EP3414099A1

EP3414099A1 - Novel colour developer for a thermo-sensitive recording medium, and a heat-sensitive recording material based on pla

Info

Publication number: EP3414099A1
Application number: EP18700648.1A
Authority: EP
Inventors: Diana Valentina Becerra Siabato; Nora Wilke; Matthias Neukirch; Martinus Adrianus Getrudus JANSEN; Armin Johannes MICHEL
Original assignee: Mitsubishi HiTec Paper Europe GmbH
Current assignee: Mitsubishi HiTec Paper Europe GmbH
Priority date: 2017-01-10
Filing date: 2018-01-10
Publication date: 2018-12-19
Also published as: EP3505358A1; WO2018130576A1; DE202018107306U1

Abstract

The present invention provides an agent capable of reacting with a leuco dye upon heating, wherein said agent meets Formula (A-I): Formula (A-I) wherein: R1 and R2 are independently a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group or a halogen atom; R3, R4, R5 and R6 are independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group; X is O, S or NH; and, a and b are integer values meeting the conditions a ≥ 0, b ≥ 0 and (a+b) ≥ 1. The present invention also provides a thermosensitive recording medium having a colour developing layer comprising: a leuco dye; and, a colour developer which reacts with said leuco dye upon heating to form a colour layer, wherein said colour developer comprises an agent meeting said Formula (A-I). The present invention also relates to a coating composition for forming a heat-sensitive recording material or heat-sensitive recording layer, comprising one or more dye precursors and one or more colour developers based on lactic acid units, and also to a coating colour for forming a coating composition or a heat-sensitive recording layer, comprising one or more dye precursors and one or more colour developers based on lactic acid units, and further to a heat-sensitive recording material comprising a supporting substrate and a heat-sensitive recording layer of the invention, and also to a method of forming this heat-sensitive recording material and to the use of this heat-sensitive recording material. The present invention here also relates to such a coating composition or heat-sensitive recording layer as further contains at least one further colour developer not based on lactic acid units. The invention lastly also relates to a compound based on lactic acid units, preferably for use as a colour developer in the above context, to such a use itself, and to a method of forming this compound based on lactic acid units.

Description

Novel Colour Developer for a Thermo-sensitive Recording Medium, and a Heat-Sensitive Recording Material based on PLA

The present invention pertains in one aspect to a novel colour developer for a thermo- sensitive recording medium, and related thereto, in a further aspect to a heat-sensitive recording material based on PLA.

Chapter A: Novel Colour Developer for a Thermo-sensitive Recording Medium Technical Field

The present invention is directed to an agent which is capable, upon heating, of reacting with a leuco dye in a colour-forming manner. More particularly, the present invention is directed to a colour developer which comprises an agent which is a macromolecular compound comprising a terminal sulfonyl group, a urea group and a linking group there- between. The colour developer is suitable for inclusion in the colour developing layer of a thermo-sensitive recording medium. Background to the Invention

The colour developing layer (5) comprises at least i) a colour developer which is usually a weak acid and which donates a proton under the action of heat to ii) a colour former, which is an initially light-coloured or colourless compound but which can change colour with the addition of said proton. The colour developer should have an appropriate melting point to react at the temperatures generated by the thermal head (7) of the printer but should equally be thermally stable at lower temperatures. It will be appreciated that there are also functional constraints on the acidity (pKa value) and solubility of such colour developers, as well as the common, practical need for the colour developer to be of improved economics given the large scale of its application.

Well established colour developers include: Bisphenol A; Bisphenol F; Bisphenol AP; Bisphenol S; 4-hydroxy-4'-isopropoxydiphenylsulfones; bis-(3-allyl-4-hydroxyphenyl)- sulfone; phenol-4-[[4-(2-propen-1 -25 yloxy)phenyl]sulfonyl]; 1 ,7-bis(4-hydroxyphenylthio)- 3,5-dioxaheptane; and, the phenol, 4, 4'-sulfonylbispolymer with 1 ,1 '-oxybis[2- chloroethane] (CAS Number 191680-83-8, D90).

The U.S. Environmental Protection Agency has documented its concerns over the use of bisphenols - in particular Bisphenol A - in thermal recording media and, particular, thermal paper and in the waste paper streams and recycled paper derived therefrom (BPA as a Developer in Thermal Paper and Alternatives: Identifying Alternative Developers, US Environmental Protection Agency (EPA), 15th July 2010). A need to find viable alternatives to these bisphenols is therefore clearly apparent, with this EPA reference mooting the use of inter alia palygorskite, attapulgite, halloysite, kaolin, colloidal silica and phenolic novolac resins. Palygorskite or attapulgite are a magnesium aluminium phyllosilicate with formula (Mg,AI)₂Si₄O₁₀(OH)-4(H₂O) that occurs in a type of clay soil, for example, common to the Southeastern United States. Halloysite is an aluminosilicate clay mineral with the empirical formula AI₂Si₂05(OH)4. Its main constituents are aluminium (20.90%), silicon (21 .76%) and hydrogen (1 .56%). Halloysite typically forms by hydrothermal alteration of alumino-silicate minerals. It can occur intermixed with other clay minerals, for example, kaolinite. Further alternatives to bisphenols have also been disclosed in the art. For instance: US 2003/0040434 A1 (Fujita et al.) and Japanese Patent Unexamined Publications (JP- Kokai) Hei 5-147357 (JP H05-147357 A) and Hei 5-32601 (JP H05-32601 A / US 4,535,176 A) disclose the use, as colour developers, of sulfonylurea compounds; aminobenzene sulfonamide derivatives are disclosed in JP H08-59603 (JP H08-59603 A / EP 0 693 386 A1 ); and, diphenyl sulfone crosslinked compounds are described in WO 97/16420 (WO 1997016420 A1 ).

US 2014/0235437 A1 (Mitsubishi HiTec Paper Europe GmbH) discloses a colour acceptor for chemical reaction with a dye precursor to form a visually recognizable colour: the colour acceptor is constructed of lactic acid monomers. This citation also discloses a heat-sensitive recording material with a substrate and a heatsensitive recording layer, wherein the heat-sensitive recording layer contains at least one dye precursor and at least one colour acceptor - which compounds react with one another in a colour-forming manner when heat is applied - and wherein the colour acceptor is constructed of lactic acid monomers.

The invention aims at providing one or more alternative colour developers having improved properties, which enable them to react with a leuco dye under optimized conditions.

Statement of the Invention

In accordance with a first aspect of the invention, there is provided an agent capable reacting with a leuco dye upon heating, wherein said agent meets Formula (A-l):

Formula (A-l) wherein: R1 and R2 are independently a hydrogen atom, a C1-C6 alkyl group, a C1- C6 alkoxy group or a halogen atom;

R3, R4, R5 and R6 are independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group;

X is O, S or NH; and, a and b are integer values meeting the conditions a > 0, b > 0 and (a+b) > 1.

Without intention to limit the present invention, the parameter (a+b) of Formula (A-l) will generally meet the condition 1 < (a+b) < 40. In an alternative expression, the molecular weight of the agent of Formula (A-l) should generally be 8000 or less, for example 6000 or less.

In an embodiment of the agent of Formula (A-l), R1 , R2, R3, R4, R5 and R6 are independently a hydrogen atom or a C1-C3 alkyl group. Preferably, R3 and R4 are inde- pendently a hydrogen atom or a methyl group and more preferably R3 is H and R4 is methyl.

In further embodiments of the agent of Formula (A-l), which embodiments are not intended to be mutually exclusive of one another: X is O; R1 and R2 are both methyl and are para- substituents of the phenyl group; and/or 1 < a < 10 and 1 < b < 10. In terms of the tackiness of the agent of Formula (A-l), good results have been obtained where 4 < a < 10 and 4 < b < 10.

In accordance with a second aspect of the present invention, there is provided a compound meeting Formula (A-l I):

Formula (A-l I) wherein: R3, R4, R5 and R6 are independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group;

Importantly, the compound of Formula (A-l I) may be obtained by a method comprising acting: i) a compound of the formula

wherein: R5 and R6 are independently a hydrogen atom, a C1-C6 alkyl group, a C3- C6 cycloalkyl group or a C2-C6 alkenyl group; and,

X is O, S or NH; and, ii) a cyclic ester of a hydroxycarboxylic acid having the formula

wherein: R3 and R4 are independently a hydrogen atom, a C1 -C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group.

The compound of Formula (A-ll) represents an important starting material for the synthesis of the agent of Formula (A-l). More particularly, the present invention provides a method for producing the agent of Formula (A-l) as defined herein above, said method comprising the steps of: a) providing a compound as defined in Formula (A-ll); and, b) reacting said compound with at least one sulfonyl isocyanate of Formula (A-l II): O

Formula (A-l II) wherein: R is a hydrogen atom, a C1 -C6 alkyl group, a C1 -C6 alkoxy group or a halogen atom

The agents of Formula (A-l) are effective as developers in the colour developing layers of thermosensitive media, in particular thermal papers. They are stable at low temperatures and particularly at temperatures below 40 °C at which thermosensitive media will usually be transported and stored prior to their use. The compounds are stable in aqueous disper- sion for an operable period of time, and their use is not compromised by the environmental concerns which surround the large scale use of bisphenols. In fact, it might be noted the reactants used to obtain compounds of Formula (A- 11 ) - and thus indirectly the agents of Formula (A-l) - can be derived from compounds of biologic origin, such as urea and lactide: as a consequence, it is postulated that the agents of Formula (A-l) may be biodegradable. In accordance with a third aspect of the invention, there is provided an aqueous dispersion comprising the agent of Formula (A-l) as defined above. In such an aqueous dispersion, it is preferred that the average particle size of the agent is less than 20 microns, for instance from 0.5 to 10 microns, as measured by dynamic light scattering.

In accordance with a fourth aspect of the present invention, there is provided a thermosen- sitive recording medium having a colour developing layer comprising; a leuco dye; and, a colour developer which reacts with said leuco dye upon heating to form a colour layer, wherein said colour developer comprises an agent as defined herein before and in the appended claims.

Typically, the leuco dye of the thermosensitive medium is selected from the group consist- ing of: triphenylmethanephthalide leuco compounds; triallylmethane leuco compounds; flu- oran leuco compounds; phenothiazine leuco compounds; thiofluoran leuco compounds; xanthene leuco compounds; indophthalyl leuco compounds; spiropyran leuco compounds; azaphthalide leuco compounds; couromeno-pyrazole leuco compounds; methine leuco compounds; rhodamineanilino-lactam leuco compounds; rhoda- minelactam leuco compounds; quinazoline leuco compounds; diazaxanthene leuco compounds; bis-lactone leuco compounds; and, mixtures thereof. In an important embodiment, the colour developing layer comprises a fluoran leuco dye.

The present invention also provides a method of producing a thermo-sensitive recording medium comprising the steps of: a) providing a preferably planar substrate; b) applying an aqueous coating composition to said substrate, said aqueous coating composition comprising a leuco dye and a dispersed developer which reacts with said leuco dye upon heating; and, c) forming a coating layer by drying the applied aqueous coating composition at a temperature below the minimum reaction temperature of the developer and the leuco dye, wherein said developer comprises the agent as defined above. Typically the substrate will comprise paper. Further, said method may be characterized in that the applied coating composition has a solids content of from 35 to 50 wt.%.

Definitions

The terms "comprising", "comprising", "comprises" and "comprised of" as used herein are synonymous with "including", "includes", "containing" or "contains": the terms should be understood to mean that the list following is non-exhaustive and may or may not include any other additional suitable items, for example one or more further feature(s), components), ingredient(s) and/or substituent(s) as appropriate.

As used herein, "and/or" refers to and encompasses any and all possible combinations of one or more of the associated listed items.

When amounts, concentrations, dimensions and other parameters are expressed in the form of a range, a preferable range, an upper limit value, a lower limit value or preferable upper and limit values, it should be understood that any ranges obtainable by combining any upper limit or preferable value with any lower limit or preferable value are also specifically disclosed, irrespective of whether the obtained ranges are clearly mentioned in the context. The words "preferred" and "preferably" are used frequently herein to refer to embodiments of the disclosure that may afford particular benefits, under certain circumstances. However, the recitation of one or more preferable or preferred embodiments does not imply that other embodiments are not useful and is not intended to exclude those other embodiments from the scope of the disclosure.

As used herein, "C1 -C6 alkyl" group refers to a monovalent group that contains 1 to 6 carbons atoms, that is a radical of an alkane and includes straight-chain and branched organic groups. Examples of alkyl groups include, but are not limited to: methyl; ethyl; propyl; isopropyl; n-butyl; isobutyl; sec-butyl; tert-butyl; n-pentyl; and, n-hexyl. In the present invention, such alkyl groups may be unsubstituted or may be substituted with one or more substituents such as halo, nitro, cyano, amido, amino, sulfonyl, sulfinyl, sulfanyl, sulfoxy, urea, thiourea, sulfamoyi, sulfamide and hydroxy. The halogenated derivatives of the exemplary hydrocarbon radicals listed above might, in particular, be mentioned as examples of suitable substituted alkyl groups. In general, however, a preference for unsubstituted alkyl groups containing from 1 -4 carbon atoms (C1 -C4 alkyl) - for example unsubstituted alkyl groups containing from 1 to 3 carbon atoms (C1 -C3 alkyl) - should be noted. As used herein, "C2-C6 alkenyl" group refers to an aliphatic carbon group that contains 2 to 6 carbon atoms and at least one double bond. Like the aforementioned alkyl group, an alkenyl group can be straight or branched, and may optionally be substituted. Examples of C2-C6 alkenyl groups include, but are not limited to: allyl; isoprenyl; 2-butenyl; and, 2-hexenyl.

The term "C3-C6 cycloalkyl" is understood to mean a saturated, mono- or bicyclic hydrocarbon group having from 3 to 6 carbon atoms. Examples of cycloalkyl groups include: cyclopropyl; cyclobutyl; cyclopentyl; and, cyclohexyl. The term "lactic acid" in this application refers to 2-hydroxypropionic acid with the chemical formula C₃H₆0₃ and, unless specified herein, can refer to either stereoisomeric form of lactic acid (L-lactic acid or D-lactic acid).

As used herein "lactide" (CAS 451 1 -42-6 and 95-96-5) refers to the cyclic diester obtained by dehydrationcondensation of two lactic acid molecules. Lactide exists as three optical isomers: L-lactide formed from two L-lactic acid molecules; D-lactide formed from two D-lactic acid molecules; and, meso-lactide formed from L20 lactic acid and D-lactic acid. Where appropriate, lactoyi units of the compounds of Formulas (A-l) and (A-ll) may be derived from one, two or three of said isomers. However, it is preferred for said lactoyl units to be derived from a source of lactide in which the level of meso-lactide is as low as possible and preferably for said lactide source to consist of L-lactide and/or D-lactide. In an embodiment, the lactide consists only of optically pure D-lactide or, preferably, optically pure L-lactide. Instructive disclosures on the preparation of purified lactide include but are not limited to: US Patent No. 6,313,319 B1 (US 6,313,319 B1 ); Japanese Examined Patent Publication No. 51 -6673 (JP S51 -6673 B1 / US 3,597,449 A); Japanese Laid- Open Patent Publication No. 63-101378 (JP S63-101378 A / EP 0 261 572 A1 ); Japanese Laid-Open Patent Publication No. 6-256340 (JP H06-256340 A / DE 44 04 838 A1 ); and, Japanese Laid-Open Patent Publication No. 7-165753 (JP H07-165753 A / EP 0 657 447 A1 ).

As used herein, a "catalytic amount" means a sub-stoichiometric amount of catalyst relative to a reactant.

As used herein "solvents" are substances capable of dissolving another substance to form a uniform solution; during dissolution neither the solvent nor the dissolved substance undergoes a chemical change. Solvents may either be polar or non-polar.

Water, for use as a (co-)solvent or carrier herein, is intended to mean water of low solids content as would be understood by a person of ordinary skill in the art. The water may, for instance, be distilled water, demineralized water, deionized water, reverse osmosis water, boiler condensate water, or ultra-filtration water. Tap water may be tolerated in certain circumstances.

Hydroxyl (OH) values are measured according to Japan Industrial Standard (JIS) K-1557, 6.4.

The measurement of the solids content of materials shall be conducted in accordance with EPA Test Method 24 (40 CFR 60, Appendix A).

The molecular weights referred to in this specification can be measured with gel permeation chromatography (GPC) using polystyrene calibration standards, such as is done according to ASTM 3536. And molecular weight as given here means "number average molecular weight (Mn)" unless specifically stated otherwise. All percentages, ratios and proportions used herein are given on a weight basis unless otherwise specified.

Detailed Description of the Invention

As noted above, the present invention is primarily directed to an agent capable of reacting with a leuco dye upon heating, wherein said agent meets Formula (A-l):

Formula (A-l) wherein: R1 and R2 are independently a hydrogen atom, a C1-C6 alkyl group, a C1- C6 alkoxy group or a halogen atom; R3, R4, R5 and R6 are independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group;

In producing a thermosensitive medium, in particular a thermal paper, it would be usual to form the colour developing layer thereof by application - to a suitable substrate - of an aqueous coating composition comprising a dispersed developer which reacts with said leuco dye upon heating; in the present invention that developer comprises the agent as defined above and further described herein below. The leuco dye of the colour developing layer may be provided within such an aqueous coating composition or may be applied in- dependently to the substrate. Within such an aqueous dispersion, it is preferred that the average particle size of any dispersed agent is less than 20 microns, for example from 0.5 to 10 microns, as measured by dynamic light scattering. Reactive Agent

The reactive agent in accordance with the present invention and having Formula (A-l) is optimally formed in a two-stage process comprising:

1 ) In a first stage, reacting at a stoichiometric ratio of 1 : (a+b): i) a compound of the formula

R^J wherein: R5 and R6 are independently a hydrogen atom, a C1-C6 alkyl group, a C3- C6 cycloalkyl group or a C2-C6 alkenyl group; and,

/ \ ^R3

o wherein: R3 and R4 are independently a hydrogen atom, a C1-C6 alkyl group, a C3- C6 cycloalkyl group or a C2-C6 alkenyl group, to thereby form an intermediate compound of Formula (A-l I): b

R³ O R° R° R O R³

— c— c-o— c— c - -N— C— N- -C— C— O— C— C-O- -H

II

R 3 O O

R^ x R^ R^q

Formula (A-ll)

2) In a second stage, reacting said intermediate compound of Formula (A-ll) with at least one sulfonyl isocyanate of Formula (A-lll):

Formula (A-lll) wherein: R is a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group or a halogen atom.

It will be recognized that a compound of Formula (A-ll) might alternatively be prepared by grafting of a preformed oligomer, such as a pre-formed polylactide, onto the appropriate starter molecule, such as urea. In this embodiment, the polylactide could be derived from either lactide or lactic acid as both alternatives are established in the art. However, no further mention will be made of said embodiment and the two stage process will be described further below.

First Stage 1 )

As regards the reactants of said first stage of the process, it is preferred that: R3, R4, R5 and R6 as defined above are independently a hydrogen atom or a C1-C3 alkyl group; and, X is O. More preferably, R3 and R4 are independently a hydrogen atom or a methyl group and most preferably R3 is H and R4 is methyl. As illustrative first stage reactants, glycolide, lactide and urea might therefore be mentioned. In the first stage of this process, polymeric blocks of unit lengths a and b may be formed by a ring-opening reaction or a ring opening polymerization of the cyclic ester using an appropriate ionic or nonionic catalyst, as described in Ring Opening Polymerization, Vol. I, pages 461 -521 , K. J. Ivin and T. Saegusa (1984). Known catalysts, which may be used alone or in combination, include but are not limited to: amine compounds or salts thereof with carboxylic acids, such as butylamine, octylamine, laurylamine, dibutylamines, mono- ethanolamines, diethanolamines, triethanolamine, diethylenetriamine, triethylenetetra- mine, oleylamines, cyclohexylamine, benzylamine, diethylaminopropylamine, xylylenediamine, triethylenediamine, guanidine, diphenylguanidine, 2,4,6- tris(dimethylaminomethyl)phenol, morpholine, N-methylmorpholine, 2-ethyl-4- methylimidazole and 1 ,8-diazabicyclo-(5,4,0)-undecene-7 (DBU) ; tin 2-ethylhexanoate (tin octanoate) ; tin dichloride (SnCI₂) ; porphyrin aluminum complexes; composite metal cyanide ; aqueous diethylzinc or diethylcadmium ; aluminum triisopropox- ide; titanium tetrabutoxide ; zirconium tetrapropoxide; tributyltin methoxide; tetraphenyltin ; lead oxide; zinc stearate; bismuth 2-ethylhexanoate; potassium alcoholate; antimony fluoride; and yttrium or lanthanide series rare earth metal based catalysts (coordination catalysts), such as described in U.S. Patent No. 5,028,667 (US 5,028,667 B1 ). In terms of yield, tin dichloride (SnCI₂) and tin 2-ethylhexanoate are particularly preferable.

There is no particular limitation on the amount of catalyst used but it will typically be 0.0001 to 5 parts by weight, and preferably from 0.05 to 1 part by weight, based on 100 parts by weight of the cyclic ester.

The ring-opening reaction or polymerization reaction can be performed at room temperature but is preferably performed with heating at a temperature of from 100 to 200 °C , or from 130 to 190 °C. If the temperature is lower than 100 °C , the reaction rate is unfa- vorably low. On the other hand, if the temperature is higher than 200 °C, the oligomer degradation rate is increased and low-molecular weight components can vaporize.

Importantly, the reaction should be performed under anhydrous conditions and in the absence of any further compounds having an active hydrogen atom. Exposure to atmospheric moisture may be avoided by providing the reaction vessel with an inert, dry gase- ous blanket. Whilst dry nitrogen, helium and argon may be used as blanket gases, precaution should be used when common nitrogen gases are used as a blanket, because such nitrogen may not be dry enough on account of its susceptibility to moisture entrain- ment; the nitrogen may require an additional drying step before use herein. The process pressure is not critical to the first-stage reaction. As such, the reaction can be run at subatmospheric, atmospheric, or super-atmospheric pressures but pressures at or above atmospheric pressure are preferred.

Furthermore, the reaction may be performed in solution or in the melt without a solvent. When used, suitable solvents for the reaction should be non-reactive, organic liquids capable of dissolving at least 1 wt.% and preferably over 10 wt.% of the compounds of Formula (A-ll) at 25 °C.

The progress of the reaction can be monitored by known methods - for instance by analyzing monomer conversion using gas chromatography or by monitoring the product hydroxyl (OH) values - and the reaction stopped when desired. This aside, the reaction generally requires a time of 0.5 to 12 hours to reach completion, and more commonly from 1 to 6 hours.

Upon completion of the first stage reaction, it is facile to remove any solid, suspended compounds by, for example, filtration, crossflow filtration or centrifugation. Further, the first stage reaction product - of Formula (A-ll) - may be worked up, using methods known in the art, to isolate and purify the product: for example, any solvent present may be removed by stripping at reduced pressure. That said, it is noted that there is no particular need to work up the first stage reaction product: the second reaction stage may proceed directly from the first stage. Second Stage 2)

The intermediate compound of Formula (A-ll) and one or more compounds of Formula (A-lll) are reacted in the second stage of the process. Preferably, a single compound of Formula (A-lll) is reacted such that the resultant terminal groups of the reactive agent (Formula (A-l)) are the same. This second stage - nominally the preparation of a sulfony- lurethane - is an addition reaction and not a polymerization reaction; therefore the molecular weights of the intermediate compound (Formula (A-ll)) and of the or each compound of Formula (A-lll) are determinative of the molecular weight of the reaction product, the compound of Formula (A-l).

Exemplary compounds of Formula (A-lll) include phenylsulfonylisocyante, toluenesolyl- sulfonyl isocyanate, and chlorophenylsulfonyl isocyanate. Where non-hydrogen substitu- ents (R) are present in the compounds of Formula (A-lll), these are preferably para- substituents of the phenyl group. As such, it is particularly preferred that p- toluenesulfonylisocyanate is used as a reactant.

For completeness, processes for the preparation of aromatic sulfonyl isocyanates of the type suitable for the present invention and their chemical behavior are described inter alia in: H. Ulrich Chem. Rev. 65, pages 369-376 (1965); US Patent No. 2,666,787 (US 2,666,787 A); and, US Patent No. 3,484,466 (US 3,484,466 A).

The molar ratio of the reactants of Formula (A-ll) and Formula (A-lll) should be selected to ensure the complete conversion of the hydroxyl groups of Formula (A-ll). Generally, the molar ratio of hydroxyl groups to sulfonyl isocyanate groups should be maintained in the range of from 1 :1 to 1 :0.8.

The second stage reaction is typically performed in organic solution and under anhydrous conditions. The intermediate compound of Formula (A-ll) is dispersed in a suitable organic solvent and, under stirring, the sulfonyl isocyanate is added thereto either in pure form or in solution. Suitable organic solvents are those capable of dissolving at least 1 wt.% and preferably over 10 wt.% of the reaction product - the compounds of Formula (A-l) - at 25 °C. As non-liming examples, mention may be made of tetrahydrofuran, ethyl acetate, nbutyl acetate, tert-butyl acetate, methyl Cellosolve acetate, toluene, xylene, methylisobutyl ketone and methylethylketone (MEK).

The compound of Formula (A-lll) may actually be sufficiently reactive towards to the hydroxyl functional, intermediate compound (Formula (A-ll)) that the reaction need not occur either at a significantly elevated temperature or under catalysis. For instance, it is envisaged that the second stage reaction may be performed at a temperature of from 30 °C or 40 °C to 80 °C and either some cooling of the reaction vessel or the introduction of the reactants at a slow rate may in fact be needed to maintain such low temperatures given the exothermic nature of the reaction. That said, in certain circumstances it may be expedient to employ one or more conventional catalysts which are known to accelerate the isocyanate-hydroxyl reaction. When employed, there is again no intended limitation on the amount of catalyst which may be used, but it will typically be 0.0001 to 5 parts by weight, and preferably from 0.05 to 1 part by weight, based on 100 parts by weight of hydroxyl functional, intermediate compound (Formula (A-ll).

In principle, any compound that can catalyze the reaction of a hydroxyl group and an isocyanato group to form a urethane bond can be used. And examples thereof include: tin carboxylates; tin alkoxides; tin oxides; reaction products between dibutyltin oxides and phthalic acid esters; dibutyltin bisacetylacetonate; titanates, such as tetrabutyl titanate and tetrapropyl titanate; organoaluminum compounds such as aluminum trisacetylaceto- nate, aluminum trisethylacetoacetate, and diisopropoxyaluminum ethylacetoacetate; chelate compounds such as zirconium tetraacetylacetonate and titanium tetraacetylace- tonate; lead octanoate; amine compounds or salts thereof with carboxylic acids, such as butylamine, octylamine, laurylamine, dibutylamines, monoethanolamines, diethanola- mines, triethanolamine, diethylenetriamine, triethylenetetramine, oleylamines, cyclohexyl- amine, benzylamine, diethylaminopropylamine, xylylenediamine, triethylenediamine, guanidine, diphenylguanidine, 2,4,6-tris(dimethylaminomethyl)phenol, morpholine, N- methylmorpholine, 2-ethyl-4-methylimidazole and 1 ,8-diazabicyclo-(5,4,0)-undecene-7 (DBU); and, aliphatic carboxylate salts or acetylacetonates of potassium, iron, indium, zinc, bismuth, or copper.

Where one elects to use a catalyst, a preference may be noted for organic tin compounds. An illustrative but non-limiting list of suitable tin compounds include: tin(ll) and tin(IV) salts of carboxylic acids, such as tin(ll) acetate, tin (II) 2-ethylhexanoate (tin octanoate), tin(ll) oleate, tin(ll) laurate, dibutyl tin diacetate, dibutyl tin dilaurate, dibutyl tin maleate, dioctyl tin diacetate, dibutyl tin di-2-ethyl hexanoate, tributyl tin acetate and triphenyl tin acetate; tin(IV) alkoxides, such as tributyl tin methoxide, tributyl tin ethoxide, dibutyl tin dimethoxide, dibutyl tin diethoxide and dibutyl tin dibutoxide; distannoxanes, such as hexabutyl distannoxane (bis(tri-n-butyl tin)-oxide); distannoxanes containing alkoxy or carboxy substituents such as tetrabutyl-1 ,3-diethoxy-distannoxane, tetrabutyl- 1 ,3-dimethoxy distannoxane and tetrabutyl-1 ,3-diacetoxydistannoxane; and, stannosilox- anes as described, for example, in DE-AS 1 ,099,743 (DE 1 099 743 A) and DE-AS 1 ,1 1 1 ,378 (DE 1 1 1 1 378 B) in particular dibutyl tin-di-(trimethyl silyloxide), tetrabutyl-1 ,3- di-(trimethyl silyloxy)-distannoxane, tetra-(dibutyl-acetoxy tin oxy)-silane and tetrabutyl3- ethoxy-1 -(triethoxy siloxy)-distannoxane.

In a particularly interesting embodiment, tin octanoate may be employed as the catalyst of both the first and second reaction stages. This allows for a "one-pot synthesis", wherein the first and second stages can be performed sequentially without the need to remove any first-stage catalyst from the intermediate product.

The progress of the second stage reaction can be monitored by known methods - again including the monitoring of reactant conversion by gas chromatography and by hydroxyl (OH) value measurement - and the reaction stopped upon completion. In practice, the reaction generally requires a time of 0.1 to 4 hours to reach completion and more commonly from 0.2 to 2 hours.

The output of the second reaction stage may be worked up, using methods known in the art, to isolate and purify the compounds of Formula (A-l): mention in this regard may be made of extraction, evaporation, distillation and chromatography as suitable techniques.

For further utility in the present invention, the compound of Formula (A-l) is dispersed in an aqueous medium in the presence or absence of a leuco dye.

Leuco Dyes

Leuco dyes, included as the so-called "colour formers" in the aqueous coating compositions and thermal sensitive recording materials of this invention, are colourless or light coloured basic substances which become coloured when oxidized by acidic substances. Exemplary leuco dyes that can be used herein, either alone or in combination, include: triphenylmethanephthalide leuco compounds; triallylmethane leuco compounds; fluoran leuco compounds; phenothiazine leuco compounds; thiofluoran leuco compounds; xan- thene leuco compounds; indophthalyl leuco compounds; spiropyran leuco compounds; azaphthalide leuco compounds; couromeno-pyrazole leuco compounds; methine leuco compounds; rhodamineanilino-lactam leuco compounds; rhodaminelactam leuco compounds; quinazoline leuco compounds; diazaxanthene leuco compounds; and, bis- lactone leuco compounds.

In an embodiment, the aqueous coating composition comprises a leuco base of a triphenylmethane dye as represented by Formula L1 :

R y

Formula L1 wherein Rx, Ry, and Rz are independently selected from the group consisting of hydrogen, hydroxyl, halogen, C1-C6 alkyl, nitro and aryl. Specific examples of dyes meeting Formula L1 include: 3,3-bis(pdimethylaminophenyl)-phthalide, 3,3-bis(p-dimethylaminophenyl)-6- dimethylaminophthalide (Crystal Violet Lactone), 3,3-bis(p-dimethylaminophenyl)-6-di- ethylaminophthalide, 3,3-bis(p-dimethylaminophenyl)-5 6-chlorophthalide, and 3,3-bis(p- dibutylaminophenyl)-phthalide.

In an alternative embodiment, the aqueous coating composition comprises a leuco dye comprises a compound represented by Formula L2:

Formula L2

Wherein: either R1 1 and R12 are independently selected from the group consisting of hydrogen, C1-C6 alkyl, substituted phenyl, unsubstituted phenyl, cyanoethyl and, R- halogenated ethyl, or R1 1 and R12 in combination form a cyclic structure and represent— (CH2— )4, (~CH2~)5; at least one of R13 and R14 is hydrogen and the other is hydrogen, C1-C6 alkyl, aralkyl, amyl, or phenyl;

X1 , X2 and X3 each independently selected from the group consisting of hydrogen, C1-C6 alkyl, halogen, halogenated methyl, nitro, amino and substituted 5 amino; and,

X4 represents hydrogen, C1-C6 alkyl or C1-C6 alkoxy and n is an integer of from 0 to 4.

Specific examples of lactone compounds meeting Formula L2 are: 3-(2'-hydroxy-4'-dime- thylaminophenyl)-3-(2' -methoxy-5'-chlorophenyl)phthalide, 3-(2'-hydroxy-4'-dimethyla- minophenyl)-3-(2'-methoxy-5'-nitrophenylphthalide, 3-(2'-hydroxy-4'-diethylaminophenyl)- 3-(2'-methoxy-5'-methylphenyl)phthalide, and 3-(2'-methoxy-10 4'-dimethylaminophenyl)- 3-(2'-hydroxy-4'-chloro-5'-methylphenyl)-phthalide. In a preferred embodiment, the aqueous coating composition comprises a fluoran leuco dye. Examples of such dyes include: 3-diethylamino-6-methyl-7-chlorofluoran; 3-pyrroli- dino-6-methyl-7-anilinofluoran; and, 2-[3,6-bis(diethylamino)-9-(0-chloroan- ilino)xanthylbenzoic acid lactam]. Equally, the dye may be a leuco base of a fluoran dye as represented by Formula L3:

R

Formula L3 wherein Rx, Ry, and Rz are independently selected from the group consisting of hydrogen, hydroxyl, halogen, C1-C6 alkyl, nitro and aryl.

As specific examples of leuco dyes conforming to Formula L3 might be mentioned 3-cyclo- hexylamino-6-chlorofluoran, 3-(N-N-diethylamino)-5-methyl-7-(N,N-dibenzylamino) fluoran, 3-dimethylamino-5,7-dimethylfluoran and 3-diethylamino-7-methylfluoran.

Coating Compositions

The amount of said colour developer included in the aqueous coating compositions is preferably selected so that the resultant thermo-sensitive medium comprises the compound of Formula (A-l) in an amount of from 0.5 and 10 parts by weight, relative to 1 part by weight of a basic leuco dye.

The colour developer may comprise or consist of the compound of Formula (A-l). By this it is meant that the present invention does not preclude the colour developer - and thereby the resultant colour developing layer of the thermosensitive medium - from comprising one or more further compounds which are supplementary to the above defined agent but which can also oxidize the constituent leuco dyes and change the colour thereof. Any co-agent should typically melt at a temperature of from 50 °C to 250 °C and be sparingly soluble in water. Suitable co-agents may be selected from the group consisting of: benzyl paraben; mono- and dihydroxy diphenyl sulfones; acidic clays; phenolic resins; and, salicylic acids and salicylates of lead, aluminum, magnesium, nickel or, preferably zinc. And specific examples of co-agents include: 4,4'-isopropylenediphenol (bisphenol A); p-tert-butylphenol, 2-4-dinitrophenol; 3,4-dichlorophenol; p-phenylphenol; 4,4- cyclohexylidenediphenol; and, 3-tert-butylsalicylic acid, 3,5-tert-butysalicylic acid, 5-a- methylbenzylsalicylic acid and zinc, lead, aluminum, magnesium or nickel salts thereof.

The amount of co-agent included in the colour developer aqueous coating composition is preferably selected so that the resultant thermosensitive medium comprises from 0.01 to 5 parts by weight thereof, relative to 1 part by weight of basic leuco dye. Whilst the use of bisphenol compounds as co-agent(s) is not precluded in the present invention, it is preferred that the thermosensitive medium comprises less than 0.1 parts by weight of such compounds, relative to 1 part by weight of basic leuco dye.

Methods In accordance with a further aspect of the invention, there is provided a method of producing a thermosensitive recording medium comprising the steps of: a) providing a preferably planar substrate; b) applying an aqueous coating composition to said substrate, said aqueous coating composition comprising a leuco dye and a dispersed developer which reacts with said leuco dye upon heating; and, c) forming a coating layer by drying the applied aqueous coating composition at a temperature below the minimum reaction temperature of the developer and the leuco dye, wherein said colour developer comprises the agent as defined hereinabove. Further, said method may be characterized in that the applied coating composition in one embodiment of the invention has a solids content of from 35 to 50 wt.%. In a further embodiment of the invention the said method may be characterized in that the applied coating composition has a solids content of from 20 to 50 wt.%. The shape, structure, size and material of the substrate to be coated will be selected based on what is appropriate for the intended purpose of the thermo-sensitive medium ; no particular limitation is intended here. Exemplary shapes of the substrate includes plates and sheets and, moreover, the substrate may have a single-layer or multi-layer structure. That aside, it is advised that the base layer (2) of the substrate can significantly affect the final characteristics of a thermosensitive medium, such as a thermal paper, and thereby must be carefully chosen on the basis of its optical and mechanical properties.

Conventionally the base layer (2) of the substrate will be selected from the group consisting of: paper, including synthetic paper; cardboard; other fibrous webs; textile materials; and, synthetic resin films. For most applications, the thickness of the base layer (2) of the substrate will be in the range from 20 to 250 microns. As is known the art, the structural properties of the base layer (2) can be modified by the provision of a backcoat (3) as illustrated in Figure 4.

The aqueous compositions may be directly coated onto the base layer (2) of the sub- strate. However, the presence of an intermediate layer (4) is not precluded and indeed may be preferable in some circumstances.

The aqueous coating compositions are liquid at their application temperature, said temperature typically being from 20 °C to 50 °C. The liquid might have a corresponding viscosity of from 2,000 to 70,000 centipoises, preferably from 3,000 to 30,000 cP as determined at application temperature using a Brookfield Thermosel Viscometer Model DV-I using a number 27 spindle. The unit centipoise ("cP") is one hundredth of a poise, or one millipascal-second (mPa-s) in SI units (1 cP = 10^"3 Pa-s = 1 mPa-s); next to the unit "cP", sometimes the abbreviations "cps", "cp", and "CPs" are used in the art. The sensitivity of the substrate and, more particularly, of the coating composition to a given tempera- ture may determine which application temperature is applicable. Such physical characteristics as the viscosity and rate of set of the compositions may be varied to accommodate such application conditions.

Illustrative techniques for the application of the aqueous coating composition to the substrate, in particular for its application in the form of a continuous surface film, include but are not limited to: roll coating; spray coating; T-die coating; knife coating; comma coating; curtain coating; dip coating; and, spin coating. The composition might also be applied by dispensing, ink-jet printing, screen printing or offset printing where more localized applica- tion of the coating composition is required or where application is required in a variety of continuous or intermittent forms such as a point, line, triangle, square, circle or arc.

The coated substrate is then dried, typically using an air dryer, with close control of the temperature and any air flow, given that the coating is sensitive to heat. The substrate may then be over-coated and/or finished by calendaring, cutting, sheeting and the like. It is quite typical for the colour developing layer (5) to be wholly or partially coated with a protective layer (6) which can protect this recording layer from organic solvents, oils, fats, water, plasticizers and the like.

The basis weight of the colour developing layer (5) is typically from 2 g/m² to 8 g/m², for example from 2 g/m² to 5.0 g/m².

Adjunct Compounds and Materials

The thermosensitive medium of the present invention may further comprise one or more of: a sensitizer; a lubricant; a binder; a filler; a pigment; a stabilizer; a dispersant; a de- foamer; a flow modifier; and, an insolubiliser. These adjunct materials may be included in the above defined aqueous coating compositions and thereby be included in the colour developing layer: it is preferred, for instance, that the colour developing layer further comprises a sensitizer. Alternatively or additionally these adjunct materials may be included in supplementary layers of the thermosensitive medium: this may be particularly appropriate for binders and pigments, for example. For completeness, it is noted that the inclusion of one of these adjunct materials in the colour developing layer (5) does not preclude the further addition of that adjunct material in such supplementary layers.

Sensitizers - sometimes referred to as thermo-sensitivity promoter agents - may be used in the coating compositions and media of the present invention to ensure a good colour density is attained. Without being bound by theory, it is considered that certain sensitizers can assist in the colour forming reaction by forming a eutectic compound with one or more of the colour forming compounds: this brings down the melting point of these compounds and thereby depresses the temperature at which the colour forming reaction takes place.

Suitable sensitizers are typically selected from the group consisting of: fatty acid amides, preferably C12-C24 fatty acid amides; methylol compounds of said fatty acid amides; p- hydroxybenzoate acid esters, preferably C1 -C6 alkyl p-hydroxybenzoates; and, mixtures thereof. As specific examples of sensitizers might be mentioned: stearic acid amide; linolenic acid amide; lauric acid amide, myristic acid amide; methylenebis (stearamide); ethylenebis (stearamide); methyl p-hydroxybenzoate; n-propyl p-hydroxybenzoate; iso- propyl p-hydroxybenzoate; and, benzyl p-hydroxybenzoate. The amount of sensitizer used is preferably selected so that the thermosensitive medium comprises from 0.5 to 10 parts by weight relative to 1 part by weight of a basic leuco dye.

Lubricants are often added to a thermosensitive medium to ensure that thermal heads contacting the medium are not abraded or worn down. Non-limiting examples of suitable lubricants are: linseed oil; tung oil; paraffin wax; oxidized paraffin wax; polyethylene wax; chlorinated paraffin wax; castor wax; metal salts of higher fatty acids, such as calcium stearate and zinc stearate; and, stearic acid amide.

Binders can often constitute an important ingredient of the aqueous coating composition used to form the colour developing layer: the inclusion of a binder may be determinative of the viscosity, rheology, water release properties and set time for the aqueous coating composition. Furthermore, binders may be important to the structural integrity of the overall thermosensitive medium, particularly where pigments and/or fillers are also included therein.

The binders may be water-soluble, emulsion or latex polymers. Without being limited thereto, water soluble binders considered suitable for the coating compositions and thermosensitive recording media of the present invention include: polyvinyl alcohol; starch and starch derivatives; cellulose derivatives, such as methoxycellulose, hydroxyethylcel- lulose, carboxymethylcellulose, methylcellulose, and ethylcellulose; sodium salts of polyacrylic acid; polyvinylpyrrolidone; acrylamide-acrylate copolymer; acrylamide- acrylatemethacrylic acid copolymer; alkali salts of styrene-maleic anhydride copolymer; alkali salts of isobutylenemaleic anhydride copolymer; polyacrylamide; sodium alginate; gelatin, and, casein. Exemplary, but nonlimiting, emulsion polymers for use as binders in the present invention include: polyvinyl acetate; polyurethane; polyacrylic acid; polyacry- late; vinyl chloride-vinyl acetate copolymer; polybuthylmethacrylate; and, ethylene-vinyl acetate copolymer. And exemplary latex polymers include styrene-butadiene copolymers and styrene-butadiene-acrylate copolymers.

Any fillers and pigments used in the thermosensitive medium should conventionally be finely pulverized. In one embodiment of the invention it is preferred that such fillers and pigments be characterized by, independently or a combination of: a mean particle diameter of less than 13 μιη, preferably less than 8 μιτι ; a maximum specific surface area of 200 m²/g; and/or, an oil absorption of at least 150 ml / 100 g, preferably at least 300 ml / 100 g. It is preferred that such fillers and pigments be characterized by: a mean particle diameter of less than 10 μιη, preferably less than 5 μιτι; a maximum specific surface area of 150 m²/g; and/or, an oil absorption of at least 150 ml / 100 g. Whilst a skilled person may be aware of further suitable inorganic and/or organic fillers, typical examples include: calcium carbonate; silica; alumina; magnesia; kaolin; talc; diatomaceous earth; barium sulfate; aluminum stearate; and, mixtures thereof. The thermo-sensitive medium should preferably contain, in total, from 0.5 to 10 parts by weight of particulate fillers and pigments relative to 1 part by weight of basic leuco dye.

In a particularly preferred embodiment, the heat-sensitive recording material according to the invention has a pigment-containing intermediate layer (4) arranged between the substrate and the heat-sensitive recording layer. On one hand, an intermediate layer of this type can positively contribute to the levelling of the surface to be coated so that the required amount of coating composition to be applied for the heat-sensitive recording layer is reduced. For this reason, levelling coating devices - such as roller coating units, knife coating units, and (roll) doctor coating units - are preferable for applying the pigmented intermediate layer. On the other hand, the pigments of this intermediate layer can absorb any wax constituents of the heat-sensitive recording layer which are liquefied by the heating effect during induced recording. The basis weight of such a pigment containing intermediate layer is suitably from 5 g/m² to 20 g/m², preferably from 5 g/m² to 10 g/m².

Illustrative Embodiment In an exemplary and non-limiting embodiment of the present invention, there is provided a thermosensitive recording medium (1 ) comprising: a planar, paper base layer (2) having a thickness of from 20 to 250 microns; and, a colour developing layer (5) having a basis weight of from 2 g/m² to 8 g/m² and containing a fluoran leuco dye and a developer which reacts with said fluoro leuco dye upon heating to form a colour layer, wherein said developer is characterized in that it comprises an agent meeting Formula (A-l):

Formula (A-l) wherein: R1 and R2 are independently a hydrogen atom or a C1-C3 alkyl group disposed as a parasubstituent of the phenyl group;

R3 and R4 are independently a hydrogen atom or a methyl group;

R5 and R6 are independently a hydrogen atom or a C1-C3 alkyl group;

X is O; and, a and b are integer values wherein 1 < a < 10 and 1 < b < 10. Example

The present invention is further defined in the following example. This example, while indicating a preferred embodiment of the invention, is presented by way of illustration only.

Materials:

Urea

Puralact B3: Available from Corbion Purac B.V.

Methyl ethyl ketone (MEK) p-toluenesulfonylisocyanate

Urea and Puralact B3 were loaded into a reaction vessel under a nitrogen atmosphere. The vessel was heated to 150 °C and 100 ppm of tin octoate catalyst was added thereto. The temperature of the vessel was then raised to 180 °C and the reaction allowed to proceed for approximately 6 hours. The vessel was cooled to 60 °C, MEK was added thereto and then p-toluenesulfonylisocyanate was added slowly to the reaction mixture over time to ensure the reaction temperature remained between 60 and 70 °C. Following the addition of the p-toluenesulfonylisocyanate, the reaction was allowed to proceed under stirring for a further 1 hour. The MEK was then removed under vacuum.

It will be apparent to those skilled in the art, upon consideration of the specification, that various modifications can be made in the disclosed embodiments without departing from the scope of the invention. It is therefore intended that the embodiments and examples be considered illustrative only, with the true scope of the invention being indicated by the Embodiments, for example, Embodiments A and/or C, and the Claims.

Chapter B: Heat-sensitive recording material based on PLA

The present invention relates to a coating composition for forming a heat-sensitive recording material or heat-sensitive recording layer, comprising one or more dye precursors and one or more colour developers based on lactic acid units, and also to a coating colour for forming a coating composition or a heat-sensitive recording layer, comprising one or more dye precursors and one or more colour developers based on lactic acid units, and further to a heat-sensitive recording material comprising a supporting substrate and a heat-sensitive recording layer of the invention, and also to a method of forming this heat-sensitive recording material and to the use of this heat- sensitive recording material. The present invention here also relates to such a coating composition or heat-sensitive recording layer as further contains at least one further colour developer not based on lactic acid units. The invention lastly also relates to a compound based on lactic acid units, preferably for use as a colour developer in the above context, to such a use itself, and to a method of forming this compound based on lactic acid units.

Heat-sensitive recording materials have been around for many years and are very popular. One of the reasons for their popularity is that their use is associated with the advantage that the colour-forming components reside in the recording material itself, allowing the use of printers that are free from toner and ink cartridges. It is accordingly no longer necessary to purchase and/or refill toner or ink cartridges. This innovative technology has thus become substantially all pervasive, particularly in public transport, public and/or cultural events, logistics, mail order, the gaming or gambling industry, biomedical engineering as well as the retail trade. In the recent past, however, increasing concerns have been voiced about the environmental compatibility of certain (colour) developers, also known as colour acceptors, partly also of dye precursors, with which the (colour) developers react by heating to form a visually discernible colour, and they cannot simply be ignored by the industry and particularly by commerce. With the (colour) developers it is for example the well-known and scientifically well-studied components known as bisphenol A (BPA) (2,2- bis(4-hydroxyphenyl)propane, 4,4'-(propane-2,2-diyl)diphenol, Dian, 4,4'-isopropylidene- diphenol, 4-[2-(4-hydroxyphenyl)propan-2-yl]phenol; CAS^® RN 80-05-7) and bisphenol S (BPS) (4,4'-dihydroxydiphenyl sulfone, bis(4-hydroxyphenyl) sulfone, 4,4'- sulfonyldiphenol; CAS^® RN 80-09-1 ) which are particularly at the centre of public criticism and are therefore occasionally replaced by Pergafast® 201 (A/-(4-methylphenylsulfonyl)- /V-(3-(4-methylphenylsulfonyloxy)phenyl)urea from BASF SE), D8, i.e. 4-hydroxy-4'- isopropoxydiphenyl sulfone, A/-[2-(3-phenylureido)phenyl]benzenesulfonamide and N-{2- [(phenylcarbamoyl)amino]phenyl}benzenesulfonamide.

The underlying chemistry and the manufacturing technology for forming heat-sensitive recording materials has been constantly further developed with the objective of improving such recording materials particularly in their use as lottery or other tickets with regard to their resistance to environmental influences such as heat, moisture and chemicals.

To meet the environmental concerns regarding particularly certain (colour) developers or colour acceptors, then, there have been more recent endeavours to develop (colour) developers or colour acceptors on the basis of natural and/or biodegradable compounds, for example on the basis of lactic acid or lactide or polymers thereof such as polylactic acid or polylactide.

EP 2 574 645 A1 for instance proposes a novel colour acceptor for chemical reaction with a dye precursor to form a visually discernible colour wherein the colour acceptor is constructed from lactic acid monomers, attention being drawn to the fact that polylactic acid is fully biodegradable. Since the lactic acid polymer, in addition to an inutile hydroxyl group, contains at the two ends of its long molecules but one carboxyl group as potential reactant with the dye precursors, there is a further proposal to increase the number of useful carboxyl groups by grouping the oligomers of polylactic acid n-fold around an n- basic acid, preferably a dibasic acid. Examples recited in respect of such a preferred dibasic acid are oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanedioic acid, dodecanedioic acid, tridecanedioic acid, tetradecanedioic acid and hexadecanedioic acid. In addition to the challenge of making heat-sensitive recording materials available whose colour developers are at least substantially biodegradable and hence very substantially ecologically unconcerning, there is in relation to a further aspect the ongoing challenge of optimizing these recording materials with regard to their printing density. This is to be understood as meaning in particular that a heat-sensitive recording material is formulated by addition of potentiating compounds so as to increase the printing density (i.e. the desired blackness or jetness) of the thermal printout versus a heat-sensitive recording material without such potentiating compounds. A person skilled in the art typically uses a densitometer to determine the printing density of a thermal printout. EP 2 784 133 A1 proposes for this a composition for forming a visually discernible colour that comprises or consists of the components a) one, two, three or more colour developer compounds each comprising one, two, three or more than three structural units of formula (B-l)

where n in any one of the structural units of formula (I) is an integer above 1 , the particular value being independent of the value in any other structural unit of formula (B-l),

one, two, three or more dye precursor compounds for forming the visually discernible colour by reaction with the colour developer(s),

and

one, two or more compounds selected from the group consisting of zinc salts, ammonium salts and zinc oxide, preferably selected from the group consisting of zinc carbonate, zinc oxide, ammonium hydrogensulfate, ammonium nitrate, ammonium hydrogenphosphate and zinc acetate. Notwithstanding the prior art achievements described above, there continues to be an unmet need for further heat-sensitive recording materials for various uses that, owing to high sales volumes in a vigorously contested market, have to be obtainable at low manufacturing costs and hence have to have a simple construction and should be biodegradable, at least partly, preferably very substantially, but more preferably ideally fully. A further challenge, especially when partial, preferably very substantial, but more preferably ideally full biodegradability is required, consists in a printed heat-sensitive recording material being exposed to a multiplicity of different environmental influences, such as moisture, heat or chemicals, in the course of its typical use as lottery ticket, entrance ticket, travel ticket, pay & display car park ticket and the like. In addition, the composition or the heat-sensitive recording material shall be obtainable at commercially acceptable expense.

This is because, during their normal use, heat-sensitive recording materials may come into contact with a multiplicity of different substances that can affect the durability of the thermal printout. These, in addition to water and organic solvents, also include fats and oils which, for example, are present in hand care products and may become transferred to the heat-sensitive recording material on touching the latter. Particularly the durability against fats and oils is therefore very relevant.

As well as durability to chemicals that may come into contact with the heat-sensitive recording materials, they also have to be very durable to thermal influences. On the one hand, the heat-sensitive recording material should be easily and energy-sparingly printable in order that little energy is consumed in the case of mobile applications for example. On the other hand, the printed image should last after printing and the action of heat should cause neither the printed image to fade nor the unprinted background to discolour, resulting in the print ceasing to be legible. Pay & display car park tickets, which, once printed, are displayed behind the windscreen and thereby become exposed in the summer to high temperatures and direct sunlight, are an example of where thermal durability is extremely relevant.

Similarly with tickets such as concert tickets or flight tickets, which are frequently generated a long time in advance, or with purchase receipts, which are needed as proof of purchase throughout a long guarantee period, the durability of the heat-sensitive recording material is very important. Especially when it has to be supposed that the heat- sensitive recording materials may come into contact with moisture, for example when the recording materials used as concert ticket, flight ticket or purchase receipt are kept close to the body (in the trouser pocket for example) and thereby may come into contact with perspiration, it has to be ensured that the recording materials remain readily legible even after any contact with moisture.

In addition to the unprinted heat-sensitive recording materials there are also printed heat- sensitive recording materials - used as flight tickets and entrance tickets for example - which are offset printed in particular. Here the heat-sensitive recording material is initially printed in a large number of copies with any unalterable data, for example with the company logo, pictures and text to create a heat-sensitive blank (a ticket blank for example). The heat-sensitive blanks obtained are loaded into a thermal printer at the point of sale and can then be individually thermoprinted with data before the individualized recording material is handed to the final customer. These data may vary with every printing operation, for example in date, event name, seat number, card number, mass, price, etc.

In the context of the present text, a distinction is made between printing of heat-sensitive recording materials (or multilayer films) by the application of printing inks to the surface of the heat-sensitive recording material, for example by offset printing, and the thermal printing of heat-sensitive recording materials by the application of heat. The application of heat, for example by use of a thermal print head as constituent part of a thermal printer, induces colour formation via a chemical reaction of the dye precursor.

It has transpired that the usable thermal print results which recording materials incorporating (colour) developers as described for example in EP 2 574 645 A1 and/or EP 2 784 133 A1 do provide are often insufficiently satisfactory, if at all, in commercial practice when judged by the high commercial expectations of the quality of the thermal printout and the durability to environmental influences.

The as yet unpublished European patent application 17150842.7 of 10 January 2017 discloses novel compounds potentially useful as (colour) developers. Thus, this as yet unpublished European patent application describes a lactide-based agent which on heating is ca able of reacting with a leucodye, wherein the agent conforms to "Formula (I)":

Formula (I) where R1 and R2 are each independently a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group or a halogen atom; R3, R4, R5 and R6 are each independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group; X is O, S or NH; and a and b are integers satisfying the conditions a > 0, b > 0 and (a + b) > 1. The unpublished patent application referred to also describes a method of forming such compounds, which comprises the reaction of i) a compound of the formula

where R5 and R6 are each independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyi group or a C2-C6 alkenyl group; X is O, S or NH; and ii) a cyclic ester of a hydroxy carboxylic acid having the formula

where R3 and R4 are each independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyi group or a C2-C6 alkenyl group, to obtain initially a compound conforming to "Formula (II)":

Formula (II) where R3, R4, R5 and R6 are each independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyi group or a C2-C6 alkenyl group; X is O, S or NH; and a and b are integers satisfying the conditions a > 0, b > 0 and (a + b) > 1 . The above method is then followed by a method of forming the agent of "Formula (I)", said method comprising the steps of: a) providing a compound of "Formula (II)"; and b) reacting the said compound with at least one sulfonyl isocyanate of "Formula (III)":

O

Formula (III) where R is a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group or a halogen atom. The first stage of this process may lead to the formation of polymeric blocks of unit lengths a and b via a ring-opening reaction or a ring-opening polymerization of the cyclic ester by using a suitable ionic or non-ionic catalyst, as described in "Ring Opening Polymerization", Vol. I, pages 461-521 , K.J. Ivin and T. Saegusa (1984). The ring-opening or polymerization reaction may be carried out at room temperature, but is preferably carried out by heating at a temperature of 100 to 200 °C or of 130 to 190 °C. When the temperature is lower than 100 °C, the reaction rate is disadvantageous^ low. When on the other hand the temperature is higher than 200 °C, the oligomer degradation rate is increased and low molecular weight components may vaporize. What is important is that the reaction should be carried out under anhydrous conditions and in the absence of further compounds having an active hydrogen atom. Exposure to atmospheric moisture may be avoided by providing an inert, dry gaseous blanket to the reaction vessel. The intermediate of "Formula (II)" and one or more compounds of "Formula (III)" are reacted in the second stage of the process. Preferably, a single compound of "Formula (III)" is reacted such that the resulting terminal groups of the reactive agent ("Formula (I)") are identical. This second stage - nominally the formation of a sulfonylurethane - is an addition reaction and not a polymerization reaction; it is therefore the molecular weights of the intermediate ("Formula (II)") and of the or each compound of "Formula (III)" which determine the molecular weight of the reaction product, the compound of "Formula (I)". Exemplary compounds of "Formula (III)" include phenylsulfonyl isocyanate, toluenesulfonyl isocyanate and chlorophenylsulfonyl isocyanate. Methods of forming suitable aromatic sulfonyl isocyanates and their chemical behaviour are described inter alia in: H. Ulrich Chem. Soc. Rev. 65, pages 369-376 (1965); U.S. Patent No. 2,666,787 (US 2,666,787 A); and U.S. Patent No. 3,484,466 (US 3,484,466 A). The reaction of the second stage is typically carried out in an organic solvent and under anhydrous conditions. The intermediate of "Formula (II)" is dispersed in a suitable organic solvent and then the sulfonyl isocyanate is admixed under agitation either in pure form or in solution. For example, the reaction of the second stage may be carried out at a temperature of 30 °C or 40 °C to 80 °C and either a certain amount of reaction vessel cooling or the introduction of the reactants at a slow rate of admixture may be required in order that such low temperatures may be maintained given the exothermic nature of the reaction.

There continues to be a great need for an improvement in the thermal printout of recording materials comprising (colour) developers based on lactic acid units, particularly as regards the quality of the thermal printout and/or the durability to various environmental influences. The problem addressed by the present invention is therefore that of providing a heat-sensitive recording material comprising at least one (colour) developer based on lactic acid units, and displaying improved properties especially as regards the quality of the thermal printout and/or the durability to various environmental influences.

A preferable embodiment of the invention shall more particularly provide a heat-sensitive recording material which, in the printed state, also has good durability to fats and oils.

This problem is solved by a coating composition for forming a heat-sensitive recording material or a heat-sensitive recording layer, comprising one or more dye precursors; and

one or more than one colour developer, wherein the one or at least one colour developer of the two or more colour developers is a compound which in the colour developer contains

a) at least one (linear) structural unit of lactic acid

and

b) two mutually independent terminal electron acceptor groups, wherein the one or the at least one colour developer of the two or more colour developers is a compound of formula (B-l),

(B-l),

where X is O, S or NH; R1 and R2 are each independently a hydrogen atom, a C1 -C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group; R3 and R4 are each independently a hydrogen atom, a C1 -C6 alkyl group, a C1 -C6 alkoxy group or a halogen atom ; and a and b are each an integer and satisfy the conditions a > 0, b > 0 and (a+b) > 1 .

It may be preferable in some cases for the colour developer to contain at least one of the terminal electron acceptor groups with one of the structural units of formula (lb),

Lactic acid and compounds derived therefrom (including, for example, lactates, lactoyllactic acid , lactide) and polymers and/or oligomers (e.g. polylactic acids, also called polylactides (PLAs)) are already well known in the prior art. Lactic acid is a hydroxy carboxylic acid having a hydroxyl group as well as a carboxyl group and therefore is known inter alia as 2-hydroxypropionic acid and has the lUPAC nomenclature name of 2-hydroxypropanoic acid . The salts and esters of lactic acid are known as lactates. Customary names for lactic acid in the prior art are: 2-hydroxypropanoic acid, 2-hydroxypropionic acid , (R)-lactic acid, (S)-lactic acid, (RS)-lactic acid, DL-lactic acid, (±)-lactic acid, and E 270. Owing to their differing optical activity, D-(-)-lactic acid (interchangeably: (R)-lactic acid) and L-(+)-lactic acid (interchangeably: (S)-lactic acid) are also referred to as laevorotatory lactic acid and dextrorotatory lactic acid, respectively. Racemic lactic acid is a 1 : 1 mixture of (R)- and (S)-lactic acid (D-/L-lactic acid). Lactic acid appears under the following Chemical Abstracts Service Registry Numbers: CAS® RN 50- 21 -5 (lactic acid, general), CAS® RN 598-82-3 (dl-form), CAS® RN 10326-41 -7 (d-form) and CAS RN 79-33-4 (l-form). The Chemical Abstracts Service Registry Number, CAS^® RN is a designation for a Registry Number (RN) used by the Chemical Abstracts Service (CAS) since 1965 to unambiguously identify chemical entities.

Lactic acid is capable of intermolecular formation of esters. Water is eliminated to form, for example as a dimer, lactoyllactic acid which on prolonged standing or on heating undergoes further esterification to polylactic acid. Lactic acid is manufactured industrially, particularly for use in the food industry and also for formation of polylactides (PLAs; also: polylactic acids). Lactic acid is preferably produced biotechnologically via a fermentation of carbohydrates (sugar, starch). About 70 to 90 % of current global lactic acid production is by the fermentative route. In addition, lactic acid can also be manufactured synthetically on the basis of petrochemical feedstocks (acetaldehyde). On a large industrial scale, only the synthesis of lactic acid from acetaldehyde with hydrogen cyanide via lactonitrile is of any importance. The latter is hydrolysed via the use of hydrochloric acid, producing ammonium chloride as well as lactic acid. Lactic acid is the monomer of the polylactides or polylactic acids (PLAs), which are widely used as biodegradable bioplastics. PLA is biodegradable by virtue of its molecular structure, although certain environmental conditions are needed for biodegradability, which are generally found in industrial composting facilities.

Lactide is the cyclic diester of lactic acid and used as starting material in the industrial production of polylactides (polylactic acids). Lactide is obtainable by acid-catalytic condensation of lactic acid. Industrially, however, it is these days mostly derived biotechnologically from glucose and molasses. Since lactide contains two stereocentres each substituted by analogous moieties, there are three isomeric lactides: (S,S)-lactide, (R.R)-lactide and (meso)-lactide. The lactide of the natural L-lactic acid [interchangeably: (S)-lactic acid] has (S,S)-configuration. (R.R)-Lactide and (meso)-lactide are not very important by comparison with (S.S)-lactide. Lactide is a colourless, odourless powder which on contact with water immediately hydrolyses into lactic acid. The lactide [or more precisely: the (S,S)-lactide] of L-lactic acid converts into polylactide by ionic polymerization.

Polylactides, also called polylactic acids (PLAs for short), are synthetic polymers which are members of the family of polyesters. They are constructed of chemically interbonded lactic acid molecules. So the customary designation of "polylactic acid" is actually misleading, since what it refers to is not a polymer having a plurality of acidic groups. Polylactides are by virtue of the asymmetrical carbon atom optically active polymers and exist in the form of D- or as L-lactides depending on whether they derive from L-(+)-lactic acid [interchangeably: (S)-(+)-lactic acid] or from D-(-)-lactic acid [interchangeably: (R)-(- )-lactic acid].

The properties of polylactides depend chiefly on the molecular mass, the crystallinity and the proportion of any copolymer. A higher molecular mass raises the glass transition and melting temperatures, the tensile strength and also the modulus of elasticity (E-modulus) and lowers the elongation at break. The methyl group renders the material water-repellent (hydrophobic), thereby reducing the water absorption and thus also the hydrolysis rate of the principal bonding. Polylactides are further soluble in many organic solvents (e.g. dichloromethane, trichloromethane; it can be reprecipitated by admixing a solvent such as ethanol in which the polylactide is less soluble). PLA has numerous properties making it advantageous for many and varied fields of use: A low degree of moisture absorption coupled with a high capillary effect, hence suitable for sports and functional apparel. A low flammability, high UV resistance and colour fastness. Moreover, the density of PLA is relatively low. Bending strength is 0.89-1 .03 MPa. UV resistance is to be understood as meaning that PLA-based products can be exposed to sunlight and other sources of ultraviolet radiation (UV radiation) without being damaged by being irradiated. UV radiation refers to that part of the electromagnetic spectrum between visible light and x- rays.

Polylactides and polylactic acids are obtainable by different methods of synthesis. Polylactides are chiefly obtainable by the ionic polymerization of lactide, a ring-shaped union of two lactic acid molecules. Whereas polylactides are produced by ring-opening polymerization, polylactic acids are formed by direct condensation reactions. Conversion of lactide (left) into polylactide (right) by thermal and catalytic ring-opening polymerization. The formation of polylactides and/or polylactic acids is described in the prior art; see for instance D. Garlotta, "A Literature Review of Poly(Lactic Acid)", Journal of Polymers and the Environment, Vol. 9, No. 2, April 2001 , 63-84 (© 2002). The conditions, especially the temperatures, in the formation of polylactides and/or polylactic acids (i.e. in the "lactide polymerization") are dependent on the catalysts used for polymerization. A ring-opening polymerization will take place for example at temperatures between 120 and 150 °C and also through the agency of catalytic tin compounds (e.g. tin oxide). Temperatures can be for example T < 100 °C for cationic polymerization and T ^« 120 °C for anionic polymerization. This gives rise to plastics having a high molecular mass and strength. Lactide itself is obtainable by fermentation of molasses or glucose using various bacteria. In addition, high molecular weight and pure polylactides are obtainable directly from lactic acid by using the so-called polycondensation. At industrial scale, however, the disposal of the solvent is problematic.

According to the invention, a coating composition for forming a heat-sensitive recording material or a heat-sensitive recording layer as defined above may be preferable wherein the one or the at least one colour developer of the two or more colour developers of formula (B-l) is a compound which contains a structural unit of formula (B-lc),

where X is O, S or NH and R1 and R2 are each independently a hydrogen atom, a methyl group, preferably a hydrogen atom. It is thus selected iminourea-, urea- or thiourea- containing colour developer structures which are present in the invention.

According to the invention, a coating composition or heat-sensitive recording layer as defined above, comprising a colour developer of formula (B-l) may be preferable wherein the colour developer has one or two terminal electron acceptors having a structural unit of formula (B-lb),

The preference in the invention is in some cases for a coating composition or heat-sensitive recording layer as defined above wherein the particle sizes, measured by laser diffraction for the one or at least one of the more than one colour developers are each independently in the range from 0.5 to 10 μιτι, preferably in the range from 0.8 to 8 μιτι and more preferably in the range from 0.8 to 4 μητι.

The preference in the invention is in some cases for a coating composition or heat-sensitive recording layer as defined above wherein the particle sizes measured as the X50 value by laser diffraction for the one or at least one of the more than one colour developers are each independently in the range from 0.8 to 2 μιτι, preferably in the range from 0.85 to 1 .7 μιτι and more preferably in the range from 0.85 to 1 .65 μιτι.

The particle sizes can be determined by use of laser diffraction (HELOS particle size analysis). An R1 Helos (H1453) & Quixel instrument from Sympatec GmbH was used in the context of the invention (analysis by WINDOX 4).

The average particle size can be determined by particle size analysis in the laser diffraction method of DIN/ISO 13320-1 [1999].

A laser scattered light spectrometer operates in the measurement range from 0.01 μιτι to 3000 μιτι on the basis of the statistical laser light scattering standardized in DIN/ISO 13320-1 [1999]. The instrument does not have to be reset for this. The automated measurement is prepared by placing the particle sample into a circulation unit for wet measurement. An integrated ultrasonic probe prevents particle reticulation and makes an external form of sample preparation superfluous. The interaction of laser light with particles creates, by diffraction, refraction, reflection and absorption, scattered light patterns characteristic of the particle size. Mie theory allows the particle size distribution to be deduced from these scattered light patterns.

In laser diffraction, particle size distributions are determined by measuring the angle dependence of the intensity of scattered light from a laser beam passing through a dispersed silica particle sample. Large particles here scatter light at small angles relative to the laser beam, whereas small particles lead to large scattering angles. The data for the angle-dependent scattered light intensity are analysed and used as a basis for computing the size of the particles responsible for the diffraction pattern. Mie theory is used for this. The particle size is reported as the diameter of the sphere having the same volume. The scattered light theory developed by Mie in 1908 is based on the supposition that the scattered light pattern generated by a particle displays characteristic features which, given knowledge of the optical parameters, enable an unambiguous assignment of size. Fraunhofer analysis is available for particles distinctly larger than 10 to 20 μιη for simplicity because only light diffraction is analysed and hence the correct optical parameters are not needed. It may be preferable in the invention for the subject invention coating composition or heat- sensitive recording layer as defined above to contain at least one further colour developer from the prior art.

The preference of the invention is for a coating composition or heat-sensitive recording layer as defined above comprising at least one colour developer which is a phenol-free compound. The at least one colour developer is then a so-called phenol-free colour developer. The term "phenol-free compound" herein also comprehends mixtures of phenol-free compounds and/or the term "phenol-free colour developer" herein also comprehends mixtures of phenol-free colour developers. By "phenol-free compound" and/or "phenol-free colour developer" are meant such compounds which as degradation products preferably release nothing by way of phenols into the environment, but at least not significant amounts of phenols, i.e. amounts of phenols which impair the environment and/or are at most below statutory limiting values. This is desirable because biodegradability is very poor for many phenols while phenols are very harmful to water courses and even in minimal concentrations impair the taste of water and fish. Phenols therefore have to be very substantially removed from wastewater.

The invention therefore in some cases provides with preference a coating composition or heat-sensitive recording layer as defined above comprising at least one phenol-free colour developer or a mixture of phenol-free colour developers. For example, a sometimes preferred coating composition or heat-sensitive recording layer containing at least one phenol-free colour developer may in addition to the compound of formula (B-l) include one or more further non-phenolic colour developers, preferably selected from the group of sulfonylureas, more preferably N'-(p-toluenesulfonyl)-N'-phenylurea, N-(p- toluenesulfonyl)-N'-3-(p-toluenesulphonyloxyphenyl)urea (A/-(4-methylphenylsulfonyl)-/V- (3-(4-methylphenylsulfonyloxy)phenyl)urea, Pergafast^® 201 ), and/or 4,4'-bis(p- tolylsulfonylureido)diphenylmethane, and/or, for example, 4-methyl-N-(2-(3-phenylureido)- phenyl)benzenesulfonamide and/or N-(2-(3-phenylureido)phenyl)benzenesulfonamide (NKK). NKK has an alpha form and a beta form, the alpha form having a melting point of 158 °C and the beta form having a melting point of 175 °C. Furthermore, NKK alpha is in a crystalline form having an absorption band at 3322 and 3229 cm^"1 in the IR spectrum and NKK beta is in a crystalline form which has an absorption band at 3401 ±20 cm^"1 in the IR spectrum. The preference of the present invention may thus be for a coating composition or heat- sensitive recording layer as defined above that further contains at least one further colour developer of formula (B-l I) ,

The compound of formula (B-l I) is likewise already known, being described in EP 2 923 851 A1 for example. It is marketed under the designation NKK (N-(2-(3- phenylureido)phenyl)benzenesulfonamide). The addition of minimal amounts of the compound of formula (B-l I) to the subject invention compound of formula (B-l) may, if necessary or desired, stabilize an even already good durability to moisture for even prolonged periods, so this durability to moisture is maintained.

The preference of the present invention may thus be for a coating composition or heat- sensitive recording layer as defined above that further contains at least one further colour developer of formula B-l II),

The compound of formula (B-lll) is the already known compound Λ/-(4- methylphenylsulfonyl)-/V-(3-(4-methylphenylsulfonyloxy)phenyl)urea, which is marketed under the designation Pergafast^® 201 and is described in EP 1 140 515 B1 for example. Pergafast^® 201 is the most frequently used phenol-free colour developer. The addition of minimal amounts of the compound of formula (B-XVI) to the subject invention compound of formula (B-l) or of formula (B-l I) may, if necessary or desired, improve the durability to fats and oils.

The preference of the invention is likewise in some cases for a coating composition or heat-sensitive recording layer according to an above described and defined type wherein the proportion of the colour developer of a colour developer mixture in the coating composition or heat-sensitive recording layer is, for example, at least 10 wt.%, especially at least 15 or 20 wt.%, and/or up to not more than 65 wt.%, especially up to not more than 60 wt.%, and preferably is 24 to 60 wt.%, preferably 35 to 58 wt.%, more preferably 39 to 56 wt.%, based on the entire solids content of the coating composition or heat-sensitive recording layer.

The preference of the invention is further for a coating composition or heat-sensitive recording layer as defined above and additionally comprising one or more constituents from the group consisting of sensitizers, pigments, dispersants, antioxidants, release agents, defoamers, light stabilizers and brighteners.

The preference of the invention is further for a coating composition or heat-sensitive recording layer as defined above and independently or combined with an above coating composition or heat-sensitive recording layer additionally comprising one or more constituents from the group consisting of sensitizers, pigments, dispersants, antioxidants, release agents, defoamers, light stabilizers and brighteners, wherein the coating composition or heat-sensitive recording layer comprises a sensitizer selected from the group consisting of benzyl naphthyl ether (BNE), diphenyl sulfone (DPS), ethylene glycol m-tolyl ether (EGTE), ethylene glycol phenoxyethane (EGPE), 1 ,2-di(m- methylphenoxy)ethane (DMPE) and 1 ,2-diphenoxyethane (DPE), or a combination thereof.

It may be particularly preferable in the present invention for pigments to be provided in the coating composition on a regular basis in order that favourable values may be obtained and ensured for the customary paper parameters.

The preference of the present invention is for a coating composition or heat-sensitive recording material wherein the supporting substrate is paper, synthetic paper or self- supporting polymeric film/sheeting. Coating basepaper which has not been surface treated is particularly preferable for use as supporting substrate by reason of its good recyclability and good environmental compatibility. Coating basepaper which has not been surface treated is coating basepaper which has not been treated in a size press or in a coating apparatus. Self-supporting film/sheeting of polypropylene or other polyolefins are preferable for use as self-supporting polymeric film/sheeting. The preference of the present invention is also for papers coated with one or more polyolefins (especially polypropylene).

In one embodiment, the supporting substrate is paper having a recycled-fibre content of not less than 70 wt.%, based on the overall fibre content of the paper. The preference of the present invention is for a heat-sensitive recording material additionally comprising an interlayer between the supporting substrate and the heat- sensitive recording layer, wherein the interlayer preferably contains pigments. The pigments may comprise organic pigments, inorganic pigments or a mixture of organic pigments and inorganic pigments.

In a preferred embodiment of the invention, the basis weight of the interlayer is in the range from 5 to 20 g/m², preferably in the range from 7 to 12 g/m².

When the interlayer contains pigments, preference in one embodiment of the invention is for organic pigments, preferably hollow-body organic pigments. ln-house studies have shown that the incorporation of organic pigments in the interlayer is advantageous because organic pigments have a high heat reflection capacity. An increased level of heat reflection for the interlayer endowed with organic pigments enhances the heat response of the heat-sensitive recording layer, since incident thermal radiation is at least partly reflected into the heat-sensitive recording layer instead of being conducted onto the supporting substrate. As a result, the sensitivity and the resolving power of the heat-sensitive recording material are distinctly up and the printing speed in the thermal printer is also increased. In addition, energy consumption during printing decreases, which is advantageous with mobile devices in particular. Hollow-body pigments contain air on the inside, as a result of which they typically have a still higher level of heat reflection and the sensitivity and the resolving power of the heat-sensitive recording material are still further enhanced.

When the interlayer contains pigments, the preference of an alternative embodiment of the invention is for the pigments to comprise inorganic pigments, preferably selected from the list consisting of calcinated kaolin, silica, bentonite, calcium carbonate, alumina and boehmite.

When inorganic pigments are incorporated in the interlayer between the recording layer and the substrate, these pigments are capable, at the script formation stage, of absorbing the constituents (waxes for example) of the heat-sensitive recording layer which are liquefied by the heating effect of the thermal head, and thereby promote a yet faster and more consistent performance of the heat-induced recording. Calcinated kaolin will be found particularly advantageous owing to its large absorption reservoir in the cavities. Mixtures of two or more different inorganic pigments are also conceivable.

The quantitative ratio between organic and inorganic pigment is a compromise between the effects engendered by the two types of pigment, which is resolved in a particularly advantageous manner when the pigment mixture consists to 5-30 wt.% or preferably to 8-20 wt.% of organic pigment and to 95-70 wt.% or preferably to 92-80 wt.% of inorganic pigment. Pigment mixtures of different organic pigments and/or inorganic pigments are conceivable. The preference of the present invention is a coating composition or heat-sensitive recording material wherein the interlayer in addition to the inorganic and/or organic pigments optionally contains at least one binder preferably based on a synthetic polymer, in which case styrene-butadiene latex delivers particularly good results. The use of a synthetic binder admixed with at least one natural polymer, such as, with particular preference, starch, constitutes a particularly suitable embodiment. Tests involving inorganic pigments have further shown that a binder-pigment ratio between 3:7 and 1 :9 within the interlayer, both based on wt.% in the interlayer, constitutes a particularly suitable embodiment.

The preference of the present invention is a coating composition or heat-sensitive recording material wherein the colour former is selected from derivatives of compounds from the group consisting of fluoran, phthalide, lactam, triphenylmethane, phenothiazine and spiropyran.

In-house studies have shown that these colour formers have particularly good properties in combination with the colour developer mixture used according to the present invention. A preferred coating composition or heat-sensitive recording material in the present invention preferably includes colour former compounds of the fluoran type selected from the group consisting of 3-diethylamino-6-methyl-7-anilinofluoran, 3-diethylamino-6- methyl-7-(3'-methylphenylamino)fluoran (6'-(diethylamino)-3'-methyl-2'-(m-tolylamino)-3H- spiro[isobenzofuran-1 ,9'-xanthen]-3-one; ODB-7), 3-di-n-pentyl-amino-6-methyl-7- anilinofluoran, 3-(diethylamino)-6-methyl-7-(3-methylphenylamino)fluoran, 3-di-n- butylamino-7-(2-chloranilino)fluoran, 3-diethylamino-7-(2-chloranilino)fluoran, 3-diethyl- amino-6-methyl-7-xylidinofluoran, 3-diethylamino-7-(2-carbomethoxyphenylamino)fluoran, 3-pyrrolidino-6-methyl-7-anilinofluoran, 3-pyrrolidino-6-methyl-7-(4-n-butyl- phenylamino)fluoran, 3-piperidino-6-methyl-7-anilinofluoran, 3-N-n-dibutylamin-6-methyl- 7-anilinofluoran (ODB-2), 3-(N-methyl-N-cyclohexyl)amino-6-methyl-7-anilinofluoran, 3- (N-Methyl-N-propyl)amino-6-methyl-7-anilinofluoran, 3-(N-methyl-N-tetrahydrofurfuryl)- amino-6-methyl-7-anilinofluoran), 3-(N-ethyl-N-isoamyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-tolyl)amino-6-methyl-7-anilinofluoran, 3-(N-ethyl-N-tetrahydrofuryl)amino-6- methyl-7-anilinofluoran, 3-(N-ethyl-N-isopentylamino)-6-methyl-7-anilinofluoran, 3-(N- ethyl-4-toluidino)6-methyl-7-(4-toluidino)fluoran and 3-(N-cyclopentyl-N-ethyl)amino-6- methyl-7-anilinofluoran.

Preference is likewise given to coating compositions or heat-sensitive recording materials of the present invention which contain the colour former compounds recited in paragraphs [0049] to [0052] of EP 2 923 851 A1 .

The invention gives particular preference to a coating composition or heat-sensitive recording material wherein the colour former is selected from the group consisting of 3-N-di-n-butylamine-6-methyl-7-anilinofluoran (ODB-2) and 3-(N-ethyl-N-isopentylamino)- 6-methyl-7-anilinofluoran.

The preference in the invention is a coating composition or heat-sensitive recording material wherein the coating composition or heat-sensitive recording layer contains a sensitizer.

When a sensitizer is used, the sensitizer first melts during the supply of heat during the printing process and the molten sensitizer dissolves the colour former and colour developer compounds present side by side in the coating composition or heat-sensitive recording layer, and/or lowers the melting temperature of the colour former and colour developer compounds to induce a colour-developing reaction. The sensitizer itself plays no part in the colour-developing reaction.

Sensitizer accordingly refers to substances used to establish the melting temperature of the coating composition or heat-sensitive recording layer and preferably capable of establishing a melting temperature of about 70 to 80 °C, without the sensitizers themselves participating in the colour-developing reaction.

Useful sensitizers for the purposes of the present invention include, for example, fatty acid salts, fatty acid esters and fatty acid amides (e.g. zinc stearate, stearamide, palmitamide, oleamide, lauramide, ethylene- and methylenebisstearamide, methylolstearamide), naphthalene derivatives, biphenyl derivatives, phthalates and terephthalates.

The invention has a particular preference for a coating composition or heat-sensitive recording material wherein the sensitizer is selected from the group consisting of 1 ,2- bis(3-methylphenoxy)ethane (other names: 3,3'-(ethylenebisoxy)bistoluene, 1 ,2-bis(3- methylphenyloxy)ethane (DMPE), ethylene glycol m-tolyl ether (EGTE) [1 ,2-di(m- methylphenoxy)ethane (DMPE, CAS^® RN is according to DB "Chemical Book" another name for EGTE)], 1 ,1 '-[1 ,2-ethanediylbis(oxy)]bis[3-methylbenzene, CAS^® RN 54914-85- 1 ), 1 ,2-diphenoxyethane (diphenoxyethane (DPE, optionally also known under the abbreviation of "EGPE"), CAS^® RN 104-66-5), 2-(2H-benzotriazol-2-yl)-p-cresol, 2,2'- bis(4-methoxyphenoxy)diethyl ether, 4,4'-diallyloxydiphenyl sulfone, 4- acetylacetophenone, 4-benzybiphenyl, acetoacetanilides, benzyl naphthyl ether (BNE, benzyl 2-naphthyl ether), benzyl 4-(benzyloxy)benzoate, benzylparaben, bis(4- chlorobenzyl) oxalate ester, bis(4-methoxyphenyl) ether, dibenzyl oxalate, dibenzyl terephthalate, dimethyl terephthalate (DMT), dimethyl sulfone, diphenyl adipate, diphenyl sulfone, ethylene glycol m-tolyl ether (EGTE), ethylenebisstearaminde, fatty acid anilides, m-terphenyl, N-hydroxymethylstearamide, N-methylolstearamide, N-stearylurea, N- stearylstearamide, p-benzylbiphenyl, phenyl benzenesulfonate ester, salicylanilide, stearamide and α,α'-diphenoxyxylene, of which benzyl naphthyl ether (BNE), diphenyl sulfone (DPS), ethylene glycol m-tolyl ether (EGTE), 1 ,2-di(m-methylphenoxy)ethane (DMPE) and 1 ,2-diphenoxyethane (DPE) are particularly preferable.

Preference is likewise given to coating compositions or heat-sensitive recording materials of the invention which contain the sensitizer compounds recited in paragraphs [0059] to [0061 ] of EP 2 923 851 A1 .

In a first preferred embodiment, these sensitizers are each used alone, that is to say, not in combination with the other named sensitizers from the above list. A second, equally preferred embodiment incorporates two or more sensitizers selected from the above list in the coating composition or heat-sensitive recording layer.

The preference of the invention is for a coating composition or heat-sensitive recording material wherein the sensitizer has a melting point of 60 °C to 180 °C, preferably a melting point of 80 °C to 140 °C. Coating compositions or heat-sensitive recording materials are preferable if desired when the heat-sensitive recording layer contains a binder, preferably a crosslinked or uncrosslinked binder selected from the group consisting of polyvinyl alcohol, carboxyl- modified polyvinyl alcohol, ethylene-vinyl alcohol copolymer, a combination of polyvinyl alcohol and ethylene-vinyl alcohol copolymer, polyvinyl alcohol modified with silanol groups, diacetone-modified polyvinyl alcohol, acrylate copolymer and film-forming acrylic copolymers.

The coating compound for forming the heat-sensitive recording layer of the heat-sensitive recording material of the present invention and/or the heat-sensitive recording material of the present invention, in addition to one or more binders, preferably contain one or more crosslinking agents for the binder or binders. The crosslinking agent is preferably selected from the group consisting of zirconium carbonate, polyamideamine epichlorohydrin resins, boric acid, glyoxal, dihydroxybis(ammonium lactato)titanium(IV) (CAS^® RN 65104- 06-5; Tyzor LA) and glyoxal derivatives.

In a coating composition of the present invention or in a heat-sensitive recroding material according to the present invention whose heat-sensitive recording layer has been formed from such a coating compound containing one or more binders and one or more crosslinking agents for the binder or binders, the heat-sensitive recording layer contains one or more binders crosslinked by reaction with one or more crosslinking agents, said crosslinking agent or agents being selected from the group consisting of zirconium carbonate, polyamideamine epichlorohydrin resins, boric acid, glyoxal, dihydroxybis(ammonium lactato)titanium(IV) (CAS^® RN 65104-06-5; Tyzor LA) and glyoxal derivatives. By "crosslinked binder" here is meant the reaction product formed by reacting a binder with one or more crosslinking agents.

The preference of the invention is in some cases likewise for a coating composition or heat-sensitive recording layer of a type described and defined above wherein the proportion of the colour developer or of a colour developer mixture in the coating composition or heat-sensitive recording layer is for example at least 10 wt.%, especially at least 15 or 20 wt.%, and/or up to not more than 65 wt.%, especially up to not more than 60 wt.%, and preferably 24 to 60 wt.%, more preferably 35 to 58 wt.%, more preferably 39 to 56 wt.%, based on the entire solids content of the coating composition or heat-sensitive recording layer. The preference of the invention is for a coating composition or heat-sensitive recording material wherein the basis weight of the heat-sensitive recording layer is in the range from 1 .5 to 8 g/m², preferably in the range from 1 .5 to 6 g/m², more preferably in the range from 2 to 6 g/m² and yet more preferably in the range from 2.0 to 5.5 g/m². Recording materials according to the invention may additionally also employ image stabilizers, dispersants, antioxidants, release agents, defoamers, light stabilizers, brighteners as known in the prior art. Every one of the components is typically used in an amount of 0.01 to 15 wt.%, especially - with the exception of defoamer - 0.1 to 15 wt.%, preferably 1 to 10 wt.%, based on the entire solids content of the heat-sensitive recording layer. When defoamers are used in the respective recipes, the recording materials of the invention may contain the defoamer in amounts of 0.03 to 0.05 wt.%, based on the entire solids content of the heat-sensitive recording layer.

In one embodiment, the invention also provides a coating colour for forming a coating composition or a heat-sensitive recording layer, comprising - one or more dye precursors; and one or more than one colour developer, wherein the one or at least one colour developer of the two or more colour developers is a compound as defined herein for the purposes of the invention.

The term "coating colour" here refers to a technical term familiar in the paper industry in relation to the production of coated papers. The term "coating colour" (also coating compound or coating mix) is familiar in the paper industry and refers to coating media containing or consisting of pigments, binders and additives which are coated on the paper surface using specific coating machines to surface finish the paper. These papers are referred to as "coated papers" and are notable for superior printability and haptics. The term "coating colour" is thus the hypernym for all coatable mixes, compounds, preparations and/or solutions in the paper industry. The precoat or intercoat is therefore a particular embodiment of a coating colour, namely that which is the first to be applied to the paper substrate. The next coat or layer applied is frequently a coating colour as functional coating, for example in order to provide a thermal functionality or a barrier functionality. The next layer or coat which may optionally be applied is a coating colour for the purpose of establishing a protective function, for example a protective topcoat layer. Alternatively, it is possible for example to coat a thermal layer with a silicone-containing coating colour to form a release layer. A silicone-containing coating colour may alternatively also be coated on a protective layer. The paper substrate side opposite the silicone-containing layer is frequently coated with an adhesive-containing coating colour. The application of the adhesive-containing coating colour may likewise be preceded by the application to the paper substrate of a coating colour as precoat.

A coating colour in the context of the present invention is to be understood as of the present invention when it can be applied as a functional coating to a substrate which may optionally already display one or more precoats, in order to provide on the substrate a thermal functionality, i.e. such a coating colour of the present invention comprises one or more dye precursors; and one or more than one colour developer, wherein the one or at least one of the more than one colour developers is a compound as defined herein as being of the present invention.

To coat the coating colour on a supporting substrate, various coating techniques are known to a person skilled in the art, examples being: blade coating, film press coating, cast coating, curtain coating, spray coating.

In a further embodiment, the invention provides a heat-sensitive material comprising a supporting substrate, and a heat-sensitive recording layer as defined herein for the purposes of the invention.

The preference of the invention is for an above heat-sensitive recording material additionally containing an interlayer between the supporting substrate and the heat- sensitive recording layer, wherein the interlayer preferably contains pigments. The preference is further for a subject invention heat-sensitive recording material wherein the pigments comprise a) organic pigments, preferably hollow-body organic pigments and/or b) inorganic pigments, preferably selected from the list consisting of calcinated kaolin, silica, bentonite, calcium carbonate, alumina and boehmite.

In one embodiment of the subject invention heat-sensitive recording material, the heat- sensitive recording layer is wholly or partly covered by a protective layer. The application of a protective layer covering the heat-sensitive recording layer also shields the heat- sensitive recording layer towards the outside and/or towards the supporting substrate of the next ply within a roll, protecting it from external influences.

A protective layer of this type, in addition to protecting from environmental influences the heat-sensitive recording layer arranged underneath the protective layer, frequently in such cases has the additional positive effect of improving the printability of the subject invention heat-sensitive recording material particularly in indigo, offset and flexographic printing. It may therefore be desirable for certain application scenarios that the heat- sensitive recording material of the present invention should have a protective layer even though the presence of a colour developer mixture as above defined in the heat-sensitive recording layer of the heat-sensitive recording material of the present invention ensures that the durability to entities selected from the group consisting of water, alcohols, fats, oils and mixtures thereof for a thermal printout obtainable on a heat-sensitive recording material of the present invention is already sufficient even without protective layer.

The protective layer of the heat-sensitive recording material according to the present invention preferably contains one or more crosslinked or uncrosslinked binders selected from the group consisting of carboxyl-modified polyvinyl alcohols, polyvinyl alcohols modified with silanol groups, diacetone-modified polyvinyl alcohols, acetoacetyl-modified polyvinyl alcohol, partially and completely hydrolysed polyvinyl alcohols and film-forming acrylic copolymers.

Preferably, if present, the coating compound for forming the protective layer of the heat- sensitive recording material according to the present invention, in addition to one or more binders, contains one or more crosslinking agents for the binder or binders. The crosslinking agent is then preferably selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, epichlorohydrin resins, adipodihydrazide, melamine-formaldehyde, urea, methylolurea, ammonium zirconium carbonate, sodium/calcium glyoxylate, polyamide-epichlorohydrin resins and Tyzor LA. In a subject invention heat-sensitive recording material whose protective layer has been formed from such a coating compound containing one or more binders and one or more crosslinking agents for the binder or binders, the protective layer contains one or more crosslinked binders due to reaction with one or more crosslinking agents, the crosslinking agent or agents being selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, epichlorohydrin resins, adipodihydrazide, melamine-formaldehyde, urea, methylolurea, ammonium zirconium carbonate and polyamide epichlorohydrin resins. By "crosslinked binder" here is meant the reaction product formed by reacting a binder with one or more crosslinking agents.

In a first embodiment, the protective layer wholly or partly covering the heat-sensitive recording layer is obtainable from a coating compound comprising one or more polyvinyl alcohols and one or more crosslinking agents. It is preferable for the polyvinyl alcohol of the protective layer to be modified with carboxyl groups or especially silanol groups. Mixtures of various carboxyl- or silanol-modified polyvinyl alcohols are usable with preference. Such a protective layer has high affinity for the preferably UV-crosslinking printing ink (UV stands for: ultraviolet radiation) used in the offset printing process. This makes a decisive contribution to meeting the demand for outstanding printability within offset printing.

The crosslinking agent or agents of the protective layer according to this embodiment are preferably selected from the group consisting of boric acid, polyamines, epoxy resins, dialdehydes, formaldehyde oligomers, polyamine epichlorohydrin resins, adipodihydrazide, melamine-formaldehyde and Tyzor LA. Mixtures of various crosslinking agents are also possible.

The weight ratio of the modified polyvinyl alcohol to the crosslinking agent in the coating compound for forming the protective layer in this embodiment is preferably in a range of 20:1 to 5:1 and more preferably in a range of 12:1 to 7:1 . Particular preference is given to a ratio in the range from 100 parts by weight to 8 to 1 1 parts by weight of the modified polyvinyl alcohol to the crosslinking agent.

Particularly good results were obtained when the protective layer in this embodiment additionally contains an inorganic pigment. This inorganic pigment is preferably selected from the group consisting of silica, bentonite, alumina, calcium carbonate, kaolin and mixtures thereof. The basis weight in which the protective layer is applied in this embodiment is preferably in a range of 1 .0 g/m² to 6 g/m² and more preferably of 1 .2 g/m² to 3.8 g/m². The protective layer therein is preferably formed as a single ply.

In a second version of this embodiment, the coating compound for forming the protective layer comprises a water-insoluble self-crosslinking acrylic polymer as binder, a crosslinking agent and a pigmentary constituent, wherein the pigmentary constituent of the protective layer consists of one or more inorganic pigments and not less than 80 wt.% is formed of a highly purified alkali-pretreated bentonite, the binder of the protective layer consists of one or more water-insoluble self-crosslinking acrylic polymers, and the binder/pigment ratio is in a range of 7:1 to 9:1 .

A self-crosslinking acrylic polymer within the protective layer in the second version described here of the embodiment is preferably selected from the group consisting of styrene-acrylic ester copolymers, copolymers formed from styrene and acrylic ester and containing acrylamide groups, and also copolymers based on acrylonitrile, methacrylamide and acrylic ester. The latter are preferred. Alkali-pretreated bentonite, natural or precipitated calcium carbonate, kaolin, silica or aluminium hydroxide may be incorporated in the protective layer as pigment. Preferred crosslinking agents are selected from the group consisting of cyclic urea, methylolurea, ammonium zirconium carbonate and polyamide epichlorohydrin resins.

The choice of a water-insoluble self-crosslinking acrylic polymer as binder and of its weight ratio (i) to pigment in a range of 7:1 to 9:1 and also (ii) to crosslinking agent at greater than 5:1 is sufficient, even in the case of a protective layer of relatively low basis weight, to ensure a high level of environmental resistance for the heat-sensitive recording material of the invention. Weight ratios of this kind are thus preferable.

The protective layer itself can be applied by employing customary coating mechanisms for which inter alia a coating colour is usable, preferably with a basis weight in a range of 1 .0 to 4.5 g/m². The protective layer has been applied by printing in an alternative version. Protective layers curable by application of actinic radiation are particularly suitable because of their processing and technological properties. The term "actinic radiation" is to be understood as meaning UV or ionizing radiations, such as electron beam rays. Actinity is to be understood as meaning the photochemical activity of electromagnetic radiation differing in wavelength. The appearance of the protective layer is dispositively determined by the type of smoothing and of the cylinder surfaces, which influence the friction in the smoothing mechanism and calender, and their materials. Existing commercial requirements in particular are the reason why a Parker Print Surf Roughness for the protective layer of less than 1 .5 μιτι (determined as per DIN ISO 8791 -4:2008-05 Paper and Board - Determination of Roughness/Smoothness (Air Leak Methods) - Part 4: Print-Surf Method (ISO 8791 -4:2007)) is deemed preferable. What proved particularly advantageous in the context of experimental work preceding this invention was the use of smoothing mechanisms employing NipcoFlex™ or zone-regulated Nipco-P™ cylinders; however, the invention is not restricted thereto.

A further aspect of the present invention relates to a use of a subject invention heat- sensitive recording material as lottery tickets, ticket-in, ticket-out (TITO) tickets, travel tickets, entrance tickets, flight, rail, ship or bus ticket, gambling ticket, pay & display car park ticket, label, sales colour, bank statements, sticker, medical and/or technical diagram paper, fax paper, security paper or barcode labels.

A further aspect of the present invention relates to products, preferably lottery tickets, ticket-in, ticket-out (TITO) tickets, travel tickets, entrance tickets, flight, rail, ship or bus ticket, gambling ticket, pay & display car park ticket, label, sales colour, bank statements, sticker, medical diagram paper, fax paper, security paper or barcode labels, comprising a subject invention heat-sensitive recording material.

Ticket-in, ticket-out (TITO) is a technology used for example in relatively modern gambling machines. A TITO machine prints out a TITO ticket (barcode ticket) which can either be exchanged for cash or inserted into other TITO machines. TITO machines have a network interface for communication with a central system which tracks the credits associated with the TITO tickets barcode tickets. This technology is useful wherever changeable credits are required yet no cash is to be used, for example in canteens, refectories, leisure parks, swimming baths and/or saunas.

A further aspect of the present invention relates to a method of forming a heat-sensitive recording material or a heat-sensitive recording layer, as respectively defined herein, said method comprising the steps of: i. providing or forming a supporting substrate; and also providing or forming a coating composition as described and defined herein according to the invention, or a coating colour, as described and defined herein according to the invention, comprising a compound of formula (B-l) as is used in a subject invention heat- sensitive recording material; ii. applying the provided or formed coating composition to the provided or formed supporting substrate or to an interlayer positioned thereon; iii. drying the applied coating composition to obtain a heat-sensitive recording layer which combines with the supporting substrate to form a heat-sensitive recording material; iv. preferably an above method comprising said steps i. to iii. for forming a heat- sensitive recording material or for forming a heat-sensitive recording layer and further comprising the step of applying a protective layer to wholly or partly cover the heat-sensitive recording layer and drying the protective layer to obtain a heat- sensitive recording layer which combines with the supporting substrate to form a heat-sensitive recording material and is wholly or partly covered by the protective layer.

The preference of the invention is for a method additionally comprising the steps of a) providing or forming a coating composition or coating colour comprising pigments; b) applying the provided or formed coating composition or coating colour to the

supporting substrate; c) drying the applied coating composition or coating colour to form an interlayer; wherein steps a) to c) are carried out before step ii. and the interlayer is between the supporting substrate and the heat-sensitive recording layer. When an interlayer is formed, the step of applying the provided or formed coating composition in step iii. of the subject invention method is effected onto the formed interlayer and not directly onto the provided or formed supporting substrate.

The invention likewise has a preference for a method additionally comprising the steps of A) providing or forming a coating composition; B) applying the provided or formed coating composition to the heat-sensitive recording layer;

C) drying the applied coating composition to form a protective layer; wherein steps A) to C) are carried out after step iv. and the protective layer is on the heat- sensitive recording layer.

The preference of the invention may further be for a method of forming a subject invention heat-sensitive recording material or a subject invention heat-sensitive recording layer that further comprises the step of applying a protective layer to wholly or partly cover the heat-sensitive recording layer and drying the protective layer to obtain a heat- sensitive recording layer which combines with the supporting substrate to form a heat- sensitive recording material and is wholly or partly covered by the protective layer.

The invention further provides a compound preferably for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the compound comprises: a) at least one structural unit of lactic acid and b) two mutually independent terminal electron acceptor groups for the colour developer, wherein the compound is a compound of formula (B-l) as indicated and defined above according to the invention, for example, in the Embodiments B and/or C, and in Claim 17.

Preferably, in the invention, the compound is a compound of formula (B-l) as indicated and defined according to the invention, the said Embodiments B and/or C, and in Claim 17 and containing a structural unit of formula (B-lc) as indicated and defined according to the invention, the said Embodiments B and/or C, and in Claim 18. More preferably, in the invention, the compound is a compound of formula (B-l) as indicated and defined according to the invention, the said Embodiments B and/or C, and in Claim 17 and as comprising two mutually independent terminal electron acceptor groups having the structural unit of formula (B-lb) as indicated and defined according to the invention, the said Embodiments B and/or C, and in Claim 17; and wherein the compound of formula (B-l) also includes a structural unit of formula (B-lc) as indicated and defined according to the invention, the said Embodiments B and/or C, and in Claim 18.

Yet more preferably, in the invention, the compound is a compound in which at least one structural unit of formula (B-llla) and/or of formula (B-lllb) of lactic acid or its lactide is present in the compound of formula (B-l), as indicated and defined according to the invention, the said Embodiments B and/or C, and in Claim 17,

wherein a and b are each independently an integer from 1 to 10, preferably from 1 to 6, more preferably from 1 to 3 and most preferably 2;

Particularly preferably, in the invention, the compound is a compound of formula (B-l) as indicated and defined according to the invention, the said Embodiments B and/or C, and in Claim 17, wherein the compound has one or two terminal structural units of formula (B-lb), preferably two terminal structural units of formula (B-lb),

In the above described and defined subject invention compound or mixtures thereof or as a mixture with at least one further compound of formula (B-XIV), the particle sizes of the one or at least one of the compounds when two or more compounds are present, as defined above, as measured by laser diffraction, of the one or at least one compound of the two or more compounds, are each independently, in the range from 0.5 to 10 μιτι, preferably in the range from 0.8 to 8 μιτι and more preferably in the range from 0.8 to 4 μιτι. The preference of the invention in some cases is for a compound or mixtures thereof or as a mixture with at least one further compound of formula (B-XIV), as defined above, wherein the particle sizes measured as X₅₀ value by laser diffraction for the one or at least one compound of the two or more compounds are each independently in the range from 0.8 to 2 μιτι, preferably in the range from 0.85 to 1 .7 μιτι and more preferably in the range from 0.85 to 1 .65 μιτι. The particle sizes can be determined by use of laser diffraction (HELOS particle size analysis). An R1 Helos (H1453) & Quixel instrument from Sympatec GmbH was used in the context of the invention (analysis by WINDOX 4).

The invention further provides for the use of a compound as defined above, i. as colour developer as indicated under A) to D), and/or ii. for forming a colour developer as indicated under A) to D), and/or iii. as colour developer for forming as indicated under A) to D), wherein the colour developer is suitable and/or intended for and/or serves for forming

A) a coating composition for forming a heat-sensitive recording material; or

B) a heat-sensitive recording layer; or

C) a coating colour for forming a coating composition for forming a heat- sensitive recording material or a heat-sensitive recording layer; or

D) a heat-sensitive recording material.

The invention finally also provides a method of forming a compound according to the invention as described and defined above, preferably a compound for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the method comprises the reaction of a compound (i.e. with a cyclic ester of a hydroxy carboxylic acid, lactide) of formula (B-IV),

by ring-opening the lactide of formula (B-IV), preferably in the presence of a catalyst, and optionally polymerizing the intermediate obtained by ring- opening the lactide of formula (B-IV) to form one or more compounds comprising at least one structural unit of formula (B-llla) and/or of formula (B- I lib) of lactic acid or its lactide,

wherein a and b are each independently an integer from 1 to 10, preferably from 1 to 6, more preferably from 1 to 3 and most preferably 2,

(ii) a compound of formula B-V),

where X is O, S or NH and R1 and R2 are each independently a hydrogen atom, a methyl group, preferably a hydrogen atom;

wherein preferably the reaction is carried out under conditions where the compound of formula (B-V) does not decompose at all or at least not wholly, preferably under conditions where the temperature in the reaction is at least 1 °C, preferably at least 2 °C or 3 °C or 4 °C or 5 °C lower, more preferably at least 5 °C to 10 °C lower, than the decomposition temperature of a compound of formula (B-V);

and (iii) the intermediate obtained by reacting compounds of formula (B-IV) and of formula (B-V), with or without preceding purification and/or with or without preceding isolation, with a compound of formula (B-Vla) and/or a compound of formula (B-Vlb),

where R3 and R4 are each independently a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group or a halogen atom, preferably a hydrogen atom or a methyl group, more preferably a methyl group, yet more preferably a p-toluenesulfonyl isocyanate of formula (B-VII) as precursor compound to an electron acceptor group,

to obtain a compound of formula (B-l) as indicated and defined according to the invention, the said Embodiments B and/or C, and in Claim 17.

The invention further provides a method of forming a compound as indicated previously, preferably a compound for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat- sensitive recording layer, wherein the method comprises the reaction of

(i) a compound (i.e. with a cyclic ester of a hydroxy carboxylic acid, lactide) of formula

(B-IV)

O

(B-IV),

by ring-opening the lactide of formula (B-IV), preferably in the presence of a catalyst, and optionally polymerizing the intermediate obtained by ring-opening the lactide of formula (B-IV) to form one or more compounds comprising at least one structural unit of formula (Ilia) and/or of formula (B-lllb) of lactic acid or its lactide,

and

(ϋ) at least one precursor compound to an electron acceptor group as defined in Claim 3, preferably at least one compound of the formula (B-Vla) and/or of formula (B-Vlb),

and

the intermediate obtained by reacting compounds of formula (B-IV) and of formula (B-VI), with or without preceding purification and/or with or without preceding isolation, with a compound of formula B-V),

H H

where X is O, S or NH and R1 and R2 are each independently a hydrogen atom, a methyl group, preferably a hydrogen atom,

to obtain a compound of formula (B-l) as indicated and defined according to the invention, the said Embodiments B and/or C, and in Claim 17. An invention example of a compound of formula (B-l) can be illustrated by a compound of the following formula (B-l-A):

The compound of formula (B-l-A) is symmetrical and contains a central structural urea unit whereto, via each nitrogen atom, a structural lactide unit is attached in each case, the compound of formula (B-l-A) thus altogether containing two structural lactide units, and wherein a p-toluenesulfonylaminocarbonyl moiety attaches terminally to the structural lactide units in each case, as an electron acceptor group.

The inventive and comparative examples which follow further clarify the invention.

On reading the description, it will become plainly evident to a person skilled in the art that various modifications can be made in the disclosed embodiments without departing the scope of the invention. The embodiments and examples should therefore only be deemed illustrative.

Example 1

The present invention is further defined in the example which follows. This example, which discloses an embodiment of the invention, is only depicted for visualization. Materials: urea; Puralact B3: commercially available from Corbion Purac B.V. ; methyl ethyl ketone (MEK); p-toluenesulfonyl isocyanate.

Urea and Puralact B3 were placed in a reaction vessel under nitrogen. The vessel was heated to 150 ^SC and 100 ppm of tin octoate catalyst were added thereto. The temperature of the vessel was then raised to 180 ^SC and the reaction was continued for about 6 hours. The vessel was cooled down to 20-60 °C, MEK was added thereto and then p-toluenesulfonyl isocyanate was gradually added to the reaction mixture over time in order to ensure that the reaction temperature stayed between 60 and 70 °C. Following completion of addition of the p-toluenesulfonyl isocyanate, the reaction proceeded for a further hour under agitation. The MEK was then removed in vacuo.

The reaction product obtained was used for the performance tests of thermal papers.

Example 2

To form a representative formula (B-l) colour developer compound of the present invention, lactide (Puralact B3, commercially available from Corbion Purac B.V., Netherlands) was subjected in the presence of urea and in a conventional manner to a catalytic ring-opening reaction and polymerization to polylactide, the conversion being effected under conditions where urea does not decompose at all or entirely. A person skilled in the art will be aware, for example, that urea disintegrates into carbon dioxide and ammonium salts on heating in an aqueous solution with acids and into carbonates and ammonia on heating with alkalis. The conversion is carried out at temperatures as indicated in the description part. In the course thereof, the urea, which is preferably also used as lactide ring opener, will react with the ring-opened lactide directly and/or with the intermediate, lactide ring opened to the desired extent after polymerization, via the carboxyl groups present therein, to form an amide group. Then, the resulting urea-lactide intermediate is made to react with p-toluenesulfonyl isocyanate (CAS^® RN 4083-64-1 ) as electron acceptor group E. The conversion product obtained contains a compound of formula (B-l). Purification and isolation of the reaction product obtained and/or of the one compound or more compounds was eschewed since it was known from the prior art (e.g. EP 2 574 645 A1 and EP 2 784 133 A1 ) that any polylactic acids present should not interfere with performance trials on thermal papers.

To carry out the ring-opening reaction, the lactide (Puralact B3) and urea were placed in a reaction vessel under inert gas before being heated to about 150 °C. A tin catalyst was admixed in ppm quantity followed by an approximately 6 hour reaction at temperatures up to 180 °C during which urea serves as ring opener and promotes the polymerization to polylactide and/or polylactic acid.

Thereafter, the reaction mixture was cooled down to room temperature up to slightly elevated temperatures (20 °C to 60 °C). To carry out the conversion with p-toluenesulfonyl isocyanate, first methyl ethyl ketone was added as solvent followed by p-toluenesulfonyl isocyanate, and under agitation the p-toluenesulfonyl isocyanate reacted away over about 1 hour. The methyl ethyl ketone solvent was stripped off in vacuo. The reaction product obtained was used for the performance trials of thermal papers. Performance examples with comparative examples

Example 3: Comminution of material, formation of coating colour, coating of paper

Initial trials were started in order to comminute the colour developer material, form a coating colour therewith and then coat this coating colour on paper. Two versions were coated. The first version was turraxed to a particle size of 8 μιτι and the second version was comminuted with a stirred ball mill (for example with LabStar stirred ball mill from Netzsch) to 1 .6 μιτι. The material was initially only turraxed (for example with ULTRA-TURRAX^® high-performance disperser from the appliance maker IKA^®-Werke GmbH & CO. KG, alternatively with POLYTRON^® PT 6100 D stand disperser from Kinematica GmbH Dispersing and Mixing technology). Comminuting with ULTRA- TURRAX^® or POLYTRON^® PT 6100 D is based on the rotor-stator principle. The turning rotor creates an underpressure whereby the sample to be dispersed is aspirated and conveyed through the stator slots to the outside. Between the rotor/stator (shearing nip) the sample is subjected to high decelerating and accelerating forces in that the individual particles are pulled apart and comminuted through further cutting and impacting effects down to a few micrometres. The high shearing effect created in the process leads to the comminution of solids in the sample. The two versions utilized the same recipe for forming the coating colour and coating on paper. The recipes for the coating colours were determined in preliminary tests using other PLA specimens. The specimens of the coating colour recipes of the invention were compared with two commercially available standard varieties (BPA and Pergafast^® 201 ). Recipes (standard formulations) containing inventive PLA specimens and any comparative recipes were coated on paper and the papers were dried in a conventional manner. Papermakers distinguish three grades for the dry matter content of paper and chemical pulp: "atro" (absolutely dry), "lutro" (air dry) and "otro" (oven dry). This is reported in each case as "% atro", "% lutro" and "% otro". Where "atro" represents a paper or chemical pulp of 0 % water. Here "lutro" utilizes a "normal" (absolutely necessary for the paper) moisture content as the basis for the computation. With chemical and mechanical wood pulps, the computational mass is generally based on 90:100, i.e. 90 parts of stuff and 10 parts of water. The state of paper or chemical pulp following drying under fixed, defined conditions is referred to as "otro".

The papers obtained were then used to carry out tests selected from the following standard tests:

- Printing out with the Epson printer:

The dynamic printing density is determined as follows: The thermal recording material described above was thermally printed with an Atlantek 400 (ATLANTEK Model 400 Thermal Response Test System from Global Media Instruments, LLC (USA)) printer using different energy settings. The thermally printed regions obtained as a result were measured with the aid of a spectral densitometer (SpectroDens from Techkon). Fig. 1 shows the printouts obtained in a comparison between an inventive PLA specimen (1 ) having a particle size of 8 μιτι and a prior art developer, BPA (2).

- Measuring the dynamic printing density:

Fig. 2 shows the measured dynamic printing density as a printout for an inventive PLA specimen (1 ) having a particle size of 8 μιτι. Fig. 2 shows the dynamic printing density as a diagram where [A] denotes the energy (mj/mm²) and [B] denotes the dynamic printing density.

- Measuring the static printing density:

The static printing density is determined as follows: The thermal recording material described above was printed with the Heat gradient tester No. 884 (Toyoseiki) at different temperatures, at defined pressure over a defined time. The thermally printed regions obtained as a result were measured with the aid of a spectral densitometer (SpectroDens from Techkon). Testinq the environmental durabilities:

The test principle:

To metrologically capture the environmental durabilities of a thermal printout on the heat-sensitive recording materials of the invention and comparative examples, thermal test printouts, chequered black and white, were prepared on each of the heat-sensitive recording materials to be tested, using an Atlantek 400 with a thermal head having a resolution of 300 dpi and a 16 mJ/mm² energy per unit area.

Following the preparation of the black and white chequered thermal test printout and after a quiescent time of more than 5 minutes, the printing density was determined with SpectroDens densitometer from Techkon at respectively three places of the black areas of the thermal test printout. The respective values measured for the black areas were averaged in each case to form the mean.

o Coat the thermal test printouts with lanolin.

o Allow to soak in for 5 minutes then wipe off carefully.

o Hang up the samples for 4 hours in a conditioned measuring space at 23 °C, 50 %. The printing density was determined with SpectroDens densitometer from Techkon at respectively the three places of the black areas of the thermal test printout which had already been measured before treating the thermal test printout. The respective values measured for the black areas were averaged in each case to form the mean. o Place the thermal test printouts in an ethanol bath (25 %).

o Allow to soak in for 20 minutes and then carefully dab off.

o Hang up the samples for 24 hours in a conditioned measuring space at 23 °C, 50 %.

o The printing density was determined with SpectroDens densitometer from Techkon at respectively the three places of the black areas of the thermal test printout which had already been measured before treating the thermal test printout. The respective values measured for the black areas were averaged in each case to form the mean. o Stick Tesa graphics film (plasticizer) to the thermal test printouts and measure at once. o Hang up the samples for 24 hours in a conditioned measuring space at 23 °C, 50 %.

o The printing density was determined with SpectroDens densitometer from Techkon at respectively the three places of the black areas of the thermal test printout which had already been measured before treating the thermal test printout. The respective values measured for the black areas were averaged in each case to form the mean. o Place the thermal test printouts in a water bath,

o Allow to soak in for 20 minutes and then carefully dab off (blotting paper).

o The printing density was determined with SpectroDens densitometer from Techkon at respectively the three places of the black areas of the thermal test printout which had already been measured before treating the thermal test printout. The respective values measured for the black areas were averaged in each case to form the mean.

Measurement criteria:

The following measurement criteria were applied to the coating colour:

Measurement 1 : particle size (TG) of 8 μιτι;

Measurement 2: particle size (TG) of 1 .6 μιτι.

Example 4:

A specimen ("PLA" specimen) formed in accordance with the present invention, for instance as described in Example 1 , or in some cases as described in Example 2, was used for performance trials of thermal papers. A recipe (standard formulation) containing an inventive PLA specimen was coated on paper, the papers were dried in a conventional manner and the papers obtained were then subjected to standard tests as indicated in Example 3.

The inventive PLA specimen used gave a D-Max of 0.96 (as determined using ATLANTEK Model 400 Thermal Response Test System from Global Media Instruments, LLC (USA)).

The Epson printout with the inventive PLA specimen used looks black. An optical printing density of 0.98 was measured here. The printout is somewhat uneven which - without wishing to be tied to one specific theory - might be due to coarse particles, since the material used was initially only turraxed to 8 μιτι and therefore some coarse particles were still also present on the coated paper. Fig. 2 shows two exemplary printouts with a comparative scale.

The 2D barcode with the inventive PLA specimen used was readable to a value of 2.4; the comparative BPA has a value of 2.2.

Still further evaluations were carried out.

Example 5: Directions for spot test

Table 1 : Substance A:

TG [%] Lutro [g] Otro [g]

ODB-2 35 170.26 59.6

PVA (NM-1 1 ) 12.5 329.74 41 .2

PVA = polyvinyl alcohol; TG = dry weight Table 2: Substance B:

TG [%] Lutro [g] Otro [g]

Dispersant (L-3266) 18 13.22 2.38

Developer 100 47.619 47.619

Water 189.16 Substance A: Colour producer dispersion with binder

Substance B: Developer

Substance C: Dispersant for developer

Mix 13.2 g of substance C, 189.2 g of water and 47.6 g of the developer and comminute this dispersion as far as possible, using for example ULTRA-TURRAX^® high performance disperser from appliance maker IKA^®-Werke GmbH & CO. KG.

Then make up the colour as follows: 55 g of substance B and 28 g of substance A (colour producer). This corresponds to the ratios typically used by a person skilled in the art.

Mix this dispersion thoroughly. A paper, a supporting substrate having an interlayer, has adhered to it a Tesa strip (adhesive strip, adhesive film, from Tesa SE, Germany; the term "adhesive strip" is a collective designation for strip-shaped supporting materials, e.g. comprising self-supporting polymeric film/sheeting) one- or both-sidedly coated with pressure-sensitive adhesives transversely. The final dispersion is distributed on the Tesa strip in one line.

Using a rod (microscope slide, magnetic stirrer, ruler) the dispersion is coated over the paper leaving little behind. The paper is air dried or at not more than 60 °C oven dried for 1 min.

A lighter is then used to briefly heat the paper from behind. This short exposure is itself sufficient to engender a (colour) reaction.

Example 6: Test procedure

Determination of the conditioning durability of heat-sensitive recording materials (at 40 °C and 90 % r.h. for 24 hours): (r.h. = relative humidity)

To metrologically capture the conditioning durability of a thermal printout on the heat- sensitive recording materials of the invention and comparative examples, thermal test printouts, chequered black and white, were prepared on each of the heat-sensitive recording materials to be tested, using an ATLANTEK 400 Thermal Response Test System from Global Media Instruments, LLC (USA) with a thermal head having a resolution of 300 dpi and a 16 mJ/mm² energy per unit area. Following the preparation of the black and white chequered thermal test printout and after a quiescent time of more than 5 minutes, the printing density was determined with RD - 1152 "B" Gretag Macbeth densitometer at respectively three places of the black areas of the thermal test printout. The respective values measured for the black areas and the uncoloured areas were averaged in each case to form the mean.

A thermal test printout was suspended in a conditioning cabinet at 40 °C and a relative humidity of 90 %. After 24 hours the thermal paper printout was removed, cooled down to room temperature and remeasured for its printing density, with an RD - 1 152 "B" Gretag Macbeth densitometer at those three places of the black areas and of the uncoloured areas of the thermal test printout. The respective values measured for the black areas and the uncoloured areas were averaged in each case to form the mean.

The durability of the printed image in % corresponds to the ratio of mean printing density of the coloured areas before and after storage in the conditioning cabinet multiplied by 100. Example 7: Test procedure

Determination of durability of heat-sensitive recording materials to lanolin (10 minutes):

To metrologically capture the lanolin durability of a thermal printout on the heat-sensitive recording materials of the invention and comparative examples, thermal test printouts, chequered black and white, were prepared on each of the heat-sensitive recording materials to be tested, using an ATLANTEK 400 Thermal Response Test System from Global Media Instruments, LLC (USA) with a thermal head having a resolution of 300 dpi and a 16 mJ/mm² energy per unit area.

Following the preparation of the black and white chequered thermal test printout and after a quiescent time of more than 5 minutes, the printing density was determined with TYPE D19C Gretag Macbeth densitometer at respectively three places of the black areas of the thermal test printout. The respective values measured for the black areas and the uncoloured areas were averaged in each case to form the mean.

The thermal test printout prepared on the heat-sensitive recording material to be tested was then generously coated with lanolin. Following a soak-in time of 10 minutes, the lanolin is carefully wiped off and remeasured for its printing density, with a TYPE D19C Gretag Macbeth densitometer at those three places of the black areas and of the uncoloured areas of the thermal test printout. The respective values measured for the black areas and the uncoloured areas were averaged in each case to form the mean.

The lanolin durability in % corresponds to the ratio of mean printing density before the lanolin treatment and after the lanolin treatment multiplied by 100.

Example 8: Test procedure

Durability to water and aqueous ethanol solutions (23 °C, 50 % r.h., 24 h):

These tests are used to evaluate the image produced on the recording layer for its durability to water and aqueous solutions. A drop of distilled water or of the aqueous 25 % ethanol solution chosen is applied to the printed areas produced using a 572 TOSHIBA TEC printer at maximum printing energy (level +1 ). The excess test liquid is dabbed off with a filter paper or cotton cloth following a soak-in time of 20 minutes and the test sheet is subsequently stored under room conditions (23 °C, 50 % relative humidity) for 24 hours. Before the particular test liquid is applied and after the storage time has expired, the optical density of the printed areas, and also their difference, is determined using a 1 150 Macbeth densitometer.

The durability to water and/or aqueous ethanol solutions corresponds to the ratio of mean printing density before and after the treatment with the particular test liquid multiplied by 100. Example 9: Bekk smoothness test procedure

The smoothness (or roughness) is a significant surface property of papers. It represents the quality of the surface structure. The Bekk smoothness relies on the principle of air leak measurement. To this end, a sample is placed on a specified glass plate and pressed in place via a rubber plate using defined pressure. This is followed by a certain volume of air being sucked from the outside through the contact area via an established vacuum. The Bekk smoothness is measured in accordance with DIN 53107:2016-05 "Testing of Paper and Board - Determination of Bekk Smoothness".

The Bekk smoothness is the time in seconds needed for a certain volume of air to be sucked out of the ambient air at a defined differential pressure and radially inwardly through between a paper surface and a ring-shaped, nearly perfectly plane area under fixed contact conditions.

The samples were each subjected to ten measurements being carried out on the overside (OS). A new sample was used for every measurement. The sample was placed with the in— test side on the glass plate so as to completely cover it. The rubber plate and the pressure plate were then placed on the sample, the areal press of 100 kPa was applied and the prepressure Pv created in the vacuum container. The vacuum container is then connected to the drilled hole in the glass plate. What is measured, then, is the time for the pressure drop between pi (measurement pressure at the start of the measurement, in kilopascals) and p∑ (measurement pressure at the end of the measurement, in kilopascals). The measurements were carried out with a Bekk smoothness tester from Messmer Biichel. This test instrument is unreservedly useful for testing according to DIN 53107 / ISO 5627.

"OS" herein in connection with Bekk smoothness instruments stands for the overside of the paper sample and hence for the coated side of the particular paper sample. List of reference signs

(1 ) = PLA specimen - 8 μιτι

(2) = BPA (2,2 bis(4-hydroxyphenyl)propane; CAS^® RN 80-05-7)

(3) = PLA specimen - 8 μιτι; dynamic printing density

[A] = energy (mj/mm²)

[B] dynamic printing density

Embodiments A1 to A16:

1. An agent capable of reacting with a leuco dye upon heating, wherein said agent meets Formula (A-l):

O θΓ R⁴ R³ O R⁵ R⁶ R⁴ O R³ H O _R2 S-N-C- -O-C-C-O-C-G -N-C-N- -C-C-O-C-C-O- -C-N R H _aL _R3 _R4 J X |_° R³ R⁴ J ° O Formula (A-l) wherein:

R1 and R2 are independently a hydrogen atom, a C1 -C6 alkyl group, a 5 C1 - C6 alkoxy group or a halogen atom;

R3, R4, R5 and R6 are independently a hydrogen atom, a C1 -C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group;

X is O, S or NH; and,

a and b are integer values meeting the conditions a > 0, b > 0 and (a+b) > 1. The agent according to Claim 1 , wherein R1 , R2, R3, R4, R5 and R6 are independently a hydrogen atom or a C1 -C3 alkyl group. The agent according to Embodiment 1 or Embodiment 2, wherein R3 and R4 are independently a hydrogen atom or a methyl group. The agent according to Embodiment 3, wherein R3 is H and R4 is methyl. The agent according to any one of Embodiments 1 to 4, wherein X is O. The agent according to any one of Embodiments 1 to 5, wherein R1 and R2 are both methyl and are parasubstituents of the phenyl group. The agent according to any one of Embodiments 1 to 6, wherein 1 < a < 10 and 1 < b < 10. A thermosensitive recording medium having a colour developing layer comprising: a leuco dye; and,

a colour developer which reacts with said leuco dye upon heating to form a colour layer, wherein said colour developer comprises an agent as defined in any one of Embodiments 1 to 7. The thermosensitive medium according to Embodiment 8, wherein said leuco dye is selected from the group consisting of: triphenylmethanephthalide leuco com- pounds; triallylmethane leuco compounds; fluoran leuco compounds; phenothiaz- ine leuco compounds; thiofluoran leuco compounds; xanthene leuco compounds; indophthalyl leuco compounds; spiropyran leuco compounds; azaphthalide leuco compounds; couromenopyrazole leuco compounds; methine leuco compounds; rhodamineanilino-lactam leuco compounds; rhodaminelactam leuco compounds; quinazoline leuco compounds; diazaxanthene leuco compounds; bislactone leuco compounds; and, mixtures thereof. The thermosensitive medium according to Embodiment 9 in which the colour developing layer comprises a fluoran leuco dye. The thermosensitive medium according to any one of Embodiments 8 to 10, wherein said colour developing layer comprises a co-developer selected from the group consisting of: benzyl paraben; mono- and dihydroxy diphenyl sulfones; acidic clays; phenolic resins; and, zinc salicylates. The thermosensitive medium according to any one of Embodiments 8 to 1 1 , wherein said colour developing layer further comprises one or more of:

i) a sensitizer;

ii) a binder;

i) a pigment;

ii) a stabilizer;

iii) a dispersant;

iv) a defoamer;

v) a flow modifier; and,

vi) an insolubilizer. A method of producing a thermo-sensitive recording medium comprising the steps of:

a) providing a preferably planar substrate;

b) applying an aqueous coating composition to said substrate, said aqueous coating composition comprising a leuco dye and a dispersed colour developer which reacts with said leuco dye upon heating; and,

c) forming a coating layer by drying the applied aqueous coating composition at a temperature below the minimum reaction temperature of the developer and the leuco dye, wherein said colour developer comprises an agent as defined in any one of Embodiments 1 to 7. A compound meeting Formula (A- II):

R^J O R° R^c R⁴ O R³

H-4-0— c— c— o— c— C4-N— c— N4-C— C— O— C— C— 04— H

X O

R 3 O R^ R^ R^q

Formula (A-ll) wherein:

X is O, S or NH; and,

a and b are integer values meeting the conditions a > 0, b > 0 and (a+b) > 1.

A method of preparing the compound as defined in Embodiment 14, said method comprising reacting:

i) a compound of the Formula

R^* wherein:

R5 and R6 are independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group; and,

X is O, S or NH; and,

a cyclic ester of a hydroxycarboxylic acid having the Formula wherein:

R3 and R4 are independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group.

A method for producing the agent as defined in any one of Embodiments 1 to 7, said method comprising the steps of:

a) providing a compound as defined in Embodiment 14; and,

b) reacting said compound with at least one sulfonyl isocyanate of Formula (A-

Embodiments B1 to B15:

1. Coating composition for forming a heat-sensitive recording material or a heat- sensitive recording layer, comprising

one or more dye precursors; and

a) at least one structural unit of lactic acid and

two mutually independent terminal electron acceptor groups, wherein the one or the at least one colour developer of the two or more colour developers is a compound of formula (B-l),

(B-l),

where X is O, S or NH; R1 and R2 are each independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group; R3 and R4 are each independently a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group or a halogen atom; and a and b are each an integer and satisfy the conditions a > 0, b > 0 and (a+b) > 1. Coating composition for forming a heat-sensitive recording material or a heat- sensitive recording layer according to Embodiment 1 , wherein the one or the at least one colour developer of the two or more colour developers of formula (B-l) is a compound which

I. contains a structural unit of formula (B-lc),

where X is O, S or NH and R1 and R2 are each independently a hydrogen atom, a methyl group, preferably a hydrogen atom; and/or

II. has one or two terminal electron acceptors having a structural unit of formula (B-lb), Coating composition or heat-sensitive recording layer according to either of Embodiments 1 and 2, wherein the particle sizes, measured by laser diffraction for the one or at least one colour developer of the two or more colour developers are each independently in the range from 0.5 to 10 μιτι, preferably in the range from 0.8 to 8 μιτι and more preferably in the range from 0.8 to 4 μητι; or wherein the particle sizes measured as the X50 value by laser diffraction for the one or at least one colour developer of the two or more colour developers are each independently in the range from 0.8 to 2 μητι, preferably in the range from 0.85 to 1.7 μητι and more preferably in the range from 0.85 to 1.65 μιτι. Coating composition or heat-sensitive recording layer according to any one of Embodiments 1 to 3, further containing at least one further colour developer of formula (B-l I) and/or of formula (B-lll),

wherein the coating composition or heat-sensitive recording layer according to any preceding Embodiment further comprises one or more constituents from the group consisting of

sensitizers,

pigments, dispersants,

antioxidants,

release agents,

defoamers,

light stabilizers,

and

brighteners; and/or wherein the coating composition or heat-sensitive recording layer comprises a sensitizer selected from the group consisting of benzyl naphthyl ether (BNE), diphenyl sulfone (DPS), ethylene glycol m-tolyl ether (EGTE), ethylene glycol phenoxyethane (EGPE), 1 ,2-di(m-methylphenoxy)ethane (DMPE) and 1 ,2- diphenoxyethane (DPE), or a combination thereof. Coating composition or heat-sensitive recording layer according to any preceding Embodiment wherein the basis weight of the coating composition or heat-sensitive recording layer is in the range from 1 .5 to 8 g/m², preferably in the range from 1 .5 to 6 g/m², more preferably in the range from 2 to 6 g/m² and yet more preferably in the range from 2.0 to 5.5 g/m². Coating colour for forming a coating composition or a heat-sensitive recording layer, comprising one or more dye precursors; and one or more than one colour developer, wherein the one or at least one colour developer of the two or more colour developers is a compound as defined in any one of Embodiments 1 to 5. Heat-sensitive recording material comprising a supporting substrate, and a heat-sensitive recording layer as defined in any one of Embodiments 1 to 5; preferably wherein the heat-sensitive recording material additionally contains an interlayer between the supporting substrate and the heat-sensitive recording layer, wherein the interlayer preferably contains pigments; more preferably wherein the pigments comprise a) organic pigments, preferably hollow-body organic pigments, and/or b) inorganic pigments, preferably selected from the list consisting of calcinated kaolin, silica, bentonite, calcium carbonate, alumina and boehmite; preferably a heat-sensitive recording material wherein the heat-sensitive recording layer is wholly or partly covered by a protective layer.

Products, preferably lottery tickets, ticket-in, ticket-out (TITO) tickets, travel tickets, entrance tickets, flight, rail, ship or bus ticket, gambling ticket, pay & display car park ticket, label, sales colour, bank statements, sticker, medical diagram paper, fax paper, security paper or barcode labels, comprising a subject invention heat- sensitive recording material according to Embodiment 7.

Use of a heat-sensitive recording material according to either of Embodiments 7 and 8 as lottery tickets, ticket-in, ticket-out (TITO) tickets, travel tickets, entrance tickets, flight, rail, ship or bus ticket, gambling ticket, pay & display car park ticket, label, sales colour, bank statements, sticker, medical and/or technical diagram paper, fax paper, security paper or barcode labels.

Method of forming a heat-sensitive recording material according to either of Embodiments 7 and 8 or a heat-sensitive recording layer according to any one of Embodiments 1 to 5, said method comprising the steps of: i. providing or forming a supporting substrate; and also providing or forming a coating composition according to any one of Embodiments 1 to 5 or a coating colour according to Embodiment 6; ii. applying the coating composition to the supporting substrate or to an interlayer positioned thereon; iii. drying the applied coating composition to obtain a heat-sensitive recording layer which combines with the supporting substrate to form a heat-sensitive recording material; iv. preferably an above method comprising said steps i. to iii. for forming a heat- sensitive recording material or for forming a heat-sensitive recording layer and further comprising the method step of applying a protective layer to wholly or partly cover the heat-sensitive recording layer and drying the protective layer to obtain a heat-sensitive recording layer which combines with the supporting substrate to form a heat-sensitive recording material and is wholly or partly covered by the protective layer.

Compound, preferably for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat- sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the compound comprises: a) at least one structural unit of lactic acid and b) two mutually independent terminal electron acceptor groups for the colour developer, wherein the compound is a compound of formula (B-l) as indicated and defined in Embodiment 1 ; preferably wherein the compound is a compound of formula (B-l) as indicated and defined in Embodiment 1 and containing a structural unit of formula (B-lc) as indicated and defined in Embodiment 2; more preferably wherein the compound is a compound of formula (B-l) as indicated and defined in Embodiment 1 and as comprising two mutually independent terminal electron acceptor groups having the structural unit of formula (B-lb) as indicated and defined in Embodiment 1 ; and wherein the compound of formula (B-l) also includes a structural unit of formula (B-lc) as indicated and defined in Embodiment 2; yet more preferably wherein the compound is a compound in which at least one structural unit of formula (B-l Ma) and/or of formula (B-lllb) of lactic acid or its lactide is present in the compound of formula (B-l),

wherein a and b are each independently an integer from 1 to 10, preferably from 1 to 6, more preferably from 1 to 3 and most preferably 2; and particularly preferably wherein the compound is a compound of formula (B-l) as indicated and defined in Embodiment 1 , wherein the compound has one or two terminal structural units of formula (B-lb), preferably two terminal structural units of formula (B-lb),

Compound according to Embodiment 1 1 , preferably for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the particle sizes, measured by laser diffraction for the one or at least one compound of two or more compounds are each independently in the range from 0.5 to 10 μιτι, preferably in the range from 0.8 to 8 μιτι and more preferably in the range from 0.8 to 4 μιτι; or wherein the particle sizes measured as the X₅₀ value by laser diffraction for the one or at least one of the more than one colour developers are each independently in the range from 0.8 to 2 μιτι, preferably in the range from 0.85 to 1 .7 μιτι and more preferably in the range from 0.85 to 1 .65 μιτι.

Use of a compound according to either of Embodiments 1 1 and 12, i. as colour developer as indicated under A) to D), and/or ii. for forming a colour developer as indicated under A) to D), and/or iii. as colour developer for forming as indicated under A) to D), wherein the colour developer is suitable and/or intended for and/or serves for forming

A) a coating composition for forming a heat-sensitive recording material; or

B) a heat-sensitive recording layer; or

D) a heat-sensitive recording material.

Method of forming a compound according to either of Embodiments 1 1 and 12, preferably a compound for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat- sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the method comprises the reaction of 0) a compound (i.e. with a cyclic ester of a hydroxy carboxylic acid, lactide) of formula (B-IV),

by ring-opening the lactide of formula (B-IV), preferably in the presence of a catalyst, and optionally polymerizing the intermediate obtained by ring- opening the lactide of formula (B-IV) to form one or more compounds comprising at least one structural unit of formula (B-llla) and/or of formula (B-lllb) of lactic acid or its lactide,

(ii) a compound of formula B-V),

and the intermediate obtained by reacting compounds of formula (B-IV) and of formula (B-V), with or without preceding purification and/or with or without preceding isolation, with a compound of formula (B-Vla) and/or a compound of formula (B-Vlb),

to obtain a compound of formula (B-l) as indicated and defined in Embodiment 1.

Method of forming a compound according to either of Embodiments 1 1 and 12, preferably a compound for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the method comprises the reaction of

(i) a compound (i.e. with a cyclic ester of a hydroxy carboxylic acid, lactide) of formula (B-IV),

O

wherein a and b are each independently an integer from 1 to 10, preferably from 1 to 6, more preferably from 1 to 3 and most preferably 2, and (ϋ) at least one precursor compound to an electron acceptor group as defined in Embodiment 3, preferably at least one compound of the formula (B-Vla) and/or of formula (B-Vlb),

and

the intermediate obtained by reacting compounds of formula (B-IV) and of formula (B-VI), with or without preceding purification and/or with or without preceding isolation, with a compound of formula (B-V),

to obtain a compound of formula (B-l) as indicated and defined in Embodiment 1.

Embodiments C1 to C19:

An agent capable of reacting with a leuco dye upon heating, wherein said agent meets Formula (A-l):

Formula (A-l) wherein:

R1 and R2 are independently a hydrogen atom, a C1-C6 alkyl group, a 5 C1- C6 alkoxy group or a halogen atom;

X is O, S or NH; preferably wherein X is O; and,

a and b are integer values meeting the conditions a > 0, b > 0 and (a+b) > 1.

The agent according to Embodiment 1 ,

wherein R1 , R2, R3, R4, R5 and R6 are independently a hydrogen atom or a C1-C3 alkyl group; preferably wherein R1 , R2, R5 and R6 are independently a hydrogen atom or a C1-C3 alkyl group, and R3 and R4 are independently a hydrogen atom or a methyl group, and more preferably wherein R3 is H and R4 is methyl; and/or wherein R1 and R2 are both methyl and are parasubstituents of the phenyl group.

The agent according to any one of Embodiments 1 to 2, wherein 1 < a < 10 and 1 < b < 10.

A compound meeting Formula (A- II):

Formula (A-ll) wherein:

X is O, S or NH; and,

a and b are integer values meeting the conditions a > 0, b > 0 and (a+b) > 1.

A method of preparing the compound as defined in Embodiment 4, said method comprising reacting:

i) a compound of the Formula

R^* wherein:

X is O, S or NH; and, a cyclic ester of a hydroxycarboxylic acid having the Formula

wherein:

A method for producing the agent as defined in any one of Embodiments 1 to 3, said method comprising the steps of:

a) providing a compound as defined in Embodiment 4; and,

b) reacting said compound with at least one sulfonyl isocyanate of Formula (A-

Coating composition for forming a heat-sensitive recording material or a heat- sensitive recording layer, comprising

one or more dye precursors; and

a) at least one structural unit of lactic acid

and two mutually independent terminal electron acceptor groups, wherein the one or the at least one colour developer of the two or more colour developers is a compound of Formula (B-l),

(B-l),

where X is O, S or NH; R1 and R2 are each independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyl group or a C2-C6 alkenyl group; R3 and R4 are each independently a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group or a halogen atom; and a and b are each an integer and satisfy the conditions a > 0, b > 0 and (a+b) > 1. Coating composition for forming a heat-sensitive recording material or a heat- sensitive recording layer according to Embodiment 7, wherein the one or the at least one colour developer of the two or more colour developers of Formula (B-l) is a compound which

I. contains a structural unit of Formula (B-lc),

and/or

II. has one or two terminal electron acceptors having a structural unit of Formula (B-lb), Coating composition or heat-sensitive recording layer according to either of Embodiments 7 and 8, wherein the particle sizes, measured by laser diffraction for the one or at least one colour developer of the two or more colour developers are each independently in the range from 0.5 to 10 μιτι, preferably in the range from 0.8 to 8 μιτι and more preferably in the range from 0.8 to 4 μητι; or wherein the particle sizes measured as the X50 value by laser diffraction for the one or at least one colour developer of the two or more colour developers are each independently in the range from 0.8 to 2 μητι, preferably in the range from 0.85 to 1.7 μητι and more preferably in the range from 0.85 to 1.65 μιτι. Coating composition or heat-sensitive recording layer according to any one of Embodiments 7 to 9, further containing at least one further colour developer of Formula (B-ll) and/or of Formula (B-lll),

sensitizers,

pigments, dispersants,

antioxidants,

release agents,

defoamers,

light stabilizers,

and

brighteners;

and/or

wherein the coating composition or heat-sensitive recording layer comprises a sensitizer selected from the group consisting of benzyl naphthyl ether (BNE), diphenyl sulfone (DPS), ethylene glycol m-tolyl ether (EGTE), ethylene glycol phenoxyethane (EGPE), 1 ,2-di(m-methylphenoxy)ethane (DMPE) and 1 ,2- diphenoxyethane (DPE), or a combination thereof. Coating colour for forming a coating composition or a heat-sensitive recording layer, comprising

one or more dye precursors; and

one or more than one colour developer, wherein the one or at least one colour developer of the two or more colour developers is a compound as defined in any one of Embodiments 7 to 10. Heat-sensitive recording material comprising

a supporting substrate,

and

a heat-sensitive recording layer as defined in any one of Embodiments 7 to 10;

preferably wherein the heat-sensitive recording material additionally contains an interlayer between the supporting substrate and the heat-sensitive recording layer, wherein the interlayer preferably contains pigments;

more preferably wherein the pigments comprise

a) organic pigments, preferably hollow-body organic pigments,

and/or b) inorganic pigments, preferably selected from the list consisting of calcinated kaolin, silica, bentonite, calcium carbonate, alumina and boehmite;

preferably a heat-sensitive recording material wherein the heat-sensitive recording layer is wholly or partly covered by a protective layer.

Products, preferably lottery tickets, ticket-in, ticket-out (TITO) tickets, travel tickets, entrance tickets, flight, rail, ship or bus ticket, gambling ticket, pay & display car park ticket, label, sales colour, bank statements, sticker, medical diagram paper, fax paper, security paper or barcode labels, comprising a subject invention heat- sensitive recording material according to Embodiment 12.

Use of a heat-sensitive recording material according to Embodiment 12 as lottery tickets, ticket-in, ticket-out (TITO) tickets, travel tickets, entrance tickets, flight, rail, ship or bus ticket, gambling ticket, pay & display car park ticket, label, sales colour, bank statements, sticker, medical and/or technical diagram paper, fax paper, security paper or barcode labels.

Method of forming a heat-sensitive recording material according to Embodiment 12 or a heat-sensitive recording layer according to any one of Embodiments 7 to 10, said method comprising the steps of:

i. providing or forming a supporting substrate; and also providing or forming a coating composition according to any one of Embodiments 7 to 10 or a coating colour according to Embodiment 1 1 ;

ii. applying the coating composition to the supporting substrate or to an interlayer positioned thereon;

iii. drying the applied coating composition to obtain a heat-sensitive recording layer which combines with the supporting substrate to form a heat-sensitive recording material;

iv. preferably an above method comprising said steps i. to iii. for forming a heat- sensitive recording material or for forming a heat-sensitive recording layer and further comprising the method step of applying a protective layer to wholly or partly cover the heat-sensitive recording layer and drying the protective layer to obtain a heat-sensitive recording layer which combines with the supporting substrate to form a heat-sensitive recording material and is wholly or partly covered by the protective layer. Compound, preferably for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the compound comprises: a) at least one structural unit of lactic acid

and

b) two mutually independent terminal electron acceptor groups for the colour developer,

wherein the compound is a compound of Formula (B-l) as indicated and defined in Embodiment 7;

preferably wherein the compound is a compound of Formula (B-l) as indicated and defined in Embodiment 7 and containing a structural unit of Formula (B-lc) as indicated and defined in Embodiment 8;

more preferably wherein the compound is a compound of Formula (B-l) as indicated and defined in Embodiment 7 and as comprising two mutually independent terminal electron acceptor groups having the structural unit of Formula (B-lb) as indicated and defined in Embodiment 7; and wherein the compound of Formula (B- I) also includes a structural unit of Formula (B-lc) as indicated and defined in Embodiment 8;

yet more preferably wherein the compound is a compound in which at least one structural unit of Formula (B-l Ma) and/or of Formula (B-lllb) of lactic acid or its lactide is present in the compound of Formula (B-l),

and particularly preferably wherein the compound is a compound of Formula (B-l) as indicated and defined in Embodiment 17, wherein the compound has one or two terminal structural units of Formula (B-lb), preferably two terminal structural units of Formula (B-lb),

Compound according to Embodiment 16, preferably for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the particle sizes, measured by laser diffraction for the one or at least one compound of two or more compounds are each independently in the range from 0.5 to 10 μιτι, preferably in the range from 0.8 to 8 μιτι and more preferably in the range from 0.8 to 4 μιη; or wherein the particle sizes measured as the X50 value by laser diffraction for the one or at least one of the more than one colour developers are each independently in the range from 0.8 to 2 μητι, preferably in the range from 0.85 to 1.7 μιη and more preferably in the range from 0.85 to 1.65 μιτι.

Use of a compound according to either of Embodiments 16 and 17,

i. as colour developer as indicated under A) to D), and/or

ii. for forming a colour developer as indicated under A) to D), and/or iii. as colour developer for forming as indicated under A) to D), wherein the colour developer is suitable and/or intended for and/or serves for forming

A) a coating composition for forming a heat-sensitive recording material; or

B) a heat-sensitive recording layer; or

C) a coating colour for forming a coating composition for forming a heat-sensitive recording material or a heat-sensitive recording layer; or

D) a heat-sensitive recording material.

Method of forming a compound according to either of Embodiments 16 and 17, preferably a compound for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the method comprises the reaction of

wherein a and b are each independently an integer from 1 to 10, preferably from 1 to 6, more preferably from 1 to 3 and most preferably 2, a compound of Formula (B-V),

and

(iii) the intermediate obtained by reacting compounds of Formula (B-IV) and of Formula (B-V), with or without preceding purification and/or with or without preceding isolation, with a compound of Formula (B-Vla) and/or a compound of Formula (B-Vlb),

to obtain a compound of Formula (B-l) as indicated and defined in Embodiment 7. Method of forming a compound according to either of Embodiments 16 and 17, preferably a compound for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the method comprises the reaction of

(B-IV),

by ring-opening the lactide of Formula (B-IV), preferably in the presence of a catalyst, and optionally polymerizing the intermediate obtained by ring- opening the lactide of Formula (B-IV) to form one or more compounds comprising at least one structural unit of Formula (B-l lla) and/or of Formula (B-l llb) of lactic acid or its lactide,

wherein a and b are each independently an integer from 1 to 10, preferably from 1 to 6, more preferably from 1 to 3 and most preferably 2, and

(ϋ) at least one precursor compound to an electron acceptor group as defined in Claim 3, preferably at least one compound of the Formula (B-VIa) and/or of Formula (B-Vlb),

where R3 and R4 are each independently a hydrogen atom, a C1 -C6 alkyl group, a C1 -C6 alkoxy group or a halogen atom , preferably a hydrogen atom or a methyl group, more preferably a methyl group, yet more preferably a p-toluenesulfonyl isocyanate of Formula (B-VI I) as precursor compound to an electron acceptor group,

(B-VI I), the intermediate obtained by reacting compounds of Formula (B-IV) and of Formula (B-VI), with or without preceding purification and/or with or without preceding isolation, with a compound of Formula (B-V),

in a compound of Formula (B-l) as indicated and defined in Embodiment 7.

Claims

Claims:

Formula (A-l) wherein:

X is O, S or NH; and,

a and b are integer values meeting the conditions a > 0, b > 0 and (a+b) > 1.

2. The agent according to Claim 1 , wherein R1 , R2, R3, R4, R5 and R6 are independently a hydrogen atom or a C1-C3 alkyl group.

3. The agent according to Claim 1 or Claim 2, wherein R3 and R4 are independently a hydrogen atom or a methyl group.

4. The agent according to Claim 3, wherein R3 is H and R4 is methyl.

5. The agent according to any one of Claims 1 to 4, wherein X is O.

6. The agent according to any one of Claims 1 to 5, wherein R1 and R2 are both methyl and are parasubstituents of the phenyl group.

7. The agent according to any one of Claims 1 to 6, wherein 1 < a < 10 and 1 < b < 10.

8. A thermosensitive recording medium having a colour developing layer comprising:

a leuco dye; and, a colour developer which reacts with said leuco dye upon heating to form a colour layer, wherein said colour developer comprises an agent as defined in any one of Claims 1 to 7.

9. The thermosensitive medium according to Claim 8, wherein said leuco dye is se- lected from the group consisting of: triphenylmethanephthalide leuco compounds; triallylmethane leuco compounds; fluoran leuco compounds; phenothiazine leuco compounds; thiofluoran leuco compounds; xanthene leuco compounds; indophthalyl leuco compounds; spiropyran leuco compounds; azaphthalide leuco compounds; couromenopyrazole leuco compounds; methine leuco compounds; rhodamineani- lino-lactam leuco compounds; rhodaminelactam leuco compounds; quinazoline leuco compounds; diazaxanthene leuco compounds; bislactone leuco compounds; and, mixtures thereof.

10. The thermosensitive medium according to Claim 9 in which the colour developing layer comprises a fluoran leuco dye. 1 1. The thermosensitive medium according to any one of Claims 8 to 10, wherein said colour developing layer comprises a co-developer selected from the group consisting of: benzyl paraben; mono- and dihydroxy diphenyl sulfones; acidic clays; phenolic resins; and, zinc salicylates.

12. The thermosensitive medium according to any one of Claims 8 to 1 1 , wherein said colour developing layer further comprises one or more of:

i) a sensitizer;

ii) a binder;

i) a pigment;

ii) a stabilizer;

iii) a dispersant;

iv) a defoamer;

v) a flow modifier; and,

vi) an insolubilizer.

13. A method of producing a thermo-sensitive recording medium comprising the steps of: a) providing a preferably planar substrate;

c) forming a coating layer by drying the applied aqueous coating composition at a temperature below the minimum reaction temperature of the developer and the leuco dye, wherein said colour developer comprises an agent as defined in any one of Claims 1 to 7.

14. A compound meeting Formula (A- II):

Formula (A-ll) wherein:

X is O, S or NH; and,

a and b are integer values meeting the conditions a > 0, b > 0 and (a+b) > 1.

A method of preparing the compound as defined in Claim 14, said method comprising reacting:

i) a compound of the Formula

X wherein:

X is O, S or NH; and,

a cyclic ester of a hydroxycarboxylic acid having the Formula

wherein:

A method for producing the agent as defined in any one of Claims 1 to 7, said method comprising the steps of:

a) providing a compound as defined in Claim 14; and,

b) reacting said compound with at least one sulfonyl isocyanate of Formula (A-

17. Coating composition for forming a heat-sensitive recording material or a heat- sensitive recording layer, comprising one or more dye precursors; and

a) at least one structural unit of lactic acid

and

(B-l),

where X is O, S or NH; R1 and R2 are each independently a hydrogen atom, a C1-C6 alkyl group, a C3-C6 cycloalkyi group or a C2-C6 alkenyl group; R3 and R4 are each independently a hydrogen atom, a C1-C6 alkyl group, a C1-C6 alkoxy group or a halogen atom; and a and b are each an integer and satisfy the conditions a > 0, b > 0 and (a+b) > 1.

Coating composition for forming a heat-sensitive recording material or a heat- sensitive recording layer according to Claim 17, wherein the one or the at least one colour developer of the two or more colour developers of Formula (B-l) is a compound which

i. contains a structural unit of Formula B-lc),

where X is O, S or NH and R1 and R2 are each independently a hydrogen atom, a methyl group, preferably a hydrogen atom; and/or has one or two terminal electron acceptors having a structural Formula (B-lb),

19. Coating composition or heat-sensitive recording layer according to either of Claims 17 and 18, wherein the particle sizes, measured by laser diffraction for the one or at least one colour developer of the two or more colour developers are each independently in the range from 0.5 to 10 μιτι, preferably in the range from 0.8 to 8 μιη and more preferably in the range from 0.8 to 4 μητι; or wherein the particle sizes measured as the X50 value by laser diffraction for the one or at least one colour developer of the two or more colour developers are each independently in the range from 0.8 to 2 μητι, preferably in the range from 0.85 to 1.7 μητι and more preferably in the range from 0.85 to 1.65 μιτι.

Coating composition or heat-sensitive recording layer according to any one of Claims 17 to 19, further containing at least one further colour developer of Formula (B-ll) and/or of Formula (B-lll),

and/or

wherein the coating composition or heat-sensitive recording layer according to any preceding claim further comprises one or more constituents from the group consisting of sensitizers,

pigments,

dispersants,

antioxidants,

release agents,

defoamers,

light stabilizers,

and

brighteners;

and/or

wherein the coating composition or heat-sensitive recording layer comprises a sensitizer selected from the group consisting of benzyl naphthyl ether (BNE), diphenyl sulfone (DPS), ethylene glycol m-tolyl ether (EGTE), ethylene glycol phenoxyethane (EGPE), 1 ,2-di(m-methylphenoxy)ethane (DMPE) and 1 ,2- diphenoxyethane (DPE), or a combination thereof.

Coating composition or heat-sensitive recording layer according to any preceding claims 17 to 20 wherein the basis weight of the coating composition or heat-sensitive recording layer is in the range from 1.5 to 8 g/m², preferably in the range from 1.5 to 6 g/m², more preferably in the range from 2 to 6 g/m² and yet more preferably in the range from 2.0 to 5.5 g/m².

Coating colour for forming a coating composition or a heat-sensitive recording layer, comprising

one or more dye precursors; and

one or more than one colour developer, wherein the one or at least one colour developer of the two or more colour developers is a compound as defined in any one of Claims 17 to 21.

Heat-sensitive recording material comprising

a supporting substrate,

and

a heat-sensitive recording layer as defined in any one of Claims 17 to

21 ; preferably wherein the heat-sensitive recording material additionally contains an interlayer between the supporting substrate and the heat-sensitive recording layer, wherein the interlayer preferably contains pigments;

more preferably wherein the pigments comprise

a) organic pigments, preferably hollow-body organic pigments,

and/or

b) inorganic pigments, preferably selected from the list consisting of calcinated kaolin, silica, bentonite, calcium carbonate, alumina and boehmite;

Products, preferably lottery tickets, ticket-in, ticket-out (TITO) tickets, travel tickets, entrance tickets, flight, rail, ship or bus ticket, gambling ticket, pay & display car park ticket, label, sales colour, bank statements, sticker, medical diagram paper, fax paper, security paper or barcode labels, comprising a subject invention heat- sensitive recording material according to Claim 23.

Use of a heat-sensitive recording material according to Claim 23 as lottery tickets, ticket-in, ticket-out (TITO) tickets, travel tickets, entrance tickets, flight, rail, ship or bus ticket, gambling ticket, pay & display car park ticket, label, sales colour, bank statements, sticker, medical and/or technical diagram paper, fax paper, security paper or barcode labels.

Method of forming a heat-sensitive recording material according to Claim 23 or a heat-sensitive recording layer according to any one of Claims 17 to 21 , said method comprising the steps of:

i. providing or forming a supporting substrate; and also providing or forming a coating composition according to any one of Claims 17 to 21 or a coating colour according to Claim 22;

iii. drying the applied coating composition to obtain a heat-sensitive recording layer which combines with the supporting substrate to form a heat-sensitive recording material; iv. preferably an above method comprising said steps i. to iii. for forming a heat- sensitive recording material or for forming a heat-sensitive recording layer and further comprising the method step of applying a protective layer to wholly or partly cover the heat-sensitive recording layer and drying the protective layer to obtain a heat-sensitive recording layer which combines with the supporting substrate to form a heat-sensitive recording material and is wholly or partly covered by the protective layer.

Compound, preferably for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the compound comprises: a) at least one structural unit of lactic acid

and

wherein the compound is a compound of Formula (B-l) as indicated and defined in Claim 17;

preferably wherein the compound is a compound of Formula (B-l) as indicated and defined in Claim 17 and containing a structural unit of Formula (B-lc) as indicated and defined in Claim 18;

more preferably wherein the compound is a compound of Formula (B-l) as indicated and defined in Claim 17 and as comprising two mutually independent terminal electron acceptor groups having the structural unit of Formula (B-lb) as indicated and defined in Claim 17; and wherein the compound of Formula (B-l) also includes a structural unit of Formula (B-lc) as indicated and defined in Claim 18; yet more preferably wherein the compound is a compound in which at least one structural unit of Formula (B-l Ma) and/or of Formula (B-lllb) of lactic acid or its lactide is present in the compound of Formula (B-l),

(B-llla), (B-lllb), wherein a and b are each independently an integer from 1 to 10, preferably from 1 to 6, more preferably from 1 to 3 and most preferably 2;

and particularly preferably wherein the compound is a compound of Formula (B-l) as indicated and defined in Claim 17, wherein the compound has one or two terminal structural units of Formula (B-lb), preferably two terminal structural units of

Formula (B-lb),

28. Compound according to Claim 27, preferably for use as colour developer in a coating composition for forming a heat-sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the particle sizes, measured by laser diffraction for the one or at least one compound of two or more compounds are each independently in the range from 0.5 to 10 μιτι, preferably in the range from 0.8 to 8 μιτι and more preferably in the range from 0.8 to 4 μητι; or wherein the particle sizes measured as the X50 value by laser diffraction for the one or at least one of the more than one colour developers are each independently in the range from 0.8 to 2 μητι, preferably in the range from 0.85 to 1.7 μητι and more preferably in the range from 0.85 to 1.65 μιτι.

Use of a compound according to either of Claims 27 and 28,

i. as colour developer as indicated under A) to D), and/or

A) a coating composition for forming a heat-sensitive recording material; or

B) a heat-sensitive recording layer; or

D) a heat-sensitive recording material.

30. Method of forming a compound according to either of Claims 27 and 28, preferably a compound for use as colour developer in a coating composition for forming a heat- sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the method comprises the reaction of

by rin rably in the presence of a catalyst, and optionally polymerizing the intermediate obtained by ring- opening the lactide of Formula (B-IV) to form one or more compounds comprising at least one structural unit of Formula (B-llla) and/or of Formula (B-lllb) of lactic acid or its lactide,

and

to obtain a compound of Formula (B-l) as indicated and defined in Claim 17.

Method of forming a compound according to either of Claims 27 and 28, preferably a compound for use as colour developer in a coating composition for forming a heat- sensitive recording material or as colour developer in a heat-sensitive recording layer or as colour developer in a coating colour for forming a coating composition or a heat-sensitive recording layer, wherein the method comprises the reaction of

O

and

(iii) the intermediate obtained by reacting compounds of Formula (B-IV) and of Formula (B-VI), with or without preceding purification and/or with or without preceding isolation, with a compound of Formula (B-V),

in a compound of Formula (B-l) as indicated and defined in Claim 17.