JP2011081236A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stable fixing device for obtaining excellent fixing over a long period by stably driving a film, also obtaining excellent color images stabilizing fixing without gloss irregularity, achieving miniaturization of the device, being superior in economical efficiency, and further reducing radiation loss, in the fixing device for arranging a radiation source on the inner side of a heating and fixing member, efficiently heating a fixing member surface, having a small heat capacity, and enabling on-demand. <P>SOLUTION: In the fixing device, concerning contact pressure in a fixing nip, downstream side contact pressure is larger than upstream side contact pressure of a transfer material passage direction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a fixing member used for fixing a toner image in an electrophotographic image forming apparatus, and a fixing device using the fixing member.

  A problem that has recently become more important in electrophotographic image forming apparatuses used in copying machines, printers, fax machines, and the like is to respond to so-called demands for energy saving. Since the conventional toner image fixing device used in the above-mentioned devices is a system in which the toner is melted and fixed to the paper, power is directly consumed as thermal energy. It accounts for a large portion of the power consumption used by the entire body.

  On the other hand, as one direction for reducing the power consumption of the fixing device, on-demand (normally, no current flows through the heater, for example, real-time when the heater is turned on only during image formation) can be achieved. ing. Specifically, by making the fixing member into a thin roller, thin belt or film, the heat capacity is significantly reduced compared to the conventional thick heating roller, and at the same time the start-up of the device is accelerated. Power consumption is reduced. By achieving on-demand, when a print signal is received, printing starts immediately with almost no waiting time, so fixing is possible even during non-printing, as with conventional heating rollers. It is not necessary to keep the member at a high temperature around the printing temperature, and it is sufficient to keep the member at room temperature at most moderately low temperature. The heat dissipation during the heat retention of the fixing device increases in proportion to the temperature difference between the environmental temperature and the set temperature of the fixing member. However, such heat dissipation always consumes electric power even when printing is not performed. Therefore, in a moving situation where printing is repeated intermittently, a very large power saving effect is brought about by making the fixing device on demand.

  However, in the so-called surf method using a film as a fixing member, it is difficult to fix a color toner image in a good state as described below, and a thin layer film is used. In the formation of many color images, there is a problem that it is difficult to obtain uniform fixing properties. In the fixing of the color toner image, when the image is formed on plain paper, the melting state of the toner image changes according to the unevenness of the paper surface, so that the unevenness of the gloss on the surface of the fixed image is generated, When an OHP (overhead projector) film is used as a transfer material, the transparency of the OHP tends to change depending on the unevenness of the toner image, and it is difficult to obtain a high-quality image.

  Therefore, the present inventors have applied for a fixing device in which an elastic layer is provided on the film and heat is transferred by high-speed radiation. According to the invention, the infrared rays generated from the heat source are transmitted or semi-transmitted through the low heat capacity film base layer and the elastic layer, and then generate heat in the absorption layer provided in the vicinity of the film surface. Good thermal responsiveness is obtained without being greatly affected by the thickness, and the fixing property in a color image is improved by sufficient elasticity of the film surface.

JP 2000-221821 A

  However, in the film fixing device using the above radiation, although the on-demand fixing device and good fixability in a color image can be achieved both by reducing the heat capacity by the film and by surface heating by radiant heat transfer, it is thin. Since the film is driven while being pressed against the transfer material, the film is likely to be wrinkled or broken.

  Moreover, in order to absorb the infrared rays generated from the heat source in the vicinity of the film surface, it is necessary to use a resin-made film base material having translucency, and it is not possible to use a metal sleeve or the like having higher mechanical strength. In order to reduce the driving torque, it was impossible to apply a large pressing force. Therefore, the toner on the transfer material cannot be crushed with sufficient pressure, the fixing property on the transfer material is lowered, and it is difficult to obtain uniform gloss without being evenly uniform.

  Accordingly, an object of the present invention is to stably drive a film in a fixing device in which a radiation source is arranged on the inner side of a heat fixing member, the surface of the fixing member can be efficiently heated, and the heat capacity is small and on demand is possible. Another object of the present invention is to provide a stable fixing device that can obtain good fixing properties over a long period of time.

  Another object of the present invention is to provide a fixing device that is excellent in economic efficiency, in which a good color image with stable fixing property without gloss unevenness can be obtained, the device can be miniaturized, and heat dissipation loss is further reduced. is there.

  The above object is achieved by the present invention described below. That is, the first invention in the present application is a heating member that is rotatable at a constant speed with the transfer material, and that has a holding member and a radiation heat source inside, and a pressurizing and driving the heating member from outside. A fixing device that heats and melts a toner image on a transfer material, and the heating member absorbs radiation light emitted from at least the radiation heat source and has a heat generation layer that generates heat or The holding member is pressed against the pressure member via the heating member to form a fixing nip, and the contact pressure in the fixing nip is higher than the upstream contact pressure in the transfer material passing direction. The fixing device is characterized in that the downstream contact pressure is larger.

  By adopting the above configuration, it is possible to reduce the thickness of the heating member, making the fixing device on-demand and quick start easy, and making the pressure (fixing) area easy by keeping the belt shape along the pressure member. The heating member can be reduced in size and heat capacity compared to a conventional roller fixing device. In addition, by setting the second half of the fixing nip to a contact pressure larger than that of the first half, the pressure can be applied when the toner is melted, and the toner can be crushed and fixed more effectively with the same contact pressure. In addition, even when a thin film is used as a heating member, even when the fixing device has a low heat capacity, an appropriate tension can be applied from the downstream side of the film, so that stable film driving can be achieved for a long time without wrinkling or breaking of the film. it can.

  According to a second aspect of the present invention, the heating member includes a base layer that is transmissive to radiation light inside the heat generating layer, and the surface of the surface is obtained by transmitting the radiation light through the film base layer. Because the heat generation layer can be directly heated, there is little deterioration in heating characteristics due to heat conduction when the film thickness is increased, and stable fixing that prevents film wrinkles and creases over time by increasing the film strength. Providing equipment.

  According to a third aspect of the present invention, the heating member includes an elastic layer that is interposed between a base layer and a heat generating layer, and transmits infrared rays from the heat generating element. Radiant light is transmitted through the elastic layer. Therefore, the heating layer near the surface is directly heated, so there is little deterioration of the heating characteristics due to the thickness of the elastic layer in heat conduction, and the heating member flexibly contacts and heats the unevenness of the toner surface on the transfer material In particular, high-quality image output with gloss uniformity in color images and color reproducibility in OHP images has become possible.

  A fourth invention according to the present application is characterized in that the holding member is formed of a thin metal plate having a protrusion with respect to the pressure member direction in the latter half of the contact nip, and an increase in pressure applied downstream of the nip. At low cost and low heat capacity. Therefore, an on-demand fixing device with a fast start-up is realized. Furthermore, since a mechanical strength is improved by providing a protrusion on the thin metal plate, a stable fixing device is provided.

  A fifth invention according to the present application is characterized in that the heating member is formed of a material containing at least a polyimide resin, and the polyimide resin has good flexibility and transmits infrared rays emitted from a radiation light source. Therefore, by directly heating the elastic layer or the release layer existing outside the heating member with radiant light, the thermal resistance in the heating process is further reduced, and high-speed color image formation is possible.

  A sixth invention according to the present application is characterized in that a silicone rubber layer is included as the elastic layer, and the silicone rubber has excellent heat resistance and flexibility, and is high in the infrared rays generated by the radiation light source. It is possible to efficiently heat the release layer that has permeability and exists outside the heating member. Further, even when unevenness on the surface of a toner image in a color image or the like is remarkable, the toner image is uniformly pressed to achieve higher image quality with further fixing properties and gloss uniformity.

  A seventh invention according to the present application is characterized in that carbon black is dispersed in a silicone rubber layer or a release layer made of a fluorine resin as an absorption layer in the heating member. Since both fluororesins have good dispersibility and infrared absorption, it is possible to effectively generate heat from the elastic layer or release layer outside the heating member, and heat is lost during continuous printing. The vicinity of the surface layer of the heating member can be rapidly heated. The release layer on the surface adheres the toner on the transfer material to the heating member, and also prevents electrostatic offset due to the conductivity, so that the image on the transfer material can be fixed without disturbing the image.

  The eighth invention according to the present application is characterized in that the heating member has a release layer made of a fluororesin on the surface layer, and the toner on the transfer material is fixed without being disturbed by an excellent release property.

  According to a ninth aspect of the present application, the holding member includes a sliding portion that slides with respect to the film at the nip forming portion, and a rotating portion that rotates together with the film, and a contact pressure generated at the nip forming portion. The contact pressure at the rotating part is higher than the contact pressure at the sliding part. By providing a sliding part upstream in the paper passing direction in the nip, a large contact nip is achieved even with a small size and low heat capacity. At the same time that the width can be taken, it is possible to locally increase the contact pressure by providing a rotating part downstream in the sheet passing direction in the nip, and to suppress an increase in driving torque when the contact pressure is increased, Realizes good fixability and high gloss.

  According to the present invention, by using a film or belt having a multilayer structure having radiation transmission and radiation absorption as the fixing member, the surface of the fixing member is directly heated despite using the internal radiation source. It became possible to do. As a result, as shown in FIG. 2, the surface heat response can be improved by performing the surface heating with respect to the normal inner surface heating, and the radiation source is arranged on the inner side of the heat fixing member to be stable and stable. It was possible to heat the fixing member surface while reducing loss due to heat dissipation, and to fix a high-speed and high-quality color image with good thermal response in good condition.

  In addition, a convex protrusion or a small diameter roller is provided in the fixing nip where the heating member and the pressure member abut within a range of 50% or less of the fixing nip width to create a sharp pressure distribution, and a large contact pressure is generated locally. Further, by setting the peak of the pressure distribution to the downstream side of the nip, the pressure was effectively applied at the stage where the toner was melted, and the fixability between the toners and between the toner and paper could be improved. In addition, since the total pressure applied between the heating member and the pressure member can be reduced by using a sharp pressure distribution, the fixing device for high-quality color image formation can be achieved by using a smaller and lower heat capacity fixing device. Made on-demand easier.

It is a whole block diagram of one Example of this invention. FIG. 3 is an explanatory diagram of the effects of radiation and heat on the fixing belt of Example 1. 1 is an overall schematic diagram of an image forming apparatus using the present invention. It is a figure which shows the pressure distribution in the contact part of the heating film in Example 1, and a pressurization member. It is a whole block diagram of the 2nd Example in this invention. It is a figure which shows the pressure distribution in the contact part of the heating film and pressurization member in Example 2. FIG. FIG. 6 is an overall configuration diagram of Example 3. 6 is a schematic configuration diagram of a cross section of a heating film in Example 3. FIG. 5 is a schematic configuration diagram of a fixing nip section in Embodiment 3.

Example 1
In this embodiment, a thin film having an elastic layer is used as a heating member, and the film is pressed by a roller as a pressure member while supporting the thin film by three rotating rollers as a holding member. Is driven stably.

  Further, in this embodiment, since the base layer and the elastic layer in the heating member have translucency and the release layer has light absorption, the radiation can directly generate heat in the release layer on the surface of the heating member. is there.

  Hereinafter, a description will be given with reference to FIG.

  FIG. 3 is a sectional view of a color image forming apparatus including the fixing device according to the first embodiment of the present invention.

  In FIG. 3, reference numeral 28 denotes a photosensitive drum, which can be configured by applying a photoconductor such as an organic photoreceptor (OPC) or amorphous silicon to the outer peripheral surface of an aluminum cylinder.

  The photosensitive drum 28 is driven at a predetermined speed (eg, 50 to 300 mm / sec) in a direction indicated by an arrow (not shown) by a driving unit (not shown), and the surface of the photosensitive drum 28 is charged to a dark portion potential (eg, −700 V) by a charger 29.

  Next, the exposure device 30 exposes the photosensitive drum 28 in accordance with the magenta image pattern, and an electrostatic latent image is formed by reducing the surface potential of only the image portion to the bright portion potential (eg, −150 V).

  The developing devices 21a, 21b, 21c, and 21d supported by the rotating support 30 include magenta, cyan, yellow, and black developer materials, respectively. Here, each color developer is a negatively chargeable toner having a weight average diameter of 6 μm which is synthesized by a suspension polymerization method and has a spherical shape and high development / transfer efficiency.

  The electrostatic latent image is first provided with a gap of 300 μm so that the magenta developing unit 21a faces the photosensitive drum 28. For example, the electrostatic latent image is developed by a developing bias obtained by superimposing AC 2 kVpp on DC-500V to form a magenta toner image. Visualized.

The visualized magenta toner image on the photosensitive drum 28 is a transfer bias supplied from a transfer power source (not shown) to an intermediate transfer drum 23 made of a medium resistance member such as PVdF subjected to a conductive treatment of 10 ⁶ to 10 ⁹ Ω. Transferred with (+0.5 to 2 kV).

  When a magenta image for one A4 size page is transferred onto the intermediate transfer drum, the rotary support 22 rotates, and the above process is sequentially performed for each color of cyan, yellow, and black, and a plurality of color toner images are formed on the intermediate transfer drum 23. Form.

  On the other hand, the pickup roller 24 feeds the transfer paper P from the transfer paper cassette 25 in synchronization with the black toner image. By applying a secondary transfer bias (+1 to 2 kV) to the transfer roller 31, the toner image on the intermediate transfer drum is transferred to the transfer paper P and carried into the fixing device 26.

  The transfer material P onto which the color image has been transferred is conveyed to the fixing device 26 by the conveying means and fixed, discharged as a color printed matter outside the apparatus, and stacked on the paper discharge tray 20.

  The transfer residual toner on the intermediate transfer drum is charged to a positive polarity by the charger 38 and then collected on the photosensitive drum 28 and cleaned by the cleaning device 27 in the same manner as the transfer residual toner on the photosensitive drum 28.

  Next, the fixing device 16 in this embodiment will be described in detail with reference to FIG.

  Reference numeral 3 in FIG. 1 denotes a heating film, which includes a halogen lamp 1 having an output of 500 to 1200 W, which is a heating element. Here, the radiation light source can be of any type as long as it efficiently radiates infrared rays at high speed, and a xenon lamp or the like can be used in addition to the halogen heater. Infrared rays of 8 μm or more can be emitted with high efficiency of 85% or more of the input power, and radiation is performed by heating a tungsten filament with a small heat capacity, so it is possible to obtain high-speed startup and responsiveness. And

  In this embodiment, the coil of the heating element in the halogen heater is wound almost uniformly, so that it is installed over the entire image area without segmentation. Therefore, a decrease in the amount of radiant light in the non-coil portion generated between the coils when the heating element is segmented is prevented, and the occurrence of the heating element coil trace (gross unevenness, fixing unevenness) in the longitudinal direction in the fixed image is prevented. . The heating film 3 is provided with a thermistor 6 which is a temperature detecting means. Electric power is supplied to the halogen heater 1 according to the surface temperature of the heating film 6 detected by the thermistor, and about 90% of the input power is a wavelength in the infrared region. Is emitted as output light.

  Around the halogen lamp 1, three metal support rollers 2a, 2b and 2c are disposed as film holding members. The heating film 3 is rotatably supported by the support roller 2 and is brought into pressure contact with the pressure roller 5.

  The support stay 2a is a roller made of metal such as stainless steel or aluminum, and may be a hollow sleeve having a wall thickness of about 0.3 to 2 mm in order to realize higher-speed startup. The support roller 2a is for downstream pressure, and is pressed toward the center of the pressure roller at 10 to 50 kgf. The support roller 2b is for upstream pressure and is pressurized toward the center of the pressure roller with 1 to 30 kg so as to realize a contact pressure lower than that of the downstream pressure roller 2a. The support roller 2c is for film control, and the tension between the support rollers 2a and 2b is generated by stretching the pressure film 3 upward, and the heating film 3 is brought into close contact with the pressure roller to form a stable fixing nip. is doing. Further, the heating film position can be moved in the axial direction by moving one end of the supporting roller 2c up and down by a cam (not shown), so that the supporting roller 2c according to information from a film position detecting means (not shown). Can be moved to suppress the meandering and displacement of the film.

  The support roller 2a is driven at the same speed as the pressure roller by a drive motor (not shown), and similarly rotates the heating film 3 at the same speed as the pressure roller 4 driven by the drive motor (not shown).

  The pressure roller 5 is formed by providing a silicone rubber layer having a thickness of 1 to 10 mm on a metal core made of metal such as aluminum, stainless steel, or iron. The surface layer has a fluororesin layer for preventing toner contamination. is doing.

  Here, the heating film 3 in the present embodiment will be described with reference to FIG.

  The heating film 3 is a seamless film in which an elastic layer 3b having a thickness of 50 to 1000 μm and an infrared absorbing layer 3c having a thickness of 5 to 50 μm are provided on a heat-resistant base layer 3a having a thickness of 20 to 200 μm and excellent in heat resistance and sliding properties. is there.

  As the film base layer 3a, a heat resistant resin such as polyimide, polyamideimide, or aramid can be used. In particular, the polyimide film has excellent mechanical strength and heat resistance and transmits 80% or more of infrared light with a wavelength of 3 μm or less emitted from a halogen lamp, so that the effect of surface heating in the present invention can be obtained more effectively. .

  As the elastic layer 3b, various silicone rubbers such as LTV, HTV, and RTV, or rubbers or sponges having high heat resistance such as fluorine rubber are formed, and those that are soft and have a small permanent strain are used. Here, the hardness of the elastic layer is preferably 50 ° or less in terms of JIS-A hardness in order to obtain flexibility corresponding to the unevenness of the toner surface. The elastic layer made of silicone rubber can also transmit 80% or more of infrared light having a wavelength of 3 μm or less, realizing efficient surface heating.

  In this embodiment, the silicone rubber layer 3b provided on the polyimide base layer 3a of the heating film 3 is formed with a thickness of 50 to 1000 [mu] m so that even a thick toner layer in a color image can be uniformly pressed. Set to In color image formation using a hard roller or film that does not have an elastic layer as a heating member, if a multicolor toner layer and a single color toner layer are present in the vicinity of a fixed image, the single color toner layer is sufficiently pressurized. In the heating film provided with the elastic layer in this embodiment, both the multicolor toner layer and the single color toner layer are used to cope with the unevenness of the toner layer. Therefore, even in a color fixed image, uniform fixing property and high transparency in OHP were obtained.

  Further, in the elastic layer 3b, fine particles may be appropriately dispersed in order to adjust the mechanical strength, electrical resistance and thermal conductivity, and by dispersing fine particles such as silica, tin oxide, titanium oxide, zinc oxide, etc. Compression set can be reduced. By suppressing the scattering of the radiation light, the amount of radiation can be suppressed, and the particle diameter of the filler fine particles in the elastic layer in the present invention is preferably less than or equal to the wavelength of transmitted infrared rays, more preferably 0. It is preferable that it is 3 micrometers or less.

  In the present embodiment, heat transfer is performed mainly by radiation rather than heat conduction in the elastic layer, so that an infrared absorption layer 3c is provided on the surface of the heating member to generate heat on the surface of the heating film.

As the absorption layer 3c, carbon-based particles such as carbon black and graphite, which are infrared absorbing materials, or various metal oxide particles such as iron oxide are dispersed in a release layer made of a conventional fluororesin such as PFA and PTFE. Therefore, infrared light can be absorbed well. Moreover, the electrical resistance of the surface can be lowered by using a conductor such as carbon black as the infrared absorbing material, and electrostatic offset can be prevented by controlling it to about 10 ⁶ to 10 ¹⁴ Ω / cm. Is also possible.

  Here, the amount of radiation (solid line) and the temperature distribution (broken line) in the heating film will be described with reference to FIG. The vertical axis of FIG. 2b represents the position y in the thickness direction in the film cross section, and the horizontal axis represents the amount of radiation (practice) and the temperature T (dashed line). Radiation light irradiated by the halogen heater inside the heating film is not attenuated so much in the film base layer 3a and the elastic layer 3b, and 70% or more of the radiation is absorbed in the release layer 3c on the surface of the heating film. Therefore, the film surface side is heated at high speed (A).

  On the other hand, when a similar film is heated by heat conduction in a conventional fixing nip, in order to obtain a temperature equivalent to A on the film surface, the inner surface of the film is considerably higher than the surface temperature (20 to 50 ° C.) as shown in B. It was necessary to set.

  Therefore, by adopting this configuration, it becomes possible to lower the film inner surface temperature, and the amount of heat required to heat the surface of the heating member to the fixing temperature is lower than that of the conventional fixing device using heat conduction, and energy saving is achieved. In addition, the life of the heating member, particularly the elastic layer, can be extended.

  The thermistor 4 may be not only a contact type but also a non-contact type thermopile. The thermistor may malfunction due to accumulation of offset toner, or the accumulated toner may fall on the transfer paper and contaminate the image. Can be prevented.

  Furthermore, according to this embodiment, the elastic layer 3b in the heating film has a low heat conductivity and rather provides a heat insulating effect. Therefore, the temperature of the support / support roller 2 constituting the nip does not need to be positively increased from the inner surface of the heating film, and the toner and the transfer material are sufficiently heated by the amount of heat stored on the film surface, which is good even during continuous printing. Fixability is realized.

  That is, according to the fixing device in this embodiment, the fixing member nip is formed by forming the supporting member of the heating member with a metal member and press-contacting with the pressure roller. Thus, the drive can be driven, and the heat capacity of the fixing device can be reduced and the startup can be achieved at high speed.

  In this embodiment, different contact pressures are applied to the support rollers 2a and 2b to enable stable film drive and high-quality image formation. FIG. 4 shows the distribution of the contact pressure in the fixing nip. The pressure distribution (dotted line) in the conventional roller fixing device has a peak value at the center of the nip, whereas the pressure distribution in this embodiment (solid line). In this case, since there is a peak on the downstream side of the nip, tension is generated in the downstream direction in the nip, so that even a thin film having high flexibility can be driven stably. Here, the distribution of the contact pressure was measured with a tactile sensor sheet manufactured by NITTA KOGYO.

  In addition, when compared with the same pressure, the peak value can be made about twice that of the conventional roller fixing device by sharpening the pressure distribution. Accordingly, the toner on the transfer material can be sufficiently crushed so that the toners and the toner and the transfer material can be combined with each other, so that high fixability can be obtained.

  Further, in the fixing device in this embodiment, the pressure peak is downstream of the nip, so that the toner melted by passing through the nip can be firmly pressed against the transfer material. Therefore, the toner melts too much when the film is hot and adheres to the heating member, so-called hot offset is reduced, high gloss is obtained, and stable image formation with little contamination to the heating member and pressure member is possible. Become.

  Here, the support roller 2a can also have a crown shape that forms a convex shape with respect to the axial direction of the roller. A flexible thin heated film is likely to wrinkle when rotated at high speed, and the wrinkle generated in the film not only causes poor fixing, but the film may break and break in the long term. In particular, in the downstream support roller 2a to which high pressure is applied, the film is easily wrinkled due to the bending of the roller. Therefore, in this embodiment, the downstream support roller 2a is crowned to end the film surface from the center in the axial direction. Tension toward the part is generated to suppress the generation of film wrinkles.

  Here, the crown amount is preferably set to 0.1 mm or more in order to obtain a sufficient tension. If the crown amount is too large, the transfer material carried into the fixing nip cannot be uniformly pressed, resulting in uneven gloss and poor fixing. The following is preferred.

  In this embodiment, the heating film has a three-layer structure including a base layer, an elastic layer, and a release layer. However, for example, a conductive primer layer or an adhesive layer may be inserted in the middle to form four or more layers. You can get an effect.

  In this embodiment, three support rollers are used as the film holding member. However, the present invention is not limited to this, and the effect of the present invention can be achieved even if two or more support rollers are used to provide the same pressure distribution. It is possible to get

(Example 2)
In this embodiment, the heating film holding member is not a roller but a support stay with a low heat capacity fixed to the fixing device so that the fixing device is on-demand and the film itself is driven to rotate. By supporting the film without tension by driving the film, the meandering of the film is suppressed, and stable film driving is realized with a simple configuration.

  Hereinafter, the fixing device in this embodiment will be described with reference to FIG. FIG. 5 is a schematic cross-sectional view as seen from the side surface of the heating film. For simplicity, the same parts as those in Example 1 are denoted by the same symbols.

  The heating film 3 in FIG. 5 includes the halogen lamp 1 as in the first embodiment, and is pressed against the pressure roller by the support stay 6 to form a fixing nip.

  The heating film 3 is driven and rotated by a pressure roller driven by a motor (not shown), and rotates at the same speed as the pressure roller and paper as a transfer material.

  In the present embodiment, two guide members 7 are arranged inside the heating film 3, and the heating film imparts straightness to suppress meandering and prevent the heating film from contacting the halogen lamp 1. The guide member 7 is composed of a sleeve made of metal such as aluminum or stainless steel, and is arranged in parallel with the shaft over the entire region in the film axial direction. Here, the guide member 7 is made of a metal member, thereby suppressing the temperature unevenness in the axial direction of the heating film, particularly the temperature rise when fixing the small size paper, thereby enabling stable image formation. .

  The surface temperature of the heated film is detected by the thermistor 4, and the halogen heater is turned on / off by a fixing power source (not shown) so as to reach a predetermined temperature (160 to 190 ° C.), and the temperature is controlled.

  Here, the support stay 6 in the present embodiment will be described in detail. The support stay 6 is formed of a thin plate of a metal material such as aluminum, stainless steel, iron, or copper having a thickness of 0.3 to 2 mm so as to satisfy heat resistance, mechanical strength, and low heat capacity. The support stay 6 is formed with a bottom plate portion that forms a nip by pressing a thin metal plate, and an edge portion that guides the film. The bottom plate portion is further provided with a protrusion toward the pressure roller on the downstream side in the sheet passing direction. .

  In this embodiment, a pressure distribution is generated in the nip in the same manner as in the first embodiment by providing the support stay 6 with a protrusion that is convex in the direction of the pressure roller.

  Here, the effect of the protrusion in the present embodiment will be described with reference to FIG. When a protrusion is provided on the bottom plate portion of the support stay 6, a sharp pressure distribution can be obtained in a relatively narrow fixing nip of 4 to 10 mm as in the first embodiment, and the effects of the present invention can be obtained. In the bottom plate part with protrusions (solid line), it is possible to obtain about twice the peak pressure when the same total pressure is applied to the fixing nip compared to the straight bottom plate part (dotted line) without protrusions. I can do it. Further, by providing a protrusion in the latter half of the nip, a wider nip width can be obtained compared to a straight bottom plate portion. Accordingly, the residence time in the nip can be increased as compared with the case where no protrusion is provided, and the toner on the transfer material can receive a sufficient amount of heat from the heating film. In addition, since a large contact pressure can be applied in the latter half of the nip, the toner on the transfer material is crushed when sufficiently melted and pressed against each other and to the paper, and good fixability can be obtained.

  The width of the protrusion is preferably 10 to 50% of the nip width, and if it is less than 10% of the nip width, the effect of forming the protrusion on the film surface is not seen, and if it exceeds 50%, a sharp pressure distribution cannot be obtained. The effect in the example could not be obtained.

  The height of the protrusion is preferably 0.2 to 2 mm. If the height is smaller than 0.2 mm, the effect of the protrusion cannot be seen due to the effect of the elastic layer. If the height is larger than 2 mm, the driving torque increases to stabilize the film. It became difficult to drive.

  In addition, the shape of the protrusion is triangular in the embodiment, but the present invention is not limited to this, and the effect of this embodiment can be obtained even if the protrusion shape is round or square.

  Here, in order to improve the slidability between the support stay and the inner surface of the film, various sliding agents such as fluorine grease, silicone grease, and silicone oil can be applied to the inner surface of the film. Since a certain amount of the sliding agent is always secured on the upstream side of the protrusion inside the nip, the friction between the support stay and the film is reduced, and the effect of keeping the rotation speed of the film constant regardless of the environment can be obtained.

  That is, according to the fixing device in this embodiment, excellent fixing performance can be realized by providing the supporting member with the protrusion on the supporting stay having a low heat capacity. In addition, it has become possible to provide an on-demand fixing device that has a small hot offset and is stable over a long period of time.

(Example 3)
In this embodiment, the heating film has a four-layer structure, and a small-diameter roller is provided on the downstream side of the nip of the support stay to realize good pressure distribution and heating efficiency and rotational stability of the film in the fixing device.

  Hereinafter, the fixing device in this embodiment will be described with reference to FIG.

  The heating film 10 contains the halogen lamp 1 as in the first embodiment, and is in pressure contact with the pressure roller 5 by a support stay 8 and a guide member 7 that rotatably support the heating film 10 to form a fixing nip. In this embodiment, the temperature of the heating film 10 is detected by the thermopile 11 in a non-contact manner with the film. A fixing power source (not shown) appropriately supplies electric power to the halogen lamp 1 based on the thermopile output signal, and keeps the film surface at a constant temperature of 160 to 190 ° C. In this embodiment, the thermopile 11 measures the temperature without contact with the film, so that stable image formation can be performed over a long period of time without damaging the film.

  In FIG. 7, reference numeral 10 denotes a heating film. In the above-described embodiment, the infrared absorbing material is dispersed in the release layer in the heating film. However, in this embodiment, the infrared absorption layer and the release layer are provided separately. Therefore, it will be described in detail with reference to FIG.

  The heating film 10 has a base layer 10a made of polyimide or the like as in Example 2 and an elastic layer 10b made of silicone rubber, and an infrared absorption layer 10c in which carbon black is formed in silicone rubber as a heat generating layer on the elastic layer, and a separating layer. A fluororesin such as perfluoroalkoxyethylene copolymer (PFA), PTFE, FEP, etc., which is the mold layer 10d, was provided as a release layer and an outermost layer. Unlike the above-described embodiments, it is not necessary to disperse an infrared absorbent such as carbon black in the release layer by separately providing an infrared absorption layer. Therefore, the ratio of the fluororesin such as PFA and FEP in the outermost layer can be increased, and the life of the fixing device can be extended by maintaining good releasability even during long-term use.

  In this embodiment, since the infrared absorption layer is not the outermost layer of the film, the effect of surface heating tends to be reduced. However, the effect of the present invention can be obtained by sufficiently reducing the outermost release layer 10d. Therefore, the thickness of the outermost release layer is preferably 5 to 50 μm, and if it is thicker than 50 μm, it is difficult to obtain the effect of surface heating, while if it is thinner than 5 μm, uniform releasability can be obtained. It became difficult.

  In this embodiment, a small-diameter roller 9 is provided on the downstream side of the support stay 8, and the downstream portion of the nip is locally pressurized as in the above-described embodiment. This will be described below with reference to FIG.

  As the small-diameter roller 9, a metal or ceramic roller or sleeve having a diameter of 1 to 5 mm can be used. In this embodiment, an aluminum roller 9 having a diameter of 2 mm is used as an example. A semi-cylindrical groove in which the aluminum roller 9 is accommodated in a substantially half circumference is inserted in parallel to the longitudinal direction on the downstream side of the support stay 8, and the aluminum roller 9 is supported rotatably.

  In order to obtain the effect of this embodiment, the diameter of the small-diameter roller 9 is preferably 10 to 50% of the fixing nip width, and if it is less than 10%, a sufficient peak pressure cannot be obtained, and if it exceeds 50%. The sharp pressure distribution could not be obtained and the effect of this example could not be obtained.

  The depth of the recess of the support stay 8 is preferably 50 to 90% of the diameter of the small-diameter roller 9. If the depth is less than 50%, it becomes difficult to hold the small-diameter roller. It became difficult to get.

  By adopting such a configuration, the pressure distribution at the fixing nip can be made substantially equal to that in Example 2 (FIG. 6).

  Here, in order to improve the lubricity between the support stay and the inner surface of the film, various sliding agents such as fluorine grease, silicone grease, and silicone oil can be applied to the inner surface of the film. By applying a sliding agent, the friction with the film is reduced, the rotation speed of the film is kept constant, and the lubricant enters the gap between the aluminum roller 9 and the support stay 8 to stabilize the aluminum roller 9. It can also be rotated.

  In this embodiment, the aluminum roller 9 is driven. However, the effect of this embodiment can be obtained even if the motor is driven from the outside at the same speed as the pressure roller.

  In addition, as shown in FIG. 9B, a sliding surface 12 made of a ceramic member such as alumina or glass can be separately provided on the support stay in order to improve wear resistance. By providing wear resistance to the friction surface with the system roller, stable film drive can be achieved over a longer period of time.

  That is, according to this embodiment, the contact pressure on the downstream side of the nip can be improved by providing a small diameter roller between the heating film and the support stay downstream of the fixing nip. Further, since the small-diameter roller provided on the downstream side of the nip is rotatable, a high contact pressure can be applied downstream of the fixing nip without increasing the driving torque of the film. Therefore, since a high pressure can be applied when the toner, which is an effect of the present invention, is melted, the toner can be effectively crushed and pressed against paper to obtain high fixability and uniform glossiness. Therefore, a high-speed and stable on-demand fixing device can be supplied even for color images that require high image quality.

DESCRIPTION OF SYMBOLS 1 Halogen lamp 2 Support roller 3 Heating film 4 Thermistor 5 Backup roller 6 Support stay 9 Small diameter roller 10 Heating film 11 Non-contact thermistor

Claims (9)

  A toner on the transfer material, having a heating member that can rotate at a constant speed with the transfer material, and that has a holding member and a radiation heat source inside, and a pressure member that pressurizes and drives the heating member from the outside. In the fixing device for fixing an image by heating and melting, the heating member is a film or a belt having a heat generating layer that generates heat by absorbing at least radiation emitted from the radiation heat source, and the holding member is the heating member. The pressure member is pressed against the pressure member to form a fixing nip, and the contact pressure in the fixing nip is higher in the downstream contact pressure than the upstream contact pressure in the transfer material passing direction. A fixing device characterized.   The fixing device according to claim 1, wherein the heating member includes a base layer that is transmissive to radiation light inside the heat generating layer.   3. The fixing device according to claim 1, wherein the heating member includes an elastic layer that is transmissive to the radiation light, between the base layer and the heat generating layer.   4. The fixing device according to claim 1, wherein the holding member is formed of a thin metal plate having a protrusion in the second half of the contact nip with respect to the direction of the pressure member.   The fixing device according to claim 1, wherein the heating member base layer is made of a material containing at least a polyimide resin.   The fixing device according to claim 3, wherein the elastic layer of the heating member includes at least a silicone rubber layer.   The fixing device according to claim 1, wherein the absorption layer in the heating member contains at least conductive carbon particles.   8. The fixing device according to claim 1, wherein the heating member has a release layer made of a fluororesin on a surface layer.   The holding member has a sliding portion that slides with respect to the film at the nip forming portion and a rotating portion that rotates together with the film, and the contact pressure generated at the nip forming portion is higher than the contact pressure at the sliding portion. 9. The fixing device according to claim 1, wherein the contact pressure at the rotating portion is higher.

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