CA1112787A

CA1112787A - Process for preparing blends of vinyl esters and reactive diluents

Info

Publication number: CA1112787A
Application number: CA296,801A
Authority: CA
Inventors: Rhetta Q. Davis
Original assignee: Dow Chemical Co
Current assignee: Dow Chemical Co
Priority date: 1977-02-14
Filing date: 1978-02-13
Publication date: 1981-11-17
Also published as: NL184846C; NL7801609A; DE2806221A1; AU3323178A; JPS53103413A; DE2806221C2; FR2380323A1; NL184846B; GB1594437A; AU524645B2; FR2380323B1

Abstract

Abstract of the Disclosure This invention is directed to an in-situ process for preparing a curable composition of a terminally unsaturated ester in a reaction diluent.
The reactive diluent is a liquid ester which is pre-first by reacting an organic hydroxyl-containing compound with an excess of equivalents of a terminally unsaturated monocarboxylic acid. A second ester is prepared by reacting the unreacted carboxylic acid from the first reaction with a glycidyl ether or a polyepoxide.
Products of this process are curable by ultraviolet, electron beam or other ionizing radiation, and by free radical catalysts such as peroxides. The products are useful as coatings for a variety of substrates such as, for example, wood, paper, metal and plastics.
The products can also be employed in radiation curable ink formulations.

Description

7~'7 The viscosity of radiation curable terminally unsaturated vinyl ester resins is often reduced to a suitable level by mixing the resins with reactive diluents such as acrylate and methacrylate esters. These esters are pre-par~d in a conventional manner by reacting suitable alcohols with acrylic acid or methacrylic acid. Water produced in the reaction is removed to drive the reaction to completion. Typically a solvent is employed which forms an azeotrope with water, and the water is removed by azeotropic distillation. The solvent is then removed from the higher boiling ester after which the ester is further purified by distillation.
This invention is directed to a process for preparing a curable composition of a liquid first ester of a terminally unsaturated monocarboxylic acid and an organic hydroxyl-containing compound and a second ester of a glycidyl ether or a polyepoxide characterized in that the first and second esters are prepared sequentially in an in situ process wherein the first ester is prepared by reacting the organic hydroxyl-containing compound with an excess of the equivalents of the terminally unsaturated carboxylic acid and the second ester is prepared by reacting the unreacted carboxylic acid from the first step with the glycidyl ether or the polyepoxide. In the formation of the first ester, the excess of equivalents of the carboxylic acid drives the reaction to completion without removing the water produced in the reaction. The in situ produced composition has improved properties compared with a simple mixture of the two esters, such as having 18, ~g-F -1-- ~ .
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lower viscosi-ty of the composition and havi~g improved adhesion to metal such as alum:inum. The in-si-tu process is more economical as the first ester is not purified ; after the reaction. The invention results in at least a 35 percent reduction in time for the overall process for synthesls o-~ the two esters and a 50 to 60 percent reduction in time for the preparation of the ~irst ester as water is not removed and the ester is not puri~ied prior to the preparation of the second ester. The l~ invention minimizes material handling and transfer operation and utilizes a minimum of equipment.
The organic hydroxyl-containing compound is a monohydroxy or polyhydroxy compound and should be free o~ other ~unctional groups which are reactive with carboxyl or oxirane groups. Among the useful compounds are monohydroxy alcohols, alXylene glycols, glycol ethers, and polyglycols. ~uitable monohydroxy alcohols include, ~or example, dicyclopentadiene alcohol. Suitable glycol ethers include, ~or example, ethylene glycol, propylene glycol, butylene glycol, and l,4-butanediol.
Suitable glycol ethers include, for example, those com-pouuds having the formula .
R O (CH -CH-O) -CH -CH-OH
R' R"
wherein R is an aromatic group or an alkyl group having ~rom l to 8 carbon atoms, R' and R" are individually hydrogen, me1;hyl, or ethyl, and n is O or l. Included , . . . ~.
tn the usefu]. compounds-are the phenyl ~ er of ethylene glyool and the methyl ether of diethylene glycol.

18l252-F -2-Suitable polyglycols include, IorOexample, novolacs of phenol and formaldehyde pre~erably reacted with two or more moles of an alkylene oxide such as ethylene oxide or propylene oxide. Other suitable polyglycols include, for example, alkylene oxide adducts of polyhydric compounds such as, for example, ethylene glycol, propylene glycol, glycerine, trimethylolpropane, 1,2,6-hexanetriol, and pentaerytheritol.
Advantageously the terminally unsaturated monocarboxylic acids useful in this invention are liquid ; - at the reaction temperature and pre~erably at room tempera-ture. Preferred acids are acrylic acid and methacrylic acid. The choice of the carboxylic acid and the hydroxyl--containing compound to prepare -the first ester must be such that the first ester is a liquid at room temperature.
Suitable glycidyl ethers include, for example, phenyl glycidyl ether and butyl glycidyl ether. Suitable polyepoxides include, ~or example, polyglycidyl ethers . o~ polyhydric phenols and polyhydric alcohols, epoxy novolac resins, epoxidized diolefins, ~atty acids or drying oils containing more than one oxirane group per molecule. The polyepoxides also include those compounds wherein the molecular weight has been increased by reacting a polyepoxide with a difunctional compound z5 such as a dicarboxylic acid or a diphenol. Preferred polyepoxides are the polyglycidyl ethers of polyhydric ;
phenols and polyhydric alcohols, the epoxy novolac resins, and mixtures thereof wherein the epoxide equiva-le~t weight ranges from lao to 600. Abo,e an epoxide - ::
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equivalent ~veight of 600 it is difficult to dissolve the polyepoxide in the first ester product.
In the first step of the process, the hydroxyl--containing compound and the carboxylic acid are mixed together with an esterification catalyst and, advantage-ously, a small amount of a polymerization inhibitor such as, for example, hydroquinone or the methyl ether of hydroquinone. The amount of acid employed is the total amount required to prepare both esters. Advan-tageously, the equivalents of acid are in the proportion of from 1.5 to 10 times the equivalents of the hydroxyl-containing compound. When the reactants are acrylic acid and a glycol ether, the optimum proportion is 5 equivalents of acid to one e~uivalent of glycol ether.
The proportions of hydroxyl-containing compound and carboxylic acid employed will depend upon the ratio of the esters desired in the final product.
The first reaction mixture is advanta~eously heated to a temperature of from 85 to 120C, preferably from 95 to 100C. The reaction is continued until the desired ester concentration is reached, usually in 3 to 6 hours, although longer or shorter reaction times may sometimes be required depending upon the reactivity of the reactants, the amount and efficiency o~ the catalyst employed and the temperature of the reaction mixture.
The product resulting ~rom the first step is a mixture of the ~irst ester and excess carboxylic - acid. The ~irst product is employed in the second step withou~ purif~catlon or any other-modification.

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In the second st~p of the process, an amount of glyciclyl ether or polyepoxide equivalent -to the amount o-f unreacted carboxylic acid reamining in the first product is added to the reaction mixture t~gether with a small amount of a catalyst such as, for example, chromium acetate or chromium chloride, to promote the carboxyl/epoxide reaction. The. second reaction mixture is heated to a temperature of ~rom 85 to 120C, pre~er-ably from 95 to 115C until the reaction is substantially complete as indicated by the drop in acid value.
Products o~ this process are curable by ultra-violet, electron beam or other ionizing radiation, and by free radical catalysts such as peroxides. The products are useful as coatings ~or a variety of substrates such as, for example, wood, paper, metal and plastics. The products can also be employed~in radiation-curable ink formulations.
Example 1 A reaction mixture o~ 360 g (5 eq~ acrylic acid, 120 g (1 eq) of the methyl ether of diethylene glycol, 1.5 g hydroquinone, and 5 g p-toluene sulfonic '~
acid were blended together in a three necked two liter ~lask equipped with a stirrer. The mix-ture was heated to 95C until the acid value-was reduced to 37.6 weight percent COOH. In the second step, 736 g (4 eq) of a diglycidyl ether of bisphenol A having an epoxy equivalent weight of 183 and 0.46 g (2 millimols) of chromium i - ~ acetate dissolved in a small amount o~ methyl alcohol O
were added to the reaction mixture. The mixture was heated to 110C until the product cQ~tained 0.71 weight ' :
18,25~-F _5_ .: ~ , .. - - .. .. ...
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percent COOII and 0.45 weigIIt p~rcent oxirane group.
When the l'inal product had cooled to 95C, 0.3 g of the monomethyl ether of hydroquinone was added. The viscosity of the final product vas 11,120 cps at 25C.
Examples 2 to 5 Comparative ~uns A to ~
Employing the procedure of Example 1, curable compositions were prepared by reacting various gram equivalent ratios o~ the pheny:L ether of eth~lene glycol and acrylic acid in step one, and then reacting the unreacted acrylic acid from step one with the diglycidyl ether of bisphenol A having an epoxy equivalent weight of 184 in step two.
For Comparative Runs A to D, mixtures of the distilled acrylate ester of the phenyl,,ether of ethylene ` 15 glycol and the acrylate ester of the diglycidyl ether ' of bisphenol A having an epoxy equivalent weight of 184 ~ere mixed in the same proportion as in Examples 2 to ~, respectively. The viscosity at 25C was measured as shown in Table I.

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Example 2 _ 3 4 5 Ratio of Equivalents of acrylic acid to the phenyl ether of ethylene glycol in Step 1 10:1 5:1 2:1 1.5:1 Ratio o~ Equivalen-ts of epoxy groups to acrylic acid in Step 2 1.0:11.12:11.09:1 1.03:1 In the final product (u;t 7/~) % Phenyl ether o~
ethylene glycol 0.5l.2 5.8 10.7 % Acrylate ester of the phenyl ether of ethylene glycol 6 16 32 43 % COOH 0.31 0.3 0.61 0.65 ~ Oxirane l.l0.68 0.56 0.53 % ~2 0.56 0.71 1.23 0.30 Viscosity, cps at 25C 132,000 31,920 1,830 780 Com~arative Run A B C D
Viscosity, cps at 25C 280,000 33,880 3,216 840 ~-, .
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Example G
A curable composition was prepared by first mixing together 285 g (1 eq) of a phenol/~ormaldehyde novolac resin having an average of 3.6 phenolic groups per molecule which was extended with an average o~ 4 moles of ethylene oxide per phenolic hydroxyl, 288 g (4 eq) o~ acrylic acid, 1.15 g of hydroquinone and 2.89 g p-~toluenesulfonic acid. The mixture was heated to 80C
- for four hours, then to 100C ~or two hours and then allowed to cool. The product contained 23.58 weight percent COOH.
In the second step of the process, 191 g (1 acid equivalent weight) of the product of the first step was mixed with 184 g (1 eq) of the digylcidyl èther lS of bisphenol A having an epoxy equivalent weight of 184 and 0.53 g of chromium acetate. The mixture was heated to 110C gradually over 5 hours. After 2 hours, an additional 30 grams o~ the digylcidyl ether of bisphenol A was added to the reaction mixture. The ~inal product after step 2 contained 28.2 weight percent novolac acrylate and had a viscosity at 25C of 42,700 centi-poise as measured with a Brookfield Viscometer at 10 rpm.
Example 7 and Comparative Run E
For Example 7, a curable composition was prepared hy mixing together 150 g (1 eq) of dicyclo-pentadiene alcohol, 288 g (4 eq) of acrylic acid, 0.88 g of hydroquinone, and 4.38 g of p-toluenesul~onic acid.
The mixture was gradually heated to 110C and maintained there for 4 hours. The product at the end of the first , ,.

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step had an acicl equivalent weigh-t of 146.48 and con-tained 2.1 weight percent of dicyclopentadiene alcohol, representing a 93.9 percent conversion.
In the second step of the process, 146.5 g (l eq) of the product from the first step was mixed with 184 g (l eq) of the diglycidyl ether of bisphenol A having an epoxy equivalent weight of 184, and 0.53 g of chromium acetate. After the mixture was heated to 75C, an additional 4.9 g of the digylcidyl ether was added to the reaction mixture. The mixture was gradually heated to 115C ovsr 2.5 hours and an additional 4.9 g of digylcidyl ether was added to the mixture. The reaction was continued for one more hour.. At the con-clusion of the reaction, 0.18 g of the methyl ether of hy.droquinone was added to.the final product. The ~inal product contained 0.45 weight percent COOH and 0.58 . ' weight, percent oxirane group.
For Comparative Run E, a mixture was prepared ~: ' of 37 weight percent of the acrylate ester of dicyclo- , ; 20 pentadiene alcohol and 63 weight percent of the diacylate ester of the diglycidyl ether of bisphenol A having an , epoxy equivalent weight of 184.
The final product from Example 7 and the mix-: ture from Comparative Run E were each coated on a sheet of aluminum and baked at 400F (204Ç) for 4 hours.
After curing, the adhesion o~ each coating to the ~j aluminum was determined by covering 100 square inches ..
(64.5 square centimeters) of. each coating with Scotch brand 610 tape and then pulling the ~ape away from the ; 30 area. In Example 7, 100 percent of the coating r~m~ined , . .

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'7 intact on the aluminum. In Comparative Run.E, none of the coating remained intact on the aluminu~.
Example 8 A curable composi-tion was prepared by first mixing toge-ther 247 g (.25 eq) of a glycerine initiated polyoxypropylene triol capped with ethylene oxide having a hydroxyl equivalent w~ight of 988, 64.5 g (0.75 eq) methacrylic acid, 0.16 g of hydroquinone, and 3.12 g of p-toluenesulfonic acid. The reaction mixture was heated to 110C for 12 hours, at which time 70 weight percent of the polyglycol had been converted to the methacrylate ester.
In the second step of the process, 33.5 g (0.587 eq) o~ a diglycidyl ether of bisphenol A having a~ epoxy equivalent weight of 568, 1.3 g of chromium acetate and 0.1 g of hydroquinone were added to the reaction product from step 1. The mixture was heated to 110C for 25 hours. At the conclusion of the reaction, 0.32 g o~ the methyl ether of hydroquinone was added to the final product. The final product contained 1.13 weight percent COOE and 0.99 weight percent oxirane groups and had a viscosity at 25C of 1,120,000 cps.

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Claims

1. A process for preparing a curable composi-tion of a liquid first ester of a terminally unsaturated monocarboxylic acid and an organic hydroxy-containing compound and a second ester of a glycidyl ether or a polyepoxide characterized in that the first and second esters are prepared sequentially in an in situ process wherein the first ester is prepared by reacting the organic hydroxyl-containing compound with an excess of the equivalents of the terminally unsaturated carboxylic acid and the second ester is prepared by reacting the unreacted carboxylic acid from the first step with the glycidyl ether or the polyepoxide.

2. The process of Claim 1 characterized in that the first ester is prepared from a reaction mixture having the proportions of from 1.5 to 10 equivalents of the carboxylic acid per equivalent of the organic hydroxyl-containing compound.

3. The process of Claim 1 characterized in that the polyepoxide has an epoxide equivalent weight of from 150 to 600.