JP2008139665A - Roller for heating, and heat fixing device with the roller for heating - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a heat fixing device where a fixing speed or the like achieved by a heat roller type heat fixing device and on-demand properties and electric power saving properties upon waiting achieved by a film heating type heat fixing device are combined, also, an image including a half-tone image can be heated and fixed in a high quality state, and consistently stable paper conveyability can be achieved without depending on paper kinds and paper passing modes. <P>SOLUTION: In the heat fixing device having a heating means for heating a roller for heating from the outside, and wherein a recording material with an unfixed toner image formed is passed through a nip part formed by the press-contact of the roller for heating and a pressurizing member, thus the unfixed toner image is heated and fixed to the surface of the recording material, the base substance of the roller for heating is made of a ceramics porous body, and an elastic layer is formed on the base substance in such a manner that both the edges are made thicker than the central part to the longitudinal direction, so as to be an inverse crown shape, and the amount of the inverse crown is 30 to 240 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a heating roller heated by an external heating means and an image forming apparatus adopting an image forming process such as an electrophotographic method or an electrostatic recording method, in a recording material (transfer material, transfer material, Related to a heating and fixing apparatus including the heating roller for heat-fixing a non-fixed toner image of image information formed and supported on a printing sheet, photosensitive sheet, electrostatic recording sheet or the like by a transfer method or a direct method as a fixed image It is.

  Conventionally, as a fixing device provided in an image forming apparatus adopting an electrophotographic method, an electrostatic recording method, etc., a heating roller and a pressure roller that rotate by pressing a recording material carrying an unfixed toner image against each other are provided. A so-called heat roller type heat fixing device that fixes an unfixed toner image on the recording material P as a permanently fixed image by passing through the nip portion N formed by the above is widely used.

  FIG. 4 shows a schematic configuration of the heat roller type heat fixing device. The heating roller 10 is provided with a heating body 16 such as a halogen lamp inside a hollow core 15 made of aluminum or stainless steel, and a release layer 11 such as a fluorine resin for preventing toner offset on the outer surface. It is a thing. The temperature of the surface of the heating roller is detected using the temperature detection means 17 such as a thermistor, and the heating body 16 is energized so that the surface temperature of the heating roller detected by the temperature detection means 17 by a current control circuit (not shown) is constant. Is controlling.

  Further, the pressure roller 20 is formed with an elastic layer formed of silicone rubber or the like on the outside of the core metal 23 or a sponge elastic layer 22 formed by foaming silicone rubber, and the outer layer is similar to the heating roller 10. A releasable layer 21 such as a fluororesin is formed.

  The heating roller 10 and the pressure roller 20 are pressed against each other with a predetermined pressure to form a fixing nip portion N, and are driven to rotate in the direction of the arrow. Then, the recording material P on which an unfixed toner image is formed and supported is introduced into the fixing nip portion N, is nipped and conveyed, and is passed therethrough, whereby the unfixed toner image is fixed on the recording material P as a permanently fixed image by heat and pressure. Is.

  However, if the above-mentioned pressurizing force is applied too much, the metal core bar bends, and in the longitudinal direction of the fixing nip portion N, the nip width is wider at the end than at the center, and the pressurizing force is also increased. Because it occurs, attention is necessary.

  The external shape of the heating roller 10 and the pressure roller 20 is formed by a die having a thin reverse crown shape at the center in the longitudinal direction and a thick reverse crown shape at both ends. In the nip portion N, both end portions having a peripheral speed faster than the central portion sandwich and convey the recording material P while pulling the recording material P toward both ends, thereby enabling paper conveyance without causing a phenomenon such as paper wrinkling.

  Further, in the case of an image forming apparatus using a high speed machine or color toner, in order to sufficiently satisfy the toner fixing property and prevent uneven fixing, the hollow core metal 15 of the heating roller 10 and the release layer 11 Some of them have an elastic layer with a thickness of about 2 mm between them, such as silicone rubber. By encapsulating the toner on the recording material with the soft heating roller surface, the efficiency of heat transmission to the recording material and toner is improved. Yes.

  However, while reduction of power consumption is strongly desired as one of the environmental problems in recent years, image output with high image quality and high speed is desired from market needs. Therefore, in order to meet such demands for reduction in power consumption and high speed and high image quality, a heat fixing apparatus using various methods has been newly proposed.

  Among them, a method of suppressing power consumption as much as possible without supplying power to the heat fixing device particularly during standby, specifically, on a recording material through a thin film with a small heat capacity between the heater unit and the pressure roller. An example of a heat fixing method using a film heating method for fixing a toner image is disclosed in JP-A-63-313182, JP-A-2-157878, JP-A-4-44075, JP-A-4-204980, and the like. Proposed. FIG. 5 shows a schematic configuration of an example of the film heating method. That is, in FIG. 5, reference numeral 40 denotes a film assembly, and a heater 42 in which an energized heating resistance layer is formed on a ceramic plate such as alumina or aluminum nitride is fixed to a stay holder 44 formed of a heat resistant resin. A heat-resistant thin film 41 (hereinafter, referred to as a fixing film) such as polyimide that is loosely fitted on the stay holder 44 is provided. A fixing nip portion N is formed by pressing the heater 42 and the pressure roller 20 of the film assembly 40 with the fixing film 41 interposed therebetween.

  The fixing film 41 is conveyed and moved in the direction of the arrow while closely contacting and sliding on the heater 42 in the fixing nip portion N by the rotational driving force of the pressure roller 20 in the direction of the arrow. The temperature of the heater 42 is detected by a temperature detection means 43 such as a thermistor disposed on the back surface of the heater, and fed back to an energization control unit (not shown) so that the heater 42 becomes a predetermined constant temperature (fixing temperature). Heated and temperature controlled.

Various image forming devices such as printers and copiers that use such a film heating type heat fixing device eliminate the need for preheating during standby and shorten the wait time due to the high heating efficiency and the rising speed. There are many advantages over conventional heat roller type heat fixing devices, such as a heat transfer device.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980

  However, the above-mentioned various conventional heat fixing devices have advantages and disadvantages, and the heat roller heat fixing device and the film heat heat fixing device have high speed and durability. Then, a heat roller type heat fixing device is excellent.

  A heat roller type heat fixing device requires a heat roller 10 having an elastic layer 12 in order to support a high-speed image forming apparatus. However, the conventional heat roller 10 has a large heat capacity and is capable of conducting heat. The time required to raise the temperature of the heating roller 10 to a predetermined temperature by heat transfer from the inner surface through the bad elastic layer 12 is long, and the temperature control reaction of the heating roller 10 surface temperature by energization control is slow.

  The heating roller 10 undergoes thermal expansion due to internal heating, and the external shape varies greatly depending on the heating state. The paper transportability is greatly affected by the shape of the heating roller 10, particularly the reverse crown amount, but it depends on the heating condition of the heating roller in the paper passing mode and the paper passing mode due to the slow surface temperature rise due to the internal heating. The external shape will change. For example, in intermittent printing in which several prints are repeated every few seconds, the heating roller is heated suddenly between prints, and the temperature of the heating roller rises and the reverse crown amount increases for each print, so paper transportability is also high. It will change a lot. In addition, it is very strict to mold the heating roller 10 with a certain range of tolerance into an effective inverse crown amount in a narrow range while considering thermal expansion, and the thermal expansion amount varies depending on the heating roller 10, so the external shape It is very difficult to obtain a consistent and stable paper transportability with precise control.

  Since the elastic layer of the heating roller 10 has an inverted crown shape, the heat conduction is also uneven due to the uneven thickness. For this reason, the speed of surface heating by internal heating is fast at the center portion and slow at both ends with respect to the longitudinal direction, so that there is a difference in fixability. Therefore, in order to accelerate the temperature rise at both ends to the same extent as the central portion, the heating body 16 in the hollow metal core is devised so that both end portions generate heat more strongly than the central portion.

  By the way, when continuously printing small-size paper, both ends of the heating roller through which the small-size paper does not pass tend to be excessively heated because heat is not taken away by the paper. However, by adopting the above-described contrivance for strongly heating the both end portions, in the case of continuously printing small-size paper, the both end portions of the heating roller 10 are further heated and melted. In order to prevent this abnormal temperature rise at both ends, when printing small-size paper, a countermeasure is taken by using a control that greatly reduces the number of printed sheets per minute. For example, in an image forming apparatus capable of printing 40 sheets of plain paper per minute, when printing on small-size paper, it is reduced to 20 sheets per minute (a 50% reduction).

  In terms of power consumption, the power consumption is high due to the length of the wait time from when the image forming apparatus is turned on until printing can be started, and the need to heat the heating roller 10 to some extent during standby, Further, due to the large heat capacity of the heating roller 10, there is a problem that the electric power required to raise the temperature of the heating roller 10 to a predetermined temperature is large.

  A film-type heat fixing device solves these problems. However, as a further improvement, due to the decrease in adhesion to the toner image due to the high rigidity of the fixing film 41, even the slight protrusions generated on the heater 42 and the fixing film 41 have a dot-like matte state. In the case where a plurality of types of toners are superimposed and fixed as in a color image, color misregistration occurs or color mixture is insufficient due to insufficient melting. On the other hand, it is desired that only the toner in the upper layer is not melted and offset.

  In addition, in the film heating method, it is difficult to apply a strong pressure to prevent deterioration of durability, and in order to further increase the fixing speed, more heat energy is used for fixing and this heat energy is efficiently used for fixing. Therefore, it is necessary to increase the nip width N, which leads to an increase in power consumption during printing and an increase in the pressure roller diameter.

  In addition, since the pressing force is relatively weak for the above-described reason, the frictional force between the film and the pressure roller is weak. The film surface is a release layer so that it is slippery with the pressure roller, and the film inner surface is slid with the heater. Because the smoothness deteriorates due to rubbing, the torque of the inner surface of the film and the heater increases, and as the durability progresses, the rotation of the film tends to be delayed with respect to the rotation of the heating roller. The image quality may be deteriorated by slightly rubbing the image.

  Therefore, the present invention has the advantages of both the heat roller type heat fixing device and the film heat type heat fixing device, that is, the fixing speed realized by the heat roller type heat fixing device, and the film heating method. It enables both on-demand performance and power saving during standby to be realized with this heat fixing device, and can heat and fix images including halftone images in a high-quality state, providing consistent and stable paper transport. It is an object of the present invention to provide a heating roller capable of realizing the heat resistance and a heat fixing device including the heating roller.

  The present invention is a heat fixing apparatus characterized by the following constitution.

  (1) A heating roller, wherein the roller base is a ceramic porous body, and an elastic layer having a non-uniform thickness is formed on the base.

  (2) The elastic layer is formed so that both end portions are thicker than the center portion with respect to the longitudinal direction of the pressure roller, and an inverted crown shape is imparted (1). The heating roller as described in).

  (3) The heating roller according to (2), wherein the amount of reverse crown provided by the elastic layer formed on the heating roller base is 30 μm to 240 μm.

  (4) The heating roller according to any one of (1) to (3), wherein a release layer is formed on the elastic layer of the heating roller.

(5) A heating means for heating the heating rotator from the outside is provided, and the recording material on which the unfixed toner image is formed is passed through a nip portion formed by pressure contact between the heating rotator and the pressure member. In the heat fixing apparatus for heat fixing the unfixed toner image on the recording material,
The heating fixing device is characterized in that the rotating body for heating is a heating roller having a base made of a ceramic porous body, and an elastic layer having a non-uniform thickness is formed on the base.

  (6) The elastic layer is formed so that both end portions are thicker than the center portion with respect to the longitudinal direction of the pressure roller, and an inverted crown shape is given (5). The heat fixing device described in the above.

  (7) The heat fixing apparatus according to (6), wherein an amount of reverse crown provided by the elastic layer formed on the heating roller base is 30 μm to 240 μm.

  (8) The heat fixing device according to any one of (5) to (7), wherein a release layer is formed on the elastic layer of the heating roller.

  (9) The heat fixing apparatus according to any one of (5) to (8), wherein the pressing member is an elastic roller formed of an elastic layer and a release layer.

  (10) The heat fixing apparatus according to any one of (5) to (9), wherein the external heating means is a radiation heating means or a direct heating means by contact.

  The ceramic porous body is remarkably excellent in heat insulation. By using this ceramic porous body as a roller base, providing at least an elastic layer on the outer peripheral surface of the roller base to form a heating roller, and combining the heating roller with an external heating means for heating from the outside of the roller, the surface layer portion of the roller It is possible to store the amount of heat necessary for the elastic layer and quickly heat up the surface of the heating roller to the required temperature, and to make the heating device on-demand and low power. .

  In addition, the combination of a heating roller based on a ceramic porous substrate with rigidity and heat insulation and a very small thermal expansion coefficient and external heating means has little thermal expansion due to the temperature rise of the heating roller, and external heating during paper feeding Thus, the heating roller can be quickly replenished with heat energy, so that the surface temperature and the external shape of the heating roller are stabilized, and consistent and stable paper transportability independent of the paper type and the paper passing mode is enabled.

  Also, by using a ceramic porous body with rigidity for the base of the heating roller, the pressure on the nip part with the rotating body for pressurization can be increased sufficiently and substantially without bending the heating roller. The heating (fixing) speed of the material to be heated can be provided, and it is possible to perform a uniform heat treatment of the material to be heated, and fixing by applying sufficient pressure to the nip. The heat energy required for printing can be reduced, so that power consumption during printing can be reduced.

  Further, since the heating roller base is a ceramic porous body, the roller base itself cannot be formed into an inverted crown shape essential for stable paper transportability, but the elastic layer on the roller base is not formed. In addition to realizing stable paper transportability that does not generate paper wrinkles by forming a thick reverse crown shape toward the center with the thickness increasing at both ends, the porous substrate surface is smoothly molded with the elastic layer Thus, high-quality heat fixing of an image including a halftone is also possible.

  In the heating roller of the present invention, the thickness of the elastic layer is not uniform as in the heating roller system, but the surface temperature of the heating roller becomes uniform in the longitudinal direction by uniform heating by external heating. Therefore, there is no problem in fixing in the longitudinal direction, which has been a problem with the heat roller method, and both ends of the heat roller are not heated as much as the heat roller method when small size paper is used for continuous printing. Even if the number of prints per minute is controlled, it is possible to cope with the case where the number of prints is not reduced as much as the heat roller method (for example, by 20% reduction when printing on plain paper).

<Example 1>
(1) Heat Fixing Device Example FIG. 1 is a schematic configuration diagram of an example of a heat fixing device. 10 is a heating roller, 20 is a pressure roller that forms a nip N with the heating roller 10, and 30 is an external heating means for heating the heating roller 10 from the outside of the roller.

  FIG. 2 is a cross-sectional view of the heating roller 10. In this heating roller 10, the roller base (base material) 14 is a ceramic porous body, and a silicone rubber layer 12 is formed as an elastic layer on the outer peripheral surface of the roller base 14, and a release layer is further provided on the outer peripheral surface. In this structure, the fluororubber layer 11 is formed as (surface layer).

  More specifically, the roller base 14 is a ceramic porous body (made by NICHIAS Corporation) having an outer diameter of about 18 mm, an inner diameter of about 8 mm, a bulk density of 0.55 g / cm 3, and a porosity of 79%, which is made of glass. Name Sereral (registered trademark) A), and the outer peripheral surface of the roller base 14 is subjected to primer treatment, and liquid silicone rubber (DY35-561A / B: manufactured by Toray Dow Corning Silicone) is coated by a blade coating method. And then cured by heating at 130 ° C. for 30 minutes, followed by secondary vulcanization for 4 hours in an oven set at 200 ° C.

  In order to improve paper transportability, the elastic layer 12 has a thickness of 1.0 mm at both ends and becomes narrower toward the center, and a thickness at the center of 0.95 mm. The elastic layer 12 has a reverse crown on the roller base. A silicone rubber layer 12 having a shape was formed.

  Although a method of forming an inverted crown shape with a ceramic porous body and forming an elastic layer with a uniform thickness on the ceramic is also conceivable, the ceramic porous body is formed by an extrusion molding method, a press molding method, or the like in the molding process. Since it is molded, its shape is easy to mold into a columnar or cylindrical shape, and it is difficult to mold into an inverted crown shape or the like. In addition, it is possible to make a reverse crown shape by cutting the central part of the columnar or cylindrical ceramic porous body, but because of the rigidity of the ceramic porous body, it takes time and labor to cut, and the cost is also expensive. End up. Therefore, the method of giving the reverse crown shape by the thickness of the elastic layer as in the present invention is most preferable.

  The surface of the silicone rubber layer 12 is subjected to a predetermined primer treatment (GLP103SR: Daikin Industries, Ltd.) and then sprayed with a fluoro rubber latex (GLS213: Daikin Industries, Ltd.) to a thickness of about 30 μm. After drying at 70 ° C., it was baked in an oven at a set temperature of 310 ° C. for 30 minutes to form a surface layer. As a result, the fluororesin in the fluororubber latex formed a surface layer having a thickness of about 1 to 3 μm, and a good release layer 11 could be formed.

  Next, an aluminum core bar 13 having a diameter of 8 mm is fixed to the inner diameter portion of the roller base 14 with an epoxy resin adhesive, and a silicone rubber having a rubber length of 240 mm, a central outer diameter of 19.9 mm, and both outer diameters of 20 mm is used as the heating roller 10. An insulating roller was prepared. Here, the reverse crown amount of the heating roller 10 is (outer diameter at both ends) − (outer diameter at the center) = 0.1 mm = 100 μm.

  By adopting such a configuration, it is possible to obtain a roll having a high heat insulating property with a heat conductivity of 0.05 to 0.1 W / m · K as the heating roller 10.

  This is markedly improved in heat insulation even when compared with 0.3 W / m · K in the case of a normal silicone rubber solid. Moreover, in the thermal conductivity with the conventional sponge, in order to prevent a permanent distortion, there exists a limit in a minimum and 0.1-0.2 W / m * K was a limit. In the case of sponge, in order to increase the heat insulation, if the foaming rate is further increased, the hardness will decrease and it may become difficult to apply pressure or permanent distortion may occur, and if excessive pressure is applied, heating will occur. Although there is a disadvantage that the roller 10 itself bends, in this embodiment, a ceramic porous body having rigidity is used as the base 14 of the heating roller 10 instead of the sponge. Applying pressure can be applied, and almost no permanent distortion or bending occurs in the heated 10 roller. Further, since the surface layer portion has the rubber layer 12 having the minimum heat capacity necessary for storing heat, the structure is more suitable for transferring the externally heated heat to the object to be heated.

  The heating roller 10 is disposed by rotatably supporting both ends of the core metal 13 between the apparatus side plates via bearings, and a predetermined peripheral speed in the clockwise direction of an arrow by a drive system (not shown). Is rotated.

  The ceramic porous body 14 that can be used in the present invention makes use of the elasticity of a thin rubber elastic layer among ceramic materials that are excellent in thermal deterioration and change with time, and that apply high pressure to a heated material (recording material P). It is porous. Under the above conditions, this is a material that obtains uniform pressure / fixability regardless of the unevenness of the heated material (recording material P).

The practical ranges of the physical properties of the ceramic porous body 14 that can be used in the present invention are bulk density: 0.35 to 1.80 g / cm ² , porosity: 30-90%, thermal conductivity: 0.1 W / m · K or less. .

  The pressure roller 20 is a heat-resistant / elastic roller comprising a metal core 23 and a solid silicone rubber layer 22 formed concentrically and integrally around the metal core.

  The pressure roller 20 is arranged in parallel to the lower side of the heating roller 10 and rotatably supports both ends of the core metal 23 and resists the elasticity of the silicone rubber layer 22 by a biasing means (not shown). Thus, the nip portion N having a predetermined width is formed by being pressed against the lower surface of the heating roller 10 with a predetermined pressure.

  The pressure roller 20 rotates in the forward direction in the rotation direction of the heating roller 10 in conjunction with the rotation of the heating roller 10, and cooperates with the heating roller 10 when the recording material P is introduced into the nip portion N. The recording material P is nipped and conveyed.

  In the first embodiment, the external heating means 30 for heating the heating roller 10 from the outside of the roller is a film heating type heater unit (heat supply unit).

  31 is an endless (cylindrical) heat-resistant film having an outer diameter of 20 mm and a thickness of 60 μm, 32 is a ceramic heater as a heating element, and 33 is a film guide member having a substantially semicircular arc shape in cross section. The heater 32 is fitted and fixedly supported in a fitting groove formed in the longitudinal direction of the film guide member at a substantially central portion on the outer surface side of the film guide member 33. The endless film 31 is loosely fitted on the film guide member 33 including the heater 32.

  In order to reduce the heat capacity and improve the quick start property, the film 31 has a film thickness of 100 μm or less, preferably 50 μm or less and 20 μm or more of heat-resistant PTFE, PFA, FEP monolayer, polyimide, polyamideimide, A composite layer film in which PTFE, PFA, FEP or the like is coated on the outer peripheral surface of PEEK, PES, PPS or the like can be used.

  The film guide member 33 is a heat-resistant and rigid member. For example, the film guide member 33 is obtained by adding glass to a heat-resistant resin such as PPS, liquid crystal polymer, or phenol resin to increase the strength. These resins are used by being injected into a mold for molding.

  The heater 32 is a heater 32 (formation heating resistor 32 having a low heat capacity formed by applying a paste such as silver / palladium alloy powder in a linear or strip shape along the length of the surface of an insulating substrate such as an elongated ceramic. Ceramic heater), which is excellent in thermal conductivity and thermal responsiveness, and can rapidly heat the surface of the heating roller 10. The surface of the heater 32 is coated with a member having good heat resistance and releasability, such as PI, so that it can withstand sliding with the heating roller 10. This heater surface side is exposed to the outside, and is fixedly supported on the film guide member 33.

  The film unit 31, the heater 32, the film guide member 33 and the like constitute a heater unit 30 as an external heating means. The heater unit 30 is opposed to the heating roller 10 with the heater 32 side facing the heating roller 10. The film guide members 33 are arranged in parallel and pressed with a predetermined pressing force against the elasticity of the elastic body layer 12 of the heating roller 10 in the axial direction of the heating roller 10 by an urging means (not shown). The heater 32 is in pressure contact with the outer surface of the heating roller 10.

  As the heating roller 10 rotates, the endless film 31 of the heater unit 30 causes a rotational force to act on the film 31 by the pressure frictional force between the outer surface of the heating roller 10 and the outer surface of the film 31, and the film 31 While rotating in close contact with the surface (outer surface) of the heater 32, the outer periphery of the film guide member 33 is rotated in a counterclockwise direction indicated by an arrow with a peripheral speed substantially corresponding to the rotational peripheral speed of the heating roller 10. By interposing a lubricant such as heat resistant grease between the heater 32 and the inner surface of the film 31, the rotation of the film 31 can be made smoother.

  As the heating roller 10 is driven to rotate, the endless film 31 of the heater unit 30 is rotated, the heater 32 is energized, the heater 32 generates heat, and the temperature is controlled to a predetermined temperature. The outer surface of the rotating heating roller 10 is heated to a predetermined fixing temperature by the heat of the heater 32 through the film 31. Here, the control temperature of the heater 32 may be adjusted by a method of changing according to the number of sheets to be passed or by detecting a temperature by bringing a temperature measuring element such as a thermistor into contact with the heating roller 10 itself.

  Then, the recording material P carrying an unfixed toner image is introduced into the nip portion N between the heating roller 10 and the pressure roller 20, and the nip portion N is nipped and conveyed so that the heating roller 10 records the unfixed toner image. Heat fixing to the material P is performed.

  By adopting such a configuration, the surface of the heating roller 10 follows the unevenness of the toner image on the recording material P, which is the material to be heated, by the elasticity of the elastic body layer 12, so that heat is applied to the uneven recesses. Also, since it can be supplied, a good fixed image without unevenness can be obtained even for a color image or a bond paper having a rough surface.

  As a feature of this configuration, a low heat capacity heating roller 10 whose base is a ceramic porous body 13 and a film heating type heater unit 30 with good heating efficiency are used as external heating means. Therefore, it is possible to quickly warm the surface of the heating roller 10 to a predetermined temperature at the time of warm-up and paper passing, and it is possible to shorten the warm-up time and reduce power consumption. In addition, compared to the film heating method, it is possible to apply a strong pressure due to the rigidity of the ceramic porous body 13, so that the heat energy required for fixing can be reduced accordingly, thereby further reducing power consumption. This makes it possible to achieve a fixing speed equivalent to that of the heat roller method.

  In addition, the combination of a heating roller based on a ceramic porous body with excellent rigidity and heat insulation and a low coefficient of thermal expansion, and external heating means, there is almost no thermal expansion due to the temperature rise of the heating roller, and from the external heating means when passing paper Since the heat energy can be quickly replenished to the heating roller, the surface temperature and the external shape of the heating roller are stabilized, and consistent and stable paper transportability independent of the paper type and the paper passing mode is enabled.

  In order to confirm the above, in the heat fixing device of Example 1 and the conventional heat roller type heat fixing device, the paper conveyance performance at the reverse crown amount of each heat roller was evaluated.

  In the heat fixing device of Example 1, the heating roller 10 has an aluminum core 13 outer diameter of 8 mm, a ceramic porous roller base 14 has an outer diameter of 18 mm, and the thickness of the silicone rubber elastic layer 12 is at both ends. Is 1.0 mm and the center is 1.0 mm to 0.87 mm, so that the amount of reverse crown due to the thickness of the elastic layer is 0 to 260 μm, and the fluororesin release layer 11 of 3 μm is formed on the outer periphery thereof.

  In the pressure roller 20, an elastic layer 22 similar to the heating roller is formed on the outer periphery of an aluminum core 23 having an outer diameter of 11 mm with a thickness of 7 mm. Further, a 30 μm PFA tube is covered as a release layer 21 on the outer periphery. The pressure roller surface hardness was 60 ° (ASKER-C, with 500 g load).

  As the heater unit 30 which is an external heating means, the film 31 is a PFA film with a film thickness of 60 μm, and the heater 32 is a ceramic heater covered with a 7 μm PI coat.

  In the heat roller type heat fixing device, the heating roller 10 has an iron core bar 13 with an outer diameter of 15 mm, a core bar 13 with a thickness of 2 mm, a silicone rubber elastic layer 12 with a thickness of 5 mm, and further on the outer periphery. The mold layer 11 is covered with a 30 μm PFA tube. The reverse crown amount of the heating roller 10 is 0 to 260 μm.

  Since the pressure roller 20 is the same roller as the pressure roller 20 of the first embodiment, description thereof is omitted.

  The heating means 16 is a halogen lamp built in the hollow core 15 of the heating roller 10.

  With the above-described configuration, when using the heat roller type heat fixing device of Example 1 and comparing the amount of paper conveyance when the reverse crown amount of the heating roller 10 is 0 to 260 μm, the comparative evaluation is performed for each number of sheets. To do.

  The evaluation results are shown in Table 1. In the table, ◯ indicates a problem-free level, Δ indicates an allowable limit level, and X indicates inferiority. Here, poor paper transportability means that paper wrinkles occur.

表1の結果より、紙搬送性が許容限界レベル以上である逆クラウン量は、熱ローラ方式では90μmから150μmであるのに対して、実施例1では30μmから240μmと広い範囲で紙搬送性が安定している。また、実施例１では通紙枚数と紙搬送性は関連性がほとんど無く一貫しているのに対して、熱ローラ方式では、通紙枚数が変わると紙搬送性も変化するといった結果が得られた。

From the results in Table 1, the amount of reverse crown whose paper transportability is above the allowable limit level is 90 μm to 150 μm in the heat roller method, whereas in Example 1, the paper transportability is in a wide range from 30 μm to 240 μm. stable. Further, in the first embodiment, the number of sheets to be passed and the paper transportability are almost unrelated and consistent, but in the heat roller method, the result is that the paper transportability changes as the number of passed sheets changes. It was.

  In the heat roller system, the heating roller 10 having a large heat capacity is slowly heated by the internal heating 16, and the external shape changes due to thermal expansion. As the heating proceeds, the amount of reverse crown increases due to thermal expansion, so that the temperature rise of the heating roller 10 due to the increase in the number of sheets passing through the paper affects the paper transportability. If the reverse crown amount is small, there is not much difference in the peripheral speed between the both ends and the center of the heating roller 10, and the paper pulling property is weak by both ends, so the paper transportability is poor, but if the reverse crown amount is excessively increased The increase in the outer diameter difference between the two ends and the central portion causes the pressurization state at the nip N extending over the recording material P to be too different between the two ends and the central portion, and the recording material end is excessively pressurized. Therefore, it was confirmed that the fibers were stretched, and the recording material P was wavy and the paper transportability was deteriorated.

  On the other hand, in the first embodiment, the external heating means 10 quickly raises the temperature of the low-heat capacity heating roller 10 having a small coefficient of thermal expansion, so that the external shape can be stabilized quickly, and consistently stable paper conveyance Can get sex. Even if the reverse crown is too small or too large, the paper transportability is deteriorated in the same manner as in the heat roller system although there is a difference in the reverse crown amount.

  Further, in the heat roller type heating roller 10, the external shape changes due to the thermal expansion in the longitudinal direction of the cored bar due to heating, so the range of the reverse crown amount that can obtain stable paper transportability is narrow. However, in the heating roller 10 of Example 1, since the ceramic porous body as the substrate hardly undergoes thermal expansion, stable paper transportability can be obtained with a wide range of reverse crown amounts.

  From the above results, it can be seen that in the heat fixing apparatus of the first embodiment, it is possible to obtain consistent and stable paper transportability independent of the number of sheets passing through a wide range of reverse crown amounts (30 μm to 240 μm). Demonstrated. However, in order to obtain good paper transportability, it is preferable that the reverse crown amount be in the range of 60 μm to 210 μm.

  Also, in this experiment, the warm-up time required for the heating roller method, which is internal heating, was 57 seconds, whereas in this example 1, which was external heating, it took only 7 seconds. It was shown that the uptime can be significantly reduced.

  However, although the heater unit is used as the part heating means in the first embodiment, the external heating means is not limited to this.

<Example 2>
(2) Heat Fixing Device Example In the first embodiment, since the pressure roller 20 has a large heat capacity in the core metal 23 and the elastic layer 22, the heat energy is transferred from the heat roller 10 to the pressure roller 20 during warm-up. The outflow occurs, the temperature rise of the heating roller 10 is delayed, and extra power is consumed. Further, since the metal core 23 of the pressure roller 20 is a metal, there is a concern that the metal core 23 may be bent when a stronger pressure is applied.

  These have little influence in the case of a low-speed image forming apparatus, but it is considered that the influence becomes large in the case of a high-speed image forming apparatus. Therefore, in the case of a high-speed image forming apparatus, it is preferable to use the heat fixing apparatus of the second embodiment.

  FIG. 3 is a schematic configuration diagram of a heat fixing apparatus as a second embodiment. In this example, both the heating roller 10 and the pressure roller 20 are configured to use the heating roller 10 based on the ceramic porous body 14 used in Example 1, and the heating roller 10 and The description of the pressure roller 20 is omitted because it is the same as the heating roller 10 of the first embodiment.

  In this embodiment, a halogen heater 34 is used as an external heating means 30 for heating the heating roller 10 from the outside of the roller, and this halogen heater 34 is an entrance of a transfer material at a fixing nip N between the heating roller 10 and the pressure roller 20. In the vicinity, it is arranged to face the heating roller 10, and the surface of the heating roller 10 is heated by the radiant heat of the halogen heater 34.

  Here, in order to efficiently use the radiant heating of the heat roller by the halogen heater 34, a curved reflecting plate 35 having a high reflectivity is disposed on the side opposite to the heating roller 10 with the halogen heater 34 in the middle, Radiant heat from the halogen heater 34 is reflected toward the heating roller 10 without being diffused.

  The heating roller 10 is driven to rotate, and the halogen heater 34 is energized. The heater 34 emits light and is controlled to have a predetermined color temperature, so that the outer surface of the rotating heating roller 10 is fixed by the radiation heat of the halogen heater 34. Heated to temperature. Here, the color temperature control of the halogen heater 34 may be adjusted by a method of changing according to the number of sheets to be passed or by detecting a temperature by bringing a temperature measuring element such as a thermistor into contact with the heating roller 10 itself.

  By adopting such a configuration, it is possible to achieve higher thermal energy efficiency and even higher speed while maintaining the on-demand and power-saving performance of the first embodiment. In other words, the heating roller 10 and the pressure roller 20 are heated quickly, and the amount of heat flowing from the heating roller 10 to the pressure roller 20 can be reduced, greatly reducing unnecessary heat energy not used for fixing. Since it becomes possible to reduce, higher-order low power consumption, on-demand characteristics, and higher speed can be realized.

  In addition, since both the heating roller 10 and the pressure roller 20 have a stable reverse crown shape with almost no external shape change due to thermal expansion at the time of temperature rise, paper transportability can be further stabilized as compared with the first embodiment.

  Also, since the ceramic porous body is the base for both the heating roller 10 and the pressure roller 20, it is possible to apply a very strong pressure, for example 100kgf, with almost no deflection, thus reducing the heat energy required for fixing. Further reduction in power consumption, high fixability, and improvement in color image gloss can be realized.

  The halogen heater used in the second embodiment is an example of external heating means, and the external heating means is not limited to this.

  The dimensions effective for the present invention are not limited to those described in the first and second embodiments.

Schematic side view of the heat fixing apparatus of Example 1 Sectional view of the heating roller in Example 1 Schematic side view of the heat fixing apparatus of Example 2 Schematic side view of a heat roller type heat fixing device as a conventional device Schematic side view of a film heating type heat fixing device as a conventional device

Explanation of symbols

10 Heating roller
11 Release layer
12 Elastic layer
13 Core
14 Ceramic porous body
15 Hollow cored bar
16 Halogen heater
17 Thermistor
20 Pressure roller
21 Release layer
22 Elastic layer
23 Core
24 Ceramic porous body
30 Heater unit
31 films
32 Heater
33 Film guide member
34 Halogen heater
35 reflector
40 film assembly
41 Heater
42 Thermistor
43 Film guide members
N Fixing nip
P Recording material

Claims (10)

  A heating roller, wherein the roller base is a ceramic porous body, and an elastic layer having a non-uniform thickness is formed on the base.   The thickness of the elastic layer is formed so that both ends are thicker than the center with respect to the longitudinal direction of the pressure roller, and an inverted crown shape is given. Roller for heating.   3. The heating roller according to claim 2, wherein the reverse crown amount provided by the elastic layer formed on the heating roller base is 30 μm to 240 μm.   4. The heating roller according to claim 1, wherein a release layer is formed on the elastic layer of the heating roller. A heating means for heating the heating rotator from the outside is provided, and the recording material on which the unfixed toner image is formed is passed through a nip formed by pressure contact between the heating rotator and the pressure member. In a heat-fixing apparatus that heat-fixes an unfixed toner image on a recording material,
The heating fixing device is characterized in that the rotating body for heating is a heating roller having a base made of a ceramic porous body, and an elastic layer having a non-uniform thickness is formed on the base.   The thickness of the elastic layer is formed so that both ends are thicker than the center with respect to the longitudinal direction of the pressure roller, and an inverted crown shape is given. Heat fixing device.   7. The heat fixing apparatus according to claim 6, wherein the reverse crown amount provided by the elastic layer formed on the heating roller base is 30 μm to 240 μm.   8. The heat fixing apparatus according to claim 5, wherein a release layer is formed on the elastic layer of the heating roller.   9. The heat fixing device according to claim 5, wherein the pressing member is an elastic roller formed of an elastic layer and a release layer.   10. The heat fixing device according to claim 5, wherein the external heating unit is a radiation heating unit or a direct heating unit by contact.

Images