JPH1069151A - Charging roller - Google Patents

Abstract

(57) [Summary] [Problem] To be excellent in release property to the surface of a photoreceptor, release property to a toner and contamination to a photoreceptor.
Provided is a charging roller capable of performing stable and uniform charging without generating minute electrical conduction portions due to a dispersion state of conductive particles. An elastic layer (2) is provided around a shaft (1), and the surface is covered with a surface layer (3). The elastic layer 2 is made of epichlorohydrin rubber, the surface layer 3 contains non-doped tin oxide, and at least nylon 6, nylon 6
6, Nylon 6-10, Nylon 11, and Nylon 12 are alcohol-soluble copolymer nylon resins containing two or more. The amount of tin oxide in the surface layer 3 is 40
It is preferable that the amount is at least 70 parts by weight.

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 charging an object to be charged such as a photoreceptor in an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art In an electrophotographic image forming apparatus such as a copying machine or a facsimile, a corona discharger is generally used as a means for charging the surface of a photoreceptor, but the corona discharger is expensive. In addition, a high-voltage power supply is required, which entails danger in safe maintenance of the machine, and furthermore, harmful substances such as ozone are generated by corona discharge, adversely affecting not only the photoreceptor but also the human body. Many problems have been pointed out from an environmental point of view.

In recent years, research and development on a contact charging system which can be charged at a low voltage and generates a small amount of ozone have been actively conducted in recent years, and are gradually being adopted.

However, in the contact charging method, charging is performed by rotating the charging roller in contact with the surface of the photoreceptor. If the roller surface is not electrically uniform, charging unevenness is likely to occur. Since the charging roller is required to have appropriate elasticity so as not to damage the photoconductor, it is generally formed of a polymer material such as rubber. For this reason, the charging potential is apt to change due to a change in environment, and for example, there is a disadvantage that charging cannot be performed uniformly at low temperature and low humidity. Therefore, the charging roller is provided with a conductive rubber layer to enhance the charging property. However, there is a problem that the low molecular weight component contained in the conductive rubber layer migrates to the photoconductor and contaminates the photoconductor. . When the conductivity of the conductive rubber layer is high, a so-called pinhole leak in which an excessive current flows in a defective portion of the photoreceptor occurs, and an image defect occurs. Further, the charging roller tends to cause problems such as sticking to the photoreceptor, adhesion of toner to the roller surface, and damage to the roller surface.

For example, Japanese Patent Application Laid-Open No. 63-149668 reports that charging uniformity can be improved by superimposing an AC voltage on a DC voltage when charging a charging roller. . Japanese Patent Application Laid-Open No. 7-64378 reports a test result in the case where an image is repeatedly created by applying an AC voltage in which a DC component is superimposed on a charging roller to charge a photoconductor, and A charging roller having a surface layer formed by coating an intermediate layer on a rubber roller coated with EPDM + carbon or the like and coating a nylon containing a conductive agent on the intermediate layer has durability, environmental stability of resistance value, and photoreceptor defects. It is shown to be good in terms of leak and photoconductor contamination.

[0006]

When the AC voltage is superimposed on the DC voltage, the operation cost and the amount of ozone generated are increased as compared with the case where only the DC voltage is applied. Then, the photoconductor and the charging roller tend to vibrate due to the influence of the AC component, thereby generating noise called charging noise, and further generating a transition from the charging roller to the photoconductor. A problem arises in that it becomes easier to do so. Since it is necessary to prevent this charging noise and the generation of migration from the charging roller, and to increase the capacity of the resistance layer by applying an AC voltage, that is, it is necessary to reduce the film thickness, the charging roller in the case of applying a DC-AC voltage is 3 It has a multi-layer structure of layers or more (excluding the support), which causes a problem that the number of manufacturing steps increases and the cost increases.

On the other hand, in a charging roller to which only a DC voltage is applied, the charging property of the roller layer is a problem. However, by using epichlorohydrin rubber for the elastic layer, the conventional conductive agent / elastomer can be used.
It is possible to obtain a sufficient charged voltage property higher than in the case of the synthetic rubber system, and it is also possible to eliminate the cause itself of the electric nonuniformity such as poor dispersion of the conductive agent in the synthetic rubber. It is also known that epichlorohydrin rubber has low elastic deformation and good mechanical strength, so that uniform and stable charging is possible.

On the other hand, the charging roller is required to have excellent releasability from the photoconductor and toner and not to contaminate the photoconductor. For this purpose, Japanese Patent Application Laid-Open No. 7-64378 discloses that. It has been shown that it is effective to use a copolymerized nylon resin as the surface layer. However, since a resin containing nylon as a polymerized unit has a high electric resistance, a charging roller using the resin as a surface layer cannot obtain a sufficient charging potential and has a low image density. In addition, as a defect when the electric resistance is high, fluctuation of the resistance due to the environment, that is, fluctuation of the charged potential occurs.

In order to adjust the resistance of the surface layer of the charging roller, conductive particles are added to the copolymerized nylon resin.

However, carbon generally used as conductive particles has a low resistance of 1 Ω · cm or less.
It is easy to be sensitive to the influence of dispersion conditions, so that the agglomerated portion of fine conductive particles becomes an electrical conduction portion, it is easy to generate sandy image density unevenness, and leaks at the contact portion with the photoconductor defect There is a problem that it easily occurs.

The conductive tin oxide of the type doped with antimony also has the same problem as the carbon because it has a low resistance of 10 Ω · cm or less.

On the other hand, non-doped conductive tin oxide is
In addition to the good dispersibility of the alcohol-soluble polymer itself, conductive portions are less likely to be formed between the dispersed tin oxides, and the image density unevenness in the sand-like state and the leak due to photoconductor defects are less likely to occur. has the property, 10 ⁴ ~10 ⁸ Ω · cm and it is necessary to increase the amount thereof to a medium resistance, for which, difficult uniform dispersion of the tin oxide into the nylon resin is Problem.

An object of the present invention is to solve such a problem. That is, the present invention is excellent in the releasability from the surface of the photoreceptor, the releasability from the toner, and the contamination on the photoreceptor, and furthermore, a minute electric conduction portion is generated due to the dispersed state of the conductive particles. An object of the present invention is to provide a charging roller capable of performing stable and uniform charging.

[0014]

The inventor of the present invention has conducted intensive studies on non-doped tin oxide, and found that nylon 6, nylon 6-6, nylon 6-10, and nylon 11 can be used.
And non-doped conductive tin oxide dispersed in an alcohol-soluble copolymerized nylon resin by dispersing at least two selected from nylon and nylon 12 as polymerized units, thereby disturbing the crystallinity of the nylon resin. It was found that even if the amount was sufficiently increased, the particles were dispersed well, and the present invention was completed.

According to a first aspect of the present invention, there is provided a charging roller having an elastic layer and a surface layer covering the elastic layer, wherein the elastic layer is made of epichlorohydrin rubber. The layer is made of an alcohol-soluble copolymerized nylon resin containing at least two selected from nylon 6, nylon 6-6, nylon 6-10, nylon 11 and nylon 12 as polymerized units in which non-doped tin oxide is dispersed. It is characterized by becoming.

According to the second invention, in the first invention, the amount of the non-doped tin oxide in the surface layer is at least 40% by weight.
% By weight.

[0017]

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a sectional view of a charging roller according to an embodiment of the present invention. This charging roller 10
Is formed by providing an elastic layer 2 around a cored bar 1 and covering the surface of the elastic layer 2 with a surface layer 3. For the elastic layer 2, epichlorohydrin rubber is used. The surface layer 3 is made of nylon 6 and nylon 6 in which non-doped tin oxide is dispersed.
6, nylon 6-10, nylon 11 and nylon 12
And an alcohol-soluble copolymerized nylon resin containing at least two selected from the group consisting of:

Since the piezoelectric roller 10 uses epichlorohydrin rubber for the elastic layer 2, electric non-uniformity does not occur unlike the case where synthetic rubber in which a conductive agent is dispersed is used. In addition, since its chargeability is higher than that of synthetic rubber in which a conductive agent is dispersed, only a DC voltage can be applied, and there is no need to laminate thin layers in consideration of the influence of an AC component. Therefore, the layer structure of the charging roller is not complicated, and the number of steps in manufacturing the roller is small, so that the charging roller can be manufactured at low cost.

The charging roller 10 is made of nylon 6, nylon 6-6, nylon 6
By using an alcohol-soluble copolymerized nylon resin containing at least two selected from the group consisting of 10, nylon 11 and nylon 12 as polymerized units, this is made into a paint and applied to the surface of the elastic layer 2 to form the surface layer 3. It can be formed and therefore has good productivity. The copolymerized nylon resin of the above polymerized unit has excellent releasability from the photoreceptor and the toner, and has high film strength and good durability, so that image density unevenness due to contamination of the photoreceptor can be prevented.

Furthermore, since the surface layer 3 contains non-doped tin oxide, unevenness in the image density in a sandy state due to uneven dispersion of tin oxide as a conductive agent and contact with a photosensitive member defect are caused. Pinhole leak occurring in the portion can be prevented. Non-doped tin oxide has a higher resistance (generally a resistivity of 10 ⁴ to 10 ⁸ ) than tin oxide doped with another atom such as antimony (generally, resistivity is 10 Ω · cm or less) or carbon. Ω
cm).

Therefore, when the non-doped tin oxide fine particles are contained in the surface layer 3, the non-doped tin oxide itself has good dispersibility with respect to the alcohol-soluble polymer. Since the resistance of the tin oxide is medium, a conductive portion is hardly generated between the dispersed non-doped tin oxides, and the image density unevenness in a sandy state and a leak due to a photoconductor defect are hardly generated. In addition, non-doped tin oxide is more advantageous in terms of pollution than tin oxide doped with antimony or the like.

If the content of the non-doped tin oxide in the surface layer 3 is less than 40% by weight, the resistance of the surface layer 3 is lowered, the charging potential is reduced, and 70% by weight. %, The flexibility of the surface layer 3 is impaired and cracks may occur. Therefore, the content of the non-doped tin oxide in the surface layer 3 is 40% by weight.
At least 70% by weight.

Prior to the description of the embodiments of the present invention, a method for evaluating the charging characteristics (charging potential and uniformity of charging) of the charging roller, a method for evaluating the releasability of the charging roller from the photosensitive member and the toner, and , The durability of the charging roller (voltage charging,
An evaluation method for (film strength) will be described.

FIG. 2 is an explanatory diagram of an apparatus for evaluating the charging characteristics of the charging roller. In the figure, reference numeral 201 denotes a charging roller to be evaluated, and 202 denotes a DC voltage V applied to the core 1 of the charging roller 201.
a, a photosensitive drum 203, a neutralizing lamp 204, and a surface potential Vs of the photosensitive drum 203.
Is an electrometer that measures

In this evaluation apparatus, the photosensitive drum 205 is rotated at a constant rotational speed v, and the charging roller 201 is brought into contact with the surface of the drum and is driven to rotate. The surface of the photoconductive drum 203 whose charge has been removed by the charge removing lamp 205 is charged, and the charged potential Vs is measured by the electrometer 205. By expressing the measurement result of the electrometer 205 in a charging characteristic chart, the charging potential Vs and its uniformity can be evaluated.

FIG. 3 is an explanatory diagram of an image forming apparatus used for evaluating the charging roller. In the figure, 301 is a photosensitive drum, 302 is a laser beam as an exposure information medium, 303 is a developing device, 304 is a cleaner for removing residual toner on the drum surface, 305 is a discharge lamp, and 306 is a transfer belt.

This device is for investigating problems in actual use of the charging roller 201. Specifically, the releasability and non-staining property of the charging roller 201 from the photosensitive drum 302 are evaluated from the horizontal streak image due to the roller trace on the photosensitive drum 302, and the image stain and the charging roller 20 are removed.
The toner releasability of the charging roller 201 is evaluated based on the state of toner adhesion to No. 1. In addition, the voltage resistance and the surface layer strength of the roller are evaluated based on the abnormal image and the damage state of the roller. In addition, pinhole leaks caused by photoconductor defects
This is performed by evaluating an image obtained by this device.

[0028]

Next, examples of the present invention will be described together with comparative examples.

(Comparative Example 1) Evaluation was made by the configuration of the charging roller described in Japanese Patent Publication No. 6-64393. Carbon dispersed chloroprene rubber (3 mm thick), N-
A methoxymethylated nylon (Toresin EF-30T, manufactured by Teikoku Chemical Industry Co., Ltd.) was applied to the roller surface under the following mixing conditions and coating conditions, and then dried to form a surface layer. Formulation conditions N-methoxymethylated nylon: 2.4% Methanol: 24.4% 2-ethoxyethanol: 73.2% Coating conditions Spray gun: TAGB-951 manufactured by Tevirbis Spray gun moving speed: 30 mm / S Spray gun and roller Distance: 93 mm Atomizing air flow rate: 50 / min Roller rotation speed: 400 rpm Alcohol-soluble nylon (CM8000, manufactured by Toray) containing carbon (Denka Black, manufactured by Denka) on an elastic layer (thickness: 3 mm) made of epichlorohydrin rubber The evaluation was performed using a charging roller having a surface layer composed of Formulation conditions-Carbon 0.36 wt%-Nylon 3.24 wt% (solid content: 3.6 wt%)-Ethanol 64.3 wt%-Xylene 32.1 wt% Coating conditions Same as Comparative Example 1. Dispersion condition at the time of preparation 90 minutes with a 300 W ultrasonic cleaner Drying temperature 150 ° C. The results are shown in Table 1 below. As shown in Table 1, since the electrical resistance of carbon is low and the conducting portion is formed between the fine particles, there is a problem in the uniformity of charging, and therefore, the image has a sand-like unevenness. Further, for the same reason, there is also a problem of a leak caused by a defect of the photoconductor.

[0030]

[Table 1]

Example 1 Alcohol-soluble copolymerized nylon containing tin oxide (S-1, manufactured by Mitsubishi Materials Corporation) on an elastic layer (3 mm thick, electric resistance of 10 ⁸ Ω · cm) made of epichlorohydrin rubber (Diamid, T1
71, Daicel Huls: a type containing nylon 12). The content of tin oxide in the surface layer was 20 wt%. Formulation conditions Tin oxide: 0.7% (solid content 3.6%) Alcohol-soluble copolymerized nylon: 2.9% (solid content 3.6%) Methanol: 64.3% 2-ethoxyethanol: 32.1% Dispersion condition Same as Comparative Example 2. Painting conditions Same as Comparative Example 1. Drying temperature 150 ° C

Example 2 A charging roller having the same structure as in Example 1 was used, and the content of tin oxide in the surface layer was 30 wt%.

Example 3 A charging roller having the same structure as in Example 1 was used, and the content of tin oxide in the surface layer was 40 wt%.

Example 4 A charging roller having the same structure as in Example 1 was used, and the content of tin oxide in the surface layer was 60 wt%.

Example 5 A charging roller having the same structure as in Example 1 was used, and the content of tin oxide in the surface layer was 71 wt%.

The evaluation results of the charging rollers of Examples 1 to 5 are shown in Table 2 below. The measurement of the charging potential was performed in a low-temperature (10 ° C.) low-humidity (15%) atmosphere in which the potential greatly decreased. The charging roller of Example 1 has a problem that the charging potential is low and the image density is low, but the other items are good. In the charging roller of the second embodiment, as in the first embodiment, there was a problem only with the charging potential. In the charging roller of Example 3, the charging potential was good, and there was no problem in image density. The charging roller of Example 4 was satisfactory over all items as in Example 3. In the charging roller of Example 5, cracks were observed in the surface layer, though slightly. In addition, the uniformity of charging and the evaluation of photoreceptor defect leak were lower than those in Example 4.

[0037]

[Table 2]

[0038]

As described above, the charging roller of the present invention has the following excellent effects. (1) The charging roller according to claim 1, wherein the elastic layer is made of a medium-resistance epichlorohydrin rubber, the surface layer contains non-doped tin oxide, and at least nylon 6, nylon 6-6, nylon 6-10, Since it is made of an alcohol-soluble copolymerized nylon resin containing two or more of nylon 11 and nylon 12, it has good releasability from the photoreceptor and toner, no contamination of the photoreceptor, and sufficient film strength. In addition, depending on the dispersion state of the non-doped tin oxide, which is a conductive agent, stable and uniform charging can be performed without generating pinhole leak due to unevenness in image density in the form of sand or a photoconductor defect. In addition, there are also production effects, such as that the resin of the surface layer is soluble in alcohol and is easily formed into a paint, and that the layer configuration is relatively simple. Furthermore, the non-doped tin oxide used as a conductive agent is also effective in terms of pollution.

(2) The charging roller according to claim 2, wherein the content of the non-doped tin oxide in the surface layer is from 40% by weight to 7% by weight.
By specifying 0% by weight, a sufficient charging potential and flexibility of the surface layer can be obtained.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a charging roller according to an embodiment of the present invention.

FIG. 2 is a schematic partial cross-sectional view illustrating a configuration of an apparatus for evaluating a charging characteristic of a charging roller.

FIG. 3 is a schematic cross-sectional view illustrating a configuration of an image forming apparatus used for evaluating a charging roller.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Axis 2 Elastic layer 3 Surface layer 10, 201 Charging roller

Claims (2)

[Claims] 1. A charging roller having an elastic layer and a surface layer covering the elastic layer, wherein the elastic layer is made of epichlorohydrin rubber, and the surface layer has non-doped tin oxide dispersed therein. ,
A charging roller comprising an alcohol-soluble copolymerized nylon resin containing as polymerized units at least two selected from nylon 6, nylon 6-6, nylon 6-10, nylon 11 and nylon 12. 2. The charging roller according to claim 1, wherein the amount of the non-doped tin oxide in the surface layer is 40% by weight or more and less than 70% by weight.