JPS6313183B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for developing an electrostatic latent image formed on an electrostatic latent image bearing member of an electrophotographic copying machine, an electrostatic recording device, etc. This relates to a method of developing by injecting charges to a predetermined polarity.

Conventionally, a one-component developer is charged using an electrode,
The method for developing the electrostatic latent image was as shown in FIG. That is, in FIG. 1, reference numeral 1 denotes a photosensitive drum which is an electrostatic latent image carrier.
A developing roller 2, which is a developer donor and rotates in contact with the developer roller 2, is provided. The developing roller 2 has conductive silicone rubber 3 on its surface, and has a core metal 4.
is grounded. 1 on the top of the developing roller 2
A toner hopper 6 containing a component developer (hereinafter referred to as toner) 5 is provided, the toner is supplied onto the developing roller 2, and an electrode 7 is used to transfer the toner to a polarity opposite to that of the electrostatic latent image on the photoreceptor. is charged with electricity. A DC voltage having a polarity opposite to that of the electrostatic latent image is applied to the electrode 7. Such a developing method is convenient for developing line images such as characters, but has poor reproducibility of halftone images.

In other words, the method of applying a DC voltage to the electrode makes the amount of charge on the toner layer on the developing roller almost uniform, so the quality of the developed image is poor in reproducibility, especially in the case of halftone images, and the gradation is poor. The result is a poor image.
This is due to the steep slope of γ (gamma) of tone reproducibility. Therefore, this is convenient for line images such as characters, but for halftone images, the γ (gamma) as described above causes the image to suddenly turn black from a certain density and cannot be reproduced at lower densities.
This results in an off-line expression and a hard-lined copy.

By the way, in general, in order to reproduce halftones,
It has been attempted to give a distribution to the amount of charge on the toner, and one method for this purpose, for example, is to change the particle size distribution of the toner since there is a correlation between the toner particle size and the amount of charge. However, with one-component developers, when copying operations are repeated for a long period of time, classification occurs due to mechanical agitation in the developing device, friction with the blade that acts as a doctor, etc., and the initial particle size distribution gradually becomes uneven. There was a characteristic that the particle size distribution changed and the image quality changed. This is considered to be a type of change in the developer over time. For this reason, it is not possible to change the charge amount distribution of the toner by changing the particle size distribution of the toner.

The present invention has been made in view of the above points, and an object of the present invention is to provide a new developing method that changes the charge amount distribution of toner without changing the particle size distribution of the toner and obtains an image with excellent gradation. This is the purpose.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows an embodiment of the present invention.
In the figure, a photosensitive drum 1 serving as an electrostatic latent image carrier is rotating at a constant speed in the direction of the arrow. Although an organic photoconductor is used as the photoreceptor, other materials such as zinc oxide, selenium, and cadmium sulfide can also be used. Furthermore, a three-layer photoreceptor having a transparent insulating layer on the surface can also be used. In this case, the image is created by a special process such as a polarity reversal method or an NP process instead of the Carlson process. Note that the photoreceptor drum 1 is not drum-shaped but may be belt-shaped or flat plate-shaped. A developing roller 8 serving as a developer donor is arranged to the left of the photoreceptor drum 1 so as to rotate at the same speed as the circumferential speed of the photoreceptor drum 1 or at a slightly higher speed. The developing roller 8 is composed of a conductive core metal 9 and a conductive elastic layer 10 formed thereon. The conductive elastic layer 10 is made of silicone rubber, polyurethane rubber, styrene rubber, etc., which has been treated to be conductive. Since this material has excellent adhesion to toner, it is suitable for conveying toner while adhering to its surface. The conductive elastic layer 10 is moving with a slight pressure applied to the surface of the photoreceptor drum 1 via the toner layer. A toner hopper 11 made of an electrically insulating material is arranged above the developing roller 8, and the non-magnetic toner 5 is accommodated inside the toner hopper 11. The volume resistivity of the toner is 10 ³ Ωcm or more, more preferably 10 ⁶ Ωcm or more. That is, the toner is an insulating toner from a semiconductor, and a conductive toner is not preferable in terms of toner charging. An electrode 12 is provided on the toner discharge side of the toner hopper 11, and the tip thereof is formed into a sharp shape. The electrodes are made of conductive material. The tip of this electrode 12 is close to the developing roller 8,
The thickness of the toner layer of the toner carried out from the toner hopper 11 is regulated to form a toner layer with a constant thickness.

Now, the core bar 9 of the developing roller 8 is connected to a DC bias power source 13, and a bias voltage _VB that is equal to or slightly higher than the background potential of the image area of the photosensitive drum 1 is applied thereto. On the other hand, the electrode 12 is connected to an AC bias power supply 14 via a switch 15, and an AC voltage V _E is applied thereto. AC bias power supply has AC100V on the primary side and electrode 12 on the secondary side.
It consists of a step-up transformer connected to By the way, the charging polarity and amount of the toner on the developing roller 8 are generally determined by the potential difference between the developing roller 8 and the electrode 12. Of course, it changes depending on the material of the toner and the rotational speed of the developing roller 8, but for the sake of explanation, these are assumed to be constant. In this embodiment, the photosensitive drum 1
The upper electrostatic latent image has a potential of -800V, and the background part has a potential of -120 to 150V. The bias voltage applied to the core bar 9 is -150V. Therefore, in order to positively charge the toner, the voltage applied to the electrode 12 must be on the positive side rather than -150V. Since an AC voltage is applied to the electrode 12, there is no problem during the positive half cycle of AC, but if it becomes more negative than -150V during the negative half cycle, the toner will be negatively charged. So you have to be careful. It goes without saying that similar precautions must be taken when toner is negatively charged. By the way, when the toner is injected with charge by the electrode 12, it is naturally tribo-electrified and the charge level is shifted. Therefore, the materials of the toner and the electrode and the alternating current voltage are adjusted in advance so that the polarity is on the shifted side. By determining the maximum and minimum values, it becomes possible to obtain only toner that is charged either positively or negatively, that is, the desired polarity. Now, when an AC voltage is applied to the electrode 12, the potential difference between the electrode 12 and the developing roller 8 changes every moment.
Therefore, the charge distribution of the toner changes. When considering only this charge distribution, it goes without saying that it is possible to further change the charge distribution to a desired one by changing the frequency of the alternating current or the rotational speed of the developing roller 8.

Now, the charged and exposed photosensitive drum 1 is sent to a developing section. The developing roller 8 carries out the toner in the toner hopper 11 in the direction of the arrow by the toner adhesion force of the conductive elastic layer 10, regulates the toner to a predetermined thickness by the electrode 12, and sends the toner to the developing section. When the toner passes under the electrode 12, its charge amount Q/m (charge amount per unit weight) is determined, but since an alternating current is applied to the electrode 12, the charge amount distribution is Depending on the voltage, the toner will have various amounts of charge.

In general, in one-component development, the amount of toner transported (the amount of toner transported per unit time) to transport the toner to the part of the photoreceptor where the electrostatic latent image is developed is much larger than in two-component development. . Therefore, as described above, there is a tendency that images tend to have a strong γ (gamma) gradient in tone reproduction characteristics. Therefore, as a means to alleviate this problem, the amount of charge injected into the toner, that is, the amount of electrification, is reduced to substantially regulate and control the amount of toner conveyed.

In this way, the toner having a charge distribution is brought into contact with the photoreceptor drum 1, and an electrostatic latent image is developed.
During development, the core metal 9 is used as the development bias voltage V _B.
Since a voltage is applied to , it is possible to obtain an image free from background stains. By the way, after copying is complete,
When the developing roller 8 stops rotating, the switch 15 is turned off to cut off the bias voltage V _E applied to the electrode 12. This is done to prevent the characteristics of the toner under the electrode 12 from changing due to the voltage being applied for a long time, and for other safety reasons.

In the above embodiment, an electrophotographic copying machine using a photoreceptor is described, but a dielectric material is used, and a recording stylus such as a multi-stylus is used to record electrostatic charges on the dielectric material in accordance with electrical signals. The same method can be applied to the development of an electrostatic recording device that imparts . Also,
Needless to say, the present invention can also be applied to the developing method of electrophotographic copying machines and direct copying machines that use zinc oxide paper as the photoreceptor.

Furthermore, although non-magnetic toner has been described as a toner, development can be similarly performed using a one-component magnetic toner. In this case, the developing roller is composed of a non-magnetic inner cylindrical sleeve with a magnet arranged inside, and the magnet and sleeve are moved relative to each other to magnetically attract the toner onto the sleeve and brush it against the magnetic brush. It is of the type that forms.
Then, in the same manner as described above, the magnetic toner on the sleeve is charged by the electrode, brought into contact with the electrostatic latent image, and developed. This toner has a volume resistivity of 10 ³ Ω.
cm or more.

As described above, according to the present invention, while the one-component developer is transported by the developer donor, it is charged by the electrode to which an alternating current voltage is applied, so that it has a charge amount distribution and has a gradation level. Images with excellent reproducibility can be obtained.

[Brief explanation of the drawing]

Figure 1 is a diagram for explaining the conventional developing method.
FIG. 2 is a sectional view of a developing device showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Electrostatic latent image carrier, 2, 8... Developer donor, 3, 10... Conductive elastic layer, 5... 1-component developer, 7, 12... Electrode, 14... AC power supply.

Claims (1)

[Claims] 1 Supplying a single-component developer to a rotating developer donor having a conductive surface, and bringing an electrode to which a voltage is applied into contact with the single-component developer. In an electrostatic latent image developing method for developing an electrostatic latent image on an electrostatic latent image carrier facing the developer donor by charging it to a predetermined polarity, a An electrostatic latent image developing method characterized by applying an alternating current voltage.