JPH0488375A - Conductive roll - Google Patents

Abstract

PURPOSE:To allow the stable transportation of a toner by forming conductive layer of a special conductive coating material contg. the silica particles set to a prescribed average particle size. CONSTITUTION:The conductive roll is constituted of a shaft body 14 and the conductive layer 15 formed on the outer periphery thereof. The conductive layer 15 is formed of the conductive coating material prepd. by dispersing and incorporating conductive powder and silica particles 16 having 1 to 3mum average particle size into a phenolic resin 17. The shaft body 14 is not particularly restricted; an arbor consisting of a solid body made of a metal and a cylindrical body made of a metal bored internally to hollow are used. The wear of the ruggedness on the surface of the conductive layer is obviated in this way and the toner is constantly and stably transported over a long period of time.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a conductive roll used as a developing roll of an electrophotographic copying machine.

[Conventional technology]

-g, the electrophotographic copying machine is constructed as shown in FIG. 6, and copies are made in the following manner. That is, the photosensitive drum 1 rotating in the direction of the arrow about the shaft 1a is uniformly charged by the corotron 2. Reference numeral 3 denotes an exposure mechanism section through which slit exposure 8 of the original optical image reaches the surface of the photosensitive drum 1, and an electrostatic latent image corresponding to the original image is formed on the surface of the photosensitive drum 1. 4 is a developing roll built into the case 4a;
Frictionally charged by the sliding contact of the layer forming member 12, the case 4
The toner in a is attached. Then, the toner flies toward the electrostatic latent image on the surface of the photosensitive drum 1, and a toner image is formed on the surface of the photosensitive drum 1.

This toner image is transported by the paper feed roller 6 in the direction of the arrow, transferred to the copy paper 11 via the transfer device 5, and fixed onto the copy paper 1 by the fixing roll 7. Copying is performed in this manner. Note that 9 is a cleaner that removes transfer afterimages and residual toner on the surface of the photosensitive drum 1, and 10 is an eraser lamp that zeroes the photosensitive drum 1 and prepares it for the next charging.

When the toner is non-magnetic, this type of developing roll 4 generally has a metal shaft (core bar) 41 as shown in FIG.
When the toner has magnetism, as shown in FIG. 8, the metal sleeve (core metal) 41b, the end caps 41c at both ends thereof, and the metal sleeve 41. Mag shaft 41d in b
and a conductive layer 42b on the outer periphery of the metal sleeve 41b. In the figure, 43 is a bearing.

These conductive layers 42a and 42b of the developing roll 4 are recently formed from a cylindrical molded body made of a conductive material made by mixing a conductive material such as carbon powder into a synthetic resin matrix from the viewpoint of cost reduction. and the above core metal (41
a, 41b). The surface thereof is formed into an uneven surface so that the attached toner can be conveyed in the circumferential direction.

[Problem to be solved by the invention]

However, in such a developing roll 4, even if an initial copy image can be secured by controlling the electrical resistance of the conductive layers 42a and 42b, the copy density tends to gradually decrease as the number of copies increases. This is because the surfaces of the conductive layers 42a and 42b are worn to a mirror surface due to the sliding contact between the layer forming member 12 and the surface of the developing roll 4 shown in FIG. 6, and the amount of toner that adheres to the surfaces and is transported is reduced. It is thought that this is because of this.

This invention was made in view of the above circumstances, and aims to provide a conductive roll that can transport toner constantly and stably over a long period of time without causing the unevenness on the surface of the conductive layer to wear out due to use. purpose.

[Means for Solving the Problems] In order to achieve the above object, a conductive roll of the present invention is a conductive roll having a conductive layer formed on the outer periphery of a shaft body, the conductive layer being made of phenolic resin. The structure is formed by a coating film of a conductive paint in which conductive powder and silica particles having an average particle size of 1 to 3 μm are dispersed.

[Function] In other words, as a result of a series of studies on the form of the surface of the conductive roll and the state of toner conveyance, the present inventors found that the average particle diameter of the toner to be conveyed (5
It has been found that the toner can be conveyed most stably by providing unevenness of about 1/10 to 1/3 of 1/10 μm). Therefore, as a result of further research on the structure of the conductive layer that would maintain the above-mentioned suitable irregularities on the surface of the conductive coal at all times without being worn out, we found that silica particles with an average particle size of 1 to 3 μm were added to the phenol resin. When a coating film is formed using a conductive paint dispersed as a filler and used as a conductive layer, the surface of the conductive layer becomes uneven and rough due to the silica particles, and even after long-term use, the silica particles gradually become uneven. It was discovered that the resin falls off in a spherical shape along with the surrounding binder resin, and the uneven surface is maintained by the marks left behind, and this invention was achieved based on this discovery.

Next, this invention will be explained in detail.

The conductive roll of the present invention is composed of a shaft and a conductive layer formed on the outer periphery of the shaft.

The above-mentioned shaft body is not particularly limited, and may include a core bar made of a solid metal body (41a in FIG. 7) or a metal cylindrical body with a hollow interior (41b in FIG. 8). used.

The conductive layer formed along the outer periphery of the shaft is made of a conductive paint containing conductive powder and silica particles dispersed in a binder resin, and has a thickness of 30 to 300 μm. It is suitable to set it to 50-200 micrometers.

Phenol resins are used as the binder resin of the conductive paint, and resol type phenol resins are particularly suitable.

In addition, the above-mentioned conductive powders include carphone black, c
-ZnOc-3nOz etc. are used. It is particularly preferable that the average particle diameter is set to 115 or less of the silica particles described below. That is, if the average particle diameter is larger than 115 of the silica particles, the influence of the conductive powder on the uneven surface of the conductive layer cannot be ignored. Note that the above "C-" means having electrical conductivity.

Furthermore, the silica particles have an average particle diameter of 1 to 3.
It is necessary to use one set to μm. In other words, if the average particle size is smaller than the above range, the surface of the conductive layer will become uneven and rough, making it impossible to transport toner.On the other hand, if the average particle size is larger than the above range, silica particles will form due to wear. The problem is that the change in the shape of the unevenness due to the falling off of the toner is too large and the amount of toner conveyed is not stable. Note that the specific surface area of the silica particles is 80 rrr/g
The following is desirable. In other words, a large specific surface area value of a silica particle means that the surface of the silica particle is composed of an uneven surface with a large difference in unevenness or an uneven surface with a high density. The marks that fall off tend to become irregularly shaped concave shapes. For this reason, it is difficult to provide the surface of the conductive layer with an uneven shape that is stable over time, and the amount of toner conveyed tends to be unstable. In addition, the specific surface area of the silica particles is 80 bo/
If it exceeds g, there is a problem that the compatibility with the binder resin increases, the viscosity of the conductive paint increases, and the coating properties deteriorate. Note that the above-mentioned "specific surface area" is determined by an iodine adsorption method (BET method).

It is suitable that such silica particles are blended in a ratio of 5 to 30 parts with respect to 100 parts by weight (hereinafter abbreviated as "parts") of the binder resin. That is, if the amount of silica particles blended is less than 5 parts, the effect of roughening the surface of the conductive layer is small, and on the other hand, if it is more than 30 parts, the effect of roughening the surface is too large and the amount of toner conveyed becomes excessive. It is from.

The conductive roll of the present invention can be manufactured using the above raw materials, for example, in the following manner. That is, first, a phenolic resin as a binder resin, the conductive powder, and the silica particles are mixed and stirred using a ball mill, etc., and this mixture is dissolved in an appropriate solvent (methanol, ethanol, etc.) to form a conductive paint. Create. Then, this conductive paint is coated to a uniform thickness on the surface of the metal shaft (core metal) by a dip method, roll coating method, spray coating method, etc., dried, and heated to harden. A conductive roll having the structure shown can be obtained. In the figure, reference numeral 14 indicates a metal core 15 that is a conductive layer.

In the above coating, it is preferable to use a dip method. More specifically, the conductive material mixed resin liquid is stored as a dip liquid in a tank 13 as shown in FIG. 2. Next, the core metal 14 is vertically erected and repeatedly dipped in the mixed resin liquid, thereby forming a coating film of the conductive paint on the outer peripheral surface of the core metal 14. The viscosity of the dip liquid at this time.

Conditions such as lifting speed and number of lifting times are such that the coating film of the conductive paint is within the range of 50 to 350 μm, especially 70 to 220 μm.
It is preferable to set the conditions so that The material on which such a coating film was formed was dried at a temperature of 50°C for 2 hours to remove the solvent, and then heated at a temperature of 150°C for 1 hour to harden the phenolic resin and form the conductive layer 15. Create. In this way, the conductive coil shown in FIG. 1 can be produced.

The conductive roll obtained in this way has the above-mentioned conductive layer 1.
5 is made of a special conductive paint containing silica particles dispersed therein, the surface becomes matte due to the silica particles 16 dispersed in the binder resin (phenol resin) 17, as shown in It is uneven.

When this conductive roll is incorporated and used as the developing roll 4 of an electrophotographic copying machine as shown in FIG. 6, as the binder resin 17 wears out, the Since the silica particles 16 drop off in a spherical shape together with the surrounding binder resin 17, the traces of the drop-off become hemispherical recesses P, and the surface of the conductive layer 15 maintains an appropriate level of unevenness. This is because the binding force between the silica particles 16 and the binder resin 17 is very strong.
Such an effect cannot be obtained if other fillers such as calcium carbonate particles are used instead of the silica particles 16 or other resins such as epoxy resin are used instead of the binder resin 17. do not have. Therefore, even after long-term use, the amount of toner that enters the recess P and is transported does not change, and toner can be stably supplied.

〔Effect of the invention〕

As described above, in the conductive roll of the present invention, the conductive layer is
Since the conductive layer is formed from a special conductive paint containing silica particles having a predetermined average particle diameter, the surface of the conductive layer always has a suitable uneven surface and can transport toner stably.

Therefore, for example, when the conductive roll is incorporated into an electrophotographic copying machine and used for a long period of time, there is an advantage that the density of the copied image hardly decreases due to an increase in the number of copies.

Next, examples will be described together with comparative examples.

[Examples 1 to 5] As a conductive layer forming material, the raw materials shown in Table 1 below were blended in the proportions shown in the table, mixed and stirred in a ball mill, then dissolved in methanol, and the viscosity was adjusted to 300 cps. We made dip liquid (conductive paint). A core metal having a diameter of 20 mm was immersed in this solution to be coated, then pulled out and dried, and then heat treated to form a conductive layer. Then, a conductive roll as shown in FIG. 1 was produced.

[Comparative Examples 1 to 5] The raw materials shown in Table 1 below were blended in the proportions shown in the same table, mixed and stirred using a ball mill, and then treated in the same manner as in the above examples.

(Margin below) For each conductive roll obtained in this way, the average electrical resistance, variation in electrical resistance, uniformity of the copied image (presence or absence of image unevenness), density, and durability were measured and evaluated using the following methods. did. The results are shown in Table 2 below.

(Average electrical resistance and variation in electrical resistance) The average electrical resistance is measured by forming electrodes 21 having the shape shown in FIG. 5(A) at 20 locations on the roll surface and using the measurement system shown in FIG. 5(B). did. In the figure, 20 is a roll, 21a is a main electrode, and 21b is a guard electrode. Then, the average value of each measurement value was determined. In addition, the variation in electrical resistance was determined by measuring the electrical resistance at 20 locations on each conductive roll in the same manner as the measurement of the average electrical resistance described above, and by calculating the difference between the maximum value and the minimum value of the measured values.

(Uniformity of Copied Image) A conductive roll was used as a developing roll, installed in a copying machine, and image ratio was performed to examine the presence or absence of image unevenness. The results are shown in Table 2 below: those in which image unevenness occurred were evaluated as x, and those in which no image unevenness occurred were evaluated as ○.

(Density of Copied Image) An image was produced in the same manner as above, and in this image production, a solid black copy was taken at the maximum density, and the density of the copy was measured using a reflection densitometer manufactured by Macbeth. Those with a measured value of 1.1 or more and those with an O1 measured value of less than 1.1 were evaluated as x, and are shown in Table 2 below.

(Durability of Copied Images) The conductive roll was used as a developing roll and installed in a copying machine, and a running test of the copying machine was conducted, and the number of copies when the copy density reached 90% of the initial copy density was shown.

(Leaving space below) From the results in Table 2 above, it can be seen that the comparison product had problems with either the electrical properties or the copy image characteristics, whereas the tested product had generally good properties in all properties and exhibited excellent development. It turned out to be a roll and a scale.

[Brief explanation of the drawing]

FIG. 1 is a box cross-sectional view of the conductive roll of the present invention, FIG. 2 is an explanatory diagram showing an example of the manufacturing method of the conductive roll of the present invention, and FIGS. 3 and 4 are conductive rolls of the conductive roll of the present invention. 5(A) is a plan view showing the configuration and shape of the electrode for investigating the electrical characteristics of the tested and comparative products; FIG. 5(B) is the above electrode. Figure 6 is a diagram showing the configuration of an electrophotographic copying machine incorporating a conductive roll, and Figures 7 and 8 are diagrams showing a measurement system used to measure the electrical resistance of a conductive roll. FIG. 14... Core metal 15... Conductive Jig 16...
Silica particles 17...Binder resin (A) Fig.

Claims (3)

[Claims] (1) A conductive roll having a conductive layer formed on the outer periphery of the shaft, wherein the conductive layer is a conductive roll containing conductive powder and silica particles having an average particle diameter of 1 to 3 μm dispersed in a phenol resin. A conductive roll characterized by being formed of a paint film. (2) The conductive roll according to claim 1, wherein the silica particles have a specific surface area of 80 m^2/g or less. (3) Claim (1) or (2) wherein the average particle diameter of the conductive powder is 1/5 or less of the average particle diameter of the silica particles.
) described conductive roll.