WO2000049097A1

WO2000049097A1 - Stable titanium dioxide containing ink jet ink composition

Info

Publication number: WO2000049097A1
Application number: PCT/US2000/001201
Authority: WO
Inventors: Michael Pierce Secord; Richard Charles Woudenberg
Original assignee: Markem Corporation
Priority date: 1999-02-19
Filing date: 2000-01-19
Publication date: 2000-08-24
Also published as: AU3210000A

Abstract

An ink jet ink composition is disclosed. The ink composition includes greater than 5% by weight titanium dioxide and a vehicle that includes a polymerizable component, wherein the ink composition is essentially solvent free.

Description

STABLE TITANIUM DIOXIDE CONTAINING INK JET INK COMPOSITION

Background of the Invention The invention relates to ink compositions for ink jet printing.

Inkjet printing, for example, continuous ink jet printing and drop-on-demand ink jet printing, involves forming characters on a substrate by ejecting ink droplets from a printhead having one or more nozzles. Inkjet printing often employs inks such as volatile solvent based inks, hot melt inks that are solid at room temperature but liquid at jetting temperatures, UV light curable inks, and e-beam curable inks.

Inkjet printers may be used for printing graphics, logos, photographic quality images, and codes (e.g., manufacturing and/or expiration dates, lot number, manufacturing location) on packaging materials for consumer products like candy bars, milk cartons, and other food products, as well as directly on some types of products such as computer chips, PVC pipe, electrical wiring, plastic and bottles.

White inks, i.e., inks containing titanium dioxide, are used to mark darker substrates such as black substrates commonly used to house computer chips. Titanium dioxide is a relatively high density pigment and tends to aggregate and form agglomerates that precipitate out of the ink compositions. Consequently, it is difficult to formulate ink compositions containing titanium dioxide that are suitable for use in ink jet printing such that they provide a sufficiently opaque mark.

Summary of the Invention

In one aspect, the invention features an ink jet ink composition that includes greater than 5% by weight titanium dioxide, and a vehicle that includes a polymerizable component, wherein the ink composition is essentially solvent free. In one embodiment, the composition exhibits a viscosity of at least about 60 centipoise at 25 C. In another embodiment, the composition exhibits a viscosity of at least about 100 centipoise at 25°C.

In other embodiments, the composition includes at least about 8% by weight titanium dioxide. In some embodiments, the composition exhibits an opacity of no greater than about 0.7 when measured according to the Opacity Test Method. In other embodiments, the composition exhibits an opacity of no greater than about 0.6 when measured according to the Opacity Test Method. In one embodiment, the titanium dioxide is in the form of a sufficiently stable homogeneous suspension such that the ink composition is suitable for use in a drop-on- demand ink jet engine. In preferred embodiments, the titanium dioxide is in the form of microencapsulated titanium dioxide particles. In some embodiments, the titanium dioxide particles include an encapsulating layer of polyvinylbutyral.

In some embodiments, the polymerizable component of the vehicle is photopolymerizable. In other embodiments, the polymerizable component is capable of being polymerized by electron beam radiation. In still other embodiments, the polymerizable component is thermosettable. Useful polymerizable components are selected from the group consisting of epoxy-functional, acrylate-functional, methacrylate-functional and vinyl ether-functional polymerizable components, and combinations thereof. In some embodiments, the polymerizable component includes a cycloaliphatic epoxide.

In one preferred embodiment, the ink jet ink composition is essentially solvent free and includes encapsulated titanium dioxide particles in an amount sufficient to provide an ink composition comprising greater than 5% by weight titanium dioxide, and a vehicle that includes a polymerizable component.

In another aspect, the invention features a hot melt ink jet ink composition that is essentially solvent free, and includes greater than 5% by weight titanium dioxide and a vehicle that includes a hot melt component. In one embodiment, the hot melt component includes hydroxy wax.

In other aspects, the invention features an ink jet ink composition that includes greater than 5% by weight titanium dioxide, and a vehicle that includes a film-forming resin and a nonvolatile solvent, wherein the titanium dioxide is in the form of a sufficiently stable homogeneous suspension such that the ink composition is suitable for use in a drop-on-demand ink jet engine, and the ink composition is essentially free of volatile components.

In one embodiment, the nonvolatile solvent includes a polar solvent. In other embodiments, the nonvolatile solvent includes a nonpolar solvent and a polar solvent. In one embodiment, the nonvolatile solvent includes tripropyleneglycol monomethylether. In other aspects, the invention features an ink jet printer that includes the above-described ink jet ink compositions. In another aspect, the invention features an ink jet printing process that includes ejecting the above-described ink jet ink compositions from an ink jet printer onto a surface.

The ink compositions of the invention employ titanium dioxide to provide a white ink that is capable of marking substrates and is particularly well-suited to marking dark substrates and clear substrates such as, e.g., housings used to encase computer chips, plastics, black plastics, bottles, and cans. The level of opacity that can be achieved by the ink compositions of the invention enables substrates to be clearly marked with opaque white indicia. In addition, the homogeneity and viscosity characteristics of the ink composition are well-suited for use in drop-on-demand ink jet printing.

Other features and advantages of the invention will be apparent from the following description of the preferred embodiments thereof, and from the claims.

Description of the Preferred Embodiments

The titanium dioxide of the ink composition is preferably in the form of a microparticle in which the titanium dioxide is surrounded by or dispersed throughout an encapsulating material. O^nfegxample of a suitable encapsulating material is poly vinyl butyral. Particularly useful microencapsulated titanium dioxide particles are commercially available under the trade designation Renol HW from Clariant (Rhode Island). The titanium dioxide preferably has an average particle size of from about 140 nm to about 1 micron, more preferably from about 140 nm to about 400 nm. The amount of titanium dioxide present in the ink composition is greater than 5% by weight, more preferably at least about 8% by weight, most preferably from about 10% to about 15% by weight. The vehicle of the ink composition is the carrier for the titanium dioxide. The vehicle and the microencapsulation material, when present, are selected to provide a substantially homogeneous suspension of titanium dioxide in the vehicle. The vehicle is further selected to permit the formation of a durable, opaque ink mark on a substrate after the ink composition has been ejected from an ink jet printer, and to provide an ink composition having a viscosity suitable for use in drop-on-demand ink jet printing. The vehicle can be selected to achieve an ink composition having a viscosity at 25 C of at least about 60 centipoise ("cPs") when measured according to the Viscosity Test Method set forth in the Examples section below. The vehicle can also be selected to achieve an ink composition that is a solid at 25 C.

The vehicle is further selected to provide an ink composition that exhibits a viscosity at the jetting temperature of an ink jet print engine that is sufficient to permit ejection of the ink composition from the ink jet printer, e.g., preferably a viscosity at the jetting temperature of no greater than about 30 cPs, more preferably no greater than about 25 cPs. Jetting temperatures of ink jet engines typically range from about 30 C to about 150°C.

The vehicle may include a polymerizable component selected to provide, upon cure, a highly cross-linked, solvent insoluble film. Preferably the polymerizable component is polymerizable upon exposure to radiation, e.g., thermal, electron beam, ultra violet ("UV") or visible radiation, and combinations thereof. Useful polymerizable components (e.g., monomers and oligomers) have at least one functional group such as, e.g., epoxy, acrylic, or vinyl ether functional groups. The polymerization process can proceed by a number of mechanisms including, e.g., cationic or free-radical mechanisms. If desired, both cationically active and free radically active functional groups may be contained in a single molecule.

Materials having cationically active functional groups include cationically polymerizable epoxy resins. Suitable epoxy functional compounds include mono-, bi-, tri-, and higher functionality epoxy compounds. Such materials are organic compounds having an oxirane ring, i.e., a group of the formula which is polymerizable by ring opening. These materials include monomeric epoxy compounds and epoxides of the polymeric type and can be aliphatic, cycloaliphatic, aromatic or heterocyclic. These materials generally have, on the average, at least 1 polymerizable epoxy group per molecule, preferably at least about 1.5 and more preferably at least about 2 polymerizable epoxy groups per molecule. The polymeric epoxides include linear polymers having terminal epoxy groups (e.g., a diglycidyl ether of a polyoxyalkylene glycol), polymers having skeletal oxirane units (e.g., polybutadiene polyepoxide), and polymers having pendent epoxy groups. The epoxides may be pure compounds or may be mixtures of compounds containing one, two, or more epoxy groups per molecule. The "average" number of epoxy groups per molecule is determined by dividing the total number of epoxy groups in the epoxy - containing material by the total number of epoxy-containing molecules present. Examples of useful epoxy functional polymerizable components include 1 ,4- butanediol diglycidyl ether, 3-bis(glycidyloxymethyl)methoxy)-l,2-propanediol, limonene oxide, 2-biphenyl glycidyl ether, 3,4-epoxycyclohexylmethyl-3',4'- epoxycyclohexane carboxylate, bis(3,4-epoxcyclohexylmethyl) adipate, 3,4- epoxcyclohexylmethyl-3,4-epoxycyclohexyl carboxylate, vinyl cyclohexene dioxide, O- cresyl glycidyl ether, and combinations thereof.

Other materials having cationically active functional groups include cationically polymerizable vinyl ethers.

Materials having free radically active functional groups include monomers, oligomers, and polymers having one or more ethylenically unsaturated groups. Suitable materials contain at least one ethylenically unsaturated bond, and are capable of undergoing addition polymerization. Such free radically polymerizable materials include mono-, di- or poly- acrylates and methacrylates. One example of a useful aery late is hydroxy polyester acrylate. Examples of useful commercially available polymerizable components include limonene dioxide (available from Elf Atochem), ERL-4206 vinyl cyclohexene diepoxide and ERL 4221 3,4-epoxy cyclohexylmethyl-3,4-epoxy cyclohexyl carboxylate (both of which are available from Union Carbide), Cyracure UVR 6128 bis-[3,4- epoxycyclohexylmethyl] adipate (available from Union Carbide), GE-21 1 ,4-butanediol diglycidyl ether and GE-10 O-cresyl glycidyl ether (both available from CVC Specialty Chemicals, Inc.), and UVR 6105 3,4-epoxy cyclohexylmethyl-3,4-epoxy cyclohexyl carboxylate (available from Union Carbide).

The ink composition may also include initiators, e.g., thermal initiators, photoinitiators, initiators sensitive to ion beam radiation, and combinations thereof. Representative examples of thermal initiators include amine blocked salts, e.g., amine blocked paratoluene sulfonic acid and trifluoromethanesulfonic acid initiators (e.g., FC- 520 resin catalyst commercially available from Minnesota Mining and Manufacturing, St. Paul, Minnesota).

Representative examples of useful cationic initiators include onium salts and mixed ligand arene cyclopentadienyl metal salts with complex metal halide ions, as described in "CRC Handbook of Organic Photochemistry," vol. II, ed. J.C. Scaiano, pp. 335-339 (1989). The initiation system may also include a sensitizer such as a visible light sensitizer.

In compositions that include both free radically active functional groups and cationically active functional groups it may be desirable to use an initiation system suitable for initiating both free radical and cationic polymerization. In the case of compositions that include both free radically active functional groups and cationically active functional groups, it may be desirable to use one initiation system for free radical polymerization and a separate initiation system for cationic polymerization. The free radical polymerization initiation system can then be selected such that upon activation, only free radical polymerization is initiated.

One class of initiators capable of initiating polymerization of free radically active functional groups, but not cationically active functional groups, includes free radical-generating photoinitiators, optionally combined with a photosensitizer or accelerator. Such initiators typically are capable of generating free radicals for addition polymerization at some wavelength between 200 and 800 nm. Examples include alpha- diketones, monoketals of alpha-diketones or ketoaldehydes, acyloins and their corresponding ethers, chromophore-substituted halomethyl-s-triazines, and chromophore- substituted halomethyl-oxadiazoles.

N second class of initiators capable of initiating polymerization of free radically active functional groups, but not cationically active functional groups, includes free radical-generating thermal initiators. Examples include peroxides and azo compounds such as NIBΝ.

The dual initiation systems further include a separate photoinitiation system for initiating polymerization of the cationically active functional groups. The cationic initiation system is selected such that activation of the free radical initiation system does not activate the cationic initiation system. Examples of suitable cationic photoinitiation systems for a dual initiation system composition include the onium salts and mixed ligand arene cyclopentadienyl metal salts with complex metal halide ions described above. The vehicle may include a hot melt component (i.e., a component that is solid at room temperature but is liquid at the jetting temperature of an ink jet printer). Examples of useful hot melt components include hydroxy wax (e.g., Castor wax MP-70 commercially available from CasChem), dimerized rosin ester (e.g., Sylvalac 295 commercially available from Arizona Chemical), phthalate plasticizer (e.g., Morflex 150 commercially available from Morflex Inc., Greensboro, North Carolina), disproportionated rosin ester (e.g., DR-10 commercially available from Arizona Chemical), and polyketone resin (e.g., Khrumbaar 1717 HMP commercially available from Lawter International Inc., Kenosha, Wisconsin).

Ink compositions that include a hot melt component may be formulated to be solid at room temperature and liquid at the jetting temperature of an ink jet engine.

The ink composition may optionally include other conventional ingredients including, e.g., accelerators, antioxidants, surfactants, rheology modifiers, adhesion promoters.

Hot melt ink compositions, for example, may include additional resins and flexibilizers/plasticizers. Examples of flexibilizers/plasticizers include aromatic sulfonamides, phthalates, acetates, adipates, amides, azelates, epoxides, glutarates, laurates, oleates, sebacates, stearates, sulfonates, tallates, phosphates, benzoin ethers, and trimellitates. A sufficient quantity of an optional ingredient may be included in the ink to provide the desired property.

The ink composition is essentially free of solvent capable of solubilizing the vehicle. Examples of such solvents include water, alcohols (e.g., ethanol, methanol and propanol), ketones (e.g., methylethyl ketone), esters, aromatics and ethers. In another embodiment, the ink composition includes titanium dioxide and a vehicle that includes a film-forming resin and a nonvolatile solvent. In this embodiment, the ink composition is essentially free of volatile components and is suitable for use in drop-on-demand ink jet print engines.

Examples of useful film-forming resins include polyketones. Examples of useful nonvolatile solvents include nonvolatile polar solvents and combinations of nonvolatile polar and nonvolatile nonpolar solvents. Suitable nonvolatile polar solvents include glycols, e.g., tripropylene glycol monomethylether.

The ink compositions are capable of forming an opaque mark on a substrate after ejection from an Inkjet printer. Preferably the titanium dioxide, the amount of titanium dioxide, and the vehicle are selected to provide an ink composition having an opacity of no greater than about 0.7, more preferably no greater than about 0.6, at 0.5 mil wet drawdown when measured according to the Opacity Test Method set forth in the Examples section below. The invention will now be described further by way of the following examples.

EXAMPLES

Test Procedures Test procedures used in the examples include the following.

Opacity Test Method

The opacity of an ink composition is determined as follows.

Three samples are prepared by coating an ink composition onto a glass substrate at a coating weight of 0.5 mil wet drawdown and then curing in an appropriate manner. An Answer II RD-922 reflection densitometer (MacBeth, Newburgh, New York), which has been calibrated prior to sampling, is placed in the "Optical Density" mode. The sample is covered with the aperture of the densitometer and the "snout" is depressed causing an optical density measurement to be taken. Three readings are taken for each of the three samples and an average to the three readings is calculated to give an approximate optical density for each sample. The average optical density for each of the three samples is then averaged to obtain an approximate optical density reading for the formulation as a whole.

Viscosity Test Method

The viscosity of an ink composition is determined as follows. From 7 to 8 g of a sample ink composition is charged into a thermosel cup of a Model DV-I+ LV viscometer (Brookfield). A SC4-18 spindle is attached to the viscometer and inserted into the ink composition. The composition is allowed to sit for five minutes. The spindle is then set to rotate for 12 minutes at a rotation speed appropriate to obtain an accurate reading, after which a viscosity measurement is taken and recorded in cPs.

Example 1

An ink composition was prepared by slowly adding 16.67% by weight Renol HW microencapsulated titanium dioxide particles, which, according to the manufacturer's literature, have a mean particle size distribution of 313 nm and contain 70% by weight titanium dioxide (Clariant), to 83.33% by weight ERL-4206 vinyl cyclohexene diepoxide (Union Carbide) and mixing with a cowles blade for about 1.5 hours. After a homogeneous mixture was obtained, 2% by weight UVI-6974 photoinitiator (Union Carbide) was added to the mixture and the composition was again mixed to form a homogeneous composition.

Example 2

An ink composition was prepared by slowly adding 14.5% by weight Renol White T-HW microencapsulated titanium dioxide (Clariant) to 58% by weight Erisys GE-21 1,4-butane diol diglycidyl ether (CVC Specialty Chemicals), 13% by weight limonene dioxide, and 14.5% by weight Cyracure 6128 bis(3,4-epoxycyclohexylmethyl) adipate (Union Carbide) and mixing with a cowles blade for about 1.5 hours. After a homogeneous mixture was obtained, 2% by weight UVI-6974 photoinitiator (Union Carbide) was added to the mixture and the composition was again mixed to form a homogeneous composition.

Example 3

A hot melt ink composition was prepared by dissolving 25% by weight Arizona DR-10 disproportionated rosin ester (Arizona Chemical), 33% by weight Castor wax hydroxy wax (CasChem), and 25% by weight Castor wax MP-70 hydroxy wax (CasChem) in acetone. 16.7% by weight Renol White HW microencapsulated titanium dioxide (Clariant) was then slowly added to the composition. The mixture was then shaken by hand for about 5 to 10 minutes, after which the acetone was evaporated off leaving an essentially solvent free mixture.

Example 4 An ink composition was prepared by slowly adding 19.1% by weight Renol

White T-HW microencapsulated titanium dioxide (Clariant) to 15.1% by weight tripropyleneglycol monomethylether, and 5.8% by weight Khrumbaar 1717 HMP polyketone resin (Lauder Chemical Company), and mixing with a cowles blade for about 1.5 hours. Two sets of samples of each of the ink compositions of Examples 1-4 were prepared by coating the ink compositions at a coating weight of 0.5 mil wet drawdown and 0.25 mil wet drawdown onto glass substrates. The samples prepared from the ink compositions of Examples 1 and 2 were then cured by passing the samples through a F-300 UV curing oven (Fusion) at 15 feet per minute while irradiating the samples with radiation from a "H" bulb.

The samples prepared from the ink composition of Example 3 were allowed to cool to room temperature.

The samples prepared from the ink composition of Example 4 were placed into a 100 C oven and the tripropyleneglycol monomethylether was allowed to evaporate.

The opacity of each of the samples was measured according to the Opacity Test Method set forth above. The results are summarized in Table I.

The viscosity of the ink compositions of Examples 1-4 was measured at 25 C according to the Viscosity Test Method set forth above. The RPMs for the viscosity measurements were as follows: 30 (Example 1), 12 (Example 2), and 12 (Example 4). Example 3 was a solid at room temperature; thus the viscosity was not measured. The results are summarized in Table I.

Table I

N.T. = not tested

Other embodiments are within the claims.

Claims

What is claimed is:

1. An ink jet ink composition comprising: greater than 5% by weight titanium dioxide; and a vehicle comprising a polymerizable component, wherein said ink composition is essentially solvent free.

2. The ink composition of claim 1, wherein said composition exhibits a viscosity of at least about 60 centipoise at 25 C.

3. The ink composition of claim 1, wherein said composition exhibits a viscosity of at least about 100 centipoise at 25 C.

4. The ink composition of claim 1, wherein said composition comprises at least about 8% by weight titanium dioxide.

5. The ink composition of claim 1 , wherein said composition exhibits an opacity of no greater than about 0.7 when measured according to the Opacity Test Method.

6. The ink composition of claim 1, wherein said composition exhibits an opacity of no greater than about 0.6 when measured according to the Opacity Test Method.

7. The ink composition of claim 1, wherein said titanium dioxide is in the form of a sufficiently stable homogeneous suspension such that said ink composition is suitable for use in a drop-on-demand ink jet engine.

8. The ink composition of claim 1, wherein said titanium dioxide is in the form of microencapsulated titanium dioxide particles.

9. The ink composition of claim 1 , wherein said titanium dioxide is in the form of microencapsulated titanium dioxide particles comprising an encapsulating layer of poly vinylbutyral.

10. The ink composition of claim 1 , wherein said polymerizable component is photopolymerizable.

11. The ink composition of claim 1 , wherein said polymerizable component is capable of being polymerized by electron beam radiation.

12. The ink composition of claim 1, wherein said polymerizable component is thermosettable.

13. The ink composition of claim 1 , wherein said polymerizable component is selected from the group consisting of epoxy-functional, acrylate-functional, methacrylate-functional and vinyl ether-functional polymerizable components, or a combination thereof.

14. The ink composition of claim 1, wherein said polymerizable component comprises a cycloaliphatic epoxide.

15. An ink j et ink composition comprising : encapsulated titanium dioxide in an amount sufficient to provide an ink composition comprising greater than 5% by weight titanium dioxide; and a vehicle comprising a polymerizable component, said ink composition being essentially solvent free.

16. A hot melt ink jet ink composition comprising: greater than 5% by weight titanium dioxide; and a vehicle comprising a hot melt component, said ink composition being essentially solvent free.

17. The hot melt ink jet ink composition of claim 16, wherein said hot melt component comprises hydroxy wax.

18. An ink j et ink composition comprising : greater than 5% by weight titanium dioxide; and a vehicle comprising film-forming resin and a nonvolatile solvent, wherein said titanium dioxide is in the form of a sufficiently stable homogeneous suspension such that said ink composition is suitable for use in a drop-on- demand ink jet engine, said ink composition being essentially free of volatile components.

19. The ink composition of claim 18, wherein said titanium dioxide is in the form of microencapsulated titanium dioxide particles.

20. The ink composition of claim 18, wherein said titanium dioxide is in the form of microencapsulated titanium dioxide particles comprising an encapsulating layer of poly vinylbutyral.

21. The ink composition of claim 18, wherein said nonvolatile solvent comprises a polar solvent.

22. The ink composition of claim 18, wherein said nonvolatile solvent comprises a nonpolar solvent and a polar solvent.

23. The ink composition of claim 18, wherein said nonvolatile solvent comprises tripropyleneglycol monomethylether.

24. An ink j et printer comprising : ink jet ink composition comprising greater than 5% by weight titanium dioxide, and a vehicle comprising a polymerizable component, said ink composition being essentially solvent free.

25. The ink jet printer of claim 24, wherein said ink composition exhibits an opacity of no greater than about 0.7 when measured according to the Opacity Test Method.

26. An ink j et printing process comprising : ejecting an ink jet ink composition from an ink jet printer onto a surface, said ink composition comprising greater than 5% by weight titanium dioxide, and a vehicle comprising a polymerizable component, said ink composition being essentially solvent free.