JPH04287074A - Fixing device for image forming device - Google Patents

Abstract

PURPOSE:To easily perform the temperature management of a heat source based on the difference of heating directions and to prevent fixing time from being extended when surface heating or back plane heating is selected corresponding to the quality of transfer paper by setting a gap between a presser roller and a heat source roller used in the backplane heating at a value less than a specific value. CONSTITUTION:The presser rollers 4, 5 are comprised of emery rollers on which irregularity are formed, for example, by scattering aluminum particle on the surfaces of RTV rubber rollers, and the gap G between the surface and that of the heating roller 2 is set at a value less than 0.1mm. Ring members 12 with plate thickness equivalent to the gap G are loaded at both terminals in the axial direction of the presser rollers 4, 5 in the gap G, and it can be obtained by abutting the ring member 12 with the circumferential plane of the heating roller 2. By forming the device in such a way, no heat insulating layer exists, therefore, the transfer of heat between the heating roller 2 can be performed satisfactorily, thereby, surface temperature almost equal to that of the heating roller 2 can be supplied to the transfer paper.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an image forming apparatus, and more particularly to a structure within a fixing device used in a wet copying machine.

0002

[Prior Art] As is well known, in a copying machine, which is one type of image forming apparatus, a wet type developer containing toner in a solvent is used to form an electrostatic latent image on a photoreceptor. Visual processing may be required. Transfer paper, on which toner is adhered using the above-mentioned wet developer, is imaged by a fixing device consisting of a heating roller and a pressure roller facing each other across a conveyance path. It is now being established. As an example of the fixing device is shown in FIG.
The main parts include a heating roller A and a pressure roller B, which face each other across the transport path of the transfer paper P. The heating roller A has a built-in heat source, and also has a pressure roller B. The heating roller B is moved by the swinging arm D which is biased by the spring C.
It is designed to come into pressure contact with A. In addition, heating roller A
Silicon oil application device E and separation device F are applied to the surface of
The image surface of the transfer paper P conveyed from the right side in the figure is brought into contact with the heating roller A to be fixed.

By the way, in the above-mentioned fixing device,
The fixing performance varies depending on the material of the transfer paper carrying the image, and a uniform fixing effect may not be obtained in some cases. In other words, the heating roller set at a uniform temperature is different between plain paper, which is relatively easy for the developer solvent to penetrate, and special transfer paper, such as OHP film or second original paper, which is difficult to penetrate. - Even if the image is in contact with the
In particular, in the case of the above-mentioned special transfer paper, image smearing tends to occur due to differences in the degree of dryness, which is affected by the amount of heat transferred.

In order to solve this problem, a structure has been proposed in which the direction of heating the transfer paper is changed depending on the material of the transfer paper. That is, FIG. 5 shows the above-mentioned fixing device, and this fixing device 1 includes, for example, a heating roller 2 made of room temperature vulcanizable silicone rubber (RTV rubber) and capable of rotating in the forward and reverse directions. A pressure roller 3 made of an elastic material such as a sponge and capable of rotating forward and backward, facing the heating roller 2 across the conveyance path of the transfer paper;
The main part is formed by a pair of pressure rollers 4 and 5 that come into contact with the heat roller 2 at different positions on the circumferential surface of the heat roller 2 on the side opposite to the contact position with the pressure roller 3. It is configured. The above-mentioned heating roller 2 and pressure roller 3 sandwich and convey a transfer paper made of plain paper that is easily penetrated by developer solvent, and apply heat from the surface corresponding to the image surface of the transfer paper. The heating roller and pressing rollers 4 and 5 constitute a first fixing section for fixing, and the heating roller and pressing rollers 4 and 5 sandwich and convey a transfer paper that is difficult to penetrate a solvent, such as an OHP film or a second original paper. It constitutes a second fixing section that performs heating from the back side of the image surface of the transfer paper.

Furthermore, in order to convey the transfer paper to the first and second fixing sections described above, a rocker is installed at the entrance of the conveyance path for the transfer paper toward each of the fixing sections to switch the direction of conveyance of the transfer paper. A movable claw 6 is arranged, and the transport path for front side heating shown by a chain double-dashed line and the transport path for back side heating shown by a broken line are switched depending on the material of the transfer paper selected at an operation part (not shown). The rocking position is set so that the

On the other hand, the above-mentioned pressing rollers 4 and 5 may be composed of emery rollers whose surfaces have irregularities formed by scattering fine particles of alumina, and in this case, To enable the transfer paper to be held and conveyed between the heating roller 2, to prevent the uneven member on the surface from falling off when it comes into contact with the heating roller 2, and to prevent the uneven member on the surface from falling off when it comes into contact with the heating roller 2.
In order to prevent the unfixed toner adhering to the roller side from being transferred onto the transfer paper again, a gap of, for example, about 0.3 to 0.5 mm is set between the heating roller 2 and the surface of the heating roller 2. (for example, Japanese Patent Application Laid-open No. 2-150877)
.

[0007]

By the way, in the fixing device 1 described above, uniform fixing is performed depending on the material of the transfer paper, but when heating is performed from the back side of the transfer paper, It has been found through experiments that the temperature on the image plane differs by about 15 degrees compared to the case of heating from the surface. In reality, sufficient fixing is achieved when the heating temperature from the front side is 140 degrees, while when heating from the back side it is 140 degrees.
It is said that unless the temperature is set at about 80 degrees, it is not possible to obtain the same fixing efficiency as in the case of surface heating described above. On the other hand, when heating the back side, the heating roller 2 is made of RTV rubber, which has inferior heat transfer efficiency compared to metal, in order to enhance the offset prevention function, so the heating temperature for the image surface is set. In order to do this, it is necessary to compensate for the thermal efficiency due to the difference in materials in addition to the difference in heating direction mentioned above. Specifically, in the case of back side heating, it is necessary to correct the temperature increase to obtain the same fixing efficiency as front side heating. Settings have to be made, which poses problems such as complicating temperature control at the heat source and lengthening the fixing time.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the above-mentioned problems in the conventional fixing device, particularly in view of the problem when the heating roller is made of silicone rubber, which has poor heat transfer efficiency compared to metal. It is equipped with a structure that allows for easy temperature control of the heat source and prevents changes in fixing efficiency, regardless of the difference in the material of the transfer paper and the difference in the heating direction for the front and back sides. The purpose is to obtain a fixing device.

[0009]

[Means for Solving the Problems] In order to achieve this object, the present invention provides a heating roller that can be rotated in forward and reverse directions and has a heat source inside it, across the transport path of the transfer paper, and a heating roller that can be rotated in both directions. A plurality of pressurizing rollers that can be rotated in forward and backward directions and facing the heating roller at a position different from the position corresponding to the pressing roller on the circumferential surface of the heating roller are a first fixing section, which is equipped with a pressure roller, and heats the surface of the transfer paper with the heating roller and pressure roller when rotating in the normal direction; In the fixing device, the heating roller constitutes a second fixing section that heats the back side of the transfer paper, and the feeding direction of each of these fixing sections is switched depending on the material of the transfer paper. and the pressure roller, the gap formed between the surfaces is set to 0.1 mm or less, and the first,
A feature is that the temperature settings for the second fixing section are the same. Further, the present invention is characterized in that the pressing roller is made of room temperature vulcanized silicone rubber having fine irregularities on its surface. Furthermore, the present invention is characterized in that the gap between the surfaces of the heating roller and the pressing roller is 0 mm.

0010

[Operation] According to the present invention, there is almost no gap between the heating roller and the pressure roller that constitute the fixing section in the case of back side heating, in other words, there is no heat insulating layer. Therefore, heat exchange between the transfer paper and the heating roller is performed well, and the transfer paper can be given a surface temperature that is approximately the same as that of the heating roller.

[0011]

[Embodiment] Details of an embodiment of the present invention will be explained below with reference to FIGS. 1 to 3. FIG. 1 is a schematic diagram corresponding to FIG. 5 showing the overall configuration of a fixing device according to an embodiment of the present invention, and the same components as those shown in FIG. 5 are designated by the same reference numerals.

That is, the fixing device 1 includes a heating roller 2 which is made of room temperature vulcanizable silicone rubber (RTV rubber) and which can rotate in the forward and reverse directions, and a heating roller that is sandwiched between a transfer paper conveyance path.
A pressure roller 3 made of an elastic body such as a sponge and capable of forward and reverse rotation faces the heating roller 2, and a heating roller The main part is composed of a pair of pressing rollers 4 and 5 that abut at different positions on the circumferential surface of the roller 2. The above-mentioned heating roller 2 and pressure roller 3 sandwich and convey a transfer paper made of plain paper that is easily penetrated by developer solvent, and apply heat from the surface corresponding to the image surface of the transfer paper. The heating roller and pressing rollers 4 and 5 constitute a first fixing section for fixing, and the heating roller and pressing rollers 4 and 5 sandwich and convey a transfer paper that is difficult to penetrate a solvent, such as an OHP film or a second original paper. It constitutes a second fixing section that performs heating from the back side of the image surface of the transfer paper.

In order to convey the transfer paper to the first and second fixing sections described above, a rocker is installed at the entrance of the conveyance path for the transfer paper toward each of the fixing sections to switch the direction of conveyance of the transfer paper. A movable claw 6 is arranged to switch between a conveyance path for back side heating shown by a chain double-dashed line and a conveyance path for front side heating shown by a broken line according to the material of the transfer paper selected at an operation section (not shown). The rocking position can be set.

Furthermore, on the surface of the heating roller 2 mentioned above,
A silicone oil application device 7 corresponds to this. That is, the silicone oil application device 7 includes an application roller 7A that is rotatable in contact with the surface of the heating roller 2, and this application roller.
A supply roller 7C contacts the roller 7A and has a coating felt 7B, which will be described later, in contact with its peripheral surface, and an oil tank 7D in which one end of the coating felt 7B is immersed and contains silicone oil. and a cleaning roller 7E that comes into contact with the surface of the heating roller 2 and is stopped by a clutch (not shown) when the heating roller 2 rotates in reverse. In addition to intermittently supplying oil to the circumferential surface of the heating roller 2, excess oil on the heating roller is recovered. In the figure, the reference numeral 8 indicates a paper feed roller, the reference numeral 10 indicates a pair of paper ejection rollers, and the reference numeral 11 indicates a cleaning roller that comes into contact with the pressure rollers 4 and 5. .

On the other hand, the above-mentioned pressing rollers 4 and 5 are constituted by, for example, emery rollers having irregularities formed by scattering fine alumina particles on the surface of an RTV rubber roller, as shown in FIG. As such, the gap G between that surface and the surface of the heating roller 2 is set to 0.1 mm or less. The above-mentioned gap G can be achieved by, for example, as shown in FIG. - It can be obtained by bringing it into contact with the circumferential surface of the rubber 2.

Furthermore, in this embodiment, the above-mentioned gap G may be eliminated and set to 0 mm; in this case,
Although not shown, the heating roller 2 is brought into direct contact with the surface of the heating roller 2 without using the ring member 12 described above.

Since this embodiment has the above structure,
The heating roller 2 and the pressing rollers 4 and 5 are close to each other in a state where they are almost in contact with each other. The rotational speeds of the pressing rollers 4 and 5 are set so that the same moving speed can be obtained at the position facing the heating roller 2. Therefore, when the transfer paper is not conveyed to the second fixing section composed of the heating roller 2 and the pressing rollers 4 and 5, the pressing rollers 4 and 5 are The temperature of the surface of the heating roller 2 is approximately the same as that of the surface of the heating roller 2, and the silicone oil applied to the surface of the heating roller 2 is also supplied. At this time,
When the heating roller 2 comes into contact with the heating roller 2, the alumina fine particles scattered on the surfaces of the pressing rollers 4 and 5 tend to be scraped off during sliding, but the heating roller 2 and the pressing roller The speeds at the opposing positions of rollers 4 and 5 must match, and heating roller 2
Since the surface is made of an elastic RTV rubber, falling off is prevented.

On the other hand, when the transfer paper is conveyed to the second fixing section, the pressure rollers 4 and 5 press the transfer paper against the surface of the heating roller 2. At this time, the transfer paper is heated not only by the heat from the heating roller 2 side but also by the heat stored in the press rollers 4 and 5, so that the temperature rise can be accelerated. Furthermore, transfer of unfixed toner toward the transfer paper, which may occur when the pressure rollers 4 and 5 come into contact with the transfer paper, can be avoided by applying a heating roller to the circumferential surface of the pressure rollers 4 and 5. The presence of the silicone oil supplied from the roller 2 prevents mold releasability.

The above-mentioned pressing rollers 4 and 5 and heating roller 2
The inventor conducted an experiment regarding the fixing efficiency and the presence or absence of offset with respect to the gap between the surface and the surface, and obtained the results shown in the following table.

[0020]

[Table 1]

The above table shows O, which is one of the special transfer papers.
The fixing performance and offset amount were evaluated on a five-point scale for back side heating of HP film. The numbers 1 to 5 for fixability rank the degree of image blurring, with 1 being a state where the image is completely blurry and difficult to read, and 2 being a state where the image is slightly blurry and solid image density. 3 is a state where there is little image blurring but the characters in the solid image are blurred, 4 is a state where there is almost no image blurring and the characters in the solid image are blurring, and 5 is a state where there is some image blurring. Not at all, it means a solid state of being in a solid image. Further, the numbers 1 to 5 regarding the offset mean that the larger the number, the smaller the offset.

As is clear from the table, according to the gap structure between the pressing roller and the heating roller in this example, the metal roller, which is effective in heat transfer, is placed between the heating roller and the pressing roller. It is possible to obtain almost or better fixing performance than in the case of using the above method, and in addition, almost no offset is observed.

As described above, according to this embodiment, the heating roller is
When a TV rubber roller is used and a pressure roller is placed close to or in contact with this heating roller, the release material from the heating roller is automatically applied to the pressing roller. This allows the toner to be unfixed to the transfer paper.
metastasis can be prevented. In addition, when the pressure roller is brought into contact with the heating roller, by making the heating roller's elastic body absorb shock and moving at the same speed, fine particles on the surface of the pressure roller will slide. It is possible to avoid a situation where it gets scraped off and falls off.

[0024]

As described above, according to the present invention, the pressure roller which cooperates with the heating roller to press the transfer paper against the heating roller is placed in the gap between the heating roller and the pressing roller. A state in which there is no
By providing the surfaces of both rollers in a state in which they are substantially in contact with each other, a heat storage effect from the heating roller can be obtained, and the temperature increase can be promoted when the back side of the transfer paper is heated. Therefore, even if the temperature is set to be substantially the same as the temperature used for heating the front surface of the transfer paper, the temperature necessary for heating the back surface can be obtained, so that the temperature control of the heat source can be simplified. Furthermore, since the same temperature can be set for both front surface heating and back surface heating, it is possible to avoid a situation where the time required to raise the temperature becomes longer.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the overall configuration of a fixing device according to an embodiment of the present invention.

FIG. 2 is a side view schematic diagram showing essential parts of the fixing device shown in FIG. 1;

FIG. 3 is a perspective view showing an example of the main components shown in FIG. 2;

FIG. 4 is a model diagram showing a conventional fixing device.

FIG. 5 is a schematic diagram corresponding to FIG. 1 showing another example of a conventional fixing device.

[Explanation of symbols]

1 Fusing device 2 Heating roller 3 Pressure roller 4, 5 Press roller 12 Ring member G Gap

Claims (3)

[Claims] [Claim 1] A heating roller that can rotate in the forward and reverse directions and has a heat source inside thereof across the conveyance path of the transfer paper, and a pressure roller and a heating roller that can rotate in the forward and reverse directions opposite to the heating roller. - a plurality of pressure rollers that are rotatable in forward and reverse directions and that face the heating roller at a position different from the position corresponding to the pressure roller on the circumferential surface of the roller; - a first fixing section that heats the front side of the transfer paper using a roller and a pressure roller, and a second fixing section that heats the back side of the transfer paper using the heating roller and a pressure roller when reversed. A gap formed between the surfaces of the heating roller and the pressing roller in a fixing device that configures a fixing section and switches the conveyance direction for each fixing section depending on the material of the transfer paper. is set to 0.1 mm or less, and the above first,
A fixing device for an image forming apparatus, characterized in that temperature settings for the second fixing section are the same. 2. A fixing device for an image forming apparatus according to claim 1, wherein the pressure roller is made of room temperature vulcanized silicone rubber having fine irregularities on its surface. 3. A fixing device for an image forming apparatus according to claim 1, wherein the gap between the surfaces of the heating roller and the pressing roller is 0 mm.