CA2116928A1 - Radiation curable composition - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

An aqueous, actinic radiation-curable coating composition containing a latex polymer emulsion and a multifunctional (meth)acrylate is disclosed. The critical aspect of the invention is that the actinic radiation-curable composition does not contain more than 5% by weight of the AOPAte ester of the multifunctional acrylate and 20% by weight of the ether resulting from a Michael addition of a multifunctional acrylate with the hydroxyl group of another multifunctional acrylate. This limitation on the maximum concentration of these components, which are typically the by-products formed in the manufacture of multifunctional (meth)acrylates, results in the improved appearance of the final cured coating.

Description

IMPROVED R~DIATION CURABLE COMPOSmON
, _ FE:LD OF THE INVENII~N ~ g 2 8 This invention relates to aqueous-based, actinic radiation-curable coating compositions. More particularly, the invention relates to aqueous-based, actinic radiation-curable coating compositions which are free of surface defects.

BACKGROUND OF THE INVENTION
, There is a need for high performance coatings that can be applied with low levels of polluting solvents. Aqueous-based thermoplastic coatings can be applied with low levels of polluting solvents, but they do not have the heat and chemical resistance required for many applications, especially where parts must be stacked soon after coating and where the substrate cannot be heated to high temperatures. Chemically-cured coatings that give good heat and chemical resistance have problems with pot life and cure speed.

Actinic radiation-curable coatings offer a solution to the above problems. However, the culTent coating technology remains costly and difficult to apply thin coatings. Conventional actinic radiation-curable coatings must be diluted with solvent so that they may be sprayed.
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Actinic radiation-curable coatings may be formulated from latex polymer emulsion and multifunctional monomers. The formulated coating composition may be ~ormed either by directly mixing the latex polymer emulsion and the multifunctional monomer or by first pre-emulsifying the multifunctional monomer 5~ and then mixing the pre-emulsified multifunctional monomer with the latex polymer emulsion. The presence of water-insoluble impurities disturbs the mixing of the two components in the coating .~ ' , ~, 1 .

.~ , ,.,, , ~ ,, , - ~, , formulation. This leads to defects and a lack of clarity in the final - radiation-cured coating.

U.S. Patent 4,101,493 is directed to an emulsion of a crosslinking type. The emulsion is made up of polymer emulsion of an oil-in-water type and at least one oligoester-(meth)acrylate whic~
has at least two (meth)acrylol groups per molecule, a molecular weight of not more than 1000 per one (meth)acrylol group and a boiling point at atmospheric pressure of at least 200C.

European Patent Application 310,472 is directed to an aqueous-based, ultraviolet radiation-curable coating composition containing a latex polymer emulsion and a multifunctional (meth)acrylate, where the latex polymer is selected to be greater than about 47 mole percent acrylate and to have a glass transition temperature less than about 28C.
-The foregoing exemplilSes attempts to make crosslinkable,radiation-curable coatings from mixtures of polymer emulsions and multifunctional compounds. However, none of the references suggests that the level of water-insoluble impurities are critical for achieving superior coatings properties, such as for example clarity.

2116g28 : ~:
SUMMARY OF THE INVENTION

This invention is an aqueous, actinic radiation-curable coating composition containing a latex polymer emulsion and a multifunctional (meth3acrylate. The critical aspect of the invention is that the actinic radiation-curable composition does not contain more than 5% by weight of the AOPAte ester of the multifunctional acrylate and 20% by weight of the ether resulting from a Michael addition of a multifunctional acrylate with the hydroxyl group of another multifunctional acrylate. This limitation on the maximum concentration of these components, which are typically the by-products formed in the manufacture of multifunctional (meth)acrylates, results in the improved appearance of the final cured coating.

DETAILED DESCRln ION OF THE INVEN'IlO~I

The actinic radiation-curable compositions of this invention contain a multifunctional (meth)acrylate, a maximum level of water-insoluble impurities, a latex polymer emulsion and optionally a photoinitiator. The final cured composition has excellent clarity which is a particularly important property for coatings on a variety of substrates and composites, including, for example, wood, plastics, and the like.

The multifunctional (meth)acrylate is present to cure with the latex polymer. The improvement accomplished in the cured coatings of the present invention are achieved by reducing or eliminating certain water-insoluble impurities which are formed as by-products in the manufacture of multifunctional (meth)acrylates.

, ; :

"Multifunctional (meth)acrylate," as used herein, refers to a material which has at least two (meth)acryloyl functional groups per molecule, a molecular weight of not more than 1000 per functional group and boiling point of at least 200~C at atmospheric pressure. The multifunctional (meth)acrylates may be used alone or in combination.
The molecular weight per one (meth)acryloyl group is less than about 1000, preferably from about 95 to about 300, and more preferably from about 95 to about 150.

Suitable multifunctional (meth)acrylates include polyfunctional (meth)acrylates obtained by reaction of a (meth)acryloxy-containing compound, such as (meth)acrylic acid, (meth)acryloyl halide, or a (meth)acrylic acid ester, with various compounds, such as hydroxy-containing alkyd resins, polyester condensates, or polyether condensates. These complex (meth)acrylated products may in some instances be termed "polymeric", since the (meth)acryloxy groups may be joined to a condensation polymer, e.g., a polyester or a polyurethane, to an addition polymer, e.g., a polyether, or to a vinyl addition polymer, e.g., a glycidyl (meth)acrylate polymer. Examples include:

(A) Urethane (meth)acrylates obtained by reacting isocyanate groups of a polyisocyanate, such as hexamethylene diisocyanate with a hydroxyalkyl (meth)acrylate, e.g., hydroxyethyl (meth)acrylate. These polyurethane poly(rneth)acrylate monomers are disclosed in U.S.
Patent 3,297,745.

(B) Polyether (meth)acrylates obtained by esterification of , .

211 ~928 , ~ "
hydroxy-terminated polyethers with (meth)acrylic acid as disclosed in U.S. Patent 3,380,831.

(C) Polyesters having at least two (meth)acrylate groups obtained by esterifymg hydroxyl groups with (meth)acrylic acid as disclosed in U.S.
Patent 3,935,173.

(D) Multifunctional (meth)acrylates disclosed in U.S. Patent 3,560,237, e.g. obtained by reaction of a hydroxyaLkyl (meth)acrylate, e.g., hydroxyethyl (me~)acrylate, with any one of: :

(a) Dicarboxylic acids having from 4 to 15 carbon atoms, (b) Polyepoxides having terminal glycidyl groups, (c) Polyis~cyanates having terminal reactive isocyanate groups.

(E) (Meth)acrylate-terminated polyesters made from (meth)acrylic acid, a polyol having at least three hydroxyl g~oups, and a dicarboxylic acid as disclosed in U.S. Patent 3,567,494.

(F) Multifuncti~nal (meth)acrylates obtained by the reaction of ~:
(meth)acrylic acid with at least two epoxy groups of epoxidized drying oils, such as soybean oil, linseed oil, and the like, e.g. epoxidized corresponding drying oil fatty acid, an ester or amide thereof, or the corresponding alcohol, containing at least 2 epoxy groups. Such ~ :
multifunctional (meth)acrylates are disclosed in U.S. Patent 3,125,592.
, (G) Multifunctional (meth)acrylates which are urethane or amine derivatives of the poly(meth)acrylated epoxidized drying oils, fatty ~ ~;

2~1 ~928 acids and the like described in (F) and U.S. Patent mentioned therein, obtained by the reaction of isocyanate(s) or amine(s) respectively with the poly(meth)acrylated epoxidized drying oils, fatty acids, and the like described in U.S. Patent 3,125,592. The urethane and amine derivatives retain some or all of the (meth)acrylate groups and are disclosed in U.S.
Patents 3,876,518 and 3,878,0'77.

(H) Multifunctional (meth)acrylates obtained by reaction of (meth)acrylic acid by addition to the epoxy groups of aromatic bisphenol-based epoxy resins as disclosed in U.S. Patent 3,373,075.

(I) Multifunctional (meth)acrylates obtained by the addition of (meth)acrylic acid to a linear vinyl polymer having pendant glycidyl groups, e.g. polymers of glycidyl (meth)acrylate or of vinyl glycidyl ether or vinyl glycidyl sulfide as disclosed in U.S. Patent 3,530,100.

(J) Multifunctional (meth)acrylates derived from (meth)acrylic acid anhydride and polyepoxides as disclosed in U.S. Patent 3,676,398.
, (K) Multifunctional (meth)acrylate urethane esters obtained from the combining of hydroxyalkyl (meth)acrylates, a diisocyanate, and a hydroxyl functional alkyd condensate as disclosed in U.S. Patent ~-3,673,140.

(L) (Meth)acrylate terminated urethane polyesters obtained by reaction of a polycaprolactone diol or triol with an organic polyisocyanate, e.g. a diisocyanate, and a hydroxyalkyl (meth)acrylate.
Such products are disclosed in U.S. Patent 3,700,643.

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2116~2~

(M~ Urethane multifunctional (meth)acrylates obtained by reaction of a hydroxyl-containing ester of a polyol with (meth)acrylic acid and a polyisocyanate, such as those described in U.S. Patent 3,759,809.

The disclosure in the patents mentioned above in each of paragraphs (A) through (M) are incorporated herein by reference insofar as they disclose the multifunctional (meth)acryloxy-containing compounds and the processes of making them.

The preferred multifunctional (meth)acrylates are trimethylolpropane triacrylate and trimethylolpropane trimethacrylate, with trimethylolpropane triacrylate more preferred.
.

The need to reduce or eliminate the water-insoluble by-products typically formed during the manufacture of the multifunctional (meth)acrylate is the crux of the present invention. These water-insoluble impurities includP the AOPAte ester product of the multifunctional acrylate and hydroxy Michael addition product of the multifunctional acrylate.
: , Although not intending to be bound by theory, I believe that the water-insoluble impurities interfere with the transfer of the multifunctional (meth)acrylate monomer into the latex polyrner. The multifunctional (rmeth)acrylate is generally soluble enough in water to rapidly transfer into the latex polymer particles. The water-insoluble impurities do not transfer into the latex polymer particles, but remair as separate particles which lead to defects, and subsequently lower clarity, in the final cured coating.

2116~28 The general structural formula of the AOPate ester product of the multifunctional acrylate is:

~ OR2 C~2 oR3 Rl--C--C H2 \ oR4 where R~ = -CH3, CH2CH3;
R2, R3 = -(CO)CH=CH2; and R4 = -(CO)CH2CH20tCO)CH= CH2 The general structural formula of the hydroxy Michael addition - product of the mul~functional acrylate is: -oR2 oR3 oR4 211~2~
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where Rl = ~H3, CH2CH3;
R2, R3 = -(CO)CH=CH2; and R4 = CH2CH2(CO) OCH2CH(RI)[CH2O(CO)CH= CH2l2.

The clarity of the final cured coating and the ease of preparation are improved when the aqueous, actinic radiation-curable compositions of the invention contain less than about 5% by weight, based on the total weight of the multifunctional (meth)acrylate and impurities, of the AOPate ester product of the multifunctional acrylate and less than 20% by weight, based on the total weight of the multifunctional (meth)acrylate and impurities, of the hydroxy Michael addition product of the multifunctional (meth)acrylate. Preferably, the aqueous, actinic radiation-curable compositions of the invention contain less than about 3% by weight, based on the total weight of the multifunctional (meth)acrylate and impurities, of the AOPate ester product of the multifunctional acrylate and less than 10% by weight, based on the total weight of the multifunctional (meth)acrylate and impurities, of the hydroxy Michael addition product of the multifunctional (meth)acrylate. ;~

The level of water-insoluble impurities may be reduced or ~;
eliminated from the multifunctional (meth)acrylate by modification of the preparation process of the multifunctional (meth)acrylate, such as ~'for example by adjusting the balance of reactant concentrations, temperature and catalyst, or by distillation, chromatography, extraction and the like.
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2 1 ~ 8 "Latex" as used herein refers to a water-insoluble polymer which may be prepared by conventional polymerization techniques such as, for example, by emulsion polymerization. "Glass transition temperature," or "Tg," as used herein means the glass transition temperature of a polymer as calculated by the Fox equation [Bulletin of :
American Physics Society 1, 3, page 123 (1956)]:

Wl_ + W?_ Tg Tg(l) Tg(2) For a copolymer, w1 and w2 refer to the weight fraction of the two comonomers and Tg(l) and TE(2) refer to the glass transition temperatures of the two corresponding homopolymers. As used herein, acrylate and methacrylate are referred to as "(meth)acrylate", acryloyl group and methacryloyl are referred to as "(meth)acryloyl" and acrylic acid and methacrylic acid are referred to as "(meth)acrylic acid".

The latex polymer used in the actinic radiation-curable composition is prepared by emulsion polymerization techniques well known in the art. The latex polymer is forrned from any monomer or mixture of monomers which yields a water-insoluble latex polymer.

A wide variety of monomers or mixture of monomers can be used to make the latex polymer. For example, acrylic ester monomers, including methyl acrylate, ethyl acrylate, propyl acrylate, isopropyl acrylate, butyl acrylate, isobutyl acrylate, secondary butyl acrylate, t-butyl acrylate, pentyl acrylate, neopentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, isooctyl aylate, 2-ethylhexyl acrylate, decyl acrylate, isodecyl acrylate, lauryl acrylate, bornyl acrylate, isobornyl acrylate, myristyl acrylate, pentadecyl acrylate, stearyl acrylate and the like; methacrylic acid ester monomers, including methyl methacrylate, ethyl methacrylate, propyl methacrylate, isopropyl methacrylate, butyl methacrylate, isobutyl methacrylate, hexyl methacrylate, octyl methacrylate, isooctyl methal rylate, decyl methacrylate, isodecyl methacrylate, lauryl methacrylate, bornyl methacrylate, isobornyl methacrylate, myristyl methacrylate, pentadecyl methacrylate, stearyl methacrylate and the like; acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, styrene, substituted styrenes, butadiene, acrylonitrile, ethylene, vinyl acetate, and the like may be used.

The latex polymer particle size should be relatively small, between about 70 nanometers (nm) to about 225 nm, preferably from about 70 nm to about 120 nm. As is well-known, given the same polymer backbone, particle size is controlled primarily by the type and level of the emulsifier used.

The latex polymer emulsion should have a level of solids from about 30% to about 50%, preferably from about 35% to about 50%.

The weight ratio of the latex polymer to the multifunctional (meth)acrylate is from about 30:70 to about 95:5, preferably from about 60:40 to about 80:20, and most preferably from about 65:35 to about 75:25.
~.The formulated coating composition may be formed either by L'.directly mixing the latex polymer emulsion and the multifunctional (meth)acrylate or by first pre-emulsifying the multifunctional (meth)acrylate and then mixing this with the latex polymer emulsion.

,7 ~' ' 2116~28 The multifunctional (meth)acrylate can be made into an oil-in-water emulsion by adding a surfactant at a level from about 2% to about 5%.

Suitable anionic surfac~ants include, for example, the higher fatty alcohol sulfates, such as sodium lauryl sulfate, and the like;
alkylaryl sulfonates such as sodium or potassium isopropylbenzene sulfonates or isopropyl naphthalene sulfonates, and the like; alkali metal higher alkyl sulfosuccinates, such as sodium octyl sulfosuccinate, sodium N-methyl- N-palmitoyltaurate, sodium oleyl isothionate, and the like; and alkali metal salts of alkylarylpolyethoxyethanol sulfates or sulfonates, such as sodium tert-octylphenoxypolyethoxyethyl sulfate having 1 to 5 oxyethylene units, and the like.

.
Suitable nonionic surfactants include alkylphenoxypoly ethoxyethanols having alkyl groups of from about 7 to 18 carbons atoms and from about 6 to about 60 oxyethylene units, such as heptyl- ~nR~
phenoxy poly~ ethoxy~ethanols, methyloctyl phenoxy^polyethoxy~ h3 ethanols, and the like; polyethoxyethanol derivatives of methylene-linked alkyl phenol; sulfur-containing agents such as those made by condensing from about 6 to about 60 moles of ethylene oxide with nonyl mercaptan, dodecyl mercaptan, and the like, or with alkylthiophenols wherein the alkyl groups contain from 6 to 16 carbons atoms; ethylene oxide derivatives of long-chained carboxylic acids, such as lauric acid, myristic acid, palrnitic acid, oleic acid, and the like, or mixtures of acids such as those found in tall oil containing frQm 6 to 60 oxyethylene units per molecule; analogous ethylene condensates of long-chained alcohols such as octyl, decyl, lauryl, or cetyl alcohols, ethylene oxide derivatives of etherified or esterified ;polyhydroxy compounds having a hydrophobic hydrocarbon chain, ;
,~ 12 .
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;~ ' 211692~

such as sorbitan monostearate containing from 6 to 60 oxyethylene units; also, ethylene oxide sections combined with one or more hydrophobic propylene oxide sections. Mixtures of alkyl benzenesulfonates and ethoxylated aL~sylphenols may be employed.

The composition may optionally contain a ultraviolet photoinitiator. The low amount of photoinitiator which can optionally be employed is an additional advantage of the present invention. The photoinitiator may be added to the composition from about 0.1% by weight of total nonvolatiles to about 0.5% by weight of total nonvolatiles and more preferably from about 0.2% by weight of total nonvolatiles to about 0.3% by weight of total nonvolatiles. Useful photoinitiators include cleavage-type initiators, halogenated polynuclear ketones, such as chlorosulfonated benzanthones, chlorosulfonated fluorenones, a-haloalkylated benzanthrones, and a-haloalkylated fluorenone as disclosed in U.S. Patents 3,827,957 and 3,827,959; benzoin, its ethers, such as methyl ether, ethyl ether, isopropyl ether, butyl ether, octyl ether and the like; carbonyl compounds such as diacetyl, benzil and the like; sulfur compounds such diphenyl sulfide, dithiocarbamate and the like; a-chloromethyl naphthalene and anthracene. Other useful photoinitiators include alkylphenones and benzophenones as disclosed in U.S. Patent 3 759,807. Photoinitiators suitable for pigrnented coatings are suggested in U.S. Patents 3,915,824 and 3,847,771. Cleavage-type photoinitiators are most preferred.

The composition may contain a thermal initiator if the coating will be cured by heat. The thermal initiator is added to the composition from about 0.5% by weight of total nonvolatiles to about 2% by weight of total nonvolatiles. Useful thermal initiators include azo compounds, such as azobisisobutyronitrile and the like; organic peroxides, such as ketone peroxides, hydroperoxides, alkyl peroxides, acryl peroxides, peroxy esters and the like; and inorganic peroxides, such as ammonium persulfate, potassium persulfate, hydrogen peroxide and the like.

In addition, conventional coating components such as, for example, pigments, dispersants, surfactants, coalescents, wetting agents, rheology modifiers, thickeners, drying retarders, antifoaming agents, colorants, waxes, preservatives, heat stabilizers, ultraviolet light stabiLizers and the like may be used in this invention.
-Techniques for applying the actinic radiation-curable coating include roller coating, curtain coating, spraying and the like.

The fbrmulated coating may be cured or crosslinked either by applying actinic radiation or by heating after most or all of the water has evaporated from the mixture. Useful actinic radiation includes ionizing radiation, electron beam radiation and ultraviolet radiation.
Sources of ultraviolet radiation include sunlight, mercury lamp, carbon-arc lamp, xenon lamp and the like. Medium pressure mercury -vapor lamps are preferred. ;

The actinic radiation-curable compositions may be used as topcoats, intermediate coats and primer coats. The compositions are useful in applications which require easy preparation and excellent clarity, such as, for example, paints, including wood lacquers; ~;
adhesives; inks, including screen printing inks and gravure and . -~::
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. , ., - , . ,, ~ . i ", , , ~ -flexographic printing inks; plastics, including vinyl sheeting and polyvinyl chloride flooring; fiber; paper, including overprint varnishes for paper and board; leather; solder mask photoresist on electronic circuit, printing plates and other composites using actinic radiation cure. The compositions are particularly useful in coating applications on wood, such as, for example, cabinets, furniture and flooring.

The following examples are intended to illustrate the invention;
they are not intended to limit the invention as other applications of the invention will be obvious to those of ordinary skill in the art.

EXAMPLE 1. PREPARATION OF LATEX POLYMER
EMULSIONS

The latex polymer emulsion is one-stage polymers which was prepared by a redox gradual-addition emulsion polymerization process.
To a kettle, 1450 grams of deionized water and 26.8 grams of sodium lauryl sulfate (28%) ("SLS") were added. The kettle was heated to 59-61C. A monomer emulsion was prepared by mixing 1485 grams of methyl acrylate and 15 grams of acrylic acid with 600 grams deionized water and a 27 grams of 28% solution of sodium lauryl sulfate. When the kettle temperature reached 59-61C, 160 grams of the monomer emulsion, 1.5 grams of ammoniurn persulfate and 0.3 grams of sodium bisulfite were added. After two minutes, a trace of ferric sulfate was added. The kettle charge exothermed to 67-69C. Fifteen minutes after the initiation, the cofeeds of the monomer emulsion, ammonium persulfate solution (1.6 grams ammonium persulfate dissolved in 60 grams of deionized water) and the sodium bisulfite solution (1.6 grams sodium bisulfite dissolved in 60 grams of deior~ized water) were begun.
The monomer emulsion was added over 3 hours and the ammonium persulfate and sodiurn bisulfite feeds were added over the same time period with a 20 minute overfeed. At the completion of the monomer emulsion feed, 40 grams of deionized water was added twice in sequence. After all the feeds were completed, the kettle was held at 63C for 20 minutes and then cooled to 55C. Any unpolymerized monomers were then incorporated into the polymer by the stepwise ~ -~
addition of redox and thermal free radical initiators over twenty minutes followed by cooling to 35C. When the kettle reached 35C, a mixture of 14.3 grams of ammonium hydroxide (28%) in 25.7 grams of deionized water and 0.2 grams of Proxel(D CRL preservative was added.
The kettle was further cooled to ambient temperature and was then , .

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21~6928 filtered. The final latex polymer emulsion was approxirnately 37.5%
solids.
XAMPLE 2. PREPARATION OF MULTIFUNCTIONAL
(METH)ACRYLATE

The multifunctional (meth)acrylate was pre-emulsified. A 1.2 liter metal bucket with a 12.5 centimeter inside diameter was equipped with a dispersator with a 6.7 centimeter Cowles serrated blade. In the bucket, 8.6 g of nonionic surfactant (Triton(9 X-15) and 2.2 g of nonionic surfactant (Triton~) X-102) were added to 125.8 g of deionized water.
360 g of trimethylolpropane triacrylate ("TMPIA") sample was added over a 20 minute period using a 3 milliliter plastic dropper with the dispersator initially at 1000-1200 rpm and increasing the stirring to 2000 rpm as foaming allowed. After the addition of the trimethylolpropane tri(meth)acrylate, the stirring was increased to 3000 rpm for 10 minutes.

211692~

EXAMPLE 3. PREPARATION OF FORMULATION

In a 2 liter metal bottle with a 5 centimeter stirrer, 0.03 grams of photoinitiator (Darocurtg) 1173) was added to 30 grams latex polymer emulsion. The samples of pre-emulsified TMPTA (6.6 grams) were then added dropwise from a 3 milliliter plastic dropper over a 15 minute period stirring to just maintain a small surface vortex. After the complete addition of the TMPTA, the mixture was stirred for an additional 30 minutes. 2.8 grams deionized water charge was added.
0.8 g associative thickener solution (Acrysol(g QR-708 ~ 2% solids in water) was added to the mixture adjusting the stirring to keep a small surface vortex. The mixture was stirred for an additional 1~5 minutes The mixture was equilibrated for at least 16 hours before use. The viscosity of the formulation was approximately 90 centipoise as measured by a Brookfield viscometer.

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EXAMPLE 4. PREPARATION OF COATED SPECIMENS AND
EVALUATION

The formulated coating was applied to a phosphatized steel panel using a wet film applicator with a 5 mil gate. The coating was allowed to dry for 15 minutes at room temperature and then for 10 minutes at 150F in a forced air oven. The coated panel was then cured with one pass through an RPC Model 1202 UV processor equipped with two 200 watts/inch medium pressure mercury arc lamps at a belt speed of 20 feet/minute (approximately 2 Joules/crn2 total energy). The final cured coating thickness was about 1 mil.

Formulation 1 having a reduced level of water-insoluble impurities had no surface defects after curing. However, Formulation 2 (Comparative) having higher levels of water-insoluble impurities had a large number of surface defects causing the final coating to be opaque.

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Claims (15)

1. A composition comprising:
(a) a latex polymer emulsion;
(b) a multifunctional (meth)acrylate;
(c) an AOPate ester product of multifunctional acrylate of the formula:

where R1=CH3,-CH2CH3;
R2,R3 = -(CO)CH=CH2; and R4=-(CO)CH2CH2O(CO)CH= CH2; and (d) a hydroxy Michael addition product of the multifunctional acrylate of the formula:

where R1 = -CH3,-CH2CH3;
R2,R3= -(CO)CH=CH2; and R4 =-CH2CH2(CO)-OCH2CH(R1)[CH2O(CO)CH= CH2]2, and wherein component (c) is present at less than 5% by weight and component (d) is present at less than 20% by weight, based on the total weight of components (b),(c) and (d).

2. The composition of claim 1 wherein said AOPate ester product is present at less than about 3% by weight, based on the total weight of components (b),(c) and (d).

3. The composition of claim 1 wherein said hydroxy Michael addition product is present at less than about 10% by weight, based on the total weight of components (b),(c) and (d).

4. The composition of claim 1 wherein the multifunctional (meth)acrylate is trimethylolpropane triacrylate.

5. The composition of claim 1 wherein the multifunctional (meth)acrylate is trimethylolpropane trimethacrylate.

6. The composition of claim 1 wherein the weight ratio of latex polymer to multifunctional (meth)acrylate is from about 30:70 to about 95:5.

7. The composition of claim 1 wherein the weight ratio of latex polymer to multifunctional (meth)acrylate is from about 60:40 to about 80:20.

8. The composition of claim 1 wherein the weight ratio of latex polymer to multifunctional (meth)acrylate is from about 65:35 to about 75:25.

9. The composition of claim 1 further comprising a photoinitiator.

10. The composition of claim 9 wherein the photoinitiator is present at a level of less than about 0.5% by weight of nonvolatiles.

11. The composition of claims 9 and 10 wherein the photoinitiator is a cleavage-type photoinitiator.

12. The composition of claim 1 further comprising a thermal initiator.

13. A process of improving the clarity of a cured coating comprising:
(a) forming a coating composition containing:
(i) a latex polymer emulsion;
(ii) a multifunctional (meth)acrylate;
(iii) an AOPate ester product of multifunctional acrylate of the formula:

where R1 = -CH3,-CH2CH3;
R2,R3 = -(CO)CH=CH2; and R4=-(CO)CH2CH2O(CO)CH= CH2; and (iv) a hydroxy Michael addition product of the multifunctional acrylate of the formula:

where R1 =-CH3,-CH2CH3;
R2,R3 = -(CO)CH=CH2; and R4=-CH2CH2(CO)-OCH2CH(R1)[CH2O(CO)CH= CH2]2, wherein component (c) is present at less than 5% by weight and component (d) is present at less than 20% by weight, based on the total weight of components (b), (c) and (d);
(b) applying the coating composition to a substrate; and (c) exposing the coating composition to a source of radiation.

14. The method of claim 13 wherein the substrate is wood.

15. A cured polymer coating comprising:
(a) a latex polymer emulsion;
(b) a multifunctional (meth)acrylate;
(c) an AOPate ester product of multifunctional acrylate of the formula:

where R1 = -CH3,-CH2CH3;
R2,R3 = -(CO)CH=CH2; and R4=-(CO)CH2CH2O(CO)CH= CH2; and (d) a hydroxy Michael addition product of the multifunctional acrylate of the formula:

where R1 =-CH3,-CH2CH3;
R2,R3 =-(CO)CH=CH2; and R4 =-CH2CH2(CO)-OCH2CH(R1)[CH2O(CO)CH= CH2]2, and wherein component (c) is present at less than 5% by weight and component (d) is present at less than 20% by weight, based on the total weight of components (b),(c) and (d).