JPH11161017A - Developing device and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the edge part of an output image sharp and to stably output an excellent image without a void and raking, in a developing device or an image forming device for outputting a monochrome image by a one-component developing system. SOLUTION: The device is provided with at least two first/second developer carriers 4a and 4b which face an image carrier 1 respectively and constitute developing parts (a) and (b) for sticking toner to an electrostatic charge image on the image carrier, to form a toner image. Then, the same electrostatic charge image on the image carrier 1 has monochrome development processing of twice or more by the one-component developing system, at least by these two first and second developer carriers 4a and 4b. In such a case, when the distance between the first developer carrier 4a and the image carrier 1 is defined as S-Da and the distance between the second developer carrier 4b and the image carrier 1 is defined as S-Dd, the condition given by S-Da<200 μm, 600 μm<S-Db satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an electrophotographic photosensitive member.
Development for developing an electrostatic charge image (electrostatic latent image) formed on an image carrier such as an electrostatic recording dielectric by an appropriate image forming means or process such as an electrophotographic process or an electrostatic recording process as a toner image. The present invention relates to an apparatus and an image forming apparatus such as a copying machine or a printer provided with the developing device.

[0002]

2. Description of the Related Art For example, in an electrophotographic apparatus, a photosensitive member (hereinafter, referred to as a photosensitive drum) having a general cylindrical shape (rotating drum type) as an image bearing member is charged by a charger and a desired pattern is formed. To form an electrostatic charge image on the photosensitive drum, and subject it to toner development processing to form a toner image corresponding to the latent image electric field, thereby obtaining an output image.

[0003] Toner development of an electrostatic charge image on a photosensitive drum is performed by a developing unit (developing nip), which is an opposing portion between the photosensitive drum and a developer carrier on the side of a developing means, between the photosensitive drum and the developer carrier. Distance (facing gap, distance between SD,
This is achieved by causing toner to fly and reciprocate an SD gap (hereinafter referred to as “SD distance”) and selectively adhere to the electrostatic charge image pattern on the photosensitive drum.

In the developing process at that time, the position of the electrostatic charge distributed on the photosensitive drum to which the toner particles adhere is determined by the magnitude of the distance between SD and the like.

[0005] Generally, in the area between the developable SD and the SD,
When the distance between S and D is small, the electrode effect works to selectively attach toner particles near the edge of the electrostatic charge image.
It is known that when the distance is large, toner particles adhere near the center of the electrostatic charge image.

[0006]

SUMMARY OF THE INVENTION As described above, SD
When the distance is reduced, toner particles selectively adhere to the vicinity of the edge of the electrostatic charge image, and an image having a sharp outline can be obtained. On the other hand, the toner particles stay near the edge, and image deterioration such as sticking and white spots occurs.

On the contrary, when the distance between SD is increased,
Stagnation of toner particles at the edge of the image is reduced, and image deterioration such as sweeping and white spots can be suppressed. However, the image lacks sharpness at the outline portion, resulting in a blurred image.

As described above, the sharpness of the image edge portion and the image deterioration due to white spots and sweeping are in a trade-off relationship under all development conditions, and it is difficult to achieve both.

An object of the present invention is to achieve both.

[0010]

According to the present invention, there is provided a developing apparatus and an image forming apparatus having the following constitution.

(1) At least first and second developing units which constitute a developing unit which forms a toner image by adhering toner to an electrostatic charge image on the image carrier, each of which faces the image carrier. Agent carrier, and at least the first and second
A developing device for performing two or more single-color development processes by a single component developing method on the same electrostatic charge image on the image carrier by using one developer carrier; and a first developer carrier and an image carrier. When the distance between the second developer carrier and the image carrier is S-Db, the following condition is satisfied: S-Da <200 μm 600 μm <S-Db Developing device.

(2) The method according to (1), wherein the electrostatic charge image on the image carrier is developed by the first developer carrier having a small distance from the image carrier. Developing device.

(3) The developing device according to (1) or (2), wherein φa ≧ φb when the diameters of the first and second developer carriers are φa and φb, respectively. .

(4) The image carrier is a photoconductive photoreceptor, and an electrostatic charge image is formed by charging means for uniformly charging the image carrier and exposure means for exposing the charged image carrier surface. The developing device according to any one of (1) to (3), wherein

(5) An image forming apparatus comprising: an electrostatic charge image forming means for forming an electrostatic charge image on an image carrier; and a developing means for forming a toner image by attaching toner to the electrostatic charge image. An image forming apparatus, wherein the developing unit is the developing device according to any one of (1) to (4).

(6) The image carrier is a photoconductive photoreceptor, and an electrostatic charge image is formed by charging means for uniformly charging the image carrier and exposure means for exposing the charged image carrier surface. The image forming apparatus according to (5), wherein is formed.

<Operation> In order to solve the above-mentioned problems, the present invention provides a first developer carrier which enhances edges and contributes to sharpness of an image, and a second developer which contributes to prevention of sweeping of white spots. By using the developing developer carrier and performing the development process by sharing the functions of these two developer carriers, a good output image with sharp edges and no white spots or sweeping is obtained. .

FIG. 1 shows a 3 × 3 mm square pattern developed using a 30 mmφ photosensitive drum as an image carrier and a 20 mmφ developing sleeve as a developer carrier of a developing device. This shows an image output immediately before the DC component at that time is lowered while the AC component of the developing bias is applied. The AC component Vac of the developing bias used at this time is Vac
The test was performed so that the value of / SD was about 400 (V / μm).

As can be seen from FIG.
At m, the edge is strongly emphasized by the electrode effect. As the distance between S and D is increased to 100 μm and 200 μm, the edge gradually weakens, and from 300 μm, the vicinity of the center is covered with toner. Further SD
As the distance is increased, the toner covers the entire surface and the entire area is reduced. This is an image symbolically representing the contribution of the edge effect, and the characteristics of the output image when a normal developing bias is applied can be estimated by the above-described method. In this case, the SD distance is 300 μm
In the following cases, the edge is sufficiently emphasized, and as a result, the sharpness of the outline of the image is increased, but the wraparound of the electric field is increased, so that white spots and sweeping are likely to occur. Conversely, S
When the distance between -D is 600 μm or more, the electrode effect is suppressed and the wraparound of the electric field is reduced, but an image lacking in sharpness of the outline of the image is output.

As described above, at least two times of development processing, that is, development that emphasizes edges and development that causes less white spots and sweeping, are performed on the same electrostatic charge image, so that white spots and sweeping are performed. For image patterns that are likely to shift and image patterns that are likely to lose sharpness at the edges,
A good output image can be obtained.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 (FIGS. 2 to 4) (1) Example of Image Forming Apparatus FIG. 2 is a schematic configuration diagram of an image forming apparatus in the present embodiment. The image forming apparatus of this embodiment is a digital printer (electrophotographic image recording apparatus) using a transfer type electrophotographic process and a laser scanning exposure system.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member (photosensitive drum) as an image carrier, which is rotated at a predetermined peripheral speed (process speed) in a clockwise direction indicated by an arrow.

In the rotating process, in the case of this embodiment as a charging means (charging device), the contact charging roller 2 receives a uniform charging process of a predetermined polarity and potential, and then a laser scanner 3 ( By receiving the laser scanning exposure L by the image exposure device, an electrostatic charge image corresponding to the target image information is formed on the surface of the rotating photosensitive drum 1. S2 is a charging bias application power source for the charging roller 2. 3a is a reflection mirror for deflecting the output laser beam from the laser scanner 3 to the exposure position of the photosensitive drum 1.

Next, the electrostatic charge image on the surface of the rotating photosensitive drum 1 is developed by the developing device 4 as a toner image. 4a
Reference numeral 4b denotes two first and second developer carrying members arranged on the upstream and downstream sides of the photosensitive drum 1 in the rotation direction.
Of the developing sleeve. The two developing sleeves 4a and 4b are arranged in parallel with and in close proximity to the photosensitive drum 1 with a predetermined small distance (SD gap) therebetween. It is driven to rotate. a
B denotes the photosensitive drum 1 and the first and second developing sleeves 4a.
First and second developing sections (developing nips) which are opposed to the developing section 4b. S4 is a power supply for applying a developing bias to the developing sleeves 4a and 4b.

In the toner development of the electrostatic charge image on the photosensitive drum 1, first, the photosensitive drum 1 and the first developing section are set in a first developing section a which is an opposing section between the photosensitive drum 1 and the first developing sleeve 4a. This is achieved by the toner flying and reciprocating between the sleeve 4a and selectively adhering to the electrostatic charge image pattern on the photosensitive drum 1.

Next, the photosensitive drum 1 and the second developing sleeve 4
b, the toner flies between the photosensitive drum 1 and the second developing sleeve 4b in a second developing section b which is a part facing the second developing sleeve 4b.
This is achieved by reciprocating and selectively adhering to the electrostatic charge image pattern on the photosensitive drum 1.

That is, the electrostatic charge image pattern on the photosensitive drum 1 is subjected to development processing twice in the first developing section a and the second developing section b.

The toner image formed on the rotating photosensitive drum 1 by the first and second developing units a and b is transferred to the photosensitive drum 1 and a transfer unit (transfer charger) brought into contact with the photosensitive drum 1. The image is sequentially transferred to a transfer portion c, which is a contact nip portion with the transfer roller 5, on a transfer material P surface side fed from a paper supply unit (not shown) at a predetermined control timing. S5 is a transfer bias application power supply for the transfer roller 5.

The transfer material P to which the toner image has been transferred through the transfer portion c is separated from the surface of the rotary photosensitive drum 1 and introduced into a fixing device (fixing device) 7 where the toner image is subjected to a fixing process and an image is formed. It is output as a formed product (print, copy).

After the transfer of the toner image to the transfer material P, the rotating photosensitive drum 1 is cleaned by the cleaning means 6 to remove contaminants remaining on the transfer material such as residual toner, and is repeatedly used for image formation. You.

In this embodiment, the photosensitive drum 1 as an image carrier is a photosensitive member (photoconductor) having a support such as aluminum as the lowermost layer. A function separation type having a charge generation layer and a charge transport layer, and a single layer type in which the charge generation layer and the charge transport layer are formed in the same layer are used. As the charge generation layer, for example, selenium-tellurium, a bilium-based pigment, a phthalocyanine-based pigment, an azo pigment, or the like can be used. As the charge transport layer, poly-N
-A polymer compound having a heterocyclic or condensed polycyclic aromatic compound such as vinyl carbazole or polystilanthracene, or a heterocyclic low molecular compound such as pyrazoline, imidazole or oxazole can be used.

The charging means 2 may be a contact type charging means using a contact charging member other than the charging roller, or a non-contact type charging means using a corona charger.

The laser scanner 3 is a combination of a semiconductor laser and a lens or a rotating mirror, and is turned ON / OFF in response to a time-series electric digital pixel signal of target image information.
This is a binary recording type exposure unit that outputs an OFF-modulated laser beam to scan and expose the surface of the rotating photosensitive drum.
As the exposure means, a binary recording method such as a line type in which an LED is combined with an optical shutter, or an exposure means such as a PWM method in which each pixel is time-resolved to form a halftone can be used.

(2) Developing Device 4 In the developing device 4, magnetic or non-magnetic particles as toner are charged by frictional charging or the like, and are applied onto the developing sleeves 4a and 4b by magnetic or mechanical force. A method is employed in which the toner particles are arrested and placed in non-contact with the photosensitive drum 1 so that toner particles fly by an electric field to form a toner image following the potential distribution or the electric field distribution on the photosensitive drum 1.

In this embodiment, as described above, the electrostatic charge image on the photosensitive drum 1 is developed twice using the first and second developing sleeves 4a and 4b. FIG. 3 is an enlarged model diagram of the first and second developing sleeves 4a and 4b.

The distance SD between the first developing unit a on the upstream side in the photosensitive drum rotation direction and the second developing unit b on the downstream side
FIG. 4 shows the evaluation results of the output image when the SD distance S-Db is changed. E, EP, P, O are shown in FIG.
As shown in the image diagram below, E: an image with excessively emphasized edges, EP: an image with insufficient edges and a sweet center, P: an image with weak edges, and O: a good image I have.

As can be seen from the table of FIG.
When the development is performed with the SD distance S-Db of the developing unit b of 500 μm or less, the first developing unit a on the upstream side
Irrespective of the SD distance S-Da, a good output image is not obtained.

This is because the toner image formed by the first developing unit a on the upstream side is rearranged by the second developing unit b on the downstream side where the distance S-Db between SD is small, and finally, It is considered that an image with an enhanced edge is output.

When the distances S-D and S-Db between the first and second developing units a and b on the upstream and downstream sides are increased, an image having weak edges and lacking sharpness is output. You.

As a result, the first developing unit a on the upstream side
The distances S-Da and S-D between the S-D of the second developing unit b on the downstream side
When Db was arranged so as to satisfy the relationship of S-Da <200 μm 600 μm <S-Db, a good image could be output.

As described above, the above condition is satisfied.
A developer carrying member (developing portion) having a small distance between SD and SD;
By developing the electrostatic charge image in combination with a developer carrier (developing unit) having a large distance between D, a good image with sharp edges and no image defects such as white spots and sweeping is output. It became possible to do.

Here, the SD of the upstream first developing unit a is described.
When the distance S-Da is about 50 μm, the edge is more emphasized, and when the distance S-Da is about 200 μm, the edge is somewhat weakened. If the distance between SD at this time is set to about 200 μm, the distance becomes somewhat weak. At this time, the SD distance is arbitrary in an area of 200 μm or less, and it is natural that an adjustment is made depending on whether the character of the output image is mainly text or graphic. Second developing section b on the downstream side
The same applies to the SD distance S-Db.

<Embodiment 2> (FIGS. 5 and 6) FIG. 5 shows the first and second developing sleeves 4a in this embodiment.
-It is an enlarged model figure of 4b part.

In this embodiment, the first and second developing sleeves 4a and 4a of the developing device 4 in the image forming apparatus of the first embodiment are used.
The output image was evaluated by variously changing the diameters φa and φb of b. Other device configurations are the same as those of the first embodiment.

That is, the first and second developing sleeves 4a and 4a
The image when the diameters φa and φb of b were selected from 15 mm, 20 mm, and 25 mm and output in combination was evaluated. FIG. 6 shows the result.

As can be seen from the table of FIG. 6, the diameters φa and φb of the first and second developing sleeves 4a and 4b are φa and φb.
When the relationship of ≧ φb is satisfied, the effect of preventing white spots and sweeping of the second developing sleeve 4b on the downstream side is increased, and a good image is obtained.

On the other hand, when the diameters are reversed between the first and second developing sleeves 4a and 4b, the effect is hardly exhibited but a slight deterioration in image quality is observed.

As described above, by making the diameter φb of the second developing sleeve 4b on the downstream side smaller than the diameter φa of the first developing sleeve 4a on the upstream side, the effect of suppressing white spots and sweeping in the developing section b can be obtained. As a result, it is possible to output an image with sharp edges and no white spots.

<Embodiment 3> (FIG. 7) FIG. 7 shows the first and second developing sleeves 4a in this embodiment.
-It is an enlarged model figure of 4b part.

This embodiment is different from the image forming apparatus of the first or second embodiment in that the second developing sleeve 4 on the downstream side of the developing process is used.
b is rotated in the opposite direction with respect to the photosensitive drum 1. Thus, the blades 4c and 4d and the rollers for regulating the developer can be arranged at the positions facing the first and second two developing sleeves 4a and 4b, respectively. Further, by rotating the developing sleeve 4b in the opposite direction with respect to the photosensitive drum 1, the effect of suppressing sweeping is increased, and a good image can be output.

[0051]

As described above, according to the present invention,
By developing using two or more developer carriers with different functions, it achieves both contradictory characteristics of edge emphasis and reduction of sweeping and white spots, and stably outputs good images It is possible to do.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a correlation between an SD distance and a developed image.

FIG. 2 is a schematic diagram of an image forming apparatus according to the first exemplary embodiment.

FIG. 3 is an enlarged model view of first and second developing sleeve portions.

Fig. 4 Evaluation result of output image

FIG. 5 illustrates first and second image forming apparatuses according to the second embodiment.
Enlarged model drawing of the developing sleeve part of

FIG. 6 is an evaluation result of an output image

FIG. 7 illustrates first and second image forming apparatuses according to a third embodiment.
Enlarged model drawing of the developing sleeve part of

[Explanation of symbols]

 Reference Signs List 1 photosensitive drum (image carrier) 2 charging roller 3 laser scanner 4 developing device 4a first developing sleeve (developer carrier) 4b second developing sleeve 5 transfer roller 6 cleaning device 7 fixing device

Claims (6)

[Claims] An at least first and second developer forming a developing unit that forms a toner image by attaching toner to an electrostatic charge image on the image carrier and facing the image carrier, respectively. A development in which a single-component development method is performed twice or more on the same electrostatic charge image on the image carrier by the at least first and second two developer carriers. S-Da, where the distance between the first developer carrier and the image carrier is S-Da and the distance between the second developer carrier and the image carrier is S-Db. A developing device that satisfies the following condition: Da <200 μm 600 μm <S−Db. 2. The image forming apparatus according to claim 1, wherein the first developer carrier having a small distance from the image carrier performs an electrostatic charge image developing process on the image carrier. Developing device. 3. The developing device according to claim 1, wherein φa ≧ φb when the diameters of the first and second developer carriers are φa and φb, respectively. 4. The image bearing member is a photoconductive photoreceptor, and a charging unit for uniformly charging the image bearing unit and an exposure unit for exposing the charged surface of the image bearing unit to form an electrostatic charge image. The developing device according to claim 1, wherein the developing device is formed. 5. An image forming apparatus comprising: an electrostatic charge image forming means for forming an electrostatic charge image on an image carrier; and a developing means for attaching a toner to the electrostatic charge image to form a toner image. An image forming apparatus, wherein the developing unit is the developing device according to any one of claims 1 to 4. 6. An image bearing member is a photoconductive photoreceptor, and an electrostatic charge image is formed by a charging device for uniformly charging the image bearing member and an exposure device for exposing the charged surface of the image bearing member. The image forming apparatus according to claim 5, wherein the image forming apparatus is formed.