Electrophotography – Control of electrophotography process – Having temperature or humidity detection
Reexamination Certificate
2001-01-03
2003-10-28
Royer, William J. (Department: 2852)
Electrophotography
Control of electrophotography process
Having temperature or humidity detection
C399S045000, C399S323000
Reexamination Certificate
active
06640062
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a toner image fixing device for use in an electrophotographic type image forming device such as a copying machine and the like.
Generally, a toner image fixing device for use in an electrophotographic type image forming device is provided with a pair of fixing rollers both of which abut at their cylindrical surface to each other and at least one of which is of a heat roller type incorporating a heater in its body. The heat roller type fixing device is generally such that a toner image developed on a recording material in an image forming step is fixed thereon by heat while the material passes, while being heated, through a nip between the paired fixing rollers, each of which is provided with a separating portion for separating the recording material from the cylindrical surface of the roller, thereby preventing the recording material from adhering to the latter surface.
In this instance, a toner image fixing device for a monochromatic type image forming device uses fixing rollers coated with a Teflon coat having a high strength against mechanical damages, so that the image quality may not be affected by separating portions being always in contact with the cylindrical surface of the rollers.
In contrast, the toner image fixing device for a color type image forming device, in which a color toner image consisting of plural toner layers, being thick and having an uneven surface formed on a recording material, is needed to have fixing rollers having a thick rubber coat capable of fusing and mixing the color toner by sufficiently heating the toner. In other words, the fixing rollers must have a thick rubber layer having a large thermal capacity and tightly covering the uneven surface of the toner image. The thick rubber coated surfaces of the fixing rollers may be damaged if the separating portions are always in contact with the roller surfaces. This results in deterioration of the toner image.
Therefore, a conventional fixing device adopts sheet separating portions capable of being detached from fixing rollers while not forming/fixing a toner image, as disclosed for example in Japanese Laid-Open Patent Publication No. 63-314582, or provides a very small gap between each sheet separating portion and a fixing roller surface.
On the other hand, for a heat roller type fixing device, a fixing roller thermally fixes a toner image developed on a recording material by directly contacting its hot surface with the toner image. Toner particles adhered onto the fixing roller may be undesirably transferred onto a toner image to be fixed on a next recording material.
As such, offset toner is apt to occur in a fixing device of the color type image forming device rather than in a fixing device of the monochromatic type image forming device. This is because the fixing device of the color type image forming device must use fixing rollers with a thick rubber coat having a large heat capacity and covering ability to fuse mixed color toners of a thick and uneven toner developed image consisting of plural toner layers. Such fixing rollers may not possess sufficient release ability due to their thick rubber layer.
For the fixing device of the color type image forming device, the fixing rollers are generally coated with a uniform coat of a release agent (e.g., silicone oil) applied with a coating roller.
By sufficiently applying an anti-offsetting agent to the surface of the fixing rollers, it is realized that a resilient recording material carrying a toner image developed thereon in normal ambient conditions can be easily separated from the fixing rollers even with a sheet separating portion apart from the roller surface.
However, at a humidity considerably higher than a normal humidity level, the recording material may lose its resiliency and not be separated from the fixing roller by the non-contacting sheet separating portions even though the rollers are sufficiently coated with release agent. The recording material may wrap around the fixing roller surfaces. In other words, in the conventional arrangement of the fixing rollers with the separating portions located apart from the roller surface, the recording material in the above condition may not be separated from the separating portions, resulting in jamming it between the fixing rollers.
In the fixing device, where sheet separating portions are used in contact with the fixing roller surfaces while a toner image is formed and fixed on a recording material, oil (anti-offsetting agent) sufficiently applied to the fixing roller may form stripes along the separating portions on the fixing roller surfaces. The oil stripes (contamination with oil) may appear and deteriorate a toner image fixed on a recording material. This contamination is not as visible on usual recording paper but may considerably deteriorate the toner image fixed on a transparent film sheet to be used for an overhead projector. In the latter case, dark stripes appear in the image projected on a screen through the overhead projector since light transmitted through the contaminated portion is reduced by scattering thereat.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a toner image fixing device capable of switching sheet separating portions into contacting positions in which the portions are in contact with corresponding roller surfaces or detached positions at which the portions are apart from corresponding roller surfaces in accordance with a condition of the resiliency of a recording material to surely prevent the recording material from wrapping around the fixing rollers and being jammed between the rollers as well as to reduce the frequency of contacting the separating portions with the surfaces of the corresponding rollers, thereby achieving a high quality toner image fixed on the recording material and extending the service life of the fixing rollers.
Another object of the present invention is to provide a toner image fixing device provided with a sheet separating portion for separating a recording material from a cylindrical surface of a fixing roller, the portion capable of changing its position from a contacting position in which it is in contact with the surface of the fixing roller to a detached position in which it is apart from the surface of the fixing roller and vice versa, a sheet separating portion driving means for turning the sheet separating portion into the contacting position or the detached position and a control means for controlling the sheet separating portion driving means based on, at least, either one of the humidity and the kind of the recording material.
Thus, the separating portion can be turned by the sheet separating portion driving means into its contacting position or detached position in accordance with at least one condition regarding the resiliency of the recording material, i.e., the humidity or the kind of the recording material. This allows the separating portion to be used in contact with the fixing roller surface for separating the recording material from the roller surface merely under the condition that the recording material may easily wrap around the fixing roller and may not depart by itself there from.
Furthermore, the frequency of putting the separating portion into contact with the fixing roller surface is restricted to the case when the recording material may easily wrap around the fixing roller, so the frequency of forming an oil stripe on the roller surface by the separating portion can be minimized, preventing possible deterioration of the toner image fixed on the material, and the possibility of damaging the roller surface by the separating portion can also be reduced, thus extending the service life of the fixing roller.
Another object of the present invention is to provide a toner image fixing device for fixing by heating a toner image formed on a recording material passing through a nip between paired fixing rollers, wherein it is provided with paired sheet separating portions, each portion being capable of changing its position from a co
Ide Atsushi
Tsubaki Yoritaka
Renner , Otto, Boisselle & Sklar, LLP
Royer William J.
Sharp Kabushiki Kaisha
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