JP4777035B2 - Heat fixing device - Google Patents

Description

  The present invention relates to a heating and fixing apparatus that heats a recording material that carries an image in a nip formed by first and second fixing members.

  More specifically, image information formed on a recording material (paper, printing paper, transfer material sheet, OHT sheet, glossy paper, glossy film, etc.) by timely image forming process means such as electrophotography, electrostatic recording, and magnetic recording. The present invention relates to a heat fixing apparatus that heat-fixes an unfixed toner image corresponding to the above on a recording material surface.

  In particular, the present invention relates to an on-demand fixing device using a thin sleeve, which is suitable for use in a color image forming apparatus, is low-cost and has a short fixing device rise time (so-called warm-up time).

  In recent years, colorization has progressed in image forming apparatuses such as printers and copiers. As a fixing device used in such a color image forming apparatus, heat roller fixing having an elastic layer on a fixing member is well known. An example of a fixing device using such a fixing roller having an elastic layer is shown in FIG.

  In this fixing device, unfixed toner is rotated at a contact nip portion (fixing nip) N of two heating rollers, which is composed of a fixing roller 1601 and a pressure roller 1602 that are rotationally driven in the direction of an arrow and adjusted to a predetermined fixing temperature. The recording material P on which the image t is placed is configured to pass therethrough.

  When the unfixed toner image t passes through the nip portion N, it is heated and pressed by the fixing roller 1601 and the pressure roller 1602 to be fixed on the recording material P as a completed image (permanently fixed image).

  Each of the rollers 1601 and 1602 includes a halogen heater H at the center, and the radiant energy generated from the heater H is absorbed by the aluminum cores 1601a and 1602a inside each roller and heated. The thermistors 1603 and 1604 are arranged in elastic contact with the surfaces of the respective rollers 1601 and 1602, and the rollers 1601 and 1602 with respect to the halogen heater H based on the temperatures detected by the thermistors 1603 and 1604. Power supply is controlled and temperature adjustment is performed.

  Elastic layers 1601b and 1602b made of silicone rubber having a thickness of 2 mm are provided around the aluminum cores 1601a and 1602a of the rollers 1601 and 1602, respectively. PFA (tetrafluoroethylene / perfluoroalkyl ether copolymer / tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin), FEP (tetrafluoroethylene / hexafluoropropylene copolymer) to prevent paper dust and the like from sticking Coating layers 1601c and 1602c are formed of a resin having good releasability and heat resistance, such as a coalescence / tetrafluoroethylene / hexafluoropropylene copolymer resin).

  The reason why the elastic layer 1601b is provided on the fixing roller 1601 side, which is a fixing member in contact with the unfixed toner t, in the fixing nip portion N is to fix the toner image surface as uniformly as possible.

  By providing the elastic layer 1601b on the fixing roller 1601 side, when the toner image t passes through the fixing nip N, the elastic layer 1601b is deformed along the toner layer, so that the toner that is unevenly placed on the image. However, it is encased in the elastic layer 1601b and uniformly heated so that uniform fixing is achieved.

  An image fixed uniformly in this way has no gloss unevenness, and has a feature that the light transmittance of the image is excellent particularly when an OHT (transparent sheet for overhead projector) is fixed.

  However, in a heat roller type fixing device having such an elastic layer, the heat capacity of the heat roller itself increases, and the time required to raise the temperature of the fixing roller 1601 to a temperature suitable for toner image fixing. There was a problem that (warm-up time) was long. Further, the cost of the fixing member is also expensive.

  On the other hand, as a low-cost fixing device with a short warm-up time, a film fixing type fixing device used in a black and white printer or the like is well known. An example of such a film fixing device is shown in FIG.

  In this fixing device, a thin fixing film 1711 is sandwiched between a heater 1712 fixedly supported by a support member 1715 and an elastic pressure roller 1714 to form a fixing nip portion N. The fixing film 1711 is attached to the heater 1712. The recording material P carrying the toner image t is nipped and conveyed between the fixing film 1711 and the pressure roller 1714 in the fixing nip portion, and is moved from the heater 1712 via the fixing film 1711. In this configuration, the toner image on the recording material is heated by heat. The unfixed toner image t on the recording material P receives heat and pressure when passing through the fixing nip portion N, and is fixed on the recording material P as a completed fixed image (permanently fixed image).

  The fixing film 1711 is, for example, an endless film made of a heat-resistant resin having a thickness of about 50 μm, and a release layer (such as a fluororesin coating layer) having a thickness of about 10 μm is formed on the surface. The heater 1712 is a ceramic. A resistance heating element is formed on a substrate. Temperature detection means 1713 is brought into contact with the heater 1712, the temperature of the heater 1712 is detected, and temperature control is performed by a control means (not shown) so that the temperature of the heater 1712 becomes a desired temperature.

  Further, in order to reduce the heat capacity of the fixing film 1711, the fixing film 1711 is not provided with an elastic layer.

  In the fixing device having such a configuration, since the heat capacity of the fixing film 1711 is very small, the power of the heater 1712 is turned on, and then the temperature of the fixing nip portion N is raised to a temperature capable of fixing the toner image in a short time. It is possible.

  In particular, from the viewpoint of energy saving, a film heating type fixing device that heats through a film having a small heat capacity has attracted attention as a method with high heat transfer efficiency and quick start-up of the device. These technologies reduce the heat capacity as much as possible to improve quick start and energy savings and improve controllability to meet the demands for high-speed, high-quality printing.

  However, when a film fixing device using the fixing film 1711 not provided with such an elastic layer is used as a fixing device of a color image forming apparatus, unevenness due to the presence or absence of the surface of the recording material P or the toner layer or unevenness of the toner itself. As a result, the surface of the fixing film 1711 cannot follow, and there is a difference in heat applied from the fixing film between the convex portion and the concave portion. The convex part that is in good contact with the fixing film conducts heat well from the fixing film, and the concave part is less likely to conduct heat from the fixing film than the convex part.

  In a color image, since a plurality of color toner layers are mixed and used, the unevenness of the toner layer is larger than that of a black and white image, and if the fixing film as a fixing member does not have an elastic layer, uneven glossiness of the fixed image may occur. When the recording material is OHT, the image quality deteriorates due to an increase in image quality, and the transparency is poor when a fixed image is projected, resulting in a decrease in image quality.

  Accordingly, a fixing device that constitutes a low-cost color on-demand fixing device by using a fixing belt (fixing film) having an elastic layer as disclosed in Patent Document 1 for a film fixing device has been proposed. Yes.

  In the heater 5 as a heating means, a heating element 8 is patterned on a heater substrate 6 made of a heat-resistant insulating material such as ceramic, the surface is protected by heat-resistant glass, and the temperature detection is performed on the back surface of the heater substrate 6. The element 7 is arranged, and the temperature control of the fixing device is performed by detecting the temperature of the back surface of the substrate. In addition, a substrate such as ALN with high thermal conductivity is used as the heater substrate, the heater surface is opposite to the film, the heater substrate side is in contact with the film, and a high heat resistant resin such as PI or PTFE is applied to the contact surface. Some are coated to make a lubricating member.

  FIG. 18 is a front view of the heating element forming surface of the heater 5, and the heating element is formed in a single band shape. The heating element 8 is an energization heating element made of silver palladium (Ag / Pd), RuO 2, Ta 2 N, or the like, and generates heat when energized from the energizing electrode 11 formed on the surface of the heater substrate 6.

  In addition, the fixing film has a heat capacity of 100 μm or less, more preferably 40 μm or less and more than 20 μm, in order to reduce the heat capacity and improve the quick start property. PTFE, PFA, PPS having both heat resistance, releasability and durability Single layer film or composite layer film with polyamide, polyamideimide, polyimide, PEEK, PES, etc. film coated with PTFE, PFA, EEP as a release layer, or a metal layer such as Ni or stainless steel It is.

As described above, various image forming apparatuses such as printers using the fixing device as described above eliminate the need for preheating during standby, lower the preheating temperature, and wait due to high heating efficiency and rising speed. It has many advantages such as elimination of time and cost. In addition to black and white machines, color machines started with introduction to small and low speed machines, and in the future, introduction to large and medium speed machines is expected. Yes.
Japanese Patent Laid-Open No. 11-15303 (Japanese Patent No. 3051085)

  However, in the conventional fixing device, it is necessary to match the heat generation positions of the fixing nip and the heater in order to ensure safety in the event of an abnormality. Therefore, it is difficult to change the structure around the nip, and it is necessary to increase the temperature and pressure in order to pursue high image quality. However, increasing the temperature and increasing the pressure increase the fixing power and the torque of the motor, that is, increase the power consumption, making it difficult to provide an image forming apparatus that has high image quality, high-speed throughput, and is energy-saving and inexpensive.

  The present invention has been made in view of the above problems, and has an object to ensure safety by controlling a temperature rising point at the time of an apparatus abnormality to make a safety element respond at a high speed and preventing an excessive temperature rising. And

The present invention for solving the above-mentioned problems is an elongated plate-like heater that generates heat by being supplied with electric power from a commercial power source and has a larger calorific value at the end than at the center in the direction perpendicular to the recording material conveyance direction, A fixing film that is rotated and heated while sliding the inner surface of the heater in contact with the heater, a pressure roller that presses the heater through the fixing film and forms a fixing nip portion, and contacts the heater to A heater holder having a heater seat surface supporting the heater, and a recess recessed from the heater seat surface in a direction perpendicular to the recording material conveyance direction in the center of the recording material conveyance direction; and in the recording material conveyance direction of the heater A protective element that is provided at a central portion in a direction perpendicular to the heater and that shuts off the power supply to the heater by being activated by an abnormal temperature rise of the heater, and records a toner image on a recording material at the fixing nip portion. Material In the fixing device for fixing, the concave portion of the heater holder includes a first bottom surface facing a central portion in a direction orthogonal to a recording material conveyance direction having a small heat generation amount in the heater, and recording having a large heat generation amount in the heater. The heater seat has a second bottom surface facing an end in a direction perpendicular to the material transport direction and having a distance from the heater shorter than the bottom surface of the first, When the surface is softened, the second bottom surface of the heater holder contacts the heater before the first bottom surface .

  According to the present invention, when an abnormality occurs without affecting the heater temperature during normal printing, it is possible to lengthen the time until failure of the heater and to increase the operating speed of the temperature protection element. It is possible to provide a fixing device with high image quality and high throughput, such as a pressure distribution in a heater and a fixing nip, at a lower cost than before.

Example 1
FIG. 1 shows the best representation of the first embodiment. In this example, as an example, the fixing device F is described as a heating device of a fixing belt heating method and a pressurizing rotator driving method (tensionless type).

1) Overall Configuration of Apparatus F Reference numeral 101 denotes a fixing belt as a first fixing member, which is a cylindrical (endless belt-like) member in which an elastic layer is provided on the belt-like member. The fixing belt 101 will be described in detail later in section 3).

Reference numeral 102 denotes a pressure roller as a second fixing member, which includes a cored bar portion 102a and a rubber portion 102b. Reference numeral 103 denotes a heat-resistant and rigid heater holder having a substantially semicircular arc shape in cross section, and 104 a fixing heater as a heat source, which is disposed on the lower surface of the heater holder 103 along the length of the holder. The fixing belt 101 is loosely fitted on the heater holder 103. In the present embodiment, the fixing heater 104 is a ceramic heater as described in detail in section 2) below.

  The heater holder 103 is a member that holds the heater 104 and rotates and holds the fixing heating sleeve. Since the heater holder is required to have heat resistance and insulating properties, strength as a structural body is required, and moldability is also important, engineering plastics reinforced with glass fibers, for example, LCP materials made of wholly aromatic polyester resins, etc. Is often used. In the present embodiment, Zenite 7755M (trade name) manufactured by DuPont is used as the liquid crystal polymer. The maximum usable temperature of Zenite 7755M is about 270 ° C.

  The pressure roller 102 is formed by forming a silicone rubber layer 102b with a thickness of about 3 mm on a stainless steel core metal 102a by injection molding and coating a PFA resin tube with a thickness of about 40 μm thereon. The pressure roller 102 is arranged such that both end portions of the core metal are rotatably supported by bearings between a side plate (not shown) and a front side plate of the apparatus frame 105. On the upper side of the pressure roller 102, the heating assembly including the heater 104, the heater holder 103, the fixing belt 101, and the like is disposed in parallel to the pressure roller 102 with the heater 104 facing downward, and is provided inside the heater holder 103. The pressurizing mechanism including the pressurizing stay 106 and the pressurizing springs 107 provided at both ends of the pressurizing stay is biased in the axial direction of the pressurizing roller 102 with the force of one side 98N (10 kgf) and the total pressure 196N (20 kgf). Thus, the fixing heater 104 has its downward surface brought into pressure contact with the elastic layer of the pressure roller 102 via the fixing belt 101 with a predetermined pressing force against the elasticity of the elastic layer, and a fixing nip having a predetermined width necessary for heat fixing. Part N is formed.

Reference numeral 40 denotes a temperature protection element which is disposed inside the pressure stay 106 and the sleeve guide 103 so as to come into contact with the fixing heater 104, and stops power supply to the fixing heater 104 when the temperature becomes abnormally high.

  The pressure roller 102 is rotationally driven by the driving means M in the counterclockwise direction indicated by the arrow at a predetermined peripheral speed. A rotational force acts on the cylindrical fixing belt 101 by the pressure frictional force at the fixing nip portion N between the outer surface of the pressure roller 102 and the fixing belt 101 by the rotational driving of the pressure roller 102, so that the fixing belt 101 is While the inner surface of the heater holder 103 slides in close contact with the downward surface of the fixing heater 104, the outer periphery of the heater holder 103 is rotated in the clockwise direction indicated by the arrow. Grease is applied to the inner surface of the fixing belt 101 to ensure slidability between the heater holder 103 and the inner surface of the fixing belt 101.

  The pressure roller 102 is rotationally driven, and accordingly, the cylindrical fixing belt 101 is driven and rotated, and the fixing heater 104 is energized. The fixing heater 104 rises in temperature and rises to a predetermined temperature. In this state, the transfer material P carrying an unfixed toner image is introduced between the fixing belt 101 and the pressure roller 102 in the fixing nip portion N, and the toner image carrying surface side of the transfer material P is fixed to the fixing nip portion N. The fixing belt 101 is in close contact with the outer surface of the fixing belt 101, and is nipped and conveyed through the fixing nip N together with the fixing belt 101. In this nipping and conveying process, heat of the fixing heater 104 is applied to the transfer material P via the fixing belt 101, and an unfixed toner image on the transfer material P is heated and pressurized on the transfer material P to be melted and fixed. . The recording material P that has passed through the fixing nip N is discharged from the fixing belt 101.

2) Fixing heater 104
In this embodiment, the fixing heater 104 serving as a heat source is formed by applying a conductive paste containing silver / palladium alloy in a film having a uniform thickness on a substrate made of aluminum oxide (alumina) or aluminum nitride by screen printing. In this way, a ceramic heater is used in which a resistance heating element is formed and a glass coat made of pressure-resistant glass is applied.

The fixing heater 104
1. A horizontally long alumina substrate or aluminum nitride substrate whose longitudinal direction is the direction orthogonal to the paper passing direction ,
2. A conductive paste containing silver palladium (Ag / Pd) alloy, which is coated on the surface side of the substrate along the longitudinal direction by screen printing in a linear or strip shape and generates heat when an electric current flows, has a thickness of about 10 μm and a width A resistance heating element layer of about 1 to 5 mm,
3. As a power supply pattern for the resistance heating element layer, the first and second electrode portions and the extended electric circuit portion, which are similarly patterned by screen printing of silver paste on the surface side of the alumina substrate a,
4). A thin glass coat or polyimide having a thickness of about 10 μm, which can withstand the rubbing against the fixing belt 101 and is formed on the resistance heating element layer and the extension circuit portion to ensure protection and insulation. coat,
Etc.

  In the heater of the present embodiment, an air layer is sandwiched between the heater and the heater holder in a portion other than the outer peripheral portion of the heater substrate, and the heat efficiency can be further improved by configuring so as not to transmit the heat generated by the heater to the heater holder side as much as possible. I am doing so.

  Further, there is provided an end stop portion that narrows the heater pattern width corresponding to the end sheet passing position in the heater longitudinal direction by about 3% to 10% compared to the center portion. The reason for this is to prevent a temperature drop at the end when the fixing unit is started up by making the resistance at the end larger than that at the center.

3) Fixing belt 101
The fixing belt 101 has a thickness of 30 μm to 50 μm after a silicone rubber layer is formed as an elastic layer on an endless film formed of a polyimide resin or a metal such as Ni or stainless steel in a cylindrical shape with a thickness of 50 μm by a ring coating method. It is formed by covering a PFA resin tube to a certain extent.

  For the silicone rubber layer, it is desirable from the viewpoint of temperature rise to use a material having as high a thermal conductivity as possible and to reduce the heat capacity of the fixing belt 101. In this example, a material having a thermal conductivity of about 4.19 × 10 −3 J / sec · cm · K and a silicone rubber having a high thermal conductivity were used.

  On the other hand, it is desirable to make the rubber layer of the fixing belt 101 as thick as possible from the viewpoint of image quality such as OHT permeability and minute gloss unevenness on the image. According to the study by the present inventors, it has been found that a rubber thickness of 200 μm or more is necessary to obtain a satisfactory level of image quality. The silicone rubber layer in this example was 250 μm thick.

  Further, by providing a fluororesin layer on the surface of the fixing belt 101, the surface releasability is improved, and an offset phenomenon that occurs when the toner once adheres to the surface of the fixing belt 101 and moves to the transfer material P again. Can be prevented.

  Further, when the fluororesin layer on the surface of the fixing belt 101 is a PFA tube, a uniform fluororesin layer can be formed more easily.

  FIG. 2 shows a cross-sectional view of a conventional heater and heater holder.

  FIG. 2 shows the structure of the heater holder and the heater around the heater. FIG. 2A is a view of the heater and the heater holder from the heater surface and the fixing sleeve side. The heater pattern is a perspective view.

In FIG. 2, 1 is a heater substrate, 2 is a resistance heating element layer , 3 is a heat insulation layer or space layer, and 4 is a heater holder. In addition, the central part of the throttle position (electrode side) of the heater in the longitudinal direction is B, the central position of the heater heat generation center is C, and the central part of the heater throttle position (counter electrode side) is D.

Figure 2-a to c are sectional views viewed sectional Dehi over data and heater holder of A-A '. 3A to 3C are cross-sectional views taken along line BB ′. A temperature rise curve is shown in FIG.

Consider a case in which power is supplied to the device and temperature control becomes impossible due to a failure in the temperature control circuit. Since there is a risk that power is continuously supplied to the heater 104 in the failed state, the seat surface portion of the heater holder 4 that is in direct contact with the heater 104 is softened. The temperature rise curve in this case is shown in FIG. In FIG. 4, point a is the temperature in this state. 2A and 3A show the positional relationship between the heater 104 and the heater holder 4 at the temperature of point a. The heater 104 is not in contact with the heater holder 4 except for the heater seat surface.

Since the heater 2 is pressed from the upper side of FIG. 3 by a pressure roller (not shown), the heater seat surface of the heater holder 4 is softened so that the heater 104 is buried in the heater holder 4. Further, since the resistance value increases as the temperature of the heater 2 rises, the input power to the heater 2 decreases. Further, when the heater 104 becomes high temperature, heat dissipation increases due to a temperature difference from the surroundings, so that the temperature rise curve of the heater 104 rises quickly and the slope becomes gentle with time.

The temperature in this state is point b in FIG. 2B and 3B show the positional relationship between the heater 104 and the heater holder 4 at the temperature of point b. The heater 2 is in a state where it does not touch the heater holder 4 except for the heater seating surface as before.

A process of increasing the temperature of the heater 104 will be described. If power is continuously supplied to the heater 104 , the temperature rise continues while the temperature gradient becomes small. The end of the heater 104 has a higher heater resistance value to correct the normal temperature distribution and has a higher heating value (provided with an aperture portion in the heater pattern). Reach temperature. Since the heater has a positive resistance-temperature characteristic, when the temperature rises, the resistance value further rises, and the heat generation ratio of the end throttle portion further increases with respect to the central portion. Therefore, the temperature of the heater end tends to rise even faster than the temperature rise of the heater in the temperature protection element at the center of the heater.

  At this time, a temperature protection element typified by a thermo switch or the like works to cut off the power supply to the heater 2.

  However, when a temperature protection element such as a thermo SW is activated, the heater end throttle is at a higher temperature than the vicinity of the temperature protection element. If the resistance value of the heater is lowered to achieve a high-throughput fixing device that requires more power, the temperature difference between the temperature protection element vicinity and the end will further increase, and the temperature at the time of abnormality will be increased. The difference becomes large, and the possibility of causing the warpage of the heater and the deformation of the holder due to the thermal stress increases.

  That is, by reducing the temperature difference between the heater end portion and the temperature protection element portion at the time of abnormality, it is possible to supply more power to the heater, and a high-throughput fixing device can be realized.

The operation according to the first embodiment will be described with reference to FIGS. Since power is continuously supplied to the heater, the portion of the heater holder 4 that is in contact with the heater 104 is softened. In FIG. 7, point a is the temperature in this state. FIGS. 5A and 6A show the positional relationship between the heater and the heater holder at the temperature of point a. The heater is not touching the heater holder except for the heater seat surface. In FIG. 5, 1 is a heater substrate, 2 is a resistance heating element layer , 3 is a heat insulating layer or space layer, 4 is a heater holder, and 5 is a heat conductive member.

Since the heater 104 is pressurized by a not-shown pressure roller, the heater 104 is buried in the heater holder 4 when the heater seating surface of the heater holder 4 is softened. When the heater end portion is buried to the good heat conduction member 5 of the heater holder 4, to take away the heat from the heater 104 good heat conductive member 5 and the heater holder 4, the temperature rise of the heater 104 becomes gentle.

  The temperature in this state is point b in FIG. FIGS. 5B and 6B show the positional relationship between the heater 2 and the heater holder 4 at the temperature of point b. It is in the state which touched the good heat conductive member 5 provided in the heater edge part heater holder 4. FIG.

  Further, it has been confirmed that the temperature rise in the portion without the good heat conducting member 5 is faster than the conventional example.

  The reason for this can be explained as follows.

  Since the temperature rise at the end of the heater is moderated by the good heat conducting member (= the resistance rises gently), the increase in the overall resistance of the heater is moderate as compared with the case where there is no good heat conducting member. As a result, the amount of power input to the entire heater is larger than in the past. At the same time, the temperature distribution in the longitudinal direction, that is, the temperature distribution at the heater end and the center (near the temperature protection element) is also reduced, so that the temperature at the center (near the temperature protection element) rises quickly. The protection element operates faster.

  FIG. 8 shows a diagram representing the configuration of this embodiment as an elevational view. Each of points A, A ′, B, C, and D in FIG. 5 corresponds to points A, A ′, B, C, and D in FIG. 8. FIG. 9 shows a block diagram of an electric circuit. In FIG. 9, 900 is a commercial AC power supply, 901 is a triac for supplying power to the heater, 902 is a main body control device including a CPU, 903 is a triac drive circuit, 904 is a line filter, 905 is a relay, and 906 is a DC power supply voltage. It is a line that supplies the same 24V voltage as the motor of the apparatus main body and the power source of the high-voltage power source. 910 is a fixing device, 911 is a heater, 912 is a thermistor, 913 is a temperature protection element, and a temperature fuse or a thermo switch is used.

  In this way, when an abnormality occurs, the temperature protection element provided in the heater unit operates and has a safe configuration in which energization to the heater is stopped.

  As described above, it is possible to apply larger electric power to the heater by reducing the temperature difference between the heater end portion and the temperature protection element portion at the time of abnormality. Accordingly, a high-throughput fixing device can be realized, and a more secure fixing device can be realized.

(Example 2)
The operation according to the second embodiment will be described with reference to FIGS.

In FIG. 10, 1 is a heater substrate, 2 is a resistance heating element layer , 3 is a space layer or a heat insulating layer, and 4 is a heater holder.

  In Example 1, the good heat conductive member was present in a portion where the space layer or the heat insulating layer 3 was small. In the present embodiment, the material of the heater holder 4 is raised instead of the good heat conducting member and is integrally formed.

Since power is continuously supplied to the heater 104 at the time of abnormality, the portion of the heater holder 4 that is in contact with the heater 104 is softened. In FIG. 12, point a is the temperature in this state. Further, FIGS. 10A and 11A show the positional relationship in the sectional view of the heater 2 and the heater holder 4 at the temperature of point a. The heater 104 is not in contact with the heater holder 4 except in contact with the heater seat surface. Since the heater 2 is pressed in such a manner that the fixing sleeve is sandwiched between the pressure rollers, the heater 2 is buried in the heater holder 4. When the heater 2 is buried up to the seat surface portion of the heater holder 4, the heat absorption surface at the end of the heater comes into contact with the heater holder 4, so that the heater holder 4 takes away the heat of the heater 104 . At the same time, at the softening point (glass transition point) of the heater holder resin, it is difficult to increase the temperature even when heated, as with the melting point. Therefore, the temperature rise of the heater becomes moderate near the softening point as point b. Furthermore, as the heater 104 is buried, the heater 104 comes into close contact with the heater holder 4, and the temperature rise of the heater 104 becomes more gradual.

  As a result, it is possible to reduce the temperature difference between the heater temperature of the temperature protection element portion and the heater end portion without attaching a special member. As a result, it is possible to input a larger amount of power to the heater, and it is possible to realize a high-throughput fixing device and to have an advantage that accuracy is easily obtained because of the integral molding. In this embodiment, the distance from the heater surface to the end heat absorption surface is about 100 μm. Moreover, since it is an integral molding, the shape is stable, and variation can be suppressed.

( Reference example )
FIG. 13 shows a diagram that best represents a reference example . A duplicate description of the first and second embodiments will be omitted. The configuration of the fixing device is the same as in FIG.

  FIG. 14 shows a comparison of the heater seating surface portion of the heater holder that holds the heater in direct contact with the heater in FIG.

  As shown in FIG. 13, the contact surface (seat surface) between the heater and the heater holder corresponding to the heater end portion is widened so that the heater seat surface area in the vicinity of the temperature protection element is minimized.

  Further, as shown in FIG. 14, the heater seat surface from the paper center position of the heater holder is also symmetrical with respect to the paper center so that the normal heater temperature is symmetric with respect to the paper position. It is trying to become. FIG. 14 shows a temperature distribution in the longitudinal direction of the fixing device corresponding to the time point d in FIG.

  The operation in such a configuration will be described.

  An example of the temperature distribution at the time of abnormality is shown in FIG. The temperature distribution at the time of abnormality is that the heater seat surface that is in direct contact with the heater is narrower at the center, so the temperature at the center of the heater (near the temperature protection element of the heater) is higher than that at the heater end. Is getting bigger. Also, because of the temperature dependence (TCR) of the resistance, the resistance value rises when the temperature starts to rise, so although the power supply power decreases, the portion where the resistance value rises compared to the surrounding area further increases the temperature. The temperature of the heater around the protection element further rises, and the temperature protection element operates quickly. FIG. 15 shows a comparison of the temperature rise process between the center and the end.

  As described above, since the temperature protection element of the fixing device can be operated quickly, even if the heater temperature is likely to rise due to the increase in fixing power and the configuration in the fixing nip, safety is sufficiently satisfied. It is possible to construct a fixing device with high image quality and high throughput.

(A) is a diagram showing the first embodiment, (b) is a lateral view of the fixing device in a pressurized state. Longitudinal cross section of heater and heater holder Cross section of the heater and heater holder in the short direction Diagram showing temperature rise Longitudinal transverse cross-sectional view of the heater and heater holder of Example 1 Cross-sectional view in the short-side direction of the heater and heater holder of Example 1 The figure showing the temperature rise of Example 1 Elevation of Example 1 Connection diagram of heater drive circuit and safety element Longitudinal transverse cross-sectional view of the heater and heater holder of Example 2 Example 2 Transverse cross-sectional view of heater and heater holder Example 2 Diagram showing temperature rise Elevation of Example 2 Diagram showing the temperature distribution in the cross-sectional direction of the fixing unit of the reference example Diagram showing temperature rise in reference example A figure showing a conventional example A figure showing a conventional example

DESCRIPTION OF SYMBOLS 101 Fixing belt 102 Pressure roller 103 Fixing belt 104 Fixing heater 105 Fixing device frame

Claims (1)

An elongated plate-like heater that generates heat when supplied with electric power from a commercial power source and has a larger calorific value at the end than at the center in the direction perpendicular to the recording material conveyance direction;
A fixing film that is heated by rotating while sliding the inner surface of the heater;
A pressure roller that presses against the heater through the fixing film to form a fixing nip portion;
A heater holder having a heater seat surface that contacts the heater and supports the heater; and a recess recessed from the heater seat surface in a direction perpendicular to the recording material conveyance direction in the center of the recording material conveyance direction;
A protection element that is provided at a central portion in a direction orthogonal to the recording material conveyance direction of the heater, and that operates by an abnormal temperature rise of the heater to cut off power supply to the heater;
In the fixing device for fixing the toner image on the recording material to the recording material at the fixing nip portion,
The concave portion of the heater holder is orthogonal to the first bottom surface of the heater facing the central portion in the direction orthogonal to the recording material conveyance direction with a small amount of heat generation, and orthogonal to the recording material conveyance direction with a large amount of heat generation in the heater. A second bottom surface facing the end in the direction and having a distance from the heater shorter than the bottom surface of the first, when the heater is heated abnormally and the heater seat surface is softened The fixing device is characterized in that the second bottom surface of the heater holder contacts the heater before the first bottom surface.

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