JP3456237B2 - Conductive roll - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive roll used in electrophotographic copying machines and the like.

[0002]

2. Description of the Related Art In an electrophotographic copying machine, an original image is formed as an electrostatic latent image on a surface of a photosensitive drum, toner is attached to the electrostatic latent image to form a toner image, and the toner image is transferred to a copy paper. Is to be copied. In this case, in order to form an electrostatic latent image on the surface of the photosensitive drum, the surface of the photosensitive drum is charged in advance, the original image is projected onto the charged portion through the optical system, and the light-transmitted portion is projected. It is practiced to create an electrostatic latent image by removing the charge.
As a method of charging the surface of the photosensitive drum prior to the formation of the electrostatic latent image, there has conventionally been a corona discharge method or a contact charging method. The corona discharge method is a method in which the surface of the photosensitive drum is subjected to a corona discharge from a corona discharger to be charged. Since this method generally uses a high voltage power supply of 5 to 10 kV, it is necessary to take thorough safety measures, and there is a drawback in that harmful ozone is generated with discharge. Therefore, recently, a contact charging method in which a conductive roll is brought into sliding contact with the surface of the photosensitive drum to charge the surface of the photosensitive drum has attracted attention. An electrophotographic copying machine to which such a contact charging system is applied is constructed as shown in FIG. 3, and copying is performed as follows. That is, the charging roller 2 made of a conductive roller is rotated around the outer peripheral surface of the photosensitive drum 1 rotating around the shaft 1a in the direction of the arrow, and a voltage is applied to the charging roller 2 to apply the voltage to the photosensitive drum 1. The outer peripheral surface of is charged. Reference numeral 3 denotes an exposure mechanism section through which 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. A developing device 4 forms toner images by attaching toner to the electrostatic latent image. Reference numeral 6 denotes a paper feed mechanism roll that supplies copy paper 11 to the surface of the photosensitive drum 1 and transfers a toner image onto the copy paper 11 via the transfer device 5. Reference numeral 7 denotes a fixing roll for passing and fixing the copy paper 11 on which the toner image is formed. In this way, a copy is obtained. Incidentally. The cleaner 9 removes transfer residual images and residual toner on the surface of the photosensitive drum 1,
Further, the entire surface is irradiated with light by the eraser lamp 10 to have a zero potential, and the next charging is prepared. In the figure, 12 is a power source for applying a voltage of about 1 to 3 kV to the charging roll 2.

A large number of conductive rolls such as a charging roll, a developing roll, a transfer roll and a cleaning roll are used in an electrophotographic copying machine or the like. Such a conductive roll is required to have a conductivity of about 10 ¹ to 10 ¹² Ω · cm, and normally, as shown in FIG. 4, a metal shaft (core metal) 21 and its outer peripheral surface are provided. The conductive elastic body layer 22 formed on is generally formed of a composition in which conductive powder (carbon black, metal powder, etc.) and conductive fibers (carbon fiber, etc.) are mixed in synthetic rubber such as silicon rubber. There is. Among the conductive rolls of this type, the charging roll is required to have an electric resistance in the semiconductive region of 10 ⁵ to 10 ⁹ Ω · cm. However, in a conductive roll having the conductive elastic layer 22 as described above, conductivity is imparted by the contact of the conductive particles mixed in the synthetic rubber, so that uniform interparticle contact is not always obtained. Not not. This is particularly remarkable in the semi-conductive region, and therefore the electric resistance is reduced to the above-mentioned semi-conductive region (10
It is difficult to store it in the range of ⁵ to 10 ⁹ Ω · cm. As a result, there is a problem that a good copy image cannot be obtained.

In order to solve such a problem, the resistance adjusting layer 2 is formed on the outer periphery of the conductive elastic layer 22 as shown in FIG.
A conductive roll provided with 3 has been proposed. However, ordinary synthetic resins (polyethylene, polyester, epoxy resin, etc.) and synthetic rubbers (ethylene-propylene rubber, styrene-butadiene rubber, chlorinated polyethylene rubber, etc.) are insulators with an electric resistance of 10 ¹² Ω · cm or more. With these synthetic resins and synthetic rubbers, the resistance adjusting layer 2
3 is formed, and 10 ⁵ to 10 ⁹ Ω required for the charging roll
In order to satisfy the electric resistance of cm, the thickness of the resistance adjusting layer 23 needs to be 1 μm or less. However,
Such a thin resistance adjusting layer 23 has no practical durability. As described above, conventional conductive rolls, in particular, charging rolls have problems such as non-uniform resistance and lack of practicality, and in reality, satisfactory ones have not yet been obtained.

[0005]

In order to solve such a problem, the present inventors have found that an excellent effect can be obtained when the resistance adjusting layer is made of epichlorohydrin-ethylene oxide copolymer rubber (CHC). A patent application has been filed (JP-A-1-142569). That is, in this way, the electric resistance is uniform throughout, and the thickness of the resistance adjusting layer can be arbitrarily adjusted to withstand practical use. However, when such a conductive roll, particularly a charging roll, is put into practical use, the electrical resistance increases when a DC voltage is continuously applied to the roll for a long period of time, the current value flowing in the roll decreases, and an image due to a charging failure occurs. There is a problem that a defect (whitening etc.) occurs. Also. Depending on the type of material forming the resistance adjustment layer, the resistance may be higher than the required initial resistance. In this way, the actual situation is that a satisfactory charging roll has not yet been obtained.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a conductive roll capable of maintaining a proper electric resistance even after long-term use and obtaining a good image.

[0007]

In order to achieve the above object, the conductive roll of the present invention has a conductive elastic body layer formed on the outer periphery of a shaft body, and a resistance is formed on the outer periphery of the conductive elastic body layer. It is a conductive roll having an adjustment layer formed, and the resistance adjustment layer is formed of a composition mainly containing the following components (A) to (C). (A) Epichlorohydrin-ethylene oxide copolymer (B) Hydrogenated nitrile rubber (C) Ion conductive agent

[0008]

That is, the present inventors mainly set the material for forming the resistance adjusting layer for the purpose of setting an appropriate electric resistance (initial value) and suppressing the increase in the electric resistance of the resistance adjusting layer. Repeated research. In the course of that research, it was found that the use of a specific rubber component (B component) and ionic conductive agent (C component) can suppress an increase in electric resistance due to long-term voltage application. As a result of further research, in addition to the ion conductive agent and the specific rubber component (B component), CHC was added.
It has been found that the addition of (Component A) makes it possible to set a desired electric resistance (initial value) together with the effect of suppressing an increase in electric resistance due to voltage application, and a good copy image can be obtained.

Next, the present invention will be described in detail. The conductive roll of the present invention comprises a shaft body, a conductive elastic body layer formed on the outer circumference thereof, and a resistance adjusting layer further formed on the outer circumference thereof. The shaft body is not particularly limited, and for example, a cored bar made of a metal cylindrical body or a metal cylindrical body having a hollowed inside is used.

The conductive elastic layer formed on the outer periphery of the shaft is not particularly limited, and polynorbornene rubber, ethylene-propylene-diene rubber (EPDM),
Examples thereof include synthetic rubbers such as styrene-butadiene rubber, which may be used alone or in combination. The conductivity of such a conductive elastic layer is usually set to about 10 ¹ to 10 ⁴ Ω · cm. And the thickness is usually 1 to 10.
mm, preferably about 2 to 4 mm.

In particular, the hardness of the conductive elastic layer (JIS
When A) is set to 25 (Hs) or less, when a conductive roll, particularly a charging roll is used by incorporating it in a device as shown in FIG. 3, it is caused by a slight vibration between the photoconductor and the conductive roll. The occurrence of image quality defects (horizontal unevenness) and fogging phenomenon can be prevented. Thus, in order to set the hardness of the conductive elastic layer itself to a desired value, a softening agent such as oil is added. As the softening agent, naphthenic oil or the like is preferably used. Further, carbon black such as Ketjen black is used as a conductive agent, if necessary.

The resistance adjusting layer formed on the outer periphery of the conductive elastic layer is a composition mainly composed of CHC (component A), hydrogenated nitrile rubber (component B), and ion conductive agent (component C). Is formed by using. And the thickness is usually set to 10 to 300 μm,
A suitable range is 80 to 200 μm.

As described above, the combination of the components (A) to (C) has been found by the present inventors as a preferable material for forming the resistance adjusting layer, and the combination of the materials for forming the resistance adjusting layer is as follows. The electric resistance used is in the range of 10 ⁸ to 10 ¹¹ Ω · cm.

The mixing ratio of the above-mentioned CHC (component A) (X) and hydrogenated nitrile rubber (component B) (Y) is X.
It is preferable to set / Y = 80/20 to 20/80. That is, when CHC is less than 20 (hydrogenated nitrile rubber exceeds 80), the initial electric resistance is high, and CHC exceeds 80 (hydrogenated nitrile rubber is 20).
This is because there is a tendency that the degree of increase in electric resistance after application of a DC voltage becomes large.

Examples of the ion conductive agent (component C) include quaternary ammonium salts, which may be used alone or in combination. The blending amount of the ionic conductive agent (C component) is preferably set to 0.5 to 5 parts with respect to 100 parts by weight (hereinafter abbreviated as “part”) of the total amount of the A component and the B component. That is, the blending amount of the ionic conductive agent is 0.
If it is less than 5 parts, the electric resistance will not decrease, and if it exceeds 5 parts, the electric resistance will increase or the ionic conductive agent will tend to bloom on the surface.

The materials for forming the resistance adjusting layer include A to
In addition to the C component, a vulcanizing agent, a filler and the like are appropriately blended.
The above-mentioned vulcanizing agent is not particularly limited, and conventionally known ones such as thiourea, triazine and sulfur can be used. In addition, examples of the filler include insulating fillers such as silica, talc, clay, and titanium oxide, which may be used alone or in combination. Since a conductive filler such as carbon black is apt to cause dielectric breakdown when used under a high voltage, it should be used in an amount of 10% by volume or less based on the rubber component.

In the conductive roll of the present invention, a softening agent migration prevention layer mainly composed of N-methoxymethylated nylon is formed between the conductive elastic layer and the resistance adjusting layer, and the resistance adjusting layer is further formed. It is particularly preferable to adopt a constitution in which a protective layer mainly composed of N-methoxymethylated nylon is formed as the outermost layer on the outer periphery of the. The softener migration-preventing layer mainly composed of N-methoxymethylated nylon formed between the conductive elastic layer and the resistance adjusting layer is made of a softening agent such as oil contained in the conductive elastic layer. It is formed to prevent bleeding. The thickness of the softening agent migration prevention layer is generally set to 3 to 20 μm, preferably 4 to 10 μm. The electric resistance of the softening agent migration prevention layer is set to about 10 ³ Ω · cm. The N-methoxymethylated nylon (8-nylon) is not particularly limited, and conventionally known ones can be used. Further, the softening agent migration prevention layer contains carbon black such as Ketjen black as a conductive agent.

The protective layer formed as the outermost layer on the outer periphery of the resistance adjusting layer is mainly composed of the N-methoxymethylated nylon described above. As the N-methoxymethylated nylon, a conventionally known one can be used as it is, as described above. Then, when a conductive agent such as carbon black is mixed and dispersed in this protective layer, the conductivity becomes good at low temperature and low humidity, and good performance is exhibited even in a low temperature and low humidity environment. Such a protective layer is
Usually, it is preferable to set the thickness to 5 to 30 μm,
A particularly preferred range is 7 to 23 μm. The electrical resistance of this protective layer is set to 10 ⁸ to 10 ¹⁰ Ω · cm. The conductive agent is not limited to carbon black, and a conventionally known conductive agent can be used in place of the carbon black.

The conductive roll of the present invention, particularly the charging roll, can be manufactured, for example, as follows. That is, an adhesive is applied to the outer peripheral surface of the cored bar, and the conductive elastic body layer is formed using the rubber composition described above and utilizing mold vulcanization. Next, a mixed resin liquid in which N-methoxymethylated nylon and a conductive agent are mixed in advance is prepared, and the surface of the conductive elastic layer is polished as necessary, and then coated by spraying, dipping, or the like. It is dried and, if necessary, heat-treated and crosslinked to form a softener migration-preventing layer. Then, the resistance adjusting layer is formed on the conductive agent-containing softener migration preventing layer thus formed.
The resistance adjusting layer is formed by kneading the components A to C with a reinforcing agent, a processing aid, a vulcanizing agent, a filler and the like by an ordinary rubber processing method (Banbury mixer, roll, etc.) and unvulcanized rubber. The composition is made, and the unvulcanized rubber composition is treated with an appropriate solvent (eg, methyl ethyl ketone, methyl isobutyl ketone, etc.)
It can be molded by dissolving it in water, coating it on the outer peripheral surface of the conductive elastic layer, drying it, and then heating and vulcanizing it. A dip method is suitable for the above coating. More specifically, the solution containing the composition containing the above-mentioned components A to C as a main component is contained as a dip solution in a tank 24 as shown in FIG. Next, the roll 25 on which the conductive elastic body layer is formed is erected vertically and repeatedly immersed in the solution to form a rubber film mainly containing components A to C on the outer peripheral surface of the conductive elastic body layer. Let it form.
At this time, the conditions such as the dip solution viscosity, the ascending / descending speed, the number of ascending / descending, and the drying condition are preferably set so that the liquid film of the solution mainly containing the components A to C is in the range of 10 to 200 μm. . The thus formed liquid film is dried at a temperature of 25 to 80 ° C. for 0.5 to 4 hours to remove the solvent, and then at a temperature of 150 to 200 ° C. for 1 hour.
By heating for 0 minutes to 2 hours, the rubber film mainly containing the components A to C is vulcanized to form a resistance adjusting layer. Next, after forming the resistance adjusting layer as described above, a resin solution made of N-methoxymethylated nylon, or a resin solution in which a conductive agent or the like is mixed therewith is coated by spraying, dipping, etc., and dried, If necessary, heat treatment is performed to crosslink and form a protective layer. In this way, a conductive roll having a layer structure as shown in FIG. 2 is obtained. In the figure, 26 is a core metal, 27 is a conductive elastic layer, 28 is a softener migration preventing layer, 29 is a resistance adjusting layer, and 30 is a protective layer. The electric resistance of the conductive roll thus obtained is set to about 10 ⁶ to 10 ⁹ Ω · cm.

[0020]

As described above, the conductive roll of the present invention has the conductive elastic body layer formed on the outer periphery of the shaft body,
A resistance adjusting layer is formed using a composition mainly containing the components A to C. Therefore, the electric resistance is uniform throughout, and the increase in the electric resistance is suppressed even after long-term use. As a result, problems such as a fog phenomenon in the copied image do not occur. Further, it becomes possible to widely control the electric resistance (initial value), and it is possible to set an appropriate electric resistance (10 ⁵ to 10 ⁹ Ω · cm for the charging roll).

Next, examples will be described together with comparative examples. Tables show Examples 1 and 2 and Comparative Examples 1 to 3. [Preparation of Conductive Elastic Body Layer Forming Material] As a conductive elastic body layer forming material, a rubber composition was prepared using the following components. Polynorbornene rubber 100 parts Ketjen black 50 parts Naphthene oil 400 parts

[Preparation of Softening Agent Migration Prevention Layer Forming Material] As a softening agent migration preventing layer forming material, a carbon black dispersion resin liquid was prepared using the following components. N-methoxymethylated nylon 100 parts Carbon black 15 parts

[Preparation of Material for Forming Resistance Adjusting Layer] As a material for forming a resistance adjusting layer, the components shown in Table 1 below were mixed in the proportions shown in the same table to prepare an unvulcanized rubber composition. The electrical resistance of the unvulcanized rubber composition is also shown in the same table.

[Preparation of Protective Layer Forming Material] As a protective layer forming material, a resin liquid was prepared using the following components. N-methoxymethylated nylon 100 parts Carbon black 8 parts

Next, an adhesive is applied to the outer periphery of the cored bar made of a metal shaft having a diameter of 8 mm, and the outer periphery of the core is vulcanized by using the rubber composition of the conductive elastic layer forming material. The conductive elastic body layer was formed so that the entire outer diameter was 15 mm. Then, the outer periphery of the conductive elastic layer was spray-coated with the carbon black dispersion resin liquid for the material for forming a softening agent migration preventing layer, and then dried to form a softening agent migration preventing layer having a thickness of 6 to 10 μm. on the other hand,
After roll-mixing the rubber composition for forming the resistance adjusting layer, methyl ethyl ketone / methyl isobutyl ketone = 3
The solution was dissolved in a solvent (weight ratio) of 1/1 and the viscosity was adjusted to 500 centipoise to prepare a dip solution. A cored bar on which the softening agent migration prevention layer was formed as described above was dipped in this solution for coating, then pulled up and dried, and then heat treated for crosslinking. Then, a resin solution for forming a protective layer was spray-coated on the surface and dried to form a protective layer. As a result, the intended conductive roll was obtained.

[0026]

[Table 1]

For each conductive roll thus obtained, 10 mm of silver paste was applied on the outer surface of the conductive roll.
The electrodes on four sides were drawn (with guard electrodes), and the electrical resistance (initial value) between the metal shaft and the electrodes was measured. Further, the electric resistance after applying a DC voltage (-550V) to this conductive roll was also measured. Further, the above conductive roll was incorporated as a charging roll into the apparatus shown in FIG. 3, and the state immediately after being incorporated into a copy (initial state) and the copied image after taking 60,000 copies were visually observed and evaluated. Then, those in which no image defect such as a fogging phenomenon occurred were displayed as ◯, and those in which the image defect occurred were displayed as x. The results are shown in Tables 2 and 3 below.

[0028]

[Table 2]

[0029]

[Table 3]

From the results of Tables 2 and 3 above, Comparative Examples 1 and 2
The degree of increase in electric resistance was as high as one digit or more, and a defect occurred in the copied image. Further, Comparative Example 3 had a high electric resistance, and a defect occurred in the copied image. On the other hand, it can be seen that the example products have a low degree of increase in electric resistance, and the increase in electric resistance is suppressed even after application of the DC voltage. Furthermore, no image defects occurred.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an example of a method for producing a conductive roll of the present invention.

FIG. 2 is a vertical sectional view of a conductive roll of the present invention.

FIG. 3 is a configuration diagram of an electrophotographic copying machine in which a conductive roll is incorporated.

FIG. 4 is a vertical cross-sectional view of a conventional conductive roll.

FIG. 5 is a vertical cross-sectional view of a conventional conductive roll.

[Explanation of symbols] 26: Core 27: Conductive elastic layer 28: Softener migration prevention layer 29: Resistance adjustment layer 30: Protective layer

─────────────────────────────────────────────────── --- Continuation of the front page (56) References JP-A-5-107874 (JP, A) JP-A-5-88509 (JP, A) JP-A-4-311972 (JP, A) JP-A-1- 142569 (JP, A) JP 58-87572 (JP, A) JP 60-150071 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) G03G 15/02 101 F16C 13/00 G03G 15/08 501 G03G 15/16 103 G03G 21/10

Claims (3)

(57) [Claims] 1. A conductive roll having a conductive elastic body layer formed on the outer circumference of a shaft body, and a resistance adjusting layer formed on the outer circumference of the conductive elastic body layer, wherein the resistance adjusting layer comprises: 1. A conductive roll formed of a composition mainly containing the components (A) to (C). (A) Epichlorohydrin-ethylene oxide copolymer (B) Hydrogenated nitrile rubber (C) Ion conductive agent 2. Between the conductive elastic body layer and the resistance adjusting layer,
2. The conductive material according to claim 1, wherein a softener migration preventing layer mainly composed of N-methoxymethyl nylon is formed, and a protective layer mainly composed of N-methoxymethyl nylon is formed as an outermost layer on the outer periphery of the resistance adjusting layer. roll. 3. The conductive roll according to claim 1, wherein the ionic conductive agent is a quaternary ammonium salt.