JP2005300980A - Fixing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the occurrence of exfoliation blisters after a paper passes through a fixing/pressurizing part, defective fixing, paper wrinkles due to the exfoliation blisters, and the occurrence of image shift phenomena at the leading end of a toner image. <P>SOLUTION: The fixing apparatus is provided with an endless rotating fixation belt; a heating apparatus for heating the fixing belt; a pressure roller for forming a fixing/pressurizing part, in press contact with the outer peripheral surface of the heated fixing belt; a support body for supporting the belt part, in contact with the inner peripheral surface of the fixing belt part entering the fixing/pressurizing part formed by the pressure roller; a heating apparatus for heating the support body; and a pressure body, coming into press contact with the outer peripheral surface of the fixing belt in an area supported by the support body so as to pressurize the recording paper which is not guided to the fixing/pressurizing part against the outer peripheral surface of the fixing belt. The temperature of the contact surface with the fixing belt of the support body is constituted so as to establish the relation where the temperature of the downstream area in the belt-rotating direction is lower than that in the upstream area (for example, a temperature difference of 10°C or larger). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a fixing device of a type that performs a fixing process by peeling a recording sheet carrying a toner image to be fixed in a state where it is in close contact with a heated and rotating endless fixing belt. It is.

  In recent years, as a fixing device used in an image forming apparatus such as a printer, a copying machine, a multifunction peripheral, etc. using an image forming method such as an electrophotographic method or an electrostatic recording method, a rotating fixing belt in a rotating state is used. While the fixing belt is heated, a recording sheet carrying an unfixed toner image is pressed against the outer peripheral surface of the belt, and the recording sheet is conveyed while cooling while being in close contact with the fixing belt, and finally the fixing belt. A belt fixing device of a type that fixes a toner image by peeling the toner image from the toner is proposed (Patent Documents 1 and 2).

  According to the fixing device of this type, the toner image on the recording paper is peeled off from the fixing belt after being cooled and solidified in a smooth state following the smooth surface of the fixing belt, so that the fixing with particularly excellent glossiness is achieved. An image can be obtained. Further, since the recording paper is peeled off from the fixing belt after the toner is cooled and solidified, there is an advantage that an offset in which the toner is transferred and adhered to the fixing belt is less likely to occur.

  However, in such a fixing device, moisture contained in the recording paper is vaporized and expanded by heating at the time of fixing and escapes to the outside of the paper and accumulates as water vapor between the fixing belt and the action of the vapor pressure of the water vapor. In this case, the recording paper may be peeled off from the fixing belt (hereinafter, this phenomenon is referred to as “peeling blister”). If this phenomenon causes the toner image to peel off from the fixing belt before cooling and solidifying, the following occurs. Gloss reduction and gloss unevenness, which are one type of poor fixing, occur. In particular, when there is a member for holding the recording paper against the fixing belt after passing through the fixing pressure unit (the portion where the recording paper is first strongly pressed against the fixing belt), the following is provided. Paper wrinkles occur.

  In other words, the toner image part peeled off from the fixing belt by the peeling blister does not solidify along the smooth surface of the belt, and the toner image surface inherently has a feeling of unevenness. As a result, the toner image in which such peeling does not occur. Compared with the portion, the glossiness is lowered, or when the peeled toner image portion is a part of the whole toner image, the gloss unevenness in which portions having different glossiness are mixed is caused. In addition, the portion of the recording paper that has been peeled off from the fixing belt by the peeling blister is bent and bent when the floating paper portion is gathered and passes through the holding member as described above. Become.

  On the other hand, although it is a conventional fixing device of a type different from the above type of fixing device (a type in which a recording paper carrying a toner image to be fixed is peeled immediately after passing through the fixing pressure unit), A fixing device having the following configuration is known.

  One of them is a fixing device including an endless fixing belt stretched between a heating roller and a driven roller, and a pressure roller provided to face the driven roller. An auxiliary roll that is in pressure contact with the fixing belt is provided on the upstream side of the inlet of the fixing nip portion formed between the fixing belt supported by the pressure roller and the pressure roller (Patent Document 3). In this fixing device, the hot offset phenomenon does not occur, and it is not necessary to bring the fixing belt and the unfixed toner image sufficiently close in the preheating process, and the unfixed toner image comes into contact with the fixing belt and image distortion occurs. It is said that effects such as no longer occurring can be obtained.

  The other is a fixing device that includes a belt member stretched between a first fixing roller and a heat generating roller, and a second fixing roller that forms a nip portion with the first fixing roller. In addition, a sheet-like heating element that abuts from the inside of the belt member and heats the belt member is provided, the transfer material is electrostatically adhered to the belt member for preliminary heating, and recording is performed at the nip portion. The toner image on the paper is fixed (Patent Document 4). In this fixing device, effects such as shortening the warm-up time of the belt member and stabilizing or equalizing the belt temperature during continuous printing can be obtained.

Japanese Patent Laid-Open No. 7-5781 (paragraph 0015, FIG. 3, etc.) JP-A-7-219366 (paragraph 0015, FIG. 2, etc.) JP-A-9-281822 (Claim 1, FIG. 1, etc.) JP 2001-166617 A (Claim 1, FIG. 3, etc.)

  However, these two different types of fixing devices both peel off the recording paper immediately after passing through the fixing nip portion and the like, and have a fixing pressure unit that presses the recording paper against the outer peripheral surface of the fixing belt. Since the sheet is not transported in close contact with the outer peripheral surface of the belt even after passing, no peeling blister occurs in the fixing device of the type described above. As a result, the gloss caused by the peeling blister Fixing defects such as unevenness and paper wrinkles do not occur. Therefore, this fixing device has nothing to do with the generation of peeling blisters after passing through the fixing pressure unit described above.

  In addition, this type of fixing device preheats toner and recording paper in a belt portion where an auxiliary roller or a planar heating element is arranged on the upstream side of the fixing nip portion. The purpose of the preheating is as follows. It does not prevent the occurrence of peeling blisters after passing through the fixing pressure unit. In addition, the preheating heating process may be performed by pressing the recording paper against a fixing belt having no support member on the inner peripheral surface side by an auxiliary roller, or by electrostatically applying to the fixing belt heated by a planar fixed heating element. Therefore, the recording paper is not pressed in a state of being firmly held between the fixing belt and, therefore, sufficient adhesion between the paper and the heated fixing belt can be obtained. However, there is a risk that image distortion or the like may occur due to pressure contact with the fixing belt that is halfway through the unfixed toner image or water vapor generated by preheating.

  The present invention has been made to solve the above-described problems, and at least prevents the occurrence of peeling blisters between the fixing belt and the recording paper after passing through the fixing pressure unit. In addition, the present invention provides a fixing device that can prevent fixing defects such as uneven gloss and paper wrinkles due to such peeling blisters. Further, the present invention can prevent the occurrence of the above-mentioned peeling blisters and the occurrence of fixing defects and paper wrinkles due to the peeling blisters, and also suppress the occurrence of an image shift phenomenon at the leading edge of the toner image as described later, for example. It is an object of the present invention to provide a fixing device that can be used.

  The fixing device of the present invention includes an endless fixing belt that rotates so as to circulate, a heating device that heats the fixing belt, and a fixing pressure unit that is in pressure contact with the outer peripheral surface of the fixing belt heated by the heating device. A pressure rotating body that introduces a recording sheet carrying a toner image to be fixed into the fixing pressure unit and presses the recording paper in contact with the outer peripheral surface of the fixing belt, and the pressure rotating body. The support is supported by the support, the support that supports the belt portion by contacting the inner peripheral surface of the fixing belt region before entering the fixing pressure unit, the heating device that heats the support, and the support. A pressing body that presses against the outer peripheral surface in the fixing belt region and presses the recording paper before being introduced into the fixing pressure unit against the outer peripheral surface in the fixing belt region, and the support The temperature of the contact surface of the body with the fixing belt is It is characterized in that the direction of belt rotation direction of the upstream region downstream region than is configured to be lower relationship.

  The temperature difference between the temperature in the upstream region of the contact surface of the support and the temperature in the downstream region is set to 10 ° C. or higher, more preferably 20 ° C. or higher. The heating device for heating the support is not particularly limited. For example, it is preferable that at least the upstream region and the downstream region of the support in the belt rotation direction are separately provided.

  The pressing body is not particularly limited. For example, the pressing body is a pressing belt that is stretched and rotated by a plurality of support rolls, and two or more support rolls among the plurality of support rolls are supported by the support body. It is preferable that the fixing belt region be installed so as to be able to rotate in a state where the pressing belt is interposed therebetween.

  According to the fixing device of the present invention, the outer peripheral surface of the fixing belt region in which the recording paper carrying the toner image to be fixed is supported and heated by at least the support before being introduced into the fixing pressure unit. As a result, the toner image is firmly pressed against the heated fixing belt supported by the support, and the toner image is preheated under pressure. After that, it is introduced into a fixing pressure unit where the fixing belt and the pressure rotating body are in pressure contact with each other.

  In addition, in this fixing device, the temperature of the contact surface of the support with the fixing belt is lower in the downstream region than in the upstream region in the belt rotation direction, and therefore the region of the fixing belt supported by the support. The recording paper that is pressed and pressed by the pressing member is affected by the temperature relationship, and is heated at a certain temperature first and then at a temperature lower than that. In particular, this makes it possible to prevent a part of the toner image that is supposedly attached to the recording paper from being excessively heated and to transfer and adhere to the fixing belt side, and to prevent the occurrence of the leading edge image shift described later. Is advantageous.

  Since the fixing operation as described above is performed, the moisture content of the recording paper slightly decreases before entering the fixing pressure unit, and accordingly, the amount of water vapor from the recording paper after passing through the fixing pressure unit. Since the generation is suppressed, the generation of peeling blisters after passing through the fixing pressure unit is reduced. In addition, by assuming the toner image, the heating temperature (for the main fixing) in the fixing pressure unit and the like is lowered from the viewpoint of suppressing the generation of peeling blisters after passing through the fixing pressure unit. It is also possible to set.

  Therefore, when this fixing device is used, it is possible to stably obtain a fixed image excellent in glossiness without at least fixing defects such as uneven gloss and paper wrinkles due to the peeling blisters. Become.

  In addition, when the temperature difference between the upstream region and the downstream region on the contact surface of the support is set to 10 ° C. or more, it is possible to more reliably prevent the occurrence of peeling blisters after passing through the fixing pressure unit. As well as being able to do so, it is possible to reliably suppress the occurrence of a tip image shift described later. In addition, when the temperature difference is set to be 20 ° C. or more, it is possible to suppress the occurrence of a highlight pattern which will be described later.

  In addition, when a heating device for heating the support is employed as a separate device that heats at least the upstream region and the downstream region in the belt rotation direction of the support, contact of the support as described above A temperature difference in the surface can be realized reliably and efficiently.

  Further, when the pressing body is a pressing belt that is stretched and rotated by a plurality of support rolls as described above, water vapor generated from a recording sheet pressed against the fixing belt by the pressing belt is put into the sheet. It becomes possible to preheat the toner image evenly by confining it and maintaining the adhesion of the recording paper to the pressing belt, which is advantageous for good assumption of the toner image. In addition, it is advantageous for suppressing the occurrence of a tip image shift described later.

  Further, the recording paper when passing through the pressing section by the pressing belt is pressed by two or more support rolls that are rotatably pressed in the fixing belt region supported by the support via the pressing belt. In response to this, the fixing belt is firmly pressed against the fixing belt, whereby the recording paper can be prevented from floating from the fixing belt by the pressure of water vapor generated from the recording paper in the pressing section. It will be heated evenly.

[Embodiment 1]
FIG. 1 is a schematic configuration diagram illustrating a main part of a fixing device according to Embodiment 1 of the present invention. The fixing device 1 is used as a fixing unit in an image forming apparatus such as a printer or a copying machine that can form a toner image and transfer it to a recording sheet.

  The fixing device 1 includes an endless fixing belt 10 that rotates in an arrow direction A, a heating plate 20 that mainly heats the fixing belt 10, and a fixing belt 10 that is heated by the heating plate 20. The fixing belt 10 is supported by a pair of pressure rolls 30 and 31 disposed in pressure contact with each other and the second pressure roll 31 disposed on the outer peripheral surface side of the fixing belt 10 among the pair of pressure rolls. And a pressure belt 35 rotating so as to move in the same direction by contacting with a predetermined distance, and an inner peripheral surface side of the fixing belt 10 after passing through the pressure rolls 30 and 31. A cooling device 40 that cools the fixing belt and the like, a belt support plate 50, a planar heater (such as a rubber heater) 55 that heats the belt support plate 50, and the fixing belt 10 supported by the support plate 50. Pressure welding Those having a pressing belt 60 such as a pressing member to be. In the figure, symbol P denotes a recording sheet, and T denotes a toner image carried on the recording sheet P. Moreover, the solid line arrow in the figure indicates the rotation direction of the main rotating component, and the one-dot chain line with an arrow indicates the conveyance path of the recording paper P.

  The fixing belt 10 includes a belt base material having a thickness of about 50 μm made of polyimide containing a conductive material such as carbon black, an elastic layer made of a silicone copolymer having a thickness of about 60 μm, a fluorine rubber, and the like. The surface release layer is made of a three-layer structure in which layers are formed in this order. The fixing belt 10 is stretched around a plurality of support rolls such as a drive roll 15, a heating roll 25, a belt support roll 16, a first pressure roll 30, a peeling roll 17, a tension roll 18, and a drive motor (not shown). It rotates in the direction of arrow A by a drive roll 15 connected to a drive source equipped with the above.

  In addition to the drive function described above, the drive roll 15 is configured to exhibit a function (steering function) for correcting the meandering travel of the fixing belt 10 by displacing one end of the roll in a predetermined direction. The peeling roll 17 supports the fixing belt 10 so that the fixing belt 10 moves while being bent sharply, and thereby the recording sheet P conveyed in close contact with the fixing belt 10 has its own waist strength (rigidity). The function of peeling off from the fixing belt 10 which is bent and travels by itself is used. The tension roll 18 applies a predetermined tension to the fixing belt 10 and adjusts the tension of the belt to stabilize the rotational drive.

  The heating plate 20 has a substrate (for example, an aluminum substrate) 21 formed on a curved mirror surface having a predetermined curvature (for example, about R900 mm) along the belt rotation direction A on the surface that contacts the fixing belt 10, and the substrate. 21 and a sheet heater 22 installed on the surface on the side where the fixing belt 10 does not contact. The heating roll 25 has a structure in which a heating source such as a halogen lamp is disposed inside a cylindrical metal (aluminum or the like) roll, and heats the fixing belt 10 from the inner peripheral surface side. The heating temperature in the heating plate 20 and the heating roll 25 is set to a temperature range of 100 to 140 ° C. Moreover, the heating temperature of the heating plate 20 and the heating roll 25 may be either the same temperature or a different temperature.

Each of the pressure rolls 30 and 31 is provided with a heat resistant elastic layer having a thickness of about 6 mm made of silicone rubber (for example, a hardness of about 17 °) or the like on a metal (aluminum or the like) roll base having a cylindrical outer diameter of about 90 mm. It is of the formed structure. The pair of pressure rolls 30 and 31 are pressed against each other with a predetermined pressure (for example, a pressure at which the nip pressure becomes about 2.5 × 10 ⁵ Pa) by a pressure mechanism (not shown), and the nip width is 20 mm. It is installed to be about. Further, the pressure rolls 30 and 31 are provided with a heating source such as a halogen lamp in the internal space, whereby the temperature required for the pressure rolls 30 and 31 during the fixing operation (preferably normal fixing). The temperature is set so as to be maintained at a temperature slightly lower than the heating temperature.

  The pressure belt 35 has an elastic layer of about 60 μm thickness made of silicone rubber or the like on a belt base material made of polyimide or the like about 50 μm thick, and a surface release layer made of silicone resin or the like and about 10 μm thick. The three-layer structure is formed by laminating in this order. The pressure belt 35 is stretched between the second pressure roll 31 and the plurality of belt support rolls 36 to 39, and is sandwiched between the first pressure roll 30 and the second pressure roll 31. The rotational force of the first pressure roll 30 is transmitted to rotate in the direction of arrow B. The pressure belt 40 rotates and moves in the same direction in contact with the outer peripheral surface of the fixing belt 10 in a predetermined section between the second pressure roll 31 and the belt support roll 39. The contact section between the pressure belt 40 and the fixing belt 10 serves as a fixing pressure unit for transporting the recording paper P in a state of being pressed against the fixing belt 10. Among the belt support rolls, the roll 38 is configured to function as a steering roll that corrects the meandering travel of the pressure belt 35 by displacing one end of the rotation shaft in a predetermined direction by a predetermined amount.

  The cooling device 40 includes a heat radiating plate 41 that is in contact with the inner peripheral surface of the fixing belt 10 between the first pressure roll 30 and the belt support roll 17, and an air cooling device 42 that air-cools the heat radiating plate 41. . The heat radiating plate 41 is a heat sink composed of a plate-like substrate formed of a metal such as aluminum and a plurality of heat radiating fins (not shown) standing on the surface opposite to the side in contact with the fixing belt. In the heat radiating plate 41, the contact surface of the substrate that contacts the fixing belt is formed as a curved surface that protrudes at least outward and is gently curved in the belt running direction. The air-cooling device 42 includes a blower fan and a duct (vent pipe) for sending (exhausting) an air flow generated by the blower fan so as to be in contact with the heat radiating plate (mainly the heat radiating fins) 41. Yes. The cooling device 40 is set so that the recording paper P conveyed in close contact with the fixing belt 10 can be cooled to such an extent that the toner image T is cooled and solidified.

  As shown in FIGS. 1 and 2, the support plate 50 is a belt region before the fixing belt 10 enters the fixing pressure unit (in other words, upstream of the first pressure roll 30 in the belt rotation direction A). The belt region in the section on the side and downstream of the belt support roll 16 in the belt rotation direction A) is supported in a state of surface contact from the inner peripheral surface side. As the support plate 50, a plate member (for example, a predetermined thickness) formed on a curved mirror surface having a belt contact surface in contact with the fixing belt 10 having a predetermined curvature (for example, about R900 mm) along the belt rotation direction A. Aluminum substrate) is used. Further, the support plate 50 is formed to have a length along the belt rotation direction A of about 200 to 400 mm.

  The planar heater 55 is for heating the support plate 50 itself on the surface opposite to the belt contact surface of the support plate 50, and fixing the support 50 by heating the support 50 with the heater 55. The belt 10 is also configured to function as a heating plate. Further, the planar heater 55 includes two planar heaters 56 and 57 (an upstream side surface heater 56 and a downstream side) that respectively heat a region portion upstream of the support plate 50 in the belt rotation direction A and a region portion downstream thereof. A side heater 57) is used. Here, the upstream region portion and the downstream region portion of the support plate are each region when divided into two at an intermediate point along the belt rotation direction A of the support 50.

  The upstream side surface heater 56 and the downstream side surface heater 57 can individually set heating temperatures, and can perform heating based on the set temperatures. In particular, in the fixing device 1, the temperature of the contact surface of the support plate 50 with the fixing belt 10 is lower than the temperature (T1) in the upstream region in the belt rotation direction A (T2 <T1). The heating temperatures of the upstream side heater 56 and the downstream side heater 57 are set so that the lower side heater 56 and the downstream side heater 57 are lower.

  At this time, the temperature difference (T1−T2) between the temperature (T1) in the upstream region and the temperature (T2) in the downstream region is set to be at least 10 ° C. from the viewpoint described later. Further, in this case, as shown in FIG. 2, the temperature (T1) of the upstream region on the support plate contact surface is the surface temperature in the vicinity of the end (50a) on the upstream side in the belt rotation direction A of the contact surface. About the temperature (T2) of a downstream area, it is set as the surface temperature in the edge part vicinity (50b) of the belt rotation direction A downstream of the contact surface. In particular, the heating temperature of the upstream side surface heater 56 is set to a temperature that is at least equal to or lower than the heating temperature of the fixing belt 10 by the heating plate 20 or the heating roll 25, but specifically 100 to 140. It is set to about ℃.

  The pressing belt 60 is formed by laminating an elastic layer having a predetermined thickness (for example, about 5 to 20 μm) made of silicone rubber or silicone resin on an endless belt base material having a predetermined thickness (for example, about 130 μm) made of polyimide or the like. The two-layer structure is formed. The pressing belt 60 is stretched between three pressing rolls 61, 62, 63 and one tension roll 64, and the fixing belt 10 is supported by the support plate 50 via the pressing belt 10. In this state, the roller is driven to rotate in the direction indicated by the arrow C while being pressed against the outer peripheral surface of the fixing belt by the three pressing rolls 61, 62, and 63 that are press-contacted to be rotatable. That is, the pressing belt 60 rotates and moves in the same direction in contact with the outer peripheral surface of the fixing belt 10 in a section between the first pressing roll 61 and the third pressing roll 63 (corresponding to a pressing section by the pressing belt 60). Become. This section is set so as to be a section that substantially covers at least both the upstream region and the downstream region on the contact surface of the support plate 50.

  Each of the three pressing rolls 61, 62, 63 is an elastic roll in which an elastic layer having a predetermined thickness made of silicone rubber or the like is formed on a metal roll core material having the same outer diameter, and is not illustrated using a spring member. The pressure mechanism is pressed with a predetermined pressing force so that the nip width between the fixing belt 10 and the support region is a predetermined width. Further, the three pressing rolls 61, 62, 63 are installed at equal intervals along the belt rotation direction B (C).

  Further, in the fixing device 1, during the fixing, the recording paper P carrying the toner image T to be fixed is rotated while the pressing belt 60 and the fixing belt 10 are in pressure contact (the pressing section E). ) Is guided by a conveyance guide or the like (not shown).

  In such a fixing device 1, the following fixing is basically performed on the recording paper P onto which the toner image T has been transferred on the image forming unit side of the image forming apparatus.

  First, the recording paper P onto which the toner image T has been transferred is conveyed in a posture in which the toner image carrying surface is brought into contact with the outer peripheral surface of the fixing belt 10 through a paper conveying belt, a conveying guide (not shown) and the like. It is introduced between the pressing sections formed with the belt 60 (on the entrance side). At this time, the fixing belt 10 reaches and reaches the pressing section in a state where the fixing belt 10 is heated to a predetermined temperature by the heating plate 20 and the heating roll 25 in advance. The fixing belt 10 is also heated by the support plate 50 on which the planar heater 55 is installed.

  The recording paper P introduced between the outer peripheral surface of the fixing belt 10 in the pressing section and the pressing belt 60 is supported by the support plate 50 and is 3% higher than the fixing belt 10 heated to a predetermined temperature or more. The pressure belt 60 passing through the two pressure rolls 61 to 63 is pressed and conveyed and heated.

  Thereby, the recording paper P is heated at high temperature under pressure. Due to this heating, moisture in the paper starts to be generated as water vapor, but most of the water vapor is recorded between the area of the fixing belt 10 supported by the support plate 50 and the pressing belt 60. The paper P is confined inside the paper P. For this reason, the recording paper P is not lifted from the fixing belt 10 due to the generation of the water vapor, and is conveyed while maintaining the close contact with the fixing belt 10, so that the toner image is preheated evenly. It is assumed that the recording paper P is attached to the recording paper P with sufficient adhesive strength.

  The support plate 50 is heated at different temperatures by the upstream side surface heater 56 and the downstream side surface heater 57, and the temperature of the upstream region is lower than the temperature of the downstream region on the belt contact surface. Therefore, the recording paper P passing through the pressing section is heated at a temperature lower than that in the upstream area when passing through the downstream area of the belt contact surface. As a result, as will be described in detail later, the recording paper P passing through the pressing section is prevented from being excessively heated, and a part of the excessively heated and melted toner image adheres to the fixing belt 10. To be suppressed.

  After passing through this pressing section, the recording paper P is conveyed by the fixing belt 10 and introduced into a fixing and pressing unit where the fixing belt 10 and the pressing belt 35 are in pressure contact. Incidentally, since the recording paper P in the section before being discharged from the pressing section and introduced into the fixing pressure unit is not subjected to the pressing action by the pressing belt 60, the recording paper P is temporarily peeled off from the fixing belt 10 in practice. Since the time is very short, it can be smoothly introduced into the fixing pressure unit without any problem.

  The recording paper P introduced into the fixing and pressing unit is strongly pressed with a load necessary for fixing by the pressure rolls 30 and 31 at the beginning of entering, and is heated mainly by preheating of the fixing belt 10. In this fixing device, since the pressure rolls 30 and 31 are heated by the heating source, the pressure rolls 30 and 31 are also heated. However, the heating by the pressure rolls 30 and 31 is performed at a temperature lower than the normal fixing temperature as described above.

  Subsequently, the recording paper P that passes through the fixing pressure unit is conveyed while being sandwiched between the fixing belt 10 and the pressure belt 35 and in close contact with the fixing belt 10, and is on the heat radiation plate 41 of the cooling device 40. When passing through the region (cooling section) of the fixing belt 10, it is cooled until it reaches a predetermined temperature (for example, 55 to 85 ° C.) together with the toner image T. The cooling by the cooling device is preferably performed so as to satisfy the condition that the surface temperature of the recording paper when being peeled from the fixing belt 10 is lower than the softening point of the toner.

  By this cooling, the toner image T is agglomerated and solidified, and the recording paper P that has passed through the heat radiating plate 41 of the cooling device 40 is fixed by the strength of the paper itself in the paper peeling means constituted by the peeling roll 17. The toner image is peeled from the belt 10 together with the toner image (a state indicated by a tip portion of an alternate long and short dash line in FIG. 1). The peeled recording paper P is discharged out of the fixing device. As a result, the toner image T is fixed on the recording paper P.

  The image fixed in this way is obtained as an image rich in glossiness that is smoothed especially in accordance with the smooth surface of the fixing belt 10.

  In particular, in the fixing device 1, as described above, the recording paper P carrying the toner image T to be attached passes through the pressing section E by the pressing belt 60 and is then introduced into the fixing pressure unit, thereby fixing the fixing belt 10. The recording paper P is heated in a state where it is firmly pressed against it, and the recording paper P is heated at a slightly lower temperature in the fixing pressure unit. For this reason, generation of water vapor from the recording paper after passing through the fixing pressure unit is suppressed.

  As a result, the occurrence of peeling blisters in which water vapor is generated after passing through the fixing pressure unit and the recording paper P peels from the fixing belt 10 is suppressed. This also prevents fixing defects such as gloss unevenness and paper wrinkles due to the occurrence of peeling blisters, and enables good fixing.

  In the fixing device 1, the pressing belt 60 is formed with an elastic layer, and the pressing rolls 61 to 63 are also formed with an elastic layer. Therefore, the recording paper P is supported by the support plate 50. The fixing belt 10 is pressed against the outer peripheral surface of the fixing belt 10 with good adhesion. As a result, the recording paper P is heated uniformly in the pressing section. In addition, since the three pressing rolls 61 to 63 are installed, the pressing (pressing) of the recording paper by the pressing belt 60 can be strengthened, so that the recording paper pressed by the pressing belt 60 generates water vapor. Peeling from the fixing belt 10 can be effectively suppressed. From this point of view, it is preferable that the number of rolls that press-contact the fixing belt 10 among the rolls that support the pressing belt 60 is plural.

  Further, since the support plate 50 is heated by the sheet heater 55, continuous fixing using recording paper such as thick paper is performed, and the recording paper having a low temperature touches the fixing belt 10 or the pressure belt 60 and the fixing is performed. Even if there is a possibility that the temperature is likely to be lowered, the fixing belt 10 and the like are continuously heated by the support plate 50, so that the temperature drop is prevented and the recording paper P is stably heated at a predetermined temperature. be able to.

  Next, each test performed for examining the configuration related to the heating condition of the support plate 50 in the fixing device 1 will be described.

<Test 1>
In this test 1, the fixing device 1 is set to the following conditions, and a fixing operation is performed by introducing recording paper P on which a constant test toner image is formed by a known color printer. The occurrence of uneven gloss and paper wrinkles due to peeling blisters in the recording paper obtained was investigated.

  The conditions are as follows. First, the heating temperature of the upstream side heater 56 and the downstream side heater 57 of the support 50 was set to the same temperature. Specifically, the same temperature was set in the range of 100 to 140 ° C. As the support plate 50, an aluminum plate having a belt contact surface made of a curved surface having the above-described curvature, a length along the belt rotation direction A of about 220 mm, and a thickness of about 3 mm was used. Here, half of the support plate 50 on the upstream side in the belt rotation direction A is defined as an upstream region, and the remaining half on the downstream side is defined as a downstream region.

Further, as the pressing belt 60, a two-layer structure in which an elastic layer made of silicone rubber and having a thickness of 10 μm was laminated on an endless belt base material made of polyimide and having a thickness of 130 μm was used. In addition, as the three pressing rolls 61, 62, and 63, an elastic roll in which an elastic layer made of silicone rubber is formed on a metal roll core material having an outer diameter of 32 mm is illustrated. The pressure mechanism was pressed with a pressure of 5.7 × 10 ⁴ Pa, and the nip width with the fixing belt 10 was set to 15 mm. The first pressing roll 61 was installed near the end of the support plate 50 on the upstream side in the belt rotation direction, and the third pressing roll 63 was installed near the end of the support plate 50 on the downstream side in the belt rotation direction. About the 2nd press roll 62, it installed so that the center distance of the 1st press roll 61 and the 2nd press roll 62 might be 80 mm, and the center distance of the 2nd press roll 62 and the 3rd press roll 63 might be 140 mm.

  Further, the fixing belt 10 was heated to a temperature of 100 to 140 ° C. by the heating plate 20 and the heating roll 25. The fixing belt 10 (including the pressure belt 35) was rotated at a speed of 350 mm / s. The cooling device 40 was set so that the surface temperature of the recording paper P between the belt support roll 39 of the pressure belt 35 and the peeling roll 17 was cooled to a temperature of 90 ° C. or lower.

The test toner image has a density of 100% when the weight of unfixed toner on the recording paper is 4 g / m ² , and is 100%, 90%, 80%,..., 20%, 10%, etc. A patch image having a density of 10% and a size of 20 × 20 mm is formed by using cyan and magenta toners so as to be sequentially arranged in a line for each color from a position 25 mm away from the leading edge of the paper. An image was used. The recording paper P has a characteristic that the adhesive phenomenon with the fixing belt 10 is relatively low and the water vapor is difficult to escape from the paper from the viewpoint that the problem phenomenon generated with the generation of water vapor is likely to occur and is easily discovered. A mat surface type coated paper (manufactured by Modo: Silver Blade Matte, basis weight 115 gsm) was used.

  As a result of Test 1 using the fixing device 1 having such a condition setting, even when the recording paper P is used, the occurrence of uneven gloss and paper wrinkles due to peeling blisters were not recognized. The occurrence of gloss unevenness and paper wrinkles was evaluated by visual observation and occurrence.

  However, when observing the fixed image on the recording paper after each fixing, a phenomenon occurs (fixed image misalignment) that the image is fixed when the leading edge of the image (the leading edge during fixing) is shifted. It was confirmed that Further, when the fixed image was observed closely, it was confirmed that an image defect (highlight pattern) that appeared as a curvilinear pattern occurred in the fixed image composed of a low density region of about 10 to 40%. It was.

  When the results of Test 1 are evaluated according to the following criteria for the occurrence of the tip image deviation and the highlight pattern, the results shown in FIGS. 3 and 4 are obtained. The leading edge image shift was evaluated based on a patch image result having a density of 100%.

・ Evaluation criteria for tip image displacement (grade: G)
G0: Not generated.
G1: Although it cannot be seen visually, it can be confirmed by confirming with a magnifying glass.
G2: Slightly generated.
G3: Clearly occurring.
G4: Remarkably generated.

・ Highlight pattern evaluation criteria (grade: G)
G0: Not generated.
G1: Very slight occurrence.
G2: Slightly generated.
G3: Clearly occurring.
G4: Remarkably generated.

  As shown in FIG. 3, the occurrence of the tip image deviation is suppressed when the heating temperature of the sheet heater 55 (upstream and downstream side heaters 56 and 57) of the support plate 50 is 130 ° C. It can be seen that this occurs in other heating temperature setting ranges. Further, as shown in FIG. 4, for the highlight pattern, although the heating temperature of the planar heater 55 (56, 57) of the support plate 50 does not occur in the set range up to 130 ° C., the heating temperature is 140 ° C. It can be seen that it occurs at a high temperature. For reference, if test 1 is performed in the same manner using plain paper (uncoated paper) or other coated paper as the recording paper P, is there any occurrence of the tip image deviation or high-ride pattern? Or it has been confirmed to be minor.

  According to the study by the present inventors, it is considered that the tip image shift and the highlight pattern are generated by the following mechanism.

  Regarding the leading edge image displacement, first, the recording paper P at the time of fixing passes through the pressing section between the fixing belt 10 and the pressing belt 60 and then enters the fixing pressure unit between the fixing belt 10 and the pressing belt 35. In the period until the introduction, the recording paper P (particularly the leading portion thereof) may be temporarily separated from the fixing belt 10 as described above. This separation phenomenon is likely to occur when the adhesion between the fixing belt 10 and the recording paper P is different due to a difference in surface condition between the fixing belt 10 and the recording paper P, a difference in toner image area, or a formation position. Then, at the first stage of the temporary separation, a part of the toner image on the recording paper P is divided and transferred to the fixing belt 10 side, and then enters the fixing pressure unit and the recording paper P enters. When pressed against the fixing belt 10 again, the toner image on the recording paper P and the portion of the toner image transferred to the fixing belt 10 side are not completely matched and are generated in a slightly shifted state. Conceivable.

  Further, as described below, the separation of the toner image due to the leading edge image deviation is different depending on the pressing time of the recording paper P by the pressing rolls 61 to 63 to the fixing belt 10 supported by the support 50. It is guessed what is happening in.

  That is, when the pressing time is relatively short, the toner image is not sufficiently heated and not sufficiently melted in the pressing section, so that the recording paper is hardly immersed (supposed), It is considered that a so-called cold offset occurs in which the toner on the side in contact with the fixing belt 10 is separated from the toner on the recording paper side and is transferred to the fixing belt side. On the other hand, when the pressing time is relatively long, the toner image is sufficiently heated and melted in the pressing section and starts to soak into the recording paper, but on the side in contact with the fixing belt 10. It is considered that so-called hot offset occurs in which the toner that exists and is excessively melted and before entering the recording paper is separated from the toner on the recording paper as it is and is transferred to the fixing belt.

  On the other hand, the highlight pattern generally tends to generate water vapor from the inside as the recording paper is heated at a high temperature. When the recording paper and the fixing belt 10 are not sufficiently adhered, the recording paper is fixed to the fixing belt 10 by the water vapor pressure. In particular, the low density part of the fixed image has a lower amount of toner than the high density part, and the degree of adhesion (adhesion) with the fixing belt 10 is low. It is thought that it is caused by this.

<Test 2>
In Test 2, when the heating temperatures of the upstream side surface heater 56 and the downstream side surface heater 57 as the surface heater 55 of the support plate 50 in the fixing device 1 used in Test 1 are different from each other, the heating temperature is relatively When the temperature was higher (140 ° C. or higher), the occurrence of tip image shift and highlight pattern was examined.

  The heating temperatures (T1, T2) of the upstream side heater 56 and the downstream side heater 57 were set as follows. That is, the temperature (T1) of the upstream side surface heater 56 is set to a heating temperature (in principle 140 ° C., 140 ° C. and 150 ° C. in the case of a highlight pattern) so that the assumed toner is sufficiently attached. The temperature (T2) of the downstream side surface heater 57 is lower than the temperature of the upstream side surface heater 56 (the temperature difference: T1-T2) from the viewpoint that it is advantageous to avoid the division of the toner image due to the hot offset described above. Is set to 10 ° C, 20 ° C, 30 ° C, 40 ° C). The results of Test 2 are shown in FIGS.

  As shown in FIG. 5, when the heating temperature of the upstream side surface heater 56 is 140 ° C., the difference in the heating temperature of the respective surface heaters 56 and 57 is set to 10 ° C. or more. Generation can be prevented, and when the heating temperature of the upstream side heater 56 is 150 ° C., the heating temperature difference (T 1 −T 2) between the respective sheet heaters 56, 57 can be prevented to 40 ° C. I understand. In the latter case, when the temperature difference is 30 ° C., the G2 level leading edge image shift occurs. This is because the toner image is heated suddenly at a high temperature of 150 ° C. of the upstream side surface heater 56. It is presumed that the toner image is divided due to the hot offset described above.

  In addition, as shown in FIG. 6, it can be seen that the occurrence of the highlight pattern can be prevented by setting the heating temperature difference (T1-T2) between the planar heaters 56 and 57 to 20 ° C. or more.

  Based on the above test results, conditions were set as follows for a part of the configuration of the fixing device 1 described above.

  First, the heating temperature (T1) of the upstream side heater 56 of the support plate 50 was set to 140 ° C., and the heating temperature (T2) of the downstream side heater 57 was set to 120 ° C. In this case, the heating temperatures of the heating plate 20 and the heating roll 25 were both set to 140 ° C. Moreover, the heating temperature of the 1st pressurization roll was set to 120 degreeC, and the heating temperature of the 2nd pressurization roll 31 was set to 70 degreeC. Furthermore, the operating conditions of the cooling device 40 were set so that the temperature of the peeling roll 16 during the fixing operation was maintained at about 70 ° C.

  When fixing is performed by using the recording paper P (the mat surface type coated paper) by the fixing device 1 set as described above, uneven gloss and paper wrinkles due to peeling blisters are not generated as described above. In addition, it was possible to perform good fixing in which the occurrence of tip image displacement was suppressed. Further, the effect of suppressing the occurrence of the leading edge image shift and the highlight pattern could be satisfactorily obtained even when the image density, the image area ratio, etc. of the toner image to be fixed were changed.

  In this case, in particular, the recording paper P introduced and conveyed in the pressing section where the fixing belt 10 supported by the support plate 50 and the pressing belt 60 are in pressure contact with each other has an upstream region in the belt rotation direction of the support plate 50. In the process of passing, recording is performed at a relatively high heating temperature (T1 = 140 ° C.) by the upstream side surface heater 56 that heats the region (at this time, the fixing belt 10 is also heated at 140 ° C. so that recording is performed). The sheet is heated at 140 ° C.), and the toner image T to be fixed is sufficiently heated and melted, soaks into the sheet, and is put on the assumption.

  Subsequently, in the process of passing through the upstream region in the belt rotation direction of the support plate 50 and then passing through the downstream region in the belt rotation direction, the heating temperature (T2 = 120.degree. C.) (at this time, the fixing belt 10 is deprived of heat by the recording paper in the upstream region and the temperature is instantaneously lowered to about 120.degree. C.), and the toner presumably attached to the recording paper P. The image is not melted by being heated again at a high temperature, and is not attached to the fixing belt 10 by hot offset. Moreover, when the downstream region passes, the recording sheet P is heated from a lower heating temperature than when passing through the upstream region of the support plate 50, so that local floating of the recording paper P from the fixing belt 10 due to the generation of water vapor also occurs. It becomes difficult to do.

  Therefore, the fixing process is performed by passing through the pressing section configured such that a temperature difference (T1−T2 = 20 ° C.) occurs in the heating temperature in the belt rotation direction upstream region and the downstream region on the support plate 50 side. It is presumed that the recording sheet P that has been produced is suppressed from the occurrence of the leading edge image deviation and the occurrence of the highlight pattern.

[Other embodiments]
In the first embodiment, as the heating device (55) for heating the support plate 50, the two planar heaters 56 that can individually heat the upstream region and the downstream region of the support plate 50 in the belt rotation direction. However, the configuration of the heating device is not particularly limited to this.

  As another example of the configuration, for example, when it is desired to increase the temperature difference between the heating temperatures, only the planar heater 56 is provided in the upstream region of the support plate 50 in the belt rotation direction. A configuration in which the planar heater 57 is not provided may be employed. Further, the entire region from the upstream end of the support plate 50 in the belt rotation direction A to the downstream end thereof is subdivided into three or more regions, and the heating temperature is changed for each of the three or more subdivided regions. It is also possible to adopt a configuration in which a planar heater or the like is installed.

  Further, when the temperature of the belt contact surface of the support plate 50 is configured such that the downstream region is lower than the upstream region in the belt rotation direction X, the following temperature relationship is set. Good. That is, as described above, the temperature (T1) in the upstream region on the contact surface of the support plate is defined as the surface temperature in the vicinity of the end (50a) on the upstream side in the belt rotation direction A of the contact surface. ) As the surface temperature in the vicinity of the end (50b) on the downstream side in the belt rotation direction of the contact surface (FIG. 2), and the boundary (50c: For example, assuming that the temperature at the boundary of the intermediate point is (T3) (FIG. 2), the temperatures (T1 to T3) may be set so as to satisfy the following conditions.

  The condition “A <B ≦ C” is preferable, but it is sufficient that the condition is at least A <C or A <B.

  In the first embodiment, the case where the pressing belt 60 stretched between a plurality of support rolls is used as the pressing body that presses the recording paper P against the fixing belt 10 supported by the support plate 50 is exemplified. As the pressing body, the pressing belt 60 may not be used and only the pressing rolls 61 to 63 may be used. In this case, it is preferable to install a plurality of pressing rolls as pressing bodies, but one pressing roll may be used as long as a required pressing time can be secured. As the pressing body, it is possible to adopt a pressing object that is fixedly set as long as there is no problem with the rotation of the fixing belt 10 or the passage of the recording paper P.

  In addition, it is also possible to form a release layer made of a material that is difficult for toner to adhere to the contact surface of the pressing member such as a pressing belt and a pressing roll that contacts the fixing belt and the recording paper. In this case, for example, when the toner image is fixed to the second surface of the recording paper during double-sided image formation, the toner of the fixed toner image on the first surface is transferred and adhered to the contact surface of the pressing body. Can be suppressed.

  In the first embodiment, the case where the whole support plate 50 is used as the support for supporting the fixing belt 10 is exemplified. However, in particular, the entire form of the support is at least the fixing belt 10. There is no particular limitation as long as it has a contact surface that comes into surface contact with the inner peripheral surface of the region in the vicinity of the front side of the fixing pressure unit.

  Furthermore, in the first embodiment, the case where the pressure belt 35 is used as the pressure rotator that forms the fixing pressure unit with the fixing belt 10 is illustrated, but as the pressure rotator, for example, It is also possible to employ a configuration constituted by only a pair of pressure rolls 30 and 31 without using the pressure belt 35 as described above. In this case, the recording paper after passing through the fixing pressure unit formed between the fixing belt 10 sandwiched between the pressure rollers 30 and 31 and the second pressure roller 31 is the fixing belt 10. In this state, the sheet is conveyed while being cooled by the cooling device 40 and finally peeled off from the fixing belt 10 that has reached the peeling roll 16. The cooling method of the cooling device 40 may be another method. Moreover, if natural cooling is possible, the cooling device 40 does not necessarily need to be installed.

  The fixing device of the present invention can be used as a fixing unit of an image forming apparatus capable of forming an image made of toner (dry developer) based on various image information and transferring it to a recording sheet. The recording paper applied to the fixing device is not limited to normal paper or coated paper (coating paper) as long as it is capable of fixing the toner image by being conveyed through the fixing device. It includes members such as OHP sheets, postcards, envelopes and the like.

FIG. 2 is a schematic configuration diagram illustrating a main part of the fixing device according to the first exemplary embodiment. FIG. 2 is an enlarged view showing a part of the fixing device in FIG. 1 (assumed wearing portion by a pressing section where a support plate and a pressing belt face each other). It is a graph which shows the result of the test 1 regarding the generation | occurrence | production state of front-end | tip image deviation. It is a graph which shows the result of the test 1 regarding the generation | occurrence | production state of a highlight pattern. It is a graph which shows the result of the test 2 regarding the generation | occurrence | production state of front-end | tip image deviation. It is a graph which shows the result of the test 2 regarding the generation | occurrence | production condition of a highlight pattern.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Fixing device, 10 ... Fixing belt, 20 ... Heating plate (heating device), 25 ... Heating roll (heating device), 30, 31 ... Pressure roll (pressure rotary body), 35 ... Pressure belt (pressure application) Rotating body), 50 ... support plate (support), 55 ... planar heater (heating device), 56 ... upstream side heater, 57 ... downstream side heater, 60 ... pressing belt (pressing body), 61-63 ... Press roll (or support roll), 64 ... tension roll (support roll), T ... toner image, P ... recording paper, A ... belt rotation direction.

Claims (4)

An endless fixing belt rotating so as to circulate;
A heating device for heating the fixing belt;
A fixing pressure unit is formed by pressure contact with the outer peripheral surface of the fixing belt heated by the heating device, and a recording sheet carrying a toner image to be fixed is introduced into the fixing pressure unit to introduce an outer peripheral surface of the fixing belt. A pressure rotator that is pressed against and passed,
A support that supports the belt portion in surface contact with the inner peripheral surface of the fixing belt region before entering the fixing pressure unit formed by the pressure rotating body;
A heating device for heating the support;
A pressing body that presses against the outer peripheral surface in the fixing belt region supported by the support and presses the recording paper before being introduced into the fixing pressure unit against the outer peripheral surface in the fixing belt region; Prepared,
The fixing device is configured so that the temperature of the contact surface of the support with the fixing belt is lower in the downstream region than in the upstream region in the belt rotation direction.   The fixing device according to claim 1, wherein a temperature difference between an upstream region temperature and a downstream region temperature of the contact surface of the support is set to 10 ° C. or more.   The fixing device according to claim 1, wherein the heating device that heats the support is a separate device that heats at least the upstream region and the downstream region of the support in the belt rotation direction.   The pressure body is a pressure belt that is stretched and rotated by a plurality of support rolls, and two or more support rolls among the plurality of support rolls are rotated upstream in the fixing belt region supported by the support body. 2. The fixing device according to claim 1, wherein the fixing device is installed so as to be rotatably contacted with the first end portion and a downstream end portion thereof via the pressing belt.

Images