JPS6255147B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for visualizing an electrostatic latent image formed on a recording medium such as an electrophotographic copying machine or an electrostatic recording device.

2. Description of the Related Art Hitherto, as a developing method of a so-called one-component developer using only toner, a method called a touch-down developing method or a pressure developing method has been known. In this developing method, the toner binding force of the developing roller is extremely large, and there is almost no movement of toner on the surface of the developing roller. The ratio of the moving speeds of the photoreceptor and the developing roller is very small compared to a normal two-component developing system. For this reason, the toner used for development is limited to a specific area on the developing roller, and toner does not move from other areas on the developing roller to be used for development.

Further, a method of developing the toner by charging the toner by charge injection is also well known. In this type of development, a voltage is applied to an electrode close to the conductive developing roller, but since the entire surface of the developing roller is uniform, the toner passing through the electrode has almost no charge distribution. Not worth it. Therefore, when an electrostatic latent image is developed with such uniformly charged toner, it will either adhere to the image bearing member or not after a certain threshold value, and the resulting image will have a γ (gamma) ), that is, the halftone reproducibility becomes poor. Therefore, it is possible to apply an AC voltage to this charge injection electrode to give the toner a distribution of charge, but due to the time constant of the toner itself, if the applied voltage is too high frequency, most of the toner will be On the other hand, at a frequency that is sufficient to charge the toner, the toner will periodically have areas that are strongly charged and areas that are weakly charged, resulting in striped development unevenness as shown in Figure 1. There are things to do. In the figure, reference numeral 1 denotes a photoreceptor drum, a shaded area 2 indicates a high-density developed area, and a white area 3 indicates a low-density developed area.

The present invention has been made in view of the above points, and an object of the present invention is to provide a developing method with excellent halftone reproduction.

The present invention is a developing method in which an electrostatic latent image is developed by imparting a charge distribution to the toner to obtain an image with excellent halftone reproduction.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 2 shows a first embodiment of the present invention.
The electrostatic latent image carrier 4 is moving in the direction of the arrow. As the electrostatic latent image carrier 4, an organic photoconductor such as polyvinyl carbazole is used in this embodiment, but other photoconductors include selenium, selenium-tellurium alloy, zinc oxide, titanium oxide, and cadmium sulfide. A three-layer photoreceptor having a transparent insulating layer on the surface can also be used. Furthermore, dielectric materials on which electrostatic latent images are formed directly, such as with multi-styli, are also used. The developing device 5 is composed of a developing roller 6, a toner hopper 7, and an electrode/doctor plate 8. The developing roller 6 rotates counterclockwise at a circumferential speed slightly faster than that of the electrostatic latent image carrier 4. The developing roller 6 is provided with a conductive elastic layer 10 around a conductive shaft 9. The conductive elastic layer 10 is made of conductive silicone rubber having a volume resistivity of 10 ⁵ Ωcm or less, which is obtained by dispersing carbon in silicone rubber. Note that not only silicone rubber but also neoprene rubber, polyurethane rubber, acrylic rubber, nitrile rubber, etc. can be used. Now, the surface of this elastic layer 10 is electrically non-uniformly processed. A method for manufacturing this electrically non-uniform surface will be described below. As shown in FIG. 3, the surface of the silicone rubber layer 10 is roughly polished to a surface roughness of 30
Set it to around μmRmax. The method for measuring surface roughness is based on JIS B0601, and in Figure 3, the difference Δ between the highest point of the mountain and the deepest point of the valley is
This means that l is 30 μm.

Next, as shown in FIG. 4, silicone rubber 11 as an insulating material is spray-coated to a thickness of about 30 μm on the silicone rubber layer 10 polished as described above. This silicone rubber has a volume resistivity of 10 ¹⁵
It is Ωcm or more. Since the applied substance and the substance on the substrate side are of the same quality, their adhesion is extremely excellent, and there is almost no risk of them peeling off during subsequent machining. After a predetermined period of time, the applied silicone rubber is polished again to give a smooth surface. The surface roughness at this time was 5 μmRmax. The final configuration is as shown in Figure 5.
The electrically conductive portion 10 and the insulating portion 11 appear approximately evenly on the surface.
Note that conductive silicone rubber has a black color due to carbon, but the insulating layer can be colored in any color, so the conductive and insulating parts appear evenly during polishing. Since it is possible to process while visually checking whether or not there is a problem, accuracy is improved and it is also simple. The developing roller manufactured as described above is used in FIG. In addition, although the material was specifically limited and described above, it is not limited to this. Referring again to FIG. 2, a toner hopper 7 is disposed above the developing roller 6, and a one-component developer T (hereinafter referred to as toner) is accommodated therein. This toner is non-magnetic and insulating to the extent that it can be charged. A portion of the toner hopper 7 has a gutter-like portion 7a surrounding the lower and right side of the developing roller 6. On the other hand, an electrode/doctor plate 8 is attached to the wall 7b of the toner hopper 7. The electrode/doctor plate 8 is lightly pressed against the developing roller 6 by a spring 12, and regulates the amount of toner carried out by the developing roller 6 from the toner hopper 7 to a predetermined thickness. A +50V DC voltage V _E is supplied to the electrode/doctor plate 8, and a -250V DC voltage _VD is supplied to the shaft 9 of the developing roller 6 by power supplies 13 and 14, respectively. next,
The operation of this developing device will be explained. When the developing roller 6 rotates, the toner T in the toner hopper 7 is attracted to its surface and conveyed. Since silicone rubber and the substances listed above have excellent toner adhesion properties, toner does not fall during transportation.
There is a potential difference (VE _- V _D ) between the electrode/doctor plate 8 and the developing roller 6, in this case a potential difference of 300V, and when the toner passes under this electrode/doctor plate 8, the above potential difference The amount of charge Q/m and the polarity of charge are determined by the direction of the electric field. However, strictly speaking, the potential difference here refers to a current, and the amount of charge Q/m is determined by the current flowing from the electrode/doctor plate 8 through the toner to the developing roller 6. As described above, the developing roller 6 of the present invention has a mixture of conductive parts and insulating parts on its surface and is electrically non-uniform, so the current flowing through the toner is not constant in all parts. do not have. Therefore, the toner has a so-called charge distribution with various amounts of charge. Of course, one toner has one charge amount. According to this method, the amount of charge on the toner is 3
It has a distribution of μc/g to 15 μc/g.

Next, experimental results of the present invention will be explained. In the apparatus shown in FIG. 2, a toner having a pressure contact resistance of 10 ¹⁶ Ωcm was used. The measurement was performed under the conditions of applying a pressure of 400 g/cm ² and an electric field of 500 V/cm. The contact pressure of the electrode/doctor plate 8 is 600 g/cm ² , and the toner layer thickness is approximately
30 μm, the circumferential speed of the developing roller 6 was 130 mm/sec, the circumferential speed of the photoreceptor was 100 mm/sec, and the contact pressure of the developing roller 6 to the photoreceptor was 1 Kg/cm ² .
I was able to obtain an image with excellent halftone reproduction. This is shown in FIG. In the figure, the broken line shows the case where a conventional developing roller having uniform conductivity is used, and the solid line shows the case where the developing roller of the present invention is used. According to this, it can be seen that the γ curve of the developing method according to the present invention is sloped compared to that of the conventional developing method. Moreover, it has become possible to reimage gradations even in high-potential areas and low-potential areas.

Now, as for a method of obtaining an electrically non-uniform surface of the developing roller 6, it is also possible to make it as follows. For example, insulating fine particles with a particle size of about 10 μm are dispersed in a conductive member, or an insulating layer is formed on the conductive member and then etched to expose the conductive part with an appropriate size and distribution density. There are ways to do this.

FIG. 7 shows yet another embodiment of the invention. This developing device is characterized by a configuration suitable for magnetic toner. The developing roller 20 is composed of a nonmagnetic sleeve 21 that rotates in the direction of the arrow and a magnet 22 fixed inside the sleeve. The magnet 22 is magnetized alternately with north and south poles. The non-magnetic sleeve 21 has the structure shown in FIG. A third layer is placed on a non-magnetic conductive substrate 23 such as aluminum.
An electrically non-uniform surface is formed by the method shown in FIGS. Normally, the appropriate thickness of the conductive rubber layer 10 is about 1 mm. A toner hopper 7 is provided above the developing roller 20, and a chargeable one-component magnetic toner T _M is accommodated therein. The electrode/doctor plate 24 is a non-magnetic sleeve 21
The toner hopper 7 is mounted opposite to the toner hopper 7. The tip of the electrode/doctor plate 24 and the sleeve 21
An appropriate gap is formed between the two. Of course, the sleeve 21 and the electrostatic latent image carrier 4 are also spaced apart by a predetermined distance. A voltage V _E is applied to the electromagnetic doctor plate 24 by the power supply 13, and the sleeve 21
The developing bias voltage V is also controlled by a power supply (not shown).
_D is applied. The magnetic toner is held on the surface of the sleeve 21 by the magnetic force of the magnet 22, is transported in the rotational direction of the sleeve 21, and is charged when passing under the electrode/doctor plate 24. In this case as well, the magnetic toner has a charge distribution. Then, the electrostatic latent image is developed with a magnetic brush formed on the sleeve 21. During development, since the sleeve 21 had an electrically non-uniform surface, the developing bias also had a wide range, and it was therefore possible to obtain a developed image with excellent halftone reproduction.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a developed image developed by applying alternating current to a conventional charge injection electrode, FIG. 2 is a sectional view of a developing device showing a first embodiment of the present invention, and FIGS. 3 to 5 6 is a diagram showing the experimental results of the present invention, and FIG. 7 is a cross section of a developing device showing a second embodiment of the present invention. 8 are partially enlarged sectional views of the nonmagnetic sleeve used in the developing device of FIG. 7. 4... Electrostatic latent image carrier, 5... Developing device, 20
...Development roller, 8, 24 ... Electrode and doctor plate, 10 ... Conductive elastic layer, 11 ... Insulating material, 21 ... Nonmagnetic sleeve, 22 ... Magnet,
T, T _M ... Toner (magnetic toner).

Claims (1)

[Claims] 1 A monocomponent developer is attached to a developer carrier whose surface has a mixed distribution of conductive parts and insulating parts, and an electrode to which a voltage is applied is brought into contact with the attached monocomponent developer. , the one-component developer is charged to a predetermined polarity with a charge distribution according to the mixed conductive portion and insulating portion by the potential difference between the electrode and the developer carrier, and then the one-component developer is An electrostatic latent image development method that develops an electrostatic latent image using a developer.