JP2001005334A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a fixing device capable of reducing the temperature difference between a paper-feeding area and a paper-nonfeeding area, even when small-sized transfer materials are continuously used, compact in structure and without the need to reduce the number of output sheets. SOLUTION: In this fixing device, having a fixing roller 1 and a pressure roller 5 which are brought into press-contact with each other and disposed freely rotatably, a heater (heating means) 4 disposed at the inside of the fixing roller 1, the thermistor of a contact type (temperature detecting means) 9 for detecting the surface temperature of the fixing roller 1 and an electric power control means for controlling electric power supplied to the heater according to temperature detected by the thermistor 9, and fixing a toner image T by heating, inserting and feeding a transfer material P on which the unfixed toner image T is carried by the fixing roller 1 and the pressure roller 5, a heat radiating sheet (sheet member) 10 opposed to the pressure roller 5 (or the fixing roller 1) and consisting of a good heat conducting body that is slidable is installed.

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 image forming apparatus.

[0002]

2. Description of the Related Art Copiers, laser beam printers, and the like employing an electrophotographic system correspond to a document image or an input image signal on the surface of a photosensitive member as an image carrier uniformly charged by a charging means. An image is exposed to form an electrostatic latent image on the surface of the photoreceptor, and the electrostatic latent image is developed as a toner image by a developing unit, and the toner image is transferred onto a transfer material as a recording material by a transfer unit. Then, the unfixed toner image on the transfer material is fixed on the transfer material by a fixing unit, and an image-formed product is output.

As a fixing method of a fixing device for permanently fixing an unfixed toner image on a transfer material on a transfer material, a heat roller method and a fixing film method are mainly used at present.

Here, in the heat roller method, a transfer material on which an unfixed toner image has been transferred is introduced into a pressure contact portion formed by a heated fixing roller and a pressure roller, and is transferred to the fixing roller and the pressure roller. And heat and pressure to fix the toner image on the transfer material.

The fixing film system is formed between the fixing film and the pressure roller by rubbing the fixing film against a heat generating member, and pressing a pressure roller against the heat generating member via the fixing film. In this method, a transfer material onto which an unfixed toner image has been transferred is introduced into the pressure contact portion, the transfer material is held and conveyed, and the toner image is fixed on the transfer material by heat and pressure.

FIG. 4 shows an example of a fixing device employing a heat roller system.

FIG. 4 is a cross-sectional view of a conventional heat roller type fixing device. The fixing device includes a fixing roller 1 having a heating source (hereinafter, referred to as a heater) 4 such as a halogen lamp as a basic configuration. The pressure roller 5 has an elastic layer 7 made of silicon rubber or the like pressed on the core bar 6 on the metal core 6. A release layer 8 made of a PFA tube or the like is provided on the elastic layer 7 of the pressure roller 5.

The fixing roller 1 has a resin surface layer 3 having a high releasability, such as a fluororesin, formed around a cored bar 2 in order to prevent adhesion due to toner viscosity.
A temperature detecting means 9 is provided on the peripheral surface of the fixing roller 1, and the temperature detecting means 9 detects the surface temperature of the fixing roller 1 so as to maintain the surface temperature substantially constant. Is controlling.

In the fixing device having the above configuration, the fixing roller 1 and the pressure roller 5 are pressed against each other with a predetermined pressure to form a pressure contact portion (hereinafter, referred to as a fixing nip portion). The transfer material P is nipped and conveyed in the fixing nip by rotating the pressure roller 5 and a driving unit (not shown). At this time, the temperature of the fixing roller 1 is controlled to a predetermined temperature by the heater 4, and the toner image T on the transfer material P is heated and melted while receiving pressure when passing between the fixing roller 1 and the pressing roller 5. After passing through the fixing nip portion, it is cooled and fixed on the transfer material P as a permanent image.

FIG. 5 shows an example of a fixing device employing a fixing film system.

FIG. 5 is a sectional view of a conventional fixing film type fixing device. In FIG. 5, reference numeral 21 denotes, for example, a ceramic heater as a heat-generating member, and the heater 21 has a high heat resistance and a high heat insulating property. It is fixed downward and supported by a stay 22 as a rigid heater support. An endless belt-like fixing film 23 made of a material having high heat resistance and covered with a material having good releasability is wound around the heater 20 between the driving roller 24 and the driven roller 25. It is arranged to rub. Note that the driving roller 24 and the driven roller 25 are disposed substantially parallel to the heater 21.

A pressing roller 26 as a rotary pressing member is pressed against the lower surface of the heater 21 so as to sandwich the fixing film 23, and the pressing roller 26 is made of silicone rubber or the like. Heater 21 having a good rubber elastic layer
And a fixing nip portion is formed therebetween. When the driving roller 24 is driven to rotate in a direction indicated by an arrow by a motor (not shown) as a rotation driving unit, the fixing film 23 to which a predetermined tension is given by a driven roller 25 also serving as a tension roller has a predetermined peripheral speed. As the fixing film 23 rotates, the pressure roller 26 also rotates.

In a state where the fixing film 23 is driven to rotate and the heater 21 is heated and controlled to a predetermined temperature, an unshown fixing roller 23 is provided between the fixing film 23 and the pressure roller 26 in the fixing nip portion. When the transfer material P carrying the unfixed toner image T is introduced from the image forming unit side to the fixing film 23 side, the transfer material P is brought into close contact with the outer surface of the fixing film 23. The fixing nip portion is conveyed while being held together with the fixing film 23. In the process, the transfer material P receives thermal energy from the heater 21 via the fixing film 23 to receive heat fixing of the unfixed toner image T, and the transfer material P that has passed through the fixing nip portion is Is discharged and transported.

[0014]

However, in an image forming apparatus using a fixing device employing a heat roller method or a fixing film method, a longer length of the transfer material than the maximum size transfer material usable in the image forming apparatus is required. When a transfer material having a small size in the direction (small size transfer material) is used, the following problem occurs.

That is, the temperature in the longitudinal direction of the range in which the maximum-size transfer material passes is generally uniform so that problems such as defective fixing do not occur when the maximum-size transfer material that can be used is used. The temperature distribution in the longitudinal direction of the heating source was set to be as follows.

However, when a small-sized transfer material is used in an image forming apparatus having only a single heating means,
When the transfer material passes through the fixing nip portion of the fixing device, the transfer material takes heat in an area where the transfer material passes (paper passing area), whereas heat is taken in an area where the transfer material does not pass (non-paper passing area). Is not deprived, the temperature of the non-sheet passing area becomes higher than that of the sheet passing area.

When the image forming operation is continuously performed, the temperature difference between the sheet passing area and the non-sheet passing area increases. The temperature of the sheet passing area becomes too high, and if a large-size transfer material is used immediately after the small size, an offset occurs in the non-sheet-passing area of the small-size transfer material. Further, if the high temperature state continues in the non-sheet passing area, components such as the fixing roller and the pressure roller may be deteriorated.

Conventionally, the following means have been used to solve the above problem.

First, there is a technique in which the heating means of the fixing device can change the temperature distribution according to the size of the transfer material. More specifically, by arranging a plurality of heaters inside the fixing roller and varying the temperature distribution in the longitudinal direction of each heater, it is possible to heat only the paper passing area when using a small-sized transfer material. Becomes

However, when a plurality of heaters are used, the diameter of the fixing roller is also large because the fixing roller accommodates the plurality of heaters, which hinders downsizing of the fixing device. In a fixing device employing a fixing film system, a similar problem occurs by providing a ceramic heater with a plurality of heating elements.

When a small-sized transfer material is continuously used in an image forming operation, the time from when the transfer material passes through the fixing nip portion to when the next transfer material enters the fixing nip portion is increased. Although the temperature of the non-sheet passing area can be reduced by heat diffusion, this method requires a reduction in the number of sheets output per unit time.

In addition, a method of making the temperature of the pressure roller uniform by bringing a roller member (radiation roller) made of a good heat conductor into contact with the pressure roller has been used. Although it is possible to reduce the temperature difference between the area and the non-sheet passing area to some extent, it is required to further reduce the temperature difference.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to reduce the temperature difference between the paper passing area and the non-paper passing area even when small size transfer materials are continuously used. It is an object of the present invention to provide a fixing device which can be suppressed, is compact and does not need to reduce the number of output sheets.

[0024]

According to a first aspect of the present invention, there is provided a fixing roller and a pressure roller which are disposed in pressure contact with each other and are rotatably disposed, and are disposed inside the fixing roller. A heating unit provided, a contact-type temperature detection unit for detecting a surface temperature of the fixing roller, and a power control unit for controlling electric power supplied to the heating unit according to the temperature detected by the temperature detection unit. A fixing device that heats and transfers a transfer material carrying an unfixed toner image by the fixing roller and the pressure roller with a narrow pressure to fix the toner image, the driven member facing the fixing roller or the pressure roller. Alternatively, a slidable sheet member made of a good heat conductor is provided.

According to a second aspect of the present invention, there is provided a heating means, a film member disposed endlessly or endlessly slidably in contact with the heating means, and being pressed against the heating means via the film member. A pressure roller disposed therein, a temperature detection unit for detecting a temperature of the heating unit, and a power control unit for controlling electric power supplied to the heating unit. In a fixing device for fixing a toner image by heating and transferring a transfer material carrying a toner image thereon with a narrow pressure, a sheet member made of a driven or slidable good heat conductor opposed to the pressure roller is provided. It is characterized by the following.

According to a third aspect of the present invention, in the first or second aspect of the invention, the sheet member is an endless belt-shaped member, and an outer peripheral surface thereof is driven or slid by the fixing roller or the pressure roller. It is characterized by rotating and moving.

According to a fourth aspect of the present invention, in the first or second aspect of the present invention, the sheet member is an endless belt-shaped member, and has a winding roller for winding and holding the belt member. It is characterized in that it moves following or sliding with the fixing roller or the pressure roller.

According to a fifth aspect of the present invention, in any one of the first to fourth aspects, a contact area between the sheet member and the fixing roller or the pressure roller is variable.

According to a sixth aspect of the present invention, in the first aspect of the present invention, the sheet member has a metal layer.

[0030]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> FIG. 1 is a cross-sectional view of a heat roller type fixing device according to a first embodiment of the present invention. In the fixing device, a fixing roller 1 is made of a metal core such as aluminum. 2, PTFE through a primer or the like,
It is configured by providing a resin layer 3 having high releasability and heat resistance such as PFA. Then, the inside of the fixing roller 1 is
A heater 4 is provided as a heating source composed of a halogen lamp or the like. Electric power to the heater 4 is determined based on a temperature detected by a thermistor 9 serving as temperature detecting means provided on an outer peripheral surface of the fixing roller 1. Is controlled so that the surface of the fixing roller 1 is heated to a predetermined temperature (about 160 ° C.
210 ° C.).

The pressure roller 5 is formed by forming an elastic layer 7 of silicon sponge rubber or the like on a cored bar 6 and coating a molded PFA tube 8 having a thickness of 100 μm or less as a release layer thereon. It is configured.

Thus, in the present embodiment, the heat radiating sheet 10 facing the pressure roller 5 is disposed over a width larger than the width of the maximum size transfer material P. The heat radiating sheet 10 is made of a metal such as nickel, aluminum, stainless steel or the like having a thickness of about 500 μm in an endless shape. The heat radiating sheet 10 is stretched by two support rollers 11 and the pressure roller 5 to rotate the pressure roller 5. It is driven and rotated with.

In the fixing device having the above-described configuration, first, when the power is turned on, the heater 4 is energized to heat the fixing roller 1, and as the temperature of the fixing roller 1 rises, the detected temperature of the thermistor 9 decreases. When the temperature rises and the thermistor 9 detects a predetermined temperature, the driving of the fixing roller 1 is started by the rotation of a motor (not shown), and the pressure roller 5 and the heat radiating sheet 10 are also rotated to transfer heat to the pressure roller 5 and the like. Can be Then, a predetermined time has elapsed or thermistor 9
When a predetermined temperature is detected, the rotation of the fixing roller 1 is stopped, the temperature is controlled at a predetermined standby temperature, and the image forming operation is in a standby state.

When the image forming operation is started, the driving of the fixing roller 1 is started, and the temperature control is started at a predetermined fixing temperature. Subsequently, when the transfer material P onto which the unfixed toner image T has been transferred enters the fixing nip, the toner is melted by heat while receiving pressure, and the toner is cooled after passing through the fixing nip, thereby becoming a permanent image. Is fixed to the transfer material P.

When the small-sized transfer material P is continuously used for the image forming operation, the temperature is controlled so that the temperature of the paper passing area becomes a predetermined temperature. For this reason, when there is a transfer material P of a small size in the fixing nip portion, heat is taken away by the transfer material P and the toner image T only in the paper passing area. Temperature is high on the exit side of. Since the core metal 2 of the fixing roller 1 is made of metal such as aluminum having high thermal conductivity, the temperature difference between the non-sheet passing area and the sheet passing area decreases relatively quickly.

On the other hand, the pressure roller 5 has a PFA tube 8 and an elastic layer 7 such as a silicone sponge. Since these materials have poor thermal conductivity, the temperature difference between the non-paper passing area and the paper passing area is low. Will be retained.

However, the temperature difference between the non-sheet passing area and the sheet passing area generated in the pressure roller 5 is rapidly reduced by contact with the heat radiation sheet 10. Since the heat radiating sheet 10 can have a large contact area with the pressure roller 5, the temperature difference between the non-sheet passing area and the sheet passing area can be suppressed as compared with the conventionally used heat radiating roller. is there. Therefore, at the entrance side of the fixing nip portion, the temperature difference between the non-sheet passing area and the sheet passing area of the pressure roller 5 is sufficiently small, and the small-sized transfer material P is continuously used for the image forming operation. However, the temperature in the non-sheet passing area does not become too high, and the fixing roller 1
The components such as the pressure roller 5 and the like do not deteriorate.

Further, even if the image forming operation is performed using the large-size transfer material P after the small-size transfer, no offset is generated, and the transfer material when the continuous image formation operation of the small-size transfer material P is performed is performed. The time between P can be shortened, and the number of output sheets per unit time can be increased.

Second Embodiment Next, a second embodiment of the present invention will be described with reference to FIG.

FIG. 2 is a sectional view of a fixing film type fixing device according to the present embodiment. In this fixing device, a fixing film 23 is fixedly provided with a driving roller 24 and a driven roller 25 and the heater 21 and the heater The stay 21 is stretched between the stay 21 and the stay 22.

The driven roller 25 also serves as a tension roller for applying tension in the direction in which the fixing film 23 is stretched outward, and the fixing film 23 is coated with silicon rubber or the like to increase the friction coefficient of the driving roller 24. It is driven at a predetermined peripheral speed without wrinkles, meandering, and speed delay with the rotation.

The surface of the pressure roller 26 is covered with a tube made of PFA or the like which is excellent in releasability and durability, and the inside is made of silicon sponge rubber or the like. The pressure roller 26 is opposed to the heater 21 via the fixing film 23 and is, for example, 5 to 15 kgf by a biasing means such as a spring.
Are pressed against each other with the contact force of
3 Followed rotation.

In this embodiment, the heat radiating sheet 28 facing the pressure roller 26 is provided over a width larger than the width of the maximum size transfer material P. The heat radiation sheet 28 is made of a metal such as nickel, aluminum, and stainless steel having a thickness of about 500 μm.
It is stretched by a book winding roller 29 and a pressure roller 26. The heat radiating sheet 28 moves while being rubbed against the pressure roller 26 by driving the winding roller 29 by driving means (not shown).

The endless fixing film 23 which is driven to rotate is repeatedly used for heat fixing of the toner image, and therefore has a thickness of 100 μm or less (preferably 40 μm) which is excellent in heat resistance, releasability and durability. The following thin film is used. As an example, a 20 μm thick polyimide, polyetherimide, polyethersulfone, polyetheretherketone, or other high heat-resistant resin, or a thin metal endless belt made of nickel, SUS, or the like, is provided on the outer peripheral surface of PTFE (tetrafluoroethylene resin). Low surface energy resin such as PFA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin) or a release coat layer obtained by adding a conductive material such as carbon black to these resins to a thickness of 10 μm. Endless belts are used.

The heater 21 having a low heat capacity forms a heat generating layer by coating a resistance material such as silver palladium or ruthenium oxide on an alumina substrate, for example, and further forms a fixing film 23 thereon.
The protective layer is formed by forming a protective layer of glass or the like in consideration of sliding with the base member, and is fixedly supported by the stay 22.

The stay 22 for thermally insulating the heater 21 with respect to the fixing device has high heat insulation, heat resistance and rigidity. For example, PPS (polyphenylene sulfide), PEEK (polyether ether ketone), liquid crystal polymer And the like, and composite materials of these resins with ceramics and metals.

Electricity is supplied to the heat generating layer of the heater 21 from both ends in the longitudinal direction, and the heat generating layer generates heat over the entire length. The temperature of the heater 21 is detected by a thermistor 27 which is bonded, pressed, or integrally formed on the back surface of the heater substrate with a thermally conductive silicone rubber adhesive or the like.

When the image forming operation is started, the driving roller 24 starts to rotate, and the fixing film 23 and the pressure roller 26 start to rotate following the rotation of the driving roller 24. And the heater 21
Of the heat generating layer is also started. When the temperature of the heater 21 is controlled at a predetermined fixing temperature in accordance with the temperature detected by the thermistor 27, and subsequently, the transfer material P on which the unfixed toner image T is transferred enters the fixing nip portion, the transfer material P receives pressure. The toner is melted by heat, and the melted toner is fixed to the transfer material P as a permanent image by being cooled after passing through the fixing nip.

Even when the transfer material P of a small size is continuously used for the image forming operation, the temperature difference between the non-sheet passing area and the sheet passing area of the pressure roller 26 by the heat radiating sheet 28 becomes small, so Deterioration and occurrence of offset can be prevented, and the number of output sheets per unit time can be increased.

Also, as in the present embodiment, the heat dissipation sheet 28
In a fixing device having a means for driving the transfer material, the transfer material P
The conveyance speed of the heat radiating sheet 28 can be changed according to the size of the sheet. In the fixing device configured as described above, for example, when the transfer material P having the maximum size is used, since the temperature difference between the non-sheet passing area and the sheet passing area of the pressure roller 26 does not occur, the heat radiation sheet 28 is stopped. The heat radiation sheet 28 is used only when a small-size transfer material P is used.
, The heat is not taken away more than necessary from the pressure roller 26.

Third Embodiment Next, a third embodiment of the present invention will be described with reference to FIG.

FIG. 3 is a cross-sectional view of a heat roller type fixing device according to the third embodiment. In this drawing, the same elements as those shown in FIG. 1 are denoted by the same reference numerals. Description is omitted.

In the present embodiment, the support roller 11 can be moved so that the contact area between the heat radiating sheet 10 and the pressure roller 5 is variable with respect to the fixing device according to the first embodiment. The contact area is changed according to the size of P. For example, when the transfer material P having the maximum size is used, no temperature difference occurs between the non-sheet passing area and the sheet passing area of the pressure roller 26. And the contact area between the pressure roller 5 and the pressure roller 5 is reduced. When a small-sized transfer material P is used, the contact area between the heat radiating sheet 10 and the pressure roller 5 is increased by disposing the support roller 11 at the position B in the drawing. With this configuration, the pressure roller 26
Will not take away the heat from it more than necessary.

[0055]

As is apparent from the above description, according to the present invention, a sheet member made of a driven or slidable good heat conductor opposed to a fixing roller or a pressure roller of a fixing device is provided. The temperature difference between the paper passing area and the non-paper passing area can be kept small even when small-sized transfer materials are continuously used, and a compact fixing device that does not need to reduce the number of output sheets can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional view of a heat roller type fixing device according to Embodiment 1 of the present invention.

FIG. 2 is a sectional view of a fixing film type fixing device according to a second embodiment of the present invention.

FIG. 3 is a sectional view of a heat roller type fixing device according to a third embodiment of the present invention.

FIG. 4 is a sectional view of a conventional heat roller type fixing device.

FIG. 5 is a sectional view of a conventional fixing film type fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller 4 Heater (heating means) 5 Pressure roller 9 Thermistor (temperature detecting means) 10 Heat dissipation sheet (sheet member) 21 Heater (heating means) 23 Fixing film (film member) 26 Pressure roller 27 Thermistor (temperature detecting means) ) 28 heat dissipation sheet (sheet member) 29 take-up roller P transfer material T unfixed toner image

Claims (6)

[Claims] A fixing roller and a pressure roller disposed so as to be rotatable by being pressed against each other; a heating means disposed inside the fixing roller; and a contact type detecting a surface temperature of the fixing roller. Temperature fixing means, and power control means for controlling electric power supplied to the heating means in accordance with the temperature detected by the temperature detecting means, wherein the fixing roller and the pressure roller carry an unfixed toner image. In a fixing device for fixing a toner image by heating and conveying a transfer material under a narrow pressure, a sheet member made of a driven or slidable good heat conductor opposed to the fixing roller or the pressure roller is provided. Fixing device. 2. A heating means, a film member disposed endlessly or endlessly movable while being in sliding contact with the heating means, and a pressurizing means disposed so as to press against the heating means via the film member. A roller, a temperature detecting unit for detecting a temperature of the heating unit, and a power control unit for controlling electric power supplied to the heating unit, and an unfixed toner image is carried by the film member and the pressure roller. A fixing device for fixing a toner image by heating and transferring a transfer material under a narrow pressure, wherein a sheet member made of a driven or slidable good heat conductor facing the pressure roller is provided. apparatus. 3. The fixing device according to claim 1, wherein the sheet member is an endless belt-shaped member, and an outer peripheral surface of the sheet member is rotated by following or sliding with the fixing roller or the pressing roller. apparatus. 4. The sheet member is an endless belt-shaped member, and has a winding roller for winding and holding the belt member, and the sheet member moves following or sliding with the fixing roller or the pressure roller. The fixing device according to claim 1, wherein: 5. The fixing device according to claim 1, wherein a contact area between the sheet member and the fixing roller or the pressure roller is variable. 6. The fixing device according to claim 1, wherein the sheet member has a layer made of metal.