JP2007010841A - Fixing apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing apparatus having reliability improved by preventing curling due to heat and jamming accompanying the curling due to heat while maintaining fixation quality (fixing strength and glossiness, etc.). <P>SOLUTION: The fixing apparatus includes a fixing part 11 where a paper 70 with an unfixed toner 71A sticking on one surface 70a thereof is conveyed through a nip part N formed by two members 61 and 62, then, the toner 71A is melted by the heat of one member 61 heated up to a prescribed temperature so as to fix the toner 71A on the surface 70a of the paper 70. Besides, the apparatus includes an auxiliary heating body 64 arranged along a conveying path 63 for conveying the paper 70 which already passed through the nip part N, for heating the opposite surface 70b of the paper 70 so as to reduce a temperature difference between both surfaces 70a and 70b of the paper 70. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device, and more particularly, to a fixing device that heats and pressurizes a sheet on which unfixed toner is adhered and fixes the toner onto the sheet.

  The present invention also relates to an image forming apparatus provided with such a fixing device. Examples of the image forming apparatus include a copying machine, a printer, and a facsimile machine.

Many fixing devices of this type include a fixing member (such as a fixing roller and a fixing belt) and a pressure member (such as a pressure roller and a pressure belt) pressed against the fixing member (for example, Patent Document 1). JP, 2001-63895, A). The temperature of the fixing member is set higher than the temperature of the pressure member so as to maintain the temperature necessary for melting the toner (fixing temperature). During operation, the sheet having unfixed toner adhered on one side is conveyed through the nip portion between the fixing member and the pressure member, so that the toner is melted by the heat of the fixing member. Fix on the surface.
JP 2001-63895 A

  By the way, in the fixing device, while the sheet passes through the nip portion, the one surface to which the toner is attached comes into contact with the fixing member and is heated to the fixing temperature, while the opposite surface serves as the pressure member. Since it is only in contact, it is heated only to a temperature lower than the fixing temperature. For this reason, there is a temperature difference between both sides of the paper after passing through the nip, and so-called heat in which the paper deforms due to a difference in the amount of thermal shrinkage between both sides of the paper as the temperature of the paper decreases due to heat dissipation. There is a problem of curling. As a result, a jam occurs in the paper conveyance path after passing through the nip portion, and reliability is impaired.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device capable of improving reliability by preventing the occurrence of heat curling and accompanying jamming while maintaining fixing quality (fixing strength, gloss, etc.).

  Another object of the present invention is to provide an image forming apparatus provided with such a fixing device.

In order to solve the above problems, the fixing device of the present invention is:
A sheet with unfixed toner on one side is conveyed through a nip formed by two members, and the toner is melted by the heat of one of the two members heated to a predetermined temperature. A fixing unit for fixing the sheet on the surface;
The surface of the sheet opposite to the surface on which the toner is fixed is arranged so as to reduce a temperature difference between both surfaces of the sheet, and is disposed along a conveyance path through which the sheet after passing the nip portion is conveyed. An auxiliary heating element for heating;
It is provided with.

  In the fixing device according to the present invention, the fixing unit conveys a sheet having unfixed toner adhered to one side through a nip formed by two members, and is heated to a predetermined temperature of the two members. The toner is melted by the heat of one member and fixed on the surface of the paper. Here, while the sheet passes through the nip portion, the one surface on which the toner is adhered is in contact with the one member and heated to the fixing temperature. On the other hand, since the opposite surface (hereinafter referred to as “back surface”) is only in contact with the other member, it is heated only to a temperature lower than the fixing temperature (the other member is also prevented from being heated). Absent.). For this reason, immediately after passing through the nip portion, there is a temperature difference between both surfaces of the paper. However, in the fixing device according to the present invention, the auxiliary heating body arranged in the conveyance path heats the back surface of the sheet so as to reduce the temperature difference between both sides of the sheet. Thereby, in the process in which the temperature of the paper is lowered due to heat radiation, the difference in heat shrinkage between both sides of the paper is reduced as compared with the conventional case. Therefore, the occurrence of heat curl and accompanying jam can be prevented, and the reliability can be improved. The auxiliary heating body heats the paper so as to reduce the temperature difference between both sides of the paper. That is, the sheet is not heated more than necessary. Therefore, fixing quality (fixing strength, gloss, etc.) can be maintained.

In one embodiment, the fixing device includes:
A paper discharge unit for receiving the paper is provided at the end of the conveyance path,
The auxiliary heating body is disposed only in the vicinity of the nip portion in the conveyance path.

  Here, “near” the nip portion means a region closer to the nip portion than an intermediate point from the nip portion to the paper discharge portion in the conveyance path. In other words, since it is “placed only in the vicinity of the nip portion”, the auxiliary heating body is not placed in a region closer to the paper discharge portion than the intermediate point.

  In the fixing device according to this embodiment, a paper discharge unit that receives the paper is provided at the end of the conveyance path. During operation, sheets in a state where the temperature difference between both sides is reduced are sequentially stacked on the paper discharge unit. Here, when sheets are sequentially stacked with the toner-fixed surface (hereinafter referred to as “toner fixing surface”) facing down, the toner fixing surface of one sheet to be stacked is the same as that of the already stacked sheets. While contacting the back surface, the back surface of the one sheet is exposed to the outside air. For this reason, if no measures are taken, the heat release on the toner fixing surface is reduced, while the heat release on the back surface is increased, resulting in a temperature difference between both sides of the paper, and heat curl is generated on the paper discharge unit. there is a possibility. Here, in the fixing device of this embodiment, the auxiliary heating body is disposed only in the vicinity of the nip portion in the conveyance path. Accordingly, each sheet dissipates heat when it passes through an area of the transport path that faces the auxiliary heating body and then passes through an area close to the paper discharge unit. Therefore, the temperature of each sheet stacked on the paper discharge unit has already decreased. As a result, the phenomenon of heat curling due to the above-described cause is suppressed for the sheets stacked on the paper discharge unit.

In one embodiment, the fixing device includes:
A guide member including a curved portion that bends the conveyance direction of the paper by contacting the paper conveyed through the conveyance path is provided in the conveyance path,
The auxiliary heating body is disposed along the curved portion.

  In the fixing device according to this embodiment, the curved portion of the guide member comes into contact with the sheet conveyed through the conveyance path and bends the conveyance direction of the sheet. While the paper is in contact with the curved portion, the auxiliary heating body disposed along the curved portion heats the paper. Therefore, the heat from the auxiliary heating body is efficiently and stably transmitted to the paper. As a result, the occurrence of heat curl can be more effectively suppressed.

In one embodiment, the fixing device includes:
A fixing temperature controller for controlling the temperature of the one member to a predetermined set value;
An auxiliary heating temperature control unit that sets a target value of the temperature of the auxiliary heating body according to the set value of the temperature of the one member, and controls the temperature of the auxiliary heating body to the target value;
It is provided with.

  The temperature difference between both sides of the sheet immediately after passing through the nip portion changes depending on the temperature difference between the one member and the other member. In particular, when only the one member is heated, it changes mainly depending on the temperature of the one member. Here, in the fixing device according to the embodiment, the auxiliary heating temperature control unit sets a target value of the temperature of the auxiliary heating body according to the set value of the temperature of the one member, and the temperature of the auxiliary heating body is set. Is controlled to the target value. Therefore, for example, even if the set value of the temperature of the one member is changed due to, for example, whether or not the paper is continuously fixed, or the thickness of the paper, the paper is heated by the auxiliary heating body. The temperature difference between the two sides is reliably reduced. As a result, the occurrence of heat curl can be more effectively suppressed.

In one embodiment, the fixing device includes:
A first temperature detection sensor for detecting the temperature of the one member;
A second temperature detection sensor for detecting the temperature of the auxiliary heating body;
In response to the outputs of the first and second temperature detection sensors, a temperature difference between the one member and the auxiliary heating body is detected, and a target value of the temperature of the auxiliary heating body is set according to the temperature difference. An auxiliary heating temperature control unit for setting and controlling the temperature of the auxiliary heating body to the target value;
It is provided with.

  The temperature difference between both sides of the sheet immediately after passing through the nip portion changes depending on the temperature difference between the one member and the other member. Here, in the fixing device according to this embodiment, the auxiliary heating temperature control unit detects the temperature difference between the one member and the auxiliary heating body in response to the outputs of the first and second temperature detection sensors. Then, a target value of the temperature of the auxiliary heating body is set according to the temperature difference, and the temperature of the auxiliary heating body is controlled to the target value. Therefore, for example, even if the temperature difference between the one member and the auxiliary heating body is changed due to, for example, whether or not the paper is continuously fixed, the difference in the thickness of the paper, etc., the auxiliary heating body The temperature difference between the two surfaces of the paper is surely reduced by the heating by. As a result, the occurrence of heat curl can be more effectively suppressed.

  The fixing device according to an embodiment is provided with a heat insulating member that blocks heat from the auxiliary heating body so as to cover a surface of the auxiliary heating body opposite to the surface facing the conveyance path. Features.

  In the fixing device according to this embodiment, heat from the auxiliary heating body is applied so as to cover a surface opposite to the surface facing the conveyance path of the auxiliary heating body (hereinafter referred to as “outer surface” as appropriate). A heat insulating member for blocking is provided. Therefore, heat is prevented from being radiated from the outer surface of the auxiliary heating body to the outside beyond the heat insulating member. Therefore, it is possible to avoid a situation in which an external element (for example, an exterior member) is unnecessarily heated by the auxiliary heater and the abnormal temperature rises.

  The fixing device according to an embodiment is characterized in that the heat insulating member is integrally attached to a surface of the auxiliary heating body opposite to the surface facing the conveyance path.

  In the fixing device of this embodiment, for example, when the device is assembled, the auxiliary heating body and the heat insulating member can be handled as one member. Therefore, handling becomes easy. Further, space can be saved as compared with the case where the auxiliary heating body and the heat insulating member are provided separately from each other.

  An image forming apparatus of the present invention is an image forming apparatus including the fixing device.

  In the image forming apparatus according to the present invention, the auxiliary heating element disposed in the conveyance path through which the toner-fixed sheet is conveyed heats the back surface of the sheet so as to reduce the temperature difference between both sides of the sheet. Thereby, in the process in which the temperature of the paper is lowered due to heat radiation, the difference in heat shrinkage between both sides of the paper is reduced as compared with the conventional case. Therefore, the occurrence of heat curl and accompanying jam can be prevented, and the reliability can be improved.

  Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.

  FIG. 1 shows a cross-sectional configuration of a fixing device 51 according to an embodiment. The fixing device 51 includes a fixing unit 11 as a fixing unit. A conveyance path 63 defined by a pair of guide members 65 and 66 is provided above the fixing unit 11. The conveyance path 63 reaches a paper discharge tray section 92 (described later) as a paper discharge section via the paper discharge roller pair 35.

  The fixing unit 11 includes a fixing roller 61 as one member heated to a predetermined temperature (referred to as a fixing temperature Tm), and a pressure roller 62 as the other member in pressure contact with the fixing roller 61. It has. Then, the sheet 70 with the unfixed toner 71A attached to one surface 70a is conveyed through the nip portion N between the fixing roller 61 and the pressure roller 62, and the toner 71A is melted by the heat of the fixing roller 61. Then, the toner image is fixed on the surface of the paper 70 (fixed toner is indicated by reference numeral 71B).

  Specifically, at least one of the fixing roller 61 and the pressure roller 62 constituting the fixing unit 11 has an elastic layer (not shown). In this embodiment, the fixing roller 61 includes a silicon rubber layer as an elastic body on a hollow core metal made of aluminum, and a polytetrafluoroethylene (PTFE) layer as a surface layer for ensuring releasability from the toner 71B. Are sequentially laminated. The pressure roller 62 is configured by sequentially laminating a silicon rubber layer as an elastic body and a PTFE layer for the same purpose on an aluminum solid cored bar. A nip portion N having a width necessary for fixing is formed by pressing the pressure roller 62 against the fixing roller 61 with a predetermined pressing force by a pressing means (not shown). As the pressure contact means, a pressure contact force changing means for changing the pressure contact force and a pressure contact force control means for controlling the pressure contact force can be provided.

  Inside the fixing roller 61, a halogen lamp heater 81 is provided as a heat source for heating the fixing roller 61. As an example of the heat source, in addition to the halogen lamp heater 81, a resistance heating element, electromagnetic induction means for generating an eddy current, or the like may be employed. In this embodiment, no heat source is provided inside the pressure roller 62. The pressure roller 62 may include a heat source in the same manner as the fixing roller 61, but in that case, there is less room for exhibiting the effects of the present invention.

  A first temperature detection sensor 82 and a second temperature detection sensor 83 are provided on the surfaces of the fixing roller 61 and the pressure roller 62, respectively (these are thermistors in this example). A fixing temperature control unit 98 composed of a CPU (Central Processing Unit) detects the temperature of the fixing roller 61 based on the output of the temperature detection sensor 82, and the halogen lamp so that the temperature of the fixing roller 61 becomes the fixing temperature Tm. The energization to the heater 81 is controlled. The outputs of the temperature detection sensors 82 and 83 can be used to control energization to an auxiliary heating body 64 described later.

  The pressure roller 62 is rotationally driven clockwise (in the direction of arrow b) in FIG. 1 by a rotation driving means (not shown), and accordingly, the fixing roller 61 is counterclockwise in FIG. 1 (in the direction of arrow a). Followed rotation. Accordingly, the sheet 70 can be conveyed upward through the nip portion N through a frictional force between the surfaces of the pressure roller 62 and the fixing roller 61 and both surfaces 70a and 70b (or toner) of the sheet 70. In this embodiment, the fixing roller 61 is only driven to rotate, but a rotation driving means is also connected to the fixing roller 61 so that the fixing roller 61 and the pressure roller 62 can be driven to rotate synchronously. Good.

  The guide members 65 and 66 forming the conveyance path 63 are plate-shaped members (may be ribs) made of a heat-resistant resin such as polyether terephthalate (PET). In FIG. 1, the guide members 65 and 66 rise from a position directly above the nip portion N and continue to the curved portion 67 that is curved to the left side and the end of the curved portion 67, and extend linearly from there to the upper left. And a straight line portion 68 that reaches the pair of paper discharge rollers 35. The curved portion 67 of the upper guide member 66 comes into contact with the sheet 70 conveyed through the conveyance path 63 and bends the conveyance direction of the sheet 70 toward the paper discharge roller pair 35. Note that the guide members 65 and 66 are divided into a plurality of parts in the axial direction of the fixing roller 61 (the same direction as the axial direction of the pressure roller 62).

  In the fixing device 51, while the sheet 70 passes through the nip portion N, the one surface 70a on which the toner 71A is adhered is in contact with the fixing roller 61 and heated to the fixing temperature Tm. Is only in contact with the pressure roller 62 that does not have a heat source, and is heated only to a temperature lower than the fixing temperature Tm. For this reason, immediately after passing through the nip portion N, a temperature difference is created between both surfaces 70a and 70b of the paper 70, as in the conventional example.

  Therefore, in the fixing device 51, the auxiliary heating body 64 is disposed along the conveyance path 63 along which the sheet 70 after passing through the nip portion N is conveyed. In this embodiment, the auxiliary heating body 64 is arranged along only the curved portion 67 in the vicinity of the nip portion N in the conveyance path 63. The auxiliary heating body 64 heats the back surface 70b of the paper 70 opposite to the toner fixing surface 70a so as to reduce the temperature difference between the both surfaces 70a and 70b of the paper 70. As a result, in the process in which the temperature of the paper 70 is lowered due to heat dissipation, the difference in thermal shrinkage between the both surfaces 70a and 70b of the paper 70 is reduced as compared with the conventional case. Therefore, the occurrence of heat curl and accompanying jam can be prevented, and the reliability can be improved. Further, since the sheet 70 is not heated more than necessary, fixing quality (fixing strength, gloss, etc.) can be maintained.

  Specifically, as shown in FIG. 5, the auxiliary heating body 64 is laminated on a base material layer 64d made of flat aluminum and on one surface of the base material layer 64d (the surface on the conveyance path 63 side in FIG. 5). The electrical insulating layer 64c, the heat generating resistor layer 64b that generates heat when energized, and the release layer 64a are provided. Further, the other surface (surface opposite to the one surface, hereinafter referred to as “outer surface”) 64g of the base material layer 64d is covered with a heat insulating layer 64e as a heat insulating member. The layers 64a, 64b, 64c, 64d, and 64e are in close contact with each other.

  The base material layer 64d is provided to give the auxiliary heating body 64 physical strength as an integral member. The base material layer 64d may be made of a heat-resistant resin such as polyethylene terephthalate (PET) or PI.

  The electrical insulating layer 64c is made of heat-resistant polyimide (PI) or the like, and electrically insulates between the base material layer 64d and the heating resistor layer 64b. When the base material layer 64d is made of an electrically insulating resin such as PET or PI, the electrical insulating layer 64c can be omitted.

  The heat insulating layer 64e is made of a non-woven fabric (aramid fiber or the like) and prevents heat from being radiated from the outer surface 64g of the auxiliary heating body 64 to the outside. Therefore, it is possible to avoid a situation in which an external element (for example, an exterior member) is unnecessarily heated by the auxiliary heating body 64 and the abnormal temperature rises. In this embodiment, since the heat insulating layer 64e is provided integrally with the auxiliary heating body 64 (the heating resistor layer 64b), the heat insulating layer 64e is separated from the auxiliary heating body 64 and provided separately. Thus, handling becomes easy. For example, when the apparatus is assembled, the auxiliary heating body 64 including the heat insulating layer 64e can be handled as one member. It also saves space.

  The release layer 64a is made of a heat-resistant tetrafluoroethylene perfluoroalkyl vinyl ether copolymer (PFA) or the like, and ensures release properties for the toner.

  The heating resistor layer 64b is made of a resistor such as ceramic and generates heat when energized. The heating resistor layer 64b is connected to an auxiliary heating temperature control unit 99 including a CPU (Central Processing Unit) and a power source 95 through wirings 96 and 97. A temperature detection sensor 84 for detecting the temperature of the auxiliary heating body 64 is attached to a surface (hereinafter referred to as “inner surface”) 64 f of the auxiliary heating body 64 on the conveyance path 63 side. Based on the output of the temperature detection sensor 84 and the like, the auxiliary heating temperature control unit 99 performs on / off control of power supply (energization) from the power source 95 to the heating resistor layer 64b.

  Specifically, the auxiliary heating temperature control unit 99 first sets a target value (this is referred to as Ttarget) of the surface temperature of the auxiliary heating body 64 (refers to the temperature of the inner surface 64f; the same applies hereinafter). How to do this later). Then, the auxiliary heating temperature control unit 99 detects the surface temperature of the auxiliary heating body 64 based on the output of the temperature detection sensor 84, and the heating resistor layer 64b from the power source 95 so that the surface temperature approaches the target value Ttarget. Turn on / off the power to the. For example, if the surface temperature of the auxiliary heater 64 is lower than the target value Ttarget while performing known PID (Proportinal, Integral, Differential) control, the energization is turned on and the auxiliary heater is turned on. If the surface temperature of 64 is higher than the target value Ttarget, the energization is turned off.

  The target value Ttarget of the surface temperature of the auxiliary heating body 64 described above is set as follows.

  i) The first setting method is to make the target value Ttarget of the surface temperature of the auxiliary heater 64 constant (fixed).

  In this case, the target value Ttarget of the surface temperature of the auxiliary heating body 64 is set higher by a certain amount with reference to the standard set value of the surface temperature of the fixing roller 61 (that is, the fixing temperature Tm). That is, as compared with the case where the sheet 70 is nipped and passes through the nip portion N, the sheet 70 is separated from the inner surface 64f of the auxiliary heating body 64 when passing through the conveyance path 63. The responsiveness of the temperature of the back surface 70b of the paper 70 is not good with respect to the temperature of 64f. Therefore, in order to sufficiently raise the temperature of the back surface 70b of the sheet 70, it is desirable that the target value Ttarget of the surface temperature of the auxiliary heating body 64 is set at least 30 ° C. higher than the set value of the surface temperature of the fixing roller 61. For example, when the set value of the surface temperature of the fixing roller 61 is 170 ° C., the target value Ttarget of the surface temperature of the auxiliary heating body 64 is set to 200 ° C., for example.

  According to this setting method, the outputs of the temperature detection sensors 82 and 83 are unnecessary, and the target value Ttarget of the surface temperature of the auxiliary heating body 64 can be set easily.

  ii) The second setting method is to set the target value Ttarget of the surface temperature of the auxiliary heating body 64 in accordance with the set value of the surface temperature of the fixing roller 61.

  That is, the surface temperature of the fixing roller 61 includes the sheet passing speed of the sheet 70, the temperature and humidity of the surrounding environment, the thickness and material of the sheet 70, the toner adhesion amount and adhesion range on the sheet 70, the presence of continuous sheet passing, It is changed depending on factors that affect the fixing quality or paper passing properties such as presence / absence and glossy image modes. In this case, the set value of the surface temperature of the fixing roller 61 is detected by, for example, the output of the temperature detection sensor 82, and the surface temperature of the auxiliary heating body 64 is changed according to the changed set value of the surface temperature of the fixing roller 61. The target value Ttarget is changed. For example, when the set value of the surface temperature of the fixing roller 61 is changed to a temperature higher than 170 ° C., it is necessary to further increase the temperature of the back surface 70b of the paper 70, and thus the target value of the surface temperature of the auxiliary heating body 64. Ttarget is set to a temperature higher than 200 ° C.

  According to this setting method, the setting method of the target value Ttarget of the surface temperature of the auxiliary heater 64 does not become complicated.

  iii) The third setting method is to set the target value Ttarget of the surface temperature of the auxiliary heating body 64 based on the temperature difference between the fixing roller 61 and the pressure roller 62 detected by the temperature detection sensors 82 and 83. It is to set.

  That is, the temperature difference between both surfaces 70a and 70b of the sheet 70 immediately after passing through the nip portion N changes depending on the temperature difference between the fixing roller 61 and the pressure roller 62 shown in FIG. Therefore, the auxiliary heating temperature control unit 99 detects the surface temperature of the fixing roller 61 and the surface temperature of the pressure roller 62 based on the outputs of the temperature detection sensors 82 and 83 described above, and the difference between the detected two temperatures. Is set higher, the target value Ttarget of the surface temperature of the auxiliary heating body 64 is set higher.

  According to this setting method, even if the surface temperature of the fixing roller 61 and the pressure roller 62 fluctuates due to the various factors described above, the temperature difference between both surfaces 70a and 70b of the paper 70 due to the heating by the auxiliary heating body 64. Can be reliably reduced. As a result, the occurrence of heat curl can be effectively suppressed.

  Note that heat radiation of the sheet 70 is performed by natural heat radiation by providing an exhaust port (louver or the like) in a cover member (not shown) for the fixing device provided above the guide member 66, or actively cooling the sheet. This is done by providing means (fan or the like).

  As described with reference to FIG. 1, in the fixing device 51, the conveyance path 63 reaches the paper discharge tray unit 92 as a paper discharge unit via the paper discharge roller pair 35. During operation, sheets 70 in a state in which the temperature difference between both surfaces 70a and 70b is reduced are sequentially stacked on the sheet discharge tray 92. Here, when the sheets 70 are sequentially stacked with the toner fixing surface 70a facing down, the toner fixing surface 70a of one stacked sheet 70 is in contact with the back surface 70b of the already stacked sheet 70, while one sheet 70 is stacked. The back surface 70b of the paper 70 is exposed to the outside air. For this reason, if no measures are taken, the heat release of the toner fixing surface 70a is reduced, while the heat release of the back surface 70b is increased, and a temperature difference occurs between the both surfaces 70a and 70b of the paper 70, and the paper discharge tray section. There is a possibility that heat curl will occur on 92. Here, in the fixing device 51, the auxiliary heating body 64 is arranged along only the curved portion 67 in the vicinity of the nip portion N in the conveyance path 63. Here, “near” the nip portion N means a region closer to the nip portion N than an intermediate point from the nip portion N to the paper discharge tray portion 92 in the conveyance path 63, in this example, a curved portion 67. That is, the auxiliary heating body 64 is not disposed in the region closer to the paper discharge tray portion 92 than the intermediate point, in this example, the linear portion 68. Therefore, each sheet 70 dissipates heat when passing through the straight portion 68 after passing through the curved portion 67 facing the auxiliary heating body 64 in the transport path 63. Therefore, the temperature of each sheet 70 loaded on the sheet discharge tray 92 has already been lowered. As a result, therefore, the phenomenon of heat curl caused by the above-described causes of the sheets 70 stacked on the discharge tray unit 92 is suppressed.

  In addition, in the fixing device 51, the curved portion 67 of the guide members 65 and 66 comes into contact with the sheet 70 conveyed through the conveyance path 63 and bends the conveyance direction of the sheet 70. While the sheet 70 is in contact with the bending portion 67, the auxiliary heating body 64 disposed along the bending portion 67 heats the sheet 70. Therefore, the heat from the auxiliary heating body 64 is efficiently and stably transmitted to the paper 70. As a result, the occurrence of heat curl can be more effectively suppressed.

  As the fixing unit 11, in addition to the configuration using the fixing roller 61 as shown in FIG. 1, the configurations 11B and 11C using the fixing belt 69 as shown in FIGS. 2 and 3, the same reference numerals are used for the same components as those in FIG. 1 (the same applies to other drawings). In the fixing device 52 shown in FIG. 2, a fixing belt 69 is wound around a pair of rollers 61A and 61B. A nip portion N is formed between a portion of the fixing belt 69 around which one of the rollers 61B is wound and the pressure roller 62. In the fixing device 53 shown in FIG. 3, a fixing belt 69 is wound around a pair of rollers 61A and 61C. A pad 78 made of an elastic material having heat resistance is interposed between one roller 61C and the fixing belt 69. The pad 78 is fixed and is held so as not to be rotated by support means (not shown). In these fixing devices 52 and 53, rotation driving means (gear, motor, etc.) not shown is connected to the pressure roller 62. When the pressure roller 62 is rotationally driven by the rotation driving means, the fixing belt 69 and the rollers 61A and 61B are driven to rotate. The heater lamp 81 is built in the other roller 61A, and the fixing belt 69 is heated to the fixing temperature Tm via the heated roller 61A.

  The auxiliary heating body 64 is shaped like a comb in order to avoid interference with the guide members 65 and 66 provided in a plurality of divisions in the axial direction of the fixing roller 61 (the same direction as the axial direction of the pressure roller 62). A configuration having a notch or a plurality of notches may be provided in the axial direction of the fixing roller 61.

  Moreover, although the base material layer 64d of the auxiliary heating body 64 and the heat insulating layer 64e as a heat insulating member are integrated, it is not limited to this. You may arrange | position the auxiliary | assistant heating body 64 and a heat insulation member as a separate member. In that case, the heat insulation member should just be laminated | stacked on heat resistant resin (PET etc.) separately from the exterior member. The configuration of the auxiliary heating body 64 is not limited to that of the present embodiment, and may be another known configuration.

  FIG. 6 shows a cross-sectional structure of a color tandem type image forming apparatus 90 to which the fixing device 51 shown in FIG. 1 is applied. The image forming apparatus 90 includes a primary transfer belt 14 wound around a pair of left and right rollers in the drawing at a substantially central position in the main body casing 91. Above the primary transfer belt 14, toner cartridges 13Bk, 13C, 13M, and 13Y containing supply toners of Bk (black), C (cyan), M (magenta), and Y (yellow) are provided in order from the right. It has been. Below the primary transfer belt 14, imaging cartridges 2Bk, 2C, 2M, and 2Y as Bk, C, M, and Y process cartridges are provided in the same order from the right. Each of the imaging cartridges 2Bk, 2C, 2M, and 2Y is configured in exactly the same manner except for the difference in the toner color that they handle. Specifically, for example, the yellow imaging cartridge 2Y includes a developing device 10 that performs development using a two-component developer including a toner and a carrier, a photosensitive drum 1, a charging device, and a transfer residue on the surface of the photosensitive drum. The photosensitive drum unit 20 including a cleaner for cleaning the toner is integrally formed. Below each of the imaging cartridges 2Bk, 2C, 2M, and 2Y, exposure devices 17Bk, 17C, 17M, and 17Y are provided for exposing the surface of the photosensitive drum of the corresponding imaging cartridge and forming a latent image thereon. ing. On the left side of the primary transfer belt 14, a cleaner unit 15 that removes residual toner from the surface of the primary transfer belt 14 and a waste toner box 16 that collects and stores the removed toner are provided. A secondary transfer roller 12 is provided on the right side of the primary transfer belt 14 with a conveyance path (shown by a broken line) 33 for paper interposed therebetween. A fixing unit 11 for fixing the toner to the paper is provided at the upper right portion in the main body casing 91. The above-described transport path 33 is connected to a paper discharge tray section 92 as a paper discharge section provided on the upper surface of the main body casing 91 via a transport path 64 provided with an auxiliary heating body 64 and a pair of paper discharge rollers 35. Yes. In addition, a paper feed cassette 31 that stores paper (not shown) is provided in the lower portion of the main body casing 91.

  At the time of image formation, the paper is fed from the paper feed cassette 31 to the transport path 33 by the paper feed roller 32, and sent to the toner transfer position 36 between the primary transfer belt 14 and the secondary transfer roller 12 by the transport roller 34. On the other hand, the surface of the photosensitive drum 1 is uniformly charged by the charging device in each of the imaging cartridges 2Bk, 2C, 2M, and 2Y, and further exposed by the exposure devices 17Bk, 17C, 17M, and 17Y to form a latent image there. Is done. Subsequently, a predetermined developing bias is applied to the developing roller 4 as a developer carrying member provided in the developing device 10, and the toner contained in the developer flies to visualize (develop) the latent images. Thereby, a toner image is formed on the surface of each photosensitive drum 1. The toner images formed on the respective photosensitive drums 1 are sequentially transferred onto the primary transfer belt 14 and further transferred onto the paper fed to the toner transfer position 36 by the secondary transfer roller 12. The sheet on which the toner image is transferred passes through the fixing unit 11. As a result, the toner image is fixed on the paper. The sheet on which the toner image is fixed is conveyed to the upper conveyance path 63 and is discharged to the discharge tray 92 by the discharge roller pair 35.

  In this image forming apparatus, the auxiliary heating body 64 disposed in the conveyance path 63 through which the sheet 70 after toner fixing is conveyed reduces the temperature difference between both surfaces 70a and 70b (see FIG. 1) of the sheet 70. The back surface 70b of the paper 70 is heated. As a result, in the process in which the temperature of the paper 70 is lowered due to heat dissipation, the difference in thermal shrinkage between the both surfaces 70a and 70b of the paper 70 is reduced as compared with the conventional case. Therefore, the occurrence of heat curl and accompanying jam can be prevented, and the reliability can be improved.

  It should be noted that during double-sided printing, it is desirable to adopt a control method different from the control method described above for the auxiliary heater 64. That is, at the time of double-sided printing, the paper 70 that has once passed through the fixing unit 11 reverses its front and back and passes through the fixing unit 11 again. . Therefore, the heat curl prevention measure by the auxiliary heating body 64 is not necessary. In addition, the toner fixed on the paper 70 after passing through the first fixing unit tends to be overmelted when passing through the second fixing unit. For this reason, if heat is supplied from the auxiliary heating body 64 to the paper 70 when passing through the fixing unit for the second time, there may occur a problem that the fixing quality (gloss or the like) differs greatly between both surfaces of the paper 70. Therefore, in order to avoid such a situation, at the time of double-sided printing, as in the fixing device 54 shown in FIG. It is desirable to provide a gap 79 between the body 64 and the guide member 66. Further, printing is performed by controlling power supply (energization) to the auxiliary heating body 64 to stop, or by providing an auxiliary heating body cooling means (fan or the like) (not shown) to cool the auxiliary heating body 64. Is desirable. In addition, when the auxiliary heating body cooling means is used in combination with the above-described paper cooling means, the cooling amount (the air volume when a fan is used) and the cooling position (the direction when a fan is used) as necessary. ) Can be changed.

  In this embodiment, the sheet 70 passes from the lower side to the upper side with respect to the fixing unit 11. However, the direction of passage and conveyance of the sheet 70 is not limited thereto, and the sheet 70 is passed and conveyed in other directions. May be.

  The image forming apparatus may be any one of a monochrome / color copying machine, a printer, a FAX, and a complex machine of these.

1 is a diagram illustrating a schematic configuration of a fixing device according to an embodiment of the present invention. FIG. 8 is a diagram illustrating a modification of the fixing device in FIG. 1. FIG. 8 is a diagram illustrating a modification of the fixing device in FIG. 1. FIG. 8 is a diagram illustrating a modification of the fixing device in FIG. 1. It is a figure which shows the cross-sectional structure of the auxiliary | assistant heating body with which the fixing apparatus of FIG. 1 is provided, and the auxiliary | assistant heating temperature control part which controls the electric power supply to the auxiliary | assistant heating body. FIG. 2 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment to which the fixing device of FIG. 1 is applied.

Explanation of symbols

61 Fixing roller 62 Pressure roller 63 Conveying path 64 Auxiliary heating element 65, 66 Guide member 70 Paper

Claims (8)

A sheet with unfixed toner on one side is conveyed through a nip formed by two members, and the toner is melted by the heat of one of the two members heated to a predetermined temperature. A fixing unit for fixing the sheet on the surface;
The surface of the sheet opposite to the surface on which the toner is fixed is arranged so as to reduce a temperature difference between both surfaces of the sheet, and is disposed along a conveyance path through which the sheet after passing the nip portion is conveyed. An auxiliary heating element for heating;
A fixing device comprising: The fixing device according to claim 1,
A paper discharge unit for receiving the paper is provided at the end of the conveyance path,
The fixing device, wherein the auxiliary heating body is disposed only in the vicinity of the nip portion in the conveyance path. The fixing device according to claim 1,
A guide member including a curved portion that bends the conveyance direction of the paper by contacting the paper conveyed through the conveyance path is provided in the conveyance path,
The fixing device, wherein the auxiliary heating body is disposed along the curved portion. The fixing device according to claim 1,
A fixing temperature controller for controlling the temperature of the one member to a predetermined set value;
An auxiliary heating temperature control unit that sets a target value of the temperature of the auxiliary heating body according to the set value of the temperature of the one member, and controls the temperature of the auxiliary heating body to the target value;
A fixing device comprising: The fixing device according to claim 1,
A first temperature detection sensor for detecting the temperature of the one member;
A second temperature detection sensor for detecting the temperature of the auxiliary heating body;
In response to the outputs of the first and second temperature detection sensors, a temperature difference between the one member and the auxiliary heating body is detected, and a target value of the temperature of the auxiliary heating body is set according to the temperature difference. An auxiliary heating temperature control unit for setting and controlling the temperature of the auxiliary heating body to the target value;
A fixing device comprising: The fixing device according to claim 1,
A fixing device, wherein a heat insulating member that blocks heat from the auxiliary heating body is provided so as to cover a surface of the auxiliary heating body opposite to the surface facing the conveyance path. The fixing device according to claim 6.
The fixing device according to claim 1, wherein the heat insulating member is integrally attached to a surface of the auxiliary heating body opposite to the surface facing the conveyance path. An image forming apparatus comprising the fixing device according to claim 1.

Images