METHOD OF PRODUCING EPOXY ESTERS

Abstract: Epoxy esters having reduced viscosity and which are curable with aminoplast resins to produce water insensitive coatings are disclosed along with a method of producing them. In this method an organic solvent solution containing a 1% to 20% stoichiometric excess of polyepoxide at least 60% of which is constituted by diglycidyl ethers of a bis­ phenol having an average molecular weight of less than 500 and a 1,2-epoxy equivalency of from 1.8 to 2.0 is slowly added to a mixture of fatty C₆-C₂₂ monocarboxylic acid and esterification catalyst maintained at elevated reaction tem­ perature under conditions appropriate for the reaction of 1,2-oxirane with carboxyl, and the reaction conditions are maintained until the acid number is less than 10.

Description: Method of Producing Epoxy Esters Field of Invention This invention relates to the production of high solids solutions of epoxy esters, especially those in which the ester group contains ethylenic unsaturation, and to thermosetting organic solvent solution coating compositions containing the same. Background Art Unsaturated epoxy esters are known compounds. In the customary production of these esters, the unsaturated fatty acid is added to a hot polyepoxide-containing solution which contains an alkaline esterification catalyst, or all the components are charged to a reactor and the mixture is heated to bring it to reaction temperature. The products produced in this fashion have exhibited a higher than desired solution viscosity which has undesirably limited the concentration of thermosetting solution coating compositions containing the same. This invention is concerned with the production of unsaturated epoxy esters having reduced solution viscosity and to low temperature-curing epoxy ester-aminoplast thermosetting solution coating compositions of high solids content. Disclosure of the Invention In accordance with this invention, the solution viscosity of epoxy esters is reduced by slowly adding at least a 1% stoichiometric excess of polyepoxide solution in organic solvent to a mixture of fatty acid and esterification catalyst maintained at elevated reaction temperature under conditions appropriate for the reaction of 1,2-oxirane with carboxyl functionality, and maintaining reaction conditions until the acid number is less than 10, preferably less than 5. The stoichiometry is based on carboxyl and epoxy functionalities. The resulting epoxy ester contains a small amount of residual unreacted epoxy functionality, but the amount thereof is too small to create solution instability in admixture with certain aminoplast resins so long as the stoichiometric excess is less than 20%, preferably less than 10%. The polyepoxides which are esterified are constituted by at least about 60X of diglycidyl ether of a bisphenol having an average molecular weight by calculation of less than 500 and a 1,2-epoxy equivalency of from 1.8-2.0. These are preferably used in admixture with an epoxidized phenolic novolac having a 1,2-epoxy equivalency of from 2.5-5.5, preferably from 3.0-4.5. The epoxidized novolac desirably constituted from 5% to 40% of the mixture, preferably froni 10% to 25X. All proportions herein are by weight, unless otherwise stated. The fatty acids which are employed may be saturated C6-C22 monocarboxylic acids, like palmitic acid, but unsaturated monocarboxylic acids, like tall oil fatty acid, are preferred, and will be illustrated herein. Other suitable acids are oleic acid, castor oil fatty acids and dehydrated castor oil fatty acids, linoleic acid and linseed fatty acids. The unsaturated acids aid adhesion and lower curing temperature, especially when drier salts are used, as is known. By high solids is meant a total solids content of at least about 50%, preferably at least about 60%. The solvents used in the coating compositions of this invention are the ones commonly used in epoxy ester -aminoplast coatings. Aromatic solvents, like xylol, alone or in admixture with alcohols, like butanol, are preferred. Ketones, like methyl amyl ketone, are desirably present. While any organic solvent-soluble heat-hardening aminoplast resin may be used herein, hexamethoxymethyl melamine is characterized by high functionality, low temperature removal of the blocking methyl ester groups, and high solubility, and is hence preferred. Formaldehyde condensates with urea, benzoguanamine and bisphenol A, will further illustrate the useful aminoplast resin curing agents. High functionality (at least two N-methylol groups or an ether thereof per molecule) is preferred. The aminoplast resin curing agents are broadly useful in an amount of from 3% to 50%, preferably from 5% to 30% based on total resin solids. The epoxy esters of reduced solution viscosity cure with aminoplast resins at relatively low temperature. In the presence of strong acid curing catalysts, like p-toluene sulfonic acid, one can obtain good cures at 250"F. using baking times of from 10-30 minutes. Driers may also be added when the fatty acids are unsaturated, but this is not essential. These driers are illustrated by cobalt naphthenate and are themselves well known. Example 760 grams of tall oil fatty acids and 6 grams of triethyl amine esterification catalyst are charged to a reactor equipped with a reflux condenser. The contents of the reactor are then heated to 80"C. In a separate tank there is mixed together 530 grams of a diglycidyl ether of bisphenol A having an average molecular weight of about 390 (the Shell product Epon 828 may be used), 100 grams of an epoxidized phenolic novolac produced by reacting the phenolic novolac with -epichloro- hydrin and then dehydrohalogenating with sodium hydroxide. This product contains an average of about 3.6 phenol glycidyl ether groups per molecule, the phenol groups being connected to one another by a methylene bridge. Also present in this separate mixture is 120 grams of methyl ethyl ketone and 80 grams of xylol. This mixture is agitated until a uniform solution is formed. The above solution is slowly added to the hot contents of the reactor over a 2-hour period, the temperature being maintained at 80 C. The 80"C. temperature is then maintained for an additional hour and then heat is applied to increase the temperature to 900C., which temperature is maintained until a specimen shows an acid value of less than 4. The product has a solids content of 87.6%, a Gardner viscosity of Q-R and an acid value (measured on nonvolatile solids) of 2.3. It is desired to point out that the reactants include a slight excess of 1,2-oxirane over carboxyl functionality (3.1 vs. 2.7) to insure the consumption of acidity. Residual acid yields water sensitive products, and the excess of oxirane functionality and the extensive reaction avoids this difficulty. Hexamethoxymethyl melamine is then added to the above solution in an amount to provide 25% of the melamine content based on total resin solids. Addition of the melamine compound is at 100% solids and it dissolves in the solution by simple mixing at room temperature. The coating composition containing the melamine curing agent is applied by spray on zinc phosphatetreated steel and polyester plastic in a thickness of 0.75-1.0 mil. Cure is then achieved by placing the wet-coated substrate in a '120"C(2500F)oven for 30 minutes In each instance a water-insensitive cured coating is obtained. The cured coatings are of HB pencil hardness and are excellently adherent to each of the tested substrates.

Claims: CLAIMS 1. A method of producing epoxy esters having reduced viscosity and which are curable with aminoplast resins to produce water insensitive coatings comprising, slowly adding an organic solvent solution containing a 1% to 20% stoichiometric excess of polyepoxide at least about 60% of which is constituted by diglycidyl ethers of a bisphenol having an average molecular weight of less than 500 and a 1,2-epoxy equivalency of from 1.82.0, to a mixture of fatty acid and esterification catalyst maintained at elevated reaction temperature under conditions appropriate for the reaction of 1,2oxirane with carboxyl, said fatty acids being C6-C22 monocarboxylic acids, and maintaining said reaction conditions until the acid number is less than 10. 2. A method as recited in claim I in which said stoichiometric excess of polyepoxide is less than 10% and said reaction conditions are maintained until the acid number is less than 5. 3. A method as recited in claim 1 in which said polyepoxide is a mixture including from 5% to 405 of the mixture of epoxidized phenolic novolac having a 1,2epoxy equivalency of from 2.5-5.5. 4. A method as recited in claim 2 in which said polyepoxide is a mixture including from 10% to 25% of the mixture of epoxidized phenol novolac having a 1,2-epoxy equivalency of from 3.0-4.5. 5. A method as recited in claim 1 in which said monocarboxylic acid is ethylenically unsaturated. 6. A method as recited in claim 4 in which said monocarboxylic acid is tall oil fatty acid. 7. The epoxy ester product of the method of claim 1. 8. The epoxy ester product of the method of claim 6. 9. A thermosetting organic solvent solution coating composition containing at least about 50% total solids content and comprising volatile organic solvent having dissolved therein the epoxy ester product of claim 7 and from 3% to 50%. of total resin solids of an aminoplast resin curing agent. 10. A thermosetting organic solvent solution coating composition containing at least about 60% total solids content and comprising volatile organic solvent having dissolved therein the epoxy ester product of claim 8 and from 5% to 30% of total resin solids of hexamethoxymethyl melamine.

Inventors: SEKMAKAS, KAZYS, SHAH, RAJ
Applicants: DESOTO, INC.
Application year: 1984
Main classification: C08G59
IPC codes: C08G59, C09D163, C08L63