JPS6317855B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing an epoxy prepreg that provides a composite material exhibiting good heat resistance. Furthermore, an aromatic polyamine containing imide groups with excellent solubility is used as an epoxy resin curing agent, and the reinforcing fibers are impregnated with a solution of a low-boiling non-amide solvent.
This invention relates to a method for producing prepreg with excellent drying properties.

[Conventional technology]

It is already known that aromatic polyamines are used as curing agents to improve the heat resistance of epoxy resins. On the other hand, attempts have been made to improve heat resistance by introducing a skeleton of polyimide, which is a type of heterocyclic polymer exhibiting high heat resistance, into epoxy resins.
However, these imide skeleton-containing polymers and oligomers generally have a high melting point and poor solubility, resulting in poor moldability. In order to improve moldability, a method is known in which polyimide is formed via intermediates such as polyamic acid, polyamide ester, alcohol half ester of tetracarboxylic acid, etc., but these intermediates are used to cure epoxy resin. If this is carried out, many side reactions occur and it is difficult not only to introduce the desired imide group but also to cure the aromatic polyamine to give a heat-resistant cured product. In order to solve these problems, attempts have been made to use solvent-soluble imide group-containing epoxy compounds, imide group-containing curing agents, etc.
Publication No. 166531. ) However, because of their imide groups, they generally have low solubility and are only soluble in high-boiling amide solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide. Prepreg impregnated with a solution of
In particular, it causes a decrease in heat resistance.

[Object of the Invention] The present invention provides a method for producing a prepreg with excellent drying properties, which improves the above-mentioned difficulties and impregnates reinforcing fibers with an excellent imide group-containing epoxy resin solution after dissolution using a low-boiling non-amide solvent. It provides:

That is, an epoxy compound having at least one epoxy group in the molecule, the general formula () (X is a tetravalent aromatic group, and each of the two sets of carbonyl groups is bonded to an adjacent carbon atom of the aromatic group,
R ₁ and R ₂ are a hydrogen atom, a halogen atom, or an alkyl group, at least one of which is an alkyl group, and n is an integer of 1 or more. It was found that a prepreg obtained by dissolving a hardening agent in a non-amide solvent having a boiling point of 150° C. or lower and impregnating reinforcing fibers with the solution has excellent drying properties, and the present invention was achieved.

[Structure of the invention]

To explain the present invention in detail, various kinds of epoxy compounds having at least one epoxy group in the molecule can be used as one component constituting the epoxy resin solution. Epibis-based epoxy compounds represented by diglycidyl ether of bisphenol A, novolak-based epoxy compounds such as polyglycidyl ethers of phenol novolak or cresol novolak, aminophenols, amine epoxy compounds such as glycidyl compounds of aromatic diamines, and Although one or more types of aliphatic and alicyclic epoxy compounds can be used, an amine epoxy compound, which is a polyfunctional epoxy compound, is preferable from the viewpoint of heat resistance.

The curing agent imide group-containing aromatic polyamine represented by the formula () constituting the epoxy resin solution is an aromatic tetracarboxylic acid or a derivative thereof and an aromatic diamine component. o-alkyl substituted aniline-formaldehyde condensate (C _1-4 as alkyl,
Ethyl group is preferred. ) can be obtained by reaction with Aromatic tetracarboxylic acids include pyromellitic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, 3,3',4,4'-
Diphenyl ether tetracarboxylic acid, 3,3',
4,4'-biphenyltetracarboxylic acid, 2,3,
6,7-naphthalenetetracarboxylic acid, 2,3,
4,5-thiophenetetracarboxylic acid, 2,2-
Bis(3,4-dicarboxyphenyl)propane and the like and one or more of these isomers are used. These aromatic tetracarboxylic acid components can be used in the form of derivatives such as lower alkyl esters and dianhydrides, but it is preferable to use dianhydrides in view of their reactivity.

Aromatic diamine components, such as o-ethylaniline-formaldehyde condensates, are disclosed in Japanese Patent Application Laid-open No. 47
- In an aqueous medium as described in Publication No. 31961,
It can be obtained by reacting at 60 to 100°C in the presence of a strong inorganic acid such as hydrochloric acid or sulfuric acid. In the above reaction, the diamine component 3,3'-diethyl-
In addition to 4,4'-diaminodiphenylmethane, triamine, tetramine, etc. are produced as by-products. Diamine components can be easily obtained by separating these by-products by distillation, but these by-products can be used in the production of imide group-containing aromatic polyamines without being separated. However, if the amount of polyamine greater than triamine increases, gelation tends to occur during production of the imide group-containing aromatic polyamine, so the amount of polyamine is preferably 70% by weight or less. In addition, by adding aniline during the condensation reaction of o-ethylaniline, 3,3'-diethyl-4,4'-diaminophenylmethane, 3-
Ethyl-4,4'-diaminophenylmethane, 4,
A mixture consisting mainly of the three components of 4'-diaminodiphenylmethane is obtained, which can also be effectively used in the present invention. o-toluidine, o- in place of aniline
An o-alkylaniline-formaldehyde condensate containing an unsubstituted aniline derivative at the p-position such as chloroaniline can also be used.

The curing agent imide group-containing aromatic polyamine represented by the formula () is combined with the above-mentioned aromatic tetracarboxylic acid or its derivative and a molar excess of o-ethylaniline-
It can be produced by reacting a formaldehyde condensate in a solvent. As the solvent, in addition to amide solvents such as N-methyl-2-pyrrolidone, N,N'-dimethylacetamide, and N,N-dimethylformamide, m-cresol, phenols, and dimethyl sulfoxide are used.
The molar ratio of the aromatic tetracarboxylic acid component and the aromatic diamine component used is n/(n+
1), and the value of the integer n is 1
~10 is preferred.

The amount of the imide group-containing aromatic polyamine in the epoxy resin solution can be selected from a wide range of 0.1 to 2.0 equivalents as the active hydrogen amount of the amine relative to the epoxy group in the epoxy compound, but it is preferably 0.5 to 1.2 equivalents, which is approximately the same amount. . Further, an aromatic diamine can be used in place of a part of the imide group-containing aromatic polyamine. Various aromatic diamines can be used, but for example, those with the formula H ₂ N-R-NH ₂
(wherein R is a divalent aromatic group having up to 30 carbon atoms and may optionally also contain oxygen atoms, nitrogen atoms, silicon atoms, phosphorus atoms and similar inert groups). The aromatic diamine shown is Suitable examples of R include monocyclic or polycyclic aromatic groups with or without substituents, and multiple aromatic groups in which these groups are bonded via a direct carbon-carbon bond or a divalent linking group. can be mentioned. As the divalent linking group, -O-, -SO ₂ -, -
S-, -CO-, alkylene groups having 1 to 3 carbon atoms, and the like.

As the organic solvent that is a component of the epoxy resin solution, a non-amide organic solvent with a boiling point of 150° C. or lower is used. Examples of these solvents include ketone solvents such as acetone, methyl ethyl ketone, and methyl isobutyl ketone, and ether solvents such as tetrahydrofuran and dioxane ethylene glycol dimethyl ether. Among these, those with a boiling point of 100° C. or less are preferred from the viewpoint of drying properties of the prepreg, and acetone, methyl ethyl ketone, tetrahydrofuran, etc. are usually used.

A prepreg can be produced by impregnating reinforcing fibers with a resin solution containing the three components described above and, if necessary, a curing accelerator such as imidazoles and a BF ₃ amine complex. The method for impregnating reinforcing fibers is to use an epoxy resin concentration of 10~
A method in which the reinforcing fibers are immersed in a bath with a low concentration solution of 50% by weight, or a method in which a three-component resin solution with a lower fluidity is made into a higher concentration solution is heated and pressed with a heated roll, etc., and directly impregnated into the reinforcing fibers. Prepreg can be produced by any method including the holt-melt method. Examples of reinforcing fibers used here include glass fibers, aramid fibers, carbon fibers, alumina fibers, and silicon carbide fibers.

〔Example〕

The present invention will be described in detail below with reference to Examples, but the present invention is not limited thereto unless it exceeds the scope of the claims.

Reference Example 1 Synthesis of imide group-containing aromatic polyamine A (hereinafter referred to as polyamine A) 3,3 obtained by vacuum distillation of o-ethylaniline-formaldehyde condensate (“Kayahard A-A” manufactured by Nippon Kayaku Co., Ltd.) 41.0 g of '-diethyl-4,4'-diaminodiphenylmethane was dissolved in 36 ml of N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP), and anhydrous 3,3',4,4'-benzophenone was added to this. Tetracarboxylic acid (hereinafter abbreviated as BTDA) 26.0g of NMP120
ml of solution was added dropwise over about 30 minutes. After stirring at room temperature for 2 hours, the mixture was heated to 200° C. for 4 hours, and the water produced was distilled off together with NMP. After cooling, polyamine A was precipitated with water/ethanol, and after washing with ethanol.
Vacuum drying was performed at 100°C for 50 hours. The yield was 94%. Furthermore, the presence of primary amino groups and imide groups was confirmed by the infrared absorption spectrum of the produced imide group-containing polyamine.

Reference Example 2 Synthesis of imide group-containing aromatic polyamine B (hereinafter abbreviated as polyamine B) Almost same as Reference Example except that 51.5 g of 3,3'-diethyl-4,4'-diaminodiphenylmethane and 43.5 g of BTDA were used. Polyamine B was synthesized in a similar manner. The yield was 96%.

Reference Example 3 Synthesis of imide group-containing aromatic polyamine C (hereinafter abbreviated as polyamine C) Reference except that 71.3 g of 3,3'-diethyl-4,4'-diaminodiphenylmethane and 30.6 g of pyromellitic anhydride were used. Polyamine C was synthesized using almost the same procedure as in Example 1. The yield was 97%.

Example 1 117 parts by weight of polyamine A1 obtained in Reference Example 1,
100 parts by weight of an amine epoxy compound ("Araldite MY-720" manufactured by Ciba Geigy) was dissolved in methyl ethyl ketone (hereinafter abbreviated as MEW) at a concentration of 35% by weight. A uniformly concentrated red solution was obtained. In this solution bath, carbon fiber (product name: Torayca T manufactured by Toray Industries, Ltd.)
-400”) was continuously immersed and spread in a cylindrical shape on a drum with a diameter of 30 cm, and then dried by heating with a far-infrared heater with a surface temperature of 100°C. After 30 minutes, the surface tackiness disappeared. At this point, the volatile content of the prepreg was 5.2% by weight.

Example 2 232 parts by weight of polyamine B obtained in Reference Example 2,
100 parts by weight of the amine epoxy compound used in Example 1 was dissolved in MEK at a concentration of 35% by weight. A deep red homogeneous solution was obtained. Using this epoxy resin solution, a prepreg was prepared by impregnating carbon fibers in the same manner as in Example 1, and dried under the same conditions.
The volatile content of the prepreg was 5.8% by weight.

Example 3 1 part by weight of polyamine C7 obtained in Reference Example 3 and 100 parts by weight of the amine epoxy compound used in Example 1 were dissolved in tetrahydrofuran at a concentration of 30% by weight. A deep red homogeneous solution was obtained. A prepreg was prepared using this epoxy resin solution in the same manner as in Example 1, and dried under the same conditions. The volatile content of the prepreg was 3.9% by weight.

Reference Example 4 Ten prepregs obtained in Example 1 were laminated in one direction and heated at a temperature increase rate of 3.3° C./min under a high vacuum of 750 to 760 mmHg. 7 for prepreg when reaching 120℃
It was pressurized at a pressure of Kg/cm ² and held at 120°C for 1 hour.
After that, the temperature was further increased to 150℃ while maintaining the pressurized state.
The curing reaction was carried out at 180°C for 1 hour and 2 hours at 180°C.
Once cooled, the pressure was restored, and the mold was demolded, followed by curing in an oven at 220° C. for 6 hours to produce a cured product with a thickness of 2 mm. The glass transition temperature (TMA method) of this cured product is 176℃
It was hot. Also, the bending strength at 180℃ is 132℃/mm ²
(V _f =57%).

Comparative Example In Reference Example 1, N, N was used instead of the solvent MEK.
- An epoxy resin solution was prepared using dimethylformamide. A prepreg was prepared using this solution in the same manner as in Example 1 and dried under the same conditions. When dried using a far-field heater at 100°C, it became extremely sticky and difficult to handle. Furthermore, the temperature inside the tank
By continuing drying in a hot air circulation constant temperature bath at 100°C, the volatile content was reduced to 5.5% by weight.

Using the thus obtained prepreg, a 2 mm thick cured product was produced in the same manner as in Reference Example 4. The glass transition temperature (TMA method) of this cured product is
It was 112℃.

〔Effect of the invention〕

According to the method of the present invention, since the obtained prepreg is a low boiling point solvent, it is easy to dry the prepreg,
Further, the amount of solvent remaining in the cured product is almost nil, and the influence of the residual solvent on the physical properties of the cured product, especially the heat resistance, can be ignored.

Claims (1)

[Claims] 1 (a) an epoxy compound having at least one epoxy group in the molecule; (b) general formula () (X is a tetravalent aromatic group, two sets of carbonyl groups are each bonded to adjacent carbon atoms of the aromatic group, R ₁ and R ₂ are a hydrogen atom, a halogen atom, or an alkyl group, and at least one of them is an alkyl group, n is an integer of 1 or more); and (c) a non-amide organic solvent with a boiling point of 150°C or less. A method for producing prepreg, characterized by impregnating it with. 2. The manufacturing method according to claim 1, wherein the epoxy compound is an amine epoxy compound.