JPH08240965A - Electrifying roller for contact electrifying - Google Patents

Abstract

PURPOSE: To uniformly discharge electricity onto a body to electrified and to obtain an image with uniform density and without unevenness as a whole image by forming a flexible sheet consisting of an inner layer of a low electric resistance, and mid-layer of a high resistance and a surface layer having lower resistance then that of the mid-layer. CONSTITUTION: The electrifying roller 1 consists of a laminated flexible sheet 2 like a seamless tube and a metal shaft penetrating through the sheet 2. Electricity is fed to the flexible sheet 2 from the metal shaft 3 via flange roller 4 and rubber ring 5, and the sheet 2 has a three-layered structure consisting of an inner layer 2a, a mid-layer 2b and a surface layer 2c. Here the mid-layer is a high-resistance layer and is usually preferred to have a volume resistivity within the range of 10<7> -10<10> Ω, while the surface layer 2c is a layer of lower resistance than the mid-layer 2b, and especially it is preferable for the surface layer to have a resistance equal to or higher than that of the inne layer 2a. Thus, a certain voltage is stably supplied via the inner layer 2a and a constant and uniform electric discharge is secured from the sheet 2. Also, the mid-layer is a layer of the highest resistance and mitigates the electric discharge onto the electrified body from the sheet 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging roller for contact charging which can charge an object to be charged such as a photosensitive member without corona discharge.

[0002]

2. Description of the Related Art In an electrophotographic image forming method, the surface of a photoconductor is uniformly charged, and image exposure is performed to form an electrostatic latent image corresponding to an original image on the surface of the photoconductor. An image is formed by developing and transferring the latent image. In such an image forming method, charging (main charging) of the surface of the photoconductor is generally performed by corona charging, but this method inevitably suffers from the problem of environmental pollution such as generation of ozone. Recently, in order to avoid the generation of ozone, a conductive rubber roller is used as a charging roller, and the conductive rubber roller is brought into frictional contact with the surface of the photoconductor while applying a bias voltage. A method for performing the above has been proposed (JP-A-63-149669 and JP-A-1-267667).

However, in the charging using the conductive rubber roller as described above, if foreign matter such as dust or paper dust is sandwiched between the conductive rubber roller and the photoconductor, the uniformity of charging is impaired. However, it was difficult to perform stable charging. Further, when an image is formed, there is a cleaning failure on the surface of the photoconductor, and if the toner remains on the surface, there is a problem that the residual toner sticks to the surface of the photoconductor, which lowers the durability of the photoconductor. The problem also occurs. Further, in order to perform uniform charging, it is not enough to apply the DC bias voltage alone, and it is necessary to apply the AC bias voltage as well.

As a charging device in which such a problem is solved, for example, Japanese Patent Laid-Open No. 6-11952 discloses a charging roller made of a flexible conductive sheet containing a conductive brush roller. According to this charging roller,
Since the flexible conductive sheet is pressed by the conductive brush roller and adheres to the surface of the photoconductor, frictional charging can be performed uniformly by applying a low DC bias voltage without applying an AC bias voltage. It is extremely excellent in that it can However, in this charging roller, when there is a defect such as a pinhole on the surface of the photoconductor, a conductive sheet comes into contact with the pinhole portion, so a large current flows into that portion, which causes the output of the power source and charging. There is an unavoidable problem that a defect occurs and a clear white streak or the like occurs in the image corresponding to the defective portion of the photoconductor.

Further, Japanese Patent Application Laid-Open No. 6-202443 discloses that
An endless flexible sheet having a built-in brush roller is disclosed, which is composed of a high resistance layer on the front surface side and a low resistance layer on the inner surface side (brush roller side). This charging roller has the advantages of the charging roller disclosed in Japanese Patent Application Laid-Open No. 6-11952 as it is, and moreover, even if there is a defect such as a pinhole on the surface of the photoconductor, the defect is caused. There is no inflow of large current to the part, and as a result, the output decrease of the power supply and charging failure are prevented,
This is satisfactory in that it is possible to effectively prevent the occurrence of white streaks due to these.

[0006]

However, Japanese Unexamined Patent Publication (Kokai) No. Hei 6
The charging roller disclosed in JP-A-202443 is
It is not always satisfactory in terms of uniform charging property. For example, when a photoreceptor is charged to form an image, density unevenness is observed in the formed image. In addition, there was a problem that the image of the portion corresponding to the central portion of the photoconductor has a lower density than the image of the peripheral portion. Therefore, further improvement is required for the above charging roller.

Therefore, the object of the present invention is that the uniform chargeability is extremely good, a good image without density unevenness can be formed, and defects such as pinholes are present on the surface of the photoreceptor. Even in such a case, it is an object of the present invention to provide a charging roller for contact charging that can effectively prevent the occurrence of white streaks and the like due to the defect.

[0008]

According to the present invention, there is provided a charging roller for contact charging, which comprises an endless flexible sheet having a conductive shaft built therein and provided so as to be electrically connected to the shaft. There is provided a charging roller, wherein the flexible sheet is composed of an inner layer having a low electric resistance, an intermediate layer having a high electric resistance, and a surface layer having an electric resistance lower than that of the intermediate layer.

In the present invention, the surface resistivity of the flexible sheet is preferably in the range of 10 ⁶ to 10 ⁷ Ω / □. The inner layer has a volume resistance value of 10 ⁷ Ω or less, the intermediate layer has a volume resistance value of 10 ⁷ to 10 ¹⁰ Ω or less, and the surface layer has a volume resistance value of 10 ⁵ to 10 ⁶ Ω. It preferably has a volume resistance value.

[0010]

In the charging roller of the present invention, a flexible sheet for contacting and charging an object to be charged such as a photoreceptor is provided with a lower electric resistance than an inner layer having a low electric resistance, an intermediate layer having a high electric resistance and an intermediate layer. It is a distinctive feature that it is composed of three layers including a surface layer of resistance. That is, the inner layer of this flexible sheet has the lowest electric resistance and forms a low resistance current path. Therefore, a constant voltage is stably supplied through the layer, ensuring a constant and uniform discharge from the flexible sheet. The intermediate layer is a layer having the highest electric resistance, and reduces the discharge from the flexible sheet to the body to be charged. That is, even when there is a defect such as a pinhole on the charged body such as a photoconductor, the layer limits the current, so that even if the flexible sheet comes into contact with the defective part, Inflow of a large current is effectively prevented, troubles such as output reduction of the power source and charging failure do not occur, and the occurrence of white streaks in the image due to these can be effectively prevented. Furthermore, the electric resistance layer of the surface layer has a lower electric resistance than the intermediate layer. In the present invention, since such a low resistance layer is formed on the high resistance intermediate layer, it is this low resistance layer that directly contacts the member to be charged. Therefore, a good current path is secured between the charged body and the charged body, and the discharge to the charged body is performed uniformly. As a result, it is possible to obtain an image with uniform density as the entire image without density unevenness. it can.

In the charging roller disclosed in JP-A-6-202443 mentioned above, since the surface of the flexible sheet that contacts the member to be charged is a high electric resistance layer, the charging roller and the member to be charged are good. No current path is formed, resulting in non-uniform discharge to the body to be charged, which tends to cause image defects due to uneven charging. Since the resistance layer is provided, such a problem can be effectively solved.

In the present invention, the flexible sheet having the three-layer structure described above preferably has a surface resistivity in the range of 10 ⁶ to 10 ⁷ Ω / □. That is, this surface resistivity is 10 ⁷ Ω
If it is larger than / □, the discharge from the surface to the body to be charged becomes uneven, and it becomes difficult to perform uniform charging,
Charge unevenness is likely to occur, resulting in image density unevenness. Again 1
If it is lower than 0 ⁶ Ω / □, it becomes difficult to prevent the inflow of a large current when there is a defect such as a pinhole in the charged body such as the photoconductor. Therefore, the electric resistance, thickness, etc. of each layer are preferably set based on the function of each layer so that the surface resistivity of the flexible sheet falls within the above range.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on specific examples shown in the accompanying drawings. FIG. 1 is a diagram showing a side cross section of a charging roller of the present invention.

This charging roller (generally designated by 1)
Roughly speaking, it is composed of a flexible laminated sheet 2 in the form of a seamless tube, and a metal shaft 3 extending through the sheet 2. The metal shaft 3 has a pair of flange rollers 4 made of a conductive and rigid material such as aluminum.
Are fitted to both ends of the flexible laminated sheet 2 via conductive rubber rings 5. That is, the flexible sheet 2 has a structure in which power is supplied from the metal shaft 3 via the flange roller 4 and the rubber ring 5. The flexible laminated sheet 2 has a three-layer structure including an inner layer 2a, an intermediate layer 2b and a surface layer 2c.

In the present invention, the electric resistance and thickness of each layer constituting the above flexible laminated sheet 2 are, as described above, the surface resistivity of the laminated sheet 2 of 10 ⁶ to 10 ⁷ Ω / □.
It is preferable that the range is set according to the function of each layer.

For example, the inner layer 2a is a layer having a low electric resistance, its volume resistance value is generally 10 ⁷ Ω or less, and its thickness is set in the range of about 50 to 150 μm. As the constituent material of the inner layer 2a, any material is used as long as the material has a predetermined conductivity and flexibility, but generally, various materials are used. Resin or rubber containing the conductive agent is used.

As the resin, various thermoplastic elastomers such as polyester elastomer, polyamide elastomer, polyurethane elastomer, soft vinyl chloride resin, styrene-butadiene-styrene block copolymer elastomer, acrylic elastomer are preferable. , Nylon 6, Nylon 6,6, Nylon 6
-Nylon 6,6 copolymer, Nylon 6,6 -Nylon 6,10
Copolymers, polyamides such as alkoxymethylated nylon such as methoxymethylated nylon, copolyamides or modified products thereof, silicone resins, acetal resins such as polyvinyl butyral, polyvinyl acetate, ethylene-
Vinyl acetate copolymers, ionomers and the like can also be used. Examples of the rubber include natural rubber, butadiene rubber, styrene rubber, butadiene-styrene rubber, nitrile-butadiene rubber, ethylene-propylene copolymer rubber, ethylene-
Propylene-non-conjugated diene copolymer rubber, chloroprene rubber, butyl rubber, silicone rubber, urethane rubber, acrylic rubber and the like are preferable. Further, a metal foil such as nickel, aluminum, copper, brass or tin can also be used.

In order to adjust the volume resistance value, as the conductive agent to be blended with the above resin or rubber, conductive carbon black and metals such as silver, gold, copper, brass, nickel, aluminum and stainless steel are used. Powder or a powdered conductive agent such as tin oxide-based conductive agent can be used. In addition, a nonionic, anionic, cationic, amphoteric-based organic conductive agent or an organic tin-based conductive agent can be used. You can also Generally, higher conductivity is obtained when these conductive agent particles form a chain structure in resin or rubber, but in this case, a dot-shaped high potential portion is generated when a voltage is applied. , There is a risk of uneven charging. Therefore, these conductive agents are preferably uniformly and finely dispersed in the resin or rubber, and for this purpose, it is important to sufficiently knead the conductive agent-containing resin or rubber.
Further, in order to effectively disperse the conductive agent uniformly, some acid-modified resins or rubbers obtained by copolymerizing an ethylenically unsaturated carboxylic acid such as acrylic acid, methacrylic acid, or maleic anhydride should be used. Is also effective.

The intermediate layer 2b is a high-resistance layer, and it is usually preferable that its volume resistance value is in the range of 10 ⁷ to 10 ¹⁰ Ω, and its thickness is set to about 10 to 150 μm.
As the material for forming the intermediate layer, the above-mentioned resin or rubber is used, and this material is set to have a volume resistance value in the above range by blending a conductive agent as described above.

The surface layer 2c is a layer having a resistance lower than that of the intermediate layer 2b, and particularly preferably has an electric resistance higher than that of the inner layer 2a. Usually, the volume resistance value thereof is 10 ⁵ to 1.
The range is preferably 0 ⁶ Ω, and the thickness is 10 to 15
It is set to about 0 μm. Further, as the surface layer forming material, the above-mentioned resins or rubbers are used. In addition to these, fluorine-based resins or rubbers such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoro Ethylene-hexafluoropropylene copolymer (PTFE.HFP), perfluoroalkoxy-based fluororesin and the like are preferably used. In particular, when these fluorine-based resins or rubbers are used, they are inactive and have a small friction coefficient, so that there is a great merit in terms of the life of the photoconductor as the charged body and the life of the sheet. Similar to the above, these resins and rubbers are set to have a volume resistance value within the above range by blending a conductive agent.

The laminated sheet 2 can be easily formed by integral molding such as simultaneous laminating extrusion or coating or the like. In this case, it is desirable to select and use a resin or rubber for forming each layer, which has a melting point or a softening point in a range close to each other in order to enhance the adhesive strength of both layers.

The surface (surface layer) of the laminated sheet 3 is preferably as smooth as possible. For example, JIS B060
The average roughness according to 1 is preferably 5 μm or less, and particularly preferably 1 μm or less.

In the charging roller 1 described above, since the conductive rubber ring 5 constitutes a current path from the metal shaft 3 to the laminated sheet 2, it must have sufficient conductivity. However, it is usually sufficient that it has a volume resistance value similar to that of the inner layer 2a. As the rubber ring forming material, the same rubber as the material exemplified for the material for forming the inner layer 2a can be used. Further, the conductive rubber ring 5 is not essential, and for example, the end portion of the laminated sheet 2 may be directly fixed to the flange roller 4 by using an adhesive or the like, but such a rubber ring 5 is usually used. Is better to use. That is, by using such a rubber ring 5, when the laminated sheet 2 is pressed against the body to be charged, the laminated sheet 2 adheres to the body to be charged at the portion where the rubber ring 5 is provided, and a sufficient nip width is obtained. Since it can be ensured, it is extremely advantageous for effective uniform charging.

In the present invention, the structure of the charging roller 1 is as follows.
The flexible laminated sheet 2 is not limited to the embodiment shown in FIG. 1 as long as it has the above-described three-layer structure, and various structures other than the above can be adopted. An example thereof is shown in FIGS.
Shown in

In the charging roller of FIG. 2, an insulating brush 10 is planted on the metal shaft 2, and an insulating rubber ring 11 is provided on the metal shaft 2 between the brush 10 and the flange roller 4. It is fitted. That is, the flexible laminated sheet 2 has its end fixed to the flange roller 4 such that a constant tension is applied by the insulating rubber ring 11. This fixing is easily performed, for example, by using a heat-shrinkable resin ring 12 and firmly sandwiching the end portion of the sheet 2 between the flange roller 4 and the resin ring 12. Of course, the laminated sheet 2 can be fixed with an appropriate adhesive without using the heat-shrinkable ring 12.

In the charging roller of FIG. 2, the insulating brush 10 is provided so that its tip contacts the inner surface of the sheet 2. Therefore, when the charging roller is pressed against a charged body such as a photosensitive member, the pressing force of the brush 10 brings the laminated sheet 2 into close contact with the charged body over the entire axial direction, which is extremely advantageous in terms of uniform charging. .

As the above-mentioned insulating brush 10, known organic or inorganic fibers can be used. Preferable examples of such organic fibers include synthetic or regenerated fibers, for example, polyamide fibers such as nylon 6, nylon 6,6, polyester fibers such as polyethylene terephthalate, acrylic fibers, polyvinyl alcohol fibers, polyvinyl chloride fibers, rayon. , Acetate, etc. Carbon fibers are suitable as the inorganic fibers. The organic or inorganic fiber has a thickness of 2 to 10 denier (d), especially 3 to 6 d, and a fiber length (hair length) of 2 to 7 mm,
Especially, it is preferable that the pressure is in the range of 3 to 5 mm, and the flocking density is in the range of 30,000 to 100,000 pieces / square inch, particularly 40,000 to 90,000 pieces / square inch. It is suitable for giving In addition, it is preferable to round the ends of the fibers (tips of the brush) in order to suppress abrasion of the laminated sheet 2.

A conductive brush may be used instead of the insulating brush 10 described above. When a conductive brush is used, electric power is supplied to the laminated sheet 2 through the brush, so that the flange ring 4 is made of an insulating material such as plastic. In this case, the volume resistivity of the conductive brush is preferably in the range of 10 ^{2 to} 10 ⁸ Ω · cm, particularly 10 ^{3 to} 10 ⁶ Ω · cm. The thickness and the fiber length of the brush fiber may be the same as those of the above-mentioned insulating brush, but the flocking density is in the range of 10,000 to 200,000 / square inch, particularly 30,000 to 100,000 / square inch. Is preferred. As such a conductive brush, a resistance is adjusted by blending a conductive agent in the above-mentioned organic fiber or by metallizing the fiber surface, conductive inorganic fiber such as carbon fiber, metal such as stainless steel and brass. Fiber is used. When the conductive agent is used, the conductive agent described above can be used.

Further, FIG. 3 shows an example in which an insulating sponge layer 20 is provided on the metal shaft 3 instead of the insulating brush 10 of FIG. 2, and other than that is exactly the same as FIG. Also in this charging roller, the laminated sheet 2 is in close contact with the member to be charged over the entire axial direction by the pressing force of the insulating sponge layer 20, which is extremely advantageous in terms of uniform charging.

Of the above-mentioned charging rollers, the one shown in FIG. 1 is suitable as a small diameter having a diameter of 10 mm or less, and the one shown in FIGS. 2 and 3 has a relatively large diameter of 10 mm or more. A diameter is suitable.

(Charging Method) The charging roller 1 described above is arranged so that the flexible laminated sheet 2 contacts the photosensitive drum 50 as shown in FIG.
Contact charging is performed. That is, a DC power source 51 is connected to the metal shaft 3, and a DC voltage is applied to the photosensitive drum 50 while the charging roller 1 is driven to rotate, so that the photosensitive drum 50 is charged. In this case, it is desirable that the charging roller 1 is charged while being pressed and biased by an elastic member (not shown) such as a spring in order to ensure a certain contact width.

The charging roller 1 does not necessarily have to be provided so as to be rotated by the photosensitive drum 50. For example, a drive mechanism is connected to the metal shaft 3 of the charging roller 1 and is independent of the photosensitive drum 50. It is also possible to drive and rotate the charging roller 1 by connecting an appropriate drive transmission mechanism to the metal shaft 3 and transmitting the drive rotation of the photosensitive drum 50 to the metal shaft 3.

The charging voltage applied to the charging roller 1 (laminated sheet 2) is set to be 1.5 to 3.5 times, especially 2 to 3 times the charging start voltage value on the surface of the photosensitive drum 1. . It is also possible to combine the AC power supply 52 with the DC power supply 51 and apply a voltage in which an AC voltage is further superimposed on the DC voltage. Such alternating current has a frequency of 300 to 1500 Hz, especially 400 to 100 Hz.
At 0 Hz, the peak-to-peak voltage is 2.5 to 4 of the above DC voltage.
It is preferred to use a double, especially 2.8 to 3.5 times alternating current.

After the above charging, image formation is carried out by means known per se. For example, although not shown, an image exposure mechanism, a developing mechanism, a transfer mechanism, a cleaning mechanism, and a charge eliminating mechanism are arranged around the photosensitive drum 50, and the image exposure is performed after the main charging to perform the original image. An electrostatic image corresponding to is formed, and the electrostatic image is developed by the developing mechanism to form a visualized toner image. This toner image is transferred to a predetermined paper by a transfer mechanism,
The transferred image is fixed on the sheet by heat, pressure or the like. On the other hand, after the transfer is completed, the cleaning mechanism removes residual toner and paper dust from the surface of the photosensitive drum 50, and then the charge removing mechanism removes the charge, thereby completing one cycle of the image forming cycle.

The above-mentioned example is an example in which the charging roller of the present invention is used for main charging of the photosensitive drum, but it goes without saying that this charging roller can also be used for static elimination of the photosensitive drum. .

The charging roller of the present invention is useful for charging photoreceptors used in various electrophotographic methods such as copying machines, facsimiles, laser printers, etc., and various photoreceptors having a single-layer or laminated structure, for example, a-Si. The present invention is applicable to charging of any photoconductor such as a photoconductor, a selenium photoconductor, and a single-layer or multi-layer organic photoconductor. Among these, when the charging roller of the present invention is applied to an organic photoconductor, ozone and NO _x are not generated, and therefore, a charge generating pigment, a charge transporting substance, a binder, a dielectric substance and the like which compose the photoconductor. It is possible to extend its life without deterioration.

[0037]

Experimental Example 1 Polyurethane as an inner layer forming resin, polyurethane as an inner layer forming resin, intermediate layer and surface layer forming resin,
Using polyvinylidene fluoride, a flexible laminated sheet having a three-layer structure having the surface resistivity and the volume resistance value shown in Table 1 was prepared. For comparison, a laminated sheet having a two-layer structure without a surface layer was also prepared. Using these laminated sheets,
Assemble the charging roller having the structure shown in Fig. 3 and install it in a modified DC-2566 electrophotographic copying machine manufactured by Mita Kogyo Co., Ltd. that uses an organic photoconductor to charge, expose, develop, and transfer without applying an AC voltage. And fixing.

The charging conditions were set as follows. Charging conditions; Applied DC voltage: + 1600V (Charging start voltage: +
600V) Charging roller rotation speed: 298.89 rpm (photoconductor and driven rotation) Photoconductor peripheral speed: 156.5 mm / sec

The image quality of the obtained image was visually evaluated. Table 1 shows the results. The judgment criteria are as follows. Criteria for image quality: Good: An image without density unevenness was obtained. Δ: Some uneven density was observed. X: White streak occurred in the image, and uneven density was clearly confirmed.

When charging was performed under the same conditions using a photoconductor having a pinhole, all the charging rollers were
No image defects such as white streaks due to concentrated leakage of charging current to the pinholes occurred.

[0041]

[Table 1]

[0042]

According to the charging roller of the present invention, since the low resistance layer is formed on the high resistance intermediate layer, the low resistance layer is brought into direct contact with the member to be charged, and the low resistance layer is contacted with the member to be charged. A good current path is secured. Therefore, the discharge to the member to be charged is uniformly performed, and it is possible to obtain an image having a uniform density as a whole image without density unevenness. In addition, since the high resistance layer is provided as the intermediate layer, even if a defect such as a pinhole occurs on the surface of the photoconductor, the charging of the surface of the photoconductor can be made uniform and stable without lowering the output of the power supply. Moreover, it can be performed without reducing the life of the photoconductor.

[Brief description of drawings]

FIG. 1 is a side sectional view showing a charging roller of the present invention.

FIG. 2 is a side sectional view showing another example of the charging roller of the present invention.

FIG. 3 is a side sectional view showing still another example of the charging roller of the present invention.

FIG. 4 is a diagram for explaining a method of charging a photosensitive drum using the charging roller of the present invention.

Front page continuation (72) Inventor Masahiro Shirai 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Kogyo Co., Ltd. (72) Masajun Matsuda 1-2-2 Tamatsukuri, Chuo-ku, Osaka Mita Kogyo Within the corporation

Claims (4)

[Claims] 1. A charging roller for contact charging, comprising an endless flexible sheet having a conductive shaft therein and provided so as to be electrically connected to the shaft, wherein the flexible sheet has a low electric resistance. A charging roller comprising an inner layer, an intermediate layer having a high electric resistance, and a surface layer having an electric resistance lower than that of the intermediate layer. 2. The flexible sheet is 10 ⁶ to 10 ⁷ Ω.
The charging roller according to claim 1, which has a surface resistivity of / □. 3. The inner layer has a volume resistance value of 10 ⁷ Ω or less, the intermediate layer has a volume resistance value of 10 ⁷ to 10 ¹⁰ Ω, and the surface layer has a volume resistance value of 10 ⁵ to 10 ^5. The charging roller according to claim 2, which has a volume resistance value of ⁶ Ω. 4. The charging roller according to claim 1, wherein the surface layer has a higher volume resistance value than the inner layer.