WO1995006675A1

WO1995006675A1 - Curable epoxy resin composition

Info

Publication number: WO1995006675A1
Application number: PCT/EP1994/002887
Authority: WO
Inventors: Takao Fukuzawa; Tetsuro Imura; Masayuki Ohta
Original assignee: Shell Internationale Research Maatschappij B.V.
Priority date: 1993-08-30
Filing date: 1994-08-29
Publication date: 1995-03-09
Also published as: JPH0762063A

Abstract

A curable epoxy resin composition comprising an expoxy resin and an acid anhydride curing agent, said epoxy resin having a bromine content of from 15 % by weight to 70 % by weight, on average more than one glycidyl group per molecule and comprising at least one of three specifically defined aromatic structures.

Description

CURABLE EPOXY RESIN COMPOSITION

The present invention relates to curable epoxy resin compositions, to articles comprising such curable coπφositions in the cured state and to the use of such a curable compositions. The curable epoxy resin compositions according to the invention in particular have excellent heat resistance and cracking resistance in the cured state.

Since epoxy resins in general have good electro-insulating properties, good heat resistance, good chemical resistance, good mechanical properties and good processability they are frequently used in the electrical and electronic fields, for example as semi¬ conductor sealants, in laminates for printed circuits, and as insulating varnishes.

Epoxy resin casting compositions used for insulating electrical and electronic instruments, are currently often based on a bisphenol-A type epoxy resin and an acid anhydride curing agent.

Since future requirements set to electrical- and electronic instruments are better heat resistance, smaller size, less weight, better resistance against exposure to high voltages and to have a higher degree of integration, the casting resins for used for insulating said instruments should as a consequence have improved heat resistance and higher mechanical strength.

Though cured epoxy resin compositions comprising a blend of a bisphenol-A type epoxy resin and a polyfunctional epoxy resin such as a novolak type epoxy resin have improved heat resistance as compared to cured epoxy resins comprising only a bisphenol-A type epoxy resin, they are often very brittle which is reflected in a very low cracking resistance.

Though the use of an epoxy resin of which the epoxy groups have been modified or wherein flexible components have been incorporated, e.g. by reacting the epoxy resin with said flexible component, may have a positive effect on the cracking resistance of to the cured composition, if negatively affects the heat resistance thereof.

The present invention aims at providing an epoxy resin composition that can be used as a casting composition for insulation of electrical and electronic instruments and that provides cured products that combine a good heat resistance with a good cracking resistance.

The present invention thus relates to a curable epoxy resin composition comprising an epoxy resin and an acid anhydride curing agent, wherein the epoxy resin has a bromine content of from 15% by weight to 70% by weight, has, on average, more than one glycidyl group per molecule and comprises at least one structure of the general formula (1), (2) or (3) as presented below:

(1)

wherein the groups X¹ to X*^° each individually may represent a hydrogen atom, a hydrocarbon residual group having from 1 to 20 carbon atoms, an alkoxy group, an aroxy group or a halogen atom; and wherein

R represents a single bond, a hydrocarbon residual group having from 1 to 20 carbon atoms, or -0-, -S-, -SO2-, -CO-, -COO-, -OCOO-, -NHCO- or -NHCOO-.

Preferred groups R in the structure according to the formula (1) are methylene, ethylidene, α-methylbenzylidene, cyclohexylidene, isopropylidene, p-xylene-α,α'-diyl or fluoren-9- ylidene, or a divalent hydrocarbon residual group derived from addition of a phenolic compound to a cyclic terpene compound such as dicyclopentadiene, limonene, terpinolene, pinene, terpinene or menthadiene.

Suitable epoxy resins used in the curable composition according to the invention comprising a structure of formula (1) are for example, epoxy resins based on tetrabromobiphenol, tetrabromobisphenol F, 4,4'-dihydroxy-3,3'-dibromo-5,5'- dimethyldiphenylme hane, tetrabromobisphenol A, 4,4'-dihydroxy- 3,3' ,5,5'-tetrabromobenzophenone, tetrabromonobisphenol S and 4,4'-dihydroxy-3,3',5,5'-tetrabromodiphenyl ether. Suitable epoxy resins comprising a structure of formula (2) are for example, epoxy resins based on hydroquinone, resorcinol and catechol derivatives.

Suitable epoxy resins comprising a structure of formula (3) are for example, dihydroxynaphthalene derivatives. If the epoxy resin has a bromine content of less than 15% by weight, the heat resistance and cracking resistance of the epoxy resin composition according to the invention in the cured state is insufficient. On the other hand, if the epoxy resin has a bromine content of more than 70% by weight, the epoxy resin composition will be extremely difficult to prepare and to process.

The epoxy resin used in the epoxy resin composition of the present invention preferably has a bromine content in the range of from 20% by weight to 65% by weight.

Suitable epoxy resins (hereafter referred to as epoxy resins I) are obtained by reacting one or more dihydroxy compounds comprising a structure of the formula (1), (2) or (3), with epichlorohydrin, optionally in the presence of one or more compounds selected from the group consisting of dihydroxy compounds, excluding the dihydroxy compounds comprising a structure of formula (1), (2) or (3), followed by cyclization of the resulting intermediate in the presence of an alkali metal hydroxide.

Other suitable epoxy resins (hereafter referred to as epoxy resins (II)) are obtained by reacting the above-mentioned epoxy resin (I) optionally in the presence of epoxy compound(s) other than the above-mentioned epoxy resins (I) with one or more compound(s) selected from the group consisting of phenols, polyphenols and carboxylic acids in the presence of a catalyst such as for example, a compound selected from the group consisting of alkali hydroxides, tertiary amines, imidazoles, quaternary ammonium salts, phosphines and phosphonium salts. Other suitable epoxy resins (hereafter referred to as epoxy resins (III)) are obtained by reacting a polyfunctional epoxy resin with one or more dihydroxy compounds comprising a structure of the formula (1), (2) or (3), optionally in the presence of one or more dihydroxy compounds other than the dihydroxy compounds having the structure of formula (1), (2) or (3), phenols, polyphenols and carboxylic acids in the presence of a catalyst, such as for example one of the above-mentioned catalytic compounds. Other suitable epoxy resins are blends of two or more of the epoxy resins (I), (II) and (III) referred to above or blends of one or more of the above referred to epoxy resins I, II and III with one or more other epoxy resin(s).

Epoxy resins that can also be used in the curable epoxy resin according to the present invention are reaction products of any one of the afore-mentioned epoxy resins with compounds having a group capable of reacting with an epoxy group such as, for example, phenols, carboxylic acids, amines and alcohols provided only part of the epoxy groups of the epoxy resin have reacted. The epoxy resins and/or the starting compounds used to prepare the epoxy resins may be subjected to recrystallization, reprecipitation, distillation, fractionation, extraction or partition chromatography in order to isolate epoxy resins or starting compounds or isomers thereof having particular chemical structures or having particular molecular weight distributions, before use.

Suitable acid anhydride curing agents for use in the epoxy resin composition according to the present invention are for example methylhexahydrophthalic anhydride, methyltetrahydro- phthalic anhydride, tetrahydrophthalic anhydride, hexa- hydrophthalic anhydride and methylnadic anhydride. The amount of the acid anhydride curing agent used in the epxoy resin composition of the present invention is generally in the range of 0.7 to 1.2 acid equivalents, preferably of from 0.8 to 1.0 acid equivalents, per equivalent epoxy group of the epoxy resin present in the composition.

The epoxy resin composition of the present invention generally contains a curing accelerator. Suitable accelerators comprise imidazoles, tertiary amines, trisdimethylaminomethyl- phenol, 1,8-diazabicyclo(5,4,0)undecene-7, phosphines, various metal salts, Lewis acid salts.

The epoxy resin composition of the present invention may further comprise contain a filler. Suitable fillers are for example, inorganic fillers such as silica, alumina, mica powder, calcium carbonate, aluminium hydroxide, magnesium carbonate, talc, clay, kaolin, dolomite, silicon carbide, glass powder, titanium dioxide, boron nitride and silicon nitride; and also sheet or tape materials such as mica, glass, polyesters, aramides and polyimides.

Mixtures of two or more of these fillers may also be used and these fillers may be surface treated if necessary.

The epoxy resin composition according to the present invention may further comprise other additives such as for example pigments, colorants, flame retardants, diluents, coupling agents, flexibility imparting agents, releasing agents, antioxidants and defoaming agents.

The epoxy resin composition according of the present invention may be prepared by uniformly mixing the epoxy resin, the acid anhydride curing agent and, if desired, the filler and various other additives by methods known in the art. The composition may be shaped by, for example, casting followed by curing at elevated temperature to give a cured article. The epoxy resin composition according to the present invention may be impregnated into a substrate, such as for example cloth or tape woven from fibers, to form a prepreg, which may subsequently be cured to form a cured article.

Articles comprising an epoxy resin composition according to the present invention in the cured state have a similar or higher glass transition point, a better heat resistance and a much higher cracking resistance than articles comprising conventional epoxy resins in the cured state.

The present invention is illustrated by means of the following examples. Example A

272 parts by weight (pbw) of tetrabromobisphenol A, 740 pbw of epichlorohydrin and 1.1 pbw of tetraethylammonium chloride were charged to a reactor equipped with thermometer, a stirrer and a condenser tube, heated to 117 °C in an oil bath and reacted under reflux for 2 hours. Next, the reaction mixture was cooled to 60 ° C, the reactor was provided with a water-separating device and 42 pbw of NaOH was added to the reaction mixture that was subsequently reacted under a reduced pressure of from 40 to 100 mmHg at a controlled temperature of from 50 to 70 °C. The water formed during the reaction, was removed by azeotropic distillation. The reaction was stopped after the theoretical amount of water was removed, (after about 2 hours) .

2500 pbw of methyl isobutyl ketone were added to the epichlorohydrin solution containing the epoxy resin thus prepared, which was then washed with a large amount of water to remove the salt formed and the excess NaOH. This solution was then neutralized with an aqueous solution of 3%-phosphoric acid. Next, epichlorohydrin and methyl isobutyl ketone were removed from the solution by means of a rotary evaporator under reduced pressure (0.1 to 100 mmHg/60 to 150 °C) . 312 pbw of an epoxy resin having an epoxy equivalent (EEW) of 390 g/eq. and a bromine content of 49% by weight (hereafter referred to as Epoxy Resin A) , was thus obtained. Example B 237 pbw of an epoxy resin was obtained in the same manner as in Example A, except that 136 pbw of tetrabromobisphenol A and 57 pbw of bisphenol A were used instead of 272 pbw of tetrabromobisphenol A. The epoxy resin thus obtained had an EEW of 285 g/eq. and a bromine content of 32% by weight (hereafter referred to as Epoxy Resin B) . Example C

230 pbw of an epoxy resin was obtained in the same manner as in Example A, except that 136 pbw of tetrabromobisphenol A and 50 pbw of bisphenol F were used instead of 272 pbw of tetrabromobisphenol A. The epoxy resin thus obtained had an EEW of 288 g/eq. and a bromine content of 33% by weight (hereafter referred to as Epoxy Resin C) . Example D

240 pbw of an epoxy resin was obtained in the same manner as in Example A, except that 136 pbw of tetrabromobisphenol A and

61 pbw of 3,3',5,5'-tetramethyl-4,4'-dihydroxybiphenyl were used in place of 272 pbw of tetrabromobisphenol A. The epoxy resin thus obtained had an EEW of 281 g/eq. and a bromine content of 32% by weight (hereafter referred to as Epoxy Resin D) . Example E

229 pbw of an epoxy resin was obtained in the same manner as in Example A, except that 136 pbw of tetrabromobisphenol A and 49 pbw of a novolak resin obtained by the condensation of phenol and salicylaldehyde in the presence of an acid catalyst and having a softening point of 105 °C, were used in place of 272 pbw of tetrabromobisphenol A. The epoxy resin thus obtained had an EEW of 272 g/eq. and a bromine content of 33% by weight (hereafter referred to as Epoxy Resin E) . Example F 100 pbw of Epoxy Resin A, 4 pbw of bisphenol A and 0.03 pbw of a catalyst (2-ethyl-4-methylimidazole) were put into a reactor equipped with a thermometer and a stirrer and reacted therein at 150 °C for 180 minutes to obtain an epoxy resin having a EEW of 480 g/eq. and a bromine content of 47% by weight (hereafter referred to as Epoxy Resin F) . Example G

100 pbw of Epoxy Resin A, 8 pbw of tetrabromobisphenol A and 0.03 pbw of 2-ethyl-4-methylimidazole were put into a reactor equipped with a thermometer and a stirrer and reacted at 150 °C for 180 minutes to obtain an epoxy resin having an EEW of

485 g/eq. and a bromine content of 50% by weight (hereafter referred to as Epoxy Resin G) . Example H

100 pbw of Epoxy Resin A, 10 pbw of a phenol-novolak-type epoxy resin having an EEW of 178 g/eq., (EPIKOTE 154 available from Yuka Shell Epoxy K.K., EPIKOTE is a trade mark), 15 pbw of tetrabromobisphenol A and 0.03 pbw of 2-ethyl-4-methyli_idazole were put into a reactor equipped with a thermometer and a stirrer and reacted at 150 °C for 180 minutes to obtain an epoxy resin having an EEW of 495 g/eq. and a bromine content of 46% by weight (hereafter referred to as Epoxy Resin H) . Example I

100 pbw of Epoxy Resin A, 5 pbw of p-t-butylphenol and 0.03 pbw of 2-ethyl-4-methylimidazole were put into a reactor equipped with a thermometer and a stirrer and reacted at 150 °C for 180 minutes to obtain an epoxy resin having an EEW of 480 g/eq. and a bromine content of 47% by weight (hereafter referred to as Epoxy Resin I) . Example J

100 pbw of Epoxy Resin A, 10 pbw of 2,4,6-tribromophenol and 0.03 pbw of 2-ethyl-4-methylimidazole were put into a reactor equipped with a thermometer and a stirrer and reacted therein at 150 °C for 180 minutes to obtain an epoxy resin having an EEW of 490 g/eq. and a bromine content of 51% by weight (hereafter referred to as Epoxy Resin J) . Example K

100 pbw of Epoxy Resin A, 3 pbw of acrylic acid and 0.03 pbw of 2-ethyl-4-methylimidazole were put into a reactor equipped with a thermometer and a stirrer and reacted at 150 °C for 180 minutes to obtain an epoxy resin having an epoxy equivalent of 490 g/eq. and a bromine content of 48% by weight (hereafter referred to as Epoxy Resin K) . Example L

143 pbw of an epoxy resin was obtained in the same manner as in Example A, except that 94.5 pbw of 4-bromoresorcinol were used in place of 272 pbw of tetrabromobisphenol A. The epoxy resin thus obtained had an EEW of 181 g/eq. and a bromine content of 26% by weight (hereafter referred to as Epoxy Resin L) . Example M 204 pbw of an epoxy resin was obtained in the same manner as in Example B, except that 159 pbw of 2,5-dibromo-l,6-dihydroxy- naphthalene were used in place of 272 pbw of tetrabromobispheol A. The epoxy resin thus obtained had an EEW of 245 g/eq. and a bromine content of 37% by weight (hereafter referred to as Epoxy Resin M) .

Examples according to the invention 1 to 20, and Comparative Examples 1 to 3:

Epoxy Resins A to M were combined with a bisphenol A-type epoxy resin having an EEW of 187 g/eq. (EPIKOTE 828 available from Yuka Shell Epoxy K.K.), a bisphenol F-type epoxy resin having an EEW of 168 g/eq. (EPIKOTE 807, available from Yuka Shell Epoxy K.K.), a phenol novolak-type epoxy resin having an epoxy equivalent of 178 g/eq. (EPIKOTE 154, available from Yuka Shell Epoxy K.K.), a low-brominated bisphenol A-type epoxy resin having an epoxy equivalent of 469 g/eq. and a bromine content of 21.0% by weight (EPIKOTE 5046, available from Yuka Shell Epoxy K.K.), and/or a flame-retardant reactive diluent having an epoxy equivalent of 360 g/eq. and a bromine content of 49.0% by weight (SHELL BROC, available from Yuka Shell Epoxy K.K.), as a curing agent: methyltetrahydrophthalic anhydride (EPIKURE DX-126, available from Yuka Shell Epoxy K.K.); as curing accelerator: 2- ethyl-4-methylimidazole (EPIKURE EMI-24, available from Yuka Shell Epoxy K.K.); and as a filler: fused quartz glass filler (FUSELEX RD-8, available from Tatsumori K.K.)

The thus prepared compositions were cast and cured in an oven at 100 °C for 2 hours followed by 5 hours at 150 °C. The articles thus obtained were tested according to the methods as described below

(a) Glass Transition Point:

A cylindrical test sample was formed from each of the articles, and its glass transition point was measured with a thermal metering apparatus (TMA) , (b) Modulus of Bending Elasticity, Bending Strength:

The modulus of bending elasticity as well as the bending strength of each of the cured bodies was measured in accordance with JISK-6911, (c) Cracking Resistance: Test articles were prepared by casting the resin compositions in accordance with JTSC-2105, using a facing ring. These articles were subjected to heating/cooling cycle tests, whereupon the number of cycles that were completed before they cracked was counted for each test piece. From the data presented in Table I below, it follows that the cured articles of examples according to the invention 1 to 20 have a similar or higher glass transition point than those of Comparative Examples 1 to 3 (conventional epoxy resins) while the cracking resistance of the former are much higher than that of the latter. Table 1

Examples

1 2 3 4 5 6 7 8 9 10 11 12

Epoxy Resin (pbw)

Epoxy Resin A 100 50 50 50 80 95

Epoxy Resin B 100

Epoxy Resin C 100

Epoxy Resin D 100

Epoxy Resin E 100

Epoxy Resin F 100

Epoxy Resin G 100

Epoxy Resin H

Epoxy Resin I

Epoxy Resin J

Epoxy Resin K

Epoxy Resin L

Epoxy Resin M

EPIKOTE 828 50

EPIKOTE 807 50 25

EPIKOTE 154 25

EPIKOTE 5046 20

SHELL BROC 5

Examples Comp. Examples

13 14 15 16 17 18 19 20 1 2 3

Epoxy Resin (wt.pts.)

Epoxy Resin A

Epoxy Resin B

Epoxy Resin C

Epoxy Resin D

Epoxy Resin E

Epoxy Resin F

Epoxy Resin G 50

Epoxy Resin H 100

Epoxy Resin I 100

Epoxy Resin J 100 50

Epoxy Resin K 100

Epoxy Resin L 100

Epoxy Resin M 100

EPIKOTE 828 50 50 100 50

EPIKOTE 807 100

EPIKOTE 154 50

EPIKOTE 5046

SHELL BROC

Claims

C L A I M S

1. A curable epoxy resin composition comprising an epoxy resin and an acid anhydride curing agent, wherein the epoxy resin has a bromine content of from 15% by weight to 70% by weight, has, on average more than one glycidyl group per molecule and comprises at least one structure of the general formula (1), (2) or (3) as presented below: (1)

wherein the groups X-*- to X^**-⁸ each individually may represent a hydrogen atom, a hydrocarbon residual group having from 1 to 20 carbon atoms, an alkoxy group, an aroxy group or a halogen atom; and wherein R represents a single bond, a hydrocarbon residual group having from 1 to 20 carbon atoms, or -0-, -S-, -SO2-, -CO-, -COO-,

-OCOO-, -NHCO- or -NHCOO-;

2. A curable epoxy resin composition as claimed in claim 1, in which the epoxy resin is prepared by reacting i) one or more dihydroxy compounds comprising a structure of formula (1), (2) or (3) with ii) epichlorohydrin; followed by cyclization of the resulting intermediate in the presence of an alkali metal hydroxide.

3. A curable epoxy resin composition as claimed in claim 1, in which the epoxy resin is prepared by reacting i) a blend of one or more dihydroxy compounds comprising a structure of formula (1), (2) or (3) and one or more compound(s) selected from the group of dihydroxy compounds such as: polyphenols, though not being the dihydroxy compounds comprising a structure of the formula (1), (2) or (3); phenols; carboxylic acids; and epoxy compounds; with (ii) epichlorohydrin.

4. A curable epoxy resin composition as claimed in claim 1, in which the epoxy resin is prepared by reacting i) an epoxy resin as claimed in claim 2 or 3 with ii) one or more compounds selected from the group of phenols, polyphenols and carboxylic acids in the presence of a catalyst.

5. An epoxy resin composition as claimed in claim 1, in which the epoxy resin is prepared by reacting i) a blend of an epoxy resin as claimed in claim 2 or 3 and one or more epoxy resin(s) other than an epoxy resin as claimed in claim 2 or 3 with ii) one or more compound(s) selected from the group of phenols, polyphenols and carboxylic acids.

6. An epoxy resin composition as claimed in claim 1, in which the epoxy resin is prepared by reacting i) one or more dihydroxy compounds comprising a structure of formula (1), (2) or (3) with ii) a polyfunctional epoxy resin in the presence of a catalyst.

7. A curable epoxy resin composition as claimed in claim 1, in which the epoxy resin is prepared by reacting i) a blend of one or more dihydroxy compounds comprising a structure of formula (1), (2) or (3) and one or more compound(s) selected from the group of: dihydroxy compound(s) such as polyphenols other than those comprising a structure of the formula (1), (2) or (3); phenols, and carboxylic acids with ii) a polyfunctional epoxy resin.

8. A curable epoxy resin composition as claimed in claim 1, in which the epoxy resin is a mixture comprising on or more epoxy resins claimed in any one of claims 2 to 7 and one or more other epoxy resin(s) .

9. A process for the preparation of a curable epoxy resin composition as claimed in any one of the claims 1 to 8 obtainable by uniformly mixing the epoxy resin the acid anhydride curing agent and if desired a filler and/or other additives.

10. Use of a curable composition as claimed in any one of the claims 1 to 8 as a casting composition for insulation of electrical and electronic articles.

11. Articles comprising a curable epoxy resin composition as claimed in any one of the claims 1 to 8 in the cured state.