JP2011138001A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that more reliably prevents toner from passing through a cleaning blade regardless of use environment and use history. <P>SOLUTION: The image forming apparatus is configured to supply developer to a surface of a photoreceptor when an image is not formed, so as to form a developer layer on the surface of the photoreceptor. The developer contains the toner and external additive having smaller particle size than the toner, and the toner and the external additive are separately supplied to the surface of the photoreceptor. When each of temperature and humidity exceeds a predetermined value and the number of recording materials subjected to image formation exceeds a predetermined value, the toner is supplied after the external additive is supplied to the surface of the photoreceptor when the image is not formed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, an electrostatic latent image is formed on the surface of a photoreceptor by charging and exposure, and the electrostatic latent image is visualized with toner by development and transferred to a recording material. After transfer, residual toner or the like is present on the surface of the photoreceptor. The residual toner and the like are peeled off from the surface of the photoreceptor by bringing a cleaning blade made of urethane rubber or the like into contact with the photoreceptor.
Cleaning blades made of an elastic material such as urethane rubber are widely used because of their simple structure, small size, and cost advantages. However, the contact state between the cleaning blade and the surface of the photosensitive member becomes unstable (chatter), so that the toner may slip through the cleaning blade.
As a countermeasure against this problem, in Patent Document 1, a toner for reducing friction is supplied to the cleaning blade, and the friction between the surface of the photoreceptor and the cleaning blade is reduced by the presence of the toner or the like. In Patent Document 2, an external additive is supplied to the photoconductor as a lubricant. In Patent Document 3, silica supply means and silica separation supply means are provided, and silica is formed as a blocking powder on a cleaning blade in contact with a cleaning object. As described above, the toner and the external additive are interposed in the contact portion between the photosensitive member and the cleaning blade, thereby reducing friction. Further, the toner existing on the upstream side in the rotation direction of the photoconductor with respect to the cleaning blade slips from the cleaning blade to the downstream side in the rotation direction of the photoconductor by the external additive layer (blocking layer) formed on the surface of the photoconductor. This is believed to be suppressed.

JP 2004-191737 A Japanese Patent Laid-Open No. 2004-4585 Japanese Patent No. 3985126

  However, in a high-temperature and high-humidity environment where friction between the photosensitive member and the cleaning blade is increased, chattering of the cleaning blade may cause a large amount of toner supplied during non-image formation to pass through the cleaning blade at the start of the next printing. There is a situation in which such toner slip easily occurs depending on use conditions such as use environment and use history.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can more reliably prevent toner from passing through a cleaning blade regardless of a use environment or a use history.

In order to achieve the above object, in the image forming apparatus according to the present invention,
A photoreceptor,
Charging means for charging the surface of the photoreceptor;
Exposure means for exposing the surface of the photoreceptor after charging to form an electrostatic latent image;
Developing means for developing the electrostatic latent image;
Transfer means for transferring an image obtained by developing the electrostatic latent image to a recording material;
Cleaning means for scraping off a substance remaining on the surface of the photoconductor after the transfer by bringing a cleaning member into contact with the surface of the photoconductor;
With
In the image forming apparatus configured to be able to supply the developer to the surface of the photosensitive member during non-image formation in order to form a layer of the developer on the surface of the photosensitive member by the developing unit,
The developer includes a toner and an external additive having a smaller particle diameter than the toner, and the toner and the external additive can be separately supplied to the surface of the photoreceptor,
When each of temperature and humidity exceeds a predetermined value and the number of the recording materials on which image formation has been performed exceeds a specified number, the external addition is first performed on the surface of the photoreceptor during non-image formation. An agent is supplied, and then the toner is supplied.

  According to the present invention, it is possible to more reliably suppress the toner cleaning blade from slipping through regardless of the use environment or use history.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment. The schematic diagram of the cleaning blade vicinity. FIG. 4 is a control block diagram for explaining toner and external additive supply control. 6 is a flowchart for describing toner and external additive supply control.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. .

<Image Forming Apparatus and Image Forming Apparatus Main Body>
An image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a schematic cross-sectional view of the image forming apparatus according to the present embodiment. The image forming apparatus according to this embodiment serves as an image forming unit that forms an image in, for example, a printer or a copier, and a driving force is supplied from an image forming apparatus main body (hereinafter simply “apparatus main body”) as a printer engine. It is comprised so that it may obtain. The image forming apparatus according to the present embodiment forms an image by electrophotography.

<Photoconductor>
In this embodiment, a drum-shaped organic photoreceptor 1 (hereinafter referred to as drum 1) is used as the photoreceptor. The drum 1 receives a driving force from the apparatus main body and rotates in the R1 direction in FIG. The drum diameter is Φ24.
<Charging means>
In this embodiment, the charging roller 2 is used as the charging means. The charging roller 2 is in contact with the drum 1 and is driven to rotate with the surface of the drum 1 (photoconductor surface). As the charging bias, only a DC component, or a DC component and an AC component can be applied. In this embodiment, a charging bias having only a DC component is applied. The surface of the drum 1 is charged by the charging roller 2 (the drum surface potential at this time is Vd). In this embodiment, Vd = −500V.
<Exposure means>
An electrostatic latent image is formed on the surface potential of the drum 1 by exposure with the laser beam output from the laser beam scanner 3 as an exposure means (the drum 1 surface potential of the exposed portion is defined as Vl). In this embodiment, Vl = −150V was set.
<Developing device>
The developing device 4 includes a developing container 5, a developing sleeve 6, and a developing blade 7, and contains a developer therein.
<Developer>
The developer is a one-component developer having a toner and an external additive. The developer according to this embodiment is a magnetic toner, and an external additive having a polarity opposite to that of the toner is used. The external additive mainly serves as an abrasive in the developer. In this embodiment, since a negatively charged toner is used, examples of the positively charged external additive include metal oxides such as magnesium, aluminum, titanium, iron, zirconium, and cerium. Furthermore, composite metal oxides such as calcium titanate, magnesium titanate, strontium titanate, and barium titanate are also included. Among these, carbides such as aluminum oxide, cerium oxide, titanium oxide, strontium titanate, magnesium titanate, silicon carbide, and titanium carbide, and nitrides such as silicon nitride and germanium nitride are often used. In this embodiment, strontium titanate is used.
The weight average particle diameter (D4) of the toner is measured with an effective measurement channel number of 25,000 channels using a fine particle size distribution measuring device by a pore electric resistance method equipped with a 100 μm aperture tube, and analysis of the measurement data is performed. To calculate. The precision particle size distribution measuring apparatus is “Coulter Counter Multisizer 3” (registered trademark, manufactured by Beckman Coulter, Inc.). “Beckman Coulter Multisizer 3 Version 3.51” (manufactured by Beckman Coulter, Inc.) was used as attached dedicated software for setting measurement conditions and analyzing measurement data. As the electrolytic aqueous solution used for the measurement, special grade sodium chloride is dissolved in ion-exchanged water so as to have a concentration of about 1% by mass, for example, “ISOTON II” (manufactured by Beckman Coulter, Inc.) can be used.
When the toner was measured using the above measuring apparatus, the average particle size was 7 μm.
The particle size of the external additive was measured with a digitizer based on an SEM photograph taken with a scanning electron microscope S-4800 (manufactured by Hitachi, Ltd.).
When the external additive was measured using the measuring apparatus, the average particle size was about 0.1 μm.
<Development sleeve>
The developing sleeve 6 is a nonmagnetic sleeve 6 formed of an aluminum or stainless steel pipe, and is supported by the developing container 5 so as to be rotatable in the direction of the arrow R2. The surface of the developing sleeve was coated with a solvent in which carbon, a charge control agent, and fine particles for roughening the surface were dispersed in a phenol resin so that an appropriate charge was given when a desired amount of toner was carried. Further, the surface of the developing sleeve 6 is rough due to the paint coat.
<Developing blade>
The developing blade 7 is formed, for example, of urethane rubber in a plate shape, and a base end portion thereof is fixed to a support metal plate. The developing blade 7 contacts the developing sleeve 6 in the counter direction with respect to the rotation direction.

<Development bias>
As the development bias, a DC component (Vdc) and an AC component (amplitude Vpp, frequency f) are applied. In this example, Vdc = −350V, Vpp = 1.4 kV, and f = 2.0 kHz. The electrostatic latent image on the drum 1 is made visible as a toner image by the developing means.
<Developing means>
The toner carried on the surface of the developing sleeve 6 is conveyed to a developing area facing the surface of the photosensitive drum 1. The toner to be conveyed includes frictional electrification between the toners caused by the rotation of the developing sleeve 6 in the R2 direction, and between the developing sleeve 6 and the developing blade 7 when the layer thickness is regulated by the developing blade 7. Appropriate charges are imparted by frictional charging by rubbing. At this time, a developing bias in which a DC component and an AC component are superimposed is applied to the developing sleeve 6 through a sliding contact. As a result, the toner on the developing sleeve 6 flies to the drum 1 in the developing region and electrostatically adheres to the electrostatic latent image, and the electrostatic latent image is visualized as a toner image.
<Transfer means>
A transfer roller 8 that abuts on the drum 1 and is driven to rotate is used as a transfer unit that transfers the toner image formed by developing the electrostatic latent image formed on the drum 1 onto the recording material P. The apparatus main body or the image forming apparatus includes environment detection means (not shown) that detects the environment from the resistance value of the transfer roller 8. The environment detection means uses the property that the resistance value of the transfer roller 8 decreases as the temperature and humidity increase, and predicts the temperature and humidity from changes in the resistance value. This environment detection means is a conventional technique and will not be described in detail. For example, a resistance value of the transfer roller 8 is measured by applying a predetermined reference voltage to the transfer roller 8 serving as a detector and measuring a current at that time. The structure provided with the electric current detection circuit etc. which can obtain | require is mentioned. The environment detection means is not limited to this, and other conventional techniques can be adopted as appropriate.

<Image forming operation>
In the image forming apparatus, when the image forming operation is started, first, the laser beam scanner 3 irradiates the drum 1 with light L corresponding to the image signal. By irradiating the light L, an electrostatic latent image is formed on the drum 1. The electrostatic latent image formed on the drum 1 is developed with the developer stored in the developing container 5, whereby a toner image (visible image) is formed on the drum 1. In parallel with such a toner image forming operation, the recording material P is fed from a recording material storage cassette (not shown). The recording material P is conveyed to a transfer unit constituted by the drum 1 and the transfer roller 8 in synchronization with a toner image formed on the drum 1 by a conveyance roller and a registration roller (not shown). In the transfer unit, a toner image is transferred to the recording material P by applying a bias to the transfer roller 8. The recording material P to which the toner image has been transferred is conveyed to a fixing device 10 as image heating means, and the toner image is fixed to the recording material P by heating.

<Cleaning means>
As the cleaning means, a cleaning blade (cleaning member) 9 made of urethane rubber is used. As shown in FIG. 1, the cleaning blade 9 is in contact with the rotation direction R1 of the drum 1 in the counter direction, and scrapes off the material remaining on the surface of the drum 1 after transfer.
<Near cleaning blade and cleaning blade in contact with drum>
The transfer residual toner not transferred to the recording material by the transfer roller 8 but remaining on the drum surface is peeled off by a cleaning blade 9 made of urethane rubber in contact with the drum surface. As shown in FIG. 2, the external additive 12 and the toner 13 are accumulated in the vicinity of the cleaning blade 9, and a blocking layer for preventing the toner from slipping is formed.

<Supplying external additives>
A method for supplying an external additive to the surface of the drum 1 during non-image formation will be described. In this embodiment, the surface of the drum 1 is charged to Vd by the charging roller 2, and then a developing bias is applied to supply the external additive to the surface of the drum 1. Here, the time of non-image formation is a timing other than the time of image formation in which an image formation operation for transferring and outputting to a recording material is performed. As non-image formation, for example, pre-rotation that is a preparatory operation before the image forming operation, post-rotation that is a rearranging operation after the image forming operation, or recording during a series of image forming operations on a plurality of recording materials For example, there is a corresponding interval between the recording material and the recording material.
The external additive used in this embodiment is positively charged and is supplied to the white portion of the image. That is, the drum surface potential is a portion of Vd, and it is necessary that Vdc> Vd. As means for supplying more external additives, if Vdc−Vd = Vback is defined, Vback is set to a value greater than the condition at the time of image formation, or Vpp is set to a magnitude greater than that at the time of image formation. This is possible by raising the frequency of the developing bias. Examples of means for increasing Vback include decreasing Vd or increasing Vdc.
In this embodiment, Vd = −600 V, Vdc = −350 V, Vpp = 1.6 kV, and f = 2.0 kHz were used for the settings during non-image formation. On the drum, an external additive was supplied in a width of 30 mm in the sub-scanning direction (parallel to the paper conveyance direction).

<Toner supply>
A method for supplying toner to the surface of the drum 1 during non-image formation will be described. In this embodiment, the surface of the drum 1 is charged to Vd by the charging roller 2, and then a thin line electrostatic latent image is formed on the surface of the drum 1 by laser light, and a developing bias is applied so that toner is transferred to the surface of the drum 1. To supply.
The toner used in this embodiment is negatively charged and is supplied to the black portion of the image. That is, it is the Vl portion of the drum surface potential, and it is necessary that Vl> Vdc. The drum surface potential Vd after charging used in the toner supply means, the drum surface potential Vl of the exposed portion, the DC component (Vdc) and AC component (amplitude Vpp, frequency f) of the developing bias are different from those in the image forming region. But you can.
In this embodiment, Vd = −500 V, Vdc = −300 V, Vl = −150 V, Vpp = 1.4 kV, and f = 2.0 kHz were used for the setting during non-image formation. In the electrostatic latent image formation, a toner image was formed by forming an electrostatic latent image having a horizontal line of 1.5 mm in the sub-scanning direction (parallel to the paper transport direction). The electrostatic latent image created for non-image formation is arbitrary, but in order to supply uniformly to the contact portion between the drum and the cleaning blade, the cleaning blade in the main scanning direction (the direction perpendicular to the paper transport direction) A horizontal line having the same length is considered preferable.

<Effects of toner supply means and external additive supply means>
By supplying toner or the like, a layer of toner or the like is formed on the surface of the drum 1. This layer is considered to prevent paper dust and the like from being sandwiched between the contact portions of the cleaning blade 9 and the drum 1. The external additive mainly serves to reduce the friction of the cleaning blade 9.
The blocking layer is formed of a toner layer and an external additive layer. Here, the blocking layer will be described with reference to FIG. As shown in FIG. 2, the external additive 12 is accumulated in the upstream direction of the cleaning blade 9 contacting the drum 1 rotating in the R1 direction in a counter manner, and the toner 13 is further accumulated so as to cover the external additive layer. The Since the small particle size has a strong adhesion to the drum 1, the external additive reaches the vicinity of the cleaning blade 9 and is dammed by the cleaning blade 9, and therefore exists in front of the cleaning blade 9.

<Selection of toner supply or external additive supply according to usage environment>
In a high-temperature and high-humidity environment, the hardness of the cleaning blade 9 made of urethane rubber or the like is lowered. Therefore, the cleaning blade 9 is likely to be distorted when the drum 1 in contact with the cleaning blade 9 starts to rotate. Furthermore, since the friction between the drum 1 and the cleaning blade 9 becomes high under a high temperature and high humidity environment, the cleaning blade 9 tends to chatter. Therefore, in the conventional method of supplying toner, a fresh toner having high fluidity is supplied in the vicinity of the cleaning blade 9 in a high temperature and high humidity environment, so that a large amount of toner passes through the cleaning blade 9 to perform cleaning. It is considered that defects are likely to occur.
As described above, the image forming apparatus according to the present embodiment is configured so that the toner and the external additive can be separately supplied to the surface of the drum 1. Therefore, in this embodiment, the external additive is supplied first, and then the toner is supplied. By supplying the external additive first, in addition to the absence of fresh toner having high fluidity, a blocking layer is formed by the supplied external additive, and chattering of the cleaning blade 9 is suppressed. Thereafter, the toner supply is performed to promote the formation of the blocking layer, and the jamming of the paper powder or the like into the contact portion between the drum 1 and the cleaning blade 9 can be suppressed.

  In this embodiment, the supply control of the toner and the external additive was performed by setting 30 ° C. and 80% as a predetermined value determined as a high temperature and high humidity environment. The temperature and humidity determined to be a high-temperature and high-humidity environment are appropriately set based on the type and particle size of the toner and external additive used, the material and dimensions of the drum 1 and the cleaning blade 9, and the like. It is. That is, the temperature and humidity determined to be a high-temperature and high-humidity environment are determined based on the temperature and humidity determined to be required to supply the external additive first in the specifications of different image forming apparatuses.

<Control configuration of toner supply and external additive supply>
FIG. 3 is a control block diagram illustrating a control configuration for controlling toner supply and external additive supply during non-image formation. A control unit (CPU) 30 as a control unit provided in the apparatus main body controls various operations such as an image forming operation in the image forming apparatus. In the apparatus main body or the image forming apparatus, an environment detecting unit 31 for detecting a use environment (temperature and humidity) of the image forming apparatus and a counter 32 for counting the number of printed sheets (the number of recording materials on which image formation has been performed) are provided. Is provided. The control unit 30 controls toner supply and external additive supply during non-image formation by controlling the bias applied to the charging roller 2 based on the output from the environment detection unit 31 and the output from the counter 32. .

<Flow chart of selection of toner supply or external additive supply according to usage environment>
With reference to FIG. 4, a flow chart for selecting whether to supply an external additive or toner on the drum 1 during non-image formation according to the use environment or the like will be described.
In response to a print command from the control unit 30, the drum 1 starts rotating by driving the apparatus main body (step 14) and pre-rotation is started (step 15). First, the use environment is determined based on the output from the environment detection means 31 during the pre-rotation (step 16). In this embodiment, the use environment is determined from the resistance value of the transfer roller 8. That is, it is determined whether or not each of the temperature and humidity predicted from the change in the resistance value of the transfer roller 8 exceeds a predetermined value.
<< In case of high temperature and high humidity >>
If it is determined in step 16 that the use environment is a high-temperature and high-humidity environment (YES), it is determined from the output of the counter 32 whether or not the specified number of sheets to be supplied with external additives (specified number) has been reached (step 17a). . If the specified number has been reached (step 17a, YES), after the printing is finished (step 18b), the external additive is supplied first (step 19a), then the toner is supplied (step 20), and the process is ended (step 21). . On the other hand, if the specified number of sheets has not been reached (step 17a, NO), after the printing is finished (step 18b), the process is finished without supplying any toner or external additive (step 21). That is, even in a high-temperature and high-humidity environment, it is considered that the influence of the residual toner is small at the initial use stage (first half of the use history), so that the blocking layer is not formed by the toner and the external additive. The blocking layer is formed with the toner and the external additive only when the specified number of sheets is considered to be affected by the residual toner.
<< When not in a high temperature and high humidity environment >>
If the use environment is not determined to be a high-temperature and high-humidity environment in step 16 (NO), it is considered that the toner cleaning blade 9 is unlikely to slip through. Therefore, the blocking layer is formed and maintained only by supplying the toner. Do. The counter 32 counts the number of printed sheets and determines whether or not the specified number of sheets to be supplied with toner has been reached (step 17b). If the specified number has been reached (step 17a, YES), toner is supplied (step 19b) after printing is performed (step 18c) to complete and maintain the blocking layer (step 19b), and the process ends (step 21). . On the other hand, if the specified number has not been reached, printing is performed (step 18d), and the process is terminated without supplying toner (step 21).

In a high-temperature and high-humidity environment, it is possible to prevent toner from passing through the cleaning blade 9 by supplying an external additive instead of toner onto the drum 1 after printing to promote formation of the blocking layer. Further, no image defect due to the contamination of the charging roller 2 occurred. In this embodiment, when the external additive is supplied 100 mm or more in the sub-scanning direction, an image defect due to contamination of the charging roller 2 occurs. Further, in the case where 10 mm or less is supplied in the sub-scanning direction, it is difficult to suppress slipping of the toner cleaning blade.
Further, the timing of supplying the toner and the external additive is always performed in a timely manner in order to reduce friction between the drum 1 and the cleaning blade 9. For example, in the first half of the usage history according to the usage history of the image forming apparatus, it is considered that the formation of the blocking layer is small, so the frequency of supplying the toner or the external additive is increased (the specified number of sheets is set to a small value). On the other hand, in the latter half of the usage history in which the number of image formations has increased, it is possible to set the frequency of toner supply or external additive supply to be reduced (the specified number of sheets is set to a large value).
Further, the position where the blocking layer is likely to be accumulated also changes depending on the particle diameter of the toner or the external additive. Smaller particle diameters are present near the cleaning blade 9. Therefore, the toner supply and the external additive supply may be performed in a timely and appropriate amount depending on the particle diameter of the toner and the particle diameter of the external additive. In other words, not only the use environment and use history but also various other use conditions may be taken into consideration, and toner supply and external additive supply during non-image formation may be performed. Thereby, the blocking layer can be stabilized.

  According to the present invention, the toner or external additive layer (blocking layer) is stabilized by controlling the toner or external additive supplied onto the drum 1 during non-image formation according to the usage environment and usage history. And has the effect of suppressing slipping of the toner cleaning blade.

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 2 ... Charging roller, 3 ... Exposure means, 4 ... Developing device, 5 ... Developing container, 6 ... Developing sleeve, 7 ... Developing blade, 8 ... Transfer roller, 9 ... Cleaning blade, 10 ... Fixing device, 12 ... external additive, 13 ... toner.

Claims (5)

A photoreceptor,
Charging means for charging the surface of the photoreceptor;
Exposure means for exposing the surface of the photoreceptor after charging to form an electrostatic latent image;
Developing means for developing the electrostatic latent image;
Transfer means for transferring an image obtained by developing the electrostatic latent image to a recording material;
Cleaning means for scraping off a substance remaining on the surface of the photoconductor after the transfer by bringing a cleaning member into contact with the surface of the photoconductor;
With
In the image forming apparatus configured to be able to supply the developer to the surface of the photosensitive member during non-image formation in order to form a layer of the developer on the surface of the photosensitive member by the developing unit,
The developer includes a toner and an external additive having a smaller particle diameter than the toner, and the toner and the external additive can be separately supplied to the surface of the photoreceptor,
When each of temperature and humidity exceeds a predetermined value and the number of the recording materials on which image formation has been performed exceeds a specified number, the external addition is first performed on the surface of the photoreceptor during non-image formation. An image forming apparatus, wherein an agent is supplied and then the toner is supplied.   Even if each of temperature and humidity exceeds a predetermined value, if the number of recording materials on which image formation has been performed is less than a specified number, the toner and the external additive are not supplied during non-image formation. The image forming apparatus according to claim 1.   When each of temperature and humidity does not exceed a predetermined value, when the number of recording materials on which image formation has been performed exceeds a specified number, only the toner is supplied during non-image formation. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   When the temperature and humidity do not exceed predetermined values and the number of recording materials on which image formation has been performed is less than a specified number, the toner and the external additive are supplied during non-image formation. The image forming apparatus according to claim 1, wherein the image forming apparatus is not provided.   The image forming apparatus according to claim 1, wherein the prescribed number is increased as the number of times of image formation increases.

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