Electrophotography – Image formation – Fixing
Reexamination Certificate
2000-10-06
2002-07-23
Chen, Sophia S. (Department: 2852)
Electrophotography
Image formation
Fixing
Reexamination Certificate
active
06424815
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to oil coating rollers for coating silicone oils as releasing agents on surfaces of fixing rollers in thermal fixing apparatuses for use in electrophotographic copying machines, laser printers, and the like.
2. Description of the Related Art
In electrophotographic processes represented by electrophotographic copying machines, toner images on copy paper are fixed by a thermal roller method. In the thermal roller method, a nip is formed by a fixing roller and a pressure roller, images formed by toner on copy paper are passed through the nip and are then heated and pressed, thereby fixing the toner by fusing. In the thermal roller method, in order to prevent toner from remaining on the fixing roller, the toner coming into direct contact therewith, so as to more preferably fix the toner images and decrease staining on a cleaner blade, a cleaner felt, and the like, a silicone oil having superior releasing properties is coated on the fixing roller.
In the case of monochrome images, the toner layer is thinner compared to the case of color images, and the amount of oil coated on a fixing roll can be further decreased concomitant with improvement of the toner itself. However, in the case of color images, since the toner layer is thick, the melting point thereof is low, and the viscosity thereof is high, the image deficiencies (toner offset) due to toner staining are easily generated, and as a result, in order to avoid the image deficiencies mentioned above, a larger amount of a silicone oil must be coated than that in the case of monochrome images.
As methods for coating silicone oil, there may be mentioned a method for coating a silicone oil, which is impregnated in a webbing, or a felt, on a surface of a fixing roller, and a method for coating a silicone oil, which is supplied by an oil coating roller, directly on a surface of a fixing roller. However, when a large amount of silicone oil is necessary as is the case with full-color images, a method for coating silicone oil is preferably performed by using an oil coating roller rather than that performed by using a webbing or a felt.
Conventionally, a topmost exterior layer of the oil coating roller is formed of a solid or a spongy silicone rubber layer. The spongy (foamed) silicone rubber is generally provided with a hollow member or the like therein for supplying a silicone oil, and the silicone oil is leached out on the spongy surface and is then coated, which is disclosed in Japanese Examined Patent Application Publications No. 5-60105, 7-15606, and the like. In the case of the solid (not spongy but solid form) silicone rubber layer, a silicone oil is transferred to an oil coating roller, which is scooped from a silicone oil bath, and it is then coated on a surface of a fixing roller by directly contacting the oil coating roller with the surface of the fixing roller. In addition, an oil-coating roller is disclosed in Japanese Unexamined Patent Application Publication No. 10-228205, in which the oil coating roller has the topmost exterior layer composed of a solid silicone rubber layer and a spongy silicone rubber layer provided therein.
In the method described above for coating silicone oil on the surface of the fixing roller by leaching the oil out on the spongy surface of the silicone rubber layer, toner adheres to the spongy surface in long-term use, oil supply is stopped at locations at which the toner adheres, and coating defects of the oil on the fixing roller occur, whereby there may be a problem in some cases in that abnormal images are produced. Accordingly, when an amount of toner offset is relatively large as is the case in which full-color images are fixed, particularly in order to perform stable and consistent oil coating over long periods of time, a method using a solid silicone rubber layer is preferably employed.
In addition, in the method for coating oil using the oil coating roller as described above, as a means for controlling the amount of silicone oil on the oil coating roller so as to be uniform, a method is generally used in which an oil control blade is provided which is urged toward the surface of the oil coating roller so as to maintain a constant pressure thereto by a pressure spring.
However, in conventional oil coating rollers in which the topmost exterior layers are composed of a solid silicone rubber layer, there are problems, which are of concern, as described below.
As a method for improving heat stability and mechanical strength of silicone rubber, a method is well known in which an inorganic filler, such as synthetic hydrated silica or silicate anhydride, is contained in the silicone rubber. However, since a large amount of synthetic hydrated silica, such as 20 to 50 parts by weight thereof to 100 parts by weight of the silicone rubber, must be added to obtain an effect of reinforcement, releasing properties of the silicone rubber may be degraded due to the addition of a large amount of synthetic hydrated silica. Consequently, an amount of offset toner transferred from the surface of the fixing roller is excessively increased, irregular and excessive coating of the oil on the oil coating roller thereby occur, and hence, excessive and irregular coating of the oil occur on the fixing roller, and ultimately, on a recording medium. As a result, it has been of concern that oil sagging, oil staining, oil stripes, and the like may be produced on images. In particular, the phenomena mentioned above may apparently be generated when an OHP sheet is fixed which will not absorb oil.
In addition, in the method for controlling an amount of silicone oil coated on the surface of the fixing roller by contacting an edge portion of the oil control blade urged toward the oil coating roller by a spring or the like, and at the same time, for smoothly and uniformly coating the oil on the oil coating roller, a uniform and desired amount of coating can be obtained at the beginning. However, as operation time passes, the edge portion of the oil control blade and the surface of the oil coating roller abrade each other, and abrasion of the edge portion thereby proceeds, whereby it may be difficult to maintain a stable coating amount of the oil in some cases after long operation time.
That is, in the case in which a coating amount of the oil is indicated by a when the oil control blade is in the initial state, and in the case in which a coating amount of the oil is indicated by b when the abrasion of the oil control blade proceeds, a <<b may occur in some cases. The reason for this is believed to be that the amount of the oil passing through is increased due to the progress in the abrasion of the edge portion of the oil control blade. Consequently, the amount of the oil transferred on the surface of the oil coating roller is excessively increased, and excessive coating on the fixing roller, and ultimately, on the recording media occurs, resulting in oil sagging, oil staining, and oil stripes. As a result, image quality is significantly degraded, and in particular, when images are fixed on an OHP sheet, sticking and degradation of tactile sensation due to excessive oil may occur in some cases.
The excessive coating amount of the oil not only increases consumption of the silicone oil but may also create problems in some cases, for example when double-sided copy is produced, paper supply defects (paper jams) due to slipping of the recording media when refed and cleaning defects, conveying defects, double images, and the like due to adhesion of excessive oil on the recording media on a photosensitive drum, a conveyer roller in a feed passage for conveying the recording media, and a conveyer belt.
On the other hand, in consideration of the increase in the coating amount of the oil due to the abrasion of the edge portion, when the oil control blade is in the initial state, the coating amount of the oil may be set to be less beforehand. In this case, the problems described above can be solved; however, new problems are of concern in which imag
Ishizuka Jiro
Kawamoto Hideo
Kishino Kazuo
Kitano Yuji
Sotome Osamu
Canon Kabushiki Kaisha
Chen Sophia S.
Fitzpatrick ,Cella, Harper & Scinto
Tran Hoan
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