JP2009139389A - Fixing device, image forming apparatus and usage of the fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure separability and ejectability of a sheet-like medium, while suppressing scratches on a fixing member. <P>SOLUTION: The fixing device includes a separation guide 255 disposed adjacent to a nip portion formed by a fixing belt 251 and a pressure roller 253 for separating the sheet P which has passed through the nip portion from the fixing belt 251; and a spacer 258 for forming a gap between the leading end of the separation guide 255 and the fixing belt 251, wherein the spacer 258 is configured to be driven independently of the separation guide 255. The spacer 258 is driven independently, according to the kind of the sheet P, and the contact position of the spacer 258 with the fixing belt 251 is varied, thereby the separation guide 255 is used in making it come close to or separate from the fixing belt 251. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device for fixing a toner image provided in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine thereof, an image forming apparatus provided with the same, and use of the fixing device Regarding the method.

2. Description of the Related Art Conventionally, image forming apparatuses such as copiers, printers, facsimiles, and multi-functional machines are equipped with a fixing device for fixing a toner image. Some sheets that pass through the fixing device are given gloss to improve the appearance of the image. The surface of the paper is coated with a resin to give gloss. Such paper is generally called coated paper, and demand is increasing. Since coated paper is coated with resin, if paper is passed through the fixing device, the heat resistance of the resin on the surface of the coated paper is insufficient, or the amount of fixing heat increases due to the compatibility between the toner and the resin. This reduces the separation of the paper with respect to the fixing roller and the fixing belt after passing through the nip portion.
In such a fixing device, a separation guide is provided in order to prevent the sheet from being rolled up by a fixing roller or a fixing belt. In order to prevent wear of the fixing roller or the fixing belt, a separation mechanism in which the fixing roller and the separation guide are not contacted is generally used. Patent Document 1 discloses a configuration in which spacers are provided at both ends of a long separation guide that is outside the paper passing area (see FIG. 1 of Patent Document). This spacer is for making the separation guide non-contact with the fixing member (fixing roller or fixing belt). The gap formed using this spacer is usually as small as 1 mm or less.

Further, since the sheet is separated from the fixing member at the margin of the leading edge of the sheet just discharged from the nip portion, the toner is likely to adhere to the leading end of the separation guide that is a short distance from the fixing member. When this amount of fixing increases, the toner comes into contact with the fixing member, causing a problem of damaging the fixing member.
In order to suppress this problem, a fluororesin layer is formed on the separation guide (see, for example, Patent Document 2). However, even if the fluororesin layer is formed, the fluororesin layer wears over time, so it cannot be said that it is a perfect countermeasure.
In addition, as a method for preventing other problems, Patent Document 3 discloses a mechanism that allows a separation claw to be taken in and out from a separation plate (separation guide). By approaching and separating the separation claw from the fixing roller, the contact time between the separation claw and the fixing roller can be shortened, and both the securing of the paper separation function by the separation claw and the prevention of wear on the surface of the fixing roller can be achieved. it can.
However, the mechanism described in Patent Document 3 described above has a structure in which the separation claw protrudes below the separation plate in the vicinity of the nip portion. It can be difficult.

Japanese Patent No. 2823168 JP 2006-317492 A JP 2007-33557 A

  Accordingly, the present invention has been made in view of the above-mentioned problems, and its object is to ensure the separation and discharge properties of the sheet-like medium while suppressing the occurrence of scratches on the fixing member. Yes.

The features of the present invention, which is a means for solving the above problems, are listed below.
The fixing device of the present invention is provided in the vicinity of a nip formed by a fixing member and a pressure member, and a separation guide for separating the sheet-like medium that has passed through the nip from the fixing member, and the separation In the fixing device having a spacer for forming a gap between the front end of the guide and the fixing member, the spacer has a structure that can be independently driven separately from the separation guide.
Further, the fixing device of the present invention is further characterized in that the tip of the separation guide has an uneven shape.
The fixing device according to the present invention is further characterized in that the separation guide is coated with a fluororesin.
The fixing device of the present invention is further characterized in that an arc having a radius of 0.3 mm or less is formed at the tip of the separation guide.
An image forming apparatus according to the present invention includes any of the above-described fixing devices.

A method of using the fixing device according to the present invention is a method of using the fixing device according to any one of the above, wherein the spacer is moved in accordance with the type of the sheet-like medium, and the contact portion of the spacer with the fixing member is determined. By changing, the separation guide approaches and separates from the fixing member.
Further, the method for using the fixing device of the present invention is characterized in that the approach and separation of the separation guide to the fixing member is performed while one sheet-like medium passes through the nip portion.
Further, in the method of using the fixing device according to the present invention, the tip of the separation guide is formed in a concavo-convex shape so that the entire length of the convex surface in the separation guide width direction is less than 50% of the sheet passing width. A sheet-like medium is supplied.

  In the fixing device as the means for solving the above, since the spacer has a structure that is driven independently from the separation guide, when the spacer is displaced with respect to the separation guide, the contact portion between the spacer and the fixing member is changed, With this change, the gap between the separation guide tip and the fixing member is also changed. When the separation member is brought close to the fixing member when the separation property of the sheet-like medium from the fixing member is low, the approach between the separation member and the fixing member is temporary, so The fixing of the toner is greatly suppressed, and the occurrence of scratches on the fixing member can be greatly reduced. That is, it is possible to ensure separation and sheet discharge of the sheet-like medium while suppressing the occurrence of scratches on the fixing member.

The best mode for carrying out the present invention will be described below with reference to the drawings. Note that it is easy for a person skilled in the art to make other embodiments by changing or correcting the present invention within the scope of the claims, and these changes and modifications are included in the scope of the claims. The following description is an example of the best mode of the present invention, and does not limit the scope of the claims.
FIG. 1 is an overall configuration diagram showing an image forming apparatus embodying the present invention. Here, a color image forming apparatus is shown as an example. This color copying machine is a tandem type electrophotographic apparatus using an intermediate transfer belt 11, a paper feeding table 2 at the bottom, a copying machine main body 1 above it, and a scanner 3 and automatic document feeding at the top. A device (ADF) 4 is provided.
The image forming apparatus main body 1 is provided with a transfer device 9 provided with an endless intermediate transfer belt 11 at substantially the center. The intermediate transfer belt 11 is stretched by a driving roller 14 and driven rollers 15 and 16 and is driven to rotate. On the left side of the driven roller 15, residual toner remaining on the surface after image transfer is removed by a belt cleaning device (not shown) to prepare for the next image formation.
Photoconductors 5Y, 5M, 5C, and 5K (hereinafter, colors are specified) along the moving direction above the linear intermediate transfer belt 11 that is stretched between the driving roller 14 and the driven roller 15. When it is not necessary, the photosensitive member 5 is simply rotatably provided, and a known exposure device 21, developing device 7, charging device 6 and photosensitive member cleaning device 8 are provided around it. Primary transfer rollers 9Y, 9C, 9M and 9B constituting primary transfer means are provided. In addition, a static eliminating device and a lubricant coating device (not shown) are provided around the photosensitive member 5, respectively, and these constitute one image forming unit 10.
On the other hand, a secondary transfer device 22 constituting secondary transfer means is provided below the intermediate transfer belt 11. The secondary transfer device 22 is configured to press the intermediate transfer belt 11 and contact the driven roller 16. The secondary transfer device 22 collectively transfers the toner images on the intermediate transfer belt 11 onto the paper P as a recording medium fed between the intermediate transfer belt 11 and the secondary transfer device 22.
A fixing device 25 for fixing the toner image formed on the paper P to the endless fixing belt 251 by heating and pressure contact with the pressure roller 252 is provided on the downstream side of the secondary transfer device 22 in the paper conveyance direction. . The sheet P after the image transfer is transported to the fixing device 25 by an endless transport belt 24 spanned between the pair of rollers 23 and 23. The secondary transfer device 22 may be a transfer system using a transfer roller or a non-contact charger. A paper reversing device 28 for reversing the paper P when an image is formed on both the front and back sides of the paper is provided below the secondary transfer device 22.

When making a color copy with the color copying machine having the above-described configuration, the document is usually set on the document table 30 of the automatic document feeder 4, but when the document is manually set, The automatic feeding device 4 is opened, a document is set on the contact glass 32 of the scanner 3, and the document is pressed against the contact glass 32 by closing the automatic document feeding device 4.
Next, when a start switch (not shown) is pressed, when the document is set on the automatic document feeder 4, the document is automatically fed onto the contact glass 32. When the document is manually set on the contact glass 32, the scanner is immediately scanned. 3 operates, and the first traveling body 33 and the second traveling body 34 start traveling. As a result, light from the light source of the first traveling body 33 is irradiated toward the original, and further, the direction is changed by 180 degrees by the pair of mirrors of the second traveling body 34 and enters the reading sensor 36 through the joint lens 35. The contents of the original are read.
When the start switch is pressed, the intermediate transfer belt 11 starts rotating, and at the same time, the photosensitive members 5Y, 5C, 5M, and 5K also start rotating, and yellow, magenta, cyan, Each black monochrome image is formed. Each single-color image formed on each photoconductor in this way is superposed on the intermediate transfer belt 11 that rotates clockwise in FIG. 1 and sequentially transferred to form a full-color composite color image.

  On the other hand, the paper feed roller 42 of the selected paper feed stage in the paper feed table 2 rotates, and the paper P is fed out from the selected paper feed tray 44 in the paper feed unit 43 and is separated into one sheet by the separation roller 45. It is separated and conveyed to the conveyance guide plate 48. The fed paper P is conveyed to the copying machine main body 1 by the conveying roller 47, contacts the registration roller 49, and temporarily stops. In the case of manual paper feed, the paper P set on the manual feed tray 51 is fed out by the rotation of the paper feed roller 50, separated into one sheet by the separation roller 52, and conveyed to the manual paper feed path 53. It comes into contact with the registration roller 49 and temporarily stops. In any case, the registration roller 49 starts rotating at an accurate timing in accordance with the color image on the intermediate transfer belt 11, and the 嫉妬 P that has been stopped is moved between the intermediate transfer belt 11 and the secondary transfer roller 22. And a color image is transferred onto the paper P by the secondary transfer device 22 described above. The sheet P on which the color image has been transferred is conveyed to the fixing device 25 by the secondary transfer device 22 having a conveyance function, and is overheated and pressurized to fix the transferred image. As a result, the paper is discharged onto the paper discharge tray 57 and stacked.

  When the double-sided copy mode is selected, the paper P on which the image is formed on the front surface is conveyed to the paper reversing device 28 side by the switching claw 55, is reversed, and is guided to the secondary transfer position 22 again. After the image is formed on the sheet, the sheet is discharged onto the sheet discharge tray by the discharge roller 56 and stacked. Further, when a black single color image is formed on the intermediate transfer belt 11, the driven rollers 15 and 16 other than the driving roller 14 are moved to place the yellow, magenta, and cyan photoconductors 5 Y, 5 M, and 5 C into the intermediate transfer belt 11. It is trying to keep away from. In the so-called 1-drum type image forming apparatus 1 having only one photoconductor, instead of the tandem type shown in FIG. 1, black is first formed in order to increase the first copy speed. In general, the remaining colors are imaged only when the original is in color.

One embodiment of the fixing device of the present invention is applied to a long roller as shown in FIG. 2 of Japanese Patent No. 2823168 (Patent Document 1), for example. Further, the fixing device of the present invention can be applied to a fixing device having a heating / pressure roller without a fixing belt and a fixing device having a fixing belt (for example, JP-A-2006-113466, FIG. 2 and FIG. 3). In the present invention, the fixing roller and the fixing belt are collectively defined as a fixing member.
FIG. 2 shows a schematic cross section of an embodiment of the fixing device of the present invention. As shown in FIG. 2, the fixing device 25 of the present embodiment includes a fixing roller 252 and a pressure roller 253 that is a pressure member. The fixing roller 252 is made of a heat resistant material such as foamed silicone rubber or liquid silicone rubber so that the pressure roller 253 and the fixing belt 251 form a nip portion on the outer periphery of a metal core such as stainless steel or aluminum alloy. An elastic layer formed into an annular shape with an elastic material is provided.
The pressure roller 253 includes an elastic layer made of a heat-resistant elastic material such as fluorine-based rubber or silicone rubber with an appropriate thickness on the outer periphery of a metal core such as stainless steel or aluminum alloy, and a surface layer made of fluorine resin or the like. A release layer is provided. For the release layer, a material having heat resistance and low surface energy is used. For example, silicone resin, fluororesin, for example, polytetrafluoroethylene (PTFE), tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), It is used as a heat-resistant tube made of a polymer resin such as tetrafluoroethylene-hexafluoropropylene copolymer (FEP). The pressure roller 253 is pressed toward the fixing roller 252 by a pressure member such as a spring (not shown). In addition, a heater 253a using a halogen lamp, nichrome wire, or the like is provided inside the pressure roller 253.

As the fixing belt 251, a metal film made of nickel alloy, aluminum alloy, stainless steel, or the like, or a resin film made of polyimide (PI) or polyamideimide (PAI) can be used as a base. A heat-resistant resin layer is formed on the substrate, and polyimide, polyamideimide, polyetheretherketone, or the like is selected as the material of the heat-resistant resin.
When the fixing roller 252 is a driving roller and the fixing roller 252 rotates, the heating roller 254 rotates via the fixing belt 251. The heating roller 254 is a member for stretching the fixing belt 251 that is stretched between the fixing roller 252 and heating the fixing belt 251. In order to heat the fixing belt 251, a heater 254 a using a halogen lamp, nichrome wire, or the like is provided inside the heating roller 254. Moreover, the heating roller 254 is a thin roller of a hollow metal cylinder such as an aluminum alloy, carbon steel, or stainless steel. Since the temperature distribution in the axial direction can be reduced if the thermal conductivity is good, an aluminum alloy cylinder is suitable. Further, the surface of the heating roller 254 is anodized to prevent abrasion with the fixing belt 251.

  A separation guide 255 is provided as a separation member in the vicinity of the discharge side of the nip formed by the contact between the fixing belt 251 and the pressure roller 253. The separation guide 255 has a function of separating the sheet P, which is a sheet-like medium on which the transfer image is fixed, from the fixing belt 251 when the sheet P is stuck to the fixing roller 252. The sheet-like medium includes paper, an OHP film, and other members capable of transferring a sheet-like image. Note that there is a margin of about 3 to 5 mm at the leading end side of the paper P, and this margin is not subjected to the winding force of the toner when the leading edge of the paper P passes through the nip portion. Already separated from the fixing belt 251 near the nip exit. Since the margin is covered by the separation guide 255, the sheet P is separated from the fixing belt 251 even if the sheet P adheres to the fixing belt 251 thereafter.

A gap 259 between the leading end of the separation guide 255 and the fixing belt 251 shown in FIG. 3 is usually 0.05 to 0.5 mm. In order to maintain the gap 259 with the fixing belt 251, the separation guide 255 keeps the gap 259 constant by abutting the spacer 258 against the fixing belt 251 at a position outside the maximum sheet passing width of the fixing belt 251. Yes. Then, when the built-in CPU receives information that the sheet P with low separation property passes, the control unit operates, and the spacer 258 is independent of the separation guide 255 around the rotation center 255b as shown in FIG. Rotate upward. That is, even if the spacer 258 rotates, the separation guide 255 is not displaced. An electric motor or a solenoid can be used as the driving source, and a well-known means using a gear or the like can be adopted as the means for transmitting the driving force.
When the spacer 258 is rotated upward from the state of FIG. 4 until it contacts the fixing belt 251, the separation guide 255 rotates at the same angle as the spacer 258 with respect to the horizontal plane. As a result, the gap 259 between the leading end 255a of the separation guide 255 and the fixing belt 251 shown in FIG.
As described above, the fixing device 25 according to this embodiment drives the spacer 258 independently and changes the contact position of the spacer 258 with the fixing belt 251, thereby moving the separation guide 255 closer to and away from the fixing belt 251. Used. In particular, it is effective to change the position of the leading end of the separation guide 255 according to the type of the paper P. For example, when the separation property of the paper P from the fixing belt 251 is low, the separation guide 255 is made to approach the fixing belt 251. In this case, since the approach between the separation guide 255 and the fixing belt 251 is temporary, the toner can be largely prevented from sticking to the leading end portion 255a of the separation guide 255, and scratches on the fixing belt 251 are generated. As a result, the occurrence of gloss streaks on the paper P can be greatly reduced. For example, in the case of a coated paper formed by coating a resin, since it is sticky, the separability is low.

As shown in FIG. 2, a temperature sensor 257 for measuring the temperature of the fixing belt 251 is provided in the vicinity of the pressure roller 253 and the heating roller 254. The temperature sensor 257 detects the temperature of the surface of the fixing belt 251 and the pressure roller 253 and performs feedback control. That is, if the CPU determines that the temperature measured by the temperature sensor 257 is lower than the predetermined temperature, heating is performed by the heaters 253a and 254a, and if the CPU determines that the temperature measured by the temperature sensor 257 is higher than the predetermined temperature, the heater Heating by 253a and 254a is not performed. A plurality of the temperature sensors 257 are provided along the longitudinal direction of the roller, and detect at least the temperatures at the center and both ends in the longitudinal direction of the roller.
The sheet P on which the toner for forming the transfer image adheres is heated by the fixing belt 251 heated by the heaters 253a and 254a at the nip portion formed by deformation of the elastic layer of the fixing roller 252 and the pressure roller 253. Get pressure. The toner is fixed on the paper P by this heat and pressure.

  FIG. 5 shows a first modification of the separation guide 255. Offset toner gradually accumulates and adheres to the leading end portion 255a of the separation guide 255 as the fixing device 25 is used over time. As a result, the surface layer of the fixing belt 251 is damaged. In order to prevent this, the front end portion 255a is covered with PFA resin 256. That is, when the PFA resin 256 is coated in this way, toner sticking to the leading end of the separation guide due to scraping of the toner adhering to the fixing belt 251 is suppressed. In addition, you may form the front-end | tip part itself with resin.

  FIG. 6 shows a second modification of the separation guide 255. The leading end portion 255a of the separation guide 255 abuts against the fixing belt 251 and separates the sheet P having low separability. At that time, if the leading end portion 255a is sharp, the sheet P is damaged, and the chamfered R of the leading end portion 255a is damaged. Is large, the leading edge of the sheet passes through between the leading edge portion 255a and the fixing belt 251 as it is. Therefore, it is preferable that an arc having a radius of 0.3 mm or less is formed at the tip end portion 255a. As a result, even when the paper is wound, it can be separated well even if it comes into contact with the leading end portion 255a.

FIG. 7 shows a modification of the sheet medium separation mechanism. A cam portion 255 c is formed at the rotation center 255 b of the separation guide 255, and the lower end side of the cam portion 255 c is in contact with the spacer 258. In FIG. 7A, the tip of the spacer 258 is not in contact with the fixing belt 251. When the rotation center 255b rotates counterclockwise in the drawing from this state, the contact portion between the spacer 258 and the cam portion 255c is pushed downward by the cam portion 255c. At this time, since the cam portion 255c and the separation guide 255 are not connected, the separation guide 255 is not directly displaced by the displacement of the cam portion 255c.
When the contact portion between the spacer 258 and the cam portion 255c is pushed downward, the spacer 258 rotates about the central shaft 258a, and the tip of the spacer 258 is connected to the fixing belt 251 as shown in FIG. Contact. At this time, simultaneously with the rotation of the spacer 258, the separation guide 255 connected to the spacer 258 rotates at the same angle as the spacer 258 with respect to the horizontal plane. That is, the separation guide 255 is indirectly displaced through the spacer 258 by the displacement of the cam portion 255c.

Then, the leading end portion 255 a of the separation guide 255 is closer to the fixing belt 251. When such a mechanism is appropriately operated in accordance with the type of paper to be passed, the gap between the leading end portion 255a and the fixing belt 251 can be changed as appropriate, so that the paper having extremely low separability can be passed. Only in this case, if the spacer 258 is brought into contact with the fixing belt 251, the amount of toner adhered to the leading end portion 255 a is greatly reduced.
Note that when the paper P is poorly separated and the paper P is wound up by the fixing belt 251, the paper P comes into contact with the separation guide 255 and the paper passing path is corrected downward (see FIG. 8A). Since the leading edge of the paper P is pulled by the paper discharge roller 7 whose linear speed is faster than that of the fixing belt 251, the paper P is not bent and the paper P is prevented from being rolled up (see FIG. 8B). In this state, even if the tip end portion 255 a is separated from the fixing belt 251, the tip end portion 255 a can be separated from the fixing belt 251 because it does not wind up again. If the approaching and separating operations are performed each time one sheet P passes, the contact time between the spacer 258 and the fixing belt 251 can be shortened as much as possible, and the occurrence of scratches on the fixing belt 251 is greatly reduced. The

  FIG. 9 shows a modification of the separation guide 255 of FIG. The separation guide 255A has a concavo-convex tip. Here, the total length of the convex surfaces in the separation guide width direction may be, for example, less than 50% of the sheet passing width. In this way, the length of the contact portion between the convex surface and the fixing belt 251 is shortened, and the toner can be prevented from sticking to the leading end portion 255a. In addition, it is particularly effective if the position of the recess corresponds to the position of another member that contacts the fixing belt 251 such as a contact thermistor.

1 is an overall configuration diagram showing an image forming apparatus embodying the present invention. 1 is a schematic cross-sectional view showing an embodiment of a fixing device according to the present invention. FIG. 6 is an explanatory diagram illustrating a positional relationship between a fixing belt and a separation guide. It is explanatory drawing which shows the form before and behind rotation of a spacer. It is explanatory drawing which shows the 1st modification of a spacer. It is explanatory drawing which shows the 2nd modification of a spacer. It is explanatory drawing which shows the modification of the separation mechanism of a sheet-like medium. (A) shows a state where the spacer is not in contact with the fixing belt, and (B) shows a state where the spacer is in contact with the fixing belt. It is explanatory drawing which shows the paper passing path of a sheet-like medium. (A) shows a state immediately after the leading edge of the sheet-like medium passes through the nip portion, and (B) shows a state in which time has elapsed from the state of (A). It is explanatory drawing which shows the modification of the separation guide of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus main body 2 Paper feed table 3 Scanner 4 Automatic document feeder (ADF)
5 Photosensitive member 6 Charging device 7 Developing device 8 Cleaning device 9 Primary transfer device 10 Image forming unit 11 Intermediate transfer member 21 Exposure device 22 Secondary transfer device 24 Secondary transfer belt 25 Fixing device 251 Fixing belt 252 Fixing roller 253 Pressure Roller 253a Heater 254 Heating roller 254a Heater 255, 255A Separation guide 255a Front end 255b Rotation center 255c Cam part 256 PFA resin 257 Temperature sensor 258 Spacer 258a Central shaft 259 Clearance 41 Guide part 42 Paper feed roller 43 Side plate 44 Paper feed tray 45 Separation Portion 46 Holding member 47 Conveying roller 48 Conveying guide plate
49 Registration roller 50 Rotating member 56 Discharge roller 57 Discharge tray P Paper

Claims (8)

A separation guide provided in the vicinity of the nip formed by the fixing member and the pressure member, for separating the sheet-like medium that has passed through the nip from the fixing member, a tip of the separation guide, and the fixing member A fixing device having a spacer for forming a gap therebetween.
The fixing device is characterized in that the spacer can be independently driven separately from the separation guide. The fixing device according to claim 1,
The fixing device is characterized in that a leading end of the separation guide is formed in an uneven shape. In the fixing device according to claim 1 or 2,
A fixing device, wherein the separation guide is coated with a fluororesin. The fixing device according to any one of claims 1 to 3,
An arc having a radius of 0.3 mm or less is formed at the tip of the separation guide.   An image forming apparatus comprising the fixing device according to claim 1. A method of using the fixing device according to any one of claims 1 to 4,
A method of using a fixing device, wherein the spacer is driven independently according to the type of the sheet-like medium, and the separation guide is moved closer to and away from the fixing member by changing the contact position of the spacer with the fixing member. . The method of using the fixing device according to claim 6.
The method of using the fixing device, wherein the separation guide approaches and separates from the fixing member while one sheet-shaped medium passes through the nip portion. The method of using the fixing device according to claim 7,
The tip of the separation guide has an uneven shape,
A method of using a fixing device, wherein the sheet-like medium is supplied so that a total length of convex surfaces in the separation guide width direction is less than 50% of a sheet passing width.

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