JPH0758403B2 - Conductive roll - Google Patents

Description

TECHNICAL FIELD The present invention relates to a conductive roll used in an electrophotographic copying machine or the like.

[Prior Art] An electrophotographic copying machine forms an original image as an electrostatic latent image on the surface of a photosensitive drum, attaches toner to the electrostatic latent image to form a toner image, and transfers the toner image to 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 portion through which the light passes is charged. 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 are conventionally known a corona discharge method and 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 source of 5 to 10 KV, it is necessary to take thorough safety measures, and there is a drawback that harmful ozone is generated due to discharge. For this reason, recently, a contact charging method in which the surface of the photosensitive drum is charged by rubbing a conductive roll on 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, a charging roll 2 made of a conductive roll is rotated on the outer peripheral surface of the photosensitive drum 1 which rotates about the shaft 1a in the direction of the arrow in a direction opposite to or in the forward direction of the photosensitive drum 1 to partially elastically deform it. Rub while rubbing. The rubbing of the charging roll 2 charges the outer surface of the photosensitive drum 1. Three
Is an exposure mechanism section through which the slit exposure 8 of the light image of the document is exposed.
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 a toner image by attaching toner to the electrostatic latent image. Reference numeral 6 denotes a paper feed mechanism roll that supplies the copying machine 11 to the surface of the photosensitive drum 1 and transfers a toner image onto the copying machine 11 via the transfer device 5. Reference numeral 7 denotes a fixing roll for passing and fixing the toner image formed on the copying machine 11. In this way, a copy is obtained. The surface of the photosensitive drum 1 is cleaned by a cleaner 9 to remove transfer residual images and residual toner, and is further irradiated with light from the entire surface by an eraser lamp 10 to be brought to a zero potential to prepare for the next charging. A power source 12 applies 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. As such a conductive roll, 10 ¹
It is required to have a conductivity of about 10 ¹² Ω · cm, and as shown in Fig. 4, it is usually a metal shaft.
21 and a conductive elastic layer 22 formed on the outer peripheral surface thereof. The conductive elastic layer 22 is generally formed of a composition in which conductive powder or conductive fibers (carbon black, metal powder, carbon fibers, etc.) are mixed in synthetic rubber such as silicon rubber. Among the conductive rolls of this type, the charging roll is required to have electric resistance in the semiconductive region of 10 ⁵ to 10 ⁷ Ω · cm.
However, in the conductive roll provided with the conductive elastic layer 22 as described above, since the conductivity is imparted by the contact of the conductive particles mixed in the synthetic rubber, a uniform interparticle contact is always obtained. Not not. This is particularly remarkable in the semi-conductive region, so that it is difficult to fit the electric resistance in the above-mentioned semi-conductive region (10 ⁵ to 10 ⁷ Ω · cm ² ). As a result, there is a problem that a good copy image cannot be obtained.

In order to solve such a problem, there has been proposed a conductive roll having a resistance adjusting layer 23 provided on the outer periphery of a conductive elastic layer as shown in FIG. However, ordinary synthetic resins, polyethylene, polyester, epoxy resins, etc.) and synthetic rubbers (ethylene-propylene rubber, styrene-butadiene rubber, chlorinated polyethylene rubber, etc.) have an electric resistance of 10 ¹²
It is an insulator of Ωcm or more, and the resistance adjustment layer 23 is formed of these synthetic resins or synthetic rubbers in order to satisfy the electric resistance of 10 ⁵ to 10 ⁷ Ωcm ² required for the charging roll. Then, 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, the conventional conductive rolls, particularly the charging rolls, have non-uniform resistance and lack of practicality. Therefore, satisfactory conditions have not yet been obtained.

[Problems to be solved by the invention]

In order to solve such a problem, the present inventors have found that when the resistance adjusting layer is composed of epichlorohydrin-ethylene oxide copolymer rubber (CHC), excellent curing can be obtained, and the patent application (Japanese Patent Application No. No. 62-301107). That is, in this case, the electric resistance is uniform throughout, and the thickness of the resistance adjusting layer can be arbitrarily adjusted so that it can be practically used. However, when such a conductive roll, in particular, a charging roll is put to practical use, the constituent rubber composition of the conductive elastic body layer located below the resistance adjusting layer may be used in the rubber composition. Softener,
For example, a phenomenon occurs in which oil permeates the resistance adjusting layer and exudes to the surface of the charging roll, whereby the oil migrates to the surface of the photosensitive drum opposite to the charging roll. When the transfer of oil occurs in this way, the toner remains attached to the transferred oil, and the toner is not transferred to the copy paper. Therefore, white spots are generated in the obtained copy body (photocopy), and the photosensitive material is not exposed. The resin film on the drum surface deteriorates due to oil permeation, and since the part where oil is attached is not charged, it becomes the same state as if that part was exposed to light and the electric charge was removed. In the case of development, there arises a problem that black streaks (oil adheres in a streak pattern in the axial direction of the roll) are formed as if the original image were formed there.

Also, if the electrophotographic copying machine incorporating the charging roll as described above is not used for a while, the resistance adjusting layer sticks to the photosensitive drum, and in extreme cases, when the electrophotographic copying machine is started, the photosensitive layer is not exposed. There is also a problem that the resin film on the drum surface is peeled off.

The present invention has been made in view of such circumstances, and the electric resistance is uniform throughout, and the thickness of the resistance adjusting layer can be arbitrarily adjusted to withstand practical use. It is an object of the present invention to provide a conductive roll that does not exude a softening agent and does not stick to a photoconductor such as a photoconductor drum.

[Means for solving problems]

In order to achieve the above object, the conductive roll of the present invention, a conductive elastic body layer is formed along the circumference on the outer circumference of the shaft body, the outer circumference of this conductive elastic body layer, along the circumference. A resistance adjusting layer mainly composed of epichlorohydrin-ethylene oxide copolymer rubber is integrally formed, and between the both layers,
A conductive agent-containing softener migration-preventing layer mainly composed of N-methoxymethylated nylon is formed integrally with both layers, and a protective layer mainly composed of N-methoxymethylated nylon is formed in the outermost layer. It is configured to be integrally formed along the lower layer.

[Action]

The present inventors have conducted a series of studies for the purpose of blocking a softening agent such as oil that oozes out from the conductive elastic layer and preventing the resistance adjusting layer from sticking to the photosensitive drum. As a result, it was found that N-methoxymethylated nylon (8-nylon) is most effective in blocking the softening agent and preventing the resistance adjusting layer from sticking. As a result of further research, when N-methoxymethylated nylon is interposed between the resistance adjusting layer and the conductive elastic body layer and a conductive agent is contained in the layer composed of N-methoxymethylated nylon, the resistance is improved. The function of the adjusting layer itself is effectively exerted without being damaged by the layer made of N-methoxymethylated nylon, and when a protective layer mainly composed of N-methoxymethylated nylon is formed on the outer periphery of the resistance adjusting layer. The inventors have found that the action of the protective layer prevents the resistance adjusting layer from sticking to the surface of the photosensitive drum, so that the resin film of the photosensitive drum is not peeled off when the electrophotographic copying machine is started.

The conductive roll of the present invention is a softening agent containing a conductive agent, which is mainly composed of a shaft body, a conductive elastic body layer formed on the outer periphery thereof, and N-methoxymethylated nylon integrally formed on the outer periphery thereof. It is composed of a migration prevention layer, a resistance adjusting layer integrally formed on the outer periphery thereof, and a protective layer mainly composed of N-methoxymethylated nylon formed on the outer periphery thereof.

The shaft is not particularly limited, for example,
A cored bar made of a metal cylindrical body or a metal cylindrical body having a hollow hollow inside is used.

The conductive elastic body layer formed along the outer periphery of the shaft body,
There is no particular limitation, and synthetic rubbers such as polynorbornene rubber, ethylene-propylene-diene rubber, and styrene-butadiene rubber may be used simply or in a blend. The conductivity of such a conductive elastic layer is usually set to about 10 ¹ to 10 ⁴ Ω · cm. The thickness is usually set to 1 to 5 mm, preferably 3 ± 1 mm.

In particular, when the hardness (Hs) of the conductive elastic layer is set to a small value of 25 or less, when the conductive roll, especially the charging roll, is used by incorporating it in a device as shown in FIG.
It is possible to prevent the occurrence of image quality defects (horizontal unevenness) and fog phenomenon (phenomenon in which the background of a copy is darkened) due to slight vibration between the photoconductor and the conductive roll, which is rare. This is what the present inventors have found as they proceed with the improvement of the conductive roll, and the conventional charging roll has a hardness
Since it is about 40 and quite hard, it is pressed against the photosensitive drum with a considerable force in order to obtain a sufficient charge amount, and it is used in that state. As a result, the contact portion has an hourglass shape with a constricted central portion as shown in FIG. 6 (a). However, ideally, the shape of the rectangular contact portion shown in FIG. 6 (b) is suitable, and when the above-mentioned drum shape is obtained, the amount of charge is reduced in the central portion, and the fog phenomenon occurs in that portion. Further, the pressing roll resonates with the frequency of the alternating current due to the above pressing and moves up and down with respect to the photosensitive drum, which causes an image quality defect (lateral unevenness). As described above, the present inventors have found out that the hardness of the conductive elastic layer and the occurrence of microvibration are closely related.

Therefore, as a result of further studies centering on the hardness of the conductive elastic layer as described above, the inventors reduced the hardness of the conductive elastic layer itself to 25 or less by adding a softening agent such as oil. It was found that the inconveniences described above would be eliminated by lowering it. In this case, usually, as the rubber material forming the conductive elastic layer, polynorbornene rubber alone or a blend rubber of polynorbornene and ethylene-propylene-diene rubber (EPDM) is used, and as an oil, for example, naphthene is used. A system oil is mixed and, if necessary, a carbon black such as a ketchen black is used as a conductive agent. And, the amount of the softening agent such as the naphthenic oil used is the above-mentioned rubber 10
200 parts of the above oil to 0 parts by weight (hereinafter abbreviated as "part")
The amount used is about 500 parts, preferably about 400 parts.
Further, the amount of the ket embracing used is set to 30 to 80 parts, preferably 40 to 60 parts, relative to 100 parts of the rubber. When a large amount of a softening agent such as oil is used, the exudation thereof sometimes occurs.

In this case, the present invention is particularly effective, and the conductive agent-containing softener migration-preventing layer mainly composed of N-methoxymethylated nylon formed on the outer periphery of the conductive elastic layer,
The exudation of softening agents such as the oil is blocked. The thickness of the softening agent migration prevention layer is generally set to 3 to 20 μm, preferably 4 to 10 μm. The term “main body” in the present invention is intended to include the case where the whole body is composed of only the main body.

N-methoxymethylated nylon (8-nylon)
Is not particularly limited, and conventionally known products can be used as they are. Further, the conductive agent used in combination with the nylon is not particularly limited to the above-mentioned ketch embrac. Conventionally used conductive agents can be used as they are. Generally, carbon black is used as the conductive agent.

The resistance adjusting layer formed on the outer periphery of the softening agent migration prevention layer is mainly composed of epichlorohydrin-ethylene oxide copolymer rubber (CHC). The thickness is usually set to 50 to 150 μm, and the preferable range is 80 ± 20 μm.

The above epichlorohydrin-ethylene oxide copolymer rubber has been found by the present inventors to be optimum for the formation of the resistance adjusting layer and has an electric resistance value of 10 ⁸ to 10 ⁹ Ω · cm. Epichlorohydrin having such characteristics
When the resistance adjusting layer is formed of ethylene oxide copolymer rubber, it does not cause non-uniformity of resistance unlike the conventional conductive particle dispersion system. As a result of further research on the epichlorohydrin-ethylene oxide copolymer rubber, the present inventors have found that the electric resistance of the copolymer rubber varies depending on the copolymerization ratio of ethylene oxide and epichlorohydrin. In particular, the epichlorohydrin-ethylene oxide copolymer rubber used in the present invention,
Epichlorohydrin / ethylene oxide molar ratio of 65
It is preferable to use one within the range of / 35 to 40/60.
That is, when the molar ratio of ethylene oxide is less than 35 mol%, the electric resistance of the epichlorohydrin-ethylene oxide copolymer rubber exceeds 10 ⁹ Ω · cm.
As a result, when the thickness of the resistance adjustment layer is set to 50 μm, which is the minimum thickness that satisfies durability and dielectric breakdown voltage, it is within the range of 10 ⁵ to 10 ⁷ Ω / cm ² under normal conditions (25 ° C x 60% RH). Fits in. However, under low temperature and low humidity (10 ℃ × 15% RH),
In some cases, it may exceed 10 ⁷ Ω · cm ² . On the other hand, when the molar ratio of ethylene oxide exceeds 60 mol%, the obtained copolymer rubber has an increased affinity for water and becomes more environmentally dependent, and tends to exceed the range of 10 ⁵ to 10 ⁷ Ωcm ^2. Because you can see. Therefore, as the epichlorohydrin-ethylene oxide copolymer rubber constituting the resistance adjusting layer, it is preferable to use one having a molar ratio of epichlorohydrin / ethylene oxide within the range of 65/35 to 40/60. That is, within this range, it is possible to obtain a conductive roll that falls within the range of 10 ⁵ to 10 ⁷ Ω · cm ² under any environment.

As the vulcanization system for the epichlorohydrin-ethylene oxide copolymer rubber, any of the thiourea-metal oxides, amine systems and triazine derivatives usually used for hydrin rubber can be used. However, from the viewpoint of environmental dependence, particularly humidity dependence, it is preferable to use a thiourea-Pb ₃ O ₄ (lead tin) vulcanization system excellent in water resistance.

The outermost protective layer formed on the outer periphery of the resistance adjustment layer,
It is mainly composed of the N-methoxymethylated nylon described above. As the N-methoxymethylated nylon, as described above, the conventionally known one can be used as it is. 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 5 to 30 μm.
It is set to the thickness of, and the preferred range is 15 ± 8μm
Is. 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, particularly the charging roll, as described above 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 by 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 is prepared in advance, and the surface of the conductive elastic layer is polished and then coated and dried by spraying, dipping or the like. If necessary, heat treatment is carried out to crosslink and form a softening agent migration prevention layer.
Then, the resistance adjusting layer is formed on the conductive agent-containing softener migration preventing layer thus formed. This resistance adjusting layer is formed by kneading epichlorohydrin-ethylene oxide copolymer rubber with a reinforcing agent, a processing aid and a vulcanizing agent by a usual rubber processing method (Banbury mixer, roll, etc.). Materialize, dissolve this unvulcanized composition in a suitable solvent (for example, methyl ethyl ketone, methyl isobutyl ketone, etc.), coat on the outer peripheral surface of the conductive elastic body layer, dry it, and then heat vulcanize it. Can be formed by. It is preferable that the above-mentioned coating is carried out by a dipped method. More specifically, the solution containing the epichlorohydrin-ethylene oxide copolymer rubber composition is contained in a tank 112a as shown in FIG. Next, the roll 110a in which the conductive elastic body tank is formed is erected vertically and repeatedly immersed in the solution to form an epichlorohydrin-ethylene oxide rubber film on the outer peripheral surface of the conductive elastic body layer. At this time, the conditions such as the viscosity of the dispersion liquid, the ascending / descending speed, the number of ascending / descending, and the drying time are preferably set such that the liquid film of the epichlorohydrin-ethylene oxide rubber solution is within the range of 40 to 150 μm. About the one in which such a liquid film is formed at a temperature of 25 to 80 ° C.
Dry for 5-4 hours to remove solvent, then 150-200
The epichlorohydrin-ethylene oxide rubber film is vulcanized by heating at a temperature of ℃ for 10 minutes to 2 hours to form a resistance adjusting layer. Next, after the resistance adjusting layer is formed as described above, the surface thereof is polished as necessary, and N
-Methoxymethylated nylon resin liquid, and in some cases mixed resin liquid mixed with a conductive agent is coated by spraying, dipping, etc. and dried, and if necessary, heat treated to crosslink to form a protective layer. To do. In this way, a conductive roll having a layer structure as shown in FIG. 2 is obtained. In the figure, 110 is a core metal, 111 is a conductive elastic layer, 112 is a softener migration preventing layer, 113 is a resistance adjusting layer, 114
Is a protective layer.

Next, examples will be described together with comparative examples.

[Examples and comparative examples]

<Preparation of conductive elastic layer forming material> As a material for forming the conductive elastic layer, the hardness of the following composition
A 20 Hs rubber composition was prepared.

Polynorbornene rubber 100 parts Ketjen black 50 parts Naphthene oil 400 parts <Preparation of softening agent migration prevention layer forming material> The materials shown in the table below as materials for forming the softening agent migration prevention layer are shown in the same table. The mixture was mixed at a ratio to prepare a carbon black dispersed resin liquid.

<Preparation of Material for Forming Resistance Adjusting Layer> As a material for forming the resistance adjusting layer, a rubber composition having the following composition was prepared.

Epichlorohydrin-ethylene oxide rubber 100 parts Pb ₃ O ₄ 5 parts Ethylene thiourea 1.2 parts Processing aid 1 part Hard clay 40 parts <Preparation of protective layer forming material> As the protective layer forming material, the materials shown in the table below are shown in the same table. A resin liquid was prepared by using the resin in the proportions shown.

Next, after applying an adhesive to the outer periphery of the core metal made of a metal shaft having a diameter of 8 mm, the outer periphery thereof is coated with a rubber composition for forming a conductive elastic body layer, and the mold vulcanization is applied to the outside of the whole. The conductive elastic layer was formed so that the diameter was 15 mm. Next, a carbon-dispersed resin liquid for forming a softening agent migration prevention layer was sprayed on the outer periphery of the conductive elastic layer for coating, and then dried to form a softening agent migration prevention layer having a thickness of 6 to 10 μm. On the other hand, the rubber composition for forming the resistance adjusting layer was roll-kneaded and then dissolved in a solvent of methylethylketone / methylisobutylketone = 3/1 to adjust the viscosity to 300 centipoise to prepare a dispersion liquid. A cored bar having the softening agent running prevention layer formed as described above was dipped in this solution for coating, then pulled up and dried, and then heat treated to crosslink. Then, a resin solution for forming a protective layer was sprayed on the surface of the resin, coated and dried to form a protective layer. As a result, the intended conductive roll was obtained.

[Comparative Example 1] The formation of the softening agent migration prevention layer was stopped. A conductive roll was obtained in the same manner as in Example 1 except for the above.

[Comparative Example 2] The formation of the softener migration preventing layer was stopped. A conductive roll was obtained in the same manner as in Example 2 except for the above.

Comparative Example 3 The formation of the softening / migration preventing layer and the formation of the protective layer were stopped. A conductive roll was obtained in the same manner as in Example 1 except for the above.

Comparative Example 4 The formation of the protective layer and the protective layer of the softening / migration preventing layer was stopped.
A conductive roll was obtained in the same manner as in Example 2 except for the above.

For each conductive roll obtained in this way, in order to evaluate the variation in electrical resistance, a 10 mm square electrode (with a guard electrode) was drawn with silver paste at five points on the outer surface of the conductive roll. And the resistance between the electrode and the electrode was measured. In addition, the electric resistance when left for 24 hours in each environment was also measured. Furthermore, the dielectric breakdown voltage was set by placing a conductive roll directly on the aluminum plate and placing a metal shaft between the aluminum plates at a direct current of 10
The voltage was applied at 0V step, and the voltage at which spark discharge was generated was measured and obtained. Regarding the oil bleeding, after the conductive roll was left in an atmosphere of 40 ° C. for 330 hours, the presence or absence of oil bleeding on the roll surface was visually measured. Regarding the generation of metallic noise and the occurrence of fog, the above conductive roll was used as a charging roll in the apparatus shown in FIG. 3 to check the occurrence of slight vibration and the number of fog during 100 copies were taken, and displayed. Regarding the adhesion to the photosensitive drum, the conductive roll was incorporated into the device shown in FIG. 3 as a charging roll, and after leaving it in that state for a predetermined time, the generation state of the adhesion when it was activated was examined and displayed. . The results are shown in the table below.

From the above results, it can be seen that the example product is superior in performance to the comparative example product and can be a good charging roll.

〔The invention's effect〕

As described above, the conductive roll of the present invention has a resistance adjusting layer mainly composed of epichlorohydrin-ethylene oxide copolymer rubber on the outer circumference of the conductive elastic body layer formed along the circumference on the outer circumference of the shaft body. Since it is formed, the electric resistance is uniform throughout, and the thickness of the resistance adjusting layer can be arbitrarily adjusted so that it can be practically used. Moreover, since the conductive agent-containing softening agent migration prevention layer containing N-methoxymethylated nylon as a main component is formed between the conductive elastic layer and the resistance adjusting layer, the conductive elastic layer bleeds. The softening agent such as oil that migrates to the output resistance adjusting layer is blocked by the softening agent migration preventing layer. Therefore, the softening agent such as oil does not exude to the surface of the resistance adjusting layer. As a result, the white spots in the copy and the black streak phenomenon caused by the oozing out of the softening agent such as oil are prevented, and the deterioration of the resin film on the surface of the photosensitive drum due to the penetration of the softening agent does not occur. In addition, since the outermost layer is formed with a protective layer mainly composed of N-methoxymethylated nylon, when this is incorporated into an electrophotographic copying machine as a charging roll, the resistance adjusting layer of the charging roll is stopped when the apparatus is stopped. Is adhered to the photosensitive drum, and when the electrophotographic copying machine is restarted, the adhesion prevents damage to the resin film on the surface of the photosensitive drum.

[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 longitudinal sectional view of an example product obtained by the above production method, and FIG. 3 is an electrophotography incorporating a conductive roll. FIG. 4 is a block diagram of a copying machine, and FIGS. 4 and 5 are explanatory diagrams of a conventional example.
FIGS. 6A and 6B are explanatory views showing the shape of the contact portion of the charging roll with respect to the photosensitive drum. 110 ... Shaft, 111 ... Conductive elastic layer, 112 ... Softener migration prevention layer, 113 ... Resistance adjustment layer, 114 ... Protective layer

Claims (1)

[Claims] 1. A conductive elastic layer is formed along the circumference on the outer circumference of a shaft body, and is mainly composed of epichlorohydrin-ethylene oxide copolymer rubber along the circumference on the outer circumference of the conductive elastic layer. A resistance adjusting layer is integrally formed, and a conductive agent-containing softening agent migration prevention layer mainly containing N-methoxymethylated nylon is integrally formed between the both layers, and A conductive roll, wherein a protective layer mainly composed of N-methoxymethylated nylon is integrally formed along the lower layer on the outermost layer.