JP2005055929A - Developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a satisfactory developing device using one-component developer in which development characteristics are stabilized by the stabilization of a toner charge ratio or the stabilization of the electrical properties of peripheral members around a development roller, and the occurrences of development ghosts are eliminated by the prevention of image quality degradation caused by dielectric break down of a toner layer or overcurrent. <P>SOLUTION: A difference in particle diameter between a white image development part and a black image development part is made small. Thereby, development ghosts caused by a change in charge ratio is prevented and satisfactory development is ensured. This hinders the occurrences of development ghosts. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention includes a developer carrying member that carries a one-component developer on the surface and that develops an electrostatic latent image in contact with the electrostatic latent image carrying member, and a developer that supplies the developer to the developer carrying member. The present invention relates to a developing device including a supply member and a developer layer regulating member that abuts the developer carrying member and regulates a layer thickness of the developer supplied by the developer supply member.

  An image forming apparatus employing an electrophotographic system such as a copying machine or a printer includes a developing device for developing an electrostatic latent image formed on the surface of the photoreceptor.

  In recent years, in response to a request for downsizing of an image forming apparatus, downsizing of a developing apparatus has been strongly demanded, and a technique for ensuring development performance at that time is required.

  For example, a developing roller of a magnetic brush system that transports a two-component developer composed of toner and a magnetic carrier to a developing area facing the photosensitive member using magnetic force is provided, and the developer is put into the developing tank after development. A developing device that can be recovered has been put into practical use.

  In order to stabilize the development in this method, it is necessary to replenish consumed toner and control the ratio of the toner contained in the developer, that is, the toner concentration to be constant.

  Usually, in the developing device using the magnetic brush developing method described above, the proportion of the carrier in the developer is larger, the developing tank for storing the developer becomes larger, and the developing device tends to be larger as a whole. In addition, it is necessary to control the toner concentration, and at the same time, a stirring member or the like for making the charge amount of the toner in the developer constant is necessary. It was.

  On the other hand, in recent years, a developing apparatus that performs development using a one-component developer, that is, a toner that is a one-component developer having no carrier, has been proposed and put into practice. In the developing device using such a one-component developer, it is not necessary to control the toner concentration, and the volume of the developing tank can be greatly reduced by the absence of the carrier, and thus the developing device can be miniaturized. In accordance with this, the simplicity of maintenance and the like is also excellent. That is, since there is no need to replace the developer due to deterioration of the deteriorated developer, especially the carrier, maintenance for the replacement becomes unnecessary.

  Further, it is only necessary to replenish the toner, it is not necessary to detect the toner density, and control for that purpose is not required. In particular, in a developing device using a one-component toner, it is only necessary to replenish the toner when necessary.

  In the developing device configured as described above, in order to faithfully develop the electrostatic latent image formed on the photoreceptor, a predetermined voltage is applied to each member constituting the developing device, such as a developing roller and a supply roller. Like to do.

  Therefore, the electrical characteristics of the toner and each member are a major factor that determines the development characteristics. In particular, the charge amount of the toner and the resistance value of the developing roller greatly affect the developing characteristics.

  The relationship between the specific charge q / m (the charge amount per unit mass) of the toner and the development characteristics is the characteristic shown in FIG. 10. When the specific charge is small, the potential difference from the development start voltage to the development end voltage is small. Hereinafter, such characteristics are referred to as “development gamma”. Conversely, when the specific charge is large, the potential difference from the development start voltage to the development end voltage increases. Hereinafter, such a characteristic is referred to as “development gamma falls asleep”. Therefore, in a developing device having a large change in toner specific charge, a change in development characteristics becomes large and a good image cannot be formed. In the conventional one-component developing apparatus, since the specific charge fluctuation cannot be sufficiently suppressed, a problem of image quality deterioration such as development ghost has occurred.

  Further, the relationship between the developing roller resistance value and the developing characteristic is the characteristic shown in FIG. 8, and the larger the resistance value, the lower the developing gamma. For example, when a conventionally proposed high-resistance developing roller is used, the resistance value fluctuates greatly due to the influence of temperature and humidity, so that the development characteristics change greatly, for example, the image density greatly fluctuates. It became. In addition, there has been a problem of image quality deterioration such as development ghost caused by charges accumulated on the surface of the high resistance layer of the developing roller.

  Therefore, in developing devices using one-component developers, it is proposed to stabilize toner charging characteristics by prescribing charge control agents and external additives, or to stabilize developing characteristics by reducing the developing roller resistance. However, it is still insufficient for high image quality.

  That is, regarding the specific charge variation of the one-component developer, specific charge variation due to the particle size distribution of the toner is fundamentally present, so that the specific charge varies at the same time as the particle size variation occurs.

  Further, regarding the developing roller resistance value, when a high resistance developing roller is used, a problem of development ghost due to the charge accumulated on the surface of the high resistance layer occurs. When the low resistance developing roller is used, the dielectric breakdown of the toner layer occurs. Further, there arises a problem that image quality is deteriorated by overcurrent.

  In view of the above problems, the present invention stabilizes development characteristics in a developing apparatus using a one-component developer by stabilizing the toner specific charge and stabilizing the electrical characteristics of peripheral members centering on the developing roller. An object of the present invention is to provide a good developing device that prevents image quality deterioration due to toner layer dielectric breakdown and overcurrent and eliminates development ghosts.

  In particular, the object of the present invention is to focus on the fact that a difference occurs in the particle size variation amount depending on the image pattern and the development ghost is generated. It is an object of the present invention to provide a developing device that can prevent the occurrence and can perform development satisfactorily.

  The present invention includes a developer carrying member that carries a one-component developer on the surface and that develops an electrostatic latent image in contact with the electrostatic latent image carrying member, and a developer that supplies the developer to the developer carrying member. A supply member, a developer layer regulating member that contacts the developer carrier and regulates a layer thickness of the developer supplied by the developer supply member, the developer carrier, and the electrostatic latent image carrier And a reset member that contacts the developer carrying member and neutralizes or removes the developer remaining on the developer carrying member, the developer has CV = 100 × The CV value [%] representing the volume particle size distribution defined as (standard deviation / average value) is 25% or more and 34.6% or less, and the voltage applied to the developer carrier is Va. [V], and the voltage applied to the reset member is Vd [V], V A developer in which the developer is formed in a predetermined layer thickness by applying a voltage so that the sign of −Vd is the same polarity as the charging polarity of the developer and | Va−Vd | ≧ 100 [V] Development carried by the developer carrying member when the carrying member has developed a black image and then the developer is supplied by the developer supplying member and is again formed to have a predetermined layer thickness by the developer layer regulating member. After the developer carrying member having an average volume particle diameter of the developer of Dbk and the developer formed in a predetermined layer thickness performs white image development, the developer is supplied by the developer supply member, and the developer layer regulating member When the average volume particle size of the developer carried by the developer carrying member when it is formed again to have a predetermined layer thickness is Dwt, Dbk and Dwt satisfy Dwt / Dbk> 0.8. In addition, the developer carried by the developer carrier In this case, the variation in particle size caused by an image pattern developed in the past is limited.

  According to the present invention, by reducing the particle size variation in the white image developing portion and the black image developing portion, it is possible to eliminate the development ghost due to the specific charge variation, and to achieve good development.

  The present invention will be described below with reference to the drawings.

  FIG. 1 is a block diagram showing a developing device according to the present invention disposed opposite to a photosensitive member as a latent image carrier of an image forming apparatus. FIG. 4 is a configuration diagram showing a main part of the structure of the image forming apparatus including the developing device in FIG.

  First, a schematic configuration of the image forming apparatus will be described with reference to FIG. The photosensitive member 1 is an image carrier that is disposed at substantially the center of the main body of the image forming apparatus and carries an electrostatic latent image formed in a drum shape that is rotationally driven at a constant speed in the direction of an arrow during an image forming operation. Various image forming process means are arranged so as to face the periphery of the photoreceptor 1.

  The means (apparatus) constituting the image forming process includes a charger 2 for uniformly charging the surface of the photoreceptor 1, an optical system (not shown) for irradiating an image 3 with light corresponding to the image, and exposure by the optical system. As a result, the developing device 4 according to the present invention for visualizing the electrostatic latent image formed on the surface of the photosensitive member 1, a sheet shape on which the developed image (image of the toner 10) is appropriately conveyed A transfer device 5 for transferring to a sheet P of paper, a cleaning device 6 for removing residual developer (toner) that has not been transferred to the surface of the photoconductor 1 after transfer, a static eliminator 7 for removing charged charges remaining on the surface of the photoconductor 1 and the like. And arranged in the rotation direction of the photosensitive member 1 in this order.

  The sheet P is stored in a large amount, for example, in a tray or a cassette, and the stored sheet is fed one sheet by a feeding means (not shown), and the photoreceptor 1 on which the transfer unit 5 described above is arranged. Are transferred to the transfer area opposite to the front end of the toner image so as to coincide with the leading edge of the toner image formed on the surface of the photoreceptor 1. The transferred paper P is peeled off from the photoreceptor 1 and sent to the fixing device 8.

  The fixing device 8 fixes an unfixed toner image transferred onto a sheet as a permanent image, and a surface opposed to the toner image is heated from a heat roller heated to a temperature for melting and fixing the toner. In other words, a pressure roller or the like that is pressed against the heat roller to bring the paper P into close contact with the heat roller is provided. The paper P that has passed through the fixing device 8 is discharged out of the image forming apparatus onto a discharge tray (not shown) via a discharge roller (not shown).

  If the image forming apparatus is a copying machine, the optical system (not shown) irradiates the copy original with light and applies reflected light from the original as the optical image 3. If the image forming apparatus is a printer or a digital copying machine, the optical system emits a light image obtained by driving a semiconductor laser on and off according to image data. Particularly in a digital copying machine, image data obtained by reading reflected light from a copy original with an image reading sensor (CCD element or the like) is input to the optical system including the semiconductor laser, and an optical image corresponding to the image data is output. Like to do. In the printer, the light image is converted into an image corresponding to the image data from another processing device such as a word processor or a personal computer, and this is irradiated. This conversion into an optical image uses not only a semiconductor laser but also an LED element, a liquid crystal shutter, and the like.

  As described above, when the image forming operation in the image forming apparatus is started, the photoconductor 1 is rotationally driven in the direction of the arrow, and the surface of the photoconductor 1 is uniformly charged by the charger 2 to a potential of a specific polarity. After this charging, the optical image 3 is irradiated by the optical system (not shown), and an electrostatic latent image corresponding to the optical image is formed on the surface of the photoreceptor 1. In order to visualize this electrostatic latent image, it is developed by the next developing device 4. In the present invention, this development is performed with a one-component developer, and the toner is selectively attracted to the electrostatic latent image formed on the surface of the photoreceptor 1 by, for example, electrostatic force, and development is performed.

  The toner image on the surface of the photoreceptor 1 developed in this manner is electrostatically transferred by a transfer device 5 disposed in the transfer area onto a sheet P that is conveyed in synchronization with the rotation of the photoreceptor 1 as appropriate. . In this transfer, the transfer device 5 charges the back surface of the paper P with a polarity opposite to the charging polarity of the toner, thereby transferring the toner image to the paper P side.

  After the transfer, a part of the toner image that has not been transferred remains on the surface of the photoconductor 1, and this residual toner is removed from the surface of the photoconductor 1 by the cleaning device 6 and removed to reuse the photoconductor 1. The surface of the photoreceptor 1 is neutralized by the electric device 7 to a uniform potential, for example, approximately zero potential.

  On the other hand, the transferred paper P is peeled off from the photoreceptor 1 and conveyed to the fixing device 8. In the fixing device 8, the toner image on the paper P is melted and pressed and fused to the paper P by pressure applied between the rollers. The sheet passing through the fixing device 8 is discharged as an image-formed sheet P to a discharge tray (not shown) provided outside the image forming apparatus.

  Next, the structure of a developing device that performs development with a one-component developer will be described with reference to FIG. The developing device 4 rotatably supplies a developing roller 41 and the one-component developer 10 to the developing roller 41 side in a developing tank 40 containing a one-component developer, for example, a non-magnetic one-component developer (toner) 10. An agitator or screw roller 9 for feeding the one-component developer 10 to be replenished as necessary into the developing tank 40 is provided on the right side of the developing tank 40 in the drawing.

  The developing roller 41 provided in the developing tank 40 is rotated in the same direction in the developing area facing the photoconductor 1 in order to convey the toner to the developing area facing the photoconductor 1 partially exposed. It is provided to be. The above-described supply roller 42 is pressed against the developing roller 41.

  The developing roller 41 is configured, for example, by coating the surface of a metal roller (including a rotating shaft) with a polymer elastic body. As the polymer elastic body, when a carbon dispersed in polyurethane or the like or an ion conductive solid rubber is used, a predetermined resistance value that does not cause toner fusion or the like can be maintained, which will be described later. Thus, it works effectively when supplying the developing bias voltage. A specific example of the configuration of the developing roller 41 used in the present invention will be described later.

A driving motor (not shown) is connected to the developing roller 41, and the developing roller 41 is rotationally driven in the direction of the arrow in the drawing. The one-component non-magnetic toner 10 is attracted to the surface of the rotating developing roller 41 and conveyed to a developing region facing the surface of the photoreceptor 1. Since the developing roller 41 is pressed against the surface of the photoreceptor 1, the pressed area becomes a developing area, and the one-component developer 10 is attracted to the electrostatic latent image on the surface of the photoreceptor 1 and developed. It will be. The development area where the developing roller 41 and the photosensitive member 1 are in contact, that is, the contact area, is set to a desired contact area S1 (cm ² ). This contact interview S1 will also be described in detail.

  The one-component developer 10 is a one-component non-magnetic toner having an average particle size of about 10 μm, for example, and a polyester toner or a styrene acrylic toner is used.

  The developing roller 41 is supplied with a developing bias voltage Va from the developing bias power supply circuit 11. The developing bias voltage Va is set to a polarity and a voltage value such that toner adheres to the electrostatic latent image formed on the photoreceptor 1 and toner does not adhere to other regions, that is, non-image regions.

  The supply roller 42 is driven to rotate in the direction opposite to the rotation direction of the developing roller 41 at the portion facing the developing roller 21 (pressure contact region). The supply roller 42 uses the same material as the developing roller 41, and the electrical resistance can be adjusted with the same resistance adjusting material as the developing roller 41. Further, in order to further increase the elasticity of the supply roller 42, a foamed (porous) material is used.

  A bias voltage Vc is applied to the supply roller 42 from the bias power supply circuit 12, and generally the toner is pushed in the direction toward the developing roller 41, that is, the toner on the supply roller 42 side is repelled to the developing roller 41. A bias voltage in the direction of supply is set. For example, when negative polarity toner is used, a larger bias voltage Vc is applied to the supply roller 42 on the negative polarity side.

  The developing roller 41 and the supply roller 42 are connected to a drive motor (not shown), and are driven to rotate in the direction of the arrow in the drawing to supply toner to the development roller 41 by the supply roller 42 and contribute to development after development. The toner on the surface of the developing roller 41 that has not been removed is peeled (removed). The toner supplied by the supply roller 42 adheres to the surface of the developing roller 41 and is conveyed to a blade 43 that is appropriately pressed against the developing roller 41 before being conveyed to the developing area facing the surface of the photoreceptor 1. Thus, the toner adhesion amount is regulated to a constant toner layer thickness.

  The blade 43 is in pressure contact with the developing roller 41 at an appropriate pressure. The blade 43 is formed of a blade constituent member made of a plate-like metal material, and a belly (surface) portion in the vicinity of the tip is pressed against the developing roller 41. Therefore, the toner 10 supplied to the developing roller 41 is regulated to a predetermined charged charge amount and thickness by a predetermined set pressure and a set position of the blade 43 and is conveyed to a developing region that is in contact with the photoreceptor 1. .

  The blade 43 serving as the regulating member is provided such that one end is fixed to the developing tank 40 side and the belly portion on the free end side of the other end is in pressure contact with the surface of the developing roller 41. The regulating member 43 is made of, for example, a phosphor bronze having a thickness of about 0.1 to 0.2 mm, or a metal plate such as stainless steel (SUS). The abdominal part in the vicinity of the tip is pressed along the direction of the rotation axis of the roller. As a result, the amount of the one-component developer 10 carried on the surface of the developing roller 41 via the supply roller 42 is made constant by the regulating member 43 and conveyed to the developing region in contact with the photoreceptor 1.

  Also in this blade 43, a predetermined voltage Vb is supplied from the bias power supply circuit 13. Also in the bias voltage Vb, a larger value is set in the direction of pushing the toner 10 toward the developing roller 41, for example, in the case of negative polarity toner, on the negative polarity side. Further, the bias voltage Vb supplied to the blade 43 may be set to the same potential as the developing bias voltage Va supplied to the developing roller 41 or a large value in absolute value thereof.

  On the other hand, the toner 10 conveyed to the developing region facing the photoreceptor 1 is selectively attached according to the electrostatic latent image formed on the surface of the photoreceptor 1, and the electrostatic latent image is visualized by the color of the toner. Turn into. Then, the toner 10 that has not contributed to the development is returned to the developing tank 40 by the rotation of the developing roller 41. At the position where the toner is returned, a toner reset member 44 is provided so as to be pressed against the developing roller 41. The reset member 44 is disposed in front of the rotation direction of the developing roller 41 of the supply roller 42, and one end portion is fixed to the developing tank 40 so as to be in pressure contact with the developing roller 41 appropriately. The contact with the developing roller 41 is made by using a spring having a region to be pressed.

  The toner that has not contributed to the development after the development by the reset member 44 is discharged and removed when it is collected into the developing tank 40 by the rotation of the developing roller 41 and reused. The reset member 44 is also supplied with a bias voltage from the power supply circuit 14 for discharging and removing toner.

  As described above, the developing device 4 conveys the toner 10 to the area facing the photoconductor 1 and visualizes the latent image on the surface of the photoconductor 1. As described above, the toner image on the surface of the photosensitive member 1 is transferred to the paper P that is appropriately conveyed in the transfer region by the action of the transfer unit 5, and the paper passes through the fixing device 8 and goes out of the image forming apparatus. Discharged.

  The photoreceptor 1 has an underlayer coated on the surface of a conductive substrate made of metal or resin, a carrier generation layer (CGL) as an upper layer, and a carrier moving layer (with a polycarbonate as a main component in the outermost layer). An OPC photosensitive member formed by applying CTL) is used. In the present invention, the photosensitive member is not limited to such a photoreceptor, and may be any carrier that carries an electrostatic latent image.

(Development roller structure)
The developing roller 41 is as described above, and the structure thereof will be described in more detail.

  For example, as shown in FIG. 5, the developing roller 41 is configured by covering a metal or a low-resistance resin cored bar (shaft 41a) with a semiconductive layer 46, which is an elastic member having a relative dielectric constant of about 10 for example. . A toner layer 45 is formed on the surface of the semiconductive layer 46.

Examples of the elastic member on the surface of the developing roller 41 include a resin selected from EPDM, urethane, silicon, nitrile butadiene rubber, chloroprene rubber, styrene butadiene rubber, butadiene rubber, and the like, and conductive fine particles such as carbon. , TiO ₂ (titanium oxide) based on a dispersion-type resistance-adjusting resin dispersed and mixed using one or a plurality of ionic conductive materials such as sodium perchlorate, perchlorine A material based on an electrical resistance adjusting resin using any one or a plurality of inorganic ionic conductive materials such as calcium acid and sodium chloride is suitable. Further, when a foaming agent is used as the foaming / mixing step for obtaining elasticity, a silicon surfactant (polydialsiloxane, polysiloxane-polyalkylenoxide block copolymer) is appropriate.

  As an example of the above-mentioned foam molding, as an example of heat blow foam molding, an appropriate amount of the above materials are mixed, stirred with a mixing injector, injected into an injection extrusion mold, heated at 80 ° C. to 120 ° C., and injected. To do. The heating time is preferably about 5 minutes to 100 minutes.

  In the case of integral molding with a cored bar by injection molding, a conductive metal cored bar (shaft) is arranged in the center in a mold prepared in advance, and the mixed material is poured in the same manner as described above, and about 10 minutes to 160 minutes. By integrally heating and vulcanizing, an integrally molded product can be obtained.

One carbon black as an electric resistance adjusting material of the developing roller 41 is a carbon black (ISAF, HAF) having a nitrogen adsorption specific surface area of 20 m ² / g to 130 m ² / g and a DBP oil absorption of 60 ml / g to 120 ml / g. , GPF, SRF, etc.) are mixed as 0.5 to 15 parts by weight (in some cases about 70 parts by weight) with respect to 100 parts by weight of polyurethane.

  As the polyurethane, flexible polyurethane foam and polyurethane elastomer are suitable. Apart from this, the above-mentioned EPDM, urethane, silicon, nitrile butadiene rubber, chloroprene rubber, butadiene rubber and the like can also be used.

  When EPDM is used as a main component constituting the developing roller 41, apart from using polyurethane, the EPDM is composed of ethylene, propylene and a third component such as zinc cyclopentadiene, ethylidene norbornene, 1.4. -Since hexadiene etc. are mix | blended suitably, it is preferable to mix | blend ethylene content 5 to 95 weight part, 5 to 95 weight part of propylene, and 0 to 50 weight part of 3rd components by the iodine value. Therefore, when the amount of carbon black is 1 to 30 parts by weight with respect to 100 parts by weight of EPDM, good dispersibility can be obtained. The carbon black used is ISAF, HAF, GPF, SRF, etc. as described above.

  In addition to carbon black, which is a resistance adjusting material, EPDM100 is used as a resistance adjusting base material such as ion conductive materials such as sodium perchlorate and tetraethylammonium chloride, and surfactants such as dimethylpolysiloxane and polyoxyethylene lauryl ether. When 0.1 to 10 parts by weight is used with respect to parts by weight, even better dispersion uniformity can be obtained.

  Examples of the ionic conductive material include ionic conductive materials, inorganic ionic conductive substances such as sodium perchlorate, calcium perchlorate, and sodium chloride, or modified aliphatic dimethylethylammonium ethosulphate, stearyl ammonium acetate, and lauryl ammonium. Organic ionic conductive materials such as acetate and octadecyltrimethylammonium perchlorate can be used. Any one or a plurality of these can be used.

(Blade structure of toner layer thickness regulating member)
As shown in FIG. 1, one end of the blade 43 is fixed to the developing tank 40 with a predetermined length, and the free end that is not fixed is pressed against the developing roller 41 with an appropriate pressure. Particularly, one end of the blade 43 is fixed to the developing tank 40 so as to be brought into pressure contact with the developing roller 41 using, for example, its own spring property.

  Further, the blade 43 is a metal plate having a plate thickness of about 0.05 to 0.5 mm, and comes into contact with the developing roller 41 with a predetermined pressure by being elastically deformed, that is, having a predetermined thickness. The toner layer and the charged charge amount are restricted. For example, the tip portion of the blade 43 that contacts the developing roller 41 is slightly bent in the direction in which the opening angle formed between the developing roller 41 and the bent blade 43 is opened by bending or the like in a direction away from the surface of the developing roller 41. It has an inclined surface. In addition, the contact portion of the blade 43 with the developing roller 41 may be subjected to a coating process or the like in order to adjust the toner charge amount or suppress toner fusion.

  As the material constituting the blade 43, a material having a normal spring property is used. For example, spring steel such as SUS, stainless steel such as SUS301, SUS304, SUS420J2, and SUS631 or copper such as C1700, C1720, C5210, and C7701. Alloys can be used.

  In addition, the fine inclined surface of the free end of the blade 43 is pasted with a conductive adhesive or the like, in addition to a mechanical cutting, polishing, bending process, or a chip-shaped tip part previously formed by molding or the like. Alternatively, the tip of the blade is processed with a step, and a metal foil is attached with a conductive adhesive or the like from the hunger.

  The blade 43 basically uses the above-described base material as it is in contact with the developing roller 41 as it is. However, coating may be performed on the contact surface with the developing roller 41 for the purpose of stabilizing the charge amount of the toner or suppressing toner sticking to the blade surface. As this coating material, a fluorine-containing resin or a graphite-containing resin is spray-coated on the blade surface, dried at about 80 ° C. for 30 minutes or more, baked at 260 ° C. for 30 minutes, and lightly polished with # 10000 sandpaper A coating having a thickness of 8 to 12 μm, or anodized aluminum formed on the blade surface and having an alumite film of about 50 to 100 μm formed on the surface is used as the coating.

(Reset member structure)
In FIG. 1, the reset member 44 is directly reused by removing the charge by directly contacting the developed toner while the developing roller 41 is in pressure contact, and removing the toner from the developing roller 41.

  In addition to this, there is one that uses a corona discharger to remove static electricity, and a contact peeling rotation member may be provided so that the toner is peeled off from the developing roller 41 and reused.

  In the reset member 44 as shown in FIG. 1, a plate-like elastic member is used, and like the blade 43, the bias voltage Vd from the power supply circuit 14 is supplied by being pressed against the developing roller 41 at an appropriate pressure. The collected toner is neutralized and removed. Therefore, as the material used for the elastic member, nylon, PET (polyethylene terephthalate), PTFE (polytetrafluoroethylene) -containing resin, polyurethane or the like is used, and this is used as a base material (main component), and an electric resistance adjusting material such as carbon. The electrical resistance is set to an appropriate value. The reset voltage Vd from the power supply 14 is supplied to the reset member 44 having such resistance.

As the carbon black used for the electrical resistance adjusting material, a carbon black having a nitrogen adsorption specific surface area of 20 m ² / g or more and 130 m ² / g or less, such as furnace or channel black such as ISAF, HAF, GPF, SRF, polyurethane (nylon or The same is used for PET and other resins). A mixture of 10 parts by weight or more (in some cases 70 parts by weight or less) is used with respect to 100 parts by weight.

(Non-magnetic one-component developer)
As a toner which is a non-magnetic one-component developer, a material having a composition of 80 to 90 parts by weight of a styrene-acrylic copolymer, 5 to 10 parts by weight of carbon black, and 0 to 5 parts by weight of a charge control agent is mixed. The negatively charged toner having an average particle diameter of about 5 to 10 μm can be obtained by kneading, pulverizing and classifying. To this toner, 0.5 to 1.5 parts by weight of silica (SiO 2) added internally or externally to improve fluidity can be added to obtain a non-magnetic one-component developer. .

  The toner is not limited to negative charging, and positively charged toner can also be obtained. This can be easily obtained by appropriately selecting a main component binder resin, a charge control agent and the like. Further, the toner is not covered with black toner for monochrome copying machines and printers, and can be applied to color toners for color copying machines and printers.

  Further, the nonmagnetic one-component developer is not limited to the above-described composition material, and even the following composition can be used in the developing device of the present invention.

  The thermoplastic resin that is the binder resin as the main component may be polystyrene, polyethylene, polyester, low molecular weight polypropylene, epoxy, polyamide, polyvinyl butyral, etc., in addition to the styrene-acrylic copolymer.

  As the colorant, in the case of black toner, besides the above-described carbon black, there are furnace black, nigrosine dye, metal-containing dye and the like. For color toners, benzidine yellow pigments for yellow, phonon yellow, acetoacetanilide anilide insoluble azo pigments, monoazo pigments, azomethine dyes, etc., xanthene magenta dyes for magenta, phosphotungstic molybdate lake pigments, anthraquinones Type dyes, colorants composed of xanthene dyes and organic carboxylic acids, thioindigo, naphthol-based insoluble azo pigments, cyan phthalocyanine pigments, and the like.

  Further, for example, colloidal silica, titanium oxide, alumina, zinc stearate, polyvinylidene fluoride, or a mixture thereof may be used in addition to silica as an external additive used as a fluidizing material for toner.

  Furthermore, as the charge control agent, azo-based metal-containing dyes, organic acid metal complex salts, chlorinated paraffins, and the like can be used for negatively charged toners. For positively charged toners, nigrosine dyes, fatty acid metal salts, amines, quaternary ammonium salts, and the like can be used.

(Development ghosting due to particle size fluctuation)
Various factors can be considered in the development ghost generation mechanism. Hereinafter, the development ghost generation mechanism due to particle size variation will be described.

  In the developing device 4 using the one-component developer as described above, the amount of toner 10 attached is regulated by the blade 43 pressed against the developing roller 41 so as to have a constant layer thickness. Thereafter, the toner 10 is transported to the development area to develop the electrostatic latent image on the surface of the photoreceptor 1. At this time, bias voltages Va, Vb, and Vc are supplied to the developing roller 41, the supply roller 42, and the blade 43, respectively. Here, when the toner 10 remaining on the developing roller 41 after developing the white image portion cannot be sufficiently removed from the developing roller 41, the same toner is again subjected to a mechanical load by the supply roller 42 and the blade 43. At the same time, it receives an electrical load (Coulomb force) due to the bias voltage. When the mechanical load is continuously received, the toner is crushed particularly in the pulverized toner, and the average particle size of the toner in the portion where the white image portion is developed may be reduced.

  Further, in a place where a bias is applied, there is a considerable particle size selectivity in the toner to be developed. That is, since the toner is moved from the small particle size toner with respect to the bias electric field, the developed portion of the white image portion becomes smaller in the vicinity of the surface of the developing roller, and the developed portion of the black image portion is refreshed by development. Therefore, the particle size hardly fluctuates. Therefore, when the toner 10 remaining on the developing roller 41 after development cannot be sufficiently removed from the developing roller 41, the average particle diameter of the toner is reduced.

  Assuming that the toner surface charge density is constant as the charging characteristics of the toner 10, the toner specific charge is a characteristic inversely proportional to the particle diameter as shown in FIG. Further, as shown in FIG. 10, the development characteristic with respect to the toner specific charge becomes such a characteristic that the development gamma becomes lower as the toner specific charge is larger. Therefore, the specific charge increases in the portion where the average particle diameter of the toner is reduced, and the development amount decreases.

  The reduction in the average particle diameter of the toner depends on an image pattern such as whether a white image is developed or a black image is developed. Therefore, the specific charge varies depending on the image pattern, and the development amount varies. That is, this is a development ghost in which the history of the past developed image pattern affects the next image, and deteriorates the image quality. In this case, the white portion has a smaller specific particle size and the specific charge increases, and the development amount decreases, so that a so-called positive ghost is formed.

(Development ghosting due to surface potential change / adhesion fluctuation)
Next, a development ghost generation mechanism due to a change in surface potential and a variation in the amount of adhesion will be described.

  The thickness of the toner layer remaining on the developing roller 41 after developing the black image portion is very thin compared to the thickness of the toner layer remaining on the developing roller 41 after developing the white image portion. Accordingly, when the supply of toner to the supply roller 42 and the blade 43 is insufficient, the amount of adhesion on the portion of the developing roller 41 that developed the previous black image is small. As shown in FIG. 9, the development characteristics with respect to the toner adhesion amount decrease as the toner adhesion amount decreases. In this case, the black portion becomes a so-called negative ghost because the adhesion amount decreases due to insufficient toner supply and the development amount decreases.

  When the bias voltages Va, Vb, and Vc are supplied to the developing roller 41, the supply roller 42, and the blade 43, respectively, the toner layer thickness remaining on the developing roller 41 after developing the black image portion is the same as the white image portion. Since the thickness of the toner layer remaining on the developing roller 41 after development is very thin, the electric field strength is stronger in the black image developing portion even with the same potential difference, and toner breakdown and overcurrent are likely to occur. Charge may be supplied to the surface of the developing roller. At this time, if the resistance value of the developing roller 41 is high, the surface potential of the black image developing portion changes because the charge does not escape. FIG. 11 shows the relationship between the surface potential change ΔV of the developing roller 41 and the development amount. For example, it can be seen that the development bias increases and the development amount increases as the surface potential increases.

  Accordingly, in the present invention, development ghosts are prevented from occurring by limiting the difference between the average particle size after black image development and the average particle size after white image development within a predetermined value. Furthermore, by limiting the resistance value and applied bias of each member, development ghosts caused by fluctuations in the amount of adhesion and changes in surface potential are prevented, and development is stabilized.

  The stability of development by the above-described developing device of the present invention was confirmed by showing examples below.

[Example 1]
As the photosensitive member 1 in the image forming apparatus shown in FIG. 4, a negatively charged photosensitive member is used, the diameter of the conductive substrate is 65 mm, and the charger 2 is charged to a potential of −550V. The substrate of the photoreceptor 1 is grounded and is rotated in the direction of the arrow at a peripheral speed of 190 mm / sec.

As shown in FIG. 5, the developing roller 41 is configured by covering a surface of a rotating shaft 41a made of stainless steel having a diameter of 18 mm with a semiconductive elastic layer 46 having a thickness of 8 mm. Asker whose rubber height conforms to SRIS (Japan Rubber Association Standard) using the above-mentioned resistance adjusting base material so that the value of the average resistance (Rd) by the developing roller 41 is 104 to 5 × 10 ⁶ (Ω). A C hardness of 65 to 70 degrees and a surface roughness of 2 to 8 μm with a 10-point average roughness Rz according to JISB0601 were used. As shown in FIG. 1, the developing roller 41 was rotationally driven at a peripheral speed of 285 mm / sec in the direction of the arrow. Further, a voltage of −400 V is supplied as the developing bias voltage Va from the power supply circuit 11 to the stainless steel rotating shaft 41a of the developing roller 41, and the toner layer on the surface of the developing roller 41 so that the developing nip width becomes 1.5 mm. Was pressed against the photoreceptor 1.

  The supply roller 42 was configured by covering a stainless steel rotating shaft surface with a conductive urethane foam having a volume resistivity of 105 (Ω · cm) and a cell density of 80 to 100 pieces / inch. The diameter of the supply roller 42 was 20 mm, and the supply roller 42 was brought into contact with the developing roller 41 with a contact depth of 0.5 mm. And it is rotationally driven in the direction of the arrow, and the peripheral speed of the supply roller 42 is rotationally driven at 170 mm / sec. The power supply circuit 12 supplies −500 V as the bias voltage Vc to the stainless steel rotating shaft of the supply roller 42.

  Further, the blade 43 serving as a regulating member was pressed against the developing roller 41 using a stainless steel plate having a thickness of about 0.1 mm. In particular, the blade 43 has a cantilever plate spring structure, and its free end is brought into contact with the developing roller 41 and is elastically deformed to be applied to the toner layer on the surface of the developing roller 41 with a predetermined pressure. The blade 43 is also supplied with −500 V as a bias voltage (Vb) from the power supply circuit 13.

  Further, the reset member 44 is configured such that a sheet-like elastic member in which carbon is dispersed in a resin base material is brought into surface contact with the developing roller 41 with a predetermined pressure. The reset member 44 is also supplied with −300 V as the reset bias voltage (Vd) by the power supply circuit 14.

  In the developing device having the above configuration, a uniform toner thin layer 45 is formed on the surface of the developing roller 41, and contact reversal development is performed on the photoreceptor 1 as described above. At this time, the toner adhesion amount m / a was set to 0.5 to 0.8 mg / cm 2, the toner charge amount q / m was set to −10 to −20 μC / g, and the toner layer thickness Dt was set to 10 to 30 μm.

  FIG. 15 shows an image pattern for evaluating the development ghost. A black and white checker pattern is arranged in a portion corresponding to one rotation of the developing roller at the head portion of the image, and the latter half of the image corresponding to the second and subsequent rotations of the developing roller is shown in FIG. Uniform halftone is arranged. Development ghosts were evaluated visually and using a Machbeth densitometer RD918.

  FIG. 2 shows the result of measuring the volume particle size distribution variation of a general pulverized one-component developer by performing a developing operation with the configuration excluding the reset member in the developing device as described above. A Coulter Multisizer 2 was used to measure the volume particle size distribution. The solid line shows the volume particle size distribution of the toner carried immediately after the black image was developed in the developing unit and the location on the developing roller that lost most of the toner rotated and passed again through the developer layer regulating member. is there. The broken line indicates the volume particle size distribution of the toner carried immediately after the white image is developed in the developing unit and the location on the developing roller where most of the toner has not been lost rotates and passes again through the developer layer regulating member. It is. The black portion volume average particle diameter Dbk indicated by the solid line is 7.6 μm, which is substantially equal to the toner volume average particle diameter in the developing tank. On the other hand, the white portion volume average particle diameter Dwt indicated by a broken line is 4.8 μm, which indicates that the particle diameter is greatly reduced. The ratio of the black part volume average particle diameter Dbk and the white part volume average particle diameter Dwt is expressed by Equation 1.

Dwt / Dbk = 0.63 (1)
The specific charge at this time was −10 μC / g in the black part and −14 μC / g in the white part, and it was confirmed that the specific charge increased as the particle size decreased. As a result of developing the development ghost evaluation pattern under these conditions, positive ghost was confirmed.

  Next, FIG. 3 shows the result of measuring the volume particle size distribution fluctuation of the toner by performing the developing operation with the configuration incorporating the reset member in the developing device. The solid line shows the volume particle size distribution of the toner carried immediately after the black image was developed in the developing unit and the location on the developing roller that lost most of the toner rotated and passed again through the developer layer regulating member. is there. The broken line indicates the volume particle size distribution of the toner carried immediately after the white image is developed in the developing unit and the location on the developing roller where most of the toner has not been lost rotates and passes again through the developer layer regulating member. It is. The black portion volume average particle diameter Dbk indicated by the solid line is 7.6 μm, which is substantially equal to the toner volume average particle diameter in the developing tank. On the other hand, the white portion volume average particle diameter Dwt indicated by a broken line is 6.1 μm, and it can be seen that the particle size reduction is considerably suppressed as compared with the case without the reset member. The ratio of the black portion volume average particle diameter Dbk and the white portion volume average particle diameter Dwt is expressed by Equation 2.

Dwt / Dbk = 0.80 (2)
The specific charge at this time was −10 μC / g in the black part and −11 μC / g in the white part, and it was confirmed that the specific charge fluctuation was small. As a result of developing the development ghost evaluation pattern under these conditions, positive ghost was not confirmed.

  In addition, various toners were used and experiments were performed under various conditions to evaluate the particle size variation and the presence or absence of ghosts. An example of the typical experimental results is shown in Table 1.

  As a specific evaluation method for the presence or absence of ghost, optical density evaluation obtained by a Machbeth densitometer and visual evaluation were used in combination.

  That is, the optical density of the white part and the black part of the development ghost of the black-and-white checker pattern appearing in the halftone portion was measured with a Machbeth densitometer, and the ghost residual rate was calculated using the following calculation formula 3.

  When the ghost residual rate calculated by the above formula 3 is 3% or more, it is determined that there is a ghost. When it is 1% or less, it is determined that there is no ghost.

  From these results, it was found that when the difference between the black part volume average particle diameter Dbk and the white part volume average particle diameter Dwt satisfies the following formula 4, development ghost does not occur.

Dwt / Dbk> 0.8 (4)
In this way, by managing and limiting the volume average particle size difference between the black image developing unit and the white image developing unit within the range of the above formula, the change of the average specific charge amount depending on the image pattern is kept within a certain value. Therefore, it is possible to provide a developing device that can prevent development ghosts and can perform development satisfactorily.

[Example 2]
Even when no reset member is used, it is described below that the development ghost caused by the volume particle size variation can be prevented by improving the volume particle size distribution of the toner.

  As an index representing the sharpness of the toner volume particle size distribution, there is a CV value [%] defined by the following formula 5. The larger the CV value, the broader the volume particle size distribution, and the smaller the CV value, the sharper the volume particle size distribution.

CV = 100 × (standard deviation / average value) (5)
The toner of Example 1 uses a toner having a CV value of 34.6%, and without the reset member, development ghosts due to volume particle size distribution fluctuations occurred.

  However, when a toner having a small CV value is used, the ratio of the small toner and the large toner to the volume average particle diameter decreases. Therefore, it is expected that the variation of the volume average particle diameter is also reduced. As a result of testing with toners having various CV values based on this expectation, it was confirmed that no development ghost occurred in toners having CV values within 25% (see Table 1).

  Further, as a result of a test using the toner layer thickness as a parameter, even when the toner has a CV value of 25%, the amount of adhesion is large, specifically, when the toner layer thickness exceeds 3 times the volume average particle diameter, It was found that particle size fluctuations occurred to a level where ghosts were generated.

  The CV value and toner layer thickness suppress the development ghost due to their synergistic effect. For example, even when the toner layer thickness exceeds 3 times the volume average particle diameter, the CV value should be 25% or less. It can be easily analogized that development ghosts can be prevented. The same applies to the synergistic effect with the reset member.

[Example 3]
In the developing device of the present invention, various members arranged in contact with the periphery of the developing roller 41 in order to stabilize the thickness and charge amount of the toner layer, that is, the developing roller 41, the supply roller 42, the blade 43, and the reset member 44. Is supplied with a bias voltage.

  In the conventional developing device, the resistance value of the above member is high, and there is little risk of discharge due to the bias voltage. However, in the developing device of the present invention, the above members are all made of a low resistance material. Therefore, it is necessary to determine the upper limit value of the bias voltage.

  For this reason, it is essential to first set the bias voltage supplied to the toner layer 45 so as not to discharge.

  Therefore, the toner layer resistance, toner layer thickness and bias applying means used in the developing device of the present invention will be described below.

  FIG. 5 is a diagram for explaining a method of measuring the resistance value Rt of the toner layer 45 between the developing roller photoreceptors.

  In the figure, an aluminum base tube 100 is used instead of the photoreceptor 1, and a toner layer 45 is uniformly formed on the surface of the developing roller 41 having the same structure as the actual development conditions, and then the aluminum base tube 100 is used in actual use. Contact with the same pressure. Then, with the respective members stationary, a developing bias voltage V1 of the same level is supplied to the conductive rotating shaft 41a of the developing roller 41 by the voltage source 101. Then, the current It flowing through the toner layer 45 was accurately measured by the microammeter 102. Thereby, the static resistance value Rt of the toner layer 45 was measured.

  In this case, by measuring each member in a stationary state, it is possible to accurately measure the amount of current by eliminating noise factors such as toner charging current and toner transfer current generated in the operating state.

  Therefore, assuming that the supply voltage V1 (V) from the voltage source 101 and the measurement current from the microammeter 102 are It (A), the static resistance value Rt (Ω) of the toner layer 45 is obtained by the following equation (6).

Rt = V1 / It (6)
However, since the resistance value of the developing roller 41 used in the present invention is sufficiently lower than the toner resistance value, the voltage drop in the semiconductive layer 46 of the developing roller 41 of the measuring apparatus shown in FIG. 5 was ignored.

  FIG. 6 shows the results of measuring the static resistance value (Rt) of the toner layer 45 by the method described above and plotting the voltage-current characteristics of the toner layer 45.

  It can be seen that the measured toner layer current exhibits a relatively linear characteristic at the low voltage portion, and suddenly an overcurrent flows when it reaches a certain value Vth (V). This value Vth is a discharge start voltage at which air discharge or creeping discharge occurs between toner particles.

  Thus, since the current-voltage characteristic is relatively linear in the voltage range equal to or lower than the discharge start voltage Vth, the resistance value obtained from Equation 6 is calculated based on the current value measured in the voltage in this range. It is defined as a static resistance value Rt.

  As a result of conducting development experiments using toners having various resistance values under various conditions similar to those in Example 1, a toner having a high insulating property having a static resistance value Rt of the toner layer of 50 MΩ or more, preferably 100 MΩ or more was used. In some cases, it has been found that the occurrence of overcurrent is extremely small and a good image quality can be obtained.

  However, even when the high-resistance toner as described above is used, the bias applied to the supply roller 42, the blade 43, and the reset member 44 arranged around the developing roller is increased, and the potential difference from the developing roller 41 is increased. If it is increased, the discharge start voltage (Vth) will be exceeded, and image quality degradation due to overcurrent will occur.

  Table 2 shows the results of measuring several types of toner layer resistance Rt [MΩ] by the measurement method based on FIG. As shown in Table 2, the measured dielectric breakdown voltage Vth [V] of the toner was 400 to 500 V with respect to the toner layer thickness T [μm] of about 20 μm. Therefore, the electric field strength Eth [MV / m] = Vth / T when the dielectric breakdown occurs is 20 to 25 MV / m. From this result, it was found that it is important to define the upper limit of the voltage that can be applied to the toner layer sandwiched between the low resistance materials as Vmax = 20 × T [V]. As a result, the voltage supplied to the supply roller 42, the blade 43, and the reset member 44 that are in contact with the developing roller 41 is set to 20 × T [V] or less as described above, thereby being defined by the layer thickness of the toner layer. Thus, it is possible to prevent development deterioration due to dielectric breakdown of the toner layer.

  Here, the developing roller 41 is supplied with a developing bias voltage Va, the supplying roller 42 is supplied with a bias voltage Vc, the blade 43 is supplied with a bias voltage Vb, and the reset member 44 is supplied with a voltage Vd. Therefore, the absolute value of each difference between the developing bias voltage Va supplied to the developing roller 41 and the bias voltage supplied to the supply roller 42, the blade 43, and the reset member 44 is 20 × T [V] or less. Various bias voltages may be set so that

[Example 4]
Next, electrical characteristics of the toner layer thickness regulating blade 43, the supply roller 42, and the reset member 44 constituting the developing device of the present invention will be described.

  Even when the voltage supplied to the toner layer 45 is within the toner layer discharge start voltage, the resistance value of the toner layer 45 in the thin layer state has a certain degree of non-uniformity, and thus a large amount of current flows through the toner layer 45. In this case, a non-uniform voltage drop of the developing roller 41 due to a non-uniform current occurs. As a result, the bias voltage supplied to the toner layer 45 becomes non-uniform. As a result, the toner layer thickness and charge amount become non-uniform, resulting in image quality degradation.

  FIG. 11 shows development characteristics using the surface potential change ΔV on the developing roller 41 as a parameter. When the surface potential increases, the graph shifts to the left. Therefore, when the portion of the halftone development potential is around 100 V, it can be seen that the development amount increases as the surface potential increases.

  If the charge adhering to the surface of the developing roller 41 for some reason does not pass through the semiconductive layer 46 of the developing roller 41 and escape to the conductive shaft 41a, the surface potential of the developing roller 41 rises. Whether the surface potential of the developing roller 41 increases depends on the time constant determined by the resistance value of the developing roller and the capacitance, and the magnitude relationship between the process speed.

  In this respect, since the resistance value of the developing roller used in the developing device of the present invention is low, the time constant is small, and when the peripheral speed of the developing roller is about 285 mm / s, charge is accumulated on the surface of the developing roller. The possibility of developing ghosts is low. However, when the same surface potential change phenomenon occurs in the toner supply unit, the layer regulation unit, and the reset unit, image quality deterioration occurs.

  On the other hand, in the toner supply roller 42, the rotation speed of the supply roller is determined by selecting a peripheral speed ratio with the developing roller between approximately 0.5 to 2.0. The resistance value is determined from the contact nip area determined from the pressing force against the developing roller and the sponge hardness, and the volume resistivity. As a result of experiment under these conditions, it was found that the surface potential change does not occur if the resistance value is 10 kΩ or less.

  Further, when a metal leaf spring blade is used as the blade 43 for regulating the toner layer, the potential change on the blade surface does not occur in principle. However, when a high-resistance resin material or the like is coated or a conductive sheet is used, a potential change occurs and the uniformity of the toner layer is greatly impaired. Since the blade 43 is a stationary member, whether or not the surface potential changes depends on the charge accumulation speed and the time constant of the member. Since the charge accumulation speed largely depends on the electrical characteristics of the toner, the theoretical value is unknown, but from the results of experiments using various toners, the blade 43 has a coating treatment or a conductive sheet. The resistance value is preferably 10 kΩ or less. If the blade 43 is formed of a metal blade, the above-described problem does not occur. Further, when a conductive sheet is used, if the electrode width is smaller than the image width as shown in FIG. 16, the current path 11 at the center and the current path 12 at the end are different, so the amount of voltage drop differs between the center and the end. A phenomenon occurs. As a result, the applied bias at the blade portion becomes non-uniform in the axial direction, causing image quality degradation. This problem can be solved by setting the electrode width longer than the effective image width.

  Further, since the toner reset portion is a stationary member like the blade portion, it has been experimentally confirmed that the problem of the surface potential change can be solved by setting the resistance value to 10 kΩ or less, which is the same as that of the supply roller. Also, when a conductive sheet is used as the reset member, the same voltage drop non-uniformity problem as that of the conductive sheet blade occurs, but this problem is also caused by making the electrode width longer than the effective image width. Can be resolved.

[Example 5]
Next, the resistance value of the developing roller 41 used in the developing device of the present invention will be described.

  In FIG. 7, a simple device for measuring the resistance value of the developing roller 41 is such that the developing roller 41 is placed on a metal detection electrode 104 disposed on an insulating flat plate 103, and shafts 41 a at both ends of the developing roller 41. A load F is applied to the portion of the portion with a weight 105. In this state, a constant voltage is supplied from the power source 106 to the shaft 41 a of the developing roller 41, and the current flowing through the detection electrode 104 is measured by the ammeter 102. Thereby, the resistance value of the resistance (Rb) in the pressure contact state by the developing roller 41 can be obtained from the supplied voltage and the flowing measurement current.

  In this case, when the resistance value has non-uniformity, an average value obtained by measuring how many points in the circumferential direction is set as a representative value of the resistance value of the developing roller 41. Therefore, after the measurement in the state of FIG. 7, the measurement is performed under the same conditions by rotating a predetermined angle.

  As the developing roller resistance layer, two types of electronic conduction type rollers (A, B) in which carbon black is dispersed in urethane resin and one type of ion conduction type roller (C) based on urethane resin are used with the above measuring device. Table 3 shows a summary of resistance values measured and average resistance values for each roller. The resistance value is obtained by measuring and converting the current value when 10 V is applied with R6871E manufactured by Advantest.

  The developing roller had an outer diameter of Φ34, a resistance layer thickness Dd of 8 mm, an axial length of 320 mm, and a width of the nip formed when the pressure F was 1 kg, which was about 1.5 mm.

  It has been experimentally found that when a developing roller having an average resistance value of 10 kΩ or less is used, the occurrence of overcurrent is extremely increased, which is not practical.

When a halftone image of gray was developed on the entire surface with the developing roller C, a phenomenon that the image density was reduced due to a high resistance value occurred. This is because a voltage drop occurs in the developing roller semiconductive layer due to the developing current, and the effective developing bias decreases. This phenomenon greatly depends on the resistance value of the developing roller semiconductive layer, and the threshold value varies somewhat depending on the process speed and the like, but becomes significant when it exceeds 10 ⁷ Ω in the developing device of the present invention, and 10 ⁷ Ω. Below it was found to be negligible.

FIG. 8 shows the development characteristics with the resistance value of the developing roller 41 as a parameter, and it can be seen that the change in the development gamma is large when it exceeds 5 × 10 ⁶ Ω. Considering the resistance value variation under the environment described below, 5 × 10 ⁶ Ω can be said to be the upper limit of the developing roller resistance value capable of maintaining good image quality.

  The resistance values shown in Table 3 are values under a standard measurement environment in accordance with JISZ-8703. For example, a high temperature and high humidity environment of 35 ° C./85% RH or a low temperature low humidity of 5 ° C./20% RH The resistance value may change in the environment, and the development characteristics may change greatly.

  The semiconductive layer of the developing roller used in the developing device of the present invention is preferably a urethane resin, but as a result of measuring the moisture absorption rate and resistance value according to the JISK-7209A method, the moisture absorption rate is In a 2 to 5% urethane base material, the resistance value changes by 1 to 2 digits between the high temperature and high humidity and the low temperature and low humidity. On the other hand, in a urethane base material having a moisture absorption rate of 0.5 to 1%, the resistance value change is 0.5 to 1 digit, and the development amount variation accompanying the resistance value change is small, and good image quality is maintained. Is possible.

[Example 6]
In the above-described embodiment, the resistance value of the toner layer is defined as a technique for preventing an overcurrent that becomes a problem when the low-resistance developing roller 41 is used. Also, by defining the toner layer thickness, overcurrent was prevented and good development was performed. Further, the overcurrent prevention is performed by defining the bias voltage supplied through various members in contact with the developing roller 41 and the difference between the bias voltages.

  However, the toner layer may be damaged due to an unexpected cause such as contamination of the developing device, which may cause an overcurrent. The overcurrent protection as a countermeasure will be described below.

  As shown in FIG. 12, a bias voltage (Vd) from the power supply circuit 14 is supplied to the reset member 44 via a resistor 50 for overcurrent protection. In this case, the resistance value of the overcurrent protection resistor 50 is very important. Therefore, in order to explain the resistance value of the resistor 50, the electrical equivalent circuit shown in FIG. 12 is shown in FIG.

  The potential difference between the developing bias voltage Va supplied to the developing roller 41 and the bias voltage Vd supplied to the reset member 44 is the voltage source 51 of FIG. The toner layer resistance Rt, the resistance Re of the reset member 44, and the protective resistance 50 are connected in series.

  Therefore, the resistance value Rd of the developing roller 41 and the resistance value Re of the reset member 44 are set sufficiently lower than the toner layer resistance value Rt, and most of the normally supplied bias voltage (51) is the toner layer 45. The value of the flowing current is very small. However, when the toner layer is damaged and the resistance value Rt of the toner layer is apparently very low, if the protective resistance 50 is not provided, the overall resistance is low, so an overcurrent flows and toner fusion occurs. Or damage to the developing roller 41 or the reset member 44 occurs.

  Even if the apparent resistance value of the toner layer resistance Rt is reduced by inserting the protective resistance 50 in series as shown in FIG. 12 (see the equivalent circuit of FIG. 13), the developing roller 41 is present due to the presence of the protective resistance 50. If the resistor Rd is set sufficiently larger than the resistor Rc of the reset member 44, the voltage (51) applied to the member is almost supplied to the protective resistor 50, and overcurrent can be prevented.

  Therefore, in order to reduce the overcurrent as much as possible, the resistance value of the protective resistor 50 should be set large. However, if the resistance value of the protective resistor 50 is large, the voltage supplied by the toner layer 45 and the protective resistor 50 in the normal state is divided and applied to the toner layer 45 due to the voltage drop by the protective resistor 50. The voltage becomes smaller. In this case, the bias voltage (Vd) initially expected is not applied. Therefore, since the upper limit of the resistance value of the protective resistor 50 is regulated, the appropriate value will be described below.

  In FIG. 12, the protective resistor 50 is provided between the reset member 44 and the power supply circuit 14, but the same applies between the supply roller 42 and the power supply circuit 12 and between the reset member 43 and the power supply circuit 13. A protective resistor is inserted as required.

  Therefore, the toner adhesion amount on the photoconductor 1 after development is m / a [kg / m2], the toner specific charge is q / m [C / kg], the effective image width is 1 [m], and the peripheral speed of the photoconductor is set. Assuming v [m / sec], the developing current Id (A) generated when the charged toner is transferred from the developing roller 41 to the photoreceptor 1 can be calculated by the following equation (7).

Id = q / m × m / a × l × v (7)
For example, assuming that the toner adhesion amount on the photoconductor after the entire black solid development is 1.0 mg / cm 2, the toner specific charge is 120 μC / g, the effective image width is 300 mm, and the peripheral speed of the photoconductor 1 is 190 mm / sec. The absolute value of the developing current is 11.4 μA from the above formula 7. The current value at the time of this black solid development is the maximum value of the development current.

  This developing current Id is due to toner transfer in the developing portion (a region where the developing roller 41 and the photoreceptor 1 are in contact), but the same applies to the supply roller 42, the blade 43, and the reset member 44 that are in contact with the developing roller 41. Can be applied.

  The voltage drop Vr of the protective resistor 50 or the like due to the toner transition current Ir is obtained from the resistance value Rr of the protective resistor 50 by the following equation (8).

Vr = Ir × Rr (8)
If the voltage drop Vr is not sufficiently small with respect to the supplied bias voltage, the voltage applied to the toner layer 45 is actually small, and the bias effect is reduced. Accordingly, the upper limit value (Rr) of the protective resistor 50 and the like is determined by how much a voltage drop due to the toner transfer current is allowed in a normal state. Further, the lower limit (Rr) of each protection resistor 50 is determined by how much overcurrent is allowed at the time of abnormality.

As a result of testing with various toners, a practical toner specific charge value is 15 to -30 μC / g, preferably 110 to 120 μC / g in the case of negatively charged toner. I was able to confirm. The amount of toner adhering to the photoreceptor 1 necessary for the black solid varies slightly depending on the toner concealment property, but is approximately 1.0 mg / cm ² . Since the effective image width is l [m] and the peripheral speed of the photoreceptor 1 is v [m / sec], which are design variables, the maximum transfer current Imax [μA] assumed in practical use is the specific charge of 1 μC / μa. When g and an adhesion amount of 1.0 mg / cm ² are substituted into Equation 7, the following Equation 9 is obtained.

Imax = 300 × l × v (9)
When the upper limit of the overcurrent allowable value that does not cause toner fusion and member damage is n times the maximum transition current, the lower limit value Rmin (MΩ) of the protective resistance 50 is expressed by the following equations 8 and 9 as follows: Become.

Rmin = V / (300 × n × l × v) (10)
“V” in Equation 10 is a difference between the bias voltage supplied to the developing roller 41 and the surface potential of the member in contact with the developing roller 41 and the photoreceptor 1 as shown in FIG.

  Therefore, in the reset member 44, toner hardly remains on the developing roller 41 after the solid black development, so that the voltage cannot be maintained by the toner layer 45 and an overcurrent tends to flow. However, since this overcurrent flows directly between the developing roller 41 and the reset member in addition to flowing inside the toner layer, the upper limit of the allowable value is slightly larger than that of the supply roller 42 and the blade 43. Then, several protection resistance values are selected based on Expression 10, and a development test of 1 to 50,000 sheets is actually performed. As a result, n = 5 for the supply roller 42 and blade 43, and n = 5 for the reset member 44. By setting the number to 10, the problem due to development degradation caused by overcurrent could be solved.

  Therefore, the minimum value Rmin of the protective resistance inserted into the reset member 44, the supply roller 42, and the blade 43 can be obtained by substituting the above-described value “5” or “10” into “n” in the above equation (10). Here, “V” in Expression 10 represents the difference between the development bias voltage (Va) and the reset bias voltage (Vd) in the reset member 44, and the difference between the development bias voltage and the supply bias voltage (Vc) in the supply roller 42. The difference is the potential of the difference between the development bias voltage and the regulation bias voltage (Vb) at the blade 43.

That is, R4min = | Vd−Va | / (3000 × v × l)
R3min = | Vb−Va | / (1500 × v × l)
R2min = | Vc−Va | / (1500 × v × l)
It becomes.

  As a result of various experiments using the toner having characteristics such as the specific charge, the toner adhesion amount, and the layer thickness as described above and changing the voltage supplied to each member, the potential difference applied to the toner layer needs to be at least 40 V or more. I got a conclusion. Such a case can be dealt with by supplying in advance a large bias voltage commensurate with the voltage drop at the protective resistance section. Assuming that the dielectric breakdown voltage of the toner layer 45 is approximately 400 V, when the set potential difference is 40 V, the voltage margin against the dielectric breakdown of the toner layer is 10 times maximum, and the allowable voltage drop at the protective resistance portion is 360 V. It becomes. In this way, it is possible to increase the range of the protective resistance. Therefore, even if unexpected toner layer non-uniformity occurs, overcurrent caused by the toner layer can be prevented and development can be performed satisfactorily.

Further, as explained in Equation 9 above, the basis for calculating the maximum value of the transition current of the toner layer is that the practical maximum value of the toner specific charge is 30 μC / g, which is necessary on the photosensitive member 1 necessary for the black solid. That is, the toner adhesion amount was approximately 1.0 mg / cm ² . However, the supply roller 42 has a function of removing the toner on the surface of the developing roller 41 after development and charging the toner in the developing tank 40 and applying it to the developing roller 41. For this reason, the mechanism for removing the toner on the developing roller 41 after development is a reverse current, and therefore the maximum current is smaller than the maximum developing current at the development position. As a result of actually measuring the current flowing through the supply roller 42, it was 1/5 or less of the maximum developing current. Therefore, the upper limit value R2max (MΩ) of the protective resistance in the supply roller 42 can be defined by the following equation 11 from the equations 8 and 9.

R2max = 6 / (l × v) (11)
However, V = 360V.

  Next, the blade 43 will be examined. Since the blade 43 is preliminarily coated with toner on the surface of the developing roller 41 by the supply roller 42, there is almost no toner transfer amount and the toner charging current is considered to be dominant. Therefore, the maximum current is smaller than the maximum developing current of the developing unit. As a result of actually measuring the current flowing through the blade 43, it was 1/3 or less of the maximum developing current.

  Further, in the development, the toner of the same amount as that before the development remains on the developing roller 41 after the white solid is developed. If all the toner is electrically removed by the reset member 44, the maximum current Imax shown in Expression 9 flows. However, in practice, it is more effective to refresh the toner on the developing roller in a balance with mechanical removal of the supply roller 42. Therefore, the removal bias voltage is set to a low value so that the toner removal amount at the reset portion is not 100%. According to this, the static elimination current is smaller than Imax. In addition, when the reset member 44 is a fixing member such as a sheet, the removed toner is not efficiently conveyed into the developing tank 40, and as a result, the static elimination current is reduced. As a result of actually measuring the current flowing through the reset member 44 after white solid development, it was 1/3 or less of the maximum development current Imax.

  Therefore, the upper limit value Rmax (Ω) of the protective resistance in the blade 43 and the reset member 44 which are toner layer regulating members is defined by the following equation 12 from the equations 8 and 9.

R3max = R4max = 3.6 / (l × v) (12)
From the above, the values of the protective resistors R4, R2, and R3 inserted between the developing roller 41 and the power supply circuits 14, 12, and 13 that apply a bias voltage to the reset member 44, the supply roller 42, and the blade 43 are
| Vc−Va | / (1500 × v × 1) <R2 <6 / (l × v)
| Vb−Va | / (1500 × v × 1) <R3 <3.6 / (l × v)
| Vd−Va | / (3000 × v × 1) <R4 <3.6 / (l × v)
It becomes.

  By inserting the protective resistance as described above between the developing roller 41 and the power supply circuit 11 which is a supply source of the developing bias voltage, an overcurrent generated between the developing roller 41 and the photoreceptor 1 is prevented. The idea is well known. However, in this case, the following side effects occur.

  For example, as the development amount increases or decreases depending on the black and white ratio of the image, the development current decreases. Then, the voltage drop amount at the developing roller 41 portion changes depending on the black and white ratio. As a result, the density unevenness accompanying the black and white ratio becomes conspicuous especially in the halftone image quality. In order to solve this problem, in the developing device of the present invention, a low resistance developing roller 41 is used, and a protective resistance is not inserted between the developing roller 41 and the power supply circuit 11 as shown in FIG. A protective resistance 50 is inserted between the reset member 44 and the power supply circuit 14. Further, as a result of experimentally examining the maximum potential difference applied to the toner layer in the developing portion, it was found that the risk of overcurrent to the photoreceptor 1 can be avoided by setting it to 400 V or less.

  Therefore, in the present invention, the protection resistance is provided between the reset member 44, the supply roller 42, and the power supply circuits 14, 12 and 13 supplied to the blade 43 as shown in FIG. Even if the potential difference is increased, overcurrent can be prevented, a pure range in which a protective resistance can be set is widened, occurrence of overcurrent is eliminated, and good development is possible.

  Further, without applying a protective resistor between the developing roller 41 and the power supply circuit 11, as described above, the developing bias voltage (Va) is set so that the potential difference at the developing portion in contact with the photosensitive member 1 is 400 V or less. To prevent overcurrent and enable stable development. Therefore, if the surface potential of the photosensitive member 1 is 1550 V, for example, and the potential of the portion irradiated with the laser beam is substantially “0”, at least the developing bias voltage is set to 1400 V or less (in absolute value). do it.

  As described above, the first aspect of the present invention has been made to achieve the above-described object, and carries a one-component developer on the surface and makes contact with an electrostatic latent image carrier to form an electrostatic latent image. A developer carrier to be developed, a developer supply member that supplies the developer to the developer carrier, and a layer thickness of the developer that is in contact with the developer carrier and supplied by the developer supply member is regulated. And a developer layer regulating member that performs a black image development on the developer carrying member having the developer formed in a predetermined layer thickness, and then supplies the developer by the developer supply member. The average volume particle diameter of the developer carried by the developer carrying member when the layer restricting member is again formed to have a predetermined layer thickness is Dbk, and the developer carrying member having the predetermined layer thickness is white. After image development, the developer is supplied by the developer supply member. When the average volume particle size of the developer carried by the developer carrying member when the developer layer regulating member is formed again to have a predetermined layer thickness is Dwt, Dwt / Dbk> 0.8 is satisfied. Is a developing device.

  In addition, the present invention 2 is characterized in that the one-component developer has a CV value [%] representing a volume particle size distribution defined as CV = 100 × (standard deviation / average value) within 25%. The developing device according to the first aspect of the present invention.

  In the present invention 3, when the layer thickness of the one-component developer carried on the developer carrying member is T [μm] and the average volume particle diameter is D [μm], T <3 × D The developing device according to the second aspect of the invention is characterized in that:

  According to the fourth aspect of the present invention, after the developer carrier and the electrostatic latent image carrier are brought into contact, the developer carrier is brought into contact with the developer carrier, and the developer remaining on the developer carrier is neutralized or removed. If the voltage applied to the developer carrying member is Va [V] and the voltage applied to the reset member is Vd [V], the sign of Va-Vd is the developer. The developing device according to the first aspect of the present invention is characterized in that a voltage is applied so as to have the same polarity as the charging polarity.

  According to a fifth aspect of the present invention, the reset member is made of a low resistance material having a resistance value of 10 kΩ or less at a portion in contact with the developer carrier via a metal material or a developer. 4 developing device.

  According to the sixth aspect of the present invention, the reset member is formed of a low-resistance thin plate-like member, and the surface other than the contact portion with respect to the front surface and the back surface is in contact with the developer layer formed on the developer carrier. The developing device according to the fifth aspect of the invention is characterized in that a conductor electrode is disposed on the surface with a width substantially equal to or greater than the effective image width, and a voltage applying means is connected to the conductor electrode.

  In addition, the present invention 7 is the developing device according to any one of the present invention 4 to 6, wherein | Va−Vd | <20 × T is satisfied when the layer thickness of the developer is T [μm].

  According to the eighth aspect of the present invention, a resistor for overcurrent protection is connected between the reset member and the voltage applying unit, and the resistance value R4 [MΩ] represents the peripheral speed of the electrostatic latent image carrier. When [m / s] and the developer carrier effective width is 1 [m], | Vd−Va | / (3000 × v × l) <R4 <3.6 / (l × v) is satisfied. The developing device according to any one of 4 to 7 of the present invention.

According to the ninth aspect of the present invention, the developer carrier is composed of a conductive shaft and a flexible semiconductive layer on the conductive shaft, and the developer carrier is interposed via the developer. In the developing device according to any one of the first to ninth aspects of the present invention, 10 ⁴ <Rd <5 × 10 ⁶ is satisfied, where Rd [Ω] is a resistance of a portion in contact with the electrostatic latent image carrier.

  According to a tenth aspect of the present invention, in the developing device of the ninth aspect, the semiconductive layer of the developer carrying member is a urethane resin having a moisture absorption rate of 1% or less.

Invention 11 is characterized in that Rt> 5 × 10 ⁷ is satisfied, where Rt [Ω] is a resistance value in a thin layer state of the developer layer formed on the developer carrier. The developing device according to the first to tenth aspects of the present invention.

  According to the present invention, by reducing the particle size variation in the white image developing portion and the black image developing portion, it is possible to eliminate the development ghost due to the specific charge variation, and to achieve good development.

  Further, by defining the resistance value of each member including the resistance value of the developing roller, the development ghost due to the surface potential fluctuation can be eliminated together.

  Furthermore, in addition to the above resistance value regulation, a protective resistor is inserted into each member, and by setting an upper limit of the applied voltage, it is possible to prevent toner layer deterioration due to overcurrent and to prevent image quality deterioration due to this. It was.

  In particular, according to the fourth aspect of the present invention, the toner remaining on the developing roller after white image development is removed by bringing the reset member into contact with the developing roller and applying a voltage that draws the charged toner toward the reset member. Eliminate static electricity to make it equivalent to that after black image development. As a result, the difference between the average toner particle diameter after developing the black image and the average toner particle diameter after developing the white image can be reduced, and the problem of development ghost can be solved.

  If the reset member is made of a conductive roller, a long-life developing device can be provided, and if it is made of a conductive film, an inexpensive developing device can be provided.

  In addition, since the toner layer thickness regulating member is brought into contact with the developing roller and a voltage for attracting the charged toner toward the developing roller is applied, variation in the toner layer thickness and specific charge amount can be reduced. The density unevenness can be reduced, and when combined with the effect of preventing the development ghost, a better development image quality can be provided.

  Further, by providing an upper limit to the applied bias or providing a protective resistor, it is possible to prevent overcurrent that makes the toner layer thickness and specific charge amount unstable, and to provide good development image quality.

  Also, the density of the halftone image can be reduced by bringing the toner supply member into contact with the developing roller and applying a voltage that draws the charged toner toward the developing roller, thereby reducing variations in the toner layer thickness and specific charge amount. Unevenness can be reduced, and in combination with the effect of preventing the development ghost, better development image quality can be provided.

  Further, according to the eighth aspect of the present invention, by setting an upper limit on the resistance value of the reset member, it is possible to prevent a change in surface potential due to charge accumulation on the surface of the reset member, thereby preventing deterioration of toner removal characteristics. Can do.

  According to the ninth aspect of the present invention, since an upper limit is set on the resistance value of the developer supply member, a change in surface potential due to charge accumulation on the surface of the developer supply member can be prevented. Can be prevented.

  According to the tenth aspect of the present invention, by setting a lower limit to the resistance value of the developing roller, it is possible to prevent problems such as dielectric breakdown and overcurrent with the member in contact with the developing roller, and to set an upper limit on the resistance value of the developing roller By providing, it is possible to prevent the development characteristics from being impaired due to the influence of toner transfer current and development roller surface potential change, and it is possible to provide good development image quality.

  Further, according to the present invention 11, if the semiconductive layer of the developing roller is formed of urethane resin having a moisture absorption rate of 1% or less, the resistance value varies due to variations in temperature and humidity. In addition, the electrostatic latent image carrier can be prevented from being contaminated, and image quality deterioration can be effectively prevented.

  Further, according to the present invention 12, by defining the lower limit of the toner layer resistance value, even when a bias is applied to each member, it is possible to improve the safety against toner layer dielectric breakdown and overcurrent, and to form a stable toner layer. Development characteristics can be realized.

  The present invention includes a developer carrying member that carries a one-component developer on the surface and that develops an electrostatic latent image in contact with the electrostatic latent image carrying member, and a developer that supplies the developer to the developer carrying member. The present invention can be applied to a developing device including a supply member and a developer layer regulating member that abuts on the developer carrying member and regulates the layer thickness of the developer supplied by the developer supply member.

FIG. 1 is a diagram illustrating a developing device that uses a one-component developer according to the present invention, and shows a structure of a developing device that performs development by making contact with a photosensitive member carrying an electrostatic latent image. FIG. 2 is a diagram for explaining a particle size distribution variation when no reset member is provided in the developing device shown in FIG. 1. FIG. 2 is a diagram for explaining a particle size distribution variation when a reset member is provided in the developing device shown in FIG. 1. FIG. 2 is a configuration diagram for explaining an outline of an overall structure of an image forming apparatus including the developing device shown in FIG. 1. It is a figure which shows the specific example of the apparatus which measures the static resistance value in the thin layer state of the toner used for the image development apparatus based on this invention. It is a figure which shows an example of the result of having measured the static resistance value in the thin layer state of the toner used for the image development apparatus based on this invention, and a voltage-current characteristic. It is explanatory drawing of the apparatus which measures the static resistance value of the developing roller which comprises the developing apparatus of this invention. In the developing device based on this invention, it is a figure for demonstrating the development characteristic which made resistance value of the developing roller the parameter. In the developing device based on this invention, it is a figure for demonstrating the development characteristic which made the adhesion amount of the toner a parameter. In the developing device according to the present invention, it is a diagram for explaining the development characteristics using the specific charge of the toner as a parameter. FIG. 4 is a diagram for explaining development characteristics using a surface potential increase amount of a developing roller constituting the developing device of the present invention as a parameter. It is a figure which shows the structure of the reset part after image development as an example explaining the protection resistance which prevents the overcurrent used for the image development apparatus based on this invention. 12 is an equivalent circuit of the reset unit shown in FIG. The relationship between the particle size and specific charge of a general one-component developer used in the developing device according to the present invention is not shown. In the developing device based on this invention, it is an image pattern for evaluating the presence or absence of a development ghost. It is a figure explaining the appropriate electrode width at the time of using an electroconductive sheet for the toner layer control member which comprises the developing device based on this invention.

Explanation of symbols

1 Photoconductor (electrostatic latent image carrier)
4 Developing Device 10 (Non-magnetic) One-Component Developer 11 Power Supply Circuit 12 for Supplying Development Bias Voltage Power Supply Circuit 13 for Supplying Voltage to Regulatory Member Voltage Circuit 40 for Supplying Voltage to Supply Roller Developing Tank 41 Developing Roller (Developing Roller) Toner carrier)
42 Supply roller (supply means)
43 Blade (Regulator)
44 reset member 45 toner layer 46 semiconductive layer Va development bias voltage Vb regulating bias voltage Vc supply bias voltage Vd reset bias voltage Rd developing roller resistance Rc toner internal resistance Ri toner contact resistance Rs toner surface resistance 50 protection resistance

Claims (1)

A developer carrier that carries a one-component developer on the surface and that develops an electrostatic latent image in contact with the electrostatic latent image carrier;
A developer supply member for supplying a developer to the developer carrier;
A developer layer regulating member that contacts the developer carrying member and regulates the layer thickness of the developer supplied by the developer supplying member;
A reset member that contacts the developer carrier after the developer carrier and the electrostatic latent image carrier are in contact with each other, and removes or removes the developer remaining on the developer carrier; In the developing device,
The developer has a CV value [%] representing a volume particle size distribution defined as CV = 100 × (standard deviation / average value) of 25% to 34.6%, and
When the voltage applied to the developer carrying member is Va [V] and the voltage applied to the reset member is Vd [V], the sign of Va-Vd is the same polarity as the charging polarity of the developer, and By applying a voltage so that | Va−Vd | ≧ 100 [V],
When the developer carrying member having a predetermined layer thickness is subjected to black image development, the developer is supplied by the developer supply member, and the developer layer restricting member is used to form the predetermined layer thickness again. The average volume particle size of the developer carried by the developer carrying member is Dbk,
When the developer carrying member having a predetermined layer thickness is subjected to white image development, the developer is supplied by the developer supply member, and is again formed to have the predetermined layer thickness by the developer layer regulating member. When the average volume particle size of the developer carried by the developer carrying member is Dwt, Dbk and Dwt are
Dwt / Dbk> 0.8
The developing device is characterized in that the amount of variation in particle size caused by an image pattern developed in the past is limited in the developer carried by the developer carrying member.

Images