Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Process of making radiation-sensitive product
Reexamination Certificate
2002-03-22
2003-11-04
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Process of making radiation-sensitive product
C430S060000
Reexamination Certificate
active
06641968
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an electrophotosensitive material comprising an intermediate layer (undercoat layer) formed between a conductive substrate and a photosensitive layer.
BACKGROUND OF THE INVENTION
As an electrophotosensitive material for use in image forming apparatuses such as electrostatic copiers, plain paper facsimiles, laser beam printers and combined devices having these functions, a so-called organic electrophotosensitive material is widespread which comprises a combination of the following components:
a charge generating material for generating electric charges (positive hole and electron) when exposed to light;
a charge transport material for transporting the generated electric charges; and
a binder resin.
The charge transport materials fall into two broad categories which include a hole transport material for transporting positive holes of the electric charges, and an electron transport material for transporting electrons.
The organic electrophotosensitive material has an advantage over an inorganic electrophotosensitive material employing an inorganic semiconductor material in that the organic electrophotosensitive material is fabricated more easily at less production costs than the latter.
In addition, the organic electrophotosensitive material also has a merit of greater freedom of function design by virtue of a wide variety of options for materials including those described above.
In this connection, the organic electrophotosensitive materials have recently been widely used in the image forming apparatuses.
The organic electrophotosensitive material is fabricated by forming either of the following photosensitive layers on a conductive substrate:
A single-layer photosensitive layer containing a charge generating material, charge transport material (hole transport material and/or electron transport material) and binder resin; and
A multi-layer photosensitive layer in which a charge generating layer containing a charge generating material, and a charge transport layer containing a charge transport material (hole transport material and/or electron transport material) are laminated in this order or vise versa.
Unfortunately, these photosensitive layers encounter the following problems when formed directly on the conductive substrate.
(a) In a charging step of the image formation, when a surface of the photosensitive layer is positively or negatively charged, a charge of the opposite polarity to the above occurs in the conductive substrate.
The photosensitive layer formed directly on the conductive substrate, however, is susceptible to the injection of the electric charge of the opposite polarity from the conductive substrate. If a large quantity of electric charge of the opposite polarity are injected into the photosensitive layer, the total amount of electric charge at the photosensitive layer surface is lowered.
Accordingly, an electrostatic latent image formed on the photosensitive layer surface in the light exposure step has a decreased potential difference between a light exposure region and a non-exposure region. This causes a printed image to sustain fogging due to the adhesion of toner particles to white areas thereof.
(b) The single-layer photosensitive layer or the lower layer of the multi-layer photosensitive layer is formed by applying a coating solution containing the above components onto the conductive substrate, followed by drying the coating film. In some cases, however, the resultant layer may be insufficiently bound onto the conductive substrate depending upon the type of the binder resin or the solution application conditions. This results in the delamination of the formed layer.
(c) If a surface of the conductive substrate contains a defect such as mars, the surface of the photosensitive layer formed directly on the conductive substrate will also sustain a similar defect. This defect causes black spots or white spots in the formed image. Whether the defect results in the black spots or the white spots depends upon whether the image forming process adopts the normal development method or the reversal development method.
With an aim at solving these problems, there has been proposed an electrophotosensitive material wherein an intermediate layer containing a binder resin is formed on a conductive substrate, and then a photosensitive layer is laid thereover.
By virtue of the intermediate layer so provided, this electrophotosensitive material is adapted to prevent the electric charge of the conductive substrate from being injected into the photosensitive layer, to achieve a firm bond between the conductive substrate and the photosensitive layer, and to cover up the defect in the surface of the conductive substrate for a smooth, defect-free surface of the photosensitive layer.
A thermosetting resin is preferably used as the binder resin for forming an intermediate layer having good thermal, chemical, physical and mechanical stabilities, especially insolubility in the dispersion medium (ex. organic solvent) contained in the coating solution for the photosensitive layer, and an excellent binding with the conductive substrate.
The intermediate layer containing the thermosetting resin is formed by applying a coating solution, such as prepared by dissolving or dispersing the thermosetting resin in a dispersion medium, to the surface of the conductive substrate and then heat treating the coating film for curing the thermosetting resin.
However, if the heat treatment is insufficient, the curing degree of the thermosetting resin is lowered so that the intermediate layer is decreased in the thermal, chemical, physical and mechanical stabilities. When a coating solution for photosensitive layer is applied to such an intermediate layer in order to overlay the photosensitive layer thereon, the intermediate layer will be dissolved or changed in properties by a dispersion medium contained in the coating solution. This may result in nonuniform thicknesses or inhomogeneous compositions of the photosensitive layer.
With a low curing degree of the thermosetting resin, the intermediate layer tends to be decreased in conductivity, leading to the likelihood of fog.
In the light exposure step of the image formation, the charge generating material generates both the positive and negative charges in the light exposure region of the photosensitive layer. One of the charges is transported to the conductive substrate while the other charge negates a charge potential of the surface of the photosensitive layer so that an electrostatic latent image is formed on the surface of the electrophotosensitive material in correspondence to a light exposure pattern.
However, if the intermediate layer between the photosensitive layer and the conductive substrate has a low conductivity, the charge (of the same polarity as that of the surface of the electrophotosensitive material) to be transported to the conductive substrate is blocked by the intermediate layer, thus remaining in the photosensitive layer.
Therefore, the electrophotosensitive material is increased in residual potential so that the printed image tends to sustain fog in its white area.
Furthermore, the intermediate layer is associated with another cause of fog. That is, a de-electrification step subsequent to an image transfer step cannot sufficiently eliminate the charge of the surface of the photosensitive layer because of the interference of the intermediate layer so that the photosensitive layer is increased in residual potential.
The present inventors have studied an approach wherein prior to the formation of the photosensitive layer, the curing degree of the thermosetting resin forming the intermediate layer is non-destructively determined so as to preclude any intermediate layer containing the thermosetting resin insufficiently cured. Then, the photosensitive layer may be laid only over an intermediate layer containing the thermosetting resin sufficiently cured.
Japanese Laid-open Patent Publication No. JP05-19518A (1993) discloses a method which comprises the steps of: applying a coating so
Goodrow John
Kyocera Mita Corporation
Smith , Gambrell & Russell, LLP
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