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Title:
CLEAR, LIQUID, PHOTOCURABLE COMPOSITION CONTAINING A MIXTURE OF AN UNSATURATED POLYESTER, VINYLPYRROLIDONE AND A NON-VOLATILE VINYL ETHER
Document Type and Number:
WIPO Patent Application WO/1992/014764
Kind Code:
A1
Abstract:
A clear, liquid, shelf-stable photocurable composition capable of cured to form a clear, hard, adherent, solvent-resistant coating on a substrate comprising a blend of substantially equivalent amounts of (a) an unsaturated polyester polymer, oligomer, or mixtures thereof; and (b) a non-volatile, polyester-compatible vinyl ether, and vinyl pyrrolidone; and (c) a free radical photoinitiator.

Inventors:
Vara, Fulvio J.
Dougherty, James A.
Application Number:
PCT/US1992/000742
Publication Date:
September 03, 1992
Filing Date:
January 29, 1992
Export Citation:
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Assignee:
ISP INVESTMENTS INC.
International Classes:
C08F2/46; C08F299/04; (IPC1-7): C08F2/46; C08J3/28
Foreign References:
US4996282A
US4956198A
US4472019A
US3874906A
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Claims:
WHAT IS CLAIMED IS:
1. A clear, liquid, shelfstable photocurable composition capable of cured to form a clear, hard, adherent, solventresistant coating on a substrate comprising a blend of substantially equivalent amounts of (a) an unsaturated polyester polymer, oligomer, or mixtures thereof; and (b) a nonvolatile, polyestercompatible vinyl ether, such as a multifunctional vinyl ether or a monofunctional vinyl ether, or mixtures thereof; for example, divinylether triethylene glycol or cyclohexane dimethanol vinyl ether; or a monofunctional vinyl ether such as the monovinyl ether of tetrahydrofurfural alcohol; such as vinyl pyrrolidone; and (c) a free radical photoinitiator, wherein said composition has a viscosity of less than 5,000 cps, and both said components of (b) are present in substantially equal equivalent amounts.
2. A composition according to claim 1 wherein the (a) component is a maleate or fumurate bisA epoxy polyester oligomer.
Description:
CLEAR, LIQUID, PHOTOCURABLE COMPOSITION CONTAINING

A MIXTURE OF AN UNSATURATED POLYESTER,

VINYLPYRROLIDONE AND A NON-VOLATILE VINYL ETHER

The use of polyester containing compositions as coatings for a variety of substrates is well known in the art. These compositions may be applied in solvent solutions and cured catalytically. Recently, the use of actinic light as a means of curing polyester compositions has minimized the need for solvents. However, the compositions without solvent are quite viscous and difficult to apply to the substrate to be coated. In order to reduce the viscosity of the polyester containing compositions to an acceptable level for application purposes, various viscosity modifiers or reducers have been added which function as diluents in the composition. However these diluents, e.g. methyl methacrylate, styrene, methyl ethyl ketone and the like, are quite volatile and odoriferous, causing air pollution during cure; also they slow the curing rate of the polyester compositions appreciably.

Pruncnal, in U.S. Pat. No. 3,874,906 discloses the use of vinylpyrrolidone as a additive for polyester compositions to reduce the viscosity of the composition for application purposes. Pruncnal suggests that vinyl monomers which are free of non-aromatic carbon-carbon conjugated double bonds, such as styrene, vinyl toluene, divinyl benzene and the like also could be included in the composition. In fact, styrene and vinyl toluene monomers were present in several of the compositions described in the examples. A list of other possible vinyl monomers.

including two monovinyl alkyl ethers, was given by Pruncnal but these were not preferred compositions. In particular, the disclosed butyl vinyl ether is a volatile component, and the disclosed cetyl vinyl ether is incompatible with the unsaturated polyester monomer or oligomer.

Friedlander, in EPA 322808, published 7/8/89, disclosed a liquid, radiation curable composition comprising an unsaturated polyester and a cocurable vinyl ether component which contained an average of at least two vinyl ether groups per molecule. Other vinyl monomers were mentioned as a third component of the composition; however these monomers were restricted to acrylates, acrylamides, vinyl aromatics, vinyl acetate and monovinyl alkyl ehters, and none were described in the examples.

Noren, in PCT Publication No. WO 90/01512, published 2/22/90, discloses a liquid composition curable by exposure to light consisting of a polyester and a vinyl ether.

However, these references have not provided a clear, liquid photocurable composition capable of being cured at a high cure rate by free-radical copolymerization to form a terpolymer of high purity, i.e. without a homopolymerized component therein, which terpolymer forms a clear, hard, adherent, solvent-resistant coating and which consists essentially of (a) an unsaturated polyester polymer, oligomer or mixtures thereof; and a mixture of (b) a multifunctional vinyl ether and (c) vinylpyrrolidone, wherein (a) and the mixture of (b) and (c) are present in substantially equivalent amounts.

There is provided herein a clear, homogeneous liquid composition curable by exposure to light of appropriate wavelength, such as ultraviolet light, which contains an unsaturated polyester polymer oligomer or blend thereof, vinylpyrrolidone and a non-volatile vinyl ether, compatible with the polyester, having a predetermined viscosity, and present in defined amounts relative to each other, which composition provides coatings upon curing at a rapid rate, which as clear, adherent and strong.

In the preferred form of the invention, the equivalent ratio of the unsaturated polyester to the sum of the vinylpyrrolidone and vinyl ether components is substantially about 1:1, and wherein the ratio of the vinylpyrrolidone to vinyl ether to about 1:99 to 99:1, most preferably including a predominance of vinyl ether. The vinyl ether component must be non-volatile and compatible with the unsaturated polyester to provide a clear composition. For effective crosslinking in the terpolymer containing coating, the vinyl ether preferably is a multifunctional vinyl ether, such as a di-, tri-, or tetravinyl ether, thereby providing a stronger coating. However, monofunctional vinyl ethers also may be used, alone or in combination with multifunctional vinyl ethers, to provide flexibility in the coating and enhanced diluency for adjustment of the viscosity of the compositions.

The viscosity of the composition suitably is less than 5,000 cps.

The composition includes a free-radical photoinitiator such as an hydroxy or alkoxy-functional acetophenone derivative, preferably an hydroxyalkyl phenone, or a benzoyl diaryl phosphine oxide. These two different types of ethylenic unsaturations interact rapidly in the presence of the specified photoinitiators to provide a rapid photocure.

The unsaturated polyester used herein is of liquid character so as to minimize the need for diluents to reduce viscosity and thus enable coating application.

The unsaturated polyester component of the liquid, radiation curable composition comprises an unsaturated polyester resin. The unsaturated (ethylenically unsaturated}r 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 polyhydriσ 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 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, trimethaltic acid, tetrahydrophthalic acid, hexahydrophthalic acid, tetrachlorophthalic acid, adipic acid, azelaic acid, sebacic acid, succinic acid, glutaric acid, malonic acid, pi ellic 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-hydroxy- propionate. 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 β C. to about 250 β 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, dibutylin diode and stannous fluoride.

A suitable unsaturated polyester is the maleate capped bis-A epoxy sold by Desoto as Desolite 1300, having a molecular weight of about 770 and a functionality of 2. The vinyl ether compounds which are used herein are non-volatile vinyl ethers which are compatible with the unsaturated polyester. A coating which is strong and durable is provided by using a multifunctional vinyl ether which will crosslink with the unsaturated polyester in the terpolymer. A composition which includes a monofunctional vinyl ether will provide a more flexible coating having less crosslinking and will also provide a diluent for viscosity adjustment of the composition. Mixtures of multifunctional and monofunctional vinyl ethers also may be used.

Examples of vinyl ether compounds include vinyl ethers made in known manner from di-, tri- or tetrafunσtional organic polyol, acetylene and a basic catalyst under high pressure. Specific examples include: tripropylene glycol divinyl ether, diethylene glycol divinyl ether, 1,4-butanediol divinyl ether, tetraethylene glycol divinyl ether and the like.

The vinyl ether compounds which are preferred are oligomeric and contain more than one vinyl ether group per molecule. To illustrate polyvinyl ether oligomers, one may use the bisvinyl ether of triethylene glycol or of any other diol, such as 1,6-hexane diol or dibutylene glycol. One may also use polyvinylates of other polyhydric alcohols, such as glycerin or trimethylol propane. Polyhydric polyethers can be used, such as ethylene oxide, propylene oxide or butylene oxide adducts of polyhydric alcohols, illustrated by ethylene glycol, butylene glycol, glycerin, trimethylol propane or pentaerythritol. Polyvinyl ether polyurethanes of the type shown in U.S. Pat. No. 4,751,273 are also useful.

Curing a composition of the invention will vary depending on such factors as the particular formulation of the radiation curable composition, thickness of the applied layer of coating composition on the substrate, temperature of the composition, and the like. However, an advantage of compositions of the invention is their excellent degree of cure at low doses of electron beam radiation. Generally, a 1 mil thick wet film of a composition of the invention can be cured in air through its thickness to a tack-free state upon exposure to from 0.5 to 5 megarads of ionizing radiation.

Ultraviolet radiation from any suitable source which emits ultraviolet light having a wavelength ranging from about 180 to about 400 nanometers may be employed to cure a composition of the invention. Because such ultraviolet light possesses insufficient energy to produce ions in a medium composed of common materials such as air or water, it is considered to be nonionizing radiation. Suitable sources of ultraviolet light are generally known and include, for example, mercury arcs, carbon arcs, low pressure mercury lamps, medium pressure mercury lamps, high

pressure mercury lamps, swirl-flow plasma arcs and ultraviolet light emitting diodes. Preferred are ultraviolet light emitting lamps of the medium pressure mercury vapor type. Such lamps usually have used quartz envelopes and are ordinarily in the formn of long tubes having an electrode at both ends. Typically, preferred medium pressure mercury lamps usually employed to cure a composition of the invention have outputs of about 200 watts per inch across the length of the tube. Another advantage of compositions of the invention is their excellent degree of cure in air at relatively low energy exposure in ultraviolet light. Generally, a 1 mil thick wet film of a composition of the invention, provided it further comprises a photocuring promoter such as a photoinitiator and/or a photosensitizer, can be cured in air through its thickness to a tack-free state upon exposure to ultraviolet light by passing the film at a rate of 20 feet per minute or more under four or fewer medium pressure mercury vapor lamps operating at 200 watts per inch at a distance of 4 inches from the surface of the wet film. Photoinitiators and photosensitizers for use in ultraviolet light curable compositions are generally known in the art of UV curable compositions. Examples of photosensitizers include benzophenone, anthraquinone, and thioxanthone. Examples of photoinitiators include isobutyl benzoin ether, mixtures of butyl isomers of butyl benzoin ether, alpha,alpha-diethoxyacetophenone, and alpha,alpha-dimethoxy-alpha-phenylacetophenone. Other examples of photoinitiators and photosensitizers can be found in U.S. Patent No. 4,017,652.

Although it is particularly preferred to cure compositions of the invention by UV and/or ionizing radiation, where desired they may be thermally cured in the presence of a thermal free radical initiator. Examples

include the generally known thermal initiators for curing unsaturated polyesters, some specific examples of which include peroxides such as benzoyl peroxide, methyl ethyl ketone peroxide, cumene hydroperoxide, cyclohexanone peroxide, 2,4-dichlorobenzoyl peroxide, bis(p-bromobenzoyl) peroxide and acetyl peroxide.

Where desired, a thermal polymerization inhibitor may be utilized in a composition of the invention. Examples of thermal polymerization inhibitors include phenolic compounds such as di-tertiary-butyl paracresol, and compounds containing secondary or tertiary nitrogen atoms.

A composition of the invention may also contain a solvent such as conventional aliphatic and aromatic solvents or diluents known in the art.

Where desired, a composition of the invention may also contain pigment, when it is desired to cure the composition with ultraviolet light, the pigment utilized is typically an ultraviolet light transparent pigment. The phrase "ultraviolet light transparent" is used to mean that the pigment does not substantially interfere with UV curing of the composition. Examples of ultraviolet light transparent pigments include: talc, calcium carbonate, aluminum silicate, magnesium silicate, barytes and silica (Si0 2 ) ♦ Coloring pigments generally employed to impart color in non-UV cured, coating compositions typically absorb or block ultraviolet light thereby interfering with UV curing of the composition. Accordingly, where some degree of color tinting of the composition is desired, such conventional coloring pigments typically are employed in only limited amounts when cure is to be effected utilizing UV.

The liquid, radiation curable compositions of the invention are especially useful as radition curable coating compositions. They can be applied to a variety of substrates, examples of which include wood, paper, particleboard, chipboard, metals, metals having primers thereon, glass, plastics, and metalized plastics. The radiation curable compositions may be applied by any known means, for example, brushing, dipping, roll coating, doctor blade coating, spraying, curtain coating, etc. They may be preliminarily dried to remove solvent if desired and then cured by radiation.

The examples which follow are submitted for the purpose of further illustrating the nature of the invention in its preferred embodiments.

As used in the body of the specification, examples, and claims, all percents, ratios and parts are by weight unless otherwise specifically indicated. Wherever used herein, "pbw" means "parts by weight".

EXAMPLE 1

A maleate-capped bis-A epoxy polyester oligomer sold by Desoto Chemical Co. under the designation "Desolite 1300", having a molecular weight of 770 and a functionality of 2, in the amount of 4.6338 g., 78.4 wt. %, an equivalency of 0.0119, vinylpyrrolidone in the amount of 0.6666 g., 11.3 wt. %, an equivalency of 0.006, and divinyl ether triethylene glycol (DVE-3) , 0.6143 g. , 10.4 wt. %, an equivalency of 0.006 were blended together to form a clear, liquid, non-volatile photocurable composition having a viscosity of less than 5,000 cps. Then 0.0050 g. of phenothiazine and 0.1725 g. of Darocur 1173 was added.

The composition then was drawn down on a polyethylene terephthalate support using a #6 rod and cured at 40 fpm in air for a period of about 1.9 minutes. An excellent, clear, hard, adherent coating was obtained having 100% adhesion to the support, a pencil hardness of H, and a solvent resistance to methyl ethyl ketone of >100 rubs.

EXAMPLE 2

The procedure of Example 1 was repeated using cyclohexane dimethanol divinyl ether as the difunctional vinyl ether in the same equivalent amounts with similar results for the coating obtained.

EXAMPLE 3

The procedure of Example 1 was repeated using the monovinyl ether of tetrahydrofurfural alcohol as a monofunctional ether in equivalent amounts with similar results for the coating obtained.

EXAMPLE 4

A blend of the difunctional vinyl ethers of Examples 2 and 3 was used in equiequivalent amounts as the difunctional vinyl ether of Example 1 with similar results for the coating obtained.

COMPARATIVE EXAMPLE 1

4.5948 g., 77.3 Wt. % of Desolite 1300, 1.3223 g. , 22.3 wt. % of vinylpyrrolidone, 0.0065 g. of phenothiazme and 0.1725 g. of Darocur 1173 was blended into a very viscous (>5,000 cps) liquid composition. The composition was applied on a substrate and cured as in Example 1. However, the coating did not adhere to the terephthalate substrate.

COMPARATIVE EXAMPLE 2

4.6028 _ . , 79.3 Wt. % of Desolite 1300, 1.2042 g. , 20.7 wt. % of DVE-3, 0.0055 g. of phenothiazme and 0.1855 g. of Darocur 1173 were blended into a liquid composition having a viscosity of less than 5,000 cps. The composition was applied onto the substrate of Example 1 and cured in a similar manner. The coating obtained was quite soft, having a pencil hardness of only less than 4B.