JPH0469690A - Developing device - Google Patents

Abstract

PURPOSE:To eliminate toner scattering and to obtain an image of excellent picture quality by putting the magnet of an upper developing sleeve and the magnet of a lower developing sleeve in well-balanced intensity relation where a developer is not carried round and no abnormal image is formed. CONSTITUTION:A developer which is carried on the lower developing sleeve 8a first moves from the sleeve 8a to the upper developing sleeve 8 as shown by a broken-line arrow B1 and passes a doctor blade 14 as shown by a broken- line arrow B2 while carried on the sleeve 8, and an excessive developer is scraped off. The developer which is proper in amount after passing the blade 14 passes an upper development area D1 between the sleeve 8 and a photosensitive body 2 as shown by an arrow B3 and then moves to the sleeve 8a again, and the developer passes a lower development area D2 between the sleeve 8a and photosensitive body 2, leaves the sleeve 8a, and flows to the bottom part of a development container 3, so that the developer is agitated by a paddle wheel 9.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an upper developing sleeve and a lower developing sleeve that are arranged in a vertical positional relationship along the surface of a latent image carrier, and The upper developing sleeve and the lower developing sleeve are rotated in the same direction, and the two-component developer is supplied to the lower developing sleeve. is transferred from the lower developing sleeve to the upper developing sleeve by the magnetic force of each magnet and the rotation of each developing sleeve, passes through the developing area between the upper developing sleeve and the latent image carrier, and then is transferred to the lower developing sleeve again. The electrostatic latent formed on the latent image carrier is transferred to the side developing sleeve and passed through the developing area between the lower developing sleeve and the latent image carrier, and the electrostatic latent formed on the latent image carrier is The present invention relates to a developing device that visualizes an image.

(Prior Art) It has been known for some time that image forming apparatuses such as electronic copying machines, printers, and facsimile machines employ the above-mentioned type of developing device using a powdered two-component developer containing toner and carrier. be.

A developing device that uses only one developing sleeve is also well known, but in this device, the developing sleeve is moved so that a predetermined amount of developer is conveyed to the developing area and a visible image of a predetermined density is obtained. It is necessary to set the linear velocity to a value greater than, for example, three times or more than the linear velocity of the latent image carrier. However, when the linear velocity ratio is set in this manner, a missing portion of the image, called a solid cross white spot, occurs at the rear end or front end of the visible image formed on the latent image carrier.

On the other hand, when two developing sleeves are used, as in the developing device described at the beginning, even if the linear velocity of each developing sleeve relative to the latent image carrier is lowered, the developing operation can be performed in the upper and lower developing areas. Therefore, it becomes possible to obtain a visible image with a predetermined density, and accordingly, it becomes possible to suppress the occurrence of the phenomenon of solid white spots.

However, when two developing sleeves are used, a portion of the developer supplied to the lower developing sleeve does not transfer to the upper developing sleeve, but passes through the gap between both developing sleeves and is directly transferred to the lower developing sleeve. A so-called tangle phenomenon occurs in which the image is transported to the development area between the image carriers. This creates a difference in the amount of developer carried by the upper and lower developing sleeves, and this has a subtle effect on the quality of the visible image, making it impossible to obtain a visible image with the desired density, or There is a possibility that the load changes and the speed of the carrier becomes uneven, resulting in striped image density unevenness in the visible image.

Therefore, the developer supplied to the lower developing sleeve is transferred to the upper developing sleeve in a stable state 1,- while preventing the occurrence of the tangled phenomenon, and then transferred from the second developing sleeve to the lower developing sleeve again. The following developing device has been proposed as a developing device capable of forming a high quality visible image by smoothly refluxing the developer.

That is, two magnets arranged along the circumferential direction of the upper developing sleeve inside the upper developing sleeve near the closest area between the upper developing sleeve and the lower developing sleeve are attached to the inner circumferential surface of the developing sleeve. The magnetic poles facing toward are set to have different polarities, and the magnetic pole of one magnet provided inside the lower developing sleeve near the closest area, the magnetic pole facing toward the inner circumferential surface of the sleeve, Of the two magnets in the upper developing sleeve, the one closer to the latent image carrier is set to have a different polarity from the magnetic pole of the one facing the inner peripheral surface of the upper developing sleeve, and This is a developing device in which the magnetic field formed by the individual magnets forms a loop.

(Problems to be Solved by the Invention) Forming a loop-shaped magnetic field as in the above-mentioned prior art means forming a curtain-shaped magnetic field that shields the space between the upper and lower developing sleeves. It is possible to avoid the tangling phenomenon.

However, even in this case, it has been found that the mutual strength of the magnets between the developing sleeves is balanced to a certain extent, causing 1) and 1) rotation.

For example, if a portion of the developer is dragged onto the upper developing sleeve, the developer in the upper developing sleeve is no longer transferred to the lower developing sleeve, and sufficient developer is not conveyed to the lower developing sleeve.

As a result, the height of the magnetic brush ear becomes lower, and the gap between the developing container and the lower developing sleeve of the developing device becomes in communication, so to speak, the cracking function of the developer is reduced, and the structure of the developer is reduced. A problem arises in that the toner is scattered outside.

This is even more remarkable because the internal pressure of the casing is increased due to the rotation of the developer stirring roller, stirring blade, screw, etc., and the replenishment of new developer from the toner supply roller.

Therefore, there are two problems: the influence on the density of one image and the scattering of toner.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that can solve problems such as insufficient replenishment of new 1 hener due to developer slipping on a developing sleeve, abnormal images caused by insufficient density, and toner scattering.

(Means for Solving the Problems) In order to achieve this object, in the developing device of the present invention, of the two magnets disposed inside the two-side developing sleeve, the one closest to the latent image carrier is P2 is the magnetic force that contributes to the transfer of the developer on the surface of the upper developing sleeve by the magnet 1, and P2 is the magnetic force on the surface of the lower developing sleeve caused by the one magnet disposed inside the lower developing sleeve. The magnetic force that contributes to receiving the developer is P4', and the magnetic force P2. is gradually increased, and the value at which no abnormal images occur is C1 magnetic force P.
4' is gradually increased, d is the value at which the developer starts to sag in the lower developing sleeve, and a and b are constants determined for each developing device.

P2=a (P4')+b''=・(1
) P2≧C (2) P4″≦d (3) Equations (1), (2), and (3) are satisfied.

(Function) The strength relationship between the magnets of the upper developing sleeve and the magnets of the lower developing sleeve is in a well-balanced state that does not cause developer drift or abnormal images.

(Example) First, the overall configuration of a developing device according to the present invention will be explained.

In FIG. 2'c, a developing device 1 is arranged close to a drum-shaped photoreceptor 2, which is an example of a latent image carrier, and its developing container 3 is
A powdered two-component developer 4 containing a magnetic carrier and magnetic or non-magnetic toner is housed inside. When the toner concentration in this developer decreases, the toner supply roller 20
7 rotates, the toner 6 in the toner container 5 is replenished into the developer 4 in the developer container 3, and is stirred by the stirring roller 7.107.

In the developing container 3, two developing sleeves, an upper developing sleeve 8 and a lower developing sleeve 8a, and a paddle wheel 9, which is an example of a rotating body for collecting developer, are arranged.

Each of the developing sleeves 8, 8a is made of a cylindrical body made of non-magnetic material, and is arranged in a vertical positional relationship along the surface of the photoreceptor, with the upper developing sleeve 8 disposed above and the lower developing sleeve 8a disposed below. has been done. Both developing sleeves 8,
8a are both rotationally driven in the counterclockwise direction in the figure by a drive device (not shown). That is, both sleeves 8
, 8a are rotated in the same direction.

Inside each developing sleeve 8, 8a, there is a code 10.
．． As generally indicated by 10a, a plurality of magnets are fixedly arranged along the circumferential direction of each sleeve 8, 8a.

The paddle wheel 9 is rotationally driven in the counterclockwise direction in the drawing, whereby the developer 4 in the developer container 3 is stirred and drawn up and supplied to the surface of the lower developing sleeve 8a.

The photoreceptor 2 is rotated in the direction of force in the figure as shown by arrow A, and at this time an electrostatic latent image is formed on its surface. This latent image moves from above to below in the area adjacent to the developing device 1.

The developer supplied to the lower developing sleeve 8a by the paddle wheel 9 as described above is applied to each developing sleeve 8a, 8.
Due to the rotation of the developer and the magnetic force of the magnets 10a and 10 inscribed therein, the developer is conveyed in the direction of the broken line arrow while being carried by the developing sleeve.

That is, first, the developer carried on the lower developing sleeve 8a moves from the lower developing sleeve 8a to the second developing sleeve 8 as shown by the broken line arrow B1, and while being carried by the sleeve 8, the developer is transferred as shown by the broken line arrow B2. like doctor blade 1
4, and excess developer is scraped off at this time. The appropriate amount of developer that has passed through the doctor blade 14 passes through the upper developing area D1 between the upper developing sleeve 8 and the photoreceptor 2 as shown by arrow B3, and then moves to the lower developing sleeve 8a again. It passes through the lower developing area D2 between the lower developing sleeve 8a and the photoreceptor 2, continues to leave the lower developing sleeve 8a, flows to the bottom of the developing container 3, and is stirred by the paddle wheel 9.

The developer scraped off by the doctor blade 14 falls downward while being guided by the separator]3.

As the developer 4 is conveyed and stirred as described above, the 1-ner and the carrier are triboelectrically charged to opposite polarities, and the developer is transferred to each development area as described above.
When passing through D, the toner in the developer electrostatically transfers to the electrostatic latent image formed on the photoreceptor 2, and the latent image is made visible.

FIG. 3 is an explanatory diagram showing the arrangement of the developing sleeves 8 and 8a shown in FIG. 2 and the magnets 10 and 10a inside them. Here, a magnet 1o installed inside the upper developing sleeve 8
The individual magnets are labeled M0 to M, and the individual magnets 10 installed inside the lower developing sleeve 8a are labeled G and G4, respectively. be. The polarity of the magnetic pole of each magnet will be explained below, but each magnetic pole explained here is for each developing sleeve 8, 8a-1.
1= means the magnetic pole facing the circumferential surface (outer magnetic pole).

Here, we will focus on the magnets installed inside each of the sleeves 8, 8a near the closest area between the upper developing sleeve 8 and the lower developing sleeve 8a. Two magnets M1.
M2, and the lower developing sleeve 8a has one magnet G1.
exists. At this time, the magnetic poles of the two magnets M11M2 in the upper developing sleeve 8 are set to have different polarities, and in the illustrated example, the former is the S pole and the latter is the N pole. Furthermore, the magnetic pole of the magnet G1 in the lower developing sleeve 8a has a different polarity than that of the magnet M1, which is closer to the photoreceptor 2 of the two magnets M□2M2 in the upper developing sleeve 8 (example in the figure). (N pole). Therefore, the magnetic poles of magnet G and magnet M are of the same polarity.

As mentioned above, three magnets M1. M2. Since the magnetic poles G and G are set respectively, the magnetic field formed by these flows in a loop shape as shown by the diagonally shaded band-shaped arrow in FIG.

That is, a magnetic field X caused by the magnet M2 and the magnet G□ and a magnetic field Y caused by the magnet M and the magnet G1 are formed between the upper and lower developing sleeves, and one magnetic field X is generated by the lower developing sleeve 8a. The upper developer is pumped up to the upper developing sleeve 8, and the other magnetic field Y is pumped up to the upper developing sleeve 8.
It serves to draw the upper developer down to the lower developing sleeve 8a. Other magnets MJ, M, , M, , G2.
The polarity of each magnetic pole G, G4 is set as illustrated in FIG.

As can be seen from FIG. 2, the magnetic poles of magnets M2 and 61 are the same (in the example shown, N pole), so the magnetic field X formed by these magnets M, G, The magnetic field extends far away from the 2 side, creating a circuitous magnetic field. Therefore, the developer can be more effectively pumped up from the lower developing sleeve 8a to the upper developing sleeve 8. If the polarities of magnets M2 and G are set to be different, the developer is temporarily held here by the magnetic field formed by these magnets, and then pushed upward by the developer that is transported later. Since the developer is drawn up into the upper developing sleeve 8 only when it reaches a position where it is attracted to the magnet P2, not only the pumping performance is reduced, but also the developer is held in the narrow gap between the developing sleeves 8 and 8a.
A slipping phenomenon becomes more likely to occur.

Furthermore, when the developer transfers from the upper developing sleeve 8 to the lower developing sleeve 8a, the amount becomes uneven, and a situation occurs in which a large amount of developer transfers at one point and a small amount transfers at another point. If this occurs, there is a risk that density unevenness will occur in the visible image.

That is, since the amount of developer passing through the upper development area D1 is regulated by the doctor blade 14,
The amount is relatively uniform, but since the lower developing sleeve 8a does not have such a developer amount regulating means, the amount of developer transferred from the upper developing sleeve 8 to the lower developing sleeve 8a may be uneven. In this case, it is impossible to correct this, and this appears as it is as density unevenness in the visible image.

However, in the developing device shown in FIGS. 1 and 2, the magnets M1 and G0 have different polarities, and a curtain-like magnetic field Y that shields the space between the developing sleeves 8 and 8a is created between them. As a result, the developer in the upper developing sleeve 8 is sequentially and uniformly delivered to the lower developing sleeve 8a.

In this way, the amount of developer transferred to the lower developing sleeve 8a can be made uniform, and the above-mentioned problems can be prevented from occurring.

Note that a magnet G2 is disposed at a position approximately 90° upstream in the rotational direction of the sleeve 8a with respect to the magnet G□ in the lower developing sleeve 8a; It serves to sequentially send out the developer supplied to the developing sleeve 8a to a developer drawing area between both developing sleeves, and transport the developer in a stable state. Without the magnet G2, developer would accumulate between the lower developing sleeve 8a and the paddle wheel 9, causing an increase in the torque of the paddle wheel 9. Moreover, the magnetic pole of this magnet G2 is
It has the same polarity as the magnetic pole of the magnet G on the downstream side,
If these have different polarities, the above-mentioned magnetic field loop will collapse and the developer will be transported from the magnet G2 to the magnet G, causing a spinning phenomenon, and the developer will be pumped up into the upper sleeve 8. There is a risk that it will not be possible.

Basically, by arranging the magnets in this manner, the developer can be conveyed smoothly and tangle can be eliminated.

However, even in this case, it is necessary to consider the strength relationship of the magnets.

In particular, in order to prevent the upper developing sleeve 8 from twisting around, it is necessary to appropriately create the loop-shaped magnetic field described in accordance with FIG. The problem is the relationship between the magnetic force P2 caused by M1 and the magnetic force P4' mainly caused by the magnet G, which contributes to the amount of developer in the lower developing sleeve 8a.

Therefore, the following experiment was conducted to explore this relationship. However, the other magnetic poles of the upper developing sleeve 8 and the lower developing sleeve 8a were set in consideration of the smooth conveyance of the developer throughout the toner container 5. Settings were made so that the peak of magnetic force appeared on each developing sleeve as shown in FIG. P shown in Figure 4
The 2 (S) pole and the P4' (N) pole are caused by magnets M, . . . , G.

In addition to these, magnet Mz8Ma9M42Ms allows P3
(N) pole, P4 (S) pole, Pg (N) pole, p6 (s) pole, and Pi (N) pole appear.

Similarly, 4 magnets, G2. G3. By G, P2'(N)
A pole, P3' (N) pole, and P□' (S) pole appear.

These values are shown in Table-1.

Table-1 (Reference values) Under the conditions of Table-1, P2 (S) pole and r', i' (N)
FIG. 5 shows the results of examining the relationship between the amount of developer carried around and the amount of toner scattering in the J-side developing sleeve 8 while varying the magnetic force of each pole.

In FIG. The amount of developer on the sleeve returned to its original position after activating the device is expressed as a percentage.

Further, the amount of toner scattering on the vertical axis represents the number of fine toner particles per hour when continuous copying was made for 2 minutes and measured at the measurement point 5 shown in FIG.

The toner concentration at this time was 5 wt%.

As can be seen from FIG. 5, there is a certain relationship between the amount of drift and the amount of toner scattering, as shown by a curve 16.

When the amount of entanglement is small, the magnetic brush Pxr P2F P3+P41 corresponds to each magnetic pole as shown in Fig. 6.
pSI P6+ P+,' * Pz' r P3'
+p4' is formed, and the toner is smoothly transported as shown by the broken line arrow. The magnetic brush p4' also maintains an appropriate height. Therefore, even at the end of the developer container 3, the developer is transferred to the magnetic brush P4' as shown in FIG.
At the same time, the toner comes into contact with the developer container 3, and the impact causes it to fly out into the container, whereupon the toner is stirred again. This cycle is repeated, so the amount of toner scattering is also small.

However, as the amount of drag increases, the amount of toner scattering tends to increase accordingly.

As mentioned above, as the amount of entanglement to the upper developing sleeve 8 increases, the amount of toner supplied to the lower developing sleeve 8a decreases, and as shown in FIG. This is because the gap becomes low and a gap is created between the developer container 3 and the end of the developer container 3, and the sealing function becomes impossible.

Here, the allowable limit value for the toner supply amount is 3.
When 000 (k/2 minutes) is selected, the allowable trailing amount of the upper developing sleeve is approximately 24%. Therefore, based on the experiment described in Section 2, the trailing amount and the upper viewing sleeve are The relationship between the peak Gauss of the p2(s) pole and the peak Gauss of the P4' (N)M of the lower developing sleeve was investigated, and the result was as shown in FIG.

In FIG. 1, a straight line 17 sloping upward to the right indicates the limit of occurrence of twisting. Here, y is p2 (
s) Peak Gauss of the pole, X is P of the lower developing sleeve 8a
If it is a peak Gaussian with 4' (N) poles, then y≦ax+b (1)
(a and b are constants) When the following is satisfied, the amount of twisting in the upper developing sleeve 8 is zero (0).

Furthermore, when the influence on the image was investigated by changing the peak Gauss of the P2(S) pole of the upper developing sleeve 8, it was found that when the peak Gauss of the P2(S) pole of the upper developing sleeve 8 becomes below a certain value C, an abnormal image (step unevenness) occurs. Therefore, as a condition for not producing an abnormal image, there is the relationship y≧C (2).

Next, when rotation occurs in the lower developing sleeve, image density is insufficient due to insufficient supply of new toner, and the amount retained on the lower developing sleeve increases. When the retained amount is large, the developer is applied too strongly to the photoreceptor 2 by the P (S) electrode, causing problems such as white spots at the trailing edge, unevenness in the image and steps, and carrier dropout.

Therefore, when the peak Gauss of the P4' (N) pole of the lower developing sleeve 8a was changed to find out the limit of occurrence of developer tangle on the lower developing sleeve, when it exceeded a certain value d, It was found that slippage occurred.

Therefore, as a condition to prevent sagging in the lower developing sleeve, X≦d (3)
There is a relationship between

In other words, the peak Gauss of the p, (s) pole of the upper developing sleeve and the p, l (N) of the lower developing sleeve within the region that satisfies the conditions of these three equations (1), (2), and (3). If the quantity condition can be met, the conventional problem of toner scattering can be solved, and background smudge images and toner stains inside the machine can be eliminated.

A specific example is as follows.

a=0.5. b=100. c=300. d
=500°P, =800 Gauss, P, =500 Gauss, P4=7oo Gauss P, =500 Gauss, P6=
500 Gauss X, P1'=650 Gauss P,'=500
Gauss, P3'=500 Gauss.

Under the above conditions, y==0.5x+lO0,3'≧300
With values of x (P4' (N) extreme peak Gauss) and y (P2 (S) extreme peak Gauss) that satisfy ゜X≦500, abnormal images such as toner scattering, background stains, and white areas will occur. do not have.

(Effect of the invention) According to the present invention, toner scattering does not occur.

Moreover, an image of good quality can be obtained.

[Brief explanation of drawings]

Fig. 1 is a diagram explaining the conditions of the developing sleeve magnetic pole to obtain a good image without toner scattering, Fig. 2 is a configuration diagram of the developing device according to the present invention, and Fig. 3 is a diagram illustrating the conditions of the developing sleeve magnetic pole in order to obtain a good image without toner scattering. A diagram illustrating the arrangement of magnets and the developer conveyance path,
Fig. 4 is a diagram explaining the position and peak of the magnetic pole of each developing sleeve, Fig. 5 is a diagram explaining the relationship between the amount of toner scattering and the amount of entanglement, and Fig. 6 is a diagram explaining the magnetic pole position and peak of each developing sleeve. Figure 7 is an explanatory diagram of the developer container at the end when toner scattering is not occurring, and Figure 8 is an illustration of the developer container when toner scattering is occurring. It is an explanatory view at the end. 8... Upper developing sleeve, 8a... Lower developing sleeve. (Idiot 1 person) - Lower 2 series) II 5 All 5 city letters (method) % formula % 3. Relationship with the person making the amendment Patent applicant name (674) Rico 4 Co., Ltd., agent address Tokyo 4-5-4-6 Kyodo, Setagaya-ku, subject of amendment

Claims (1)

[Claims] An upper developing sleeve and a lower developing sleeve arranged in a vertical positional relationship along the surface of the latent image carrier, and fixedly arranged inside each developing sleeve along its circumferential direction. The upper developing sleeve and the lower developing sleeve are rotated in the same direction, and the two-component developer supplied to the lower developing sleeve is controlled by the magnetic force of each of the magnets and the developing sleeve. The image is transferred from the lower developing sleeve to the upper developing sleeve by rotation, passes through the developing area between the upper developing sleeve and the latent image carrier, and then transferred to the lower developing sleeve again. A developing device that causes an electrostatic latent image formed on the latent image carrier to be visualized by toner in a developer that passes through a development area between the latent image carrier and the latent image carrier. , two magnets arranged along the circumferential direction of the sleeve inside the upper developing sleeve in the vicinity of the closest area between the upper developing sleeve and the lower developing sleeve. The magnetic poles facing toward each other are set to have different polarities, and the magnetic pole facing the inner peripheral surface of the sleeve of one magnet provided inside the lower developing sleeve near the nearest area is set to have opposite polarity to the upper side. Of the two magnets in the developing sleeve, the one closer to the latent image carrier is set to have a different polarity with respect to the magnetic pole of the one facing the inner circumferential surface of the upper developing sleeve, and the three magnets In a developing device in which a magnetic field formed by a magnet has a loop shape, the upper developing device is developed by the magnet closer to the latent image carrier among the two magnets disposed inside the upper developing sleeve. The magnetic force that contributes to the transfer of developer on the sleeve surface is P.
_2, said 1 disposed inside said lower developing sleeve
The magnetic force that contributes to the reception of the developer on the surface of the lower developing sleeve by the magnets is P_4', and the magnetic force P
_2 is gradually increased, and the value at which abnormal images no longer occur is c; the magnetic force P_4' is gradually increased, and the value at which the developer starts to roll around in the lower developing sleeve is d; The constants determined for the developing device are a and b.
When P_2=a(P_4')+b...(1) P_2≧c...(2) P_4'≦d...(3) (1), (2 ) and (3).