JP2004286932A - Belt fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt fixing device capable of preventing the occurrence of an image noise even when a cardboard is passed through. <P>SOLUTION: The belt fixing device 10 is provided with an endless sheet-like fixing belt 12 which is stretched to be laid between a rotatable heat roller 14 and a nip forming member 20 fixedly arranged so as not to be rotated, a rotary-driven pressure roller 50 which is brought in press contact with the nip forming member 20 across the fixing belt 12 and which has a contact part with the fixing belt 12 functioning as a fixation nip 40, and the fixing belt 12 is rotated while sliding on the nip forming member 20 in accordance with the rotary driving of the pressure roller 50, the nip forming member 20 has an elastic layer 20b formed on a base material 20a. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a belt fixing device used in an electrophotographic image forming apparatus.
[0002]
[Prior art]
Prior art documents related to the present invention include the following.
[0003]
[Patent Document 1]
JP 2001-356625 A [Patent Document 2]
JP-A-11-133776 [Patent Document 3]
JP-A-2002-148979
Patent Documents 1 to 3 disclose, as shown in FIG. 9, a rotatable pressure roller 101 having an elastic layer 101a made of sponge or rubber on an outer peripheral portion, a fixing belt holding section 102, and a fixing belt holding section. A belt fixing device 100 including an endless sheet-shaped fixing belt 103 wound around 102 is disclosed.
[0005]
In the belt fixing device 100, a contact portion between the pressure roller 101 and the fixing belt 103 forms a fixing nip 104, and the fixing belt 103 is moved by the pressure roller 101 to a nip forming member 102 a of the fixing belt holding unit 102. The pressure roller 101 is pressed and rotated in the direction of the arrow C to rotate in the direction of the arrow D. Further, the pressure roller 101 is heated by a heater lamp 105 as a heat source disposed therein, so as to be heated to a predetermined fixing temperature (for example, 180 ° C.). Then, in the belt fixing device 100, after the pressure roller 101 is heated to a predetermined temperature, the recording medium 107 on which the unfixed toner image 106 is formed is introduced into the fixing nip 104 in the paper passing direction indicated by an arrow E, and When passing through the fixing nip 104, the toner image 106 is heated and fixed on the recording medium 107. As described above, by using the nip forming member 102a that is fixedly arranged so as not to rotate, the wide fixing nip 104 is formed to secure the nip time, and the heat capacity is reduced to shorten the warm-up time. ing.
[0006]
However, in the belt fixing device 100 having the above-described configuration, since the nip pressure distribution in the paper passing direction is not uniform, a difference occurs in the amount of deformation in the elastic layer 101a in the fixing nip 104, and the conveyance speed of the recording medium 107 in the fixing nip 104 is reduced. This causes a problem that image noise is generated or torque is increased. Therefore, in another patent application filed on the same date as the present application, the present applicant made the shape of the nip forming member 102a in the fixing nip 104 substantially the same as the shape of the pressure roller 101, that is, added the nip forming member 102a. A belt in which the surface facing the pressure roller 101 is curved along the outer peripheral surface of the pressure roller 101 so that the nip pressure distribution is made substantially uniform and fluctuations in the conveyance speed of the recording medium 107 in the fixing nip 104 are suppressed. A fixing device is proposed.
[0007]
[Problems to be solved by the invention]
In the belt fixing device in which the conveyance speed fluctuation is suppressed, when thin paper such as plain paper is passed through the fixing nip 104, the nip pressure distribution is substantially uniform in the paper passing direction as shown by a solid line in FIG. When thick paper such as thick paper is passed, the radius of curvature of the paper contacting the pressure roller 101 is slightly smaller than the radius of curvature of the outer peripheral surface of the pressure roller 101, so that the elastic layer 101a in the fixing nip 104 is It is greatly deformed on the inlet side and the outlet side compared to the part. As a result, as shown by the dotted line in FIG. 10, the nip pressure distribution increases at both ends in the sheet passing direction and decreases at the center in the sheet passing direction. As a result, there is a problem that the conveyance speed of the recording medium 107 fluctuates and image noise occurs.
[0008]
SUMMARY OF THE INVENTION It is an object of the present invention to provide a belt fixing device capable of preventing occurrence of image noise even when thick paper is passed.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides
An endless sheet-like fixing belt wound around a rotatable or non-rotatable heating member and a non-rotatably fixed nip forming member, and pressed against the nip forming member with the fixing belt interposed therebetween. And a rotatable pressure roller having a fixing nip at a contact portion with the fixing belt. The fixing belt slides on the nip forming member by rotating the pressure roller. The nip forming member is configured by providing an elastic layer on a base material.
[0010]
In the belt fixing device having the above-described configuration, since the elastic layer is provided on the base material of the nip forming member, the elastic layer of the nip forming member is deformed when the thick paper is passed, so that the nip is formed at the entrance side and the exit side of the fixing nip. Although the pressure is slightly higher than the central part of the nip, the nip pressure distribution in the fixing nip becomes substantially uniform in the paper passing direction. As a result, fluctuations in the paper conveyance speed are suppressed, and image noise can be prevented.
[0011]
The thickness of the elastic layer is preferably 0.3 to 2.0 mm.
[0012]
A low friction layer having a thickness of 5 to 300 μm may be provided on the elastic layer.
[0013]
It is preferable that the deformation amount of the pressure roller is larger than the deformation amount of the elastic layer of the nip forming member.
[0014]
Preferably, the base material of the nip forming member is sufficiently harder than the elastic layer.
[0015]
Further, the surface of the nip forming member facing the pressure roller may be a curved surface along the outer peripheral surface of the pressure roller so that the pressure distribution in the fixing nip is substantially flat in the sheet passing direction.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 shows a belt fixing device 10 according to an embodiment of the present invention. The belt fixing device 10 includes an endless sheet-shaped fixing belt 12. The fixing belt 12 has, for example, a cylindrical shape having an outer diameter of 50 mm, a base material made of PI (polyimide) having a thickness of 70 μm, an elastic layer made of silicone rubber having a thickness of 200 μm, and a PFA having a thickness of 30 μm. (Tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer). The fixing belt 12 is wound around a heating roller (heating member) 14 whose both ends are rotatably supported, and a nip forming member 20 which is non-rotatably fixed at a position distant from the heating roller 14.
[0017]
The heating roller 14 is formed of, for example, a metal cylindrical tube having an outer diameter of 35 mm, and has a heater lamp 16 as a heat source inside. Further, a predetermined tension is applied to the fixing belt 12 by urging the heating roller 14 in a direction away from the nip forming member 20 by a spring (not shown).
[0018]
The fixing belt 12 is heated by a heating roller 14 heated from the inside by a heater lamp 16. Further, a thermistor 18 is disposed in contact with the heating roller 14, and the on / off of the heater lamp 16 is controlled in accordance with the temperature detected by the thermistor 18, so that the heating roller 14 and the fixing belt 12 are maintained at a predetermined temperature. It can be set.
[0019]
The nip forming member 20 is disposed inside the fixing belt 12, and a pressure roller 50 is pressed against the nip forming member 20 with the fixing belt 12 interposed therebetween. Thus, the contact portion between the fixing belt 12 and the pressure roller 50 forms the fixing nip 40.
[0020]
The pressure roller 50 has, for example, an elastic layer 54 made of rubber or sponge with a thickness of 4 mm around the outer periphery of a metal cylindrical core bar 52 having an outer diameter of 30 mm and an outer diameter of 22 mm. A release layer (not shown) having a thickness of 40 μm is formed on the surface of 54. The pressure roller 50 is driven to rotate in the direction of arrow A by a motor (not shown). Note that an auxiliary heater may be arranged inside the pressure roller 50.
[0021]
The elastic layer 54 of the pressure roller 50 has a length of, for example, 240 mm in the axial direction (the depth direction in FIG. 1). The fixing belt 12 has a greater width so that the elastic layer 54 of the pressure roller 50 is pressed against the entire length. Further, the nip forming member 20 extends so as to support the fixing belt 12 over the entire width.
[0022]
The nip load in the fixing nip 40 (that is, the pressure contact load of the pressure roller 50) is set in the range of 160 to 240 N, and the average pressure in the fixing nip 40 at this time is in the range of 50 kPa to 250 kPa. When the pressure is lower than 50 kPa, the driving force of the pressure roller 50 cannot be stably transmitted to the fixing belt 12. On the other hand, when the pressure is higher than 250 kPa, the driving load of the fixing belt 12 increases only, Is necessary.
[0023]
As shown in FIG. 2, the nip forming member 20 includes a base material 20a, an elastic layer 20b provided on the base material 20a, and a low friction layer 20c provided on the elastic layer 20b. I have. The base material 20a of the nip forming member 20 is formed of a material having low thermal conductivity and sufficiently harder than the elastic layer 20b, and is made of, for example, heat-resistant resin or ceramic. The elastic layer 20b is made of, for example, rubber, and preferably has a thickness of 0.3 to 2.0 mm. Further, the low friction layer 20c is made of, for example, PFA or PTFE (polytetrafluoroethylene), and preferably has a thickness of 5 to 300 μm. In order to reduce the frictional resistance between the nip forming member 20 and the fixing belt 12, a heat-resistant lubricant such as fluorine-based grease may be applied to the inner surface of the fixing belt 12.
[0024]
The surface 22 of the nip forming member 20 facing the pressure roller 50 (that is, the surface of the low friction layer 20c) is a curved surface along the outer peripheral surface of the pressure roller 50. Specifically, the radius of curvature of the facing surface 22 of the nip forming member 20 is the same as the radius of curvature of the outer peripheral surface of the pressure roller 50, for example, 15 mm, or is slightly larger, for example, 15.4 mm. As a result, the circumferential length (so-called nip width) of the fixing nip 40 is about 12 mm. In this manner, by forming the surface 22 of the nip forming member 20 facing the pressure roller 50 as a curved surface along the outer peripheral surface of the pressure roller 50, the pressure distribution in the fixing nip 40 becomes substantially flat in the paper passing direction. It has become. As a result, the paper conveyance speed becomes constant in the entire area inside the fixing nip 40, and as a result, stress does not occur on the paper passing through the fixing nip 40, and image noise such as image bleeding and paper wrinkles can be prevented. . In the “approximately flat”, the nip pressure is slightly higher at the nip center than at the inlet and outlet, or slightly higher at the inlet and outlet than at the nip center. The state shall be included.
[0025]
On the back surface of the nip forming member 20, a sheet metal reinforcing member 30 bent in an S-shaped cross section is provided along the longitudinal direction of the nip forming member 20. The reinforcing member 30 is for minimizing bending of the nip forming member 20 in a direction orthogonal to the longitudinal direction due to being pressed by the pressure roller 50. Further, a space 32 for heat insulation is provided between the nip forming member 20 and the reinforcing member 30. The reinforcing member is not limited to a sheet metal member, and may be, for example, a solid metal rod.
[0026]
A plunging guide 60 is arranged below the fixing nip 40, and the paper P on which the unfixed toner image T is formed is introduced into the fixing nip 40 by the plunging guide 60. Further, a pair of discharge guides 62 are disposed above the fixing nip 40. These discharge guides 62 serve to assist the paper P coming out of the fixing nip 40 and to separate the paper P to be wound around the fixing belt 12 or the pressure roller 50.
[0027]
In the belt fixing device 10 having the above configuration, when the pressure roller 50 is driven to rotate in the direction of arrow A, the fixing belt 12 moves while sliding on the surface of the nip forming member 20 and moves in the direction of arrow B. To rotate. While the fixing belt 12 is rotated in this way, the entire circumference thereof is heated by the heating roller 14 and the temperature is raised to a predetermined fixing temperature (for example, 180 ° C.).
[0028]
After the fixing belt 12 is heated to a predetermined fixing temperature, the paper P on which the unfixed toner image T is formed is introduced into the fixing nip 40 from below. Thus, the toner image T is fixed on the sheet P while passing through the fixing nip 40. Then, the sheet P having passed through the fixing nip 40 is transported upward while being assisted by a discharge guide 62, and is discharged outside the image forming apparatus.
[0029]
As described above, according to the belt fixing device 10 of the present embodiment, since the nip forming member 20 has the elastic layer 20b, the elastic layer 20b of the nip forming member 20 is deformed when the thick paper passes, as shown in FIG. In addition, although the nip pressure distribution in the fixing nip 40 is slightly higher on the inlet side and the outlet side than in the case of plain paper, it becomes substantially uniform in the paper passing direction. As a result, fluctuations in the conveyance speed of the paper are suppressed, and no stress is generated on the paper passing through the fixing nip 40, and occurrence of image noise such as image bleeding and paper wrinkles can be prevented.
[0030]
In addition, by arbitrarily setting the width of the nip forming member 20, a fixing nip 40 having a desired width of, for example, 12 mm can be obtained. Therefore, in a conventional fixing device in which a fixing nip is formed between two rollers, a large pressing force of, for example, 480 N is required to obtain a fixing nip having a width of, for example, 9 mm. A wide fixing nip 40 can be easily realized by the pressing force. By setting the fixing nip 40 wide as described above, a nip time required for fixing can be obtained, and as a result, it is possible to cope with an increase in the system speed of the apparatus.
[0031]
Further, by using the nip forming member 20 instead of the fixing roller having an elastic layer on the outer peripheral portion used in the conventional belt fixing device, the fixing device can be downsized and the circumference of the fixing belt 12 can be shortened. it can. Since the fixing belt 12 can be shortened in this way, the heat capacity of the fixing belt 12 is reduced, and the amount of heat radiated from the fixing belt 12 is also reduced. In addition, instead of a fixing roller having an elastic layer having a large heat capacity, for example, resin By using the nip forming member 20, the speed at which the temperature of the fixing belt 12 rises due to the heat transfer from the heating roller 14 is increased, and as a result, the warm-up time at the start and the recovery time from the printing standby time Can be shortened.
[0032]
Further, even when the pressing load of the pressure roller 50 is made variable according to the type of paper, the positions of the entrance and the exit of the fixing nip 40 are large as in a conventional fixing device in which a fixing nip is formed between two rollers. Since it does not fluctuate, the performance of the sheet entering the fixing nip 40 and the performance of separating the sheet exiting the fixing nip 40 do not deteriorate.
[0033]
Here, the relationship between the thickness of the elastic layer 20b of the nip forming member 20 and the occurrence of image noise was examined using the belt fixing device 10 of the embodiment. At this time, silicon solid rubber (JIS-A20 °) was used for the elastic layer 20b of the nip forming member 20. The nip forming member 20 was constituted by providing a low friction layer 20c (PTFE) having a thickness of 0.1 mm on the elastic layer 20b, and the radius of curvature of the facing surface 22 of the nip forming member 20 was 15.4 mm. The paper used was 210 g / m ² thick paper.
[0034]
In the belt fixing device 10, as shown in FIG. 4, image noise was generated when the thickness of the elastic layer 20b of the nip forming member 20 was 0.1 mm, and no image noise was generated when the thickness was 0.3 mm or more. Therefore, in order to prevent image noise, the thickness of the elastic layer 20b is preferably 0.3 mm or more.
[0035]
Further, the relationship between the thickness of the elastic layer 20b of the nip forming member 20 and the durability of the elastic layer 20b was examined using the belt fixing device 10 of the embodiment. At this time, silicon solid rubber (JIS-A20 °) was used for the elastic layer 20b of the nip forming member 20. The nip forming member 20 was constituted by providing a low friction layer 20c (PTFE) having a thickness of 0.1 mm on the elastic layer 20b, and the radius of curvature of the facing surface 22 of the nip forming member 20 was 15.4 mm. Then, the fixing belt 12 was heated to 185 ° C. and continuously operated for 100 hours, and then the presence or absence of breakage of the elastic layer 20b was examined.
[0036]
As shown in FIG. 5, the elastic layer 20b of the nip forming member 20 did not break down until the layer thickness of the elastic layer 20b reached 2.0 mm. Near the adhesive interface with the substrate 20a. . This is because the shear force to the rubber interface due to the sliding load increased as the layer thickness of the elastic layer 20b increased. Therefore, the layer thickness of the elastic layer 20b of the nip forming member 20 is preferably 2.0 mm or less.
[0037]
Further, the relationship between the layer thickness of the low friction layer 20c on the elastic layer 20b and the durability was examined using the belt fixing device 10 of the embodiment. At this time, a silicon solid rubber (JIS-A20 °) having a thickness of 0.5 mm was used for the elastic layer 20b of the nip forming member 20. The nip forming member 20 was configured by providing a low friction layer 20c (PTFE) on the elastic layer 20b. Further, as the low friction layer 20c, a glass coat sprayed and baked was used. The radius of curvature of the opposing surface 22 of the nip forming member 20 was 15.4 mm. Then, the fixing belt 12 was heated to 185 ° C., and after a continuous operation for 24 hours, the amount of increase in torque was examined.
[0038]
In the belt fixing device 10, as shown in FIG. 6, the torque increase amount is 0.1 Nm up to the layer thickness of the low friction layer 20c of the nip forming member 20 of 5 μm, which is within an allowable range. However, when the layer thickness is 2 μm, the torque increases by 0.45 Nm. This is because the glass coat was worn and the elastic layer 20b was exposed. Therefore, the layer thickness of the low friction layer 20c is preferably 5 μm or more.
[0039]
Further, the relationship between the layer thickness of the low friction layer 20c on the elastic layer 20b and the image noise was examined using the belt fixing device 10 of the embodiment. At this time, a silicon solid rubber (JIS-A20 °) having a thickness of 0.5 mm was used for the elastic layer 20b of the nip forming member 20. Further, a PTFE film was used as the low friction layer 20c. The radius of curvature of the opposing surface 22 of the nip forming member 20 was 15.4 mm. The paper used was 210 g / m ² thick paper.
[0040]
In the belt fixing device 10, as shown in FIG. 7, when the layer thickness of the low friction layer 20c of the nip forming member 20 is 0.3 mm or less, no image noise occurs even with the thick paper, but the low friction layer 20c Image noise occurred when the layer thickness was 0.4 mm. Therefore, it is preferable that the layer thickness of the low friction layer 20c is 0.3 mm or less.
[0041]
Further, when the deformation amount of the elastic layer 20b of the nip forming member 20 becomes larger than the deformation amount of the elastic layer 54 of the pressure roller 50, the curvature at the exit of the fixing nip 40 becomes small, and the separation property and the curl of the paper are deteriorated. Therefore, the amount of deformation of the elastic layer 54 of the pressure roller 50 is preferably larger than the amount of deformation of the elastic layer 20 b of the nip forming member 20. In order to obtain the appropriate amount of deformation, it is preferable to set the necessary rubber thickness and rubber hardness using, for example, a graph shown in FIG. The graph shown in FIG. 8 shows the relationship between the rubber thickness and the rubber hardness necessary to obtain a rubber deformation of 0.075 mm at a pressure of 0.128 N / mm ² .
[0042]
In the belt fixing device 10, the fixing belt 12 is heated by the heating roller 14 having the built-in heater lamp 16, but the heater lamp 16 may be arranged in the pressure roller 50. Further, unlike the present embodiment, the unfixed toner image T formed on the paper P may be contacted with the pressure roller 50 and fixed.
[0043]
Further, in the belt fixing device 10, the rotatable heating roller 14 is used as the heating member, but a non-rotatable sheet heater may be used instead. In this case, the fixing belt 12 is wound around the curved sheet heater and the nip forming member 20, and the sliding fixing belt 12 is heated by the sheet heater.
[0044]
【The invention's effect】
As is clear from the above description, according to the present invention, the elastic layer is provided on the base material of the nip forming member. Although the nip pressure at the side and the outlet side is slightly higher than that at the nip center, the nip pressure distribution in the fixing nip is substantially uniform in the paper passing direction. As a result, fluctuations in the paper conveyance speed are suppressed, and image noise can be prevented.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of a belt fixing device.
FIG. 2 is a partially enlarged view of FIG. 1;
FIG. 3 is a graph showing a nip pressure distribution in the fixing nip of FIG.
FIG. 4 is a table showing the relationship between the thickness of an elastic layer of a nip forming member and the occurrence of image noise.
FIG. 5 is a table showing the relationship between the thickness of an elastic layer of a nip forming member and durability.
FIG. 6 is a table showing the relationship between the thickness of the low friction layer of the nip forming member and the amount of increase in torque.
FIG. 7 is a table showing a relationship between a layer thickness of a low friction layer of a nip forming member and occurrence of image noise.
FIG. 8 is a graph showing the relationship between rubber thickness and rubber hardness.
FIG. 9 is a diagram illustrating an example of a conventional belt fixing device.
FIG. 10 is a graph showing a nip pressure distribution in the fixing nip of FIG. 9;
[Explanation of symbols]
10 belt fixing device 12 fixing belt 14 heating roller (heating member)
20 nip forming member 20a substrate 20b elastic layer 40 fixing nip 50 pressure roller

Claims (5)

An endless sheet-shaped fixing belt wound around a rotatable or non-rotatable heating member and a non-rotatably fixed nip forming member, and pressed against the nip forming member with the fixing belt interposed therebetween. And a rotatable pressure roller having a fixing nip at a contact portion with the fixing belt, wherein the fixing belt slides on the nip forming member by rotating the pressure roller. A belt fixing device that rotates while rotating, wherein the nip forming member is configured by providing an elastic layer on a base material. The belt fixing device according to claim 1, wherein the thickness of the elastic layer is 0.3 to 2.0 mm. The belt fixing device according to claim 1, wherein a low friction layer having a thickness of 5 to 300 μm is provided on the elastic layer. The belt fixing device according to claim 1, wherein an amount of deformation of the pressure roller is greater than an amount of deformation of the elastic layer of the nip forming member. The belt fixing device according to claim 1, wherein the base material of the nip forming member is sufficiently harder than the elastic layer.

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