JPS6321678A - Developing device - Google Patents

Abstract

PURPOSE:To easily fetch toner and to maintain the density of an image regardless of whether the image is a solid black image or color copy by arranging developer straightening members separately on the center line of the angle of the center of a developer carrier to the centers of two magnetic field production parts. CONSTITUTION:The developer 4 circulated by screws 5, 6, and 7 which rotate as shown by arrows consists of magnetic particles and nonmagnetic particles. The developer 4 carried to a developing sleeve 8 is conveyed to a development part having a gap of 300mum between the sleeve 8 and a photosensitive drum 1. Nonmagnetic toner is scattered over an electrostatic latent image formed on the drum 1 from on the sleeve 8 by an alternating electric field to develop the image. The developer 4 is passed between the sleeve 8 and the nonmagnetic developer straightening member 15 arranged at the intermediate point of the peak value of magnetic flux concentration between conveyance poles N2 and S2. When its is passed, a fresh developer is compressed mechanically to be pressed against the sleeve 8, and toner is fetched effectively into magnetic particles whose toner is consumed.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a developing device used in electrostatic recording devices such as black-and-white and color electrophotographic copying machines. The present invention relates to a developing device for forming a brush of a small amount of magnetic particles and subjecting it to development.

(Prior Art) FIG. 3 shows a cross section of a conventional developing device, in which the developing device 2 is arranged around a photosensitive drum 1 that rotates in the direction of the arrow. The inside of this developing device z is divided into two chambers by a partition plate 3, and a screw 5 is installed in one of the chambers.
In the other room, screw 6.7 is placed perpendicular to the page.
Moreover, it is arranged so as to be freely rotatable. 1 in Figure 3 of partition plate 3
Gaps (not shown) through which the developer 4 passes are formed at the back and front sides of the paper, and the screw 5 rotates in the direction of the arrow in the figure to move the developer 4 from one position to the rear in the figure. The screws 6 and 7 conversely transport the developer 4 from the back to the front, so that the developer 4 is circulated between the two chambers.

A developing sleeve 8 is rotatably disposed in the developing device 2 at a position facing the photosensitive drum 1, and the developing sleeve 8 has four poles (N1).

N2, S+, N2) fixed permanent magnets are provided.

The developing sleeve 8 forms a developer brush in contact with the photosensitive drum 1 by the action of a permanent magnet, and develops the electrostatic latent image formed on the photosensitive drum 1 by rotating in the direction of the arrow in the figure. In this case, a non-magnetic doctor blade 9 disposed close to the developing sleeve 8 controls the amount of developer 4 forming the brush.

Further, the developing device 2 is provided with a toner hopper 10 and a toner replenishment port 11. Replenishment toner 12 is stored in the toner hopper 10, and an amount of toner commensurate with the consumed toner is supplied from the replenishment port 11. It is replenished and falls onto the screw 5. Here, the developer 4 in the developing sleeve 8 circulates as shown by arrows 13 in the figure. The magnetic brush (magnetic particles) on the developing sleeve 8, which has consumed toner during development, takes in the toner in the magnetic particle layer by the circulation of the developer 4 as shown by the arrow 13 and contributes to the next development.

(Problems to be Solved by the Invention) However, such prior art has the following problems. That is, the magnetic particles that have consumed toner are transported by the magnetic pole Sl of polarity S in the developing sleeve 8, and begin to stand up from the upstream side of the magnetic pole N2 of polarity N, and the density of the polar particles gradually becomes coarser and the magnetic flux density decreases. Magnetic pole N showing peak value
At position 2, the coarse ratio is maximum. However, since the magnetic pole N2 where the density of the magnetic particles is the coarsest is located away from the position of the screw 6, there is a problem that the amount of new toner incorporated into the magnetic particles by the conveying action of the screw 6 is insufficient. there were.

Therefore, if you develop more than 10 solid black images in a row,
Even though the toner density within the developing device 2 is constant, the image density gradually decreases. In particular, systems that require a relatively large number of peta images, such as full-color copying machines, use several types of toner, so if a single color developing device does not take in enough toner, a subtle difference in color reproduction may occur. There are problems in that the overall image density decreases as the number of constants increases.

To solve the above problem, 1. Using a so-called scraper, the developer layer that contributed to the development is mechanically and forcibly stripped off from the developing sleeve, mixed with new developer, and then supplied to the developing sleeve again. Then do the next development.

2. A repulsion magnetic field is provided in the magnetic configuration on the side of the developer container in the developer sleeve to magnetically peel off the developer layer, and this is re-stirred with new developer and supplied to the developer sleeve again for the next development.

3. Increase the number of rotations of the screw to improve the fluidity of the developer and increase the chances of toner being taken in near the developing sleeve.

Such techniques are well known.

However, in the technique described in item 1 above, the scraper is in contact with the developing sleeve, so if the developing sleeve is surface-treated, the amount of charge may change slightly due to changes in the surface condition. Toner often fuses onto the developing sleeve due to the friction between the developing sleeve and the scraper, and once this fusion occurs, it remains in that state semi-permanently, and the developing system coats a thin layer of developer. In this case, this fused toner is blocked by the doctor blade, resulting in coating defects and causing white spots on the image. Further, it requires some effort to return the scraped developer to the developing sleeve again, resulting in a complicated structure and an increased size of the device.

This also applies to the technique described in item 2 above.

Further, in the technique described in item 3 above, toner uptake is promoted and almost satisfactory results are obtained, but since the screw is rotated at high speed, the life of the developer itself is shortened, and the supplied toner is insufficient. If the toner is supplied to the developing sleeve without being stirred, there is a problem that toner scattering and image fogging occur in the developing section.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a developing device that has a simple configuration and can easily take in toner without increasing the rotational speed of the stirring means. There is something to do.

(Means for Solving the Problems) In order to achieve the above object, the present invention has a rotatable magnetic field generator which has a plurality of fixed magnetic field generating parts inside and which holds developer like a brush on its surface. In a developing device that makes a developer carrier face an image carrier holding an electrostatic latent image in a developing section and visualizes the electrostatic latent image on the image carrier, an adjacent part of the developer carrier A developer rectifying member is provided over the entire axial direction of the developer carrier near the center line of the angle formed by the centers of the two matching magnetic field generating portions with respect to the center of the developer carrier.

The developer rectifying member and the developer carrier are arranged apart from each other.

(Function) When the magnetic particles that have consumed toner are transported between the two transport magnets in the developer carrier, the density of the developer becomes maximum at that position on the developer carrier. With,
Since a large amount of developer holding fresh toner with a sufficient amount of charge coexists near the magnetic particles on the developer carrier, the developer rectifying plate is placed opposite the developer carrier under the above conditions. When the developer is set to do so, when the developer passes between the current plate and the developer carrier, it is subjected to a mechanical compression force that presses fresh developer toward the developer carrier, and the toner is transferred to the spent magnetic particles. The import is carried out effectively.

(Example) Embodiments of the present invention will be described below based on the accompanying drawings.

FIG. 1 is a cutaway side view of a developing device according to the present invention, in which the same elements as shown in FIG. 3 are designated by the same reference numerals.

Thus, the screw 5.6.7 rotates in the direction of the arrow shown in the figure.
The developer 4 that is circulated in the system includes magnetic particles having an average particle size of 50 g, which are made by coating a ferrite-based magnetic material with a non-magnetic material such as a styrene-skewered acrylic copolymer, and 10 parts of carbon and 90 parts of polystyrene as a non-magnetic toner. The mixture ratio is 15% (weight) in terms of toner concentration, and the magnetic particles are positively charged and the non-magnetic toner is negatively charged. . In addition, the electric resistance value of the brush in the developing section is 1Q.
It is about 12Ωφcm.

When the developing sleeve 8 as a developer carrier (including the belt) and the screw 5.degree. 6.7 are driven by the developer 4, they rotate in the directions of arrows in the figure. The amount of developer 4 supported on the developing sleeve 8 is regulated by a doctor blade 9 provided at a distance of 250 gm from the developing sleeve 8, and the amount of the developer 4 carried by the developing sleeve 8 is 300 gm between the developing sleeve 8 and the photosensitive drum l. It is transported to a developing section with a gap. At this time, the developing sleeve 8 receives a DC component of -500V and a DC component of 1.5V as a developing bias.
KVpp, 1.5 KHz (1') While applying a superimposed AC component, the photosensitive drum 1 was heated at 200 ra.
ts/sec speed 200~210
It rotates at am/sec in the direction of the arrow shown in the figure, and develops the image area of the electrostatic latent image formed on the photosensitive drum 1 by flying non-magnetic toner from above the developing sleeve 8 and above the magnetic particles using an alternating electric field.

After development, the magnetic particles and undeveloped non-magnetic toner on the developing sleeve 8 are collected into the developing device z by rotation of the developing sleeve 8.

Here, the developer 4 transported by the transport poles S1 and N2 as magnetic field generating parts in the non-magnetic sleeve 8 is transferred to the transport poles N2 and S.
2 (in other words, N
The shortest pressure fi14 was set to 4■ at the position between poles 2 and 52). It passes between the sleeve 8 and a non-magnetic developer rectifying member 15 that extends over the entire axial direction of the sleeve 8 .

To explain one embodiment in detail under the above conditions, when the magnetic particles that have consumed the non-magnetic toner pass through the N2 pole and are transported to the position between the N2 pole and the 82 pole, the sleeve 8 At the upper position, the density of the developer 4 is maximum because it is between the poles, and the developer 4 retains fresh non-magnetic toner with a sufficient amount of charge near the magnetic particles on the sleeve 8.
coexist in large quantities. At this time, if the developer baffle plate 15 is set so as to face the sleeve 8, when the developer 4 passes through this point, it receives a mechanical compression action that presses fresh developer 4 against the sleeve 8 side, thereby consuming toner. The toner is effectively incorporated into the magnetic particles. In addition to this, it is thought that a phenomenon occurs in which the compressed developer 4 breaks down the magnetic particle layer on the surface of the sleeve 8, which has consumed toner, and is replaced with fresh developer 4.

Due to the action explained above, the toner is effectively taken into the magnetic particles that have consumed the toner and the magnetic particles are replaced, and the developer 4, which has reached the normal toner concentration, is transferred to S2.
It is transported to the electrode and subjected to the next development. The effects here are as follows, listing the governing elements and numerical values.

1. Relative position of N2 pole and S2 pole of developer rectifying member 15: N2. It is preferable that the position be located between the S2 poles, but as an allowable range that does not impair the present invention, the position may be within the half width of the peak value of each magnetic flux density, but in this case, the distance from the sleeve 8 should be It is preferable to shrink it.

2. Distance between developer rectifying member 15 and sleeve 8 2. N2.
When placing it in the middle of the S2 pole, use letters, small figures,
For photography, approximately 5cm is sufficient, but considering continuous copying of solid images, it is preferable to use within 4+wm.N2
, 52 poles near the half-width of the peak value of the magnetic flux density, it is preferably within 3■, and it is expected that the closer the position is, the more effective the effect can be expected, but 1■
If it is less than that, the impulsivity of the developer in the gap will deteriorate and the compressed developer will coagulate.

Another embodiment will be explained with reference to FIG. This is a modified example in which the non-magnetic developer rectifying member 16 is made of a round piece (3φ) instead of the square piece (2×6 am) shown in FIG. At this time, the distance f$17 to the sleeve 8 is set to 4■, which is N2.

It is located between the S2 poles.

When I experimented with this example, I expected that the effect of the present invention would depend on the absolute area of the rectifying member facing the sleeve 8, and I thought that round material would have a weaker effect, but contrary to my expectations, The same effect as square timber was obtained.

Although the present invention is particularly effective in a system in which a developer layer is coated in a thin layer, it is also sufficiently effective in forward development in a conventional two-component contact development system.

(Effects of the Invention) As is clear from the above description, according to the present invention, toner can be easily taken in with a simple configuration, and the image density can be improved even during continuous copying of solid black images and in full-color copying machines. can be maintained, and in the latter case in particular, subtle deviations in color reproduction can be eliminated. In addition, since toner can be taken in without increasing the rotational speed of stirring means such as a screw, the life of the developer is extended, and the supplied toner is not sufficiently stirred and contributes to development, causing capri. It can also solve the traditional problems of

[Brief explanation of the drawing]

FIG. 1 is a cutaway side view of a developing device according to the present invention, FIG. 2 is a cutaway side view of a developing device according to a modified embodiment of the present invention, and FIG.
The figure is a cutaway side view of a conventional developing device. Explanation of symbols 1...Photosensitive drum 2...Developing device 4...
Developer 5.6.7...Screw 8...Developing sleeve 9...Doctor blade 10...Toner hopper 11...Replenishment port 12...
・Replenishment toner 14.17...Distance 15...Developer rectifying member Fig. 1 2It (&'Ai et =e2 Fig. 2

Claims (2)

[Claims] (1) An image carrier that retains an electrostatic latent image in a developing section, including a rotatable developer carrier that has a plurality of fixed magnetic field generating sections inside and holds developer like a brush on its surface. In a developing device that visualizes an electrostatic latent image on an image carrier, the center line of the angle formed by the centers of two adjacent magnetic field generating parts in the developer carrier with respect to the center of the developer carrier. A developing device characterized in that a developer rectifying member is provided in the vicinity over the entire axial direction of the developer carrier, and the developer rectifying member and the developer carrier are spaced apart from each other. (2) The developing device according to claim 1, wherein the closest distance between the rectifying member and the carrier is 5 mm or less.