JP2007093915A - Conductive rubber member, conductive rubber roller, transfer roller and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-resistance conductive rubber member free of bleeding and having low volume resistivity and electrical uniformity, with respect to a member for use in an electrophotographic process in a copying machine, a laser beam printer or the like. <P>SOLUTION: The conductive rubber member comprises a rubber component having epichlorohydrin-based rubber and a copolymer of ethylene oxide (A)/propylene oxide (B)/allyl glycidyl ether (C), wherein copolymerization ratios in the copolymer are A+B<90 mol% and B+C<20 mol%. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a conductive rubber member, a conductive rubber roller, and a transfer roller used in an electrophotographic process such as a copying machine or a laser beam printer.

Various electroconductive rubber parts such as electroconductive rollers are used in various electrophotographic apparatuses such as electrostatic copying machines, laser printers, and facsimile machines. As the conductive rubber member, epichlorohydrin rubber / acrylonitrile rubber having moderate elasticity and moderate conductivity is widely used (for example, Patent Document 1). However, in order to prepare a rubber material in a medium resistance region having a volume resistivity of 10 ⁵ to 10 ¹⁰ Ω · cm, such as for a roll of an electrophotographic apparatus, a conductive particle / ionic conductivity imparting agent such as carbon black is used. It was necessary to adjust the volume resistivity by adding it.

Since carbon black has a larger effect of reducing the volume resistance value as the particle size is smaller, carbon black having a particle size of 45 nm or less is usually used. When carbon black having such a small particle size is used, the volume specific resistance value of rubber decreases as the amount of carbon black added increases, and the conductive rubber composition has a volume specific resistance value of 10 ⁴ Ω · cm or less. Can be easily prepared.

However, the volume specific resistance of the rubber composition depends on slight differences in the carbon black content caused by losses during kneading, and on the rubber condition and slight fluctuations in the dispersion of carbon black that occur during processing such as injection molding and extrusion molding. The value varies greatly. Therefore, the rubber composition having a volume resistivity of 10 ⁵ to 10 ¹⁰ Ω · cm, which is required for electrostatic countermeasures, has a problem that the electrical uniformity is inferior. .

  On the other hand, when a rubber composition having conductivity in the middle resistance region is prepared using carbon black having a large particle size, the electrical uniformity of the rubber composition can be improved. However, in order to prepare a rubber composition in the middle resistance region using such carbon black, a large amount of carbon black is required, and the obtained cross-linked product has poor processability and has limited applications. .

  There are also some examples in which a conductive agent is used in order to obtain a conductive part rubber material with little variation and low volume resistivity. However, since the molecular weight is small and liquid, there is a problem that the photoreceptor is easily contaminated.

  As a method for reducing the volume specific resistance value, an ionic conductivity imparting agent may be added. Thus, a method in which an organic metal salt such as a Li salt is contained in a polar rubber as an ionic conductivity imparting agent has been studied so far. In this case, although the resistance value as a semiconductive rubber is lowered, the above-mentioned organometallic salt has poor compatibility with polar rubber, and when added in a large amount, bloom occurs, contaminates the photoconductor, and has a current-carrying durability. It gets worse. In order to solve this problem, a method in which a rubber composition contains a quaternary ammonium salt (for example, Patent Document 2) or a quaternary phosphonium salt (for example, Patent Document 3) as an ionic conductivity imparting agent has also been proposed. . In the case of this method, a low resistance conductive rubber member can be obtained by adding 10 parts by mass or more with respect to 100 parts by mass of the rubber component, but the roller surface bleeds out and causes contamination of the photoreceptor.

Therefore, in order to obtain a low resistance conductive rubber member with less bleed and less variation in resistance value, those mainly composed of ion conductive rubber are mainly used, and epichlorohydrin rubber alone or blended with other materials A low resistance conductive rubber member obtained in this manner has been proposed. The epichlorohydrin rubber is a copolymer of epichlorohydrin-ethylene oxide-allyl glycidyl ether, and has ethylene oxide as its constituent unit, so that low resistance is realized. There are also many proposals regarding the copolymer ratio of epichlorohydrin-ethylene oxide-allyl glycidyl ether. However, when the content of ethylene oxide is 90 mol% or more, crystallization occurs, the volume resistivity increases, and the compression set increases. Therefore, when the epichlorohydrin rubber is used alone, the volume resistivity value is 1 × 10 ⁷ Ω · cm or more, for example, 1 × 10 ⁷ Ω · cm or less required for a roller of an electrophotographic apparatus. It becomes difficult to achieve medium resistance.

Further, an ethylene oxide / propylene oxide / allyl glycidyl ether copolymerization ratio of 50 to 95 mol% / 1 to 49 mol% / 1 to 10 mol% and an ethylene oxide-propylene oxide having a number average molecular weight Mn of 10,000 or more. A proposal has been made to lower the volume resistivity by mixing an allyl glycidyl ether terpolymer with an epichlorohydrin rubber in a mass ratio of 0.01 to 4.00 (for example, Patent Document 4). However, when the copolymerization ratio of allyl glycidyl ether exceeds 10 mol%, the number of crosslinking points after vulcanization increases, and resistance reduction cannot be realized, and the copolymerization ratio of allyl glycidyl ether that is a crosslinking site is Even if the number average molecular weight Mn is 10,000 or more because it is as small as 1 to 10 mol%, problems such as bleeding on the surface of the member and contamination of the photoreceptor are not solved.
JP 2001-115005 A JP-A-7-28301 Japanese Patent Laid-Open No. 9-101652 JP 2002-105305 A

  The present invention has been made in view of the above-mentioned problems, and relates to a member used in an electrophotographic process such as a copying machine or a laser beam printer, and has no bleed, low volume resistivity, and electrically uniform. An object of the present invention is to provide a low resistance conductive rubber member.

  The conductive rubber member according to the present invention is composed of a rubber component having epichlorohydrin rubber and a copolymer of ethylene oxide (A) / propylene oxide (B) / allyl glycidyl ether (C). The copolymerization ratio of the copolymer is A + B <90 mol% and B + C <20 mol%.

  In addition, a conductive rubber roller and a transfer roller using the conductive rubber member, and an image forming apparatus including the transfer roller are provided.

  According to the present invention, the volume specific resistance value is low, and when used for a member involved in the chargeability of an electrophotographic process, it is electrically uniform and bleed does not occur.

  The conductive rubber member according to the present invention is composed of a rubber component having epichlorohydrin rubber and a copolymer of ethylene oxide (A) / propylene oxide (B) / allyl glycidyl ether (C). The copolymerization ratio of the copolymer is A + B <90 mol% and B + C <20 mol%. In addition, the above-mentioned A, B, and C say each polymerization ratio which concerns on the ethylene oxide, propylene oxide, and allyl glycidyl ether which are the structural units of this copolymer, respectively.

  Sum of copolymerization ratios A and B related to the copolymer of ethylene oxide (A) / propylene oxide (B) / allyl glycidyl ether (C) constituting the conductive rubber member according to the present invention, and A + B is 90 mol% or more. As a result, the increase in crystallinity inhibits electrical conduction, and the volume resistivity value also increases. Since allyl glycidyl ether (C) decreases relative to the increase in the ratio, the crosslinking sites derived from allyl glycidyl ether (C) become insufficient, and the copolymer and the epichlorohydrin rubber are co-polymerized. Cross-linking becomes difficult. As a result, it becomes difficult to form a three-dimensional structure by cross-linking, so that the surface of the member is bleed and the charged member is contaminated.

  In addition, when the sum of the polymerization ratios B and C relating to this copolymer, B + C is 20 mol% or more, ethylene oxide (A), which is a structural unit contributing to electrical conduction, is relatively reduced. Resistance value will increase. Therefore, it is difficult to reduce the resistance unless the copolymerization ratio is as described above.

  The epichlorohydrin rubber constituting the conductive rubber member according to the present invention may be a homopolymer of epichlorohydrin, which is a copolymer of epichlorohydrin and another cross-linking agent having polymerizability. May be. Examples of other crosslinking agents include ethylene oxide, propylene oxide and / or allyl glycidyl ether. Among these, in consideration of the crosslinkability with the above-mentioned ethylene oxide / propylene oxide / allyl glycidyl ether copolymer, the epichlorohydrin rubber is a terpolymer of epichlorohydrin / ethylene oxide / allyl glycidyl ether. It is preferably a coalescence. As a result, the epichlorohydrin rubber and the ethylene oxide / propylene oxide / allyl glycidyl ether copolymer are sufficiently crosslinked to form a three-dimensional structure properly, and bleed can be suppressed. Further, the volume resistivity value is reduced by copolymerizing ethylene oxide.

  On the other hand, in the conductive rubber member according to the present invention, the constituent ratio of the ethylene oxide in the rubber component constituting the conductive rubber member is preferably less than 84 mol%. When the composition ratio of ethylene oxide is 84 mol% or more, the crystallinity that inhibits electrical conduction increases and the volume resistivity value tends to increase.

  Moreover, the rubber component used for the conductive rubber member of the present invention may contain other components used for general rubber as necessary. For example, vulcanizing agents such as sulfur and organic sulfur-containing compounds, various vulcanization accelerators, various processing aids such as lubricants and subs, various anti-aging agents, p, p'-oxybissulfonylhydrazide (OBSH) and azodicarbon Various foaming agents such as amide (ADCA) and dinitrosopentamethylenetetramine (DPT), various foaming aids such as urea, vulcanization aids such as zinc oxide and stearic acid, various types such as calcium carbonate, talc, silica and clay You may mix | blend a filler as needed.

  The conductive rubber member according to the present invention is manufactured by melt-kneading and vulcanizing a rubber component having at least an epichlorohydrin rubber and a copolymer of ethylene oxide / propylene oxide / allyl glycidyl ether. This melt-kneading may be performed by a method known in this technical field, and may be kneaded using, for example, an open roll or a closed kneader. The above vulcanization may be performed by a method known in the art, for example, a method performed in a vulcanizing can under steam pressure. In that case, you may carry out at 160 degreeC and 10 to 60 minutes. Furthermore, secondary vulcanization may be performed as necessary in terms of increasing the crosslinking density and suppressing bleeding. In these vulcanizations, it is preferable to use sulfur in terms of crosslinkability, low resistance and / or low contamination. Further, hydrotalcite may be further used in terms of low contamination.

(Conductive rubber roller and transfer roller)
The conductive rubber roller and / or the transfer roller according to the present invention includes the above-described conductive rubber member according to the present invention. FIG. 1 schematically shows an example of a conductive rubber member according to the present invention. The conductive rubber roller according to the present invention includes a conductive metal core 61 and an elastic layer 62 laminated around the metal core 61.

  The conductive rubber roller according to the present invention is manufactured using the above-mentioned molded product of the conductive rubber member. For forming the conductive rubber member, conventionally known various molding methods can be applied. For example, an unvulcanized conductive rubber composition is extruded into a tube shape by an extruder, and a vulcanized can or a continuous vulcanizing furnace is used. It may be heated to form a conductive rubber (elastic body) tube. The conductive rubber member molded in this way is inserted into the cored bar 61 coated with an adhesive and heated to be bonded to the cored bar 61, and then polished to a predetermined outer diameter. The conductive rubber roller according to the present invention having the elastic layer 62 around the periphery thereof. Further, the conductive rubber roller according to the present invention is a conventionally known one such as extruding the unvulcanized conductive rubber material and the cored bar 61 at the same time or loading the extruded rubber composition into a mold and vulcanizing. It may be manufactured by various manufacturing methods. Furthermore, the conductive rubber roller of the present invention may have a layer of resin or the like on the outer periphery of the elastic layer 62 as necessary.

  As described above, the conductive rubber member according to the present invention is used as a transfer roller for black and white and / or color, when a low electrical resistance value is required such as a charging roller, a toner supply roller, a developing roller, etc. Particularly preferably used.

(Electrophotographic equipment)
FIG. 2 shows an example in which the transfer roller having the conductive rubber member of the present invention is used in an image forming apparatus. This image forming apparatus is formed on an electrophotographic photosensitive member (hereinafter referred to as a photosensitive drum 1) as an image carrier, a charging device 2 for uniformly charging the surface of the photosensitive drum 1, and a surface of the photosensitive drum 1. The developing device 4 for attaching the charged toner 5 to the electrostatic latent image formed in accordance with the target image information by the exposure light 3 from the formed electrostatic latent image, and the toner 5 attached to the surface of the photosensitive drum 1 A transfer roller 6 for transferring the toner to a recording medium 7 such as paper fed from a paper feed unit (not shown) and toner 5 (residual toner) remaining on the surface of the photosensitive drum 1 without being transferred to the recording medium 7. A cleaning blade 8 that is removed from the surface, a waste toner container 9 that stores the toner, and a fixing device 10 that fixes the toner 5 transferred to the recording medium 7 are provided.

  Next, image formation control by this image forming apparatus will be described.

  The photosensitive drum 1 is rotationally driven by a driving means (not shown) in the direction of arrow R1 at a predetermined process speed (circumferential speed), for example, 50 mm / second. The surface of the photosensitive drum 1 is electrically and uniformly charged by the charging device 2. The charging device 2 is disposed in contact with the surface of the photosensitive drum 1, and is driven to rotate (R2 direction in FIG. 1) as the photosensitive drum 1 rotates (R1 direction in FIG. 1). The charging device 2 is applied with an oscillating voltage (AC voltage VAC + DC voltage VDC) by a charging bias application power source (not shown), whereby the surface of the photosensitive drum 1 is uniformly charged to, for example, −600 V (dark part potential Vd). It is processed. Thereafter, the surface of the photosensitive drum 1 is exposed to exposure light 3 such as a laser beam modulated in accordance with a time-series electric digital image signal of target image information, and an electrostatic latent image corresponding to the target image information. Is formed. The toner 5 having a chargeability opposite to that of the electrostatic latent image is attached to the electrostatic latent image formed in this manner, and a toner image is formed on the surface of the photosensitive drum 1. The toner image thus formed is transferred to a recording medium 7 fed and conveyed between the photosensitive drum 1 and a transfer roller 6 made of a conductive rubber member according to the present invention. At this time, a transfer bias is applied to the transfer roller 6 by a transfer bias application power source (not shown), whereby the toner image on the surface of the photosensitive drum 1 is transferred to the recording medium 7. The recording medium 7 onto which the toner image has been transferred is discharged to the outside of the image forming apparatus main body as an image formed product (print) after the toner image is fixed by the fixing device 10.

  Hereinafter, the present invention will be described in detail using examples and comparative examples, but the present invention is not limited to these examples. The blending ratios and test results of the rubber materials used in the examples and comparative examples are as shown in the table. In addition, the unit of a compounding quantity is a mass part.

The rubber materials used in each example and comparative example are as follows.
1: Epichlorohydrin rubber [ethylene oxide content 56 mol%; trade name Zeklon 3106 (manufactured by ZEON CORPORATION)]
2: ethylene oxide (A) / propylene oxide (B) / allyl glycidyl ether (C) copolymer [ethylene oxide-propylene oxide-allyl glycidyl ether copolymerization ratio = 87: 1: 12] (for each example)
3: Ethylene oxide (A) / Propylene oxide (B) / Allyl glycidyl ether (C) copolymer [Ethylene oxide-propylene oxide-allyl glycidyl ether copolymerization ratio = 90: 6: 4; (Made by Co., Ltd.)] (for each comparative example)
4: Filler [Calcium carbonate; trade name Silver W (manufactured by Maruo Calcium Co., Ltd.)]
5: Ionic conductive agent [quaternary ammonium salt; trade name Adeka Sizer LV70 (Asahi Denka Kogyo Co., Ltd.)]
6: Vulcanizing agent [Sulfur (S); trade name Sulfax PMC (manufactured by Tsurumi Chemical Co., Ltd.)]
7: Vulcanization accelerator [Dibenzothiazyl disulfide (DM); trade name Noxeller DM (Ouchi Shinsei Chemical Co., Ltd.)]
[Tetraethylthiuram disulfide (TET); trade name Noxeller TET (Ouchi Shinsei Chemical Co., Ltd.)]
8: Vulcanization accelerating aid [Zinc oxide; trade name: Zinc Hana, Class 2 Hakusui Tech Co., Ltd.]
[Stearic acid; trade name LUNAC S manufactured by Kao Corporation]

  In addition, the conductive rubber member of an Example and a comparative example vulcanized | cured using the said rubber material using the metal mold | die of 150 mm x 150 mm x 2 mm, and shape | molded it in the sheet form. The conductive rubber roller was formed into a tube shape by using the rubber material and extruding into a tube shape using an extruder and then vulcanizing with a vulcanizing can. Next, a φ6 mm cored bar was inserted into the inner diameter portion of the tubular rubber vulcanizate to obtain a roller-shaped molded body. This molded body was prepared by polishing so that the outer diameter was 14 mm.

(About measurement evaluation)
<Volume specific resistance value>
A sheet made by vulcanization using a 150 mm x 150 mm x 2 mm mold, using a super insulation meter SM-8220, manufactured by Toa Denpa Kogyo Co., Ltd., in an environment of 23 ° C / 55% RH (N / N) Then, a voltage of 100 V was applied to measure the volume resistivity. In the present invention, a volume resistivity value of 7.4 (Log ₁₀ R) or less was set as a favorable range.

<Photoconductor contamination>
Under an N / N environment (23 ° C / 50% RH), a rubber roller is incorporated into the Hewlett-Packard laser printer Laserjet 4000N, printing 30 sheets of solid black, and image evaluation for charging roller unevenness in charging density and image defects Went. Among the obtained images, those having no image density unevenness and image defect due to the charging roller were marked with ◯, and those having image density unevenness and image defect and not practical were marked with ×.

<Circle unevenness>
In a state where the conductive rubber roller is pressed against a stainless steel drum having an outer diameter of 30 mm and rotated at 0.5 Hz so that a load of 500 g is applied to both sides of the elastic layer of the produced conductive rubber roller, A voltage of 1000 V is applied between the steel drum and the current value is measured in an environment of 23 ° C./55% RH (N / N), and the ratio between the maximum value and the minimum value of the current value is determined as unevenness in the circumference. did. The same level or more as in the case of ionic conduction that can reduce resistance unevenness (comparative example) was considered good.

  In Examples 1 to 6, a low resistance conductive rubber member having little variation and no photoconductor contamination was obtained when the ethylene oxide component ratio in the rubber component was less than 84 mol%.

  In addition, it can be seen that even when the copolymerization ratio of allyl glycidyl ether exceeds 10 mol%, low resistance is realized.

  In Comparative Example 1, the copolymerization ratio of allyl glycidyl ether is 10 mol% or less, and in Comparative Examples 2 and 3, an ionic conductive agent is added. In Comparative Example 1, since the copolymerization ratio of allyl glycidyl ether is 10 mol% or less and co-crosslinking is difficult, the photoreceptor is contaminated. Moreover, although the resistance reduction is realized with the addition of the ionic conductive agent of Comparative Examples 2 and 3, the photoreceptor contamination is insufficient.

  From the above, a conductive rubber member comprising a rubber component having epichlorohydrin rubber and a copolymer of ethylene oxide (A) / propylene oxide (B) / allyl glycidyl ether (C), If the conductive rubber member is characterized in that the copolymerization ratio of the copolymer is A + B <90 mol% and B + C <20 mol%, there is little bleed, A low-resistance conductive rubber member can be obtained without using an electronic conductive agent / ion conductive imparting agent.

1 is an overall cross-sectional view of a conductive rubber roller according to the present invention. 1 is an overall cross-sectional view of an image forming apparatus according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device 3 Exposure light 4 Developing device 5 Toner 6 Transfer roller 7 Recording medium 8 Cleaning blade 9 Waste toner container 10 Fixing device 61 Core metal 62 Elastic layer

Claims (6)

A conductive rubber member comprising a rubber component having an epichlorohydrin rubber and a copolymer of ethylene oxide (A) / propylene oxide (B) / allyl glycidyl ether (C),
A conductive rubber member, wherein a copolymerization ratio of the copolymer is A + B <90 mol% and B + C <20 mol%.   The conductive rubber member according to claim 1, wherein the epichlorohydrin rubber is a terpolymer of epichlorohydrin / ethylene oxide / allyl glycidyl ether.   The conductive rubber member according to claim 1 or 2, wherein a constituent ratio of the ethylene oxide in the rubber component is less than 84 mol%.   A conductive rubber roller comprising the conductive rubber member according to claim 1.   A transfer roller comprising the conductive rubber member according to claim 1.   An image forming apparatus comprising the transfer roller according to claim 5.

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