JP3134544B2 - Fixing device - Google Patents

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 and a copying machine.
More specifically, the present invention relates to a method for heating a heating roller.

[0002]

2. Description of the Related Art Conventionally, a fixing device of an electrophotographic image forming apparatus includes a heating roller which is maintained at a predetermined temperature by applying radiant heat from a lamp heater such as a halogen lamp, and a heating roller having an elastic layer. A heat roller system in which a recording material carrying an unfixed toner image is heated and pressurized by a pressure roller pressed in contact with the recording medium is typically used.

A method of heating a heating roller without using a lamp heater is disclosed in Japanese Patent Application Laid-Open No. 56-12358.
As disclosed in Japanese Patent Application Laid-Open No. H. 0, there has been a method of heating by energizing a resistance heating layer on the peripheral surface of a heating roller. In addition, Japanese Unexamined Patent Publication
As disclosed in JP-A-3-313182, there has been a method of heating with a fixed resistance heating element via a film moving at the same speed as a recording material without using a heating roller.

[0004]

However, the above-mentioned prior art has the following problems. That is,
In the method using a lamp heater, the filament portion of the lamp needs to be extremely high at 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 sealed by a glass tube. Further, if the glass heater is touched with a bare hand, the life is remarkably impaired, so that the assemblability of the apparatus is deteriorated and the cost is increased. It was also expensive.

In order to obtain a necessary heat generation length, an extra length is required for a filament sealing portion, a terminal, and the like, resulting in an increase in the size of the apparatus.

[0007] The service life is short and the reliability of the device is reduced.

In Japanese Patent Application Laid-Open No. 63-313182, since the film is conveyed at the same speed as the recording material, its handling is not easy and the structure is complicated. In addition, the cost was also high.

[0009] Since the film comes into contact with the recording material, there is a problem in reliability such that the film is damaged by jamming of the recording material.

In Japanese Patent Application Laid-Open No. Sho 56-123580, a brush electrode is required, and there is a problem in that a contact portion generates heat and electric noise is generated.

[0011] A heating layer and electrodes must be formed on the peripheral surface of the heating roller, so that the production is not easy and the cost is high.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to eliminate the above-mentioned problems and to provide a small-sized and low-cost fixing device which is high in safety and reliability. It is.

[0013]

According to the present invention, there is provided a heating roller for heating a recording material by contacting the surface of the recording material, and the heating roller while rubbing a part of a peripheral surface of the heating roller .
A heating means for transferring heat to the roller , and a pressure means for heating and pressing the recording material together with the heating roller to form a nip portion , wherein the heating means is provided on the peripheral surface of the heating roller.
And a film-shaped resistance heating element fixedly disposed in contact with a portion different from the nip portion , preferably,
The film-shaped resistance heating element has at least a pair of electrodes arranged in parallel in the axial direction of the heating roller, and more preferably, a temperature detection element is provided on the film-shaped resistance heating element. It is characterized by.

[0014]

Embodiments of the present invention will be described below.

First, the structure of the entire fixing device will be described with reference to FIGS.
This will be described with reference to FIGS. 1 is a side sectional view of the present embodiment, FIG. 2 is a front sectional view, and FIG. 3 is a view showing a configuration of a heat generating film, wherein a) is a plan view and b) is a side sectional view.

The heating roller 2 made of aluminum is fixed coaxially with a heating roller shaft 22 made of metal via a sleeve 21 made of heat-resistant resin such as PPS (polyphenylene sulfide). The heating roller shaft 22 is rotatably supported by upper support plates 64 and 65 formed integrally 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 driven to rotate by a motor (not shown). On the surface of the heating roller 2, PFA (ethylene tetrafluoride-perfluoroalkyl vinyl ether copolymer), FEP (ethylene tetrafluoride-propylene hexafluoride copolymer), PTFE (polytetrafluoroethylene)
A release layer such as that described above is applied to improve the offset property of the toner and reduce the coefficient of friction between the heating film 1 and a part of the peripheral surface of the heating roller 2.

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 to the upper case 6 via a leaf spring 63 by means of film pressing plates 61 and 62 and an adhesive, respectively. Have been. Fix the heating film 2
Is set at a predetermined position, and then film holding plates 61 and 62 are fixed from above with screws or the like.
An adhesive may be poured between the film holding plates 61 and 62. The length of the rectangular short side of the heat generating film 2 is set to such a size that when the heating roller 2 is set at a predetermined position, the leaf spring 63 bends to generate a tension on the heat generating film 2. The heat generating film is made of a material having resistance, for example, PI (polyimide) in which carbon beads are dispersed. As shown in FIG. 3, a pair of electrodes 13 made of silver paste or the like are arranged on the heat generating film 1 in the axial direction of the heating roller 2. When a predetermined voltage is applied between the electrodes, a current flows through a gap (heating region 12) between the electrodes, which is linear and parallel to the axial direction of the heating roller 2, and generates heat. A temperature sensor 11 is fixed on the heating area 12, and the temperature of the heating roller 2 is controlled by adjusting the power applied to the heating film based on the detected temperature information.

In addition, a separating claw 5 for preventing the recording material 8 from being wound around the heating roller 2 is provided around the outer periphery of the heating roller 2.
Cleaning pad 4 made of felt for removing toner adhered to heating roller 2 with a slight offset
Are arranged. The cleaning pad 4 is provided with a heating roller 2 to prevent the toner from adhering to the heat generating film 1 and thereby deteriorating the thermal conductivity and to prevent the heat generating film 1 from being stuck to the heat roller 2 to damage the heat generating film 1. Are disposed upstream of the heat generating film 1 in the rotation direction. In order to further secure the breakage 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, for example, immediately after the power is turned on.
When the toner is in a state where the two are fixed, that is, when 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 periphery of a pressure roller shaft 32.
A nip portion for heating and pressing the recording material 8 together with the heating roller 2 is formed. The pressure roller 3 is rotatably supported by lower support plates 71 and 72 formed integrally with the lower frame 7 via a 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 urged by a pressing spring 91 in a direction in which the pressing roller 3 is pressed against the heating roller 2.

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

The appropriate value of the electric power applied to the heat generating film is determined by setting a warm-up time from when the power is turned on to when fixing is possible, and by setting a heat capacity of the heating roller 2 in order to stabilize temperature fluctuation. It depends on whether it is set to a degree or the like. The present embodiment is intended to minimize the power consumption and the warm-up time as much as possible. In such a case, for example, the diameter of the heating roller 2 is changed from φ12 mm to φ20 mm,
When the 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 seconds. In this embodiment, the resistance value of the heat generating film 1 is determined so that the maximum applied power is 200 W. Specifically, the resistance value of the heating film 1 is 5
The volume resistivity of the heat generating film 1 is set to 10
It is sufficient to set the effective value of the maximum applied voltage to 100 V by setting 00 Ωcm, the electrode length Le220 mm in FIG. 3, the electrode width De2.2 mm, the heat generation film thickness to 50 μm.

The heat generation conditions are not limited to the above-mentioned values, but the volume resistivity of the heat generation film 1 may be in the range of about 10 ² Ωcm to 10 ⁵ Ωcm from the viewpoints of manufacturability and stability of resistivity. Is desirable. In addition, the thickness of the heat generating film is 12 μm or more from the viewpoint of handleability and difficulty in generating wrinkles.
From the viewpoint of thermal conductivity, the thickness is desirably 200 μm or less. The electrode length Le is Lr> L, where Lr is the length of the heating roller.
e> Lr-20 mm is desirable. The upper limit of Le is to prevent a partial excessive rise in the temperature of the heating film 1 due to the occurrence of a portion that does not contact the heating roller 2 at the end of the heating region 12, and the lower limit is that both ends of the heating roller 2 are heated. This is to prevent non-uniformity of the temperature distribution by not being performed. Here, it is appropriate that the length Lr of the heating roller is longer than the maximum recording material width by about 5 mm to 50 mm. Assuming that the contact width between the heating roller 2 and the heat generating film 1 shown in FIG. 1 is Dr, Dr>De>
About 1 mm is desirable. The upper limit of De is to prevent a partial excessive rise in the temperature of the heat generating film 1 due to the occurrence of a portion that does not contact the heating roller 2 in the heat generating region 12. By reducing the contact area required for conduction, the temperature gradient between the heating film 1 and the heating roller 2 becomes too large, so that the temperature control of the heating roller becomes inaccurate. This is to prevent it.

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

FIG. 4 is a block diagram relating to the temperature control of the present embodiment. Temperature information from the temperature sensor 11 by the thermistor is input to an arithmetic processing unit through an AD converter, an appropriate amount of applied electric power is set, and an amount of electricity to the electrode 13 of the heating film 1 is controlled by an electricity supply control unit.

FIG. 5 shows the structure of the temperature sensor 11. The thermistor 112 and the electrode 113 are provided on the base 111 of the insulating PI.
The substrate 111 is adhered to the heat generating film 1 such that the thermistor 112 is located at the center of the heat generating region 12 of the heat generating film 1. In the case of the conventional heat roller method of heating with a lamp heater, the temperature sensor is of a method in which the thermistor slides on the heat roller via a PI film, so the structure is complicated, such as pressing with an elastic member. According to the invention, the structure can be simplified because it can be fixed by bonding, and the accuracy of temperature control can be improved because of good thermal conductivity from the heat generating portion.

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

In addition to the above, as a method of temperature control,
A method of performing on / off control according to the level of the detected temperature and the target temperature, a method of adjusting the amount of applied heat based on a deviation between the detected temperature and the target temperature, and giving an applied amount of heat in accordance with a warm-up time and a passing point of a recording material in advance. Various methods such as so-called feed-forward control can be applied. Further, as a method of changing the amount of energization, phase control that changes the phase range of energization within one cycle of the AC waveform can be applied.

As described above, according to the present invention, a heating element can be obtained simply by forming an electrode on a plastic film such as a conductive PI, and it is extremely low-cost and easy to assemble. In addition, since the heating is performed in direct contact with the heating roller, the temperature is almost the same as that of the heating roller, that is, the temperature is only one hundred and several tens of degrees. Further, the dimensions of the heating film 1 are set within the length of the heating roller, which does not lead to an increase in the size of the apparatus. Further, the life of the heating element is semi-permanent, and the reliability can be greatly improved. Also,
Since it is a fixed heating element, it has a simple structure and does not require a brush electrode.

As described above, although the present invention has many excellent features, it has been further found that this embodiment has a remarkable effect of actively eliminating the axial temperature distribution of the heating roller 2. In the heat roller method, the temperature distribution in the axial direction is inevitable, and it is necessary to take sufficient measures especially in the case of reducing the heat capacity as in this embodiment. The main causes of this are that the temperature at both ends decreases due to heat transfer from the bearings at both ends of the roller, and that the temperature at the center decreases due to the recording material taking heat from the roller. Incidentally, the resistance value of the resistance heating element generally increases as the temperature increases, and the heating value decreases under a constant applied voltage. In the case of a linear heating region sandwiched between a pair of electrodes as in the present embodiment, it can be approximately regarded that a constant voltage is applied between the electrodes at each linear location. When the temperature rises, the resistance at both ends increases, and the calorific value at both ends decreases as compared with that at the center. Conversely, when the temperature at both ends becomes low, the resistance value at that portion decreases and the amount of heat generated increases. In other words, the calorific value distribution that positively corrects the generated temperature distribution,
That is, the temperature distribution is made uniform.

In the above-described embodiment, the heat-generating film has a structure in which electrodes are formed on a conductive base material. However, a heat-generating region is formed by coating a resistive layer and electrodes on an insulating film such as a polyimide film. May be formed.

In the above-described embodiment, the heat generating film 1 is pressed against the heating roller 2 by the tension applied to the heat generating film 1. However, a method in which the heat generating film 1 is pressed by a heat insulating elastic member such as felt may be used.

As described above, the present invention has the effect of positively eliminating the temperature distribution. However, in order to forcibly correct the temperature distribution, a plurality of electrodes are formed on the heating film 1. By providing a pair, it is also possible to independently control and apply different amounts of heat in the axial direction of the heating roller 2. In the present invention, such a configuration can be achieved only by patterning the electrodes, so that it can be easily realized as compared with the conventional example.

Further, a substance having a positive temperature coefficient of resistance, that is, a substance having PTC characteristics may be used as the resistance heating element. FIG. 7 shows typical PTC characteristics. Materials exhibiting such characteristics include, for example, barium titanate (BaTi
There is an O ₃ ) -based ceramic. Specifically, JP-A-56-1
As disclosed in Japanese Patent No. 23581, if powder of Postar (trade name, manufactured by Murata Manufacturing Co., Ltd.) is bound using an insulating binder, PTC characteristics suitable for a fixing device can be obtained. In order to apply the present invention, the above substance and electrodes may be applied on an insulating film to form a film heating element. It is also known that PTC characteristics appear even when carbon beads are dispersed in a specific resin, and can be applied to the present invention. As shown in FIG. 7, in the substance having the PTC characteristic, the resistance value decreases as the temperature increases until the temperature reaches a certain predetermined temperature, so that the applied power does not decrease and the temperature rises quickly. After the temperature reaches a predetermined temperature, the resistance value rises sharply and the applied power automatically decreases. Therefore, the device has a self-temperature adjusting function without externally controlling the temperature using a temperature sensor. Japanese Patent Application Laid-Open No. 56-123581 discloses a configuration in which PTC ceramics is applied to a roller such as a heating roller.
Although it has the same problems as No. 0, the effects of the above-mentioned PTC characteristics can be exerted while solving those problems by applying to the present invention. It can be said that the application to is very suitable.

[0034]

As described above, according to the present invention,
A high-safety heating element without a high-temperature portion such as a lamp heater can be formed, and a compact, low-cost, and high-performance fixing device can be provided. Furthermore, the heating element is different from the nip
Heating element breaks due to recording material jam, etc.
This has the effect of preventing loss .

[Brief description of the 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.

FIGS. 3A and 3B are a plan view and a side sectional view, respectively, showing a heat generating film according to an embodiment of the present invention.

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

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

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

FIG. 7 is a view showing PTC characteristics.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat generation 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)

(57) [Claims] A heating roller for heating the recording material by contacting the surface of the recording material ;
Heating means for transferring heat to the heating roller while rubbing a part thereof, and heating and pressing the recording material together with the heating roller
Pressurizing means for forming a nip portion , wherein the heating means is a peripheral surface of the heating roller, and the nip portion
A fixing device comprising a film-shaped resistance heating element fixedly arranged in contact with a portion different from the above . 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 an 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.