Patent Application
20140233978
The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2013-027575, filed Feb. 15, 2013. The contents of this application are incorporated herein by reference in their entirety.
The present disclosure relates to image forming apparatuses, such as electrographic copiers, printers, and facsimile machines, as well as multifunction peripherals combining their functions.
Recent years, amorphous silicon (a-Si) photosensitive drums have been widely used as an image bearing member for an image forming apparatus utilizing an electrographic process. An a-Si photosensitive drum has high hardness and excellent durability, and its characteristics as a photosensitive member are substantially without degradation even after a prolonged usage. Therefore, high image quality can be maintained. That is to say, an a-Si photosensitive drum is an excellent image bearing member for its low running cost, easy handling characteristics, and high level of safety to the environment.
An image forming apparatus using such an a-Si photosensitive drum is known to involve a greater risk of image deletion owing to the characteristics of the a-Si photosensitive member. Image deletion refers to a phenomenon in which an image is blurred or smudged. Image deletion occurs when ion products adhere to the surface of the photosensitive drum and the ion products absorb moisture from the atmosphere. In particular, when the surface of the photosensitive drum is charged by a charging unit, nitrogen oxide (NOx) adheres to the surface of the photosensitive drum. The nitrogen oxide absorbs moisture, causing the latent charges to flow along the surface on which the latent image is formed. As a result, image deletion occurs in the electrostatic latent image formed on the surface of the photosensitive drum. Image deletion tends to occur especially at the edge portions of an electrostatic latent image.
Various methods have been suggested to reduce occurrence of image deletion. In one example, a heating element (heater) is provided inside the photosensitive drum, and a hygrothermograph sensor is provided inside the image forming apparatus. The heating element is heated based on the temperature and humidity measured by the hygrothermograph sensor. With this arrangement, even if moisture adheres to the surface of the photosensitive drum, the moisture can be evaporated. Consequently, occurrence of image deletion can be prevented.
Unfortunately, in the case where the heater is provided inside the photosensitive drum, a sliding electrode is required to connect the heater and the power supply. Therefore, there is a sliding portion connecting the heater to the power supply. As the total rotation time of the photosensitive drum is prolonged, connection failure may occur at the sliding portion.
In view of the above, a suggestion is made to provide the heating element in a static eliminating section. In particular, the static eliminating section includes a substrate, a light-emitting element, and a heating element. The light-emitting element is attached to one main surface of the substrate and emits light toward the photosensitive drum. The light emission by the light-emitting element eliminates the charges on the photosensitive drum. The heating element is disposed on the other main surface of the substrate. The heating element heats the photosensitive drum.
An image forming apparatus according to one aspect of the present disclosure includes an image bearing member, a charging unit, a laser scanning unit, a developing unit, a transfer member, a recording medium conveyance path, a heating element, and a cleaning unit. The image bearing member includes a photosensitive layer. The charging unit charges a surface of the photosensitive layer by applying a charging bias to the surface of the photosensitive layer. The laser scanning unit forms an electrostatic latent image on the photosensitive layer by scanning light on the surface of the photosensitive layer, the surface having been uniformly charged by the charging unit. The developing unit includes a developing-agent bearing member. The developing-agent bearing member has an outer peripheral surface. The developing-agent bearing member bears a developing agent on the outer peripheral surface. The developing unit forms, on a surface of the image bearing member, a toner image conforming to the electrostatic latent image by using the developing-agent bearing member to cause toner to adhere to the surface of the image bearing member. The transfer member transfers the toner image formed on the surface of the image bearing member by the developing unit to a recording medium. The recording medium conveyance path is disposed between the transfer member and the image bearing member. The recording medium is conveyed through the recording medium conveyance path. The recording medium conveyance path includes a resin member that forms a conveyance surface. The resin member has a concave portion at a location closer to the transfer member than to the image bearing member. The heating element is accommodated in the concave portion and heats the image bearing member. The heating element is disposed downstream from the contact point between the image bearing member and the transfer member in the conveyance direction in which the recording medium is conveyed through the recording medium conveyance path. The cleaning unit removes residual toner from the surface of the image bearing member. The charging unit, the developing unit, the transfer member, and the cleaning unit are disposed in the stated order in a rotation direction of the image bearing member. The developing unit is located upstream from the contact point between the image bearing member and the transfer member in the conveyance direction of the recording medium.
The following describes embodiments of the present disclosure, with reference to the accompanying drawings. In the figures, the same or corresponding parts are denoted by the same reference sings, and a description of such parts is not repeated.
The sheet feed cassette 2 is provided with a sheet stacking plate 12. The sheet stacking plate 12 is supported to be freely pivotable about a pivotal fulcrum 12a relative to the sheet feed cassette 2. The pivotal fulcrum 12a is disposed on the rear edge in the sheet conveyance direction. Sheets are stacked on the sheet stacking plate 12. As the sheet stacking plate 12 pivots, the stack of sheets on the sheet stacking plate 12 comes to be pressed by the pickup roller 5. Disposed at a location forward of the sheet feed cassette 2 is a retard roller 13. The retard roller 13 is pressed against the feed roller 6. In the event that the pickup roller 5 simultaneously feeds a plurality of sheets, the sheets are separated by the feed roller 6 and the retard roller 13 so that only the topmost sheet is forwarded.
Having passed through the roller pair made up of the feed roller 6 and the retard roller 13, the sheet is conveyed to the intermediate conveyance roller 7. The intermediate conveyance roller 7 changes the sheet conveyance direction (the recording medium conveyance direction) from the direction toward the front side to the direction toward the rear side of the apparatus. Having passed the intermediate conveyance roller 7, the sheet is conveyed to the image forming section 9 via the registration roller pair 8. The registration roller pair 8 is provided for adjusting the timing for feeding the sheet to the image forming section 9.
The image forming section 9 forms a predetermined toner image on the sheet through an electrographic process. The image forming section 9 includes a photosensitive drum 14, which is one example of an image bearing member, a charging unit 15, a developing unit 16, a cleaning unit 17, a transfer roller 18, which is one example of a transfer member, and a laser scanning unit (LSU) 19. The photosensitive drum 14 is axially supported to be rotatable in the clockwise direction in
In this embodiment, the photosensitive drum 14 is an amorphous silicon (a-Si) photosensitive member. The a-Si photosensitive drum includes a conductive substrate (tubular body) made, for example, of aluminum, an a-Si based photoconductive layer, and a surface protective layer. The a-Si based photoconductive layer is disposed as a photosensitive layer over the conductive substrate (tubular body). The surface protective layer is disposed on the upper surface of the photoconductive layer. The surface protective layer is made from an inorganic insulator or an inorganic semiconductor, such as a-Si based SiC, SiN, SiO, SiON, or SiCN.
When image data is input to the CPU 30 from a higher-level device, such as a personal computer, first, the charging unit 15 uniformly charges the surface of the photosensitive layer included in the photosensitive drum 14. Next, the laser scanning unit (LSU) 19 emits a laser beam based on the inputted image data so as to form an electrostatic latent image on the surface of the photosensitive layer included in the photosensitive drum 14. Then, the developing unit 16 supplies toner to the surface of the photosensitive drum 14. As a result, toner adheres to the surface of the photosensitive drum 14 in conformity with the electrostatic latent image. This forms a toner image on the surface of the photosensitive drum 14. The toner image is then transferred to the sheet fed to a nip portion (transfer position). The nip portion is formed at the contact point between the photosensitive drum 14 and the transfer roller 18. The sheet is fed to the nip portion by the transfer roller 18.
The sheet onto which the toner image has been transferred is separated from the photosensitive drum 14 and conveyed toward the fixing unit 10. The fixing unit 10 is disposed downstream from the image forming section 9 in the sheet conveyance direction. The fixing unit 10 includes a heating roller 22 and a pressure roller 23. The heating roller 22 is one example of a heating member, and the pressure roller 23 is one example of a pressure member. The pressure roller 23 is pressed against the heating roller 22. The sheet to which the toner image has been transferred is heated and pressed by the heating roller 22 and the pressure roller 23. As a result, the toner image transferred to the sheet is fixed. In the manner described above, an image is formed on the sheet by the image forming section 9 and the fixing unit 10. The sheet on which an image has been formed is ejected to the sheet ejecting section 3 by the ejection roller pair 11.
Note that some toner may remain on the surface of the photosensitive drum 14 even after the image transfer. The residual toner is removed by the cleaning unit 17. In addition, after the image transfer, a static eliminating unit 25 (see
As the photosensitive drum 14 rotates in the clockwise direction in
The fixing unit 16 includes a developing roller 16a. The developing roller 16a is one example of a developing-agent bearing member. The developing roller 16a supplies toner to the surface of the photosensitive drum 14. The supplied toner adheres to the surface of the photosensitive drum 14 in conformity with the electrostatic latent image. To the developing unit 16, toner is supplied (fed) from the toner container 20 (see
The cleaning unit 17 includes a slide-and-friction roller 45, a cleaning blade 47, and a toner collecting roller 50. The slide-and-friction roller 45 is one example of a polishing member. The slide-and-friction roller 45 is pressed against the photosensitive drum 14 at a predetermine pressure. In addition, the slide-and-friction roller 45 rotates in the counterclockwise direction shown in
The linear velocity of the slide-and-friction roller 45 is higher than that of the photosensitive drum 14. For example, the linear velocity of the slide-and-friction roller 45 is 1.2 times higher than the linear velocity of the photosensitive drum 14. As an example of its structure, the slide-and-friction roller 45 may adopt a structure in which, for example, a foam layer of EPDM rubber having an Asker C hardness of 55° is used as a roller body wrapped around a metal shaft.
The material of the roller body is not limited to the EPDM rubber mentioned above. The roller body may be made of rubber or foam rubber of a different material. As the material of the roller body, one having an Asker C hardness ranging from 10° to 90° is suitably used. Note that Asker C is one of the durometers (spring type hardness meters) specified in the standard by the Society of Rubber Science and Technology, Japan. In short, Asker C is a device for measuring hardness (hardness meter). The Asker C hardness refers to a hardness measured by Asker C, and a greater value of Asker C hardness indicates material of higher hardness.
The cleaning blade 47 is disposed downstream from the slide-and-friction roller 45 in the rotation direction of the photosensitive drum 14 at the abutment surface between the slide-and-friction roller 45 and the photosensitive drum 14. The cleaning blade 47 is secured in abutment with the photosensitive drum 14. In one example of the cleaning blade 47, a blade made of polyurethane rubber having a JIS hardness of 78° is used. The cleaning blade 47 is secured so as to form a predetermined angle with the tangent to the surface of the photosensitive drum 14 at the point of abutment between the cleaning blade 47 and the photosensitive drum 14. The cleaning blade 47 removes toner remaining on the surface of the photosensitive drum 14 (residual toner) from the surface of the photosensitive drum 14. The material of the cleaning blade 47, the hardness of the cleaning blade 47, the dimensions of the cleaning blade 47, the amount by which the cleaning blade 47 bites into the photosensitive drum 14, the pressure under which the cleaning blade 47 is pressed against the photosensitive drum 14, and so on may be appropriately set according to the specifications of the photosensitive drum 14. Note that the JIS hardness refers to the hardness specified in the Japanese Industrial Standards (JIS).
The toner collecting roller 50 rotates in the clockwise direction in
The transfer roller 18 transfers the toner image formed on the surface of the photosensitive drum 14 to the sheet P being conveyed along the sheet conveyance path 4, without disturbing the toner image. The transfer roller 18 is connected to a transfer bias supply and also to a bias control circuit (both not shown). By the transfer bias supply and the bias control circuit, a transfer bias which is of a reversed polarity to the toner is applied to the transfer roller 18.
The sheet conveyance path 4 has a conveyance surface that is formed by a conveyance-path resin member 51. A heating element 53 is disposed on the conveyance-path resin member 51. The heating element 53 heats the photosensitive drum 14. In
As described above, the heating element 53 that heats the photosensitive drum 14 is disposed outside the photosensitive drum 14. Therefore, a sliding electrode is no longer required to connect the heating element 53 to the power supply, and thus the risk of connection failure is eliminated. In addition, since the heating element 53 is disposed at the opposite side from the developing unit 16 across the straight line L1, heat generated by the heating element 53 is conducted less easily to the developing unit 16. This is effective to prevent caking and blocking of the toner in the developing unit 16.
In addition, the heating element 53 is accommodated in a concave portion 51a formed in the conveyance-path resin member 51. The concave portion 51a is located closer to the transfer roller 18 than to the photosensitive drum 14. Such disposition of the heating element 53 ensures that the heating element 53 does not obstruct the conveyance of the sheet P along the sheet conveyance path 4. Such disposition is also effective in that the heating element 53 is more distant from the cleaning unit 17. Thus, caking and blocking of the waste toner in the cleaning unit 17 can be prevented.
In addition, in the image forming apparatus 100 of a horizontal conveyance type as shown in
As shown in
In this way, the substrate 53a is located between the resistor chips 53b and the first inner wall surface of the concave portion 51a. Therefore, the temperature rise of the inner wall surfaces of the concave portion 51a is lessened. In addition, since the space is left between the resistor-chip mounting surface and the partition wall 51b, the air warmed by heat generated by the resistor chips 53b is assisted to flow toward the photosensitive drum 14 (upward in
As shown in
To prevent occurrence of image deletion on the photosensitive drum 14, it has been empirically confirmed that the relative humidity in the vicinity of the photosensitive drum 14 needs to be 60% or below. When the outside air temperature is from 10° C. to 40° C. and the relative humidity is 80%, keeping the relative humidity in the vicinity of the surface of the photosensitive drum 14 below 60% requires that the surface temperature of the photosensitive drum 14 be raised higher than the atmospheric temperature by 6° C. The output power of the heating element 53 required for raising the temperature by 6° C. or more is on the order of 1 W to 3 W.
For example, by providing as the resistor chips 53b twenty-eight 10Ω resistor chips on the substrate 53a and supplying 24 volts direct current, the heating element 53 achieves the output power of 2.05 W.
In addition, the heating element 53 is connected to a power supply circuit 60. The power supply circuit 60 is provided with a switch 55 that can be turned on and off. The switch 55 turns off the conduction of electric current to the heating element 53 during the heating period (conduction period) of the heating roller 22 of the fixing unit 10 (see
Preferably, the conveyance-path resin member 51 is made from a material having a relative temperature index (hereinafter, RTI) greater than the surface temperature of the heating element 53. The RTI is an index of degradation of the mechanical characteristics (tensile strength and tensile impact strength) and the electrical characteristics (disruptive strength) after prolonged use in an environment associated with exposure to high temperature. The RTI is defined based on UL 746B (the UL Standard for Safety for Polymeric Materials—Long Term Property Evaluations) by Underwriters Laboratories Inc. in the United States of America. For example, a resin having an RTI of 110 means that the resin will have 50% of the initial mechanical characteristics and of the initial electrical characteristics after a 100,000—hour exposure at 110° C. Thus, by keeping the surface temperature of the heating element 53 below the RTI of the conveyance-path resin member 51, the mechanical characteristics and the electrical characteristics of the conveyance-path resin member 51 can be maintained until the end of the useful life of the image forming apparatus 100.
In addition to the polyphenylene sulfide resin mentioned above, examples of the material usable for the conveyance-path resin member 51 include modified-polyphenyleneether (m-PPE) (for example, Xyron SZ800 manufactured by Asahi Kasei Chemicals Corporation).
In addition, the heating element 53 is not conducted at the time of power-up of the image forming apparatus 100. When the conduction of electric current to the heating element 53 is turned on simultaneously with the power-up, the output power of the heating element 53 is low and requires three to four hours until the surface temperature of the photosensitive drum 14 is raised by 6° C. Therefore, when image formation is performed immediately after the power-up under the condition that the relative humidity inside the image forming apparatus 100 is 60% or higher, image deletion may occur. To prevent such occurrence of image deletion, it is preferable to perform drum refresh immediately after the power-up.
The following is an example of a specific method for the drum refresh. First, toner is ejected toward the photosensitive drum 14 from the developing roller 16a included in the developing unit 16. Then, the photosensitive drum 14 and the slide-and-friction roller 45 rotate for a predetermined period of time. Consequently, the surface of the photosensitive drum 14 (the surface of the surface protective layer) is polished by the toner present between the photosensitive drum 14 and the slide-and-friction roller 45.
With this structure, the photosensitive drum 14 is heated by convection of air warmed by the heating element 53 and also directly by radiant heat from the resistor chips 53b. Thus, the photosensitive drum 14 is more efficiently heated as compared to the disposition of the heating element 53 shown in
As shown in
As shown in
In the second embodiment, the sheet P is charged by the transfer bias applied to the transfer roller 18 and thus electrically attracted to the conveyance metal plate 70 that is disposed on the upper surface of the conveyance-path resin member 51. This ensures that the sheet P is attracted toward the upper surface of the conveyance-path resin member 51 and thus smoothly conveyed along the conveyance-path resin member 51. Each rib 71 is disposed on the top surface of the conveyance-path resin member 51 and protrudes beyond the surface of the conveyance metal plate 70. This arrangement keeps the sheet P out of direct contact with the conveyance metal plate 70 and eliminates the risk of bias current flowing into the conveyance metal plate 70.
In addition, the conveyance metal plate 70 is formed from a material having a higher thermal conductivity than that of the conveyance-path resin member 51, and the substrate 53a of the heating element 53 is secured to the conveyance metal plate 70. Examples of the usable materials include: an electrolytic zinc-coated steel sheet (SECC) manufactured by Sumitomo Metal Industries, Ltd. and having a thermal conductivity of 50.0 W/(m·k) for the conveyance metal plate 70; Xyron SZ800 manufactured by Asahi Kasei Chemicals Corporation and having a thermal conductivity from 0.16 W/(m·k) to 0.20 W/(m·k)) for the conveyance-path resin member 51; and CCL-EL190T manufactured by MITSUBISHI GAS CHEMICAL COMPANY, INC. and having a thermal conductivity of 0.45 W/(m·k) for the substrate 53a.
Use of such materials enables the conveyance metal plate 70 to function as a heat-dissipating plate (heat sink), so that the conveyance metal plate 70 efficiently dissipates heat conducted from the resistor chips 53b to the substrate 53a. Thus, deterioration and damage of the substrate 53a by heat can be reduced.
The present disclosure is not limited to the first or second embodiment described above, and various modifications are possible without departing from the gist of the present disclosure. For example, alternatively to the charging unit 15 of a contact charging type that includes the charging roller 41 as shown in
In addition, the image forming apparatus according to the present disclosure is not limited to a monochrome printer as shown in
The image forming apparatuses 100 as shown in
After the 48-hour period, each image forming apparatus 100 was used to produce prints of a test image containing both characters and a half-tone image. The first print of the test image was visually inspected for occurrence of image deletion. As Comparative Examples, the same experiment was conducted on image forming apparatuses having the same structure as the image forming apparatuses 100 except that the heating element was not mounted. Tables 1 and 2 below show the experimental results (evaluation results).
Table 1 shows the evaluation results on the apparatuses each without the heating element 53, whereas Table 2 shows the evaluation results on the apparatuses each with the heating element 53. As Table 1 indicates, Comparative Examples employing the image forming apparatuses without the heating element 53 were used in the high-humidity environment with the relative humidity of 80%, and all resulted in image deletion occurred in both the characters and the half-tone image irrespective of the temperatures. On the other hand, as Table 2 indicates, the image forming apparatuses 100 each with the heating element 53 were used in the high-humidity environment with the relative humidity of 80%, and all capable of preventing occurrence of image deletion in both the characters and the half-tone image irrespective of the temperatures.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-027575 | Feb 2013 | JP | national |
