JPS6355709B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an apparatus for developing an electrostatic image, and more specifically, the present invention relates to an apparatus for developing an electrostatic image, and more specifically, the present invention relates to an apparatus for developing an electrostatic image, and more specifically, a thin layer of developer formed on the surface of a developer carrier and the surface of the electrostatic image carrier are brought into contact with each other in a non-contact state. The present invention relates to a developing device that selectively transfers toner to a high-potential electrostatic image portion and visualizes the same while maintaining a high-potential electrostatic image.

Conventionally, methods employed in developing devices for electrophotography and electrostatic recording are broadly classified into dry developing methods and wet developing methods. The former method is further divided into methods using a two-component developer and methods using a single-component developer.

In the two-component contact development method, a developer mixture of carrier particles and toner particles is inevitably used, and since the toner particles are normally consumed in much larger quantities than the carrier particles as the development process progresses, the mixture of both carrier particles and toner particles is required. It inherently has drawbacks such as a change in the ratio, resulting in fluctuations in the density of the image, and a deterioration in image quality due to deterioration of the carrier particles, which are difficult to consume, due to long-term use.

On the other hand, in the one-component contact development method, the Magne Dry method using magnetic toner and the contact development method without magnetic toner, the toner contacts the entire surface of the surface to be developed, that is, both the image area and the non-image area. Therefore, there is a problem in that toner tends to adhere even to non-image areas, resulting in so-called background fog and dirt.
(This fog stain is also a drawback that occurs in two-component development methods.) Furthermore, as a so-called jumping development method, which belongs to one-component development methods, toner is uniformly applied to a carrier such as a sheet. After that, a method is known in which the electrostatic image holding surface is opposed to the electrostatic image holding surface with a small gap, and the toner is attracted from the toner carrier to the electrostatic image holding surface by the electric charge of the electrostatic image, and the toner is adhered to the electrostatic image holding surface, thereby developing the image. (Tokuko Showa 41-
9475, US Pat. No. 2,839,400, etc.). This method has the advantage that not only the toner is not attracted to the non-image area where there is no static charge, but also the toner and the non-image area do not come into contact with each other, so that the above-mentioned fogging is less likely to occur. In addition, since carrier particles are not used, there is no variation in the mixing ratio as described above.
Furthermore, there is no deterioration of carrier particles.

However, this method (1) Practical uniform application is difficult.

(2) It is difficult to uniformly release the toner from the toner support.

(3) Due to low resolution, etc., it has not been put into full-scale practical use.

In order to prevent such drawbacks, the applicant first forms a uniform thin layer of toner on the surface, maintains a minute gap between the electrostatic image holding surface facing the sleeve, and selectively applies the high potential latent image surface. has proposed a developing method in which toner is transferred to (Japanese Patent Application No. 109237-109242, etc.).

FIG. 1 is a sectional view showing an example of such a developing device. In the figure, 1 is an electrostatic image holding means, 2
3 is a sleeve, 3 is a hopper containing a monocomponent toner 4, and 5 is a doctor blade that regulates the thickness of the toner to form a toner layer 6 of uniform thickness on the sleeve. A minute gap is maintained between the toner layer 6 and the electrostatic image holding means, and the toner flies through this gap and is attracted to the electrostatic image. 7 is Magnetrol. When an electrostatic image was visualized using this developing device, a fog-free image with high gradation could be obtained.

However, when images were continuously produced using this developing device, the following phenomenon occurred.

(1) After making 300 to 500 copies of an original with a large amount of white background, which consumes extremely little toner, when a black original was copied, the image density D had decreased from 1.3 to 1.0. Moreover, the image had noticeable unevenness in development.

(2) When I continuously copied black originals using a developing device whose image density had decreased, the image density began to recover to 1.3 after 30 to 50 copies had been made. Also, development unevenness has decreased.

(3) When the toner on the sleeve surface of the developer device where the image density had decreased in (1) above was removed and the toner in the hopper was newly adsorbed to produce an image, the image density recovered to 1.3. .

Therefore, when we measured the toner particle size on the surface of the developer sleeve where the image density had decreased in (1) above, we found that toner with a particle size of 1 to 3μ was the main component, and the toner in the hopper (average particle size of 5 to 10μ) In comparison, the particle size is clearly smaller, and it has been found that this change in toner particle size seems to cause a change in image density and uneven development.

SUMMARY OF THE INVENTION An object of the present invention is to provide a developing device that solves the above problems and prevents changes in image density due to changes in toner particle size around the sleeve.

The present invention, which achieves the above object, forms a thin layer of developer on the surface of a developer carrier, maintains a minute gap between this thin layer of developer and the surface of the electrostatic image carrier, and
A developing device for visualizing an electrostatic image by causing developer to fly from the surface of a developer carrier to the surface of an electrostatic image holder, characterized in that a thin insulating layer is formed on the surface of the developer carrier. This is a developing device. Therefore, according to this developing device of the present invention, there is no change in image density even when continuous copying is performed, and uneven development can also be prevented.

The present invention will be described in more detail below.

The phenomena (1) to (3) above are explained as follows using FIG. Here, 2 is the sleeve surface,
Assume that it is grounded. 8 indicates the magnetic toner adhering to the sleeve 2, and 0' indicates the point at which the reflection force of the magnetic toner 8 acts.

The toner that is thinly coated on the sleeve surface is always attracted by the toner charge and the toner's reflection charge, and the toner is electrostatically attracted to the sleeve surface. The magnitude of this adsorption force is expressed as f ₁ =Kq ² /r ² where r is the toner radius and q is the toner charge amount. (K; constant of proportionality). Also the radius is mr
In the case of toner, it is considered to have a charge amount m ² q proportional to the surface area, and its adsorption force is expressed as f ₂ =Km ² q ² /r ² . At this time, the adsorption force per unit weight of toner is expressed as f' = k'q ² / mr ⁵ (K'; proportionality constant), so the average particle size is 8μ (radius 4μ) and 2μ (radius 1μ).
2μ toner is adsorbed to the sleeve surface with four times the force per unit weight.

By the way, as the sleeve rotates, forces act on the toner, such as magnetic force that fluffs the toner and force that loosens the toner, such as rolling force on the sleeve, but the magnetic force acting on the toner per unit weight is
It is the same for 8μ toner and 2μ toner. For this reason,
2μ toner is more easily adsorbed to the sleeve surface layer than 8μ toner.

Once the toner is adsorbed onto the sleeve through this process, as the sleeve rotates, more charges are applied from the sleeve surface, and the toner is even more strongly adsorbed to the sleeve surface, causing the sleeve surface to be covered with a layer of fine toner powder. Become. In such a situation, the newly replenished toner is blocked by the fine toner layer and cannot contact the sleeve surface, resulting in insufficient charge, resulting in reduced density and unevenness in the reproduced image. It is thought that this will make it more noticeable.

Therefore, the present invention is characterized in that in order to prevent the formation of a fine powder toner layer on the sleeve surface, the sleeve surface is processed with an extremely thin insulator to reduce the reflection force of the fine powder toner. .

The function of the sleeve whose surface is insulated will be explained using FIG.

Here, 2 is the conductor surface of the sleeve, which is assumed to be grounded. The conductor surface has a dielectric constant ε,
An insulator layer 9 of thickness d is coded,
Magnetic toner with a radius mr is adsorbed on its surface. The thickness of this insulating layer is exaggerated for convenience of explanation. At this time, the toner reflection point is a point 2 (mr + d/ε) away from the toner center.
becomes O′.

The reflection force acting on the toner per unit weight is expressed as f″=K″mq ² /(mr+d/ε) ² r ³ (K″; constant of proportionality).

Here, when 1/(r+d/ε) ² =m/(mr+d/ε) ² holds true, it means that the toner of radius r and mr adsorbed to the sleeve per unit weight are equal.
Furthermore, since the magnetic loosening force per unit weight of toner by the magnet is equal, when the above equation holds true, selective adsorption of toner to the sleeve surface can be prevented. In order for this equation to hold true for toners with a particle size of 8μ (radius 4μ) and a particle size 2μ (radius 1μ), it is sufficient to obtain the relationship d/ε=2. When making an insulator sleeve using an insulator with a dielectric constant of 3, it is sufficient to form an insulator layer of about 6 μm on the conductive cylinder. Of course, if a toner with a different particle size is used, d/ε will change, so
Needless to say, the material and thickness of the insulator must be changed accordingly.

FIG. 4 is a sectional view of a developing device showing an embodiment of the present invention, in which the same members as in the device of FIG. 1 are given the same reference numerals.

In the figure, reference numeral 1 denotes a photosensitive drum as an electrostatic image holding means, which may of course be in the form of a belt or sheet. Reference numeral 2 denotes a developer carrying means provided opposite to this holding means, and the illustrated one is a non-magnetic cylinder (sleeve).

The electrostatic image holding means 1 moves in the direction of the arrow. At this time, by rotating the sleeve 2 in the same direction as the electrostatic image holding surface, the one-component insulating ferromagnetic toner 4 sent from the hopper 3 is applied onto the surface of the sleeve 2,
And due to the friction between this cylindrical surface and the toner particles,
Gives toner particles a charge of opposite polarity to the electrostatic image charge. The surface of this sleeve 2 is provided with an extremely thin insulating layer 10. Furthermore, the iron doctor blade 5 is placed close to the sleeve surface (with a spacing of 50 μm or more).
500μ) to reduce the thickness of the toner layer 6 (30μ to 500μ, preferably 30μ to 100μ).
and uniformly regulated. Note that 6 is a magnet roller fixedly installed inside the sleeve 2.

When the doctor blade 5 is made of a magnetic material as described above, the toner layer can be regulated to be thin and uniform.
The reason for this is shown in FIG. Now magnet roller 7
On the outer circumference of the sleeve 2, which is almost opposite to the magnetic pole N of the
When the magnetic blade 5 is provided, the magnetic lines of force 11 from the magnetic pole N are concentrated at the tip of the magnetic blade 5, and the brush-like toner continues like a curtain between the sleeve and the doctor blade, thereby preventing the toner from passing through. The toner 6 slightly dragged by the sleeve 2 only passes through the sleeve surface a little. Therefore, the toner layer 6 can be made extremely thin as described above. If a magnet is used as the doctor blade 5, the magnetic field in this part will be even stronger and more effective.

When producing an image using a developing device with this configuration, first, as a magnetic toner, 50 parts of polystyrene, 40 parts of magnetite, 3 parts of a charge control agent, and 6 parts of carbon are mixed in a well-known ratio. Particles having an average particle diameter of 5 to 10 μm were used. Of course, other known magnetic toners can also be used. As the developer carrier, an aluminum material was used as a non-magnetic material, and this was made into a cylindrical shape as shown in the figure to form a sleeve. The magnet has a magnetic pole located closest to the sleeve and the electrostatic image holding member (potential contrast of about 600 V), and the surface magnetic flux density at that time is selected to be 800 Gauss from a range of about 600 to 1300 Gauss. is.

I actually created an image based on the above content. First, the polystyrene toner was negatively charged by contact. Nylon was selected as the insulating material for the sleeve surface, and was dissolved in an organic solvent to form a thin nylon layer about 6μ thick on the aluminum sleeve by spraying or dipping. Then, using mostly blank manuscripts, 2000~
I continued to copy 3000 sheets, but the image density drop as described above did not occur.

In addition, a sleeve having the insulating layer of the present invention can be prototyped by using other insulating materials (e.g., eponite, glass, etc.) located in the same polar direction as the latent image charge on the triboelectrification series, that is, at a point away from the toner. It was hot.
When the insulating material is selected as described above, the toner can receive a sufficient amount of triboelectric charge due to the insulating material, so that a clear and good image can be obtained.

The results of experiments using prototype sleeves with different insulating layer thicknesses showed that it was possible to prevent toner from selectively adsorbing to the sleeve surface when the insulating layer had a thickness of 2μ or more. However, it was found that when the thickness of the insulating layer exceeds 20 μm, the electric field between the static image holding surface and the sleeve surface decreases significantly, resulting in a thin image in which development is suppressed from the beginning. From this, it can be said that in order to obtain sufficient image density from the beginning to the end of continuous copying, the thickness of the insulating layer on the sleeve surface is preferably about 2 to 15 microns.

The insulating layer material may be selected from materials other than resin materials. For example, using an aluminum sleeve with a 5μ thick alumite layer formed on its surface by anodizing in a 15% sulfuric acid solution, 3000~3000~
Even after 4,000 copies were made, no decrease in density occurred. Furthermore, since the sleeve has a hard surface, no scratches occur on the sleeve surface, and it exhibits stable jumping characteristics over a long period of time. At this time, when the toner particle size on the surface of the alumite sleeve was measured, it was found that the toner was mainly 5 to 10 microns in size, and there was no difference in particle size from the toner in the hopper circle.

In order to further improve the quality of the image, it is preferable to apply a bias voltage between the latent image holding means 1 and the sleeve 2 by means of a power supply 12, as shown in FIG. This bias power source 12 may be a direct current, but if it is one that provides a positive and negative alternating electric field, such as an alternating current or an alternating current that is a superimposed direct current, the edges will be clear and there will be less background fog, and the gradation will be high. An image is obtained. The reason for this is detailed in Japanese Patent Application No. Sho 53-92108, which was previously proposed by the present applicant, so the explanation thereof will be omitted here. In addition, blade 5 is also sleeve 2.
to prevent bias voltage from leaking to the blade 5.

In explaining the embodiments of the present invention so far,
We have shown an example of a method in which one-component insulating ferromagnetic toner is used to fly this toner into a minute gap between the developer support and the electrostatic image holder, but it is also possible to The present invention can also be applied to a developing method in which toner, nonmagnetic toner, or even a two-component developer is used to fly the toner from the gap toward the electrostatic image surface.

As described in detail above, the present invention maintains a minute gap between the thin layer of developer and the surface of the electrostatic image carrier, and allows the developer to fly onto the electrostatic image carrier surface through this gap. Since a thin insulating layer is formed on the surface of the developer carrier in the developing device that performs development, it is possible to prevent toner with small particle size from strongly electrostatically adsorbing on the surface of the developer carrier. It is possible to prevent changes in image density and uneven development.
In the present invention, since a thin insulating layer is formed on the surface of the developer carrier, the electrostatic adsorption force due to the mirror force of the developer to the developer carrier is reduced, and when the developer flies, the developer is not developed. The agent can be easily detached from the agent carrier, the amount of flight is increased, and the image density is improved, and the acceleration performance is also improved and the reproducibility of fine lines is also improved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional developing device, FIGS. 2 and 3 are explanatory diagrams illustrating the electrostatic attraction force between toner and a sleeve in the conventional example and the present invention, and FIG. 4 is an embodiment of the present invention. FIG. 5 is a cross-sectional view of the developing device according to an example, and FIG. 5 is an explanatory diagram of the operation of the magnetic blade. In the figure, 1... electrostatic image holding means, 2... sleeve, 3... hopper, 4... toner, 5...
Doctor blade, 6... Toner layer, 7... Magnetic roller, 8... Magnetic toner, 9, 10...
... Insulator thin layer, 12 ... Bias power supply.

Claims (1)

[Claims] 1. Forming a thin layer of developer on the surface of a developer carrier,
While maintaining a small gap between this thin layer of developer and the electrostatic image holder, the developer is caused to fly from the surface of the developer carrier to the surface of the electrostatic image holder to visualize the electrostatic image. 1. A developing device, characterized in that a thin insulating layer is formed on the surface of the developer carrier. 2. The developing device according to claim 1, wherein the developer is a one-component toner. 3. The developing device according to claim 1, wherein the toner of the developer is a magnetic toner. 4. The developing device according to claim 2, wherein the developer carrier has a magnetic field generating means for conveying magnetic toner. 5. The developing device according to claim 4, wherein the developer carrier includes a non-magnetic cylindrical body and a magnet roll. 6. The developing device according to claim 1, wherein the toner of the developer is an insulating toner. 7. The developing device according to claim 6, wherein the developer carrier is electrically conductive and a bias voltage is applied thereto. 8. The developing device according to claim 7, wherein the bias voltage is an alternating bias voltage. 9. The developing device according to claim 1, wherein the insulating thin layer is made of a material that is separated from the toner material on the triboelectrification series and located in the same direction as the electrostatic image polarity.