Composite papyraceous material

Abstract

A composite papyraceous material comprising a fibrous polytetrafluoroethylene (in particular, fibrous powder thereof) and fibrous polyimide.

Description

TECHNICAL FIELD [0001] The present invention relates to a composite papyraceous material comprising a fibrous polyimide and a fibrous polytetrafluoroethylene (PTFE). BACKGROUND ART [0002] Various papyraceous materials containing a high-performance engineering plastic as a fiber component were proposed and expected to be used widely, for example, as members in electronic devices such as board material and heat-resistant structural materials. Among them, the one containing a fluoroplastic fiber as a constituent, which is advantageous in dielectric and friction properties etc. has been studied intensively. [0003] For example, Patent Document 1 proposes a papyraceous material made of a fluoroplastic fiber and a heat-resistant engineering plastic fiber. [0004] Patent Document 2 proposes a sheet insulator made of a base fiber material, mixture of an insulation fiber and a fluoroplastic fiber, impregnated with an impregnating agent. [0005] Patent Document 3 proposes a low-dielectric printe...

AI Technical Summary

Benefits of technology

[0048] One or more of these additives may be added in an amount that does not impair the advantage of the present invention, the total mass after drying preferably remains 30 percent by mass or less with respect to the total mass of the composite paper according to the present invention, for preserving various favorable properties.

[0049] As described above, the composite papyraceous material according to the present invention may be processed into the state in which the fibrous powder of polytetrafluoroethylene is fused and bonded to the fibrous polyimide in the heat-pressurization step, and such a densified papyraceous material has a superior strength. In addition, such a papyraceous material, even when laminated in the heat-pressurization step, does not show a phenomenon of breakage from the interlayer during use and retains a strength at a substantially same level as that of a single-layer papyraceous material. The strength thereof is determined by the blending ratio of fibrous powder of polytetrafluoroethylene to fibrous polyimide, the degree of densification, or the amount of the third component blended, but, for example, the average breaking length, as determined according to the test method specified by JIS-P8113, is normally in the range of 0.5 to 7 km.

[0050] The composite papyraceous material according to the present invention is resistant to thermal dimensional change and superior in dimensional stability when used at high temperature. As for the dimensional stability, both the average linear expansion coefficients at 20 to 230° C. in the production and width directions of the composite papyraceous material are preferably in the range of −20 to 30 μm / m·° C. (as determined according to JIS-K7197). The average linear expansion coefficient outside the region of −20 to 30 μm / m·° C. may lead to increase in the dimensional stability when used at high temperature and make the papyraceous material unsuitable for use.

[0051] In the present invention, it is possible to prepare a papyraceous material superior in dimensional stability and its directional balance, by preparing a papyraceous material wherein the fibrous polyimide and the polytetrafluoroethylene described above are dispersed randomly.

[0052] The composite papyraceous material preferably has lower water absorption, and in a preferred embodiment of the present invention, the water absorption, as calculated according to the following formula when left in an environment at 25° C. and a relative humidity 60% for 24 hours, is preferably 0.5% or less. Water⁢ ⁢absorption=W-WoWo⨯100⁢(%)(Formula⁢ ⁢I) (wherein W represents mass of nonwoven fabric after moisture absorption, and W0 represents mass of nonwoven fabric when absolutely dried).

[0053] Generally, polyimides are known to have a relatively higher water absorption because of the strong polarity of the imide groups therein, and the molded products thereof often had problems of the change in dimension and electrical characteristic after absorption of moisture. Papyraceous materials of conventional amorphous polyimide fibers also had the problem in dimensional change by water absorption; but in the present invention, it is possible to prepare a high-performance composite papyraceous material lower in water absorption than ever, by using a crystalline polyimide fiber and a fibrous powder of polytetrafluoroethylene lower in water absorption as the main components. In particular, the polyimide represented by Chemical Formula (1) or (2) has crystallinity and a low imide-group content in the chemical structure, and thus, has especially lower water absorption among polyimides; and from these viewpoints, use of the fibrous polyimide above is preferable.

Problems solved by technology

In addition, the fluorine fibers used are sufficiently burned in the manufacturing process of the fluoroplastic fiber, and thus, do not function sufficiently as a binder for binding fibers with each other.

In many cases, the binder component added causes deterioration of the properties of the papyraceous material obtained.

Although the shape etc. of the polytetrafluoroethylene resin in Patent Document 4 are not specified and are still unknown, it seems practically impossible to prepare a thin paper-shaped composite product, considering the manufacturing process.

As described above, it is only possible to prepare a papyraceous material having the properties inherent to polyimide fiber impaired by such a thermosetting resin.

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