JP2888949B2 - Conductive roll - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a conductive roll used for a developing roll of an electrophotographic copying machine.

[Conventional technology]

Generally, an electrophotographic copying machine is configured as shown in FIG.
Copying is performed as follows. That is, the photosensitive drum 1 rotating in the direction of the arrow around the axis 1a is uniformly charged by the corotron 2. Reference numeral 3 denotes an exposure mechanism through which a slit exposure 8 of the original light 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. Reference numeral 4 denotes a developing roll built in the case 4a.
The toner is frictionally charged by the sliding contact of the layer forming member 12, and the toner in the case 4a adheres. 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 fed to the paper feed roller 6
Is transferred as indicated by an arrow, is transferred to the copy paper 11 via the transfer device 5, and is fixed on the copy paper 11 by the fixing roll 7. Copying is performed in this manner. Note that 9
Reference numeral denotes a cleaner for removing transfer residual images and residual toner on the surface of the photosensitive drum 1, and reference numeral 10 denotes an eraser lamp for making the photosensitive drum 1 zero and preparing for the next charging.

When the toner is non-magnetic, this type of developing roll 4
Generally, as shown in FIG.
When the toner has magnetism, as shown in FIG. 7, a metal sleeve (core bar) 41b, end caps 41c at both ends and a metal sleeve 41b are formed. 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 formed of a cylindrical body formed of a conductive material obtained by introducing a conductive material into a synthetic resin matrix from the viewpoint of cost reduction and the like. It is externally fitted to the outer peripheral surface of the cored bar (41a, 41b). And, as such a conductive material, generally,
They are broadly classified into carbon-based materials and metal oxide-based materials.

[Problems to be solved by the invention]

However, in the case of a conductive roll using a carbon-based conductive material, electrons move even when the carbon-based conductive materials are slightly separated from each other. Therefore, as shown in FIG. Potential (white area is V
_BK , the electrostatic latent image portion is V _Image , and the darkest portion is V _H ) and the bias potential (V _Bias ) on the side of the developing roll 4 causes the toner to fly in a structure in which the toner always flies.
Towards _Bias has the advantage of excellent low state (see FIG. 9) and bias characteristics than V _BK (i.e., shading is clearly distinguished) contrary, unevenness is likely to occur in the variation is large copy image of electrical resistance There is a problem that.

On the other hand, a conductive roll using a metal oxide-based conductive material has the advantage that the electric resistance is small and unevenness of a copied image is unlikely to occur, but the metal oxide-based conductive materials are in contact with each other. Since electron transfer is performed only in the metal oxide conductive material, depending on the dispersion state of the metal oxide conductive material,
As shown in FIG. 10, there is a problem that the bias characteristic becomes poor when V _Bias becomes higher than V _BK (the toner is also scattered on a white background portion to make the shading unclear).

The present invention has been made in view of such circumstances,
There is no unevenness in the copied image and good bias characteristics (V
Its purpose is to provide a conductive roll having a _Bias <V _BK ).

[Means for solving the problem]

In order to achieve the above object, a conductive roll of the present invention is a conductive roll in which a conductive layer is formed on the outer periphery of a shaft, wherein the conductive layer is formed of a metal oxide conductive material in a binder resin. by the coating of conductive paint which contains a carbon-based conductive material are connexion formed, the average particle diameter D _M of the metal oxide-based conductive material is larger than the average particle diameter D _C of the carbon-based conductive material so as configured, and the addition amount C _C of amount C _M and the carbon-based conductive material of the metal oxide-based conductive material, a configuration that is set to satisfy the following conditions (a).

(A) the electrical resistance Rv of the coating film obtained by containing only the metal oxide-based conductive material in the binder resin in the amount C _M
M is smaller than the electric resistance Rv _{C of the} coating film obtained by adding only the carbon-based conductive material to the binder resin at the added amount C _C.

[Action]

That is, the present inventors use a carbon-based conductive material having good bias characteristics and easily causing unevenness of a copied image and a metal oxide-based conductive material having poor bias characteristics and hardly causing unevenness of a copied image. A series of studies were conducted on the idea that an excellent conductive roll in which the drawbacks of the above were offset could be obtained.However, carbon-based conductive materials and metal oxide-based conductive materials that have been used conventionally were compared. It has been found that there are many points that are insufficient in the variation of the electric resistance by simply using them together, and that no preferable one can be obtained. Therefore, as a result of further research, it was decided that the conductive layer of the conductive roll was formed by a conductive paint containing a metal oxide-based conductive material and a carbon-based conductive material. The average particle diameter D _M is set to be larger than the average particle diameter D _C of the carbon-based conductive material, and the electric resistance Rv _M of the coating film obtained by having only the metal oxide-based conductive material in the binder resin. The electrical resistance Rv of a coating film obtained by containing only the carbon-based conductive material in a binder resin.
To be smaller than _C, and adjusting the addition amount C _M, C _C of the metal oxide-based conductive material and the carbon-based conductive material, the bias characteristics are excellent, yet without unevenness to copy image without variation in electrical resistance The present inventors have found that an excellent conductive roll can be obtained, and have reached the present invention.

 Next, the present invention will be described in detail.

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

The shaft body is not particularly limited, and may be a metal core (41a in FIG. 6) made of a solid metal body, or a metal cylindrical body hollowed in the interior (FIG. 7).
41b) is used.

Further, the conductive layer formed along the outer periphery of the shaft body,
It is formed of a conductive paint in which a metal oxide conductive material and a carbon conductive material, which are conductive materials, are dispersed and contained in a binder resin, and the thickness thereof is set to 30 to 300 μm, especially 50 to 200 μm. Is preferred.

The binder resin is not particularly limited, but a resol type phenol resin is preferable from the viewpoint of hardness and abrasion resistance.

Further, as the metal oxide-based conductive material, c-ZnO, c
—SnO ₂ , c-TiO _2, etc., which may be used alone or in combination of two or more. Here, “c−” means having conductivity.

Further, examples of the carbon-based conductive material include conductive carbon, general-purpose carbon, color carbon, graphite, and the like, and they may be used alone or in combination of two or more.

And the average particle diameter D _M of the metal oxide-based conductive material is
It is necessary to set larger than the average particle diameter D _C of the carbon-based conductive material. The metal amount C _C of amount C _M and the carbon-based conductive material of the oxide conductive agent, the coating film obtained by containing a binder resin only the metal oxide-based conductive material with the added amount C _M resistance Rv _M of, it is necessary to set to be smaller than the electrical resistance Rv _C of the coating film obtained by containing a binder resin only the carbon-based conductive material in the amount of addition C _C. By satisfying these two conditions,
As shown in FIG. 2, the carbon-based conductive material 17 enters between the metal oxide-based conductive materials 16 through which current flows only in the contact state, and the current flow is improved by the tunnel effect, so that the bias characteristics are improved. And metal oxide conductive material
Since the uniformity of electric resistance, which is the 16 characteristic, is utilized, an extremely clear copy image can be obtained.

The conductive roll of the present invention can be manufactured using the above-mentioned raw materials, for example, as follows. That is,
First, a binder resin, a metal oxide-based conductive material, and a carbon-based conductive material are mixed and stirred using a ball mill or the like, and the mixture is dissolved in an appropriate solvent (methanol, ethanol, or the like) to form a conductive paint. And this conductive paint,
A uniform thickness is applied to the surface of the metal shaft (core metal) by dipping, roll coating, spray coating, or the like, dried, and heat-cured to obtain a structure as shown in FIG. A conductive roll can be obtained. In the figure, 14 is a cored bar, and 15 is a conductive layer.

In the above coating, it is preferable to use a dipping method. More specifically, the conductive paint is stored as a dipping liquid in a tank 13 as shown in FIG. And
The metal core 14 is set upright, and is repeatedly immersed in the conductive paint in the tank 13 to form a coating film of the conductive paint on the outer peripheral surface of the metal core 14. At this time, the conditions such as the viscosity of the dipping liquid, the elevating speed, and the number of elevating times are as follows.
It is preferable to set the conditions so as to fall within the range of 0 μm. The thus formed coating film was dried at a temperature of 50 ° C. for 2 hours to remove the solvent.
For one hour to cure the binder resin and form the conductive layer 15. Thus, the conductive roll shown in FIG. 1 can be made.

As described above, the conductive roll obtained as described above has a carbon-based conductive material 17 penetrating between the metal oxide-based conductive materials 16 in the conductive layer 15 to exhibit a tunnel effect and transfer electrons. Is performed smoothly, the bias characteristics are kept good, and the electric resistance becomes uniform due to the presence of the metal oxide conductive material 16 (see FIG. 2).

〔The invention's effect〕

As described above, the conductive roll of the present invention, the conductive layer, the metal oxide-based conductive material and the carbon-based conductive material, each of which is set so that the average particle diameter of each other has a specific magnitude relationship, respectively, a specific Since it is formed by a special conductive paint film that is contained in a proportion, there is no variation in the electrical resistance on the surface of the conductive layer, and the flow of electrons moving in the conductive layer is smooth and V _BIAS is V _BK Never be higher. Therefore, for example, when incorporated in the above-mentioned electroconductive roll electrophotographic copying machine and used for a long period of time, there is an effect that the copied image has no unevenness and its density is clearly displayed.

 Next, examples will be described together with comparative examples.

[Examples 1 to 4] As the conductive layer forming material, the raw materials shown in Table 1 described below were blended in the proportions shown in the same table, mixed and stirred by a ball mill, dissolved in methanol, and adjusted to a viscosity of 300 cps. A dipping solution (conductive paint) was prepared. In this liquid, the diameter 20
After immersing and coating a core metal of mm, the core was pulled up and dried, and then subjected to a heat treatment to form a conductive layer. Then, a conductive roll as shown in FIG. 1 was produced.

[Comparative Examples 1 to 8] The raw materials shown in Table 1 below were blended in the proportions shown in the table,
After mixing and stirring with a ball mill, the same treatment as in the above example was performed.

For each of the conductive rolls thus obtained, the average electric resistance, the variation of the electric resistance, the uniformity of the copied image,
The density and bias characteristics were measured and evaluated by the following methods. The results are shown in Table 2 below.

<< Average Electric Resistance and Variation of Electric Resistance >> The average electric resistance is measured by a measuring system shown in FIG. 4B by forming 20 electrodes 21 having the shape shown in FIG. 4A on the roll surface. did. In the figure, 20 is a roll, 21a is a main electrode, and 21b is a guard electrode. And the average value of each measured value was calculated. Further, the variation of the electric resistance was determined by measuring the electric resistance of 20 places of each conductive roll in the same manner as the measurement of the average electric resistance, and determining the difference between the maximum value and the minimum value of the measured values.

<< Uniformity of copied image >> An electroconductive roll was used as a developing roll, and was incorporated into a copying machine to perform image output to check for image unevenness. Then, x indicates that the image unevenness has occurred, and o indicates that the image unevenness has not occurred.
The results are shown in Table 2 below.

<< Density of Copy Image >> An image was formed in the same manner as described above. In this image formation, a solid black copy was taken at the maximum density, and the density of the copy was measured with a reflection densitometer manufactured by Macbeth. Then, those having a measured value of 1.1 or more were evaluated as ○, and those having a measured value of less than 1.1 were evaluated as x, and the results are shown in Table 2 below.

<< _Bias Characteristic of Copy Image >> An image is obtained in the same manner as above, and (V _Bias −V _BK ) <
The case of 0 (minus charge) was _evaluated as ○, and the case of (V _Bias −V _BK ) ≧ 0 was _evaluated as ×.

From the results shown in Table 2 above, the product of the comparative example has a problem in either the electrical characteristics or the copied image characteristics (including the bias characteristics), whereas the product of the example is excellent in all of the characteristics and excellent. It can be seen that it can be a developing roll.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of the conductive roll of the present invention, FIG. 2 is a schematic sectional view of the conductive layer of the conductive roll of the present invention, and FIG. 3 is an example of a method of manufacturing the conductive roll of the present invention. FIG. 4 (A) is a plan view showing the configuration and shape of an electrode for examining electrical characteristics of an example product and a comparative example product, and FIG. 4 (B) is a conductive roll using the above electrode. FIG. 5 is a configuration diagram showing a measuring system for measuring the electric resistance of the electrophotographic copying machine, FIG. 5 is a configuration diagram of an electrophotographic copying machine incorporating a conductive roll, and FIGS. 6 and 7 are longitudinal sectional views of a conventional conductive roll. FIG. 8 is an explanatory diagram of the relationship between the potential of the photosensitive drum surface and the potential of the developing roll surface. FIG. 9 is an explanatory diagram of an undesirable bias characteristic.
FIG. 10 is an explanatory diagram of good bias characteristics. 14 core metal, 15 conductive layer, 16 metal oxide conductive material, 17 carbon conductive material

Continued on the front page (72) Inventor Eiji Yasui Komaki City, Aichi Prefecture, Kita-gaiyama, Gezu 3600 Tokai Rubber Industries Co., Ltd. Field (Int.Cl. ⁶ , DB name) G03G 15/08

Claims (1)

(57) [Claims] 1. A conductive roll having a conductive layer formed on the outer periphery of a shaft body, wherein the conductive layer contains a metal oxide-based conductive material and a carbon-based conductive material in a binder resin. The metal oxide-based conductive material is set so that the average particle size D _M of the metal oxide-based conductive material is larger than the average particle size D _C of the carbon-based conductive material, and Addition amount of conductive material C _M and addition amount of carbon-based conductive material C _C
Is set so as to satisfy the following condition (A). (A) the electrical resistance Rv of the coating film obtained by containing only the metal oxide-based conductive material in the binder resin in the amount C _M
M is smaller than the electric resistance Rv _{C of the} coating film obtained by adding only the carbon-based conductive material to the binder resin at the added amount C _C.