JPH03259169A - Developing device - Google Patents

Abstract

PURPOSE:To carry out a high-definition image formation without having a defective image caused by density irregularities, etc., by composing a shaft center part with an elastic layer on a developing roll disposed opposite to the outside surface of an electrostatic latent image carrier, forming a conductive tank on the outer periphery of the elastic layer, and simultaneously, specifying the hardness ratio of the hardness developing roll of the the elastic layer. CONSTITUTION:The developing roll 9 disposed opposite to the outside surface of the electrostatic latent image carrier 2 is constituted that its shaft center part is composed of the elastic layer 9b, its conductive layer 9c is formed on the outer periphery of the elastic body, and simultaneously, the ratio Y of the hardness of the elastic layer 9b to that of the developing roll 9 is set at Y <=1.5. Thus, the difference of the hardness of the developing roll 9, that is, the elastic layer 9b + the conductive layer 9c is put together, and the hardness of the elastic layer 9b of the shaft center part is reduced, and the hardness of the developing roller is minimized, so that a sufficient developing nip width is obtained with a small load. Thus, the defective image caused by the density irregularities, etc., and the increasing of the torque of this developing device are eliminated, and a stable high-definition image formation is carried out.

Description

[Detailed Description of the Invention] [Objective of the Invention] (Industrial Field of Application) This invention relates to the improvement of a developing device used in an image forming apparatus using an electrophotographic recording method or an electrostatic recording method. More specifically, the present invention relates to development iW that forms high-quality images using a one-component developer.

(Prior Art) Image forming apparatuses using an electronic recording horn type or an electrostatic recording type usually make a visible image by attaching a developing agent to an electrostatic latent image formed on a photosensitive image holding surface. , a method is adopted in which the obtained iiT visual image is transferred to a transfer body. (Visualization of such an electrostatic latent image) The developer used is a two-component developer consisting of toner particles and carrier particles, and a one-component developer that carries and adheres toner particles to the electrostatic latent image. There is a method using

- One of the developing methods using component developers is the pressure development method.
t) is known. This method is characterized by bringing the electrostatic latent image into contact with toner particles or toner carriers at substantially zero relative peripheral velocity, and since magnetic materials such as carriers in two-component developers are not required, the device It has many advantages, such as being able to be simplified and miniaturized, and easily coloring images using multicolor toner.

In the above-mentioned pressure development method, since the toner carrier is pressed against or brought into contact with the electrostatic latent image for development, it is necessary to use a developing roller having elasticity and conductivity. In particular, when the electrostatic latent image holder is a rigid body, the developing roller must be made of an elastic body to avoid damaging it. Further, in order to obtain the well-known developing electrode effect and bias effect, it is desirable to provide a conductive layer on or near the surface of the developing roller and apply a bias voltage as necessary.

When the developing roller is made of an elastic material, distortion occurs in the developing roller at a portion where the developing roller and the means for forming the toner layer and the developing roller and the photoreceptor drum come into contact with each other. Especially for developing electrostatic latent images on photoreceptor drums.
In order to obtain a sufficient contact width, i.e., nip width, it is necessary to press the developing roller against the photosensitive drum with a constant pressure, which tends to cause large distortions. If an electrostatic latent image on a photoreceptor drum is developed with distortion remaining on the developing roller, image defects such as white spots and density unevenness will appear in the image at the locations where distortion has occurred. This tendency becomes particularly noticeable when the developing roller is left pressed against the photosensitive drum. It was also confirmed that the problem was more pronounced when a developing roller with a rubber hardness of 506 or less was used.

(Problems to be Solved by the Invention) The present invention has been made to solve the problems of the prior art, and it is possible to obtain high-quality images without defective images such as density unevenness, and even after long-term use. , it is an object of the present invention to provide a developing device for use in an image forming apparatus that does not cause deterioration in image quality.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above problems, a developing device according to the present invention includes: a developing roller having elasticity disposed opposite to the outer surface of the electrostatic latent image holder; means for forming a toner layer on the outer surface of the developing roller, and by bringing the toner layer into contact with the outer surface of the electrostatic latent image carrier, the electrostatic latent image on the electrostatic latent image carrier is visualized. In the developing device, the developing roll disposed opposite to the outer surface of the electrostatic latent image holder has an axial center formed of an elastic layer, a conductive layer is formed on the outer circumferential surface of the elastic body, and a conductive layer is formed on the outer circumferential surface of the elastic body. The ratio Y of hardness to hardness of the developing roll is Y≦1. 5.

(Function) As described above, the developing device according to the present invention reduces the difference between the hardness B of the developing roller (combined elastic layer + conductive layer and the hardness A of the elastic layer at the shaft center), Since the hardness of the roller is kept low, a sufficient developing nip width can be obtained with a small load.

(Embodiment) Hereinafter, a developing device according to an embodiment of the present invention will be described with reference to the drawings.

FIG. 1 shows a longitudinal section of a pressure-type component nonmagnetic developing device according to an embodiment of the present invention. In the developing device of this embodiment, a thin layer of non-magnetic toner is formed by a toner supply roller 11 on the outer surface of a developing roller 9 having conductivity and elasticity, and this non-magnetic toner layer is brought into contact with the surface of the photoreceptor drum 2. This developing device does not require a magnetic carrier, an Mg roller, a toner density controller, etc., and can be made smaller and less expensive.

The developing process by the developing device 3 according to this embodiment will be described below.

The non-magnetic toner 13 in the developer container 12 is sent to the toner supply roller 11 while being stirred by the mixer 14, and the toner supply roller 11 supplies the toner to the developing roller 9. The supplied toner particles are charged by friction with the surface of the developing roller 9, and are electrostatically attracted and conveyed. Thereafter, the amount of toner conveyed is regulated by the blade 1o that is in contact with the developing roller 9 held by the blade holder A17, the spacer 18, and the blade holder B19, and at the same time, the toner is triboelectrically charged by the friction between the roller and the toner particles. be exposed. In the present invention, since reversal development is performed using a negatively charged organic photoreceptor drum 2, a negatively charged toner is used for the tri-color, and a material that easily imparts a negative charge is also used for the blur 11 (). j: Photoreceptor surface potential -55
With respect to 0 V, the developing bias potential is -200 V, which is supplied to the shaft (9a) of the developing roller 9 through a protective resistor, and the developing temperature is approximately 4 times higher than that of the photoconductor Drano 2 and approximately 1.2. photoreceptor in the direction of the arrow at a speed]. 2 and approx.]
It has a contact width (developing nip) of about 4 mm and rotates in contact. Furthermore, since the toner particles are triboelectrically charged even at the development position, extremely sharp images can be obtained with little fogging. The toner remaining after development is removed by scraping off the cover blur 7-de (Mylar film) 15 and returns to the inside of the developing device.

Furthermore, if the toner falls from the developing roller 9 for some reason, it will stain the inside of the machine or the transfer paper. This eliminates the problem of the transfer paper falling and staining the transfer paper.

Furthermore, even if the developing device 3 is placed in the 1-down return position, toner can be prevented from falling. In addition, in Fig. 1, the buckle plate 21 (attached to the plastic holder A) is in contact with the foam material 21 that comes out of the maltblen etc. attached to the front of the replacement plate 10 [11, Vibrations of the seal and the plate 7-10 can be suppressed, and a good toner layer can be formed on the developing port/layer 9. Also, the blade]-〇 indicates the rotating shaft 1.7a of the blade node holder 17 and the plurality of compression springs 2 for pressurizing.
0, it is pressed against the developing roller 9. compression spring 2
0 is lower than the spring constant of the thin plate spring H of the blade 1 node 10, so even if the contact portion of the blade 10 wears out, the pressing force remains unchanged and a good toner layer can be maintained. ing.

Next, a description will be given of the developing roller, which is a main component of the developing device W3 according to the present invention. FIG. 2 is a perspective sectional view of an embodiment of the developing roller 9 used in the present invention C1. .

In the developing method used in the present invention, the first requirement is that the developing roller 9 is "conductive and elastic", and the simplest configuration that satisfies this requirement is a metal shaft and a conductive rubber roller. This combination requires the toner to be brought into pressure contact with the developing roller surface, and the surface must be smooth in order to be conveyed.

The developing roller of this embodiment has a two-layer structure of an elastic layer 9b and a surface conductive layer 9c around a metal shaft 9a as shown in FIG. When selecting the elastic layer 9b, there are two possible options: conductive and non-conductive, but it is preferable to use a conductive layer in consideration of the possibility that the conductive layer 9C may be peeled off or scratched. Moreover, the elastic body Jii9b
is in pressure contact with the blade 1(,) and the photoreceptor 2, so if it is packed or left for a long time, JIS K, 6
The permanent strain (%) shown in 301 becomes a problem, and if this strain exceeds 10%, uneven development roller cycles will occur in the image, so the compressive strain (%) of the elastic layer 9b should preferably be 10% or less. It's good to keep the power below 5%. Regarding the relationship between rubber hardness and permanent set (%), generally speaking, the larger the rubber hardness, the smaller the permanent set, so the balance between the materials and each other is important. As described above, conductive silicon was selected in this embodiment as a material that satisfies the characteristics required for the elastic layer 9b.
However, not only conductive silicon but also conductive EPD
M rubber and conductive urethane rubber can also meet the required characteristics.

The elastic layer 9 made of conductive silicon of the embodiment described above.
b has a hardness of 28° on a JIS standard 6301 type A hardness tester and an outer diameter of 18 nm. In addition, the electrical resistance value of conductive silicon is the elastic low mentioned above.

The stainless steel row with a diameter of 60 mm has a contact width of 2
The result was calculated by measuring the current observed when the rollers were arranged in parallel so that rn, m and a potential difference of 100V was established between the metal shafts of both rollers.The result was 3.4X103.
It was Ω・Cnl. Also, the permanent deformation is J l5K6301
As a result of measurement using the measuring force method shown in , it was 1.8%. Since the conductive layer 9c (see FIG. 2) directly contacts the toner and the photoreceptor, it must not contaminate the toner or the photoreceptor drum by seeping out plasticizer, vulcanizing agent, process oil, etc. In addition, regarding surface smoothness, 3I
Jm Rz or less is desirable, and if it is higher than that, a pattern of surface irregularities tends to appear in the image. In order to achieve a smoothness of 3 μmRz, it is conceivable to attach a sufficiently thick conductive layer 9c to the elastic layer 9b and then finish it to a predetermined outer diameter and surface roughness through post-processing (polishing). Cost increases. Therefore, in order to achieve this without post-processing, the surface roughness of the elastic layer 9b, the thickness of the conductive layer 9c, and the viscosity of its paint must be optimally selected. FIG. 3 shows the elastic layer 9b.
This figure shows a typical method for applying a conductive layer 9c to the wafer. FIG. 3(a) shows the coating method by spraying, FIG. 3(b) shows the method by dipping, and FIG. 3(C) shows the method by using a knife.

The viscosity of the paint in each method is as follows: spray method, dipping method ≦ Knifetsu method, and the paint film thickness T (μm) necessary to achieve the above-mentioned surface smoothness of 3 μmRz is determined by the surface of the elastic layer 9b. The roughness is S (μmRz
), it becomes possible if T≦10XS is satisfied in the spray method, and T≦5XS in the dipping method and the knife method.

In this embodiment, the conductive layer 9b is made of a polyurethane resin that has conductivity of 10 3 Ω·cm by dispersing conductive carbon particles therein.

A conductive polyurethane paint was applied to the surface of the elastic layer 9b made of conductive silicone by the following steps, and after drying, heat treatment was performed to form the elastic layer 9b.

First, as a conductive polyurethane paint, the product name "Sparex DH202313" manufactured by Nippon Miractron Co., Ltd.
Using the trade name, an equal amount of a diluting solvent prepared by mixing methyl ethyl ketone (MEK) and tetrahydrofuran (THE) at a ratio of 1:1 is added thereto. This “Subarex DH2
02313'' is a solution type conductive polyurethane paint based on thermoplastic polyurethane.

After thoroughly stirring the paint diluted in this manner, it is applied by dipping onto the surface of the elastic layer 9b that has been washed with a solvent. The pulling speed of the elastic layer 9b is 3.5 mm/
sec. After application, dry in the air for about 30 minutes,
Thereafter, heat treatment was performed at 100° C. for 20 minutes. As a result,
A conductive layer 9C having a layer thickness of about 50 μm was obtained. The thickness of the conductive layer 9C can range from 10 μm to 100 μm by changing the pulling speed of the dipping method.

Through the above steps, the developing roller 9 has a resistance value of 5 x 103 Ω·cm between the metal shaft 9a and the conductive layer 9C, and a hardness of the rubber on the roller of 36° with an A-type hardness needle of 6301 according to the JIS standard. , a surface roughness of 3 μmRz could be obtained. Further, the hardness ratio Y between the elastic layer 9b and the developing roller 9 was 1.29.

Note that if the ratio Y of the hardness A of the elastic layer to the hardness B of the phenomenon roll is 1.7 or more, it is too hard and causes "unevenness" in the image, and if it is 1.7 or less, the "unevenness" in the image decreases; When the value is .5, a good quality image without "unevenness" can be obtained. However, in addition 1.
It has been confirmed that an excellent image with no unevenness can be formed when the rating is 3 or less and 1 or more.

Next, in order to confirm the change in characteristics due to the resistance value between the shaft and surface of the developing roller 9 using this contact type component non-magnetic developing device 3, an arbitrary resistance value is interposed between the developing bias power source and the metal shaft. A development experiment was conducted to obtain the correlation between the potential of the developing roller surface, the resistance value, and the image. The results obtained are shown in FIG. However, the voltage of the developing bias power supply at this time is -200V.

As is clear from FIG. 4, at a resistance value of 107Ω or more, the developing roller surface potential shows different values when developing a solid white image and a solid black image, and in the case of a solid white image, the potential of the white background latent image changes. A solid black image shows a tendency to approach the potential of a black solid latent image. In other words, when an image has a large image area, the potential difference between the latent image potential of the image area and the surface potential of the developing roller becomes small, resulting in a low-density image. Since the potential approaches the white background latent image potential, the potential difference with the image area increases, making thin lines thicker and resulting in an image with no sharpness.

Such fluctuations in the surface potential of the developing roller are caused by the current flowing through the resistor during development.

During black solid development, negatively charged toner particles are transferred from the developing roller 9 to the photoreceptor drum 2, so the developing o-
-L8] to the developing bias power supply.

During development to white, the surface charge on the photoreceptor 2 is removed by the developing roller (5), and a current flows from the developing bias to the developing roller.

Such a current generates a potential difference across the resistor, causing the above-mentioned fluctuation in the surface potential of the developing roller at t5.

This tendency was remarkable at I x ] 08 Ω or higher.

That is, the actual resistance value between the metal shaft and the surface conductive layer is IX], 08Ω or more, preferably 11. < is 1×107
It has been confirmed that good images can be obtained with a ratio of Ω or less.

FIG. 2 is a perspective cross-sectional view showing an example of a roller. Figure 3 (a), (
i)) and (c) are diagrams illustrating the method of forming a conductive layer on the developed Ti1i7 film according to the example. FIG. 4 shows the correlation between the potential, resistance value, and image on the surface near development 1 in one embodiment of the developing device according to the embodiment.

[Effects of the Invention] As is clear from the above description, the developing device according to the present invention has an axial center portion formed of an elastic layer 1.
11. In order to form a conductive layer on the outer circumferential surface of this elastic layer, and to set the ratio Y of the hardness of the developed vJ-ra to the hardness of the elastic layer to be Y≦1.5, 2. Develop 171 width by 1
It is possible to obtain a stable high-quality image in minutes, and it is possible to eliminate undesired images such as "density unevenness" and to reduce the torque of the developing device.

[Brief explanation of drawings]

Fig. 1 shows the configuration of a developing device according to an embodiment of the present invention. Fig. 2 shows an embodiment of the developing device according to the embodiment. Perspective sectional view 6 (a), (b), and (c) are process diagrams showing a method for forming the conductive layer of the developed Iγ-layer according to the example. Development 0- of an embodiment of the development device
Graph A shows the correlation between the electric potential J resistance value of the surface of La and the image. 9... Current image roller 9a... Metal shaft 0 [] -
Bullet body layer ≦7 (...conductive layer) 0...Blade 1
()a...thin plate fence], Ob...-f knob 1
0c Seal Shrine Ryo, (Ina' Rijuzo Hidekazu Figure 3 (a) ↑ 3rd Th': 1 (b)

Claims (1)

[Scope of Claims] A developing roller having elasticity disposed opposite to the outer surface of the electrostatic latent image holder, and means for forming a toner layer only on the surface of the developing roller, the toner layer being formed on the surface of the electrostatic latent image. In a developing device that visualizes an electrostatic latent image on an electrostatic latent image holder by bringing it into contact with the outer surface of the holder, a developing roll disposed opposite to the outer surface of the electrostatic latent image holder has an axial center portion. A conductive tank is formed on the outer peripheral surface of the elastic body layer, and the ratio Y of the hardness of the elastic body layer to the hardness of the phenomenon roll is Y≦1.5. A developing device.