JP2017003850A - Fixation device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixation device which can alleviate reduction in a heating amount of a fixation member from an end of a heating part in a heating source to the outer side thereof.SOLUTION: A fixation device 20 comprises: a rotatable fixation belt 21; a rotatable pressure roller 22 which forms a fixation nip N with the fixation belt 21; a nip formation member 24 which faces the pressure roller 22 via the fixation belt 21 and forms the fixation nip N; and a halogen heater 23 which includes a heating part 231 for heating the fixation belt 21. The nip formation member 24 includes: a base part 241; and a uniform-heating part 242 which is composed of a member with high heat conductivity than that of the base part 241. The length in the width direction of the uniform-heating part 242 is longer than a heating width E being the length in the width direction in which the heating part 231 is provided.SELECTED DRAWING: Figure 10

Description

  The present invention relates to a fixing device and an image forming apparatus in a copying machine, a printer, a facsimile, or a complex machine including the fixing device.

  In an image forming apparatus in a copying machine, a printer, a facsimile machine, or a complex machine thereof, a fixing device for fixing an unfixed toner image is provided. The fixing device includes a heat roller method, a film heating method, and electromagnetic induction. A contact heating type fixing device such as a heating method is widely used.

  In the film heating type fixing device, a configuration in which an endless belt having a low heat capacity is directly heated without using a metal heat conductor is already known for the purpose of energy saving and speeding up of the device.

  In the case of such a fixing device using an endless belt having a low heat capacity, it has been difficult to maintain a uniform temperature distribution in the longitudinal direction during sheet passing. That is, in the area (sheet passing portion) through which a small-sized recording medium passes, heat is consumed to heat the unfixed toner on the recording medium and the recording medium. I will not be taken away. For this reason, heat accumulates on the heating roller (fixing roller) and the belt, and the temperature of the nip portion of the non-sheet passing portion becomes higher than the temperature of the nip portion of the sheet passing portion maintained at a predetermined temperature. Temperature rise. As an invention for the problem of such an end temperature increase, for example, the invention of Patent Document 1 (Japanese Patent Laid-Open No. 2015-64560) is already known.

  In Patent Document 1, a fixing rotator, an opposing rotator facing the fixing rotator, and a nip forming member provided inside the fixing rotator for forming a fixing nip between the fixing rotator and the counter rotator. The nip forming member has a high heat conduction portion having a large thermal conductivity in the thickness direction and a low heat conduction portion having a small heat conductivity, and the high heat conduction portion serves as a heating source for the fixing rotator. The structure provided with the same width | variety as the light emission length of this is disclosed. By providing the nip forming member with the high heat conduction portion, the amount of heat at the end portion where the temperature has risen can be moved to the center, and the above-described non-uniformity of the temperature distribution between the paper passing portion and the non-paper passing portion can be alleviated.

  By the way, the heat generating part of a heating source such as a halogen heater used in the fixing device as described above is reduced in energy consumption and cost by reducing the width as much as possible. In general, the width of the heat generating portion is set in accordance with the width of the high recording medium, and a recording medium having a width wider than the heat generating portion may be conveyed to the fixing device (for example, A3). This is a case where a heat generating part is provided in accordance with the width of the size paper, and A3 Nobi size paper is carried).

  However, since the amount of heating of the fixing member suddenly drops from the end of the heat generating portion to the outside thereof, when a recording medium having a width wider than the heat generating portion is conveyed to the fixing device, the recording There is a problem in that the edge of the medium is not sufficiently heated, and toner offset and glossiness are reduced.

  Under such circumstances, an object of the present invention is to provide a fixing device that can alleviate a decrease in the amount of heat of the fixing member from the end of the heat generating portion of the heating source to the outside thereof.

  In order to solve the above problems, the present invention provides a rotatable first fixing member, a rotatable second fixing member that forms a fixing nip between the first fixing member, and the first constant member. A fixing device having a nip forming member for forming the fixing nip opposite to the second fixing member via a fixing member, and a heating source having a heat generating portion for heating the first fixing member The nip forming member includes a base portion and a high heat conduction portion configured by a member having a higher thermal conductivity than the base portion, and the length of the high heat conduction portion in the width direction is the heat generation portion. Is provided longer than the heat generation width which is the length in the width direction.

  According to the fixing device of the present invention, the amount of heat is also supplied to the outer portion in the width direction from the heat generating part through the high heat conduction part provided longer in the width direction than the heat generating part. From the outside to the outside, it is possible to mitigate a rapid decrease in the amount of heating of the first fixing member.

1 is a schematic configuration diagram of an image forming apparatus. 1 is a cross-sectional view of a fixing device according to an embodiment of the present invention. It is a schematic diagram which shows the structure of the halogen heater of embodiment. FIG. 6 is a cross-sectional view of a fixing device according to a comparative example. FIG. 5 is a diagram illustrating an arrangement in a width direction of a nip forming member and a temperature distribution of a fixing belt in the fixing device of FIG. 4. FIG. 6 is a cross-sectional view of a fixing device according to a comparative example. FIG. 7 is a diagram illustrating an arrangement in a width direction of a nip forming member and a temperature distribution of a fixing belt in the fixing device of FIG. 6. It is a schematic diagram which shows schematic structure of the halogen heater edge part which concerns on a comparative example. It is a schematic diagram which shows schematic structure of the halogen heater edge part which concerns on embodiment of this invention. It is sectional drawing of the fixing device which concerns on different embodiment of this invention. It is a schematic diagram which shows the structure of the halogen heater of different embodiment. It is a perspective view which shows the structure of the fixing device of different embodiment. It is a schematic diagram which shows the heating method by the heater part according to the width | variety of paper. FIG. 3 is a cross-sectional view showing a shape of a fixing nip according to an embodiment of the present invention.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

First, an overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.
An image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided in the center of the apparatus main body. Each of the image forming units 4Y, 4M, 4C, and 4K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K has a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a surface of the photoconductor 5. A developing device 7 for supplying toner and a cleaning device 8 for cleaning the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are denoted by reference numerals. In the other image forming units 4 </ b> Y, 4 </ b> M, and 4 </ b> C, The reference numerals are omitted.

  Under the image forming units 4Y, 4M, 4C, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transfer member, four primary transfer rollers 31 as primary transfer means, a secondary transfer roller 36 as secondary transfer means, a secondary transfer backup roller 32, A cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35 are provided.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, by rotating the secondary transfer backup roller 32, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. Each primary transfer roller 31 is connected to a power source, and a predetermined direct current voltage (DC) and / or alternating current voltage (AC) is applied to each primary transfer roller 31.

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, a power source is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It is like that.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. The waste toner collected by the belt cleaning device 35 is accommodated in a waste toner container via a waste toner transfer hose.

  A bottle container 2 is provided at the upper part of the main body of the image forming apparatus, and four toner bottles 2Y, 2M, 2C, and 2K that store replenishing toner are detachably attached to the bottle container 2. ing. Toner is supplied from each toner bottle 2Y, 2M, 2C, 2K to each developing device 7 via a supply path provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7.

  On the other hand, at the lower part of the main body of the image forming apparatus, a paper feed tray 10 that stores paper P as a recording medium, a paper feed roller 11 that carries out the paper P from the paper feed tray 10, and the like are provided. In addition to plain paper, the recording medium includes cardboard, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. A manual paper feed mechanism may be provided.

  In the image forming apparatus main body, a conveyance path R is disposed for discharging the paper P from the paper feed tray 10 through the secondary transfer nip and out of the apparatus. In the transport path R, a pair of registration rollers 12 serving as timing rollers for transporting the paper P to the secondary transfer nip at a transport timing is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction. ing.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. A discharge tray 14 for stocking sheets discharged outside the apparatus is provided on the upper surface of the apparatus main body.

  Next, a basic operation of the printer according to the present embodiment will be described with reference to FIG. When the image forming operation is started, the respective photoconductors 5 in the respective image forming units 4Y, 4M, 4C, and 4K are rotationally driven clockwise in the drawing, and the surface of each photoconductor 5 is set to a predetermined polarity by the charging device 6. Uniformly charged. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is monochromatic image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Further, by applying a constant voltage having a polarity opposite to the toner charging polarity or a voltage controlled by a constant current to each primary transfer roller 31, the primary transfer nip between each primary transfer roller 31 and each photoreceptor 5 is applied. A transfer electric field is formed.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Then, the surface of each photoconductor 5 is neutralized by the neutralization device, and the surface potential is initialized.

  In the lower part of the printer, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The paper P sent to the transport path R is temporarily stopped by the registration rollers 12.

  Thereafter, rotation of the registration roller 12 is started at a predetermined timing, and the paper P is conveyed to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip. . Then, the toner images on the intermediate transfer belt 30 are collectively transferred onto the paper P by this transfer electric field. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35 and conveyed to a waste toner container.

  Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

Next, the configuration of the fixing device 20 will be described with reference to FIG.
As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a rotatable first fixing member, and a pressure roller 22 as a second fixing member that is rotatably provided facing the fixing belt 21. A halogen heater 23 as a heating source for heating the fixing belt 21, a nip forming member 24 disposed inside the fixing belt 21, a stay 25 as a support member for supporting the nip forming member 24, and a halogen heater A reflection member 26 that reflects the light emitted from the fixing belt 21 to the fixing belt 21, a temperature sensor 27 that detects the temperature of the fixing belt 21, a separation member 28 that separates the paper from the fixing belt 21, A pressing means for pressing the pressure roller 22 to the fixing belt 21 is provided.

  The fixing belt 21 is composed of a thin and flexible endless belt member (including a film). Specifically, the fixing belt 21 includes a base material on the inner peripheral side formed of a metal material such as nickel or SUS or a resin material such as polyimide (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Or it is comprised by the release layer of the outer peripheral side formed with polytetrafluoroethylene (PTFE) etc. Further, an elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluorine rubber provided on the surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22b. Alternatively, it is constituted by a release layer 22c made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by a pressing unit and is in contact with the nip forming member 24 via the fixing belt 21. At the place where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor provided in the printer body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heating source such as a halogen heater may be disposed inside the pressure roller 22. In addition, when there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image, and uneven glossiness is formed on the solid portion of the image. It can happen. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing an elastic layer having a thickness of 100 μm or more, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided. The elastic layer 22b may be solid rubber, but if there is no heat source inside the pressure roller 22, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  Both ends of the halogen heater 23 are fixed to the side plate of the fixing device 20. The halogen heater 23 is configured to generate heat by being output controlled by a power supply unit provided in the printer body, and the output control is performed based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 27. Is called. By such output control of the halogen heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature. In addition to the halogen heater, an IH, a resistance heating element, a carbon heater, or the like may be used as a heating source for heating the fixing belt 21.

  As shown in FIG. 3, the halogen heater 23 has a heater portion 231 as a heat generating portion in the range of the width E, and heats the fixing belt 21 in this range. Hereinafter, the width in which the halogen heater 23 has the heater portion 231 is referred to as a heater width E as a heat generation width.

  As shown in FIG. 2, the nip forming member 24 is disposed in a longitudinal shape over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22. The nip forming member 24 includes a base portion 241 and a heat equalizing portion 242 as a high heat conduction portion that is configured by a member having a higher thermal conductivity than the base portion 241. The soaking part 242 faces the pressure roller 22 with the fixing belt 21 in between.

  The nip forming member 24 is fixedly supported by a stay 25. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained in the axial direction of the pressure roller 22. The stay 25 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the bending prevention function of the nip forming member 24. However, the stay 25 may be made of resin. It is.

  The soaking part 242 faces the pressure roller 22 with the fixing belt 21 in between. The base portion 241 is made of a heat-resistant resin material such as polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethernitrile (PEN), polyamideimide (PAI), polyetheretherketone ( PEEK) or the like. The soaking part 242 is configured by a member having higher thermal conductivity than the base part 241. For example, carbon nanotubes, graphite sheets, silver, copper, aluminum, SECC (electrogalvanized steel), or the like can be used.

  The nip forming member 24 can also be provided with a low friction sheet on the surface of the soaking part 242. When the fixing belt 21 rotates, the fixing belt 21 slides with respect to the low friction sheet, so that the driving torque generated in the fixing belt 21 is reduced and the load due to the frictional force on the fixing belt 21 is reduced. As a material of the low friction sheet, for example, Toyoflon (registered trademark) 401 manufactured by Toray Industries, Inc. is preferable.

  The reflection member 26 is disposed between the stay 25 and the halogen heater 23. In the present embodiment, the reflecting member 26 is fixed to the stay 25. Moreover, since the reflecting member 26 is directly heated by the halogen heater 23, it is desirable that the reflecting member 26 be formed of a high melting point metal material or the like. For example, examples of the material of the reflecting member 26 include aluminum and stainless steel. By arranging the reflection member 26 in this way, the light emitted from the halogen heater 23 toward the stay 25 is reflected to the fixing belt 21. As a result, the amount of light applied to the fixing belt 21 can be increased, and the fixing belt 21 can be efficiently heated. Further, since it is possible to suppress the radiant heat from the halogen heater 23 from being transmitted to the stay 25 and the like, energy saving can be achieved.

  Further, the reflective surface may be formed by subjecting the surface of the stay 25 on the side of the halogen heater 23 to mirror processing such as polishing or painting without providing the reflective member 26 as in the present embodiment. The reflectance of the reflecting surface of the reflecting member 26 or the stay 25 is desirably 90% or more.

  However, since the shape and material of the stay 25 cannot be freely selected in order to ensure the strength, the separate provision of the reflecting member 26 as in this embodiment increases the degree of freedom in selecting the shape and material, and the reflection. The member 26 and the stay 25 can be specialized for each function. Further, since the reflecting member 26 is provided between the halogen heater 23 and the stay 25, the position of the reflecting member 26 with respect to the halogen heater 23 is reduced, so that the fixing belt 21 can be efficiently heated.

In addition, the fixing device 20 according to the present embodiment is devised in various configurations in order to further improve energy saving and first print time.
Specifically, the fixing belt 21 can be directly heated at a place other than the nip portion N by the halogen heater 23 (direct heating method). In the present embodiment, nothing is interposed between the halogen heater 23 and the left portion of the fixing belt 21 in FIG. 2, and the radiant heat from the halogen heater 23 is directly applied to the fixing belt 21 in that portion.

  Further, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is made thinner and smaller in diameter. Specifically, the thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm, and the overall thickness is set. It is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  In this embodiment, the diameter of the pressure roller 22 is set to 20 to 40 mm, and the diameter of the fixing belt 21 and the diameter of the pressure roller 22 are configured to be equal. However, it is not limited to this configuration. For example, the fixing belt 21 may be formed so that the diameter thereof is smaller than the diameter of the pressure roller 22. In that case, since the curvature of the fixing belt 21 at the nip portion N is smaller than the curvature of the pressure roller 22, the recording medium discharged from the nip portion N is easily separated from the fixing belt 21.

  Here, the problem of an increase in the end portion temperature of the fixing belt 21 will be described using the configuration of FIG. 4 different from the present embodiment. In the configuration of FIG. 4, the nip forming member 24 is formed of a heat resistant resin member without providing a soaking part in the nip forming member 24.

5 (a) is, the fixing device described in FIG. 4, in the case of fed four paper P _A to P _D of different sheet width (see FIG. 5c), the fixing belt 21 in the fixing nip N It shows the temperature distribution on the surface. Paper P _D is paper frequent that is fed to the fixing device 20 (e.g., A3 size paper) heater width E, it is set to the same width as the width of the paper P _D. 5B is a cross-sectional view taken along the line GG in FIG. 4. In the example of FIG. 4, the heater width E of the halogen heater 23 (see FIG. 3) and the width of the nip forming member 24 are set to be the same. The 5A to 5C, the left side of the figure shows the center side in the width direction of the fixing belt 21, and the right side of the figure shows the end side. The width direction of the fixing belt 21 refers to the same direction as the axial direction of the pressure roller 22.

The distance from the center indicated on the horizontal axis in FIG. 5A indicates the distance from the center in the width direction of the fixing belt 21. Further, when the sheet passing the respective sheets P _A to P _D, shows the temperature of the sheet passing portion of the fixing belt 21 (fixing temperature) in t _A ~t _D, the temperature rise of the non-sheet passing portion T _A ~ It is shown by the T _C. Incidentally, there is no non-sheet passing portion when the sheet P _D is fed.

If you passed a small paper P _A to P _C width than the heater width E, the temperature only T _A through T _C respectively non-sheet-passing portion is rising. This is because in the non-sheet passing portion, the heat generated by the heater unit 231 is not transmitted to the sheet or toner on the sheet, and heat is accumulated in the non-sheet passing portion.

Then, (as the width of the paper P to be fed is small) width of the non-sheet-passing portion is larger the temperature rise in the non-sheet passing portion is larger, when it is especially fed paper P _A, The temperature rises exceeding the target upper limit temperature of the fixing belt 21. It is difficult to keep the temperature distribution in the width direction of the fixing belt 21 uniform due to the temperature rise (edge temperature rise) in such a non-sheet passing portion.

  In the fixing device of FIG. 4, since the nip forming member 24 is made only of a resin member, almost no heat is transferred from the fixing belt 21 to the nip forming member 24, and a temperature drop does not occur in the sheet passing portion.

  The fixing device shown in FIG. 6 has a configuration different from that of the present embodiment, and shows a configuration that alleviates the end temperature rise in the non-sheet passing portion. The fixing device 20 shown in FIG. 6 is provided with a soaking part 242 on the nip forming member 24 as in the present embodiment.

FIG. 7A shows the result of the temperature distribution on the surface of the fixing belt 21 in the fixing device 20 of FIG.
As shown in FIG. 7 (a), in the case where the fed each sheet P _A to P _C, when the temperature rise T _A through T _C in the non-sheet passing portion of the fixing belt 21 is shown in FIG. 5 (a) and It is smaller than that. This is because the soaking part 242 having high thermal conductivity is provided on the side of the nip forming member 24 that contacts the fixing belt 21, so that the non-sheet passing part of the fixing belt 21 is passed through the soaking part 242. This is because the heat is transmitted and the heat of the non-sheet passing portion is partially absorbed by the soaking portion 242.

  In this way, by providing the soaking part 242 in the nip forming member 24, it is possible to mitigate the rise in the end temperature at the non-sheet passing part of the fixing belt 21.

Further, by providing the soaking part 242 in contact with the fixing belt 21, a part of the heat amount of the sheet passing part is absorbed by the soaking part 242, and the temperatures t _{A to} t _D of the sheet passing part are shown in FIG. It is lower than the fixing temperature in the case of a) (dotted line in FIG. 7a).

Next, problems to be solved by the present embodiment will be described.
8A is a diagram showing a distribution in the width direction of the temperature T of the halogen heater 23 in the configuration of FIG. 6, and FIG. 8B is a diagram showing a positional relationship in the width direction of the halogen heater 23 and the like. It is. The left side of the figure shows the center side in the width direction of the halogen heater 23, and the right side of the figure shows the end side.

  As shown in FIGS. 8A and 8B, the temperature T of the halogen heater 23 maintains a high temperature within the range of the heater width E in which the heater portion 231 is provided. A drop in temperature T occurs from the boundary portion toward the outside (right side in the figure).

In the configuration of FIG. 8, the width of the soaking part 242 is set to be the same as the heater width E. The heater section 231 has a heater width E set in accordance with the width of the frequently used paper P. As shown in FIG. 8B, the paper PE having a width larger than the heater width _E is fixed. which may be fed to the device 20 (e.g., if you were set according to the heater width E in the paper width of A3 size, A3 Nobisaizu of paper P _E is fed).

  In such a case, the end portion P1 of the paper P overlaps with the temperature T drop region of the halogen heater 23, and the end portion P1 is not sufficiently heated. As a result, the toner image is not sufficiently fixed at the end portion P1, and the toner offset and the glossiness are reduced.

Therefore, in the present embodiment, as shown in FIGS. 9A and 9B, the soaking part 242 has a width longer than the heater width E, and the soaking part reaches the temperature T drop region. 242 is provided. Thus, the paper P _E of greater width than the heater width E even when is passed, since the soaking unit 242 at a position corresponding to the widthwise end portion of the sheet P _E is disposed, soaking is heat transfer to the edge of the sheet of paper P _E via the section 242, it is possible to alleviate the problem of the above-mentioned heating is not enough.

  The respective end positions in the width direction are provided in the order of heater width E <maximum width of paper P <heat equalizing portion 242 <halogen heater 23.

  As described above, when heat is transferred to the edge of the paper P by the heat equalizing unit 242 in the temperature drop region outside the heater width E, a certain amount of heat is accumulated in the heat equalizing unit 242, and then the fixing device. 20 need to pass through. For this reason, in the image forming apparatus 1, when a sheet P having a width exceeding the heater width E is selected by an operator or the like and the image forming operation is started, the sheet feeding roller is fed from the sheet feeding tray 10 shown in FIG. 11 delays the timing at which the paper P is sent out to the transport path, and makes the heat storage time (heating time by the halogen heater 23) of the heat equalizing section 242 until the paper P is transported to the fixing nip N longer than usual. . Further, during the heat accumulation of the heat equalizing unit 242 until the paper P is conveyed to the fixing nip N, it is possible to easily store heat in the heat equalizing unit 242 by reducing the rotation speed of the fixing belt 21.

  The stay 25 (see FIG. 2) abuts on the heat equalizing part 242 at its convex part. Thereby, the contact area of the stay 25 and the heat equalization part 242 can be reduced, and the heat transfer to the stay 25 can be made as small as possible.

  On the outer side in the width direction of the soaking part 242, an end part 243 that makes it difficult to transfer heat compared to the soaking part 242 is provided by providing a hole 243 a in a part thereof.

  Further, the reason why the both ends of the nip forming member 24 are the end portions 243 where heat transfer is difficult to be performed is as follows. In other words, both ends of the nip forming member 24 are provided outside the maximum width of the paper P to be passed, and it is not necessary to conduct heat to the paper P, and the heat equalizing portion 242 is made longer than necessary. This is because heat transfer is performed to a portion where no soaking action is required, and the heat transfer effect by the soaking part 242 to the end of the paper P arranged in the temperature drop region is weakened. It is not always necessary to provide the end portions 243 at both ends of the heat equalizing portion 242, but, for example, when the engaging portion between the heat equalizing portion 242 and the base portion 241 is provided at this position, the aforementioned hole portion 243a is provided. Thus, the end portion 243 that serves as an engaging portion can be provided while minimizing the heat transfer effect. The end portion 243 is provided with a hole 243a to make it difficult to transfer heat at the portion. However, the method is not limited to this, and for example, by reducing the thickness of the end portion 243, the end portion 243 is compared with the heat equalizing portion 242. Heat transfer may be difficult.

  By providing the soaking part 242 not only at the width direction end part side of the nip forming member 24 but also at the center side, the heat soaking part 242 can receive the heat generation at the center side in the width direction of the halogen heater 23, and so on. The heat part 242 can transfer heat to the end part side more efficiently.

  The halogen heater 23 of the present embodiment is provided so as to be movable in the circumferential direction of the fixing belt 21 shown in FIG. As a result, the distance between the halogen heater 23 and the fixing nip N can be adjusted, and adjustment can be made so that an appropriate heating amount can be obtained.

  Next, a fixing device according to an embodiment different from that in FIG. 2 will be described with reference to FIG. The description of the configuration common to FIG. 2 is omitted as appropriate.

  As shown in FIG. 10, the fixing device 20 includes a shielding member 29 that shields heat from the halogen heater 23 to the fixing belt 21 between the halogen heater 23 and the fixing belt 21.

  The shielding member 29 is configured by forming a metal plate having a thickness of 0.1 mm to 1.0 mm into an arc-shaped cross-sectional shape along the inner peripheral surface of the fixing belt 21. The shielding member 29 is provided so as to be movable between the fixing belt 21 and the halogen heater 23 in the circumferential direction. In the present embodiment, in the circumferential region of the fixing belt 21, the other side fixed to a side plate or the like between the halogen heater 23 and the heated region α that is directly heated by the halogen heater 23. A member (reflecting member 26, stay 25, nip forming member 24, etc.) is interposed, and a non-heated region β that is not directly heated by the halogen heater 23 is formed. When there is no need for heat shielding, the shielding member 29 is moved to the non-heated region β side, and when it is necessary to shield heat, the shielding member 29 can be moved to the heated region α side. .

  By rotating the shielding member 29 in this way, the area of the heated region α of the fixing belt 21 is changed, and the amount of radiant heat applied to the fixing belt 21 from the halogen heater 23 is adjusted. Thereby, an excessive temperature rise in the non-sheet passing region of the fixing belt 21 during continuous sheet feeding can be suppressed, and deterioration and damage of the fixing belt 21 due to heat can be prevented. Since the shielding member 29 requires heat resistance, it is preferable to use a metal material such as aluminum, iron, stainless steel, or ceramic as the material.

  The halogen heater 23 is provided with two heaters, and has an end heater 23a on the shielding member 29 side and a central heater 23b on the opposite side. As shown in FIG. 11, the end heater 23 a and the center heater 23 b have heater portions 231 on the end side and the center side in the axial direction of the halogen heater 23, respectively. The width in which the heater portion 231 is provided is the heater width E. In this embodiment, two halogen heaters 23 are provided. However, the number of halogen heaters 23 may be three or more according to the size of the paper used in the printer.

  As shown in FIG. 12, belt holding members 40 are inserted on the inner circumferences of both ends of the fixing belt 21. The fixing belt 21 is rotatably supported by belt holding members 40 at both ends, and basically there is no member that supports the fixing belt 21 other than the belt holding member 40. That is, the fixing belt 21 is in a non-tensioned state that is not stretched over a roller or the like. The belt holding member 40, together with the halogen heater 23 and the stay 25, is fixed to a pair of side plates provided on both sides in the axial direction of the fixing device 20 (the same direction as the axial direction of the pressure roller 22). The overall length of the stay 25 is longer than that of the halogen heater 23.

  A slip ring that protects the end portion of the fixing belt 21 is provided between the end surface of the fixing belt 21 and the opposing surface of the belt holding member 40 that faces the fixing belt 21. As a result, when the fixing belt 21 is displaced in the axial direction, the end portion of the fixing belt 21 can be prevented from coming into direct contact with the belt holding member 40, and the end portion can be prevented from being worn or damaged. it can. Further, the slip ring is fitted to the belt holding member 40 with a margin with respect to the outer periphery. For this reason, when the end of the fixing belt 21 comes into contact with the slip ring, the slip ring can be rotated with the fixing belt 21, but the slip ring may not be rotated and may be stationary. As a material for the slip ring, it is preferable to apply a so-called super engineering plastic excellent in heat resistance, for example, PEEK, PPS, PAI, PTFE and the like.

  In the present embodiment, the range in which the fixing belt 21 is heated is changed according to the width of the paper P to be passed through the fixing device 20 by using the end heater 23a, the central heater 23b, and the shielding member 29. Hereinafter, a method for changing the heating range of the fixing belt 21 will be described.

Figure 13 is a diagram showing the width direction of the relationship between respective sizes of the sheet P _A to P _D and the heater unit 231 and the shielding member 29.

First, when the smallest paper P _A is passed, the heater portion 231 of the end heaters 23a without heating, the fixing belt 21 is heated only by the central heater 23b. The width of the heater portion 231 of the central heater 23b is set to the same width as the sheet P _A, since the fixing belt 21 does not occur non-sheet passing portion in the heated region is heated by the heater unit, the aforementioned end The problem of temperature rise does not occur.

When the small sheet P _B in the second is fed, similarly to the case of the paper P _A, the heater portion 231 of the end heaters 23a without heating, the heating of the fixing belt 21 only by the central heater 23b Is done. In this case, the regions J1 at both ends of the paper P _B are not directly heated by the heater unit 231, but are thermally fixed by transferring heat through the soaking unit 242. The non-sheet-passing portion does not occur in the heated area where the fixing belt 21 is heated by the heater portion, so that the above-described problem of the end temperature rise does not occur. As described above, even when the paper P _B having a width larger than that of the heater portion 231 of the central heater 23b is passed, by using the heat equalizing portion 242, the heat can be sufficiently transmitted to the end portion of the paper. Is possible. The second smallest paper P _B is heated only by the heater portion 231 of the central heater 23b. However, as in the case of the third smallest paper P _C described later, the heater portion 231 of the end heater 23a is simultaneously turned on. It is good also as a structure which heats and shields the one part by the shielding member 29. FIG. Thereby, the temperature drop at the portion corresponding to the end portion of the paper P _B of the heat equalizing section 242 can be suppressed, and the end portion of the paper P _B can be thermally fixed at a sufficient temperature.

If the third small paper P _C is fed to a fixing belt 21 is heated by both the heater portion 231 of the central heater 23b and the end heater 23a. In this case, the end portion J2 of the heater portion 231 of the end heater 23a is disposed in the non-sheet passing area outside in the width direction than the edge of the sheet of paper P _C, the end temperature increase problems set forth above.

Therefore, in this embodiment, when the sheet P _C is fed to the fixing device 20, heat from the heater 231 by the shielding member 29 covers the end portion J2 moves toward the end heaters 23a Shield. Thereby, the end portion temperature of the fixing belt 21 due to the non-sheet passing portion of the fixing belt 21 being heated from the heater portion 231 is prevented.

If the largest sheet P _D at four in is passed causes fever both heater 231 of the central heater 23b and the end heater 23a. Heater width E is provided in accordance with the width of the paper P _D, the heater portion 231 of the central heater 23b and the end heaters 23a, without providing a non-sheet passing portion in the fixing belt 21, heating the sheet P _D I can do it.

  As described above, in the present embodiment, since the shielding member 29 is used to shield the heater portion 231 of the end heater 23a, the end heater 23a is disposed on the shielding member 29 side. Thereby, the moving distance of the shielding member 29 can be made small.

When the second smallest paper P _B is passed, heat is transferred to the end portion of the paper P _B by the heat equalizing section 242 as described above, so that the paper PE having a width larger than the heater width _E is passed. Similarly to the case of paper, the heat storage time of the heat equalization unit 242 may be made longer than usual, or the circulation speed of the fixing belt 21 may be delayed to make it easier to store heat in the heat equalization unit 242.

  In the embodiment of FIG. 2, the fixing nip N has a planar configuration, but as shown in FIG. 10, the fixing nip N may be configured by a combined surface of a curved surface and a plane. Hereinafter, the shape of the fixing nip N formed in the fixing device 20 of the present embodiment will be described.

  FIG. 14 is a cross-sectional view schematically showing the fixing nip N formed by the soaking part (nip forming part) 242. In FIG. 14, the step between the first flat surface A and the second flat surface C of the nip forming member 24 is exaggerated to clearly represent the shape of the fixing nip N. For this reason, the shapes of the front surface 242a of the heat equalizing section 242 and the fixing nip N are different from actual shapes. Further, in FIG. 14, the illustration of the fixing belt 21 is omitted to simplify the drawing.

  As shown in FIG. 14, the surface 242a (front surface) of the heat equalizing section 242 facing the pressure roller 22 has a length in the transport direction that is larger than the fixing nip N in the paper transport direction. A first flat surface A, a connection surface B, a second flat surface C, and a guide surface D are formed on the front surface 242a from the entrance side (lower side of the drawing) of the fixing nip N.

  Two of the flat surfaces A and C are formed so as to be parallel to each other. One flat surface A (first flat surface) is disposed on the inlet side of the fixing nip N, and the other flat surface C (second flat surface) is more at the outlet of the fixing nip N than the first flat surface A. Arranged on the side. Further, the second flat surface C is located closer to the pressure roller 22 than the first flat surface A (right side of the drawing). The first and second flat surfaces A and C are preferably formed so as to be parallel to the entry direction of the paper P with respect to the inlet portion N1 of the fixing nip N. Specifically, in the present embodiment, the first flatness is along a direction substantially orthogonal to an imaginary line m (see FIG. 14) connecting the rotation center O1 of the fixing belt 21 and the rotation center O2 of the pressure roller 22. The surface A and the second flat surface C are arranged.

  The first flat surface A and the second flat surface C are smoothly connected via the connection surface B. The shape of the connection surface B is arbitrary, and can be formed as a flat surface, a curved surface, or a composite surface combining these. FIG. 14 illustrates a case where the connection surface B is formed by a composite curved surface including a first curved surface portion B1 on the inlet side of the fixing nip N and a second curved surface portion B2 on the outlet side of the fixing nip N.

  In this embodiment, the first curved surface portion B1 and the second curved surface portion B2 have opposite curvature directions. Specifically, the first curved surface portion B1 is a concave cylindrical surface as viewed from the pressure roller 22 side having a single radius of curvature, and the second curved surface portion B2 is a pressure having a single radius of curvature. The cylindrical surface is convex when viewed from the roller 22 side.

The shape of the guide surface D is arbitrary, and can be formed by, for example, a flat surface, a curved surface, or a composite surface combining these. The guide surface D of the present embodiment is a concave cylindrical surface having a single radius of curvature as viewed from the pressure roller 22 side. The guide surface D and the second flat surface C are connected so as to have a common tangent at the boundary.
Here, the first curved surface portion B1, the second curved surface portion B2, and the guide surface D have been described as having a single radius of curvature, but the first curved surface portion B1, the second curved surface portion B2, and Each of the guide surfaces D may be composed of a plurality of curved surfaces having different curvatures.

  When the pressure roller 22 is pressed against the heat equalizing portion 242 described above via the fixing belt 21, the elastic layer 22 b of the pressure roller 22 is elastically deformed, and the fixing is performed between the fixing belt 21 and the pressure roller 22. A nip N is formed. At this time, the fixing belt 21 is deformed following the shape of the front surface 242a of the soaking part 242.

  In the fixing nip N, the portion formed by the first flat surface A and the second flat surface C of the soaking part 242 has a flat shape corresponding to the shapes of both flat surfaces A and C. Moreover, the part formed in the connection surface B of the heat equalization part 242 becomes a shape (in this embodiment, curved surface shape) corresponding to the shape of the connection surface B. In the following description, in the fixing nip N, a region formed by the first flat surface A of the soaking portion 242 is referred to as a first flat portion Na, and a region formed by the connection surface B is referred to as a connection portion Nb. A region formed by the second flat surface C is referred to as a second flat portion Nc.

  In the fixing nip N, the inlet portion N1 is composed of the first flat portion Na (the first flat surface A of the heat equalizing portion 242 forms the inlet portion N1), and the outlet portion N2 is the second flat portion Nc. (The second flat surface C of the soaking part 242 forms the outlet part N2). In addition, the length of the second flat portion Nc is shorter than the length of the first flat portion Na.

  The sheet P reaches the entrance N1 of the fixing nip N with the toner T directed toward the fixing belt 21 and enters the first flat portion Na. In the first flat portion Na, the compressibility Xa of the elastic layer 22b of the pressure roller 22 increases toward the downstream side, and the surface pressure acting on the paper P gradually increases accordingly. Next, the paper P enters the connection portion Nb. At the connection portion Nb, the compression rate Xb of the elastic layer 22b increases rapidly to take a maximum value, and the surface pressure acting on the paper P becomes maximum. Thereafter, while the sheet P moves through the connecting portion Nb and the second flat portion Nc, the compression rate Xb of the elastic layer 22b decreases toward the downstream side, so that the surface pressure acting on the sheet P gradually decreases. Therefore, the toner fixing process (melting / fluidizing / merging / penetrating / solidifying) proceeds mainly in the region from the connecting portion Nb to the second flat portion Nc.

  The sheet P that has reached the outlet portion N2 of the fixing nip N is discharged in a direction F slightly inclined toward the pressure roller 22 with respect to the extending direction of the second flat portion Nc by the guide surface D of the nip forming member 24. Further, it comes into contact with the separation claw and is separated from the fixing belt 21. A curved surface portion 242b having a small radius of curvature is provided at the downstream end of the front surface 242a of the heat equalizing portion 242 in the conveying direction, and the fixing belt 21 has a large curvature along the curved surface portion 242b and the pressure roller 22. It is bent in the direction away from. Therefore, the separation property of the paper P discharged from the fixing nip N is good.

  As described above, in the present invention, the high surface pressure region in the fixing nip N is provided on the outlet side of the fixing nip N. In order to realize this surface pressure distribution, the portion of the fixing nip N where the compression rate of the elastic layer 22b is maximized (the connecting portion Nb in the present embodiment) is more fixed than the fixing nip N than the rotation center O2 of the pressure roller 22. Is provided on the exit side of the fixing nip N from the intersection when the perpendicular is drawn from the rotation center O2 of the pressure roller 22 to the first flat surface A (or an extension thereof) of the heat equalizing section 242. In the present embodiment, as shown in FIG. 14, a boundary portion between the first flat portion Na and the connection portion Nb is disposed in the vicinity of an imaginary line m connecting the rotation center O1 of the fixing belt 21 and the rotation center O2 of the pressure roller 22. Therefore, the maximum compression portion of the elastic layer 22b can be reliably arranged under the above conditions.

Hereinafter, the function and effect obtained by configuring the fixing nip N as described above will be described.
In the first flat portion Na of the fixing nip N, the surface of the fixing belt 21 is less likely to be wrinkled as compared with a case where the first flat portion Na is formed into a concave curved surface when viewed from the pressure roller 22 side. Further, in the first flat portion Na, since the compression amount Xa of the elastic layer 22b of the pressure roller 22 is small, the linear velocity difference between the fixing belt 21 and the pressure roller 22 is also small. Further, even when considering the displacement force acting on the unfixed toner, the influence of the displacement force is small because the first flat portion Na is in the low surface pressure region. For the above reasons, it is possible to suppress the deviation of the unfixed toner on the upstream side of the fixing nip N and prevent the image quality from being deteriorated due to the fixing.

  On the other hand, since the second flat surface C of the nip forming member 24 is disposed closer to the pressure roller 22 than the first flat surface A, the second flat surface C is located downstream of the first flat portion Na. A compression amount larger than the compression amount Xa of the elastic layer 22b in the first flat portion Na can be obtained at least at the connection portion Nb (or both the connection portion Nb and the second flat portion Nc). As a result, the exit side of the fixing nip N can be set to a high surface pressure region, and sufficient heat and pressure can be applied to the toner to reliably fix the unfixed image.

  Thus, by locally increasing the contact surface pressure of the fixing nip, it is possible to save energy by suppressing the heating amount by the halogen heater 23. Further, the heat equalizing portion 242 and the fixing belt 21 can be brought into contact with each other under a high surface pressure, and heat conduction from the fixing belt 21 to the heat equalizing portion 242 can be efficiently performed. Heat can be efficiently transferred to the part.

  In the present embodiment, the second flat surface C is formed so as to be continuous with the arc surface of the connection surface B in order to prevent the fixing belt 21 and the nip forming member 24 from being damaged due to a local increase in surface pressure. Has been.

The embodiment of the present invention has been described above, but the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.
The image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may be a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a complex machine thereof.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 20 Fixing apparatus 21 Fixing belt (1st fixing member)
22 Pressure roller (second fixing member)
23 Halogen heater (heating source)
23a End heater 23b Central heater 231 Heater (heat generating part)
24 Nip forming member 241 Base portion 242 Heat equalization portion (high heat conduction portion)
A First flat surface B Connection surface C Second flat surface E Heater width (heat generation width)
N fixing nip

Japanese Patent Laying-Open No. 2015-64560

Claims (7)

A rotatable first fixing member, a rotatable second fixing member forming a fixing nip between the first fixing member, and the second fixing member through the first fixing member And a fixing device having a nip forming member for forming the fixing nip and a heating source having a heat generating part for heating the first fixing member.
The nip forming member has a base part and a high heat conduction part constituted by a member having a higher thermal conductivity than the base part,
The fixing device according to claim 1, wherein a length in the width direction of the high heat conduction portion is longer than a heat generation width that is a length in the width direction in which the heat generation portion is provided.   The heating time by the heating source during heat storage before the recording medium is transported to the fixing nip is changed depending on the length in the width direction of the recording medium transported to the apparatus, and is longer in the width direction than the heat generation width. The fixing device according to claim 1, wherein the heating time is increased when a long recording medium is conveyed.   When a recording medium having a longer length in the width direction than the heat generation width is conveyed, the rotation speed of the first fixing member during heat accumulation before the recording medium is conveyed to the fixing nip is decreased. The fixing device according to claim 1.   A first flat surface and a second flat surface that are parallel to each other and a connection surface that connects the two flat surfaces are provided in a region where the fixing nip of the nip forming member is to be formed. 4. The fixing device according to claim 1, wherein the fixing device is disposed closer to an exit side of the fixing nip than the one flat surface and closer to the second fixing member.   The fixing device according to claim 1, wherein the heat source is provided so as to be movable in a circumferential direction of the first fixing member.   6. The fixing device according to claim 1, wherein a width of the high heat conduction portion is provided longer than a recording medium having a maximum width conveyed to the fixing device.   An image forming apparatus comprising the fixing device according to claim 1.

Images