JPS61166572A - Dry type developing device - Google Patents

Abstract

PURPOSE:To eliminate the existence of an insufficiently triboelectrified toner in a developing area by forming the crests of the magnetic brush of the developer in an area, where the developer is carrier upward from below, before the developer is used for development and allowing the crests of the magnetic brush to collide against a control member facing this area. CONSTITUTION:The magnetic developer on the peripheral surface of a developing sleeve 12 is formed into the crests of the magnetic brush by the magnetic force of a magnetic roll 13, and these crests of the magnetic brush are raised in areas corresponding to magnetic poles N1, N2, S1, and S2 of the magnetic roll 13. An insulating toner supplied from a slit 18 is formed into the crests of the magnetic brush in an area D corresponding to the magnetic pole S2. The developer is carrier upward from below in this area D, and the crests of the magnetic brush formed in this area D collide against a control plate 11, and the toner stuck to a magnetic carrier is shaked off. Most of the toner shaked off at this time is the excess toner whose triboelectrification to the magnetic carrier is insufficient.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a dry developing device used in electrophotographic copying processes and the like.

The conventional technology and its problems are summarized by Rokuji Ichita Takara, Tei A Inui, Q Hosha 1. They can be roughly divided into two-component developing methods using a powder developer consisting of a mixture of toner and magnetic carrier, and one-component developing methods using a powder developer consisting only of magnetic toner.

By the way, in the conventional two-component developing method, it is necessary to sufficiently stir and mix the toner and magnetic carrier, and to keep the toner concentration constant by appropriately replenishing new toner in proportion to the amount of toner consumed. A mixing section, a toner replenishing device, etc. are required, leading to an increase in the size of the developing device.

Therefore, the present applicant prepared a two-component magnetic developer by allowing a magnetic carrier to exist only on the circumferential surface of a developing sleeve containing a magnet therein, and by supplying insulating toner to the magnetic carrier. , a developing method or a developing device for developing an electrostatic latent image using this developer has been proposed. According to this developing method or developing device, the agitation mixing section and toner replenishing device that were required in the conventional two-component developing method are no longer necessary, the developing device is considerably miniaturized, and basically the one-component developing method is A developing device similar to the method can be used.

FIG. 4 shows an example of a dry developing device used in the developing method proposed by the present applicant. (1) is a cylindrical developing sleeve, (2) is a magnetic roller with S and N poles sequentially magnetized on the outer periphery, (3) is a height regulating plate, (4) is a carrier reservoir space,
(5) is a toner hopper forming plate, (6) is a toner supply blade, and (7) is a photosensitive drum.

The magnetic carrier is supplied in advance onto the circumferential surface of the developing sleeve (1), and together with the toner supplied by the rotation of the toner supply vane (6) in the direction of the arrow (d), the magnetic carrier is transported along the direction of the arrow (a) of the magnetic roller (2). Based on the rotation of the developing sleeve (12) in the direction of the arrow (b), the developing sleeve (12) is circulated in the direction of the arrow (b) and rotationally driven in the direction of the arrow (c). An electrostatic latent image previously formed on the surface of the photosensitive drum (7) is developed by rubbing.

However, with development using this dry developing device, images of good quality could be obtained in the initial state by setting the amount of magnetic carrier to an appropriate level, but as the number of copies increased, the image density increased and toner The problem of background fogging occurs.

Such problems are thought to be due to the following reasons. That is, the insulating toner adheres to the surface of the magnetic carrier due to frictional electrification with the magnetic carrier, is transported to the development area together with the magnetic carrier, and is attracted by the electrostatic attractive force of the electrostatic latent image in the development area and becomes magnetic. away from the surface of the carrier,
Adheres to the electrostatic latent image. However, if more toner adheres to the surface of the magnetic carrier, triboelectric charging between the two becomes insufficient, and the toner separates from the magnetic carrier relatively easily. In the above-mentioned dry type developing device, as development is repeated, toner is over-supplied to the developing area with multiple layers attached to the surface of the magnetic carrier, and insufficiently charged toner increases, resulting in the above-mentioned image density. 1).
'1 Therefore, when the relationship between the toner charge amount and the toner mixing ratio was experimentally investigated in the above-mentioned dry type developing device, the results shown in FIG. 5 were obtained. As is clear from the graph in Figure 5, as the toner mixture ratio increases, the toner charge amount tends to decrease, and the above-mentioned problem occurs only when the toner charge amount is less than about 5 μc/g, that is, when the toner mixture ratio increases. It was found that this is the case when the amount is 30 wt% or more. Therefore, if the toner mixing ratio is always kept below 30wt%,
It is believed that excessive supply of toner can be prevented by maintaining a sufficient amount of toner charge.

Note that the experiment that yielded the results shown in FIG. 5 was conducted using a specific type of developer, and the specific numerical values and characteristic curves vary depending on the type of developer, the setting conditions of the apparatus, and the like. However, the characteristic curve shows that the amount of toner charge tends to decrease as the toner mixing ratio increases, and it is clear that by keeping the toner mixing ratio below a certain value, it is possible to maintain a sufficient amount of toner charge and prevent oversupply of toner. It is.

[Means for Solving the Problems] Therefore, although the dry type developing device according to the present invention basically has the same configuration as the above-mentioned developing device already proposed by the applicant, it can be used for developing. Prior to this, the magnetic brush ears of the developer are formed in a region where the developer is conveyed from the bottom to the top, and the magnetic brush ears are made to collide with a control member opposed to this region. shall be.

[Function] That is, the ears of the magnetic brush of the developer formed on the circumferential surface of the developing sleeve before being used for development collide with the control member, thereby removing excess toner adhering to the surface of the magnetic carrier. The toner mixture ratio in the developer that is shaken off and eventually reaches the development area is controlled to be below a certain value, thereby preventing insufficiently charged toner from being supplied to the development area.

[Embodiment] Hereinafter, an embodiment of a dry developing device according to the present invention will be described with reference to FIGS. 1 to 3.

First, in FIG. 1, this dry developing device has a developing tank (l
O) is transferred to the developing section (A) using a control plate (11) made of a non-magnetic material.
) and a toner hopper section (B), and the developing section (A) has a developing sleeve (
12), a magnetic roller (13) is housed in the developing sleeve (12), a brush height regulating plate (14) is provided on the upstream side of the developing area (C), and a brush height regulating plate (14) is provided on the upstream side of the developing area (C). A carrier reservoir space (16) is formed by the and ceiling member (15), and a toner supply blade (
17).

The developing sleeve (12) is made of a conductive non-magnetic material and has a cylindrical shape, and can be rotated in the direction of arrow (b). The magnetic roller (13) has S and N poles sequentially magnetized at equal intervals on its outer periphery and is fixed inside the developing sleeve (12), so that the S1 pole is in the developing area (C) and the S2 pole is in the control area. Board (
11), and the N1 pole faces the space (I6). Therefore, the developer is transferred to the arrow (b) of the developing sleeve (12).
) direction, the developing sleeve (12) is conveyed in the direction of arrow (b) on the circumferential surface of the developing sleeve (12).

The toner supply vane (17) can be driven to rotate in the direction of the arrow (d), and the toner in the toner hopper section (B) is supplied to the control plate (11) based on the rotation of the toner supply vane (17).
) and the bottom of the developer tank (IO).

Next, the operation of the dry developing device having the above structure will be explained.

First, a magnetic carrier is first loaded into the space (16), and the developing sleeve (12) is pre-rotated in the direction of the arrow (b).
) is supplied to the circumferential surface of the Note that in this case, not only a magnetic carrier but also a magnetic carrier mixed with an insulating toner may be used. After that, the insulating toner is transferred to the hopper section (B
), and by rotating the developing sleeve (12) again, a magnetic developer is prepared on the circumferential surface of the developing sleeve (12), and the electrostatic latent image can be developed by this device. .

That is, the insulating toner is supplied from the slit (18) to the developing section (A) based on the rotation of the toner supply vane (I7) in the direction of arrow (d), and is applied onto the circumferential surface of the developing sleeve (12). is mixed with the magnetic carrier present in the developing sleeve (12), stirred, and moved along with the magnetic carrier on the circumferential surface of the developing sleeve (12) in the direction of the arrow (b).
) direction, is sufficiently mixed and stirred in the space (16), and is sufficiently triboelectrically charged at a constant mixing ratio, and then rotates in the direction of arrow (a) in the development area (C). The surface of 20) is rubbed and the electrostatic latent image formed on the surface is developed. After being subjected to development, insulating toner is sequentially supplied to the developer through the slit (18), mixed and stirred in the same manner as described above, and then subjected to development again.

In this case, the magnetic developer on the circumferential surface of the developing sleeve (12) is formed as the ears of a magnetic brush by the magnetic force of the magnetic roller (13). , N, , S, , rises in the region corresponding to S2. The insulating toner supplied from the slit (I8) is first formed as an ear of a magnetic brush in a region (D) corresponding to the magnetic pole S. This area (D) is an area where the developer is conveyed from the bottom to the top, and the ears of the magnetic brush formed in this area (D) are attached to the control plate (11) as shown in FIG. Upon collision, the toner adhering to the magnetic carrier is shaken off. Most of the toner that is shaken off at this time is excess toner that is insufficiently charged by friction with the magnetic carrier, and the excess toner is transferred to the carrier reservoir space (16) and the development area (C), which will be the subsequent transport path. It is prevented from being transported to. As a result, an increase in image density and toner fogging are prevented.

Note that the slit (18) has a function of regulating the supply of toner, but this is also to ensure a place where excess toner shaken off in the collision area (D) can accumulate.

Further, as a developing bias, a DC voltage is applied to the developing sleeve (12) based on a normal method, but an AC voltage may be superimposed on this, or alternatively, a DC voltage is applied to the developing sleeve (12) based on a normal method.
2) may be grounded.

Here, experimental data conducted by the inventors using the present dry developing apparatus will be shown. Experiments were conducted by changing the type of magnetic carrier or insulating toner, or by changing the development gap (Ds).
The height regulation gap (Db), slit width (Sg), and collision area gap (Dr) were varied. The data shown below is an example of the Hotaka regulation gap (Db)
: 0.35mm development gap (Ds)
: 0.45mm collision area gap (Dr)
: 0.55mm slit (Sg)
・1. O+nm magnetic roller: fixed magnetic pole, magnetic force of 4 magnetic poles: 740 Gauss magnetic pole direction
Developing sleeve in the direction shown in Figure 1 - Non-magnetic diameter - 20+ nm Rotation speed 42 rpm Carrier: Magnetic binder type toner with average particle size of 55 μm: Non-magnetic insulating toner with average particle size of 12 μm In the above experimental examples, a large number of copies were made. However, even when the number of copies was increased, there was no increase in image density and no toner fogging occurred.

Figure 3 shows the density (highest density part) of the copied image (image obtained by transferring the developed image to transfer paper and then fixing it) obtained when changing the collision area gap (DI). Yes, as the gap (D f) becomes narrower, the amount of toner that is shaken off increases, and the toner concentration in the developer that reaches the development area (C) decreases, resulting in a decrease in the density of the copied image. is found. That is, the gap (Dr)
This is because as the width becomes narrower, the impact of the developer colliding with the control plate (It) becomes greater, and the amount of toner that is shaken off also increases. On the other hand, and this means that the gap (Dr)
This means that a stable toner density level can be adjusted by changing .

[Effects of the Invention] As is clear from the above description, according to the present invention, before being used for development, the ear of the magnetic brush containing the developer is placed in the area where the developer is conveyed from the bottom to the top. 1.1 Control member formed in the area and facing this area
: Since the ears of the magnetic brush are made to collide with □, the excess toner is shaken off from the developer by this collision, and the increase in the toner mixing ratio in the developer that reaches the development area is suppressed. The presence of undercharged toner in the area is eliminated. Therefore, there is no problem that the image density increases as the number of copies increases or that toner background fog occurs.

Further, although the developing device uses toner and carrier, it does not require an agitating/mixing section or a toner replenishing device, which are required in conventional two-component developing devices, making it possible to downsize the developing device.

Further, as shown in the above embodiment, if the magnetic roller (13) is fixed and only the developing sleeve (12) is driven to rotate, the rotational speed of the developing sleeve (12) can be adjusted to the magnetic roller (13).
Since there is no need for high-speed rotation as in 13), vibrations are reduced, carrier flow to the toner hopper portion (B') due to vibrations is eliminated, and manufacturing costs are also reduced.

Furthermore, if non-magnetic toner is used, color toner can be used.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing an embodiment of a dry developing device according to the present invention, FIG. 2 is an explanatory cross-sectional view of the main part thereof, and FIG. 3 is a case where the collision area gap is changed in this embodiment. 3 is a graph showing changes in image density. FIG. 4 is a sectional view of a dry type developing device as a prior art, and FIG. 5 is a graph showing changes in toner charge amount with respect to toner mixing ratio in this type of device. (11)...control board, (12) developing sleeve, (13)
)...Magnetic roller, (14)...Hot height regulation plate, (1
6)...Carrier/reservoir space, (20)...Photosensitive drum, (A)...Developing section, (B)...Toner hopper section, (C)...Developing area, ( D)...Collision area.

Claims (1)

[Claims] 1. A two-component magnetic developer is prepared by making a magnetic carrier exist only on the circumferential surface of a developing sleeve that has a magnet inside, and supplying an insulating toner to this magnetic carrier. This is a dry type developing device that develops an electrostatic latent image using a magnetic brush, and prior to being used for development, the magnetic brush head of the developer is placed in an area where the developer is conveyed from below to above. A dry-type developing device characterized in that the ears of the magnetic brush are caused to collide with a control member which is formed and opposed to this area.