JP2004191514A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of realizing a rapid fixing start-up and preventing the occurrence of a satin image thereby improving the image quality. <P>SOLUTION: A fixing belt 51 that is heated with a heat roll 52 is brought into pressure contact with a pressure roller 57 by a pressing member 56. The fixing belt 51 has an elastic layer. The pressing member 56 is constructed of different springs such that the exit side is higher in pressure distributed in a fixing nip than the entrance side. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a fixing device in an image forming apparatus such as a copying machine, a printer, and a facsimile.
[0002]
[Prior art]
Patent Document 1 JP-A-09-44014
Patent Document 2 JP-A-2002-148983
2. Description of the Related Art A heat roller (heat roll) type fixing device is widely used in an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction peripheral having a plurality of functions thereof. As a heat source of the fixing roller, a halogen heater using a halogen lamp has been often used.
[0003]
Due to recent environmental regulations and an increase in environmental protection consciousness, in various image forming apparatuses, power supply to the fixing heater is cut off during standby and power is supplied only when necessary, thereby reducing power consumption. In such an energy saving type image forming apparatus, the surface temperature of the fixing roller needs to quickly reach the set temperature during printing. In the conventional method of heating with a halogen heater, the thickness of the fixing roller base is reduced to 1 mm or less in thickness, thereby reducing the heat capacity of the fixing roller and rapidly raising the fixing roller to a set temperature. Can be raised.
[0004]
However, when the fixing roller is formed of a rigid body, the contact surface at the time of fixing does not follow irregularities on the recording medium. Even if the level is not a problem in the monochrome machine, it is particularly noticeable in the color machine. Therefore, it is essential to provide the fixing surface with elasticity for improving the image quality of the color machine.
[0005]
Therefore, in a color machine, a fixing device in which both a fixing roller and a pressure roller have an elastic layer (mainly silicone rubber) and heats the inside from inside by a halogen heater disposed inside the roller is mainly used. However, in such a roller fixing method, the heat capacity becomes enormous, heat transfer from the inside of the roller to the surface layer is poor, the start-up becomes extremely slow, and it is necessary to always perform residual heat during standby, thereby saving energy. Not be.
[0006]
As a countermeasure, a fixing method other than a roller method having an elastic layer in a color machine has been studied in recent years. For example, Patent Document 1 discloses a heating film including a heat generating layer that generates heat by electromagnetic induction due to the action of a magnetic field, and that at least the heat generating layer, the elastic layer, and the release layer are laminated in this order. A heating film, a pressurizing member that presses against the film to form a nip portion, and a magnetic field generating means that causes a magnetic field to act on the heating layer portion of the film by electromagnetic induction to produce a nip portion. A heating device has been proposed in which a material to be heated is introduced between the film and the pressing member and conveyed together with the film to heat the material to be heated.
[0007]
Further, in Patent Document 2, a thin heating belt having a conductive layer is induction-heated by a magnetic field generated by a magnetic field generating means, and a nip portion between the heating belt and a pressing member provided opposite to the heating belt forms In a fixing device for fixing an unfixed toner image, a pressing member having an elastic layer is disposed inside the loop of the heating belt, and the pressing member is pressed against the pressing member via the heating belt to perform fixing. A fixing device in which a nip portion is formed has been proposed.
[0008]
[Problems to be solved by the invention]
However, in the device described in Patent Document 1, since the excitation coil support opposed to the pressing member with the heating film interposed therebetween is not an elastic body, good image quality can be obtained even if the heating film has an elastic layer. And the pressure distribution inside the nip is not specified, so that an abnormal image called satin may occur. When the thickness of the elastic layer of the heating film is increased, the heat capacity of the film itself increases, and the rise time is significantly increased.
[0009]
Further, in the case of Patent Document 2, the rise time is almost zero and good paper peeling performance can be obtained even in a color image due to the pressure distribution in the nip portion, but the fixing belt itself does not have an elastic layer. Therefore, there is still a problem that the effect of improving the image quality is limited. Unless a certain amount of pressure is applied to the image surface on the exit side of the nip after using the elastic layer for the fixing belt, an abnormal image called a satin having minute gloss unevenness occurs. That is, even when good paper peeling performance is obtained, a matte texture often occurs.
[0010]
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems in the conventional fixing device and image forming apparatus, and to provide a fixing device and an image forming apparatus capable of simultaneously achieving high image quality and energy saving.
[0011]
[Means for Solving the Problems]
According to the present invention, there is provided an endless loop-shaped fixing member heated by a heating unit, a pressing member pressed against the fixing member, and a fixing member disposed in a loop of the fixing member. And a fixing member having a pressing member for pressing the recording material carrying an unfixed toner image through a nip formed by contact between the fixing member and the pressing member. Is composed of at least a base material layer, an elastic layer, and a surface release layer. The pressing member is configured such that a portion for pressing the fixing member to form the nip is formed of an elastic member, and the pressing member is This problem is solved by the fact that the pressure distribution of the fixing member to the pressure member is higher on the outlet side than on the inlet side of the nip.
[0012]
Moreover, in order to solve the above-mentioned problem, the present invention proposes that the hardness of the elastic member of the pressing member is larger on the outlet side than on the inlet side of the nip.
According to another aspect of the present invention, the elastic member of the pressing member is formed of solid rubber and foamed rubber, the solid rubber is provided on an outlet side of the nip, and the foamed rubber is provided on the nip. It is proposed to be located at the entrance side of the.
[0013]
Further, in order to solve the above-mentioned problem, the present invention provides a pressing member in which the elastic member has two layers made of solid rubber and foamed rubber, and the layer thickness of the solid rubber is more than the outlet of the nip from the inlet side. Suggest that it is getting bigger on the side.
[0014]
In order to solve the above-mentioned problem, according to the present invention, the elastic member of the pressing member is formed of foamed rubber, and the expansion ratio of the foamed rubber is smaller at the outlet side than at the entrance side of the nip. Propose that.
[0015]
Moreover, in order to solve the above-mentioned problem, the present invention proposes that the amount of deflection of the pressing member is smaller on the exit side than on the entrance side of the nip.
Further, in order to solve the above-mentioned problem, the present invention proposes that the pressing member has a thickness of a support member for supporting the elastic member, which is larger at an exit side than at an entrance side of the nip.
[0016]
Moreover, in order to solve the above-mentioned problem, the present invention proposes that the pressing member has a support member that supports the elastic member formed of ceramics.
In order to solve the above-mentioned problem, the present invention proposes that, in the pressing member, a portion of the support member supporting the elastic member, which comes into contact with the fixing member, is formed of ceramics.
[0017]
According to the present invention, the above-mentioned object is achieved by an image forming apparatus including the fixing device according to any one of claims 1 to 9.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus to which an example of a fixing device according to the present invention is attached. The overall configuration and operation of the image forming apparatus will be described later, and the fixing device will be described first.
[0019]
FIG. 2 is a sectional view showing a first embodiment of the fixing device. The fixing device 50A shown in FIG. 1 includes a fixing belt 51, a heating roll 52, a halogen heater 53 as a fixing heater, a pressing member 56 including an elastic member 54 and a supporting member 55, a pressure roller 57, and the like. These are housed in a fixing casing (not shown).
[0020]
A heating roll 52 and a pressing member 56 are arranged in a loop of the fixing belt 51 having an endless shape. The heating roll 52 has a built-in halogen heater 53. The pressing member 56 is installed opposite to the pressing roller 57 so that the elastic member 54 is in contact with the inside of the fixing belt 51, and is fixed to the pressing roller 57 by the pressing means (not shown) with the fixing belt 51 interposed therebetween. Pressing force is applied. That is, the fixing nip is formed by pressing the elastic member 54 of the pressing member 56 and the pressing roller 57 through the fixing belt 51.
[0021]
A constant pressure is applied to the pressing member 56 by a pressing unit (not shown) such as a spring, but the pressure distribution in the fixing nip portion (the pressure distribution in the paper advancing direction) is more than the inlet side (the right side in the drawing). The side (the left side in the figure) is configured to be higher. For example, different springs are used from the fixing member nip inlet side and the outlet side of the pressing member, and from the back side (the upper side in the figure), so that the pressure distribution is higher on the outlet side.
[0022]
When the pressure roller 57 is driven to rotate by a driving mechanism (not shown), the fixing belt 51 rotates clockwise in the drawing. The fixing belt 51 rotates while the inner side of the belt frictionally slides with the elastic member 54 and the supporting member 55. Further, the fixing belt 51 is suspended on a heating roller 52 heated by a halogen heater 53, and is heated at a contact surface thereof. In this example, in order to realize a quick start-up, the pressure roller 57 and the heating roller 52 are thin rollers having a metal pipe with a thickness of 1 mm or less.
[0023]
By passing the transfer paper P as a recording medium through a fixing nip where the fixing belt 51 and the pressure roller 57 are pressed against each other by the pressing member 56, the unfixed toner carried on the transfer paper P is changed by heat and pressure. The image is fixed on the transfer paper P.
[0024]
FIG. 3 is a cross-sectional view illustrating a configuration of the fixing belt 51.
As shown in this figure, the fixing belt 51 has a three-layer structure including a release layer 51a, an elastic layer 51b, and a base layer 51c, and the base layer 51c, the elastic layer 51b, and the release layer from inside the loop. 51a.
[0025]
The release layer 51a is a heat-resistant release layer made of a fluorine resin, a high release silicone rubber, or the like, and the thickness thereof is preferably in the range of 10 to 30 μm as a condition for obtaining good fixing properties, durability and thermal responsiveness.
[0026]
The elastic layer 51b is desirably made of a sufficiently soft and heat-resistant material. In this embodiment, silicone rubber is used. The thickness is desirably in the range of 100 to 300 μm. If the thickness is smaller than this, the effect of the elastic layer is not sufficiently utilized, and it is difficult to follow the unevenness of the surface of the recording medium. On the other hand, if the thickness is larger than this, the heat capacity of the fixing belt itself becomes large, which hinders the high-speed startup of the entire fixing device.
[0027]
The base layer 51c is made of a heat-resistant resin, and is made of polyimide, polyamideimide, polyetherketone (PEEK), or the like. A thickness of 50 to 125 μm is desirable. If the thickness is smaller than this, problems such as insufficient strength, low durability, low rigidity, and poor transportability of the rotating belt occur. In this case, the heat capacity of the fixing belt itself becomes large, which hinders the high-speed startup of the entire fixing device.
[0028]
The fixing belt 51 has an elastic layer, and the fixing belt 51 is pressed against the pressure roller 57 via the elastic member 54 of the pressing member 56, thereby realizing a quick start-up by the belt fixing method. Since the pressure distribution is configured to be higher on the outlet side than on the inlet side, sufficient pressurization is performed on the outlet side of the nip, and the occurrence of a matte image can be prevented.
[0029]
FIG. 4 is a sectional view showing a second embodiment of the fixing device. In the fixing device 50B shown in this figure, a heating roller is not used to heat the fixing belt 51, and a halogen heater 53 as a fixing heater is arranged outside the loop of the fixing belt 51. The other basic configuration is the same as that of the fixing device 50A of FIG.
[0030]
In the fixing device 50B of this embodiment, the halogen heater 53 is disposed outside the loop of the fixing belt 51 and at a position upstream of the fixing nip, and the fixing belt 51 is externally heated by radiant heat. A reflection plate 58 having an opening on the side of the fixing belt is provided around the halogen heater 53 to reduce radiation loss. The pressing member 56 is the same as the fixing device 50A of FIG. 2, and the configuration of the fixing belt 51 is also the same as that described with reference to FIG.
[0031]
In the fixing device 50B of this example, since there is no heating roll that suspends the fixing belt 51, the fixing belt 51 is driven by the pressure roller 57 while maintaining a cylindrical cross-sectional shape due to its own rigidity. As in the fixing device 50A of FIG. 2, the fixing is performed by passing the transfer paper P through the fixing nip between the fixing belt 51 and the pressure roller 57 pressed by the pressing member 56.
[0032]
FIG. 5 is a sectional view showing the configuration of a third embodiment of the fixing device. In the fixing device 50C shown in this figure, a halogen heater 53 as a fixing heater is disposed inside a pressure roller 57 without using a heating roll for heating the fixing belt 51. The other basic configuration is the same as that of the fixing device 50B of FIG.
[0033]
In the fixing device 50C of this example, the halogen heater 53 is disposed inside the pressure roller 57 to heat the pressure roller 57, and the fixing roller 51 is heated while the pressure roller 57 rotates. The pressing member 56 is the same as the fixing device 50A of FIG. 2, and the configuration of the fixing belt 51 is also the same as that described with reference to FIG.
[0034]
In the fixing device 50C of this example, since there is no heating roll for suspending the fixing belt 51, the fixing belt 51 is driven by the pressure roller 57 while maintaining a cylindrical cross-sectional shape due to its own rigidity. As in the fixing device 50A of FIG. 2, the fixing is performed by passing the transfer paper P through the fixing nip between the fixing belt 51 and the pressure roller 57 pressed by the pressing member 56.
[0035]
FIG. 6 is a sectional view showing the configuration of a fourth embodiment of the fixing device. The fixing device 50D shown in this figure does not use a halogen heater as a fixing heater, but heats the fixing belt 51 by a heating unit 59 which is a resistance heating unit. The other basic configuration is the same as that of the fixing device 50B of FIG.
[0036]
The heating means 59 includes a sliding heating layer 60, an electric insulating layer 61, and a resistance heating layer 62, and has a circular cross section in this example.
The sliding heating layer 60 is a base layer having high strength and high thermal conductivity such as metal. The resistance heating layer 62 is made of a metal thin film or a conductive paint containing a metal, receives power from electrodes (not shown), generates heat, and transmits heat to the sliding heating layer 60 via the electric insulating layer 61. The electric insulating layer 61 is made of ceramics, insulating paint, or the like, and prevents current flowing through the resistance heating layer 62 from leaking to the sliding heating layer 60.
[0037]
The heating means 59 is disposed inside the fixing belt 51, and the fixing belt 51 is suspended on a surface corresponding to the outside of the arc of the heating means 59. The heating means 59 heats the fixing belt 51 from the inside of the loop, and frictionally slides on the fixing belt 51 by the rotation of the fixing belt 51. Therefore, a friction layer having heat resistance may be provided on the sliding portion (surface layer) of the heating means 59. The pressing member 56 is the same as the fixing device 50A of FIG. 2, and the configuration of the fixing belt 51 is also the same as that described with reference to FIG. As in the fixing device 50A of FIG. 2, the fixing is performed by passing the transfer paper P through the fixing nip between the fixing belt 51 and the pressure roller 57 pressed by the pressing member 56.
[0038]
In the fixing device of each of the above-described embodiments, the fixing belt (film) system is used to achieve a quick rise, and the fixing belt has an elastic layer. Is applied to the recording medium (unfixed toner), so that an abnormal image such as a satin image can be prevented. That is, it is possible to simultaneously achieve the energy saving effect and the high image quality due to the startup of the fixing device in a short time.
[0039]
FIG. 7 is a cross-sectional view illustrating another example of a pressing member that presses the fixing belt 51 against the pressing roller 57. This pressing member 56B can be used as a pressing member of the fixing device of each of the above embodiments.
[0040]
The pressing member 56B of the present example includes an elastic member 54B made of a solid rubber 54a and a sponge (foamed rubber) 54b and a support member 55. The elastic member 54B has a solid rubber 54a on the outlet side of the fixing nip and a sponge 54b on the inlet side. When comparing the hardness of the solid rubber 54a and the hardness of the sponge 54b, the hardness of the solid rubber 54a is higher. Accordingly, when the fixing belt 51 is pressed against the pressure roller 57 in opposition to the pressure roller 57, the pressure on the outlet side in the nip is reduced by uniformly displacing (pressing) the pressing member 56B as a whole. It can be higher than the entrance side. That is, there is no need to use springs having different pressing forces as in the case of the pressing member 56 (the elastic member 54 is formed of one type of member) described above.
[0041]
FIG. 8 is a cross-sectional view illustrating still another example of a pressing member that presses the fixing belt 51 against the pressing roller 57. This pressing member 56C can be used as a pressing member of the fixing device of each of the above embodiments.
[0042]
The pressing member 56C of this example is similar to the pressing member 56B of FIG. 7 in that the elastic member 54C is made of solid rubber and sponge, but the arrangement and shape of the solid rubber and the sponge are different from those of the elastic member 54B of FIG. Is different.
[0043]
That is, in this example, as shown in FIG. 8, the solid rubber 54c and the sponge 54d of the elastic member 54C have a triangular cross section that is opposite to each other, and the sponge 54d is thick at the entrance side of the fixing nip. The solid rubber 54c is thin. The solid rubber 54c is configured such that the thickness thereof increases toward the nip outlet. When comparing the hardness of the solid rubber 54c and the hardness of the sponge 54d, the hardness of the solid rubber 54c is higher. Thus, when the fixing belt 51 is pressed against the pressure roller 57 in opposition to the pressure roller 57, the pressure on the outlet side in the nip is reduced by uniformly displacing (pressing) the pressing member 56C as a whole. It can be higher than the entrance side. That is, there is no need to use springs having different pressing forces as in the case of the pressing member 56 (the elastic member 54 is formed of one type of member) described above.
[0044]
Further, in the pressing member 56C of the present example, the sliding surface with the fixing belt 51 is the solid rubber 54a. Therefore, if fluorine rubber is used as the solid rubber material, the frictional resistance of the sliding surface can be suppressed and the fixing belt The transfer capacity can be improved.
[0045]
FIG. 9 is a cross-sectional view showing still another example of a pressing member for pressing the fixing belt 51 against the pressing roller 57. This pressing member 56D can be used as a pressing member of the fixing device of each of the above embodiments.
[0046]
In the pressing member 56D of this example, the elastic member 54D is composed of two types of sponges 54c and 54d having different expansion ratios. The sponge 54c on the exit side of the fixing nip has a smaller expansion ratio than the sponge 54d on the entrance side. Accordingly, when the fixing belt 51 is pressed against the pressure roller 57 in opposition to the pressure roller 57, the pressure on the outlet side in the nip is reduced by uniformly displacing (pressing) the pressing member 56D as a whole. It can be higher than the entrance side. That is, there is no need to use springs having different pressing forces as in the case of the pressing member 56 (the elastic member 54 is formed of one type of member) described above.
[0047]
FIG. 10 is a cross-sectional view showing still another example of a pressing member for pressing the fixing belt 51 against the pressing roller 57. This pressing member 56E can be used as a pressing member of the fixing device of each of the above embodiments.
[0048]
The pressing member 56E of this example is different from the pressing member 56 described in FIG. 2 in that a reinforcing member 63 is provided on the upper surface of the support member 55 (the side opposite to the pressing roller 57) at the nip exit side. The elastic member 54 is one kind of elastic member. Due to the reinforcing member 63, the strength of the support member 55 on the nip exit side becomes larger than that on the nip entrance side, and the amount of deflection on the nip exit side during pressurization becomes smaller than on the entrance side. Therefore, when the fixing belt 51 is pressed against the pressure roller 57 in opposition to the pressure roller 57, the pressure on the outlet side in the nip is reduced by uniformly displacing (pressing) the pressing member 56E as a whole. It can be higher than the side. Therefore, it is not necessary to use springs having different pressing forces.
[0049]
FIG. 11 is a cross-sectional view showing still another example of the pressing member for pressing the fixing belt 51 against the pressing roller 57. This pressing member 56F can be used as a pressing member of the fixing device of each of the above embodiments.
[0050]
In the pressing member 56F of this example, as shown in FIG. 11, the elastic member 54 is one kind of elastic member. However, the shape of the support member 55F is thin on the nip entrance side and thick on the exit side. Accordingly, the amount of bending of the support member 55F on the nip outlet side during pressurization becomes smaller than that on the inlet side. Therefore, when the fixing belt 51 is pressed against the pressure roller 57 in opposition to the pressure roller 57, the pressure on the outlet side in the nip is reduced by uniformly displacing (pressing) the pressing member 56E as a whole. It can be higher than the side. Therefore, it is not necessary to use springs having different pressing forces.
[0051]
FIG. 12 is a cross-sectional view showing still another example of a pressing member for pressing the fixing belt 51 against the pressing roller 57. This pressing member 56G can be used as a pressing member of the fixing device of each of the above embodiments.
[0052]
The pressing member 56G of this example uses a supporting member 55G made of ceramics having excellent properties in both heat insulation and strength as a supporting member. It is the same as the pressing member 55 in FIG. 2 except that the material of the supporting member 55G is different. In the pressing member 56G of this example, by using a material having a low thermal conductivity for the supporting member, it is possible to reduce the loss caused by transferring heat to the pressing member (the supporting member), and to further shorten the rising time. Can be. In each of the pressing members 56 and 56B to 56F described above, the support member can be made of ceramics.
[0053]
FIG. 13 is a cross-sectional view showing still another example of a pressing member for pressing the fixing belt 51 against the pressing roller 57. This pressing member 56H can be used as a pressing member of the fixing device of each of the above embodiments.
[0054]
The pressing member 56H of the present example is configured such that the portions on the inlet side and the outlet side of the fixing nip of the support member 55H (the portions on which the fixing belt 51 slides in contact) 55a, 55a are heat insulating portions. The supporting member main body portion (center portion) other than the heat insulating portions 55a, 55a is formed of a material having high strength but high thermal conductivity such as metal. In the present example, the heat insulating portions 55a, 55a are made of ceramics having excellent heat insulating properties and strength.
[0055]
In the pressing member 56H of the present example, it is possible to reduce the loss caused by transferring heat to the pressing member (supporting member) while maintaining the strength of the supporting member 55H (pressing member 56H), and further shorten the rising time. be able to. In each of the pressing members 56 and 56B to 56F described above, the portion of the support member that contacts the fixing belt 51 may be made of ceramic.
[0056]
FIG. 14 is a sectional view showing a fifth embodiment of the fixing device. The fixing device 50E shown in this figure directly heats the fixing belt 151 by an induction heating method without using a halogen heater as a fixing heater. That is, an induction heating means including a core 63 and an induction coil 64 is arranged in a loop of the fixing belt 151 near the upstream side of the fixing nip, and the magnetic flux generated by this induction heating means acts on the fixing belt 151, which will be described later. An eddy current is generated in the heat generating layer inside the belt to generate heat.
[0057]
FIG. 15 is a cross-sectional view illustrating the configuration of the fixing belt 151 used in this embodiment. The lower side of the figure is inside the belt loop, and the upper side of the figure is outside the belt loop. That is, the base layer 151d, the heat generating layer 151c, the elastic layer 151B, and the release layer 151a are sequentially stacked from the inside of the belt. The heat generating layer 151c is preferably made of a ferromagnetic metal such as nickel and iron. The thickness of the heat generating layer is desirably in the range of 10 to 100 μm. If the thickness is smaller than this, the electromagnetic energy cannot be completely absorbed, so that the heating efficiency deteriorates. On the other hand, if the thickness is larger than this, the rigidity of the fixing belt itself becomes too high, and the flexibility is reduced, which causes a problem in the transportability of the belt.
[0058]
Finally, the schematic configuration and operation of the printer shown in FIG. 1 will be briefly described. As the fixing device, the fixing device of each of the embodiments described above can be mounted. In FIG.
[0059]
The color laser printer 1 shown in FIG. 1 has a configuration in which a paper feed unit 2 is provided at a lower portion of the apparatus main body, and an image forming unit 3 is arranged above the paper feed unit 2. A paper discharge tray 40 is formed on the upper surface of the apparatus. The paper is fed from the paper supply unit 2, the image formed by the image forming unit 3 is transferred onto the paper, and is fixed by the fixing device 50, and the paper is discharged, as shown by the dashed line in FIG. The sheet is discharged to the tray 40. Note that manual sheet feeding (symbol: h) is possible from the side of the apparatus.
[0060]
Further, a double-sided device 90 is mounted on the side of the apparatus main body, and it is also possible to reverse the sheet after fixing and feed the sheet again via the double-sided conveyance unit 30. Further, it is possible to discharge the paper from the double-sided device 90 to a discharge tray (not shown) in the side direction of the device.
[0061]
The image forming section 3 is provided with a transfer / conveyance belt device 20 which is arranged so as to be inclined such that the paper supply side is downward and the paper discharge side is upward. Four image forming units 4M, 4C, 4Y, and 4Bk for magenta (M), cyan (C), yellow (Y), and black (Bk) in this order from the bottom along the upper running side of the transfer and transport belt device 20. Are arranged side by side.
[0062]
Since the configuration of each of the image forming units 4M, 4C, 4Y, and 4Bk is the same, the description will be made with the alphabets (M, C, Y, and Bk) indicating each color omitted.
Each image forming unit 4 includes a photosensitive drum 5 as an image carrier, and the photosensitive drum 5 is driven to rotate clockwise in the figure by a driving unit (not shown). Around the photosensitive drum 5, a charging roll, a developing device, a cleaning device, and the like are provided. The developing device is a two-component developing device including a toner and a carrier in this embodiment, and applies the toner carried on the developing roll to the photosensitive drum 5. The laser beam from the optical writing device 8 is applied to the photosensitive drum 5 from between the charging roll and the developing roll.
[0063]
The transfer conveyance belt 21 having an endless loop shape is wound around a driving roller 22, a driven roller 23, and two opposing rollers 24, 24. A transfer brush 28 is disposed at a position inside the upper running side of the transfer / conveying belt 21 at a position facing the photosensitive drum 5 of each of the color image forming units 4M, 4C, 4Y, and 4Bk so as to contact the belt 21. . A transfer bias is applied to the transfer brush 28. A paper suction roller 27 is provided above the driven roller 23 with the belt 21 interposed therebetween. The recording paper is sent out onto the belt 21 from between the driven roller 23 and the suction roller 27, and is conveyed while being electrostatically adsorbed on the transfer conveyance belt 21 by the bias voltage applied to the suction roller 27.
[0064]
The transfer / conveyance belt device 20 is held by a mechanism (not shown) in a state where the belt 21 is in contact with the four-color image forming units 4M, 4C, 4Y, and 4Bk (the photosensitive drums thereof) in the case of color printing, so In the case of (1), the state where the belt 21 is in contact with only the image forming unit 4Bk (the photosensitive drum thereof) is maintained.
[0065]
Next, the printing operation will be described.
In the image forming unit 4M for magenta, the surface of the photosensitive drum 5 is uniformly charged to a predetermined potential by the charging roll 6. In the exposure device 8, an LD (laser diode), not shown, is driven based on image data sent from a host machine such as a personal computer to irradiate the polygon mirror 7 with laser light, and reflects reflected light via a cylinder lens or the like. An electrostatic latent image to be developed with magenta toner is formed on the photoconductor drum 5M by guiding the photoconductor onto the photoconductor drum 5M. Toner is applied from the developing device 10 to the latent image to form a visible image of magenta toner.
[0066]
On the other hand, a sheet designated as a transfer material is fed from the sheet feeding unit 2, and the fed sheet is once hit by a pair of registration rollers 40 provided on the upstream side in the transport direction of the transfer transport belt device 20. At the time of color printing, in the transfer / conveyance belt device 20, the transfer / conveyance belt 21 is pushed up as described above, and the belt 21 is in contact with (the photosensitive drums of) the image forming units 4M, 4C, 4Y, and 4Bk of four colors. . Then, the sheet is fed onto the belt 21 in synchronization with the visible image, and reaches the transfer position facing the photosensitive drum 5M by running of the belt. At this transfer position, the visible image of the magenta toner is transferred to the sheet by the action of the transfer brush 28 disposed on the back side of the transfer belt 20.
[0067]
Similarly to the case of the magenta color, in the other image forming units 4C, 4Y, and 4Bk, visible images are formed on the surfaces of the respective photosensitive drums 5 by the respective toners. Each time the conveyed sheet arrives at each transfer position, the sheet is overlaid and transferred. Therefore, in the color printer of the present embodiment, a full-color image is overlaid and transferred onto a sheet in almost the same short time as a monochrome image.
[0068]
On the other hand, in the case of monochrome printing, in the transfer / conveyance belt device 20, the transfer / conveyance belt 21 is lowered as described above, and the belt 21 is in contact only with (the photosensitive drum of) the image forming unit 4Bk. Then, only in the black image forming unit 4Bk, a visible image of black toner is formed on the surface of the photosensitive drum 5, and the black sheet is fed onto the belt 21 in synchronization with the visible image of Bk. On the other hand, the Bk toner image is transferred.
[0069]
The sheet after the transfer of the toner image is separated from the transfer conveyance belt 21 and fixed by the fixing device 50. The sheet on which the fixing has been completed is discharged to a discharge tray 40 provided on the upper surface of the apparatus main body or transferred to the duplex apparatus 90.
[0070]
The paper can also be discharged from the duplex device 90 to a discharge tray (not shown) in the side direction of the device. In the case of double-sided recording, the sheet is turned upside down by the duplex device 90, and passed through the duplex transport unit 30 to the image forming unit 3 Paper can be fed again, and an image forming apparatus can be formed on the back of the paper. The paper after the double-sided recording is discharged to a paper discharge tray 40 on the upper surface of the apparatus or a paper discharge tray (not shown) in the side direction of the apparatus.
[0071]
As described above, the present invention has been described with reference to the illustrated examples. However, the present invention is not limited to these examples, and appropriate changes can be made. The configuration of each part of the image forming apparatus is also arbitrary, and the image forming apparatus is not limited to a printer, but may be a copying machine, a facsimile, or a multifunction peripheral.
[0072]
【The invention's effect】
As described above, according to the fixing device and the image forming apparatus of the present invention, the belt fixing method using the endless loop-shaped fixing member realizes quick start-up, and the fixing belt has an elastic layer, and The fixing belt is pressed against the pressing means via the elastic member of the pressing member, and the pressure distribution in the fixing nip is configured to be higher on the outlet side than on the inlet side. Pressurization can prevent generation of a matte image.
[0073]
According to the configuration of claim 2, since the hardness of the elastic member of the pressing member is larger at the outlet side than at the inlet side of the nip, the pressure distribution in the fixing nip portion can be reduced from the inlet side with a simple configuration at low cost. Can also be higher on the exit side.
[0074]
According to the structure of the third aspect, the elastic member of the pressing member is made of solid rubber and foamed rubber, and the solid rubber is arranged on the outlet side of the nip and the foamed rubber is arranged on the entrance side of the nip, so that the structure is simple. Therefore, the pressure distribution in the fixing nip can be made higher at the outlet side than at the inlet side at low cost.
[0075]
According to the configuration of the fourth aspect, the elastic member of the pressing member has two layers made of solid rubber and foamed rubber, and the layer thickness of the solid rubber is larger at the exit side than at the entrance side of the nip, so that it is simple. With this configuration, the pressure distribution in the fixing nip portion can be made higher at the outlet side than at the inlet side at low cost.
[0076]
According to the configuration of claim 5, since the elastic member of the pressing member is formed of foamed rubber and its expansion ratio is smaller at the exit side than at the entrance side of the nip, the inside of the fixing nip portion can be formed with a simple configuration at low cost. Can be made higher on the outlet side than on the inlet side.
[0077]
According to the configuration of claim 6, since the amount of deflection of the pressing member is smaller at the outlet side than at the inlet side of the nip, the pressure distribution in the fixing nip portion is reduced at the outlet side than at the inlet side with a simple configuration at low cost. Can be higher.
[0078]
According to the configuration of the seventh aspect, since the thickness of the support member that supports the elastic member is larger at the exit side than at the entrance side of the nip, the pressure member has a simple configuration and can reduce the pressure distribution in the fixing nip portion at low cost. Can be higher on the outlet side than on the inlet side.
[0079]
According to the configuration of the eighth aspect, since the support member for supporting the elastic member is formed of ceramic mix, the heat transfer loss can be reduced, and the rise time can be further reduced.
[0080]
According to the configuration of the ninth aspect, in the pressing member, a portion of the support member that supports the elastic member, which comes into contact with the fixing member, is formed of ceramic mixed material, so that heat transfer loss can be reduced and the rising time can be further reduced. it can.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of an image forming apparatus to which an example of a fixing device according to the present invention is attached.
FIG. 2 is a cross-sectional configuration diagram illustrating a first embodiment of a fixing device.
FIG. 3 is a cross-sectional view illustrating a configuration of a fixing belt used in the fixing device.
FIG. 4 is a cross-sectional configuration diagram illustrating a second embodiment of the fixing device.
FIG. 5 is a cross-sectional configuration diagram illustrating a third embodiment of the fixing device.
FIG. 6 is a cross-sectional configuration diagram illustrating a fourth embodiment of a fixing device.
FIG. 7 is a cross-sectional view illustrating another example of a pressing member that presses a fixing belt against a pressing roller.
FIG. 8 is a sectional view showing still another example of the pressing member.
FIG. 9 is a sectional view showing still another example of the pressing member.
FIG. 10 is a sectional view showing still another example of the pressing member.
FIG. 11 is a sectional view showing still another example of the pressing member.
FIG. 12 is a sectional view showing still another example of the pressing member.
FIG. 13 is a sectional view showing still another example of the pressing member.
FIG. 14 is a cross-sectional configuration diagram illustrating a fifth embodiment of the fixing device.
FIG. 15 is a cross-sectional view illustrating a configuration of a fixing belt used in the fixing device.
[Explanation of symbols]
50 Fixing device
51 fixing belt (endless loop fixing member)
51a Release layer
51b elastic layer
51c Base layer
52 heating roll
53 Fixing heater (heating member)
54 elastic member
55 support members
56 Pressing member
57 pressure roller (pressure member)
59 heating means
60 Sliding heating layer
61 Electrical insulation layer
62 Resistance heating layer
63 core
64 induction coil
151 fixing belt
151c Heating layer (ferromagnetic material)

Claims (10)

An endless loop-shaped fixing member heated by a heating unit, a pressing member pressed against the fixing member, and a pressing member disposed in the loop of the fixing member and pressing the fixing member against the pressing member are provided. A fixing device that performs fixing by passing a recording material carrying an unfixed toner image through a nip formed by contact between the fixing member and the pressing member;
The fixing member includes at least a base material layer, an elastic layer, and a surface release layer,
In the pressing member, a portion that presses the fixing member to form the nip is formed of an elastic member, and the pressure distribution of the fixing member to the pressing member by the pressing member is from the entrance side of the nip. The fixing device is also characterized in that it is higher on the exit side. 2. The fixing device according to claim 1, wherein a hardness of the elastic member of the pressing member is larger on an outlet side than on an inlet side of the nip. 3. The elastic member of the pressing member is formed of solid rubber and foamed rubber, wherein the solid rubber is arranged on an outlet side of the nip and the foamed rubber is arranged on an entrance side of the nip. Item 3. The fixing device according to item 1 or 2. The elastic member of the pressing member has two layers made of solid rubber and foamed rubber, and a layer thickness of the solid rubber is larger at an outlet side than at an inlet side of the nip. 3. The fixing device according to 1 or 2. The elastic member of the pressing member is made of foamed rubber, and the expansion ratio of the foamed rubber is smaller at an outlet side than at an inlet side of the nip, according to claim 1 or 2, wherein Fixing device. 2. The fixing device according to claim 1, wherein a bending amount of the pressing member is smaller on an outlet side than on an inlet side of the nip. 3. 7. The fixing device according to claim 6, wherein the pressing member has a support member that supports the elastic member, and a thickness of the support member is larger on an exit side than on an entrance side of the nip. 8. 8. The fixing device according to claim 1, wherein the pressing member has a support member that supports the elastic member formed of ceramics. 9. 8. The fixing device according to claim 1, wherein a portion of the pressing member that contacts the fixing member of the supporting member that supports the elastic member is formed by ceramics. 9. An image forming apparatus comprising the fixing device according to claim 1.

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