JP2009288539A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which can perform high quality image formation by preventing a decrease in density followability in low temperature and low humidity environment and fog due to a low speed in high temperature and high humidity environment. <P>SOLUTION: The image forming apparatus includes: a photosensitive drum 1; a developing device 7 having a developing roller 3, a developing blade 4, and a toner supply roller 5; a development bias power source 12; and a blade bias power source 14. In the image forming apparatus, the photosensitive drum 1 has a plurality of rotating speeds. Toner T whose volume average particle diameter R<SB>T</SB>(μm) is 4.0 μm≤R<SB>T</SB>≤8.2 μm is used. Voltages with a polarity same as that of the toner are applied to the developing roller 3 and the developing blade 4. The voltage applied to the developing blade 4 is greater in absolute value than the voltage applied to the developing roller 3. The arithmetic average roughness R<SB>D</SB>(μm) of the surface of the developing roller 3 is 0.5 or less times that of the volume average particle diameter R<SB>T</SB>(μm) of the toner. The width L of the contact between the developing blade 4 and the developing roller 3 is 0.3 mm≤L≤1.4 mm. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet material.

  Conventionally, as an image forming apparatus that forms an image on a sheet material by an electrophotographic method, an image forming apparatus including a developing device 102 as shown in FIG. 8 is known.

  The conventional image forming apparatus shown in FIG. 8 has a charging process in which the surface of the photosensitive drum 100 charged to a predetermined bias by the charging roller 101 is exposed by a laser beam emitted from a scanning optical system (not shown). It has an exposure process. Then, the electrostatic latent image formed on the surface of the photosensitive drum 100 by the exposure process is developed as a toner image by the developing device 102 to obtain a desired image.

  Further, the developing device 102 includes a developing roller 103 as a developer carrying member, a supply roller 105 that supplies non-magnetic one-component toner (negative polarity) to the developing roller 103, and an agitation that conveys toner in the vicinity of the supply roller 105. And a member 106. The developing roller 103 is connected to a developing bias power source 107, and a bias having a predetermined polarity is applied thereto.

  Further, the developing device 102 is provided with a thin metal plate developing blade 104 that regulates the toner amount (developer amount) on the surface of the developing roller 103. The developing blade 104 is a blade bias power source 108 (see Patent Document 1). It is connected to the. As a result, the developing blade 104 slidably rubs with the toner on the developing roller 103 using spring elasticity, so that the toner can be charged to a predetermined polarity while regulating the toner amount.

  According to the developing device 102 having such a configuration, the toner is stirred by the stirring member 106 in the developing container, the toner is supplied from the supply roller 105 to the developing roller 103, and the toner is electrostatically supplied from the developing roller 103 to the photosensitive drum 100. I can do it.

  The toner image developed on the surface of the photosensitive drum 100 is transferred to the sheet material P at the nip portion between the photosensitive drum 100 and the transfer roller 111. Note that a transfer bias is applied to the transfer roller 111 from a power source (not shown), whereby a toner image can be electrostatically transferred from the photosensitive drum 100 onto the sheet material P. Further, the toner remaining on the surface of the photosensitive drum 100 without being transferred is peeled off by the cleaning member 109.

The sheet material P to which the toner image has been transferred is sent to a fixing device 110 provided on the downstream side in the transport direction, and the toner image on the sheet material P is heated and fixed to the sheet material P in the fixing device 110. Then, the sheet material P on which the toner image is heat-fixed is discharged from the image forming apparatus main body by a discharge unit (not shown).
JP 05-011599 A JP 2005-215057 A

  In recent years, for the purpose of improving work efficiency, image forming apparatuses have been required to increase printing speed. However, when the printing speed is increased, the conventional image forming apparatus has the following problems.

[Concentration following in low temperature and low humidity environment]
In low-temperature and low-humidity environments (temperature 15 ° C / humidity 10%) in which the toner fluidity decreases due to electrostatic aggregation or the like, the density difference between the leading edge and trailing edge of the sheet material as the transfer material increases as the printing speed increases. Become.

  Specifically, when the printing speed is increased in a low temperature / low humidity environment, a phenomenon that the density at the leading edge of the paper increases and the density at the trailing edge of the paper decreases conversely is noticeable. That is, when the printing speed is increased, it becomes difficult to follow the density of the image along the direction in which the sheet material is conveyed (density followability is lowered), and the image quality is lowered.

[Cover at low speed in high temperature and high humidity environment]
Even when printing speed is required to be increased, if thick paper (for example, paper with a basis weight of 105 g / m ² or more) is used, printing can be performed in order to ensure fixability with limited usable power. It is necessary to fix the speed at a low speed.

  In other words, when heat-fixing a toner image on cardboard, if the sheet material is conveyed to the fixing device at a high speed, the heat applied in the fixing device is absorbed by the cardboard, and the unfixed toner correspondingly. A situation occurs where the image cannot be heated sufficiently. Therefore, when using thick paper, a method is employed in which the unfixed toner is sufficiently heated by reducing the printing speed.

In particular, when a color image or the like is used, the amount of unfixed toner placed on the sheet material increases, so that the printing speed (hereinafter referred to as normal paper speed) of plain paper (for example, 72 g / m ² sheet material) or the like is increased. In comparison, the speed is often reduced to 20 to 50% (hereinafter referred to as cardboard speed).

  However, the conventional image forming apparatus has a problem that “fogging at low speed” occurs when the printing speed is reduced. This “fogging at low speed” is a phenomenon in which toner adheres to the white portion of the sheet material, but the occurrence of fogging is small at normal paper speed, but the amount of fogging is increased at low speed for thick paper. A phenomenon.

The occurrence of “fogging at low speed” has been found to be prominent in high temperature and high humidity environments (temperature 30 ° C./humidity 80%). Become.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to prevent a decrease in density followability in a low temperature / low humidity environment and to prevent fogging at a low speed in a high temperature / high humidity environment. An object of the present invention is to provide an image forming apparatus capable of forming an image.

In order to achieve the above object, the present invention provides:
A rotatable image carrier on which an electrostatic latent image is formed;
A developer carrying member configured to be rotatable in contact with the image carrier, a developer carrying member that carries the developer, a developer supply member that supplies the developer to the developer carrier, and a surface of the developer carrier. Developing means having a developer regulating member for regulating the amount of developer carried on the surface;
Voltage application means for applying a voltage to each of the developer carrier and the developer regulating member;
In an image forming apparatus comprising:
Control means for controlling the rotational speed so that the image carrier has a plurality of rotational speeds;
As the developer, a developer having a volume average particle size R _T (μm) of 4.0 μm ≦ R _T ≦ 8.2 μm is used.
A voltage having the same polarity as the charging polarity of the developer is applied to the developer carrier and the developer regulating member, and the absolute value of the applied voltage value is applied to the developer carrier. The voltage applied to the developer regulating member is larger than the voltage,
A semiconductive resin or a semiconductive rubber is used in at least a portion of the developer regulating member that contacts the surface of the developer carrier.
The arithmetic average roughness R _D (μm) of the surface of the developer carrying member is 0.5 times or less with respect to the volume average particle diameter R _T (μm) of the developer,
The abutting width where the developer carrying member and the developer regulating member abut via the developer, and the abutting width L (mm) in the rotation direction of the developer carrying member is 0.3 mm ≦ L It is characterized by being ≦ 1.4 mm.

  According to the present invention, it is possible to provide an image forming apparatus capable of performing high-quality image formation by preventing a decrease in density followability in a low-temperature / low-humidity environment and low-speed fogging in a high-temperature / high-humidity environment. It becomes possible.

  The best mode for carrying out the present invention will be exemplarily described in detail below based on the embodiments 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. Absent.

[Embodiment]
An image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS.

(Overall configuration of image forming apparatus)
First, the overall configuration of the image forming apparatus according to the present embodiment will be described. FIG. 2 shows a schematic configuration of the image forming apparatus according to the present embodiment. Here, a case where a full color laser printer employing an electrophotographic method is used as the image forming apparatus will be described. The service life of the image forming apparatus 8 is a service life capable of printing about 2000 sheets when printing is performed at a print rate of 5% using A4 paper.

  In the image forming apparatus 8, a charging unit, a developing unit, a cleaning unit, and an image carrier are integrated, and a process cartridge 9 that is detachable from the apparatus main body is connected to yellow (Y), magenta (M), cyan ( C) and four for each color of black (K). As the photosensitive drum 1 used as the image carrier in the present embodiment, an organic photosensitive drum in which an outer peripheral surface of an aluminum cylinder is coated with a functional undercoat layer, a carrier generation layer, and a carrier transfer layer in this order is used. It has been. The photosensitive drum 1 is configured to be rotatable. The members provided for each toner color will be described by adding the corresponding toner color initials (Y, M, C, K) to numerals.

  In the vicinity of the process cartridges 9Y, 9M, 9C, and 9K, scanner units 10Y, 10M, 10C, and 10K that emit laser beams to the photosensitive drums 1Y, 1M, 1C, and 1K are provided. Further, charging rollers 2Y, 2M, 2C, and 2K are provided so as to be in contact with the photosensitive drums 1Y, 1M, 1C, and 1K, and the charging rollers 2Y, 2M, 2C, and 2K are connected to a bias applying unit (not shown). .

The charging rollers 2 </ b> Y, 2 </ b> M, 2 </ b> C, and 2 </ b> K are driven to rotate by bringing a roller portion of conductive rubber into pressure contact with the photosensitive drum 1. In addition, a DC voltage of −1100 V is applied to the cores of the charging rollers 2Y, 2M, 2C, and 2K, thereby reducing the surface potential of the photosensitive drum 1 to about −550.
It is possible to obtain a uniform dark portion potential (Vd) of v.

  When performing the image forming process, the surfaces of the photosensitive drums 1Y, 1M, 1C, and 1K are uniformly charged by the charging rollers 2Y, 2M, 2C, and 2K, and based on the image data from the scanner units 10Y, 10M, 10C, and 10K. The laser beam is emitted and the photosensitive drum 1 is exposed.

  The surface potential of the exposed portions of the photosensitive drums 1Y, 1M, 1C, and 1K is lowered by the carrier generated from the carrier generation layer formed on the photosensitive drums 1Y, 1M, 1C, and 1K. As a result, the potential of the exposed part (bright part potential) is V1 = −100v, and the potential of the unexposed part (dark part potential) is Vd = −550v, which causes the surface of the photosensitive drums 1Y, 1M, 1C, and 1K. The electrostatic latent image based on the image data is formed.

  The electrostatic latent images formed on the respective photosensitive drums 1 are developed as toner images by developing means included in the process cartridges 9Y, 9M, 9C, and 9K. The configuration of the process cartridges 9Y, 9M, 9C, 9K will be described in detail later.

  For the photosensitive drums 1Y, 1M, 1C, and 1K, transfer rollers 22Y, 22M, 22C, and 22K are provided so as to face the respective photosensitive drums 1, and both contact to form a primary transfer nip portion. Is done. An endless intermediate transfer belt 20 is sandwiched between four primary transfer nip portions formed for each of the process cartridges 9Y, 9M, 9C, and 9K, and the photosensitive drums 1Y, 1M, 1C, and 1K are transferred to the intermediate transfer belt 20. The toner images are sequentially superimposed and transferred (primary transfer).

  Note that a transfer bias power source (not shown) is connected to the primary transfer rollers 22Y, 22M, 22C, and 22K, and a DC voltage is applied thereto. As a result, an electric field is generated between each of the primary transfer rollers 22Y, 22M, 22C, and 22K and the photosensitive drums 1Y, 1M, 1C, and 1K, and the electrostatic force generated by the electric field causes the photosensitive drum 1 to transfer to the intermediate transfer belt 20. The toner image can be primarily transferred.

  The toner image transferred onto the intermediate transfer belt 20 is conveyed to the secondary transfer nip portion formed by the secondary transfer roller 23 and the secondary transfer counter roller 29 along with the rotational movement of the intermediate transfer belt 20, where the sheet material is transferred. A toner image is transferred onto P (secondary transfer). The toner remaining on the intermediate transfer belt 20 without being transferred is collected by the intermediate transfer belt cleaner 21.

  Note that a plurality of sheet materials P are stacked in a cassette 24 provided below the image forming apparatus 8, and are fed one by one from the feeding roller 25 at the start of the image forming process, and the secondary timing is measured. It is conveyed to the transfer nip part.

  The sheet material P to which the toner image has been transferred is heated and fixed in a fixing unit 26 provided downstream in the conveyance path, further conveyed downstream, and discharged from the discharge unit 27 to the outside of the image forming apparatus 8.

(Process cartridge configuration)
The configuration of the process cartridges 9Y, 9M, 9C, and 9K will be described. Since the four process cartridges 9Y, 9M, 9C, and 9K in the present embodiment all have the same configuration, the explanation of the configuration of one process cartridge 9 is used here to describe the other process cartridges. Description is omitted.

FIG. 3 shows a schematic configuration of the process cartridge 9 according to the present embodiment. The process cartridge 9 includes a photosensitive drum (image carrier) 1, a charging roller (charging means) 2, a developing device (developing means) 7, and a cleaning member (cleaning means) 6 that can rotate in the x direction in the figure. It is constructed integrally. The process cartridge 9 is configured to be detachable from the image forming apparatus main body.

  The developing device 7 includes a stirring member 11, a toner supply roller (developer supply member) 5, a development roller (developer carrier) 3, and a development roller in a toner storage portion that stores the nonmagnetic one-component toner T (developer). 3 is provided with a developing blade (developer regulating member) 4 for regulating the amount of toner on the surface 3. The image forming apparatus according to the present embodiment is a one-component image forming apparatus that performs development by bringing the developing roller 3 carrying negatively charged toner into contact with the photosensitive drum 1. However, a positively charged toner may be used. In that case, a bias may be applied to each member so that the direction of the electric field generated in each process described below is reversed.

  The agitating member 11 is provided for the purpose of agitating the toner in the toner accommodating portion and spreading the toner T to the toner supply roller 5 side while maintaining fluidity. The toner supply roller 5 rotates in the z direction in the drawing while being in contact with the developing roller 3, and supplies toner to the surface of the developing roller 3. An RS bias power source 13 is connected to the toner supply roller 5.

  The developing roller 3 contacts the photosensitive drum 1 and rotates in the y direction in the figure. Further, the toner T on the surface of the developing roller 3 comes into contact with the developing blade 4 connected to the blade bias power source 14 and is rubbed, so that the surface of the developing roller 3 has a predetermined coating amount and charge amount of toner. A coat layer is formed. The photosensitive drum 1 and the developing roller 3 are rotationally driven by a motor 15, and the motor 15 further rotationally drives a pressure roller and the like (not shown) in the fixing unit 26.

  When developing the electrostatic latent image formed on the surface of the photosensitive drum 1, a DC bias = −350 V is applied to the developing roller 3 by the developing bias power source (voltage applying unit) 12, and the photosensitive drum 1 and the developing roller 3 are Using the potential difference, toner is supplied to the electrostatic latent image. As described above, this embodiment is a so-called reversal development system that supplies toner to an exposed portion.

  Further, the image forming apparatus 8 includes a control circuit (control unit) that controls the rotation drive of the motor 15 and controls the voltage values of the developing bias power source 12, the RS bias power source 13, and the blade bias power source (voltage applying unit) 14. 16 is provided.

In the present embodiment, the control circuit 16 controls the rotation of the photosensitive drum 1 so that the photosensitive drum 1 has a plurality of rotational speeds. Specifically, when image formation is performed on plain paper (for example, 72 g / m ² paper) or the like, the printing speed (hereinafter referred to as normal paper speed) is set to 200 mm / sec, and thick paper (for example, basis weight 105 g / m ² or more). In the case of using paper, etc.), it was set to 65 mm / sec. The printing speed here is almost the same as the rotation speed of the photosensitive drum 1.

  However, the rotational speed of the photosensitive drum 1 is not limited to two types. Depending on the type of sheet material used, the basis weight of the paper, the type, and the like, the rotational speed may be increased. For example, when using OHP paper (transmission film for an over head projector) or the like, the rotational speed may be controlled to be lower.

As described above, when the photosensitive drum 1 has a plurality of rotational speeds, it is possible to improve the fixability of the unfixed toner to the sheet material even in a limited usable power. That is, when an unfixed toner image placed on a cardboard or the like is fixed and the printing speed is normal, the heat applied at the time of fixing is first absorbed by the sheet material. Therefore, sufficient heat cannot be applied to the unfixed toner.

On the other hand, if the printing speed is controlled to be reduced when fixing thick paper or the like, a sufficient amount of heat can be applied to the unfixed toner, and the unfixed toner can be surely fused and fixed to the sheet material. In particular, when a color image or the like is used, the amount of toner placed on the sheet material increases, so that the printing speed (hereinafter referred to as normal paper speed) used for plain paper (for example, 72 g / m ² paper) is used. In many cases, the speed is reduced to 20% to 50% (hereinafter referred to as cardboard speed).

  Next, each member provided in the process cartridge 9 mentioned above is demonstrated in detail. Here, (development roller configuration), (development roller material), (development roller resistance measurement method), (development roller surface roughness), (development roller rubber hardness), (development roller manufacturing method) Will be described. Furthermore, (Configuration of toner supply roller), (Configuration of development blade), (Surface roughness of development blade), (Abutting width between development blade and development roller), (Measurement method of resistance of development blade), (Development roller) And the contact pressure of the photosensitive drum) and (used toner) will be described.

(Development roller configuration)
The developing roller 3 is a so-called elastic developing roller having an elastic layer on a cored bar. In the present embodiment, a first layer (base layer) made of solid rubber in which carbon is dispersed in silicone rubber is formed on a stainless steel core having a diameter of 6 mm.

  Further, as the second layer (intermediate layer), a layer in which a spherical resin of about 20 μm to 60 μm was dispersed in a urethane resin whose resistance was adjusted by a conductive agent was formed to a thickness of about 10 μm. The spherical resin dispersed in the second layer is for adjusting the surface roughness of the developing roller 3.

  Further, a third layer (surface layer) was formed on the second layer. The surface layer is made of a urethane resin whose resistance is adjusted by a conductive agent, and has a layer thickness of about 10 μm. As the resin for the surface layer, a resin capable of charging the toner to a predetermined polarity is preferably used in order to charge the toner by friction with the toner.

(Development roller material)
As materials used for the base layer and the intermediate layer of the developing roller 3, in addition to the above, butyl rubber, budadiene rubber (BR), natural rubber, acrylic rubber, EPDM (ethylene / propylene copolymer), or rubber in which these are mixed A generally used rubber can be used.

  A desired resistance value can be obtained by dispersing carbon resin particles, metal particles, an ionic conductive agent, and the like using these rubbers as a base material. Further, as the conductive agent, an ionic conductive agent such as lithium perchlorate or quaternary ammonium salt is used, and the conductivity can be adjusted by dispersing these conductive agents in a binder.

  As the resin binder for the surface layer, when a negatively chargeable toner is used, a urethane resin, a silicone resin, a polyamide resin, or the like is preferably used. If a positively chargeable toner is used, a fluorine resin or the like is preferably used. A desired resistance value can be obtained by dispersing the aforementioned carbon resin particles, metal particles, ionic conductive agent, and the like in these resins.

In the present embodiment, the developing roller 3 has a three-layer structure, but the layer structure of the developing roller 3 is not limited to this. For example, a spherical resin is used for the intermediate layer to form a desired surface roughness, but a two-layer structure may be used by utilizing the surface roughness of the base layer. Also, after polishing the surface of the base layer to form the desired surface roughness, the surface is modified by UV irradiation or the like,
It may be configured to obtain a desired surface roughness.

The resistance value of the developing roller 3 is desirably 2 × 10 ⁴ Ω to 5 × 10 ⁶ Ω. 2x1
This is because if it is 0 ⁴ Ω or less, the current flowing in the elastic layer increases, and the required current capacity increases. Further, if it is 5 × 10 ⁶ Ω or more, the current flowing during development is likely to be inhibited. In this embodiment, a resistor having a resistance value of 5 × 10 ⁵ Ω is used.

(Development roller resistance measurement method)
A method for measuring the resistance of the developing roller 3 will be described. FIG. 4 is a diagram for explaining a method of measuring the resistance of the developing roller 3 in the present embodiment.

  As shown in FIG. 4, the roller 63 to be measured has a multilayer structure composed of a conductive metal core 62 made of stainless steel or the like, an elastic layer 61 formed on the outer periphery thereof, and a roller surface 60. On the other hand, when the roller 63 has a single layer structure, it can be considered that the elastic layer 61 and the roller surface 60 are made of the same kind of material. The width of the roller 63 in the longitudinal direction is about 230 mm.

  In this measuring method, a cylindrical member 66 which is stainless steel of φ30 mm and rotates in the direction of the arrow at a speed of about 48 mm / sec is used. When measuring the resistance, the roller 63 rotates following the rotation of the cylindrical member 66.

  An end roller 69 is fitted to the end of the roller 63 to restrict the amount of penetration into the cylindrical member 66 to 50 μm (in order to make the contact area between the roller 63 and the cylindrical member 66 constant). The end roller 69 has a cylindrical shape whose outer diameter is 100 μm smaller than the outer diameter of the roller 63.

  4 indicates the load applied to both ends of the roller 63 (both ends of the conductive core metal 62). In the measurement, the roller is loaded with a load of 1 kg in weight of 500 g on each side. 63 is pressed to the cylindrical member 66 side.

In addition, a measurement circuit 68 is used for this measurement method. The measurement circuit 68 includes a power source Ein2, a resistor Ro2, and a voltmeter Eout2. In this measurement method, measurement was performed with Ein2: 300 V (DC). The resistor Ro2 may have a resistance value of 100Ω to 10MΩ. In addition, since resistance Ro2 is for measuring a weak electric current, it is good to use the resistance value of * 10 ^<-2> -* 10 ^{< -4>} of the resistance of the roller 63 which is a measuring object. That is, if the resistance value of the roller 63 is about 1 × 10 ⁶ Ω, the resistance value of the resistor Ro2 may be about 1 kΩ.

When this measuring circuit 68 is used, the resistance value Rb of the roller 63 is calculated by the following equation. In addition, Eout2 measured the value 10 seconds after applying a voltage.
(Equation 1) Rb = Ro2 × (Ein2 / Eout2-1) (Ω)

(Development roller surface roughness)
The arithmetic average roughness Ra (hereinafter referred to as _RD ) of the surface of the developing roller 3 is desirably 0.5 times or less with respect to the volume average particle diameter _{RT of} the toner to be used. When the volume average particle size _RT exceeds 0.5, the toner does not rub against the surface of the developing roller 3 or the surface of the developing blade 4, and as a result, uncharged toner increases and fogging at normal printing speed occurs. Because it will increase.

In order to further improve the image quality, it has been found that it is preferable to set _RD to 0.17 times or less of the volume average particle diameter _{RT of} the toner used. That is, when _RD is reduced (surface roughness is reduced), improvement in image quality can be achieved.

Note that when _RD is further reduced as described above, the magnitude relationship between the RS bias power supply 13 and the development bias power supply 12 is adjusted, and a bias relation in which more negative toner T is more likely to be supplied to the developing roller 3 side. It is desirable to do.

That is, as described above, if the arithmetic average roughness _RD of the surface of the developing roller 3 is 0.17 times or more and 0.5 times or less than the volume average particle diameter _{RT of the} toner, The toner T can be suitably conveyed by the surface roughness. However, if the arithmetic average roughness _RD of the surface of the developing roller 3 is 0.17 times or less with respect to the volume average particle diameter of the toner T, a sufficient amount of the toner T can be obtained using the surface roughness of the developing roller 3. Can not be expected to carry.

  For this reason, an electric field is formed between the developing roller 3 and the toner supply roller 5 so as to press the toner T against the developing roller 3, and the toner T is pressed against the developing roller 3 by the action of the electric field. Is adsorbed on the surface of the developing roller 3.

Further, when the arithmetic average roughness _RD of the surface of the developing roller 3 is 0.17 times or less than the volume average particle diameter _RT of the toner T, the toner T on the developing roller 3 is transferred to the photosensitive drum 1. There is an advantage that sometimes the image is not disturbed. That is, when the arithmetic average roughness R _D of the surface of the developing roller 3 is greater than 0.17 times the volume average particle diameter R _T of the toner T is in a developing area where the developing roller 3 photosensitive drum 1 is in contact, the photosensitive A phenomenon occurs in which the toner transferred to the drum 1 is rubbed by the convex portions on the surface of the developing roller 3. As a result, the convex portion on the surface of the developing roller 3 moved the toner on the surface of the photosensitive drum 1, or the toner was peeled off again to the developing roller 3 side by the convex portion.

However, when the arithmetic average roughness _RD of the surface of the developing roller 3 is 0.17 times or less than the volume average particle diameter _{RT of the} toner, the convex portion of the developing roller 3 is transferred to the photosensitive drum 1. It is difficult for toner to move or scrape off. As a result, the edge of the character becomes sharp and the uniformity of the solid image is improved.

In the present embodiment, since the toner T having a volume average particle size _RT of 4.0 μm or more and 8.2 μm or less is used (the details will be described later), the maximum value of the arithmetic average roughness _RD is the volume average particle size R _D It becomes 2.0 times or more and 4.1 micrometers or less which is 0.5 times or less. Further, the lower limit value of the arithmetic average roughness _RD of the developing roller 3 may be 0 (that is, a mirror surface state). Even when R _D = 0, such a developing roller 3 can be manufactured. That is, for example, when the toner T having a volume average particle size of 8.2 μm is used, the arithmetic average roughness _RD of the developing roller 3 may be set to 0 μm or more and 4.1 μm or less.

In the present embodiment, the arithmetic average roughness _RD of the surface of the developing roller 3 was measured by a surface roughness tester “SE-30H” (manufactured by Kosaka Laboratory Ltd.).

(Developer roller rubber hardness)
The rubber hardness of the developing roller 3 was measured using an Asker C rubber hardness meter (manufactured by Kobunshi Keiki Co., Ltd.). In the present embodiment, the developing roller 3 having a rubber hardness of 30 degrees to 75 degrees (Asker C) or less is preferably used.

  If the rubber hardness is 75 degrees (Asker C) or more, the toner is melted by the rubbing of the developing roller 3 and blade fusion or roller fusion occurs, which is not preferable. Further, the contact state between the developing roller 3 and the photosensitive drum 1 tends to become unstable.

When the rubber hardness is 30 degrees (Asker C) or less, it becomes difficult to use as the developing roller 3 due to permanent deformation due to compression set. More preferably, the rubber hardness is 35 degrees to 60 degrees, and by setting the hardness in this range, the toner T can be rubbed and charged without applying excessive stress to the toner T. In the present embodiment, the developing roller 3 having a rubber hardness of 45 degrees (Asker C) is used.

(Development roller manufacturing method)
A method for manufacturing the developing roller 3 in the present embodiment will be described. First, an adhesive for securing rubber and ensuring electrical conductivity is applied on the cored bar. Then, a solid rubber in which carbon resin particles and the like are dispersed is wound around the core bar and placed in a mold.

  Thereafter, the mold is vulcanized by applying heat and pressure with a press machine, and the surface is polished after vulcanization to obtain a solid elastic roller. The intermediate layer and the surface layer can be formed by a roll coater method, a spray method, a dipping method, or the like.

  The coating thickness of the outermost layer is preferably about 3 μm to 50 μm. If the thickness is 3 μm or less, there is a concern about scraping due to rubbing with the photosensitive drum 1. If the thickness is 50 μm or more, coating must be repeated many times in order to obtain a desired coating thickness. It is not.

(Configuration of toner supply roller)
The toner supply roller 5 is constituted by a foamed foam (hereinafter referred to as a foamed layer) formed on the outer periphery of a conductive metal core. The foam layer of the toner supply roller 5 has two roles of supplying the toner T to the developing roller 3 and stripping off the toner that has not contributed to the development.

  The toner on the developing roller 3 is peeled off by rubbing the edge of the foam layer of the toner supply roller 5 against the surface of the developing roller 3. When the outermost layer of the toner supply roller 5 is formed of solid rubber or single-foam sponge rubber, the amount of toner carried tends to be small, so that it is difficult to supply the toner amount necessary for development to the developing roller 3. However, when the outermost layer is formed of open-cell foam as in the present embodiment, toner can be included in the cells of the foam, so that the necessary toner can be supplied to the developing roller 3. Is possible.

  In the present embodiment, the toner supply roller 5 is an elastic sponge having an outer diameter of φ16 mm formed by forming 5.5 mm (cell diameter of 200 μm to 350 μm) of polyurethane foam having a foamed skeleton structure on a core metal having an outer diameter of φ5 mm. A roller was used. As described above, the toner supply roller 5 is made of open-cell foam, so that the toner supply roller 5 can be brought into contact with the developing roller 3 without applying excessive pressure. Therefore, it is possible to remove the residual toner without being consumed at the time of supplying and developing the toner onto the developing roller 3 with moderate unevenness on the surface.

  Note that the function of scraping off the toner T from the surface of the developing roller 3 by such a foam layer is not limited to urethane foam. In this embodiment, polyurethane foam is used. However, as a material for the foam layer, NBR rubber (NBR: nitrile rubber), silicone rubber, acrylic rubber, hydrin rubber, and ethylene propylene rubber (EPDM) may be used. . In addition, a commonly used rubber such as chloroprene rubber, styrene butadiene rubber, isoprene rubber, acrylonitrile butadiene rubber, and a composite mixture thereof may be used. Furthermore, in order to adjust the resistance of the foam layer, a known ionic conductive agent, inorganic fine particles, carbon black, or the like may be appropriately dispersed.

Further, in order to assist the toner supply to the developing roller 3, a bias that moves the toner from the toner supplying roller 5 side to the developing roller 3 side may be applied to the toner supplying roller 5. For example, by applying a bias that moves the negatively charged toner to the developing roller 3 side, the amount of toner carried on the developing roller 3 is increased upstream of the developing blade 4 in the rotation direction of the developing roller 3. Is possible. Further, by applying a bias, the toner density on the developing roller 3 can be increased, and a uniform toner density can be obtained even when the surface roughness of the developing roller 3 is low. In the present embodiment, −500 V is applied by the Rs bias power source 13.

(Development blade configuration)
The developing blade 4 in the present embodiment is provided so as to abut on the surface of the developing roller 3 from the contact portion between the toner supply roller 5 and the developing roller 3 on the downstream side in the rotation direction of the developing roller 3. With this configuration, the amount of toner supplied from the toner supply roller 5 to the developing roller 3 can be regulated, and the toner T can be charged by sliding the developing blade 4 and the toner T against each other.

  FIG. 1 shows an enlarged view of a portion where the developing blade 4 abuts against the developing roller 3. The developing blade 4 includes a thin metal plate 4a as a support member and a semiconductive rubber 4b as a contact member that actually contacts the toner. The developing blade 4 can be brought into contact with the surface of the developing roller 3 through the toner T with a predetermined pressure by using the spring elasticity of the thin metal plate 4a, and the semiconductive rubber 4b can be in contact with the surface of the developing roller 3. It contacts the upper toner and the surface of the developing roller 3.

  As the material of the metal thin plate 4a, a thin plate such as stainless steel or phosphor bronze can be used. In the present embodiment, a phosphor bronze thin plate having a thickness of 0.1 mm is used. A predetermined voltage is supplied from the blade bias power supply 14 to the support member 4a of the developing blade 4 (see FIG. 3).

  The voltage of the blade bias power supply 14 is applied to the surface of the semiconductive rubber 4b through the metal thin plate 4a of the developing blade 4. On the other hand, an electric field can be formed between the surface of the semiconductive rubber 4b where the toner T is interposed and the surface of the developing roller 3 by applying the voltage of the developing bias power source 12 to the developing roller 3.

  As described above, in the present embodiment, the semiconductive rubber 4b is used for at least the portion of the developing blade 4 that contacts the developing roller 3, that is, the contact member. Here, as the form of the abutting member, a semiconductive rubber is molded on the thin metal plate 4a, a conductive rubber is molded on the thin metal plate 4a, and the surface is coated with a semiconductive resin. A thin plate 4a directly coated with a semiconductive resin is used.

  Thus, the form of the semiconductive rubber 4b used in the present invention is not limited to one. However, in any case, when a predetermined voltage is applied to the developing blade 4, a predetermined resistance value is obtained. It is necessary to satisfy

  However, among these, it is preferable to mold semiconductive rubber on the thin metal plate 4a and further disperse conductive powder in an elastomer on the surface of the semiconductive rubber 4b. Molding conductive rubber on the metal thin plate 4a and coating the surface with a semiconductive resin has the advantage that it can be manufactured at low cost and can have sufficient elasticity and conductivity. Furthermore, the range of selection of the resin to be applied to the surface layer is expanded. Furthermore, since the elasticity does not give extra stress to the toner T, it is possible to suppress the deterioration of the toner T.

The semiconductive rubber 4b obtained by dispersing conductive powder in the elastomer described here may be any elastomer that can be used as long as it exhibits fluidity before curing, and may be appropriately selected from materials known per se. Can do. Examples thereof include urethane rubber, silicone rubber, ethylene / propylene rubber (EPM), liquid rubber such as fluorine rubber latex, polymer blend, and the like. Among these, liquid rubber is preferable, urethane rubber and silicone rubber are more preferable in terms of having appropriate polarity and appropriate compatibility with conductive powder, and two-component urethane rubber and one-component silicone rubber are preferable. Particularly preferred.

  In addition, as the conductive powder, a so-called electronic conductive system whose resistance decreases as the so-called bias to be applied is increased is used. The conductive form having the electronic conductive form has a characteristic that the resistance is changed by an increase in voltage, but is effective in the present invention because the resistance change due to environmental fluctuation (particularly, fluctuation due to humidity) is small. In the present invention, as the conductive powder, only an electronic conductive system or a mixture of an electronic conductive system and an ionic conductive system is used.

  The conductive powder can be appropriately selected from materials known per se, and examples thereof include conductive inorganic powders such as carbon black, carbon beads, carbon filler, potassium titanate, zinc oxide, and titanium oxide. It is done. In addition, conductive inorganic particles, conductive inorganic fillers, metal oxides, and the like are also suitable.

  Among these, conductive inorganic powder is preferable in terms of easy control of curing conditions, and carbon black is preferable in terms of excellent dispersibility in the elastomer before curing and good balance of density, specific gravity, and the like. preferable. Carbon black having a secondary particle size of several tens of μm to 500 μm and a DBP oil absorption of 50 to 500 g / dl exhibits appropriate compatibilization in the elastomer before curing. And it is especially preferable at the point which can achieve favorable gradient dispersion | distribution as a result of diffusing at the time of centrifugal molding. In the present invention, these conductive powders may be used alone or in combination of two or more.

  Further, in the present invention, when the metal thin plate 4a as the support member and the semiconductive rubber 4b as the contact member are separately formed and then integrated, the urethane type, the silicone type, the epoxy type or the like is known. A conductive adhesive can be used. Further, the conductive adhesive is not particularly limited as long as it has conductivity and can function as an adhesive, and examples thereof include a conductive hot melt adhesive and a conductive paint.

(Surface roughness of developing blade)
A surface of the semiconductive rubber 4b of the present embodiment, the portion in contact with the toner T and the developing roller 3 surface arithmetic average roughness Ra (hereinafter referred to as R _B), the roughness like a mirror It can be set from a state where there is no toner to a volume average particle diameter of the toner. Since an electric field that moves the negative toner T from the developing blade 4 toward the developing roller 3 is formed, the toner T can be regulated even when the surface roughness is substantially mirror-like.

More preferably, it is desirable to increase the _{R B} from the arithmetic mean roughness _{R D} of the developing roller 3 _{(R B> R} D). That is, the surface of the developing blade 4 may be rougher (uneven) than the surface of the developing roller 3.

  When the surface of the developing blade 4 is rough, the contact area between the developing blade 4 and the toner T is increased, and the toner weight per unit area on the developing roller 3 after the developing blade 4 has passed can be stabilized.

  However, if the surface of the developing blade 4 is rough, there is a concern that the toner T melts and adheres to the surface of the developing blade 4 so-called blade fusion occurs.

However, in the case of the present embodiment, an electric field is formed so that the negatively charged toner T moves from the developing blade 4 side to the developing roller 3 side, so that even if the surface of the developing blade 4 is rough. The possibility of blade fusion is low. For the surface roughness of the developing blade 4, the surface roughness tester “SE-30H” (manufactured by Kosaka Laboratory Ltd.) described above was used.

(Contact width between developing blade and developing roller)
A contact width L between the developing blade 4 and the developing roller 3 will be described with reference to FIG. In FIG. 1, L indicates the contact width between the developing blade 4 and the developing roller 3. Here, the contact width L is an area where the developing blade 4 actually presses the developing roller 3 through the toner, and the length of the developing blade 4 in the short side direction (the rotating direction of the developing roller 3) is defined as the contact width L. Say.

  In the present embodiment, it is desirable that the contact width L between the developing blade 4 and the developing roller 3 is 0.3 mm or more and 1.4 mm or less. Although details will be described later, if it is less than 0.3 mm, the toner T cannot be sufficiently regulated, and the contact state tends to become unstable due to vibration of the image forming apparatus main body.

  Further, if the contact width L between the developing blade 4 and the developing roller 3 is larger than 1.4 mm, the charge is lost between the developing blade 4 and the developing roller 3 when the image forming apparatus is used in a high temperature / high humidity environment. Since there is sufficient time to perform fogging, fogging easily occurs at low speed.

  The contact width L between the developing blade 4 and the developing roller 3 can be freely changed by adjusting the length of the developing blade 4 in the short direction. It is also possible to change the curvature of the developing roller 3. When a small-diameter developing roller is used, the contact width L is smaller than that of the large-diameter developing roller.

  Further, the contact width L is measured by once assembling the developing roller 3 in a developing device that does not contain the toner T in a state where a toner is carried on the developing roller 3 and removing the developing roller 3 again to the developing blade 4. It was determined by measuring the width of the adhered toner T.

(Development blade resistance measurement method)
A method for measuring the resistance of the developing blade 4 will be described with reference to FIG. First, a thin film conductive film or the like is applied to the surface of the developing roller 3 to ground the developing roller 3. The developing blade 4 is connected to a measuring power source 18 and an ammeter 19 that monitors a current that flows when a voltage is applied to the developing blade 4. The resistance value of the developing blade 4 can be measured by the portion of the surface of the developing blade 4 in contact with the normal toner coming into contact with the surface of the developing roller 3.

  At the time of measurement, first, the voltage of the measuring power supply 18 is changed between about 80 V to 400 V, and the resistance value of the developing blade 4 is measured from the voltage value applied to the developing blade 4 and the numerical value indicated by the ammeter 19. Is done. When the dielectric strength of the abutting member (semiconductive rubber 4b) of the developing blade 4 is low, measurement is performed simultaneously with the developing roller 3 without using a thin film conductive film, and then development is performed by subtracting the three resistance values of the developing roller 3. The resistance value of the blade may be calculated.

The resistance value of the developing blade 4 in the present invention is set as follows under a low temperature / low humidity environment (temperature 15 ° C./humidity 10%) to a high temperature / high humidity environment (temperature 30 ° C./humidity 80%). Good. That is, in the region where the potential difference between the blade bias and the developing roller bias is 80 V to 400 V, it is desirable that the resistance value of the developing blade 4 is set so as to exhibit a resistance value of 5 × 10 ⁶ Ω to 1 × 10 ⁹ Ω.

  The resistance value of the developing blade 4 includes the type / specific gravity / amount of conductive powder added to the contact member (semiconductive rubber 4b) of the developing blade 4, the type / polarity of the elastomer, and molding conditions (for example, in the case of centrifugal molding). By appropriately changing the rotation speed, G), etc., it is possible to adjust to the above range.

Further, if the resistance value of the developing blade 4 exceeds 1 × 10 ⁹ Ω when the voltage of the measuring power supply 18 is in the range of 80V to 400V, almost no current flows through the developing blade 4, and the developing blade 4 and the developing The force of the electric field does not reach the toner passing between the rollers 3.

  Further, when the developing blade 4 is composed only of a conductive blade such as a phosphor bronze thin plate, when the developing blade 4 abuts against the developing roller 3, charge injection is likely to occur in a high temperature / high humidity environment. , Fogging is likely to occur at low speeds.

Further, when the voltage of the measurement power supply 18 is in the range of 80V to 400V, the electric field is formed between the developing blade 4 and the developing roller 3 by setting the resistance value of the developing blade 4 to 1 × 10 ⁹ Ω or less. Become. When an electric field is formed between the developing blade 4 and the developing roller 3, the toner T moving between them is frictionally charged, and at the same time, the toner is pressed against the developing roller 3 side. At this time, as the toner T is pressed, a larger amount of current flows through the developing blade 4, and at the same time, the amount of toner (M / A) per unit area coated on the developing roller 3 increases.

  FIG. 6 shows the relationship between the potential difference (V) between the developing roller and the developing blade and the resistance value (Ω) of the developing blade obtained by the measurement. As shown in FIG. 6, as the potential difference between the two increases, the resistance value of the developing blade 4 decreases. Therefore, in a low temperature / low humidity environment, the voltage applied to the developing blade 4 is increased in order to obtain a sufficient electric field, and in a high temperature / high humidity environment, the developing blade 4 is used to eliminate the influence of charge injection described later. You may set the voltage applied to to small.

  The thickness of the contact member (semiconductive rubber 4b) of the present invention can be appropriately determined according to the molding method of the developing blade, cost, etc., but is usually 10 μm to 5 mm, and preferably 30 μm to 2 mm. If the thickness of the abutting member (semiconductive rubber 4b) is less than 10 μm, resistance adjustment becomes difficult and resistance tends to vary. If the thickness exceeds 5 mm, uneven distribution of the conductive powder increases, and the dielectric layer becomes This is not practical because it forms a large resistance loss.

  The contact pressure of the developing blade 4 against the surface of the developing roller 3 is preferably about 20 g / cm to 100 g / cm of linear pressure. If it is 20 g / cm or less, sufficient toner regulation cannot be performed, and the amount of toner carried on the developing roller 3 changes due to the influence of vibration or the like. When it is 100 g / cm or more, the external additive mixed in the toner T due to pressure or the like is easily peeled off from the surface of the toner T, the toner T is deteriorated, and the charging property of the toner T is lowered.

  As a method for measuring the linear pressure, a stainless steel thin plate having a length of 100 mm × width 15 mm × thickness 30 μm as a drawing plate and a stainless steel thin plate having a length of 180 mm × width 30 mm × thickness 30 μm as a sandwiching plate are halved in length. Prepare something folded in Then, a drawing plate is inserted between the sandwiching plates, and the sandwiching plate is inserted between the developing roller 3 and the developing blade 4.

  In this state, the pulling plate is pulled out at a constant speed with only a spring or the like, and the value of the spring only at that time (unit: g) is read. Then, the value indicated by the spring alone is divided by 1.5 to obtain the linear pressure with the unit of g / cm.

  The voltage applied to the developing blade 4 from the blade bias power supply 14 is the same polarity as the charging polarity of the toner T, and a voltage whose absolute value is larger than the voltage applied to the developing roller 3 may be applied. preferable. That is, if a voltage of DC = −350 V is supplied to the developing roller 3 from the developing bias power supply 12, for example, a voltage of −500 V may be supplied to the developing blade 4. The potential difference at this time is indicated as “Δ−150 V”.

  In the present embodiment, if the blade bias power supply 14 is larger on the negative polarity side than the development bias power supply 12, when negative polarity toner enters the space between the development blade 4 and the development roller 3 (hereinafter, regulation nip), The negative toner is pressed against the developing roller 3 side.

  Since the developing roller 3 rotates at a speed, the negative toner pressed near the surface of the developing roller 3 passes through the developing roller 3. Conversely, the toner charged to positive polarity is pressed against the developing blade 4 at the regulation nip. Since the developing blade 4 is stationary, the speed of passing through the developing nip is very slow.

(Contact pressure between developing roller and photosensitive drum)
The contact pressure of the developing roller 3 with respect to the photosensitive drum 1 is preferably set to a linear pressure of 20 g / cm to 120 g / cm in the same measurement as the measurement of the linear pressure. When the linear pressure is 20 g / cm or less, the contact state between the developing roller 3 and the photosensitive drum 1 becomes unstable, and when the linear pressure is 120 g / cm or more, the external additive mixed with the toner due to the pressure is peeled off from the toner surface. It becomes easy to do. As a result, the toner is deteriorated and the chargeability of the toner by the developing blade 4 is lowered.

(Toner used)
In the present embodiment, a one-component nonmagnetic toner T is used as the toner (developer) T. The toner T is prepared by a suspension polymerization method including a binder resin and a charge control agent, and can be produced by adding a fluidizing agent or the like as an external additive.

Here, the volume average particle size _RT is obtained by attaching a liquid module to an LS-230 type laser diffraction particle size distribution measuring device (manufactured by Beckman Coulter, Inc.) and measuring a particle size of 0.04 μm to 2000 μm. The volume-based particle size distribution was calculated.

In the present embodiment, the image quality can be improved by using the toner T having a volume average particle size _RT of 4.0 μm to 8.2 μm. When the volume average particle size _{RT of} the toner exceeds 8.2 μm, roughness occurs on the halftone image or in the minute dot area. When the volume average particle size _RT is less than 4.0 μm, the toner is applied to the developing roller 3. Since stable coating is not possible, image quality is degraded.

  The toner T in the present embodiment preferably has a shape factor SF-1 value of 100 to 160 and a shape factor SF-2 value of 100 to 140 measured by the image analysis apparatus. Further, it is more preferable that the value of the shape factor SF-1 is 100 to 140 and the value of the shape factor SF-2 is 100 to 120. Further, by satisfying the above conditions and setting the value of (SF-2) / (SF-1) to 1.0 or less, not only the characteristics of the toner but also matching with the image analysis apparatus is extremely good. I know it will be something.

The shape factors SF-1 and SF-2 are parameters obtained as follows. First, using FE-SEM (S-800) (manufactured by Hitachi, Ltd.), 100 toner images enlarged at a magnification of 500 times are sampled randomly. Then, the image information is introduced into an image analysis apparatus (Luxex 3) (manufactured by Nicole) via an interface, analyzed, and calculated from the following equation.
(Expression 2) SF-1 = {(MXXLNG) 2 / AREA} × (π / 4) × 100
SF-2 = {(PERI) 2 / AREA} × (1 / 4π) × 100
AREA: toner projected area, MXLNG: absolute maximum length, PERI: circumference

The toner shape factor SF-1 indicates the degree of roundness of the toner particles, and gradually increases from a spherical shape to an irregular shape as the value increases. SF-2 indicates the degree of unevenness of the toner particles, and the unevenness of the toner surface becomes remarkable. When the shape factor SF-1 exceeds 160, the rolling resistance becomes low, and the torque increases. In addition, since friction increases, frictional heat increases and toner deterioration is likely to occur.

  FIG. 7 shows the relationship between the blade bias potential (V) and the toner coat amount (M / A) on the developing roller in a low temperature / low humidity environment. Here, the horizontal axis indicates the potential difference between the developing blade 4 and the developing roller 3, and the vertical axis indicates the toner amount (M / A) per unit area carried on the developing roller 3 after passing through the developing blade 4.

Black circles (●) show the results when the developing blade 4 in the present embodiment shown in FIG. 6 is used. Squares (□) are results when a developing blade having a resistance value of approximately 1 × 10 ⁹ Ω or more is used even when a potential difference of −400 V or more is applied. The cross (×) is the result when phosphor bronze (conductor) is used for the developing blade.

  Here, in order to obtain a desired toner density on the developing roller 3, M / A needs to be 0.35 (dotted line portion in FIG. 7) or more. Therefore, as shown in FIG. 7, it is possible to obtain a desired density by using the developing blade 4 in the present embodiment and forming an electric field that presses the toner T toward the developing roller 3 in the regulating nip. It is.

  However, when the resistance value is high (□), the amount of toner on the developing roller 3 does not increase because an electric field sufficient to transfer the toner T to the developing roller side is hardly generated in the regulation nip. On the contrary, even when the resistance of the developing roller 3 is low (x), the image density can be obtained, but the following low-speed fog occurs.

  Since the contact resistance between the toner T and the developing roller 3 and the like is lowered in an environment of high temperature and high humidity, the electric field easily loses the electric charge of the toner T once charged to the developing roller 3 side and easily disappears. Is in a state. That is, even if there is frictional charging or charge injection from the developing blade 4, fogging tends to occur at a low speed as a result of those charges escaping and disappearing to the developing roller 3 side.

  Therefore, since the fog at low speed is determined by the ease of charge removal, the longer the electric field is applied (the longer the contact width between the developing blade and the developing roller), or the lower the resistance value of the developing blade (development) A large electric field is formed between the blade and the developing roller).

  In the present embodiment, the surface of the developing blade 4 that contacts the developing roller 3 through the toner T is formed by the semiconductive rubber 4b (contact member). Therefore, a potential drop occurs in the blade bias voltage due to the semiconductivity of the semiconductive rubber 4b, and the potential appearing on the surface of the contact member 4b becomes low. As a result, the electric field generated in the regulation nip is smaller than that of the conductive one, and the positive charge injection to the toner T is reduced.

  As described above, in the present embodiment, it is possible to obtain image density followability in a low temperature / low humidity environment while minimizing the effect of charge loss due to a high temperature / high humidity environment. Furthermore, by making the arithmetic average roughness of the developing blade 4 larger than the arithmetic average roughness of the developing roller 3, the area where the developing blade 4 can inject charges into the toner T is increased from the surface area through which charges are released to the developing roller 3 side. It becomes possible to give an electric charge suitably.

(Comparison result of Example and Comparative Example)
Next, the arithmetic average roughness R _{D of} the developing roller surface, the volume average particle diameter R _{T of} the toner, the arithmetic average roughness R _{B of} the developing blade surface, the resistance value of the developing blade, the difference Δ between the blade bias power source and the developing bias power source Δ The contact width L between the developing blade and the developing roller is set as follows. Then, (Example 1) to (Example 13) set in a range that can be taken by the image forming apparatus according to the present invention described above, and (Comparative Example 1) to (Comparative Example 7) which are conventional examples. The comparison result will be described.

Example 1
In Example 1, 1.5 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 6.1 [mu] m volume average particle diameter _{R T} of the toner, the arithmetic mean roughness 1.3μm to _{R B} of the developing blade surface, a set did. According to this, the arithmetic average roughness R _D of the developing roller surface is 0.25 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

The resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment). Further, the difference Δ between the blade bias power source and the development bias power source is −150 V (blade bias power source: −500 V, development bias power source: −350 V). The contact width L between the developing blade and the developing roller is 0.9 mm. The resistance value of the developing blade 4 is measured by applying a voltage difference between the blade bias power source and the developing bias power source in each environment.

(Example 2)
The second embodiment is different from the first embodiment in that the contact width L between the developing blade 4 and the developing roller 3 is reduced, and the other settings are the same as those in the first embodiment. That is, in the same manner as in Example 1, 1.5 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 6.1 [mu] m volume average particle diameter _{R T} of the toner, the arithmetic mean roughness _{R B} of the developing blade surface 1. Set to 3 μm. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.25 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

Further, the resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment). The difference Δ is −150V. The contact width L between the developing blade 4 and the developing roller 3 was set to 0.4 mm.

(Example 3)
The third embodiment is different from the first embodiment in that the contact width L between the developing blade 4 and the developing roller 3 is increased, and the other settings are the same as those in the first embodiment. That is, in the same manner as in Example 1, 1.5 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 6.1 [mu] m volume average particle diameter _{R T} of the toner, the arithmetic mean roughness _{R B} of the developing blade surface 1. Set to 3 μm. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.25 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

Further, the resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment). The difference Δ is −150V. The contact width L between the developing blade 4 and the developing roller 3 is 1.3 mm.

(Comparative Example 1)
Comparative Example 1 differs from Example 3 in that the contact width L between the developing blade and the developing roller is further increased, and the other settings are the same as those in Example 3. That is, in the same manner as in Example 3, 1.5 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 6.1 [mu] m volume average particle diameter _{R T} of the toner, the arithmetic mean roughness _{R B} of the developing blade surface 1. Set to 3 μm. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.25 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

Further, the resistance value of the developing blade used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference between the blade bias power supply and the development bias power supply Δ is −150V. The contact width L between the developing blade and the developing roller is 1.5 mm.

(Comparative Example 2)
Comparative Example 2 differs from Example 2 in that the contact width L between the developing blade and the developing roller is further narrowed, and the other settings are the same as in Example 2. That is, in the same manner as in Example 2, 1.5 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 6.1 [mu] m volume average particle diameter _{R T} of the toner, the arithmetic mean roughness _{R B} of the developing blade surface 1. Set to 3 μm. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.25 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

The resistance value of the developing blade used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference Δ between the blade bias power source and the developing bias power source Δ Is -150V. The contact width L between the developing blade and the developing roller is 0.2 mm.

Example 4
The fourth embodiment is different from the first embodiment in that the resistance value of the developing blade 4 is increased, and the other settings are the same as those in the first embodiment. That is, in the same manner as in Example 1, 1.5 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 6.1 [mu] m volume average particle diameter _{R T} of the toner, the arithmetic mean roughness _{R B} of the developing blade surface 1. Set to 3 μm. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.25 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

The resistance value of the developing blade used at this time is 8 × 10 ⁸ Ω (low temperature / low humidity environment) / 5 × 10 ⁸ Ω (high temperature / high humidity environment), and the difference Δ between the blade bias power source and the developing bias power source Δ Is -250V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm as in the first embodiment.

(Example 5)
The fifth embodiment is different from the first embodiment in that the resistance value of the developing blade 4 is reduced, and the other settings are the same as those in the first embodiment. That is, in the same manner as in Example 1, 1.5 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 6.1 [mu] m volume average particle diameter _{R T} of the toner, the arithmetic mean roughness _{R B} of the developing blade surface 1. Set to 3 μm. Therefore, the arithmetic average roughness R _D of the surface of the developing roller 3 is 0.25 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

The resistance value of the developing blade 4 used at this time is 6 × 10 ⁶ Ω (low temperature / low humidity environment) / 3 × 10 ⁶ Ω (high temperature / high humidity environment), and the difference between the blade bias power supply and the development bias power supply Δ is −100V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm as in the first embodiment.

(Comparative Example 3)
Comparative Example 3 is different from Example 5 in that the resistance value of the developing blade is reduced, and the other settings are the same as in Example 5. That is, in the same manner as in Example 5, 1.5 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 6.1 [mu] m volume average particle diameter _{R T} of the toner, the arithmetic mean roughness _{R B} of the developing blade surface 1. Set to 3 μm. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.25 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

Further, the resistance value of the developing blade used at this time is 4 × 10 ⁵ Ω (low temperature / low humidity environment) / 1 × 10 ⁵ Ω (high temperature / high humidity environment), and the difference Δ between the blade bias power source and the developing bias power source Δ Is -100V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm as in the fifth embodiment.

(Comparative Example 4)
Comparative Example 4 is different from Example 4 in that the resistance value of the developing blade is increased, and the other settings are the same as in Example 4. That is, in the same manner as in Example 4, 1.5 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 6.1 [mu] m volume average particle diameter _{R T} of the toner, the arithmetic mean roughness _{R B} of the developing blade surface 1. Set to 3 μm. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.25 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

The resistance value of the developing blade used at this time is 5 × 10 ⁹ Ω (low temperature / low humidity environment) /
1 × 10 ⁸ Ω (high temperature / high humidity environment), and the difference Δ between the blade bias power source and the developing bias power source is −400V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm as in the fourth embodiment.

(Example 6)
Example 6 is different from Example 1 in that the arithmetic average roughness R _D of the surface of the developing roller 3, the volume average particle diameter R _{T of} the toner, and the arithmetic average roughness R _B of the surface of the developing blade 4 are changed. Other settings are the same as those in the first embodiment. That is, the arithmetic mean roughness _{R D} of the developing roller surface 2.2 .mu.m, 4.5 [mu] m volume average particle diameter _{R T} of the toner, and the arithmetic average roughness _{R B} of the developing blade surface is set to 2.0 .mu.m. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.49 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

Further, the resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference between the blade bias power supply and the development bias power supply Δ is −150V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm.

(Example 7)
Example 7 differs from Example 1 in that the arithmetic average roughness R _D of the surface of the developing roller 3, the volume average particle diameter R _{T of} the toner, and the arithmetic average roughness R _B of the surface of the developing blade 4 are changed. Other settings are the same as those in the first embodiment. That is, the arithmetic mean roughness _{R D} of the developing roller 3 surface 3.6 [mu] m, a volume average particle diameter _{R T} of the toner T 7.9 .mu.m, and the arithmetic average roughness _{R B} of the developing blade 4 surface is set to 1.0μm . Accordingly, the arithmetic average roughness R _D of the surface of the developing roller 3 is 0.46 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner T.

Further, the resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference between the blade bias power supply and the development bias power supply Δ is −150V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm.

(Comparative Example 5)
Comparative Example 5 is different from Example 6 in that the arithmetic average roughness _RD of the developing roller surface is increased, and the other settings are the same as in Example 6. That is, the arithmetic mean roughness _{R D} of the developing roller surface 2.7 .mu.m, 4.5 [mu] m volume average particle diameter _{R T} of the toner, and the arithmetic average roughness _{R B} of the developing blade surface is set to 2.0 .mu.m. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.6 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

The resistance value of the developing blade used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference Δ between the blade bias power source and the developing bias power source Δ Is -150V. The contact width L between the developing blade and the developing roller is 0.9 mm.

(Comparative Example 6)
Comparative Example 6 differs from Example 7 in that the arithmetic average roughness _RD of the surface of the developing roller 3 is increased, and the other settings are the same as in Example 7. That is, the arithmetic mean roughness _{R D} of the developing roller surface 4.3 [mu] m, a volume average particle diameter _{R T} of the toner 7.9 .mu.m, and the arithmetic average roughness _{R B} of the developing blade surface is set to 1.0 .mu.m. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.54 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

The resistance value of the developing blade used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference Δ between the blade bias power source and the developing bias power source Δ Is -150V. The contact width L between the developing blade and the developing roller is 0.9 mm.

(Example 8)
Example 8 differs from Example 1 in that the arithmetic average roughness R _D of the surface of the developing roller 3, the volume average particle diameter R _{T of} the toner, and the arithmetic average roughness R _B of the surface of the developing blade 4 are changed. Other settings are the same as those in the first embodiment. That, 1.0 .mu.m arithmetic mean roughness _{R D} of the developing roller 3 surface, 4.5 [mu] m volume average particle diameter _{R T} of the toner, and the arithmetic average roughness _{R B} of the developing blade 4 surface is set to 1.6 [mu] m. Therefore, the arithmetic average roughness R _D of the surface of the developing roller 3 is 0.22 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner. At this time, the relationship of R _B > R _D is established.

Further, the resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference between the blade bias power supply and the development bias power supply Δ is −150V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm.

Example 9
Example 9 differs from Example 1 in that the arithmetic average roughness R _D of the surface of the developing roller 3, the volume average particle diameter R _{T of} the toner, and the arithmetic average roughness R _B of the surface of the developing blade 4 are changed. Other settings are the same as those in the first embodiment. That, 1.0 .mu.m arithmetic mean roughness _{R D} of the developing roller 3 surface, 4.5 [mu] m volume average particle diameter _{R T} of the toner, and the arithmetic average roughness _{R B} of the developing blade surface is set to 0.8 [mu] m. Therefore, the arithmetic average roughness R _D of the surface of the developing roller 3 is 0.22 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner. At this time, the relationship of R _B <R _D is established.

Further, the resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference between the blade bias power supply and the development bias power supply Δ is −150V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm.

(Example 10)
Example 10 differs from Example 1 in that the arithmetic average roughness R _D of the surface of the developing roller 3, the volume average particle diameter R _{T of} the toner, and the arithmetic average roughness R _B of the surface of the developing blade 4 are changed. Other settings are the same as those in the first embodiment. That is, the arithmetic mean roughness _{R D} of the developing roller 3 surface 3.2 .mu.m, the volume average particle diameter _{R T} of the toner 7.9 .mu.m, and the arithmetic average roughness _{R B} of the developing blade 4 surface is set to 2.8 .mu.m. Therefore, the arithmetic average roughness R _D of the surface of the developing roller 3 is 0.41 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner. At this time, the relationship of R _B <R _D is established.

Further, the resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference between the blade bias power supply and the development bias power supply Δ is −150V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm.

Example 11
Example 11 differs from Example 1 in that the arithmetic average roughness R _D of the surface of the developing roller 3, the volume average particle diameter R _{T of} the toner, and the arithmetic average roughness R _B of the surface of the developing blade 4 are changed. Other settings are the same as those in the first embodiment. That is, the arithmetic mean roughness _{R D} of the developing roller surface 3.2 .mu.m, the volume average particle diameter _{R T} of the toner 7.9 .mu.m, and the arithmetic average roughness _{R B} of the developing blade 4 surface is set to 2.8 .mu.m. Therefore, the arithmetic average roughness R _D of the surface of the developing roller 3 is 0.41 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner. At this time, the relationship of R _B > R _D is established.

Further, the resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference between the blade bias power supply and the development bias power supply Δ is −150V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm.

Example 12
Example 12 differs from Example 1 in that the arithmetic average roughness R _D of the surface of the developing roller 3, the volume average particle diameter R _{T of} the toner, and the arithmetic average roughness R _B of the surface of the developing blade 4 are changed. Other settings are the same as those in the first embodiment. That, 0.1 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 4.5 [mu] m volume average particle diameter _{R T} of the toner, and the arithmetic average roughness _{R B} of the developing blade 4 surface is set to 0.12 .mu.m. Therefore, the arithmetic average roughness R _D of the surface of the developing roller 3 is 0.02 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

Further, the resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference between the blade bias power supply and the development bias power supply Δ is −150V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm.

(Example 13)
Example 13 differs from Example 1 in that the arithmetic average roughness R _D of the surface of the developing roller 3, the volume average particle diameter R _{T of} the toner, and the arithmetic average roughness R _B of the surface of the developing blade 4 are changed. Other settings are the same as those in the first embodiment. That, 0.6 .mu.m arithmetic mean roughness _{R D} of the developing roller 3 surface, 4.5 [mu] m volume average particle diameter _{R T} of the toner, and the arithmetic average roughness _{R B} of the developing blade 4 surface is set to 0.7 [mu] m. Therefore, the arithmetic average roughness R _D of the surface of the developing roller 3 is 0.16 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

Further, the resistance value of the developing blade 4 used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference between the blade bias power supply and the development bias power supply Δ is −150V. The contact width L between the developing blade 4 and the developing roller 3 is 0.9 mm.

(Comparative Example 7)
Comparative Example 7 differs from Example 1 in that when the electric field direction of the developing blade is reversed, the contact width L between the developing blade and the developing roller is increased. That is, an electric field in which the negatively charged toner is pressed against the developing blade side. Also, 1.5 [mu] m and an arithmetic mean roughness _{R D} of the developing roller surface, 6.1 [mu] m volume average particle diameter _{R T} of the toner, the arithmetic mean roughness _{R B} of the developing blade surface
Was set to 1.3 μm. Therefore, the arithmetic average roughness R _D of the developing roller surface is 0.25 (R _D / R _T ) with respect to the volume average particle diameter R _T of the toner.

The resistance value of the developing blade used at this time is 5 × 10 ⁷ Ω (low temperature / low humidity environment) / 2 × 10 ⁷ Ω (high temperature / high humidity environment), and the difference Δ between the blade bias power source and the developing bias power source Δ Is + 150V. The contact width L between the developing blade and the developing roller is 1.5 mm.

  The following evaluation was performed for the above (Example 1) to (Example 13) and (Comparative Example 1) to (Comparative Example 7).

(1) Density follow-up evaluation under low temperature and low humidity environment The density follow-up evaluation is performed by leaving the image forming apparatus in an evaluation environment at 15.0 ° C. and 10% Rh for 1 day to adjust to the environment, and then printing 100 sheets. I went later. The printing test for 100 sheets was performed by continuously passing a horizontal line recorded image having an image ratio of 5%. Image evaluation was performed by using a spectrum densitometer 500 (manufactured by X-Rite Co., Ltd.) based on the density difference between the leading edge and the trailing edge of the tenth solid black image. The print test and the evaluation image are monochromatic and output at a normal paper speed (200 mm / sec). And it evaluated by the symbol of (circle), (triangle | delta), and x demonstrated below.
◯: The density difference between the leading edge and the trailing edge of the paper in a solid black image is less than 0.2. Δ: The density difference between the leading edge of the paper and the trailing edge in the solid black image is 0.2 or more and less than 0.3. In solid black images, the density difference between the leading edge and the trailing edge of the paper is 0.3 or more

(2) Evaluation of low-speed fogging in a high-temperature and high-humidity environment Low-speed fogging evaluation was performed after the image forming apparatus was allowed to stand in the evaluation environment at 30.0 ° C. and 80% Rh for one day, and then adjusted to the environment. This was carried out after the sheet was left in the environment for another 2 days after printing. The 1000-sheet printing test was performed by continuously passing a horizontal line recorded image having an image ratio of 5%. After being left in the environment for 2 days, the image evaluation was performed by continuously outputting three solid white images and measuring the amount of fogging of the third solid white image.

The fog amount was measured by measuring the density of the image surface with a reflection densitometer TC-6DS (manufactured by Tokyo Denshoku). The fog due to image formation is obtained by subtracting the reflection density (%) of the solid white image from the reflection density (%) of the paper of the same lot. The print test was output at a normal paper speed (200 mm / sec), and the evaluation image was output at a thick paper speed (65 mm / sec). At the time of evaluation, the evaluation was performed using a single color. And it evaluated by the symbol of (circle), (triangle | delta), and x demonstrated below.
○: The maximum fog value in the paper is less than 3%. Δ: The maximum fog value in the paper is 3% or more and less than 7%. X: The maximum fog value in the paper is 7% or more. This is because when the fog exceeds 3%, discoloration of the paper due to fog toner becomes conspicuous.

(3) Evaluation of change in durable image density Evaluation of change in durable image density is carried out by leaving the image forming apparatus in the evaluation environment at 15.0 ° C. and 10% Rh for one day to adjust to the environment, and then every 100 sheets. An evaluation image was output, and printing was performed up to 1000 sheets. The printing test was performed by continuously passing a horizontal line of recorded images having an image ratio of 5%. For the image evaluation, one solid black image was output, and the average density of the solid black image was evaluated using a spectrum densitometer 500 (manufactured by X-Rite). The print test and the evaluation image are monochromatic and output at a normal paper speed (200 mm / sec). As the evaluation, the evaluation was performed by the difference between the maximum value and the minimum value in the transition of the average density of the solid image output every 100 sheets.
○: The difference between the maximum value and the minimum value of the average concentration during endurance is less than 0.2. Δ: The difference between the maximum value and the minimum value of the average concentration during endurance is 0.2 or more and less than 0.3. The difference in density between the maximum and minimum average concentrations during endurance is 0.3 or more

(4) Image Uniformity Evaluation Image uniformity was evaluated after 100 sheets were printed after the image forming apparatus was allowed to stand for 1 day at an evaluation environment of 15.0 ° C. and 10% Rh for one day. The printing test for 100 sheets was performed by continuously passing a horizontal line recorded image having an image ratio of 5%. In the image evaluation, after outputting one sheet of solid black, a solid black image is output again and the image forming apparatus is forcibly stopped halfway. The state of the toner on the photosensitive drum in the state where it was forcibly stopped was observed, and at the same time, the uniformity of the density of the solid black image output previously was visually observed. And it evaluated by the symbol of (circle), (triangle | delta), and x demonstrated below.
○: There is no rubbing trace on the photosensitive drum, and the solid black image on the paper is uniform.
Δ: A rubbing trace is seen on the photosensitive drum, but there is no problem with the solid black image on the paper. The trace refers to a minute vertical streak trace that is peeled off by the convex portion of the developing roller in the toner layer on the photosensitive drum, and the surface of the photosensitive drum can be seen at the rubbing trace portion.

(Evaluation results)
The evaluation results are shown in Tables 1 and 2 below.

  First, Comparative Example 1 and Comparative Example 2, which are conventional techniques, and Examples 1 to 3 are compared. In Comparative Example 1, the contact width L between the developing blade and the developing roller is as wide as 1.5 mm. The results of low speed fogging in Comparative Example 1 will be described. When output at a thick paper speed (65 mm / sec) in a high-temperature and high-humidity environment, toner is present in a region between the developing roller and the developing blade (hereinafter referred to as a regulation nip) for a long time.

  The negatively charged toner in the regulation nip is pressed against the developing roller by an electric field. The pressed toner is pressed to the developing roller side, and electrons existing on the toner surface are neutralized or reversely charged by holes injected from the developing roller side.

  This phenomenon is more likely to occur as the time in the regulation nip is longer (the longer the time affected by the electric field). Furthermore, since the electric charge injection is promoted as the electric field strength in the regulation nip increases, fogging at low speed with low resistance of the contact member of the developing blade is likely to occur.

  Next, we will describe the results of concentration follow-up evaluation in a low temperature and low humidity environment. In Comparative Example 1, since the contact width L between the developing blade and the developing roller is as wide as 1.5 mm, the force with which the developing blade presses the developing sleeve in the regulation nip tends to be weak, and the density follows slightly. Sexual decline was observed.

In Comparative Example 2, since the contact width L between the developing blade and the developing roller is as narrow as 0.2 mm, the time for sliding against the developing blade is short, so the chance of frictional charging is greatly reduced. . For this reason, when a solid black image is output, a desired image density is easily obtained in the length of one round of the developing roller at the leading end of the paper. However, at the rear end, toner that is not frictionally charged enters the regulation nip. As a result, the uncharged toner cannot pass through the developing blade, and the image density becomes thin. On the contrary, in a high temperature / high humidity environment, the time for injecting the charge is short, but since there is little opportunity for the original triboelectric charging, a slight fog is generated.

  On the other hand, in Examples 1 to 3, in a low temperature and low humidity environment, an appropriate electric field is formed in the regulation nip and charges are given to the toner. On the other hand, in a high-temperature and high-humidity environment, charge neutralization and reverse charging are suppressed in order to suppress the current flowing through the developing blade.

  Next, Examples 4 and 5 and Comparative Examples 3 and 4 will be described. In Comparative Example 3, the resistance of the developing blade is low. Therefore, as described above, an electric field in which the charge of the toner is neutralized or reversely charged is formed from the developing roller side in a high temperature / high humidity environment. As a result, fogging occurs at a low speed.

  On the other hand, when the resistance of the developing blade is high as in Comparative Example 4, a sufficient electric field is formed between the developing blade and the developing roller to bias the negative toner toward the developing roller at a low temperature and low humidity. This makes it difficult to obtain the desired density followability.

  On the other hand, in Examples 4 and 5, in a low temperature / low humidity environment, an appropriate electric field is formed in the regulation nip, and the toner is charged. On the other hand, in a high-temperature and high-humidity environment, charge neutralization and reverse charging are suppressed in order to suppress the current flowing through the developing blade.

Next, Examples 6 and 7 and Comparative Examples 5 and 6 will be described. In Comparative Examples 5 and 6, the arithmetic average roughness _RD of the developing roller surface is increased. Comparative Example 5 uses a toner having a small volume average particle size _RT , and Comparative Example 6 uses a toner having a large volume average particle size _RT .

  In Comparative Examples 5 and 6, the arithmetic average roughness of the surface of the developing roller is larger than 0.5 times the volume average particle diameter of the toner, so that the triboelectric charging of the toner is easily inhibited. That is, the toner exists between the protrusions on the surface of the developing roller, and the chance that the toner is directly frictionally charged with the developing blade and the surface of the developing roller is reduced. As a result, the toner passes through the developing blade in a low temperature / low humidity environment. Thus, the following property of the concentration is deteriorated without obtaining the charge.

  Similarly, there are few opportunities for frictional charging in a high temperature / high humidity environment, and the influence is greater than in a low temperature / low humidity environment. That is, not only a large amount of fog occurs at low speed, but also fog occurs at normal paper speed.

  On the other hand, in Examples 6 and 7, in a low temperature / low humidity environment, the regulation nip has an appropriate surface roughness, and a large amount of regulation nip is formed by urging the toner toward the developing roller by an electric field. The toner can pass through. On the other hand, in a high-temperature and high-humidity environment, as described above, neutralization of charge and reverse charging are suppressed in order to suppress the current flowing through the developing blade.

  Next, Comparative Example 7 will be described. In Comparative Example 7, the bias applied to the developing blade is on the positive polarity side. Under this bias condition, the negatively charged toner is pressed against the developing blade, and as a result, the amount of toner passing through the developing blade is reduced. Therefore, the average density of the solid black image is also lowered.

Next, evaluation of durable image density change will be described. In Examples 8 and 11, the relationship between the arithmetic average roughness R _D on the surface of the developing roller and the arithmetic average roughness R _B on the surface of the developing blade is R _B > R _D. By comparison, Example 9, Example 10 and Example 1-7 _has a _R B <R _D.

When R _B < _RD , the average density of the initial solid black image is particularly low, and the average density of the solid black image tends to increase as the number of print tests increases. In the initial stage, a toner having a relatively small particle diameter among the toner in the developing container is likely to be selectively carried on the developing roller. The cause is that the toner amount of the small particle size toner has a larger charge amount per unit weight of the toner.

  As the number of print tests increases, the small-diameter toner is gradually consumed from the developing device, and the average particle density of the solid image increases as the particle diameter of the toner carried on the developing roller gradually increases. To go.

On the other hand, when R _B > _RD , the toner near the surface of the developing blade easily passes through the developing blade. That is, since the convex portion on the surface of the developing blade presses the developing roller, it is difficult to apply a physical regulating force to the toner existing in the concave portion therebetween.

  Therefore, the toner in the concave portion can also pass through the developing blade, and the selectivity of the toner particle size by the developing blade is reduced. As a result, a decrease in the initial solid black image density is suppressed, so that an overall change in image density due to durability is reduced.

Next, image uniformity evaluation will be described. In Examples 12 and 13, the ratio of the arithmetic average roughness _RD on the surface of the developing roller to the volume average particle diameter _RT of the toner is very small as compared with the above-described Examples. Specifically, _RD / _RT is less than 0.17.

Therefore, the image is not disturbed when the toner T on the developing roller is transferred to the photosensitive drum 1. That is, when the arithmetic average roughness _RD of the surface of the developing roller is 0.17 times or more with respect to the volume average particle diameter of the toner, the surface is transferred to the photosensitive drum side in a so-called developing region where the developing roller and the photosensitive drum are in contact with each other. The convex portions on the surface of the developing roller rub the toner. Therefore, the toner is moved, or the toner is peeled off again on the developing roller side by the convex portion.

However, when the arithmetic average roughness _RD of the surface of the developing roller is less than 0.17 times the volume average particle diameter of the toner, the toner transferred to the photosensitive drum by the convex portion of the developing roller is moved. There is no scratching or scraping. As a result, the edge of the character becomes sharp and the uniformity of the solid image is improved.

  As described above, according to the image forming apparatus of the present invention, it is possible to perform high-quality image formation by preventing a decrease in density followability in a low-temperature / low-humidity environment and low-speed fogging in a high-temperature / high-humidity environment. It is possible to provide a possible image forming apparatus.

The figure which shows the contact part vicinity of the image development blade and image development roller in this invention. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention. 1 is a schematic configuration diagram of a process cartridge according to the present invention. Explanatory drawing of the method to measure the resistance of the developing roller in this invention. Explanatory drawing of the method of measuring the resistance of the image development blade in this invention. The figure which shows the relationship between the electrical potential difference between a developing roller and a developing blade, and resistance. The figure which shows the relationship between the blade bias potential (V) and the toner coat amount (M / A) on a developing roller in a low temperature and low humidity environment. 1 is a schematic configuration diagram of a conventional image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Developing roller 4 Developing blade 5 Toner supply roller 7 Developing apparatus 8 Image forming apparatus 9 Process cartridge 10 Scanner unit 11 Stirring member 12 Developing bias power supply 13RS bias power supply 14 Blade bias power supply 15 Motor 16 Control circuit T Toner

Claims (7)

A rotatable image carrier on which an electrostatic latent image is formed;
A developer carrying member configured to be rotatable in contact with the image carrier, a developer carrying member that carries the developer, a developer supply member that supplies the developer to the developer carrier, and a surface of the developer carrier. Developing means having a developer regulating member for regulating the amount of developer carried on the surface;
Voltage application means for applying a voltage to each of the developer carrier and the developer regulating member;
In an image forming apparatus comprising:
Control means for controlling the rotational speed so that the image carrier has a plurality of rotational speeds;
As the developer, a developer having a volume average particle size R _T (μm) of 4.0 μm ≦ R _T ≦ 8.2 μm is used.
A voltage having the same polarity as the charging polarity of the developer is applied to the developer carrier and the developer regulating member, and the absolute value of the applied voltage value is applied to the developer carrier. The voltage applied to the developer regulating member is larger than the voltage,
A semiconductive resin or a semiconductive rubber is used in at least a portion of the developer regulating member that contacts the surface of the developer carrier.
The arithmetic average roughness R _D (μm) of the surface of the developer carrying member is 0.5 times or less with respect to the volume average particle diameter R _T (μm) of the developer,
The abutting width where the developer carrying member and the developer regulating member abut via the developer, and the abutting width L (mm) in the rotation direction of the developer carrying member is 0.3 mm ≦ L An image forming apparatus, wherein ≦ 1.4 mm. 2. The arithmetic average roughness R _D (μm) of the surface of the developer carrying member is 0.17 times or less with respect to the volume average particle diameter R _T (μm) of the developer. The image forming apparatus described in 1. On the surface of the developer regulating member, the arithmetic average roughness R _B (μm) of the portion in contact with the developer carrier via the developer is the arithmetic average roughness R _D on the surface of the developer carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is larger than (μm). In the semiconductive resin or the semiconductive rubber,
The image forming apparatus according to claim 1, wherein conductive powder is dispersed. The resistance value of the semiconductive resin or the semiconductive rubber is
The voltage is set so as to exhibit a resistance value of 5 × 10 ⁶ to 1 × 10 ⁹ (Ω) when a voltage of 80 V to 400 V is applied thereto. The image forming apparatus described in the item. The developer particles are:
6. The image forming apparatus according to claim 1, wherein the shape factor SF-1 has a value of 100 to 160, and the shape factor SF-2 has a value of 100 to 140. The developing means includes
The image forming apparatus according to claim 1, wherein the image forming apparatus is configured as a cartridge that is detachable from the apparatus main body.

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