JPH06118825A - Fixing device - Google Patents

Abstract

PURPOSE:To attain safety by dropping the temperature of the heat generating source of a heating roller, to improve reliability and to reduce size and cost, in a thermal roller type fixing device used for an electrophotographic device, etc. CONSTITUTION:A pair of electrodes lined up in the axial direction of a heating roller 2 and a temperature sensor 11 fixed on the central part of a heat generating region between a pair of the electrodes are disposed on a resistant film 1, has the impartation of tensile force by a leaf spring 63 and is pressed with contact with a part of the periphery of the heating roller 2. The heat generating region generates heat to maintain the heating roller 2 at a prescribed temperature by the energization of the electrodes. A recording material 8 is heated, pressurized and fixed between the heating roller 2 and a pressurizing roller 3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device used in an electrophotographic image forming apparatus such as a printer or a copying machine.
More specifically, it relates to a method for heating a heating roller.

[0002]

2. Description of the Related Art Conventionally, a fixing device for an electrophotographic image forming apparatus has a heating roller that is maintained at a predetermined temperature by being radiated from a lamp heater such as a halogen lamp, and a heating roller that has an elastic layer. A typical example is a heat roller system in which a recording material carrying an unfixed toner image is heated and pressed by a pressure roller that is pressed against.

Further, as a method for heating a heating roller without using a lamp heater, JP-A-56-12358 is known.
No. 0, there is a method of heating by energizing the resistance heating layer on the peripheral surface of the heating roller. In addition, JP-A-6
As disclosed in JP-A-3-313182, there is a method of heating with a fixed resistance heating element through a film that moves at the same speed as a recording material without using a heating roller.

[0004]

However, the above-mentioned conventional example has the following problems. That is,
In the method using a lamp heater, the filament part of the lamp needs to be heated to an extremely high temperature around 3000 ° C. in order to obtain sufficient radiant heat, which is a safety problem.

The lamp heater has a structure in which a filament is enclosed by a glass tube, and further, if the glass tube is touched with bare hands, the life of the lamp heater may be remarkably impaired, and the assemblability of the device is deteriorated, resulting in cost increase. It was also expensive in itself.

In order to obtain the required heat generation length, an extra length is required due to the filament sealing portion, terminals, etc., leading to an increase in the size of the device.

It has a short life and lowers the reliability of the device.

In Japanese Patent Laid-Open No. 63-313182, the film is conveyed at the same speed as the recording material, so that its handling is not easy and its structure is complicated. In addition, this has led to high costs.

Since the film comes into contact with the recording material, there is a problem in reliability such as the film being damaged by a jam of the recording material.

In Japanese Unexamined Patent Publication No. 56-123580, a brush electrode is required, and there is a problem of resistance heating of the contact portion and generation of electrical noise.

Since the heat generating layer and the electrodes have to be formed on the peripheral surface of the heating roller, the manufacture is not easy and the cost is high.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a fixing device which eliminates the above problems, has high safety and reliability, and is small in size and low in cost. Is.

[0013]

According to the present invention, a heating roller that heats a recording material by contacting the surface of the recording material, a heating means of the heating roller, and the recording material are brought into pressure contact with the heating roller. A heating means, and the heating means is a film-shaped resistance heating element fixedly arranged in contact with the surface of the heating roller, preferably, the film-shaped resistance heating element is arranged in parallel in the axial direction of the heating roller. It is characterized in that it has at least a pair of electrodes arranged as described above, and more preferably, a temperature detecting element is provided on the film-shaped resistance heating element.

[0014]

EXAMPLES Examples of the present invention will be described below.

First of all, referring to FIG.
This will be described with reference to FIGS. 2 and 3. FIG. 1 is a side sectional view of this embodiment, FIG. 2 is a front sectional view, FIG. 3 is a diagram showing a structure of a heat generating film, a) is a plan view, and b) is a side sectional view.

The aluminum heating roller 2 is fixed coaxially with a metal heating roller shaft 22 via a sleeve 21 made of a heat resistant resin such as PPS (polyphenylene sulfide). The heating roller shaft 22 is rotatably supported by upper support plates 64 and 65 integrally formed with the upper case 6 via slide bearings 24 and 24. A drive gear 23 is fixed to one end of the heating roller shaft 22 and is rotationally driven by a motor (not shown). On the surface of the heating roller 2, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer), PTFE (polytetrafluoroethylene).
A release layer such as the above is applied to improve the offset property of the toner and reduce the friction coefficient between the heating film 1 and a part of the peripheral surface of the heating roller 2 to rub.

The heat generating film 1 has a rectangular shape, and one of its long sides is fixed to the upper case 6 and the other is fixed to the upper case 6 via a leaf spring 63 by film pressing plates 61 and 62 and an adhesive agent, respectively. Has been done. Fix the heating film 2
After setting it to a predetermined position, fix the film pressing plates 61 and 62 from above with screws or the like, and finally, the upper case 6
The adhesive may be poured between the film pressing plates 61 and 62. The length of the rectangular short side of the heat generating film 2 is set to a dimension such that when the heating roller 2 is set at a predetermined position, the leaf spring 63 bends to generate tension in the heat generating film 2. The material of the heat generating film is resistive, for example, PI (polyimide) in which carbon beads are dispersed, and as shown in FIG. 3, a pair of electrodes 13 made of silver paste or the like are arranged in parallel in the axial direction of the heating roller 2 on the heat generating film 1. When a predetermined voltage is applied between the electrodes, an electric current flows through the gap (heat generating region 12) between the electrodes, which is linear and parallel to the axial direction of the heating roller 2, to generate heat. A temperature sensor 11 is fixed on the heat generating area 12, and the temperature of the heating roller 2 is controlled by adjusting the electric power applied to the heat generating film based on the detected temperature information.

In addition, on the outer periphery of the heating roller 2, a separation claw 5 for preventing the recording material 8 from winding around the heating roller 2,
Felt cleaning pad 4 for slightly offsetting and removing the toner adhering to the heating roller 2.
Is provided. The cleaning pad 4 includes a heating roller 2 to prevent the toner from adhering to the heating film 1 to deteriorate the thermal conductivity and to prevent the heating film 1 and the heating roller 2 from sticking and damaging the heating film 1. It is arranged on the upstream side of the heat-generating film 1 in the rotating direction of. In order to further safeguard the damage of the heat generating film 1 due to the sticking of the heat generating film 1 and the heat roller 2, the temperature of the heat roller 2 is low such as immediately after the power is turned on, and the toner between the heat generating film 1 and the heat roller 2 is used.
If there is such a state, the toner may be fixed to each other, that is, if the temperature is equal to or lower than a predetermined temperature determined by the characteristics of the toner, the rotation drive may be controlled so as not to rotate the heating roller 2.

The pressure roller 3 is provided with an elastic member 31 such as silicon rubber on the outer circumference of a pressure roller shaft 32.
A nip portion for heating and pressing the recording material 8 is formed together with the heating roller 2. The pressure roller 3 is rotatably supported by the lower support plates 71 and 72 integrally formed with the lower frame 7 via the pressure roller bearing 33. The lower frame 7 is rotatably supported by the frame rotation shaft 90 with respect to the upper frame 6, and is biased by a pressure spring 91 in a direction in which the pressure roller 3 is pressed against the heating roller 2.

Next, setting of heat generation conditions for the heat generating film 1 will be described.

Regarding the appropriate value of the electric power applied to the heat-generating film, what is set as the warm-up time from power-on until fixing is possible, and what is the heat capacity of the heating roller 2 in order to stabilize temperature fluctuations? It depends on whether or not it is set to a certain level. In this embodiment, the power consumption is made as small as possible and the warm-up time is made as short as possible. In such a case, for example, the diameter of the heating roller 2 is 12 mm to 20 mm,
When the wall thickness is set to about 0.4 mm to 1 mm and the maximum applied power is set to 150 W to 300 W, the warm-up time is 10 seconds to several tens of seconds. In this embodiment, the resistance value of the heat generating film 1 is set so that the maximum applied power is 200W. Specifically, the resistance value of the heating film 1 is 5
The volume resistivity of the heating film 1 is set to 10 Ω so that it becomes 0 Ω.
00Ωcm, the electrode length Le 220 mm in FIG. 3, the interelectrode width De 2.2 mm, the heating film thickness 50 μm, and the effective value of the maximum applied voltage may be 100V.

The setting of heat generation conditions is not limited to the above values, but the volume resistivity of the heat generating film 1 is about 10 ² Ωcm to 10 ⁵ Ωcm in view of manufacturability, stability of resistivity and the like. Is desirable. In addition, the thickness of the heat-generating film is 12 μm or more from the viewpoint of handleability and the difficulty of generating wrinkles,
From the viewpoint of thermal conductivity, 200 μm or less is desirable. If the heating roller length is Lr, the electrode length Le is Lr> L
It is desirable that e> Lr-20 mm. The upper limit of Le is to prevent a partial excessive temperature rise of the heat-generating film 1 due to the occurrence of a portion that does not come into contact with the heating roller 2 at the end of the heat-generating region 12, and the lower limit thereof heats both ends of the heating roller 2. This is to prevent non-uniformity of the temperature distribution by not doing so. Here, the heating roller length Lr is appropriately longer than the maximum recording material width by about 5 mm to 50 mm. If the contact width between the heating roller 2 and the heat-generating film 1 shown in FIG. 1 is Dr, the inter-electrode width De is Dr>De>
About 1 mm is desirable. The upper limit of De is to prevent a partial excessive temperature rise of the heat generating film 1 due to the generation of a portion that does not contact the heating roller 2 in the heat generating region 12, and the lower limit is to increase the heat generation density and heat. Since the contact area required for conduction is reduced, the temperature gradient between the heating film 1 and the heating roller 2 becomes too large, the temperature control of the heating roller becomes inaccurate, and further, the temperature of the heating film is excessively increased. This is to prevent it.

Next, the temperature control of the fixing device of this embodiment will be described.

FIG. 4 shows a block diagram relating to the temperature control of this embodiment. The temperature information from the temperature sensor 11 by the thermistor is input to the arithmetic processing unit through the AD converter, an appropriate applied power amount is set, and the energization control unit controls the energization amount to the electrode 13 of the heat generating film 1.

FIG. 5 shows the structure of the temperature sensor 11. A thermistor 112 and an electrode 113 are provided on the base material 111 of the insulating PI.
The base material 111 is bonded to the heat generating film 1 so that the thermistor 112 is located at the center of the heat generating area 12 of the heat generating film 1. In the case of the conventional heat roller method of heating with a lamp heater, since the temperature sensor is a method of sliding the thermistor on the heat roller through the PI film, the structure becomes complicated by pressing with an elastic member. According to the invention, since the structure can be fixed by adhesion, the structure is simple, and since the heat conductivity from the heat generating portion is good, the accuracy of temperature control is also improved.

In the present embodiment, since the heat capacity of the heating roller 2 is reduced, the temperature fluctuation of the heating roller 2 is sensitive to the change of the heat value of the heat generating film 1 and the passage of the recording material 8. Therefore, it is desirable to finely control the energization amount of the heat generating film 1 from the information of the temperature sensor 11. In this embodiment, the temperature information is converted into an 8-bit digital signal, and the arithmetic processing unit calculates the applied heat quantity based on the deviation from the target temperature, the differential value of the deviation, and the integrated value. That is, discrete PID control is performed. The energization control unit changes the energization amount to the heat generating film 1 based on the calculated heat amount. As shown in FIG. 6, the change of the energization amount is performed by the change of the wave number divided at the zero cross point of the commercial AC power source.

In addition to the above, as a temperature control method,
ON / OFF control method based on the detected temperature and target temperature, adjusting the applied heat quantity from the deviation between the detected temperature and the target temperature, and giving the applied heat quantity according to the warm-up time and the passing time of the recording material in advance Various methods such as so-called feedforward control can be applied. Further, as a method of changing the energization amount, phase control for changing the energized phase range within one cycle of the AC waveform can be applied.

As described above, according to the present invention, a heating body can be obtained by simply forming electrodes on a plastic film such as conductive PI, which is extremely low cost and easy to assemble. Further, since the heating roller is heated in direct contact with the heating roller, the temperature is about the same as that of the heating roller, that is, only a hundred and several tens of degrees, and the temperature is not as high as several thousand degrees as in a lamp heater, which is highly safe. Moreover, the dimensions of the heating film 1 are within the length of the heating roller, which does not lead to an increase in the size of the apparatus. Also, the life of the heating element is semi-permanent, and the reliability can be greatly improved. Also,
Since it is a fixed electric heating element, its structure is simple and no brush electrode is required.

As described above, although the present invention has many excellent features, it was further discovered that this embodiment has a remarkable effect of actively eliminating the temperature distribution in the axial direction of the heating roller 2. In the heat roller system, temperature distribution in the axial direction is unavoidable, and particularly in the case of the one having a low heat capacity as in this embodiment, it is necessary to take sufficient measures. The main causes of the occurrence are that the temperature at both ends of the roller is lowered by heat transfer from the bearings at both ends of the roller, and the temperature at the center is lowered as the recording material removes heat from the roller. By the way, in general, the resistance value of the resistance heating element increases as the temperature rises, and the amount of heat generation decreases under a constant applied voltage. In the case of a linear heating region sandwiched by a pair of electrodes as in this embodiment, it can be approximately regarded that a constant voltage is applied between the electrodes at each linear position, and therefore, for example, both ends are When the temperature becomes high, the resistance at both ends increases, and then the heat generation amount at both ends decreases as compared with the central part. On the contrary, if the temperature of both ends becomes low, the resistance value of that part decreases and the amount of heat generation increases. In other words, the calorific value distribution is such that the generated temperature distribution is positively corrected,
The temperature distribution is made uniform.

In the above-mentioned embodiment, the heat-generating film has an electrode formed on a conductive base material. However, for example, a resistance layer and an electrode are coated on an insulating film such as a polyimide film to form a heat-generating region. It may be formed with.

Further, in the above-mentioned embodiment, the heat generating film 1 is pressed against the heating roller 2 depending on the tension applied to the heat generating film 1, but it may be pressed by a heat insulating elastic member such as felt.

Further, as described above, the present invention has the effect of actively canceling the temperature distribution, but in order to further forcibly correct the temperature distribution, a plurality of electrodes are formed on the heating film 1. It is also possible to provide pairs and independently control and give different amounts of heat in the axial direction of the heating roller 2. In the present invention, since such a structure can be achieved by only patterning the electrodes, it can be realized more easily than the conventional example.

As the resistance heating element, a material having a positive temperature coefficient of resistance, that is, a material having PTC characteristics may be used. FIG. 7 shows a typical PTC characteristic. Examples of substances having such characteristics include barium titanate (BaTi).
O ₃₎ system there is a ceramic. Specifically, JP-A-56-1
As disclosed in Japanese Patent No. 23581, if Posistar (trade name) Murata Manufacturing Co., Ltd. powder is bound by using an insulating binder, a PTC characteristic suitable for a fixing device can be obtained. For application to the present invention, the above substance and electrodes may be coated on an insulating film to form a film heating element. It is also known that PTC characteristics are exhibited by dispersing carbon beads in a specific resin, which is applicable to the present invention. As shown in FIG. 7, in the case of a substance having PTC characteristics, the resistance value decreases as the temperature rises until a certain predetermined temperature is reached, so that the applied power does not decrease and the temperature rises quickly. Further, after reaching the predetermined temperature, the resistance value suddenly rises and the applied power automatically decreases. Therefore, it has a self-temperature adjusting function without using the temperature sensor to control the temperature from the outside. By the way, in JP-A-56-123581, PTC ceramics is coated on a roller such as a heating roller. In that case, JP-A-56-12358 is used.
Although it has the same problems as No. 0, by applying to the present invention, since it is possible to solve the problems and exert the effects due to the above PTC characteristics, the present invention of a heating element having PTC characteristics is provided. It can be said that the application to is extremely suitable.

[0034]

As described above, according to the present invention,
A heating roller that heats the recording material by contacting the surface of the recording material, a heating means of the heating roller, and a pressing means that presses the recording material into contact with the heating roller. A film resistance heating element fixedly arranged in contact with the surface of the roller, preferably, the film resistance heating element has at least a pair of electrodes arranged in parallel in the axial direction of the heating roller,
More preferably, since the temperature detecting element is provided on the film-shaped resistance heating element, a heating element having a high safety without a high temperature portion such as a lamp heater can be configured, and the fixing is small in size, low in cost and high in performance. It has an effect that a device can be provided.

[Brief description of drawings]

FIG. 1 is a side sectional view showing an embodiment of the present invention.

FIG. 2 is a front sectional view showing an embodiment of the present invention.

FIG. 3 is a plan view showing a heat generating film of an embodiment of the present invention, and b) is a side sectional view.

FIG. 4 is a block diagram showing a temperature control method according to an embodiment of the present invention.

5A is a plan view showing a temperature sensor according to an embodiment of the present invention, and FIG. 5B is a side sectional view.

FIG. 6 is a diagram showing a method of changing an energization amount according to the embodiment of the present invention.

FIG. 7 is a diagram showing PTC characteristics.

[Explanation of symbols]

 1 Heating Film 2 Heating Roller 3 Pressure Roller 4 Cleaning Pad 5 Separation Claw 6 Upper Case 7 Lower Case 8 Recording Material 11 Temperature Sensor 13 Electrode

Claims (3)

[Claims] 1. A heating roller for heating the recording material by contacting the surface of the recording material, a heating means for the heating roller, and a pressing means for pressing the recording material to the heating roller. The fixing device, wherein the heating means is a film-shaped resistance heating element fixedly arranged in contact with the surface of the heating roller. 2. The fixing device according to claim 1, wherein the film-shaped resistance heating element has at least a pair of electrodes arranged in parallel in the axial direction of the heating roller. 3. The fixing device according to claim 1, wherein a temperature detecting element is provided on the film-shaped resistance heating element.