JP2006285076A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve a problem that an exit guide member may damage the surface of a pressure roller when the diameter of a fixing roller is reduced with the lapse of time in a fixing device constituted so as to guide and discharge a sheet material on which a toner image is fixed from a nip part between the fixing roller around which a fixing belt is stretched and the pressure roller by the exit guide member. <P>SOLUTION: A projected portion 23 is formed on the tip part of the exit guide member 22, and when the diameter of the fixing roller 11 is reduced and the pressure roller 14 approaches the fixing roller 11 to maintain the nip part 15, the outer circumferential surface of the pressure roller 14 is brought into contact with the projected portion 23 without being brought into contact with the tip part of the exit guide member 22. The projected portion 23 is formed on both longitudinal-direction end parts of the exit guide member 22 while evading a paper feeding area between the exit guide member 22 and the pressure roller 14. The outer diameter line of the projected portion 23 is formed like a smooth curve projected to the outside. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device and an electrophotographic image forming apparatus including the same. The present invention particularly relates to a structure of a sheet material peeling assist mechanism in a fixing device.

  A sheet material (paper, recording paper) on which a toner image is formed is nipped by a pressure roller facing the fixing belt or a pressure roller facing the fixing roller, and pressure is applied, or heat and pressure are applied. In the electrophotographic image forming apparatus having a fixing device for fixing the toner image on the sheet material, the sheet material on which the toner image is fixed at the nip portion is moved to the fixing belt or the fixing roller side by the adhesive force of the toner. In order to prevent winding easily, it is necessary to provide a separation assisting member such as a separation claw or a separation plate.

Examples of the sheet material peeling assist mechanism in the fixing device include those disclosed in the following Patent Documents 1 to 3.
In the belt-type fixing device described in Patent Document 1, a nip portion is formed by a support roller on which a fixing belt is hung and a pressure roller, and a transfer material on which a toner image is fixed at the nip portion is ejected by a discharge guide. The structure is such that the sheet is guided and discharged. In a high humidity atmosphere where the transfer material is likely to stick to the fixing belt, the discharge guide member is brought closer to the fixing belt, and in a low humidity atmosphere where the transfer material is difficult to stick to the fixing belt, the discharge guide member should be kept away from the fixing belt. I have to.

  In the fixing device described in Patent Document 2, a nip portion is formed by a fixing roller and a pressure roller, and a transfer material on which a toner image is fixed at the nip portion is guided by a discharge upper guide and a discharge lower guide. The paper is then discharged. A constant interval is always maintained between the front end of the sheet discharge lower guide and the pressure roller. In other words, even if the position of the pressure roller moves to adjust the nip pressure, or the position of the pressure roller changes due to variations in rubber hardness, the tip of the lower discharge guide abuts the positioning member with a predetermined configuration. By doing so, the above-mentioned fixed interval is maintained.

  The fixing device described in Patent Document 3 includes a guide member that guides a transfer sheet after passing through a nip portion between a fixing roller and a pressure roller to a paper discharge portion. The guide member is provided in a variable position. When passing thin transfer paper, move the tip of the guide member closer to the nip to reduce the amount of thin paper back curl caused by the heat in the nip, thereby reducing the jam of the thin paper. Yes.

JP 2004-53899 A JP-A-8-179651 JP-A-6-175526

  By the way, when performing double-sided printing in an electrophotographic image forming apparatus or when printing on the back side of a sheet material that has already been printed on one side, there is a toner image on the pressure roller side. Sheet material may wrap around the side. For this reason, it is necessary to arrange a guide member (exit guide member) for assisting sheet material separation on the pressure roller side as well as on the fixing side. The guide member on the pressure roller side is disposed on a fixing frame or the like. The position is determined, and the tip of the guide member is configured to maintain a gap in a non-contact state with the pressure roller.

[First object of the present invention]
However, when the diameter of the fixing roller becomes small due to wear over time or the like, the pressure roller approaches the fixing roller side by that amount (to form the nip portion), and the gap with the guide member is also narrowed. In the worst case, the pressure roller may come into contact with the guide member, and the guide member may damage the pressure roller. Accordingly, an object of the present invention is to solve the problem that the guide member damages the pressure roller due to the pressure roller approaching the guide member.

[Second object of the present invention]
3. The fixing device according to claim 1, wherein the convex portion is originally in a non-contact position with respect to the pressure roller. However, when the diameter of the fixing roller is reduced with time, the pressure roller is in contact with the convex portion. Therefore, there is a possibility that the contact portion affects the surface property of the pressure roller and causes a problem that the quality of the fixed toner image is deteriorated. Accordingly, an object of the invention of claim 3 is to prevent quality deterioration of the toner image.

[Third object of the present invention]
4. The fixing device according to claim 1, wherein when the convex portion provided on the guide member has an edge shape, the pressure roller may be damaged even when the contact pressure of the convex portion with the pressure roller is low. . The object of the present invention is to prevent such a problem.

  In order to achieve the first object, in the fixing device according to the first and second aspects of the present invention, the pressure roller is provided by providing a convex portion at the tip of the outlet guide member which is a guide member on the pressure roller side. Even when approaching the fixing roller side, only the convex part is in contact with the pressure roller, so that the contact part between the guide member and the pressure roller is kept to a minimum, and further contact between the two is prevented. I made it.

  That is, in the invention according to claim 1, the fixing belt is hung on the heating roller and the fixing roller (supporting roller), a nip portion is formed by the fixing roller hung portion of the fixing belt and the pressure roller, and the toner The toner image on the sheet material is fixed by pressing and heating the sheet material on which the image is formed and conveyed from the transfer device at the nip portion, and the fixed sheet material is disposed close to the pressure roller. In the fixing device that is guided and discharged by the outlet guide member, a convex portion is provided at the tip of the outlet guide member, the fixing roller is reduced in diameter (reduced diameter) over time, and the pressure roller is a nip portion. The outer peripheral surface of the pressure roller is in contact with the convex portion without being in contact with the distal end portion of the outlet guide member when approaching the fixing roller in order to maintain the fixing roller. .

  Similarly, in order to achieve the first object, in the invention according to claim 2, a sheet material on which a toner image is formed and conveyed from the transfer device is formed by a pressure roller and a fixing roller having a built-in heating means. The toner image on the sheet material is fixed by pressurizing and heating at the nip portion, and the sheet material after the fixing is guided and discharged by an exit guide member disposed in the vicinity of the pressure roller. In the apparatus, a convex portion is provided at a tip portion of the outlet guide member, and when the fixing roller is reduced in diameter with time and the pressure roller approaches the fixing roller to maintain the nip portion, the outer peripheral surface of the pressure roller is The fixing device is characterized in that it contacts the convex portion without contacting the front end portion of the outlet guide member.

  In order to achieve the second object, in the fixing device according to the third aspect of the present invention, the arrangement positions of the convex portions provided at the front end portion of the exit guide member are the both end portions which become the non-sheet passing region. That is, the invention according to claim 3 is characterized in that the convex portions are provided at both ends in the longitudinal direction of the outlet guide member, avoiding a sheet passing region between the outlet guide member and the pressure roller. The fixing device according to claim 1.

  In order to achieve the third object, the invention according to claim 4 is characterized in that the contact surface of the convex portion with the outer peripheral surface of the pressure roller is formed smoothly (thus having sliding property), and the contact surface. 4. The fixing device according to claim 3, wherein the outer diameter line (contour line) is formed in an outwardly convex curved shape (for example, an arc shape or an elliptical arc shape).

  Similarly, in order to achieve the third object, in the invention according to claim 5, the contact surface of the convex portion with the outer peripheral surface of the pressure roller is formed in a smooth planar shape (and thus has sliding property). The fixing device according to claim 3, wherein the fixing device is a fixing device.

  Furthermore, an invention according to claim 6 is an image forming apparatus comprising the fixing device according to any one of claims 1 to 5.

  According to the first and second aspects of the present invention, when the diameter of the fixing roller becomes small due to wear over time, the outer peripheral surface of the pressure roller contacts the convex portion without contacting the tip of the outlet guide member. Thus, the problem that the guide member damages the outer peripheral surface of the pressure roller is solved. Further, in the first and second aspects of the invention, the pressure roller is in contact with the convex portion as described above. Therefore, when the diameter of the fixing roller is reduced, the pressure roller outer peripheral surface and the outlet guide member tip It can suppress that the space | interval (gap) with a part narrows more than this.

  In the third aspect of the invention, since the convex portions provided at the tip of the exit guide member are arranged at both end portions which are non-sheet passing regions, the fixing roller is fixed even when the diameter of the fixing roller is reduced over time. There is no problem that the quality of the toner image deteriorates due to the surface property of the pressure roller, and a fixed image with good quality can be obtained at all times.

  According to the fourth and fifth aspects of the present invention, when the fixing roller diameter is reduced due to wear over time or the like, the pressure roller outer peripheral surface is in contact with the convex portion having the above characteristics. This prevents the pressure roller surface from being damaged by the contact.

  According to the sixth aspect of the present invention, there is provided a high-performance image forming apparatus capable of obtaining the above-described effect by the fixing device according to any one of the first to fifth aspects.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[First embodiment]
FIG. 1 is a schematic explanatory diagram illustrating the configuration of a belt-type fixing device. In this figure, reference numeral 14 denotes a pressure roller, and reference numeral 23 denotes a convex portion provided at the lower end portion of the outlet guide member 22. It shows that it is in position. Further, the pressure roller 14 indicated by a solid line shows a state in which the roller approaches the fixing roller 11 side and comes into contact with the convex portion 23 as the diameter decreases. This will be described in detail later.

  In the fixing device of FIG. 1, a fixing roller (support roller) 11 is fixed to a fixing frame (not shown) via a bearing. The endless fixing belt 12 is hung on the fixing roller 11 and the heating roller 13, and the pressure roller 14 facing the fixing roller 11 is not fixed, and the fixing roller 11 can be pressurized and depressurized. Yes. That is, the pressure roller 14 is pressed against the fixing roller 11 by a spring or the like (not shown) during operation, and a nip portion 15 is formed by the fixing roller hooking portion of the fixing belt 12 and the pressure roller 14. . Further, the pressure roller 14 is configured to be separated from the fixing roller 11 in a depressurized state at the time of jam processing or the like.

  However, in the configuration as described above, the sheet material on which the toner image is fixed at the nip portion 15 is discharged so as to be wound around the fixing belt 12 by the adhesive force of the toner. As a member for preventing wrapping, a separation assisting member 21 (a separation claw, a separation plate, etc.) is provided. Further, in a sheet material for double-sided printing or the like, a toner image is also present on the pressure roller 14 side, and therefore the sheet material may be wound around and discharged on the pressure roller 14 side. Similarly to the fixing side, an outlet guide member 22 is arranged as a member for preventing winding.

  That is, in this fixing device, the peeling auxiliary member 21 is disposed in the vicinity of the nip portion 15 and in the vicinity of the fixing roller 11, and the outlet guide member 22 is disposed in the vicinity of the nip portion 15 and in the vicinity of the pressure roller 14. The auxiliary member 21 and the outlet guide member 22 are opposed to each other. The outlet guide member 22 is rotated around the shaft 22a so as to be positioned in the vicinity of the pressure roller 14 to form the nip portion 15 or away from the pressure roller 14 during jam processing or the like. The upper space of the nip portion 15 is open. Further, the outlet guide member 22 is positioned by a fixing frame or the like, and is configured to maintain a gap in a non-contact state between the distal end portion of the outlet guide member 22 and the pressure roller 14. The peeling assisting member 21 is configured to move the distal end portion (lower end portion) of the peeling assisting member 21 toward and away from the nip portion 15 by operating an operation portion provided on the upper portion thereof.

  Further, in this fixing device, a predetermined convex portion 23 is provided at the tip of the outlet guide member 22 on the pressure roller 14 side, the fixing roller 11 is reduced in diameter (reduced diameter) over time, and the pressure roller 14 is in the nip portion. 15, the outer peripheral surface of the pressure roller 14 is configured to contact the convex portion 23 without contacting the tip portion of the outlet guide member 22 when approaching the fixing roller 11 side to maintain 15. . This will be described in detail below.

  In such a belt-type fixing device, a heating source can be disposed outside the fixing roller. Therefore, by using a sponge roller having a low hardness as the fixing roller, the sheet material can be placed at the exit of the nip portion. Although it is easy to adopt a structure in which the curvature is separated, the diameter of a sponge fixing roller may be reduced by heat or pressure over time. For example, when a sponge roller having an outer diameter of 30 mm was subjected to a running test equivalent to 100K sheets, the diameter was reduced to about 29 mm.

  Since the necessary nip does not change even when the diameter of the fixing roller 11 is reduced, the pressure roller 14 must approach the fixing roller side when forming the nip by the amount of the diameter of the fixing roller. The gap with the outlet guide member 22 is narrowed, and in the worst case, the tip of the outlet guide member 22 comes into contact with the pressure roller 14 and damages the pressure roller.

In this embodiment, as shown in FIG. 1, a convex portion 23 is provided at the distal end portion (on the pressure roller 14 side) of the outlet guide member 22 as a countermeasure. Thus, even when the pressure roller 14 approaches the outlet guide member 22 from the position indicated by the one-dot chain line in FIG. 1, that is, the position indicated by the solid line in FIG. 2A, the solid line in FIG. As shown in (b), the pressure roller 14 and the outlet guide member 22 are in contact with each other only by the convex portion 23, and even when the pressure roller is further approached, the gap is prevented from further narrowing. It becomes possible.
In addition, as a material of the convex part 23, elastic materials, such as silicone rubber and a self-lubricating rubber, or a soft plastic or a self-lubricating plastic can be used. These are all well-known materials.

Second Embodiment In the first embodiment, the above effect can be obtained by providing a convex portion at the distal end portion of the outlet guide member 22. However, when the convex portion 23 and the pressure roller 14 come into contact with each other. In this portion, friction is generated, which affects the surface roughness of the pressure roller 14, and therefore, on the surface of the pressure roller, there is a difference in surface roughness between the friction portion and other portions. As a result, in the paper passing image, the gloss that the gloss looks different between the image portion that has passed through the contact portion between the convex portion 23 and the pressure roller 14 and the other image portion that does not pass through the contact portion. Problems such as unevenness may occur.

  Therefore, in the fixing device of this embodiment, as shown in FIG. 3, the convex portions 23 are provided at both ends in the longitudinal direction of the outlet guide member, avoiding the sheet passing area between the outlet guide member 22 and the pressure roller 14. It is a thing. By doing so, the problem that gloss unevenness occurs in the toner image of the sheet material after fixing is solved. FIG. 3 is a schematic perspective view showing a main part structure of the fixing device, and shows a half side in the longitudinal direction of the pressure roller 14 and the like. It is configured in an area-oriented manner. In this figure, reference numeral 22b denotes a streak rib for reinforcing the plate-like portion of the outlet guide member 22.

Third Embodiment According to the first and second embodiments, the above-described effects can be obtained. However, when the convex portion 23 has an edge shape, the pressure roller 14 contacts the convex portion 23. Even when the pressure is low, the outer peripheral surface of the pressure roller is damaged (particularly, when the convex portion 23 is made of a relatively hard material).

  Therefore, in the present embodiment, as the convex portion, the contact surface with the outer peripheral surface of the pressure roller is formed smoothly, and the outer diameter line of the contact surface is curved outward (that is, a smooth convex curve). What is formed, or the one in which the contact surface with the outer peripheral surface of the pressure roller is formed in a smooth flat shape is provided. If it does in this way, what consists of metals, such as aluminum, stainless steel, and a satin finish metal, can also be provided as said convex part.

1 is a schematic explanatory diagram illustrating a structure of a fixing device according to a first embodiment of the present invention. FIGS. 2A and 2B are explanatory diagrams of a main part of the fixing device of FIG. 1, in which FIG. 1A shows a state before the fixing roller is reduced in diameter, FIG. 1B is a state where the fixing roller is reduced in diameter, and an outer peripheral surface of the pressure roller is an outlet guide member; The state which contacted the convex part is each shown. FIG. 6 is a schematic perspective view showing a main part structure of a fixing device according to a second embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Fixing roller 12 Fixing belt 13 Heating roller 14 Pressure roller 15 Nip part 21 Peeling auxiliary member 22 Exit guide member 23 Convex part

Claims (6)

A fixing belt is hung on the heating roller and the fixing roller, a nip portion is formed by the fixing roller hung portion of the fixing belt and the pressure roller, and a sheet material on which a toner image is formed and conveyed from the transfer device The toner image on the sheet material is fixed by pressurizing and heating at the nip portion, and the fixed sheet material is guided and discharged by an outlet guide member disposed close to the pressure roller. In the device
Providing a convex portion at the tip of the outlet guide member,
When the diameter of the fixing roller decreases with time and the pressure roller approaches the fixing roller so as to maintain the nip portion, the outer peripheral surface of the pressure roller does not contact the tip of the exit guide member, and the convex portion A fixing device characterized by being in contact with the fixing device. The toner image on the sheet material is fixed by pressing and heating the sheet material on which the toner image is formed and conveyed from the transfer device at a nip formed by a pressure roller and a fixing roller incorporating a heating unit. In the fixing device in which the sheet material after fixing is guided and discharged by an outlet guide member disposed close to the pressure roller,
Providing a convex portion at the tip of the outlet guide member,
When the diameter of the fixing roller decreases with time and the pressure roller approaches the fixing roller so as to maintain the nip portion, the outer peripheral surface of the pressure roller does not contact the tip of the exit guide member, and the convex portion A fixing device characterized by being in contact with the fixing device.   The fixing device according to claim 1, wherein the convex portions are provided at both ends in the longitudinal direction of the outlet guide member, avoiding a sheet passing region between the outlet guide member and the pressure roller. .   The fixing device according to claim 3, wherein the convex portion is formed in a smooth curved shape in which an outer diameter line of a contact surface with the outer peripheral surface of the pressure roller is convex outward.   The fixing device according to claim 3, wherein the convex portion is formed in a flat surface with a smooth contact surface with the outer peripheral surface of the pressure roller. An image forming apparatus comprising the fixing device according to claim 1.

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