JPH0226224B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a developing device for electrophotography or electrostatic recording, and more specifically, the present invention relates to a developing device for electrophotography, electrostatic recording, etc. The present invention relates to a developing device that performs development by supplying developer to the photosensitive drum using the developing roll.

Prior Art Developers are broadly classified into so-called two-component developers that use a carrier and toner, and single-component developers that use only toner. The former is a toner in which a coloring agent such as carbon black is dispersed in a binder resin, and a carrier such as iron powder glass beads are stirred and mixed together and triboelectrically charged. The development method using this developer has the advantage of providing excellent image quality, but on the other hand, it is necessary to control the toner concentration in the developer at a constant level, and the toner adheres to the carrier surface and gradually becomes triboelectrically charged. However, this method has the disadvantage that the performance is lowered and the image deteriorates. Furthermore, the entire device used for carrying out the method is large in size, and it has the disadvantage that it is not satisfactory in terms of cost and maintenance.

The latter is largely divided into so-called one-component non-magnetic toner, which has a colorant such as carbon black dispersed in a binder resin, and so-called one-component magnetic toner, which has magnetic powder dispersed together with a colorant such as carbon black in a binder resin. Separated. Although the development method using one-component magnetic toner can be carried out with a simple device using a magnetic roll, it lacks image quality, especially the reproducibility of fine lines, and the uniform reproducibility of low-density solid images, and furthermore, it is difficult to use a magnetic roll. There is a limit in terms of cost. In particular, in the case of development using one-component magnetic toner, in a method in which charge is applied to the toner by electrostatic induction, the toner charge amount and image quality depend on the development electric field strength determined by the gap between the photoreceptor and the development roll. On the other hand, the direction in which the electric field is made stronger has problems such as damage to the photoreceptor and maintaining the gap between the photoreceptor and the developing roll.

On the other hand, a developing method using a one-component non-magnetic toner (a toner material in a so-called two-component developer) charges the one-component non-magnetic toner with a corona, a blade, a charging roll, etc. to form a strong electric field and generate a low potential. By fully developing the latent image, it is possible to obtain a solid image with excellent uniformity without edge effects, and because it does not use a magnetic roll, it is small, lightweight, and
This has the advantage that an inexpensive developing device can be obtained.

Conventional developing devices using single-component non-magnetic toner are
JP-A-47-13089, JP-A-53-26135, JP-A-56-
14242, etc., are known, and the developing roll is made of silicone rubber with a conductive treatment applied to the core metal, or one coated with a porous rubber layer (sponge), and furthermore, a conductive silicon tube is coated on the surface of the developing roll. Adhesive coatings are used, and surface hardness etc. are taken into consideration. (Hereinafter, the developing roll will be referred to as a donor roll.) In addition, as a method of imparting a charge to the toner, a blade or a corona charger whose charging polarity and charging sequence with respect to the toner material are appropriately selected,
Furthermore, a method has been proposed in which the carrier material and toner are triboelectrically charged to a sufficient level on a roll, and then the toner is transferred onto a donor roll.

However, although donor roll development methods using these one-component nonmagnetic toners can obtain the desired toner charge amount and charge polarity, when developing an electrostatic latent image, the toner layer on the donor roll is extremely thin. (20 to 50 μ), it is impossible to maintain the gap between the latent image carrier and the donor roll using mechanical methods. A pressure welding method is also used. However, when the donor roll is pressed against the latent image carrier, charged toner uniformly adheres to image areas and non-image areas on the carrier, resulting in a serious problem of fogging. Countermeasures for this problem include applying a bias voltage to the donor roll, controlling the hardness, conductivity, etc. of the elastic body, and selecting the adhesion force between the toner material and the donor material from each other, and using it as a development drag. Attempts have been made to make this work, but the method of controlling using the developing bias has the disadvantage that low density reproducibility is poor and high-contrast images cannot be obtained due to the application of a bias potential higher than the background potential of the photoreceptor. have. Furthermore, no effective means has been found for achieving both fogging and image quality in any of the countermeasures. Furthermore, in order to obtain a sufficient amount of toner charge, it is essential that the toner layer on the donor roll be a thin layer, and if an elastic member such as a rubber roll is used, the accuracy with respect to the straightness of the roll will decrease. Therefore, the toner has the disadvantage that it tends to have uneven thickness and even pressure unevenness on the donor roll, which tends to cause density unevenness in the image.

Purpose of the Invention In view of the above-mentioned drawbacks of conventional devices, it is an object of the present invention to provide a developing device using a single-component non-magnetic toner that can provide image quality with excellent gradation without fogging. .

Structure of the Invention As a result of extensive studies, the inventors have found that suppressing fog density and improving gradation reproducibility depend not only on the charge amount of the toner and the adhesion force (development drag) between toner particles and the surface of the donor roll, but also on photosensitive We have found that the pressure between the body and the donor roll has the most influence, and we have found a means for adjusting the pressure that can be implemented in a simple manner by suppressing the dependence of the above-mentioned pressing force on the hardness of the elastic roll.

That is, in the present invention, an elastic developing roll having a conductive surface is brought into rotational contact with the surface of a photoreceptor drum, and development is carried out by supplying a developer, for example, a one-component non-magnetic toner, to the photoreceptor drum using the developing roll. A dry-type developing device for carrying out the above-described method includes a pressing member for pressing the elastic developing roll against the surface of the photoreceptor drum, and a pressing member disposed coaxially with the developing roll and having a predetermined diameter slightly smaller than the diameter of the developing roll. , a tracking roll whose outer peripheral surface comes into contact with the photoreceptor drum when the elastic developing roll is pressed against the photoreceptor drum by the pressing member, and adjusts the pressing force of the pressing member to a specified value. It is characterized by this.

Embodiments Hereinafter, a developing device according to a preferred embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic side view of a developing device according to an embodiment of the invention, and FIG. 2 is a longitudinal sectional view of a portion of a donor roll.

In the figure, the reference numeral "1" indicates a photoreceptor drum, and the photoreceptor drum 1 is rotating in the direction of arrow a, and the donor roll 2 is in contact with the outer periphery of the photoreceptor drum 1. As shown in FIG. 2, this donor roll 2 has a core metal 3 coated with a conductive urethane foam 4, and the surface of which is covered with a conductive fluorine rubber layer 5.
The structure is coated with A hopper 6 for supplying toner is provided above the donor roll 2, and a toner spill prevention member 7 and a toner layer thickness adjustment member 8 are provided at the tip of the hopper 6. A conductive scraping member 9 is disposed within the hopper so as to come into contact with the surface of the donor roll.

Here, the toner 10 in the hopper is transferred to the photoreceptor drum 1.
The process of adhering to the upper latent image will be explained. The photoreceptor drum 1 rotates in the direction of arrow a, and the donor roll 2 is rotated at a substantially constant speed in the direction of arrow b while being in pressure contact with the photoreceptor drum. The toner 10 in the hopper passes through a toner layer thickness adjustment member 8 and a thin layer (20-50 microns) of toner is formed on the donor roll. Next, it passes under the corona charger 11 and is connected to the high voltage DC power supply.
A desired amount of charge and polarity are imparted by V ₁ , and in this state it advances to the development area and adheres to the latent image, where development is performed. After passing through the development area, residual toner remains on the donor roll 2 corresponding to the non-latent image pattern on the photoreceptor drum 1. This residual toner is removed again by hopper 6.
When the conductive fluorocarbon rubber layer 5 is returned to the inside, the charge is peeled off from the surface of the donor roll by the conductive scraping member 9 and the electric charge remaining on the conductive fluorocarbon rubber layer 5 is neutralized by grounding. The symbol "V ₂ " indicates a DC bias power supply for the donor roll 2, which controls toner adhesion to non-image areas on the photoreceptor. Development is performed continuously by repeating the above cycle.

The donor roll 2 is pressed against the photosensitive drum 1 by a pressing member P. This pressing member P
Although a spring is shown in the embodiment, a locking pawl may be used instead of the spring, or a drive gear for driving the donor roll 2 may also be used as the pressing member.

In order to regulate the pressing force of the donor roll 2 against the photoreceptor drum 1 by the pressing member P, in the present invention, the tracking roll 12 is attached to the core metal 3 of the donor roll 2 via a bearing 13. There is. This tracking roller 12 is desirably made of polyacetal resin or the like, and its outer diameter is slightly smaller than the outer diameter of the donor roll 2.

Here, the degree of pressing (or contact width) of the donor roll 2 against the photoreceptor drum 1, that is, the magnitude of the pressing force, is determined by assuming that the outer diameter of the donor roll 2 is d and the outer diameter of the tracking roll 12 is c. , (d-
c)/2. Therefore,
Generally, the outer diameter d of the donor roll 2 is constant, so by appropriately selecting the outer diameter c of the tracking roll 12, the pressing force of the donor roll 2 against the photoreceptor drum 1 can be set to a desired value. As a result, good development can be performed.

An experimental example will be explained below.

Experimental example Γ Sensitivity Light body Se Γ surface potential Image area 800V Non-image area 150V Γ donor roll Conductive urethane foam (made by Achilles: resistor) on an aluminum core roll with an outer diameter of 10 mm
The surface of the elastic ^roll coated with conductive fluorocarbon rubber (GL-252 manufactured by Shin-Etsu Chemical, surface resistance 10 ⁸ Ω/cm ² ) was coated on an Al sheet with a bar ^coater to a thickness of about 5 μm. coating).

Donor roll outer diameter 37mm Γ Conductive scraping member Conductive rubber (Hokushin Chemical resistance 10 ⁶ to 10 ⁸ Ω・cm) Γ Toner fall prevention member Toner layer thickness adjustment member 50μ, PET film Γ Tracking roll Polyacetal resin Outside Diameter 36mm ΓV ₁ , V ₂ = -5.8KV, 0V Γ Photoreceptor rotation speed 127mm/sec Γ Donor roll rotation speed 127mm/sec As a result of image formation using the above materials and setting conditions, the fog density was low and sufficient Good image quality with high image density and excellent gradation reproducibility was obtained.

Effects of the Invention According to the present invention, as in the above-mentioned embodiments, it is possible to stably maintain any desired pressure (contact width) between the photoreceptor and the donor roll by a simple and reliable method. It solves both fog and gradation reproducibility, which were the biggest drawbacks of developing methods using donor rolls, all at once, and also makes it possible to reduce the accuracy of the elastic roll's straightness, thereby achieving uniform image density. You can get something. Although the present invention has been explained using a single-component non-magnetic toner as an example, it is also applicable to a donor roll or donor sheet development system in which a single-component magnetic toner is conveyed and supplied using a magnetic tape, an elastic roll, etc. .

Further, the type of latent image is not limited to an electrostatic latent image, and it is also possible to develop a magnetic latent image using a donor roll development method using an elastic rubber roll, such as in magnetography.

[Brief explanation of drawings]

FIG. 1 is a schematic side view of a developing device according to an embodiment of the present invention, and FIG. 2 is a longitudinal sectional view of a portion of a donor roll used in the developing device of FIG. 1... Photoreceptor drum, 2... Donor roll, 5
... Conductive fluorine rubber layer, 12 ... Tracking roll, P ... Pressing means.

Claims (1)

[Claims] 1. In a dry type developing device that performs development by bringing an elastic developing roll having a conductive surface into rotational contact with the surface of a photoreceptor drum and supplying developer to the photoreceptor drum by this developing roll, the elastic developing roll a pressing member for pressing the surface of the photoreceptor drum, and a pressing member disposed coaxially with the developing roll and having a predetermined diameter slightly smaller than the diameter of the developing roll, and the elastic developing roll is pressed by the pressing member. A developing device comprising a tracking roll whose outer circumferential surface contacts the photosensitive drum when the roller is pressed against the photosensitive drum to define a pressing force of the pressing member.