JPH06186824A - Electrostatic charging roll - Google Patents

Abstract

PURPOSE:To provide the electrostatic charging roll capable of maintaining a smooth surface, lowering the vibration noise by the AC component of an electric field when the roll is brought into pressurized contact with a photosensitive body and forming a stable nip by providing a conductive elastic material layer which is not a foam on the outer periphery of a foam layer. CONSTITUTION:The foam layer 14 consisting of a conductive foam is provided on the outer periphery of a shaft body (arbor) 12 and the conductive elastic material layer 16 is provided on the outer periphery thereof, by which a base layer is formed. The outer periphery of the base layer is coated with a resistance control layer 18 and a protective layer 20 in this order. Conductive rubber compsns. and conductive thermoplastic elastomers formed by incorporating conductive powders and conductive fibers, such as metallic powder, carbon black and carbon fibers, into various kinds of rubber compsns. and thermoplastic elastomers are optimum as the material for forming the conductive elastic material layer 16. The thickness of the conductive elastic material layer 16 is preferably specified to 100 to 1200mum.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a charging roll used in a copying machine, a printer or the like using an electrophotographic system.

[0002]

2. Description of the Related Art In electrophotography, there is a step of uniformly charging the surface of a photoconductor (photosensitive drum) to a predetermined potential, and in the past, a method of charging by using a corona discharger was mostly used. However, this method has the following problems: (1) high voltage needs to be applied, (2) low charging efficiency, (3) high concentration ozone is generated, and (4) uneven charging due to wire contamination. Since it has some points, the contact charging method, in particular, the roll charging method using a conductive roll has started to be used in recent years.

That is, in the roll charging system, the charging roll is pressed against the photosensitive member by a spring or the like, and the charging roll is rotated in a rotating state in accordance with the driving of the photosensitive member. Then, by applying a predetermined voltage to the shaft of the charging roll, charges are directly injected into the surface of the photoconductor to charge the surface of the photoconductor to a predetermined potential. Further, at that time, if the applied voltage is only the DC component, microscopic contact unevenness occurs between the charging roll and the photoconductor, and spot-like charging unevenness occurs, so the AC component is superimposed on the DC component. A voltage is applied. And the frequency of the AC electric field is determined according to the process speed, and when the process speed is slow, it is a low frequency,
The frequency is set higher as the process speed increases.

By the way, the charging roll used therein generally has a structure as shown in FIG. 3, and a conductive material made of a low hardness conductive rubber composition is provided on the outer periphery of the shaft body (core metal) 2. The elastic layer 4 is provided. Further, on the outer periphery of the conductive elastic layer 4, the softener migration preventing layer 6,
The resistance adjusting layer 8 and the protective layer 10 are sequentially laminated as a coating layer.

When a voltage is applied while the charging roll is pressed against the photoconductor, the photoconductor is composed of a thin metal pipe as a base material. Therefore, the action of an AC component acts on the photoconductor and the charging roll. There is a problem in that the force acts in correlation with the frequency to vibrate the photoconductor and generate noise. Then, in order to prevent such noise, conventionally, it has been necessary to take vibration damping measures such as applying a damping paint to the inner surface of the photoconductor or filling a damping material inside. However, there is a need for sound insulation measures that reduce the sound leakage from the housing.

Further, in such a charging roll, the shafts 2 and 2 at both ends are pressed by the spring pressure or the like to be pressed against the photoconductor, so that the nip width is widened at both ends of the roll, while the central part of the roll is widened. However, there is a problem that the drum-shaped contact is made as a whole and a gap is easily formed between the photosensitive member and the photosensitive member at the center of the roll. Was.

On the other hand, in recent years, a charging roll having a structure in which a foam layer made of a conductive foam is provided on the outer periphery of a shaft body, and a resistance adjusting layer and a protective layer are further coated on the outer periphery thereof has been proposed. Therefore, it has been studied to obtain a noise reduction effect by reducing the hardness of the roll with a conductive foam.

However, in order to obtain a sufficient noise reduction effect with such a charging roll, the foaming ratio of the conductive foam must be increased so that the hardness of the roll becomes sufficiently low. When the foam has such a low hardness, wrinkles easily occur on the roll surface due to shrinkage of the coating layer, and it becomes difficult to obtain a smooth roll surface. If the smoothness of the roll is poor, there is a problem that image defects occur during use.

Further, since the foam layer has a large variation in size, in such a charging roll, in order to make the outer diameter of the roll uniform and to bring it into the range of the outer diameter accuracy required for the charging roll, the coating is performed prior to coating. It was necessary to polish the outer peripheral surface. When inserting a shaft into a cylindrically shaped foam, the inner peripheral surface of the roll has a large variation (because of the poor flatness of the surface). There was a necessary defect.

[0010]

The present invention has been made in view of such circumstances, and the problem to be solved is to satisfy the electrical properties required for a charging roll and maintain a smooth surface. SUMMARY OF THE INVENTION It is an object of the present invention to provide a charging roll in which vibration noise due to an AC component when pressed against a photoconductor is reduced and which forms a stable nip.

Incidentally, the noise generated when an AC electric field is applied to the charging roll repeats attraction and repulsion between the photoconductor and the charging roll according to the frequency of the AC electric field, and the aluminum pipe which is the base material of the photoconductor vibrates. It is caused by doing. Therefore, in order to prevent noise, it is highly effective to reduce the hardness of the charging roll so as to prevent vibration of the photoconductor, and a method of forming a charging roll base layer into a sponge has been studied, but as described above, It is difficult to achieve both the noise reduction and the required characteristics of the charging roll.

Therefore, the present inventors have made various studies in order to obtain a smooth roll surface property while lowering the roll hardness.
It is considered that the low hardness foam has an effect on noise reduction (= vibration prevention) because the charging roll side is deformed when an AC electric field is applied and the vibration of the photoconductor is suppressed. I thought that if there was a foam layer with low hardness in the part, it would be effective in reducing noise, and conducted a concrete study. That is, a roll having a conductive elastic layer provided on the outer periphery of the foam layer was created and investigated. As a result, if the thickness of the conductive elastic layer is reduced, it is effective in reducing noise, similar to the foam. I found something.

[0013]

The present invention has been completed based on such findings, and the gist of the invention is to:
A foam layer made of a conductive foam or a partially conductive foam is provided on the outer circumference of the shaft body, and a thin conductive elastic body layer is provided on the outer circumference of the foam layer. A charging roll is characterized in that a resistance adjusting layer and a protective layer are coated on the outer periphery of a conductive elastic layer.

In the present invention, it is advantageous that the conductive elastic layer is formed with a thickness of 100 μm to 1200 μm using a conductive rubber composition or a conductive thermoplastic elastomer.

[0015]

In summary, in the charging roll according to the present invention, a solid conductive elastic body layer which is not a foam body is provided on the outer periphery of the foam body layer. With this configuration, the cell defects of the foam are covered with the conductive elastic layer, the influence on the roll surface can be reduced, and the surface can be made substantially smooth like the solid rubber surface. Also, since the coating layers (resistance adjusting layer and protective layer) are provided on the outer periphery of the conductive elastic body layer, they can be handled in the same manner as coating on the solid rubber surface, and when directly coating on the foam layer. Wrinkles are less likely to occur due to drying and heat treatment of the coating layer. Therefore, the surface properties of the charging roll are significantly improved and smoothed,
It is possible to effectively prevent the accumulation of toner and the like, and effectively improve the reliability of image quality. Further, since the solid conductive elastic body layer has high dimensional accuracy, there is also an advantage that polishing for obtaining the outer diameter accuracy of the roll is unnecessary.

In such a charging roll, the hardness can be sufficiently lowered by making the conductive elastic layer sufficiently thin so that the foam occupies most of the base layer of the roll, so that the hardness is low. The same effective noise reduction effect as that of the hardness foam can be obtained. Therefore, it is not necessary to take noise prevention measures or sound insulation measures on the photoconductor side or the main body side of a copying machine, printer, or the like.

Further, when the charging roll is pressed against the photoreceptor, the roll as a whole can obtain the same uniform contact as the low hardness foam because of the effect of the volume shrinkage of the foam when compressed. Form a stable nip. Therefore, the charging of the photoconductor is made uniform, the accumulation of toner is prevented, and the reliability of the image quality is improved.

In such a charging roll, the conductive elastic layer is formed with a thickness of 100 μm to 1200 μm using a conductive rubber composition or a conductive thermoplastic elastomer, so that any of the above effects can be obtained. You can get it.

[0019]

Concrete Structure By the way, FIG. 1 shows an example of a charging roll having a structure according to the present invention. In this charging roll, a foam layer 14 made of a conductive foam is provided on the outer periphery of a shaft body (core bar) 12, and a conductive elastic layer 16 is provided on the outer periphery thereof to form a base layer. Has been done. The resistance adjusting layer 18 and then the protective layer 20 are coated on the outer periphery of the base layer.

The foam material forming the foam layer 14 is not particularly limited as long as it prevents settling and satisfies the characteristics required of the charging roll, and various known foam materials are used. However, normally, a conductive foam material in which conductive powder or conductive fiber such as metal powder, carbon black, carbon fiber is mixed in a rubber foam such as urethane foam or hydrin rubber foam is used. .

Even if the foam material is insulative, if a part of the foam material is subjected to a conductive treatment so that the shaft 12 and the conductive elastic layer 16 can be electrically connected, there is no problem. FIG. 2 shows an example of a charging roll which can be used and in which the foam layer 22 is formed of an insulating foam and both ends 24, 24 of which are subjected to a conductive treatment. The conductive treatment can be performed by, for example, allowing a conductive powder such as carbon black or carbon fiber or a liquid in which conductive fibers are dispersed in water to soak into the foam layer 22 and then drying.

Further, the lower the hardness (H _S ) of the foam is, the more effective it is in reducing noise. Therefore, in order to obtain an effective noise-preventing effect, the foaming ratio and the like are adjusted to increase the hardness. It is desirable that the angle be 35 ° or less.

Further, as a material for forming the conductive elastic layer 16, various rubber compositions or thermoplastic elastomers are mixed with conductive powders or conductive fibers such as metal powder, carbon black or carbon fibers. A rubber composition or a conductive thermoplastic elastomer is most suitable. It should be noted that even hard resin can be used if it can be thinned to the extent that it can be easily elastically deformed, but even if it is thin, hard resin has high roll hardness, so it is necessary to obtain a sufficient contact width between the charging roll and the photoreceptor. It can be difficult. Further, in the case of a hard resin, it is necessary to reduce the thickness to substantially 50 μm, which makes molding difficult, and easily causes breakage and the like, which makes handling difficult.

The thickness of the conductive elastic layer 16 is preferably 100 μm to 1200 μm.
This is because if the thickness of the conductive elastic layer 16 is smaller than 100 μm, the cell defects of the foam layers 14 and 22 cannot be covered sufficiently, and the conductive elastic layer 16 is not covered by the cell defective portion. This is because dents and the like are likely to appear and the roll surface property is impaired. On the other hand, if the thickness of the conductive elastic layer 16 exceeds 1200 μm, the noise reduction effect is reduced.

In order to integrally form the foam layers 14 and 22 and the conductive elastic layer 16 around the shaft body 12, for example, a cylindrical molding die is used, and the center thereof is used. A thin tube of conductive elastic material that will provide the conductive elastic layer 16 is concentrically arranged while the shaft body 12 is arranged, and the molding material that provides the foam layers 14 and 22 is pressed between them. However, the foaming operation may be performed.

Further, between the foam layers 14 and 22 and the conductive elastic layer 16, and between the foam layers 14 and 22 and the shaft body 1.
Between the two, sufficient durability can be obtained only by the pressure of the foam without adhesion, but they may be adhered if necessary, thereby not adversely affecting the effects of the present invention.

Further, when the resistance adjusting layer 18 is coated on the outer periphery of the conductive elastic layer 16, the conductive elastic layer 16 may be swollen by the solvent of the coating liquid that provides the resistance adjusting layer 18. In this case, it is desirable to coat the conductive elastic layer 16 with a resistance adjusting layer 18 after coating a conductive resin layer that does not swell with a solvent. The conductive resin layer may be formed of a material containing a nylon polymer such as N-methoxymethylated nylon as a main component and having a thickness of about several μm.

The resistance adjusting layer 18 is preferably made of epichlorohydrin rubber or the like, and is usually 50 to 50 by a known coating method such as a dipping method.
It is formed with a thickness of about 500 μm, preferably about 80 to 160 μm. Further, on the surface of the resistance adjusting layer 18, a protective layer 20 made of a material containing a nylon-based polymer such as N-methoxymethylated nylon as a main component or the like is provided in a thickness of several μm in order to prevent sticking to the photoreceptor. The target charging roll is produced by coating with a moderate thickness.

[0029]

EXAMPLES Some examples of the present invention will be shown below to clarify the present invention in more detail. However, the present invention is not limited by the description of such examples. Needless to say, it is not something to receive. Further, in addition to the following specific examples, in addition to the following embodiments, the present invention includes various modifications based on the knowledge of those skilled in the art without departing from the spirit of the present invention.
It should be understood that modifications, improvements, etc. may be made.

First, various materials shown below were prepared as materials for forming the charging roll. (1) Urethane foam polyether polyol [Sanyo Kasei Co., Ltd. "FA7030"] ... 100 parts by weight of H ₂ O · 1 part by weight fatty acid sulfonate solution [Sumitomo Bayer Urethane Co. "additive SV" ] 1 part by weight Silicone-based foam stabilizer ("SRX274C" manufactured by Toray Silicone Co., Ltd.) 2 parts by weight triethanolamine ... 1.5 parts by weight N, N'-dimethylbenzylamine (catalyst ) [Kaolyzer No. 20 manufactured by Kao Corporation] 2 parts by weight Triethylenediamine (catalyst) [Dabco33 LV manufactured by Mitsui Air Products Co., Ltd.] 1 part by weight Polyol mixture and isocyanate (Sumijour T- manufactured by Sumitomo Bayer Urethane Co., Ltd.
80 ") was mixed with a ratio of 5.3: 1.0 immediately before casting.

(2) Conductive hydrin rubber foam Epichlorohydrin rubber ["Epichromer C" manufactured by Daiso Co., Ltd.] ... 100 parts by weight Carbon [Toast Carbon Co., Ltd. "SEAST SO"] ... 40 parts by weight Light Calcium carbonate: 20 parts by weight Processing aid: 3 parts by weight Anti-aging agent: 3 parts by weight Ethylenethiourea: 1.5 parts by weight N, N'-dinitroso-pentamethylene-tetramine (foaming agent ) [Sankyo Kasei's "Celmic A"] ... 5 parts by weight Urea and its derivatives (foaming auxiliary) [Sankyo Kasei's "Celton N"] ... 5 parts by weight After kneading with the closed type mixer, the vulcanizing agent and the foaming agent were mixed with a two-roll mill.

(3) Conductive rubber (solid) Polynorbornene rubber ・ ・ ・ 80 parts by weight Ethylene propylene rubber ・ ・ ・ 20 parts by weight Ketjen Black ・ ・ ・ 40 parts by weight Naphthenic oil ・ ・ ・ 350 parts by weight After kneading with an ordinary closed mixer, a vulcanizing agent and a vulcanization accelerator were mixed with a two-roll mill.

(4) Conductive EPDM rubber Ethylene propylene rubber ・ ・ ・ 100 parts by weight Ketjen Black ・ ・ ・ 40 parts by weight Naphthenic oil ・ ・ ・ 20 parts by weight After kneading with an ordinary closed mixer A vulcanizing agent and a vulcanization accelerator were mixed with a two-roll mill. (5) Conductive polyester elastomer Toray DuPont KK "Hytrel 4047 x 08" is used. (6) Conductive polyamide elastomer "Pebax" manufactured by Toray Industries, Inc. is used. (7) Conductive N-methoxymethylated nylon N-methoxymethylated nylon: After dissolving 100 parts by weight in a mixed solution of methanol and water, 15 parts by weight of Ketjen Black was added and dispersed by a bead type disperser. did.

(8) Material for forming resistance adjusting layer Epichlorohydrin rubber [“Epichromer C” manufactured by Daiso Co., Ltd.] ・ ・ ・ 100 parts by weight Hard clay ・ ・ ・ 40 parts by weight Rintan ・ ・ ・ 5 parts by weight Processing aid ・.. 1 part by weight Ethylenethiourea ... 1.5 parts by weight was kneaded with a two-roll mill and then dissolved in a mixed solution of methyl ethyl ketone and toluene. (9) Material for Forming Protective Layer N-methoxymethylated nylon: 100 parts by weight was dissolved in a mixed solution of methanol and water, and then 5 parts by weight of Ketjen Black was added and dispersed by a bead type disperser.

Examples 1 to 4 and Comparative Example 1 First, using a predetermined mold, a tube having an outer diameter of 12 mmφ and a wall thickness set to a value shown in Table 1 below was prepared from the conductive EPDM rubber. After that, the division marks of the mold on the surface of the tube were removed by polishing to smooth the surface. Next, a shaft (core metal) having a diameter of 6 mm and the tube were concentrically set in a cylindrical mold, and the urethane foam was poured between the shaft and the tube and then immediately sealed, Foaming and heat treatment were performed to provide a foam layer and a conductive elastic body layer on the outer periphery of the shaft body.

Then, the resistance adjusting layer forming material is coated on the outer periphery of the conductive elastic material layer by a dipping method to a thickness of 80 μm, dried and heat-treated, and further, by a dipping method, the protective layer forming material. Was coated to a thickness of 5 μm, dried and heat treated. Thereafter, a liquid in which carbon black is dispersed in water is permeated into both ends of the foam layer and dried to conduct conductivity, so that the shaft body and the conductive elastic body layer are electrically connected to each other. Thus, a desired charging roll was obtained.

With respect to the charging roll thus obtained, the current value, roll hardness, noise level, and surface roughness are measured, the appearance of the roll is evaluated, and the charging roll is attached to the actual machine to evaluate the performance of the actual machine. The results are also shown in Table 1 below.

The measurement conditions for each measurement are as follows. (Current value) In an environment of 23 ° C. × 53% RH, a charging metal roll (30 g) is loaded on the shafts at both ends with a load of 500 gf, and the smoothing metal roll (30 rpm) is rotated at 17 rpm.
(mmφ) and presses it to the shaft of the charging roll at 500Vp-p
A voltage of (300 Hz) -200V _DC was applied and measured. (Roll hardness) It was measured by applying a load of 1 kg using an Asker C hardness meter. (Noise level) 2000Vp-p (500Hz) -on the shaft of the charging roll by using the measuring device having the structure shown in FIG.
The measurement was performed by applying a voltage of 550V _DC . (Surface roughness) Tokyo Seimitsu Co., Ltd. surface roughness meter "Surfcom"
Was measured using. (Actual image rendering performance) Using a laser beam printer "Laser Jet III _SI " manufactured by Hewlett Packard, under an environment of 10 ° C x 15% RH, 5000
The sheet durability was evaluated as follows. ○ No abnormality △ Minor image unevenness × Image unevenness

[0039]

[Table 1]

As is clear from the results shown in Table 1, the charging rolls of Examples 1 to 4 have a low noise level and have an excellent performance for displaying images on an actual machine. However, in the charging roll of Comparative Example 1 in which the thickness of the conductive elastic layer was 1400 μm, the roll hardness was high and the noise was large.

Examples 5 and 6 and Comparative Example 2 First, using an extruder, a tube having an outer diameter of 12 mmφ and a wall thickness set to the value shown in Table 2 below was prepared. After that, in the same manner as in Example 1, a foam layer and a conductive elastic layer were provided on the outer periphery of the shaft body, and a resistance adjusting layer and a protective layer were further formed. Then, the shaft and the conductive elastic layer were made conductive by the same conductive treatment as in Example 1 to obtain a target charging roll as shown in FIG.

The charging roll thus obtained was measured and evaluated in the same manner as in Example 1, and the results are also shown in Table 2 below. As is clear from the result,
The charging rolls of Examples 5 and 6 are low in noise and have an excellent performance for displaying images on an actual machine. However, in the charging roll of Comparative Example 2 in which the thickness of the conductive elastic body layer was 80 μm, the dents due to the cell defects of the foam layer could not be covered well, the roll appearance was deteriorated, and the surface roughness of the roll was deteriorated. The degree of image rendering becomes worse, and the actual image output performance is inferior.

[0043]

[Table 2]

Examples 7 and 8 First, using an extruder, an unfoamed tube for forming a foam layer was prepared from the conductive hydrin rubber. Further, similarly, a tube having an outer diameter of 12 mmφ and a wall thickness set to a value shown in the above Table 2 was prepared by extruding the conductive polyester elastomer and the conductive polyamide elastomer to provide a conductive elastic layer. . Next, the unfoamed conductive hydrin rubber tube and the conductive elastomer tube are concentrically set together with a shaft body (core metal) having a diameter of 6 mm in a cylindrical mold and heated in an oven to foam and vulcanize. Then, the foam layer and the conductive elastic body layer were provided on the outer circumference of the shaft body. Then, a resistance adjusting layer and a protective layer were formed on the outer periphery of the conductive elastic layer by the dipping method in the same manner as in Example 1 to obtain the target charging roll as shown in FIG.

The charging roll thus obtained was measured and evaluated in the same manner as in Example 1, and the results are also shown in Table 2 above. As a result, it was clarified that such a charging roll has a low noise and has an excellent performance for displaying an actual image.

Comparative Examples 3 to 5 First, an unfoamed tube was prepared from the conductive hydrin rubber using an extruder. Then, the tube and a shaft body (core metal) having a diameter of 6 mmφ are concentrically set in a cylindrical mold, heated in an oven, foamed and vulcanized, and foamed on the outer periphery of the shaft body. The layers were applied with a thickness of 3 mm. However, the expansion ratio was changed in each of Comparative Examples 3 to 5. Next, in order to prevent the foam layer from swelling with the solvent of the resistance adjusting layer,
The conductive N-methoxymethylated nylon was coated to a thickness of 10 μm by a dipping method, dried and heat treated. Then, in the same manner as in Example 1, a resistance adjusting layer and a protective layer were formed by a dipping method to obtain a target charging roll.

The charging roll thus obtained was subjected to the same measurements and evaluations as in Example 1, and the results are shown in Table 3 below. As is clear from the results, when the expansion ratio is increased and the hardness is decreased (Comparative Examples 3 and 4), noise can be reduced satisfactorily, but shrinkage wrinkles are formed in the coating layer and the roll appearance deteriorates. However, the surface roughness of the roll becomes large, and the performance of actual image drawing deteriorates. On the other hand, when the expansion ratio is lowered to prevent the shrinkage wrinkles of the coating layer (Comparative Example 5), the roll hardness is increased and the noise is increased.

[0048]

[Table 3]

Comparative Example 6 A shaft body (core bar) having a diameter of 6 mm and the conductive rubber (solid) were set in a mold and heated by a press to form a conductive rubber layer of 3 mm on the outer circumference of the shaft body. Provided in the thickness of. Next, after smoothing the surface of the conductive rubber layer by polishing, the conductive N-methoxymethylated nylon was coated with a thickness of 10 μm by a dipping method, dried and heat treated.
Then, in the same manner as in Example 1, a resistance adjusting layer and a protective layer were formed by a dipping method to obtain a target charging roll.

The charging roll thus obtained was subjected to the same measurements and evaluations as in Example 1, and the results are shown in Table 3 above. As is clear from the result, such a charging roll has a high roll hardness of 61 and a lot of noise.

[Brief description of drawings]

FIG. 1 is a cross-sectional explanatory view showing an example of a charging roll according to the present invention.

FIG. 2 is a cross-sectional explanatory view showing a different example of the charging roll according to the present invention.

FIG. 3 is a cross-sectional explanatory view showing an example of a conventional charging roll.

FIG. 4 is an explanatory diagram showing a configuration of an apparatus used for measuring a noise level in an example.

[Explanation of symbols]

 12 Shaft 14 Foam Layer 16 Conductive Elastic Layer 18 Resistance Adjustment Layer 20 Protective Layer 22 Foam Layer 24 End

Claims (2)

[Claims] 1. A foam layer made of a conductive foam or a partially conductive foam is provided on the outer circumference of a shaft body, and a thin conductive elastic layer is provided on the outer circumference of the foam layer. And a resistance adjusting layer and a protective layer are coated on the outer periphery of the conductive elastic layer. 2. The conductive elastic layer is made of a conductive rubber composition or a conductive thermoplastic elastomer, and has a thickness of 100 μm.
The charging roll according to claim 1, wherein the charging roll has a thickness of m to 1200 μm.