JPH08262900A - Fixing device - Google Patents

Abstract

PURPOSE: To provide a fixing device capable of preventing fixation defect by restraining a temp. unevenness of a heat roller, and to provide the fixing device capable of preventing the temp. drop on the heat roller end part at the rise time of the device, while preventing the heat roller end part from the temp. accession at the time of allowing papers in a small size transfer paper to pass successively. CONSTITUTION: In the fixing device 10 provided with the heat roller 11 and a pressure roller 12 held in press contact with the heat roller 11, for fixing a toner image on the transfer paper, by allowing the transfer paper on which the toner image is formed to pass through a contact part between the heat roller 11 and the pressure roller 12, the heat roller 11 is provided with a base 11a whose surface is coated 15 and 16 formed on the surface of the base 11a and severally insulated, and a heat resistive released layer 13 formed on the resistance heating layer 16 as the outermost layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a copying machine, a facsimile,
The present invention relates to a fixing device applied to an image forming apparatus such as a printer.

[0002]

2. Description of the Related Art As a fixing device for fixing a toner image on a transfer paper, it has a core metal, a resistance heating layer, and a heat-resistant release layer, as disclosed in Japanese Patent Application Laid-Open No. 5-35137. A device having a heat roller and a pressure roller that is in pressure contact with the heat roller is well known. The heat resistant release layer has a plurality of resistance heating elements extending from one end to the other end of the heat roller.

In general, when the fixing device is started up, the temperature of the end portion of the heat roller does not rise as compared with the center portion of the heat roller due to heat radiation from the end portion of the heat roller, and fixing failure is likely to occur. Therefore, the above-mentioned publication discloses a technique in which the density of the resistance heating element is increased from the center of the heat roller toward both ends to increase the amount of heat generation.

[0004]

In the above-mentioned device, since the resistance heating elements of the heat roller are separated by the insulators, the resistance heating elements are separated from the portions where the resistance heating elements are present. However, there is a problem in that there is a difference in temperature and fixing failure occurs.

Further, when a small-sized transfer paper is continuously fixed by the above-mentioned apparatus, the heat of the central portion of the heat roller is carried away by the transfer paper, so that the temperature of the central portion of the heat roller decreases and the end portion of the heat roller lowers. There is also a problem that the temperature rises and the heat-resistant release layer is damaged.

Therefore, the present invention has been made in view of the above problems, and provides a fixing device capable of preventing the fixing failure by eliminating the temperature unevenness of the heat roller, and lowering the temperature of the end portion of the heat roller when the device starts up. It is an object of the present invention to provide a fixing device capable of preventing the temperature rise and preventing the temperature rise of the end portion of the heat roller at the time of continuously passing the small size transfer paper.

[0007]

According to the first aspect of the present invention,
A transfer roller having a heat roller and a pressure roller in pressure contact with the heat roller is passed through the transfer paper on which a toner image is formed at the contact portion between the heat roller and the pressure roller to transfer the toner image to the transfer paper. In the fixing device for fixing to the heat roller, the heat roller has a base whose surface is covered with an insulating material, a plurality of resistance heating layers which are formed on the surface of the base and are insulated from each other, and a resistance heating layer of the outermost layer. It has a heat-resistant release layer formed on it.

According to a second aspect of the present invention, in the fixing device according to the first aspect, each of the resistance heating layers extends in the axial direction and is arranged at a predetermined interval in the circumferential direction. And the resistance heating element of the outer resistance heating layer is disposed outside the resistance heating element of the inner resistance heating layer between the above-mentioned intervals.

According to a third aspect of the present invention, in the fixing device according to the first aspect, the two resistance heating layers are formed, and one resistance heating layer extends in the central portion in the axial direction, and It has a plurality of resistance heating elements arranged at a predetermined interval in the circumferential direction, and the other resistance heating layer is located at both ends in the axial direction and separated at a predetermined interval in the circumferential direction. It has a plurality of resistance heating elements arranged in a line, and the resistance heating element of the outer resistance heating layer is arranged outside the resistance heating element of the inner resistance heating layer between the above-mentioned intervals.

According to a fourth aspect of the present invention, in the fixing device according to the third aspect, a thermistor for detecting the temperature of the heat roller and a control means for controlling the temperature of the resistance heating element based on the temperature information of the thermistor are provided. It is characterized by being provided.

[0011]

According to the invention described in claim 1, since the heat roller has a plurality of resistance heating layers, the temperature of the surface of the heat roller becomes uniform.

According to the second aspect of the present invention, since the resistance heating element of the outer resistance heating layer is arranged outside the space between the resistance heating elements of the inner resistance heating layer, the temperature of the surface of the heat roller is increased. Becomes uniform.

According to the third aspect of the present invention, one resistance heating layer has a plurality of resistance heating elements extending in the central portion in the axial direction, and the other resistance heating layer is positioned at both ends in the axial direction. Since the resistance heating element of the outer layer has a plurality of resistance heating elements, and the resistance heating element of the outer layer of the resistance heating layer is disposed outside the space between the resistance heating elements of the inner layer of the resistance heating layer, the axial end portion and the center of the heat roller are The temperature difference between the parts is corrected.

According to the fourth aspect of the present invention, the control means controls the temperature of the resistance heating element of each layer so as to eliminate the temperature difference between the end portion and the central portion in the axial direction of the heat roller based on the temperature information from the thermistor. .

[0015]

Embodiments of the present invention will be described below with reference to the drawings. In FIG. 1, reference numeral 10 represents a fixing device applied to the image forming apparatus. First, the image forming apparatus will be described.

The image forming apparatus reads a document image, a reading unit 2, an image processing unit 3 that converts the read image information into an electric image signal, a photoconductor 1, and the photoconductor 1 is uniformly charged. The charging unit 4 includes a charging unit 4, a writing unit 5 that forms an electrostatic latent image on the charged photoconductor 1 corresponding to an original, a developing device 6 that visualizes the electrostatic latent image, and a developing unit 6. A transfer device 7 that transfers the visible image from the paper feed cassette 8 to the transfer paper that is transferred by the registration rollers 21, and a fixing device 1 that fixes the transferred toner image.
0, and a cleaning unit 16 for cleaning the photoconductor 1 by removing the toner remaining on the photoconductor 11 after transfer.
And a static elimination lamp 22.

As shown in FIG. 1, the fixing device 10 includes a heat roller 11, a pressure roller 12 pressed against the heat roller 11 by a pressure means 23, and a release agent on the outer peripheral surface of the heat roller 11. The release agent application felt 17 to be applied, a blade 18 for scraping off the excess release agent of the release agent applied by the release agent application felt 17, the heat roller 11 and the pressure roller 12 to remove the toner. Separation claw 19 for separating the fixed transfer paper from heat roller 11, and separation claw 19
Discharge roller pair 20a, 2 for discharging the transfer paper separated by
Mainly from 0b. In the figure, reference numeral 14 represents a thermal fuse.

The pressing means 23 comprises a pressing arm 24 which is in contact with the bearing 12c of the pressing roller 12 and a spring 25 which urges the pressing arm 24. A central thermistor 26 that detects the temperature of the heat roller 11 is arranged on the surface of the heat roller 11 in the axial direction, and a thermistor 27 is also arranged on the surface of the pressure roller 12. Both thermistors 2
The temperature information of 6 and 27 is input to the control means (not shown). The control means controls energization to a resistance heating element, which will be described later, based on the temperature information of the thermistors 26 and 27, and keeps the temperature of the heat roller 11 at a predetermined temperature.

The pressure roller 12 is composed of a cored bar 12a made of aluminum or the like, and a rubber layer 12b made of silicon rubber provided outside the cored bar 12a.

As shown in FIGS. 3 to 5, the heat roller 11 includes a base 11a having a surface made of aluminum, nickel, iron or the like coated with an insulating material, and a first resistance heating element formed on the surface of the base 11a. A layer 15 and a second resistance heating layer 16 formed on the surface of the first resistance heating layer 15;
The heat-resistant release layer 13 made of fluororesin or the like is formed on the second resistance heating layer 16. In this example, the base 11a has a cylindrical shape, but may have a cylindrical shape. Further, as the base 11a, glass, enamel,
A material having low thermal conductivity such as ceramic may be used.

The first and second resistance heating layers 15 and 16 have a plurality of resistance heating elements 15a and 16a which extend in the axial direction and are arranged at predetermined intervals in the circumferential direction. The resistance heating elements 1 of the second resistance heating layer 16 are provided outside the space between the resistance heating elements 15a of the first resistance heating layer 15.
6a is arranged. The resistance heating elements 15a and 16a are
Both ends of the heat roller 11 are exposed on the surface of the heat-resistant release layer 13 to form electrode portions 28a and 28b. The first and second resistance heating layers 15 and 16 are respectively insulated, and the resistance heating elements 15a and 16b are electrically independent.

Electrode portions 28a at both ends of the heat roller 11,
Power supply brushes 29a and 29b are arranged in sliding contact with 28b to energize the resistance heating elements 15a and 16a. As shown in FIG. 6, the power supply brushes 29a and 29b generate heat only in the pressure contact position between the heat roller 11 and the pressure roller 12 and in the first and second resistance heat generation layers 15 and 16 near the upstream side thereof. Area A of about 1/4 in the circumferential direction of the heat roller 11
Are in sliding contact with the electrode portions 28a and 28b in the range corresponding to. In the figure, the symbol P indicates a transfer sheet.

The operation of the above configuration will be briefly described below. The image information of the document is read by the reading unit 2 and converted into an electrical image signal by the image processing unit 3. The image of the document is projected by the writing unit 5 onto the surface of the photoconductor 1 whose surface is uniformly charged by the charging charger 4, and an electrostatic latent image is formed. The electrostatic latent image on the photoconductor 1 is formed with a visible image by toner being attached by the developing device 6 after the electric charge in the non-image portion is erased by an eraser (not shown).

On the other hand, one transfer sheet is fed from one of the sheet feeding cassettes 8 of the sheet feeding device and sent to the registration roller 21. The registration roller 21 sends the transfer paper to the transfer separation charger 7 at the timing when the visible image on the photoconductor 1 and the transfer paper coincide with each other at the transfer separation charger 7. An image is transferred by the transfer / separation charger 7, and the transfer paper separated from the photoconductor 1 is sent to the fixing device 10.

As shown in FIG. 2, the toner image on the transfer paper is inserted between the heat roller 11 heated to a predetermined temperature by the control means and the pressure roller 12, and heat-fixed. Thereafter, the transfer paper P is separated from the surface of the heat roller 11 by the separation claw 19 (see FIG. 1), and the paper discharge roller pair 2
It is transported and discharged at 0a and 20b.

The toner remaining on the photoconductor 1 is removed and cleaned by the cleaning unit 9 so as to be prepared for the next image formation.

FIG. 7 shows another embodiment. In the figure, the same components as those of the heat roller 11 described above are designated by the same reference numerals, and the description thereof will be omitted.

The heat roller 31 includes a base 11a and an end resistance heating layer 35 formed on the surface of the base 11a.
And a central resistance heating layer 36 formed on the surface thereof, and a heat-resistant release layer 13 formed thereon.

The central resistance heating layer 36 is composed of the heat roller 31.
Has a plurality of resistance heating elements 36a extending in the central portion in the axial direction and spaced apart from each other in the circumferential direction at a predetermined interval, and the end resistance heating layer 35 has an axial direction of the heat roller 31. Has a plurality of resistance heating elements 35a and 35b which are located at both ends and are arranged at a predetermined interval in the circumferential direction. The resistance heating elements 35a, 3 of the end resistance heating layer 35
The central resistance heating layer 36 is provided on the outer side between the circumferential intervals of 5b.
The resistance heating elements 36a are arranged so as to exist.

The resistance heating element 35a and the resistance heating element 35b are connected by a conductor 37 at the center of the heat roller 31, and are exposed on the surface of the heat-resistant release layer 13 at both ends of the heat roller 11. The electrodes 38a and 38b are formed.

Electrode portions 40a and 40b, which are exposed on the surface of the heat-resistant release layer 13 via conductors 39, are arranged at both ends of the resistance heating element 36a. The position of one electrode portion 40b is different from that of the above-mentioned electrode portion 38b.
It is displaced in the axial direction of the heat roller 31.

Edge resistance heating layer 35 and central resistance heating layer 36
Are insulated from each other, and the resistance heating elements 35a, 3a,
5b and the resistance heating element 16b are electrically independent.

A power supply brush 41a is disposed so as to be in sliding contact with the electrode portions 38a and 40a, a power supply brush 41b is disposed so as to be in sliding contact with the electrode portion 38b, and a power supply brush 41c is disposed so as to be in sliding contact with the electrode portion 40b.

At the center and the end of the heat roller 31,
The central thermistor 26 and the end thermistor 42 are arranged, and the temperature information of these thermistors 26, 42 is input to the control means 43. The control unit 43 controls the power supply to the power supply brushes 41a, 41b, 41c based on the temperature information of the central thermistor 26 and the end thermistor 42, and keeps the heat roller 31 at a predetermined fixing temperature.

The operation of the control means 43 when the apparatus is started up and when small size transfer sheets are continuously passed will be briefly described. When the device is started up, the heat roller 3
The temperature at the end of 1 is lower than that at the center. The temperature information at this time is the central thermistor 26, the end thermistor 4
2 and the temperature information is input to the control means 43. The control unit 43 lowers the voltage applied to the resistance heating elements 35a and 35b to raise the temperature of the end portion of the heat roller 31.

On the other hand, when a small size transfer paper is continuously fed, the temperature of the end portion of the heat roller 31 becomes lower than that of the central portion. The temperature information at this time is detected by the central thermistor 26 and the end thermistor 42, and the temperature information is input to the control means 43. The control means 43 raises the voltage applied to the resistance heating elements 35a and 35b to lower the temperature of the end portion of the heat roller 31.

In this embodiment, the end resistance heating layer 35 is arranged inside the central resistance heating layer 36, but the arrangement may be reversed. Further, although the resistance heating element of the central resistance heating layer 36 is composed of two resistance heating elements 35a and 35b, it may be formed of one resistance heating element.

[0038]

According to the first aspect of the present invention, since the heat roller has a plurality of resistance heating layers, the temperature of the surface of the heat roller becomes uniform and defective fixing can be prevented.

According to the second aspect of the invention, since the resistance heating element of the outer resistance heating layer is arranged outside the space between the resistance heating elements of the inner resistance heating layer, the temperature of the surface of the heat roller is increased. Is uniform, and fixing failure can be prevented.

According to the third aspect of the invention, one resistance heating layer has a plurality of resistance heating elements extending in the central portion in the axial direction, and the other resistance heating layer is positioned at both ends in the axial direction. Since the resistance heating element of the outer layer has a plurality of resistance heating elements, and the resistance heating element of the outer layer of the resistance heating layer is disposed outside the space between the resistance heating elements of the inner layer of the resistance heating layer, the axial end portion and the center of the heat roller are The temperature difference between the parts can be corrected, the temperature rise of the heat roller end can be prevented when the small size transfer paper is continuously passed, and the temperature decrease of the heat roller end can be prevented when the apparatus is started up.

According to the fourth aspect of the invention, the control means controls the temperature of the resistance heating element of each layer so as to eliminate the temperature difference between the end portion and the central portion in the axial direction of the heat roller based on the temperature information from the thermistor. Therefore, the same effect as the third aspect can be obtained.

[Brief description of drawings]

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

FIG. 2 is a side view of an image forming apparatus to which the fixing device shown in FIG. 1 is applied.

3 is an end view of a cross section of a heat roller of the fixing device shown in FIG.

4 is a partially cutaway perspective view of a heat roller of the fixing device shown in FIG.

5 is a cross-sectional view taken along line VV of the heat roller shown in FIG.

FIG. 6 is a diagram for explaining a heat generating portion of the heat roller shown in FIG.

FIG. 7 is a sectional view showing a schematic configuration of a heat roller according to another embodiment of the present invention.

[Explanation of Codes] 10 Fixing Device 11 Heat Roller 12 Pressure Roller 13 Heat Resistant Release Layer 14 Thermal Fuse 15 First Resistance Heating Layer 16 Second Resistance Heating Layer 17 Release Agent Coating Felt 18 Blade 19 Separation Claw 20a, 20b Paper ejection roller pair

Claims (4)

[Claims] 1. A transfer roller having a heat roller and a pressure roller pressed against the heat roller and having a toner image formed at the contact portion between the heat roller and the pressure roller is passed through the toner. In a fixing device for fixing an image on the transfer paper, the heat roller comprises a base having at least a surface covered with an insulating material, a plurality of resistance heating layers formed on the surface of the base and insulated from each other, and an outermost layer. And a heat-resistant release layer formed on the resistance heating layer of 1. 2. The fixing device according to claim 1, wherein each of the resistance heating layers comprises a plurality of resistance heating elements that extend in the axial direction and are arranged at predetermined intervals in the circumferential direction. A fixing device characterized in that the resistance heating element of the outer resistance heating layer is disposed outside the resistance heating element of the inner resistance heating layer between the above-mentioned intervals. 3. The fixing device according to claim 1, wherein two resistance heating layers are formed, one resistance heating layer extending in a central portion in the axial direction and having a predetermined interval in the circumferential direction. Having a plurality of resistance heating elements arranged apart from each other,
The other resistance heating layer has a plurality of resistance heating elements located at both ends in the axial direction and arranged at a predetermined interval in the circumferential direction. A fixing device in which a resistance heating element of an outer resistance heating layer is arranged outside the space. 4. The fixing device according to claim 3, further comprising a thermistor for detecting the temperature of the heat roller and a control means for controlling the temperature of the resistance heating element based on temperature information of the thermistor. Fixing device.