JP7374641B2 - Pressure roller for fixing device, fixing device, and image forming device - Google Patents

Description

The present invention relates to a pressure roller for a fixing device installed in an image forming apparatus such as a copying machine, a printer (laser printer, an LED printer, etc.), a facsimile machine, etc. using an electrophotographic method or an electrostatic recording method; The present invention relates to a fixing device equipped with a roller and an image forming apparatus.

2. Description of the Related Art An image forming apparatus using an electrophotographic method uses an image heating device such as a fixing device that heats a recording material carrying a toner image to fix the toner image on the recording material. For example, the fixing device includes a heating member (fixing member) that comes into contact with unfixed toner on the recording material, and a pressure roller that comes into pressure contact with the heating member to form a nip (fixing nip). This fixing device supplies thermal energy to the recording material and toner in a fixing nip formed between the heating member and the pressure roller. As a result, the toner on the recording material is melted in the fixing nip, cooled and solidified after passing through the fixing nip, and fixed on the recording material.

As a fixing device, a film heating type fixing device is known which is excellent in energy saving properties and can be started quickly. A film heating type fixing device includes a heating member that includes a flexible cylindrical fixing film and a heating element such as a ceramic heater, and a heating member that is pressed into contact with the heating member (more specifically, through the fixing film). and a pressure roller that presses against the heating element. In this fixing device, thermal energy from a heating element is supplied to the recording material and toner via the fixing film in a fixing nip where a heating member and a pressure roller are in pressure contact.

For example, in the film heating type fixing device as described above, one is known that is equipped with the following pressure roller for the purpose of efficiently transmitting thermal energy from a heating member to a recording material and toner. In other words, it is a pressure roller that includes an elastic layer that has a plurality of dispersed voids and thus has low thermal conductivity. However, when such a pressure roller with low thermal conductivity is used, when a recording material whose width is narrower than the maximum usable width as a recording material is used, the temperature of the non-paper-passing area is likely to rise. Here, "temperature rise in non-sheet passing area" refers to the temperature of the area of the fixing device through which the recording material does not pass in a direction substantially perpendicular to the conveyance direction of the recording material (herein also referred to as "non-sheet passing area"). This is a phenomenon in which the amount of energy increases excessively. The temperature increase in the non-paper-passing area becomes noticeable when paper passes continuously without time for cooling.

To address these issues, we have provided multiple elastic layers in order to achieve both quick start performance (fusing ready state in a short time after power is turned on) and suppression of temperature rise in non-paper passing areas. A pressure roller having separate functions for each elastic layer has been proposed (Patent Document 1). In other words, in this pressure roller, the outer elastic layer that is relatively close to the heat source is made of foamed rubber or the like to have low thermal conductivity, while the inner elastic layer that is relatively far from the heat source is used as a heat storage layer. There is. Then, when the thermal conductivity in the thickness direction of the outer elastic layer is λ1, and the thermal conductivity in the thickness direction of the inner elastic layer is λ2, there is a relationship of λ1<λ2. As a result, the surface of the pressure roller easily heats up at the start of printing, resulting in a quick start, and excess heat at the edges is evenly heated by the inner elastic layer (heat storage layer), allowing the non-sheet passing area to rise. Temperature can be suppressed.

On the other hand, in recent years, with the demand for faster and more compact fixing devices, the fixing nip passage time (duel time), which is the time it takes for a recording material to pass through the fixing nip, has tended to be shortened. Along with this, the elastic layer constituting the pressure roller can maintain sufficient flexibility (responsiveness and followability to vibrations during compression and release) even during high-speed operation, and ensure a sufficient fixing nip. In addition, it has become necessary to be able to suppress the temperature increase in the non-sheet passing portion described above.

Japanese Patent Application Publication No. 2012-163812

In the pressure roller described in Patent Document 1, the heat storage layer is non-porous and contains a thermally conductive filler such as alumina and zinc oxide. The thermally conductive filler has the effect of improving thermal conductivity, but if its content is high, the flexibility of the elastic layer will be impaired. Therefore, it is conceivable to mix a thermally conductive filler with a low hardness rubber as a base rubber, but since the low hardness rubber has low strength, the durability may be insufficient. It has also been found that the non-porous heat storage layer may not be able to secure the necessary fixing nip during high-speed operation where pressurization and release are performed at high speed. This is because the deformation speed of the rubber at the fixing nip is insufficient to form the nip, so the rubber is not sufficiently crushed while passing through the fixing nip.

Therefore, an object of the present invention is to provide a pressure roller for a fixing device, a fixing device, and an image forming apparatus that can both ensure appropriate flexibility of an elastic layer and suppress temperature rise in non-sheet passing areas. It is to be.

The above object is achieved by a pressure roller for a fixing device, a fixing device, and an image forming apparatus according to the present invention. In summary, the present invention provides a pressure roller used in a fixing device that heats and fixes a toner image formed on a recording material, the pressure roller comprising a first elastic layer; a second elastic layer provided on the outside of the first elastic layer, the first elastic layer has a higher thermal conductivity than the second elastic layer, and the first elastic layer has a plurality of , a hole connecting the plurality of voids, and a acicular highly thermally conductive filler. When dynamic viscoelastic properties are measured by applying compressive stress in the thickness direction of the roller, the complex elastic modulus E* (1 Hz) when the stress frequency is 1 Hz and the complex elastic modulus when the stress frequency is 50 Hz. The rate E*(50Hz) and the ratio E*(50Hz)/E*(1Hz) satisfy the following formula, 1.0≦E*(50Hz)/E*(1Hz)≦1.3. This is a pressure roller characterized by:

According to another aspect of the present invention, there is provided a fixing device that fixes a toner image formed on a recording material on a recording material by nipping and conveying the toner image formed on the recording material in a fixing nip portion, the fixing device including a heating unit and a toner image formed on the recording material together with the heating unit. There is provided a fixing device comprising: a pressure roller forming a nip portion, the pressure roller being the pressure roller of the present invention.

According to another aspect of the present invention, there is provided an image forming apparatus for forming a toner image on a recording material, the image forming device for forming a toner image on the recording material, and fixing the toner image formed on the recording material on the recording material. There is provided an image forming apparatus comprising: a fixing means, wherein the fixing means is the fixing device of the present invention.

According to the present invention, it is possible to both ensure appropriate flexibility of the elastic layer and suppress temperature rise in non-paper-passing areas.

FIG. 1 is a schematic cross-sectional view of an image forming apparatus. FIG. 2 is a schematic cross-sectional view of a fixing device and a schematic perspective view of a pressure roller. (a) A schematic cross-sectional view of an inner elastic layer of a pressure roller, and (b) a schematic cross-sectional view of an outer elastic layer of a pressure roller. FIG. 2 is a schematic perspective view of a mold for forming a pressure roller. FIG. 2 is a schematic cross-sectional view of a mold for forming a pressure roller.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a pressure member for an image heating device, an image heating device, and an image forming device according to the present invention will be described in more detail with reference to the drawings.

[First embodiment]
1. Image Forming Apparatus FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a laser printer using an electrophotographic method. Here, a direction substantially orthogonal to the conveying direction of recording material P, which will be described later, is also referred to as a "longitudinal direction." This longitudinal direction is approximately parallel to the rotational axis direction of the photosensitive drum 1, which will be described later, and the pressure roller 20 of the fixing device 6, which will be described later.

The image forming apparatus 100 includes a photosensitive drum 1 that is a rotatable drum-shaped (cylindrical) photosensitive member (electrophotographic photosensitive member) and serves as an image carrier that carries a toner image. The photosensitive drum 1 is constructed by disposing a photosensitive material such as OPC (organic optical semiconductor), amorphous selenium, or amorphous silicon on a cylindrical drum base made of aluminum alloy, nickel, or the like. The photosensitive drum 1 is rotated at a predetermined process speed (circumferential speed) in the direction of arrow R1 in the drawing by a drive motor (not shown) serving as a drive means. The surface of the photosensitive drum 1 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 2, which is a roller-shaped charging member serving as a charging means. The charging roller 2 is placed in contact with the surface of the photosensitive drum 1 . The charged surface of the photosensitive drum 1 is scanned and exposed by an exposure device (laser scanner) 3 serving as an exposure means, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 1. The laser scanner 3 irradiates the surface of the photosensitive drum 1 with a laser beam E that is ON/OFF controlled according to image information, and forms an electrostatic image by removing electric charge from the exposed portion. The electrostatic image formed on the photosensitive drum 1 is developed (visualized) by supplying toner as a developer by a developing device 4 serving as a developing means, and a toner image (developer image) is formed on the photosensitive drum 1. be done. The developing device 4 includes a developing roller 41 as a developer carrier that carries toner and conveys it to a portion (developing portion) facing the photosensitive drum 1 . As the developing method, a jumping developing method, a two-component developing method, etc. are used. In this embodiment, the charged polarity of the photosensitive drum 1 is applied to the exposed area (image area) on the photosensitive drum 1 whose absolute value has decreased by being exposed according to image information after being uniformly charged. Toner charged to the same polarity (negative polarity in this embodiment) is attached (reversal development).

A transfer roller 5, which is a roller-shaped transfer member serving as a transfer means, is arranged opposite to the photosensitive drum 1. The transfer roller 5 is urged toward the photosensitive drum 1 to form a transfer portion (transfer nip) T where the photosensitive drum 1 and the transfer roller 5 come into contact. The toner image formed on the photosensitive drum 1 as described above is transferred in the transfer section T onto a recording material (transfer material, sheet) P that is conveyed while being sandwiched between the photosensitive drum 1 and the transfer roller 5. . During transfer, a transfer voltage (transfer bias) having a polarity opposite to the normal charging polarity of the toner (charging polarity during development) (positive polarity in this embodiment) is applied to the transfer roller 5 during transfer. Recording materials P are stored in a recording material tray 101, are fed one by one by a feeding roller 102, and are supplied to a transfer section T at a predetermined timing by a conveying roller 103 or the like. At this time, the leading edge of the recording material P is detected by the top sensor 104, and based on the positional relationship between the top sensor 104 and the transfer section T and the transport speed of the recording material P, the leading edge of the recording material P reaches the transfer section T. The timing is detected.

The recording material P onto which the toner image has been transferred is conveyed to a fixing device 6, which is a fixing means serving as an image heating device. The fixing device 6 heats and pressurizes the recording material carrying an unfixed toner image (image) to fix (melt, fix) the toner image on the surface of the recording material P. The fixing device 6 will be described in more detail later. The recording material P with the toner image fixed thereon is discharged (output) by a discharge roller 106 onto a discharge tray 107 formed outside (on the top surface) of the apparatus main body 110 of the image forming apparatus 100 . During this time, the timing at which the leading and trailing ends of the recording material P pass is detected by the discharge sensor 105, and the occurrence of jamming or the like is monitored.

On the other hand, toner remaining on the surface of the photosensitive drum 1 without being transferred to the recording material P during transfer (transfer residual toner) is removed from the photosensitive drum 1 by a cleaning device 7 serving as a cleaning means and collected. The cleaning device 7 uses a cleaning blade 71 as a cleaning member disposed in contact with the surface of the photosensitive drum 1 to scrape and remove residual toner from the surface of the rotating photosensitive drum 1 .

In this embodiment, the photosensitive drum 1, the charging roller 2, the exposure device 3, the developing device 4, the transfer roller 5, and the like constitute an image forming unit that forms an image on the recording material P.

2. Overall Configuration of Fixing Device FIG. 2A is a schematic cross-sectional view (a cross section substantially perpendicular to the rotational axis direction of a pressure roller 20, which will be described later) of the fixing device 6 as an image heating device of this embodiment.

The fixing device 6 of this embodiment is a film heating type fixing device. The fixing device 6 includes a heating member 10 and a pressure roller 20 that presses against the heating member 10. The heating member (heating unit) 10 includes a fixing film 13, a heater 11, and a holder (insulating stay holder) 12. The fixing film 13 is an example of a heating rotating body as a heat transfer member, which is made of a flexible cylindrical heat-resistant film. The heater 11 is an example of a heating element (heat source, heating source, heating body). The holder 12 is an example of a holding member that holds the heater 11. The heater 11 is fixedly arranged on the holder 12. The holder 12 also functions as a guide that regulates the rotation locus of the fixing film 13. Pressure roller 20 is arranged to face heater 11 with fixing film 13 in between.

In this embodiment, the holder 12 to which the heater 11 is fixed is urged toward the pressure roller 20. As a result, a fixing nip N is formed in which the heater 11 and holder 12 are brought into pressure contact with the pressure roller 20 via the fixing film 13. That is, the fixing nip N is formed by applying pressure between the heater 11 and the pressure roller 20 via the fixing film 13. Further, in this embodiment, the pressure roller 20 is rotationally driven in the direction of arrow R2 in the figure by a drive motor (not shown) serving as a drive means. Accordingly, in the present embodiment, the fixing film 13 is rotated (circularly moved) in the direction of arrow R3 in the figure by the pressure roller 20 while being held between the heater 11, the holder 12, and the pressure roller 20. The fixing device 6 nips and conveys the recording material P carrying the unfixed toner image t together with the fixing film 13 in the fixing nip N. As a result, thermal energy is supplied from the heating member 10 to the recording material P and the toner image t, and the toner image t is fixed (melted, fixed) on the recording material P. That is, the fixing device 6 fixes the toner image formed on the recording material P at the fixing nip N by heating it while nipping and conveying it.

A thermistor 14, which is a temperature sensing element serving as temperature sensing means, is disposed in contact with the surface of the heater 11 opposite to the surface that slides on the fixing film 13. A signal indicating the detection result of the thermistor 14 is input to the engine control section 302. Based on this signal, the engine control unit 302 controls the current supplied to the heater 11 so that the temperature of the heater 11 becomes a desired temperature.

The heater 11 has a resistance heating layer 112 on a substrate (insulating substrate) 113 made of ceramic (alumina, aluminum nitride, etc.). Further, the resistance heating layer 112 is covered with an overcoat glass 111 for electrical insulation and wear resistance. The heater 11 is configured such that the overcoat glass 111 contacts the inner circumferential surface (inner surface) of the fixing film 13.

3. Fixing Film In this embodiment, the fixing film 13 includes a base layer formed of a thin metal tube such as SUS (stainless steel) or a heat-resistant resin film such as polyimide or PEEK, and a mold release layer formed on the base layer. It is a composite layer film having a sexual layer. The releasable layer is formed by coating a material such as PFA, PTFE, FEP, etc. directly or via a primer layer on the surface of the base layer, or by coating a tube made of a similar material. Can be configured. In this embodiment, in particular, the fixing film 13 was constructed by coating a base layer made of polyimide with PFA to form a releasable layer. In this embodiment, the entire thickness (total film thickness) of the fixing film 13 is 70 μm, and the outer circumferential length of the fixing film 13 is 56.7 mm.

Since the fixing film 13 rotates while rubbing against the heater 11 and holder 12 disposed on its inner peripheral surface side, it is desirable to keep the frictional resistance between the heater 11 and holder 12 and the fixing film 13 small. . Therefore, an appropriate amount of lubricant such as heat-resistant grease is interposed between the surfaces of the heater 11 and holder 12 and the inner peripheral surface of the fixing film 13. This allows the fixing film 13 to rotate smoothly.

4. Pressure roller <Overall configuration of pressure roller>
FIG. 2(b) is a schematic perspective view of the pressure roller 20 of this embodiment. The pressure roller 20 has an inner elastic layer (first elastic layer) 22 , an outer elastic layer (second elastic layer) 23 , and a surface release layer 24 on a core metal (base material) 21 . It has a multi-layer structure in which layers are sequentially laminated.

The core metal 21 includes a rigid main body at the center in the longitudinal direction, and shaft parts provided at both ends in the longitudinal direction and having a smaller diameter than the main body. An elastic layer 25 is composed of the inner elastic layer 22 and the outer elastic layer 23. The inner elastic layer 22 , the outer elastic layer 23 , and the surface release layer 24 are provided on the outer periphery of the main body of the core bar 21 . The inner elastic layer 22 and the outer elastic layer 23 are made of heat-resistant rubber. The surface release layer 24 is made of fluororesin. In this embodiment, the outer diameter of the pressure roller 20 is 20 mm, and the thickness of the elastic layer 25 (total thickness of the inner elastic layer 22 and outer elastic layer 23) is 2.5 mm. In this embodiment, the length (total length) of the pressure roller 20 in the longitudinal direction is 289 mm (the length in the longitudinal direction of the main body of the core bar 21, the inner elastic layer 22, the outer elastic layer 23, and the surface release layer 24). The length is approximately 250 mm).

As will be described in more detail below, in this embodiment, the inner elastic layer 22 is made of heat-resistant silicone rubber, and includes voids, pores connecting the voids, and needle-shaped holes. filler (high thermal conductivity filler). Furthermore, in this embodiment, the outer elastic layer 23 is made of heat-resistant silicone rubber and has voids.

<Core metal>
Solid core metals and hollow pipe-shaped core metals are known as the core metal of the pressure roller for the fixing device, and in the case of a hollow pipe-shaped core metal, a heating element is arranged inside the core metal. In some cases.

In this embodiment, the core metal 21 can be either solid or hollow pipe-shaped. However, it is preferable that no heating element is disposed inside the core bar 21. This is to promote heat dissipation from the inner elastic layer 22 through the core metal 21 in order to suppress temperature rise in the non-paper-passing area.

The core metal 21 can be made of a metal material such as aluminum, aluminum alloy, steel, or stainless steel alloy. Further, the shape and the like of the core bar 21 can be selected so that it has a strength capable of applying a load necessary for forming the fixing nip N and forming a desired nip shape.

In this embodiment, the core bar 21 is made of solid steel, and has a main body at the center in the longitudinal direction, and shaft parts provided at both ends in the longitudinal direction and having a smaller diameter than the main body. It is configured. In this embodiment, the outer diameter of the main body of the core bar 21 is 15 mm. Further, in this embodiment, the length (total length) of the cored metal 21 in the longitudinal direction is 289 mm (the length of the main body of the cored metal 21 in the longitudinal direction is about 250 mm).

<Inner elastic layer (first elastic layer)>
FIG. 3A is a schematic cross-sectional view showing the fine structure of the inner elastic layer 22. FIG. The main component of the inner elastic layer 22 is heat-resistant silicone rubber 22a. The inner elastic layer 22 includes, in a silicone rubber 22a, a plurality of dispersed voids 22b, pores 22c that connect the voids 22b to each other (i.e., the voids), and a dispersed acicular filler. 22d. That is, the voids 22b of the inner elastic layer 22 have a structure (communicating holes) in which adjacent voids 22b among the plurality of voids 22b are connected to each other by the hole passages 22c. In this embodiment, the silicone rubber 22a of the inner elastic layer 22 is blended with a silane coupling agent, an adhesive, etc., and the inner elastic layer 22 is integrated with the core metal 21 by the adhesive or the like. . The inner elastic layer 22 will be described in more detail later.

<Outer elastic layer (second elastic layer)>
FIG. 3(b) is a schematic cross-sectional view showing the fine structure of the outer elastic layer 23. The main component of the outer elastic layer 23 is heat-resistant silicone rubber 23a. The silicone rubber 23a of the outer elastic layer 23 preferably contains an adhesive component for integration with the surface release layer 24 and the silicone rubber 22a of the inner elastic layer 22. Specifically, in order to integrate with the surface mold release layer 24, it is preferable that a silane coupling agent is blended. In addition, in order to integrate with the inner elastic layer 22, a silicone rubber raw material component (a raw material component having a functional group such as a Si-vinyl group or a Si-hydrogen group) that participates in the hydrosilylation reaction may be blended. preferable. In this way, the outer elastic layer 23, the surface release layer 24, and the inner elastic layer 22 can be integrated.

Moreover, it is preferable that the outer elastic layer 23 has a plurality of dispersed voids 23b within the silicone rubber 23a. The outer elastic layer 23 contacts the heating member 10 via the surface release layer 24 until the recording material P is conveyed to the fixing nip N. By providing the void portion 23b in the outer elastic layer 23, heat penetration from the surface release layer 24 side to the inner elastic layer 22 side in the outer elastic layer 23 is prevented, and thermal energy from the heating member 10 is recorded without waste. It can be transmitted to the material P. Here, the void portions 23b of the outer elastic layer 23 may have a structure (communicating holes) in which the void portions 23b are connected to each other by hole passages, similar to the void portions 22b of the inner elastic layer 22. However, the voids 23b of the outer elastic layer 23 may have a structure (independent holes) in which the voids 23b are not connected to each other by a hole. This is because the thickness of the outer elastic layer 23 is relatively thin, so even if the holes are independent, the pressure roller 20 may be pushed out due to the expansion and contraction of air existing inside the gap 23b during heating or cooling. This is because the effect on the change in diameter is small. Note that the outer elastic layer 23 may include both communicating holes and independent holes. Note that the thermal conductivity of the inner elastic layer 22 is higher than that of the outer elastic layer 23.

The thickness of the outer elastic layer 23 is determined in consideration of the quick start performance of the fixing device 6 and the temperature increase characteristics of the non-sheet passing portion. On a relatively short time scale of several seconds (at the time of heating start-up), heat penetration from the heating member 10 is hindered, while on a relatively long time scale of several minutes (such as during continuous sheet feeding), heat transfer to the inner elastic layer 22 occurs. It needs to be possible. The thickness of the outer elastic layer 23 is preferably 150 μm or more and less than 500 μm, more preferably 200 μm or more and less than 400 μm. If the thickness of the outer elastic layer 23 is less than 150 μm, heat will be transferred even in a short time scale, making it difficult to exhibit sufficient quick start performance. Furthermore, if the thickness of the outer elastic layer 23 is 500 μm or more, it will take too long for heat to be transferred to the inner elastic layer 22, resulting in heat accumulation, making it difficult to sufficiently suppress temperature rise in the non-paper-passing area. .

The outer elastic layer 23 can be formed of a known porous material. As the porous material, for example, the following materials can be used. First, there is a material in which the rubber component is crosslinked by heating and at the same time made porous by using a thermally decomposable organic foaming agent. Another example is a material that is made porous using an emulsion obtained by mixing an uncrosslinked liquid silicone rubber material and water with a thickener, an emulsifier, and the like. Another example is a material that is made porous by using hollow particles (hollow filler) dispersed in a silicone rubber raw material. In this embodiment, as the outer elastic layer 23, a porous material is used in which the voids 23b are formed using the same resin microballoons (hollow particles) as in the case of the voids 22b of the inner elastic layer 22, which will be described in detail later. . Note that as the silicone rubber 23a of the outer elastic layer 23, the same silicone rubber 22a of the inner elastic layer 22, which will be described in detail later, can be used.

<Surface release layer>
The main component of the surface release layer 24 is a fluororesin. Examples of the fluororesin include fluorine-based resins selected from tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), and polytetrafluoroethylene (PTFE). Resins, mixtures thereof, or dispersions of these polymers in heat-resistant resins or rubbers can be used. In this embodiment, a resin tube (fluororesin tube) formed of these resins was used as the surface release layer 24.

Examples of methods for molding the surface release layer 24 made of a resin tube include the following methods. After forming the elastic layer 25, a resin tube is later fixed to the outer periphery of the elastic layer 25 using an adhesive.The resin tube is placed inside a cylindrical outer mold, and the resin tube is attached at the same time as the elastic layer 25 is formed. For example, a method of adhesion is used. In this embodiment, as shown in FIG. A method of integrating the release layer 24) and the outer elastic layer 23 was used. FIG. 4 shows a state in which the resin tube installed inside the cylindrical outer mold is folded back and fixed at both ends of the opening. Note that the method for manufacturing the pressure roller 20 will be described in more detail later.

The thickness of the surface release layer 24 is about 100 μm or less, preferably about 10 μm or more and 50 μm or less. If the surface release layer 24 is too thick, the pressure roller 20 will have a high hardness, which may make it difficult to stably form the fixing nip N. In this embodiment, the thickness of the surface release layer 24 is 30 μm. That is, the pressure roller 20 may have a fluororesin layer, and the thickness of this fluororesin layer is preferably 10 μm or more and 100 μm or less. In the present embodiment (experimental examples described later), for simplicity, the thickness of the surface release layer 24 is ignored, and the thickness of the inner elastic layer 22 or the thickness of the inner elastic layer 22 and the outer elastic layer 23 is The total thickness may be displayed.

5. Details of Inner Elastic Layer Next, the structure of the inner elastic layer 22 will be described in more detail. According to this embodiment, since the inner elastic layer 22 has a microstructure as described below, it is possible to impart desired dynamic viscoelastic properties and thermal conductivity properties to the pressure roller 20. In other words, in order to achieve both quick start performance during high-speed operation and suppression of temperature rise in non-paper passing areas, the following configuration is desired. Even during high-speed operation, the pressure roller exhibits the same flexibility (responsiveness and followability to vibrations during compression and release) as during low-speed operation, and the fixing nip N is maintained stably from low-speed to high-speed operation. This is a configuration that can ensure the following. According to the present embodiment, it is possible to provide the pressure roller 20 that exhibits the same degree of flexibility during high-speed operation as during low-speed operation, and achieves both quick start performance and suppression of temperature rise in non-paper passing areas. . In this embodiment, the inner elastic layer 22 is a silicone rubber layer formed by curing and molding liquid silicone rubber containing resin microballoons, an aggregating agent, and a highly thermally conductive filler with heat.

<Silicone rubber>
The silicone rubber 22a is preferably formed from a silicone rubber raw material that exhibits rubber-like elasticity when cured by heat, but its type is not particularly limited. The silicone rubber raw material is, for example, composed of (1) an alkenyl group-containing diorganopolysiloxane, a silicon-bonded hydrogen atom-containing organohydrogenpolysiloxane, and a reinforcing filler, and is cured with a platinum-based catalyst to become a silicone rubber. Addition reaction-curing liquid silicone rubber composition; (2) an organic peroxide-curing silicone rubber composition comprising an alkenyl group-containing diorganopolysiloxane and a reinforcing filler and becoming a silicone rubber when cured with an organic peroxide; (3) consisting of a hydroxyl group-containing diorganopolysiloxane, a silicon-bonded hydrogen atom-containing organohydrogenpolysiloxane, and a reinforcing filler; Examples include condensation reaction-curable liquid silicone rubber compositions that cure into silicone rubber.

Among these, addition reaction curing liquid silicone rubber compositions are preferred from the viewpoint of processability. For example, if the viscosity at 25°C of a liquid material whose main component is diorganopolysiloxane as a starting material is 0.1 Pa·S or more, it can be easily made into a rubber material using a known processing method such as mold casting. A shaped article can be obtained. Commercially available liquid silicone rubbers can be used, and in addition to the compounding materials described below, thickeners, reinforcing agents, etc. can be added as necessary.

<Void part>
By providing the void portion 22b in the inner elastic layer 22, it becomes possible to achieve both quick start performance and suppression of temperature rise in the non-sheet passing portion during high-speed operation.

When the pressure roller 20 is repeatedly compressed and released in the fixing nip N, the elastic layer 25 (inner elastic layer 22 and outer elastic layer 23) is also repeatedly compressed and released. According to the studies conducted by the present inventors, when the inner elastic layer 22 is non-porous and is not provided with the voids 22b, the necessary There were cases in which the fixing nip N could not be secured (see experimental examples described later). As a result of evaluating the frequency-dependent characteristics of the dynamic viscoelasticity of the inner elastic layer 22, it is believed that this is caused by the following. In other words, in the non-porous inner elastic layer 22, when the repetition period of pressurization and release is fast (short), the inner elastic layer 22 lacks flexibility (responsiveness and followability to vibrations during compression and release). This results in insufficient deformation. Here, the high-speed operation is assumed to be when the process speed (corresponding to the transport speed of the recording material P in the fixing nip N) is 250 mm/sec or more, for example, about 270 mm/sec. Furthermore, here, the low-speed operation is assumed to be when the process speed (corresponding to the transport speed of the recording material P in the fixing nip N) is less than 200 mm/sec, for example, about 180 mm/sec.

Specifically, as the dynamic viscoelastic property of the inner elastic layer 22, the following complex modulus ratio E* (50 Hz)/E* (1 Hz) was evaluated by a method described in detail later. In other words, the complex modulus of elasticity E* (1Hz) when the frequency of stress is 1Hz, which is a relatively low frequency, and the complex modulus of elasticity E* (50Hz) when the frequency of stress is 50Hz, which is a relatively high frequency. The ratio of E*(50Hz)/E*(1Hz) was evaluated. As a result, it was found that the dynamic viscoelastic properties of the non-porous elastic layer had a ratio of E*(50Hz)/E*(1Hz) of about 1.5, and had a relatively large frequency dependence.

On the other hand, the dynamic viscoelastic property of the porous inner elastic layer 22 provided with the voids 22b according to the present embodiment is such that E*(50Hz)/E*(1Hz) is within 1.3, typically 1 .1 or less, and almost no frequency dependence is observed. That is, it was confirmed that it is possible to stably secure the fixing nip N even if pressurization and release are repeated at low speeds and even if pressurization and release are repeated at high speeds.

As will be described in detail later, when dynamic viscoelastic properties of a sample of the inner elastic layer 22 are measured by applying compressive stress in the thickness direction of the pressure roller 20 at a temperature of 100° C. and an amplitude of 3 μm, the stress frequency The ratio E*(50Hz)/E*(1Hz) of the complex modulus of elasticity E*(1Hz) when is 1Hz and the complex modulus of elasticity E*(50Hz) when the frequency of stress is 50Hz is given by the following formula. , 1.0≦E*(50Hz)/E*(1Hz)≦1.3.

Here, most of the voids 22b of the inner elastic layer 22 are so-called communicating holes that communicate with the "outside" through the hole passages 22c. Note that the "outside" means the area around the pressure roller 20. In this embodiment, the outer periphery of the elastic layer 25 (the inner elastic layer 22 and the outer elastic layer 23) is covered with the surface release layer 24, but the inner elastic layer 22 is coated at both ends of the pressure roller 20 in the longitudinal direction. The side surface (end surface) is exposed around the pressure roller 20 and is in communication with the "outside". A porous elastic body that has a continuous pore structure allows air existing inside the void to move in and out more easily than a porous elastic body that does not have a continuous pore structure (i.e., has an independent pore structure). . For example, when the pressure roller 20 is heated, the air thermally expanded inside the voids 22b of the inner elastic layer 22 is discharged to the outside via the holes 22c, causing a change in the outer diameter of the pressure roller 20. is suppressed.

Examples of methods for forming the void portion 22b having such a communicating hole structure include the following methods. These methods include a method in which a thermally decomposable organic foaming agent is used at the same time as crosslinking of the rubber component by heating, and a method in which an emulsion is used in which an uncrosslinked liquid silicone rubber material and water are mixed with a thickener, an emulsifier, and the like. In this embodiment, as a method for forming the voids 22b of the inner elastic layer 22, it is preferable to use resin microballoons, which are hollow particles dispersed in liquid silicone rubber. That is, it is preferable that the void 22b of the inner elastic layer 22 is a void derived from the resin microballoon. In this case, by adding a resin microballoon aggregating agent that has a high affinity with resin microballoons and a poor affinity with silicone rubber materials, the hole passages 22c can be formed simultaneously with heat molding.

Various types of resin microballoons are available. In this embodiment, in consideration of dispersibility in liquid silicone rubber, dimensional stability during molding, and ease of handling, a pre-expanded resin microballoon (trade name :F80-DE, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd.) was used. The amount of resin microballoons added to the liquid silicone rubber can be selected appropriately taking into account the specific gravity of the molded product, but it is usually 0.5 to 8 parts by weight, and 2. The amount is preferably from 5 parts by weight to 5 parts by weight. If the blending amount of the resin microballoon is less than 2 parts by weight, the molded product may have a high specific gravity and become hard, and the formation of the pores 22c in response to the addition of the flocculant may become unstable. . Furthermore, if the blending amount of the resin microballoon is more than 5 parts by weight, the volume of the resin microballoon becomes large, and special consideration may be required when blending it into the liquid silicone rubber.

In this embodiment, tetraethylene glycol was used as the aggregating agent. The amount of aggregating agent added to the liquid silicone rubber depends on the amount of resin microballoons added to the liquid silicone rubber, but is approximately 3 to 15 parts by weight per 100 parts by weight of the liquid silicone rubber. If the amount of the agglomerating agent added is less than 3 parts by weight, there may be many isolated voids 22b that are not communicating with each other. Furthermore, if the amount of the aggregating agent added is more than 15 parts by weight, the heat moldability may be poor.

In addition, it is preferable that the volume ratio of the interconnected void portions 22b (communicating holes) is 35 vol% or more and 65 vol% or less with respect to the entire volume of the inner elastic layer 22. If the volume ratio of the void portion 22b is less than 35 vol%, the durability of the rubber may be poor, and if it is 65 vol% or more, the rubber may be too hard to form the fixing nip N. Note that the voids 22b of the inner elastic layer 22 are not all limited to being continuous holes, and the inner elastic layer 22 may include independent holes.

<Acicular filler>
The acicular filler 22d is almost randomly dispersed within the silicone rubber 22a. As will be described in detail later, the inner elastic layer 22 is formed by injecting a liquid material containing an acicular filler into a mold and causing it to flow. At this time, the acicular filler 22d with a high aspect ratio is generally oriented in accordance with the flow. When hollow particles (hollow filler) are used as the material for forming the voids 22b, orientation of the acicular fillers 22d in the flow direction can be suppressed. This is considered to be because the hollow particles act as so-called disturbing particles. Therefore, when the hollow particles for forming the void portion 22b are present, the connection based on the contact between the needle-like fillers enables the characteristic peculiar to the needle-like fillers to be exhibited, compared to the case where the hollow particles do not exist. A relatively large number of paths are formed in the thickness direction of the inner elastic layer 22.

Examples of the acicular filler 22d include pitch-based carbon fibers, PAN-based carbon fibers, glass fibers, and other inorganic whiskers. The acicular filler 22d may be at least one of these examples. For example, when carbon fiber with high thermal conductivity is used as an acicular filler, the above-mentioned connected path functions as a heat conduction path, and the thickness direction of the inner elastic layer 22 is Improves heat transfer. Since the inner elastic layer 22 is laminated on the metal core 21 as described above, the heat accumulated in the non-sheet passing portion of the pressure roller 20 is effectively transferred via the heat conduction path. It is possible to escape to the core metal 21. Here, the acicular filler (or fibrous filler) refers to a filler having an acicular (or fibrous) shape that is long in one direction. More specifically, although not limited thereto, fillers with an aspect ratio (length/diameter) of 10 or more, preferably 20 or more can be suitably used as needle-like fillers (or fibrous fillers).

The thermal conductivity λ of the pressure roller 20 can be measured by the method described below. The thermal conductivity λ of the pressure roller 20 depends on the amount of resin microballoons and acicular filler blended into the silicone rubber, which is the main component of the elastic layer 25, but is from 0.5 [W/m·K]. It is preferably large, and 3.0 [W/m·K] or less. If the thermal conductivity λ of the pressure roller 20 is 0.5 [W/m·K] or less, it may be difficult to suppress the temperature rise in the non-sheet passing area. Furthermore, if the thermal conductivity λ of the pressure roller 20 is higher than 3.0 [W/m·K], a large amount of acicular filler is required, which may make molding difficult.

Further, as described above, the thermal conductivity λ2 of the inner elastic layer 22 is higher than the thermal conductivity λ1 of the outer elastic layer 23. The thermal conductivity λ2 of the inner elastic layer 22 is preferably 0.2 [W/m·K] or more and 1.0 [W/m·K] or less, and the thermal conductivity λ1 of the outer elastic layer 23 is 0.2 [W/m·K] or more and 1.0 [W/m·K] or less. 05 [W/m·K] or more and 0.2 [W/m·K] or less is preferable. A method for measuring the thermal conductivities λ1 and λ2 will also be described later.

That is, it is preferable that the thermal conductivity λ of the pressure roller 20 satisfies the following formula: 0.5 [W/m·K]<λ≦3.0 [W/m·K]. Further, the thermal conductivity of the first elastic layer 22 is 0.2 [W/m·K] or more and 1.0 [W/m·K] or less, and the thermal conductivity of the second elastic layer 23 is is preferably 0.05 [W/m·K] or more and 0.2 [W/m·K] or less.

In this embodiment, the acicular filler 22d is made of pitch-based carbon fiber exhibiting high thermal conductivity (product name: GRANOC Milled Fiber , aspect ratio 28, density 2.2 g/cm ³ ).

6. Method for Manufacturing Pressure Roller Next, a method for manufacturing the pressure roller 20 in this embodiment will be described. Here, an outline of a method for manufacturing the pressure roller 20 will be described using Experimental Example A1, which will be described later, as an example. Details of settings such as materials, compounding amounts, and dimensions of each part in each experimental example will be described later. 4 and 5 are a schematic external perspective view and a schematic cross-sectional view along the longitudinal direction of a cast molding mold used for manufacturing the pressure roller 20 in this embodiment, respectively.

Note that the present invention does not limit the method of manufacturing the pressure roller 20 to the method described below. In addition, a plurality of pressure rollers 20 for each experimental example to be described later were created and used for evaluation.

<Preparation process of liquid composition for outer elastic layer (first step)>
A liquid silicone rubber containing a silane coupling agent (methacryloxypropyltrimethoxysilane) is further blended with resin microballoons, and thoroughly stirred to form a liquid composition for the outer elastic layer. was prepared.

<Outer elastic layer molding process (second process)>
As shown in FIG. 4, a fluororesin tube 75 was tightly fixed inside a cylindrical metal outer mold 71 having a longitudinal length of 250 mm, an outer diameter of 28 mm, and an inner diameter of 20 mm by a known method. Note that the above dimensions are the dimensions of the portions of the pressure roller 20 that correspond to the main body portion of the core bar 21, the inner elastic layer 22, the outer elastic layer 23, and the surface release layer 24. Next, the liquid composition for the outer elastic layer prepared in the first step is applied to the inside of the fluororesin tube 75 using a ring coating method until the outer elastic layer 79 (FIG. 5) has a predetermined thickness. The coating was applied so that the thickness (approximately 300 μm in Experimental Example A1) was obtained. In addition, when setting the thickness of the outer elastic layer 79 (FIG. 5) to 200 μm or less, the outer mold 71 and a ring coating nozzle (not shown) are precisely aligned so that they are concentric. . The entire outer mold 71 to which the fluororesin tube 75 is fixed is heated to 130° C. to form a molded body in which the fluororesin tube 75 fixed to the outer mold 71 and the outer elastic layer 79 are integrated (FIG. 5). I got it. The fluororesin tube 75 serves as the surface release layer 24 of the pressure roller 20, and the outer elastic layer 79 serves as the outer elastic layer 23 of the pressure roller 20.

<Preparation step of liquid composition for inner elastic layer (third step)>
A needle filler and a resin microballoon were each weighed and blended into an uncrosslinked addition-curing liquid silicone rubber. Then, the mixture was mixed using a known mixing and stirring means such as a planetary universal mixing and stirring machine. Subsequently, tetraethylene glycol was added as an aggregating agent for the resin microballoons, and mixing was continued for a certain period of time to prepare a liquid composition for the inner elastic layer.

<Layer formation step of inner elastic layer (fourth step)>
As shown in FIG. 5, the molded body obtained in the second step fixed to the outer mold 71 and the core bar 74 with a diameter of 15 mm whose surface has been treated with a primer are used to form a cavity in a casting mold. 72 was formed. The core metal 74 is supported by the outer mold 71 by bearings 76-1 and 76-2. The cavity 72 is formed between the outer peripheral surface of the core bar 74 and the inner peripheral surface of the outer elastic layer 79 formed in the second step. The cavity 72 communicates with the outside of the outer mold 71 through communication paths 73-1 and 73-2. Then, the liquid composition for the inner elastic layer prepared in the third step was injected from the communication path 73-1, which is a flow path, to fill the inside of the cavity 72 with the liquid composition. Next, the cavity 72 filled with the liquid composition for the inner elastic layer was sealed using a sealing means (not shown). Note that the core metal 74 becomes the core metal 21 in the pressure roller 20.

<Crosslinking and curing step of silicone rubber component (fifth step)>
The cast molding mold with the cavity 72 sealed was heated at 130° C. for 60 minutes to harden the silicone rubber component of the inner elastic layer.

<Demolding process (6th process)>
After the cast molding mold is appropriately cooled by water cooling or air cooling, the pressure roller 20 in which the core bar 21, the inner elastic layer 22, the outer elastic layer 23, and the surface release layer 24 are integrated is used for cast molding. Removed from mold.

<Secondary crosslinking step (7th step)>
The pressure roller 20 taken out from the casting mold was placed in a hot air circulation oven and maintained at a temperature of 230° C. for 4 hours to perform secondary crosslinking.

7. Evaluation Method Next, a method for evaluating the pressure roller 20 will be described.

<Evaluation method of dynamic viscoelastic properties of inner elastic layer>
A destructive test was conducted to evaluate the material properties of the inner elastic layer 22 of the molded pressure roller 20. The inner elastic layer 22 was cut out, and the frequency dependence of dynamic viscoelasticity during compression was measured using a dynamic viscoelasticity measuring device (Rheogel-E4000: UBM Corporation).

The size of the cut sample of the inner elastic layer 22 was 5 mm in length, 5 mm in width, and 2 mm in thickness. Further, a load of 50 g was applied in a static load constant mode in which compressive stress was applied in the thickness direction of the sample corresponding to the thickness direction of the pressure roller 20 (substantially radial direction in this embodiment). In addition, the test was conducted at a temperature of 100°C and a strain amplitude of 3 μm (sine wave), using the complex modulus of elasticity E* (1 Hz) at a stress frequency of 1 Hz as an index during low-speed operation, and the complex elastic modulus at a stress frequency of 50 Hz. The rate E* (50 Hz) was used as an index during high-speed operation. The complex modulus of elasticity E* (1Hz) and the complex modulus of elasticity E* (50Hz) are determined by the amplitude ratio (σ*/ε*) of stress and strain at each frequency and the phase difference ( The value (unit: is represented by [Pa]).

<Evaluation method of thermal conductivity of pressure roller>
The thermal conductivity λ of the pressure roller 20 is measured using a surface thermal conductivity meter (product name: QTM-500, manufactured by Kyoto Denshi Co., Ltd.). Measurements were made by contacting a sensor probe of a surface thermal conductivity meter (model: PD-11, manufactured by Kyoto Denshi Co., Ltd.) approximately in parallel. In the measurement, the sensor probe was calibrated with a quartz cylinder having the same diameter as the pressure roller 20 and used.

In addition, the thermal conductivity λ2 of the inner elastic layer 22 and the thermal conductivity λ1 of the outer elastic layer 23 can be measured in the same manner as the thermal conductivity λ of the pressure roller 20 using a surface thermal conductivity meter (product name: QTM- 500, manufactured by Kyoto Denshi Co., Ltd.). Note that the inner elastic layer 22 and the outer elastic layer 23 were stacked to form a measurement sample so that each had a thickness that could be measured with a surface thermal conductivity meter.

<Evaluation method of temperature rise in non-paper passing area of pressure roller>
The pressure roller 20 of each example was incorporated into the fixing device 6 of this embodiment shown in FIG. 2(a), and the fixing device 6 was installed in the image forming apparatus 100 of this embodiment shown in FIG. Then, 50 sheets of recording material (paper) P on which a predetermined image pattern has been formed are continuously conveyed (passed) to the fixing nip N under the following predetermined conditions, and the non-sheet passing portion of the pressure roller 20 is (More specifically, the surface temperature of the pressure roller 20) was measured. The above predetermined conditions include a process speed (corresponding to the transport speed of the recording material P in the fixing nip N) of 270 mm/sec, an environment of an air temperature of 25° C., and a humidity of 50%, and a target temperature for temperature control of the heater 11 of the fixing device 6 (temperature Temperature control) 200°C. As the paper, CANON Red Label 80 g/cm ² was cut into B5 size.

It should be noted that the pressure roller 20 is unlikely to break immediately when 50 sheets of paper are continuously passed. Here, the temperature of the non-paper passing portion of the pressure roller 20 reaches 230°C, which is the temperature at which the pressure roller 20 is likely to break due to oxidative deterioration of silicone rubber. The paper section temperature rise was evaluated.

8. Structure of Experimental Example Next, the present invention will be explained in more detail by giving an experimental example.

<Experiment example A1>
The pressure roller 20 of Experimental Example A1 was manufactured as follows.

・Preparation process of liquid composition for outer elastic layer (first step)
To 100 parts by weight of liquid silicone rubber, 1 part by weight of a silane coupling agent (methacryloxypropyltrimethoxysilane) was added, and resin microballoons (trade name: F80-DE, Matsumoto Yushi) with an average particle size of 100 μm were added. (manufactured by Yakuhin Co., Ltd.) was added thereto and thoroughly stirred to prepare a liquid composition for the outer elastic layer.

・Outer elastic layer molding process (second process)
As described above with reference to FIGS. 4 and 5, a molded article in which the fluororesin tube 75 fixed to the outer mold 71 and the outer elastic layer 79 were integrated was obtained. At this time, the liquid composition for the outer elastic layer prepared in the first step was applied to the inside of the fluororesin tube 75, and the entire outer mold 71 was heated to 130°C. Further, the thickness of the outer elastic layer 23 formed by the ring coat was approximately 300 μm.

・Preparation process of liquid composition for inner elastic layer (third process)
For 100 parts by weight of uncrosslinked addition-curing liquid silicone rubber, 15 parts by weight of needle filler (product name: GRANOC Milled Fiber XN-100-25M, manufactured by Nippon Graphite Fiber Co., Ltd.) and resin microballoon (product name) :F80-DE, manufactured by Matsumoto Yushi Pharmaceutical Co., Ltd., 5 parts by weight were each weighed and blended. Then, the mixture was stirred using a universal mixing stirrer (trade name: T.K. Hibismix 2P-1, manufactured by Primix Co., Ltd.) with the rotation speed of the stirring blade at 80 rpm. Subsequently, 5 parts by weight of tetraethylene glycol was added as an aggregating agent for resin microballoons, and the mixture was further stirred to prepare a liquid composition for the inner elastic layer.

・Layer formation process of inner elastic layer (4th process)
A core bar 74 whose surface was treated with a primer (trade name: DY39-051, manufactured by Dow Corning Toray Co., Ltd.) and whose main body had an outer diameter of 15 mm was prepared. Further, as described above with reference to FIG. 5, this core metal 74, the outer mold 71 to which the molded body obtained in the second step is fixed, and the bearings 76-1 and 76-2 are combined. , a casting mold having a cavity 72 was formed. Then, the liquid composition for the inner elastic layer prepared in the third step was injected at a rate of 50 cm ³ /min to fill the cavity 72 with the liquid composition, and flow-out was confirmed. Then, the cavity 72 was sealed using a sealing means (not shown).

・Crosslinking and curing process of silicone rubber component (5th process), demolding process (6th process), and secondary crosslinking process (7th process)
The cast mold with the cavity 72 sealed was heated in a hot air oven at 130° C. for 1 hour to cure the silicone rubber (fifth step). After cooling the cast molding mold, the pressure roller was taken out from the cast molding mold (sixth step). Next, it was heated in a hot air oven at 230°C for 4 hours (seventh step). Finally, a secondary process was performed to cut off the excess end portions to obtain the pressure roller 20 of Experimental Example A1.

<Experiment example A2>
A pressure roller 20 of Experimental Example A2 was obtained by the same manufacturing method as Experimental Example A1, except that in the third step, 2 parts by weight of resin microballoons were mixed into the liquid silicone rubber.

<Experiment example A3>
In the third step, the processing of Experimental Example A3 was performed using the same manufacturing method as Experimental Example A1, except that the resin microballoons were not blended and the blended amounts of the acicular filler and flocculant were the same as those of Experimental Example A1. A pressure roller 20 was obtained.

<Experiment example A4>
In the third step, the pressurization of Experimental Example A4 was performed using the same manufacturing method as Experimental Example A1, except that the resin microballoons and agglomerating agent were not blended, and the amount of needle-like filler was the same as that of Experimental Example A1. A roller 20 was obtained.

<Experiment example B2>
A pressure roller 20 of Experimental Example B2 was obtained by the same manufacturing method as Experimental Example A1, except that in the third step, 25 parts by weight of the acicular filler was mixed into the liquid silicone rubber.

<Experiment example B3>
A pressure roller 20 of Experimental Example B3 was obtained by the same manufacturing method as Experimental Example A1, except that in the third step, 10 parts by weight of the acicular filler was added to the liquid silicone rubber.

<Experiment example B4>
A pressure roller 20 of Experimental Example B4 was obtained by the same manufacturing method as Experimental Example A1, except that in the third step, 5 parts by weight of the acicular filler was mixed into the liquid silicone rubber.

<Experiment example C2>
The manufacturing method is the same as in Experimental Example A1, except that in the second step, the thickness of the outer elastic layer 23 formed by ring coating is 150 μm, and in the fourth step, the thickness of the inner elastic layer 22 is 2350 μm. Thus, a pressure roller 20 of Experimental Example C2 was obtained.

<Experiment example C3>
The manufacturing method is the same as in Experimental Example A1, except that in the second step, the thickness of the outer elastic layer 23 formed by ring coating is 500 μm, and in the fourth step, the thickness of the inner elastic layer 22 is 2000 μm. Thus, a pressure roller 20 of Experimental Example C3 was obtained.

<Experiment example C4>
In the second step, the thickness of the outer elastic layer 23 formed by ring coating is set to 300 μm, and in the fourth step, the thickness of the inner elastic layer 22 is set to 3200 μm using a core bar 74 whose main body has an outer diameter of 13 mm. Except for this, a pressure roller 20 of Experimental Example C4 was obtained using the same manufacturing method as Experimental Example A1.

9. Evaluation Experiment Table 1 summarizes the thickness of the elastic layer, the addition-curing liquid silicone rubber, the acicular filler, the resin microballoon, and the blending ratio of the aggregating agent in each of the above-mentioned experimental examples. As mentioned above, for simplicity, the thickness of the surface release layer 24 is ignored here, and the thickness of the inner elastic layer 22 and the total thickness of the inner elastic layer 22 and the outer elastic layer 23 are shown. are doing. More specifically, the thickness of the inner elastic layer 22 and the total thickness of the inner elastic layer 22 and the outer elastic layer 23 are the thicknesses obtained by subtracting the thickness of the surface release layer 24 from the indicated value.

For each of the above-mentioned experimental examples, an evaluation experiment was conducted regarding the dynamic viscoelastic properties of the inner elastic layer 22, the thermal conductivity of the pressure roller 20, and the temperature rise of the non-sheet passing portion of the pressure roller 20. Table 2 shows the evaluation results. The methods for evaluating the dynamic viscoelastic properties of the inner elastic layer 22, the thermal conductivity of the pressure roller 20, and the temperature rise in the non-sheet passing portion of the pressure roller 20 are as described above.

(1) Experimental examples A1 to A4
In Experimental Example A1, E*(50Hz)/E*(1Hz) was 1.05, and the frequency dependence of the dynamic viscoelasticity of the inner elastic layer 22 was small. Further, in Experimental Example A1, the thermal conductivity of the pressure roller 20 was 1.36 [W/m·K]. In addition, in the fixing device 6 equipped with this pressure roller 20, when the temperature control temperature was set to 200°C, the temperature of the non-paper-passing portion of the pressure roller 20 at the 50th continuous sheet passing was 212°C. . Experimental example A1 is OK from the viewpoint of ensuring the flexibility of the elastic layer and suppressing the temperature rise in the non-paper-passing area.

In Experimental Example A2, E*(50Hz)/E*(1Hz) was 1.17, and although the frequency dependence of the dynamic viscoelasticity of the inner elastic layer 22 was larger than that in Experimental Example A1, it was still sufficiently small. Ta. Further, in Experimental Example A2, the thermal conductivity of the pressure roller 20 was 1.02 [W/m·K], which was smaller than that in Experimental Example A1. This is considered to be because the amount of resin microballoons blended into the inner elastic layer 22 was smaller than in Experimental Example A1, so that the acicular filler was oriented in the longitudinal direction during cast molding. In addition, in the fixing device 6 equipped with this pressure roller 20, when the temperature control temperature was set to 200°C, the temperature of the non-sheet-passing portion of the pressure roller 20 at the 50th continuous sheet passing was 222°C. . Experimental example A2 is OK from the viewpoint of ensuring the flexibility of the elastic layer and suppressing the temperature rise in the non-paper-passing area.

In Experimental Example A3, during the preparation of the liquid composition for the inner elastic layer, the liquid silicone rubber and the flocculant were not compatible. When molded as is, a plurality of depressions were found here and there on the surface of the pressure roller 20 after molding, and it was thought that the incompatible agglomerating agent was the cause of the depressions. For this reason, evaluations of thermal conductivity and temperature rise in non-sheet passing areas were not performed when this pressure roller 20 was incorporated into the fixing device 6. In Experimental Example A3, E*(50Hz)/E*(1Hz) was 1.41, and the frequency dependence of the dynamic viscoelasticity of the inner elastic layer 22 was large. Experimental example A3 is NG from the viewpoint of ensuring the flexibility of the elastic layer and suppressing the temperature rise in the non-paper-passing area.

In Experimental Example A4, E*(50Hz)/E*(1Hz) was 1.52, and the frequency dependence of the conductive viscoelasticity of the inner elastic layer 22 was large. In addition, in Experimental Example A4, the thermal conductivity of the pressure roller 20 was 0.88 [W/m·K], but in the fixing device 6 equipped with this pressure roller 20, the thermal conductivity was equivalent to that in Experimental Example A1. In order to obtain image quality, it was necessary to make the controlled temperature higher than in Experimental Example A1. That is, in Experimental Example A4, the fixing nip N was considered to be narrower than in Experimental Example A1, suggesting that the deformation of the pressure roller 20 was insufficient. In addition, in the fixing device 6 equipped with this pressure roller 20, when the temperature control temperature was set to 200°C, the temperature of the non-sheet passing portion of the pressure roller 20 at the 50th continuous sheet passing was 225°C. . Experimental example A4 is NG from the viewpoint of ensuring the flexibility of the elastic layer and suppressing the temperature rise in the non-paper-passing area.

Note that, as an example of the above-mentioned image quality, the fixing quality of a test image formed on the recording material P was evaluated. The fixing quality is determined by forming a predetermined test image on the recording material P, measuring the reflection density before and after rubbing the test image under predetermined conditions, and calculating the ratio of reflection density after rubbing/reflection density before rubbing (fixing rate). ) can be evaluated.

(2) Experimental examples B2 to B4
In Experimental Example B2, when preparing the liquid composition for the inner elastic layer, it was necessary to add the acicular filler in multiple doses. Further, in Experimental Example B2, E*(50Hz)/E*(1Hz) was 1.11, and the frequency dependence of the dynamic viscoelasticity of the inner elastic layer 22 was small. Further, in Experimental Example B2, the thermal conductivity of the pressure roller 20 was 3.00 [W/m·K]. In addition, in the fixing device 6 equipped with this pressure roller 20, when the temperature control temperature was set to 200°C, the temperature of the non-paper-passing portion of the pressure roller 20 at the 50th consecutive sheet passing was 195°C. . If the amount of acicular filler blended is larger than in this experimental example, the preparation of the liquid composition may become complicated and molding may become difficult. In other words, it can be seen that a thermal conductivity of the pressure roller 20 of 3.0 [W/m·K] or less is sufficient. Experimental example B2 is OK from the viewpoint of ensuring the flexibility of the elastic layer and suppressing the temperature rise in the non-paper-passing area.

In Experimental Example B3, E*(50Hz)/E*(1Hz) was 1.30, and although the frequency dependence of the dynamic viscoelasticity of the inner elastic layer 22 was larger than that in Experimental Example A1, it was still sufficiently small. Ta. Further, in Experimental Example B3, the thermal conductivity of the pressure roller 20 was 0.82 [W/m·K]. In addition, in the fixing device 6 equipped with this pressure roller 20, when the temperature control temperature was set to 200°C, the temperature of the non-paper-passing portion of the pressure roller 20 at the 50th continuous sheet passing was 226°C. . Experimental example B3 is OK from the viewpoint of ensuring the flexibility of the elastic layer and suppressing the temperature rise in the non-paper-passing area.

In Experimental Example B4, E*(50Hz)/E*(1Hz) was 1.09, and the frequency dependence of the dynamic viscoelasticity of the inner elastic layer 22 was small. However, in Experimental Example B4, the thermal conductivity of the pressure roller 20 was 0.45 [W/m·K]. In the fixing device 6 equipped with this pressure roller 20, when the temperature control temperature is set to 200°C, the temperature of the non-paper passing portion of the pressure roller 20 for the 50th continuous sheet of paper passing is 250°C. The temperature exceeded 230°C, which is an indicator of temperature rise in the non-paper passing area. In other words, in order to sufficiently suppress the temperature rise in the non-sheet passing area, the amount of acicular filler blended is larger than in this experimental example, and the thermal conductivity of the pressure roller 20 is increased to 0.5 [W/m· It can be seen that it is preferable to make the value larger than [K]. Experimental example B4 is NG from the viewpoint of ensuring flexibility of the elastic layer and suppressing temperature rise in the non-paper-passing area.

(3) Experimental examples C2 to C4
In Experimental Example C2, when molding the outer elastic layer 23, precise positioning was performed so that the outer mold and the ring coating nozzle were concentric. Further, in Experimental Example C2, E*(50Hz)/E*(1Hz) was 1.01, and the frequency dependence of the dynamic viscoelasticity of the inner elastic layer 22 was small. Further, in Experimental Example C2, the thermal conductivity of the pressure roller 20 was 1.85 [W/m·K]. This is considered to be because the thickness of the outer elastic layer 23 was thinner than that in Experimental Example A1, so that the thermal conductivity of the pressure roller 20 was higher than that in Experimental Example A1. In the fixing device 6 equipped with this pressure roller 20, when the temperature control temperature was set at 200°C, the temperature of the non-paper passing portion of the pressure roller 20 after the 50th continuous sheet was 209°C. In other words, it can be seen that in order to exhibit sufficient quick start performance, it is preferable that the thickness of the outer elastic layer 23 is 150 μm or more as in this experimental example. Experimental example C2 is OK from the viewpoint of ensuring the flexibility of the elastic layer and suppressing the temperature rise in the non-paper-passing area.

In Experimental Example C3, E*(50Hz)/E*(1Hz) was 1.08, and the frequency dependence of the dynamic viscoelasticity of the inner elastic layer 22 was small. However, in Experimental Example C4, the thermal conductivity of the pressure roller 20 was 0.50 [W/m·K]. This is considered to be because the outer elastic layer 23 was thicker than in Experimental Example A1, so the thermal conductivity of the pressure roller 20 was lower than in Experimental Example A1. In the fixing device 6 equipped with this pressure roller 20, when the temperature control temperature is set to 200°C, the temperature of the non-paper-passing portion of the pressure roller 20 for the 50th sheet of continuous paper passing is 230°C. The temperature reached 230°C, which was used as an index for the temperature increase in the non-paper passing area. In other words, in order to sufficiently suppress the temperature rise in the non-sheet passing area, the thickness of the outer elastic layer 23 should be smaller than 500 μm in this experimental example, and the thermal conductivity of the pressure roller 20 should be 0.5 [W/ m·K] is preferable. Experimental example C3 is NG from the viewpoint of ensuring the flexibility of the elastic layer and suppressing the temperature rise in the non-paper-passing area.

In Experimental Example C4, E*(50Hz)/E*(1Hz) was 1.05, and the frequency dependence of the dynamic viscoelasticity of the inner elastic layer 22 was small. However, in Experimental Example C4, the thermal conductivity of the pressure roller 20 was 0.25 [W/m·K]. This is because the inner elastic layer 22 is thicker than in Experimental Example A1, and the heat dissipation to the core metal 21 is inferior, so the thermal conductivity of the pressure roller 20 is lower than in Experimental Example A1. Conceivable. In the fixing device 6 equipped with this pressure roller 20, when the temperature control temperature is set to 200°C, the temperature of the non-paper-passing portion of the pressure roller 20 for the 50th continuous sheet of paper is 265°C. The temperature exceeded 230°C, which is an indicator of temperature rise in the non-paper passing area. The thickness of the inner elastic layer 22 is preferably 2 mm or more and 3 mm or less (2000 μm or more and 3000 μm or less). Experimental example C4 is NG from the viewpoint of ensuring the flexibility of the elastic layer and suppressing the temperature rise in the non-paper-passing area.

In addition, when the inner elastic layer 22 does not have a communicating hole and has only substantially independent holes, the expansion and contraction of the air existing inside the void portion 22b during heating and cooling may be applied. Due to a change in the outer diameter of the pressure roller 20, the formation of the fixing nip N may become unstable. Furthermore, in the structure in which the inner elastic layer 22 is provided with the void portion 22b and the hole passage portion 22c, if the heat conductive filler is not acicular (or fibrous), the heat conduction path in the thickness direction of the inner elastic layer 22 is The formation may be insufficient, and it may not be possible to sufficiently suppress the temperature rise in the non-sheet passing area.

As explained above, the pressure roller 20 of this embodiment can exhibit the same degree of flexibility during high-speed operation as during low-speed operation. As a result, the fixing device 6 of the present embodiment can stably secure the fixing nip N from low-speed operation to high-speed operation, and achieve both quick start performance and suppression of temperature rise in non-paper passing areas. can. Further, as a result, the image forming apparatus 100 of this embodiment can provide images with stable quality from low speed operation to high speed operation. In other words, according to the present embodiment, it is possible to stably form the nip portion, and also achieve both quick start performance and suppression of temperature rise in the non-sheet passing portion.

[Other embodiments]
Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

In the above-described embodiment, the heating member has an endless film (or belt) as a heating rotating body, but the present invention is not limited to this, and the heating member has an endless film (or belt) as a heating rotating body. A roller-shaped member (fixing roller) may be included as a fixing roller. Furthermore, in the above-described embodiment, the heating rotating body of the heating member is heated by the heater provided inside (on the inner peripheral surface side), but the present invention is not limited to this, and the rotating body for heating of the heating member is The rotating body for heating, such as a belt, may self-generate heat when energized. Further, the heating rotating body, such as an endless belt, may be electromagnetically generated to generate heat by an excitation coil provided on the outside (outer peripheral surface side) thereof.

6 Fixing device 10 Heating member 11 Heater 12 Holder 13 Fixing film 14 Thermistor 20 Pressure roller 21 Core bar 22 Inner elastic layer 22a Silicone rubber 22b Cavity 22c Hole 22d Needle filler 23 Outer elastic layer 24 Surface release layer 25 Elasticity layer

Claims (18)

A pressure roller used in a fixing device that heats and fixes a toner image formed on a recording material, the pressure roller comprising:
a first elastic layer;
a second elastic layer provided outside the first elastic layer;
has
The thermal conductivity of the first elastic layer is higher than the thermal conductivity of the second elastic layer,
The first elastic layer includes a plurality of voids, a hole connecting the plurality of voids, and an acicular highly thermally conductive filler,
Regarding the sample of the first elastic layer, when the dynamic viscoelastic properties were measured by applying compressive stress in the thickness direction of the pressure roller at a temperature of 100°C and an amplitude of 3 μm, when the stress frequency was 1 Hz, The ratio E*(50Hz)/E*(1Hz) of the complex modulus of elasticity E*(1Hz) and the complex modulus of elasticity E*(50Hz) when the frequency of stress is 50Hz is given by the following formula,
1.0≦E*(50Hz)/E*(1Hz)≦1.3
A pressure roller that satisfies the following. The thermal conductivity λ of the pressure roller is expressed by the following formula,
0.5[W/m・K]<λ≦3.0[W/m・K]
The pressure roller according to claim 1 , wherein the pressure roller satisfies the following. The first elastic layer has a thermal conductivity of 0.2 [W/m·K] or more and 1.0 [W/m·K] or less, and the second elastic layer has a thermal conductivity of The pressure roller according to claim 1 or 2, wherein the pressure roller is 0.05 [W/m·K] or more and 0.2 [W/m·K] or less. 4. The pressure roller according to claim 1, wherein the void in the first elastic layer is a void derived from a resin microballoon. 5. The first elastic layer is a silicone rubber layer formed by curing and molding liquid silicone rubber containing the resin microballoons, an agglomerating agent, and the high heat conductive filler with heat. Pressure roller as described. The pressure roller according to claim 5 , wherein the amount of the resin microballoons is 0.5 to 8 parts by weight based on 100 parts by weight of the liquid silicone rubber. The flocculant is tetraethylene glycol,
7. The pressure roller according to claim 5 , wherein the amount of the tetraethylene glycol is 3 to 15 parts by weight based on 100 parts by weight of the liquid silicone rubber. Claims 1 to 7 , characterized in that the communicating voids including the voids and the pores are provided in the first elastic layer at a volume ratio of 35 vol% or more and 65 vol% or less. The pressure roller according to any one of the items. The pressure roller according to any one of claims 1 to 8 , wherein the highly thermally conductive filler is at least one of pitch-based carbon fiber, PAN-based carbon fiber, glass fiber, and inorganic whisker. The pressure roller according to any one of claims 1 to 9 , wherein the second elastic layer has a thickness of 150 μm or more and less than 500 μm. The pressure roller according to any one of claims 1 to 10 , wherein the second elastic layer includes a plurality of voids. The pressure roller according to any one of claims 1 to 11 , wherein the void in the second elastic layer is a void derived from a resin microballoon. The pressure roller according to any one of claims 1 to 12 , wherein the first elastic layer has a thickness of 2 mm or more and 3 mm or less. The pressure roller according to any one of claims 1 to 13 , wherein the pressure roller further includes a fluororesin layer, and the thickness of the fluororesin layer is 10 μm or more and 100 μm or less. . A fixing device that heats and fixes a toner image formed on a recording material in a fixing nip portion while nipping and conveying it to the recording material, the fixing device comprising:
heating unit;
a pressure roller forming the fixing nip portion together with the heating unit;
has
A fixing device, wherein the pressure roller is the pressure roller according to any one of claims 1 to 14 . The fixing device according to claim 15 , wherein the heating unit includes a cylindrical fixing film and a heater that contacts an inner surface of the fixing film. 17. The fixing device according to claim 16 , wherein the fixing nip is formed by applying pressure between the heater and the pressure roller via the fixing film. An image forming apparatus that forms a toner image on a recording material,
an image forming means for forming a toner image on a recording material;
a fixing means for fixing the toner image formed on the recording material to the recording material;
has
An image forming apparatus, wherein the fixing means is the fixing device according to any one of claims 15 to 17 .

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