JPH01113476A - Epoxy adhesive composition - Google Patents

Abstract

PURPOSE:To obtain the title pregel composition excellent in bonding strength, by mixing a liquid epoxy resin with a specified acrylic resin and a dibasic acid dihydrazide compound. CONSTITUTION:An epoxy monomer or polymer (a) (e.g., glycidyl methacrylate) and a (meth)acrylate monomer or polymer (b) (e.g., methyl methacrylate) are subjected to treatment such as copolymerization, graft polymerization, posttreatment or mixing to obtain a powdery acrylic resin (B) having an epoxy group content >=0.2wt.% and a mean particle diameter <=50mu. 100 pts.wt. liquid epoxy resin (A) having at least one epoxy group on the molecule (e.g., diglycidyl ether) is mixed with 5-100 pts.wt. component B, a curing agent (C) comprising a dibasic acid dihydrazide compound (C) (e.g., succino-hydrazide) and, optionally, other curing agents and, optionally, a cure accelerator, a viscosity modifier, a filler, a pigment, a plasticizer, etc., (D).

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) This invention relates to an epoxy adhesive composition.

(Prior Art) In recent years, thermosetting epoxy adhesives have been widely used in the automobile industry, electrical industry, and the like. Among these, for structural adhesives used for structural parts, especially one-component thermosetting adhesives, epoxy resin is mixed with polyamide resin, acrylonitrile-butadiene rubber (NBR)-based liquid rubber, etc. as the second component resin. Efforts are being made to improve the brittleness of epoxy resins and improve their adhesive strength and durability.

It is believed that by dispersing the mixed second component resin or rubber in the epoxy resin matrix in the form of islands, these islands absorb stress and improve the properties of the adhesive (Adhesion 1984 Vol. 28, No. 9, pp. 9-11 (published by Kobunshi Kankankai).

(Problem to be solved by the invention) However, in conventional epoxy adhesives, it is difficult to obtain pregel properties (the property of changing from a sol to a gel by short heating in a temperature range of about 100 to 200°C). However, this method involved mixing a powdered acrylic resin with a liquid epoxy resin and using a catalytic curing agent, which resulted in the problem that sufficient adhesive strength could not be obtained.

(Means for Solving the Problems) This invention was made by focusing on the above-mentioned conventional problems, and as a result of the inventors' intensive study on the strength of epoxy resins for the development of structural adhesives, We have discovered a new method of strengthening epoxy resin that was previously unknown. That is, by using 5 to 100 parts by weight of a powdered acrylic resin containing 0.2% by weight or more of epoxy groups in 100 parts by weight of a liquid epoxy resin and a dibasic acid dihydrazide compound as an essential component as a curing agent. It has been found that a pre-gel type adhesive composition having excellent adhesive properties can be obtained, leading to the present invention.

The present invention will be explained in more detail below.

The epoxy resin used in the present invention may be any liquid resin having one or more epoxy groups in one molecule, and even a solid epoxy resin can be used after being dissolved in a liquid epoxy resin. Examples include diglycidyl ethers such as the usual reaction product of bisphenol A and epichlorohydrin, the reaction product of bisphenol F and epichlorohydrin, aliphatic diglycidyl ethers, alicyclic epoxides, and the reaction product of phthalic acid derivatives and epichlorohydrin. Diglycidyl esters, hydantoin epoxy resins, novolak epoxy resins, glycidylamine epoxy resins and the like can be used alone or in combination of two or more.

Next, the powdered epoxy group-containing acrylic resin used in this adhesive composition will be explained.

The epoxy group-containing acrylic resin is a powdery reactive polymer, which is a finely powdered (meth)acrylate polymer containing at least 0.2% by weight or more of epoxy groups based on the polymer.
Hereinafter, it is referred to as an epoxy group-containing copolymer). To introduce an epoxy group into a polymer, an epoxy group-containing monomer or polymer is added to a (meth)acrylate monomer or polymer by any known method such as copolymerization, graft polymerization, post-treatment, or mixing. It can also be done.

Examples of epoxy group-containing monomers or polymers for introducing epoxy groups include allyl glycidyl ether, glycidyl acrylate, glycidyl methacrylate, glycidyl-p-vinyl benzoate, methylglycidyl itaconate, glycidyl ethyl maleate, glycidyl Monomers such as glycidyl esters of unsaturated acids such as vinyl sulfonate and glycidyl (meth)allylsulfonate, epoxy olefins such as butadiene monoxide, vinylcyclohexene monooxide, and 2-methyl-5,6-epoxyhexene. Or polymers formed by polymerizing them can be mentioned. Particularly preferred are allyl glycidyl ether, glycidyl acrylate, and glycidyl methacrylate.

Monomers constituting the (meth)acrylate polymer include alkyl methacrylates such as methyl methacrylate, ethyl methacrylate, and stearyl methacrylate; alkyl acrylates such as methyl acrylate and butyl acrylate; and alkyl glycols such as butoxyethyl (meth)acrylate. Examples include meth)acrylate and alkylene glycol mono(meth)acrylate. A preferred (meth)acrylate is methyl methacrylate.

A method for obtaining an epoxy group-containing polymer by copolymerization will be explained. Copolymerizing at least one selected from the epoxy group-containing monomer group and at least one monomer selected from the (meth)acrylate monomer group together with other monomers as necessary in a medium, It is then separated from the medium and dried.

As an example of a method for obtaining it by graft polymerization, it can be obtained by polymerizing one monomer in advance and then adding and polymerizing the other monomer.

It is also possible to sequentially polymerize two or more monomer mixtures having different ratios in advance.

As an example of a method for obtaining it through post-treatment, it can be obtained by bringing an epoxy group-containing monomer into contact with a (meth)acrylate polymer and adding it thereto.

As an example of a method of obtaining by mixing, a polymer obtained by polymerizing an epoxy group-containing monomer and a (meth)acrylate polymer,
Obtained by mixing in a dispersion medium.

The method for incorporating epoxy groups is not limited, and it is sufficient to contain 0.2% by weight or more of epoxy groups per epoxy group-containing polymer.

If the epoxy group content is less than 0.2% by weight, the adhesiveness will be poor.

The polymer needs to have a fine particle size, and it is desirable that the average particle size is 50 μm or less, preferably 0.1 to 5 μm. If the average particle size is too large, the curability will be poor when used as an adhesive composition, and the cured product will exhibit brittle properties; if it is too small, the powder properties will be poor, causing problems during production and mixing. Emulsion polymerization, milk suspension polymerization, and suspension polymerization are often used to obtain an epoxy group-containing polymer having a preferred basic particle size. After the polymerization reaction, spray drying,
Fluidized bed drying, coagulation dehydration drying, etc. are preferably used.

If the basic average particle size is 50 μm or less, a weak agglomeration state may be exhibited in order to improve powder properties, and the apparent upper particle size may be coarsened. The higher the molecular weight of the epoxy group-containing polymer, the more desirable the average molecular weight is 300,000 or more.

If the molecular weight is lower than this, there is a tendency for performance as an adhesive, ie, performance such as tensile shear strength and T-peel strength, to decrease when used as an adhesive composition.

The epoxy group-containing polymer can be used in an amount of 5 to 100 parts by weight based on 100 parts by weight of the liquid epoxy resin. More preferably, it can be used in an amount of 10 to 70 parts by weight. When the amount of the epoxy group-containing polymer used is less than 5 parts by weight, no effect of adding the acrylic resin is observed, and when it is more than 100 parts by weight, the adhesive performance tends to decrease.

In the present invention, a dibasic acid dihydrazide compound is used as an essential curing agent. Conventionally, catalytic curing agents such as dicyandiamide and imidazole type curing agents have been used in corrugated epoxy adhesives.

The catalytic type is used here for the following reason. Taking dicyandiamide as an example, the amount of dicyandiamide added to bisphenol A type epoxy resin (epoxy equivalent: 190) calculated from the active hydrogen equivalent is 11.1 phr.
For practical use, a lower amount of 4 to 10 phr is sufficient. This is thought to be due to the decomposition of dicyandiamide during the reaction, causing self-polymerization of the epoxy resin (Polymer Processing 1
Published by Kobunshi Kagaku Kankai, March 1977 issue, p. 17).

However, as shown in the examples, it can be seen that such catalyst-type curing agents have low reactivity with acrylic resins containing epoxy groups. That is, even if an acrylic resin containing an epoxy group is mixed with a liquid epoxy resin and cured with dicyandiamide, the adhesive strength is reduced. On the other hand, it can be seen that when a dibasic acid dihydrazide compound is used as a curing agent, the effect of blending the epoxy group-containing acrylic resin becomes extremely effective.

Dibasic acid dihydrazide compounds used as curing agents include the following and are easily available industrially. That is, succinic acid dihydrazide, adipic acid dihydrazide, isophthalic acid dihydrazide, p-oxybenzoic acid dihydrazide, salicylic acid dihydrazide, and the like. These curing agents generally react in a ratio of 1:1 with the epoxy group and the active hydrogen contained in the dibasic acid dihydrazide, so when using only the dibasic acid dihydrazide compound as a curing agent, it is necessary to The basic idea is to consider the epoxy equivalent of the epoxy group-containing acrylic resin to be mixed and mix the equivalent amount. On the other hand, when a catalyst type curing agent such as dicyandiamide or imidazole type curing agent is used in combination, the equivalent amount is not necessarily required as shown in the examples. This is thought to be because the above-mentioned catalytic curing agent preferentially reacts with the liquid epoxy resin and has poor reactivity with the epoxy group of the acrylic resin used in the present invention. Therefore, it is sufficient to use dibasic acid dihydrazide in an amount equivalent to the epoxy group contained in the acrylic resin.

Other curing agents mainly include the dibasic acid dihydrazide mentioned above.
Furthermore, in order to shorten the curing time, a curing accelerator can also be used in combination. As the curing accelerator, N,N'-dialkyl urea derivatives and alkylaminophenol derivatives can be used. These curing accelerators are appropriately blended into the composition depending on the equivalent weight of the epoxy resin used and the curing conditions.
It is usually desirable to use 0.1 to 15 parts by weight per 100 parts by weight of the epoxy resin.

Further, although not essential components, viscosity modifiers, fillers, pigments, plasticizers, and the like can be added depending on the purpose.

As the viscosity modifier, thickeners such as anhydrous silicic acid, hydrated silicic acid, asbestos, finely divided calcium carbonate, and bentonite, and reactive diluents such as monoepoxide can be used in the same way as in normal applications, if necessary.

As the filler, calcium carbonate, talc, clay, etc. can be added according to the usual method.

Colorants such as carbon can be used as pigments in the same way as in normal applications.

Plasticizers such as phthalate esters and phosphate esters can also be added to impart flexibility to the adhesive after it is cured. If the plasticizer is used in a large amount, it may cause a decrease in adhesive strength or cause bleeding, so it is preferable that the plasticizer is compatible with the epoxy resin, and the amount used is in the range of 0 to 80 parts by weight per 100 parts by weight of the epoxy resin. is appropriate.

The epoxy group-containing polymer can be mixed with the epoxy resin using a conventional mixer. For example, a Niegoo, Henschel mixer, Disper, planetarium mixer, etc. can be used. In order to further form a smooth paste, it can be pulverized into fine particles using an ink roll or three rolls. The mixed epoxy resin adhesive composition is applied onto the substrate to be bonded by a conventional method such as spraying, sealer gun, brushing, etc. The substrate is generally a metal, and even if antirust oil is attached to the substrate, the adhesiveness of the composition will not be impaired after the composition is fully cured.

(Example) The present invention will be explained below with reference to Examples and Comparative Examples.

The powdered acrylic resin containing an epoxy group was a combination of methyl methacrylate (MMA), glycidyl methacrylate (GMA), and aliglycidyl ether (AGllt) as shown in Table 1. These acrylic resins include, for example, glycidyl methacrylate (
GMA) 5 parts by weight, methyl methacrylate (HMA)
) was obtained by emulsion polymerization of 95 parts by weight, followed by spray drying, and the basic particle size was about 1.0 μm and the average molecular weight was about 1.5 million.

Table 1 Powdered acrylic resin Acrylic A used in Examples MMA: GMA±95:5 2
．． 1 Acrylic B HMA: GMA=90: 10
3.2 Acrylic CHMA: AGE=95:
5 2.2 Acrylic D MMA:GMA=99:
1 0.4 Backyard ■ Tsuchifutagawa liquid epoxy resin Epicoat 482B (epoxy equivalent 190, manufactured by Yuka Shell Epoxy ■) 100 parts by weight was mixed with epoxy group-containing powder acrylic resin A-D according to the formulation shown in Table 2, and two as a curing agent. Basic acid dihydrazide was blended alone or in combination with dicyandiamide and kneaded using three rolls to obtain an adhesive composition.

This was applied to a degreased mild steel plate and a tensile shear test piece was prepared.
JIS K 6850, JIS K
6854, and was cured at 180° C. for 30 minutes to determine adhesive strength and single-character peel strength.

As in the Examples, various materials were blended according to Table 3 to prepare adhesive compositions, and the adhesive strength and T-peel force of each were determined.

As a result, it was found that the adhesive strength of each sample was lower than that of the example.

(Effects of the Invention) As explained above, by using dibasic acid dihydrazide as a curing agent in an epoxy composition prepared by mixing a liquid epoxy resin and an acrylic resin containing 0.2% by weight or more of epoxy groups, It has been found that a pregel type adhesive composition with excellent adhesive properties can be obtained. - The adhesive of the present invention changes from a sol to a gel when heated for a short time in a temperature range of about 100 to 200°C, so it can be used as a preheated adhesive with excellent adhesive strength.

Patent applicant: Nissan Motor Co., Ltd.

Claims (1)

[Claims] 1. Epoxy group content is 0 for 100 parts by weight of liquid epoxy resin containing one or more epoxy groups in the molecule.
．． 5 to 10% of powdered acrylic resin that is 2% by weight or more
An epoxy adhesive composition comprising 0 parts by weight of a dibasic acid dihydrazide compound as a curing agent.