JPH0376457B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adjusting toner concentration and an apparatus therefor, and more particularly, the present invention relates to a method for adjusting toner concentration and an apparatus for the same. The present invention relates to a method and device for freely adjusting within a wide range.

In electrophotography and electrostatic recording, an electrostatic latent image is formed on a photoreceptor or recording medium, and this electrostatic latent image is brought into contact with a developer to form a visible image corresponding to the electrostatic latent image. let The developer for this electrostatic latent image is a two-component system in which a magnetic carrier made of iron powder or the like is mixed with an electrostatic toner made of resin binder particles in which a pigment is dispersed, for ease of development operation. Magnetic developers are the most widely used. When the two-component developer is mixed, the toner particles are triboelectrically charged and held on the surface of the magnetic carrier.
When this two-component developer is rubbed in the form of a magnetic brush against a substrate having an electrostatic latent image, toner particles are attracted to the electrostatic latent image to form a toner image.

As described above, two-component magnetic developers have the advantage that the developing operation is easy and the quality of the images formed is generally good. However, on the other hand, the toner concentration in the developer decreases as the developing operation continues. There is a problem in that the concentration decreases over time and it is difficult to control the concentration to a constant level. In other words, when the toner concentration in the developer decreases, the image density formed also decreases, while if the toner concentration is too high, toner adheres to the background (non-image area) and toner flows from the magnetic brush roller. Problems such as scattering will occur.

For this reason, a decrease in toner concentration in a two-component developer is detected by a decrease in image density, a change in the inductance of the developer, a change in the volume of the developer, etc., and the toner is replenished manually. . However, when replenishing toner manually, the toner concentration changes stepwise, making it difficult to adjust the toner concentration in the developer to a constant set value. Furthermore, devices are known that detect toner concentration and automatically replenish toner based on this detection signal, but such devices require a complicated detection control system and are expensive. In addition, it is inevitable that the toner density adjustment will be gradual.

Moreover, these known toner concentration adjustment mechanisms cannot achieve the function of lowering the toner concentration when the toner concentration in the two-component developer becomes higher than the set value.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a method and apparatus that can automatically and continuously adjust the toner concentration in a two-component developer using simple means.

Another object of the present invention is to provide a method and apparatus that can freely adjust the toner concentration in a two-component developer to any set value within a wide range.

Still another object of the present invention is to maintain a uniform toner density as a whole with respect to the area where the toner density has decreased, even when the density decreases due to local toner consumption on the magnetic brush on the developing sleeve. It is an object of the present invention to provide a toner concentration adjusting method and apparatus in which toner is supplied so that the toner is supplied.

Further advantages of the invention will become apparent from the following description of the specification.

According to the present invention, a magnetic brush of a two-component developer made of a mixture of a magnetic carrier and an electrostatic toner is formed on a developing sleeve, and a mesh is inserted into an opening of a toner reservoir containing only an electrostatic toner.・A screen is arranged so that the electrostatic toner in the toner reservoir and the magnetic brush of the two-component developer come into contact with each other through the mesh screen, and the magnetic brush is rubbed against the mesh screen, and the sleeve and the mesh are brought into contact with each other.・Adjust the toner concentration in the two-component developer by applying a bias voltage between the mesh screen and the electrostatic toner moving to the magnetic brush side or toner reservoir side through the openings of the mesh screen. A method for adjusting toner concentration in a two-component developer is provided.

The invention also provides a magnetic carrier and a microelectromagnetic carrier comprising a sleeve made of an electrically conductive non-magnetic material and a magnet with a plurality of magnetic poles built into the sleeve, at least one of which is movable. a mechanism for forming and transporting a magnetic brush made of a mixture with electrostatic toner; a toner reservoir that contains only electrostatic toner therein and has an opening at the bottom;
a mesh screen made of a conductive material provided at the opening of the toner reservoir, the upper surface side of which supports electrostatic toner, and the lower surface side of which is arranged to rub against the magnetic brush; and the sleeve and the mesh screen; An apparatus for adjusting toner concentration in a two-component magnetic developer is provided, which is characterized by comprising a bias pressure applying mechanism for applying a bias voltage between the two components.

The present invention will be described in detail below based on specific examples shown in the accompanying drawings.

In FIG. 1 for explaining the present invention, a magnet roll 2 having a large number of magnetic poles is housed inside a sleeve 1 made of a non-magnetic material such as aluminum, and these sleeve 1 and magnet roll 2 are ,
At least one of them is rotatably supported by a machine frame (not shown).

A magnetic brush 3 of a two-component developer made of a mixture of a magnetic carrier and electrostatic toner is formed on the surface of the sleeve 1 . A rotating drum 5 having an electrophotographic photosensitive layer 4 adjacent to this sleeve 1
is provided. Magnetic brush 3 on sleeve 1
As the sleeve 1 rotates or the magnet roll 2 rotates, the toner image 7 moves, for example in the direction of the arrow in the figure, and slides against the surface of the photosensitive layer 4 to form a toner image 7 corresponding to the electrostatic latent image 6 on the photosensitive layer 4. will be formed.

According to the invention, the magnetic brush 3 on the sleeve 1
Let's see it as mesh screen 8. In FIG. 2, which schematically shows an enlarged view of the sliding state between the magnetic brush 3 and the mesh screen 8, the mesh screen 8 has a mesh opening 9 and a dielectric mesh strand or shielding portion 10. On the other hand, the magnetic brush 3 has a magnetic carrier 1 on the surface of which the toner particles 11 are electrostatically attracted and held.
2 are connected in a tuft-like and chain-like structure. Only the toner particles 11 are accommodated above the mesh screen 8 to form a toner reservoir 13, while only the magnetic brush 3 is located below the mesh screen 8. Depending on the size of the magnetic brush 3, the tip of the magnetic brush 3 may protrude upward from the mesh opening 9.

According to the invention, a bias voltage is applied between the mesh screen 8 and the magnetic brush support or sleeve 1, as shown in FIG. For this purpose, a voltage-adjustable variable DC power supply 14 for applying a bias voltage is provided, which power supply 14 is connected to the mesh screen 8 via the contact S ₁ and the connection 15 of the double-throw double-pole switch and to the mesh screen 8 of the switch. It is connected to the sleeve 1 via the contact S ₂ and the connection 16 . Thus, with the sleeve 1 as a reference, a positive bias voltage or a negative bias voltage can be applied to the mesh screen 8 by switching the switch, and the magnitude of this bias voltage can also be freely adjusted. It's summery.

In the present invention, the magnetic brush 3 and mesh
When the screen 8 is rubbed, the toner particles 11 are sucked in or the toner particles 11 are discharged through the mesh screen 8, depending on the toner concentration in the two-component developer forming the magnetic brush. At this time, if a bias voltage is applied between the sleeve 1 supporting the magnetic brush and the mesh screen 8, the amount of toner movement and the toner movement can be substantially controlled depending on the polarity and magnitude of this bias voltage. This method utilizes the new knowledge that the toner concentration in the magnetic brush (hereinafter sometimes simply referred to as the reference concentration C _S ) changes, which is the upper zero.

In FIG. 3, which shows the relationship between the toner concentration C in a two-component developer for developing a positive electrostatic latent image and the toner movement amount M through the mesh screen in relation to the bias voltage, the toner movement The positive amount is the toner reservoir 1 on the mesh screen 8.
3 indicates the toner transfer through the screen 8 to the magnetic brush 3, while the minus sign indicates the toner transfer from the magnetic brush 3 through the screen 8 to the toner reservoir 13. Thus, referring to the principle diagram in FIG. 3, first, when the two-component developer and toner concentration C are lower than a certain standard concentration C _S , the toner is transferred from the toner reservoir 13 to the magnetic brush 3 through the screen 8. On the other hand, if the toner concentration is higher than this standard concentration C _S , toner movement occurs from the magnetic brush 3 through the screen 8 to the toner reservoir 13, and the toner concentration is higher than the standard concentration.
The fact that when equal to C _S no toner movement through the screen 8 occurs is evident.
In addition, in the case of a two-component developer for positive latent images, when a negative bias voltage is applied to the mesh screen 8 with respect to the sleeve 1, the reference density C _S mentioned above shifts to the high density side and , the amount of toner movement through the screen 8 also increases significantly,
Furthermore, when a positive bias voltage is applied to the mesh screen 8 with the sleeve 1 as a reference, the reference density C _S shifts to the lower density side and the amount of toner movement through the screen 8 can be significantly reduced. Become.

Furthermore, FIGS. 4, 5, and 6 are diagrams showing the relationship between the toner concentration in the magnetic brush and elapsed time, and in these diagrams, the curve A indicates the initial toner concentration in the magnetic brush. When the density is higher than the reference density C _S , the curve B shows the density change when the initial toner density in the magnetic brush is lower than the reference density C _S . Furthermore, Fig. 4 shows that when the voltage applied to the mesh screen based on the sleeve is 0 volts,
Figure 5 shows that when this applied voltage is -150 volts, the 6th
The figures show the case where this applied voltage is +100 volts. From these drawings, it can be seen that the toner concentration C is the standard value C _S
Whether the toner concentration C is at a higher density (curve A) or lower than the standard value C _S (curve B), it converges to the standard concentration C _S over time and this convergence. It is clear that the reference concentration C _S is on the high concentration side when the bias voltage is on the negative side, and on the low concentration side when the bias voltage is on the positive side.

From the above facts, according to the present invention, sleeve 1
A bias voltage is applied to the mesh screen 8 that rubs against the upper developer magnetic brush 3, and if this developer contains toner for a positively charged latent image, the bias voltage is increased to the negative side. Therefore, it becomes clear that the toner concentration in the magnetic brush can be shifted to the low density side by shifting the toner concentration in the magnetic brush to the high density side and shifting this bias voltage to the positive side.

Of course, if the two-component developer used contains toner for forming a negative charge latent image, contrary to the above, by increasing the bias voltage to the positive side, the toner concentration in the magnetic brush can be adjusted to the high density side. By shifting the toner density to the negative side and shifting the bias voltage to the negative side, it is possible to shift the toner density to the low density side.

Thus, according to the present invention, by adjusting the magnitude of the bias voltage and, if necessary, also changing its polarity, the toner concentration in the magnetic brush can be adjusted.
The advantage is achieved that any selected concentration can be precisely and automatically and continuously adjusted within a fairly wide range.

Furthermore, a photosensitive layer of a certain width and a developing sleeve,
When using for a long time to copy an original whose width is narrower than this width, and then when using it to copy a full width raw material, or when copying an original whose image is unevenly distributed in a certain part in the width direction, and then When copying a document in which an image exists uniformly across the entire width, a low-density image is formed in the area where the toner of the developing sleeve is consumed due to a decrease in toner density, and other areas are In some areas, the toner concentration is too high, which tends to cause fogging.

On the other hand, according to the present invention, even when the density decreases due to local toner consumption on the magnetic brush on the developing sleeve, the density decrease area is treated as follows, as is clear from FIG. Toner is selectively replenished, making it possible to maintain a uniform toner concentration over the entire magnetic brush.

In the present invention, toner is ejected from the magnetic brush 3 through the mesh screen 8 and toner is sucked into the magnetic brush 3, and these are further changed by the bias voltage applied to the mesh screen 8. Although the exact reason for this has not yet been elucidated, the present inventors speculate that the reason is as follows. That is, as described above, the electrostatic toner particles 11 are attracted and held on the surface of the magnetic carrier 12 by electrostatic force to form the magnetic brush 3, but the mesh
The screen 8 allows contact and mutual friction between the magnetic carrier 12 forming the magnetic brush 3 and the toner particles 11 in the toner reservoir 13 through its openings 9 and also allows its mesh strands or shield 10 to Therefore, it is believed that the magnetic brush 3 acts like a scraper to scrape off the toner particles 11 in the magnetic brush 3. Thus, when the toner concentration in the magnetic brush is low, toner particles 11 are electrostatically attracted into the magnetic brush through the mesh openings, and conversely, when the toner concentration is high, excess toner particles are attracted to the magnetic brush 3. It is recognized that the material is scraped off from the surface and stored on the mesh screen. In the case of toner for a positive electrostatic latent image, the toner particles are of course negatively charged, but when a negative bias voltage is applied to the mesh screen 8, the mesh screen 8 By applying a repulsive force to push the toner toward the sleeve 1 side or the carrier 12 side of opposite polarity, toner suction through the mesh screen 8 is increased.On the other hand, when applying a positive bias voltage, the negative It is recognized that an attractive force acts between the charged toner particles 11 and the mesh screen 8, and the suction of the toner into the mesh screen 8 is suppressed.

The size of the mesh openings 9 of the mesh screen 8 used in the present invention is at least larger than the particle size of the electrostatic toner 11, but when the electrostatic toner 11 is placed on the mesh screen 8, , the size of the toner 11 is determined to be smaller than the size at which the toner 11 falls freely due to gravity. The specific dimensions of the mesh openings 9 vary depending on the particle size and fluidity (angle of sway) of the toner particles, so it is difficult to define them unconditionally.

However, two-component developers commonly used commercially typically consist of a relatively coarse magnetic carrier with a particle size of 10 to 200 microns and a relatively fine electrostatic carrier with a particle size of 1 to 40 microns. These electrostatic toner particles are often manufactured by a kneading/pulverizing method and have an amorphous shape and relatively poor fluidity. It has been found that for such a two-component developer, satisfactory results can be obtained by using a screen of 50 to 500 meshes (tire standard), particularly 80 to 200 meshes. That is, in a two-component magnetic developer,
3 to 20% based on the total amount of magnetic carrier and toner
However, by using the mesh screen described above, it is possible to bring the toner standard concentration C _S (see FIGS. 3 to 6) approximately within this range.

Of course, this reference concentration C _S of toner varies slightly depending on not only the bias voltage but also the mesh size of the screen used and the degree of rubbing of the screen against the magnetic brush. Generally, as the mesh size of the screen increases, this reference density C _S shifts to the higher density side, and on the other hand, as the degree of rubbing of the screen against the magnetic brush increases, the standard density of toner tends to shift to the lower density side. It will be done.

In the present invention, the bias voltage applied between the mesh screen and the sleeve can be freely varied within a range that does not cause problems such as discharge breakdown between the two, but it is generally from -500V to +500V, particularly -200V. It is best to use between +200V and +200V.

In the present invention, the mesh screen may be made of any material as long as it is electrically conductive. For example, screen materials include non-magnetic metal materials such as stainless steel, brass, copper, bronze, phosphor bronze, aluminum, and monel; magnetic metal materials such as nickel, galvanized copper, and hard steel; conductive-treated nylon, and polyester. Organic polymer materials such as polyvinyl chloride, vinylidene chloride resin, acrylic, and silk can be used. The screen may be a so-called woven net made by weaving fibers or wires made of these materials into a plain weave, twill weave, etc., or a punched net made by punching the above-mentioned materials, or a metal material. It may be an electroformed wire mesh manufactured by the electroforming method. The porosity of the screen, that is, the ratio of the area of the mesh openings to the total area of the screen, is generally speaking:
A range of 20 to 80%, particularly 40 to 70%, is desirable from the viewpoint of the mechanical strength or durability of the screen and the speed of concentration adjustment.

The toner concentration adjusting method of the present invention can be applied, for example, to a magnetic brush roller for developing electrostatic latent images to directly adjust the toner concentration in a developer, and can also be applied to a cleaning roller using a magnetic brush to perform cleaning. It can be used to separate or collect toner from magnetic brushes.

According to the present invention, as explained above, an exceptional detection mechanism and an exceptional A significant advantage is that the toner concentration is automatically and precisely adjusted without the need for any control mechanism or the like.

The invention is illustrated by the following example.

Experiment 1 We prototyped a measurement container with a 20 mm x 12 mm 100-mesh screen mesh made of brass at the bottom, put 0.5 g of toner in this container, and used two-component development with the toner concentration set to a low value. The toner concentration in the developer and the toner being replenished through the mesh screen are determined by placing the developer in moderate contact with the tip of a magnetic brush and measuring the difference between the initial weight of the container and the weight after aging for 60 seconds. We investigated the relationship with quantity. The toner concentration was determined by taking a 1 g sample from the magnetic brush in contact with the drum and cleaning it.

Further, a bias power source is connected to the brass mesh, so that the voltage between the developing sleeve and the mesh can be arbitrarily set.

The results are shown in FIG.

As a result, the amount of toner replenishment changes depending on the toner concentration in the developer, and furthermore, there is a large change in the current bias potential of the screen mesh with respect to the sleeve.

Although polar toner was used in the experiment, there was a large change in the amount of toner replenishment and the toner concentration value at which toner replenishment stopped for the screen mesh potential of 100V, 0V, and 150V, and the value was It became 9%, 10%, and 11%.

Example 1 Next, we actually used a test developer (DC-
A mesh screen (12 mm x 230 mm) of the same type as that used in Experiment 1 was installed at the bottom of the toner hopper, extending almost the entire length of the developing roller in the axial direction of the developing device (modified for 161). It was set to make contact with the brush.

The initial developer toner concentration is lower than the set value.
The relationship between the aging time of the developing device and the toner concentration was investigated using a mesh voltage of 100 V and a setting of C ₁ .

The results are shown in FIG.

Example 2 The initial developer toner concentration was set higher than the set value.
The relationship between the aging time and the toner concentration was investigated in the same manner as in Example 1, with the mesh voltage set at _C2 and the mesh voltage at 100V.

The results are shown in FIG.

From the results of curves a and b shown in FIG. 2, it was found that the toner concentration converged and stabilized at C _S with time, both when it was lower than the reference value C _S and when it was higher.

Figures 5 and 6 show the screen mesh voltages, respectively, in the same manner as in Examples 1 and 2.
These are characteristic curves when changing the voltage to 0 V and 150 V. As is clear from these curves, it is possible to arbitrarily control the focusing and stable value C _S of the toner concentration of the developer by adjusting the screen mesh voltage.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a developing device using the developing method of the present invention, FIG. 2 is an enlarged view of main parts of the developing method of the present invention, and FIG. 3 is a diagram showing toner concentration and toner movement amount. FIG. 4, FIG. 5, and FIG. 6 are diagrams showing the relationship between the toner concentration in the magnetic brush and the elapsed time. The reference numbers are 1 for the sleeve, 2 for the magnet, 3 for the magnetic brush, 8 for the mesh screen, 11 for the toner, 12 for the magnetic carrier, and 14 for the bias variable DC power supply.

Claims (1)

[Scope of Claims] 1. A magnetic brush made of a two-component developer consisting of a mixture of a magnetic carrier and electrostatic toner is formed on a developing sleeve, and a mesh is inserted into the opening of a toner reservoir containing only electrostatic toner. - By arranging a screen, the electrostatic toner in the toner reservoir and the magnetic brush of the two-component developer are brought into contact through the mesh screen, and the magnetic brush is rubbed against the mesh screen, and the sleeve By applying a bias voltage between the mesh screen and the mesh screen, the toner concentration in the two-component developer can be adjusted by moving the electrostatic toner through the openings of the mesh screen to the rear of the magnetic brush or to the toner reservoir side. A method for adjusting toner concentration in a two-component developer, the method comprising: adjusting the toner concentration in a two-component developer. 2. A mixture of a magnetic carrier and electrostatic toner, comprising a sleeve made of an electrically conductive non-magnetic material and a magnet with a large number of magnetic poles built into the sleeve, at least one of which is movable. A mechanism for forming and transporting a magnetic brush consisting of; a toner reservoir that stores only electrostatic toner inside and has an opening at the bottom; a mechanism provided at the opening of the toner reservoir, and whose upper surface side supports the electrostatic toner; and a mesh screen made of a conductive material, the lower surface of which is arranged to rub against the magnetic brush;
and a bias pressure applying mechanism for applying a bias voltage between the sleeve and the mesh screen.