JPS6348324A - Epoxy resin composition - Google Patents

Abstract

PURPOSE:To obtain the titled composition excellent in heat resistance, mechanical strength, water resistance and flexibility, by mixing a specific polyepoxy resin with a curing agent for epoxy resin. CONSTITUTION:100pts.wt. mixture of 90-60wt% diepoxy resin of an epoxy equivalent of 170-800, represented by the formula (wherein R1-2 are each H or methyl and X1-2 are each H or Br) and obtained by reacting at least one bisphenol (i) selected from among (tetrabromo)bisphenol A and bisphenol F with epichlorohydrin (ii), with 10-40wt% bisphenol a novolak epoxy resin of an average of glycidyl groups per molecule of 2.3-10, obtained by reacting a bisphenol A novolak resin obtained by reacting bisphenol A with form-aldehyde with epichlorohydrin, is reacted with 20-70pts.wt. component (i) at 110-180 deg.C in the presence of a catalyst (e.g., NaOH) to obtain a polyepoxy resin (a) of an epoxy equivalent of 200-2,000. 100pts.wt. component (a) is mixed with 2-70pts.wt. curing agent (b) for epoxy resin (e.g., diethylenetriamine).

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a new and useful epoxy resin composition, and more particularly, to a trifunctional epoxy equivalent resin having a specific bisphenol as a backbone and a bisphenol A monomer. The polyfunctional epoxy resin obtained by reacting such specific bisphenols with a mixture with a lac-type epoxy resin is an essential base resin component, and on the other hand, a heat-resistant epoxy resin that has a curing agent for epoxy resin as an essential curing agent component. The present invention relates to a resin composition having excellent cured product properties such as hardness, water resistance, rock-like strength, and flexibility, and is therefore suitable for lamination, molding, coating, or adhesion.

[Problems to be Solved by the Prior Art and the Invention] Bisphenol A type epoxy resins, which are the most widely used ones, are difunctional and therefore may lack heat resistance depending on their use.

In order to improve heat resistance in such cases, a polyfunctional novolac type epoxy resin is often used in combination.

In addition, in fields where flame retardancy is required, brominated epoxy resins containing tetrabromobisphenols as a single bisphenol component, or brominated epoxy resins that are co-condensed with tetrabromobisphenols and bisphenols, are commonly used. In addition, when heat resistance is also required, Yabari Nogelac type epoxy resin is often used in combination.

In addition, so-called bisphenol F type epoxy resins, in which part or all of the bisphenol human skeleton has a bisphenol F skeleton, are also used, although in rare cases.

In any case, if a novolak type epoxy resin is used in combination with a bifunctional epoxy resin using various bisphenols as mentioned above for the purpose of imparting heat resistance, the improvement in heat resistance will be certain. On the other hand, since the cured product tends to be hard and brittle and has reduced flexibility, it is problematic to increase the amount of novolac-type epoxy resin based only on heat resistance, and it is also costly. is also generally disadvantageous.

For example, in epoxy resin laminates, the so-called G-10 grade, which has not been flame retardated, uses bisphenol A type solid epoxy resin as the main raw material, and phenol noblack type or cresol novolac type epoxy resin is used to impart heat resistance. A mixture of both of these components is often used.

On the other hand, the flame-retardant PR-4 grade is based on a bisphenol A type liquid epoxy resin modified with tetrabromobisphenol A, and has a low bromine content of 20 to 30% by weight at most. Type 2 I-oxy resin is used as the main raw material, and a mixture of 7-enol novolac type epoxy resin, cresol novolac type epoxy resin, etc. is also used for the purpose of imparting heat resistance.

However, when such laminates are used, the combined use of Tsumerac-type epoxy resin deteriorates the dimensional stability of the laminates and makes them hard and brittle, resulting in poor drill resistance. The reality is that similar problems arise in the fields of insulating powder coatings and molding materials, where similar resins are used in combination.

[Means for solving problems]

However, in view of the various shortcomings in the prior art as described above, the present inventors have developed
In order to obtain an epoxy mia paraboloid with a well-balanced performance such as mechanical strength, water resistance, and flexibility, as a result of extensive research, we found that we did not simply mix a tumerac type epoxy resin with a bifunctional epoxy resin. If a bifunctional di-d soxy resin and a Tumerac type epoxy resin, particularly a bisphenol A7M lac type epoxy resin, are prepared in advance to have a structure in which they are grafted, it is extremely effective to meet the above purpose. The present inventors have discovered that a caepoxy resin composition can be obtained, and have completed the present invention.

The reason why the bisphenol A Tumerac epoxy resin used in the present invention is limited to the bisphenol A Tumerac epoxy resin is that it is heat resistant compared to those grafted with phenol novilac epoxy resins or cresol novolac epoxy resins based on the same idea. This is because it has much better water resistance. This is due to the fact that lac-type epoxy resin itself has better heat resistance and water resistance than phenol novolac-type epoxy resin or cresol novolac-type epoxy resin, but also because these lac-type epoxy resins and bifunctional epoxy resins ( The reactivity with bisphenols (a-3) used for grafting with a-1) is higher in bisphenol A tumerac-type epoxy resin than in phenol or cresol novolac-type epoxy resins, and as a result, tumerac-type epoxy resin One of the reasons is thought to be that the grafting rate of epoxy resin to bifunctional epoxy resin is much higher.

That is, the present invention provides a trifunctional epoxy resin (a-1
) and bisphenol A novolak type epoxy resin (a-2 ) with at least one kind of bisphenol (a-3) selected from the group consisting of bisphenol A, bisphenol F and tetrabromobisphenol A, with an epoxy equivalent of 200 to 2,000. The present invention provides an epoxy resin composition comprising a functional epoxy resin and (B) a curing agent for epoxy resin as essential components.

Here, the trifunctional epoxy resin (R-1) used to prepare the polyfunctional epoxy resin matrix, which is the first essential component constituting the composition of the present invention, refers to the trifunctional epoxy resin (R-1) used as the bisphenol (a-3). bisphenol A, bisphenol F and tetra2o bisphenol/L/
By using at least one compound selected from A and epichlorohydrin, for example, by a known method as described in "Epoxy Resin" published by Shokodo Co., Ltd.
Easily obtained liquid or solid (brominated) epoxy resins having two glycidyl ethers in the same molecule, or the epoxy resin thus obtained, can be used as a paste for bispheno-#s (a-3). The following general compound is obtained by reacting at least one compound selected from bisphenol A, bisphenol F and tetrabromobisphenol A by a known method as described in the further refined "K4Ki Resin". It is a synonym for (brominated) epoxy resin with the structure shown in , and has a bisphenol skeleton,
and an epoxy equivalent of 170 to 800, preferably 190
This is a general term for resins ranging from 5004 to 5004.

The polyfunctional epoxy resin (4), the thus obtained trifunctional epoxy resin (a-1), and the bisphenol A lac type epoxy resin (a-2) as described below
Because it is obtained by reacting bisphenols (a-3) with a mixture of The effect of grafting using bisphenols (a-3) will not last long.

For example, the trifunctional epoxy resin (a-t) has a high molecular weight, that is, the molecular weight of the resin (&-1) is high, and you do not want the molecular weight of the desired polyfunctional epoxy resin (4) to be too high. In this case, the amount of bisphenols (a-3) used, which also has the role of increasing the molecular weight, is
Naturally, we have no choice but to suppress it, but the result is inevitably that the effect of grafting is diluted by that amount.

Therefore, the molecular weight of the trifunctional epoxy resin (a-1) to be used is preferably lower, except in cases where a polyfunctional epoxy resin with a relatively high molecular weight is to be obtained.

Next, the above-mentioned bisphenol A sogelac type epoxy Mt resin (&-2) is a bisphenol/l/A nogolac type resin obtained from bisphenol and formaldehyde and epichlorohydrin, which is described in the above-mentioned "epoxy resin". The number of glycidyl groups in one molecule is on average 2.3 to 2.
It is made of a novolak type epoxy resin having 10, preferably 4 to 8 epoxy resins.

The polyfunctional epoxy resin (4) usually has an epoxy equivalent of 200 to 2,000, preferably 300.
-1,200, but the above-mentioned 92-functional epoxy resin (a-1), bisphenol A novolak type epoxy resin (a-2) and bisphenols (a- 3) The usage ratio of each raw material component is not uniform because it varies depending on the use and required performance of the composition of the present invention. For example, when heat resistance is to be emphasized as much as possible, bisphenol A novolak Epoxy resin (a
-2) should be increased, and in order to also increase the grafting rate to this resin (a-2),
The amount of bisphenols (a-3) used also needs to be increased.

In addition, when obtaining the composition of the present invention for use in laminates, impregnating properties are important, so as mentioned above, it is not possible to increase the molecular weight of the polyfunctional epoxy resin (A) so much. Trifunctional epoxy resin (a-1
) It should be noted that the molecular weight of bisphenol (a-3) itself should be kept as low as possible while increasing the amount of bisphenol (a-3) used to an appropriate level.

Furthermore, when using the polyfunctional epoxy resin (4) for applications such as powder coatings, it is difficult to use low molecular weight or low melting point substances for blocking purposes.
), but in such a case, if a low molecular weight trifunctional epoxy resin (a-1) is also used, it will increase the molecular weight of bisphenols (a-3).
The amount of bisphenol A used increases, and at the same time, bisphenol A
If a large amount of novolac type epoxy resin (a-2) is used, there is also a risk of dulling of the polyfunctional epoxy resin, so care must be taken.

Therefore, in such cases, bisphenols (a-3
) In order to reduce the amount of use of - layer, bifunctional engineering with higher molecular weight? It becomes necessary to use xy resin (a-1).

In any case, when designing to obtain the resin (A) having the desired molecular weight and desired heat resistance, special attention should be paid to the grafting of the bisphenol A novolac type epoxy resin (a-2). It is important to ensure that the degree of grafting is not too low or, conversely, that it does not exceed the desired range of grafting and reach dulling, and sufficient preliminary experiments are required for this. In addition, it is important to design while confirming the effect of grafting compared to the conventional simple blending method. In normal cases, the usage ratio of each raw material component is as follows:
Weight ratio (a-1)/(a-2) is 90710-60/
40, ((a=1)+(a-2))/(a-3)
is in the range of 100/20 to 100/70.

Thus, each of the aforementioned bifunctional epoxy trees JIW (
a-1), the reaction using bisphenol A novolak type epoxy resin (a-2) and bisphenols (a-3) can be carried out using the above-mentioned "epoxy resin" or JP-A-48-83199. As described in the publication, known methods are used, for example, alkali hydroxides such as sodium hydroxide, tertiary amines such as triethylamine and benzyldimethylamine, and quaternary ammonium salts such as tetramethylammonium chloride. , imidazole compound, triphenylphosphine nanocatalyst 1
By reacting at 10 to 180°C, the desired polyfunctional epoxy resin (4) having excellent heat resistance, mechanical strength, water resistance, flexibility, etc. can be obtained.

In the present invention, the use of the multifunctional epoxy resin (A) obtained as described above is achieved by grafting this resin (a-2) in advance on the lac-type epoxy side (a-2) in which bisphenol A is used. On the other hand, the polyfunctional epoxy resin compound of the present invention obtained by taking the method of leaving the resin (a-2), and novolac type epoxy resins such as phenol nogelac type epoxy resin and cresol novolac type epoxy resin Conventional epoxy blends obtained by simply blending epoxy resins differ in the heat resistance of cured products of these two resins, such as heat distortion temperature and glass transition point (Tg).
) are designed to be the same, in the former method, that is, when using a polyfunctional epoxy resin (N), the usage amount of this bisphenol A novolac type edexy resin (a-2) is the same as in the latter method. Compared to using a jepoxy blend, less phlegm is produced, and as a result, the former method naturally has better toughness, and furthermore, the former method also has better water resistance. It can be said that it is indeed advantageous, as the surprising results have been obtained.

Furthermore, when designing the amount of novolac type epoxy resin to be the same between the case of using the polyfunctional epoxy resin (A) in the present invention and the case of using a conventional simple blend, Results have been obtained that the cured product according to the present invention has much better heat resistance, mechanical strength, water resistance, etc., and is also tougher.

Furthermore, in the present invention, by limiting the novilac type epoxy resin to be grafted to bisphenol A novilac type epoxy resin, compared to the case where other novilac type epoxy resins such as phenol or cresol novolac type epoxy resin are grafted. It has been found that a product with even better heat resistance and water resistance can be obtained.

On the other hand, as the curing agent (B) for epoxy resin, which is the second essential component constituting the composition of the present invention, any compound known and commonly used as a curing agent for epoxy resin can be used. Examples include aliphatic amines such as diethylenetriamine and triethylenetetramine; aromatic amines such as metaphenylenediamine, diaminodiphenylmethane, and diaminodiphenylsulfone;
Polyamide resins or modified products thereof; or anhydrides such as maleic anhydride, hexahydrophthalic anhydride, pyromellitic anhydride, dicyandiamide,
Examples include latent curing agents such as imidazole, BF3-amide, complexes or guanidine derivatives.

When using each of these compounds as a curing agent, it is often necessary to also use a curing accelerator, but in such cases, tertiary amines such as dimethylbenzylamine, imidazole, etc. It goes without saying that known and commonly used compounds including metal compounds of the same type or various types can be used.

In addition, the above-mentioned polyfunctional epoxy resin (A) in the present invention
The term polyfunctional shall mean a resin with an average functionality of greater than two.

Therefore, the epoxy resin composition of the present invention contains the above-described two essential components, the polyfunctional epoxy resin (4) and the curing agent for epoxy resin (B), based on 100 parts by weight of the solid content of the resin component. It is obtained by blending in a proportion of 2 to 70 parts by weight. However, it should be noted that this blending ratio varies greatly depending on the type of curing agent (B) component used.

The composition of the present invention obtained in this manner may further contain various additives such as fillers and colorants, if necessary, and may also contain tar, pitch, amino resin, alkyd resin, phenol resin, etc. can also be used together.

〔Effect of the invention〕

The epoxy resin composition of the present invention not only has excellent heat resistance, fundamental strength, and water resistance, but also provides an extremely useful cured product that is tough and not brittle.

Because of these properties, the composition of the present invention is extremely useful for a wide range of applications such as laminated materials, molding materials, coating materials, and adhesives.

〔Example〕

Next, the present invention will be specifically explained with reference to Reference Examples, Examples, and Comparative Examples. In the following, all parts and parts are expressed on a weight basis unless otherwise specified.

Reference Example 1 [Example of Preparation of Multifunctional Epoxy Resin (4)] 53 parts of liquid Epiclon 850J (bisphenol A type epoxy resin manufactured by Dainippon Ink and Chemicals Co., Ltd.) with an epoxy equivalent of 190, and bisphenol A novolak. Type epoxy resin [epoxy 1=210, softening point=78℃,
Average number of glycidyl groups = 6.5, hereinafter referred to as bisphenol A)
Melac-type epoxy resin (1)] was added with 34 parts of tetrabromobisphenol A, heated to 120°C and stirred, and further 0.01 part of 2-methyl-imidazole was added. After reacting at 150° C. for 4 hours, a solid desired resin having an epoxy equivalent of 475 and a bromine content of 20% was obtained. Hereinafter, this will be abbreviated as resin (A-1).

Reference example 2 (same as above) The amount of "Epicron 850" used was increased from 53 parts to 56 parts,
Also, bisphenol A is a lac type epoxy resin (1)
A solid target resin having an epoxy equivalent weight of 471 and a bromine content of 20 inches was obtained in the same manner as in Reference Example 1, except that the amount used was changed from 13 parts to 10 parts. Hereinafter, this will be abbreviated as resin (A-2).

Reference Example 3 (same as above) Epoxy equivalent = 208. A resin with an epoxy equivalent of 470 and a bromine content of 20% was prepared in the same manner as in Reference Example 1, except that a bisphenol A novolak type epoxy resin (n) having a softening point of 68°C and an average number of glycidyl groups of 5.0 was used. A solid target resin was obtained. Below, this is resin (
It is abbreviated as A-3).

Reference Example 4 (same as above) Same as Reference Example 1 except that 28 parts of bisphenol A was added to the mixture consisting of 52 parts of Epiclon 850J and 20 parts of bisphenol A novolac type epoxy resin (1). As a result, a desired resin having an epoxy equivalent of 830 and a softening point of 95° C. was obtained.Hereinafter, this will be abbreviated as resin (A-4).

Reference Example 5 (same as above) "Epiclon 152JC Tetrabromobisphenol A type epoxy resin manufactured by Dainippon Ink & Chemicals (Riki); Epoxy equivalent = 360. Softening point = 60°C, Bromine content = 47
%) and 15 parts of bisphenol A novolac type epoxy resin (I) in the same manner as in Reference Example 1, except that 20 parts of tetrabromobisphenol A was added to the mixture, and the epoxy equivalent was 540, a target resin having a softening point of \83°C and a bromine content of 42% was obtained. Hereinafter, this will be abbreviated as resin (A-5).

Reference Example 6 [Multifunctional epoxy resin for control (preparation example A)] Bisphenol A novolac type epoxy resin (1) 1
Instead of 3 parts, all 13 parts of semi-solid "Epicron N-740" (Inu Nippon Ink Chemical Industry Co., Ltd. (lead phenol novolac type epoxy resin; epoxy equivalent = 180, average number of glycidyl groups = 4.0) were used. Except for this, the same procedure as Reference Example 1 was carried out, and the epoxy equivalent was 450 and the bromine content was 20.
% solid control resin was obtained. Hereinafter, this resin (A
'-1).

Reference example 7 (same as above) Bisphenol A novolac mold? Kishiju Jffj (
1) Add "Epiclon N-680J (cresol novolac type epoxy resin manufactured by the same company) to 13 parts of glue; 1 per epoxy = 210, softening point = 84 ° C., average number of glycidyl groups =
6.6') was used in the same manner as in Reference Example 1, the epoxy equivalent was 473, and the bromine content was 2.
A control resin of 0% solids was obtained. Below, this resin (A
'-2).

Reference Example 8 (same as above) The epoxy equivalent was 83 in the same manner as Reference Example 4, except that the same amount of "Epicron N-680J" was used instead of the bisphenol A novolac type epoxy resin (I).
A control resin having a softening point of 93° C. was obtained. Hereinafter, this will be abbreviated as resin (A'-3).

Reference Example 9 [Example of preparation of bifunctional epoxy resin (A") for comparison] A mixture of 46 parts of "Epiclon 850" and 34 parts of tetrabromobisphenol A was heated to 120°C, stirred, and further mixed with 2-methyl - Addition of 0.01 part of imidazole and reaction at 150 DEG C. for 4 hours yielded a solid control resin with an epoxy equivalent weight of 695 and a bromine content of 25 inches. Hereinafter, this will be abbreviated as resin (Al/-1).

Reference Example 10 (same as above) The same procedure as Reference Example 8 was carried out except that the amounts of "Epiclon 850" and tetrabromobisphenol A were changed to 52 parts and 35 parts, respectively, and the epoxy equivalent was 615.
A solid control resin with a bromine content of 23% was obtained. Hereinafter, this will be abbreviated as resin (A"-2).

Reference Example 11 (same as above) A mixture of 68 parts of "Evicron 152" and 17 parts of tetrabromobisphenol was heated to 120°C, stirred, and then 0.01 part of 2-methyl-imidazole was added and the mixture was heated to 150°C. After 4 hours of reaction, the epoxy equivalent was 68.
7, a control resin with a softening point of 86° C. and a bromine content of 49% was obtained.

Hereinafter, this will be abbreviated as resin (A"-3).

Examples 1 to 3 and Comparative Examples 1 to 2 Each resin (A-1), (A-2), (A-3), (A') obtained in Reference Examples 1 to 3 and Reference Examples 6 to 7 -1
) and (A'-2) separately in methyl ethyl ketone, and then add the hardening agent dicyandiamide and the hardening accelerator dimethylbenzylamine, which had been previously dissolved in methyl cellosolve, in the amounts shown in Table 1 below, to form a non-volatile solution. A mixed solution with a minute (NV) of 55 was prepared. The amount of curing agent (B) at this time is set at a ratio of 0.25 mol per epoxy group in the polyfunctional epoxy resin diagram, and the amount of curing accelerator is set at a ratio of 0.25 mol to one epoxy group in the polyfunctional epoxy resin diagram.
CA) The ratio was set to 0.2 parts per 100 parts of solid content.

Thereafter, each mixed solution was used and cured under the following conditions to produce a laminate.

Next, each laminate was tested for physical properties of the cured product.
The results shown in the same table were obtained.

Laminate production conditions Base material: rWE-18 to -104-BZ2J (Nittobo ■
[glass cloth] Number of plies = 9 Resin content: approximately 40% Comparative Example 3 Comprised of 80 parts of the control resin (A"-1) obtained in Reference Example 9 and 20 parts of [Epicron N-740J] blend(
A laminate was produced in the same manner as in Example 1, except that a mixed solution was used, and the cured physical properties were evaluated in the same manner. Table 1 shows the results.

Comparative Example 4 A yC layer plate was prepared in the same manner as in Example 1, except that 87 parts of the control resin (A''-2) obtained in Reference Example 10 and 13 parts of Epicron N-740J were used. was prepared and the physical properties of the cured product were evaluated in the same manner.The results are shown in Table 1.

Comparative Example 5 Table 1 shows the results of testing in the same manner as Comparative Example 3 except that the same amount of Epiclon N-6804'e was used instead of Epiclon N-740j.

Comparative Example 6 Comparative Example 4 except that the same amount of Epiclon N-680J was used instead of Epiclon N-740J.
Tested in the same manner. The results are shown in Table 1.

Comparative Example 7 Tests were carried out in the same manner as in Comparative Example 4, except that the same amount of bisphenol A novolak epoxy resin was used in place of Epiclon N-740J. The results are shown in Table 1.

Examples 4 to 5 and Comparative Example 8 Control resins obtained in Reference Examples 4 to 5 and Reference Example 8 (A
-4), (A-5) and (A'-3) separately,
The amount of curing agent “Epiclon B-5704 [:
Methyltetrahydrophthalic anhydride, which is liquid at room temperature, manufactured by Dainippon Ink Chemical Industry ■ and the curing accelerator 2-ethyl-4-
The epoxy resin composition of the present invention was obtained by adding methyl-imidazole. The amount of curing agent (B) at this time is 1 per epoxy group in the polyfunctional epoxy resin (A).
On the other hand, the amount of the curing accelerator was determined to be 1 part per 100 parts of the polyfunctional epoxy resin (A).

Thereafter, each epoxy resin composition was cured under the conditions described below to produce a cast plate.

Next, the physical properties of the cured products of each cast plate were tested, and the results shown in the table were obtained.

Curing conditions: held at 100°C for 1 hour, then held at 160°C for 2 hours, and further held at 180°C for 2 hours.

Casting piece thickness: Approximately 3 times Comparative Examples 9 and 10 Solid bisphenol A type epoxy resin for control Nibukron 3050J [manufactured by Inu Nippon Ink Chemical Co., Ltd., epoxy equivalent = 835, softening point = 98°C] and " Epicron N
-680J separately at a weight ratio of 8o:20 and 70:30, and then a casting plate was prepared in the same manner as in Example 4, except that the respective blends were used. The physical properties of the cured product were evaluated. The results are shown in Table 2.

Comparative Example 11 A blend of Epiclon 3050J and bisphenol A Tumerac type epoxy resin (I) in a weight ratio of 80:20 was tested in the same manner as in Comparative Example 9.
Shown in the table.

Comparative Example 12 The same procedure as Example 4 was carried out except that a blend of 85 parts of the control resin (A''-3) obtained in Reference Example 11 and 15 parts of Epiclon N-740j was used. A casting plate was prepared using the same method, and the physical properties of the cured product were evaluated.The results are shown in Table 2.

*1): Pressure Kutzker Test J (PCT).

*2): Two test pieces were subjected to PCT at 120℃ for 4 hours.
The test piece was floated on a melting solder at 60° C., and the appearance of the test piece, especially the presence or absence of “blister”, was visually evaluated.

◎・・・No abnormality at all ○... There is almost no abnormality, but there is a slight "bulge" ×・・・“Blistering” occurs

Claims (1)

Scope of Claims: (A) A bifunctional epoxy resin having an epoxy equivalent of 170 to 800 and having a backbone of at least one bisphenol selected from the group consisting of bisphenol A, bisphenol F, and tetrabromobisphenol A ( a-1
), and a bisphenol A novolac type epoxy resin (a-2) having an average number of glycidyl groups in one molecule of 2.3 to 10, which is obtained by reacting epichlorohydrin with a bisphenol A novolac resin derived from bisphenol A and formaldehyde. A polyfunctional compound having an epoxy equivalent of 200 to 2,000, obtained by reacting a mixture of with at least one bisphenol (a-3) selected from the group consisting of bisphenol A, bisphenol F, and tetrabromobisphenol A. An epoxy resin composition comprising an epoxy resin and (B) a curing agent for epoxy resin as essential components.