Patent Application
20110026990
The present invention relates to a rotational heating member which is suitable as a fixing member of an image fixing apparatus (fixing device) mountable in image forming apparatuses such as an electrophotographic copy machines, electrophotographic printers, and the like. It also relates image heating apparatuses which use a rotational image heating member.
There have been increasing activities to reduce in energy consumption, image heating apparatuses (fixing devices) which are mounted in electrophotographic copy machines, electrophotographic printers, and the like. More specifically, various efforts have been made to reduce image heating apparatuses in the so-called “startup” time, that is, the length of time it takes for an image heating apparatus to become ready for image formation after it is turned on. As one of such efforts, a fixing apparatus of the belt type has been proposed, which uses a belt as a part of the fixing means. It is structured so that an unfixed toner image on recording medium is heated through a belt (fixation belt). For example, Japanese Laid-open Patent Application 2006-293225 and Japanese Laid-open Patent Application H04-204980 propose fixing apparatuses of the belt type. These fixing apparatuses have a ceramic heater (which hereafter will be referred to simply as heater), a belt (fixation belt), and a pressure roller. The fixation belt is made of thin film. It is pressed against the heater by the pressure roller, forming a nip between itself and pressure roller. In operation, the fixation belt is moved in contact with the heater. Fixing apparatuses of this type have various advantages over fixing apparatuses of the other types. For example, their heater and fixation belt are relatively small in thermal capacity, and therefore, relatively short (quick start) in the length of time it takes for them to become ready for image formation after they are turned on. Further, they are substantially smaller in electric power consumption (reduction in electric power consumption) while they are kept on standby. Japanese Laid-open Patent Applications H01-177576, H04-328594, H04-326386, and H09-114295 disclose another example of the image heating apparatus of the aforementioned type. This image heating apparatus heats the toner image on recording medium with the use of a rotational heating member made up of a rotational core, and a heat generating cylindrical heating member which rotates with the core. The heat generating cylindrical member is made of a substance which generates heat as electric current is flowed through it.
Fixing apparatuses which employ a fixation belt suffer from the following weaknesses. That is, if they become unstable in the transmission of electric power to their heater, they become unreliable in the length of startup time. Further, if the transmission of electric power to the heater becomes unstable while recording medium is conveyed through their fixation nip, they fail to supply the fixation belt with heat by the amount necessary to properly fix the toner image, and therefore, cannot properly fix the toner image on the recording medium; the so-called cold offset occur. Thus, the primary object of the present invention is to provide a rotational heating member which is significantly shorter than any of conventional rotational heating members, in the startup time, that is, the length of time it takes for the rotational heating member to become ready for properly heating recording medium, on which an image is present, and also, does not cause the cold offset. It is also to provide an image heating apparatus which employs the rotational heating member in accordance with the present invention.
The primary object of the present invention is to provide a rotational heating member which is significantly shorter in startup time than any of conventional heating members, and an image heating apparatus which employs such a rotational heating member.
According to an aspect of the present invention, there is provided an image heating rotatable member for heating an image on a recording material, comprising: a base layer; a heat generation layer, provided on said base layer, for generating heat by being supplied with electric power; an electrode layer, provided outside of said heat generation layer with respect to a widthwise direction and having an electric resistance which is smaller than that of said heat generation layer, for supplying the electric power to heat generation layer; an elastic layer provided on said electrode layer and having a length longer than that of said electrode layer measured in the widthwise direction; and a parting layer provided on said elastic layer and having a length which is substantially equal to the length of said electrode layer measured in the widthwise direction.
These and other objects, features, and advantages of the present invention will become more apparent upon consideration of the following description of the preferred embodiments of the present invention, taken in conjunction with the accompanying drawings.
a) is a schematic sectional view of a typical fixing apparatus, at a plane perpendicular to the lengthwise direction of the fixing apparatus.
a) is a perspective view of the pressure application stay and fixation flange of the fixing apparatus shown in
a) is a schematic sectional view of one of the lengthwise end portions of the fixation belt, and shows the laminar structure of the fixation belt.
This image forming apparatus is an electrophotographic color printer. The image forming apparatus in this embodiment has four image forming portions, that is, first to fourth image forming portions Py, Pm, Pc, and Pb, which are disposed in parallel in the image forming apparatus. The four image forming portions form four monochromatic toner images, different in color, one for one, through the charging, exposing, developing, and transfer processes. The image forming apparatus forms images by performing a preset image formation sequence in response to print signals outputted from external apparatus (unshown) such as a host computer. More specifically, the image forming portions Py, Pm, Pc, and Pb are sequentially driven, whereby the photosensitive drum 1 (image bearing member) of each image forming portion P is rotated at a preset peripheral velocity (process speed) in the direction indicated by an arrow mark. The image forming apparatus is provided also with an intermediary transfer belt 7, which is supported, and kept stretched, by a driver roller 6a, a follower roller 6b, and a tension roller 6c so that it is kept in contact with the photosensitive drum 1 of each of the image forming portions Py, Pm, Pc, and Pb. The intermediary transfer belt 7 is circularly driven by the driver roller 6a at a peripheral velocity which corresponds to the peripheral velocity of each photosensitive drum 1, in the direction indicated by another arrow mark. In the yellow (first color) image forming portion Py, the peripheral surface of the photosensitive drum 1 is uniformly charged to preset polarity and potential level by a charging device 2. Then, an exposing apparatus 3 scans (exposes) the charged portion of the peripheral surface of the photosensitive drum 1, with a beam of laser light it projects while modulating the beam of laser light with image formation signals (information) sent from an external apparatus. As a result, an electrostatic latent image which reflects the image formation signals is formed on the peripheral surface of the photosensitive drum 1. This latent image is developed by a developing apparatus 4, which uses yellow toner (developer), into a visible image; a visible image of yellow color (which hereafter will be referred to as yellow toner image) is formed of the yellow toner, on the peripheral surface of the photosensitive drum 1. Processes similar to the above described processes for forming a yellow toner image are carried out in the magenta (second color) image forming portion Pm, cyan (third color) image forming portion Pc, and black (fourth color) image forming portion Pb, one for one. The four toner images which were formed in the image forming portions Py, Pm, Pc, and Pb, one for one, and are different in color, are sequentially transferred in layers onto the outward (surface) of the intermediary transfer belt 7 by four primary transfer rollers 8 which oppose the four photosensitive drums 1 with the presence of the intermediary transfer belt 7 between the transfer rollers 8 and photosensitive drums 1, one for one. As a result, a full-color toner image is borne on the outward surface of the intermediary transfer belt 7. Meanwhile, one of the sheets of recording mediums P which are stored in layers in a recording medium feeding-and-conveying cassette 10 is moved out of the cassette 10, while being separated from the rest, and into the main assembly of the image forming apparatus, by a feed roller 11. Then, the sheet of recording medium P (which hereafter will be referred to simply as recording medium P) is sent by the feed roller 11 to a pair of registration rollers 13 through a recording medium guidance path 12. Then, the recording medium P is conveyed by the pair of registration rollers 13 to a second transfer nip Tn, which is the interface between the intermediary transfer belt 7 and a second transfer roller 14. Then, the recording medium P is conveyed through the second transfer nip Tn while remaining pinched by the intermediary transfer belt 7 and second transfer roller 14. While the recording medium P is conveyed through the second transfer nip Tn, the full color toner image on the outward surface of the intermediary transfer belt 7 is transferred by the second transfer roller 14 onto the recording medium P. Then, the recording medium P, on which the unfixed full-color toner image is present, is introduced into a fixing apparatus 15, and conveyed through the nip (which will be described later in detail) of the fixing apparatus 15, while remaining pinched by the nip. As the recording medium P is conveyed through the nip, the unfixed toner image on the recording medium P is thermally fixed to the recording medium P. After coming out of the fixing apparatus 15, the recording medium P is discharged into a delivery tray 16. After the transfer of a toner image from each photosensitive drum 1, the transfer residual toner, that is, the toner remaining on the peripheral surface of the photosensitive drum 1, is removed by a drum cleaner 5. Then, the photosensitive drum 1 is used for the next round of image formation. After the transfer of the full-color toner image from the intermediary transfer belt 7, the transfer residual toner, that is, the toner remaining of the outward surface of the intermediary transfer belt 7, is removed by a belt cleaner 9. Then the intermediary transfer belt 7 is used for the next round of image formation.
In the following description of the fixing apparatus, and the components, members, etc., which makes up the fixing apparatus 15, the “lengthwise direction” means the direction which is perpendicular to the recoding medium conveyance direction. The “widthwise direction” means the direction parallel to the recording medium conveyance direction. The “length” of a given component means the dimension of the component in the “lengthwise direction”. The width of a given component means the measurement of the component in the “widthwise direction”. The “widthwise direction” of the recording medium P means the direction of the edges of the recording medium, which is perpendicular to the recording medium conveyance direction. The “width” of the recording medium P means the dimension of the recording medium P, which is parallel to the widthwise direction of the recording medium P.
The fixing apparatus 15 in this embodiment has the fixation belt 20, belt holder 16, and pressure application stay 17, as described above. The fixation belt 20 is cylindrical (endless). The belt holder 16 is roughly semicircular in cross section, heat resistant, and rigid, and is on the inward side of the cylindrical fixation belt 20. The pressure application stay 17 is roughly U-shaped in cross section, and is also on inward side of the fixation belt 20. Further, the pressure application stay 17 is placed on inward side of the belt holder 16, being positioned in contact with the inward side of the belt holder 16 in such a manner that its open side faces the belt holder 16. From the standpoint of reducing the fixing apparatus 15 in energy consumption, the belt holder 16 is desired to be formed of a substance which is low in thermal conductivity. In this embodiment, therefore, a heat resist substance, for example, heat resistant glass, or heat resistant resin such as polycarbonate, is used as the material for the belt holder 16. The pressure application stay 17 is desired to be unlikely to flex even if it comes under a large amount of pressure. In the first embodiment, therefore, SUS 304 is used as the material for the pressure application stay 17. The pressure roller 22 is below the fixation belt 20, and is parallel to the fixation belt 20. The pressure roller 22 is made up of a metallic core 22a and an elastic layer 2b. The metallic core 22a is made of stainless steel. The elastic layer 22b is made of silicone rubber, and is roughly 3 mm in thickness. It covers the entirety of the peripheral surface of the metallic core 22a. The pressure roller 22 has also a parting layer 22c which covers the entirety of the peripheral surface of the elastic layer 22b. It is a piece of PFA resin tube, and is roughly 40 μm in thickness. The pressure roller 22 is rotatably supported by the frame 24 of the fixing apparatus 15. More specifically, the lengthwise end portions of the metallic core 22a of the pressure roller 22 are rotatably supported by a pair of bearings 25a and 25b attached to the front and rear plates of the frame 24, respectively. The adiabatic sheet 30 is for preventing the heat from the fixing belt 20 conducting to the belt holder 16 and pressure application stay 17. It is between the inward surface of the fixation belt 20 and the outward surface of the belt holder 16, and is held to the outward surface of the belt holder by adhesive. The adiabatic sheet 30 is a piece of silicone sponge, and is 500 μm in thickness. The fixation flanges 40 and 40 are at the lengthwise ends of the pressure application stay 17, one for one. Each pressure application stay 40 has a substrate 40a (
b) is a sectional view of a part of the heat generating portion of the fixation belt 20 of the fixing apparatus 15, and depicts the laminar structure of the fixation belt 20.
Next, the various sublayers of fixation belt 20, and the elastic layer of the pressure roller 22, will be described regarding their length. The width of the largest recording medium P, in terms of the lengthwise direction, usable with the image forming apparatus in this embodiment is 297 mm. The image forming apparatus in this embodiment is designed so that when the recording medium P is conveyed through the apparatus, the center of the recording medium passage in the apparatus in the “lengthwise direction” coincides with the center of the recording medium P in the “widthwise direction” of the recording medium P. That is, a broken line A in
The operation of the fixing apparatus 15 in this embodiment is as follows: the fixation motor (unshown) of the fixing apparatus 15 is rotationally driven in response to a print signal, whereby the pressure roller driving gear G (
The length of the elastic layer 22b of the pressure roller 22 is such that when a sheet of recording medium (P), which is maximum in “width”, is conveyed through the fixing apparatus 15, the elastic layer 2b extends beyond the edge of the recording medium P by 7.5 mm at both of its lengthwise ends. Further, the substrate layer 20a, heat generation layer 20b, elastic layer 20c, and parting layer of the fixation belt 20 are longer than the elastic layer 22b of the pressure roller 22. If the dimension of the elastic layer 22b is less than the dimension of the recording medium P in terms of the lengthwise direction (“widthwise direction of recording medium P), the “widthwise” end portions of the recording medium P fail to be pressed by the elastic layer 22b (pressure roller 22). Consequently, the recording medium P is bent along the border lines between the pressed portion of the recording medium P and the unpressed portions of the recording medium P. In the case of the fixing apparatus 15 in this embodiment, the length of its elastic layer 22b is greater than the maximum “width” for the recording medium P. Therefore, the recording medium P is always pressed across its entirety when it is conveyed through the fixing apparatus 15. Therefore, it does not occur that the recording medium P is bent along the border line between the portion pressed by the elastic layer 22b (pressure roller 22) and the portions which were not pressed by the elastic layer 22b (pressure roller 22). Also in the case of the fixing apparatus in this embodiment, the parting layer 20d of the fixation belt 20 is made longer than the elastic layer 22b of the pressure roller 22, by such a length that it extends by 2 mm beyond the elastic layer 22b at both lengthwise ends. Further, the heat generation layer 20b does not come into contact with the elastic layer 22b of the pressure roller 22. Therefore, it does not occur that the heat generation layer 20b is frictionally worn by the elastic layer 22b. Therefore, it is ensured that even when the fixing apparatus 15 is used for a long time, electric current is reliably flowed through the heat generation layer 20b.
The following is the description of the relationship between the length of the heat generation layer 20b and the temperature increase which occurred to the lengthwise end portions of the fixation belt 20.
In the case of the fixation belt 20 in this embodiment, a silicone resin is used as the adhesive to keep the parting layer 20d adhered to the elastic layer 20c. This silicone resin softens at 210° C., and therefore, becomes ineffective as adhesive. Thus, in the case of a fixation belt (20), the heat generation layer (20b) of which is no less the 310 mm in length, its parting layer (20d) is likely to separate from the elastic layer 20c; the fixation belt (20) is likely to break.
The length of the heat generation layer 20b of the fixation belt 20 in this embodiment is 307 mm. Therefore, it is possible to prevent the so-called cold offset from occurring across the “widthwise” end portion of the recording medium P, and also, to prevent the parting layer 20d of the fixation belt 20 from separating from the elastic layer 20c of the fixation belt 20.
In terms of the widthwise direction of the recording medium P, the electrode layer 20e and 20e of the fixation belt 20 in this embodiment is on the outward side of the heat generation layer 20b of the fixation belt 20. Therefore, the fixing apparatus 15 is stable in the flow of the electric current to the heat generation layer 20b. Therefore, it is faster in startup time, that is, the length of time it takes for the fixing apparatus 15 to become ready to properly heat the recording medium P on which the toner image t is present. Also in this embodiment, the heat generation layer 20b of the fixation belt 20 is longer than the “width” of the recording medium P, and the parting layer 20d of the fixation belt 20 is longer than the heat generation layer 20b. Therefore, the so-called cold offset does not occur. Further, the electrode layers 20e and 20e are smaller in electrical resistance than the heat generation layer 20b. Therefore, the fixation belt 20 is unlikely to break across its lengthwise end portions.
The electric power supplying member 45 of the fixing apparatus 15 in this embodiment is the electrically conductive leaf spring 45b. However, the electric power supplying member does not need to be the electrically conductive leaf spring 45b. For example, it may be an electrically conductive member which is in the form of a brush (unshown). In a case where the electric power supplying member 45 is an electrically conductive member in the form of a brush, it is connected to the exposed portion 20e1 of the electrode layer 20e of the fixation belt 20. The employment of the above described fixation belt 20 in this embodiment can reduce a fixing apparatus 15 in startup time, that is, the length of time it takes for the fixing apparatus to become ready for properly heating (fixing) the recording medium P, on which the toner image t is present, after electric power begins to be flowed through the fixation belt 20. Further, it can prevent the occurrence of the cold offset, and also, to prevent the lengthwise end portions of the fixation belt 20 from breaking.
The following is the description of the method for forming the heat generation layer 20b and electrode layer 20e on the substrate layer 20a by coating the materials for the layers 20b and 20e on the substrate layer 20a. It is possible to coat the substrate layer 20a first with the material for the heat generation layer 20b, and then, with the material for the electrode layer 20e. In this case, the step 20b2 is formed on the substrate layer side, that is, not on the elastic layer side, at the lengthwise end of the heat generation layer 20b, which faces the substrate layer 20a as shown in
According to the present invention, it is possible to provide a rotational heating member which is significantly shorter than any of the conventional rotational heating members, in terms of startup time, that is, the length of time it takes for the apparatus to become ready for properly heating recording medium, on which an unfixed image is present, after electric power begins to be supplied to the apparatus, and does not cause the so-called cold offset, and also, to provide an image heating apparatus which employs the rotational image heating member.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth, and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No 179026/2009 filed Jul. 31, 2009 which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-179026 | Jul 2009 | JP | national |
