JP7655835B2 - Charging roll for electrophotographic equipment and method for producing the charging roll for electrophotographic equipment - Google Patents

Description

The present invention relates to a charging roll for electrophotographic equipment suitable for use in electrophotographic equipment such as copying machines, printers, and facsimiles that employ electrophotography, and a method for manufacturing the charging roll for electrophotographic equipment.

In electrostatic charge rolls for electrophotographic devices, carbon black is sometimes mixed into the surface layer to improve the amount of charge. Fluorine resin is sometimes used as a binder for the surface layer (Patent Document 1).

Japanese Patent Application Publication No. 10-268613

When fluororesin is used as a binder for the surface layer, it is incompatible with carbon black, which reduces the dispersibility of the carbon black and causes uneven discharge. This impairs uniform charging.

The problem that the present invention aims to solve is to provide a charging roll for electrophotographic devices that has excellent charging properties and uniform charging properties, and a method for manufacturing a charging roll for electrophotographic devices.

The charging roll for an electrophotographic device according to the present invention comprises a shaft body, an elastic layer formed on the outer peripheral surface of the shaft body, and a surface layer formed on the outer peripheral surface of the elastic layer, and the surface layer contains the following (A) to (D):
(A) one or more polymers selected from fluoropolymers and silicone polymers, each having a dielectric constant of 2.2 to 2.5; (B) carbon black; (C) one or more polymer dispersants selected from ester-type polyurethane polymer dispersants and polyethyleneimine polymer dispersants, each having a carboxyl group; (D) a polyamine polymer dispersant having a polyester structure in the side chain.

The DBP absorption of the (B) is preferably 115 cm ³ /100 g or more and 160 cm ³ /100 g or less, the specific surface area of the (B) is preferably 25 m ² /g or more and 75 m ² /g or less, and the average particle size of the (B) is preferably 35 nm or more and 75 nm or less. The surface layer contains roughness forming particles that form surface roughness, and the roughness forming particles may have either or both of a carbonyl group and a hydroxyl group. The content of the (D) relative to the (B) may be 1.5 to 3.0 in mass ratio. The content of the (C) relative to the (B) may be 1.5 to 3.0 in mass ratio. The polyester terminal of the (D) may be a ring. The (C) may have a polyalkylene oxide structure in the main chain. The carboxyl group of the (C) may be a carboxylate group having a quaternary amine structure.

The method for producing a charging roll for an electrophotographic device according to the present invention is such that the surface layer is formed from a surface layer composition containing the above-mentioned (A) to (D), and the surface layer composition is formed by mixing the above-mentioned (B) and the above-mentioned (D), then mixing the above-mentioned (C), and then mixing the above-mentioned (A).

The electrostatic charge roll for electrophotographic equipment according to the present invention comprises a shaft body, an elastic layer formed on the outer peripheral surface of the shaft body, and a surface layer formed on the outer peripheral surface of the elastic layer, and since the surface layer contains the above-mentioned (A) to (D), it has excellent electrostatic chargeability and uniform electrostatic chargeability.

When the DBP absorption of (B) is 115 ^cm3 /100g or more and 160 ^cm3 /100g or less, the specific surface area of (B) is 25 ^m2 /g or more and 75 ^m2 /g or less, and the average particle size of (B) is 35 nm or more and 75 nm or less, (B) can exhibit low resistance and high capacitance, thereby improving the charging property.

When the surface layer contains roughness-forming particles that form surface roughness and the roughness-forming particles have either or both of a carbonyl group and a hydroxyl group, the roughness-forming particles are made of a material with a high dielectric constant, which can improve charging properties.

When the content of (D) relative to (B) is 1.5 or more and 3.0 or less in mass ratio, the dispersion effect of (D) due to the steric hindrance of (B) is excellent, and the uniform charging property is improved.

When the content of (D) relative to (C) is 1.5 or more and 3.0 or less in mass ratio, the dispersion effect of the electrostatic repulsion of (B) by (C) is excellent, and the uniform charging property is improved.

If the polyester end of (D) is cyclic, the dispersion effect due to steric hindrance can be further improved.

When (C) has a polyalkylene oxide structure in the main chain, the electrostatic repulsion of (C) is enhanced, improving the dispersion effect of the electrostatic repulsion of (B) by (C), and improving the uniform charging property.

When the carboxyl group of (C) is a carboxylate group having a quaternary amine structure, the steric hindrance of (C) is enhanced, the dispersion effect of (B) due to the steric hindrance of (C) is improved, and the uniform charging property is improved.

And according to the manufacturing method of the electrophotographic device charge roll of the present invention, the surface layer is formed from a surface layer composition containing the above-mentioned (A) to (D), and the surface layer composition is formed by mixing the above-mentioned (B) and the above-mentioned (D), then mixing the above-mentioned (C), and then mixing the above-mentioned (A), so that it is possible to provide an electrophotographic device charge roll with excellent chargeability and uniform chargeability.

1A is a schematic external view of a charging roll for an electrophotographic device according to one embodiment of the present invention, and FIG. 1B is a cross-sectional view taken along line AA thereof.

The charging roll for electrophotographic equipment (hereinafter, simply referred to as the charging roll) according to the present invention will be described in detail. Figure 1 shows (a) a schematic view of the appearance of the charging roll for electrophotographic equipment according to one embodiment of the present invention, and (b) a cross-sectional view taken along line A-A.

The charged roll 10 comprises a shaft 12, an elastic layer 14 formed on the outer peripheral surface of the shaft 12, and a surface layer 16 formed on the outer peripheral surface of the elastic layer 14. The elastic layer 14 is a layer (base layer) that forms the base of the charged roll 10. The surface layer 16 is a layer that appears on the surface of the charged roll 10.

The shaft body 12 is not particularly limited as long as it is conductive. Specific examples include a core bar made of a solid or hollow body made of a metal such as iron, stainless steel, or aluminum. The surface of the shaft body 12 may be coated with an adhesive, primer, or the like as needed. In other words, the elastic layer 14 may be adhered to the shaft body 12 via an adhesive layer (primer layer). The adhesive, primer, or the like may be made conductive as needed.

The elastic layer 14 contains a crosslinked rubber. The elastic layer 14 is formed from a conductive rubber composition that contains uncrosslinked rubber. The crosslinked rubber is obtained by crosslinking the uncrosslinked rubber. The uncrosslinked rubber may be a polar rubber or a non-polar rubber.

Polar rubber is a rubber having polar groups, such as chloro groups, nitrile groups, carboxyl groups, and epoxy groups. Specific examples of polar rubber include hydrin rubber, nitrile rubber (NBR), urethane rubber (U), acrylic rubber (a copolymer of acrylic acid ester and 2-chloroethyl vinyl ether, ACM), chloroprene rubber (CR), and epoxidized natural rubber (ENR). Of the polar rubbers, hydrin rubber and nitrile rubber (NBR) are more preferred, as they tend to have a particularly low volume resistivity.

Examples of hydrin rubbers include epichlorohydrin homopolymer (CO), epichlorohydrin-ethylene oxide binary copolymer (ECO), epichlorohydrin-allyl glycidyl ether binary copolymer (GCO), and epichlorohydrin-ethylene oxide-allyl glycidyl ether terpolymer (GECO).

As an example of urethane rubber, there can be mentioned polyether-type urethane rubber having an ether bond in the molecule. Polyether-type urethane rubber can be produced by reacting a polyether having hydroxyl groups at both ends with a diisocyanate. As polyether, there is no particular limitation, but there can be mentioned polyethylene glycol, polypropylene glycol, etc. As diisocyanate, there is no particular limitation, but there can be mentioned tolylene diisocyanate, diphenylmethane diisocyanate, etc.

Non-polar rubbers include silicone rubber (Q), isoprene rubber (IR), natural rubber (NR), styrene butadiene rubber (SBR), butadiene rubber (BR), etc.

Examples of crosslinking agents include sulfur crosslinking agents, peroxide crosslinking agents, and dechlorination crosslinking agents. These crosslinking agents may be used alone or in combination of two or more.

Examples of sulfur crosslinking agents include powdered sulfur, precipitated sulfur, colloidal sulfur, surface-treated sulfur, insoluble sulfur, sulfur chloride, thiuram vulcanization accelerators, polymeric polysulfides, and other conventionally known sulfur crosslinking agents.

Examples of peroxide crosslinking agents include peroxyketals, dialkyl peroxides, peroxyesters, ketone peroxides, peroxydicarbonates, diacyl peroxides, and hydroperoxides.

Examples of dechlorinating crosslinking agents include dithiocarbonate compounds. More specifically, examples include quinoxaline-2,3-dithiocarbonate, 6-methylquinoxaline-2,3-dithiocarbonate, 6-isopropylquinoxaline-2,3-dithiocarbonate, and 5,8-dimethylquinoxaline-2,3-dithiocarbonate.

The amount of crosslinking agent to be mixed is preferably within the range of 0.1 to 2 parts by mass, more preferably within the range of 0.3 to 1.8 parts by mass, and even more preferably within the range of 0.5 to 1.5 parts by mass, per 100 parts by mass of uncrosslinked rubber, from the viewpoint of preventing bleeding.

When a dechlorination crosslinking agent is used as the crosslinking agent, a dechlorination crosslinking accelerator may be used in combination. Examples of the dechlorination crosslinking accelerator include 1,8-diazabicyclo(5,4,0)undecene-7 (hereinafter abbreviated as DBU) or its weak acid salt. The dechlorination crosslinking accelerator may be used in the form of DBU, but from the viewpoint of handling, it is preferable to use it in the form of its weak acid salt. Examples of the weak acid salt of DBU include carbonate, stearate, 2-ethylhexyl acid salt, benzoate, salicylate, 3-hydroxy-2-naphthoate, phenol resin salt, 2-mercaptobenzothiazole salt, and 2-mercaptobenzimidazole salt.

The content of the dechlorination crosslinking accelerator is preferably within the range of 0.1 to 2 parts by mass per 100 parts by mass of uncrosslinked rubber, from the viewpoint of preventing bleeding. It is more preferably within the range of 0.3 to 1.8 parts by mass, and even more preferably within the range of 0.5 to 1.5 parts by mass.

The elastic layer 14 may contain a conductive agent to provide electrical conductivity. Examples of the conductive agent include electronic conductive agents and ionic conductive agents. Examples of the electronic conductive agent include carbon black, graphite, and conductive metal oxides. Examples of the conductive metal oxide include conductive titanium oxide, conductive zinc oxide, and conductive tin oxide. Examples of the ionic conductive agent include quaternary ammonium salts, borates, and surfactants. In addition, various additives may be added to the elastic layer 14 as necessary. Examples of the additives include lubricants, vulcanization accelerators, antioxidants, light stabilizers, viscosity adjusters, processing aids, flame retardants, plasticizers, foaming agents, fillers, dispersants, defoamers, pigments, and mold release agents.

The elastic layer 14 can be adjusted to a predetermined volume resistivity by the type of crosslinked rubber, the amount of ionic conductive agent, the amount of electronic conductive agent, etc. The volume resistivity of the elastic layer 14 may be appropriately set to a range of ¹⁰ to ¹⁰ Ω·cm, ¹⁰ to 10 Ω·cm, 10 to ¹⁰ Ω·cm, or ¹⁰ to ¹⁰ Ω·cm depending on the application, etc.

The thickness of the elastic layer 14 is not particularly limited and may be set appropriately within the range of 0.1 to 10 mm depending on the application.

The surface layer 16 contains the following (A) to (D).
(A) one or more polymers selected from fluoropolymers and silicone polymers, each having a dielectric constant of 2.2 to 2.5; (B) carbon black; (C) one or more polymer dispersants selected from ester-type polyurethane polymer dispersants and polyethyleneimine polymer dispersants, each having a carboxyl group; (D) a polyamine polymer dispersant having a polyester structure in the side chain.

(A) is one or more polymers selected from fluoropolymers and silicone polymers. In this way, since (A) is a material with low dielectric constant and low abrasion, it is possible to suppress contamination of toner and toner additives. On the other hand, if (A) has a low dielectric constant, it has poor compatibility with (B) carbon black, and the dispersibility of (B) carbon black decreases. This reduces the uniform charging ability. For this reason, in the present invention, the above-mentioned two types of dispersants (C) and (D) with different properties are used in combination. This makes it possible to increase the dispersibility of (B) carbon black and achieve excellent uniform charging ability even when using a binder with a low dielectric constant such as (A).

In (A), the fluoropolymer is a polymer containing a fluorine group. Examples of the fluoropolymer include polytetrafluoroethylene (PTFE), perfluoroalkoxyalkane (PFA), perfluoroethylenepropene copolymer (FEP), ethylenetetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVDF), and the like. The silicone polymer may be one that is generally and widely known as organopolysiloxane. The silicone polymer may have a modified group. Examples of the modified silicone polymer include phenyl-modified silicone, ether-modified silicone, and ester-modified silicone.

The one or more polymers selected from fluoropolymers and silicone polymers (A) have a dielectric constant of 2.2 or more and 2.5 or less. In this way, since (A) is a material with a low dielectric constant and low wear properties, it is possible to suppress contamination of toner and toner external additives. In addition, since the dielectric constant of (A) is within the above range, the charging roll 10 can exhibit excellent charging properties. If the dielectric constant of (A) is less than 2.2, the electrostatic capacitance of (A) becomes small and the charging properties become poor. From this viewpoint, the dielectric constant of (A) is preferably 2.3 or more. On the other hand, if the dielectric constant of (A) is more than 2.5, the dipole moment of (A) increases, and the dispersants of (C) and (D) tend to adhere to (A), the interaction between (C) and (D) and (B) becomes small, and the dispersibility of (B) carbon black decreases. In addition, if the dielectric constant of (A) is more than 2.5, the charging properties become more environmentally dependent and the environmental dependency becomes poor. From this perspective, the relative dielectric constant of (A) is preferably 2.4 or less.

(B) Carbon black contributes to improving electrostatic chargeability. From the viewpoint of improving electrostatic chargeability, it is preferable that (B) carbon black has a DBP absorption amount, specific surface area, and average particle size within a specified range in order to exhibit low resistance and high electrostatic capacity.

From the viewpoint of improving capacitance, the DBP absorption of the carbon black (B) is preferably 115 ^cm3 /100g or more, more preferably 120 ^cm3 /100g or more, and even more preferably 130 ^cm3 /100g or more. On the other hand, from the viewpoint of improving dischargeability, the DBP absorption of the carbon black (B) is preferably 160 ^cm3 /100g or less, more preferably 150 ^cm3 /100g or less, and even more preferably 140 ^cm3 /100g or less. The DBP absorption of the carbon black is calculated from the amount of DBP (dibutyl phthalate) absorbed by 100 g of carbon black in accordance with JIS K6221.

From the viewpoint of improving the electrostatic capacity, it is preferable that the (B) carbon black has a relatively small specific surface area and a large particle size. Specifically, the (B) carbon black has a specific surface area of preferably 75 m ² /g or less, more preferably 70 m ² /g or less, and even more preferably 60 m ² /g or less. The average particle size is preferably 35 nm or more, and more preferably 40 nm or more. On the other hand, from the viewpoint of low resistance, the (B) carbon black has a specific surface area of preferably 25 m ² /g or more, more preferably 30 m ² /g or more. The average particle size is preferably 75 nm or less, more preferably 70 nm or less, and even more preferably 60 nm or less. The specific surface area of the carbon black is a value measured by the BET method. The average particle size of the carbon black is represented by an arithmetic mean diameter obtained by observing the carbon black with an electron microscope.

From the viewpoint of easily securing capacitance, the content of (B) carbon black is preferably 5 parts by mass or more per 100 parts by mass of (A). More preferably, it is 10 parts by mass or more, and even more preferably, it is 20 parts by mass or more. Also, from the viewpoint of easily suppressing insufficient discharge, the content of (B) carbon black is preferably 75 parts by mass or less per 100 parts by mass of (A). More preferably, it is 70 parts by mass or less, and even more preferably, it is 60 parts by mass or less. And, when the content of (B) carbon black is 5 parts by mass or more and 75 parts by mass or less per 100 parts by mass of (A), it is easy to maintain the resistance and capacitance within a suitable range.

(C) and (D) are used in combination to improve the dispersibility of (B) carbon black in (A) with a low dielectric constant. Using only (C) or (D) alone does not provide sufficient dispersion effect of (B) in (A), and uniform charging is not possible.

(C) is a dispersant having a carboxyl group. The carboxyl group includes both carboxylic acid (-COOH) and carboxylate (-COOM). M represents a metal having a valence of one or more or a quaternary amine. (C) is adsorbed to the surface of (B) carbon black, and by having a carboxyl group, it suppresses the aggregation of the particles of (B) carbon black due to electrical repulsion, thereby improving the dispersibility of (B) carbon black. As the carboxyl group, a carboxylate salt group having a quaternary amine structure is particularly preferable. The steric hindrance of (C) is increased, the dispersion effect of (B) due to the steric hindrance of (C) is improved, and the uniform charging is improved.

(C) is a polymeric dispersant composed of a polymer. Because it has a larger molecular weight than low-molecular-weight dispersants such as fatty acids and fatty acid salts, it is expected to have a dispersing effect on the carbon black (B) by utilizing steric hindrance. Examples of polymeric dispersants (C) include ester-type polyurethane polymeric dispersants and polyethyleneimine polymeric dispersants. These may be included alone as (C), or two or more types may be combined.

Ester-type polyurethane polymer dispersants tend to achieve a large electrostatic repulsion effect due to the large dipole moment of the ester-type urethane group (-NH-COO-). Polyethyleneimine polymer dispersants also tend to achieve a large electrostatic repulsion effect due to the large dipole moment of the imine group and the large number of NH groups in the polyethyleneimine.

Ester type polyurethane has an ester bond in the molecule. Ester type polyurethane contains polyester polyol as a polyol component. Examples of polyester polyol include polyethylene adipate, polybutylene adipate, polyhexylene adipate, copolymers of ethylene adipate and butylene adipate, carbonate diol, etc. Examples of the isocyanate component of polyurethane include, but are not limited to, tolylene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), etc.

(C) may have a polyalkylene oxide structure in the main chain. Having a polyalkylene oxide structure in the main chain increases the electrostatic repulsion. Examples of polyalkylene oxide structures include a polyethylene oxide structure and a polypropylene oxide structure.

Examples of ester-type polyurethane polymer dispersants having carboxyl groups include Lubrizol's Solsperse 75500, 76500, 82500, and 83500. Examples of polyethyleneimine polymer dispersants having carboxyl groups include Lubrizol's Solsperse 32500.

The content of (C) is preferably 1.5 or more and 3.0 or less in mass ratio to (B). By making the content 3.0 or less, aggregation of (C) is suppressed, and the decrease in chargeability is suppressed. From this viewpoint, the content is more preferably 2.5 or less. On the other hand, by making the content 1.5 or more, the dispersion effect of (B) due to the electrostatic repulsion of (C) can be increased. From this viewpoint, the content is more preferably 2.0 or more.

(D) is a polyamine-based polymer dispersant. The amino groups at the ends of the polyamine molecular chain have good affinity with the carboxyl and hydroxyl groups on the carbon black surface, and can preferentially adsorb to the carbon black surface. (D) is a polyamine-based polymer dispersant (a polymer dispersant composed of polymers), which suppresses the aggregation of (B) carbon black particles due to steric hindrance, thereby improving the dispersibility of (B) carbon black.

(D) has a polyester structure in the side chain. This can further improve the dispersion effect due to steric hindrance. Furthermore, if the polyester end is a cyclic unit, the dispersion effect due to steric hindrance can be further improved. Examples of cyclic units at the polyester end include caprolactone.

Examples of polyamine-based polymer dispersants with a polyester structure in the side chain include Lubrizol's Solsperse 13240 and 24000. Other examples include Ajisper PB821 manufactured by Ajinomoto Fine-Techno.

The content of (D) is preferably 1.5 or more and 3.0 or less in mass ratio to (B). When the content is 3.0 or less, it is easy to secure a portion to which (C) can adhere to the surface of the (B) carbon black, and it is easy to secure the dispersion effect of (B) by (C). This makes it easy to secure the combined effect of (C) and (D). From this viewpoint, the content is more preferably 2.5 or less. On the other hand, when the content is 1.5 or more, it is possible to increase the dispersion effect of (B) due to the steric hindrance of (D). From this viewpoint, the content is more preferably 2.0 or more.

The ratio of the amounts of (C) and (D) is preferably 0.6 to 1.5 by mass ratio relative to (C), from the viewpoint that the dispersion effect of (B) by (C) and the dispersion effect of (B) by (D) can be easily achieved at the same time.

The surface layer 16 may contain roughness-forming particles. The roughness-forming particles are particles for imparting roughness to the surface of the surface layer 16. In other words, they are particles for imparting unevenness to the surface of the surface layer 16. The surface unevenness of the surface layer 16 increases the discharge space between the photoreceptor and the charging roll 10, promoting discharge. This improves charging properties and suppresses image defects such as horizontal streaks and unevenness.

The roughness-forming particles are made of resin particles or the like. The material of the roughness-forming particles is not particularly limited. The roughness-forming particles are preferably made of a polymer having a carbonyl group or a polymer having a hydroxyl group. This is because a polymer having a carbonyl group or a polymer having a hydroxyl group is a material with a relatively high dielectric constant, and the charging roll 10 can easily ensure excellent charging properties. Examples of polymers having carbonyl groups include urethane resin, polyamide resin, acrylic resin, acrylic silicone resin, silicone graft acrylic polymer, acrylic graft silicone polymer, and urethane rubber. Examples of polymers having hydroxyl groups include epoxy resin.

The size of the roughness-forming particles is not particularly limited, but from the viewpoint of easily ensuring uniform charging properties, an average particle diameter of 3.0 μm or more and 50 μm or less is preferable. More preferably, an average particle diameter of 5.0 μm or more and 30 μm or less is preferable. The average particle diameter of the roughness-forming particles is expressed as the average of any 20 points when the surface of the surface layer 16 is observed with a laser microscope, and the diameter of the roughness-forming particles visible when observing the surface is taken as the particle diameter.

The content of the roughness-forming particles in the surface layer 16 is not particularly limited, but from the viewpoint of easily ensuring uniform charging properties, it is preferably 3 parts by mass or more and 50 parts by mass or less per 100 parts by mass of the binder polymer (A) in the surface layer 16. More preferably, it is 5 parts by mass or more and 30 parts by mass or less.

The volume resistivity of the surface layer 16 is preferably set in the semiconductive region from the viewpoint of electrostatic chargeability. Specifically, for example, it is preferably set in the range of 1.0×10 ⁷ to 1.0×10 ¹⁰ Ω·cm. The volume resistivity can be measured in accordance with JIS K6911. The thickness of the surface layer 16 is not particularly limited, and is preferably set in the range of 0.1 to 3.0 μm. The thickness of the surface layer 16 can be measured by observing the cross section using a laser microscope (for example, Keyence's "VK-9510"). For example, the distance from the surface of the elastic layer 14 to the surface of the surface layer 16 is measured at five arbitrary positions, and the thickness can be expressed by the average of the measured distances.

The charged roll 10 can be produced by forming an elastic layer 14 on the outer circumferential surface of the shaft and forming a surface layer 16 on the outer circumferential surface of the elastic layer 14.

The elastic layer 14 can be formed, for example, as follows. First, the shaft is placed coaxially in the hollow portion of a roll molding die, and an uncrosslinked elastic layer forming composition is injected and heated and cured (crosslinked), after which the composition is demolded, or the uncrosslinked elastic layer forming composition is extruded onto the surface of the shaft to form the elastic layer 14 on the outer periphery of the shaft.

To form the surface layer 16, a surface layer composition is used. The surface layer composition includes the above (A) to (D). The surface layer composition can be formed by mixing (B) and (D), then mixing (C), and then mixing (A). By mixing (D) with (B) before (C), (C) and (D) can be appropriately adsorbed to (B). If (C) is mixed with (B) before (D), (D) is less likely to be adsorbed to (B), and the dispersion effect of (D) for (B) is less likely to be obtained.

The surface layer composition may contain an appropriate solvent, such as organic solvents such as methyl ethyl ketone, toluene, acetone, ethyl acetate, butyl acetate, methyl isobutyl ketone (MIBK), THF, or DMF, or water-soluble solvents such as methanol or ethanol, in order to adjust the viscosity.

The surface layer 16 can be formed by a method such as coating a surface layer composition on the outer peripheral surface of the elastic layer 14. Various coating methods such as roll coating, dipping, and spray coating can be used as the coating method. The coated surface layer 16 may be irradiated with ultraviolet light or heat treated as necessary.

According to the charging roll 10 having the above configuration, the surface layer 16 uses two types of dispersants (C) and (D) in combination as a dispersant for the carbon black (B), so that the carbon black can be well dispersed even in fluoropolymers and silicone polymers, which are binders in which carbon black is difficult to disperse. Furthermore, due to the charging effect of the carbon black and the dispersing effect of that carbon black, the charging roll 10 has excellent charging properties and uniform charging properties.

The present invention will be described in detail below using examples and comparative examples.

Example 1
<Preparation of Conductive Rubber Composition>
A conductive rubber composition was prepared by compounding 100 parts by mass of isoprene rubber with 30 parts by mass of carbon black, 6 parts by mass of zinc oxide, 2 parts by mass of stearic acid, 1 part by mass of sulfur, 0.5 parts by mass of a thiazole-based vulcanization accelerator, 0.5 parts by mass of a thiuranium-based vulcanization accelerator, and 50 parts by mass of heavy calcium carbonate, and kneading the mixture for 10 minutes using an internal mixer adjusted to a temperature of 50°C.

As materials for the conductive rubber composition, the following materials were prepared.
・Isoprene rubber (IR): JSR "JSR IR2200"
・Carbon black: Cabot Japan "Show Black N762"
・Zinc oxide: Sakai Chemical Industry's "Zinc oxide type 2"
・Stearic acid: "Sakura Stearic Acid" manufactured by Nippon Oil & Fats
・Sulfur: "Powdered sulfur" manufactured by Tsurumi Chemical Industry Co., Ltd.
- Thiazole-based vulcanization accelerator: "Noccela DM" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
- Thiam-based vulcanization accelerator: "Noccela TRA" manufactured by Ouchi Shinko Chemical Industry Co., Ltd.
Heavy calcium carbonate: "Whiten B" manufactured by Shiraishi Calcium, average particle size 3.6 μm

<Preparation of Elastic Layer>
A core bar (diameter 8 mm) was set in a molding die (pipe-shaped), the above composition was injected, and the die was heated at 180°C for 30 minutes. The die was then cooled and demolded to form an elastomer layer made of a conductive rubber elastomer having a thickness of 1.9 mm around the outer periphery of the core bar.

<Preparation of surface layer>
In the compounding composition (parts by mass) shown in Table 1, the carbon black <B-1> was mixed with the dispersant <D-1> having an aromatic ring, then mixed with the dispersant <C-1> having a carboxyl group, then mixed with the binder <A-1> and the roughness forming particles <1>, and 200 parts by mass of methyl ethyl ketone (MEK) was added, and the mixture was mixed and stirred at a predetermined stirring speed to prepare a surface layer composition. Next, while continuing to stir, this surface layer composition was roll-coated on the outer peripheral surface of the elastic layer, and a heat treatment was performed to form a surface layer having a thickness of 1.0 μm on the outer periphery of the elastic layer. In this way, the charging roll of Example 1 was produced.

(Examples 2 to 11, Comparative Examples 1 to 4)
A charging roll was produced in the same manner as in Example 1, except that the surface layer composition had the composition shown in Table 1.

The following materials were prepared as the surface layer composition.
(binder)
A-1: Silicone polymer (dielectric constant 2.2), "SLK" manufactured by Shin-Etsu Chemical Co., Ltd.
A-2: Fluoropolymer (dielectric constant 2.5), Daikin's "Neoflon PCTFE"
・X-1: Fluorine polymer (dielectric constant 2.1), Daikin's "Neoflon PFA"
・X-2: Fluoropolymer (dielectric constant 2.6), Daikin's "Neoflon ETFE"
(Carbon Black)
B-1 (DBP absorption capacity 124 ml/100 g, BET specific surface area 43 ^{m 2} /g, average particle size 41 nm): Asahi #60H (N-568) manufactured by Asahi Carbon
B-2 (DBP absorption capacity 160 ml/100 g, BET specific surface area 75 ^{m 2} /g, average particle size 35 nm): "Denka Black" manufactured by Denka
B-3 (DBP absorption capacity 115 ml/100 g, BET specific surface area 42 m ² /g, average particle size 44 nm): "Seest SO" manufactured by Tokai Carbon
B-4 (DBP absorption capacity 155 ml/100 g, BET specific surface area 25 m ² /g, average particle size 75 nm): "Seest GFY" manufactured by Tokai Carbon
B-5 (DBP absorption capacity 125 ml/100 g, BET specific surface area 126 ^{m 2} /g, average particle size 25 nm): "Seest 7HM" manufactured by Tokai Carbon
Y-1 (DBP absorption capacity 175 ml/100 g, BET specific surface area 165 ^{m 2} /g, average particle size 20 nm): "#3400B" manufactured by Mitsubishi Chemical
Y-2 (DBP absorption capacity 58 ml/100 g, BET specific surface area 180 ^{m 2} /g, average particle size 18 nm): "#1000" manufactured by Mitsubishi Chemical
Y-3 (DBP absorption capacity 360 ml/100 g, BET specific surface area 800 m ² /g, average particle size 32 nm): "Ketjen EC300J" manufactured by Ketjen Black International
(Dispersant)
C-1: Carboxyl group-containing ester-type polyurethane polymer dispersant, Lubrizol's "Solsperse 75500"
C-2: Polyethyleneimine-based polymer dispersant having a carboxyl group, "Solsperse 32500" manufactured by Lubrizol
D-1: Polyamine polymer dispersant with polyester structure in the side chain, Lubrizol's "Solsperse 24000"
D-2: Polyethyleneimine-based polymer dispersant with polyester structure in the side chain, "Ajisper PB821" manufactured by Ajinomoto Fine Techno
Z-1: An ester-type polyurethane polymer dispersant that does not have a carboxyl group, "Solsperse 32600" manufactured by Lubrizol
Z-2: Polyamine polymer dispersant that does not have a polyester structure in the side chain, "Disparlon DA-234" manufactured by Kusumoto Chemicals
(Roughness forming particles)
PMMA: "Chemisnow MX3000" manufactured by Soken Chemical, average particle size 30 μm
Epoxy: Toray "Trepearl EP", average particle size 30 μm
Urethane: Negami Industrial Co., Ltd. "Art Pearl C200", average particle size 30 μm

The following image evaluations were performed on the prepared charging roll.

(White dots: Evaluation of carbon black dispersibility)
The produced charging roll was attached to a unit (black) of an actual machine (RICOH "MP C6004"), and images were output in 25% density halftone in a 10°C x 10% RH environment, and evaluation was performed after 500,000 sheets were printed. Images with no white spots were rated as particularly good "◎", images with white spots found in the image but within the acceptable range were rated as good "◯", and images with white spots found in the image but outside the acceptable range were rated as poor "×".

(Black dots: Evaluation of dispersibility of dispersant C)
The produced charging roll was attached to a unit (black) of an actual machine ("MP C6004" manufactured by RICOH), and images were output in 25% density halftone in an environment of 10°C x 10% RH, and evaluation was performed after 500,000 sheets were printed. Images with no black spots were rated as particularly good "◎", images with black spots found in the image but within the acceptable range were rated as good "◯", and images with black spots found in the image but outside the acceptable range were rated as poor "×".

(Fog: Low dielectric constant)
The produced charging roll was attached to a unit (black) of an actual machine ("MP C6004" manufactured by RICOH), and images were output in 25% density halftone in an environment of 10°C x 10% RH, and evaluation was performed after 500,000 sheets were printed. Images with no fog were rated as particularly good "◎", images with fog found in the image but within the acceptable range were rated as good "◯", and images with fog found in the image but outside the acceptable range were rated as poor "×".

(White stripes: high dielectric constant)
The produced charging roll was attached to a unit (black) of an actual machine (RICOH "MP C6004"), and images were output in 25% density halftone in an environment of 35°C x 80% RH, and evaluation was performed after 500,000 sheets were printed. Images with no white streaks were rated as particularly good "◎", images with white streaks found in the image but within the acceptable range were rated as good "◯", and images with white streaks found in the image but outside the acceptable range were rated as poor "×".

In Comparative Example 1, the relative dielectric constant of the binder polymer in the surface layer is too low, so the capacitance is small and the charging property is poor, resulting in fogging. In Comparative Example 2, the relative dielectric constant of the binder polymer in the surface layer is too high, so the compatibility between the binder polymer and dispersant C is too high, which reduces the dispersion effect of the carbon black and causes white spots outside the allowable range. In addition, the charging property becomes highly environmentally dependent, and white streaks occur in a high temperature and high humidity environment (LL environment). In Comparative Example 3, in a specified binder polymer, a polyethyleneimine-based polymer dispersant D having a polyester structure in the side chain is blended with carbon black, but a dispersant C having a carboxyl group is not blended. As a result, the dispersibility of carbon black is poor, and white spots outside the allowable range occur. In Comparative Example 4, in a specified binder polymer, a dispersant C having a carboxyl group is blended with carbon black, but a polyethyleneimine-based polymer dispersant D having a polyester structure in the side chain is not blended. As a result, the dispersibility of carbon black is poor, and white spots outside the allowable range occur.

On the other hand, in the examples, the surface layer contains (A) one or more polymers selected from fluoropolymers and silicone polymers having a dielectric constant of 2.2 to 2.5, (B) carbon black, (C) one or more polymer dispersants selected from ester-type polyurethane polymer dispersants and polyethyleneimine polymer dispersants having a carboxyl group, and (D) a polyamine polymer dispersant having a polyester structure in the side chain, and therefore it is understood that the dispersibility of carbon black is excellent, and the uniform charging property and charging property are excellent.

And, from a comparison between the Examples (Examples 1-2 and Examples 4-6), it can be seen that when the DBP absorption amount, specific surface area, and average particle size of carbon black are within the specified ranges, no fogging is observed in the image, the resistance is low, the electrostatic capacity is high, and the charging properties are excellent. And, from a comparison between the Examples (Examples 1-3 and Examples 7-8), it can be seen that when the content of (C) relative to (B) is within the specified ranges, no black spots are observed in the image, and the charging properties are excellent. It can also be seen that no white spots are observed in the image, and the charging properties are excellent. And, from a comparison between the Examples (Examples 1-3 and Examples 9-10), it can be seen that when the content of (D) relative to (B) is within the specified ranges, no white spots are observed in the image, and the charging properties are excellent.

Although the embodiments and examples of the present invention have been described above, the present invention is in no way limited to the above embodiments and examples, and various modifications are possible without departing from the spirit of the present invention.

10: charging roll 12: shaft body 14: elastic layer 16: surface layer

Claims (9)

The shaft body includes an elastic layer formed on an outer peripheral surface of the shaft body, and a surface layer formed on the outer peripheral surface of the elastic layer,
The surface layer of the charging roll for electrophotographic equipment contains the following (A) to (D):
(A) one or more polymers selected from fluoropolymers and silicone polymers, each having a dielectric constant of 2.2 to 2.5; (B) carbon black; (C) one or more polymer dispersants selected from ester-type polyurethane polymer dispersants and polyethyleneimine polymer dispersants, each having a carboxyl group; (D) a polyamine polymer dispersant having a polyester structure in the side chain. ^2. The charging roll for an electrophotographic device according to claim 1, wherein the DBP absorption of said (B) is 115 ^cm3 /100g or more and 160 ^cm3 /100g or less, the specific surface area of said (B) is 25 ^m2 /g or more and 75 m2/g or less, and the average particle size of said (B) is 35 nm or more and 75 nm or less. The electrostatic charge roll for electrophotographic equipment according to claim 1 or 2, wherein the surface layer contains roughness-forming particles that form surface roughness, and the roughness-forming particles have either or both of a carbonyl group and a hydroxyl group. The electrostatic charge roll for electrophotographic equipment according to any one of claims 1 to 3, wherein the content of (D) relative to (B) is 1.5 or more and 3.0 or less in mass ratio. The electrostatic charge roll for electrophotographic equipment according to any one of claims 1 to 4, wherein the content of (C) relative to (B) is 1.5 or more and 3.0 or less in mass ratio. The electrostatic charge roll for electrophotographic equipment according to any one of claims 1 to 5, wherein the polyester end of (D) is a cyclic body. The electrostatic charge roll for electrophotographic equipment according to any one of claims 1 to 6, wherein (C) has a polyalkylene oxide structure in the main chain. The electrostatic charge roll for electrophotographic equipment according to any one of claims 1 to 7, wherein the carboxyl group of (C) is a carboxylate group having a quaternary amine structure. A method for producing a charging roll for an electrophotographic device according to any one of claims 1 to 8, comprising the steps of:
the surface layer is formed of a surface layer composition containing the components (A) to (D),
the surface layer composition is formed by mixing (B) and (D), then mixing (C), and then mixing (A).

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