JP2009288490A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To uniformize a quantity of heat applied to a toner image, even when continuous paper is stopped or conveyed in a reverse direction in an image forming apparatus which fixes a toner image on the continuous paper by a radiation system fixing device. <P>SOLUTION: The image forming apparatus includes: a heat source 811 for heating paper in a heating area by radiation; and a blocking means 812 disposed between the heat source 811 and the heating area and used for blocking radiation of heat to the heating area from the heat source 811. A control means 50 changes a blocking area where a blocking means 812 blocks radiation of heat to the heating area from the heat source 811, so as to correspond to the position of a toner image formed on continuous paper P conveyed to the heating area. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a fixing device that heat-fixes a toner image and fixes the toner image on a sheet.

  Non-contact fixing that uses a heat source such as an infrared lamp or a ceramic heater as a fixing means for fixing the toner image on the paper, and heats the toner image formed on the paper by the radiant heat emitted from the heating source to fix the toner image on the paper. There exists an apparatus (for example, patent document 1).

  When continuous paper is used, the paper is continuous from paper feeding to toner image transfer and toner image fixing. Therefore, at the time of forming a color image, (1) toner image superimposing step at the intermediate transfer portion , (2) Toner image superimposition process by forward / reverse conveyance of continuous paper, (3) Image adjustment, (4) Switching of image forming conditions, (5) Waiting for image processing response to image data, etc. Due to these factors, there are cases where continuous paper needs to be stopped or reversely conveyed in the fixing device.

  In a fixing device that heats a toner image by non-contact heating, the amount of heat to be applied depends on the time of heating by the heating source, that is, the time that the paper faces the heating source, but when the continuous paper is stopped or reversely conveyed as described above In some cases, the amount of heating may be excessive due to radiation for a long time or multiple times.

  For such a problem, in the fixing device disclosed in Patent Document 1, as the developed electrophotographic photoreceptor (heated body) progresses, the infrared heaters arranged in parallel in the traveling path are sequentially turned on, The lights are turned off sequentially.

Patent Document 2 discloses a fixing device that shuts the entire heating area with a shutter in the event of an abnormality such as a paper jam during conveyance.
Japanese Utility Model Publication No. 2-17760 JP-A-62-264082

  In the fixing device disclosed in Patent Document 1, since the heater is turned on and off in accordance with the progress of the heated object, the response of the heater to the high-speed operation in which the heated object is conveyed at high speed. However, in reality, it is difficult to respond. Halogen lamps and xenon lamps, which are frequently used as heat sources in electrophotography and have a large proportion of radiant energy in the visible light region, are color images that are composed of yellow toner or the like and have a low visible light absorption rate. If the toner is fixed, the black toner having a large absorption factor for visible light is excessively heated, and may cause smoke and fire.

  In order to uniformly heat different color toners, it is necessary to use a radiation wavelength of a heating source having a long wavelength such as far infrared rays. As a heating source having such a radiation wavelength characteristic, a ceramic heater or the like is generally used. However, a ceramic heater has a low response and it is difficult to cope with a higher speed.

  Further, the fixing device disclosed in Patent Document 2 blocks the entire heating area as a unit, and has a problem that it cannot cope with the optimization of the heating amount when stopping continuous paper or transporting in the reverse direction.

  In view of the above problems, the present invention provides an image forming apparatus in which a toner image is fixed to a continuous paper by a radiation-type fixing device, even if the continuous paper is stopped or conveyed in the reverse direction. An object of the present invention is to provide an image forming apparatus capable of making the amount of heating to an image uniform.

1. Conveying means for feeding and conveying continuous paper;
A plurality of developing means for forming a toner image on the image carrier;
A transfer unit that includes a pressure release unit, and transfers a toner image formed on the image carrier to a continuous paper transported by the transport unit in a transfer nip formed at the time of pressure bonding;
A fixing device for heating and fixing a toner image formed on continuous paper;
An image forming apparatus having a control unit,
The transport means can switch the transport direction of the continuous paper between the forward direction and the reverse direction,
The transfer unit includes a step of transferring a toner image to a continuous paper conveyed in a forward direction to a transfer nip formed at the time of pressure bonding, and a step of releasing the pressure bonding of the transfer unit and conveying the continuous paper in a reverse direction. By repeating alternately to form a superimposed toner image on continuous paper,
The fixing device includes:
A heating source for heating the paper in the heating area by radiation;
A shielding unit that is provided between the heating source and the heating region and shields radiation from the heating source to the heating region;
The control means changes the shielding area that shields radiation from the heating source to the heating area by the shielding means in accordance with the position of the toner image formed on the continuous paper conveyed to the heating area. An image forming apparatus.

2. Conveying means for feeding and conveying continuous paper;
A plurality of developing means for forming a toner image on the image carrier;
An intermediate transfer body for sequentially superimposing and transferring the toner images formed on the image carrier to form a superimposed toner image;
A transfer unit that includes a pressure release unit, and transfers a toner image formed on the intermediate transfer body to a continuous paper transported by the transport unit in a transfer nip formed at the time of pressure bonding;
A fixing device for heating and fixing a toner image formed on continuous paper;
An image forming apparatus having a control unit,
The fixing device includes:
A heating source for heating the paper in the heating area by radiation;
A shielding unit that is provided between the heating source and the heating region and shields radiation from the heating source to the heating region;
The control means changes the shielding area that shields radiation from the heating source to the heating area by the shielding means in accordance with the position of the toner image formed on the continuous paper conveyed to the heating area. An image forming apparatus.

3. The shielding means is
It has two shielding plates that can move in the transport direction of continuous paper,
3. The image forming apparatus according to 1 or 2, wherein the shielding area is changed by moving the shielding plate in accordance with the position of the toner image formed on the continuous paper to be conveyed.

4). The shielding means is
A plurality of strip-shaped slats having long sides in the direction orthogonal to the continuous paper transport direction are arranged in parallel in the continuous paper transport direction,
Each of the plurality of slats can be independently rotated by a drive source with a rotation axis extending in a direction orthogonal to the conveyance direction of continuous paper as a rotation center,
3. The image forming apparatus according to 1 or 2, wherein the shielding area is changed by rotating the wing plate corresponding to the position of the toner image formed on the continuous paper to be conveyed.

5. 5. The image forming apparatus according to item 4, wherein the image forming apparatus includes a sheet amount information acquisition unit, and the control unit changes the shielding area based on the amount information of the continuous sheet from the sheet amount information acquisition unit.

6). The change of the shielding area based on the weight information is
The vanes are stopped by rotating to a shielded position that shields radiation from the heating source to the heating area and are not rotated, and the vanes that are stopped to the shielded position and are not rotated are approximately equidistant. 6. The image forming apparatus as described in 5 above, wherein

7). The heating source can change the heating width in a direction orthogonal to the conveyance direction of the continuous paper,
The image forming apparatus according to any one of 1 to 6, wherein the heating width is changed in accordance with a width of the continuous paper to be conveyed.

  According to the present invention, in an image forming apparatus for fixing a toner image to a continuous sheet by a radiation-type fixing device, even when the continuous sheet is stopped or conveyed in the reverse direction, the toner image is displayed. Thus, it is possible to provide an image forming apparatus capable of making the heating amount uniform.

  Although the present invention will be described based on an embodiment, the present invention is not limited to the embodiment.

[Image forming apparatus]
The image forming apparatus according to the first embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a main part of the image forming apparatus.

  The image forming apparatus includes a photosensitive member 1 that functions as an image carrier, a strip electrode 2 that charges the photosensitive member 1, and an exposure unit 3 that exposes the photosensitive member 1 based on image data to form a latent image. A plurality of developing devices 4Y, 4M, 4C, and 4K that develop the latent image with toner and a cleaning unit 5 are provided.

  The transfer unit 9 transfers the toner image formed on the photoconductor 1 onto a sheet. The cleaning unit 5 cleans the transfer residual toner on the photoreceptor 1.

  The photoconductor 1 is made of an organic photoconductor in which a photosensitive layer made of a resin containing an organic photoconductor is formed on the outer peripheral surface of a drum-shaped metal substrate, for example, in the width direction of the conveyed continuous paper P. It is arranged in an extended state. Examples of the resin constituting the photosensitive layer include polycarbonate. In the embodiment shown in FIG. 1, the configuration example using the drum-shaped photoconductor 1 has been described. However, the present invention is not limited to this, and a belt-shaped photoconductor may be used.

  The developing device 4 functions as a developing unit, and includes a two-component developer composed of a toner having a small particle diameter of different colors of yellow (Y), magenta (M), cyan (C), and black (K) and a carrier. .

  The transport unit 20 feeds and transports continuous paper. The conveying means 20 includes an original winding 29 in which a sheet is wound in a roll shape, and conveying roller pairs 21, 22, 23, 24, and the like. The original winding 29 and the conveying roller pair can be rotated forward and backward by a drive motor M20 described later, and the forward direction in which the continuous paper P of the original winding 29 is conveyed (the original winding 29 shown in FIG. 1 rotates clockwise). , And in the reverse direction. The forward conveyance speed is 300 mm / s, and the reverse conveyance speed is 2000 mm / s. If the conveyance speed in the reverse direction of the paper is low, the time until the start of the image formation of the subsequent color is shortened and the effect on productivity is large. It is desirable. The speed and position control of conveyance / reverse conveyance may be non-feedback control by a motor rotation angle or the like, but a marking for position detection is given to a non-image area outside the image forming area of the continuous paper P, and the marking is detected by a sensor. By detecting in S1, the transport position of the continuous paper P can be adjusted. The marking may be formed with toner using the image forming means, or may be provided with a cut in advance at the end of the continuous paper P. The configuration of the conveyance roller pair 23 in the paper width direction is in contact with the continuous paper P only at both ends of the non-image area of the continuous paper P.

[Crimping release mechanism]
FIG. 2 is an enlarged view of the periphery of the transfer unit 9. The crimp release function will be described with reference to FIG. FIG. 2A is a diagram showing a released state, and FIG. 2B is a diagram showing a crimped state. In the pressure-bonded state, the transfer roller 90 is pressure-bonded to the photoreceptor 1, and a transfer nip N is formed between the photoreceptor 1 and the transfer roller 90.

  The transfer roller 90 is rotatably supported by a support portion 962 provided on a support lever 960 that is rotatably supported with a shaft 961 as a fulcrum. The support lever 960 is biased by a coil spring 970 as biasing means. A roller 963 is provided at the end of the support lever 960 opposite to the shaft 961, and the roller 963 is in contact with the rotating cam 980. The rotary cam 980 is driven to rotate by a motor M9.

  By driving the motor M9, the angle of the rotating cam 980 can be changed to switch between the released state and the crimped state. In addition, the conveyance roller pair 22 that is moved back and forth to the transfer unit 9 can be shifted downward by a mechanism similar to the pressure-release releasing mechanism shown in FIG.

Here, an image forming process at the time of forming a color image will be described. In the present embodiment, toner images of the respective colors are formed on the photoreceptor 1 and the formed toner images are sequentially superimposed on the continuous paper P. This will be described below.
(1) Step of developing and transferring a Y-color toner image: The toner image is developed by the developing device 4Y, and the continuous paper is aligned with the timing when the toner image formed on the photoreceptor 1 moves to the transfer nip N. P is conveyed in the forward direction (left direction in FIG. 1).
(2) Step of transporting the continuous paper P in the reverse direction: After the transfer of the Y-color toner image is completed, the transfer roller 90 is released by the pressure-release releasing mechanism shown in FIG. Further, the conveying roller pairs 22 and 23 are simultaneously shifted downward. In such a state, the transport unit 20 transports the continuous paper P in the reverse direction (right direction in FIG. 1).
(3) Step of developing and transferring the M color toner image: The toner image is developed by the developing device 4M, and the continuous paper is aligned with the timing at which the toner image formed on the photoreceptor 1 moves to the transfer nip N. Transport P again in the forward direction. The image leading edge position at this time is made to coincide with the image leading edge position when the Y color is transferred by referring to the detection value of the sensor S1.

  Thereafter, by repeating the steps (2) and (3), the C and K toner images are superimposed on the transfer paper, and a full-color superimposed toner image on the continuous paper P (hereinafter also simply referred to as a toner image). ).

[Fixing device 8]
The configuration of the fixing device 8 will be described with reference to FIGS. FIG. 3 is an enlarged view of the periphery of the fixing device 8, and FIG. 4 is a perspective view of the fixing device 8.

  The fixing device 8 includes a housing 810, a ceramic heater 811, a shielding unit 812, a transport plate 815, and the like. In this embodiment, the ceramic heater 811 functions as a “heating source”, and the shielding unit 812 functions as a “shielding unit”. The distance between the upper surface of the transport plate 815 and the shielding portion 812 is 100 mm, and the upper surface of the transport plate 815 becomes a heating region that is heated by the radiation of the heating source.

  The ceramic heater 811 is obtained by wrapping and firing a resistance heating element such as a heating wire in ceramic. Electric power is supplied to the resistance heating element to generate heat, the ceramic is heated by the generated heat, and the object to be heated is heated by radiant heat of far infrared rays radiated from the heated ceramic. Since ceramic has a high emissivity in the infrared region of 0.9 to 1.0, highly efficient radiation heating is possible. In the present embodiment, the ceramic heater 811 has a length of 440 mm in the conveyance direction of the continuous paper P (hereinafter simply referred to as the conveyance direction) and a paper width direction (hereinafter simply referred to as the paper width direction) perpendicular to the conveyance direction. The length is 350 mm, and it has a substantially rectangular parallelepiped shape as a whole. The length in the paper width direction is longer than the maximum usable paper width. The control temperature of the ceramic heater 811 is 720 ° C.

  Further, when the resistance heating element is constituted by heating wire wiring, the wiring inside the ceramic heater is constituted by a plurality of wiring paths corresponding to the paper width direction, and the heating area is changed by selecting the power feeding path. It is good also as a structure. By adopting such a configuration, it becomes possible to change the heating width in the direction orthogonal to the paper conveyance direction, and the heating area and the shielding area are changed according to the position of the width of the conveyed paper. It becomes possible to make it. Although the response of the ceramic heater is low, the paper width is not changed so frequently in normal use, so when fixing a narrow paper, the temperature outside the paper rises to the extent that the above-mentioned problems occur. There is nothing.

  As shown in FIG. 3, the shielding part 812 in the first embodiment includes a first shielding plate w11 and a second shielding plate w12.

  In the perspective view shown in FIG. 4, only one shielding plate w11 (or w12) is shown, and the other shielding plate w12 is not shown. The shielding plate w11 and the shielding plate w12 have the same configuration, and the shielding plate w11 will be described as a representative. The shielding plate w11 is supported by wires L1 and L2 attached between pulleys (not shown), and the shielding plate w11 is moved by operating the wires L1 and L2. In the case where the shielding is not performed, the film is wound around one axis r.

  As the material of the shielding plates w11 and w12, a metal is preferable because of its high heat resistance and low emissivity, and SUS is more preferable from the viewpoint of rust prevention because the emissivity increases when rusted. By selecting a low emissivity material, it is possible to suppress both a temperature rise due to radiation from the heating source and heating of the conveyance path due to radiation from the shielding plates w11 and w12. Since the emissivity is also affected by the surface shape, it is desirable that the surfaces of the shielding plates w11 and w12 be as close to a mirror surface as possible. The thicknesses of the shielding plates w11 and w12 are both 0.05 mm. In FIG. 4, the thickness of the shielding plate w11 (or w12) is exaggerated and drawn.

  The size of the shielding plates w11 and w12 in the unrolled and unrolled state is 520 mm (conveying direction) × 400 mm (paper width direction). As described above, in this embodiment, the size of the ceramic heater 811 is 440 mm (conveyance direction) × 350 mm (paper width direction), and the shielding plates w11 and w12 are larger than the ceramic heater 811. Can be covered.

  The shield plates w11 and w12 can be driven independently by the drive motor M1, and the moving speed is 300 mm / s, which is the same as the conveying speed of the continuous paper P in normal times. As a problem that occurs when the angular velocity is rotated at the time of winding, there is a problem that the winding speed varies depending on whether the winding start diameter is small or the winding end diameter is large. An encoder that rotates by moving the wire may be installed, and the amount of movement of the wire may be detected and controlled so as to reach a predetermined wire moving speed. The rotational speed may be controlled so that the speed is constant.

  The emissivity of the shielding plate w11 made of SUS is 0.1 or less, and most of the radiation from the ceramic heater 811 is reflected. When the temperature of the ceramic heater 811 is controlled at 720 ° C. in the shielded state, the shield plate w11 itself is gradually heated by the radiation from the ceramic heater 811. In this embodiment, the temperature rises to 400 to 500 ° C. Is low and the temperature itself is lower than the temperature of the ceramic heater 811, the irradiation energy from the shielding plate w 11 or the like to the heating area (upper surface of the conveyor belt) in the “shielded state” radiates from the ceramic heater 811. It stays on the order of a few tenths compared with the “heated state”.

  The control unit 50 includes a CPU and a memory, and executes various controls when the CPU executes a program stored in the memory. The control unit 50 controls the driving motor M1 that drives the shielding unit and the driving motor M20 that drives the conveying unit 20, and performs the non-feedback control or the position of the continuous paper P conveyed to the fixing device 8 detected by the sensor S1 (image). The shielding area of the shielding part 812 is controlled in synchronization with the position of the area.

[Change of shielding area corresponding to position of toner image on continuous paper P]
Next, based on FIG. 5, FIG. 6, operation | movement of the shielding part 812 in 1st Embodiment is demonstrated. 5 and 6 are schematic diagrams for explaining the change of the shielding area corresponding to the position of the toner image on the continuous paper P. FIG.

  FIG. 5A shows a standby state. In the standby state shown in the figure, the entire range of the heating region is shielded by the spread shielding plate w12.

  FIG. 5B is a diagram showing a state where the toner image area m (1) of the first page formed in the image area on the continuous paper P is conveyed to the fixing device 8. The shielding plate w12 is moved downstream in the conveyance direction in synchronization with the conveyance of the toner image area m (1) of the first page to the heating area on the conveyance plate 815 of the fixing device 8. The shield plate w12 moved at this time is wound around the axis r on the downstream side in the transport direction. The toner image area m (1) is heated by radiation from the ceramic heater 811.

FIG. 5C is a diagram for explaining the length of a necessary heating region. FIG. 5B is a continuation of FIG. 5B, and the shielding plate w12 is stopped at a predetermined position so that the length of the heating region becomes a predetermined length x1. The length x1 is a length determined by a heating time necessary for providing a necessary heating amount. The necessary heating amount differs when the thickness of the continuous paper P is different or when the glossiness is changed. Note that if the heating operation is continuously performed with the heating amount limited, the heating source temperature corresponding to the shielded region may increase excessively. As with the configuration that can be changed by selection, the feeding path of the heating source can be divided in the transport direction according to the number of paper thickness levels, and the necessary heating width (= heating time) can be selected. It is preferable to configure. Levels of paper thickness may be appropriately selected but, for example ^{80~105g / m 2, 106~160g / m} 2, 161~220g / m 2, divided into 4 levels 221~300g / ^{m 2,} a heat source 4 Dividing and selecting from energizing only one area to energizing all areas corresponding to the four levels, and controlling the opening position of the shielding portion 812 according to the energizing area.

  FIG. 6A is a schematic diagram for explaining a state following FIG. 5C. In FIG. 6A, in synchronization with the rear end position of the toner image area m (1) of the first page of the continuous paper P. FIG. The shielding plate w11 is moved.

  FIG. 6B is a schematic diagram for explaining a state following FIG. 6A, in which heating of the toner image region m (1) in the heating region (length of x1) is completed ( The fixing process is completed).

  FIG. 6C is a schematic diagram for explaining the state following FIG. 6B, in which the continuous paper P is reversed in order to form the toner image of the subsequent page on the continuous paper P. It shows a state of being conveyed in the direction. While the toner image of the subsequent page of the continuous paper P is being formed, the shielding plates w11 and w12 are also rewound in the reverse direction to return to the initial state shown in FIG.

  As described above, the conveyance speed of the continuous paper in the reverse direction is 2000 mm / s faster than 300 mm / s in the forward direction. However, the rewinding of the shielding plates w11 and w12 in the reverse direction is subsequent. Since it is only necessary to be performed during the formation of the toner image of the current page (during the image formation of the Y, M, and C toners), it is not particularly necessary to perform at a high speed.

  As described above, according to the present exemplary embodiment, in the image forming apparatus in which the toner image is fixed to the continuous paper by the radiation-type fixing device, the toner is used even when the continuous paper is conveyed in the reverse direction. It is possible to provide an image forming apparatus capable of making the amount of heating to an image uniform.

  In this embodiment, an example in which paper is sandwiched between a transfer roller and a photoreceptor has been described. However, transfer using corona discharge or transfer means via an intermediate transfer member such as an intermediate transfer roller is used. The present invention is effective even with the above configuration.

[Second Embodiment]
A fixing device according to the second embodiment will be described with reference to FIGS. In the second embodiment, the configuration of the shielding portion 812 is different from the first to third embodiments, but the other configurations are the same as those of the embodiment shown in FIGS. .

  FIG. 7 is a schematic diagram of the periphery of the fixing device 8 according to the second embodiment. FIG. 8 is an enlarged view of the slat w.

  The shielding part 812 in the second embodiment is configured by arranging a plurality of strip-like slats w shown in FIG. 8 in parallel as shown in FIG. As shown in FIG. 8, each vane w is provided with a rotation axis ax extending in the sheet width direction at the center in the short side direction. Each rotation shaft ax is connected to a stepping motor M1 that can be driven independently, and can be rotated by a stepping motor (not shown). Since it is desirable that the blades can rotate at a high speed, and therefore it is necessary to have a low rotation moment, the rotation axis is provided at the center of the blades.

Moreover, although the example which rotates each wing board w independently by a stepping motor is demonstrated, it is not restricted to this, It is good also as any one of the following (1) thru | or (3).
(1) The wing plate w is urged to rotate in one direction by a spring such as a helical spring and held so as to be stopped by a stopper, which is attracted by an electromagnet and rotated in the direction opposite to the urging direction by the spring. To do.
(2) The wing plate w is supported in the same manner as in (1), and the flip-up member supported by a wire or the like is caused to run in synchronization between the sheets of paper to be conveyed so that the wing plate w is operated.
(3) The screw is fitted and supported on a screw coaxial with the rotation axis ax of the slat w, and is moved in the axial direction by an electromagnet or the like by a quarter rotation of the screw.

  Each wing plate w has a width of 30 mm (conveying direction), a length of 400 mm (paper width direction), and a wing thickness of 0.5 mm. The gap between adjacent slats w is 0.6 mm at room temperature. As a material, metal is preferable from the characteristics of high heat resistance and low emissivity, and SUS is more preferable from the viewpoint of rust prevention because emissivity increases when rusted. By selecting a low emissivity material, it is possible to suppress both a temperature rise due to radiation from the heating source and heating of the conveyance path due to radiation from the blades. Since the emissivity is also affected by the surface shape, it is desirable that the blade surface be as close to the mirror surface as possible.

  The distance between the blades is preferably small from the viewpoint of shielding performance, but when the blades are rotated in one direction, the blades should not overlap at the shielding position. The blade rises in temperature by shielding radiation from the heating source, and expands thermally. In this embodiment, since the width of the blade is increased by 0.2 to 0.3 mm, the interval is set in consideration of the processing / assembly accuracy of the apparatus.

  In the second embodiment, the ceramic heater 811 is 540 mm (conveyance direction) × 350 mm (paper width direction) and is used at a control temperature of 600 ° C. The shielding part 812 has an area larger than that of the ceramic heater 811 as a whole. In the present embodiment, 18 blades w (10 sheets are shown in FIG. 7 for simplification) are used, so that the shielding portion 812 is 540 mm (conveyance direction) × 400 mm (paper width direction). It is.

  The position of the heating region is changed by rotating the blade w in correspondence with the position of the toner image formed on the continuous paper. By setting the wing plate w of the shielding part 812 to the horizontal position, the “heated state” in which the heating region shown in FIG. By setting the wing plate w to a vertical position, a “heating state” in which the heating region shown in FIG.

  Although the blades are rotated at a high speed as a low moment, radiation is reflected by the inclined blades when the position of the blades is changed for a short time. If this goes to between the sheets, it will lead to an increase in the temperature of the conveying path due to heating between the sheets and a decrease in heating efficiency. By making the rotation direction of the blades clockwise in FIG. 7, radiation reflected by the inclined blades can be directed to the paper, and there are more problems such as an increase in the conveyance path temperature and a decrease in heating efficiency due to the heating between the papers. Can be small.

  Priority may be given to the shielding performance when the blade is in the shielding position, and the blade and the blade may overlap each other at the time of shielding. In this case, since the rotation of the blades is reciprocating, the radiation reflected during the rotation of the blades at either the front or rear edge of the paper is directed between the papers. The conveyance path heating suppression performance during standby of the apparatus can be further increased.

  According to the present embodiment, in an image forming apparatus that fixes a toner image to continuous paper by a radiation-type fixing device, even if the continuous paper is stopped or conveyed in the reverse direction, the toner image It is possible to provide an image forming apparatus capable of making the heating amount to be uniform.

  In addition, since the shielding plate in the present embodiment can be switched between the heating state and the shielding state in a very short time, it prevents smoke and ignition of paper left behind in the heating area when a problem such as a paper jam occurs. It is also extremely effective as a shielding device.

[Third Embodiment]
FIG. 9 is a schematic diagram for explaining the correspondence between the amount of wrinkles of the continuous paper P and the shielding area in the third embodiment. This figure is a schematic diagram corresponding to FIG. 7, and other configurations are the same as those of the second embodiment shown in FIG.

  The image forming apparatus according to the third embodiment acquires the amount information of the continuous paper conveyed to the fixing device 8. Then, the shielding area is changed based on the acquired soot amount information. The user inputs the amount information of the continuous paper P of the original winding 29 of the transport unit 20 in advance through an operation panel or the like. The inputted information is stored in the storage unit of the image forming apparatus, and the control unit 50 calls the information on the amount of paper corresponding to the continuous paper P of the original winding 29 to be used from the storage unit, and so on. To get. Of course, a device for detecting the thickness of the continuous paper P may be provided in the transport path of the transport unit 20 of the image forming apparatus. Known thickness detection means can be used.

  The reason why the shielding area is changed based on the amount information of the continuous paper P conveyed to the fixing device 8 is as follows. The size and control temperature of the ceramic heater 811 as a heat source are set according to the maximum amount of heat required for the material to be heated. The required maximum amount of heat corresponds to the maximum amount of paper that can be used in the image forming apparatus. For this reason, the amount of heat given by the fixing device 8 is appropriate for the maximum amount of paper, that is, thick paper with a large amount of paper, but is excessive for thin paper with a small amount of paper. If an excessive amount of heat is applied, problems such as hot offset and paper curl will occur.

  For this reason, it is preferable to optimize the amount of heat applied according to the amount of paper curled. The amount of heat applied may be changed for the purpose of varying the glossiness of the paper so that the glossiness of the toner image surface of the paper can be selected.

  The optimization of the amount of heat is performed by changing the shielding area as shown in FIG. FIG. 9 (a) shows the state of the slats w when heated with thick paper P having a large amount of soot, and FIG. 9 (b) shows the slats w when heating with thin paper having a small amount of soot. This shows the state. As shown in FIG. 9B, in a thin paper with a small amount of necessary heat, a part of the slat w is stopped without rotating, and the horizontal position is in spite of the continuous paper P immediately below. It is in the shielding state. Compared to FIG. 9A, in FIG. 9B, 30% of the slats w2 are in a shielded state, so the amount of heat applied to the paper is reduced by about 30%.

  The slats w other than the slats w that maintain the stopped state are rotated in correspondence with the position of the continuous paper P. Further, in FIG. 9B, the slats w that maintain the stopped state are arranged every two sheets in the sheet transport direction. This is for the purpose of preventing the temperature distribution in the heating region from being greatly different. Of course, it is not restricted to this, It is good also as the wing board w which maintains the state which stopped only the downstream or the upstream.

  Further, when the same wing plate w is kept stopped at the horizontal position while the ceramic heater 811 is continuously supplied with power, the temperature of the ceramic heater 811 at the position at the opposite position due to reflection by the wing plate w rises. Therefore, the wing plate w to be stopped may be shifted to another wing plate w every predetermined time or every predetermined number of sheets conveyed.

  When the heating region is divided, the time from the start of heating of the paper to the end of heating becomes longer, and the amount of heat released during heating increases, so the heating efficiency decreases slightly. Heat is generated according to the thickness of the paper and required gloss by making the heater temperature uniform by dividing the heater temperature by using metal as part of the heater base material, or by dividing the heating area of the heater in the paper transport direction. As a configuration for limiting the region, it is desirable to use one continuous heating region.

[Fourth Embodiment]
FIG. 10 is a diagram illustrating an image forming apparatus according to the fourth embodiment. Unlike the image forming apparatus shown in FIG. 1, the image forming apparatus shown in FIG. 1 uses an intermediate transfer belt 6 in the image forming apparatus.

The belt-like intermediate transfer belt 6 is rotatably supported by a plurality of rollers 61, 62, 63, 64. The intermediate transfer belt 6 is an endless belt having a volume resistivity of 10 ⁶ to 10 ¹² Ω · cm. A semiconductive seamless belt having a thickness of 0.04 to 0.10 mm, in which a conductive material is dispersed.

  The toner image formed on the photoreceptor 1 by the developing device 4Y (or 4M, 4C, 4K) is transferred onto the rotating intermediate transfer belt 6 by the transfer roller 63 functioning as a primary transfer portion (primary transfer process). . By repeating the primary transfer process four times, a synthesized color image is formed on the intermediate transfer belt 6. Note that in the primary transfer process for Y, M, and C toners, the transfer unit 9 is in a released state (see FIG. 2A). In order to perform the following secondary transfer process, only the K toner process is in a press-bonded state ( 2 (b)).

  The combined color image is collectively transferred onto the continuous paper P by the transfer unit 9 functioning as a secondary transfer unit (secondary transfer process), and a toner image is formed on the continuous paper P.

  In the image forming process, it is necessary to perform four rotations in order to perform the primary transfer process for four colors of Y, M, C, and K, and secondary transfer is performed for three rotations of Y, M, and C colors. In order not to carry out, it is necessary to stop the conveyance of the continuous paper P and to wait.

  The ceramic heater 811 in this embodiment has a size of 500 mm (conveying direction) × 350 mm (paper width direction), and a control temperature of 600 ° C. The conveyance speed of the continuous paper P is 500 mm / s. Further, as shown in FIG. 11, the shielding portion 812 includes two shielding plates w11 and w12. The shielding plate w11 is 300 mm (conveyance direction) × 400 mm (paper width direction), and the shielding portion w12 is 570 mm (conveyance direction) × 400 mm. (Paper width direction).

  FIG. 11 is a schematic diagram for explaining the change of the shielding region corresponding to the position of the toner image on the continuous paper P, and the operation of the shielding plates w11 and w12 will be described based on the same drawing.

  FIG. 11A shows an initial state, and the continuous paper P is stopped in this state. In the figure, the entire range of the heating region is shielded by the shielding plate w11 and the shielding plate w12. Further, the end b1 on the downstream side in the transport direction of the shielding plate w11 is stopped in a predetermined positional relationship from the front end of the toner image region m (1) at the time of stop. The positional relationship will be described later.

  In FIG. 11B, as the continuous paper P moves, the shielding plate w12 is moved at the same speed. Since the front end of the toner image area m (1) and the rear end of the shielding plate w12 are made to coincide with each other, the leading side of the toner image area m (1) is always in a heated state that is not shielded.

  FIG. 11C shows a state following FIG. 11B. In FIG. 11C, since the rear end of the toner image region m (1) has reached the end b1 of the shielding plate w11, the shielding plate is shown. The state where the movement of w12 and the conveyance of the continuous paper P are stopped is shown. In the stopped state of FIG. 11C, the radiant heating by the ceramic heater 811 is continued. After stopping for a predetermined time, the shielding plate w12 is moved in the direction opposite to the conveying direction of the continuous paper P as shown in FIG. The moving speed at this time is 500 mm / s, which is the same speed as the conveying direction. By performing the operations of FIG. 11A to FIG. 11D, the same heating amount can be applied over the entire surface of the toner image region m (1).

Further, the amount of heating can be increased or decreased by controlling the stop time ts of the predetermined time in FIG. This will be described below. In this embodiment, if the soot amount of the continuous paper P is 100 g / m ² , the stop time ts is 0 s, the heating time is about 0.8 s, and if the soot amount is 300 g / m ² , the stop time ts is 1 .2 s and the heating time is about 2.0 s. The stop time may be appropriately selected according to the amount of the continuous paper P or the physical properties. In the case of forming a four-color full color image, it is possible to secure a maximum heating time of 3.0 s. When the maximum amount of soot used is limited to 300 g / m ² , the toner can be fixed even if the control temperature of the ceramic heater 811 is lowered to 450 ° C.

  FIG. 12 is a schematic diagram for explaining the relationship between the length of the toner image region m in the transport direction and the position of the end b1. FIG. 12A shows the positional relationship between the end b1 of the shielding plate w11 and the tip of the toner image area m when the toner image area m is short, and FIG. Is shown.

  As shown in the figure, the heating area is an unshielded area between the end b2 of the shielding plate w12 and the end b1 (b11 or b12) of the shielding plate w11, and a toner image for one page is formed in the heating area. The position of the end b1 of the shielding plate w11 is moved so that the area m is accommodated.

  According to the present embodiment, in an image forming apparatus that fixes a toner image to a continuous sheet using a radiation type fixing device, even when the continuous sheet is stopped, the heating amount to the toner image is uniform. An image forming apparatus capable of achieving the above can be provided.

1 is a diagram illustrating a main part of an image forming apparatus. FIG. 6 is an enlarged view around the transfer unit 9. 3 is an enlarged view of the periphery of the fixing device 8. 2 is a perspective view of a fixing device 8. FIG. FIG. 6 is a schematic diagram for explaining a change of a shielding area corresponding to the position of a toner image on continuous paper P. FIG. 6 is a schematic diagram for explaining a change of a shielding area corresponding to the position of a toner image on continuous paper P. FIG. 6 is a schematic diagram around a fixing device 8 according to a second embodiment. It is an enlarged view of the wing board w. It is a schematic diagram explaining the correspondence between the amount of wrinkles of the continuous paper P and the shielding area in the third embodiment. It is a figure explaining the image forming apparatus in 4th Embodiment. FIG. 10 is a schematic diagram for explaining a change of a shielding area corresponding to the position of a toner image on a continuous paper P in a fourth embodiment. FIG. 6 is a schematic diagram for explaining a relationship between a length of a toner image region m in a conveyance direction and a position of an end b1.

Explanation of symbols

4Y, 4M, 4C, 4K Developing device 811 Ceramic heater 812 Shielding unit 815 Conveying plate w11, w12 Shielding plate w Wing plate L1, L2 Wire 9 Transfer unit 90 Transfer roller 50 Control unit M1 Drive motor M20 Drive motor

Claims (7)

Conveying means for feeding and conveying continuous paper;
A plurality of developing means for forming a toner image on the image carrier;
A transfer unit that includes a pressure release unit, and transfers a toner image formed on the image carrier to a continuous paper transported by the transport unit in a transfer nip formed at the time of pressure bonding;
A fixing device for heating and fixing a toner image formed on continuous paper;
An image forming apparatus having a control unit,
The transport means can switch the transport direction of the continuous paper between the forward direction and the reverse direction,
The transfer unit includes a step of transferring a toner image to a continuous paper conveyed in a forward direction to a transfer nip formed at the time of pressure bonding, and a step of releasing the pressure bonding of the transfer unit and conveying the continuous paper in a reverse direction. By repeating alternately to form a superimposed toner image on continuous paper,
The fixing device includes:
A heating source for heating the paper in the heating area by radiation;
A shielding unit that is provided between the heating source and the heating region and shields radiation from the heating source to the heating region;
The control means changes the shielding area that shields radiation from the heating source to the heating area by the shielding means in accordance with the position of the toner image formed on the continuous paper conveyed to the heating area. An image forming apparatus. Conveying means for feeding and conveying continuous paper;
A plurality of developing means for forming a toner image on the image carrier;
An intermediate transfer body for sequentially superimposing and transferring the toner images formed on the image carrier to form a superimposed toner image;
A transfer unit that includes a pressure release unit, and transfers a toner image formed on the intermediate transfer body to a continuous paper transported by the transport unit in a transfer nip formed at the time of pressure bonding;
A fixing device for heating and fixing a toner image formed on continuous paper;
An image forming apparatus having a control unit,
The fixing device includes:
A heating source for heating the paper in the heating area by radiation;
A shielding unit that is provided between the heating source and the heating region and shields radiation from the heating source to the heating region;
The control means changes the shielding area that shields radiation from the heating source to the heating area by the shielding means in accordance with the position of the toner image formed on the continuous paper conveyed to the heating area. An image forming apparatus. The shielding means is
It has two shielding plates that can move in the transport direction of continuous paper,
The image forming apparatus according to claim 1, wherein the shielding area is changed by moving the shielding plate in accordance with a position of a toner image formed on the continuous paper to be conveyed. The shielding means is
A plurality of strip-shaped slats having long sides in the direction orthogonal to the continuous paper transport direction are arranged in parallel in the continuous paper transport direction,
Each of the plurality of slats can be independently rotated by a drive source with a rotation axis extending in a direction orthogonal to the conveyance direction of continuous paper as a rotation center,
3. The image forming apparatus according to claim 1, wherein the shielding region is changed by rotating the wing plate according to a position of a toner image formed on the continuous paper to be conveyed. 5. The image forming apparatus according to claim 4, further comprising: a sheet weight information acquisition unit, wherein the control unit changes the shielding area on the basis of continuous sheet weight information from the sheet weight information acquisition unit. The change of the shielding area based on the weight information is
The vanes are stopped by rotating to a shielded position that shields radiation from the heating source to the heating area and are not rotated, and the vanes that are stopped to the shielded position and are not rotated are approximately equidistant. The image forming apparatus according to claim 5, wherein the image forming apparatus is arranged as follows. The heating source can change the heating width in a direction orthogonal to the conveyance direction of the continuous paper,
The image forming apparatus according to claim 1, wherein the heating width is changed in accordance with a width of the continuous paper that is conveyed.

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