Heating device, fixing device, image forming apparatus

Abstract

To solve electrical problems occurring in and around a heating device.SOLUTION: A fixing device 9 comprises: a planar heater 22 that has a substrate 30 and a resistance heating element 40; a rotating fixing belt 20; a pressure roller 21 that applies pressure to the fixing belt 20; and a static eliminating brush 27. The fixing belt 20 has a conductive substrate 20a. The fixing belt 20 has an exposed part 20d where the substrate 20a is exposed to an outer surface side. The pressure roller 21 has its outer surface formed of conductive material. The static eliminating brush 27 is in contact with the substrate 20a or the outer surface of the pressure roller 21. A projection 35a projecting toward an inner surface of the fixing belt 20 is provided inside the fixing belt 20 at a position corresponding to the exposed part 20d.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a heating device, a fixing device, and an image forming apparatus. [Background technology]

[0002] In a fixing device serving as a heating device, the toner on the paper is heated and pressurized as the paper passes through a fixing nip formed between a fixing belt (heating member) and a pressure roller (pressure member).

[0003] A planar heater (heating element) that heats the fixing belt is provided on the inside of the fixing belt. This heater generates heat when an AC voltage is applied to a resistance heating element formed on a base material, and contacts the inner surface of the fixing belt via an insulating layer or the like provided on the heater, thereby heating the fixing belt.

[0004] However, in an image forming apparatus equipped with such a fixing device, there are some electrical problems.

[0005] For example, when a charged paper passes through the fixing nip, or when frictional charging occurs due to the rotation of the fixing belt and pressure roller, the surfaces of the fixing belt and pressure roller become charged. If such charging is not suppressed, the toner image on the paper will electrostatically offset during the fixing process, causing abnormal images. This problem is particularly noticeable in low-humidity environments and when forming images on paper whose surface has been made low-resistance by a coating agent.

[0006] In addition, in a configuration in which an AC voltage is applied to the heater, the insulating layer provided on the heater and the surface layer of the fixing belt are equivalent to a capacitor, and an AC voltage is applied to the fixing nip via the fixing belt. When the paper is in contact with both the transfer nip and the fixing nip, this AC voltage is transmitted to the transfer nip via the paper. This causes the AC voltage to affect the transfer electric field, resulting in periodic density unevenness in the transferred image, which is known as a banding image. In particular, the above problem becomes more pronounced when the paper has low resistance, such as in a high humidity environment or when thin paper is used.

[0007] For example, in Patent Document 1 (JP 2015-84084 A), a fixing inlet guide is disposed upstream of the fixing nip in the paper transport direction. A resistor and a capacitor are connected in parallel to the fixing inlet guide, and the fixing inlet guide is grounded via these resistors and capacitors. This allows the AC voltage that flows from the fixing belt through the paper to the transfer nip to flow to the fixing inlet guide, preventing the occurrence of banding images due to the propagation of the AC voltage to the transfer side.

[0008] However, the configuration of Patent Document 1 could not solve all of the electrical problems described above. Summary of the Invention [Problem to be solved by the invention]

[0009] The objective of the present invention is to solve electrical problems occurring in and around a heating device. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides a heating device comprising a planar heating element having a base material and a resistive heating element, a rotating heating member, a pressure member that pressurizes the heating member, and a static elimination member, wherein the heating member has a conductive layer, the heating member has an exposed portion where the conductive layer is exposed to its outer surface, the pressure member has an outer surface formed of a conductive material, the static elimination member is in contact with the conductive layer or the outer surface of the pressure member, and a convex portion is provided on the inside of the heating member at a position corresponding to the exposed portion, which protrudes toward the inner surface of the heating member and presses the heating member from the inner surface. Effect of the Invention

[0011] According to the heating device of the present invention, electrical problems occurring in or around the heating device can be solved. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of an image forming apparatus. [Diagram 2] 1 is a schematic diagram of a fixing device according to an embodiment of the present invention; [Diagram 3] FIG. 1 shows a heater, in which FIG. 1(a) is a plan view and FIG. 1(b) is a cross-sectional view taken along the line AA in FIG. [Figure 4] FIG. 13 is a diagram showing a state in which a connector is attached to a heater and a heater holder. [Diagram 5] FIG. 4 is a diagram showing power supply to a heater. [Figure 6] 11 is a diagram showing the propagation of an AC voltage from a fixing nip to a transfer nip in a fixing device different from that of the present embodiment. [Figure 7] 4 is a perspective view showing the configuration of a charge removing member, an exposed portion, and a convex portion that come into contact with a pressure roller; FIG. [Figure 8] 4 is a schematic diagram showing a charge removing member in contact with a pressure roller. FIG. [Figure 9] FIG. 2 is a diagram showing a fixing device having a configuration in which a discharging brush is in contact with a fixing belt; [Figure 10] FIG. 2 is a side cross-sectional view of a fixing device having a heat equalizing plate. [Figure 11] FIG. 2 is a side cross-sectional view of a fixing device having an antistatic sheet. [Figure 12] FIG. 1 is a schematic diagram illustrating a color image forming apparatus. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. In each drawing, the same or corresponding parts are denoted by the same reference numerals, and the duplicated description will be appropriately simplified or omitted. In the following description, a fixing device that fixes a toner image onto a paper surface will be described as an example of a heating device.

[0014] For example, a monochrome image forming apparatus 100 shown in Fig. 1 has a drum-shaped photoconductor 110 as an image carrier. Around the photoconductor 110, a charging roller 111, a developing device 112, a cleaning blade 113, etc. are provided. The developing device 112 has a developing roller 115, etc. The charging roller 111 charges the surface of the photoconductor 110. The developing device 112 supplies toner as a developer to the surface of the photoconductor 110 to form a toner image. The cleaning blade 113 cleans the surface of the photoconductor 110.

[0015] A transfer roller 116 is provided at a position facing the photoconductor 110 across the paper transport path B. Between the photoconductor 110 and the transfer roller 116, a transfer nip N1 is formed as a nip portion.

[0016] The image forming apparatus 100 also includes an exposure device 102, a paper feed device 103, and a fixing device 9 as a heating device. The exposure device 102 has a mirror 117. The paper feed device 103 has a paper feed tray 118 and a paper feed roller 119. The exposure device 102 exposes the surface of each photoconductor 110 to light and forms an electrostatic latent image on the surface. The paper feed device 103 supplies paper P as a recording medium to a paper transport path B. The fixing device 9 fixes the toner image transferred to the paper P on the surface of the paper P. The photoconductor 110, the charging roller 111, the developing device 112, the transfer roller 116, the fixing device 9, etc. constitute an image forming means for forming an image on paper.

[0017] Hereinafter, the basic operation of the image forming apparatus 100 will be described with reference to FIG.

[0018] When the image forming operation is started, first, the charging roller 111 charges the surface of the photoconductor 110. Then, the exposure device 102 irradiates the photoconductor 110 with a laser beam Lb based on image data. This reduces the potential of the irradiated portion of the photoconductor 110, and an electrostatic latent image is formed in that portion. Toner is supplied from the developing device 112 to the surface portion of the photoconductor 110 on which the electrostatic latent image has been formed, and the electrostatic latent image is visualized as a toner image (developer image). Then, the toner and the like remaining on the photoconductor 110 after transfer is removed from the surface of the photoconductor 110 by the cleaning blade 113.

[0019] On the other hand, when an image forming operation is started, at the bottom of the image forming apparatus 100, a paper feed roller 119 of the paper feed device 103 is rotated to send out paper P accommodated in a paper feed tray 118 to a conveying path B.

[0020] The paper P sent to the conveying path B is timed by the registration rollers 120 and conveyed to the transfer nip N1 at a timing that faces the toner image on the surface of the photoconductor 110. Then, the toner image is transferred onto the surface of the paper P in the transfer nip N1.

[0021] The paper P onto which the toner image has been transferred is transported to the fixing device 9. The paper P is heated and pressurized by the heated fixing belt 20 and pressure roller 21, and the toner image is fixed onto the surface of the paper P. Then, the paper P onto which the toner image has been fixed is separated from the fixing belt 20, transported by a pair of transport rollers provided downstream of the fixing device 9, and discharged onto a paper output tray. The paper output tray is provided outside the device.

[0022] Next, the configuration of the fixing device will be described in more detail.

[0023] As shown in FIG. 2, the fixing device 9 according to the present embodiment includes an endless fixing belt 20 as a rotating member or fixing member, a pressure roller 21 as an opposing member or pressure member, a heater 22 as a heating body, a heater holder 23 as a holding member, a stay 24 as a supporting member, and a thermistor 25 as a temperature detection means. The pressure roller 21 contacts the outer peripheral surface of the fixing belt 20 to form a fixing nip N2 as a nip portion. The heater 22 heats the fixing belt 20. The heater holder 23 holds the heater 22. The stay 24 supports the heater holder 23 from its rear side. The fixing belt 20, the pressure roller 21, the heater 22, the heater holder 23, and the stay 24 extend in a direction perpendicular to the plane of FIG. 2, and hereinafter this direction is also referred to as the longitudinal direction of each member, or simply the longitudinal direction. This longitudinal direction is also the rotation axis direction of the pressure roller 21 and the width direction of the paper P passed through the fixing device 9.

[0024] The fixing belt 20 has a cylindrical substrate made of polyimide (PI) having an outer diameter of 25 mm and a thickness of 50 to 70 μm, for example. A release layer having a thickness of 7 to 20 μm is formed on the outermost layer of the fixing belt 20. An elastic layer made of rubber or the like having a thickness of 100 to 300 μm may be provided between the substrate and the release layer. The substrate of the fixing belt 20 is not limited to polyimide, and may be a heat-resistant resin such as PEEK or a metal substrate such as nickel (Ni) or SUS. The inner peripheral surface of the fixing belt 20 may be coated with polyimide, polyamideimide, PTFE, or the like. The fixing belt 20 is a member to be heated by the heater 22, and is a heating member that heats the paper (toner thereon) in the fixing nip N2.

[0025] The pressure roller 21 has an outer diameter of, for example, 25 mm. The pressure roller 21 is composed of a solid iron core 21a, an elastic layer 21b as an intermediate layer, and a release layer 21c. The elastic layer 21b is formed on the surface of the core 21a. The elastic layer 21b is made of silicone rubber and has a thickness of, for example, 3.5 to 4.0 mm. The release layer 21c is formed on the outside of the elastic layer 21b. In order to increase the releasability of the surface of the pressure roller 21, it is desirable for the release layer 21c to be a fluororesin layer having a thickness of, for example, about 30 to 50 μm.

[0026] The pressure roller 21 is urged toward the fixing belt 20 by the urging means, and is pressed against the heater 22 via the fixing belt 20. As a result, a fixing nip N2 is formed between the fixing belt 20 and the pressure roller 21. The pressure roller 21 is configured to be rotationally driven by a driving means. When the pressure roller 21 rotates in the direction of the arrow in FIG. 2, the fixing belt 20 is rotated accordingly.

[0027] The heater 22 is a planar heating element provided along the longitudinal direction. The heater 22 heats the inner surface of the fixing belt 20 by heat generated by a resistance heating element 40 provided on the base material 30. A detailed configuration of the heater 22 will be described later.

[0028] The heater holder 23 and the stay 24 are disposed on the inner circumferential side of the fixing belt 20. The stay 24 is made of a metal channel material, and both ends thereof are supported by both side plates of the fixing device 9. The stay 24 supports the heater holder 23 and the heater 22 held by the heater holder 23. As a result, when the pressure roller 21 is pressed against the fixing belt 20, the heater 22 reliably receives the pressing force of the pressure roller 21, and the fixing nip N2 is stably formed between the fixing belt 20 and the pressure roller 21.

[0029] The heater holder 23 is desirably formed of a heat-resistant material because it is likely to become hot due to the heat of the heater 22. For example, when the heater holder 23 is formed of a heat-resistant resin with low thermal conductivity such as LCP, the heat transfer from the heater 22 to the heater holder 23 is suppressed, and the heater 22 can efficiently heat the fixing belt 20.

[0030] The heater holder 23 also has a protrusion 23a that is partially provided in the short side direction and protrudes toward the heater 22. The heater holder 23 abuts against the heater 22 by the protrusion 23a. Providing the protrusion 23a reduces the contact area of ​​the heater holder 23 with the heater 22, and the amount of heat transferred from the heater 22 to the heater holder 23. However, the heater holder 23 may not be provided with the protrusion 23a, and may be made to contact the heater 22 over the entire short side. This increases the amount of heat transferred from the heater 22 to the heater holder 23, and suppresses temperature rises in the heater 22 and the fixing belt 20.

[0031] The thermistor 25 is in contact with the rear surface of the substrate 30 to detect the temperature thereof.

[0032] 2, when the fixing device 9 according to this embodiment starts a printing operation, the pressure roller 21 is driven to rotate, and the fixing belt 20 starts to rotate. Furthermore, power is supplied to the resistance heating element 40 of the heater 22, thereby heating the fixing belt 20. Then, when the temperature of the fixing belt 20 reaches a predetermined target temperature (fixing temperature), the paper P carrying the unfixed toner image is transported between the fixing belt 20 and the pressure roller 21 (fixing nip N2). As a result, the unfixed toner image is heated and pressurized to be fixed to the paper P.

[0033] Next, a more detailed configuration of the heater 22 will be described with reference to Fig. 3. Fig. 3(a) is a plan view of the heater 22, and Fig. 3(b) is a cross-sectional view taken along line AA of Fig. 3(a).

[0034] The heater 22 includes, in order from the heater holder 23 side (the left side in FIG. 2), a first insulating protective layer 31, a first insulating glass layer 32, a substrate 30, a second insulating protective layer 33, a conductor layer 34, and a second insulating glass layer 35.

[0035] The substrate 30 is a plate-like member extending in the longitudinal direction. In this embodiment, the substrate 30 has a longitudinal width of 270 mm, a lateral width of 8 mm, and a thickness of 0.3 mm. The longitudinal direction of the heater 22 is the direction of the double-headed arrow X in FIG. 3(a), and the lateral direction is the direction of the double-headed arrow Y. The lateral direction of the heater 22 is a direction along the surface of the substrate 30 on which the resistance heating element 40 and the like are provided, and is a direction intersecting the longitudinal direction (a direction perpendicular to the longitudinal direction in this embodiment).

[0036] In this embodiment, the base material 30 is made of stainless steel. Alternatively, the base material 30 may be made of an iron-based alloy, an aluminum alloy, or a copper alloy. The base material 30 may also be made of ceramics such as alumina or aluminum nitride.

[0037] A conductor layer 34 is formed on the base material 30 via a second insulating protective layer 33. This ensures insulation between the conductor layer 34 and the base material 30. A resistance heating element 40, electrode portions 41 (41a, 41b), and a power supply line 42 are provided on the conductor layer 34. When the base material 30 is formed from ceramic, which is an insulating material, the second insulating protective layer 33 is not necessary.

[0038] The resistance heating element 40 can be formed, for example, by applying a paste prepared by mixing silver palladium (AgPd) and glass powder to the substrate 30 by screen printing or the like, and then firing the substrate 30. In this embodiment, the resistance value of the resistance heating element 40 is set to 10Ω at room temperature. The material of the resistance heating element 40 may be a resistance material such as silver alloy (AgPt) or ruthenium oxide (RuO2) in addition to the above-mentioned materials. The material of the power supply line 42 and the electrode part 41 can be formed by screen printing or the like using silver (Ag) or silver palladium (AgPd). The power supply line 42 is made of a conductor having a smaller resistance value than the resistance heating element 40.

[0039] The first insulating protective layer 31, the first insulating glass layer 32, the second insulating protective layer 33, the conductor layer 34, and the second insulating glass layer 35 are made of heat-resistant glass having a thickness of, for example, 75 μm.

[0040] The second insulating glass layer 35 covers the resistance heating element 40 and the power supply line 42 to insulate and protect them and maintain their sliding properties with the fixing belt 20. The electrode portion 41 is not covered by the second insulating glass layer 35.

[0041] Fig. 4 is a perspective view showing a state in which the connector 70 is attached to the heater 22 and the heater holder 23. As shown in Fig. 4, the connector 70 has a resin housing 71 and a leaf spring contact terminal 72 fixed to the housing 71. The contact terminal 72 has a pair of contact portions 72a that come into contact with the electrode portions 41 of the heater 22. In addition, a harness 73 for power supply is connected to the connector 70 (contact terminals 72).

[0042] The connector 70 is attached so as to sandwich the heater 22 and the heater holder 23 from the front and back sides together. As a result, each contact portion 72a of the contact terminal 72 elastically contacts (pressure-welds) with the electrode portion 41. As a result, the resistance heating element 40 and a power source provided in the image forming apparatus are electrically connected via the connector 70, and the resistance heating element 40 becomes capable of being supplied with power from the power source.

[0043] FIG. 5 is a diagram showing a power supply circuit to the heater according to this embodiment.

[0044] As shown in FIG. 5, in this embodiment, a power supply circuit for supplying power to each resistance heating element 40 is configured by electrically connecting an AC power source 200 and an electrode portion 41 of the heater 22.

[0045] In addition, a switch 210 is provided between the AC power supply 200 and the electrode unit 41. By turning the switch 210 on and off, it is possible to switch between the supply of electricity to the resistance heating element 40 and the absence or presence of electricity.

[0046] The control unit 220 controls the power supply to the resistance heating element 40 based on the temperature detected by thermistor 25 (see FIG. 2) and also taking into consideration the amount of heat transferred to the paper when the paper is passed. The control unit 220 is composed of a microcomputer including a CPU, ROM, RAM, an I / O interface, etc. In this embodiment, the control unit 220 is provided in the main body of the image forming apparatus, but may also be provided in the fixing device.

[0047] However, in an image forming apparatus equipped with the above-mentioned fixing device, there is a problem that electrical problems may occur, which may result in abnormal images.

[0048] For example, the surface layers of the fixing belt 20 and the pressure roller 21 become charged when the charged paper P passes through the fixing nip N2 during the transfer operation. In addition, the surfaces of the fixing belt 20 and the pressure roller 21 become frictionally charged due to the rotation of the fixing belt 20 and the pressure roller 21. Then, when the paper P passes through the fixing nip N2 with the surface layers of the fixing belt 20 and the pressure roller 21 charged, the toner image on the paper P is electrostatically offset, causing an abnormal image. The above problem is particularly noticeable in a low-humidity environment or when forming an image on paper whose surface has become highly resistive due to a coating agent.

[0049] In addition, in the fixing device 9 of the present embodiment in which an AC voltage is applied to the heater 22, the insulating layer provided on the heater 22 and the surface layer of the fixing belt 20 are equivalent to a capacitor. Therefore, in a configuration in which the heater 22 and the fixing belt 20 are in physical contact with each other (however, they may be indirectly in contact with each other via a sheet material or the like), an AC voltage is applied to the fixing nip N2 via the fixing belt 20. As shown in FIG. 6, when the paper P is in contact with both the transfer nip N1 and the fixing nip N2, this AC voltage propagates to the transfer nip N1 via the paper P (see the direction of the arrow in FIG. 6). This AC voltage affects the transfer electric field, causing periodic density unevenness in the transferred image, which is the cause of so-called banding images. In particular, when the paper P has low resistance, such as in a high humidity environment or when thin paper is used as the paper P, the above problem becomes more pronounced. Also, in areas where the AC power supply is 220-240 [V], the above problem becomes more pronounced. This banding image problem occurs when a sheet P having a transport length longer than the sheet transport distance L between the transfer nip N1 (the center position of the transfer nip N1) and the fixing nip N2 (the center position of the fixing nip N2) is passed through. For convenience, FIG. 6 shows a case in which the transfer nip N1 and the fixing nip N2 are arranged on a straight line, but this is not limited to this, and the path may be curved along the way. In this case, the total distance the sheet is transported between both nips is taken as the transport distance L. FIG. 6 also shows a fixing device having a configuration in which the static elimination member of this embodiment, which will be described later, is not provided. A transfer power source 230 is connected to the transfer roller 116.

[0050] Next, the configuration of the fixing device of this embodiment with respect to the above electrical problem will be described.

[0051] As shown in Fig. 6, the fixing belt 20 has, from the inside, a base 20a as a conductive layer and a release layer 20b. The inner surface of the base 20a constitutes the inner circumferential surface of the fixing belt 20. The outer surface of the release layer 20b constitutes the outer circumferential surface of the fixing belt 20. The release layer 20b of this embodiment is a non-conductive layer formed of PFA from the viewpoint of increasing durability and ensuring releasability. Alternatively, a fluorine-based resin such as PTFE can be used as the release layer 20b.

[0052] The pressure roller 21 has a solid iron core 21a, an elastic layer 21b, and a release layer 21c. The elastic layer 21b is made of insulating silicone rubber. The release layer 21c of the pressure roller 21 is a conductive layer formed by adding a conductive filler such as carbon to PFA. The outer surface of the release layer 21c constitutes the outer circumferential surface of the pressure roller 21. The outer circumferential surface of the pressure roller 21 has a surface resistivity of 40×10 6 [Ω / □]~160×10 6 The surface resistivity is set in the range of [Ω / □]. The surface resistivity was measured using a high resistance resistivity meter (product name: Hiresta IP [MCP-HT450], manufactured by Mitsubishi Chemical Analytech) under the following conditions. Probe used: Type HA (2-pin type: pitch 20 mm) Measurement mode: ρs Measurement time: 10 seconds Applied voltage: 250V Measurement environment: 27℃80%RH after being left for 24 hours Measurement points: 4 points in the circumferential direction (90° intervals), 3 points in the axial direction (center, 20 mm inside from both ends), total of 12 points Surface resistivity: Average value of the above 12 points

[0053] 7, an exposed portion 20d is provided on one end side in the longitudinal direction of the fixing belt 20. The exposed portion 20d is a portion of the fixing belt 20 where the release layer 20b is not provided and the base 20a, which is a conductive layer, is exposed to the outside. The exposed portion 20d is provided outside the paper passing area in the longitudinal direction, and in this embodiment, it is provided within a range of 5 mm from one end of the fixing belt 20.

[0054] 7 and 8, a charge removing brush 27 as a charge removing member is in contact with the pressure roller 21 outside the paper passing area at one end side in the longitudinal direction of the pressure roller 21. In this embodiment, the charge removing brush 27 is made of stainless steel.

[0055] The charge removing brush 27 is grounded via a resistor 46. The resistor 46 has a resistance of 1.1×10 3 ~2×10 7 It is set in the range of [Ω].

[0056] In this embodiment, the electric charges on the surface layers of the fixing belt 20 and the pressure roller 21 are removed by the charge removal brush 27 through the surface layer of the pressure roller 21. This makes it possible to suppress the charge on the surface layers of the fixing belt 20 and the pressure roller 21 and to prevent electrostatic offset of the toner image on the paper P during the fixing process.

[0057] Incidentally, in the above-described configuration in which the charge removal brush 27 is in contact with the surface layer of the pressure roller 21, when the paper P is in contact with both the transfer nip N1 and the fixing nip N2 (see FIG. 6), the transfer current may leak from the transfer roller 116 to the ground side via the paper P, the pressure roller 21, and the charge removal brush 27. This makes it impossible to obtain the electric field necessary for transfer, resulting in poor transfer. In particular, in an environment with high relative humidity, the resistance value of the paper P decreases, making this problem more noticeable.

[0058] In contrast to this, in this embodiment, by setting the surface resistivity of the pressure roller 21 to the above value, it is possible to set an appropriate resistance value of the ground path from the pressure roller 21 to ground via the resistor 46. This makes it possible to suppress the current flowing to the discharging brush 27 side and suppress the leakage of the transfer current.

[0059] The greater the surface resistivity of the pressure roller 21, the more the leakage of the transfer current can be suppressed. However, on the other hand, the greater the surface resistivity of the pressure roller 21, the lower the ability to remove static electricity from the surface layers of the fixing belt 20 and the pressure roller 21. Therefore, it is necessary to set the surface resistivity of the pressure roller 21 to an appropriate value, taking into account the balance between these two factors.

[0060] Therefore, in this embodiment, the resistance value of the paper actually used in the image forming apparatus is measured, and the surface resistivity of the pressure roller 21 is set based on the measurement results. Specifically, multiple brands of PPC paper were left for 24 hours or more in an environment of 27°C and 80% RH. Then, the surface resistivity was measured with a Type HA probe using a measuring instrument Hiresta IP (MCP-HT450) manufactured by Mitsubishi Chemical Analytech. As a result, the paper with the lowest resistivity had a resistance of 100×106 [Ω / □] (100V applied, 10sec value). Therefore, the resistance per 1mm in the paper transport direction is 1×10 6 Since the length L in Figure 6 is 80 mm, the resistance of the paper is 80 × 10 6 It becomes [Ω].

[0061] In this embodiment, taking the above balance into consideration, the resistance value of the surface layer of the pressure roller 21 is set in the range of 0.5 to 2 times the resistance value of the paper. 6 [Ω / □] Larger than 160×10 6 It is preferable to set it in the range smaller than [Ω / □], specifically, 100×10 6 This makes it possible to suppress leakage of the transfer current and obtain an appropriate static elimination capability for the surfaces of the fixing belt 20 and the pressure roller 21.

[0062] In this way, the resistance per mm of paper is 1 × 10 6 [Ω / mm] and the distance between the transfer nip and the fixing nip is L [mm], the surface resistivity Rp [Ω / □] of the surface layer of the pressure roller 21 can be set to satisfy the range of the following formula 1. This makes it possible to suppress the leakage of the transfer current to the surface layer side of the pressure roller 21 as described above, and to ensure the static elimination capability for the surfaces of the fixing belt 20 and the pressure roller 21.

[0063]

number

[0064] Furthermore, the resistance value per mm in the length in the paper transport direction is RA [Ω / mm], and the surface resistivity Rp [Ω / □] of the surface layer of the pressure roller 21 may be set by the following equation 2. This makes it possible to suppress leakage of the transfer current to the surface layer side of the pressure roller 21 and ensure the static elimination capability for the surfaces of the fixing belt 20 and the pressure roller 21.

[0065]

number

[0066] 7, the second insulating glass layer 35 of the heater 22 is provided with a protrusion 35a and another protrusion 35b. The protrusion 35a and the other protrusion 35b protrude toward the inner surface of the fixing belt 20 (the right side in FIG. 2 and the upper side in FIG. 3b) and apply pressure to the inner surface of the fixing belt 20. The protrusion 35a and the other protrusion 35b are integrally formed when the second insulating glass layer 35 is formed by the above-mentioned screen printing.

[0067] The protruding portion 35a and the other protruding portions 35b are provided so that their height (protruding amount) is greater than the thickness of the release layer 20b of the fixing belt 20. Specifically, the height is formed to be 25 μm to 100 μm.

[0068] In the longitudinal direction, the convex portion 35a and the other convex portion 35b are provided outside the maximum paper passing area C of the fixing device. The convex portion 35a is provided at a position corresponding to the exposed portion 20d in the longitudinal direction. In this embodiment, the convex portion 35a and the other convex portion 35b extend in the paper conveying direction (in other words, the direction of rotation of the fixing belt 20 in the fixing nip N2, the direction of the arrow A in FIG. 2), and are provided with a length longer than the fixing nip N2. The convex portion 35a and the other convex portion 35b are inclined toward the center side in the longitudinal direction of the fixing belt 20 (in other words, toward the center side of the maximum paper passing area C) as they move from the upstream side to the downstream side in the paper conveying direction. In other words, the interval between the convex portion 35a and the other convex portion 35b becomes smaller from the upstream side to the downstream side in the paper conveying direction.

[0069] In this embodiment, the protrusion 35a is provided at a position corresponding to the exposed portion 20d, so that the exposed portion 20d and the surface layer of the pressure roller 21 can be stably contacted. In other words, since the release layer 20b is not provided on the exposed portion 20d, the thickness of the fixing belt 20 is accordingly thin, and the fixing belt 20 is less likely to contact the pressure roller 21. However, the protrusion 35a abuts the fixing belt 20 from its inner surface at the position of the exposed portion 20d, so that the exposed portion 20d can be brought into contact with the release layer 21c of the pressure roller 21. In other words, the conductive layer of the fixing belt 20 can be brought into contact with the conductive layer of the pressure roller 21, and the fixing belt 20 can be grounded via the pressure roller 21 and the charge removal brush 27. As a result, a part of the AC component (50 Hz) of the AC power source 200 that propagates from the resistance heating element 40 of the heater 22 to the fixing belt 20 and the paper P to the transfer nip N1 can be released to the ground side via the charge removal brush 27. That is, the AC component is prevented from being transmitted from the resistance heating element 40 to the second insulating glass layer 35 to the fixing belt 20 (the cylindrical body 20a to the release layer 20b) to the paper P to the transfer nip N1, and is transmitted from the resistance heating element 40 to the second insulating glass layer 35 to the exposed portion 20d of the cylindrical body 20a to the release layer 21c of the pressure roller 21 to the charge removing brush 27, so that the AC component can be released to the ground side. This makes it possible to prevent the banding image from occurring.

[0070] As described above, the above-described configuration of this embodiment can solve the electrical problems in the fixing device 9 and the transfer section therearound.

[0071] In addition, the capacitive reactance Xc of the second insulating glass layer 35 of the heater 22 is 5×10 6 ~12×10 6 Considering that the resistance of resistor 46 is 3 × 10 6 It is preferable to set the resistance of the resistor 46 to 2×10 [Ω] or less. This makes it possible to suppress the propagation of AC components to the transfer side. 6 It is set to [Ω].

[0072] In this embodiment, the surface resistivity of the surface layer of the pressure roller 21 and the resistance value of the resistor 46 are set to the required values, respectively, to appropriately control the flow of current. In other words, the release layer 21c of the pressure roller 21 is set to the required surface resistivity to suppress charging of the surface layer while suppressing leakage of transfer current. In addition, the resistance value of the resistor 46 is set to the required value to appropriately suppress propagation of the AC component (50 Hz) of the AC power source 200. However, the surface resistivity of the surface layer of the pressure roller 21 and the resistance value of the resistor 46 are not limited to the above, and it goes without saying that appropriate values ​​can be set according to the paper conveyance distance L and the capacitive reactance Xc of the second insulating glass layer 35, etc.

[0073] Moreover, by making the height of the protrusions 35a greater than the thickness of the release layer 20b of the fixing belt 20, the exposed portion 20d can be brought into contact with the pressure roller 21 more reliably.

[0074] As shown in FIG. 7, by providing the convex portion 35a and the other convex portion 35b outside the maximum paper passing area C, the fixing belt 20 can be pressed against the pressure roller 21 without affecting the image on the paper P or the image fixing operation.

[0075] In addition, the protrusions 35a and the other protrusions 35b can suppress leakage of lubricant such as grease applied to the sliding portion between the fixing belt 20 and the pressure roller 21. In other words, the protrusions 35a and the other protrusions 35b extend in the paper conveying direction, so that the protrusions 35a and the other protrusions 35b function as wall surfaces that fill the gap between the other portion of the second insulating glass layer 35 and the inner surface of the fixing belt 20, and can suppress leakage of the lubricant to the outside in the longitudinal direction. In particular, in this embodiment, the protrusions 35a and the other protrusions 35b are inclined in a direction in which the distance between them becomes smaller as they move from the upstream side to the downstream side in the rotation direction of the fixing belt 20. This allows the lubricant to be guided toward the center in the longitudinal direction toward the downstream side, and can effectively suppress leakage of the lubricant to the outside in the longitudinal direction.

[0076] Although an embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the gist of the present invention.

[0077] Although the case where the charge removal brush 27 is in contact with the surface layer of the pressure roller 21 has been described, the present invention is not limited thereto. For example, as shown in FIG. 9, the charge removal brush 27 may be in contact with the cylindrical body 20a, which is the conductive layer of the fixing belt 20. Even in this case, the fixing belt 20 is provided with an exposed portion 20d (see FIG. 7) that is in contact with the surface layer of the pressure roller 21. In this embodiment, the charge on the surface layer of the pressure roller 21 can be discharged to the ground side via the exposed portion 20d and the charge removal brush 27. In addition, the AC component of the AC power source 200 can be transmitted from the resistance heating element 40 to the second insulating glass layer 35, the cylindrical body 20a, and the charge removal brush 27, and can be released to the ground side.

[0078] In the above description, the second insulating glass layer 35 of the heater 22 is in direct contact with the inner surface of the fixing belt 20, but another conductive member may be interposed therebetween. For example, as shown in FIG. 10, the fixing device 9 has a heat equalizing plate 50 as a high thermal conductive member between the second insulating glass layer 35 and the fixing belt 20.

[0079] The heat equalizing plate 50 is a member that contacts the fixing belt 20 from its inner circumferential surface side. The heat equalizing plate 50 is made of a member having a higher thermal conductivity than the base material 30. In this embodiment, aluminum is used as the material for the heat equalizing plate 50, and the thermal conductivity is set to about 236 W / m·K, for example. Alternatively, SUS (thermal conductivity is 16.7 to 20.9 W / m·K) or a copper-based material (thermal conductivity is 381 W / m·K, for example) can be used for the heat equalizing plate 50.

[0080] Next, a method for calculating the thermal conductivity will be described. When calculating the thermal conductivity, first, the thermal diffusivity of the object is measured, and then the thermal conductivity is calculated using the measured thermal diffusivity.

[0081] The thermal diffusivity was measured using a thermal diffusivity / thermal conductivity measuring device (product name: ai-Phase Mobile 1u, ai-Phase Corporation).

[0082] In order to convert the thermal diffusivity to thermal conductivity, the values ​​of density and specific heat capacity are necessary. A dry automatic density meter (product name: Accupyc 1330, manufactured by Shimadzu Corporation) was used to measure the density. A differential scanning calorimeter (product name: DSC-60, manufactured by Shimadzu Corporation) was used to measure the specific heat capacity, and sapphire was used as a reference material with a known specific heat capacity. In this embodiment, the specific heat capacity was measured five times, and the average value at 50°C was used. If the density and specific heat capacity are ρ and C, respectively, the thermal conductivity λ can be obtained from the thermal diffusivity α obtained by the thermal diffusivity measurement by the following formula 3.

[0083]

number

[0084] Furthermore, by bringing the heat equalizing plate 50 into contact with the fixing belt 20 in the longitudinal direction, the heat of the fixing belt 20 can be transferred and equalized in the longitudinal direction, thereby making it possible to suppress temperature unevenness in the fixing belt 20 in the longitudinal direction.

[0085] In this embodiment, a convex portion is provided on the surface of the heat equalizing plate 50 facing the inner surface of the fixing belt 20, as in the previously described embodiment. This allows the exposed portion 20d to come into contact with the surface layer of the pressure roller 21. Also, a charge removing member is in contact with the base 20a of the fixing belt 20 or the surface layer of the pressure roller 21. This allows electrical problems occurring in the fixing device and its surroundings to be solved, as in the previously described embodiment.

[0086] Furthermore, the static elimination member of the present invention is not limited to the static elimination brush described in the above embodiment. For example, as shown in Fig. 11, in this embodiment, a static elimination sheet 28 as a static elimination member is provided on the inside of the fixing belt 20. The static elimination sheet 28 contacts the inner surface of the fixing belt 20. The static elimination sheet 28 is sandwiched between the heater holder 23 and the stay 24, and the part protruding from the sandwiched part contacts the inner surface of the fixing belt 20 at its tip side. The static elimination sheet 28 is grounded via the metal stay 24 and a resistor 46.

[0087] In this embodiment, the static elimination sheet 28 is made of the same polyimide as the base body 20a of the fixing belt 20. This allows the static elimination sheet 28 and the inner surface of the fixing belt 20 to slide smoothly with each other.

[0088] In this embodiment, the heater holder 23 is provided with a guide portion 26, and a static elimination sheet 28 is disposed between the guide portion 26 and the stay 24. When the fixing belt 20 rotates following the rotation of the pressure roller 21, the inner peripheral surface of the fixing belt 20 comes into contact with and is guided by the belt facing surface 260 of the guide portion 26, so that the fixing belt 20 rotates stably and smoothly. However, the guide portion 26 is not necessarily provided.

[0089] In the fixing device described above, by providing the antistatic sheet 28, electrical problems occurring in the fixing device and its surroundings can be solved, as in the previous embodiment.

[0090] The image forming apparatus according to the present invention is not limited to the monochrome image forming apparatus shown in FIG. 1, but may be a color image forming apparatus, a copying machine, a printer, a facsimile, or a combination machine of these.

[0091] For example, the image forming apparatus 100 shown in Fig. 12 includes four imaging units 1Y, 1M, 1C, and 1Bk that are detachable from the image forming apparatus main body. Each imaging unit 1Y, 1M, 1C, and 1Bk has the same configuration except that it contains a developer of a different color, yellow, magenta, cyan, or black. These developers correspond to the color separation components of a color image. Each imaging unit 1Y, 1M, 1C, and 1Bk includes a photoconductor 2, a charging device 3, a developing device 4, and a cleaning device 5.

[0092] The image forming apparatus 100 also includes an exposure device 6, a paper feeder 7, a transfer device 8, a fixing device 9, and a paper discharge device 10. The transfer device 8 transfers the toner image formed on each photoconductor 2 onto a sheet of paper P. The paper discharge device 10 discharges the sheet of paper P to the outside of the apparatus. The imaging units 1, the photoconductor 2, the charging device 3, the exposure device 6, the transfer device 8, etc. constitute an image forming means for forming an image on a sheet of paper.

[0093] The transfer device 8 has an endless intermediate transfer belt 11 as an intermediate transfer body, four primary transfer rollers 12 as primary transfer members, a secondary transfer roller 13 as a secondary transfer member, and an opposing roller 14. The intermediate transfer belt 11 is stretched by a plurality of rollers. The primary transfer rollers 12 transfer the toner images on the photoconductors 2 to the intermediate transfer belt 11. The secondary transfer rollers 13 transfer the toner images transferred onto the intermediate transfer belt 11 to a sheet of paper P. Each of the primary transfer rollers 12 contacts the photoconductor 2 via the intermediate transfer belt 11. As a result, the intermediate transfer belt 11 and each photoconductor 2 come into contact with each other, and a primary transfer nip is formed between them. Meanwhile, the secondary transfer roller 13 contacts the opposing roller 14 via the intermediate transfer belt 11. As a result, a secondary transfer nip N1 as a nip portion or transfer portion is formed between the secondary transfer roller 13 and the intermediate transfer belt 11. The opposing roller 14 is a roller that stretches the intermediate transfer belt 11.

[0094] Further, a pair of timing rollers 15 is provided on the paper transport path B between the paper feeder 7 and the secondary transfer nip N1.

[0095] Next, the printing operation of the image forming apparatus will be described with reference to FIG.

[0096] When an instruction to start a printing operation is given, in each of the imaging units 1Y, 1M, 1C, and 1Bk, the photoconductor 2 is rotated clockwise in FIG. 13, and the surface of the photoconductor 2 is charged to a uniform high potential by the charging device 3. Next, the exposure device 6 exposes the surface of each photoconductor 2 based on the image information of the original document read by the original reading device or the print information instructed to be printed from the terminal. This reduces the potential of the exposed portion, forming an electrostatic latent image. Then, toner is supplied from the developing device 4 to this electrostatic latent image, and a toner image is formed on each photoconductor 2.

[0097] The toner images formed on each photoconductor 2 rotate with the rotation of each photoconductor 2 and reach the primary transfer nip (the position of the primary transfer roller 12). The toner images are then transferred to the intermediate transfer belt 11, which rotates counterclockwise in FIG. 13, so as to be superimposed one on the other. The toner images transferred onto the intermediate transfer belt 11 are then transported to the secondary transfer nip (the position of the secondary transfer roller 13) with the rotation of the intermediate transfer belt 11. The toner images are transferred to the paper P that has been transported at the secondary transfer nip. This paper P is supplied from the paper supply device 7. The paper P supplied from the paper supply device 7 is stopped once by the timing roller 15, and then transported to the secondary transfer nip in accordance with the timing at which the toner image on the intermediate transfer belt 11 reaches the secondary transfer nip. Thus, a full-color toner image is carried on the paper P. After the toner image is transferred, the toner remaining on each photoconductor 2 is removed by each cleaning device 5.

[0098] The paper P onto which the toner image has been transferred is transported to a fixing device 9, which fixes the toner image onto the paper P. Thereafter, the paper P is discharged outside the apparatus by a paper discharge device 10, completing a series of printing operations.

[0099] Examples of recording media include paper P (plain paper), as well as cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheets, plastic film, prepreg, copper foil, and the like.

[0100] Furthermore, the present invention is not limited to the fixing device described in the above embodiment, but can also be applied to a drying device that dries ink applied to paper, and further to a heating device such as a laminator that thermocompresses a film as a covering member onto the surface of a sheet such as paper, or a heat sealer that thermocompresses the seal portion of a packaging material, thereby solving electrical problems that occur in and around the heating device. [Explanation of symbols]

[0101] 1. Image forming device 9 Fixing device (heating device) 20 Fixing belt (heating member) 20a Base (conductor layer) 20b Release layer 21 Pressure roller (pressure member) 21a Core metal 21b Elastic layer (middle layer) 21c Release layer 22 Heater (heating element) 24 Stay (support member) 27 Antistatic brush (antistatic material) 28 Antistatic sheet (antistatic material) 30 Base material 35 Second insulating glass layer 35a Convex part 40 Resistance heating element 46 Resistance N1 Transfer nip (nip or transfer area) N2 Fixing nip (nip part) X Longitudinal direction Y Short side [Prior art documents] [Patent documents]

[0102] [Patent Document 1] JP 2015-84084 A

Claims

1. a planar heating element having a base material and a resistance heating element; A rotating heating element; A pressure member that presses the heating member; A heating device including a static eliminator, The heating element has a conductive layer; the heating member has an exposed portion where the conductive layer is exposed to an outer surface side, The pressure member has an outer surface made of a conductive material, the static eliminator is in contact with the conductive layer or the outer surface of the pressure member, A heating device characterized in that a protrusion is provided on the inside of the heating member at a position corresponding to the exposed portion, the protrusion protruding toward the inner surface of the heating member and applying pressure to the heating member from the inner surface side.

2. The heating device according to claim 1 , wherein the protrusion is provided on the heating element.

3. The heating element has an insulating layer, 3. The heating device according to claim 2, wherein the protrusion is made of the same material as the insulating layer.

4. 4. The heating device according to claim 1, wherein in a rotation direction of the heating member at a nip portion between the heating member and the pressure member, the convex portion is inclined from an end side of the heating body in a longitudinal direction toward a center side from an upstream side to a downstream side in the rotation direction of the heating member.

5. The heating device according to claim 1 , wherein the charge removing member is grounded via a resistor.

6. 6. The heating device according to claim 1, wherein the charge removing member is a conductive brush and is in contact with the exposed portion or the outer surface of the pressure member.

7. 6. The heating device according to claim 1, wherein the static eliminator is a conductive sheet and is in contact with the conductive layer from its inner surface side.

8. 8. The heating device according to claim 7, further comprising a support member for supporting the heating body from the side opposite to the pressing member. The charge removing member is in contact with the supporting member and is grounded via the supporting member.

9. The surface resistivity of the pressure member is 1×10 ７ [Ω / □] ~ 1 x 10 ９ The heating device according to any one of claims 1 to 8, wherein the resistance is [Ω / □].

10. The heating device according to claim 1 , wherein the pressure member has a non-conductive intermediate layer.

11. 11. The heating device according to claim 1, which is a fixing device for fixing an image on a recording medium by heat.

12. An image forming apparatus comprising the fixing device according to claim 11.

Images