JPH06274059A - Fixing device for image forming device - Google Patents

Abstract

PURPOSE:To uniformalize the temp. over the entire length in the axial line direction of an elastic roller in pressurized contact with a rigid roller and to enable stable and good fixing regardless of the sizes and quantities of transfer materials by providing this elastic roller with a high thermal conductivity in its axial line direction. CONSTITUTION:A pressure roller 1 is held in pressurized contact with a heating roller 3 internally having a heat source 4 and an arbor 2 of the pressure roller 1 formed by covering the front layer of silicone rubber or silicone sponge with a PFA tube has the spirally formed parts existing within the roller. The material of this arbor 2 is a heat resistant material which is selected from the heat resistant materials having >=237W/mk thermal conductivity, for example, low- alloy heat resisting coppers, ferritic heat resisting steels, iron base (iron-Ni base) super heat resisting alloy sheets, Co base super heat resisting alloys, dispersion strengthened alloys, eutectic unidirectionally solidified alloys, etc. The temp. distribution in the axial line direction of a fixing roller pair is uniformalized by constituting the roller in such a manner, by which the generation of wrinkles in the transfer material and the generation of local fixing defects are prevented.

Description

Detailed Description of the Invention

[0001]

[Object of the Invention]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus utilizing an electrostatic transfer process, such as an electrostatic copying machine and a dynamic printer.
Above all, it relates to the fixing device.

[0002]

2. Description of the Related Art In a known image forming apparatus including a step of electrostatically transferring a toner image electrostatically formed on the surface of an image carrier to a transfer material such as paper It is necessary to heat and press the transfer material carrying the image to fix and fix the toner image on the transfer material, and a typical example of a fixing device for this purpose will be briefly described with reference to FIG.

FIG. 1 is a side sectional view of the fixing device, in which a casing 6 is provided with a heating roller 3 and a pressure roller 7 which are in pressure contact with each other, and a toner image is transferred at a transfer portion (not shown). The material P is conveyed in the direction of the arrow in the figure and passes through the pressure contact nip portion of both rollers.

The heating roller 3 is made of a rigid material such as a stainless steel material coated with a fluororesin film for offset prevention, and has a heat source 4 for heating therein. The pressure roller 7 is provided with a surface layer made of an elastic material such as rubber or sponge, and is pressed against the heating roller 3 by the force applied by the springs 8 at both ends of its core shaft so that the transfer material P moves in the traveling direction. The nip portion N having an appropriate length is formed. The length of the nip portion is set so that the toner image of the transfer material passing therethrough is sufficiently melted and fixed to the transfer material.

Reference numeral 9 in the drawing denotes a thermistor for detecting the roller temperature, reference numeral 10 denotes a thermoswitch which is a safety device, and reference numeral 11
Is a separation claw for preventing the transfer material from sticking to the roller 3 due to the viscosity of the molten toner.

In such a known fixing device, the thermistor 9 is usually arranged at the end portion of the roller and the non-sheet passing portion, and cannot detect all the temperatures over the entire length of the roller in the axial direction. Therefore, when passing a small size transfer material through the center of the roller, the non-paper passing area becomes an inverted crown shape due to thermal expansion.
There is a problem that the transfer speed is different between the end portion and the central portion of the roller, and the transfer material is wrinkled.

Further, when the small size paper is continuously fed, the heat of the portion is taken by the transfer material to lower the temperature, and when the large size transfer material is passed thereafter, the portion where the small size transfer material has passed There was a case where the fixing failure occurred in the part corresponding to.

The present invention has been made to cope with such a situation, and in a fixing device configured to pass a transfer material through a nip portion between a heating roller and a pressure roller, an axis line of these rollers is provided. An object of the present invention is to provide a fixing device capable of performing stable and good fixing at all times regardless of the size and amount of the transfer material passing through by making the temperature as uniform as possible over the entire length in the direction. It is a thing.

[0009]

[Constitution of the invention]

In order to achieve the above object, the present invention provides a transfer material carrying an unfixed toner image in a pressure contact nip portion between a rigid roller and an elastic roller in pressure contact with the rigid roller. In the fixing device that allows the toner to pass through and heats and presses the transfer material and the toner image by the roller at this time,
A fixing device for an image forming apparatus, wherein at least a part of the elastic roller in the axial direction is configured to have high thermal conductivity,
The means for forming high thermal conductivity is formed by winding a core metal of an elastic roller in a spiral shape, or is a cylindrical mesh member arranged in the elastic roller, or is arranged in the elastic roller. It is characterized in that it is a plurality of ring members.

With this structure, the temperature distribution in the axial direction of the fixing roller pair can be made as uniform as possible, and it is possible to effectively prevent wrinkles and local fixing defects from occurring on the transfer material.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS "FIG. 1" is a perspective view of a main part of a fixing device showing an embodiment of the present invention. The entire structure of the fixing device is the same as that shown in "FIG. 4". However, in FIG. 1, only a pair of rollers arranged opposite to each other are shown, and other parts are omitted.

A pressure roller 1 is in pressure contact with a heating roller 3 having a heat source 4 inside, and a core metal 2 of the pressure roller 1 is provided.
As shown in the figure, the portion located inside the roller is formed in a spiral shape. The fixing action is the same as that shown in FIG. 4 and the description thereof is omitted.

The material of the core metal 2 is a heat resistant material having a thermal conductivity of 237 W / mk or more, such as low alloy heat resistant steel, ferritic heat resistant steel, austenite heat resistant steel,
Iron-based (iron-Ni-based) super heat-resistant plywood, Co-based super heat-resistant alloy, N
i-base super heat-resistant alloy, dispersion strengthened alloy, eutectic directionally solidified alloy,
It can be appropriately selected from Mo-based alloys, Cr-based alloys, W-based alloys, and the like.

Next, the experimental results of the fixing device having the roller having the spiral cored bar as described above will be described. A fixing device capable of processing a transfer material of maximum A3 size, with a heating roller having a thickness of 3.0 mm, an outer diameter of 28 mm, and an axial length of 365 mm, a heat source of a halogen heater, a rated power of 750 W, and a flat light distribution. The temperature is 180.
Set to C. The speed of the heating roller is 14πmm
/ Sec.

As the pressure roller, the outer diameter was 30 mm, the wall thickness was 5.0 mm, the length was 320 mm, the hardness was 47 degrees, the material was silicon rubber or silicon sponge, and the PFA tube was used as the surface layer. Note that the transfer material was conveyed at the center.

Under these conditions, 100 sheets of A4 size paper were continuously fed, and immediately 50 sheets of A3 size paper were continuously fed, and no paper wrinkles were formed on these 50 sheets.
This is because the core metal of the pressure roller is formed in a spiral shape, so that the heat biased to the non-sheet passing portion is quickly transferred to the low temperature portion through the core metal to make the temperature distribution in the longitudinal direction of the roller surface uniform. it is conceivable that.

When an experiment was conducted under the same conditions as described above using an ordinary fixing device equipped with a linear cored bar, wrinkles were found on 7 of the subsequent 50 sheets.

FIG. 2 is a perspective view showing only the heating roller and pressure roller of the fixing device according to another embodiment. In this device, a mesh member 13a corresponding to a width of A4 size is arranged in the center of the pressure roller so as to surround the core metal 13. The material of the mesh member is selected from the materials having high thermal conductivity as described above.

A roller similar to the above is used by using such a roller.
Immediately after 100 sheets of 4 size paper were continuously fed, 50 sheets of A3 size paper were immediately passed, but no fixing failure occurred in the following 50 sheets.

A small amount of heat is biased to both ends of the roller by passing the transfer material through the core metal to be distributed and supplied to the central A4 size width portion where the mesh member exists, so that a small size A4 size sheet is passed. Even after that, it is considered that the transfer failure is unlikely to occur even when the A3 size paper, which is a large size sheet, is supplemented with the amount of heat taken away by the heat from both sides.

For comparison, when a similar type of paper was carried out using a known type fixing device equipped with a bar-shaped core metal,
12 out of 50 sheets of A3 size had a defective fixing in the central portion.

FIG. 3 shows still another embodiment, which is also a perspective view showing the fixing roller 3, the pressure roller 1 and the recess which are in pressure contact with each other in the fixing device. In this apparatus, a large number of ring members 14 are arranged inside the pressure roller 1 via spoke-shaped members connected to a cored bar. The ring member 14 in this case also uses the high thermal conductivity material as described above.

With such a configuration, as in the case described above,
When 100 sheets of A4 size paper and 50 sheets of A3 size paper were continuously fed, the A3 size paper did not show wrinkles or defective fixing at the center.

Even in such an apparatus, when the amount of heat biased to both ends of the pressure roller is dispersed in the central portion by the cored bar and the ring member 14, and when the transfer materials of different sizes as described above are passed, However, it is considered that the local temperature change on the roller surface due to this is small and good fixing is performed.

When a similar experiment was carried out using a known fixing device, 6 wrinkles of 50 sheets of A3 size paper were generated and 12 sheets of the fixing failure occurred in the central portion.

[0026]

As described above, according to the present invention, in the fixing device for fixing the toner image by passing the transferred transfer material through the nip portion of the heating roller and the elastic pressure roller which is in pressure contact with the heating roller. Since it is possible to prevent local fluctuations in the temperature distribution in the axial direction on the pressure roller side, it is possible to prevent wrinkling of the transfer material and partial fixing failure, and to perform stable and good fixing. This is effective for obtaining high quality images.

[Brief description of drawings]

FIG. 1 is a perspective view of a fixing device according to an embodiment of the present invention, particularly showing only a heating roller and a pressure roller portion.

FIG. 2 and

FIG. 3 is a perspective view of a main part of the fixing device showing another actual use.

FIG. 4 is a side sectional view showing the configuration of a known fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pressure roller 2 Core metal 3 Heating roller 6 Casing 8 Spring 11 Separation claw 13a Net-like member 14 Ring member

Claims (4)

[Claims] 1. A transfer material carrying an unfixed toner image is passed through a pressure-contact nip portion between a rigid roller and an elastic roller which is in pressure contact with the rigid roller, at which time the transfer material and the toner image are heated and pressed. In the fixing device, the fixing device of the image forming apparatus is configured such that at least a part of the elastic roller in the axial direction has a high thermal conductivity. 2. The fixing device as set forth in claim 1, wherein the means having a high thermal conductivity is formed by winding a core metal of an elastic roller in a spiral shape. 3. The fixing device according to claim 1, wherein the means having a high thermal conductivity is a cylindrical mesh member arranged in the elastic roller. 4. The fixing device according to claim 1, wherein the means having a high thermal conductivity is a plurality of ring members arranged in the elastic roller.