Patent Application
20070295707
An embodiment of the present invention is described below with reference to the attached drawings.
First, an image forming apparatus using an image heating device according to the embodiment of the present invention is described with reference to
In addition, dedicated charging units 13a to 13d and laser scanning units 11a to 11d are provided at the peripheries of the photosensitive drums 12a to 12d, respectively. The laser scanning units 11a to 11d emit light on the photosensitive drums 12a to 12d in accordance with image information. Developing units 15a to 15d develop formed electrostatic latent images. Drum cleaning units 14a to 14d remove toner remained on the photosensitive drums 12a to 12d after the transfer operation. Transfer units 16a to 16d transfer the toner images formed on the photosensitive drums 12a to 12d to an intermediate transfer body or a recording material. Also, cylindrical toner cartridges 51a to 51d are disposed directly below horizontal portions and along vertical portions of the laser scanning units 11a to 11d. The toner cartridges 51a to 51d correspond to the developing units 14a to 14d, respectively. The toner cartridges 51a to 51d are detachably attached for supplement of toner. The image forming stations Pa to Pd form a cyan image, a magenta image, a yellow image, and a black image, respectively.
An endless intermediate transfer belt 61 is disposed below the photosensitive drums 12a to 12d in a manner passing through the image forming stations Pa to Pd.
The intermediate transfer belt 61 extends over a driving roller 62 and driven rollers 63 and 65. A cleaning unit 64 is provided for cleaning the surface of the intermediate transfer belt 61.
With the above configuration, an electrostatic latent image is formed on the photosensitive drum 12a by charging of a charging unit 13a of the first image forming station Pa and exposure of the laser scanning unit 11a. The developing unit 15a visualizes the electrostatic latent image as a cyan toner image by using a developing agent containing cyan toner. The transfer unit 16a transfers the cyan toner image on the surface of the intermediate transfer belt 61.
While the cyan toner image is transferred on the intermediate transfer belt 61, a magenta toner image is formed in the second image forming station Pb in a manner similar to the cyan toner image. The transfer unit 16b superposes the magenta toner image accurately on the cyan toner image of the intermediate transfer belt 61 that has completed the former transfer of the first image forming station Pa.
Yellow and black images are formed in a manner similar to the former color images. Thus, the four toner images are superposed on the intermediate transfer belt 61. A secondary transfer roller 66 transfers (secondarily transfers) the four color toner images that have been formed on the intermediate transfer belt 61, on a recording material S that is stored in a sheet feeding cassette 70 and conveyed by a sheet feeding roller 71, a conveying roller pair 72, and a registration roller pair 73, in an appropriate timing. The recording material S with the secondary transfer completed is heated so that the transferred toner images are fixed to the recording material S by a fixing roller pair 74. Accordingly, a full color image can be formed on the recording material S.
The cleaning units 14a to 14d remove the remaining toner from the photosensitive drums 12a to 12d after the transfer is completed, to prepare the next image formation.
Next, the structure of the cross section of a heating roller 1 (image heating member) is described below with reference to
A heating roller core metal 2 made of ferrous metal is a conductive layer of the heating roller 1. Typically, to make a thin heating roller core metal 2, ends of a plate are welded to be a cylinder, the cylinder is stretched and polished, and formed in a predetermined shape. In the present embodiment, a heating roller longitudinal center core metal portion 5 (hereinafter, referred to as a center core metal portion) as a first region, and a heating roller longitudinal end core metal portion 6 (hereinafter, referred to as an end core metal portion) as a second region, are made in the above-mentioned processing manner.
The center core metal portion 5 and the end core metal portion 6 are made of ferrous metal, but have different Curie temperatures.
In general, a Curie temperature may be changed by varying the chemical composition of the base metal. In this embodiment, the Curie temperature is changed by varying the composition amount of nickel (Ni) mainly contained in the ferrous metal.
As shown in
As described above, in the case where the second regions are provided at both ends of the first region, the following conditions are satisfied:
0° C.≦|TQe1−TQe2|≦10° C.,
and more particularly,
0° C.≦|TQe1−TQe2|≦5° C.,
where TQe1 is a Curie temperature of the second region at one end, and TQe2 is a Curie temperature of the second region at another end.
The Curie temperature TQe1 of the end core metal portion 6 is adjusted to be 100° C. TQe1 is a temperature lower than 180° C. which is an image heating temperature (described below), namely, a preset temperature for heating an image. A Curie temperature TQc of the center core metal portion 5 is adjusted to be 200° C. The Curie temperature TQc is set to be lower than an allowable temperature limit for the image heating device, i.e., an allowable temperature limit for the coating of the coil in this embodiment, with regard to a temperature rise of an area not occupied by the sheet-passing region. TQc is a temperature higher than 180° C. which is the image heating temperature. If TQc is equal to or lower than the image heating temperature, then the magnetic permeability given around the image heating temperature may be small, and this may decrease heating efficiency.
Connection portions 4 of both ends of the center core metal portion 5 with respect to the respective ends of the end core metal portions 6 are processed by welding in a manner similar to the cylinder-forming process as described above.
Then, the product is stretched and polished similarly, and formed in a predetermined shape.
The center core metal portion 5 has the composition amount of Ni different from those of the end core metal portions 6, however, the center core metal portion 5 and the end core metal portions 6 are made of substantially the same ferrous metal. Thus, the weld strength of the center core metal portion 5 with respect to the end core metal portions 6 is not deteriorated. In the manner as described above, the heating roller core metal 2 is made.
A release layer 3 is provided on the outer periphery of the heating roller core metal 2. The release layer 3 is made of polytetrafluoroethylene (PTFE) for preventing melted unfixed toner from adhering on the heating roller core metal 2. The heating roller core metal 2 and the release layer 3 are coupled to each other with an adhesive 110 interposed therebetween as a binder layer.
Alternatively, a thin rubber layer may be provided between the release layer 3 and the heating roller core metal 2.
An exemplary measurement method of the Curie temperature is described below. In this embodiment, a B-H analyzer (model No.: SY-8232) manufactured by Iwatsu Test Instruments Corporation is used for the measurement. Predetermined first and second coils of the measurement device are wound around a part of a fixing roller as a measurement sample, and the fixing roller is measured with the frequency of 20 kHz. The shape of the measurement sample is not limited particularly as long as the coils can be wound. (The absolute value of the magnetic permeability may vary when the shape varies, however, almost no change is found in the Curie temperature.)
After the coils are set on the sample, the sample is placed in a temperature-controlled room and the temperature is saturated. Then the magnetic permeability at the temperature is plotted. By varying the temperature of the temperature-controlled room, a temperature dependence curve of the magnetic permeability can be obtained. At this time, the temperature, at which the magnetic permeability is 1, is determined as the Curie temperature. In particular, the temperature, at which the magnetic permeability is 1, is obtained as follows. As the temperature of the temperature-controlled room is increased, the variation in the magnetic permeability is stopped at a certain point. The point is assumed as the temperature at which the magnetic permeability is 1, namely, the Curie temperature.
Next, the relationship among the width of the coil of the heating roller 1 in the longitudinal direction, the width of the recording material of the maximum size to be fed, and the length of the center core metal portion 5, is described with reference to
To be more specific, since the maximum dimension of the sheet-passing region in this embodiment is 305 mm, the width of the sheet-passing region is increased at both ends by 5 mm each so as to heat the end portions sufficiently. As a result, the length of the center core metal portion 5 is determined to 315 mm in total. The coil width is increased at both ends by 5 mm each, and determined to 325 mm. In this embodiment, various sizes of sheets can pass through the sheet-passing region as long as the width of the recording material is equal to or smaller than the width of the sheet-passing region. Even when the size of the sheet is changed, the sheet-passing region is designed such that the center portion of the sheet constantly passes through the same point (center reference).
Next, the relationship between an induction heating material and the heating roller 1 is described below with reference to
The heating roller 1 as an induction heating material generates heat by electromagnetic induction.
To generate heat at the heating roller 1, a magnetic flux generating unit (coil unit) including an exciting coil 7 and a magnetic material core 8 is disposed in the heating roller 1. A high frequency power source 9a applies a high frequency alternating voltage to the exciting coil 7. Also, a thermistor 304 is mounted to the heating roller 1, as a temperature detecting member that detects the temperature of the surface of the heating roller 1. The output of the thermistor 304 is transmitted to a control section 9b such as a CPU, and the control section 9b controls power distribution to the coil so that the surface temperature of the heating roller 1 becomes the preset temperature for heating an image, namely, 180° C. in this embodiment. In this embodiment, a power distribution controlling unit has the high frequency power source 9a and the control section 9b. Accordingly, the magnetic flux generating unit generates the magnetic flux. This causes eddy current to be generated in the conductive layer of the heating roller 1, and the heating roller 1 generates heat. The power distribution controlling unit can hold the temperature of the heating roller 1 at the preset temperature.
In this embodiment, the fixer is used as the image heating device. A pressure roller 302 presses the heating roller 1. The pressure roller 302 is a pressing member that forms a nip 301 for nipping and conveying the recording material. The recording material is conveyed by a sheet feeding unit, and the recording material having the toner images transferred thereon enters the nip 301 through a fixing inlet guide 303. Then, the toner images formed on the recording material are fixed to the recording material by the heat and pressure. The pressure roller 302 of the present embodiment is formed such that an elastic layer is provided on a core metal made of iron, aluminum, or the like, and a release layer (surface layer) made of PTFE or the like is provided on the elastic layer.
The heating roller 1 is rotated using power generated by a motor 17 and transmitted through a heating roller gear 18, as shown in
The heating roller gear 18 connected to the heating roller 1 has been requested to have the allowable temperature limit of about 230° C. when employing the known halogen system. However, with the present invention, a resin material having the allowable temperature limit of 100° C. can be used. The advantage of the allowable temperature limit can be applied to a driving motor for the heating roller 1 as well as its peripheral electric components. In addition, the distance between the image heating device and those components can be decreased.
In this embodiment, while the material of the heating roller 1 is ferrous metal as an example, a ferromagnetic material (metal having a large magnetic permeability) may be used. For example, metal such as nickel or cobalt is suitable instead of the ferrous metal. By using such a ferromagnetic material, a larger quantity of the magnetic flux generated by the magnetic flux generating unit can be kept in the ferromagnetic metal, i.e., the magnetic flux density can be increased. Accordingly, the eddy current can be efficiently generated at the surface of the ferromagnetic metal, and hence, heat can be generated.
The manufacturing method of the heating roller 1 is not limited to that described above, and the following method may be used. Generally, the heating roller core metal 2 is manufactured by electroforming if the thickness of the heating roller core metal 2 is extremely small. For example, a metal material with a high purity, for instance, the Ni material in this embodiment is completely melted in an electric furnace, injected to a fireproof mold, and molded in a predetermined shape. In this embodiment, the center core metal portion 5 is coupled to the end core metal portions 6 by bonding.
Next, temperature distribution data of the present embodiment and comparative examples is shown in
This is comparison data of the present invention with respect to Comparative Examples 1 to 3. Comparative Example 1 is the configuration disclosed in Japanese Patent No. 02975435, Comparative Example 2 is the configuration having a relatively high Curie temperature, and Comparative Example 3 is the configuration having a relatively large magnetic flux generating unit and a relatively large heating region. The lateral axis indicates the longitudinal position of the heating roller, and the vertical axis indicates the surface temperature of the heating roller at predetermined points.
Referring to the result of the experiment, in the case of Comparative Example 1, if the temperature of the center portion is set to 180° C., the temperature of the maximum sheet-passing region is about 155° C., and consequently, the temperature is decreased, possibly causing defective fixing.
If the temperature of the maximum sheet-passing region is held at 180° C., the temperature of the center portion is necessary to be 205° C., and consequently, the temperature is unnecessarily increased, possibly causing phenomenon called high temperature offset. The high temperature offset is phenomenon where excessively melted toner adheres on the fixing roller. This may cause dirt on the image of the next sheet.
Since the magnetic flux generating unit and the heating region are relatively large, the temperature of the center portion and the temperature of the maximum sheet-passing region can be held at appropriate values. However, the temperature of the connection portion of the heating roller gear is increased to about 180° C. A resin material and electric components exhibiting sliding ability under the high-temperature environment may be extremely expensive, and thus may not satisfy the demand of cost reduction which is popular demand today. If the heating roller is mounted to a position where the temperature is sufficiently low as required for the present invention, then the size of the image forming apparatus becomes extremely large.
In the case of the present embodiment as compared with comparative examples described above, since the magnetic flux generating unit (coil) and the heating region are relatively large, the temperature of the center portion and the temperature of the maximum sheet-passing region can be held at appropriate values.
In addition, the temperature of the connection portion of the heating roller gear can be suppressed to about 100° C., a relatively inexpensive resin material and electric components can be used.
In the present embodiment, while the preset temperature is 180° C., if a plurality of preset temperatures are provided, the Curie temperature of the first region may be higher than the highest preset temperature. The Curie temperature of the second region may be lower than the lowest preset temperature.
While the end core metal portion 6 is used as the second region in the embodiment, a third region having a Curie temperature lower than that of the first region may be provided outside the first region.
With the present invention, even if the portions outside the sheet-passing region of the image heating member generate heat, the influence of the heat with respect to the components disposed in the vicinity of the end portions of the image heating member can be suppressed.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions.
This application claims the benefit of Japanese Application No. 2006-172719 filed Jun. 22, 2006, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-172719 | Jun 2006 | JP | national |
