JP2003295677A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the rubbing of an image at a leading edge when an envelope or cardboard passes, and to prevent toner scattering caused by peeling electrification when thin paper passes. <P>SOLUTION: In a fixing device having a pressuring force changing mechanism, a pressure abutting angle is simultaneously changed when pressuring force is changed, whereby the optimum pressuring force and the pressure abutting angle in accordance with recording material are realized. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine and a laser printer.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a laser beam printer, a developing device for developing a latent image drawn by laser light or the like, and a transfer means for transferring the developed toner image to a recording material, The one having a fixing device for fixing the transferred toner image on the recording material is mainly used. Among them, in a fixing device for fixing the transferred toner image onto a recording material, a heater, a fixing roller rotating while being kept at a predetermined temperature by a temperature sensor, and abutting on the fixing roller with a predetermined pressing force. The method in which the toner, which is the developer, is melted by heat and pressure by the pressure roller that is driven to rotate and the toner image is fixed on the recording material is the mainstream.

FIG. 6 shows a conventional laser beam printer as a typical example. The components of the laser beam printer of FIG. 6 will be described below. A laser scanner 10 and a photosensitive drum 11 are provided in the printer body (image forming apparatus body).
A print process unit 15 including a primary charger 12 and a developing roller 13, a transfer roller 16, a fixing device 30, a pair of conveyance rollers 18, a paper feed cassette 20, a paper feed roller (including a pickup roller) 21, and the like are installed. There is.

The sheet-shaped recording materials P stacked and stored in the paper feeding cassette 20 are fed by the paper feeding roller 2 which rotates counterclockwise.
The sheet is fed by 1, and is guided to the sheet metal 22 and is sent to the nip portion of the pair of conveying rollers 18.

Next, the recording material P is sent between the photosensitive drum 11 and the transfer roller 16 by the pair of conveying rollers 18.
The photosensitive drum 11 is rotating clockwise and is uniformly charged by the primary charger 12. Then, an electrostatic latent image is sequentially formed on the outer peripheral surface by the laser light L of the laser scanner 10, and then the electrostatic latent image is developed by the developing roller 13 to form a toner image. The toner image on the photosensitive drum 11 is sequentially transferred from the transfer roller 16 to the recording material P sent between the photosensitive drum 11 and the transfer roller 16. The recording material P on which the toner image has been transferred in this manner is guided to the fixing device 30 by the entrance guide 5, and is heated and pressed there to fix the toner image on the recording material P. After that, the recording material P is conveyed along the guide 38 by the fixed paper ejection conveyance roller pair 70, and is ejected onto the paper ejection tray 80 on the upper surface of the printer body by the paper ejection rollers 81.

In this conventional laser beam printer, the units such as the process cartridge 15 and the fixing device 30 and the roller relations such as the paper feed roller 21 and the transfer roller 16 are consumable parts, and the life of the product is reduced. It needs to be replaced several times. As the heat fixing device described above, a heat roller type device or a film heating type device is widely used.

In this conventional example, a heat roller type fixing device as shown in FIG. 7 will be described. In FIG. 7A, reference numeral 50 is a fixing roller, and as an example, an elastic layer 52 and PFA on a core metal 51 such as aluminum or iron,
A releasable resin layer 53 such as PTFE is provided, and the inside is heated by a heater 54. The temperature of the fixing roller 50 is detected as the surface temperature of the fixing roller 50 by the temperature detecting element 35 which is in contact with the fixing roller 50, and the surface temperature is determined by intermittently operating the heater 54 by the temperature control circuit. It is controlled to a predetermined temperature.

On the other hand, reference numeral 60 denotes a pressure roller which is rotated in pressure contact with the fixing roller 50. For example, a metal core 61 made of aluminum, iron or the like is provided on a metal core 61 having heat resistance and low hardness, such as silicon rubber or silicon sponge. And the like, and a coating layer 63 made of a conductive PFA resin containing carbon is provided on the surface thereof.

Reference numeral 55 denotes a fixing separation claw, which is formed of a heat resistant resin such as PEK and has its tip brought into contact with the fixing roller by a spring pressure of several tens N. 64 is a pressure separation guide, P
It is made of heat-resistant resin such as ET, and is in contact with the pressure roller with a PFA roller while keeping a constant gap. The fixing / separating claw 55 and the pressure-separating guide 64 prevent the recording material from winding around the fixing / pressure roller.

As a measure against offset, a method of applying a bias having the same polarity as the toner to the core metal of the fixing roller or a bias of the opposite polarity to the toner to the core metal or the surface of the pressure roller is used. In this conventional example, by the power feeding member,
An example of a fixing device that prevents an offset by applying a bias to the surface of the pressure roller will be described. Reference numeral 65 denotes a power feeding brush, which is installed at both ends of the roller so that the tip of the brush contacts the non-sheet passing area on the surface of the pressure roller. A fixing bias having a polarity opposite to that of the toner is applied from the power feeding brush to prevent electrostatic offset. At this time, the fixing roller is grounded from the core metal 51 to prevent the surface of the fixing roller from having a potential having a polarity opposite to that of the toner.

Reference numeral 1 is a pressing force changing lever. When the user manually lifts the pressing force changing lever 1 in the direction of the arrow, the discharge side of the pressure stay 3 is pushed down and the pressure position by the pressure spring 2 is regulated, so that the pressure roller is fixed. The force to press against is weakened.

FIG. 8 shows a schematic longitudinal view of the pressure stay.
The pressure roller is attached to the pressure stay via the ball bearings and the heat insulating bush on both ends of the core metal. By incorporating the pressure springs 2 at both ends of the fixing frame and the pressure stay, the pressure roller is pressed against the fixing roller together with the pressure stay. Further, the pressure separation guide 64 and the power feeding brush 65 are attached to the pressure stay, and always keep a constant distance from the pressure roller.

When the pressing force changing lever 1 is lifted,
The pressing force changing lever rotates with the fixed shafts 8 attached to both ends of the fixing frame as fulcrums. As a result, the discharge side of the pressure stay is pushed down, and the upstream side of the pressure stay is pushed up with the fixed shafts 4 attached to both ends of the fixing frame as fulcrums. At this time, the pressure stay is slid upward along the groove to the state shown in FIG. 7B.
The dotted lines in the figure show the positions of the pressing force changing lever, the pressure stay and the pressure roller in the state of (a).

Here, as shown in FIG. 9, the fixing roller 5
0 and the center position of the pressure roller 60 are connected, and the inclination α of the pressure roller from the vertical direction is defined as the pressure contact angle. After that,
This pressure contact angle is used as a parameter indicating the positional relationship between the fixing roller and the pressure roller. In this conventional example, when the pressing force changing lever is lifted, the pressing contact angle does not change and the pressing force decreases.

The pressing force changing mechanism may be manually operated by the user as in the conventional example, or may be automatically changed by rotating the pressing force changing lever. Further, as shown in FIG. 10, there is a type in which the pressing force changing lever has a plurality of fixing positions and the pressing force can be set in multiple stages. The pressing force becomes smaller as the pressing position of the pressing spring 2 to the pressing stay 3 is regulated downward. That is, FIG.
At 0, the pressing force decreases in the order of (a) → (b) → (c). There is also a type that can change the applied pressure by tightening screws. This is because the pressure roller is pressed against the fixing roller by the metal stay 6 as shown in FIG. 11, and the user can change it to a desired pressure by adjusting the tightening degree of the screw 7 with a driver. Is.

The pressing force changing mechanism as described above is used for the following purposes.

(1) Fixing by leaving it for a long time, and preventing deformation of the pressure roller elastic layer.

If the fixing device is left for a long time while the applied pressure is large, the elastic layer of the roller is deformed in the nip portion formed by the fixing and pressure rollers. As a result, abnormal noise when the fixing device is driven, a horizontal streak image of the roller cycle, and paper wrinkles are generated. Particularly, it occurs remarkably when the thickness of the elastic layer is large and the hardness of the elastic layer is large.

As a countermeasure against this, when the power is turned on and the standby is performed, the pressure is automatically changed to a small value. When the power is turned off for a long time, the user manually changes the pressure to a small value. Measures such as doing are implemented.

(2) Improving usability during jam processing By changing the pressing force to be small when a fixing jam occurs, the user can easily remove the jammed paper jammed in the fixing nip. In some cases, the user manually changes the pressing force to a small value, and in other cases, the pressing force is automatically changed to a small value when the door is opened.

(3) The pressure is optimized according to the recording material.

When the envelope is passed, the pressure is set small.

The envelope is a stack of two sheets, and if a difference in the conveying force between the fixing roller and the pressure roller is generated, the envelope is easily wrinkled. Therefore, the wrinkle is prevented by changing the pressing force to a small value. . At this time, the fixing property is deteriorated, but the throughput is reduced to lengthen the fixing nip passage time of the envelope.
Alternatively, it is usually practiced to secure the fixability by widening the space between sheets and warming the fixing and pressure roller between the sheets.

When the thin paper is passed, the fixing property is set to be small so that the fixing property is good. However, when the thin paper is liable to cause wrinkles, it is possible to prevent the wrinkles from occurring by reducing the pressing force. Since the load is not applied to the fixing and pressure roller, the life of the fixing and pressure roller is extended.

When a thick paper or a rough paper is passed, a wrinkle that sets a large pressing force is unlikely to occur, but for a thick paper or a rough paper, which has a poor fixing property, the fixing property is increased by increasing the pressing force. Improve.

[0026]

However, the following problems cannot be solved only by changing the pressing force according to the recording material.

"Rubbing of leading edge image" As shown in FIG. 12 (a), when the fixing roller is protruding beyond the line segment connecting the transfer nip outlet and the fixing nip inlet, envelopes, thick paper, and rough paper are Since the stiffness of the paper is strong, there is a problem that the front end of the paper touches the fixing roller and the unfixed image printed on the front end of the paper rubs.

The larger the pressure contact angle α is, the more the fixing roller is bulged to the upstream side, and the image tends to be disturbed by rubbing against the fixing roller before the leading edge of the paper enters the fixing nip.

Particularly, thick cardboard and envelopes having strong elasticity are conveyed in such a manner as to bridge the transfer nip outlet and the leading end of the paper, so that rubbing of the leading edge image easily occurs. Further, in the case of double-sided printing using an automatic double-sided machine, the curl on the first side also influences, and the image rubbing on the front side of the second side, which is even worse, occurs at the front end of the second side.

"Toner Scattering Due to Peeling Charging" This is a phenomenon in which peeling charging occurs when the trailing edge of the paper is separated from the fixing roller, and toner scatters thereafter in the fixing roller cycle. This is because the bias having the opposite polarity to the toner supplied to the surface of the pressure roller is also supplied to the back surface of the paper, and when the bias is separated from the fixing roller, the charge having the opposite polarity to the toner remains on the surface of the fixing roller. . The fixing roller is set to have the same polarity as the toner, but due to this phenomenon, the potential of the polarity opposite to that of the toner is applied at the position where the trailing edge of the paper is separated, and toner scatters at that position. Resulting in.

Particularly in the case of thin paper having a weak stiffness, the separation of the trailing edge of the paper from the fixing roller tends to be delayed, and when continuous paper feeding is performed, peeling charge is accumulated on the fixing roller, and the fixing pressure roller The potential difference between them cannot be taken. As a result, the force of electrostatically holding the toner on the paper becomes weak, and there is a case where "tailing" occurs in which the unfixed toner on the paper is scattered and fixed in the direction opposite to the paper conveyance direction.

As the pressure contact angle is smaller, the paper trailing edge separating position from the fixing roller is moved to the paper discharge side, and this phenomenon is more likely to occur. As compared with the paper trailing edge separating position from the fixing roller indicated by the arrow in FIG. 12A, when the pressure contact angle is small (b), the paper trailing edge separating position from the fixing roller indicated by the arrow is downstream. You can see that it is moving to the side. Further, as in this conventional example, the fixing bias surface power feeding method of feeding the actual electric charge to the surface of the pressure roller, and when the surface layer of the fixing roller is covered with an insulating PFA tube, this phenomenon remarkably occurs. To do.

Therefore, an object of the present invention is to provide an image fixing device having a pressing force changing mechanism, which can realize the optimum pressing force and pressure contact angle depending on the recording material.

[0034]

In order to solve the above problems, in a fixing device having a pressing force changing mechanism, the pressing contact angle is also changed when the pressing force is changed.

As a first aspect of the invention for achieving the above object, when an envelope is passed, the pressing force changing member is operated to change the pressing force to a smaller value than usual, and at the same time, the pressing contact is performed. Change the angle to a smaller value.

This is effective in preventing wrinkles and rubbing of the leading edge image when the envelope is passed.

As a second invention, in an image forming apparatus provided with a special paper mode, the pressing force and the pressure contact angle are automatically changed simultaneously according to the type of recording material.

As a result, it is effective in improving the fixing property when passing thick paper or rough paper and preventing rubbing of the leading edge image, at the same time as fixing when passing thin paper, extending the life of the pressure roller and preventing toner scattering due to peeling electrification. .

As a third invention, in an image forming apparatus equipped with an automatic double-sided machine, when performing double-sided printing, the pressing force and the pressure contact angle are automatically set simultaneously on the first and second sides of the recording material. change.

As a result, it is possible to prevent the leading edge image rubbing which is generated on the second surface of the recording material and has a poor level.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION (First Embodiment) In the first embodiment, in a fixing device provided with a pressing force changing mechanism with a pressing force changing member, when a paper is passed through an envelope, the pressing force and An example is shown in which the pressure contact angle is changed to be smaller than that in the normal state. FIG. 1 shows a sectional view of the fixing device according to the present embodiment. This fixing device is an example of a central reference that conveys a recording material having a maximum paper passing size of A3 (297 mm) width with reference to the paper passing center of the device, and the heater 54 outputs a rated output of 800 W when 120 V is input. The heater light distribution is also symmetrical with respect to the paper passing standard. The fixing roller 50 in this embodiment is a roller having a core metal 51 of stainless steel and a diameter of 50 mm. On the core metal having a thickness of 2.5 mm, there is an insulating silicone rubber layer 52 having a thickness of 250 μm,
The surface layer is a thin roller having a release layer 53 of PFA coated thereon. The pressure roller 60 is made of an aluminum core metal 61.
An elastic layer 62 of insulating silicon rubber is provided on the upper side, and a resistor 106 is provided on the surface layer.
Having a release layer 63 of conductive PFA of Ω and having a diameter of 40 mm,
A product having a hardness of 60 ° is used, and a nip width of about 8.0 mm can be formed between the fixing roller and the fixing roller by applying a pressure of 500 N. The pressure contact angle between the fixing roller and the pressure roller is 30 °. Further, as a countermeasure against toner offset and trailing, a fixing bias of +1 kV is applied to the surface of the pressure roller 60 by the power supply brush 65. The power feeding brush 65 is configured so that the tip of the brush contacts the non-sheet passing area on the surface of the pressure roller.
It is installed at both ends of the pressure roller. On the other hand, the fixing roller is grounded from the core metal 51 to prevent the surface from having a positive potential.

The recording material, which has been fixed by the pair of rollers, is conveyed by the fixing and discharging roller. The process speed is 240 mm / sec, and with this configuration, it is possible to print 50 sheets / minute with A4 transverse feed.

The fixing device in this embodiment is provided with a pressing force changing lever 1, and by lifting the lever in the direction of the arrow in FIG. 1, the fixing shaft 8 attached to both ends of the fixing frame serves as a fulcrum to apply the force. The pressure change lever rotates. As a result, the position of the pressure spring 2 that presses the pressure stay 3 is restricted downward, and the applied pressure becomes 100N.
At the same time, the upstream side of the pressure stay 3 is lifted upward with the fixed shafts 4 attached to both ends of the fixing frame as fulcrums.
At this time, since the pressure stay is slid along the groove by the fixed shaft 4, the pressure roller moves to the upstream side together with the pressure stay so that the pressure contact angle becomes 15 °.

When passing an envelope, the user sets the envelope position by raising the pressing force changing lever 1 in the direction of the arrow from the paper discharge side, and as shown in FIG. It is possible to change the pressing force and the pressing contact angle that are optimum for the paper. The dotted line in the figure indicates the normal time (Fig. 1
The positions of the pressing force changing lever, the pressure stay and the pressure roller at the time of (a)) are shown.

Since the two envelopes are stacked, the envelope is likely to be wrinkled while passing through the fixing nip. Therefore, the wrinkle of the envelope is prevented by reducing the applied pressure from 500 N to 100 N. At this time, although the fixing property is deteriorated, the fixing property can be secured by lowering the throughput to lengthen the fixing nip passage time of the envelope, or by widening the interval between sheets to heat the fixing and the pressure roller between the sheets. .

At the same time, the pressure contact angle is changed from 30 ° to 1
By reducing the angle to 5 °, the front end of the envelope does not come into contact with the fixing roller before the fixing nip enters, and the front end image rubbing can be prevented. Also, since the envelope has a strong paper,
Separability of the trailing edge of the paper from the fixing roller is good. Therefore, even if the pressure contact angle is small, the separation of the trailing edge of the paper from the fixing roller is quick, and toner scattering due to peeling charging does not occur.

At this time, the fixing roller 50 is fixed to the fixing frame. The fixing inlet guide 5 may be fixed to the fixing frame, or may be attached to the pressure stay 3. However, when attaching to a pressure stay,
Since the entrance guide is also tilted by the change in the pressure contact angle, the positional relationship between the fixing roller and the entrance guide changes greatly. Even in this case, it must be installed at a position where it functions as an entrance guide and does not affect the paper conveyance.

Further, in the present embodiment, the pressure separation guide 64
Is attached to the pressure stay 3 so that the positional relationship between the pressure roller and the pressure separation guide is not always changed. However, the pressure separation guide 64 is attached to the fixing frame side,
The roller contact position of the pressure separation guide may be changed according to the change of the pressure contact angle. At this time, the pressure separation guide is tilted about the fulcrum by the amount of change in the pressure contact angle while the pressure roller and the roller are always in contact with each other.

Further, in this embodiment, the power feeding brush 65 is attached to the pressure stay 3, so that the positional relationship between the pressure roller and the power feeding brush does not always change, but the power feeding brush 65 is placed on the fixing frame side. The contact position between the pressure roller and the tip of the power feeding brush may be changed according to the attachment and the change of the pressure contact angle. If the power supply brushes do not come into contact with each other when the pressure roller moves, the fixing bias will not be applied, so care must be taken in the installation location of the power supply brushes.

In addition, by putting an internal heater in the pressure roller,
When controlling the pressure roller temperature with a temperature detection element such as a thermistor, the temperature detection element is attached to the pressure stay 3, and if the temperature detection element is a contact type temperature detection element, the pressure roller is always in contact or non-contact with the same pressure. In the case of the temperature detecting element of the formula, it is desirable to always keep the same gap as the pressure roller. Even when a safety device such as a thermoswitch is attached to the pressure roller side, it is desirable to attach it to the pressure stay 3 so that the gap with the pressure roller is always kept constant.

The present embodiment can be similarly applied to the multi-step pressing force changing method and the screw tightening pressing force changing method described in the conventional example.

As described above, in the fixing device having the pressurizing force changing mechanism, when the envelope is passed, the pressurizing force is changed to be small to prevent the envelope from wrinkling and the pressurizing contact angle to be decreased. It is possible to prevent rubbing of the tip image.

(Second Embodiment) In the second embodiment, in an image forming apparatus provided with a special paper mode, the pressing force and the pressure contact angle are automatically set at the same time depending on the type of recording material. An example of changing is shown.

The image forming apparatus according to the present embodiment has a special paper mode, and a switch for setting special paper is provided on the operator operation panel of the apparatus (not shown), and the user selects the mode to print. Part of the process conditions can be changed depending on the type of material.

For example, when thick paper is set, the process conditions are partially changed in order to reduce the offset and improve the fixability by raising the fixing temperature and decreasing the throughput. For papers with a basis weight of 128 g / m2 or more, users are recommended to use thick paper settings.

FIG. 2 shows a sectional view of the fixing device of this embodiment. In the configuration of the fixing device in this embodiment, the description of the same parts as those in the first embodiment described above will be omitted.

In this embodiment, normally, the pressing force is set to 100 N and the pressing contact angle is set to 30 ° as shown in FIG. 2A, but in the case of thick paper setting, the pressing force changing lever 1 is used. Rotates in the direction of the arrow and the applied pressure is automatically set to 5 as shown in (b).
The pressure contact angle is 15 degrees. In this embodiment, the groove of the pressure stay 3 is in the opposite direction to that of the first embodiment. That is, when the position of the pressure spring rises upward, the upstream side of the pressure stay is pushed downward, and the pressure stay slides along the notch of the groove by the fixed shaft 4, so that the pressure roller moves. It is designed to move upstream.

In the case of thin paper in a normal state, the fixing property is good without applying a large pressing force, so the pressing force is set to 100N. As a result, a large load is not normally applied to the fixing and pressure rollers, which has the effect of extending the life of the rollers. Furthermore, the pressure contact angle is 30
By setting the angle to °, the separation of the trailing edge of the paper from the fixing roller is promoted to prevent toner scattering due to peeling charging.

On the other hand, when thick paper is set, the pressure is changed to 500 N in order to improve the fixing property. At this time, if the fixing property can be secured only by changing the pressing force, it is not necessary to change the process conditions such as the fixing temperature and the throughput by setting the thick paper. Further, in order to prevent rubbing of the leading edge image, the pressure contact angle is set to be 15 °, which is smaller than that in the normal state. Since thick paper has a strong elasticity, the separability of the trailing edge of the paper from the fixing roller is good. Therefore, even if the pressure contact angle is small, the separation of the trailing edge of the paper from the fixing roller is quick, and toner scattering due to peeling charging does not occur. When the thick paper setting is released and returns to the normal setting, the pressing force changing lever 1 reversely rotates to automatically return to the state (a).

As described above, in the image forming apparatus provided with the special paper mode, the pressurizing force and the press contacting angle are automatically changed simultaneously according to the kind of the recording material, so that the thick paper and the rough paper can be passed. It is effective in improving fixability when paper, prevention of rubbing of leading edge image, fixation when passing thin paper, extension of life of pressure roller, and prevention of toner scattering due to peeling charge. Further, since the pressurizing force and the pressurizing contact angle are automatically switched in association with the special paper mode setting, the user does not have to switch them manually, which leads to an improvement in usability.

(Third Embodiment) In the third embodiment, when double-sided printing is performed in an image forming apparatus equipped with an automatic duplexer, pressure is automatically applied to the first and second sides of the recording material. And an example of changing the pressure contact angle will be shown.

FIG. 3 shows an example of an image forming apparatus for performing double-sided printing on a recording material. When performing double-sided printing, first, the recording material P on the paper feed cassette 20 is fed one by one by the paper feed roller 21, and is conveyed to the conveyance roller pair 18 along the conveyance sheet metal 22. The recording material P on which the toner image has been transferred at the transfer portion is fixed by the fixing device 30 to obtain a fixed image. The paper discharged from the fixing device 30 is discharged downward by a flapper 37 rotatably attached, and is conveyed to a reversing roller 40 along a guide 39. While being supported by the guide 41, the recording material P is conveyed in the conveying roller pair 43 along the guide 42 while being reversed in the traveling direction by the forward and reverse rotations of the reversing roller 40. The conveying roller pair 43 conveys the recording material P to the conveying roller pair 18, and the recording material P is subjected to the image transfer fixing step again. The recording material P, on which the second surface is fixed on the transfer material, is ejected upward by the flapper 37 and is guided by the guide 3
Then, the sheet is conveyed along the sheet 8 and is ejected onto the sheet ejection tray 80 by the sheet ejection roller 81.

FIG. 4 is a sectional view of the fixing device of this embodiment. In the configuration of the fixing device in this embodiment, the description of the same parts as those in the first embodiment described above will be omitted.

In this embodiment, the pressing force is set to 500 N and the pressing contact angle is set to 30 ° on the first side as shown in FIG. 4 (a), but when the second side is printed, the pressing force is changed. By rotating the lever in the direction of the arrow, the pressing force is automatically set to 100 N and the pressing contact angle is 15 ° as shown in (b).

Since the second surface of the recording material which has passed through the fixing nip once on the first surface and is preheated has a better fixing property than the first surface, a pressure of 100 N is set. Further, on the second side, the recording material P has a chevron shape as shown in FIG. 5 due to the curl that is thermally generated when passing through the fixing device on the first side, and the rubbing of the leading edge image with a poor level occurs. It's easy to do. Therefore, on the second side of the recording material, the pressure contact angle is set to a small angle of 15 ° to prevent rubbing of the leading edge image having a poor level. If you want to print the first side again,
By the reverse rotation of the pressing force changing lever, the state of (a) is automatically returned.

As described above, in the image forming apparatus equipped with the automatic double-sided machine, when double-sided printing is performed, the pressing force and the pressure contact angle are automatically changed on the first side and the second side of the recording material. Poor level when printing on the second side. Effective for preventing rubbing of leading edge image.

[0067]

As described above, according to the present invention,
In a fixing device with a pressurizing force changing mechanism, by changing the pressurizing force and pressurizing contact angle to the optimum value according to the recording material, while ensuring the fixability, the front image rubbing during envelope and cardboard passage is prevented. , It is effective in promoting the separation of the trailing edge of thin paper.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a fixing device according to a first exemplary embodiment.

FIG. 2 is a cross-sectional view of a fixing device according to a second exemplary embodiment.

FIG. 3 is a sectional view of an image forming apparatus according to a third embodiment.

FIG. 4 is a cross-sectional view of a fixing device according to a third exemplary embodiment.

FIG. 5 is a diagram illustrating curling on the second side of a recording material.

FIG. 6 is a sectional view of a conventional image forming apparatus.

FIG. 7 is a sectional view of a conventional fixing device.

FIG. 8 is a schematic longitudinal view of a pressure stay.

FIG. 9 is a diagram showing a pressure contact angle.

FIG. 10 is a diagram showing an example of changing the multi-step pressing force.

FIG. 11 is a diagram showing an example of changing the screw tightening pressure.

FIG. 12 is a diagram illustrating “tip image rubbing”.

[Explanation of symbols]

1 Pressurization force change lever 2 pressure spring 3 pressure stay 4, 8 fixed shaft 50 fixing roller 60 pressure roller

   ─────────────────────────────────────────────────── ─── Continued front page    F term (reference) 2H027 DC02 EA18 FA13 FA30 FA35                 2H028 BA05 BB02 BB04                 2H033 AA06 AA15 AA23 AA46 AA47                       BB03 BB05 BB06 BB13 BB14                       BB15 BB18 BB28 BB34 CA01                       CA09 CA39

Claims (3)

[Claims] 1. A recording material on which an unfixed toner image is formed,
A heating and fixing device that permanently fixes the unfixed toner image on a recording material by passing through a fixing nip formed by pressing a fixing member and a pressure member against each other, and pressing force of the fixing member and the pressure member. Is variable, and when the pressing force of the fixing member and the pressure member is changed, the pressure contact angle of the fixing member and the pressure member is changed at the same time. 2. An image forming apparatus having a plurality of modes in which fixing process conditions can be changed and the setting of which can be changed by the user arbitrarily selecting a mode, according to the type of recording material. 2. The image forming apparatus according to claim 1, wherein the pressing force and the pressing contact angle of the fixing member and the pressing member are automatically changed simultaneously. 3. An image forming apparatus equipped with an automatic double-sided machine, when performing double-sided printing, automatically presses and pressurizes the fixing member and the pressing member on the first and second sides of the recording material. The image forming apparatus according to claim 1, wherein the contact angle is changed at the same time.