Radiation imagery chemistry: process – composition – or product th – Electric or magnetic imagery – e.g. – xerography,... – Radiation-sensitive composition or product
Reexamination Certificate
2002-02-20
2004-03-02
Chapman, Mark A. (Department: 1756)
Radiation imagery chemistry: process, composition, or product th
Electric or magnetic imagery, e.g., xerography,...
Radiation-sensitive composition or product
C430S030000, C399S159000
Reexamination Certificate
active
06699631
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a photoconductor, an image forming apparatus, an image forming method and a process cartridge using the same. The present invention is also directed to a method of preparing a photoconductor.
In recent years, with an increasing demand for reproduction of image information with a high definition, image forming with higher definition and resolution is highly required. In high resolution image forming, characteristics of a photoconductor are likely to be reflected in a formed image in addition to the image information itself. An image forming process employing coherent light such as laser beam for writing light is widely used in a field of electrophotography for forming a digital image, for example in copying machines, printers and facsimiles. In such a process, there tends to arise a problem of occurrence of interference fringes in a formed image due to interference of coherent light in a photoconductor.
It is known that when the photoconductor meets with the following relation:
2nd=m&lgr;
(wherein n is a reflective index of a charge transporting layer, d is a thickness of the charge transporting layer, &lgr; is a wavelength of the writing light and m is an integer), the writing light is enhanced to cause interference fringes.
For example, when &lgr;=780 nm and n=2.0, a set of interference fringes is generated every time the thickness of the charge transporting layer is changed by 0.195 &mgr;m. In order to eliminate such interference fringes completely, therefore, the charge transporting layer should have a thickness variation not greater than 0.195 &mgr;m all over the image forming area. However, it is very difficult to produce such a photoconductor for an economical reason. Thus, various methods for restraining interference fringes have been proposed.
For example, Japanese Laid-Open Patent Publication No. S57-165845 discloses a photoconductor having a charge generating layer containing amorphous Si, wherein a light absorbing layer is provided on a surface of an aluminum support to prevent mirror reflection of light on the surface of the support, thereby preventing occurrence of interference fringes. This method is effective to a photoconductor having a layer structure consisting of an aluminum support/a charge transporting layer/a charge generating layer such as an amorphous Si photoconductor but is not very effective to a photoconductor having a layer structure consisting of an aluminum support/a charge generating layer/a charge transporting layer as seen in many organic photoconductors.
Japanese Laid-Open Patent Publication No. H07-295269 discloses a photoconductor having a layer structure consisting of an aluminum support/an under coat layer/a charge generating layer/a charge transporting layer, wherein a light absorbing layer is provided on the aluminum support to prevent interference fringes. However, even with this photoconductor, it is impossible to prevent interference fringes completely.
Japanese Examined Patent Publication No. H07-27262 discloses an image forming apparatus having a photoconductor including a cylindrical support having a convex shape obtained by superimposing a sub-peak on a main peak in a cross-section cut along a plane including the central axis thereof, and an optical system for irradiating coherent light with a diameter smaller than one cycle of the main peak to the photoconductor. The image forming apparatus can restrain interference fringes to a large extent with some limited types of photoconductors. However, many of photoconductors including a support having a convex shape obtained by superimposing a sub-peak on a main peak in a cross-section cut along a plane including the central axis thereof still generate interference fringes.
A photoconductor including a support having a specified parameter of surface roughness is proposed (for example, Japanese Laid-Open Patent Publication No. H10-301311). The photoconductor can restrain interference fringes when used in an image forming apparatus having a low resolution. However, in the case of an image forming apparatus having a high resolution, it is impossible to determine conditions to eliminate interference fringes completely even though the surface roughness of the support is specified with conventionally used parameters (maximum height roughness (Ry), ten point-average roughness (Rz), center line-average roughness (Ra) etc.).
A photoconductor in which surface roughness of an intermediate layer and surface roughness of an outermost layer are specified in addition to surface roughness of a support is also known. For example, Japanese Laid-Open Patent Publication No. H6-138685 discloses a photoconductor including a conductive support having an Rz of 0.01-0.5 &mgr;m and a surface protective layer having an Rz of 0.2-1.2 &mgr;m. However, a surface protective layer is generally poor in hole transferring ability so that the photoconductor tends to cause a problem of an increase in electric potential of a latent image and to produce an unclear image by influences of ion species generated by electrification, oxidizing or reducing gas, humidity and so on. Also, it is extremely difficult to specify an Rz to eliminate interference fringes completely. When the writing light of the image forming apparatus has a high resolution, image defects such as interference fringes tends to occur.
Japanese Laid-Open Patent Publication No. H7-13379 discloses a photoconductor including an intermediate layer having an Rz of not greater than 1.0 &mgr;m and a surface protective layer having an Rz of not greater than 1.0 &mgr;m, for the purpose of preventing interference fringes such as moire. It is thought to be effective to provide the surfaces of the layers with roughness in a certain degree or greater. However, an upper limit of the Rz for each layer is disclosed but an Rz necessary to prevent interference fringes such as moire is not disclosed.
Japanese Laid-Open Patent Publication No. H08-248663 discloses a photoconductor including a support having a surface roughness of 0.01 to 2.0 &mgr;m, an outermost layer having a surface roughness of 0.1 to 0.5 &mgr;m and containing inorganic particles having an average particle diameter of 0.05-0.5 &mgr;m. However, it is not specified what kind of surface roughness is the surface roughness of the support and the outermost layer. As mentioned above, conventional parameters of surface roughness include Ry, Rz and Ra. It is well known that even if one solid surface is measured for the surface roughness, the measurements are largely varied depending upon the parameters and upon the measurement conditions such as measurement length. Even if the roughness of the support and the outermost layer is Rz provided in JIS and so on, there are many cases where interference fringes cannot be prevented completely.
As mentioned above, conditions to prevent interference fringes completely are unknown but interference fringes are frequently reduced when a support, an intermediate layer or an outermost layer has a roughened surface. However, it is impossible to obtain a photoconductor capable of preventing interference fringes completely even if surface conditions of a support, undercoat layer (intermediate layer) and an outermost layer of a photoconductor are specified with conventionally used parameters of surface roughness, and this tendency increases as the resolution of a printed image becomes higher.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide an image forming apparatus which has overcome the problems of the prior arts.
Another object of the present invention is to provide an image forming apparatus of the above-mentioned type which is capable of producing a high-quality image free from image defects such as interference fringes, streaks, and black spots.
It is a further object of the present invention to provide an image forming apparatus capable of producing a high-quality image free from image defects such as blur without lowering the resolution of an output image.
It
Aruga Tamotsu
Kabata Toshiyuki
Miyamoto Yuka
Chapman Mark A.
Ricoh & Company, Ltd.
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