JP2000172045A - Color image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of an image density irregularity caused by a change in an amount of carrying and to satisfactorily form an image, by moving and carrying developer from an upstream to downstream developer- carrier in an area where they are close to a latent-image carrier. SOLUTION: By stirring screws 136 and 137 rotating at the same speed in opposite directions, toner supplied into a developing-unit casing 130 is stirred and mixed with developer, stored in the developing-unit casing 130, so that developer having uniform toner concentration is obtained, and carried to a layer-thickness regulating plate 133 by a supply roller 135. It is regulated into a specific layer-thickness, and steadily supplied onto a developing sleeve 131a disposed upstream in the direction of the rotation of a photoreceptor drum 10. By the rotations of the developing sleeves 131a and 131b rotated in the same direction and the magnetic actions of fixed magnets 132a and 132b, the developer is carried from the developing sleeve 131a, disposed upstream, onto the developing sleeve 131b, disposed downstream in the direction of the rotation of the photoreceptor drum 10, so as to be stable in amount of carrying.

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 such as a copying machine, a printer, a facsimile, etc., in which a charging means, an image exposing means and a developing means are arranged around a latent image carrier and the latent image carrier is placed on the latent image carrier. The present invention relates to an electrophotographic color image forming apparatus that forms a color image by superimposing toner images.

[0002]

2. Description of the Related Art Conventionally, as a method of forming a multi-color image by superposing a toner image on a latent image carrier, a charging means, an image exposing means and a plurality of sets of developing means are provided around the latent image carrier. The latent image carrier is rotated a plurality of times to form a latent image by charging the latent image carrier by a charging unit, forming a latent image by image exposure light from an image exposing unit, and developing the latent image by a developing unit. Is repeated for each color to form a color toner image by superimposing a plurality of toner images on the peripheral surface of the latent image carrier, or a plurality of sets of charging around the latent image carrier. Means, an image exposing means and a developing means, and within one rotation of the latent image carrier, charging of the latent image carrier by the charging means and formation of a latent image by image exposure light from the image exposing means and development by the developing means Toner image formation by developing the latent image for each color Repeatedly performed, the color image forming apparatus that forms a color toner image by superimposing a plurality of toner images on the peripheral surface of the latent image carrier are known.

Further, an apparatus using a plurality of developer carriers as a developing means is disclosed in Japanese Patent No. 273619 or the like.

[0004]

In a color image forming apparatus for forming a multi-color image by superposing a toner image on a latent image carrier as described above, a toner image of a previous color is used in the development of the second and subsequent colors. The magnetic brush of the developer on the developer carrier must be extremely thin so as not to contact the latent image carrier, that is, in a so-called thin layer state so as not to disturb the toner image.

In thin layer development in which the latent image carrier and the magnetic brush on the developer carrier are not in contact with each other, a DC electric field in which an AC electric field is superimposed on a development electric field may be used, or the peripheral speed of the latent image carrier may be changed. V
peripheral speed of the developer carrier (referred to as Vs)
Has been set quickly (Vs / Vp = 1 or more) to ensure developability (development density).

However, it becomes more difficult to secure developability as the speed increases. As one of means for securing the developing property, there is a method using a plurality of developer carrying members in the developing means as in the above proposal. It is difficult to secure the amount of the developer, the amount of the developer conveyed is not stabilized, and image density unevenness occurs due to the fluctuation of the amount of conveyed toner.

The present invention solves the above-mentioned problems, stabilizes the amount of developer transported by a plurality of developer carriers, and prevents the occurrence of image density unevenness due to variations in the transported amount, thereby improving image quality. It is an object to provide a color image forming apparatus capable of forming.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a latent image carrier for carrying a latent image, and a plurality of developer carriers having a fixed magnet therein for carrying and transporting a developer comprising a toner and a carrier. In a color image forming apparatus in which a plurality of color toner images are formed on the latent image carrier by a plurality of developing means having a plurality of members, the plurality of developer carriers are all transferred in the same direction. And moving the developer between the developer carriers in the vicinity of the latent image carrier, moving the developer from the upstream developer carrier to the downstream developer carrier, and transporting the developer. Is achieved by a color image forming apparatus.

[0009]

Embodiments of the present invention will be described below. Note that the description in this column does not limit the technical scope of the claims and the meaning of terms. Also, the following assertive description in the embodiment of the present invention indicates the best mode, and does not limit the meaning of the terms of the present invention or the technical scope. In the following description of the embodiment, two developer carriers will be described. However, the present invention is also applicable to a case where two or more developer carriers are used.

An image forming process of a color printer, which is an example of an image forming apparatus according to the present invention, and each mechanism and a developing means used in the image forming apparatus will be described with reference to FIGS. FIG. 1 is a cross-sectional configuration diagram of a color printer which is an example of an image forming apparatus according to the present invention, FIG. 2 is an enlarged cross-sectional configuration diagram of a developing unit in FIG. 1, and FIG. FIG. 4 is a diagram showing an example of a configuration in which the developer can be easily delivered to the body, FIG. 4 is a diagram showing a configuration in which the developer is more easily delivered in FIG. 3, and FIG.
FIG. 9 is a diagram illustrating another example of a configuration in which a plurality of developer carriers easily transfer developer.

According to FIG. 1, reference numeral 10 denotes a photosensitive drum which is a latent image carrier, which is formed by applying an OPC photosensitive member (organic photosensitive member) on a drum base, and is grounded and driven clockwise in the drawing. Rotated. Reference numeral 11 denotes a scorotron charger, which is a charging means, has a control grid and a discharge electrode, is mounted to face the photosensitive layer of the photosensitive drum 10, and has a corona having the same polarity as the toner (minus polarity in this embodiment). A uniform charging potential (white portion potential) _VH , for example, -750 V, is applied to the peripheral surface of the photosensitive drum 10 by the discharge. Prior to charging by the scorotron charger 11, in order to eliminate the history of the photosensitive drum 10 up to the previous printing, exposure is performed by a PCL 11a, which is a pre-charging static eliminator using a light emitting diode or the like, and the peripheral surface of the photosensitive drum 10 is neutralized. Keep it. The history of the photoconductor drum 10 refers to an image pattern remaining on the photoconductor formed by charging and image exposure at the time of preceding image formation, and is also referred to as a photoconductor memory.

After the photosensitive drum 10 is uniformly charged, an image exposure based on an image signal is performed by an exposure optical system 12 as image exposure means. The exposure optical system 12 includes a polygon mirror 12a, an fθ lens 12b, and a cylindrical lens 12 that rotate using a laser diode (not shown) as a light source.
The main scanning is performed by bending the optical path by the reflection mirror 12d after the rotation of the photosensitive drum 10 and rotating the photosensitive drum 10 (sub-scanning).
Forms a latent image. In this embodiment performs exposure for a character portion, the exposed portion potential (black portion potential) V _L, for example, to form a -50 V, lower than the white area potential V _H is more in absolute value Kurobe potential V _L A reversal latent image having a potential is formed.

Around the periphery of the photosensitive drum 10, Y, Y and M containing a two-component developer composed of a toner such as yellow (Y), magenta (M), cyan (C), and black (K) and a magnetic carrier, respectively. A developing device 13 as M, C, and K developing means is provided. The developing device 13 for each color includes a developing sleeve 131a, which is a developer carrying member that carries a developer and rotates on the upstream side and the downstream side with respect to the rotation direction of the photosensitive drum 10, which will be described in detail later. , 131b
Is provided.

First, yellow development by the Y developing device 14 for the first color is performed by the developing sleeves 131a and 131b which rotate while holding the Y developer. The developer is a magnetic carrier (carrier) with magnetite as a core and an insulating resin coated around it, and a pigment and a charge control agent, silica,
It is made of a toner to which titanium oxide or the like is added, and is conveyed to the developing area on the developing sleeves 131a and 131b with the developer layer thickness being regulated to 100 to 400 μm.

The developing sleeves 131a, 131a,
The gap between the photosensitive drum 131b and the photosensitive drum 10 is 0.4 to 1.0 mm, which is larger than the thickness of the developer layer. During this time, the AC bias is applied to the DC of the same polarity as the toner (minus polarity in the present embodiment). The developing bias superimposed on the bias is applied to the respective developing sleeves 131a and 131b, so that the latent image on the photosensitive drum 10 is developed (developed) by non-contact reversal development, and the Y toner image is It is formed on the drum 10.

After the visualization of the first color is completed, a magenta image forming process for the second color is started, and the scorotron charger 1 is again activated.
1 is performed, and a latent image based on the image data of the second color is formed by the exposure optical system 12. At this time 1
The charge elimination by the PCL 11a performed in the color image forming process is not performed when the Y toner image attached to the image portion of the first color scatters due to a sharp drop in the surrounding potential.

The portion of the photoreceptor charged to the white portion potential V _H (−750 V in the present embodiment) again over the entire surface of the photoreceptor drum 10 has 1 A latent image similar to the color image is formed, and an M toner image is formed by development in the M developing unit 13. However, in the portion where the image of the first color is developed again, the adhesion of the first color image is performed. Due to the shading by the toner and the influence of the charge of the toner itself, a latent image having a potential slightly higher than the black portion potential _VL of the first color (-50 V in the present embodiment) is formed, and a DC bias (for example, in the present embodiment). Is -60
0 V).

For the third color cyan and the fourth color black, an image forming process similar to that for the second color magenta is performed, and the Y, M, C and K toner images are formed on the peripheral surface of the photosensitive drum 10. A color superimposed color toner image is formed.

A toner supply device 16 for controlling and replenishing each of the Y, M, C and K developing units 13 with a new color toner.
Are detachable Y, M, C and K toner cartridges 16a, Y, M, C and K toner storage means 16b;
The toner supply unit 16c includes Y, M, C, and K toner supply units. For each color, unused toner passes through a toner supply unit (not shown) from the toner cartridge 16a through the toner storage unit 16b and the toner transport unit 16c. It is supplied and supplied into the developing unit 13 for each.

On the other hand, the half moon roller 1
Recording paper P, which is one sheet of transfer material carried out via
Is temporarily stopped by a timing roller 15d provided with a registration sensor (not shown) through a pair of intermediate paper feed rollers 15b and 15c. The sheet is fed to the transfer area by the rotation of the registration roller 15d in synchronization with the transfer.

In the transfer area, a transfer roller 14a, which is a transfer means for applying a voltage for transferring the color toner image on the peripheral surface of the photosensitive drum 10 to the recording paper P in synchronization with the transfer timing, is pressed into contact with the transfer roller 14a. The color toner image on the peripheral surface of the photosensitive drum 10 is collectively transferred to the recording paper P while sandwiching the fed recording paper P.

Next, the recording paper P is neutralized by a sawtooth electrode 14b serving as a separating means, separated from the peripheral surface of the photosensitive drum 10, and conveyed to a fixing device 17 serving as a fixing means. Crimping roller (lower roller) 1
After the toner image on the recording paper P is welded by heating and pressurizing the recording paper 7b, the recording paper P is discharged onto a discharge tray 20 outside the apparatus via discharge rollers 18a, 18b, and 18c. After the recording paper P passes through the transfer roller 14a, the transfer roller 14a is retracted and separated from the peripheral surface of the photosensitive drum 10 to prepare for the formation of the next toner image.

On the other hand, the photosensitive drum 1 from which the recording paper P is separated
In the case of No. 0, the residual toner is removed and cleaned by the pressure contact of the blade 19a of the cleaning device 19, and the charge is removed by the PCL 11a and charged by the scorotron charger 11 again to start the next image forming process. The blade 19
“a” immediately moves after the cleaning of the photosensitive drum surface and moves away from the peripheral surface of the photosensitive drum 10. Blade 19a
The waste toner scraped into the cleaning device 19 by the screw 19b is discharged and stored in a waste toner collecting container (not shown).

According to FIGS. 2 and 3, in the color image forming apparatus described with reference to FIG. 1, in the thin layer development in which the photosensitive drum 10 and the magnetic brush are not in contact, an AC electric field is applied to the developing electric field at the developing bias. Use a superimposed DC electric field,
The developing sleeve 131 as a developer carrier is compared with the peripheral speed (referred to as Vp) of the photosensitive drum 10 as a latent image carrier.
The peripheral speeds of a and 131b (both are referred to as Vs) are set fast (Vs / Vp = 1 or more) to secure developability. However, as the speed increases, it becomes more difficult to secure developability.
As one of means for securing the developing property, there is a method using a plurality of developer carrying members in the developing means as in the above proposal. It is difficult to secure the amount, and the amount of the developer conveyed is not stabilized, and image density unevenness occurs due to the fluctuation of the amount of conveyed, and a good image is not formed.

Therefore, as shown in FIG. 2, a plurality of developer carrying members (two developer carrying members in the present embodiment)
The developing sleeves 131a and 131b are all moved in the same direction at the developing position (in the present embodiment, in the forward direction with respect to the rotation direction of the photosensitive drum 10 rotated clockwise in FIG. 2, the counterclockwise direction in FIG. 2). Direction).

The developing device 13, which is a developing means for each color, is configured as follows. The flow of the developer inside the developing device 13 is shown by a dotted line in FIG.

In the developing device 13, 130 is a developing device casing which is a developer accommodating portion for accommodating a two-component developer composed of toner and carrier, and 131a is a photosensitive drum 10
The developing sleeve 131b, which is a developer carrying member disposed upstream with respect to the rotation direction of the photosensitive drum 10, has a developing sleeve 132a, which is a developer carrying member disposed downstream with respect to the rotating direction of the photosensitive drum 10. Reference numeral 132b denotes a fixed magnet which is a magnetic field generating means fixedly disposed inside each of the rotating developing sleeves 131a and 131b, and 133 denotes a predetermined amount of layer for supplying the developer onto the upstream developing sleeve 131a. A layer thickness regulating plate 134, which is a layer thickness regulating means made of a magnetic material to be regulated, is a transport roller 135 composed of a roller-shaped magnet body for peeling off and transporting the developer from the developing sleeve 131b on the downstream side. Supply rollers, 136 and 13
7 is a pair of stirring screws.

Developing sleeve 131 as a developer carrier
Each of a and 131b is made of a nonmagnetic cylindrical member having an outer diameter of, for example, about 8 mm to 30 mm using an aluminum material or a stainless steel material, and maintains a predetermined gap with respect to the peripheral surface of the photosensitive drum 10. In the developing position, all the developing sleeves 131a and 131b are in the same direction (in this embodiment, in the forward direction with respect to the rotation direction of the photosensitive drum 10 rotated clockwise in FIG. 2, the counterclockwise direction in FIG. 2). Direction). The photosensitive drum 10 is rotated in the forward direction with respect to the rotation (clockwise rotation in FIG. 2) (counterclockwise rotation in FIG. 2).

Fixed magnets 132a, 13 which are magnetic field generating means disposed inside the developing sleeves 131a, 131b
Reference numeral 2b designates a plurality of magnetic poles N and S, which are fixed in the developing sleeves 131a and 131b, respectively, and form a magnetic field on the peripheral surface of the non-magnetic sleeve.

The layer thickness regulating plate 133, which is a layer thickness regulating means,
For example, it is made of a rod-shaped or plate-shaped magnetic stainless steel material, and is disposed at a predetermined gap from the fixed magnet 132a of the upstream developing sleeve 131a, for example, the magnetic pole S, and on the peripheral surface of the developing sleeve 131a. The layer thickness of the formed two-component developer is regulated stably and uniformly. In particular, the present method using the magnetic layer thickness regulating plate 133 is excellent in forming a thin layer of developer on the surface of the developing sleeve 131a.

The transport roller 134 has a plurality of magnetic poles N, S
Are alternately arranged, and the repelling magnetic field of the magnetic poles N and N of the developing sleeve 131b and the conveying roller 13
4, the developing sleeve 131b on the downstream side
Stripping of the developer from above and transport of the stripped developer to the stirring screw 136 are performed.

The stirring screw 136 and the stirring screw 137 rotate at a constant speed in directions opposite to each other, stir and mix the toner and the magnetic carrier in the developing unit 13, and form a two-component containing a predetermined toner component uniformly. Developer.

The supply roller 135 is provided with the stirring screw 13
6,137, the developer stirred by the layer thickness regulating plate 133.
To supply.

The toner supplied into the developing device casing 130 from a toner supply port (not shown) in the upper portion of the developing device casing 130 above the stirring screw 137 is supplied to the stirring screws 136 and 13 rotating at opposite speeds in opposite directions.
7, is stirred and mixed with the developer contained in the developing device casing 130 to become a developer having a uniform toner concentration.
The developer is conveyed to the layer thickness regulating plate 133 by the rotating supply roller 135. The developer, which is regulated to a predetermined layer thickness by the layer thickness regulating plate 133 and is stably supplied onto the developing sleeve 131a arranged on the upstream side with respect to the rotation direction of the photosensitive drum 10, rotates in the same direction. Rotation of the developing sleeves 131a, 131b and the fixed magnets 132a, 132
3B, the developing sleeve 13a disposed on the downstream side with respect to the rotation direction of the photosensitive drum 10 from the developing sleeve 131a disposed on the upstream side as shown in FIG.
The developer is transported onto the upper portion 1b with a stable developer transport amount. The developer on the developing sleeve 131b, which has developed the latent image on the photosensitive drum 10 by the developing sleeves 131a and 131b,
The feed roller 1 is peeled off by the action of the transport roller 134 and
By 35, it is conveyed again to the stirring screw 136.

As described above, the two-component developer and the fixed magnet are used inside the developer carrier, and a plurality of developer carriers are further rotated in the same direction. Is moved from the upstream developer carrier to the downstream developer carrier in the vicinity of the developer carrier and conveyed, so that the amount of developer transport set by the upstream developer carrier is set. To
It is also possible to stably supply the developer carrying member on the downstream side, stabilize the developer carrying amount in the plurality of developer carrying members, and prevent the occurrence of image density unevenness due to the fluctuation of the carrying amount, Good images can be supplied.

Further, as shown in FIG. 4, the outer diameter of the developing sleeve 131a on the upstream side with respect to the moving direction of the developer is such that the outer diameter of the developing sleeve 131a on the downstream side is relatively small. The diameter is set to be larger than the outer diameter of the developing sleeve 131b. This makes it possible to more smoothly move the developer from the upstream developing sleeve 131a having a large outer diameter to the downstream developing sleeve 131b. Further, the outer diameter of the upstream developing sleeve 131a is 1.5 times or more the outer diameter of the downstream developing sleeve 131b.
It is preferable that the ratio be equal to or less than twice in order to more smoothly move the developer. When the outer diameter is less than 1.5 times, the delivery of the developer from the upstream developing sleeve 131a is not easy, and when the outer diameter exceeds 3 times, the outer diameter of the upstream developing sleeve 131a is not increased. Is too large to stably deliver the developer.

As described above, the transfer of the developer between the plurality of developer carrying members is facilitated, and the amount of the developer transported is stabilized.

As another example of a configuration in which a plurality of developer carrying members can easily transfer the developer, as shown in FIG. 5, a plurality of developer carrying members (in the present embodiment, two developer carrying members are used). Developing sleeve 131a and developing sleeve 131
b) in the rotation direction and the driven direction (forward direction) of the photosensitive drum 10 and the developing sleeves 131a and 131b.
b rotates at the same speed as the peripheral speed of the photosensitive drum 10.

As described above, the plurality of developer carriers are rotated in the rotation direction and the driven direction (forward direction) of the latent image carrier and at the same speed as the peripheral speed of the latent image carrier. In other words, by making the plurality of developer carrying members Vs / Vp = 1 in the forward rotation development, the occurrence of the deviation of the developing portion during the development of the latent image on the latent image carrying member is reduced, and the plurality of developer carrying members are reduced. Delivery of the developer to and from the developer carrier is facilitated, and the amount of the developer transported is stabilized.

In the color printer described with reference to FIG. 1, each color toner image sequentially formed on the image carrier is superimposed, and then the superimposed color toner image formed on the image carrier is transferred to the transfer unit. Is a color image forming apparatus of a type in which a color image is formed by transferring onto a transfer material at one time, but the color image forming apparatus of the present invention is not limited to this, A plurality of sets of charging means, image exposing means and developing means are arranged, within one rotation of the latent image carrier,
The charging of the latent image carrier by the charging unit and the formation of the latent image by the image exposure light from the image exposure unit and the toner image formation by the development of the latent image by the developing unit are repeatedly performed for each color,
Of course, the present invention is also applied to a color image forming apparatus that forms a color toner image by superposing a plurality of toner images on the peripheral surface of the latent image carrier.

Although a two-component magnetic developer has been described as the developer used in the developing means, a one-component developer may be used as the developer.

[0042]

According to the first aspect of the present invention, the amount of developer conveyed by the plurality of developer carriers is stabilized, and the occurrence of uneven image density due to the fluctuation of the amount of conveyed toner is prevented, thereby providing a good image supply. Becomes possible.

According to the second or third aspect, the transfer of the developer between the plurality of developer carrying members is facilitated, and the developer transport amount is further stabilized.

According to the fourth aspect of the invention, the occurrence of deviation of the developing piece during the development of the latent image on the latent image carrier is reduced, and the transfer of the developer between the plurality of developer carriers is facilitated. The transport amount is stabilized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional configuration diagram of a color printer as an example of an image forming apparatus according to the present invention.

FIG. 2 is an enlarged cross-sectional configuration diagram of a developing unit in FIG.

FIG. 3 is a diagram illustrating an example of a configuration in which a plurality of developer carriers easily transfer developer.

FIG. 4 is a diagram showing a configuration in which developer can be more easily delivered in FIG. 3;

FIG. 5 is a diagram illustrating another example of a configuration in which a plurality of developer carriers easily transfer developer.

DESCRIPTION OF SYMBOLS 10 Photoconductor drum 11 Scorotron charger 12 Exposure optical system 13 Developing device 17 Fixing device 19 Cleaning device 131a, 131b Developing sleeve P Recording paper

Claims (4)

[Claims] 1. A latent image carrier for carrying a latent image and a plurality of developing means having a plurality of developer carriers having a fixed magnet therein for carrying and transporting a developer comprising a toner and a carrier. In a color image forming apparatus that forms a plurality of color toner images on the latent image carrier and then collectively transfers the toner images onto a transfer material, the plurality of developer carriers are all rotated in the same direction, and the developer is A color image forming apparatus comprising: moving from an upstream developer carrier to a downstream developer carrier in a portion adjacent to the latent image carrier; 2. The developer carrier according to claim 1, wherein the upstream developer carrier has a larger outer diameter than the downstream developer carrier with respect to the direction of movement of the developer. Color image forming apparatus. 3. The developer carrier on the upstream side has an outer diameter that is 1.5 times or more and 3 times or less than the outer diameter of the developer carrier on the downstream side. Color image forming apparatus. 4. The developer carrier according to claim 1, wherein the plurality of developer carriers rotate in a rotation direction and a driven direction of the latent image carrier, and rotate at the same speed as the peripheral speed of the latent image carrier. The color image forming apparatus according to claim 1.