JP2008064934A - Image fixing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image fixing device of a belt nip system which has fewer components, is low in cost and suitable for reduction in its size. <P>SOLUTION: The image fixing device includes a heat roller 1 having an elastic layer on its surface; an endless belt 3 rotated following the rotation of the heat roller; and a pressure pad 5 for pressing the endless belt against the heat roller. The image fixing device fixes a toner image to the recording medium 9, by passing the recording medium 9 with the toner image thereon, through a fixing nip part to be formed in the firm contact part of the heat roller and the endless belt. In the image fixing device, the pressure pad includes a center portion 51 curved along the surface of the heat roller; an entrance-side projecting portion 52, projecting toward the surface of the heat roller on the recording medium entrance side; and an exit-side projecting portion 53, projecting with respect to the surface of the heat roller on the recording medium exit side. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, and a printer, and more particularly to an image fixing apparatus that fixes a toner image carried on a recording by contact heating and an image forming apparatus using the same. is there.

  In an image forming apparatus using an electrophotographic method, as a general method for fixing a toner image carried on a sheet as a recording medium to a sheet, a pair of heated rollers are pressed against each other, and the sheet is placed on the pressed area. A heat and pressure roller type fixing method for fixing a toner image by passing the toner image is known.

  A belt nip fixing method disclosed in Patent Document 1 has been proposed as a method that is smaller and has better fixing efficiency than the heating and pressure roller type fixing method. An apparatus using the belt nip fixing method is configured to bring an endless belt into contact with a heating roller and press the endless belt against the heating roller with a pressure pad.

  This belt nip fixing method has the advantage that the fixing efficiency can be improved because the nip portion formed between the endless belt pressed by the pressure pad and the heating roller can be widened. There is a problem that many parts are required to press the heating roller, and the number of parts increases. Further, when the number of parts increases, it is necessary to increase the diameter of the endless belt, and there is a problem that the entire fixing device must be increased in size.

JP-A-8-262903

  SUMMARY OF THE INVENTION An object of the present invention is to solve the above-described problems, and to provide a small and inexpensive image fixing apparatus having good fixing efficiency and an image forming apparatus using the same.

  In order to achieve the above object, the present invention comprises a heat roller having an elastic layer on its surface, an endless belt that rotates following the rotation of the heat roller, and a pressure pad that presses the endless belt against the heat roller. An image fixing apparatus that fixes the toner image to the recording body by passing the recording body carrying the toner image through a fixing nip formed at a pressure contact portion between the heat roller and the endless belt. The pressure pad includes a central portion that is curved along the surface of the heat roller, an inlet-side convex portion that is convex with respect to the surface of the heat roller on the inlet side of the recording member, and the recording member. One feature resides in that an outlet-side convex portion that is convex with respect to the surface of the heat roller is provided on the outlet side.

  Another feature of the present invention is that the inlet-side convex portion and the outlet-side convex portion have curved surfaces with curvatures R1 and R2 at the tips of the convex members, respectively.

  Another feature of the present invention is that the curvature R2 of the outlet-side convex portion is smaller than the curvature R1 of the inlet-side convex portion.

  Another feature of the present invention is that the central portion of the pressure pad has a curved surface with a curvature R3, and the curvature R3 is larger than the curvature R of the outer surface of the heat roller.

  Another feature of the present invention is that an end of the inlet-side convex portion of the pressure pad has an inclination of an angle of 30 degrees or more with respect to a line connecting the center of the heat roller and the center of the pressure pad. It is in.

  Another feature of the present invention is that an end of the outlet-side convex portion of the pressure pad has an inclination of an angle of 20 degrees or more with respect to a line connecting the center of the heat roller and the center of the pressure pad. It is in.

  According to the present invention, by devising the shape of the pressure pad, it becomes possible to transport the recording body more smoothly while applying an appropriate pressure to the nip portion. can do. Therefore, the number of necessary parts can be reduced, and a small and inexpensive belt-nip type fixing device can be realized.

  An embodiment of the image fixing device according to the present invention will be described below with reference to FIGS.

  In FIG. 1, reference numeral 1 denotes a heat roller. An elastic body layer 1b such as silicone rubber is formed on the surface of a cylindrical member 1a having an outer diameter of 25 mm, and a heater 2 is disposed therein. Reference numeral 3 denotes an endless belt, which is configured to be pressed against the heat roller 1 by the pressure mechanism 4 and to be driven to rotate by the rotation of the heat roller 1.

  The pressurizing mechanism 4 includes a pressure pad 5, a holder 6 that fixes the pressure pad 5, a support member 7 that supports the holder 6, and the like. The pressure pad 5 is made of rubber having a rubber hardness of 30 degrees (ASKERC), and the endless belt 3 rotates between the pressure pad 5 and the heat roller 1.

  A low friction member 5 a is formed on the surface of the pressure pad 5 so as to align with the outer peripheral surface of the heat roller 1. The dimensions of the pressure pad 5 were 320 mm in the direction perpendicular to the paper surface of FIG. 1, 12 mm in the vertical direction in the figure, 6 mm in the longest portion in the horizontal direction, and 4 mm in the shortest portion.

  The holder 6 has a C-shape, and supports and fixes the pressure pad 5 at two upper and lower points. This is to reduce the number of parts and to make the pressure pad 5 always contact the heat roller 1 on the surface. The holder 6 is supported on the support member 7 by springs 8a and 8b. Although not shown in the drawing, the holder 6 is supported by the support member 7 by providing holes at both ends of the holder 6 and fitting convex portions provided on the side surfaces of the U-shaped support member 7 into the holes. Yes.

The sheet 9 as a recording medium is conveyed in the direction of the arrow, and the toner image is heated and fixed at the nip portion between the heat roller 1 and the endless belt 3. The spring constants of the springs 8a and 8b are selected so that the load applied to the heat roller 1 by the pressure pad 5 is about 40 kgf / mm ² .

  FIG. 2 is a sectional view showing details of the pressure pad 5 of the image fixing apparatus according to the present invention. The lower side of the drawing corresponds to the entrance portion of the recording sheet 9, and the upper side corresponds to the output portion.

  The pressure pad 5 includes a central portion 51, an inlet side portion 52, and an outlet side portion 53, and is formed of rubber having a rubber hardness of 30 degrees as described above. This rubber hardness is a value selected in consideration that the width of the fixing nip can be sufficiently maintained and the load of the pressure mechanism 4 can be sufficiently received.

  The surface of the central portion 51 of the pressure pad 5 has a curved shape with a curvature R3, and in this example, R3 = 15.6 mm. The curvature R3 of the pressure pad central portion 51 is selected to be slightly larger than the curvature R of the surface of the heat roller 1. This is because, according to experiments by the present inventors, it has been found that if the curvature R3 and the curvature R are equal, a sufficient nip width necessary for fixing cannot be obtained, and fixing efficiency cannot be improved. .

  The inlet side portion 52 of the pressure pad 5 has a convex shape in which an end portion thereof rises at an angle α with respect to a line connecting the center of the heat roller 1 and the center of the pressure pad 5, and has a curvature R1 on the tip surface thereof. The curved surface is formed.

  By adopting such a shape, the endless belt 3 can be smoothly conveyed, and the inlet side portion 52 of the pressure pad 5 can be prevented from being caught in the nip by driving the endless belt 3. It was confirmed. In particular, when thick paper is used as the recording sheet 9, the pressure pad inlet side portion 52 has a phenomenon of being caught in the fixing nip direction. It was. Particularly good results were obtained when the angle α was 30 degrees or more with respect to the horizontal direction.

  On the other hand, in the present embodiment, the end portion of the outlet side portion 53 of the pressure pad 5 also has a convex shape that falls at an angle β with respect to a horizontal line (a line connecting the center of the heat roller 1 and the center of the pressure pad 5). A curved surface having a curvature R2 is formed on the tip surface.

  Here, if the curvature R2 of the surface of the output convex portion 53 is smaller than the curvature R1 of the surface of the inlet convex portion 52, the pressure applied to the heat roller 1 can be locally increased on the outlet side, As a result, it has been found that there is an effect of preventing the sheet 9 from being distorted and sticking to the heat roller 1 when the recording sheet 9 passes.

  According to the experiment by the present inventor, when the angle β is less than 20 degrees, when the pressure pad 5 is pressed toward the heat roller 1, the end of the pad 5 is bent and a sufficient load cannot be applied. Therefore, it is desirable that β be 20 degrees or more.

  As a result of attaching the pressure pad 5 configured as described above to the fixing device and driving it alone, it was confirmed that the endless belt 3 can be driven at the same speed as the heat roller 1. Thus, driving the heat roller 1 and the endless belt 3 at the same speed is important for preventing the recording sheet 9 from meandering and wrinkling when the recording sheet 9 is passed.

Next, an image forming apparatus using the fixing device according to the present invention will be described with reference to FIG.
In FIG. 3, reference numeral 12 denotes an endless photosensitive belt, which is rotated counterclockwise by a motor (not shown). A charger 16, an exposure device 20, and black K, yellow Y, magenta M, and cyan C developing machines 19K, 19Y, 19M, and 19C are disposed along the photosensitive belt 12.

  The surface of the photosensitive belt 12 is uniformly charged by the charger 16. An electrostatic latent image is formed on the charged photosensitive belt 12 by a laser irradiated from the exposure device 20. The photosensitive belt 12 on which the electrostatic latent image is formed sequentially passes through developing machines 19C, 19M, 19Y, and 19K having developing rollers. Each of the developing machines 19C, 19M, 19Y, and 19K is prepared with toners of four colors, cyan, magenta, yellow, and black. Each time the exposed photosensitive belt 12 passes, a toner image of each color is generated. It is formed. That is, a one-color toner image is formed on the photosensitive belt 12 per rotation.

  The photosensitive belt 12 on which the toner image is formed contacts the intermediate transfer belt 11 at the first transfer position T1. The intermediate transfer belt 11 is rotated clockwise in the figure following the rotation of the photosensitive belt 12. The reason why the intermediate transfer belt 11 is driven is to make the configuration simple and inexpensive, and to eliminate the speed difference from the photosensitive belt 12 and to eliminate image shift.

  At the first transfer position T1, the toner image formed on the surface of the photosensitive belt 12 due to the potential difference between the photosensitive belt 12 and the intermediate transfer belt 11 is transferred to the surface of the intermediate transfer belt 11. The potential of the photosensitive belt 12 that has passed the first transfer position T1 is subsequently reduced to a certain level by light irradiation for removing afterimages, and the electrostatic latent image is erased. Further, the remaining toner on the surface remaining without being transferred at the first transfer position T1 is cleaned by the photosensitive member cleaning means, and the next toner image can be formed.

  By repeating the above steps as many times as necessary by the developing machines 19K, 19Y, 19M, and 19C, a toner image corresponding to an image to be printed and a character is formed on the surface of the intermediate transfer belt 11. The toner image on the intermediate transfer belt 11 is transferred onto the recording sheet by the transfer roller 13 at the second transfer position T2.

  A sheet holding device 21 for storing sheets is disposed below the image forming apparatus. The paper in the paper holding device 21 is guided to the transfer roller 13 by the paper supply device 22. The toner image transferred to the paper at the second transfer position T2 is fixed by the fixing device 10 and then discharged from the paper discharge device 23.

  In the image forming apparatus configured as described above, since the fixing device is small, the apparatus main body can also be small. In addition, since the occurrence of wrinkles in the fixing unit is small, a stable high-quality image can be formed.

  As mentioned above, although the Example of this invention was described, various deformation | transformation and a change are possible in the range which does not change the basic concept of this invention. For example, the image forming apparatus is not limited to the configuration in FIG. 3, and the present invention can be applied to any image forming apparatus having a fixing unit.

1 is a schematic configuration diagram illustrating an embodiment of an image fixing device according to the present invention. FIG. 3 is a cross-sectional view of a pressure pad in the image fixing device according to the present invention. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus using a fixing device of the present invention.

Explanation of symbols

1: heat roller, 1a: cylindrical member, 1b: elastic layer, 2: heater, 3: endless belt,
4: Pressurization mechanism, 5: Pressure pad, 5a: Low friction member, 51: Center part, 52: Entrance side part,
53: Exit side, 6: Holder, 7: Support member, 8a, 8b: Spring, 9: Recording body,
10: fixing device, 11: intermediate transfer belt, 12: photosensitive belt, 13: transfer roller,
16: charger, 17: photoconductor cleaning means, 19K, 19Y, 19M, 19C: developing machine,
20: Exposure device, 21: Paper holding device, 22: Paper supply device, 23: Paper discharge device

Claims (7)

  A recording medium having a heat roller having an elastic layer on its surface, an endless belt driven to rotate by rotation of the heat roller, and a pressure pad for pressing the endless belt against the heat roller, and carrying a toner image In the image fixing apparatus for fixing the toner image to the recording body by passing through a fixing nip portion formed at a pressure contact portion between the heat roller and the endless belt, the pressure pad is a surface of the heat roller. A central portion that curves along the inlet, a convex portion on the inlet side that is convex with respect to the surface of the heat roller on the inlet side of the recording member, and a convex portion on the surface of the heat roller with respect to the outlet side of the recording member. An image fixing device comprising an outlet-side convex portion.   2. The image fixing apparatus according to claim 1, wherein the inlet-side convex portion and the outlet-side convex portion have curved surfaces with curvatures R1 and R2, respectively, at the tips of the convex members.   3. The image fixing device according to claim 2, wherein a curvature R2 of the outlet convex portion is smaller than a curvature R1 of the inlet convex portion.   4. The pressure pad according to claim 1, wherein a central portion of the pressure pad has a curved surface with a curvature R3, and the curvature R3 is larger than a curvature R of an outer surface of the heat roller. Image fixing device.   2. The end of the inlet-side convex portion of the pressure pad according to claim 1, having an inclination of an angle of 30 degrees or more with respect to a line connecting the center of the heat roller and the center of the pressure pad. Image fixing device.   The end of the outlet-side convex portion of the pressure pad according to claim 1 has an inclination of an angle of 20 degrees or more with respect to a line connecting the center of the heat roller and the center of the pressure pad. Image fixing device. A charging unit that uniformly charges the surface of the photoconductor, an exposure unit that irradiates the charged photoconductor surface with a laser beam to form an electrostatic latent image, and a toner image corresponding to the electrostatic latent image on the surface of the photoconductor. In an image forming apparatus comprising a developing unit to be formed, a transfer unit for transferring a toner image to a recording medium, and a fixing unit for fixing a toner image carried on the recording medium, the fixing unit has an elastic layer on the surface. A heat roller, an endless belt driven to rotate by rotation of the heat roller, and a pressure pad that presses the endless belt against the heat roller, and a recording medium carrying a toner image is the heat roller and the The toner image is fixed to the recording medium by passing through a fixing nip formed at a pressure contact portion with an endless belt, and the pressure pad is curved along the surface of the heat roller. Department and An inlet-side convex portion that is convex with respect to the surface of the heat roller on the inlet side of the recording member, and an outlet-side convex portion that is convex with respect to the surface of the heat roller on the outlet side of the recording member. An image forming apparatus comprising:

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