JP2001215842A - Fixing device, fixing method, and image forming apparatus - Google Patents

Abstract

(57) [Summary] [Problem] To provide a structure capable of controlling the amount of heat applied to a recording medium to be introduced into a fixing device according to the type of the recording medium and accurately preventing the offset according to the type of the recording medium. A fixing device is provided. SOLUTION: In a fixing device provided with a heating roller 12A capable of contacting a toner image carried on a recording medium and a pressure roller 12B opposed to and abutting against the toner image, the heating roller 12A and the pressure roller 12B are provided. The structure 17 is characterized in that the holding pressure on the recording medium can be changed according to the type of the recording medium.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device and an image forming apparatus, and more particularly, to a device for preventing offset of a member used for fixing an unfixed toner image.

[0002]

2. Description of the Related Art An image forming apparatus such as a copying machine or a printer is provided with a step of fixing a visible image transferred to a recording medium. In the fixing step, as an example, a configuration is known in which a heating roller having a built-in heat source and a pressure roller that is opposed to and abuts against the heating roller are combined. In this configuration, the unfixed toner image carried on the recording medium is fixed by heating and fusing while nipping and conveying the recording medium. The fixing device is provided with a configuration for preventing the toner on the heated recording medium from causing hot offset, transferring to the surface of the heating roller and being soiled.

[0003] As a configuration for preventing offset, for example, an oil application roller that can be brought into contact with and separated from the heating roller is provided, the oil application roller is brought into contact only when the heating roller is in operation, and follows the heating roller when it comes into contact. (For example, Japanese Patent Application Laid-Open No. Hei 5-88579, filed by the present applicant).

According to the configuration described in the above publication, the oil application roller does not come into contact with the heating roller for a long time.
There is no permanent deformation occurring in a part of the peripheral surface of the oil application roller and the surface is not deformed. Further, the surfaces of the heating roller and the oil application roller are constituted by low friction resistance surfaces. Even in this case, it is possible to enhance the cleaning effect on the surface of the heating roller by rotating the heating roller.

[0005]

The heating roller used in the fixing device is a member that consumes a great deal of electric power. In recent years, toners having a low melting point have been used in order to suppress power consumption. Assuming that low-melting toner is used, power consumption can be suppressed regardless of the type of recording medium introduced into the fixing device, but there are the following problems. Depending on the type of recording medium, hot offset tends to occur when a preset fixing temperature is used. In other words, the main recording medium used in image forming apparatuses such as copiers and printers is plain paper, but contains cellulose more than plain paper in order to improve properties such as light transmittance as compared with plain paper. Tracing paper with an increased rate may be used as a recording medium.
As described above, when the above-mentioned low melting point toner is used for plain paper having characteristics as a recording medium due to the difference in the contained components, in this case, the characteristics of light transmittance, the fixing temperature of the toner is lowered. In some cases, it is insufficient to prevent wrinkling of the racing paper. For this reason, the fixing temperature of the tracing paper is increased with respect to the fixing temperature of plain paper using the low melting point toner. However, when the fixing temperature is increased, a hot offset easily occurs with respect to the tracing paper. . The above publication does not discuss this point, that is, the offset phenomenon according to the type of recording medium.

On the other hand, the oil application roller can have not only the function of preventing offset but also the function of removing foreign matter such as paper powder attached to the heating roller. For this reason, normally, in a case where the heating roller comes into contact with the heating roller, the stopped state may be maintained without following the heating roller. Thereby, the same function as a known cleaning blade is exhibited. However, in a configuration in which a part of the peripheral surface abuts on the heating roller, foreign matter always accumulates only on a part of the peripheral surface in contact with the heating roller, and the foreign matter transfers to the heating roller and adheres to the recording medium. There is a risk of doing so.

SUMMARY OF THE INVENTION In view of the above-mentioned problems in the conventional fixing device, an object of the present invention is to control the amount of fixing heat to a recording medium according to the type of the recording medium introduced into the fixing device.
An object of the present invention is to provide a fixing device having a configuration capable of accurately preventing offset according to a type of a recording medium.

Another object of the present invention is to provide a fixing device having a structure capable of improving the cleaning quality when cleaning the surface of the heating roller by the offset prevention device.

Still another object of the present invention is to provide an image forming apparatus capable of preventing retransfer of toner and adhesion of foreign matter during fixing to a recording medium so as not to deteriorate image quality. It is in.

[0010]

According to the first aspect of the present invention,
In a fixing device including a heating roller capable of contacting a toner image carried on a recording medium and a pressing roller opposed to and abutting against the toner image, the heating roller and the pressing roller may include a type of the recording medium. The structure is such that the holding pressure on the recording medium can be changed according to the pressure.

According to a second aspect of the present invention, the heating roller and the pressure roller can change the holding pressure according to the amount of heat required for the recording medium.

According to a third aspect of the present invention, there is provided an offset preventing lubricant applying means which is capable of coming in contact with and separating from the heating roller in accordance with the type of the recording medium.

The invention according to claim 4 is characterized in that a structure capable of changing the holding pressure between the heating roller and the pressure roller is provided so as to be interlocked with the offset preventing lubricant applying means.

According to a fifth aspect of the present invention, there is provided a pressure control device in which the nipping pressure between the heating roller and the pressure roller is changed, wherein the pressure roller is movable in the direction of contact and separation with respect to the heating roller. Means, and the offset-preventing lubricant applying means is provided so as to be interlocked with a part of the driving force transmitting means for the pressurizing control means, and is provided with moving means for moving toward and away from the heating roller. It is characterized by:

According to a sixth aspect of the present invention, the pressure control means and the moving means use the same drive source.

According to a seventh aspect of the present invention, the anti-offset lubricant applying means rolls the peripheral surface of the heating roller before reaching a predetermined contact position from a separation position with respect to the heating roller. It is characterized by having a movable roller.

According to a still further aspect of the present invention, there is provided an image forming apparatus provided with a fixing device for fixing the unfixed image by heating and fusing the recording medium carrying the unfixed image while nipping and transporting the recording medium. A configuration for changing the amount of heat to the recording medium using a heating unit provided in the fixing device according to the type, and an anti-offset lubricant to the heating unit in conjunction with a configuration for changing the amount of heat in the heating unit And a configuration for performing supply control.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram for explaining a schematic configuration of an image forming apparatus using a fixing device according to an embodiment of the present invention. In FIG. 1, an image forming apparatus 1 of the present invention
Is an in-body discharge type image forming apparatus capable of discharging paper inside the housing without discharging the paper to the outside of the housing.
A paper discharge unit 2 is provided substantially at the center in the height direction, and a document reading unit 3 is provided at an upper part of the paper discharge tray 2 and an image forming unit 4 described below is provided at a lower part. . In this embodiment, the image forming unit 4 includes a photosensitive drum 5 corresponding to a drum-shaped latent image carrier, and the photosensitive drum 5 is rotated in a counterclockwise direction in the figure by a driving source (not shown). I do. Around the photoconductor drum 5, a charging device 6, a writing device 7, a developing device 8, a transfer device 9, and a cleaning device 10 for executing an electrophotographic copying process along the rotation direction are arranged. A paper feeder 11 is provided below the photosensitive drum 5, and a fixing device 12 and a paper output device are provided behind the transfer device 9 and in front of the paper output unit 2 in the paper feeding direction indicated by the dashed line arrow. 13 are arranged respectively.

The original reading section 3 is provided with a light source 3A and an optical path changing reflecting mirror 3B for scanning the original placed on the original placing table, and the reflected light from the original is read via a reading optical system 3C. The light is incident on an optical element 3D such as a CCD, and is output to the control unit 14 as image information of the original by the optical element 3D.

The writing device 7 irradiates the photosensitive drum 5 with scanning light from a polygon mirror 7A via a reflecting mirror and an imaging lens which form an imaging optical system with a semiconductor laser (not shown) to form an electrostatic latent image. Is formed.

The light emission of the semiconductor laser is controlled based on an image signal from the control unit 14. The control unit 14 not only controls the image information from the document reading unit 3 but also controls the light emission when used as a printer. The drive control of the semiconductor laser is performed by an image signal corresponding to a print signal and a transmission signal when used as a facsimile machine. As a result, the control unit 14 allows the image forming apparatus 1 to have a character as a digital multifunction peripheral having functions as a printer and a facsimile machine as well as a copying machine.

The paper feeding device 11 is a device for feeding out paper, and includes a paper feeding cassette 11A which can be pulled out toward the front of the image forming apparatus 1 (on the front side of the paper surface shown in FIG. 1) at the lower part of the housing. I have. The paper accommodated in the paper feed cassette 11A is lifted at the leading end in the feeding direction by the loading table 11B being given a rising behavior by the spring 11B1, and is held between the feeding roller 11B and the friction pad 11C. The paper whose leading end is sandwiched between the feeding roller 11B and the friction pad 11C is prevented from being double-fed by utilizing the difference in the frictional force between the two, and the registration roller 11D determines the matching relationship with the image position on the photosensitive drum 5. The sheet is fed toward the transfer portion of the photosensitive drum 5 where the transfer device 9 is set. As the sheet feeding mechanism, in addition to the above-mentioned sheet feeding cassette 11A, there is a case where an upside down sheet feeding tray 11E which forms a part of a side wall of the image forming apparatus 1 is used. 1, the sheet can be placed down from the storage position indicated by the solid line. The paper placed on the paper feed tray 11E is to be fed in the manual feed mode.
As in the case of feeding from 1A, the feeding timing is set by the registration roller 11D and the photosensitive drum 5 is fed to the transfer unit. In FIG. 1, reference numeral 11E1 denotes an auxiliary tray provided at the swinging end side of the paper feed tray 11E so as to be able to move forward and backward. The auxiliary tray 11E1 can be drawn out and used according to the sheet size.

In FIG. 1, the paper discharge unit 2 is formed of a space formed substantially at the center in the height direction of the housing 1A so that a hand can be inserted from the near side of the paper surface. Has become. The above-described paper feed cassette 11 </ b> A is provided below the paper discharge unit 2. As described above, the image forming apparatus 1 is configured such that the sheet discharge unit 2 and the sheet feeding cassette 11A are operated from the front of the image forming apparatus 1 (on the front side of the sheet of FIG. 1).

As shown in FIG. 2, the fixing device 12 includes a heating roller 12A and a pressure roller 12B opposed to the sheet conveyance path. Note that FIG. 2 shows a state different from the arrangement of the rollers shown in FIG. 1 for convenience of explanation. The heating roller 12A has a PFA, PTEF
The roller is made of a thermal conductor having a heat-resistant release layer coated thereon, and has a heat source 12A1 inside. Heat source 1
As 2A1, a halogen heater, an infrared heater (nichrome wire), or the like is used.

The pressure roller 12B has an outer peripheral surface made of a heat-resistant rubber layer such as silicon rubber.
When pressed against 2A, a part of the peripheral surface
2A, the contact width in the circumferential direction,
The nip width can be set. Pressure roller 1
2B can be rotated in conjunction with the rotation of the heating roller 12A by a driving unit (not shown) provided on the heating roller 12A side, and can pinch and convey the sheet. The pressing roller 12B is normally set in a state of being separated from the heating roller 12A by urging means (not shown).

A fixing temperature sensor 15 and a pressing temperature sensor 16 are provided on the outer peripheral surfaces of the heating roller 12A and the pressing roller 12B, respectively. The fixing temperature sensor 15 and the pressurized temperature sensor 16 are connected to a control unit 14. The control unit 14 controls the power supply to the heat source 12A1 according to the detection result, and the surface temperature of each of the rollers 12A and 12B is controlled. The temperature is kept constant.

Heating roller 12A and pressure roller 12B
Are configured to be able to move in a direction in which they come into contact with and separate from each other, and to be able to change the sandwiching pressure of the sheet by moving in a direction in which they make contact. In FIG. 2, the pressure control means 17 which corresponds to a configuration for changing the clamping pressure below the peripheral surface is provided on the rotation shaft 12B1 of the pressure roller 12B, which is normally given a habit of separating from the heating roller 12A. Is arranged.

The pressure control means 17 includes a swingable pressure urging lever 18 which is in contact with a lower surface of the rotating shaft 12B1 of the pressure roller 12B and a link member 19 which swings the pressure urging lever 18. And The pressure urging lever 18 can swing in a direction in which the pressure roller 12B is brought into contact with or separated from the heating roller 12A by the support shaft 18A, and in the case of this embodiment, swings in the vertical direction. The link member 19 is a member having one end engaged with one of the swing ends of the pressure urging lever 18 and capable of swinging in a horizontal plane by a support shaft 19A.

The other end of the link member 19 has a spring 2
0 is locked at one end, and the other end of the spring 20 is locked at one end of an anchor member 21 that can move in the horizontal direction. The spring 20 is a member for transmitting the movement of the anchor member 21 to the link member 19, and urges the link member 19 and the pressure urging lever 18 so that they are always engaged. The anchor member 21 is a member that transmits the oscillating power to the pressure urging lever 18 and the driving force to the later-described lubricant applying means for preventing offset by moving in the horizontal direction. A feed screw 23 that is rotated by a rotational force from a drive source using a stepping motor 22 is fastened to a part of the anchor member 21.

The feed screw 23 is formed on the rotation shaft of a driven gear 23A that meshes with an idle gear 24 that transmits the rotation force from the stepping motor 22. The feed screw 23 is used to move the anchor member 21 in accordance with the rotation direction and the rotation amount of the stepping motor 22. Move horizontally. Stepping motor 22
Is rotated in the counterclockwise direction in the direction of the arrow shown in the figure, the anchor member 21 moves in the direction shown by the symbol (B), and the link member 19 is moved via the spring 20 to the link member 19 with the support shaft 19A as a fulcrum. The other end where the spring 20 is locked is pulled toward the anchor member 21 side, and the pressure urging lever 18 is pushed by the link member 19 and swings in a direction to push up the pressure roller 12B. At this time, the contact pressure of the pressure roller 12B against the heating roller 12A,
The so-called pinching pressure on the paper is increased. When the stepping motor 22 rotates in a direction opposite to that described above, the pressure urging lever 18 swings in a direction away from the pressure roller 12B, and the contact pressure of the pressure roller 12B with the heating roller 12 is reduced.

The pressure roller 12 with respect to the heating roller 12A
When the anchor member 21 moves in the direction in which the contact pressure of B decreases, the return position is detected by the position sensor 25 provided near the anchor member 21. The position sensor 25 prevents the anchor member 21 from inadvertently returning too much so that the contact pressure after the pressing roller 12B and the heating roller 12 cannot be obtained. Therefore, even if the contact pressure with the pressure roller 12B after the heating roller 12 is the lowest, the state in which the sheet to be fixed can be nipped and conveyed is maintained.

In FIG. 2, the heating roller 12A is provided with an application roller 26, which is a means for applying a lubricant for preventing offset, so as to be able to contact and separate therefrom. The application roller 26 is
This is a roller formed by winding a heat-resistant felt around the surface of a metal cored bar. The felt on the surface is impregnated with silicone oil which is a lubricant for preventing offset. The application roller 26 is maintained so as not to follow when the heating roller 12A rotates by a one-way clutch provided between the application roller 26 and the rotation shaft. For this reason, when it comes into contact with the heating roller 12A, it is kept in a non-rotating state, so that it functions as a scraping member for collecting the toner and paper powder attached to the surface of the heating roller 12A, that is, a so-called cleaning member. .

As shown in FIG. 2, the application roller 26 is provided at a swinging end of a swinging lever 27 having a support shaft 27A as a fulcrum. The swing lever 27 has a configuration for moving the application roller 26 toward and away from the heating roller 12A in conjunction with the pressure control means 17 provided on the pressure roller 12B side. In this embodiment, the contact / separation link 28 is used as the contact / separation structure.
And a swing link 29. In FIG. 2, the swinging lever 27 has a swinging end opposed to one longitudinal end of a vertically movable contacting / separating link 28,
The other end in the longitudinal direction of 8 is opposed to one of the swing ends of a swing link 29 that can swing in a vertical plane with the support shaft 29A as a fulcrum. The other of the swing ends of the swing link 29 is engaged with a pin 21A provided on the anchor member 21. According to the moving direction of the anchor member 21, one of the swing ends and the contact / separation link 28 are connected. Raise and lower. The swing lever 27 swings in accordance with the elevating operation of the contact / separation link 28, and the application roller 26 provided at the swing end is moved toward and away from the heating roller 12A.

An arrangement is set such that a part of the peripheral surface can bite into the peripheral surface of the heating roller 12A when it comes into contact with the application roller 26 and the heating roller 12A, as shown in FIG. When it comes into contact with the heating roller 12A, a part of the peripheral surface thereof comes into pressure contact with the peripheral surface of the heating roller 12A and collapses. Therefore, the application roller 26 is
Before reaching the contact position with A, the heating roller 12A can come into contact with the peripheral surface of the heating roller 12A, and can roll with the swing of the swing lever 27 until reaching the contact position.

The stepping motor 22 for moving the anchor member 21 for setting the nipping pressure of the pressure roller 12B and the contact / separation state of the application roller 26 is controlled by a command from the control unit 14 according to the type of paper to be fixed. The rotation amount and the rotation direction are set accordingly. FIG. 4 is a block diagram for explaining the configuration of the control unit 14. In FIG. 4, the control unit 14 includes an operation panel 30 for specifying the type of paper, The temperature sensors 15 and 16 for pressure fixing and the home position sensor 25 are respectively connected to the input side, and a stepping motor (indicated by M in FIG. 4) 22 is connected to the output side.

In the control unit 14, the type of paper, that is,
The pressure control means 17 and the application roller 26 are simultaneously controlled in accordance with paper having different characteristics such as light transmittance depending on the contained components, and the control contents are as follows. When plain paper is to be fixed as paper, the contact pressure of the pressure roller 12B against the heating roller 12A is reduced, and the application roller 26 is
2A, when the tracing paper is to be fixed, the contact pressure of the pressing roller 12B is increased to increase the amount of fixing heat, and the coating is performed to prevent hot offset due to the fixing heat. The roller 26 is brought into contact with the heating roller 12A. When the latter case is set, there is a case where thin paper among the plain papers is to be fixed.

Since the present embodiment has the above configuration,
The operation of the control unit 14 will be described with reference to the flowchart shown in FIG. When the type of paper is designated from the operation panel 30, the control unit 14 determines whether the paper is tracing paper (ST1). In the case of tracing paper, the stepping motor (expressed as a motor in FIG. 5) 22 is rotated counterclockwise in FIG. 2 by a predetermined amount (ST2).

If it is not tracing paper, the position of the anchor member 21 is determined (ST3). The position of the anchor member 21 can be determined by a signal from the home position sensor 25. When the anchor member 21 is not at the initial position according to the signal from the sensor 25, the stepping motor 22 is returned to the initial position in FIG. Rotate clockwise (ST4). Position sensor 2
The rotation is continued until it is determined that the position of the anchor member 21 is determined by Step 5 (ST5).

When the stepping motor 22 rotates counterclockwise in step ST2, the anchor member 21 is drawn toward the stepping motor 22, so that the link member 19 swings in a horizontal plane via the spring 20, and the one end of the link member 19 The engaging pressure urging lever 18 is swung in a vertical plane to move the pressure roller 12B to the heating roller 12B.
Push up to A side. Thereby, the heating roller 12A
The nip width of the pressure roller 12B is increased, so that the heat receiving range on the paper side is widened and the amount of fixing heat is increased.

On the other hand, with the movement of the anchor member 21, the swing link 29 swings in a vertical plane via the pin 21A,
The swing lever 27 is connected via the contact / separation link 28 which is linked to this.
The application roller 26 provided at the swinging end of the roller moves toward the heating roller 12A.

At this time, before reaching the contact position after the heating roller 12 shown by a solid line in FIG. 3, the application roller 26 swings by coming into contact with the peripheral surface of the heating roller 12A as shown by a dashed line. The roller 27 rolls on the peripheral surface of the heating roller 12A in accordance with the swing of the lever 27. Thereby, when the contact position indicated by the solid line is reached, a new peripheral surface of the application roller 26 faces the heating roller 12A. Therefore, each time the swing lever 27 swings, the application roller 26 causes a new surface to face the heating roller 12A and stops rotating when the heating roller 12A rotates, so that deformation of the peripheral surface is prevented. Needless to say, there is no accumulation of foreign matter as in the case where the same surface is in contact, and it is possible to prevent the heating roller 12A from being soiled. As a result, when the contact area of the sheet with the heating roller 12A is increased to increase the amount of fixing heat, hot offset is likely to occur. Hot offset can be prevented beforehand by contacting the heating roller 12A.

When fixing plain paper, the pressure between the pressing roller 12B and the heating roller 12A is reduced, and the coating roller 26 is separated from the heating roller 12A. Can be prevented from deteriorating with time, and the consumption of the lubricant for preventing offset can be reduced.

By preventing the re-transfer of the deposit from the application roller 26 to the heating roller 12A, the contamination of the sheet during the fixing process is prevented, so that a defective image can be prevented from occurring.

[0044]

According to the first and second aspects of the present invention,
Since the pinching pressure on the recording medium can be adjusted to match the amount of heat according to the type of recording medium, hot offset can be applied even when fixing to plain paper or tracing paper that can fix even at low heat quantity. It is possible to make it hard to cause.

According to the third aspect of the present invention, it is possible to set the position of the means for applying the lubricant for preventing offset to the heating roller in accordance with the type of the recording medium. In this case, hot offset can be efficiently prevented by applying an anti-offset lubricant, and if the recording medium is unlikely to be hot-applied, excessive application of the anti-offset lubricant is stopped. This makes it possible to extend the service life of the application unit.

According to the fourth and fifth aspects of the present invention, the pressure control means for changing the holding pressure between the heating roller and the pressure roller contacts the offset preventing lubricant applying means to the heating roller. Since the moving means for separating can be interlocked with, the offset controlling lubricant applying means adjusts the clamping pressure according to the type of the recording medium and the offset preventing lubricant applying means contacts the heating roller at the same time. Can be set automatically. Therefore, when a recording medium that requires a large amount of fixing heat is used, hot offset that easily occurs due to the amount of heat can be prevented by applying the lubricant.

According to the sixth aspect of the present invention, since the pressurizing control means and the moving means use the same driving source, the apparatus can be adapted to the type of the recording medium without increasing the size and complexity of the apparatus. Hot offset can be prevented.

According to the seventh aspect of the present invention, the roller used as the offset preventing lubricant applying means before reaching the contact position of the preset offset preventing lubricant applying means with respect to the heating roller is provided. Since the rolling can be performed on the peripheral surface of the heating roller, a new surface can be brought into contact with the peripheral surface of the heating roller. Therefore, the roller of the anti-offset lubricant applying means, which is a lubricant application surface and functions as a cleaning surface, does not deform a part of the peripheral surface, and furthermore, the foreign matter on the heating roller due to foreign matter accumulation Can be prevented from retransferring.

According to the eighth aspect of the present invention, the unfixed toner image can be fixed by changing the contact pressure between the heating roller and the pressure roller according to the type of recording medium. It is possible to prevent the occurrence of fixing failure when using the melting point toner, and to prevent the adverse effects such as wrinkles due to the difference in the characteristics of the recording medium, and it is possible to perform satisfactory fixing regardless of the type of the recording medium. Become.

According to the ninth aspect of the present invention, the supply of the offset preventing lubricant to the heating means is controlled in conjunction with the arrangement for changing the amount of heat to the recording medium according to the type of the recording medium. With this arrangement, when a fixing heat amount that easily causes a hot offset is set according to the type of the recording medium, the hot offset can be automatically prevented.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus using a fixing device according to an embodiment of the present invention.

FIG. 2 is a perspective view for explaining a main configuration of a fixing device according to an embodiment of the present invention.

FIG. 3 is a schematic diagram for explaining the operation of the fixing device shown in FIG. 2;

4 is a block diagram for explaining a configuration of a control unit of the fixing device shown in FIG.

FIG. 5 is a flowchart for explaining the operation of the control unit shown in FIG. 4;

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 12 Fixing apparatus 12A Heating roller 12B Pressure roller 14 Control part 17 Pressure control means 18 Pressure urging lever used for pressure control means 19 Link member used for pressure control means 21 Anchor member used for moving means 22 Stepping motor 26 serving as a drive source 26 Application roller serving as lubricant applying means for offset prevention 28 Contacting / separating link used for moving means 29 Swinging link used for moving means 30 Operation panel for specifying the type of recording medium

Claims (9)

[Claims] A fixing roller for fixing an unfixed toner image on the recording medium, the heating roller including a heating roller capable of contacting the unfixed toner image carried on the recording medium; In the fixing device, the heating roller and the pressure roller are configured to be capable of changing a holding pressure on the recording medium according to a type of the recording medium. 2. The fixing device according to claim 1, wherein the nipping pressure of the heating roller and the pressing roller can be changed according to the amount of heat required for the recording medium. 3. The fixing device according to claim 1, further comprising an offset preventing lubricant applying means which can contact and separate from the heating roller in accordance with a type of the recording medium. 4. The fixing device according to claim 3, wherein the structure capable of changing the holding pressure between the heating roller and the pressure roller and the offset preventing lubricant applying means are provided in an interlockable manner. apparatus. 5. A structure for changing a holding pressure between the heating roller and the pressure roller, comprising: pressure control means capable of moving the pressure roller in a direction of coming and going with respect to the heating roller; The lubricant applying means for prevention is provided so as to be interlocked with a part of the driving force transmitting means for the pressurizing control means, and comprises a moving means for moving toward and away from the heating roller. Item 5. The fixing device according to Item 4. 6. The fixing device according to claim 5, wherein the same driving source is used for the pressure control unit and the moving unit. 7. The offset preventing lubricant applying means,
6. A roller capable of rolling on a peripheral surface of the heating roller before reaching a preset contact position from a separation position with respect to the heating roller.
A fixing device according to any one of the preceding claims. 8. A fixing method for heating and fixing an unfixed toner image carried on a recording medium by a heating roller and a pressure roller in contact with the heating roller. A fixing method characterized by fixing the unfixed toner image by changing a contact pressure with a pressure roller. 9. An image forming apparatus provided with a fixing device for fixing a non-fixed toner image by heating and fusing the recording medium carrying the unfixed toner image while nipping and transporting the recording medium. A configuration for changing the amount of heat to the recording medium using a heating unit provided in the fixing device, and a lubricant for preventing offset to the heating unit in conjunction with a configuration for changing the amount of heat in the heating unit. An image forming apparatus having a configuration for performing supply control.