Curable compositions containing an epoxy resin, a difunctional phenol and a polyfunctional phenol

Claims

What is claimed is:

1. A compositon which comprises

(A) at least one aromatic based epoxy resin having an average number of epoxide groups per molecule of more than 2; and

(B) a phenolic hydroxyl-containing component consisting essentially of a mixture of

(1) at least one phenolic hydroxyl-containing compound having an average of not more than 2 phenolic hydroxyl groups per molecule; and

(2) at least one phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule;

(C) optionally, at least one ketone solvent as the only solvent for components (A) and (B); and

(D) optionally, one or more stabilizers; and

wherein components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.75:1 to about 1.5:1; component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.1:1 to about 0.65:1; (C) is present in an amount of from about zero to about 75 weight percent based upon the combined weight of components (A), (B), (C) and (D); and component (D) is present in an amount of from about zero to about 1 percent by weight based upon the weight of component (A).

2. A composition of claim 1 wherein

(a) component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.2:1 to about 0.6:1;

(b) components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.85:1 to about 1:4:1; and

(c) component (C) is present in an amount of from about 5 to about 50 percent by weight based upon the combined weight of components (A), (B), (C) and (D); and

(d) component (D) is present in an amount of from about 0.05 to about 1 percent by weight based upon the weight of component (A).

3. A composition of claim 2 wherein

(a) component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.3:1 to about 0.55:1;

(b) components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group from about 0.9:1 to about 1.3:1;

(c) component (C) is present in an amount of from about 10 to about 25 percent by weight based upon the combined weight of components (A), (B), (C) and (D); and (d) component (D) is present in an amount of from about 0.1 to about 0.8 percent by weight based upon the weight of component (A).

4. A composition of claim 1, 2 or 3 wherein

(a) component A is an epoxy resin represented by the following formulas I or II or a combination of such epoxy resins ##STR4## wherein each A' is independently a divalent hydrocarbyl group having from 1 to about 10 carbon atoms; each R is as defined above; each R' is independently hydrogen or a hydrocarbyl group having from 1 to about 10 carbon atoms; m has a value from about 0.1 to about 7; and m' has a value from zero to about 3;

(b) component (B-1) is a phenolic hydroxyl-containing compound represented by the following formulas III or IV or a combination of such phenolic hydroxyl-containing compounds ##STR5## wherein each A, is independently a divalent hydrocarbyl or a halogen substituted divalent hydrocarbyl group having from 1 to about 12, preferably from 1 to about 6, carbon atoms, --O--, --S--, --S--S--, --SO--, --SO.sub.2 --, or --CO--; each X is independently hydrogen, an alkyl or an alkoxy group having suitably from 1 to about 10 carbon atoms or a halogen; and n has a value of zero or 1;

(c) component (B-2) is a phenolic hydroxyl-containing compound represented by the following formulas V or VI or a combination of such phenolic hydroxyl-containing compounds ##STR6## wherein each A', R', X and m are as defined above; and (d) component (D), when present, is selected from the group consisting of organic and inorganic acids, and salts of organic and inorganic acids.

5. A composition of claim 4 wherein

(a) component (A-1) is a diglycidyl ether represented by formula II wherein n has a value of 1 and n' has a value from zero to about 2;

(a) component A is a polyglycidyl ether represented by formula II wherein m has a value from about 1 to about 5

(b) component (B-1) is a phenolic hydroxyl-containing compound represented by formula IV wherein n has a value of 1;

(c) component (B-2) is a phenolic hydroxyl-containing compound represented by formula V wherein m has a value from about 1.01 to about 7; and

(d) component (D) is p-toluene sulfonic acid, benzene sulfonic acid, methyl p-toluene sulfonate, ammonium perchlorate, fluoboric acid, perchloric acid, nitric acid or any combination thereof.

6. A composition of claim 5 wherein

(a) component A-2 is a polyglycidyl ether of a phenol-formaldehyde novolac epoxy resin;

(b) component (B-1) is bisphenol A or tetrabromo bisphenol A;

(c) component (B-2) is a phenol-formaldehyde novolac resin;

(d) component (C) is acetone; and

(e) component (D) is p-toluene sulfonic acid, benzene sulfonic acid, or methyl p-toluene sulfonate.

7. A curable composition which comprises

(A) at least one aromatic based epoxy resin having an average number of epoxide groups per molecule of more than 2;

(B) a phenolic hydroxyl-containing component consisting essentially of a mixture of

(1) at least one phenolic hydroxyl-containing compound having an average of not more than 2 phenolic hydroxyl groups per molecule; and

(2) at least one phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule;

(c) optionally, at least one ketone solvent for component (A) as the only solvent in the composition except for minor amounts of any solvent for component (C);

(D) optionally, one or more stabilizers; and

(D) a catalytic quantity of at least one catalyst for effecting the reaction between components (A) and (B); and

wherein components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.75:1 to about 1.5:1; component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.1:1 to about 0.65:1; component (C) is present in an amount of from about zero to about 75 weight percent based upon the combined weight of components (A), (B), (C), (D) and (E); component (D) is present in an amount of from about zero to about 1 percent by weight based upon the weight of component (A) and component (E) is present in an amount of from about 0.00005 to about 0.01 mole of catalyst per 100 parts by weight of the combined weight of component (A) and component (B).

8. A curable composition of claim 7 wherein

(a) component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.2:1 to about 0.6:1;

(b) components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.85:1 to about 1.4:1;

(c) component (C) is present in an amount of from about zero to about 50 weight percent based upon the combined weight of components (A), (B), (C), (D) and (E);

(d) component (D) is present in an amount of from about 0.05 to about 1 percent by weight based upon the weight of component (A); and

(e) component (E) is present in an amount of from about 0.00005 to about 0.05 mole per 100 parts by weight of the combined weight of component (A) and component (B).

9. A curable composition of claim 8 wherein

(a) component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.3:1 to about 0.55:1;

(b) components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.9:1 to about 1.3:1;

(c) component (C) is present in an amount of from about zero to about 25 weight percent based upon the combined weight of components (A), (B), (C), (D) and (E);

(d) component (D) is present in an amount of from about 0.0.1 to about 0.8 percent by weight based upon the weight of component (A); and

(e) component (E) is present in an amount of from about 0.0001 to about 0.03 mole per 100 parts by weight of the combined weight of component (A) and component (B).

10. A curable composition of claim 7, 8 or 9 wherein

(a) A-2 is an epoxy resin represented by the following formulas I or II or a combination of such epoxy resins ##STR7## wherein each A' is independently a divalent hydrocarbyl group having from 1 to about 10 carbon atoms; each R is as defined above; each R' is independently hydrogen or a hydrocarbyl group having from 1 to about 10 carbon atoms; m has a value from about 0.1 to about 7; and m' has a value from zero to about 3;

(b) component (B-1) is a phenolic hydroxyl-containing compound represented by the following formulas III or IV or a combination of such phenolic hydroxyl-containing compounds ##STR8## wherein each A, is independently a divalent hydrocarbyl or a halogen substituted divalent hydrocarbyl group having from 1 to about 12, preferably from 1 to about 6, carbon atoms --O--, --S--, --S--S--, --SO--, --SO.sub.2 --, or --CO--; each X is independently hydrogen, an alkyl or an alkoxy group having suitably from 1 to about 10 carbon atoms or a halogen; and n has a value of zero or 1;

(c) component (B-2) is a phenolic hydroxyl-containing compound represented by the following formulas V or VI or a combination of such phenolic hydroxyl-containing compounds ##STR9## wherein each A', R', X and m are as defined above; (d) component (E) is a phosphonium compound or an imidazole.

11. A curable composition of claim 10 wherein

(a) component A is a polyglycidyl ether represented by formula I wherein m has a value from about 1 to about 5;

(b) component (B-1) is a phenolic hydroxyl-containing compound represented by formula III wherein n has a value of 1;

(c) component (B-2) is a phenolic hydroxyl-containing compound represented by formula V wherein m has a value from about 1.01 to about 7;

(d) component (D) is selected from the group consisting of organic and inorganic acids, salts of inorganic acids; esters of organic acids; and any combination thereof; and

(e) component (E) is selected from the group consisting of phosphonium compounds, ammonium compounds, imidazoles and any combination thereof.

12. A curable composition of claim 11 wherein

(a) component A is a polyglycidyl ether of a phenol-formaldehyde novoalc epoxy resin;

(b) component (B-1) is bisphenol A or tetrabromo bisphenol A;

(c) component (B-2) is a phenol-formaldehyde novolac resin;

(d) component (C) is acetone;

(e) component (D) is p-toluene sulfonic acid, benzene sulfonic acid, methyl p-toluene sulfonate or any combination thereof; and

(f) component (E) is a quaternary phosphonium halide, a quaternary phosphonium acetate.multidot.acetic acid complex, 2-methylimidazole, the reaction product of a quaternary phosphonium acetate.multidot.acetic acid complex and fluoboric acid in a respective molar ratio of from about 1:0.9 to about 1:1.25, or any combination thereof.

13. In a laminating varnish comprising (A) an epoxy resin component, (B) a curing agent from said epoxy resin and (C) a solvent; the improvement which comprises employing as the epoxy resin, component (A), at least one aromatic based epoxy resin having an average number of epoxide groups per molecule of more than 2; employing as said curing agent, component (B), a phenolic hydroxyl-containing composition consisting essentially of a mixture of (1) at least one phenolic hydroxyl-containing compound having an average of more than 1 but not more than 2 phenolic hydroxyl groups per molecule; and (2) at least one phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule; employing as the solvent, component (C), at least one ketone solvent as the only solvent present in the composition except for minor amounts of any solvent for component (D); and optionally, (D) a catalytic quantity of at least one catalyst for effecting the reaction between components (A) and (B); and wherein components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.75:1 to about 1.5:1; component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.1:1 to about 0.65:1; and component (C) is present in an amount of from about 5 to about 75 percent by weight based upon the total weight of the varnish composition; and component (D) is present in an amount which provides from about zero to about 0.01 moles of component (D) per 100 parts by weight of the combined weight of component (A) and component (B).

14. A laminating varnish of claim 13 wherein

(a) component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.2:1 to about 0.6:1;

(b) components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.85:1 to about 1.4:1;

(c) component (C) is present in an amount of from about 5 to about 50 percent by weight based upon the total weight of the varnish composition; and

(d) component (D) is present in an amount of from about 0.00005 to about 0.01 mole of catalyst per 100 parts by weight of the combined weight of component (A) and component (B).

15. A laminating varnish of claim 14 wherein

(a) component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component (A) of from about 0.3:1 to about 0.55:1;

(b) components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.9:1 to about 1.3:1;

(c) component (C) is present in an amount of from about 10 to about 25 percent by weight based upon the total weight of the varnish composition; and

(d) component (D) is present in an amount of from about 0.0001 to about 0.03 mole of catalyst per 100 parts by weight of the combined weight of component (A) and component (B).

16. A laminating varnish of claim 13, 14 or 15 wherein

(a) component A-2 is an epoxy resin represented by the following formulas I or II or a combination of such epoxy resins ##STR10## wherein each A' is independently a divalent hydrocarbyl group having from -b 1 to about 10 carbon atoms; each R is as defined above; each R' is independently hydrogen or a hydrocarbyl group having from 1 to about 10 carbon atoms; m has a value from about 0.1 to about 7; and m' has a value from zero to about 3;

(b) component (B-1) is a phenolic hydroxyl-containing compound represented by the following formulas III or IV or a combination of such phenolic hydroxyl-containing compounds ##STR11## wherein each A, is independently a divalent hydrocarbyl or a halogen substituted divalent hydrocarbyl group having from 1 to about 12, preferably from 1 to about 6, carbon atoms, --O--, --S--, --S--S--, --SO--, --SO.sub.2 --, or --CO--; each X is independently hydrogen, an alkyl or an alkoxy group having suitably from 1 to about 10 carbon atoms or a halogen; and n has value of zero or 1;

(c) component (B-2) is a phenolic hydroxyl-containing compound represented by the following formulas V or VI or a combination of such phenolic hydroxyl-containing compounds ##STR12## wherein each A', R', and X and m are as defined above; and (d) component (D) is a phosphonium compound, an ammonium compound or an imidazole.

17. A laminating varnish of claim 16 wherein

(a) component A is a polyglycidyl ether represented by formula I wherein m has a value from about 1 to about 5;

(b) component (B-1) is a phenolic hydroxyl-containing compound represented by formula IV wherein n has a value of 1; and

(c) component (B-2) is a phenolic hydroxyl-containing compound represented by formula V wherein m has a value from about 1.01 to about 7.

18. A laminating varnish of claim 17 wherein component A is a polyglycidyl ether of a phenol-formaldehyde novolac epoxy resin;

(B) component (B-1) is bisphenol A or tetrabromo bisphenol A;

(c) component (B-2) is a phenol-formaldehyde novolac resin;

(d) component (C) is acetone; and

(e) component (D) is a quaternary phosphonium halide, a quaternary phosphonium acetate.multidot.acetic acid complex, an imidazole, the reaction product of a quaternary phosphonium acetate.multidot.acetic acid complex and fluoboric acid in a respective molar ratio of from about 1:0.9 to about 1:1.25, or any combination thereof.

19. A substrate impregnated with a laminating varnish of claims 13, 14, or 15.

20. A substrate impregnated with a laminating varnish of claim 16.

21. A substrate impregnated with a laminating varnish of claim 17.

22. A substrate impregnated with a laminating varnish of claim 18.

23. A laminate resulting from curing one or more plies of a substrate of claim 19.

24. A laminate of claim 23 which has an outer layer of an electrical conducting material.

25. A laminate of claim 24 wherein the electrical conducting material is copper.

26. A laminate resulting from curing one or more plies of a substrate of claim 20.

27. A laminate of claim 26 which has an outer layer of an electrical conducting material.

28. A laminate of claim 27 wherein the electrical conducting material is copper.

29. A laminate resulting from curing one or more plies of a substrate of claim 21.

30. A laminate of claim 29 which has an outer layer of an electrical conducting material.

31. A laminate of claim 30 wherein the electrical conducting material is copper.

32. A laminate resulting from curing one or more plies of a substrate of claim 22.

33. A laminate of claim 32 which has an outer layer of an electrical conducting material.

34. A laminate of claim 33 wherein the electrical conducting material is copper.

35. The product resulting from curing the curable composition of claim 7, 8, or 9.

36. The product resulting from curing the curable composition of claim 10.

37. The product resulting from curing the curable composition of claim 11.

38. The product resulting from curing the curable composition of claim 12.

39. A curing agent composition for epoxy resins which comprises a mixture of

(A) a phenolic hydroxyl-containing component consisting essentially of a mixture of

(1) from about 7 to about 81 equivalent percent of at least one phenolic hydroxyl-containing compound having an average of more than 1 but not more than 2 phenolic hydroxyl groups per molecule; and

(2) from about 93 to about 19 equivalent percent of at least one phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule;

(B) at least one ketone solvent for component

(A) as the only solvent in the composition except for minor amounts of any solvent for component (C); and

(C) optionally, a catalytic quantity of at least one catalyst for effecting the reaction between an epoxy resin and component (A); and

wherein component (B) is present in quantities of from about 5 to about 75 percent by weight based upon the total weight of the curing agent composition.

40. A curing agent composition of claim 39 wherein

(a) component (A) comprises from about 30 to about 70 equivalent percent of component (1) and from about 70 to about 30 equivalent percent of component (2); and

(b) component (B) is present in an amount of from about 5 to about 50 weight percent based upon the total weight of the curing agent composition.

41. A curing agent composition of claim 40 wherein

(a) component (a) comprises from about 40 to about 50 equivalent percent of component (1) and from about 60 to about 50 equivalent percent of component (2); and

(b) component (B) is present in an amount of from about 10 to about 25 percent by weight based upon the total weight of the curing agent composition.

42. A curing agent compositon of claim 39, 40 or 41 wherein

(a) component (A-1) is a phenolic hydroxyl-containing compound represented by the following formulas III or IV or a combination of such phenolic hydroxyl-containing compounds ##STR13## wherein each A, is independently a divalent hydrocarbyl or a halogen substituted divalent hydrocarbyl group having from 1 to about 12, preferably from 1 to about 6, carbon atoms, --O--, --S--, --S--S--, --SO--, --SO.sub.2 --, or --CO--; each X is independently hydrogen, an alkyl or an alkoxyl group having suitably from 1 to about 10 carbon atoms or a halogen; and n has a value of zero or 1;

(b) component (A-2) is a phenolic hydroxyl-containing compound represented by the following formulas V or VI or a combination of such phenolic hydroxyl-containing compounds ##STR14## wherein each A' is independently a divalent hydrocarbyl group having from 1 to about 10 carbon atoms; each R is as defined above; each R' is independently hydrogen or a hydrocarbyl group having from 1 to about 10 carbon atoms; and m has a value from about 0.1 to about 7; and

(c) component (C) is a phosphonium compound, an ammonium compound or an imidazole.

43. A curing agent composition of claim 42 wherein

(a) component (A-1) is a phenolic hydroxyl-containing compound represented by formula IV wherein n has a value of 1; and

(b) component (A-2) is a phenolic hydroxyl-containing compound represented by formula V wherein m has a value from about 1.01 to about 7.

44. A curing agent composition of claim 43 wherein

(a) component (A-1) is bisphenol A or tetrabromo bisphenol A;

(b) component (A-2) is a phenol-formaldehyde novolac resin;

(c) component (B) is acetone; and

(d) component (C) is a quaternary phosphonium halide, a quaternary phosphonium acetate.multidot.acetic acid complex, an imidazole, the reaction product of a quaternary phosphonium acetate.multidot.acetic acid complex and fluoboric acid in a respective molar ratio of from about 1:0.9 to about 1:1.25, or any combination thereof.

FIELD OF THE INVENTION

The present invention concerns curable compositions containing an epoxy resin, difunctional phenols and polyfunctional phenols as well as cured products thereof. The invention also concerns a curing agent composition for epoxy resin comprising a mixture of difunctional phenols and polyfunctional phenols.

BACKGROUND OF THE INVENTION

Electrical laminates are usually prepared from bisphenol A based epoxy resins advanced with tetrabromobisphenol A and cured with a biguanide such as dicyandiamide. These electrical laminates usually require curing at 350.degree. F. for about an hour to obtain an adequate cure. It would be desirable to obtain an adequate cure. It would be desirable to have laminates which are cured in much less time e.g. within about ten minutes without a substantial loss in its physical properties.

SUMMARY OF THE INVENTION

One aspect of the present invention pertains to a composition which comprises

(A) at least one aromatic based epoxy resin having an average number of epoxide groups per molecule of more than 2; and

(B) a phenolic hydroxyl-containing component consisting essentially of

(1) at least one phenolic hydroxyl-containing compound having an average of more than 1 but not more than 2 phenolic hydroxyl groups per molecule; and

(2) at least one phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule;

(C) optionally, at least one ketone solvent as the only solvent for components (A) and (B); and

(D) optionally, one or more stabilizers; and

wherein components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.75:1 to about 1.5:1; component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.1:1 to about 0.65:1; component (C) is present in an amount of from about zero to about 75 weight percent based upon the combined weight of components (A), (B), (C) and (D); and component (D) is present in an amount of from about 0.05 to about 1 percent by weight based upon the weight of component (A).

Another aspect of the present invention pertains to a curable composition which comprises

(A) at least one aromatic based epoxy resin having an average number of epoxide groups per molecule of more than 2; (B) a phenolic hydroxyl-containing component consisting essentially of

(1) at least one phenolic hydroxyl-containing compound having an average of more than 1 but not more than 2 phenolic hydroxyl groups per molecule; and

(2) at least one phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule;

(C) optionally, at least one ketone solvent for component (A) as the only solvent in the composition except for minor amounts of any solvent for component (C);

(D) optionally, one or more stabilizers; and

(E) a catalytic quantity of at least one catalyst for effecting the reaction between components (A) and (B); and

wherein components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.75:1 to about 1.5:1; component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.1:1 to about 0.65:1; component (C) is present in an amount of from about zero to about 75 weight percent based upon the combined weight of components (A), (B), (C), (D), and (E); component (D) is present in an amount of from about zero to about 1 percent by weight based upon the weight of component (A) and component (E) is present in an amount of from about 0.00005 to about 0.01 mole of catalyst per 100 parts by weight of the combined weight of the epoxy-containing component and the phenolic hydroxyl-containing component.

Another aspect of the present invention pertains to an improvement in a laminating varnish comprising (A) an epoxy resin component, (B) a curing agent for said epoxy resin and (C) a solvent; wherein the improvement resides in employing as the epoxy resin component (A) at least one aromatic based epoxy resin having an average number of epoxide groups per molecule of more than 2; said curing agent component (B) is a phenolic hydroxyl-containing composition consisting essentially of a mixture of (1) at least one phenolic hydroxyl-containing compound having an average of more than 1 but not more than 2 phenolic hydroxyl groups per molecule; and (2) at least one phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule; as the solvent component (C), at least one ketone solvent as the only solvent present in the composition except for minor amount, of any solvent for component (D); and optionally, (D) a catalytic quantity of at least one catalyst for effecting the reaction between components (A) and (B); and wherein components (A) and (B) are present in quantities which provide a ratio of phenolic hydroxyl groups for each epoxy group of from about 0.75:1 to about 1.2:1; component (B1) is present in an amount which provides a ratio of phenolic hydroxyl groups per epoxide group contained in component A of from about 0.1:1 to about 0.65:1; and component (C) is present in an amount of from about 5 to about 75 weight percent based upon the combined weight of the laminating varnish composition.

Another aspect of the present invention pertains to a laminate resulting from curing one or more plies of a substrate material which has been impregnated with the aforementioned laminating varnish.

Still another aspect of the present invention pertains to a curing agent composition for epoxy resins which comprises a mixture of

(A) a phenolic hydroxyl-containing component consisting essentially of

(1) from about 7 to about 81 equivalent percent of at least one phenolic hydroxyl-containing compound having an average of more than 1 but not more than 2 phenolic hydroxyl groups per molecule; and

(2) from about 93 to about 19 equivalent percent of at least one phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule;

(B) at least one ketone solvent for component (A) as the only solvent in the composition except for minor amount of any solvent for component (C); and

(C) optionally, a catalytic quantity of at least one catalyst for effecting the reaction between an epoxy resin and component (A); and

wherein component (B) is present in quantities of from about 5 to about 75 percent by weight based upon the total weight of the composition and component (C) is present in an amount which provides from about zero to about 0.01 mole of component (C) per 100 parts by weight of component (A).

The curable compositions described above cure in less than about 10 minutes at 350.degree. F.

DETAILED DESCRIPTION OF THE INVENTION

The curing agent of the present invention is suitably prepared by melt mixing the components in the absence of a suitable solvent or inert liquid diluent at temperatures of from about 150.degree. C. to about 200.degree. C, suitably from about 175.degree. C. to about 200.degree. C., more suitably from about 175.degree. C. to about 190.degree. C. The curing agent can also be prepared by mixing the components in the presence of a suitable solvent or inert liquid diluent or mixture of inert liquids and/or diluents at temperatures of from about 5.degree. C. to about 80.degree. C., suitably from about 10.degree. C., to about 70.degree. C., more suitably from about 15.degree. C. to about 60.degree. C., more suitably from about 20.degree. C. to about 50.degree. C. Suitable solvents or liquid diluents include, for example, ketones, alcohols, glycol ethers, aromatic hydrocarbons, polar aprotic solvents, combinations thereof and the like. Particularly suitable such solvents or liquid diluents include, for example, acetone, methyl ethyl ketone, ethylene glycol monomethyl ether, propylene glycol monomethyl ether, dimethylformamide, dimethyl sulfoxide, sulfolane, N-methylpyrrolidone, toluene, xylene, combinations thereof and the like.

Any epoxy resin having an average of more than 2 vicinal epoxy groups per molecule can be employed herein. Particularly suitable such resins include, for example, those represented by the formulas I and II ##STR1## wherein each A' is independently a divalent hydrocarbyl group suitably having from 1 to about 10, more suitably from 1 to about 4, most suitably from 1 to about 2, carbon atoms or a divalent polycyclopentadiene group; each R is independently hydrogen or an alkyl group having from 1 to about 3 carbon atoms; each R' is independently hydrogen or a hydrocarbyl group having suitably from 1 to about 10, more suitably from 1 to about 5, most suitably from 1 to about 2, carbon atoms; each X is independently hydrogen, an alkyl or an alkoxy group having suitably from 1 to about 10, more suitably from 1 to about 5, most suitably from 1 to about 3 carbon atoms or a halogen, preferably chlorine or bromine; m suitably has a value from about 0.1 to about 7, more suitably from about 1 to about 5, most suitably from about 1 to about 4; and m' suitably has a value from zero to about 3, more suitably from zero to about 2, most suitably from zero to about 1.

The phenolic hydroxyl-containing component suitably contains from about 7 to about 81, more suitably from about 30 to about 70, most suitably from about 40 to about 50, equivalent percent phenolic hydroxyl-containing compound having an average of more than 1 but not more than 2 phenolic hydroxyl groups per molecule based upon the combined weight of phenolic hydroxyl-containing compound having an average of not more than 2 phenolic hydroxyl groups per molecule and phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule. Correspondingly, the phenolic hydroxyl-containing component suitably contains from about 93 to about 19, more suitably from about 70 to about 30, most suitably from about 60 to about 50, equivalent percent phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule based upon the combined weight of phenolic hydroxyl-containing compound having an average of not more than 2 phenolic hydroxyl groups per molecule and phenolic hydroxyl-containing compound having an average of more than 2 phenolic hydroxyl groups per molecule.

Among the compounds which are suitable as the phenolic hydroxyl-containing compound having an average of more than 1 but not more than 2 phenolic hydroxyl groups per molecule include, for example, those represented by the following formulas III and IV ##STR2## wherein each A, is independently a divalent hydrocarbyl or a halogen substituted divalent hydrocarbyl group having from 1 to about 12, preferably from 1 to about 6, carbon atoms, --O--, --S--, --S--S--, --SO--, --SO.sub.2 --, or --CO--; and X and n are as previously defined. Particularly suitable phenolic hydroxyl-containing compounds having an average of more than 1 but not more than 2 phenolic hydroxy groups per molecule include, for example, bisphenol A, bisphenol K, bisphenol F, bisphenol S, the halo