JPH04201304A - Manufacture of laminated sheet - Google Patents

Abstract

PURPOSE:To improve impregnation and moldability at the time of molding by making use of an existing coating machine and molding press as they are by hardly improving them, by a method wherein at the time of manufacturing of prepreg by two stage impregnation, the melting point of undercoating varnish resin is made lower by at least a fixed temperature than the melting point of finish coating varnish resin. CONSTITUTION:Glass cloth is impregnated, for example, respectively with undercoating varnish and finish coating varnish, dried and prepreg is manufactured. On this occasion, a difference in the melting points between undercoating varnish resin and finish coating varnish resin is made at least 15 deg.C. With this construction, at the time of molding to a laminated sheet, at the time of a temperature rise, the undercoating varnish resin is melted and then the finish coating varnish resin is melted. Since the undercoating varnish resin and finish coating varnish are melted in order at time intervals at the time of the temperature rise like this, removal of a bubble from the prepreg becomes easy. Therefore, the laminated sheet whose dimensional stability and moisture resistance are favorable can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a method for producing a laminate with few voids, good dimensional stability, and moisture absorption resistance.

[Conventional technology]

Conventionally, a two-stage impregnation method has been employed to improve various properties of laminates. Resin formulations for undercoat varnishes for two-stage impregnation include low molecular weight resins with good impregnation properties and varnishes with low resin content. Apart from this, there are other methods that do not rely on varnish formulations, such as squeezing air bubbles with a roll or the like during the impregnation process, or using ultrasonic waves to improve impregnation properties.These methods simply improve the impregnation of the prepreg. It was something to do. Furthermore, there are methods using vacuum impregnation, vacuum presses that improve impregnation during pressing, and methods that combine these methods.

[Problem to be solved by the invention]

The purpose of the present invention is to provide a laminate with improved dimensional stability by improving impregnation and moldability during molding by using existing coating machines and molding presses as they are without much improvement. It's about doing.

In the present invention, only the resin formulation of the undercoat varnish is changed, so other properties of the laminate remain almost unchanged.

[Failure to solve the problem]

In the present invention, in producing prepreg by separately impregnating a fiber base material with two types of varnishes, the varnish to be impregnated first (
This is a method for producing a laminate, characterized in that the melting point of the resin of the undercoat varnish is 15° C. or more lower than the melting point of the resin of the varnish to be impregnated later (topcoat varnish).

The resin for the undercoat varnish used in the present invention is a bisphenol A type epoxy resin, a noholac type epoxy resin, etc., and is not particularly limited, or may have a melting point that is 15°C or more lower than that of the resin for the top coat varnish. .

However, if the resin content of the undercoat varnish is low and the amount adhered to the fiber base material is small, the effect will be small, so the resin content in the fiber base material (prepreg) after application of the undercoat varnish is preferably 25% by weight or more.

Because the difference in melting point between the resin of the undercoat varnish and the resin of the topcoat varnish is 15°C or more, when forming into a laminate,
When the temperature rises, first the resin of the undercoat varnish melts, and then the resin of the top coat varnish melts. In this way, since the resin of the undercoat varnish and the resin of the topcoat varnish are sequentially melted at time intervals when the temperature is increased, air bubbles can be easily removed from the prepreg. If this temperature is lower than 15° C., it will be difficult to melt the two resins during heating, and it will be difficult to remove air bubbles.

Next, it is impregnated with an undercoat varnish to have a predetermined resin content. This resin content is about 40 to 60% in the prepreg.

Preferably, the prepreg thus obtained is laminated and molded under the following conditions. That is, when layer-molding prepreg, at a temperature between the melting points of the two types of varnish resins,
After holding for 5 minutes or more and 30 minutes or less, the temperature is raised to a predetermined temperature and molded.

Under these molding conditions, only the resin of the undercoat varnish is melted, and the resin of the topcoat varnish is hardly melted.

By keeping this temperature for a long time, air bubbles between the monofilaments will be defoamed or will reach the interface between the resin of the undercoat varnish and the resin of the top coat varnish, and then the remaining air bubbles will be removed from the laminate by raising the temperature to a normal temperature and heating and pressurizing it. It becomes easier to go outside.

In this way, molding became easy, and it became possible to obtain a laminate with good dimensional accuracy and less warping and wrinkling by molding at low pressure.

〔Example〕

The present invention will be explained below using Examples and Comparative Examples.

A glass cloth having a thickness of 200 μm was impregnated with the undercoat varnish and topcoat varnish shown in Table 1, respectively, and dried to obtain a prepreg. The properties of the prepreg are shown in the middle column of Table 1. Next, eight sheets of this prepreg were stacked, 18μ copper foil was stacked on both sides, and lamination molding was carried out under the pressing conditions shown in the lower column of Table 1.

Formability and laminate properties are also shown in Table 1.

(Measuring method) Gel time = I Measured at 70°C.

Determine the amount of air bubbles by visually observing the nib leg.

Formability After etching and removing the steel foil, visually inspect the surface condition of the laminate and judge by the presence or absence of voids.

Dimensional stability After etching and removing the copper foil, it was treated at 170°C for 30 minutes and determined from the dimensions before and after the treatment using the following formula.

Dimensions before treatment Glass transition point (Tg): Determined by viscoelasticity measurement method.

〔Effect of the invention〕

As is clear from the above examples, the present invention, when manufacturing a prepreg by two-stage impregnation, lowers the melting point of the resin of the undercoat varnish by 15°C or more lower than the melting point of the resin of the topcoat varnish. Air bubbles in the prepreg can be easily removed, and a laminate with good dimensional stability and moisture absorption resistance can be obtained.

Furthermore, during lamination molding, a laminate with better properties as described above can be obtained by holding the resin in a greenhouse for a certain period of time at a temperature between the melting points of the two resins mentioned above.

Claims (2)

[Claims] (1) In manufacturing a prepreg by separately impregnating a fiber base material with two types of varnish, the melting point of the resin of the varnish to be impregnated first is 15°C or more lower than the melting point of the resin of the varnish to be impregnated later. A method for manufacturing a laminate. (2) When laminating and molding the prepreg obtained in claim 1, the temperature is maintained at a temperature between the melting points of the two types of varnish resins for 5 minutes to 30 minutes, and then the temperature is raised to a predetermined temperature. Characteristic manufacturing method for laminates.