Electrophotographic conductive roller

Abstract

The purpose of this invention is to provide a conductive roller that can suppress the electrical degradation of the conductive elastic layer caused by continuous use, and can also suppress the deformation of the conductive elastic layer itself and the contamination of components in contact with the conductive elastic layer during storage. The conductive roller (1) for electrophotography has a conductive core (2) and a conductive elastic layer (3), wherein the conductive elastic layer (3) is formed by vulcanizing a conductive rubber composition containing a specified amount of a base polymer, sulfur, a first carbon black, and a second carbon black. The base polymer contains styrene-butadiene rubber and chloroprene rubber. The first carbon black has a primary particle size of 18 nm to 30 nm and a DBP absorption of 50 ml / 100 g to 130 ml / 100 g. The second carbon black has a primary particle size of 80 nm to 125 nm and a DBP absorption of 10 ml / 100 g to 47 ml / 100 g.

Description

Technical Field

[0001] The present invention relates to a conductive roller used in an image forming apparatus utilizing electrophotography. Background Technology

[0002] In image forming apparatuses utilizing electrophotography, such as laser printers, electrostatic copiers, plain paper fax machines, or their multifunction printers, a charged roller is used to uniformly charge the surface of the photoreceptor. As a charged roller, a conductive roller is used, for example, which is formed by inserting a conductive core made of metal or the like into a conductive rubber tube formed by molding and cross-linking a conductive rubber composition into a cylindrical shape. Methods for imparting conductivity to rubber include, for example, using ionically conductive rubbers such as epichlorohydrin rubber, or utilizing the electronic conductivity of carbon black dispersed in the rubber.

[0003] In addition, to prevent the components contained in the rubber from being transferred relative to the photoreceptor in contact with the roller, thus causing poor image quality, and to prevent the performance of the charged roller itself from being reduced due to toners or external additives attached to the charged roller during continuous printing, methods such as local modification of the roller surface using ultraviolet light or electron beams, or coating with urethane resins or fluorine resins are used.

[0004] With increasing demands for high image quality, long lifespan, and low cost, more and more problems cannot be addressed using existing technologies. Therefore, various conductive rollers have been proposed. For example, Patent Document 1 describes a semi-conductive roller formed from a crosslinked rubber composition containing epichlorohydrin rubber, diene rubber, anionic potassium salt, and reactive silicone oil, and includes an oxide film on its outer peripheral surface (see Patent Document 1 (Technical Solution 1)).

[0005] Patent Document 2 describes a semiconductive roller that includes an oxide film on the outer peripheral surface of a crosslinked material formed from a rubber composition. The rubber composition contains only two rubber components: acrylonitrile butadiene rubber (NBR) and ethylene propylene diene rubber (EPDM), a specific carbon black, sulfur as a crosslinking component, a peroxide crosslinking agent, and a sulfenamide accelerator (see Patent Document 2 (Technical Solution 1)).

[0006] Patent document 3 describes a conductive roller in which the conductive rubber layer comprises polar rubber and carbon black, wherein the carbon black contains a specified amount of carbon black A (average primary particle size: 31 nm to 50 nm, dibutyl phthalate (DBP) absorption: 90 cm⁻¹). 2 / 100g~180cm 2 / 100g), and carbon black B (average primary particle size: 90nm~300nm, DBP absorption: 20cm).2 / 100g~80cm 2 / 100g)(Refer to Patent Document 3 (Technical Solution 1)).

[0007] [Existing technical documents]

[0008] [Patent Literature]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2018-197791

[0010] [Patent Document 2] Japanese Patent No. 5936282

[0011] [Patent Document 3] Japanese Patent Application Publication No. 2008-256908 Summary of the Invention

[0012] [The problem the invention aims to solve]

[0013] In rollers containing epichlorohydrin as a rubber component, the epichlorohydrin itself is contaminating the photoreceptor. Therefore, given the required image quality, the oxide film on the outer surface alone cannot provide sufficient anti-fouling properties. Furthermore, the combination of epichlorohydrin and anionic potassium salts as a rubber material is relatively expensive, and even a structure omitting the coating film cannot adequately meet the market's demand for low prices.

[0014] In rollers using only NBR and EPDM as rubber components, co-crosslinking is difficult when NBR (diene-based rubber) and EPDM (non-diene-based rubber) are combined. Therefore, depending on the photoreceptor material, unreacted low-molecular-weight components may sometimes transfer to the photoreceptor during storage and transport, resulting in image defects. Furthermore, in crosslinking operations performed in oxygen-containing vulcanizing tanks or continuous crosslinking devices, peroxide crosslinking agents sometimes fail to induce crosslinking reactions in the rubber components. In such cases, for example, when in contact with the photoreceptor as a charged roller, problems may arise with the roller adhering to the charged roller. Moreover, if rollers with this structure are applied to long-life image forming apparatuses or toner cartridges, a phenomenon known as "electrical degradation" occurs, where the roller's resistance increases during continuous use. Therefore, they cannot be used in long-life image forming apparatuses or toner cartridges.

[0015] In rollers using NBR as the polar rubber, NBR has low weather resistance and may deteriorate and crack due to ozone within the image forming apparatus. Furthermore, when forming an oxide film through ultraviolet (UV) treatment, NBR is prone to cracking due to the ozone inevitably generated during UV treatment, making it impossible to design a stable manufacturing process. In addition, polar rubber exhibits environmental variations in resistivity; depending on the type of rubber chosen, its discharge characteristics relative to the photoreceptor can change in low-temperature, low-humidity environments versus high-temperature, high-humidity environments.

[0016] The present invention was made in view of the above circumstances, and its object is to provide a conductive roller that can suppress the electrical degradation of the conductive elastic layer caused by continuous use, and can suppress the deformation of the conductive elastic layer itself and the contamination of the components in contact with the conductive elastic layer during storage.

[0017] [Technical means to solve the problem]

[0018] The conductive roller for electrophotography of the present invention, which solves the aforementioned problem, has a conductive shaft core and a conductive elastic layer covering the conductive shaft core. The conductive elastic layer is formed by vulcanizing a conductive rubber composition containing (a) a base polymer, (b) sulfur, and (c) carbon black. The (a) base polymer contains (a1) styrene-butadiene rubber and (a2) chloroprene rubber, with a mass ratio (a1 / a2) of 1.0 to 5.0 for the (a1) styrene-butadiene rubber to (a2) chloroprene rubber. The (c) carbon black contains... (c1) a first carbon black with a primary particle size of 18 nm to 30 nm and a dibutyl phthalate absorption of 50 ml / 100 g to 130 ml / 100 g, and (c2) a second carbon black with a primary particle size of 80 nm to 125 nm and a dibutyl phthalate absorption of 10 ml / 100 g to 47 ml / 100 g, wherein the total mass (c1+c2) of the first carbon black (c1) and the second carbon black (c2) in the conductive rubber composition is 38 to 65 parts by mass relative to 100 parts by mass of the base polymer (a).

[0019] Regarding the base polymer (a) constituting the conductive elastic layer, by mixing (a1) styrene-butadiene rubber and (a2) chloroprene rubber at a ratio of 1.0 to 5.0, there are no environmentally induced polymer-derived resistance variations, and because both are diene-based rubbers, they exhibit co-crosslinking properties, making it less likely to contaminate components in contact with the conductive elastic layer (e.g., photosensitive drums). Furthermore, carbon black, as a conductive agent, can be stably dispersed, and it can possess weather resistance resistant to ozone exposure.

[0020] By dispersing (c1) the first carbon black and (c2) the second carbon black in the conductive elastic layer, the conductive elastic layer can be made to have high electrical conductivity durability. In addition, by adjusting the total mass of (c1) the first carbon black and (c2) the second carbon black, the conductive elastic layer can be made to have moderate semiconductivity.

[0021] [The effects of the invention]

[0022] When the conductive roller for electrophotography of the present invention is used as the charged roller of an image forming apparatus utilizing electrophotography, the degradation of the conductive elastic layer due to continuous use is suppressed, thus suppressing the generation of haze caused by degradation of charged properties and extending the lifespan of the image forming apparatus. Furthermore, it suppresses the generation of image defects caused by deformation of the charged roller itself and contamination of the photoreceptor during storage and transport of the image forming apparatus. Attached Figure Description

[0023] Figure 1 This is a perspective view showing an example of the conductive rubber roller of the present invention.

[0024] Explanation of symbols

[0025] 1: Conductive rollers for electrophotography

[0026] 2: Conductive shaft core

[0027] 3: Conductive elastic layer Detailed Implementation

[0028] The conductive roller for electrophotography of the present invention has a conductive core and a conductive elastic layer covering the conductive core, the conductive elastic layer being formed by vulcanizing a conductive rubber composition containing (a) a base polymer, (b) sulfur, and (c) carbon black.

[0029] The following describes the raw materials used in the conductive rubber composition.

[0030] (a) Basic polymers

[0031] The (a) base polymer contains (a1) styrene-butadiene rubber (SBR) and (a2) chloroprene rubber (CR).

[0032] (a1)SBR

[0033] As the SBR, any type of cross-linking SBR synthesized by copolymerizing styrene and butadiene through various polymerization methods such as emulsion polymerization and solution polymerization can be used. As the SBR, any type of high-styrene, medium-styrene, and low-styrene SBR classified according to the amount of styrene bonded can be used. Furthermore, as the SBR, there are oil-filled SBRs with added filler oil to adjust flexibility, and non-oil-filled SBRs without added filler oil, but non-oil-filled SBRs are preferred. Additionally, as the SBR, non-polluting is preferred.

[0034] The amount of bonded styrene in the SBR is preferably 15% by mass or more, more preferably 20% by mass or more, and preferably 45% by mass or less, more preferably 35% by mass or less, and even more preferably 27% by mass or less. The amount of bonded styrene is determined in accordance with Japanese Industrial Standards (JIS) 6236 (2001).

[0035] (a2)CR

[0036] As the CR, any of various crosslinking CRs synthesized by emulsifying chloroprene can be used. Depending on the type of molecular weight modifier used in the emulsification polymerization of chloroprene, CRs are classified as sulfur-modified and non-sulfur-modified. Furthermore, copolymers of chloroprene with other copolymers can also be used as CRs. Examples of such other copolymers include, for example, one or more of 2,3-dichloro-1,3-butadiene, 1-chloro-1,3-butadiene, styrene, acrylonitrile, methacrylonitrile, isoprene, butadiene, acrylic acid, acrylates, methacrylic acid, and methacrylates. As CRs, there are oil-extended CRs with added filler oil to adjust flexibility, and non-oil-extended CRs without added filler oil, but non-oil-extended CRs are preferred.

[0037] The mass ratio (a1 / a2) of the (a1) styrene-butadiene rubber to the (a2) chloroprene rubber in the base polymer is preferably 1.0 or more, more preferably 1.3 or more, even more preferably 1.5 or more, particularly preferably 1.7 or more, and preferably 5.0 or less, more preferably 4.5 or less, even more preferably 4.0 or less, and particularly preferably 3.5 or less. If the mass ratio (a1 / a2) is 1.0 or more, the dispersion of carbon black in the rubber composition is improved, and the resistivity of the obtained conductive elastic layer becomes good. Furthermore, if the mass ratio (a1 / a2) is 5.0 or less, the weather resistance of the obtained conductive elastic layer is improved, and the occurrence of cracking or other defects on the surface of the conductive elastic layer after ultraviolet irradiation treatment is suppressed.

[0038] The base polymer (a) may also contain other rubber components besides the (a1) styrene-butadiene rubber and (a2) chloroprene rubber, but preferably contains only the (a1) styrene-butadiene rubber and (a2) chloroprene rubber. When the base polymer (a) contains other rubber components, the total content of the (a1) styrene-butadiene rubber and (a2) chloroprene rubber in the base polymer (a) is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0039] As other rubber components, rubber components previously used in conductive rubber rollers are preferably used. Examples of such other rubber components include acrylonitrile butadiene rubber (NBR), ethylene propylene diene rubber (EPDM), epichlorohydrin rubber, acrylic rubber, butyl rubber, and silicone rubber. These other rubber components may be used alone or in combination of two or more.

[0040] (b) Sulfur

[0041] The conductive rubber composition contains (b) sulfur as a crosslinking agent. Examples of sulfur include: powdered sulfur, oil-treated powdered sulfur, precipitated sulfur, colloidal sulfur, and dispersed sulfur.

[0042] The content of sulfur (b) in the conductive rubber composition is preferably 0.5 parts by mass or more, more preferably 0.75 parts by mass or more, and even more preferably 1.0 parts by mass or more, particularly preferably 1.2 parts by mass or more, and preferably 2.0 parts by mass or less, more preferably 1.75 parts by mass or less, and even more preferably 1.65 parts by mass or less, relative to 100 parts by mass of the base polymer (a). If the content of sulfur (b) is 0.5 parts by mass or more, the base polymer (a) can be fully crosslinked, and the collapse of the conductive elastic layer during storage can be suppressed. Furthermore, if the content of sulfur (b) is 2.0 parts by mass or less, the hardness of the conductive elastic layer can be prevented from becoming excessively high.

[0043] (c) Carbon black

[0044] The conductive rubber composition contains (c1) a first carbon black and (c2) a second carbon black as (c) carbon black. The conductivity of the conductive elastic layer is achieved by using carbon black with small particle size, while the high filling capacity brought about by carbon black with large particle size is used to stabilize the conductive path of carbon (resistance to mechanical and electrical stress).

[0045] (c1) First carbon black

[0046] The primary particle size of the first carbon black is 18 nm to 30 nm. In this invention, the primary particle size refers to the average particle size of the primary particles as measured using an electron microscope. The DBP absorption of the (c1) first carbon black is preferably 50 ml / 100 g or more, more preferably 75 ml / 100 g or more, even more preferably 100 ml / 100 g or more, and preferably 130 ml / 100 g or less, more preferably 125 ml / 100 g or less. The DBP absorption is measured on an uncompressed sample according to JIS K6217-4 (2017).

[0047] (c2) Second carbon black

[0048] The primary particle size of the second carbon black is 80 nm to 125 nm. The DBP absorption of the second carbon black (c2) is preferably 10 ml / 100 g or more, more preferably 20 ml / 100 g or more, even more preferably 25 ml / 100 g or more, and preferably 47 ml / 100 g or less, more preferably 45 ml / 100 g or less.

[0049] In the conductive rubber composition, the mass ratio (c1 / c2) of the first carbon black (c1) to the second carbon black (c2) is preferably 0.5 or more, more preferably 0.8 or more, further preferably 1.0 or more, particularly preferably 1.5 or more, and preferably 3.0 or less, more preferably 2.5 or less, further preferably 2.4 or less, and particularly preferably 2.2 or less. If the mass ratio (c1 / c2) is 0.5 or more, uneven discharge of the conductive elastic layer is suppressed; if it is 3.0 or less, the electrical conductivity durability of the conductive elastic layer becomes good.

[0050] The total mass (c1+c2) of the first carbon black (c1) and the second carbon black (c2) in the conductive rubber composition is preferably 38 parts by mass or more, more preferably 40 parts by mass or more, even more preferably 42 parts by mass or more, particularly preferably 44 parts by mass or more, and preferably 65 parts by mass or less, more preferably 60 parts by mass or less, even more preferably 57 parts by mass or less, and particularly preferably 55 parts by mass or less. If the total mass (c1+c2) is 38 parts by mass or more, the resistance value of the conductive elastic layer decreases and the discharge amount of the conductive elastic layer increases; if it is 65 parts by mass or less, the formability of the rubber composition becomes good.

[0051] The mass of the first carbon black (c1) in the conductive rubber composition is preferably 10 parts by mass or more, more preferably 15 parts by mass or more, more preferably 20 parts by mass or more, and preferably 60 parts by mass or less, more preferably 52 parts by mass or less, more preferably 50 parts by mass or less, and especially preferably 45 parts by mass or less, relative to 100 parts by mass of the base polymer (a).

[0052] The mass of the second carbon black (c2) in the conductive rubber composition is preferably 5 parts by mass or more, more preferably 7 parts by mass or more, and even more preferably 10 parts by mass or more, and preferably 55 parts by mass or less, more preferably 45 parts by mass or less, even more preferably 42 parts by mass or less, and particularly preferably 35 parts by mass or less, relative to 100 parts by mass of the base polymer (a).

[0053] The conductive rubber composition may contain a third carbon black (c3) other than (c1) first carbon black and (c2) second carbon black, but preferably contains only (c1) first carbon black and (c2) second carbon black as (c) carbon black. Furthermore, when (c3) third carbon black is contained, the total content of (c1) first carbon black and (c2) second carbon black in (c) carbon black is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0054] The conductive rubber composition may also contain crosslinking accelerators, crosslinking aids, acid absorbers, fillers, anti-aging agents, processing aids, lubricants, dispersants, and other formulation agents as needed. These formulation agents are preferably selected to minimize the occurrence of blooming and bleeding.

[0055] Crosslinking accelerator

[0056] The conductive rubber composition may also contain a crosslinking accelerator. As the crosslinking accelerator, any one of inorganic or organic accelerators may be used. Examples of inorganic accelerators include slaked lime, magnesium oxide (MgO), and lead oxide (PbO). Examples of organic accelerators include thiazole-based accelerators, thiuram-based accelerators, sulfenamide-based accelerators, and dithiocarbamate-based accelerators. The crosslinking accelerator may be used alone or in combination with two or more. As a crosslinking accelerator combined with the sulfur, it is preferable to use a combination of a thiazole-based accelerator and a thiuram-based accelerator.

[0057] Examples of thiazole-based accelerators include 2-mercaptobenzothiazole, di-2-benzothiazole disulfide, zinc salt of 2-mercaptobenzothiazole, cyclohexylamine salt of 2-mercaptobenzothiazole, 2-(N,N-diethylthiocarbamoylthio)benzothiazole, and 2-(4'-morpholinodithio)benzothiazole, with di-2-benzothiazole disulfide being preferred. The amount of the thiazole-based accelerator used is preferably 0.5 parts by weight or more and 2.0 parts by weight or less relative to 100 parts by weight of the base polymer (a).

[0058] Examples of thiuram-based accelerators include tetramethylthiuram monosulfide, tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, tetra(2-ethylhexyl)thiuram disulfide, and di-pentamethylenethiuram tetrasulfide, with tetramethylthiuram monosulfide being preferred. The amount of the thiuram-based accelerator used is preferably 0.3 parts by weight or more and 2.0 parts by weight or less relative to 100 parts by weight of the base polymer (a).

[0059] Crosslinking aids

[0060] Examples of crosslinking aids include: metal compounds such as zinc oxide (zinc oxide); fatty acids such as stearic acid, oleic acid, and cottonseed fatty acids; and one or more other previously known crosslinking aids. The amount of the crosslinking aid used is preferably 0.1 parts by mass or more, and more preferably 7 parts by mass or less, relative to 100 parts by mass of the base polymer (a).

[0061] acid absorbent

[0062] An acid absorber prevents chlorine-based gases generated during the crosslinking of the base polymer from remaining in the conductive elastic layer, or from causing crosslinking obstacles or contamination of components (e.g., photoreceptor drums) in contact with the conductive elastic layer. Various substances that function as acid acceptors can be used as acid absorbers, with hydrotalcite or MAGSARAT, which have excellent dispersibility, being particularly preferred. The amount of acid absorber used is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and preferably 8 parts by mass or less, more preferably 6 parts by mass or less, relative to 100 parts by mass of the base polymer (a).

[0063] Examples of fillers include silica, clay, talc, calcium carbonate, magnesium carbonate, and aluminum hydroxide. By adjusting the filler composition, the mechanical strength of the conductive elastic layer can be improved.

[0064] Various anti-deterioration agents and antioxidants can be listed as examples. Examples of anti-aging agents include nickel diethyldithiocarbamate and nickel dibutyldithiocarbamate.

[0065] The conductive rubber composition can be prepared by mixing (a) a base polymer, (b) sulfur and (c) carbon black, and other raw materials as needed, using a pressure kneader, a Banbury mixer, an open roll, etc. The mixing method and conditions can be appropriately selected according to the production scale.

[0066] [Conductive rollers for electrophotography]

[0067] The conductive roller for electrophotography of the present invention has a conductive core and a conductive elastic layer covering the conductive core, the conductive elastic layer being formed from the conductive rubber composition. The conductive roller for electrophotography of the present invention can be used in charged rollers, transfer rollers, etc., of image forming apparatuses utilizing electrophotography, and is particularly preferably used in charged rollers. Figure 1This is a perspective view showing an example of the conductive roller for electrophotography according to the present invention. The conductive roller 1 for electrophotography has a conductive core 2 and a conductive elastic layer 3 covering the conductive core 2. The conductive elastic layer 3 is formed of a crosslinked product of the conductive rubber composition and is formed in a cylindrical shape. The conductive core is inserted into and fixed in a through hole at the center of the conductive elastic layer 3.

[0068] The conductive shaft core 2 is not particularly limited as long as at least its surface is conductive and it functions as a support for the conductive roller. The diameter of the conductive shaft core 2 is not particularly limited, and is typically 4.0 mm to 12.0 mm. The conductive shaft core 2 may be formed of metals such as aluminum, aluminum alloy, or stainless steel.

[0069] The conductive shaft core 2 is electrically bonded to the conductive elastic layer 3 via a conductive adhesive and then mechanically fixed, for example, by pressing a conductive shaft core with an outer diameter larger than the inner diameter of the through-hole in the conductive elastic layer into the through-hole, thereby electrically bonding to the conductive elastic layer 3 and then mechanically fixed. Alternatively, the conductive shaft core 2 can be electrically bonded and mechanically fixed to the conductive elastic layer 3 using both of these methods.

[0070] The conductive elastic layer 3 can be a solid structure or a porous structure. Additionally, a resistance adjustment layer or surface protective layer for the roller can be disposed on the outer or inner circumferential surface of the conductive elastic layer 3. The thickness of the conductive elastic layer 3 is not particularly limited and can be adjusted appropriately according to the intended use, typically ranging from 0.5 mm to 6.0 mm.

[0071] The conductive elastic layer 3 can also be coated with polyurethane resin, acrylate resin, fluororesin, fluorinated acrylic resin, fluorinated silane resin, etc. Alternatively, the surface of the conductive elastic layer 3 can be modified by dry treatments such as electron beam, ultraviolet light, or corona discharge. Preferably, the surface of the conductive elastic layer 3 is treated with ultraviolet light irradiation. Furthermore, the conductive elastic layer 3 preferably has an oxide film formed on its outer peripheral surface. The oxide film is a film formed by the oxidation of a base polymer. This oxide film can be formed by ultraviolet irradiation of the surface of the conductive elastic layer 3 in the presence of oxygen.

[0072] To manufacture the conductive roller 1 for electrophotography, firstly, the prepared conductive rubber composition is extruded into a cylindrical shape using an extruder, then cut to a specified length, and cross-linked by pressurizing and heating in a vulcanizing tank. Next, the cross-linked (and foamed) cylindrical body is heated in an oven or similar device to undergo secondary cross-linking, and then cooled to form a conductive elastic layer 3. Here, the outer peripheral surface can also be ground to achieve a specified outer diameter. Various grinding methods, such as dry longitudinal grinding, can be used as the grinding method.

[0073] The conductive core 2 can be inserted and fixed in the through-hole of the conductive elastic layer 3 at any point between the cutting of the cylindrical body and the grinding. However, it is preferable to perform secondary cross-linking and grinding after cutting, with the conductive core 2 first inserted in the through-hole. This suppresses warping or deformation of the conductive elastic layer 3 caused by expansion and contraction during secondary cross-linking. In addition, grinding while rotating around the conductive core 2 improves the workability of the grinding and suppresses runout of the outer peripheral surface.

[0074] The conductive core 2 can be formed by pressing a conductive core with an outer diameter larger than the inner diameter of the through hole into the through hole, or by inserting it into the through hole of the cylindrical body before secondary cross-linking via a conductive thermosetting adhesive. In the former case, electrical bonding and mechanical fixation with the conductive elastic layer 3 are completed simultaneously with pressing in the conductive core 2. In the latter case, the thermosetting adhesive hardens while the cylindrical body undergoes secondary cross-linking through heating in an oven, and the conductive core 2 is electrically bonded to the conductive elastic layer 3 and mechanically fixed. Alternatively, as described above, the conductive core 2 can also be electrically bonded and mechanically fixed to the conductive elastic layer 3 using both methods.

[0075] When forming an oxide film by subjecting the surface of the conductive elastic layer 3 to ultraviolet irradiation treatment, a low-pressure mercury lamp is preferably used. Low-pressure mercury lamps primarily emit ultraviolet light with wavelengths of 185 nm and 254 nm, thus enabling efficient surface modification of the conductive elastic layer. Furthermore, when using a low-pressure mercury lamp, the ultraviolet irradiation dose is preferably set to 100 mJ / cm². 2 ~5000mJ / cm 2 .

[0076] The conductive roller for electrophotography of the present invention can preferably be used as an electrified roller in image forming apparatuses that utilize electrophotography, such as laser printers, electrostatic copiers, plain paper fax machines and their multifunction printers. In addition, it can also be used as a developing roller, transfer roller, cleaning roller, etc.

[0077] [Example]

[0078] The present invention will be described in detail below through embodiments, but the present invention is not limited to the following embodiments. Any changes and implementation methods that do not depart from the spirit of the present invention are included within the scope of the present invention.

[0079] [Evaluation Method]

[0080] In the initial image, storage test, and paper feed durability test, the existing charged roller in a commercially available new toner cartridge for laser printers (a component that integrates a toner container containing toner, a photoreceptor, and a charged roller and a developing roller in contact with the photoreceptor) was replaced with the conductive roller of the present invention to produce a test toner cartridge.

[0081] (1) Initial image

[0082] Image formation was performed using a test toner kit to visually confirm the initial image.

[0083] 〇: No image defects were produced in either actual use of the image or the halftone image.

[0084] △: Image defects were confirmed in actual used images and / or halftone images.

[0085] (2) Storage test

[0086] The test toner cartridge was placed in an ambient oven at 50°C / 90% Rh for 2 weeks before image evaluation was performed to confirm whether there were any image defects caused by the photoreceptor cycle and the charged roller cycle.

[0087] 〇: No image defects were produced in either actual use of the image or the halftone image.

[0088] △: No image defects were detected in actual use images. Slight image defects were detected in the electrified roller cycle and photosensitive drum cycle in halftone images.

[0089] ×: This produces a level of image defect that is unusable in either actual use images or halftone images.

[0090] (3) Paper feed durability test

[0091] Using a test toner cartridge, after 5 days of paper feeding at a rate of 6 sheets per minute and 2000 sheets per day, a pure white image was output to confirm the generation of haze.

[0092] 〇: No visually identifiable haze was produced in the white background area.

[0093] △: A small amount of gray haze was produced in the white area, but it is at a level that is not a problem for practical use.

[0094] ×: Gray fog was generated on the white background area, making it an unusable level.

[0095] (4) Power-on durability test

[0096] A conductive roller connected to a metal shaft is placed in an oven at 22°C and 55% RH for at least 12 hours. The conductive roller is then axially supported and positioned above a metal cylinder (SUS material, 30mm in diameter) so that the roller abuts against the cylinder. A DC power supply and a resistor are connected in series between the metal shaft and the metal cylinder to create a resistance measurement circuit. Furthermore, one side of the DC power supply is connected to the metal shaft, and the positive side is connected to the resistor.

[0097] A load of 500 gf is applied to both ends of a metal shaft, pressing a conductive roller against a metal cylinder. Both the conductive roller and the metal cylinder remain stationary. A direct current (200 V) is continuously applied from one side of the exposed portion of the metal shaft for 1 hour. Using a data logger, data on the voltage applied to a resistor (0.1 kΩ) connected in series with the metal cylinder is collected. The resistance value of the conductive roller is calculated based on the voltage applied to the resistor (0.1 kΩ), and the resistance rise rate (resistance value after 1 hour / initial resistance value) is calculated based on the initial and 1-hour resistance values.

[0098] 〇: The resistance rise rate is 1.00 to 1.50 times, which has good power-carrying durability.

[0099] △: The resistance rise rate is 1.51 times to 3.00 times, and it has practical electrical durability.

[0100] ×: The resistance rise rate is more than 3.01 times, which is an impractical level.

[0101] [Manufacturing of conductive rollers]

[0102] Following the formulations shown in Tables 1 and 2, the base polymers were kneaded using a pressure kneader, then first carbon black, second carbon black, crosslinking aid, and acid scavenger were added, and the mixture was further kneaded using a kneader. Finally, the crosslinking agent and crosslinking accelerator were kneaded using a roller mill to obtain a conductive rubber composition.

[0103] The obtained conductive rubber composition was formed into a rubber tube (11 mm outer diameter, 5 mm inner diameter) using an extruder. The obtained rubber tube was then subjected to direct steam vulcanization at 150°C for 40 minutes in a vulcanizing tank. A metal shaft (6 mm diameter) was pressed into the vulcanized rubber tube, and a secondary vulcanization was performed at 160°C for 30 minutes in a Geer oven. The ends were then cut off to obtain a rubber roller with the rubber length adjusted to a specified length. The outer circumferential surface of the rubber roller was longitudinally ground using a cylindrical grinding mill to produce a conductive roller.

[0104] After wiping the outer circumferential surface of the ground conductive roller with alcohol, it is placed in an ultraviolet treatment device at a distance of 50mm from the low-pressure mercury lamp to the outer circumferential surface. The conductive roller is then irradiated with ultraviolet light while rotating at 60 rpm. The ultraviolet irradiation dose at the outer circumferential surface is thus set to 3000 mJ / cm². 2 The UV irradiation time was set using a specific method. The conductive rollers that underwent UV irradiation treatment were evaluated, and the results are shown in Tables 1 and 2.

[0105] [Table 1]

[0106]

[0107] [Table 2]

[0108]

[0109] The raw materials used in Tables 1 and 2 are as follows.

[0110] SBR: Manufactured by ZEON Corporation, Japan, Nipol (registered trademark) 1502 (non-oil-extended styrene-butadiene rubber, bonded styrene content: 23.5% by mass)

[0111] CR: Manufactured by Showa Denko Corporation, SHOPRENE (registered trademark) WRT (chloroprene rubber)

[0112] NBR: Manufactured by JSR Corporation, N250SL (Acrylonitrile Butadiene Rubber)

[0113] EPDM: Manufactured by Sumitomo Chemical Co., Ltd., Esprene (registered trademark) 505A (ethylene propylene diene rubber)

[0114] SEAST (registered trademark) 3: Manufactured by Tokai Carbon Co., Ltd., carbon black (primary particle size: 28nm, DBP absorption: 101ml / 100g)

[0115] SEAST 7HM: Manufactured by Tokai Carbon Co., Ltd., carbon black (primary particle size: 19nm, DBP absorption: 125ml / 100g)

[0116] SEAST 116: Manufactured by Tokai Carbon Co., Ltd., carbon black (primary particle size: 38nm, DBP absorption: 133ml / 100g)

[0117] Asahi #15: Manufactured by Asahi Carbon, carbon black (primary particle size: 122nm, DBP absorption: 41ml / 100g)

[0118] Asahi Thermal (registered trademark): Manufactured by Asahi Carbon Co., Ltd., carbon black (primary particle size: 80nm, DBP absorption: 28ml / 100g)

[0119] Asahi #35: Manufactured by Asahi Carbon, carbon black (primary particle size: 78nm, DBP absorption: 50ml / 100g)

[0120] Zinc oxide: Manufactured by Mitsui Metals & Mining Co., Ltd., two types of zinc oxide.

[0121] DHT-4A-2: Manufactured by Kyowa Chemical Industry Co., Ltd., a hydrotalcite compound.

[0122] Sulfur: Manufactured by Tsurumi Chemical Industry Co., Ltd., 5% oil-impregnated sulfur

[0123] MBTS: SUNSINE MBTS (di-2-benzothiazolyl disulfide) manufactured by Shandong Shanxian Chemical Co., Ltd.

[0124] SANCELER (registered trademark) TS: Manufactured by Sanxin Chemical Industry Co., Ltd., tetramethylthiuram monosulfide

[0125] The conductive elastic layer of conductive rollers No. 1 to No. 11 is formed from a conductive rubber composition containing specified amounts of (a) a base polymer, (b) sulfur, (c1) a first carbon black, and (c2) a second carbon black. Although slight image defects are confirmed in conductive rollers No. 1 to No. 11 depending on the level, they are usable at any level.

[0126] Regarding conductive roller No. 12, since the conductive rubber composition does not contain (c2) second carbon black, its electrical durability is poor, and haze was also observed in the paper feeding durability.

[0127] The conductive roller No. 13 has a low CR ratio in its base polymer (a), resulting in poor weather resistance. Consequently, due to ozone generated during UV irradiation treatment, the surface of the conductive elastic layer cracks, making it impossible to obtain prototypes suitable for image evaluation and electrical durability testing.

[0128] The conductive roller No. 14 has a high DBP absorption of (c1) the first carbon black and (c2) the second carbon black, resulting in an excessively high resistance value and low discharge, making it impossible to perform an evaluable printing operation.

[0129] The conductive roller No. 15 has an excessively high resistance value and low discharge capacity due to the low total mass (c1+c2) of carbon black in the conductive rubber composition, making it impossible to perform an evaluable printing operation.

[0130] The conductive rubber composition of conductive roller No. 16 contains too much carbon black (c1+c2) to be extruded.

[0131] Conductive roller No. 17, lacking SBR and CR as its (a) base polymers, exhibits poor co-crosslinking properties, resulting in both flattening marks on the charged roller and contamination marks on the photoreceptor. Furthermore, conductive roller No. 17 shows a significant increase in current carrying capacity and poor post-paper feeding haze.

[0132] Conductive roller No. 18 is an improvement over conductive roller No. 17, but tends to be the same.

Claims

1. A conductive roller for electrophotography, characterized in that: It has a conductive shaft core and a conductive elastic layer covering the conductive shaft core. The conductive elastic layer is formed by vulcanizing a conductive rubber composition containing (a) a base polymer, (b) sulfur, and (c) carbon black. The base polymer (a) contains (a1) styrene-butadiene rubber and (a2) chloroprene rubber, wherein the mass ratio of (a1) styrene-butadiene rubber to (a2) chloroprene rubber, a1 / a2, is 1.0 to 5.

0. The carbon black (c) comprises (c1) a first carbon black with a primary particle size of 18 nm to 30 nm and a dibutyl phthalate absorption of 50 ml / 100 g to 130 ml / 100 g, and (c2) a second carbon black with a primary particle size of 80 nm to 125 nm and a dibutyl phthalate absorption of 10 ml / 100 g to 47 ml / 100 g. The total mass of the first carbon black (c1) and the second carbon black (c2) in the conductive rubber composition, c1+c2, is 38 to 65 parts by mass relative to 100 parts by mass of the base polymer (a).

2. The conductive roller for electrophotography according to claim 1, wherein, The mass ratio of (a1) styrene-butadiene rubber to (a2) chloroprene rubber, a1 / a2, is 1.3 to 4.

5.

3. The conductive roller for electrophotography according to claim 1 or 2, wherein, The mass of the second carbon black (c2) in the conductive rubber composition is 5 to 55 parts by mass relative to 100 parts by mass of the base polymer (a).

4. The conductive roller for electrophotography according to any one of claims 1 to 3, wherein, The mass ratio of (c1) first carbon black to (c2) second carbon black, c1 / c2, is 0.5 to 3.

0.

5. The conductive roller for electrophotography according to any one of claims 1 to 4, wherein, The content of sulfur in (b) of the conductive rubber composition is 0.5 to 2.0 parts by mass relative to 100 parts by mass of the base polymer (a).

6. The conductive roller for electrophotography according to any one of claims 1 to 5, wherein, An oxide film is formed on the outer peripheral surface of the conductive elastic layer.

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