JP3679613B2 - Fixing device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device that sandwiches and conveys a recording material between a heating rotator and a pressure rotator, and heats and melts unfixed toner on the recording material.
[0002]
[Prior art]
2. Description of the Related Art Image forming apparatuses using an electrophotographic system are applied to printers, copiers, and the like, and their spread has been remarkable in recent years because of the advantages of high speed and high image quality. In the electrophotographic method, a latent image corresponding to image information is formed on an image carrier represented by a drum or a belt-shaped photoconductor, and the latent image is developed as a toner image using toner, and is further formed on paper or OHP. The toner image is transferred onto a recording material such as a resin film to be used, and the toner image is fixed by a fixing device. From the viewpoint of environmental protection and effective use of resources, duplex copying, in which images are formed on both sides of a recording material, has become increasingly important in recent years. Actually, double-sided copying that forms an image on the surface of the recording material (hereinafter referred to as the first surface) by development, transfer, and fixing, and then forms an image on the reverse side of the recording material (hereinafter referred to as the second surface) as well. Many possible image forming apparatuses have been realized.
[0003]
In the fixing device, the heat roller method is the most commonly used fixing method at present. The configuration of the heating roller system includes a pair of a heating roller as a heating rotator and a pressure roller as a pressure rotator. The two rollers are pressed against each other by a spring or the like and pressed against each other (hereinafter referred to as a “nip portion”). And the toner image which is not fixed on the recording material is nipped and conveyed to be thermally melted and fixed on the recording material. One of the major problems with this heat generating roller system is that wrinkles are likely to occur in the recording material when the recording material is passed through the nip portion. For this reason, various solutions have been proposed to suppress wrinkling. A commonly used measure is to make the roller shape an inverted crown. As a result, the conveyance speed at the end of the recording material becomes faster than the central portion of the recording material, and a force for expanding the trailing end of the recording material is generated to prevent wrinkling.
[0004]
[Problems to be solved by the invention]
However, when such a fixing device is used to form an image on the second surface of the recording material, there is a problem that wrinkles are likely to occur at the trailing edge of the recording material. It has been found that the occurrence of can not be effectively suppressed. This problem occurs remarkably in the color image forming apparatus, and is also affected by the position of the image to be formed. That is, when the image of the first surface is formed at the center of the recording material and the end of the recording material is blank, wrinkles occur frequently. This is because the surface state of the image portion on the first surface and the surface of the blank paper portion is different and the image portion in the center of the recording paper is slippery. Therefore, when an image is formed on the second surface, Slip occurs between the pressure roller (driven side). For this reason, the frictional resistance between the image portion on the first surface and the pressure roller is reduced, and a driving force is applied to the second surface from the heating roller on the driving side. Therefore, when an image is formed on the second surface, recording is performed. The conveyance speed of the central portion of the material becomes faster than that on the first surface, and vertical paper wrinkles are generated at the rear end by receiving force on the central direction of the recording material.
[0005]
As a countermeasure against such wrinkles that occur during double-sided image formation, a silicon rubber layer is provided on the surface of the rotating body for heating and the rotating body for pressure, and the thickness of the silicon rubber layer and the width of the nip portion of each roller are tested. There has been proposed a fixing device that performs image fixing in a region where wrinkles do not occur, which is defined by a value (Japanese Patent Laid-Open No. 6-301306). Specifically, the sum of the thicknesses of the elastic layers of the fixing roller and the pressure roller is set to 4 mm or more, the thickness difference between these elastic layers is set to 1 mm or less, the width of the nip portion is secured, and the contact pressure is set to 30 kgf or less. By preventing the wrinkle, the generation of paper wrinkles is prevented. However, Japanese Patent Application Laid-Open No. 6-301306 has a problem that wrinkles are reduced by keeping the contact pressure as low as 30 kgf or less, and it cannot be applied to high-speed image formation that requires high contact pressure. .
The present invention relates to a fixing device capable of reliably reducing wrinkles generated when an image is formed on both sides of a recording material even if the contact pressure between a heating rotator and a pressurizing rotator is increased. The purpose is to provide.
[0006]
[Means for Solving the Problems]
According to the first aspect of the present invention, there is provided a heating rotator that is rotated by being provided with a driving force, a pressurizing rotator that is disposed so as to face the heating rotator and is in pressure contact with the member, and at least a heating rotator. Heating means for heating the body, and means for reducing a load torque applied to the pressurizing rotating body when forming an image on the second surface of the recording material, compared to when forming an image on the first surface of the recording material. The load torque on the pressurizing rotator during image formation on the first surface and the second surface of the recording material can be changed.
The invention according to claim 2 is a load member which is provided so as to be able to contact and separate from the pressurizing rotator and presses the pressurizing rotator. The load torque to the pressure rotating body can be controlled.
[0007]
According to the third aspect of the present invention, the load member is constituted by an oil application member, and the load member and the oil application member are made common, and the load member is added during image formation on the first surface and the second surface. The load torque to the pressure rotating body can be controlled, and oil is applied to the surface of the pressure rotating body to improve the peelability of the recording material.
The invention described in claim 4 is characterized in that the means for reducing the rotational load torque electrically controls the fluctuation of the load torque.
[0008]
【Example】
Embodiments of the present invention will be described below with reference to the drawings. The fixing device shown in FIG. 2 is installed in a full-color copying machine which is an example of a color image forming apparatus compatible with double-sided copying (not shown). The fixing device includes a fixing roller 1 as a heating rotator, and a pressure roller 2 as a pressure rotator disposed opposite to the fixing roller 1, and is a resin sheet-like material used for paper or OHP (overhead projector). The recording material 3 is nipped and conveyed, and the unfixed toner image 4 transferred to the first surface 3a or the second surface 3b is heated and melted and fixed while being pressed. The toner image 4 is transferred onto the recording paper 3 by a transfer unit of an image forming apparatus (not shown).
[0009]
The fixing roller 1 is given a driving force from the outside and rotates in the clockwise direction in FIG. The fixing roller 1 has a configuration in which an elastic layer 1b is coated on a cored bar 1a. In many cases, the core metal 1a is mainly made of roller-like aluminum, iron, or an alloy thereof, and becomes high temperature due to heat generated by the halogen heater 11 serving as a heating means provided in the roller. The elastic layer 1b is coated to increase the nip portion 16 serving as a mutual pressure contact portion with the pressure roller 2 and to obtain image gloss, and is formed of silicon rubber on the core metal 1a. In this example, the fixing roller 1 includes the elastic layer 1b of silicon rubber. However, a configuration without the elastic layer 1b may be used. The outer diameter of the fixing roller 1 is appropriately set to 60 mm, and the thickness of the elastic layer 1b is appropriately set to 1 to 3 mm.
[0010]
An oil application felt 5 for applying release oil is in contact with the elastic layer 1b, and an oil blade 6 for controlling the oil amount is in contact with the downstream side in the rotational direction. The mold release oil is dimethyl silicone oil and has a viscosity of 300 CS. In the present embodiment, the oil application mechanism having the oil application felt 5 and the oil blade 6 enables the oil application amount to be regulated to 10 mg or less (2 to 10 mg) per A4 size. A cleaning roller 7 and a separation claw 9 are in contact with the elastic layer 1b, and a scraper 8 is in contact with the cleaning roller 7.
[0011]
The pressure roller 2 is in pressure contact with the fixing roller 1 and is driven to rotate counterclockwise in FIG. The pressure roller 2 is coated with an elastic layer 2b on a core metal 2a in the same manner as the fixing roller 1. The outer diameter of the pressure roller 2 is set to 60 mm, and the thickness of the elastic layer is set to 1 to 4 mm. The width W (length of the nip portion in the paper transport direction) of the nip portion 16 by the fixing roller 1 and the pressure roller 2 is 9.5 mm, and the fixing speed is 180 mm / s. In this configuration, the pressure roller 2 is also provided with a halogen heater 12 serving as a heating means so as to generate heat at a high temperature. Of course, the halogen heater 12 may be omitted. The contact pressure of both rollers is set to about 80 kgf. This contact pressure is a contact pressure when fixing a color image to the recording material 3 at six sheets per minute. The contact pressure of both rollers is not limited to this example, and may be a general contact pressure corresponding to the number of recording materials 3 to be fixed (printed) per unit time, and is at least larger than 30 kgf. Pressure.
[0012]
In the vicinity of the outer periphery of the pressure roller 2, a pressure roller blade 13 for scraping paper dust and dust of the recording material 3 and a toner image 4 fixed on the second surface 3 b of the recording material 3 to form a copy image In this case, a load member 10 serving as means for reducing the load torque as compared with the time of image formation on the first surface 3a is disposed. The pressure roller blade 13 is provided in sliding contact with the elastic layer 2b.
[0013]
The load member 10 is in contact with the pressure roller 2 as shown in FIGS. 2 and 3 when an image is formed on the first surface 3a, and as shown in FIG. 1 when an image is formed on the second surface 3b. It is provided so as to be able to contact and separate from the pressure roller 2. The load member 10 is an oil application member made of an oil application felt for applying release oil, and is configured to act as a load member for the rotational torque of the pressure roller 2. That is, the load torque of the pressure roller 2 is controlled by the load member 10. The oil application member used as the loading member 10 is not limited to felt impregnated with oil, and may be a rotatable roller. In this case, the roller may be constituted by a sponge or an impregnating member similar to the sponge, and the roller may be used by impregnating the release oil. Alternatively, when the roller is constituted by a member having no impregnation property, release oil may be appropriately supplied to the roller surface and then supplied to the pressure roller 2.
[0014]
The drive system of the fixing device shown in FIGS. 1, 2, and 3 will be described. As shown in FIG. 4, a shaft 14 is provided on the fixing roller 1 so as to be integrally rotatable. A driving force input gear 17 is fixed to one end of the shaft 14. The driving force input gear 17 is engaged with an output gear 19 that is rotated by a driving motor (not shown) to transmit the driving force from the driving motor. The shaft 14 is rotatably supported by a side plate (not shown). The pressure roller 2 is provided integrally with the shaft 15 and is supported and rotated by bearings 18 and 18 provided at both ends of the shaft 15. The bearings 18 and 18 are provided on a side plate (not shown).
[0015]
The operation of the fixing device having such a configuration will be described.
The recording material 3 carrying the unfixed toner image 4 is conveyed from the right to the left in FIG. 3 and passes through the nip portion 16 where the fixing roller 1 and the pressure roller 2 are pressed against each other. The toner image 4 is melted on the recording material 3 and fixed as the image portion 140.
[0016]
Here, if the toner image 4 is carried on the first surface 3a, the recording material 3 is formed with an image portion 140 on the first surface 3a as shown in FIG. The paper is discharged from a fixing device to a paper discharge tray (not shown). In the case of duplex copying, the toner image 4 is carried on the second surface 3b of the recording material 3, and the first surface 3a moves in contact with the pressure roller 2 and passes through the nip portion 16 to pass through the nip portion 16. The toner image 4 is fixed on the second surface 3b and discharged onto a discharge tray (not shown).
[0017]
The inventor conducted an experiment in which the load member 10 was brought into and out of contact with the pressure roller 2 when fixing the image on the recording material 3, and the following results were obtained. In this experiment, after forming the first surface 3a, the apparatus is temporarily stopped, and after removing the load member 10 (oil application member) from the fixing device to the pressure roller 2 outside the apparatus, the second surface 3b is formed. In the experiment, the wrinkles generated in the recording material 3 were confirmed.
[0018]
The outline of the experiment is as follows. A4 size paper was conveyed in the vertical direction to form an image. The width of the paper is 210 mm and the formed image width is 120 mm. First, when the load member 10 was brought into pressure contact with the pressure roller 2 to form the image portion 140 on the second surface 3b, all three of the three sheets were wrinkled at the trailing edge of the sheet. On the other hand, when the load member 10 was removed, that is, the image portion 140 was formed on the second surface 3b away from the pressure roller 2, no wrinkles were generated on the paper in three of the three sheets. It should be noted that when forming an image on the first surface 3a, no wrinkle was generated in either case of contact or separation between the load member 10 and the pressure roller 2.
[0019]
In order to separate and confirm the effects of oil application and load on the pressure roller 2, the non-sheet passing region is not the load member 10 having the oil application function but the rotation of the pressure roller 2 itself. The result of an experiment using a configuration in which the load member 10 that does not have an oil application function is press-contacted is also similar to the above. It should be noted that no image disturbance was observed even when no release oil was supplied during image formation on the second surface 3b.
[0020]
From the above experiment, it was confirmed that the wrinkle generation of the recording paper 3 can be suppressed by adjusting the load torque of the pressure roller 2. Therefore, it is not necessary to reduce the contact pressure between the heating roller 1 and the pressure roller 2 as in the conventional example, and it is possible to cope with high-speed image formation.
[0021]
The reason why the load torque affects wrinkles is that the friction coefficient of the recording material 3 is different between the blank paper portion and the image portion 140, and the image portion, that is, the central portion of the recording material 3 in this example slips and the conveyance speed is increased. It is considered that the speed difference between the central portion of the recording material 3 and the white paper portion (both side portions) becomes smaller when the load torque with respect to the pressure roller 2 on the driven side is smaller.
[0022]
As in the conventional example, when the contact pressure between the heating roller and the pressure roller is set to 30 kgf to obtain a sufficient nip width, the rubber layer constituting the roller must be thickened. Generally, rubber does not have a good thermal conductivity compared to metal, etc., so to obtain a sufficient nip width with the configuration of the conventional example, the heating time of both rollers becomes longer and the heating energy must be increased. not. In this respect, if the generation of wrinkles is prevented by the load torque as in this embodiment, it is not necessary to reduce the contact pressure of both rollers, the heating time and heating energy of each roller can be prevented, and energy saving can be performed quickly and reliably. Fixing can be done. By mounting such a fixing device on the image forming apparatus, the printing speed can be increased while saving energy.
[0023]
In this embodiment, the means for reducing the load torque with respect to the pressure roller 2 is configured to bring the load member 10 into and out of contact with the pressure roller 2, but is not limited thereto. As this means, a gear is attached to the pressure roller 2, and the torque of a drive motor (not shown) for driving the pressure roller 2 is varied when forming an image on the first surface 3a and the second surface 3b. Is attached to the first surface 3a and the second surface 2a by rotating or rotating the driven member such as a paper discharge roller (not shown) driven by this gear. It may be changed when an image is formed on the surface 3b. Alternatively, a known electromagnetic brake is provided on the shaft 15 of the pressure roller 2 to electrically control the fluctuation of the load torque, or the rotational resistance of the bearings 18 and 18 of the pressure roller 2 is mechanically changed. It may be configured.
[0024]
An example of mechanically changing the rotational resistance of the bearings 18 and 18 includes attaching a gear to the pressure roller 2 and changing the driving or load torque as described above. This may be any configuration in which the pressure roller 2 is driven without transmitting the driving force to the gear when the first surface 3a is formed and the driving force is applied to the gear when the second surface 3b is formed.
[0025]
Further, in this embodiment, a color image is fixed, and in order to ensure releasability from an image forming agent such as toner, release oil is applied to the surfaces of the rollers 1 and 2. The structure which does not apply | coat this may be sufficient. When the release oil is not applied, it is desirable to form a fluorine-based resin layer of about 10 to 30 microns on the surfaces of the rollers 1 and 2 in order to improve the release property.
[0026]
5 and 6 show a modification of the fixing device. Hereinafter, the same components as those in the above-described embodiment will be denoted by the same reference numerals and detailed description thereof will be omitted. The fixing device shown in FIG. 5 is provided with a halogen heater 22 serving as a heating means, a roller 21 that rotates integrally with a shaft 23 is provided in parallel with the heating roller 1, and a belt wound around the roller 21 and the heating roller 1. 20 is a rotating body for heating. The belt 20 is in pressure contact with the pressure roller 2, and a mutual pressure contact portion with the pressure roller 2 is a nip portion 16. In this example, the oil application felt 5, the oil blade 6, the cleaning roller 7, and the separation claw 9 are in contact with the outer peripheral surface 20 a of the belt 20.
[0027]
In the fixing device shown in FIG. 6, a belt 33 wound around rollers 31 and 32 respectively supported by shafts 35 and 36 is used as a heating rotary member, and at least one of the shafts 35 and 36 constitutes a drive shaft. . The belt 33 is projected toward the pressure roller 2 by a heating and pressing unit 37 having a halogen heater 34 serving as a heating means. In this example, the pressure roller 2 is disposed so as to face the heating and pressure unit 37, and the opposite pressure portion is pressed against the surface 33 a of the belt 33 to form the mutual pressure contact portion as the nip portion 16. The oil application felt 5, the oil blade 6, the cleaning roller 7, and the separation claw 9 are in contact with the outer peripheral surface 33 a of the belt 33.
[0028]
Even with such a configuration, when the image is formed on the second surface 3a, the load member 10 is separated from the pressure roller 2 to reliably prevent the recording material 3 from being wrinkled for the reasons described above. .
[0029]
5 and 6, the heating rotator side is a belt and the pressing rotator is a pressure roller 2. However, the heating rotator shown in FIGS. 1 to 3 is used as the heating rotator, and the pressing rotator is used. As shown in FIGS. 5 and 6, it may be configured in a belt shape.
[0030]
【The invention's effect】
According to the first and second aspects of the invention, the occurrence of vertical wrinkles occurring in the latter half of the recording material during double-sided image formation can be reliably suppressed, and high-speed copying can be performed.
[0031]
According to the third aspect of the invention, since the oil is applied while pressing the rotary member for pressurization with the load member, it is possible to surely suppress the occurrence of vertical wrinkles occurring in the latter half of the recording material and enable high speed copying. At the same time, the peelability of the recording material can be improved.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a configuration of a fixing device according to an embodiment of the present invention and a state during duplex printing.
FIG. 2 is a diagram illustrating a state before printing in the fixing device illustrated in FIG.
FIG. 3 is a diagram illustrating a state during single-sided printing in the fixing device illustrated in FIG. 1;
FIG. 4 is a diagram illustrating a configuration of a driving system of the fixing device.
FIG. 5 is a diagram illustrating the configuration and operation of a fixing device according to a modification of the present invention.
FIG. 6 is a diagram illustrating the configuration and operation of a fixing device according to a modification of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Rotating body for heating 2 Rotating body for pressurization 3 Recording material 3a First surface 3b of recording material Second surface of recording material 4 Unfixed toner 10 Load member

Claims (4)

A heating rotator that is rotationally driven, a pressurizing rotator that is driven to rotate in pressure contact with the heating rotator, and a heating means that heats at least the heating rotator, the heating rotator In the fixing device capable of nipping and transporting the recording material between the pressure rotating body and the pressure rotating body, and fixing the unfixed toner on the recording material by heating and melting to form images on both sides of the recording material,
A fixing device comprising: means for reducing a load torque applied to the pressurizing rotator when an image is formed on the second surface of the recording material than when an image is formed on the first surface of the recording material. The fixing device according to claim 1.
The fixing device is characterized in that the means for reducing the load torque is a load member which is provided so as to be able to come into contact with and separate from the surface of the pressurizing rotating body and presses the rotating body. The fixing device according to claim 2.
The fixing device, wherein the load member is an oil application member. The fixing device according to claim 1.
The fixing device according to claim 1, wherein the means for reducing the load torque electrically controls fluctuations in the load torque .

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