JPH10288906A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the adhesion of toner with the lapse of time, to uniformize the temperature of a pressure roller and a heating roller without lowering heat conductivity and to eliminate the need of exchanging a heat conduction roller so as to reduce a running cost by providing the heat conduction roller abutting on the pressure roller with a mold-released layer. SOLUTION: This device is provided with the heating roller 1 equipped with a heater 2 inside, the pressure roller 3 coming in press-contact and rotating with the roller 1 and the heat conduction roller 4 rotating with the roller 3. Fixation is performed by advancing transfer paper P holding unfixed toner T into a nip part between both rollers 1 and 3 from a direction shown by an arrow. The roller 3 freely rotates following the rotation of the roller 1. The roller 4 has such the constitution that the mold-released layers 4b consisting of heat resistant releasing material are laminated and formed on the outside surface of a cylindrical core bar 4a formed of metal excellent in the heat conductivity, and freely rotates following the rotation of the roller 3 while its outer peripheral surface abuts on the roller 3 nearly all over the length in the axial direction thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement of a fixing device used in an image forming apparatus such as a laser beam printer, a plain paper copying machine, a plain paper facsimile machine, etc. using an electrophotographic process, and more particularly, to a fixing device. The present invention relates to a fixing device capable of efficiently achieving uniform temperature of a heating roller and a pressure roller.

[0002]

2. Description of the Related Art In an image forming apparatus utilizing an electrophotographic process, a toner image formed on a photoreceptor is transferred onto a transfer sheet, and then the transfer sheet is guided to a fixing device and heated and pressurized while being heated. The toner image is fixed.
The fixing device includes a heating roller having a heater and a pressure roller, and presses the transfer paper while heating the transfer paper in a process of passing the transfer paper holding the unfixed toner image through a nip portion of both rollers. Thereby, the toner image is fixed. By the way, when a small-sized transfer sheet is passed through the fixing device, the temperature of the central portion of the heating roller in the axial direction is deprived of the heat by the transfer sheet, so that the temperature is lower than the set fixing temperature. Then, based on a temperature detection signal from a thermistor provided at the axial center portion of the heating roller, the control unit further causes the heater to generate heat in order to return the temperature of the heating roller to the fixing set temperature. Since the heater is configured to heat uniformly over the entire length of the heating roller, if the heating is performed to raise the temperature of the central portion to the fixing set temperature, the temperature does not decrease when the small-size transfer paper passes. The temperature at the end of the heating roller further rises above the fixing temperature. As a result, the temperature distribution in the axial direction of the heating roller becomes non-uniform, and wrinkles occur when the transfer paper is fixed, or when the temperature at the end is higher than the endurance temperature of the release layer on the surface of the heating roller. Offset occurs due to deterioration of the release layer.

The following method is generally known as a measure against such a problem. 1. A method in which a plurality of heaters are provided, and the central portion and the end portion in the axial direction of the heating roller are separately heated and controlled by each heater, thereby preventing a rise in the temperature of the end portion when the central portion is heated. This method has a disadvantage that the cost is extremely increased by the increased number of heaters, power supplies, and circuits in order to increase the number of heaters. 2. A method in which the temperature of the pressure roller and the heating roller is made uniform by contacting the heat transfer roller having the same configuration as the conventional cleaning roller over the entire length of the pressure roller surface in the axial direction. In this method, the toner on the transfer paper is fixed on the transfer paper at the nip portion, but a very small amount of toner remains on the heating roller, and after the transfer paper passes, this toner moves to the pressure roller. Even in the case of a small amount of toner that does not cause a problem with the back of the transfer paper, etc. in the conventional method, the heat transfer roller with the same configuration as the cleaning roller attempts to equalize the heat. A toner layer is formed by being adhered and fixed on the surface of the substrate, and the thermal conductivity is deteriorated, so that the temperature cannot be made uniform.

As a conventional example for solving such a problem, Japanese Utility Model Laid-Open No. Sho 60-39065 (Fuji Xerox)
The toner on the surface of the heating roller is moved to the pressure roller side by forming the release layer on the surface of the pressure roller from a material having a lower releasability to toner than the release layer on the surface of the heating roller. Then, a method of removing toner by a cleaning roller and then contacting a blade or felt with the cleaning roller to remove toner from the cleaning roller is introduced. However, in this method, the toner cannot completely be removed because the toner enters the concave portion of the minute uneven portion on the surface of the cleaning roller. Over time, the toners are combined and become hard and cover the entire cleaning roller. I will. Further, there is a problem that the toner scraped off by the blade is scattered and adheres to the transfer paper, thereby deteriorating the image. The present invention has been made in view of the above, and by providing a release layer on the surface of a heat conductive roller that abuts on a pressure roller, improves the releasability of the heat conductive roller and prevents toner from adhering over time. It is another object of the present invention to make the temperature of the pressure roller and the heating roller uniform without lowering the heat conductivity, and to reduce the running cost by eliminating the need to replace the heat conduction roller.

[0005]

In order to achieve the above object,
According to a first aspect of the present invention, there is provided a fixing device having a thin cylindrical heating roller having a heat source, a pressure roller in contact with a peripheral surface of the heating roller, and a heat conducting roller in contact with the peripheral surface of the pressure roller. A release layer is provided on the surface of the heat conduction roller. The invention according to claim 2 is characterized in that the release layer of the heat conductive roller is formed of a conductive heat-resistant release material, and a charge removal brush that slides on the release layer and electrically grounds the release layer is provided. Features. According to a third aspect of the present invention, when the heating roller is not heated, the two rollers are arranged so that a gap is formed between the heat conduction roller and the pressure roller, and the width of the gap is set by fixing the heating roller. The width is such that the elastic layer and the release layer on the surface of the pressure roller heated by the heating roller when the temperature rises to the temperature and the diameter of the release layer abuts on the heat conduction roller by expanding the diameter. The invention of claim 4 is characterized in that the elastic layer of the pressure roller is made of foamed silicone rubber. The invention according to claim 5 is characterized in that an application roller for applying oil having good releasability to the surface of the heat conduction roller is disposed in contact with the surface of the heat conduction roller.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments shown in the drawings. FIG. 1 is a schematic diagram illustrating the configuration of a fixing device according to an embodiment of the present invention. The fixing device includes a heating roller 1 having a heater 2 therein, and a pressure roller that presses against and rotates with the pressure roller 1. The fixing is performed by allowing the transfer paper P, which has the roller 3 and the heat conductive roller 4 that rotates with the pressure roller 2 and holds the unfixed toner T, to enter the nip portion of both rollers from the direction of the arrow. Heating roller 1 is A
1, a hollow cylindrical thin metal core 1a made of a metal such as Fe or the like is provided with a release layer 1b made of a heat-resistant release material such as PTFE or PFA on the outer surface thereof. A heater 2 for heating the metal core is disposed in the section. The heater 2 has a structure for uniformly heating the cored bar 1a over the entire length in the axial direction, and receives a temperature detection signal from a thermistor (not shown) provided at the center in the axial direction of the heating roller, as in the related art. The control unit controls the power supply to the heater to maintain the set fixing temperature. The pressure roller 3 is made of Al,
An elastic layer 3b made of silicon rubber or the like is provided on the outer surface of a cylindrical metal core 3a made of a metal such as Fe, and a release layer made of a heat-resistant release material such as PTFE or PFA is provided on the outer surface. 3c is formed. The pressure roller 3 is brought into contact with the heating roller 1 to form a nip portion, and the transfer paper P
The upper unfixed toner T is fixed. The pressure roller 3 comes into pressure contact with the heating roller 1 and rotates freely as the heating roller rotates. The heat conductive roller 4 is formed by laminating a release layer 4b made of a heat-resistant release material such as PTFE or PFA on the outer surface of a cylindrical cored bar 4a formed of a metal having good thermal conductivity such as Al or Cu. The outer peripheral surface of the pressure roller 3 contacts the entire length of the pressure roller 3 in the axial direction, and freely rotates in accordance with the rotation of the pressure roller.

When a small-size transfer sheet is passed through the fixing device, the heat is taken away by the transfer sheet at the central portion of the heating roller 1 and the pressure roller 3 in the axial direction. Then, the control unit, which has received a temperature detection signal from a thermistor (not shown) provided at the center of the heating roller 3, heats the heater to a high temperature in order to return the heating roller to the fixing set temperature. For this reason, the temperature difference between the central part and the end part increases due to the temperature of the end part in the axial direction of the heating roller 1 and the pressure roller 3 rising beyond the fixing set temperature. Since the same phenomenon also appears in the pressure roller 3 that is in pressure contact with the heating roller 1, the heat conduction roller 4 that is in contact with the pressure roller 3 (made of a metal material having a high heat conductivity such as Al or the like). ), The temperature at the end of the pressure roller 3 is transmitted to the lower temperature center,
While the temperature at the end of the pressure roller 3 decreases, the temperature at the center increases moderately. As a result, the temperature of the end portion of the heating roller 1 also decreases, and the temperature of the central portion increases, so that the temperature of the heating roller 1 is made uniform over the entire length. The toner T on the transfer paper P is fixed on the transfer paper P at the nip portion,
A very small amount of toner adheres and remains on the heating roller 1 side, and a part of the toner is further transferred to the pressure roller 3 after the transfer paper P is passed. However, in the present invention, since the release layer 4b is provided on the surface of the heat conductive roller 4, the adhesion of the minute amount of toner can be reduced, and the adhesion of the toner layer to the surface of the heat conductive roller and It is possible to prevent the heat conduction function from being deteriorated due to the deterioration.

Next, FIG. 2 is a block diagram of another embodiment of the present invention. The same parts as those of the embodiment of FIG. The release layer 4b of the heat conductive roller 4 is formed of a conductive heat-resistant release material such as PTFE or PFA, and the release layer 4b is slidably contacted with a neutralization brush 10 made of carbon fiber or the like. It is characteristic that the brush 10 is supported by a unit base (conductive material) 11 which is electrically grounded, so that the discharging brush 10 is grounded. With this configuration, the release layer 4b on the surface of the heat conductive roller 4 falls to the ground through the charge removing brush 10, so that
The small amount of toner attached to the pressure roller 3 is no longer charged,
The movement of the minute amount of toner to the heat conduction roller 4 due to static electricity can be effectively prevented, and the prevention effect can be further enhanced.

FIG. 3 is a block diagram of another embodiment of the present invention. The same parts as those in FIG. 2 are denoted by the same reference numerals, and the duplicated description is omitted. However, the heater 2 is not turned on. In the state,
A feature is that a gap S is provided between the peripheral surfaces of the pressure roller 3 and the heat conduction roller 4. The size of the gap S is such that when the surface temperature of the heating roller 3 reaches the set temperature, when the pressure roller 4 rises to a fixing temperature, the elastic layer 3b and the release layer 3c of the pressure roller are It is set so as to expand and expand and come into contact with the heat conduction roller 4. If the material of the elastic layer 3b is, for example, foamed silicon rubber, the elastic layer 3b has a shell layer with air, so that the expansion coefficient becomes larger than that of normal silicon rubber, and even if the gap S is set to be large. In addition, the contact between the elastic layer 3b and the heat conductive roller 4 can be reliably ensured by the expansion of the elastic layer 3b during thermal expansion. As described above, the size of the gap S can be increased, and the gap S does not need to be set strictly. Therefore, it is not necessary to tighten the assembly tolerance of each part, and the manufacturing cost and the maintenance cost can be reduced.

In the above arrangement, when the main switch of the copier is turned on to turn on the heater 2 and the heating roller 1 rises to the fixing temperature, the control unit controls the temperature based on a detection signal from the thermistor. Control to keep At this time, the heat of the heating roller 1 is also transmitted from the nip to the pressing roller 3. However, at this time, since the temperature of the elastic layer 3b of the pressure roller 3 is not sufficiently raised, there is a gap S between the pressure roller 3 and the heat conduction roller 4, and the heat is released to the heat conduction roller 4. I can't go. Therefore, the warm-up time is not delayed. On the other hand, when the heating roller 3 rises to the set temperature and shifts to the fixing-possible state, the control unit starts the rotation of the heating roller 1 and the pressing roller 3, so that the elastic layer 3b of the pressing roller 3 as a whole is sufficient. Expands when heated
It contacts the heat conduction roller 4. The heat transfer function of the heat transfer roller 4 and the charge removal function of the charge removal brush 10 are the same as those described in the above embodiments.

FIG. 4 is a schematic structural view of a fixing device according to another embodiment of the present invention. Instead of eliminating the static elimination brush 10 and the unit base 11 of the embodiment of FIG.
The coating roller 15 is made of an elastic material impregnated with an oil having a releasability such as silicone oil. This application roller 15
Has a configuration in which a roller-shaped oil holding member 15b made of a soft, porous, and highly oil-absorbing material is fixed around an axis 15a.
And apply silicon oil to the surface of the heat transfer roller 4. As a result, the surface releasability of the heat conductive roller 4 is further improved, and the adhesion of toner can be prevented. In addition, since the silicone oil moves to and adheres to the surfaces of the pressure roller 3 and the heating roller 1, the releasability of each roller is also improved, and the effect of preventing toner adhesion can be enhanced. The application roller 15 of FIG. 4 may be applied to the embodiment of FIG. In the above-described embodiment, the example in which the heat conductive roller is applied to the fixing device having the heating roller in which the heater such as the halogen lamp is disposed at the center of the roller has been described. The present invention can also be applied to a fixing device using a core material provided with a heating resistor, or a core material having a heating resistor itself.

[0012]

In the fixing device, the toner T on the transfer paper P is fixed to the transfer paper P at the nip portion between the heating roller and the pressure roller, but a very small amount of toner remains on the heating roller 1. After the transfer paper P has passed, the process further proceeds to the pressure roller 3.
Even in the case of a small amount of toner that does not cause a problem without causing back contamination of transfer paper or the like in the conventional method, when heat uniformity is intended by a heat conductive roller having the same configuration as the cleaning roller,
The toner adheres to the surface of the heat conductive roller, and the toner layer, which is a resin, is solidified on the surface, and the thermal conductivity is deteriorated. In order to solve such a problem, the first aspect of the present invention improves the releasability of the surface of the heat-conducting roller in contact with the pressure roller, thereby preventing toner from adhering and preventing the thermal conductivity from decreasing over time. The temperature of the pressing roller and the heating roller can be made uniform. Next, in the second aspect of the present invention, the release layer 4b on the surface of the heat conductive roller 4 is grounded through the static elimination brush 10, so that a small amount of toner attached to the pressure roller 3 is transferred to the heat conductive roller 4 due to static electricity. Can be prevented, and the prevention effect can be further enhanced.

In the third aspect of the present invention, when the copying machine is started up, there is a gap between the pressure roller 3 and the heat conduction roller 4, and the width of the gap is determined by the elastic layer 3b of the pressure roller. Since the heat conductive roller 4 is set to have a size that comes into contact with the heat conductive roller 4 when expanded, the heat does not escape to the heat conductive roller at the time of startup, and the warm-up time is not delayed. Next, in the invention of claim 4, the elastic layer 3b of the pressure roller is provided.
Is made of foamed silicone rubber, the presence of a shell layer with air makes the expansion coefficient larger than that of ordinary silicone rubber, and the size of the gap S can be increased. You do n’t have to
Assembly cost can be reduced. Next, in the fifth aspect of the present invention, the surface of the heat conductive roller 4 is coated with silicone oil to further improve the surface releasability of the heat conductive roller 4 and prevent the toner from adhering. In addition, since the silicone oil also adheres to the surfaces of the pressure roller 3 and the heating roller 1, the releasability of each roller is also improved, and it is possible to effectively prevent the adhesion of toner and the resulting problems such as deterioration of image quality. Will be able to

[Brief description of the drawings]

FIG. 1 is a schematic structural explanatory view of a fixing device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a fixing device according to another embodiment of the present invention.

FIG. 3 is a schematic diagram illustrating the configuration of a fixing device according to another embodiment of the present invention.

FIG. 4 is a schematic structural explanatory view of a fixing device according to another embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Heating roller, 1a core metal, 2 heaters, 3 pressure rollers, 3a core metal, 3b elastic layer, 3c release layer, 4 heat conduction roller, 4a core metal, 4b release layer, 10 static removal brush, 11 unit base , 15 application roller.

Claims (5)

[Claims] 1. A thin cylindrical heating roller having a heat source,
In a fixing device having a pressure roller in contact with the peripheral surface of the heating roller and a heat conductive roller in contact with the peripheral surface of the pressure roller, a release layer is provided on the surface of the heat conductive roller. Fixing device. 2. The method according to claim 1, wherein the release layer of the heat-conducting roller is formed of a conductive heat-resistant release material, and a charge removing brush is provided for slidingly contacting the release layer to electrically ground the release layer. The fixing device according to claim 1, wherein: 3. The heat roller and the pressure roller are arranged such that a gap is formed between the heat conduction roller and the pressure roller when the heating roller is not heated, and the width of the gap is raised to a fixing temperature of the heating roller. The width of the elastic layer and the release layer on the surface of the pressure roller heated by the heating roller when heated to have a width in which the elastic layer and the release layer expand in diameter and abut on the heat conductive roller. 3. The fixing device according to item 2. 4. The fixing device according to claim 3, wherein the elastic layer of the pressure roller is made of foamed silicone rubber. 5. An application roller for applying oil having good releasability to the surface of the heat conductive roller in contact with the surface of the heat conductive roller. Fixing device.