Stock material or miscellaneous articles – Hollow or container type article – Polymer or resin containing
Reexamination Certificate
2000-08-14
2002-03-05
Hampton-Hightower, P. (Department: 1711)
Stock material or miscellaneous articles
Hollow or container type article
Polymer or resin containing
C428S034100, C428S035700, C428S036920, C428S338000, C428S473500, C264S209100, C264S209500
Reexamination Certificate
active
06352750
ABSTRACT:
FIELD OF THE INVENTION
The present invention provides an seamless tubular electrically-semiconductive aromatic polyimide film having, in particular, electrical resistance properties (surface resistivity, volume resistivity and dielectric strength) improved in stability and a process for producing the film. The film is used remarkably advantageously as, for example, an intermediate transfer belt member in a color copying machine employing an intermediate transfer system.
BACKGROUND OF THE INVENTION
In the field of color copying, for example, a copying system using an intermediate transfer belt (hereinafter referred to as “intermediate transfer system”) is known and part thereof is put to practical use. In the intermediate transfer system, which is different from the xerography method wherein a color toner image formed on a photosensitive drum is transferred in sequence to be directly fixed on a transfer paper, a plurality of toner images are transferred firstly onto an electrically-semiconductive belt which is electrostatically charged and mounted between a photosensitive drum and a transfer paper, and then fixed on transfer papers.
The color copying techniques according to the intermediate transfer system attracts widespread attention since the techniques enable to reproduce images with maintaining high image quality, to lower the level of ozonization and to reproduce toner images on a wider range of image acceptors including cardboards, envelopes, etc., thereby serving for many uses.
It is known to use, as the intermediate transfer belt, an electrically-semiconductive seamless belt prepared by dispersing an electrically-conductive carbon black in a thermosetting polyimide. This electrically-semiconductive seamless belt is excellent in heat resistance, mechanical properties, chemical resistance and the like as compared to that made from other resins.
However, an seamless tubular film to which an electrical semiconductivity is imparted by dispersing an electrically-conductive carbon black in a thermosetting polyimide generally tend to be unstable in the electrical semiconductivity, i.e., in electrical resistance properties and, therefore, it is difficult to utilize such seamless tubular film with maintaining high quality thereof. For example, in the case where the seamless tubular film having the unstable electrical resistance properties is used as the intermediate transfer belt, toner scatter will occur to cause irregularity in image density and spots at non-image area, thereby deteriorating quality of reproduced images. Moreover, change in the applied voltage during a copying process immediately affects the quality of the reproduced images, so that constant quality of reproduced images cannot be achieved.
DISCLOSURE OF THE INVENTION
The present invention was accomplished as a result of extensive researches carried out to provide an seamless tubular electrically-semiconductive aromatic polyimide film improved in its quality and performance, to thereby solve the above-described problems.
The present invention is characterized by, as claimed in claim
1
, an seamless tubular electrically-semiconductive aromatic polyimide film comprising an aromatic polyimide and an electrically-conductive carbon black having a volatile content of 10-25% which consists mainly of volatile acidic ingredients having a pH of not more than 4, which is capable of efficiently solving the above problems.
The aromatic polyimide may preferably have a Tg (glass transition temperature) of 210-350° C. (claim
2
), and the electrically-conductive carbon black may preferably be treated by a surface oxidation (claim
3
).
Pursuant to claims
2
and
3
, a surface resistivity/volume resistivity ratio of the seamless tubular electrically-semiconductive aromatic polyimide film is easily regulated to be two digits (10
2
) or less, preferably in the range of 1≦a surface resistivity/volume resistivity ratio≦10
2
, thereby enabling to solve the above problems in a preferred manner.
Pursuant to claims
1
-
3
, variation in the surface resistivity caused by variation in an applied voltage for charging is easily regulated to be half a digit or less, thereby enabling to solve the above problems in a preferred manner (claim
5
).
Pursuant to claims
2
and
3
, it is found that not only the surface resistivity/volume resistivity ratio tends to be within two digits or less, but also the variation in the surface resistivity caused by variation in an applied voltage for charging tends to be within half a digit or less, which is provided in claim
6
. The triune relationship among the surface resistivity, the volume resistivity and the voltage applied for charging, which is established on the basis of the invention which is recited in claims
2
and
3
, characterizes the invention as a whole from the viewpoint of solving the above problems in most effective manner.
In claim
7
, there is provided a preferred embodiment of a process for the production of the seamless tubular electrically-semiconductive aromatic polyimide film as claimed in claims
1
-
6
. The production process is excellent in producing an seamless tubular electrically-semiconductive aromatic polyimide film having a remarkably high surface smoothness and thickness precision (hereinafter referred to as “surface quality”) as compared to others.
The invention will hereafter be described in detail.
As a resin to form a basis of the seamless tubular electrically-semiconductive aromatic polyimide film (hereinafter referred to as “SL film”) of the invention is selected an aromatic polyimide in view of its excellent characteristics as compared to other resins as described above. The aromatic polyimide may preferably have a Tg (at second-order transition point) of about 210-350° C., more preferably about 250-350° C. Use of such aromatic polyimide enables to easily achieve stable electrical resistance properties which are imparted to the SL film by dispersing the electrically-conductive carbon black and to easily ensure the surface quality required for the SL film. Further, the SL film obtained by using the aromatic polyimide is so excellent in flexing resistance that dimensional change of the SL film after repetitive and long-term use can be made smaller.
Now that reasons why the aromatic polyimide having a Tg of 210-350° C. is preferred are as explained above, mechanism of action of the aromatic polyimide will hereafter be explained. Polyimide having a Tg in the above ranges has, as described specifically later on, 2 to 3 groups selected from —O—, —SO
2
—, —CO— and alkylene groups, etc. in its aromatic group which is bound to an imide group. Therefore, there occurs a weak bond similar to a hydrogen bond between the selected groups and the volatile acidic ingredients having a pH of not more than 4, preferably 1.5-3.5, which are contained in the carbon black, thereby producing a greater affinity for each other and achieving a state of dispersion improved in uniformity and stability. As a result, the electrical resistance properties are improved. Further, the polyimide itself acquires flexibility and, therefore, even if there are imide rings formed in the polyimide, i.e. even if the polyimide is not in the state of a poly(amic acid) which is a precursor thereof, the polyimide shows solubility for an organic polar solvent (aprotic organic solvent such as N-methylpyrrolidone, dimethylacetoamide and dimethylformamide). As a result, the polyimide enables to improve the surface precision of the SL film and to carry out imidation at a lower temperature.
The followings are specific examples of the aromatic polyimide. The aromatic polyimide having a Tg of higher than 350° C. may be a polyimide (Tg 500° C.) obtained from 3,3′,4,4′-biphenyl-tetracarboxylic dianhydride and p-phenylenediamine, a polyimide (Tg 420° C.) obtained from pyromellitic dianhydride and 4,4′-diaminodiphenylether, etc. The aromatic polyimide having a Tg of 210-350° C. may be a polyimide (Tg 303° C.) obtained from 3,3′,4,4′-biphenyl-tetracarboxylic dianhydride and 4,4′-
Gunze Limited
Hampton-Hightower P.
Knobbe Martens Olson & Bear LLP
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