Fixing device

Abstract

To provide a fixing device capable of suppressing an increase in electrical resistance of a conductive layer.SOLUTION: A fixing device satisfies a relationship expressed as: D>R+C-F, where F represents a film width, C represents a width of a conductive layer, R represents a distance between two limiting surfaces, and D represents a width of a pressing member.SELECTED DRAWING: Figure 11

Description

[Technical field]

[0001] The present invention relates to a fixing device mounted in an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer. [Background technology]

[0002] As one form of fixing device to be installed in electrophotographic printers and the like, a fixing device has been proposed that uses a cylindrical film (also called a belt) with a conductive layer, in which the film itself generates Joule heat by passing an electric current through the conductive layer (Patent Document 1).

[0003] A fixing device using a film has a restricting member that restricts the movement (lateral movement) of the film in the longitudinal direction of the film. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2014-26267 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a configuration in which the regulating member regulates the shifting of the film, if the regulating member receives the edge of the film and the lateral force of the film becomes even stronger, the film may be damaged. In a fixing device in which the film itself heats up due to the current flowing through the film, if the film is damaged at the position where the current flows, the electrical resistance may increase, which may lead to poor heating or abnormal heating.

[0006] An object of the present invention is to provide a fixing device capable of suppressing an increase in the electrical resistance of a conductive layer. [Means for solving the problem]

[0007] The present invention for solving the above-mentioned problems comprises a cylindrical film having a base layer and a conductive layer having a lower resistance than the base layer, a contact member disposed in an internal space of the film and against which the rotating film slides, a pressure member contacting an outer peripheral surface of the film, the pressure member sandwiching the film together with the contact member to form a fixing nip between the film and the pressure member, and a regulating member having a regulating surface that regulates movement of the film in the longitudinal direction when the film moves in the longitudinal direction of the film, wherein a current is passed through the conductive layer in a circumferential direction to cause Joule heating in the conductive layer, and this heat is a fixing device which fixes a toner image formed on a recording material to the recording material by heating the recording material being sandwiched and transported in the fixing nip portion by a fixing member, the regulating members are respectively arranged at positions facing both end faces of the film in the longitudinal direction, the conductive layer through which the current flows in the circumferential direction in the longitudinal direction is not provided in both end regions of the film but is provided in a region between the both end regions, and the relationship D>R+CF is satisfied when the width of the film is F, the width of the conductive layer is C, the distance between the two regulating surfaces is R, and the width of the pressure member is D in the longitudinal direction. Effect of the Invention

[0008] According to the present invention, it is possible to provide a fixing device capable of suppressing an increase in the electrical resistance of a conductive layer. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus. [Diagram 2] Cross-sectional view of the fixing device [Diagram 3] Front view of the fixing device [Figure 4] Exploded perspective view of the film unit [Diagram 5] Cross-sectional structure of the film [Figure 6] A perspective view of a magnetic core and an excitation coil. [Figure 7] A diagram showing a part of an alternating magnetic field and an induced current [Figure 8] Flange structure diagram [Figure 9] Schematic diagram of film shifting [Figure 10] Schematic diagram of induced current when the resistance of a part of a conductive layer increases [Figure 11] FIG. 1 is a schematic diagram illustrating a film-side state in Example 1. [Figure 12] Schematic diagram illustrating the film-side state in Comparative Example 1. [Figure 13] Schematic diagram illustrating the film-side state in Comparative Example 2. [Figure 14] FIG. 5 is a schematic diagram illustrating a film-side state in Comparative Example 3. [Figure 15] FIG. 13 is a schematic diagram illustrating a film-side state in Comparative Example 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Example 1 1 is a cross-sectional view showing the schematic configuration of a laser beam printer 1 (hereinafter referred to as printer 1) as an image forming apparatus that uses electrophotographic technology to form a toner image on a recording material P. This is an A4 printer that can also handle letter-size (215.9 mm wide) recording materials P.

[0011] The printer 1 has a photosensitive drum 2 which is an image carrier, charging means 3 which charges the surface of the photosensitive drum 2 almost uniformly, and a scanner unit 4 which scans the photosensitive drum 2 with a laser beam according to image information to form an electrostatic latent image on the photosensitive drum 2. Further provided are developing means 5 which develops the electrostatic latent image with toner, a transfer member 6 which transfers the toner image on the photosensitive drum 2 to a recording material P, and cleaning means 7 which cleans toner remaining on the photosensitive drum 2 without being transferred to the recording material P. Further provided is a fixing device A which fixes the toner image transferred to the recording material P to the recording material P. The fixing device A will be described in detail later.

[0012] A cassette 8 that contains recording material P such as paper is attached to the bottom of the printer 1. The recording material P contained in the cassette 8 is fed one sheet at a time by rollers 9. The fed recording material P is transported by transport rollers 10, 11, 30, transfer member 6, fixing device A, etc., and is finally discharged to a paper output tray 31 via the path indicated by the dotted line in FIG.

[0013] Next, the fixing device A (fixing section) will be described in detail. Fig. 2 is a cross-sectional view of the fixing device A, Fig. 3 is a front view of the fixing device A, and Fig. 4 is an exploded perspective view of the film unit 50. Here, the front of the fixing device A is the entrance side of the fixing device A for the recording material P, and the back side is the exit side of the fixing device A for the recording material P. The left is the left when the fixing device A is viewed from the front (i.e., in Fig. 3), and the right is the right when viewed from the front. The fixing device A is an electromagnetic induction heating type fixing device. The fixing device A has, broadly speaking, a film unit 50, a pressure roller 15 as a pressure member, and a chassis 60 that houses these.

[0014] The film unit 50 includes a cylindrical film 13, a contact member 14 that is disposed in the internal space of the film 13 and against which the rotating film 13 slides, a holder 17 that holds the contact member 14, and a metal stay 16 for ensuring the rigidity of the fixing device A. The film unit 50 further includes an excitation coil 19 that is disposed in the internal space of the film 13 and has a helical portion whose helical axis is approximately parallel to the longitudinal direction of the film 13, and an end-shaped magnetic core 18 that is disposed inside the helical portion. The film unit 50 further includes a temperature sensor 20 that contacts the inner surface of the film 13 and detects the temperature of the film 13, and flanges 40 (regulating members) that are disposed on both ends of the stay 16 in the longitudinal direction of the film 13. The flanges 40 have a regulating surface that regulates the movement of the film 13 in the longitudinal direction of the film 13 when the film 13 moves in the longitudinal direction of the film 13.

[0015] The contact target member 14, stay 16, and holder 17 are all longer than the width (left-right length) of film 13, and the left and right sides protrude from both ends of film 13 to the outside. A flange 40L fits into a protruding portion 16aL on the left side of the stay 16, and a flange 40R fits into a protruding portion 16aR on the right side. That is, the flanges 40L and 40R are disposed at positions facing both end faces of film 13 in the longitudinal direction of film 13.

[0016] Next, the film 13 will be described. FIG. 5 is a cross-sectional view of the central portion of the film 13 in the longitudinal direction thereof, and includes a base layer 13a, a conductive layer 13b, a protective layer 13c, and a release layer 13d. In the film 13, an induced current flows through the conductive layer 13b, which has a low electrical resistance, due to an induced electromotive force, and the conductive layer 13b generates Joule heat. The base layer 13a is preferably made of a material having a higher resistance value than the conductive layer 13b in order to ensure insulation between the conductive layer 13b through which the induced current flows and the members disposed in the internal space of the film 13. The base layer 13a is also required to have heat resistance. For this reason, the material of the base layer 13a is preferably an insulating heat-resistant resin such as polyimide, polyamide-imide, PEEK, or PES. The size of the base layer 13a in this embodiment is an inner diameter of 30 mm, a width F of 240 mm, and a thickness of about 40 μm, and the material is polyimide.

[0017] The conductive layer 13b is a resistance heating element having a lower electrical resistance than the base layer 13a and the protective layer 13c. As the material, metals having a low volume resistivity such as iron, copper, silver, aluminum, nickel, chromium, tungsten, and metals containing these such as SUS304 (stainless steel) and nichrome are preferable. Conductive materials such as CFRP (carbon fiber reinforced plastic) and carbon nanotubes may be used as long as the volume resistivity is low. Methods for forming the conductive layer 13b include coating, plating, sputtering, and deposition. The conductive layer 13b in this embodiment is formed of copper with a thickness of about 2 μm by electroplating. The width (length in the left-right direction) of the conductive layer 13b is longer than the maximum size of the recording material P that can be used in the printer 1 and shorter than the width of the base layer 13a. In this embodiment, the conductive layer 13b is formed on the base layer 13a by masking both ends of the base layer 13a by 8 mm and electroplating so that the width C of the conductive layer 13b is 224 mm. Since conductive layer 13b is not present in the regions at both ends of film 13, the cross section of film 13 in these regions at both ends is the cross section of FIG. 5 excluding conductive layer 13b.

[0018] The protective layer 13c is provided for the purpose of preventing the conductive layer 13b made of copper from deteriorating due to oxidation, etc. For the same reason as the base layer 13a, the protective layer 13c is also desirably higher in resistance than the conductive layer 13b, and is preferably made of an insulating heat-resistant resin. The protective layer 13c in this embodiment is made of polyimide with a thickness of about 20 μm.

[0019] The material of the release layer 13d is preferably a material having good releasability and heat resistance, such as PFA, PTFE, or FEP. The release layer 13d in this embodiment is a PFA tube having a thickness of about 15 μm. An elastic layer such as sponge or rubber may be provided between the release layer 13d and the protective layer 13c. By providing an elastic layer, the surface of the film 13 can easily follow the unevenness of the surface of the recording material P, improving the adhesion to the toner image. As a result, uneven heating of the toner image is reduced, and a good image with little uneven gloss can be obtained. In addition, a primer layer may be provided between each layer in order to strengthen the adhesion between each layer.

[0020] Next, the sliding contact member 14 will be described. The sliding contact member 14 is required to have excellent sliding properties with the inner surface of the film 13 and heat resistance. The sliding contact member 14 in this embodiment is composed of a base material with a surface layer on the surface with which the film 13 slides. The base material is preferably a heat-resistant resin such as polyimide, polyamide-imide, PEEK, PES, etc., which have excellent heat resistance, or a metal such as aluminum or iron. In this embodiment, pure aluminum with a thickness of 0.8 mm is used as the base material. The surface layer is a PTFE coating with a thickness of about 30 μm, which has low sliding resistance with the inner surface of the film 13 and has excellent heat resistance and abrasion resistance. In addition, in order to further reduce the sliding resistance between the sliding contact member 14 and the film 13, a heat-resistant lubricant is also interposed between them. As the lubricant, fluorine-based or silicone-based grease or oil is preferable. The lubricant in this embodiment is a fluorine grease based on fluorine oil and using PTFE as a thickener.

[0021] Next, the guide member 17 will be described. The guide member 17 is a member formed from a heat-resistant resin, and has the function of supporting the contact member 14 and guiding the rotation of the film 13. A groove is formed in the lower surface of the guide member 17 along the longitudinal direction of the film 13, and the contact member 14 is fitted and supported in the groove with the surface that comes into contact with the film 13 facing outward. The material of the guide member 17 is preferably a heat-resistant resin such as liquid crystal polymer, phenolic resin, PPS, or PEEK, and in this embodiment, the guide member is formed from a liquid crystal polymer.

[0022] Next, the magnetic flux generating means will be described. In the internal space of the stay 16, which has a U-shaped cross section, a magnetic core 18 and an excitation coil 19, which are magnetic flux generating means, are provided. FIG. 6 is a perspective view of the magnetic core 18 and the excitation coil 19, and the excitation coil 19 is wound in a spiral shape around the outer periphery of the magnetic core 18. The magnetic core 18 is cylindrical and has ends, and is disposed at approximately the center of the film 13 in the radial direction of the film 13. The magnetic core 18 has a role of inducing the magnetic flux (magnetic flux) of the alternating magnetic field generated by the excitation coil 19 and forming a path (magnetic path) for the magnetic flux. The material of this magnetic core 18 is preferably a material with low iron loss (hysteresis loss and eddy current loss) and high relative permeability, such as a ferromagnetic material with high permeability, such as sintered ferrite or ferrite resin. The cross-sectional shape of the magnetic core 18 may be any shape that can be accommodated in the internal space of the film 13, and is preferably a shape that can maximize the cross-sectional area. Although the cross section does not need to be circular, when winding the excitation coil 19 around the magnetic core 18, the shorter the wire length, the smaller the copper loss (coil current Joule loss), so it is preferable to make it as close to a circle as possible. In this embodiment, the magnetic core 18 has a diameter of 10 mm and is made of ferrite with a length of 245 mm. The excitation coil 19 is formed by winding a copper wire (single conductor) with a diameter of 1 to 2 mm coated with heat-resistant polyamide imide in a spiral shape around the magnetic core 18. The number of turns is 18. The spiral axis of the excitation coil 19 is parallel to the axial direction of the magnetic core 18. When a high-frequency current is applied to the excitation coil 19, an induced current flows in the conductive layer 13b according to a principle described later, causing the conductive layer 13b to heat up. In this way, the fixing device A has an excitation coil 19 disposed in the internal space of the film 13, which has a spiral-shaped portion with a spiral axis approximately parallel to the longitudinal direction, and an end-shaped magnetic core 18 disposed inside the spiral-shaped portion. An alternating voltage is applied to the exciting coil 19 to generate an induced current in the conductive layer 13b.

[0023] Here, the principle of induction heating in the fixing device A of this embodiment will be described. Fig. 7 is a conceptual diagram showing the moment when the current flowing in the direction of the arrow I1 to the exciting coil 19 is increasing. When a high-frequency current is applied to the exciting coil 19, the fixing device A forms a magnetic field in which most (90% or more) of the magnetic flux emitted from one end of the magnetic core 18 passes outside the film 13 and returns to the other end of the magnetic core 18. S in Fig. 7 indicates a portion of the induced current (circulating current) flowing in the conductive layer 13b, and when such a magnetic field is formed, the induced current flows in the direction of the arrow I2.

[0024] Next, the temperature detection means will be described. Since the conductive layer 13b of the film 13 generates heat according to the principle described above, it is desirable to directly detect the temperature of the film 13 itself as the temperature detection means. Therefore, as shown in FIG. 2, the temperature sensor 20, which is the temperature detection means, is in contact with the inner surface of the film 13. The temperature sensor 20 is composed of a leaf spring 20a, one end of which is fixed to the stay 16, a thermistor (temperature detection element) 20b installed at the other end of the leaf spring 20a, and a sponge 20c interposed between the leaf spring 20a and thermistor 20b. The surface of the thermistor 20b is covered with a polyimide tape (not shown) having a thickness of 50 μm to ensure sliding properties with the inner surface of the film 13 and electrical insulation. The sponge 20c functions as a heat insulator for the thermistor 20b, and also has the function of flexibly fitting the thermistor 20b to the film 13, which is the object of measurement.

[0025] Next, we will explain flange 40. Flanges 40L and 40R are disposed at positions facing both end faces of film 13 in the longitudinal direction of film 13. Flanges 40L and 40R have bilaterally symmetrical shapes and are molded products made of heat-resistant resin.

[0026] 8(a), (b), and (c) are views of the flange 40 as viewed from the inner surface, side surface, and top surface, and (d) is a vertical cross-sectional view. As shown in these figures, the flanges 40L and 40R have a regulating surface 40a, a guide surface 40b, a force receiving portion 40c, a fitting portion 40d, and a vertical groove portion 40e. The regulating surface 40a faces the end surface of the film 13, and is the surface against which the end surface of the film 13 abuts when the film 13 moves in the longitudinal direction. This serves to regulate the movement (deviation) of the film 13, so that the film 13 stays at a predetermined position in the longitudinal direction. The guide surface 40b guides the inner surface of the rotating film 13 in the end region in the longitudinal direction of the film 13. That is, the guide surface 40b supports the inner peripheral surface of the longitudinal end portion of the film 13 from the inside, thereby allowing the film 13 to describe a desired rotation trajectory. The fitting portion 40d is a portion that fits into the protruding portion 16a of the stay 16. The fitting portion 40d also has an empty hole for connecting the exciting coil 19 and a power circuit (not shown). The force receiving portion 40c is a surface that receives the urging force of the pressure springs 48L and 40R for forming the fixing nip portion N, and the back surface of this force receiving portion 40c is in direct contact with the protruding portion 16a of the stay 16. The force receiving portion 40c serves to press down the stay 16 by receiving the urging force of the pressure springs 48L and 40R. The flange 40 is molded from a resin containing glass fiber, such as PPS, liquid crystal polymer, PET, PA, etc., which is a material that has excellent heat resistance, relatively low thermal conductivity, and excellent slip properties. In this embodiment, PPS is used.

[0027] The pressure roller 15 is in contact with the outer peripheral surface of the film 13, and forms a fixing nip N with the contacted member 14 via the film 13. The pressure roller 15 also serves as a driving roller for rotating the film 13. The pressure roller 15 has a core 15a and an elastic layer 15b that is molded and coated concentrically around the core in a roller shape, and is a roller with a release layer 15c as a surface layer, and has an outer diameter of 30 mm and a width D (length of the elastic layer 15b) of 232 mm. The elastic layer 15b is preferably made of a material with excellent heat resistance, and silicone rubber, fluororubber, fluorosilicone rubber, etc. are preferable. The elastic layer 15b in this embodiment is silicone rubber with a thickness of about 4 mm. The release layer 15c is preferably made of a material with good releasability and heat resistance, and fluorine-based resin such as PFA, PTFE, and FEP is preferable. The release layer 15c in this embodiment is PFA with a thickness of about 50 μm.

[0028] The pressure roller 15 is rotatably disposed between left and right side plates 61L, 61R of the device frame 60 on the left and right sides of the core shaft portion 15d via bearing members 62. A drive gear 47 is disposed concentrically on the right side of the core shaft portion 15d. The driving force of a motor (not shown) controlled by a control portion (not shown) is transmitted to this gear 47 via a drive transmission portion (not shown), whereby the pressure roller 15 is driven to rotate at a predetermined peripheral speed as a driving rotor.

[0029] Next, the pressure mechanism will be described. Pressure springs 48L and 48R are in contact with the force receiving portions 40c of the flanges 40L and 40R, respectively. The pressure spring 48L is compressed and disposed between the spring receiving portion 67L on the left side of the top plate 66 of the device frame body 60 and the force receiving portion 40c of the flange 40L. The pressure spring 48R is compressed and disposed between the spring receiving portion 67R on the right side of the top plate 66 of the device frame body 60 and the force receiving portion 40c of the flange 40R. The reaction force of these pressure springs 48L and 48R acts on the left and right protruding portions 16aL and 16aR of the stay 16 of the film unit 50 through the flanges 40L and 40R, respectively. As a result, the guide member 17 having the sliding contact member 14 and the pressure roller 15 sandwich the film 13 against the elasticity of the elastic layer 15b of the pressure roller 15. A fixing nip portion N is formed between the film 13 and the pressure roller 15.

[0030] The pressure roller 13 and the film unit 50 are arranged substantially parallel to each other and disposed between the side plates 61L, 61R of the device frame 60. The vertical grooves 40e of the flanges 40L, 40R of the film unit 50 are engaged with the vertical edges of guide slits (not shown) provided in the side plates 61L, 61R, respectively. This allows the flanges 40L, 40R to be held slidably toward the pressure roller 13 relative to the side plates 61L, 61R, respectively.

[0031] The distance R between the restriction surfaces 40a of the flanges 40 disposed on the left and right sides is set to be wider than the width of the film 13. In this embodiment, the distance R between the restriction surfaces 40a of the flanges 40 was set to 246 mm.

[0032] 9 is a diagram showing a state in which a leftward shift force is generated on film 13, causing film 13 to come into contact with left flange 40L. Film 13 cannot move further leftward because it is restricted by flange 40L. If the leftward shift force continues to be generated in this state, a large deformation stress will be applied to the portion of film 13 corresponding to end position E of pressure roller 15, as indicated by the dotted arrow in the figure. As a result, the resistance value of conductive layer 13b may increase.

[0033] FIG. 10 is a schematic diagram for explaining the change in the flow of induced current when the resistance of a part of the conductive layer 13b increases. FIG. 10(a) is a conceptual diagram showing the moment when induced current flows through the conductive layer 13b due to the magnetic flux generated by the excitation coil 19 when no resistance increase occurs. In this case, a predetermined amount of current flows almost uniformly throughout the conductive layer 13b, generating heat uniformly. On the other hand, FIG. 10(b) shows the case where the resistance increases at the ● part in the figure. Since the induced current flows to bypass the ● part, the amount of heat generated at the ● part decreases. In addition, the current density becomes high at both sides of the ● part, causing the amount of heat generated to increase. In this way, in a method in which a current is passed through the film 13 itself to generate Joule heat, it is necessary to minimize damage to the parts through which the current flows.

[0034] On the other hand, even if film 13 is biased and deformation stress occurs at end position E of pressure roller 15, there is no problem as long as that location is a non-current-carrying area. Therefore, by utilizing the fact that the width of conductive layer 13b can be set independently of the width of film 13, an apparatus configuration is adopted that satisfies the relationship of the following formula 1.

[0035] If the pressure roller width is D, the flange distance is R, the conductive layer width is C, and the film width is F, then D>R+CF...(Formula 1) The effectiveness of the configuration that satisfies the relationship of formula 1 in terms of the above-mentioned problem will be described below in comparison with comparative examples. The flange distance R, which is the distance between flanges 40L and 40R, is 246 mm, and the width F of film 13 is 240 mm, and the comparison was made for cases in which the width C of conductive layer 13b and the width D of pressure roller 15 are different. Table 1 is a table summarizing the configurations in Example 1 and Comparative Examples 1 and 2, the calculated values ​​of the flange distance R + conductive layer width C - film width F, and whether formula 1 is satisfied or not.

[0036] [Table 1]

[0037] Fig. 11 is a schematic diagram for explaining a state in which film shift occurs in Example 1. Fig. 11(a) shows a state in which film shift does not occur, and Fig. 11(b) shows a state in which film shift occurs to the left and the left end of film 13 contacts left flange 40L. In Example 1, width C of conductive layer 13b is 224 mm, width D of pressure roller 15 is 232 mm, and conductive layer 13b is not present at end position E of pressure roller 15 where deformation stress occurs. In other words, it is possible to suppress an increase in resistance of conductive layer 13b due to deformation stress.

[0038] Comparative Example 1 Fig. 12 is a schematic diagram for explaining a state in which film shift occurs in Comparative Example 1, and the difference between Fig. 12(a) and (b) is the same as in Example 1. Comparative Example 1 is a case in which the pressure roller 13 is shorter than that in Example 1, and the width of the conductive layer 13b is 224 mm, and the length of the pressure roller 15 is 228 mm. When the film 13 comes into contact with the left flange 40L, the conductive layer 13b is present at end position E of the pressure roller 15 where deformation stress occurs. As a result, an increase in the resistance of the conductive layer 13b occurs due to the deformation stress (NG1 in Fig. 12).

[0039] Comparative Example 2 Fig. 13 is a schematic diagram for explaining a state in which film shift occurs in Comparative Example 2, and the difference between Figs. 13(a) and (b) is the same as in Example 1. Comparative Example 2 is a case in which the width of conductive layer 13b is wider than that of Example 1, the width of conductive layer 13b is 228 mm, and the length of pressure roller 15 is 232 mm. When film 13 comes into contact with left flange 40L, conductive layer 13b is present at end position E of pressure roller 15 where deformation stress occurs. As a result, an increase in resistance of conductive layer 13b occurs due to deformation stress (NG1 in Fig. 13).

[0040] Comparative Example 3 FIG. 14 is a schematic diagram for explaining the state where film deviation occurred in Comparative Example 3. The difference between FIGS. 14(a) and 14(b) is the same as that in Example 1. As shown in Table 2, Comparative Example 3 is a case where the width of the conductive layer is narrow compared to Example 1. The width of the conductive layer 13b is 220 mm, and the width of the pressure roller 15 is 232 mm. Even when the film 13 is in contact with the left flange 40L, the conductive layer 13b does not exist at the end position E of the pressure roller 15 where deformation stress is generated. That is, an increase in the resistance of the conductive layer 13b due to deformation stress can be suppressed.

[0041]

Table 2

[0042] However, in the state where the film 13 is deviated, the conductive layer 13b cannot cover the width (the maximum width T of the toner image formed on the recording material) that should guarantee the fixing property with the maximum size recording material through which the paper can pass. Here, it cannot cover the maximum width T (width 214.9 mm) of the toner image in the letter size width (NG2 in FIG. 14). That is, it is impossible to apply a predetermined amount of heat to the recording material P substantially uniformly. Therefore, as shown in Table 3, it is preferable to add constraint conditions so that Equation 2 is also satisfied in addition to Equation 1.

[0043] When the fixing guarantee width is T, T < C + F - R ··· (Equation 2)

[0044]

Table 3

[0045] In Example 1 where Equation 2 is satisfied, even when the film is deviated, the conductive layer 13b covers the maximum width T (214.9 mm). Therefore, it is possible to apply a predetermined amount of heat to the recording material P substantially uniformly.

[0046] (Comparative Example 4) FIG. 15 is a schematic diagram for explaining the state where film deviation occurred in Comparative Example 4. The difference between FIGS. 15(a) and 15(b) is the same as that in Example 1. Comparative Example 4 is a case where the pressure roller 15 is long with respect to Example 1. The width of the conductive layer 13b is 220 mm, and the width of the pressure roller 15 is 236 mm. Even when film deviation occurs and the film 13 contacts the left flange 40L, the conductive layer 13b does not exist at the end position E of the pressure roller 15 where deformation stress occurs. That is, an increase in the resistance of the conductive layer 13b due to deformation stress can be suppressed.

[0047]

Table 4

[0048] However, at the right end of the pressure roller 15, the surface of the pressure roller 15 comes into sliding contact with the sliding contact member 14, and the pressure roller is damaged (NG3 in FIG. 15). Therefore, it is preferable to add a constraint condition so that Equation 3 also holds.

[0049] D < F × 2 - R ··· (Equation 3)

[0050]

Table 5

[0051] In Example 1 where Equation 3 holds, the right end of the pressure roller 15 is in a state of pressing the sliding contact member 14 via the film 13, and the pressure roller 15 does not directly touch the sliding contact member 14.

[0052] As described above, by configuring the fixing device A to satisfy Equation 1, it is possible to suppress an increase in the resistance of the conductive layer 13b. Furthermore, by also satisfying Equation 2, it is possible to suppress an increase in the resistance of the conductive layer 13b while applying a predetermined amount of heat to the recording material P substantially uniformly. Furthermore, by also satisfying Equation 3, it is possible to suppress an increase in the resistance of the conductive layer 13b while preventing the pressure roller 15 from directly touching the sliding contact member 14.

[0053] (Additional Note) The above-described embodiment discloses at least the following fixing device.

[0054] (Item 1) A cylindrical film having a base layer and a conductive layer having a lower resistance than the base layer; a sliding contact member that is disposed in an internal space of the film and with which the rotating film slides; a pressing member that contacts an outer peripheral surface of the film, the pressing member sandwiching the film together with the contacted member to form a fixing nip portion between the film and the pressing member; a regulating member having a regulating surface that regulates movement of the film in the longitudinal direction when the film moves in the longitudinal direction of the film; having A fixing device that fixes a toner image formed on a recording material to the recording material by passing a circumferential current through the conductive layer to generate Joule heat in the conductive layer and heating the recording material being nipped and conveyed in the fixing nip portion with the generated heat, the regulating members are disposed at positions facing both end surfaces of the film in the longitudinal direction, The conductive layer through which the current flows in the circumferential direction is not provided in both end regions of the film with respect to the longitudinal direction, but is provided in a region between the both end regions, In the longitudinal direction, the width of the film is F, the width of the conductive layer is C, the distance between the two regulating surfaces is R, and the width of the pressure member is D. D>R+CF A fixing device characterized in that the above relationship is satisfied.

[0055] (Item 2) In the longitudinal direction, if the maximum width of the toner image formed on the recording material is T, T <C+F-R 2. The fixing device according to item 1, wherein the following relationship is satisfied.

[0056] (Item 3) D <F×2-R 3. The fixing device according to item 1 or 2, wherein the following relationship is satisfied.

[0057] (Item 4) The fixing device described in any one of items 1 to 3 further includes an excitation coil disposed in an internal space of the film and having a helical portion whose helical axis is approximately parallel to the longitudinal direction, and an end-shaped magnetic core disposed inside the helical portion, and is characterized in that an induced current is generated in the conductive layer by applying an alternating voltage to the excitation coil.

[0058] (Item 5) 5. The fixing device according to item 4, wherein the induced current flows in the direction of rotation of the film. [Explanation of symbols]

[0059] A Fixing device 13 Film 14 Contact material 15 Pressure roller 18 Magnetic Core 19 Excitation coil 40 Flange

Claims

1. A cylindrical film having a base layer and a conductive layer having a lower resistance than the base layer; a sliding contact member that is disposed in an internal space of the film and with which the rotating film slides; a pressing member that contacts an outer peripheral surface of the film, the pressing member sandwiching the film together with the contacted member to form a fixing nip portion between the film and the pressing member; a regulating member having a regulating surface that regulates movement of the film in the longitudinal direction when the film moves in the longitudinal direction of the film; having A fixing device that fixes a toner image formed on a recording material to the recording material by passing a current through the conductive layer in a circumferential direction to generate Joule heat in the conductive layer and heating the recording material being nipped and conveyed in the fixing nip portion with the generated heat, the regulating members are disposed at positions facing both end surfaces of the film in the longitudinal direction, The conductive layer through which the current flows in the circumferential direction is not provided in both end regions of the film with respect to the longitudinal direction, but is provided in a region between the both end regions, In the longitudinal direction, the width of the film is F, the width of the conductive layer is C, the distance between the two regulating surfaces is R, and the width of the pressure member is D. D>R+C-F A fixing device characterized in that the above relationship is satisfied.

2. In the longitudinal direction, if the maximum width of the toner image formed on the recording material is T, T<C+F-R 2. The fixing device according to claim 1, wherein the following relationship is satisfied:

3. D<F×2-R 3. The fixing device according to claim 2, wherein the following relationship is satisfied:

4. The fixing device according to any one of claims 1 to 3, further comprising: an excitation coil disposed in an internal space of the film, the excitation coil having a helical portion whose helical axis is substantially parallel to the longitudinal direction; and an end-shaped magnetic core disposed inside the helical portion, wherein an induced current is generated in the conductive layer by applying an alternating voltage to the excitation coil.

5. 5. The fixing device according to claim 4, wherein the induced current flows in a direction of rotation of the film.

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