JP6136147B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device for fixing toner onto a recording medium by heat and pressure, and image formation such as a FAX, a printer, a copying machine, or a complex machine using the electrophotographic method, electrostatic recording method, etc. provided with the fixing device. It relates to the device.

  Conventionally, various image forming apparatuses using an electrophotographic system have been devised as image forming apparatuses such as copying machines and printers, and are well known in the art. In the image forming process, an electrostatic latent image is formed on the surface of the photosensitive drum as an image carrier, and the electrostatic latent image on the photosensitive drum is developed with a toner as a developer to be visualized and developed. This process is established by a process in which the transferred image is transferred onto a recording paper (also referred to as a recording medium or paper) by a transfer device to carry the image, and a toner image on the recording paper is fixed by a fixing device using pressure, heat, or the like.

  In this fixing device, a fixing member and a pressure member constituted by opposing rollers or belts or a combination thereof are arranged so as to contact each other to form a nip portion, and a recording sheet is sandwiched in the nip portion, Heat and pressure are applied to fix the toner image on the recording paper.

  As an example of a fixing device, a technique using a fixing belt stretched around a plurality of roller members as a fixing member is known (for example, Patent Document 1). As shown in FIG. 4, the apparatus using such a fixing belt has a fixing belt (endless belt) 204 as a fixing member, a plurality of roller members 202 and 203 for stretching and supporting the fixing belt 204, and a plurality of rollers. Of the roller members 202 and 203, a heater 201 provided in one roller member 202, a pressure roller (pressure member) 205, and the like are configured. The heater 201 heats the fixing belt 204 via the roller member 202. The toner image on the recording medium P conveyed toward the fixing nip portion (nip portion) N formed between the fixing belt 204 and the pressure roller 205 receives heat and pressure at the nip portion. Then, it is fixed on the recording medium (belt fixing method).

  There is also a fixing device having a fixing member that is in sliding contact with the inner surface of the fixing member that is a rotating body. For example, in Patent Document 2, as shown in FIG. 5, a heat-resistant film (fixing film) 213 is sandwiched between a ceramic heater 211 serving as a heating element and a pressure roller 212 serving as a pressure member. A recording medium on which an unfixed toner image to be image-fixed is formed and carried is introduced between the film 213 and the pressure roller 212 in the fixing nip portion N, and is nipped and conveyed together with the film 213. Thus, the heat of the ceramic heater 211 is applied to the recording medium through the film 213 in the nip portion N, and the film heating method is used for fixing the unfixed toner image to the recording medium by the pressure of the fixing nip portion N. A fixing device is disclosed.

  This film heating type fixing device can be configured as an on-demand type device using a ceramic heater and a member having a low heat capacity as a film, and energizes the ceramic heater as a heat source only when the image forming apparatus performs image formation. Thus, it is only necessary to generate heat at a predetermined fixing temperature, the waiting time from the power-on of the image forming apparatus to the image forming executable state is short (quick start property), and the power consumption during standby is greatly reduced ( There are advantages such as (power saving).

  In Patent Documents 3 and 4, a rotatable heat-fixing roll whose surface is elastically deformed, an endless belt (pressure belt) that can run while being in contact with the heat-fixing roll, and a non-rotating state inside the endless belt. And a pressure pad that elastically deforms the surface of the heat-fixing roll, and is provided with a belt nip through which the recording paper can pass between the endless belt and the heat-fixing roll. A pressure belt type image fixing device is proposed. According to this fixing method, the lower pressure member is used as a belt, and the contact area between the paper and the roll is widened to greatly improve the heat conduction efficiency, and it is possible to reduce the energy consumption and at the same time realize the miniaturization. It has become.

  However, although the fixing device described in Patent Document 1 described above is suitable for speeding up the device as compared with a device using a fixing roller, the warm-up time (time required to reach a printable temperature) and the first print There is a limit to shortening the time (the time from when a print request is received to when the print operation is performed and the paper discharge is completed).

  On the other hand, the fixing device described in Patent Document 2 can reduce the warm-up time and the first print time by reducing the heat capacity, and also reduce the size of the device. However, the fixing device described in Patent Document 2 has a problem of durability and a problem of belt temperature stability.

  In other words, the wear resistance due to sliding between the ceramic heater, which is a heat source, and the inner surface of the belt is inadequate, and the surface that repeats continuous friction is roughened when operated for a long time, increasing the frictional resistance and making the belt run unstable. Or, a phenomenon such as an increase in the driving torque of the fixing device occurs, and as a result, the transfer paper forming the image slips and the image shifts, or the stress on the driving gear increases, causing damage to the gear. (Problem 1).

  In the film heating type fixing device, since the belt is locally heated at the nip portion, when the rotating belt returns to the nip entrance, the belt temperature becomes the coldest state (especially at high speed rotation). , There was a problem that fixing failure was likely to occur (Problem 2).

  On the other hand, in Patent Document 3, a glass fiber sheet (PTFE-impregnated glass cloth) impregnated with PTFE as a low friction sheet (sheet-like sliding material) on the surface layer of the pressure pad is used, and the slidability of the belt inner surface and the fixing member is improved. Means for improving the problem are disclosed. However, such a pressure belt type fixing device (Patent Documents 3 and 4) has a problem that it takes a long time to warm up because the heat capacity of the fixing roller is large and the temperature rise is slow. (Problem 3).

  With respect to the above problems 1 to 3, in Patent Document 5, a substantially pipe-shaped counter member (metal thermal conductor, support member) disposed on the inner peripheral side of the endless fixing belt, and the counter member By providing a resistance heating element such as a ceramic heater that is disposed on the inner peripheral side and heats the opposing member, the entire fixing belt can be warmed, the warm-up time and the first print time can be shortened, and There has been proposed a fixing device that can solve the shortage of heat during high-speed rotation.

  However, in the fixing device described in Patent Document 5, the nip portion formed by pressing a pressure roller as a pressure member on the fixing belt side is supported by a metal thermal conductor, so the nip width in the nip portion, The pressure was unstable.

  Therefore, in Patent Document 6, in order to maintain and stabilize the state, shape, position, and the like of the nip portion and the pipe-shaped heating member formed by the fixing belt and the pressure roller, a nip portion corresponding to the portion where the nip portion is formed is used. A configuration in which a forming member (abutting member, fixing member), a reinforcing member, and the like are provided has been proposed.

  The nip forming member is in pressure contact with the pressure roller via the fixing belt and is in sliding contact with the fixing belt that rotates in the circumferential direction. For this reason, the surface of the nip forming member needs to have low friction. At the same time, in order to improve the image quality, it is necessary to follow minute irregularities on the surface of the recording medium, and an elastic function like rubber is also required. However, since rubber is generally a high friction body, it is difficult to use it as it is.

  Therefore, by providing a sliding sheet (low friction sheet) on the surface of the nip forming member, it is possible to achieve both rubber elasticity and low friction. However, the sliding sheet is moved downstream in the rotational direction by the rotational movement of the fixing belt. In order to continue receiving the shearing force, it is necessary to firmly fix the sliding sheet to the surface on the nip portion side of the nip forming member.

  As a technique for fixing the sliding sheet to the nip forming member, a screw hole for fastening the wound sliding sheet is provided on the surface on the opposite side of the nip portion of the nip forming member and fixed with a screw. As shown in FIG. 7, a method is disclosed in which a nip forming member is fitted to a convex portion and a concave portion, and a sliding sheet is sandwiched and fixed between them. This led to an increase in manufacturing cost of the nip forming member.

  Therefore, the present invention eliminates the configuration for fixing the sliding sheet from the nip forming member by holding the sliding sheet by a holding means provided on a member other than the nip forming member and fixing it to the nip forming member. An object of the present invention is to provide a fixing device and an image forming apparatus capable of simplifying the configuration of the nip forming member and reducing the cost.

In order to achieve this object, a fixing device according to the present invention includes a rotatable endless fixing belt, a pressure roller disposed on the outer peripheral side of the fixing belt so as to be in pressure contact with the fixing belt, and the fixing belt. A nip forming member disposed on the inner peripheral side of the fixing belt and press-contacted with the pressure roller via the fixing belt to form a nip portion, and fixed to an inner diameter portion of the fixing belt, and the nip forming member is fixed to the nip portion. A reinforcing member that is supported from the opposite side of the fixing portion, and a heat source that is provided at a position sandwiching the nip forming member and the reinforcing member with respect to the nip portion on the inner peripheral side of the fixing belt, and that heats the fixing belt. A fixing device that guides a recording medium carrying an unfixed image to the nip portion, and passes the unfixed image in contact with the fixing belt. It has a sliding sheet between the inner peripheral surface of the wearing belt, sliding seat, retaining means provided on both sides of the upstream side and the downstream side of the nip portion in the rotational direction of the fixing belt of the reinforcing member The nip forming member is held in close contact with the surface on the nip portion side of the nip forming member, and the nip forming member is disposed in a space formed between the reinforcing member and the sliding sheet fixed to the reinforcing member. In addition, the nip forming member is in contact with the reinforcing member only on the surface opposite to the nip portion .

  According to the present invention, the configuration for fixing the sliding sheet from the nip forming member can be eliminated, the configuration of the nip forming member can be simplified, and the cost can be reduced.

1 is a cross-sectional view illustrating an embodiment of an image forming apparatus according to the present invention. 1 is a cross-sectional view illustrating a configuration of an embodiment of a fixing device according to the present invention. It is the perspective view which looked at the nip formation member from the surface on the opposite side to a nip part. It is a schematic block diagram which shows the fixing device of the conventional belt fixing system. It is a schematic block diagram which shows the conventional fixing device of a film heating system.

  Hereinafter, a configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

(Image forming device)
FIG. 1 is a schematic configuration diagram illustrating the overall configuration of a tandem type color printer which is an embodiment of an image forming apparatus according to the present invention. The outline and operation of the internal configuration of the image forming apparatus will be described with reference to FIG.

  Four bottles 102Y, 102M, 102C, and 102K corresponding to each color (yellow, magenta, cyan, and black) are detachably (replaceable) installed in the bottle housing portion 101 above the image forming apparatus main body 1. ing.

  An intermediate transfer unit 85 is disposed below the bottle housing portion 101. Image forming units 4Y, 4M, 4C, and 4K corresponding to the respective colors (yellow, magenta, cyan, and black) are arranged in parallel so as to face the intermediate transfer belt 78 of the intermediate transfer unit 85.

  Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively.

  Further, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing unit 76, a cleaning unit 77, a charge eliminating unit (not shown), and the like are disposed.

  Then, an image forming process (charging process, exposure process, development process, transfer process, cleaning process) is performed on each photoconductor drum 5Y, 5M, 5C, 5K, and each photoconductor drum 5Y, 5M, 5C, An image of each color is formed on 5K.

  The photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven in a clockwise direction in FIG. 1 by a drive motor (not shown). The surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75 (charging process).

  Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser beam emitted from the exposure unit 3, and electrostatic latent images corresponding to the respective colors are formed by exposure scanning at this position. (Exposure process).

  Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the developing unit 76, and the electrostatic latent image is developed at this position to form toner images of each color (development process). ).

  Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the positions facing the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K, and at these positions, the photosensitive drums 5Y, 5M. , 5C, 5K are transferred onto the intermediate transfer belt 78 (primary transfer step).

  At this time, a small amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K.

  Thereafter, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, and untransferred toner remaining on the photosensitive drums 5Y, 5M, 5C, and 5K is removed at this position. It is mechanically recovered by a cleaning blade 77 (cleaning process).

Finally, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing a neutralization unit (not shown), and the residual potential on the photosensitive drums 5Y, 5M, 5C, and 5K is removed at this position. The
Thus, a series of image forming processes performed on the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

  Thereafter, the toner images of the respective colors formed on the respective photosensitive drums through the developing process are transferred onto the intermediate transfer belt 78 in an overlapping manner. In this way, a color image is formed on the intermediate transfer belt 78.

  Here, the intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning unit 80. , Etc.

  The intermediate transfer belt 78 is stretched and supported by the three rollers 82 to 84 and is endlessly moved in the direction of the arrow in FIG. The four primary transfer bias rollers 79Y, 79M, 79C, and 79K respectively sandwich the intermediate transfer belt 78 with the photosensitive drums 5Y, 5M, 5C, and 5K to form primary transfer nips.

  Then, a transfer bias reverse to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K. The intermediate transfer belt 78 travels in the direction of the arrow, and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K.

  In this way, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred while being superimposed on the intermediate transfer belt 78. Thereafter, the intermediate transfer belt 78 onto which the toner images of the respective colors are transferred in an overlapping manner reaches a position facing the secondary transfer roller 89.

  At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 and forms a secondary transfer nip. The four color toner images formed on the intermediate transfer belt 78 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip.

  At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 78. Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected.

  Thus, a series of transfer processes performed on the intermediate transfer belt 78 is completed. Here, the recording medium P transported to the position of the secondary transfer nip is transported from the paper feeding unit 12 disposed below the apparatus main body 1 via the paper feeding roller 97 and the registration roller pair 98. It is a thing.

Specifically, a plurality of recording media P such as transfer paper are stored in the paper supply unit 12 in an overlapping manner.
When the paper feed roller 97 is rotationally driven in the counterclockwise direction in FIG. 1, the uppermost recording medium P is fed between the rollers of the registration roller pair 98.

  The recording medium P conveyed to the registration roller pair 98 is temporarily stopped at the position of the roller nip of the registration roller pair 98 that has stopped rotating. Then, the registration roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the recording medium P is conveyed toward the secondary transfer nip.

  In this way, a desired color image is transferred onto the recording medium P. Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing device 20.

  At this position, the color image transferred on the surface is fixed on the recording medium P by heat and pressure generated by the fixing belt 21 and the pressure roller 31. Thereafter, the recording medium P is discharged out of the apparatus through a pair of paper discharge rollers 99.

  The recording medium P discharged out of the apparatus by the discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image. Thus, a series of image forming processes in the image forming apparatus is completed.

(Fixing device)
Next, the configuration and operation of the fixing device 20 provided in the image forming apparatus 1 will be described. FIG. 2 is a schematic cross-sectional view illustrating an example of the fixing device 20.

  The fixing device (fixing device 20) according to this embodiment includes a rotatable endless fixing member (fixing belt 21), a heat source (heater 25) for heating the fixing member, and the fixing member on the outer peripheral side of the fixing member. A pressure member (pressure roller 31) arranged so as to be in pressure contact with the member, and arranged on the inner peripheral side of the fixing member, and press-contacted with the pressure member via the fixing member to form a nip portion (nip portion N). And a reinforcing member (reinforcing member 23) that is fixed to an inner diameter portion of the fixing member and supports the nip forming member from the side opposite to the nip portion. A sliding sheet (sliding sheet 22) between the nip forming member and the inner peripheral surface of the fixing member, and the sliding sheet is a holding means (holding means) provided on a member different from the nip forming member. 27) on the nip portion side of the nip forming member. It is intended to be held in close contact with the. In addition, the code | symbol in embodiment and the example of application are shown in a parenthesis.

  As shown in FIG. 2, the fixing device 20 includes an endless belt-like member, a fixing belt 21, a nip forming member (base member) 26, a reinforcing member (pressing stay) 23, a heater (heat source) 25, and pressurization. The pressure roller 31 is a rotating body.

  Here, the fixing belt 21 is a thin and flexible endless belt, and rotates (runs) in an arrow direction (counterclockwise) in FIG. The fixing belt 21 has a base material layer, an elastic layer, and a release layer sequentially laminated from the inner peripheral surface side, and the total thickness thereof is set to 1 mm or less, for example. The base material layer of the fixing belt 21 has a layer thickness of, for example, 30 to 100 μm, and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide.

  The elastic layer of the fixing belt 21 has a layer thickness of, for example, 100 to 300 μm, and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber. By providing the elastic layer, minute irregularities on the surface of the fixing belt 21 in the nip portion N are not formed, and heat is uniformly transmitted to the toner image T on the recording medium P, thereby suppressing the occurrence of a satin skin image.

  The release layer of the fixing belt 21 has a layer thickness of, for example, 10 to 50 μm, and includes PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, and polyetherimide. , PES (polyether sulfide), and the like. By providing this release layer, releasability (peelability) with respect to the toner image T is ensured. The diameter of the fixing belt 21 is set to be 15 to 120 mm, for example.

  The pressure roller 31 as a pressure rotating body that contacts the outer peripheral surface of the fixing belt 21 at the position of the nip portion N has a diameter of about 30 to 40 mm and has an elastic layer 33 on a hollow cored bar 32. Is formed.

  The elastic layer 33 of the pressure roller 31 is formed of a material such as foamable silicone rubber, silicone rubber, or fluorine rubber. Moreover, in order to obtain mold release properties, a thin mold release layer (PFA or PTFE layer) may be provided on the surface.

  The pressure roller 31 is provided with a gear that meshes with a drive gear of a drive mechanism (not shown), and the pressure roller 31 is rotationally driven in an arrow direction (clockwise direction) in FIG. In addition, the pressure roller 31 is rotatably supported at both ends in the width direction on a side plate (not shown) of the fixing device 20 via a bearing. A heat source such as a halogen heater can be provided inside the pressure roller 31.

  The pressure roller 31 is pressed against the fixing belt 21 by the contact / separation mechanism, thereby forming a predetermined nip width in the nip portion N. The pressure roller 31 may be a solid roller, but a hollow roller may have a smaller heat capacity.

  Note that when the elastic layer 33 of the pressure roller 31 is formed of a sponge-like material such as foamable silicone rubber, the pressure applied to the nip portion N can be reduced, so that it occurs in the nip forming member 26. Deflection can be reduced. Further, since the heat insulation of the pressure roller 31 is enhanced and the heat of the fixing belt 21 is less likely to move to the pressure roller 31 side, the heating efficiency of the fixing belt 21 is improved.

  A nip forming member 26 held by the reinforcing member 23 is provided inside the fixing belt 21. In the nip portion N, the driving force is received from the pressure roller 31 and the fixing belt 21 rotates. On the other hand, the heater 25, the reinforcing member 23, and the nip forming member 26 inside the fixing belt 21 are fixed. The fixing belt 21 and the nip forming member 26 are in sliding contact.

  Further, a sliding sheet 22 made of a porous sheet made of PTFE resin is disposed between the inner peripheral surface of the fixing belt 21 and the surface of the nip forming member 26 on the nip portion side. Thus, the nip forming member 26 slides on the fixing belt 21. By providing the sliding sheet 22, the sliding load can be reduced and the life can be extended.

  The nip forming member 26 is made of a heat-resistant resin material such as PPS (polyphenylene sulfide), PAI (polyamideimide), PI (polyimide), or LCP (liquid crystal polymer). For example, both ends in the width direction are fixedly supported by side plates (not shown) of the fixing device 20. In FIG. 2, the cross-sectional shape of the nip forming member 26 that forms the nip portion N is formed in a flat shape, but the shape of the nip forming member 26 that forms the nip portion N is formed in a concave shape, It is also preferable to form it so as to continuously change from a concave shape to a concave shape.

  When the nip forming member 26 is on a plane and the shape of the nip portion N is substantially parallel to the image surface of the recording medium P, there is an effect of preventing the recording medium P from being wrinkled. Further, by bringing the shape close to the concave cross-sectional shape, the adhesion between the fixing belt 21 and the recording medium P is increased, and the fixing property is improved. Further, since the curvature of the fixing belt 21 on the exit side of the nip portion N increases, the recording medium P sent out from the nip portion N can be easily separated from the fixing belt 21.

  The reinforcing member 23 is for reinforcing and supporting the nip forming member 26 that forms the nip portion N, and is fixed to the inner peripheral surface side of the fixing belt 21. Further, the reinforcing member 23 is formed so that the length in the width direction is equal to that of the nip forming member 26, and both end portions in the width direction are fixedly supported by side plates (not shown) of the fixing device 20.

  The reinforcing member 23 abuts on the pressure roller 31 via the nip forming member 26 and the fixing belt 21, thereby preventing a problem that the nip forming member 26 is greatly deformed by the pressure applied by the pressure roller 31 in the nip portion N. doing. The reinforcing member 23 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron alloy in order to satisfy the above-described function.

  In addition, when the heater 25 is a heat source of a heating method using radiant heat such as a halogen heater, a reflecting member (reflector) 24 is provided on a part or all of the surface of the reinforcing member 23 facing the heater 25. preferable. Further, a heat insulating member can be provided, or BA (bright annealing) treatment or mirror polishing treatment can be performed. Since the radiant heat from the heater 25 toward the reinforcing member 23 (heat for heating the reinforcing member 23) is insulated or reflected and used for heating the fixing belt 21, the heating efficiency is further improved.

  The output control of the heater 25 is performed based on the detection result of the belt surface temperature by a temperature sensor (not shown) such as a thermistor facing the surface of the fixing belt 21. Further, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature by such output control of the heater 25. In FIG. 2, a halogen heater is used as an example of the heater 25. However, the type of the heat source is not limited to the halogen heater. For example, a fixing device having an induction heating type heat source, a resistance heating element, a carbon heater, or the like. It may be.

  In FIG. 2, the diameter of the fixing belt 21 is formed to be equal to the diameter of the pressure roller 31, but the diameter of the fixing belt 21 may be formed to be smaller than the diameter of the pressure roller 31. it can. In this case, since the curvature of the fixing belt 21 at the nip portion N is smaller than the curvature of the pressure roller 31, the recording medium P sent out from the nip portion N is easily separated from the fixing belt 21.

  Further, the fixing device 20 is provided with a contact / separation mechanism (not shown) for contacting and separating the pressure roller 31 with respect to the fixing belt 21, and the pressure roller 31 is fixed to the fixing belt 21 during a normal fixing process. Is pressed to form a desired nip portion N, and the pressure roller 31 is detached from the fixing belt 21 (or the fixing belt 21) at times other than the normal fixing process (during jam processing or standby). Is reduced pressure).

  Hereinafter, the normal operation of the fixing device 20 configured as described above will be briefly described. When the power switch of the image forming apparatus main body 1 is turned on, power is supplied to the heater 25, and the rotational driving of the pressure roller 31 in the direction of the arrow in FIG.

  Thereby, the fixing belt 21 is also driven (rotated) in the direction of the arrow in FIG. 2 by the frictional force with the pressure roller 31. Thereafter, the recording medium P is fed from the paper supply unit 12 and an unfixed color image is carried (transferred) on the recording medium P at the position of the secondary transfer roller 89 in FIG.

  The recording medium P carrying the unfixed image (toner image T) is conveyed while being guided by a guide plate (not shown), and is sent to the nip portion N of the fixing belt 21 and the pressure roller 31 that are in a pressure contact state. The The toner image T on the surface of the recording medium P is fixed by the heating by the fixing belt 21 heated by the heater 25 and the pressing force of the nip forming member 26 reinforced by the reinforcing member 23 and the pressure roller 31. The Thereafter, the recording medium P sent out from the nip portion N is conveyed to the paper discharge roller pair 99. With the fixing device 20 described above, the warm-up time can be shortened.

  Further, a heat transfer member (holding member) (not shown) made of a pipe-like metal body as a shape maintaining member that holds the inner peripheral surface of the fixing belt 21 and maintains the shape may be provided in the fixing belt 21. . The heat transfer member is provided at a position excluding the nip forming member 26 in the rotation direction of the fixing belt 21.

  The heat transfer member is, for example, a pipe-like member having a wall thickness of 0.2 mm or less. As a material for the heat transfer member, a metal heat conductor (a metal having heat conductivity) such as aluminum, iron, and stainless steel can be used. By setting the thickness of the heat transfer member to 0.2 mm or less, the heating efficiency of the fixing belt 21 can be improved.

  The gap A between the fixing belt 21 and the heat transfer member at normal temperature (gap at a position excluding the nip portion) is preferably greater than 0 mm and 1 mm or less (0 mm <A ≦ 1 mm).

  As a result, the area where the heat transfer member and the fixing belt 21 are in sliding contact with each other is increased, and the problem that the wear of the fixing belt 21 is accelerated is suppressed, and the heat transfer member and the fixing belt 21 are separated too much to heat the fixing belt 21. Inconveniences that reduce efficiency can be suppressed.

  Furthermore, since the heat transfer member is provided close to the fixing belt 21, the circular posture of the flexible fixing belt 21 is maintained to some extent, so that deterioration / breakage due to deformation of the fixing belt 21 can be reduced. .

  Further, in order to reduce the sliding resistance between the heat transfer member and the fixing belt 21, the sliding contact surface of the heat transfer member is formed of a material having a low friction coefficient, or a material containing fluorine on the inner peripheral surface of the fixing belt 21. A surface layer made of may be formed. Even if it forms so that the cross-sectional shape of a heat-transfer member may become substantially circular, you may form so that the cross-sectional shape of a heat-transfer member may become a polygon.

  Both ends of the heat transfer member in the width direction are fixedly supported by side plates (not shown) of the fixing device 20. The heat transfer member is heated by the radiant heat (radiant light) of the heater 25 configured by a halogen heater, a carbon heater, or the like, and heats the fixing belt 21. That is, the heat transfer member is directly heated by the heater 25 (heating means), and the fixing belt 21 is indirectly heated by the heater 25 through the heat transfer member.

(Holding of sliding sheet)
Hereinafter, a method for holding and fixing the sliding sheet 22 will be described in detail. As described above, in the nip portion N, the fixing belt 21 and the nip forming member 26 are in sliding contact. In order to reduce this sliding load, the nip forming member 26 and the inner peripheral surface of the fixing belt 21 are in contact with each other. A sliding sheet 22, which is a sheet-like member having high slidability, is interposed therebetween.

  Since the sliding sheet 22 must always be held between the nip forming member 26 and the fixing belt 21, when the sliding sheet 22 is provided, the sliding sheet 22 is provided on the surface of the nip forming member 26 as described above. The nip forming member 26 is superposed on the surface opposite to the nip portion and fastened with screws.

  The nip forming member 26 is pressed from the pressure roller 31 and abuts against the reinforcing member 23. The position of the nip forming member 26 directly affects the nip width and the nip pressure. Since the thickness of the sliding sheet 22 is likely to fluctuate depending on the pressurized state, the contact of the sliding sheet 22 with the reinforcing member 23 increases the variation in the nip shape.

  In order to solve this problem, a plurality of protrusions (convex shapes) are provided on the surface of the nip forming member 26 opposite to the nip portion, and the protrusions are exposed even when the sliding sheet 22 is wound. It has become. The exposed protrusions not including the sliding sheet 22 abut against the reinforcing member 23 so that the accuracy of the nip position can be maintained.

  However, several disadvantages can occur when the nip forming member 26 is configured as described above.

  First, it is necessary to provide a screw hole for fastening the wound slide sheet 22 on the surface opposite to the nip portion of the nip forming member 26. Here, as described above, a heat resistant resin material such as LCP or PPS is used for the nip forming member 26. However, generally, the process of making a screw hole is a secondary process, which requires a manufacturing cost. Although it is conceivable to mold the screw holes at the time of mold molding (primary processing), the degree of difficulty is high and manufacturing costs are increased. Further, since the nip forming member 26 is an important member that directly affects the nip shape, a molding method including a foreign matter such as an insert screw cannot be taken.

  In any processing method, it is necessary to provide a screw hole in the nip forming member 26 and fasten it. However, since it is a resin material, it is difficult to ensure the strength of the screw hole, and there is a possibility that it will be crushed during assembly. The sex was decreasing.

  Further, as described above, a plurality of protrusions are provided on the surface of the nip forming member 26 opposite to the nip portion, and are formed so as to come into contact with the reinforcing member 23 when pressed. Since the screw hole is provided in the surface opposite to the nip portion of the nip forming member 26, the protrusions cannot be molded integrally.

  Here, the shape connecting the vertices of the plurality of protrusions is an R for canceling (absorbing) the deflection of the reinforcing member 23 when receiving pressure from the pressure roller 31 in order to make the nip shape uniform. It has a shape.

  Accordingly, the heights of the protrusions are slightly different, and the heights on both sides of each protrusion are different. Thus, since the shape of the protrusion is complicated, high processing accuracy is required, the manufacturing difficulty is high, and time is also required for component inspection after completion, so it is difficult to reduce the cost.

  Furthermore, in order for the plurality of protrusions provided on the surface opposite to the nip portion of the nip forming member 26 to abut on the reinforcing member 23, it is necessary to make it higher than the screw head of the screw that fixes the sliding sheet 22.

  For this reason, the total thickness of the nip forming member 26 is increased at least by the height of the protruding portion. However, if the diameter of the fixing belt 21 is determined, the reinforcing member 23 disposed in the nip forming member 26 in the direction of the pressing force. It will be placed at the expense of height. Since the height of the reinforcing member 23 in the pressing force direction is the dimension that contributes most to the strength, the height of the reinforcing member 23 in the pressing force direction is as high as possible in the nip shape against variations in the pressing force. It can be said that stability can be improved.

  With respect to these points, in the fixing device 20 according to the present embodiment, the sliding sheet 22 is held in close contact with the nip forming member 26 by holding means 27 provided on a member different from the nip forming member 26. In this way, the holding means for the sliding sheet 22 is separated from the nip forming member 26.

  In the present embodiment, as shown in FIG. 2, the holding means 27 is provided on both the upstream side and the downstream side of the nip portion N in the rotation direction of the fixing belt 21 of the reinforcing member 23. For example, a fastening member (screw) is fastened to a screw hole provided in the reinforcing member 23. The holding means 27 is not limited to the reinforcing member 23, and for example, a dedicated holding member other than the nip forming member 26 fixed to the side plate of the fixing device 20 may be provided. Further, the holding method of the holding means 27 is not limited to the screw hole and the fastening member (screw), and any method can be used as long as the sliding sheet 22 can be fixed.

  As a result, there is no need to provide a screw hole for fixing the sliding sheet 22 on the surface opposite to the nip portion of the nip forming member 26, so that the above-described problem in processing does not occur, and the nip forming member 26 Is easy to mold. As a result, the processing cost can be reduced, and the screw holes are not crushed, so that the product yield can be improved and the manufacturing cost can be greatly reduced.

  In addition, as shown in FIG. 2, the nip forming member 26 is disposed in a bag-like space formed between the reinforcing member 23 and the sliding sheet 22 fixed to the reinforcing member 23. Can always be interposed between the nip forming member 26 and the fixing belt 21, and the sliding sheet 22 and the fixing belt 21 can be rotated both in the forward rotation (in the direction of the arrow in FIG. 2) and in the reverse rotation. The nip forming member 26 can be held in close contact.

  Further, since the sliding sheet 22 is not in close contact with the surface of the nip forming member 26 opposite to the nip portion, it is not necessary to secure a corresponding area (sheet fixing area) in addition to the screw hole. Further, since the nip forming member 26 is directly contacted and pressed against the reinforcing member 23 without using the sliding sheet 22, the positional accuracy of the nip forming member 26 can be improved.

  FIG. 3 is a perspective view of the nip forming member 26 as viewed from the surface opposite to the nip portion. In this embodiment, since it is not necessary to provide a screw hole in the nip forming member 26, as shown in FIG. 3, all the protruding portions 26a can be integrated with the connecting portion 26b so as to be integrally formed, and one unconnected portion is connected. From this point, the nip forming member 26 can be easily molded, and the manufacturing cost can be reduced.

  At the time of pressurization, the continuous protrusions come into contact with the reinforcing member 23, thereby canceling the deflection of the reinforcing member 23 due to the applied pressure and preventing local pressure loss, and having a uniform width in the axial direction. A uniform pressure nip can be obtained.

  Further, since there is no screw for fixing the sliding sheet 22 to the nip forming member 26, the height of the protrusion 26a can be reduced without considering the height relationship with the screw head. The total thickness of the forming member 26 can be greatly reduced.

Since this reduction can increase the strength of the reinforcing member 23 in order to improve the strength of the reinforcing member 23, it is possible to reduce fluctuations in the nip width and pressure against variations in the pressing force. it can.

  According to the fixing device 20 described above, the sliding sheet 22 is held by the holding means 27 other than the nip forming member 26 and fixed to the nip forming member 26, thereby fixing the sliding sheet 22 from the nip forming member 26. Therefore, the configuration of the nip forming member 26 can be simplified and the cost can be reduced.

  Further, the sliding sheet 22 is held and fixed to the reinforcing member 23, and the nip forming member 26 is disposed in a space formed between the reinforcing member 23 and the sliding sheet 22, thereby facilitating assembly. The sliding sheet 22 can be arranged uniformly over the entire nip surface of the nip forming member 26. Further, the sliding sheet 22 can be firmly held and fixed.

  Further, the sliding sheet 22 is not wound on the surface of the nip forming member 26 opposite to the nip portion, and the nip forming member 26 directly contacts the reinforcing member 23, thereby reducing the increase in dimensions. The nip position accuracy can be increased.

  In addition, by using the image forming apparatus (FIG. 1) including the fixing device 20 having the above-described configuration, a fixing device that can be easily assembled, is low-cost, and can obtain a uniform nip with little nip fluctuation is used. An image forming apparatus can be provided.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus main body 3 Exposure part 4Y, 4M, 4C, 4K Image forming part 5Y, 5M, 5C, 5K Photosensitive drum 12 Paper feed part 20 Fixing apparatus 21 Fixing belt 22 Sliding sheet 23 Reinforcing member (pressure stay)
24 Reflective member 25 Heater (heat source)
26 Nipping member 27 Holding means 31 Pressure roller 32 Core 33 Elastic layer 75 Charging unit 76 Developing unit 77 Cleaning unit 78 Intermediate transfer belts 79Y, 79M, 79C, 79K First transfer bias roller 80 Intermediate transfer cleaning unit 82 Secondary Transfer backup roller 83 Cleaning backup roller 84 Tension roller 85 Intermediate transfer unit 89 Secondary transfer roller 97 Paper feed roller 98 Registration roller pair 99 Paper discharge roller pair 100 Stack unit 101 Bottle storage units 102Y, 102M, 102C, 102K Toner bottle N Nip Part P Recording medium T Toner image

Japanese Patent Laid-Open No. 11-2982 JP-A-4-44075 JP-A-8-262903 JP-A-10-213984 JP 2007-334205 A JP 2010-96782 A JP 2011-70070 A

Claims (5)

A rotatable endless fixing belt;
A pressure roller disposed on the outer peripheral side of the fixing belt so as to be in pressure contact with the fixing belt;
A nip forming member that is disposed on the inner peripheral side of the fixing belt and forms a nip portion by pressure contact with the pressure roller via the fixing belt;
A reinforcing member fixed to an inner diameter portion of the fixing belt and supporting the nip forming member from a side opposite to the nip portion;
A heat source provided at a position sandwiching the nip forming member and the reinforcing member with respect to the nip portion on the inner peripheral side of the fixing belt, and heating the fixing belt,
In a fixing device that guides a recording medium carrying an unfixed image to the nip portion and causes the unfixed image to contact the fixing belt and pass the paper,
Having a sliding sheet between the nip forming member and the inner peripheral surface of the fixing belt;
The sliding sheet is held in close contact with the surface on the nip portion side of the nip forming member by holding means provided on both the upstream and downstream sides of the nip portion in the rotation direction of the fixing belt of the reinforcing member. It is,
The nip forming member is disposed in a space formed between the reinforcing member and the sliding sheet fixed to the reinforcing member,
The fixing device , wherein the nip forming member is in contact with the reinforcing member only on a surface opposite to the nip portion . The holding means holds the sliding sheet between the fixing belt and the nip forming member, and holds the sliding sheet and the nip forming member in close contact regardless of the rotation direction of the fixing belt. The fixing device according to claim 1 . Opposite side of the nip portion of the nip forming member, the fixing device according to claim 1 or 2, characterized in the reinforcing member and to abut without passing through the sliding sheet. The surface of the nip forming member opposite to the nip portion has a plurality of protrusions that come into contact with the reinforcing member,
The fixing device according to any one of what is protruding formed integrally via a raised portion connecting portion from claim 1, wherein up to 3. An image forming apparatus comprising: a fixing device according to any one of claims 1 to 4.

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