JPH1048981A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device having a nonpassing part temperature rise reforming means which can reform the nonpassing part temperature rise generated by passing numerous sheets of small size recorders, generates no hot setoff, no deterioration of heating roller, and the like, can obtain a high quality of recording image, gives hardly an influence to the temperature rising time, has no operating part to reform the nonpassing part temperature rise, and of a low cost. SOLUTION: In a fixing device which has a heating roller 2 and a pressurizing roller 4 abutted to the heating roller 2, and heats and fixes a toner image T on a recorder P by passing the recorder P between both rollers 2 and 4, a pressurizing roller cooling means 9 to cool a nonpassing part of the pressurizing roller 4 where a small size of recorder does not pass is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to an electrophotographic copying machine,
The present invention relates to a toner image fixing device used in an image forming apparatus such as a printer and a facsimile.

2. Description of the Related Art As a method of fixing a toner image formed on a recording medium such as paper or a film, a heat fixing method is generally used in which a toner is melted by heat and fixed. Among the heat fixing systems, the heat roller system is most widely used because of its high thermal efficiency and safety. In this method, for example, two rollers are pressed against each other, at least one of the rollers is heated, and the unfixed toner is heated at a nip portion, which is a pressed portion of the fixing roller pair, to fix the toner on a recording medium. When heating one of the two rollers, the roller to be heated is called a heating roller, and the other roller is called a pressure roller. Inside the heating roller, a heat source of the halogen lamp is provided in the axial direction of the heating roller. As another heat source, a heat source using a ceramic heater or the like is known. A temperature sensor is attached to the outer surface of the heating roller, and power supply to the heat source is controlled so that the temperature of the nip is maintained at a temperature suitable for fixing. Conventionally, in such a heat fixing device, it has been difficult to make the temperature distribution in the axial direction of the fixing roller pair uniform when the size of the recording medium to be fixed is different in size. That is, in a region through which a small-sized recording medium passes (hereinafter, referred to as a “passing portion”), heat is consumed for heating the recording body and unfixed toner on the recording medium, but an area through which the small-size recording medium does not pass ( Since the heat is not taken away by the recording medium in the non-passing portion, the heat of the heating roller accumulates, and the temperature of the non-passing portion is higher than the temperature of the nip portion of the passing portion which is maintained at a predetermined temperature. That is, a so-called non-passing portion temperature rise occurs. Therefore, when a large-size recording medium is passed after a small-size recording medium is continuously passed, for example, when an A4-size sheet is passed after a B5-size sheet is continuously passed, fixing to a large-size recording medium is performed. There have been problems such as unevenness and wrinkles, and the so-called hot offset that toner in a portion corresponding to the non-passing portion of the unfixed toner image is excessively melted and adheres to the heating roller to stain the surface of the recording medium. Also, if the temperature of the non-passing portion B is too high, a large temperature difference occurs between the non-passing portion and the passing portion in the heating roller, and a difference in thermal expansion between the high temperature portion and the low temperature portion causes distortion in the heating roller, There is also a problem of deterioration. In particular, among the heating rollers, the surface heating roller, in which a heating resistor is formed on the surface of a glass or ceramic pipe, directly heats the surface of the fixing roller, so that the heat efficiency is good, and the heat capacity of the heating roller can be reduced. This is a fixing method that is excellent in that the heating time can be shortened and the power supply to the heating roller can be turned off when it is not used, which is energy saving. Due to the difference in thermal expansion due to the temperature rise, the diameters of the heating roller and the pressure roller differ from each other between the passing portion and the non-passing portion, and the heating roller may be damaged. By making the temperature distribution in the axial direction of the fixing roller pair uniform,
Means for solving these problems and disadvantages are described in JP-A-4-51799, JP-A-6-11983, JP-A-5-281877, and JP-A-6-250540.
JP, JP-A-3-139682, JP-A-5-1
No. 81382, but each has its own problems and disadvantages.

The above publications, their defects, and problems will be outlined below. A cooling means for selectively cooling the non-passing portion of the fixing device is provided, and the temperature distribution of the fixing device is made uniform by the cooling means. Specifically, the fan and the duct selectively send air to the non-passing portion only during paper passing to prevent an increase in temperature in the non-passing portion. However, since the air is blown to the heating roller on the side where the toner image is formed, there is a possibility that the toner is blown off by the blow and the image quality is often deteriorated. Since the heating roller is directly cooled, even if only the end portion is to be cooled, the temperature tends to be lowered to the temperature at the central portion where fixing is performed. Therefore, there is also a problem that the heated heat is not used effectively, the thermal efficiency is reduced, and the power consumption is increased. The heat radiating member is brought into contact with the end of the heating roller according to the size of the paper to prevent the temperature of the non-passing portion from rising due to heat radiation. Specifically, a roller-shaped heat dissipating member is arranged in a non-passing portion when small-size paper is passed, and when the temperature of the non-passing portion rises, the heat dissipating member abuts on the heating roller to increase the heat generated. By dissipating the heat, the temperature distribution in the axial direction of the heating roller is made uniform. However, a movable portion is required for pressing and detaching the heat radiating member to and from the heating roller, and there is a problem that a failure or breakage is liable to occur over a long period of use.
In addition, since the heat roller is in direct contact with the surface, the surface is easily scratched. In particular, when a material that is easily broken, such as glass or ceramics, is used as the heating roller in this configuration, there is a problem that the heating roller itself is damaged by an impact at the time of long-term contact. JP, 5-281877, A Two or more heating elements are provided inside a heating roller, and these heating elements are controlled according to paper width. Specifically, two heating elements having different heating distributions in the axial direction of the heating roller are provided inside the heating roller, and the heating elements are appropriately selected and driven according to the surface temperature of the fixing unit and the width of the recording material. This prevents the non-passing portion temperature from rising. However, when two or more heating elements are provided inside the heating roller, there is a problem that it is difficult to reduce the diameter of the heating roller. Especially,
When a variety of paper sizes are used, for example, when fixing an A4, B4, or B5 size recording paper or a toner image on a postcard using an A3 machine, the temperature of the non-passing portion of any recording paper increases. In order to solve the problem and accurately equalize the surface temperature of the heating roller, it is necessary to use a heating element with a different heat generation distribution.If the heating element is provided inside the heating roller, it must be arranged unless the diameter of the heating roller is increased. Since it is not possible, there is a problem that the apparatus becomes large, its structure becomes complicated, and the cost increases. JP, 6-250540, A A heat transfer member provided in contact with a heating roller via a film on an endless belt via a film on an endless belt, or a heat transfer member provided in a non-contact manner. Providing means,
The heat stored in the pressure roller is made uniform, thereby eliminating temperature unevenness and eliminating the temperature difference between the passing portion and the non-passing portion.
Generally, the pressure roller is warmer in the warm state than in the cold state, and the melted toner is easy to penetrate the recording paper,
Improves fixability. However, if the heat conduction member is simply brought into contact, not only the non-passing portion but also the passing portion is deprived of heat, and the fixing property is reduced. Further, when the temperature of the heating roller is raised, the heated heat is also transmitted to the pressure roller. Therefore, if the heat transfer member of the pressure roller is simply provided, there is a problem that heat is radiated from the pressure roller to the heat transfer member, and the temperature rise of the heating roller is delayed. SUMMARY OF THE INVENTION An air cooling means for generating an air flow is provided outside a cover which covers the periphery of a heating roller, and the air blowing to the heating roller is made variable. Generally, a recording paper on which an unfixed toner image is formed is conveyed such that the heating roller side is the toner image surface, and is configured to be fixed by heat of the heating roller whose surface temperature is controlled to be constant. . In the technique described in this publication, since air is blown toward the heat roller (heat roller), an unfixed image is blown off by the air flow, resulting in a problem that the image quality is deteriorated. SUMMARY OF THE INVENTION The amount of air blown to the heating roller is made variable by a blowing means and a heat radiating window. However, even though the amount of air can be changed, since air is being sent to the heating roller, it is undeniable that the image is disturbed. The present invention has been made in view of these problems and problems of the related art, and improves a non-passing portion temperature rise caused by passing a large number of small-sized recording media, and generates a hot offset and a heating roller. Provided is a fixing device that does not cause deterioration of the fixing device. Provided is a fixing device in which a heating roller having a heating resistor provided on a surface of glass, ceramics or the like does not cause damage to the heating roller due to a rise in non-passing portion temperature. Due to the rise in the temperature of the non-passing portion, a difference occurs in the diameter of the passing portion and the non-passing portion of the heating roller, and when a recording material having a normal size or a maximum paper passing width that is not a small size passes through the nip portion, Provided is a fixing device capable of obtaining a high-quality recorded image, in which a difference in paper conveyance speed between a passing portion and a non-passing portion is prevented from causing a wrinkle on a recording medium and resulting in a poor image. A low-cost fixing device that has a non-passing portion temperature rise improvement unit that does not easily affect the temperature rise time, does not have an operating unit for improving the non-passing portion temperature rise, and does not require a special device. I will provide a.

According to the first aspect of the present invention,
A fixing device that has a heating roller and a pressure roller that is in pressure contact with the heating roller, and heat-fixes a toner image on the recording material by passing a recording material between the two rollers; And a pressure roller cooling means for cooling a non-passing portion through which the small-sized recording medium does not pass. The invention according to claim 2 includes a heating roller,
A pressure roller that is in pressure contact with the heating roller; and a fixing device that heats and fixes the toner image on the recording material by passing the recording material between the two rollers. Pressure roller cooling means for cooling the
Control means for controlling the operation timing of the pressure roller cooling means. According to a third aspect of the present invention, in the fixing device according to the second aspect, the control unit includes a recording body detection unit that detects a size of the recording body. The invention according to claim 4 is the invention according to claim 2.
In the fixing device described above, the control unit includes a temperature detection unit that detects a temperature of the non-passing portion. According to a fifth aspect of the present invention, in the fixing device according to the first or second or third or fourth aspect, the pressure roller cooling unit increases an amount of air blown to the non-passing portion than an amount of air blown to another portion. It is a blower. According to a sixth aspect of the present invention, in the fixing device according to the first or second or third or fourth aspect, the pressure roller cooling means is opposed to the pressure roller and is close to the pressure roller at the non-passing portion. It is a heat absorbing means. According to a seventh aspect of the present invention, in the fixing device according to the first or second or third or fourth aspect, the pressure roller cooling unit faces the blower and the pressure roller at the non-passing portion facing the pressure roller. And heat absorbing means close to the roller. According to an eighth aspect of the present invention, in the fixing device according to the sixth or seventh aspect, the heat absorbing means is configured such that a portion facing the non-passing portion is set to be thicker than other portions. Features. According to a ninth aspect of the present invention, in the fixing device according to the first or second or third or fourth or fifth or sixth or seventh or eighth aspect, the heating roller has a heat source in a surface layer or an inner layer near the surface. Features.

According to the present invention, since the cooling means for cooling the pressure roller is provided, it is possible to prevent the temperature of the non-passing portion of the pressure roller from rising greatly, and to prevent the heating roller from contacting the pressure roller. Reduce the temperature rise in the passage section. By cooling around the non-passing portion of the pressure roller, the temperature of the central portion of the pressure roller does not decrease, and the temperature of the central portion of the heating roller does not greatly decrease during paper passing. By changing the distance between the pressure roller and the cover as a heat absorbing means that covers the pressure roller between the passing portion and the non-passing portion of the pressure roller, the heat release amount of the pressure roller from the pressure roller changes, and the heating roller The rise in the temperature of the non-passing portion of the pressure roller caused by the rise in the temperature of the non-passing portion is suppressed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1 and 2, in a first embodiment of the present invention, a heating roller 2 having a heat source 1 therein, and a heating roller 2 and a pressure roller 4 are pressed against the heating roller 2. And a pressure roller 4 forming a nip portion 3 which is a contact portion between the nip portion 3 and a transfer paper P as a recording material on which the toner image T is transferred.
Guide member 5 for guiding the rollers 2 and 4
And a cover 6 having an inlet for taking in air for cooling the pressure roller and an outlet for discharging the taken-in air, and for keeping the surface temperature of the heating roller 2 at a set temperature. A first sensor 7 provided in contact with the heating roller 2 for detecting the temperature of the surface of the heating roller 2, a second sensor 8 provided as a temperature detecting means provided in contact with the pressure roller 4, An air blower 9 is provided at the inlet and serves as a pressure roller cooling means for cooling the pressure roller 4. The two rollers 2 and 4 forming the fixing roller pair have a passing portion A, which is an area through which a recording medium (hereinafter, referred to as a small size paper) having a relatively small size with respect to the length of the fixing roller pair passes. , A non-passing portion B which is a region that does not pass through.
When the transfer paper P passes through the nip portion 3 on the basis of the center (FIG. 2A), the non-passing portion B
Passes through the nip 3 on the basis of the end (FIG. 2B)
Is located at the end opposite to the reference end.
The first sensor 7 is in contact with the upper portion of the passing portion A of the heating roller 2, and the second sensor 8 as a temperature detecting means for detecting the temperature of the non-passing portion B is provided at the non-passing portion B of the pressure roller 4. Each is provided so as to be in contact with the lower part, and detects the temperature of the part in contact with them. The number of the first sensors 7 is not limited to one, and a plurality of the first sensors 7 may be provided in order to reliably detect the temperature of the passage portion A made of transfer paper of various sizes. Similarly, the number of the second sensors 8 is not limited to one, and a plurality of the second sensors 8 may be provided in order to reliably detect the temperature of the non-passing portion B formed by transfer papers of various sizes. The heat source 1 is composed of a halogen lamp, and is disposed in the axial direction of the heating roller 2 so as to have a length substantially equal to the entire length of the heating roller 2. Heat to The pressure roller 4 is configured to be able to freely contact and separate from the heating roller 2 by a pressing mechanism (not shown). In the present embodiment, the heating roller 2 employs Al as a base material, but may use a metal such as SUS as a base material. A release layer is provided on the surface of the substrate for the purpose of preventing the toner from adhering thereto. As the material of the release layer, Teflon is used, but a PFA tube or the like can also be used. As a method for forming the release layer, there are a method of directly coating a heating roller, a method of heating a tube-shaped material at a high temperature, and shrinking and adhering to the heating roller. As for the thickness of the heating roller, the thinner the heat capacity, the smaller the heat capacity and the faster the temperature rise time, which is preferable. Since an inconvenience such as variation in properties occurs, it is necessary to select an optimal thickness. In the present embodiment, the pressure roller 4 employs SUS as a core rod, but other metals such as iron, Al, and brass may be used as the core rod. An elastic layer of silicon rubber is formed on the core rod. As the elastic layer, a relatively soft material such as foamed silicone rubber may be used in order to reduce a pressing force for securing a nip width necessary for fixing. On the surface of the elastic layer, a release layer for imparting releasability, or silicon rubber, which is an insulating material, is charged by friction or the like, and an unfixed toner image is formed due to the electrostatic force or generation of electric discharge. As a conductive layer for preventing disorder, a Teflon layer containing a conductive material such as carbon may be provided. The pressing force of the pressing roller 4 against the heating roller 2 may be a pressing force that can secure a necessary nip width.
C, laser printer, PPF, usually 1kgf ~
It is about 20 kgf. An air passage for cooling the pressure roller 4 is formed between the pressure roller 4 and the bottom of the cover 6. An air blower 9 as a cooling means for sending air to the air passage has a plurality of blades rotating about an axis provided in parallel with the pressure roller 4 and having a length substantially equal to the length of the pressure roller 4 in the axial direction. Consists of fans. The blowing device 9 varies the blowing amount in the axial direction of the pressure roller 4 so that the air flow rate to the non-passing portion B, which becomes high when small-size paper is continuously passed, becomes larger than that of the passing portion A. Therefore, the size of the blade changes in the axial direction. As a configuration for changing the air flow rate in the axial direction, in addition to the above, an air flow control plate for shielding or changing the direction of the air flow was provided, and the size of the air inlet and the outlet was changed. A configuration, a configuration in which a plurality of blowers are provided in the axial direction, and the like are given.
In a configuration in which a plurality of blowers are provided, only the non-passing portion B can be selectively cooled. The operation timing of the blower 9 is determined by a control unit having a recording body detection unit for detecting the number and size of the transfer paper P to be sent to the fixing device and a second sensor 8. The recording body detecting means detects a command from an operator or the size of the transfer sheet when transferring the toner image onto the transfer sheet, and a control unit (not shown) for selecting the same also serves as the transfer unit. To detect the size of the paper, a sensor or the like may be provided in the fixing device. The control means may include one of the recording body detection means and the second sensor 8. With such a configuration, it is possible to reduce a decrease in the temperature of the pressure roller in the passing portion and effectively reduce an increase in the temperature in the non-passing portion. It is preferable to generate an air flow in the transfer paper transport direction of the pressure roller 4 from the viewpoint that the passage portion A of the pressure roller 4 can be selectively cooled. You can also shed. In this embodiment, the blower 9 is used as the cooling means.
A Peltier element or the like may be used as long as the pressure roller 4 is actively cooled. From the viewpoint of cost, cooling by a blower is preferable. The blower 9 may be provided not only on the air intake side but also on the discharge side. In cooling by blowing air, the size and shape of the air intake and exhaust ports are appropriately set, and the smooth flow of air can reduce the generation of abnormal noise due to the air flow. In an image forming apparatus used for a PPC, a laser printer, a PPF, or the like, a toner image T is formed on the surface of the transfer paper P by a known electrophotographic process of charging, exposure, development, and transfer. The transfer paper P on which the toner image T is formed is conveyed in the direction of arrow C in FIG. 1 and is guided by the guide member 5 to the fixing portion, that is, the nip portion 3, where the heat of the heating roller 2 causes the toner image T to be transferred.
Is heat-fixed. Thereafter, the transfer paper P on which the toner image T has been heated and fixed is discharged from the fixing device. In the fixing process,
The heat energy of the heating roller 2 is deprived by the transfer paper P,
As a result, the temperature of the heating roller 2 decreases, so that the first sensor 7 detects this, the heat source 1 is driven, and the temperature of the heating roller 2 is heated to the set temperature. When small-size paper is continuously printed, the heat energy of the heating roller 2 is taken only in the passing portion B. Since the temperature detection of the heating roller 2 is performed in the passage portion A of the heating roller, when the temperature decreases, the heat source 1 is driven to increase the temperature of the heating roller 2 to a set temperature. Since the non-passing portion B is similarly heated, the temperature of the non-passing portion B rises above the set temperature by heating even though the temperature does not decrease in the non-passing portion B. At this time, from the experiment of the present inventors, it was found that the temperature of the non-passing portion B becomes higher than that of the passing portion A even in the pressure roller 4. Since the heat capacity of the heating roller 2 is small, the temperature rise in the non-passing portion can be relatively quickly eliminated after a while, but the heat capacity of the pressure roller 4 is large, and the heat conductivity of silicon rubber as a material of the elastic layer is large. Is low, the pressure roller 4
The temperature of the non-passing portion B on the side does not readily decrease. Therefore,
Thereafter, when the heating roller 2 is rotated again, the heating roller 2
The non-passing portion B contacts the high-temperature pressure roller 4 and immediately becomes hot again. In the present embodiment, the blower 9 is driven by driving the blower 9 at the time when it is determined that the small size paper is continuously passed and when the temperature of the non-passing portion B is detected to be equal to or higher than the predetermined temperature. At least the non-passing portion B of the pressure roller 4 is cooled. Therefore, the phenomenon that the non-passing portion B of the pressure roller 4 becomes much hotter than the passing portion A is eliminated, and the temperature rise of the non-passing portion of the heating roller 2 in contact with the pressure roller 4 is suppressed. Experimental Example 1 With the configuration of this example, a fixing device for A3 recording paper as shown below was prepared, and the temperature rise of the non-passing portion B when continuous transfer paper of B5 width was continuously measured. As Comparative Example 1, measurement was also made without the blower 9. Heat roller size: width 335 mm, diameter 30 mm, heat 0.6 mm Heat roller material: aluminum Heat source: halogen lamp Heat source supply power: 1000 W Pressure roller: diameter 30 mm, core material = iron, elastic layer = silicone rubber Cooling means: Suction by a fan Recording paper: Ricoh type 6200 paper Recording paper feed speed: 90 mm / s Heating roller set temperature: 180 ° C. The non-passing portion temperature rise in the present embodiment on the heating roller 2 side and the blower of Comparative Example 1 are not provided. And the temperature rise in the non-passing part in the case. In FIG. 3, a indicates the temperature of the passage section A measured by the first sensor 7. b and c are the second
5 shows a temperature rise characteristic of the non-passing portion B of the pressure roller 4 measured by the sensor 8 of FIG.
c is a characteristic when no air blower is provided. As shown in FIG. 3, according to the present embodiment, the rise in the temperature of the non-passing portion when small-size paper is continuously passed is reduced, and the difference from the temperature of the passing portion A is reduced. Immediately after 50 sheets of B5 size paper were continuously passed using the fixing device of the present embodiment, A4 size paper on which a toner image was formed was passed and the fixed image was evaluated. In the case of the example, a good fixed image was obtained, whereas in Comparative Example 1, an offset occurred in the non-passing portion B, and the occurrence of wrinkles on the transfer paper P was confirmed, resulting in a poor image. Was. In addition, when the heating time from the room temperature to the set temperature of the heating roller was compared, the temperature could be increased in the same time as Comparative Example 1 by operating the blower 9 only during continuous paper feeding. Further, the air flow rate is small in the passage portion A and increased in the non-passage portion B, that is, the cooling capacity is large in the non-passage portion B and small in the passage portion A, or only the non-passage portion B is selectively cooled. As a result, the temperature of the passage A is not greatly reduced, so that the temperature is detected by the first sensor 7 and the temperature of the passage A, which controls the temperature, is the same as that when the blower 9 is not used. , And there is no effect on power consumption during continuous paper passing. FIG. 4 shows three examples of the heating roller 10 in which the heating roller itself has a heat storage layer. FIG.
In the heating roller 10 shown in FIG. 1A, a heating resistor 10b is formed on the surface of a base material 10a, on which a releasability from a toner is improved, and heat is generated by contact between another member and the heating element. In order to prevent the body from being damaged and to electrically insulate the heating resistor, a heat-resistant resin layer 10c made of Teflon is formed. The heating roller 10 shown in FIG. The heating resistor 10b is formed on the inner surface of the base material 10a, and the above-described heat-resistant resin layer 10c is formed on the surface of the base material 10a. The heating roller 10 shown in FIG. 4C has a configuration in which a heat-resistant resin layer 10c is formed on the surface of a roller 10d made of a material that generates heat. The roller 21d is formed of conductive fibers, but may be formed of carbon-dispersed ceramics, so-called self-heating ceramics. As a material of the base material 10a, glass is used, but is not limited thereto.
Ceramics or metals such as Al and SUS may be used. However, when metal is used, it is necessary to provide an insulating layer made of a resin material such as SiO ₂ or polyimide on the surface layer for electrical insulation from the heating resistor. As the heating roller 10, although not shown, there is another heating roller in which the base material 10 a itself is a heating element. Examples of the heating element include a material in which a conductive material is dispersed in ceramics, a material in which conductive fibers are formed in a cylindrical shape, and the like. These heating rollers 10 have a heat source and a heating roller 10 integrated with each other as compared with the heating roller 2 using a halogen lamp or the like. Since the vicinity of the surface 10 is directly heated, the heating efficiency is good and the power consumption can be reduced. By thinning the base material 10a, the heat capacity becomes small and the heating time becomes short.
This is a very excellent fixing method in that a so-called wait time until printing by C, laser printer, PPF or the like is shortened. When glass is used for the base material 10a,
Another advantage is that the cost of the glass itself is low. During standby, the power supply to the heating roller 10 can be stopped or slightly supplied to maintain a low temperature. The waiting time of the user at the time of reprinting is desirably to shorten the heating rise time to the fixing temperature within 30 seconds, preferably within 15 seconds. Therefore, when the heat of the heating roller is made of Al, SUS, or glass as a base material, 1 mm
Hereinafter, in the case of ceramics, it is necessary to reduce the thickness to just the processing limit (usually 1 to 2 mm). However, on the other hand, in the case of a heating roller having a small heat capacity, when used in a high-speed machine, the thickness of the heating roller is thin, so that heat transfer in the horizontal direction is unlikely to occur, and a non-passing portion temperature rise is likely to occur. There is also a problem that. Above all, when glass or ceramics is used as the base material, there is a problem that the temperature rise in the non-passing portion tends to be further increased due to poor thermal conductivity. In the case where a heating roller having a heat source on or near the surface is used as the heating roller 10, the above-described problem can be solved particularly effectively. Experimental Example 2 A fixing device for A3 as shown below was formed with the configuration using the heating roller 10, and the temperature rise of the non-passing portion when the transfer paper P of A4 width was continuously passed through the fixing device was measured. As Comparative Example 2, measurement was performed using the heating roller 10 and without the blower 9. Heating roller configuration: Fig. 4 (a) Heat source supply power: 700W Heating roller size: width 335mm, diameter 30mm, thickness 0.6mm, heating section length 305mm Heating roller material: glass Pressure roller: diameter 30mm, core Material = iron, elastic layer = silicone rubber Cooling means: suction with a fan Recording paper: Ricoh type 6200 paper Recording paper feed speed: 90 mm / s Heating roller set temperature: 180 ° C. Non-passing portion in the present embodiment on the side of the heating roller 10 The temperature rise is compared with the temperature rise in the non-passage portion of the comparative example 2 without the blower. In FIG. 5, a indicates the temperature of the passage section A measured by the first sensor 7. b and c are the second
5 shows a temperature rise characteristic of the non-passing portion B of the pressure roller 4 measured by the sensor 8 of FIG.
c is a characteristic when no air blower is provided. As shown in FIG. 5, the temperature rise in the non-passing portion when small-size paper is continuously passed according to the present invention is reduced, the difference between the temperature of the passing portion A is significantly reduced, and the temperature is greatly improved. I understand. Immediately after 50 sheets of B5 size paper were continuously passed using the fixing device of the present embodiment, A4 size paper on which a toner image was formed was passed and the fixed image was evaluated. In the case of the example, a good fixed image was obtained, whereas in Comparative Example 2, an offset occurred in the non-passing portion, and the occurrence of wrinkles on the recording paper was confirmed, resulting in a poor image. Comparing the temperature rise time from room temperature to the heating roller set temperature, the temperature could be raised in the same time as Comparative Example 2 by operating the blower 9 only during continuous paper passing. In addition, the amount of air flow is small in the passing portion A and large in the non-passing portion B, that is, the cooling capacity is large in the non-passing portion B and small in the passing portion A, or only the non-passing portion B is selectively used. By cooling, the temperature of the passage portion A does not drop significantly, so that the first sensor 7
The temperature of the passage A, which performs temperature detection and controls the temperature, is the same as when the blower 9 is not used,
There is no effect on power consumption during continuous paper feeding. FIG. 6 (a),
(B) shows a second embodiment of the present invention. In this embodiment, the cover 11 also serves as a heat absorbing means. The pressure roller cooling means does not have the air inlet and outlet of the cover 6 and the air blower in the first embodiment, and
The first embodiment differs from the first embodiment in that the heat absorbing means is opposed to the pressure roller 4 in the non-passing portion B and is adjacent to the pressure roller 4, that is, the cover 11 also serves as a heat absorbing means as a cooling means. FIGS. 6A and 6B show a case where the sheet feeding device is based on the center and a case where the sheet feeding device is based on the end. The heating roller shown in FIG. 4A is employed. The other configuration is the same as that of the first embodiment, and therefore, the description is omitted by attaching the reference numerals. The distance between the pressure roller 4 and the cover 11 is different at portions corresponding to the passing portion A and the non-passing portion B of the pressure roller 4. In the non-passing portion B, the distance is close, and in the passing portion A, the distance is larger. In the non-passing portion B, the heat of the pressure roller 4 is easily radiated to the cover 11, and in the passing portion A, the heat is hardly radiated. In general, fixing in a warm state is better than fixing in a cold state in terms of fixing performance and power consumption during fixing of a heating roller. This is because the recording paper is heated not only by the heating roller but also by the pressure roller because the pressure roller is warmed, and the recording paper itself is easily heated. To improve the fixability, reduce the decrease in the temperature of the heating roller, and reduce the electric power for reheating. In the present embodiment, the temperature drop of the pressure roller 4 in the passing portion A is reduced, the fixing property of the toner image is secured, and the power consumption of the heating roller 10 is reduced. Since excess heat is taken away and the temperature rise in the non-passing portion of the pressure roller 4 is reduced, the temperature rise in the non-passing portion of the heating roller 10 in contact therewith can be reduced. The distance between the pressure roller 4 and the cover 11 in the passing portion A and the non-passing portion B is set to 10 mm and 5 mm, respectively.
It can be set to a value of not less than 1 mm and less than 10 mm. If the non-passing portion B is too close, the pressing roller 4
And the pressure roller 4 may be damaged. In order to make the temperature inside the cover 11 uniform, a high heat conductive layer such as an Al film may be provided on the inner surface of the cover 11. This can prevent the cover at the position corresponding to the non-passing portion B from becoming hot and reducing the heat absorbing effect, and can prevent the temperature from being abnormally high and the user's safety from being impaired. If the temperature of the pressure roller 4 is particularly high, the distance may be changed in accordance with a delicate tendency of the temperature of the pressure roller 4, such that the pressure roller 4 is closer to the temperature, and is relatively far away at a slightly lower temperature. Conceivable. EXPERIMENTAL EXAMPLE 3 A fixing device for A3 as shown below was formed with the configuration of the present embodiment using the cover 11, and the temperature rise of the non-passing portion B when the recording paper of A4 width was continuously passed was measured. . As Comparative Example 3, measurement was also performed when the distance was constant at 12 mm, that is, when there was no heat absorbing means. Heating roller configuration: FIG. 4 (a) Heat source supply power: 700 W Heating roller size: 335 mm in width, 30 mm in diameter, 0.6 mm in thickness, 305 mm in length of heating section Heating roller material: glass Pressure roller: 30 mm in diameter, core Material = iron, elastic layer = silicon rubber Distance between pressure roller and cover: center = 12 mm, end (between both ends of pressure roller and 30 mm each) = 2 mm Recording paper: Ricoh type 6200 paper Recording paper feed Speed: 90 mm / s Heating roller set temperature: 180 ° C. The non-passing portion temperature rise in the present embodiment on the heating roller 10 side and the distance between the pressure roller 4 and the cover 6 in Comparative Example 3 were 12
The temperature rise in the non-passage portion when the temperature is kept constant in mm is compared.
In FIG. 7, a is a passing portion A measured by the first sensor 7.
Shows the temperature. b and c show the temperature rise characteristics of the non-passing portion B of the pressure roller 4 measured by the second sensor 8, and b
Is the characteristic when the cover as the heat absorbing means is provided, and c is the characteristic when the cover is not provided as the heat absorbing means. As shown in FIG. 7, according to the present embodiment, the rise in the temperature of the non-passing portion when the small-size paper is continuously passed is reduced, the difference between the temperature of the passing portion A is significantly reduced, and the temperature is greatly improved. You can see that there is. In addition, when compared with the case where the distance between the pressure roller 4 and the cover 6 is fixed at 2 mm, the same effect can be obtained with respect to the rise in the temperature at the non-passing portion. But it turned out to be fast. The power consumption during continuous feeding of small-size paper was also smaller in this embodiment. Immediately after 50 sheets of A4 size paper were continuously passed using the fixing device of the present embodiment, A3 size paper on which a toner image was formed was passed, and the fixed image was evaluated. In the case of the example, while a good fixed image was obtained, in Comparative Example 3, an offset occurred in the non-passing portion B, and the occurrence of wrinkles on the recording paper was confirmed.
Poor image. The cover 12 as the heat absorbing means shown in FIGS. 8A and 8B has a different thickness in the axial direction of the pressure roller. FIGS. 8A and 8B show a case where the sheet feeding position is based on the center and a case where the sheet feeding position is based on the end. By increasing the thickness of the portion facing the non-passing portion B of the cover 12 and reducing the thickness of the other portions, the heat capacity of the cover 12 at each portion facing the passing portion A and the non-passing portion B is reduced. Are different. This is suitable in that the non-passing portion B needs a larger amount of heat in order to keep the temperature in the axial direction of the pressure roller 4 constant. By using the cover 12, the pressure roller 4
When the heat of the cover 12 is radiated to the cover more than the passing portion A, the heat capacity of the non-passing portion B is large, so that the portion of the cover 12 facing the non-passing portion B is hard to warm, and the cover 12 and the pressure roller 4 Can be maintained for a long time, so that the heat radiation effect of the non-passing portion B of the pressure roller 4 can be maintained for a long time, thereby increasing the temperature rise of the non-passing portion of the heating roller 2 for a long time. Can be kept. Therefore, even when a large number of small-size sheets are printed, the non-passing portion B
The temperature of the pressure roller 4 is reduced, and the fixing property is secured.
In order to reduce the power consumption of the heating roller 2, the non-passing portion B takes away excess heat generated by the rise in the temperature of the non-passing portion, and reduces the rise in the temperature of the non-passing portion of the pressure roller 4, so that the heating in contact therewith The temperature rise in the non-passing portion of the roller 2 can be reduced. The thickness of the portion of the cover 12 facing the non-passing portion B is set to 10 mm. As for this thickness, it is more difficult to warm as thick as possible,
If the thickness is too large, the entire fixing device becomes large, so that the fixing device is formed in a range of 7 to 20 mm. Experimental Example 4 A fixing device for A3 as shown below was formed with the configuration using the cover 12, and the temperature rise of the non-passing portion when recording paper of A4 width was continuously passed through the fixing device was measured. Heating roller configuration: FIG. 4 (a) Heat source supply power: 700 W Heating roller size: 335 mm in width, 30 mm in diameter, 0.6 mm in thickness, 305 mm in length of heating section Heating roller material: glass Pressure roller: 30 mm in diameter, core Material = iron, elastic layer = silicon rubber Distance between pressure roller and cover: center = 12 mm, end (between both ends of pressure roller and 30 mm each) = 2 mm Recording paper: Ricoh type 6200 paper Recording paper feed Speed: 90 mm / s Heating roller set temperature: 180 ° C With this configuration, even if 100 sheets of A4 size paper are continuously passed, the temperature rise in the non-passing portion of the heating roller 2 can be maintained at 20 ° C or less. Immediately after this, as a result of passing the A3 size paper on which the toner image was formed and evaluating the fixed image, a good fixed image was obtained without offset or wrinkling of the recording paper. Was. For convenience of explanation, the pressure roller cooling means is only a blower in the first embodiment, and only a heat absorbing means in the second embodiment. It is possible to use both at the same time, and the combination of these, including the specific arrangement positions of the recording medium detecting means and the temperature detecting means, can be appropriately selected.

According to the present invention, the cooling means for cooling the pressure roller is provided, so that the temperature of the non-passing portion of the pressure roller is prevented from greatly increasing, and the heating which contacts the pressure roller is prevented. The temperature rise in the non-passing portion of the roller could be reduced. As a result, even if a large-sized recording medium is passed after the small-size paper is continuously passed, hot offset does not occur,
In addition, it was possible to obtain a high-quality recorded image without wrinkling of the recording medium. By cooling around the non-passing portion of the pressure roller, the temperature of the central portion of the pressure roller does not drop, and the temperature of the central portion of the heating roller does not drop significantly during paper passing, and the set temperature is maintained. Power consumption was reduced. Further, the cooling means can be operated only when the non-passage portion temperature rises, so that the heating time is not affected and the heating time is shortened.
By changing the distance between the pressure roller and the cover as a heat absorbing means that covers the pressure roller between the passing portion and the non-passing portion of the pressure roller, the heat release amount of the pressure roller from the pressure roller changes, and the heating roller The rise in the temperature of the non-passing portion of the pressure roller caused by the rise in the temperature of the non-passing portion is suppressed. Not only was it possible to obtain, but also the passing part was not cooled and was appropriately heated, and the temperature of the heating roller was detected near the center, which is the passing part of the heating roller. The power supply to the rollers can be reduced.
Compared to when the distance between the pressure roller and the cover is fixed,
Since the amount of heat transferred from the heating roller to the pressure roller is reduced, it is possible to achieve both the solution of the rise in the temperature at the non-passing portion and the shortening of the heating time without increasing the heating time. Since the thickness of the heat absorbing means in the portion facing the non-passing portion is increased, the ability of the pressure roller to deprive the temperature of the non-passing portion increases, and even if the number of small-size paper sheets continuously passed is increased. , The rise in the temperature of the non-passing portion can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a fixing device according to a first embodiment of the present invention in which a blower is used as a pressure roller cooling unit.

FIG. 2 is a schematic diagram showing a passing portion and a non-passing portion in the first embodiment of the present invention.

FIG. 3 is a diagram for comparing the temperature rise of each part of a heating roller between a transfer device using the first embodiment having a blower and a transfer device not having a blower according to the present invention. It is.

FIG. 4 is a cross-sectional view showing a structure of a heating roller having a configuration different from that of the heating roller shown in FIG. 1 in the first embodiment of the present invention.

FIG. 5 shows how the temperature of each part of the heating roller of the transfer device in the first embodiment of the present invention in which the heating roller is the one shown in FIG. 4 and that of the transfer device without a blower are increased. It is a figure for comparing.

FIG. 6 is a schematic diagram of a fixing device according to a second embodiment of the present invention in which a heat absorbing unit is used as a pressing roller cooling unit.

FIG. 7 is a diagram for comparing the temperature rise of each part of the heating roller between the fixing device having the pressure roller cooling unit shown in FIG. 6 and the fixing device not having the pressure roller cooling unit. It is.

FIG. 8 shows a second embodiment of the present invention in which a portion of the heat absorbing means facing the non-passing portion of the pressure roller is thicker than other portions as the pressure roller cooling means. FIG. 2 is a schematic diagram of the fixing device shown.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Heat source 2, 10 Heating roller 4 Pressure roller 8 Temperature detecting means 9 Blower 11, 12 Heat absorber A Passing part B Non-passing part P Recording material T Toner image

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[Procedure amendment]

[Submission date] July 31, 1996

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

[Title of the Invention] Fixing device

[Claims]

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electrophotographic copying machine,
The present invention relates to a toner image fixing device used in an image forming apparatus such as a printer and a facsimile.

[0002]

2. Description of the Related Art As a method of fixing a toner image formed on a recording medium such as paper or a film, a heat fixing method is generally used in which a toner is melted by heat and fixed. Among the heat fixing systems, the heat roller system is most widely used because of its high thermal efficiency and safety. In this method, for example, two rollers are pressed against each other, at least one of the rollers is heated, and the unfixed toner is heated at a nip portion, which is a pressed portion of the fixing roller pair, to fix the toner on a recording medium.

When heating one of the two rollers,
The roller to be heated is called a heating roller, and the other roller is called a pressure roller. Inside the heating roller, a heat source of the halogen lamp is provided in the axial direction of the heating roller. As another heat source, a heat source using a ceramic heater or the like is known. A temperature sensor is attached to the outer surface of the heating roller, and power supply to the heat source is controlled so that the temperature of the nip is maintained at a temperature suitable for fixing.

Conventionally, in such a heat fixing device, it has been difficult to equalize the temperature distribution in the axial direction of the fixing roller pair when the size of the recording medium to be fixed differs. That is, in a region through which a small-sized recording medium passes (hereinafter, referred to as a “passing portion”), heat is consumed to heat the recording body and unfixed toner on the recording medium, but an area through which the small-size recording medium does not pass ( Since the heat is not taken away by the recording medium at the non-passing portion, the heat of the heating roller is accumulated,
The so-called non-passing portion temperature rise occurs in which the temperature of the non-passing portion becomes higher than the temperature of the nip portion of the passing portion maintained and controlled at a predetermined temperature.

Therefore, when a large-sized recording medium is passed after a small-sized recording medium is continuously passed, for example, when an A4 size paper is passed after a B5 size paper is continuously passed, a large-sized recording medium is passed. Fixation unevenness and wrinkles occur on the body,
The toner corresponding to the non-passing portion of the unfixed toner image is excessively melted, adheres to the heating roller, and stains the surface of the recording medium. Also, if the temperature of the non-passing portion B is too high, a large temperature difference occurs between the non-passing portion and the passing portion in the heating roller, and a difference in thermal expansion between the high temperature portion and the low temperature portion causes distortion in the heating roller, There is also a problem of deterioration.

In particular, among the heating rollers, the surface heating roller in which a heating resistor is formed on the surface of a glass or ceramic pipe directly heats the surface of the fixing roller. This is a fixing method that is excellent in that it can turn off the power to the heating roller when it is not in use and saves energy.However, in the case of this surface heating roller, Due to the difference in thermal expansion due to the rise in the temperature of the non-passing portion, the diameters of the heating roller and the pressure roller in the passing portion and the non-passing portion are different from each other, and the heating roller is broken.

Means for making the temperature distribution in the axial direction of the fixing roller pair uniform to solve these problems and disadvantages include:
JP-A-4-51799, JP-A-6-11983, JP-A-5-281877, JP-A-6-250
540, JP-A-3-139682 and JP-A-5-181382, but each has its own problems and disadvantages.

[0008]

The above publications, their defects, and problems will be outlined below.

[0009] A cooling means for selectively cooling the non-passing portion of the fixing device is provided, and the temperature distribution of the fixing device is made uniform by the cooling means. Specifically, the fan and the duct selectively send air to the non-passing portion only during paper passing to prevent an increase in temperature in the non-passing portion. However, since the air is blown to the heating roller on the side where the toner image is formed, there is a possibility that the toner is blown off by the blow and the image quality is often deteriorated. Since the heating roller is directly cooled, even if only the end portion is to be cooled, the temperature tends to be lowered to the temperature at the central portion where fixing is performed. Therefore, there is also a problem that the heated heat is not used effectively, the thermal efficiency is reduced, and the power consumption is increased.

The heat radiation member is brought into contact with the end of the heating roller according to the size of the paper to prevent the temperature of the non-passing portion from rising due to heat radiation. Specifically, a roller-shaped heat dissipating member is arranged in a non-passing portion when small-size paper is passed, and when the temperature of the non-passing portion rises, the heat dissipating member abuts on the heating roller to increase the heat generated. By dissipating the heat, the temperature distribution in the axial direction of the heating roller is made uniform. However, a movable portion is required for pressing and detaching the heat radiating member to and from the heating roller, and there is a problem that a failure or breakage is liable to occur over a long period of use.
In addition, since the heat roller is in direct contact with the surface, the surface is easily scratched. In particular, when a material that is easily broken, such as glass or ceramics, is used as the heating roller in this configuration, there is a problem that the heating roller itself is damaged by an impact at the time of long-term contact.

[0011] Two or more heating elements are provided inside the heating roller, and these heating elements are controlled according to the paper width. Specifically, two heating elements having different heating distributions in the axial direction of the heating roller are provided inside the heating roller, and the heating elements are appropriately selected and driven according to the surface temperature of the fixing unit and the width of the recording material. This prevents the non-passing portion temperature from rising. However, when two or more heating elements are provided inside the heating roller, there is a problem that it is difficult to reduce the diameter of the heating roller. Especially,
When a variety of paper sizes are used, for example, when fixing an A4, B4, or B5 size recording paper or a toner image on a postcard using an A3 machine, the temperature of the non-passing portion of any recording paper increases. In order to solve the problem and accurately equalize the surface temperature of the heating roller, it is necessary to use a heating element with a different heat generation distribution.If the heating element is provided inside the heating roller, it must be arranged unless the diameter of the heating roller is increased. Since it is not possible, there is a problem that the apparatus becomes large, its structure becomes complicated, and the cost increases.

A heat transfer member provided in contact with the pressure roller or a non-contact heat transfer member is provided on a part of the pressure roller which comes into pressure contact with the heating body via the film on the endless belt. Heat transfer means,
The heat stored in the pressure roller is made uniform, thereby eliminating temperature unevenness and eliminating the temperature difference between the passing portion and the non-passing portion.
Generally, the pressure roller is warmer in the warm state than in the cold state, and the melted toner is easy to penetrate the recording paper,
Improves fixability. However, if the heat conduction member is simply brought into contact, not only the non-passing portion but also the passing portion is deprived of heat, and the fixing property is reduced. Further, when the temperature of the heating roller is raised, the heated heat is also transmitted to the pressure roller. Therefore, if the heat transfer member of the pressure roller is simply provided, there is a problem that heat is radiated from the pressure roller to the heat transfer member, and the temperature rise of the heating roller is delayed.

[0013] An air cooling means for generating an air flow is provided outside a cover for covering the periphery of the heating roller, and air blowing to the heating roller is made variable. Generally, a recording paper on which an unfixed toner image is formed is conveyed such that the heating roller side is the toner image surface, and is configured to be fixed by heat of the heating roller whose surface temperature is controlled to be constant. . In the technique described in this publication, since air is blown toward the heat roller (heat roller), an unfixed image is blown off by the air flow, resulting in a problem that the image quality is deteriorated.

[0014] Japanese Patent Application Laid-Open No. 5-181382 discloses an air blower and a heat radiating window that make it possible to change the amount of air blown to the heating roller. However, even though the amount of air can be changed, since air is being sent to the heating roller, it is undeniable that the image is disturbed.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems and problems of the prior art, and improves the temperature rise in a non-passing portion caused by passing a large number of small-sized recording media, thereby generating a hot offset. And a fixing device that does not cause deterioration of the heating roller. Provided is a fixing device in which a heating roller having a heating resistor provided on a surface of glass, ceramics or the like does not cause damage to the heating roller due to a rise in non-passing portion temperature. Due to the rise in the temperature of the non-passing portion, a difference occurs in the diameter of the passing portion and the non-passing portion of the heating roller, and when a recording material having a normal size or a maximum paper passing width that is not a small size passes through the nip portion, Provided is a fixing device capable of obtaining a high-quality recorded image, in which a difference in paper conveyance speed between a passing portion and a non-passing portion is prevented from causing a wrinkle on a recording medium and resulting in a poor image. A low-cost fixing device that has a non-passing portion temperature rise improvement unit that does not easily affect the temperature rise time, does not have an operating unit for improving the non-passing portion temperature rise, and does not require a special device. I will provide a.

[0016]

According to the first aspect of the present invention,
A fixing device that has a heating roller and a pressure roller that is in pressure contact with the heating roller, and heat-fixes a toner image on the recording material by passing a recording material between the two rollers; And a pressure roller cooling means for cooling a non-passing portion through which the small-sized recording medium does not pass.

According to a second aspect of the present invention, there is provided a heating roller and a pressure roller which is in pressure contact with the heating roller. The toner image on the recording material is formed by passing the recording material between the two rollers. A fixing device for performing heat fixing includes a pressure roller cooling unit that cools a non-passing portion of the pressure roller, and a control unit that controls an operation timing of the pressure roller cooling unit.

According to a third aspect of the present invention, in the fixing device according to the second aspect, the control unit includes a recording body detection unit that detects a size of the recording body.

According to a fourth aspect of the present invention, in the fixing device of the second aspect, the control means includes a temperature detecting means for detecting a temperature of the non-passing portion.

According to a fifth aspect of the present invention, in the fixing device according to the first or second or third or fourth aspect, the pressure roller cooling means causes the amount of air blown to the non-passing portion to be smaller than the amount of air blown to another portion. This is characterized in that the number of blowers is increased.

According to a sixth aspect of the present invention, in the fixing device according to the first or second or third or fourth aspect, the pressure roller cooling means is opposed to the pressure roller and the pressure roller is provided at the non-passing portion. Characterized in that it is a heat-absorbing means close to.

According to a seventh aspect of the present invention, in the fixing device according to the first or second or third or fourth aspect, the pressure roller cooling means is provided at the non-passing portion which faces the blower and the pressure roller. And a heat absorbing means adjacent to the pressure roller.

According to an eighth aspect of the present invention, in the fixing device of the sixth or seventh aspect, the heat absorbing means is configured such that a thickness of a portion facing the non-passing portion is set to be thicker than other portions. It is characterized by being.

According to a ninth aspect of the present invention, in the fixing device according to the first or second or third or fourth or fifth or sixth or seventh or eighth aspect, the heating roller has a heat source on its surface layer or an inner layer near the surface. It is characterized by having.

[0025]

According to the present invention, since the cooling means for cooling the pressure roller is provided, it is possible to prevent the temperature of the non-passing portion of the pressure roller from rising greatly, and to prevent the heating roller from contacting the pressure roller. Reduce the temperature rise in the passage section. By cooling around the non-passing portion of the pressure roller, the temperature of the central portion of the pressure roller does not decrease, and the temperature of the central portion of the heating roller does not greatly decrease during paper passing. By changing the distance between the pressure roller and the cover as a heat absorbing means that covers the pressure roller between the passing portion and the non-passing portion of the pressure roller, the heat release amount of the pressure roller from the pressure roller changes, and the heating roller The rise in the temperature of the non-passing portion of the pressure roller caused by the rise in the temperature of the non-passing portion is suppressed.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1 and 2, in a first embodiment of the present invention, a heating roller 2 having a heat source 1 therein, and a heating roller 2 and a pressure roller 4 are pressed against the heating roller 2. And a pressure roller 4 forming a nip portion 3 which is a contact portion between the nip portion 3 and a transfer paper P as a recording material on which the toner image T is transferred.
Guide member 5 for guiding the rollers 2 and 4
And a cover 6 having an inlet for taking in air for cooling the pressure roller and an outlet for discharging the taken-in air, and for keeping the surface temperature of the heating roller 2 at a set temperature. A first sensor 7 provided in contact with the heating roller 2 for detecting the temperature of the surface of the heating roller 2, a second sensor 8 provided as a temperature detecting means provided in contact with the pressure roller 4, An air blower 9 is provided at the inlet and serves as a pressure roller cooling means for cooling the pressure roller 4.

The rollers 2 and 4 forming the fixing roller pair are areas through which a recording medium (hereinafter, referred to as small size paper) having a relatively small size relative to the length of the fixing roller pair passes. It has a passing portion A and a non-passing portion B which is a region that does not pass. The non-passing portion B is the transfer paper P
Passes through the nip 3 on the basis of the center (FIG. 2A)
Is a nip portion 3 at both ends of the roller and the transfer paper P is
(FIG. 2B), it is located at the end opposite to the reference end. The first sensor 7 is in contact with the upper portion of the passing portion A of the heating roller 2, and the second sensor 8 as a temperature detecting means for detecting the temperature of the non-passing portion B is provided at the non-passing portion B of the pressure roller 4. Each is provided so as to be in contact with the lower part, and detects the temperature of the part in contact with them. The number of the first sensors 7 is not limited to one, and a plurality of the first sensors 7 may be provided in order to reliably detect the temperature of the passage portion A made of transfer paper of various sizes. Similarly, the number of the second sensors 8 is not limited to one, and a plurality of the second sensors 8 may be provided in order to reliably detect the temperature of the non-passing portion B formed by transfer papers of various sizes.

The heat source 1 is composed of a halogen lamp, and is disposed in the axial direction of the heating roller 2 so as to have a length substantially equal to the entire length of the heating roller 2. Heat 2 uniformly. The pressure roller 4
The heating roller 2 is configured to be able to freely contact and separate from the heating roller 2 by a pressing mechanism (not shown).

In the present embodiment, the heating roller 2 employs Al as a base material, but may use a metal such as SUS as a base material. A release layer is provided on the surface of the substrate for the purpose of preventing the toner from adhering thereto. As the material of the release layer, Teflon is used, but a PFA tube or the like can also be used.

As a method for forming the release layer, there are a method of directly coating a heating roller, a method of heating a tube-shaped material at a high temperature, and shrinking and adhering to the heating roller.
As for the thickness of the heating roller, the thinner the heat capacity, the smaller the heat capacity and the faster the temperature rise time, which is preferable. Since an inconvenience such as variation in properties occurs, it is necessary to select an optimal thickness.

In the present embodiment, the pressing roller 4 employs SUS as a core rod, but other metals such as iron, Al, and brass may be used as the core rod. An elastic layer of silicon rubber is formed on the core rod. In order to reduce the pressure required to secure the nip width required for fixing as the elastic layer,
A relatively soft material such as foamed silicone rubber may be used. On the surface of the elastic layer, a release layer for imparting releasability, or silicon rubber, which is an insulating material, is charged by friction or the like, and an unfixed toner image is formed due to the electrostatic force or generation of electric discharge. As a conductive layer for preventing disorder, a Teflon layer containing a conductive material such as carbon may be provided.

The pressing force of the pressing roller 4 against the heating roller 2 only needs to have a pressing force capable of securing a required nip width.

An air passage for cooling the pressure roller 4 is formed between the pressure roller 4 and the bottom of the cover 6. Blower 9 as cooling means for sending air to ventilation passage
Consists of a fan having a plurality of blades rotating about an axis provided in parallel with the pressure roller 4 and having the same length in the axial direction as the pressure roller 4. The blowing device 9 varies the blowing amount in the axial direction of the pressure roller 4 so that the air flow rate to the non-passing portion B, which becomes high when small-size paper is continuously passed, becomes larger than that of the passing portion A. Therefore, the size of the blade changes in the axial direction. As a configuration for changing the air flow rate in the axial direction, in addition to the above, an air flow control plate for shielding or changing the direction of the air flow was provided, and the size of the air inlet and the outlet was changed. A configuration, a configuration in which a plurality of blowers are provided in the axial direction, and the like are given. In a configuration in which a plurality of blowers are provided, only the non-passing portion B can be selectively cooled.

The operation timing of the blower 9 is determined by a control unit having a recording body detection unit for detecting the number and size of the transfer paper P to be sent to the fixing device and a second sensor 8. The recording body detecting means detects a command from an operator or the size of the transfer sheet when transferring the toner image onto the transfer sheet, and a control unit (not shown) for selecting the same also serves as the transfer unit. To detect the size of the paper, a sensor or the like may be provided in the fixing device. The control means may include one of the recording body detection means and the second sensor 8. With such a configuration, it is possible to reduce a decrease in the temperature of the pressure roller in the passing portion and effectively reduce an increase in the temperature in the non-passing portion.

It is preferable to generate an air flow in the transfer paper transfer direction of the pressure roller 4 from the viewpoint that the passage portion A of the pressure roller 4 can be selectively cooled. It can also flow in the axial direction. In this embodiment, the air blower 9 is used as the cooling means. However, a Peltier element or the like may be used as long as the pressure roller 4 is actively cooled. From the viewpoint of cost, cooling by a blower is preferable. The blower 9 may be provided not only on the air intake side but also on the discharge side. In cooling by blowing air, the size and shape of the air intake and exhaust ports are appropriately set, and the smooth flow of air can reduce the generation of abnormal noise due to the air flow.

In an image forming apparatus used for a PPC, a laser printer, a PPF, or the like, a toner image T is formed on the surface of the transfer paper P by a well-known electrophotographic process of charging, exposing, developing, and transferring. The transfer paper P on which the toner image T is formed is conveyed in the direction of arrow C in FIG. 1 and guided to a fixing section, that is, a nip section 3 by a guide member 5, where the toner image T is heated and fixed by the heat of the heating roller 2. You. Thereafter, the transfer paper P on which the toner image T has been heated and fixed is discharged from the fixing device. In the fixing step, the transfer sheet P removes the heat energy of the heating roller 2,
Since the temperature of the heating roller 2 decreases, the first sensor 7 detects this, the heat source 1 is driven, and the temperature of the heating roller 2 is heated to the set temperature.

When small size paper is continuously printed, the passing portion B
Only the heat energy of the heating roller 2 is taken away. Since the temperature detection of the heating roller 2 is performed at the passage A of the heating roller,
When the temperature decreases, the heat source 1 is driven to increase the temperature of the heating roller 2 to a set temperature. Since the non-passing portion B is similarly heated, the temperature of the non-passing portion B rises above the set temperature by heating even though the temperature does not decrease in the non-passing portion B. At this time, from the experiment of the present inventors, the temperature of the non-passing portion B of the pressure roller 4 is
It turned out to be higher.

Since the heat capacity of the heating roller 2 is small, the temperature rise in the non-passing portion can be relatively quickly eliminated after a while, but the heat capacity of the pressure roller 4 is large, and silicon rubber which is a material of the elastic layer is made of silicon rubber. Since the thermal conductivity is low, the temperature of the non-passing portion B on the pressure roller 4 side does not readily decrease. Therefore, when the heating roller 2 is rotated again thereafter, the non-passing portion B of the heating roller 2 comes into contact with the high-temperature pressure roller 4 and becomes hot immediately.

In this embodiment, the blower 9 is driven at the time when it is determined that the small size paper is continuously passed and when the temperature of the non-passing portion B is detected to be higher than the predetermined temperature. Thereby, at least the non-passing portion B of the pressure roller 4 is cooled. Therefore, the phenomenon that the non-passing portion B of the pressure roller 4 becomes much hotter than the passing portion A is eliminated, and the temperature rise of the non-passing portion of the heating roller 2 in contact with the pressure roller 4 is suppressed.

EXPERIMENTAL EXAMPLE 1 With the configuration of this embodiment, a fixing device for A3 recording paper as shown below was prepared, and the temperature rise of the non-passing portion B when the transfer paper of B5 width was continuously passed. It was measured. As Comparative Example 1, measurement was also made without the blower 9.

Heating roller size: width 335 mm, diameter 30 mm, heat 0.6 mm Heating roller material: aluminum Heat source: halogen lamp Heat source supply power: 1000 W Pressure roller: diameter 30 mm, core material = iron, elastic layer = silicone rubber Cooling means: Suction by fan Recording paper: Ricoh type 6200 paper Recording paper feed speed: 90 mm / s Heating roller set temperature: 180 ° C. Non-passage temperature rise in the present embodiment on the heating roller 2 side Is compared with the non-passing portion temperature rise in the case where is not provided. In FIG. 3, a indicates the temperature of the passage section A measured by the first sensor 7. b and c are the second
5 shows a temperature rise characteristic of the non-passing portion B of the pressure roller 4 measured by the sensor 8 of FIG.
c is a characteristic when no air blower is provided. As shown in FIG. 3, according to the present embodiment, the rise in the temperature of the non-passing portion when small-size paper is continuously passed is reduced, and the difference from the temperature of the passing portion A is reduced.

Further, using the fixing device of this embodiment,
Immediately after 50 sheets of B5 size paper were continuously passed, A4 size paper on which a toner image was formed was passed and the fixed image was evaluated. As a result, in the case of this embodiment, a good fixed image was obtained. On the other hand, in Comparative Example 1, offset was generated in the non-passing portion B, and wrinkles were confirmed on the transfer paper P, resulting in a poor image. In addition, when the heating time from the room temperature to the set temperature of the heating roller was compared, the temperature could be increased in the same time as Comparative Example 1 by operating the blower 9 only during continuous paper feeding.

Further, the air flow rate is small in the passage portion A and large in the non-passage portion B, that is, the cooling capacity is increased.
By increasing the size in the passage portion A and decreasing the size in the passage portion A, or selectively cooling only the non-passage portion B,
The temperature of the passage section A, which detects the temperature by the first sensor 7 and controls the temperature, is the same as when the air blower 9 is not used, and the continuous paper passing is not performed. There is no effect on power consumption during operation.

FIG. 4 shows three examples of the heating roller 10 in which the heating roller itself has a heat storage layer. The heating roller 10 shown in FIG. 4A has a heating resistor 10b formed on the surface of a base material 10a, on which a releasability from a toner is improved, and a contact between another member and the heating element. The heat-resistant resin layer 10c of Teflon is formed for the purpose of preventing the heat-generating element from being damaged and electrically insulating the heat-generating resistor.
The heating roller 10 shown in FIG.
A heat-generating resistor 10b is formed on the inner surface of the substrate, and the above-described heat-resistant resin layer 10c is formed on the surface of the substrate 10a. Then, the heating roller 10 shown in FIG.
Is formed by forming a heat-resistant resin layer 10c on the surface of a roller 10d made of a material that generates heat itself.

The roller 21d is made of conductive fibers, but may be made of carbon-dispersed ceramics, so-called self-heating ceramics. Glass is used as the material of the base material 10a, but the material is not limited to this, and ceramics or metals such as Al and SUS may be used. However, when metal is used, it is necessary to provide an insulating layer made of a resin material such as SiO ₂ or polyimide on the surface layer for electrical insulation from the heating resistor.

As the heating roller 10, although not shown, there is another heating roller in which the base material 10a itself is a heating element. Examples of the heating element include a material in which a conductive material is dispersed in ceramics, a material in which conductive fibers are formed in a cylindrical shape, and the like. These heating rollers 1
0 is smaller than that of the heating roller 2 using a halogen lamp or the like.
Since the heat source and the heating roller 10 are integrated, the heating efficiency of the heating roller 10 is good. Further, since the heat source directly heats the vicinity of the surface of the heating roller 10 where fixing is performed, the heating efficiency is good and the power consumption is reduced. The fixing method is extremely excellent in that the heat capacity is reduced by reducing the thickness of the base material 10a, the heating time is shortened, and the so-called wait time until printing of a PPC, laser printer, PPF, or the like is shortened. It is.

When glass is used for the substrate 10a, there is also an advantage that the cost of the glass itself is low. During standby, the power supply to the heating roller 10 can be stopped or slightly supplied to maintain a low temperature. The waiting time of the user at the time of reprinting is desirably to shorten the heating rise time to the fixing temperature within 30 seconds, preferably within 15 seconds. Therefore, when the heat of the heating roller is made of Al, SUS, or glass as a base material, 1 mm
Hereinafter, in the case of ceramics, it is necessary to reduce the thickness to just the processing limit (usually 1 to 2 mm).

However, on the other hand, in the case of a heating roller having a small heat capacity, when it is used in a high-speed machine, its thickness is so thin that heat transfer in the horizontal direction is unlikely to occur, and the temperature rise in the non-passing portion is reduced. It also has a disadvantage that it is easily generated. Above all, when glass or ceramics is used as the base material, there is a problem that the temperature rise in the non-passing portion tends to be further increased due to poor thermal conductivity. Heating roller 1
When the heat roller is provided with a heat source at or near the surface as 0, the above-described disadvantage can be particularly effectively solved.

EXPERIMENTAL EXAMPLE 2 A fixing device for A3 as shown below was constructed with the configuration using the heating roller 10, and the temperature rise of the non-passing portion when the transfer paper P of A4 width was continuously passed was measured. . As Comparative Example 2, measurement was performed using the heating roller 10 and without the blower 9.

Heating roller configuration: FIG. 4 (a) Heat source supply power: 700 W Heating roller size: width 335 mm, diameter 30 mm, thickness 0.6 mm, heating section length 305 mm Heating roller material: glass Pressure roller: diameter 30 mm, core material = iron, elastic layer = silicone rubber Cooling means: suction by fan Recording paper: Ricoh type 6200 paper Recording paper feed speed: 90 mm / s Heating roller set temperature: 180 ° C. In this embodiment on the heating roller 10 side The non-passing portion temperature rise and the non-passing portion temperature rise in the case where the air blower of Comparative Example 2 is not provided are compared. In FIG. 5, a indicates the temperature of the passage section A measured by the first sensor 7. b and c are the second
5 shows a temperature rise characteristic of the non-passing portion B of the pressure roller 4 measured by the sensor 8 of FIG.
c is a characteristic when no air blower is provided. As shown in FIG. 5, the temperature rise in the non-passing portion when small-size paper is continuously passed according to the present invention is reduced, the difference between the temperature of the passing portion A is significantly reduced, and the temperature is greatly improved. I understand.

Further, using the fixing device of this embodiment,
Immediately after 50 sheets of B5 size paper were continuously passed, A4 size paper on which a toner image was formed was passed and the fixed image was evaluated. As a result, in the case of this embodiment, a good fixed image was obtained. On the other hand, in Comparative Example 2, offset was generated in the non-passing portion, and wrinkling was confirmed on the recording paper, resulting in a poor image.

When the temperature rise time from room temperature to the set temperature of the heating roller was compared, the temperature could be raised in the same time as Comparative Example 2 by operating the blower 9 only during continuous paper feeding. In addition, the amount of the air flow is small in the passage portion A,
By increasing the cooling capacity in the non-passing portion B, that is, by increasing the cooling capacity in the non-passing portion B and decreasing it in the passing portion A, or by selectively cooling only the non-passing portion B, the temperature of the passing portion A is greatly reduced. Since the temperature is controlled by the first sensor 7 and the temperature is controlled, the passing portion A that controls the temperature is the same as when the air blower 9 is not used, and the power consumption during continuous paper passing is not affected. Absent.

FIGS. 6A and 6B show a second embodiment of the present invention. In this embodiment, the cover 11 also serves as a heat absorbing means. In the first embodiment, the pressure roller cooling means does not have the air inlet and outlet of the cover 6 and the blower, and the pressure roller cooling means is opposed to the pressure roller 4 and is provided to the pressure roller 4 at the non-passing portion B. Being an endothermic means that is close,
The difference from the first embodiment is that the cover 11 also serves as a heat absorbing means as a cooling means. 6 (a), 6
(B) shows the case where the paper feeding device is based on the center and the case where the paper feeding device is based on the end. The heating roller shown in FIG. 4A is employed. The other configuration is the same as that of the first embodiment, and therefore, the description is omitted by attaching the reference numerals.

The distance between the pressure roller 4 and the cover 11 is different at portions corresponding to the passing portion A and the non-passing portion B of the pressure roller 4. In the non-passing portion B, the distance is close, and in the passing portion A, the distance is larger. In the non-passing portion B, the heat of the pressure roller 4 is easily radiated to the cover 11, and in the passing portion A, the heat is hardly radiated.

In general, fixing in a warm state is better than fixing in a cold state of a pressure roller in terms of fixing performance and power consumption during fixing of a heating roller. This is because the recording paper is heated not only by the heating roller but also by the pressure roller because the pressure roller is warmed, and the recording paper itself is easily heated. To improve the fixability, reduce the decrease in the temperature of the heating roller, and reduce the electric power for reheating.

In the present embodiment, the temperature drop of the pressure roller 4 in the passing section A is reduced, the fixing of the toner image is secured, and the power consumption of the heating roller 10 is reduced. Since the excess heat generated by the rise is taken away and the temperature rise in the non-passing portion of the pressure roller 4 is reduced, the temperature rise in the non-passing portion of the heating roller 10 in contact therewith can be reduced.

The distance between the pressure roller 4 and the cover 11 in the passing portion A and the non-passing portion B is 10 mm and 5 mm, respectively.
Is set to 10 mm or more and 1 mm, respectively.
It can be set to be less than 10 mm. Non-passing part B
If the distance is too close, the pressure roller 4 may be damaged by contact with the pressure roller 4.

In order to make the temperature inside the cover 11 uniform, a high heat conductive layer such as an Al film may be provided on the inner surface of the cover 11. This can prevent the cover at the position corresponding to the non-passing portion B from becoming hot and reducing the heat absorbing effect, and can prevent the temperature from being abnormally high and the user's safety from being impaired. If the temperature of the pressure roller 4 is particularly high, the distance may be changed in accordance with a delicate tendency of the temperature of the pressure roller 4, such that the pressure roller 4 is closer to the temperature, and is relatively far away at a slightly lower temperature. Conceivable.

EXPERIMENTAL EXAMPLE 3 With the configuration of the present embodiment using the cover 11, a fixing device for A3 as shown below was prepared, and the temperature rise of the non-passing portion B when recording paper of A4 width was continuously fed. Was measured. As Comparative Example 3, measurement was also performed when the distance was constant at 12 mm, that is, when there was no heat absorbing means.

Heating roller configuration: FIG. 4A Heat source supply power: 700 W Heating roller size: 335 mm wide, 30 mm diameter, 0.6 mm thick, 305 mm length of heating section Heating roller material: glass Pressure roller: diameter 30 mm, core material = iron, elastic layer = silicone rubber Distance between pressure roller and cover: central part = 12 mm, edge part (between both ends of pressure roller 30 mm) = 2 mm Recording paper: Ricoh type 6200 paper Recording paper feed speed: 90 mm / s Heating roller set temperature: 180 ° C. The non-passing portion temperature rise in the present embodiment on the heating roller 10 side and the distance between the pressure roller 4 and the cover 6 in Comparative Example 3 are 12
The temperature rise in the non-passage portion when the temperature is kept constant in mm is compared.
In FIG. 7, a is a passing portion A measured by the first sensor 7.
Shows the temperature. b and c show the temperature rise characteristics of the non-passing portion B of the pressure roller 4 measured by the second sensor 8, and b
Is the characteristic when the cover as the heat absorbing means is provided, and c is the characteristic when the cover is not provided as the heat absorbing means. As shown in FIG. 7, according to the present embodiment, the rise in the temperature of the non-passing portion when the small-size paper is continuously passed is reduced, the difference between the temperature of the passing portion A is significantly reduced, and the temperature is greatly improved. You can see that there is. In addition, when compared with the case where the distance between the pressure roller 4 and the cover 6 is fixed at 2 mm, the same effect can be obtained with respect to the rise in the temperature at the non-passing portion. But it turned out to be fast. The power consumption during continuous feeding of small-size paper was also smaller in this embodiment.

Further, using the fixing device of this embodiment,
Immediately after passing 50 sheets of A4 size paper continuously, the A3 size paper on which the toner image was formed was passed and the fixed image was evaluated. As a result, in the case of this embodiment, a good fixed image was obtained. On the other hand, in Comparative Example 3, an offset occurred in the non-passing portion B, and the occurrence of wrinkles on the recording paper was confirmed, resulting in a poor image.

The cover 12 as the heat absorbing means shown in FIGS. 8A and 8B has a different thickness in the axial direction of the pressure roller. FIGS. 8A and 8B show a case where the sheet feeding position is based on the center and a case where the sheet feeding position is based on the end. Cover 1
By increasing the thickness of the portion facing the non-passing portion B and reducing the thickness of the other portions, the heat capacity of the cover 12 at each portion facing the passing portion A and the non-passing portion B is reduced. Is different. This is suitable in that the non-passing portion B needs a larger amount of heat in order to keep the temperature in the axial direction of the pressure roller 4 constant.

By using the cover 12, even if the heat of the pressure roller 4 is radiated to the cover in the non-passing portion B more than in the passing portion A, the heat capacity of the non-passing portion B is large, so that the non-passing portion B faces the non-passing portion B. The part of the cover 12 that does
Since the state where the temperature difference between the cover 12 and the pressure roller 4 is large can be maintained for a long time, the heat radiation effect of the non-passing portion B of the pressure roller 4 can be maintained for a long time. The rise in the temperature of the passage section can be reduced for a long time.

Accordingly, even when a large number of small-size sheets are printed, the temperature of the pressure roller 4 in the non-passing portion B is reduced, the fixing property is secured, and the power consumption of the heating roller 2 is reduced. In the portion B, excess heat generated by the rise in the temperature of the non-passing portion is taken away, and the rise in the temperature of the non-passing portion of the pressure roller 4 is reduced. I can do it.

The thickness of the portion of the cover 12 facing the non-passing portion B is set to 10 mm. As for this thickness, it is preferable that the thickness is as thick as possible, because it is more difficult to warm up.
It is formed in a range of up to 20 mm.

Experimental Example 4 A fixing device for A3 as shown below was constructed with the configuration using the cover 12, and the temperature rise of the non-passing portion when recording paper of A4 width was continuously passed was measured.

Heating roller configuration: FIG. 4 (a) Heat source supply power: 700 W Heating roller size: 335 mm wide, 30 mm diameter, 0.6 mm thick, 305 mm length of heating section Heating roller material: glass Pressure roller: diameter 30 mm, core material = iron, elastic layer = silicone rubber Distance between pressure roller and cover: central part = 12 mm, edge part (between both ends of pressure roller 30 mm) = 2 mm Recording paper: Ricoh type 6200 paper Recording paper feed speed: 90 mm / s Heating roller set temperature: 180 ° C. With this configuration, even if 100 sheets of A4 size paper are continuously passed, the temperature rise in the non-passing portion of the heating roller 2 is maintained at 20 ° C. or less. Immediately after this, the A3 size paper on which the toner image was formed was passed through and the fixed image was evaluated. Chakugazo was obtained.

For the sake of explanation, the pressure roller cooling means is only a blower in the first embodiment and only a heat absorbing means in the second embodiment. Both can be used at the same time as the roller cooling means, and a combination of these can be appropriately selected, including the specific arrangement positions of the recording body detecting means and the temperature detecting means.

[0069]

According to the present invention, the cooling means for cooling the pressure roller is provided, so that the temperature of the non-passing portion of the pressure roller is prevented from greatly increasing, and the heating which contacts the pressure roller is prevented. The temperature rise in the non-passing portion of the roller could be reduced. As a result, even if a large-sized recording medium is passed after the small-size paper is continuously passed, hot offset does not occur,
In addition, it was possible to obtain a high-quality recorded image without wrinkling of the recording medium.

By cooling around the non-passing portion of the pressure roller, the temperature of the central portion of the pressure roller does not decrease, and the temperature of the central portion of the heating roller does not greatly decrease during the paper passing. The power consumption for maintaining is reduced. Further, the cooling means can be operated only when the non-passage portion temperature rises, so that the heating time is not affected and the heating time is shortened.

By changing the distance between the pressure roller and the cover as a heat absorbing means for covering the pressure roller between the passing portion and the non-passing portion of the pressure roller, the amount of heat radiated from the pressure roller changes. In addition, the rise in temperature of the non-passing portion of the pressure roller caused by the rise in the temperature of the non-passing portion of the heating roller is suppressed. In addition to being able to obtain a recorded image, the passing portion is not cooled and is appropriately warmed. Since the temperature detection of the heating roller is performed near the central portion which is the passing portion of the heating roller, fixing is performed. The power supplied to the heating roller at the time can be reduced.

As compared with the case where the distance between the pressure roller and the cover is fixed, the amount of heat transferred from the heating roller to the pressure roller is reduced. And shortening of the heating time can be achieved. Since the thickness of the heat absorbing means in the portion facing the non-passing portion is increased, the ability of the pressure roller to deprive the temperature of the non-passing portion increases, and even if the number of small-size paper sheets continuously passed is increased. , The rise in the temperature of the non-passing portion can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic side view of a fixing device according to a first embodiment of the present invention in which a blower is used as a pressure roller cooling unit.

FIG. 2 is a schematic diagram showing a passing portion and a non-passing portion in the first embodiment of the present invention.

FIG. 3 is a diagram for comparing the temperature rise of each part of a heating roller between a transfer device using the first embodiment having a blower and a transfer device not having a blower according to the present invention. It is.

FIG. 4 is a cross-sectional view showing a structure of a heating roller having a configuration different from that of the heating roller shown in FIG. 1 in the first embodiment of the present invention.

FIG. 5 shows how the temperature of each part of the heating roller of the transfer device in the first embodiment of the present invention in which the heating roller is the one shown in FIG. 4 and that of the transfer device without a blower are increased. It is a figure for comparing.

FIG. 6 is a schematic diagram of a fixing device according to a second embodiment of the present invention in which a heat absorbing unit is used as a pressing roller cooling unit.

FIG. 7 is a diagram for comparing the temperature rise of each part of the heating roller between the fixing device having the pressure roller cooling unit shown in FIG. 6 and the fixing device not having the pressure roller cooling unit. It is.

FIG. 8 shows a second embodiment of the present invention in which a portion of the heat absorbing means facing the non-passing portion of the pressure roller is thicker than other portions as the pressure roller cooling means. FIG. 2 is a schematic diagram of the fixing device shown.

[Description of Signs] 1 Heat source 2, 10 Heating roller 4 Pressure roller 8 Temperature detecting means 9 Blower 11, 12 Heat absorbing device A Passing part B Non-passing part P Recording material T

Claims (9)

[Claims] A fixing device for heating and fixing a toner image on the recording material by allowing a recording material to pass between the two rollers; And a pressure roller cooling means for cooling a non-passing portion through which the small-sized recording medium of the pressure roller does not pass. 2. A fixing device comprising: a heating roller; and a pressure roller in pressure contact with the heating roller. A pressure roller cooling means for cooling a non-passing portion of the pressure roller; and a control means for controlling operation timing of the pressure roller cooling means. 3. A fixing device according to claim 2, wherein said control means includes a recording body detecting means for detecting a size of said recording body. 4. A fixing device according to claim 2, wherein said control means includes a temperature detecting means for detecting a temperature of said non-passing portion. 5. The fixing device according to claim 1, wherein the pressure roller cooling means is configured such that an amount of air blown to the non-passing portion is larger than an amount of air blown to another portion. A fixing device. 6. A fixing device according to claim 1, wherein said pressure roller cooling means is a heat absorbing means opposed to said pressure roller and adjacent to said pressure roller at said non-passing portion. The fixing device as described in the above. 7. The fixing device according to claim 1, wherein said pressure roller cooling means comprises: a blowing device;
And a heat absorbing means facing the pressure roller and approaching the pressure roller at the non-passing portion. 8. The fixing device according to claim 6, wherein
The fixing device according to claim 1, wherein a thickness of a portion of the heat absorbing unit facing the non-passing portion is set to be thicker than thicknesses of other portions. 9. The method of claim 1, 2 or 3, 4 or 5, or 6.
9. The fixing device according to claim 7, wherein the heating roller has a heat source in a surface layer or an inner layer near a surface thereof.