JPH032372B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a curing agent for epoxy resins. More specifically, the present invention relates to a curing agent for aromatic amine-based epoxy resins that provides a cured product with excellent heat resistance, strength (tensile, bending, compression), hardness, and flexibility by heat curing. Conventionally, aromatic amine curing agents (for example, 4,
4'-diaminodiphenylmethane, 4,4'diaminodiphenyl sulfone, metaphenylenediamine, etc.) are known to provide cured epoxy resins with excellent heat resistance, strength, and hardness, and are useful for electrical and electronic applications. It is used in applications such as casting resins, anticorrosion paints, high-hardness jigs and cast products, and structural adhesives. However, cured epoxy resin products using conventional aromatic amine curing agents have a low bending deflection rate or tensile elongation rate, that is, they lack flexibility, and for example, in paints, the paint film is likely to crack due to impact.
Adhesives have problems such as not having the expected peel strength, and cast products tend to crack due to thermal shock, etc., so there is a strong desire to improve flexibility. On the other hand, as a method to increase the flexibility of cured epoxy resin products, it is known to add a flexible epoxy resin, a flexible curing agent, a flexibility imparting agent, etc. , diglycidyl ether of polyalkylene glycol, diglycidyl ester of dimer acid, etc.
Examples of flexibility curing agents include polyamide amines made of dimer acid and polyamines, dodecenylsuccinic anhydride, polyethers containing NH ₂ or COOH groups at the ends, and polyesters containing COOH groups at the ends. There are polyesters with OH groups at the ends, polyalkylene ethers, polysulfides with thiol groups at the ends, etc., but the cured products obtained by blending these with the conventional combination of aromatic amine and epoxy resin are not flexible. Although it was improved, it still had the disadvantage that its original features of high heat resistance, strength, and hardness were significantly reduced. The present inventors have discovered that epoxy resin cured products obtained using conventional aromatic amine curing agents have excellent heat resistance,
As a result of repeated studies on an epoxy resin curing agent that improves the pending flexibility without substantially impairing strength or hardness, the present invention was achieved. That is, the present invention has the general formula (In the formula, R is H, an alkyl group having 1 to 3 carbon atoms (however, H is 50 mol% or less of the total aniline skeleton),
X represents H, a group selected from an alkyl group having 1 to 3 carbon atoms, and an electron-withdrawing group, and n represents an arbitrary number from 1 to 5. ) is a curing agent for epoxy resins (hereinafter referred to as AF amine). In the general formula [1], R is H or an alkyl group having 1 to 3 carbon atoms. However, H is at most 50 mol%, preferably at most 30 mol%, of the total aniline skeleton. When R is H, the amount of primary aniline skeleton is
If it is more than 50 mol%, there is a drawback that the flexibility of the cured epoxy resin product decreases. Examples of the alkyl group having 1 to 3 carbon atoms include a methyl group, an ethyl group, an n-propyl group, and an i-propyl group. Among these, methyl and ethyl groups are particularly preferred. When the number of carbon atoms in R is 4 or more, there is a drawback that the hardness and heat resistance of the cured epoxy resin decrease. In the general formula [1], R is not limited to one type, and two or more types may be mixed. In general formula [1], Examples of electron-withdrawing groups include halogen groups such as F, Cl, and Br, nitro groups, and trifluoromethyl groups. Among these, preferred are H, a methyl group, an ethyl group, or a halogen group. In the general formula [1], X is not limited to one type, and two or more types may be mixed. In general formula [1], n is any number from 1 to 5, preferably from 1 to 4. If n is smaller than 1, heat resistance and hardness will decrease, and if n is larger than 5, heat resistance and hardness will improve, but flexibility will deteriorate. This n is a number related to the degree of condensation of aromatic rings, and indicates that the larger n is, the larger the molecular weight of AF amine is. In the method for producing AF amine described below, for example, when AF amine is produced from x moles of N-methylaniline and y moles of formaldehyde, n is calculated by the following formula. n=(2y-x)/(x-y) To give a specific example of the AF amine represented by the general formula [1], for example, etc. AF amine can be prepared by known methods, for example, from 1 to 1 carbon atoms.
It can be obtained by condensing N-alkylaniline of No. 3 or a mixture of N-alkylaniline and primary aniline with formaldehyde under acidic conditions,
The method is not limited to this method, but primary aniline may be condensed with formaldehyde and then N-alkylated, or a condensed aromatic hydrocarbon may be nitrated, reduced, and further N-alkylated. of the present invention
AF amine may be a single compound where n is an integer, but
From the viewpoint of compatibility with the epoxy resin, a mixture of various single compounds is better, and more preferably n=0
0 to 30% of compounds, n=1 10 to 60%, n=2
It is a mixture of about 10 to 50% of n = 3 to 5, 0 to 40% of n = 3 to 5, and 0 to 30% of n = 6 or more. Under acidic conditions, N
- AF amines obtained by condensation of alkylanilines and formaldehyde are usually such mixtures. The epoxy resin used in combination with AF amine may be any ordinary one, such as (1) phenol ether epoxy resin [condensate of bisphenols and epichlorohydrin, condensate of novolac phenol resin and epichlorohydrin], (2) ) Ether-based epoxy resin (condensation product of polyol, polyether polyol, etc. and epichlorohydrin), (3) Ester-based epoxy resin [copolymer of methacrylic acid glycidyl ester and ethylenic double bond monomer (acrylonitrile, etc.) (4) Glycidyl-type epoxy resins such as glycidylamine-based epoxy resins [condensates of amines and epichlorohydrin] and non-glycidyl-type epoxy resins such as cycloaliphatic epoxy resins, epoxidized polybutadiene, and epoxidized soybean oil. Details of epoxy resins are described in "Basic Synthetic Resin Chemistry (New Edition)" (1975 edition), written by Tadahiro Miba, published by Gihodo, pp. 371-392. Among epoxy resins, phenol ether is preferred. type epoxy resins and glycidylamine type epoxy resins.These epoxy resins may be used alone or in combination of two or more types.The curing agent of the present invention contains 1 equivalent of epoxy resin. Normally active hydrogen equivalent is 0.5 to 1.5, preferably 0.8 to
It is blended at a ratio of 1.2. If the active hydrogen equivalent ratio of the curing agent is less than 0.5 or greater than 1.5, the heat resistance and hardness of the cured epoxy resin product decreases, which is undesirable.
When using a curing agent, the epoxy resin and the curing agent may be mixed as they are or dissolved in a solvent at room temperature or under heating. Examples of the solvent include ketones (acetone, methyl ethyl ketone, methyl isobutyl ketone, etc.), cellosolves (methyl cellosolve, ethyl cellosolve), amides (dimethylformamide, etc.). The curing temperature is usually 70-220°C, preferably 100-200°C.
The curing time is 0.5 to 15 hours, preferably 1 to 10 hours. The curing agent of the present invention can be used in combination with other curing agents for epoxy resins, if necessary. For example, amine curing agents {aliphatic amines (triethylenetetramine, tetraethylenepentamine, etc.), polyamide amines (condensates of dimer acids and polyamines),
Aromatic amines (4,4'-diaminodiphenyl sulfone, 4,4'-diaminodiphenylmethane, N,
N'-dimethyl-4,4'-diaminodiphenylmethane, N,N'-diethyl-4,4'-diaminodiphenylmethane, N,N'-dimethyl 3,3'-diaminodiphenylmethane)}, Phenol curing agent {Bisphenols (bisphenol A, bisphenol F, bisphenol S, etc.), phenolic resins (novolac phenol resin, novolac cresol resin), vinylphenol polymers (poly-
P-vinylphenol, etc.)}.
The amount of other curing agents for epoxy resins is 0 to 50% by weight, preferably 0 to 30% by weight based on the total curing agent, in view of heat resistance, strength, hardness, and flexibility. When using the curing agent of the present invention, reactive diluents such as olefin oxide, glycidyl methacrylate, styrene oxide, phenyl glycidyl ether, phenols, tertiary
Curing accelerators such as class amines, imidazoles, boron trifluoride complex salts, pyrazoles, and aminotriazoles may be added. Fillers such as silica powder, aluminum powder, mica, and calcium carbonate may also be added. These amounts are typically 0 to 15% by weight for reactive diluents, 0 to 5% for accelerators, and 0 to 70% by weight for fillers based on the curing agent and epoxy resin formulation. It is. The cured epoxy resin obtained using the curing agent of the present invention has superior flexibility compared to that obtained using conventional aromatic amine curing agents, and has comparable heat resistance and Because of its strength and hardness, it is useful in electrical and electronic encapsulants, anticorrosion paints, structural adhesives, jigs, molded products, and other applications that require particularly high mechanical properties. The present invention will be further explained below with reference to Examples, but is not limited thereto. Production example of the curing agent (AF amine, a to i) of the present invention In a four-necked flask equipped with a reflux condenser, thermometer, dropping funnel, and stirrer, 321 g (3 mol) of N-methylaniline, 36% Hydrochloric acid 319.4g (3.15mol)
was charged, and 162.2 g (2 mol) of a 37% formaldehyde aqueous solution was added dropwise from the dropping funnel over 1 hour while maintaining the liquid temperature at 30 to 40°C. After stirring at 30-40°C for 2 hours, the temperature was raised to 90-95°C and further stirred for 2 hours. The reaction solution was cooled to room temperature, neutralized with 262.5 g (3.15 mol) of 48% sodium hydroxide solution, and the condensate was extracted with 300 c.c. of toluene.
Washed 4 times with cc water. Under reduced pressure (13mmHg), 160
Toluene was distilled off at 50°C to obtain AF amine a having a viscosity of 33 poise at 50°C and an amine value of 477. In the same manner, b to i listed in Table 1 were obtained.

[Table] Example 1 Sumiepoxy ELM434 (manufactured by Sumitomo Chemical Co., Ltd., epoxy equivalent
124) and uniformly melted at 100°C, this was molded into a 2 mm layer sheet under the conditions of 120°C x 2 hours + 160°C x 2 hours. The physical properties of these cured products are 4,4'-
Comparison was made with a cured epoxy resin obtained in a similar manner using diaminodiphenyl sulfone, aniline formaldehyde condensate (n = 1), and N,N'-dimethyl-4,4'-diaminodiphenylmethane as a curing agent. . The results are shown in Table 2.

[Table] Table 2 shows that the curing agent of the present invention is an epoxy resin that has the same level of heat resistance, strength, and hardness as the conventional aromatic amine curing agent, and exhibits far superior flexibility. It can be seen that a cured resin product is obtained.

Claims (1)

[Claims] 1. General formula (In the formula, R is H, an alkyl group having 1 to 3 carbon atoms (however, H is 50 mol% or less of the total aniline skeleton),
X represents H, a group selected from an alkyl group having 1 to 3 carbon atoms, and an electron-withdrawing group, and n represents an arbitrary number from 1 to 5. ) A curing agent for epoxy resins.