JP2005115188A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device and an image forming apparatus capable of flexibly reducing troubles in carrying a transfer paper, even under different conditions such as the kinds of paper and characteristic change in the paper due to a using environment. <P>SOLUTION: The fixing device 6 is provided with a separation voltage apply roller 66 and a separation voltage source 67. The roller 66 is made of metal and arranged in contact with the inside of a pressure belt while facing a heat roller 61. A retrieval of a voltage storage part 11 is performed by a voltage setting part 10, and a separation voltage which corresponds to the kind of the transfer paper, distinction between a full color image forming mode and a monochromatic image forming mode, and the surface of the transfer paper to be carried to the fixing device next and where DC components and AC components are superposed is obtained by the part 10, and the obtained voltage is set in the separation voltage source 67. The separation voltage is supplied by the separation voltage source 67 to the separation voltage apply roller 66 so as to indirectly form an uneven electrical field on the pressure belt 62. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using electrophotography and a fixing device thereof, and more particularly to a technique for preventing a transfer material conveyed from being wound around a fixing device.

  An image forming apparatus using an electrophotographic system holds a charge on the surface of a photosensitive member by a charging device, and irradiates the photosensitive member with light from a light source such as laser light or LED light that is emitted based on an input image signal. Then, an electrostatic latent image is formed on the surface of the photoconductor, and the toner charged in the developing device is attached to the photoconductor to visualize the electrostatic latent image on the photoconductor to form a toner image and transfer The toner image is transferred onto the transfer paper by the apparatus, and the toner image is fixed on the transfer paper by heating and pressurizing with the fixing device to form a color image.

  There are various image forming apparatuses that create color images at high speed. For example, an intermediate transfer member is provided, and images formed on four photosensitive members corresponding to toner colors such as yellow, magenta, cyan, and black are primarily transferred so as to overlap on the intermediate transfer member, and further transferred onto the transfer paper. There is an image forming apparatus that performs secondary transfer in a batch. In addition, there is an image forming apparatus in which a transfer sheet is sent between each photoconductor and a conveyance transfer belt disposed so as to face the photoreceptor, and an image of each toner color is sequentially formed on the transfer sheet.

  When toner having a negative charge is used, a positive charge is applied to the transfer paper in order to adsorb the toner. Here, in order to transfer four color images, a large amount of positive charge is applied to the transfer paper. When the transfer paper is separated from a transfer member such as a transfer roller or a transfer belt, the transfer paper retains a positive charge without being neutralized, or the positive charge on the transfer paper is not completely eliminated even if the charge is eliminated. Therefore, the transfer paper that has reached the fixing device has a positive charge.

  Here, a problem called toner offset, in which the toner scattered from the transfer paper in the fixing device adheres to the heating fixing roller and the fixing belt stretched around the heating roller, becomes a problem. In order to prevent this, various methods have been proposed. For example, a fluorine-based material has a strong tendency to be negatively charged in the charge train. Therefore, this fluorine-based material is used for a fixing roller and a fixing belt. There is a method for preventing adhesion of negatively charged toner. In this case, transfer paper having a positive charge is likely to be attracted to the fixing roller or the fixing belt.

  In addition, the fixing device disclosed in Patent Document 1 has a fixing belt provided with a fluorine resin or the like on the outer periphery of a conductive member, and applies a potential having the same polarity as that of toner to the conductive member of the fixing belt through a fixing roller. An electric field is generated between the fixing belt and the transfer paper. When a toner having a negative charge is used, the toner is given a force toward the transfer paper having a positive charge, so that the fixing of the toner to the transfer paper is enhanced and the offset of the toner is reduced. Also in this case, the transfer paper having a positive charge is easily attracted to the fixing belt side.

  On the other hand, the fixing device disclosed in Patent Document 2 has a pressure roller having a shaft to which a potential is applied, an inner layer having low resistance and elasticity, and an outer layer having high resistance, and toner is applied to the inner layer through the shaft of the pressure roller. Give a potential of the opposite polarity. When toner having a negative charge is used, the toner is given a force toward the pressure roller having a positive charge, so that the fixing to the transfer paper having the positive charge on the pressure roller side is enhanced and the toner offset is reduced. Decrease. In this case, the transfer paper having a positive charge is difficult to be adsorbed to the pressure roller side, but is adsorbed to the fixing belt side as in the conventional case.

  As described above, since the transfer paper is easily attracted to the fixing roller, it is not separated from the fixing roller even when it is discharged from the fixing device, and is likely to cause a conveyance trouble. For this reason, various fixing devices for separating the transfer paper from the fixing roller have been proposed. For example, in the fixing device disclosed in Patent Document 3, the pressure roller is pressed against the fixing roller to reduce the curvature of the fixing belt at a portion where the transfer paper is separated from the fixing belt, and the transfer paper is easily separated from the fixing belt. To do.

However, paper used in the image forming apparatus is diversified in terms of weight, hardness, and the like, and the characteristics of the paper change depending on the use environment of the apparatus. In the fixing device disclosed in Patent Document 3, since only the curvature of the fixing roller and the fixing belt is used, it is difficult to cope with changes in paper characteristics depending on the type of paper and the environment, and it is difficult to cope with differences in conditions. It is.
JP-A-9-190099 Japanese Patent No. 3102317 JP 2002-268436 A

  The present invention provides a fixing device and an image forming apparatus capable of flexibly reducing transfer paper conveyance troubles even under different conditions such as changes in paper characteristics depending on the type of paper and usage environment.

  The fixing device includes a heating member, a pressure member, and a voltage applying unit. The heating member is rotatable and has a heating source for heating the surface inside. The pressure member has a pressure belt, an entrance side roller, and an exit side roller, the entrance side roller and the exit side roller are rotatably installed, and the pressure belt is an endless sheet in the rotation direction. It is stretched around the inlet side roller and the outlet side roller so as to be rotatable, and the surface is pressed against the heating member. The voltage application means includes a separation voltage application roller and a separation voltage source. The separation voltage application roller is rotatably installed in contact with the pressure belt, and the separation voltage source has a variable voltage value, and the separation voltage A separation voltage in which a direct current component and an alternating current component are superimposed is applied to the separation voltage application roller, which is electrically connected to the application roller.

  The pressure belt has at least a two-layer structure, the innermost layer of the layer structure is composed of a low resistance member, the outermost layer of the layer structure is composed of a high resistance member, and the separation voltage application roller is It may be in contact with the inner periphery of the pressure belt. Alternatively, at least the outermost layer of the pressure belt may be formed of a high resistance member, and the separation voltage application roller may be in contact with the outer periphery of the pressure belt.

  The separation voltage application roller may have a surface electrical resistance value that varies in a striped manner in either a direction parallel or perpendicular to the axial direction. The separation voltage source starts applying the separation voltage before the transfer paper is carried onto the pressure belt, and after the transfer paper passes through the portion sandwiched between the pressure belt and the heating roller, The application should be stopped.

  The image forming apparatus according to the present invention may be an image forming apparatus equipped with the above-described fixing device, and may include a voltage storage unit and a voltage setting unit. The voltage storage unit is provided with a separation voltage according to different thicknesses of the transfer paper, a separation voltage according to the case where the toner image transferred onto the transfer paper is a full-color image or a monochrome image, or next to the fixing device. The separation voltage corresponding to the case where the surface on which the transfer paper that is carried in is fixed is the first side and the second side in double-sided printing is stored, and the stored separation voltage has a DC component and an AC component, The voltage setting unit is a separation voltage according to the thickness of the transfer paper carried into the transfer device, a separation voltage according to whether the toner image transferred to the transfer paper is a full color image or a monochrome image, or Next, the separation voltage corresponding to the surface on which the transfer paper carried into the fixing device is fixed may be read from the voltage storage unit and set for the separation voltage source.

  According to this fixing device, the transfer paper, the heating roller, and the pressure belt can be easily separated. Further, a space-saving image forming apparatus can be realized according to the configuration of the apparatus. In addition, by generating a non-uniform electric field on the pressure belt, the transfer paper and the pressure belt can be easily separated. Also, by applying different separation voltages depending on the conditions, it is possible to easily cope with various usage environments. In addition, an effective voltage application and power saving effect can be obtained by controlling the on / off timing of the separation voltage source. By making the curvature radius of the exit side roller appropriate, separation between the transfer paper and the pressure belt can be ensured. Further, by providing such a fixing device, it is possible to realize an image forming apparatus that can easily separate the transfer paper and the heating roller, and the transfer paper and the pressure belt.

  A composite image forming apparatus is shown in FIG. 1 as an example of the image forming apparatus, and a functional block diagram of the image forming apparatus 1 is shown in FIG. The image forming apparatus 1 includes an image reading unit 2, a receiving unit 3, an input operation unit 4, a transfer device 5, a fixing device 6, a paper feeding unit 7, a paper reversing unit 8, a paper discharging unit 9, a voltage setting unit 10, and printing. A surface storage unit 11, a voltage storage unit 12, an image processing unit 13, and a processing unit 14 are provided, and an image is formed on a transfer sheet and output according to the input image signal. Although a composite image forming apparatus will be described here as an example of the image forming apparatus, a facsimile transmission / reception apparatus, a printing apparatus, a copying apparatus, or an image forming apparatus that arbitrarily combines these may be used.

  The image reading unit 2 includes a carriage 22 having an automatic document feeder 21, a light source, and a plurality of mirrors, a lens 23, a CCD 24, and a buffer 25. The carriage 22 scans light on the document fed by the automatic document feeder 21. The reflected light is collected by the lens 23, the image of the original is read by the CCD 24, and the read image is stored in the buffer 25 as an image signal. Note that the image reading unit 2 may have other structures. The receiving unit 3 has a communication function such as wired, wireless, and optical, and is connected to an external device such as a host computer, a facsimile communication device, a digital camera, and a scanner, and receives an image signal of an image formed on a transfer sheet. The receiving unit 3 receives information such as start and stop of image formation, selection of a full-color image formation mode or monochrome image formation mode, selection of double-sided printing or single-sided printing, transfer paper type, and the like. The image reading unit 2 is not necessarily required when the image forming apparatus 1 is a printing device, and the receiving unit 3 is not necessarily required when the image forming device 1 is a copying apparatus.

  The input operation unit 4 includes an image display device and an input key, and includes start and stop of image formation, selection of full color image formation mode or monochrome image formation mode, selection of double-sided printing or single-sided printing, transfer paper type, etc. Receive input of information.

  The transfer device 5 includes a transfer unit 51, a registration roller 52, and a guide 53. The transfer unit 51 includes a photoconductor 510, a charging device 511, an exposure device 512, a developing device 513, an intermediate transfer belt 514, and a belt roller 515. A primary transfer roller 516, a primary bias power source 517, a secondary transfer roller 518, and a secondary bias power source 519 are provided. The photoconductor 510, the charging device 511, the exposure device 512, the primary transfer roller 516, and the primary bias power source 517 form a set of yellow (Y), magenta (M), cyan (C), and black (B). Separately provided for each toner color.

  The photoconductor 510 is a cylindrical drum having a diameter of 30 mm coated with negatively chargeable OPC, and rotates in conjunction with the intermediate transfer belt 514 to be charged, exposed and developed to form a toner image. It is. The charging device 511 is a charging roller that applies a negative charge to the surface of the rotating photoreceptor 510 to uniformly charge the surface. The exposure apparatus 512 includes a laser light source 5121 and a rotating polygon mirror (polygon mirror) 5122.

  The laser light source 5121 emits laser light whose intensity has changed according to the write signal input from the image processing unit 13. The rotating polygon mirror 5122 rotates the laser beam at a high speed and a constant speed by a motor, and scans the photosensitive member 510 with the laser beam. Further, an optical system is appropriately arranged so that the laser light output from the laser light source 5121 is irradiated by scanning the surface of the photoconductor 510 with the rotary polygon mirror 5122. Note that a light emitting diode may be used for the exposure device 512.

  The developing device 513 attaches negatively charged toner to the surface of the photoconductor 510 to form a toner image from the electrostatic latent image. For the development, a two-component development system using a toner charged by stirring a carrier having a negative charge and a toner material is used. On the surface of the photoconductor 510, the electric charge is released according to the intensity of the irradiated laser beam to generate a potential distribution, and an electrostatic latent image corresponding to the image signal is formed. Here, since the toner is negatively charged, the toner is adsorbed on a portion of the surface of the photoreceptor 510 that is weakly negatively charged.

The intermediate transfer belt 514 has two layers of a base layer and a surface layer, and the entire thickness is formed to 150 μm. The surface layer is a layer to which a toner image is transferred, and is preferably formed of a material with little residual toner adhesion (good releasability). In this embodiment, the surface layer is formed to a thickness of about 10 μm by a resin in which PTEF, which is a fluororesin having a volume resistivity of about 1 × 10 ¹² Ω · cm, is dispersed. On the other hand, the base layer has a volume resistance value of at least 10 ⁶ to 10 ¹¹ Ω · so that primary transfer from the four photoconductors and secondary transfer to the transfer paper are surely performed and abnormal image formation can be prevented. It is desirable to be in the range of cm. In this embodiment, it is formed of NBR and EPDM rubber having a volume resistance of about 1 × 10 ⁷ to 1 × 10 ⁹ Ω · cm.

  The intermediate transfer belt 514 is stretched around a belt roller 515 so as to be rotatable, and is disposed in contact with each photoconductor 510, the primary transfer roller 516, and the secondary transfer roller 518. The primary transfer roller 316 is a metal rod and is disposed to face the photoconductor 510 with the intermediate transfer belt 514 interposed therebetween. The primary bias power source 517 applies a high voltage to the primary transfer roller 516 to positively charge the intermediate transfer belt 514 that is in contact with the primary transfer roller 516 so that the negatively charged toner is easily adsorbed. The intermediate transfer belt 514 moves in the direction of the arrow in conjunction with the rotation of each photoconductor 510, and the yellow (Y) photoconductor 510y, the magenta (M) photoconductor 510m, the cyan (C) photoconductor 510c, The toner images are sequentially transferred from the black (B) photoconductor 510b. Each toner image is transferred in a superimposed manner (hereinafter referred to as primary transfer) at the same position so that all the toner colors are aligned to form one color toner image.

The secondary transfer roller 518 is opposed to one of the belt rollers 515 with the intermediate transfer belt 514 interposed therebetween, and is rotatably disposed while applying pressure to the intermediate transfer belt 514 by the elastic force of the spring. The belt roller 515 facing the secondary transfer roller 518 is grounded. The secondary transfer roller 518 is formed of a core metal having a diameter of 10 mm and a surrounding resin layer, and rotates by receiving a driving force from a motor via a gear. The resin layer is formed of a conductive rubber having a volume resistivity of about 1 × 10 ⁸ Ω · cm, such as chloroprene rubber or urethane rubber, or an elastomer resin. The cored bar is connected to a secondary bias power source 519 via a power supply spring. The secondary bias power supply 519 applies a voltage to the secondary transfer roller 518 to positively charge the transfer paper sent from the registration roller 52 and to easily adsorb the negatively charged toner.

  The registration roller 52 receives the supply of transfer paper from the paper feed unit 7 or the paper reversing unit 8, stops the transfer paper as necessary, and adjusts the timing of sending the transfer paper to the secondary transfer roller 518. The registration roller 52 sends the transfer paper to the secondary transfer roller 518 in synchronization with the timing at which the primary transfer toner image of the intermediate transfer belt 514 reaches the secondary transfer roller 518. The toner image that has been primarily transferred to the intermediate transfer belt 514 is collectively transferred (hereinafter referred to as secondary transfer) to a transfer sheet that is sandwiched between the intermediate transfer belt 514 and the secondary transfer roller 518 and conveyed. ) The guide 53 guides the transfer paper from the transfer unit 51 to the fixing device 6.

  An enlarged view of the fixing device 6 is shown in FIG. The fixing device 6 includes a heating roller 61, a pressure belt 62, an entrance side roller 63, an exit side roller 64, a pressure spring 65, a separation voltage application roller 66, and a separation voltage source 67. The heating roller 61 includes a metal core 611, a release layer 612, a heater 613, and a thermistor 614. The cored bar 611 has a pipe shape and is driven to rotate by a motor. The release layer 612 is formed to cover the peripheral surface of the cored bar 611 with a fluororesin such as PFA or PTTFE having heat resistance and good release properties. The heater 613 heats the entire heating roller 61. The thermistor 614 is disposed in contact with the peripheral surface of the release layer 612, and detects the temperature and turns the heater 613 on and off to maintain an appropriate fixing temperature.

The pressure belt 62 is stretched around the entrance side roller 63 and the exit side roller 64, contacts the heating roller 61 on the outside, and contacts the separation voltage application roller 66 on the inside. As shown in FIG. 4, the pressure belt 62 is formed of two layers of a base layer 621 and a surface layer 622, the base layer 621 is formed of a member having a relatively low resistance value, and the surface layer 622 is a member having a relatively high resistance value. Formed with. The base layer 621 is a layer obtained by adding carbon or an ionic conductive member to polyethersulfone (PES) having an endless sheet shape in the rotation direction, and has a resistance value of about 10 ¹⁰ Ω · cm, and has a surface layer 622. Is formed by coating the base layer 621 with a fluororesin of 10 μm. In addition to PES, a heat-resistant resin such as polyimide (PI) or polyether ether ketone (PEEK) may be used as a sheet shape having a thickness of about 500 μm to 5 mm.

  The separation voltage application roller 66 is made of metal and is disposed at a position in contact with the inside of the pressure belt 62 and facing the heating roller 61. The separation voltage source 67 supplies a separation voltage obtained by superimposing the direct current component and the alternating current component set by the voltage setting unit 10 to the separation voltage application roller 66 and indirectly forms a non-uniform electric field on the pressure belt 62. Let This electric field causes the transfer paper carried in from the transfer device 5 to be adsorbed to the pressure belt 62 to suppress adverse effects such as entanglement in the heating roller, and the transfer paper discharged from the fixing device 6 from the pressure belt 62. Strip efficiently.

  The inlet side roller 63 is located on the side where the transfer paper is carried into the pressure belt 62, is connected to the other end of the pressure spring 65 with one end fixed, and presses the pressure belt 62 against the heating roller 61 side. Apply pressure in the direction. Due to this pressure, a contact portion called a nip portion is formed between the heating roller 61 and the pressure belt 62. The exit side roller 64 is located on the side where the transfer paper is carried out from the pressure belt 62 and is rotated by a motor to rotate the pressure belt 62.

  In order to reliably separate the pressure belt 62 and the transfer paper in the vicinity of the exit side roller 64, it is desirable that the radius of curvature of the exit side roller 64 is 12 mm to 16 mm. In order to obtain this radius of curvature, the radius of curvature of the outlet side roller 64 and the environment were changed, and an experiment was conducted to determine in which case separation is effectively performed.

  First, when the radius of curvature is smaller than 10 mm, there is a possibility that the force pulled by the pressure belt 62 cannot withstand the distortion. Therefore, it is desirable that the radius of curvature is larger than 10 mm. Next, three types, a first environment having a temperature of 10 ° C. and a humidity of 15%, a second environment having a temperature of 23 ° C. and a humidity of 65%, and a third environment having a temperature of 30 ° C. and a humidity of 90% Experiments were conducted to determine whether various types of paper were separable in the environment. In the case of a curvature radius of 12 mm, the paper having the basis weight above 45K paper was separable in any environment. In the case of a curvature radius of 14 mm and a curvature radius of 16 mm, the paper with the basis weight above 55K paper was separable in any environment.

  However, in the case of the curvature radius of 18 mm, in the second environment and the third environment, the paper having the basis weight above 55K paper was separable, but in the first environment, the 55K paper might not be separated. It was. In the case of 20 mm, the 55K paper was separable in the second environment, but the basis weight paper above the 55K paper was not separated in any other environment.

  From this result, it can be seen that it is desirable to use a roller having a radius of curvature of 12 mm to 16 mm as the outlet side roller 64 in order to be separable in any environment. When the usage environment is limited, a roller having a radius of curvature of about 20 mm may be used as the outlet side roller 64.

  The paper feeding unit 7 receives a signal instructing the start of paper feeding from the processing unit 14, and the registration roller of the transfer device 5 according to the type of transfer paper received by the receiving unit 3 or input by the input operation unit 4. The transfer paper is sent to 52. A sensor may be provided in the paper supply unit 7 to determine the type of transfer paper. The sheet reversing unit 8 includes a branching pawl 81 and a reversing unit 82, and the branching pawl 81 changes a path for feeding a transfer sheet conveyed from the fixing device 6. When the paper reversing unit 8 receives a signal for instructing paper discharge from the processing unit 14, the paper reversing unit 8 operates the branch pawl 81 to form a path for sending the transfer paper from the fixing device 6 to the paper discharging unit 9. When a signal instructing reversal is received, the branch pawl 81 is operated to form a path for sending transfer paper from the fixing device 6 to the reversing unit 82. The reversing unit 82 reverses the front and back of the transfer paper sent through the branch pawl 81 and sends it to the registration roller 52 of the transfer device 5. The paper discharge unit 9 discharges the transfer paper sent from the fixing device 6 through the branch pawl 81 to the outside.

  The printing surface storage unit 11 stores information on whether the transfer paper conveyed next to the fixing device 6 performs the first surface fixing or the second surface fixing at the time of duplex printing. The voltage storage unit 12 corresponds to three types of information: the type of transfer paper, whether it is a full-color image formation mode or a monochrome image formation mode, and the side on which the transfer paper that is next carried into the fixing device is fixed. The separation voltage is stored. The stored separation voltage is divided into a direct current component and an alternating current component.

  Depending on the type of transfer paper, the optimum suction force to the pressure belt varies, and when a thicker transfer paper is sucked, a stronger electric field is generated around the transfer paper to increase the suction force. Good. In addition, the transfer paper that has been directly transferred from the paper supply unit 7 and secondarily transferred, and the transfer paper that has been reversely transferred by the paper reversing unit 8 once through the fixing device 6 and secondarily transferred again has a higher resistance value. Become. That is, since the charge amount of the transfer paper is different between the case where the first side is fixed and the case where the second side is fixed during double-sided printing, it is preferable that the separation voltage is also different. In general, even in a full-color image forming apparatus, a full-color image forming mode and a monochrome image forming mode can be switched by user selection or automatic discrimination. The applied voltage from the primary transfer roller 516 to the intermediate transfer belt 514 and the applied voltage from the secondary transfer roller 518 to the transfer paper are different depending on the image forming mode, so that the charged state of the transfer paper carried into the transfer device 5 is different. It is preferable to make them different.

  Specifically, for both the absolute value of the direct current component of the separation voltage and the peak-to-peak voltage value of the alternating current component, the value corresponding to the thick transfer paper should be equal to or greater than the value corresponding to the thin transfer paper. The value corresponding to the full-color image formation mode is preferably set to be equal to or greater than the value corresponding to the monochrome image formation mode. Furthermore, it is preferable that the value corresponding to the first surface is greater than or equal to the value corresponding to the second surface.

  The correspondence between the type of transfer paper, the distinction between the full-color image formation mode and the monochrome image formation mode, and the surface on which the transfer paper that is next carried into the fixing device is fixed and the separation voltage are as follows, for example. . When the transfer paper is plain paper and the first side is printed in the full color image forming mode, the separation voltage is a voltage obtained by superimposing a DC component of −200 V, a peak-to-peak voltage of 2000 V, and a rectangular wave AC component of a frequency of 40 Hz. . When the transfer paper is thin paper (55K paper), the separation voltage is a voltage obtained by superimposing a DC component of −100 V and an AC component of a rectangular wave with a peak-to-peak voltage of 1500 V and a frequency of 40 Hz. When the transfer paper is thick paper (135K paper), postcard, OHP paper, or the like, the separation voltage is a voltage obtained by superimposing a DC component of −500 V and a rectangular wave with a peak-to-peak voltage of 2000 V and a frequency of 40 Hz.

  Further, when the transfer paper is plain paper and the second side is printed in the full color image forming mode, the separation voltage is a voltage obtained by superimposing a DC component of −300 V, a peak-to-peak voltage of 3000 V, and a rectangular wave AC component of frequency 40 Hz. It is. When the transfer paper is plain paper and the second side is printed in the monochrome image forming mode, the separation voltage is a rectangular wave with a peak-to-peak voltage of 3000 V and a frequency of 40 Hz. The separation voltage may be a voltage obtained by superimposing a DC component of −1200 V and an AC component of a peak-to-peak voltage of 0 V depending on the paper type, environment, and the like.

  The image processing unit 13 includes an image signal read by the image reading unit 2 or received by the receiving unit 3 and a full-color image forming mode or a monochrome image forming mode received by the receiving unit 3 or input by the input operation unit 4. The laser light is turned on in synchronization with the rotation of the rotary polygon mirror 5122 and the photosensitive member 510 so that an electrostatic latent image is formed on the photosensitive member 510 based on the information such as the type of transfer paper. A write signal for instructing the laser light source 5121 to be generated is created. The processing unit 14 controls the overall operation of the image forming apparatus 1.

  As shown in FIG. 5, the image forming apparatus may sequentially transfer the toner color photoreceptors to the transfer paper without providing an intermediate transfer belt.

  The operation of the image forming apparatus 1 will be described with reference to FIG. The processing unit 14 receives the print start signal received by the receiving unit 3 or input from the input operation unit 4 and causes the image processing unit 13 to create a writing signal for each toner color. The processing unit 14 causes the printing surface storage unit 11 to store the surface of the transfer paper that is next carried into the fixing device as the first surface. The image processing unit 13 outputs a writing signal to the transfer device 5. The transfer device 5 performs primary transfer and secondary transfer. In the primary transfer, the transfer device 5 rotates the photosensitive member 510, the charging device 511 negatively charges the surface of the photosensitive member 510, and blinks the laser light source 5121 in accordance with the writing signal. An electrostatic latent image is formed on the surface due to the strength of negative charging, and toner is attached to a portion with weak negative charging to form a toner image on the surface of the photoreceptor 510. Further, the transfer device 5 rotates the intermediate transfer belt 514 to cause the primary bias power source 517 to apply a positive high voltage to the primary transfer roller 516, and sequentially from each toner color photoreceptor 510 to the intermediate transfer belt. The toner image is transferred to 514, and one color toner image is formed at the same position on the intermediate transfer belt 514.

  In the secondary transfer, the processing unit 14 designates the transfer paper to the paper feeding unit 7 according to the type of transfer paper received by the receiving unit 3 or input from the input operation unit 4 and starts supply. . The paper feed unit 7 sends the designated transfer paper to the registration roller 52 of the transfer device 5. The transfer device 5 causes the secondary bias power source 519 to apply a positive voltage to the secondary transfer roller 518 to rotate the secondary transfer roller 518. On the other hand, the transfer device 5 transfers the transfer paper from the registration roller 52 to the secondary transfer roller 518 and the intermediate transfer belt 514 in accordance with the timing at which the toner image formed on the intermediate transfer belt 514 is sent to the secondary transfer roller 518. The toner image is transferred to the contact portion and transferred onto the transfer paper. The transfer paper that has passed through the secondary transfer roller 518 is positively charged, and a negatively charged toner image is formed on the surface thereof. The transfer device 5 sends the transfer paper from the secondary transfer roller 518 to the guide 53 and sends it to the fixing device 6.

  The voltage setting unit 10 searches the print surface storage unit 11 for the type of transfer sheet and the full color image formation mode or monochrome image formation mode received by the reception unit 3 or input from the input operation unit 4. The voltage storage unit 11 is searched based on the acquired information on whether the surface on which the transfer paper carried into the fixing device is to be fixed is the first side or the second side. As a result of the search, the voltage setting unit 10 determines whether the transfer sheet type, the full-color image formation mode or the monochrome image formation mode, and the separation information corresponding to the information on the surface on which the transfer sheet carried into the fixing device is fixed next. The voltage is read and set to the separation voltage source 67.

  The processing unit 14 causes the fixing device 6 to fix the conveyed transfer paper. The fixing device 6 heats the heating roller 61 by the heater 613 and rotates the pressure belt 62 by rotating the outlet side roller 64. The separation voltage source 67 applies the separation voltage set by the voltage setting unit 10 to the separation voltage application roller 66 to generate an electric field in the pressure belt 62. For example, when the transfer paper is plain paper and the first side is printed in the full color image forming mode, the separation voltage source 67 is supplied with a DC component of −200 V and a square wave AC component of a peak-to-peak voltage of 2000 V and a frequency of 40 Hz. The superimposed separation voltage is set. When the pressure belt 62 moves at a speed of 200 mm / second, a non-uniform electric field having a period of 5 mm is formed on the pressure belt 62 by applying a separation voltage.

  Since the pressure belt 62 has a high resistance portion, there is a time lag from the start of application of the separation voltage to the generation of an electric field on the surface of the pressure belt 62. Therefore, the separation voltage source 67 needs to start applying the separation voltage before the transfer paper is sent to the pressure belt 62. In the experiment, as shown in FIG. 6, it was found that the start of application of the separation voltage is desirably 4 ms or more, preferably 10 ms or more before the transfer paper is supplied to the heating roller 61. Further, if the application of the separation voltage to the pressure belt 62 is continued, the opposing heating roller 61 is likely to be deteriorated, and the power consumption increases. In order to prevent this, the voltage setting unit 10 adjusts the start of application of the separation voltage to the timing at which the registration roller 52 starts supplying the transfer paper to the secondary transfer roller 518, and also stops application of the separation voltage. Adjust after the paper is discharged.

  When the transfer paper is conveyed between the heating roller 61 and the pressure belt 62, the toner image is fixed to the transfer paper by heat and pressure. In addition, the transfer paper is attracted to the pressure belt 62 and conveyed by the electric field generated in the pressure belt 62, so that it is prevented from being caught in the heating roller 61. The transfer paper sent to the outlet side roller 64 is easily removed from the pressure belt 62 due to the influence of the radius of curvature of the outlet side roller 64 or the influence of the non-uniform electric field generated by the AC component of the separation voltage on the pressure belt 62. And are sent to the branching pawl 81.

  The processing unit 14 sends a signal for instructing the paper reversing unit 8 to discharge paper when the fixing of the first side of single-sided printing or the second side of double-sided printing is completed. The sheet reversing unit 8 operates the branch pawl 81 to send the transfer sheet to the sheet discharge unit 9 to be discharged outside. On the other hand, when the fixing of the first side of double-sided printing is completed, the processing unit 14 sends a signal to instruct the paper inversion unit 8 to invert. The paper reversing unit 8 operates the branch pawl 81 to cause the transfer paper to be sent to the reversing unit 82 and to cause the printing surface storage unit 11 to store the surface of the transfer paper that is next carried into the fixing device as the second surface. The transfer paper is reversed and sent to the registration roller 52 to perform transfer and fixing on the second side.

  The separation voltage application roller 66 may be disposed so as to come into contact with the pressure belt 62 from the outside, as shown in FIG. In this case, a single-layer pressure belt may be used instead of the two-layer pressure belt. As the single-layer pressure belt, one formed by molding a PES film to a thickness of 500 μm is used. The polarity of the separation voltage is reversed between when the separation voltage application roller 66 contacts the pressure belt 62 from the outside and when it contacts from the inside. Further, as shown in FIG. 7B, the separation voltage application roller 66 is opposed to the heating roller 61 with the pressure belt 62 interposed therebetween, and is disposed downstream of the heating roller 61 in the rotation direction of the pressure belt 62. May be. As a result, the contact area between the heating roller 61 and the pressure belt 62 is large, and the pressure applied to the transfer paper increases. Further, since the adhesion between the transfer paper and the separation voltage application roller 66 is increased, the attractive force between the two is further increased. Further, the separation voltage application roller 66 may also be used as the outlet side roller 64 as shown in FIG.

  The separation voltage application roller 66 may be one in which an insulating member and a conductive member are mixed on the surface. The insulating member is urethane rubber, chloroprene rubber or the like, and the conductive member is obtained by adding carbon or the like to these insulating members. For example, as shown in FIG. 8A, insulating members and conductive members may be alternately arranged at a pitch of 5 mm to 15 mm in the rotation direction. In this case, the separation voltage application roller 66 is disposed inside the pressure belt 62, and the pressure belt 62 has a two-layer structure. When a DC voltage is applied from the separation voltage source 67, the separation voltage application roller 66 forms a non-uniform electric field on the pressure belt 62 that is rotated at a constant speed by the outlet side roller 64. Moreover, as shown in FIG.8 (b), you may arrange | position an insulating member and an electroconductive member alternately with a pitch of 5 mm-15 mm in a longitudinal direction. In this case, the separation voltage application roller 66 is disposed outside the pressure belt 62. A single layer structure may be used as the pressure belt 62. When a voltage in which a DC voltage and an AC component are superimposed is applied by the pressure belt 62 and the separation voltage source 67, a non-uniform electric field is generated on the pressure belt 62 rotated at a constant speed by the outlet side roller 64. Let it form.

  In this embodiment, a reversal development method using negatively charged toner is adopted, but a positively charged toner may be used to provide a similar device of reverse polarity.

1 is a configuration diagram of an image forming apparatus. 2 is a functional block diagram of the image forming apparatus. FIG. It is an enlarged view of a fixing device. It is sectional drawing of a pressure belt. It is a block diagram of another image forming apparatus. It is a figure which shows the application timing of a separation voltage. It is an enlarged view of another fixing device. It is an enlarged view of another separation voltage application roller.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1; Image forming apparatus, 2; Image reading part, 3; Receiving part, 4; Input operation part,
5; transfer device, 6; fixing device, 7; paper feeding unit, 8; paper reversing unit, 9; paper ejection unit,
10; voltage setting unit, 11; printing surface storage unit, 12; voltage storage unit,
13; Image processing unit, 14; Processing unit, 21; Automatic document feeder,
22; Carriage, 23; Lens, 24; CCD, 25; Buffer 51; Transfer section, 52; Registration roller, 53;
61; heating roller, 62; pressure belt, 63; inlet side roller,
64; outlet side roller, 65; pressure spring, 66; separation voltage application roller,
67; separation voltage source; 81; branch claw; 82;
510; photosensitive member, 511; charging roller, 512; exposure device,
513; developing device, 514; intermediate transfer belt, 515; belt roller,
516; primary transfer roller, 517; primary bias power source,
518; secondary transfer roller, 519; secondary bias power supply,
611; Metal core, 612; Release layer, 613; Heater, 614; Thermistor,
621; base layer, 622; surface layer, 5121; laser light source, 5122; rotating polyhedron

Claims (9)

A heating member, a pressure member, and a voltage applying means;
The heating member is rotatable and has a heating source for heating the surface inside,
The pressure member includes a pressure belt, an entrance-side roller, and an exit-side roller. The entrance-side roller and the exit-side roller are rotatably installed, and the pressure belt is endless in the rotation direction. A sheet, which is rotatably stretched around the inlet side roller and the outlet side roller, and the surface is pressed against the heating member,
The voltage application means includes a separation voltage application roller and a separation voltage source, the separation voltage application roller is rotatably installed in contact with the pressure belt, and the separation voltage source has a variable voltage value. A fixing device, wherein the fixing device is electrically connected to the separation voltage application roller and applies a separation voltage in which a direct current component and an alternating current component are superimposed on the separation voltage application roller. The pressure belt has a layer structure of at least two layers, the innermost layer of the layer structure is configured by a low resistance member, and the outermost layer of the layer structure is configured by a high resistance member,
The fixing device according to claim 1, wherein the separation voltage application roller is in contact with an inner periphery of the pressure belt. At least the outermost layer of the pressure belt is constituted by a high resistance member,
The fixing device according to claim 1, wherein the separation voltage application roller is in contact with an outer periphery of the pressure belt.   The fixing device according to claim 1, wherein the separation voltage application roller has a surface electrical resistance value that differs in a stripe shape in either a direction parallel to or perpendicular to an axial direction.   The separation voltage source starts application of the separation voltage before the transfer paper is carried onto the pressure belt, and the transfer paper has passed through a portion sandwiched between the pressure belt and the heating roller. The fixing device according to claim 1, wherein after that, application of the separation voltage is stopped.   An image forming apparatus equipped with the fixing device according to claim 1. The image forming apparatus includes a voltage storage unit and a voltage setting unit,
The voltage storage unit stores separation voltages corresponding to different thicknesses of transfer paper, and the stored separation voltage has a direct current component and an alternating current component,
The image forming apparatus according to claim 6, wherein the voltage setting unit reads a separation voltage corresponding to a thickness of a transfer sheet carried into the transfer device from the voltage storage unit and sets the separation voltage with respect to the separation voltage source. . The image forming apparatus includes a voltage storage unit and a voltage setting unit,
The voltage storage unit stores a separation voltage according to a case where the toner image transferred onto the transfer paper is a full color image or a monochrome image, and the stored separation voltage has a direct current component and an alternating current component,
The voltage setting unit reads a separation voltage according to whether the toner image transferred onto the transfer paper is a full-color image or a monochrome image from the voltage storage unit and sets the separation voltage for the separation voltage source. Item 7. The image forming apparatus according to Item 6. The image forming apparatus includes a voltage storage unit and a voltage setting unit,
The voltage storage unit stores a separation voltage according to the case where the surface on which the transfer paper to be carried next to the fixing device is fixed is the first side and the second side in double-sided printing, and the stored separation The voltage has a DC component and an AC component,
The voltage setting unit reads out from the voltage storage unit and sets the separation voltage corresponding to the surface on which the transfer paper that is next carried into the fixing device is fixed to the separation voltage source. Image forming apparatus.

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