JPH09114315A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize stable fixing performance and to comparatively easily exchange a heating roller by safely, inexpensively and accurately detecting the temperature of a heating roller and submitting it for controlling the temperature of the heating roller. SOLUTION: This device is provided with the heating roller 100 for thermally fixing an unfixed image. The roller 100 includes a hollow core roller 110, a release layer 140 formed on the outer peripheral surface of the roller 110, and a resistance heating element layer 130 formed on the inner peripheral surface of the roller 110 through an electric insulating layer 120 and generating heat when it is energized. The layer 140 is formed to be wider than maximum recording material width and the layer 130 is formed to be wider than the layer 140. The layer 120 is formed wider than the layer 130, and a thermistor TM (temperature detecting means) is arranged in contact with the outer peripheral surface of the roller 110 in the outside area of the layer 140 and the width area of the layer 130.

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 heating and fixing an unfixed image such as a toner image on a recording material in an image forming apparatus such as an electrophotographic copying machine and a printer.

[0002]

2. Description of the Related Art A fixing device in an image forming apparatus such as a printer or a copying machine usually has a heating roller for heating and fixing an unfixed image on a recording material, and holds an unfixed image such as a toner image. The recording material is generally passed between the heating roller and a backup member (generally a pressure roller) arranged to face the heating roller, and heat-fixed under pressure between them.

Hitherto, a heating roller having a built-in heating heater such as a halogen lamp heater and heating the roller by radiant heat from the heater has been widely used. However, according to the heating roller having a built-in heating heater such as a halogen lamp heater as a heat source, the temperature rising rate from the start of energization of the heater to the predetermined fixing temperature on the surface of the heating roller is slow, and therefore the power switch of the image forming apparatus is turned on. The preheating time (so-called warm-up time) from when the fixing device reaches a predetermined fixing temperature becomes long, and the device becomes difficult to use.

Therefore, as a heating roller which can be heated in a short time until the predetermined fixing temperature is reached, for example, Japanese Patent Laid-Open No. 59-
As disclosed in Japanese Patent No. 189381, a heating roller is proposed in which a core roller is formed with a resistance heating element made of a substance that generates heat when energized so as to rotate together with the core roller. This type of heating roller has a high electric-heat conversion efficiency, and the surface temperature of the heating roller can be quickly raised to a predetermined fixing temperature after the energization of the resistance heating element is started, thereby shortening the preheating time of the fixing device. be able to.

Even in a fixing device employing such a heating roller, it is essential to detect the temperature of the heating roller in order to secure image fixing performance and safety. With respect to this point, a method is generally known in which a temperature detecting means is brought into contact with a release layer on the outer peripheral surface of the core roller which holds a resistance heating element, and in addition to this, JP-A-59-151177 and As taught in Japanese Patent Application Laid-Open No. 62-18582, forming a resistance heating element on the outer peripheral surface of a hollow core roller and arranging a temperature detecting means in contact with or close to the inner peripheral surface of the core roller, Japanese Patent Publication No.
As taught in Japanese Patent No. 58543, it is also proposed to stack temperature detecting means on the resistance heating element layer.

Further, in Japanese Unexamined Patent Publication No. 62-157080, the heating roller temperature is controlled by detecting a change in the resistance value of the resistance heating element and controlling the energization to the resistance heating element based on the change in the resistance value. It is also suggested to do so.

[0007]

However, when the temperature detecting means is brought into contact with the release layer on the outer peripheral surface of the core roller holding the resistance heating element, the temperature detecting means relatively slides in contact with the release layer. Therefore, the release layer is easily worn, scratched or deteriorated. JP-A-59-151177 and JP-A-62.
As taught in Japanese Patent No. -18582, when the temperature detecting means is placed in contact with or close to the inner peripheral surface of the core roller, it is difficult to remove the temperature detecting means inside the core roller when the heating roller is replaced for maintenance or the like. It takes time to replace. In order to save this trouble, when the temperature detecting means is also replaced when the heating roller is replaced, the cost is increased accordingly.

As disclosed in Japanese Examined Patent Publication No. 5-58543, when the temperature detecting means is laminated on the resistance heating layer, a large current flowing through the resistance heating layer also flows into the temperature detecting means. The control unit for controlling the temperature of the heating roller according to the signal from the controller must be configured to handle a large current, and must be configured independently from other control means that configure the image forming apparatus. Therefore, the cost is increased accordingly.

As disclosed in Japanese Patent Laid-Open No. 62-157080, a method of detecting a change in resistance value of a resistance heating element and controlling energization to the resistance heating element based on the variation in the resistance value is a resistance heating element. Since the temperature coefficient of resistance is used to detect the resistance value change of the resistance heating element, the temperature is adjusted.
The resistance value fluctuates greatly due to variations in the composition mixing ratio of the substances forming the resistance heating element and the thickness of the resistance heating element. Therefore,
This method, which substitutes the actual fluctuation of the heating roller surface temperature by the change of the resistance value of the resistance heating element, has a problem that the set temperature varies depending on the fixing device and it is difficult to obtain stable fixing performance.

In any case, when the resistance heating element is provided on the outer peripheral surface of the core roller, if the recording material with the clips, staples, etc. attached by mistake is fed into the fixing device, the recording material is fed by them. The release layer on the resistance heating element may be damaged and they may come into contact with the resistance heating element, which causes electric leakage through the recording material. Therefore, the present invention
A fixing device of a type including a core roller, comprising a heating roller formed so as to rotate together with the resistance heating element that generates heat by energizing the core roller. An object of the present invention is to provide a fixing device that can be detected and used for temperature control of a heating roller, thereby achieving stable fixing performance, and replacing the heating roller relatively easily.

[0011]

In order to solve the above-mentioned problems, the present invention is a fixing device for heating and fixing an unfixed image on a recording material holding the unfixed image, which comprises a heating roller for fixing the unfixed image. The heating roller is a hollow core roller,
It includes a release layer formed on the outer peripheral surface of the core roller and a resistance heating element formed on the inner peripheral surface of the core roller via an electric insulating layer to generate heat by energization. The resistance heating element is formed wider than the width of the material, the resistance heating element is formed wider than the release layer, and the width of the electric insulating layer is formed to be larger than the width of the resistance heating element. And a temperature detecting means in contact with the outer peripheral surface of the core roller in the outer region of the resistance heating element and in the width region of the resistance heating element.

The core roller is usually formed of a metal material such as aluminum or an iron-based alloy in order to obtain the rigidity of the heating roller and to obtain good thermal conductivity. The resistance heating element itself generates Joule heat when a current flows. Examples of the material of the resistance heating element include barium titanate-based ceramics having a positive temperature coefficient of resistance. As a material of the electric insulating layer,
A heat resistant insulating resin such as polyimide or polyamide imide can be exemplified. From the viewpoint of safety, it is desirable that this electrical insulating layer has an electrical breakdown voltage equal to or higher than the maximum applied voltage applied to the resistance heating element. The material of the release layer may be a copolymer of tetrafluoroethylene and perfluoroalkoxyethylene (PFA) or polytetrafluoroethylene (PT).
FE) can be illustrated.

According to the fixing device of the present invention, an electric current is passed through the resistance heating element to heat the entire heating roller by the heat generated by the resistance heating element itself. Then, the energization of the resistance heating element is controlled based on the temperature detected by the temperature detecting means arranged in contact with the outer peripheral surface of the core roller, and the heating roller is kept at a predetermined fixing temperature. Between the heating roller that has reached the predetermined fixing temperature in this manner and the backup member that is normally included in the fixing device and that faces the roller,
The image is heated and fixed on the recording material by passing the recording material holding the unfixed image.

According to the fixing device of the present invention, since the temperature detecting means is arranged in contact with the outer peripheral surface of the core roller within the outer region of the release layer and the width region of the resistance heating element, the wall thickness of the core roller is reduced. The heat of the resistance heating element is satisfactorily transmitted to the temperature detecting means via the heating roller, and the temperature of the heating roller can be detected directly and accurately, and can be used for temperature control of the heating roller without causing an extra cost increase. As a result, stable fixing performance is achieved.

Further, in the fixing device of the present invention, since the temperature detecting means is arranged at a position where it does not make sliding contact with the release layer, the release layer is worn or damaged by the temperature detecting means. It does not deteriorate and can be used stably for a long period of time. Further, even if a recording material with clips, staples, etc. attached by mistake is sent to the fixing device, the resistance heating element is formed on the inner peripheral surface of the core roller through the electric insulating layer, so that those clips There is no danger that staples, etc., will come into contact with the resistance heating element and cause electric leakage, which is just that safe.

Further, since the temperature detecting means is disposed in contact with the outer peripheral surface of the core roller, the temperature detecting means can be easily removed when the heating roller is replaced, and the heating roller can be replaced easily and inexpensively. be able to.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view of a fixing device according to an embodiment of the present invention. The fixing device heat-fixes a toner image, which is an unfixed image, onto a recording sheet that is a recording material that holds the image. Is.

This fixing device has a heating roller 100 and a pressure roller 200 pressed against the heating roller 100. In the heating roller 100, a core roller 110 described later is fitted to a bearing portion 150 including a ball bearing portion fitted in a circular through hole 310 provided in the side plate member 300 in advance, and an outer peripheral surface of the roller 110 is fitted. Both ends are supported rotatably by being supported by the ball bearing portion of the bearing portion 150. Further, the pressure roller 200 is
The supporting shaft 210 is rotatably supported by the side plate member 300 via a bearing portion (not shown), and is pressed toward the heating roller 100 by pressing means (not shown). The heating roller 100 and the pressure roller 200 are rotationally driven in the recording paper feeding direction by a driving unit (not shown).

The heating roller 100 has a hollow cylindrical aluminum core roller 110. Core roller 1
A release layer 140 is formed on the outer peripheral surface of 10. In addition, the inner surface of the core roller 110 has an electrically insulating layer 120.
However, a layered resistance heating element 130 is sequentially formed on the inner peripheral surface of the electric insulating layer 120. The electric insulation layer 120 is made of polyimide, which is a heat-resistant insulating resin, the resistance heating element layer 130 is made of barium titanate-based ceramic having a positive temperature coefficient, and the release layer 140 is polytetrafluoro, which is a heat-resistant resin. It is made of ethylene (PTFE). The release layer 140, the electrical insulating layer 120, and the resistance heating layer 130 rotate integrally with the core roller 110.

The width of the release layer 140 is formed to be larger than the maximum width of the recording paper carrying the toner image which is passed between the heating roller 100 and the pressure roller 200. Resistance heating element layer 13
The width of 0 is formed wider than the release layer 140,
The width of the electric insulation layer 120 is set to maintain the electric insulation between the core roller 110 and the resistance heating layer 130.
The width is wider than that of the core roller 110 in this embodiment, and is formed over the entire width in the rotation axis direction of the core roller 110. Therefore, the release layer 140, the resistance heating element layer 130, and the electrical insulating layer 120 are formed in the order of increasing width.

As described above, since the resistance heating element layer 130 is formed on the inner peripheral surface of the core roller 110 via the electric insulating layer 120, the recording paper on which the clips, staples, etc. are erroneously attached is fixed. Even if it is sent into the device, there is no danger that those clips, staples, etc. will come into contact with the resistance heating element layer 130 and cause electrical leakage, and that is the only safety. A pair of ring-shaped power receiving members 161a and 161b made of a conductive copper alloy are fitted and fixed to the heating element layer 130 on the inner peripheral surfaces of both ends of the resistance heating element layer 130. Therefore, the power receiving members 161a and 161b and the resistance heating layer 130
And are electrically connected to. Power receiving members 161a, 16
Similarly to the electric insulating layer 120, the resistance heating element layer 130, and the release layer 140, 1b also rotates integrally with the core roller 110.
A pair of conductive carbon power feeding members 162a and 162b are pressed against the power receiving members 161a and 161b by springs 163a and 163b, respectively. Then, the power receiving member 161a (161b) and the power feeding member 162a
Even if the power receiving member 161a (161b) rotates integrally with the core roller (162b), electrical connection is maintained at the contact surface between the two.

The power supply member 162a is provided at one end of the power source 400,
The power feeding member 162b is connected to the other end of the power source 400 via the relay RY. The heating roller temperature control unit 500 is provided in the relay RY so that the contact of the relay RY can be opened and closed according to the temperature detected by the thermistor TM described later.
Is connected. With such a configuration, the resistance heating element layer 13
A voltage is applied to 0 by the power supply 400.

A thermistor TM, which is a temperature detecting means, is arranged in contact with the outer surface of the release layer 140 and on the outer peripheral surface of the core roller 110 within the width of the resistance heating layer 130. Even if a relatively large current that flows through the resistance heating element layer 130 flows into the core roller 110, the thermistor TM and the control unit 500 do not interfere with the thermal response of the thermistor TM due to this current, or destroy it. To prevent this, an electric insulating layer may be provided between the core roller 110 and the thermistor TM for safety.

As described above, since the thermistor TM, which is the temperature detecting means, is arranged at a position where it does not contact the mold release layer 140, the mold release layer 140 is worn or scratched by the thermistor TM and deteriorates. Therefore, the fixing device can be stably used for a long time. According to the fixing device shown in FIG. 1, the unfixed toner image is heated and fixed on the recording paper as follows.

First, in the initial state, the heating roller 1
Since the temperature of 00 is lower than the predetermined fixing temperature necessary for heat fixing, the contact of the relay RY is closed by the control unit 500, and the power supply 400 causes the power feeding member 162a and the power receiving member 1 to operate.
A voltage is applied to the resistance heating element layer 130 via the relay 61, the relay RY, the power feeding member 162b, and the power receiving member 161b. The resistance heating element layer 130 generates heat due to its own Joule loss to raise the temperature of the heating roller 100. While the heating roller 100 is in operation, the heating roller 1 is heated by the thermistor TM.
A temperature of 00 is detected, is input to the control unit 500, is compared with a predetermined fixing temperature, and a contact opening / closing signal of the relay RY is output from the control unit 500 to the relay RY accordingly. The contact opening / closing signal opens / closes the contact of the relay RY to control the voltage application to the resistance heating layer 130 by the power supply 400, and the temperature of the heating roller 100 is maintained at a predetermined temperature.

The recording paper bearing the toner image is pressed against the heating roller 100 and the heating roller 100, one end of which is heated to a predetermined fixing temperature as described above by a conveying means (not shown). It is conveyed to the nip portion of the roller 200. Since both rollers are rotated by the driving means (not shown), the recording paper conveyed is sandwiched by both rollers and passes between both rollers, so that the toner image is heated and fixed on the recording paper.

Since the thermistor TM for detecting the temperature of the heating roller 100 is arranged in contact with the outer peripheral surface of the core roller 110 in the outer area of the release layer 140 and the width area of the resistance heating layer 130, the core roller 110. The heat of the resistance heating element layer 130 is satisfactorily transferred to the thermistor TM through the thickness of the above, and thus the temperature of the heating roller 100 can be directly and accurately detected, whereby stable fixing property is achieved. . Further, since the temperature detecting means has a relatively simple structure as described above, the cost can be reduced.

Further, the thermistor TM is a core roller 110.
Since it is placed in contact with the outer peripheral surface of the heating roller 100,
The thermistor TM can be easily removed upon replacement, and the heating roller can be replaced easily and inexpensively. The material of each part of the fixing device shown in the above-mentioned embodiment is not limited to the above.

[0029]

According to the present invention, there is provided a fixing device of the type including a core roller, and a heating roller formed so that a resistance heating element that generates heat by energizing the core roller is rotated together with the roller. (EN) Provided is a fixing device which can detect a roller temperature safely and accurately at low cost and can be used for heating roller temperature control, thereby achieving stable fixing performance and relatively easy replacement of a heating roller. be able to.

[Brief description of the drawings]

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

[Explanation of symbols]

 100 heating roller 110 core roller 120 electric insulation layer 130 resistance heating layer 140 release layer 150 bearing parts 161a, 161b power receiving members 162a, 162b power feeding members 163a, 163b springs 200 pressure roller 210 support shaft 300 of pressure roller 200 side plate Member 310 Through hole 400 Power supply 500 Control unit RY relay TM thermistor

Claims (1)

[Claims] 1. A fixing device for heating and fixing an unfixed image on a recording material, which comprises a heating roller for fixing the unfixed image, wherein the heating roller is a hollow core roller, and the core. It includes a release layer formed on the outer peripheral surface of the roller and a resistance heating element formed on the inner peripheral surface of the core roller through an electric insulating layer to generate heat by energization, and the release layer has a maximum recording material width. The resistance heating element is formed to be wider than the release layer, and the resistance heating element is formed to be wider than the release layer. A fixing device characterized in that a temperature detecting means used for temperature control of the heating roller is arranged in contact with the outer peripheral surface of the core roller within the area and the width of the resistance heating element.