Patent Description:
Conventionally, there has been widespread an image forming apparatus (referred to also as a printer) that performs a printing process by making an image forming section form a developing agent image by using toners (referred to also as developing agents) based on an image supplied from computer equipment or the like, transferring the developing agent image onto a medium such as paper, and making a fixing device fix the image on the medium by applying heat and pressure to the image.

As an example of the fixing device, there is a fixing device in which a heating member is arranged to face an inner peripheral surface of an annular belt and a fixation nip part transmits heat to the fixation belt via a facing member (see Patent Reference <NUM>, for example). Patent Reference <NUM> is <CIT>.

Document <CIT> relates to a pressing member, a fixing device including the pressing member, and an electrophotographic image forming apparatus, such as a copier, a printer, or a facsimile machine, including the fixing device.

While it is desirable to efficiently transmit the heat generated by the heating member provided on the inner peripheral surface of the annular belt to the annular belt, the heat generated by the heating member is not transmitted efficiently to the annular belt.

An object of the disclosure is to provide a fixing device and an image forming apparatus capable of increasing the efficiency of the transmission of the heat from the heating member to the annular belt.

The present invention is defined in independent claims <NUM>, <NUM> and <NUM>.

A fixing device according to an aspect includes, among other features, an annular belt; a heating member provided on an inner peripheral surface's side of the annular belt; a facing member provided on a facing surface of the heating member facing the inner peripheral surface; and a pressing member that is provided on an outer peripheral surface's side of the annular belt and forms a nip region between the pressing member and the facing member via the annular belt, wherein the facing member includes resin and carbon.

Further, a fixing device according to another aspect includes, among other features, an annular belt; a heating member provided on an inner peripheral surface's side of the annular belt; and a facing member provided on a facing surface of the heating member facing the inner peripheral surface, wherein the facing member includes resin and a thermally conductive material having higher thermal conductivity than the resin, and a weight compound ratio of the thermally conductive material as a compound ratio of the thermally conductive material added relative to a weight ratio of the facing member is higher than or equal to <NUM> [wt%].

Furthermore, a fixing device according to yet another aspect includes, among other features, an annular belt; a heating member provided on an inner peripheral surface's side of the annular belt; and a facing member provided on a facing surface of the heating member facing the inner peripheral surface, wherein the facing member includes resin and a thermally conductive material having higher thermal conductivity than the resin, and a volume compound ratio of the thermally conductive material as a compound ratio of the thermally conductive material added relative to a volume ratio of the facing member is higher than or equal to <NUM> [vol%].

An image forming apparatus according to an aspect includes the above-described fixing device.

According to the disclosure, it is possible to realize a fixing device and an image forming apparatus capable of increasing the efficiency of the transmission of the heat from the heating member to the annular belt.

A fixing device and an image forming apparatus according to each embodiment will be described below with reference to drawings. The following embodiments are just examples and it is possible to appropriately modify the embodiments.

As shown in <FIG>, an image forming apparatus <NUM> is a printer using the electrophotographic method, for example, and forms a black and white image or a color image on a record medium P such as paper by performing an image forming operation by using one or more developing agents such as toners. In the following description, a position close to a sheet feed tray <NUM> or a direction heading towards the sheet feed tray <NUM> as viewed from an arbitrary position in a conveyance path through which the record medium P is conveyed will be referred to as an upper stream or being upstream. Further, a position close to a stacker <NUM> onto which the record medium P is ejected and loaded or a direction heading towards the stacker <NUM> as viewed from an arbitrary position in the conveyance path will be referred to as a lower stream or being downstream. Furthermore, a direction heading from the upper stream towards the lower stream will be referred to as a conveyance direction.

In a box-shaped printer housing <NUM>, the image forming apparatus <NUM> includes the sheet feed tray <NUM>, a hopping roller <NUM>, a registration roller pair <NUM>, an image forming section <NUM>, a fixing device <NUM> and an ejection roller pair <NUM>.

The sheet feed tray <NUM> is arranged in a lower part of the printer housing <NUM> and stores a plurality of record media P in a stacked state. The hopping roller <NUM> is provided downstream of the sheet feed tray <NUM>.

The hopping roller <NUM> presses against the surface of the record medium P and sends out the record medium P downstream along the conveyance path. The hopping roller <NUM> is rotated around a central axis of the hopping roller <NUM> as a rotation axis by motive power transmitted from a hopping motor (not shown). The registration roller pair <NUM> is provided downstream of the hopping roller <NUM>.

The registration roller pair <NUM> conveys the record medium P towards the image forming section <NUM>. While conveying the record medium P, the registration roller pair <NUM> corrects the skewing of the record medium P by catching a front end part of the record medium P butting against the registration roller pair <NUM>. The image forming section <NUM> is provided downstream of the registration roller pair <NUM>. The image forming section <NUM> transfers an image onto the record medium P and conveys the record medium P to the fixing device <NUM>.

The fixing device <NUM> fixes the image, transferred onto the record medium P conveyed from a transfer belt unit <NUM> of the image forming section <NUM>, on the record medium P by applying heat and pressure to the image, and conveys the record medium P towards the ejection roller pair <NUM> along the conveyance path. The ejection roller pair <NUM> is provided downstream of the fixing device <NUM>.

The ejection roller pair <NUM> conveys the record medium P towards the stacker <NUM>. By this operation, the image forming apparatus <NUM> ejects the record medium P to the stacker <NUM> provided outside the printer housing <NUM> and loaded with record media P having images fixed thereon.

The image forming section <NUM> is a mechanism that forms an image (toner image) and transfers the image onto the record medium P. The image forming section <NUM> includes four development units <NUM> (development units <NUM>, 11Y, <NUM> and 11C), four exposure units <NUM> (exposure units <NUM>, 17Y, <NUM> and 17C) and the transfer belt unit <NUM>. The development units <NUM>, 11Y, <NUM> and 11C are arranged in this order along the conveyance direction of the record medium P. In the following description, the development units <NUM>, 11Y, <NUM> and 11C will also be referred to collectively as a development unit <NUM>, and the exposure units <NUM>, 17Y, <NUM> and 17C will also be referred to collectively as an exposure unit <NUM>.

The development unit <NUM> forms images by using toners as developing agents based on print data transmitted from a host device such as a personal computer. The development units <NUM>, 11Y, <NUM> and 11C respectively form black, yellow, magenta and cyan images. The development units <NUM>, 11Y, <NUM> and 11C have the same configuration except in that the development units <NUM>, 11Y, <NUM> respectively form images by using toners of colors different from each other. Each development unit <NUM> includes a photosensitive drum <NUM>, a charging roller <NUM>, a development roller <NUM>, a cleaning blade <NUM> and a toner storage section <NUM>.

The photosensitive drum <NUM>, as a cylindrical member for carrying an electrostatic latent image on its surface (surface part), is formed by using a photo conductor (e.g., organic photo conductor). This photosensitive drum <NUM> is rotated clockwise in <FIG> by motive power transmitted from a photo conductor motor (not shown). The photosensitive drum <NUM> is electrically charged by the charging roller <NUM> and is exposed to light by a corresponding exposure unit <NUM>. By this operation, an electrostatic latent image is formed on the surface of the photosensitive drum <NUM>. Then, the toner is supplied from the development roller <NUM>, by which an image corresponding to the electrostatic latent image is formed (developed) on the photosensitive drum <NUM>.

The charging roller <NUM> is configured to electrically charge the surface (surface part) of the photosensitive drum <NUM>. The charging roller <NUM> is arranged to make contact with the surface (circumferential surface) of the photosensitive drum <NUM> and to be pressed against the photosensitive drum <NUM> at a prescribed pressing level. The charging roller <NUM> rotates counterclockwise in <FIG> according to the rotation of the photosensitive drum <NUM>. A prescribed charging voltage is applied to the charging roller <NUM>.

The development roller <NUM> is configured to carry the electrically charged toner on its surface. This development roller <NUM> is arranged to make contact with the surface (circumferential side face) of the photosensitive drum <NUM> and to be pressed against the photosensitive drum <NUM> at a prescribed pressing level. The development roller <NUM> is rotated counterclockwise in <FIG> by motive power transmitted from the photo conductor motor (not shown). A prescribed development voltage is applied to the development roller <NUM>.

The cleaning blade <NUM> is a member that cleans the surface of the photosensitive drum <NUM> by scraping off the toner remaining on the surface of the photosensitive drum <NUM>. This cleaning blade <NUM> is arranged to make contact with the surface of the photosensitive drum <NUM> in a counter direction and to be pressed against the photosensitive drum <NUM> at a prescribed pressing level.

The toner storage section <NUM> is configured to store the toner. Specifically, the toner storage sections <NUM> of the development units <NUM>, 11Y, <NUM> and 11C respectively store black, yellow, magenta and cyan toners.

Each exposure unit <NUM> (exposure unit <NUM>, 17Y, <NUM>, 17C), as a mechanism that applies light to the photosensitive drum <NUM> of the development unit <NUM>, is formed by using an LED (Light Emitting Diode) head, for example. By the exposure unit <NUM>, the electrostatic latent image is formed on the surface of the photosensitive drum <NUM>. Then, an image corresponding to the electrostatic latent image is formed on the photosensitive drum <NUM>.

The transfer belt unit <NUM> is a mechanism that transfers the image formed on the surface of each photosensitive drum <NUM> onto the surface of the record medium P by means of Coulomb force and conveys the record medium P in the conveyance direction. The transfer belt unit <NUM> conveys the record medium P having the transferred image thereon towards the fixing device <NUM>. The transfer belt unit <NUM> includes a transfer belt <NUM>, a drive roller <NUM>, a driven roller <NUM>, four transfer rollers <NUM> (transfer rollers <NUM>, 22Y, <NUM> and 22C) and a cleaning blade <NUM>.

The transfer belt <NUM> is an annular belt formed seamlessly and capable of holding and carrying the record medium P. The transfer belt <NUM> is stretched between the drive roller <NUM> and the driven roller <NUM>. The drive roller <NUM>, as a rotary member rotated by motive power transmitted from a belt motor (not shown) so as to convey the record medium P towards the fixing device <NUM>, rotates the transfer belt <NUM> in a circulating manner. The driven roller <NUM> is a member that stretches the transfer belt <NUM> in cooperation with the drive roller <NUM> while adjusting tension applied to the transfer belt <NUM>. The four transfer rollers <NUM> are rotary members that respectively transfer the image formed on the surface of the photosensitive drum <NUM> of the corresponding development unit <NUM> onto a transfer target surface of the record medium P. The transfer rollers <NUM>, 22Y, <NUM> and 22C are respectively arranged to face the photosensitive drums <NUM> of the development units <NUM>, 11Y, <NUM> and 11C via the transfer belt <NUM>. A prescribed transfer voltage is applied to each of the transfer rollers <NUM>, 22Y, <NUM> and 22C, by which the image formed on the photosensitive drum <NUM> by the development unit <NUM> is transferred onto the transfer target surface of the record medium P. The cleaning blade <NUM> is a member that cleans the surface of the transfer belt <NUM> by scraping off waste toners remaining on the surface of the transfer belt <NUM>. The fixing device <NUM> is provided downstream of the image forming section <NUM>.

The detailed configuration of the fixing device <NUM> will be described below with reference to <FIG>, <FIG>, <FIG>, <FIG>, <FIG>, <FIG>. As shown in <FIG>, the fixing device <NUM> includes side frames <NUM> and 31R, springs <NUM> and 32R, levers <NUM> and 33R, a drive gear <NUM>, a fixation belt unit <NUM> and a pressure roller <NUM>.

The side frames <NUM> and 31R are, for example, members fixed to the printer housing <NUM> of the image forming apparatus <NUM> by using screws or the like. As shown in <FIG> and <FIG>, the spring <NUM> is an elastic member such as a spring, for example, and applies biasing force to the lever <NUM>. One end of the spring <NUM> is fixed to the side frame <NUM> and the other end of the spring <NUM> is fixed to the lever <NUM>. Similarly to the spring <NUM>, the spring 32R is an elastic member such as a spring and applies biasing force to the lever 33R. Due to the biasing force applied from the spring <NUM>, the lever <NUM> rotates in a direction D1 around a rotary bearing <NUM> extending in a transverse direction as a rotary shaft. The lever <NUM> is attached to the side frame <NUM>. Similarly to the lever <NUM>, due to the biasing force applied from the spring 32R, the lever 33R rotates in the direction D1 around a rotary bearing 34R extending in the transverse direction as a rotary shaft. When the fixing device <NUM> does not perform the fixing operation, the levers <NUM> and 33R are pressed and retained at prescribed positions by lever retaining members (not shown). Specifically, since the spring <NUM> is compressed by the lever retaining member via the lever <NUM>, the spring <NUM> can apply the biasing force to the lever <NUM> when the lever <NUM> is released from the lever retaining member. The same goes for the spring 32R. The drive gear <NUM> transmits motive power supplied from an annular belt motor (not shown) to the pressure roller <NUM>.

With this configuration, when the fixing device <NUM> performs the fixing operation, the drive gear <NUM> transmits the motive power supplied from the annular belt motor to the pressure roller <NUM>. Further, due to the release of the levers <NUM> and 33R from the lever retaining members in response to the operation of the drive gear <NUM>, the levers <NUM> and 33R rotate in the direction D1 around the rotary bearings <NUM> and 34R as the rotary shafts. Accordingly, the fixation belt unit <NUM> attached to the levers <NUM> and 33R is pressed against the pressure roller <NUM>, by which a nip part N is formed in the fixation belt unit <NUM> and the pressure roller <NUM>. <FIG> shows the state in which the nip part N has been formed in the fixation belt unit <NUM> and the pressure roller <NUM>. By the passage of the record medium P through the nip part N, heat and pressure are applied to the image transferred onto the record medium P and the image is fixed on the record medium P.

The fixation belt unit <NUM> is configured to apply heat to the image on the record medium P. As shown in <FIG>, the fixation belt unit <NUM> includes a stay <NUM>, a holding member <NUM>, a heater <NUM>, a heat storage plate <NUM>, a heat diffusion member <NUM> and a fixation belt <NUM>. The stay <NUM> is a member that supports the fixation belt <NUM>. The stay <NUM> is fixed to the lever <NUM> by using a screw <NUM> and fixed to the lever 33R by using a screw 42R. The holding member <NUM> is a member that holds the heater <NUM>, the heat storage plate <NUM> and the heat diffusion member <NUM>. The holding member <NUM> is fixed to the stay <NUM>. As shown in <FIG> and <FIG>, the heat storage plate <NUM>, the heater <NUM>, the heat diffusion member <NUM> and the fixation belt <NUM> are arranged in this order from top to bottom. Namely, the heat storage plate <NUM> faces the heater <NUM>, the heater <NUM> faces the heat diffusion member <NUM>, and the heat diffusion member <NUM> faces the fixation belt <NUM>. In the following description, the heat diffusion member <NUM> and the heater <NUM> will also be referred to collectively as a heating member <NUM>.

The heater <NUM>, as a plate-shaped member extending in the transverse direction, is a heat source for heating the fixation belt <NUM> and includes a plurality of (e.g., five) heating parts aligned in a width direction (transverse direction) orthogonal to a rotation direction of the fixation belt <NUM>. For example, when an image is formed on a record medium P that is wide in the transverse direction such as a A3 sheet, the fixation belt unit <NUM> makes all the heating parts of the heater <NUM> generate heat. In contrast, when an image is formed on a record medium P that is narrow in the transverse direction such as a postcard, for example, the fixation belt unit <NUM> makes only heating parts in a central part in the transverse direction generate heat and thereby holds down the energy consumption. As above, the fixation belt unit <NUM> selectively energizes the heating parts depending on the width of the record medium P in the transverse direction and makes the energized heating parts generate heat.

The heat storage plate <NUM> is a member that stores the heat generated by the heater <NUM>. In this example, the heat storage plate <NUM> is a plate-shaped member extending in the transverse direction along the heater <NUM>. The heat storage plate <NUM> inhibits the heat generated by the heater <NUM> from being transmitted to a side of the heat storage plate <NUM> opposite to a side facing the heater <NUM>. Incidentally, while the fixation belt unit <NUM> is configured to include the heat storage plate <NUM> in this example, the configuration of the fixation belt unit <NUM> is not limited to this example; the fixation belt unit <NUM> may also be configured to include no heat storage plate <NUM>.

Between the heater <NUM> and the heat storage plate <NUM>, thermally conductive grease is applied in order to efficiently transmit the heat generated by the heater <NUM>. Similarly, the thermally conductive grease is applied between the heater <NUM> and the heat diffusion member <NUM>. The heater <NUM> and the heat storage plate <NUM> are arranged to be sandwiched between the holding member <NUM> and the heat diffusion member <NUM>, and are fixed by the holding member <NUM>. Incidentally, while the thermally conductive grease is applied between the heater <NUM> and the heat storage plate <NUM> in this example, the configuration is not limited to this example; it is permissible even if no thermally conductive grease is applied between the heater <NUM> and the heat storage plate <NUM>. Further, while the thermally conductive grease is applied between the heater <NUM> and the heat diffusion member <NUM> in this example, the configuration is not limited to this example; it is permissible even if no thermally conductive grease is applied between the heater <NUM> and the heat diffusion member <NUM>.

The heat diffusion member <NUM> is a metal plate member in a substantially flat plate shape extending in the transverse direction along the heater <NUM> and is configured to transmit the heat generated by the heater <NUM> to the fixation belt <NUM>. The heat diffusion member <NUM> is in a shape like the upper case character "U" in a right side view and its front and rear end parts are bent upward in a vertical direction as a thickness direction. Namely, the heat diffusion member <NUM> has a concave part facing the heater <NUM>. As shown in <FIG>, convex parts of the heat diffusion member <NUM> formed by bending the front and rear end parts upward are inserted into holding grooves 49F and 49B formed in the holding member <NUM>. Since the holding grooves 49F and 49B are spaces wider than the convex parts of the heat diffusion member <NUM>, the heat diffusion member <NUM> inserted into the holding grooves 49F and 49B can move in the thickness direction (substantially vertical direction) when the fixation belt unit <NUM> is pressed against the pressure roller <NUM>. Specifically, when the fixing device <NUM> performs the fixing operation, the heat diffusion member <NUM> is pressed against the heater <NUM>. At that time, the heat diffusion member <NUM> transmits the heat generated by the heater <NUM> to the fixation belt <NUM>. As shown in <FIG>, the heat diffusion member <NUM> includes a base member <NUM> and a slide member <NUM>.

The base member <NUM> has a counter facing surface 51A facing the heater <NUM> and a facing surface 51B on a side opposite to the counter facing surface 51A. The slide member <NUM> is formed on the facing surface 51B of the base member <NUM>. The counter facing surface 51A faces an inner peripheral surface <NUM> (<FIG>) of the fixation belt <NUM>. As mentioned earlier, the base member <NUM> is in a shape like the upper case character "U" in a right side view and its front and rear end parts are bent upward in the vertical direction as the thickness direction. The base member <NUM> uniformizes temperature difference at seams between heating parts in the heater <NUM>.

The base member <NUM> is configured to include a metal whose thermal diffusivity indicating the speed of heat transmission is high, for example. In this example, the main component of the base member <NUM> is aluminum (Al). Here, the main component means a component that occupies at least <NUM> [wt%] of the whole of the base member <NUM>. Namely, the content percentage of Al in the base member <NUM> is higher than those of other materials. Incidentally, while the base member <NUM> is configured to include Al in this example, the configuration of the base member <NUM> is not limited to this example; the base member <NUM> may also be configured to include a different metal whose thermal diffusivity is high. The base member <NUM>, which is required to have sufficient thermal conductivity capable of uniformizing the temperature difference at the seams between heating parts in the heater <NUM>, may also be configured to include stainless steel (SUS), copper or zinc (Zn), for example. Incidentally, the thickness of the base member <NUM> is not limited to the illustrated thickness.

The slide member <NUM> is a contact member that has a slide surface SF facing the inner peripheral surface <NUM> (<FIG>) of the fixation belt <NUM> and makes contact with the inner peripheral surface <NUM> of the fixation belt <NUM> via slide grease GR (described later). Here, "the slide surface SF of the slide member <NUM> faces the inner peripheral surface <NUM> of the fixation belt <NUM>" means that the slide surface SF is in an arrangement relationship of facing each other with the inner peripheral surface <NUM>. In this case, to "face" also means that the slide surface SF is in an arrangement relationship of contacting and facing each other with the inner peripheral surface <NUM> or that the slide surface SF is in an arrangement relationship of facing each other with the inner peripheral surface <NUM> via another member such as the slide grease GR which will be described later. The heater <NUM> is situated on a side of the base member <NUM> opposite to the slide surface SF. The slide member <NUM> is configured to include resin having high slidability on the inner peripheral surface <NUM> of the fixation belt <NUM>, for example. The thickness of the slide member <NUM> is greater than or equal to <NUM> [µm] and is desired to be less than or equal to <NUM> [µm]. Here, the thickness of the slide member <NUM> is the distance from the facing surface 51B of the base member <NUM> of the heat diffusion member <NUM> to the slide surface SF of the slide member <NUM> in a direction orthogonal to the facing surface 51B and heading towards the nip part N. Further, the thickness of the slide member <NUM> is not limited to the illustrated thickness.

As shown in <FIG>, the slide member <NUM> includes binder resin 52B as the main component. The binder resin 52B forming the slide member <NUM> is, for example, polyamideimide (PAI) having high tenacity. Here, the main component means a component that occupies at least <NUM> [wt%] of the whole of the slide member <NUM>. Namely, the content percentage of PAI in the slide member <NUM> is higher than those of other materials.

Further, the slide member <NUM> includes a plurality of particulate fillers (hereinafter referred to as thermally conductive filler particles 52F) of graphite as carbon being a thermally conductive material. By including the thermally conductive filler particles 52F being graphite, the slide member <NUM> has increased further in the slidability and the thermal conductivity.

As shown in <FIG>, the plurality of thermally conductive filler particles 52F are distributed discretely in the binder resin 52B, for example. Some of the plurality of thermally conductive filler particles 52F have a part exposed to the slide surface SF. Therefore, minute concave and convex structures are formed on the slide surface SF. Further, even when the slide surface SF has worn down due to the sliding on the inner peripheral surface <NUM>, the slide surface SF is capable of maintaining the minute concave and convex structures thanks to the plurality of thermally conductive filler particles 52F embedded in the binder resin 52B.

In this example, the slide member <NUM> is formed on the base member <NUM> by, for example, spraying a solvent of PAI on a surface of the base member <NUM> and hardening the resin by means of heating. The thickness of the slide member <NUM> is controlled by adjusting the number of times of the spraying, for example. In this example, the length of the slide member <NUM> in its lengthwise direction (transverse direction) is approximately <NUM> [mm], and the length of the slide member <NUM> in its short-side direction (depth direction) is approximately <NUM> [mm]. Thus, the slide member <NUM> covers substantially the whole of the facing surface 51B of the base member <NUM> facing the inner peripheral surface <NUM> of the fixation belt <NUM>. The slide surface SF of the slide member <NUM> faces the fixation belt <NUM> as described earlier, and the inner peripheral surface <NUM> of the fixation belt <NUM> rotating in the circulating manner slides on the slide surface SF. A surface roughness of the slide surface SF of the slide member <NUM> in contact with the inner peripheral surface <NUM> of the fixation belt <NUM> is preferably higher than or equal to <NUM> [µm] and less than or equal to <NUM> [µm].

Therefore, in order to increase the slidability of the inner peripheral surface <NUM> on the slide surface SF, the slide grease GR is provided between the fixation belt <NUM> and the slide surface SF of the slide member <NUM> as shown in <FIG> and <FIG> by applying the slide grease GR as a lubricant on the slide surface SF, for example. Thus, the fixation belt <NUM> slides on the slide surface SF via the slide grease GR. The slide grease GR is, for example, gel-like grease and includes a silicone-based material or a fluorine-based material.

Incidentally, while the binder resin 52B of the slide member <NUM> includes PAI in this example, the binder resin 52B is not limited to this example and can include a different resin. As such a different resin, polyimide (PI) realizing excellent slidability of the fixation belt <NUM> and also excelling in heat resistance and mechanical strength can be taken as an example. Further, while the slide member <NUM> is configured to cover substantially the whole of the facing surface 51B of the base member <NUM> facing the inner peripheral surface <NUM> of the fixation belt <NUM>, the configuration of the slide member <NUM> is not limited to this example; the slide member <NUM> may also be configured to cover part of the facing surface 51B of the base member <NUM>, for example.

The fixation belt <NUM> is an annular belt stretched by the stay <NUM> at prescribed tension, and is configured to be held to be rotatable. Further, the fixation belt <NUM> has the inner peripheral surface <NUM> facing the slide surface SF, and is provided so that the inner peripheral surface <NUM> slides on the slide surface SF. The fixation belt <NUM> forms the nip part N (<FIG>) between the fixation belt <NUM> and the pressure roller <NUM>. As shown in <FIG>, the fixation belt <NUM> includes a surface layer <NUM>, an elastic layer <NUM> and a base member layer <NUM>. Namely, in the fixation belt <NUM>, the elastic layer <NUM> is formed on the base member layer <NUM>, and the surface layer <NUM> is formed on the elastic layer <NUM>.

In this example, the surface layer <NUM> is configured to include a copolymer (PFA) of tetrafluoroethylene and perfluoro alkyl vinyl ether. The thickness of the surface layer <NUM> is <NUM> [µm], for example. The thickness of the surface layer <NUM> is desired to be a size that enables the surface layer <NUM> to follow the deformation of the elastic layer <NUM>. In contrast, if the thickness of the surface layer <NUM> is too small, wrinkles occur to the surface layer <NUM> due to the sliding on the pressure roller <NUM> and the sliding on the record medium P, and thus the thickness of the surface layer <NUM> is desired to be <NUM> to <NUM> [µm]. Further, the surface layer <NUM> is desired to have heat resistance to withstand the fixation temperature and to have releasability to inhibit toners remaining on the fixation belt <NUM> and paper dust deriving from the record medium P from sticking to the surface layer <NUM>, and thus is desired to be made of material obtained by fluorine substitution. Incidentally, the material of the surface layer <NUM> is not limited to the illustrated material, and the thickness of the surface layer <NUM> is not limited to the illustrated thickness.

In this example, the elastic layer <NUM> is configured to include silicone rubber having the heat resistance to withstand the fixation temperature. The rubber hardness of the elastic layer <NUM> is <NUM>°, for example, and the thickness of the elastic layer <NUM> is <NUM> [µm], for example. The elastic layer <NUM> is desired to have rubber hardness and thickness with which the nip part N can be formed. On the other hand, the elastic layer <NUM> is desired to inhibit heat loss of the heat emitted from the heater <NUM> and to efficiently transmit the heat emitted from the heater <NUM> to an outer peripheral surface (toner contact surface) of the fixation belt <NUM>. A great thickness of the elastic layer <NUM> facilitates the formation of a uniform nip part N, but is undesirable since heat capacity becomes high and heat loss becomes high. The thickness of the elastic layer <NUM> is desired to be <NUM> to <NUM> [µm]. The rubber hardness of the elastic layer <NUM> is desired to be <NUM>° to <NUM>° in order to increase the uniformity of the nip part N. Incidentally, while the elastic layer <NUM> is configured to include silicone rubber in this example, the configuration of the elastic layer <NUM> is not limited to this example; the elastic layer <NUM> may also be configured to include a different material having heat resistance to withstand the fixation temperature. For example, the elastic layer <NUM> may be configured to include fluororubber. Incidentally, the thickness of the elastic layer <NUM> is not limited to the illustrated thickness.

In this example, the base member layer <NUM> is configured to include polyimide (PI), and the main component of the base member layer <NUM> is PI. Here, the main component means a component that occupies at least <NUM> [wt%] of the whole of the base member layer <NUM>. Namely, the content percentage of PI in the base member layer <NUM> is higher than those of other materials. The internal diameter of the base member layer <NUM> is <NUM> [mm], for example, and the thickness of the base member layer <NUM> is <NUM> [µm], for example. The base member layer <NUM> lets the fixation belt <NUM> exhibit high durability and high mechanical strength, and excels in mechanical strength, resistance to repetitive bending, and durability against buckling. In other words, since the base member layer <NUM> has a high Young's modulus and high buckling strength, the fixation belt <NUM> is unlikely to tear. Incidentally, while the base member layer <NUM> is configured to include PI in this example, the configuration of the base member layer <NUM> is not limited to this example; the base member layer <NUM> may also be configured to include a different material having high heat resistance, a high Young's modulus and high buckling strength, for example. For example, the base member layer <NUM> may be configured to include stainless steel or polyether ether ketone (PEEK)-based material. Especially, resin material excelling in heat resistance is desirable, such as polytetrafluoroethylene (PTFE), for example. The base member layer <NUM> may also be configured to include a material to which carbon black or electrically conductive filler including a metallic element such as zinc has been added, in which case the base member layer <NUM> is enabled to exhibit conductivity. The base member layer <NUM> may also be configured to include PTFE to which filler such as boron nitride has been added, in which case the slidability and the thermal conductivity of the base member layer <NUM> can be increased. Incidentally, the thickness of the base member layer <NUM> is not limited to the illustrated thickness.

As shown in <FIG>, the pressure roller <NUM> is a rotary member that is provided to be capable of making contact with the outer peripheral surface of the fixation belt <NUM> in the fixation belt unit <NUM> so that the nip part N is formed between the pressure roller <NUM> and the fixation belt unit <NUM>, and applies pressure to the image on the record medium P. The external diameter of the pressure roller <NUM> is <NUM> [mm] and the hardness of the pressure roller <NUM> is desired to be <NUM>° to <NUM>°. The pressure roller <NUM> includes a surface layer <NUM>, an adhesive layer <NUM>, an elastic layer <NUM> and a shaft <NUM>. Specifically, in the pressure roller <NUM>, the elastic layer <NUM> is formed on the shaft <NUM>, the adhesive layer <NUM> is formed on the elastic layer <NUM>, and the surface layer <NUM> is formed on the adhesive layer <NUM>. Incidentally, an adhesive layer may be provided between the shaft <NUM> and the elastic layer <NUM>.

In this example, the surface layer <NUM> is configured to include PFA. The thickness of the surface layer <NUM> is <NUM> [µm], for example. The surface layer <NUM> slides on the record medium P and the fixation belt <NUM>. Similarly to the surface layer <NUM> of the fixation belt <NUM>, the thickness of the surface layer <NUM> is desired to be a size that enables the surface layer <NUM> to follow the deformation of the elastic layer <NUM>. In contrast, if the thickness of the surface layer <NUM> is too small, wrinkles occur to the surface layer <NUM> due to the sliding on the fixation belt <NUM> and the sliding on the record medium P, and thus the thickness of the surface layer <NUM> is desired to be <NUM> to <NUM> [µm]. Further, the surface layer <NUM> is desired to have heat resistance to withstand the fixation temperature and to have releasability to inhibit toners remaining on the fixation belt <NUM> and paper dust deriving from the record medium P from sticking to the surface layer <NUM>, and thus is desired to be made of material obtained by fluorine substitution. The material of the surface layer <NUM> is not limited to the illustrated material, and the thickness of the surface layer <NUM> is not limited to the illustrated thickness.

In this example, the adhesive layer <NUM> is configured to include a silicone adhesive agent having sufficient adhesivity, including electrically conductive material added thereto, and capable of withstanding the fixation temperature. The adhesive layer <NUM> bonds the elastic layer <NUM> and the surface layer <NUM> together to inhibit the peeling of the surface layer <NUM> from the elastic layer <NUM> and the occurrence of wrinkles. Since the adhesive layer <NUM> has electrical conductivity, the adhesive layer <NUM> inhibits accumulation of electric charge in the pressure roller <NUM> in continuous printing and electrostatic adhesion of paper dust or the like to the pressure roller <NUM>, for example. Incidentally, while electrically conductive material is added to the adhesive layer <NUM> in this example, the adhesive layer <NUM> is not limited to this example; it is permissible even if no electrically conductive material is added to the adhesive layer <NUM>. The material of the adhesive layer <NUM> is not limited to the illustrated materials.

In this example, the elastic layer <NUM> is configured to include silicone sponge having foamed cells to which electrically conductive material has been added. The thickness of the elastic layer <NUM> is <NUM> [mm], for example. Since the elastic layer <NUM> has electrical conductivity, the elastic layer <NUM> inhibits accumulation of electric charge in the pressure roller <NUM> in continuous printing and electrostatic adhesion of paper dust or the like to the pressure roller <NUM>, for example. The elastic layer <NUM> is desired to have rubber hardness and thickness with which the nip part N can be formed. Further, the elastic layer <NUM> is desired to have sufficient heat storage performance so that the heat transmitted from the fixation belt <NUM> to the image and the record medium P is not lost. Furthermore, to prevent a nip mark from remaining in the compressed nip part N, the cell diameter of the foamed cells is desired to be small, and specifically, the average cell diameter of the foamed cells is desired to be <NUM> to <NUM> [µm]. In this example, the average cell diameter is <NUM> [µm]. Measurement of the average cell diameter was carried out by slicing silicone sponge by using a razor or the like, observing the slice of silicone sponge by using a CCD (charged-coupled device) microscope, measuring the cell diameters of ten foamed cells in an observation viewing angle, and obtaining the average value of these cell diameters as the measurement value. Incidentally, while electrically conductive material is added to the elastic layer <NUM> in this example, the elastic layer <NUM> is not limited to this example; it is permissible even if no electrically conductive material is added to the elastic layer <NUM>. Further, while the elastic layer <NUM> is configured to include silicone sponge in this example, the configuration of the elastic layer <NUM> is not limited to this example; the elastic layer <NUM> may also be configured to include a different material. For example, the elastic layer <NUM> may be configured to include solid rubber. Incidentally, the thickness of the elastic layer <NUM> is not limited to the illustrated thickness.

The shaft <NUM> is a member having sufficient pressure resistance not to be deformed by the fixation pressure, and is configured to include solid stainless steel (SUS304), for example. Incidentally, while the shaft <NUM> includes SUS304 in this example, the shaft <NUM> is not limited to this example; the shaft <NUM> may also be configured to include a different material instead of SUS304. Further, while a solid shaft is used in this example, the shaft is not limited to this example; it is also possible to use a hollow shaft instead, for example.

With the configuration described above, the image forming apparatus <NUM> forms an image on the record medium P as follows: Upon receiving the print data from the host device, the image forming apparatus <NUM> executes an image forming process by rotating the photosensitive drum <NUM> of each development unit <NUM>.

The image forming apparatus <NUM> forms the electrostatic latent image on the surface of the photosensitive drum <NUM> in each development unit <NUM> by selectively applying light from the exposure unit <NUM> to the electrically charged surface of the photosensitive drum <NUM>. Then, an image corresponding to the electrostatic latent image is formed on the photosensitive drum <NUM>.

The image forming apparatus <NUM> rotates the hopping roller <NUM> by transmitting the motive power from the hopping motor (not shown) to the hopping roller <NUM>, and thereby sends out the record medium P towards the registration roller pair <NUM>. The registration roller pair <NUM> conveys the record medium P towards the image forming section <NUM>. At that time, the front edge of the record medium P butts against the registration roller pair <NUM>, by which the skewing of the record medium P is corrected.

Thereafter, the image forming apparatus <NUM> conveys the record medium P towards the fixing device <NUM> by rotating the transfer belt <NUM> in the circulating manner in the image forming section <NUM>. At that time, the record medium P passes between the photosensitive drum <NUM> and the transfer roller <NUM>.

In the image forming apparatus <NUM>, upon forming the image on the surface of each photosensitive drum <NUM>, a transfer process is executed by the transfer belt unit <NUM>. At that time, in the transfer belt unit <NUM>, while the transfer belt <NUM> conveys the record medium P, the transfer roller <NUM> attracts the image formed on the surface of the photosensitive drum <NUM>. Consequently, the image is transferred from the photosensitive drum <NUM> onto the record medium P.

After the image has been transferred from each photosensitive drums <NUM> onto the record medium P, the image forming apparatus <NUM> conveys the record medium P to the fixing device <NUM>. When the record medium P is conveyed thereto, the fixing device <NUM> executes a fixation process. At that time, the fixing device <NUM> fuses the image transferred onto the surface of the record medium P by heating and compressing the image, and thereby fixes the image on the record medium P.

After the image is fixed on the record medium P, the image forming apparatus <NUM> conveys the record medium P towards the stacker <NUM> and ejects the record medium P onto the stacker <NUM>.

Next, a description will be given of the behavior of the heat diffusion member <NUM> in the fixing operation when the record medium P onto which the image has been transferred is conveyed from the image forming section <NUM> towards the fixing device <NUM>.

When the fixing device <NUM> executes the fixing operation, the drive gear <NUM> transmits the motive power supplied from the annular belt motor to the pressure roller <NUM>. At that time, due to the release of the levers <NUM> and 33R from the lever retaining members in response to the operation of the drive gear <NUM>, the levers <NUM> and 33R rotate in the direction D1 (<FIG>) respectively around the rotary bearings <NUM> and 34R as the rotary shafts. Accordingly, the fixation belt unit <NUM> is pressed against the pressure roller <NUM>, by which the nip part N is formed in the fixation belt unit <NUM> and the pressure roller <NUM>. In this example, the length of the nip part N in its lengthwise direction (transverse direction) is <NUM> [mm], and the length of the nip part N in its short-side direction (depth direction) orthogonal to the lengthwise direction is <NUM> to <NUM> [mm]. The load placed on the fixation belt unit <NUM> is <NUM> to <NUM> [kg] in regard to the whole of the nip part N, and is specifically <NUM> [kg], for example. Nip pressure corresponding to the load of <NUM> [kg] is <NUM> to <NUM> [kg/cm<NUM>].

The pressure roller <NUM> is rotated by the motive power transmitted from the annular belt motor. The fixation belt <NUM> rotates accompanying the pressure roller <NUM> according to the rotation of the pressure roller <NUM>. Accordingly, in the fixation belt unit <NUM>, the inner peripheral surface <NUM> of the fixation belt <NUM> slides on the slide surface SF of the slide member <NUM> of the heat diffusion member <NUM> via the slide grease GR. At that time, in the fixation belt unit <NUM>, the heat diffusion member <NUM> is pressed against the heater <NUM>. In the fixing operation, electric current supplied from an external power supply is fed to each heating part through electric wires (not shown), by which the heater <NUM> generates heat. The heat generated by the heater <NUM> is transmitted to the heat diffusion member <NUM> via the thermally conductive grease and thereafter transmitted to the fixation belt <NUM> via the slide grease GR. By the passage of the record medium P through the nip part N, the image transferred onto the record medium P is supplied with heat from the fixation belt <NUM> and pressure from the nip part N. Consequently, the image is fixed on the record medium P.

By using the image forming apparatus <NUM> and the fixing device <NUM> described above, examination of the heat diffusion member <NUM> was conducted. In this examination, the slide member <NUM> was formed with the thermally conductive filler particles 52F and the binder resin 52B as shown in <FIG>, samples Sa, Sb, Sc, Sd, Se and Sf of the heat diffusion member <NUM> differing from each other in the compound ratio of the thermally conductive filler particles 52F included in the slide member <NUM> (namely, graphite weight compound ratio) were made, and thermal diffusivity in the thickness direction of the heat diffusion member <NUM> and arithmetic mean roughness Ra of the slide surface SF of the slide member <NUM> in the heat diffusion member <NUM> were measured in regard to each sample. The thickness of the heat diffusion member <NUM> in this example was designed so that the base member <NUM> is <NUM> [µm] thick, the slide member <NUM> is <NUM> [µm] thick, and the heat diffusion member <NUM> is <NUM> [µm] thick in total.

The graphite weight compound ratio in the embodiment was obtained from a weight decrement in thermogravimetry-differential thermal analysis (TG-DTA measurement) of the slide member <NUM>. In the TG-DTA measurement, thermogravimeter-differential thermal analyzer TG/DTA <NUM> (manufactured by Hitachi High-Tech Corporation) was used. Measurement conditions were as described below.

Here, dry air is generally obtained by removing water vapor from atmospheric air, and the oxygen concentration of the dry air is assumed to be <NUM>%.

The weight decrements in measurement step <NUM> and measurement step <NUM> in Table TB1 in <FIG> were caused by pyrolysis of the binder resin 52B in a nitrogen atmosphere. The weight decrement in the subsequent measurement step <NUM> was caused by combustion of carbon components in an oxygen atmosphere. In the measurement step <NUM>, the weight decrement occurring from <NUM> [°C] to <NUM> [°C] was caused by combustion of carbon components of the pyrolyzed binder resin 52B, and the weight decrement occurring from <NUM> [°C] to <NUM> [°C] was caused by combustion of graphite alone. Based on this knowledge, the graphite weight was regarded as the weight decrement due to combustion from <NUM> [°C] to <NUM> [°C] in an air atmosphere after the pyrolysis in the nitrogen atmosphere, and the ratio of the graphite weight in the measurement sample weight was obtained as the graphite weight compound ratio in the embodiment.

In this measurement, the thermal diffusivity in the thickness direction was used as an index representing the thermal conductivity. In this measurement, the thermal diffusivity of the heat diffusion member <NUM> was measured by using a thermowave analyzer TA35 (manufactured by BETHEL Co. Measurement conditions were as described below.

In this measurement, the arithmetic mean roughness Ra stipulated in JIS (Japanese Industrial Standards) B0601: <NUM> was measured as an index representing the roughness. In this measurement, the roughness was measured by using a Surfcoder SEF3500 (manufactured by Kosaka Laboratory Ltd. Measurement conditions were as described below.

The roughness was measured at three positions on the heat diffusion member <NUM> and the mean value of the three roughness values was obtained as the arithmetic mean roughness Ra of the sample.

Further, in this measurement, fixation limit temperature when using each of the samples Sa to Sf of the heat diffusion member <NUM> was measured.

The fixation limit temperature is the lower limit of the surface temperature of the fixation belt <NUM> at which a fixation ratio is <NUM>% or higher. The fixation ratio was obtained by sticking Mending tape (manufactured by <NUM> Company) on the image after the fixation, rolling a cylindrical weight <NUM> [cm] wide and <NUM> [g] in weight on the mending tape back and forth, thereafter slowly peeling away the mending tape, measuring the image density before and after the tape peeling by using a reflection densitometer, and calculating the fixation ratio according to the following expression: <MAT>.

Furthermore, evaluation was performed on the printed image obtained by using each of the samples Sa to Sf of the heat diffusion member <NUM>.

In the evaluation of the printed image, the presence/absence of occurrence of a vertical streak-like image defect in fill-page <NUM>% solid color printing was evaluated. In cases where the surface roughness Ra is high and the slide grease GR not uniformly but unevenly and partially exists between the fixation belt <NUM> and the heat diffusion member <NUM>, temperature unevenness occurs on the surface of the fixation belt <NUM> due to the difference in the thermal conductivity, and a vertical streak appears as a level difference in gloss. Therefore, the vertical streak-like image defect is employed as an evaluation item. As the image evaluation, the presence/absence of a vertical streak having a width of <NUM> [mm] or more in the printed image was evaluated.

Table TB2 in <FIG> shows the graphite weight compound ratio, the thermal diffusivity, the arithmetic mean roughness Ra, a decrement in the fixation limit temperature, the judgment on the printed image (presence/absence of occurrence of a vertical streak), and fixability improvement in regard to each of the samples Sa to Sf of the heat diffusion member <NUM> used for the judgment on the printed image. About the presence/absence of occurrence of a vertical streak, the circle mark "O" was put when no vertical streak occurred, and the cross mark "×" was put when a vertical streak occurred. About the fixability improvement, the cross mark "×" was put when the graphite weight compound ratio was <NUM> [wt%], and the circle mark "O" was put when the fixation limit temperature lowered compared to the case where the graphite weight compound ratio was <NUM> [wt%].

From the result shown in Table TB2, it became clear that the thermal diffusivity of the heat diffusion member <NUM> in the thickness direction increases and the fixation limit temperature can be lowered with the increase in the graphite weight compound ratio. This can be understood as follows: The addition of graphite as the thermally conductive filler particles 52F improves the thermal conductivity of the slide member <NUM>, the heat from the heating member <NUM> can be quickly transmitted to the toners on the paper via the fixation belt <NUM>, and the need of excessively heating the fixation belt <NUM> is eliminated.

Here, if the graphite weight compound ratio is higher than <NUM> [wt%], the ratio of the binder resin 52B in the slide member <NUM> is too low, and thus the slide member <NUM> peels off without sticking fast to the base member <NUM> and no slide layer can be formed. Thus, the slide member <NUM> sticks fast to the base member <NUM> and the slide layer can be formed if the graphite weight compound ratio is less than or equal to <NUM> [wt%].

On the other hand, it was found that the vertical streak-like image defect occurs to the printed image when using the sample whose graphite weight compound ratio is <NUM> [wt%]. This can be understood as follows: Tops of graphite particles and the inner peripheral surface <NUM> of the fixation belt <NUM> locally adhere to each other, the slide grease GR between the slide member <NUM> and the inner peripheral surface <NUM> of the fixation belt <NUM> is unlikely to uniformly spread in surface directions, and parts with a large amount of grease and parts with a small amount of grease are formed locally during the sliding. Since the surface roughness of the slide member <NUM> increases with the increase in the graphite weight compound ratio, even supposing that a slide member <NUM> whose graphite weight compound ratio is over <NUM> [wt%] successfully sticks to the base member <NUM>, it can be considered that the slide grease GR becomes nonuniform and the vertical streak-like image defect occurs similarly to the case where the graphite weight compound ratio is <NUM> [wt%].

Further, it was found that the vertical streak-like image defect does not occur to the printed image with the samples whose graphite weight compound ratio is less than or equal to <NUM> [wt%]. Thus, it appears that the vertical streak-like image defect does not occur to the printed image with samples whose graphite weight compound ratio is less than or equal to a prescribed value between <NUM> [wt%] and <NUM> [wt%].

As above, it was found that the fixation limit temperature can be lowered by adding graphite to the slide member <NUM>. Further, it was found that the image defect can be inhibited if the graphite weight compound ratio is less than or equal to <NUM> [wt%].

As an example of a side effect of the addition of graphite to the slide member <NUM>, the slide member <NUM> becomes more likely to wear down and the base member <NUM> is exposed. When the base member <NUM> is exposed, deterioration in the slidability leads to an increase in abrasiveness of the inner peripheral surface <NUM> of the fixation belt <NUM>, and a tear occurs to the fixation belt <NUM>. Thus, breakage of the fixation belt <NUM> due to the exposure of the base member <NUM> in long-term use of an actual device can be inhibited by deriving the relationship between the compound ratio of graphite and wear depth and providing a slide member <NUM> whose film thickness is greater than the wear depth.

In this measurement, wear depth measurement of the slide member <NUM> by means of a frictional wear test was conducted in regard to the prepared samples Sa to Se in Table TB2 (<FIG>) differing in the graphite weight compound ratio by using a load variable frictional wear test system HHS2000 (manufactured by Shinto Scientific Co. Measurement conditions were as described below.

The product of the load and the slide distance in the frictional wear test in this example is equal to the product of the nip pressure and the slide (travel) distance of the fixation belt <NUM> in an actual device in longitudinal feed printing of <NUM> (= <NUM> × <NUM>) A4 sheets, from which the wear depth of the slide member <NUM> in long-term use of the actual device can be obtained. Table TB3 in <FIG> shows the pressure and the slide distance in the frictional wear test and in the actual device <NUM>-sheet printing. In this frictional wear test, the slide distance was set at a distance corresponding to longitudinally fed <NUM> A4 sheets. On the other hand, the operating life of the fixing device <NUM> is a distance corresponding to longitudinally fed <NUM> A4 sheets. Therefore, the slide distance in the frictional wear test reaches a range over the operating life of the fixing device <NUM>, and the result of the frictional wear test is a test result taking a safety margin (margin) into account.

The relationship between the graphite weight compound ratio and the wear depth in regard to the samples Sa to Se of the heat diffusion member <NUM> is shown in Table TB4 in <FIG> and a graph in <FIG>.

The tear of the fixation belt <NUM> due to the exposure of the base member <NUM> can be inhibited if the film thickness of the slide member <NUM> is made thicker than the wear depth corresponding to the graphite weight compound ratio. It became clear from the result in Table TB4 (<FIG>) that the wear depth increases with the increase in the graphite weight compound ratio and a relationship y = <NUM>. 198x holds in regard to the graphite weight compound ratio x and the wear depth y when an approximate straight line is drawn in <FIG>. Accordingly, the tear of the fixation belt <NUM> can be inhibited if a relationship t > <NUM>. 198Rw holds in regard to the film thickness t [µm] of the slide member <NUM> and the graphite weight compound ratio Rw [wt%] in the slide member <NUM>.

While the weight compound ratio Rw was used as the compound ratio of graphite in the above example, the compound ratio is not limited to the weight compound ratio; it is also possible to use a volume compound ratio Rv. In that case, the relationship between the film thickness and the graphite volume compound ratio can be obtained by converting the weight compound ratio into the volume compound ratio as described below.

Assuming that the weight of graphite is A [g] , the weight of the whole of the slide member <NUM> is B [g] , the density of graphite is α [g/cm<NUM>] and the density of the binder resin 52B is β [g/cm<NUM>], the weight compound ratio Rw [wt%] of graphite is represented by the following expression (<NUM>): <MAT>.

The following expression (<NUM>) is derived from the expression (<NUM>) : <MAT>.

Next, the volume compound ratio Rv [vol%] of graphite is represented by the following expression (<NUM>): <MAT>.

The following expression (<NUM>) is derived by substituting the expression (<NUM>) into the expression (<NUM>): <MAT>.

Further, the following expression (<NUM>) is derived by transposing Rw in the expression (<NUM>) to the left side: <MAT>.

Accordingly, the relationship between the film thickness of the slide member <NUM> and the graphite volume compound ratio is derived by substituting the expression (<NUM>) into the relational expression between the film thickness of the slide member <NUM> and the graphite weight compound ratio.

Namely, the tear of the fixation belt <NUM> can be inhibited if a relationship of the following expression (<NUM>) holds in regard to the film thickness t [µm] of the slide member <NUM>, the graphite volume compound ratio Rv [vol%] in the slide member <NUM>, the density α [g/cm<NUM>] of graphite and the density β [g/cm<NUM>] of the binder resin 52B: <MAT>.

Assuming that the density of graphite in the slide member <NUM> is <NUM> [g/cm<NUM>] and the density of the binder resin 52B is <NUM> [g/cm<NUM>], the relationship between the graphite volume compound ratio and the wear depth in regard to the samples Sa to Se of the heat diffusion member <NUM> is shown in Table TB4 in <FIG> and a graph in <FIG>.

The tear of the fixation belt <NUM> due to the exposure of the base member <NUM> can be inhibited if the film thickness of the slide member <NUM> is made thicker than the wear depth corresponding to the graphite volume compound ratio. According to the result in Table TB4, the wear depth increases with the increase in the graphite volume compound ratio similarly to the relationship with the graphite weight compound ratio. An approximate curved line can be drawn in <FIG> by substituting the right side of the aforementioned expression (<NUM>) into x in the approximate straight line y = <NUM>. 198x drawn in <FIG>, and it was found that a relationship y = <NUM>. 56x/(<NUM>. 8x + <NUM>) holds in regard to the graphite volume compound ratio x and the wear depth y. In this case, the density of graphite in the slide member <NUM> was assumed to be <NUM> [g/cm<NUM>] and the density of the binder resin 52B was assumed to be <NUM> [g/cm<NUM>]. Accordingly, the tear of the fixation belt <NUM> can be inhibited if a relationship t > <NUM>. 56x/(<NUM>. 8x + <NUM>) holds in regard to the film thickness t [µm] of the slide member <NUM> and the graphite volume compound ratio x [vol%] in the slide member <NUM>.

The aforementioned Table TB2 in <FIG> further describes the graphite volume compound ratios in addition to the graphite weight compound ratios of the samples Sa to Se of the heat diffusion member <NUM>. From the result shown in Table TB2, it became clear that the thermal diffusivity of the heat diffusion member <NUM> in the thickness direction increases and the fixation limit temperature can be lowered with the increase in the graphite volume compound ratio similarly to the relationship with the graphite weight compound ratio.

Here, if the graphite volume compound ratio is higher than <NUM> [vol%], the ratio of the binder resin 52B in the slide member <NUM> is too low, and thus the slide member <NUM> peels off without sticking fast to the base member <NUM> and no slide layer can be formed. Thus, the slide member <NUM> sticks fast to the base member <NUM> and the slide layer can be formed if the graphite volume compound ratio is less than or equal to <NUM> [vol%].

On the other hand, it was found that the vertical streak-like image defect occurs to the printed image when using the sample whose graphite volume compound ratio is <NUM> [vol%]. Since the surface roughness of the heat diffusion member <NUM> increases with the increase in the graphite volume compound ratio, even supposing that a slide member <NUM> whose graphite volume compound ratio is over <NUM> [vol%] successfully sticks to the base member <NUM>, it can be considered that the slide grease GR becomes nonuniform and the vertical streak-like image defect occurs similarly to the case where the graphite volume compound ratio is <NUM> [vol%].

Further, it was found that the vertical streak-like image defect does not occur to the printed image with the samples whose graphite volume compound ratio is less than or equal to <NUM> [vol%]. Thus, it appears that the vertical streak-like image defect does not occur to the printed image with samples whose graphite volume compound ratio is less than or equal to a prescribed value between <NUM> [vol%] and <NUM> [vol%].

As above, it was found that the fixation limit temperature can be lowered by adding graphite to the slide member <NUM>. Further, it was found that the image defect can be inhibited if the graphite volume compound ratio is less than or equal to <NUM> [vol%].

In the above-described configuration, the fixing device <NUM> of the image forming apparatus <NUM> is configured so that the slide member <NUM> provided on the facing surface 51B of the heating member <NUM> for forming the nip part N, facing the inner peripheral surface <NUM> of the fixation belt <NUM>, is configured to include the binder resin 52B and the thermally conductive filler particles 52F. Accordingly, with the thermally conductive filler particles 52F having higher thermal conductivity than the binder resin 52B, the fixing device <NUM> is capable of increasing the thermal diffusivity of the heat diffusion member <NUM> in the thickness direction and lowering the fixation limit temperature.

Accordingly, the fixing device <NUM> is capable of increasing the efficiency of the heat transmission from the heater <NUM> to the fixation belt <NUM> and reducing the power consumption of the heater <NUM>. Further, the fixing device <NUM> is capable of increasing the printing speed by the lowering of the fixation limit temperature.

Furthermore, when the record medium P is fed to pass through the nip part N, heat in the fixation belt <NUM> in the first round is taken away to the record medium P; however, the fixing device <NUM> is capable of quickly heating the fixation belt <NUM> before the sheet feed to the fixation belt <NUM> in the second round thanks to the high efficiency of the heat transmission from the heater <NUM> to the fixation belt <NUM>. Accordingly, the fixing device <NUM> is capable of securing sufficient fixation temperature even for a medium like thick paper that is likely to take away a lot of heat at the time of sheet feed, and thus the printing can be performed at the same printing speed irrespective of whether the medium is thin paper or thick paper and the medium versatility can be increased.

Specifically, in the fixing device <NUM>, the graphite weight compound ratio is set higher than or equal to <NUM> [wt%] (i.e., the graphite volume compound ratio is set higher than or equal to <NUM> [vol%]).

Here, graphite as a carbon material is fragile and is softer and more easily scraped off compared to the fixation belt <NUM>, and thus is capable of reducing the abrasiveness of the inner peripheral surface <NUM> of the fixation belt <NUM> sliding on the slide member <NUM> in comparison with other inorganic thermally conductive materials.

However, even though the increase in the amount of addition of graphite to the slide member <NUM> improves the thermal diffusiveness, the surface roughness of the slide member <NUM> increases, the slide grease GR becomes nonuniform on the slide surface SF, and there occurs a print failure in which the vertical streak-like image defect occurs.

To deal with this problem, in the fixing device <NUM>, the graphite weight compound ratio is set less than or equal to <NUM> [wt%], and preferably less than or equal to <NUM> [wt%]. To describe this condition in terms of the graphite volume compound ratio, in the fixing device <NUM>, the graphite volume compound ratio is set less than or equal to <NUM> [vol%], and preferably less than or equal to <NUM> [vol%]. Therefore, the fixing device <NUM> is capable of holding down the surface roughness of the slide member <NUM> and mitigating the nonuniformity of the slide grease GR on the slide surface SF. Accordingly, the fixing device <NUM> is capable of reducing the occurrence of the vertical streak and maintaining high print quality.

Further, as an example of the side effect of the addition of graphite to the slide member <NUM>, the slide member <NUM> becomes more likely to wear down and the base member <NUM> is exposed. When the base member <NUM> is exposed, deterioration in the slidability leads to an increase in the abrasiveness of the inner peripheral surface <NUM> of the fixation belt <NUM>, and a tear occurs to the fixation belt <NUM>.

To deal with this problem, the fixing device <NUM> is configured so that the relationship t > <NUM>. 198Rw is satisfied in regard to the film thickness t [µm] of the slide member <NUM> and the graphite weight compound ratio Rw [wt%] in the slide member <NUM>. To describe this condition in terms of the graphite volume compound ratio, the fixing device <NUM> is configured to satisfy the aforementioned expression (<NUM>) in regard to the film thickness t [µm] of the slide member <NUM>, the graphite volume compound ratio Rv [vol%] in the slide member <NUM>, the density α [g/cm<NUM>] of graphite and the density β [g/cm<NUM>] of the binder resin 52B.

Thus, the fixing device <NUM> is capable of inhibiting the breakage of the fixation belt <NUM> due to the exposure of the base member <NUM> in long-term use of the actual device by providing the slide member <NUM> whose film thickness is greater than the wear depth of the slide member <NUM> corresponding to the compound ratio of graphite. Accordingly, the fixing device <NUM> is capable of securing excellent fixation performance while avoiding the occurrence of the wear or abrasion to the inner peripheral surface <NUM> of the fixation belt <NUM>. As above, the fixing device <NUM> prescribes the thickness of the slide member <NUM> corresponding to the compound ratio of graphite and that makes it possible to let the slide member <NUM> have sufficient durability, maintain the slide member <NUM> until the end of the operating life of the device, and inhibit the breakage of the fixation belt <NUM>.

As above, in the fixing device <NUM>, the slide member <NUM> is configured to include the thermally conductive filler particles 52F only less than or equal to a prescribed compound ratio and the film thickness of the slide member <NUM> is set at a sufficient film thickness corresponding to the compound ratio of the thermally conductive filler particles 52F. With this configuration, the fixing device <NUM> is capable of increasing the efficiency of the heat transmission from the heating member <NUM> and increasing the durability of the slide member <NUM>, by which both the increase in the heat transmission efficiency of the heat diffusion member <NUM> and the increase in the durability of the slide member <NUM> can be achieved.

According to the configuration described above, the fixing device <NUM> of the image forming apparatus <NUM> includes the fixation belt <NUM>, the heating member <NUM> provided on the inner peripheral surface <NUM>'s side of the fixation belt <NUM>, the slide member <NUM> provided on the facing surface 51B of the heating member <NUM> facing the inner peripheral surface <NUM>, and the pressure roller <NUM> that is provided on the outer peripheral surface's side of the fixation belt <NUM> and forms the nip part N as a nip region between the pressure roller <NUM> and the slide member <NUM> via the fixation belt <NUM>, wherein the slide member <NUM> is configured to include at least the binder resin 52B as resin and the thermally conductive filler particles 52F as carbon.

Alternatively, the fixing device <NUM> of the image forming apparatus <NUM> includes the fixation belt <NUM>, the heating member <NUM> provided on the inner peripheral surface <NUM>'s side of the fixation belt <NUM>, and the slide member <NUM> provided on the facing surface 51B of the heating member <NUM> facing the inner peripheral surface <NUM>, wherein the slide member <NUM> is configured to include at least the binder resin 52B as resin and the thermally conductive filler particles 52F as a thermally conductive material having higher thermal conductivity than the binder resin 52B so that a weight compound ratio of the thermally conductive filler particles 52F as the compound ratio of the thermally conductive filler particles 52F added relative to the weight ratio of the slide member <NUM> is higher than or equal to <NUM> [wt%] (i.e., a volume compound ratio of the thermally conductive filler particles 52F as the compound ratio of the thermally conductive filler particles 52F added relative to the volume ratio of the slide member <NUM> is higher than or equal to <NUM> [vol%]).

Accordingly, with the thermally conductive filler particles 52F having higher thermal conductivity than the binder resin 52B, the fixing device <NUM> is capable of increasing the thermal diffusivity of the heat diffusion member <NUM> in the thickness direction and lowering the fixation limit temperature.

In the above-described embodiment, a description was given of a case where graphite is used as the thermally conductive filler particles 52F. The embodiment is not limited to such a configuration; it is also possible to use carbon black or the like, being a carbon material similarly to graphite, as the thermally conductive filler particles 52F. As the thermally conductive filler particles 52F, it is also possible to use metal-based, metallic oxide-based, metal coating-based or metallic oxide coating-based material, such as boron nitride, aluminum oxide, zinc oxide or the like, as a thermally conductive material having high thermal conductivity. However, in the case where graphite is used as the thermally conductive filler particles 52F, the abrasiveness of the inner peripheral surface <NUM> of the fixation belt <NUM> sliding on the slide member <NUM> can be reduced since graphite as a carbon material is fragile and is softer and more easily scraped off compared to the fixation belt <NUM>.

In the above-described embodiment, a description was given of a case where the slide member <NUM> is provided on the facing surface 51B of the heat diffusion member <NUM>. The embodiment is not limited to such a configuration; it is also possible to leave out the heat diffusion member <NUM> and provide the slide member <NUM> on a surface of the heater <NUM> facing the inner peripheral surface <NUM> of the fixation belt <NUM>. However, in the case where the heat diffusion member <NUM> is provided, the temperature unevenness in the lengthwise direction of the heater <NUM> can be mitigated when using the heater <NUM> controlling a plurality of heating elements aligned in the lengthwise direction of the heater <NUM>, and rigidity of the whole of the heating member <NUM> can be increased compared to cases where the heating member <NUM> includes the heater <NUM> alone.

In the above-described embodiment, a description was given of a case where the slide grease GR is applied on the slide surface SF of the slide member <NUM>. The embodiment is not limited to such a configuration; it is also possible to apply the slide grease GR not on the slide surface SF of the slide member <NUM> but on the inner peripheral surface <NUM> of the fixation belt <NUM>, or to apply the slide grease GR on both of the slide surface SF of the slide member <NUM> and the inner peripheral surface <NUM> of the fixation belt <NUM>. In short, it is permissible if the slide grease GR is situated between the slide surface SF of the slide member <NUM> and the inner peripheral surface <NUM> of the fixation belt <NUM>.

In the above-described embodiment, a description was given of a case where the embodiment is applied to the image forming apparatus <NUM> of the so-called direct transfer type in which the toner image is directly transferred from the photosensitive drum <NUM> of each development unit <NUM> onto the record medium P. The embodiment is not limited to such application; it is also possible to apply the embodiment to an image forming apparatus of the so-called intermediate transfer type (or secondary transfer type) in which the toner image of each color is successively transferred from the photosensitive drum <NUM> of the corresponding development unit <NUM> onto an intermediate transfer belt in an overlaying manner and then the toner image is transferred from the intermediate transfer belt onto the record medium P.

In the above-described embodiment, a description was given of a case where the embodiment is applied to developing agents used for the single component development method. The embodiment is not limited to such application; it is also possible to apply the embodiment to developing agents used for the two-component development method in which the toner is provided with an appropriate amount of electrification by mixing the toner with a carrier and using friction between the carrier and the toner.

In the above-described embodiment, a description was given of a case where the embodiment is applied to the image forming apparatus <NUM> that includes four development units <NUM> and forms a color image by use of toners of four colors. The embodiment is not limited to such application; it is also possible to apply the embodiment to an image forming apparatus that includes three or less or five or more development units <NUM> and forms a color image by use of toners of a prescribed number of colors.

In the above-described embodiment, a description was given of a case where the embodiment is applied to the image forming apparatus <NUM> that is a single-function device as a printer. The embodiment is not limited to such application; it is also possible to apply the embodiment to an image forming apparatus having various other functions such as an MFP (Multi-Function Peripheral) having the functions of a copy machine and a facsimile machine, for example. The embodiment may be applied also to various types of electronic devices that form an image on a record medium P such as paper by the electrophotographic method by using a developing agent.

Further, the embodiment is not limited to the embodiment and the other embodiments described above. Namely, the scope of application of the embodiment ranges also to embodiments obtained by arbitrarily combining the above-described embodiment and part or all of the above-described other embodiments and embodiments obtained by extracting parts from the above-described embodiments.

In the above-described embodiment, a description was given of a case where the fixing device <NUM> is formed with the fixation belt <NUM> as an annular belt, the heating member <NUM>, the slide member <NUM> as a facing member and the pressure roller <NUM> as a pressing member. The embodiment is not limited to such a configuration; the fixing device may also be formed with an annular belt, a heating member, a facing member and a pressing member having various other configurations.

In the above-described embodiment, a description was given of a case where the fixing device <NUM> is formed with the fixation belt <NUM> as an annular belt, the heating member <NUM>, the slide member <NUM> as a facing member and the slide grease GR as a lubricant. The embodiment is not limited to such a configuration; the fixing device may also be formed with an annular belt, a heating member, a facing member and a lubricant having various other configurations.

The embodiment is applicable to cases where an image is printed on a specific medium by using an image forming apparatus of the electrophotographic type.

Claim 1:
A fixing device (<NUM>) comprising:
an annular belt (<NUM>);
a heating member (<NUM>) provided on an inner peripheral surface's side of the annular belt (<NUM>);
a facing member (<NUM>) provided on a facing surface (51B) of the heating member (<NUM>) facing the inner peripheral surface; and
a pressing member (<NUM>) that is provided on an outer peripheral surface's side of the annular belt (<NUM>) and forms a nip region (N) between the pressing member (<NUM>) and the facing member (<NUM>) via the annular belt (<NUM>),
wherein the facing member (<NUM>) includes resin and carbon, and
wherein a relationship t > <NUM>.198Rw is satisfied in regard to a thickness t [µm] of the facing member (<NUM>) and a weight compound ratio Rw [wt%] of the carbon.