JPH07271151A - Electrostatic charging roll - Google Patents

Abstract

PURPOSE:To obtain an electrostatic charging roll with which the longer life of a photosensitive drum is realized by forming high-polymer coating layers for preventing etching on at least one end side of the electrostatic charging roll in contact with the photosensitive drum. CONSTITUTION:This electrostatic charging roll consists of an arbor 20, a conductive elastic material layer 21, a resistance adjusting layer 22, a protective layer 23 and the high-polymer coating layers 24 for preventing etching. The high-polymer coating layers 24 for preventing etching are formed at both end parts of the front surface of the protective layer 23 in Fig. This layer may be formed only at either one end side. The high-polymer coating layers 24 for preventing etching are formed on at least one ends of the electrostatic charging roll in such a manner. As a result, dropping of the AC voltage at the time of voltage impression only at the parts of the photosensitive drum where the film thickness is small and which come into contact with the parts formed with the high-polymer coating layers 24 for preventing etching is made possible and the etching effect on the photosensitive drum is suppressed. Consequently, the durability of both of the photosensitive drum and the electrostatic charging roll is improved and the longer life is realized. Further, the leak reliability at the roll ends is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging roll used in a copying machine, a printer or the like using an electrophotographic copying system.

[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 electrostatic latent image is formed by charging the surface of the photosensitive drum in advance, projecting a document image onto the charged portion through an optical system, and canceling the charging of the exposed portion. As a method of charging the surface of the photosensitive drum prior to the formation of the electrostatic latent image, a roll charging method of directly charging the surface of the photosensitive drum to directly charge the surface of the photosensitive drum has recently attracted attention. An electrophotographic copying machine to which such a roll charging system is applied is configured as shown in FIG. 4 and performs copying as follows. That is, the charging roll 2 is rotated around the outer peripheral surface of the photosensitive drum 1 which rotates about the shaft 1a in the direction of the arrow, and is brought into sliding contact with the photosensitive drum 1 while being partially elastically deformed. 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. Note that the transfer residual image and the residual toner are removed by the cleaner 9 on the surface of the photosensitive drum 1. A power source 12 applies a voltage of about 1 to 3 kV to the charging roll 2.

In the charging roll 2, as shown in FIG. 3, a conductive elastic layer 15 is formed on the outer peripheral surface of a core metal 14, and a semiconductive polymer is formed on the outer peripheral surface of the conductive elastic layer 15. A layer 16 is provided, and if necessary, a protective layer 17 is provided on the outer periphery of the semiconductive polymer layer 16 for the purpose of preventing contamination of the photosensitive drum and toner adhesion. Such a charging roll is configured to have a uniform resistance distribution in the axial direction. For example, as described above, the one in which the semiconductive polymer layer 16 and the protective layer 17 are provided on the outer periphery of the conductive elastic body layer 15 is an ordinary charging roll. An example of the charging roll is a softening agent migration prevention layer provided between the elastic layer 15 and the semiconductive polymer layer 16 to prevent migration of the softening agent or the like of the conductive elastic layer 15 forming material. Further, there is a charging roll in which the conductive elastic layer 15 is made semi-conductive, and the protective layer 17 is directly provided on the outer periphery of the semi-conductive conductive elastic layer 15. From the viewpoint of axial resistance distribution, the above-mentioned softening agent migration prevention layer and the one in which the protective layer 17 is directly provided on the outer periphery of the semiconductive conductive elastic body layer 15 are the same as above. , Are configured to have a uniform resistance distribution in the axial direction.

[0004]

In the charging method using the charging roll having the above structure, in order to ensure uniform charging,
An application method using both AC voltage and DC voltage as the applied voltage is predominant. The frequency of the AC voltage is appropriately determined according to the copying process speed. That is, as the process speed increases, the frequency of the AC voltage also increases. On the other hand, as the photosensitive drum, an organic (OPC) photosensitive drum is mainly used.
The PC photosensitive drum is manufactured by the dip method.
That is, for example, a mandrel serving as a shaft is erected vertically, and an organic material is applied to this to form an organic layer having a desired film thickness. The film thickness distribution in the axial direction of the photosensitive drum manufactured by this dip method tends to become thinner near the start of coating on one end side (upper side) because the coating material flows downward due to its own weight due to the manufacturing method. There is. When a voltage is applied to such a photosensitive drum in combination with a charging roll having a uniform resistance distribution in the axial direction and used for a long time, the AC voltage between the surface of the photosensitive drum and the surface of the charging roll causes the film thickness of the photosensitive drum to change. The phenomenon that the height is higher in other parts than in other parts occurs. This AC voltage has an electric etching action on the photosensitive drum, and there is a problem that the degree of the etching action increases as the voltage increases in the thin film portion. Therefore, due to this phenomenon, the portion of the photosensitive drum where the film thickness is thin, that is, near one end formed by the dipping method (width of about 10 m
(within m), the protective layer of the photosensitive drum is removed, the surface of the charging roll is grounded, and insufficient charging occurs in the vicinity thereof, or sometimes the charging roll is destroyed by discharge.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a charging roll capable of extending the life of the photosensitive drum.

[0006]

In order to achieve the above object, the charging roll of the present invention is a charging roll in contact with a photosensitive drum, and a polymer coating layer for preventing etching is provided on at least one end side of the charging roll. Is formed.

[0007]

That is, the present inventor has conducted a series of studies in order to solve the etching phenomenon caused by the contact of the charging roll with the photosensitive drum. As described above, the thin-film portion of the photosensitive drum is the extremely narrow end portion, and this thin-film portion is formed outside the actually required copy image area (width of copy paper). To form a polymer coating layer for etching prevention so that the electric resistance value becomes higher than other surface portions only on the surface portion of the charging roll facing the thin portion of the photosensitive drum. The idea was to set the axial resistance distribution high only at the roll ends. As described above, when the etching preventing polymer coating layer is formed, it is possible to reduce the AC voltage when a voltage is applied only to the thin film portion of the photosensitive drum which is in contact with the coating layer forming portion, and the etching voltage for the photosensitive drum is reduced. The inventors have found that the action is suppressed and, as a result, the life of the photosensitive drum is extended, and the present invention has been reached. further,
When the etching preventing polymer coating layer and the outermost layer surface other than that are formed in different colors, the formation region of the etching preventing polymer coating layer becomes apparent from the appearance without measuring the resistance distribution of the roll surface, This is more effective because complicated steps such as inspection can be omitted.

Next, the present invention will be described in detail.

The charging roll of the present invention comprises a shaft body, a polymer layer formed of a plurality of layers on the outer circumference of the shaft body, and an etching layer formed on at least one end of the outermost surface of the polymer layer. And a polymer coating layer for prevention.

The shaft body is not particularly limited, and a metal core made of a solid metal body, a metal cylindrical body having a hollow hollow inside, or the like is used. The metal material is not particularly limited to iron, aluminum or the like.

The polymer layer composed of a plurality of layers formed on the outer periphery of the shaft body includes, for example, a conductive elastic body layer and a resistance adjusting layer (semiconductive elastic body) formed on the outer periphery of the conductive elastic body layer. Body layer) and a protective layer formed on the outer periphery of the resistance adjusting layer.

The conductive elastic layer is preferably formed to have a low hardness [Asker C (sponge hardness meter) 60 ° or less / 1 kg load] and an electric resistance of 10 ⁴ Ω · cm or less. And, as the matrix component, ethylene-propylene-diene rubber (EPDM), polynorbornene rubber, styrene-butadiene rubber (SBR), chloroprene rubber (CR), silicone rubber, epichlorohydrin rubber, acrylonitrile-butadiene rubber (NBR) and the like can be mentioned. It is formed using a forming material in which a conductive powder such as carbon black is mixed. Above all, polynorbornene rubber is used as the matrix component, and a mixture of carbon black and this is preferably used as the forming material.

The resistance adjusting layer formed on the outer periphery of the conductive elastic layer is preferably set within the range of a semiconductive region (10 ⁵ to 10 ⁸ Ω · cm). Then, the resistance adjusting layer is a polymer material mainly composed of epichlorohydrin-ethylene oxide rubber, hydrogenated acrylonitrile-butadiene rubber, acrylic resin, carbon black, conductive powder such as metal oxide, and an ionic conductivity control agent. It is formed using the forming material. Examples of the metal oxide include trilead tetraoxide (Pb ₃ O ₄ ), a solid solution of zinc oxide and aluminum oxide, a solid solution of tin oxide and antimony oxide,
Examples thereof include solid solutions of indium oxide and tin oxide. Examples of the ionic conductivity control agent include quaternary ammonium compounds such as trimethyloctadecyl ammonium chloride, benzyl trimethyl ammonium chloride, trioctyl propyl ammonium bromide, and trimethyl octadecyl ammonium perchlorate, and benzoates and nitrites of these quaternary ammonium compounds. Examples thereof include sulfates and the like, which may be used alone or in combination of two or more. As the material for forming the resistance adjusting layer, for example, as a polymer substance, hydrogenated acrylonitrile-butadiene rubber, epichlorohydrin-ethylene oxide rubber is used, and at least quaternary ammonium salt such as trimethyloctadecyl ammonium chloride and trilead tetraoxide are used. A mixture of one is preferably used.

The protective layer formed on the outer periphery of the resistance adjusting layer preferably has a surface resistance of 10 ⁵ Ω · cm or more, particularly preferably 10 ⁵ to 10 ⁸ Ω · cm.
Is. Then, for example, N-methoxymethylated nylon (8-nylon) and, if necessary, a forming material to which a conductive agent such as tin oxide is added are used.

The etching preventing polymer coating layer formed on the surface of at least one end side of the protective layer is formed so that the electric resistance value thereof is higher than the electric resistance value of the protective layer by 0.3 digit or more. It Examples of the forming material include urethane resin, binary fluororesin, and ternary fluororesin. Furthermore, since the coated surface using only the above various resins becomes transparent, the coating range, that is, in order to clarify the polymer coating layer forming region for etching prevention, a pigment is added in addition to the above forming material. May be. In this case, the pigment to be blended is preferably one that can be colored in a color that is easily distinguishable from the protective layer. And, as the above-mentioned pigment, those which do not affect the electric resistance value of the above-mentioned various resins are used. For example, titanium oxide, zinc oxide or the like is colored in white, and other than white. Inorganic pigments such as red iron oxide are preferably used. It is particularly preferable to use titanium oxide in terms of color developability and electric resistance. The blending amount of the pigment is not particularly set as long as the transparent resin can be colored in a desired color, but is, for example, 10 to 100 parts by weight of the various resins (hereinafter abbreviated as “part”). It is preferable to set in the range of 15 parts. As the material for forming the polymer layer for preventing etching, a binary fluororesin mixed with titanium oxide as a pigment is particularly preferable from the viewpoint of electrical resistance and color developability.

The charging roll of the present invention is manufactured, for example, as follows. That is, first, a conductive elastic layer forming material is prepared, and the conductive elastic layer is formed by filling the material in a molding die in which a shaft body (core bar) is arranged and heating and vulcanizing. . Next, a resistance adjusting layer forming material is prepared, and the outer peripheral surface of the conductive elastic body layer is coated with the resistance adjusting layer forming material by a spraying method, a dipping method, a roll coating method or the like, and heat vulcanized to form a resistance adjusting layer. To do. Next, as a material for forming a protective layer, a conductive agent is added to a methanol solution of N-methoxymethylated nylon and sufficiently dispersed by a disperser to adjust the viscosity, and then the protective layer is formed on the surface of the resistance adjusting layer by dipping or the like. The forming material is coated and heat-crosslinked to form a protective layer. Furthermore, as a polymer coating layer forming material for etching prevention,
The above resin and, if necessary, a pigment is added to this resin,
This is dissolved in an organic solvent such as methyl ethyl ketone or toluene to prepare a coating liquid. Then, the coating liquid, which is the material for forming the polymer layer for preventing etching, is applied to the surface of at least one end of the protective layer to form the polymer layer for preventing etching. In this way, the charging roll as shown in FIGS. 1 and 2 is manufactured. In the figure, 20 is a core bar,
Reference numeral 21 is a conductive elastic layer, 22 is a resistance adjusting layer, 23 is a protective layer, and 24 is a polymer coating layer for preventing etching. In the charging roll shown in FIGS. 1 and 2, the polymer layer 2 for preventing etching is formed on both end portions of the surface of the protective layer 23.
Although 4 is formed, it may be formed only on one end side. However, when the etching preventing polymer coating layer 24 is formed only on the one end side, when the charging roll is incorporated into a copying machine or the like and brought into contact with the photosensitive drum,
The charging roll must be installed so that the thin portion of the organic layer formed on the surface of the photosensitive drum is in contact with the etching preventing polymer coating layer 24 of the charging roll.

In addition, between the conductive elastic layer 21 and the resistance adjusting layer 22, a softening agent migration preventing layer for preventing migration / contamination of the softening agent in the conductive elastic layer 21 to another layer. May be formed. As the material for forming the softening agent migration prevention layer, N-methoxymethylated nylon containing a conductive agent such as carbon black is used.

In the charging roll thus obtained, the thickness of each layer and the thickness of the conductive elastic layer 21 are 3 to 4 m.
m, the thickness of the resistance adjusting layer 22 is 160 to 200 μm,
The thickness of the protective layer 23 is preferably set within the range of 5 to 10 μm. Then, the polymer coating layer 24 for preventing etching formed on at least one end side of the charging roll
Is preferably set to 10 to 30 μm,
It is particularly preferably 20 to 30 μm. The width in the axial direction depends on the contacting photosensitive drum, but is generally preferably set to 5 to 10 mm, particularly preferably 7 to 8 mm. Further, when the softener migration preventing layer is formed between the conductive elastic body layer 21 and the resistance adjusting layer 22, the thickness thereof is preferably set to 5 to 10 μm.

When the above-mentioned pigment is blended with the material for forming the polymer layer for preventing etching 24 and the polymer is used for forming the polymer layer for preventing etching 24 colored in a color different from that of the protective layer 23. It is possible to easily visually confirm the formation region of the etching preventing polymer coating layer 24 without measuring the resistance distribution of the charging roll. Therefore, a complicated process such as an inspection for confirming the formation region of the polymer layer for preventing etching 24 can be omitted, which is more effective.

[0020]

As described above, the charging roll of the present invention has the polymer coating layer for preventing etching formed on at least one end of the charging roll. Therefore, it is possible to reduce the AC voltage when a voltage is applied only to the thin film thickness portion of the photosensitive drum that is in contact with the etching preventing polymer coating layer forming portion, and the etching action on the photosensitive drum is suppressed. The durability of both the photosensitive drum and the charging roll is improved, and the service life is extended. Further, the leak reliability at the roll end portion is improved. Moreover, by forming the etching-preventing polymer coating layer and the other exposed portion of the roll surface in different colors, the region where the etching-preventing polymer coating layer is formed can be easily confirmed from the appearance. Therefore, it is not necessary to measure the resistance distribution on the roll surface, and complicated steps such as inspection can be omitted.

Next, examples will be described together with comparative examples.

[0022]

Example 1 [Material for forming conductive elastic layer] First, a material for forming a conductive elastic layer was prepared by blending the following components. Polynorbornene rubber 100 parts Ketjen Black 50 parts Naphthene system oil 400 parts

Then, the conductive elastic layer forming material is filled in a molding die having an iron cored bar (diameter 6 mm) and heated and vulcanized (200 ° C. × 30 minutes) to give a thickness of about 3 mm. A conductive elastic layer (Asker C hardness 58 °) was formed. Then, a resistance adjusting layer forming material containing the following respective components was prepared, and the forming material was used to dip the outer periphery of the conductive elastic layer to a thickness of 160 μm.
And vulcanize by heating in an oven (160 ° C
X 30 minutes) to form a resistance adjusting layer.

Epichlorohydrin-ethylene oxide rubber 100 parts Pb ₃ O ₄ 5 parts ethylenethiourea 1.2 parts processing aid 1 part hard clay 40 parts

Further, a protective layer forming material containing the following components is prepared, and the outer periphery of the resistance adjusting layer is coated with the forming material by dipping to a thickness of 10 μm and heated and dried (60 ° C. × 30 minutes). ) Was performed to form a protective layer.

N-methoxymethylated nylon 100 parts Carbon black 8 parts

Then, a material for forming a polymer coating layer for etching prevention containing the following components was prepared, and the outer peripheral portions of both ends of the protective layer were coated with this forming material by dipping to a thickness of 4 μm × width of 10 mm. Then, by heating and drying (60 ° C. × 30 minutes), a white etching preventing polymer coating layer was formed. In this way
And the charging roll shown in FIG. 2 was manufactured.

Binary fluororesin 100 parts Titanium oxide (white) 10 parts

[0029]

Example 2 As a material for forming a polymer coating layer for preventing etching, a material containing the following components was used. Then, using the forming material on the outer peripheral portions of both ends of the protective layer,
By coating with a thickness of 12 μm × width of 10 mm by dipping and heating and drying (60 ° C. × 30 minutes), a white polymer layer for preventing etching was formed. Other than that was carried out similarly to Example 1, and manufactured the charging roll shown in FIG. 1 and FIG.

Urethane resin 100 parts Titanium oxide (white) 10 parts

[0031]

Example 3 As a material for forming a polymer coating layer for preventing etching, a mixture of the following components was used. Then, using the forming material on the outer peripheral portions of both ends of the protective layer,
By coating with a thickness of 26 μm × width of 10 mm by dipping, and heating and drying (60 ° C. × 30 minutes), a white polymer layer for preventing etching was formed. A charging roll was manufactured in the same manner as in Example 1 except for the above.

Urethane resin 100 parts Titanium oxide (white) 10 parts

[0033]

Comparative Example A polymer coating layer for preventing etching was not formed on both outer peripheral edges of the protective layer. Other than that was carried out similarly to Example 1, and manufactured the normal charging roll shown in FIG.

The charging rolls of the example product and the comparative example product thus obtained were incorporated into a laser beam printer so as to be in sliding contact with the photosensitive drum. And 32 ℃ ×
Copies were made under 85% harsh conditions. In addition,
The copying was stopped for each sheet. The results are shown in Table 1 below.

[0035]

[Table 1]

From the results shown in Table 1 above, the comparative example product was only 9%.
After copying 000 sheets, scraping occurred on both ends of the photosensitive drum. On the other hand, in the product of Example 1, scraping occurred at the edge of the photosensitive drum after copying 14,000 sheets. Further, in the products of Examples 2 and 3, even after copying 15,000 sheets, scraping did not occur at the end portion of the photosensitive drum. From this, it is understood that the durability of the photosensitive drum is improved in copying when the charging roll of the example product is incorporated.

The current values at 7 points A to G on the surfaces of the charging rolls of Examples 1, 2, 3 and Comparative Example were measured (conditions: when 300 Hz-500 V _{PP was} applied). The results are shown in FIGS. 5 and 6. The curve A in FIG. 5 is the first embodiment.
The product, the curve B is the product of Example 2, and the curve C is the product of Example 3.
The curve D in FIG. 6 is a comparative example product. From the above-mentioned FIGS. 5 and 6, it can be seen that the comparative example product has substantially the same current value measured in the axial direction of the roll, and the axial resistance distribution of the comparative example product is substantially uniform. On the other hand, in each of the example products, the current value at both end portions of the charging roll is lower than that at the other portions, so it can be seen that the resistance is high at both end portions of the roll.

Further, in the case of the example product, since the portions where the polymer coating layer for preventing etching was formed on both ends were white, it could be easily distinguished from other surface portions by visual observation.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a charging roll of the present invention.

FIG. 2 is a front view showing an example of a charging roll of the present invention.

FIG. 3 is a cross-sectional view showing a conventional charging roll.

FIG. 4 is a configuration diagram of an electrophotographic copying machine using a roll charging method.

FIG. 5 is a curve diagram showing a current value in the axial direction of the surface of the charging roll of the example product.

FIG. 6 is a curve diagram showing the current value in the axial direction of the surface of the charging roll of the comparative example product.

[Explanation of symbols]

 20 Core Bar 21 Conductive Elastic Layer 22 Resistance Adjustment Layer 23 Protective Layer 24 Polymer Coating Layer for Etching Prevention

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[Procedure amendment]

[Submission date] April 26, 1994

[Procedure Amendment 1]

[Document name to be corrected] Drawing

[Correction target item name] All drawings

[Correction method] Change

[Correction content]

[Figure 1]

[Fig. 2]

[Figure 3]

[Figure 4]

[Figure 5]

[Figure 6]

Claims (2)

[Claims] 1. A charging roll in contact with a photosensitive drum, characterized in that a polymer coating layer for preventing etching is formed on at least one end side of the charging roll. 2. The charging roll according to claim 1, wherein the polymer coating layer for preventing etching and the other roll surface exposed portion are formed in different colors.