JP4544882B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device of an image forming apparatus.

  In the fixing mechanism of the image forming apparatus, in order to stably fix the toner image, heat and pressure are applied to the paper carrying the unfixed toner image, and a predetermined width is secured in the nip portion between the pressure roller and the fixing roller. There is a need to. Therefore, it is necessary to apply a certain pressure or more to the pressure roller.

  On the other hand, with the recent progress in energy saving measures, a sponge roller having a small heat capacity capable of shortening the warm-up time is used for the pressure roller. In this case, when the applied pressure is increased, the elasticity of the material is lost while the pressure roller is repeatedly deformed at the nip portion, and the sponge cells that are crushed by the pressure are less likely to return to the original shape. As a result, the pressure applied to the paper changes or becomes non-uniform compared to that in the early stage of use, and the quality of the fixed image is deteriorated.

Therefore, in order to obtain an appropriate nip width without applying pressure as much as possible, a proposal has been made to facilitate deformation by providing a through hole in the axial direction of the pressure roller and to reduce the heat capacity (Patent Document 1,). 2). There has also been a proposal that the same effect can be obtained by increasing the foaming rate while improving the durability by increasing the hardness of the sponge roller (Patent Document 3).
JP-A-7-295418 (page 4, FIG. 1) JP 2002-244466 (5th page, FIG. 2) Japanese Patent Laid-Open No. 9-212025 (page 3, FIG. 1)

  However, with the techniques disclosed in the above-mentioned patent documents, since the pressure applied is low, the durability against repeated deformation at the nip portion of the pressure roller is improved, but both are durable under high-speed rotation due to an increase in process speed. It does not satisfy. First, in the case where the through holes are provided (Patent Documents 1 and 2), the deformation at the nip portion can be easily performed, but the durability is lowered at the portion refracted by the deformation. In addition, even if the hardness of the sponge roller is increased (Patent Document 3), since the cell is easily crushed due to the increased foaming rate, a refracting part is generated, and the durability is lowered as a whole, and the elasticity is further increased. However, under high-speed rotation, the cells crushed at the nip portion do not return to the original state until the roller makes one round and then reaches the nip portion, and the image quality is also deteriorated.

  Therefore, an object of the present invention is to provide a pressure roller that achieves both sufficient elasticity and durability, and an image forming apparatus including the pressure roller.

In order to achieve the above object, the fixing device of the present invention is a fixing device having a fixing roller provided with a heater therein and a pressure roller that presses against the fixing roller and forms a nip through which a sheet passes. The pressure roller is formed by embedding a plurality of elastic pipes in an elastic body surrounding the cored bar substantially parallel to the axial direction, and the elastic modulus of the elastic pipe is higher than the elastic modulus of the elastic body. And

In the fixing device of the present invention, the elastic pipes may be arranged in a line so as to be concentric with the cored bar.

In the fixing device of the present invention, the elastic pipes may be arranged at substantially equal intervals on the concentric circles.

In the fixing device of the present invention, the elastic body may be a silicone-based elastic body, and the elastic pipe may be a PFA resin.

  In the present invention, the image forming apparatus is provided with any of the fixing devices described above.

A fixing device according to the present invention includes a fixing roller provided with a heater therein, and a pressure roller that forms a nip through which a sheet passes by being in pressure contact with the fixing roller, and the pressure roller is an elastic material that surrounds a cored bar. Since multiple elastic pipes are embedded inside the body approximately parallel to the axial direction, it will return to its original shape even when it is repeatedly deformed by applying pressure under high-speed rotation, compared to a normal sponge. It is easy to fix a good image continuously. Moreover, since the air in the pipe serves as a heat insulating layer and the heat capacity is reduced, the warm-up time can be shortened. Furthermore, by making the elastic modulus of the elastic pipe higher than the elastic modulus of the elastic body, the pressure roller can easily return to its original shape, and a good image can be continuously fixed.

Further, according to the present invention, by arranging the elastic pipes in a line so as to form a concentric circle with the cored bar, the nip width becomes uniform and a good image can be fixed.

In addition, according to the present invention, the elastic pipes are arranged on the concentric circles at substantially equal intervals, so that the nip width becomes more uniform and a good image can be fixed.

Further, according to the present invention, the elastic body is made of a silicone-based elastic body, and the elastic pipe is made of a PFA resin having a high elastic modulus, thereby reducing the thermal deformation of the elastic pipe and continuously fixing the image on the paper. However, since the hardness necessary to stably fix the image can be ensured, a good image can be continuously fixed on the paper.

  In addition, since the image forming apparatus according to the present invention includes any one of the fixing devices described above, an image having good fixability can be formed over a long period of time.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of a copier, which is one of the embodiments of the image forming apparatus of the present invention, in which the fixing device according to the first embodiment of the present invention is installed. The main body housing 1 includes an upper housing 11, a lower housing 13, and a connecting housing 12 positioned between the upper housing 11, and the document conveying unit 2 is placed on the upper housing 11. The document transport unit 2 is attached to be openable and closable with the back side of the paper as a fulcrum.

  The document transport unit 2 includes a document feed tray 21, a document transport unit body 22, a document discharge tray 23, and a document cover 24. The document discharge tray 23 is integrally formed as a part of the upper surface of the document cover 24. The document feed tray 21 forms the upstream end of the document transport path d, and the document discharge tray 23 forms the downstream end of the document transport path d. A pickup roller 22a, a conveyance roller pair 22b, a registration roller pair 22c, and a discharge roller pair 22d are provided in order from the upstream side in the document conveyance direction in the document conveyance path d in the document conveyance unit main body 22. An image reading unit 25 is provided between the registration roller pair 22c and the discharge roller pair 22d. An image document (not shown) set on the document feed tray 21 with its image surface facing upward is conveyed through the document conveyance path d by the rollers when a copy start button (not shown) is pressed, and an intermediate image reading unit. In 25, the image is read by the exposure unit 3.

  The exposure unit 3 is built in the upper housing 11. The exposure unit 3 includes an exposure lamp 31 and a reflecting plate 32, a first mirror 33, a second mirror 34, a third mirror 35, a condenser lens 36, and an image sensor (for example, a line type CCD) 37. The exposure lamp 31 and the first mirror 33 are mounted on a first carriage (not shown), and the second mirror 34 and the third mirror 35 are mounted on a second carriage (not shown). When reading a document image by a so-called sheet-through method, the first carriage moves directly below the image reading unit 25, and the light irradiation light from the exposure lamp 31 exposes the moving document. Irradiation light reaches the CCD 37 through the first mirror 33, the second mirror 34, the third mirror 35, and the condenser lens 36, and is read out as an electric signal through a photoelectric conversion process. On the other hand, when the original image is read by the original fixing method, the original image placed on the original placement plate 26 is read and scanned by the exposure unit 3, and is reduced and imaged on the CCD 37 to be subjected to photoelectric conversion processing. After that, it is read to become an electric signal.

  In the lower housing 13, a paper feeding unit 4, an image forming unit 5, and a fixing device 6 are incorporated. First, the sheet feeding unit 4 will be described. A paper feed cassette 41 containing paper P is disposed below the lower housing 13, and the paper P is sent out one by one by a roller 42 to the conveyance path. Further, an openable / closable paper feed tray 43 is provided at the lower left portion of the lower housing 13, and the paper P is placed on the tray 13 so that the paper is conveyed one by one by the rollers 44 in the same manner as described above. Sent out.

  Next, the image forming unit 5 will be described. The image forming unit 5 includes a photosensitive drum 51 and a charger 52, an optical scanning unit 53, a developing device 54, a transfer roller 55, and a cleaning device 56 disposed around the photosensitive drum 51. The photosensitive drum 51 rotates clockwise. First, the surface of the photosensitive drum 51 is uniformly charged by the charger 52. Next, the surface of the photosensitive drum 51 is irradiated with laser light from the optical scanning unit 53, and the charge corresponding to the portion of the image formed on the paper P or the portion other than the image is erased. An electrostatic latent image is formed on the surface. Then, the developing device 54 supplies toner to the electrostatic latent image on the photosensitive drum 51, and the electrostatic latent image is visualized.

  When the photosensitive drum 51 further rotates and the toner image comes to a position facing the transfer roller 55, the paper P is conveyed between the photosensitive drum 51 and the transfer roller 55 accordingly. At this time, the toner image on the photosensitive drum 51 is transferred onto the paper P by applying a voltage having a polarity opposite to the charging polarity of the toner to the transfer roller 55. Residual toner that has not been transferred onto the photosensitive drum 51 is removed from the photosensitive drum 51 by the cleaning device 56. On the other hand, the paper P onto which the toner image has been transferred is conveyed to a fixing device 6 described later, where the toner image is heated and pressurized and fixed on the paper. Thereafter, the paper P is discharged to the paper discharge trays 7a and 7b through the paper discharge path.

  Next, the fixing device 6 will be described. The fixing device 6 includes a fixing roller 61 and a pressure roller 62 that are in pressure contact with each other. FIG. 2 is a perspective view of the fixing device 6 according to the first embodiment, and FIG. 3 is a front view thereof. The fixing roller 61 includes a heater (not shown). The pressure roller 62 includes a cored bar 63, an elastic body 64 surrounding the cored bar 63, and a surface release layer 66 covering the surface. A nip portion 67 for fixing the toner image is formed.

  The pressure roller 62 has a nip portion length of 310 mm so that A3 paper (420 mm × 297 mm) can be used, and a silicone-based elastic body as an elastic body 64 so as to surround the iron core 63 having an outer diameter of 14 mm. And a PFA tube having a film thickness of 50 μm is coated on the outside as a surface release layer 66 so that the entire outer diameter is 25 mm. This numerical value is one preferred example and does not limit the scope of the invention.

  The first embodiment is characterized in that a large number of elastic pipes 65 are embedded in the silicone-based elastic body 64 substantially parallel to the core metal 63. The elastic pipes 65 preferably have a substantially circular cross section and have substantially the same diameter. The reason why the elastic pipe 65 is disposed substantially parallel to the core metal 63 is to reduce the variation in elasticity in the axial direction of the pressure roller 62.

  Moreover, it is preferable that the both end surfaces of the embedded elastic pipe 65 have an open structure rather than a closed structure. This is because in the closed structure, the air inside the elastic pipe 65 is not released, and there is a concern that the pressure roller 62 cannot be sufficiently deformed at the nip portion 67 with the fixing roller 61. In addition, there is a concern that thermal deformation increases as air expands and contracts.

  The elastic pipes 65 may be in contact with each other or may not be in contact with each other. The elastic pipe 65 is made of a copolymer (PFA resin) of tetrafluoroethylene, perfluoroalkyl, and perfluorovinyl ether, and its elastic modulus is preferably higher than that of the elastic body 64. PFA resin is preferably used as the material for the elastic pipe 65, but fluorocarbon resin (polytetrafluoroethylene, ethylenetetrafluoroethylene, etc.), urethane resin, silicone resin, etc. can also be used.

  Further, the number and diameter of the elastic pipes 65 are set so that the total area of the holes of the elastic pipe 65 occupies 40 to 60% of the cross-sectional area of the pressure roller 62 in the cross section perpendicular to the axis of the pressure roller 62. It is preferable to set. Below the range, there is a concern that the durability of the pressure roller 62 is deteriorated, and when the range is exceeded, the heat capacity of the pressure roller 62 tends to be too low, and the fixability is fixed when continuously fixing the toner image. Concerns such as deterioration and a decrease in hardness of the pressure roller 62 occur.

  By configuring as described above, the void ratio of the pressure roller 62 is increased and the heat capacity is decreased, so that the warm-up time can be shortened. In addition, since the elastic pipe 65 embedded in the elastic body 64 is less thermally deformed, even if the toner image is repeatedly fixed, the hardness necessary for stable fixing can be secured, so that good images can be continuously displayed. Can be established. The elastic pipe 65 made of PFA resin preferably has an outer diameter of 0.5 to 2 mm and a thickness of 5 to 20 μm when the diameter of the pressure roller 62 is 25 mm.

  The pressure roller 62 is produced by, for example, arranging elastic pipes 65 made of a plurality of PFA resins in a bundle in a substantially parallel manner around the core metal 63 and fixing both ends thereof, and elastic pipes 65 by a mold. What is necessary is just to vulcanize-mold (for example, 250 degreeC, 20 minutes) the silicone type elastic body 64 in the space | gap between. Thereafter, a cored bar 63 coated with an adhesive is inserted into the outer peripheral surface, and after the adhesive is cured, the roller outer peripheral surface is cut to a desired outer diameter. In particular, it is preferable to apply air pressure to prevent deformation of the elastic pipe 65 during molding.

  FIG. 4 is a front view of the pressure roller 62 of the fixing device 6 according to the second embodiment of the present invention. The second embodiment is characterized in that the elastic pipes 65 similar to those in the first embodiment are arranged in a line so as to form a concentric circle with the core metal 63, and it is particularly preferable to arrange them at substantially equal intervals. Further, it is preferable to arrange the envelope circles outside the arranged elastic pipes 65 so that the diameter of the circle is 90 to 98% of the diameter of the pressure roller 62. If the temperature is below the range, the heat insulation effect due to the air layer in the elastic pipe 65 tends to deteriorate, and there is a concern that the warm-up time is increased. The unevenness due to the air layer affects the area, and there is a concern of uneven fixing.

  Note that it is preferable that both end surfaces of the elastic pipe 65 have an open structure rather than a closed structure, the elastic pipes 65 may be in contact with each other or may not be in contact with each other, About a diameter and wall thickness, it is the same as that of the said 1st Embodiment.

  The pressure roller 62 is manufactured by, for example, arranging an elastic pipe 65 made of a plurality of PFA resins in a circular shape around the core metal 63 and fixing both ends so as to maintain the circular shape. What is necessary is just to vulcanize-mold the silicone type elastic body 64 in the space | gap between 65 similarly to 1st Embodiment. In particular, it is preferable to apply air pressure to prevent deformation of the elastic pipe 65 during molding. The subsequent steps are the same as in the first embodiment.

  With the configuration as described above, the air layer of the elastic pipe 65 serves as a heat insulating layer, and the heat capacity of the pressure roller 62 as a whole is reduced, so that the warm-up time can be shortened and the first implementation is performed. Compared to the configuration, the variation in elasticity in the axial direction of the pressure roller 62 can be reduced, and the number of elastic pipes 65 to be embedded can be reduced, so that the heat capacity of the pressure roller 62 is reduced. There is no excess and the fixing property does not deteriorate.

<Example>
The above effects were investigated using a printer FS-1920 manufactured by Kyocera Mita Corporation. In the experiment, the unprocessed pressure roller of the first and second embodiments was used as the pressure roller, the warm-up time was measured, the initial (unused state), and the pressure roller after fixing 200,000 sheets This was done by measuring Asker hardness. The results are shown in Table 1.

表１より、未処理の加圧ローラに比べて、空隙率の高い第１、第２実施形態の加圧ローラを使用した場合に、ウォームアップ時間が１．５〜２秒短縮されることが明確となった。しかも、トナー画像定着後のアスカー硬度の低下が未処理に比べて少ないことも明確となった。これは、未処理の加圧ローラの場合、トナー画像の定着を繰返すに従い、弾性層のスポンジが潰れやすいために硬度を維持することができなかったのに対して、第１、第２実施形態ではシリコーン系弾性体に埋設されたＰＦＡ弾性パイプの変形が少ないために硬度を維持し続けたためである。

From Table 1, the warm-up time can be shortened by 1.5 to 2 seconds when the pressure roller according to the first and second embodiments having a high porosity is used compared to the untreated pressure roller. It became clear. In addition, it became clear that the decrease in Asker hardness after fixing the toner image is smaller than that in the untreated case. This is because, in the case of an untreated pressure roller, the hardness of the elastic layer sponge was easily crushed as the toner image was repeatedly fixed, whereas the hardness could not be maintained. This is because the hardness of the PFA elastic pipe embedded in the silicone-based elastic body is kept low because the deformation is small.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. 1 is a perspective view of a fixing device according to a first embodiment of the present invention. 1 is a front view of a fixing device according to a first embodiment of the present invention. The front view of the pressure roller of the fixing device which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

6 Fixing Device 61 Fixing Roller 62 Pressure Roller 63 Core Bar 64 Elastic Body 65 Elastic Pipe 66 Surface Release Layer 67 Nip Portion

Claims (5)

A fixing device having a fixing roller provided with a heater therein and a pressure roller that forms a nip through which a sheet passes by being pressed against the fixing roller,
The pressure roller is all SANYO was embedded a plurality of elastic pipes axial direction substantially parallel to the inside of the elastic body surrounding the metal core,
A fixing device for an image forming apparatus, wherein an elastic modulus of the elastic pipe is higher than an elastic modulus of the elastic body . The fixing device according to claim 1, wherein the elastic pipes are arranged in a line so as to form a concentric circle with the cored bar. The fixing device according to claim 2, wherein the elastic pipes are arranged at substantially equal intervals on the concentric circles. The elastic body is a silicone-based elastic body;
The fixing device according to claim 1, wherein the elastic pipe is a PFA resin.   An image forming apparatus comprising the fixing device according to claim 1.

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