JP2019012171A - Fixation member and heating fixation device - Google Patents

Abstract

To improve heat insulation performance in a thickness direction of an elastic layer for shortening a period since printing start time until fixation can be started, to provide an elastic layer in which voids are arranged, namely a porous elastic layer for shortening a build-up time, to solve problems in which, when the void ratio is increased, heat insulation performance is improved however, a fixation member is easily crushed in a thickness direction and durability is reduced, therefore, to improve heat insulation performance while maintaining a void ratio of the elastic layer.SOLUTION: There is provided a compression roller comprising a core grid and an elastic layer and being used for an image heating device, in the elastic layer, there are provided ellipsoid gap parts, an orientation of a long diameter of each gap is a shaft direction of a compression roller.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a pressure member and a fixing device used in a heat fixing device of an image forming apparatus using an electrophotographic system.

  In general, a heat and pressure fixing device used in a toner image forming apparatus using an electrophotographic system functions by a pair of members including a rotating member such as a heated roller and a roller, a film and a roller, and a belt and a roller being pressed against each other. It has the composition to do. When a recording material such as paper to which toner has been transferred passes between the pair of members (nip portion), the unfixed toner image is heated and softened in the nip and pressed against the paper by the applied pressure. Fixing is performed after solidification, and a fixed image of toner is formed on the paper (FIG. 1).

  With these fixing devices, when a small-sized recording material is continuously printed at the same print interval as a large-sized recording material, the temperature of the non-sheet-passing area is excessively increased (hereinafter referred to as non-sheet-passing portion temperature rise). Are known. When the non-sheet passing portion temperature rise occurs, the heat resistance temperature of each member constituting the fixing device is exceeded, and there is a possibility of damaging them. In addition, if a large size recording material is printed while the temperature of the non-sheet passing portion is raised, the toner melts too much in the portion corresponding to the non-sheet passing area of the small size recording material, and a high temperature offset occurs. End up.

  On the other hand, from the viewpoint of speeding up the first print time and saving energy, it is necessary to shorten the time required for the fixing film and the fixing roller to reach a temperature sufficient to heat and fix the toner image (hereinafter referred to as the rise time). It has been. Therefore, in recent years, the elastic layer of the pressure member is an elastic layer in which voids are arranged, that is, a porous elastic layer, thereby reducing the heat capacity and the thermal conductivity (FIG. 2). By reducing the heat capacity and heat conductivity of the pressure member, the amount of heat taken away by the pressure member at the start of operation of the heating device is kept small, and the film-like rotating body or fixing roller in contact with the pressure member The temperature rise rate can be improved.

  The following three methods have been proposed as a method for forming the gap. In Patent Document 1, a void is formed by mixing an uncrosslinked silicone rubber with a foaming agent and foaming and curing. In Patent Document 2, a hollow filler is mixed in advance with uncrosslinked silicone rubber to form voids after molding and crosslinking. In Patent Document 3, a water-containing material in which water is contained in a water-absorbing polymer is dispersed in uncrosslinked silicone rubber and dehydrated during crosslinking to form voids. Moreover, in patent document 4, the acicular high heat conductive filler is orientated to the bridge | crosslinking silicone rubber which has a non-gap | gap, and the non-sheet passing part temperature rising of a pressure roller is suppressed.

JP 2008-150552 A JP 2001-265147 A JP 2002-114860 A JP 2012-37874 A

  However, there is a problem in that the durability of the pressure roller elastic layer due to the pressing force is lowered because the air gap is easily crushed in the radial direction as described above. Therefore, a pressure roller having an improved heat insulating effect while maintaining the porosity is required. The present invention has been devised in view of this, and provides a pressure roller that can shorten the rise time while maintaining the durability by the pressing force (while maintaining the gap ratio below a certain value). For the purpose.

  In a pressure member used for an image heating apparatus, the pressure member including a cored bar and an elastic layer, the elastic layer has an ellipsoidal void portion, and the major axis direction of the void is the direction of the pressure member. A pressure member in the axial direction.

  By aligning the void shape of the elastic body in the axial direction and deforming it into an ellipse, more voids can be arranged in the elastic layer thickness direction than the perfect circular void. Thereby, the thermal conductivity in the elastic layer thickness direction can be reduced. Therefore, it is possible to provide a pressure member capable of shortening the rise time while maintaining the void ratio below a certain value, and a heat fixing device including the pressure member.

FIG. 2 is a schematic diagram illustrating an example of a configuration of a fixing device and a layer configuration of a pressure member according to the present invention. It is the schematic which shows the cross section of the porous elastic layer which concerns on a prior example. It is the schematic which shows the cross section of the porous elastic layer which concerns on this invention. It is the schematic which shows the cross section of the porous elastic layer which mixed the acicular filler which concerns on this invention.

  Next, embodiments of the present invention will be described with reference to the drawings.

<Fixing device>
The fixing device according to the present invention will be described. A fixing device according to the present invention is a fixing device used in an electrophotographic image forming apparatus, in which the above-described pressure member of the present invention is arranged as a pressure roller or a pressure belt. The electrophotographic image forming apparatus includes a photosensitive member, a latent image forming unit, a unit for developing the formed latent image with toner, a unit for transferring the developed toner image to a recording material, and fixing the toner image on the recording material. An electrophotographic image forming apparatus having means and the like can be mentioned.

  FIG. 1 is a sectional view showing one embodiment of the fixing device according to the present invention. The pressure member according to the present invention is arranged as a pressure roller 4. In the following description, regarding the fixing device and members constituting the fixing device, the longitudinal direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The short side direction is a direction parallel to the recording material conveyance direction on the surface of the recording material. The length is a dimension in the longitudinal direction. The width is a dimension in the short direction. Regarding the recording material, the width direction is a direction orthogonal to the recording material conveyance direction on the surface of the recording material. The width is a dimension in the width direction.

  Such a fixing device includes a ceramic heater 1 as a heating body, a heater holder 2 as a support member, an endless fixing belt 3 as a heating rotator, a pressure roller 4 as a pressure rotator (backup member), and the like. have.

  The heater holder 2 is formed in a substantially bowl shape with a rigid heat-resistant material. A ceramic heater (hereinafter referred to as a heater) 1 is supported by a groove provided on the lower surface of the center of the heater holder 2 in the short direction.

  The fixing belt 3 is loosely fitted around the outer periphery of the heater holder 2 that supports the heater 1. Further, grease is applied to the inner peripheral surface (inner surface) of the fixing belt 3 in order to improve the slidability with the heater 1.

  The fixing belt 3 will be described in more detail. The fixing belt 3 is an endless belt member having a multilayer structure in which a base layer 3a, an elastic layer 3b, and a release layer 3c are provided from the inside as shown in a fixing belt layer configuration diagram in FIG. The base layer 3a is a thin endless belt having flexibility. As the material of the base layer 3a, a thin heat-resistant resin such as polyimide, polyamideimide, PEEK or the like is used. In order to further increase the thermal conductivity, a thin metal such as SUS or Ni may be used. In addition, since the base layer 3a needs to satisfy the quick start property by reducing the heat capacity and further satisfy a certain mechanical strength, the thickness is desirably 5 μm to 100 μm, preferably 20 μm to 85 μm. .

  An elastic layer 3b made of silicone rubber or the like is formed on the outer periphery of the base layer 3a. By providing the elastic layer 3b, it is possible to obtain a high-quality image having high gloss and no fixing unevenness. That is, the release layer 3c is deformed with respect to the shape of the toner T on the recording material P and the paper fiber of the recording material P at the fixing nip N, and wraps an unfixed toner image, thereby Heat can be applied uniformly. If the thickness of the elastic layer 3b is too thin, the elasticity cannot be sufficiently exerted, so that an image having high gloss and no fixing unevenness cannot be obtained, and if it is too thick, the heat capacity of the fixing belt 3 becomes large and the quick start property is improved. It will decline. Therefore, the thickness of the elastic layer 3b is 30 μm or more and 500 μm or less, preferably 100 μm or more and 300 μm or less.

  The silicone rubber according to the present invention is a polymer having fluidity at room temperature, which cures by heating, has a moderately low hardness after curing, and has sufficient heat resistance and deformation to be used in a heat and pressure fixing device. It is a liquid silicone rubber having resilience. In particular, it is more preferable to use an addition reaction cross-linkable liquid silicone rubber because it has excellent processability, high dimensional accuracy stability, and excellent productivity such that no reaction by-product is generated during the curing reaction.

  The addition reaction crosslinking type liquid silicone rubber is a composition containing, for example, organopolysiloxane (A liquid) and organohydrogenpolysiloxane (B liquid), and further containing a catalyst and other additives as appropriate. Organopolysiloxane is a base polymer of a silicone rubber raw material, and its molecular weight is a number average molecular weight of 5,000 to 100,000 in order to bring the mixing and stirring of various fillers and the fluidity of the resulting mixture into an appropriate range. The weight average molecular weight is preferably 10,000 or more and 500,000 or less.

  The elastic layer 3b has a low thermal conductivity when silicone rubber is used alone. If the thermal conductivity is low, it becomes difficult to effectively transfer heat from the heater 1 to the recording material P, and there is a risk of causing image defects such as uneven fixing due to insufficient heating. Therefore, in the Example which concerns on this invention, in order to raise the heat conductivity of the elastic layer 3b, a highly heat conductive filler is mixed and disperse | distributed to the elastic layer 3b. As the granular high thermal conductive filler, SiC, ZnO, Al2O3, AlN, MgO, carbon or the like is used. Moreover, you may use a needle-shaped highly heat conductive filler according to the objective. Details of the acicular high thermal conductive filler will be described later. These fillers may be used alone or in combination of two or more. It is possible to impart conductivity to the elastic layer 3b by mixing these fillers into the elastic layer 3b.

  On the outer periphery of the elastic layer 3b, there are tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin (PFA), tetrafluoroethylene resin (PTFE), and tetrafluoroethylene / hexafluoropropylene copolymer resin (FEP). A release layer 3c formed from a fluororesin such as is provided. The release layer 3c has a thickness of 1 to 50 μm, preferably 8 to 25 μm. The release layer 3c may be a tube coated or a surface coated with a paint.

  The pressure roller 4 is disposed below the fixing belt 3 and parallel to the fixing belt 3. The pressure roller 4 and the heater 1 press the fixing belt 3 toward the heater 1 by a predetermined pressure mechanism. As a result, the outer peripheral surface (surface) of the pressure roller 4 is brought into contact with the outer peripheral surface (surface) of the fixing belt 3 in a pressurized state, and an elastic layer 4b described later is elastically deformed to thereby elastically deform the surface of the fixing belt 3 and the pressure roller 4. A fixing nip portion (nip portion) N having a predetermined width is formed between the surface and the surface.

  The pressure roller 4 will be described in more detail. The pressure roller 4 includes a shaft core body and a cylindrical body 4a, a porous rubber elastic layer 4b provided on the outer peripheral surface thereof, and a release layer 4c provided on the outer peripheral surface of the porous rubber elastic layer. Is a multi-layer structure.

(Shaft core and cylindrical body 4a)
The material used as the shaft core 4a is preferably stainless steel, phosphor bronze, aluminum or the like including a SUM material such as nickel-plated or chrome-plated surface. Further, when used as a pressure belt, examples of the material used for the cylindrical base material include a thin heat-resistant resin such as polyimide, polyamideimide, and PEEK, or an endless belt made of a thin metal such as SUS and Ni. It is done. As a standard of the outer diameter of the shaft core and the cylinder, it is 4 mm or more and 80 mm or less.

(Porous elastic layer 4b, release layer 4c)
The porous elastic layer 4b has a needle-like shape to increase the thermal conductivity λy in the longitudinal direction of the roller and the thermal conductivity λx in the lateral direction to rubber made of a flexible and heat resistant material such as silicone rubber. The high thermal conductive filler 4c1 is mixed and dispersed. In addition, by setting the gap 4c2, the heat capacity is set to be low.

  The porous elastic layer 4b is formed with a substantially uniform thickness on the elastic layer 4b. The thickness of the porous elastic layer 4b is not particularly limited as long as the nip portion N having a desired width can be formed, but is preferably 2.0 to 10.0 mm. The hardness of the porous elastic layer 4b is preferably in the range of 20 ° to 70 ° from the viewpoint of securing the nip portion N having a desired width.

  Next, the acicular high thermal conductive filler dispersed in the porous elastic layer 4b will be described in detail. A heat flow path can be formed by dispersing a needle-like highly thermally conductive filler in the elastic layer. Further, when the acicular high thermal conductive filler is kneaded and dispersed in the above-mentioned addition-reaction-crosslinking liquid silicone rubber before curing, the high thermal conductive filler has an elongated fiber shape. It tends to be oriented along the direction of flow of the liquid rubber during molding.

  Therefore, by flowing and molding the liquid rubber in the direction in which it is desired to increase the heat flow in the elastic layer and the pressure member, the heat flow in that direction can be made larger than the heat flow in the other direction. It becomes possible. By making the flow direction of the liquid rubber when molding the porous elastic layer 4b the longitudinal direction of the pressure member, efficient thermal diffusion from the high temperature side such as the non-sheet passing portion to the sheet passing portion is possible. Become. In addition, since the needle-like filler is oriented not only in the longitudinal direction but also in the lateral direction, it is effective in alleviating the temperature rise of the non-sheet passing portion. Therefore, the liquid rubber used for molding the porous elastic layer 4b There is no problem even if the flow direction is disturbed in the recording material conveyance direction in the pressure member, that is, in the short direction.

The acicular filler is a material having a large ratio of the length L to the diameter D, that is, a high aspect ratio. The shape of the bottom surface of the filler may be circular or square, and can be applied as long as the material is oriented by the molding method described later. Examples of such a material include pitch-based carbon fibers having a thermal conductivity λ _L in the length direction of 500 W / (m · K) or more. More specifically, the needle-like pitch-based carbon fiber has an average diameter D of 5 to 11 μm and an average length L of about 50 μm to 1000 μm, and is easily industrially available. If the average length L of the pitch-based carbon fibers is shorter than 50 μm, the thermal conductivity anisotropy effect in the porous elastic layer 4b is difficult to appear.

  On the other hand, when the average length L is longer than 1000 μm, it becomes difficult to perform dispersion processing molding into the porous elastic layer 4b. In order to shorten the rise time which is the object of the present invention, it is not always necessary to mix the needle filler.

  The release layer 4c may be formed by covering the porous elastic layer 4b with a PFA tube, or by coating the high thermal conductive elastic layer 4c with a paint made of fluororesin such as PFA, PTFE, FEP or the like. It may be formed. Although the thickness of the release layer 4c will not be specifically limited if it is the thickness which can provide sufficient mold release property, Preferably it is 15-80 micrometers.

  Next, a method for forming the porous elastic layer 4b and the release layer 4c in the embodiment of the present invention will be described in detail.

(I) Compounding step of liquid rubber mixture The above-mentioned needle-like filler 4b1 and a water-containing material containing water in a water-absorbing polymer are mixed in an uncured addition-reaction-crosslinking liquid silicone rubber and dispersed and mixed. The compounding can be carried out by weighing a predetermined amount of the liquid silicone rubber, the needle-like filler 4b1, and the water-containing material and dispersing them by a known filler mixing and stirring means such as a planetary universal mixing and stirring machine. In order to shorten the rise time which is the object of the present invention, it is not always necessary to mix the needle filler.

(Ii) Layer formation process of liquid rubber mixture A liquid rubber mixture is formed using a general mold. The core metal is placed in the mold, and the liquid rubber mixture is poured (cast) along the longitudinal direction of the shaft core body. Due to this flow, the needle-like filler 4b1 is oriented along the flow direction of the liquid rubber mixture, so that the thermal conductivity in the longitudinal direction can be effectively increased. At this time, the flow direction of the liquid rubber mixture is disturbed in the mold, so even if the needle-like filler is oriented in the short direction and the thermal conductivity in the short direction is increased, the non-sheet-passing portion is heated. The mitigation effect will not fade and there is no problem. The method is not particularly limited as long as the liquid rubber mixture can be layered while flowing in the longitudinal direction.

  Here, by increasing the flow rate during casting, a shear stress σ can be applied to the liquid rubber mixture, and a desired elliptical void shape can be obtained by crushing the void in the longitudinal direction. When the flow rate of the liquid rubber mixture is increased, a flow rate distribution is generated inside and a shear stress σ is generated. The shear stress σ is directly proportional to viscosity (Pa · s) and shear rate: casting speed (mm 2 / s) / mold diameter (mm). In order to sufficiently orient the voids in the longitudinal direction, the shear rate is desirably 20 (1 / s) or more. When the shear rate is 35 (1 / s) or more, emulsion breakage occurs inside the rubber mixture. Therefore, the shear rate is suitably less than 35 (1 / s). In order to increase the shear stress or prevent relaxation of the oriented rubber mixture, the viscosity of the liquid rubber mixture is preferably 10 (Pa) or more.

  By the above process, it becomes possible to produce a pressure roller having an elliptical gap shape. The gap is configured such that the direction of the major axis of the ellipsoid is the axial direction of the roller. Accordingly, the cross-sectional shape of the roller in the axial direction is an oval. On the other hand, in the cross section in the roller radial direction, the cross-sectional shape is circular. The ratio between the minor axis and the major axis of the ellipsoidal diameter is 1: 1.5 to 1: 2, preferably 1: 3 or more.

(Iii) Silicone rubber component cross-linking curing step The mold filled with the liquid rubber mixture is sealed, and the silicon rubber component is cured by heat treatment at a temperature not higher than the boiling point of water for 5 to 120 minutes. As heat processing temperature, 60-90 degreeC is desirable. Since it is hermetically sealed, the silicone rubber component can be crosslinked and cured while retaining moisture in the water-containing material.

(Iv) Demolding process The mold is appropriately cooled with water or air, and then the elastic roller on which the cured rubber mixture layer is laminated is demolded.

(V) Dehydration step The laminated rubber mixture layer is dehydrated by heat treatment to form the gap 4c2. The heat treatment conditions are preferably 100 ° C. to 250 ° C. and 1 to 5 hours. Through the above steps, the porous elastic layer 4b is formed on the cored bar.

(Vi) Lamination process of mold release layer 4c Using the adhesive, the fluororesin tube which is mold release layer 4c is coat | covered and integrated on the porous elastic layer 4b. When the porous elastic layer 4b and the release layer 4c are adhered to each other without using an adhesive, it is not necessary to use an adhesive. It is not always necessary to form the release layer 4c at the end of the process, and the release layer can also be laminated by a method in which a liquid resin mixture is cast after a fluororesin tube is previously placed inside the mold. Further, after forming the porous elastic layer 4b, the release layer 4c can be formed by a known method such as coating with a fluororesin paint.

[Example]
Hereinafter, details of the present invention will be described by way of examples. First, measurement methods and various evaluations performed in each example and comparative example will be described.

<Performance evaluation>
Next, performance evaluation will be described. In the performance evaluation, the pressure roller of this example and the comparative example are incorporated in the heat fixing apparatus shown in FIG. 1, respectively, and A3 size paper is supported, and the pressure roller surface moving speed (circumferential speed) is 246 mm / sec. This was done using a laser printer. A pressure roller having an outer diameter of 30 mm and an elastic layer thickness of 3.0 mm was used.

<Method of measuring thermal diffusivity>
For measurement of thermal diffusivity, a thermal diffusivity / thermal conductivity measuring device (trade name: ai-Phase Mobile2, manufactured by Eye Phase Co., Ltd.) using a temperature variable thermal wave thermal analysis method was used.

  The recording material conveyance direction of the porous elastic layer (short direction of the roller, hereinafter referred to as x direction), the direction orthogonal to the x direction (longer direction of the roller, hereinafter referred to as y direction), and the thickness direction of the elastic layer (roller) The cross-sectional direction, hereinafter referred to as the z direction) was measured. In the measurement of the thermal diffusivity in the x direction, a cut was made in the yz plane of the elastic layer, and the sample in the x direction was cut out to a predetermined sample size of 1 mm or less to obtain a sample to be measured.

  Similarly, in the measurement of the thermal conductivity in the y direction and the z direction, cuts were made in the zx plane and the xy plane, respectively, so that the thicknesses in the respective directions were 1 mm or less, thereby obtaining samples to be measured. In this example, the thermal diffusivity measurement was performed 5 times at 50 ° C. in each of the short direction, the long direction, and the cross-sectional direction, and the average values thereof were respectively the circumferential thermal diffusivity αx, the longitudinal thermal diffusivity αy, and the thickness. The directional thermal diffusivity αz was used.

<Calculation of thermal conductivity>
In order to convert the measured value of the thermal diffusivity into thermal conductivity, values of density and specific heat capacity are required. A dry automatic densimeter (trade name: Accupyc 1330, manufactured by Shimadzu Corporation) was used for density measurement. Further, the specific heat capacity was measured using a differential scanning calorimeter (trade name: DSC823, manufactured by METTLER TOLEDO Co., Ltd.) using sapphire as a reference material with a known specific heat capacity.

  In this example, the specific heat capacity was measured five times, and the average value at 50 ° C. was used. If the obtained density and specific heat capacity are ρ and C, respectively, the thermal conductivity λ can be obtained from the thermal diffusivity α obtained by the above thermal diffusivity measurement by the formula λ = ρ × C × α. Can do. The thermal conductivities obtained from the thermal diffusivities αx, αy, αz in the respective directions were λx, λy, λz, respectively.

<Calculation of ratio of major axis / minor axis of void>
The porous elastic layer 4b of the pressure roller was cut out in the thickness direction, and the shape of the gap in the plane defined by the roller axial direction and the thickness direction of the elastic layer was observed with a scanning electron microscope. From this observation image, the major axis / minor axis of the void was measured. The ratio of the major axis to the minor axis was calculated using the average value of 20 voids.

<Rise time evaluation>
The rise time was also evaluated in a low-temperature and low-humidity environment (15 ° C./10%) in order to compare performance under conditions where the temperature rise at the non-sheet passing portion was very severe. The rise time was measured from the time when the heater power was turned on to the time when the fixing belt surface temperature reached 170 ° C. in the idling state where no paper was passed.

  Hereinafter, the present invention will be described more specifically with reference to examples.

<Example 1>
In this embodiment, a φ24 iron cored bar was used as the shaft core. The porous elastic layer 4b was formed with a thickness of 3.0 mm on the peripheral surface of the core metal. The water-containing material used for the liquid rubber mixture is water containing sodium polyacrylate (trade name: Rheojic 250H, manufactured by Nippon Pure Chemical Co., Ltd.), and the proportion of the water-containing material in the liquid rubber mixture is 50% by volume. It is mixed and dispersed so that The proportion of sodium polyacrylate in the water-containing material is 1 wt%. In the casting process, a core metal is installed in the center of a cylindrical molding die having an inner diameter of 30 mm, a PFA tube is installed on the inner surface of the molding die, and the liquid rubber is interposed between the porous elastic layer 4b and the PFA tube. The mixture was poured so that the needle-like filler 4b1 was oriented along the longitudinal direction of the roller.

In this study, in order to orient the voids in the longitudinal direction, the liquid rubber mixture was poured at a constant speed of 50 mm / s to 150 mm / s during casting. The porous elastic layer 4b was formed with a thickness of 3.0 mm on the peripheral surface of the core metal by the liquid rubber mixture blending step and the casting step.
The inner surface of the PFA tube used at this time is etched, and a primer (trade name: DY39-067, manufactured by Toray Dow Corning) is applied and dried in advance on the inner surface. After sealing the mold, the mold was heat-treated in a hot air circulating oven at 90 ° C. for 1 hour to cure the silicone rubber component. After performing water cooling and demolding, a pressure roller of Example 1 was obtained by heat treatment at 200 ° C. for 4 hours in a hot air circulation oven and dehydration. A cross section of the porous elastic layer 4b of the pressure roller is shown in FIG. This pressure roller was incorporated in the heat fixing apparatus shown in FIG. 1, and the rise time was evaluated.

<Example 2>
In Example 1, the needle-like filler 4b1 was mixed at the time of casting the rubber mixture. The acicular filler 4b1 includes pitch-based carbon fibers (trade name: GRANOC milled) which are acicular fillers having an average fiber diameter D = 9 μm, an average fiber length L = 250 μm, and a thermal conductivity λ _L = 900 W / (m · k). Fiber, XN-100-25M, manufactured by Nippon Graphite Fiber Co., Ltd.) and mixed and dispersed in an addition reaction crosslinked liquid silicone rubber at a ratio of 10% by volume. In the casting process, a PFA tube is installed in the center of the cylindrical molding die having an inner diameter of 30 mm and on the inner surface of the molding die. The casting speed was increased from 50 mm / s to 100 mm / s so that the gaps were oriented along the longitudinal direction of the roller. A cross section of the porous elastic layer 4b of the pressure roller is shown in FIG. This pressure roller was incorporated in the heat fixing apparatus shown in FIG. 1, and the rise time was evaluated.

<Comparative Example 1>
The pressure roller was produced by changing the flow rate of the liquid rubber mixture for the porous elastic layer 4b to 20 mm / s. Other than that was carried out similarly to Example 1, and obtained the pressure roller of this comparative example 1. Evaluation similar to Example 1 was performed.

<Comparative Example 2>
The liquid rubber mixture for the porous elastic layer 4b mixed with the needle-like filler 4b1 was poured into 20 mm / s. Other than that was carried out similarly to Example 2, and obtained the pressure roller of this comparative example 2. The same evaluation as in Example 2 was performed.

<Evaluation results>
Table 1 shows the measurement results of the pressure rollers and the evaluation results of the rise time. In addition, when the flow rate was 150 mm / s, the rubber mixture was emulsified and destroyed, and a pressure roller that could be studied could not be obtained.

  In Example 1, by increasing the ratio of the major axis to the minor axis in the axial direction of the void shape of the pressure member elastic layer, the thermal conductivity in the thickness direction is reduced, and the rise time is sufficiently shortened compared to Comparative Example 1. The effect is obtained. It was also shown that the pressure roller added with the heat conductive filler has a sufficient rise time shortening effect.

  From these results, it can be seen that by applying the present invention, it is possible to provide a pressure member capable of shortening the rise time while maintaining the void ratio, and a heat fixing device including the pressure member.

1. Ceramic heater 2. 2. Heater holder Fixing belt 3a. Base layer 3b. Elastic layer 3c. Release layer 4. Pressure roller 4a. Shaft core 4b. Porous elastic layer 4b1. Needle-like filler 4b2. Air gap 4c. Release layer

Claims (4)

  In a pressure member used for an image heating apparatus, the pressure member including a cored bar and an elastic layer, the elastic layer has an ellipsoidal void portion, and the major axis direction of the void is the direction of the pressure member. A pressure member in the axial direction.   2. The pressure member according to claim 1, wherein a ratio α / β of a major axis α and a minor axis β of the ellipsoid of the void is 1.5 or more.   3. The pressure member according to claim 1, wherein the void ratio is 50% or less when the void ratio of the elastic layer is a volume occupation ratio of the void.   The pressure member according to any one of claims 1 to 3, wherein the elastic layer includes a needle-like highly thermally conductive filler having thermal conductivity anisotropy, and the highly thermally conductive filler is in an axial direction. And a pressure member distributed along the surface.