Electrophotography – Image formation – Development
Reexamination Certificate
2000-02-24
2001-08-07
Royer, William J. (Department: 2852)
Electrophotography
Image formation
Development
C430S102000, C430S117200
Reexamination Certificate
active
06272304
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The invention relates to image forming apparatus which used liquid development agent.
(2) Description of the Related Art
Development apparatus can be divided into 2 kinds, dry type and wet, by whether powder-like thing is used as developer, or liquid is used. Although dry-type development apparatus had advantages that it is easy to deal with developer, there are faults of that it is hard to acquire quality image, and developer often adheres to record media, etc. since powder-like developer is used.
In order to eliminate easily powder-like developer adhering to record media, applying release agent on the surface of record media, before developing, was also considered (Japanese Patent Disclosure Syo 6-242688). However, this type apparatus also has many other faults because of using powder-like developer.
Electrophotographic recording device and electrostatic recording apparatus using liquid-development agent have advantage unrealizable in dry type, and the value is being improved in recent years.
The main advantages of wet image forming apparatus to dry type are that high quality image is obtained since very fine toner of submicron size can be used, it is economical since sufficient density image is obtained with a little toner, high quality image is realizable about the same as printing (for example, offset printing), and energy saving is realizable since toner can be fixed to paper at comparatively low temperature, etc.
On the one hand, some essential troubles were included in wet image forming apparatus using conventional liquid toner, and, for the reason, dry-type development has outpaced wet-type development for a long time. There are several problems regarding transferring process in wet-type development.
The first problem in transfer was degradation of image quality. That is, since transfer of the developer which has adhered on latent image layer with transfer measure was conventionally carried out to media directly by work of electric field, transfer unevenness by electric field fluctuation which responded to irregularity on surface of paper had caused.
Moreover, it was easy to cause poor transfer by variation, environmental dependency, etc. of electrical characteristic of paper.
These problems were degrading quality of transferred image remarkably.
In order to solve such problems, the apparatus, in which after transfer from latent image layer to intermediate member is carried out, and transfer from the intermediate member to paper is carried out, is proposed.
U.S. Pat. Nos. 5,148,222, 5,166,734, 5,208,637, etc. disclose the apparatus, in which transfer from latent image layer by electric field to intermediate member is carried out, and then transfer from intermediate with pressure (and heat) to paper is carried out.
Moreover, Japanese Patent Publication Sho 46-41679 and Japanese Patent Disclosure Sho 62-280882 disclose the apparatus using pressure (and heat) in both processes of transfer to intermediate member, and transfer to paper, without using electric field.
Since it is comparatively easy to formulate intermediate member from smooth material with few variations and fluctuations in electric resistance, compared with case where direct electric field transfer is performed to paper, image quality degradation by transfer is improved by leaps and bounds.
When carrying out transfer to intermediate member with pressure and heat, degradation of quality of image is inhibited remarkably. In these proposals, since transfer to paper is carried out with heat and pressure, problem which was seen in the case of electric field transfer is not caused.
However, also in these proposals, the following problems were left behind practically. First, process is complicated by providing intermediate transfer member.
Moreover, quality of image varied in connection with degradation of intermediate transfer member, and depreciation of the reliability of system is brought.
Since good intermediate transfer member generally requests high elasticity and high release characteristic, that intermediate transfer member prepared release layer of silicone system or fluorine system on surface of elastic layers, such as rubber, is used in many cases, and the durability is inferior compared with other component parts.
Furthermore, toner image is transferred from intermediate member to paper, it is difficult to maintain 100% of transfer efficiency, and the cleaner to eliminate residual on intermediate member after transfer is necessary.
Therefore, while system is complicated much more, the durability becomes still shorter because of damage by cleaner.
Apparatus which carries out transfer of the toner image from latent image layer directly to image support (paper) is proposed with heat and pressure to solve these problems in connection with such a intermediate transfer member.
U.S. Pat. No. 5,608,507 discloses the apparatus in which the image by liquid toner is directly transferred with heat and pressure from latent image support having release layer on surface to paper.
In the invention shown in the above U.S. Patent, since the liquid toner image adhering to latent image of sensitization body surface side is transferred to paper after drying out, no solvent adheres in the paper and it can prevent discharging detrimental solvent steam outside the apparatus.
However, according to supplementary examination experiments by the inventor of this invention, it became clear that the following problems exist also in the above apparatus. It is very difficult to carry out transfer of the toner image by pressure (and heat) to paper, after solvent has dried completely.
Therefore, in order to improve transfer efficiency as explained by this patent in full detail, photosensitive layer is formed on elastic fleshing layer, and it is necessary to raise the adhesion of paper surface and toner using the elastic deformation.
In this case, since photosensitive layer deformed in connection with transformation of elastomer under pressure of pressure member applied to rear of paper repeatedly, fatigue failure occurred to binder resin which constitutes photosensitive member, and life of photosensitive member became remarkably short.
Because photosensitive member needs to have flexibility, it cannot use photosensitive member of metal system like amorphous silicon system or selenium system.
Since photosensitive member of binder system like organic photosensitive member must be used, improvement of life is difficult.
Since it is necessary to constitute photosensitive member surface layer by material of remarkable high release characteristic to acquire good transfer efficiency, coexistence of high photosensitive property and high release characteristic was very difficult.
Moreover, in order to acquire transfer [about 100% of] efficiency, while photosensitive layer and pressurization member (backup roller) are heated at 100 degrees C. or more and toner is fully melted, paper must be pressed to photosensitive member by high pressure. This brought the problems, such as the further degradation of photosensitive member by heat, and waste of energy, enhancement of driving torque.
As mentioned above, in conventional wet image formation apparatus, acquiring good transfer efficiency brought several problems, such as shortening of photosensitive member life, difficulty of material selection, waste of heat energy, enhancement of driving torque, etc.
SUMMARY OF THE INVENTION
The invention aims at offering an image forming apparatus which can maintain transfer property good and high quality of image for a long time.
By the present invention, such image forming apparatus is obtainable.
The image forming apparatus using liquid development agent is comprised of a latent image retaining layer; a release agent providing unit configured to provide the release agent on the latent image retaining layer, the release agent releases the liquid development agent from the latent image retaining layer; a latent image formation unit configured to form an electrostatic latent image on the latent image
Hosoya Masahiro
Ishii Koichi
Saito Mitsunaga
Shinjo Yasushi
Yagi Hitoshi
Kabushiki Kaisha Toshiba
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Royer William J.
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