JP2014059358A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device and an image forming apparatus having good productivity and durability, and manufactured at a low cost.SOLUTION: A fixing device includes a fixing member 111, a heat source 112 that is provided inside the fixing member to heat the fixing member from the inside, and a pressure member 110 that presses the fixing member to form a nip part. The fixing device further includes a shield member 120 that extends in a main scanning direction between the heat source and the fixing member; the shield member includes at least one opening; an opening width of the opening corresponds to a sheet width of a recording medium; and the edge of the shield member forming the opening width is formed in a shape to prevent diffraction of light.

Description

  The present invention relates to a fixing device provided in a copying machine, a facsimile, a printer, a printing machine, or an ink jet recording apparatus. Furthermore, the present invention relates to an image forming apparatus formed by combining at least one of these.

  Conventionally, an image forming apparatus using an electrophotographic system is known. The image forming process in the image forming apparatus can be performed by forming an electrostatic latent image on the surface of the photosensitive drum as an image carrier and developing the electrostatic latent image on the photosensitive drum with toner as a developer. The toner image visualized and developed is transferred onto a recording paper by a transfer device to carry the toner image, and the toner image on the recording paper is fixed by a fixing device.

  The fixing device is provided with a fixing rotator constituted by opposing rollers, a belt, or a combination thereof. The fixing rotator sandwiches the recording paper onto which the toner image has been transferred and applies heat and pressure to fix the toner image transferred onto the recording paper.

  Specifically, a belt fixing method, which is an example of a known fixing device, will be described below with reference to FIG. The fixing rotator of the fixing device includes a fixing belt 1-j including a heating roller 1-d having a heater 1-f as a heat source and a fixing roller 1-b having a rubber layer on the surface, The pressure roller 1-a is in contact with the fixing belt 1-j.

  The recording sheet 1-h to which the toner image conveyed to the fixing device is transferred is conveyed to the nip between the fixing belt 1-j and the pressure roller 1-a. Then, in the process in which the recording paper 1-h having the toner image transferred passes through the fixing nip, the toner image is heated and pressurized and fixed.

  Also known are a fixing device employing a film fixing method and a fixing device provided with an IH heater outside the fixing belt. Such fixing devices are described in, for example, Patent Documents 1 to 4.

The fixing device described in Patent Document 1 includes a fixing member that is in sliding contact with the inner surface of the rotating body.
Further, the fixing device described in Patent Document 2 has a configuration having a shielding member.
Further, the fixing device described in Patent Document 3 includes a heat dissipation member.
Further, the fixing device described in Patent Document 4 has a configuration in which a heater is provided inside the pressure roller.

The fixing belt and the metal heat conductor of the fixing device described in Patent Document 1 have a thin plate thickness, and thus the heat conduction in the main scanning direction is not good. Specifically, the heat quantity Q is obtained by the following equation.
Q = kSt (T1-T2) / L
It is assumed that the thermal conductivity of the material of the metal heat conductor is k, the cross-sectional area of the metal heat conductor is S, the length in the main scanning direction is L, and the temperatures of both surfaces of the metal heat conductor are T1 and T2. Therefore, if the metal heat conductor is thin (the cross-sectional area S is small), the amount of heat Q transmitted per unit time is reduced. As a result, when a sheet having a short length in the main scanning direction is continuously passed, the temperature of the end of the sheet passing portion of the fixing belt rises, and there is a risk that thermal degradation or hot offset may occur. When the temperature of the fixing belt rises, it is necessary to limit sheet passing in order to prevent this thermal deterioration and hot offset. Therefore, there has been a demand for a fixing device that does not require paper passing restrictions and has improved productivity.

  In the fixing device described in Patent Document 2, in order to prevent the temperature rise of the non-sheet passing portion of the fixing roller, a shielding member is installed in a range corresponding to the non-sheet passing portion of the fixing roller. It seems that the heat transfer to the non-sheet passing portion is shielded by this shielding member. However, since light is diffracted by Huygens' principle, after all, the non-sheet passing portion of the fixing roller is heated. As a result, the temperature of the non-sheet passing portion of the fixing roller increases, the fixing roller may deteriorate, and the life may be shortened. In order to avoid such a possibility, it is conceivable to install the shielding member in a range corresponding to the sheet passing portion of the fixing roller in consideration of light diffraction. However, the diffractive portion has a low light density, and there is a problem that a temperature drop occurs at the end of the paper during fixing, resulting in an abnormal image.

  In the fixing device described in Patent Document 3, in order to prevent the temperature of the fixing belt from rising, the heat of the fixing belt can be radiated by the heat radiating member. However, when the heat of the fixing belt is radiated by the heat radiating member, it is necessary to stop the operation of the fixing belt. Therefore, there has been a demand for a fixing device that does not require the operation of the fixing belt to be stopped and has improved productivity.

  In the fixing device described in Patent Document 4, preheating can be applied from the back surface of the paper by providing a heater inside the pressure roller and the fixing member. Therefore, there is no need for heat deterioration or hot offset in the fixing member, and it is not necessary to restrict paper passing or stop the operation of the heating belt, thereby improving productivity. However, this fixing device requires two heat lamps and is expensive. Therefore, cost reduction has been desired.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an inexpensive fixing device and an image forming apparatus that are highly productive and durable.

In order to solve the above-described problem, a fixing device according to a first aspect of the present invention includes:
A fixing member;
A heat source provided inside the fixing member for heating the fixing member from the inside;
A pressure member that presses the fixing member to form a nip portion;
In a fixing device having
A shielding member extending in the main scanning direction between the heat source and the fixing member;
The shielding member has at least one opening;
The opening width of the opening corresponds to the paper width of the recording medium,
The shape of the edge of the light shielding member that forms the opening width is a shape that prevents diffraction of light.

  According to the present invention, it is possible to provide a low-cost fixing device and image forming apparatus that are highly productive and durable.

1 is a configuration diagram schematically illustrating an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating a partial cross section of a fixing device of the image forming apparatus illustrated in FIG. 1. FIG. 3 is a perspective view schematically showing a fixing device of the image forming apparatus shown in FIG. 1, and FIG. 3A is a perspective view showing the fixing device when a paper having a small paper width is passed. FIG. 3B is a perspective view illustrating a fixing device when a sheet having a large sheet width is passed. FIG. 4A is an explanatory diagram showing a light amount distribution from a heat source to a fixing belt, FIG. 4A is an explanatory diagram showing a light amount distribution of a conventional fixing device, and FIG. 4B is a light amount of the fixing device shown in FIG. It is explanatory drawing which shows distribution. It is a perspective view which shows the light-shielding plate of the various aspect which concerns on one Embodiment of this invention. FIG. 10 is a cross-sectional view schematically showing a conventional fixing device.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram schematically showing an image forming apparatus according to an embodiment of the present invention. The image forming apparatus of the present embodiment is a color printer (hereinafter referred to as “printer”) capable of forming a full-color image adopting an electrophotographic tandem method. The image forming apparatus is not limited to the printer shown in FIG. 1, and may be a copying machine, a facsimile, a printing machine, an ink jet recording apparatus, or the like.

  First, the basic configuration and operation of the printer will be described with reference to FIG. 1, and then the configuration and operation unique to the present embodiment will be described.

  The printer shown in FIG. 1 has a paper feed cassette 2 in which a transfer paper 29 as a recording medium is stored at the bottom of the image forming apparatus main body 1 serving as a base, and an image forming unit 3 is arranged above the paper cassette. It has been configured.

  The image forming unit 3 includes an image forming unit 8 including four image forming units 8Y, 8C, 8M, and 8K as a plurality of image forming units including an image carrier, and a plurality of rollers 4, 5, 6 An intermediate transfer unit 7 having an intermediate transfer belt 7a as an intermediate transfer member constituted by a flexible endless belt wound around these rollers, and light as an optical writing unit that performs optical writing on each image carrier A writing unit 15 and a fixing device 22 for fixing the toner image on the transfer paper 29 are provided.

  The image forming units 8Y, 8C, 8M, 8K and the intermediate transfer unit 7 are detachable from the apparatus main body 1. A conveyance path R for conveying the transfer paper 29 is formed between the paper feeding unit 2 and the fixing device 22. The roller 6 is arranged facing the conveyance path R. In the present embodiment, the intermediate transfer unit 7, the image forming unit 8, the optical writing unit 15, and the fixing device 22 constitute constituent elements inside the apparatus, and are arranged at the approximate center in the apparatus main body 1.

  The space between the roller 4 and the roller 5 of the intermediate transfer belt 7a corresponds to the lower belt running side of this belt. In the intermediate transfer belt 7 a, a secondary transfer roller 20 serving as a secondary transfer device is disposed at a portion facing the roller 6 so as to face the conveyance path R, and a belt for cleaning the belt surface at a portion facing the roller 4. A cleaning device 21 is provided.

  The image forming unit 8 is disposed below the intermediate transfer belt 7a as desired on the lower running side. Each image forming unit includes a photosensitive drum 10 as an image carrier that is in contact with the intermediate transfer belt 7a. Around each photosensitive drum 10, a charging device 11, a developing device 12, and a cleaning device 13 are arranged. Transfer rollers 14 as transfer means for performing primary transfer are provided inside the intermediate transfer belt 7a at positions where the respective photosensitive drums 10 are in contact with the intermediate transfer belt 7a.

  In the present embodiment, the image forming units 8Y, 8C, 8M, and 8K are basically configured in the same structure. In FIG. 1, only the configuration of the image forming unit 8K is represented by a reference numeral. The difference in each image forming unit is only the color of toner as a developer stored in each developing device 12. The developing devices 12 of the image forming units 8Y, 8C, 8M, and 8K store yellow, cyan, magenta, and black toners, respectively. When the toner decreases, each developing device 12 is supplied with replenishing toner from toner replenishing bottles T1, T3, T3, and T4 disposed on the upper portion of the apparatus main body 1, respectively.

  The optical writing unit 15 irradiates the surface of each photoconductive drum with the light-modulated laser light L to form a latent image for each color on the photoconductive surface. In the present embodiment, the image forming unit 8 It is arranged below.

  The toner supply bottles T1, T2, T3, T4, the intermediate transfer unit 7, the image forming unit 8, and the optical writing unit 15 are disposed in the apparatus main body 1 so as to be inclined in the same direction. The installation area is reduced compared to the case where it is horizontally arranged in 1.

  When the image forming operation is started, the photosensitive drums 10 of the respective image forming units 8 are rotationally driven clockwise by a driving device (not shown), and the surface of each photosensitive drum is uniformly made to have a predetermined polarity by the charging device 11. Charged. The surface of each charged photosensitive drum is irradiated with laser light from the optical writing unit 15 to form an electrostatic latent image on each surface.

  At this time, image information for exposing each photosensitive drum is single-color image information obtained by separating a desired full-color image into color information of yellow, cyan, magenta, and black. The electrostatic latent image formed in this way is visualized as a toner image by the toner of each developing device 12 when passing between each photoconductor and the developing device 12.

  Of the plurality of rollers 4, 5 and 6 around which the intermediate transfer belt 7a is wound, one roller is driven to rotate counterclockwise by a driving device (not shown), whereby the intermediate transfer belt 7a is counterclockwise indicated by an arrow. Driven in the clockwise direction, the other rollers are driven to rotate. A yellow toner image formed by the image forming unit 8Y including the developing device 12 having yellow toner is transferred by the transfer roller 14 to the intermediate transfer belt 7a that travels in this manner.

  To the transferred yellow toner image, a cyan toner image formed by the image forming units 8C, 8M, and 8K, a magenta toner image, and a black toner image are sequentially superimposed and transferred by the transfer roller 14, and thus the intermediate transfer belt 7a. Carries a full-color toner image on its surface.

  Residual toner adhering to the surface of each photoconductive drum after the toner image is transferred is removed from the surface of the photoconductive drum by each cleaning device 13. Next, the surface is subjected to a static elimination action by a static eliminator (not shown), and the surface potential is initialized to prepare for the next image formation.

  The transfer paper 29 fed from the paper feed unit 2 is sent to the transport path R and is fed by a registration roller pair (timing matching roller pair) 24 disposed on the paper feed side with respect to the secondary transfer roller 20. Is fed to the opposite portion between the roller 6 and the secondary transfer roller 20. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the surface of the intermediate transfer belt is applied to the secondary transfer roller 20, whereby the toner image on the surface of the intermediate transfer belt 7 a is transferred onto the transfer paper 29. Are collectively transferred.

  The transfer paper 29 onto which the toner image has been transferred is conveyed to the fixing device 22, and when passing through the fixing device 22, heat and pressure are applied to melt and fix the toner image. The transfer sheet 29 on which the toner image is fixed is located at the end of the transport path R, and is transported to the discharge unit 23 configured at the upper part of the apparatus main body 1 and to the stacking unit 36 configured at the upper part of the apparatus main body 1. And discharged. After the toner image is transferred to the transfer paper 29, the toner remaining on the intermediate transfer belt 7a is removed from the cleaning device 21.

  The printer configured as described above is provided with four image forming units 8Y, 8C, 8M and 8K facing the intermediate transfer belt 7a, and sequentially transfers the toner images of the respective colors onto the intermediate transfer belt 7a. For this reason, the image forming time is greatly reduced compared to a type in which a single image forming means has a four-color developing device, and a toner image is transferred onto an intermediate transfer belt and then transferred onto a transfer paper. Can do. In addition, since the stacking portion 36 is formed on the upper portion of the apparatus main body 1, the stacking section 36 does not jump out from the apparatus main body 1, and the installation area and the occupied area are reduced.

  The above description is an image forming operation when a full-color image is formed on the transfer paper 29. A single color image can be formed by using any one of the image forming units of the image forming unit 8 or two colors. Alternatively, a three-color image can be formed. When monochrome printing is performed using the printer of the present embodiment, an electrostatic latent image is formed only on the photosensitive drum of the image forming unit 8K, developed by the unit, transferred to the transfer paper 29, Fixing may be performed by the fixing device 22.

  Next, a fixing device mounted on the image forming apparatus according to the present embodiment will be described below with reference to FIG. The fixing device 22 according to the present embodiment includes a pressure roller (pressure member) 110, a metal pipe (not shown) as a heat conducting member, and a fixing belt (fixing member) 111 including a nip forming member 113, A light shielding plate (shielding member) 120, a halogen heater (heat source) 112 that heats the metal pipe, a support member 115 that supports the nip forming member 113, and a reinforcing member that functions to absorb and shield the heat of the halogen heater 112. 116, a temperature sensor 117, and the like.

  The pressure roller 110 is provided with a silicone rubber layer (not shown) on a hollow metal roller, and a release layer (PFA or PTFE layer) is provided on the surface thereof in order to obtain release properties.

  The pressure roller 110 is rotated by a driving force transmitted from a driving source such as a motor (not shown) provided in the image forming apparatus main body via a gear (not shown). The pressure roller 110 is pressed against the fixing belt 111 by a spring (not shown) or the like, and the silicone rubber layer of the pressure roller is crushed and deformed. Therefore, a predetermined nip width is secured in the nip portion 130 between the pressure roller 110 and the fixing belt 111.

  In the present embodiment, the pressure roller 110 can be made hollow to reduce the heat capacity. The pressure roller 110 is not limited to this aspect, and may be a solid roller. Further, the pressure roller 110 may have a heat source such as the halogen heater 112.

  The silicone rubber layer of the pressure roller 110 is preferably made of sponge rubber. By using sponge rubber, the heat insulation performance is improved, and even when the heat source such as the heater 112 is not provided inside the pressure roller, the heat of the fixing belt 111 can be hardly taken away. The silicone rubber layer is not limited to this aspect, and solid rubber or the like may be used.

  The fixing belt 111 is a thin and flexible endless belt or film. An elastic layer and a surface layer are laminated on the base material of the fixing belt 111.

  The base material of the fixing belt 111 is formed of a metal such as nickel or SUS or a resin material such as polyimide.

  The elastic layer of the fixing belt 111 is an elastic layer of 100 μm or more formed of a silicone rubber layer or the like, and is provided between the base material of the fixing belt 111 and the surface layer (PFA layer or PTFE layer) of the fixing belt 111. Therefore, when an unfixed image is crushed and fixed in the nip portion 130 formed by being pressed against the pressure roller 110, fine irregularities on the surface of the fixing belt are transferred to the image, and the solid image is printed. It is possible to prevent a defect that a mark with a crusty skin remains on the part. Specifically, fine irregularities on the surface of the fixing belt are absorbed by elastic deformation of an elastic layer such as a silicone rubber layer, and the formation of a crusty skin-like image can be improved.

  The surface layer of the fixing belt 111 has a release layer (not shown) such as a PFA or PTFE layer to improve the releasability with respect to the toner.

  Inside the fixing belt 111 (inner peripheral surface side), a nip forming member 113, a support 115, a reinforcing member 116, a halogen heater 112, a light shielding plate (shielding member) 120, and the like are installed.

  The support member 115 prevents the nip forming member 113 from being deformed (deformed) by the pressure applied by the pressure roller 110 at the nip portion 130.

  The reinforcing member 116 has a square U shape, and the halogen heater 112 is disposed inside thereof. Note that in the case where the support 115 or the reinforcing member 116 is heated by radiation heat from a heat source such as the halogen heater 112, the surface of the support 115 or the reinforcing member 116 is subjected to heat insulation treatment or mirror surface treatment, and the support 115 or By preventing the reinforcing member 116 from being heated, wasteful energy consumption can be suppressed. In this embodiment, the support body 115 and the reinforcing member 116 are separated from each other, but may be integrated.

  The nip forming member 113 is provided so as to be in contact with the inner peripheral surface side of the fixing belt 111, and is pressed against the pressure roller 110 via the fixing belt 111 to form a nip portion (nip) 130.

  The nip portion 130 has a concave shape in the inner direction of the fixing belt 111. Therefore, the discharge direction of the paper 29 from the nip portion 130 is closer to the pressure roller (in the diagonally upper right direction in FIG. 2), the separation performance of the paper 29 from the fixing belt 111 is improved, and the occurrence of jam is suppressed. The shape of the nip portion is not limited to this aspect, and may be a flat shape or other shapes.

  The heat source 112 employs a halogen heater. The heat conducting member is heated by the radiant heat from the halogen heater 112. The fixing belt 111 is heated by the heated heat conducting member, and heat is applied to the toner image on the paper from the surface of the heated fixing belt 111 in the nip portion 130. Although the halogen heater 112 is used in the present embodiment, the present invention is not limited to this aspect, and may be IH. Furthermore, a resistance heating element, a carbon heater, or the like can be used.

  The light shielding plate (shielding member) 120 is provided between the fixing belt 111 and the reinforcing member 116 so as to extend in the main scanning direction. As shown in FIG. 3, the light shielding plate 120 has openings corresponding to two types of paper that are passed through the nip portion 130. Specifically, the opening has a notch shape having an opening width corresponding to a sheet having a small sheet width and a sheet having a large sheet width. Here, the width of the paper width and the opening width means a width in a direction perpendicular to the paper transport direction, that is, a width in the main scanning direction. The notched shape allows radiant heat from the halogen heater 112 to be transferred to the fixing belt 111 via the heat conductor. The light shielding plate is bent at 90 ° toward the fixing belt 111 to form a flange portion 121 with a notch-shaped edge forming the width direction of the paper as a base point.

  Note that the light shielding plate may have a plurality of notches having a plurality of widths in order to cope with various widths of paper to be passed. Moreover, it cannot be overemphasized that an opening part is not limited to a notch shape. Further, the size of the opening may be changed by moving the light shielding plate in the main scanning direction by a known driving mechanism so as to cope with various sizes of paper.

  As shown in FIG. 2, the fixing belt 111 rotates along with the pressure roller 110 being rotated by a driving source (not shown) and the driving force transmitted to the fixing belt 111 through the nip portion 130. The fixing belt 111 rotates while being sandwiched by the nip portion 130, but is guided by a metal body (not shown) outside the nip portion, and the position of the fixing belt 111 is not separated from the heat conductor beyond a certain distance. It is like that.

  Note that the output control of the halogen heater 112 is performed based on the detection result of the belt surface temperature by a temperature sensor 117 such as a thermistor installed facing the surface of the fixing belt 111. Further, the temperature of the fixing belt 111 (fixing temperature) can be set to a desired temperature by such output control of the halogen heater 112.

  Next, the light shielding operation of the fixing device mounted on the image forming apparatus according to the present embodiment will be described below with reference to FIG. For convenience of explanation, FIG. 3 shows only the halogen heater 112, the reinforcing member 116, and the light shielding plate 120.

  A transfer paper (not shown) having a small paper width on which the toner image is transferred is detected by a paper width detection device (not shown). Then, the detected information is sent to a light shielding plate position control means (not shown). Then, as shown in FIG. 3A, the light shielding plate 120 is configured so that the notch width of the light shielding plate 120 corresponds to the sheet width of the transfer paper based on the detection information by a known driving means (not shown). Move to. That is, the radiant heat from the halogen heater is transferred to the fixing belt (not shown) through the notch of the light shielding plate 120 corresponding to the paper width of the transfer paper. The toner image transferred onto the transfer paper is passed through a fixing device (not shown) by a fixing belt (not shown) heated by a halogen heater 112 and a pressure roller (not shown). Heat and pressure are applied and melted and fixed.

  At this time, the shape of the edge of the light shielding plate 120 that forms the opening width of the cutout of the light shielding plate 120 has a flange 121a that extends toward the fixing belt from the edge of the light shielding plate 120 as a base point. , Can prevent the diffraction of light by Huygens principle. Therefore, the paper passing portion of the fixing belt is not heated excessively, and the heat of the fixing belt heated by the halogen heater 112 is taken away by the transfer paper to be passed.

  The transfer paper (not shown) having a large paper width to which the toner image is transferred is detected by a paper width detection device (not shown). Then, the detected information is sent to a light shielding plate position control means (not shown). Then, as shown in FIG. 3 (b), the light shielding plate 120 is configured so that the notch width of the light shielding plate 120 corresponds to the sheet width of the transfer paper based on the detection information by a known driving means (not shown). Move to. That is, the radiant heat from the halogen heater is transferred to the fixing belt (not shown) through the notch of the light shielding plate 120 corresponding to the paper width of the transfer paper. The toner image transferred onto the transfer paper is passed through a fixing device (not shown) by a fixing belt (not shown) heated by a halogen heater 112 and a pressure roller (not shown). Heat and pressure are applied and melted and fixed.

  At this time, the shape of the edge of the light shielding plate 120 forming the opening width of the cutout of the light shielding plate 120 has a flange 121b extending from the edge of the light shielding plate 120 toward the fixing belt. , Can prevent the diffraction of light by Huygens principle. Therefore, the paper passing portion of the fixing belt is not heated excessively, and the heat of the fixing belt heated by the halogen heater 112 is taken away by the transfer paper to be passed.

  Next, the light amount distribution to the fixing belt of the fixing device mounted on the image forming apparatus according to the present embodiment will be described below with reference to FIG. As shown in FIG. 4A, the fixing device having the light shielding plate described in Patent Document 2 has a thin knife edge at the tip of the light shielding plate in the main scanning direction. For this reason, when light propagates from the halogen heater 112 to the fixing belt 111, the light diffraction amount and diffraction angle increase, and a large amount of light is distributed to the non-sheet passing range of the fixing belt 111.

  On the other hand, as shown in FIG. 4B, the fixing device according to the present embodiment has a flange shape in which the front end of the light shielding plate 120 in the main scanning direction is bent in an L shape, and has a knife edge shape. It is avoiding. Therefore, when light propagates from the halogen heater 112 to the fixing belt 111, the amount of diffraction and angle of light can be reduced, and the amount of light hardly distributes in the non-sheet passing range of the fixing belt 111.

  Next, various aspects of the edge of the light shielding plate, which is a characteristic part of the present invention, will be described below with reference to FIG. Here, the edge of the light shielding plate 120 refers to the edge of the light shielding plate 120 forming the opening width of the notch of the light shielding plate 120 as shown in FIGS. 5 (a) and 5 (b). In this embodiment, as shown in FIG. 5C, the edge of the light shielding plate 120 is bent to the fixing belt (heating belt) side as a base point. However, as shown in FIG. It may be bent. Further, the edge of the light shielding plate 120 may have a folded shape as shown in FIG.

  Next, the operation of the image forming apparatus according to this embodiment will be described. In the image forming apparatus according to the present exemplary embodiment, the edge shape of the light shielding plate 120 is a shape that prevents diffraction of light generated by Huygens' principle, so that the temperature of the end portion of the sheet passing portion in the fixing belt 111 is increased. There is no increase, and neither heat deterioration nor hot offset of the fixing belt 111 occurs. In addition, there is no need to restrict paper passing, and productivity can be improved.

  Further, the shape of the edge of the light shielding plate 120 that forms the opening width of the notch of the light shielding plate 120 is a shape bent from this edge, so that the light shielding plate in the direction of irradiation from the heat source to the fixing belt is formed. The length can be increased, and it has a simple configuration that prevents the diffraction of light generated by the Huygens principle, preventing heat conduction from the heat source to the non-sheet-passing area of the fixing belt. Temperature rise can be prevented. Specifically, the fixing device described in Patent Document 2 has a so-called knife-edge shielding member with a thin plate thickness at the tip, so that the light diffraction amount and diffraction angle increase. On the other hand, according to the fixing device of the second aspect, the state of the knife edge can be avoided and the shape of the tip of the shielding member can be widened. Therefore, the amount of diffraction and the angle of light can be prevented.

  Further, as shown in FIG. 5C, the edge of the light shielding plate 120 that forms the opening width of the cutout of the light shielding plate 120 is bent toward the endless belt from this edge as a starting point. By adopting the shape, the gap between the heating member and the light shielding plate can be reduced. Therefore, the light from the heat source is efficiently applied to the fixing belt, and energy saving can be achieved. Further, it is possible to reduce the size of the fixing device.

  Further, as shown in FIG. 5D, the edge of the light shielding plate 120 that forms the opening width of the cutout of the light shielding plate 120 is bent toward the heat source starting from this edge. By adopting the shape, the gap between the endless belt and the light shielding plate can be reduced. Therefore, the light from the heat source is efficiently applied to the fixing belt, and energy saving can be achieved. Further, it is possible to reduce the size of the fixing device.

  In addition, as shown in FIG. 5E, the edge of the light shielding plate 120 that forms the opening width of the notch of the light shielding plate 120 has a shape that is folded back starting from this edge. Thus, the diffraction of heat generated by the Huygens principle can be prevented, the heat conduction from the heat source to the non-sheet passing portion of the fixing belt can be prevented, and the temperature rise of the fixing member can be prevented. Further, space can be saved from the fixing device according to claim 3 or 4, and the image forming apparatus can be downsized.

  Further, it is possible to provide an image forming apparatus that is stable in both productivity and image quality.

  Although one embodiment of the present invention has been described above, the present invention is not limited to this.

  It should be noted that the materials and dimensions of each component introduced in the above-described embodiment are merely examples, and it is needless to say that various materials and dimensions can be selected within a range where the effects of the present invention can be exhibited.

1 Image forming apparatus body 22 Fixing device 29 Paper (transfer paper, recording medium)
110 Pressure roller (an example of a pressure member)
111 Fixing belt (an example of a fixing member)
112 Halogen heater (example of heat source)
113 Nip forming member 115 Support body 116 Reinforcing member 117 Thermistor (example of temperature sensor)
120 Shading plate (shielding member)
130 Nip 1-a Pressure roller 1-b Fixing roller 1-d Heating roller 1-f Heater 1-h Recording paper 1-j Fixing belt

JP 2007-334205 A JP 2008-139779 A JP 2011-59388 A JP 2010-20124 A

Claims (6)

A fixing member;
A heat source provided inside the fixing member for heating the fixing member from the inside;
A pressure member that presses the fixing member to form a nip portion;
In a fixing device having
A shielding member extending in the main scanning direction between the heat source and the fixing member;
The shielding member has at least one opening;
The opening width of the opening corresponds to the paper width of the recording medium,
The fixing device according to claim 1, wherein a shape of an edge of the light shielding member that forms the opening width is a shape that prevents diffraction of light.   The fixing device according to claim 1, wherein a shape of an edge of the light shielding member forming the opening width is a shape bent from an edge of the opening.   The fixing device according to claim 2, wherein the bent shape is bent toward the fixing member.   The fixing device according to claim 2, wherein the bent shape is bent toward the heat source.   The fixing device according to claim 3, wherein the bent shape is a folded shape.   An image forming apparatus comprising the fixing device according to claim 1.

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