JPH0915937A - Member for electrostatic charging roller - Google Patents

Abstract

PURPOSE: To make it possible to obtain good images free from the occurrence of white striation by providing the outer periphery of a conductive elastic layer with a resin surface layer consisting of a mixture composed of a polyamide resin and a conductive material. CONSTITUTION: The surface of a photoreceptor drum is electrostatically charged uniformly to high potential by feeding DC voltage from a power source to an electrostatic charging roller held in contact with this photoreceptor drum. In such a case, the electrostatic charging roller is constituted by winding the conductive elastic layer 102 consisting of a conductive rubber material around the outer periphery of a conductive supporting shaft (arbor) 101 consisting of a conductive material, such as stainless materials, and further, winding the resin surface layer 103 consisting of a mixture composed of the polyamide resin and conductive resin in contact with the photoreceptor around the outer periphery of the conductive elastic layer 102. The conductive resin consists mainly of acrylonitrile butadiene rubber. The good images free from the occurrence of the white striation are obtd. and the stable electrostatic charge characteristic unaffected by a change in temp. and humidity is obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging roller member used in an electrophotographic image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus represented by the Carlson process, a corona discharge method which is a non-contact charging method is often used in order to uniformly charge the surface of a photosensitive member. In this corona discharge method, a high voltage is applied to a tungsten wire called corona wire having a thickness of about 30 to 100 μm to perform discharge. Therefore, it is known that the air around the corona wire is ionized to generate a large amount of undesirable gases such as ozone and nitric oxide. At high concentrations, this ozone and the like are not only harmful to the human body, but also adversely affect the characteristics of the photoconductor and its components. Also,
In recent years, the photosensitive member has become an organic photosensitive member for negative charging for the purpose of improving image quality. However, in the conventional corona discharge method, the amount of ozone generated remarkably increases when negative discharge is performed. Furthermore, safety standards for the concentration of ozone discharged out of the machine have been more strictly regulated both inside and outside Japan, and the corona discharge method has a limit in reducing the amount of ozone generated during charging.

In contrast to the corona discharge method described above, a contact charging method is used in which a charging member such as a charging roller, a charging blade or a charging brush is brought into contact with the surface of the photosensitive member to carry out a charging process. This contact charging method has the advantages that the voltage applied to the charging member is as small as about 1 to 2 KV and the amount of ozone generated is very small. In particular, the contact state with the photosensitive member is more stable when the charging roller is used than when the charging blade or the charging brush is used.

FIG. 2 is an explanatory view showing the main configuration of the image forming apparatus of the charging roller type. 201 is a photosensitive drum on which an electrostatic latent image is formed, and 202 is a photosensitive drum 201.
A charging roller for performing a charging process by contacting with the developing roller, a developing roller 204 for adhering toner to the electrostatic latent image on the photosensitive member 201, a power source 205 for applying a DC voltage to the charging roller 202, and a photosensitive drum 201. A transfer roller for transferring the toner image on the recording paper 207 conveyed from the paper feeding unit, a cleaning device 208 for removing and collecting residual toner on the surface of the photosensitive drum 201,
Reference numeral 09 is a surface electrometer for measuring the surface potential of the photosensitive drum 201. A wavy arrow indicates exposure of laser light or reflected light of a document. In FIG. 2, functional units normally required in other electrophotographic processes are omitted.

A basic image forming operation in the image forming apparatus configured as described above will be described. The surface of the photoconductor drum 201 is uniformly charged to a high potential by supplying a DC voltage from the power supply 205 to the charging roller 202 in contact with the photoconductor drum 201. Immediately after that, when the surface of the photosensitive drum 201 is irradiated with the image forming light (exposure), the potential of the irradiated portion decreases. Since the image forming light has a light amount distribution corresponding to black / white of the image, the potential distribution corresponding to the recorded image, that is, an electrostatic latent image is formed on the surface of the photosensitive drum 201 by the irradiation of the image forming light.
When the portion where the electrostatic latent image is formed passes through the developing roller 204, toner adheres according to the level of the potential, and a toner image is formed by visualizing the electrostatic latent image. The recording paper 207 is conveyed to a portion where the toner image is formed by a registration roller (not shown) at a predetermined timing and overlaps the toner image. After the toner image is transferred onto the recording paper 207 by the transfer roller 206, the recording paper 207 is separated from the photosensitive drum 201. The separated recording paper 207 is conveyed through a conveyance path and is fixed in a fixing unit (not shown).
And then discharged out of the machine. After the transfer is completed, the surface of the photosensitive drum 201 is cleaned by the cleaning device 208, and the residual charge is erased by a quenching lamp (not shown) to prepare for the next image forming process.

By the way, since the charging roller 202 is in pressure contact with the photoconductor drum 201, if the state remains as it is, the charge roller 202 sticks to the photoconductor drum 201, or the resin between the surfaces becomes compatible at the contact portion. Some of the components may be transferred from the charging roller 202 to the photosensitive drum 201 side. Therefore, in the portion where the charging roller 202 is in contact with the photosensitive drum 201, the toner supplied from the developing roller 204 does not adhere to the photosensitive drum 201 in the image forming process of FIG. There is a problem that an abnormal image is generated in which a portion corresponding to the contact portion becomes white and streaky.

On the other hand, conventionally, the photosensitive drum 201
And a charging roller 202 provided with a contact / separation mechanism, a charging roller 202 having a rough surface to reduce a contact area with the photosensitive drum 201, a charging roller 202 having a surface layer material selected, and the like. Is.

However, in the case where the contacting / separating mechanism is provided, the mechanism around the charging roller 202 becomes complicated and the cost increases. In addition, roughening the surface causes problems such as non-uniform charging and toner that is not removed by the cleaning blade 208 easily adheres to the surface of the charging roller 202 and deteriorates the charging function after long-term use.
In addition, since the resin surface layer containing phosphate has hygroscopicity, the conductivity changes due to changes in temperature and humidity. Further, in the case of containing graphite, since carbon, which is the same as the toner that has slipped through the cleaning blade 208 due to long-term use, is a main component, there is a problem that the compatibility is high and the toner is fixed and the charging performance is deteriorated. .

The cause of the white streaks is that the low molecular weight component of the surface resin layer itself, the low molecular weight component contained in the underlying conductive elastic layer, the oil component such as a softening agent, and other volatile components cause the surface resin layer to form. It is considered to be due to permeation and bleeding into the surface layer. Typical examples thereof include low molecular weight siloxane in silicone rubber, paraffin contained to soften the underlying conductivity, and naphthenic oil. In addition, the charging roller 202 is the photosensitive drum 20.
In order to obtain a uniform contact state with No. 1, it is required to be soft, and rubber is mainly used as the base elastic layer.

[0010]

Generally, rubber is used together with various other additives of polymers, and the major ones are vulcanizing agents, vulcanization accelerators, processing aids, softening agents, fillers (carbonic acid). Calcium), reinforcing agent (carbon silica), lubricant (stearic acid), etc. Among these substances, for example, sulfur as a vulcanizing agent causes a phenomenon of so-called bloom, which is deposited or sublimated on the surface in a long period of time, and is considered to be one of the causative substances of white streaks.

As described above, as a material that does not cause white streaks, a polyamide-based material having a low gas permeability, a high barrier property with respect to the underlying elastic layer, and a low migration of a substance from the material itself to the photosensitive drum 201 is used. Resin is often used as the surface resin layer of the charging roller 202.

The reason why polyamides have good gas barrier properties is that they generally have crystallinity and hydrogen bonds that suppress gas diffusion. It is said. Regarding crystallinity, it is generally said that the higher the degree of crystallinity, the denser the film and the more improved the gas barrier property.

A member for a charging roller is generally semiconductive (10 ⁶ to 10 ¹² Ωc) for the purpose of charging efficiency and prevention of charging defects such as voltage drop due to leakage to a photoreceptor defect.
m) is required, but in the above-mentioned polyamides, the conductivity is low, and the polyamide itself does not have a sufficient charging function. In addition, the polyamide generally has high water absorption and high temperature / high humidity to normal temperature. There is a problem in that it exhibits some conductivity due to water absorption under normal humidity, but dehydrates and loses conductivity under low temperature and low humidity environment.

The present invention has been made against the background of such circumstances, and it is free from sticking to the photoconductor and white streaks, and the charging function is stable regardless of changes in temperature and humidity. An object is to provide a member for a charging roller.

[0015]

In order to achieve the above object, the invention according to claim 1 provides a charging roller member having a conductive elastic layer around the outer periphery of a conductive support shaft.
A resin surface layer made of a mixture of a polyamide resin and a conductive substance is provided around the outer circumference of the conductive elastic layer.

The invention according to claim 2 is characterized in that the conductive material is mainly composed of acrylonitrile-butadiene rubber.

The invention according to claim 3 is characterized in that the conductive material has crystallinity.

The invention according to claim 4 is characterized in that the conductive material is mainly composed of urethane rubber.

According to a fifth aspect of the present invention, the resin surface layer has a thickness of 10 μm or more.

[0020]

According to the charging roller member of the first aspect,
By providing a resin surface layer composed of a mixture of a polyamide resin and a conductive substance around the outer circumference of the conductive elastic layer, a good image without white streaks can be obtained, and it is affected by changes in temperature and humidity. It is possible to obtain stable charging characteristics. Further, according to claim 2, the charging characteristic becomes more stable even if there are changes in temperature and humidity.
According to No. 4, the occurrence of white lines is further reduced, and a better image can be obtained. Further, according to the fifth aspect, the occurrence of white streaks is related to the film thickness of the resin surface layer, and a better image can be obtained by controlling it.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to illustrated embodiments. FIG. 1 is a sectional view showing the structure of the charging roller of the present invention. In the charging roller 1, a conductive elastic layer 102 made of a conductive rubber material is wound around an outer circumference of a conductive support shaft (core bar) 101 made of a conductive material such as stainless steel,
Further, a resin surface layer 103 made of a mixture of a polyamide resin and a conductive resin, which is in contact with the photoconductor, is wound around the outer periphery of the conductive elastic layer 102. Hereinafter, the material forming the resin surface layer 103 and its characteristics will be described based on Table 1.

As a comparative example, a nylon pellet was dissolved in a methanol solvent at 60 ° C., and then ethylcellosolve was added as a paint, which was spray-coated and dried to form a resin surface layer having a thickness of 10 μm. adopt.

The mixing ratio of each material is as follows.

CM8000 10 g Methanol 90 g Ethyl cellosolve 50 g

[Table 1] In addition, in Examples 1 to 4, a 5 wt% solution of each conductive resin in toluene as a solvent was prepared and mixed with a nylon solution of Comparative Example prepared in advance to obtain coating materials. The mixing ratio is such that the solid content ratio shown in the polyamide / conductive resin ratio in Table 1 is obtained. The mixing ratio was determined so that the volume resistance of the resin surface layer was 10 ¹⁰ Ωcm. The polyamide resin is 6/66 /
6/66/12 series other than 610 series (for example, trade name Daiamide T171 Daicel Huls), polyamide elastomer (for example, trade name Daiamide E40 Daicel Huls), and methylmethoxylated nylon (for example, trade name Toresin EF- 30T Teikoku Kagaku Sangyo) may be used. The spray coating and drying conditions are as follows.

The spray coating conditions are: roller rotation speed: 400 rpm, spray gun moving speed: 32 mm / min, spray gun: ps-3K Fuso Seiki, roller gun distance: 90 mm, atomizing air amount: 120 l / min, drying conditions: hot air circulating drying oven It is dried at 100 ° C. for 60 minutes.

Next, each charging roller manufactured under the above respective conditions is attached using a plain paper copying machine (trade name: FT-3350) manufactured by Ricoh instead of the charging charge. A half-tone image was evaluated by applying a DC voltage of -1.6 KV to the charging roller via the stainless steel shaft (conductive support shaft 101) while rotating the photosensitive member. Further, the image is output after leaving it for 2 days in an environment of 30 ° C. and 90% RH in a state where the charging roller is in pressure contact with the photosensitive member, and the number of printed sheets until the disappearance of white streaks is counted. Further, the charging roller is set in a resistance measuring device as shown in FIG. 3, and low temperature and low humidity (10 ° C. 15% RH), normal temperature and normal humidity (23 ° C. 50% RH), high temperature and high humidity (30 ° C. 90% R).
The resistance was measured under three environments (H). In this device,
Electrode roller 302 (SUS φ30 m
m) is placed from above as shown in the figure, and a current flowing between the charging roller 301 and the electrode roller 302 is applied by an ammeter 303 when a high voltage power supply 304 is applied between the electrode roller 302 and the charging roller 301 and -100 V is applied. The resistance value was measured and determined.

(Example 5) Example 4 The same as Examples 1 to 4 in which the resin surface layer was provided so that the film thickness after spray coating was 3, 7, 10, 12, and 15 µm. Method, take a halftone image and count the number of prints until the white streak disappears.

Table 2 shows the evaluation results of Examples 1 to 5 and Comparative Example.

[0029]

[Table 2] As shown by the above experimental results, the combination of Example 4 is the best in terms of the ease of white streak disappearance, and then Example 3 is the result showing a good tendency. In addition, this Example 4
Also, as shown in Example 5, depending on the film thickness,
If the film thickness is smaller than 10 μm as a boundary, streaks are hard to disappear, and 10 μm or more is a good result.

Regarding the resistance, when the resin surface layer made of only the polyamide of Comparative Example was provided, the resistance value remarkably changed due to changes in temperature and humidity (in the measurement method, the result changed by two orders or more). . However, when this polyamide is mixed with the conductive resin of Example 2 or later, the change of the resistance value becomes small with respect to the change of the temperature and the humidity, and the change amount of each of Example 1, Example 2, Example 3, and Example 4 is changed. Good results were obtained in the order of 5.

Regarding the number of white streaks disappeared, as described above, the polyamides have a good gas barrier property due to the crystallinity and suppress the volatilization from the underlying elastic layer and the exudation of the sublimation component to the surface. Therefore, it is considered that the polyamide showed a relatively good result, but the polyamide itself has residual low molecular weight, and it may be transferred to a contact substance such as a photoconductor. Polyamide was detected as a result of qualitative analysis of the contact portion on the photoconductor by infrared spectroscopic analysis, and is considered to be the causative agent of white streaks. When a conductive substance was added to this polyamide, Examples 3 and 4 in which the conductive substance showed crystallinity gave better results than the comparative example, but this resulted in a decrease in the polyamide content, and the polyamide was reduced by that amount. There is less migration of low molecules from the photoconductor to the photoconductor, and the conductive resin added in place of polyamide has a high crystallinity similar to polyamide and acts as a barrier to the underlying elastic layer. It is considered that the white streak disappeared better than the polyamide alone.

Further, regarding Example 5, there is a difference in the disappearance of white streaks depending on the film thickness, which confirms that the migration of volatile matters in the elastic layer of the underlayer to the surface is suppressed by the resin surface layer. This is a phenomenon, and it is considered that the thicker the film thickness, the higher the barrier effect and the faster the disappearance of white streaks.

Next, regarding the influence of changes in temperature and humidity on the resistance value, as described in the section of the prior art, the resistance of the polyamide simple substance shown in the comparative example becomes high because of its high water absorption. It was On the other hand, the conductive resins of 1 to 5 shown in the examples have a lower water absorption rate than polyamide, and therefore the increase in resistance is small especially under low temperature and low humidity. Particularly, in Examples 2 to 4, the water absorption is low and the resistance value is stable against changes in temperature and humidity, which are preferable results.

[0034]

As described above, according to the charging roller member of the present invention, by providing the resin surface layer made of the mixture of the polyamide resin and the conductive substance around the outer periphery of the conductive elastic layer, It is possible to obtain a good image without generation of streaks, and it is possible to obtain stable charging characteristics that are not affected by changes in temperature and humidity. Further, according to claim 2, the charging characteristics are more stable even if the temperature and humidity are changed, and according to claims 3 and 4, the occurrence of white streaks is further reduced and a better image can be obtained. it can. Further, according to the fifth aspect, the occurrence of white streaks is related to the film thickness of the resin surface layer, and a better image can be obtained by controlling it.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing the structure of a charging roller member according to the present invention.

FIG. 2 is an explanatory diagram showing a main part of an electrophotographic process apparatus using a charging member.

FIG. 3 is an explanatory diagram showing a resistance measuring device adopted in the present invention.

[Explanation of symbols]

 101 conductive support shaft 102 conductive elastic layer 103 surface layer

Claims (5)

[Claims] 1. A charging roller member having a conductive elastic layer provided around the outer periphery of a conductive support shaft, wherein a resin surface layer made of a mixture of a polyamide resin and a conductive substance is provided around the outer periphery of the conductive elastic layer. A charging roller member characterized by being provided. 2. The charging roller member according to claim 1, wherein the conductive material is mainly composed of acrylonitrile-butadiene rubber. 3. The charging roller member according to claim 1, wherein the conductive material has crystallinity. 4. The charging roller member according to claim 3, wherein the conductive material is mainly composed of urethane rubber. 5. The charging roller member according to claim 4, wherein the resin surface layer has a thickness of 10 μm or more.