JPH0441173B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a hardener solution for dicyandiamide-based epoxy resin materials and the use of this hardener solution to produce storage-stable epoxy resin solutions, in particular glass fiber reinforced The present invention relates to a method for producing storage stable epoxy resin solutions such as those used to impregnate fabrics.

Prior art Epoxy resin has high impact strength and decay resistance,
Due to its outstanding properties such as outstanding adhesion ability to both large and small materials and good light, water and chemical resistance, it has numerous uses, inter alia as lacquer resin, casting resin and binder. Used in printed circuits, and in adhesives and reinforced plastics.

In addition, in order to produce glass fiber reinforced laminates, customary epoxy resins or epoxy resin mixtures, hardeners and optionally hardening accelerators and certain amounts of hardening agents and hardening agents are generally used to adjust the viscosity constant. An epoxy resin mixture consisting of a solvent or a mixture of solvents is obtained. Dicyandiamide (see U.S. Pat. No. 2,637,715 and U.S. Pat. No. 3,391,113) is often used as a curing agent, which may also be combined with e.g. dimethylbenzylamine, 2- Curing accelerators such as methylimidazole and tetraalkylguanidine may be included.

Solvents or solvent mixtures having the task of completely dissolving all the components of the epoxy resin mixture in order to obtain a uniform distribution on the fabric to be impregnated as well as a uniform curing of the impregnated fabric are described in East German Patent Application No. 133955, methyl- or ethyl glycols, which may contain other solvents such as aromatic hydrocarbons, alkylformamides or ketones, for example as described in German Patent Application No. 3026706. Consists of glycol ethers such as

One of the main drawbacks of glycol ethers is the limited solubility of dicyandiamide in this solvent, which can lead to significant difficulties in the production and use of epoxy resin mixtures.

Problem to be Solved by the Invention It is therefore an object of the invention to develop curing agent solutions based on dicyandiamide which have particularly good solubility and good compatibility with epoxy resin mixtures.

Means for Solving the Problem According to the present invention, this problem is solved by: a) 50 to 95 parts by weight of dimethylformamide; b) a low-boiling ketone and/or a low-boiling alcohol;
~50 parts by weight and c. A curing agent solution characterized in that it contains from 5 to 32 parts by weight of dicyandiamide per 100 parts by weight of the sum of components a) and b).

Furthermore, it has surprisingly been found that the curing agent solution according to the invention has a significant solubility for dicyandiamide, both alone and in combination with other components of the epoxy resin mixture. In this way, crystal separation is prevented before or during the impregnation of the glass fiber-reinforced fabric as well as during drying.

Furthermore, the curing time is shortened with the solution according to the invention due to the synergistic effect between dicyandiamide and the solvent mixture, which was likewise unexpected.

The curing agent solution of the present invention generally comprises 50 to 95 parts by weight of dimethylformamide, a low boiling ketone and/or
Alternatively, it consists of 5 to 50 parts by weight of a low-boiling alcohol and 5 to 32 parts by weight of dicyandiamide per 100 parts by weight of the total of these components a) and b). Low-boiling ketones and low-boiling alcohols are within the scope of the present invention such solvents with a boiling point of up to 150°C.
As low-boiling ketones, acetone and/or methyl ethyl ketone are preferred, but other ketones are also suitable, such as for example diethyl ketone, dipropyl ketone, acetylacetone, vinyl methyl ketone and mesityl oxide. In the case of low-boiling alcohols, methanol, ethanol and 1-methyl-2-propanol have been found to be particularly preferred, but in principle it is possible to use, for example, n-propanol, isopropanol, n-butanol and n-pene Other alcohols such as tanol can also be used. In all cases, the boiling point of the solvent mixture must not exceed 160°C. That's because
This is because the drying conditions when producing glass fiber reinforced epoxy resin laminates are observed and no high boiling points occur. It is clear that the hardener dicyandiamide has a significant solubility in the hardener solution of up to 25% by weight at 20° C., thus exceeding the solubility of dicyandiamide in pure dimethylformamide.

This is therefore surprising since dicyandiamide is only very poorly soluble in low-boiling alcohols and low-boiling ketones.

The curing agent solutions according to the invention may optionally also contain customary curing accelerators such as dimethylbenzylamine in proportion to the dicyandiamide content.
It can be contained in amounts of up to 10% by weight, especially 2 to 5% by weight.

This curing agent solution usually has an epoxy resin content of 40~
It is particularly suitable for obtaining storage-stable epoxy resin solutions having a content of 60% by weight and used for impregnating glass fiber reinforced fabrics. As for epoxy resins, this applies to all the conventional types existing on the market. i.e. for example the trademark Epikote 828 or Araldit
An epoxy resin commercially available under the name LZ7065N-75sp can be used. The hardener solution is added to the epoxy resin, which may also be already dissolved in a suitable solvent, in such an amount that the dicyandiamide content is from 1 to 10% by weight, based on the epoxy resin content. Ru. Moreover, even after storing the epoxy resin solution for several weeks under these conditions, no crystallization of dicyandiamide or any change in the viscosity of the solution can be observed. Moreover, even after drying the impregnated fabric, no dicyandiamide crystals, which would be a hindrance during the production of laminates, can be detected.

Examples Next, the present invention will be explained in detail with reference to Examples, but the present invention is not limited thereto.

Example 1: A 20% solution of dicyandiamide was obtained from 20 g of dicyandiamide, 68 g of dimethylformamide, and 12 g of acetone, and this was mixed with the following resin materials: 50 parts by weight of Epikote 828, 7.5 parts by weight of dimethylformamide, 30 parts by weight of acetone, and cured. 12.5 parts by weight of curing agent solution is used as curing agent solution for curing.

The resin material obtained is clearly soluble and shows no increase in viscosity during storage for 3 weeks at room temperature. The gelation time of the sample at 180°C is 4 minutes.

A resin material obtained for comparison consisting of 50 parts by weight of Epikote 828, 30 parts by weight of acetone and 25 parts by weight of a curing agent solution consisting of a 10% solution of dicyandiamide in monomethyl glycol was cured for 5 minutes under the same conditions. It will gel later.

Example 2: A 10% solution from 10 g of dicyandiamide, 45 g of dimethylformamide, and 45 g of methyl ethyl ketone was obtained and mixed into the following resin material: Araldit LZ7065N−75sp
135 parts by weight, 30 parts by weight of hardening agent solution, and 10 parts by weight of dimethylformamide are used as a hardening agent solution for hardening.

This impregnating solution does not change its viscosity during 3 weeks. The gelation time for one sample at 180°C is 4.5 minutes.

Example 3: dicyandiamide 20g, Dimethylformamide 68g, 1-methoxy-2-propanol 12g Obtain a 20% solution from and combine this with the following resin material: Epikote 828 50 parts by weight, Hardener solution 12.5 parts by weight used for curing.

The resulting viscous resinous material is clearly soluble and shows only a slight increase in viscosity during storage for 3 weeks. The gelation time for one sample at 180°C is 4 minutes.

Example 4: A 20% solution from 20 g of dicyandiamide, 68 g of dimethylformamide, and 12 g of ketylethyl ketone was obtained and mixed into the following resin material: Araldit LZ7065N-75sp
133 parts by weight, 15 parts by weight of hardener solution, 12.5 parts by weight of dimethylformamide, and 12.5 parts by weight of methyl ethyl ketone are used for curing.

The viscosity of this impregnating solution remains stable. 180
The gelation time for one sample at °C is 4.5 minutes.

Example 5: 0.2 parts by weight of dimethylbenzylamine curing accelerator are added to the resin mixture described in Example 4. A piece of glass fiber fabric is impregnated with this solution, crushed and dried for 10 minutes at 160° C. in a drying box. Non-stick prepreg has a resin content of 35%. When observed under a polarizing microscope, no intervening dicyandiamide crystals can be measured.

Claims (1)

[Claims] 1. A curing agent solution for an epoxy resin material based on dicyandiamide comprises: a) 50 to 90 parts by weight of dimethylformamide; b) a low-boiling ketone and/or a low-boiling alcohol.
Curing agent for epoxy resin materials based on dicyandiamide, characterized in that it contains 5 to 50 parts by weight and c 5 to 32 parts by weight of dicyandiamide per 100 parts by weight of the sum of components a) and b) solution. 2 Claim 1 containing acetone and/or methyl ethyl ketone as a low boiling point ketone
Curing agent solution as described in section. 3. The curing agent solution according to claim 1 or 2, which contains methanol and/or ethanol and/or 1-methoxy-2-propanol as the low-boiling alcohol. 4 a Dimethylformamide 50 to 90 parts by weight, b Low boiling point ketone and/or low boiling point alcohol
c) a curing agent solution for epoxy resin materials based on dicyandiamide containing 5 to 32 parts by weight of dicyandiamide per 100 parts by weight of the sum of components a) and b); Hardener solution for epoxy resin materials based on dicyandiamide, characterized in that this hardener solution contains a hardening accelerator in an amount of 1 to 10% by weight, based on the dicyandiamide content. 5 A storage-stable epoxy resin solution, a. 50 to 90 parts by weight of dimethylformamide, b. a low-boiling ketone and/or a low-boiling alcohol.
5 to 50 parts by weight and a curing agent solution containing 5 to 32 parts by weight of dicyandiamide per 100 parts by weight of the sum of components a) and b),
A process for producing a storage-stable epoxy resin solution, characterized in that the curing agent solution is initially introduced in such an amount that the dicyandiamide content is from 1 to 10% by weight, based on the epoxy resin content.