JP2002296870A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of yielding a stable high-quality image excellent in reproducibility in both a primary color and a secondary color or yielding a stable high-quality image excellent in reproducibility in both a primary color and a secondary color even when the electrified charge amount of developer is changed because the number of image forming times is increased. SOLUTION: In this image forming device A equipped with a plurality of developing devices 4, 1st bias and 2nd bias are respectively applied to the developer carrier 23 and the developer electrifying member 26 of the respective developing devices 4 of the image forming device A, and a potential difference between the 1st bias and the 2nd bias in the developing device which performs image forming later is set to be larger than that in the developing device which performs image forming earlier. Then, the image forming device A is constituted to control the potential difference between the 1st bias and the 2nd bias in the respective developing devices 4 according to information in a storage means 30 for storing the using circumstances of the respective developing devices 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using an electrophotographic system, an electrostatic recording system, or the like, for example, a copying machine or a printer. The present invention can be applied to a multicolor image forming apparatus capable of forming an image.

[0002]

2. Description of the Related Art For example, in an electrophotographic image forming apparatus, an electrostatic latent image formed on an image carrier is visualized as a toner image with a developer (toner) using a developing device.

As such a developing device, for example, a dry single-component contact developing device has been proposed and put to practical use. In this case, an electrostatic latent image is often developed by pressing or contacting a rotating image carrier and a similarly rotating developer carrier at an appropriate relative peripheral speed difference. According to such a development method,
There are many advantages, such as the elimination of a magnetic material, the simplification of the apparatus and the miniaturization of the apparatus are easy, and the use of a non-magnetic toner for application to a full-color image forming apparatus.

[0004] As the developer carrying member, a developing roller which is a rotating member having elasticity and conductivity can be used. That is, to perform development by pressing or contacting the electrostatic latent image carrier, especially when the image carrier is a rigid body,
In order to avoid damaging this, the developing roller is made of an elastic body.

Alternatively, a conductive layer may be provided on or near the surface of the developing roller, and a DC bias may be applied as a developing bias.

FIG. 11 shows an example of a conventional multicolor image forming apparatus capable of forming a full-color image. This image forming apparatus forms a toner image by performing charging, exposure, and development processes for each color based on image data separated into four colors of cyan, yellow, magenta, and black, and sequentially forms them.
This is to obtain a full-color image by superimposing and transferring on a recording medium such as recording paper.

In other words, four full-color image forming apparatuses A are arranged side by side in a direction substantially perpendicular (substantially in the direction of gravity).
A photosensitive drum 101 (101A to 101D), which is a cylindrical image carrier rotatable in one direction, is provided. Around the photosensitive drum 101, charging means 102 (102A to 102A) for uniformly charging the surface of the photosensitive drum 101 is provided.
D), a scanner 103 (10) that irradiates a laser based on image information to form an electrostatic latent image on the photosensitive drum 101;
3A to 103D), a developing device 104 (104A to 104D) for developing the electrostatic latent image as a toner image, a transfer device 106 for transferring the toner image on the photoconductor drum 101 to the recording medium 105, and a photoconductor after the transfer Cleaner 107 (107A) for removing transfer residual toner remaining on the surface of drum 101
To 107D).

The transfer device 106 includes an electrostatic transport belt 109 for electrostatically attracting and transporting the recording medium 105, and a roller-like transfer member disposed in contact with the four photosensitive drums 101 in contact therewith. Transfer roller 110 (110A-
110D). These transfer rollers 110
Forms transfer portions T1 to T4 in opposition to the photosensitive drum 101. For example, when a negatively charged toner is used as the developer, a positive charge is applied to the recording medium 105 from the transfer roller 110 via the electrostatic transport belt 109. The electric field generated by the charge causes the photosensitive drum 10
The negative toner on the photosensitive drum 101 is transferred to the recording medium 105 that is in contact with 1. The multicolor toner images transferred to the recording medium 105 are thereafter fixed by the fixing device 108.

FIG. 12 shows a schematic cross section of an example of a conventional developing device 104 of a dry one-component contact developing system. The developing roller 201, which is a developer carrying member disposed in contact with the photosensitive drum 101, is formed of a conductive elastic roller.
It is driven to rotate in the direction of arrow R2 in the figure. Developing roller 201
, A DC bias is applied to develop the electrostatic latent image formed on the photosensitive drum 101.

A developing blade 202 serving as a developer layer thickness regulating member is abutted so that the vicinity of the free end is in contact with the outer peripheral surface of the developing roller 201. When the toner carried on the surface of the developing roller 201 passes through the contact portion between the developing roller 201 and the developing blade 202, charge is applied to the toner and a thin toner layer is formed.

Further, an elastic roller 204 which is driven to rotate in the direction of arrow R3 in FIG. The elastic roller 204 can be formed by a sponge roller, and supplies the toner to the developing roller 201 and removes the toner remaining on the surface of the developing roller 204 without being used for development. It is disposed on the upstream side of the developing roller 201 in the rotation direction.

In such a developing device 104, the toner 2
As 03, a non-magnetic one-component developer can be used.
Usually, an appropriate amount of hydrophobic silica is externally added for the purpose of improving the chargeability and transferability of the toner.

Incidentally, in the developing system using the DC one-component contact developing system, recently, Japanese Patent Application Laid-Open No. H11-119546 has been proposed.
As disclosed in Japanese Patent Application Laid-Open No. 11-19547 and Japanese Patent Application Laid-Open No. H11-119547, for the purpose of high tribo stability and reduction of fog, a method using a toner charging roller and using means for electrically charging the toner has been proposed. ing.

FIG. 13 shows the toner charging roller 30.
1 shows an example of a conventional developing device using No. 1. This developing device 104 is obtained by attaching a toner charging roller 301 to the developing device 104 shown in FIG. Therefore, first,
As described above, the toner is carried on the surface of the developing roller 201.

The electric charge is applied to the toner by the discharge from the toner charging roller 301. The charged toner is conveyed by the rotation of the developing roller 201, and develops the electrostatic latent image formed on the photosensitive drum 101. The toner charging roller 301 is in contact with the developing roller 201, and is driven to rotate in the direction indicated by an arrow R4 in FIG.

[0016]

In a conventional full-color image forming apparatus, the primary colors of yellow, magenta, cyan and black, red formed of yellow and magenta, green formed of yellow and cyan, magenta and cyan It was difficult to stably form an image with the secondary color of blue formed by the above-mentioned method with good reproducibility.

That is, the positive transfer voltage is applied to the photosensitive drum 1 from the transfer roller 110 facing the photosensitive drum 101 through the electrostatic transport belt 109 and the recording medium 105.
01 is applied to the negative toner. Therefore, the transfer voltage is controlled by the electrostatic transport belt 109, the recording medium 105, and the transfer unit T.
, And the electrostatic capacity ratio of the toner on the photosensitive drum 101. Further, when a secondary color is formed, the capacitance of the toner on which an image has been formed on the recording medium 105 is added. In order to always perform constant transfer, transfer conditions must be set so that a necessary voltage is applied to the transfer gap.

However, even if such transfer conditions are achieved, the toner charge amount of the toner image formed on the photosensitive drum 101 is not specified, and, for example, a secondary color is formed by overlapping the toner images. At this time, first, the recording medium 105
The toner charge amount of the toner image formed thereon is large,
When the toner charge amount of the toner image formed next is small, the latter toner image may not be transferred from the photosensitive drum 101 to the recording medium 15 in some cases.

Further, when the toner deteriorates due to an increase in the number of times of image formation, the charge amount of the toner changes, and the optimum transfer condition is further narrowed, so that an image cannot be stably formed with good reproducibility.

Accordingly, an object of the present invention is to provide an image forming apparatus capable of obtaining stable and high-quality images with good reproducibility for both primary colors and secondary colors.

Another object of the present invention is to improve the reproducibility of both the primary and secondary colors even when the charge amount of the developer changes due to an increase in the number of times of image formation, and to achieve stable and high-quality images. An object of the present invention is to provide an image forming apparatus capable of obtaining an image.

[0022]

The above object is achieved by an image forming apparatus according to the present invention. In summary, a first aspect of the present invention is a developer carrying member that transports a developer to an image carrying member, and a developer charging member that applies a voltage to the developer on the developer carrying member to charge the developer. , Having a plurality of developing devices,
An image forming apparatus for supplying a developer to the image carrier by the developing device to form an image, wherein the developer carrier and the developer charging member of each developing device are respectively provided with a first member.
And a second bias are applied, and the potential difference between the first bias and the second bias in the developing device that forms an image first is greater than the potential difference between the first bias and the developing device that forms an image later. An image forming apparatus is characterized in that a potential difference from the second bias is larger.

According to a second aspect of the present invention, there is provided a developer carrier for transporting a developer to an image carrier, and a developer charging member for applying a voltage to the developer on the developer carrier to charge the developer. ,
An image forming apparatus comprising: a plurality of developing devices each including a developing device, wherein the developing device supplies a developer to the image carrier to form an image, wherein the developer carrier of each developing device; A first bias and a second bias are respectively applied to the member, and the developer of the developing device that forms an image later than the charge amount of the developer on the developer carrier of the developing device that forms the image first An image forming apparatus is provided, wherein the charge amount of the developer on the carrier is increased.

According to a third aspect of the present invention, there is provided a developer carrier for transporting a developer to an image carrier, and a developer charging member for applying a voltage to the developer on the developer carrier to charge the developer. ,
An image forming apparatus, comprising: a plurality of developing devices each including: and a storage unit for storing a use state of each developing device, wherein the developing device supplies a developer to the image carrier to form an image. Wherein a first bias and a second bias are respectively applied to the developer carrier and the developer charging member of each developing device, and the first bias and the second bias are applied to each developing device. Is controlled by information stored in the storage means, and the maximum potential difference in the variable range of the potential difference between the first bias and the second bias in each developing device is determined by the developing An image forming apparatus is characterized in that the maximum potential difference in a developing device that forms an image later is greater than the maximum potential difference in the device.

According to a fourth aspect of the present invention, there is provided a developer carrier for transporting a developer to an image carrier, and a developer charging member for applying a voltage to the developer on the developer carrier to charge the developer. ,
An image forming apparatus comprising: a plurality of developing devices each comprising: a storage unit for storing a use state of each developing device; and supplying a developer to an image carrier by the developing device to form an image. A first bias and a second bias are applied to the developer carrier and the developer charging member of each developing device, respectively, so that the first bias and the second bias are applied to each developing device. Is controlled by the information stored in the storage means, and the minimum potential difference in the variable range of the potential difference between the first bias and the second bias in each developing device is determined by the developing device which performs image formation first. An image forming apparatus is characterized in that the minimum potential difference in a developing device for forming an image later is larger than the minimum potential difference in the above.

According to a fifth aspect of the present invention, there is provided a developer carrier for conveying a developer to an image carrier, and a developer charging member for applying a voltage to the developer on the developer carrier to charge the developer. ,
An image forming apparatus, comprising: a plurality of developing devices each including: and a storage unit for storing a use state of each developing device, wherein the developing device supplies a developer to the image carrier to form an image. Wherein a first bias and a second bias are respectively applied to the developer carrier and the developer charging member of each developing device, and the first bias and the second bias are applied to each developing device. The potential difference between the developer and the developer is controlled by the information stored in the storage unit, so that the amount of the developer charged on the developer carrier of the developing device that forms the image first becomes greater than the amount of the developer charged on the developer carrier. An image forming apparatus is provided, wherein the charge amount of the developer on the carrier is increased.

According to a sixth aspect of the present invention, there is provided a developer carrier for transporting a developer to an image carrier, and a developer charging device for applying a voltage to the developer on the developer carrier to charge the developer. A plurality of developing devices each including a member, and storage means for storing a use state of each developing device, and the developing device supplies a developer to the image carrier to form an image. An image forming apparatus, wherein the developer carrier of each developing device;
A first bias and a second bias are respectively applied to the developer charging member, and the first and second biases are applied to each of the developing devices.
Controlling the potential difference between the first bias and the second bias based on the information stored in the storage means, thereby increasing the developer charge amount on the developer carrier in the order of image formation. An apparatus is provided.

According to one embodiment of the present invention, the image forming apparatus sequentially transfers the images formed by the developers formed on the image carrier by the plurality of developing devices to a recording medium. According to another embodiment, the image forming apparatus sequentially transfers images formed by the developers formed on the image carrier by the plurality of developing devices to an intermediate transfer body, and thereafter, transfers the images to the intermediate transfer body. The image is transferred from the body to the recording medium at once.

In one embodiment of the present invention, a plurality of image carriers can be provided corresponding to the plurality of developing devices.

According to one embodiment of the present invention, at least the developing device and the image carrier are integrally formed, and a cartridge detachable from the image forming apparatus main body can be provided. Also, according to another embodiment,
The cartridge further has at least one of a charging unit for charging the image carrier and a cleaning unit for cleaning the image carrier. Further, in each of the above-described embodiments of the present invention, according to another embodiment, the developing device can be a cartridge that can be attached to and detached from the image forming apparatus main body. In the present invention, the image bearing member may be an electrophotographic photosensitive member.

In the third to sixth aspects of the present invention, the use condition of the developing device stored in the storage means includes the number of times of image formation, the number of sheets passed through the recording medium in the image forming device, and the number of rotations of the developer carrier. , Or the application time of the first bias or the second bias. The storage means may be a contact or non-contact type nonvolatile memory. In the third to sixth aspects of the present invention, according to one embodiment, the storage means is attached to each cartridge, and can store the use state of the developing device of each attached cartridge. it can.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings. The embodiments described below are intended to exemplify the present invention, and the dimensions, materials, shapes, relative arrangements, and the like of the components described below are not particularly described. It is not intended to limit the scope of the invention.

Embodiment 1 An embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS.

FIG. 1 shows a schematic cross section of the image forming apparatus of this embodiment capable of forming a full-color image of four colors.

As shown in FIG. 1, the image forming apparatus A has four cylindrical image carriers, ie, photosensitive drums 1 (1A, 1B, 1C) arranged in a substantially vertical direction (substantially in the direction of gravity). , 1
D). The photosensitive drum 1 is driven to rotate in the direction of arrow R1 by driving means (not shown). Around the photoreceptor drum 1, a charging unit 2 (2A, 2B, 2C, 2D) for uniformly charging the surface of the photoreceptor drum 1 irradiates a laser based on the image information. A scanner 3 (3A, 3A) serving as an exposure unit for forming an electrostatic latent image.
B, 3C, 3D), a developing device 4 (4A, 4B, 4C, 4D) for developing the electrostatic latent image as a toner image, and a transfer device for transferring the toner image formed on the photosensitive drum 1 to a recording medium 5 6. A cleaner 7 (7) serving as a cleaning means for removing transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer.
A, 7B, 7C, 7D) are sequentially arranged according to the rotation direction of the photosensitive drum 1.

The image forming apparatus A of this embodiment is a process in which an electrophotographic photosensitive member and process means acting on the electrophotographic photosensitive member are integrally formed into a cartridge, and this cartridge is detachably mountable to the main body of the electrophotographic image forming apparatus. It is a cartridge system. Here, as the process means,
A charging unit for charging the electrophotographic photosensitive member, a developing unit for supplying a developer to the electrophotographic photosensitive member, and a cleaning unit for cleaning the electrophotographic photosensitive member are included. In other words, the process cartridge is a cartridge in which the charging unit, the developing unit, the cleaning unit, and the electrophotographic photosensitive member are integrally formed into a cartridge, and this cartridge is detachable from the main body of the electrophotographic image forming apparatus. At least one of the developing means and the cleaning means and the electrophotographic photosensitive member are integrally formed as a cartridge so as to be detachable from the main body of the electrophotographic image forming apparatus, or at least the developing means and the electrophotographic photosensitive member The body is integrally formed into a cartridge, and this cartridge is made detachable from the main body of the electrophotographic image forming apparatus.

In this embodiment, the photosensitive drum 1, the charging means 2, the developing device 4, and the cleaner 7 are integrally formed as a cartridge, and the process cartridge 8 (8A, 8B, 8) is formed.
C, 8D), and is detachable from the apparatus main body 17. Each process cartridge 8A, 8B, 8C, 8D
Are mounting means 18A, 18B, 1
It is detachably attached to the apparatus main body 17 via 8C and 18D. In the present embodiment, the process cartridges 8A, 8B, 8C, and 8D all have the same shape, and contain cyan (yellow), yellow, magenta, and black developers (toners) therein. I have.

The transfer device 6 serves as a means for transporting the recording medium, and circulates so as to come into contact with all the photosensitive drums 1A, 1B, 1C, and 1D, and electrostatically attracts and transports the recording medium 5 to transport. 9 is provided. The electrostatic transport belt 9 has a thickness of 50 to 200 μm and a volume resistivity of 10 ⁸ to 10 ¹⁴ Ω.
A resin film such as PvdF, ETFE, polyamide, polyimide, PET, or polycarbonate having a thickness of about 0.5 cm, or a resin layer formed on a rubber base layer having a thickness of about 0.5 to 2 mm can be used. Here, the volume resistivity was measured using a high resistance meter R83 manufactured by ADVANTEST, using a measurement probe according to JIS K6911.
The measured value obtained by applying 100 V to 40 is normalized by the thickness of the electrostatic transport belt 9.

Further, the transfer device 6 is brought into contact with the inside of the electrostatic transport belt 9 and has four photosensitive drums 1A, 1B, 1C,
The transfer rollers 10 (10A, 10B, 10C, and 10D), which are roller-shaped transfer members, provided corresponding to 1D are arranged side by side. These transfer rollers 10 face the photosensitive drum 1 to form transfer portions T1, T2, T3, T4. In this embodiment, since a negatively chargeable toner is used as the developer,
Positive charges are applied to the recording medium 5 from the transfer roller 10 via the electrostatic transport belt 9. The electric field generated by the electric charge causes the recording medium 5 in contact with the photosensitive drum 1
Then, the negative toner on the photosensitive drum 1 is transferred. In this embodiment, the transfer rollers 10A, 10B, 10
C and 10D each have a transfer bias of about Vt.
r = + 1200V is applied.

The image forming apparatus A includes a fixing device 11 for fixing a plurality of toner images transferred to the recording medium 5.
Is provided. The fixing device 11 applies heat and pressure when the recording medium 5 onto which the toner image on the photosensitive drum 1 has been transferred passes. Thus, the toner images of a plurality of colors are permanently fixed on the surface of the recording medium 5.

Next, the process cartridge 8 will be described with reference to FIG.

In this embodiment, the photosensitive drum 1 is a rigid body formed by applying a photosensitive layer to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm, and is driven to rotate in the direction of arrow R1 in the figure. In the present embodiment, the charging means 2 is a conductive roller (charging roller) formed in a roller shape, and the charging roller 2 is brought into contact with the photosensitive drum to apply a charging bias to the photosensitive member. Vd = −700 on the surface of the drum 1
It is charged to V.

The uniformly charged surface of the photosensitive drum 1 is irradiated with a laser beam corresponding to an image signal of each color. As a result, the selectively exposed portion is Vl =
It becomes -100 V, and an electrostatic latent image is formed.

The electrostatic latent image formed on the photosensitive drum 1 is developed by the developing device 4 (4A, 4B, 4C, 4D). That is, the developing device 4 includes the developing container 21 that stores the non-magnetic toner 22 having a negative charge as a one-component developer. The developing device 4 has an opening 2 extending in the longitudinal direction of the developing container 21 (a direction orthogonal to the conveying direction of the recording medium 5).
1a. At the opening 21a, a developing roller 23 as a roller-like developer carrying member (developing means) is provided which is opposed to the photosensitive drum 1 over substantially the entire length thereof. Then, the developer is supplied by the developing roller 23 to develop and visualize the electrostatic latent image on the photosensitive drum 1. In the present embodiment, as the non-magnetic toner 22 having a negative charge, a substantially spherical toner excellent in particle size distribution and having 1.0 wt% of hydrophobic silica externally added was used.

The developing roller 23 has a diameter 16 having elasticity.
In the opening 21 a of the developing container 21, approximately a right half in the figure protrudes into the developing container 21, and a substantially left half peripheral surface is exposed from the developing container 21. The surface exposed from the developing container 21 is pressed and brought into contact with the photosensitive drum 1 located on the left side of the developing device 4 in the figure with a predetermined penetration amount. In this embodiment, the developing roller 23 enters the photosensitive drum 1 by 50 μm and comes into contact therewith.

The developing roller 23 is driven to rotate in the direction of arrow R2 in FIG. The surface has moderate irregularities in order to increase the probability of rubbing with the toner 22 and to favorably transport the toner 22. The developing roller 23 of this embodiment has a two-layer structure in which silicone rubber is used as a base layer and an acrylic / urethane-based rubber is coated on the surface, and the roughness of Rz (JIS ten-point average roughness) = 10 μm and 10 ⁴ to It has a resistance of 10 ⁶ Ω. The developing roller 23 is in contact with the photosensitive drum 1 with a contact load of 500 gf (4900N). In this embodiment, a DC voltage of Vdc = −400 V is applied to the developing roller 23 as a developing bias.

The method of measuring the resistance of the developing roller 23 is as follows. The developing roller 23 is mounted on an aluminum sleeve having the same diameter as the photosensitive drum 1 with a contact load of 500 gf (4
900N). Further, the aluminum sleeve is rotated at a peripheral speed equal to that of the photosensitive drum 1. In this embodiment, the photosensitive drum 1 rotates at a peripheral speed of 90 mm / sec,
The developing roller 23 has a peripheral speed 120 higher than that of the photosensitive drum 1.
Rotate at mm / sec. Next, a DC voltage of -400 V, which is equal to the developing bias in this embodiment, is applied to the developing roller 23. At that time, a 10 kΩ resistor was provided on the ground side, and the current was calculated by measuring the voltage at both ends.
The resistance of the developing roller 23 is calculated.

Below the developing roller 23 in the figure, an elastic roller 24 rotatably supported by the developing container 21 is abutted as developer supplying means for supplying a developer to the developing roller 23. As the elastic roller 24, a sponge structure or a fur brush structure in which fibers such as rayon and nylon are planted on a cored bar are preferable in terms of supplying toner to the developing roller 23 and stripping undeveloped toner. In this embodiment, a urethane sponge roller having a diameter of 14 mm is used, and is driven to rotate in a direction indicated by an arrow R3 in the same direction as the developing roller 23.

On the upper side of the developing roller 23 in the figure, an elastic developing blade 25 is provided as a developer layer thickness regulating member.
Is provided. The developing blade 25 is supported by a supporting metal plate, and the vicinity of the free end of the developing blade 25 is in surface contact with the outer peripheral surface of the developing roller 23. The contact direction is a so-called counter direction in which the tip on the free end side with respect to the contact portion is located on the upstream side in the rotation direction of the developing roller 23. In this embodiment, the developing blade 25 has a thickness of 100 μm.
Was used.

The toner carried on the surface of the developing roller 23 by the rubbing between the developing roller 23 and the elastic roller 24 is
When passing through the contact portion between the developing blade 25 and the developing roller 23, electric charge is given by frictional charging and is regulated to a thin layer.

Further, the rotation direction (R2) of the developing roller 23
A toner charging roller 26, which is a developer charging member, is disposed between a contact portion between the developing roller 23 and the developing blade 25 and a contact portion between the developing roller 23 and the photosensitive drum. I have. In this embodiment, as the toner charging roller 26, a rubber roller formed of hydrin rubber having a diameter of 7 mm and extending over substantially the entire length of the developing roller 23 is used. In this embodiment, the toner charging roller 26 has a resistance of 10 ⁸ Ω.
Resistance. Then, the toner charging roller 26
Is in contact with the developing roller 23 by a pressing member (not shown) with a contact load of 100 gf (980 N).
Due to the rotation of the developing roller 23, the developing roller 23 is driven to rotate in a direction indicated by an arrow R4.

By the contact of the toner charging roller 26,
The toner on the developing roller 23 is closest packed and is uniformly coated on the surface of the developing roller 23. Toner charging roller 26
, A toner charging bias is applied from a power supply (not shown), and the thin toner layer on the developing roller 23 is charged by discharging.

Next, a method of applying charge to the toner by the toner charging roller 26 will be described. FIG. 3 shows the discharge of the toner charging roller 26 (toner discharge) in this embodiment.
The characteristics are shown. That is, when the resistance of the toner charging roller 26 is 10 ⁸ Ω, the toner surface potential shows the behavior shown in the figure with respect to the voltage applied to the toner charging roller 26.
The toner surface potential has a surface potential of -20 V even when the applied voltage is 0 V. This consists of the elastic roller 24 and the developing blade 2
This is because the toner received frictional charging in No. 5.

Excluding the surface potential due to the triboelectric charging, as shown in FIG. 4, the discharge start voltage with the toner rises at a slope of 1 from approximately -600 V. This is the same behavior as the DC discharge charging of the photosensitive drum 1.

Here, the toner charging roller 26 and the toner 2
The discharge starting voltage of No. 2 is determined by the intersection of the following equations (1) and (2).

Vb = 312 + 6.2g (1) Vg = g (Va−Vc) / [(Lt / Kt) + g] (2) In the above equation, g: spatial distance Vb: g> Approximate expression of Paschen's rule at 8 μm Vg: Air gap voltage on toner charging roller and toner layer surface Va: Toner charging roller applied voltage Vc: Toner layer surface potential Lt: Toner layer thickness Kt: Toner layer relative dielectric constant

Since the toner 22 used in this embodiment has an excellent particle size distribution and a substantially spherical shape, the ratio between the toner and air in the toner layer is constant. Therefore, in equation (2), Kt
Are stabilized, and charge is provided by stable discharge.

FIGS. 3 and 4 show the toner charging roller 2.
6 is an experimental result when the entire longitudinal area (230 mm) of 6 is in contact with the toner coat portion.

In the configuration of the present embodiment, the appropriate range of the resistance of the toner charging roller 26 capable of discharging toner is 10 ⁷ to 10 ⁷ .
10 ¹¹ Ω. That is, when the resistance of the toner charging roller 26 is 10 ⁷ Ω or less, a voltage between the toner charging roller 26 and the toner coat portion where toner can be discharged cannot be obtained, and when the resistance of the toner charging roller 26 is 10 ¹¹ Ω or more. In the configuration of this embodiment, the discharge starting voltage is too high, which is not appropriate. In the present embodiment, when the toner charging roller 26 having a resistance of 10 ⁸ Ω is used, the above-mentioned range of the resistance of the toner charging roller 26 is appropriate.

The method of measuring the resistance of the toner charging roller 26 is as follows. A 16 mm diameter aluminum roller is brought into contact with the toner charging roller 26 with a contact load of 100 gf (980 N), and the 16 mm diameter aluminum roller is 90 mm / sec.
Rotate with. Next, −400 is applied to the toner charging roller 26.
A DC voltage of V is applied. At that time, 10 kΩ on the ground side
The current is calculated by measuring the voltage at both ends of the resistance, and the resistance of the toner charging roller 26 is calculated.

Next, the amount of toner charge with respect to the difference in the applied voltage between the developing roller 23 and the toner charging roller 26 will be described. In the following description, when the applied voltage, the difference between the applied voltages, the potential difference, and the toner charge amount have a magnitude relationship such as a large or an increased amount, the comparison is an absolute value. In the present embodiment, the negative toner is used as the developer, but the present invention can of course be applied to the case where the positive toner is used.

FIG. 5 shows the relationship between the applied voltage difference between the toner charging roller 26 and the developing roller 23 with respect to the developing roller 2.
3 shows the relationship between the charge amounts of the toners on No. 3. As shown in FIG. 5, the charge amount of the toner is saturated from an applied voltage difference (potential difference) of about 1200 V. In addition, as can be seen from FIG. 5, by changing the voltage between the toner charging roller 26 and the toner 22 on the developing roller 23, the charge amount of the toner can be changed to a desired value.

Further, after the toner (toner image) transferred to the photosensitive drum 1 by the developing device 4 is transferred to the recording medium 5, the cleaner 7 provided in the process cartridge 8 is not transferred to the surface of the photosensitive drum 1. The transfer residual toner remaining in the toner is removed.

Now, an image forming operation using the process cartridge 8 and the image forming apparatus A having the above configuration will be described.

The image forming apparatus A is connected to a host 14 such as a personal computer, receives a print request signal from the host 14, and receives image data. The image data is supplied to the controller unit 36 (not shown) by cyan,
The color data is expanded to yellow, magenta, and black color data.

The recording medium 5, for example, recording paper, OHP sheet, etc., is separated and fed from the paper supply unit 15 and temporarily stops at the registration roller 16. The registration roller 16 waits for the scanner 3 to rise and for the charging unit 2 to stabilize the potential of the photosensitive drum 1, and synchronizes the recording position of the recording medium 5 with the image formation timing of the four color toner images to quiesce the transfer device 6. The recording medium 5 is sent out to the electric transport belt 9. Thus, the recording medium 5 is electrostatically attracted to the electrostatic transport belt 9 and is transported sequentially to the transfer units T1 to T4.

On the other hand, in this embodiment, first, an image of cyan as the first color is formed. That is, the scanner 3A is attached to the photosensitive drum 1A uniformly charged by the charging device 2A.
Performs a laser exposure based on the cyan image data to form an electrostatic latent image on the photosensitive drum 1A.

A developing device 4A containing cyan toner
The cyan toner is carried on the developing roller 23A by sliding friction with the elastic roller 24A. When the developing roller 23 is driven to rotate, the cyan toner carried on the developing roller 23A passes through a contact portion with the developing blade 25A. At this time, the cyan toner is charged by frictional charging and is regulated to a uniform thin layer. Further, the cyan toner layer formed as a thin layer on the developing roller 23A is transported to a contact portion with the toner charging roller 26A.

A DC voltage of Vdc = −400 V is applied to the developing roller 23A as a developing bias. on the other hand,
A DC voltage of VeA = -1000 V is applied to the toner charging roller 26A. As a result, the difference between the applied voltages of the developing roller 23A and the toner charging roller 26A is 600 V
Becomes As described above, the electric charge is applied to the toner by the discharge according to the voltage difference. By the application of charge to the toner by this discharge, the charge amount of the cyan toner becomes -3.
It is controlled at 0 μC / g.

-30 μC by toner charging roller 26A
The cyan toner layer on the developing roller 23A charged to / g is uniformly conveyed to a developing section which is a section facing the photosensitive drum 1A. In the developing section, the cyan toner layer develops the electrostatic latent image on the photosensitive drum 1A by the action of a developing bias applied to the developing roller 23A, and visualizes it as a cyan toner image.

The cyan toner image on the photosensitive drum 1A, which has been visualized, is conveyed to the transfer portion T1, which is a portion facing the transfer roller 10A, by the rotation of the photosensitive drum 1A. At the same time, the recording medium 5 is transported to the transfer section T1 by the electrostatic transport belt 9.

Vtr = 1100 is applied to the transfer roller 10A.
A transfer bias of V is applied. Thus, the cyan toner image on the photosensitive drum 1A is transferred to the recording medium 5 in contact with the photosensitive drum 1A.

Next, in the present embodiment, a yellow image, which is the second color, is formed. That is, through the same process as described above, the yellow toner layer formed as a thin layer on the developing roller 23B is transported to the contact portion with the toner charging roller 26B.

A DC voltage of Vdc = −400 V is applied to the developing roller 23B as a developing bias. On the other hand, VeB = −1 is applied to the toner charging roller 26B.
A DC voltage of 200 V is applied. Thus, the difference between the applied voltages of the developing roller 23B and the toner charging roller 26B becomes 800V. Then, the charge amount of the yellow toner is controlled to −35 μC / g.

-35 μC by the toner charging roller 26B
The yellow toner layer on the developing roller 23B charged to / g develops the electrostatic latent image on the photosensitive drum 1B by the action of the developing bias applied to the developing roller 23B, and is visualized as a yellow toner image.

The visualized yellow toner image is conveyed to the transfer portion T2 which is the portion facing the transfer roller 10B by rotating the photosensitive drum 1B. At the same time, the recording medium 5 on which the cyan toner image has been transferred
Is transported to the transfer section T2.

Here, the secondary color green is formed by superimposing a cyan toner image and a yellow toner image. Therefore, to form a secondary color green image, the charged electric charge amount on the photosensitive drum 1B is -35 μm, which is superimposed on the charged electric charge amount −30 μC / g cyan toner image formed on the recording medium 5.
A C / g yellow toner image is transferred. Transfer roller 10
A transfer bias of Vtr = 1150 V is applied to B.

Further, in this embodiment, magenta image formation, which is the third color, is performed. That is, the magenta toner layer thinly formed on the developing roller 23C is transported to the contact portion with the toner charging roller 26C through the same process as described above.

A DC voltage of Vdc = −400 V is also applied to the developing roller 23 C as a developing bias. On the other hand, VeC = −14 is applied to the toner charging roller 26C.
A DC voltage of 00V is applied. As a result, the difference between the applied voltages of the developing roller 23C and the toner charging roller 26C becomes 1000V. Then, the charge amount of the magenta toner is controlled to −40 μC / g.

-40 μC by the toner charging roller 26C
The magenta toner layer on the developing roller 23C charged to / g develops the electrostatic latent image on the photosensitive drum 1C by the action of the developing bias applied to the developing roller 23C and visualizes it as a magenta toner image.

The visualized magenta toner image is conveyed to the transfer portion T3, which is the portion facing the transfer roller 10C, by rotating the photosensitive drum 1C. At the same time, the recording medium 5 on which the cyan toner image and the yellow toner image have been transferred is conveyed to the transfer unit by the electrostatic conveyance belt 9.

Here, the secondary colors blue and red are formed by superimposing a cyan toner image and a magenta toner image, and a yellow toner image and a magenta toner image, respectively.
Therefore, in order to form a secondary color blue image, the charge amount on the photosensitive drum 1C is −40, superimposed on the charge amount −30 μC / g cyan toner image formed on the recording medium 5.
A mC / g magenta toner image is transferred. To form the secondary color red image, the secondary color red image was superimposed on the yellow toner image having a charge amount of −35 μC / g formed on the recording medium 5.
A magenta toner image having a charge amount of −40 μC / g on the photosensitive drum 1C is transferred. Vt is applied to the transfer roller 10C.
A transfer bias of r = 1200 V is applied.

Finally, in this embodiment, a black image, which is the fourth color, is formed. That is, through the same process as described above, the black toner layer formed as a thin layer on the developing roller 23D is transported to the contact portion with the toner charging roller 26D.

A DC voltage of Vdc = −400 V is also applied to the developing roller 23D as a developing bias. On the other hand, VeD = −16 is applied to the toner charging roller 26D.
A DC voltage of 00V is applied. Thus, the difference between the applied voltages of the developing roller 23D and the toner charging roller 26D becomes 1200V. Then, the charge amount of the black toner is controlled to −45 μC / g.

-45 μC by the toner charging roller 26D
The black toner layer on the developing roller 23D charged to / g develops the electrostatic latent image on the photosensitive drum 1D by the action of the developing bias applied to the developing roller 23D, and is visualized as a black toner image.

The visualized black toner image is conveyed to the transfer portion T4, which is the portion facing the transfer roller 10D, by the rotational driving of the photosensitive drum 1D. At the same time, the recording medium 5 on which the cyan toner image, the yellow toner image, and the magenta toner image have been transferred by the electrostatic transport belt 9 is transferred to a transfer unit T4.
Transported to

The black toner image can be used for inking. Accordingly, a cyan toner image having a charge amount of −30 μC / g, a yellow toner image having a charge amount of −35 μC / g, and a magenta toner image having a charge amount of −40 μC / g formed on the recording medium 5, of course. Green formed by superimposing toner images as described above,
A black toner image having a charge amount of -45 μC / g on the photosensitive drum 1D is transferred so as to be superimposed on the toner images of the blue and red secondary colors. Vtr is applied to the transfer roller 10D.
A transfer bias of = 1250 V is applied.

As described above, the cyan toner image, the yellow toner image, the magenta toner image, and the black toner image are sequentially transferred while the recording medium 5 is being conveyed to the electrostatic conveyance belt 9.

Recording medium 5 on which four color toner images have been transferred
Is then separated from the electrostatic transport belt 9 and the fixing device 1
Sent to 1. Then, the toner image on the recording medium 5 is
The fixing device 11 permanently fixes the recording medium 5
Is discharged outside the aircraft.

Table 1 shows the voltages applied to the developing roller 23 and the toner charging roller 26, the difference (potential difference) between the applied voltages between the developing roller 23 and the toner charging roller 26, and the amount of toner charge in this embodiment.

[0091]

[Table 1]

As described above, in the present embodiment, the voltage applied to the toner charging roller 26 provided in the developing device 4 used in the image forming apparatus (multi-color image forming apparatus) A having a plurality of developing devices 4 is controlled. When forming a secondary color, the charge amount of the toner image formed later can always be made larger than the charge amount of the toner image formed first among the overlapping toner images. . As a result, the charge amount of the toner image previously transferred to the recording medium 5 is always larger than the charge amount of the toner image.
Since the charge amount of the toner image formed later becomes large, stable transfer of the toner image from the photosensitive drum 1 to the recording medium 5 is achieved without causing secondary color transfer failure.

Here, in this embodiment, the developing bias applied to the developing roller 23 is fixed. However, even when the developing bias is variable, the voltage applied between the developing roller 23 and the toner charging roller 26 can be reduced. By controlling the difference (potential difference), the toner charge amount can be changed to a desired value.

That is, the plurality of developing devices 4 used in the image forming apparatus A are provided with the toner charging rollers 26, respectively. Then, the potential difference between the developing bias (first bias) applied to the developing roller 23 and the toner charging bias (second bias) applied to the toner charging roller 26 is calculated from the potential difference in the developing device 4 that performs image formation first. Also, the potential difference in the developing device 4 for forming an image later is increased. That is, the potential difference between the developing bias (first bias) applied to the developing roller 23 and the toner charging bias (second bias) applied to the toner charging roller 26 is sequentially increased in the order of image formation.

As a result, the amount of toner charge on the developing roller 4 of the developing device 4 for forming an image later is always smaller than the amount of toner charge on the developing roller 23 of the developing device 4 for forming an image first. Can be bigger. That is, the developing roller 23 of each developing device 4 is formed in the order of image formation.
The above-mentioned toner charge amount can be increased. Therefore, the charge amount of the toner image transferred to the recording medium 5 later can be always larger than the charge amount of the toner image transferred to the recording medium 5 first.

As described above, according to the present embodiment, the photosensitive drum 1
The stable transfer of the toner image from the recording medium 5 to the recording medium 5 is achieved, and good image quality can be obtained. That is, a stable high-quality image can be obtained with good reproducibility for both the primary color and the secondary color with the toner charge amount being a desired value.

In this embodiment, the photosensitive drum 1
However, the present invention is not limited to this. For example, a toner image formed on the photosensitive drum 1 is transferred to a belt-like or drum-like intermediate transfer body, and a plurality of colors are superimposed and then collectively transferred to a recording medium 5. It is needless to say that the present invention can be applied to a device and the same effects as described above can be obtained.

In this embodiment, the developing devices 4A to 4D are:
Although it has been described that the process cartridges 8A to 8D are formed into cartridges and can be attached to and detached from the image forming apparatus main body 17, the present invention is not limited to this.
The plurality of developing devices 4 may be fixed to the device main body 17 and may be configured to supply toner as needed. Or,
The plurality of developing devices 4 may be independently configured as a cartridge that is detachable from the device main body 17.

Further, in this embodiment, a plurality of photosensitive drums 1 (1A, 1B, 1C, 1D) are provided as an image carrier, but the present invention is not limited to this. For example,
A plurality of developing devices sequentially form toner images on a single photosensitive drum as an image carrier, and each time the toner image is carried on a recording medium carrier circulating with respect to a portion (transfer portion) facing the photosensitive drum. The present invention also suitably works in an image forming apparatus configured to transfer this toner image onto a recorded recording medium or onto an intermediate transfer member as described above.

Embodiment 2 Next, another embodiment of the image forming apparatus according to the present invention will be described.

In this embodiment, in consideration of the case where the toner as the developer changes with time in the developing device 4 and the image forming apparatus described in the first embodiment, the toner charging roller 2 is used.
6 is characterized in that the difference between the applied voltages of the developing roller 6 and the developing roller 23 is changed. Thereby, regardless of the change over time of the characteristics of the developer, particularly, the change of the charging characteristics of the toner,
Control is performed so that the charge amount of the toner image formed later is larger than the charge amount of the toner image formed earlier. In the image forming apparatus of the present embodiment, elements having the same functions and configurations as those of the image forming apparatus A of the first embodiment are denoted by the same reference numerals, and detailed description is omitted.

FIG. 6 shows the difference between the applied voltage between the toner charging roller 26 and the developing roller 23 in the image forming apparatus A in the present embodiment at the time of initial use and 2500 sheets and 5000 sheets. The relationship between the charge amounts of the toner is shown. As shown in FIG. 6, the charge amount of the toner saturates from the applied voltage difference (potential difference) of about 1200 V at any number of passed sheets. However, 5
It can be seen that the charge amount of the toner has decreased and the saturation charge amount has also decreased by 000 sheets. This is considered to be mainly due to toner deterioration due to release of external additives of the toner.

Normally, in the image forming apparatus, when the developer runs out, the developer is supplied to the developing device 4 or, if the developing device 4 is in the form of the process cartridge B, a known toner presence / absence detection. By notifying the absence of toner by means or the like, for example, when the user replaces the process cartridge 8, the image can be formed again.

Therefore, usually, in an image forming apparatus provided with a plurality of developing devices 4 (multicolor image forming device), each developing device 4
, The number of sheets passed and the number of image formation are different. For example, in a full-color image forming apparatus including cyan, yellow, magenta, and black, the yellow cartridge is initially used immediately after the yellow cartridge is replaced, while the other process cartridges
A case where 500 sheets are passed is considered. That is,
The charge amount of the toner varies depending on the usage of the developer.

Accordingly, as shown in FIG. 7, the process cartridge 8 used in the image forming apparatus A of the present embodiment is used.
A, 8B, 8C, and 8D have storage means 30 (3
0A, 30B, 30C, 30D). Each storage unit 30 stores the number of image formations performed by each developing device 4 as usage status information of each developing device 4. Then, the difference between the applied voltages of the toner charging roller 26 and the developing roller 23 is changed in accordance with the number of formed images. As a result, control is performed such that the charge amount of the toner image formed later is always larger than the charge amount of the toner image formed earlier. That is, based on the use status information of each developing device 4 stored in each storage unit 30, control is performed so that the charge amount of the toner image is sequentially increased according to the order of image formation.

FIG. 8 shows the difference (potential difference) between the applied voltages between the toner charging roller 26 of the first color, the second color, the third color, and the fourth color and the developing roller 23 in the relationship shown in FIG. The variable range according to the number of image formation is superimposed.

The developing roller 23A of the developing device 4A containing the first color cyan toner has a developing bias of V
A DC voltage of dc = −400 V is applied. On the other hand, the difference between the applied voltages between the toner charging roller 26A and the developing roller 23A changes from 500 V to 900
The bias applied to the toner charging roller 26A is changed in the range of -900V to -1300V so as to increase to V. As a result, the charge amount of the cyan toner is controlled to be always -30 [mu] C / g.

A DC voltage of -400 V is applied as a developing bias to the developing roller 23B of the developing device 4B containing the second color yellow toner. On the other hand, the difference between the applied voltages between the toner charging roller 26B and the developing roller 23B changes from 700 V to 11
The bias applied to the toner charging roller 26B is changed in the range of -1100V to 1500V so as to increase to 00V. As a result, the charge amount of the yellow toner is always controlled to −35 μC / g.

A DC voltage of Vdc = −400 V is applied as a developing bias to the developing roller 23 C of the developing device 4 C containing the magenta toner of the third color. On the other hand, the difference of the applied voltage between the toner charging roller 26C and the developing roller 23C changes from 800 V to 12
The bias applied to the toner charging roller 26C is changed in the range of -1200V to -1600V so as to increase to 00V. As a result, the charge amount of the magenta toner is always controlled to −40 μC / g.

A DC voltage of Vdc = −400 V is applied as a developing bias to the developing roller 23D of the developing device 4D containing the fourth color black toner. On the other hand, the difference of the applied voltage between the toner charging roller 26D and the developing roller 23D is 1000 V
Charging roller 2 so as to increase from
The bias applied to 6D is changed from -1400V to -1800.
V is changed in the range. As a result, the charge amount of the black toner is always controlled to −45 μC / g.

In this embodiment, the difference (potential difference) between the applied voltage to the developing roller 23 and the toner charging roller 26, and the applied voltage between the developing roller 23 and the toner charging roller 26.
Table 2 shows the variable range and the toner charge amount.

[0112]

[Table 2]

As described above, in this embodiment, the applied voltage range of the toner charging roller 26 is set for each developing device, and the toner charging roller 26 is set in accordance with the number of images formed by each developing device stored in the storage means. The applied voltage is variably controlled. Thus, the charge amount of the toner image formed later can always be larger than the charge amount of the toner image formed earlier. Therefore, the charge amount of the toner image transferred to the recording medium 5 later can always be made larger than the charge amount of the toner image transferred to the recording medium 5 first, and the recording from the photosensitive drum 1 can be performed. To medium 5
Stable transfer of the toner image is achieved.

That is, in this embodiment, the maximum potential difference in the variable range of the potential difference between the developing bias (first bias) applied to the developing roller 23 and the toner charging bias (second bias) applied to the toner charging roller 26. However, the maximum potential difference in the developing device 4 that forms an image later is set to be larger than the maximum potential difference in the developing device 4 that forms an image first. Further, in the present embodiment, the minimum potential difference in the variable range of the potential difference is set to be larger than the minimum potential difference in the developing device 4 which forms an image first, in the developing device 4 which forms an image later.

The developing bias (first bias) applied to the developing roller 23 and the toner charging roller 26 are applied to the developing roller 23 in accordance with the number of images formed by each developing device 4 stored in the storage means 30 of each process cartridge 8. The potential difference between the applied toner charging bias (second bias) and
Control is performed in the above variable range. Thus, the amount of charged toner on the developing roller 23 of the developing device 4 that forms an image later is always larger than the amount of charged toner on the developing roller 23 of the developing device 4 that forms an image first. To control. That is, control is performed so that the amount of toner charge on the developing roller 23 of each developing device 4 is increased in the order of image formation.

In this embodiment, the developing bias applied to the developing roller 23 is fixed. However, even when the developing bias is variable, the applied voltage between the developing roller 23 and the toner charging roller 26 is not changed. By controlling the difference (potential difference), the toner charge amount can be changed to a desired value.

An example of a method of changing the bias applied to the toner charging roller will be further described with reference to the flowchart of FIG. FIG. 10 schematically shows a control mode of the developing bias and the toner charging bias in this embodiment.

As shown in FIGS. 7 and 10, the process cartridge 8 (8A, 8B, 8C, 8D) of this embodiment has storage means 30 (30A, 30B, 30C, 30D). Reference numeral 30 stores the number of images formed using each process cartridge.

When a print signal is input from the host 14 (S1), the control means (CPU) 31 provided in the image forming apparatus main body 17 causes each process cartridge 8 (8A,
8B, 8C, 8D).
A, 30B, 30C, and 30D), and reads the number of formed images (P) for each process cartridge (S).
2).

Next, the CPU 31 determines, for each process cartridge, the contents of the ROM 32 of the image forming apparatus main body 17 in which bias information to be applied to the toner charging roller 26 in accordance with the number of formed images is stored in advance, as described above. CPU31
Is compared with the value (P) of the number of image formations read in (S)
3). Then, the power supply 34 is
(34A, 34B, 34C, 34D) and power supply 35 (3
5A, 35B, 35C, 35D) to set optimal biases to be applied to the toner charging roller 26 (26A, 26B, 26C, 26D) and the developing roller 23 (23A, 23B, 23C, 23D), The operation shifts to the forming operation (S4).

When the image forming operation is completed, the count of the number of formed images is increased by one (S5), and the storage means 30 (30A, 30B, 30C, 30) of each process cartridge 8 is stored.
The count of the number of images formed in D) is rewritten (S6).
Subsequently, it is determined whether there is a request for continuous printing (S
7) If there is no request, shift to print end operation (S)
8) If there is a request, the operations of S3 to S7 are repeated until there is no request for continuous printing.

In the present embodiment, the bias applied to the toner charging roller 26 is set to be variable every 500 sheets of image formation. That is, the bias applied to the toner charging roller 26 that is changed within the above-described range is set in the ROM 32 for each of the process cartridges 8 every 500 sheets of image formation from the time of initial use. Incidentally, the bias variable frequency can of course be changed according to the stability of the toner.

By performing such control, a stable transfer of the toner image from the photosensitive drum 1 to the recording medium 5 is achieved without causing a transfer failure of the secondary color, and an image which always provides high image quality is obtained. A forming device could be provided.

In this embodiment, the NVRAM provided in the process cartridge B is used as the storage means 30, and is electrically communicated with the image forming apparatus main body 17 through a contact point to read and write the number of formed images. However, the present invention is not limited to this, and a non-contact memory or the like may be used. Thereby, for example, there is no possibility that paper dust or the like generated in the apparatus main body 17 adheres to the contact point between the storage means 30 and the apparatus main body 17 to cause a contact failure.

The contents stored in the storage means 30 include the developing roller rotation time, the number of sheets passed, the bias application time, and the like.
The number of image formation is not particularly limited as long as there is a correlation with the aging of the toner.

Further, the storage means 30 may be provided in the main body 17 of the image forming apparatus. For example, if the developing device 4 is
7, and in the image forming apparatus that supplies toner, the usage status information of each developing device 4 is
May be stored in the storage means 30, and the number of image formation for the developing device 4 may be reset when toner is supplied. This makes it possible to variably control the bias applied to the toner charging roller 26 in accordance with the change over time of the toner in each developing device 4.

The present embodiment is also applicable to a case where the developing device 4 is a cartridge that can be individually attached to and detached from the apparatus main body 17. In this case, the storage unit 3 is stored in each developing device 4.
0 is provided, and the usage status information of each developing device 4 is held.
Then, the same control as described above may be performed.

As described above, according to this embodiment, even if the amount of charge of the developer changes due to the increase in the number of times of image formation, the transfer from the photosensitive drum 1 to the recording medium 5 is always performed.
Stable transfer of the toner image is achieved, and good image quality can be obtained. Therefore, a stable high-quality image can be obtained with good reproducibility for both the primary color and the secondary color with the toner charge amount always being a desired value without being affected by the deterioration of the developer.

[0129]

As described above, according to the present invention,
A first bias and a second bias are respectively applied to a developer carrier and a developer charging member of each developing device of the image forming apparatus having a plurality of developing devices, and the developing device performs image forming first. The configuration is such that the potential difference between the first bias and the second bias in the developing device for forming an image later is larger than the potential difference between the first bias and the second bias. The first bias and the second bias are applied to the carrier and the developer charging member, respectively, so that the image formation is performed later than the developer charge amount on the developer carrier of the developing device that forms the image first. Since the charge amount of the developer on the developer carrying member of the developing device to be performed can be made larger, stable and high-quality images can be obtained with good reproducibility for both the primary color and the secondary color.

Further, according to the present invention, there is further provided a storage means for storing a use condition of each developing device provided in the image forming apparatus, and a potential difference between the first bias and the second bias in each developing device is provided. Since it can be controlled by the information stored in the storage means, by increasing the number of image formation,
Even when the charge amount of the developer changes, a stable high-quality image can be obtained with good reproducibility for both the primary color and the secondary color.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic sectional view of a process cartridge used in the image forming apparatus of FIG.

FIG. 3 is a graph illustrating a discharge characteristic of a toner charging roller.

FIG. 4 is a graph showing discharge characteristics (excluding toner potential) of a toner charging roller.

FIG. 5 is a graph illustrating a relationship between an applied voltage of a toner charging roller and a toner charge amount.

FIG. 6 is a graph showing the relationship between the voltage applied to the toner charging roller and the amount of toner charge, which changes depending on the use condition of the developer.

FIG. 7 is a schematic sectional view of another embodiment of the image forming apparatus according to the present invention.

FIG. 8 is a graph for explaining a control range of a voltage applied to a toner charging roller.

FIG. 9 is a flowchart for explaining one embodiment of a control procedure of a voltage applied to the toner charging roller according to the present invention.

FIG. 10 is a control block diagram of an embodiment of the image forming apparatus according to the present invention.

FIG. 11 is a schematic sectional view of an example of a conventional image forming apparatus.

FIG. 12 is a schematic sectional view of an example of a conventional developing device.

FIG. 13 is a schematic sectional view of another example of a conventional developing device.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum (image carrier) 2 charging roller (charging means) 3 scanner (exposure means) 4 developing device 7 cleaner (cleaning means) 9 transport belt 10 transfer roller 22 toner (developer) 23 developing roller (developer carrying) Body) 24 elastic roller 25 developing blade 26 toner charging roller (developer charging member) 30 storage means 31 CPU (control means)

────────────────────────────────────────────────── ─── of the front page continued (51) Int.Cl. ⁷ identification mark FI theme Court Bu (reference) G03G 15/06 101 G03G 15/08 503A 15/08 503 15/00 556 507 15/08 507Z 21/14 21 / 00 372 F term (reference) 2H027 DA04 DA39 DA41 DA45 DE04 DE07 DE10 EA04 EA05 EB04 EC06 EC20 ED09 EE07 EE08 2H030 AB02 AD17 BB23 BB34 BB42 BB44 BB63 2H071 BA03 BA04 BA13 BA22 BA27 BA03 DA05 DA06 A08 DA08 A08 BA22 BA36 BA41 CA02 CA22 2H077 AD06 AD13 AD17 AD36 AE10 DA01 DA22 DA24 DB08 DB25 EA14 EA15 GA13 GA17

Claims (23)

[Claims] 1. A developing device comprising: a developer carrying member for conveying a developer to an image carrying member; and a developer charging member for applying a voltage to the developer on the developer carrying member to charge the developer. An image forming apparatus that supplies a developer to the image carrier by the developing device to form an image, wherein each of the developer carrier and the developer charging member of each developing device has a first And a second bias are applied, and the potential difference between the first bias and the second bias in the developing device that forms an image first is greater than the potential difference between the first bias and the developing device that forms an image later. An image forming apparatus, wherein the potential difference from the second bias is larger. 2. A developing device comprising: a developer carrier for conveying a developer to an image carrier; and a developer charging member for applying a voltage to the developer on the developer carrier to charge the developer. An image forming apparatus that supplies a developer to the image carrier by the developing device to form an image, wherein each of the developer carrier and the developer charging member of each developing device has a first And the second bias are applied, and the developer charge on the developer carrier of the developing device that forms the image later than the developer charge amount on the developer carrier of the developing device that forms the image first An image forming apparatus characterized by increasing the amount. 3. The image forming apparatus according to claim 1, wherein the images formed by the developers formed on the image carrier by the plurality of developing devices are sequentially transferred to a recording medium. 4. An image formed by a developer formed on the image carrier by the plurality of developing devices is sequentially transferred to an intermediate transfer member, and then transferred collectively from the intermediate transfer member to a recording medium. The image forming apparatus according to claim 1, wherein: 5. The image carrier according to claim 1, wherein a plurality of image carriers are provided corresponding to the plurality of developing devices.
Or the image forming apparatus of 2. 6. The image forming apparatus according to claim 5, wherein at least the developing device and the image carrier are integrally formed, and the cartridge is detachable from the image forming apparatus main body. 7. The image forming apparatus according to claim 6, wherein the cartridge further includes at least one of a charging unit for charging the image carrier and a cleaning unit for cleaning the image carrier. apparatus. 8. An image forming apparatus according to claim 6, wherein said image bearing member is an electrophotographic photosensitive member. 9. The image forming apparatus according to claim 1, wherein the developing device is a cartridge that is detachable from the image forming apparatus main body. 10. A plurality of developer carrying members each comprising: a developer carrying member for conveying a developer to an image carrying member; and a developer charging member for applying a voltage to the developer on the developer carrying member to charge the developer. A developing device, and storage means for storing a use state of each developing device,
An image forming apparatus that forms an image by supplying a developer to the image carrier by the developing device, wherein the developer carrier and the developer charging member of each developing device have The first bias and the second bias are applied, and the potential difference between the first bias and the second bias in each developing device is controlled by information stored in the storage means, and the potential difference between the first bias and the second bias in each developing device is controlled. The maximum potential difference in the variable range of the potential difference between the first bias and the second bias is such that the maximum potential difference in the developing device that performs image formation later is larger than the maximum potential difference in the developing device that performs image formation first. Image forming apparatus. 11. A plurality of developer carrying members each comprising: a developer carrying member for conveying a developer to an image carrying member; and a developer charging member for applying a voltage to the developer on the developer carrying member to charge the developer. A developing device, and storage means for storing a use state of each developing device,
An image forming apparatus for forming an image by supplying a developer to an image carrier by the developing device, wherein each of the developer carrier and the developer charging member of each developing device has a first And the second bias are applied, and the potential difference between the first bias and the second bias in each developing device is controlled by the information stored in the storage means. The minimum potential difference in the variable range of the potential difference between the bias and the second bias is larger in the developing device that performs image formation later than in the developing device that performs image formation first. Image forming apparatus. 12. A plurality of developer carrying members each comprising: a developer carrying member for conveying a developer to an image carrying member; and a developer charging member for applying a voltage to the developer on the developer carrying member to charge the developer. A developing device, and storage means for storing a use state of each developing device,
And an image forming apparatus for forming an image by supplying a developer to the image carrier by the developing device, wherein the developer carrier and the developer charging member of each developing device have The first bias and the second bias are applied, and the potential difference between the first bias and the second bias in each developing device is controlled by the information stored in the storage unit, thereby forming an image first. An image forming apparatus, wherein the developer charge amount on a developer carrier of a developing device that forms an image later is larger than the developer charge amount on a developer carrier of a developing device. 13. A plurality of developer carrying members each comprising: a developer carrying member for carrying a developer to an image carrying member; and a developer charging member for applying a voltage to the developer on the developer carrying member to charge the developer. A developing device, and storage means for storing a use state of each developing device,
And an image forming apparatus for forming an image by supplying a developer to the image carrier by the developing device, wherein the developer carrier and the developer charging member of each developing device have The first bias and the second bias are applied, and the potential difference between the first bias and the second bias in each developing device is controlled based on the information stored in the storage means, so that the developing is performed in the image forming order. An image forming apparatus characterized in that a charge amount of a developer on a developer carrier is increased. 14. The state of use of the developing device stored in the storage means includes the number of times of image formation, the number of sheets passing through a recording medium in the image forming device, the number of rotations of a developer carrier, the first bias or the second The image forming apparatus according to any one of claims 10 to 13, wherein the application time is one of bias application times. 15. The memory according to claim 10, wherein said storage means is a contact or non-contact type nonvolatile memory.
14. The image forming apparatus according to any one of items 13 to 13. 16. The image forming apparatus according to claim 10, wherein the images formed by the developers formed on the image carrier by the plurality of developing devices are sequentially transferred to a recording medium. Image forming device. 17. An image formed by a developer formed on the image carrier by the plurality of developing devices, sequentially transferred to an intermediate transfer member, and then transferred collectively from the intermediate transfer member to a recording medium. 10. The method according to claim 10, wherein
3. The image forming apparatus according to any one of items 3. 18. The image forming apparatus according to claim 10, wherein a plurality of said image carriers are provided corresponding to said plurality of developing devices. 19. The image forming apparatus according to claim 18, wherein at least the developing device and the image carrier are integrally formed, and the cartridge is detachable from the image forming apparatus main body. 20. The image forming apparatus according to claim 19, wherein the cartridge further comprises at least one of a charging unit for charging the image carrier and a cleaning unit for cleaning the image carrier. apparatus. 21. An image forming apparatus according to claim 19, wherein said image bearing member is an electrophotographic photosensitive member. 22. The image forming apparatus according to claim 10, wherein the developing device is a cartridge that is detachable from the image forming apparatus main body. 23. The image according to claim 19, wherein said storage means is attached to each cartridge, and stores a use state of the developing device of each of the attached cartridges. Forming equipment.