JP7822838B2 - Fixing member and thermal fixing device - Google Patents

Description

This disclosure relates to fixing members and thermal fixing devices used in electrophotographic image forming apparatuses such as copiers and printers.

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.

In addition, from the perspective of energy conservation, the elastic layer of the fixing member is required to have high thermal conductivity as well as elasticity. 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 more thermally conductive filler to achieve high thermal conductivity can harden the elastic layer and cause it to lose its elasticity. 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 cause the elastic layer to break under conditions of repeated high stress. Therefore, a method is needed to increase thermal conductivity without increasing the amount of thermally conductive filler blended.

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 at the trailing edge of the first rotation. As a result, the gloss of the image at the leading edge of the second rotation is lower than that at the trailing edge of the first rotation in the conveyance direction of the recording material on the same recording material, which can result in a steep 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, which can result 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 (= circumference of the fixing member divided by conveyance speed), and therefore the gloss step tends to be more noticeable.

As a conventional technique for improving the gloss difference between the first and second revolutions of the fixing member, Japanese Patent Laid-Open No. 2003-222262 proposes a heat fixing device in which the surface of the heat fixing member is cooled by a cooling means 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 device 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.

Japanese Patent Application Publication No. 11-038826 Japanese Patent Application Laid-Open No. 2018-205336

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.

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 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 greater and a λnd of 1.3 W/(m·K) or greater.

According to another aspect of the present disclosure, there is provided a thermal fixing device having a heating member and a pressure member disposed opposite the heating member, wherein the heating member is the fixing member described above.

According to one aspect of the present disclosure, a fixing member for a thermal fixing device can be obtained that can prevent the occurrence of gloss variations in electrophotographic images caused by the temperature difference between the first and second revolutions of the fixing member while minimizing a decrease in heat utilization efficiency. According to one aspect of the present disclosure, a thermal fixing device that can form high-quality electrophotographic images can be obtained.

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. 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 FIG. 1A is a top view and FIG. 1B is a cross-sectional view. 1A and 1B are explanatory diagrams of 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. 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. 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. 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. 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. 1 is a cross-sectional view of a thermal fixing device according to one embodiment of the present disclosure. FIG. 10 is a cross-sectional view of a thermal fixing device according to another embodiment of the present disclosure.

The inventors conducted extensive research to achieve the above objective. In the process, they investigated incorporating a thermally conductive filler into the elastic layer of the fixing member to increase 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 has dropped. Hereinafter, circumferential thermal conductivity will also be referred to as "λtd." While incorporating a large amount of thermally conductive filler into the elastic layer can improve λtd, incorporating a large amount of thermally conductive filler increases the hardness of the elastic layer. Therefore, in order to suppress the increase in hardness of the elastic layer, they investigated increasing λtd to 2.0 W/(m·K) or more, assuming that the content of thermally conductive filler in the elastic layer is 30% by volume or less based on the total volume of the elastic layer.

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, at 600 W/(m·K), for example. Furthermore, because hexagonal boron nitride has a plate shape, they found that λtd can be increased by incorporating it in the elastic layer so that it is circumferentially oriented.

However, when hexagonal boron nitride is oriented in the circumferential direction, the thermal conductivity of the hexagonal boron nitride 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 disposed on the back surface of the fixing member, heat conduction to the surface of the fixing member is hindered, which is not desirable in terms of efficiently applying heat to fix unfixed toner.
Therefore, the inventors conducted further studies 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.

That is, according to one embodiment of the present disclosure, an endless-shaped electrophotographic fixing member has an endless-shaped 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 in 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, λtd is 2.0 W/(m·K) or more, and λnd is 1.3 W/(m·K) or more.

Because λtd is high at 2.0 W/(m·K) or more, heat from an area where the recording material has not passed (leading edge of the second revolution) is efficiently replenished to an area where the surface temperature of the fixing member has dropped after the recording material has passed (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 from the heating source to be transferred to the surface of the fixing member also contributes to the reduction of 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.

(1) Outline of the Configuration of the Fixing Member The fixing member of this embodiment will be described in detail with reference to the drawings.
6(a) and 6(b) are schematic cross-sectional views showing a fixing member according to this embodiment. Fig. 6(a) shows an example of a fixing member in the form of a belt, and Fig. 6(b) shows an example of a fixing member in the form of a roller. In Fig. 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 Fig. 6, the radial direction corresponds to the thickness direction of the elastic layer.

As such, the fixing member according to this embodiment has a base 3 and an elastic layer 4 containing silicone rubber on the base 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 Figure 6 have an endless shape. An endless shape is a shape that allows the same portion to pass through the fixing nip area multiple times (endlessly) by rotating in the circumferential direction. Specific examples include an endless belt shape and a roller shape.

(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, alloys primarily containing nickel or iron are 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 fixing member 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 therein and prevents the fixing device from becoming too large.

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

(3) Elastic Layer The elastic layer 4 includes silicone rubber as a binder and a 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, it is possible to prevent the rubber component in the elastic layer from becoming too low. As a result, the elastic layer can be provided with sufficient elasticity and durability to withstand long-term use. 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 irregularities of the paper, contributing to the formation of higher-quality electrophotographic images. 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.

As mentioned above, the elastic layer according to the present disclosure has a high λtd of 2.0 W/(m·K) or more, which allows the area (trailing end of the first lap) where the surface temperature of the fixing member has dropped after the recording material has passed to be efficiently replenished with heat from the area where the recording material has not passed (leading end of the second lap). This reduces the temperature difference at the boundary between the first and second laps of the fixing member. Furthermore, since λnd is also high at 1.3 W/(m·K) or more, it is believed that the reduction in the time it takes for heat generated from 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.

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 Formula (2)
In equation (2), λnd is the thermal conductivity of the elastic layer in the thickness direction (W/(m·K)), _αnd is the thermal diffusivity in the thickness direction (m ² /s), _Cp is the specific heat at constant pressure (J/(kg·K)), and ρ is the density (kg/m ³ ).

λmd=α _md ×C _p ×ρ Formula (3)
λtd= _αtd × _Cp ×ρ. Formula (4)
In equations (3) and (4), _αmd is the thermal diffusivity in the width direction ( ^m2 /s), _αtd is the thermal diffusivity in the circumferential direction ( ^m2 /s), _Cp is the specific heat at constant pressure (J/(kg·K)), and ρ is the density (kg/ ^m3 ). The method for measuring each parameter will be described in detail in the examples.

An elastic layer with the above-described thermal properties according to the present disclosure can be achieved, for example, by orienting a filler with a plate-like crystal structure, such as hexagonal boron nitride, in the circumferential and thickness directions of the elastic layer. Such an elastic layer can be manufactured, for example, by the following method. A layer of a composition for forming the elastic layer (hereinafter also referred to as the "composition layer") containing a filler with a plate-like crystal structure and liquid silicone rubber is formed on a substrate. At this time, because 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.

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 during this process, the filler particles are connected to 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.

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, exhibits strong infrared absorption at a wavenumber of around 1020 cm ⁻¹ due to stretching vibration. Furthermore, the methyl group (Si—CH ₃ ) bonded to the silicon atom exhibits strong infrared absorption at a wavenumber of around 1260 cm ⁻¹ due to deformation vibration caused by the structure, making it possible to confirm its presence.

The content of cured silicone rubber and filler in the elastic layer can also be confirmed using a thermogravimetric analyzer (TGA) (e.g., TGA851, manufactured by Mettler-Toledo). A sample of the elastic layer is cut out with a razor blade or similar tool, and approximately 20 mg is accurately weighed and placed in an alumina pan used in the analyzer. The alumina pan containing the sample is then placed in the analyzer and heated in a nitrogen atmosphere from room temperature to 800°C at a rate of 20°C per minute, 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 cured silicone rubber component and filler contained in the elastic layer can be confirmed.

(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 conform to the unevenness of the paper during fixing. Silicone rubber has high heat resistance, allowing it to maintain flexibility even in environments where the temperature reaches as high as about 240°C in the non-paper passing area, and is therefore particularly suitable for use as a binder for the elastic layer. Furthermore, the silicone rubber is preferably electrically insulating or semiconductive, since it imparts an electric charge to the surface of the layer of the surface layer-forming composition to charge it in the filler orientation step described below. Examples of such silicone rubber include a cured product of an addition-curing liquid silicone rubber.

(3-1-1) Addition-Cure Liquid Silicone Rubber The liquid addition-cure silicone rubber can contain (a) an organopolysiloxane having an unsaturated aliphatic group, (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 to accelerate the curing reaction. (d) is a curing retarder (inhibitor) to control the reaction start time. In addition to these, fillers suitable for each purpose can also be mixed and dispersed to impart heat resistance, reinforcing properties, etc.
(a) to (d) will be explained below.

(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.
A linear organopolysiloxane having one or both of intermediate units selected from the group consisting of intermediate units represented by R ₁ R ₁ SiO and intermediate units represented by R ₁ R ₂ SiO, and molecular terminals represented by R ₁ R ₁ R ₂ SiO _1/2 (see formula 1 below).

A linear organopolysiloxane having one or both of intermediate units selected from the group consisting of intermediate units represented by R ₁ R ₁ SiO and intermediate units represented by R ₁ R ₂ SiO, and molecular terminals represented by R ₁ R ₁ R ₁ SiO _1/2 (see formula 2 below).

(In Formula 1 and Formula 2, _R1 's each independently represent an unsubstituted hydrocarbon group that does not contain an unsaturated aliphatic group, _R2 's each independently represent an unsaturated aliphatic group, and m and n each independently represent an integer of 0 or greater.)

Examples of the unsubstituted hydrocarbon group not containing an unsaturated aliphatic group represented by _R1 in Formula 1 and Formula 2 include a methyl group, an ethyl group, a propyl group, and an aryl group (e.g., a phenyl group). In particular, a methyl group is preferred.
In addition, in Formula 1 and Formula 2, examples of the unsaturated aliphatic group represented by R ₂ include a vinyl group, an allyl group (CH ₂ ═CH—CH ₂ —), and a 3-butenyl group, with a vinyl group being preferred.

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 in Formula 2 have unsaturated aliphatic groups only in the side chain. Component a may be used alone or in combination of two or more types.

Furthermore, when component (a) is used as a raw material for silicone rubber, the viscosity is preferably 100 mm ² /s or more and 50,000 mm ² /s or less, from the viewpoint of obtaining excellent moldability. The viscosity (kinematic viscosity) can be measured using a capillary viscometer, rotational viscometer, or the like, in accordance with JIS Z 8803:2011. Furthermore, when using a commercially available component (a), the catalog value can be referenced.

(3-1-3) Component (b)
The organopolysiloxane having silicon-bonded active hydrogen is a crosslinking agent that reacts with the unsaturated aliphatic groups in component a under the catalytic action of the platinum compound to form a crosslinked structure.
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.

- From the viewpoint of being able to promote the formation of a crosslinked structure by reaction with an organopolysiloxane having an unsaturated aliphatic group, the number of hydrogen atoms bonded to silicon atoms is an average of 3 or more per molecule.
The organic group bonded to the silicon atom may be, for example, an unsubstituted hydrocarbon group such as those mentioned 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.

(In Formula 3 and Formula 4, _R1 's each independently represent an unsubstituted hydrocarbon group not containing 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, R ₁ is an unsubstituted hydrocarbon group that does not contain unsaturated aliphatic groups, and is preferably a methyl group.

(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, these may be referred to as component c.

(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 retarder may be referred to as "component d."

(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 having a plate-like crystal structure, such as hexagonal boron nitride. For example, 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 in-plane direction are alternately stacked. Furthermore, the filler 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.

This section describes the case where a layer of an elastic layer-forming composition containing a filler with a plate-like crystalline structure and a silicone rubber raw material is formed to obtain an elastic layer with a thickness of, for example, approximately 100 to 500 μm. Due to its plate shape, the filler tends to be oriented (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 the "longitudinal direction"), as shown in Figures 4(a) and (b). As a result, the λtd and λmd of the elastic layer obtained by curing the layer of this composition can be very high. On the other hand, because the thermal conductivity of the filler with a plate-like crystalline structure in the thickness direction is low, the λnd of the elastic layer is very small.

Therefore, in the present disclosure, in order to increase λnd, it is preferable to have the filler oriented in the thickness direction of the elastic layer. A non-limiting method for manufacturing such an elastic layer is described below using Figures 2 and 3. This manufacturing method includes the following steps (i) to (iii).

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.

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 of the composition layer 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 direction of rotation). As a result, the filler 7, which was present in the composition layer 401 in the state shown in FIGS. 4(a) and (b) before charging, changes to the state shown in FIGS. 5(a) and (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 due to the rotation of the filler 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.

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.

(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 achieve substantially uniform charging. 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.
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.

As shown in Figures 2(a) and 2(b), the corona charger 2 comprises 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, which serves as a charged body. 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 the 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), controlling the surface potential of the composition layer 401 makes it possible to generate a predetermined electric field in the composition layer 401.

To explain in detail one example of a method for manufacturing an elastic layer using the corona charger 2 described above, first, a composition layer is formed on the outer peripheral surface of the substrate 3. There are no particular restrictions on the method for forming the composition layer, and known methods such as ring coating and blade coating can be used. However, ring coating is particularly preferred, as it tends to allow the filler to be oriented in the in-plane direction of the composition layer.

Next, as shown in FIG. 2(a), corona chargers 2 are positioned closely opposite each other across the width of the composition layer 401. A voltage is applied to the grid 206 of the corona charger 2, and while the grid 206 is discharged, the substrate 3 is rotated, for example, at 141 rpm for 160 seconds 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, along with the inertial force associated with the rotation, orients the filler as shown in FIGS. 5(a) and (b). The composition layer is then cured by heating or the like to fix the orientation of the filler and form the elastic layer according to the present disclosure.

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 Vpp (peak-to-peak voltage) when AC is applied) in order to generate effective electrostatic interactions with the filler. When using an electric field to orient the filler 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 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.

The orientation of the filler can be adjusted, for example, by controlling the voltage applied to the grid 206. This is thought to be related to the dielectric constant of the silicone rubber and the dielectric constant of the filler. If the difference between the dielectric constants of the silicone rubber and the filler is large, the filler can be more oriented even with a relatively small applied voltage. However, if the voltage applied to the grid 206 is too high, the electrostatic repulsion force due to the surface charge of the elastic layer will increase, causing liquid surface flow and reducing the surface properties of the elastic layer 4. Therefore, it is more preferable that the voltage applied to the grid 206 be in the absolute value range of 0.6 kV to 1.5 kV (1.2 to 3 kV Vpp (peak-to-peak voltage) when AC is applied). This liquid surface flow can be alleviated by applying AC charging.

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

The discharge wire 205 may be made of stainless steel, nickel, molybdenum, tungsten, or other materials. 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-section or a sawtooth shape. The diameter of the discharge wire 205 is preferably between 40 μm and 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. Either a DC or AC voltage can be applied to the discharge wire 205. 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 rectangular wave, sine wave, or other waveform using an arbitrary waveform generator.

(3-4) Hexagonal boron nitride Hexagonal boron nitride has a low volumetric specific heat among heat-conductive fillers, and therefore can reduce the volumetric specific heat of the elastic layer. Therefore, it is effective in shortening the warm-up time of the fixing device and saving energy. Furthermore, because it has insulating properties, it can maintain its insulating properties as a composition layer, and is also 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.
By setting the content to 20% by volume or more, it is possible to impart sufficiently high thermal conductivity (λtd, λnd) to the elastic layer, and by setting the content to 25% by volume or less, it is possible to prevent the viscosity of the composition from becoming too high, and it is difficult to interfere with the application of the composition layer and the orientation of the filler when an electric field is applied.

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°

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 resulted in more filler being oriented in the thickness direction.

In order to fill the gaps between the main thermally conductive fillers, a secondary thermally conductive filler other than the main thermally conductive filler may be blended in. Examples of the secondary thermally conductive filler to be blended in include alumina, zinc oxide, magnesium oxide, silicon metal, silicon carbide, silica, and carbon. The thermally conductive filler may be surface-treated to provide excellent affinity with silicone and excellent electrical resistance.

(4) Adhesive Layer of Fixing Member As shown in FIG. 6 , the adhesive layer 5 is formed by adhering the elastic layer 4 and the surface layer (release layer) 6 together using, for example, an addition-cure silicone rubber adhesive. The adhesive is preferably an addition-cure 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 addition reaction. Any known adhesive can be used.
Examples of self-adhesive components include:

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.

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 side (substrate side) can be efficiently transmitted to the recording material (recording medium).

(5) Surface Layer of Fixing Member The surface layer 6 is made of a fluororesin, and a tubing method or a coating method is used as a molding method. The tubing method, in which a resin exemplified below is molded into a tube shape and coated, is exemplified below.
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 allows the elasticity of the underlying elastic layer to be maintained when laminated, and the surface hardness as a fixing member to be prevented from becoming too high, while ensuring abrasion resistance.
The inner surface of the fluororesin tube can be preliminarily treated with sodium, excimer laser, ammonia, or the like to improve adhesiveness.

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.

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, it is preferable that the thickness of the adhesive layer 5 after being squeezed out be 20 μm or less.
Next, the addition-curing silicone rubber adhesive 5 is hardened 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.

(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 entire 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 thereon with unfixed toner, is sandwiched and conveyed through this fixing nip N. The image formed with the 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.

(6-1) Fixing Belt-Pressure Belt Type Thermal Fixing Device Figure 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 pressed together, and which has a fixing belt as the fixing member.
It should be noted that 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 where 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.

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 fixing belt 11 is heated by a heating source (induction heating element, excitation coil) capable of heating by highly energy-efficient electromagnetic induction heating. The induction heating element 13 is composed of 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 loss in the induction coil 13a and excitation core 13b and enables efficient heating of the fixing belt 11.

When a high-frequency current is applied from the excitation circuit 14 to the induction coil 13a of the induction heating member 13, the base of the fixing belt 11 is induced to heat, and the fixing belt 11 is heated from the base side. The surface temperature of the fixing belt 11 is detected by a temperature detection element 15 such as a thermistor. A signal related to the temperature of the fixing belt 11 detected by this temperature detection element 15 is sent to the control circuit unit 16. The control circuit unit 16 controls the power supplied from the excitation circuit 14 to the induction coil 13a so that the temperature information received from the temperature detection element 15 maintains the predetermined fixing temperature, thereby adjusting the temperature of the fixing belt 11 to the predetermined fixing temperature.
The fixing belt 11 is stretched by 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.

The 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 the fixing belt 11. The 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 thickness of 1 mm, and an iron alloy core metal, on which a silicone rubber layer is provided as an elastic layer.
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 rotated clockwise as indicated by the arrow at a predetermined speed.
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. The provision of the elastic layer in the heating side roller 18 also reduces heat conduction to the heating side roller, which is also effective in shortening the warm-up time.

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 to match 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 they can support a fixing belt 11 with an inner diameter of 55 mm when not installed.

The pressure belt 12 is tensioned 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 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.

The pressure 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 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 with a predetermined pressure force.

Furthermore, to obtain a wide nip N without increasing the size of the device, a pressure pad is employed. 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 base, 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 neutralization brush (not shown), and the pressure belt is provided with a contact neutralization brush (not shown).

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 part of the fixing nip is configured so that the fixing belt 11 and pressure belt 12 are sandwiched between the pair of rollers, the heating side roller 18 and the pressure side roller 20, and transported, thereby preventing belt slippage. The most downstream part of the fixing nip is where the pressure distribution in the recording medium transport direction of the fixing nip is greatest.

Once the fixing belt 11 has reached and maintained a predetermined fixing temperature (referred to as temperature regulation), a recording medium S bearing an unfixed toner image t is transported through the nip N between the fixing belt 11 and 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 transported while remaining in close contact with the outer 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 through pressure. During this process, 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 transported.

(6-2) Fixing Belt-Pressure Roller Type Thermal Fixing Device Figure 9 is a schematic diagram showing an example of a fixing belt-pressure roller type thermal fixing device using a ceramic heater as a heating element. In Figure 9, reference numeral 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 fixedly supported by being fitted into a groove formed along the length of the guide 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.

A pressure roller 33 is disposed below the fixing belt 11, facing the fixing belt 11. In this example, the pressure roller is an elastic pressure roller, i.e., 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 provided between both ends of the rigid pressure stay 32 and spring bearing members (not shown) on the device chassis side, respectively, to apply a downward force to the rigid pressure 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, sandwiching the fixing belt 11, to form a fixing nip N.

The pressure roller 33 is driven to rotate in the counterclockwise direction indicated by arrow 41 by a driving means (not shown). This rotational drive of the pressure roller 33 exerts a rotational force on the fixing belt 11 due to the friction between the pressure roller 33 and the outer surface of the fixing belt 11. 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 roughly corresponds to the rotational peripheral speed of the pressure roller 33, with its inner surface sliding against the underside of the ceramic heater 31 at the fixing nip N.

(Pressure roller drive system).
The pressure roller 33 starts rotating based on a print start signal, and the ceramic heater 31 starts heating up. Thereafter, 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 rotational peripheral speed of the fixing belt 11 due to 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.

The ceramic heater 31 used as the heating element is a horizontally elongated linear heating element with 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 this heater substrate 31a along its longitudinal direction, and a protective layer 31c made of glass, fluororesin, or the like provided on top of that. The heat-generating layer 31b is preferably made of an electrically resistive material such as Ag/Pd (silver/palladium), applied by screen printing or the like to a thickness of approximately 10 μm and a width of 1 to 5 mm. However, the ceramic heater used is not limited to this type.

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 where the ceramic heater 31 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, thereby suppressing the occurrence of gloss variations in an electrophotographic image due to the temperature difference between the first and second revolutions of the fixing member, and enabling the heat to be efficiently used for thermal fixing of unfixed toner.

The present disclosure will be described in more detail below using examples.
[Example 1]
(1) Preparation of an addition-curable liquid silicone rubber composition First, 98.6 parts by mass of a silicone polymer containing vinyl unsaturated aliphatic groups at both ends of the molecular chain and methyl groups as unsubstituted hydrocarbon groups with 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 hereinafter be referred to as "Vi."
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 the mixture was thoroughly mixed to obtain mixture 1.

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

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.

Furthermore, 1.4 parts by mass of a silicone polymer (trade name: HMS-301, manufactured by Gelest, viscosity 30 mm ² /s, hereinafter referred to as "SiH") having a linear siloxane skeleton and having active hydrogen groups bonded to silicon only on the side chains was weighed out as component b. 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.

(2) Preparation of Fixing Belt An electroformed nickel endless belt having an inner diameter of 55 mm, a width of 420 mm, and a thickness of 65 μm was prepared as a substrate. During the series of manufacturing steps, the endless belt was handled with a core inserted therein.
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 so that the dry weight was 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 this primer-treated substrate by ring coating, forming a layer of the addition-curable liquid silicone rubber composition 450 μm thick. This is referred to as the uncured endless belt.

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, thereby charging the outer surface of the layer of addition-curable liquid silicone rubber composition. The electric field application conditions were as follows: current supplied to the discharge wire of the corona charger was ±150 μA, grid electrode potential was ±1500 V (Vp-p: 3000 V), frequency was 0.025 Hz, charging time was 160 seconds, and the distance between the grid electrode and the belt was 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.

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 form an adhesive layer with a thickness of approximately 20 μm. 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 the adhesive 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, thereby fixing the fluororesin tube to the elastic layer. Both ends of the resulting endless belt were cut to obtain a fixing belt with a width of 368 mm.

(3) Evaluation of Fixing Belt Characteristics (3-1) Thermal Conductivity of 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× _Cp ×ρ
In the formula, λnd is the thermal conductivity of the elastic layer in the thickness direction (W/(m·K)), α is the thermal diffusivity in the thickness direction (m ² /s), _Cp is the specific heat at constant pressure (J/(kg·K)), and ρ is the density (kg/m ³ ).
Here, the values of the thermal diffusivity α in the thickness direction, the specific heat at constant pressure _Cp , and the density ρ were determined by the following methods.

・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 probe φ4 mm; manufactured by Nikon Corporation. Next, the thermal diffusivity α of each sample was measured five times, and the average value (m ² /s) was calculated. The measurements were performed 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.

・Specific heat at constant pressure 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. Measurements were then performed using the same program. Next, 10 mg of synthetic sapphire with a known constant-pressure specific heat was used as a 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 placed in the sample pan, and measurements were performed using the same program. These measurement results were analyzed using the specific heat analysis software provided with the differential scanning calorimeter, and the constant-pressure specific heat ( _Cp) at 25°C was calculated from the average of five measurement results.
As a result, the specific heat at constant pressure of the silicone rubber elastic layer was 1.27 J/(g·K).

・Density ρ
The density of the elastic layer was measured using a dry automatic densitometer (product name: Accupyc 1330-01, manufactured by Shimadzu Corporation). Specifically, a 10 ^cm3 sample cell was used, and a sample piece was cut out from the elastic layer so as to fill 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 apparatus, and helium was used as the measurement gas. After gas replacement, volume measurements were performed 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 .
From the above, the thermal conductivity λnd of the elastic layer in the thickness direction was calculated from the unit-converted constant pressure specific heat _Cp (J/(kg·K)) and density ρ (kg/m ³ ) of the elastic layer, and the measured thermal diffusivity α (m ² /s), and was found to be 1.40 W/(m·K).

(3-2) Thermal Conductivity of Elastic Layer in Longitudinal and Circumferential Directions The thermal conductivity λmd of the elastic layer in the longitudinal direction and the thermal conductivity λtd in the circumferential direction 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)), and ρ is the density (kg/m ³ ).
Here, the constant pressure specific heat Cp and density ρ were determined by the above-described method, and the longitudinal thermal diffusivity αmd and circumferential thermal diffusivity αtd were determined 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.

Next, a black paint (trade 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 at 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 sec, Sampling 2, Period (1/frequency) 5, Rate (movement speed of sample mounting table) 10 μm/s, and Level (movement distance of sample mounting table) 3000 μm.
The thermal conductivity λmd in the longitudinal direction and the thermal conductivity λtd in the circumferential direction of the elastic layer were calculated from the constant pressure specific heat Cp (J/(kg·K)), density ρ (kg/m ³ ), and the measured thermal diffusivities αmd (m ² /s) and αtd (m ² /s). The results were λmd = 1.94 W/(m·K) and λtd = 2.47 W/(m·K).

(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-shaped), and the thickness of the sample piece near the center, which was the measurement point, was measured. Next, the cut-out sample piece was tested using a tensile tester (device name: Strograph EII-L1, manufactured by Toyo Seiki Seisakusho, Ltd.) at a tensile speed of 200 mm/min and room temperature. The tensile modulus was measured by creating a graph from the measurement results with the strain of the sample piece 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.

(4) Actual machine evaluation (fixing ability, image quality, durability)
<Fixability evaluation (fixability)>
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.). This thermal fixing device was then attached to the copying machine. Using this copying machine, a cyan solid image was formed on thick paper having a basis weight of 300 g/ ^m2 (product name: UPM Finesse Gloss 300 g/m2, manufactured by UPM Co., Ltd.) at a fixing temperature set lower than the standard fixing temperature.

Specifically, the fixing temperature of the thermal fixing device was adjusted from 195°C, the standard fixing temperature for the copier, to 185°C, and five cyan solid images were formed consecutively. The image density of the fifth solid image was measured. Next, the toner surface of the solid image was rubbed three times in the same direction with Silbon paper under a load of 4.9 kPa (50 g/ ^cm2 ), and the image density after rubbing was measured. If the reduction rate of image density before and after rubbing (= [image density difference before and after rubbing/image density before rubbing] x 100) was less than 5%, it was determined that the toner had fixed to the cardboard.
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.

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 cardboard 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 was not fixed to the cardboard even at a fixing temperature of 185°C.

<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 gloss difference 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, but the 60° gloss difference 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.

<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 the number of images reached 740,000, image formation was stopped at 740,000.
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 100,000 images were formed, but breakage or plastic deformation occurred in the elastic layer of the fixing belt after 300,000 images were formed.

[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 3 volume % of spherical alumina (product name: CB-P02, manufactured by Showa Denko K.K.) was used as another filler.

[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 set to 25 volume % and spherical alumina (product name: CB-P02, manufactured by Showa Denko K.K.) was used in an amount of 3 volume % as another filler.
[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 volume %.

[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-curing 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).

[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 an elastic layer of a fixing belt by ring coating.

[Comparative Example 5]
The 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 addition-curable liquid silicone rubber composition layer.
A fixing belt was produced and evaluated in the same manner as in Example 1 except for these points.
[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 the content was set to 57% by volume. In addition, no charge was applied to the surface of the addition-curable liquid silicone rubber composition layer. Except for these points, a fixing belt was produced and evaluated in the same manner as in Example 1.
The results are shown in Table 1.

In all examples, the total filler content was 30% by volume or less, the relationship λtd>λmd>λnd was satisfied, λtd was 2.0 W/(m K) or more, and λnd was 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 examples, the filler content and thermal conductivity were outside the above ranges, and a result of 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.

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 member 13a Induction coil 13b Excitation core 13c Coil holder 14 Excitation circuit 15 Temperature detection element 16 Control circuit unit 17 Roller 18 Heating side roller 19 Tension roller 20 Pressure side roller 21 Fixing pad 22 Pressure pad 23, 24 Sliding sheet 25 Separating member 30 Belt guide 31 Ceramic heater 31a Heater substrate 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 Unfixed toner S Recording medium M Motor

Claims (8)

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. The fixing member according to claim 1, which has a surface layer on the elastic layer. The fixing member according to claim 1 or 2, wherein the filler contains hexagonal boron nitride. The fixing member described in 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. The fixing member according to any one of claims 1 to 4, wherein the elastic modulus of the elastic layer is 0.20 MPa or more and 1.20 MPa or less. The fixing member according to any one of claims 1 to 5, wherein the fixing member is a fixing belt, and the inner diameter of the fixing belt is 20 mm or more and 130 mm or less. 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. 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.