JP4752973B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

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

  2. Description of the Related Art Conventionally, there is an electromagnetic induction heating type fixing device using a coil that generates a magnetic field when energized and a heating element that generates heat by generating an eddy current by electromagnetic induction of the magnetic field as a heat source.

  As a first example of a fixing device using an electromagnetic induction heat generation method, a fixing roller is composed of a heating roller that is made of a temperature-sensitive magnetic material having a predetermined Curie temperature and generates heat by electromagnetic induction action of a magnetic field generated by an exciting coil. There is one in which a belt is suspended and a conductive member which can be rotated and moved is disposed in a heat generating roller (for example, see Patent Document 1).

  The fixing device of Patent Document 1 moves the conductive member to a position not facing the excitation coil when the heating roller is heated, and when the temperature rises to a predetermined temperature, moves the conductive member to a position facing the excitation coil. In particular, the temperature rise of the heat generating roller in the non-sheet passing portion is prevented.

  In addition, as a second example of a fixing device using an electromagnetic induction heat generation method, an induction heating coil disposed in a pressure roll, a temperature-sensitive magnetic pipe as a fixing roll having a predetermined Curie temperature characteristic and generating heat, Some have a non-magnetic material disposed in a non-contact state inside the temperature-sensitive magnetic pipe (see, for example, Patent Document 2).

  In the fixing device disclosed in Patent Document 2, when the temperature of the temperature-sensitive magnetic pipe is lower than the Curie temperature, an induced current flows through the temperature-sensitive magnetic pipe to generate heat, but when the temperature is higher than the Curie temperature, the temperature-sensitive magnetic pipe is nonmagnetic. The magnetic flux passes through the body, an induced current flows through the nonmagnetic material, and the temperature rise stops.

  Furthermore, as a third example of a fixing device using an electromagnetic induction heating method, there is a fixing belt having a conductive layer and a magnetically permeable layer (see, for example, Patent Document 3).

  In the fixing device of Patent Document 3, the heating layer generates heat due to electromagnetic induction when the temperature rises. When the fixing belt reaches a fixing set temperature or higher, the magnetic flux penetrates the magnetically permeable layer and the magnetic field is weakened, and excessive heat generation of the heat generating layer is suppressed.

  In the fixing devices of Patent Documents 1 to 3, a heat generation layer that generates heat by electromagnetic induction and a temperature-sensitive magnetic layer for preventing temperature rise are integrated, and the temperature-sensitive magnetic layer also generates heat by electromagnetic induction. The temperature is excessively increased by the heat generation of both the layer and the temperature-sensitive magnetic layer.

Patent 3527442 JP2000-030850 JP-A-11-288190

  SUMMARY OF THE INVENTION An object of the present invention is to obtain a fixing device and an image forming apparatus in which a temperature rise of a temperature-sensitive rotating body is suppressed more than necessary.

The fixing device according to claim 1 of the present invention generates heat by electromagnetic induction of a magnetic field, and has a cylindrical shape in which the magnetic permeability starts to continuously decrease from the magnetic permeability change start temperature in the temperature region that is higher than the heating set temperature and lower than the heat resistance temperature. and the temperature-sensitive layer formed, while being more formed at intervals in the circumferential direction of the temperature sensing layer, a plurality of formed by shifting so that the staggered arrangement in the axial direction of the temperature sensing layer, wherein the electromagnetic induction A temperature-sensitive rotating body having a slit-like cut extending in the circumferential direction for blocking a part of the eddy current generated by the above-mentioned structure, a tension rotating body spaced apart from the temperature-sensitive rotating body, and the temperature-sensitive rotating body A fixing belt having a heat generating layer having a thickness at least thinner than the skin depth, a magnetic field generating means for generating a magnetic field disposed opposite to the temperature-sensitive rotating body, and a fixing belt. Contacting the outer peripheral surface, the fixing belt A pressure rotator that pressurizes the rotator to fix the developer image on the recording medium passing between the fixing belt and the fixing belt, and from the heat generating layer of the fixing belt The notches are formed so that the heat generation amount of the temperature-sensitive layer of the temperature-sensitive rotating body is reduced.

According to a second aspect of the present invention, the fixing device generates heat by electromagnetic induction of a magnetic field, and has a cylindrical shape in which the magnetic permeability starts to continuously decrease from the magnetic permeability change start temperature in the temperature region that is higher than the heating set temperature and lower than the heat resistance temperature. A plurality of temperature-sensitive layers formed at intervals in the circumferential direction of the temperature-sensitive layer, and a plurality of the temperature-sensitive layers formed so as to be staggered in the circumferential direction of the temperature-sensitive layer. A temperature-sensitive rotating body extending in the axial direction of the temperature-sensitive layer that cuts off part of the eddy current generated by the temperature-sensitive rotating body, a tension rotating body spaced apart from the temperature-sensitive rotating body, and A fixing belt stretched between the temperature-sensitive rotating body and the stretched rotating body and having a heat generation layer having a thickness smaller than the skin depth; and a magnetic field generating means that is disposed opposite to the temperature-sensitive rotating body and generates a magnetic field; The fixing bell is in contact with the outer peripheral surface of the fixing belt. And a pressure rotator for fixing the developer image on the recording medium passing between the fixing belt and the fixing belt to the tension rotator, and generating heat from the fixing belt. The notch is formed so that the heat generation amount of the temperature-sensitive layer of the temperature-sensitive rotating body is smaller than that of the layer. In the fixing device according to a third aspect of the present invention, the heat generating layer includes a nonmagnetic metal material having a thickness of 2 to 20 μm and a specific resistance of 2.7 × 10 ⁻⁸ Ωcm or less.

An image forming apparatus according to claim 4 of the present invention, a fixing device according to any one of claims 1 to 3, an exposure unit that emits the exposure light, the latent image formed by the exposure light Is developed with a developer to form a developer image, a transfer unit that transfers the developer image made visible at the development unit onto a recording medium, and the developer image is transferred at the transfer unit. A transport unit that transports the recorded recording medium to the fixing device.

According to the first and second aspects of the present invention, an unnecessarily high temperature rise of the temperature-sensitive rotating body is suppressed as compared with the case where the present configuration is not provided.

According to the invention of claim 3 , the heat capacity of the heat generating layer can be reduced as compared with the case where this configuration is not provided.

According to the fourth aspect of the present invention, image defects are less likely to occur as compared with the case where the present configuration is not provided.

1 is an overall view of an image forming apparatus according to an embodiment of the present invention. 1 is a cross-sectional view of a fixing device according to an embodiment of the present invention. (A) It is a perspective view which shows the state by which the slit was formed in the temperature sensitive roll which concerns on embodiment of this invention. (B) It is a schematic diagram which shows the state which interrupted | blocked the eddy current which flows into the temperature sensitive layer which concerns on embodiment of this invention with the slit. (A) It is sectional drawing of the temperature-sensitive roll and fixing belt which concern on embodiment of this invention. (B) It is a connection diagram of the control circuit and energization circuit which concern on embodiment of this invention. It is the schematic diagram which showed the relationship between the magnetic permeability of the temperature-sensitive magnetic member which concerns on embodiment of this invention, and temperature. (A), (b) It is the schematic diagram which showed the state which a magnetic field penetrates the fixing belt and temperature-sensitive roll which concern on embodiment of this invention. It is the graph which compared the relationship between time and temperature about the temperature-sensitive roll and fixing belt which concern on embodiment of this invention, and the heating roll of a prior art example. (A) It is a perspective view which shows the state by which the slit was formed in the temperature-sensitive roll as another Example of this invention. (B) It is a schematic diagram which shows the state which interrupted | blocked the eddy current which flows into a temperature sensitive layer as another Example of this invention with the slit.

  Embodiments of a fixing device and an image forming apparatus of the present invention will be described with reference to the drawings.

  FIG. 1 shows a printer 10 as an image forming apparatus. In the printer 10, the optical scanning device 54 is fixed to the housing 12 that constitutes the main body of the printer 10, and the control for controlling the operation of each part of the optical scanning device 54 and the printer 10 is positioned adjacent to the optical scanning device 54. A unit 50 is provided.

  The optical scanning device 54 scans a light beam emitted from a light source (not shown) with a rotating polygon mirror (polygon mirror), reflects it with a plurality of optical components such as a reflection mirror, and produces yellow (Y), magenta (M), Light beams 60Y, 60M, 60C, and 60K corresponding to cyan (C) and black (K) toners are emitted. The light beams 60Y, 60M, 60C, and 60K are guided to the corresponding photoreceptors 20Y, 20M, 20C, and 20K, respectively.

  A paper tray 14 for storing the recording paper P is provided below the printer 10. A pair of registration rolls 16 for adjusting the position of the leading end of the recording paper P are provided above the paper tray 14. An image forming unit 18 is provided at the center of the printer 10. The image forming unit 18 includes the above-described four photoconductors 20Y, 20M, 20C, and 20K, which are arranged in a vertical line.

  Charging rollers 22Y, 22M, 22C, and 22K that charge the surfaces of the photoreceptors 20Y, 20M, 20C, and 20K are provided on the upstream side in the rotation direction of the photoreceptors 20Y, 20M, 20C, and 20K. Further, on the downstream side in the rotation direction of the photoconductors 20Y, 20M, 20C, and 20K, developing units 24Y, 24M that develop the Y, M, C, and K toners on the photoconductors 20Y, 20M, 20C, and 20K, respectively. 24C and 24K are provided.

  On the other hand, the first intermediate transfer member 26 is in contact with the photoconductors 20Y and 20M, and the second intermediate transfer member 28 is in contact with the photoconductors 20C and 20K. The third intermediate transfer member 30 is in contact with the first intermediate transfer member 26 and the second intermediate transfer member 28. A transfer roll 32 is provided at a position facing the third intermediate transfer member 30. As a result, the recording paper P is conveyed between the transfer roll 32 and the third intermediate transfer body 30, and the toner image on the third intermediate transfer body 30 is transferred to the recording paper P.

  A fixing device 100 is provided downstream of the paper conveyance path 34 through which the recording paper P is conveyed. The fixing device 100 includes a fixing belt 122 and a pressure roll 104, and heats and presses the recording paper P to fix the toner image on the recording paper P. The recording paper P on which the toner image is fixed is discharged to a tray 38 provided on the upper portion of the printer 10 by a paper transport roll 36.

  Here, image formation of the printer 10 will be described.

  When image formation is started, the surfaces of the photoreceptors 20Y to 20K are uniformly charged by the charging rollers 22Y to 22K. Then, light beams 60Y to 60K corresponding to the output image are irradiated from the optical scanning device 54 onto the surfaces of the charged photoconductors 20Y to 20K, and electrostatic latent images corresponding to the respective color separation images are formed on the photoconductors 20Y to 20K. Is formed. Developers 24Y to 24K selectively apply toners of respective colors, that is, Y to K, to the electrostatic latent images, and Y to K color toner images are formed on the photoreceptors 20Y to 20K.

  Thereafter, a magenta toner image is primarily transferred from the magenta photosensitive member 20M to the first intermediate transfer member 26. Further, a yellow toner image is primarily transferred from the yellow photoreceptor 20Y to the first intermediate transfer member 26, and is superimposed on the magenta toner image on the first intermediate transfer member 26.

  On the other hand, similarly, a black toner image is primarily transferred from the black photosensitive member 20K to the second intermediate transfer member 28. Further, a cyan toner image is primarily transferred from the cyan photoconductor 20 </ b> C to the second intermediate transfer member 28, and is superimposed on the black toner image on the second intermediate transfer member 28.

  The magenta and yellow toner images primarily transferred to the first intermediate transfer member 26 are secondarily transferred to the third intermediate transfer member 30. On the other hand, the black and cyan toner images primarily transferred to the second intermediate transfer member 28 are also secondarily transferred to the third intermediate transfer member 30. Here, the magenta and yellow toner images that have been secondarily transferred first and the cyan and black toner images are superimposed, and the color (three colors) and black full-color toner images are formed on the third intermediate transfer member 30. It is formed.

  The secondary-transferred full color toner image reaches the nip portion between the third intermediate transfer member 30 and the transfer roll 32. In synchronization with the timing, the recording paper P is conveyed from the registration roll 16 to the nip portion, and a full-color toner image is thirdarily transferred (final transfer) onto the recording paper P.

  The recording paper P is then sent to the fixing device 100 and passes through the nip portion between the fixing belt 122 and the pressure roll 104. At that time, the full color toner image is fixed on the recording paper P by the action of heat and pressure applied from the fixing belt 122 and the pressure roll 104. After fixing, the recording paper P is discharged to the tray 38 by the paper transport roll 36, and the formation of the full color image on the recording paper P is completed.

  Next, the fixing device 100 according to the present embodiment will be described.

  As shown in FIG. 2, the fixing device 100 includes a housing 120 in which openings 120 </ b> A and 120 </ b> B for entering or discharging the recording paper P are formed. Inside the housing 120, a temperature-sensitive roll 102 as a heating rotator is provided. Both end portions of the temperature-sensitive roll 102 are rotatably supported by a hollow shaft portion formed on a side wall (not shown) of the housing 120 via a bearing. A gear connected to a motor (not shown) that rotationally drives the temperature sensitive roll 102 is bonded to one end of the temperature sensitive roll 102. Here, when the motor operates, the temperature-sensitive roll 102 rotates in the direction of the arrow.

  A bobbin 108 made of an insulating material is disposed at a position facing the outer peripheral surface of the temperature sensitive roll 102. The bobbin 108 is formed in a substantially arc shape that follows the outer peripheral surface of the temperature-sensitive roll 102, and a convex portion 108 </ b> A projects from a substantially central portion on the surface opposite to the temperature-sensitive roll 102. The distance between the bobbin 108 and the temperature sensitive roll 102 is about 1 to 3 mm.

  An excitation coil 110 that generates a magnetic field H by energization is wound around the bobbin 108 a plurality of times in the axial direction (the depth direction in FIG. 2) around the convex portion 108A. A magnetic core 112 formed in a substantially arc shape following the arc shape of the bobbin 108 is disposed at a position facing the exciting coil 110 and supported by the bobbin 108. In the fixing device 100, the exciting coil 110 and the temperature sensitive roll 102 constitute a heating unit 111 as a heating device.

  In addition, a derivative 118 is provided inside the temperature-sensitive roll 102 at a position 1.0 to 1.5 mm away from the inner peripheral surface of the temperature-sensitive roll 102. The derivative 118 is made of aluminum, which is a nonmagnetic material, and has a circular arc shape facing the inner peripheral surface of the temperature-sensitive roll 102. Note that both ends of the derivative 118 are fixed to the shaft portion of the casing 120 described above. In addition, the derivative 118 is disposed in advance at a position that induces the magnetic flux of the magnetic field H when the magnetic flux of the magnetic field H penetrates a temperature-sensitive layer 103 (described later) of the temperature-sensitive roll 102.

  On the other hand, on the side opposite to the bobbin 108 of the temperature sensitive roll 102, a tension roll 114 as a tension rotating body is disposed at a position separated by a predetermined distance (for example, 30 mm). The tension roll 114 includes a cored bar 116 and a silicon rubber layer and a release layer coated around the cored bar 116. Further, the tension roll 114 is provided with a cored bar 116 rotatably on the housing 120.

  A fixing belt 122 as a fixing member is wound around the temperature-sensitive roll 102 and the tension roll 114. Here, when the temperature-sensitive roll 102 rotates in the direction of the arrow by the rotation of the motor, the fixing belt 122 rotates, and the tension roll 114 rotates in the same direction as the temperature-sensitive roll 102.

  A pressure roll 104 that rotates following the rotation of the fixing belt 122 is provided at a position facing the stretching roll 114 with the fixing belt 122 interposed therebetween. The pressure roll 104 is provided with a foamed silicon rubber sponge elastic layer having a thickness of 5 mm around a metal core 106 made of a metal such as aluminum, and a PFA containing carbon having a thickness of 50 μm outside the foamed silicon rubber sponge elastic layer. It is the structure which coat | covered the mold release layer which consists of.

  Further, since the pressure roll 104 is pressed against the outer peripheral surface of the fixing belt 122, the outer peripheral surface of the pressure roll 104 is concave at the contact portion (nip portion) between the fixing belt 122 and the pressure roll 104. . Here, the pressure roll 104 contacts the outer peripheral surface of the fixing belt 122, presses the fixing belt 122 toward the stretching roll 114, and causes the toner image T passing between the fixing belt 122 to be recorded on the recording paper P. To settle.

  On the other hand, a non-contact temperature sensor 124 that measures the temperature of the fixing belt 122 is provided at a position facing the outer peripheral surface of the fixing belt 122 on the temperature sensitive roll 102 side. The temperature sensor 124 has a thermocouple and converts the amount of heat given from the fixing belt 122 into a temperature, thereby indirectly predicting and measuring the surface temperature of the fixing belt 122. The attachment position of the temperature sensor 124 is approximately the center in the width direction of the fixing belt 122 so that the measured value does not change depending on the size of the recording paper P.

  As shown in FIG. 4B, the temperature sensor 124 is connected to the control circuit 128 provided in the control unit 50 (see FIG. 1) via the wiring 127. The control circuit 128 is connected to the energizing circuit 132 via the wiring 130, and the energizing circuit 132 is connected to the above-described exciting coil 110 via the wirings 134 and 136. The energization circuit 132 is driven or stopped based on an electric signal sent from the control circuit 128 so that an alternating current of a predetermined frequency is supplied to the exciting coil 110 via the wires 134 and 136 (in the arrow direction) or stopped. It has become.

  Here, the control circuit 128 performs temperature conversion based on the amount of electricity sent from the temperature sensor 124 and measures the temperature of the surface of the fixing belt 122. Then, the measured temperature is compared with a preset fixing temperature (170 ° C. in the present embodiment) stored in advance. When the measured temperature is lower than the fixed set temperature, the energizing circuit 132 is driven to drive the exciting coil. 110 is energized to generate a magnetic field H (see FIG. 2) as a magnetic circuit. When the measured temperature is higher than the fixing set temperature, the energization circuit 132 is stopped.

  On the other hand, a peeling member 126 is provided on the exit side of the contact portion (nip portion) between the fixing belt 122 and the pressure roll 104. The peeling member 126 includes a support portion 126A having one end fixed and a release sheet 126B supported by the support portion 126A. The leading edge of the release sheet 126B is disposed so as to be close to or in contact with the fixing belt 122.

  Next, the configuration of the temperature sensitive roll 102 will be described.

  As shown in FIGS. 3A, 3B, and 4A, the temperature-sensitive roll 102 has a temperature-sensitive layer 103 having a thickness of 200 μm (150 to 200 μm or less) and a thickness from the inside toward the outside. A multilayer roll 107 in which a release layer 105 made of 30 μm PFA is laminated and integrated, and a plurality of slits 109 formed on the outer peripheral surface of the multilayer roll 107 are configured.

  The temperature-sensitive layer 103 is located on the base layer for maintaining the strength of the temperature-sensitive roll 102, and is a metal composed of an alloy made of iron, nickel, chromium, silicon, boron, niobium, copper, zirconium, cobalt, or the like. A soft magnetic material is used. The temperature-sensitive layer 103 is equal to or lower than the heat-resistant temperature of the temperature-sensitive roll 102 (temperature at which functional degradation or deformation starts due to heat), and the fixing setting temperature of the fixing device 100 (fixing temperature required for the temperature-sensitive roll 102) A material having a magnetic permeability change start temperature is used in the above temperature range.

  As shown in FIG. 5, the magnetic permeability change start temperature is a temperature at which the magnetic permeability (measured by JIS-C2531) starts to decrease continuously, and means the point at which the magnetic flux penetration amount starts to change. . Further, the permeability change start temperature is different from the Curie point, and is preferably set at 150 ° C. to 230 ° C.

In this embodiment, the heat-resistant temperature is set to 240 ° C. and the fixing set temperature is set to 170 ° C., and an iron-nickel alloy having a permeability change start temperature of about 210 ° C. is used as the temperature-sensitive layer 103. The specific resistance of the temperature sensitive layer 103 is 60 × 10 ⁻⁸ Ωm or more, and the thickness is 200 μm.

  Further, the temperature sensitive layer 103 is a ferromagnetic material at a temperature lower than the permeability change start temperature, and allows the aforementioned magnetic field H (see FIG. 2) to enter. Further, when the permeability change start temperature is exceeded, the magnetic permeability starts to decrease, and when the Curie point is reached, the magnetic density becomes low due to the nonmagnetic material (paramagnetic material), and the magnetic flux penetration of the magnetic field H is very large. Become.

  In order to fully develop the temperature-sensing function of the temperature-sensitive layer 103, the skin depth δ indicating the depth at which the magnetic field H can penetrate at a temperature lower than the permeability change start temperature is set to be equal to or less than the thickness of the temperature-sensitive layer 103. There is a need. The skin depth δ is given by equation (1). Conversely, it can be said that the thickness of the temperature-sensitive layer 103 needs to be equal to or greater than the skin depth δ.

In the equation (1), ρ is a specific resistance, f is a frequency (electromagnetic induction heating frequency), and μr is a relative permeability (room temperature). For example, assuming that ρ ≧ 70 × 10 ⁻⁸ Ωm and f ≧ 20 kHz are the necessary conditions and the relative permeability satisfying, for example, δ ≦ 200 μm is obtained based on the equation (1), at least the relative permeability μr ≧ 230 is required. Become. The temperature sensitive layer 124 of the present embodiment is previously made highly magnetically permeable by heat treatment (annealing) so that the relative magnetic permeability μr is 230 or more. The specific resistance ρ of the material of the temperature sensitive layer 103 is obtained by a method such as JIS K7194.

  On the other hand, the slit 109 has a length of 10 mm and a width of 0.2 mm. The slit 109 intersects the direction in which the eddy current B1 generated by the electromagnetic induction action of the exciting coil 110 (see FIG. 2) flows (a loop is formed). (Direction to shut off). In this embodiment, the formation direction of the slit 109 is the same as the rotation direction of the temperature-sensitive roll 102 (arrow R direction).

  The plurality of slits 109 are the first slit row 109A formed at 11 positions at equal intervals of 15 mm in the width direction (direction of arrow X) of the temperature sensitive roll 102, and the second is formed at 10 positions at equal intervals of 15 mm. It is composed of a slit row 109B. The slits of the first slit row 109 </ b> A and the second slit row 109 </ b> B are staggered so as to be shifted from each other, and all of them are arranged uniformly in the entire circumferential direction of the temperature-sensitive roll 102.

  In addition, the first slit row 109A and the second slit row 109B have both ends of each slit 109 extending from the center line M in the width direction of the temperature-sensitive roll 102, and each end as viewed in the width direction. The parts overlap. Here, the amount of eddy current generated in the temperature sensitive roll 102 is adjusted by changing the amount of the slit 109, the slit interval, and the overlap range of the slits.

  Next, the configuration of the fixing belt 122 will be described.

  As shown in FIG. 4A, the fixing belt 122 includes a base layer 138 made of polyimide having a thickness of 200 μm (150 to 200 μm or less) from the inside to the outside, a heat generating layer 140 having a thickness of 12 μm (5 to 20 μm), The elastic layer 142 having a thickness of 400 μm and the release layer 144 having a thickness of 30 μm are stacked and integrated. The fixing belt 122 has a diameter of 30 mm and a width direction length of 300 mm.

The heat generating layer 140 is made of a metal material that generates heat by an electromagnetic induction effect in which an eddy current flows so as to generate a magnetic field that cancels the magnetic field H (see FIG. 2). As such a metal material, for example, gold, silver, copper, aluminum, zinc, tin, lead, bismuth, beryllium, antimony, or an alloy thereof can be used. Further, in order to shorten the warm-up time of the fixing device 100, the thickness of the heat generating layer 140 should be as thin as possible. The heat generating layer 140 has a thickness of 5 to 20 μm and a specific resistance of 2.7 × 10 ⁻⁸ Ωcm. If the following non-magnetic metal material is used, a necessary amount of heat generation can be efficiently obtained in the range of AC frequency 20 kHz to 100 kHz where a general-purpose power source can be utilized. When the thickness is 5 μm or less, it is difficult to form a uniform layer when formed by plating or metal paste, and the temperature distribution can be uneven. Further, if it is 20 μm or more, the resistance value of the heat generating layer 140 becomes small and eddy current loss becomes difficult to obtain, so 20 μm or less is desirable. In this embodiment, from the viewpoint of heat generation efficiency and cost, copper is used and the thickness is 12 μm. Since this is sufficiently thinner than the skin depth δ, the magnetic flux penetrates.

  The elastic layer 142 is made of silicon rubber or fluorine rubber from the viewpoint of obtaining excellent elasticity and heat resistance, and in this embodiment, silicon rubber is used.

  The release layer 144 is provided in order to weaken the adhesive force with the toner T (see FIG. 2) melted on the recording paper P so that the recording paper P can be easily separated from the fixing belt 122. In order to obtain excellent surface releasability, a fluororesin, a silicon resin, or a polyimide resin is used as the release layer 144. In this embodiment, PFA (tetrafluoroethylene / perfluoroalkoxyethylene copolymer) is used. Polymerization resin).

  Next, the operation of the embodiment of the present invention will be described.

  As shown in FIG. 1, the recording paper P onto which the toner T has been transferred is sent to the fixing device 100 through the image forming process of the printer 10 described above.

  Subsequently, in the fixing device 100, a motor (not shown) is driven by the control unit 50, and the temperature-sensitive roll 102 rotates in the arrow direction. As a result, the fixing belt 122, the tension roll 114, and the pressure roll 104 are rotated. At this time, the energization circuit 132 is driven based on the electrical signal from the control circuit 128, and an alternating current is supplied to the excitation coil 110.

  Here, as shown in FIG. 6A, when an alternating current is supplied to the exciting coil 110, the magnetic field H as a magnetic circuit repeats generation and disappearance around the exciting coil 110. When the magnetic field H crosses the heat generating layer 140 of the fixing belt 122, an eddy current is generated in the heat generating layer 140 so that a magnetic field that prevents the magnetic field H from changing is generated. The heat generating layer 140 generates heat in proportion to the skin resistance of the heat generating layer 140 and the magnitude of the eddy current flowing through the heat generating layer 140, whereby the fixing belt 122 is heated. The magnetic field H reaches the temperature-sensitive layer 103 of the temperature-sensitive roll 102 and forms a closed magnetic circuit.

  Subsequently, as shown in FIG. 1, the recording paper P sent to the fixing device 100 is fed by a fixing belt 122, a tension roll 114, and a pressure roll 104 that are at a predetermined fixing set temperature (170 ° C.). The toner image is fixed on the surface of the recording paper P by being heated and pressed. The recording paper P discharged from the fixing device 100 is discharged to the tray 38 by the paper transport roll 36.

  Here, the operation of the temperature-sensitive roll 102 will be described.

  As shown in FIG. 6A, the magnetic field H <b> 1 generated by the exciting coil 110 enters the temperature sensitive layer 103. Since the temperature-sensitive layer 103 is a metal, the temperature-sensitive layer 103 also generates eddy current due to the electromagnetic induction effect of the magnetic field H1 and tends to generate heat.

  However, as shown in FIG. 3B, a large flow of eddy current B 1 that is to be generated in the temperature-sensitive layer 103 is blocked by the slit 109. Only a very small eddy current is generated between the slits 109 of the temperature-sensitive layer 103, and an excessive temperature increase of the temperature-sensitive roll 102 is suppressed. For this reason, the heat generation amount of the temperature sensitive layer 103 is such that it hardly affects the heat generation amount of the heat generation layer 140 of the fixing belt 122.

  As a result, as shown in FIG. 7, the peak temperature of the fixing belt 122 at the time of temperature rise is suppressed to be lower than that in the case of using a conventional heating roll in which excessive heating is performed without the slit 109. Further, when the temperature of the fixing belt 122 decreases due to continuous fixing of a plurality of recording sheets P, even if the temperature is raised by energizing the exciting coil 110, almost only the heat generation layer 140 of the fixing belt 122 generates heat. The temperature of the fixing belt 122 can be set to a temperature close to the fixing set temperature.

  As described above, when the fixing device 100 according to this embodiment is used, the amount of heat generated by self-heating of the temperature-sensitive roll 102 is suppressed, and excessive temperature increase of the temperature-sensitive roll 102 and the fixing belt 122 is suppressed. T becomes difficult to be in a high-temperature molten state more than necessary, and image contamination is suppressed.

  Subsequently, as shown in FIG. 6B, when the temperature of the temperature-sensitive layer 103 becomes equal to or higher than the magnetic permeability change start temperature, the magnetic permeability of the temperature-sensitive layer 103 decreases, so that the magnetic field H1 is changed to the temperature-sensitive layer. 103 is passed to the derivative 118. At this time, since the magnetic field H1 is also penetrated in the derivative 118, it is difficult to form a closed magnetic circuit, the magnetic field H1 is weakened to become the magnetic field H2, and the heat generation amount of the heat generating layer 140 is reduced. Thereby, as shown in FIG. 7, the temperature increase of the fixing belt 122 more than necessary is suppressed.

  As shown in FIGS. 8A and 8B, as another embodiment of the temperature-sensitive roll 102, a temperature-sensitive roll 150 that includes an exciting coil can be used.

  The temperature-sensitive roll 150 includes a cylindrical multilayer roll 154 in which a temperature-sensitive layer 152 made of the same material as that of the temperature-sensitive layer 103 is disposed on the inner side and a release layer is laminated on the outer side. A spiral excitation coil 156 is inserted from one end to the other end of the multilayer roll 154 in the center.

  The exciting coil 156 is connected to an energization circuit (not shown), and generates a magnetic field by energization. In addition, a derivative made of a nonmagnetic material (not shown) is provided at a position facing the outer peripheral surface of the multilayer roll 154.

  A plurality of slits 160 are formed in the multilayer roll 154. The slit 160 is formed by a notch having a length of 10 mm and a width of 0.2 mm, and is formed in a direction intersecting the direction in which the eddy current B2 generated by the electromagnetic induction action of the exciting coil 156 flows (direction in which the loop is interrupted). ing. Here, the forming direction of the slit 160 is the same as the width direction (arrow X direction) of the multilayer roll 154.

  The plurality of slits 160 have a first slit row 160A formed at five equal intervals of 15 mm in the width direction (arrow X direction) of the multi-layer roll 154, and a width at a position shifted by 15 mm from the first slit row 160A in the circumferential direction. The second slit row 160B is formed at four locations at equal intervals of 15 mm in the direction.

  The slits of the first slit row 160A and the second slit row 160B are staggered so as to be shifted from each other. The first slit row 160A and the second slit row 160B are alternately provided at equal intervals over the entire circumferential direction of the multilayer roll 154. Further, the first slit row 160 </ b> A and the second slit row 160 </ b> B overlap each other when viewed in the width direction of the multilayer roll 154. Here, the amount of eddy current generated in the temperature sensitive roll 150 is adjusted by changing the amount of the slit 160, the interval between the slits, and the overlapping range of the slits.

  When forming a plurality of loops in which the eddy current B2 extends in the circumferential direction like the temperature sensitive roll 150, the loop of the eddy current B2 is blocked by forming the slit 160 extending in the width direction, and the temperature sensitive layer 152 is formed. Heat generation is suppressed. Thereby, the excessive temperature rise of the temperature sensitive roll 150 is suppressed.

  In addition, this invention is not limited to said embodiment.

  The printer 10 may use a liquid developer as well as a dry electrophotographic system using a solid developer. Further, as the temperature detecting means of the fixing belt 122, a thermistor disposed inside the fixing belt 122 and in contact with the inner peripheral surface may be used instead of the non-contact type temperature sensor 124. Further, if temperature conversion is set in advance, the temperature sensor 124 may be provided at a position facing the surface of the pressure roll 104.

  The slits 109 and 160 may be formed in an oblique direction as long as the eddy current can be cut off. Further, the eddy current blocking means is not limited to the slits 109 and 160, and for example, a resin material having low conductivity may be partially embedded in the temperature sensitive layers 103 and 152.

10 Printer (image forming device)
18 Image forming unit (exposure section)
24 Developer (Developer)
32 Transfer roll (transfer section)
34 Paper transport path (transport section)
100 Fixing device (fixing device)
102 Temperature-sensitive roll (temperature-sensitive rotating body)
103 Temperature sensitive layer (temperature sensitive layer)
107 Multi-layer roll (rotating body)
104 Pressurizing roll (Pressurizing rotating body)
109 slit (eddy current blocking means, cutting)
110 Excitation coil (magnetic field generating means)
111 Heating unit (heating device)
114 Tension roll (Tension roll)
122 Fixing belt (fixing member)
140 Heat generation layer (heat generation layer)
150 Temperature sensitive roll (temperature sensitive rotating body)
152 Temperature sensitive layer (temperature sensitive layer)
154 Multi-layer roll (rotating body)
H Magnetic field P Recording medium (recording medium)
T Toner (Developer)

Claims (4)

A temperature-sensitive layer formed in a cylindrical shape that generates heat due to electromagnetic induction of a magnetic field, and whose magnetic permeability begins to continuously decrease from a magnetic permeability change start temperature in a temperature range that is higher than a heating set temperature and lower than a heat-resistant temperature, with the plurality of formed at intervals in the circumferential direction of the layer, a plurality of formed by shifting so that the staggered arrangement in the axial direction of the temperature sensing layer, wherein the circumferential blocking the portion of the eddy current generated by the electromagnetic induction A temperature-sensitive rotating body having a slit-like cut extending in a direction ;
A tension rotator spaced apart from the temperature-sensitive rotator;
A fixing belt stretched between the temperature-sensitive rotating body and the tension rotating body and having a heat generation layer having a thickness smaller than at least the skin depth;
A magnetic field generating means arranged to be opposed to the temperature-sensitive rotating body and generating a magnetic field;
The developer belt is brought into contact with the outer peripheral surface of the fixing belt, and the fixing belt is pressurized toward the tension rotating body so that the developer image on the recording medium passing between the fixing belt and the fixing belt is fixed to the recording medium. A pressure rotating body,
The fixing device in which the cut is formed so that the heat generation amount of the temperature-sensitive layer of the temperature-sensitive rotating body is smaller than the heat generation layer of the fixing belt. A temperature-sensitive layer formed in a cylindrical shape that generates heat due to electromagnetic induction of a magnetic field, and whose magnetic permeability begins to continuously decrease from a magnetic permeability change start temperature in a temperature range that is higher than a heating set temperature and lower than a heat-resistant temperature, A plurality of layers formed at intervals in the circumferential direction of the layers, and formed in a staggered arrangement in the circumferential direction of the temperature-sensitive layer, and the sensation that blocks a part of the eddy current generated by the electromagnetic induction. A temperature-sensitive rotating body having a slit-like cut extending in the axial direction of the warm layer;
A tension rotator spaced apart from the temperature-sensitive rotator;
A fixing belt stretched between the temperature-sensitive rotating body and the tension rotating body and having a heat generation layer having a thickness smaller than at least the skin depth;
A magnetic field generating means arranged to be opposed to the temperature-sensitive rotating body and generating a magnetic field;
The developer belt is brought into contact with the outer peripheral surface of the fixing belt, and the fixing belt is pressurized toward the tension rotating body so that the developer image on the recording medium passing between the fixing belt and the fixing belt is fixed to the recording medium. A pressure rotating body,
The fixing device in which the cut is formed so that the heat generation amount of the temperature-sensitive layer of the temperature-sensitive rotating body is smaller than the heat generation layer of the fixing belt . The fixing device according to claim 1 , wherein the heat generating layer includes a nonmagnetic metal material having a thickness of 2 to 20 μm and a specific resistance of 2.7 × 10 ⁻⁸ Ωcm or less . A fixing device according to any one of claims 1 to 3,
An exposure unit that emits exposure light; and
A developing unit that exposes the latent image formed by the exposure light with a developer to form a developer image; and
A transfer unit that transfers the developer image made visible in the developing unit onto a recording medium;
A transport unit that transports the recording medium onto which the developer image has been transferred in the transfer unit to the fixing device;
An image forming apparatus .