WO2000024786A1

WO2000024786A1 - Method of stabilizing a radiation curable, water insoluble monomer/prepolymer in an aqueous medium

Info

Publication number: WO2000024786A1
Application number: PCT/US1998/022634
Authority: WO
Inventors: Andrew J. Naisby
Original assignee: Rexam Graphics Inc.
Priority date: 1998-10-28
Filing date: 1998-10-28
Publication date: 2000-05-04
Also published as: AU1277499A

Abstract

Provided is a method of stabilizing water insoluble monomer and/or prepolymer in an aqueous medium. The method comprises mixing the radiation curable, water insoluble monomer and/or prepolymer with an aqueous mixture containing a colloidal suspension of water insoluble particles. The result is a stable mixture. The resulting stable mixture can be used as a coating for various substrates to impart characteristics such as abrasion resistence as well as in inks, e.g., useful as ink jet inks.

Description

METHOD OF STABILIZING A RADIATION CURABLE, WATER

INSOLUBLE MONOMER/PREPOLYMER

IN AN AQUEOUS MEDIUM

Field of the Invention

The invention pertains to a method of stabilizing a radiation curable water insoluble monomer /prepolymer in an aqueous medium. The stable colloidal emulsion composition, once processed, offers all the advantages associated with UV/EB curable systems containing a hydrophobic monomer /prepolymer, but from an environmentally friendly medium.

Description of the Related Art

The resurgence of interest in water-based radiation curable technology has been prompted by a recognition of a number of unique advantages of waterborne resin systems. Inversely, this refers to some of the limitations of a traditional 100% solids radiation curable resins. The following are perceived advantages of water based systems:

• unique viscosity reduction since water is the solvent;

• potential for non-hazardous spray applications;

• improved toxicology since zero or reduced quantities of acrylate monomers; • tack-free coatings prior to UV/EB cure;

• easy equipment clean-up;

• reduced flammability; zero VOC potential. In the wood industry, for example, waterborne UN cure formulations offer many advantages; such as the coating is easily sprayed; low shrinkage; reduced or zero monomer content or waterborne UV coatings; water will not penetrate wood pores and remain uncured; better mattability; and improved adhesion. The alternative of using water soluble radiation curable chemicals has limitations, e.g., in the availability of such chemicals, water resistance of the cured material, and controlling the viscosity of the solution. Generally, the more water soluble the material and higher the molecular weight, the higher the viscosity. The industry, therefore, would welcome a procedure for stabilizing a radiation curable, water insoluble monomer and/or prepolymer in an aqueous medium so that the properties associated with highly crosslinked, hydrophobic radiation curable materials can be achieved, but from an environmentally friendly medium. Thus, it is an objective of the present invention to provide a method for stabilizing such a radiation curable, water insoluble and/or prepolymer in an aqueous medium.

It is still another object of the present invention to provide a novel aqueous composition containing a radiation curable, water insoluble monomer and/or prepolymer.

Still another object of the present invention is to provide one with the opportunity to employ a stable aqueous emulsion composition to form coatings, inks, finishes and the like, from an environmentally friendly medium, while also realizing the advantages and the properties associated with highly crosslinked hydrophobic radiation curable materials.

These and other objects of the present invention will become apparent upon a review of the following specification and the claims appended thereto. Summary of the Invention

In accordance with the foregoing objectives, the present invention provides a method of stabilizing a radiation curable, water insoluble monomer/prepolymer in an aqueous medium. The method comprises mixing a radiation curable, water insoluble monomer and/or prepolymer, or mixture of same, with an aqueous mixture containing a colloidal suspension of water insoluble particles. The resultant mixture is stable and can be used to form coatings, inks, finishes and the like, with the desirable properties associated with highly crosslinked hydrophobic radiation curable materials, e.g., solvent and abrasion resistance, while employing an environmentally friendly medium.

The stable colloidal solution formed includes two phases, an aqueous phase and a non-aqueous phase. The non-aqueous phase includes a non- water soluble monomer/prepolymer together with a colloidal suspension of water insoluble particles, within the aqueous phase. The mixture remains stable over time.

Detailed Description of the Preferred Embodiments

The invention provided herein is a method of stabilizing a radiation curable water insoluble monomer/prepolymer in an aqueous mixture. The method comprises mixing a radiation curable, water insoluble monomer and/or prepolymer with an aqueous mixture conta-iiing a colloidal suspension of water insoluble particles. The result is a stable mixture, which remains stable over time. The water insoluble monomer and/or prepolymer is generally unstable in an aqueous medium, but is believed to become adsorbed onto the water insoluble particles in colloidal suspension within the aqueous mixture. The result is an aqueous emulsion composition or mixture which allows one to employ the benefits of a radiation curable, water insoluble monomer/prepolymer material, yet from an aqueous medium. It is preferred that the radiation curable, water insoluble monomer/prepolymer contain ethylenic unsaturated groups that can be polymerized and/or crosslinked by irradiation with electron bombardment or ultraviolet radiation, generally in the presence of a photoinitiator system. The preferred monomers/pre-polymers are urethane acrylates, carboxy ethyl acrylates, trimethylol propane triacrylate and ethoxylated derivatives thereof, and acrylated amines, although other like materials will be obvious to those skilled in the art. The monomer/prepolymer is preferably mixed with an aqueous mixture containing a colloidal suspension of water insoluble particles of ethylene vinyl acetate, polyvinyl acetate, poly urethane, ethylene vinyl chloride, silicone emulsions and the like. Other suitable particles will be known to those of skill in the art. It is believed that the normally aqueous unstable monomer/prepolymer is stabilized by adsorption onto the colloidally suspended particles, thus allowing the radiation curable monomer/prepolymer to remain itself in colloidal suspension in the aqueous medium. The amount of monomer/prepolymer (e.g., aery late) that can be successfully stabilized on the colloidal particle will vary based on the acrylate and the type of colloidal particle used. Values typically vary between 20% and 100% by weight of the acrylate to the weight of colloidal particle. Generally, the mixture can be even further stabilized by adjustments in pH, or preferably, by the presence of a suitable surfactant.

The mir-L-mum film forming temperature (M.F.F.T.) and glass transition temperature (Tg) of the emulsion particle used to stabilize the acrylate influences the gloss and physical properties of the fully processed mixture (i.e., once the water has been evaporated and the dried film exposed to radiation). The M.F.F.T. may be from about -20°C to +50°C, preferably between about -5°C to +40°. The Tg is preferably between about -40 °C to +40 °C, and most preferably between 0°C and +40°C. However, one of ordinary skill in the art will recognize that the M.F.F.T. and Tg may in fact be higher or lower than the given ranges in any particular composition.

Once coated, and the water removed, the monomer/prepolymer may be cured by electron bombardment or ultraviolet radiation. Optional photoinitiators for use in an ultraviolet light cured system may include alpha hydroxy ketones and phosphine oxides. Other suitable photoinitiators are -mown to those skilled in the art.

The stabilized mixture of the present invention has also found particular application in inks. The stable emulsion, containing the radiation curable monomer/prepolymer, are particularly useful in the manufacture of aqueous UN curable ink jet inks. Presence in the ink would allow for subsequent curing of the ink once applied to an ink jet medium, after the water has been removed by wicking so that only the ink remains on the medium.

In general, it is believed that the present invention provides many advantages. Among those is that the present invention provides a method incorporating water insoluble, radiation curable chemicals into an aqueous medium to facilitate a unification of the advantages of using hydrophobic radiation curable chemicals in an environmentally friendly medium, i.e., specifically an aqueous medium. Among the advantages of hydrophobic radiation curable chemicals are solvent and water resistance, as well as abrasion resistance.

Furthermore, low viscosities are easily obtainable as the curable chemicals are not in a solution. This is useful in the manufacture of aqueous based radiation curable ink jet inks and spray coatings. Additionally, as a direct consequence of the method of stabilization and the low viscosity it affords, hybrid systems are possible where a water soluble polymer can be dissolved into the aqueous phase thereby creating a method for enhancing the properties of aqueous ink jet receptive medium. A coating can be manufactured that has both the properties associated with water soluble polymers and the capturing, drying and smear resistance of the water based ink with additional properties of gloss, abrasion, and water resistance associated with hydrophobic radiation cured chemicals.

Example 1

A mixture was prepared in the following proportions.

Mixture A

* Photomer RCC 13-429 55 JO grams (polyester acrylate oligomer)

* Photomer 3015 31.10 grams (bisphenol A epoxy diacrylate)

* Monomer RCC 13-361 7.70 grams (1,6 hexanediol ethoxylate diacrylate)

Darocur 4265 5.50 grams (50:50 blend of 2-hydroxy-2-methyl-l- phenyl-propan-1-one and 2,4,6- trimethyl benzoyl diphenyl phosphine oxide)

* Supplied by Henkel Corporation; Darocur 4265 is available from Ciba Additives.

A mixture of lOg of mixture A was added to 25g of Airflex 110 (an ethylene vinyl acetate aqueous emulsion). This was mixed thoroughly before adding 5.0g of water thereby making mixture B.

Mixture B

Mixture A 10.0 grams

Airflex 110 25.0 grams

Water 5.0 grams Airflex 110 is supplied as a 55% solids emulsion in water by Air Products.

Both mixture A and mixture B were coated using a Meyer rod to give the appropriate film thicknesses.

The support for each coating was a clear biaxially orientated polyester film supplied by ICI Melineax division. The grade used was Melineax 401.

Mixture A was coated to a thickness of 10 microns and then irradiated with UV radiation in the region of 200-350 nm with an energy dose of 1000 mJ/cπr². Mixture B was coated to a wet thickness of 60 microns, the water content was totally removed in a thermal convection oven at 220 °F. The resultant coating was then irradiated (10 microns in thickness) with UV identically to that used with mixture A (i.e., UV wavelength 200nm-250nm, energy of 1000 mJ/cm"²).

All of the monomers/epoxy acrylate and polyester acrylate are water insoluble.

A mixture was attempted adding water directly to mixture A. i.e.,

Mixture A 10.0 grams Water 5.0 grams

Coating preparation from this mixture was impossible due to the inhomogenecity caused. The properties of each cured coating was evaluated in terms of hardness, adhesion to a polyester film, solvent and water resistance as follows:

Test methods.

Pencil hardness. The hardness of pencil required to leave a permanent abrasion on the surface of the cured coating. Adhesion. The percentage removed of the cured coating after the coating has been scored with a knife. Solvent Resistance. Methyl ethyl ketone was applied to the coating. The number of subsequent rubs required to destroy the coating was recorded.

Water Resistance. The test for solvent resistance was repeated using water instead of methyl ethyl ketone.

Results

Coating A Coating B

Pencil hardness 6H 6H

Adhesion 15% removed <5% removed

Solvent resistance 75 rubs 75 rubs

Water resistance > 100 rubs > 100 rubs.

The example illustrates that a mixture of hydrophic monomers/prepolymers was stabilized in an aqueous medium and that the final coating demonstrated equal if not superior performance in the key physical properties. Yet, Coating B provides distinct advantages in handling and the coating procedure since it is of lower viscosity and is from an aqueous medium as opposed to the organic based solvent of Coating A. As well, surprising adhesion of Coating B to the polyester substrate was observed.

Example 2

This example illustrates the incorporation of the present invention into an aqueous ink jet ink. A non UV curable aqueous ink jet ink was compared against a UV curable ink jet ink. The method of incorporating the UV curable species into an aqueous medium is identical to that used in Example 1.

Ink-jet ink 1. (Non UV curable).

Commercially available as RSP101-4

Ink-jet ink 2. (Invention)

At the "LETDOWN" stage the following mixture was made and added instead of 51.06 % by weight of "DISTILLED WATER" .

Mixture B (see example 1) 0.96

Distilled Water 50J0

51.06

(i.e., 50.06 of the above added to RSP101-7 instead of 51.06 of distilled water). Therefore a UV reactive ink-jet was created.

An ink-jet cartridge was filled with ink-jet ink 1 (RSP101-4) and one was filled with ink-jet ink 2. The ink-jet cartridge used was the Hewlett Packard 51626A. The filled cartridges were installed into an ink jet printer, the Encad Novajet π. A test plot was made onto plain paper so that a direct comparison could be made of the two ink types. The printed sheet was irradiated with UV light in the region of 200-350nm at an energy dose between 500-1000 mJ/cm^"2.

The resultant print was tested for water resistance, solvent resistance and abrasion resistance, using test the methods outlined in Example 1. Results

Ink Jet Ink 1 Ink Jet Ink 2

Water Resistance 0 50 Solvent resistance 0 50 Abrasion resistance 2B 4H

The example illustrates that the physical performance of an ink-jet ink can be improved using UV reactive species and that these can easily be incorporated into an aqueous ink using the stabilization technique of the present invention.

While the invention has been described with preferred embodiments, it is to be understood that variations and modifications may be resorted to as will be apparent to those skilled in the art. Such variations and modifications are to be considered within the purview and the scope of the claims appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A method of stabilizing a water insoluble monomer and/or prepolymer in an aqueous medium comprising: mixing a radiation curable, water insoluble monomer and/or prepolymer, with an aqueous mixture containing a colloidal suspension of water insoluble particles, to thereby create a stable mixture.

2. The method of claim 1, wherein the stable mixture containing the radiation curable, water insoluble monomer and/or prepolymer further comprises a photoinitiator.

3. The method of claim 2, wherein the photoinitiator is an alpha hydroxy ketone or a phosphine oxide.

4. The method of claim 1, wherein the radiation curable monomer and/or prepolymer is UV curable or EB curable.

5. The method of claim 1, wherein the radiation curable, water insoluble monomer and/or prepolymer contain ethylenic unsaturated groups.

6. The method of claim 1, wherein additional water is added during the mixing stage of the radiation curable, water insoluble monomer and/or prepolymer with the aqueous mixture.

7. The method of claim 1, wherein the radiation curable, water insoluble monomer and/or prepolymer comprises a urethane acrylate, carboxyethyl acrylate, trimethylol propane triacrylate and ethoxylated derivatives thereof, or an acrylated amine, or a mixture thereof.

8. The method of claim 1, wherein the aqueous mixture contains a colloidal suspension of ethylene vinyl acetate, poly vinyl acetate, polyurethane, ethylene vinyl chloride or silicone particles, or a mixture thereof.

9. The method of claim 1, wherein the aqueous mixture further comprises a surfactant.

10. An aqueous emulsion composition comprised of an aqueous phase and a non-aqueous phase, with the non-aqueous phase comprising a colloidal suspension of water insoluble particles within the aqueous phase, said suspension being comprised of a radiation curable water insoluble monomer and/or prepolymer together with water insoluble solid particles in stable colloidal suspension within the aqueous phase.

11. The aqueous emulsion composition of claim 10, wherein the mixture of the radiation curable, water insoluble monomer and/or prepolymer further comprises a photoinitiator.

12. The aqueous emulsion composition of claim 10, wherein the photoinitiator is an alpha hydroxy ketone or a phosphine oxide.

13. The aqueous emulsion composition of claim 10, wherein the radiation curable, water insoluble monomer and/or prepolymer is UV curable or EB curable.

14. The aqueous emulsion composition of claim 10, wherein the radiation curable, water insoluble monomer and/or prepolymer contains ethylenic unsaturated groups.

15. The aqueous emulsion composition of claim 10, wherein the radiation curable, water insoluble monomer and/or prepolymer comprises a urethane acrylate, carboxyethyl acrylate, trimethylol propane triacrylate and ethoxylated derivatives thereof, or an acrylated amine, or a mixture thereof.

16. The aqueous emulsion composition of claim 10, wherein the aqueous emulsion contains a colloidal suspension of ethylene vinyl acetate, poly vinyl acetate, polyurethane, ethylene vinyl chloride or silicone particles, or a mixture thereof.

17. The aqueous emulsion composition of claim 10, wherein the aqueous emulsion further comprises a surfactant.

18. A method of coating a substrate, which comprises preparing the aqueous emulsion composition of claim 10 containing a radiation curable, water insoluble monomer and/or prepolymer, coating a substrate with the composition, removing the water from the coating, and subjecting the coating to radiation to cure the radiation curable monomer and/or prepolymer remaining in the coating.

19. The method of claim 18, wherein the aqueous emulsion composition containing the radiation curable monomer and/or prepolymer further comprises a photoinitiator.

20. The method of claim 19, wherein the photoinitiator is an alpha hydroxy ketone or a phosphine oxide.

21. The method of claim 18, wherein the aqueous emulsion composition containing the radiation curable monomer and/or prepolymer contains a monomer and/or prepolymer which is UV curable or EB curable.

22. The method of claim 18, wherein the aqueous emulsion composition containing the radiation curable monomer and/or prepolymer contains a radiation curable, water insoluble monomer and/or prepolymer with ethylenic unsaturated groups.

23. The method of claim 18, wherein the aqueous emulsion composition containing the radiation curable monomer and/or prepolymer contains a radiation curable, water insoluble monomer and/or prepolymer comprised of a urethane acrylate, carboxyethyl acrylate, trimethylol propane triacrylate and ethoxylated derivatives thereof, or an acrylated amine, or a mixture thereof.

24. The method of claim 18, wherein the aqueous emulsion composition contains a colloidal suspension of ethylene vinyl acetate, poly vinyl acetate, poly urethane, ethylene vinyl chloride or silicone particles, or a mixture thereof.

25. The method of claim 18, wherein the aqueous emulsion composition further comprises a surfactant.

26. The method of claim 18, wherein the substrate coated comprises paper, textile, wood, ceramic and/or plastic.

27. The method of claim 26, wherein the substrate is a polyester substrate.

28. A coated substrate having a uniform, glossy coating thereon, with the coating being comprised of a radiation cured, water insoluble monomer and/or prepolymer, and with the coating having no residue of organic solvent.