Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2001-09-04
2002-10-29
Goodrow, John (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S133000
Reexamination Certificate
active
06472114
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a laminate type organic electrophotographic receptor used in an image forming device such as a copying machine, a printer or a facsimile, and especially relates to an improved coating fluid for forming an improved electric charge generating layer and the organic electrophotographic receptor formed using the coating fluid, and the method of manufacturing the same.
Heretofore, along with the improvement in developing the material for an electrophotographic receptor, the material for the receptor has changed from inorganic materials such as zinc oxide, cadmium sulfide, selenium amorphous and amorphous silicon, to organic photoconductive materials (OPC). The electrophotographic receptor formed using the organic photoconductive material has some problems related to its sensitivity, durability and environmental stability, but it has greater advantages compared to the inorganic material in its toxicity, cost, and freedom of material design and the like.
Therefore, many proposals for improving the sensitization of the organic electrophotographic receptor exist.
There are two types of photoconductive layer of the organic electrophotographic receptor, a single layered type and a laminated type. Since the laminate type receptor (hereinafter called “separated-function receptor”) composed mainly of a layer (hereinafter called “charge generating layer:CGL”) including a material that generates a charge carrier when exposed to light (hereinafter called “charge generating material:CGM”) and a layer (hereinafter called “charge transferring layer:CTL”) mainly formed of a material that receives the charge carrier generated at the CGL and transfers the same (hereinafter called “charge transferring material:CTM”) is known to provide advantageous sensitization, it constitutes the main portion of organic receptors that are currently utilized. Further, since recent studies have improved the durability of the above-mentioned laminated receptor, it is considered to become the mainline of receptors in the near future.
Moreover, the durability of the receptor is further improved by providing an undercoating layer (hereinafter called “UCL”) on the conductive base so as to improve the electrification, to prevent unnecessary charge injection from the conductive base, to cover the defects on the surface of the conductive base, to prevent the creation of pinholes, and to improve the adhesiveness of the photosensitive layer.
These photosensitive layers are formed by creating a coating fluid including photosensitive material by dissolving or dispersing the organic photoconductive material for each layer together with a binding resin in an organic solvent, and applying and drying the coating fluids including the photosensitive material on the conductive base in order.
The method for applying the organic electrophotographic photosensitive layer includes a spraying method, a bar-coat method, a roll coat method, a blade method, a ring method, and a dip coating method. The dip coating method is a method where the (cylindrical) conductive base is immersed into a coating tank (filled with the photosensitive material) and then pulled out either at constant speed or at varying speeds set freely so as to form the photosensitive layer. This dip coating method is relatively easy and advantageous in its productivity and its low cost, so it is often used when manufacturing the electrophotographic receptor.
One example of the device used for dip coating is shown in FIG.
1
.
A coating fluid
5
including the photosensitive material is stored in a coating tank
4
. A cylindrical conductive base
1
, the upper end of which is supported in an airtight manner by a chucking device
8
, is immersed into the coating solution
5
of the coating tank
4
. Upon dipping, the chucking device
8
is lowered by an elevating machine
2
equipped with a motor
3
, and the base
1
is immersed into the coating fluid
5
. After enough dipping has been performed, the chucking device
8
is raised by the elevator
2
. The elevator
2
enables the base
1
to be immersed into the coating tank for a desired depth by controlling and confirming the rotation of the motor
3
. According to another example, the coating tank can be elevated when performing the coating.
Upon dipping, the fluid that has overflown from the tank
4
is collected into an auxiliary tank as shown in arrow
13
, and the coating fluid is adjusted so as to maintain a constant viscosity using a viscometer
16
and a fluid adding device
10
. After stirring the fluid with a stirring device (impeller)
12
, foreign matter in the fluid is removed through a filter
9
, and as shown in arrow
14
, the fluid is returned to the coating tank by a pump
6
, and the tank
4
is filled with the coating fluid
5
before repeating the next coating steps.
In order to realize supersensitivity in a separated-function type laminated receptor, not only is it necessary to use a charge generating material having high quantum efficiency, but it is also necessary to form a very thin charge generating layer in order to increase the ratio of charge generating material within the charge generating layer or to move the electrons toward the substrate faster, the speed of the electrons being very slow compared to the speed in which the holes move toward the charge transferring layer.
However, during the application of the electric charge generating layer, external defects can be generated such as the unevenness of the film thickness, the ring-like stripes, the fluid droppings, and the belt-like liquid pool formed on the lower end of the base. Further, since the coating fluid for the charge generating layer is a pigment dispersion fluid, if the dispersion is of poor quality, the pigments can aggregate and create black dots or white dots.
These defects are caused by the fouling of the base body, the uneven dispersion of the application fluid, or the convection within the coated layer when the coated solvent is evaporating. Therefore, the charge generating material can be in some locations while not being in other areas of the layer. Such unevenness of the coated layer causes fatal image defects especially in the charge generating layer of the supersensitive receptor required to be thin, and deteriorates the quality of the image forming device.
Japanese Patent Laid-Open Publication No. 2-203348, Japanese Patent Laid-Open Publication No. 4-14053, and Registered patent Publication No. 2853336 disclose methods for improving the coating fluid for the charge generating layer in order to overcome the above-mentioned problems. These references disclose a method for using and mixing two kinds of organic solvents as the coating fluid (each using dioxane/cyclohexanone, low boiler/high boiler solvents, or low viscosity/high viscosity solvents), and the references all insist that these. solvents improve the dispersibility, the stability and the application performance of the coating fluid.
However, in the case of the coating fluid formed of more than two kinds of mixed solvents, the difference in the boiling point, the vapor pressure, the vapor rate and the like of the different solvents causes the quantity of evaporation of each solvent to differ, causing the composition ratio including the mixed solvent ratio within the coating fluid to vary. If the composition ratio of the mixed solvents is varied, the quality of the coated layer can be deteriorated by the change in color or forming of dews on the layer, or the dispersibility or solubility of the solution can be deteriorated.
Moreover, though the prior art references insist that the coating unevenness is solved by their inventions, since they mix different solvents that have different properties, the applicability is deteriorated and coating unevenness is still caused by the change or bias in surface tension when the solvents in the applied layer evaporate.
Therefore, other references (refer to Japanese Patent Laid-Open Publication Nos. 6-208230 and 7-295247) disclose method of including polydimethylsiloxane in the
Kakui Mikio
Kawahara Akihiko
Matsuo Rikiya
Morita Tatsuhiro
Nakamura Tomomi
Goodrow John
Sharp Kabushiki Kaisha
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