Paper making and fiber liberation – Processes and products – Plural fiber containing
Reexamination Certificate
1995-04-27
2001-09-25
Chin, Peter (Department: 1731)
Paper making and fiber liberation
Processes and products
Plural fiber containing
C162S157300
Reexamination Certificate
active
06294049
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to polyimide precursor fibrid materials which do not contain aprotic polar organic solvents, and further to polyimide paper products, polyimide composite paper products and polyimide composite boards obtained from the fibrids and to processes for the production of the fibrids and the paper products.
BACKGROUND OF THE INVENTION
It is known that polyimides have excellent properties in terms of heat resistance, mechanical characteristics, electrical characteristics, weatherability and the like and are useful as materials for films and moldings. For example, a polyimide prepared from 4,4′-diaminodiphenyl ether and pyromellitic acid dianhydride can produce films and moldings having excellent heat stability, and these products are widely used in electrical insulation and the like.
In the field of heat-resistant synthetic paper, on the other hand, aramid synthetic paper is known and is widely used. However, with the improvement in advanced materials for use in spacecraft and aircraft, great interest has recently been directed toward the development of synthetic paper products having excellent heat resistance and strength which are superior to those of aramid paper.
Attempts have been made to obtain polyimide paper by subjecting a polyimide fibrid material to paper making. For example, JP-A-62-297330 discloses a process for the production of a polyimide fibrid material in which a poly(amic acid), which dissolved in an aprotic polar organic solvent, is injected into a coagulation bath containing acetic acid and/or acetic anhydride under high speed agitation. Further, JP-A-64-26718 discloses a process for the production of a polyimide fibrid material in which a poly(amic acid) solution is injected under high shear force into a coagulation bath containing a mixture comprising a chemical cyclization agent and a cyclization catalyst. (The term “JP-A” as used herein means an “unexamined published Japanese patent application”.) However, polyimide paper made of the polyimide fibrid material obtained by such processes has a problem in terms of its practical use because of poor strength.
In addition, JP-B-60-1402 discloses a process for the production of pulpy particles in which a polymer solution prepared by solution polymerization in the presence of staple fibers is dispersed in a precipitant. (The term “JP-B” as used herein means an “examined Japanese patent publication”.) According to this process, pulpy poly(amic acid) particles containing staple fibers are obtained. However, this process has a problem of causing a reduction in polymerization degree, because an aprotic polar solvent remains inside the pulpy particles, and the poly(amic acid) is apt to be hydrolyzed by the remaining aprotic polar solvent. In addition, the aprotic polar solvent that remains inside the pulpy particles in a large amount causes other problems in that a high purity polyimide paper cannot be obtained when the pulpy particles are subjected to paper making and imidization. In particular, the product becomes a film-like paper with no appearance of pulpy particles when pressurized after paper making because of the remaining aprotic polar solvent which oozes out due to the applied pressure and dissolves the pulpy particles and causes mutual adhesion of the particles.
With the recently increasing demand for materials having improved mechanical properties and heat resistance, complexing of polyimide resins and other materials has been proposed, and processes in which polyimide resin powder and staple fibers are mixed and molded in the same manner as the case of polyimide moldings have been examined. Polyimide moldings are produced by subjecting polyimide resin powder to press molding and heat treatment, as disclosed for example in JP-A-2-18420, JP-B-49-5737, JP-A-61-250030 and JP-A-1-292035. It is difficult, however, to obtain a composite material having high strength because of the difficulty in uniformly mixing and dispersing the resin powder and staple fibers.
SUMMARY OF THE INVENTION
In view of the above, it is an object of the present invention to provide a polyimide precursor fibrid material which does not contain aprotic polar organic solvents, as well as to provide a process for the production of the polyimide precursor fibrid material.
It is a further object of the present invention to provide a polyimide paper product having excellent strength which comprises a polyimide fibrid material resulting from a ring closure reaction of the polyimide precursor that constitutes the above described polyimide precursor fibrid material, as well as to provide a process for the production of the polyimide paper product.
A still further object of the present invention is to provide a polyimide composite paper product having excellent strength which comprises a polyimide fibrid material resulting from a ring closure reaction of the polyimide precursor that constitutes the polyimide precursor fibrid material and other staple fibers wherein these components are uniformly dispersed, as well as to provide a process for the production of the polyimide composite paper product.
Another object of the present invention is to provide a polyimide composite board having excellent strength which comprises a polyimide fibrid material resulting from a ring closure reaction of the polyimide precursor that constitutes the polyimide precursor fibrid material and other staple fibers wherein these components are uniformly dispersed, as well as to provide a process for the production of the polyimide composite board.
Other objects and advantages of the present invention will be made apparent as the description progresses.
DETAILED DESCRIPTION OF THE INVENTION
With the aim of overcoming the aforementioned problems involved in the prior art, the inventors of the present invention have conducted intensive studies and found that a polyimide precursor fibrid material free from aprotic polar organic solvents can be produced when a polyimide precursor solution prepared from a polyimide precursor material and a solvent or a mixture of solvents which do not exhibit a strong solvation with the polyimide precursor is injected into a coagulation bath and treated under a shear force. Further, a polyimide paper, polyimide composite paper and polyimide composite board obtained from paper made of the thus produced polyimide precursor fibrid material are also free from the aforementioned problems. The present invention has been accomplished on the basis of these findings.
Accordingly, the present invention is directed to: a polyimide precursor fibrid material which comprises a polyimide precursor that forms a polyimide having a property of no thermal melting when subjected to a ring closure reaction and which are substantially free from aprotic polar organic solvents, and a process for the production of the polyimide precursor fibrid material; a polyimide paper product which comprises a polyimide fibrid material resulting from a ring closure reaction of the polyimide precursor that constitutes the just described polyimide precursor fibrid material, and a process for the production of the polyimide paper product; a polyimide composite paper product which comprises a polyimide fibrid material resulting from a ring closure reaction of the polyimide precursor that constitutes of the polyimide precursor fibrid material and other staple fibers, and a process for the production of the polyimide composite paper product; and a polyimide composite board which comprises a polyimide fibrid resulting from a ring closure reaction of the polyimide precursor that constitutes the polyimide precursor fibrid material and other staple fibers, and a process for the production of the polyimide composite board.
The following describes each aspect of the present invention in detail.
1. Polyimide precursor fibrid material and its production process
According to the present invention, any type of polyimide precursor may be used, provided that it becomes a polyimide having a property of no thermal melting when subjected to ring closure. T
Echigo Yoshiaki
Furukawa Mikio
Nakano Takeshi
Tomioka Isao
Wada Masato
Chin Peter
Sughrue Mion Zinn Macpeak & Seas, PLLC
Unitika Ltd.
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