Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-01-12
2002-10-08
Brase, Sandra (Department: 2852)
Electrophotography
Image formation
Fixing
Reexamination Certificate
active
06463249
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an offset preventing liquid supplying device for a toner image fixing device for use in an electro-photographic type image forming device such as a copying machine and the like and also relates to an image forming device provided with the same offset preventing liquid supplying device.
Generally, a toner image fixing device for use in the electro-photographic type image forming device is provided with a pair of fixing rollers both of which abut at their cylindrical surfaces to each other and at least one of which is of the heat-roller type incorporating a heater in its cylindrical body. The heat-roller type toner image 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, being heated, through a nip between the paired fixing rollers. Direct contact of the fixing roller with a toner image developed on a recording material may cause toner particles to adhere to the working surface of the fixing roller, which particles is then undesirably transferred onto a toner image to be fixed on a next recording material.
As such, so-called “offset toner” is apt to occur in the fixing device of the color type image forming device rather than in the 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 (e.g., Magenta, cyan, yellow and black layers) by heating. Such fixing rollers may not possess sufficient release ability due to its thick rubber layer.
In the conventional fixing devices of the color-type image forming device, as shown for example in
FIG. 1
, offset preventing liquid (g) stored in a storage tank (a) being able to supply is sucked by a piezoelectric or electromagnetic type pump (b) disposed above the tank (a) through a tubular piping (c) and applied by an applying means (e) to a working surface of a heat roller (fixing roller) (d). The applying means (e) is provided with a supplying pipe (f) that extends above and along the heat roller body (d) and has plural supplying ports (h) arranged in the same direction thereof to feed droplets of offset preventing liquid (g) onto a felt material (i) and a surface of an applying roller (t). Rotating in contact with the heat roller (d), the applying roller (t) applies a uniform coat of the offset preventing liquid (g) over a whole length of the cylindrical surface of the heat roller (d). An excess of the offset preventing liquid (g) falling from the applying roller is collected in a pan (j) disposed under the heat roller (d), wherefrom it is returned through a tubular return piping (k) to the storage tank (a).
The offset preventing liquid (g) is thus circulated from the storage tank (a) to the applying means (e). When a level of the offset preventing liquid (g) in the storage tank (a) lowered below a specified level, a sensor (s) for controlling the amount of the liquid in the tank (a) actuates to warn the user of the need for supplying the liquid (g) in the tank (a) and/or to temporally stop the toner image forming process.
In the offset preventing liquid supplying device, it is very important to maintain a constant feed rate of the offset preventing liquid to a full length of the working surface of the heat roller (d). A partial break of a coat of offset preventing liquid (g) applied on the working surface of the heat roller in its longitudinal direction may result in wrapping of the recording sheet around the heat roller (d) and/or unintentional transferring of offset toner to an image fixed on a next recording sheet. Partially excessive supplying of the offset preventing liquid to the heat roller (d) in its longitudinal direction may cause leakage of the liquid from the fixing device.
Therefore, the offset preventing liquid supplying device has the pipe (f) with upwardly opening ports (h) made in its wall relative to the applying means (e) as shown in
FIGS. 2 and 3
to simultaneously supply the offset preventing liquid (g) through all the supplying ports (h) on the condition that the image forming device is horizontally mounted.
The equally balanced feed of the offset preventing liquid (g) relative to the longitudinal direction of the heat roller (d) is realized by differentiating diameters of the supplying ports on the upstream (front side in
FIGS. 4 and 5
) and downstream (rear side in
FIGS. 4 and 5
) sides of the offset preventing liquid supplying pipe (f) as shown in
FIGS. 4 and 5
. In practice, the offset preventing liquid supplying ports (h) disposed closer to the upstream (front) end of the offset preventing liquid supplying pipe (f) are smaller in diameter and the ports disposed closer to the downstream (rear) end of the supplying pipe (f) are larger in diameter.
Recently, there has been a steady trend of space-saving design (miniaturization) of the image forming devices. As the result, the image-forming devices may be used as mounted at various places including not-horizontal places. Accordingly, it is necessary to consider a margin for tilting angle of the device.
In this instance, the conventional offset preventing liquid supplying device uses a liquid supplying pipe (f) having a series of upwardly opening ports (h) made in its upper wall of the applying means (e). When the image forming device is mounted in a tilted state with the supplying pipe (f) tilted up in the downstream (rear side) direction relative to the length of the heat roller (d), the upstream side (front side) of the supplying pipe (f) is located at a lower level as shown in
FIG. 6
, resulting in supplying offset preventing liquid (g) merely from the upstream side ports (h). Namely, in this case, the liquid (g) hardly flows out through the downstream side ports (h), causing unbalanced (uneven) supplying of the offset preventing liquid (g) relative to the length of the heat roller (d). In
FIG. 6
, letter “n” designates a horizontal line.
When the image forming device is mounted in a position tilted in the transverse direction perpendicular to the longitudinal direction of the heat roller (d) as shown in
FIGS. 7 and 8
, the upwardly opening ports (h) in the wall of the supplying pipe (f) may correspondingly reduce their cross-sectional areas, causing reduction of outflows (feeds) though every port (h). Furthermore, no feed of the offset preventing liquid (g) from the downstream side ports (h) may occur because the feed of the liquid (g) through the upstream side ports under a higher pressure is accompanied by forming an air layer (v) due to the viscosity of the offset preventing liquid (g) in the downstream portion of the supplying pipe (f) with a low pressure.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an offset preventing liquid supplying device of a toner image fixing device for use in an image forming device, which system is capable of uniformly supplying offset preventing liquid to a working surface of a heat roller with an evenly balanced feed over a full length of the roller irrespective of the tilted state of the image forming device, and an image forming device provided with the same offset preventing liquid supplying device.
The present invention relates to an offset preventing liquid supplying device for supplying offset preventing liquid to a working surface of a fixing roller of an toner image fixing device for thermally fixing a toner image developed on a recording material. This system includes a storage means for storing the offset preventing liquid, a liquid applying means for applying the offset preventing liquid to the working surface of the heat roller and a pump for supplying the offset preventing liquid from the storage means to the liquid applying means. The liquid applying means has a supplying pipe with series of supplying ports made in a wall thereof
Brase Sandra
Kenner Otto, Boisselle & Sklar
Sharp Kabushiki Kaisha
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