JP4696846B2 - Fixing device - Google Patents

Description

The present invention, for example, relates to a fixing device used in an image forming apparatus utilizing an electrophotographic system, and more particularly, to a fixing equipment having 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 or the like having a large heat capacity is used as the recording paper, the amount of heat taken from the surface of the fixing roll is increased, so that the fixing performance is deteriorated and the temperature droop phenomenon is increased. It will cause deterioration.

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, when the separation claw is used, it becomes mechanically complicated, and it becomes difficult to reduce the size and cost of the apparatus.

  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, a nip where the fixing roll and the pressure roll are pressed against each other is provided. 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 the equipment.
Another object is to provide a fixing equipment to prevent in rapid simple configuration the image defects generated by heating the paper.
Still another object is to be reduced in size and cost of the apparatus for providing an easy fixing equipment.

  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 a downstream side of the pressure contact portion between the fixing roll and the pressure member, It includes a peeling member that presses the outer surface of the belt member against the pressure member, and a pressing member that presses the peeling member so as to contact the fixing roll.

  It further includes a protruding portion provided on the peeling member and protruding from the belt member in the width direction of the belt member, and the pressing member presses the protruding portion of the peeling member so as to contact the fixing roll. . The peeling member is formed of a first member that receives a pressing force by the pressing member and a material different from the first member, and the first member presses the outer surface of the belt member by the pressing force received by the pressing member. And a second member that contacts the fixing roll. Further, the peeling member can be characterized by being formed in substantially the same shape as the shape of the surface of the pressure member and the surface of the fixing roll in a state where the nip portion is formed.

  From another point of view, the fixing device to which the present invention is applied includes a rotatable fixing roll, a belt member stretched around the fixing roll, a tension roll that stretches the belt member, and a fixing roll. A pressure member that forms a first nip portion between which the recording material passes between the belt member and the belt member that is arranged to press and stretched around the fixing roll; and a downstream side of the pressure contact portion between the fixing roll and the pressure member A release member that slides on the surface of the fixing roll and presses the outer surface of the belt member against the pressure member to form a second nip portion through which the recording material passes. It is a waste.

  It may further include a sliding layer provided on the surface of the peeling member. Further, the inner surface of the belt member may be made of a resin material. Further, the first nip portion formed by the fixing roll and the pressure member and the second nip portion formed by the peeling member and the pressure member are continuously formed. it can.

  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. And a fixing unit that fixes the toner image transferred onto the recording material to the recording material. The fixing unit stretches the heater, a rotatable belt member, and the belt member. At the same time, a nip portion through which the recording material passes is formed between a fixing roll that fixes the toner image using the heat of the heater and a belt member that is arranged to press the fixing roll and is stretched over the fixing roll. For pressing the outer surface of the belt member against the pressure member on the downstream side of the pressure member and the pressure contact portion between the fixing roll and the pressure member, and bending the belt member to peel the recording material from the belt member A peeling member; Provided, the peeling member is a non-fixed to the fixing means, and is characterized in that the sliding contact surface of the fixing roll by receiving the pressing force.

  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 downstream nip formed by the peeling member and the pressure member on the downstream side of the nip formed by the belt member and the pressure member is a pressure distribution that monotonously decreases from the upstream side to the downstream side. It can be characterized by being. 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 that rotates in the direction of arrow B. . 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 each of the image forming units 1Y, 1M, 1C, and 1K in the present embodiment, various electrophotographic devices are sequentially arranged around the photosensitive drum 11 that rotates in the direction of arrow A. 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 that guides the paper P discharged from the fixing device 60 and a paper discharge roll 66 that outputs 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 is formed of a fixing belt 610 as an example of a belt member rotating in the direction of an arrow D, a fixing roll 611, columnar stretching rolls 612 and 613 made of aluminum, and stainless steel. A main part is constituted by a columnar stretching roll 615, a posture correction roll 614, and a peeling pad 64 as an example of a peeling member. 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. In order to prevent the peeling pad 64 from being worn, it is preferable to form the inner surface of the fixing belt 610 and the surface of the fixing roll 611 with a resin material. Specifically, a resin having high heat resistance such as PFA or polyimide is preferable. Further, it is preferable to apply sliding oil such as silicone oil to the inner surface of the fixing belt 610.

The fixing roll 611 is formed by coating a cylindrical core roll (core metal) made of aluminum with a predetermined thickness on a surface layer of 300 μm thick PFA as a protective layer for preventing metal wear on the core roll surface. Is a hard roll. However, the fixing roll 611 is not limited to this configuration, and when the nip portion N is formed with the pressure roll 62, the fixing roll 611 hardly deforms with respect to the pressing force from the pressure roll 62. Any structure that functions as a sufficiently hard roll may 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 stainless steel. 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 disposed across the entire axial direction of the fixing roll 611 at a position near the downstream side of the area where the pressure roll 62 is pressed against the fixing roll 611 via the fixing belt 610. 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. The peeling pad 64 is a block member having a substantially arc shape in cross section. The detailed configuration of the peeling pad 64 will be described later.

  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 conveyed in the direction of the arrow F and guided in the traveling direction together with the fixing belt 610 cannot follow the change in the traveling direction of the fixing belt 610 when it exits 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 a peeling guide plate 83, a paper discharge guide 65, and a paper discharge roll 66.

FIG. 3 is a schematic configuration diagram of the fixing device 60 shown in FIG.
As shown in FIG. 3, support shafts 74 that support the fixing roll 611 protrude from both sides of the fixing roll 611 that rotates the fixing belt 610. Both ends of the support shaft 74 are rotatably held by the housing 76 via bearings 71. A drive gear 75 is provided at the end of the support shaft 74 on the apparatus rear side (back side, in side). A driving force is transmitted to the driving gear 75 from a driving source such as a driving motor (not shown), whereby the support shaft 74 and the fixing roll 611 are rotated. The bearing 71 and the casing 76 are not shown in FIG.

The peeling pad 64 is formed longer than the width of the fixing bell and 610 in the axial direction of the support shaft 74. That is, the peeling pad 64 has protruding portions 64 </ b> A that protrude from the fixing belt 610. Each of the protrusions 64A is pressed by the pressing member 73 in the direction of the fixing roll 611 (left direction in FIG. 3).
As described above, in this embodiment, the pressing to the peeling pad 64 is performed at the portions exposed from both ends of the fixing belt 610. Accordingly, it is not necessary to provide a pressing mechanism on the inner surface of the fixing belt 610, and the design of the apparatus can be facilitated.

FIG. 4 is a cross-sectional view for explaining the configuration of the peeling pad 64.
As shown in FIG. 4, the peeling pad 64 includes a main body portion 641 made of a highly rigid member such as stainless steel (SUS) and a pad portion 642 made of aluminum. The main body portion 641 and the pad portion 642 are bonded and integrated with a heat-resistant silicone adhesive. Thus, the required rigidity of the peeling pad 64 is ensured by the stainless steel body 641. That is, as described above, the protrusion 64A (see FIG. 3) of the peeling pad 64 receives a pressing force from the pressing member 73 in the arrow Y direction, so that the main body 641 is made of stainless steel so as not to bend more than necessary due to the pressing force. It is made of steel to ensure the rigidity of the peeling pad 64. In addition, the pressing force (pad pressing load) by which the main body portion 641 of the peeling pad 64 is pressed is, for example, 196N (20 kgf).

In addition, the shape of the pad portion 642 was obtained by two methods: calculation of the outer shape of the pressure roll 62 by simulation, and the shape of a piece obtained by molding the outlet shape of the pressure roll 62 in the nip state with resin. Based on the results, the design was made so as to be substantially the same shape as the exit shape of the fixing nip. The pad portion 642 is made of aluminum in consideration of heat resistance, rigidity to withstand pressing, hardness to withstand sliding with the fixing belt 610, and workability at the time of manufacture. Therefore, when the main body portion 641 is a highly rigid member, it is possible to use a relatively soft material such as a heat resistant resin.
The pad portion 642 is formed with a peeling portion 64B having a small curvature radius. The peeling portion 64B can reduce the curvature of the fixing belt 610 and ensure the self-strip performance of the paper P.

  The peeling pad 64 also includes a sliding sheet (sliding layer) 643 as a sliding layer that covers the outer periphery of the integrated main body portion 641 and pad portion 642. As the sliding sheet 643, for example, a fluororesin-impregnated glass fiber sheet can be used. Since the sliding pad 64 includes the sliding sheet 643, the sliding between the inner surface of the fixing belt 610 and the surface of the fixing roll 611 is smoothly performed.

Next, the nip portion N (see FIG. 2) where the fixing belt module 61 and the pressure roll 62 are pressed against each other will be described.
FIG. 5 is a schematic cross-sectional view showing the vicinity region of the nip portion N.
As shown in FIG. 5, in the nip portion N where the fixing belt module 61 (see FIG. 2) and the pressure roll 62 are pressed, an area (wrapped) where the fixing belt 610 is wound (wrapped) around the fixing roll 611 (see FIG. 5). In the lapping region), the pressure roll 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. Accordingly, a peeling pad nip portion (second nip portion, downstream nip portion) N2 in which the fixing belt 610 is wrapped on the surface of the pressure roll 62 is formed on the downstream side of the roll nip portion N1. That is, the nip portion N has a roll nip portion N1 and a peeling pad nip portion N2.

Further, as described above, the peeling pad 64 is pressed in the direction of the fixing roll 611 by the pressing member 73 (see FIG. 3). As a result, the peeling pad 64 is in contact with both the rigid body surface of the fixing roll 611 and the elastic body surface of the pressure roll 62 to apply a pressing force. In addition, the gap between the roll nip portion N1 and the peeling pad nip portion N2 is eliminated by making the peeling pad 64 extremely close to the roll nip portion N1 and making the interval as small as possible.
Thus, by making the peeling pad 64 positively contact the fixing roll 611, the peeling pad nip portion N2 can be configured to be continuous at the downstream end portion N1E of the roll nip portion N1. Thus, a predetermined pressing force can be applied over substantially the entire nip portion N. Therefore, it is possible to prevent an image defect called “blister” in which air or water vapor existing in the paper P or toner gap (a space between powder toners) is heated and expanded to disturb the toner image.

  The outer peripheral surface of the peeling pad 64 mainly includes an inner side surface 64a facing the fixing roll 611 side, an outer side surface 64b that rapidly changes the advancing direction of the fixing belt 610 that has passed through the peeling pad nip portion N2, and a fixing belt 610. Can be divided into a pressing surface 64 c that presses the pressure roll 62.

FIG. 6 is an explanatory diagram showing a schematic configuration diagram for explaining a nip state by the peeling pad 64 and a graph of the pressure state. FIG. 6A shows the case of the present embodiment, and FIG. 6B 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. 6A, the peeling pad 64 is formed so as to be substantially the same as the exit shape of the nip between the fixing roll 611 that is a hard roll and the pressure roll 62 that is a soft roll. The shape is formed. A pressing load was applied to the peeling pad 64 in the direction of the arrow. That is, the peeling pad 64 is pressed in a direction in contact with the fixing roll 611. In other words, the peeling pad 64 is configured to be pressed in a direction opposite to the conveyance direction of the paper P.

  Under such conditions, the peeling pad 64 is in contact with both the fixing roll 611 and the pressure roll 62, and applies a pressing force to the fixing roll 611 and the pressure roll 62. For this reason, there is no gap between the roll nip portion N1 and the peeling pad nip portion N2, and there is no section (gap) without pressing force. That is, a pressure distribution in which the roll nip portion N1 and the peeling pad nip portion N2 are continuous is formed. Thus, in the case of the present embodiment, a predetermined pressing force can be applied over substantially the entire nip portion N. Note that the length of the peeling pad nip portion N2 is 8 mm.

Further, the pressure distribution in the peeling pad nip portion N2 monotonously decreases from the upstream side toward the downstream side. That is, the pressure distribution in the peeling pad nip portion N2 is not a distribution in which the pressing force increases after the pressing force suddenly decreases in the middle, but a distribution that gradually decreases.
The pressure distribution by the peeling pad 64 can be adjusted by the shape of the peeling pad 64, and the total pressing force can be adjusted by the magnitude of the load of the pressing member 73.

In the case of the comparative example shown in FIG. 6B, the peeling pad 94 having a conventional shape is used, and the peeling pad 94 presses the pressure roll 62. Yes. That is, the peeling pad 94 is not in contact with the fixing roll 611, and a gap Q is formed between the peeling pad 94 and the fixing roll 611. The peeling pad 94 does not apply a pressing force to the fixing roll 611.
In the pressure distribution of the nip portion N, a section (gap Q) where no pressing force is present is formed on the way. That is, in the pressure distribution of the nip portion N, the roll nip portion N1 and the peeling pad nip portion N2 are not continuously formed. In addition, the length of the peeling pad nip portion N2 is 8 mm, and the gap Q is 2 mm.

  Table 1 shows the results of evaluating the peeling performance for each of the present embodiment and the comparative example shown in FIG. Table 2 shows the results of evaluating the blister prevention performance for each of the present embodiment and the comparative example.

Specific experimental conditions are as follows. The paper P used in the evaluation of the peeling performance is an OK top coat (basis weight 85 gsm (g / m ² )), and the fixing belt temperature thereof is 150 ° C. The paper P used in the evaluation of the blister prevention performance is an OK top coat (basis weight 127.9 gsm), and the fixing belt temperature is 180 ° C. In any case, the process speed is 264 mm / s, the fixing nip load is 1470 N (150 kgf), and the pad pressing load is 196 N (20 kgf). Other conditions are the same as those in the above-described embodiment.
As an image type, in the evaluation of peeling performance, a solid image of C (cyan) (density 100%) was formed and evaluated. In the evaluation of the blister prevention performance, process black (100% density C (cyan), M (magenta) and Y (yellow) were overlapped to form an image (density 300%), and the blister was visually evaluated. .

  As shown in Table 1, it has been clarified that both the present embodiment and the comparative example have sufficient performance for sheet peeling. That is, self-strip performance can be ensured.

  Further, as shown in Table 2, in the case of the present embodiment, the occurrence of blisters at the visual level could not be confirmed. That is, no visible blister is generated. On the other hand, in the case of the comparative example, blisters that are minor but can be confirmed at the visual level are generated.

As described above, in the case of this embodiment, the gap between the peeling pad 64 and the fixing roll 611 can be eliminated by bringing the peeling pad 64 into contact with the fixing roll 611. That is, in the case of the present embodiment, the gap is eliminated by adopting a simple pressing structure. In this pressing structure, for example, both ends of the peeling pad 64 are held so as to be movable in the pressing direction with respect to the casing 76 (see FIG. 3), and as described above, the peeling pad 64 is formed by the pressing member 73. Is urged so as to be pressed in the direction of the fixing roll 611.
By adopting such a pressing structure, it is not necessary to set a gap, so that the configuration can be simplified. On the other hand, by covering the peeling pad 64 with the sliding sheet 643, the peeling pad 64 is configured so as not to be inconvenient even if it always slides.
For this reason, in the case of this embodiment, it was confirmed that by eliminating the gap, the blister prevention performance was higher than that of the comparative example, and sufficient paper peeling performance could be secured.
In addition, in the present embodiment, the sheet is not peeled off by a peeling claw as in the conventional structure, but a portion having a small curvature is provided in the peeling pad 64 to ensure self-strip performance, thereby simplifying the apparatus. It is possible to achieve downsizing and cost reduction of the apparatus.

1 is a diagram illustrating a schematic 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. FIG. 3 is a schematic configuration diagram when the fixing device illustrated in FIG. 2 is viewed from an arrow X. It is a cross-sectional view for demonstrating the structure of a peeling pad. It is a schematic sectional drawing showing the vicinity area | region of a nip part. It is explanatory drawing which shows the schematic block diagram for demonstrating the nip state by a peeling pad, and shows 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, 612, 613, 615 ... Stretching roll, 62 ... Pressure roll, 64 ... Peeling pad, 64A ... Protruding part, 64B ... Peeling , 641... Body portion, 642... Pad portion, 643... Sliding sheet, 73 .. pressing member, N .. nip portion, N1 .. roll nip portion, N2.

Claims (9)

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 which is arranged to press the fixing roll and forms a first nip portion through which the recording material passes between the belt member and the belt member stretched around the fixing roll;
The surface of the fixing roll slides on the downstream side of the press-contact portion between the fixing roll and the pressure member, and the outer surface of the belt member is pressed against the pressure member between the belt member and the belt. A peeling member that forms a second nip through which the recording material passes,
Only including,
The first nip portion formed by the fixing roll and the pressure member, and the second nip portion formed by the peeling member and the pressure member are continuously formed. A fixing device. A protruding portion provided on the peeling member and protruding from the belt member in the width direction of the belt member ;
A pressing member for pressing the protruding portion of the release member into contact with the fixing roll,
The fixing device according to claim 1, further comprising: A pressing member that presses the peeling member in the direction of the fixing roll and makes contact with the fixing roll;
The peeling member is formed of a first member that receives a pressing force by the pressing member, and a material different from the first member, and the outer surface of the belt member by the pressing force that the first member receives by the pressing member. The fixing device according to claim 1, further comprising: a second member that presses and contacts the fixing roll. The peeling member includes a surface of the pressure member in a state where the first nip portion and the second nip portion are formed, and a shape of a surface of the fixing roll in a state where the first nip portion is formed. The fixing device according to claim 1, wherein the fixing device has substantially the same shape. The fixing device according to claim 1 , further comprising a sliding layer provided on a surface of the peeling member. The fixing device according to claim 1 , wherein an inner surface of the belt member is made of a resin material. The fixing device according to claim 1 , wherein a deformation amount of the pressure member in the first nip portion and the second nip portion formed by the pressure member is larger than a deformation amount of the fixing roll. . Wherein the second nip formed by the peeling member and the pressure member, the fixing device according to claim 1, characterized in that the monotonically decreasing pressure distribution toward the downstream side from the upstream side. The fixing device according to claim 1 , wherein the pressure member is formed of a roll member.

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