GB2447659A

GB2447659A - Laser markable compositions

Info

Publication number: GB2447659A
Application number: GB0705232A
Authority: GB
Inventors: Christopher Anthony Wyres; Anthony N Jarvis; Martin Robert Walker
Original assignee: DataLase Ltd
Current assignee: DataLase Ltd
Priority date: 2007-03-19
Filing date: 2007-03-19
Publication date: 2008-09-24
Also published as: GB0705232D0

Abstract

A laser-markable composition comprises a compound which is metal oxyanion or metal thioanion. Also shown is a method of producing a readable image by exposing the compound and a near infrared-absorbing agent to laser irradiation in the wavelength range 780 to 2500 nm. The metal oxyanion may be selected from chromates or polychromates and the metalthioanion may be selected from thiovanadates and polythiovanadates.

Description

Intellectual Property Of:o Fon CeaIoty and Inn0voIOfl Application No.

GB0705232.7 RTM Date:10 July 2008 The following terms are registered trademarks and should be read as such wherever they occur in this document: LUMOGEN, PRO-JET, TEXICRYL, WITCOBOND, PIOLOFORM, ELVACITE,

OCTAFORM

UK Intellectual Property Office is an operating name of The Patent Office

I

LASER MARKABLE COMPOSITIONS

It has been found that the following compounds when incorporated into an ink * formulation and printed on to a substrate surprisingly give rise to readable images when exposed to CO2 laser radiation. It was also observed that readable images could be produced by combining said compounds with a near infrared absorbing agent and exposing the system to laser radiation in the wavelength range 780 to 2500rm.

The compounds are complex polyanions such as metal oxyanions and metal thioanions. Preferred compounds being oxyanlons.

Examples of metal oxyanions include: Chromates and polychromates such as dichromate, peroxychromates, hydrogen arsenates, orthoarsenates, molybdates and polymolybdates such as tn, tetra, penta, hexa, nona, deca, undeca and dodecamolybdate, borates and polyborates such as tetra and pentaborates, peroxyborates, perrhenates, phosphomolYbdates permolybdates and perpolymolybdates, molybdotellurates, phosphotungstates, selenates, bis(oxalate)oxotitaflates, silicomolybdates, vanadates and polyvanadates such as metavanadate, fluoroniobate and polyfluoronlobates such as hexafluorofliObateS. niobate oxalates, tellurates, tungstates and polytungstates such as mete, di, tn, tetra, penta, hexa, hepta, octa, nona, deca, undecatungstates and dodecatungstateS. oxalatopalladiums. cobaltphosphates, Examples of metal thioanions include: Thiovanadates and polythiovandates such as tetra thiovanadates, thiomolybdates and polythiomolybdates such as tetrathiomolybdate, thlotungstates and polythiotungstates such as tetrathiotungstate.

The cationic counter ions of the complex polyanion can be protons, ammonium and other quatemary nitrogen salts, alkali or alkaline earth metals. Preferred are ammonium and alkali earth such as sodium.

The laser radiation that can be used to initiate the colour change reaction can be ultraviolet, visible, near infrared or CO2 laser radiation ("-10.6 microns). Preferred is near infrared and CO2 laser radiation. It has been found that the said compounds of the present invention can used without the need for other absorbing additives whenever CO2 laser radiation is employed. However, if near infrared laser radiation (i.e. with a wavelength of 780 to 2500nm) Is employed it is desirable to also employ a near * infrared absorbing additive. Near infrared radiation is that which falls in the wavelength range 780 to 2500nm. The near infrared laser can be a diode, fibre or a diode array system. Preferred near infrared absorbing compounds are those that have an absorbance maximum similar to the wavelength of the near infrared radiation employed and have little or no visible colour. Suitable examples include copper compounds such as copper (II) hydroxyl phosphate (CHP), non- stoichiometriC mixed metal oxide compounds such as reduced indium tin oxide and reduced antimony tin oxide, organic polymers such as the conductive polymer product Baytron P supplied by HC Starck, and near Infrared absorbing organic molecules, known to those skilled In the art as NIR dyeslpigmentS. Types of NIR dyes/pigments than can be used comprise, but are not limited to: families of metallo-porphyrins, metallo-thiolenes and polythiolenes, metallo-phthalocyanine$, aza-variants of these, annellated variants of these, pyrylium salts, squaryliums, croconiums, amminiums, diimoniums, cyanines and Indolenine cyanines.

Examples of organic compounds that can be used in the present invention are taught in US691 1262, and are given in Developments in the Chemistry and Technology of Organic dyes, J Griffiths (ed), Oxford: Blackwell Scientific, 1984, and Infrared Absorbing Dyes, M Matsuoka (ed), New York: Plenum Press 1990. Further examples of the NIR dyes or pigments of the present invention can be found in the EpoIight1' series supplied by Epolin, Newark, NJ, USA; the ADS series supplied by American Dye Source lnc, Quebec, Canada; the SDA and 8DB series supplied by HW Sands, Jupiter, FL, USA; the Lumogentm' series supplied by BASF, Germany, particularly LumogenN lR765 and lR788; and the Pro-Jet series of dyes supplied by FujiFilm Imaging Colorants, Blackley, Manchester, UK, particularly ProJet 830NP, 900NP, 825LD1 and 83OLDI.

The ink formulation can be aqueous or non-aqueous based. The binder system can be anything suitable that is used In ink formulations. Suitable examples include the Texicryl series supplied by Scott-Bader (NorthamptOflShire, England), the WitcoBond series supplied by Baxenden Chemicals (Accnngton, England), the Pioloform series supplied by Wacker-Chemie (Munich, Germany), the Elvacite series supplied by Lucite International Inc (Southampton, England), the Paranol series supplied by Para-Chem (South Carolina, USA) and the nitrocellulose series supplied by. Nobel Enterprises (Ayrshire, Scotland).

* It can be applied to any known substrate such as: paper, card, board and corrugate, polymer films, and other packaging/box materials.

Examples

Ammonium metatungstate was purchased from Aldrich.

Silicomolybdic acid was purchased from Aldrich.

Paranol 1-6320 -aqueous acrylic-urethane resin, ex. Para-Chem.

Octafoam E-235 -defoamer, ex. Octel Copper (II) hydroxyl phosphate (CHP) -near infrared absorber, ex. Aldrich.

Pioloform 8N18 -poly(vinyl butyrat), ex. Wacker-Chemie.

Other substances were standard laboratory grade.

1. Synthesis of ammonium silicomolybdate.

Silicomolybdic acid (25g) was suspended in water (500ml) at 20 C. To this suspension, 33% aqueous ammonia solution was added until the silicomolybdate had dissolved. The reaction mixture pH was 8.0. The reaction was then stirred for a further two hours and the solid ammonium silicomolybdate product collected by rotary evaporation.

Examole 1. aqueous Inks

Example IA

Paranol T-6320 64g Octafoam E-235 Ig Ammonium metatungstate 35g

Example lB

Paranol T-6320 32g Octafoam E-235 0.Sg Ammonium metatungstate 17.5g

Example IC

ParanolT-6320 44g Octafoam E-235 ig Ammonium metatungstate 35g S CHP 20g

Example ID

Paranol T-6320 22g Octafoam E-235 0.Sg Ammonium metatungstate 17.5g CHP lOg ExamDle 2. non-aoueous inks

Example2A

Ploloform BN-18 15g Ammonium metatungstate 35g Methyl ethyl ketone 50g

Example 2B

Ploloform BN-18 7.5g Ammonium silicomolybdate 17.5g Methyl ethyl ketone 25g

Example 2C

Pioloform BN-I 8 1 5g Ammonium metatungstate 35g CHP 20g Methyl ethyl ketone 30g

Example 2D

PiotoformBN-18 7.5g Ammonium silicomolybdate 17.5g CHP lOg Methyl ethyl ketone 159 Analogous inks were also prepared that did not contain any metatungstate or silicomolybdate colour former.

* Each ink was milled using an Eiger-TorraflCe bead mill (50m1 capacity) and then drawn down on to 50 micron PET film (cx. HiFi) using an RK-Cqater bar.

The approximate coat weight applied was 5.0 gem.

The laser systems employed were: 1. A Videojet CO2 laser, rated at 30W, connected to a galvo scanning head controlled by an IBM compatible PC. Used with inks IA, IB, 2A and 2B 2. A 1066nm fibre laser, rated at 5W, connected to a galvo scanning head controlled by an IBM compatible PC. Used with inks IC, ID, 2C and 2D.

RESULTS

Inks IA, 18, IC and ID produced dark readable text images upon exposure to CO2 laser radiation.

Inks I C, ID, 2C and 2D produced dark readable text images upon exposure to 1066nm laser radiation.

The inks prepared without metatungsate and silicomolybdate colour formers yielded barely perceivable brown marks.

Claims

1. A laser-markable composition comprising a compound which is a metal oxyanion or metal thioanion.

2. A composition according to claim 1, wherein the metal oxyanion is selected from chromates and polychromates such as dichromate, peroxychromates, hydrogen arsenates, orthoarsenates1 molybdates and polymolybdates such as tn, tetra, penta, hexa, nona, deca, undeca and dodecamolybdate, borates and polyborates such as tetra and pentaborates, peroxyborates, perrhenates, phosphomolybdates, permolybdates and perpolymolybdates, molybdotellurates, phosphotungstates. selenates, bis(oxalate)oxotitanateS, silicomolybdates, vanadates and polyvanadates such as metavanadate, fluoroniobate and polyfluoroniobates such as hexafluoroniobates. niobate oxalates, tellurates, tungstates and polytungstates such as meta, di, tn, tetra, penta, hexa, hepta, octa, nona, deca, undecatungstateS and dodecatungstates, oxalatopalladiums, cobaltphosphates.

3. A composition according to claim I, wherein the metal thioanion is selected from thiovanadates and polythiovandates such as tetra thiovanadates, thiomolybdates and polythiomolybdates such as tetrathiomotybdate, thiotungstates and polythiotu ngstates such as tetrathiotungstate.

4. A composition according to any preceding claim, wherein the cationic counter ion of the metal oxyanion or metal thioanion is ammonium, a quaternary nitrogen or an alkali or alkaline earth metal.

5. A substrate to which a composition according to any preceding claim has been applied.

6. A method for producing a readable image by exposing a compound as defined in any of claims I to 4 and a near infrared-absorbing agent to laser irradiation in the wavelength range 780 to 2500 nm.