JP2005338761A - Fixing apparatus, silicon rubber composition and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of a temperature droop phenomenon correspondingly to speed-up of an image forming apparatus and to shorten warm-up time as much as possible. <P>SOLUTION: A fixing apparatus 60 for fixing a toner image carried on paper P is provided with: a halogen heater 66; a fixing roll 61 on which a heat resisting elastic layer 612 is arranged; and an endless belt 62 forming a nip part N through which the paper P passes while pressing it with contact with the fixing roll 61. The fixing roll 61 is molded by blending a heat conductivity providing agent and low melting point metallic alloy particles with silicon rubber. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device and the like, and more particularly to a fixing device used in an image forming apparatus using an electrophotographic system.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, for example, a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged, and the photosensitive drum is controlled based on image information. An electrostatic latent image is formed on the photosensitive drum by exposure with the exposed light. The electrostatic latent image is converted into a visible image (toner image) with toner, and the toner image is further transferred onto a recording sheet and fixed by a fixing device to form an image.

  As shown in FIG. 10, the fixing device used in such an image forming apparatus includes a heating source 114 inside a cylindrical cored bar 111, a heat resistant elastic layer 112 on the cored bar 111, and an outer peripheral surface thereof. A fixing roll 110 formed by laminating a release layer 113 on the core, a pressure-contacting arrangement with respect to the fixing roll 110, a heat-resistant elastic body layer 122 on a core metal 121, and a heat-resistant resin film or It comprises a pressure roll 120 formed by laminating a release layer 123 made of a heat resistant rubber coating. Then, the recording paper carrying the unfixed toner image is passed between the fixing roll 110 and the pressure roll 120, and the unfixed toner image is heated and pressed to thereby apply the toner to the recording paper. The image is fixed. Such a fixing device is called a two-roll system and is generally widely used.

By the way, in order to increase the speed in the two-roll type fixing device, it is necessary to increase the nip width in proportion to the fixing speed in order to supply a sufficient amount of heat to the toner and the recording paper. As a method of widening the nip width, there are a method of increasing the load between the fixing roll and the pressure roll, a method of increasing the thickness of the elastic body, and a method of increasing the roll diameter.
However, in the method of increasing the load and the method of increasing the thickness of the elastic body, the uneven nip width and paper wrinkle occur because the shape of the nip width due to the deflection of the roll becomes non-uniform along the roll axis. This causes image quality problems such as In addition, the method of increasing the roll diameter causes problems that the apparatus is increased in size and the time (warm-up time) until the fixing roll is raised from room temperature to a fixable temperature is increased.

  Accordingly, in order to cope with these problems and to realize a fixing device corresponding to the speeding up of the image forming apparatus, the applicant of the present invention has a rotatable fixing roll whose surface is elastically deformed and remains in contact with the fixing roll. An endless belt capable of traveling and a pressure pad arranged in a non-rotating state inside the endless belt, and the endless belt is pressed against the fixing roll so that a contact surface with the fixing roll is formed by the pressure pad. And a belt nip so that the sheet can be passed between the endless belt and the fixing roll, and a fixing device configured to locally elastically deform the exit side of the sheet on the surface of the fixing roll. The technique regarding this is proposed (for example, refer patent document 1).

  In the fixing device (referred to as “belt nip method”) described in Patent Document 1, an endless belt is pressed against the fixing roll using a pressure pad instead of the pressure roll in the conventional two-roll type fixing device. . By adopting such a configuration, the width of the belt nip formed by the fixing roll and the endless belt can be easily made larger than the width of the roll nip between the conventional fixing roll and the pressure roll. It is easy to reduce the size of the apparatus.

  In particular, the heat capacity of the endless belt brought into pressure contact with the fixing roll is small, and further, the heat transmitted from the fixing roll is hardly dissipated because the pressure pad is arranged in a non-rotating state. Therefore, even when rotation of the fixing roll is started, the amount of heat taken from the fixing roll to the endless belt side is small, and the efficiency of using heat for melting the toner is increased, and the temperature decrease amount at the belt nip is also small. There is an advantage that the fixing property of the toner can be improved.

Japanese Patent No. 3298354 (pages 4-7)

  However, even in the belt nip type fixing device described above, when the speed of the image forming apparatus is advanced and fixing processing is performed on a large number of recording papers that are continuously fed in a short time, image forming is performed. A so-called “temperature droop” phenomenon occurs in which the surface temperature of the fixing roll temporarily decreases when the apparatus starts up. This temperature droop phenomenon is caused even when a sufficient amount of heat is supplied from the inside of the fixing roll because the elastic body layer made of silicone rubber or the like coated on the core metal of the fixing roll acts as a thermal resistor. This is because a time lag occurs before the toner is transmitted to the surface of the fixing roll. In particular, when fixing thick paper or the like having a large heat capacity, the amount of heat taken away from the surface of the fixing roll increases, so that the temperature droop tends to increase. Therefore, when the image forming apparatus is further increased in speed, there arises a new problem that a fixing defect is likely to occur in a certain number of recording sheets until the surface temperature of the fixing roll is recovered.

Further, even in the belt nip type fixing device, since the elastic layer made of silicone rubber or the like coated on the core metal of the fixing roll acts as a thermal resistor, the fixing roll at the time of starting up the image forming apparatus There is also a problem that there is a warm-up time until the temperature is raised from room temperature to a fixable temperature, and the warm-up time tends to become longer due to the increase in the diameter and heat capacity of the fixing roll accompanying the increase in the speed of the image forming apparatus. Arise.
These problems also exist in the conventional two-roll fixing device, and become more serious in the two-roll fixing device.

Accordingly, the present invention has been made to solve the technical problems as described above, and an object of the present invention is to suppress the occurrence of the temperature droop phenomenon corresponding to the speeding up of the image forming apparatus. It is an object of the present invention to provide a fixing device capable of achieving the above.
Another object is to shorten the warm-up time as much as possible.

  For this purpose, the fixing device of the present invention is a fixing device for fixing a toner image carried on a recording material, and includes a fixing member having a heating source and provided with an elastic layer, and a fixing member. A pressure member that forms a nip through which the recording paper passes while being pressed, and the fixing member was formed by blending a thermal conductivity-imparting agent and low-melting-point metal alloy particles in silicone rubber. It is characterized by.

Here, the elastic layer of the fixing member is characterized in that the low melting point metal alloy particles are melted and the melted low melting point metal alloy particles form a state in which the thermal conductivity-imparting agents are bonded to each other. it can. Further, the elastic layer of the fixing member may be characterized in that the low melting point metal alloy particles have a melting point not higher than the processing maximum temperature of the silicone rubber. Further, the elastic layer of the fixing member may be characterized in that the average particle diameter of the low melting point metal alloy particles is 1.0 to 1000 μm. Moreover, the compounding quantity of a low melting metal alloy particle can also be characterized by being 10-1000 weight part with respect to 100 weight part of silicone rubber.
Further, the fixing member may be a fixing roll or a fixing belt. Further, the pressure member is a belt member, and is disposed inside the belt member, and presses the belt member against the fixing member to form a nip portion through which the recording material passes between the fixing member and the belt member. It can also be characterized by further comprising.

Further, the present invention is regarded as a silicone rubber composition, and the silicone rubber composition of the present invention can be characterized by blending a silicone rubber base material with a heat conductive filler and low melting point metal alloy particles.
Here, the low melting point metal alloy particles may be characterized by having a melting point not higher than the maximum processing temperature of the silicone rubber base material. The low melting point metal alloy particles may be characterized by having an average particle size of 1.0 to 1000 μm. Furthermore, the blending amount of the low melting point metal alloy particles may be 10 to 1000 parts by weight with respect to 100 parts by weight of the silicone rubber.

  Further, the present invention is regarded as an image forming apparatus. The image forming apparatus of the present invention includes a toner image forming unit that forms a toner image, and a transfer unit that transfers the toner image formed by the toner image forming unit onto a recording material. A fixing means for fixing the toner image transferred onto the recording material to the recording material, the fixing means having a heating source, and blending a silicone rubber with a thermal conductivity-imparting agent and low melting point metal alloy particles. The fixing member is provided with a molded elastic layer, and a pressure member that forms a nip portion through which the recording paper passes while being pressed against the fixing member.

  As an effect of the present invention, it is possible to suppress the occurrence of the temperature droop phenomenon in the fixing device corresponding to the speeding up of the image forming apparatus. At the same time, the warm-up time can be shortened.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus shown in FIG. 1 is an intermediate transfer type image forming apparatus generally called a tandem type, and a plurality of image forming units 1Y, 1M, 1C, and 1K on which toner images of respective color components are formed by electrophotography. The primary transfer unit 10 that sequentially transfers (primary transfer) the color component toner images formed by the image forming units 1Y, 1M, 1C, and 1K to the intermediate transfer belt 15, and the superimposed toner image transferred onto the intermediate transfer belt 15. Are provided with a secondary transfer unit 20 that collectively transfers (secondary transfer) to a paper P that is a recording material (recording paper), and a fixing device 60 that fixes the secondary transferred image onto the paper P. Moreover, it has the control part 40 which controls operation | movement of each apparatus (each part).

  In the present embodiment, each of the image forming units 1Y, 1M, 1C, and 1K has a charger 12 that charges the photosensitive drum 11 around the photosensitive drum 11 that rotates in the direction of arrow A, and the photosensitive drum 11. A laser exposure device 13 for writing an electrostatic latent image thereon (exposure beam is indicated by a symbol Bm in the figure), each color component toner is accommodated, and the electrostatic latent image on the photosensitive drum 11 is visualized with toner. A developing unit 14, a primary transfer roll 16 that transfers each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15 in the primary transfer unit 10, and a drum cleaner that removes residual toner on the photosensitive drum 11. 17 and the like are sequentially arranged. These image forming units 1Y, 1M, 1C, and 1K are arranged in a substantially straight line from the upstream side of the intermediate transfer belt 15 in the order of yellow (Y), magenta (M), cyan (C), and black (K). Has been.

The intermediate transfer belt 15 as an intermediate transfer member is constituted by a film-like endless belt in which an appropriate amount of an antistatic agent such as carbon black is contained in a resin such as polyimide or polyamide. And the volume resistivity is formed so that it may become 10 < ⁶ > -10 < ¹⁴ > (omega | ohm) cm, The thickness is comprised by about 0.1 mm, for example. The intermediate transfer belt 15 is circulated and driven (rotated) at a predetermined speed in the direction B shown in FIG. 1 by various rolls. As these various rolls, a drive roll 31 that is driven by a motor (not shown) excellent in constant speed and rotates the intermediate transfer belt 15, and an intermediate that extends substantially linearly along the arrangement direction of the photosensitive drums 11. A support roll 32 that supports the transfer belt 15, a tension roll 33 that functions as a correction roll that applies a constant tension to the intermediate transfer belt 15 and prevents meandering of the intermediate transfer belt 15, and a backup provided in the secondary transfer unit 20. A cleaning backup roll 34 provided in a cleaning unit for scraping off residual toner on the roll 25 and the intermediate transfer belt 15 is provided.

The primary transfer unit 10 includes a primary transfer roll 16 that is disposed to face the photosensitive drum 11 with the intermediate transfer belt 15 interposed therebetween. The primary transfer roll 16 includes a shaft and a sponge layer as an elastic layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll formed of a blend rubber of NBR, SBR and EPDM containing a conductive agent such as carbon black and having a volume resistivity of 10 ^7.5 to 10 ^8.5 Ωcm. The primary transfer roll 16 is placed in pressure contact with the photosensitive drum 11 with the intermediate transfer belt 15 in between, and the primary transfer roll 16 has a voltage (with negative polarity; the same applies hereinafter) having a polarity opposite to that of the toner. (Primary transfer bias) is applied. As a result, the toner images on the respective photosensitive drums 11 are sequentially electrostatically attracted to the intermediate transfer belt 15 so as to form superimposed toner images on the intermediate transfer belt 15.

The secondary transfer unit 20 includes a secondary transfer roll 22 disposed on the toner image carrying surface side of the intermediate transfer belt 15 and a backup roll 25. The backup roll 25 is composed of a tube of EPDM and NBR blend rubber with carbon dispersed on the surface, and EPDM rubber on the inside. And it forms so that the surface resistivity may be 10 < ⁷ > -10 < ¹⁰ > (omega | ohm) / square, and hardness is set to 70 degrees (Asker C), for example. The backup roll 25 is disposed on the back side of the intermediate transfer belt 15 to form a counter electrode of the secondary transfer roll 22, and a metal power supply roll 26 to which a secondary transfer bias is stably applied is disposed in contact with the backup roll 25. ing.

On the other hand, the secondary transfer roll 22 includes a shaft and a sponge layer as an elastic layer fixed around the shaft. The shaft is a cylindrical bar made of metal such as iron or SUS. The sponge layer is a sponge-like cylindrical roll formed of a blend rubber of NBR, SBR and EPDM containing a conductive agent such as carbon black and having a volume resistivity of 10 ^7.5 to 10 ^8.5 Ωcm. The secondary transfer roll 22 is disposed in pressure contact with the backup roll 25 with the intermediate transfer belt 15 interposed therebetween. Further, the secondary transfer roll 22 is grounded, and a secondary transfer bias is formed between the secondary transfer roll 22 and the backup roll 25. The toner image is secondarily transferred onto the paper P conveyed to the transfer unit 20.

  Further, on the downstream side of the secondary transfer portion 20 of the intermediate transfer belt 15, an intermediate transfer belt that removes residual toner and paper dust on the intermediate transfer belt 15 after the secondary transfer and cleans the surface of the intermediate transfer belt 15. A cleaner 35 is provided so as to be able to contact and separate. On the other hand, on the upstream side of the yellow image forming unit 1Y, a reference sensor (home position sensor) 42 that generates a reference signal serving as a reference for taking image forming timings in the image forming units 1Y, 1M, 1C, and 1K. It is arranged. Further, an image density sensor 43 for adjusting image quality is disposed on the downstream side of the black image forming unit 1K. The reference sensor 42 recognizes a predetermined mark provided on the back side of the intermediate transfer belt 15 and generates a reference signal. Each image forming unit is instructed by an instruction from the control unit 40 based on the recognition of the reference signal. 1Y, 1M, 1C, and 1K are configured to start image formation.

  Further, in the image forming apparatus according to the present embodiment, as a paper transport system, a paper tray 50 that stores paper P, a pickup roll 51 that picks up and transports the paper P accumulated in the paper tray 50 at a predetermined timing, and a pickup A transport roll 52 that transports the paper P fed by the roll 51, a transport chute 53 that feeds the paper P transported by the transport roll 52 to the secondary transfer unit 20, and transported after being secondarily transferred by the secondary transfer roll 22. A conveyance belt 55 that conveys the paper P to be fixed to the fixing device 60 and a fixing inlet guide 56 that guides the paper P to the fixing device 60 are provided.

  Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. In the image forming apparatus as shown in FIG. 1, image data output from an image reading device (IIT) not shown or a personal computer (PC) not shown is subjected to predetermined image processing by an image processing device (IPS) not shown. After being applied, the image forming operation is executed by the image forming units 1Y, 1M, 1C, and 1K. In IPS, the input reflectance data is subjected to predetermined image processing such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color editing, moving editing, and other various image editing. Is done. The image data that has undergone image processing is converted into color material gradation data of four colors, Y, M, C, and K, and is output to the laser exposure unit 13.

  The laser exposure unit 13 irradiates the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K, for example, with an exposure beam Bm emitted from a semiconductor laser in accordance with the input color material gradation data. Yes. In each of the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K, the surface is charged by the charger 12, and then the surface is scanned and exposed by the laser exposure unit 13 to form an electrostatic latent image. The formed electrostatic latent images are developed as toner images of respective colors Y, M, C, and K by the respective image forming units 1Y, 1M, 1C, and 1K.

  The toner images formed on the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K are transferred onto the intermediate transfer belt 15 in the primary transfer unit 10 where the photosensitive drums 11 and the intermediate transfer belt 15 come into contact with each other. Transcribed. More specifically, in the primary transfer portion 10, a voltage (primary transfer bias) having a polarity opposite to the toner charging polarity (minus polarity) is applied to the base material of the intermediate transfer belt 15 by the primary transfer roll 16, and the toner image. Are sequentially superimposed on the surface of the intermediate transfer belt 15 to perform primary transfer.

  After the toner images are sequentially primary transferred onto the surface of the intermediate transfer belt 15, the intermediate transfer belt 15 moves and the toner image is conveyed to the secondary transfer unit 20. When the toner image is transported to the secondary transfer unit 20, in the paper transport system, the pick-up roll 51 rotates in accordance with the timing at which the toner image is transported to the secondary transfer unit 20, and the paper of a predetermined size is transferred from the paper tray 50. P is supplied. The paper P supplied by the pickup roll 51 is transported by the transport roll 52 and reaches the secondary transfer unit 20 via the transport chute 53. Before reaching the secondary transfer unit 20, the paper P is temporarily stopped, and a registration roll (not shown) rotates in accordance with the movement timing of the intermediate transfer belt 15 on which the toner image is carried. And the position of the toner image are aligned.

  In the secondary transfer unit 20, the secondary transfer roll 22 is pressed against the backup roll 25 via the intermediate transfer belt 15. At this time, the sheet P conveyed at the same timing is sandwiched between the intermediate transfer belt 15 and the secondary transfer roll 22. At this time, when a voltage (secondary transfer bias) having the same polarity as the toner charging polarity (negative polarity) is applied from the power supply roll 26, a transfer electric field is formed between the secondary transfer roll 22 and the backup roll 25. Is done. The unfixed toner image carried on the intermediate transfer belt 15 is collectively electrostatically transferred onto the paper P in the secondary transfer unit 20 pressed by the secondary transfer roll 22 and the backup roll 25. .

Thereafter, the sheet P on which the toner image has been electrostatically transferred is transported as it is while being peeled off from the intermediate transfer belt 15 by the secondary transfer roll 22, and transported downstream of the secondary transfer roll 22 in the sheet transport direction. It is conveyed to the belt 55. The conveyance belt 55 conveys the paper P to the fixing device 60 in accordance with the optimum conveyance speed in the fixing device 60. The unfixed toner image on the paper P conveyed to the fixing device 60 is fixed on the paper P by being subjected to a fixing process by heat and pressure by the fixing device 60. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge placement unit provided in a discharge unit of the image forming apparatus.
On the other hand, after the transfer onto the paper P is completed, the residual toner remaining on the intermediate transfer belt 15 is conveyed to the cleaning unit as the intermediate transfer belt 15 rotates, and the cleaning backup roll 34 and the intermediate transfer belt cleaner 35 are transferred. Is removed from the intermediate transfer belt 15.

  Next, the fixing device 60 used in the image forming apparatus of the present embodiment will be described. FIG. 2 is a side sectional view showing a configuration of the fixing device 60 of the present embodiment. The fixing device 60 includes a fixing roll 61 as an example of a fixing member, an endless belt 62 as an example of a belt member (pressure member), and an example of a pressure member that is pressed from the fixing roll 61 via the endless belt 62. The main part is constituted by the pressure pad 64.

The fixing roll 61 is a cylindrical roll whose surface has elasticity, is rotatably supported, and rotates at a surface speed of, for example, 194 mm / s.
In addition, a halogen heater 66 as a heating source is disposed inside the fixing roll 61 and is configured to supply heat to the fixing roll 61. At this time, a temperature sensor 69 is disposed in contact with the surface of the fixing roll 61, and the control unit 40 of the image forming apparatus controls lighting of the halogen heater 66 based on a temperature measurement value by the temperature sensor 69. The surface temperature of the fixing roll 61 is adjusted to maintain a predetermined set temperature (for example, 175 ° C.).

The endless belt 62 is rotatable by a pressure pad 64 and a belt guide member 63 disposed inside the endless belt 62, and edge guide members 80 (see FIG. 3 in the subsequent stage) disposed at both ends of the endless belt 62. It is supported by. Then, it is arranged so as to be in pressure contact with the fixing roll 61 at the nip portion N, and rotates at a moving speed of 194 mm / s following the fixing roll 61.
Here, FIG. 3 is a cross-sectional configuration diagram illustrating a configuration in which the endless belt 62 is supported, and shows one end region of the fixing device 60 as viewed from the downstream side in the conveyance direction of the paper P.
As shown in FIG. 3, edge guide members 80 are fixed to both ends of a holder 65 disposed inside the endless belt 62. The edge guide member 80 is provided on the outer side of the belt traveling guide portion 801 having a cylindrical shape in which a notch is formed in a portion corresponding to the nip portion N and the vicinity thereof, that is, a C-shaped cross section, A flange portion 802 formed with an outer diameter larger than the inner diameter of the endless belt 62 and a holding portion 803 provided outside the flange portion 802 for positioning and fixing the edge guide member 80 to the fixing device 60 main body. Has been.

The endless belt 62 is supported by the outer peripheral surface of the belt traveling guide portion 801 except for the nip portion N and the vicinity thereof, and rotates along the outer peripheral surface of the belt traveling guide portion 801. . Accordingly, the belt traveling guide portion 801 is formed of a material having a small friction coefficient so that the endless belt 62 can smoothly rotate, and further has a low thermal conductivity so that it is difficult to remove heat from the endless belt 62. It is made of material.
Further, the flange portion 802 is disposed such that inner surfaces of both flange portions 802 disposed so as to face each other at both end portions of the holder 65 have an interval substantially matching the width of the endless belt 62. When the endless belt 62 rotates, the end of the endless belt 62 abuts against the inner surface of the flange portion 802, so that the movement of the endless belt 62 in the width direction (belt walk) is limited. . As described above, the endless belt 62 is supported by the edge guide member 80 so that the deviation is regulated.

Further, the endless belt 62 is supported by the pressure pad 64 and the belt guide member 63 in the longitudinal region excluding both ends of the endless belt 62 (see also FIG. 2). In the region excluding both ends of the endless belt 62, the inner peripheral surface of the endless belt 62 rotates while sliding on the pressure pad 64 and the belt guide member 63.
The belt guide member 63 is attached to a holder 65 disposed inside the endless belt 62, and is formed of a material having a small friction coefficient so that the endless belt 62 can smoothly rotate. Further, it is preferable that the endless belt 62 is made of a material having low thermal conductivity so that it is difficult to remove heat from the endless belt 62.

Next, the pressure pad 64 is disposed inside the endless belt 62 while being pressed against the fixing roll 61 via the endless belt 62, and forms a nip portion N with the fixing roll 61. In the pressure pad 64, a pre-nip member 64 a for securing a wide nip portion N is disposed on the inlet side (upstream side) of the nip portion N. Further, by locally pressing the surface of the fixing roll 61, the toner image surface is smoothed to give image gloss, and the surface of the fixing roll 61 is distorted (dented) to form a down curl on the paper P. The peeling nip member 64b is disposed on the outlet side (downstream side) of the nip portion N. Further, the pressure pad 64 is provided with a low friction sheet 68 on the surface in contact with the endless belt 62 in order to reduce the sliding resistance between the inner peripheral surface of the endless belt 62 and the pressure pad 64.
The pressure pad 64 and the low friction sheet 68 are supported by a metal holder 65.

  The fixing roll 61 is connected to a drive motor (not shown) and rotates in the direction of arrow C. Following this rotation, the endless belt 62 also rotates in the same direction as the fixing roll 61. The sheet P on which the toner image is electrostatically transferred in the secondary transfer unit 20 of the image forming apparatus shown in FIG. 1 is guided by the fixing inlet guide 56 and conveyed to the nip N. When the paper P passes through the nip portion N, the toner image on the paper P is fixed by the pressure acting on the nip portion N and the heat supplied from the fixing roll 61. In the fixing device 60 of the present embodiment, since the nip portion N can be configured widely by the concave pre-nip member 64a that substantially follows the outer peripheral surface of the fixing roll 61, stable fixing performance can be ensured.

  In the vicinity of the downstream side of the nip portion N, the paper P peeled off from the fixing roll 61 by the peeling nip member 64b is completely separated from the fixing roll 61 and guided to the paper discharge path toward the discharge portion of the image forming apparatus. A peeling assisting member 70 is provided for this purpose. The peeling auxiliary member 70 is held by a baffle holder 72 in a state in which the peeling baffle 71 is close to the fixing roll 61 in a direction (counter direction) opposite to the rotation direction of the fixing roll 61.

Next, each member constituting the fixing device 60 will be described in detail.
First, the endless belt 62 is a seamless endless belt whose original shape is formed in a cylindrical shape so that a defect due to the seam does not occur in the output image. The base layer and the surface of the base layer on the fixing roll 61 side Or it is comprised from the release layer coat | covered on both surfaces. The base layer is formed of a polymer such as thermosetting polyimide, thermoplastic polyimide, polyamide, or polyamideimide, and has a thickness of 30 to 200 μm, preferably 50 to 125 μm, and more preferably about 75 to 100 μm. As the release layer to be coated on the surface of the base layer, fluororesin such as tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer It is formed of coalescence (FEP) and has a thickness of about 5 to 100 μm, preferably about 10 to 30 μm.
In the fixing device 60 of the present embodiment, an endless belt 62 having a configuration in which a release layer made of PFA having a thickness of 30 μm is laminated on a base layer made of thermosetting polyimide having a circumferential length of 94 mm, a thickness of 75 μm, and a width of 320 mm. Used.

As described above, the pressure pad 64 disposed inside the endless belt 62 includes the pre-nip member 64a and the peeling nip member 64b, and is a holder that presses the fixing roll 61 with a load of, for example, 35 kgf by a spring or an elastic body. 65 is supported. An elastic body such as silicone rubber or fluororubber, a leaf spring, or the like can be used for the prenip member 64 a, and the surface on the fixing roll 61 side is formed with a concave curved surface that substantially follows the outer peripheral surface of the fixing roll 61. In the fixing device 60 of the present embodiment, silicone rubber having a width of 10 mm, a thickness of 5 mm, and a length of 320 mm is used.
The peeling nip member 64b is formed of a heat-resistant resin such as PPS (polyphenylene sulfide), polyimide, polyester, polyamide, or a metal such as iron, aluminum, or SUS. As the shape of the peeling nip member 64b, the outer surface shape in the nip portion N is formed as a convex curved surface having a constant radius of curvature.
In the fixing device 60 of the present embodiment, the endless belt 62 is wrapped around the fixing roll 61 by the pressure pad 64 at a winding angle of about 40 ° to form a nip portion N having a width of about 10 mm.

The low friction sheet 68 is provided on the inner peripheral surface side of the endless belt 62 of the pressure pad 64 in order to reduce sliding resistance (friction resistance) between the inner peripheral surface of the endless belt 62 and the pressure pad 64, and has a small friction coefficient. Materials with excellent wear resistance and heat resistance are suitable. Specifically, sintered molded PTFE resin sheets, glass fiber sheets impregnated with Teflon (registered trademark), laminated sheets in which a glass fiber sheet made of a fluororesin is heated and fused, sand, FEP film, polyimide film Etc. can be used.
The low friction sheet 68 is preferably formed of a material that does not have a hole on the surface and does not have wettability and permeability to the lubricant. Since the low friction sheet 68 is formed of a material that has no holes on the surface and does not penetrate or permeate the lubricant, the lubricant can be prevented from seeping into the low friction sheet 68. The lubricant can be maintained stably without being lost. Further, it is possible to prevent the lubricant from penetrating into the pre-nip member 64a to swell and the nip pressure from being lowered.
Here, if the low friction sheet 68 is disposed on the inner peripheral surface side of the endless belt 62 of the pressure pad 64, the low friction sheet 68 may be separated from the pressure pad 64 even if the low friction sheet 68 is configured separately from the pressure pad 64. It may be configured integrally or any of them.

  Also, the belt guide member 63 disposed in the holder 65 is formed with a plurality of ribs in the rotational direction of the endless belt 62 so as to minimize the contact area with the inner peripheral surface of the endless belt 62. As described above, the belt guide member 63 is made of a material having a low coefficient of friction and low thermal conductivity so that the endless belt 62 does not easily take heat because it rubs against the inner peripheral surface of the endless belt 62. A heat-resistant resin such as PFA or PPS is used.

  Further, the holder 65 is provided with a lubricant application member 67 along the longitudinal direction of the fixing device 60. The lubricant application member 67 is disposed so as to contact the inner peripheral surface of the endless belt 62 and supplies an appropriate amount of lubricant. As a result, the lubricant is supplied to the sliding portion between the endless belt 62 and the low friction sheet 68, and the sliding resistance between the endless belt 62 and the pressure pad 64 via the low friction sheet 68 is further reduced. 62 is smoothly rotated. Further, it has an effect of suppressing wear on the inner peripheral surface of the endless belt 62 and the surface of the low friction sheet 68.

  Here, as the lubricant, a lubricant having durability against long-term use under a fixing temperature environment and capable of maintaining wettability with the inner peripheral surface of the endless belt 62 is suitable. For example, liquid oil such as silicone oil or fluorine oil, grease in which a solid substance and a liquid are mixed, or a combination thereof can be used. Examples of the silicone oil include dimethyl silicone oil, amino-modified silicone oil, carboxy-modified silicone oil, silanol-modified silicone oil, sulfonic acid-modified silicone oil, and the like. Modified silicone oil is preferred.

Next, the fixing roll 61 according to this embodiment will be described.
FIG. 4 is a cross-sectional view showing the structure of the fixing roll 61. As shown in FIG. 4, the fixing roll 61 is configured by laminating a heat-resistant elastic body layer 612 and a release layer 613 as an elastic layer on a core (cylindrical core metal) 611. The core 611 is formed of a metal having high thermal conductivity such as iron, aluminum, SUS, and the fixing device 60 of the present embodiment is configured by a cylindrical body having an outer diameter of 30 mm and a length of 360 mm.
For the release layer 613, for example, a heat-resistant resin such as a silicone resin or a fluororesin is used, and a fluororesin is suitable from the viewpoint of the releasability to the toner and the wear resistance. As the fluororesin, PFA, PTFE, FEP or the like can be used. The thickness of the release layer 613 is preferably 5 to 30 μm. In the fixing device 60 of the present embodiment, PFA with a thickness of 30 μm is coated and the surface is finished close to a mirror surface state.

Next, the heat resistant elastic layer 612 will be described. The heat-resistant elastic body layer 612 used for the fixing roll 61 of the present embodiment is made of a silicone rubber as a base material, a base material silicone rubber, a heat conductive filler as a thermal conductivity imparting agent, and a base material silicone rubber. A silicone rubber composition containing low melting point metal alloy particles having a melting point equal to or lower than the processing temperature (molding temperature) is molded.
Thus, the heat conductivity of the heat resistant elastic body layer 612 can be improved by forming the heat resistant elastic body layer 612 by molding the silicone rubber composition. For this reason, the occurrence of a so-called “temperature droop” phenomenon in which the surface temperature of the fixing roll 61 temporarily decreases when the image forming apparatus starts up, and further, the time until the fixing roll 61 is raised from room temperature to a fixable temperature. (Warm-up time) can be shortened.

FIG. 5 is a view for explaining the structure of the silicone rubber composition constituting the heat resistant elastic layer 612. As shown in FIG. 5, in such a silicone rubber composition, the low-melting point metal alloy particles dispersed in the silicone rubber base material are melted during the processing (molding) of the silicone rubber. Similarly, dispersed thermal conductive fillers are bonded together to form a thermal conduction path between the thermal conductive filler and the thermal conductive filler. For this reason, in the silicone rubber composition, the heat conduction stretched organically with the heat conductive filler as a core by the heat conductive filler and the low melting point metal alloy bonding the heat conductive fillers. A highly meshed network is built. Thereby, in the silicone rubber composition, a structure in which heat is easily transmitted through the mesh is formed, and the heat conduction efficiency can be extremely increased.
That is, in the conventional configuration in which only the heat conductive filler is dispersed, the heat conductive fillers are isolated from each other and exist in the base material silicone rubber, and therefore, between the heat conductive filler and the heat conductive filler. Since the base material silicone rubber having low thermal conductivity is interposed, there is a certain limit to the heat conduction efficiency. On the other hand, in the silicone rubber composition constituting the heat-resistant elastic body layer 612 of the present embodiment, the heat is an organically stretched mesh having a thermally conductive filler as a core and having a high thermal conductivity. Therefore, the heat conduction efficiency can be made extremely high.

In addition, although the method of increasing the heat conductive efficiency by increasing the blending amount of the heat conductive filler internally added to the base material silicone rubber and increasing the density of the heat conductive filler is also conceivable, the blending amount of the heat conductive filler However, it is possible to increase the heat conduction efficiency to some extent, but the heat conductive filler in the base silicone rubber becomes rich, for example, the rubber hardness increases or the rubber elasticity decreases. Such as deterioration of the rubber properties of the silicone rubber itself, such as deterioration of heat resistance and processability, and it is difficult to satisfy the use of the fixing roll 61 as the heat resistant elastic body layer 612. Become.
However, in the silicone rubber composition that constitutes the heat-resistant elastic body layer 612 of the present embodiment, by forming a mesh of high thermal conductivity stretched organically with the thermal conductive filler as a core. Since extremely high heat conduction efficiency is realized, the blending amount of the heat conductive filler to be internally added can be suppressed to the minimum necessary amount. Further, the mechanical bonding force between the heat conductive filler and the heat conductive filler due to the low melting point metal alloy is extremely moderate, and the influence on the rubber properties of the base material silicone rubber is negligible. Therefore, it is possible to ensure desired rubber characteristics of the silicone rubber itself.

Here, the operation of the heat-resistant elastic body layer 612 used in the fixing roll 61 of this embodiment will be described.
In the fixing device 60, when the paper P is successively conveyed to the nip portion N and continuous fixing is performed, the paper P and the unfixed toner image are deprived of heat at the nip portion N and heat is radiated from the endless belt 62. For this reason, the surface temperature of the fixing roll 61 decreases. On the other hand, although heat energy is supplied from the inside of the fixing roll 61 by the halogen heater 66, the heat-resistant elastic body layer 612 of the fixing roll 61 becomes a thermal resistor until the heat reaches the surface of the fixing roll 61. There is a time lag.
Therefore, in the conventional general two-roll type or belt nip type fixing device, as the speed of the image forming apparatus progresses, the fixing roller 61 passes through a region (nip portion N) where it contacts the paper P. After that, it is likely to be extremely difficult to return the fixing roll 61 having a large heat capacity to a predetermined fixing temperature during one rotation until the nip portion N is returned again. If the predetermined fixing temperature is not reached during one rotation of the fixing roll 61, particularly when the image forming apparatus starts up, a temperature droop occurs to cause a fixing defect, or for the same reason, warm-up is performed. The time is getting longer.

On the other hand, in the heat resistant elastic layer 612 using the silicone rubber composition of the present embodiment, the low melting point metal alloy particles dispersed in the silicone rubber base material in the heat resistant elastic layer 612 are silicone rubber. The heat conductive filler melted at the time of processing (molding) and bonded together in the same manner in the base material of the silicone rubber and bonded with the heat conductive filler. A high meshwork is built to form a path for heat transfer. Thereby, the heat conduction efficiency of the heat-resistant elastic layer 612 is extremely high.
Therefore, the heat resistance in the heat-resistant elastic body layer 612 can be configured to be extremely low with respect to the heat energy supplied from the inside of the fixing roll 61 by the halogen heater 66, so that the time lag until the heat reaches the surface of the fixing roll 61 is reduced. It can be shortened. As a result, the fixing roll 61 can be returned to a predetermined fixing temperature during one rotation after the fixing roll 61 passes through the nip portion N and then returns to the nip portion N again. In addition, the warm-up time can be shortened.

By the way, the low-melting-point metal alloy particles that bond the thermally conductive fillers are not more than the molding temperature of the base material silicone rubber, that is, not more than the maximum temperature used when processing the base material silicone rubber (maximum processing temperature: for example, 250 ° C.). It has a melting point. That is, as the low melting point metal alloy particles, those having a temperature below the maximum processing temperature of the base material silicone rubber are used.
By using the low melting point metal alloy particles having such a melting point, when the heat resistant elastic layer 612 is molded on the fixing roll 61, the low melting point metal alloy particles are melted and dispersed in the base material of the silicone rubber. It is possible to construct a mesh having a high thermal conductivity that is organically stretched with the thermally conductive filler as a core by bonding the thermally conductive fillers that have been formed. At the same time, even when the low-melting-point metal alloy is melted when the fixing device 60 is used, the form of the organically stretched high-heat-conducting mesh centered on the heat-conductive filler changes its form. Thus, when the fixing device 60 is used, it can function as the heat-resistant elastic layer 612 with extremely high heat conduction efficiency.

Next, the composition of the silicone rubber composition constituting the heat-resistant elastic body layer 612 of the present embodiment will be specifically described.
The silicone rubber composition of the present embodiment is basically (A) a polyorganosiloxane composition that becomes a rubber elastic body by being cured by heating or the like, (B) a thermally conductive filler, and (C) It is a blend of low melting point metal alloy particles. The blending amount in this case is 10 to 1000 parts by weight, more preferably 100 to 800 parts by weight of the thermally conductive filler of the component (B) with respect to 100 parts by weight of the polysiloxane base polymer. The low melting point metal alloy particles are 10 to 1000 parts by weight, more preferably 50 to 500 parts by weight.
With regard to the thermally conductive filler of component (B), when it is less than 10 parts by weight, the desired thermal conductivity cannot be obtained, and when it is more than 1000 parts by weight, the rubber hardness is increased. This is because elasticity is lost and rubber processability deteriorates. In addition, regarding the low melting point metal alloy particles of the component (C), when the amount is less than 10 parts by weight, the desired thermal conductivity cannot be obtained, and when it is more than 1000 parts by weight, the rubber hardness is increased. This is because elasticity is lost and rubber processability deteriorates.

Here, as the thermally conductive filler of the component (B), inorganic fillers such as alumina, aluminum nitride, boron nitride, silicon nitride, pulverized quartz, and magnesium oxide can be used.
Further, as the low melting point metal alloy particles of the component (C), easy fusion gold (alloy for solder) can be used. The easily fused gold (alloy for solder) includes Sn—Pb, Sn—Sb, Sn—Ag, Sn—Bi, Sn—Al, Sn—Cu, Sn—Mn, Sn—Mg. In addition to binary alloys such as Zn-Mg and Sn-Pb-Bi, Sn-Sb-Bi, Sn-Ag-Bi, and Sn-In-Ag are also included. The composition selection of the low melting point metal alloy particles is determined by the processing temperature of the silicone rubber composition as the base material. In particular, it is desirable to select a Pb-free alloy system in consideration of recent environmental regulations.
(C) As a particle size of the low melting metal alloy particle of a component, it is 1.0-1000 micrometers, More preferably, it is 10-100 micrometers. This is because when the particle size is smaller than 1.0 μm, the dispersion into the silicone rubber is deteriorated and the desired high thermal conductivity cannot be obtained, and when it is larger than 1000 μm, the processability of the silicone rubber itself is deteriorated.

  Further, as the polyorganosiloxane composition of component (A), a composition in which (a) a polyorganosiloxane base polymer, (b) a curing agent, and various additives as required is uniformly dispersed is used. be able to. Among various components used in such a polyorganosiloxane composition, (a) the polyorganosiloxane base polymer and (b) the curing agent are appropriately selected according to the reaction mechanism for obtaining a rubber elastic body. It is. As the reaction mechanism, (1) a crosslinking method using an organic peroxide vulcanizing agent, (2) a condensation reaction method, (3) an addition reaction method, etc. are known. It is well known that a preferred combination of the component and the component (b), that is, a curing catalyst or a crosslinking agent is determined. The organic group in the polyorganosiloxane as the base polymer of the component (a) used in such various reaction mechanisms is a monovalent substituted or unsubstituted hydrocarbon group, methyl group, ethyl group, propyl group, Unsubstituted hydrocarbon groups such as alkyl groups such as butyl, hexyl and dodecyl, aryl groups such as phenyl, aralkyl groups such as β-phenylethyl and β-phenylpropyl, and chloromethyl Examples thereof include substituted hydrocarbon groups such as a 3,3,3-trifluoropropyl group. In general, methyl groups are frequently used because of their ease of synthesis.

  Hereinafter, (a) the polyorganosiloxane base polymer and (b) the curing agent in each of the reaction mechanisms (1) to (3) described above will be described. First, in the case of applying the crosslinking method using the organic peroxide vulcanizing agent (1), the base polymer of the component (a) is usually at least of organic groups bonded to silicon atoms in one molecule. Polyorganosiloxanes in which two are alkenyl groups such as vinyl, propenyl, butenyl, hexenyl are used. Of these groups, a vinyl group is preferred because of ease of synthesis and availability of raw materials. In addition, as the curing agent for component (b), benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxy Various organic peroxide vulcanizing agents such as hexane and di-t-butyl peroxide are used and give particularly low compression set. Therefore, dicumyl peroxide, cumyl-t-butyl peroxide, 2,5-dimethyl- 2,5-di-t-butylperoxyhexane and di-t-butylperoxide are preferred. These organic peroxide vulcanizing agents are used as one kind or a mixture of two or more kinds. The blending amount of the organic peroxide that is the curing agent of the component (b) is preferably in the range of 0.05 to 15 parts by weight with respect to 100 parts by weight of the polyorganosiloxane base polymer of the component (a). When the amount of the organic peroxide is less than 0.05 parts by weight, the vulcanization is not sufficiently performed, and even when the amount exceeds 15 parts by weight, there is no particular effect. This is because physical properties may be adversely affected.

  When the condensation reaction (2) is applied, a polyorganosiloxane having hydroxyl groups at both ends is used as the base polymer of the component (a). As the curing agent for component (b), first, as a crosslinking agent, ethyl silicate, propyl silicate, methyltrimethoxysilane, vinyltrimethoxysilane, methyltriethoxysilane, vinyltriethoxysilane, methyltris (methoxyethoxy) silane, vinyltris ( Alkoxy type such as methoxyethoxy) silane and methyltripropenoxysilane; acetoxy type such as methyltriacetoxysilane and vinyltriacetoxysilane; methyltri (acetoneoxime) silane, vinyltri (acetoneoxime) silane, methyltri (methylethylketoxime) silane, Examples thereof include vinyltri (methylethylketoxime) silane and the like, and partial hydrolysates thereof. Hexamethyl-bis (diethylaminoxy) cyclotetrasiloxane, tetramethyldibutyl-bis (diethylaminoxy) cyclotetrasiloxane, heptamethyl (diethylaminoxy) cyclotetrasiloxane, pentamethyl-tris (diethylaminoxy) cyclotetrasiloxane, hexamethyl-bis ( Examples thereof include cyclic siloxanes such as methylethylaminoxy) cyclotetrasiloxane and tetramethyl-bis (diethylaminoxy) -mono (methylethylaminoxy) cyclotetrasiloxane. Thus, the cross-linking agent may be either a silane or siloxane structure, and the siloxane structure may be linear, branched or cyclic. Furthermore, when using these, it is not necessary to be limited to one type, and two or more types can be used together. Among the curing agents of component (b), the curing catalyst includes carboxylic acid metal salts such as iron octoate, cobalt octoate, manganese octoate, tin naphthenate, tin caprylate, tin oleate; dimethyltin dioleate, Organotin compounds such as dimethyltin dilaurate, dibutyltin diacetate, dibutyltin dioctoate, dibutyltin dilaurate, dibutyltin dioleate, diphenyltin diacetate, dibutyltin oxide, dibutyltin dimethoxide, dibutylbis (triethoxysiloxy) tin, dioctyltin dilaurate Used. (B) Among the hardening | curing agents of a component, 0.1-20 weight part is preferable with respect to 100 weight part of base polymers of (a) component. This is because if the amount of the crosslinking agent used is less than 0.1 parts by weight, sufficient strength cannot be obtained in the cured rubber, and if it exceeds 20 parts by weight, the resulting rubber becomes brittle, and it is difficult to endure practical use. The amount of the curing catalyst is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the component (a) base polymer. If the amount is less than 0.01 parts by weight, it is not sufficient as a curing catalyst, and it takes a long time for curing, and curing in the interior far from the contact surface with air becomes poor. On the other hand, when the amount is more than 5 parts by weight, the storage stability is lowered. In addition, as a range of a more preferable compounding quantity, it is the range of 0.1-3 weight part.

  Furthermore, as the base polymer of the component (a) when the addition reaction of (3) is applied, the same base polymer as that in the crosslinking method of (1) described above is used. As the curing agent for component (b), a platinum catalyst such as chloroplatinic acid, platinum olefin complex, platinum vinylsiloxane complex, platinum black, platinum triphenylphosphine complex, etc. is used as a curing catalyst, and as a crosslinking agent. Polyorganosiloxane having an average number of hydrogen atoms bonded to silicon atoms exceeding at least two per molecule is used. Among the curing agents of component (b), the blending amount of the curing catalyst is preferably an amount that is in the range of 1 to 1000 ppm in terms of platinum element relative to the base polymer of component (a). If the blending amount of the curing catalyst is less than 1 ppm as the platinum element amount, curing does not proceed sufficiently, and if it exceeds 1000 ppm, no improvement in the curing rate can be expected. The amount of the crosslinking agent is preferably such that the number of hydrogen atoms bonded to silicon atoms in the crosslinking agent is 0.5 to 4.0 with respect to one alkenyl group in component (a), More preferably, the amount is 1.0 to 3.0. When the amount of hydrogen atoms is less than 0.5, the curing of the composition does not proceed sufficiently, the hardness of the composition after curing is reduced, and the amount of hydrogen atoms is 4.0. When it exceeds, the physical property and heat resistance of the composition after hardening will fall. In the thermally conductive silicone rubber composition of the present embodiment, the above-described curing mechanism and polysiloxane base polymer are not particularly limited, but from the viewpoint of thermal conductivity properties, the addition reaction of (3) or (1 ) By organic peroxide vulcanization, and a polysiloxane base polymer having a polymerization degree of 1000 or more, that is, a so-called millable type is preferable. This is because since the shear stress at the time of mixing is moderate, it is presumed that the above-described effects are more exhibited by blending.

  Note that various additives such as a reinforcing filler, a heat resistance improver, a flame retardant, and the like may be added to the thermally conductive silicone rubber composition of the present embodiment as needed. As such, usually, fumed silica, precipitated silica, diatomaceous earth and other reinforcing fillers, aluminum oxide, mica, clay, zinc carbonate, glass beads, polydimethylsiloxane, alkenyl group-containing polysiloxane, etc. Is exemplified.

Hereinafter, the silicone rubber composition constituting the heat-resistant elastic body layer 612 in the fixing roll 61 of the present embodiment will be specifically described based on examples and comparative examples. In addition, the silicone rubber composition which comprises the heat resistant elastic body layer 612 of this Embodiment is not limited to an Example.
(Example 1)
100 parts by weight of polydimethylsiloxane (degree of polymerization of about 6000) containing 0.15 mol% of a methylvinylsiloxane unit, which is blocked with a trimethylsilyl group, and 200 parts by weight of alumina (Al ₂ O ₃ ) as a thermally conductive filler Then, 100 parts by weight of Sn—Pb alloy powder (average particle size: 50 μm, melting point 183 ° C.) as low melting point alloy particles was charged into a kneader and kneaded to take out the compound after it was collected. To this, 0.5 part by weight of 2,5-dimethyl-2,5-di-t-butylperoxyhexane as a crosslinking agent was uniformly mixed to prepare a heat conductive silicone rubber composition.

(Comparative Example 1)
A heat conductive silicone rubber composition was prepared in the same manner as in Example 1 except that the low melting point alloy particles (Sn—Pb alloy powder) were not mixed.

(Comparative Example 2)
A heat conductive filler prepared in the same manner as in Example 1 except that 300 parts by weight of alumina (Al ₂ O ₃ ) is used as the heat conductive filler and the low melting point alloy particles (Sn—Pb alloy powder) are not mixed. A silicone rubber composition was obtained.

(Example 2)
100 parts by weight of polydimethylsiloxane (degree of polymerization: about 6000) containing 0.15 mol% of a methylvinylsiloxane unit, which is blocked with a trimethylsilyl group, and 300 parts by weight of magnesia (MgO) as a heat conductive filler, have a low melting point 200 parts by weight of Sn—Ag—Bi alloy powder (average particle size: 80 μm, melting point 197 ° C.) as alloy particles was charged into a kneader and kneaded to take out the compound after it had been collected. To this, 0.5 part by weight of 2,5-dimethyl-2,5-di-t-butylperoxyhexane as a crosslinking agent was uniformly mixed to prepare a heat conductive silicone rubber composition.

(Comparative Example 3)
A heat conductive silicone rubber composition was prepared in the same manner as in Example 1 except that the low melting point alloy particles (Sn—Ag—Bi alloy powder) were not mixed.

(Comparative Example 4)
A thermally conductive silicone was prepared in the same manner as in Example 1 except that 500 parts by weight of magnesia (MgO) was used as the thermally conductive filler and the low melting point alloy particles (Sn—Ag—Bi alloy powder) were not mixed. A rubber composition was obtained.

Using the heat conductive silicone rubber compositions of Examples 1 and 2 and Comparative Examples 1 to 4 thus obtained, the characteristics were evaluated by the methods shown below. First, for the purpose of confirming roll workability and sheeting performance, a sheet was taken out with a roll and the state was evaluated. As the roll, an 8-inch test row was used, the interval between the rubber contact plates was set to 20 cm, and the sheet was seated while making the bank on the roll. The sheet thickness was set to two types of 1 mm and 3 mm, and it was confirmed whether or not sheeting was possible. Further, in the sheet, the dispersibility of the compound was confirmed by holding the sheet over the light bulb of the light source 100W. The sheet that could not be seated was artificially molded to produce a sheet.
Further, each heat conductive silicone rubber composition described above is formed into a 2 mm thick rubber sheet, subjected to press vulcanization under conditions of 180 ° C. atmosphere for 10 minutes as primary vulcanization, and then at 250 ° C. atmosphere as secondary vulcanization. Post-vulcanization was performed under the conditions of time, and after returning to normal temperature and 24 hours passed, the hardness, tensile strength, and elongation of each rubber sheet were measured according to JIS-K6301 (vulcanized rubber physical test method). In addition, as a heat resistance test, the sample was left in a constant temperature bath at 200 ° C. for 96 hours, then returned to room temperature, and measured for physical properties after 24 hours to compare heat resistance. Furthermore, the thermal conductivity was measured using a QTM rapid thermal conductivity meter (trade name: manufactured by Kyoto Electronics Industry Co., Ltd.).

FIG. 6 shows the evaluation results of these examples and comparative examples together with the blending ratios of the respective compositions. As shown in FIG. 6, in the rubber sheet of Example 1, the thermal conductivity is remarkably improved as compared with the rubber sheets of Comparative Examples 1 and 2 in which the low melting point alloy particles (Sn—Pb alloy powder) are not mixed. It has been demonstrated that Even in such a case, the sheeting property and filler dispersibility are good, and the hardness, tensile strength, and elongation have good characteristics with little change even in the initial state and after the heat test. The same applies to the rubber sheet of Example 2, and the thermal conductivity is remarkably improved as compared with the rubber sheets of Comparative Examples 3 and 4 in which the low melting point alloy particles (Sn—Ag—Bi alloy powder) are not mixed. It was proved that Even in such a case, the sheeting property and filler dispersibility are good, and the hardness, tensile strength, and elongation have good characteristics with little change even in the initial state and after the heat test.
Thus, by comparing the examples and comparative examples, the silicone rubber composition of the present embodiment achieves a high value of thermal conductivity of about 7 to 10 (× 10 ⁻³ cal / cm · sec · ° C.). And its superiority was confirmed. In the silicone rubber composition of the present embodiment, it has been confirmed by the inventors' experiments that it is possible to set the thermal conductivity to 5 (× 10 ⁻³ cal / cm · sec · ° C.) or more. However, from the viewpoint of maintaining rubber properties such as hardness, tensile strength, and elongation, the thermal conductivity is 15 (× 10 ⁻³ cal / cm) in consideration of the blending amount of each compound into the silicone rubber composition. · Sec · ° C) or less is preferable.

Furthermore, the silicone rubber compositions of Examples 1 and 2 and Comparative Examples 1 and 3 were prepared by vulcanizing the fixing roll 61 as a heat-resistant elastic body layer 612 under the same conditions as those for manufacturing the sheet, and incorporating them. Using the apparatus 60, the time (minutes) from when the energization of the halogen heater 66 is started until the surface of the fixing roll 61 reaches a set temperature (150 ° C. in this experiment), and unevenness of image gloss (microscopic) An experiment to evaluate (gross) was conducted.
In this experiment, the fixing roll 61 is made of the silicone rubber composition used in Examples 1 and 2 and Comparative Examples 1 and 3 as the heat-resistant elastic body layer 612 on the aluminum core 611 with 3 mm. After coating to a thickness, the surface of this heat resistant elastic layer 612 was spray coated with a fluororesin paint EN-710CL (manufactured by Mitsui DuPont) to a thickness of 30 μm to prepare four types of fixing rolls 61. An 800 W halogen heater 66 is disposed inside the fixing roll 61, and the set temperature is set to 150 ° C. The nip width of the nip portion N was set to 8 mm, and the process speed was 150 mm / sec. Then, a fixing device 60 incorporating these four types of fixing rolls 61 was attached to the image forming apparatus, and the fixing performance was evaluated. As the toner, color toner (cyan) for DocuCenterColor400 manufactured by Fuji Xerox Co., Ltd. was used, and “J paper” (trade name) manufactured by Fuji Xerox Co., Ltd. was used. At that time, the toner density of the toner image formed on the paper P was set to 1 mg / cm ² .

  FIG. 7 shows the result. As shown in FIG. 7, in the fixing device 60 of the present embodiment using the silicone rubber compositions of Examples 1 and 2 as the heat resistant elastic layer 612, the silicone rubber compositions of Comparative Examples 1 and 3 are used. It was proved that the set temperature arrival time was shortened to ¼ to 2/5, compared with the case where it was. In addition, regarding the image cross unevenness, no occurrence was observed both when the silicone rubber composition of Examples 1 and 2 and the silicone rubber composition of Comparative Examples 1 and 3 were used, and good image quality. showed that. This is probably because both the silicone rubber compositions of Examples 1 and 2 and the silicone rubber compositions of Comparative Examples 1 and 3 have low hardness and large elongation.

  As described above, in the fixing device 60 of the present embodiment, the heat-resistant elastic body layer 612 of the fixing roll 61 has a silicone rubber as a base material, and the base material silicone rubber has a heat conductivity as a thermal conductivity imparting agent. It is formed by molding a silicone rubber composition containing a conductive filler and low melting point metal alloy particles having a melting point equal to or lower than the processing temperature of the base material silicone rubber (molding temperature (secondary vulcanization temperature)). ing. With such a configuration, in the heat resistant elastic layer 612, the low melting point metal alloy particles dispersed in the silicone rubber base material are melted during the processing (molding) of the silicone rubber, and the silicone rubber base material is melted. Similarly, the dispersed heat conductive fillers are bonded to each other to construct a network of high thermal conductivity organically stretched around the heat conductive fillers, so that the heat of the heat resistant elastic body layer 612 is increased. The conduction efficiency can be made extremely high.

  Therefore, the thermal resistance in the heat-resistant elastic body layer 612 can be configured to be extremely low with respect to the heat energy supplied from the inside of the fixing roll 61 by the halogen heater 66, and the time lag until the heat reaches the surface of the fixing roll 61 is shortened. It becomes possible to do. Accordingly, the fixing roll 61 can be returned to a predetermined fixing temperature during one rotation after the fixing roll 61 passes through the nip portion N and then returns to the nip portion N again. Occurrence can be suppressed and, similarly, the warm-up time can be shortened.

  In this embodiment, the belt nip type fixing device 60 in which the endless belt 62 is pressed against the fixing roll 61 has been described. However, the present invention is a two-roll type in which a pressure roller is pressed against a general fixing roll. The present invention can be widely applied to a fixing device using a fixing member provided with a heat-resistant elastic body layer and other fixing devices.

[Embodiment 2]
In the first embodiment, the image forming apparatus is described in which the fixing roll 61 having a heat source is used as the heating unit and the fixing device 60 using the endless belt 62 with the pressure pad 64 pressed as the pressing unit is mounted. In the second embodiment, a fixing device mounted on the image forming apparatus shown in FIG. 1 is a fixing device using a fixing belt with a heat generation source pressed as a heating unit and a pressure roll as a pressing unit. explain. In addition, the same code | symbol is used about the structure similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

  FIG. 8 is a side sectional view showing a configuration of the fixing device 90 in the present embodiment. As shown in FIG. 8, the fixing device 90 according to the present exemplary embodiment includes a fixing belt 92 as an example of a fixing member and a pressure roll 91 as an example of a pressure member. The fixing belt 92 is disposed on the toner image carrying surface side of the paper P, and a ceramic heater 82 which is a resistance heating element as an example of a heating source is disposed inside the fixing belt 92. The nip portion N is configured to supply heat.

The ceramic heater 82 has a substantially flat surface on the pressure roll 91 side. Then, it is arranged in a state of being pressed against the pressure roll 91 via the fixing belt 92 and forms a nip portion N. Therefore, the ceramic heater 82 also functions as a pressure member. The sheet P that has passed through the nip portion N is peeled off from the fixing belt 92 by the change in the curvature of the fixing belt 92 in the exit region (peeling nip portion) of the nip portion N.
Further, a low friction sheet 68 is disposed between the inner peripheral surface of the fixing belt 92 and the ceramic heater 82 in order to reduce sliding resistance between the inner peripheral surface of the fixing belt 92 and the ceramic heater 82. The low friction sheet 68 may be configured separately from the ceramic heater 82 or may be configured integrally with the ceramic heater 82.

  On the other hand, the pressure roll 91 is disposed so as to face the fixing belt 92, and is configured to rotate in the direction of arrow D by a drive motor (not shown), and the fixing belt 92 is rotated following the rotation. The pressure roll 91 includes a core (cylindrical cored bar) 911, a heat-resistant elastic body layer 912 coated on the outer peripheral surface of the core 911, and a release layer 913 made of a heat-resistant resin coating or a heat-resistant rubber coating. Has been configured.

Further, in the fixing device 90 according to the present embodiment, the fixing belt 92 is an endless belt having an original shape formed in a cylindrical shape, for example, a diameter of 30 mm. As shown in FIG. 9, the layer structure of the fixing belt 92 includes a base material layer 921 made of a sheet member having high heat resistance, an elastic layer 922 laminated on the outer peripheral surface of the base material layer 921, and an elastic layer. The surface release layer 923 is laminated on the 922.
The base material layer 921 of the fixing belt 92 is formed of a highly heat-resistant sheet having a thickness of 10 to 150 μm, more preferably 50 to 100 μm. For example, polyester, polyethylene terephthalate, polyethersulfone, polyetherketone, polysulfone, polyimide Further, synthetic resins having high heat resistance such as polyimide amide and polyamide, and those made of metal such as SUS and nickel can be used. Note that the base material layer 921 has sufficient rigidity to prevent buckling or the like even when both ends of the fixing belt 62 abut against an edge guide (not shown).

The elastic layer 922 of the fixing belt 92 has silicone rubber as a base material, a heat conductive filler as a thermal conductivity imparting agent, and a melting point equal to or lower than the processing temperature (molding temperature) of the base material silicone rubber. Is formed by molding a silicone rubber composition containing low melting point metal alloy particles having a thickness of about 100 to 600 μm.
By providing the elastic layer 922, the toner image formed by laminating the toner as powder is wrapped in the nip portion N without being crushed, and the entire toner image is uniform. Since heat can be supplied, it is possible to fix a fine line or fine dot-shaped toner image with high definition. Particularly for color images, four color toners can be sufficiently dissolved and mixed, so that good color developability can be obtained.

Further, in the elastic layer 922 of the present embodiment, the low-melting point metal alloy particles dispersed in the silicone rubber base material are melted during the processing (molding) of the silicone rubber, and similarly in the silicone rubber base material. Since the dispersed heat conductive fillers are bonded to each other and a network of high thermal conductivity organically stretched around the heat conductive filler as a core is constructed, the heat conduction efficiency of the elastic layer 922 is extremely improved. Can be expensive.
Therefore, the thermal resistance in the elastic layer 922 can be configured to be extremely low with respect to the thermal energy supplied from the inside by the ceramic heater 82, and the time lag until the heat reaches the outer peripheral surface from the inner peripheral surface of the fixing belt 92 is shortened. It becomes possible. As a result, in the nip portion N, rapid heat conduction is performed from the ceramic heater 82 to the outer peripheral surface of the fixing belt 92. Therefore, even when the speed of the image forming apparatus is increased, good fixability can be obtained. Can be maintained.

  Further, since the surface release layer 923 of the fixing belt 62 is in direct contact with the unfixed toner image carried on the paper P, it is necessary to use a material having good releasability. Examples of the material constituting the surface release layer 923 include PFA, PTFE, a silicone copolymer, or a composite layer thereof. The surface release layer 923 is provided on the uppermost layer of the fixing belt 62 with a thickness of 1 to 50 μm appropriately selected from these materials.

Note that edge guide members (not shown) are disposed at both ends of the holder 65. The edge guide members are disposed such that the inner surfaces of both edge guide members disposed so as to face each other at both end portions of the holder 65 have an interval substantially matching the width of the fixing belt 92. When the fixing belt 92 rotates, movement of the fixing belt 92 in the width direction (belt walk) is restricted by the end portions of the fixing belt 92 coming into contact with the inner surfaces of both edge guide members. Yes. Thus, the fixing belt 92 is set so that the deviation is regulated by the edge guide member.
Further, as a peeling auxiliary means, a peeling auxiliary member 70 can be disposed on the downstream side of the nip portion N of the fixing belt 92. The peeling auxiliary member 70 is held by a baffle holder 72 in a state where the peeling baffle 71 is close to the fixing belt 92 in a direction (counter direction) opposite to the rotation direction of the fixing belt 92.

  The paper P on which the toner image has been electrostatically transferred in the secondary transfer unit 20 of the image forming apparatus shown in FIG. 1 is guided to the nip N of the fixing device 90 by the fixing inlet guide 56. When the paper P passes through the nip portion N, the toner image on the paper P is fixed by the pressure acting on the nip portion N and the heat supplied from the ceramic heater 82 on the fixing belt 92 side. Also in the fixing device 90 of the present embodiment, since the nip portion N can be configured widely between the pressure roll 91 and the ceramic heater 82, stable fixing performance can be ensured.

As described above, in the fixing device 90 according to the present embodiment, the elastic layer 922 is provided on the fixing belt 92, and the elastic layer 922 uses silicone rubber as a base material, and the base material silicone rubber is provided with a thermal conductivity-imparting agent. A silicone rubber composition in which a heat conductive filler and a low melting point metal alloy particle having a melting point equal to or lower than the processing temperature (molding temperature) of the base silicone rubber is molded.
With such a configuration, a fine line or fine dot-shaped toner image is fixed with high definition, and particularly good color developability is obtained for a color image. Furthermore, the low melting point metal alloy particles dispersed in the silicone rubber base material are melted during the processing (molding) of the silicone rubber, so that the thermally conductive fillers dispersed in the silicone rubber base material are similarly dispersed. Bonding and organically stretched meshes with high thermal conductivity centered on the thermally conductive filler are constructed, so that the heat conduction efficiency of the elastic layer 922 can be made extremely high. Therefore, the thermal resistance in the elastic layer 922 can be configured to be extremely low with respect to the thermal energy supplied from the inside by the ceramic heater 82, and the time lag until the heat reaches the outer peripheral surface from the inner peripheral surface of the fixing belt 92 is shortened. Therefore, in the nip portion N, rapid heat conduction is performed from the ceramic heater 82 to the outer peripheral surface of the fixing belt 92, which is satisfactory even when the speed of the image forming apparatus is increased. Fixability can be maintained.

  As an application example of the present invention, application to an image forming apparatus such as a copying machine or a printer using an electrophotographic method, for example, application to a fixing apparatus that fixes an unfixed toner image carried on a recording paper (paper). is there. Further, there is application to an image forming apparatus such as a copying machine or a printer using an ink jet method, for example, a fixing device that dries an undried ink image carried on a recording paper (paper).

1 is a schematic configuration diagram showing an image forming apparatus of the present invention. 2 is a side cross-sectional view illustrating a configuration of a fixing device according to Embodiment 1. FIG. It is a cross-sectional block diagram explaining the structure by which an endless belt is supported. FIG. 3 is a cross-sectional view illustrating a structure of a fixing roll. It is a figure explaining the structure of the silicone rubber composition which comprises a heat resistant elastic body layer. It is the figure which put together the evaluation result of the Example and the comparative example with the compounding ratio of each composition. FIG. 6 is a diagram illustrating a result of evaluating time until a fixing roll surface reaches a set temperature and image gloss unevenness of a fixed image. FIG. 4 is a side sectional view illustrating a configuration of a fixing device according to a second embodiment. 2 is a cross-sectional view illustrating a layer structure of a fixing belt. FIG. FIG. 10 is a side sectional view showing a configuration of a conventional fixing device.

Explanation of symbols

1Y, 1M, 1C, 1K ... image forming unit, 11 ... photosensitive drum, 12 ... charger, 13 ... laser exposure device, 14 ... developing device, 15 ... intermediate transfer belt, 16 ... primary transfer roll, 17 ... drum cleaner , 20 ... secondary transfer part, 60, 90 ... fixing device, 61 ... fixing roll, 611 ... core (cylindrical cored bar), 612 ... heat-resistant elastic body layer, 613 ... release layer, 62 ... endless belt, 63 ... belt guide member, 64 ... pressure pad, 64a ... pre-nip member, 64b ... peeling nip member, 65 ... holder, 66 ... halogen heater, 67 ... lubricant supply member, 68 ... low friction sheet, 69 ... temperature sensor, 70 ... Peeling assisting member, 80 ... edge guide member, 82 ... ceramic heater, 91 ... pressure roll, 92 ... fixing belt, 921 ... base material layer, 922 ... elastic layer, 923 ... surface release layer

Claims (12)

A fixing device for fixing a toner image carried on a recording material,
A fixing member having a heating source and provided with an elastic layer;
A pressure member that forms a nip portion through which the recording paper passes while being pressed against the fixing member,
The fixing device is characterized in that the elastic layer is formed by blending a silicone rubber with a thermal conductivity-imparting agent and low melting point metal alloy particles.   The elastic layer of the fixing member is characterized in that the low-melting point metal alloy particles are melted and the melted low-melting point metal alloy particles form a state in which the thermal conductivity-imparting agents are bonded together. The fixing device according to claim 1.   The fixing device according to claim 1, wherein the elastic layer of the fixing member has the low melting point metal alloy particles having a melting point equal to or lower than a maximum processing temperature of silicone rubber.   The fixing device according to claim 1, wherein the elastic layer of the fixing member has an average particle diameter of the low melting point metal alloy particles of 1.0 to 1000 μm.   2. The fixing device according to claim 1, wherein the elastic layer of the fixing member includes 10 to 1000 parts by weight of the low melting point metal alloy particles based on 100 parts by weight of the silicone rubber.   The fixing device according to claim 1, wherein the fixing member is a fixing roll or a fixing belt.   The pressure member is a belt member, and is disposed inside the belt member, and presses the belt member against the fixing member to form a nip portion through which the recording material passes between the fixing member and the belt member. The fixing device according to claim 1, further comprising a pressure member to be formed.   A silicone rubber composition comprising a silicone rubber base material and a thermally conductive filler and low melting point metal alloy particles.   9. The silicone rubber composition according to claim 8, wherein the low-melting-point metal alloy particles have a melting point equal to or lower than a maximum processing temperature of the silicone rubber base material.   9. The silicone rubber composition according to claim 8, wherein the low melting point metal alloy particles have an average particle size of 1.0 to 1000 [mu] m.   9. The silicone rubber composition according to claim 8, wherein the amount of the low melting point metal alloy particles is 10 to 1000 parts by weight with respect to 100 parts by weight of the silicone rubber. Toner image forming means for forming a toner image;
Transfer means for transferring the toner image formed by the toner image forming means onto a recording material;
Fixing means for fixing the toner image transferred onto the recording material to the recording material,
The fixing means is
A fixing member having a heating source and provided with an elastic layer formed by blending a silicone rubber with a thermal conductivity-imparting agent and low melting point metal alloy particles;
An image forming apparatus comprising: a pressure member that forms a nip portion through which the recording paper passes while being pressed against the fixing member.

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