JP4206788B2 - Belt fixing device - Google Patents

Description

[0001]
BACKGROUND 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]
Japanese Patent Laid-Open No. 11-133776 [Patent Document 3]
Japanese Patent Laid-Open No. 2002-148979
In Patent Documents 1 to 3, as shown in FIG. 9, as shown in FIG. 9, a rotatable pressure roller 101 having an elastic layer 101 a made of sponge or rubber on the outer peripheral portion, a fixing belt holding portion 102, and this fixing belt holding portion. A belt fixing device 100 including an endless sheet-like fixing belt 103 wound around 102 is disclosed.
[0005]
In this belt fixing device 100, the contact portion between the pressure roller 101 and the fixing belt 103 is a fixing nip 104, and the fixing belt 103 is fixed to the nip forming member 102 a of the fixing belt holding portion 102 by the pressure roller 101. The pressure roller 101 is driven to rotate in the direction of arrow C and is rotated in the direction of arrow D. The pressure roller 101 is heated to a predetermined fixing temperature (for example, 180 ° C.) by being heated by a heater lamp 105 that is a heat source disposed inside. 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 sheet passing direction indicated by the arrow E. When passing through the fixing nip 104, the toner image 106 is heated and fixed to the recording medium 107. In this way, by using the nip forming member 102a that is fixedly arranged so as not to rotate, a wide fixing nip 104 is formed to secure a nip time, and a low heat capacity is reduced to shorten a warm-up time. ing.
[0006]
However, since the nip pressure distribution in the sheet passing direction is not uniform in the belt fixing apparatus 100 having the above-described configuration, a difference occurs in the deformation amount 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 high. As a result, there is a problem that image noise occurs and torque increases. Therefore, in another patent application filed on the same date as the present application, the present applicant makes 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, adds the nip forming member 102a. By making the surface facing the pressure roller 101 a curved surface along the outer peripheral surface of the pressure roller 101, a belt in which the nip pressure distribution is made substantially uniform and fluctuation in the conveyance speed of the recording medium 107 in the fixing nip 104 is suppressed. A fixing device is proposed.
[0007]
[Problems to be solved by the invention]
In the belt fixing device in which the fluctuation in the conveyance speed is suppressed, when a thin sheet such as plain paper is passed through the fixing nip 104, the nip pressure distribution is substantially uniform with respect to the sheet passing direction as shown by a solid line in FIG. When a thick sheet such as a thick sheet is passed, the radius of curvature of the sheet 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 in the center. It is greatly deformed on the inlet side and outlet side compared to the part. As a result, as indicated 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 Accordingly, an object of the present invention is to provide a belt fixing device that can prevent image noise from occurring even when a cardboard is passed.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the belt fixing device of the present invention includes an endless sheet-like fixing belt, a nip forming member disposed in a non-rotatable manner inside the fixing belt, and the fixing to the nip forming member. A pressure roller that is rotationally driven and is in pressure contact with the fixing belt, and a contact portion with the fixing belt is a fixing nip. The fixing belt is configured to form the nip by rotating the pressure roller. A sheet carrying unfixed toner is inserted into the fixing nip so that the surface of the unfixed toner is in contact with the fixing belt, and the sheet between the nip forming member and the pressure roller is rotated. a belt fixing device for fixing the unfixed toner to the sheet by only the fixing nip formed between a curved, the nip forming member, along the outer periphery surface of the pressure roller An elastic layer having a thickness of 0.3 to 2.0 mm is provided on the base material formed on the substrate, and the surface of the nip forming member facing the pressure roller is along the outer peripheral surface of the pressure roller. It is characterized by being a curved surface.
[0010]
In the belt fixing apparatus 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 fed so that the nip is formed on the inlet side and the outlet side of the fixing nip. Although the pressure is slightly higher than that at the center of the nip, the nip pressure distribution in the fixing nip is substantially uniform over the sheet passing direction. As a result, fluctuations in the sheet conveyance speed are suppressed, and image noise can be prevented.
[0011]
In the belt fixing device of the present invention, radius of curvature or the same of the outer peripheral surface of the curvature radius of the pressure roller of the opposite surfaces of said nip forming member, or is preferably large heard.
[0013]
In the belt fixing device of the present invention, a low friction layer having a thickness of 5 to 300 μm may be provided on the elastic layer.
[0014]
In the belt fixing device of the present invention, 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.
[0015]
Further, a belt fixing device of the present invention, the base material of the nip forming member is hard Ikoto is preferred over the elastic layer.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below 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-like fixing belt 12. The fixing belt 12 has, for example, a base material made of PI (polyimide) having a diameter of 50 mm and a thickness of 70 μm, an elastic layer made of silicon rubber having a thickness of 200 μm, and a PFA having a thickness of 30 μm. A release layer composed of (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) is laminated in order from the inside. The fixing belt 12 is wound around a heating roller (heating member) 14 that is rotatably supported at both ends, and a nip forming member 20 that is fixedly disposed at a position away from the heating roller 14 so as not to rotate.
[0017]
The heating roller 14 is made of a metal cylindrical tube having an outer diameter of 35 mm, for example, and has a heater lamp 16 as a heat source therein. 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 heating roller 14 and the fixing belt 12 are brought to a predetermined temperature by controlling on / off of the heater lamp 16 according to the temperature detected by the thermistor 18. It can be set.
[0019]
The nip forming member 20 is disposed inside the fixing belt 12, and the pressure roller 50 is pressed against the nip forming member 20 with the fixing belt 12 sandwiched therebetween. Accordingly, the contact portion between the fixing belt 12 and the pressure roller 50 is a fixing nip 40.
[0020]
The pressure roller 50 has, for example, an elastic layer 54 made of rubber or sponge having a thickness of 4 mm on the outer peripheral portion of a metal cylindrical cored 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). An auxiliary heater may be disposed 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 width larger than that so that the elastic layer 54 of the pressure roller 50 is pressed over 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 is increased and the motor with higher power consumption. Because it becomes 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. Yes. The base material 20a of the nip forming member 20 has a low thermal conductivity and is made of a material that is sufficiently harder than the elastic layer 20b, and is made of, for example, a 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 the thickness thereof is preferably 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]
Further, the surface 22 of the nip forming member 20 facing the pressure roller 50 (that is, the surface of the low friction layer 20 c) 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, for example, 15 mm, which is the same as the radius of curvature of the outer peripheral surface of the pressure roller 50, or is slightly larger, for example, 15.4 mm. As a result, the circumferential length of the fixing nip 40 (so-called nip width) is about 12 mm. Thus, by making the surface 22 of the nip forming member 20 facing the pressure roller 50 a curved surface along the outer peripheral surface of the pressure roller 50, the pressure distribution in the fixing nip 40 is approximately flat with respect to the sheet passing direction. It is supposed to be. As a result, the paper conveyance speed is constant throughout the fixing nip 40, and as a result, no stress is generated on the paper passing through the fixing nip 40, and image noise such as image blurring and paper wrinkles can be prevented. . In the above "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. It also includes the state.
[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 suppressing the nip forming member 20 from being bent in a direction perpendicular to the longitudinal direction when pressed by the pressure roller 50 as much as possible. 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 a solid metal rod, for example.
[0026]
A rush guide 60 is disposed below the fixing nip 40, and the paper P having an unfixed toner image T formed on the surface thereof is introduced into the fixing nip 40 by the rush guide 60. A pair of discharge guides 62 are disposed above the fixing nip 40. These discharge guides 62 assist the paper P that has come out from the fixing nip 40 and also serve to separate the paper P that is to be wound around the fixing belt 12 or the pressure roller 50.
[0027]
In the belt fixing device 10 having the above-described configuration, when the pressure roller 50 is rotationally driven in the direction of the arrow A, the fixing belt 12 moves while sliding on the surface of the nip forming member 20 and moves in the direction of the arrow B. Rotate to. While the fixing belt 12 is rotated in this manner, the entire circumference 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 on the surface is introduced into the fixing nip 40 from below. As a result, the toner image T is fixed on the paper P while passing through the fixing nip 40. Then, the sheet P that has passed through the fixing nip 40 is conveyed upward while being supplementarily guided by the discharge guide 62, and is discharged to the outside of 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 paper is passed through 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 is substantially uniform over the sheet passing direction. As a result, fluctuations in the conveyance speed of the sheet are suppressed, no stress is generated on the sheet passing through the fixing nip 40, and 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. Accordingly, in a conventional fixing device that forms a fixing nip between two rollers, a large pressure contact force of, for example, 480 N is required to obtain a fixing nip of, for example, 9 mm width, whereas it is relatively small, for example, 160 to 240 N. A wide fixing nip 40 can be easily realized by the pressure contact force. By using the wide fixing nip 40 as described above, a nip time necessary for fixing can be gained, and as a result, the system speed of the apparatus can be increased.
[0031]
Further, by using the nip forming member 20 in place of the fixing roller having the elastic layer on the outer peripheral portion used in the conventional belt fixing device, the fixing device can be downsized and the peripheral length of the fixing belt 12 can be shortened. it can. Since the fixing belt 12 can be shortened in this manner, the heat capacity of the fixing belt 12 is reduced and the amount of heat released from the fixing belt 12 is reduced. In addition, instead of the fixing roller having an elastic layer having a large heat capacity, the heat capacity is small, for example By using the nip forming member 20, the speed at which the fixing belt 12 rises in temperature as a result of heat transfer from the heating roller 14 increases, and as a result, the warm-up time at start-up and the recovery time from waiting for printing are increased. Can be shortened.
[0032]
Furthermore, even when the pressure contact load of the pressure roller 50 is variable according to the type of paper, the positions of the inlet and outlet of the fixing nip 40 are large as in the conventional fixing device that forms the fixing nip between the two rollers. Since it does not fluctuate, the paper entry performance to the fixing nip 40 and the paper separation performance from the fixing nip 40 are not deteriorated.
[0033]
Here, the relationship between the layer 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 above embodiment. At this time, silicon solid rubber (JIS-A 20 °) was used for the elastic layer 20b of the nip forming member 20. The nip forming member 20 is configured by providing a low friction layer 20c (PTFE) having a thickness of 0.1 mm on the elastic layer 20b, and the curvature radius of the facing surface 22 of the nip forming member 20 is 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 layer 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-A 20 °) was used for the elastic layer 20b of the nip forming member 20. The nip forming member 20 is configured by providing a low friction layer 20c (PTFE) having a thickness of 0.1 mm on the elastic layer 20b, and the curvature radius of the facing surface 22 of the nip forming member 20 is 15.4 mm. The fixing belt 12 was heated to 185 ° C. and continuously operated for 100 hours, and then the presence or absence of the elastic layer 20b was examined.
[0036]
As shown in FIG. 5, the elastic layer 20b did not break until the thickness of the elastic layer 20b of the nip forming member 20 was 2.0 mm. However, when the thickness was 2.5 mm or more, the nip forming member 20 increased with an increase in torque. Breakage occurred in the vicinity of the adhesive interface with the substrate 20a. . This is because the shearing force to the rubber interface due to the sliding load increases as the thickness of the elastic layer 20b increases. 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-A 20 °) 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 baked by spraying was used. Further, 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 after 24 hours of continuous operation, the amount of torque increase was examined.
[0038]
In this belt fixing device 10, as shown in FIG. 6, the amount of torque increase is 0.1 Nm until the layer thickness of the low friction layer 20c of the nip forming member 20 is 5 μm, which is in an allowable range. However, when the layer thickness is 2 μm, the torque increases by 0.45 Nm. This is because the glass coat is worn and the elastic layer 20b is 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-A 20 °) 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. Further, 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.
[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 is generated even with thick paper. Image noise occurred when the layer thickness was 0.4 mm. Therefore, the layer thickness of the low friction layer 20c is preferably 0.3 mm or less.
[0041]
Further, when the deformation amount of the elastic layer 20b of the nip forming member 20 is 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 is reduced, and the separation property and curl of paper are deteriorated. Therefore, the deformation amount of the elastic layer 54 of the pressure roller 50 is preferably larger than the deformation amount of the elastic layer 20b of the nip forming member 20. In order to obtain this appropriate amount of deformation, for example, it is preferable to set the necessary rubber thickness and rubber hardness using the graph shown in FIG. The graph shown in FIG. 8 represents the relationship between the rubber thickness and the rubber hardness necessary for obtaining a rubber deformation amount 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 including the heater lamp 16, but the heater lamp 16 may be disposed in the pressure roller 50. Further, unlike the present embodiment, the unfixed toner image T formed on the paper P may be fixed in contact with the pressure roller 50.
[0043]
In the belt fixing device 10, the rotatable heating roller 14 is used as the heating member. However, a non-rotatable sheet heater may be used instead. In this case, the fixing belt 12 is wound around the curved sheet-like heater and the nip forming member 20, and the sliding fixing belt 12 is heated by the sheet-like heater.
[0044]
【The invention's effect】
As is apparent 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 is slightly higher at the nip side and at the outlet side than at the nip center, the nip pressure distribution in the fixing nip is substantially uniform in the sheet passing direction. As a result, fluctuations in the sheet 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.
FIG. 3 is a graph showing a nip pressure distribution in the fixing nip of FIG. 1;
FIG. 4 is a table showing the relationship between the thickness of the elastic layer of the nip forming member and the occurrence of image noise.
FIG. 5 is a table showing the relationship between the thickness of the elastic layer of the nip forming member and the 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 torque increase.
FIG. 7 is a table showing the relationship between the layer thickness of the low friction layer of the nip forming member and the 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.
10 is a graph showing a nip pressure distribution in the fixing nip of FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Belt fixing apparatus 12 ... Fixing belt 14 ... Heating roller (heating member)
20 ... Nip forming member 20a ... Base material 20b ... Elastic layer 40 ... Fixing nip 50 ... Pressure roller

Claims (5)

An endless sheet-shaped fixing belt, a nip forming member disposed in a non-rotatable manner inside the fixing belt, and press-contacted to the nip forming member with the fixing belt interposed therebetween, and a contact portion with the fixing belt is fixed. A pressure roller that can be driven to rotate in a nip, and the fixing belt rotates while sliding on the nip forming member when the pressure roller is driven to rotate so that unfixed toner is carried thereon. The unfixed toner is inserted into the fixing nip so that the unfixed toner surface is in contact with the fixing belt, and the unfixed toner is transferred to the sheet only by the fixing nip formed between the nip forming member and the pressure roller. A belt fixing device for fixing;
The nip forming member is configured by providing an elastic layer having a thickness of 0.3 to 2.0 mm on a base formed on a curved surface along the outer peripheral surface of the pressure roller. A belt fixing device, wherein a surface facing the pressure roller is a curved surface along an outer peripheral surface of the pressure roller. The nip the radius of curvature of the opposed surfaces of the forming member is either identical to the radius of curvature of the outer peripheral surface of the pressure roller, or a belt fixing device according to claim 1, wherein the large heard.   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 a deformation amount of the pressure roller is larger than a deformation amount of an elastic layer of the nip forming member. The substrate of the nip forming member, a belt fixing device as claimed in claim 1, wherein the hard Ikoto than that of the elastic layer.

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