JP2002268437A - Fixing device, and image forming apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the defect that a recording medium coming out of a press- contact part is wound around a fixing roller in a fixing device which fixes a toner image on the recording medium by the action of heat and pressure by passing the recording medium through the press-contact part between the fixing roller and a pressure roller. SOLUTION: A voltage having the reverse polarity of the charge polarity of the rear surface of the recording medium is applied to a separation guide 9 positioned at the rear side of the recording medium coming out of the press- contact part of the fixing roller 3 and the pressure roller 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for fixing a toner image to a recording medium by passing a recording medium carrying a toner image through a pressure contact portion between a fixing member and a pressing member, and the fixing device. And an image forming apparatus having the same.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electronic copying machine, a printer, a facsimile, or a multifunction machine having at least two of these functions, a toner image formed on a recording medium is pressed by a fixing member. 2. Description of the Related Art A fixing device that fixes a toner image to a recording medium by passing the toner image through a member is employed. In such a fixing device, when the recording medium that has come out of the pressure contact portion between the fixing member and the pressing member winds around the peripheral surface of the fixing member, a recording medium conveyance trouble occurs, and the recording medium is wound around the fixing member. Various measures have been taken to prevent sticking. For example, when a recording medium separating unit that separates the recording medium from the fixing member is provided, or when the toner image is not formed at the leading end of the recording medium, and the leading end comes out of the pressure contact portion between the fixing member and the pressing member, A configuration is employed in which the leading end is easily separated from the peripheral surface of the fixing member. However, since the peripheral surface of the fixing member is generally charged, even if a toner image is not formed on the leading end of the recording medium, the leading end of the fixing member is a pressure contact portion between the fixing member and the pressing member. , The tip comes into close contact with the peripheral surface of the fixing member by electrostatic force. For this reason, it is difficult to completely prevent the recording medium from being wound around the fixing member by the recording medium separating unit. In particular, if the surface of the recording medium that has passed between the fixing member and the pressing member, the surface facing the fixing member is charged to a polarity opposite to the charging polarity of the fixing member.
The above problems are likely to occur.

[0003]

SUMMARY OF THE INVENTION It is a first object of the present invention to provide a fixing device which can prevent the above-mentioned problems from occurring, and a second object of the present invention is to provide an image forming apparatus having the fixing device. And

[0004]

According to the present invention, in order to achieve the first object, a pressure contact portion between a fixing member and a pressing member includes:
In a fixing device that passes a recording medium carrying a toner image and fixes the toner image on the recording medium, the recording medium is fixed such that the leading end of the recording medium that has exited the pressure contact portion is separated from the peripheral surface of the fixing member. A fixing device having a separation guide for electrostatic attraction is provided (claim 1).

At this time, a separation claw is provided for separating the recording medium that has exited from the pressure contact portion from the fixing member, and the separation guide is configured to electrostatically attract the recording medium surface facing the fixing member. When the separation guide is not subjected to an external force from the recording medium, the tip of the separation guide is located upstream of the separation claw in the surface movement direction of the fixing member. Advantageously, it is located on the side (claim 2).

In the fixing device according to the first aspect of the present invention, a voltage having a polarity that electrostatically attracts the surface of the recording medium opposite to the fixing member from the surface of the recording medium opposite to the fixing member is applied to the separation guide. When the polarity of the charge on the opposite surface is the same as the polarity of the voltage applied to the separation guide, it is advantageous that the voltage application to the separation guide is turned off. ).

Further, in the fixing device according to the first or third aspect, a voltage having a polarity to electrostatically attract a surface of the recording medium opposite to the fixing member from a surface of the recording medium opposite to the fixing member is applied to the separation guide. It is advantageous that the polarity of the voltage applied to the separation guide is switched in accordance with the charging polarity of the opposite surface (claim 4).

Further, in the fixing device according to any one of claims 1 to 4, a fluorine resin layer is provided on a surface side of the fixing member, and a surface of the recording medium facing the fixing member is positively charged. (Claim 5).

In order to achieve the second object, the present invention proposes an image forming apparatus having the fixing device according to any one of claims 1 to 5 (claim 6).

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a vertical sectional view schematically showing an image forming apparatus. In an image forming apparatus main body 31, an image forming means 32 for forming a toner image on a recording medium and recording on the image forming means is performed. The fixing device includes a feeding unit 33 that feeds a medium, and a fixing device 1 that fixes a toner image formed on a recording medium. First, the outline of the image forming means 32 will be clarified.

The image forming means 32 exemplified here has a drum-shaped photosensitive member 35 as an example of an image carrier, and when the photosensitive member 35 rotates clockwise, the surface of the photosensitive member is charged by a charging device 36. It is charged to a predetermined polarity. In this example, it is assumed that the photoconductor 35 is negatively charged. A laser writing unit 37 which is an example of an exposure device is provided on the charged surface.
Is irradiated with a light-modulated laser beam L emitted from
As a result, an electrostatic latent image is formed on the surface of the photoconductor. In this example, the surface portion of the photoconductor whose laser beam is irradiated and whose absolute value of the surface potential is reduced forms an electrostatic latent image, that is, an image portion. When passing through the developing device 38, the electrostatic latent image is visualized as a toner image by the negatively charged toner. The electrostatic latent image is visualized by reversal development. This toner image is transferred onto the recording medium P fed by the feeding means 33 by the transfer device 39 to which a positive transfer voltage is applied. In the image forming apparatus shown in FIG. 1, a transfer device 39 composed of a roller is used, but a transfer device using a corona discharger, a transfer belt, or the like may be employed. In any case, in order to electrostatically transfer the toner on the photoconductor to the recording medium during the transfer of the toner image, the transfer device needs to have a polarity opposite to that of the toner charged on the toner image formed on the photoconductor. Since a positive voltage is applied, the surface of the recording medium that has passed through the transfer area, that is, the surface in contact with the photoconductor 35 is positively charged. On the other hand, the transfer residual toner adhering to the photoconductor surface after the transfer of the toner image is removed by the cleaning device 40.

The feeding means 33 has a cassette 41 containing a recording medium P made of, for example, a resin sheet or transfer paper, and the uppermost recording medium P is sent out of the cassette 41 by the rotation of the feeding roller 42. The fed recording medium is fed to the transfer area between the photoconductor 35 and the transfer device 39 by the rotation of the pair of registration rollers 43, where the toner image on the photoconductor 35 is recorded as described above. It is transferred onto a medium. The recording medium to which the toner image has been transferred is continuously sent to the fixing device 1 as shown by an arrow A,
The toner image is fixed on the recording medium through the fixing device 1. The recording medium that has passed through the fixing device 1 is discharged onto a tray 44 outside the apparatus.

FIG. 2 is an enlarged view of the fixing device 1. The fixing device 1 shown here has a fixing roller 3 as an example of a fixing member and a pressing roller 4 as an example of a pressing member pressed against the fixing roller 3. FIG.
In the directions indicated by arrows. Fixing roller 3
Is heated by a heater 2 provided therein,
The surface temperature of the fixing roller 3 is detected by the thermistor 5, and based on the detection result, the power supply to the heater 2 is turned on,
By performing the OFF control, the surface temperature of the fixing roller 3 is maintained at a temperature suitable for fixing the toner image.

The recording medium P carrying the unfixed toner image transferred from the photoreceptor 35 has a pressure contact portion between the fixing roller 3 and the pressure roller 4 as shown by an arrow A in FIG. And passed through the pressure contact portion. At this time, heat and pressure are applied to the toner, and the recording medium P that has exited the pressure contact portion between the fixing roller 3 and the pressure roller 4
Is separated from the peripheral surface of the fixing roller 3 by a separation claw 6 that contacts the peripheral surface of the fixing roller 3. Thus, the toner image is fixed on the recording medium.

As described above, in the fixing device 1 of the present embodiment, the recording medium carrying the toner image is placed on the press contact portion between the rotating fixing member and the pressing member which also rotates, and the toner image is applied to the fixing member. The toner image is passed in the contact direction, and the toner image is fixed on the recording medium by the action of heat and pressure.

The recording medium P includes a fixing roller 3 and a pressure roller 4
When the toner passes through the gap, the toner is heated and melted, so that the toner has high adhesiveness to the peripheral surface of the fixing roller 3. Therefore, the surface side of the fixing roller 3 is coated with a fluorine-based resin having good releasability. As a result, it is possible to prevent the melted toner from migrating to the peripheral surface of the fixing roller 3 and to reduce the force of the recording medium wrapping around the peripheral surface of the fixing roller 3. Further, no toner image is formed at the leading end of the recording medium P in the transport direction, and thus the recording medium P that has exited between the fixing roller 3 and the pressure roller 4
Is easily separated from the peripheral surface of the fixing roller 3. Normally, a toner image is not formed over a range of, for example, 2 mm from the leading edge of the recording medium P, and this is a margin.

As described above, measures have been taken to prevent the recording medium P, which has come out of the pressure contact portion between the fixing roller 3 and the pressure roller 4, from being wound around the peripheral surface of the fixing roller 3.
It has been found that it is difficult to completely prevent the winding of the recording medium with only the above-described configuration. That is, if the recording medium surface on the side carrying the toner image to be fixed is referred to as a front surface as needed, and the opposite surface is referred to as a back surface, the front surface is, as described above, When the toner image is transferred from the photoconductor 35 to the recording medium P, the toner image is positively charged. Since the toner charging polarity of the toner image formed on the photoconductor 35 by the developing device 38 is negative, and the transfer device 39 is applied with a positive transfer voltage having a polarity opposite to the polarity, the surface of the recording medium is It is positively charged. On the other hand, since a fluorine resin layer is provided on the surface side of the fixing roller 3, the surface thereof is
And the surface is negatively charged, and is hardly attenuated once the surface is charged. For this reason, the leading end of the recording medium that has exited between the fixing roller 3 and the pressure roller 4 is electrostatically attracted to the peripheral surface of the fixing roller 3. Therefore, the recording medium cannot be separated from the fixing roller by the separation claw, and there is a possibility that a conveyance trouble of the recording medium, that is, a jam occurs. When the leading end of the recording medium is curled toward the side wound around the peripheral surface of the fixing roller, the tendency is further increased. In the image forming apparatus of the type that performs double-sided printing in which the front and back of the recording medium that has passed through the fixing device is reversed, the toner image is transferred again to the back surface of the recording medium, and the toner image is fixed by the fixing device, Easily curls.

Therefore, the fixing device 1 of this embodiment is configured as follows in order to prevent the above-mentioned problems.

The charging polarity of the back surface of the recording medium P, which has passed the pressure contact portion between the fixing roller 3 and the pressing roller 4, that is, the surface facing the pressing roller 4, depends on the type of the recording medium, its properties,
Although it differs depending on the type of the transfer device, the surface condition of the pressure roller 4 (whether it is coated with a fluororesin or conductive), the environment, or the difference between single-sided printing and double-sided printing. It is assumed that the back surface of the recording medium P is negatively charged as shown in FIG. The fixing device 1 shown in FIG. 2 is provided with upper and lower guide members 7 and 8 for guiding the recording medium P that has exited the fixing roller 3 and the pressure roller 4. A separation guide 9 made of a conductive material is fixed, and a positive high voltage is applied to the separation guide 9 by a power source (not shown), and the separation guide 9 is positively charged. The recording medium P that has passed between the fixing roller 3 and the pressure roller 4 is transported above the separation guide 9.

The leading end of the recording medium P, which has passed through the pressure contact portion between the fixing roller 3 and the pressure roller 4, is electrostatically attracted to the peripheral surface of the fixing roller 3 as described above, and is wound around the peripheral surface. Try to do this. However, the separation guide 9 is located below the leading end of the recording medium, and a voltage having a polarity opposite to the charging polarity of the back surface of the recording medium P is applied to the separating guide 9. Is attracted to the separation guide 9 by a large electrostatic force. For this reason, the leading end of the recording medium P is smoothly peeled off from the peripheral surface of the fixing roller 3, and the recording medium P is smoothly carried out of the fixing device while being guided by the separation guide 9 without causing a conveyance trouble. You. As described above, the separation guide 9 electrostatically attracts the recording medium so that the leading end of the recording medium that has come out of the pressure contact portion between the fixing member and the pressing member is separated from the peripheral surface of the fixing member, and the recording medium is recorded. It serves to guide the medium P. This is the same in the case of the separation guide of the example described later.

As described above, the charging polarity on the back surface of the recording medium P differs depending on various conditions and the charging amount also differs.
In accordance with this, it is necessary to set the voltage polarity applied to the separation guide 9 and its voltage value. For example, when the back surface of the recording medium P is positively charged, a negative polarity voltage is applied to the separation guide 9. The separation guide 9 can be made of, for example, a conductive resin (PC, PPS), a metal, or a metal coated with a resin.

In the fixing device 1 shown in FIG. 2, a fixing roller 3 is used as a fixing member, and a separation claw 6 is used as a recording medium separating means for separating the recording medium from the fixing member.
However, as shown in FIG. 3, a fixing member including an endless fixing belt 3A wound around a pair of belt winding rollers 11 and 12 may be used.
The pressure roller 4 is in pressure contact with one of the belt winding rollers 11 on the downstream side in the recording medium conveyance direction or both of the belt winding rollers via the fixing belt 3A. The pair of belt winding rollers 11 and 12, the fixing belt 3A, and the pressure roller 4 are respectively rotated in directions indicated by arrows in FIG. A heater 2A is provided in the other belt winding roller 12, whereby the fixing belt 3A is heated to a temperature suitable for fixing a toner image. Also in this case, the recording medium P carrying the toner image is fixed on the recording medium P carrying the toner image at the pressure contact portion between the fixing member composed of the fixing belt 3A and the pressure member composed of the pressure roller 4 as shown by the arrow A. The toner image is fixed on the recording medium P by applying heat and pressure to the toner and passing the toner image in a direction in which the toner image contacts the member. In this example, no separate recording medium separating means is provided, and instead, the radius of one of the belt winding rollers 11 is set to be small, and the recording medium that has come out of the pressure contact portion is applied to the belt winding roller 11. The recording medium P is configured to be separated from the peripheral surface of the fixing belt 3A without being able to follow the curved surface of the belt 3A. Belt wrapping roller 1
1 constitutes a recording medium separating means. This method is called a curvature separation method. The diameter of the winding roller 11 is set, for example, to 20 mm or less.

Since the surface of the fixing belt 3A is also coated with a fluorine-based resin layer, the surface thereof is negatively charged, and the recording medium P which has exited the pressure contact portion between the fixing belt 3A and the pressure roller 4 is formed. Is positively charged, the leading end of the recording medium P where the toner image is not formed is electrostatically attracted to the peripheral surface of the fixing belt 3A. In the example shown in FIG. Since the separation guide 9A to which a negative voltage is applied by the power supply is fixed to the upper guide member 7, the leading end of the recording medium P is electrostatically attracted to the separation guide 9A, and the fixing belt 3A Peeled from the peripheral surface. In this way, the normal curvature separation of the leading end of the recording medium P is reliably performed, and the recording medium P is smoothly carried out of the fixing device without being jammed while being guided by the separation guide 9A.

The fixing device 1 shown in FIG.
Although there is no difference from the fixing device shown in FIG.

The fixing device 1 shown in FIG.
And a separation claw 6 for separating the recording medium that has come out of the pressure contact portion between the fixing member formed of the pressure roller 4 and the fixing member from the fixing member. 3 are provided along the longitudinal direction. Separation guides 9B are arranged between the separation claws 6, and these separation guides 9B are swingably supported by the separation claws 6 via a shaft 13. At this time, when the separation guide 9B is not subjected to an external force from the recording medium P, the separation guide 9B balances the weight of the separation guide 9B and a spring (not shown) so that the leading end of the separation guide 9B Is the separation claw 6
Is located upstream (downward in the example in the figure) of the surface of the fixing member including the fixing roller 3 in the surface movement direction. A fixing member (the fixing roller 3 in this example) is provided on the separation guide 9B.
A negative voltage is applied by a power source (not shown) so as to electrostatically attract the surface of the recording medium facing the side, that is, the surface thereof.

The leading end of the recording medium P which has come out of the pressure contact portion between the fixing belt 3A and the pressure roller 4 hits the leading end of the separating guide 9B before hitting the leading end of the separating claw 6 and the separating guide 9B.
While being electrostatically attracted to B, the separation guide 9B is pushed up in the direction of arrow a. The state of the separation guide 9B at this time is shown by a chain line in FIG. When the separation guide 9B is pushed up in this way, the leading end of the recording medium P hits the separation claw 6 and is separated from the peripheral surface of the fixing belt 3A. The recording medium P is reliably separated from the peripheral surface of the fixing belt 3A by the cooperation of the electrostatic attraction force of the separation guide 9B and the separation claw 6. Next, the recording medium P is smoothly carried out of the fixing device 1 while being guided by the separation guide 9B.

Further, depending on the curl of the recording medium or the charging state of the recording medium, the leading end of the recording medium P may be located at the position indicated by the solid line.
However, even in such a case, the separation guide 9B is pressed by the recording medium P, rotates in the direction of the arrow b, and occupies the position shown by the broken line. Thus, the conveyance of the recording medium is not hindered. As described above, the recording medium P is smoothly peeled off from the fixing roller 3, and the occurrence of jam is prevented.

By the way, as described above, the charge polarity and the charge amount on the back surface of the recording medium P differ depending on various conditions, and in the example shown in FIG. Although the recording medium P is charged, for example, in the case of the recording medium P made of OHP paper, the back surface of the recording medium P may be positively charged as shown in FIG. At that time, the pressure roller 4
When the fluorine-based resin layer is also coated on the surface of the recording medium P, the surface thereof is also negatively charged.
Is electrostatically attracted to the peripheral surface of the pressure roller 4 and the fixing roller 3
Easier to separate from Conversely, if a positive voltage is still applied to the separation guide 9, the back surface of the recording medium P and the separation guide 9 repel each other, and the recording medium P is urged toward the peripheral surface of the fixing roller 3. Rather, it is difficult to separate from the fixing roller 3.

Therefore, as shown in FIG. 2, a voltage having a polarity to electrostatically attract the surface of the recording medium opposite to the fixing member from the surface of the recording medium opposite to the fixing member is applied to the separation guide 9. In this case, as shown in FIG. 5, when the charged polarity on the opposite surface is the same as the polarity of the voltage applied to the separation guide 9, the voltage application to the separation guide 9 is turned off. Is preferred. For example, in a general image forming apparatus, when OHP paper is used, the OHP mode is selected. When such a mode is selected, voltage application to the separation guide 9 is automatically performed as shown in FIG. It is turned off. In this way, the recording medium P made of OHP paper can be smoothly separated from the peripheral surface of the fixing roller 3 and can be smoothly carried out of the fixing device 1 while being guided by the separation guide 9.

In addition to turning off the voltage application to the separation guide 9 as described above, when the charging polarity on the back surface of the recording medium P is positive as shown in FIG. When a negative voltage is applied to the separation guide 9 by a power supply that is not connected, the leading end of the recording medium P is moved to the separation guide 9.
Therefore, the recording medium P can be more effectively separated from the fixing roller 3. When the back surface of the recording medium P is negatively charged, the polarity of the voltage applied to the separation guide 9 is switched to positive. A voltage having a polarity to electrostatically attract the surface opposite to the recording medium surface opposite to the fixing member is applied to the separation guide 9, and the voltage to the separation guide 9 is adjusted according to the charging polarity of the opposite surface. By switching the polarity of the applied voltage, the recording medium P is efficiently separated from the fixing roller 3 regardless of the charging polarity of the back surface of the recording medium P, and the separated recording medium is smoothly guided by the separation guide 9. Can be transported. Also in this case, it is possible to configure so that the voltage application to the separation guide 9 can be turned off according to various conditions.

In the above, an example has been described in which the fluorine resin layer is provided on the surface side of the fixing member, and the recording medium surface on the side facing the fixing member is positively charged. The present invention can be widely applied to fixing devices other than the above or an image forming apparatus having the fixing device.

[0033]

According to the first to fifth aspects of the present invention,
The problem that the recording medium wraps around the peripheral surface of the fixing member and causes trouble in transporting the recording medium can be effectively suppressed. According to the invention according to claim 6, an image forming apparatus provided with a fixing device exhibiting this effect can be provided. Can be offered.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus.

FIG. 2 is an enlarged view of a fixing device.

FIG. 3 is a diagram illustrating a fixing device different from the fixing device illustrated in FIG. 2;

FIG. 4 is a view showing still another fixing device.

FIG. 5 is a diagram illustrating another example of a fixing device.

FIG. 6 is a view showing still another fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing device 6 Separation claw 9 Separation guide 9A Separation guide 9B Separation guide P Recording medium

Claims (6)

[Claims] 1. A fixing device for fixing a toner image on a recording medium by passing a recording medium carrying a toner image through a pressure contact portion between a fixing member and a pressing member, wherein A fixing device provided with a separation guide for electrostatically attracting the recording medium such that a leading end portion is separated from a peripheral surface of the fixing member. 2. The image forming apparatus according to claim 1, further comprising a separation claw for separating the recording medium that has exited from the pressure contact portion from the fixing member, wherein the separation guide electrostatically attracts the recording medium surface facing the fixing member. The separation guide is configured to be swingably supported, and when the separation guide is not subjected to an external force from the recording medium, the tip of the separation guide is located upstream of the separation claw in the surface movement direction of the fixing member. Claim 1 which is located in
3. The fixing device according to claim 1. 3. A voltage having a polarity that electrostatically attracts a surface of the recording medium opposite to the fixing member and opposite to the surface of the recording medium opposite to the fixing member is applied to the separation guide. 2. The fixing device according to claim 1, wherein the voltage application to the separation guide is turned off when the polarity of the voltage applied to the guide is the same. 4. A voltage having a polarity for electrostatically attracting a surface of the separation guide opposite to the surface of the recording medium opposite to the fixing member is applied to the separation guide in accordance with a charging polarity of the opposite surface. 4. The fixing device according to claim 1, wherein the polarity of the voltage applied to the separation guide is switched. 5. The fixing device according to claim 1, wherein a fluorine-based resin layer is provided on a surface side of the fixing member, and a surface of the recording medium facing the fixing member is positively charged. . 6. An image forming apparatus comprising the fixing device according to claim 1.