JP2649163B2 - Conductive roll - Google Patents

Description

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

[Conventional technology]

2. Description of the Related Art An electrophotographic copying machine forms an original image as an electrostatic latent image on the surface of a photosensitive drum, forms a toner image by attaching toner to the image, and transfers the toner image to copy paper to perform copying. It is. 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, and an original image is projected on the charged portion via an optical system, and a portion of the light-transmitted portion is exposed. It has been practiced to create an electrostatic latent image by eliminating charge. the above,
As a method of charging the surface of the photosensitive drum prior to the formation of an electrostatic latent image, a corona discharge method or a friction charging method has conventionally been used. In the corona discharge method, a corona discharge is applied to the surface of the photosensitive drum from a corona discharger to perform a charging process. Since this system generally uses a high-voltage power supply of 5 to 10 KV, it is necessary to take thorough safety measures, and there is a problem that harmful ozone is generated with the discharge. For this reason, recently, a frictional charging system in which a conductive roll is rubbed against 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 triboelectric charging system is applied is configured as shown in FIG. 4, and performs copying as follows. That is, the charging roller 2 made of a conductive roll is rotated in the opposite direction to the photosensitive drum 1 on the outer peripheral surface of the photosensitive drum 1 rotating in the direction of the arrow about the axis 1a, and rubbed while partially elastically deforming. . The outer surface of the photosensitive drum 1 is charged by the rubbing of the charging roll 2. Reference numeral 3 denotes an exposure mechanism through which the slit exposure 8 of the light image of the original 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. 6
Reference numeral denotes a paper feed mechanism roll, which supplies copy paper 11 to the surface of the photosensitive drum 1 and transfers the toner image via the transfer device 5 to the copy paper.
Transfer to 11 Reference numeral 7 denotes a fixing roll that passes the copy paper 11 on which the toner image is formed and fixes it. Thus, a copy is obtained. The photosensitive drum 1
The transfer surface and the remaining toner are removed by the cleaner 9 from the surface, and the entire surface is irradiated with light by the eraser lamp 10 to be zero potential, so that the surface is prepared for the next charging. Reference numeral 12 denotes a power supply for applying a voltage of about 1 to 3 KV to the charging roll 2.

[Problems to be solved by the invention]

Many electroconductive rolls such as a charging roll, a developing roll, a transfer roll, and a cleaning roll are used in an electrophotographic copying machine and the like. As such a conductive roll, 10
It is required to have a conductivity of about ¹ to 10 ¹² Ω · cm, and usually, as shown in FIG. 5, a metal shaft (core metal)
1 and a conductive elastic layer 2 formed on the outer peripheral surface thereof. The conductive elastic layer 2 is generally formed of a composition in which conductive powder and conductive fibers (carbon black, metal powder, carbon fibers, and the like) are mixed in synthetic rubber such as silica rubber. Of this type of conductive roll, the charging roll is required to have an electric resistance in a semiconductive region of 10 ⁵ to 10 ⁷ Ω / cm ² . However, in the conductive roll provided with the conductive elastic layer 2 as described above, conductivity is given by the contact between the conductive particles mixed in the synthetic rubber, so that uniform contact between particles is not necessarily obtained. Not. This is particularly remarkable in the semiconductive region, so that it is difficult to keep the electric resistance in the above semiconductive region (10 ⁵ to 10 ⁷ Ω / cm ² ).
In particular, when the hardness of the synthetic rubber serving as the matrix is low, the conductive elastic layer is easily deformed largely by pressurization, so that the degree of contact between the conductive particles changes and the electric resistance changes greatly. Therefore, in the charging roll, the charging of the photosensitive drum becomes non-uniform due to the non-uniformity of the conductivity and the change of the electric resistance as described above. As a result, there is a problem that a good copied image cannot be obtained. In addition, there is also a disadvantage that a dielectric breakdown easily occurs under a high voltage, and a fatal problem of damaging the photosensitive drum is likely to occur.

In order to solve such a problem, there has been proposed a conductive roll in which a resistance adjusting layer 3 is provided on the outer periphery of a conductive elastic layer as shown in FIG. However, ordinary synthetic resins,
Polyethylene, polyester, epoxy resin, etc.) and synthetic rubber (ethylene-propylene rubber, styrene-butadiene rubber, chlorinated polyethylene rubber, etc.) have an electrical resistance of 10
It is an insulator of ¹² Ω / cm ² or more, and forms the resistance adjustment layer 3 with these synthetic resins and synthetic rubbers to satisfy the electric resistance of 10 ⁵ to 10 ⁷ Ω / cm ² required for the charging roll. In this case, the thickness of the resistance adjusting layer 3 needs to be 1 μm or less. However, such a thin-film resistance adjusting layer 3 has no practical durability.

Since the highly hygroscopic resin such as 6-nylon and 8-nylon itself has an electric resistance in a semiconductive region of 10 ⁸ to 10 ⁹ Ω / cm, the thickness of the electric resistance layer 3 is set to a practical durability. Is 100 μm, the electrical resistance of the charging roll is 1
0 ⁶ ~10 ⁷ Ω / cm ² and summer and so enter the desired resistance region. However, since the electric resistance of the highly hygroscopic resin greatly depends on the humidity, the resin has a low temperature and low humidity (10 ° C x 15%
RH) to high temperature and high humidity (30 ° C x 85% RH), the electrical resistance fluctuates by about 3.5 digits.
There is a drawback that the range immediately exceeds the range of 0 ⁵ to 10 ⁷ Ω / cm ² . Therefore, when such a resin is used for the resistance adjusting layer 3, the electric resistance of the charging roll greatly depends on the humidity, and there is a problem that a sufficient image quality cannot be obtained depending on the surrounding environment. Further, such a charging roll cannot satisfy a dielectric breakdown voltage (preferably 2 KV or more is required) required for this type of roll.

As a method of reducing the electric resistance without using the method of providing the resistance adjusting layer 3 as described above, a method of adding a high dielectric liquid such as an ester plasticizer to a synthetic rubber such as a nitrile rubber or a chloroprene rubber. is there. According to this method, the electric resistance can be stored in the semiconductive region as described above. However, there is a problem that the liquid such as the added ester plasticizer migrates to the surface of the photosensitive drum and is contaminated, and the contaminated portion deteriorates the image quality.

As described above, conventional conductive rolls, particularly charging rolls, have non-uniform resistance, lack practicality, have high humidity dependency, and have problems such as contamination of the photosensitive drum surface. The fact is that no kimono has been obtained.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a conductive roll that has uniform resistance, is practically useful, has low humidity dependency, and does not contaminate the photosensitive drum surface.

[Means for solving the problem]

In order to achieve the above object, the conductive roll of the present invention has a conductive elastic layer formed along the circumference of the shaft body, and a resistance adjusting layer formed along the circumference on the circumference of the conductive elastic layer. Is an integrally formed conductive roll, wherein the resistance adjusting layer is mainly composed of epichlorohydrin-ethylene oxide copolymer rubber.

[Action]

The present inventors consider that a conductive roll having the above-mentioned resistance adjusting layer is most practical, and as a result of repeated studies mainly on this, as a result, when the above-mentioned resistance adjusting layer is composed of epichlorohydrin-ethylene oxide copolymer rubber, The present inventors have found that the object of the present invention is achieved, and reached the present invention.

The conductive roll of the present invention includes a shaft, a conductive elastic layer formed on the outer periphery thereof, and a resistance adjustment layer integrally formed on the outer periphery of the conductive elastic layer.

The shaft is not particularly limited, and a metal core made of a metal cylindrical body or a metal cylindrical body whose inside is hollowed out is used.

The conductive elastic layer formed along the circumference on the outer periphery of the shaft body is not particularly limited, and synthetic rubber such as polynorbornene rubber, ethylene propylene diene rubber, styrene butadiene rubber alone or as a blend is used. Used as

The resistance adjusting layer formed on the outer periphery of the conductive elastic layer is mainly composed of epichlorohydrin-ethylene oxide copolymer rubber. Here, “subject” means to include a case where the whole consists only of the subject. The epichlorohydrin-ethylene oxide copolymer rubber,
The present inventors have found that it is most suitable for forming the resistance adjusting layer, and have an electric resistance value of 10 ⁸ to 10 ⁹ Ω / cm.
When the resistance adjusting layer is formed of epichlorohydrin-ethylene oxide copolymer rubber having such characteristics, the resistance does not become non-uniform unlike the conventional conductive particle dispersion system. As a result of further studies 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. Particularly, the epichlorohydrin-ethylene oxide copolymer rubber used in the present invention has an epichlorohydrin / ethylene oxide molar ratio of 65/35 to 40/60.
It is preferable to use the one within the range. 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 the minimum thickness of 50 μm that satisfies the durability and dielectric breakdown voltage, the normal state (25 ° C x 60%
RH) falls within the range of 10 ⁵ to 10 ⁷ Ω / cm ² . However, in the low temperature and low humidity (10 ℃ × 15% RH) below, by the case connexion is because so more than 10 ⁷ Ω / cm ^2. vice versa,
When the molar ratio of ethylene oxide exceeds 60 mol%, the obtained copolymer rubber has an increased affinity for water, has a high environmental dependency, and tends to exceed the range of 10 ⁵ to 10 ⁷ Ω / cm ^2. Because. Therefore, it is preferable to use an epichlorohydrin / ethylene oxide copolymer rubber having a molar ratio of 65/35 to 40/60 as the epichlorohydrin-ethylene oxide copolymer rubber constituting the resistance adjusting layer. That is, within this range, a conductive roll falling within the range of 10 ⁵ to 10 ⁷ Ω / cm ² under any environment can be obtained.

As the vulcanization system for the epichlorohydrin-ethylene oxide copolymer rubber, any of thiourea-metal oxide, amine, and triazine derivatives usually used for hydrin rubber can be used. However, it is preferable to use a thiourea-Pb ₃ O ₄ (lead red) vulcanized material having excellent water resistance from the viewpoint of environmental dependency, particularly humidity dependency. The filler is appropriately selected from insulating fillers such as silica, tall, clay, and titanium oxide. Conductive fillers such as carbon black are liable to cause dielectric breakdown when used under high voltage, so they are not suitable for epichlorohydrin-ethylene oxide copolymer rubber.
It should be kept below 10% by volume.

The above-mentioned conductive roll, particularly the charging roll, can be manufactured, for example, as follows. That is, a conductive elastic material layer is formed on the outer peripheral surface of the core metal by using mold vulcanization using a rubber composition. Next, after polishing the surface of the conductive elastic body layer, a resistance adjusting layer is formed thereon. The resistance adjusting layer is formed by adding a reinforcing agent, a processing aid, and an epichlorohydrin-ethylene oxide copolymer rubber.
The vulcanizing agent is used in the usual rubber processing method (Banbury mixer,
A non-vulcanized rubber composition by kneading with a roll or the like, dissolving this unvulcanized composition in an appropriate solvent (eg, methyl ethyl ketone, methyl isobutyl ketone, etc.) and coating the outer peripheral surface of the conductive elastic layer. It can be formed by drying after processing, and then heating and vulcanizing. In the above coating, a dipping method is preferably used. More specifically, a solution containing the above epichlorohydrin-ethylene oxide copolymer rubber composition is stored as a dipping solution in a tank 112a as shown in FIG. Next, the roll 110a on which the conductive elastic layer is formed is set upright, and is repeatedly immersed in the above solution to form an epichlorohydrin-ethylene oxide rubber film on the outer peripheral surface of the conductive elastic layer. At this time, the conditions such as the elevating speed, the number of elevating times, the drying time, etc.
It is preferable to set the conditions so that the liquid film of the ethylene oxide rubber solution is in the range of 50 to 500 μm. At a temperature of 25 to 80 ° C, the liquid film formed
The solvent is removed by drying for 0.5 to 4 hours, followed by 150 to 20 hours.
By heating at a temperature of 0 ° C. for 10 minutes to 2 hours, the epichlorohydrin-ethylene oxide rubber film is vulcanized to form a resistance adjusting layer. Thus, a conductive roll having a layer structure as shown in FIG. 1 is obtained. In the figure, 11
0 is a metal core, 111 is a conductive elastic layer, and 112 is a resistance adjusting layer.

As shown in FIG. 2, in order to prevent adverse effects due to the adhesiveness of the resistance adjusting layer 112 made of the epichlorohydrin-ethylene oxide copolymer rubber, as shown in FIG.
A protective layer 113 having an electric resistance lower than that of the resistance adjusting layer 112 may be provided on the outer periphery of 2. Such a protective layer is generally made of a rubber material.

 Next, examples will be described.

[Examples 1 to 6] Rubber compositions having the following compositions were prepared.

Next, the rubber composition having the above composition is roll-kneaded in a conventional manner, and then methyl ethyl ketone / methyl isobutyl ketone is added.
It was dissolved in a 3/1 solvent, the viscosity was adjusted to 300 centipoise, and the solution was poured as a dipping solution into the dipping layer 112a shown in FIG. On the other hand, a metal shaft having a diameter of 8 mm was prepared as a core metal, and a rubber composition comprising ethylene, propylene, diene rubber [EPDM] and carbon black was vulcanized and polished according to a conventional method through an adhesive layer on the outer periphery of the shaft. A conductive elastic layer having an outer diameter of 15 mm was formed. This conductive elastic layer has a hardness of 33.
The degree of electrical resistance was 1 × 10 ³ Ω · cm. Next, the metal shaft with the conductive elastic layer is immersed in the previously prepared dipping solution, coated to a thickness shown in Table 2 below, dried at room temperature, and then dried at 70 ° C. for 2 hours. The mixture was further vulcanized at 160 ° C. for 1 hour to obtain a desired conductive roll.

[Comparative Example 1] 8-Nylon (metal methoxylated nylon: AQ nylon K-80, manufactured by Toray Industries, Inc.) was dissolved in a mixed solvent of methanol / n-butanol = 3/1, and the same procedure as in the above example was performed. Coating was performed on the obtained conductive elastic layer. This was dried at room temperature and then heated at 70 ° C. for 2 hours to obtain a conductive roll.

[Comparative Example 2] Using a rubber composition in which conductive zinc white (23-K, manufactured by Shimizu Chemical Co., Ltd.) was mixed with EPDM, a conductive roll was obtained in the same procedure as in the above example.

In order to evaluate the variation of the electric resistance of each of the conductive rolls obtained in this way, electrodes of 10 mm square were drawn in five places on the outer surface of the conductive roll in silver space (with a guard electrode), and the metal shaft and The resistance with the electrode was measured. In addition, the electric resistance when left in each environment for 24 hours was measured. In addition, the dielectric breakdown voltage is set by placing a conductive roll directly on an aluminum
A voltage was applied at a step, and a voltage causing spark discharge was measured and obtained.

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

〔The invention's effect〕

As described above, in the conductive roll of the present invention, the resistance adjusting layer mainly composed of epichlorohydrin-ethylene oxide copolymer rubber is formed on the outer periphery of the conductive elastic layer formed along the circumference of the shaft body. Therefore, the electric resistance is uniform throughout, and the thickness of the resistance adjusting layer can be arbitrarily adjusted so as to be practically usable. In addition, since the resistance adjustment layer has low humidity dependency, the electric resistance of the resistance adjustment layer does not deviate from a suitable range due to a change in the surrounding environment. In addition, since it is not necessary to use a plasticizer solution or the like to adjust the electric resistance, a situation in which the surface of the photosensitive drum or the like is contaminated with the plasticizer or the like does not occur.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of one embodiment of the present invention, FIG. 2 is a vertical cross-sectional view of another embodiment, FIG. 3 is a manufacturing explanatory view of FIG. 1, and FIG. FIG. 5 and FIG. 6 are explanatory diagrams of a conventional example of an electrophotographic copying machine in which is incorporated. 110: shaft, 111: conductive elastic layer, 112: resistance adjusting layer

Continued on the front page (72) Inventor Yuji Ota Komaki City, Aichi Prefecture, Kokugaiyama, Gezu 3600 Tokai Rubber Industry Co., Ltd. (56) References JP-A-58-87572 (JP, A) Japanese Patent Application No. 56-87633 (Japanese Utility Model Application No. 57-199349) Microfilm (JP, U)

Claims (2)

(57) [Claims] 1. A conductive roll in which a conductive elastic layer is formed on the outer periphery of a shaft along the circumference, and a resistance adjusting layer is integrally formed on the outer periphery of the conductive elastic layer along the circumference. A conductive roll, wherein the resistance adjusting layer is mainly composed of epichlorohydrin-ethylene oxide copolymer rubber. 2. The conductive roll according to claim 1, wherein the epichlorohydrin-ethylene oxide copolymer rubber has a molar ratio of epichlorohydrin / ethylene oxide of 65/35 to 40/60.