JPS5948068B2 - epoxy resin varnish - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to fiber reinforced plastic (hereinafter abbreviated as FRP)
The present invention relates to an epoxy resin varnish for prepregs used in the production of prepregs, and more specifically to a varnish for producing prepregs that cures at low temperatures, particularly at temperatures of 140° C. or lower, and has a long shelf life.

Conventionally, the demand for prepreg for use in fishing rods and golf club shafts has increased dramatically, and along with this, there has been a strong demand for the provision of FRP that is inexpensive and has good quality and performance.

Especially carbon fiber reinforced plastic (hereinafter referred to as CFRP)
In this case, there is a demand for prepreg or CFRP using epoxy resin instead of phenolic resin in terms of quality and performance, but in general, epoxy resin is difficult to cure at low temperatures, and carbon fiber itself hardly expands when heated. , which exhibits the characteristic of slight shrinkage, increases the residual stress during molding as the curing temperature increases, causing problems such as bending and cracking of the molded product even if the thread arrangement is slightly disturbed. In terms of performance, especially with thin tubular fishing rods,
It was becoming a big problem. Additionally, if any organic solvent remains in the prepreg, it will impair the heat resistance of the cured resin and cause blistering in the molded product.For this reason, conditions were adopted to increase the curing temperature and reduce the amount of residual solvent as much as possible. I had no choice but to do it.

Furthermore, the conditions required for prepreg include not only hardening properties but also long shelf life of the prepreg.
There are not many known epoxy resin varnishes that simultaneously satisfy these requirements, such as appropriate tackiness and drapability, and the ability to cure in a short time. There are major restrictions.

For example, low-temperature curing hot-melt epoxy resins have been developed to avoid problems caused by solvents, but these hot-melt epoxy resins have poor impregnation properties, at least for the manufacture of cloth prepregs, and cannot be made into prepregs. It's normal. It is known that by using dicyandiamide as a curing agent and using an imidazole derivative or a urea derivative as a curing accelerator, an epoxy resin with not only curability but also improved shelf life and heat resistance can be obtained. Generally, only methyl cellosolve, dimethylformamide, etc., which are poorly soluble in organic solvents and have a high boiling point, are used, and troubles caused by the residual solvents cannot be avoided.

The present inventors have focused on the low-temperature curing properties of epoxy resins using dicyandiamide as a curing agent, and have conducted intensive research into epoxy resin varnishes that are free from the above-mentioned drawbacks, especially troubles caused by solvents, and have thus arrived at the present invention. It is.

That is, the purpose of the present invention is to provide low temperature curability,
An object of the present invention is to provide an epoxy resin canis that has excellent shelf life and heat resistance and is useful for FRP or CFRP.

Another object is to provide an epoxy resin varnish that has a small amount of residual organic solvent even when cured at a low temperature and is free from troubles caused by residual solvent. Such objects of the present invention can be achieved by the invention described in the claims.
In other words, the feature of the present invention is that one component is a solvent that can dissolve well the epoxy resin and dicyandiamide, which are components that have different solubility behavior in the solvent, and have a low boiling point and a small amount of residual solvent after curing. As an epoxy resin varnish, as a solvent for the epoxy resin varnish,
Ketones and alcohols with a boiling point of 110°C or less, respectively, in a weight ratio of 40 to 60 for ketones and 60 for alcohols.
The point is to use solvents mixed at a ratio of ~40%. In other words, dicyandiamide is water-soluble and relatively easy to dissolve in alcohols, but hardly dissolves in ketones, whereas epoxy resins, especially solid epoxy resins, dissolve well in ketones. is difficult to dissolve in alcohols, and there are no known examples of using alcohols as a solvent for epoxy resins. However, when ketones and alcohols, especially low-boiling ketones and alcohols each having a boiling point of 110°C or less, are mixed together under certain conditions, both the epoxy resin and dicyandiamide, which have different solubility, are mixed together. It dissolves well and forms a homogeneous solution. However, if the mixing ratio of ketones or alcohols is outside the range of 40 to 60 by weight, the solubility of either the dicyandiamide or the epoxy resin decreases, and the stability deteriorates, causing one of the components to deteriorate over time. may precipitate, which is not preferable.

In addition, ketones and alcohols should preferably have as low a boiling point as possible, as higher boiling points make it more difficult to remove the solvent from the prepreg, and also reduce the drying rate of the prepreg, reducing productivity. do not have.

However, if ketones and alcohols each having a boiling point of 110°C or lower are used, the amount of residual solvent in the prepreg can be sufficiently reduced to a level that poses no practical problems, and the drying speed is fast, improving productivity. It is. Examples of the ketones used in the present invention include acetone, methyl ethyl ketone, methyl-n-propyl ketone, diethyl ketone, etc., and examples of the alcohols include methyl alcohol, ethyl alcohol, n-propyl alcohol, and isopropyl alcohol. Examples include alcohol, isobutyl alcohol, sec-butyl alcohol, tertiary-butyl alcohol, etc., and one or more of these may be used in combination. In addition, as the epoxy resin, various known epoxy resins can be used, including, but not limited to, EP-828, EP-
1001, EP-1004, EP-1009, EP-1
52, EP-154, ELM- manufactured by Sumitomo Chemical Co., Ltd.
120, ELM-434, ESM-1402, ESCH
-220 etc.

In addition to dicyandiamide as a curing agent, the epoxy resin varnish of the present invention contains an imidazole derivative as a curing accelerator. There is no problem in adding urea derivatives such as "Kyuazol" 2p4MHZ manufactured by Shikoku Kasei Kogyo Co., Ltd. and DCMU manufactured by Hodogaya Chemical Industry Co., Ltd. as desired. By blending, it cures at a low temperature of 140℃ or less, has a shelf life of at least 1 month at 20℃, and does not leave any solvent remaining in the prepreg after curing, reducing heat resistance caused by residual solvent. This method has an excellent effect of reducing molded product defects such as blisters and cracks.Moreover, it is possible to produce high-quality, high-performance prepregs with high productivity and even resin impregnation at low temperatures using a wet method. , which is extremely advantageous industrially.Hereinafter,
The present invention will be explained in more detail with reference to Examples.

Example 1 60 parts of Epicoat 154 manufactured by Siel Kagaku Co., Ltd., 40 parts of Epicoat 1007, 4 parts of dicyandiamide, 5 parts of dichlorophenyl-1,1 dimethylurea, methyl ethyl ketone and ethyl alcohol were mixed in various proportions. A resin varnish having a resin concentration of 40% by weight was prepared by dissolving it in a mixed solvent, and the solubility and stability of the varnish were investigated.

The results are shown in Table 1. When the ethyl alcohol content was less than 40% by weight, dicyandiamide was not sufficiently dissolved, and when it exceeded 60% by weight, the epoxy resin was not sufficiently dissolved.

Example 2 Of the resin varnishes prepared in Example 1, a varnish containing 50% by weight of ethyl alcohol was used to prepreg a hybrid fabric using glass fibers and carbon fibers for the warp yarns and glass fibers for the weft yarns.

That is, the cloth was immersed in an impregnation bath filled with varnish to be impregnated with the resin solution, and then continuously placed in an oven to dry. The maximum temperature in the oven was set at 120°C. The running speed of the cloth was adjusted to dry between 3 and 5 minutes, but in all cases the amount of residual solvent in the prepreg after drying was 0.5% by weight or less, and the shelf life of the prepreg was 20% by weight or less. ℃ for more than 1 month, and a good prepreg was obtained. In addition, the obtained prepreg was heated to 130°C.
After curing for 1 hour, it was cured normally. Example 3 A resin varnish was prepared under the same conditions as in Example 1, except that the following mixed solvent was used.

Claims (1)

[Claims] 1. An epoxy resin varnish obtained by dissolving an epoxy resin and dicyandiamide in a mixed solvent consisting of a ketone having a boiling point of 110°C or less in a weight ratio of 40 to 60 and an alcohol having a boiling point of 110°C or less in a weight ratio of 60 to 40.