JP2006072270A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which prevents slippage between a photoreceptor and a charging roller rotating following the rotation of the photoreceptor, or sticking of toner, and which can form a stable image for a long period of time. <P>SOLUTION: The image forming apparatus is equipped with at least: an image carrier; a charging roller which is in contact with the image carrier and driven to rotate to charge the image carrier; an exposing means to expose the charged image carrier to form an electrostatic latent image; a developing means to develop the electrostatic latent image with toner to obtain a toner image; and a transfer means to transfer the toner image onto a material to be transferred. The image forming apparatus is characterized in that: a resin layer is provided as the surface layer of the charging roller; the surface of the charging roller shows the ten-point average roughness Rz satisfying 0.14 μm≤Rz≤1.4 μm and the micro hardness K satisfying 0°<K≤60°; the nip pressure P of the charging roller against the image carrier is controlled to satisfy 6.3 N/m≤P≤16.7 N/m. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus including a charging roller that rotates in contact with an image carrier and charges the image carrier.

  In an image forming apparatus such as a printer or a copier that includes a charging roller that rotates following contact with a photosensitive member as an image bearing member and charges the photosensitive member, when the toner remaining on the photosensitive member adheres to the charging roller, the charging roller Increases in resistance value, and the photosensitive member cannot be uniformly charged, resulting in uneven image density. For this reason, various countermeasures for preventing toner from adhering to the charging roller have been conventionally devised (see, for example, Patent Documents 1 to 4).

  In recent years, so-called cleanerless system image forming apparatuses that do not use a cleaning blade have been devised, and various cleaning systems for such image forming apparatuses have been devised. Among them, the toner remaining on the photosensitive member without being transferred to the transfer belt is transferred to the brush roller as a holding unit disposed between the transfer belt (transferred member) and the charging roller in the moving direction of the photosensitive member. And retransfer toner offset from the transfer belt to the photoconductor, and temporarily applying a reverse bias voltage to the brush roller during non-image formation to release the toner from the brush roller to the photoconductor, A system has been devised in which toner is collected by a cleaning device that collects toner on a developing device or a transfer belt.

  In this system, when the cleaning cycle is long, such as when a large number of sheets are continuously printed, or when the toner image is not transferred to the transfer belt due to a jam, The amount increases, and the amount of toner discharged from the brush roller to the photoreceptor also increases.

  When the amount of toner discharged from the brush roller to the photoconductor increases, the charging roller that is originally driven by the photoconductor and rotates is not driven by the photoconductor, causing a slip. Toner accumulates in the part. The toner accumulation causes a slip every time the charging roller makes one revolution. Accordingly, there has been a problem that charging failure occurs periodically and periodic white spots and density unevenness occur in the image.

In this case, if the nip pressure of the charging roller with respect to the photosensitive member is high, there is a problem that toner adheres to the photosensitive member.
Therefore, in order to put the cleanerless system using the charging roller into practical use, it is necessary to solve various problems caused by the toner interposed between the photoreceptor and the charging roller.
JP 2002-040756 A Japanese Patent Laid-Open No. 2002-221829 JP 2003-098725 A Japanese Patent Application Laid-Open No. 08-211698

The present invention aims to solve the above-mentioned problems.
In other words, the present invention provides an image forming apparatus capable of preventing slippage and toner sticking between a charging roller that rotates following the photosensitive member and the photosensitive member, and forming a stable image over a long period of time. With the goal.

The above-mentioned subject is achieved by the following present invention. That is, the present invention
<1> At least an image carrier, a charging roller that is driven to rotate in contact with the image carrier and charges the image carrier, and an exposure that exposes the charged image carrier to form an electrostatic latent image An image forming apparatus comprising: a developing unit; a developing unit that develops the electrostatic latent image with toner to form a toner image; and a transfer unit that transfers the toner image to a transfer target.
A resin layer is provided as a surface layer of the charging roller, the charging roller surface has a ten-point average roughness Rz of 0.14 μm ≦ Rz ≦ 1.4 μm, a micro hardness K of 0 ° <K ≦ 60 °, and the image In the image forming apparatus, the nip pressure P of the charging roller with respect to the carrier is 6.3 N / m ≦ P ≦ 16.7 N / m.

<2> Further, a part or all of the toner that is disposed between the transfer position and the contact position of the charging roller in the moving direction of the image carrier and adheres to the surface of the image carrier after the transfer is collected. The image forming apparatus according to <1>, further comprising a holding unit that temporarily holds the toner and releases the toner to the image carrier during non-image formation.

<3> The image forming apparatus according to <1> or <2>, wherein the resin layer includes polyamide.

<4> The toner according to any one of <1> to <3>, wherein the toner is a polymerized toner having a shape factor SF1 in the range of 100 to 140 and a volume average particle diameter in the range of 2 to 8 μm. An image forming apparatus.

  According to the present invention, there is provided an image forming apparatus capable of preventing the occurrence of slip and toner sticking between a charging roller that rotates following the photosensitive member and the photosensitive member, and can form a stable image over a long period of time. can do.

Hereinafter, the present invention will be described in detail.
The image forming apparatus of the present invention includes at least an image carrier, a charging roller that is driven to rotate in contact with the image carrier, and charges the image carrier, and the charged image carrier is exposed to electrostatic latent image. An image forming apparatus comprising: an exposure unit that forms an image; a developing unit that develops the electrostatic latent image with toner to form a toner image; and a transfer unit that transfers the toner image to a transfer target. A resin layer is provided as a surface layer of the charging roller, the 10-point average roughness Rz of the charging roller surface is 0.14 μm ≦ Rz ≦ 1.4 μm, the micro hardness K is 0 ° <K ≦ 60 °, and the image bearing The nip pressure P of the charging roller with respect to the body is set to 6.3 N / m ≦ P ≦ 16.7 N / m.

As described above, in the cleanerless system using the charging roller, it is necessary to solve the problem caused by the toner interposed between the photosensitive member (image carrier) and the charging roller.
In the present invention, in an image forming apparatus having a contact-type charging roller as a charging means, not only the hardness and surface property of the charging roller are controlled, but also the nip pressure with respect to the photosensitive member (image carrier) is kept below a certain level. Thus, it has been found that not only can the slip during the follower rotation with the photoreceptor in the cleaner-less system be prevented, but also the toner sticking can be avoided.

The image forming apparatus of the present invention will be described below with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an example of an image forming apparatus of the present invention. As shown in the figure, a color laser printer (hereinafter simply referred to as “printer”) 10 as an image forming apparatus includes developing units (developing units) 12C, 12M, 12Y, and 12K for cyan, magenta, yellow, and black. Photoconductors (image carriers) 13C, 13M, 13Y, and 13K are arranged in parallel facing the intermediate transfer belt (transfer target) 14, and the intermediate transfer belt 14 makes one round in the direction of arrow A. This is a so-called tandem full-color laser printer that superimposes four color toner images.

  The printer 10 includes a paper feed tray 16 at the bottom. A paper feed roller 18 is in contact with the leading end of the paper P set in the paper feed tray 16 in the conveying direction (arrow B). The paper P is fed by the paper feed roller 18 and a paper winding means (not shown). The sheets are fed one by one from the sheet feeding tray 16 to the downstream side in the transport direction. A pair of transport rollers 20 is arranged on the downstream side of the paper feed roller 18 in the transport direction, and the paper P is transported to the transfer unit 22 above the drawing by the transport force from the transport rollers 20.

  The transfer unit 22 is provided with a belt conveyance roller 24A around which the intermediate transfer belt 14 is wound, and a transfer roller 26 pressed against the belt conveyance roller 24A. The intermediate transfer belt 14 is sandwiched between the nip portion between the belt conveyance roller 24A and the transfer roller 26, and the toner image is transferred from the intermediate transfer belt 14 when the sheet P passes through the nip portion.

  A fixing unit 28 is disposed above the transfer unit 22 and on the downstream side in the transport direction. The fixing unit 28 is provided with a heat roller 28A that reaches a high temperature and a backup roller 28B that is in pressure contact with the heat roller 28A, and the sheet P passes through the nip portion between the heat roller 28A and the backup roller 28B. When passing, the toner is melted and solidified to be fixed on the paper P. Then, the paper P is discharged by a paper discharge roller 29 disposed on the downstream side in the transport direction of the fixing unit 28.

  Here, the printing unit 30 in which the photoreceptors 13C, 13M, 13Y, and 13K superimpose the toner image on the intermediate transfer belt 14 will be described. In addition, when distinguishing each color of cyan, magenta, yellow, and black, explanation is made by adding C, M, Y, K after the code. However, when it is not necessary to distinguish each color, C, M, Y, and K are omitted.

FIG. 2 shows a schematic configuration of the print unit 30.
As shown in FIG. 2, the intermediate transfer belt 14 includes the above-described belt conveyance roller 24A, a belt conveyance roller 24B disposed below the belt conveyance roller 24A, and a sheet conveyance path diagonally above the belt conveyance roller 24B. Is wound around a belt conveyance roller 24C disposed on the opposite side.

  The surface of the intermediate transfer belt 14 between the belt conveyance roller 24B and the belt conveyance roller 24C that faces obliquely downward is a transfer surface 14A on which the toner image is transferred from the photoreceptors 13C, 13M, 13Y, and 13K. The developing units 12C, 12M, 12Y, and 12K and the photoconductors 13C, 13M, 13Y, and 13K are arranged in parallel so as to face the transfer surface 14A, and the photoconductors 13C, 13M, 13Y, and 13K are transferred to the transfer surface. 14A. The four transfer rollers 32 are pressed against the photoreceptors 13C, 13M, 13Y, and 13K through the intermediate transfer belt 14, respectively.

  A sensor 15 for detecting the density of toner transferred to the intermediate transfer belt 14 is disposed on the transfer surface 14A downstream of the photosensitive member 13K in the transport direction.

FIG. 3 shows an enlarged image forming portion of one color in the printing unit.
As shown in FIG. 3, the intermediate transfer belt 14, the brush roller 34, the charging roller 36, and the developing roller 38 are in contact with the photosensitive surface 13 </ b> A of the photosensitive member 13 in order in the rotation direction. The developing roller 38 rotates in the same direction as the rotation direction of the photoconductor 13. That is, the developing roller 38 rotates in the reverse direction with respect to the photoreceptor 13 at the nip portion. Thereby, the transfer efficiency from the developing roller 38 to the photosensitive member 13 is enhanced. Further, between the charging roller 36 and the developing roller 38, an LED array head (exposure means) 40 that performs line exposure of the photosensitive surface 13A is disposed.

Hereinafter, a flow until the toner image is transferred to the intermediate transfer belt 14 will be described.
When the photosensitive member 13 rotates counterclockwise in the figure, first, the photosensitive surface 13A is uniformly charged to a predetermined polarity potential by the charging roller 38. When the photosensitive member 13 further rotates, the charged surface of the photosensitive surface 13A is exposed by the LED array head 40, and the potential of the exposed portion of the charged surface is lowered to form an electrostatic latent image. After that, the developing toner T1 charged to the same polarity as the charging polarity of the photosensitive member 13 is electrically attached to the potential lowering portion of the charging surface by the developing roller 38, thereby developing the electrostatic latent image and developing the toner image. And The toner is electrically attracted to the transfer roller 32 to which a transfer voltage having a polarity opposite to that of the toner is applied. As a result, the toner image is transferred from the photoreceptor 13 to the intermediate transfer belt 14.

  Here, when the toner image is transferred from the photoreceptor 13 to the intermediate transfer belt 14, untransferred toner T <b> 2 that remains on the photoreceptor 13 without being transferred to the intermediate transfer belt 14 is generated. Further, retransfer toner (hereinafter referred to as “retratoner”) T3 is generated in which the toner transferred to the intermediate transfer belt 14 on the upstream side in the moving direction is offset to the downstream photoreceptor 13.

Therefore, it is necessary to remove the transfer residual toner T2 and the retraction toner T3 from the photoconductor 13. In the present invention, the removal method is not particularly limited, but the charging roller according to the present invention is preferably used in the case of a so-called cleaningless system having a holding means for temporarily collecting and holding the residual toner as described below.
Hereinafter, cleaning of the transfer residual toner T2 and the retraction toner T3 will be described. In the present invention, the transfer residual toner and the retra toner are combined and used as the toner adhered on the photosensitive member after transfer.

4 and 5 are schematic views showing the process from the development of the toner onto the photoreceptor to the transfer and collection.
First, the printing process will be described. As shown in FIG. 4A, first, the developing toner T1 moves from the developing roller 38 to the photosensitive member 13. Thereafter, the transfer residual toner T2 remains on the photoconductor 13 at the transfer portion, and the re-tray toner T3 is offset from the intermediate transfer belt 14 to the photoconductor 13.

  Then, as shown in FIG. 4B, a voltage (for example, −500 V) having a polarity opposite to the polarity (for example, +) of the retraction toner T3 is applied to the brush roller (holding body) 34, and the retraction toner T3 is applied to the brush roller 34. It is electrically adsorbed (collected and retained). Further, the transfer residual toner T <b> 2 passes through the charging area by the charging roller 36 and the exposure area by the LED array head 40 while being attached to the photoreceptor 13. That is, charging and exposure are performed while the transfer residual toner T2 remains attached to the photosensitive member 13.

  As shown in FIG. 5A, the untransferred toner T2 adhered to the non-exposed non-image area (for example, −500 V) is electrically collected by the developing roller 38 to which a voltage of −200 V is applied, for example. Then, the toner is scraped off from the developing roller 38 to the toner containing portion 41 by the blade 39 slidably contacting the developing roller 38 in the developing unit 12. At the same time, the developing roller 38 moves the developing toner T1 to the potential lowering portion of the photosensitive surface 13A. Thus, a toner image can be formed while removing the transfer residual toner T2 from the photosensitive member 13.

  Next, the flow of cleaning the re-toner T3 temporarily held by the brush roller 34 in the cleaning mode or at the job end will be described.

  As shown in FIG. 5B, first, the polarity of the voltage applied to the brush roller 34 is reversed from minus (−) to plus (+), and the retraction toner T3 charged to + from the brush roller 34 to the photosensitive member 13 is loaded. Release.

Then, by turning off the minus (−) voltage applied to the developing roller 38, the retractor toner T 3 passes through the developing region without being collected by the developing roller 38. Then, the voltage polarity of the transfer roller 32 is reversed from plus (+) to minus (−) and transferred to the intermediate transfer belt 14. Thereafter, the re-toner T3 is collected by the cleaner 42 (see FIG. 2) on the intermediate transfer belt 14.
In the present embodiment, the mode in which only the retraction toner T3 is collected on the brush roller 34 is shown. However, in the present invention, both the transfer residual toner T2 and the retraction toner T3 are collected on the brush roller 34 by changing the mechanism. You can also.

Here, the configuration of the charging roller used in the present invention will be described.
FIG. 7 shows a cross-sectional view of an example of the configuration of the charging roller in the present invention. The layer structure of the charging roller preferably has at least two or more conductive layers including a surface layer on the surface of the conductive support, and may be composed of three layers or four layers. At least one of the conductive layers is a conductive elastic layer so that the charging roller is pressed against the surface of the photoconductor with an appropriate pressure to form a nip between the photoconductor and the surface of the photoconductor can be uniformly charged. It is preferable.

  The conductive support functions as an electrode and a support member of the charging roller. For example, a metal or alloy such as aluminum, copper alloy, or stainless steel; iron plated with chromium, nickel, etc .; conductive It is made of a conductive material such as resin.

  The conductive elastic layer is formed, for example, by dispersing a conductive agent in a rubber material. Rubber materials include isoprene rubber, chloroprene rubber, epichlorohydrin rubber, butyl rubber, urethane rubber, silicone rubber, fluorine rubber, styrene-butadiene rubber, butadiene rubber, nitrile rubber, ethylene propylene rubber, epichlorohydrin-ethylene oxide copolymer rubber, ethylene-propylene. -Diene terpolymer rubber (EPDM), acrylonitrile-butadiene copolymer rubber, natural rubber, etc., and blended rubbers thereof. Of these, silicone rubber, epichlorohydrin rubber, and acrylonitrile-butadiene copolymer rubber are preferably used. These rubber materials may be foamed or non-foamed.

  As the conductive agent, an electronic conductive agent or an ionic conductive agent is used. Examples of electronic conductive agents include carbon blacks such as ketjen black and acetylene black; pyrolytic carbon, graphite; various conductive metals or alloys such as aluminum, copper, nickel, and stainless steel; tin oxide, indium oxide, titanium oxide Examples thereof include fine powders such as various conductive metal oxides such as tin oxide-antimony oxide solid solution and tin oxide-indium oxide solid solution; Examples of ionic conductive agents include perchlorates and chlorates such as tetraethylammonium and lauryltrimethylammonium; alkali metals such as lithium and magnesium; perchlorates and chlorates of alkaline earth metals Can be mentioned.

These conductive agents may be used alone or in combination of two or more. The addition amount is not particularly limited, but it is preferable to adjust the volume resistance value of the conductive elastic layer to a range of 1 × 10 ⁶ to 1 × 10 ¹⁰ Ω · cm.

A resin layer is provided as the surface layer. The polymer material constituting the resin layer is not particularly limited, but polyamide, polyurethane, polyvinylidene fluoride, tetrafluoroethylene copolymer, polyester, polyimide, silicone resin, acrylic resin, polyvinyl butyral, ethylene tetrafluoroethylene copolymer Examples thereof include polymers, melamine resins, fluororubbers, epoxy resins, polycarbonates, polyvinyl alcohol, cellulose, polyvinylidene chloride, polyvinyl chloride, polyethylene, and ethylene vinyl acetate copolymers.
Among these, a resin containing polyamide is preferably used from the viewpoint of releasability from the toner.

  The surface layer is formed as a composition by mixing the polymer material with the conductive agent used in the conductive elastic layer and various fine particles. As the fine particles, metal oxides such as silicon oxide, aluminum oxide, and barium titanate and composite metal oxides, polymer fine powders such as polytetrafluoroethylene and polyvinylidene fluoride are used alone or in combination. It is not limited to these.

Further, the film thickness of the surface layer is preferably 20 μm or less, and more preferably 5 μm or less. Furthermore, in addition to the conductive elastic layer and the surface layer, for example, a resistance adjusting layer can be provided between these layers.
The method for forming the surface layer is not particularly limited, but it is preferably formed by coating the surface of the conductive elastic layer with a solution containing the resin, a conductive agent and the like. As a coating method, a normal coating method such as a spray method, a dipping method, or a spin coating method can be used.

The hardness of the charging roller produced as described above is preferably 70 ° or less in terms of Asker C hardness. When the Asker C hardness is higher than 70 °, not only the uniformity of the nip with the photoconductor is impaired and image quality defects are generated, but the photoconductor surface may be gradually worn by long-term use, for example.
The Asker C hardness was measured under the condition of a load of 1000 g with a pusher of an Asker C-type hardness meter (manufactured by Kobunshi Keiki Co., Ltd.) in contact with the surface of the charging roller.

The resistance value of the charging roller is preferably in the range of 2 × 10 ^{4 to} 5 × 10 ¹⁰ Ω. If the resistance value is less than 2 × 10 ⁴ Ω, excessive current may flow on the surface of the photoreceptor, and pinhole leakage may easily occur on the surface of the photoreceptor. On the other hand, if the resistance value is greater than 5 × 10 ¹⁰ Ω, it is difficult to charge the photoconductor with a low voltage, and image quality defects occur due to insufficient charging potential.

  The resistance value is set by placing a charging roller on a metal plate, applying a load of 500 g to both ends of the roller, and using a high resistance measuring instrument (R8340A digital high resistance / microammeter: manufactured by Advantest). After applying a voltage of 100 V between the metal core and the metal plate for 10 seconds, the obtained current value was measured to obtain the roller resistance value.

The slip and toner adhesion that may occur in the cleanerless type image forming apparatus using the charging roller described above will be further described.
FIG. 6 is a conceptual diagram illustrating a state in which toner is discharged from the brush roller. As shown in FIG. 6A, a charging roller 36 is disposed downstream of the brush roller 34 in the photosensitive member rotation direction. For this reason, the charging roller 36 that is originally rotated by the rotation of the photosensitive member 13 by the retraction toner T3 (which may include the transfer residual toner T2) discharged from the brush roller 34 to the photosensitive member 13 is the photosensitive member. Accordingly, the photosensitive member 13 may be slipped (illustrated by a dotted line in the figure).

In the present invention, the ten-point average roughness Rz and the micro hardness K on the surface of the charging roller 36 can be set to predetermined values to prevent this slip.
Specifically, by setting the surface roughness Rz (μm) of the charging roller 36 to 0.14 μm ≦ Rz ≦ 1.4 μm and the microhardness K to 0 ° <K ≦ 60 °, the retraction toner T3 and the like can be transferred to the photoconductor. 13 can be suppressed even if it is interposed between the charging roller 36 and the charging roller 36.

  The ten-point average roughness Rz of the roller surface is preferably 0.3 μm ≦ Rz ≦ 0.9 μm. If Rz is less than 0.14 μm, slippage with the photoreceptor tends to occur. On the other hand, if Rz exceeds 1.4 μm, the photosensitive member is easily affected by the toner interposed between the charging roller and the toner, which will be described later.

  Rz is measured using a surface roughness meter surfcom 1400A (manufactured by Tokyo Seimitsu Co., Ltd.) according to JIS B 0601-1994, with a measuring length of 5.0 mm, a cutoff value of 0.8 mm, and a measuring speed of 0.30 mm / It measured on the conditions of sec.

  The micro hardness K of the charging roller is preferably 40 ° ≦ K ≦ 50 °. When the micro hardness exceeds 60 °, not only slipping is likely to occur, but also toner sticking described later is likely to occur.

The “micro hardness” in the present invention refers to a sample (roller) cut out to prepare a sample, and the hardness in the thickness direction of the sample is measured by a micro rubber hardness meter (MD-manufactured by Kobunshi Keiki Co., Ltd.). The value measured using 1).
To describe a specific measurement method, the micro hardness is in principle according to the type A durometer described in JIS K6253, and the push needle is pressed against the surface of the sample by the force of a spring to give deformation. It can be measured based on the push-in depth of the push needle in a state where the resistance of the sample and the force of the spring are balanced.

  More specifically, the diameter of the push needle is 0.16 mm, and when not measured, that is, when the displacement of the push needle is 0 mm, the protruding amount from the pressure surface is 0.5 mm, and the push needle is 22 mN by a spring. Pressed with force. The micro hardness at this time is 0 °. When the pushing depth of the push needle is 0 mm (displacement 0.5 mm), the push needle is pushed with a force of 330 mN by the spring. At this time, the micro hardness is set to 100 °, and this interval is graduated at equal intervals to obtain a micro hardness measurement scale. The pressing surface has an outer diameter of 4 mm, and a hole having a diameter of 1.5 mm through which the push needle is passed.

With the measuring machine configured as described above, a push needle was pressed against the sample, and the value in the balanced state was read as micro hardness.
The relationship between the micro hardness Hm (°) and the needle tip load F (mN) is expressed by the following equation (1).
F = 22 + 3.1Hm Formula (1)

  Further, as shown in FIG. 6, when the amount of the retraction toner T3 interposed in the contact portion (charging region) between the charging roller 36 and the photosensitive member 13 increases, toner adhesion occurs on the surface of the photosensitive member 13. . Here, the toner fixing means that the toner adhering to the surface of the photoconductor after the transfer is crushed on the surface of the photoconductor during the press contact with the charging roller 36 or the driven rotation with the charging roller 36, or more than the glass transition temperature of the toner. Or the like, it is in the form of a lump or a film and is in close contact with the surface of the photoreceptor.

Therefore, in order to avoid the occurrence of toner sticking, it is desirable to reduce the pressure contact force (nip pressure) of the charging roller 36 to the photosensitive member as much as possible.
In the present invention, with respect to the charging roller having the surface property and the hardness, the nip pressure P is set to 6.3 N / m ≦ P ≦ 16.7 N / m (17 gf / cm), so that the occurrence of toner fixation and the photosensitivity can be achieved. It has been found that both slipping against the body can be avoided. Hereinafter, how the nip pressure is set will be described.

  As shown in the cross-sectional view of FIG. 7, the charging roller used in the experiment has a urethane foam layer (thickness: 2.5 mm) on a metal shaft, and an epichlorohydrin rubber (ECO) tube layer (thickness: 0) on the metal shaft. 0.5 mm), and a surface layer (coating layer, thickness: 3 μm) in which tin oxide is dispersed in nylon resin (polyamide) is further laminated thereon. The metal shaft was 8 mm in diameter and the roller diameter was 14 mm.

The charging roller surface had a 10-point average roughness Rz of 0.14 μm and a micro hardness K of 60 °. The Asker C hardness of the roller was 40 ° and the roller resistance was 10 ⁷ Ω.

The experimental method is described below.
The experiment was performed by forcibly supplying toner from a developing unit to a photoconductor provided with a charging roller as a model, and examining the toner fixing state on the surface of the charging roller. The charging roller and the photosensitive member are positioned at three locations on the vertical line passing through the photosensitive member center, on the vertical line passing through the photosensitive member center, and on the straight line that forms an angle of 90 degrees with the vertical line passing through the photosensitive member center. The spring load F at both ends of the charging roller was changed. Toner fixation is performed by rotating for 20 hours at a peripheral speed of 100 mm / sec in a state where only fog toner is supplied by bias development (the photosensitive substrate is grounded and +150 V bias is applied to the developing roller of the developing device). Using the charging roller, an image was evaluated with an actual machine, and the presence or absence of toner adhesion was confirmed.

  As the toner, a polymerized toner having a shape factor SF1 of 120 having a volume average particle size of 20 nm and silica and titania as external additives and a volume average particle size of 6 μm was used (the shape factor will be described later). .

The degree of toner fixation was evaluated according to the following criteria.
Grade 1: Adherence cannot be visually recognized on the photoreceptor, and there is no defect in the image.
Grade 2: Adherence is slightly observed on the photoreceptor, but there is no defect in the image.
Grade 3: Sticking is seen on the photoreceptor, and there is a defect on a 45 ° screen with a 30% halftone image.
Grade 4: Fixation is seen on the photoreceptor, and a defect occurs in the halftone image.
Grade 5: Adherence is seen on the photoreceptor, and a defect occurs in the solid image.

  FIG. 8 shows the relationship between the nip load (nip pressure) and the toner sticking occurrence level. As shown in FIG. 8, toner fixation occurs with a weak spring load in the order of the charging roller downward, 90 degrees, and upward. This is because the weight w of the charging roller is not taken into consideration, and when w is converted into a substantial nip load in consideration of the w, the nip load at which toner fixation occurs at any position as shown in FIG. It becomes equivalent.

  Note that the actual nip load per unit length is (2 × F + w) / L when the roller position is up and L is 90 degrees, where L is the length in the axial direction where the charging roller contacts the photoconductor. Is converted as (2 × F) / L, and (2 × F−w) / L in the lower case. Here, L is 31 cm.

  From the results of FIG. 9, it can be seen that image quality deterioration due to toner fixation can be prevented if the substantial nip load is 17 gf / cm (16.7 N / m) or less regardless of the position of the charging roller. However, when the nip load was made smaller than 6.5 gf / cm (6.3 N / m), the charging roller slipped.

  The nip pressure (nip load) P is preferably 9.8 N / m ≦ P ≦ 15 N / m, and more preferably 9.8 N / m ≦ P ≦ 13 N / m. If the nip pressure P is less than 6.3 N / m, toner sticking does not occur but the slip occurs. If P exceeds 16.7 N / m, toner sticking cannot be avoided.

  The nip pressure P can be easily adjusted to the above range by adjusting the type and the type of a pressing member such as a spring fixed to both ends of the roller to press the charging roller 36 against the photosensitive member 13 as described above. it can.

Next, the toner used in the present invention will be described.
Examples of the method for producing the toner used in the present invention include a kneading and pulverizing method, a suspension polymerization method, an emulsion polymerization method, a dry granulation method in liquid, and the like. In order to obtain the toner, a polymerized toner such as a suspension polymerization method or an emulsion polymerization method is preferred, and a toner production method by emulsion polymerization is most desirable.

  A method for producing a toner using an emulsion polymerization method is described in JP-A-6-250439. In this method, a resin fine particle dispersion is prepared by emulsion polymerization using a surfactant. On the other hand, a colorant dispersion in which a colorant is dispersed is prepared. A surfactant having the opposite electrical polarity to the agent is added to agglomerate the fine resin particles and colorant until the desired particle size is reached (aggregation step), and then the aggregated particles are stabilized at the desired particle size. Then, the aggregated particles are fused at a temperature equal to or higher than the glass transition point (Tg) of the resin fine particles (fusion process) to produce a toner. The nonionic surfactant is added to ensure dispersion stability of the fine particles when preparing emulsion polymerization or a colorant dispersion.

  Further, between the agglomeration step and the fusion step, a step of forming adhering particles by adding a fine particle dispersion in which fine particles are dispersed to the agglomerated particle dispersion and adhering the fine particles to the agglomerated particles (adhesion) Step) may be provided. In this adhesion step, the fine particle dispersion is added to and mixed with the aggregated particle dispersion prepared in the aggregation step, and the fine particles are adhered to the aggregated particles to form adhered particles. Since it corresponds to newly added particles as seen from the aggregated particles, they may be added fine particles.

  As the additional fine particles, in addition to resin fine particles, release agent fine particles, colorant fine particles and the like may be used singly or in combination. The method of additionally mixing the fine particle dispersion is not particularly limited, and may be performed gradually, for example, or may be performed stepwise by dividing into a plurality of times. In this way, by adding and mixing fine particles (additional fine particles), the generation of fine particles can be suppressed, and the particle size distribution of the resulting toner particles can be sharpened, contributing to higher image quality. It becomes.

  In addition, by providing an adhesion step, a pseudo shell structure can be formed, and the toner surface exposure of internal additives such as colorants and release agents can be reduced, resulting in improved chargeability and life. In addition, it is possible to maintain the particle size distribution during fusion in the fusion process, to suppress fluctuations, and to add a stabilizer such as a surfactant or base or acid to enhance stability during fusion. This is advantageous in that it can be eliminated or the amount of addition can be minimized, and costs can be reduced and quality can be improved. Therefore, when using a release agent, it is preferable to add additional fine particles mainly composed of resin fine particles. Furthermore, if this method is used, the toner shape can be easily controlled by adjusting the temperature, the number of stirring, the pH and the like in the fusing step.

The toner used in the present invention preferably has a volume average particle diameter D _50v in the range of ₂ to 8 μm, more preferably in the range of 2.0 to 5.0 μm, and further in the range of 2.5 to 3.5 μm. preferable. When the volume average particle diameter of the toner exceeds 8 μm, the ratio of coarse particles increases, and the reproducibility and gradation of fine lines and fine dots of an image obtained through the fixing process are deteriorated. On the other hand, when the volume average particle size of the toner is less than 2 μm, the powder fluidity, developability, or transferability of the toner deteriorates, and the cleaning property of the toner remaining on the surface of the latent image carrier decreases. Various problems occur in other processes due to the deterioration of body characteristics.

The volume particle size distribution index GSDv of the toner in the present invention is preferably 1.3 or less, and more preferably 1.25 or less. The number particle size distribution index GSDp is preferably 1.4 or less, and more preferably 1.3 or less.
If GSDv is greater than 1.3, the amount of coarse powder in the toner increases and image scattering may occur. When GSDp is larger than 1.4, the amount of fine powder in the toner increases, and toner contamination in the machine due to toner scattering may increase.

The volume average particle diameter, GSDv, and GSDp are determined as follows. First, for example, based on the particle size distribution measured by a measuring instrument such as Coulter Counter TAII (manufactured by Nikka Machine Co., Ltd.), the volume and number are each subtracted from the small particle size side, and the accumulation is 16%. particle size volume D _16v made, the number D _16p, 50% accumulation become volume particle diameter D50v (this is the volume average particle diameter), the number D _50p, 84% accumulation becomes volume particle diameter D _84v, number D _84p is defined.
The volume particle size distribution index GSDv is calculated as (D _84v / D _16v ) ^1/2 , and the number average particle size distribution index GSDp is calculated as (D _84p / D _16p ) ^1/2 .

Furthermore, the toner shape factor SF1 in the present invention is preferably in the range of 100 to 140. If the shape factor is smaller than 100, the shape is very close to a sphere, and thus it has fluidity like water, and the transportability may deteriorate. When the shape factor is larger than 140, the fluidity of the toner is lowered, and a strong stress is partially applied, or it is necessary to increase the conveyance force and the stirring force, thereby promoting the deterioration of the developer.
The SF1 is more preferably in the range of 105 to 130.

Here, the shape factor SF1 is obtained by the following equation (2).
SF1 = (ML ² / A) × (π / 4) × 100 (2)
In the above formula (2), ML represents the absolute maximum length of the toner particles, and A represents the projected area of the toner particles.

  The SF1 is quantified mainly by analyzing a microscope image or a scanning electron microscope (SEM) image using an image analyzer, and can be calculated as follows, for example. That is, an optical microscope image of the toner scattered on the surface of the slide glass is taken into a Luzex image analyzer through a video camera, the maximum length and the projected area of 100 or more toner particles are obtained, calculated by the above formula (1), and the average Obtained by determining the value.

  As described above, the nip pressure P between the charging roller and the photosensitive member for a charging roller having a ten-point average roughness Rz of the roller surface of 0.14 μm ≦ Rz ≦ 1.4 μm and a micro hardness K of 0 ° <K ≦ 60 °. Is set to 6.3 N / m ≦ P ≦ 16.7 N / m, so that the charging roller and the photosensitive roller are also exposed in the cleaningless system in which the toner is discharged from the brush roller 34 to the photosensitive member 13 as shown in FIG. Slip with the body does not occur, and toner sticking to the surface of the photoreceptor can be avoided. As a result, it is possible to prevent the occurrence of charging defects and image quality defects (white spots in images, uneven density, etc.) due to slip and toner fixation.

  Although the present invention has been described by the embodiment that prevents the charging roller 36 from slipping or toner sticking due to the toner discharged from the brush roller 34, the present invention is not limited to this, and the toner remains on the photosensitive member 13. The present invention can also be applied to toner that passes through the nip portion between the charging roller 36 and the photosensitive member 13 when the collected toner is collected in the developing unit 12.

  Further, the present invention has been described by taking as an example a color laser printer that superimposes toner images of a plurality of colors on an intermediate transfer belt. However, the present invention is not limited to this, and a color or monochrome printer that directly transfers a toner image from a photoreceptor to a sheet. The present invention can also be applied to.

<Test example>
In order to confirm the operation of the above embodiment, the following comparative test was performed.
(Evaluation equipment)
As an image forming apparatus, a cleaning device for DCC400 manufactured by Fuji Xerox Co., Ltd. was used. A conductive brush roller having a diameter of 17 mm (2-denier nylon brush fibers implanted at a density of 120,000 fibers / inch, the amount of biting into the photoreceptor: 1 .6 mm, surface speed: 150 mm / sec), modified as shown in FIG. 3, and adjusted by a fixed spring load so that the nip pressure of the charging roller to the photosensitive member is 12.6 N / m. It was.

  As the charging roller, in the charging roller configured as described above, the thickness of the polyamide layer of the surface layer is changed to 1 to 10 μm, and the ten-point average roughness Rz (μm) of the charging roller surface is 0.13, 0. .14, 0.30, 0.60, 0.90, 1.40, 1.50, and micro hardness K (°) changed to 40, 50, 60, 70 were prepared.

The evaluation conditions were as follows.
(Developer)
As the toner, emulsion polymerization aggregation using resin fine particles made of styrene / n-butyl acrylate / β-carboethyl acrylate copolymer, colorant particles containing magenta pigment, and release agent fine particles containing polyethylene wax. A magenta toner (volume average particle diameter: 6 μm, shape factor SF1: 120) prepared by the above method, and a silica-treated product and a polymethyl methacrylate having carbon black dispersed as a conductive agent on the surface of ferrite particles. A two-component developer obtained by mixing a polymer-coated carrier having a volume average particle size of 45 μm with a toner concentration (TC) of 8% by weight was used.

(Printing conditions)
As an apparatus, the voltage applied to the charging roller was 1.6 kV (Peak to Peak) as an AC voltage, and the frequency was 2 kHz. The test environment was a high-temperature and high-humidity environment (28 ° C., 85% RH) in which toner sticking easily occurs.

  Under the above-mentioned conditions, 5000 images were continuously formed for a 4% halftone image, and thereafter, the appearance of the charging roller and the photoreceptor was observed, and the evaluation of slip and toner fixing was performed. In the continuous image output, the cleaning mode is set for every 100 sheets, and the toner is discharged from the brush roller onto the photosensitive member.

(Evaluation methods)
-Slip-
Marking was performed on the charging roller after the continuous image was output, and a defective charging was intentionally generated in the marking portion, and a defective image in which white spots occurred at regular intervals was printed as an evaluation print. At the time of printing, a reverse bias voltage was applied to the brush roller to release the toner from the brush roller to the photoreceptor. Then, the pitch of white spots formed on the defective image is measured, and the presence or absence of slip is confirmed by comparing the pitch and the circumferential length of the charging roller. When no slip occurs, ○, when slip occurs Is x.

-Toner fixing-
The evaluation criteria for toner adhesion were Grade 1 to Grade 5, with Grades 1 and 2 being ◯, Grade 3 being Δ, and Grades 4 and 5 being ×.
The above evaluation was performed on the various charging rollers. The results are shown in Table 1.

  As shown in Table 1, when the nip pressure is 12.6 N / m, the charging roller having the surface roughness and the micro hardness specified in the present invention does not cause any problems with slip and toner fixation. However, when the surface roughness was 0.13 μm, slip occurred even at the same nip pressure, and when the micro hardness was 70 °, toner fixation occurred.

  On the other hand, for comparison, in the image evaluation apparatus, a similar experiment was performed with the nip pressure between the charging roller and the photoconductor set to 17.5 N / m. However, toner fixation occurred in all the charging rollers. In addition, when the nip pressure was 5.0 N / m, it was not possible to avoid slipping with the photoreceptor even if any of the above charging rollers was used.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus of the present invention. FIG. 2 is a cross-sectional view illustrating a schematic configuration of a printing unit of the image forming apparatus of the present invention. FIG. 3 is an enlarged schematic diagram illustrating an image forming portion of a print unit. (A) and (B) are schematic views showing a process in which toner is transferred and collected in the image forming apparatus. (A) is a schematic diagram for explaining a method for collecting transfer residual toner at the time of printing by the image forming apparatus, and (B) is a schematic diagram for explaining a method for collecting retraction toner at the time of cleaning mode or the like. (A) and (B) are schematic views showing a state in which toner is discharged from the brush roller to the photosensitive member. It is sectional drawing which shows the structural example of the charging roller in this invention. It is a figure which shows the relationship between a nip load (nip pressure) and a toner adhesion generation | occurrence | production level. It is a figure which shows the relationship between a substantial nip load and a toner adhesion generation | occurrence | production level.

Explanation of symbols

10 Color laser printer (image forming device)
13 Photoconductor (image carrier)
14 Intermediate transfer belt (transfer object)
34 Brush roller (holding means)
36 Charging roller 36B Rubber layer (base material)
36C Surface layer (resin layer)
38 Developing roller (developing means)
40 LED array head (exposure means)

Claims (4)

At least an image carrier, a charging roller that is driven to rotate in contact with the image carrier and charges the image carrier, and an exposure unit that exposes the charged image carrier to form an electrostatic latent image; An image forming apparatus comprising: a developing unit that develops the electrostatic latent image with toner to form a toner image; and a transfer unit that transfers the toner image to a transfer target.
A resin layer is provided as a surface layer of the charging roller, the charging roller surface has a ten-point average roughness Rz of 0.14 μm ≦ Rz ≦ 1.4 μm, a micro hardness K of 0 ° <K ≦ 60 °, and the image An image forming apparatus, wherein a nip pressure P of the charging roller with respect to the carrier is 6.3 N / m ≦ P ≦ 16.7 N / m.   Further, the toner is disposed between the transfer position and the contact position of the charging roller in the moving direction of the image carrier, and collects part or all of the toner adhering to the surface of the image carrier after the transfer. The image forming apparatus according to claim 1, further comprising a holding unit that holds the toner and releases the toner to the image carrier during non-image formation.   The image forming apparatus according to claim 1, wherein the resin layer includes polyamide.   The image forming apparatus according to claim 1, wherein the toner is a polymerized toner having a shape factor SF1 in the range of 100 to 140 and a volume average particle diameter in the range of 2 to 8 μm.

Images