Fixing member and thermal fixing device

Abstract

To provide a fixation member for heat fixation devices which is effective for further improving a gloss step between first and second rounds and the effective utilization of heat to thermally fix an unfixed toner, as well as for having high durability against repeated compressions.SOLUTION: Provided is a fixation member for electrophotography having an endless shape, comprising a base layer of an endless shape and an elastic layer on the outer circumferential surface of the base layer, the elastic layer including silicone rubber and a filler dispersed in the silicone rubber. The total blending amount of the filler in the elastic layer is 30% or less by volume with respect to the total volume of the elastic layer. When it is assumed that λtd represents a coefficient of thermal conductivity in the circumferential direction, λnd represents a coefficient of thermal conductivity in the thickness direction, and λmd represents a coefficient of thermal conductivity in the longitudinal direction of the elastic layer, then the relationship λtd>λmd>λnd is satisfied, where λtd is 2.0 W / (m K) or greater and λnd is 1.3 W / (m K) or greater.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a fixing member and a thermal fixing device used in an electrophotographic image forming apparatus such as a copier or a printer. [Background technology]

[0002] Due to the recent increase in demand for chromatic images, there is a demand for image forming apparatuses that form chromatic images to output uniformly glossy images. Furthermore, from the viewpoint of energy conservation, there is a growing trend to make the most efficient use of energy consumed by fixing devices, and at the same time, there is a demand for miniaturization of image forming apparatuses. In order to provide a uniformly glossy image, a fixing member of a fixing device generally has a structure in which an elastic layer containing heat-resistant silicone rubber is disposed on a substrate formed of metal or heat-resistant resin, and further coated or formed with a thin layer of fluororesin via an adhesive. By providing the fixing member with an elastic layer, the fixing member can conform to the uneven shape of the paper in the fixing nip, and can apply heat and pressure uniformly to the unfixed toner image.

[0003] Furthermore, from the perspective of energy conservation, the elastic layer of a fixing member requires high thermal conductivity in addition to its elastic function. Generally, a heat-resistant rubber material such as silicone rubber is blended with a highly thermally conductive inorganic filler as a thermally conductive filler to achieve the desired thermal conductivity and elasticity. However, blending a large amount of thermally conductive filler to achieve high thermal conductivity can harden the elastic layer and cause it to lose its elastic function. Furthermore, repeated compression within the fixing nip increases the number of areas where localized stress concentrations occur at the interface between the thermally conductive filler and the silicone rubber, which can lead to fracture of the elastic layer under conditions of repeated high stress. Therefore, a method is needed to increase thermal conductivity without increasing the amount of thermally conductive filler.

[0004] Because the fixing member applies heat to the toner and recording material, its surface temperature drops as the recording material passes due to a time lag with respect to the temperature control by the temperature control circuit. Therefore, the amount of heat applied to the recording material and toner at the leading edge of the fixing member on the second rotation is smaller than that at the trailing edge of the first rotation. As a result, the gloss of the image on the same recording material at the leading edge of the fixing member on the second rotation relative to the direction of transport of the recording material may be lower than that at the trailing edge of the fixing member on the first rotation, resulting in a sharp gloss difference (gloss unevenness, hereafter referred to as gloss step) in the image. In other words, the temperature difference between the fixing member is particularly large between the first and second rotations, resulting in a large gloss step between the portion of a fixed image fixed at the trailing edge of the fixing member on the first rotation and the portion fixed at the leading edge of the fixing member on the second rotation. Especially from the perspective of energy conservation, the smaller the fixing member, the shorter the rotation time of the fixing member (= circumferential length of the fixing member divided by transport speed), which tends to make the gloss step more noticeable.

[0005] As a conventional technique for improving the gloss difference between the first and second revolutions of the fixing member, Patent Document 1 proposes a heat fixing device in which a cooling means cools the surface of the heat fixing member before the recording material is inserted. By lowering the temperature of the fixing member before the recording material is inserted, the temperature difference between the rear end of the first revolution and the front end of the second revolution of the fixing member is reduced, thereby reducing the gloss difference. Furthermore, Patent Document 2 discloses a fixing unit that has a heat transfer sheet that transfers heat from a heating member located inside the fixing member in the conveying direction of the recording material, thereby reducing the difference in heat quantity in the conveying direction of the recording material. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 11-038826 [Patent Document 2] Japanese Patent Application Publication No. 2018-205336 Summary of the Invention [Problem to be solved by the invention]

[0007] According to the inventors' investigations, the heat fixing device disclosed in Patent Document 1 can mitigate the steep gloss difference described above. However, the temperature of the fixing member, once heated, is lowered, and the amount of heat applied to the fixing member is not fully utilized. Furthermore, the fixing device disclosed in Patent Document 2 has an increased heat capacity as a fixing device due to the heat transfer sheet, and requires more energy to heat the fixing device to a predetermined temperature. One aspect of the present disclosure is to provide a fixing member for a thermal fixing device that can prevent the occurrence of gloss variations in an electrophotographic image due to a temperature difference between the first and second revolutions of the fixing member while suppressing a decrease in heat utilization efficiency. Another aspect of the present disclosure is to provide a thermal fixing device that can form high-quality electrophotographic images. [Means for solving the problem]

[0008] According to one aspect of the present disclosure, An electrophotographic fixing member having an endless shape, The device has an endless base layer and an elastic layer on an outer peripheral surface of the base layer, the elastic layer includes a silicone rubber and a filler dispersed in the silicone rubber; the total blending amount of the filler in the elastic layer is 30% by volume or less based on the total volume of the elastic layer; When the thermal conductivity of the elastic layer in the circumferential direction is λtd, the thermal conductivity in the thickness direction is λnd, and the thermal conductivity in the longitudinal direction is λmd, The relationship λtd>λmd>λnd is satisfied, A fuser member is provided having a λtd of 2.0 W / (m·K) or more and a λnd of 1.3 W / (m·K) or more.

[0009] According to another aspect of the present disclosure, there is provided a thermal fixing device having a heating member and a pressure member arranged opposite the heating member, wherein the heating member is the fixing member described above. [Effects of the Invention]

[0010] According to one aspect of the present disclosure, it is possible to obtain a fixing member for a thermal fixing device that can prevent the occurrence of gloss variations in an electrophotographic image caused by a temperature difference between the first and second revolutions of the fixing member while suppressing a decrease in heat utilization efficiency. According to one aspect of the present disclosure, it is possible to obtain a thermal fixing device that can form high-quality electrophotographic images. [Brief explanation of the drawings]

[0011] [Figure 1] 4A and 4B are explanatory diagrams illustrating the direction of heat conduction of an elastic layer of a fixing member according to an embodiment of the present disclosure. [Figure 2] 1A and 1B are explanatory views of a charging step of a layer of an elastic layer-forming composition in a method for manufacturing a fixing member according to one embodiment of the present disclosure, in which (a) is a top view and (b) is a cross-sectional view. [Figure 3] 1A and 1B are explanatory diagrams illustrating the mechanism of filler orientation when a composition layer for forming an elastic layer is placed in an electric field, where (a) is a schematic diagram showing an example of the filler orientation state in a circumferential-thickness cross section, and (b) is an explanatory diagram of the force applied to the filler. [Figure 4] 1A and 1B are explanatory views of the state before the elastic layer-forming composition layer is placed in an electric field, in which (a) is a cross-sectional view in the circumferential direction-thickness direction, and (b) is a cross-sectional view in the longitudinal direction-thickness direction. [Figure 5] 1A and 1B are explanatory diagrams of the state when a composition layer for forming an elastic layer is placed in an electric field to orient the filler, where (a) is a cross-sectional view in the circumferential direction-thickness direction, and (b) is a cross-sectional view in the longitudinal direction-thickness direction. [Figure 6] 1A and 1B are explanatory diagrams of examples of endless-shaped fixing members according to the present disclosure, in which (a) is a cross-sectional view parallel to the circumferential direction of an endless belt-shaped fixing member, and (b) is a cross-sectional view parallel to the circumferential direction of a roller-shaped fixing member. [Figure 7] 10A and 10B are explanatory diagrams illustrating a surface layer forming step in a method for manufacturing a fixing member according to one embodiment of the present disclosure. [Figure 8] 1 is a cross-sectional view of a thermal fixing device according to one embodiment of the present disclosure. [Figure 9] FIG. 10 is a cross-sectional view of a thermal fixing device according to another embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012] The inventors conducted extensive research to achieve the above objective. In the process, they investigated a configuration in which a thermally conductive filler was incorporated into the elastic layer of the fixing member to increase the thermal conductivity in the circumferential direction. This would allow heat to be absorbed by the recording material, and heat would be supplied from the upstream and downstream sides of the circumferential direction to the area where the temperature had dropped. Hereinafter, the thermal conductivity in the circumferential direction will also be referred to as "λtd." While incorporating a large amount of thermally conductive filler into the elastic layer can improve λtd, the inclusion of a large amount of thermally conductive filler increases the hardness of the elastic layer. Therefore, to prevent the increase in hardness of the elastic layer, they investigated a λtd of 2.0 W / (m·K) or more, assuming that the thermally conductive filler content in the elastic layer is 30% by volume or less based on the total volume of the elastic layer.

[0013] As a result, they found that using a filler with a plate-like crystal structure, such as hexagonal boron nitride, as a thermally conductive filler is effective. Hexagonal boron nitride has a layered structure in which two-dimensional structures in which multiple six-membered rings formed by alternating covalent bonds between nitrogen and boron are bonded in the plane direction are alternately stacked. The thermal conductivity in the plane direction is extremely high, for example, 600 W / (m·K). Furthermore, because hexagonal boron nitride has a plate shape, they found that λtd can be increased by incorporating it in the elastic layer with a circumferential orientation.

[0014] However, when hexagonal boron nitride is oriented in the circumferential direction, its thermal conductivity in the direction perpendicular to the crystal plane is extremely low at approximately 3 W / (m·K), and the thermal conductivity in the thickness direction of the elastic layer is low. This means that when a heat source is placed on the back surface of the fixing member, heat conduction to the surface of the fixing member is hindered, which is not desirable for efficiently applying heat to fix unfixed toner. Therefore, the inventors conducted further research and discovered a new elastic layer configuration that can achieve high values ​​for both λtd and λnd while keeping the content of thermally conductive filler to 30 volume % or less of the total volume of the elastic layer.

[0015] Specifically, an endless electrophotographic fixing member according to one embodiment of the present disclosure includes an endless base layer and an elastic layer on the outer peripheral surface of the base layer. The elastic layer contains silicone rubber and a filler dispersed in the silicone rubber, and the total filler content of the elastic layer is 30 volume % or less based on the total volume of the elastic layer. Furthermore, when the thermal conductivity of the elastic layer in the circumferential direction is λtd, the thermal conductivity in the thickness direction is λnd, and the thermal conductivity in the longitudinal direction is λmd, the relationship λtd > λmd > λnd is satisfied, and λtd is 2.0 W / (m·K) or more and λnd is 1.3 W / (m·K) or more.

[0016] Because λtd is high at 2.0 W / (m·K) or more, heat from the area where the recording material has not passed (the leading edge of the second revolution) is efficiently replenished to the area where the surface temperature of the fixing member has dropped after the recording material has passed (the trailing edge of the first revolution).This makes it possible to reduce the temperature difference at the boundary between the first and second revolutions of the fixing member.In addition, because λnd is high at 1.3 W / (m·K) or more, it is thought that shortening the time it takes for heat generated by the heating source to be transferred to the surface of the fixing member also contributes to reducing the temperature difference. A fixing member and a thermal fixing device according to an embodiment of the present disclosure will be described in detail below based on a specific configuration.

[0017] (1) Outline of the fixing member The fixing member of this embodiment will be described in detail with reference to the drawings. Figures 6(a) and (b) are schematic cross-sectional views showing a fixing member according to this embodiment. Figure 6(a) shows an example of a fixing member in the form of a belt, and Figure 6(b) shows an example of a fixing member in the form of a roller. In Figures 6(a) and 6(b), reference numeral 3 denotes a base (base layer), and reference numeral 4 denotes an elastic layer containing silicone rubber that covers the outer peripheral surface of the base 3. In Figure 6, the radial direction corresponds to the thickness direction of the elastic layer.

[0018] As described above, the fixing member according to this embodiment has a substrate 3 and an elastic layer 4 containing silicone rubber on the substrate 3. As shown in these figures, the fixing member can have a surface layer 6 on the elastic layer 4 containing silicone rubber. An adhesive layer 5 can also be provided between the elastic layer 4 containing silicone rubber and the surface layer 6. In this case, the surface layer 6 is fixed to the outer peripheral surface of the elastic layer 4 containing silicone rubber by the adhesive layer 5. All of the fixing members shown in FIG. 6 have an endless shape. An endless shape is a shape that allows the same part to pass through the fixing nip portion multiple times (endlessly) by rotating in the circumferential direction. Specific examples include an endless belt shape and a roller shape.

[0019] (2) Substrate When the fixing member is in the form of a belt as shown in FIG. 6(a), the substrate 3 can be made of a metal such as an electroformed nickel sleeve or a stainless steel sleeve, or a heat-resistant resin such as polyimide. In particular, when the thermal fixing device uses an electromagnetic induction heating method, an alloy primarily composed of nickel or iron is used to improve heat generation efficiency. The outer surface of the substrate 3 (the surface facing the elastic layer) can be provided with a layer to improve adhesion to the elastic layer. That is, the elastic layer 4 need only be provided on the outer peripheral surface of the substrate 3, and other layers can be provided between the elastic layer 4 and the substrate 3. Furthermore, the inner surface of the substrate 3 (the surface opposite the outer surface) can be provided with an additional layer to impart functions such as wear resistance and lubricity. When the substrate is in the form of a belt, a core is inserted into the sleeve during the following manufacturing process. When the fixing member is a fixing belt, the fixing belt preferably has an inner diameter of 20 mm to 130 mm, which limits the downsizing of the heater and heater holder inserted inside and prevents the fixing device from becoming too large.

[0020] When the fixing member is in the form of a roller as shown in Fig. 6(b), a conductive mandrel (hereinafter also referred to as a core metal) made of a metal or alloy such as aluminum or iron can be used for the base 3, as long as it has the strength to withstand the heat and pressure in the thermal fixing device. In Fig. 6(b), a solid core metal is used for the base 3, but a hollow core metal may also be used for the base 3, and a heat source such as a halogen lamp may be provided inside.

[0021] (3) Elastic layer The elastic layer 4 contains silicone rubber as a binder and filler 7 dispersed in the silicone rubber. The content of the filler in the elastic layer is 30% by volume or less, based on the volume of the elastic layer. Furthermore, when the thermal conductivity of the elastic layer 4 in the circumferential direction is λtd, the thermal conductivity in the thickness direction is λnd, and the thermal conductivity in the direction perpendicular to the circumferential direction is λmd, the relationships λtd>λmd>λnd are satisfied, λtd is 2.0 W / (m·K) or more, and λnd is 1.3 W / (m·K) or more. By setting the total filler content in the elastic layer to 30% by volume or less, based on the volume of the elastic layer, the rubber component content in the elastic layer can be prevented from becoming too low. As a result, the elastic layer can be provided with sufficient elasticity and durability to withstand long-term use. Here, the tensile modulus of the elastic layer is preferably 0.20 MPa or more and 1.20 MPa or less. By setting the modulus of the elastic layer within this range, the outer surface of the fixing member can be made to conform well to the unevenness of the paper, contributing to the formation of higher-quality electrophotographic images. Note that the modulus of the elastic layer can be adjusted by the filler content as well as the type and amount of each of the components (a) to (d) of the addition-curable liquid silicone rubber described below.

[0022] Furthermore, as described above, the elastic layer according to the present disclosure has a high λtd of 2.0 W / (m·K) or more. This allows the heat from the area where the recording material has not passed (the leading edge of the second revolution) to be efficiently replenished to the area where the surface temperature of the fixing member has dropped after the recording material has passed (the trailing edge of the first revolution). This reduces the temperature difference at the boundary between the first and second revolutions of the fixing member. Furthermore, since the λnd is also high at 1.3 W / (m·K) or more, it is believed that the reduction in the time required for heat generated by the heat source to be transferred to the surface of the fixing member also contributes to the reduction in the temperature difference. Furthermore, even when a heat source is located on the inner periphery of the fixing member, the heat supplied from the heat source to the fixing member is efficiently transferred to the outer periphery of the fixing member, thereby improving the efficiency of heat utilization for thermally fixing unfixed toner.

[0023] The thermal conductivity λnd of the elastic layer in the thickness direction can be calculated from the following formula (2): The thermal conductivity λmd of the elastic layer in the width direction and the thermal conductivity λtd of the elastic layer in the circumferential direction can be calculated from the following formulas (3) and (4). λnd=α nd ×C p ×ρ Equation (2) In equation (2), λnd is the thermal conductivity of the elastic layer in the thickness direction (W / (m·K)), α nd is the thermal diffusivity in the thickness direction (m 2 / s), C p is the specific heat at constant pressure (J / (kg·K)), and ρ is the density (kg / m 3 )

[0024] λmd=α md ×C p ×ρ Equation (3) λtd=α td ×C p ×ρ. Formula (4) In formula (3) and formula (4), α md is the thermal diffusivity in the width direction (m 2 / s), α td is the thermal diffusivity in the circumferential direction (m 2 / s), C p is the specific heat at constant pressure (J / (kg·K)), and ρ is the density (kg / m 3 The method for measuring each parameter will be described in detail in the Examples.

[0025] The elastic layer according to the present disclosure, which has the above-described thermal properties, can be achieved, for example, by orienting a filler having a plate-like crystal structure, such as hexagonal boron nitride, in the circumferential direction and thickness direction of the elastic layer. Such an elastic layer can be produced, for example, by the following method. A layer of a composition for forming an elastic layer (hereinafter also referred to as a "composition layer") containing a filler having a plate-like crystal structure and liquid silicone rubber is formed on a substrate. Since the filler has a plate-like crystal structure, it tends to be oriented in-plane within the composition layer. When the composition layer in this state is cured, an elastic layer with a large λtd and a small λnd is obtained.

[0026] Therefore, the outer surface of the composition layer, in which the filler is present and oriented in the plane, is charged. This causes dielectric polarization of the filler in the composition layer, resulting in orientation in the thickness direction. Furthermore, it is believed that this process causes the filler to bond with each other, forming a circumferential heat transfer path. As a result, an elastic layer can be produced in which λtd is 2.0 W / (m·K) or more, λnd is 1.3 W / (m·K) or more, and the relationship λtd > λmd > λnd is satisfied. The assumed mechanism for orienting the filler by charging the outer surface of the composition layer and the charging method will be described later.

[0027] The composition of the silicone rubber in the elastic layer can be confirmed by performing attenuated total reflection (ATR) measurement using an infrared spectrometer (FT-IR) (for example, product name: Frontier FT IR, manufactured by PerkinElmer). The silicon-oxygen bond (Si-O), which is the main chain structure of silicone, generates a stretching vibration at a wave number of 1020 cm. -1 Furthermore, the methyl group bonded to the silicon atom (Si-CH3) exhibits strong infrared absorption at a wavenumber of 1260 cm due to the deformation vibration caused by its structure. -1 Its presence can be confirmed by the strong infrared absorption in the vicinity.

[0028] The content of cured silicone rubber and filler in the elastic layer can be confirmed using a thermogravimetric analyzer (TGA) (e.g., product name: TGA851, manufactured by Mettler-Toledo). A sample of the elastic layer is cut out with a razor blade, and approximately 20 mg is accurately weighed and placed in an alumina pan used in the instrument. The alumina pan containing the sample is placed in the instrument and heated from room temperature to 800°C at a rate of 20°C per minute under a nitrogen atmosphere, and then maintained at 800°C for one hour. In a nitrogen atmosphere, as the temperature rises, the cured silicone rubber component is decomposed and removed by cracking without being oxidized, resulting in a decrease in the mass of the sample. By comparing the mass before and after measurement, the content of the cured silicone rubber component and filler in the elastic layer can be confirmed.

[0029] (3-1) Silicone rubber When the fixing member is used as a heating member, the elastic layer containing silicone rubber functions as a layer that imparts excellent flexibility to follow the unevenness of the paper during fixing. Silicone rubber has high heat resistance that allows it to maintain flexibility even in environments where the temperature reaches as high as 240°C in the non-paper passing area, making it particularly suitable for use as a binder for the elastic layer. Furthermore, the silicone rubber is preferably electrically insulating or semiconductive so that it can be charged by imparting an electric charge to the surface of the layer of the surface layer-forming composition in the filler orientation process described below. Examples of such silicone rubber include a cured product of an addition-curing liquid silicone rubber.

[0030] (3-1-1) Addition-curing liquid silicone rubber The liquid addition-curable silicone rubber can include (a) an organopolysiloxane having unsaturated aliphatic groups, (b) an organopolysiloxane having silicon-bonded active hydrogen, (c) a catalyst (e.g., a platinum compound), and (d) a cure retarder. (a) functions as a crosslinking point during the curing reaction. (b) is a crosslinking agent. (c) is a catalyst that accelerates the curing reaction. (d) is a curing retarder (inhibitor) that controls the reaction start time. In addition to these, fillers suitable for each purpose can also be mixed and dispersed to impart heat resistance, reinforcement, etc. (a) to (d) will be explained below.

[0031] (3-1-2) Component (a) Any organopolysiloxane having an unsaturated aliphatic group (hereinafter sometimes referred to as component a) can be used as long as it has an unsaturated aliphatic group such as a vinyl group. For example, the following formulas 1 and 2 can be used as component a. one or both of intermediate units selected from the group consisting of intermediate units represented by R1R1SiO and intermediate units represented by R1R2SiO, and R1R1R2SiO 1 / 2 and a molecular terminal represented by the following formula 1.

[0032] [ka]

[0033] one or both of intermediate units selected from the group consisting of intermediate units represented by R1R1SiO and intermediate units represented by R1R2SiO, and R1R1R1SiO 1 / 2 and a molecular terminal represented by the following formula 2.

[0034] [ka]

[0035] (In Formula 1 and Formula 2, each R1 independently represents an unsubstituted hydrocarbon group that does not contain an unsaturated aliphatic group, each R2 independently represents an unsaturated aliphatic group, and each m and n independently represents an integer of 0 or greater.)

[0036] Examples of the unsubstituted hydrocarbon group not containing unsaturated aliphatic groups represented by R1 in Formulas 1 and 2 include methyl, ethyl, propyl, and aryl groups (e.g., phenyl). Methyl is particularly preferred. In addition, in Formula 1 and Formula 2, examples of the unsaturated aliphatic group represented by R2 include a vinyl group, an allyl group (CH2=CH-CH2-), and a 3-butenyl group, with a vinyl group being preferred.

[0037] In Formula 1, linear organosiloxanes where n=0 have unsaturated aliphatic groups only at both ends, while linear organosiloxanes where n=1 or more have unsaturated aliphatic groups at both ends and in the side chain. Furthermore, linear organosiloxanes of Formula 2 have unsaturated aliphatic groups only in the side chain. One type of component a may be used alone, or two or more types may be used in combination.

[0038] Furthermore, when component (a) is used as a raw material for silicone rubber, the viscosity is set to 100 mm from the viewpoint of obtaining excellent moldability. 2 / s or more, 50000mm 2 / s or less. The viscosity (kinematic viscosity) can be measured using a capillary viscometer, a rotational viscometer, or the like in accordance with JIS Z 8803:2011. When using a commercially available component a, the catalog value can be referenced.

[0039] (3-1-3) Component (b) The organopolysiloxane having active hydrogen bonded to silicon is a crosslinking agent that forms a crosslinked structure by reacting with the unsaturated aliphatic groups in component (a) under the catalytic action of the platinum compound. Any organopolysiloxane having a Si-H bond can be used as component (b), but for example, those that satisfy the following conditions can be suitably used. The component b may be used alone or in combination of two or more.

[0040] - The number of hydrogen atoms bonded to silicon atoms is three or more per molecule, from the viewpoint of being able to promote the formation of a crosslinked structure through a reaction with organopolysiloxanes having unsaturated aliphatic groups. The organic group bonded to the silicon atom may be, for example, an unsubstituted hydrocarbon group such as those described above, but is preferably a methyl group. The siloxane skeleton (-Si-O-Si-) may be linear, branched, or cyclic. The Si-H bond may be present in any siloxane unit in the molecule. For example, the linear organopolysiloxanes shown in the following formulas 3 and 4 can be used as component b.

[0041] [ka]

[0042] [ka]

[0043] (In Formula 3 and Formula 4, each R1 independently represents an unsubstituted hydrocarbon group that does not contain an unsaturated aliphatic group, p represents an integer of 0 or greater, and q represents an integer of 1 or greater.) As explained in Formula 1 and Formula 2, R1 is an unsubstituted hydrocarbon group that does not contain unsaturated aliphatic groups, and is preferably a methyl group.

[0044] (3-1-4) Component (c) Examples of the hydrosilylation (addition curing) catalyst that can be used include platinum compounds. Specific examples include platinum carbonylcyclovinylmethylsiloxane complex and 1,3-divinyltetramethyldisiloxane platinum complex. Hereinafter, this may be referred to as component c.

[0045] (3-1-5) Component (d) To adjust the curing reaction rate of hydrosilylation (addition curing), a curing retarder can be added. Specific examples include 2-methyl-3-butyn-2-ol and 1-ethynyl-1-cyclohexanol. Hereinafter, this will be referred to as component d.

[0046] (3-2) Filler The filler 7 in the elastic layer 4 functions to adjust the thermal conductivity of the elastic layer. In the present disclosure, it is preferable to use a filler with a plate-like crystal structure, such as hexagonal boron nitride. For example, hexagonal boron nitride has a layered structure in which two-dimensional structures, each consisting of a large number of six-membered rings formed by alternating covalent bonds between nitrogen and boron, are alternately stacked in the in-plane direction. The filler also has anisotropic thermal conductivity, with a value of approximately 600 W / (m·K) in the in-plane direction and approximately 3 W / (m·K) in the direction perpendicular to the plane.

[0047] This section describes a case where a layer of a composition for forming an elastic layer, which contains a filler having a plate-like crystalline structure and a silicone rubber raw material, is formed to obtain an elastic layer having a thickness of, for example, approximately 100 to 500 μm. Due to its plate shape, the filler tends to be oriented (hereinafter sometimes referred to as "in-plane orientation") in the circumferential direction and in a direction perpendicular to the circumferential direction (hereinafter also referred to as "longitudinal direction"), as shown in FIGS. 4(a) and 4(b). As a result, the λtd and λmd of the elastic layer obtained by curing the layer of the composition can be very high. Meanwhile, because the thermal conductivity of the filler having a plate-like crystalline structure in the thickness direction is low, the λnd of the elastic layer is very small.

[0048] Therefore, in the present disclosure, in order to increase λnd, it is preferable that the filler be oriented in the thickness direction of the elastic layer. A non-limiting method for producing such an elastic layer will be described below with reference to Figures 2 and 3. The production method includes the following steps (i) to (iii).

[0049] Process (i) A layer 401 of a composition for forming an elastic layer (hereinafter also referred to as a "composition layer") containing a thermally conductive filler and silicone rubber raw materials (for example, the above-mentioned components (a), (b), and (c)) is formed on the outer peripheral surface of the base 3.

[0050] Process (ii) The surface of the composition layer 401 is charged while the substrate 3 on which the composition layer 401 is formed is rotated in the direction of arrow A2. Note that although a positive charge is applied in Fig. 2, the present invention is not limited thereto and the surface may be charged negatively. An electric field is formed in the thickness direction of the composition layer whose surface is charged. This causes dielectric polarization of the filler, and the polarization charge generated in the filler generates a rotational torque in the direction of the electric field (thickness direction of the composition layer). Furthermore, as the composition layer rotates, as shown in FIG. 3, a diagonal vector force is applied to the filler 7 in the elastic layer 4 relative to the film thickness, which is the sum of a force in the electric field direction and an inertial force in the tangential direction (opposite to the rotation direction). As a result, the filler 7, which was present in the composition layer 401 in the state shown in FIGS. 4(a) and 4(b) before charging, changes to the state shown in FIGS. 5(a) and 5(b). Specifically, the longitudinal direction is oriented in the direction of the resultant force of the force in the electric field direction and the inertial force, and the filler gradually moves through the composition layer due to its charge, resulting in a state in which adjacent fillers are in contact with each other. As a result, λnd can be increased. It was thought that the thermal conductivity (λtd) of the composition layer in the circumferential direction would relatively decrease as a result of the filler rotating in the thickness direction of the composition layer 401. However, the thermal conductivity λtd in the circumferential direction could also be increased, possibly because the rotation of the filler caused adjacent fillers to come into contact with each other, forming a heat transfer path in the circumferential direction.

[0051] Process (iii) The composition layer in which the filler is present in the state shown in FIGS. 5(a) and 5(b) is cured to form the elastic layer according to the present disclosure.

[0052] (3-3) Charging method The method for charging the surface of the composition layer in the above step (ii) is preferably a non-contact method, and more preferably a corona charger, which can easily and inexpensively charge the surface uniformly. As a non-limiting example of the charging method, a method for charging the composition layer using a corona charger will be described below with reference to FIG. 2. There are two types of corona charging methods: the scorotron method, which has a grid electrode between the corona wire and the object to be charged, and the corotron method, which does not have a grid electrode.The scorotron method is preferred from the viewpoint of superior controllability of the surface potential of the object to be charged.

[0053] As shown in FIGS. 2(a) and 2(b), the corona charger 2 includes a front block 201, a rear block 202, and shields 203 and 204. A discharge wire 205 is stretched between the front block 201 and the rear block 202. When a charging bias is applied from a high-voltage power supply, the discharge wire 205 discharges and charges the surface of a composition layer 401 on a substrate (a body to be charged). Similar to the configuration of a typical corona charger, a high voltage is applied to the discharge wire 205, which serves as a discharging member. The ion flow resulting from the discharge to the shields 203 and 204 is controlled by applying a high voltage to a grid 206, thereby charging the surface of the composition layer 401 to a predetermined potential. Since the substrate 3 or the core 1 holding the substrate 3 is grounded (not shown), a predetermined electric field can be generated in the composition layer 401 by controlling the surface potential of the composition layer 401.

[0054] To describe in detail an example of a method for producing an elastic layer using the corona charger 2, first, a composition layer is formed on the outer peripheral surface of the substrate 3. The method for forming the composition layer is not particularly limited, and known methods such as ring coating and blade coating can be used. However, the ring coating method is particularly preferred because it is easy to make the filler present in a state oriented in the in-plane direction of the composition layer.

[0055] Next, as shown in FIG. 2(a), corona chargers 2 are placed adjacent to and facing each other along the width direction of the composition layer 401. A voltage is applied to the grid 206 of the corona charger 2, and while the grid 206 is in a discharged state, the substrate 3 is rotated at 141 rpm for 160 seconds, for example, to charge the surface of the composition layer. The distance between the surface of the composition layer 401 and the grid 206 can be 1 mm to 10 mm. By charging the surface of the composition layer 401 in this manner, an electric field is generated within the composition layer 401. The rotational force resulting from the dielectric polarization of the filler when the composition layer is placed in the electric field and the inertial force associated with the rotation orient the filler as shown in FIGS. 5(a) and 5(b). The composition layer is then cured by heating or the like to fix the orientation of the filler and form an elastic layer according to the present disclosure.

[0056] From the viewpoint of generating effective electrostatic interactions with the filler, the voltage applied to the grid 206 is preferably in the range of 0.6 kV to 3.0 kV in absolute value (1.2 to 6 kV in Vp-p (peak-to-peak voltage) in the case of AC application). When using an electric field to form filler orientation in the thickness direction of the elastic layer, it is important to generate an electric field in the thickness direction of the elastic layer 4. If the sign of the applied voltage is the same as the sign of the voltage applied to the wire, the effect obtained is the same, even though the direction of the electric field will be opposite whether it is negative or positive. Furthermore, when AC charging is used to suppress the liquid surface flow described below, it is preferable to match the phase of the waveforms of the wire and grid.

[0057] The orientation state of the filler can be adjusted, for example, by controlling the voltage applied to the grid 206. This is presumably related to the dielectric constant of the silicone rubber and the dielectric constant of the filler. When the difference between the dielectric constant of the silicone rubber and the dielectric constant of the filler is large, the filler can be more oriented even with a relatively small applied voltage. Note that if the voltage applied to the grid 206 is too high, the electrostatic repulsion force due to the surface charge of the elastic layer increases, causing the liquid surface to flow, which may deteriorate the surface properties of the elastic layer 4. Therefore, it is more preferable that the voltage applied to the grid 206 be in the range of 0.6 kV to 1.5 kV in absolute value (1.2 to 3 kV in Vp-p (peak-to-peak voltage) when AC is applied). This liquid surface flow can be alleviated by applying AC charging.

[0058] The rotation speed of the substrate in the charging step (ii) is not particularly limited, but is preferably 10 rpm to 500 rpm as a guideline. The treatment time is preferably 20 seconds or more to ensure that the composition layer is charged reliably.

[0059] The discharge wire 205 may be made of stainless steel, nickel, molybdenum, tungsten, or the like. However, tungsten is preferred because it is one of the most stable metals. The discharge wire stretched inside the shield may have either a circular cross-sectional shape or a sawtooth shape. The diameter of the discharge wire 205 is preferably 40 μm to 100 μm. By keeping the diameter of the discharge wire within this range, cutting of the discharge wire by ions during discharge can be suppressed, and the voltage required to generate a corona discharge does not need to be excessively high. The voltage applied to the discharge wire 205 can be either a DC voltage or an AC voltage. In the case of an AC voltage, a frequency of approximately 0.01 Hz to 1000 Hz is preferred. The voltage can be generated by outputting a square wave, a sine wave, or the like using an arbitrary waveform generator.

[0060] (3-4) Hexagonal boron nitride Hexagonal boron nitride has a low volumetric specific heat among heat-conductive fillers, which can reduce the volumetric specific heat of the elastic layer. This is effective in shortening the warm-up time of the fixing device and saving energy. In addition, because it has insulating properties, it can maintain its insulating properties as a composition layer and is suitable for applying a high electric field using a corona charger. When hexagonal boron nitride is used as the filler, the content of hexagonal boron nitride in the elastic layer is preferably 20% by volume or more and 25% by volume or less based on the total volume of the elastic layer. A content of 20% by volume or more can impart sufficiently high thermal conductivity (λtd, λnd) to the elastic layer, while a content of 25% by volume or less prevents the viscosity of the composition from becoming too high, making it less likely to interfere with application of the composition layer and with the orientation of the filler when an electric field is applied.

[0061] The orientation state of hexagonal boron nitride can be evaluated by the diffraction intensity ratio calculated by substituting the diffraction intensity of the (002) plane and the diffraction intensity of the (100) plane obtained by X-ray diffraction (XRD) into the following equation. Intensity ratio = I(100) / (I(100)+I(002)) I(100): Diffraction intensity at 2θ=41.6° I(002): Diffraction intensity at 2θ=26.7°

[0062] The diffraction intensity ratio increases as the filler becomes more oriented in the film thickness direction. The diffraction intensity ratio of the rubber layer cured in an uncharged state was 0.007, while the diffraction intensity ratio of the rubber layer of the present disclosure cured after charging was 1.222, confirming that the influence of charging increased the filler orientation in the film thickness direction.

[0063] To fill the gaps between the main thermally conductive fillers, a sub-thermally conductive filler other than the main thermally conductive filler may be blended. Examples of the sub-thermally conductive filler to be blended include alumina, zinc oxide, magnesium oxide, silicon metal, silicon carbide, silica, and carbon. The thermally conductive filler may be surface-treated to obtain excellent affinity with silicone and excellent electrical resistance.

[0064] (4) Adhesive layer of fixing member As shown in FIG. 6, the adhesive layer 5 is a layer formed by adhering the elastic layer 4 and the surface layer (release layer) 6 together using, for example, an addition-curing silicone rubber adhesive. The adhesive is preferably an addition-curing silicone rubber containing a self-adhesive component. Specifically, the adhesive contains an organopolysiloxane having multiple unsaturated aliphatic groups, typically vinyl groups, in its molecular chain, a hydrogenorganopolysiloxane, and a platinum compound as a crosslinking catalyst. The adhesive cures by an addition reaction. Any known adhesive can be used. Examples of self-adhesive components include:

[0065] a silane having at least one, preferably two or more functional groups selected from the group consisting of an alkenyl group such as a vinyl group, a (meth)acryloxy group, a hydrosilyl group (SiH group), an epoxy group, an alkoxysilyl group, a carbonyl group, and a phenyl group; Organosilicon compounds such as cyclic or linear siloxanes having 2 to 30 silicon atoms, preferably 4 to 20 silicon atoms; A non-silicon-based (i.e., silicon-free) organic compound that may contain oxygen atoms in the molecule, provided that it contains one to four, preferably one to two, aromatic rings such as monovalent to tetravalent, preferably divalent to tetravalent, phenylene structures per molecule, and at least one, preferably two to four, functional groups capable of participating in a hydrosilylation addition reaction (e.g., alkenyl group, (meth)acryloxy group) per molecule. The above self-adhesive components may be used singly or in combination of two or more.

[0066] Filler components can be added to the adhesive to adjust viscosity and ensure heat resistance within the scope of the present disclosure. Examples of such filler components include the following: Silica, alumina, iron oxide, titanium oxide, cerium oxide, cerium hydroxide, carbon black, etc. Such addition-curing silicone rubber adhesives are commercially available and readily available. The thickness of the adhesive layer is preferably 20 μm or less. By setting the thickness to 20 μm or less, the thermal resistance of the fixing member can be set low, and heat from the inner surface (substrate side) can be efficiently transferred to the recording material (recording medium).

[0067] (5) Surface layer of fixing member The surface layer 6 is made of a fluororesin, and a tube method or a coating method is used as a molding method. The following describes the tube method, in which a resin exemplified below is molded into a tube shape and then coated. Tetrafluoroethylene-perfluoro(alkyl vinyl ether) copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), etc. Among the resin materials listed above, PFA is preferred from the viewpoint of excellent moldability and toner releasability. The thickness of the fluororesin layer (surface layer) is preferably 10 μm or more and 50 μm or less, because this maintains the elasticity of the underlying elastic layer when laminated, prevents the surface hardness as a fixing member from becoming too high, and ensures abrasion resistance. The inner surface of the fluororesin tube can be preliminarily treated with sodium, excimer laser, ammonia, or the like to improve adhesiveness.

[0068] 7 is a schematic diagram of an example of a process for laminating a surface layer 6 onto an elastic layer 4 containing silicone rubber via an addition-curing silicone rubber adhesive 5. The addition-curing silicone rubber adhesive 5 is applied to the surface of the elastic layer 4 formed on the outer peripheral surface of the base 3. The outer surface is then coated with a fluororesin tube 6 as the surface layer 6, and laminated. The method for covering the fluororesin tube is not particularly limited, but methods such as covering with an addition-curing silicone rubber adhesive as a lubricant or expanding and covering the fluororesin tube from the outside can be used.

[0069] Using a means not shown, the excess addition-curing silicone rubber adhesive 5 remaining between the elastic layer 4 and the surface layer 6 made of fluororesin is removed by squeezing it out. From the viewpoint of obtaining excellent heat conductivity, the thickness of the adhesive layer 5 after squeezing out is preferably 20 μm or less. Next, the addition-curing silicone rubber adhesive 5 is cured and adhered by heating for a predetermined time using a heating means such as an electric furnace, and both ends in the width direction are cut to the desired length to obtain a fixing member.

[0070] (6) Thermal fixing device The thermal fixing device according to this embodiment is configured so that a pair of heated rollers, belts, or belts are pressed against each other. The type of thermal fixing device is appropriately selected taking into consideration the processing speed, size, and other conditions of the image forming apparatus in which the thermal fixing device is installed. In a thermal fixing device, a fixing nip N is formed by pressing a heated fixing member and a pressure member together, and a recording medium S, which serves as a heated object and has an image formed with unfixed toner, is sandwiched and conveyed through this fixing nip N. The image formed with unfixed toner is called a toner image t. When the toner image t is heated and pressurized, the toner image t is melted and mixed, and then cooled to fix the image on the recording medium. Below, specific examples of thermal fixing devices will be given and their configurations will be described, but the scope and applications of the present disclosure are not limited to these.

[0071] (6-1) Fixing belt-pressure belt type thermal fixing device FIG. 8 is a schematic cross-sectional view of an example of a so-called twin-belt type thermal fixing device in which a pair of rotating bodies, namely, a fixing belt 11 and a pressure belt 12, are in pressure contact with each other, and which includes a fixing belt as a fixing member. Note that here, the width direction of the thermal fixing device or the components that make it up is the direction perpendicular to the plane of the paper in Figure 8. The front of the thermal fixing device is the side on which the recording medium S is introduced. Left and right are left and right when viewed from the front of the device. The belt width is the belt dimension in the left-right direction when viewed from the front of the device. The width of the recording medium S is the dimension of the recording medium S in a direction perpendicular to the conveying direction of the recording medium S. Furthermore, upstream and downstream are upstream and downstream with respect to the conveying direction of the recording medium S.

[0072] This thermal fixing device includes fixing members, a fixing belt 11 and a pressure belt 12. The fixing belt 11 and the pressure belt 12 are each a fixing belt including a flexible base made of a metal whose main component is nickel, as shown in FIG. 6(a), stretched over two rollers. The heating means for the fixing belt 11 employs a heating source (induction heating element, excitation coil) capable of heating by highly energy-efficient electromagnetic induction heating. The induction heating element 13 comprises an induction coil 13a, an excitation core 13b, and a coil holder 13c that holds them. The induction coil 13a uses a litz wire wound flat in an oval shape and is placed inside a horizontal E-shaped excitation core 13b that protrudes from the center and both sides of the induction coil. The excitation core 13b is made of a material with high magnetic permeability and low residual magnetic velocity density, such as ferrite or permalloy, which reduces losses in the induction coil 13a and excitation core 13b and enables the fixing belt 11 to be heated efficiently.

[0073] When a high-frequency current is applied from excitation circuit 14 to induction coil 13a of induction heating member 13, the base of fixing belt 11 is inductively heated, and fixing belt 11 is heated from the base side. The surface temperature of fixing belt 11 is detected by temperature detection element 15 such as a thermistor. A signal related to the temperature of fixing belt 11 detected by temperature detection element 15 is sent to control circuit 16. Control circuit 16 controls the power supplied from excitation circuit 14 to induction coil 13a so that the temperature information received from temperature detection element 15 maintains the predetermined fixing temperature, thereby adjusting the temperature of fixing belt 11 to the predetermined fixing temperature. The fixing belt 11 is stretched over a roller 17 as a belt rotating member and a heating side roller 18. The roller 17 and the heating side roller 18 are supported by bearings that allow them to rotate freely between left and right side plates (not shown) of the device.

[0074] Roller 17 is, for example, a hollow iron roller having an outer diameter of 20 mm, an inner diameter of 18 mm, and a thickness of 1 mm, and functions as a tension roller that applies tension to fixing belt 11. Heating side roller 18 is, for example, a highly slidable elastic roller having an outer diameter of 20 mm, an inner diameter of 18 mm, a 1 mm thick iron alloy core metal, and a silicone rubber layer as an elastic layer provided on the core metal. This heating side roller 18 is a drive roller that receives a driving force from a drive source (motor) M via a drive gear train (not shown), and is driven to rotate at a predetermined speed in the clockwise direction indicated by the arrow. By providing the heating side roller 18 with the elastic layer as described above, the driving force input to the heating side roller 18 can be effectively transmitted to the fixing belt 11, and a fixing nip can be formed to ensure separation of the recording medium from the fixing belt 11. Providing the heating side roller 18 with the elastic layer also reduces heat conduction to the heating side roller, which is also effective in shortening the warm-up time.

[0075] When the heating side roller 18 is driven to rotate, the fixing belt 11 rotates together with the roller 17 due to friction between the silicone rubber surface of the heating side roller 18 and the inner surface of the fixing belt 11. The arrangement and size of the roller 17 and the heating side roller 18 are selected according to the size of the fixing belt 11. For example, the dimensions of the roller 17 and the heating side roller 18 are selected so that a fixing belt 11 having an inner diameter of 55 mm when not installed can be stretched over them.

[0076] The pressure belt 12 is stretched by a tension roller 19 and a pressure side roller 20, which serve as belt rotation members. The inner diameter of the pressure belt when not in use is, for example, 55 mm. Like the roller 17 and the heating side roller 18, the tension roller 19 and the pressure side roller 20 are also rotatably supported by bearings between the left and right side plates (not shown) of the device. The tension roller 19 is, for example, a 2 mm thick iron alloy core having an outer diameter of 20 mm, an inner diameter of 16 mm, and a silicone sponge layer to reduce thermal conductivity and reduce heat conduction from the pressure belt 12.

[0077] The pressure side roller 20 is a low-sliding, rigid roller made of an iron alloy, for example, with an outer diameter of 20 mm, an inner diameter of 16 mm, and a thickness of 2 mm. The dimensions of the tension roller 19 and the pressure side roller 20 are also selected to match the dimensions of the pressure belt 12. Here, in order to form a nip portion N between the fixing belt 11 and the pressure belt 12, the pressure side roller 20 is pressed toward the heating side roller 18 at both left and right ends of the rotating shaft in the direction of arrow F by a pressure mechanism not shown in the figure with a predetermined pressure.

[0078] Furthermore, a pressure pad is employed to obtain a wide nip portion N without increasing the size of the device. Specifically, a fixing pad 21 serves as a first pressure pad that presses the fixing belt 11 against the pressure belt 12, and a pressure pad 22 serves as a second pressure pad that presses the pressure belt 12 against the fixing belt 11. The fixing pad 21 and the pressure pad 22 are supported and disposed between left and right side plates (not shown) of the device. The pressure pad 22 is pressed against the fixing pad 21 with a predetermined pressure in the direction of arrow G by a pressure mechanism (not shown). The fixing pad 21, which is the first pressure pad, has a pad base and a sliding sheet (low-friction sheet) 23 that contacts the belt. The pressure pad 22, which is the second pressure pad, also has a pad base and a sliding sheet 24 that contacts the belt. This is because there is a problem of significant wear at the portion of the pad that rubs against the inner circumferential surface of the belt. By interposing the sliding sheets 23 and 24 between the belt and the pad substrate, pad wear can be suppressed and sliding resistance can be reduced, ensuring good belt running performance and durability. The fixing belt is provided with a non-contact discharging brush (not shown), and the pressure belt is provided with a contact discharging brush (not shown).

[0079] The control circuit unit 16 drives the motor M at least when image formation is being performed. This rotates the heating side roller 18, which in turn rotates the fixing belt 11 in the same direction. The pressure belt 12 rotates following the rotation of the fixing belt 11. Here, the most downstream portion of the fixing nip is configured so that the fixing belt 11 and the pressure belt 12 are sandwiched and transported between the roller pair of the heating side roller 18 and the pressure side roller 20, thereby preventing belt slippage. The most downstream portion of the fixing nip is where the pressure distribution in the recording medium transport direction of the fixing nip is greatest.

[0080] When the fixing belt 11 is heated to a predetermined fixing temperature and maintained at that temperature (referred to as temperature regulation), a recording medium S bearing an unfixed toner image t is conveyed to the nip N between the fixing belt 11 and the pressure belt 12. The recording medium S is introduced with the side bearing the unfixed toner image t facing the fixing belt 11. As the unfixed toner image t of the recording medium S is nipped and conveyed while remaining in close contact with the outer peripheral surface of the fixing belt 11, heat is applied from the fixing belt 11, and the unfixed toner image t is fixed to the surface of the recording medium S by the application of pressure. At this time, heat from the heated substrate of the fixing belt 11 is efficiently transported toward the recording medium S through an elastic layer with enhanced thermal conductivity in the thickness direction. The recording medium S is then separated from the fixing belt by a separating member 25 and conveyed.

[0081] (6-2) Fixing belt-pressure roller type thermal fixing device FIG. 9 is a schematic diagram showing an example of a fixing device using a fixing belt and pressure roller system with a ceramic heater as the heating element. In FIG. 9, 11 denotes a cylindrical or endless fixing belt, such as that described above. A heat-resistant and heat-insulating belt guide 30 holds the fixing belt 11. A ceramic heater 31 for heating the fixing belt 11 is fitted into a groove formed along the length of the guide and fixedly supported at the position where the belt guide 30 contacts the fixing belt 11 (approximately the center of the underside of the belt guide 30). The fixing belt 11 is loosely fitted around the belt guide 30. A pressure-applying rigid stay 32 is inserted inside the belt guide 30.

[0082] A pressure roller 33 is disposed below the fixing belt 11 so as to oppose the fixing belt 11. In this example, the pressure roller is an elastic pressure roller, that is, a core 33a with an elastic silicone rubber layer 33b provided on it to reduce hardness. The elastic pressure roller is disposed with both ends of the core 33a rotatably supported by bearings between the front and rear chassis side plates (not shown) of the device. The elastic pressure roller is covered with a PFA (tetrafluoroethylene / perfluoroalkyl ether copolymer) tube to improve surface properties. Compressed pressure springs (not shown) are respectively provided between both ends of the pressure rigid stay 32 and spring bearing members (not shown) on the device chassis side, thereby applying a downward force to the pressure rigid stay 32. As a result, the lower surface of the ceramic heater 31 disposed on the lower surface of the heat-resistant resin belt guide 30 and the upper surface of the pressure roller 33 come into pressure contact with each other with the fixing belt 11 sandwiched therebetween, forming a fixing nip N.

[0083] The pressure roller 33 is driven to rotate in the counterclockwise direction indicated by arrow 41 by a driving means (not shown). A rotational force acts on the fixing belt 11 due to friction between the outer surfaces of the pressure roller 33 and the fixing belt 11 caused by the rotational driving of the pressure roller 33. The fixing belt 11 then rotates around the outside of the belt guide 30 in the clockwise direction indicated by arrow 42 at a peripheral speed that corresponds approximately to the rotational peripheral speed of the pressure roller 33, while its inner surface slides in close contact with the lower surface of the ceramic heater 31 at the fixing nip N.

[0084] (Pressure roller drive system). The pressure roller 33 starts rotating in response to a print start signal, and the ceramic heater 31 starts heating up. After that, at a predetermined moment, a recording medium S bearing an unfixed toner image t as a heated material is introduced between the fixing belt 11 and the pressure roller 33 in the fixing nip N, with the toner image bearing surface facing the fixing belt 11. The predetermined moment refers to the moment when the peripheral speed of the fixing belt 11, caused by the rotation of the pressure roller 33, becomes steady and the temperature of the temperature detection element 34 on the upper surface of the ceramic heater reaches a predetermined temperature, for example, 180°C. The recording medium S then comes into close contact with the lower surface of the ceramic heater 31 via the fixing belt 11 in the fixing nip N and moves through the fixing nip N together with the fixing belt 11. During this movement and passage, heat from the fixing belt 11 is applied to the recording medium S, and the toner image t is heat-fixed to the surface of the recording medium S. After passing through the fixing nip N, the recording medium S is separated from the outer surface of the fixing belt 11 and transported.

[0085] The ceramic heater 31 serving as the heating element is a horizontally elongated linear heating element with a low heat capacity, with its longitudinal direction perpendicular to the direction of movement of the fixing belt 11 and recording medium S. The ceramic heater 31 preferably has a basic configuration consisting of a heater substrate 31a made of aluminum nitride or the like, a heat-generating layer 31b provided on the surface of the heater substrate 31a along its longitudinal direction, and a protective layer 31c made of glass, fluororesin, or the like provided on top of the heater substrate 31a. The heat-generating layer 31b is preferably formed by applying an electrically resistive material such as Ag / Pd (silver / palladium) to a thickness of approximately 10 μm and a width of 1 to 5 mm by screen printing or the like. However, the ceramic heater used is not limited to this type of material.

[0086] When a current is applied between both ends of the heat generating layer 31b of the ceramic heater 31, the heat generating layer 31b generates heat, and the temperature of the heater 31 rises rapidly. The ceramic heater 31 is fixedly supported by being fitted with the protective layer 31c side facing upward into a groove formed along the longitudinal direction of the guide at approximately the center of the underside of the belt guide 30. In the fixing nip N that comes into contact with the fixing belt 11, the surface of the sliding member 31d of the ceramic heater 31 and the inner peripheral surface of the fixing belt 11 come into contact with each other and slide against each other. As described above, in the thermal fixing device using the fixing belt 11 according to the present disclosure as a heating belt, heat supplied to the fixing belt by the heating means (heater) arranged in contact with the inner circumferential surface of the fixing belt flows easily in the circumferential direction and thickness direction of the elastic layer. Therefore, it is possible to suppress the occurrence of gloss unevenness in an electrophotographic image caused by the temperature difference between the first and second revolutions of the fixing member, and it is possible to efficiently use the heat for thermal fixing of unfixed toner. [Example]

[0087] The present disclosure will be described in more detail below using examples. [Example 1] (1) Preparation of addition-curable liquid silicone rubber composition First, 98.6 parts by mass of a silicone polymer having vinyl groups, which are unsaturated aliphatic groups, only at both ends of the molecular chain and methyl groups as unsubstituted hydrocarbon groups containing no other unsaturated aliphatic groups, was prepared as component a. This silicone polymer (trade name: DMS-V35, manufactured by Gelest, viscosity 5000 mm) 2 / s) will be referred to as "Vi" from here on. Next, 80 parts by mass of hexagonal boron nitride (trade name: SGP, manufactured by Denka Co., Ltd.) was added as a thermally conductive filler to this Vi and mixed thoroughly to obtain mixture 1.

[0088] Next, 0.2 parts by mass of 1-ethynyl-1-cyclohexanol (manufactured by Tokyo Chemical Industry Co., Ltd.), a cure retarder as component d, dissolved in the same mass of toluene was added to mixture 1 to obtain mixture 2.

[0089] Next, 0.1 parts by mass of a hydrosilylation catalyst (platinum catalyst: a mixture of 1,3-divinyltetramethyldisiloxane platinum complex, 1,3-divinyltetramethyldisiloxane, and 2-propanol) as component c was added to mixture 2 to obtain mixture 3.

[0090] Furthermore, as component b, a silicone polymer (trade name: HMS-301, manufactured by Gelest, viscosity 30 mm) with a linear siloxane skeleton and silicon-bonded active hydrogen groups only on the side chains was used. 2 1.4 parts by mass of SiH / s (hereinafter referred to as "SiH") was weighed out. This was added to Mixture 3 and mixed thoroughly to obtain an addition-curable liquid silicone rubber composition. The content of hexagonal boron nitride (filler) in the silicone rubber composition was 25% by volume based on the total volume of the elastic layer.

[0091] (2) Fabrication of the fixing belt An electroformed nickel endless belt with an inner diameter of 55 mm, a width of 420 mm, and a thickness of 65 μm was prepared as the substrate. During the series of manufacturing steps, the endless belt was handled with a core inserted inside. A primer (product name: DY39-051A / B; manufactured by Dow Corning Toray Co., Ltd.) was applied almost uniformly to the outer peripheral surface of the substrate to a dry weight of 50 mg, and after the solvent was dried, the substrate was baked for 30 minutes in an electric furnace set to 160°C. The addition-curable liquid silicone rubber composition prepared above was applied to the primer-treated substrate by ring coating to form a layer of the addition-curable liquid silicone rubber composition 450 μm thick. This is referred to as the uncured endless belt.

[0092] Next, a corona charger was placed facing the uncured endless belt along its generating line, and while the uncured endless belt was rotating at 100 rpm, an AC electric field was applied to the surface of the uncured elastic layer to charge the outer surface of the addition-curable liquid silicone rubber composition layer. The electric field application conditions were as follows: current supplied to the discharge wire of the corona charger: ±150 μA, grid electrode potential: ±1500 V (Vp-p: 3000 V), frequency: 0.025 Hz, charging time: 160 seconds, distance between the grid electrode and the belt: 3 mm. This charged uncured endless belt was placed in an electric furnace and heated at 160°C for 1 minute (primary curing), and then heated at 200°C for 30 minutes (secondary curing). In this way, the layer of addition-curable liquid silicone rubber composition was cured to form an elastic layer.

[0093] Next, an addition-curing silicone rubber adhesive (product name: SE1819CV A / B; manufactured by Dow Corning Toray Co., Ltd.) was applied uniformly to the surface of the elastic layer to a thickness of approximately 20 μm as an adhesive layer. A fluororesin tube (product name: NSE; manufactured by Gunze Co., Ltd.) with an inner diameter of 52 mm and a thickness of 40 μm was then laminated onto this as a release layer while expanding its diameter. The belt surface was then uniformly rubbed from above the fluororesin tube to remove excess adhesive from between the elastic layer and the fluororesin tube, thinning the thickness to approximately 5 μm. The endless belt was heated for 1 hour in an electric furnace set at 200°C to harden the adhesive and fix the fluororesin tube onto the elastic layer. Both ends of the resulting endless belt were cut to obtain a fixing belt with a width of 368 mm.

[0094] (3) Evaluation of fixing belt characteristics (3-1) Thermal conductivity of the elastic layer in the thickness direction The thermal conductivity λnd of the elastic layer in the thickness direction was calculated from the following formula. λnd=α×C p ×ρ In the formula, λnd is the thermal conductivity of the elastic layer in the thickness direction (W / (m K)), and α is the thermal diffusivity in the thickness direction (m 2 / s), C p is the specific heat at constant pressure (J / (kg·K)), and ρ is the density (kg / m 3 ) Here, the thermal diffusivity in the thickness direction α and the specific heat at constant pressure C p The values ​​of ρ and density were determined by the following method.

[0095] ·Thermal diffusivity α The thermal diffusivity α of the elastic layer in the thickness direction was measured at room temperature (25°C) using a cyclic heating method thermal property measurement device (product name: FTC-1, manufactured by Advance Riko Co., Ltd.) Rectangular sample pieces with short sides of 8 mm and long sides of 12 mm were cut out of the elastic layer with a cutter to prepare a total of five sample pieces, and the thickness of each sample piece was measured using the following digital length measuring device. Digital length measuring instrument: Product name: DIGIMICRO (registered trademark) MF-501 flat stylus φ4 mm; manufactured by Nikon Corporation Next, the thermal diffusivity α of each sample was measured five times, and the average value (m 2 The measurement was carried out while applying pressure to the sample using a 1 kg weight. As a result, the thermal diffusivity α of the silicone rubber elastic layer in the thickness direction was 7.95 × 10 -7 m 2 / s.

[0096] Constant pressure specific heat C P The constant pressure specific heat of the elastic layer was measured using a differential scanning calorimeter (trade name: DSC823e, manufactured by Mettler-Toledo K.K.). Specifically, aluminum pans were used as the sample pan and the reference pan. First, as a blank measurement, both pans were empty and the temperature was kept constant at 15°C for 10 minutes, then the temperature was increased to 215°C at a rate of 10°C / min, and the temperature was kept constant at 215°C for another 10 minutes. Measurement was then performed using the same program. Next, 10 mg of synthetic sapphire, whose isobaric specific heat is known, was used as the reference material, and measurements were performed using the same program. Next, a 10 mg measurement sample, the same amount as the synthetic sapphire reference material, was cut out from the elastic layer and set in the sample pan, and measurements were performed using the same program. These measurement results were analyzed using the specific heat analysis software attached to the differential scanning calorimeter, and the isobaric specific heat at 25°C, C, was calculated from the average of the five measurement results. P was calculated. As a result, the specific heat at constant pressure of the silicone rubber elastic layer was found to be 1.27 J / (g·K).

[0097] ·Density ρ The density of the elastic layer was measured using a dry automatic density meter (product name: Accupyc 1330-01, manufactured by Shimadzu Corporation). 3 A sample cell was used, and a sample piece was cut out from the elastic layer so that it filled approximately 80% of the cell volume. The mass of this sample piece was measured and then placed in the sample cell. This sample cell was set in the measurement section of the device, and after gas replacement using helium as the measurement gas, the volume measurement was carried out 10 times. The density of the elastic layer was calculated from the mass of the sample piece and the measured volume for each measurement, and the average value was calculated. As a result, the density of the silicone rubber elastic layer was 1.29 g / cm 3 It was. From the above, the unit converted specific heat of the elastic layer at constant pressure C p (J / (kg·K)) and density ρ(kg / m 3 ), and the measured thermal diffusivity α(m 2 / s), the thermal conductivity λnd in the thickness direction of the elastic layer was calculated to be 1.40 W / (m·K).

[0098] (3-2) Thermal conductivity of the elastic layer in the longitudinal and circumferential directions The thermal conductivity λmd in the longitudinal direction and the thermal conductivity λtd in the circumferential direction of the elastic layer were calculated using the following formulas. λmd=αmd×Cp×ρ λtd=αtd×Cp×ρ In the formula, αmd is the thermal diffusivity in the width direction (m 2 / s), αtd is the thermal diffusivity in the circumferential direction (m 2 / s), Cp is the specific heat at constant pressure (J / (kg K)), ρ is the density (kg / m 3 ) Here, the values ​​of the specific heat at constant pressure Cp and density ρ obtained by the above-mentioned method were used, and the thermal diffusivity αmd in the longitudinal direction and the thermal diffusivity αtd in the circumferential direction were obtained by the following method. Measurements were performed at room temperature (25°C) using an AC light thermal diffusivity measuring device (trade name: LaserPIT, manufactured by Advance Riko Co., Ltd.) First, the elastic layer sample was cut into a sample piece with a short side of 5 mm and a long side of 30 mm using a cutter, so that the longitudinal or circumferential direction of the sample was 30 mm.

[0099] Next, a black paint (product name: JSC-3, manufactured by Japan Sensor Co., Ltd.) was applied to the surface of the sample piece and baked for 20 minutes in an electric furnace set to 150°C to prepare a sample. Each sample was measured twice under the following conditions, and the average value was calculated. The measurement conditions were room temperature, reduced pressure, total time (total measurement time) 1500 seconds, sampling 2, period (1 / frequency) 5, rate (movement speed of the sample mounting stage) 10 μm / s, and level (movement distance of the sample mounting stage) 3000 μm. The constant pressure specific heat Cp (J / (kg·K)) and density ρ (kg / m 3 ), and the measured thermal diffusivity αmd(m 2 / s) and αtd(m 2 The thermal conductivity of the elastic layer in the longitudinal direction, λmd, and the thermal conductivity in the circumferential direction, λtd, were calculated from the thermal conductivity (λmd / s), and the results were λmd = 1.94 W / (m K) and λtd = 2.47 W / (m K).

[0100] (3-3) Elastic modulus of elastic layer The tensile modulus of the elastic layer was measured. Specifically, an elastic layer sample was cut out using a punch (JIS K6251 tensile No. 8 dumbbell shape), and the thickness of the sample piece near the center, which was the measurement point, was measured. Next, the cut sample piece was tested using a tensile tester (device name: Strograph EII-L1, manufactured by Toyo Seiki Seisakusho Co., Ltd.) at a tensile speed of 200 mm / min at room temperature. The tensile modulus was determined by creating a graph from the measurement results with the sample strain on the horizontal axis and the tensile stress on the vertical axis, and the slope of the linear approximation of the measurement data in the strain range of 0 to 10% was used.

[0101] (4) Actual machine evaluation (fixing ability, image quality, durability) <Adhesion evaluation (adhesion)> The fixing belt thus obtained was incorporated into a thermal fixing device of an electrophotographic copying machine (product name: imagePRESS C850, manufactured by Canon Inc.). Then, this thermal fixing device was installed in the copying machine. Using this copying machine, the fixing temperature was set lower than the standard fixing temperature, and a sheet having a basis weight of 300 g / m was fixed. 2 A cyan solid image was formed on thick paper (trade name: UPM Finesse gloss 300 g / m 2 , manufactured by UPM Co., Ltd.).

[0102] Specifically, the fixing temperature of the thermal fixing device was adjusted from 195°C, which is the standard fixing temperature of the copier, to 185°C, and five solid cyan images were formed consecutively, and the image density of the fifth solid image was measured. Next, the toner surface of the solid image was heated at 4.9 kPa (50 g / cm 2 The toner surface was rubbed three times in the same direction with a piece of Silbon paper under a load of 10 ... Further, the fixing state of the toner on the cardboard was evaluated in the same manner as above, except that the fixing temperature was adjusted to 180°C.

[0103] The results were evaluated according to the following criteria: Image density was measured using a reflection densitometer (manufactured by Macbeth). Rank A: The toner was fixed to the thick paper at a fixing temperature of 180°C. Rank B: The toner was not fixed to the cardboard at a fixing temperature of 180°C, but was fixed to the cardboard at a fixing temperature of 185°C. Rank C: The toner did not fuse to the thick paper even at a fixing temperature of 185°C.

[0104] <Image quality evaluation (image quality)> The fifth solid image produced in the above fixation evaluation was visually observed, and the degree of gloss difference between the trailing edge of the first round and the leading edge of the second round was evaluated visually and using a gloss meter (PG-1M manufactured by Nippon Denshoku Industries Co., Ltd.) according to the following criteria. Rank A: No difference in gloss was observed. That is, the 60° gloss difference between the trailing edge of the first turn and the leading edge of the second turn was Δ0. Rank B: A slight difference in gloss was observed. However, the difference in 60° gloss between the trailing edge of the first turn and the leading edge of the second turn was greater than Δ0 but less than Δ2. Rank C: Gloss step was observed. Also, the 60° gloss difference between the trailing edge of the first turn and the leading edge of the second turn was Δ2 or more.

[0105] <Durability evaluation (durability)> With the fixing temperature set to the standard fixing temperature (195°C), cyan solid images were continuously formed on A4-sized plain paper, and the number of sheets at which the elastic layer of the fixing belt broke or plastically deformed was recorded and evaluated according to the following criteria. If the elastic layer of the fixing belt did not break or plastically deform even after 740,000 images had been formed, image formation was stopped at 740,000 sheets. Rank A: No breakage or plastic deformation occurred in the elastic layer of the fixing belt even after 740,000 images were formed. Rank B: No breakage or plastic deformation occurred in the elastic layer of the fixing belt even after 300,000 images were formed, but breakage or plastic deformation occurred in the elastic layer of the fixing belt after 740,000 images were formed. Rank C: No breakage or plastic deformation occurred in the elastic layer of the fixing belt even after forming images on 100,000 sheets, but breakage or plastic deformation occurred in the elastic layer of the fixing belt after forming images on 300,000 sheets.

[0106] [Example 2] A fixing belt was produced and evaluated in the same manner as in Example 1, except that the volume ratio of hexagonal boron nitride was set to 20% by volume. [Example 3] A fixing belt was produced and evaluated in the same manner as in Example 1, except that the volume ratio of hexagonal boron nitride was set to 20 volume % and spherical alumina (product name: CB-P02, manufactured by Showa Denko K.K.) was used as another filler in an amount of 3 volume %.

[0107] [Example 4] A fixing belt was produced and evaluated in the same manner as in Example 1, except that the volume ratio of hexagonal boron nitride was 25 volume % and spherical alumina (product name: CB-P02, manufactured by Showa Denko K.K.) was used as another filler at 3 volume %. [Example 5] A fixing belt was produced and evaluated in the same manner as in Example 1, except that the volume ratio of hexagonal boron nitride was set to 30% by volume.

[0108] [Comparative Example 1] A fixing belt was produced and evaluated in the same manner as in Example 1, except that no charge was applied to the surface of the layer of the addition-curable liquid silicone rubber composition. Comparative Example 2 A fixing belt was produced and evaluated in the same manner as in Example 1, except that the grid electrode potential was changed to ±200 V (Vp-p: 400 V).

[0109] Comparative Example 3 A fixing belt was produced and evaluated in the same manner as in Example 1, except that the volume ratio of hexagonal boron nitride was set to 18 volume %. Comparative Example 4 An addition-curable liquid silicone rubber composition was prepared in the same manner as in Example 1, except that the volume ratio of the hexagonal boron nitride filler was changed to 33 volume %. However, the resulting addition-curable liquid silicone rubber composition had a high viscosity, making it difficult to form the elastic layer of the fixing belt by ring coating.

[0110] Comparative Example 5 Hexagonal boron nitride was changed to cubic boron nitride (product name: SGPS, manufactured by Denka Co., Ltd.) Furthermore, no charge was applied to the surface of the layer of addition-curable liquid silicone rubber composition. Except for these, the same procedures as in Example 1 were carried out to prepare a fixing belt and evaluate it. Comparative Example 6 A fixing belt was produced and evaluated in the same manner as in Example 1, except that hexagonal boron nitride was replaced with cubic boron nitride (product name: SGPS, manufactured by Denka Co., Ltd.). Comparative Example 7 The hexagonal boron nitride was replaced with spherical alumina (product name: CB-P10, manufactured by Showa Denko K.K.), and its content was set to 57% by volume. In addition, no charge was applied to the surface of the addition-curing liquid silicone rubber composition layer. Except for these, a fixing belt was produced and evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0111] [Table 1]

[0112] In all examples, the total filler content was 30% by volume or less, and the relationship λtd>λmd>λnd was satisfied, with λtd being 2.0 W / (m·K) or more and λnd being 1.3 W / (m·K) or more. As a result, good results of ranks A or B were obtained in fixation, gloss difference, and durability. In particular, in examples 1 to 4, in which the hexagonal boron nitride filler content was 20% by volume or more and 25% by volume or less, all indicators were ranked A. On the other hand, in the comparative example, the filler content and thermal conductivity were outside the above ranges, and a C rank was obtained in either item. Although the above examples and comparative examples have been described with respect to fixing belts, it is easily understood that the same tendency also applies to fixing rollers. [Explanation of symbols]

[0113] 1 core 2 Corona charger 3 Substrate (base layer) 4 Elastic Layer 5 Adhesive layer 6 Surface layer 7. Filler 100 Fixing member 11 Fixing belt 12 Pressure Belt 13 Induction heating components 13a Induction coil 13b Excitation core 13c coil holder 14 Excitation circuit 15 Temperature detection element 16 Control circuit section 17 Laura 18 Heating roller 19 Tension roller 20 Pressure roller 21 Fixing Pad 22 Pressure pad 23, 24 Sliding sheet 25 Separation member 30 Belt guide 31 Ceramic heater 31a Heater board 31b Heat generating layer 31c protective layer 31d Sliding member 32 Stay 33 Pressure roller 33a Core metal 33b Elastic layer 34 Temperature detection element N Fixing nip t Unfused toner S Recording media Medium motor

Claims

1. An electrophotographic fixing member having an endless shape, The device has an endless base layer and an elastic layer on an outer peripheral surface of the base layer, the elastic layer includes a silicone rubber and a filler dispersed in the silicone rubber; the content of the filler in the elastic layer is 30% by volume or less based on the volume of the elastic layer; When the thermal conductivity of the elastic layer in the circumferential direction is λtd, the thermal conductivity in the thickness direction is λnd, and the thermal conductivity in the longitudinal direction is λmd, The relationship λtd>λmd>λnd is satisfied, A fixing member having a λtd of 2.0 W / (m·K) or more and a λnd of 1.3 W / (m·K) or more.

2. The fixing member according to claim 1 , further comprising a surface layer on the elastic layer.

3. 3. The fuser member of claim 1, wherein the filler comprises hexagonal boron nitride.

4. 4. The fixing member according to claim 3, wherein the content of the hexagonal boron nitride is 20% by volume or more and 25% by volume or less based on the volume of the elastic layer.

5. 5. The fixing member according to claim 1, wherein the elastic layer has a modulus of elasticity of 0.20 MPa or more and 1.20 MPa or less.

6. 6. The fixing member according to claim 1, wherein the fixing member is a fixing belt, and the fixing belt has an inner diameter of 20 mm or more and 130 mm or less.

7. A thermal fixing device having a heating member and a pressure member disposed opposite the heating member, wherein the heating member is a fixing member, The fixing member comprises: The device has an endless base layer and an elastic layer on an outer peripheral surface of the base layer, the elastic layer includes a silicone rubber and a filler dispersed in the silicone rubber; the content of the filler in the elastic layer is 30% by volume or less based on the volume of the elastic layer; When the thermal conductivity of the elastic layer in the circumferential direction is λtd, the thermal conductivity in the thickness direction is λnd, and the thermal conductivity in the longitudinal direction is λmd, The relationship λtd>λmd>λnd is satisfied, A thermal fixing device, characterized in that the fixing member has an endless shape, λtd of 2.0 W / (m·K) or more, and λnd of 1.3 W / (m·K) or more.

8. A thermal fixing device having a heating member, a pressure member arranged opposite the heating member, and a heater for heating the heating member, wherein the heating member is the fixing member described in claim 6, and the heater is arranged in contact with the inner surface of the base of the fixing member.

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