JP2004145360A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem that molten toner may stick to a guide member as a high fixing degree is needed when forming a color image on an OHP sheet. <P>SOLUTION: The color image forming apparatus is provided with a switchable guide member which guides a sheet after fixing. Under a mode in which an image is formed on an OHP sheet with color toner, the color image forming apparatus retracts the guide member. <P>COPYRIGHT: (C)2004,JPO

Description

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

(2) 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.

In addition, many color image forming apparatuses can form an image on paper and also can form an image on an OHP sheet.

When an image is formed on an OHP sheet, particularly when a color image is formed, it is necessary that the image be light-transmissive. Fixing an image is performed. Specifically, the degree of melting of the toner forming the image is increased to form an image with high transparency.

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

The object of the present invention is to solve the above-mentioned problem in a mode for forming a color image on an OHP sheet.

The above object is achieved by the following invention.
(1) a fixing roller having a heat-resistant elastic layer, and a pressure roller that presses against the fixing roller, and a nip portion is formed by pressing the fixing roller and the pressure roller to form a nip portion; In a color image forming apparatus having a fixing device that causes a sheet to pass between pressure contact rollers and discharges the sheet from the nip portion in a direction away from the fixing roller side,
A first guide member located on the pressure roller side and a switchable second guide member located on the fixing roller side;
When a color image is formed on an OHP sheet, the second guide member is retracted from a sheet guide position.
(2) The color image forming apparatus having the fixing device according to (1), wherein the fixing speed is lower in the OHP mode for fixing the color toner on the OHP sheet than in the normal mode.

According to the first aspect of the present invention, in the mode of forming a color image on the OHP sheet, the fused toner is prevented from adhering to the guide member, so that image contamination and defective conveyance due to such toner adhesion are favorably prevented. .

According to the invention of claim 2, a color image having 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 the configuration and a series of operations will be described based on the drawings.

For example, a photosensitive drum 10 as an image carrier having an OPC photosensitive layer applied on its surface is driven and rotated at a linear speed of 75 mm / sec in one direction (clockwise in the figure). 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 unit 13 performs image exposure based on the image signal. The image exposure means 13 is rotated and scanned by a rotary polygon mirror 131 with laser light emitted from a laser light source to be described later, the optical path of which is bent by a reflection mirror 133 through an fθ lens 132 and the like, and the charged photosensitive drum 10 is charged in advance. And a latent image is formed on the surface of the photosensitive drum 10.

The peripheral edge of the photosensitive drum 10 is filled with a developer composed of a mixture of a toner such as yellow (Y), magenta (M), cyan (C), and black (K) and a carrier having magnetic properties. The devices 14A, 14B, 14C, and 14D are provided. First, the development of the first color is performed by a developing rotary sleeve 141 that includes a magnet and rotates while holding a developer. The developer is conveyed to the developing area while being regulated to a predetermined thickness on the developing rotary sleeve 141 by the layer forming rod. 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 which has been triggered to be separated from the carrier by the AC bias voltage VAC does not adhere to the VH portion having a higher potential than VDC, and does not adhere to the exposed portion having the potential VL having a lower potential than VDC. Attached, visualized and developed.

After the development of the first color has been completed in this way, the image forming process of the second color (for example, magenta) is started, the photosensitive drum 10 is uniformly charged again, and the latent image based on the image data of the second color is exposed to the image exposure unit 13. Formed by For the third color (cyan) and the fourth color (black), the same image forming process as 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 for supplying toner to the yellow (Y), magenta (M), cyan (C), and black (K), respectively. The toner replenishing tube 45 is supplied to the device 14B, the toner replenishing tube 46 is supplied to the developing device 14C, and the toner replenishing tube 47 is supplied to the developing device 14D. On the other hand, the recording paper P, which is the transfer material fed by the paper feeding mechanism 22 from the paper feeding cassette 21, is guided by the recording paper guiding means 211, the recording paper P is detected by the detecting member S, and Is transferred to a nip portion (transfer area) 35 formed between the photosensitive drum 10 and the transfer belt 31 by a transfer belt device 30 having a transfer belt 31 stretched thereon. The multicolor image formed on the surface is transferred to the recording paper P at a time. Here, a high voltage is applied to the shaft 32a of the upstream holding roller 32 of the transfer belt 31, and the conductive brush 34 installed at a position facing the shaft 32a with the transfer belt 31 interposed therebetween is grounded. Then, 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 photoreceptor drum 10 is separated from the transfer belt 31 while being neutralized by using the shaft 33b of the downstream holding roller 33 on which the transfer belt 31 is stretched as a counter electrode. The toner adhered 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 the multicolor image.

The recording paper P separated from the transfer belt device 30 has a heating heater 232 inside at least one pressure roller 231 and receives heat from the pressure roller 231 to fix the toner image on the recording paper P. The toner image on the recording paper P is conveyed to the fixing device 23 composed of a roller 233, and heat and pressure are applied between the pressing roller 231 and the heat fixing roller 233, so that the toner image is fused and fixed. In the case where the sheet is discharged from the first sheet discharging roller 235 to the outside of the apparatus as it is, the sheet discharge switching means 234 causes the sheet to be discharged to the sheet discharge tray 237 via the second sheet discharging roller 236 provided in the upper part of the image forming apparatus 100. By switching, the recording paper P can be inverted and discharged.

The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the static eliminator 15, reaches the cleaning device 16, and is scraped 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 has been removed by the cleaning device 16 is neutralized by the neutralizer 11 and then uniformly charged by the charger 12 to start the next image forming cycle. Further, if the recording paper P is not separated from the transfer belt 31 and 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 for detecting winding is mounted near the static eliminator 15.

FIG. 2 shows the fixing device 23 and the paper ejection guide device for the recording paper P. The pressing roller 231 having the heating heater 232 therein as described above forms the fluororesin layer 231B on the surface of the metal roller 231A. Further, 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 pressing roller 231 and the heat fixing roller 233 formed as described above to each other, a nip 233 </ b> D having a width L is formed at a pressing portion on the side of the heat fixing roller 233. An elastic member such as a spring is used as the crimping means. 231C and 233E are cleaning members for cleaning the pressing roller 231 and the surface of the heat fixing roller 233. When fixing the recording paper P onto which the multicolor image has been transferred from the photosensitive drum 10 by the fixing device 23 configured as described above, the pressing roller 231 is heated to the fixing temperature by the heating heater 232, The surface of the heat fixing roller 233 is heated by the heated pressure contact roller 231. When the surface of the heat fixing roller 233 reaches the fixing temperature, the operation of the image forming apparatus 100 is enabled, and the recording paper P enters the fixing device 23 as described above to start fixing. As described above, the nip 233D having the width L is formed on the surface of the heat fixing roller 233, and the toner of the multicolor image is melted and fixed while passing through the nip 233D. Reference numeral 24 denotes a lower separation claw provided on the paper discharge side of the pressing roller 231. The lower separation claw 24 is rotatably supported by a shaft 241, and a separating tip 242 is provided at a center point of the pressing roller 231. It is in contact with the surface of the pressure contact 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. The separating claw 24 is pressed by a spring 243 in the direction of the pressing roller 231 in order to always maintain contact between the separating tip 242 and the surface of the pressing roller 231, and the other end of the lower separating claw 24 is stopped by a stopper 244. And maintain the predetermined position. Further, a guide surface 245 for guiding the recording paper P is formed in the discharge direction of the recording paper P from the separation tip 242 of the lower separation claw 24. On the other hand, an upper separating claw 246 is also provided on the paper discharge side of the heat fixing roller 233 so that the leading end thereof is brought into contact with an urging member. 3, a plurality of lower separating claws 24A, 24B are provided side by side on the lower separating claw 24 as shown in FIG. The portions 242 # A and 242 # B are provided so as to be retracted by the width L1 from the separation tip 242 of the lower separation claw 24 and to be in contact with the pressing roller 231.

The recording paper P1 on which the fixing has been completed is curved downward at the nip 233D formed on the surface of the heat fixing roller 233 and is about to be discharged. 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, so that the recording paper P1 is discharged without causing an irregular state. However, since the recording paper P1 to be discharged has a curl slightly downward at the nip 233D, the paper discharge guide plates 25, 251 provided above and below are provided along the paper discharge direction of the recording paper P1. S1 is a paper discharge detection member, which detects a paper discharge state of the recording paper P1 by the operation of an operation member S2 which is operated by the discharge conveyance of the recording paper P1. The recording paper P1 to be discharged and conveyed is guided by the discharge switching means 234 shown in FIG. 1 and discharged out of the apparatus from the first discharge roller 235, and if necessary, the discharge switching means 234. And the recording paper P1 can be inverted and discharged onto the discharge tray 237 from the second discharge roller 236 via the transport roller 26.

In FIG. 4, the horizontal axis represents the angle θ, and the vertical axis represents the generation rate (%) of the ribs. When the angle θ of the separation tip 242 and the generation rate of the rosettes are measured, the angle θ of the separation tip 242 is measured. When the angle is around 28 °, the generation rate of the rubbing is 0% and hardly occurs. When the angle exceeds 30 °, the generation rate of the rubbing becomes close to 100%.

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

FIG. 5 shows another embodiment of the fixing device 23 and the recording paper discharging device. FIG. 5 shows a configuration in which a movable recording sheet guide rotating member is provided in the sheet discharge section of the fixing device 23.

定 着 Also in this embodiment, the fixing device 23 has the same configuration as that described with reference to FIG. 2 shows a paper ejection guide device for the recording paper P together with the fixing device 23. As shown in FIG. 4, the pressing roller 231 having a heater 232 therein has a fluororesin layer 231B formed on the surface of a metal roller 231A. Further, 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 pressing roller 231 and the heat fixing roller 233 formed as described above to each other, a nip 233 </ b> D is formed at a pressing portion on the heat fixing roller 233 side. An elastic member such as a spring is used as the crimping means. 231C and 233E are cleaning members for cleaning the pressing roller 231 and the surface of the heat fixing roller 233. When fixing the recording paper P onto which the multicolor image has been transferred from the photosensitive drum 10 by the fixing device 23 configured as described above, the pressing roller 231 is heated to the fixing temperature by the heating heater 232, The surface of the heat fixing roller 233 is heated by the heated pressure contact roller 231. When the surface of the heat fixing roller 233 reaches the fixing temperature, the operation of the image forming apparatus 100 is enabled, 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 while passing through the nip 233D. Reference numeral 24 denotes a lower separation claw provided on the paper discharge side of the pressing roller 231. The lower separation claw 24 is rotatably supported by a shaft 241 and a separation tip 242 provided on the lower separation claw 24. Is in contact with the surface of the pressure contact roller 231 at a position of an angle X that forms an angle θ on the paper discharge side from the center point O1 with respect to the central axis Y passing through the center point O1 of the pressure contact roller 231. The angle θ is a maximum angle of 40 °, and is preferably set to 40 ° or less. In order to always maintain the separation tip 242 in contact with the pressure roller 231, the separation tip 242 is pressed in the direction 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. Maintain position. On the other hand, an upper separating 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 separating claws 24A and 24B are provided side by side on the lower separating claw 24 as in FIG. Separation front ends 242 # A and 242 # B of 24A and 24B are provided so as to be retracted from the separation front end 242 of the lower separation claw 24 by L1 width and contact the pressing roller 231.

The recording paper P1 that has completed the fixing is bent downward at the nip 233D portion formed on the surface of the heat fixing roller 233 and is about to be discharged. However, the leading end of the recording paper P1 is immediately The sheet is separated from the pressing roller 231 and discharged. The discharged recording paper P1 has a curving tendency slightly downward at the nip 233D, and is discharged downward as it is. First, the leading end of the recording paper P1 hits the paper discharge guide plate 25, and The sheet is guided in a manner sequentially bent in the sheet discharging direction. Next, as shown in FIG. 6, the recording paper guide plate 25 is inserted between the recording paper guide rotating member 27 provided at a predetermined interval L2 (1.5 mm or less, preferably 1 mm or less) on the paper ejection guide plate 25 and ejected. It is guided and transported in the paper direction. The recording paper guide rotating member 27 is provided at the tip of a support plate 271 supported by a support shaft 273 so as to be rotatable about the support shaft 273. First, the recording paper P1 is ejected in a horizontal state by the action of the waist, and then the recording paper P1 is deformed and guided downward by the recording paper guiding rotating member 27 sequentially from the leading end of the recording paper P1, so that the recording paper P1 has a stable force. As a result, the vertical movement is suppressed, so that the recording paper P1 does not have an irregular 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 which is operated by the paper discharge of the recording paper P1. The recording paper P1 to be discharged and conveyed is guided by the discharge switching means 234 shown in FIG. 1 and discharged out of the apparatus from the first discharge roller 235, and if necessary, the discharge switching means 234. And the recording paper P1 can be inverted and discharged onto the discharge tray 237 from the second discharge roller 236 via the transport roller 26.

In FIG. 7, the horizontal axis represents the distance L2 (unit: mm) between the paper discharge guide plate 25 and the recording paper guiding rotary member 27 shown in FIG. 6, and the vertical axis represents the occurrence of rubbing (%). As a result, when the distance L2 was 1 mm, the occurrence rate of the irregularities at the leading end of the recording paper P1 was 0%, and even at 1.5 mm, the occurrence rate of the irregularities was 10% or less, and the occurrence rate was extremely small. I understand.

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

FIG. 9 is an embodiment showing a state in which the rotating member 27 for guiding the recording paper shown in FIG. 5 is operated to the upper position. In this embodiment, an OHP sheet P3 is used as a recording sheet. The OHP sheet P3 in the image forming apparatus 100 is guided by the recording sheet guide means 211, and the detection member S detects that the OHP sheet P3 is used. Is done. Then, in the image forming apparatus 100, the multicolor image is transferred onto the OHP sheet P3 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. 2 shows a paper ejection guide device for the OHP sheet P3 together with the fixing device 23. As shown in FIG. 9, the pressing roller 231 having a heater 232 inside has a fluororesin layer 231B formed on the surface of a metal roller 231A. Further, 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 pressing roller 231 and the heat fixing roller 233 formed as described above to each other, a nip 233 </ b> D is formed at a pressing portion on the heat fixing roller 233 side. An elastic member such as a spring is used as the crimping means. 231C and 233E are cleaning members for cleaning the pressing roller 231 and the surface of the heat fixing roller 233. When fixing the OHP sheet P3 onto which the multicolor image has been transferred from the photosensitive drum 10 by the fixing device 23 configured as described above, the pressing roller 231 is heated to the fixing temperature by the heating heater 232, The surface of the heat fixing roller 233 is heated by the heated pressure contact roller 231. When the surface of the heat fixing roller 233 reaches the temperature at which the OHP sheet P3 can be fixed, the operation of the image forming apparatus 100 becomes possible, and the OHP sheet P3 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 while passing through the nip 233D. Reference numeral 24 denotes a lower separation claw provided on the paper discharge side of the pressing roller 231. The lower separation claw 24 is rotatably supported by a shaft 241 and a separation tip 242 provided on the lower separation claw 24. Is in contact with the surface of the pressure contact roller 231 at a position of an angle X that forms an angle θ on the paper discharge side from the center point O1 with respect to the central axis Y passing through the center point O1 of the pressure contact roller 231. For example, the angle θ is set to 40 °. In order to always keep the separation tip 242 in contact with the surface of the pressure roller 231, the tip 242 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. Maintain position. On the other hand, an upper separating claw 246 is also provided on the paper discharge side of the heat fixing roller 233 so as to be biased by an elastic member. Also, in the present embodiment, the lower separating claw 24 is provided in parallel with the lower separating claw 24 as shown in FIG. Separation front ends 242 # A and 242 # B of 24A and 24B are provided so as to retreat from the separation front end 242 of the lower separation claw 24 by L1 width and to contact the pressure contact roller 231.

(4) When the color toner is transferred on the OHP sheet P3, transparency is required for the OHP sheet P3, and the fixing device 23 is operated at a lower speed than the fixing speed of the recording P1. The switching of the low-speed operation is not shown, but a speed switching means may be used. Alternatively, the switching may be automatically performed by the development with the color toner and the detection of the OHP sheet P3. In this manner, the color toner of the OHP sheet P3 discharged from the fixing device 23 at a low speed is in a molten state without being cured, and when the recording sheet guide rotating member 27 comes into contact with the color toner, the molten color toner is discharged. The recording paper guide rotating member 27 is retracted to adhere to the surface of the OHP sheet P4 on which fixing has been completed. However, in the case of a monochrome which does not require transparency, heat fixing is performed at the same speed as the fixing speed of the recording P1 for improving the performance. Therefore, the rotary member 27 for guiding the preceding recording paper is retracted to the position shown in FIG. In this case, the paper discharge guide portion is widened and the jam easily occurs. Therefore, as shown in FIG. 5, the pre-recording paper guide rotating member 27 is switched to a position close to the OHP sheet P1.

In the case of the OHP mode for fixing a color toner, the fixing speed is 12.4 mm / sec, which is 1/6 of the normal mode, which is 74.4 mm / sec. Is set to 195 ° C. and the heat fixing roller 233 is set to 145 ° C. to perform fixing.

S1 is a paper discharge detection member, which detects the paper discharge state of the OHP sheet P4 by the operation of the operation member S2 which is operated by the paper discharge conveyance of the OHP sheet P4. The OHP sheet P4 to be discharged and conveyed is guided by the discharge switching means 234 shown in FIG. 1 and is discharged outside the apparatus from the first discharge roller 235, and if necessary, the discharge switching means 234 is used. And the OHP sheet P4 can be inverted and discharged to the discharge tray 237 from the second discharge roller 236 via the transport roller 26.

FIG. 1 is a cross-sectional view illustrating an overall configuration of an image forming apparatus embodying the present invention. FIG. 2 is a longitudinal sectional view of the fixing device of the present invention. FIG. 3 is a plan view illustrating a pressure roller in the fixing device of the present invention. FIG. 4 is an explanatory diagram showing the occurrence rate of horns and the angle of the separation claw tip of the present invention. FIG. 6 is a longitudinal sectional view showing another embodiment of the fixing device of the present invention. FIG. 4 is a front view showing a gap between the recording paper guide rotating member and the paper ejection guide plate in the present invention. FIG. 3 is an explanatory diagram showing the relationship between the generation rate of the rubs and the gap in the present invention. FIG. 7 is an exploded perspective view showing a recording paper guiding rotating member and a paper ejection 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 reference numerals

DESCRIPTION OF SYMBOLS 10 Photoreceptor drum 12 Charger 13 Image exposure means 14A, 14B, 14C, 14D Developing device 31 Transfer belt 141, 111 Rotating sleeve for development 143, 211 Magnetic pole 23 Fixing device 231 Pressure contact roller 233 Heat fixing roller 24 Lower separation claw 25 Discharge 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 pressing roller that presses against the fixing roller, a nip portion is formed by pressing the fixing roller and the pressing roller, and a nip is formed between the fixing roller and the pressing roller. In a color image forming apparatus having a fixing device that discharges the sheet from the nip portion in a direction away from the fixing roller side.
A first guide member located on the pressure roller side and a switchable second guide member located on the fixing roller side;
When a color image is formed 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 the fixing speed is lower in the OHP mode for fixing the color toner on the OHP sheet than in the normal mode.

Images