JPH05148337A - Epoxy resin composition suitable for structural adhesive - Google Patents

Abstract

PURPOSE:To provide the subject composition excellent in peeling strength without substantial detriment to the excellent tensile shear strength inherent in a cured epoxy resin. CONSTITUTION:The objective composition comprises 65-98 pts.wt. bisphenol epoxy resin (A), 35-2wt.% urethane-modified epoxy resin (B) containing blocked isocyanate groups (the total of components A and B being 100 pts.wt.), 5-50 pts.wt. carboxylated butadiene/acrylonitrile liquid rubber (C) and a curing agent (D).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an epoxy resin suitable as a structural adhesive used for bonding hoods, doors, hem / flange parts of fenders, etc. in car body assembly of automobiles or for bonding car body frame parts by the weld bond method It relates to a composition.

[0002]

Conventionally, various epoxy resin compositions comprising bisphenol type epoxy resin, rubber modified epoxy resin, synthetic rubber, urethane modified epoxy resin, filler and curing agent have been used as structural adhesives based on epoxy resin. Are known.

On the other hand, an adhesive used for a structure is subjected to not only shearing stress but also stress in various directions on the bonded portion depending on the usage form of the structure, so that the structural adhesive has both shear adhesiveness and peel strength. On the other hand, advanced equipment is required. Epoxy resin compositions used for conventionally known structural adhesives do not always completely meet such requirements, and there is room for improvement, especially in peel strength.

[0004]

Therefore, the present invention provides an epoxy resin composition suitable as a structural adhesive having excellent peel strength without substantially impairing the shear adhesiveness originally possessed by a bisphenol epoxy resin cured product. The purpose is to provide.

As a result of diligent research, the present inventor has blended a special urethane-modified epoxy resin having a blocked isocyanate and a special butadiene-acrylonitrile liquid rubber containing a carboxyl group into a system comprising a bisphenol type resin and a curing agent. As a result, they have found that the above objects can be achieved, and have completed the present invention.

[0006]

According to the present invention, 65 to 98 parts by weight of a bisphenol type epoxy resin (A) and 35 to 2 parts by weight of a urethane-modified epoxy resin (B) containing a blocked isocyanate (wherein the epoxy resin is used). The total amount of (A) and modified epoxy resin (B) is 100 parts by weight), a structure comprising 5 to 50 parts by weight of a carboxyl group-containing butadiene-acrylonitrile liquid rubber (C) and a curing agent (D). An epoxy resin composition suitable for an adhesive for use is provided.

When the composition of the present invention is used as an adhesive,
It has a high shear adhesive strength originally possessed by an epoxy resin-based adhesive, and is also excellent in peel strength, so it is extremely suitable as a structural adhesive.

Hereinafter, the constitution of the present invention will be described in detail, but the objects and advantages of the present invention will become clearer.

Epoxy Resin (A ) The bisphenol type epoxy resin (A) is 2,2-bis (4-hydroxyphenyl) propane: bisphenol A, 2,2-bis (4-hydroxyphenyl) ethane:
Bisphenol AD, bis (4-hydroxyphenyl)
Methane: An epoxy resin derived from bisphenol exemplified by bisphenol F and epichlorohydrin, and is typically represented by the following structural formula (1).

[0010]

[Chemical 1] (In the above formula, R is a hydrogen atom or a methyl group)

The number average molecular weight of the epoxy resin (A) is 35.
0-5000, especially 350-2000 are preferable.
When the molecular weight is too high, since the content of epoxy groups is low, the crosslink density after curing is low, sufficient shear adhesive strength cannot be obtained, and the viscosity of the adhesive becomes large, which makes application work difficult.

Modified urethane containing blocked isocyanate
Epoxy resin (B) Modified epoxy resin (B) is prepared by the following method. That is, an excess diisocyanate (b) is reacted with the polyol (a) to prepare a urethane prepolymer (c) having an isocyanate group at the terminal, and then a part of the terminal isocyanate of this prepolymer (c) contains a hydroxyl group. It reacts with compound (d) to form a blocked isocyanate.

A prepolymer (c) in which a part of the isocyanate is blocked and a bisphenol A type epoxy resin,
The modified epoxy resin (B) is produced by reacting with an epoxy resin (e) such as a bisphenol F type epoxy resin, a glycidyl ester type epoxy resin, or a polyglycol type epoxy resin.

In the above, examples of the polyol (a) include polyether polyols such as polytetramethylene glycol, polyethylene glycol and polypropylene glycol, other polyester polyols, polyether ester polyols, polyester amide polyols, acrylic polyols and polyurethane polyols. Although preferred, polyether polyols are preferred.

Examples of the diisocyanate (b) include tolylene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, tetramethylene diisocyanate, isophorone diisocyanate, methylene bis (4-cyclohexyl isocyanate), xylylene diisocyanate, and the like.
Tolylene diisocyanate and diphenylmethane diisocyanate are preferred.

The urethane prepolymer (c) obtained by the above reaction has an isocyanate group at the polymer terminal, and as the hydroxyl group-containing compound (d) used for blocking a part of the isocyanate, phenol, cresol, xylenol, etc. , Lactams such as γ-butyrolactam and ε-caprolactam, oximes such as acetoxime, methylethylketoxime and cyclohexanone oxime, imides such as succinimide and phthalimide, alcohols such as ethanol, butanol and isopropanol. Is mentioned.

Such a blocked isocyanate-containing urethane-modified epoxy resin (B) is commercially available, for example, as R-1541 of AC R Co., Ltd.

When the epoxy resin composition of the present invention is heated to a high temperature for the purpose of curing, the modified epoxy resin is dissociated from the blocked isocyanate to form an isocyanate group and a hydroxyl group-containing compound, which react with the epoxy group and the curing agent and are tough. Form a bond. The presence of this bond and the liquid rubber (C) described below makes the cured product of the composition of the present invention excellent in shear adhesiveness and peel strength.

The weight ratio ((A) / (B)) of the epoxy resin (A) and the modified epoxy resin (B) is 65 /.
35 to 98/2, preferably 80/20 to 95/5.

Carboxyl group-containing butadiene acrylo
Nitrile liquid rubber A preferable liquid rubber (C) has a carboxyl group represented by the following structural formula (2) bonded to the terminal.

[0021]

[Chemical 2] (Where x, y and m are the number of repeating units and x / y is 95 /
5-50 / 50, m is 10-50. )

The liquid rubber (c) can be produced by a method known per se, and it can also be produced by Ube Industries, Ltd. Hycar.
CTBN 1300x31, CTBN 1300x
8, CTBN 1300x13, CTBN 1300x
It is marketed as 9 and is easily available. Liquid rubber (C)
The compatibility with the epoxy resin (A) increases with an increase in the content of acrylonitrile, but if it is too much, the rubber-like property is lost, so x / y (molar ratio) in the above formula (2)
Is preferably 90/10 to 70/30.

When this liquid rubber (C) is compounded in an appropriate amount, it reacts with the epoxy resins (A) and (B) during curing and bonds with the rigid polymer chains of the epoxy resin, giving flexibility to the cured product. , Increases peel adhesion strength. In that sense, the compounding amount of the liquid rubber (C) is 5 to 5 per 100 parts by weight of the total of the epoxy resin (A) and the modified epoxy resin (B).
It is 0 part by weight, preferably 10 to 30 parts by weight.

Curing agent (D) The curing agent used in the present invention has a curing temperature of 100 to 200 ° C.
Any substance may be used as long as the curing reaction of the epoxy resin is substantially started in the temperature range of, but specifically, dicyandiaside, isophthalic acid hydrazide,
Latent curing agents such as N, N′-dialkylurea derivatives and N, N′-dialkylthiourea derivatives, aromatic diamine-based curing agents such as 4,4′-diaminodiphenylmethane and 4,4′-diaminodiphenylsulfone, Other examples include imidazole and its derivatives, and among them, dicyandiamide, N, N'-dialkylurea derivative and the like can be preferably used. The amount of the curing agent used can be appropriately determined in consideration of the type of the curing agent and the amount of the epoxy group present in the composition, but generally, the epoxy resin ((A) + (B)) 100 1-3 parts by weight
About 0 parts by weight is blended. Further, a curing accelerator can be used in combination if necessary.

Further, in the composition of the present invention, (A) to
In addition to the essential components of (D), calcium carbonate, aluminum hydroxide, titanium oxide, barium sulfate, if necessary,
Fillers such as calcium metasilicate, carbon filler, and carbon chop can be contained.

[0026]

EXAMPLES The present invention will be specifically described below with reference to examples. Mix the components in the mixing ratios listed in Table 1,
An adhesive was obtained by sufficiently dispersing it with three rolls.

This adhesive is applied to an adherend (steel plate SCP-28C
(Rust prevention oil surface treatment), for tensile shear adhesion test: 25 x 150
× 1.6mm For T-type peel test: 25 × 200 × 0.8m
m) to a thickness of 0.15 mm and cured and adhered under the curing condition of 180 ° C. for 20 minutes, and the obtained test piece is subjected to a tensile shear adhesion test (pulling speed 5 mm / min) and a peel strength test (pulling speed 50 mm). / min). The results are shown in Table 1. Comparative Example 1 is an example in which 60 phr of liquid rubber is added, Comparative Example 2 is an example in which neither liquid rubber nor urethane-modified epoxy resin is added,
It can be seen that Comparative Example 3 is an example in which the urethane-modified epoxy resin is not added, and Comparative Example 4 is an example in which the urethane-modified epoxy resin is excessively added, and the adhesiveness is lowered.

[0028]

[Table 1]

[0029]

INDUSTRIAL APPLICABILITY As described above, the epoxy resin composition of the present invention is excellent in shear adhesive strength and peel adhesive strength, and therefore is extremely suitable and advantageously used as a structural adhesive.

Claims (1)

[Claims] 1. A bisphenol type epoxy resin (A) 65.
˜98 parts by weight, 35 to 2 parts by weight of urethane modified epoxy resin (B) containing blocked isocyanate (wherein the total amount of epoxy resin (A) and modified epoxy resin (B) is 100 parts by weight) ), Carboxyl group-containing butadiene / acrylonitrile liquid rubber (C) 5 to 5
An epoxy resin composition suitable for a structural adhesive comprising 0 parts by weight and a curing agent (D).