Patent Grant
8913943
This application is based on Japanese Patent Application No. 2012-58686 filed on Mar. 15, 2012, the content of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an image forming apparatus with an application unit for applying a lubricant to an image support.
2. Description of Related Art
In an electrographic image forming apparatus, as shown in
In recent years, to reduce downtime of the image forming apparatus, there is demand for extended service lives of the image support 102 and the cleaning blade 105. A factor that limits the service lives is an amount of abrasion. In an abrasion reduction technique in practical use, an application brush 107 is used to apply a solid lubricant 106 onto the circumferential surface of the image support 102, thereby forming a film of solid lubricant (referred to below as a lubricant film) thereon.
However, reducing the amount of abrasion of the image support 102 means reducing the force of the application brush 107 scrubbing the circumferential surface of the image support 102, resulting in other issues. The most critical of all is an image defect. Specifically, charged products (such as O3 and NOx) generated by the charging unit 101 adhere to the image support 102. The adhering charged products might be left unscrubbed when the lubricant film weakens the scrubbing force of the image support 102. The remaining charged products might lower the surface resistance of the image support 102, making the electrostatic latent image on the image support 102 defective. Accordingly, for example, a resultant print includes an image with blurry edges or a half-tone image with white spots. Such image noise is included in the image defect. Note that in the case where the amount of abrasion of the image support 102 is high, charged products are scrubbed together with the film on the surface of the image support 102, so that no image defect is caused.
The mechanism of the image defect will now be described in more detail. In the following, the percentage of applied lubricant is a value obtained by dividing the amount of solid lubricant 106 applied to the image support 102 by the amount of lubricant scraped by the application brush 107. In the configuration of
An image forming apparatus capable of reducing the image defect is described in, for example, Japanese Patent Laid-Open Publication No. 2001-265185. This image forming apparatus includes a lubricity providing member, an application roller, and a friction coefficient adjusting member. The lubricity providing member and the friction coefficient adjusting member are arranged in this order along the rotational direction of the application roller. The lubricity providing member supplies a lubricant to the application roller. The application roller with the lubricant contacts the friction coefficient adjusting member, thereby removing excess lubricant from the application roller. Thereafter, the application roller applies the lubricant to the image support.
Incidentally, the lubricant film on the image support adsorbs charged products, and therefore, to prevent image defects, it is important to scrub the lubricant film with charged product adsorbed thereon, and form a new lubricant film without any charged product being adsorbed thereon.
However, simply adjusting the amount of lubricant to be supplied as in the approach described in Japanese Patent Laid-Open Publication No. 2001-265185 might not successfully remove the lubricant film with charged product adsorbed thereon, so that the lubricant film with charged product adsorbed thereon possibly remains on the image support, causing an image defect.
An image forming apparatus according to an embodiment of the present invention includes: a rotatable image support; a charging unit that charges the image support; an exposing unit that exposes the image support charged by the charging unit, thereby forming an electrostatic latent image; a developing unit that develops the electrostatic latent image formed by the exposing unit, thereby forming a toner image on the image support; a transfer unit that transfers the toner image formed on the image support to a transfer target in a transfer area; and a cleaning unit, in which the cleaning unit includes: a cleaning blade that is provided downstream from the transfer area in a rotational direction of the image support and scrapes off untransferred toner remaining on the image support; an application brush that contacts the image support on the downstream side in the rotational direction of the image support relative to the cleaning blade, the application brush rotating in a counter direction at a contact position with the image support, thereby scratching off lubricant particles from a solid lubricant provided at its periphery, and supporting and feeding the lubricant particles toward the contact position with the image support; and a moving force providing unit that provides the lubricant being fed by the application brush with an electrical moving force toward the image support, on the upstream side in the rotational direction of the application brush relative to the contact position of the image support and the application brush.
Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, the directions of X, Y, and Z-axes represent right-left (horizontal) direction, front-rear (depth) direction and top-bottom (height) direction, respectively, of the image forming apparatus. The lower-case alphabet letters a, b, c, and d suffixed to reference numerals are affixes that denote yellow (Y), magenta (M), cyan (C), and black (Bk). For example, a photoreceptor drum 21a is intended to mean a photoreceptor drum 21 for yellow.
In
In the main unit of the image forming apparatus, arranged to the right of the intermediate transfer belt 11 are imaging units, from top to bottom, 2a, 2b, 2c, and 2d. The imaging units 2a to 2d include photoreceptor drums 21a to 21d, which are typical examples of image supports. The photoreceptor drums 21a to 21d are in the form of cylinders extending in the depth direction of the image forming apparatus, and rotate about their central axes (counterclockwise as indicated by arrows B). Arranged around the photoreceptor drums 21a to 21d are, in order along their rotational directions B, charging units 22a to 22d, developing units 24a to 24d, cleaning units 26a to 26d, and diselectrifying units 27a to 27d.
Primary transfer rollers 14a to 14d are provided so as to be opposed to the photoreceptor drums 21a to 21d with respect to the intermediate transfer belt 11. Primary transfer areas 141a to 141d are created between the primary transfer rollers 14a to 14d and the intermediate transfer belt 11. In addition, a secondary transfer roller 15 is disposed so as to be opposed to the roller 12 with respect to the intermediate transfer belt 11 and tightly contact the intermediate transfer belt 11. A nip is created between the secondary transfer roller 15 and the intermediate transfer belt 11 as a secondary transfer area 16.
Furthermore, an exposing unit 3 is provided to the right of the imaging units 2a to 2d.
Furthermore, disposed below the main unit of the image forming apparatus is a sheet cassette in which sheet materials are placed, although the cassette is not shown in the figure. A feed roller provided in the sheet cassette forwards the sheet materials one by one to a feeding path R indicated by a dotted arrow. Provided in the feeding path R are a timing roller pair, a secondary transfer area 16, and a fusing unit 4, which are omitted in the figure.
Next, the general operation of the image forming apparatus thus configured will be described. In the image forming apparatus, the charging units 22a to 22d negatively charge the photoreceptor drums 21a to 21d uniformly across their circumferential surfaces. The exposing unit 3 irradiates the charged circumferential surfaces of the photoreceptor drums 21a to 21d with optical beams Ba to Bd modulated with image data (i.e., exposure). As a result, the photoreceptor drums 21a to 21d have electrostatic latent images of corresponding colors formed on their circumferential surfaces.
The developing units 24a to 24d supply toner, which is negatively charged by friction, to the photoreceptor drums 21a to 21d with the electrostatic latent images supported thereon (i.e., development). As a result, of the photoreceptor drums 21a to 21d has toner images of the corresponding colors formed on their circumferential surfaces. Here, a negative voltage (developing bias) is applied to the developing rollers included in the developing units 24a to 24d, for reversal development being selectively performed on the photoreceptor drums 21a to 21d when their potentials drop due to exposure.
Due to the voltage being applied to the primary transfer rollers 14a to 14d, the toner images on the photoreceptor drums 21a to 21d are electrostatically transferred to the intermediate transfer belt 11 (i.e., primary transfer), such that the transfer takes place at the same portion of the intermediate transfer belt 11, sequentially in the primary transfer areas 141a to 141d. In this manner, the toner images on the photoreceptor drums 21a to 21d are transferred to the intermediate transfer belt 11, and in this regard, the intermediate transfer belt 11 is an example of a transfer target which is a material to which an image is to be transferred. Moreover, combinations of the intermediate transfer belt 11 and the primary transfer rollers 14a to 14d are examples of transfer units. As a result of the primary transfer, a full-color composite toner image is formed on the intermediate transfer belt 11. The composite toner image is fed to the secondary transfer area 16 while being supported on the intermediate transfer belt 11.
Here, Van der Waals forces are applied between the photoreceptor drums 21a to 21d and the toner supported thereon, and therefore, any toner that is not subjected to primary transfer remains on the circumferential surfaces of the photoreceptor drums 21a to 21d as untransferred toner. The untransferred toner is fed to the cleaning units 26a to 26d through rotation of the photoreceptor drums 21a to 21d.
The cleaning units 26a to 26d are provided downstream from the primary transfer areas 141a to 141d in the rotational directions B, and scrape and recover the untransferred toner on the photoreceptor drums 21a to 21d (i.e., cleaning). The recovered toner in the cleaning units 26a to 26d is fed by recovery screws to be collected in an unillustrated waste toner box.
Furthermore, the electrostatic latent images that remain on the circumferential surfaces of the photoreceptor drums 21a to 21d are erased through whole image exposure by the diselectrifying units 27a to 27d. Here, the diselectrifying units 27a to 27d are arrays of luminous elements, such as LEDs, provided between the cleaning units 26a to 26d and the charging units 22a to 22d in the rotational directions B, each array extending in the depth direction of the image forming apparatus. The circumferential surfaces of the photoreceptor drums 21a to 21d are illuminated by the arrays of luminous elements, thereby lowering potentials that are persisting on the circumferential surfaces, so that the current image history (memory image) does not remain for the next image formation.
Furthermore, a sheet material fed from the sheet cassette travels in the feeding path R and contacts the timing roller pair (not shown) at rest without rotation. Thereafter, the timing roller pair starts rotating in synchronization with transfer timing in the secondary transfer area 16, thereby feeding the sheet material at temporary rest to the secondary transfer area 16.
In the secondary transfer area 16, the composite toner image on the intermediate transfer belt 11 is transferred to the sheet material introduced from the timing roller pair by the roller 12 and the secondary transfer roller 15 (i.e., secondary transfer). The sheet material subjected to secondary transfer is fed further downstream of the feeding path R by the secondary transfer roller 15 and the intermediate transfer belt 11.
The fusing unit 4 includes a fusing roller and a pressure roller. The sheet material fed from the secondary transfer area 16 is introduced to a nip created by these rollers. The fusing roller heats the toner image on the sheet material passing through the nip, and simultaneously, the pressure roller presses the sheet material. As a result, a full-color toner image is fixed on the sheet material. Thereafter, the fusing roller and the pressure roller forward the sheet material subjected to the fusing process, further downstream of the feeding path R. The forwarded sheet material is ejected onto an output tray after passing through an unillustrated ejection roller.
Next, the configuration of the cleaning units 26a to 26d will be described in detail. The cleaning units 26a to 26d include cleaning blades 51a to 51d, application units 52a to 52d, leveling units 53a to 53d, solid lubricants 54a to 54d, and biasing units 55a to 55d, as shown in
In the cleaning unit 26a, the cleaning blade 51a, the application unit 52a, and the leveling unit 53a are arranged in this order, from upstream to downstream in the rotational direction B.
The cleaning blade 51a is made of strips of polyurethane rubber processed by a centrifugal molding machine. The cleaning blade 51a is bonded to a retaining plate by a hot-melt adhesive so as to extend in the depth direction of the image forming apparatus. The cleaning blade 51a is pressed against the photoreceptor drum 21a, thereby scraping untransferred toner adhering to the rotating photoreceptor drum 21a.
The application unit 52a extends in the depth direction of the image forming apparatus, and at least includes a metal shaft 521a and an application brush 522a, as explicitly shown in
Here, example specifications of the application unit 52a will be described in detail. The material of the application brush 522a is conductive polyester, and the fiber resistance thereof is about 106Ω. The application brush 522a has a fiber thickness of 3 T (decitex) and a fiber density of 225 kF/inch2. Moreover, the shaft 521a is made of iron and has a diameter of 6 mm. Furthermore, the application brush 522a has an outer diameter of 12 mm, but the fiber length thereof is about 2.5 mm because it is woven on the ground cloth whose thickness is about 0.5 mm.
Furthermore, as with the cleaning blade 51a, the leveling unit 53a is polyurethane rubber produced in the form of a plate by a centrifugal molding machine, and fixed to a retaining plate via a hot-melt adhesive, and the leveling unit 53a is angled against rotation of the photoreceptor drum 21a.
Next, the operation of the cleaning unit 26a thus configured will be described in detail. In
The lubricant particles 54a′ adhere to the application brush 522a, and are fed to immediately before the contact area of the photoreceptor drum 21a through rotation of the application unit 52a, and thereafter the lubricant particles 54a′ are supplied to the circumferential surface of the photoreceptor drum 21a by action of a moving force providing unit 56a to be described later.
The lubricant particles 54a′ on the photoreceptor drum 21a are fed to the leveling unit 53a shown in
As has already been described, conventional cleaning units have a problem where the lubricant film with charged products adsorbed thereon remains on the image support, causing image defects. To solve such a problem, the cleaning units 26a to 26d include, in addition to the features described above, moving force providing units 56a to 56d, as shown in
In
On the upstream side of the rotational direction C relative to the contact D, the moving force providing unit 56a provides the lubricant particles 54a′ (represented by small circles in the figure) on the application brush 522a with a moving force toward the circumferential surface of the photoreceptor drum 21a. The lubricant particles 54a′ move onto the circumferential surface of the photoreceptor drum 21a once it approaches so close to the contact D that the moving force provided to the lubricant particles 54a′ exceeds the adhesion to the application brush 522a. Here, the position from which the lubricant particles 54a′ move onto the photoreceptor drum 21a is position E on the circumferential surface of the application brush 522a, which is located on the upstream side of the rotational direction C relative to the contact D and is determined mainly by the moving force provided to the lubricant particles 54a′.
The moving force providing unit 56a is capable of electrically providing the moving force. In a typical example of such a case, a power unit 57a applies a bias voltage to the shaft 521a. Here, the polarity of the difference in the potential on the circumferential surface of the photoreceptor drum 21a relative to the application unit 52a is taken as a. In addition, when comparing positions in a triboelectric series for the lubricant particles 54a′ and the application brush 522a upon which the lubricant particles 54a′ are pressed, if the polarity β of the application brush 522a coincides with the polarity α, the moving force can be provided to the lubricant particles 54a′. Specific examples will be given below.
For example, the surface potential at the contact D of the photoreceptor drum 21a is about −100V, and the bias potential applied to the application unit 52a is about −300V. In this case, the difference in the potential of the photoreceptor drum 21a relative to the application unit 52a is +200V, and therefore the polarity α is positive. Moreover, the material of the solid lubricant 54a is zinc stearate, and the material of the application brush 522a to be brought into contact therewith is polyester. In this case, the position of polyester in the triboelectric series is on the positive side relative to zinc stearate, the polarity β is positive, and coincides with the polarity α. In this case, the lubricant particles 54a′ are negatively charged, and therefore the lubricant particles 54a′ receive an electric force applied by the application unit 52a toward the photoreceptor drum 21a, and move onto the circumferential surface of the photoreceptor drum 21a with high efficiency.
The above embodiment has been described with respect to the example where an electric force from the power unit 57a acts on the lubricant particles 54a′. However, in addition to this, a first auxiliary charge member 59a and a second auxiliary charge member 60a may be provided between the position F of the solid lubricant 54a and the contact D in the rotational direction C, as shown in
Here, if the auxiliary charge member 60a has a corrugated surface profile in a plan view from the depth direction (i.e., the direction parallel to the shaft 521a), contact area with the application brush 522a can be increased. As a result, the lubricant particles 54a′ can be increased in frictional charge quantity, and the moving force applied thereto can be further increased. The surface profile may be in the form of sinusoidal, triangular, or rectangular waves, or may be a combination thereof.
Furthermore, the power unit 57a may apply a direct-current voltage superimposed with an alternating-current voltage to the application unit 52a as a bias voltage, thereby applying an oscillating electric field to the lubricant particles 54a′. As a result, the lubricant particles 54a′ can further readily move onto the photoreceptor drum 21a. Moreover, the superimposition of the alternating-current voltage produces the effect of causing the application brush 522a to be in microoscillations, so that the mobility of the lubricant particles 54a′ can be further enhanced. In addition, the application brush 522a in microoscillations rubs the photoreceptor drum 21a, producing the effect of enhancing the scrubbing force of the photoreceptor drum 21a.
Furthermore, a bias voltage of the same polarity as the charge polarity of the lubricant particles 54a′ can be applied to the auxiliary charge members 59a and 60a, as shown in
The moving force providing unit 56a can mechanically provide the moving force without using the power unit 57a. In a typical example of such a case, the first deforming unit 58a is provided at position E, as shown in
By using both the power unit 57a and the first deforming unit 58a, it is rendered possible for the lubricant particles 54a to further readily move from the application brush 522a onto the circumferential surface of the photoreceptor drum 21a. Note that in the case where both of the units are used, it is necessary that a bias voltage opposite in polarity to the lubricant particles 54a′ is applied to the first deforming unit 58a.
Furthermore, as in the present embodiment, the application unit 52a rotates at a higher linear velocity than the photoreceptor drum 21a. This is more desirable because foreign matter scraped from the photoreceptor drum 21a by the application brush 522a can be prevented from readhering to the drum 21a.
Furthermore, a second deforming unit 61a having the same configuration as the first deforming unit 58a is preferably provided between the contact D and the position F of the solid lubricant 54a in the rotational direction C, as shown in
Furthermore, the example where both of the polarities α and β are positive is presented in the above embodiment. However, this is not restrictive, and a similar effect can be achieved even in the case where both of the polarities α and β are negative so long as the potentials of the photoreceptor drum 21a and the application unit 52a, and the materials of the solid lubricant 54a and the application brush 522 are appropriately selected.
Furthermore, in the above embodiment, the image forming apparatus uses the intermediate transfer belt 11 to form a full-color toner image. However, this is not restrictive, and the image forming apparatus may be capable of simply forming a monochrome image without using the intermediate transfer belt. In such a case, the transfer roller and the photoreceptor drum, which also acts as an image support, function as transfer members, and a toner image on the photoreceptor drum is directly transferred onto a sheet material (e.g., paper; another example of the transfer target) introduced between the roller and the drum.
As described above, the moving force providing unit 56a causes the lubricant particles 54a′ to move from position E at the upstream relative to the contact D, onto the circumferential surface of the photoreceptor drum 21a, so that the amount of lubricant particles 54a′ to be fed to the contact D can be suppressed much more significantly than can conventionally be suppressed. As a result, the application unit 52a can apply a constant scrubbing force to the photoreceptor drum 21a, thereby scraping charged products adsorbed on the circumferential surface thereof. Thus, occurrence of image defects can be prevented.
Here, to confirm the effect of the moving force providing unit 56a, the present inventors evaluated image defect occurrence levels for a conventional image forming apparatus and the image forming apparatus according to the present embodiment.
The equipment used for evaluation was bizhub C8000 (A4Y: 80 pages/min.) manufactured by Konica Minolta Business Technologies, Inc. The present inventors used this equipment to intermittently print six pages of character image at 5% image coverage in a hygrothermal environment at 23° C. and 65% RH, and also print 1,000 pages of character image at 5% image coverage in a hot and humid (HH) environment (30° C. and 85% RH) every 200,000 revolutions of the photoreceptor drum. Immediately after completion of the printing, the equipment was turned off, and after an eight-hour halt, half-tone images were outputted and then evaluated. The above evaluation was carried out until the cumulative number of photoreceptor drum revolutions reached 1,200,000.
Table 1 below shows the results of evaluation performed on the image forming apparatus according to the present embodiment.
In the image defect evaluation results of Table 1, each “A” denotes no occurrence of image defect, each “B” denotes occurrence of minor image defect, and each “C” denotes occurrence of major image defect. In addition, the solid lubricant used was zinc stearate, the materials used for the auxiliary charge member and the flexible members were nylon sheets, and the material used for the application brush 522a of the application unit was polyester. Moreover, a −300V direct-current bias voltage superimposed with an alternating-current bias voltage having amplitude of −800V and a frequency of 1 kHz was applied to the application unit. However, as for Example 5, the direct-current bias voltage was applied alone without being superimposed with the alternating-current bias voltage. Moreover, the surface potential of the photoreceptor drum was −100V in a section downstream from the primary transfer roller 14 but upstream from the diselectrifying unit 27.
As can be appreciated from Table 1, in the image forming apparatus according to the present embodiment, no major image defect occurred up to 1,000,000 pages of printing, although some minor image defects occurred. Particularly as in Example 1 shown in the top panel of Table 1, where the application brush 522a shown in
Furthermore, the conventional image forming apparatus was evaluated in the same manner as above, and the results of the evaluation are shown in Table 2. Here, in Table 2, the material of the application brush used in Comparative Examples 1 to 5, 7, and 8 was polytetrafluoroethylene pile, and the material used in Comparative Example 6 was polyester. Moreover, the specifications of the application brush in the conventional image forming apparatus were the same as those of the application brush 522a, except for the material. In addition, the position of polytetrafluoroethylene pile in the triboelectric series is on the negative side relative to zinc stearate, and therefore the polarity β was negative and did not coincide with the polarity α.
As shown in Table 2, for Comparative Examples 1 to 5 without the moving force providing unit 56a, image defects occurred in a short period of time.
Furthermore, as shown in
Furthermore, in Comparative Examples 1 to 5, 7, and 8, the material of the application brush was polytetrafluoroethylene pile. The position of polytetrafluoroethylene pile in the triboelectric series is on the negative side relative to zinc stearate, and therefore the polarity β was negative, and did not coincide with the polarity α. In this case, lubricant particles did not receive electric force applied by the application brush toward the photoreceptor drum, and therefore did not move onto the photoreceptor drum, leading to image defect occurrence in a short time frame.
Furthermore, in a preferred example of the present embodiment, the power unit 57a applies a direct-current voltage superimposed with an alternating-current voltage to the application unit 52a as a bias voltage, thereby applying an oscillating electric field to the lubricant particles 54a′. As a result, the lubricant particles 54a′ can further readily move onto the photoreceptor drum 21a.
Furthermore, in the present embodiment, the first and second auxiliary charge members 59a and 60a frictionally charge the lubricant particles 54a′. Thus, the lubricant particles 54a′ can move onto the photoreceptor drum 21a with higher efficiency.
Furthermore, if the second auxiliary charge member 60a has a corrugated surface profile in a plan view from the direction parallel to the shaft 521a, contact area with the application brush 522a can be increased. Thus, the lubricant particles 54a′ can be increased in frictional charge quantity.
Furthermore, a bias voltage of the same polarity as the lubricant particles 54a′ is applied to the first and second auxiliary charge members 59a and 60a. This produces the effect of further increasing the moving force applied to the lubricant particles 54a′.
Furthermore, in the present embodiment, the second deforming unit 61a flexibly deforms the rotating application brush 522a after the rotating application brush 522a scrapes foreign matter from the circumferential surface of the photoreceptor drum 21a. The application brush 522a returns to its original shape after it passes the second deforming unit 61a, and therefore the scraped foreign matter is forcibly taken away from the application brush 522a. Thus, the foreign matter can be prevented from readhering to the photoreceptor drum 21a.
Although the present invention has been described in connection with the preferred embodiment above, it is to be noted that various changes and modifications are possible to those who are skilled in the art. Such changes and modifications are to be understood as being within the scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-058686 | Mar 2012 | JP | national |
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| Number | Date | Country |
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| 2001-265185 | Sep 2001 | JP |
| 2005-189594 | Jul 2005 | JP |
| 2007-310336 | Nov 2007 | JP |
| 2008-275724 | Nov 2008 | JP |
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| Entry |
|---|
| Office Action (Notification of Reason for Refusal) issued on Jan. 21, 2014, by the Japan Patent Office in corresponding Japanese Patent Application No. 2012-058686, and an English Translation of the Office Action (7 pages). |
| Office Action (Notification of Reason for Refusal) issued on Jul. 8, 2014, by the Japan Patent Office in corresponding Japanese Patent Application No. 2012-058686, and an English Translation of the Office Action (6 pages). |
| Number | Date | Country | |
|---|---|---|---|
| 20130243505 A1 | Sep 2013 | US |
