JP2010039255A - Fixing device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device not affected by micro unevenness even when the unevenness exists on a surface of a pressing member, eliminating a nip pressure change in an axial-direction, and thereby preventing nonuniform glossiness from being generated in a fixed image. <P>SOLUTION: This fixing device is provided with: a rotating fixing roller; an endless fixing belt; the pressurizing member deforming itself by pressing the fixing belt from an inner circumferential face side to bring the fixing belt into pressure contact with the fixing roller; and a separation member arranged in a downstream with respect to the pressurizing member, and for deforming elastically an elastic layer of the fixing roller by pressing the fixing belt from the inner circumferential face side to bring the fixing belt into pressure contact with the fixing roller. The pressurizing member is constituted to layer the first elastic member positioned in a fixing belt side and formed of a sponge, onto the second elastic member formed of a sponge, the first elastic member and the second elastic member are continuously extended along a center axial direction of the fixing belt, and a hardness of the first elastic member is lower than a hardness of the second elastic member. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an FBN-type fixing device having a fixing belt, and an image forming apparatus including the fixing device.

  In an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine having these functions, a latent image corresponding to an original is formed on a photosensitive drum, and toner is applied to the latent image. Thus, the visualized toner image is transferred onto a recording material, and then the toner image on the recording material is fixed and discharged.

  When a color image is formed, Y, M, C, and K latent images corresponding to the original color are formed on four photosensitive drums, and the visualized four color toner images are endless. After the primary transfer onto the intermediate transfer belt, the toner image transferred onto the recording material is fixed on the recording material, and the toner image transferred onto the recording material is fixed and discharged.

  As a fixing device for fixing a toner image in this way, a recording material on which the toner image is transferred at a nip formed by a fixing roller incorporating a heating means such as a halogen lamp and a pressure roller for pressing the fixing roller. There is a heat roller fixing type fixing device that heats and pressurizes while sandwiching and conveying the sheet, and such a fixing device is widely used because of its simple configuration.

  By the way, in such a fixing device, in order to increase the speed, it is necessary to supply a sufficient amount of heat to the toner and the recording material. For this purpose, it is necessary to widen the nip width. In order to increase the nip width, it is possible to increase the load by which the pressure roller presses the fixing roller, the thickness of the elastic layer formed of silicone rubber or the like in the pressure roller, the diameter of the two rollers, and the like. Conceivable.

  However, when the load on the pressure roller and the thickness of the elastic layer are increased, the nip width in the central axis direction (hereinafter referred to as the axial direction) of the fixing belt may become non-uniform. There is a risk of wandering. Further, when the diameter of the roller is increased, there is a problem that not only the fixing device is increased in size but also the warm-up time is increased.

  In order to solve this problem, a fixing roller (fixing roll 61) that contains a halogen lamp and rotates with an elastic layer, and an endless fixing belt (endless belt 62) that rotates by being driven by the fixing roller; A pressure pad (pressure pad 64) disposed on the inner peripheral surface side of the fixing belt, and a nip portion formed between the fixing roller and the fixing belt by the pressure pad pressing the fixing belt. A so-called FBN (Free Belt Nip) type fixing device that heats and pressurizes a recording material onto which a toner image has been transferred is held and conveyed (see, for example, Patent Document 1).

  According to this fixing device, the fixing belt pressed against the fixing roller by the pressure pad is elastically deformed toward the pressure pad, and a wide nip portion is formed between the fixing roller and the fixing belt. Therefore, although it is a small shape, it can cope with high speed, and since the heat capacity of the fixing belt is small, the warm-up time is shortened and energy is saved.

Further, the recording material that has passed through the nip portion may stick to the fixing roller due to the adhesive force of the molten toner. In order to prevent this, in this fixing device, the fixing belt is pressed toward the fixing roller from the inner peripheral surface side toward the fixing roller on the downstream side in the conveyance direction of the recording material with respect to the pressure pad. A separation member (peeling nip member 64b) is provided that presses and elastically deforms the elastic layer of the fixing roller into a concave shape with a large curvature. As a result, it is possible to separate the recording material from the fixing roller without providing a special separating member such as a separation claw.
JP 2006-126536 A

  In the FBN type fixing device as disclosed in Patent Document 1, the pressure pad is formed of silicone rubber, fluorine rubber, or the like. When the rubber is crushed, the crushed portion has a characteristic of spreading and spreading in the lateral direction. . Therefore, when there are fine irregularities on the surface of the pressure pad, the irregularities spread over a wide range due to the nip pressure, and there is a possibility that gloss unevenness may occur in the fixed image due to the pressure difference caused by the irregularities.

  Further, in the FBN type fixing device as disclosed in Patent Document 1, a support member (pad holder 160) for supporting the pressure pad is provided, and the support member is urged by a compression spring (pressure spring 180) to fix. A pressure pad is pressed against the fixing roller via a belt. A plurality of compression springs are provided at predetermined intervals in the axial direction. In this way, a plurality of compression springs press the pressure pad through the support member, and in the pressure pad, the pressing force to the fixing roller is the portion where the compression spring is directly below and the portion where there is no compression spring. That is, a difference occurs in the nip pressure. As a result, gloss unevenness may occur in the fixed image as well.

  The present invention has been made in view of such a problem, and even if there are fine irregularities on the surface of the pressure member (pressure pad), the irregularities are not affected, and the nip pressure changes in the axial direction. As a result, it is an object of the present invention to propose a fixing device that does not cause gloss unevenness in a fixed image and an image forming apparatus including the fixing device.

  The object is achieved by the invention described below.

1. A fixing roller having an elastic layer and rotating with a heating means;
An endless fixing belt driven and rotated by the fixing roller;
A pressure member that elastically deforms itself by pressing the fixing belt from the inner peripheral surface side and pressing the fixing belt against the fixing roller;
The elastic layer of the fixing roller is elastically disposed by being downstream of the pressure member in the recording material conveyance direction and pressing the fixing belt from the inner peripheral surface side to press the fixing belt against the fixing roller. A separating member to be deformed;
With
In a fixing device for fixing a toner image on a recording material conveyed at a nip portion formed between the fixing roller and the fixing belt,
The pressure member is formed by laminating a first elastic member formed of a sponge positioned on the fixing belt side and a second elastic member formed of a sponge or rubber. The elastic member and the second elastic member extend continuously in the central axis direction of the fixing belt, and the hardness of the first elastic member is lower than the hardness of the second elastic member. Fixing device.

  2. When the fixing belt is not pressed against the fixing roller, the first elastic member has the same thickness, and the second elastic member increases in thickness as it advances downstream in the recording material conveyance direction. The fixing device according to 1.

  3. When the fixing belt is not pressed against the fixing roller, the thickness of the first elastic member is equal, and the thickness of the second elastic member decreases as it advances toward the end of the fixing belt in the central axis direction. The fixing device according to 1 or 2 above.

  4). An image forming apparatus comprising the fixing device according to claim 1.

  According to the fixing device of the present invention and the image forming apparatus provided with the fixing device, even if there are fine irregularities on the surface of the pressure member, the irregularities are not affected by the irregularities, and the nip pressure in the axial direction is not affected. There is no change, and as a result, no gloss unevenness occurs in the fixed image.

  Hereinafter, the present invention will be described based on an embodiment of the present invention, but the present invention is not limited to this embodiment.

  First, an image forming apparatus according to the present invention will be described with reference to the block diagram of FIG.

  The image forming apparatus includes an image reading apparatus YS, an image forming apparatus GH, and the like. The image forming unit GH is called a tandem color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, an intermediate transfer member 6, a secondary transfer unit 7A, a fixing device 100, and a paper feeding unit. 20 etc.

  An image reading device YS including an automatic document feeder 501 and a document image scanning exposure device 502 is installed above the image forming unit GH. The document d placed on the document table of the automatic document feeder 501 is transported by a transport unit, and an image on one or both sides of the document is scanned and exposed by the optical system of the document image scanning exposure device 502, and the line image sensor CCD is scanned. Is read.

  An image signal formed by photoelectric conversion by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, and the like in an image processing unit (not shown), and then exposure means 3Y, 3M. , 3C, 3K.

  The image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an exposure unit 3Y, a developing device 4Y, a primary transfer unit 7Y, and a cleaning unit 8Y around the photosensitive drum 1Y. The image forming unit 10M that forms a magenta (M) color image includes a charging unit 2M, an exposure unit 3M, a developing device 4M, a primary transfer unit 7M, and a cleaning unit 8M around the photosensitive drum 1M. An image forming unit 10C for forming a cyan (C) color image includes a charging unit 2C, an exposure unit 3C, a developing device 4C, a primary transfer unit 7C, and a cleaning unit 8C around the photosensitive drum 1C. The image forming unit 10K that forms a black (Bk) image includes a charging unit 2K, an exposure unit 3K, a developing device 4K, a primary transfer unit 7K, and a cleaning unit 8K around the photosensitive drum 1K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit.

  The developing devices 4Y, 4M, 4C, and 4K include a two-component developer including yellow (Y), magenta (M), cyan (C), and black (K) toner having a small particle diameter and a carrier.

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported.

  The fixing device 100 fixes a toner image on the recording paper P (recording material) by heating and pressing at a nip portion formed between a fixing roller 101 having a halogen lamp and a fixing belt 102.

  Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially primary-transferred onto the rotating intermediate transfer body 6 by the primary transfer means 7Y, 7M, 7C, and 7K, and color image synthesis is performed. A toner image is formed.

  The recording paper P stored in the paper feed tray 21 is separated and fed by the paper feed roller 22 of the paper feed means 20, passes through a plurality of paper feed rollers 23, and enters the stopped registration roller 24. Paper is fed. Therefore, the roller is temporarily stopped, and the registration roller 24 starts to rotate at the timing when the positional relationship between the leading end and the toner image on the intermediate transfer member 6 accurately coincides, and is fed to the secondary transfer unit 7A for recording. A color image is secondarily transferred onto the paper P. The recording paper P to which the color image has been transferred is heated and pressurized by the fixing device 100, and the color toner image on the recording paper P is fixed. Thereafter, the sheet is sandwiched between the sheet discharge rollers 25 and placed on the sheet discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred to the recording paper P by the secondary transfer means 7A, the residual toner is removed by the intermediate transfer body cleaning means 8A from the intermediate transfer body 6 from which the recording paper P is separated by curvature.

  Although the above is an image forming apparatus that forms a color image, an image forming apparatus that forms a monochrome image may be used.

  Next, the fixing device 100 according to the present invention will be described with reference to the enlarged sectional view of FIG. The fixing device 100 is an FBN type fixing device.

  The fixing roller 101 includes a halogen lamp (heating means) H in the center, and a cylindrical cored bar 101A formed of aluminum, iron, or the like, and an elastic made of silicone rubber that covers the cylindrical cored bar 101A and has high heat resistance. A layer 101B and a release layer 101C made of a fluororesin such as PFA (perfluoroalkoxy) or PTFE (polytetrafluoroethylene) which further covers the elastic layer 101B.

  The fixing belt 102 includes a base formed of polyimide and a release layer formed of PFA or PTFE that covers the outer surface of the base, and is formed in an endless shape.

  Then, a pressure member composed of the first elastic member 103 and the second elastic member 104 presses the fixing belt 102 from the inner peripheral surface side to press the fixing belt 102 against the fixing roller 101.

  Both the first elastic member 103 and the second elastic member 104 are formed of a heat-resistant sponge, and the first elastic member 103 located on the fixing belt 102 side is laminated on the second elastic member 104. . The first elastic member 103 and the second elastic member 104 extend continuously in the central axis direction of the fixing belt 102 (hereinafter referred to as the axial direction). Further, the first elastic member 103 is formed of a low hardness sponge, and the second elastic member 104 is formed of a high hardness sponge. For example, the hardness of the first elastic member 103 is ASKER C 24 °, and the hardness of the second elastic member 104 is ASKER C 40 °. As described above, since the hardness of the first elastic member 103 is lower than the hardness of the second elastic member 104, only the first elastic member 103 is deformed when the pressing force is low, and the first elastic member 103 is increased when the pressing force is high. The second elastic member 104 is also deformed together with the member 103.

  The first elastic member 103 and the second elastic member 104 are held by a holder 108 made of a heat resistant resin.

  The separation member 107 is disposed on the downstream side in the transport direction of the recording paper P with respect to the first elastic member 103 and the like in order to improve the separation of the fixed recording paper P. The separation member 107 is made of a heat-resistant resin such as PPS or a metal such as aluminum, and has a narrow width and a distal end formed in an arc having a large curvature. A metal frame 110 that holds the holders 108 and 109 is disposed in the center, and the separation member 107 is supported by the holder 108 and the frame 110.

  The sliding sheet 111 is formed by coating a glass fiber sheet with fluororesin (PTFE) or Teflon (registered trademark), between the inner peripheral surface of the fixing belt 102 and the first elastic member 103, and the fixing belt 102. Between the inner peripheral surface and the separation member 107, and one end is fixed to the frame 110.

  The oil pad 112 is formed of a sponge or the like and impregnated with a lubricant made of silicone oil or the like, is held by the holder 109, and is pressed against the inner peripheral surface of the fixing belt 102.

  When the fixing belt 102 is rotated, the holder 108 guides the fixing belt 102 via the sliding sheet 111, and the holder 109 also has a function as a guide member that directly guides the fixing belt 102.

  Here, FIG. 2 is a diagram in which the first elastic member 103 and the second elastic member 104 press the fixing belt 102 against the fixing roller 101 and the first elastic member 103 having low hardness is greatly deformed. However, when the first elastic member 103 and the second elastic member 104 are not deformed without pressing the fixing belt 102 against the fixing roller 101, the shape is as shown in FIG. In FIG. 3, the first elastic member 103 has the same thickness, but the contact surface 104 </ b> A of the second elastic member 104 with the first elastic member 103 advances toward the fixing roller 101 as the recording paper P is conveyed downstream. The thickness of the second elastic member 104 is gradually increased by gradually projecting. This is due to the following reasons.

  That is, regarding the pressing force on the fixing roller 101, the pressing force of the separation member 107 is considerably larger than the pressing force of the first elastic member 103 and the second elastic member 104. There is a risk that the conveyance speed of the image becomes unstable and image defects occur. Therefore, the thickness of the second elastic member 104 having high hardness is increased as the separation member 107 is advanced, so that the pressing force is gradually increased so as not to change suddenly.

  When the first elastic member 103 and the second elastic member 104 are not deformed without the fixing belt 102 being pressed against the fixing roller 101, the shape shown in FIG. In FIG. 4, the first elastic member 103 has the same thickness, but the thickness of the second elastic member 104 decreases as it proceeds to both ends in the axial direction. Thereby, in the axial direction, the pressing force at the center is higher than that at the end, so that the possibility of wrinkles on the recording paper P is eliminated.

  In the fixing device 100 configured as described above, the fixing roller 101 heated by the halogen lamp H and driven by a driving unit (not shown) rotates in the clockwise direction. Also, the first elastic member 103 is pressed by the second elastic member 104, and the first elastic member 103 presses the fixing belt 102 against the fixing roller 101 via the sliding sheet 111. However, since the first elastic member 103 is softer than the fixing roller 101, the first elastic member 103 elastically deforms itself. As a result, the fixing belt 102 is elastically deformed toward the first elastic member 103, and a wide nip portion N is formed between the fixing belt 102 and the fixing roller 101. The fixing belt 102 rotates counterclockwise by the rotation of the fixing roller 101, and the unfixed toner on the conveyed recording paper P is heated and pressed at the nip portion N and fixed.

  On the other hand, the separating member 107 presses the fixing belt 102 against the fixing roller 101 via the sliding sheet 111, and elastically deforms the elastic layer 101B and the release layer 101C of the fixing roller 101 into a concave shape having a large curvature. Accordingly, the recording paper P fixed at the nip portion N is reliably peeled off and separated from the fixing roller 101 without using a separation claw or the like.

  Further, the inner peripheral surface of the fixing belt 102 slides on the sliding sheet 111 during rotation, but since the sliding sheet 111 has a small coefficient of friction, the sliding resistance between the two is small. Furthermore, since the silicone oil as a lubricant is supplied from the oil pad 112 to the inner peripheral surface of the fixing belt 102 and the outer surface of the sliding sheet 111, the sliding resistance is further reduced.

  In the fixing device 100 described above, the first elastic member 103 having a low hardness made of sponge is in pressure contact with the fixing belt 102 through the sliding sheet 111. When the sponge is pressed and crushed, only the apparent volume in the pressing direction is reduced, and the lateral portion thereof is not greatly deformed like rubber. Therefore, even if there is a fine unevenness on the surface of the first elastic member 103 before pressing, the unevenness is eliminated by pressing, and unlike rubber, this unevenness does not spread over a wide range due to the nip pressure, and the pressure generated by the unevenness Due to the difference, no gloss unevenness occurs in the fixed image.

  Further, since the first elastic member 103 with low hardness is easily crushed, the pressing force is made uniform at the nip portion, and the pressure distribution at the nip portion can be formed into a desired distribution by the second elastic member 104 with high hardness. it can.

  Further, the first elastic member 103 and the second elastic member 104 continuously extend in the axial direction to form a nip portion N. The high hardness second elastic member 104 presses the low hardness first elastic member 103. Therefore, the compression spring disclosed in Patent Document 1 and essential for the conventional FBN type fixing device is not required.

Therefore, a comparison experiment between the fixing device as disclosed in Patent Document 1 and the fixing device 100 was performed.
(1) Experimental conditions Fixing device as in Patent Document 1 Pressure member: formed from silicone rubber with a shape and dimensions as shown in FIG. 5 (a), length in the axial direction is 350 mm
Compression spring: In order to press the pressure member, the measurement fixing device 100 is arranged at intervals of 35 mm in the axial direction.
Pressurizing member: A low-hardness heat-resistant sponge having a shape and dimension as shown in FIG. 5B and a high-hardness heat-resistant sponge are laminated, and the axial length is 350 mm.
Compression spring: None For both fixing devices, the value of the axial pressing force was measured near the exit in the conveyance direction. (2) Experimental results FIG. 6 shows the results.

In Table 1, the horizontal axis represents the axial length, and the vertical axis represents the pressing force (kPa) on the fixing roller. Further, the broken line in the line graph is the pressing force of the fixing device as in Patent Document 1 provided with a compression spring, and the solid line is the pressing force of the fixing device 100 without the compression spring.
(3) Consideration In the case of the fixing device as disclosed in Patent Document 1, peaks and valleys with a significant difference in pressing force are generated, and the peak is a portion where a compression spring for generating the pressing force is disposed. Since the compression springs are discontinuously arranged at predetermined intervals, a change occurs in the pressing force, and gloss unevenness occurs in the fixed image.

  On the other hand, in the case of the fixing device 100, it is the second elastic member 104 that mainly generates the pressing force and extends continuously in the axial direction. Does not occur. There are peaks and valleys with a small difference in height, but this is due to measurement errors and component accuracy, and gloss unevenness does not occur in the fixed image.

  In the fixing device 100 described above, the first elastic member 103 is formed of a low-hardness sponge and the second elastic member 104 is formed of a high-hardness sponge. The same effect can be obtained by forming only silicone rubber or fluororubber having the same hardness as that of sponge.

  Further, since the optimum values of the hardness of the first elastic member 103 and the hardness of the second elastic member 104 vary depending on the shape and size of each member of the fixing device, it is necessary to obtain the value by experiment according to the fixing device used.

1 is a configuration diagram of an image forming apparatus. 2 is an enlarged cross-sectional view of the fixing device 100. FIG. It is a figure of the paper feeding direction when the 1st elastic member 103 and the 2nd elastic member 104 are not deform | transforming. FIG. 6 is an axial view when the first elastic member 103 and the second elastic member 104 are not deformed. 6 is a cross-sectional view of a pressure member in the fixing device and the fixing device 100 as disclosed in Patent Document 1. FIG. 10 is a graph of pressure distribution in the axial direction between a fixing device and a fixing device 100 as in Patent Document 1;

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Fixing apparatus 101 Fixing roller 102 Fixing belt 103 First elastic member 104 Second elastic member 104A Contact surface 107 Separating member H Halogen lamp

Claims (4)

A fixing roller having an elastic layer and rotating with a heating means;
An endless fixing belt driven and rotated by the fixing roller;
A pressure member that elastically deforms itself by pressing the fixing belt from the inner peripheral surface side and pressing the fixing belt against the fixing roller;
The elastic layer of the fixing roller is elastically disposed by being downstream of the pressure member in the recording material conveyance direction and pressing the fixing belt from the inner peripheral surface side to press the fixing belt against the fixing roller. A separating member to be deformed;
With
In a fixing device for fixing a toner image on a recording material conveyed at a nip portion formed between the fixing roller and the fixing belt,
The pressure member is formed by laminating a first elastic member formed of a sponge positioned on the fixing belt side and a second elastic member formed of a sponge or rubber. The elastic member and the second elastic member extend continuously in the central axis direction of the fixing belt, and the hardness of the first elastic member is lower than the hardness of the second elastic member. Fixing device. The first elastic member is equal in thickness when the fixing belt is not pressed against the fixing roller, and the thickness of the second elastic member increases as the recording material moves downstream in the conveyance direction. Item 4. The fixing device according to Item 1. When the fixing belt is not pressed against the fixing roller, the thickness of the first elastic member is equal, and the thickness of the second elastic member decreases as it advances toward the end of the fixing belt in the central axis direction. The fixing device according to claim 1 or 2. An image forming apparatus comprising the fixing device according to claim 1.

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