JP2013114166A - Charging roller, electrophotographic device, and manufacturing method of charging roller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a charging roller that is formed in a single-layer structure, has a conductive elastic layer having low-resistance particles exposed on the surface, and prevents the appearance of a contact part on an image even after being in contact with a photoreceptor in a high-temperature and high-humidity environment for a long period.SOLUTION: A charging roller includes a conductive elastic layer 12 having conductive particles 42 partially exposed on the surface. The conductive elastic layer has needle-like bodies comprising a zinc salt having a structure represented by the following formula (1) as a vulcanization accelerator; and the needle-like bodies are present in overlapping one another with gaps on the surface of the conductive elastic layer.

Description

  The present invention relates to a charging roller, an electrophotographic apparatus, and a method for manufacturing a charging roller.

  In the electrophotographic apparatus, a charging roller used for contact charging of the electrophotographic photosensitive member abuts on the electrophotographic photosensitive member and is rotated by the rotation of the electrophotographic photosensitive member. For this reason, the charging roller is provided with an elastic layer in order to secure a nip width with the electrophotographic photosensitive member and to improve the followability of the electrophotographic photosensitive member.

However, when such a charging member is in contact with the electrophotographic photosensitive member for a long period of time, a deformation that does not easily recover, that is, a so-called C set may occur in a part of the elastic layer of the charging roller. When a charging roller having such a partial deformation is used for contact charging, the deformation portion of the charging roller passes through the nip portion with the photosensitive drum at the gap between the charging roller surface and the photosensitive drum surface. The state of the generated discharge may become unstable. In some cases, the electrophotographic photosensitive member may be unevenly charged to cause an image defect.
In order to avoid these problems, Patent Document 1 discloses a surface having a high hardness and a low friction by adding an additive comprising a fluorine-based block copolymer or a silicon-based block copolymer to the elastic layer surface. Techniques for forming layers are disclosed.

JP 2000-267394 A

However, in the case of a charging roller in which only one elastic layer is formed on the substrate, it is not easy to suppress the occurrence of C set that causes image defects in a high temperature and high humidity environment.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a charging roller and a method for manufacturing the same that are unlikely to generate C-sets that cause image defects even when contacted with an electrophotographic photosensitive member for a long period of time in a high-temperature and high-humidity environment. That is.

  According to the present invention, a charging roller having a conductive shaft core and a conductive elastic layer, the conductive elastic layer being a compound zinc having a structure represented by the following formula (1): There is provided a charging roller having a needle-like body made of salt, and the needle-like body is present on the surface of the conductive elastic layer with a gap.

According to the present invention, there is provided an electrophotographic apparatus having a charging roller and a member to be charged that can be charged by the charging roller, wherein the charging roller is the above-described charging roller. An electrophotographic apparatus is provided.
Furthermore, according to the present invention, there is provided a method for producing a charging roller having a conductive shaft core and a conductive elastic layer, wherein the conductive roller contains a vulcanization accelerator having a structure represented by the above formula (1). The surface of the conductive elastic layer is polished, immersed in an organic solvent in a state where the surface of the conductive elastic layer is heated, and then the organic solvent is dried, thereby adding the structure represented by the above formula (1). There is provided a method for producing a charging roller, wherein a needle-like body made of a zinc salt derived from a sulfur accelerator is deposited on the surface of the conductive elastic layer.

  According to the present invention, even in a charging roller having a single-layer structure and a conductive elastic layer in which low-resistance particles are exposed on the surface, an image defect is caused when a long-term contact is made with a photoconductor in a high-temperature and high-humidity environment. It is possible to obtain a charging roller that is less likely to cause the occurrence of the problem. Further, it is possible to obtain an electrophotographic apparatus capable of obtaining a good electrophotographic image without causing image defects due to long-term contact in a high temperature and high humidity environment. Furthermore, a simple method for manufacturing a charging roller is provided that is less likely to cause image defects even in the above environment.

It is a figure which shows the contact state of a photoreceptor and the charging roller of this invention. 1 is a diagram showing a schematic configuration of an electrophotographic apparatus having a charging roller of the present invention. It is a figure which shows the spread of discharge. It is a figure which shows schematic structure of the charging roller of this invention. It is a figure explaining the measuring method of triboelectric charge amount. It is a graph which shows the triboelectric charge amount of the Example and comparative example in this invention.

First, a charging process during image formation will be described.
FIG. 2 shows a schematic configuration of an electrophotographic apparatus having the charging roller of the present invention. Reference numeral 21 denotes an electrophotographic photosensitive member (hereinafter abbreviated as “photosensitive member”) as a member to be charged. The photosensitive member of this example is formed on a support 21b having conductivity such as aluminum and the support 21b. This is a drum-shaped photoreceptor having the photosensitive layer 21a as a basic constituent layer. The shaft 21c is rotationally driven at a predetermined peripheral speed in the clockwise direction in the figure.
The charging roller 10 is disposed so that the photosensitive member 21 can be charged. In this example, the charging roller 10 is disposed in contact with the photoconductor 21, and the photoconductor 21 is charged (primarily charged) to a predetermined polarity and potential.
The charging roller 10 includes a conductive shaft core body 11 and an elastic layer 12 formed on the conductive shaft core body 11, and both ends of the conductive shaft core body 11 are attached to the photoconductor 21 by a pressing unit (not shown). It is pressed and rotates following the rotation of the photosensitive member 21.

  When a predetermined direct current (DC) bias of the conductive shaft core 11 is applied by the rubbing power source 23a with the power source 23, a weak discharge is generated in the gap in the vicinity of the photosensitive member 21, the charging roller 10, and the contact portion (nip). Occurs, and the surface of the photoreceptor 21 is charged to a predetermined polarity and potential. The photosensitive member 21 whose peripheral surface is charged by the charging roller 10 is then subjected to exposure of target image information (laser beam scanning exposure, slit exposure of a document image, etc.) by the exposure means 24, and the target image is then formed on the peripheral surface. An electrostatic latent image for information is formed. The electrostatic latent image is then successively visualized as a toner image by the developing member 25. Next, the toner image is synchronized with the rotation of the photosensitive member 21 from a paper feeding unit (not shown) by the transfer roller 26 and conveyed to the transfer unit between the photosensitive member 21 and the transfer roller 26 at an appropriate timing. The transfer material 27 is sequentially transferred. The toner image on the photosensitive member 21 side is transferred to the transfer material 27 by charging with the reverse polarity to the toner from the back of the transfer material 27.

The transfer material 27 that has received the transfer of the toner image on the surface is separated from the photoconductor 21 and conveyed to a fixing means (not shown) to receive image fixing and output as an image formed product. Alternatively, in the case of forming an image on the back side, it is conveyed to a re-conveying means to the transfer unit.
The peripheral surface of the photoreceptor 21 after the image transfer is cleaned by the cleaning member 28 after removal of adhering contaminants such as toner remaining after transfer, and is repeatedly used for image formation.

  Single-layer charging roller, especially when low-resistance particles are exposed on the surface of the charging roller, in addition to the above-mentioned weak discharge, the direct charging phenomenon in which the charge moves directly from the charging roller to the photoconductor in the nip. Happens. This is considered to be a kind of contact charging phenomenon in which charges move from the low-resistance particles present on the surface of the charging roller to the photoreceptor, and the amount of charge is greatly increased by rubbing and friction. In addition, in the case of a contact charging type charging roller that is driven to rotate with the photoconductor, the outer diameter becomes narrower toward the end with respect to the central portion of the roller. Realized. However, if the charging roller has a crown shape, an outer diameter difference can be made in the longitudinal direction of the charging roller. Therefore, slip (friction) occurs so as to fill the outer diameter difference at the time of rotation with the photoreceptor, and contact charging is promoted. .

Next, a description will be given of a mechanism for generating a C set that causes an image defect that occurs when left in contact with a photoconductor in a high temperature and high humidity environment. Generally, a small amount of polymer having no crosslinking point is present in rubber. In addition, when the elastic layer is polished into a crown shape, molecular cutting of the rubber polymer itself occurs, and there are relatively many rubber polymers near the surface of the rubber roller after polishing that do not have crosslink points compared to the inside. I think that.
In a high temperature and high humidity environment where molecular mobility is high, when the charging roller is in contact with the photoreceptor for a long period of time, the low molecular rubber component moves to the periphery of the contact portion with the charging roller, and the elastic layer Results in C set. Further, the low-molecular rubber component that has moved to the periphery of the contact portion of the charging roller with the photosensitive member moves to the surface of the charging roller. As a result, charge transfer from the low-resistance particles in the elastic layer to the photoconductor is suppressed, and coupled with uneven charging due to deformation of the elastic layer, the frictional charge amount of the contact portion changes, resulting in image defects. It is considered a thing.

Next, the principle of the present invention will be described.
FIG. 4 is a schematic view showing the form of the surface of the charging roller of the present invention. In the present invention, on the surface of the elastic layer 12 of the charging roller, a needle-like body made of a zinc salt of a compound having a structure represented by the following formula (1) used as a vulcanization accelerator has a gap. As a result, the needle-like body group 51 is formed.

  Here, the acicular bodies are stacked with a gap, as shown in FIG. 1A, the acicular bodies are present at random positions, and the axes of the acicular bodies are in a random orientation. , Meaning to overlap while maintaining a twisted relationship. Here, the needle shape means an elongated shape having an aspect ratio of 2.0 or more. Since the needle-like bodies are stacked in such a positional relationship, it is possible to discharge from the surface of the charging roller. Examples of the vulcanization accelerator having the formula (1) include tetrabenzylthiuram disulfide, 1,6-bis (N, N'-benzylthiocarbamoyldithio) hexane, and zinc dibenzyldithiocarbamate. Since the acicular bodies are stacked on the surface of the charging roller, the low-resistance particles exposed from the surface of the charging roller do not come into direct contact with the photoconductor when contacting the photoconductor that is the object to be charged. In other words, the needle-like body acts as spacer particles 42 on the surface of the charging roller, and the contact between the low resistance particles exposed on the surface of the elastic layer 12 of the charging roller and the surface layer (photosensitive layer) 21a of the photoreceptor is prevented. Since the effect (spacer effect) is exhibited, the triboelectric charge amount is greatly reduced. For this reason, the occurrence of uneven charging due to the variation in the triboelectric charge amount at the contact portion with the photosensitive member is suppressed.

  Further, since the needle-like bodies are elongated as shown in FIG. 1 (a), when the spacer effect is exhibited by overlapping each other, the spacer effect is produced with a single object as shown in FIG. 1 (b). The area F where the spacer effect of the surface of the charging roller and the photosensitive member is exhibited can be made wider. Moreover, since it is not necessary to cover the whole roller in order for crystals to pile up and exhibit the spacer effect, the discharge from the roller surface is not hindered. Even when pressed against the photoconductor, the contact pressure is dispersed over a wide range, so that the spacer effect is buried in the elastic layer as shown in FIG. It is difficult to reduce the spacer effect. In addition, the zinc salt crystal having the structure represented by the above formula (1) has a hardness that does not greatly deform or crack at the contact pressure with the photoreceptor. The effect as a spacer can be expected. Further, as shown in FIG. 3, the discharge for charging the photoconductor occurs like an avalanche between the gap between the photoconductor and the charging roller, so that it has a certain spatial extent and is on the surface of the elastic layer 12. The creeping discharge that occurs in the area is also wide. Therefore, if the area occupied by the spacer particles 42 on the surface of the charging roller on the elastic layer 12 of the charging roller is extremely small, even if discharge unevenness occurs, the discharge spreads as shown by the arrow 41, so Potential is leveled and hardly affects the image. That is, unlike the case where the same spacer effect is produced by the large particle size as shown in FIG. 3B, in the case of the needle-like body having a small short diameter as shown in FIG. It is difficult to affect the image due to the leveling effect.

  In addition, since the zinc salt having the structure represented by the above formula (1) has low electrical conductivity, abnormal discharge due to leakage or electric field concentration hardly occurs even in a sharp shape like a needle-like body. The effect on the image is small. As a guide for the size of the needle-like body, it is preferable that the minor axis is 10 μm or more and 30 μm or less and the aspect ratio is 4.0 or more and 10.0 or less. By setting the minor axis in the above range, the spacer effect can be exhibited with an appropriate number density of needle-like bodies, and image defects are suppressed. In addition, by setting the aspect ratio within the above range, the strength of the needle-like body can be maintained, and separation from the charging roller surface hardly occurs.

  In addition, when the surface of a 200 μm square charging roller is observed at an arbitrary location on the surface of the charging roller, if two or more needle-like bodies having a height of 40 μm or more can be confirmed, a spacer effect can be expected. Further, it is sufficient that crystals are present on the surface of the charging roller with a coverage of 30% or less. By setting the coverage to the above range, an appropriate charge amount can be secured without hindering discharge from the surface of the charging roller.

The charging roller of the present invention can be manufactured by the following method. First, a mixture of a base rubber polymer constituting an elastic body as a base layer, a vulcanization accelerator having a structure represented by the above formula (1), and zinc oxide as a vulcanization aid is prepared. Alternatively, a mixture of a base rubber polymer and a zinc salt vulcanization accelerator having a structure represented by the above formula (1) is prepared.
Subsequently, the obtained mixture is formed into a predetermined shape. A needle-shaped body made of a zinc salt derived from a vulcanization accelerator having a structure represented by the above formula (1) is polished after polishing the elastic body surface of the molded member, and finally dipped in an organic solvent. Precipitate.

By adjusting the solvent type and immersion conditions (time, solvent temperature, rubber roller surface temperature, etc.), the size of the needle-like body deposited on the rubber roller surface can be controlled. Further, the density of the needle-like body on the roller surface can be controlled by the number of parts added to the rubber polymer of the vulcanization accelerator or zinc oxide having the structure represented by the above formula (1) and the vulcanization conditions. Since crystals are deposited as the organic solvent volatilizes, the direction of the axis of the needle-like body grows in a random direction. In addition, since it has a needle-like and elongated shape, it is possible to form an overlap of needle-like bodies that maintain a twisted relationship with each other in a random orientation as described above by growing crystals to some extent. Further, since it is deposited from the roller base layer, the needle-like body adheres to the surface of the charging roller and does not peel off to the extent that it is driven and rotated by the photoreceptor. In order to increase the deposition rate, a zinc salt having a structure represented by the above formula (1) may be dissolved in an organic solvent to be immersed in advance.
Here, as the organic solvent, a solvent in which the zinc salt of the vulcanization accelerator having the structure represented by the above formula (1) is soluble is used. Specifically, toluene, ethanol, methanol, etc. are mentioned.

  Since the zinc salt having the structure represented by the above formula (1) does not exhibit electrical conductivity, it does not become a leak point and hardly causes image defects. Moreover, since the particles for exhibiting the spacer effect are formed from a substance blended in the rubber, compatibility with the rubber is good. Therefore, from the viewpoint of the material, it is considered that the discharge from the surface of the charging roller is hardly inhibited during image formation, and the influence on the image is small even though it is attached to the surface of the charging roller.

  Moreover, the zinc salt having the structure represented by the above formula (1) is precipitated and crystallized. For this reason, even when pressed against the photoconductor, it has a high hardness that does not collapse due to the contact pressure and an adhesive property with the surface of the charging roller that does not collapse, so that the spacer effect can be sufficiently exerted.

Details of the preferred embodiment will be described below.
FIG. 4 shows a schematic configuration of a charging roller as the charging member of the present invention. The charging roller 10 includes a conductive shaft core body 11 and an elastic layer 12 formed on the outer periphery of the conductive shaft core body 11.
The elastic layer is a mixture of a base rubber polymer and an additive. The base rubber polymer is not particularly limited as long as it is a material that exhibits rubber elasticity in the actual use temperature range of the elastic member. Specific rubber materials include natural rubber (NR), isoprene rubber (IR), butadiene rubber (BR), styrene-butadiene (SBR), butyl rubber (IIR), ethylene-propylene-diene terpolymer rubber ( EPDM), epichlorohydrin homopolymer (CHC), epichlorohydrin-ethylene oxide copolymer (CHR), epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (CHR-AGE), acrylonitrile-butadiene copolymer (NBR), A thermosetting rubber material obtained by blending a raw material rubber such as hydrogenated acrylonitrile-butadiene copolymer (H-NBR), chloroprene rubber (CR), and acrylic rubber (ACM, ANM) with a crosslinking agent is used.

  In the present invention, the elastic layer contains at least one spherical particle selected from spherical silica particles, spherical alumina particles, and spherical zirconia particles as an additive. Since the spherical particles made of silica, alumina, and zirconia have high hardness, the particles themselves are not ground even in the polishing process described later, and can remain on the surface of the elastic layer while maintaining a spherical shape. These particles are particles composed mainly of silica, alumina, and zirconia, and may contain other impurities.

  Moreover, it is preferable to add a conductive agent to the base rubber polymer for the purpose of adjusting the electric resistance of the elastic layer. Examples of the conductive agent include carbon materials such as carbon black and graphite; oxides such as titanium oxide and tin oxide; metals such as Cu and Ag; electrons such as conductive particles obtained by coating the surface of the particles with oxide or metal to make the particles conductive. Conductive agents and inorganic ionic substances such as lithium perchlorate, sodium perchlorate, calcium perchlorate; lauryltrimethylammonium chloride, stearyltrimethylammonium chloride, octadecyltrimethylammonium chloride, dodecyltrimethylammonium chloride, hexadecyltrimethylammonium chloride, Cationic surfactants such as trioctylpropylammonium bromide, modified aliphatic dimethylethylammonium etosulphate; lauryl betaine, stearyl betaine, dimethylalkyl lauryl betaine, etc. Zwitterionic surfactants; quaternary ammonium salts such as tetraethylammonium perchlorate, tetrabutylammonium perchlorate, and trimethyloctadecylammonium perchlorate; ionic conducting agents such as organic acid lithium salts such as lithium trifluoromethanesulfonate Can be mentioned.

Base rubber polymers include fillers, processing aids, anti-aging agents, vulcanization aids, vulcanization accelerators, vulcanization accelerators, and vulcanization delays that are commonly used as rubber compounding agents as required. An agent, a dispersing agent, etc. can be added. Further, a vulcanization accelerator having a structure represented by the above formula (1) necessary for forming a needle-like body and, optionally, zinc oxide are added.
Examples of a mixing method of these materials include a mixing method using a closed mixer such as a Banbury mixer and a pressure kneader, a mixing method using an open mixer such as an open roll, and the like.

The rubber roller can be formed by extruding the elastic body composition into a tube shape with an extruder and press-fitting the conductive shaft core into the tube, or centering the conductive shaft core with an extruder equipped with a crosshead. And a method of coextruding into a cylindrical shape to obtain a molded body having a desired outer diameter. Moreover, the method of inject | pouring the composition for elastic bodies into the metal mold | die of a desired outer diameter with an injection molding machine can also be mentioned. Among them, the extrusion molding method using a crosshead extruder is most preferable because continuous production is easy, the number of steps is small, and it is suitable for low-cost production.
The molded rubber roller exposes spherical particles on the surface of the elastic layer by polishing the surface. The grinding method for the surface of the rubber roller is a traverse grinding method in which the grinding wheel is moved in the thrust direction of the rubber roller, and the grinding wheel that is wider than the roller length is not reciprocated while the rubber roller is rotated about the axis of the conductive shaft core. A plunge-cut grinding method that cuts into The plunge cut cylindrical grinding method is more preferable because it has the advantage that the entire width of the elastic roller can be ground at once, and the processing time can be shorter than the traverse cylindrical grinding method. Here, the rubber roller means a roller-shaped member comprising a conductive shaft core and a rubber elastic layer provided on the outer periphery of the conductive shaft core, and the rubber roller can be used as a charging roller as it is. is there.
Further, the surface of the charging roller may be subjected to surface modification from the viewpoint of stabilizing the drive with the photosensitive member and preventing toner contamination. Examples of the surface modification method include ultraviolet irradiation, electron beam irradiation, plasma treatment, and corona discharge treatment. These surface treatments may be combined.

Hereinafter, the present invention will be described in more detail by way of examples. In the following, commercially available high-purity products were used unless otherwise specified.
[Example 1]
(Preparation of A-kneaded rubber material for elastic layer)
The materials listed in Table 1 were mixed using a 6 liter pressure kneader (trade name: TD6-15MDX, manufactured by Toshin Co., Ltd.) for 16 minutes at a filling rate of 70 vol% and a blade rotation speed of 30 rpm. A kneaded rubber composition A1 Got.

(Preparation of unvulcanized rubber material for elastic layer)
The materials shown in Table 2 were turned 20 times in total on the open roll with a roll diameter of 12 inches at a front roll rotation speed of 8 rpm, a rear roll rotation speed of 10 rpm, and a roll gap of 2 mm. Thereafter, the roll gap was set to 0.5 mm, and thinning was performed 10 times to obtain an unvulcanized rubber composition A1 for an elastic layer.

(Molding of elastic layer)
A conductive vulcanizing adhesive (trade name: METALOC U-20, Toyo) is attached to 226 mm in the axial center of the cylindrical surface of a cylindrical conductive shaft core (steel, surface is nickel-plated) having a diameter of 6 mm and a length of 252 mm. Chemical Laboratory) was applied and dried at a temperature of 80 ° C. for 30 minutes.
Next, the unvulcanized rubber composition A1 is simultaneously extruded into a cylindrical shape coaxially with the conductive shaft core as the center by extrusion molding using a crosshead, and the unvulcanized rubber composition A1 is not added to the outer periphery of the conductive shaft core. An unvulcanized rubber roller having a diameter of 8.8 mm coated with a vulcanized rubber composition was produced. The extruder used was an extruder having a cylinder diameter of 45 mm and L / D = 20. The temperature during extrusion was adjusted to a head temperature of 90 ° C., a cylinder temperature of 90 ° C., and a screw temperature of 90 ° C. Both ends of the molded unvulcanized rubber roller were cut so that the axial width of the elastic layer portion was 228 mm, followed by heat treatment at 160 ° C. for 30 minutes in an electric furnace to obtain a vulcanized rubber roller. The surface of the obtained vulcanized rubber roller was polished with a plunge cut grinding type polishing machine to obtain a rubber roller A1 having a crown-shaped elastic layer having an end diameter of 8.35 mm and a center diameter of 8.50 mm.

(Needle formation)
The rubber roller A1 was heated in an oven at a temperature of 80 ° C. for 15 minutes, immersed in toluene for 30 minutes, and then dried at room temperature for 72 hours, whereby the TBzTD zinc salt represented by the following formula (3) was formed on the roller surface. The acicular body was deposited and the charging roller 1 was obtained.

[Example 2]
As a method for forming the needle-like body, a charging roller of Example 2 was a roller manufactured by the same method as in Example 1 except that the solvent to be immersed was methanol and the immersion time was 2 hours.
Example 3
A roller produced by the same method as in Example 1 was used as the charging roller of Example 3 except that the needle-like body on the roller surface was formed by the following method.
First, the rubber roller A1 in Example 1 was placed in a pressure vessel. This pressure vessel is connected in advance to a pipe that becomes a flow path for the supercritical fluid. This pressure vessel was immersed in a water bath heated to a predetermined temperature. Subsequently, carbon dioxide pump (trade name: PU-2080-CO2, manufactured by JASCO Corporation) and ethanol pump (trade name: PU-2080, manufactured by JASCO Corporation), preheater, inner diameter is 30 mm. In a flow path connected in the order of a cylindrical pressure vessel made of stainless steel (SUS) having a height of 500 mm, a back pressure valve (trade name: BU-2080, manufactured by JASCO Corporation), and a recovery vessel, carbon dioxide And ethanol was flowed so that ethanol might be 5 mol%. The flow rate of carbon dioxide was 10 ml / min.
Then, after processing for 60 minutes in the steady state (temperature 70 degreeC, pressure 10MPa), the press injection of carbon dioxide and ethanol was stopped, and carbon dioxide and ethanol were discharged from the back pressure valve. The rubber roller A1 was taken out of the pressure vessel whose interior returned to atmospheric pressure, and then left to stand for 24 hours in an environment of a temperature of 23 ° C. and a humidity of 50% RH.

Example 4
The blending amount of zinc oxide in the kneaded rubber composition is 10 parts by mass, the blending amount of tetrabenzyl thiuram disulfide in the unvulcanized rubber composition is 9 parts by mass, and the heat treatment of the vulcanized rubber roller is performed at a temperature of 150 ° C. for 30 minutes. It was. Other than that, a roller manufactured by the same method as in Example 1 was used as the charging roller of Example 4.

Example 5
A roller produced in the same manner as in Example 1 was carried out except that the amount of tetrabenzylthiuram disulfide in the unvulcanized rubber composition was 3 parts by mass and the temperature of the vulcanized rubber roller was 160 ° C for 1 hour. The charging roller of Example 5 was obtained.
Example 6
A roller produced by the same method as in Example 1 except that the terminal-modified copolymer rubber A2 polymerized by the following method was used instead of NBR (trade name: JSR N230SV, manufactured by JSR) as the raw rubber. 6 charging roller.
(Method for synthesizing terminal-modified copolymer rubber A2)
The materials listed in Table 3 were charged into an autoclave reactor with an internal volume of 15 liters purged with nitrogen.

After adjusting the temperature of the reactor contents to 20 ° C., 645 mg (10.08 mmol) of n-butyllithium was added to initiate polymerization.
When the polymerization conversion rate reached 99%, 30 g of butadiene was added, and after further polymerizing for 5 minutes, 3381 mg of N, N-bis (trimethylsilyl) aminopropylmethyldimethoxysilane was added and reacted for 15 minutes. 2,6-Di-tert-butyl-p-cresol was added to the polymer solution after the reaction, and then the resulting polymer was coagulated. Thereafter, it was dried under reduced pressure at a temperature of 60 ° C. for 24 hours to obtain a terminal-modified styrene-butadiene copolymer (terminal-modified copolymer rubber A2).

Example 7
As a vulcanization accelerator to be added to the unvulcanized rubber composition A1 for the elastic layer, a zinc salt of TBzTD represented by the following formula (3) instead of TBzTD (trade name: ZTC (zinc dibenzyldithiocarbamate) Ouchi Shinsei Chemical Industry Co., Ltd.) was used. The heat treatment conditions for the vulcanized rubber roller were set at a temperature of 160 ° C. for 20 minutes. Other than that, a roller prepared by the same method as in Example 1 was used as the charging roller of Example 7.

Example 8
As a vulcanization accelerator to be added to the unvulcanized rubber composition 1 for the elastic layer, 1,6-bis (N, N′-benzylthiocarbamoyldithio) represented by the following formula (4) instead of TBzTD Hexane (trade name: Vulcuren, VPKA9188, manufactured by Bayer AG) was used. Other than that, a roller manufactured by the same method as in Example 1 was used as the charging roller of Example 8. The zinc salt needles deposited on the surface of the charging roller 8 have a structural formula represented by the following formula (5).

Example 9
As a method for forming the needle-like body, a roller manufactured in the same manner as in Example 1 except that the heating temperature of the rubber roller A1 is 50 ° C., the immersion solvent is isopropyl alcohol, and the immersion time is 45 minutes. A roller.

[Comparative Example 1]
The rubber roller A1 was used as the charging roller of Comparative Example 1.
[Comparative Example 2]
A powdery TBzTD zinc salt (trade name: ZTC (Zinc Dibenzyldithiocarbamate), manufactured by Ouchi Shinsei Chemical Industry Co., Ltd.) is applied to the outer peripheral surface of the rubber roller A1 with an adhesive roller to produce a powder application roller B1. did. A powder roller of Comparative Example 2 was obtained by wiping the powder of TBzTD on the surface of the powder application roller B1 by the following wiping method.
As a result of observing the surface of the charging roller of Comparative Example 2, it was confirmed that the entire roller was covered with zinc salt powder of TBzTD. However, a spacer having a height of 40 μm or more from the rubber surface where a spacer effect is expected could not be confirmed.

(Wiping method)
While rotating the powder application roller B1 at 700 rpm, a sponge roller wrapped with a thin 2 μm polyester fiber cloth was pressed as a wiping member so that a load of 3000 Pa was applied, and the wiping member was moved at a speed of 300 mm / sec in the longitudinal direction of the roller. Made 12 round trips.

[Comparative Example 3]
Spherical silica particles-3 (trade name: FB-40S, manufactured by Denki Kagaku Kogyo Co., Ltd.) were dispersed in polyethylene glycol (trade name: polyethylene glycol 600, manufactured by Kishida Chemical Co., Ltd.) to 50% by mass. The rubber roller A1 was dipped using this dispersion.
The dipping coating conditions were a dipping time of 9 seconds, a dipping coating lifting speed of an initial speed of 20 mm / s, and a final speed of 2 mm / s. Thereafter, a roller in which the solvent was volatilized under an environment of a temperature of 23 ° C. and a humidity of 50% RH was used as a charging roller of Comparative Example 3.
When the surface of the charging roller in Comparative Example 3 was observed, it was confirmed that the spacer surface had a height of 40 μm or more from the rubber surface where a spacer effect could be expected, but it was formed of one spherical particle.

[Comparative Example 4]
In Comparative Example 2, a roller produced in the same manner as in Comparative Example 2 except that zinc stearate (manufactured by Sakai Chemical Industry Co., Ltd.) was used as the powder to be applied to the roller surface was used as the charging roller of Comparative Example 4.
When the surface of the charging roller of Comparative Example 4 was observed, it was confirmed that the entire charging roller was covered with zinc stearate powder, but the height of 40 μm or more from the rubber surface where a spacer effect can be expected. Could not be confirmed.

(Image evaluation)
The produced charging roller and photoconductor were assembled in a process cartridge that integrally supports them, and allowed to stand for 1 month in a constant temperature and humidity chamber having a room temperature of 40 ° C. and a humidity of 95% to prevent condensation. After taking out from the thermostatic chamber and leaving it in an environment of temperature 23 ° C. and humidity 50% RH for 24 hours, this process cartridge is electrophotographic apparatus for A4 paper longitudinal output (trade name: LaserJet P1215, Hewlett-Packard Co., Ltd.) ) Made).
The image evaluation was performed under the environment of a temperature of 23 ° C. and a humidity of 50% RH, and was performed by visually determining the printed halftone image. Table 4 shows the evaluation criteria for the contact portion, and Table 5 shows the evaluation criteria for image spots.

About what can confirm the spot on an image visually, it measured with the video micro (brand name: VHX-500, product made by Keyence Corporation), and the size of the largest spot was described in Table 6 and Table 7.
In addition, the surface of the charging roller in each of the examples and comparative examples was observed with a video micro (trade name: VHX-500, manufactured by Keyence Corporation) on a 200 μm square, the coverage by crystals on the roller surface, and the needle-like body The minor axis and the aspect ratio were measured. The roller surface was randomly observed at 10 points, and the average was taken to obtain the roller coverage, needle body short diameter, and needle body aspect ratio, respectively.
Furthermore, the 200 μm square on the surface of the charging roller in each example and comparative example was observed with a laser microscope (trade name: VK-8700, manufactured by Keyence Corporation), and the overlapping of needle-like bodies having a height of 40 μm or more was observed. The number was measured. Ten points on the surface of the charging roller were randomly observed and the average was taken to determine the number of spacers of the roller. The evaluation results are shown in Tables 6 and 7.

  As is apparent from Tables 6 and 7, in Comparative Example 1, there is no roller surface that exhibits the spacer effect, so the contact portion image rank is D rank. In Comparative Example 2 and Comparative Example 4, powder is applied to the roller surface, but the contact portion image rank is not improved. This is because there are no spacer particles having a height necessary to prevent contact between the low resistance particles on the roller surface and the photoreceptor. In Comparative Example 3, spacer particles having a height necessary to prevent contact between the low resistance particles on the roller surface and the photoreceptor can be confirmed on the roller surface. However, since the spacer is formed by one particle, the discharge from the roller surface is inhibited as shown in FIG. 3B, and a spot-like defect occurs on the image. The initial improvement in the contact portion image rank can also be confirmed, but the rank decreases as the number of images to be printed out. On the other hand, the spots on the image are confirmed in the initial stage, but improve as the number of images is printed. This is presumably because the spacer effect is exhibited in the initial stage, but the spacer particles are not fixed to the roller surface, so that they are removed from the roller surface by the driven rotation with the photoreceptor.

On the other hand, in Examples 1 to 9, both the contact portion image rank and the spot image are B rank or higher, and good images having no practical problem are obtained. FIG. 6 shows the triboelectric charge amount at the roller end 10 mm position in each example and the comparative example.
Here, the triboelectric charge amount was determined by the following method using the apparatus shown in FIG. A simulated photoreceptor B in which a polycarbonate film having a thickness of 15 μm is formed on a rough aluminum tube, the simulated photoreceptor B and the charging roller 10 are brought into contact with each other, and the simulated photoreceptor B is rotated in the rotational direction C at 60 rpm. .
Further, an applied voltage (-500 V in the measurement of FIG. 6) whose absolute value is 10 V smaller than the discharge start voltage is applied to the conductive shaft core of the charging roller by a high voltage power source D (trade name: Model 615-3, manufactured by Trek). Applied.
The surface potential of the simulated photoconductor B is measured by a surface potential meter A (trade name: Model 344, manufactured by Trek). From the change in surface potential of the simulated photoconductor B after three rotations, The charge amount was calculated and defined as the triboelectric charge amount. FIG. 6 also shows the triboelectric charge amounts after 20 sheets are printed in Comparative Example 3 and Comparative Example 4.
As can be seen from FIG. 6, it can be confirmed that the triboelectric charge amount significantly decreases when the improvement in the set portion image rank can be confirmed. In other words, the spacer effect of the needle-like body is exhibited, so that the contact between the photosensitive member and the low-resistance particles exposed on the roller surface is avoided, and the frictional charge is reduced. As a result, the image defect at the contact portion is greatly reduced. It is thought that it improved.

F Region 12 where the spacer effect is exerted between the surface of the charging roller and the object to be charged 12 Elastic layer 21a Photosensitive layer 42 Spacer particles on the surface of the charging roller

Claims (3)

A charging roller having a conductive shaft core and a conductive elastic layer,
The elastic layer has an acicular body made of a zinc salt of a compound having a structure represented by the following formula (1):
The needle roller is present on the surface of the elastic layer in a stacked manner with a gap:
.
An electrophotographic apparatus comprising: a charging roller; and a member to be charged that can be charged by the charging roller, wherein the charging roller is the charging roller according to claim 1. .
A method of manufacturing a charging roller having a conductive shaft core and a conductive elastic layer,
Polishing the surface of a conductive elastic layer containing a compound having a structure represented by the following formula (1), immersing the surface of the elastic layer in an organic solvent in a heated state, and then drying the organic solvent A process for depositing a needle-like body made of a zinc salt derived from a vulcanization accelerator having a structure represented by the following formula (1) on the surface of the elastic layer: :
.