JP2009031777A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which controls an appropriate developer amount with respect to a desired image, and can thereby prevent image defects, such as, damaged characters or voids and form a stable image over a long time. <P>SOLUTION: A developer regulating member 9 has a resistance value varying depending on a voltage to be applied. A control device 14 changes over the voltage to be applied to the developer regulating member 9, during image formation corresponding to image information. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system or an electrostatic recording system such as a copying machine or a printer.

  Conventionally, as this type of image forming apparatus, for example, one having the configuration shown in FIG. 13 is known. FIG. 13 schematically shows an example of the basic configuration of a conventional image forming apparatus.

  In this example, a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 100 is used as an image carrier. The photosensitive drum 100 has a photosensitive material layer (for example, an organic photosensitive material layer) formed on the surface of a cylindrical base made of aluminum, for example, and is driven to rotate in the direction of an arrow. Around the photosensitive drum 100, a charging roller 101, a laser beam scanning optical system E, a developing device 102 as a developing device, a transfer roller 111, and a cleaner 109 are arranged in order from the upstream side in the rotation direction.

  After the photosensitive drum 100 is uniformly charged by the charging roller 101, an electrostatic latent image is formed on the photosensitive drum 100 by light image irradiation by the laser beam scanning optical system E. Then, a visible image is developed (developed) with toner (developer) in the developing device 102 in accordance with the electrostatic latent image. The charging polarity of the developer is negative. The charge polarity of the developer is the charge polarity of the development that adheres to the image area of the latent image when development is performed, and is the same as the charge polarity of the photosensitive drum in the case of reverse development. That is, when the photosensitive drum is negatively charged by reversal development, the charging polarity of the toner is negative.

  The recording medium, that is, the transfer material P, is fed in synchronism with the formation of the visible image (toner image) from a paper feed port (not shown), and is substantially contacted between the photosensitive drum 100 and the transfer roller 111. A visible image (toner image) is transferred. The image on the transfer material P is melted and fixed by the fixing device 110.

  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 a stirring member 106 that conveys toner in a container to the vicinity of the supply roller 105. It has. Further, a developer regulating blade 104 is provided as a developer regulating member that regulates the amount of toner on the developing roller 103.

  Since the developing roller 103 is in contact with the photosensitive drum 100, the developing roller 103 is formed of an elastic body. Further, the developer regulating blade 104 regulates the toner layer thickness by utilizing the spring elasticity of the metal thin plate.

  A developing bias is applied to the developing roller 103 so that the toner is transferred from the developing roller 103 to the photosensitive drum 100 side by a developing bias power source 107 to have a predetermined potential. Further, as described in Patent Document 1, a blade bias power source 108 is connected to the developer regulating blade 104 in order to stabilize the charge amount of the toner, and a blade bias is applied so as to have a predetermined potential. . There are various types of blade bias power sources 108, such as those having the same potential as the developing bias power source 107 and those supplying different potentials.

  In the conventional system, as described above, in order to keep the toner layer thickness on the developing roller 103 constant, a layer thickness regulating blade pressed against the developing roller 103 with a predetermined pressing force is used. Since the developer regulating blade 104 is made of a metal blade harder than the toner, the developer regulating blade 104 has a problem that the toner deteriorates.

Therefore, in order to solve such problems, a method has been proposed in which a layer thickness regulating blade uses a conductive material that is softer than a toner such as rubber or resin at least at a portion that rubs against the toner (patent). Reference 2).
JP-A-5-11599 JP 11-327291 A

  However, when the image forming operation was performed with the configuration of the conventional example, the following problems were observed.

  FIG. 14 shows the image density for a desired gradation. The horizontal axis becomes closer to a solid image as it goes to the right in the gradation.

  First, in the image forming apparatus shown in the conventional example, a potential difference of 300 V larger (that is, −300 V) is applied to the blade bias power source 108 on the charging polarity (for example, minus) side of the developer than the developing bias power source 107. . The gradation at this time is shown by a broken line G in FIG. As for the image density, although a desired image density was obtained, the gradation of the image density was low. That is, a phenomenon in which toner cannot be developed (hereinafter referred to as “whiteout”) occurs in a highlight portion (a so-called low density image portion, (A) portion in FIG. 14). Further, in the shadow part (so-called medium density part to high density part region, part (B) in FIG. 14), the maximum density is reached quickly. Such gradation is suitable for an image that requires a clear contrast such as characters, but is not suitable for an image that emphasizes gradation such as a photographic image.

  However, when the amount of toner to be developed is suppressed by lowering the voltage of the developing bias power source 107, as shown by the solid line H in FIG. 14, although the density is lowered as a whole, the halftone portion (( The slope between A) and (B) does not change.

  Furthermore, even if the voltage applied to the blade bias power supply 108 is lowered, the amount of toner carried on the developing roller 103 can be suppressed to some extent. However, in this case, so-called toner fusion occurs in which the toner adheres to the developer regulating blade 104.

  When a similar image output is performed by changing the conductivity of the developer regulating blade 104 to an insulating rubber, gradation can be obtained, but conversely, the sharpness of characters is lowered. In addition, a phenomenon that a desired density cannot be obtained at the time of output in the initial stage of use as a developing device occurred.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to control image development that is appropriate for a desired image, thereby preventing image defects such as character crushing and whiteout, and image formation capable of stable image formation over a long period of time. To provide an apparatus.

The above object is achieved by the image forming apparatus according to the present invention. The present invention
An image carrier on which an electrostatic latent image is formed;
A device for visualizing the electrostatic latent image with a developer, comprising: a rotatable developer carrying member; and a developer regulating member for regulating the amount of developer carried on the developer carrying member. A developing device;
A voltage applying device for applying a voltage to each of the developer carrier and the developer regulating member;
A control device for controlling the voltage application device;
In an image forming apparatus having
The developer regulating member changes its resistance value depending on the applied voltage,
The control device can change a voltage applied to the developer regulating member according to image information relating to an image to be formed, and can change a potential difference between the developer carrying member and the developer regulating member. The image forming apparatus is characterized by the above.

  According to the present invention, optimal image formation can be performed according to image information relating to an image to be formed.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

First Embodiment A first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1 shows a schematic configuration of an image forming apparatus 100 according to the first embodiment of the present invention.

  The image forming apparatus 100 according to the present embodiment is a reversal developing system that visualizes a developer (toner) attached to an exposed portion of an electrophotographic photosensitive member as an image carrier, and carries a developer carrying negatively charged toner. A one-component image forming apparatus that performs development by bringing a body into contact with an image carrier. When a positively chargeable toner is used, it can be used as appropriate by reversing the direction of the electric field formed by the voltage applied to each member.

  In this embodiment, the drum-shaped electrophotographic photosensitive member as the image carrier, that is, the photosensitive drum 1 is rotatable in the arrow x direction. The surface of the photosensitive drum 1 is uniformly charged to a negative polarity by a charging roller 2 that is a primary charger (charging device). As the photosensitive drum 1 rotates, the uniformly charged surface is exposed by the exposure device (exposure device) 3. An electrostatic latent image is formed on the photosensitive drum 1 by the disappearance of the charge of the exposed portion.

  To the exposed portion of the electrostatic latent image on the photosensitive drum 1, toner as the developer T contained in the developing device (developing device) 4 is transferred to make the electrostatic latent image visible. In this embodiment, as the developer T, a non-magnetic one-component toner is used. The charging polarity of the toner is negative. The present embodiment is a so-called reversal development system that transfers toner to an exposed portion.

  The toner transferred onto the photosensitive drum 1 is transferred to the transfer material P by a transfer roller 5 as a transfer charger (transfer device). The toner remaining on the photosensitive drum 1 without being transferred is removed from the photosensitive drum 1 by the cleaning device 6.

  The toner on the transfer material P is thermally melted by a fixing device (fixing device) 7 and fixed on the transfer material P to form a permanent image.

  The developing device 4 includes a developing roller 8 as a developer carrying member, a supply roller 12 that supplies toner to the developing roller 8, and a developer as a developer regulating member that regulates the developer amount (toner amount) on the developing roller 8. A regulating blade 9 and a stirring member 13 for conveying toner are provided on the supply roller 12 side. The developer regulating blade 9 has a support member 9a and a contact member 9b.

  The developing roller 8 can be rotated in the direction of the arrow y by a motor 15 as a driving device. Since the developing roller 8 is so-called contact development in which development is performed in contact with the surface of the photosensitive drum 1, the developing roller 8 preferably has elasticity such as rubber. In the present embodiment, a voltage of about −300 V is supplied to the developing roller 8 from the developing bias power source 10. The toner on the developing roller 8 is transferred to the exposed portion on the photosensitive drum 1 due to the difference between the exposed portion potential on the photosensitive drum 1 and the potential supplied from the developing bias power supply 10.

  The developer regulating blade 9 has a metal thin plate as the support member 9a and a semiconductive rubber as the contact member 9b that actually contacts the toner, and uses the spring elasticity of the thin plate to apply the contact pressure. Then, the contact member 9b is brought into contact and contact with the toner and the developing roller 8. As the material of the metal thin plate, stainless steel, phosphor bronze, or the like can be used. In this embodiment, a phosphor bronze thin plate having a thickness of 0.1 mm was used. The toner T is triboelectrically charged by being rubbed with the developer regulating blade 9 and the developing roller 8 to be charged, and at the same time the layer thickness is regulated. A predetermined voltage is supplied from a blade bias power supply 11 to the support member 9 a of the developer regulating blade 9. Reference numeral 117 denotes a power source that is a voltage application device, and includes a developing bias power source 10 and a blade bias power source 11.

  A control circuit (control device) 14 controls the rotational driving of the developing roller 8 and controls the voltage values of the developing bias power supply 10 and the blade bias power supply 11 as voltage application devices.

  The blade bias power supply 11 supplies a voltage to the surface of the contact member 9 b through the support member 9 a of the developer regulating blade 9. The developing bias power supply 10 supplies a voltage to the developing roller 8. As a result, an electric field is formed between the surface of the contact member 9b of the developer regulating blade 9 where the toner is interposed and the surface of the developing roller 8.

  In the conventional image forming apparatus described with reference to FIG. 13, the material of the portion that contacts the toner as the developer regulating blade 104 is conductive rubber or resin, stainless steel, phosphor bronze, or the like. These metals are used.

  In this embodiment, the developer regulating blade 9 is characterized in that, in particular, a semiconductive rubber or resin having an electronic conductive material is used as the material of the contact member 9b, and the resistance value is in the following range. Yes. The resistance value of the developer regulating blade using the material varies depending on the applied voltage.

For example, when the potential difference between the blade bias and the developing roller bias is 10 V, the resistance value of the developer regulating blade 9 (that is, the contact member 9b) is 2 × 10 ⁸ Ω or more. Further, in the region where the potential difference is 100 V or more and at least a part of 100 V to 400 V, the resistance value of the developer regulating blade 9 (that is, the contact member 9b) has a resistance value of 1 × 10 ⁸ Ω or less. To do. That is, by changing the potential difference between the blade bias and the developing roller bias, the resistance value of the developer regulating blade can be 2 × 10 ⁸ Ω or more or 1 × 10 ⁸ Ω or less.

  In this specification, when “the potential difference between the blade bias and the developing roller bias is 10 V”, the “blade bias and developing when the blade bias is increased by 10 V on the charging polarity side of the developer (toner) from the developing roller bias. It means “potential difference of roller bias”.

  Image information relating to the image to be formed is determined, and the potential difference between the blade bias and the developing roller bias is changed to obtain an appropriate amount of toner. By controlling the amount of toner in this manner, image defects such as character collapse and whiteout can be prevented, and stable image formation can be performed over a long period of time.

  FIG. 2 shows an example of resistance characteristics of the developer regulating blade 9 (contact member 9b) used in the present embodiment. Here, the X axis represents the potential difference between the developer regulating blade 9 and the developing roller 8, and the Y axis represents the resistance value of the developer regulating blade 9 (contact member 9b). A method for measuring the resistance value will be described later.

  FIG. 3 shows the amount of toner (hereinafter referred to as “M / A”) per unit area carried on the developing roller 8 with respect to the blade bias. Here, the black circle is a case where the developer regulating blade 9 corresponding to the present invention is used. The white square is when the resistance value of the developer regulating blade is high, the white triangle is when a metal blade whose surface is phosphor bronze is used, and the x mark is when the surface is conductive rubber and a potential difference of 10 V is applied. This is the case when it is lower than a predetermined resistance value.

In the developer regulating blade 9 of the present invention, when the potential difference between the developer regulating blade 9 and the developing roller 8 is 10 V or less, the resistance value of the developer regulating blade 9 shows 5 × 10 ⁸ Ω (FIG. 2). reference). When image formation is performed with the developer regulating blade having the potential difference, the resistance value of the developer regulating blade behaves in the same manner as during insulation. That is, the amount of charge per unit area (hereinafter referred to as “Q / M”) coated on the developing roller 8 that has passed through the developer regulating blade 9 becomes high, and as a result, the amount of toner per unit area (M / M). A) becomes lower. This is because the resistance value of the developer regulating blade 9 is high, and an electric field that can move the toner is not formed between the developer regulating blade 9 and the developing roller 8. Therefore, only the amount of toner carried on the developing roller 8 is carried as if it was worn out by the developer regulating blade 9. As a result, about one toner layer is carried. Accordingly, a high charge amount is obtained by increasing the chances of contact with the developing roller 8 and the developer regulating blade 9. Furthermore, since the surface is close to insulation, the mirror image force acting in the case of a conductor is difficult to work, and blade fusion in which toner stays in the vicinity of the developer regulating blade and the toner melts and adheres to the blade is unlikely to occur. Since the toner has a high Q / M, the gradation property at the time of development becomes high (the gradient of the increase in density becomes small with respect to the increase in the development electric field). The reason why the gradation property at the time of development is high is that when Q / M is high, the charge of the toner layer increases. Therefore, the highlight image is easily developed by the charge of the toner itself. In addition, the toner in the vicinity of the developing roller has a high electrostatic adhesion force to the shadow portion, so that it becomes difficult to develop, and as a whole, the increase in density is small with respect to the increase in the developing electric field, and the inclination becomes small. .

On the other hand, when the potential difference between the developer regulating blade 9 and the developing roller 8 is 100 V or more, the resistance value of the developer regulating blade 9 is 9 × 10 ⁷ Ω (see FIG. 2). When image formation is performed with the developer regulating blade 9 having the potential difference, the developer regulating blade 9 behaves in a manner similar to that during conduction. That is, the Q / M coated on the developing roller that has passed the developer regulating blade 9 becomes low, and the M / A increases conversely. This is because the electric field on the side where the negatively charged toner is urged is formed on the developing roller side between the developing roller and the developer regulating blade, and the toner is pressed against the developing roller side. As a result, the moving speed of the toner becomes close to the rotating speed of the developing roller, and the toner in the developing device more easily enters the developer regulating blade and the nip of the developing roller, thereby increasing the M / A. However, although the M / A increases, since the toner is restricted by the electric field, the opportunity to contact the developing roller and the developer regulating blade is reduced. As a result, Q / M decreases. A toner layer having a low Q / M and a large M / A has low gradation during development. However, from the opposite point of view, an image with excellent contrast can be reproduced instead of reproducing the halftone. Furthermore, M / A becomes larger by widening the potential difference. That is, it is suitable for the case where it is desired to sharpen the outline around the character as in the character image (black circle in FIG. 3).

  A case where the resistance value deviates from the region will be described.

When the potential difference between the developer regulating blade 9 and the developing roller 8 is 10 V or less, when the resistance value is 2 × 10 ⁸ Ω lower, it behaves like the conductive blade. In the case of the conductive blade, when the developing roller is rotated, a current flows between the developing roller and the developer regulating blade even when no voltage is applied (the developing roller and the developer regulating blade have the same potential). The current flows in a direction in which electric charges are supplied from the developer regulating blade to the toner. This is because when the toner that is frictionally charged with the developer regulating blade receives the charge from the developer regulating blade and contacts the developing roller as the toner moves, the charge is transferred to the developing roller and acts as if current flows. Conceivable. It can be considered that the current flows, the mirror image force also works and causes blade fusion. This threshold value is 2 × 10 ⁸ Ω, and when the resistance value falls below this resistance value, current gradually flows due to the rotation of the developing roller without applying a potential difference between the developer regulating blade and the developing roller. At this time, M / A increases, and at the same time, blade fusion is likely to occur when the voltage is 0 V (white Δ and x in FIG. 3).

Conversely, if the resistance of the developer regulating blade is 2 × 10 ⁸ Ω or more, the observed current is a very small amount of 1 μA or less. The upper limit of the resistance value is about 1 × 10 ¹² Ω. This is because at higher resistance values, the resistance value does not decrease even when a potential difference is applied.

Next, if the resistance value of the developer regulating blade does not become 1 × 10 ⁸ Ω or less even when a potential difference of 100 V to 400 V is applied between the developing roller and the developer regulating blade, the increase in M / A cannot be expected. A toner coat suitable for character reproduction cannot be obtained (white square in FIG. 3).

  In the present invention, the case where the potential difference is 10 V as the resistance value of the developer regulating blade 9 is measured for the following reason.

  That is, when the surface potential of the toner carried on the developing roller 8 by the insulating developer regulating blade 9 is measured, a potential of about −10 V is observed as the toner surface potential. That is, it is considered that a potential difference of about 10 V is generated between the toner layer surface and the support member 9a. Furthermore, in the conductive blade 9, current flows even at the same potential as the developing roller 8 rotates. However, even if 0 V is applied during measurement of the developer regulating blade 9, no current flows. It is.

  From the above, a plurality of modes are set as voltages to be applied to the developer regulating blade 9 during image formation. In one mode, that is, when an image that emphasizes gradation, such as a photographic image, is desired, the potential difference applied to the developing roller 8 and the developer regulating blade 9 is set to substantially the same potential. . In the other mode, that is, in the case of obtaining contrast as in a character image, the potential difference is 100V or more, preferably 100V to 400V. This is because if it is less than 100 V, it is easily affected by the resistance of the developing roller or the like, and the effect of the gradient of gradation cannot be obtained sufficiently. Further, if the voltage is set to 400 V or less, discharge easily occurs between the developing roller and the developer regulating blade. Further, the current flowing between the developer regulating blade and the developing roller becomes large, and a high-capacity power source is required. A desirable current value is about 1 to 40 μA.

  When the value of the shape factor SF-1 measured by the image analysis apparatus for toner particles is 100 to 160 and the value of the shape factor SF-2 is 100 to 140, transferability is improved, and the effect of the bias is obtained. It is possible to make it larger.

  Further, it is preferable that at least the developing device is configured as a cartridge that is detachable from the image forming apparatus main body 100A. In this case, the developing device (developing device 4) alone may be a developing cartridge, or in addition to the developing device, the image carrier (photosensitive drum 1), charging device (charging roller 2), cleaning device 6 and the like are integrated. A process cartridge may be used. As a result, the user's labor related to various maintenance work such as toner replenishment and replacement of the developing device after the end of the service life can be reduced, and a stable output image can be obtained with a simple operation.

  Hereinafter, the developing roller 8 and other members, which are features of the present embodiment, will be described.

(Development roller configuration)
As shown in FIG. 4A, the developing roller 8 is a so-called elastic developing roller having an elastic layer 8b on a cored bar 8a.

  In the present embodiment, the elastic layer 8b includes a first layer (base layer) 8b1 made of solid rubber in which carbon is dispersed in budadiene rubber (BR) on a stainless steel core 8a having a diameter of 8 mm (layer 4 mm). Thickness) to form.

  Further, as the second layer (intermediate layer) 8b2, a layer in which a spherical resin of about 20 to 60 μm is dispersed in nitrile rubber (NBR) is formed to have a thickness of about 10 μm (layer thickness). The spherical resin serves to adjust the surface roughness of the developing roller 8.

  A third layer (surface layer) 8b3 is formed on the second layer 8b2. The surface layer 8b3 is made of urethane rubber whose resistance is adjusted by carbon, and has a layer thickness of about 10 μm. Since the resin of the surface layer 8b3 has a purpose of charging the toner by being rubbed with the toner, a resin that can charge the toner to a predetermined polarity is preferably used.

(Development roller material)
As materials for the base layer 8b1 and the intermediate layer 8b2 of the developing roller 8, in addition to the above, silicone rubber, butyl rubber, natural rubber, acrylic rubber, EPDM (ethylene / propylene copolymer), or a rubber mixed thereof, etc. A commonly 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. As the ionic conductive agent, conductivity can be obtained by dispersing an ionic conductive agent such as lithium perchlorate or a quaternary ammonium salt in a binder.

  As the resin binder for the surface layer 8b3, 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, a three-layer structure is used, but the present invention is not limited to this. In order to form the desired surface roughness, a spherical resin is used for the intermediate layer, but it is also possible to use a two-layer structure by utilizing the surface roughness of the base layer.

(Development roller resistance)
As the resistance value of the developing roller 8, it is preferable to adapt the surface resistance and bulk resistance described later to the following values.

As the surface resistance, 2 × 10 ³ Ω to 8 × 10 ¹⁴ Ω can be used. Preferably, it is desirable to use in the range of 5 × 10 ⁴ Ω to 1 × 10 ¹² Ω. This is because if it is less than 2 × 10 ³ Ω, frictional charging to the toner becomes difficult. This is because if it exceeds 8 × 10 ¹⁴ Ω, image density unevenness (ghost) in the previous circumference is likely to occur due to residual charges due to frictional charging.

The bulk resistance is desirably 2 × 10 ⁴ Ω to 5 × 10 ⁸ Ω. Is less than 2 × 10 ⁴ Ω, becomes large current flowing through the elastic layer, because the necessary current capacity is increased. Further, if it exceeds 5 × 10 ⁸ Ω, the current flowing during development tends to be hindered.

(Development roller resistance measurement method)
(1) Roller surface resistance measurement method A roller surface resistance measurement method will be described with reference to FIG. In FIG. 5, a roller 63 to be measured includes a conductive metal core 62 made of stainless steel, an elastic layer 61 formed on the outer periphery thereof, and a roller surface 60. When the roller 63 is a single layer, the elastic layer 61 and the roller surface 60 are made of the same kind of material.

  The electrode 64 includes application electrodes 64a and 64c for applying a voltage, which will be described later, and a measurement electrode 64b. Each of the electrodes has a thickness of 5 mm, and the center is cut into a circular shape. The inner surface of the electrode hollowed out in the circular shape is in contact with the outer periphery of the roller 63 to be measured, and each electrode is disposed with an interval of 5 mm.

The measurement circuit 65 includes a power source Ein1, a resistor Ro1, and a voltmeter Eout1. In this measurement, Ein1: 100V (DC) was performed. For the resistor Ro1, Ro1: 100Ω to 10MΩ can be used. Since the resistance Ro1 is for measuring a weak current, it is preferable to use a resistance value 2 to 4 digits lower than the roller surface resistance to be measured. That is, as long as the roller surface resistance has a resistance of about 1 × 10 ⁸ Ω, or a resistance of 100kΩ as Ro1.

The surface resistance value Rs of the roller is calculated by the following formula (1).
Rs = 2 × Ro1 × (Ein1 / Eout1-1) (Ω) (1)

  Since the surface resistance is measured between the electrodes 64a and 64b and the resistance between the electrodes 64c and 64b in parallel, the substantial resistance value at the 5 mm interval on the roller surface is doubled. 2 ”.

  In this embodiment, the value of Eout1 10 seconds after applying the voltage was measured and obtained.

(2) Method for Measuring Bulk Resistance of Roller Measurement of bulk resistance of a roller will be described with reference to FIG. In FIG. 6, a roller 63 to be measured includes a conductive core 62 made of stainless steel, an elastic layer 61 formed on the outer periphery thereof, and a roller surface 60. When the roller 63 is a single layer, the elastic layer 61 and the roller surface 60 are made of the same kind of material.

  The stainless steel cylindrical member 66 having a diameter of 30 mm rotates in the direction of the arrow at a speed of about 48 mm / sec. At this time, the roller 63 rotates following the rotation of the cylindrical member 66. An end roller 69 is fitted to the end of the roller so as to restrict the amount of penetration into the cylindrical member 66 to 50 μm (in order to make the contact area between the roller and the cylindrical member constant). The end roller 69 has a cylindrical shape whose outer diameter is 100 μm smaller than the outer diameter of the roller 63.

  The load 67 applied to both ends of the roller 63 (62 parts of the conductive core metal) is a load of 1 kg in weight of 500 g on one side, and the roller 63 is pressed against the cylindrical member 66.

The measurement circuit 68 includes a power source Ein2, a resistor Ro2, and a voltmeter Eout2. In this measurement, Ein2: 300 V (DC) was performed. For the resistor Ro2, Ro2: 100Ω to 10MΩ can be used. Since the resistance Ro2 is for measuring a weak current, it is preferable to use a resistance value 2 to 4 digits lower than the bulk resistance of the roller to be measured. That is, if the bulk resistance of the roller has a resistance of about 1 × 10 ⁶ Ω, a resistance of 1 kΩ may be used as Ro2.

The bulk resistance value Rb of the roller is calculated by the following formula (2).
Rb = Ro2 × (Ein2 / Eout2-1) (Ω) (2)

  In the present embodiment, the value of Eout2 10 seconds after applying the voltage was measured and obtained.

(Development roller surface roughness)
The surface roughness of the developing roller 8 is preferably 1 μm to 10 μm in terms of the ten-point average roughness Rz, although it depends on the particle size of the toner used. If the toner particle size to be used is an average volume particle size of 6 μm, a 10-point average roughness Rz of 2 μm to 8 μm can be preferably used. When the toner particle size is smaller, it is preferable to slightly reduce the ten-point average roughness Rz. If the ten-point average roughness Rz is less than 1 μm, sufficient toner conveying force cannot be obtained, resulting in insufficient density. If the average roughness Rz exceeds 10 μm, the toner cannot be sufficiently charged, and so-called “fogging” occurs in which toner adheres to non-image areas. Will occur.

  The ten-point average roughness Rz was defined according to JIS B0601, and a surface roughness tester “SE-30H” manufactured by Kosaka Laboratory was used for measurement.

(Rubber hardness)
The rubber hardness of the developing roller 8 was an Asker C rubber hardness meter (manufactured by Kobunshi Keiki Co., Ltd.). A rubber hardness of 30 to 75 degrees (Asker C) is preferably used. If it exceeds 75 degrees (Asker C), the toner melts due to the rubbing of the developing roller 8 and causes blade fusion or roller fusion, which is not preferable. In addition, the contact state between the developing roller 8 and the photosensitive drum 1 tends to be unstable. If it is less than 30 degrees, it is difficult to use as a developing roller due to permanent deformation due to compression set. More preferably, it is 35 degrees to 60 degrees, and by setting the hardness in this range, triboelectric charging can be performed without applying excessive stress to the toner.

(Development roller manufacturing method)
An example of a method for manufacturing the developing roller 8 in the present embodiment will be described.

  First, an adhesive for adhering rubber and ensuring conductivity is applied onto the cored bar 8a. Then, a solid rubber 8b1 in which carbon resin particles and the like are dispersed is wound around the core metal and placed in a mold. The mold is vulcanized by applying heat and pressure with a press, and the surface is polished after vulcanization to obtain a solid elastic roller. The intermediate layer 8b2 and the surface layer 8b3 can be formed by a roll coater method, a spray method, a dipping method, or the like. The coating thickness of the ion conductive layer is preferably about 3 μm to 50 μm. If it is less than 3 μm, there is a concern about scraping due to rubbing with the photosensitive drum 1, and if it exceeds 50 μm, coating must be repeated many times in order to obtain a desired coating thickness, which is not realistic for production. Because.

(Developer regulating blade)
The developer regulating blade 9 has a thin metal plate as a support member 9a and a contact member 9b that actually contacts the toner. Using the spring elasticity of the thin plate, the toner and the developing roller 8 are brought into contact contact with each other.

  As the form of the contact member 9b, a semiconductive rubber is molded on the support member 9a, a conductive rubber is molded on the support member 9a, and the surface is coated with a semiconductive resin, the support member 9a. The one directly coated with a semiconductive resin can be used. In the present invention, it is necessary to satisfy a resistance value at a predetermined potential difference.

  Among the above-described embodiments, the most preferable one is one in which semiconductive rubber is molded on the support member 9a. The contact member 9a of the developer regulating blade 9 is formed by dispersing conductive powder in an elastomer.

  In the case where a conductive rubber is molded on the support member 9a and the surface thereof is coated with a semiconductive resin, there is an advantage that an inexpensive elastic and conductive rubber can be used. Furthermore, the range of selection as a resin to be applied to the surface layer is expanded.

  Furthermore, the toner can be prevented from deteriorating due to its elasticity.

  A material obtained by directly coating the support member 9a with a semiconductive resin is inexpensive, but can be suitably used for a developer having a short life because it is easily affected by a resistance change due to the film thickness.

  In the contact member 9b formed by dispersing conductive powder in the elastomer, any elastomer may be used as long as it exhibits fluidity before curing, and can be appropriately selected from materials known per se. 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.

  The conductive powder is an electronic conductive material, that is, a so-called electronic conductive system, that is, a material whose resistance decreases as the applied bias is increased. Therefore, a so-called ion conductive system, that is, a so-called resistance that does not change even when the applied bias is increased, cannot be used to obtain a desired resistance. Accordingly, 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. Examples thereof include conductive inorganic powders such as carbon black, carbon beads, carbon filler, potassium titanate, zinc oxide, and titanium oxide, conductive inorganic particles, conductive inorganic filler, and metal oxide. 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 to 500 μm and a DBP oil absorption of 50 to 500 g / dl exhibits an appropriate compatibilization in the elastomer before curing, and diffuses during centrifugal molding. This is particularly preferable in that the gradient dispersion can be achieved. In the present invention, these conductive powders may be used alone or in combination of two or more.

  In the present invention, as one embodiment, after the support member 9a and the contact member 9b are separately formed, when these are integrated, a known conductive adhesive such as urethane, silicone or epoxy is used. be able to. 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.

(Measurement method of resistance of developer regulating blade)
The resistance measurement of the developer regulating blade will be described with reference to FIG. A developing roller 8 and a developer regulating blade 9 are disposed in the developing device 4. The developing roller 8 is coated with a conductive layer of approximately 0Ω around it, or a thin aluminum thin film or the like is wound around to ground the surface. The developer regulating blade 9 is connected to a measuring power source 18A and an ammeter 18B for monitoring current when a voltage is applied. The resistance value with respect to the voltage of the developer regulating blade 9 can be measured by contacting the portion of the surface of the developer regulating blade 9 where the normal toner comes into contact with the aluminum thin film.

  The resistance value of the developer regulating blade 9 is measured from the applied voltage and the ammeter value by changing the voltage of the measurement power supply 18A between about 0 to 400V. When the withstand voltage of the contact member 9b of the developer regulating blade 9 is low, the resistance value of the developer regulating blade 9 may be calculated by subtracting the resistance value of the developing roller 8 after measurement simultaneously with the developing roller 8. .

As the resistance value of the developer regulating blade 9 (that is, the contact member 9b) in this embodiment, the resistance value of the developer regulating blade is 0 V to 10 V when the potential difference between the developing roller 8 and the developer regulating blade 9 is 0V to 10V. Preferably it has 2 × 10 ⁸ Ω or more. Further, it is preferable that the resistance value of the developer regulating blade has a resistance value of 1 × 10 ⁸ Ω or less in at least a part of the region where the potential difference is 100V to 400V.

  The resistance value of the developer regulating blade 9 is the type / specific gravity / amount of the conductive powder added to the contact member 9b, the type / polarity of the elastomer, and molding conditions (for example, the rotational speed and G in the case of centrifugal molding). By appropriately changing the above, it is possible to adjust to the above range.

More specifically, if the resistance value of the developer regulating blade 9 is 2 × 10 ⁸ Ω or more when the potential difference is 0 V to 10 V, almost no current flows through the developer regulating blade 9, and the developer regulating blade 9 The force of the electric field does not reach the toner passing between the developing rollers 8. Further, since the image forming force on the blade surface is small because the resistance value of the developer regulating blade 9 is high, blade fusion does not occur as in the case where a conductive blade is used.

  When the developer regulating blade 9 is in contact with the developing roller 8 using a conductive blade such as only a phosphor bronze thin plate, blade fusion is likely to occur.

Further, in the region where the potential difference is 100 V to 400 V, the resistance value of the developer regulating blade has a resistance value of 1 × 10 ⁸ Ω or less at least in a part of the region. As a result, when there is a potential difference between the developer regulating blade 9 and the developing roller 8, an electric field is formed between the developer regulating blade 9 and the developing roller 8. When an electric field is formed between the developer regulating blade 9 and the developing roller 8, the toner moving between them is frictionally charged, and at the same time, the toner is urged toward the developing roller. At this time, as the toner is energized, more current flows through the developer regulating blade 9 and at the same time, M / A coated on the developing roller 8 increases.

  That is, the action of the developer regulating blade 9 of the present invention has a high resistance value when the potential difference between the developing roller 8 and the developer regulating blade 9 is small. Accordingly, the toner carried on the developing roller 8 is frayed and regulated, and the high Q / M suitable for a photographic image is obtained. Further, in this state, blade fusion hardly occurs as a result. When the potential difference is large, the resistance value is low, and a high M / A suitable for a character image is obtained.

  The thickness of the contact member 9b in the developer regulating blade 9 of the present embodiment can be appropriately determined according to the developer regulating blade molding method, cost, etc., but is usually 10 μm to 5 mm, and 30 μm to 2 mm. Is preferred. If the thickness of the abutting member 9b is less than 10 μm, resistance adjustment becomes difficult, and the resistance tends to vary. If the thickness exceeds 5 mm, the uneven distribution of the conductive powder increases and a dielectric layer is formed, resulting in resistance loss. In terms of practically increasing performance, both are undesirable.

  In the contact member 9b of this embodiment, the surface of the contact member 9b that is in contact with the toner and the developing roller may be a mold surface on the mold side that is in contact with the mold at the time of molding. A mirror surface is preferred. Specifically, the 10-point average roughness Ra is preferably 0.2 μm or less. In this case, it is advantageous in that foreign matters such as dust and dust are less likely to adhere to the surface of the contact portion, and the charging property to the toner can be stabilized for a long time. The toner passing through the blade is difficult to stop, and blade fusion can be prevented.

(Manufacturing method of developer regulating blade)
In this embodiment, after forming the support member 9a and the contact member 9b separately, these are integrated. For example, when the support member 9a and the contact member 9b are integrated, a known conductive adhesive such as urethane, silicone, or epoxy can be used. 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.

  The manufacturing method of the contact member 9b of this embodiment formed the electroconductive layer by carrying out the centrifugal molding using the liquid for electroconductive layer formation containing an elastomer and electroconductive powder.

  The conductive layer forming liquid contains at least conductive powder and an elastomer, and further contains a curing agent, a solvent, and the like as necessary. The concentration, viscosity, and the like of the conductive layer forming liquid can be appropriately adjusted according to the purpose.

  The specific method of centrifugal molding can be appropriately selected depending on the purpose, and examples thereof include a method of applying (flowing) a conductive layer forming liquid to the inner peripheral surface of a rotating mold. There is no restriction | limiting in particular about the shape of a type | mold, a magnitude | size, a structure, etc., Although it can select suitably according to the objective, For example, a cylindrical type | mold etc. whose internal diameter is about 5-100 cm are used.

  In centrifugal molding, it is necessary to solidify and mold the conductive layer forming liquid under centrifugal conditions. That is, it is necessary to proceed simultaneously with the curing reaction of the elastomer such as liquid rubber contained in the conductive layer forming liquid and the dispersion of the conductive powder. Here, if the curing reaction of the elastomer is too early than the dispersion of the conductive powder, the dispersion of the conductive powder is not sufficient. Conversely, if the dispersion of the conductive powder is too early than the curing reaction of the elastomer, the elastomer and the conductive powder cause a phase separation state, and in any case, a conductive layer as a good gradient material cannot be obtained. .

  In order for the curing reaction of the elastomer and the dispersion of the conductive powder to proceed simultaneously, the type / polarity of the elastomer, the type / amount / specific gravity of the conductive powder, the compatibility between the elastomer and the conductive powder, It is preferable to appropriately adjust G, molding temperature, and the like. In the manufacturing method of this embodiment, it is particularly preferable to use two-component urethane rubber or one-component silicone rubber as the elastomer and carbon black as the conductive powder. In the case of this combination, since the compatibility between the two is good, there is an advantage that the conductive layer can be easily made into a good gradient material, and the curing conditions of the elastomer can be easily controlled.

  In general, the rotation speed of the centrifuge is preferably about 400 to 800 rpm when the diameter is about 500 to 1000 mm, and preferably about 1800 to 2500 rpm when the diameter is about 50 to 300 mm. The molding temperature is generally preferably about room temperature to about 180 ° C, but is preferably about 100 to 130 ° C for a urethane system, and preferably about room temperature to about 160 ° C for a silicone system.

  The contact pressure of the developer regulating blade with respect to the developing roller is preferably about 20 g / cm to 100 g / cm of linear pressure. If it is less than 20 g / cm, proper charge cannot be imparted to the toner, resulting in “fogging” and lowering the image quality. If it exceeds 100 g / cm, the external additive mixed in the toner due to pressure or the like is easily peeled off from the toner surface, the toner is deteriorated, and the chargeability of the toner 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 8 and the developer regulating blade 9. 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. The linear pressure is determined when the value of the spring is divided by 1.5 and the unit is g / cm.

(Contact pressure between developing roller and photosensitive drum)
The contact pressure of the developing roller 8 against the photosensitive drum 1 is preferably a linear pressure of 20 g / cm to 120 g / cm in the same measurement as the linear pressure. If the linear pressure is less than 20 g / cm, the contact state becomes unstable. When the linear pressure exceeds 120 g / cm, the external additive mixed with the toner is easily peeled off from the toner surface due to the pressure and the like, and the toner is deteriorated and the chargeability of the toner by the developer regulating blade 9 is lowered. Because it will go.

  FIG. 8 is a diagram showing a sequence according to the present embodiment.

  In FIG. 8, a print output is requested from a personal computer (not shown) or the like (step 1: hereinafter referred to as “S1”). When the print request is confirmed, whether the requested image is an image that emphasizes gradation, such as a photograph, or an image that emphasizes density, such as text, is determined by image area separation (S2) or the like. Determine (S3). An image area separation method in this case, that is, a method for distinguishing characters from images (graphs, photographs, drawings, etc.) is well known to those skilled in the art, and any method can be used. In addition, the request may be entered by a user by entering it on a print request screen of a personal computer or the like without depending on the image area separation and the like may be determined. Moreover, when outputting from a personal computer, since a font is embedded, it is separable also by a font etc.

  As a result of the determination, when an image that emphasizes gradation such as a photographic image is requested, the first mode is set. That is, a bias (-300 V) having substantially the same potential as the developing bias power source is applied to the blade bias power source (S4). As a result, Q / M increases and M / A decreases due to the high resistance value of the blade. As a result of the development, an image with high gradation is obtained (S6). Here, in (S4) of FIG. 8, Vb indicates the output value of the blade bias power source, and Vdc indicates the output value of the developing bias power source. Therefore, in (S4), the output value of the blade bias power supply is the same value as the output value of the developing bias power supply.

  If it is determined that the image is a character image as a result of the image area separation, a bias (−400 V or less) Vb (Vb <Vdc−100) smaller than the developing bias Vdc by −100 V or more is applied to the blade bias power supply in the second mode. Applied (S5). As a result, a current necessary for the toner coating can flow from the developer regulating blade 9. Since the charge can move in the developer regulating blade 9, the toner that has received the charge from the developer regulating blade 9 due to frictional charging is easily transferred to the developing roller 8 side, and the M / A on the developing roller is increased. By developing characters and the like with a lot of toner, it is possible to reproduce characters with very high contrast (S6).

  Then, after confirming the additional print request (S7), the image formation is terminated.

In the present embodiment, as an example, when a blade bias is applied, the bias is set to be −100 V or more lower than the developing bias. However, this applies a voltage such that the resistance value of the blade is 1 × 10 ⁸ Ω or less. Desirably, −400 to −700 V is applied to the blade bias power supply. In other words, the blade bias power supply is applied with a voltage 100V to 400V larger than the developing bias (−300V) on the charging polarity side of the developer, that is, −400 to −700V in this embodiment.

  As described above, the time for applying the blade bias needs to be the same during the formation of at least one image. Here, “under image formation” refers to the time during which an image is formed on one sheet of transfer paper P1. The blade bias is not switched in one sheet of transfer paper P (switching between step 4 and step 5). This is because a gradation discontinuity occurs when the blade bias is switched within one transfer sheet. However, when the transfer paper P is output continuously, it is possible to perform the first and second sheets with different blade biases as shown in FIG.

(Supply roller)
As shown in FIG. 4B, the supply roller 12 includes a foamed foam (hereinafter referred to as “foamed layer”) 12 b on the outer periphery of the conductive core 12 a.

  The foam layer 12b of the supply roller 12 has two functions of supplying the toner to the developing roller 8 and removing the toner that has not contributed to the development.

  The toner on the developing roller 8 is mechanically removed by rubbing the edge of the foam cell.

  Further, when the outermost layer is solid rubber or single-foam sponge rubber, the amount of toner to be carried tends to be small, so that it is difficult to carry the amount of toner necessary for development on the developing roller 8. However, since the toner can be contained in the cell if it is open-celled, it is possible to supply the necessary toner to the developing roller 8.

  As the thickness of the foam layer 12b, 1 to 6 mm can be used. If the thickness of the foamed layer 12b is less than 1 mm, the amount of toner transport decreases, making it difficult to transport the desired toner. Further, if it exceeds 6 mm, the outer diameter shape becomes larger than necessary.

  In the present embodiment, the supply roller 12 is formed of urethane foam rubber (cell diameter 200 to 350 μm) 12b made of open-cell foam on a stainless steel core 12a having an outer diameter of 5 mm with a layer thickness of 5.5 mm. did.

  Examples of the material of the foam layer 12b include NBR rubber (NBR: nitrile rubber), silicone rubber, acrylic rubber, hydrin rubber, ethylene propylene rubber (EPDM), chloroprene rubber, styrene butadiene rubber, isoprene rubber, acrylonitrile butadiene rubber, and composites thereof. Commonly used rubbers such as a mixture can be used.

  As the resistance adjustment of the foam layer 12b, a known ionic conductive agent, inorganic fine particles, carbon black, or the like can be dispersed as appropriate.

  Further, a bias may be applied to the supply roller 12 in order to assist the toner supply to the developing roller 8. By applying a bias for urging negatively charged toner to the developing roller 8 side, the amount of toner carried on the developing roller before the developer regulating blade can be increased. Furthermore, the bias tends to increase the toner density on the developing roller, making it easier to obtain a uniform toner density.

(toner)
In the present embodiment, the one-component developing toner is substantially spherical and / or spindle-shaped in a state where the wax component is not compatible with the binder resin in the tomographic observation of the toner particles using a transmission electron microscope (TEM). And is preferably dispersed in an island shape.

  By dispersing the wax component as described above and encapsulating it in the toner, it is possible to prevent deterioration of the toner, contamination of the image forming apparatus, etc. An image can be formed over a long period of time. Further, since the wax component acts efficiently during heating, the low-temperature fixability and offset resistance are satisfied.

  As a specific method for observing the tomographic plane of the toner particles, the toner particles are sufficiently dispersed in a room temperature curable epoxy resin and then cured in an atmosphere at a temperature of 40 ° C. for 2 days. Use ruthenium trioxide and, if necessary, osmium tetroxide in combination. Thereafter, a flaky sample is cut out using a microtome with diamond teeth, and the tomographic morphology of the toner particles is observed using a transmission electron microscope (TEM).

  In the present embodiment, it is preferable to use a ruthenium tetroxide dyeing method in order to provide a contrast between materials by utilizing a slight difference in crystallinity between the wax component to be used and the resin constituting the outer shell. In the toner particles used in this embodiment, it was observed that the wax component was encapsulated with the outer shell resin.

  In the present embodiment, the wax component having a maximum endothermic peak in the region of 40 ° C. to 130 ° C. at the time of temperature rise in the DSC curve measured by a differential scanning calorimeter is used. Having a maximum endothermic peak in the above temperature range greatly contributes to low-temperature fixing, and effectively exhibits releasability.

  When this maximum endothermic peak is less than 40 ° C., the self-aggregation force of the wax component becomes weak, resulting in deterioration of the high temperature offset resistance and excessively high gloss. On the other hand, if the maximum endothermic peak exceeds 130 ° C., the fixing temperature increases, and it becomes difficult to appropriately smooth the surface of the fixed image. Absent. Further, in the case where granulation and polymerization are carried out in an aqueous medium and a toner is obtained directly by the polymerization method, if the maximum endothermic peak temperature is high, problems such as precipitation of a wax component mainly during granulation are undesirable.

  The maximum endothermic peak temperature of the wax component is measured according to “ASTM D 3418-8”. For the measurement, for example, DSC-7 manufactured by PerkinElmer is used. The temperature correction of the device detection unit uses the melting points of indium and zinc, and the correction of heat uses the heat of fusion of indium. An aluminum pan is used as a measurement sample, and an empty pan is set as a control. After the temperature is raised and lowered once to obtain a previous history, measurement is performed at a rate of temperature rise of 10 ° C./min.

  Specific examples of the wax component include paraffin wax, polyolefin wax, Fischer tropish wax, amide wax, higher fatty acid, ester wax and derivatives thereof, or graft / block compounds thereof.

  In this embodiment, the toner 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. More preferably, 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. It will be something.

  For the shape factors SF-1 and SF-2, 100 toner images enlarged by a magnification of 500 times using FE-SEM (S-800) manufactured by Hitachi, Ltd. are randomly sampled. The image information is a parameter defined by values obtained by introducing the image information into the image analysis apparatus (Luxex 3) manufactured by Nicole through an interface and performing analysis, and calculating from the following formulas (3) and (4).

SF-1 = {(MXLNG) ² / AREA} × (π / 4) × 100 (3)
SF-2 = {(PERI) ² / AREA} × (1 / 4π) × 100 (4)
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 becomes indefinite from a spherical shape. SF-2 indicates the degree of unevenness of the toner particles, and the unevenness of the toner surface becomes remarkable.

  When the above-described 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.

  In terms of rolling resistance, it is desirable that the shape factor SF-1 is small in order to move efficiently in the developer regulating blade.

  In order to increase the transfer efficiency of the toner image, the shape factor SF-2 of the toner particles is 100 to 140, and the value of (SF-2) / (SF-1) is preferably 1.0 or less. . When the toner particle shape factor SF-2 is greater than 140 and the value of (SF-2) / (SF-1) exceeds 1.0, the toner particle surface is not smooth, and the toner particles have a large number of irregularities. The transfer efficiency from the photosensitive drum 1 to the transfer material P or the like tends to be reduced.

  In particular, when the shape factor SF-1 is 160 or less and the shape factor SF-2 is 140, the toner is separated from the developer regulating blade 9 when a potential difference is provided between the developer regulating blade 9 and the developing roller 8. This is effective for preventing blade fusion.

  The weight average particle diameter of the toner can be measured by various methods. In this embodiment, the toner is a multisizer using a Coulter counter. That is, a multisizer II type Coulter counter (manufactured by Coulter Co.) is used as a measuring device, and an interface (manufactured by Nikkiki) that outputs number distribution and volume distribution and a CX-1 personal computer (manufactured by Canon) are connected. Then, a 1% NaCl aqueous solution is prepared using a special grade or first grade sodium chloride as the electrolytic solution. As a measuring method, 0.1 to 5 ml of a surfactant, preferably alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the electrolytic aqueous solution, and 2 to 20 mg of a measurement sample is further added thereto. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 to 3 minutes, and when measuring the toner particle size as an aperture by the multisizer type II of the Coulter counter, a 100 μm aperture is used. taking measurement. The volume and number of toners were measured, and the volume distribution and number distribution were calculated. Then, a weight-based weight average particle diameter obtained from the volume distribution is obtained. In this embodiment, a toner having a weight average particle diameter of 7 μm and a toner having a weight average particle diameter of 4 μm or less is less than 5%.

  Further, as the toner particles used in the present embodiment, it is preferable to use toner particles whose surfaces are coated with an external additive so that the toner has a desired charge amount.

  In this sense, the external additive coverage on the toner surface is preferably 5% to 99%, more preferably 10% to 99%.

  As for the external additive coverage on the toner surface, 100 toner images were randomly sampled using FE-SEM (S-800) manufactured by Hitachi, Ltd., and the image information was obtained from the image analysis device (Luxex 3) manufactured by Nicole via the interface. ) And measure. The obtained image information is binarized since the brightness of the toner particle surface portion and the external additive portion are different, and the area SG of the external additive portion and the area of the toner particle portion (including the area of the external additive portion) are also obtained. Even if it divides into ST, it calculates by following formula (5).

External additive coverage (%) = (SG / ST) × 100 (5)

  The external additive used in this embodiment preferably has a particle size of 1/10 or less of the weight average diameter of the toner particles from the viewpoint of durability when added to the toner. The particle size of the additive means the average particle size obtained by observing the surface of the toner particles with an electron microscope. As the external additive, for example, the following are used.

  Metal oxide (aluminum oxide, titanium oxide, strontium titanate, cerium oxide, magnesium oxide, chromium oxide, tin oxide, zinc oxide, etc.), nitride (silicon nitride, etc.), carbide (silicon carbide, etc.), metal salt (sulfuric acid) Calcium, barium sulfate, calcium carbonate, etc.), fatty acid metal salts (zinc stearate, calcium stearate, etc.), carbon black, silica, etc.

  In this embodiment, auxiliary particles are externally added to the toner particles (100 parts by weight). The externally added auxiliary particles added 1 part by weight of silica as a negative-polarity external additive and 0.1 part by weight of titanium oxide as a positive-polarity external additive. In particular, when a positive external additive is added, it is possible to adjust the fluidity of the toner and to impart stable chargeability to the toner.

  These external additives are used in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 5 parts by weight, based on 100 parts by weight of toner particles. These external additives may be used alone or in combination. Those subjected to hydrophobic treatment are more preferable.

  When the amount of the external additive is less than 0.01 parts by weight, the fluidity of the one-component developer is deteriorated, and the efficiency of transfer and development is lowered. So-called scattering occurs in which toner is scattered.

  On the other hand, when the amount of the external additive exceeds 10 parts by weight, excessive external additive adheres to the photosensitive drum 1 and the developing roller 8 to deteriorate the chargeability of the toner or disturb the image. .

  To measure Q / M and M / A of the toner, the charge amount Q is measured by sucking the toner on the developing roller with a suction type small charge amount measuring device Model 210HS-2A manufactured by Trek. And the weight M attracted | sucked is measurable by taking the difference before and behind suction about the weight of a suction nozzle. Further, by measuring the area of the sucked portion, the area A is measured, and Q / M and M / A can be calculated.

As described above, in this embodiment, it is preferable to use semiconductive rubber or resin as the material of the contact member 9b in the developer regulating blade 9 and set the resistance value within the following range. That is, it is preferable that the resistance value of the developer regulating blade is 2 × 10 ⁸ Ω or more when at least the potential difference between the blade bias and the developing roller bias is 10V. In the region where the potential difference is 100 V to 400 V, it is preferable that the resistance value of the developer regulating blade has a resistance value of 1 × 10 ⁸ Ω or less in at least a part of the region.

  Furthermore, by determining the desired image, changing the potential difference between the blade bias and the developing roller bias, and controlling the appropriate amount of toner to prevent image defects such as text crushing and whiteout, and stable image formation over a long period of time Is possible.

(Examples 1, 2, and 3)
The following evaluation was performed using the developer regulating blade 9 used in the above embodiment of the present invention. The evaluation results are shown in Table 1.

  As an evaluation, it is output immediately after the initial state of the developing device and 5% printing (a state in which toner is attached to an area area of 5% in the image formable area of paper), and at the time of 5000 sheets The sample was output again.

  As evaluation items, image gradation, character reproducibility, fogging, development streaks, and measurements were performed on Q / M and M / A.

(1) Sensory evaluation was performed for image gradation and character reproducibility.
Image gradation ○: The gradation is sufficient △: The gradation is insufficient The character reproducibility ○: The reproduction is sufficient △: The reproduction is insufficient

(2) Measurement of fog The measurement of fog was performed 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 evaluation was performed based on the following evaluation criteria.
○: All fog is less than 1.5% through image endurance.
X: The image output durability is 1.5% or more.
The reason why 1.5% is used as the evaluation criterion is that the fogging of the paper becomes conspicuous when the fog exceeds 1.5%.

(3) Development streaks When development streaks occur, vertical streaks occur in solid images.
○: No vertical stripe ×: Vertical stripe generated

  About Examples 1-3, it has the desired resistance value in this invention. As a result, a desired image can be printed in an optimum state by switching the potential difference between the developing roller and the developer regulating blade according to the image sample. In Example 3, although some resistance values deviate from a desired part, it is possible to obtain a desired image by controlling with, for example, 100 V removed by control. Accordingly, both photographic images and character images can be handled.

  In Table 1, the potential difference between the developing roller and the developer regulating blade is an output difference between the developing bias power source and the blade bias power source, and the blade bias power source side has a larger negative polarity (that is, a charging polarity side of the developer). Have Further, at the potential difference of 0V, the developer regulating blade was measured using a potential difference of 10V.

  However, in Comparative Example 1, since the resistance value with respect to the potential difference was too high, it was suitable for a photographic image but not suitable for a character image. On the contrary, Comparative Example 2 was in a state not suitable for a photographic image even if controlled because of its low resistance.

  In Comparative Example 3, a developer regulating blade made of only phosphor bronze was used, and the potential difference was 0V. As a result, blade fusion occurred, and the toner charge was inhibited by the fusion, resulting in deterioration of fog.

Second Embodiment A second embodiment of the present invention will be described. The image forming apparatus according to the second embodiment is the same as the image forming apparatus according to the first embodiment described with reference to FIG. 1, and the same portions are denoted by the same reference numerals and description thereof is omitted. However, the image forming apparatus of the present embodiment is provided with a counting device 30 that counts the number of printed sheets (see FIG. 1).

  In the first embodiment, the toner is a toner having a weight average particle diameter of 7 μm, and the ratio of the toner having a weight average particle diameter of 4 μm or less is less than 5%. However, considering the cost, it is desirable to reduce the toner classification (particle size selection) and to use many toners. However, when the conventional toner has a wide particle size distribution, especially when a small amount of toner is included in the toner, the small particle size toner tends to be carried on the developing roller in the initial stage of the endurance. Likely to happen. In particular, when a developer regulating blade having a high resistance is used as the resistance value of the developer regulating blade, it is difficult to satisfy the image density.

  In the second embodiment of the present invention, a toner having a weight average particle diameter of 6.5 μm and a toner having a weight average particle diameter of 4 μm or less is 35%.

  Next, the operation of this embodiment will be described with reference to FIG.

  In FIG. 9, a print output is requested from a personal computer (not shown) (S11). When the print request is confirmed, the control device 14 confirms the number of sheets output so far based on the signal from the counting device 30 (S12). N in Step 12 (S12) is a count value of the counting device 30 that counts the number of sheets printed so far. Every time one sheet is printed, the count is incremented by one. The M / A is increased by forcibly applying a large blade bias until the number of prints reaches a certain number. In this embodiment, the desired number of sheets is set to 500. It is desirable that the set number of sheets is suitably changed according to the size of the developing device, the printing speed, and the like. As a guide for the number of sheets, the average particle size of the toner carried on the developing roller is about the same as the average particle size of the toner in the developing device.

  When the number is smaller than the predetermined number, a bias (that is, −400 V or less) smaller by −100 V or more than the developing bias (−300 V in the present embodiment) is applied to the blade bias power source (S17). As a result, a current necessary for the toner coating can flow from the developer regulating blade 9. Since the electric charge can move in the developer regulating blade, the toner that has received the electric charge from the blade due to frictional charging is easily transferred to the developing roller side, and the M / A on the developing roller 8 is increased. Even when a large amount of toner having a small particle size is carried on the developing roller by the supply roller 12, it is possible to output an image satisfying the image density by applying a voltage to the developer regulating blade 9 (S18).

  When the predetermined number of sheets is reached, the toner carried on the developing roller 8 approaches the center particle diameter, and thus image area separation is performed as in the above embodiment. Whether the requested image is an image that emphasizes gradation like a photograph or an image that emphasizes density such as text is determined by image area separation (S14) or the like (S15). As the image area separation method in this case, the above-described known methods can be used. Further, it may be determined by inputting a user's request by describing it on a print request screen of a personal computer without depending on image area separation or the like.

  As a result of the determination, if an image that emphasizes gradation, such as a photographic image, is requested, a bias (-300 V) having substantially the same potential as the developing bias power supply is applied to the blade bias power supply (S16). As a result, Q / M increases and M / A decreases due to the high resistance value of the blade. As a result of development, an image with high gradation is obtained (S18).

  When it is determined that the image is a character image as a result of the image area separation, a bias (−400 V or less) smaller than the developing bias is applied to the blade bias power source (S17). As a result, a current necessary for the toner coating can flow from the developer regulating blade 9. Since the electric charge can move in the developer regulating blade, the toner that has received the electric charge by frictional charging from the blade easily transfers to the developing roller side, and the M / A on the developing roller increases. By developing characters and the like with many toners, it is possible to reproduce characters with very high contrast (S18).

  Then, after confirming the additional print request (S19), the image formation is terminated (S20).

  As described above, in addition to the first embodiment, the developer regulating blade bias is forcibly applied up to a predetermined number of sheets, so that an output satisfying a desired image density can be achieved even for a toner containing a large amount of small particle size toner. Is possible. Thus, the control operation may be switched according to the result of the counting device.

Third Embodiment A third embodiment of the present invention will be described with reference to FIG. FIG. 10 is a schematic diagram of an image forming apparatus according to the present embodiment.

  In this embodiment, the image forming apparatus 100 is a color image forming apparatus, and includes a single drum-shaped electrophotographic photosensitive member, that is, a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, a charging roller 2 as a charging device, an exposure device (exposure device) 3 for providing image information, a developing device 22 for visualizing an electrostatic latent image on the photosensitive drum 1, and an intermediate The transfer member 24 is used.

  The developing device 22 is a rotary developing device and includes a rotary 22x as a rotary support. In this embodiment, a plurality of developing devices (developing devices), that is, a yellow developing cartridge 22Y, a magenta developing cartridge 22M, a cyan developing cartridge 22C, and a black developing cartridge 22K are mounted on the rotary 22x.

  In this embodiment, the color image forming apparatus is an electrophotographic color printer, and image data is input from a personal computer, a workstation, or the like (not shown). Then, based on this image data, it is decomposed into four colors of yellow Y, magenta M, cyan C, and black K, and toner images of each color are sequentially formed from the decomposed image data. Next, the toner images of the respective colors are superimposed on the intermediate transfer member 24 to form a color image, and this color image is collectively transferred to a transfer material (recording medium) P such as paper to obtain a full color image.

  As described above, the image forming apparatus according to the present embodiment employs a rotary developing device configured by mounting a plurality of developing units (developing devices), that is, developing cartridges 22Y, 22M, 22C, and 22K in the rotary 22x. Thus, a so-called rotary color printer is obtained.

  In this embodiment, the image forming apparatus includes a photoconductive organic photosensitive drum 1 as an image carrier, and when the image forming operation starts, the photosensitive drum 1 is rotationally driven in the direction of an arrow q. . The surface of the photosensitive drum 1 is uniformly charged to a predetermined dark portion potential by applying a bias to a core of a charging roller 2 as a contact charging device. Next, scanning exposure is performed with a laser beam that is ON / OFF controlled by the exposure device 3 in accordance with yellow (Y) image data of the first color, and a first electrostatic latent image is formed as a bright portion potential. Is done.

  The electrostatic latent image formed in this manner is developed and visualized by a developing device (developing cartridge) mounted in the rotary 22x of the developing device 22. The rotary 22x has a configuration in which the first developing cartridge 22Y, the second developing cartridge 22M, the third developing cartridge 22C, and the fourth developing cartridge 22K are mounted and integrated. Then, when the image of each color is formed, it is rotated and moved to the position opposite to the photosensitive drum (in the direction of the arrow r).

  The first developing cartridge 22Y includes yellow (Y) toner as the first color toner, and the second cartridge 22M includes magenta (M) toner as the second color toner. . Further, the third developing cartridge C contains cyan (C) toner as the third color toner, and the fourth developing cartridge 22K contains black (K) toner as the fourth color toner. .

  A developing cartridge (22Y, 22M, 22C, 22K) positioned at a developing position facing the photosensitive drum 1 is a developing roller 8 (8Y) as a developer carrying member carrying toner regulated to a predetermined layer thickness. , 8M, 8C, 8K) are rotationally driven by the motor 23. Then, development is performed by applying a predetermined bias to the core of the developing roller 8. The yellow Y, magenta M, cyan C, and black K developing cartridges 22Y, 22M, 22C, and 22K can be individually replaced as one cartridge (developing cartridge) depending on the degree of wear.

  First, the first electrostatic latent image is developed and visualized by a first developing cartridge 22Y containing yellow (Y) toner as a first color toner. The developing method can be used regardless of contact / non-contact, but in this embodiment, a contact developing method using a non-magnetic one-component toner in which image exposure and reversal development are combined is used.

  The visualized toner image of the first color has a releasability from the conductive elastic layer on the cylinder at the first transfer portion N1, which is a nip portion with the intermediate transfer member 24 as the second image carrier. Electrostatic transfer (primary transfer) is performed on the surface of the intermediate transfer member 24 formed from the surface layer.

  The intermediate transfer member 24 has a circumferential length longer than the length of the maximum transfer material that can be passed, and is pressed against the photosensitive drum 1 with a predetermined pressing force. Then, the photosensitive drum 1 is rotationally driven in a direction opposite to the rotational direction (q direction) of the photosensitive drum 1 (direction of the arrow u) at a circumferential speed substantially equal to the circumferential speed of the photosensitive drum 1 (the photosensitive drum 1 at the contact portion N1). The surface and the surface of the intermediate transfer member 24 move in the same direction).

  The toner image formed on the surface of the photosensitive drum 1 as described above is applied by applying a voltage (primary transfer bias) having a polarity opposite to the charging polarity of the toner to the cylinder portion of the intermediate transfer member 24. Then, electrostatic transfer (primary transfer) is performed on the surface of the intermediate transfer member 24.

  The toner remaining on the surface of the photosensitive drum 1 after the primary transfer is removed by the cleaning device 6 to prepare for the next latent image formation.

  The same process is repeated. That is, a second color toner image developed with magenta (M) toner, a third color toner image developed with cyan (C) toner, and a fourth color toner image developed with black (K) toner. Sequentially transferred and laminated on the surface of the intermediate transfer member 24. As a result, a color toner image is formed.

  Thereafter, the transfer belt 25 that has been separated from the surface of the intermediate transfer member 24 is pressed against the surface of the intermediate transfer member 24 with a predetermined pressing force and is driven to rotate. The transfer belt 25 includes a transfer roller 17. At the second transfer site N2, a voltage (secondary transfer bias) having a polarity opposite to the charging polarity of the toner is applied to the transfer roller 17. As a result, the color toner image laminated on the surface of the intermediate transfer member 24 is batch transferred (secondary transfer) onto the surface of the transfer material P conveyed at a predetermined timing, and the transfer material P is transferred to the fixing device 7. Be transported. The transfer material P is discharged to the outside after the toner image is fixed as a permanent image by the fixing device 7, and a desired color print image is obtained.

  Further, the toner remaining on the surface of the intermediate transfer member 24 after the secondary transfer is removed by the intermediate transfer member cleaning device 16 that comes into contact with the surface of the intermediate transfer member 24 at a predetermined timing.

  FIG. 11 is a configuration diagram illustrating developing cartridges 22Y, 22M, 22C, and 22K that store toners of yellow Y, magenta M, cyan C, and black K, which are the developing devices of this embodiment.

  The developing cartridges 22Y, 22M, 22C, and 22K can be attached to and detached from the rotary color printer that is the image forming apparatus 100 shown in FIG. 10 by opening and closing a developing cartridge replacement cover (not shown). The In FIG. 10, the cyan developing cartridge 22C at the take-out position can be taken out in the upward arrow D direction.

  In the rotary color printer 100 shown in FIG. 10, it is necessary to attach and detach the developing cartridge at the take-out position. Therefore, in FIG. 10, when replacing the yellow, magenta, and black developing cartridges 22Y, 22M, and 22K other than the cyan developing cartridge 22C, the rotary 22x is rotated. Then, it is necessary to rotate the cartridge to be taken out to the attaching / detaching position (the position of the developing cartridge 22C in FIG. 10).

  Hereinafter, for the sake of simplicity, the case of the yellow (Y) toner developing cartridge 22Y will be described, but the same applies to the developing cartridges 22M, 22C, and 22K of other colors. FIG. 12 is a flowchart showing this embodiment.

  A developing cartridge 22Y of the present embodiment shown in FIG. 11 is a reversal developing device in which nonmagnetic one-component Y toner is accommodated as a developer.

  The developing cartridge 22Y is a developing roller 8Y that performs development by contacting the photosensitive drum 1 while being rotated in the direction of arrow e in the figure, and a toner supply device that supplies toner to the developing roller 8Y by being rotated in the direction f in the figure. As a supply roller 12Y. Further, a developer regulating blade 32Y as a developer regulating member for regulating the toner application amount and the charge amount on the developing roller 8Y, and an agitating member 13Y for feeding and agitating the toner to the supply roller 12Y are provided.

  This will be described with reference to FIG. When a print output is requested from a personal computer (not shown) (S21), it is determined whether the requested image is an image that emphasizes gradation like a photograph or an image that emphasizes density such as text. Then, determination is made by image area separation (S22) or the like (S23). As the image area separation method in this case, the above-described known methods can be used. In addition, the request may be entered by a user by entering it on a print request screen of a personal computer or the like without depending on the image area separation and the like may be determined.

  As a result of the above determination, when an image that emphasizes gradation, such as a full-color photographic image, is requested, all blade bias power supplies have a bias (for example, approximately the same potential as the development bias power supply) according to the first mode. , -300V) is applied (S24). As a result, it is possible to output a full color image that emphasizes gradation. Here, in (S24) of FIG. 12, Vb indicates the output value of the blade bias power source, and Vdc indicates the output value of the developing bias power source for each color. In Vb and Vdc of FIG. 12, Y, M, C, and K in parentheses indicate each color of the developing device.

  If it is not only a photographic image (NO in S23), it is determined whether it is only a character (S25). If it is determined that only the characters are present, a bias (−400 V or less) smaller than the developing bias by −100 V or more is applied to all blade bias power supplies (S26).

  As a result, a current necessary for the toner coating can flow from the developer regulating blade 9. Since the charge can move in the developer regulating blade 9, the toner that has received the charge from the blade 9 due to frictional charging is easily transferred to the developing roller, and the M / A on the developing roller 8 is increased. By developing characters and the like with a large amount of toner, it is possible to reproduce characters with very high contrast (S28).

  If it is determined that characters and photographs are mixed (S25), a bias that emphasizes gradation is applied to yellow Y, magenta M, and cyan C, and a bias that emphasizes character reproduction is applied to black K. That is, a bias (-300 V) having substantially the same potential as that of the developing bias power supply is applied to the blade bias power supplies of yellow Y, magenta M, and cyan C that are chromatic colors. That is, Vb (Y), (M), (C) = Vdc (Y), (M), (C). A bias (−400 V or less) smaller than the developing bias is applied to the black K blade bias power source. That is, Vb (K) <Vdc (K) -100. In other words, in a mixed image of images and characters, gradation properties such as photographs and black character quality are required. Therefore, in the mixed image, the portion and color character determined to be photographic tone are reproduced with yellow Y, magenta M, and cyan C, and the character portion is performed with black K.

  After the blade bias is determined, the operation for image formation (S28) is started.

  In FIG. 10, as the photosensitive drum 1 rotates, the rotary 22 x starts to revolve so that the first color developing cartridge 22 </ b> Y comes to a position facing the photosensitive drum 1.

  When the developing cartridge 22Y for the first color (yellow Y) comes to a position facing the photosensitive drum 1, the developing roller 8Y starts to rotate before preparation. At the same time, a voltage is supplied from the developing bias power source 19 and the blade bias power source 20 as voltage applying devices according to the control of the control unit (control device) 21. At this time, a voltage of about −300 V is applied from the developing bias power source 19 to the developing roller 8Y in this embodiment, and a bias as a result of the above determination is applied from the blade bias power source 20.

  When the image formation for the first color is completed, the rotation of the developing roller 8Y is turned off, and the rotary 22x revolves during the next color (magenta M) image formation. During the revolution of the rotary 22x, the voltage supply from the developing bias power source 19 and the blade bias power source 20 is turned off.

  The revolution of the rotary 22x is completed, and the developing cartridge 22M for the second color (magenta M) stops at the position facing the photosensitive drum 1.

  Then, similarly to the first color (yellow), the developing roller 8M starts to rotate before preparation. At the same time, a voltage is supplied from the developing bias power source 19 and the blade bias power source 20.

  The above operation is performed up to the third color (cyan C) and the fourth color (black K).

  As described above, it is possible to provide an image forming apparatus capable of outputting a desired image by determining the blade bias for each color.

  When the image formation up to the fourth color is completed, the rotation of the developing roller 8K is turned off, and the rotary 22x revolves. Prior to the revolution of the rotary 22x, the voltage supply from the developing bias power source 19 and the blade bias power source 20 is turned off.

  Then, after confirming the additional print request (S29), the image formation is terminated (S30).

  In the end operation of image formation, the revolution of the rotary 22x is completed, the intermediate transfer member 24, the photosensitive drum 1 and the like are rotated to the rear of the main body for the next printing, and the photosensitive drum 1 is stopped when the main body is rotated backward.

As described above, in this embodiment, it is preferable to use semiconductive rubber or resin as the material of the contact member 9b in the developer regulating blade 9 and set the resistance value within the following range. That is, it is preferable that the resistance value of the developer regulating blade can be 2 × 10 ⁸ Ω or more at least when the potential difference between the blade bias and the developing roller bias is 10V. In the region where the potential difference is 100 V to 400 V, it is preferable that the resistance value of the developer regulating blade has a resistance value of 1 × 10 ⁸ Ω or less in at least a part of the region.

  Furthermore, the desired image including the color image is judged, the potential difference between the blade bias and the developing roller bias is changed for each color, and an appropriate amount of toner is controlled to prevent image defects such as text crushing and whiteout, for a long period of time. Stable image formation can be performed.

1 is a schematic configuration diagram illustrating an image forming apparatus according to a first embodiment of the present invention. It is a figure which shows the resistance value of the developer control blade which concerns on the 1st Embodiment of this invention. It is a figure which shows the toner coat amount which concerns on the 1st Embodiment of this invention. FIG. 3 is a schematic sectional view of a developing roller and a supply roller. It is explanatory drawing of the surface resistance measuring method of a roller. It is explanatory drawing of the method of measuring the resistance of the bulk of a roller. It is explanatory drawing of the method of measuring the resistance of a developer control blade. It is a figure for demonstrating the sequence which concerns on the 1st Embodiment of this invention. It is a figure for demonstrating the sequence which concerns on the 2nd Embodiment of this invention. It is a schematic block diagram which shows the image forming apparatus which concerns on the 3rd Embodiment of this invention. It is a schematic block diagram of the developing cartridge which concerns on the 3rd Embodiment of this invention. It is a figure for demonstrating the sequence which concerns on the 3rd Embodiment of this invention. It is a schematic block diagram which shows the conventional image forming apparatus. It is a figure explaining the relationship between gradation and image density.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging roller (charging device)
3 Exposure unit (exposure device)
4 Developer (Developer)
5 Transfer roller (transfer device)
6 Cleaning device 7 Fixing device (fixing device)
8, 8Y, 8M, 8C, 8K Development roller (developer carrier)
9 Developer regulating blade (Developer regulating member)
9a Developer regulating blade support member 9b Developer regulating blade contact member 10 Development bias power supply (voltage application device)
11 Blade bias power supply (voltage application device)
12, 12Y, 12M, 12C, 12K Supply roller 13, 13Y, 13M, 13C, 13K Stirring member 14 Control circuit (control device)
15 Motor 16 Intermediate transfer member cleaning device 17 Transfer roller 19 Development bias power supply (voltage application device)
20 Blade bias power supply (voltage application device)
21 Control unit (control device)
22 Developing units 22a, 22b, 22c, 22d Developing cartridge (developing device)
22x Rotary 23 Motor 24 Intermediate transfer member 25 Transfer belt 30 (30Y, 30M, 30C, 30K) Developer regulating blade support member 31 (31Y, 31M, 31C, 31K) Developer regulating blade contact member 32 (32Y, 32M, 32C, 32K) Developer regulating blade (Developer regulating member)
117 Power P Transfer material T Toner (Developer)

Claims (9)

An image carrier on which an electrostatic latent image is formed;
A device for visualizing the electrostatic latent image with a developer, comprising: a rotatable developer carrying member; and a developer regulating member for regulating the amount of developer carried on the developer carrying member. A developing device;
A voltage applying device for applying a voltage to each of the developer carrier and the developer regulating member;
A control device for controlling the voltage application device;
In an image forming apparatus having
The developer regulating member changes its resistance value depending on the applied voltage,
The control device can change a voltage applied to the developer regulating member according to image information relating to an image to be formed, and can change a potential difference between the developer carrying member and the developer regulating member. An image forming apparatus. The resistance value of the developer regulating member is 2 × 10 ⁸ Ω or more when the potential difference between the developer carrying member and the developer regulating member is 10V, and 1 × 10 ⁸ Ω or less when the potential difference is 100V or more. The image forming apparatus according to claim 1, wherein:   The image forming apparatus according to claim 1, wherein the developer regulating member is a semiconductive resin or a semiconductive rubber containing an electronic conductive material.   4. The control device according to claim 1, wherein the image information is a character image or a photographic image, and changes a voltage applied to the developer regulating member. 5. Image forming apparatus.   The control device is configured so that the voltage applied to the developer regulating member is larger on the charging polarity side of the developer when the image information is a character image than when the image information is a photographic image. 5. The image forming apparatus according to claim 4, wherein control is performed. The controller is
When the image information is a character image, a voltage higher than the voltage applied to the developer carrying member by at least 100 V or more and on the charging polarity side of the developer is applied to the developer regulating member,
6. The image according to claim 4, wherein, when the image information is a photographic image, a voltage is applied to the developer regulating member so as to be approximately the same potential as a voltage applied to the developer carrying member. Forming equipment.   The image forming apparatus according to claim 1, further comprising a counting device that counts the number of printed sheets, wherein the control operation of the control device is switched according to a result of the counting device.   The image according to any one of claims 1 to 7, wherein the developer has a shape factor SF-1 of 100 to 160 and a shape factor SF-2 of 100 to 140. Forming equipment.   The image forming apparatus according to claim 1, wherein the developing device is configured as a cartridge that is detachable from the main body of the image forming apparatus.

Images