JP4857708B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device used in an image forming apparatus using, for example, an electrophotographic system, and more particularly to a fixing device and an image forming apparatus provided with a rotatable belt member.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic system, image formation is performed as follows. First, for example, the surface of a photosensitive member (photosensitive drum) formed in a drum shape is uniformly charged by a charging device. The charged photosensitive drum is scanned and exposed with light controlled based on the image information, and an electrostatic latent image is formed on the surface thereof. Subsequently, the electrostatic latent image formed on the photosensitive drum is made a visible image (toner image) by the developing device, and then the toner image is conveyed to the transfer unit along with the rotation of the photosensitive drum to be recorded. It is electrostatically transferred onto paper (hereinafter also referred to as paper). The toner image carried on the recording paper is subjected to a fixing process by a fixing device to complete the toner image.

  As a fixing device used in such an image forming apparatus, a configuration called a two-roll system has been widely used. This two-roll fixing device includes a fixing roll formed by laminating a heat-resistant elastic layer and a release layer on the surface of a cylindrical cored bar in which a heating source (heater) is disposed; A pressure roll formed by laminating a heat-resistant elastic layer and a release layer made of a heat-resistant resin film or a heat-resistant rubber film on a metal core is configured to be in pressure contact with each other. Then, the recording paper carrying the unfixed toner image is passed through the pressure contact area (nip portion) between the fixing roll and the pressure roll, and the toner image is heated and pressed against the unfixed toner image. Is firmly established.

By the way, in recent years, high productivity and colorization have rapidly progressed in image forming apparatuses, and many apparatuses having a double-sided printing mechanism have become widespread. Therefore, it is necessary to further cope with the high speed in the fixing device mounted on the image forming apparatus.
However, the conventional two-roll type fixing device has a problem that it is difficult to perform a sufficient fixing process on a large number of recording sheets continuously fed at a high speed. That is, in the two-roll type fixing device, a core metal constituting the fixing roll, an elastic layer made of silicone rubber coated on the core metal, or the like acts as a thermal resistor. Therefore, in the two-roll type fixing device, it is structurally difficult to supply the heat corresponding to the amount of heat taken by the recording paper from the surface of the fixing roll promptly and sufficiently from the heater disposed inside the fixing roll. .
As a result, when the recording paper is continuously fed to the two-roll type fixing device at a high speed, the surface temperature of the fixing roll gradually decreases and the fixing performance gradually decreases. In addition, when the image forming apparatus starts up, a so-called “temperature droop phenomenon” in which the surface temperature of the fixing roll temporarily drops tends to occur. In particular, when thick paper with a large heat capacity is used as recording paper, the amount of heat taken away from the surface of the fixing roll increases, so that the fixing performance decreases and the temperature droop increases, resulting in image quality deterioration due to poor fixing. Will be generated.

Under such circumstances, a technique has been developed that solves the above-described problems that occur when a two-roll type fixing device is used, and realizes a fixing device that can cope with higher speed of the image forming apparatus. For example, there is a technique related to a fixing device in which a heating member that heats recording paper is configured by a film-like belt member (fixing belt) stretched by a plurality of stretching rolls (see, for example, Patent Document 1).
In such a fixing device using a fixing belt, the fixing belt is sufficiently heated by a heater provided in the stretching roll in advance before entering the nip portion, and the fixing belt heated in the nip portion is heated. The toner image is fixed by applying heat to the recording paper and the toner image. Therefore, even if the fixing belt is deprived of heat by the recording paper during the fixing process, the heat capacity of the fixing belt itself is small, so that the fixing belt is recovered to a predetermined fixing temperature in a short time by the heater in the stretching roll. It is possible to make it. Accordingly, in the fixing device using the fixing belt as the heating member, it becomes easy to maintain the temperature of the fixing belt when entering the nip portion at a predetermined value, and even if the image forming apparatus is speeded up, It is possible to supply a sufficient amount of heat.

  However, even in a fixing device using a fixing belt, since a toner image is carried on the surface of the recording paper, when the toner image is melted by the heat of the fixing belt, the toner image becomes an adhesive and becomes a recording paper. Adhesive force acts between the toner and the fixing belt. Therefore, it is necessary to provide a mechanism for peeling the recording paper from the surface of the fixing belt as in the conventional two-roll type fixing device. In particular, when the speed of the image forming apparatus is increased, if a separation failure occurs once in the fixing device and a paper jam occurs, the number of subsequent recording papers damaged by the influence increases. For this reason, it is necessary to stably and reliably peel the recording paper that has passed through the nip portion at a high speed from the fixing belt side.

  As a mechanism for peeling the recording paper from the surface of the fixing belt, as described in Patent Document 1 described above, a structure in which a separation claw is disposed in contact with the fixing belt on the downstream side of the nip portion is conventionally used. ing. In a fixing device having a configuration in which a pressure roll is disposed in pressure contact with a fixing belt stretched between a fixing roll and a heating roll, a position corresponding to an outlet portion (the most downstream portion) of the nip portion A fixing member for setting a large curvature of the fixing belt at the outlet is provided inside the fixing belt, and the recording paper is peeled off by changing the curvature of the fixing belt (see, for example, Patent Document 2). .

JP-A-3-133871 (page 4, FIG. 3) Japanese Patent Laying-Open No. 2003-5566 (page 6-8, FIG. 4)

  However, in the fixing device using the fixing belt, when the separation claw is used as a mechanism for separating the recording paper from the surface of the fixing belt, the separation claw is used to stably peel the recording paper from the fixing belt side. It is necessary to be disposed in contact with the. Therefore, when the fixing claw is used and the high-speed fixing is performed, the surface of the fixing belt is easily worn by the separating claw. If wear due to the separation claw occurs on the surface of the fixing belt, fixing unevenness corresponding to the wear mark on the surface of the fixing belt may occur on the fixed image, which may deteriorate the image quality. Further, the offset toner may gradually adhere to and accumulate on the wear scar, causing stain on the fixed image. Furthermore, when the surface of the fixing belt progresses, the thin-layer fixing belt eventually breaks, and the function of the fixing device may be impaired.

  Further, as a mechanism for peeling the recording paper from the surface of the fixing belt, when a fixing member for forming a large curvature of the fixing belt is provided at the exit portion of the nip portion, the nip where the fixing roll and the pressure roll are pressed against each other In the nip intermediate region between the inlet portion of the portion and the outlet portion where the fixing member is disposed, the fixing belt is pressed against the pressure roll only by the tension of the fixing belt. For this reason, the nip pressure in the intermediate nip region is relatively low. When the recording paper or toner is heated in such a low nip pressure region, the water in the recording paper is vaporized to become water vapor, or the air in the toner is thermally expanded, so that the fixing belt and the toner are heated. An air gap (bubbles) may be formed between the pressure rolls. When such an air gap is generated, if the toner on the recording paper existing in the nip portion is not completely fixed yet, the unfixed toner is easily disturbed by the bubbles moving around. As a result, an image defect such as unevenness occurs in the fixed image, and there is a possibility that the image quality is deteriorated.

The present invention has been made to solve the technical problems as described above, and an object of the present invention is to fix the sheet peeling performance even when the fixing speed is increased. It is to provide a device or the like.
Another object is to prevent image defects caused by sudden heating of the paper.

For this purpose, a fixing device to which the present invention is applied includes a rotatable fixing roll, a belt member that is stretched around the fixing roll, a tension roll that stretches the belt member, and presses the fixing roll. A pressure member that forms a nip portion through which the recording material passes between the belt member and the belt member that is stretched around the fixing roll, and in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressure member , together to press the outer surface of the belt member to the pressure member, it viewed including a release member, a having the surface shape and the pressing surface is substantially the same pressure member in a pressed state to pressure member, pressure The member has a surface shape in which the curvature decreases as the pressure member moves away from the vicinity of the downstream end of the pressure contact region where the pressure member is pressed against the outer peripheral surface of the belt member in the region where the belt member is wound around the fixing roll. The pressing surface of the peeling member A first pressing surface on the upstream side in which an arc of radius is formed, and a second pressing surface in which an arc having a radius of curvature larger than the radius of curvature of the first pressing surface is formed on the downstream side and continuous with the first pressing surface. The pressure at which the pressing surface of the peeling member presses the pressing member is substantially equal in the conveying direction of the belt member .

The pressing surface of the peeling member can be characterized in that it is formed so as to follow the surface shape of the pressing member while being pressed by the pressing member .

Further, from another point of view of the present invention, an image forming apparatus to which the present invention is applied transfers a toner image forming means for forming a toner image and a toner image formed by the toner image forming means onto a recording material. tension and transfer means, and fixing means for fixing to the recording material a toner image transferred onto a recording material, only including, a fixing unit includes a heater, a belt member provided rotatably, a belt member In addition, a nip is formed between the fixing roll that fixes the toner image using the heat of the heater and the belt member that is arranged to press the fixing roll and that is stretched over the fixing roll. The outer surface of the belt member is pressed against the pressure member near the downstream side of the pressure contact portion between the pressure member and the fixing roll and the pressure member, and the recording material is peeled from the belt member by bending the belt member. Peeling member for Comprises, the pressure member, the curvature becomes smaller as the pressure member in the region where the belt member wound around the fixing roll away from the vicinity of the downstream end of the press-contact region pressed against the outer peripheral surface of the belt member The pressing surface of the peeling member has a first pressing surface on the upstream side where an arc having a predetermined curvature radius is formed, and a curvature radius of the first pressing surface that is continuous with the first pressing surface on the downstream side. anda second pressing surface which arc is formed of radius of curvature greater than the pressure the pressing surface of the peeling member presses the pressing member, and wherein the substantially uniform der Rukoto in the transport direction of the belt member To do.

  The deformation amount of the pressure member in the nip portion formed by the pressure member may be larger than the deformation amount of the fixing roll. The pressure member of the fixing unit may be formed of a roll member.

  According to the present invention, it is possible to ensure the sheet peeling performance even when the fixing speed is increased.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
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 in which toner images of respective color components are formed by electrophotography. And a 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. In addition, the image forming apparatus has a secondary transfer unit 20 that performs batch transfer (secondary transfer) of the superimposed toner image transferred onto the intermediate transfer belt 15 onto a sheet P that is a recording material (recording paper), and is secondarily transferred. And a fixing device 60 for fixing the image on 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 is sequentially provided with various electrophotographic devices around the photosensitive drum 11 that rotates in the arrow A direction. This device includes a charger 12 for charging the photosensitive drum 11, a laser exposure device 13 for writing an electrostatic latent image on the photosensitive drum 11 (the exposure beam is indicated by Bm in the figure), and each color component toner. And a developing device 14 that visualizes the electrostatic latent image on the photosensitive drum 11 with toner. Further, a primary transfer roll 16 that transfers each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15 by the primary transfer unit 10, and a drum cleaner 17 from which residual toner on the photosensitive drum 11 is removed. And are included. These image forming units 1Y, 1M, 1C, and 1K are arranged substantially linearly in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the upstream side of the intermediate transfer belt 15. Has been.

  The image forming apparatus according to the present embodiment includes, as a paper transport system, a unit that takes out the paper P from the paper tray at a predetermined timing and sends it to the secondary transfer unit 20. Further, as a paper transport system, a transport belt 55 for transporting the paper P transported after the secondary transfer to the fixing device 60 and a fixing entrance guide 56 for guiding the paper P to the fixing device 60 are provided. Further, as a paper transport system, a paper discharge guide 65 for guiding the paper P discharged from the fixing device 60 and a paper discharge roll 66 for discharging the paper P guided by the paper discharge guide 65 to the outside of the apparatus are provided. Yes.

  That is, the sheet P on which the toner image is electrostatically transferred by the secondary transfer unit 20 is conveyed to the conveyance belt 55 as it is while being peeled off from the intermediate transfer belt 15. The conveying belt 55 conveys the paper P to the fixing device 60 through the fixing inlet guide 56 at an optimum conveying speed in accordance with the conveying 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 fixing processing by heat and pressure by the fixing device 60. Then, the paper P on which the fixed image is formed is conveyed via a paper discharge guide 65 and a paper discharge roll 66 to a paper discharge mounting portion (not shown) provided in a discharge portion of the image forming apparatus.

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 schematic configuration of the fixing device 60 of the present embodiment.
As shown in FIG. 2, the fixing device 60 includes a fixing belt module 61 as an example of a heating member, and a pressure roll 62 as an example of a pressure member disposed in pressure contact with the fixing belt module 61. The main part is composed of.

  The fixing belt module 61 includes a fixing belt 610 as an example of a belt member, a fixing roll 611, columnar stretching rolls 612, 613, and 615 formed of aluminum, an attitude correction roll 614, and an example of a peeling member. The main part is constituted by the peeling pad 64. The fixing roll 611 is rotationally driven while the fixing belt 610 is stretched. The tension roll 612 stretches the fixing belt 610 from the inside, and the tension roll 613 stretches the fixing belt 610 from the outside. The attitude correction roll 614 corrects the attitude of the fixing belt 610 between the fixing roll 611 and the stretching roll 612. The peeling pad 64 is a downstream region in the nip portion N where the fixing belt module 61 and the pressure roll 62 are in pressure contact with each other, and is disposed in the vicinity of the fixing roll 611. The tension roll 615 stretches the fixing belt 610 on the downstream side of the nip portion N.

  The fixing belt 610 includes a base layer formed of a polyimide resin having a thickness of 80 μm, an elastic layer made of 200 μm thick silicone rubber laminated on the surface side (outer peripheral surface side) of the base layer, And a release layer made of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin (PFA) tube having a thickness of 30 μm, which is further coated. Here, the elastic layer is provided in order to improve the image quality especially for color images. The fixing belt 610 is a flexible endless belt, and the material, thickness, hardness, and the like can be selected as appropriate for the configuration according to the device design conditions such as the purpose of use and conditions of use.

The fixing roll 611 is a hard core having a diameter of 100 mm formed by coating a cylindrical core roll (core metal) made of aluminum having a predetermined thickness with a 200 μm-thick fluororesin film as a protective layer for preventing metal wear on the core roll surface. It is a roll. However, the fixing roll 611 is not limited to this configuration. When the nip portion N is formed between the fixing roll 611 and the pressure roll 62, the fixing roll 611 is sufficiently deformed with respect to the pressing force from the pressure roll 62. Any configuration that functions as a hard roll can be used. The fixing roll 611 receives a driving force from a driving motor (not shown) and rotates in the direction of arrow C at a high speed, for example, a surface speed (process speed) of 264 mm / s.
A halogen heater 616a as a heating source is disposed inside the fixing roll 611. Then, based on the measurement value of the temperature sensor 617a arranged so as to contact the surface of the fixing roll 611, the control unit 40 (see FIG. 1) of the image forming apparatus sets the surface temperature of the fixing roll 611 to a predetermined value. I have control.

The tension roll 612 is provided with a halogen heater 616b as a heating source therein, and is controlled by the temperature sensor 617b and the control unit 40 (see FIG. 1) so that the surface temperature becomes a predetermined value. Accordingly, the tension roll 612 has a function of stretching the fixing belt 610 and a function of heating the fixing belt 610 from the inner peripheral surface side.
In addition, spring members (not shown) that press the fixing belt 610 outward are disposed at both ends of the tension roll 612. The tension roll 612 is provided with a shaft displacement mechanism that displaces the contact position in the axial direction of the fixing belt 610 according to the detection result of the belt edge position detection mechanism. It is configured to control (walk).

A release layer made of PFA having a thickness of 20 μm is formed on the surface of the tension roll 613. This release layer is formed to prevent slight offset toner and paper powder from the outer peripheral surface of the fixing belt 610 from accumulating on the stretching roll 613.
A halogen heater 616c as a heating source is disposed inside the tension roll 613, and is controlled so that the surface temperature becomes a predetermined value by the temperature sensor 617c and the control unit 40 (see FIG. 1). Yes. Therefore, the tension roll 613 has a function of stretching the fixing belt 610 and a function of heating the fixing belt 610 from the outer peripheral surface side. Therefore, in this embodiment, a configuration in which the fixing belt 610 is heated by the fixing roll 611, the stretching roll 612, and the stretching roll 613 is employed.

  The posture correction roll 614 is a cylindrical roll made of aluminum. A belt edge position detection mechanism (not shown) that detects the edge position of the fixing belt 610 is disposed in the vicinity of the posture correction roll 614.

The pressure roll 62 has a cylindrical roll 621 made of aluminum having a diameter of 80 mm as a base, and an elastic layer (Si rubber intermediate layer) made of silicone rubber having a rubber hardness of 30 ° (JIS-A) in order from the base side. ) And a release roll 623 made of a PFA tube having a film thickness of 100 μm. The pressure roll 62 is installed so as to be pressed against the fixing belt module 61. As the fixing roll 611 of the fixing belt module 61 rotates in the direction of arrow C, the pressure roll 62 follows the fixing roll 611 and moves in the direction of arrow E. To turn. The traveling speed is 264 mm / s, which is the same as the surface speed of the fixing roll 611.
Further, the tension roll 615 is disposed in the vicinity of the downstream side of the fixing pad 610 in the traveling direction of the fixing belt 610 so that the fixing belt 610 that has passed through the peeling pad 64 smoothly rotates toward the fixing roll 611.

  The peeling pad 64 is a block member made of stainless steel (SUS) and having a substantially arc-shaped cross section. The pressure roller 62 is disposed over the entire region in the axial direction of the fixing roller 611 at a position near the downstream side of the region where the pressure roller 62 is pressed against the fixing roller 611 via the fixing belt 610. Further, the peeling pad 64 is installed so as to uniformly press the pressure roll 62 over a predetermined width region with a predetermined load (for example, 30 kgf) through the fixing belt 610.

  In the fixing device 60 configured as described above, the fixing belt 610 after passing through the nip portion N rotates following the side surface of the peeling pad 64. Accordingly, the advancing direction of the fixing belt 610 is rapidly changed so as to be bent in the direction of the tension roll 615 by the peeling pad 64. Therefore, the sheet P guided in the traveling direction together with the fixing belt 610 cannot follow the change in the traveling direction of the fixing belt 610 at the time of exiting the nip portion N. As a result, the sheet P is peeled off from the fixing belt 610 by the so-called “koshi”, and the fixing process is completed. In this way, the curvature separation with respect to the paper P is stably performed at the exit of the nip portion N. The paper P peeled off from the fixing belt 610 is discharged out of the apparatus by the peeling guide plate 83 and the paper discharge guide 65.

Next, the nip portion N where the fixing belt module 61 and the pressure roll 62 are pressed against each other will be described.
FIG. 3 is a schematic cross-sectional view showing the vicinity of the nip N. As shown in FIG.
As shown in FIG. 3, in the nip portion N where the fixing belt module 61 and the pressure roll 62 are pressed against each other, the fixing belt 610 is wound (wrapped) in the region (wrapped region) around the fixing roll 611. , The pressure nip 62 is disposed so as to be in pressure contact with the outer peripheral surface of the fixing belt 610, thereby including a roll nip portion (first nip portion) N1.

  Further, as described above, the peeling pad 64 is disposed in the vicinity of the downstream side of the roll nip portion N 1, and the peeling pad 64 presses the fixing belt 610 against the surface of the pressure roll 62. As a result, a separation pad nip portion (second nip portion) N2 in which the fixing belt 610 is wrapped on the surface of the pressure roll 62 is formed downstream of the roll nip portion N1. That is, the nip portion N includes a roll nip portion N1 and a peeling pad nip portion N2 (N = N1 + N2). Further, the roll nip portion N1 and the peeling pad nip portion N2 are continuous at the downstream end N1E of the roll nip portion N1.

The peeling pad nip portion N2 includes a region (a pressure contact portion between the peeling pad 64 and the pressure roll 62) N2T in the peeling pad nip portion N2 and a boundary located on the roll nip portion N1 side from the region N2T. It consists of a region N2S (N2 = N2S + N2T).
Here, no member that directly presses the fixing belt 610 against either the fixing roll 611 or the pressure roll 62 exists in the boundary region N2S. Therefore, the boundary region N2S is pressed against the pressure roll 62 only by the tension of the fixing belt 610, and thus the nip pressure in the boundary region N2S is formed only by the tension of the fixing belt 610.

FIG. 4 is an enlarged schematic configuration diagram for explaining the peeling pad 64.
As shown in FIG. 4, the advancing direction of the fixing belt 610 that has mainly passed through the inner surface 64 a facing the fixing roll 611 and the peeling pad nip portion N <b> 2 (see FIG. 3) is suddenly changed. An outer side surface 64b and a pressing surface 64c that presses the fixing belt 610 against the pressing roll 62 are formed.

  The inner surface 64a of the peeling pad 64 is arranged around the fixing roll 611 in order to place the peeling pad 64 as close as possible to the fixing roll 611 side (for example, the gap between the peeling pad 64 and the fixing roll 611 is 0.5 mm). It is formed with a curved surface following the surface. That is, in order to set the boundary region N2S shown in FIG. 5 as narrow as possible, it is defined by the fixing roll 611 and the pressure roll 62 in the vicinity of the downstream side of the roll nip portion N1 (see also FIG. 3). In the wedge-shaped region Q, it is necessary to arrange the peeling pad 64 so as to press the surface of the pressure roll 62. Therefore, the upstream end portion (upstream end portion, tip portion of the pressing surface 64c) 64p of the inner surface 64a is fixed in the vicinity of the downstream end portion (exit) N1E of the roll nip portion N1, that is, in the wedge-shaped region Q described above. The inner side surface 64 a is formed in a curved surface following the peripheral surface of the fixing roll 611 so that the inner side surface 64 a can be installed at a position close to the roll 611.

The pressing surface 64 c of the peeling pad 64 is a surface that presses the fixing belt 610 against the pressure roll 62 and presses against the surface of the pressure roll 62, and is formed in a concave curved surface. The pressing surface 64c will be described in more detail. The pressing surface 64c has regions having different radii of curvature. That is, in the state where no contact with the surface of the pressure roll 62, the pressing surface 64c, the second pressing of the curvature radius of the first press surface 64c1 of R _1, radius of curvature _{R 2 (R 2 ≠ R 1} ) It consists of surface 64c2.
Here, the curvature radii R ₁ and R ₂ shown in FIG. 4 are the curvature radii in a state where they are not in contact with the surface of the pressure roll 62. As the radii of curvature R ₁ and R ₂ , values corresponding to various conditions such as the dimensions of the pressure roll 62 may be adopted, but in this embodiment, R ₁ = 40 mm and R ₂ = 50 mm. Moreover, the 1st press surface 64c1 is formed in the range of 2 mm from the upstream edge part 64p, and after that, the 2nd press surface 64c2 is formed in the range of 6 mm along the advancing direction.

As described above, in this embodiment, the release pad 64 is formed with the press surface 64c including the first press surface 64c1 and the second press surface 64c2 having different curvature radii. The pressure state of 64 and the pressure roll 62 can be maintained in a good state.
In this embodiment, the shape of the pressing surface 64c of the peeling pad 64 is a shape in which two arcs having different radii of curvature are continuous. However, as will be described later, the pressing surface 64c is formed in an arc shape composed of one arc. Such a modification (see FIG. 5B) is also conceivable.

FIG. 5 is an explanatory diagram showing a schematic configuration diagram for explaining the shape of the pressing surface 64c of the peeling pad 64 in the nipped state and a graph of the pressure state. 5A shows the case of the present embodiment, FIG. 5B shows the case of a modification of the present embodiment, and FIG. 5C shows a comparative example. Here, in the graph of the pressure state, the vertical axis represents the pressing force, and the horizontal axis represents the position in the traveling direction of the paper P.
Note that the contact shape by the nip is obtained by two methods of calculating the outer shape by simulation and the piece shape in which the roll outlet shape in the nip state is molded with resin. Further, the pressure profile in the pressure state graph is measured by a pressure sensor (tactile).

In the case of the present embodiment shown in FIG. 5A, the pressing surface 64c of the peeling pad 64 has a shape formed by connecting two or more kinds of arcs. Specifically, as described above, the radii of curvature are 40 mm and 50 mm.
The pressing surface 64 c having such a shape is substantially the same as the surface shape of the pressure roll 62 in the nip state with the pressure roll 62. That is, the pressing surface 64 c is formed along the surface shape of the pressure roll 62 in a nip state with the pressure roll 62. Further, the pressing force by the peeling pad 64 has a pressure distribution applied almost uniformly. In addition, the boundary area | region N2S in Fig.5 (a) is 2 mm, and area | region (pressure-contact part) N2T is 6 mm.

Here, the surface shape of the pressure roll 62 in the vicinity of the downstream end N1E (see FIG. 3) of the roll nip portion N1 takes a complicated shape due to the influence of the distortion of the roll nip portion N1. That is, the pressure roll 62 has a large curvature in the vicinity of the downstream end N1E (see FIG. 3) of the roll nip N1, and the curvature decreases as the distance from the pressure roll 62 increases. For this reason, as shown in FIG. 5A, when the pressing surface 64c of the peeling pad 64 is formed with the radii of curvature R ₁ and R ₂ as in the present embodiment, the pressing force by the peeling pad 64 is increased. It becomes possible to add almost evenly to the roll 62. In other words, the pressing force to the pressure roll 62 is substantially the same on the upstream side and the downstream side of the pressing surface 64c of the peeling pad 64.

  In the case of the modification shown in FIG. 5B, the pressing surface 91c of the peeling pad 91 has a shape composed of one arc, and specifically has a curvature radius of 50 mm. In the nip state with the pressure roll 62, the pressing surface 91c having such a shape ensures contact over almost the entire area of the pressing surface 91c, but in the region J near the upstream end 64p (see FIG. 4). The pressing force is reduced and the contact is uneven.

  In the case of the comparative example shown in FIG. 5C, the pressing surface 92c of the peeling pad 92 has a linear shape. The pressing surface 92c having such a shape is completely lifted from the pressure roll 62 in a region K near the upstream end portion 64p (see FIG. 4) when in the nip state with the pressure roll 62. For this reason, the boundary region N2S ′ becomes larger than those in the present embodiment and the modified example, and the region (pressure contact portion) N2T ′ becomes smaller. In FIG. 5C, the boundary region N2S and the region (pressure contact portion) N2T in the case of the present embodiment (FIG. 5A) and the modified example (FIG. 5B) are shown by broken lines. Show.

Table 1 shows the experimental results comparing image defects (blisters) for each of the present embodiment, modification, and comparative example shown in FIG. Specific experimental conditions are as follows. There are two types of paper used: OK top coat (basis weight 127 g / m ² ) and mirror coat platinum (basis weight 256 g / m ² ). In the OK top coat, the fixing belt temperature is 160 ° C., and the fixing belt temperature of the mirror coat platinum is 190 ° C. The fixing nip load is 1470 N (150 kgf). Other conditions are the same as those in the above-described embodiment. In addition, as an image type, process black (100% density C (cyan), M (magenta), and Y (yellow)) were superimposed to form an image, and the blister was visually evaluated.

As shown in Table 1, in the case of this embodiment, no blister was observed on any of the sheets. In the case of the modification, blisters did not occur in the mirror coat platinum, but blisters occurred slightly in the OK top coat.
On the other hand, in the case of the comparative example, blisters occurred on any paper. In this comparative example, the shape of the pressing surface 92c of the peeling pad 92 is a simple shape such as a straight line, and cannot cope with the complicated shape of the pressure roll 62. For this reason, it is considered that a region K, which is a reduced pressure portion due to a mismatch between the surface shape of the pressure roll 62 and the shape of the pressing surface 92c of the peeling pad 92, is generated, and a blister is generated from that region.

  Here, even if the pressing surface 91c of the peeling pad 91 is approximated to an arc shape as in the modification, a certain blister suppressing effect can be obtained. For this reason, when the fixing temperature is low, the pressing surface 91c can use the arc-shaped peeling pad 91.

Thus, it turns out that there exists a difference in the suppression effect of a blister by the shape of the pressing surface of a peeling pad. That is, in order to sufficiently suppress the blister, the peeling pad is placed in close proximity to the roll nip portion N1, the interval is made as small as possible, and the pressing force of the peeling pad is uniform and there is no low pressure portion. It is necessary to satisfy two conditions at the same time. Although it overlaps with the above-mentioned content, if this embodiment, a modification, and a comparative example are examined from these viewpoints, in the case of this embodiment ((a) in FIG. 5), the two conditions are satisfied at the same time. And a sufficient suppression effect can be expected. In the case of the modified example (FIG. 5B), although there is a low-pressure portion, the blister suppression effect can be expected to some extent in that the interval is as small as possible. Further, in the case of the comparative example ((c) in FIG. 5), it can be said that it is difficult to expect a blister suppressing effect because the interval is large.
In addition, since the shape of the pressure roll 62 changes with roll specifications (diameter / layer structure / material hardness, etc.), it is necessary to design the shape of the pressing surface of the peeling pad for each roll specification.

  As described above, by using the peeling pad 64 (see FIG. 5A) of the present embodiment or the peeling pad 91 of the modified example (see FIG. 5B), the sheet peeling performance is secured. However, blisters can be effectively prevented. In particular, blisters are likely to occur during high-speed fixing in which paper and toner are rapidly heated. Therefore, the blister prevention performance of this embodiment is effective when performing high-speed fixing. In order to obtain a higher gloss image, blisters are likely to occur because it is necessary to heat the toner and paper to a high temperature in order to reduce the viscosity of the toner. Therefore, the present embodiment is also effective for a fixing device that obtains a high gloss image.

1 is a diagram illustrating an overall configuration of an image forming apparatus to which the exemplary embodiment is applied. FIG. 2 is a side sectional view showing a schematic configuration of a fixing device according to the present embodiment. It is a schematic sectional drawing showing the vicinity area of a nip part. It is a schematic block diagram enlarged and shown in order to demonstrate a peeling pad. It is explanatory drawing which shows the schematic block diagram for demonstrating the shape of the press surface of the peeling pad of the state nipped, and the graph of the pressure state.

Explanation of symbols

DESCRIPTION OF SYMBOLS 60 ... Fixing device, 61 ... Fixing belt module, 610 ... Fixing belt, 611 ... Fixing roll, 62 ... Pressure roll, 64, 91 ... Release pad, 64c, 91c ... Pressing surface, 64c1 ... First pressing surface, 64c2 ... Second pressing surface, N ... nip part, N2 ... peeling pad nip part, N2T ... region (pressure contact part), R ₁ , R ₂ ... curvature radius

Claims (5)

A fixing device for fixing a toner image carried on a recording material,
A rotatable fixing roll;
A belt member stretched around the fixing roll;
A tension roll that stretches the belt member;
A pressure member that is arranged to press the fixing roll and forms a nip portion through which the recording material passes between the belt member and the belt member stretched around the fixing roll;
In the vicinity of the downstream side of the press-contact portion between the fixing roll and the pressure member, the pressure member is pressed against the pressure member while the outer surface of the belt member is pressed against the pressure member. A peeling member having a pressing surface substantially the same as the surface shape of
Only including,
The curvature of the pressure member decreases as the pressure member moves away from the vicinity of the downstream end of the pressure contact area where the pressure member presses the outer peripheral surface of the belt member in the area where the belt member is wound around the fixing roll. The surface shape
The pressing surface of the peeling member is continuous with the first pressing surface on the upstream side where an arc having a predetermined radius of curvature is formed, and the first pressing surface on the downstream side, and is more than the curvature radius of the first pressing surface. A second pressing surface formed with an arc having a large radius of curvature,
The fixing device according to claim 1, wherein a pressure with which the pressing surface of the peeling member presses the pressing member is substantially equal in a conveying direction of the belt member . The fixing device according to claim 1, wherein the pressing surface of the peeling member is formed so as to follow a surface shape of the pressing member in a state where the pressing surface is pressed by the pressing member. 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 heater,
A belt member rotatably provided;
A fixing roll that stretches the belt member and fixes a toner image using heat of the heater;
A pressure member that is arranged to press the fixing roll and forms a nip portion through which the recording material passes between the belt member and the belt member stretched around the fixing roll;
The outer surface of the belt member is pressed against the pressure member in the vicinity of the downstream side of the pressure contact portion between the fixing roll and the pressure member, and the recording material is peeled from the belt member by bending the belt member. A peeling member for,
The curvature of the pressure member decreases as the pressure member moves away from the vicinity of the downstream end of the pressure contact area where the pressure member presses the outer peripheral surface of the belt member in the area where the belt member is wound around the fixing roll. The surface shape
The pressing surface of the peeling member is continuous with the first pressing surface on the upstream side where an arc having a predetermined radius of curvature is formed, and is continuous with the first pressing surface on the downstream side, and is larger than the curvature radius of the first pressing surface. A second pressing surface formed with an arc of curvature radius,
The pressure of the pressing surface presses the pressing member of the peeling member, an image forming apparatus, wherein a substantially uniform der Rukoto in the conveying direction of the belt member. The image forming apparatus according to claim 3 , wherein a deformation amount of the pressure member in a nip portion formed by the pressure member is larger than a deformation amount of the fixing roll . The image forming apparatus according to claim 3 , wherein the pressure member of the fixing unit is formed of a roll member .

Images