JP2003122090A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of obtaining a good image while reducing the toner consumption and preventing the color mixture in toner. SOLUTION: The image forming device constituted so that developer may be applied on a photoreceptor drum 1 by a fixed developer carrier installed in a fixed developing device 4a, and arranged close to or in contact with the photoreceptor drum 1 while facing the photoreceptor drum 1, and several rotary developer carriers which are held in the circumferential direction of a freely rotatable rotary developing device 4b, and for carrying the developer while selectively coming close to face the photoreceptor drum 1 in accordance with the rotation of the rotary developing device 4b, is provided with a varying means for varying a gap between the fixed developer carrier and the photoreceptor drum 1.

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 and a facsimile machine.

[0002]

2. Description of the Related Art An image forming apparatus such as a copying machine, a printer, a facsimile machine, or the like, includes, for example, a photosensitive drum which is an electrophotographic photosensitive member which is a latent image carrier for carrying a latent image formed by exposure processing, and the photosensitive drum. A developing unit that visualizes the latent image as a toner image by applying a toner as a developer to the toner, and a transfer unit that transfers the toner image on the photosensitive drum to a recording material.

Conventionally, in such an image forming apparatus, for example, the developing means has a fixed developer carrying member which is disposed close to or in contact with the photosensitive drum so as to face, for example, black (Bk) toner. A plurality of Bk developing devices and a rotatable support member are held in the circumferential direction, and selectively rotate in close proximity to the photosensitive drum by rotation of the support member so that magenta (M), cyan (C), and yellow (Y) A developing bias voltage can be applied between the M, C, and Y developing devices each having a plurality of rotary developer carrying members carrying toner, and the photosensitive drum, the fixed developer carrying member, and the rotary developer carrying member. There is known an image forming apparatus which is provided with a bias applying means and is configured to apply a developer to the photosensitive drum from the fixed developer bearing member or the rotating developer bearing member.

[0004]

However, as described above, the exposure position in the circumferential direction of the photosensitive drum, M,
When the Bk developing device is arranged between the C and Y developing devices,
When the image-exposed latent image portion on the photosensitive drum passes the Bk toner developing position during the development with the M, C, and Y toners, the Bk toner is exposed before the M, C, and Y toners. There is a risk that the color will be transferred to and mixed.

This is because even if the Bk developing device is arranged in non-contact with the electrophotographic photosensitive member 1, the Bk toner may be transferred to the photosensitive drum, although it is in a small amount. For example, when developing with a Y toner developing device, Bk
The color mixture of the toners is conspicuous on the image due to the high brightness of the Y toner, and the color mixture of the Bk toners is very conspicuous even in a slight amount especially in a highlight portion (a portion having a low density). Damages.

Therefore, the present invention reduces toner waste,
An object of the present invention is to provide an image forming apparatus capable of preventing color mixture of toner and providing a good image.

[0007]

According to the present application, the above object is to provide a latent image bearing member carrying a latent image, and to apply the developer to the latent image bearing member to form the latent image with the developer image. An image forming apparatus comprising: a developing unit that visualizes the latent image bearing member and a transfer unit that transfers the developer image on the latent image bearing member to a recording material. A fixed developer carrier that is arranged to face each other and carries a developer, and a plurality of rotatable support members are held in the circumferential direction, and the developer is selectively opposed to the latent image carrier by the rotation of the support members to carry the developer. And a bias applying unit capable of applying a developing bias voltage between the latent image carrier, the fixed developer carrier and the rotary developer carrier. The above-mentioned fixed developer carrier or the above-mentioned rotary developer carrier is carried on the image carrier. The present invention provides an image forming apparatus in which a developer is applied from the first invention, which comprises variable means for varying the gap between the fixed developer carrier and the latent image carrier. It

Further, according to the present application, in the first aspect of the present invention, there is provided an exposing means for forming a latent image on the latent image carrier by exposing the surface of the latent image carrier.
The fixed developer carrying member is also achieved by the second invention in which the fixed developer carrying member is located between the rotating developer carrying member and the exposing means in the circumferential direction of the latent image carrying member.

Further, according to the present application, the above-mentioned object is, in the first invention or the second invention, that the fixed developer carrying member is
It has a magnet inside and is disposed close to and in contact with the latent image carrier, and the layer thickness of the developer on the fixed developer carrier is the same as that of the fixed developer carrier and the latent image carrier. A third invention in which the bias applying means is smaller than the gap and is adapted to apply a developing bias voltage in which an AC voltage is superimposed on a DC voltage between the fixed developer carrier and the latent image carrier. Also achieved by.

According to the present application, the above-mentioned object is the developing means in any one of the first to third inventions,
The present invention can also be achieved by the fourth invention, which has a developer regulating member that regulates the layer thickness of the developer on the fixed developer carrier, and the developer regulating member is a magnetic body.

Further, according to the present application, in any one of the first to fourth inventions, the above-mentioned object is that the developer on the fixed developer carrier is a one-component developer containing a magnetic material. It is also achieved by the fifth invention.

According to the present invention, the above-mentioned object is that in any of the first to fifth inventions, the latent image carrier is an electrophotographic photoreceptor containing amorphous silicon in the surface layer. It is also achieved by the sixth invention.

Further, according to the present invention, the above-mentioned object is, in any one of the first to sixth inventions, that the developing step by the developing means is the reversal development for the latent image formation. Also achieved by.

Further, according to the present invention, in any one of the first to seventh inventions, the above-mentioned object is such that the fixed developer carrying member stops rotating during non-development by the fixed developer carrying member. It is also achieved by the eighth invention that is.

Further, according to the present invention, in the above object, in any one of the first to eighth inventions, the gap between the fixed developer carrier and the latent image carrier is the fixed developer carrier. It can also be achieved by the ninth invention in which development is different from development.

Further, according to the present application, in the above-mentioned object, in any one of the first to ninth inventions, the gap between the fixed developer carrying member and the latent image carrying member is changed by the developing means. It is also achieved by the tenth invention, which is designed to be performed after the end of the process.

Further, according to the present application, in the above-mentioned object, in any one of the first to tenth inventions, the fixed developer carrying member is post-rotated after development by the fixed developer carrying member, The change of the gap between the fixed developer bearing member and the latent image bearing member is also achieved by the eleventh invention, which is adapted to be performed at the time of the post-rotation.

According to the present invention, in the above-mentioned object, in any one of the first to eleventh inventions, the fixed developer carrying member is pre-rotated before development by the fixed developer carrying member. The twelfth aspect of the invention is also capable of changing the gap between the fixed developer bearing member and the latent image bearing member during the pre-rotation.

Further, according to the present invention, in the above-mentioned object, in any one of the first invention to the twelfth invention, the gap between the fixed developer carrying member and the latent image carrying member is changed by plural recording. The present invention can also be achieved by a thirteenth invention, which is designed to be performed between two continuous recording materials at the time of continuous image formation on the material.

According to the present application, the above-mentioned object is, in any one of the first to thirteenth inventions, a fixed developer carrying member and a latent image carrying member during non-development by the fixed developer carrying member. The gap with the body is also achieved by the fourteenth invention, which is 4 times to 20 times as large as that at the time of development by the fixed developer carrying body.

Further, according to the present application, in the above-mentioned object, in any one of the first to fourteenth inventions, the bias applying means is the fixed developer carrying member at the time of non-development by the fixed developer carrying member. It is also achieved by the fifteenth invention that a developing bias voltage of a DC voltage is applied to.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described.

FIG. 1 is a schematic sectional view showing a schematic structure of an image forming apparatus according to this embodiment.

This image forming apparatus is an image forming apparatus for forming a color image by superposing toner images of a plurality of colors, and for the purpose of obtaining a color image without color deviation.
The copying machine or laser beam printer uses an electrophotographic process using the intermediate transfer member as shown in FIG. The configuration and operation of the image forming apparatus shown in FIG. 1 will be briefly described below.

A rotary drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1 as a latent image carrier is disposed inside the main body of the image forming apparatus (hereinafter referred to as "inside the apparatus"). An amorphous silicon photoconductor is used here, and a schematic diagram thereof is shown in FIG.

The photosensitive drum 1 is made of Al as shown in FIG.
And the like, a conductive support 101, a conductive support 104, a charge injection blocking layer for blocking injection of charges from the conductive support 101, and a photoconductive layer made of at least an amorphous silicon-based material. Photoconductive layer 102 exhibiting a property, and the photoconductive layer 1
Surface protection layer 103 for protecting 02, conductive support 1
01 long-wavelength light absorption layer 105 for preventing reflection from 01 and the like.

The photosensitive drum 1 is rotationally driven in the direction of arrow R1 at a predetermined peripheral speed (process speed), and each image forming process described later is repeatedly performed on the surface thereof.

The photosensitive drum 1 is charged with a predetermined polarity and a predetermined surface potential by a primary charger 2 such as a corona discharger in the course of rotation in the direction of the arrow R1, and then the exposure unit 3 (color original image color). A target color by receiving an image exposure L by an image-forming exposure optical system based on decomposition, or a scanning exposure optical system by a laser scanner that outputs a laser beam modulated corresponding to a time-series electric digital pixel signal of image information. An electrostatic latent image corresponding to the color component image of the image (for example, M (magenta) component image) is formed.

An intermediate transfer belt is used as the intermediate transfer member. The intermediate transfer belt 5 is stretched around a total of five rollers including one conductive roller 6 and four turn rollers 7a, 7b, 7c and 7d. In this embodiment, the intermediate transfer belt 5, the conductive roller 6, the turn roller 7a,
The transfer means is constituted by 7b, 7c, 7d and the like.

The conductive roller 6 holds the intermediate transfer belt 5 in a state of being pressed against the photosensitive drum 1 with a predetermined pressing force. The intermediate transfer belt 5 is rotationally driven in the direction of arrow R5 at the same peripheral speed as the photosensitive drum 1, and the conductive roller 6 is biased by a bias power source to form and carry a toner image (hereinafter referred to as “toner image”) on the photosensitive drum 1. A transfer bias having a polarity (plus) opposite to that of the toner charging polarity (negative in this embodiment) is applied.

The intermediate transfer belt 5 is, for example, a dielectric film of polyester, polyethylene or the like, or a composite layer type dielectric film in which the back surface (inner surface side) of a medium resistance rubber or the like is lined with a conductor. The magenta toner image of the first color, which is formed and carried on the surface of the photosensitive drum 1 described above, is generated by the electric field formed by the application of the transfer bias to the conductive roller 6.
In the process of passing through the transfer section, on the outer surface of the intermediate transfer belt 5,
Intermediate transfer is performed in sequence.

The developing device as a developing means is a black (Bk) developing device (hereinafter referred to as "Bk developing device") 401 fixedly arranged on the upstream side in the rotation direction of the photosensitive drum 1 (direction of arrow R1). And a rotary developing device 4b having another three-color developing device rotatably arranged on the downstream side. The rotary developing device 4b includes a rotating body that is a supporting member that rotates in the direction of arrow R4, and three developing devices that are held and mounted on the rotating body, that is, magenta (M), cyan (C), and yellow ( Y) developing device 402 containing toner of each color,
403 and 404 (hereinafter, respectively referred to as "M developing device 402, C developing device 403, Y developing device 404"). Further, M developing device 402, Y developing device 403, C
Each of the developing devices 404 is a rotary developer carrying member (not shown) that selectively faces the photosensitive drum 1 by a rotary developing device 4b accompanying the rotation of a rotatable support member (not shown) and selectively faces the photosensitive drum 1 to carry toner of each color. Have).

Further, the Bk developing device 401 is fixedly arranged between the exposure unit 3 on the upstream side and the rotary developing device 4b on the downstream side so as to separate them.

By rotating in the direction of arrow R4, the rotary developing device 4b positions the developing device (M developing device 402 in FIG. 1) for development at the developing position facing the surface of the photosensitive drum 1. Rotational direction R4 of the rotary developing device 4b
Is the same as the rotation direction R1 of the photosensitive drum 1 and is opposite to the rotation direction of the intermediate transfer belt 5 (direction of arrow R5).

The direction of rotation of the rotary developing device 4b is indicated by the arrow R.
If the four colors are set and the four colors are developed in the order of M-C-Y-Bk as in the conventional example, the M developing device 402, the C developing device 403, and the Y developing device 403 of the rotary developing device 4b. The developing device 404 is arranged as shown in FIG.
Along the rotation direction (direction of arrow R4) of the M developing device 402,
The Y developing device 403 and the C developing device 404 are in this order.

The image forming operation in the image forming apparatus of this embodiment shown in FIG. 1 will be described below by dividing it into processes (1) to (5). Incidentally, FIG. 1 shows the M developing device 402 among the three developing devices in the rotary developing device 4b.
Indicates that it is standing by at the current position.

(1) First, a latent image for the M image of the first color is formed on the photosensitive drum 1, and development is performed in the state shown in FIG. The M toner image on the photosensitive drum 1 which is visualized with the M toner by the developing device 402 is sequentially transferred onto the outer peripheral surface of the intermediate transfer belt 5 while being rotated in the arrow Rl direction (counterclockwise). Then, the surface of the photosensitive drum 1 that has finished transferring the M toner image of the first color to the intermediate transfer belt 5 is cleaned by the cleaning device 8.

(2) Subsequently, a latent image for the C image of the second color is formed, but in order to perform the C development, the rotary developing device 4b moves in the direction of arrow R4 (the same counterclockwise direction as the photosensitive drum 1). ) To rotate.

(3) Similarly, C development → C toner development on the intermediate transfer belt 5 → intermediate transfer of the C image on the intermediate transfer belt 5 → cleaning of the surface of the photosensitive drum 1 by the cleaning device 8.

(4) And Y as in (2) to (3)
Phenomenon → Intermediate transfer of Y image onto intermediate transfer belt 5 → Cleaning of the surface of the photosensitive drum 1 by the cleaning device 8.

(5) Next, image exposure L corresponding to the fourth Bk component image → Development with Bk toner of the Bk developing device 401 → Intermediate transfer of Bk toner image to the intermediate transfer belt 5 → Surface of the photosensitive drum 1 Cleaning with the cleaning device 8.

The above four toner images (toner images of magenta, cyan, yellow, and black) are superposed on the outer surface of the intermediate transfer belt 5 by sequentially performing the above processes (1) to (5). Transferred to form a composite color toner image (mirror image) corresponding to the target color image.

Next, from the paper feed cassette 9 to the paper feed roller 1
The recording material (paper sheet) P is separated and conveyed by 0 by 0, passes through the registration roller pair 11 and the transfer guide 12, and is transferred to the transfer portion formed by the transfer device 13 (corona charger) and the turn roller 13a. It is fed at a predetermined timing.

The conductive roller 6 is applied with 0 V or a bias (negative in this example) having the same charge polarity as that of the toner, which is opposite to the transfer process, from a bias power source. Further, on the recording material P fed at a predetermined timing, when the toner image is transferred, a bias power source transfers a transfer bias having a toner charge polarity (negative in this example) and a reverse polarity (plus). Applied to the device 13.

By repeating the above-described series of image forming processes, the transfer composite color images are sequentially intermediate-transferred onto the intermediate transfer belt 5, and the intermediate-transferred color toner images are successively sent to the transfer section. The final transfer is performed on the succeeding recording material P.

Upon completion of the transfer process, a transfer bias (minus) of 0 V or the same polarity as the toner charging polarity (minus in this example) is applied to the intermediate transfer belt 5.

The recording material P on which the toner image on the intermediate transfer belt 5 has been transferred through the transfer portion is introduced into the fixing device 15 via the conveyance guide 14 and added to the fixing roller 15a which is heated and controlled to a predetermined value. The toner image is fixed by being heated and pressed by the pressure roller 15b, and is output as a final color image formed product.

On the other hand, the intermediate transfer belt 5 after the toner image transfer
Are cleaned by the belt cleaning device 16.
The belt cleaning device 16 is a cleaning device for the intermediate transfer belt 5, and is normally held in a non-operating state with respect to the intermediate transfer belt 5. However, when the transfer of the toner image onto the recording material P is finished, The outer surface of the intermediate transfer belt 5 is cleaned by the belt cleaning device 16 acting on the outer surface of the transfer belt 5.

Depending on the outer peripheral length of the intermediate transfer belt 5, it is possible to carry two or more recording materials P at one time and form two images at once by one rotation.

Next, the Bk developing device 4 in the fixed developing device 4a.
The configuration of 01 will be described with reference to FIG.

In the fixed developing device 4a, the developing container 4
0 has an opening extending in the longitudinal direction of the apparatus (direction perpendicular to the paper surface of FIG. 1), and a developing sleeve 41 as a fixed developer carrier is installed in the opening.

The developing sleeve 41 is made of a material such as aluminum or SUS. Also, the developing sleeve 41
Is a rotatably arranged so that the left substantially semi-peripheral surface thereof projects into the developing container 40 and the right substantially semi-peripheral surface thereof is exposed to the outside of the developing container 40 as viewed in the drawing of the opening and faces the photosensitive drum 1. Has been done. A small gap S-Dgap is provided between the developing sleeve 41 and the photosensitive drum 1, and the developing sleeve 41 is rotationally driven in the arrow R4a direction with respect to the rotational direction Rl of the photosensitive drum 1.

Further, this minute gap S-Dgap is Bk with respect to the fixed developing device 4a by a variable means (not shown).
The developing device 401 is variable while being pressed in the direction of arrow R4c.

A magnet 42 is provided in the developing sleeve 41 as a magnetic field generating means. In this embodiment, the magnet 42 is a permanent magnet. The magnet 42 is non-rotatably arranged in the developing sleeve 41 so as to generate a fixed magnetic field regardless of the rotation of the developing sleeve 41.

In the vicinity of the developing sleeve 41 in the developing container 40, a plate-shaped magnetic blade having a fixed end supported by an opening portion of the developing container 40 as a developer regulating member and a free end facing the developing sleeve 41 is brought close to the developing sleeve 41. 43 is provided, and one pole of the magnetic pole of the magnet 42 is positioned to face the magnetic blade 43.

The magnetic toner 45 carried on the developing sleeve 41 by the stirring member 44 is then transferred to the developing sleeve 41.
Is rotated, the magnetic blade 43 is conveyed to a portion facing the developing sleeve 41. The magnetic regulation formed in the gap between the magnetic blade 43 and the developing sleeve 41: S
-Bgap regulates the layer thickness, and the developing sleeve 41
After being formed into a thin layer on the upper side, it exits the regulating portion: S-Bgap and is conveyed to the developing area facing the photosensitive drum 1 with a minute gap: S-Dgap. In the developing area, a bias applying unit (not shown) applies an alternating voltage, which is a direct current and an alternating current, as a developing bias voltage between the developing sleeve 41 and the photosensitive drum 1. Transfer and adhere to the electrostatic latent image on the photosensitive drum 1 to visualize and develop the electrostatic latent image as a toner image.

Subsequently, the Bk developing device 401 according to the present embodiment.
The development by will be described.

First, the surface of the photosensitive drum 1 is uniformly charged by the primary charger 2 to the drum surface potential vd = + 400V. Next, the surface of the photosensitive drum 1 has a wavelength of 680 μm.
An exposure L by PWM is received at 600 dpi by a semiconductor laser of m, and an electrostatic latent image is formed on the photosensitive drum 1.
The laser power at this time is set so that the electrostatic latent image becomes V1 = + 50V.

Then, S-Bgap: 250 μm, S-
Development is performed by a Bk developing device 401 having a Dgap of 250 μm to visualize the toner image. In the above-mentioned conventional example, the color image formation by the normal development has been described, but in the present embodiment, the case where the reverse development is adopted will be described.

The developer used in this embodiment is a negative magnetic one-component toner, and the developing bias voltage Vdc is + 200V.
DC voltage of 2700Hz, 1500Vpp, 50% D
The AC voltage of the duty is superimposed to realize jumping development. This is because the Bk development contrast Vcont (= Vd-Vdc) = 200V and the fog removal bias Vback (= Vdc-Vl) = + 150V in reversal development.
This is because it is set to (Fig. 4).

On the other hand, M in the rotary developing device 4b,
Color image formation in the C, Y developing devices (402, 403, 404) is Vd = + 400V, Vl = + 5 for all three colors.
It is set to 0V. Also, Vcont = + 150V, V
Since back = + 200V is required, Vdc = 25
It is set to 0 V (2000 Hz, 2000 Vpp, 50% superposition) (FIG. 5).

That is, the development processing similar to Bk is performed for M, C and Y. Therefore, the latent image for color is also developed by the Bk developing device 401 which is a fixed developing device.

Therefore, in the present embodiment, Bk is set when no image is formed.
The developing device 401 is separated from the photosensitive drum 1 at the time of image formation.

As described above, the Bk developing device 401 has SD =
The thickness is set to 250 μm in order to achieve a reflection density of 1.50 in a solid image. Therefore, by changing the direction of pressing by the arrow R4c, S-Dga
Change so that p becomes large. As a result, the electric field strength between the photosensitive drum 1 and the developing sleeve 41 is reduced, and the transfer of Bk toner onto the photosensitive drum due to electrostatic force can be prevented.

As described above, the Bk developing device 401 is set to SD: 250 μm in order to achieve the reflection density of 1.50 in a solid image. Therefore, by changing the direction of pressing by the arrow R4c, S
-Change Dgap (here, 150 μm to 1000 μm
m) and the reflection density measured at that time is shown in FIG.

As shown in FIG. 6, the solid image reflection density is S
It can be seen that when −Dgap is increased, the value is drastically decreased particularly after 500 μm. This is S-Dga
It is conceivable that the electric field strength between the photosensitive drum 1 and the developing sleeve 41 is reduced due to the increase of p, and the transfer of the Bk toner onto the photosensitive drum due to the electrostatic force is reduced.

Immediately after increasing S-Dgap, S-
The image was evaluated by returning to Dgap = 250 μm and using Bk single color (Table 1).

[0069]

[Table 1]

As a result, the S-Dgap is 15 mm.
If the above setting is made, image defects (particularly image density unevenness and bleeding) occur. This is considered to be caused by S-Dgap shake and Bk toner leakage from the lower portion of the Bk developing device 401 when the developing sleeve 41 approaches the photosensitive drum 1 again during development.

Therefore, in order to obtain a good image in a full-color image, S in the non-developing process by the Bk developing device 401
It is considered that -Dgap is 6 to 10 mm, that is, 24 to 40 times as large as S-Dgap at the time of development.

(Second Embodiment) Next, a second embodiment of the present invention will be described. The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In this embodiment, in addition to the above-described first embodiment, as shown in FIG. 7, the Bk developing device 401 is replaced by S-Dg.
While the ap is moved so as to increase, the developing bias voltage is changed to Vdc = + 600V during M, C, and Y development.

As a result, by keeping Vback = + 200V or higher for the electrostatic latent image in color in any case, it is possible to prevent the transfer of the Bk toner to the image exposure portion. Further, since the Bk developing device adopts the jumping developing method, it is supported in a non-contact manner with the photosensitive drum, and the influence on the photosensitive drum when the developing bias voltage is changed (for example, in the case of two-component developing, There is almost no transfer of magnetic particles).

(Third Embodiment) Next, a third embodiment of the present invention will be described. The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the first embodiment described above, S-Dgap is used.
And the relationship between image quality and image quality. In this embodiment, for the purpose of further improving the image quality, the non-image-developing developing bias voltage of the Bk developing device 401 is set to only the DC voltage.

The developing bias voltage configuration of the Bk developing device 401 has been described with reference to FIG. 4 in the above-described first embodiment. However, in practice, as shown in FIG. 8, in order to realize jumping development, an AC voltage (2700 Hz,
1500 Vpp, 50% superposition) is superposed. As a result, the Bk development contrast is always Vcont = 200.
The maximum contrast is Vcmax (= Vco
nt + 1 / 2Vpp) = 950V.

Therefore, when no development is performed by the Bk developing device 401, a developing bias voltage of only a DC voltage is applied between the developing sleeve 41 and the photosensitive drum 1 to further reduce the electric field strength, and the Bk on the photosensitive drum 1 is reduced. Toner can be reduced.

Actually, under that condition, the direction of pressing by the arrow R4c is changed as in the first embodiment, so that S
-Change Dgap (here 150 μm to 1.5 mm)
FIG. 9 shows the measured reflection density at that time.

According to FIG. 9, when the S-Dgap is set to 1 mm or more, the transfer of Bk toner to the photosensitive drum 1 at the time of non-development by the Bk developing device 401 is almost eliminated.

Further, since the S-Dgap is sufficiently narrower than that in the first embodiment, the image when the developing sleeve 41 and the photosensitive drum 1 come close again is also good (Table 2).

[0082]

[Table 2]

(Fourth Embodiment) Next, a fourth embodiment of the present invention will be described. The same components as those in the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the above-described first and second embodiments, the durability test of 1 million sheets was actually performed in the full-color image formation by M, C, Y and Bk.

However, as a practical result, some fog images due to Bk toner have been confirmed after 250,000 sheets after the durability test. The cause is considered as follows.

Originally, the Bk developer is a negative magnetic one-component toner, but there is a toner which becomes a positive toner by reversing the polarity of a very small amount of toner. This is Vd during M, C, Y development.
It is considered that by increasing c = 200V → 600V, the extremely small amount of the positive toner was developed on the photosensitive drum and was manifested as a fog image on the recording material.

Therefore, in the present embodiment, the rotary developing device 4b in the first embodiment or the second embodiment described above is used.
The driving of the developing sleeve of the Bk developing device 401 is stopped during the development by.

Further, in this embodiment, in consideration of the matters described in the first and second embodiments described above, the Bk developing device at the time of color image formation is set to satisfy the conditions of Table 3. Then, the durability test of 1 million sheets was actually performed in the full-color image formation by M, C, Y, and Bk.

[0089]

[Table 3]

As a result, the development with the Bk reversal positive toner is suppressed within the minimum range on the Bk sleeve.
In addition, since the Bk reversal positive toner is sufficiently discharged in the non-image area, fogging in the image area is prevented and high image quality is realized.

In the durability test of this embodiment, 1
A good image free from fog could be obtained even after the completion of, 000,000 sheets. Further, the effect of raising the temperature of the Bk developing device 401 by stopping the driving and improving the life are also obtained.

[0092]

As described above, according to the first invention of the present application, the variable means makes the gap between the fixed developer carrier and the latent image carrier variable, so that the toner is wasted. It is possible to reduce the amount of toner, prevent color mixture of toner, and provide a good image.

According to the second invention of the present application,
Since the variable means makes the gap between the fixed developer carrier and the latent image carrier variable, it is possible to reduce toner waste, prevent toner color mixture, and provide a good image.

Further, according to the third invention of the present application, the variable means makes the gap between the fixed developer carrying member and the latent image carrying member variable, and at the same time, on the fixed developer carrying member. The layer thickness of the developer is smaller than the gap between the fixed developer bearing member and the latent image bearing member, and the bias applying means applies a developing bias voltage obtained by superimposing an AC voltage on a DC voltage to the fixed developer bearing member. Since the voltage is applied between the latent image carrier and the latent image carrier, it is possible to more effectively reduce toner waste, prevent toner color mixing, and provide a good image.

According to the fourth invention of the present application,
Since the variable means makes the gap between the fixed developer carrier and the latent image carrier variable, it is possible to reduce toner waste, prevent toner color mixture, and provide a good image.

Further, according to the fifth invention of the present application, since the variable means makes the gap between the fixed developer carrier and the latent image carrier variable, the toner waste is reduced and the toner amount is reduced. It is possible to prevent color mixture and provide a good image.

According to the sixth invention of the present application,
Since the variable means makes the gap between the fixed developer carrier and the latent image carrier variable, it is possible to reduce toner waste, prevent toner color mixture, and provide a good image.

Further, according to the seventh invention of the present application, since the variable means makes the gap between the fixed developer carrying member and the latent image carrying member variable, waste of toner is reduced and the toner amount is reduced. It is possible to prevent color mixture and provide a good image.

According to the eighth invention of the present application,
The changing means changes the gap between the fixed developer carrying member and the latent image carrying member, and the fixed developer carrying member stops rotation when the fixed developer carrying member is not developing. Therefore, it is possible to more effectively reduce waste of toner, prevent color mixture of toner, and provide a good image.

Further, according to the ninth invention of the present application, the changing means can change the gap between the fixed developer bearing member and the latent image bearing member, and at the same time, the fixed developer bearing member and the latent image bearing member. Since the gap between the carrier and the fixed developer is different between the time of development by the fixed developer carrier and the time of non-development, it is possible to more effectively reduce toner waste, prevent toner color mixture, and provide a good image. It will be possible.

According to the tenth invention of the present application,
Since the variable means makes the gap between the fixed developer carrier and the latent image carrier variable, it is possible to reduce toner waste, prevent toner color mixture, and provide a good image.

Further, according to the eleventh invention of the present application, since the variable means makes the gap between the fixed developer carrier and the latent image carrier variable, toner waste is reduced and the toner is reduced. It is possible to prevent the color mixture of and to provide a good image.

Further, according to the twelfth invention of the present application, since the variable means makes the gap between the fixed developer carrier and the latent image carrier variable, toner waste is reduced and the toner is reduced. It is possible to prevent the color mixture of and to provide a good image.

Further, according to the thirteenth invention of the present application, since the variable means makes the gap between the fixed developer carrier and the latent image carrier variable, toner waste is reduced and the toner is reduced. It is possible to prevent the color mixture of and to provide a good image.

According to the fourteenth invention of the present application, the changing means changes the gap between the fixed developer carrying member and the latent image carrying member, and at the same time the non-fixed developer carrying member prevents the gap. Since the gap between the fixed developer carrying member and the latent image carrying member at the time of development is 4 to 20 times as much as that at the time of developing by the fixed developer carrying member, the toner waste is reduced more effectively, It is possible to prevent color mixture of toner and provide a good image.

Further, according to the fifteenth invention of the present application, the variable means makes the gap between the fixed developer carrier and the latent image carrier variable, and the bias applying means is fixed. Since the developing bias voltage of DC voltage is applied to the fixed developer carrying member at the time of non-development by the developer carrying member, it is possible to more effectively reduce toner waste and prevent toner color mixture, It is possible to provide a clear image.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a layer structure of a latent image carrier which is an electrophotographic photosensitive member containing amorphous silicon, which is provided in the image forming apparatus of FIG.

FIG. 3 is a diagram for explaining a fixed developer carrier according to the first embodiment of the present invention.

FIG. 4 is a diagram for explaining a developing bias voltage between a latent image carrier and a fixed developing carrier by the bias applying means in the first embodiment of the present invention.

FIG. 5 is a diagram for explaining a developing bias voltage between a latent image carrier and a rotary developing carrier by the bias applying means in the first embodiment of the present invention.

FIG. 6 is a graph showing the relationship between the image density and the gap between the latent image carrier and the fixed developer carrier in the first embodiment of the present invention.

FIG. 7 is a diagram for explaining a developing bias voltage between a latent image carrier and a fixed developing carrier by the bias applying means in the second embodiment of the present invention.

FIG. 8 is a diagram for explaining a developing bias voltage between a latent image carrier and a fixed developing carrier by a bias applying unit according to a third embodiment of the present invention.

FIG. 9 is a graph showing the relationship between the image density and the gap between the latent image carrier and the fixed developer carrier in the third embodiment of the invention.

[Explanation of symbols]

1 Electrophotographic photoreceptor (latent image carrier) 41 Development sleeve (fixed developer carrier) 43 Magnetic blade (developer regulating member) 45 toner (developer) P recording material

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/08 503 G03G 15/08 503C 504 504A 507 507L F term (reference) 2H030 AA04 AD01 AD16 BB02 BB23 BB24 BB33 BB34 BB42 BB63 BB71 2H071 DA02 DA08 EA04 EA18 2H073 AA01 BA02 BA04 BA13 BA22 BA43 CA02 CA14 CA22 2H077 AD02 AD06 AD13 AD24 AD35 AD36 BA07 BA10 DA24 DB08 DB25 EA13 EA16 GA13 GA17

Claims (15)

[Claims] 1. A latent image carrier carrying a latent image, developing means for visualizing the latent image as a developer image by applying a developer to the latent image carrier, and a latent image carrier on the latent image carrier. An image forming apparatus, comprising: a transfer unit that transfers the developer image to a recording material, wherein the developing unit is disposed in proximity to or in contact with the latent image carrier to face the latent developer carrier to carry the developer. A plurality of rotary developer carriers that are held in the circumferential direction of a rotatable support member and selectively oppose the latent image carrier by the rotation of the support members to carry a developer; and the latent image carrier. And a fixed developer carrying member and a rotating developer carrying member, and a bias applying means for applying a developing bias voltage between the latent image carrying member and the fixed developer carrying member or the rotary developing member. Image in which the developer is applied from the agent carrier A developing device, wherein the forming device is provided with a varying means for varying a gap between the fixed developer carrier and the latent image carrier. 2. An exposure means for forming a latent image on the latent image bearing member by exposing the surface of the latent image bearing member to light,
The image forming apparatus according to claim 1, wherein the fixed developer carrying member is located between the rotating developer carrying member and the exposing means in the circumferential direction of the latent image carrying member. 3. The fixed developer carrier has a magnet inside and is disposed in close proximity to the latent image carrier in a non-contact manner, and the layer thickness of the developer on the fixed developer carrier is the fixed thickness. It is smaller than the gap between the developer carrying member and the latent image carrying member, and the bias applying means applies a developing bias voltage, which is a DC voltage superimposed with an AC voltage, between the fixed developer carrying member and the latent image carrying member. Claim 1 or Claim 2 to be applied.
The image forming apparatus according to item 1. 4. The developing means has a developer regulating member for regulating the layer thickness of the developer on the fixed developer carrying member, and the developer regulating member is a magnetic body. The image forming apparatus according to claim 3. 5. The image forming apparatus according to claim 1, wherein the developer on the fixed developer carrier is a one-component developer containing a magnetic material. 6. The image forming apparatus according to claim 1, wherein the latent image carrier is an electrophotographic photoreceptor containing amorphous silicon in a surface layer. 7. The image forming apparatus according to claim 1, wherein the developing process by the developing unit is reverse development for latent image formation. 8. The image according to any one of claims 1 to 7, wherein the fixed developer carrying member is adapted to stop rotation when the fixed developer carrying member is not developing. Forming equipment. 9. The method according to claim 1, wherein a gap between the fixed developer carrying member and the latent image carrying member is different between when developing with the fixed developing agent carrier and when not developing. The image forming apparatus according to item 1. 10. The method according to claim 1, wherein the gap between the fixed developer bearing member and the latent image bearing member is changed after the developing process by the developing means is completed. The image forming apparatus according to item. 11. The fixed developer carrying member is post-rotated after development by the fixed developer carrying member, and the gap between the fixed developer carrying member and the latent image carrying member is changed during the post-rotation. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured as follows. 12. The fixed developer carrying member is pre-rotated before development with the fixed developer carrying member, and the gap between the fixed developer carrying member and the latent image carrying member is changed during the pre-rotating process. The image forming apparatus according to claim 1, wherein the image forming apparatus is configured as described above. 13. The gap between the fixed developer bearing member and the latent image bearing member is changed between two continuous recording materials during continuous image formation on a plurality of recording materials. The image forming apparatus according to any one of claims 1 to 12. 14. The gap between the fixed developer carrying member and the latent image carrying member during non-development with the fixed developer carrying member is 4 to 20 times as large as that during development with the fixed developer carrying member. The image forming apparatus according to any one of claims 1 to 13. 15. The bias applying means is adapted to apply a developing bias voltage of a DC voltage to the fixed developer carrying member during non-development by the fixed developer carrying member. The image forming apparatus according to claim 1.