Compositions – Electrically conductive or emissive compositions – Elemental carbon containing
Reexamination Certificate
2000-08-14
2001-10-16
Kopec, Mark (Department: 1751)
Compositions
Electrically conductive or emissive compositions
Elemental carbon containing
Reexamination Certificate
active
06303054
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an electrically-semiconductive poly(amic acid) liquid composition excellent in storage stability and to a use thereof for producing an electrically-semiconductive seamless tubular polyimide film. The electrically-semiconductive seamless tubular polyimide film is useful, for example, as an intermediate belt member for fixation and transfer in a copying machine.
BACKGROUND OF THE INVENTION
It is well known to prepare an electrically-semiconductive polyimide by incorporating an electrically-conductive carbon black and to mold the electrically-semiconductive polyimide in the form of a film (sheet, tube, etc), for example, for using the film for various types of applications. Conventionally, in the production process, a liquid composition of poly(amic acid) (hereinafter referred to as “conventional liquid composition”) is first prepared by synthesizing poly(amic acid), which is a precursor of polyimide, in an organic polar solvent, followed by adding thereto the electrically-conductive carbon black to be mixed therewith. Viscosity of the resultant liquid composition can be adjusted by adding the organic polar solvent to suit preferable molding conditions. Thereafter, the liquid composition is used for molding a film, for example, wherein the following two steps are necessary. In the first step, the liquid composition is molded under the molding conditions where the poly(amic acid) used as a main ingredient is not imidated (the molding temperature is less than 250° C.) and by desired means to obtain the molded product in a desired form. The organic polar solvent contained in the liquid composition is removed by evaporation to give a solid poly(amic acid) film containing the carbon black. In the second step, the poly(amic acid) film is gradually heated until the temperature reaches about 350° C. so that the imidation is complete to give an electrically-semiconductive polyimide film with removing the remaining solvent by evaporation, thereby finishing the production process.
The inventors of the present invention have filed a number of patent applications in connection with the techniques explained above. However, during various types of research for improving the techniques, the inventors have found the following problems which should have been resolved at once.
One of the problems relates especially to the conventional liquid composition. The inventors found that the conventional liquid composition sharply changes in the electrical resistivity day by day when stored in ordinary state (at ordinary temperature and under atmospheric pressure). The electrical resistivity changes with time; it decreases in some cases and increases in other cases. The change in the electrical resistivity makes it impossible to obtain a desired molded product having a desired electrical resistivity unless the liquid composition is subjected to a molding immediately after the production. Because of the unstable electrical resistivity, the liquid composition cannot be prepared in a large scale to be stored and used in such a manner that a portion required for the production process is taken out of the stock. That is, a mass-production of the liquid composition is practically impossible.
Another problem is a nonuniform electrical resistivity of a molded product. It is possible to produce a molded product having a desired electrical resistivity from the unstable liquid composition if the liquid composition is molded immediately after the preparation. However, depending on use conditions of the molded product (for example, a long-term use with repetitive electrification and destaticization under a high voltage, such as an intermediate transfer belt in a color copying machine; a long-term use under a high temperature and high humidity; etc.), variations in the electrical resistivity occur, thereby preventing the molded product from maintaining the uniformity in the electrical resistivity once applied to the molded product.
The inventors carried out an extensive research to solve the above problems at once, and found a novel electrically-semiconductive poly(amic acid) composition which has a higher storage stability and maintains a stable electrical resistivity as being molded into a molded product, thereby to accomplish the present invention. The invention is easily achieved as described below.
SUMMARY OF THE INVENTION
The invention provides an electrically-semiconductive poly(amic acid) liquid composition (PA liquid composition) as recited in claim
1
, whose electric semiconductivity is imparted by an electrically-conductive carbon black contained therein, characterized in that a change in an electrical resistivity of the liquid composition is 7% or less with respect to an initial electrical resistivity after being stored at least for 180 days at a temperature of 23° C. and in an atmosphere of RH of 65%. The electrically-semiconductive poly(amic acid) liquid composition having the above characteristics can solve the problems mentioned above. Thus, a novel electrically-semiconductive poly(amic acid) liquid composition (hereinafter “PA liquid composition”) is provided.
One of the embodiments of the PA liquid composition is provided by claim
2
, wherein the PA liquid composition comprises 5-40 parts by weight based on poly(amic acid), of a poly(amic acid), 95-60 parts by weight of an organic polar solvent and 10-40% by weight of an electrically-conductive carbon black having a volatile content of 5-20% by weight, a specific surface area of 100-300 m
2
/g and a pH of 2-4. Of course, this is one of the examples for the preferred embodiments of the PA liquid composition, and the invention is not limited thereto.
A preferred example of the use of the PA composition is recited in claim
4
, wherein an electrically-semiconductive seamless tubular polyimide film is produced by using the PA composition. The electrically-semiconductive seamless tubular polyimide film (hereinafter referred to as SL film) thus obtained is usable, for example, as an intermediate belt member for fixation and transfer in a color copying machine.
In claim
3
, the poly(amic acid) which is a thermosetting polyimide precursor is provided. Not only the thermosetting polyimide precursor, but also a polyamideimide precursor is included in poly(amic acids); however, the thermosetting polyimide precursor is more effectively used as described below.
REFERENCES:
patent: 5021036 (1991-06-01), Tanaka et al.
patent: 5078936 (1992-01-01), Parish et al.
patent: 5174924 (1992-12-01), Yamada et al.
patent: 5389412 (1995-02-01), Tanaka et al.
patent: 6001440 (1999-12-01), Miyamoto et al.
patent: 5-77252 (1993-03-01), None
patent: 10-2968264 (1998-11-01), None
Kanetake Junya
Kuraoka Takashi
Miyamoto Tsuneo
Nishiura Naoki
Yoshida Tsutomu
Gunze Limited
Knobbe Martens Olson & Bear LLP
Kopec Mark
LandOfFree
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