JPH0364307B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a laminate suitable for printed wiring. BACKGROUND OF THE INVENTION In recent years, laminates formed by impregnating a glass nonwoven fabric as a base material with an epoxy resin, which is a thermosetting resin, have come into widespread use as laminates for printed wiring. This is because properties such as electrical insulation are comparable to epoxy resin laminates made of glass cloth as a base material, and furthermore, they have excellent punching workability. However, glass nonwoven fabrics are usually made by cutting glass fibers into appropriate lengths.
It is manufactured by dispersing it in water and forming it on a running net, and epoxy resin powder or emulsion is used as the binder for the glass fibers. Problems with the Prior Art Therefore, in the laminate using the above glass nonwoven fabric as a base material, the bonding agent of the glass fibers is thermally softened during the molding process, making it difficult to withstand the flow of the thermosetting resin impregnated into the base material. The problem was that the non-woven fabric could break due to the failure, and a normal laminate could not be obtained. Furthermore, this phenomenon of nonwoven fabric breakage occurs because the binder that can be used in the nonwoven fabric papermaking process is inherently susceptible to thermal softening, and cannot be prevented even if the amount of binder used is increased. For this reason, during lamination molding, compared to the case of glass cloth base laminates, it is necessary to slow the clamping speed of the hot platen or lower the molding pressure to reduce resin flow. Naturally, the number of air bubbles included in the glass nonwoven fabric base laminate increased, which caused deterioration of properties such as moisture resistance and heat resistance. An object of the present invention is to provide a laminate that does not cause breakage of the glass nonwoven fabric during molding, does not contain air bubbles, and has excellent moisture resistance and heat resistance by applying sufficient molding pressure. Means for Solving the Problems In order to achieve the above object, the laminate of the present invention uses glass fibers with a fiber length of 2 mm as a sheet-like base material.
A glass nonwoven fabric containing 10 to 40% by weight of the above softwood kraft pulp is used. To prevent nonwoven fabric from breaking, the upper limit of the fiber length of softwood kraft pulp in glass nonwoven fabric is 10 mm. Function Softwood kraft pulp mixed with glass fiber has the effect of binding the glass fibers, increasing the strength of the glass nonwoven fabric, and reducing its strength deterioration even at high temperatures. As cellulose fibers to be mixed with glass fibers, in addition to softwood kraft pulp, vascular fibers such as bamboo and Manila hemp, bast fibers of flax, hemp, and mitsumata, and wood fibers of hardwood have been extensively tested. Coniferous kraft pulp was selected because it was the best in terms of electrical insulation properties of the laminate. The glass nonwoven fabric used in the present invention is produced by mixing softwood kraft pulp with glass fibers cut into appropriate lengths, dispersing the mixture in water, and forming it onto a running net. If the fiber length of the softwood kraft pulp to be mixed is shorter than 2 mm, its dispersibility is good, but the strength of the glass nonwoven fabric cannot be increased and breakage of the nonwoven fabric during molding cannot be prevented. On the other hand, if long fibers are mixed,
As the dispersibility is poor and the longitudinal/lateral strength ratio of the glass nonwoven fabric increases, the directionality of the laminate using this increases, causing warping, twisting, etc. In order to maintain the same characteristics as the above, it is preferable to use one with a length of up to 10 mm. Furthermore, if the content of softwood kraft pulp is less than 10% by weight, the strength of the glass nonwoven fabric will deteriorate significantly at high temperatures, making it impossible to achieve the object of the present invention. On the other hand, if the content of softwood kraft pulp exceeds 40% by weight, there will be no problem in terms of nonwoven fabric breakage during molding, but softwood kraft pulp will inherently have inferior dimensional stability and moisture resistance compared to glass fiber. Therefore, the resulting laminate has poor properties, and there is no value in using glass nonwoven fabric. Examples E-glass fibers are commonly used as the glass fibers constituting the glass nonwoven fabric used in the present invention.
Glass fibers of other compositions with excellent electrical properties may also be used. Further, as a method for producing glass fibers, any method may be used, such as a method in which long fibers are cut into appropriate lengths by melt spinning, or a method in which molten glass is directly made into short fibers by centrifugation or blowing. In addition to epoxy resins, the thermosetting resins used are those normally used for laminated boards. Next, examples of the present invention will be described. Various glass nonwoven fabrics shown in Table 1 were used as base materials, and a prepreg obtained by impregnating and drying an epoxy resin was layered on the base material, and heat and pressure molding was performed at a temperature of 160° C. and a pressure of 40 kg/cm ² for 30 minutes. These molding conditions are equivalent to the molding conditions for a glass cloth base epoxy resin laminate. The presence or absence of nonwoven fabric breakage during molding of each of the obtained laminates is shown in Table 1.

【table】

[Table] Figure 1 also shows the tensile strength of each glass nonwoven fabric at room temperature and when heated. The tensile testing machine is a shovel type tensile machine with a crosshead speed of 0.5 mm/
It's a minute. Next, using the various glass nonwoven fabrics shown in Table 2 (however, conventional example 3 was glass fabric) as a base material, impregnating this with epoxy resin to a resin content of 60% by weight and drying it, overlaying the prepreg obtained, 160℃, pressure 40Kg/
cm ² for 30 minutes to form a laminate with a thickness of 1.6 mm. However, only in Conventional Example 2, in order to prevent the nonwoven fabric from breaking, heat and pressure molding was carried out at a temperature of 160° C. and a pressure of 15 kg/cm ² for 30 minutes. Note that these laminates do not have metal foil pasted on the surface, but the same applies if metal foil is pasted on the surface.

[Table] Table 3 shows the results of characteristic tests of laminates using each of the glass nonwoven fabrics and glass cloths shown in Table 2. In Table 3, moisture resistance and soldering heat resistance are as follows:
Measured in accordance with JIS-C-6481. The amount of warpage is
The warpage after E-0.5/150 treatment was based on JIS-C-6481 (specimen size is 300 x 300 mm). The dimensional change rate was calculated by calculating the amount of dimensional change in the longitudinal direction after the E-0.5/150 treatment using the following formula (specimen size was 50 x 200 mm). Dimensional change rate = (dimensions upon receipt) - (E-0.5/1
50 (dimensions after processing) / (dimensions upon receipt) x 100 Punching workability was based on ASTM method.

【table】

[Table] From Table 1 and Figure 1, it can be seen that the softwood kraft pulp mixed with the glass nonwoven fabric needs to have a fiber length of 2 mm or more and a content of 10% by weight or more in order to prevent the nonwoven fabric from breaking. It was also found that if the glass nonwoven fabric has a tensile strength of 3.5 kg/mm width or more at 120°C, the nonwoven fabric will not break under normal molding conditions for glass fabric base epoxy resin laminates. Next, from Table 3, it can be seen that a softwood kraft pulp with a content of 50% by weight has poor moisture resistance and heat resistance, so it is necessary to reduce the content to 40% by weight or less.
Furthermore, by setting the fiber length of the softwood kraft pulp to 10 mm or less, the warp of the laminate can be reduced, and in this case, the same properties as glass cloth base laminates can be maintained. Effects of the Invention As mentioned above, since the present invention uses a glass nonwoven fabric that has little strength deterioration when heated, the nonwoven fabric does not break during molding and has excellent moisture resistance and heat resistance. Its industrial value is extremely great as it also has good punching workability.

[Brief explanation of drawings]

FIG. 1 is a comparison diagram of the tensile strength of various glass nonwoven fabrics.

Claims (1)

[Claims] 1. A laminate in which a sheet-like base material is impregnated with a thermosetting resin and then stacked and molded under heat and pressure. A laminate characterized by using glass nonwoven fabric mixed with ~40% by weight. 2. The laminate according to claim 1, wherein the softwood kraft pulp has a fiber length of 2 to 10 mm.