JP2010072468A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device capable of responding to high-speed printing without bringing about heat generation of the device and capable of preventing an image memory from being formed while securing an image density, in a hybrid developing system. <P>SOLUTION: Two developing rollers 21A, 21B arranged opposite to a developer-conveying roller 23 and an image carrier 1 are disposed, a vibrational electric field, on the average, in the direction of transferring toner from the developer-conveying roller to the developing rollers is formed between the developer-conveying roller and the developing rollers, the moving direction of a developer on the developer-conveying roller and the moving direction of the toner on the developing rollers are set in the inverse direction to each other on the opposite part and, with respect to the first developing roller located on the upstream side in the rotation direction of the image carrier, a toner conveyance amount Q [g/m<SP>2</SP>], a ratio Rd of peripheral speed of the developing roller to peripheral speed of the image carrier, a process speed Pv [mm/sec], a diameter D [mm] of the developing roller and the number n of the developing rollers satisfy the following relations: 1≤Q≤4, Rd≤(100/Pv)D, 4/n≤Rd×Q. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing device used for electrophotographic image formation that can be applied to, for example, a copying machine, a facsimile machine, a printer, or a combination of these, and an image forming apparatus including the developing device.

  In an electrophotographic image forming apparatus, a developing method employed for developing an electrostatic latent image formed on an image carrier includes a one-component developing method using only toner as a main component of a developer, and a developing method. A two-component development method using toner and carrier as the main components of the agent, and a so-called hybrid development method intended to enjoy the advantages of both by combining the one-component development method and the two-component development method. It has been known.

In the two-component development system, development is performed by supplying only the toner to the latent image on the image carrier directly from the developer carrier carrying the developer composed of toner and carrier without going through the toner carrier. Done.
On the other hand, in the hybrid development method, only the toner is supplied to the toner carrier from the developer carrier that carries the developer composed of toner and carrier, and the latent image on the image carrier is developed by the one-component development method. Done. It is known that the so-called image memory (image history) problem is more prominent in this hybrid development method than in the one-component development method and the two-component development method.

  In the one-component development method, a supply roller that is composed of a sponge or the like and has a toner collecting function is in contact with the toner carrier, and the toner on the toner carrier is accurately adjusted by the contact pressure between the sponge and the toner carrier surface. It can be recovered well. In the two-component development system, generally, a part of the developer carrying member is disposed so as to come into contact with the developer in the developing tank, and toner is supplied and recovered in the process of passing therethrough.

  On the other hand, in the case of the hybrid development method, the toner on the toner carrier must be collected by the rising of the carrier on the developer carrier, and sufficient recoverability can be secured stably. In general, it is considered difficult to generate a memory image due to a difficult relationship. As a method for improving the toner recoverability in this hybrid developing system, it may be possible to provide a separate member for toner recovery, but there is a problem that the apparatus cost increases and the apparatus becomes large.

In relation to such a problem, for example, Patent Document 1 includes two donor rolls (toner carrier) in the hybrid development system, and includes a detection unit that detects a memory image, and takes into account toner deterioration. There has been disclosed a developing device in which the rotational speed of a magnetic roll (developer carrier) is increased only when an image is detected, thereby attempting to eliminate the image memory. In this developing device, in the toner supply and recovery unit between the two toner carriers and the developer carrier, the movement directions of the peripheral surface of the toner carrier and the peripheral surface of the developer carrier are opposite to each other. In the developing portion between the two toner carriers and the photoconductive belt (image carrier), the movement direction of the peripheral surface of the toner carrier and the belt surface is set in the same direction.
JP 2006-276853 A

  However, in the conventional hybrid development type developing device, while the memory image is detected and the rotation speed of the developer carrier is increased, the deterioration of the toner is also promoted, and the memory image is detected. Therefore, there is a problem that the apparatus becomes large.

  Conventionally, in a development device of a hybrid development system, when a configuration in which toner is supplied to and collected from a toner carrier with a single member is used and development is attempted in a high-speed print region, the toner supply amount required for development When the supply electric field necessary for securing the toner is applied, the recovery electric field necessary for the recovery cannot be obtained, and as a result, the image memory appears, and the apparatus generates heat (specifically, in the toner carrier). Problems arise.

  In order to improve the toner recoverability, the average potential difference in the toner supply / recovery unit is set in a direction that is advantageous for toner recovery, or the toner carrying amount on the toner carrier is reduced to increase the toner adhesion. Although it is generally effective to reduce the toner density, if the toner adhesion force is excessively reduced, it will hinder the securing of the image density.

  The present invention has been made in view of such technical problems, and in the hybrid development system, it can cope with high-speed printing without causing heat generation of the apparatus, and prevents image memory from being generated while ensuring image density. It is a basic object to provide a developing device and an image forming apparatus that can be used.

For this reason, the developing device according to the first invention of the present application includes a developer carrying member that encloses a magnet and carries a developer containing toner and magnetic particles on a peripheral surface, the developer carrying member, and an electrostatic latent image. A plurality of toner carriers disposed opposite to the carrier, and a first toner in the direction of transferring toner from the developer carrier to the toner carrier between the developer carrier and the toner carrier. A first electric field forming means for forming an electric field; and a latent image portion on the electrostatic latent image carrier that transfers the toner transferred to the toner carrier between the toner carrier and the electrostatic latent image carrier. And a second electric field forming unit that visualizes the electrostatic latent image as a toner image by transferring to
The first electric field forming means, on the average, forms an oscillating electric field in a direction in which the toner is transferred from the developer carrier to the toner carrier,
The moving direction of the developer on the developer carrying member and the moving direction of the toner on the toner carrying member are set in opposite directions at the facing portion thereof.
At least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner transport amount on the toner carrier is Q [g / m ² ], and the peripheral speed of the electrostatic latent image carrier is The ratio of the peripheral speed of the toner carrier to the development side peripheral speed ratio Rd, the process speed Pv [mm / sec], the diameter of the toner carrier D [mm], and the number of toner carriers n [number] The following conditions: a) 1 ≦ Q ≦ 4, b) Rd ≦ (100 / Pv) · D, c) 4 / n ≦ Rd · Q
It is characterized by satisfying.

In addition, a developing device according to a second invention of the present application includes a developer carrying body that encloses a magnet and carries a developer containing toner and magnetic particles on a peripheral surface, the developer carrying body, and an electrostatic latent image carrying body. And a first electric field in a direction in which the toner is transferred from the developer carrier to the toner carrier between the developer carrier and the toner carrier. Between the toner carrier and the electrostatic latent image carrier, the toner transferred to the toner carrier to the latent image portion on the electrostatic latent image carrier. A developing device comprising: a second electric field forming unit that transfers the electrostatic latent image to a visible image as a toner image;
At least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner transport amount on the toner carrier is Q [g / m ² ], and the peripheral speed of the electrostatic latent image carrier is The ratio of the peripheral speed of the toner carrier to the development side peripheral speed ratio Rd, the process speed Pv [mm / sec], the diameter of the toner carrier D [mm], and the number of toner carriers n [number] , The average potential difference ΔV _avg of the toner supply / recovery unit in the oscillating electric field formed by the first electric field forming means {(toner supply side potential difference × supply side duty ratio) − (toner recovery side potential difference × collection side duty ratio) } / 100 and the following conditions: a) 1 ≦ Q ≦ 4.5, b) Rd ≦ (100 / Pv) · D, c) 4 / n ≦ Rd · Q, d) ΔV _avg ≦ 200
It is characterized by satisfying.

Furthermore, a developing device according to a third invention of the present application includes a developer carrying member that encloses a magnet and carries a developer containing toner and magnetic particles on a peripheral surface thereof, and the developer carrying member and an electrostatic latent image carrying member. And a first electric field in a direction in which the toner is transferred from the developer carrier to the toner carrier between the developer carrier and the toner carrier. Between the toner carrier and the electrostatic latent image carrier, the toner transferred to the toner carrier to the latent image portion on the electrostatic latent image carrier. A developing device comprising: a second electric field forming unit that transfers the electrostatic latent image to a visible image as a toner image;
At least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner transport amount on the toner carrier is Q [g / m ² ], and the peripheral speed of the electrostatic latent image carrier is The ratio of the peripheral speed of the toner carrier to the developing side peripheral speed ratio Rd, the ratio of the peripheral speed of the developer carrier to the peripheral speed of the toner carrier is the supply side peripheral speed ratio Rs, and the process speed is Pv [mm]. / Sec], where the diameter of the toner carrier is D [mm], and the number of toner carriers is n [pieces], a) 1 ≦ Q ≦ 4.5, b) Rd ≦ (100 / Pv) D, c) 4 / n ≦ Rd · Q, d) Rs ≧ 1
It is characterized by satisfying.

Furthermore, a developing device according to a fourth invention of the present application includes a developer carrying member that encloses a magnet and carries a developer containing toner and magnetic particles on a peripheral surface, the developer carrying member, and an electrostatic latent image. A plurality of toner carriers disposed opposite to the carrier, and a first toner in the direction of transferring toner from the developer carrier to the toner carrier between the developer carrier and the toner carrier. A first electric field forming means for forming an electric field; and a latent image portion on the electrostatic latent image carrier that transfers the toner transferred to the toner carrier between the toner carrier and the electrostatic latent image carrier. And a second electric field forming unit that visualizes the electrostatic latent image as a toner image by transferring to
At least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner transport amount on the toner carrier is Q [g / m ² ], and the peripheral speed of the electrostatic latent image carrier is The ratio of the peripheral speed of the toner carrier to the development side peripheral speed ratio Rd, the process speed Pv [mm / sec], the diameter of the toner carrier D [mm], and the number of toner carriers n [number] The following conditions are used: a) 1 ≦ Q ≦ 4.5, b) Rd ≦ (100 / Pv) · D, c) 4 / n ≦ Rd · Q, d) E ≦ 40
It is characterized by satisfying.

  In the above case, it is preferable to use a small diameter toner having a particle diameter of 8 [μm] or less.

  According to the first invention of the present application, by providing a plurality of toner carriers, the rotational speed of each toner carrier required for supplying toner to the image carrier at high speed even when high-speed printing is required. And the heat generation of the toner carrier (and hence the heat generation of the apparatus) can be suppressed. That is, it is possible to cope with high-speed printing without causing heat generation of the apparatus. In particular, by setting the moving direction of the developer on the developer carrying member and the moving direction of the toner on the toner carrying member in the opposite directions at the opposite portions, a higher rubbing / disturbing effect can be obtained, The toner recoverability can be improved. Moreover, at least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner carrier (Q) on the toner carrier and the toner carrier relative to the peripheral speed of the electrostatic latent image carrier. The image density is ensured by suitably setting the peripheral speed ratio (development side peripheral speed ratio Rd), the process speed (Pv), the diameter (D) of the toner carrier and the number (n) of the toner carriers. In addition, the generation of the image memory can be effectively prevented.

According to the second invention of the present application, since a plurality of toner carriers are provided, each toner carrier required for supplying toner to the image carrier at high speed can be obtained even when high-speed printing is required. The rotation speed can be reduced, and the heat generation of the toner carrier (and hence the heat generation of the apparatus) can be suppressed. That is, it is possible to cope with high-speed printing without causing heat generation of the apparatus. In particular, by setting the moving direction of the developer on the developer carrying member and the moving direction of the toner on the toner carrying member in the opposite directions at the opposite portions, a higher rubbing / disturbing effect can be obtained, The toner recoverability can be improved. Moreover, at least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner carrier (Q) on the toner carrier and the toner carrier relative to the peripheral speed of the electrostatic latent image carrier. Peripheral speed ratio (development side peripheral speed ratio Rd), process speed (Pv), the diameter (D) of the toner carrier, the number of toner carriers (n), and the first electric field forming means formed by the first electric field forming means. By appropriately setting the average potential difference (ΔV _avg ) of the toner supply / recovery unit in the electric field (average, the oscillating electric field in the direction in which the toner is transferred from the developer carrier to the toner carrier), the image density can be reduced. The generation of the image memory can be effectively prevented after being secured.

  Further, according to the third invention of the present application, by providing a plurality of toner carriers, each toner carrier required for supplying toner to the image carrier at high speed can be obtained even when high-speed printing is required. The rotation speed can be reduced, and the heat generation of the toner carrier (and hence the heat generation of the apparatus) can be suppressed. That is, it is possible to cope with high-speed printing without causing heat generation of the apparatus. In particular, by setting the moving direction of the developer on the developer carrying member and the moving direction of the toner on the toner carrying member in the opposite directions at the opposite portions, a higher rubbing / disturbing effect can be obtained, The toner recoverability can be improved. Moreover, at least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner carrier (Q) on the toner carrier and the toner carrier relative to the peripheral speed of the electrostatic latent image carrier. The peripheral speed ratio (development side peripheral speed ratio Rd), the process speed (Pv), the diameter (D) of the toner carrier, the number of toner carriers (n), and the supply side peripheral speed ratio (Rs) are preferably used. By setting, it is possible to effectively prevent the generation of the image memory while ensuring the image density.

  Further, according to the fourth invention of the present application, since a plurality of toner carriers are provided, each toner carrier required for supplying toner to the image carrier at high speed even when high-speed printing is required. The rotation speed of the toner can be reduced, and the heat generation of the toner carrier (and hence the heat generation of the apparatus) can be suppressed. That is, it is possible to cope with high-speed printing without causing heat generation of the apparatus. In particular, by setting the moving direction of the developer on the developer carrying member and the moving direction of the toner on the toner carrying member in the opposite directions at the opposite portions, a higher rubbing / disturbing effect can be obtained, The toner recoverability can be improved. Moreover, at least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner carrier (Q) on the toner carrier and the toner carrier relative to the peripheral speed of the electrostatic latent image carrier. The peripheral speed ratio (development side peripheral speed ratio Rd), the process speed (Pv), the diameter (D) of the toner carrier, the number of toner carriers (n), and the saturated charge amount (E) of the toner are preferably By setting, it is possible to effectively prevent the generation of the image memory while ensuring the image density.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, terms indicating a specific direction (for example, “up”, “down”, “left”, “right”, and other terms including them, “clockwise direction”, “counterclockwise” ”) Is used to facilitate understanding of the invention with reference to the drawings, and the present invention should not be construed as being limited by the meaning of these terms. Further, in the image forming apparatus and the developing apparatus described below, the same reference numerals are used for the same or similar components.

[Image forming apparatus]
FIG. 1 shows a portion related to image formation of an electrophotographic image forming apparatus according to an embodiment of the present invention.
The image forming apparatus M1 according to the present embodiment performs image formation by transferring a toner image formed on an image carrier (photoconductor) 1 to a transfer medium P such as paper by an electrophotographic method. , A printer, a facsimile machine, or a multi-function machine having these functions in combination.

The image forming apparatus M1 has an image carrier 1 (so-called photoconductor) for carrying an electrostatic latent image. The image carrier 1 is connected to a motor (not shown) and is driven by the motor. Rotate in the direction of the arrow based on Around the image carrier 1, there are charging means 6 for charging the image carrier 1, exposure means 7 for exposing the image carrier 1 to form an electrostatic latent image, and the electrostatic latent image. A developing device 2 for developing the toner, a transfer means 8 for transferring the developed toner image on the image carrier 1, and a cleaning means 9 for removing residual toner on the image carrier 1. They are arranged in order along the direction.
For the image carrier 1, the charging means 6, the exposure means 7, the transfer means 8, the cleaning means 9 and the like used in the electrophotographic apparatus, a well-known electrophotographic technique can be arbitrarily used. For example, although a charging roller is shown in FIG. 1 as the charging unit 6, a charging device that is not in contact with the image carrier 1 may be used.

The developing device 2 includes a developer tank 28 that stores the developer 25 and a developer transport roller 23 that transports the developer 25 supplied from the developer tank 28 while supporting the developer 25 on the surface. As developing rollers capable of separating the toner from the developer 25 of the roller 23, first and second developing rollers 21A and 21B are provided.
These first and second developing rollers 21A and 21B are both arranged in the vertical direction in FIG. 1 so as to face both the image carrier 1 and the developer transport roller 23. With respect to the circumferential movement direction (arrow Y4 direction), the first developing roller 21A is positioned upstream and the second developing roller 21B is positioned downstream.

  The developer 25 in the developing tank 28 is mixed and stirred by the rotation of the mixing and stirring means 26 and is frictionally charged, and then supplied to the sleeve roller 23 s on the surface of the developer transport roller 23. The developer 25 is held on the surface side of the sleeve roller 23s by the magnetic force of the magnet roller 23m inside the developer transport roller 23, and rotates together with the sleeve roller 23s. Then, after the passage amount is regulated by a regulating member 24 provided opposite to the developer conveying roller 23, it is sent to a portion facing the first and second developing rollers 21A and 21B.

  An electric field that causes the toner in the developer to be electrically separated and carried on the surfaces of the developing rollers 21A and 21B by the first electric field forming unit 4 at the opposing portion between the developer conveying roller 23 and the developing rollers 21A and 21B. Is formed. The toner layers 22a and 22b respectively carried on the developing rollers 21A and 21B are conveyed to a position facing the image carrier 1 by the developing rollers 21A and 21B, and the developing electric field formed by the second electric field forming unit 5 is transferred. Below, the electrostatic latent image on the image carrier 1 is developed. The development method may be a reversal development method or a regular development method.

  After development, the toner remaining on the developing rollers 21A and 21B is rubbed and disturbed by a magnetic brush formed on the developer conveying roller 23 at a portion facing the developer conveying roller 23, and collected in the developer. Is done.

The movement direction (arrow Y2, Y3 direction) of the peripheral surfaces of the first and second developing rollers 21A, 21B is the movement direction (arrow Y1 direction) of the peripheral surface of the developer transport roller 23 (that is, the sleeve roller 23s). ) Is set to be in the opposite direction at each facing portion. That is, the moving direction of the developer on the developer conveying roller 23 (that is, on the sleeve roller 23s) and the moving direction of the toner on the first and second developing rollers 21A and 21B are opposite to each other at the opposite portion. The direction is set. By setting in this way, a higher rubbing / disturbing effect can be obtained, and toner recoverability can be improved.
The developer on the developer transport roller 23 that collects the remaining toner is peeled off from the developer transport roller 23 at a position facing the developer tank 28, collected in the developer tank 28, and mixed and stirred in the developer tank 28. .

Next, each component in the developing device 2 will be described in more detail.
As described above, the developer transport roller 23 includes the magnet roller 23m that is fixedly arranged, and a rotatable sleeve roller 23s that includes the magnet roller 23m. The magnet roller 23m has seven magnetic poles N1, S2, N2, S3, N3, N4, and S1 along the rotation direction of the sleeve roller 23s.

  Of these magnetic poles, the main magnetic poles N1 and N2 are disposed at positions facing the first and second developing rollers 21A and 21B, respectively, and are used to peel off the developer on the sleeve roller 23s. The magnetic poles N3 and N4 having the same polarity for generating a repulsive magnetic field are arranged at positions facing the inside of the developing tank 28.

  As described above, the rotation directions of the first and second developing rollers 21A and 21B (in the directions of arrows Y2 and Y3) are the same as the rotation direction of the sleeve roller 23s of the developer transport roller 23 (in the direction of arrow Y1). Are set so as to be in opposite directions. The rotation direction (arrow Y2, Y3 direction) is opposite to the rotation direction of the image carrier 1 (arrow Y4 direction), that is, the same direction at the opposing portion.

  The developing tank 28 is formed by a casing 29, and normally contains a stirring and conveying means 26 for feeding the developer 25 to the developer conveying roller 23 while mixing and stirring. A magnetic permeability sensor (not shown) for detecting a toner ratio (weight ratio) in the developer 25 is preferably disposed in the vicinity of the stirring and conveying means 26.

  The developing device 2 normally regulates the amount of developer on the developer transport roller 23 and a replenishment unit for replenishing the developer tank 28 with toner that has been developed into the latent image on the image carrier 1. It has a regulating member 24 for thinning the developer. The replenishing unit includes a toner bottle 3 that stores replenished toner, and a toner replenishing roller 27 for controlling the amount of toner replenished into the developing tank 28.

  Examples of the material used for the developing rollers 21A and 21B include an aluminum (aluminum) roller that has been subjected to a surface treatment. In addition, on a conductive substrate such as aluminum, for example, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, polysulfone resin, polyether ketone resin, vinyl chloride resin, acetic acid A resin coating such as a vinyl resin, a silicone resin, or a fluorine resin, or a rubber coating such as a silicone rubber, urethane rubber, nitrile rubber, natural rubber, or isoprene rubber may be used.

  The coating material is not limited to these. Furthermore, a conductive agent may be added to the bulk or surface of the coating. Examples of the conductive agent include an electronic conductive agent or an ionic conductive agent. Examples of the electronic conductive agent include carbon black such as ketjen black, acetylene black, and furnace black, metal powder, metal oxide fine particles, and the like, but are not limited thereto. Examples of the ionic conductive agent include, but are not limited to, cationic compounds such as quaternary ammonium salts, amphoteric compounds, and other ionic polymer materials. Furthermore, a conductive roller made of a metal material such as aluminum may be used.

[Bias to be applied]
Below, the conditions of bias application that can be used in the present invention will be described.
By the first electric field forming means 4 and the second electric field forming means 5, two conditions can be set when the toner supply portion electric field is an oscillating electric field, and when the developing portion electric field is a direct current electric field and when it is an oscillating electric field. 2A and 2B, FIG. 3 and FIG. 4 show connection examples of the bias power source when the toner is negative and performs reversal development.

  In the connection example shown in FIG. 2A, a first power source S1 connected to the developer conveying roller 23 and a second power source S2 connected to the developing roller 21 (first and second developing rollers 21A and 21B) are provided. The second power source S2 is provided with a DC power source connected between the developing roller 21 (21A, 21B) and the ground G, and develops a second DC voltage having the same polarity as the charging polarity of the toner. The roller 21 (21A, 21B) is applied. The first power source S1 includes a DC power source and an AC power source between the developer transport roller 23 and the ground G. The DC power supply applies a first DC voltage having the same polarity as the charging polarity of the toner and higher than the second DC voltage to the developer transport roller 23. The AC power source applies an AC voltage as shown in FIG. 2B between the developer transport roller 23 and the ground G. As a result, in the toner supply area, the negatively charged toner is conveyed to the developer by the action of the pulsating electric field formed between the developing roller 21 (21A, 21B) and the developer conveying roller 23. The roller 23 is electrically attracted to the developing roller 21 (21A, 21B). At this time, the positively charged carrier is held by the developer conveying roller 23 by the magnetic force of the fixed magnet inside the developer conveying roller 23 and is not supplied to the developing roller 21 (21A, 21B). . In the developing region, the negative toner held on the developer transport roller 23 is based on the potential difference between the developer transport roller 23 and the electrostatic latent image portion of the image carrier 1. Adhere to.

In the connection example shown in FIG. 3, the second power source S4 connected to the developing roller 21 (first and second developing rollers 21A and 21B) is also connected between the developing roller 21 (21A and 21B) and the ground G. A DC power supply and an AC power supply are connected. The voltage of the AC power source of the first power source S3 connected to the developer transport roller 23 and the voltage of the AC power source of the second power source S4 may be the same or different.
In the connection example shown in FIG. 4, the first power source S5 connected to the developer transport roller 23 has only a DC power source between the developer transport roller 23 and the ground G, and does not have an AC power source. . The second power source S6 connected to the developing roller 21 (first and second developing rollers 21A and 21B) is a DC power source and an AC power source connected between the developing roller 21 (21A and 21B) and the ground G. And have.

  In any case, toner can be supplied from the developer conveying roller 23 to the developing roller 21 (21A, 21B), and the toner is developed from the developing roller 21 (21A, 21B) to the electrostatic latent image portion on the image carrier 1. It must be in a potential relationship that can be achieved. The developing unit may be contact development in which the developing roller 21 (21A, 21B) and the image carrier 1 are in contact with each other via toner, or the space between the developing roller 21 and the image carrier 1 is the toner. It may be non-contact development in which the flying occurs.

[About usable developers]
The developer that can be used in the present invention will be described below.
In the present embodiment, the developer is composed of toner and a carrier for charging the toner.
The toner is not particularly limited, and commonly used known toners can be used. The binder resin contains a colorant and, if necessary, a charge control material or a release material, and the external additive is processed. Can be used. The toner particle size is not limited to this, but is preferably about 3 to 15 μm. In manufacturing such a toner, it can be manufactured by a publicly known method, for example, a pulverization method, an emulsion polymerization method, a suspension polymerization method, or the like.

  The binder resin used in the toner is not limited to this. For example, styrene resin (monopolymer or copolymer containing styrene or a styrene substitution product), polyester resin, epoxy resin, vinyl chloride Resins, phenol resins, polyethylene resins, polypropylene resins, polyurethane resins, silicone resins and the like can be mentioned. It is preferable to use those having a softening temperature in the range of 80 to 160 ° C. and those having a glass transition point in the range of 50 to 75 ° C., depending on the single resin or composite.

  As the colorant, known ones that are generally used can be used. For example, carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, ultramarine blue , Rose bengal, lake red, etc., and generally 2 to 20 parts by weight with respect to 100 parts by weight of the binder resin is preferred.

  As the charge control material, known materials can be used. Examples of the charge control material for positively chargeable toner include nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazole compounds. And polyamine resins. Examples of charge control materials for negatively chargeable toners include metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkyl salicylic acid metal compounds, and curlyx allene compounds. In general, the charge control material is preferably used at a rate of 0.1 to 10 weight capital with respect to 100 parts by weight of the binder resin.

  Further, as the above-mentioned mold release material, publicly known ones can be used, for example, polyethylene, polypropylene, carnauba wax, sazol wax and the like can be used alone or in combination of two or more kinds, Generally, it is preferable to use it in the ratio of 0.1-10 weight part with respect to 100 weight part of said binder resin.

  As particles externally added to the toner, commonly used known particles can be used. For the purpose of improving fluidity, for example, silica, titanium oxide, aluminum oxide or the like can be used, and it is particularly preferable to use a water-repellent material such as a silane coupling agent, a titanium coupling agent, or silicon oil. . Such a fluidizing agent is added at a ratio of 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner. The number average primary particle size of the external additive is preferably 10 to 100 nm.

It does not specifically limit as a carrier, The well-known carrier generally used can be used, A binder type carrier, a coat type carrier, etc. can be used. Although it is not limited to this as a carrier particle size, 15-100 micrometers is preferable.
The binder type carrier is obtained by dispersing magnetic fine particles in a binder resin, and positive or negative chargeable fine particles can be fixed to the carrier surface or a surface coating layer can be provided. The charging characteristics such as the polarity of the binder type carrier can be controlled by the material of the binder resin, the chargeable fine particles, the type of the surface coating layer, and the like.

  Examples of the binder resin used for the binder-type carrier include thermoplastic resins such as vinyl resins, polyester resins, nylon resins, polyolefin resins, and the like, as exemplified by polystyrene resins, and thermosetting resins such as phenol resins. The

  Magnetic fine particles of the binder type carrier include spinel ferrites such as magnetite and gamma iron oxide, and magnets such as spinel ferrite and barium ferrite containing one or more metals other than iron (Mn, Ni, Mg, Cu, etc.). Plumbite type ferrite, iron or alloy particles having iron oxide on the surface can be used. The shape may be any of a granular shape, a spherical shape, and a needle shape. In particular, when high magnetization is required, it is preferable to use iron-based ferromagnetic fine particles. In consideration of chemical stability, it is preferable to use ferromagnetic fine particles of magnetoplumbite type ferrite such as spinel ferrite and barium ferrite containing magnetite and gamma iron oxide. A magnetic resin carrier having a desired magnetization can be obtained by appropriately selecting the type and content of the ferromagnetic fine particles. The magnetic fine particles are suitably added in an amount of 50 to 90% by weight in the magnetic resin carrier.

Silicone resin, acrylic resin, epoxy resin, fluorine resin, etc. are used as the surface coating material of the binder type carrier, and these resins are coated on the surface and cured to form a coating layer, thereby providing a charge imparting ability. Can be improved.
For example, the charging fine particles or the conductive fine particles can be fixed to the surface of the binder type carrier by, for example, mixing the magnetic resin carrier and the fine particles uniformly, adhering these fine particles to the surface of the magnetic resin carrier, This is performed by applying a strong impact force and fixing the fine particles so as to be driven into the magnetic resin carrier. In this case, the fine particles are not completely embedded in the magnetic resin carrier, but are fixed so that a part thereof protrudes from the surface of the magnetic resin carrier.

  As the chargeable fine particles, an organic or inorganic insulating material is used. Specifically, organic insulating fine particles such as polystyrene, styrene copolymers, acrylic resins, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesin, and cross-linked products thereof are used. As for the charge level and polarity, a desired level of charge and polarity can be obtained by a material, a polymerization catalyst, a surface treatment, and the like. Further, as the inorganic type, negatively charged inorganic fine particles such as silica and titanium dioxide, and positively charged inorganic fine particles such as strontium titanate and alumina are used.

  On the other hand, a coated carrier is a carrier in which a carrier core particle made of a magnetic material is coated with a resin, and also in a coated carrier, like a binder carrier, positive or negatively chargeable fine particles are fixed on a carrier surface. You can make it. Charging characteristics such as polarity of the coat type carrier can be controlled by the type of the surface coating layer and the chargeable fine particles, and the same material as the binder type carrier can be used. In particular, the same resin as the binder resin of the binder type carrier can be used as the coating resin.

  The charging polarity of the toner by the combination of the toner and the carrier can be easily known from the direction of the electric field for separating the toner from the developer after mixing and stirring each to make the developer. The mixing ratio of the toner and the carrier may be adjusted so as to obtain a desired toner charge amount. The toner ratio is 3 to 50% by weight, preferably 6 to 30% by weight based on the total amount of the toner and the carrier. Is preferred.

[Experiment]
In the present embodiment, in the hybrid development system, the number of developing rollers can be used from the viewpoint of being able to cope with high-speed printing without causing heat generation of the developing device and preventing image memory from being generated while ensuring image density. Starting from heat generation due to differences in toner, the amount of toner transported on the toner carrier, the peripheral speed ratio between the rollers, the process speed, the diameter of the toner carrier, the average potential difference in the toner supply and recovery unit, and the toner saturation charge amount The exothermic test and the image-drawing test were conducted by changing the above.

First, the sample toner used in the experiment will be described. In the experiment, two types of toner manufactured by the following method were prepared.
Toner A: 0.2 parts by weight of the first hydrophobic silica and 0.2% of the second hydrophobic silica with respect to 100 parts by weight of the toner base material having a volume average particle diameter of about 6.5 μm prepared by the wet granulation method. By adding 5 parts by weight and 0.5 parts by weight of hydrophobic titanium oxide using a Henschel mixer (manufactured by Mitsui Kinzoku Mining Co., Ltd.) and subjecting them to a surface treatment for 3 minutes at a mixer rotational speed of 40 m / s, negative addition is performed. Toner A was obtained.
The first hydrophobic silica used here is a silica (# 130: manufactured by Nippon Aerosil Co., Ltd.) having a number average primary particle size of 16 nm and surface-treated with hexamethyldisilazane (HMDS) as a hydrophobizing agent. is there. The second hydrophobic silica is obtained by surface-treating silica (# 90: manufactured by Nippon Aerosil Co., Ltd.) having a number average primary particle size of 20 nm with HMDS. Hydrophobic titanium oxide is an anatase-type titanium oxide having a number average primary particle size of 30 nm and surface-treated with isobutyltrimethoxysilane as a hydrophobizing agent in an aqueous wet process.

  Toner B: Negative toner B was obtained in the same manner as in the toner A described above except that a toner base material having a volume average particle diameter of about 9 μm prepared by a wet granulation method was used. .

  Carrier: A carrier for bizhub C350 manufactured by Konica Minolta Business Technologies Co., Ltd., having an average particle size of about 33 μm, which is a coat type carrier in which carrier core particles made of a magnetic material are coated with an acrylic resin.

Next, each test will be described.
Example 1
Developing device: A developing device 2 having the form shown in FIG. 1 was used.
Developer: The above carrier and toner A were used. The toner ratio in the developer was 8%. In this case, the toner ratio is the ratio of the total amount of toner and external additive to the total amount of developer (hereinafter the same).
Development bias: A rectangular wave development bias having an amplitude of 1 kV, a DC component of -190 V, a negative duty ratio of 60%, and a frequency of 3 kHz was applied to the developer transport roller. A rectangular wave developing bias having an amplitude of 1.5 kV, a DC component of −350 V, a negative duty ratio of 40%, and a frequency of 3 kHz was applied to the developing roller 21A and the developing roller 21B.

FIG. 5 illustrates the bias applied to each roller. Thus, the potential difference in the direction in which the negatively charged toner is supplied from the developer conveying roller 23 to the first developing roller 21A and the second developing roller 21B is 1090 V, and conversely, on the first developing roller 21A and the second developing roller 21B. It can be seen that the potential difference in the direction in which the upper toner is collected by the developer conveying roller 23 is 1410V.
Here, the average potential difference ΔV _avg of the toner supply and recovery unit can be expressed by the following equation.
ΔV _avg = {(toner supply side potential difference × supply side duty ratio) − (toner recovery side potential difference × recovery side duty ratio)} / 100
In this case, ΔV _avg = {(1090 × 60) − (1410 × 40)} / 100 = 90V.

The developing rollers 21A and 21B are made of anodized aluminum rollers. The gaps between the developer transport roller 23 and the first and second developing rollers 21A and 21B are 0.3 mm, respectively. . Accordingly, the electric field in the toner supply direction formed between the developer conveying roller 23, the developing roller 21A, and the developing roller 21B is 1090 V / 0.3 mm = 3.6 × 10 ⁶ V / m. The distance between the regulating member 24 and the developer transport roller 23 was set to 0.4 mm so that the magnetic brush on the developer transport roller 23 slid onto the developing rollers 21A and 21B. The developer moving direction on the developer conveying roller 23 and the toner moving direction on the developing rollers 21A and 21B are opposite to each other at the opposed portions. The background potential of the electrostatic latent image formed on the image carrier 1 is −550 V, and the image portion potential is −60 V. The closest portion between the image carrier 1, the developing roller 21A, and the developing roller 21B is The gap was 0.135 mm.

Here, the ratio of the peripheral speeds of the developing rollers 21A and 21B to the peripheral speed of the image carrier 1 is Rd (development-side peripheral speed ratio: Rd = peripheral speed of the developing rollers 21A and 21B / peripheral speed of the image carrier 1). The ratio of the peripheral speed of the developer transport roller 23 to the peripheral speed of the developing rollers 21A and 21B is Rs (supply-side peripheral speed ratio: Rs = peripheral speed of the developer transport roller 23 / peripheral speed of the developing rollers 21A and 21B). In addition, the toner conveyance amount (toner carrying amount per unit area) on the developing rollers 21A and 21B is Q [g / m ² ].

In the first embodiment, the rotation speed of the developer conveying roller 23 and the rotation speeds of the first and second developing rollers 21A and 21B are set so that the supply-side peripheral speed ratio Rs = 1.
Further, the developing-side peripheral speed ratio Rd = 2.5, the toner transport amount Q of the first developing roller 21A = 3 [g / m ² ], and the toner transport amount Q of the second developing roller 21B = 2.8 [g / m]. ² ], the rotation speeds of the first and second developing rollers 21A and 21B were adjusted, and the electric field of the toner supply and recovery unit was adjusted as described above.

[Test 1]
In Test 1, a conventional hybrid developing device having only one developing roller and a developing device having the configuration shown in FIG. 1 (two developing rollers) according to this embodiment are used under the same conditions. By driving, both heat generation properties were compared. The test results are shown in Table 1 described later.

(Comparative Example 1)
This comparative example 1 uses a conventional hybrid developing device having only one developing roller, and FIG. 6 shows a portion related to image formation of an image forming apparatus provided with such a developing device. In the image forming apparatus M2 according to the comparative example 1, except that the developing device 102 includes only a single developing roller 121, and the number and arrangement of magnetic poles in the magnet roller 123m of the developer transport roller 123 are different. The image forming apparatus M1 according to the present embodiment shown in FIG. 1 has the same basic configuration, and the material of each component is also the same. Note that the image forming apparatus M2 shown in FIG. 6 has the same configuration as that in the image forming apparatus M1 shown in FIG. Description is omitted.
In the developing device 102 according to the comparative example 1, the rotation direction of the sleeve roller 123s of the developer conveying roller 123 is the same as the rotation direction of the developing roller 121 (that is, the opposite portions of the two are opposite directions). Is set.

  Using the developing device 102 having the conventional hybrid configuration (one developing roller) shown in FIG. 6, a developing roller 121 having a diameter D = 18 mm is used, and a development-side peripheral speed ratio Rd = 2 is set. Table 1 shows the number of rotations of the developing roller when the speed Pv is 300, 600, and 900 [mm / s].

(Example 2)
This Example 2 is for comparison with Comparative Example 1, and the developing device 2 having the configuration (two developing rollers) shown in FIG. 1 according to this embodiment is used to develop with a diameter D = 18 mm. Table 1 shows the number of rotations of the developing roller when the roller 121 is used, the development-side peripheral speed ratio Rd = 2, and the process speed Pv is 300, 600, 900 [mm / s].

The results of Test 1 were as shown in Table 1.

In the second embodiment, even if the process speed Pv is increased to 900 [mm / s], the rotation speed of the developing rollers 21A and 21B does not exceed 1000 rpm, the heat generation of the developing device 2 is low, and there is no practical problem. Did not occur. On the other hand, in Comparative Example 1, when the process speed Pv is set to 600 and 900 [mm / s], the rotation speed of the developing roller 121 greatly exceeds 1200 rpm. A large amount of heat was generated, causing practical problems.
Accordingly, it has been confirmed that it is effective to use the image forming apparatus M1 incorporating the developing device 2 according to the present embodiment including the two developing rollers 21A and 21B in order to cope with the speeding up of the process. did it.

[Test 2]
In Test 2, the appropriate ranges of the amount of toner that can be supplied to the image carrier per unit time, the size of the developing-side peripheral speed ratio, the toner transport amount of the developing roller, and the like were determined. The test results are shown in FIG. 7 and Table 2 described later.

(Comparative Example 2)
This comparative example 2 exemplifies a case where the amount of toner that can be supplied to the image carrier 1 per unit time is excessively small. Using the same developing device 2 and developer as in the first embodiment, Speed ratio Rd = 1.5, toner transport amount Q of the first developing roller 21A = 1.2 [g / m ² ], toner transport amount Q of the second developing roller 21B = 1.1 [g / m ² ] The DC component of the bias applied to the first and second developing rollers 21A and 21B and the developer conveying roller 23 is changed, and the first and second developing rollers 21A and 21B and the developer conveying roller 23 are changed. The rotation speed was adjusted. In this case, for the first developing roller 21A, the Rd · Q value that is an index indicating the amount of toner supplied to the image carrier 1 per unit time is 1.8. The condition of Comparative Example 2 corresponds to the point (× 2) in FIG.

(Comparative Example 3)
This comparative example 3 exemplifies a case where the development side peripheral speed ratio Rd is excessively large. The development side peripheral speed ratio Rd = 5, the first developing apparatus 2 and the developer similar to those in the first embodiment are used. The first and ^second toner conveying amounts Q of the developing roller 21A are 1.5 [g / m ² ] and the toner conveying amount Q of the second developing roller 21B is 1.4 [g / m ² ]. The bias DC components applied to the developing rollers 21A and 21B and the developer conveying roller 23 were changed, and the rotation speeds of the first and second developing rollers 21A and 21B and the developer conveying roller 23 were adjusted. In this case, for the first developing roller 21A, the Rd · Q value, which is an index indicating the amount of toner supplied to the image carrier 1 per unit time, is 7.5. The condition of Comparative Example 3 corresponds to the point (× 3) in FIG.

(Comparative Example 4)
The comparative example 4 exemplifies a case where the toner conveyance amount of the developing rollers 21A and 21B is excessively large, and the developing side peripheral speed ratio Rd = using the developing device 2 and the developer similar to those in the first embodiment. 3. Toner transport amount Q of first developing roller 21A = 5 [g / m ² ], toner transport amount Q of second developing roller 21B = 4.7 [g / m ² ] 2 The DC component of the bias applied to the developing rollers 21A and 21B and the developer conveying roller 23 was changed, and the rotation speeds of the first and second developing rollers 21A and 21B and the developer conveying roller 23 were adjusted. In this case, for the first developing roller 21A, the Rd · Q value, which is an index indicating the amount of toner supplied to the image carrier 1 per unit time, is 15. The condition of Comparative Example 4 corresponds to the point (× 4) in FIG.

Under the conditions of Example 1 and Comparative Examples 2 to 4, image image evaluation (image memory and solid density) and heat generation by driving the developing roller were evaluated.
Further, as conditions for evaluating heat generation by driving the developing roller, the process speed Pv was set to 450 [mm / s], and the diameters D of the first and second developing rollers 21A and 21B were both unified to 18 mm. Therefore, (100 / Pv) · D is about 4.

The results of Test 2 were as shown in Table 2.

In the first embodiment, an image memory is not generated, the density of a solid image is sufficiently secured, and no heat is generated by the developing roller. Therefore, the developing device can provide a good image.
In Comparative Example 2, there is a problem that the image density cannot be secured (solid image: x) because the amount of toner per unit time that can be provided to the developing unit is too small. In this case, if the number of developing rollers is n (n = 2), 4 / n = 2, and the relationship 4 / n ≦ Rd · Q is not satisfied.
In Comparative Example 3, the development-side peripheral speed ratio Rd was large, and the number of rotations of the developing roller was too high at 1590 rpm.
Further, in Comparative Example 4, there was a problem that an image memory was generated due to poor recovery of the toner on the developing roller.

The conditions of Example 1 and Comparative Examples 2 to 4 are indicated by point (◯ 1) and point (× 2) to point (× 4) in the graph of FIG.
As shown in FIG. 7, in this test, in addition to the above-described Example 1 and Comparative Examples 2 to 4, similar tests were performed by variously changing the toner transport amount Q and Rd · Q value of the developing roller. The image memory was checked for occurrence. In FIG. 7, a point (●) and a point (x) not accompanied by a numerical symbol represent these test examples, where a mark ● indicates no image memory and a mark × indicates that there is an image memory. In FIG. 7, the hatched area represents an area where there is no practical problem with respect to the image memory.

As described above, in order to realize a good image without an image memory, at least for the first developing roller 21A, the toner transport amount Q [g / m2] of the developing roller, the number of developing rollers n [lines], the developing peripheral speed It can be said that it is most preferable that the following conditions are satisfied for the ratio Rd and Rd · Q value.
・ 1 ≦ Q ≦ 4
・ Rd ≦ (100 / Pv) ・ D = 4
・ 4 / n ≦ Rd ・ Q

[Test 3]
In Test 3, it was examined in Comparative Example 5 below whether which toner conveyance amount Q of the first developing roller 21A or the second developing roller 21B has a greater influence on the occurrence of the image memory.
(Comparative Example 5)
In Comparative Example 5, using the same developing device 2 and developer as in Example 1, the development-side peripheral speed ratio Rd = 2.5, the toner transport amount Q of the first developing roller 21A = 4.2 [g / ^m 2], so that the toner conveyance amount of the second developing roller ^{21B Q = 4 [g / m} 2], the first, second developing roller 21A, 21B and DC bias applied to the developer conveying roller 23 The components were changed, and the rotation speeds of the first and second developing rollers 21A and 21B and the developer conveying roller 23 were adjusted. In this case, for the first developing roller 21A, the Rd · Q value that is an index indicating the amount of toner supplied to the image carrier 1 per unit time is 10.5. The condition of Comparative Example 5 corresponds to the point (Δ5) in FIG.

  According to the test 3 using the comparative example 5, although it is not particularly problematic in practical use, some instability was recognized in the image memory characteristics (this evaluation is indicated by Δ in FIG. 7). ). In other words, even when the toner transport amount Q of the second developing roller 21B located downstream in the rotation direction of the image carrier 1 is 4 or less (Q = 4), some instability occurs in the image memory characteristics. Therefore, it can be said that the generation of the image memory is dominant because the influence of the toner conveyance amount Q of the first developing roller 21A located on the upstream side in the rotation direction of the image carrier 1 is larger. Therefore, in the following, only the toner conveyance amount of the first developing roller 21A is displayed as the toner conveyance amount Q of the developing roller.

[Test 4]
In Test 4, the average potential difference ΔV _avg of the toner supply / recovery unit in the oscillating electric field formed by the first electric field forming unit is {(toner supply side potential difference × supply side duty ratio) − (toner recovery side potential difference × collection side duty). Ratio)} / 100, the influence of the average potential difference ΔV _{avg of the} toner supply / recovery unit on the occurrence of image memory was examined.

(Example 3)
In the third embodiment, using the same developing device 2 and developer as in the first embodiment, the development-side peripheral speed ratio Rd = 2.5, the toner transport amount Q of the first developing roller 21A = 4.5 [g / M ² ], the DC component of the bias applied to the first and second developing rollers 21A and 21B and the developer transport roller 23 is changed, and the first and second developing rollers 21A and 21B and The number of rotations of the developer transport roller 23 was adjusted. At that time, the amplitude on the developer conveying roller 23 side was set to 1 [kV], and the average potential difference ΔV _avg of the toner supply / recovery unit was 140V. In this case, for the first developing roller 21A, the Rd · Q value, which is an index indicating the amount of toner supplied to the image carrier 1 per unit time, is 11.25. The condition of Example 3 corresponds to the point (Δ6) in FIG.

(Comparative Example 6)
In Comparative Example 6, using the same developing device 2 and developer as in Example 1, as in Example 3, the development-side peripheral speed ratio Rd = 2.5, the toner conveyance amount of the first developing roller 21A The DC component of the bias applied to the first and second developing rollers 21A and 21B and the developer transport roller 23 is changed so that Q = 4.5 [g / m ² ], and the first and first 2 The rotational speeds of the developing rollers 21A and 21B and the developer conveying roller 23 were adjusted. At that time, the amplitude on the developer conveying roller 23 side was set to 0.5 [kV], and the average potential difference ΔV _avg of the toner supply / recovery unit was 210V. The condition of Comparative Example 6 corresponds to the point (Δ6) in FIG.

The results of Test 4 were as shown in Table 3.

In Comparative Example 6, a slight instability was observed in the image memory characteristics, although this was not a practical problem. On the other hand, in Example 3, no image memory was recognized.
FIG. 8 is a graph showing experimental results of examining the toner particle size distribution using the average potential difference ΔV _avg of the toner supply / recovery unit as a parameter. The horizontal axis represents the toner particle size [μm], and the vertical axis represents the integrated [%]. Respectively. As can be seen from the experimental results, when ΔVavg ≧ 200, particle size selection is likely to occur in the toner layers carried on the developing rollers 21A and 21B, which adversely affects the image memory. Therefore, it is preferable to set ΔVavg ≦ 200.

[Test 5]
In Test 5, the influence of the toner particle size on the image density was examined.
(Comparative Example 7)
In Comparative Example 7, the same developing device 2 as in Example 1 is used, but the toner used in the developer is changed from toner A (toner particle size: 6.5 μm) to toner B (toner particle size: 9 μm). Changed to As in the first embodiment, the first and first developing speed ratios Rd = 2.5 and the toner transport amount Q of the first developing roller 21A = 3 [g / m ² ]. 2 The DC component of the bias applied to the developing rollers 21A and 21B and the developer conveying roller 23 was changed, and the rotation speeds of the first and second developing rollers 21A and 21B and the developer conveying roller 23 were adjusted. The condition of Comparative Example 7 corresponds to the point (◯ 1) in FIG.

  When the image was developed with the developing device described in Example 1 and the image was developed with the developing device described in Comparative Example 7, when the adhesion density [g / m 2] on the paper was made uniform, The occupied area of Example 1 was larger in Example 1, resulting in a darker image. When producing the same image density, it can be said that it is preferable to use a small diameter toner having a particle diameter of 8 μm or less because the toner conveyance amount Q on the developing roller can be set smaller for the small diameter toner.

[Test 6]
In Test 6, the influence of the supply-side peripheral speed ratio Rs (ratio of the peripheral speed of the developer conveying roller to the peripheral speed of the developing roller) on whether or not the image memory is generated was examined.
Example 4
In the fourth embodiment, using the same developing device 2 and developer as in the first embodiment, the development-side peripheral speed ratio Rd = 2 and the supply-side peripheral speed ratio Rs are the same as in the first embodiment, Rs = 1, The DC component of the bias applied to the first and second developing rollers 21A and 21B and the developer conveying roller 23 is changed so that the toner conveying amount Q of the developing roller 21A is 4.5 [g / m ² ]. In addition, the rotation speeds of the first and second developing rollers 21A and 21B and the developer conveying roller 23 were adjusted. In this case, for the first developing roller 21A, the Rd · Q value, which is an index indicating the amount of toner supplied to the image carrier 1 per unit time, is 9. The condition of Example 4 corresponds to the point (Δ7) in FIG.

(Comparative Example 8)
In Comparative Example 8, the same developing device 2 and developer as in Example 1 were used, but the supply-side peripheral speed ratio Rs was changed to Rs = 0.5. As in the case of the fourth embodiment, the first and first developing speed ratios Rd = 2 and the toner transport amount Q of the first developing roller 21A is 4.5 [g / m ² ]. 2 The DC component of the bias applied to the developing rollers 21A and 21B and the developer conveying roller 23 was changed, and the rotation speeds of the first and second developing rollers 21A and 21B and the developer conveying roller 23 were adjusted. The condition of Comparative Example 8 corresponds to the point (Δ7) in FIG.

  In the image output using the developing device of Comparative Example 8, although it was not particularly problematic in practical use, some instability was recognized in the image memory characteristics. On the other hand, no image memory was generated in image output using the developing device of Example 4. A larger amount of the magnetic brush carried on the developer transport roller 23 that contacts the first and second developing rollers 21A and 21B per unit time is advantageous for toner collection. Therefore, the supply-side peripheral speed ratio Rs It is preferable to set ≧ 1.

[Test 7]
In Test 7, the influence of the toner charge amount on the occurrence of image memory was examined.
(Example 5)
In the fifth embodiment, using the same developing device 2 and developer (toner ratio: 8%) as in the first embodiment, the developing-side peripheral speed ratio Rd = 2.3, the toner transport amount of the first developing roller 21A. The DC component of the bias applied to the first and second developing rollers 21A and 21B and the developer transport roller 23 is changed so that Q = 4.5 [g / m ² ], and the first and first 2 The rotational speeds of the developing rollers 21A and 21B and the developer conveying roller 23 were adjusted. In this case, for the first developing roller 21A, the Rd · Q value, which is an index indicating the amount of toner supplied to the image carrier 1 per unit time, is 10.35. The condition of Example 5 corresponds to the point (Δ8) in FIG.

(Comparative Example 9)
In Comparative Example 9, the same developing device 2 as in Example 1 was used, but the toner ratio in the developer was changed to 6%. Similarly to the case of the fifth embodiment, the first circumferential speed ratio Rd = 2.3 and the toner transport amount Q of the first developing roller 21A Q = 4.5 [g / m ² ]. The DC components of the bias applied to the second developing rollers 21A and 21B and the developer transport roller 23 were changed, and the rotation speeds of the first and second developing rollers 21A and 21B and the developer transport roller 23 were adjusted. The condition of Comparative Example 9 corresponds to the point (Δ8) in FIG.

  In the image output using the developing device of Comparative Example 9, a slight instability was recognized in the image memory characteristics, although not particularly problematic in practical use. On the other hand, no image memory was generated in image output using the developing device of Example 5.

  In each case of Comparative Example 9 and Example 5, the toner charge amount in the used developing tank was examined. The toner charge amount was measured using a known measuring device. As a result, the toner charge amount in Comparative Example 9 was 50 [μc / g], whereas in Example 5, the toner charge amount was 35 [μc / g]. Accordingly, when the toner charge amount is low, the adhesion between the developing rollers 21A and 21B and the toner is reduced, and the toner recoverability is enhanced. Therefore, it is preferable to set the toner saturation charge amount E ≦ 40.

  For Examples 1, 3 to 5 and Comparative Examples 2 to 9 used in Test 2 to Test 7, development-side peripheral speed ratio Rd, toner transport amount Q of first developing roller 21A, image memory evaluation, image density evaluation, A list of heat generation evaluation and comprehensive evaluation as an image forming device is shown. The overall evaluation as an image forming apparatus is evaluated as “◯” when all the evaluations of the image memory, the image density, and the heat generation are satisfactory (◯). For Example 2 and Comparative Example 1, only the evaluation of heat generation was performed in Test 1 as described above.

  As described above, according to the present embodiment, by providing a plurality of developing rollers 21A and 21B, it is necessary for supplying toner to the image carrier 1 at high speed even when high-speed printing is required. The rotation speeds of the developing rollers 21A and 21B can be reduced, and the heat generation of the developing rollers 21A and 21B (and hence the heat generation of the apparatus) can be suppressed. That is, it is possible to cope with high-speed printing without causing heat generation of the apparatus. In particular, a higher rubbing / disturbing effect can be obtained by setting the moving direction of the developer on the developer conveying roller 23 and the moving direction of the toner on the developing rollers 21A and 21B in the opposite directions. In addition, the toner recoverability can be improved.

Moreover, at least for the first developing roller 21A located upstream in the rotation direction of the image carrier 1, the developing roller 21A with respect to the toner conveyance amount (Q) on the first developing roller 21A and the peripheral speed of the image carrier 1 The peripheral speed ratio (development side peripheral speed ratio Rd), the ratio of the peripheral speed of the developer transport roller 23 to the peripheral speed of the developing roller 21A (supply side peripheral speed ratio Rs), the process speed (Pv), the first development The diameter (D) of the roller 21A, the number of developing rollers (n), and the first electric field formed by the first electric field forming means (on the average, the toner is transferred from the developer transport roller 23 to the developing rollers 21A and 21B. The required combination of the average potential difference (ΔV _avg ) of the toner supply / recovery unit (vibrating electric field in the direction), the toner saturation charge amount (E), etc. is suitably set to ensure the image density. Generation of image memory can be effectively prevented.

Although the above description is about the case where two developing rollers are provided, the present invention can be effectively applied to the case where three or more developing rollers are provided.
Thus, it goes without saying that the present invention is not limited to the above-described embodiments, and that changes and improvements can be made without departing from the scope of the invention.

It is explanatory drawing which shows the part relevant to the image formation of the electrophotographic image forming apparatus which concerns on embodiment of this invention. It is explanatory drawing which shows the example of 1 connection of an electric field formation means. It is explanatory drawing which shows the relationship between the voltage supplied to the developing agent conveyance roller and the developing roller from the electric field formation means shown in FIG. 2A. It is explanatory drawing which shows the other example of a connection of an electric field formation means. It is explanatory drawing which shows the other example of a connection of an electric field formation means. It is a figure which shows the specific example of the bias voltage by the electric field formation means which concerns on Example 1 of this invention. It is explanatory drawing which shows the part relevant to the image formation of the image forming apparatus provided with the developing device of the conventional hybrid system. It is a figure which shows each test result in the experiment of this embodiment. FIG. 6 is a diagram illustrating an experimental result of examining a toner particle size distribution using an average potential difference of a toner supply and recovery unit as a parameter.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image carrier 2 Developing apparatus 4 1st electric field formation means 5 2nd electric field formation means 21A 1st developing roller 21B 2nd developing roller 22a, 22b Toner layer 23 Developer conveyance roller 23m Magnet roller 23s Sleeve roller 24 Restriction member 25 Developer 28 Developing tank M1 Image forming apparatus n Number of developing rollers Q Amount of toner transported on developing roller Rd Development-side peripheral speed ratio ΔV _avg Average potential difference of toner supply / recovery unit

Claims (6)

A developer carrying body that encloses a magnet and carries a developer containing toner and magnetic particles on the peripheral surface thereof, and a plurality of toner carrying bodies that are arranged to face the developer carrying body and the electrostatic latent image carrying body A first electric field forming means for forming a first electric field in a direction in which the toner is transferred from the developer carrier to the toner carrier between the developer carrier and the toner carrier; and the toner carrier Between the toner and the electrostatic latent image carrier, the toner transferred to the toner carrier is transferred to a latent image portion on the electrostatic latent image carrier, and the electrostatic latent image is visualized as a toner image. A developing device comprising: a second electric field forming means that comprises:
The first electric field forming means, on the average, forms an oscillating electric field in a direction in which the toner is transferred from the developer carrier to the toner carrier,
The moving direction of the developer on the developer carrying member and the moving direction of the toner on the toner carrying member are set in opposite directions at the facing portion thereof.
At least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner transport amount on the toner carrier is Q [g / m ² ], and the peripheral speed of the electrostatic latent image carrier is The ratio of the peripheral speed of the toner carrier to the development side peripheral speed ratio Rd, the process speed Pv [mm / sec], the diameter of the toner carrier D [mm], and the number of toner carriers n [number] The following conditions a) 1 ≦ Q ≦ 4
b) Rd ≦ (100 / Pv) · D
c) 4 / n ≦ Rd · Q
A developing device characterized by satisfying: A developer carrying body that encloses a magnet and carries a developer containing toner and magnetic particles on the peripheral surface thereof, and a plurality of toner carrying bodies that are arranged to face the developer carrying body and the electrostatic latent image carrying body A first electric field forming means for forming a first electric field in a direction in which the toner is transferred from the developer carrier to the toner carrier between the developer carrier and the toner carrier; and the toner carrier Between the toner and the electrostatic latent image carrier, the toner transferred to the toner carrier is transferred to a latent image portion on the electrostatic latent image carrier, and the electrostatic latent image is visualized as a toner image. A developing device comprising: a second electric field forming means that comprises:
At least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner transport amount on the toner carrier is Q [g / m ² ], and the peripheral speed of the electrostatic latent image carrier is The ratio of the peripheral speed of the toner carrier to the development side peripheral speed ratio Rd, the process speed Pv [mm / sec], the diameter of the toner carrier D [mm], and the number of toner carriers n [number] , The average potential difference ΔV _avg of the toner supply / recovery unit in the oscillating electric field formed by the first electric field forming means {(toner supply side potential difference × supply side duty ratio) − (toner recovery side potential difference × collection side duty ratio) } / 100, the following conditions a) 1 ≦ Q ≦ 4.5
b) Rd ≦ (100 / Pv) · D
c) 4 / n ≦ Rd · Q
d) ΔV _avg ≦ 200
A developing device characterized by satisfying: A developer carrying body that encloses a magnet and carries a developer containing toner and magnetic particles on the peripheral surface thereof, and a plurality of toner carrying bodies that are arranged to face the developer carrying body and the electrostatic latent image carrying body A first electric field forming means for forming a first electric field in a direction in which the toner is transferred from the developer carrier to the toner carrier between the developer carrier and the toner carrier; and the toner carrier Between the toner and the electrostatic latent image carrier, the toner transferred to the toner carrier is transferred to a latent image portion on the electrostatic latent image carrier, and the electrostatic latent image is visualized as a toner image. A developing device comprising: a second electric field forming means that comprises:
At least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner transport amount on the toner carrier is Q [g / m ² ], and the peripheral speed of the electrostatic latent image carrier is The ratio of the peripheral speed of the toner carrier to the developing side peripheral speed ratio Rd, the ratio of the peripheral speed of the developer carrier to the peripheral speed of the toner carrier is the supply side peripheral speed ratio Rs, and the process speed is Pv [mm]. / Sec], the diameter of the toner carrier is D [mm], and the number of toner carriers is n [pieces] a) 1 ≦ Q ≦ 4.5
b) Rd ≦ (100 / Pv) · D
c) 4 / n ≦ Rd · Q
d) Rs ≧ 1
A developing device characterized by satisfying: A developer carrying body that encloses a magnet and carries a developer containing toner and magnetic particles on the peripheral surface thereof, and a plurality of toner carrying bodies that are arranged to face the developer carrying body and the electrostatic latent image carrying body A first electric field forming means for forming a first electric field in a direction in which the toner is transferred from the developer carrier to the toner carrier between the developer carrier and the toner carrier; and the toner carrier Between the toner and the electrostatic latent image carrier, the toner transferred to the toner carrier is transferred to a latent image portion on the electrostatic latent image carrier, and the electrostatic latent image is visualized as a toner image. A developing device comprising: a second electric field forming means that comprises:
At least for the toner carrier positioned upstream in the rotation direction of the electrostatic latent image carrier, the toner transport amount on the toner carrier is Q [g / m ² ], and the peripheral speed of the electrostatic latent image carrier is The ratio of the peripheral speed of the toner carrier to the development side peripheral speed ratio Rd, the process speed Pv [mm / sec], the diameter of the toner carrier D [mm], and the number of toner carriers n [number] , Where S is the saturation charge amount of the toner, and a) 1 ≦ Q ≦ 4.5
b) Rd ≦ (100 / Pv) · D
c) 4 / n ≦ Rd · Q
d) E ≦ 40
A developing device characterized by satisfying:   5. The developing device according to claim 1, wherein a small-diameter toner having a particle diameter of 8 [μm] or less is used.   An image forming apparatus comprising the developing device according to claim 1.

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