EPOXY RESIN COMPOSITION FOR LAMINATING VARNISHES AND LAMINATES PREPARED THEREFROM

Abstract: Compositions comprising (A) a halogenated phenoxy resin and (B) an advanced epoxy resin are useful in the preparation of electrical laminates when admixed with a suitable curing agent such as dicyan­ diamide.

Description: The present invention pertains to a mixture of a halogenated phenoxy resin and an advanced epoxy resin, laminating varnishes containing same and laminates prepared therefrom. Electrical laminates are prepared by blending minor amounts of a phenoxy resin with an advanced epoxy resin, curing agent therefor and solvents if required. The phenoxy resin provides flow control for the composition during the laminating stage which involves pressure molding of layers of substrates impregnated with the laminating varnish. This prevents the resin from flowing out of the press or mold which prevents resin poor areas in the resultant laminate. While the phenoxy resins employed provide for good flow control during molding or pressing of the impregnated substrates, the resultant laminates exhibit a decrease in one or more of their mechanical properties such as, for example, glass transition temperature, moisture and blister resistance and flame retardant properties. The present invention provides a method for eliminating or decreasing the loss in one or more of the physical properties such as, for example, glass transition temperature, moisture and blister resistance and flame retardant properties by employing as the phenoxy resin a halogenated phenoxy resin. The present invention in one aspect pertains to a composition which comprises (A) at least one phenoxy resin and (B) at least one advanced epoxy resin, characterized in that said phenoxy resin is a nuclearly halogenated phenoxy resin having a halogen content of at least 5 percent by weight, said phenoxy resin being present in an amount of from 0.5 to 50 , preferably from 1 to 20, most preferably from 3 to 10 percent by weight of the combined weight of components (A) and (B); and said advance epoxy resin is a nuclearly brominated advanced epoxy resin present in an amount of form 99.5 to 50, preferably from 99 to 80, most preferably from 97 to 90 percent by weight of the combined weight of components (A) and (B). US-A-3,888,942 discloses an epoxy resin composition comprising a phenoxy resin, which is not halogenated, and an advanced epoxy resin obtained by reacting a diglycidyl ether with a polyhydric phenol which need not, but can be brominated, such as tetrabromobisphenol-A. The compositions of the present invention, using a halogenated phenoxy resin, not only have increased flame retardent properties, but surprisingly also a significantly improved blister resisistance, as shown in Table I below. Another aspect of the present invention pertains to a laminating varnish which comprises: (A) the aforementioned composition; (B) curing amount of at least one curing agent for the advanced epoxy resin; and (C) optionally one or more solvents. Another aspect of the present invention pertains to a substrate impregnated with the aforementioned laminating varnish. Still another aspect of the present invention pertains to a laminate prepared from one or more of the aforementioned impregnated substrates. A further aspect of the present invention pertains to an electrical laminate comprising at least one electroconductive layer and one or more layers of the aforementioned impregnated substrates. Phenoxy resins are well known and are prepared, by reacting a diglycidyl ether of a dihydric phenol with a dihydric phenol in the presence of a suitable catalyst in quantities which provide a phenolic hydroxyl to epoxy ratio of from 0.9:1 to 1:1, preferably from 0.92:1 to 0.99:1, most preferably from 0.95:1 to 0.98:1. The halogenated phenoxy resins employed in the present invention can be prepared as above employing (a) an aromatic halogenated epoxy resin and a non-halogenated phenolic material, (b) a non-halogenated epoxy resin and an aromatic halogenated phenolic material or (c) an aromatic halogenated epoxy resin and an aromatic halogenated phenolic material. Suitable phenolic materials which can be employed to prepare the aromatic halogenated phenoxy resins which can be employed herein include, for example, those represented by the following Formulas I and II: wherein A is a divalent hydrocarbyl group having from 1 to 20, preferably from 2 to 10, most preferably from 3 to 5 carbon atoms, -S-, -S-S-, each R is independently hydrogen, a hydrocarbyl group having from 1 to 6, preferably from 1 to 4, most preferably from 1 to 2 carbon atoms or a halogen, preferably bromine; and n has a value of zero or 1. Particularly suitable phenolic hydroxyl-containing materials include, for example, tetrabromobisphenol A, resorcinol, bisphenol A, bisphenol S, and mixtures thereof. Suitable epoxy resins which can be employed in the preparation of the aromatic halogenated phenoxy resins include, for example, those represented by the following Formulas III and IV: wherein each A is independently a divalent hydrocarbyl group having from 1 to 20, preferably from 2 to 10, most preferably from 3 to 5 carbon atoms, -S-, -S-S-, each R is independently hydrogen, a hydrocarbyl group having from 1 to 6, preferably from 1 to 4, most preferably from 1 to 2 carbon atoms or a halogen, preferably bromine; R' is hydrogen or an alkyl group having from 1 to 4 carbon atoms; n has a value of zero or 1 and n' has an average value from zero to 10, preferably from 0.1 to 7, most preferably from 0.1 to 3. Particularly suitable epoxy resins include, for example, the diglycidyl ether of tetrabromobisphenol A, the diglycidyl ether of bisphenol A, the diglycidyl ether of bisphenol F, the diglycidyl ether of bisphenol S, the diglycidyl ether of resorcinol, the diglycidyl ether of bisphenol, and mixtures thereof. The phenoxy resin employed herein should contain a sufficient number of aromatic halogen atoms so as to provide the phenoxy resin with an aromatic halogen content of at least 5, preferably from 15 to 50, most preferably from 20 to 40 percent by weight. The phenolic halogenated phenoxy resins of the present invention can be represented by the following Formula V: wherein A, R, R' and n are as defined above, each Z is independently a terminal group which is -OH or and n" has a value of at least 15, preferably from 30 to 100, most preferably from 40 to 70 with the proviso that at least a sufficient number of the R groups are a halogen to provide the aromatic halogenated phenoxy resin with the required halogen content. The advanced epoxy resins which can be employed herein can be prepared by reacting a dihydric phenolic material with a material containing an average of more than one and preferably from 2 to 10, and most preferably from 2 to 4 vicinal epoxy groups per molecule in the presence of a suitable catalyst. In their preparation, the ratio of phenolic hydroxyl groups to epoxy groups is from 0.05:1 to 0.75:1, preferably from 0.2:1 to 0.6:1, most preferably from 0.3:1 to 0.4:1. These advanced epoxy resins must contain aromatic halogen atoms. Suitable advanced epoxy resins which can be employed in admixture with the halogenated phenoxy resins include, for example, those represented by the Formulas III and IV wherein A, R, R' and n are as defined above and n' has a value from 1 to 10, preferably from 2 to 7, most preferably from 3 to 5. Particularly suitable advanced epoxy resins include, for example, the diglycidyl ether of bisphenol A advanced with tetrabromobisphenol A, the diglycidyl ether of tetrabromobisphenol A advanced with tetrabromobisphenol A, and mixtures thereof. Each of these advanced epoxy resins have an average n' value as illustrated in Formula IV within the scope of the aforementioned range. Suitable catalysts which can be employed to prepare the aromatic halogenated phenoxy resins and the advanced epoxy resins include, for example, quaternary ammonium compounds, phosphonium compounds, imidazoles, phosphines, tertiary amines, inorganic bases, mixtures thereof and the like. Particularly suitable catalysts include, for example, ethyltriphenylphosphonium acetate.acetic acid complex, ethyltriphenylphosphonium bromide, bensyl dimethyl amine, 2-methylimidazole, triphenyl phosphine, potassium hydroxide, and mixtures thereof. Suitable solvents which can be employed herein include, for example, ketones, alcohols, glycol ethers, aromatic hydrocarbons, and combinations thereof. Particularly suitable solvents include, for example, methyl ethyl ketone, methyl isobutyl ketone, propylene glycol methyl ether, ethylene glycol methyl ether, methyl amyl ketone, methanol, isopropanol, toluene, xylene, dimethyl formamide, and mixtures thereof. The solvents can be employed in the preparation of the aromatic halogenated phenoxy resins, in the preparation of the advanced epoxy resins and in the compositions of the present invention. They are present in any desirable quantity depending upon the particular application which is known by those skilled in the art. Suitable curing agents which can be employed herein include, for example, biguanides, imidazoles, guanidines, aliphatic amines, aromatic amines, multifunctional phenols, thiols, sulfonamides, and combinations thereof. Particularly suitable curing agents include, for example, dicyandiamide, 2-methyl imidazole, tetramethylguanidine, cyanamide, 2-ethyl-4-methyl imidazole, ethylenediamine, methylene dianiline, diaminodiphenylsulfone, meta-phenylene diamine, phenolic novolac resins from phenol/formaldehyde condensation products, 1,2-benzenedithiol, sulfanilamide, and mixtures thereof. Suitable substrates which can be employed herein include, for example, glass, graphite, aromatic polyamides, carbon quartz, ceramic, synthetic and natural fibers, and combinations thereof in woven matt or fibrous form. The compositions of the present invention may also contain, if desired, pigments, dyes, mold release agents, flow control agents, fillers, fire retardant agents, rubber modifiers, surfactants, accelerators, reactive diluents, combinations thereof and the like. The compositions of the present invention are suitable for such applications as structural or electrical laminates or composites, coatings, adhesives, castings, moldings, electronic encapsulations and in potting compositions and the like. The following examples are exemplary of the invention but are not to be construed as to limiting the scope thereof in any manner. Epoxy Resin A was a diglycidyl ether of bisphenol A having an epoxide equivalent weight of 181.3. Advanced Epoxy Resin A was the reaction product of a diglycidyl ether of bisphenol A having an epoxy equivalent weight of 188 and tetraorthobromo-bisphenol A having a phenolic hydroxyl equivalent weight of 272 and a bromine content of 58.7 percent by weight. The resultant advanced epoxy resin had an epoxy equivalent weight of 483 and a bromine content of 21 percent by weight. Halogenated Phenol A was tetraorthobromo-bisphenol A having a bromine content of about 58.7 percent by weight and a phenolic hydroxyl equivalent weight of 272. Catalyst A was ethyltriphenylphosphonium acetate·acetic acid complex as a 70% by weight solution in methanol. Catalyst B was tetrabutylphosphonium acetate·acetic acid complex as a 70% by weight solution in methanol. EXAMPLE 1 A. Preparation of Brominated Phenoxy Resin Into a 2-liter Parr reactor was charged 235.8 g (1.3006 epoxy equiv.) of Epoxy Resin A and 349.5 g (1.2849 phenolic hydroxyl equiv.) of Halogenated Phenol A followed by the addition of 715 g of methyl ethyl ketone, 1.358 g (0.0023 equiv.) of Catalyst A and 1.010 g (0.0019 equiv.) of Catalyst B. The reactor was sealed and heated while stirring to 145°C. The pressure in the Parr reactor reached 68 psig (469 kPa). The temperature was controlled at 145°C for 3 hours at which time the solution was cooled to room temperature. The resultant brominated phenoxy resin had an epoxide content of 0.12 percent and a solids content of 35% by weight. B. Preparation of Blend of Halogenated Phenoxy Resin and Advanced Epoxy Resin 6.718 g (1.8748 x 10⁻⁴ equiv.) of the brominated phenoxy resin prepared in A above was placed in an aluminum dish and heated in a vacuum oven at 175°C at 5 mm Hg for 2 hours. The resultant solid brominated phenoxy resin, 0.611 (2.273 x 10⁻⁴ equiv.) was blended with 6.176 g (0.0128 equiv.) of Advanced Epoxy Resin A by dissolving both in methylene dichloride and then placing on a 175°C hot plate to drive off the methylene dichloride. The resultant blend had a melt viscosity of 1300 cp (1.3 Pa·s) as 150°C. The Advanced Epoxy Resin A had a melt viscosity of 500 cp (0.5 pa·s) at 150°C. C. Varnish Preparation (1) 2992 g (6.1927 equiv.) of Advance Epoxy Resin A dissolved in 748 g of acetone. (2) 450 g (0.0126 equiv.) of the brominated phenoxy solution prepared in Example 1-A. (3) 89.8 g of dicyandiamide dissolved in 808 g of a 50/50 by weight blend of propylene glycol methyl ether/dimethylformamide. (4) 2.99 g of 2-methylimidazole dissolved in 56.81 g of dimethylformamide. The above four components were blended together along with an additional 1143 g of acetone. This formulation had a Zahn cup viscosity of 22 seconds and a gel time at 171°C of 270 seconds. D. Prepreg and Laminate Preparation Burlington style 7628 glass cloth with an I617 finish was impregnated with the varnish formulation of Example 1-C in a forced air vertical treater having a total length of 26 feet (7.9 meters) with the first 19.5 feet (5.9 meters) heated to 350°F (176.67°C) at a rate of 9 feet per minute (45.72 mm/sec.). The solid resin contained in the impregnated glass cloth had a 102 second gel time at 171°C. The resultant impregnated glass cloth had a resin content of 42.2% by weight. Unclad laminates were made from the prepreg by pressing eight 12" x 12" (3048 mm x 3048 mm) plies at 500 psig (3447.4 kPa). The temperature in the press was initially 200°F (93.3°C) and was increased to 290°F (143.3°C) at 7°F/min. (0.0648°C/sec.). Then the temperature was raised to 350°F (176.67°C) at 20°F/min. (0.185°C/sec.) and held at 350°F (176.67°C) for 60 minutes. There was no post cure. The physical properties of the laminate are recorded in Table I. COMPARATIVE EXPERIMENT A A. Varnish Preparation (1) 3200 g (6.6233 equiv.) of Advanced Epoxy Resin A dissolved in 800 g of acetone. (2) 168.3 g of PKHH (a phenoxy resin based upon bisphenol A and commercially available from Union Carbide Corp.) dissolved in 561 g of methyl ethyl ketone. (3) 96 g of dicyandiamide dissolved in 864 g of a 50/50 blend of dimethylformamide/propylene glycol methyl ether. (4) 3.2 g of 2-methylimidazole dissolved in 60.8 g of dimethylformamide. The above components were blended together along with an additional 1293 g of acetone. This formulation had a Zahn cup viscosity of 21 seconds and a gel time at 171°C of 247 seconds. B. Prepreg and Laminate Preparation The prepreg and laminate were prepared as in Example 1-D. The prepreg gel time was 85 seconds at 171°C and the resin content on the glass was 42 percent by weight. The physical properties of the laminate are given in Table I. COMPARATIVE EXPERIMENT B A. Varnish Preparation (1) 3200 g (6.6233 equiv.) of Advanced Epoxy Resin A dissolved in 800 g of acetone. (2) 96 g of dicyandiamide dissolved in 864 g of a 50/50 blend of dimethylformamide/propylene glycol methyl ether. (3) 3.2 g of 2-methylimidazole dissolved in 60.8 g of dimethylformamide. The above components were blended together along with an additional 1014 g of acetone. This formulation had a Zahn cup viscosity of 19 seconds and a gel time at 171°C of 210 seconds. B. Prepreg and Laminate Preparation The prepreg and laminate were prepared as in Example 1-D. The prepreg gel time was 90 seconds at 171°C and the resin content on the glass was 41.4 percent by weight. The physical properties of the laminate are given in Table I.

Claims: A composition which comprises (A) at least one phenoxy resin and (B) at least one advanced epoxy resin, characterized in that said phenoxy resin is a nuclearly halogenated phenoxy resin having a halogen content of at least 5 percent by weight, said phenoxy resin being present in an amount of from 0.5 to 50 percent by weight of the combined weight of components (A) and (B); and said advanced epoxy resin is a nuclearly brominated epoxy resin present in an amount of from 99.5 to a 50 percent by weight of the combined weight of components (A) and (B). A composition of Claim 1 characterized in that (i) component (A) is present in an amount of from 3 to 10 percent by weight of the combined weight of components (A) and (B); (ii) component (B) is present in an amount of from 97 to 90 percent by weight of the combined weight of components (A) and (B); and (iii) component (A) has a halogen content of from 20 to 40 percent by weight. A composition of Claim 2 characterized in that (i) component (A) is represented by the Formula V: (ii) and component (B) is represented by Formula III: or Formula IV: in which formulas each A is independently a divalent hydrocarbyl group having from 1 to 20 carbon atoms, -S-, -S-S-, each R is independently hydrogen, a hydrocarbyl group having from 1 to 6 carbon atoms or a halogen; R' is hydrogen or an alkyl group having from 1 to 4 carbon atoms; each Z is independently a terminal group -OH or n has a value of zero or 1; n' has a value from zero to 10 and n" has a value of at least 15; with the proviso that at least a sufficient number of the R groups in Formula V are a halogen so as to provide the aromatic halogenated phenoxy resin with the required halogen content. A composition of Claim 3 wherein each A is independently a divalent hydrocarbyl group having from 1 to 4 carbon atoms; each R is independently hydrogen, methyl or bromine; each R' is hydrogen; n has a value of 1; n' has a value of from 0.1 to 7; and n" has a value of from 15 to 150. A laminating varnish which comprises (A) the composition of any one of Claims 1 to 4; and (B) a curing quantity of at least one curing agent for the advanced epoxy resin. A laminating varnish of Claim 5 wherein said curing agent is selected from quanidines, biquanidines, aromatic amines, sulfonic acid amides or mixtures thereof. A laminating varnish of Claim 5 or Claim 6 further containing one or more solvents. A substrate impregnated with a laminating varnish of anyone of Claims 5 to 7. An impregnated substrate of Claim 8 wherein said substrate is glass or graphite in woven, mat or fibrous form. A laminate prepared from one or more layers of the impregnated substrate of Claims 8 to 9.

Inventors: BERMAN, JODY R., MCCRARY, AVIS L., STEELE, DENNIS L.
Applicants: THE DOW CHEMICAL COMPANY
Application year: 1987
Main classification: C08L63
IPC codes: C08L63, C08G59, C08J5, C08L71, H05K1