WO2022043181A1 - Method for the uv curing of lacquers containing non-aqueous poly(meth)acrylates without a photoinitiator - Google Patents

Method for the uv curing of lacquers containing non-aqueous poly(meth)acrylates without a photoinitiator Download PDF

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Publication number
WO2022043181A1
WO2022043181A1 PCT/EP2021/073041 EP2021073041W WO2022043181A1 WO 2022043181 A1 WO2022043181 A1 WO 2022043181A1 EP 2021073041 W EP2021073041 W EP 2021073041W WO 2022043181 A1 WO2022043181 A1 WO 2022043181A1
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WO
WIPO (PCT)
Prior art keywords
paint formulation
acrylates
meth
weight
paint
Prior art date
Application number
PCT/EP2021/073041
Other languages
French (fr)
Inventor
Axel Becker
Oliver Starzmann
Michael Stengle
Frederik FEIL
Original Assignee
Basf Se
Ist Metz Gmbh
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Basf Se, Ist Metz Gmbh filed Critical Basf Se
Priority to EP21766435.8A priority Critical patent/EP4204463A1/en
Publication of WO2022043181A1 publication Critical patent/WO2022043181A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F8/00—Chemical modification by after-treatment
    • C08F8/30—Introducing nitrogen atoms or nitrogen-containing groups
    • C08F8/32—Introducing nitrogen atoms or nitrogen-containing groups by reaction with amines
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F2/00—Processes of polymerisation
    • C08F2/46—Polymerisation initiated by wave energy or particle radiation
    • C08F2/48—Polymerisation initiated by wave energy or particle radiation by ultraviolet or visible light
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F290/00—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups
    • C08F290/08—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups on to polymers modified by introduction of unsaturated side groups
    • C08F290/14—Polymers provided for in subclass C08G
    • C08F290/142—Polyethers
    • C—CHEMISTRY; METALLURGY
    • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
    • C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
    • C08F290/00—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups
    • C08F290/08—Macromolecular compounds obtained by polymerising monomers on to polymers modified by introduction of aliphatic unsaturated end or side groups on to polymers modified by introduction of unsaturated side groups
    • C08F290/14—Polymers provided for in subclass C08G
    • C08F290/147—Polyurethanes; Polyureas
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D151/00—Coating compositions based on graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Coating compositions based on derivatives of such polymers
    • C09D151/08—Coating compositions based on graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Coating compositions based on derivatives of such polymers grafted on to macromolecular compounds obtained otherwise than by reactions only involving carbon-to-carbon unsaturated bonds
    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
    • C09D4/00—Coating compositions, e.g. paints, varnishes or lacquers, based on organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond ; Coating compositions, based on monomers of macromolecular compounds of groups C09D183/00 - C09D183/16
    • C09D4/06—Organic non-macromolecular compounds having at least one polymerisable carbon-to-carbon unsaturated bond in combination with a macromolecular compound other than an unsaturated polymer of groups C09D159/00 - C09D187/00
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J61/00—Gas-discharge or vapour-discharge lamps
    • H01J61/82—Lamps with high-pressure unconstricted discharge having a cold pressure > 400 Torr
    • H01J61/822—High-pressure mercury lamps

Definitions

  • the present invention relates to a method for producing a paint coating on an in particular flat substrate by means of a radiation-curing, nonaqueous paint formulation comprising at least 80% by weight of curable constituents having (meth)acrylate groups, in particular on substrates such as paper, wood, woodbase materials, metals, and plastics.
  • Coating systems cured by exposure to actinic radiation are formulations comprising oligomers or polymers having a plurality of ethylenically unsaturated double bonds, commonly present in the form of acrylate groups or methacrylate groups, and optionally low-molecular-weight ethylenically unsaturated monomers.
  • the formulations are applied to the substrate surface to be coated and cured by irradiating with actinic radiation or else with electron beams. What takes place here is a free-radical polymerization of the ethylenically unsaturated double bonds to form a crosslinked polymer film.
  • One embodiment of radiation-curable coating systems comprises formulations in which essentially all constituents, i.e. at least 80% by weight, in particular at least 90% by weight, of the constituents of the formulation undergo crosslinking through free-radical polymerization.
  • Such coating systems typically comprise no non-polymerizable volatile constituents (VOCs) and are also referred to as 100% systems.
  • the curing of the photosensitive mixtures with UV radiation involves the addition to the coating composition of photoinitiators that absorb the UV radiation, generate radicals or protons, and initiate photopolymerization or photocrosslinking.
  • the amount of photoinitiators added here is generally over 0.5% by weight of the curable unsaturated compounds, often over 1% by weight.
  • UV curing under an inert gas atmosphere allows the amount of photoinitiator required to be reduced.
  • the presence of atmospheric oxygen inhibits the photopolymerization, since reactive oxygen, which is itself a diradical, scavenges the radicals formed from the photoinitiator or occurring during the free-radical polymerization, thereby taking them out of the polymerization reaction.
  • a photocurable paint formulation comprising a photoinitiator is often more unstable than a corresponding formulation without photoinitiator. Since photoinitiators rank among the costly constituents of a UV-curable paint formulations, it is advantageous for the amounts of photoinitiators in UV-curable paint formulations to be only small. Moreover, photoinitiators and fragments thereof that form on irradiation with UV light often result in yellowing of the paint films or obtrusive odors due to volatile substances. There may also be toxicological concerns about the use of photoinitiators. Furniture manufacturers accordingly impose strict requirements on the type and amount of photoinitiators used in UV-curable paint coatings.
  • the object of the invention is to provide UV-curable paint formulations in which photoinitiators or particular types of photoinitiators are present only in small amounts or are absent altogether, and also to provide a method for producing paint coatings on a flat substrate by UV curing of the paint formulations that may in particular be carried out in air too.
  • the object is achieved by a method for producing a paint coating on a substrate by UV curing of a liquid, nonaqueous paint formulation comprising at least 80% by weight of curable constituents having (meth)acrylate groups, said method comprising the steps of:
  • the curing of the paint formulation with UV-C light in step (ii) uses according to the invention an irradiation device that in the 180 to 280 nm UV-C range, in particular in the 180 to 240 nm range, has a distinctly higher power output compared with conventional UV-C radiation sources.
  • the radiation source used is according to the invention a mercury lamp, in particular, a mediumpressure mercury lamp.
  • the curing (ii) of the liquid paint formulation occurs exclusively with UV-C radiation in the 180 to 280 nm, wavelength range using a mercury lamp. No other type of UV-C irradiation source is used.
  • the mercury lamp has according to the invention an electrical power consumption (power input) of > 150 W/cm, preferably > 180 W/cm.
  • an undoped mercury lamp is used.
  • the mercury lamp used according to the invention is constructed in the form of a hollow cylinder, the jacket tube of which is made of a material that is transparent to UV radiation.
  • the hollow tube is sealed at its end faces, with the result that the interior of the hollow cylinder forms a closed volume in which a filling gas is enclosed.
  • the hollow cylinder has electrical connections at least at its end faces for transferring energy into the filling gas in the interior of the hollow cylinder.
  • the filling gas consists of at least one noble gas and a proportion of mercury, it being possible for the filling gas to additionally be doped with proportions of metals. Doping may be for example with lead, iron, gallium, indium or other metals, according to individual requirement.
  • the jacket tube of the mercury lamp has in accordance with the invention high transparency for shortwave UV radiation in the 180 to 240 nm range. It is preferable that the jacket tube is made of a quartz material having high transparency to IIV-C.
  • the jacket tube has high thermal stability.
  • the quartz material used can for example be one of the Suprasil series type from Heraeus, for example Suprasil 3001 130021300.
  • the filling gas has in operation a working pressure within a range from 1 bar to 10 bar, preferably within a range from 1.5 bar to 8 bar, more preferably within a range from 1.7 bar to 5 bar.
  • the working voltage per cm arc length is within a range from 5 V/cm to 30 V/cm, preferably within a range from 8 V/cm to 20 V/cm, more preferably within a range from 10 V/cm to 15 V/cm.
  • the electrical power input of the mercury lamp is in general within a range from 150 to 500 W/cm, preferably within a range from 180 to 500 W/cm, more preferably within a range from 200 to 500 W/cm arc length, even more preferably within a range from 200 to 400 W/cm, more preferably within a range from 200 to 350 W/cm.
  • the current and voltage per cm arc length are in accordance with the invention optimized for a maximum output in the 180 to 240 nm UV range; the conversion efficiency in this wavelength range is > 13%, preferably > 15%, more preferably > 17%, based on the power input.
  • the IIV-C output per cm arc length in the 180 to 240 nm range is thus in accordance with the invention at least 19.5 W/cm, preferably at least 23.4 W/cm, more preferably at least 25.5 W/cm or at least
  • 23.4 W/cm preferably at least 27 W/cm and more preferably at least 30.6 W/cm.
  • it is in general within a range from 22.5 to 75 W/cm, preferably within a range from 27 to 75 W/cm, even more preferably within a range from 30 to 75 W/cm, more preferably within a range from 30 to 60 W/cm, and in particular within a range from 30 to
  • the radiation unit accordingly has optical elements such as reflectors for optically deflecting the shortwave radiation emitted by the radiation source into the process plane.
  • the reflectors reflect the UV radiation in the 180 to 240 nm range, preferably in the 180 to 300 nm range, more preferably in the 180 to 400 nm range.
  • the reflectance of the reflectors in the 180 to 240 nm range is in particular greater than or equal to 80%, preferably greater than 90%, more preferably greater than 95%.
  • the reflectors may be metallic reflectors, for example aluminum reflectors, dielectric reflectors or combinations of metallic and dielectric reflectors.
  • the reflectors may have focusing, scattering or collimating properties. Further optical elements for the deflection of light may be provided, for example lenses or diffractive elements.
  • the IIV-C curing (ii) of the paint film with the mercury lamp used according to the invention can be carried out in the absence of photoinitiators and in the presence of oxygen, i.e. without an inert gas atmosphere.
  • curing step (ii) is carried out in air.
  • Photoinitiators activatable by UV radiation having a wavelength of > 350 nm generally have an absorption band with a maximum in the 260 to 340 nm range.
  • These include in particular alphahydroxyalkylphenones and alpha-dialkoxyacetophenones such as 1 -hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1 -propanone, 2- hydroxy- 1- ⁇ 4-[4-(2-hydroxy-2- methylpropionyl)benzyl]phenyl ⁇ -2-methylpropan-1-one, 2-hydroxy-1-[4-(2- hydroxyethoxy)phenyl]-2-methyl-1 -propanone or 2, 2-dimethoxy-1 -phenylethanone; phenylglyoxalic esters such as methyl phenylglyoxalate; benzophenones such as benzophenone, 2-hydroxybenzophenone, 3-hydroxybenzophenone, 4-hydroxybenzophenone, 2-methylbenz
  • the abovementioned photoinitiators are present in amounts totaling ⁇ 0.01% by weight based on the solids content of the paint formulation and are preferably absent.
  • the total content of photoinitiators of any kind i.e. including those activatable at wavelengths of > 350 nm, based on the solids content of the paint formulation, is preferably ⁇ 0.01% by weight, in particular photoinitiators are absent altogether.
  • the liquid paint formulations used in the method of the invention comprise at least 80% by weight, in particular at least 85% by weight, e.g. 80% to 99.9% by weight, in particular 85% to 99.5% by weight, based on the total weight of the coating-forming constituents present in the paint formulation, of curable constituents, i.e. substances that have ethylenically unsaturated double bonds.
  • curable constituents i.e. substances that have ethylenically unsaturated double bonds.
  • Substances having ethylenically unsaturated double bonds may be oligomers or polymers as well as monomers. Whereas oligomers and polymers typically have a numberaverage molecular weight Mn of at least 450 g/mol, in particular of at least 500 g/mol, e.g.
  • the number-average molecular weight Mn of monomers is below 450 g/mol and is typically within a range from 100 to 400 daltons.
  • the curable constituents are generally here selected such that the paint formulation F comprises at least 2.0 mol, in particular at least 2.5 mol, and especially at least 3.0 mol, e.g. 2.0 to 8.0 mol, in particular 2.5 to 7.5 mol, and especially 3.0 to 7.0 mol, of ethylenically unsaturated double bonds per kg of the coating-forming constituents present in the liquid paint formulation.
  • the ethylenically unsaturated double bonds in the curable constituents of the paint formulation are present in the form of acrylate groups or methacrylate groups, more particularly to an extent of at least 90% or 100%, based on the total amount of the ethylenically unsaturated double bonds present in the paint formulation, in the form of acrylate or methacrylate groups and especially in the form of acrylate groups.
  • the curable constituents of the paint formulation consist to an extent of at least 90% or 100%, based on the total amount of ethylenically unsaturated double bonds present in the paint formulation, of acrylate groups.
  • the liquid paint formulation comprises according to the invention at least one oligomer or polymer having ethylenically unsaturated double bonds and an average double-bond functionality of at least 1.5, in particular at least 1.8.
  • the oligomers/polymers in the liquid paint formulation preferably have a double-bond functionality within a range from 1.5 to 10, in particular within a range from 1.8 to 8.5, i.e. the average number of ethylenically unsaturated double bonds per molecule of oligomer/polymer is within a range from 1.5 to 10 and in particular within a range from 1.8 to 8.5.
  • oligomers/polymers typically have a linear or branched backbone bearing the ethylenically unsaturated double bonds, which are preferably present in the form of the abovementioned acrylic groups and especially in the form of acrylate groups, it being possible for the ethylenically unsaturated double bonds to be attached to the backbone via a linker or to be a constituent of the backbone.
  • Suitable oligomers and polymers are in particular oligomers and polymers from the group comprising polyethers, polyesters, melamine resins, silicone resins, polyurethanes, polycarbonates, and epoxy resins.
  • the oligomers and polymers are generally selected from polyether (meth)acrylates, i.e. polyethers having acrylate groups and/or methacrylate groups, polycarbonate (meth)acrylates, i.e. polycarbonates having acrylate groups and/or methacrylate groups, polyester (meth)acrylates, i.e. polyesters having acrylate groups and/or methacrylate groups, epoxy (meth)acrylates, i.e. reaction products of polyepoxides with hydroxyl-, amino- or carboxyl- functionalized (meth)acrylate compounds, urethane (meth)acrylates, i.e.
  • oligomers and polymers having a (poly)urethane backbone and acrylate groups and/or methacrylate groups for example reaction products of polyisocyanates with hydroxyl- or amino-functionalized acrylate compounds.
  • unsaturated polyester resins i.e. polyesters having a plurality of ethylenically unsaturated double bonds, which are preferably present in the polymer backbone, e.g. condensation products with aliphatic di- or polyols of itaconic acid, maleic acid or fumaric acid and anhydrides thereof, and mixtures thereof.
  • the curable constituents of the paint formulation having (meth)acrylate groups are preferably selected from compounds of groups (a) to (e) and mixtures thereof:
  • Suitable polyether (meth)acrylates (a) are in particular polyether acrylates, especially those having an average of 1.8 to 6 acrylate groups.
  • Suitable polyether (meth)acrylates are in particular those having an amine modification.
  • Amine-modified polyether (meth)acrylates are modified by Michael addition of amines to the (meth)acrylate double bond.
  • Particularly suitable for the amine modification are diethylamine, dibutylamine, triethylamine, 3- (dimethylamino)propylamine (DMAPA), monoethanolamine, and isopropanolamine.
  • Preferred amine-modified polyether (meth)acrylates have an average of 2.0 to 6.0, more preferably 2.5 to 6.0, (meth) acrylate groups.
  • Preferred amine-modified polyether (meth)acrylates have an amine value of 30 to 90 mg KOH/g. Their number-average molecular weight is preferably within a range from 400 to 1500 g/mol.
  • Preferred liquid, nonaqueous paint formulations comprise at least 20% by weight of amine- modified polyether acrylates. They particularly preferably comprise at least 30% by weight, in particular at least 50% by weight, of amine-modified polyether acrylates.
  • Suitable polyester (meth)acrylates (b) are in particular polyester acrylates, preferably those having an average of 1.8 to 6, more particularly 2.0 to 6.0, acrylate groups. Particular preference is given to aliphatic polyester acrylates having a number-average molecular weight Mn within a range from 500 to 4000 g/mol. Particularly preferred polyester acrylates have a number-average molecular weight within a range from 1000 to 2000 g/mol.
  • Suitable epoxy (meth)acrylates (c) are in particular aromatic epoxy (meth)acrylates, especially aromatic epoxy acrylates.
  • Examples of epoxy acrylates are in particular the reaction products of aliphatic polyglycidyl ethers with acrylic acid or with hydroxy-functionalized acrylic compounds and also the reaction products of aromatic polyglycidyl ethers with acrylic acid or with hydroxyfunctionalized acrylic compounds.
  • the term polyglycidyl ethers encompasses diglycidyl ethers of aliphatic or aromatic diols and also oligomers obtained by reaction of diglycidyl ethers with dihydric or polyhydric alcohols and which besides epoxy groups also have esterifiable hydroxyl groups.
  • Suitable hydroxy-functionalized acrylic compounds are in particular hydroxyalkyl acrylates, e.g. hydroxyethyl acrylate, hydroxypropyl acrylate or hydroxybutyl acrylate.
  • the polyglycidyl ethers used for preparation of the epoxy acrylates typically have an average of 2 to 4 glycidyl groups per molecule and may also have 1 to 4 esterifiable hydroxyl groups.
  • Preferred epoxy acrylates are aromatic epoxy acrylates. Preference among these is given to the reaction products of polyglycidyl ethers based on novolaks and the reaction products of polyglycidyl ethers based on bisphenols, e.g. based on bisphenol A or bisphenol F.
  • aromatic polyglycidyl ethers in particular those based on novolaks, or based on bisphenols such as bisphenol A or bisphenol F, with acrylic acid and/or hydroxyalkyl acrylates.
  • aromatic epoxy acrylates having a number-average molecular weight Mn within a range from 500 to 4000 g/mol.
  • aromatic epoxy acrylates having an average of 1.9 to 5, especially 2 to 4, acrylate groups.
  • the epoxy (meth)acrylates (c) are preferably used together with reactive diluents (e).
  • Particularly preferred reactive diluents for epoxy (meth)acrylates are dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), hexanediol diacrylate (HDDA), and trimethylolpropane triacrylate (TMPTA).
  • Suitable urethane (meth)acrylates (d) are especially urethane acrylates, in particular urethane- group-containing oligomers and polymers having an average of 1.8 to 10, in particular 1.9 to 8.5, acrylate groups and preferably obtainable by reaction of aromatic or aliphatic di- or oligoisocyanates with hydroxyalkyl acrylates.
  • the crosslinkable components of the liquid paint formulation may comprise one or more low-molecular-weight (meth)acrylic esters (e), which are also referred to as reactive diluents.
  • the monomers typically have molecular weights below 450 g/mol, e.g. within a range from 100 to 400 g/mol.
  • Suitable monomers generally have an average of 1 to 6, in particular 2 to 4, ethylenically unsaturated double bonds per molecule.
  • the ethylenically unsaturated double bonds are present here in the form of acrylate or methacrylate groups, preferably as acrylate groups.
  • Preferred monomeric reactive diluents (e) are: esters of acrylic acid with mono- to hexahydric, in particular mono- to tetrahydric, aliphatic or cycloaliphatic alcohols, which may optionally be ethoxylated or propoxylated, and which preferably have 2 to 20 carbon atoms, for example monoesters of acrylic acid with mono- or difunctional alcohols, e.g.
  • Ci to C20 alkanols benzyl alcohol, furfuryl alcohol, tetrahydrofurfuryl alcohol, (5-ethyl-1 ,3-dioxan-5-yl)methanol, phenoxyethanol, cyclic trimethylolpropane formal, butane-1 ,4-diol or with 4-tert-butylcyclohexanol; diesters of acrylic acid with di- or trifunctional alcohols, for example with ethylene glycol, propane-1, 3-diol, propane-1, 2-diol, butane-1 ,4-diol, neopentyl glycol, ethoxylated neopentyl glycol, hexane-1,6-diol, diethylene glycol, triethylene glycol, dipropylene glycol or with tripropylene glycol; triesters of acrylic acid with tri- or tetrafunctional alcohols, for example with glycerol, propoxylated
  • reactive diluents are in particular trimethylolpropane diacrylate, trimethylolpropane triacrylate, ethylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, phenoxyethyl acrylate, furfuryl acrylate, tetrahydrofurfuryl acrylate, 4-t-butylcyclohexyl acrylate, 4-hydroxybutyl acrylate, and trimethylol formal monoacrylate (acrylic acid (5-ethyl-1,3-dioxan-5-yl)methyl ester), the triester with acrylic acid of trimethylolpropane ethoxylated with 2 to 4 moles of ethylene oxide, the diester with acrylic acid of neopentyl glycol ethoxylated with 1 to 3 moles of ethylene oxide, and the diester with acrylic acid of o
  • Particular preferred reactive diluents are selected from dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), hexanediol diacrylate (HDDA), trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, bis(dimethylolpropane) tetraacrylate, and bis(pentaerythritol) hexaacrylate.
  • DPGDA dipropylene glycol diacrylate
  • TPGDA tripropylene glycol diacrylate
  • HDDA hexanediol diacrylate
  • TMPTA trimethylolpropane triacrylate
  • trimethacrylate pentaerythritol tetraacrylate
  • bis(dimethylolpropane) tetraacrylate bis(pentaerythritol) hexa
  • Particularly preferred liquid paint formulations comprise at least 20% by weight, in particular at least 30% by weight, especially at least 50% by weight, of amine-modified polyether acrylates and in addition one or more further curable constituents selected from epoxy acrylates (c), urethane acrylates (d), and reactive diluents (e) or mixtures of two or more of constituents (c), (d), and (e).
  • the liquid paint formulations comprise one or more amine-modified polyether acrylates and one or more epoxy acrylates in a weight ratio of 1 :4 to 4:1.
  • the liquid paint formulations comprise one or more amine-modified polyether acrylates and one or more urethane acrylates in a weight ratio of 1 : 1 to 9: 1.
  • the nonaqueous liquid paint formulations may also comprise one or more organic solvents.
  • Suitable organic solvents are inert toward the functional groups present in the coating composition from the time of addition until the end of the process and have no ethylenically unsaturated double bonds.
  • Suitable solvents are for example those used in coatings technology, such as hydrocarbons, alcohols, ketones, and esters, for example toluene, xylene, isooctane, acetone, butanone, methyl isobutyl ketone, ethyl acetate, butyl acetate, tetra hydrofuran, N-methylpyrrolidone, dimethylacetamide, dimethylformamide.
  • Such solvents preferably constitute not more than 10% by weight, in particular not more than 5% by weight.
  • the paint formulations preferably do not comprise any such organic solvents.
  • the paint formulations of the invention are generally clearcoat formulations.
  • liquid paint formulations are carried out by the methods known to those skilled in the art, for example by spraying, troweling, knifecoating, brushing, rolling, roller coating, pouring or nozzle application. It is likewise possible to apply the paint formulations to a substrate by means of a printing process such as offset printing, flexographic printing, intaglio printing, screen printing or inkjet printing, or by means of a similar method.
  • the amount applied is generally chosen such that, after flashing off, i.e. after removal of any volatile constituents of the paint formulation F, an application of at least 1 g/m 2 (or less, e.g. in the case of offset printing), e.g.
  • 3 to 400 g/m 2 in particular 3 to 200 g/m 2 , and especially 3 to 80 g/m 2 results.
  • Such application volumes result, after step iv. has been carried out, typically in film thicknesses of at least 3 pm, e.g. 3 to 400 pm, in particular 3 to 200 pm, and especially 3 to 80 pm.
  • the film thickness in pm here approximates to the applied amount in g/m 2 after flashing off. This is particularly the case with so-called 100% systems, since these consist exclusively of substances that remain in the cured film and paint formulations of this type show no significant shrinkage in volume during curing, i.e. the shrinkage in volume is typically less than 10% by volume.
  • the liquid nonaqueous paint formulations are preferably paint formulations for the coating of wood, paper, textile, leather, nonwoven, plastics surfaces, glass, ceramic, mineral building materials, such as cement moldings and fiber-cement slabs, and of coated or uncoated metals.
  • liquid nonaqueous paint formulations and the method of the invention are suitable in particular for the coating of wood and woodbase materials and wood-containing substrates, such as fiberboard, and also for the coating of substrates containing cellulose fibers, for example paper, paperboard or cardboard.
  • Wood substrates can for example be pure-wood substrates, for example oak, spruce, pine, beech, maple, walnut, makore, chestnut, plane, robinia, ash, birch, pine, and elm, pure-wood woodbase materials, such as cross-laminated timber, block plywood, glued laminated timber or similar, laminated plywood, veneer wood materials such as veneer plywood, laminated veneer lumber, veneer strip lumber, flexible plywood, or else chipboard materials such as MDF panels, HDF panels or OSB panels, and also cork.
  • pure-wood substrates for example oak, spruce, pine, beech, maple, walnut, makore, chestnut, plane, robinia, ash, birch, pine, and elm
  • pure-wood woodbase materials such as cross-laminated timber, block plywood, glued laminated timber or similar, laminated plywood, veneer wood materials such as veneer plywood, laminated veneer lumber, veneer strip lumber, flexible plywood, or else chipboard materials such as MDF panels, HD
  • Tables 1 to 8 below show the results of the curing experiments with amine-modified polyether acrylates (Laromer PO 9137 and Laromer PO 9139), hexafunctional urethane acrylate (Laromer UA 9162), and epoxy acrylate (Laromer EA 9138) under the following conditions:
  • UV-C lamp from 1ST Metz GmbH High-voltage mercury lamp
  • Lamp power 200 W/cm arc length electrical power consumption
  • the cotton pad is immersed in isopropanol and the soaked pad is rubbed across the cured paint film in 5 double-stroke steps (movement back and forth). After 5 double strokes, the paint surface is in each case assessed for changes in appearance (matting, removal of paint, wear).
  • the double-bond conversion of the EA/POA mixtures without photoinitiator in air is about 85%.
  • Table 7 The same coatings were tested with a film thickness of 10 pm on polypropylene film at a belt speed of 15 m/min and a lamp power of 300 W/cm in air (distance from substrate: 95 mm). The results are shown in Table 8.

Abstract

The invention relates to a method for producing a paint coating on a substrate by UV curing of a liquid, nonaqueous paint formulation comprising at least 80% by weight of curable constituents having (meth)acrylate groups, said method comprising the steps of: (i) applying the liquid paint formulation to the substrate; (ii) curing the paint formulation by irradiating with UV-C radiation in the 180 to 280 nm 10 wavelength range; wherein the total content in the paint formulation of photoinitiators activatable by UV radiation having a wavelength of < 350 nm is < 0.01% by weight based on the paint formulation.

Description

METHOD FOR THE UV CURING OF LACQUERS CONTAINING NON-AQUEOUS POLY(METH)ACRYLATES WITHOUT A PHOTOINITIATOR
Description
The present invention relates to a method for producing a paint coating on an in particular flat substrate by means of a radiation-curing, nonaqueous paint formulation comprising at least 80% by weight of curable constituents having (meth)acrylate groups, in particular on substrates such as paper, wood, woodbase materials, metals, and plastics.
Coating systems cured by exposure to actinic radiation are formulations comprising oligomers or polymers having a plurality of ethylenically unsaturated double bonds, commonly present in the form of acrylate groups or methacrylate groups, and optionally low-molecular-weight ethylenically unsaturated monomers. For production of the coatings, the formulations are applied to the substrate surface to be coated and cured by irradiating with actinic radiation or else with electron beams. What takes place here is a free-radical polymerization of the ethylenically unsaturated double bonds to form a crosslinked polymer film.
One embodiment of radiation-curable coating systems comprises formulations in which essentially all constituents, i.e. at least 80% by weight, in particular at least 90% by weight, of the constituents of the formulation undergo crosslinking through free-radical polymerization. Such coating systems typically comprise no non-polymerizable volatile constituents (VOCs) and are also referred to as 100% systems.
Whereas the presence of photoinitiators is not necessary for the curing of coating compositions with electron beams, the curing of the photosensitive mixtures with UV radiation involves the addition to the coating composition of photoinitiators that absorb the UV radiation, generate radicals or protons, and initiate photopolymerization or photocrosslinking.
The amount of photoinitiators added here is generally over 0.5% by weight of the curable unsaturated compounds, often over 1% by weight. UV curing under an inert gas atmosphere allows the amount of photoinitiator required to be reduced. The presence of atmospheric oxygen inhibits the photopolymerization, since reactive oxygen, which is itself a diradical, scavenges the radicals formed from the photoinitiator or occurring during the free-radical polymerization, thereby taking them out of the polymerization reaction.
It is known that a photocurable paint formulation comprising a photoinitiator is often more unstable than a corresponding formulation without photoinitiator. Since photoinitiators rank among the costly constituents of a UV-curable paint formulations, it is advantageous for the amounts of photoinitiators in UV-curable paint formulations to be only small. Moreover, photoinitiators and fragments thereof that form on irradiation with UV light often result in yellowing of the paint films or obtrusive odors due to volatile substances. There may also be toxicological concerns about the use of photoinitiators. Furniture manufacturers accordingly impose strict requirements on the type and amount of photoinitiators used in UV-curable paint coatings.
The object of the invention is to provide UV-curable paint formulations in which photoinitiators or particular types of photoinitiators are present only in small amounts or are absent altogether, and also to provide a method for producing paint coatings on a flat substrate by UV curing of the paint formulations that may in particular be carried out in air too.
The object is achieved by a method for producing a paint coating on a substrate by UV curing of a liquid, nonaqueous paint formulation comprising at least 80% by weight of curable constituents having (meth)acrylate groups, said method comprising the steps of:
(i) applying the liquid paint formulation to the substrate;
(ii) curing the liquid paint formulation by irradiating with UV-C radiation in the 180 to 280 nm wavelength range; wherein the total content in the paint formulation of photoinitiators activatable by UV radiation having a wavelength of < 350 nm is < 0.01% by weight based on the paint formulation.
The curing of the paint formulation with UV-C light in step (ii) uses according to the invention an irradiation device that in the 180 to 280 nm UV-C range, in particular in the 180 to 240 nm range, has a distinctly higher power output compared with conventional UV-C radiation sources. The radiation source used is according to the invention a mercury lamp, in particular, a mediumpressure mercury lamp. Preferably, the curing (ii) of the liquid paint formulation occurs exclusively with UV-C radiation in the 180 to 280 nm, wavelength range using a mercury lamp. No other type of UV-C irradiation source is used.
The mercury lamp has according to the invention an electrical power consumption (power input) of > 150 W/cm, preferably > 180 W/cm.
In a preferred embodiment, an undoped mercury lamp is used.
The mercury lamp used according to the invention is constructed in the form of a hollow cylinder, the jacket tube of which is made of a material that is transparent to UV radiation. The hollow tube is sealed at its end faces, with the result that the interior of the hollow cylinder forms a closed volume in which a filling gas is enclosed. The hollow cylinder has electrical connections at least at its end faces for transferring energy into the filling gas in the interior of the hollow cylinder. The filling gas consists of at least one noble gas and a proportion of mercury, it being possible for the filling gas to additionally be doped with proportions of metals. Doping may be for example with lead, iron, gallium, indium or other metals, according to individual requirement.
The jacket tube of the mercury lamp has in accordance with the invention high transparency for shortwave UV radiation in the 180 to 240 nm range. It is preferable that the jacket tube is made of a quartz material having high transparency to IIV-C. The jacket tube has high thermal stability. The quartz material used can for example be one of the Suprasil series type from Heraeus, for example Suprasil 3001 130021300.
The filling gas has in operation a working pressure within a range from 1 bar to 10 bar, preferably within a range from 1.5 bar to 8 bar, more preferably within a range from 1.7 bar to 5 bar.
The working voltage per cm arc length is within a range from 5 V/cm to 30 V/cm, preferably within a range from 8 V/cm to 20 V/cm, more preferably within a range from 10 V/cm to 15 V/cm.
The electrical power input of the mercury lamp is in general within a range from 150 to 500 W/cm, preferably within a range from 180 to 500 W/cm, more preferably within a range from 200 to 500 W/cm arc length, even more preferably within a range from 200 to 400 W/cm, more preferably within a range from 200 to 350 W/cm.
The current and voltage per cm arc length are in accordance with the invention optimized for a maximum output in the 180 to 240 nm UV range; the conversion efficiency in this wavelength range is > 13%, preferably > 15%, more preferably > 17%, based on the power input. The IIV-C output per cm arc length in the 180 to 240 nm range is thus in accordance with the invention at least 19.5 W/cm, preferably at least 23.4 W/cm, more preferably at least 25.5 W/cm or at least
23.4 W/cm, preferably at least 27 W/cm and more preferably at least 30.6 W/cm. At a conversion efficiency of 15%, it is in general within a range from 22.5 to 75 W/cm, preferably within a range from 27 to 75 W/cm, even more preferably within a range from 30 to 75 W/cm, more preferably within a range from 30 to 60 W/cm, and in particular within a range from 30 to
52.5 W/cm.
Because of the rotational symmetry of the radiation emissions from the cylindrical lamp, it is expedient to deflect the radiation that is not directly incident on the process plane so as to achieve a higher irradiation effect and thus greater efficiency in the polymerization. The radiation unit accordingly has optical elements such as reflectors for optically deflecting the shortwave radiation emitted by the radiation source into the process plane. The reflectors reflect the UV radiation in the 180 to 240 nm range, preferably in the 180 to 300 nm range, more preferably in the 180 to 400 nm range. The reflectance of the reflectors in the 180 to 240 nm range is in particular greater than or equal to 80%, preferably greater than 90%, more preferably greater than 95%.
The reflectors may be metallic reflectors, for example aluminum reflectors, dielectric reflectors or combinations of metallic and dielectric reflectors. The reflectors may have focusing, scattering or collimating properties. Further optical elements for the deflection of light may be provided, for example lenses or diffractive elements.
It has been found that the IIV-C curing (ii) of the paint film with the mercury lamp used according to the invention can be carried out in the absence of photoinitiators and in the presence of oxygen, i.e. without an inert gas atmosphere.
In a preferred embodiment of the method of the invention, curing step (ii) is carried out in air.
Photoinitiators activatable by UV radiation having a wavelength of > 350 nm generally have an absorption band with a maximum in the 260 to 340 nm range. These include in particular alphahydroxyalkylphenones and alpha-dialkoxyacetophenones such as 1 -hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1 -propanone, 2- hydroxy- 1-{4-[4-(2-hydroxy-2- methylpropionyl)benzyl]phenyl}-2-methylpropan-1-one, 2-hydroxy-1-[4-(2- hydroxyethoxy)phenyl]-2-methyl-1 -propanone or 2, 2-dimethoxy-1 -phenylethanone; phenylglyoxalic esters such as methyl phenylglyoxalate; benzophenones such as benzophenone, 2-hydroxybenzophenone, 3-hydroxybenzophenone, 4-hydroxybenzophenone, 2-methylbenzophenone, 3-methylbenzophenone, 4-methylbenzophenone, 2,4- dimethylbenzophenone, 3,4-dimethylbenzophenone, 2,5-dimethylbenzophenone, 4- benzoylbiphenyl, or 4- methoxybenzophenone; benzoins such as benzoin, benzoin ethyl ether, benzoin isopropyl ether, and benzoin methyl ether; thioxanthones such as 2,4- dimethylthioxanthone, 2,4-diethylthioxanthone, 2,4-diisopropylthioxanthone, and 2,4- dichlorothioxanthone.
The abovementioned photoinitiators are present in amounts totaling < 0.01% by weight based on the solids content of the paint formulation and are preferably absent.
The total content of photoinitiators of any kind, i.e. including those activatable at wavelengths of > 350 nm, based on the solids content of the paint formulation, is preferably < 0.01% by weight, in particular photoinitiators are absent altogether.
The liquid paint formulations used in the method of the invention comprise at least 80% by weight, in particular at least 85% by weight, e.g. 80% to 99.9% by weight, in particular 85% to 99.5% by weight, based on the total weight of the coating-forming constituents present in the paint formulation, of curable constituents, i.e. substances that have ethylenically unsaturated double bonds. Substances having ethylenically unsaturated double bonds may be oligomers or polymers as well as monomers. Whereas oligomers and polymers typically have a numberaverage molecular weight Mn of at least 450 g/mol, in particular of at least 500 g/mol, e.g. within a range from 450 to 10 000 g/mol and especially within a range from 500 to 10 000 g/mol, the number-average molecular weight Mn of monomers is below 450 g/mol and is typically within a range from 100 to 400 daltons. The curable constituents are generally here selected such that the paint formulation F comprises at least 2.0 mol, in particular at least 2.5 mol, and especially at least 3.0 mol, e.g. 2.0 to 8.0 mol, in particular 2.5 to 7.5 mol, and especially 3.0 to 7.0 mol, of ethylenically unsaturated double bonds per kg of the coating-forming constituents present in the liquid paint formulation.
The ethylenically unsaturated double bonds in the curable constituents of the paint formulation are present in the form of acrylate groups or methacrylate groups, more particularly to an extent of at least 90% or 100%, based on the total amount of the ethylenically unsaturated double bonds present in the paint formulation, in the form of acrylate or methacrylate groups and especially in the form of acrylate groups. In particular, the curable constituents of the paint formulation consist to an extent of at least 90% or 100%, based on the total amount of ethylenically unsaturated double bonds present in the paint formulation, of acrylate groups.
The liquid paint formulation comprises according to the invention at least one oligomer or polymer having ethylenically unsaturated double bonds and an average double-bond functionality of at least 1.5, in particular at least 1.8. The oligomers/polymers in the liquid paint formulation preferably have a double-bond functionality within a range from 1.5 to 10, in particular within a range from 1.8 to 8.5, i.e. the average number of ethylenically unsaturated double bonds per molecule of oligomer/polymer is within a range from 1.5 to 10 and in particular within a range from 1.8 to 8.5. Also suitable are mixtures of different oligomers having different functionality, the average double-bond functionality preferably being within a range from 1.5 to 10, in particular within a range from 1.8 to 8.5. The oligomers/polymers typically have a linear or branched backbone bearing the ethylenically unsaturated double bonds, which are preferably present in the form of the abovementioned acrylic groups and especially in the form of acrylate groups, it being possible for the ethylenically unsaturated double bonds to be attached to the backbone via a linker or to be a constituent of the backbone. Suitable oligomers and polymers are in particular oligomers and polymers from the group comprising polyethers, polyesters, melamine resins, silicone resins, polyurethanes, polycarbonates, and epoxy resins.
The oligomers and polymers are generally selected from polyether (meth)acrylates, i.e. polyethers having acrylate groups and/or methacrylate groups, polycarbonate (meth)acrylates, i.e. polycarbonates having acrylate groups and/or methacrylate groups, polyester (meth)acrylates, i.e. polyesters having acrylate groups and/or methacrylate groups, epoxy (meth)acrylates, i.e. reaction products of polyepoxides with hydroxyl-, amino- or carboxyl- functionalized (meth)acrylate compounds, urethane (meth)acrylates, i.e. oligomers and polymers having a (poly)urethane backbone and acrylate groups and/or methacrylate groups, for example reaction products of polyisocyanates with hydroxyl- or amino-functionalized acrylate compounds. Also suitable are unsaturated polyester resins, i.e. polyesters having a plurality of ethylenically unsaturated double bonds, which are preferably present in the polymer backbone, e.g. condensation products with aliphatic di- or polyols of itaconic acid, maleic acid or fumaric acid and anhydrides thereof, and mixtures thereof. The curable constituents of the paint formulation having (meth)acrylate groups are preferably selected from compounds of groups (a) to (e) and mixtures thereof:
(a) polyether (meth)acrylates;
(b) polyester (meth)acrylates;
(c) epoxy (meth)acrylates;
(d) urethane (meth)acrylates;
(e) (meth)acrylate esters of low-molecular-weight diols or polyols as reactive diluents.
Suitable polyether (meth)acrylates (a) are in particular polyether acrylates, especially those having an average of 1.8 to 6 acrylate groups. Suitable polyether (meth)acrylates are in particular those having an amine modification. Amine-modified polyether (meth)acrylates are modified by Michael addition of amines to the (meth)acrylate double bond. Particularly suitable for the amine modification are diethylamine, dibutylamine, triethylamine, 3- (dimethylamino)propylamine (DMAPA), monoethanolamine, and isopropanolamine. Preferred amine-modified polyether (meth)acrylates have an average of 2.0 to 6.0, more preferably 2.5 to 6.0, (meth) acrylate groups. Preferred amine-modified polyether (meth)acrylates have an amine value of 30 to 90 mg KOH/g. Their number-average molecular weight is preferably within a range from 400 to 1500 g/mol.
Preferred liquid, nonaqueous paint formulations comprise at least 20% by weight of amine- modified polyether acrylates. They particularly preferably comprise at least 30% by weight, in particular at least 50% by weight, of amine-modified polyether acrylates.
Suitable polyester (meth)acrylates (b) are in particular polyester acrylates, preferably those having an average of 1.8 to 6, more particularly 2.0 to 6.0, acrylate groups. Particular preference is given to aliphatic polyester acrylates having a number-average molecular weight Mn within a range from 500 to 4000 g/mol. Particularly preferred polyester acrylates have a number-average molecular weight within a range from 1000 to 2000 g/mol.
Suitable epoxy (meth)acrylates (c) are in particular aromatic epoxy (meth)acrylates, especially aromatic epoxy acrylates. Examples of epoxy acrylates are in particular the reaction products of aliphatic polyglycidyl ethers with acrylic acid or with hydroxy-functionalized acrylic compounds and also the reaction products of aromatic polyglycidyl ethers with acrylic acid or with hydroxyfunctionalized acrylic compounds. The term polyglycidyl ethers encompasses diglycidyl ethers of aliphatic or aromatic diols and also oligomers obtained by reaction of diglycidyl ethers with dihydric or polyhydric alcohols and which besides epoxy groups also have esterifiable hydroxyl groups. Suitable hydroxy-functionalized acrylic compounds are in particular hydroxyalkyl acrylates, e.g. hydroxyethyl acrylate, hydroxypropyl acrylate or hydroxybutyl acrylate. The polyglycidyl ethers used for preparation of the epoxy acrylates typically have an average of 2 to 4 glycidyl groups per molecule and may also have 1 to 4 esterifiable hydroxyl groups. Preferred epoxy acrylates are aromatic epoxy acrylates. Preference among these is given to the reaction products of polyglycidyl ethers based on novolaks and the reaction products of polyglycidyl ethers based on bisphenols, e.g. based on bisphenol A or bisphenol F. Preference among these is given to the reaction products of aromatic polyglycidyl ethers, in particular those based on novolaks, or based on bisphenols such as bisphenol A or bisphenol F, with acrylic acid and/or hydroxyalkyl acrylates. Particular preference is given to aromatic epoxy acrylates having a number-average molecular weight Mn within a range from 500 to 4000 g/mol. Particular preference is given to aromatic epoxy acrylates having an average of 1.9 to 5, especially 2 to 4, acrylate groups.
The epoxy (meth)acrylates (c) are preferably used together with reactive diluents (e). Particularly preferred reactive diluents for epoxy (meth)acrylates are dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), hexanediol diacrylate (HDDA), and trimethylolpropane triacrylate (TMPTA).
Suitable urethane (meth)acrylates (d) are especially urethane acrylates, in particular urethane- group-containing oligomers and polymers having an average of 1.8 to 10, in particular 1.9 to 8.5, acrylate groups and preferably obtainable by reaction of aromatic or aliphatic di- or oligoisocyanates with hydroxyalkyl acrylates.
Besides oligomers or polymers having ethylenically unsaturated double bonds, the crosslinkable components of the liquid paint formulation may comprise one or more low-molecular-weight (meth)acrylic esters (e), which are also referred to as reactive diluents. The monomers typically have molecular weights below 450 g/mol, e.g. within a range from 100 to 400 g/mol. Suitable monomers generally have an average of 1 to 6, in particular 2 to 4, ethylenically unsaturated double bonds per molecule. The ethylenically unsaturated double bonds are present here in the form of acrylate or methacrylate groups, preferably as acrylate groups.
Preferred monomeric reactive diluents (e) are: esters of acrylic acid with mono- to hexahydric, in particular mono- to tetrahydric, aliphatic or cycloaliphatic alcohols, which may optionally be ethoxylated or propoxylated, and which preferably have 2 to 20 carbon atoms, for example monoesters of acrylic acid with mono- or difunctional alcohols, e.g. with Ci to C20 alkanols, benzyl alcohol, furfuryl alcohol, tetrahydrofurfuryl alcohol, (5-ethyl-1 ,3-dioxan-5-yl)methanol, phenoxyethanol, cyclic trimethylolpropane formal, butane-1 ,4-diol or with 4-tert-butylcyclohexanol; diesters of acrylic acid with di- or trifunctional alcohols, for example with ethylene glycol, propane-1, 3-diol, propane-1, 2-diol, butane-1 ,4-diol, neopentyl glycol, ethoxylated neopentyl glycol, hexane-1,6-diol, diethylene glycol, triethylene glycol, dipropylene glycol or with tripropylene glycol; triesters of acrylic acid with tri- or tetrafunctional alcohols, for example with glycerol, propoxylated glycerol, trimethylolpropane, ethoxylated trimethylolpropane, propoxylated trimethylolpropane, mixed ethoxylated and propoxylated trimethylolpropane, or with pentaerythritol (ethoxylated or propoxylated) or di(trimethylolpropane); tetraesters of acrylic acid with tetra- or hexafunctional alcohols, for example with pentaerythritol, di(trimethylolpropane) or with ethoxylated pentaerythritol; pentaesters of acrylic acid with hexafunctional alcohols, for example with dipentaerythritol, isosorbide or with ethoxylated and/or propoxylated dipentaerythritol or isosorbide; and also hexaesters of acrylic acid with hexafunctional alcohols, for example with dipentaerythritol, isosorbide or with ethoxylated and/or propoxylated dipentaerythritol or isosorbide.
Examples of reactive diluents are in particular trimethylolpropane diacrylate, trimethylolpropane triacrylate, ethylene glycol diacrylate, butanediol diacrylate, hexanediol diacrylate, dipropylene glycol diacrylate, tripropylene glycol diacrylate, phenoxyethyl acrylate, furfuryl acrylate, tetrahydrofurfuryl acrylate, 4-t-butylcyclohexyl acrylate, 4-hydroxybutyl acrylate, and trimethylol formal monoacrylate (acrylic acid (5-ethyl-1,3-dioxan-5-yl)methyl ester), the triester with acrylic acid of trimethylolpropane ethoxylated with 2 to 4 moles of ethylene oxide, the diester with acrylic acid of neopentyl glycol ethoxylated with 1 to 3 moles of ethylene oxide, and the diester with acrylic acid of neopentyl glycol propoxylated with 1 to 3 moles of propylene oxide.
Particular preferred reactive diluents are selected from dipropylene glycol diacrylate (DPGDA), tripropylene glycol diacrylate (TPGDA), hexanediol diacrylate (HDDA), trimethylolpropane triacrylate (TMPTA), trimethylolpropane trimethacrylate, pentaerythritol tetraacrylate, bis(dimethylolpropane) tetraacrylate, and bis(pentaerythritol) hexaacrylate.
Particularly preferred liquid paint formulations comprise at least 20% by weight, in particular at least 30% by weight, especially at least 50% by weight, of amine-modified polyether acrylates and in addition one or more further curable constituents selected from epoxy acrylates (c), urethane acrylates (d), and reactive diluents (e) or mixtures of two or more of constituents (c), (d), and (e).
In especially preferred embodiments of the invention, the liquid paint formulations comprise one or more amine-modified polyether acrylates and one or more epoxy acrylates in a weight ratio of 1 :4 to 4:1.
In further especially preferred embodiment of the invention, the liquid paint formulations comprise one or more amine-modified polyether acrylates and one or more urethane acrylates in a weight ratio of 1 : 1 to 9: 1.
The nonaqueous liquid paint formulations may also comprise one or more organic solvents.
Suitable organic solvents are inert toward the functional groups present in the coating composition from the time of addition until the end of the process and have no ethylenically unsaturated double bonds. Suitable solvents are for example those used in coatings technology, such as hydrocarbons, alcohols, ketones, and esters, for example toluene, xylene, isooctane, acetone, butanone, methyl isobutyl ketone, ethyl acetate, butyl acetate, tetra hydrofuran, N-methylpyrrolidone, dimethylacetamide, dimethylformamide. Such solvents preferably constitute not more than 10% by weight, in particular not more than 5% by weight. The paint formulations preferably do not comprise any such organic solvents.
The paint formulations of the invention are generally clearcoat formulations.
Application of the liquid paint formulations is carried out by the methods known to those skilled in the art, for example by spraying, troweling, knifecoating, brushing, rolling, roller coating, pouring or nozzle application. It is likewise possible to apply the paint formulations to a substrate by means of a printing process such as offset printing, flexographic printing, intaglio printing, screen printing or inkjet printing, or by means of a similar method. The amount applied is generally chosen such that, after flashing off, i.e. after removal of any volatile constituents of the paint formulation F, an application of at least 1 g/m2 (or less, e.g. in the case of offset printing), e.g. 3 to 400 g/m2, in particular 3 to 200 g/m2, and especially 3 to 80 g/m2 results. Such application volumes result, after step iv. has been carried out, typically in film thicknesses of at least 3 pm, e.g. 3 to 400 pm, in particular 3 to 200 pm, and especially 3 to 80 pm. The film thickness in pm here approximates to the applied amount in g/m2 after flashing off. This is particularly the case with so-called 100% systems, since these consist exclusively of substances that remain in the cured film and paint formulations of this type show no significant shrinkage in volume during curing, i.e. the shrinkage in volume is typically less than 10% by volume.
The liquid nonaqueous paint formulations are preferably paint formulations for the coating of wood, paper, textile, leather, nonwoven, plastics surfaces, glass, ceramic, mineral building materials, such as cement moldings and fiber-cement slabs, and of coated or uncoated metals.
The liquid nonaqueous paint formulations and the method of the invention are suitable in particular for the coating of wood and woodbase materials and wood-containing substrates, such as fiberboard, and also for the coating of substrates containing cellulose fibers, for example paper, paperboard or cardboard. Wood substrates can for example be pure-wood substrates, for example oak, spruce, pine, beech, maple, walnut, makore, chestnut, plane, robinia, ash, birch, pine, and elm, pure-wood woodbase materials, such as cross-laminated timber, block plywood, glued laminated timber or similar, laminated plywood, veneer wood materials such as veneer plywood, laminated veneer lumber, veneer strip lumber, flexible plywood, or else chipboard materials such as MDF panels, HDF panels or OSB panels, and also cork.
The invention is more particularly elucidated by the following examples. Examples
Examples 1-31
Tables 1 to 8 below show the results of the curing experiments with amine-modified polyether acrylates (Laromer PO 9137 and Laromer PO 9139), hexafunctional urethane acrylate (Laromer UA 9162), and epoxy acrylate (Laromer EA 9138) under the following conditions:
UV-C lamp from 1ST Metz GmbH: High-voltage mercury lamp
Reflector: Elliptical, aluminum
Glass: Synthetic quartz glass
Application and curing parameters:
Substrate: Paper
Application device Spiral film applicator, 20 pm
Curing rate: 30 m/min
Lamp power: 200 W/cm arc length electrical power consumption
Distance from substrate: 95 mm
Atmosphere: Ambient air
Assessment of the cured paint films:
Isopropyl alcohol double strokes:
The cotton pad is immersed in isopropanol and the soaked pad is rubbed across the cured paint film in 5 double-stroke steps (movement back and forth). After 5 double strokes, the paint surface is in each case assessed for changes in appearance (matting, removal of paint, wear).
Double-bond conversion in clearcoat:
Raman microscope (A = 523 nm, 100x lens, 30 s) Aliphatic (2925-2945 cm’1) vs. C=C (1631-1641) Reference: Liquid paint
Film thickness: 200 pm gap frame draw down bar Drying: 20 min at 50°C Examples 1-4
Table 1
Figure imgf000012_0001
Examples 5-27
Based on the results from Table 1 , various mixtures were tested. The results are shown in Tables 2 to 6: Table 2
Figure imgf000012_0002
Table 3
Figure imgf000012_0003
Figure imgf000013_0001
Table 4
Figure imgf000013_0002
Table 5
Figure imgf000013_0003
Table 6
Figure imgf000014_0001
The double-bond conversion of the EA/POA mixtures without photoinitiator in air is about 85%.
Examples 28-31
In the experiments below, the curing parameters were kept constant, but the coatings were cured 1-5 times and then the double-bond conversion determined. The results are shown in Table ?.
Table 7
Figure imgf000014_0002
The same coatings were tested with a film thickness of 10 pm on polypropylene film at a belt speed of 15 m/min and a lamp power of 300 W/cm in air (distance from substrate: 95 mm). The results are shown in Table 8.
Examples 32-35
Table 8
Figure imgf000015_0001

Claims

Claims
1. A method for producing a paint coating on a substrate by UV curing of a liquid, nonaqueous paint formulation comprising at least 80% by weight of curable constituents having (meth)acrylate groups, said method comprising the steps of:
(i) applying the liquid paint formulation to the substrate;
(ii) curing the paint formulation by irradiating with IIV-C radiation in the 180 to 280 nm wavelength range; wherein the total content in the paint formulation of photoinitiators activatable by UV radiation having a wavelength of < 350 nm is < 0.01% by weight based on the paint formulation.
2. The method according to claim 1 , wherein the paint formulation is cured in step (ii) with a mercury lamp.
3. The method according to claim 2, wherein the power consumption of the mercury lamp per cm arc length is > 150 W/cm, preferably > 180 W/cm, and the conversion efficiency for UV-C radiation in the 180 to 240 nm wavelength range is at least 13% based on the power consumption.
4. The method according to claim 3, wherein the conversion efficiency for UV radiation in the 180 to 240 wavelength range is at least 15 % and the power consumption is from 200 to 500 W/cm.
5. The method according to any one of claims 1 to 4, wherein curing step (ii) is carried out in air.
6. The method according to any of claims 1 to 5, wherein the paint formulation does not comprise any photoinitiators activatable by UV radiation having a wavelength of < 350 nm and preferably photoinitiators are absent altogether.
7. The method according to any of claims 1 to 6, wherein the curable constituents of the paint formulation having (meth)acrylate groups are selected from:
(a) polyether (meth)acrylates;
(b) polyester (meth)acrylates;
(c) epoxy (meth)acrylates;
(d) urethane (meth)acrylates;
(e) (meth)acrylate esters of low-molecular-weight diols or polyols as reactive diluents.
8. The method according to any of claims 1 to 7, wherein the paint formulation comprises amine-modified polyether acrylates (a).
9. The method according to claim 8, wherein the paint formulation comprises at least 20% by weight of amine-modified polyether acrylates (a).
10. The method according to claim 8 or 9, wherein the paint formulation comprises one or more further curable constituents selected from epoxy acrylates (c), urethane acrylates (d), and reactive diluents (e).
11. The method according to any of claims 1 to 10, wherein the paint formulation comprises
< 10% by weight of non-UV-curable solvents.
12. The method according to any of claims 1 to 11 , wherein the paint formulation is a clearcoat formulation.
13. The method according to any of claims 1 to 12, wherein curing step (ii) is carried out by means of a mercury lamp.
14. The method according to claim 13, wherein the mercury lamp is an undoped mercury lamp.
15. The method according to claim 13, wherein the mercury lamp is a mercury lamp doped with gallium, indium, iron or lead or with a combination thereof.
16 The method according to any of claims 1 to 15, wherein the substrate used is a wood substrate.
17. The method according to claim 16, wherein the wood substrate is selected from pure- wood substrates, such as oak, spruce, pine, beech, maple, walnut, makore, chestnut, plane, robinia, ash, birch, pine, and elm, pure-wood woodbase materials, such as crosslaminated timber, block plywood, glued laminated timber, and laminated plywood, veneer wood materials such as veneer plywood, laminated veneer lumber, veneer strip lumber, and flexible plywood, chipboard materials such as MDF panels, HDF panels or OSB panels, and also cork.
18. A liquid, nonaqueous paint formulation comprising at least 80% by weight of curable constituents having (meth)acrylate groups and comprising < 0.01% by weight, based on the paint formulation, of photoinitiators activatable by UV radiation having a wavelength of
< 350 nm.
19. The liquid, nonaqueous paint formulation according to claim 18, wherein the curable constituents of the paint formulation having (meth)acrylate groups are selected from
(a) polyether acrylates;
(b) polyester acrylates; 17
(c) epoxy acrylates;
(d) urethane acrylates;
(e) (meth)acrylate esters of low-molecular-weight diols or polyols as reactive diluents.
20. The liquid, nonaqueous paint formulation according to claim 18 or 19, wherein the paint formulation comprises at least 20% by weight of amine-modified polyether acrylates (a).
21. The liquid, nonaqueous paint formulation according to any of claims 18 to 20, wherein the paint formulation comprises one or more further curable constituents selected from epoxy acrylates (c), urethane acrylates (d), and reactive diluents (e).
22. The liquid, nonaqueous paint formulation according to any of claims 18 to 21 , wherein the paint formulation comprises < 10% by weight of non-UV-curable solvents.
23. The liquid, nonaqueous paint formulation according to any of claims 18 to 22, wherein the paint formulation is a clearcoat formulation.
PCT/EP2021/073041 2020-08-28 2021-08-19 Method for the uv curing of lacquers containing non-aqueous poly(meth)acrylates without a photoinitiator WO2022043181A1 (en)

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EP20193395.9 2020-08-28
EP20193395 2020-08-28

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Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006117163A1 (en) * 2005-05-02 2006-11-09 Basf Aktiengesellschaft Method for treating wood surfaces
WO2010054711A1 (en) * 2008-11-15 2010-05-20 Basf Coatings Ag High-transparency polycarbonates with scratch-resistant coating, process for production thereof and use thereof
EP2198981A1 (en) * 2008-12-10 2010-06-23 Innovative Oberflächentechnologie GmbH Method and apparatus for direct radiation-induced polymerisation and integration of acrylates and methacrylates
WO2010089203A1 (en) * 2009-02-05 2010-08-12 Tesa Se Pressure-sensitive adhesive transfer tape with differentiated adhesion on either side and method for producing the tape

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006117163A1 (en) * 2005-05-02 2006-11-09 Basf Aktiengesellschaft Method for treating wood surfaces
WO2010054711A1 (en) * 2008-11-15 2010-05-20 Basf Coatings Ag High-transparency polycarbonates with scratch-resistant coating, process for production thereof and use thereof
EP2198981A1 (en) * 2008-12-10 2010-06-23 Innovative Oberflächentechnologie GmbH Method and apparatus for direct radiation-induced polymerisation and integration of acrylates and methacrylates
WO2010089203A1 (en) * 2009-02-05 2010-08-12 Tesa Se Pressure-sensitive adhesive transfer tape with differentiated adhesion on either side and method for producing the tape

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