JPH1184882A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device never generating a scavenging phenomenon by improving developability and preventing a phenomenon such as a void. SOLUTION: The image forming device is constituted so that all developer after passing through a developing region P, by a developing sleeve 42 on the downstream side in the rotational direction of a photoreceptive drum 39 is carried onto a developing sleeve 43 on the downstream side and in a developing region P2 on the downstream side, a fixed developing bias is applied to the developing sleeve 43, to transfer nonmagnetic toner 5 in the developer 4 onto the photoreceptive drum 39 and attain development. Further, the density of a magnetic flux at a developing pole S1 which is arranged in the developing sleeve 43 and in the vicinity of the developing region P2 is made lower than that at a developing pole N1 which is arranged in the developing sleeve 42 and in the vicinity of the developing region P1 , to make the nap length of an electromagnetic brush in the developing region P2 shorter than that in the developing region P1 .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using electrophotography, such as a copying machine, an image recording apparatus, a printer, a facsimile, etc., and more particularly, to the same electrostatic latent image which is visible in two development steps. The present invention relates to an image forming apparatus for forming an image.

[0002]

2. Description of the Related Art Conventionally, a two-component developer comprising a magnetic carrier and a non-magnetic toner has been magnetically carried on a developing sleeve as a developer carrying member having a magnet fixedly disposed therein. Is a so-called two-component magnetic brush that visualizes the electrostatic latent image on the photosensitive drum by rotating the developing roller and passing the developing area between the photosensitive drum as the electrostatic latent image carrier and the developing sleeve. Developing devices are known. Further, as one of such developing devices, there are two developing sleeves on the upstream side and the downstream side in the rotation direction of the photosensitive drum, a first developing step using the upstream developing sleeve, and a developing step on the downstream side. A second developing step using a sleeve visualizes the same electrostatic latent image on the photosensitive drum, thereby improving developability and preventing white spots at the rear end of the image. An image forming apparatus using a multi-stage developing method has been proposed.

[0003]

However, in the above-mentioned conventional developing method, among the plurality of magnets provided inside the developing sleeve on the downstream side, the magnet located closest to the photosensitive drum, that is, the so-called magnet. Since the magnetic flux density of the developing pole is equivalent to the magnetic flux density of the developing pole of the developing sleeve on the upstream side, the so-called magnetic brush formed by the developer is the same as the magnetic brush on the upstream side, The toner image developed in the first developing step with the developing sleeve of
During the second developing step on the downstream developing sleeve, the magnetic brush is again rubbed with the same pressure by the magnetic brush, and as a result, a so-called scavenging phenomenon that disturbs the image may occur.

In the conventional developing method, the half width of the developing pole of the downstream developing sleeve is equal to the half width of the developing pole on the upstream side. The density of the magnetic brush becomes the same as the density of the magnetic brush ears on the upstream developing sleeve, so that the toner image may be rubbed again by the same pressure, and the above-described scavenging phenomenon may be more likely to occur. was there. SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus capable of preventing the above-described scavenging phenomenon from occurring by improving the developing property and preventing a decrease in white spots or the like.

[0005]

According to a first aspect of the present invention, an object of the present invention is to provide an electrostatic latent image carrier having a surface movably provided endlessly, and the electrostatic latent image carrier. And a developing device having two developer carriers disposed along the surface moving direction of the electrostatic latent image carrier, wherein each of the developer carriers has a plurality of magnets therein. The developing device is arranged such that the developer in the developing region on the developer carrier on the downstream side in the surface moving direction is all conveyed from the developer carrier on the upstream side in the surface moving direction. A developing device that performs two-component magnetic brush development using a magnetic carrier and a non-magnetic toner by two developer carriers, and exposes the electrostatic latent image carrier uniformly charged by a charging device to an image exposure device. To form an electrostatic latent image, and the electrostatic latent image is In the image forming apparatus for forming a toner image on the electrostatic latent image carrier by forming a visible image by a developing process using the developer carrier, a plurality of magnets of the developer carrier on the downstream side in the surface moving direction are used. The magnetic flux density of the magnet located closest to the electrostatic latent image carrier is increased by the magnets located closest to the electrostatic latent image carrier among the plurality of magnets of the developer carrier upstream in the surface movement direction. Is achieved by making the magnetic flux density smaller than the magnetic flux density.

According to a second aspect of the present invention, the above object is attained by providing a plurality of magnets of a developer carrying member on the downstream side in the surface moving direction of the electrostatic latent image carrier of the first invention. The half-value width of the magnet located closest to the electrostatic latent image carrier is set to a value selected from among a plurality of magnets of the developer carrier on the upstream side in the surface movement direction.
This is achieved by making the half width of the magnet closest to the electrostatic latent image carrier smaller than the half width.

That is, in the first invention according to the present application, the magnetic flux density of the magnet located closest to the electrostatic latent image carrier downstream of the electrostatic latent image carrier in the surface moving direction is determined by the surface moving direction. By making the magnetic flux density smaller than the magnetic flux density of the magnet positioned closest to the electrostatic latent image carrier on the upstream side, the development-related portion of the developer carrier on the downstream side in the surface movement direction of the electrostatic latent image carrier is reduced. The magnetic brush is shorter than the magnetic brush of a portion related to development on the developer carrier on the upstream side in the surface movement direction,
Since the sliding force can be reduced as compared with the case where the downstream and upstream magnetic brushes have the same length, the toner image developed in the first developing step is disturbed further in the second developing step. Therefore, the so-called scavenging phenomenon is less likely to occur.

In the second invention according to the present application, the half width of the magnet located closest to the electrostatic latent image carrier downstream in the surface moving direction is changed to the electrostatic latent image upstream in the surface moving direction. By making the half width of the magnet positioned closest to the carrier smaller than the half width of the magnet, the density of the magnetic brush ears of the portion related to the development on the developer carrier on the downstream side in the surface movement direction is increased on the upstream side in the surface movement direction. The density of the spikes of the magnetic brush at the portion related to the development on the developer carrier becomes larger, the sliding force per spike is weakened, and the scavenging phenomenon can be more effectively prevented.

[0009]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS. 1, 2 and 3. FIG.
FIG. 1 is a sectional view showing a schematic configuration of an example of an image forming apparatus using the developing device of the present invention. As shown in FIG. 1, the image forming apparatus according to the present embodiment is an electrophotographic copying apparatus of a fixed platen type, a movable optical system type, a rotary drum type, and a transfer type.

In the apparatus according to the present embodiment, the original 19 is placed on the original platen glass 20 which is fixedly set, the required copy conditions are set, and the copy start key is pressed. The photosensitive drum 39 as an electrostatic latent image carrier is rotationally driven at a predetermined peripheral speed in a clockwise direction indicated by an arrow, and the following image forming operation is performed.

First, the light source 21, together with the reflection shade 22 and the first mirror 23, moves at a predetermined speed V from the home position on the left side of the glass to the right side of the glass along the lower surface of the platen glass 20, and the second mirror By moving the mirror 24 and the third mirror 25 in the same direction at a speed of V / 2, the downward image surface of the document 19 placed on the document table glass 20 is illuminated and scanned from the left side to the right side.

The original surface reflected light of the illumination scanning light is imagewise exposed on the surface of the photosensitive drum 39 via the image forming lens 29, the fixed fourth mirror 26, the fixed fifth mirror 27 and the fixed sixth mirror 28 (FIG. Slit exposure).

Therefore, the surface of the photosensitive drum 39 which has been uniformly charged to a predetermined positive or negative potential by the primary charger 30 before the exposure by these image exposure means is exposed to the above-mentioned exposure to the charged surface. Then, an electrostatic latent image having a pattern corresponding to the original image is sequentially formed, and this electrostatic latent image is visualized as a toner image by the developing sleeves 42 and 43 of the developing device 40 as the photosensitive drum 39 rotates in the arrow direction. It is imaged.

On the other hand, a recording material sheet P is fed from a paper feeding means (not shown), and the recording material sheet P passes through a guide 33 between a photosensitive drum 39 and a transfer charger 34 at a predetermined timing. To the transfer section. Then, the recording material sheet P receives the transfer corona at the transfer portion, comes into contact with the photosensitive drum 39, and the toner visible image on the photosensitive drum 39 surface side is sequentially transferred to the recording material sheet P surface.

Next, the recording material sheet P that has passed through the transfer section is sequentially separated from the surface of the photosensitive drum 39 by, for example, a separation belt (not shown) disposed at the end of the drum. Transfer guide 3
8. The toner image is introduced into the fixing device 31 via the guide 18 and is fixed to the toner image, and is discharged out of the apparatus as an image formed product.

The surface of the photosensitive drum 39 after the transfer is
Dirt such as remaining toner is cleaned and removed by the cleaning blade 37 of the cleaning device 36, and is repeatedly provided for image formation.

The moving optical members (the light source 21, the reflection shade 22, the first mirror 23, the second
The mirror 24 and the third mirror 25) are set so as to move in the return path when reaching a predetermined forward end point, return to the initial home position, and wait until the start of the next copy cycle.

Next, the developing device 40 of the present embodiment will be described with reference to FIG. The developing device 40 includes developing sleeves 42 and 43 as developer carrying members and developer circulation and stirring spaces 47 and 48 on the upstream and downstream sides in the rotation direction of the photosensitive drum 39, respectively. The developing sleeves 42 and 43 rotate in the direction of the arrow at a peripheral speed difference of 1.7 times the photosensitive drum 39.

In the first developing step, the upstream developer 4 sufficiently stirred by the stirring screw 44 is carried on the developing sleeve 42 in which a fixed magnet (not shown) is disposed, and the doctor blade is used. After being adjusted to an appropriate coating amount by 46, a developing bias in which an AC bias is superimposed on a DC bias is applied to the developing sleeve 43 in a developing area P ₁ near a position facing the photosensitive drum 39.
The non-magnetic toner in the developer 4 is transferred onto the photosensitive drum 39 carrying an electrostatic latent image (not shown), and development is performed.

Next, in the second developing step, the developer 4 having passed through the developing area P ₁ is all conveyed onto the developing sleeve 43 on the downstream side, and the developing bias is applied to the developing area P ₂ on the downstream side. Is applied to the developing sleeve 43, the non-magnetic toner 5 in the developer 4 is transferred onto the photosensitive drum 39,
Perform development.

In the present embodiment, the upstream developing sleeve 4
2 internal (inner circumference near) to which five fixed magnets are arranged spaced an appropriate interval, the flux density of the developing pole N ₁ in the developing region P ₁ near of which 1000 G, half width 30 °. Further, the inside of the developing sleeve 43 on the downstream side (near the inner circumference) are arranged to open the appropriate intervals are three stationary magnets, the magnetic flux of the developing pole S ₁ in the vicinity developing region P ₂ of them The density is 800 G and the half width is 30 °. Note that the half-value width in the present embodiment is set so that the magnetic field strength is の of the maximum value in the magnetic flux distribution shape (represented by the relationship between the circumferential position and the magnetic field strength) formed by the fixed magnet. At a certain position in the circumferential direction. Further, the number of magnets provided in the developing sleeve, the magnetic flux density of the developing pole in the vicinity of the developing area, and the half-value width are not limited to the above settings, and may deviate from the gist of the present invention. If it is not in the range, it can be changed as appropriate.

The shape of the magnetic brush formed in the developing region P ₁ to FIG. 3 (a), shows the shape of the magnetic brush formed in the developing region P ₂ to the respective schematically in FIG. 3 (b). As can be seen, the length of the bristles of the magnetic brush formed in the developing region P ₂ is shorter than the length of the bristles of the magnetic brush formed in the developing region P _1. This is a developing apparatus of the present embodiment, because the magnetic flux density of the developing pole S ₁ of the developing region P ₂ near the downstream side is smaller than the magnetic flux density of the developing pole N ₁ of the developing region P ₁ near the upstream side is there.

When development is performed by the above-described developing device, the development area P
₁ (first developing step) toner image developed, since it is the peripheral speed difference between the photosensitive drum 39 and the developing sleeve 42, but undergoes a certain degree of rubbing by the magnetic brush at the developing region P _1, 1 ° The scrubbing phenomenon does not occur by the rubbing, and the process proceeds to the second developing step with a normal toner image.

Here, if the magnetic flux densities of the magnets located in the vicinity of the upstream and downstream developing regions are equal, in the second developing step (downstream in the surface moving direction), the developing region P
_The toner image is rubbed with a magnetic brush having the same shape as that of _{No. 1,} and the toner image is disturbed and a scavenging phenomenon occurs, so that a normal toner image cannot be obtained. However, as shown in this embodiment, the downstream development area P ₂
The magnetic flux density of the developing pole near the developing sleeve 42 is
Is made smaller than the magnetic flux density in the developing region P ₁ near the developing pole, the length of the bristles of the magnetic brush in the developing region P _2, when shorter than the length of the ears in the developing regions P _1, the second In the developing step, the rubbing force on the toner image by the magnetic brush is weakened, and a normal toner image can be maintained without causing a scavenging phenomenon.

(Second Embodiment) A second embodiment of the present invention will be described with reference to FIG. In the present embodiment, the magnetic flux density at the developing pole near the developing area on the upstream side in the surface movement direction,
Without changing the values of the half-width and the magnetic flux density at the downstream development pole, the half-width of the development pole near the downstream development area is set to 20 °.
It is smaller.

FIG. 4 schematically shows the shape of the magnetic brush formed near the downstream development area P ₂ ′. Since the developing poles near the downstream developing region P ₂ ′ of the present embodiment have the same magnetic flux density as the developing poles near the downstream developing region of the first embodiment, each of the ears of the downstream magnetic brush is different. Is almost the same as that of the first embodiment, but the developing pole near the downstream developing region P ₂ ′ has a small half-width, so that it is formed in the downstream developing region of the first embodiment. The density of each ear is larger than that of the magnetic brush, and the interval between the ears is narrower.

As a result, the number of spikes that come into contact with the toner image in the second development step increases, and the sliding force per spike becomes weaker than in the first embodiment in which the spike interval is wide. In addition, the scavenging phenomenon can be more effectively prevented.

[0029]

As described above, according to the first aspect of the present invention, a plurality of magnets provided inside a developer carrier on the downstream side in the surface moving direction of the electrostatic latent image carrier are used. Of these, the magnetic flux density of the magnet located closest to the electrostatic latent image carrier is determined by the static density of the plurality of magnets arranged inside the developer carrier on the upstream side in the surface movement direction of the electrostatic latent image carrier. By making the magnetic flux density smaller than the magnetic flux density of the magnet located closest to the electrostatic latent image carrier, the magnetic brush on the downstream side in the surface movement direction of the electrostatic latent image carrier is shortened, and the magnetic flux for the toner image on the upstream side is reduced. Since the sliding force of the brush can be reduced, a normal toner image can be obtained while suppressing the occurrence of the scavenging phenomenon.

According to the second aspect of the present invention, there is provided a magnet among a plurality of magnets disposed inside the developer carrier on the downstream side in the surface moving direction of the electrostatic latent image carrier of the first aspect. The half-width of the magnet located closest to the electrostatic latent image carrier is set to the electrostatic capacity of the plurality of magnets disposed inside the developer carrier on the upstream side in the surface movement direction of the electrostatic latent image carrier. By making the half width of the magnet closest to the latent image carrier smaller than the half width of the magnet, the density of the magnetic brush ears on the downstream side in the surface movement direction of the electrostatic latent image carrier is increased, and the ears contacting the toner image are formed. The scrubbing phenomena can be more effectively prevented because the rubbing force per spike is weakened by increasing the number of spikes.

[Brief description of the drawings]

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

FIG. 2 is a schematic view of a developing device of the present invention.

Figure 3 is a schematic view showing the shape of the electromagnetic brush formed in the developing region P ₁ of the first embodiment of the present invention and (a), a schematic view showing the shape of the electromagnetic brush formed in the developing region P ₂ (B).

FIG. 4 is a schematic diagram illustrating a shape of an electromagnetic brush formed in a developing area P ₂ ′ according to a _second embodiment of the present invention.

[Explanation of symbols]

Reference Signs List 4 developer 5 non-magnetic toner 21 light source (image exposure unit) 22 reflector (image exposure unit) 23 first mirror (image exposure unit) 24 second mirror (image exposure unit) 25 third mirror (image exposure unit) 26 Fixed fourth mirror (image exposure unit) 27 Fixed fifth mirror (image exposure unit) 28 Fixed sixth mirror (image exposure unit) 29 Imaging lens (image exposure unit) 39 Photosensitive drum (electrostatic latent image carrier) 40 Developing device 42 Upstream developing sleeve (developer carrier on the upstream side in the surface moving direction of the electrostatic latent image carrier) 43 Downstream developing sleeve (downstream developer carrier on the surface moving direction of the electrostatic latent image carrier) 50 stirring roller (stirring member) P ₁ (development area of the electrostatic latent image bearing member surface movement direction upstream side of the developer carrying member) developing area of the upstream developing sleeve P ₂ downstream developing region of the developing sleeve (electrostatic Submarine P ₂ ′ Developing area of downstream developing sleeve (developing area of developer carrier downstream of surface moving direction of electrostatic latent image carrier)

Claims (2)

[Claims] 1. An electrostatic latent image carrier having a surface disposed endlessly movably, and disposed near the electrostatic latent image carrier along a surface moving direction of the electrostatic latent image carrier. And a developing device having two developer carriers, wherein each of the developer carriers has a plurality of magnets disposed therein, and the developing device has
All of the developer in the developing region on the developer carrier on the downstream side in the surface movement direction has been transported from the developer carrier on the upstream side in the surface movement direction, and the two developer carriers have a magnetic property. A developing device that performs two-component magnetic brush development using a carrier and a non-magnetic toner, and forms an electrostatic latent image by exposing the electrostatic latent image carrier uniformly charged by a charging unit to image by an image exposing unit. An image forming apparatus that visualizes the electrostatic latent image by a developing process using two developer carriers of the developing device to form a toner image on the electrostatic latent image carrier; The magnetic flux density of the magnet located closest to the electrostatic latent image carrier among the plurality of magnets of the developer carrier on the side of the developer carrier is higher than that of the magnets of the developer carrier on the upstream side in the surface movement direction. Magnetic flux of the magnet located closest to the latent image carrier An image forming apparatus comprising less than degrees. 2. A method according to claim 1, wherein, among a plurality of magnets of the developer carrier on the downstream side in the surface movement direction of the electrostatic latent image carrier, a half width of a magnet arranged closest to the electrostatic latent image carrier is determined by the surface movement. 2. The image forming apparatus according to claim 1, wherein, among the plurality of magnets of the developer carrier on the upstream side in the direction, the half width of the magnet located closest to the electrostatic latent image carrier is smaller than the half width.