JP2017156669A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device including a fixing member that can suppress wear to improve durability and prevent electrostatic offset and hot offset.SOLUTION: A fixing device 16 comprises a fixing member 31 to be heated and a pressure member 33 that forms a fixing nip 45 with the fixing member 31, and sandwiches and conveys a sheet to which a toner is transferred while applying heat and pressure to the toner to fix the toner to the sheet at the fixing nip part 45. The fixing member 31 includes a surface layer 37 in contact with the sheet. The surface layer 37 contains a fluorine resin 40 and a conductive needle-like filler 41 that is dispersed in the fluorine resin 40. The conductive needle-like filler 41 has an aspect ratio L1/L2 of 7 or more and 30 or less, where L1 is the length in the longitudinal direction and L2 is the length in the short direction, a powder resistance of 5 Ω cm or more and 100 Ω cm or less, and a volume content relative to the fluorine resin 40 of 1% or more and 9% or less.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a fixing device that fixes a toner image onto a sheet and an image forming apparatus including the fixing device.

  In the image forming apparatus, the toner image transferred to the paper is heated and pressed by the fixing device and fixed on the paper. The fixing device includes a fixing member such as a fixing roller to be heated and a fixing belt, and a pressure member. When the sheet passes through a fixing nip formed between the fixing member and the pressure member, the toner image Is heated and pressurized to be fixed on the paper.

  The fixing member generally has a conductive base layer and a surface layer that contacts the paper. For the surface layer, a fluororesin having a good releasability is often used. The fixing device may be provided with a separation member for separating the paper from the fixing member after the toner image is transferred.

  Such a fixing member needs to satisfy the following problems. The first problem is prevention of surface wear due to contact between the separation member or the trailing edge of the paper and the surface layer. The second problem is that when the resistance value of the surface layer is high, the surface layer is charged by friction with the paper or the like, and the toner transferred to the paper is electrostatically attracted to this charge, and the attracted toner is This is to prevent a phenomenon (electrostatic offset) that is retransferred and fixed on the paper. A third problem is prevention of a phenomenon (tailing offset) in which toner is scattered and tailing occurs when the resistance value of the surface layer is low. The fourth problem is prevention of a phenomenon (hot offset) in which the toner melted by heating adheres to the fixing member and causes an image defect due to a decrease in surface layer releasability.

  As a countermeasure for solving the first problem and the second problem, it is conceivable to include a conductive filler in the surface layer. However, in this case, since the releasability of the surface layer is lowered, prevention of hot offset, which is the fourth problem, cannot be satisfied. In order to satisfy all of these problems, it is necessary to contain a small amount of a conductive filler in the surface layer. However, if the resistance of the surface layer is too low, prevention of tailing offset, which is the third problem, cannot be satisfied. Thus, it is difficult to satisfy all the problems.

  For such a problem, Patent Document 1 describes a fixing member having a surface layer in which conductive needle-like fibers are contained in a fluororesin. Patent Document 2 describes a fixing member having a surface layer in which silicon carbide is contained in a fluororesin. Furthermore, Patent Document 3 describes a fixing member having a surface layer formed of a fluororesin, a fiber material coated with a conductive oxide, an acrylic resin, and a liquid medium.

  Further, Patent Document 4 describes a fixing member having a surface layer in which graphite powder having a particle size of 5 μm or less is contained in 1 to 10 wt% of a fluororesin. Furthermore, Patent Document 5 describes a fixing member having a surface layer in which carbon nanotubes or carbon nanofibers are contained in a fluororesin. Further, Patent Document 6 describes a fixing member having a surface layer in which two kinds of fluororesins having different melting points are provided and the periphery of the fluororesin particles having a high melting point is coated with metal particles.

JP-A-3-284781 JP 60-107670 A Japanese Patent Laid-Open No. 2-85 JP-A-9-237007 JP 2007-304374 A JP 2005-302691 A

However, in the fixing member described in Patent Document 2, since the volume resistivity of silicon carbide is as high as about 10 ⁶ Ω · cm, the conductivity of the surface layer may be insufficient. Further, in the fixing member described in Patent Document 4, since the particle diameter of the graphite powder is large, the surface roughness of the surface layer is increased, and the releasability may be deteriorated. In the fixing member described in Patent Document 5, when carbon nanotubes are used, the cost increases. Moreover, when using carbon nanofiber, since the aspect ratio is large, the surface roughness of the surface layer is increased, and the releasability may be deteriorated. In the fixing member described in Patent Document 6, the process of forming the surface layer is complicated, and mass production is difficult.

  On the other hand, the conductive fibrous filler contained in the fixing member described in Patent Document 1 and Patent Document 3 is considered a preferable material, but by selecting material characteristics such as aspect ratio and powder resistance. There is a possibility that better fixing characteristics can be exhibited.

  In view of the above circumstances, an object of the present invention is to provide a fixing device including a fixing member that can improve durability and prevent electrostatic offset, hot offset, and the like, and an image forming apparatus including the fixing device. To do.

  In order to achieve the above object, a fixing device according to the present invention includes a fixing member to be heated and a pressure member that forms a fixing nip between the fixing member, and after the toner transfer in the fixing nip. A fixing device that heats and pressurizes toner while fixing and conveying a sheet, and the fixing member includes a surface layer in contact with the sheet, and the surface layer includes a fluororesin and a fluororesin in the fluororesin The conductive needle filler is dispersed, and the conductive needle filler has an aspect ratio L1 / L2 of 7 or more when the length in the longitudinal direction is L1 and the length in the short direction is L2. 30 or less, the powder resistance is 5 Ω · cm or more and 100 Ω · cm or less, and the volume content with respect to the fluororesin is 1% or more and 9% or less.

  By adopting such a configuration, it is possible to maintain wear resistance without impairing the surface layer releasability. Furthermore, electrostatic offset and hot offset can be prevented by imparting appropriate electrical conductivity to the surface layer.

  In the fixing device of the present invention, the conductive needle filler may be any one of tin oxide, antimony-doped tin oxide, and antimony-doped tin oxide-coated titanium oxide.

  By adopting such a configuration, appropriate conductivity can be imparted to the surface layer.

  In the fixing device of the present invention, the fluororesin may have a melt flow rate of 2 or less.

  By adopting such a configuration, the mechanical strength of the surface layer can be increased and the wear resistance can be improved.

  In the fixing device of the present invention, the fixing member may have a conductive base layer, and the surface layer may be provided on a surface of the base layer.

  By adopting such a configuration, the configuration of the fixing member can be simplified.

  The image forming apparatus of the present invention includes any one of the fixing devices described above.

  According to the present invention, wear of the surface layer can be suppressed to improve durability, and electrostatic offset and hot offset can be prevented.

1 is a schematic diagram illustrating an outline of a printer according to an embodiment of the present invention. 1 is a front view schematically showing a fixing device according to an embodiment of the present invention. 1 is a cross-sectional view schematically showing a fixing member in a fixing device according to an embodiment of the present invention.

  Hereinafter, a fixing device and an image forming apparatus according to an embodiment of the present disclosure will be described with reference to the drawings.

  First, the overall configuration of the printer 1 (image forming apparatus) will be described with reference to FIG. FIG. 1 is a schematic diagram showing an outline of a printer according to an embodiment of the present invention. In the following description, the front side of the paper in FIG. 1 is the front side (front side) of the printer 1, and the direction when the left and right orientation printers are viewed from the front is used as a reference.

  The printer 1 includes a box-shaped housing 2, and a paper feed cassette 3 that stores paper is detachably housed in a lower portion of the housing 2. A paper feeding device 4 that feeds paper from the paper feeding cassette 3 is provided at the upper right of the paper feeding cassette 3. A paper discharge tray 5 is provided on the upper surface of the housing 2.

  Above the paper feed cassette 3, an exposure device 7 composed of a laser scanning unit (LSU) and an image forming unit 8 are provided. The image forming unit 8 includes a photosensitive drum 9 that is rotatably provided. Around the photosensitive drum 9, a charging device 10, a developing device 11, a transfer roller 12, and a cleaning device 13 are photosensitive. It arrange | positions along the rotation direction (refer arrow X of FIG. 1) of the body drum 9. FIG. The developing device 11 is connected to a toner container 14 that contains toner. A fixing device 16 is provided above the image forming unit 8, and a paper discharge device 17 is provided above the fixing device 16.

  Further, inside the housing 2, paper is fed from the paper feeding device 4 to the paper discharge device 17 through the transfer unit 20 formed between the photosensitive drum 9 and the transfer roller 12 and the fixing device 16. Transport path 22 is provided.

  Next, an image forming operation of the printer 1 having such a configuration will be described. After the surface of the photosensitive drum 9 is charged by the charging device 10, exposure corresponding to image data is performed on the photosensitive drum 9 by laser light from the exposure device 7 (see the dashed line P in FIG. 1). An electrostatic latent image is formed on the surface of the photosensitive drum 9. The electrostatic latent image is developed into a toner image by the toner supplied from the toner container 13 in the developing device 11.

  On the other hand, the sheet taken out from the sheet feeding cassette 3 by the sheet feeding device 4 is conveyed to the image forming unit 8 in synchronization with the image forming operation described above, and the toner image on the photosensitive drum 9 is transferred by the transfer unit 20. Transferred to paper. The sheet on which the toner image has been transferred is conveyed downstream in the conveyance path 22 and enters the fixing device 16 where the toner image is fixed on the sheet. The paper on which the toner image is fixed is discharged to the paper discharge tray 5 by the paper discharge device 17. The toner remaining on the photosensitive drum 9 is collected by the cleaning device 13.

  Next, the fixing device 16 will be described with reference to FIGS. 2 is a side view schematically illustrating the fixing device, FIG. 3 is a diagram schematically illustrating a primer layer of the fixing device, FIG. 3A is a plan view, and FIG. 3B is a cross-sectional view. .

  As shown in FIG. 2, the fixing device 16 includes a fixing roller 31 as a fixing member that is heated from the inside, a halogen heater 32 that heats the fixing roller 31, and a pressure member that is pressed against the fixing roller 31. A pressure roller 33 and a separation member 34 pressed against the fixing roller are provided.

  As shown in FIG. 3, the fixing roller 31 includes a cylindrical cored bar 35 that is a conductive base layer, and a surface layer 37 provided on the outer peripheral surface of the cored bar 35 via a primer layer 36. Yes. As the core metal 35, for example, an aluminum tube having a thickness of 0.55 mm and a diameter of 30 mm can be used. For example, an insulating binder resin can be used for the primer layer 36.

  The surface layer 37 has a fluororesin 40 and a conductive needle filler 41 dispersed in the fluororesin 40. As the fluororesin 40, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), or the like can be used. As the conductive needle filler 41, tin oxide, antimony-doped tin oxide, antimony-doped tin oxide-coated titanium oxide, or the like can be used. Further, as shown in FIG. 3, the tips T of some of the conductive needle fillers 41 may protrude from the surface of the surface layer 37.

  The fixing roller 31 is rotatably supported. The core bar 35 is grounded via the housing 2.

  As shown in FIG. 2, the halogen heater 32 is disposed inside the fixing roller 31, and radiates heat to the inner peripheral surface of the fixing roller 31 to heat the fixing roller 31. The pressure roller 33 has a cylindrical metal core, an elastic layer provided on the outer peripheral surface of the metal core, and a release layer provided on the outer peripheral surface of the elastic layer via an adhesive layer. . The pressure roller 33 is rotatably supported, and presses against the fixing roller 31 to form a fixing nip 45 with the fixing roller 31. The separation member 34 is disposed downstream of the fixing nip 45 in the rotation direction of the fixing roller 31, and abuts on the surface of the fixing roller 31 from the counter direction with respect to the rotation direction of the fixing roller 31.

  In the fixing device 16 described above, when fixing toner on a sheet, the halogen roller 32 is operated to heat the fixing roller 31. When the paper transported along the transport path 22 passes through the fixing nip 45, the toner image is heated and pressurized and fixed on the paper. The paper that has passed through the fixing nip 45 is separated from the fixing roller by the separation member 34 and is discharged to the paper discharge tray 5 by the paper discharge device 17.

  Next, a result of selecting preferable values of material characteristics of the fluororesin 40 and the conductive needle filler 41 in the surface layer 37 of the fixing roller 31 based on the evaluation result of the image formed using the image forming apparatus 1. explain. The material characteristics are the melt flow rate (MFR) of the fluororesin 40, the aspect ratio of the conductive needle-like filler 41, the powder resistance, and the content of the fluororesin 40. Using a predetermined testing machine (printer LS-4200DN (trade name) manufactured by Kyocera Document Solutions Co., Ltd.), a test chart with a predetermined printing rate is formed on plain paper, and the wear durability number, hot offset temperature, electrostatic offset, The tailing offset was evaluated.

  The wear durability number indicates the number of prints on which the formed image is visually observed and an image defect due to wear or damage occurring on the fixing roller 31 occurs. The hot offset temperature indicates a temperature at which the hot offset first occurs when the temperature of the fixing roller 31 is increased stepwise from a predetermined temperature. The electrostatic offset and the tailing offset indicate the number of printed sheets in which the formed image is visually observed and the offset and the tailing respectively occur.

  First, the melt flow rate of the fluororesin 40 will be described. The melt flow rate was measured by a measuring method according to JIS K7210 under conditions of a predetermined temperature and load. As a measuring apparatus, a melt indexer L280 manufactured by Tateyama Scientific Industry Co., Ltd. was used. The fixing roller 31 is formed by using a fluororesin 40 (PFA) having a melt flow rate (MFR) of 2, 7, 15, and 30, with the material characteristics and content of the conductive needle filler 41 being constant, and this fixing. The fixing device 16 provided with the roller 31 was mounted on a testing machine, a printing test was performed, and the number of wear-resistant sheets was determined. The results are shown in Table 1.

  From Table 1, it is confirmed that the melt flow rate of the fluororesin 40 is preferably 2 or less. This is presumably because if the melt flow rate is small, the fixing roller 31 is not softened easily even if it is heated by the halogen heater 32 or pressed by the separation member 34, so the wear resistance is improved.

  Next, the aspect ratio of the conductive needle filler 41 will be described. The aspect ratio is a ratio L1 / L2 of the length L2 in the lateral direction to the length L1 in the longitudinal direction of the conductive needle-like filler 41.

  The melt flow rate of the fluororesin 40 is constant, the powder resistance of the conductive acicular filler 41 is 10 Ω · cm, the volume content with respect to the fluororesin 40 is 5%, and the aspect ratio is 3, 7, 12, 30, The fixing roller 31 is formed using the conductive needle fillers 41 of 50, 80, and 120, the fixing device 16 including the fixing roller 31 is mounted on a test machine, a printing test is performed, and the wear durability number and the hot offset are measured. The temperature was determined. The results are shown in Table 2.

  From Table 2, it can be seen that the aspect ratio is preferably 7 or more with respect to the wear durability. This is because when the aspect ratio is high, the conductive needle-like filler 41 is dispersed in a mesh shape in the fluororesin 40, so that high mechanical strength can be obtained. However, when the aspect ratio is small, mechanical strength is obtained. This is probably because the wear durability is insufficient.

  Regarding the hot offset temperature, it can be seen that the aspect ratio is preferably 30 or less. This is considered to be because when the aspect ratio is high, the conductive needle-like filler 41 is easily exposed on the surface of the surface layer 37 and the releasability of the surface layer 37 is lowered, so that hot offset is likely to occur. . The conductive needle-like filler 41 is contained so that the tip protrudes from the surface of the surface layer 37, and the area exposed on the surface can be made relatively narrow, so that the releasability of the surface layer 37 is greatly impaired. Absent.

  Next, the powder resistance of the conductive needle filler 41 will be described. The powder resistance indicates the resistance measured at a predetermined applied voltage after the conductive needle filler 41 is hardened at an arbitrary pressure (9.8 MPa) to form a powder molded product (pellet). A powder resistance measurement system MCP-PD51 manufactured by Mitsubishi Chemical Analytech Co., Ltd. was used as a measuring device.

  The melt rate of the fluororesin 40 is constant, the aspect ratio of the conductive needle filler 41 is 12, the volume content with respect to the fluororesin 40 is 5%, and the powder resistance is 0.16, 5, 10, 60, 100. , 2000, 1000000 Ω · cm of conductive needle filler 41 is used to form a fixing roller 31, and the fixing device 16 including the fixing roller 31 is mounted on a test machine to perform a print test, and electrostatic offset and tail The pull offset was determined. The results are shown in Table 3.

  From Table 3, it can be seen that regarding the electrostatic offset, the powder resistance is preferably 100 Ω · cm or less. This is presumably because when the powder resistance is as high as 2000 Ω · cm or more, the surface layer 37 is not sufficiently reduced in resistance and is easily charged, and electrostatic offset is likely to occur.

  Regarding the tailing offset, it can be seen that the powder resistance is preferably 5 Ω · cm or more. This is presumably because when the powder resistance is low, the resistance of the surface layer 37 is low and the toner is likely to be scattered.

  Next, the volume content of the conductive needle filler 41 with respect to the fluororesin 40 will be described. The melt flow rate of the fluororesin 40 is constant, the conductive needle filler 41 has an aspect ratio of 12, the powder resistance is 10 Ω · cm, and the volume content is 0, 1, 3, 5, 9, 12, 20 % Fixing roller 31 was formed, and the fixing device 16 equipped with this fixing roller 31 was mounted on a test machine to perform a printing test, and the wear durability, electrostatic offset, tailing offset, and hot offset were determined. The results are shown in Table 4.

  From Table 4, it can be seen that the conductive needle-like filler 41 is preferably contained in an amount of 1% or more with respect to wear durability. This is presumably because the mechanical strength of the surface layer 37 is increased and the wear resistance is improved by containing the conductive needle-like filler 41.

  Regarding the electrostatic offset, it can be seen that the conductive needle-like filler 41 is preferably contained in an amount of 1% or more. This is considered because the electroconductivity of the surface layer 37 falls because the electroconductive needle filler 41 is contained in the fluororesin 40.

  As for the tailing offset, it can be seen that the volume content is preferably 12% or less. This is considered to be because when the volume content of the conductive needle-like filler 41 is increased, the conductivity of the surface layer 37 is excessively decreased or the releasability of the surface layer 37 is decreased, and tailing occurs. .

  As for the hot offset temperature, it can be seen that the volume content is preferably 9% or less. This is because when the volume content is high, the conductive needle-like filler 41 is likely to be exposed on the surface of the surface layer 37 and the releasability of the surface layer 37 is lowered, so that hot offset is likely to occur. It is done.

  From the above results, it is understood that the melt flow rate of the fluororesin 40 is preferably 2 or less. The conductive needle-like filler 41 preferably has an aspect ratio of 7 or more and 30 or less, a powder resistance of 5 Ω · cm or more and 100 Ω · cm or less, and a volume content with respect to the fluororesin of 1% or more and 9% or less. Recognize.

  As described above, in the fixing roller 31 of the fixing device 16 according to the present invention, the wear resistance of the surface layer 37 can be improved by setting the melt flow rate of the fluororesin 40 of the surface layer 37 to 2 or less. Furthermore, electroconductivity can be provided, without impairing mold release property by making the fluororesin 40 contain the electroconductive needle filler 41. FIG. Specifically, the conductive needle-like filler 41 having an aspect ratio of 2 or less, a powder resistance of 5 Ω · cm or more and 100 Ω · cm or less with respect to the fluororesin 40 at a volume content of 1% or more and 9% or less. By containing, electrostatic offset, hot offset, and tailing can be prevented while maintaining wear resistance. Therefore, wear due to contact with the separation member 34 and the paper can be suppressed, and a good image free from electrostatic offset, hot offset, and tailing can be formed.

  Further, the fixing roller 31 is formed of a core metal 35 and a surface layer 37 provided on the outer peripheral surface of the core metal 35 via a primer layer 36 and does not have an elastic layer. A simple configuration is possible.

  In addition, as the fluororesin 40, materials other than PFA and PTFE can be used. As the conductive needle filler 41, materials other than tin oxide, antimony-doped tin oxide, and antimony-doped tin oxide-coated titanium oxide can be used. The “needle shape” includes a fiber shape or a rod shape having an aspect ratio of 2 or less.

  In this embodiment, the roller fixing type fixing device 16 using the fixing roller 31 has been described. However, the present invention can also be applied to a belt fixing type fixing device using a fixing belt.

  Further, in the embodiment of the present invention, the case where the configuration of the present invention is applied to the printer 1 has been described. However, in another different embodiment, the present invention is applied to an image forming apparatus other than the printer 1 such as a copying machine, a facsimile machine, and a multifunction machine. You may apply the structure of invention.

  Furthermore, since the above description of the embodiments of the present invention describes preferred embodiments of the fixing device and the image forming apparatus according to the present invention, various technically preferable limitations may be imposed. However, the technical scope of the present invention is not limited to these embodiments unless specifically described to limit the present invention. That is, the above-described components in the embodiment of the present invention can be appropriately replaced with existing components and the like, and various variations including combinations with other existing components are possible. The description of the embodiment of the present invention described above does not limit the contents of the invention described in the claims.

1 Printer (image forming device)
31 Fixing roller (fixing member)
33 Pressure roller (Pressure member)
35 Core (base layer)
37 Surface layer 40 Fluororesin 41 Conductive needle filler 45 Fixing nip

Claims (5)

A fixing member to be heated, and a pressure member that forms a fixing nip between the fixing member, and the paper is heated and pressurized while holding and conveying the paper after toner transfer in the fixing nip. A fixing device for fixing to
The fixing member includes a surface layer in contact with the paper,
The surface layer has a fluororesin and a conductive needle filler dispersed in the fluororesin,
The conductive needle-like filler has an aspect ratio L1 / L2 of 7 or more and 30 or less, and a powder resistance of 5 Ω · cm or more and 100Ω when the length in the longitudinal direction is L1 and the length in the short direction is L2. A fixing device having a volume content of 1% or more and 9% or less with respect to the fluororesin.   The fixing device according to claim 1, wherein the conductive acicular filler is any one of tin oxide, antimony-doped tin oxide, and antimony-doped tin oxide-coated titanium oxide.   The fixing device according to claim 1, wherein the fluororesin has a melt flow rate of 2 or less.   The fixing device according to claim 1, wherein the fixing member has a conductive base layer, and the surface layer is provided on a surface of the base layer.   An image forming apparatus comprising the fixing device according to claim 1.

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