Radiation curable compositions based on unsaturated polyesters and compounds having at least two vinyl ether groups

Claims

What is claimed is:

1. A liquid, radiation curable coating composition comprising:

an unsaturated polyester having a plurality of maleate and/or fumarate groups; and

a non-polymerized, cocurable vinyl ether component free radically reactive with said unsaturation of said polyester and selected from the group consisting of: (a) vinyl ether compounds containing an average of at least two reactive vinyl ether groups per molecule and (b) a vinyl ether containing group bonded to the polyester;

the composition being free of components that would destabilize the composition under coating application conditions, whereby polymerization of the vinyl ether component is substantially avoided until cocured with the unsaturated polyester when initiated by exposure to radiation.

2. The composition of claim 1 comprising a photoinitiator.

3. The composition of claim 1 wherein the ratio of carbon-carbon double bond equivalents of said vinyl ether groups to carbon-carbon double bond equivalents from said polyester is in a range of from 0.1:1.0 to 1.5:1.0.

4. The composition of claim 3 comprising a thermal polymerization inhibitor.

5. The composition of claim 3 wherein said unsaturated polyester comprises an unsaturated polyester polymer having a peak molecular weight, as measured by gel permeation chromatography using a polystyrene standard, in a range of from 800 to 50,000.

6. The composition of claim 5 wherein the ratio of carbon-carbon double bond equivalents of said vinyl ether groups to carbon-carbon double bond equivalents of said polyester is in a range of from 0.25:1.0 to 1.1:1.0.

7. The composition of claim 5 wherein said unsaturated polyester comprises an unsaturated polyester polymer having a peak molecular weight, as measured by gel permeation chromatography using a polystyrene standard, in a range of from 1,200 to 5,000.

8. The composition of claim 1 wherein said unsaturated polyester is an unsaturated polyester-urethane polymer, an unsaturated polyester-urethane oligomer or a mixture thereof.

9. The composition of claim 1 wherein the composition consists essentially of the unsaturated polyester and the vinyl ether component, and optionally a photoinitiator and/or a thermal polymerization inhibitor.

10. The composition of claim 1 wherein the polyester component comprises the reaction product of a polyhydric alcohol with an unsaturated carboxylic acid selected from the group consisting of maleic acid, fumaric acid, and itaconic acid.

11. The composition of claim 10 wherein the backbone of the unsaturated polyester includes a plurality of unsaturated ester groups selected from the group consisting of maleate, fumarate, and itaconate.

12. The composition of claim 1 wherein the unsaturated polyester contains a plurality of fumarate groups.

13. The composition of claim 1 wherein the vinyl ether component includes a reaction product of a di-, tri-, or tetra-functional organic polyol and acetylene.

14. The composition of claim 1 wherein the vinyl ether component includes a member selected from the group consisting of: tripropylene glycol divinyl ether, diethylene glycol divinyl ether, 1,4,-butanediol divinyl ether, and tetraethylene glycol divinyl ether.

15. A substrate having thereon a cured film comprising the crosslinked product of the unsaturated polyester containing and vinyl ether containing coating composition of claim 1.

16. The coated article of claim 15 wherein the polyester component comprises the reaction product of a polyhydric alcohol with an unsaturated carboxylic acid selected from the group consisting of maleic acid, fumaric acid, and itaconic acid.

17. The coated article of claim 16 wherein the backbone of the unsaturated polyester includes a plurality of unsaturated ester groups selected from the group consisting of maleate, fumarate, and itaconate.

18. The substrate of claim 15 wherein the unsaturated polyester contains a plurality of fumarate groups.

19. The coated article of claim 15 wherein the vinyl ether component includes a reaction product of a di-, tri-, or tetra-functional organic polyol and acetylene.

20. The coated article of claim 15 wherein the vinyl ether component includes a member selected from the group consisting of: tripropylene glycol divinyl ether, diethylene glycol divinyl ether, 1,4,-butanediol divinyl ether, and tetraethylene glycol divinyl ether.

21. A method of coating comprising:

(A) applying to a substrate a film of a liquid, radiation curable composition containing an unsaturated polyester having a plurality of maleate and/or fumarate groups and a non-polymerized, cocurable vinyl ether component free radically reactive with said unsaturation of said polyester and selected from the group consisting of: (a) vinyl ether compounds containing an average of at least two reactive vinyl ether groups per molecule and (b) a vinyl ether containing group bonded to the polyester, the composition being free of components that would destabilize the composition under coating application conditions, whereby polymerization of the vinyl ether component is substantially avoided until cocured with the unsaturated polyester when initiated by exposure to radiation; and

(B) curing said composition through its thickness to a tack-free state by means of crosslinking the polyester component using the vinyl ether groups as the primary crosslinking agent, the curing being effected by exposing said film to ionizing radiation and/or ultraviolet light.

22. The method of claim 21 wherein the ratio of carbon-carbon double bond equivalents of said vinyl ether groups to carbon-carbon double bond equivalents from said polyester is in a range of from 0.1:1.0 to 1.5:1.0.

23. The method of claim 22 wherein said composition contains a photoinitiator.

24. The method of claim 22 wherein said composition contains a thermal polymerization inhibitor.

25. The method of claim 22 wherein said unsaturated polyester comprises an unsaturated polyester polymer having a peak molecular weight, as measured by gel permeation chromatography using a polystyrene standard, in a range of from 800 to 50,000.

26. The method of claim 25 wherein the ratio of carbon-carbon double bond equivalents of said vinyl ether groups to carbon-carbon double bond equivalents of said polyester is in a range of from 0.25:1.0 to 1.1:1.0.

27. The method of claim 25 wherein said unsaturated polyester comprises an unsaturated polyester polymer having a peak molecular weight, as measured by gel permeation chromatography using a polystyrene standard, in a range of from 1,200 to 5,000.

28. The method of claim 21 wherein said unsaturated polyester is an unsaturated polyester-urethane polymer, an unsaturated polyester-urethane oligomer or a mixture thereof.

29. The method of claim 21 wherein said unsaturated polyester is present in the radiation curable composition as a separate compound from said vinyl ether component.

30. The method of claim 21 wherein the composition applied to the substrate consists essentially of the unsaturated polyester and the vinyl ether component, and optionally a photoinitiator and/or a thermal polymerization inhibitor.

31. The method of claim 30 wherein the backbone of the unsaturated polyester in the composition applied to the substrate includes a plurality of unsaturated ester groups selected from the group consisting of maleate, fumarate, and itaconate.

32. The method of claim 21 wherein the unsaturated polyester contains a plurality of fumarate groups.

33. The method of claim 21 wherein the vinyl ether component of the composition applied to the substrate includes a reaction product of a di-, tri-, or tetra-functional organic polyol and acetylene.

34. The method of claim 21 wherein the vinyl ether component of the composition applied to the substrate includes a member selected from the group consisting of: tripropylene glycol divinyl ether, diethylene glycol divinyl ether, 1,4,-butanediol divinyl ether, and tetraethylene glycol divinyl ether.

BACKGROUND AND FIELD OF THE INVENTION

The present invention relates to liquid, radiation curable compositions, particularly coating compositions, containing an unsaturated polyester component in combination with compounds containing at least two vinyl ether groups.

The use of radiation curable coating compositions based on unsaturated polyesters is limited by the rate of radiation cure and degree of radiation cure in air of known compositions containing unsaturated polyesters. For example, liquid films of known unsaturated polyesters cured with styrene typically require doses of 10 to 20 megarads of ionizing radiation (electron beam) for cure or, when cured using actinic radiation (ultraviolet light), cure at typical rates of from 5 to 10 feet/minute/lamp upon exposure to ultraviolet light (UV) from a medium pressure mercury vapor lamp operating at 200 watts/inch at a distance of about 4 inches from the surface of the wet film. Also such known compositions tend to exhibit disadvantages in surface curing characteristics.

The present invention is primarily directed to improving the radiation curing properties of liquid, compositions based on unsaturated polyester polymers and unsaturated polyester oligomers. Other objects of the invention will become apparent to the reader infra.

SUMMARY OF THE INVENTION

The present invention is for a liquid, radiation curable composition comprising: (A) an unsaturated polyester component containing an unsaturated polyester polymer, an unsaturated polyester oligomer or a mixture thereof; and (B) a non-polymerized, cocurable vinyl ether component which may be separate from or structurally incorporated in the unsaturated polyester component, provided that the vinyl ether component contains an average of at least two vinyl ether groups per molecule of the vinyl ether component.

The present invention is also for a method of coating comprising: applying to a substrate a film of a liquid, radiation curable composition of the invention, and curing the composition through its thickness to a tack-free state by exposing the film to ionizing radiation and/or ultraviolet light.

DETAILED DESCRIPTION OF THE INVENTION

A composition of the invention is liquid and is capable of being cured by the application of ionizing radiation, such as electron beam radiation, or actinic light, such as ultraviolet light (UV). The composition is liquid such that it can be applied to a substrate utilizing conventional coating application techniques such as roll coating, curtain coating, doctor blade coating, and/or spray coating. Generally, a composition of the invention will have a viscosity at 25 degrees Celsius (.degree.C.) of from 200 to 20,000 centipoises (cp), preferably from 200 to 4,000 cp. Moreover, vinyl unsaturation of the vinyl ether component which is present in a liquid composition of the invention in combination with the unsaturated polyester component, is available for curing (crosslinking) with ethylenic unsaturation in the backbone of the unsaturated polyester component.

The unsaturated polyester component of the liquid, radiation curable composition comprises an unsaturated polyester resin. The unsaturated (ethylenically unsaturated) polyester resin can be an unsaturated polyester polymer, an unsaturated polyester oligomer or a mixture thereof. The preparation of unsaturated polyesters, for example by the reaction of unsaturated polycarboxylic acid or anhydride with polyhydric alcohol, is well-known in the art. Processes for making unsaturated polyesters include batch processes and continuous processes. As used herein, the term "unsaturated polyester" is to be distinguished from unsaturated alkyd resins such as drying-oil modified alkyds.

Unsaturated polyesters for compositions of the invention ordinarily are esterification products of ethylenically unsaturated carboxylic acids and organic polyhydric alcohols (organic polyols). Usually, an unsaturated carboxylic acid having an acid functionality of at least two, more particularly a dicarboxylic acid or its anhydride, is utilized as a starting reactant. Examples of unsaturated dicarboxylic acids and anhydrides include: maleic acid, maleic anhydride, fumaric acid and itaconic acid. Maleic anhydride is a desirable dicarboxylic component to make the unsaturated polyester resin since it is relatively inexpensive. However, the maleate esters do not copolymerize with monomers such as vinyl ethers as readily as do the fumarate esters (i.e., esters derived from the trans isomer of maleic acid, i.e., fumaric acid). Accordingly, fumarate esters are preferred for making the unsaturated polyester for a composition of the invention.

Unsaturated polyesters for a composition of the invention, where desired, also can be prepared utilizing a saturated polycarboxylic acid as a portion of the polycarboxylic component. Preferred unsaturated polyester resins for the present invention, however, typically are prepared utilizing just the unsaturated polycarboxylic acid or its anhydride with the polyhydric alcohol component. Examples of saturated polycarboxylic acids which optionally may be used include: phthalic acid, isophthalic acid, terephthalic acid, trimellitic acid, tetrahydrophthalic acid, hexahydrophthalic acid, tetrachlorophthalic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, malonic acid, pimelic acid, suberic acid, 2,2-dimethylsuccinic acid, 3,3-dimethylglutaric acid, and 2,2-dimethylglutaric acid. Of course, anhydrides of the aforementioned acids, where they exist, also can be utilized.

Examples of organic polyols suitable for preparing the unsaturated polyester resin include: diethylene glycol, ethylene glycol, propylene glycol, dipropylene glycol, butylene glycol, glycerol, trimethylolpropane, pentaerythritol, sorbitol, 1,6-hexanediol, 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, 1,2-bis(hydroxyethyl)cyclohexane, and 2,2-dimethyl-3-hydroxypropyl-2,2-dimethyl-3-hydroxypropionate. Organic polyols which are diols are preferred. Diethylene glycol is particularly preferred since it is readily available and is relatively inexpensive. While organic polyols having a hydroxyl functionality of greater than 2 may be employed in the preparation of the unsaturated polyester resin, it is preferred that the major portion, if not all of the unsaturated polyester resin, be comprised of unsaturated polyester molecules which are linear; hence the preference for diols.

The molecular weight of unsaturated polyester resins suitable for a composition of the invention may vary widely. However, generally the unsaturated polyester resin has a peak molecular weight, as measured by gel permeation chromatography using a polystyrene standard, of from 800 to 50,000, preferably of from 1,200 to 5,000. The unsaturated polyester resins may be prepared by heating the polycarboxylic component and organic polyol component together for about 1 to 10 hours to temperatures of from about 165.degree. C. to about 250.degree. C., with water formed during the esterification being distilled off using a sparge of an inert gas such as nitrogen. Esterification catalysts for increasing the rate of reaction can also be used. Examples of known catalysts useful for this purpose include para-toluenesulfonic acid, butylstannoic acid, dibutyltin oxide and stannous fluoride.

Radiation curable compositions of the present invention utilize a vinyl ether component that provides an average of at least two vinyl ether groups per molecule of the