Electrophotography – Cleaning of imaging surface – Plural diverse
Reexamination Certificate
2001-05-01
2002-11-12
Tran, Hoan (Department: 2852)
Electrophotography
Cleaning of imaging surface
Plural diverse
C399S071000, C399S350000, C399S353000, C399S354000
Reexamination Certificate
active
06480695
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a cleaning system to clean an image bearing member used in electrophotographic process and an image forming system equipped with said cleaning system.
In the field of image forming technology where images are formed by an electrophotographic system, efforts have been made in recent years to reduce toner particle size, thereby improving image quality. Resolution can be improved and sharp images can be formed by reducing toner particle size. However, the following problems arise in the cleaning process:
With the reduced size of toner particles, there is an apparent increase in adhesion of toner to the image bearing member. This makes it difficult to clean the image bearing member by removing it from the toner remaining after transfer. When using the cleaning method of using only the cleaning blade, cleaning failure occurs to deteriorate image quality. Especially when image is formed using the toner whose particles are formed by emulsion polymerization method or suspension polymerization method, cleaning failure called “sneaking-through” occurs, wherein remaining toner on the image bearing member passes through the cleaning system without being scraped off by the cleaning blade of the cleaning system. This is because the particle size is very small and toner particles are roughly spherical in shape.
Study is currently under way in an effort to solve the problem resulting from the reduced particle size of such toner particles. For example, Official Gazette of Japanese Patent Laid-Open NO.52808/1999 proposes the cleaning technology wherein conductive or semiconductive rubber is used as the material constituting the cleaning blade, and voltage having polarity reverse to that of toner is applied to the cleaning blade, thereby applying mechanical and electrical removing force to toner remaining on the image bearing member.
Official Gazette of Japanese Patent Laid-Open NO.189675/1991 discloses a cleaning technology which permits cleaning by installing a cleaning brush to apply electrostatic force and a cleaning blade to apply mechanical cleaning force on the downstream side of said cleaning brush.
In the image forming system based on electrophotographic method so far, a cleaning method using an elastic cleaning blade is known as a means of cleaning toner remaining on the image bearing member. This is extensively use for simple structure and lower cost.
In addition to cleaning of the toner after transfer, an image bearing member cleaning means is used to clean the surface of the image bearing member with a great deal of toner remaining thereon without being transferred, for example, after sudden suspension of the operation due to paper jamming or the like or on the patch created for image adjustment or the like.
When pulverized toner created by the conventional pulverization method is used, toner has been successfully scraped off for a long time without cleaning failure, even if a great deal of toner has reached the cleaning blade without being transferred.
In the image forming system based on electrophotographic method, many proposals have been put forth regarding the cleaning system laid out on the periphery of the carrier to clean the surface of the image bearing member.
In the normal image forming process, electrostatic latent image is formed on the image bearing member. After that, said electrostatic latent image is developed by toner to create a toner image. After said toner image is transferred, paper powder adhering to said carrier surface or remaining toner having failed to be transferred is removed by the cleaning system.
Amorphous toner produced according to the conventional pulverization method (average circularity of 0.95 or less) has been sufficiently scraped off only when the end of an elastic plate member called a cleaning blade is brought into mechanical contact with the surface of the image bearing member to scrape it off.
Said conventional cleaning technology, however, has the following problems:
(1) Sufficient cleaning cannot be performed when the potential distribution on the image bearing member is not uniform.
(2) If high voltage is applied to the cleaning blade for cleaning work, electric discharge or injection of electric charge into the image bearing member takes place. This results in image quality or image bearing member.
(3) Toner electrostatically attached to the cleaning blade is deposited with time, and deposited toner falls down to contaminate the image or interior of the equipment.
(4) If bias voltage applied to the cleaning roller in order to raise the cleaning performance of said cleaning roller, toner is absent between the downstream cleaning blade and image bearing member. This will deteriorate friction reducing effect by toner, and is likely to cause separation of the cleaning blade.
The cleaning system disclosed in said Official Gazette allows the cleaning function to be shared between a cleaning brush and cleaning blade, thereby ensuring improved cleaning performance. However, it has the following problems:
(5) Since the greater part of toner is removed by the brush located on the upstream side, the amount of toner between the toner carrier and cleaning blade can be very small. If this occurs, friction between the image bearing member and cleaning blade will be increased. This is likely to cause chattering where the cleaning blade vibrates, or curling where the cleaning blade tip rotates in the reverse direction following the image bearing member.
(6) According to an example disclosed in the Official Gazette of Japanese Patent Laid-Open NO.189675/1991, a high voltage is applied to the upstream brush roller and the image forming surface is likely to be damaged by electrical discharge. Especially in the initial phase of development, foreign substances (carrier in the developer, magnetic substance and mixed metal chip) are likely to deposit on an image former due to overshooting of the development bias. If a brush charged with said voltage is brought in contact with that portion, electric discharge will easily occur with the result that the image former is damaged and image failure occurs.
(7) In the real-world usage, toner deposits over the range in excess of the image forming area by scatters from the development device. When the disclosed art alone is used, it may be difficult to recover the toner having dispersed over said range. A simple countermeasure is to increase the width of the cleaning brush (roller). In this case, electric discharge occurs from the cleaning brush (roller) to which bias is applied to the substrate (aluminum used normally) of both image forming ends. This makes it difficult to maintain stable cleaning performances.
(8) In keeping with improvement of image quality in an image forming system, roughly spherical and small-sized toner is coming into use. Roughly spherical shape of toner is effective in increasing the development quality. Small-sized toner is essential to formation of a high resolution image. If the weight mean particle size is below 3 microns, however, deposition of toner on the image bearing member is caused by van der Waals force, with the result that fogging is produced to deteriorate image quality.
(9) Said roughly spherical and small-sized toner can be obtained with relative ease if it is made into polymerized toner (to be discussed later). Polymerized toner is preferably used to ensure high quality image. It is known in the related art that, when such polymerized toner is used, however, it is difficult to scrape said toner off the surface of the image bearing member with the cleaning blade as a cleaning means if much toner remains on the image bearing member.
(10) This is commonly explained by the following argument: The tip of said cleaning blade in contact with the image bearing member surface is vibrated by the rotation of the image bearing member, and a gap is produced between the tip of said cleaning blade and image bearing member surface due to said vibration. Since the polymerized toner is roughly spherical, it easily escapes through th
Endo Isao
Morimoto Hiroshi
Bierman, Muserlian & Lucas
Konica Corporation
Tran Hoan
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