JPH0486857A - Developing device - Google Patents

Abstract

PURPOSE:To completely and electrostatically charge developer at the contact spot of an electrostatic latent image holding body with a developing roller and to prevent the drop of the developer from the developing roller and surface fogging from occurring by satisfying the relation of Rs<=Rd between the center line average height Rs(mum) of the surface of the electrostatic latent image holding body and the center line average height Rd(mum) of the surface of the developing roller. CONSTITUTION:Toner A is supplied to the developing roller 12 by a toner supply roller 15. The toner A is electrostatically charged to be negative by the surface friction with the rotating developing roller 12 and electrostatically attracted to the surface of the roller 12. Thereafter, it is formed to a thin layer by a blade 16 and simultaneously triboelectrified again by the friction with the roller 12 and the blade 16. After this, the toner A is completely electrostatically charged at the contact spot of the roller 12 with the photosensitive drum 11, and transferred to an electrostatic latent image on the surface of the photosensitive drum 11. The relation Rs<=Rd is satisfied between the center line average height Rs(mum) of the surface of the photosensitive drum 11 and the center line average height Rd(mum) of the surface of the roller 12.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a developing device for visualizing an electrostatic latent image in an electrophotographic device or an electrostatic recording device.

(Prior art) One of the development methods using a one-component developer is the pressure development method (
Impression Development) is known. One of the characteristics of this pressure development method is that toner charged by friction is electrostatically attracted to the surface of a developing roller and transported. Therefore, there are many advantages such as no magnetic material is required, the device is simpler and smaller, and furthermore, it is easier to use colored toner.

In this pressure development method, when development is performed by pressing or bringing the developing roller into contact with the electrostatic latent image on the photoreceptor drum, the developing roller is required to have elasticity and conductivity. Particularly when the photosensitive drum is a rigid body, it is essential that the developing roller be made of an elastic body. Further, in order to obtain the well-known developing electrode effect and bias effect, it is preferable to provide a conductive layer on or near the surface of the developing roller and apply a bias voltage as necessary.

In a developing device that employs such a developing method, the toner is charged by contact friction with the developing roller, is electrostatically attracted to the surface of the developing roller, and is conveyed. The layer is thinned by Here, the toner is charged again by friction between the blade and the developing roller, becomes a dense toner layer, and is conveyed to a contact position (development position) with the photoreceptor drum. Then, the toner becomes charged enough to obtain a good image due to contact friction with the photoreceptor drum, and is transferred onto the electrostatic latent image on the photoreceptor drum.

(Problem to be Solved by the Invention) However, in such a developing device, if the toner is insufficiently charged by contact with the photoreceptor drum, which is an electrostatic latent image holder, the toner may be charged from the developing roller. Toner dropout and background fogging may occur, resulting in a decline in image quality.

The present invention was made to solve such problems,
The developer can be sufficiently charged at the contact point between the electrostatic latent image holder and the developing roller, which prevents the developer from falling off the developing roller and from causing background fog, resulting in high-quality images. The purpose of the present invention is to provide a developing device that can be obtained.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above object, the developing device of the present invention includes a developing roller disposed facing the electrostatic latent image holder, and a developing roller disposed opposite to the electrostatic latent image holder. a developer thin layer forming means for forming a developer thin layer, and the electrostatic latent image carrier is moved by bringing the developer thin layer formed on the developing roller close to or in contact with the electrostatic latent image carrier. In a developing device that visualizes the electrostatic latent image held, the center line average roughness of the surface of the electrostatic latent image holder is expressed as Rs (
μm), and the center line average roughness of the surface of the developing roller is Rd(μm).
m), it is characterized by satisfying the relationship Rs≦Rd.

(Function) In the developing device of the present invention, if the center line average roughness of the surface of the electrostatic latent image holder is Rs (μm) and the center line average roughness of the surface of the developing roller is Rd (μm), Rs By satisfying the relationship ≦Rd, the developer can be sufficiently charged at the contact point between the electrostatic latent image holder and the developing roller, which prevents the developer from falling off the developing roller and causing background fog. can be prevented and high-quality images can be obtained.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view showing the overall structure of a contact type component nonmagnetic developing device (hereinafter simply referred to as a developing device) according to an embodiment of the present invention.

As shown in the figure, this developing device 1o uses non-magnetic toner (hereinafter simply referred to as toner), which is a developer, on an electrostatic latent image formed on the surface of a photoreceptor drum 11, which is an electrostatic latent image holder. ) A developing roller 12 for transferring toner A to visualize an electrostatic latent image, a toner container 13 containing toner A, a mixer 14 for stirring toner A in this toner container 13, and a toner A toner supply roller 15 that supplies toner A in the container 13 to the developing roller 12, and a developing roller 1.
The main part thereof includes a blade 16 which is a developer thin layer forming means for forming a toner thin layer on the two surfaces.

Next, the developing process in this developing device 10 will be explained.

The toner A contained in the toner container 13 is transferred to the mixer 1.
4 and sent to the toner supply roller 15 while being agitated by the toner supply roller 15.
Furthermore, this toner supply roller 15 causes the developing roller 12 to
supplied to Here, the toner A is negatively charged due to surface friction with the rotating developing roller 12, and is electrostatically attracted to the surface of the developing roller 12 and transported. Thereafter, the amount of toner A attached to the surface of the developing roller 12 is regulated by the blade 16 to become a thin layer, and at the same time, it is triboelectrically charged again due to the friction between the developing roller 12 and the blade 16, forming a dense toner. It is transported in layers. Thereafter, the toner A adhering to the surface of the developing roller 12 is sufficiently charged at the point of contact with the photoreceptor drum 11, and then transferred onto the electrostatic latent image on the surface of the photoreceptor drum 11. This makes the electrostatic latent image visible. Developing roller 1 that did not transfer
The toner A on the second surface is scraped through the recovery blade (Mylar film) 17 and returned to the toner container 14.

By the way, in this embodiment, since a reversal development method using a negatively charged organic photoreceptor drum 11 is adopted, a negatively charged toner is used as the toner A, and the blade 16
A material that easily charges the toner A negatively is used. Further, the surface potential of the photosensitive drum 11 is -550
In contrast, -200 V is applied to the metal shaft 12a of the developing roller 12 via a protective resistor as a developing bias potential. Further, the developing roller 12 is
While always having a contact width (developing nip) of about 1 to 5 mm with the surface of the photoreceptor drum 11, it rotates in the direction of arrow a in the figure at a speed of about 1 to 4 times the diameter of the rotation speed of the photoreceptor drum 11. are doing.

In addition, in the above-mentioned development process, if toner A falls from the developing roller 12 for some reason, it will stain the main unit or the transfer paper, so in this embodiment, toner welding made of a plasticizer or the like that welds toner A is used. A member 18 is attached to the lower part of the developing bag f10. Also, this allows
Even when the developing device 10 is placed upside down, scattering of the toner A can be prevented.

The above blade 16 is attached to a first blade holder 16a1.
It is supported by the device main body by a spacer 16b and a second blade holder 16c. Reference numeral 19 denotes a baffle plate attached to the first blade boulder 16a to sandwich a foamed material 20 made of maltbrene or the like between it and the back surface of the blade 16. By sandwiching the foamed material 20 between the baffle plate 19 and the back surface of the blade 16 in this manner, leakage of toner A from the toner container 13 and vibration of the blade 16 are prevented.

Further, this blade 16 has a tip portion (tip 162).
) to press the surface of the developing roller 12 with an appropriate force.
It is constantly biased by a plurality of compression springs 22 with the rotating shaft 21 as a fulcrum. Since the spring constant of these compression springs 22 is lower than that of the blade 16 (thin spring material 161), even if the tip portion (tip 162) is worn, there is almost no change in the pressing force.

Further, in this example, as toner A, carbon, a charge control agent, and wax are kneaded and dispersed in an epoxy resin, and
The crushed and classified product was used. The volume average particle diameter of Toner A was 11.5 μm as measured using a Coulter Counter Model TA-II manufactured by Coulter Electronics.

Next, the above-mentioned developing roller 12 will be explained in detail.

FIG. 2 is a perspective sectional view showing the developing roller 12.

The characteristics required of the developing roller 12 are that it has "conductivity and elasticity".

The simplest configuration that satisfies this requirement is, for example, one in which the outer periphery of a metal shaft is covered with a conductive rubber roller. However, in the developing system of this embodiment, the toner is conveyed while being pressed against the surface of the developing roller 12. Therefore, surface smoothness is required.

Therefore, in the developing roller 12 of this embodiment, an elastic layer 12b is provided on the outer periphery of the metal shaft 12a, and a conductive polyurethane-based conductive layer 12 is further provided on the surface of the elastic layer 12b.
It has a two-layer structure with c.

The elastic layer 12b may be conductive or non-conductive, but it is preferable to use a conductive layer in consideration of the possibility that the conductive layer 12c may be peeled off or scratched.

Further, the rubber hardness of the elastic layer 12b is a factor that directly affects the load and torque of the developing roller 12 for obtaining an appropriate nip width between the developing roller 12 and the photoreceptor drum 11. In addition, regarding the permanent strain shown in JIS standard 6301 due to packaging or long-term storage, if this exceeds 10%, uneven rotation period of the developing roller will occur in the image, so the compressive strain of the elastic layer 12b is 10%. Below, preferably 5
% or less. Regarding the relationship between rubber hardness and permanent set, there is generally a tendency that the higher the rubber hardness, the smaller the permanent set, so the balance between the materials and each other is important.

As described above, conductive silicone was selected in this embodiment as a material that satisfies the characteristics required for the elastic layer 12b, but other materials such as conductive EPDM rubber and conductive urethane rubber also meet the required characteristics. It can be used as

The elastic layer 12b made of conductive silicon has a hardness of 28@ with an A-type hardness needle of 6301 according to the JIs standard, and has an outer diameter of 18 mm as an elastic roller. In addition, the electrical resistance value of conductive silicon was observed when this elastic roller was placed parallel to a stainless steel roller with a diameter of 60 mm so that the contact width was 2 mm, and a potential difference of 100 V was established between the metal shafts of both rollers. The result was 3.4 x 10'' Ω·cm, which was calculated by measuring the electric current.The permanent set was 1.8%, which was measured using the measurement method specified in JIS standard 6301.

Further, the conductive layer 12c is directly coated with toner and the photosensitive drum 11.
As long as the toner and the surface of the photoreceptor drum 11 are not contaminated by seepage of plasticizer, vulcanizing agent, process oil, etc., the smoothness of the surface must comply with JIS standards.
Center line average roughness shown in standard BO601 is 5 μm R
a or less, the maximum height is preferably 10 μm or less,
If it is more than that, the pattern of unevenness on the surface tends to appear in the image.

In order to realize a developing roller 12 that satisfies these conditions, a sufficiently thick conductive layer 12c is applied on the elastic layer 12b, and then post-processed (polishing) to obtain a predetermined outer diameter and surface roughness. There is a way to achieve this, but this method would be expensive. Therefore, a method of finishing without requiring post-processing is desired, but for this purpose, the surface roughness of the elastic layer 12b,
The thickness of the conductive layer 12c and the viscosity of the paint used to form the conductive layer 12c must be optimally selected. That is, the lower the viscosity of the paint and the greater the surface roughness of the elastic layer 12b, the greater the thickness of the conductive layer 12c must be.

FIGS. 3 to 5 show typical methods of applying conductive layer paint.

FIG. 3 shows a spray coating method, FIG. 4 shows a dipping coating method, and FIG. 5 shows a knife coating method.

The viscosity of the paint in each method is spray method, dipping method ≦ Naifetsu method,
Required smoothness of the surface of the conductive layer 12c (center line average roughness is 5 μmRa or less, maximum height is 10 μmRmax or less)
The film thickness T (μm) of the paint necessary to achieve this is as follows, assuming that the maximum surface roughness of the elastic layer 12b is S (μmRa).
This is possible if T≧10XS is satisfied in the spray method, and T≧5XS in the dipping method and the knife method.

In this example, conductive carbon fine particles are dispersed in polyurethane resin as a paint for forming the conductive layer 12c. A conductive polyurethane paint with conductivity of Ω/cm was used. Then, in the following steps, a conductive polyurethane paint was applied to the surface of the elastic layer 12b made of conductive silicone, and after drying, heat treatment was performed to form a conductive layer 12C.

First, Nippon Miractron ■ as a conductive polyurethane paint.
A diluting solvent prepared by mixing methyl ethyl ketone (MEK) and tetrahydrofuran (THF) in a ratio of 1:1 was added to the same solution using the product name "Sparex D) 120Z313" manufactured by Co., Ltd. "Sparex DH202313" is a solution-type conductive polyurethane paint based on thermoplastic polyurethane. After sufficiently stirring this diluted paint, it is applied onto the surface of the elastic layer 12b washed with a solvent using a dipping method. In addition, the pulling speed of the treated material in this dipping method is 5.5 mm/s.
It was set as ec. Thereafter, it was dried in air for about 30 minutes, and then heat-treated at 100° C. for 20 minutes. As a result, a conductive layer 12c having a layer thickness of 80 μm was obtained. Conductive layer 12c
The layer thickness can be changed within the range of 10 μm to 300 μm by changing the pulling speed of the dipping method and the viscosity of the solvent.

The center line average roughness of the surface of the developing roller 12 obtained through the above steps was measured using the apparatus shown in FIG. This device is manufactured by Koita Research Institute Co., Ltd. and has the product name “Surfcog 5E-”.
This is a 40D'' contact type surface roughness meter, which includes a detector 201, an amplification calculation device 202, a recorder 203, and a support for the object to be measured 20.
It consists of 4. Using this device, the developing roller 12
When measuring the center line average roughness of the surface, use the developing roller 1.
2 is placed on the object to be measured support 204, and the contact needle 205 of the detector 201 is brought into contact with the surface of the developing roller 12 with a predetermined pressure. The roughness state of the surface of the developing roller 12 obtained by the contact needle 205 is sent to the recorder 203 via the amplification calculation device 202.
is output to. As shown in Fig. 7, the center line average roughness Ra here refers to the center line of the roughness curve f(x), which is obtained by extracting a portion of the measurement length from the roughness curve f(x) in the direction of the center line. When the line is the Y-axis, the direction of vertical magnification is the Y-axis, and the roughness curve is expressed as Y-f(x), the following formula can be used to calculate δI
The II conditions are as follows.

Cutoff value (mm): 0.8 Fill constant length (mm): 2.5 As a result of measurement under these conditions, the centerline average roughness Ra of the surface of the developing roller 12 was 4.2 μm.

The developing roller 12 has a resistance value of 5×10 Ω”cm between the metal shaft 12a and the conductive layer 12C, and a rubber hardness of 36° with an A-type hardness needle of 6301 according to the JIS standard.

On the other hand, the photoreceptor drum 11 is made of C0 made of the materials shown below, respectively, on an aluminum tube with an outer diameter of 5Qmm.
A functionally separated photoreceptor, so-called OPC, which was constructed by sequentially stacking layers and CT layers was used.

C0 layer: Binder... phenoxy resin CGM
...Hydrazone derivative CT layer: Binder...Polyester carbonate C
TM...Hydrazone derivative or the surface of the aluminum tube is used as a measure against interference fringes.
Sandblasting is performed using 000 abrasive.

The center line average roughness Ra of the surface of the photoreceptor drum 11 was measured using the above-mentioned surface roughness measuring device and was found to be 0.8 μm.
Met.

FIG. 8 shows the center line average roughness of the surface of the photoreceptor drum 11, Rs.
(μm), the center line average roughness of the surface of the developing roller 12 is Rd
It is a graph showing changes in fog on paper when the value of Rs/Rd is changed as (μm) and image data is collected each time.

As is clear from this graph, it was confirmed that in the range where Rs≦Rd is satisfied, good images with almost no fogging on the paper can be obtained.

Furthermore, in order to sufficiently charge the toner, it is advantageous to increase the width of the developing nip between the developing roller 12, the blade 16, and the photosensitive drum 1. For this purpose, it is advantageous for the developing roller 12 to be soft;
If 2 is made too soft, distortion will occur at the contact point between the blade 16 and the photoreceptor drum 11, and if the developing nip width is made too large, the pressing force of the blade 16 and the photoreceptor drum 11 against the developing roller 12 will increase accordingly. Since it is necessary to increase the torque, problems such as decreased durability and the need to increase the torque of the developing device motor arise.

Figure 9 shows the rubber hardness of the developing roller 12 from 15° to 80'.
This figure shows the relationship between image density and paper fog when image data is collected by changing the density to .

From this graph, it can be seen that the image density decreases when the rubber hardness of the developing roller 12 is 20" or less and when the rubber hardness is 70" or more, and furthermore, the paper fog increases rapidly. If the rubber hardness of the roller 12 is less than 20'', the adhesion between the developing roller 12 and the photoreceptor drum 11 will be too high, causing the toner to roll within the developing nip width, making it impossible to apply sufficient charge to the toner. It seems to be for a reason.

Further, when the rubber hardness is 70 degrees or more, the load on the motor rotating the developing roller 12 becomes large, and the rotation speed of the developing roller 12 becomes slow.

From this, it has become clear that the comb hardness of the developing roller 12 is preferably in the range of 20'' to 70''.

In addition, the blade 16 was pressed against the developing roller 12 with a linear pressure of 50 g/cm;
It was also confirmed through experiments that a good toner layer could be formed within the range of g/cm.

Now, the above-described developing device 1o can be used as a so-called laser printer, which forms a latent image by irradiating a laser beam onto a photoreceptor whose surface is negatively charged, and converts it into a visible image using a reversal development method. The image part potential, that is, the exposed part potential, is -40 V, the non-image part potential, that is, the unexposed part potential, is -550 V, the developing bias is -200 V, the contact width with the photosensitive drum 11 is 2 mm, and the circumferential speed of the developing roller 12. When reversal development was carried out with the image density set to 2.5 times that of the photoreceptor drum 11, a printed sample with an image density of 1.4 and an extremely sharp line image with no blurring on the paper was obtained. Further, when a life test of 20,000 sheets was carried out using this developing device 1o, it was possible to obtain extremely good images equivalent to the initial images even after the life was over.

From the above, in order to obtain high-quality images without toner drop or background fog, the center line average roughness Rs (μm) of the surface of the photoreceptor drum 11 and the center line average roughness Rd of the surface of the developing roller 12 are required. (μm) satisfies the relationship Rs≦Rd, and more preferably, the rubber hardness of the developing roller 12 is in the range of 20@ to 706.

The developing device of this embodiment uses a negatively charged organic photoreceptor as the photoreceptor drum 11 to perform reversal development, but the developing device uses a positively charged organic photoreceptor or an inorganic photoreceptor to perform regular development. The present invention is also applicable to

It is also possible to use a developing device in which a resistor is used for the elastic layer 12b of the developing roller 12, or a resistive layer is formed on the conductive layer 12c, and the developing bias is directly supplied to the metal shaft 12a without using a protective resistor. The invention can be similarly applied.

Further, in this embodiment, the blade 16 is supported at a position against the rotation of the developing roller 12, but may be supported at a position with respect to the rotation of the developing roller 12.

[Effects of the Invention] As explained above, according to the present invention, the developer can be sufficiently charged at the contact point between the electrostatic latent image holder and the developing roller, thereby preventing the developer from falling off the developing roller. It is possible to realize a developing device that can prevent the occurrence of background fog and produce high-quality images.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the overall structure of a developing device according to an embodiment of the present invention, FIG. 2 is a perspective sectional view illustrating the structure of a developing roller in the developing device of FIG. 1, and FIGS. Figure 5 is a diagram showing a typical method of applying the conductive layer paint on the developing roller in Figure 2, Figure 6 is a diagram schematically showing the configuration of a surface roughness measuring device, and Figure 7 is based on the JIS standard. FIG. 8 is a graph showing the relationship between the ratio of the center line average roughness of the photoreceptor drum surface to the center line average roughness of the developing roller surface and paper overburden; FIG. 9 is a graph showing the relationship between the rubber hardness of the developing roller according to the JIS standard, the image density, and the number of occurrences of curling on the paper. 10...Developing device 11...Photoconductor drum 12...Developing roller 16...Blade applicant Toshiba Corporation Toshiba Intelligent Technology Corporation

Claims (1)

[Claims] A developing roller disposed opposite to the electrostatic latent image holder;
The developing roller is provided with a developer thin layer forming means for forming a developer thin layer, and the developer thin layer formed on the developing roller is brought close to or in contact with the electrostatic latent image holder to generate the electrostatic latent image. In a developing device that visualizes an electrostatic latent image held by an electrostatic latent image carrier, the center line average roughness of the surface of the electrostatic latent image carrier is expressed as Rs (μ
m), and the center line average roughness of the surface of the developing roller is Rd(
μm), a developing device satisfying the relationship Rs≦Rd.