JP3873969B2 - Color image forming apparatus - Google Patents

Description

  The present invention relates to a color image forming apparatus that feeds a sheet, forms an image on the sheet by an image forming unit, and fixes and discharges the image by a fixing device.

  In an electrophotographic image forming apparatus, a toner image is generally formed on a sheet and then fixed by a fixing device. An image to be formed includes a monochrome image and a color image, and a general color image forming apparatus has a monochrome mode and a color mode, and can form a monochrome image and a color image.

  Many color image forming apparatuses can form an image on an OHP sheet while forming an image on paper.

  When forming an image on an OHP sheet, particularly when forming a color image, the image needs to be light-transmitting, so that the conditions are different from those in other image forming modes such as a monochrome mode. An image is fixed, and specifically, a high-transparency image is formed by increasing the melting degree of toner forming the image.

  However, when the melting degree of the toner is increased, there is a problem that when the sheet comes into contact with the guide member immediately after fixing, the molten toner adheres to the guide member.

  An object of the present invention is to solve the above-described problem in a mode in which a color image is formed on an OHP sheet.

The object is achieved by the following invention.
(1) a fixing roller having a heat-resistant elastic layer, and a pressure roller that is in pressure contact with the fixing roller, and by pressing the fixing roller and the pressure roller, a nip portion is formed, and the fixing roller; In a color image forming apparatus having a fixing device that passes a sheet between pressure rollers and discharges the sheet from the nip portion in a direction away from the fixing roller side.
Wherein as the pressing roller is positioned on the side of the first guide member and Rutotomoni provided a switchable second guide member positioned in the fixing roller side, the toner adhering surface on said sheet is opposed to the second guide member A second guide member is disposed;
A color image forming apparatus having a fixing device, wherein when forming a color image on an OHP sheet, the second guide member is retracted from a sheet guide position.
(2) In the OHP mode in which color toner is fixed on the OHP sheet, the fixing speed is slower than that in the normal mode.

  According to the first aspect of the present invention, in the mode in which a color image is formed on the OHP sheet, the molten toner is prevented from adhering to the guide member, so that image smear and conveyance failure due to the toner adhering can be prevented well. .

  According to the invention of claim 2, a color image with high transparency is formed on the OHP sheet.

  FIG. 1 is a cross-sectional view showing a configuration of a color image forming apparatus which is an image forming apparatus using the fixing device of the present invention. An outline of a configuration and a series of operations will be described based on the drawings.

  For example, the photosensitive drum 10 as an image carrier having an OPC photosensitive layer coated on the surface thereof is driven and rotated at a linear speed of 75 mm / sec in one direction (clockwise in the figure), and the static eliminator 11 performs static elimination before. After the charge during printing is removed, the peripheral surface is uniformly charged by the charger 12 to prepare for a new print. After this uniform charging, the image exposure means 13 performs image exposure based on the image signal. The image exposure means 13 rotates and scans a laser beam emitted from a laser light source, which will be described later, by a rotary polygon mirror 131, bends an optical path by a reflection mirror 133 through an fθ lens 132 and the like, and is charged in advance. And a latent image is formed on the surface of the photosensitive drum 10.

  Development in which the periphery of the photosensitive drum 10 is filled with a developer composed of a mixture of toner such as yellow (Y), magenta (M), cyan (C), and black (K) and a magnetic carrier. The devices 14A, 14B, 14C, and 14D are provided. First, development of the first color is performed by a developing rotary sleeve 141 that contains a magnet and rotates while holding the developer. The developer is regulated to a predetermined thickness on the developing rotary sleeve 141 by the layer forming rod and conveyed to the developing area. An AC bias voltage VAC and a DC bias voltage VDC are superimposed and applied between the photosensitive drum 10 and the developing rotary sleeve 141. Here, the potential of the exposed portion of the photosensitive drum 10 is VL, the surface potential of the charged photosensitive layer other than the exposed portion is VH, and the DC bias voltage VDC is | VH |> | VDC |> | VL | By setting so as to be established, the toner that has been triggered to leave the carrier by the AC bias voltage VAC does not adhere to the VH portion having a higher potential than VDC, but to the exposed portion of the potential VL having a lower potential than VDC. It adheres, is visualized and developed.

  After the development of the first color is completed in this way, the second color (for example, magenta) image forming process is started, the photosensitive drum 10 is uniformly charged again, and the latent image based on the second color image data becomes the image exposure means 13. Formed by. For the third color (cyan) and the fourth color (black), an image forming process similar to that for the second color is performed, and a total of four colors are developed on the photosensitive drum 10.

  Four toner replenishing devices 40 are provided to supply toner to yellow (Y), magenta (M), cyan (C), and black (K), respectively. The toner supply pipe 45 is supplied to the apparatus 14B, the toner supply pipe 46 is supplied to the developing apparatus 14C, and the toner supply pipe 47 is supplied to the developing apparatus 14D from the toner supply apparatus 40. On the other hand, the recording paper P, which is a transfer material fed by the paper feeding mechanism 22 by the paper feeding cassette 21, is guided by the recording paper guiding means 211, the recording paper P is detected by the detection member S, and is conveyed to the transport roller 221. And is fed to a nip portion (transfer area) 35 formed between the photosensitive drum 10 and the transfer belt 31 by the transfer belt device 30 that stretches the transfer belt 31. The multicolor images formed on the surface are transferred to the recording paper P all at once. Here, a high voltage is applied to the shaft 32 a of the upstream holding roller 32 of the transfer belt 31, and the conductive brush 34 placed at a position facing the shaft 32 a across the transfer belt 31 is grounded. The fed recording paper P enters between the brush 34 and the transfer belt 31 and enters the transfer area while being attracted to the transfer belt 31 by the electric charge injected into the recording paper P from the brush 34. The recording paper P separated from the photosensitive drum 10 is separated from the transfer belt 31 while being neutralized by using the shaft 33b of the holding roller 33 on the downstream side of the transfer belt 31 as a counter electrode. The toner attached to the transfer belt 31 is removed by the cleaning blade 37. Note that the transfer belt 31 is separated from the photosensitive drum 10 around the shaft 33b of the holding roller 33 on the downstream side during the formation of a multicolor image.

  The recording paper P separated from the transfer belt device 30 has a heating heater 232 in at least one of the pressure contact rollers 231 and receives heat from the pressure contact roller 231 to fix the toner image on the recording paper P. The toner image on the recording paper P is melted and fixed by being conveyed to the fixing device 23 constituted by the roller 233 and applying heat and pressure between the pressure contact roller 231 and the heat fixing roller 233. In the case of discharging from the first discharge roller 235 to the outside of the apparatus, the discharge switching unit 234 discharges the sheet to the discharge tray 237 via the second discharge roller 236 provided on the upper part of the image forming apparatus 100. The recording paper P can be reversed and discharged by switching.

  The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is discharged by the static eliminator 15, reaches the cleaning device 16, and is scraped off into the cleaning device 16 by the cleaning blade 16 a contacting the photosensitive drum 10. Then, it is carried out by a screw or the like and stored in a collection box. The photosensitive drum 10 from which the residual toner is removed by the cleaning device 16 is discharged by the charge remover 11 and then uniformly charged by the charger 12 and enters the next image forming cycle. Further, if the recording paper P is not separated from the transfer belt 31 but is wound around the photosensitive drum 10 and enters above the static eliminator 15, the cleaning blade 16a and the electrode wire may be damaged. A jam sensor 36 that detects winding is mounted in the vicinity of the static eliminator 15.

  FIG. 2 shows a fixing device 23 and a discharge guide device for the recording paper P. As described above, the pressure roller 231 having the heater 232 inside forms the fluororesin layer 231B on the surface of the metal roller 231A. The heat fixing roller 233 covers the outer periphery of the core shaft 233A with silicon rubber 233B, and further forms a fluororesin layer 233C on the surface. By press-bonding the pressure roller 231 and the heat fixing roller 233 formed as described above, a nip 233D having a width L is formed in the pressure-bonding portion on the heat fixing roller 233 side. As the crimping means, an elastic member such as a spring is used. 231C and 233E are cleaning members for cleaning the pressure roller 231 and the surface of the heat fixing roller 233. When fixing the recording paper P onto which the multicolor image is transferred from the photosensitive drum 10 with the fixing device 23 configured as described above, the pressure roller 231 is heated to the fixing temperature by the heater 232, The surface of the heat fixing roller 233 is heated by the heated pressure roller 231. When the surface of the heat fixing roller 233 reaches the fixable temperature, the image forming apparatus 100 can be operated, and the recording paper P enters the fixing device 23 as described above to start fixing. As described above, a nip 233D having a width L is formed on the surface of the heat fixing roller 233, and the toner of the multicolor image is melted and fixed in the process of passing through the nip 233D. Reference numeral 24 denotes a lower separation claw provided on the paper discharge side of the pressure roller 231. The lower separation claw 24 is rotatably supported by a shaft 241 and the separation tip 242 is a center point of the pressure roller 231. The surface is in contact with the surface of the pressure roller 231 at a position of a central axis Y passing through O1 and an angle X forming an angle θ on the paper discharge side from the central point O1. The angle θ is a maximum angle of 28 °, and is preferably set to 28 ° or less. In order to keep the separation claw 24 in contact with the separation tip 242 and the surface of the pressure roller 231 at all times, the separation claw 24 is pressed by a spring 243 toward the surface of the pressure roller 231, and the other end of the lower separation claw 24 is stoppered 244. To prevent and maintain a predetermined position. A guide surface 245 for guiding the recording paper P is formed in the paper discharge direction of the recording paper P from the separation leading end 242 of the lower separation claw 24. On the other hand, an upper separation claw 246 is also provided on the paper discharge side of the heat fixing roller 233 so that the tip is brought into contact with the urging member. Further, as shown in FIG. 3, the lower separation claw 24 is provided side by side on both sides with the lower separation claw 24 as a center to provide a plurality of lower separation claws 24A and 24B, and the separation tips of the lower separation claws 24A and 24B are provided. The parts 242 A and 242 B are provided so as to recede by L1 width from the separation tip 242 of the lower separation claw 24 and to contact the pressure roller 231.

  The recording paper P1 that has been fixed is bent downward by a nip 233D formed on the surface of the heat fixing roller 233 and is about to be discharged. However, the leading edge of the recording paper P1 is immediately pressed against the pressure at the separation leading edge 242. Since the recording paper P1 is separated from the surface of the roller 231 and is smoothly guided along the guide surface 245 of the lower separation claw 24, the recording paper P1 is discharged without causing any irregularity. However, since the recording paper P1 to be discharged has a curved ridge slightly downward at the nip 233D, upper and lower discharge guide plates 25 and 251 are provided along the discharge direction of the recording paper P1. S1 is a paper discharge detection member, which detects the paper discharge state of the recording paper P1 by the operation of the operation member S2 that operates by paper discharge conveyance of the recording paper P1. The recording paper P1 to be discharged and conveyed is guided by the discharge switching unit 234 shown in FIG. 1 and discharged from the first discharge roller 235, and if necessary, the discharge switching unit 234. The recording paper P1 can be reversed and discharged from the second discharge roller 236 to the discharge tray 237 via the transport roller 26.

  In FIG. 4, when the angle θ is plotted on the horizontal axis and the incidence rate (%) is plotted on the vertical axis, the angle θ of the separation tip 242 and the incidence rate are measured. It can be seen that when the angle is around 28 °, the occurrence rate of looseness is almost 0%, and when the angle exceeds 30 °, the incidence rate of looseness is close to 100%.

  As a specific configuration of the fixing device 23, the pressure roller 231 has a thickness of 3 mm of the metal roller 231A and an inner surface is coated with heat resistant paint (black). The layer thickness of the fluororesin layer 231B formed on the surface of the metal roller 231A is 15 to 25 μm. The heat fixing roller 233 has a hardness of silicon rubber 233B of 18 °. The thickness of the fluororesin layer 233C is 50 μm, and each layer has a hardness of 56 °. The fixing speed is 74.4 mm / sec during normal fixing. In this case, the pressure roller 231 rotates at 48.16 rpm, and the heat fixing roller 233 rotates at 48.1 rpm even when slipping. . The fixing temperature is set to 190 ° C. for the pressure roller 231 and 150 ° C. for the heat fixing roller 233. When the pressure roller 231 is pressed against the heat fixing roller 233 (1.13 kg / cm), the width of the nip 233D is 5 to 6 mm.

  FIG. 5 shows another embodiment of the fixing device 23 and a recording paper discharge device. FIG. 5 is a diagram in which a movable recording paper guiding rotation member is provided in the paper discharge section of the fixing device 23.

  Also in this embodiment, the fixing device 23 has the same configuration as that described with reference to FIG. A discharge guide device for the recording paper P together with the fixing device 23 is shown. As shown in FIG. 4, the pressure roller 231 having a heater 232 inside forms a fluororesin layer 231B on the surface of the metal roller 231A. The heat fixing roller 233 covers the outer periphery of the core shaft 233A with silicon rubber 233B, and further forms a fluororesin layer 233C on the surface. By pressing the pressure contact roller 231 and the heat fixing roller 233 formed as described above, a nip 233D is formed at the pressure-bonding portion on the heat fixing roller 233 side. As the crimping means, an elastic member such as a spring is used. 231C and 233E are cleaning members for cleaning the pressure roller 231 and the surface of the heat fixing roller 233. When fixing the recording paper P onto which the multicolor image is transferred from the photosensitive drum 10 with the fixing device 23 configured as described above, the pressure roller 231 is heated to the fixing temperature by the heater 232, The surface of the heat fixing roller 233 is heated by the heated pressure roller 231. When the surface of the heat fixing roller 233 reaches the fixable temperature, the image forming apparatus 100 can be operated, and the recording paper P enters the fixing device 23 as described above to start fixing. As described above, the nip 233D is formed on the surface of the heat fixing roller 233, and the toner of the multicolor image is melted and fixed in the process of passing through the portion of the nip 233D. Reference numeral 24 denotes a lower separation claw provided on the paper discharge side of the pressure roller 231. The lower separation claw 24 is rotatably supported by a shaft 241 and is provided with a separation tip 242 provided on the lower separation claw 24. Is in contact with the surface of the pressure roller 231 at a position of a central axis Y passing through the center point O1 of the pressure roller 231 and an angle X that forms an angle θ on the paper discharge side from the center point O1. The angle θ is a maximum angle of 40 °, and is preferably set to 40 ° or less. In order to keep the separation tip 242 in contact with the surface of the pressure roller 231 at all times, it is pressed in the direction of the surface of the pressure roller 231 by a spring 243 and the other end of the lower separation claw 24 is blocked by a stopper 244 to be predetermined. Maintaining position. On the other hand, an upper separation claw 246 is also provided on the paper discharge side of the heat fixing roller 233 by being urged by an elastic member. Also in the present embodiment, the lower separation claw 24 is provided side by side on both sides with the lower separation claw 24 in the same manner as in FIG. The separation tips 242 A and 242 B of 24 A and 24 B are provided so as to recede by L1 width from the separation tip 242 of the lower separation claw 24 and contact the pressure roller 231.

  The recording sheet P1 that has been fixed is bent downward by the nip 233D formed on the surface of the heat fixing roller 233 and is about to be discharged. However, the leading edge of the recording sheet P1 is immediately pushed out by the separation leading edge 242. The paper is separated from the surface of the pressure roller 231 and discharged. Since the discharged recording paper P1 has a curved ridge slightly downward at the nip 233D, the recording paper P1 is discharged toward the lower side of the nip. First, the leading edge of the recording paper P1 hits the discharge guide plate 25, and the leading edge The guides are sequentially bent in the paper discharge direction. Next, as shown in FIG. 6, the paper is guided between the paper guide rotating member 27 provided at a constant interval L2 (1.5 mm or less, preferably 1 mm or less) on the paper discharge guide plate 25, and then discharged. Guide and transport in the paper direction. The recording paper guiding rotation member 27 is provided at the tip of a support plate 271 supported by a support shaft 273 so as to be rotatable by the support shaft 273. First, the recording paper P1 is ejected in a horizontal state by the action of the waist of the recording paper P1, and then the recording paper P1 is deformed and guided downward by the recording paper guiding rotating member 27 sequentially from the leading edge of the recording paper P1, thereby stabilizing the recording paper P1. Therefore, since the vertical movement is suppressed, the recording paper P1 does not have a loose state.

  S1 is a paper discharge detection member, which detects the paper discharge state of the recording paper P1 by the operation of the operation member S2 that operates by paper discharge conveyance of the recording paper P1. The recording paper P1 to be discharged and conveyed is guided by the discharge switching unit 234 shown in FIG. 1 and discharged from the first discharge roller 235, and if necessary, the discharge switching unit 234. The recording paper P1 can be reversed and discharged from the second discharge roller 236 to the discharge tray 237 via the transport roller 26.

  In FIG. 7, the horizontal axis indicates the interval L2 (unit: mm) between the paper discharge guide plate 25 and the recording paper guide rotating member 27 shown in FIG. 6, and the vertical axis indicates the occurrence rate (%). As a result, when the distance L2 is 1 mm, the occurrence rate of flutter at the leading edge of the recording paper P1 is 0%, and even when the distance is 1.5 mm, the occurrence rate is 10% or less and the occurrence rate is extremely low. I understand.

  FIG. 8 is a perspective view of the paper discharge guide plate 25 and the recording paper guide rotation member 27. One end of the shaft 272 of the support plate 271 provided with the recording paper guide rotation member 27 is operated as shown in the figure. A lever 273 is provided, and a solenoid 274 is connected to the other end of the operating lever 2731. By actuating the solenoid 274, the recording paper guide rotating member 27 can be raised and separated from the paper discharge guide plate 25 via the operating lever 2731 and the support plate 271. Further, as shown in the figure, a plurality of recording paper guiding rotating members 27 are provided in parallel at a constant interval.

  FIG. 9 shows an embodiment in which the recording paper guiding rotating member 27 shown in FIG. 5 is moved to the upper position. In this embodiment, an OHP sheet P3 is used as the recording paper, and the OHP sheet P3 in the image forming apparatus 100 is guided by the recording paper guiding means 211 and is detected by the detection member S as the OHP sheet P3. Is done. In the image forming apparatus 100, the multicolor image is transferred onto the OHP sheet P 3 by the image forming process described with reference to FIG. Also in this embodiment, the fixing device 23 has the same configuration as that described with reference to FIG. A discharge guide device for the OHP sheet P3 together with the fixing device 23 is shown. As shown in FIG. 9, the pressure roller 231 having a heater 232 inside forms a fluororesin layer 231B on the surface of the metal roller 231A. The heat fixing roller 233 covers the outer periphery of the core shaft 233A with silicon rubber 233B, and further forms a fluororesin layer 233C on the surface. By pressing the pressure contact roller 231 and the heat fixing roller 233 formed as described above, a nip 233D is formed at the pressure-bonding portion on the heat fixing roller 233 side. As the crimping means, an elastic member such as a spring is used. 231C and 233E are cleaning members for cleaning the pressure roller 231 and the surface of the heat fixing roller 233. When fixing the OHP sheet P3 onto which the multicolor image is transferred from the photosensitive drum 10 with the fixing device 23 configured as described above, the pressure roller 231 is heated to the fixing temperature by the heater 232, and The surface of the heat fixing roller 233 is heated by the heated pressure roller 231. When the surface of the heat fixing roller 233 reaches the fixable temperature of the OHP sheet P3, the image forming apparatus 100 can be operated, and the OHP sheet P3 enters the fixing apparatus 23 as described above to start fixing. As described above, the nip 233D is formed on the surface of the heat fixing roller 233, and the toner of the multicolor image is melted and fixed in the process of passing through the portion of the nip 233D. Reference numeral 24 denotes a lower separation claw provided on the paper discharge side of the pressure roller 231. The lower separation claw 24 is rotatably supported by a shaft 241 and is provided with a separation tip 242 provided on the lower separation claw 24. Is in contact with the surface of the pressure roller 231 at a position of a central axis Y passing through the center point O1 of the pressure roller 231 and an angle X that forms an angle θ on the paper discharge side from the center point O1. For example, the angle θ is set to 40 °. In order to keep the separation tip 242 in contact with the surface of the pressure roller 231 at all times, it is pressed in the direction of the surface of the pressure roller 231 by a spring 243 and the other end of the lower separation claw 24 is blocked by a stopper 244 to be predetermined. Maintaining position. On the other hand, an upper separation claw 246 is also provided on the paper discharge side of the heat fixing roller 233 so as to be urged by an elastic member. Also in the present embodiment, the lower separation claw 24 is provided in parallel with the lower separation claw 24 at the center and provided with lower separation claws 24A and 24B on both sides in the same manner as in FIG. The separation tips 242 A and 242 B of 24 A and 24 B are provided so as to recede by L1 width from the separation tip 242 of the lower separation claw 24 and contact the pressure roller 231.

  When transferring color toner on the OHP sheet P3, the OHP sheet P3 needs to be transparent, and the fixing device 23 is operated at a speed lower than the fixing speed of the recording P1. Although not shown, the low speed operation may be switched by using a speed switching means, or may be automatically performed by developing with color toner and detecting the OHP sheet P3. In this way, the color toner of the OHP sheet P3 discharged from the fixing device 23 at low speed is in a molten state without being cured. When the recording paper guiding rotation member 27 comes into contact therewith, the molten color toner is The sheet is retracted because it adheres to the surface of the OHP sheet P4 that has been fixed by way of the recording paper guide rotating member 27. However, in the case of monochrome that does not require transparency, the front recording paper guiding rotation member 27 is retracted to the position shown in FIG. 9 in order to perform heat fixing at the same speed as the fixing speed of the recording P1 in order to improve performance. Since the paper discharge guide portion becomes wider and jamming is likely to occur, the front recording paper guide rotation member 27 is switched to a position close to the OHP sheet P1 as shown in FIG.

  In the OHP mode for fixing color toner, the fixing speed is 12.4 mm / sec, which is 1/6 of the normal mode of 74.4 mm / sec. The fixing temperature is the pressure roller 231. Is set at 195 ° C., and the heat fixing roller 233 is set at 145 ° C. for fixing.

  S1 is a discharge detection member, which detects the discharge state of the OHP sheet P4 by the operation of the operation member S2 that is operated by discharging the OHP sheet P4. The OHP sheet P4 to be discharged and conveyed is guided by the discharge switching unit 234 shown in FIG. 1 and discharged from the first discharge roller 235, and if necessary, the discharge switching unit 234. The OHP sheet P4 can be reversed and discharged from the second discharge roller 236 to the discharge tray 237 via the transport roller 26.

1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus embodying the present invention. 1 is a longitudinal sectional view of a fixing device of the present invention. FIG. 3 is a plan view showing a pressure roller in the fixing device of the present invention. Explanatory drawing which shows the angle of incidence of the present invention and the angle of the separation claw tip. FIG. 6 is a longitudinal sectional view showing another embodiment of the fixing device of the present invention. FIG. 3 is a front view showing a gap between a recording paper guide rotating member and a paper discharge guide plate in the present invention. Explanatory drawing which shows the relationship between the loose incidence in the present invention, and the gap. FIG. 7 is an exploded perspective view showing a recording paper guide rotation member and a paper discharge guide plate in FIG. 6. FIG. 6 is a longitudinal sectional view showing another embodiment of the fixing device of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photosensitive drum 12 Charger 13 Image exposure means 14A, 14B, 14C, 14D Developing device 31 Transfer belt 141, 111 Developing rotary sleeve 143, 211 Magnetic pole 23 Fixing device 231 Pressing roller 233 Thermal fixing roller 24 Lower separation claw 25 Exhaust Paper guide plate 27 Rotating member for recording paper guide 100 Image forming apparatus

Claims (2)

A fixing roller having a heat-resistant elastic layer; and a pressure contact roller that is in pressure contact with the fixing roller, and presses the fixing roller and the pressure contact roller to form a nip portion between the fixing roller and the pressure contact roller. A color image forming apparatus having a fixing device that passes the sheet through the nip portion and discharges the sheet in a direction away from the fixing roller side.
Wherein as the pressing roller is positioned on the side of the first guide member and Rutotomoni provided a switchable second guide member positioned in the fixing roller side, the toner adhering surface on said sheet is opposed to the second guide member A second guide member is disposed;
A color image forming apparatus having a fixing device, wherein when forming a color image on an OHP sheet, the second guide member is retracted from a sheet guide position. 2. The color image forming apparatus having a fixing device according to claim 1, wherein an OHP mode in which color toner is fixed on an OHP sheet has a slower fixing speed than in the normal mode.

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