JPH0360436B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dry developing device that visualizes an electrostatic latent image formed on a latent image carrier using a one-component developer carried on a developer carrier.

Developing devices of the above type used in electronic copying machines, electrostatic recording devices, and other various recording devices are well known in the art. In this case, the electrostatic latent image to be visualized can be roughly divided into high and low spatial frequencies: so-called line images (linear electrostatic latent images) consisting of high spatial frequency components, and low-spatial latent images. It can be divided into so-called solid images (planar electrostatic latent images) consisting of frequency components, and different requirements are imposed on visualizing these line images and solid images. In other words, for a solid image, it is necessary to obtain a visible image with a density that roughly corresponds to the height of the surface potential, and for a line image, it is necessary to obtain a visible image with a density that approximately corresponds to the level of the surface potential, and for a line image, the surface potential is It is required to obtain a visible image with high density considering the potential. These requirements can be met relatively easily by using a two-component developer containing toner and carrier. However, with conventionally known developing devices that use a one-component developer that does not contain a carrier, it is not easy to meet the above requirements, or even if this requirement can be met, the development efficiency is significantly reduced. I couldn't escape the inconvenience.

From the above-mentioned viewpoint, the present applicant has developed a developing device that can satisfy the above-mentioned requirements to a fairly high degree even when a one-component developer is used, without significantly reducing development efficiency. The structure of the developer carrier was proposed (Japanese Patent Application No. 185726/1982).
The developer carrier according to this proposal includes a conductive support and a large number of minute float electrodes that are substantially electrically insulated from the support and from each other. This float electrode acts in the same manner as a carrier in a two-component developer, and can substantially satisfy the requirements described above. As described above, the developing device according to this proposal can provide excellent advantages.
However, one problem with this type of developing device is that charge accumulates on the float electrode, and if the amount of charge becomes excessive, the quality of the visible image deteriorates.

The present invention has been made based on the above recognition,
It is an object of the present invention to provide a dry type developing device that can prevent an excessive amount of charge from accumulating on a float electrode with a simple configuration.

Advantageous embodiments of the invention will be explained below with reference to the drawings.

FIG. 1 is a partial view of an electronic copying machine having a developing device according to the present invention. Although the present invention is applicable to various types of developing devices other than the developing device shown in FIG. 1, in order to understand the present invention, an outline of the configuration shown in FIG. 1 and an outline of its operation will first be explained. do.

A developing device 1 shown in FIG. 1 has a developer carrier formed as a sleeve 2.
A plurality of magnets 3, four in this example, are provided inside, and these magnets are fixedly supported by a support roller 4. The magnetic poles of each magnet 3 facing the sleeve 2 are alternately of opposite polarity. In this example, magnet 3
is rotated counterclockwise together with its support roller 4, and the sleeve 2 is also rotated counterclockwise. It is well known that one of the two may be fixed immovably. The sleeve 2 is provided with a large number of float electrodes, which will be explained in detail later.

Reference numeral 5 denotes a tank containing developer 6, and the sleeve 2 is located in the lower opening of this tank. In this example, a one-component high-resistance magnetic developer (hereinafter referred to as toner) consisting of toner particles and other components other than a carrier, which are mixed with the toner particles as necessary, is used as the developer 6. There is. The specific volume resistivity of this toner as a whole is 10 ¹⁰ Ω-cm or more, particularly 10 ¹³ to 10 ¹⁴ Ω-cm or more. 7 is a stirring blade that stirs the toner 6 in the tank;
is a blade that regulates the layer thickness of the toner on the sleeve 2, and the blade 8 in this example is made of an elastic magnetic material, and is supported with its tip pressed against the surface of the sleeve 2. ing. It goes without saying that modifications can be made, such as making the blade 8 of a non-magnetic material or pressing the surface of the blade against the sleeve 2. Further, 9 is a conductive support 10 (second
It is a power supply that applies a bias voltage to 11
is a static elimination lamp, and the operation of this lamp 11 will be explained later.

In the copying machine shown in FIG. 1, the latent image carrier is constructed as a drum-shaped photoreceptor 12, and this photoreceptor 12 is positioned parallel to the sleeve 2. It goes without saying that a sheet-like or belt-like photoreceptor may be used instead of such a drum-like photoreceptor.

When the copying operation is started, the photoreceptor 12 is rotationally driven in a predetermined direction (clockwise in this example), and at this time, an electrostatic latent is formed on the surface of the photoreceptor by a latent image forming means (not shown). An image is formed. This latent image is formed between the sleeve 2 and the photoreceptor 12 as the photoreceptor 12 rotates.
, the developing area D.

On the other hand, the toner 6 in the tank 5 is supplied to the circumferential surface of the sleeve 2 while being stirred by the rotation of the stirring blade 7 . At this time, both the sleeve 2 and the magnet 3 rotate counterclockwise, and the toner supplied to the circumferential surface of the sleeve 2 is attracted and repelled by the action of the rotating magnetic field generated by the rotating magnet 3, as is well known. Under the force, it is conveyed counterclockwise along the circumferential surface of the sleeve while vibrating, and is sent out of the tank. In this case, in this example, the magnet 3 rotates counterclockwise, so the toner on the sleeve 2 receives a clockwise conveying force, but the counterclockwise rotation of the sleeve 2 causes a force to be conveyed. Since the force for conveying the toner in the counterclockwise direction is greater, the toner is conveyed in the predetermined counterclockwise direction. Note that by rotating the magnet 3 in this manner, the quality of the visible image on the photoreceptor, which will be described later, can be improved. Furthermore, since the blade 8 is made of a magnetic material, the blade is attracted to the sleeve side not only by the elastic force of the blade itself but also by the magnetic force of the magnet 3 installed inside the sleeve 2, and as shown in the figure, the blade 8 is attracted to the sleeve side by the magnetic force of the magnet 3 installed inside the sleeve 2. It is pressed against the surrounding surface. Therefore, the toner sent out from the tank 5 is pressed against the sleeve surface by the blade 8, and the amount of toner passing through the blade 8 is
Therefore, the thickness of the toner layer on the sleeve is regulated to be thin. The thickness of the toner layer 6a after passing under the blade is preferably about one to two toner particles. 6b shows a toner pool scraped off by the blade 2.

The toner whose thickness is regulated to be thin is carried on the circumferential surface of the sleeve 2 and continuously conveyed in the counterclockwise direction, and is brought to the development area D described above. In this case, by the time the toner reaches the development area D, it has been charged to a predetermined polarity, which in this example is opposite to the polarity of the charge forming the electrostatic latent image. As will be explained in more detail below, it electrostatically adheres to the latent image, rendering the latent image visible. Toner that does not adhere to the photoreceptor is returned to the tank. As is known per se, toner charging is
This can be carried out as appropriate by friction between the surface of the blade 8 or sleeve 2 and the toner, friction between the toner and a charging member (not shown), or charge injection into the toner using a corona discharger (not shown).

The structure of the developing device shown in FIG. 1 and its operation have been outlined above. Next, the float electrode and its related structure will be explained in detail. The float electrode can produce a line image and a solid image of an electrostatic latent image while almost satisfying the above-mentioned requirements.
This is a configuration for visualization, and FIGS. 2a and 2b are explanatory diagrams schematically showing how a line image and a solid image are visualized.

In FIGS. 2a and 2b, the photoreceptor 12, also shown in FIG. 1, and the sleeve 2 face each other in the development area D (see also FIG. 1). The photoreceptor 12 shown as an example consists of a conductive substrate 13 and a photosensitive layer (for example, a photoconductor layer of selenium, organic semiconductor, etc.) 14 provided on the surface of the conductive substrate 13, as is well known. The sleeve 2 includes the previously described conductive support 10 formed into a cylindrical shape, the electrode support material 15 provided on the surface thereof, and the many previously described micro float electrodes 16 fixedly supported thereby. It has Each float electrode 16 has a diameter of, for example, 10μ to 500μ.
It consists of conductive fine particles having a suitable shape and size, and the fine particles may be magnetic or non-magnetic. For example, fine particles of copper, bronze, iron, nickel, ferrite, stainless steel, etc. can be advantageously used. Preferably, at least a portion of the float electrode is exposed on the surface of the sleeve, and each float electrode is attached to the electrode support material 15.
They are spaced apart from each other and also from the support 10 via. Further, when the toner is conveyed by magnetic force as in this example, a non-magnetic material such as aluminum or stainless steel is used as the conductive support 10. The electrode support material 15 that supports the float electrode 16 is selectively made of a material that exhibits conductivity and insulation properties, and at least the portion of the electrode support material that exists in the development area D during the development operation is made of a material that exhibits insulation properties. It is composed of In this example, the electrode supporting material 15 is made of a photoconductive material, such as selenium or an organic semiconductor, which exhibits insulating properties in the dark and becomes conductive when irradiated with light. In the electronic copying machine, development is performed in the dark, and therefore the electrode support material portion existing in the development area D exhibits insulating properties, and each float electrode 16 is substantially insulated from the support 10 and also from each other. can maintain an insulated state.

Now, as described above, toner charged to a predetermined polarity is located between the sleeve 2 placed in the above-described state and the photoreceptor 12 in the developing area D. Toner is not shown in a and b for clarity of illustration. In this case, in the configuration shown in FIG. 2, for convenience of explanation, the charging polarity of the toner is assumed to be negative. Further, electrostatic latent images L ₁ and L ₂ are formed on the photosensitive layer 14 of the photoreceptor 12 by charges having a polarity opposite to that of the toner, that is, positive charges in this example, and one latent image L ₁ is a linear line image, and the other latent image is a planar solid image. Other than the form of the latent images L ₁ and L ₂ , the configurations shown in FIGS. 2a and 2b are exactly the same.

As explained above _, the toner carried on the sleeve ₂ and not shown in FIG. The image is visualized, but the amount of toner that adheres to the latent images L ₁ and L ₂ at this time largely depends on the strength of the electric field near the surface of the photosensitive layer 14.
The stronger the electric field, the more toner adheres to the latent images L ₁ and L ₂ , and the higher the density of the developed visible image. Therefore, let us consider the strength of the electric field generated based on the charge of each latent image L ₁ and L ₂ . First, if the electrostatic latent image is a line image as shown in _FIG . However, as shown in FIG. 2a, the light is directed toward the background portion of the photosensitive layer 14 (the portion where the latent image _L1 is not formed). This is because, despite the presence of the conductive support 10 that acts as a counter electrode to the photoreceptor 12, they are electrically insulated from each other and from the support 10. This is because a large number of minute conductive float electrodes 16 are located near the photosensitive layer 14. In other words, when the float electrode 16 is present, the number of electric lines of force coming out from the latent image L ₁ and heading toward the background increases compared to when the float electrode 16 is not present. This means that when the float electrode 16 is provided, the latent image L ₁
This is because the dielectric thickness from the to the bare surface can be reduced. The phenomenon in which an electric field is generated between the latent image _L1 and the background is called the edge effect, and by providing the float electrode 16, this edge effect can be increased. It is. Therefore, the strength of the electric field in the vicinity of the surface of _the latent image _L1 shown in FIG. The density of the visible image increases.

On the other hand, the electrostatic latent image L ₂ of the solid image shown in FIG.
In this case, the electric lines of force emanating from the central region excluding the edges of the latent image L ₂ are directed toward the conductive support 10 as the counter electrode. This is because the dielectric thickness from this central region to the support 10 is smaller than the dielectric thickness from the central region of the latent image L ₂ to the background portion of the photosensitive layer 14 . Such a phenomenon occurs in the same manner even if the float electrode 16 is not present. In other words, for solid images,
The electric field strength near the surface of the central region of the latent image _L2 is not greatly affected by the presence or absence of the float electrode.

As can be seen from the above description, by providing the float electrode 16, it is possible to particularly improve the efficiency of line image processing. This relationship is expressed as the relationship between the density of the original image to be copied and the density of the copied visible image as shown in FIG. FIG. 3 is a graph showing the density of the original image on the horizontal axis and the density of the copied visible image on the vertical axis.
A broken line A indicates the density of a visible image obtained from a line image, and a solid line B indicates the density of a visible image obtained from a solid image. As can be seen by comparing the dashed line A and the solid line B, the rising slope of the dashed line A is the same as that of the solid line B.
This means that line images are visualized with higher development efficiency than solid images. Ordinary operators usually want to clearly reproduce thin line images (line images) of originals even if the density is low, and want to obtain high-density copied images. Regarding (solid images), it is normal to want to obtain a copy image with a density that corresponds to the density of the original image. Considering this point, it is possible to perform the phenomenon in the form shown by broken line A and solid line B. I can understand that this is a good thing. This also corresponds to the requirements described above as a requirement when visualizing a line image and a solid image.

The configuration of the float electrode described above and its effects are the same as in the previously proposed configurations. Then, the sleeve portion that has undergone the development operation as described above and passed through the development area D moves toward the tank 5 again, and the above-mentioned operation is repeated again, but when this operation is repeated, the float electrode is constantly If the electrodes are insulated from each other with respect to the support 10, there is a risk that charges will accumulate in the float electrode. In order to prevent this inconvenience, in the illustrated embodiment, the above-mentioned static elimination lamp 11 is provided at a location other than the developing area D, and this lamp 11 is configured to irradiate light onto the sleeve surface that has passed through the developing area D. It's getting old. As a result, the electrode support 15 made of a photoconductive material in the sleeve 2 becomes a conductor, and the charges that would have accumulated in the float electrode 16 are discharged, and the potential of the float electrode 16 becomes substantially equal to the potential of the conductive support 10. are identical. When no bias voltage is applied to the conductive support, the potential of the float electrode can be lowered to approximately 0 volts by grounding the sleeve. In this way, the inconvenience caused by the accumulation of charge on the float electrode can be easily eliminated.

The cause of charge accumulation on the float electrode 16 when the static elimination lamp 11 is not provided is as follows.
Various types can be mentioned, but the representative ones are as follows.

When a high-resistance toner is used as the toner, as in the developing device shown in Figure 1, the toner is forced to a predetermined polarity before being used for development so that the latent image can be visualized without any trouble. As explained above, it is necessary to electrically charge the battery. At that time, the surface of the sleeve 2, especially the float electrode 16
When the toner is charged by friction between the toner and the toner carried while being carried on the surface, the float electrode 1 exposed on the surface of the sleeve
6 is triboelectrically charged to have a polarity opposite to that of the toner, and the charge is thereby accumulated on the float electrode. and,
If the accumulated charge is left undischarged, each float electrode will become electrically saturated, and even if the toner is brought into frictional contact with the float electrode,
It becomes impossible to substantially charge the toner, and if such a situation occurs, the toner does not adhere to the latent image or becomes difficult to adhere to the latent image, and it is impossible to avoid a decrease in development efficiency and a decrease in the quality of the visible image. Can not.

Furthermore, the float electrode 16 that has reached the development area D is
When facing the latent image on the surface of the photoreceptor, the electrode 16
However, it is also conceivable that the float electrode 16 is charged by electrostatic induction due to the charges forming the latent image, and that the charges are accumulated in the float electrode 16. In this case, the float electrode is given a charge of opposite polarity to that of the latent image, that is, the same polarity as the charge polarity of the toner in this example, but this charge accumulates on the float electrode, and If the amount is too large, toner tends to adhere to the background portion of the photoreceptor surface during the next developing operation, and so-called background staining becomes noticeable. Furthermore, a large amount of toner usually adheres to the local area of the latent image, causing image unevenness in the visible image.

As described above, depending on the form of the developing device, there is a possibility that charge may accumulate on the float electrode due to various causes, but with the configuration according to the present invention, this inconvenience can be easily eliminated, as explained earlier. .

In the above embodiment, the electrode support material was made of a photoconductive material, and a static elimination lamp was used as a means to make it conductive. A known pressure conductive material is used, and as shown in FIG. 4, a pressure roller 111 rotating in the direction of the arrow is brought into pressure contact with the sleeve 2 in place of the static elimination lamp, and the electrode support material 15 after passing through the development area D. (Second
It is also possible to apply pressure using the roller 111 to make the float electrode conductive, thereby dissipating the charge on the float electrode. It goes without saying that a pressure plate or the like may be used instead of the pressure roller 111.

The means for making the electrode support material 15 conductive, that is, the pressure plate, the pressure roller 111, or the static elimination lamp 11,
It can be clearly understood from the above description that it can be provided at any appropriate location other than the development area D. However, in the case where the toner sent out from the tank 5 and conveyed to the development area D is attracted to the sleeve not only by magnetic force but also by electrostatic force acting on the float electrode and the toner. However, if the above means is provided between the toner outlet area and the development area of the tank, the charge on the float electrode will become too small and it will be difficult to connect the float electrode and toner with electrical force. It is advantageous to provide the means downstream of the development area D in the toner transport direction, as shown in FIGS. 1 and 4.

Further, in each of the above embodiments, the entire electrode support material 15 was made of a photoconductive material or a pressure conductive material, but as shown in FIG. and the electrode 1
The electrode support material 15 is divided into a second electrode support material portion 15b that is not in direct contact with the electrode support material 6, and only the first portion 15a is made of a photoconductive material or a pressure conductive material, It is also possible to configure this portion 15a to be grounded, for example.

The present invention can also be applied to developing devices other than those shown in the drawings, for example, developing devices using a one-component resistive magnetic developer or a one-component non-magnetic developer (regardless of whether it is a low-resistance developer or a high-resistance developer). It is well known that when a non-magnetic developer is used, it is not necessary to use a magnet to transport it, and when a low-resistance developer is used, the toner is charged by electrostatic induction due to the charge of the latent image. It is as follows. Further, the present invention is applicable not only to electronic copying machines, but also to developing devices in electrostatic recording devices or other various printers, developing devices in direct copying type recording devices that use a latent image carrier as the final recording paper, and developer It goes without saying that the present invention can also be advantageously applied to a developing device or the like in which the carrier is configured as a belt rather than a sleeve.

As can be understood from the above description, according to the present invention, the intended purpose can be achieved with a simple configuration.

[Brief explanation of drawings]

FIG. 1 is a partial diagram of an electronic copying machine equipped with a developing device according to the present invention, FIGS. 2a and b are explanatory diagrams illustrating the operation of visualizing a latent image, and FIG. 3 is an original image FIG. 4 is a graph similar to FIG. 1 showing an example different from FIG. 1, and FIG. It is a cross-sectional explanatory view showing a specific example. DESCRIPTION OF SYMBOLS 1...Development device, 6...Developer, 10...Support, 15...Electrode support material, 16...Float electrode, L1 _{, L2} ...Latent image.

Claims (1)

[Scope of Claims] 1. A dry developing device that visualizes an electrostatic latent image formed on a latent image carrier using a one-component developer carried on a developer carrier, comprising: The carrier has a plurality of minute float electrodes supported on a conductive support via an electrode support material, and at least a part of the electrode support material is a material that selectively exhibits conductivity and insulation. and a means for making at least a portion of the electrode support material conductive is provided at a location other than the development area where the electrostatic latent image is visualized. The dry developing device.