ADVANCED EPOXY RESIN FOR CAN COATING APPLICATIONS AND PROCESS FOR THE PREPARATION THEREOF

Abstract: Advanced epoxy resins are prepared from a liquid diglycidyl ether of bisphenol A and bisphenol A which advanced epoxy resins have an equivalent weight in the range of 3,000 to 3,900 and a weight average molecular weight of 13,000 to 17,000. These resins are prepared by heating a heat­ ing a mixture of (A) a liquid diglycidyl ether of bisphenol A having an average epoxide equivalent weight of from 170 to 195, (B).bisphenol A, (C) a catalytic quantity of one or more catalysts for effecting the reaction between components A and B and (D) a solvent or mixture of solvents such that the exotherm temper­ ature is between 190°C and 210°C; cooling the resultant reaction mixture to a temperature between 150°C and 185°C and maintaining the temperature thereat until the desired epoxide equivalent weight and weight average molecular weight are obtained; and thereafter quenching the resulting reaction product to a tem­ perature between 90°C and 130°C with (E) one or more solvents. In the process of this invention, component A is employed in an amount which comprises from 54 to 62 percent by weight of the combined weight of components A, B, C and D; component B is employed in an amount which comprises from 30 to 35 percent by weight of the combined weight of components A, B, C and D; component C is employed in an amount which comprises from 0.01 to 0.2 percent by weight of the combined weight of compon­ ents A, B, C and D; component D is employed in an amount which comprises from 5 to 30 percent by weight of the combined weight of components A, B, C and D; and component E is employed in an amount which comprises from 30 to 80 percent by weight of components A, B, C, D and E. When these advanced epoxy resins are formu­ lated into can coating compositions they result in coatings having good wet and dry adhesion.

Description: The present invention is directed to advanced epoxy resin compositions which when formulated into a can coating result in a coating which has good wet adhesion as well as good dry adhesion and a method for preparing these resins. Can coatings have heretofore been formulated from advanced epoxy resins. These coatings usually have good dry adhesion, but relatively poor wet adhesion. It is desirable that such coatings have both good wet and dry adhesion, particularly for food and beverage cans. It has been discovered that when the advanced epoxy resin employed in the coating formulation has an epoxide equivalent weight of from 3,000 to 3,900 and a weight average molecular weight of from 13,000 to 17,000 the resultant coating has good wet adhesion as well as good dry adhesion. The present invention concerns advanced epoxy resins prepared from a diglycidyl ether of bisphenol A having an epoxide equivalent weight of from 170 to 195 and bisphenol A wherein the resultant advanced epoxy resin has an epoxide equivalent weight of from 3,000 to 3,900 and a weight average molecular weight of from 13,000 to 17,000. Another aspect of the present invention pertains to a process for preparing an epoxy resin having an epoxide equivalent weight of from 3,000 to 3,900 and a weight average molecular weight of from 13,000 to 17,000 which process comprises (I) heating a mixture of (A) a liquid diglycidyl ether of bisphenol A having an average epoxide equivalent weight of from 170 to 195, and (B) bisphenol A, (C) a catalytic quantity of one or more phosphonium compounds for effecting the reaction between components A and B and (D) a solvent or mixture of solvents such that the exotherm temperature is between 190°C and 210°C; (II) cooling the reaction mixture from step I to a temperature between 150°C and 185°C, preferably between 125°C and 175°C and maintaining the temperature thereat until the desired epoxide equivalent weight and weight average molecular weight are obtained; and thereafter (III) quenching the reaction product from step II to a temperature between 90°C and 130°C with (E) one or more solvents; and wherein (i) component A is employed in an amount which comprises from 54 to 62 percent by weight of the combined weight of components A, B, C and D; (ii) component B is employed in an amount which comprises from 30 to 35 percent by weight of the combined weight of components A, B, C and D; (iii) component C is employed in an amount which comprises from 0.01 to 0.2 percent by weight of the combined weight of components A, B, C and D; (iv) component D is employed in an amount which comprises from 5 to 30 percent by weight of the combined weight of components A, B, C and D; (v) component E is employed in an amount which comprises from 30 to 80 percent by weight of components A, B, C, D and E. Suitable solvents which can be employed in step I of the process of the present invention as component D and in step III of the process of the present invention as component E include, for example, glycol ethers, alcohols, ketones, aromatic hydrocarbons, and mixtures thereof. Particularly suitable solvents which can be employed in step I and step III of the process of the present invention as components D and component E include, for example, 2-butoxyethanol (n-butyl ether of ethylene glycol), aromatic solvents having a flash point of 43°C and a boiling range of 155°C to 173°C, aromatic solvents having a flash point of 66°C and a boiling range of 183°C to 210°C, methyl amyl ketone, diacetone alcohol, methyl ether of dipropylene glycol, 3-methyl-3-methoxy butanol, xylene, methyl ethyl ketone, methyl isobutyl ketone, acetone, n-butanol, sec-butanol, isopropanol, butyl acetate, and mixtures thereof. Particularly suitable solvents which can be employed in step I of the process of the present invention as component D include 2-butoxyethanol, xylene, aromatic hydrocarbon solvent, 3-methyl-3-methoxy butanol, methyl ether of dipropylene glycol or a mixture thereof. Particularly suitable solvents which can be employed in step III of the process of the present invention as component E include 2-butoxyethanol, xylene, aromatic hydrocarbon solvent, cyclohexanone, n-butanol, or a mixture thereof. The catalysts which can be employed herein as component C are phosphonium compounds such as, for example, phosphonium carboxylates, phosphonium carboxylate·carboxylic acid complexes, phosphonium halides, phosphonium biscarbonates, phosphonium phosphates, and mixtures thereof. Particularly suitable phosphonium compounds include, for example, ethyltriphenylphosphonium acetate·acetic acid complex, ethyltriphenylphosphonium phosphate, and mixtures thereof. The advanced epoxy resins of the present invention are particularly useful in can coating formulations wherein such formulations contain said advanced epoxy resin, suitable solvents and suitable curing agents and optionally fillers, pigments, flow control agents, surfactants and the like. Suitable curing agents which can be employed in the formulation of can coatings include, for example, phenol-aldehyde (resole) resins, urea-aldehyde resins, melamine-aldehyde resins, polyamides, acid anhydrides, primary ,secondary and tertiary amines, imidazoles, guanadines, mixtures thereof and the like. The following examples are illustrative of the present invention. In the following examples, the epoxide equivalent weight was determined by titration with perchloric acid. The weight average molecular weight was determined by gel permeation chromatography using polystyrene standards. Coatings were tested for wet and dry adhesion using the T-peel test ASTM D1876. The wet adhesion test was performed after the test panels had been immersed in 90°C water for four days (345,600 s). EXAMPLE 1 A. Preparation of Advanced Epoxy Resin To a one liter 5-necked round bottom glass reaction vessel equipped with a means for stirring and temperature control was added 315 g (1.67 equiv.) of a diglycidyl ether of bisphenol A having an epoxide equivalent weight (EEW) of 188, 13.13 g of xylene, 1.05 g of ethyltriphenylphosphonium phosphate (30 percent solids in methanol), 172.3 g (1.51 equiv.) of bisphenol A and 39.56 g of the n-butyl ether of ethylene glycol. The contents were heated with stirring to a temperature of 160°C over a period of 62 minutes (3720 s). The contents were then allowed to exotherm to a temperature of 206°C after which the contents were cooled to a temperature of 171°C and maintained at a temperature of 170°C for a period of 90 minutes (5400 s). A sample was taken and an analysis revealed it to have an EEW of 3,362 and a weight average molecular weight of 14,457. The resultant product was then quenched to a 40 percent by weight non volatiles level with 678.3 g of a 60/40 mixture, by weight, of xylene and the n-butyl ether of ethylene glycol, respectively. B. Preparation of Coating Composition A coating was prepared by mixing the following components: 25 g of the advanced epoxy resin prepared in A above; 8.3 g of a phenol formaldehyde resole curing agent of 30 percent solids; 8.3 g of 60/40 by weight xylene/n-butyl ether of ethylene glycol mixture. The above mixture was heated for 4 hours (14,400 s) at a temperature of 110°C. After cooling to ambient temperature, the resultant coating composition was coated onto tin-free steel panels and cured in an oven at 210°C for 0.22 hour (780 s). The thus coated panel was then cut into 5 mm wide strips and between each pair of strips was placed 0.08 mm thick Nylon-12 tape. Each pair of strips was then heat bonded under a pressure of 150 psig (1034.22 kPa) at a temperature of 205°C for 0.50 minute (30 s). The panels were then tested for wet and dry adhesion. The results are given in Table I. COMPARATIVE EXPERIMENT A A coating composition was prepared and evaluated as in Example 1-B from ®EPIKOTE 1009 (Shell Chemical Co.), a diglycidyl ether of bisphenol A having an EEW of 2600 and a 16,900 weight average molecular weight. Performance results are given in Table I. COMPARATIVE EXPERIMENT B To a 100 gallon (378.5 1) kettle equipped with a means of stirring and temperature control was added 134.6 lbs. (61 kg, 0.72 lb. equiv.) of a diglycidyl ether of bisphenol A having an epoxide equivalent weight (EEW) of 187, 5.6 lbs. (2.54 kg) of xylene, 0.45 lbs. (0.2 kg) of ethyltriphenylphosphonium phosphate (30 percent solids in methanol), 73.7 lbs. (33.43 kg, 0.65 lb. equiv.) of bisphenol A and 17.5 lbs. (7.94 kg) of the n-butyl ether of ethylene glycol. The contents were heated with stirring to a temperature of 160°C over 75 minutes (4500 s). The contents were then allowed to exotherm to a temperature of 180°C and cooled to a temperature of 170°C and reacted for 134 minutes (8040 s) post maximum exotherm. A sample was taken and analysis revealed it to have an EEW of 3760 and a 17,600 weight average molecular weight. The resultant product was then quenched to a 40 percent by weight non-volatiles level with 114.8 lbs. (52.1 kg) of the n-butyl ether of ethylene glycol and 171.7 lbs. (77.88 kg) of xylene. COMPARATIVE EXPERIMENT C To a 300 gallon (1135.6 l) kettle equipped with a means of stirring and temperature control was added 595 lbs. (269.89 kg, 3.16 lb. equiv.) of a diglycidyl ether of bisphenol A having an epoxide equivalent weight (EEW) of 186, 25 lbs. (11.34 kg) of xylene, 2 lbs. (0.91 kg) of ethyltriphenylphosphonium phosphate (30 percent solids in methanol), 327 lbs. (148.33 kg, 2.87 lb. equiv.) of bisphenol A and 78 lbs. (35.38 kg) of the n-butyl ether of ethylene glycol. The contents were heated with stirring to a temperature of 154°C over 63 minutes (3780 s). The contents were then allowed to exotherm to a temperature of 197°C and cooled to a temperature of 171°C and reacted for 65 minutes (3900 s) past maximum exotherm. A sample was taken and analysis revealed it to have an EEW of 2756 and a 10,700 weight average molecular weight. The resultant product was then quenched to a 40 percent by weight non-volatiles level with 200 lbs. (90.72 kg) of the n-butyl ether of ethylene glycol, 278 lbs. (126.1 kg) of cyclohexanone, 278 lbs. (126.1 kg) of n-butanol, 253 lbs. (114.76 kg) of xylene, and 278 lbs. (126.1 kg) of an aromatic solvent having a flash point of 43°C and a boiling range of 155°C to 173°C. COMPARATIVE EXPERIMENT D To a 300 gallon (1135.6 1) kettle equipped with a means of stirring and temperature control was added 595 lbs. (269.89 kg, 3.2 lb. equiv.) of a diglycidyl ether of bisphenol A having an epoxide equivalent weight (EEW) of 186, 25 lbs. (11.34 kg) of xylene, 2 lbs. (0.91 kg) of ethyltriphenylphosphonium phosphate (30 percent solids in methanol), 327 lbs. (148.33 kg, 2.87 lb. equiv.) of bisphenol A and 78 lbs. (35.38 kg) of the n-butyl ether of ethylene glycol. The contents were heated with stirring to a temperature of 170°C over 74 minutes (4440 s). The contents were then allowed to exotherm to a temperature of 216°C and cooled to a temperature of 170°C and reacted for 80 minutes (4800 s) post maximum exotherm. A sample was taken and analysis revealed it to have an EEW of 3675 and a 17,400 weight average molecular weight. The resultant product was then quenched to a 40 percent by weight non-volatiles level with 200 lbs. (90.72 kg) of the n-butyl ether of ethylene glycol, EB, 278 lbs. (126.1 kg) of cyclohexanone, 278 lbs. (126.1 kg) of n-butanol, 253 lbs. (114.76 kg) of xylene, and 278 lbs, (126.1 kg) of an aromatic solvent having a flash point of 43°C and a boiling range of 155°C to 173°C. EXAMPLE 2 To a 300 gallon (1135.6 1) kettle equipped with a means of stirring and temperature control was added 596 lbs. (269.89 kg, 3.2 lb. equiv.) of a diglycidyl ether of bisphenol A having an epoxide equivalent weight (EEW) of 186, 25 lbs. (11.34 kg) of xylene, 2 lbs. (0.91 kg) of ethyltriphenylphosphonium phosphate (30 percent solids in methanol), 327 lbs. (148.33 kg, 2.87 lb. equiv.) of bisphenol A and 78 lbs. (35.38 kg) of the n-butyl ether of ethylene glycol. The contents were heated with stirring to a temperature of 160°C over 74 minutes (4440 s). The contents were then allowed to exotherm to a temperature of 206°C and cooled to a temperature of 175°C and reacted for 69 minutes (4140 s) post maximum exotherm. A sample was taken and analysis revealed it to have an EEW of 3583 and a 15,700 weight average molecular weight. The resultant product was then quenched to a 40 percent by weight non-volatiles level with 200 lbs. (90.72 kg) of the n-butyl ether of ethylene glycol, 278 lbs. (126.1 kg) of cyclohexanone, 278 lbs. (126.1 kg) of n-butanol, 253 lbs. (114.76 kg) of xylene, and 278 lbs. (126.1 kg) of an aromatic solvent having a flash point of 43°C and a boiling range of 155°C to 173°C. EXAMPLE 3 To a 300 gallon (1135.6 1) kettle equipped with a means of stirring and temperature control was added 596 lbs. (270.34 kg, 3.2 lb. equiv.) of a diglycidyl ether of bisphenol A having an epoxide equivalent weight (EEW) of 186, 25 lbs. (11.34 kg) of xylene 2 lbs. (0.91 kg) of ethyltriphenylphosphonium phosphate (30 percent solids in methanol), 327 lbs. (148.33 kg, 2.87 lb. equiv.) of bisphenol A and 78 lbs. (35.38 kg) of the n-butyl ether of ethylene glycol. The contents were heated with stirring to a temperature of 153°C over 76 minutes (4560 s). The contents were then allowed to exotherm to a temperature of 200°C and cooled to a temperature of 170°C and reacted for 94 minutes (5640 s) post maximum exotherm. A sample was taken and analysis revealed it to have an EEW of 3116 and a 13,200 weight average molecular weight. The resultant product was then quenched to a 40 percent by weight non-volatiles level with 200 lbs. (90.72 kg) of the n-butyl ether of ethylene glycol, 278 lbs. (126.1 kg) of cyclohexanone, 278 lbs. (126.1 kg) of n-butanol, 253 lbs. (114.76 kg) of xylene, and 278 lbs. (126.1 kg) of an aromatic solvent having a flash point of 43°C and a boiling range of 155°C to 173°C. EXAMPLE 4 To a 100 gallon (378.54 1) kettle equipped with a means of stirring and temperature control was added 132.6 lbs. (60.15 kg, 0.71 lb. equiv.) of a diglycidyl ether of bisphenol A having an epoxide equivalent weight (EEW) of 187, 5.5 lbs. (2.5 kg) of xylene, 0.45 lb. (0.2 kg) of ethyltriphenylphosphonium phosphate (30 percent solids in methanol), 73 lbs. (33.11 kg, 0.64 lb. equiv.) of bisphenol A and 17.3 lbs. (7.85 kg) of the n-butyl ether of ethylene glycol. The contents were heated with stirring to a temperature of 180°C over 68 minutes (4080 s). The contents were then allowed to exotherm to a temperature of 202°C and cooled to a temperature of 172°C and reacted for 127 minutes (7620 s) post maximum exotherm. A sample was taken and analysis revealed it to have an EEW of 3870 and a 15,200 weight average molecular weight. The resultant product was then quenched to a 40 percent by weight non-volatiles level with 113.1 lbs. (51.3 kg) of the n-butyl ether of ethylene glycol and 169.2 lbs. (76.75 kg) of xylene. EXAMPLE 5 To a 2000 gallon (7570.8 1) kettle equipped with a means of stirring and temperature control was added 3159 lbs. (1432.92 kg, 16.71 lb. equiv.) of a diglycidyl ether of bisphenol A having an epoxide equivalent weight (EEW) of 189, 133 lbs. (60.33 kg) of xylene, 10.5 lbs. (4.76 kg) of ethyltriphenylphosphonium phosphate (30 percent solids in methanol), 1720.5 lbs. (781.11 kg, 15.09 lb. equiv.) of bisphenol A and 411 lbs. (186.43 kg) of the n-butyl ether of ethylene glycol. The contents were heated with stirring to a temperature of 150°C over 60 minutes (3600 s). The contents were then allowed to exotherm to a temperature of 198°C and cooled to a temperature of 178°C and reacted for 60 minutes (3600 s) post maximum exotherm. A sample was taken and analysis revealed it to have an EEW of 3210 and a 14,200 weight average molecular weight. The resultant product was then quenched to a 40 percent by weight non-volatiles level with 1056 lbs. (479 kg) of the n-butyl ether of ethylene glycol, 1467 lbs. (665.43 kg) of cyclohexanone, 1467 lbs. (665.43 kg) of n-butanol, 1334 lbs. (605.1 kg) of xylene, and 1467 lbs. (665.43 kg) of an aromatic solvent having a flash point of 43°C and a boiling range of 155°C to 173°C. COMPARATIVE EXPERIMENT E Example 2 of EPO Application Publication No. 0,115,432 was essentially duplicated. In this experiment a commercially available liquid epoxy resin which was a diglycidyl ether of bisphenol A having an epoxide equivalent weight of 187 (available from The Dow Chemical Company as D.E.R.® 331) was employed as the starting resin. The results are given in Table II. COMPARATIVE EXPERIMENT F Example 8 of EPO Application Publication No. 0,115,432 was essentially duplicated. In this experiment a commercially available liquid epoxy resin which was a diglycidyl ether of bisphenol A having an epoxide equivalent weight of 187 (available from The Dow Chemical Company as D.E.R.® 331) was employed as the starting resin. The results are given in Table II.

Claims: A process for preparing an epoxy resin having an epoxide equivalent weight of from 3,000 to 3,900 and a weight average molecular weight of from 13,000 to 17,000 which process comprises (I) heating a mixture of (A) a liquid diglycidyl ether of bisphenol A having an average epoxy equivalent weight of from 170 to 195, (B) bisphenol A, (C) a catalytic quantity of one or more phosphonium compounds for effecting the reaction between components A and B, and (D) a solvent or mixture of solvents such that the exotherm temperature is between 190 °C and 210 °C; (II) cooling the reaction mixture from step I to a temperature between 150 °C and 185 °C and maintaining the temperature thereat until the desired epoxide equivalent weight and average molecular weight are obtained ; and thereafter (III) quenching the reaction product from step II to a temperature between 90 °C and 130 °C with (E) one or more solvents; and wherein (i) component A is employed in an amount which comprises from 54 to 62 percent by weight of the combined weight of components A, B, C, and D; (ii) component B is employed in an amount which comprises from 30 to 35 percent by weight of the combined weight of components A, B, C, and D; (iii) component C is employed in an amount which comprises from 0.01 to 0.2 percent by weight of the combined weight of components A, B, C, and D; (iv) component D is employed in an amount which comprises from 5 to 30 percent by weight of the combined weight of components A, B, C, and D; (v) component E is is employed in an amount which comprises from 30 to 80 percent by weight of the combined weight of components A, B, C, D, and E. A process of Claim 1 wherein the reaction mixture from step I is cooled to a temperature between 175°C and 165 °C. A process of Claims 1 or 2 wherein component C is ethyltriphenylphosphonium phosphate, ethyltriphenylphosphonium acetate / acetic acid complex or a mixture thereof. A process of any of Claims 1 to 3 wherein said component D in step I is a glycol ether, an alcohol, a ketone, an aromatic hydrocarbon or a mixture thereof. A process of Claim 4 wherein the glycolether is 2-butoxyethanol, 3-methyl-3-methoxy butanol, or methyl ether of dipropylene glycol, and the aromatic hydrocarbon is xylene. A process of any of Claims 1 to 5 wherein said component E in step III is a glycol ether, an alcohol, a ketone, an aromatic hydrocarbon or a mixture thereof. A process of Claim 6 wherein the glycol ether is 2-butoxyethanol, the alcohol is n-butanol, the ketone is cyclohexanone, and the aromatic hydrocarbon is xylene. An advanced epoxy resin prepared from a diglycidyl ether of bisphenol A having an epoxide equivalent weight of from 170 to 195 and bisphenol A wherein the resultant advanced epoxy resin has an epoxy equivalent weight of from 3,000 to 3,900 and a weight average molecular weight of from 13,000 to 17,000.

Inventors: SHEIH, PONG SU, TYLER, MANUEL C., JR.
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1986
Main classification: C08G59
IPC codes: C08G59, C09D163