JP2005091418A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus having a fixing device which maintains glossiness, without raising the lower limit temperature and which will not cause deviation in images, in the fixing device of a belt system. <P>SOLUTION: The image forming apparatus has: the fixing device, which includes a support roller member parallel to a heating roller member and separated therefrom; a belt member stretched endlessly in between both of the roller members; and a pressure roller member disposed opposite the support roller member via the belt member. The pressure roller member and the support roller member constitute a second fixing process, and the abutment region between the pressure roller member and the belt member constitutes a first fixing process other than the region of the second fixing process. A pressing member is provided to a part of the first fixing process, so that the pressing force of the pressing member, with respect to the pressure roller member near the central part of the pressure roller, is larger than that near both the end parts. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus having a fixing device using an electrophotographic system such as a copying machine, a printer, and a FAX, and more particularly to an image forming device having a fixing device using a belt member.

In recent years, in electrophotographic image forming apparatuses such as copying machines, printers, and fax machines, there has been an increasing demand for image quality, and there has been a movement to increase or control the glossiness of an image by a fixing device of the image forming apparatus. It has been.

  Conventionally, as a fixing device of an electrophotographic image forming apparatus, a heat generating rubber roller having an elastic layer and maintained at a predetermined temperature, and a pressure rubber roller in pressure contact with the heat generating rubber roller and having an elastic layer are undetermined. A heat roller fixing method in which a transfer material on which a toner image (toner image) is formed is nipped and conveyed while being heated is frequently used.

  In addition, a transfer material for holding an unfixed toner image is fed to the surface of the endless fixing belt maintained in a predetermined temperature range so that the toner image surface side faces, and the fixing belt is sandwiched therebetween. The transfer material is pressed against the fixing belt by an arranged belt support roller and pressure roller, and the toner image is transferred through heating and pressure action by the fixing belt, the belt support roller and the pressure roller. An image forming apparatus using a belt fixing system configured to be fixed on a material is also generally known.

Further, in the belt fixing method, a pressure member for the purpose of a preceding pressure effect in which a predetermined load distribution is applied in the roller axial direction in addition to pressing the belt and the transfer material with the pressure roller and the belt support roller A technique for avoiding image misalignment and wrinkles by applying the technique is also disclosed (for example, see Patent Document 1).
Japanese Patent Laid-Open No. 10-228199

  However, a belt fixing device having a pressure member for the purpose of the preceding pressure effect, which is the first fixing step, is advantageous in reducing the minimum fixing temperature and improving the glossiness, but causes image misalignment. Tend to. Image misalignment is resolved by raising the fixing temperature and fixing at a higher temperature, but raising the fixing temperature is the same as raising the lower limit temperature, and does not reduce the lower limit fixing temperature. The in-flight temperature rises and the viewpoint of energy saving is not good.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus having a fixing device that maintains glossiness without increasing the minimum temperature and does not cause image displacement.

  The above object is achieved by the following means.

  (1) A heating roller member having heating means, a support roller member disposed in parallel with and spaced from the heating roller member, and a belt member that is endlessly stretched between the heating roller member and the support roller member And a pressure roller member provided to face the support roller member via the belt member, and the pressure roller member and the support roller member are pressed against each other via the belt member The image forming apparatus includes a belt fixing device that constitutes a second fixing process unit and that constitutes the first fixing process part in a region where the pressure roller member and the belt member are in contact with each other except the second fixing process unit. In the forming apparatus, the portion that performs the first fixing step has a member that presses the pressure roller member via the belt member, and the sheet of the pressing member passes through the pressure roller member. The pressing force in the direction perpendicular to the direction the image forming apparatus characterized by a larger near the center than near both ends of the pressure roller member (first invention).

  (2) A heating roller member having a heating means, a support roller member disposed in parallel with and spaced from the heating roller member, and a belt member that is endlessly stretched between the heating roller member and the support roller member And a pressure roller member provided to face the support roller member via the belt member, and the pressure roller member and the support roller member are pressed against each other via the belt member The image forming apparatus includes a belt fixing device that constitutes a second fixing process unit and that constitutes the first fixing process part in a region where the pressure roller member and the belt member are in contact with each other except the second fixing process unit. In the forming apparatus, the portion that performs the first fixing step has a member that presses the pressure roller member via the belt member, and is formed by the pressure roller member of the pressing member. Image forming apparatus sheet passing width of the-up unit is characterized in that is larger near the center than near both ends of the pressure roller member (second invention).

  The pressure distribution in the axial direction of the pressure roller of the auxiliary pressure member, which is the pre-pressing section, is made higher at the center of the shaft than at both ends, and the nip width distribution is made wider at the center of the shaft than at both ends. Accordingly, image shift can be prevented at a lower temperature.

  First, the image forming apparatus of the present invention will be described.

  In the description of the embodiment of the present invention, the technical scope is not limited by the terms used in this specification.

  FIG. 1 is a schematic diagram illustrating an example of the overall configuration of the image forming apparatus.

  In the figure, 10 is a photoconductor, 11 is a scorotron charger as charging means, 12 is a writing device as image writing means, 13 is a developing device as developing means, and 14 is a cleaning for cleaning the surface of the photoconductor 10. An apparatus, 15 is a cleaning blade, 16 is a developing sleeve, and 20 is an intermediate transfer belt. The image forming unit 1 includes a photoconductor 10, a scorotron charger 11, a developing unit 13, a cleaning device 14, and the like. Since the mechanical configuration of the image forming unit 1 for each color is the same, Y ( Reference numerals are given to the configuration of only the yellow (yellow) series, and reference symbols are omitted for the constituent elements of M (magenta), C (cyan), and K (black).

  The arrangement of the image forming means 1 for each color is in the order of Y, M, C, K with respect to the running direction of the intermediate transfer belt 20, and each photoconductor 10 contacts the stretched surface of the intermediate transfer belt 20. The contact point rotates in the same direction as the traveling direction of the intermediate transfer belt 20 and at the same linear speed.

  The intermediate transfer belt 20 is stretched around a driving roller 21, an earth roller 22, a tension roller 23, a static elimination roller 27, and a driven roller 24. The belt unit 3 includes these rollers, the intermediate transfer belt 20, a transfer device 25, a cleaning device 28, and the like. Configure.

  The intermediate transfer belt 20 is driven by rotation of the driving roller 21 by a driving motor (not shown).

  The photosensitive member 10 is formed by forming a photosensitive layer such as a conductive layer, an a-Si layer, or an organic photosensitive member (OPC) on the outer periphery of a cylindrical metal base formed of, for example, an aluminum material, and the conductive layer is grounded. It rotates in the counterclockwise direction indicated by the arrow in the figure.

  An electrical signal corresponding to the image data from the reading device 80 is converted into an optical signal by the image forming laser, and is projected onto the photoconductor 10 by the writing device 12.

  The developing unit 13 is a developing sleeve formed of a cylindrical nonmagnetic stainless steel or aluminum material that keeps a predetermined interval with respect to the circumferential surface of the photoconductor 10 and rotates in the same direction as the rotation direction of the photoconductor 10. 16.

The intermediate transfer belt 20 is an endless belt having a volume resistivity of 10 ⁶ to 10 ¹² Ω · cm. For example, the intermediate transfer belt 20 may be an engineering plastic such as modified polyimide, thermosetting polyimide, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, and nylon alloy. A seamless two-layer structure in which a conductive film is dispersed on the outside of a semiconductive film substrate having a thickness of 0.1 to 1.0 mm, and a fluorine coating having a thickness of 5 to 50 μm is preferably applied as a toner filming prevention layer. It is a belt. In addition to this, a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber, urethane rubber, or the like can also be used.

  A transfer unit 25 has a function of transferring a toner image formed on the photoreceptor 10 onto the intermediate transfer belt 20 by applying a direct current having a polarity opposite to that of the toner. As the transfer unit 25, a transfer roller can be used in addition to the corona discharger.

  Reference numeral 26 denotes a transfer roller which can be brought into contact with and released from the earth roller 22 and retransfers the toner image formed on the intermediate transfer belt 20 onto the transfer material P.

  A cleaning device 28 is provided to face the driven roller 24 with the intermediate transfer belt 20 interposed therebetween.

  After the toner image is transferred onto the transfer material P, the intermediate transfer belt 20 has its residual toner charge weakened by a neutralizing roller 27 to which an AC voltage superimposed with a DC voltage having the same or opposite polarity as that of the toner is applied. Residual toner on the peripheral surface is cleaned.

  A fixing device 4 includes a fixing belt 40 formed by molding a metal or resin base and silicon rubber into a belt shape, a belt support roller 41 that supports and conveys the belt, a heating roller 42 that is a heating roller member, and the fixing belt 40. The pressure roller 43 is a pressure roller member that presses with the transfer material P interposed therebetween, the auxiliary pressure mechanism 45 that is a pressure member in the first fixing step, a belt cleaning web (not shown), and the like. . The auxiliary pressure member will be described later.

  The heating roller 42 has a cylindrical shape made of thin aluminum, and has a halogen heater 47 and the like for heating from the inside to a predetermined temperature. Heated by heat. The temperature is detected by a contact temperature sensor 48 installed on the heating roller 42, and the temperature is controlled by the control unit B1.

  The heating roller 42 is slidable in the direction of arrow F by a spring 421 (see FIG. 2) via a bearing (not shown), and urges the fixing belt 40 with tension.

  Further, the belt support roller 41 has a silicone-based elastic layer 411 (see FIG. 2), which is an elastic body, baked on a cylindrical cored bar 410 (see FIG. 2) formed from iron, so that the main body side drive (not shown) is driven. Power is obtained from the device and it rotates clockwise as shown. Accordingly, the drive transmission path is (1) main body side drive source, (2) belt support roller 41, (3) fixing belt 40, and (4) heating roller 42.

  As described above, the belt fixing device with an auxiliary pressure member is advantageous in that the lower limit temperature of fixing can be reduced and the glossiness of the toner image can be improved. However, image misalignment tends to occur as a problem.

  The present invention is characterized in that image displacement can be prevented and eliminated without increasing the fixing temperature by lowering the pressure distribution in the axial direction of the pressure roller of the auxiliary pressure member at both ends than at the center. .

  FIG. 2 is a schematic diagram showing a belt fixing mechanism and an auxiliary pressure mechanism.

  FIG. 3 is a view showing a cross section of the auxiliary pressurizing mechanism taken along the line AA.

  2 and 3, the auxiliary pressure mechanism 45 includes a support frame 454, a sponge 452 as an auxiliary pressure member, a sponge support plate 453, compression springs 45A and 45B, a back plate 451, and the like. Compression springs 45 </ b> A and 45 </ b> B are included inside, and the sponge support plate 453 can be slid by the rising portion h with the inner surface of the back plate 451 as a guide. Further, the back plate 451 is fixed to the support frame body 454, and the support frame body 454 has fixing pins 455 on both sides, and the fixing pins 455 engage with the frame body 457 of the fixing device and are positioned. The compression springs 45 </ b> A and 45 </ b> B are engaged at both ends of each spring at predetermined positions in the back plate 451 and the sponge support plate 453.

  The central compression spring 45A has a larger spring coefficient than the compression springs 45B at both ends. That is, both ends of the sponge support plate 453 are in a slightly distorted state, and the sponge 452 is configured to have a pressure distribution such that the pressing force against the pressure roller 43 via the fixing belt 40 becomes a central high pressure and a low pressure on both ends. .

  Alternatively, the width in the sheet passing direction of the nip portion d formed by the sponge 452 and the pressure roller 43 is configured to be larger in the vicinity of the center portion than in the vicinity of both end portions of the pressure roller 43.

  It has been confirmed through experiments that the above-described configuration can prevent and eliminate image shift.

  FIG. 4 is an enlarged view (photograph) showing an example of image misalignment.

  In FIG. 4, the line of width S inherently causes image misalignment e, f, m in the reverse direction of the sheet passing.

  Hereinafter, the confirmation experiment will be described.

Experimental conditions
Sponge support plate thickness: 1mm
Sponge thickness: 6mm
Sponge length: 350mm
Total pressing force between auxiliary pressure member and pressure roller: 150N
Fixing temperature: 140-200 ° C
Transfer material used (A): POD100 (Glossy paper for color PPC made by Oji Paper, 100 g / m ² )
Used transfer material (B): 4024-28 lb (about 105 g / m ^{2 of} plain paper for color PPC manufactured by Xerox)
Next, the experimental results under the above conditions are shown in the table.

  From Table 1, it was confirmed that in both of the transfer materials (A) and (B), when the central portion of the auxiliary pressure member was set to a high pressure, no image displacement occurred even when the fixing temperature was lowered by about 10 ° C.

  Further, the width in the sheet passing direction of the nip portion d formed by the auxiliary pressure member and the pressure roller member is 8.5 mm in the central portion and 8.0 mm in the end portion compared to the conventional central portion 7.5 mm and the end portion 9 mm. It can be seen that image displacement does not occur as the value increases.

  In the table, “x” indicates that there is an image shift in the reverse direction of the transfer material, and “◯” indicates that there is no image shift. The determination was made by visual confirmation using a loupe.

  FIG. 5 is a view showing another embodiment of the auxiliary pressure mechanism.

  FIG. 5A corresponds to a cross section taken along arrow AA in FIG. FIG.5 (b) has shown the DD arrow cross section of Fig.5 (a).

  5, the auxiliary pressure mechanism 46 presses the pressure roller 43 via the fixing belt 40 at substantially the same position as the auxiliary pressure mechanism 45 in FIG.

  The auxiliary pressure mechanism 46 includes a sponge 462, which is an auxiliary pressure member, a sponge support plate 463, a pressure plate 464, a support block 465 that holds the pressure plate 464, and a support frame body 466 that supports both ends of the support block 465. Etc. The support frame 466 is supported at both ends by a support shaft 467 supported by a frame 457 (see FIG. 3) of the fixing device 4, and can be rotated in the direction of the arrow w with the support shaft 467 as a fulcrum. Further, the support frame body 466 rotates counterclockwise by a pressing spring 470 that is hung on a spring hook pin 468 provided at both ends and a spring hook pin 469 fitted to the frame body 457. The force acts, and the sponge 462 presses the fixing belt 40 and the pressure roller 43.

  The pressing plate 464 is inserted between pins 46A that are attached to the sponge support plate 463 in two rows in the axial direction, abuts against the sponge support plate, presses the sponge 462 against the pressure roller 43, and supports the sponge. The plate 463 can perform a pendulum movement as indicated by an arrow u with a contact portion (line) with the pressing plate 464 as a fulcrum.

  The edge portion of the pressing plate 464 is formed in a curved shape so that a gap g between the center portion and both end portions that contact the sponge support plate 463 is formed, and in the embodiment, g = 0.3 mm. Therefore, when the sponge support plate 463 is pressed by the pressing spring 470, the pressing force against the pressure roller 43 at the central portion is maximized via the sponge 462, and both ends become smaller due to the bending of the sponge support plate 463. As a result, the pressure distribution on the pressure roller 43 is such that the central high pressure is low and the both ends are low pressure, and it has been confirmed by experiments that image displacement can be prevented and eliminated.

  Alternatively, due to the bending of the sponge support plate 463, the width in the sheet passing direction of the nip formed by the sponge 262 and the pressure roller member 43 is larger in the vicinity of the center than in the vicinity of both ends of the pressure roller member 43. Configure to be

  It has been confirmed through experiments that the above-described configuration can prevent and eliminate image shift.

  Note that it is preferable to cover the sponge 462 with a thin film having a low coefficient of friction such as PTFE (tetrafluoroethylene resin) and press the fixing belt 40 through the thin film, so that damage such as scratches on the belt can be avoided.

  Hereinafter, the confirmation experiment will be described.

Experimental conditions
Sponge support plate thickness: 2mm
Sponge thickness: 6mm
Sponge length: 350mm
Total pressing force between auxiliary pressure member and pressure roller: 150N
Fixing temperature: 140-200 ° C
Transfer material used (A): POD100 (Glossy paper for color PPC made by Oji Paper Co., Ltd., 100 g / m ² )
Used transfer material (C): X4024-28lb (plain paper for color PPC manufactured by Xerox, about 105 g / m ² )
The experimental results under the above conditions are shown in the table.

  From Table 2, it was confirmed that in both of the transfer materials (A) and (C), when the central portion of the auxiliary pressure member was set to a high pressure, no image displacement occurred even when the fixing temperature was lowered by about 10 ° C.

  Further, the width in the sheet passing direction of the nip portion d by the auxiliary pressurizing member is larger with the central portion of 8.0 mm and the end portion of 7.0 mm than the conventional central portion of 7.5 mm and the end portion of 8.5 mm. It can be seen that there is no image displacement.

  In the table, “x” indicates that there is an image shift in the reverse direction of the transfer material, and “◯” indicates that there is no image shift. The determination was made by visual confirmation with a loupe.

  Next, the image forming process will be described with reference to FIG.

  Simultaneously with the start of image recording, the photoconductor drive motor (not shown) starts to rotate the photoconductor 10 of the color signal Y in the counterclockwise direction indicated by the arrow, and at the same time, a potential is applied to the photoconductor 10 by the charging action of the scorotron charger 11. Is started.

  After the potential is applied to the photoconductor 10, the writing device 12 starts writing an image corresponding to the Y image data, and an electrostatic latent image corresponding to the Y image of the original image is formed on the surface of the photoconductor 10. Is done.

  The electrostatic latent image is reversely developed in a non-contact state by a Y developing device 13, and a Y toner image is formed on the photoconductor 10 as the photoconductor 10 rotates.

  The Y toner image formed on the photoconductor 10 is transferred onto the intermediate transfer belt 20 by the action of the Y transfer unit 25.

  Thereafter, the photosensitive member 10 is cleaned by the cleaning device 14 and enters the next image forming cycle (hereinafter, the same applies to the M, C, and K cleaning processes, and thus the description is omitted).

  Next, the writing device 12 performs image writing corresponding to an M (magenta) color signal, that is, M image data, and an electrostatic latent image corresponding to the M image of the original image is formed on the surface of the photoconductor 10. . The electrostatic latent image is converted into an M toner image on the photosensitive member 10 by the M developing unit 13, and is synchronized with the Y toner image on the intermediate transfer belt 20 by the M transfer unit 25. Is superimposed on the toner image.

  By a similar process, the Y and M superimposed toner images are synchronized, and the C (cyan) toner image is superimposed on the Y and M superimposed toner images by the C transfer unit 25. Further, synchronization with the Y, M, and C superimposed toner images is performed, and the K (black) toner image is superimposed on the Y, M, and C superimposed toner images in the K transfer device 25, A superimposed toner image of Y, M, C, and K is formed on the intermediate transfer belt 20.

  The intermediate transfer belt 20 carrying the superimposed toner image is fed clockwise as indicated by the arrow, and the transfer material P is fed from the paper cassette 72 by the paper feed roller 70, passes through the transport roller 73, and then the timing roller 71. The transfer roller 26 (to the intermediate transfer belt 20) to which the DC voltage having the opposite polarity to the toner is applied is synchronized with the superimposed toner image on the intermediate transfer belt 20 by driving the timing roller 71. The toner image is fed to the transfer area S in the contact state, and the superimposed toner image on the intermediate transfer belt 20 is transferred to the transfer material P.

  Thereafter, the intermediate transfer belt 20 travels, the charge of the residual toner is weakened by the neutralizing roller 27, and is cleaned by the cleaning blade 29 that is in contact with the intermediate transfer belt 20, and the next image forming cycle starts.

  The transfer material P onto which the superimposed toner image has been transferred is further sent to the fixing device 4, and is sandwiched and pressed between the belt support roller 41 and the pressure roller 43 via the fixing belt 40 to be fixed. The transfer material P on which the toner image has been melted and fixed is conveyed to a discharge tray 82 by a discharge roller 81.

1 is a schematic diagram illustrating an example of an overall configuration of an image forming apparatus. 4 is a schematic diagram showing a belt fixing mechanism and an auxiliary pressure mechanism. It is a figure which shows the AA arrow cross section of an auxiliary pressurization mechanism. It is an enlarged view (photograph) which shows the example of image gap. It is a figure which shows other embodiment of an auxiliary pressurization mechanism.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photoconductor 20 Intermediate transfer belt 4 Fixing device 40 Fixing belt 42 Heating roller 41 Belt support roller 43 Pressure roller 45, 46 Auxiliary pressure mechanism 451 Back plate 452, 462 Sponge 453, 463 Sponge support plate 45A, 45B Compression spring 464 Press plate 465 Support block 466 Support frame 470 Press spring

Claims (2)

A heating roller member having heating means, a support roller member disposed in parallel with and spaced from the heating roller member, a belt member stretched endlessly between the heating roller member and the support roller member, and A pressure roller member provided opposite to the support roller member via a belt member, and a second region in a region where the pressure roller member and the support roller member press each other via the belt member. An image forming apparatus having a belt fixing device that constitutes a first fixing step in a region where the pressure roller member and the belt member are in contact with each other except for the second fixing step. The portion that performs the first fixing step has a member that presses the pressure roller member via the belt member, and the sheet passing direction of the pressing member with respect to the pressure roller member is The image forming apparatus pressing force in a direction line, characterized in that the larger near the center than near both ends of the pressure roller member. A heating roller member having heating means, a support roller member disposed in parallel with and spaced from the heating roller member, a belt member stretched endlessly between the heating roller member and the support roller member, and A pressure roller member provided opposite to the support roller member via a belt member, and a second region in a region where the pressure roller member and the support roller member press each other via the belt member. An image forming apparatus having a belt fixing device that constitutes a first fixing step in a region where the pressure roller member and the belt member are in contact with each other except for the second fixing step. A nip formed by the pressure roller member of the pressing member having a member that presses the pressure roller member via the belt member at a portion where the first fixing step is performed. Image forming apparatus where the width of the sheet passing direction is equal to or greater in the vicinity of the center portion than near both ends of the pressure roller member.

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