Fixing unit and image forming apparatus

Abstract

To transmit heat of a heating member to an annular belt while preventing variations in the heat with respect to a longitudinal direction, thereby improving image quality.SOLUTION: A fuser 8 of an image forming apparatus 1 includes: a fixing belt 28; a planar heater 30 that is provided on an inner peripheral surface of the fixing belt 28; a thermal diffusion member 32 that is formed of metal, and is provided between the planar heater 30 and the fixing belt 28; and a back plate 34 that is formed of metal, has a lower thermal conductivity than the thermal diffusion member 32, and is provided on the opposite side of the fixing belt 28 with respect to the planar heater 30.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a fixing unit and an image forming apparatus, and is suitably applied to, for example, an electrophotographic printer. [Background technology]

[0002] Conventionally, a widespread type of image forming device (also called a printer) performs printing processing by forming a developer image using toner (also called a developer) in an image forming unit based on an image supplied from a computer device or the like, transferring the developer image to a medium such as paper, and then fixing the image by applying heat and pressure in a fixing unit.

[0003] One such fixing unit is one in which a heating member is disposed on the inner circumferential side of the circular belt, a heat diffusion member is provided between the heating member and the circular belt, and a heat storage member is provided on the opposite side of the heating member from the circular belt side, and the heat of the heating member is transferred to the circular belt via the heat diffusion member. One such fixing unit has been proposed that makes the thermal conductivity of the heat diffusion member higher than that of the heat storage member, thereby making it easier to transfer the heat of the heating member to the circular belt and making it compatible with high-speed printing (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Application No. 2022-115000 Summary of the Invention [Problem to be solved by the invention]

[0005] In such a fixing unit, it is desirable to improve image quality by suppressing the variation in heat of the heating member in the longitudinal direction and transmitting the heat to the circular belt.

[0006] The present invention has been made in consideration of the above points, and aims to propose a fixing unit and an image forming apparatus that can improve image quality. [Means for solving the problem]

[0007] In order to solve this problem, the fixing unit of the present invention includes a circular belt, a heating member provided on the inner surface side of the circular belt, a first heat diffusion member made of metal and provided between the heating member and the circular belt, and a second heat diffusion member made of metal, having a lower thermal conductivity than the first heat diffusion member, and provided on the opposite side of the heating member from the circular belt.

[0008] The image forming apparatus of the present invention is provided with the fixing unit described above.

[0009] The present invention can efficiently heat the nip portion while suppressing the variation in heat of the heating member in the longitudinal direction. Effect of the Invention

[0010] According to the present invention, it is possible to realize a fixing unit and an image forming apparatus that can efficiently heat a nip portion while suppressing the heat variation of a heating member in the longitudinal direction, thereby improving image quality. [Brief description of the drawings]

[0011] [Figure 1] FIG. 2 is a left side view illustrating a configuration of the image forming apparatus. [Diagram 2] FIG. 2 is a front view showing the configuration (1) of the fixing unit. [Diagram 3] FIG. 3 is a cross-sectional view taken along the line AA in FIG. 2, showing the configuration (2) of the fixing unit. [Figure 4] FIG. 2 is a block diagram showing a control configuration of the image forming apparatus. [Diagram 5] 4 is a block diagram showing the configuration of a fixing control unit and a sheet heater; FIG. [Figure 6] 5A and 5B are diagrams illustrating the relationship between the thermal conductivity and the amount of heat transfer of a heat diffusion member and a back plate. [Figure 7] 4 is a graph showing the relationship between the thermal conductivity of the heat diffusion member and the back plate and the temperature of the fixing unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, modes for carrying out the invention (hereinafter referred to as embodiments) will be described with reference to the drawings.

[0013] [1. Configuration of image forming device] As shown in FIG. 1, the image forming device 1 is, for example, a printer using an electrophotographic method, and forms a black-and-white image or a color image on a print medium P such as paper by performing an image forming operation using a developer such as toner. In the following, a position close to the paper feed cassette 3 as viewed from an arbitrary position on the conveying path along which the print medium P is conveyed, or a direction toward the paper feed cassette 3, is referred to as upstream. Also, a position close to the stacker 11 into which the print medium P is discharged and stacked as viewed from an arbitrary position on the conveying path, or a direction toward the stacker 11, is referred to as downstream. Furthermore, a direction from upstream to downstream is referred to as a conveying direction. Furthermore, in the following, the right end portion in FIG. 1 is the front of the image forming device 1, and the up-down direction, left-right direction, and front-rear direction are defined when viewed from the front, and the description will be given after the above-mentioned. The image forming device 1 is a so-called direct transfer type, that is, a toner image as a developer image is directly transferred from a photoconductor drum 20 (described later) of an image forming unit 14 (described later) to the print medium P.

[0014] The image forming apparatus 1 is controlled by a print control unit 50 (FIG. 4). The print control unit 50 has a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), which are not shown, and executes various processes by reading and executing predetermined programs. The image forming apparatus 1 also has a paper feed cassette 3, a hopping roller 4, a registration roller 5, a conveying roller 6, an image forming unit 7, a fixing unit 8, and discharge rollers 9 and 10 inside a box-shaped housing 2.

[0015] The paper feed cassette 3 is disposed at the bottom of the housing 2 and accommodates a plurality of stacked print media P. A hopping roller 4 is provided downstream of the paper feed cassette 3. The hopping roller 4 rotates while being in pressure contact with the surface of the print medium P, thereby feeding the print medium P downstream along the transport path.

[0016] A registration roller 5 is provided downstream of the hopping roller 4. The registration roller 5 transports the printing medium P toward the transport roller 6. When the printing medium P is transported, the leading edge of the printing medium P is abutted against the registration roller 5, thereby correcting any skew of the printing medium P. A transport roller 6 is provided downstream of the registration roller 5. The transport roller 6 transports the printing medium P toward the image forming unit 7 provided downstream. The image forming unit 7 transfers an image onto the printing medium P and transports it to a fixing unit 8.

[0017] The fixing device 8 applies heat and pressure to the toner image transferred onto the printing medium P transported from the transfer belt unit 16 of the image forming section 7, thereby fixing the toner image onto the printing medium P, and also transports the printing medium P along the transport path toward the discharge rollers 9.

[0018] Discharge rollers 9 are provided downstream of the fixing unit 8. The discharge rollers 9 transport the print medium P toward the discharge rollers 10 provided downstream. The discharge rollers 10 transport the print medium P toward a stacker 11. In this way, the image forming apparatus 1 loads the print medium P, on which the toner image has been fixed, into the stacker 11 provided outside the housing 2.

[0019] A write sensor 12 and an EXIT sensor 13, which are sensors for detecting the presence or absence of a print medium P, are provided on the transport path of the print medium P. The detection signal of the write sensor 12 serves as a reference for the exposure timing of an LED head 15 (described later) and the timing for applying a high voltage to a transfer roller 25 (described later). The detection signal of the EXIT sensor 13 serves as a reference for whether or not a series of image formation processes for the print medium P has been completed.

[0020] [2. Configuration of image forming unit] The image forming section 7 is a mechanism that forms an image (toner image) and transfers the image onto the print medium P. The image forming section 7 has four image forming units 14 (image forming units 14K, 14Y, 14M, and 14C), four LED heads 15 (LED heads 15K, 15Y, 15M, and 15C), and a transfer belt unit 16. The image forming units 14K, 14Y, 14M, and 14C are arranged in this order along the transport direction of the print medium P. Hereinafter, the image forming units 14K, 14Y, 14M, and 14C are collectively referred to as image forming units 14, and the LED heads 15K, 15Y, 15M, and 15C are collectively referred to as LED heads 15.

[0021] The image forming unit 14 forms an image using toner, which is a developer, based on print data transmitted from a higher-level device such as a personal computer. The image forming units 14K, 14Y, 14M, and 14C form images of black, yellow, magenta, and cyan, respectively. The image forming units 14K, 14Y, 14M, and 14C have the same configuration, except that they form images using toners of different colors. Each image forming unit 14 has a photoconductor drum 20 (photoconductor drums 20K, 20Y, 20M, and 20C) and a toner cartridge 21 (toner cartridges 21K, 21Y, 21M, and 21C). Hereinafter, the photoconductor drums 20K, 20Y, 20M, and 20C are collectively referred to as photoconductor drums 20, and the toner cartridges 21K, 21Y, 21M, and 21C are collectively referred to as toner cartridges 21.

[0022] The photoconductor drum 20 is a cylindrical member that carries an electrostatic latent image on its surface (surface layer portion), and is constructed using a photoconductor (e.g., an organic photoconductor). This photoconductor drum 20 rotates clockwise in FIG. 1 by power transmitted from an ID motor 58 (FIG. 4). The photoconductor drum 20 is charged by a charging roller (not shown) and exposed by a corresponding LED head 15. As a result, an electrostatic latent image is formed on the surface of the photoconductor drum 20. Then, an image corresponding to the electrostatic latent image is formed (developed) on the photoconductor drum 20 by supplying toner from a developing roller (not shown).

[0023] The toner cartridges 21 are configured to accommodate toner. Specifically, the toner cartridges 21 of the image forming units 14K, 14Y, 14M, and 14C accommodate black, yellow, magenta, and cyan toner, respectively.

[0024] The LED heads 15 (LED heads 15K, 15Y, 15M, and 15C) are mechanisms that irradiate light onto the photoconductor drums 20 of the image forming units 14K, 14Y, 14M, and 14C, respectively, and are configured using LEDs (Light Emitting Diodes).

[0025] The transfer belt unit 16 is a mechanism that transfers an image formed on the surface of the photoconductor drum 20 to the surface of the print medium P by Coulomb force, and transports the print medium P in the transport direction. The transfer belt unit 16 transports the print medium P to which the image has been transferred toward the fixing device 8. The transfer belt unit 16 has a transfer belt 22, a drive roller 23, a driven roller 24, and four transfer rollers 25 (transfer rollers 25K, 25Y, 25M, and 25C). Hereinafter, the transfer rollers 25K, 25Y, 25M, and 25C are also collectively referred to as transfer rollers 25.

[0026] The transfer belt 22 is a seamless circular belt capable of carrying the print medium P. The transfer belt 22 is tensioned by a drive roller 23 and a driven roller 24. The drive roller 23 is a rotating member that rotates by power transmitted from a belt motor 56 (FIG. 4) so ​​as to transport the print medium P toward the fixing device 8, and circulates the transfer belt 22. The driven roller 24 is a member that adjusts the tension applied to the transfer belt 22 while tensioning the transfer belt 22 together with the drive roller 23.

[0027] The four transfer rollers 25 are rotating members that transfer images formed on the surfaces of the photoconductor drums 20 of the corresponding image forming units 14 onto the transfer surface of the print medium P. The transfer rollers 25K, 25Y, 25M, and 25C are disposed opposite the photoconductor drums 20 of the image forming units 14K, 14Y, 14M, and 14C, respectively, via the transfer belt 22. A predetermined transfer voltage is applied to each of the transfer rollers 25K, 25Y, 25M, and 25C, so that the images formed on the photoconductor drums 20 by the image forming units 14 are transferred onto the transfer surface of the print medium P.

[0028] [3. Configuration of the fixing unit] 2 and 3, the fixing unit 8 is roughly composed of a fixing belt 28 arranged above the transport path, and a backup roller 29 arranged below the transport path. The fixing unit 8 is generally surrounded by a housing (not shown). This housing is appropriately formed with holes and the like for passing the print medium P along the transport path.

[0029] [3-1. Structure of the fixing belt] The fixing belt 28 is an endless belt made of a cylindrical film made of a material having flexibility and heat resistance, and is formed into a cylindrical shape with a central axis aligned in the left-right direction. The fixing belt 28 has a multi-layer structure in which a heat-resistant resin such as PI (polyimide) or a metal such as SUS (stainless steel) is used as a base material, an elastic layer made of silicone rubber, and a surface layer made of a fluororesin coating such as PFA (perfluoroalkoxyalkane) or a tube made of the same are superimposed. Inside the fixing belt 28, a planar heater 30, a heat diffusion member 32, and a back plate 34 are provided.

[0030] [3-2. Configuration of Planar Heater] The planar heater 30 is a plate-shaped planar heating element extending in the longitudinal direction, i.e., the left-right direction, with a thickness of 0.25 to 2.0 mm. An electrical insulating layer, a resistive heating layer, an electrode, and a protective layer are laminated in this order on a stainless steel substrate, and the planar heater 30 generates heat when power is supplied. In the planar heater 30, the heating portion, which is the region that generates heat, is divided into five regions in the longitudinal direction. In the following, the central region of the planar heater 30 is referred to as the main heater 31c, the regions on both the left and right sides of the main heater 31c are referred to as the first side heaters 31Li and 31Ri, and the outermost region is referred to as the second side heaters 31Lo and 31Ro. In the following, the first side heaters 31Li and 31Ri are also collectively referred to as the first side heaters 31i, and the second side heaters 31Lo and 31Ro are also collectively referred to as the second side heaters 31o. Further, hereinafter, the main heater 31c, the first side heater 31i, and the second side heater 31o are collectively referred to as the heater 31. The first side heater 31Li and the first side heater 31Ri are electrically connected to each other, and generate heat simultaneously when current is applied. Similarly, the second side heater 31Lo and the second side heater 31Ro are electrically connected to each other, and generate heat simultaneously when current is applied.

[0031] The main heater 31c has a length in the left-right direction (i.e., width) of 138 mm, which corresponds to the width of B6 vertical size (128 mm). The first side heater 31i, when combined with the main heater 31c, has a width of 230 mm, which corresponds to the width of A4 vertical size (210 mm). The second side heater 31o, when combined with the main heater 31c and the first side heater 31i, has a width of 306 mm, which corresponds to the width of A4 horizontal size (297 mm).

[0032] [3-3. Composition of heat diffusion material] The heat diffusion member 32 is a substantially flat plate extending in the left-right direction along the planar heater 30, and its upper surface is in contact with the lower surface of the planar heater 30. The heat diffusion member 32 is made of an aluminum alloy such as AL5052, and is a metal plate member with high thermal conductivity. The heat diffusion member 32 is shaped like a capital letter "U" when viewed from the left side, and both front and rear ends are bent upward in the vertical direction, which is the thickness direction. That is, the heat diffusion member 32 has a recess facing the planar heater 30. The heat diffusion member 32 is fixed to a heater fixing member 39 fixed to a stay metal plate 38. The heat diffusion member 32 efficiently transfers heat due to the properties of the metal material, and transfers the heat generated by the planar heater 30 to the fixing belt 28 while diffusing it evenly in the longitudinal direction. The thermal conductivity of the heat diffusion member 32 is 138 [W / mK], which is about 8.47 times higher than the thermal conductivity of the back plate 34, which is 16.3 [W / mK]. The thermal conductivity of the heat diffusion member 32 is also significantly higher than that of the fixing belt 28.

[0033] [3-4. Back panel configuration] The back plate 34 is a generally flat plate with a thickness of 0.25 to 2.0 mm extending in the left-right direction along the planar heater 30, and its lower surface is in contact with the upper surface of the planar heater 30. That is, the back plate 34 is in contact with the planar heater 30 on the surface opposite to the heat diffusion member 32. The back plate 34 is made of stainless steel such as SUS304, and is a metal plate member with high thermal conductivity. The back plate 34 is fixed to a heater fixing member 39 fixed to a stay metal plate 38. Due to the nature of the metal material, the back plate 34 stores the heat generated by the planar heater 30 and efficiently transmits it, diffusing it evenly in the longitudinal direction. The thermal conductivity of the back plate 34 is significantly higher than that of the fixing belt 28.

[0034] [3-5. Thermostat configuration] The thermostat 40 abuts against the upper surface of the back plate 34, and is pressed downward toward the sheet heater 30 by a spring 41. The thermostat 40 cuts off the flow of electricity to the sheet heater 30 when the temperature of the sheet heater 30 rises abnormally.

[0035] [3-6. Grease composition] Thermally conductive grease 44, mainly composed of zinc oxide and silicone oil, is applied from the front end to the other end in the gap between the planar heater 30 and the heat diffusion member 32. In addition, sliding grease 45, mainly composed of PFPE (perfluoropolyether), is applied from the front end to the other end on the underside of the heat diffusion member 32 in the gap between the heat diffusion member 32 and the fixing belt 28.

[0036] [3-7. Configuration of thermistor behind the heater] Furthermore, at the center of the main heater 31c, the first side heater 31Li, the first side heater 31Ri, the second side heater 31Lo, and the second side heater 31Ro in the left-right direction, a heater back side main thermistor 36c, a first heater back side thermistor 36Li, a first heater back side thermistor 36Ri, a second heater back side thermistor 36Lo, and a second heater back side thermistor 36Ro are provided so as to abut against the upper surface of the back plate 34. Hereinafter, the first heater back side thermistors 36Li and 36Ri are also collectively referred to as the first heater back side thermistor 36i, and the second heater back side thermistors 36Lo and 36Ro are also collectively referred to as the second heater back side thermistor 36o. In the following description, the heater back main thermistor 36c, the first heater back side thermistor 36i, and the second heater back side thermistor 36o are collectively referred to as heater back thermistors 36. Each heater back thermistor 36 is urged downward toward the planar heater 30 by a spring 42. Since each heater back thermistor 36 changes resistance depending on the temperature of the portion of the planar heater 30 it is in contact with, it generates an electrical signal according to this temperature and supplies this to the fixing control unit 52 (FIG. 5). In other words, each heater back thermistor 36 detects the temperature of the planar heater 30 itself and generates an electrical signal representing that temperature.

[0037] [3-8. Sensor configuration] A non-contact temperature sensor 46 is provided at a position slightly away from the front of the exterior of the fixing belt 28. The non-contact temperature sensor 46 receives infrared rays emitted from the fixing belt 28, generates an electrical signal according to the surface temperature of the fixing belt 28 based on the amount of infrared light received, etc., and supplies this to the fixing control unit 52 (FIG. 5). The non-contact temperature sensor 46 is preferably provided at the center of the main heater 31c in the longitudinal direction of the planar heater 30.

[0038] [3-9. Configuration of backup roller] On the other hand, backup roller 29 as a pressure member is formed in a cylindrical shape with its central axis aligned in the left-right direction, is rotatably supported by a support member (not shown), and is urged toward fixing belt 28. Therefore, in fixing unit 8, backup roller 29 is pressed against fixing belt 28, and a nip portion NP is formed between them to sandwich print medium P transported from transfer belt 22 (FIG. 1).

[0039] [3-10. Operation of the fixing unit] In this configuration, the fixing unit 8 detects the temperature by the non-contact temperature sensor 46 and the heater back thermistor 36, and controls the power supplied to each heater 31 under the control of the fixing control unit 52 (FIG. 5), thereby controlling each heater 31 to a desired temperature. The fixing control unit 52 also controls the fixing unit 8 mainly based on the temperature of the non-contact temperature sensor 46 during printing operations. On the other hand, the fixing control unit 52 uses the heater back thermistor 36 mainly to detect alarm states, such as abnormal temperature rise of the planar heater 30 and excessive temperature rise of non-paper passing areas when printing on narrow media.

[0040] In addition, the fixing device 8 switches the heating length of the planar heater 30 along the main scanning direction (left-right direction) by switching between heating only the main heater 31c, heating the main heater 31c and the first side heater 31i, and heating all of the main heater 31c, the first side heater 31i, and the second side heater 31o.

[0041] Specifically, the fixing unit 8 controls the planar heater 30 so as to heat an area slightly wider in the medium width direction than the print area, so as to include the print area, which is the range in the medium width direction where image data for adhering toner to the print medium P exists, as indicated by the print data. In this way, the fixing unit 8 is able to fix an image over a size wider than the print area while suppressing excessive heating in non-paper passing areas of the fixing belt 28, and fixes the toner image transferred to the print medium P to the print medium P in the fixing operation. In this way, the fixing unit 8 selectively energizes the planar heater 30 to generate heat depending on the width of the print medium P in the left-right direction.

[0042] [4. Control configuration of image forming device] As shown in FIG. 4, the print control unit 50 is connected to a fixing control unit 52, a paper feed motor 54, a belt motor 56, an ID motor 58, a fixing motor 60, an LED head 15, and a high voltage unit 62, and performs print control of the image forming apparatus 1.

[0043] The fixing control unit 52 controls the fixing unit 8 to a target temperature according to printing conditions such as medium thickness and medium width. The paper feed motor 54 is a stepping motor or a DC motor that drives the hopping roller 4, the registration roller 5, and the transport roller 6 that feed and transport the print medium P. The belt motor 56 is a stepping motor or a DC motor that drives the transfer belt 22. The ID motor 58 is a DC motor that drives various rollers in the image forming unit 14. The fixing motor 60 is a DC motor that drives the fixing unit 8 and the discharge rollers 9 and 10.

[0044] The LED head 15 exposes the charged surface of the photoconductor drum 20. The high voltage unit 62 is a circuit that generates a high voltage for charging and developing in the image forming unit 14 and for transferring to the transfer belt 22. The fixing motor 60 generates a driving force that is decelerated via a gear train (not shown) and transmitted to the backup roller 29, thereby rotating the backup roller 29.

[0045] [5. Configuration of the fixing control unit] As shown in FIG. 5, the fixing control unit 52 receives electrical signals output from the heater back-side main thermistor 36c, the first heater back-side thermistors 36Li and 36Ri, the second heater back-side thermistors 36Lo and 36Ro, and the non-contact temperature sensor 46.

[0046] One terminal of a commercial power supply 70 is connected to one electrode of each heater 31 of the sheet heater 30. The other terminal of the commercial power supply 70 is connected to terminal terminals T1 of the triacs 72c, 72i, and 72o. The triac 72c has a terminal terminal T2 connected to the other electrode of the main heater 31c. The triac 72i has a terminal terminal T2 connected to the other electrode of the first side heater 31i (first side heaters 31Li and 31Ri). The triac 72o has a terminal terminal T2 connected to the other electrode of the second side heater 31o (second side heaters 31Lo and 31Ro). The gate terminals G of the triacs 72c, 72i, and 72o are connected to a triac drive circuit 74.

[0047] The triac driving circuit 74 is configured to insulate the primary side from the secondary side using a photocoupler, and turns the triacs 72c, 72i and 72o ON / OFF in response to heater ON signals 76c, 76i and 76o (collectively referred to below as heater ON signals 76) input from the fixing control unit 52.

[0048] The fixing control unit 52 supplies an ON pulse to the triac driving circuit 74 as a heater ON signal 76c, thereby conducting the terminals T1 and T2 of the triac 72c (i.e., turning the triac 72c ON), and causing the current of the commercial power supply 70 to flow to the main heater 31c. The fixing control unit 52 also supplies an ON pulse to the triac driving circuit 74 as a heater ON signal 76i, thereby turning the triac 72i ON, and causing the current of the commercial power supply 70 to flow to the first side heaters 31Li and 31Ri. The fixing control unit 52 also supplies an ON pulse to the triac driving circuit 74 as a heater ON signal 76o, thereby turning the triac 72o ON, and causing the current of the commercial power supply 70 to flow to the second side heaters 31Lo and 31Ro. At this time, the fixing control unit 52 can adjust the power supply to the planar heater 30 by adjusting the ON pulse width (ie, the duty value) of the heater ON signal 76 to change the time during which the triac 72 is turned ON.

[0049] [6. Relationship between the thermal conductivity of the heat diffusion material and the back plate and the amount of heat transfer] The relationship between the thermal conductivity and the amount of heat transfer of the heat diffusion member 32 and the back plate 34 will be described with reference to FIG. 6. In the case of the fixing device 8 according to the present embodiment, as shown in FIG. 6(A), for the heat diffusion member 32 and the back plate 34 in contact with the planar heater 30, when the thermal conductivity of the heat diffusion member 32 is thermal conductivity α and the thermal conductivity of the back plate 34 is thermal conductivity β, the thermal conductivity α>thermal conductivity β always holds. Since the amount of heat transferred by a material is proportional to the thermal conductivity of the material, when the thermal conductivity α is higher than the thermal conductivity β (i.e., the thermal conductivity α>thermal conductivity β), the amount of heat transfer Aα, which is the amount of heat (amount of heat transfer) transferred by the heat diffusion member 32, is larger than the amount of heat transfer B1, which is the amount of heat (amount of heat transfer) transferred by the back plate 34, among the amount of heat W generated by the planar heater 30, compared to when the thermal conductivity α is set to be equal to or lower than the thermal conductivity β (i.e., the thermal conductivity α≦thermal conductivity β). In FIG. 6, the amount of heat transfer is represented by the size of the arrow.

[0050] 6(B) shows a comparative example in which the thermal conductivity value of the heat diffusion member 32 is the same as that of the back plate 34, that is, thermal conductivity β. For this reason, in the comparative example, the thermal conductivity of the heat diffusion member 32 is thermal conductivity β, the thermal conductivity of the back plate 34 is thermal conductivity β, the heat transfer amount of the heat diffusion member 32 is heat transfer amount Aβ, and the heat transfer amount of the back plate 34 is heat transfer amount B2.

[0051] In addition, in both the fixing device 8 according to the present embodiment (FIG. 6A) and the comparative example (FIG. 6B), the heat generation amount of the planar heater 30 is defined as heat generation amount W, and the heat generation amount of the planar heater 30 is entirely transferred from the heat diffusion member 32 or the back plate 34. This can be expressed as a formula: heat generation amount W=heat transfer amount Aα+heat transfer amount B1=heat transfer amount Aβ+heat transfer amount B2. In this case, if the thermal conductivity α>thermal conductivity β, the heat transfer amount Aα>heat transfer amount Aβ holds. As a result, when the thermal conductivity of the heat diffusion member 32 is made higher than that of the back plate 34, the heat transfer amount of the heat diffusion member 32 is larger than when the thermal conductivity of the heat diffusion member 32 is made lower than that of the back plate 34.

[0052] [7. Relationship between the thermal conductivity of the heat diffusion material and back plate and the temperature of the fixing unit] 7 shows a graph obtained by measuring the relationship between the thermal conductivity of the heat diffusion member 32 and the back plate 34 and the actual temperature of the fixing device 8. In the fixing device 8 of the image forming apparatus 1, the material of the heat diffusion member 32 is AL5052 (thermal conductivity 138 [W / mK]) and the material of the back plate 34 is SUS304 (thermal conductivity 16.3 [W / mK]), which is referred to as a fixing device 8a. The material of the heat diffusion member 32 is SUS430 (thermal conductivity 26 [W / mK]) and the material of the back plate 34 is SUS304 (thermal conductivity 16.3 [W / mK]), which is referred to as a fixing device 8b. That is, in the case of the fixing device 8a, the thermal conductivity of the heat diffusion member 32 is about 8.5 times higher than that of the back plate 34, whereas in the case of the fixing device 8b, the thermal conductivity of the heat diffusion member 32 is about 1.6 times higher than that of the back plate 34.

[0053] The image forming apparatus 1 using the fixing unit 8a and the image forming apparatus 1 using the fixing unit 8b perform a warm-up operation from room temperature, and the temperatures of the non-contact temperature sensor 46 are plotted so that the heater ON signals 76a of all the heaters 31 in the image forming apparatus 1 using the fixing unit 8a and the heater ON signals 76b of all the heaters 31 in the image forming apparatus 1 using the fixing unit 8b are turned ON at the same time. These are shown as heater temperature curves La and La. The heater temperature curve La is for the fixing unit 8a, and the heater temperature curve Lb is for the fixing unit 8b.

[0054] The heater temperature curve La reaches the print start temperature Ts about 7.2 seconds after the start of the warm-up operation. On the other hand, the heater temperature curve Lb reaches the print start temperature Ts about 8.2 seconds after the start of the warm-up operation. Thus, compared to the heater temperature curve Lb, the heater temperature curve La starts to rise at almost the same timing, but rises faster and reaches the print start temperature Ts about 1 second earlier. Thus, as a result of the warm-up operation, the temperature rise speed of the fixer 8a is faster than that of the fixer 8b, and it reaches the print start temperature Ts more quickly.

[0055] These fusers 8a and 8b have the same material for the back plate 34, and differ only in the material of the heat diffusion member 32. The fuser 8a, which has a faster warm-up operation, has a heat diffusion member 32 with a higher thermal conductivity than the fuser 8b. From this result, it can be seen that the higher the thermal conductivity of the heat diffusion member 32 is made higher than that of the back plate 34, the more efficiently the temperature of the fuser 8 can be increased.

[0056] [8. Effects, etc.] Here, it is also conceivable to configure the back plate 34 from, for example, a polyimide film, which is not a metal. However, in that case, since the thermal conductivity of the polyimide film is significantly lower than that of the metal aluminum alloy, the thermal variation of the planar heater 30 in the longitudinal direction cannot be evened out, and in particular, the heat transferred to the nip portion NP decreases in the portion between the adjacent heaters 31, which may result in a decrease in image quality when forming an image on a print medium P that is wide in the left-right direction.

[0057] In contrast, the image forming apparatus 1 configures the back plate 34 from an aluminum alloy, which is a metal and has a significantly higher thermal conductivity than polyimide film, which is not a metal. This allows the image forming apparatus 1 to suppress the variation in heat from the planar heater 30 in the longitudinal direction, compared to when the back plate 34 is configured from a polyimide film. This allows the image forming apparatus 1 to suppress a decrease in image quality, particularly when forming an image on a print medium P that is wide in the left-right direction.

[0058] Furthermore, in the image forming apparatus 1, the thermal conductivity of the thermal diffusion member 32 is set to be higher than that of the back plate 34. Therefore, in the image forming apparatus 1, more of the heat generated in the planar heater 30 can be transferred to the thermal diffusion member 32 than to the back plate 34, compared to a case in which the thermal conductivity of the thermal diffusion member 32 is set to be equal to or lower than that of the back plate 34. As a result, in the image forming apparatus 1, the heating efficiency of the nip portion NP can be increased, the fixing unit 8 can be heated efficiently, and the warm-up time can be shortened, compared to a case in which the thermal conductivity of the thermal diffusion member 32 is set to be equal to or lower than that of the back plate 34.

[0059] In this way, the image forming apparatus 1 suppresses the thermal variation of the planar heater 30 in the longitudinal direction by constructing the back plate 34 from an aluminum alloy, which is a metal, while making the thermal conductivity of the heat diffusion member 32 higher than that of the back plate 34, thereby efficiently heating the fixing unit 8 and shortening the warm-up time.

[0060] Furthermore, the back plate 34 of the image forming apparatus 1 is made of an aluminum alloy, which is a metal and has a significantly higher thermal conductivity than polyimide film, which is not a metal. This makes it easier for the image forming apparatus 1 to transfer heat from the planar heater 30 to the heater back thermistor 36, compared to when the back plate 34 is made of polyimide film. This improves the thermal response of the heat transferred to the heater back thermistor 36 via the back plate 34, and allows the temperature of the planar heater 30 to be monitored more closely using the heater back thermistor 36.

[0061] According to the above-mentioned configuration, the fixing device 8 of the image forming apparatus 1 includes a fixing belt 28, a planar heater 30 provided on the inner surface of the fixing belt 28, a heat diffusion member 32 made of metal and provided between the planar heater 30 and the fixing belt 28, and a back plate 34 made of metal, having a lower thermal conductivity than the heat diffusion member 32, and provided on the opposite side of the planar heater 30 from the fixing belt 28.

[0062] This allows the fixing device 8 to efficiently heat the nip portion NP while suppressing the variation in heat of the planar heater 30 in the longitudinal direction.

[0063] 9. Other Embodiments In the above embodiment, the image forming apparatus 1 has been described as being made of the heat diffusion member 32 of AL5052. The present invention is not limited to this, and the image forming apparatus 1 may be made of various other aluminum alloys such as AL5056 (thermal conductivity 117 [W / mK]). The image forming apparatus 1 may be made of various other metals such as silver (thermal conductivity 427 [W / mK]), copper (thermal conductivity 398 [W / mK]), tungsten (thermal conductivity 178 [W / mK]), silicon (thermal conductivity 148 [W / mK]), zinc (thermal conductivity 121 [W / mK]), etc. In short, the image forming apparatus 1 may be made of the heat diffusion member 32 of a metal having a higher thermal conductivity than the back plate 34. In this case, it is preferable that the thermal conductivity of the heat diffusion member 32 is 8.4 times or more higher than the thermal conductivity of the back plate 34.

[0064] In the above embodiment, the image forming apparatus 1 has been described with the back plate 34 made of SUS304. The present invention is not limited to this, and the image forming apparatus 1 may have the back plate 34 made of various other stainless steels, such as SUS430 (thermal conductivity 26 [W / mK]). The image forming apparatus 1 may have the back plate 34 made of various other metals, such as titanium (thermal conductivity 21.9 [W / mK]) and manganese (thermal conductivity 7.82 [W / mK]). In short, the image forming apparatus 1 may have the back plate 34 made of a metal having a lower thermal conductivity than the thermal diffusion member 32. In this case, as described above, it is preferable that the thermal conductivity of the thermal diffusion member 32 is 8.4 times or more higher than the thermal conductivity of the back plate 34.

[0065] In this way, in the image forming apparatus 1, it is preferable that the heat diffusion member 32 is made of various metals having a thermal conductivity of 100 [W / mK] or more, and the back plate 34 is made of various metals having a thermal conductivity of 30 [W / mK] or less. The upper limit of the thermal conductivity of the heat diffusion member 32 is 427 [W / mK] when the heat diffusion member 32 is made of silver.

[0066] Furthermore, in the above-described embodiment, the present invention has been described as being applied to a so-called direct transfer type image forming apparatus 1 in which a toner image is directly transferred from the photoconductor drum 20 of the image forming unit 14 to the print medium P. However, the present invention is not limited to this, and the present invention may also be applied to an image forming apparatus of a so-called intermediate transfer type (or secondary transfer type) in which a toner image of each color is transferred from the photoconductor drum 20 of the image forming unit 14 to an intermediate transfer belt so as to be sequentially superimposed on top of each other, and the toner image is then transferred from this intermediate transfer belt to the print medium P.

[0067] Furthermore, in the above embodiment, the present invention has been described as being applied to a developer used in a one-component development system, but the present invention is not limited to this, and may be applied to a developer in a two-component development system in which a carrier and a toner are mixed together and friction between the carrier and the toner is used to impart an appropriate amount of charge to the toner.

[0068] Furthermore, in the above-described embodiment, the present invention has been described as being applied to an image forming apparatus 1 having four image forming units 14 and forming a color image using toner of four colors. However, the present invention is not limited to this, and the present invention may be applied to an image forming apparatus having three or less image forming units 14 or five or more image forming units 14 and forming an image using toner of a predetermined number of colors.

[0069] Furthermore, in the above-described embodiment, the present invention has been described as being applied to the image forming apparatus 1, which is a single-function printer. The present invention is not limited to this, and may be applied to image forming apparatuses having various other functions, such as an MFP (Multi Function Peripheral) having the functions of a copier or facsimile machine. The present invention may also be applied to various electronic devices that form images on a print medium P, such as paper, using a developer by electrophotography.

[0070] Furthermore, the present invention is not limited to the above-mentioned embodiment and other embodiments. That is, the scope of application of the present invention extends to an embodiment in which the above-mentioned embodiment and the other embodiments are combined in part or in whole in any manner. The scope of application of the present invention also extends to an embodiment in which a part of the configuration described in any of the above-mentioned embodiment and other embodiments is extracted and replaced or diverted with a part of the configuration of any of the above-mentioned embodiment and other embodiments, or an embodiment in which a part of the extracted configuration is added to any of the embodiments.

[0071] Furthermore, in the above-described embodiment, the fixing device 8 as a fixing unit is configured by the fixing belt 28 as a circular belt, the planar heater 30 as a heating member, the heat diffusion member 32 as a first heat diffusion member, and the back plate 34 as a second heat diffusion member. However, the present invention is not limited to this, and the fixing unit may be configured by a circular belt, a heating member, a first heat diffusion member, and a second heat diffusion member having various other configurations. [Industrial Applicability]

[0072] The present invention can be used when printing images on a medium using an electrophotographic image forming apparatus. [Explanation of symbols]

[0073] 1: image forming apparatus, 2: housing, 3: paper feed cassette, 4: hopping roller, 5: registration roller, 6: transport roller, 7: image forming section, 8: fixing unit, 9, 10: discharge roller, 11: stacker, 12: write sensor, 13: EXIT sensor, 14: image forming unit, 15: LED head, 16: transfer belt unit, 20: photosensitive drum, 21: toner cartridge, 22: transfer belt, 23: drive roller, 24: driven roller, 25: transfer roller, 28: fixing belt, 29: backup roller, 30: surface heater, 31c: main heater, 31Li, 31Ri: first side heater, 31Lo, 31Ro: second side heater, 31: heater, 32: heat diffusion member, 34...back plate, 36...heater back thermistor, 36c...heater back main thermistor, 36Li, 36Ri...first heater back side thermistor, 36Lo, 36Ro...second heater back side thermistor, 38...stay metal plate, 39...heater fixing member, 40...thermostat, 41, 42...spring, NP...nip portion, 44...thermal conductive grease, 45...sliding grease, 46...non-contact temperature sensor, 50...print control unit, 52...fixing control unit, 54...paper feed motor, 56...belt motor, 58...ID motor, 60...fixing motor, 62...high voltage unit, 70...commercial power supply, 72c, 72i, 72o...triac, 74...triac drive circuit, 76c, 76i, 76o...heater ON signal, P...printing medium.

Claims

1. A circular belt; a heating member provided on an inner peripheral surface side of the circular belt; a first heat diffusion member made of metal and disposed between the heating member and the circular belt; a second heat diffusion member made of metal, having a thermal conductivity lower than that of the first heat diffusion member, and provided on the opposite side of the heating member from the circular belt side; A fixing unit having a fixing member.

2. The first heat diffusion member has a thermal conductivity 8.4 times or more higher than that of the second heat diffusion member. The fixing unit according to claim 1 .

3. The thermal conductivity of the first heat diffusion member is 100 [W / mK] or more, The thermal conductivity of the second heat diffusion member is 30 [W / mK] or less. The fixing unit according to claim 2 .

4. the first heat diffusion member includes aluminum; The second heat diffusion member includes stainless steel. The fixing unit according to claim 3 .

5. The first heat diffusion member is made of AL5052, The second heat diffusion member is made of SUS304. The fixing unit according to claim 4 .

6. The heating member includes a plurality of heat generating portions arranged in a longitudinal direction. The fixing unit according to claim 1 .

7. a pressure member provided on an outer peripheral surface side of the circular belt, the pressure member forming a nip portion between the circular belt and the first heat diffusion member via the circular belt; The fusing unit of claim 1 further comprising:

8. 8. An image forming apparatus comprising the fixing unit according to claim 1.

Images