Developing roller, process cartridge and electrophotographic image forming apparatus

Abstract

To provide a developing roller that can suppress occurrence of density unevenness even when printing a large number of sheets in a low-temperature and low-humidity environment.SOLUTION: A developing roller has: an electric conductive base body; and an electric conductive elastic layer that is a single layer on an exterior circumference of the base body. The elastic layer includes a dien-based rubber, and the elastic layer has a crown shape in which an outer diameter of a central part in a longitudinal direction along an axis of the base body is larger than that of both end parts in the longitudinal direction. A thickness of the elastic layer is equal to or more than 0.30 mm. Let a length in the longitudinal direction of the elastic layer be L, each position of (1 / 10)L, (1 / 2)L and (9 / 10)L from one end in the longitudinal direction of the elastic layer toward other end therein be P1, P2 and P3 respectively, in a cross-section in a thickness direction of the P1, P2 and P3, and an elasticity modulus in a first area from an outer surface of the elastic layer to 0.1 μm of a depth thereof be E11, E12 and E13 respectively, E11, E12 and E13 are all more than 500 MPa.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present disclosure relates to a developing roller incorporated in an apparatus employing an electrophotographic system, and also to a process cartridge and an electrophotographic image forming apparatus using the developing roller. [Background technology]

[0002] In electrophotographic image forming devices (also called electrophotographic devices) such as copying machines, facsimiles, and printers that use the electrophotographic method, images are formed through the following steps: a step of charging the surface of an image carrier, a step of forming an electrostatic latent image on the surface of the image carrier using a laser or the like, a step of developing the electrostatic latent image with toner, a step of transferring the developed toner image to recording paper, and a step of fixing the transferred image on the recording paper using heat and pressure. In addition, after transfer to the recording paper, there is a cleaning step in which any toner remaining on the image carrier is removed with a cleaning blade. The development of an electrostatic latent image with toner is achieved by applying toner from a developer container to the surface of a developing roller using a toner supply member and a toner regulating member, and then the developing roller comes into contact with or is close to an image carrier, whereby the toner is attracted to the electrostatic latent image. A commonly used developing roller has a conductive substrate and an elastic layer provided on the outer periphery of the conductive substrate. The elastic layer may be a laminate of multiple layers or a single layer. A diene rubber with high impact resilience may be used for the single-layer elastic layer. However, when a developing roller equipped with a single-layer elastic layer containing a diene rubber is brought into contact with an image carrier, the developing roller may bend due to the rubber elasticity of the elastic layer. As a result, the width of the nip in the axial direction (longitudinal direction) may become uneven. This unevenness in the axial width of the nip can be solved by changing the shape of the elastic layer of the developing roller, as disclosed in Patent Document 1, so that the outer diameter is larger at the center than at the longitudinal ends of the developing roller (hereinafter referred to as a crown shape). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 4-336561 Summary of the Invention [Problem to be solved by the invention]

[0004] However, when the present inventors investigated a developing roller having a single elastic layer containing a diene rubber and having a crown shape, they found that when the developing roller was used to form a large number of electrophotographic images, for example, 300,000 sheets, in a low-temperature, low-humidity environment, density unevenness sometimes occurred in the electrophotographic images. One aspect of the present disclosure is directed to providing a developing roller that contributes to the stable formation of high-quality electrophotographic images even when used to form electrophotographic images over a long period of time in a low-temperature, low-humidity environment. Another aspect of the present disclosure is directed to providing an electrophotographic process cartridge that contributes to the stable formation of high-quality electrophotographic images over a long period of time. Still another aspect of the present disclosure is directed to providing an electrophotographic image forming apparatus that can stably form high-quality electrophotographic images over a long period of time. [Means for solving the problem]

[0005] According to one aspect of the present disclosure, a conductive substrate; a conductive elastic layer consisting of a single layer on the outer periphery of the substrate; A developing roller having The elastic layer 、 Contains diene rubber, The elastic layer has an outer diameter of a central portion in a longitudinal direction along the axis of the base. is applicable The crown shape is larger than the outer diameter of both ends in the longitudinal direction, The thickness of the elastic layer is 、 0.30 mm or more, The length of the elastic layer in the longitudinal direction is L, and the positions of (1 / 10)L, (1 / 2)L, and (9 / 10)L from one end to the other end of the elastic layer in the longitudinal direction are respectively P1, P2 and P3, Said P1, Applicable P2 and Applicable In the cross section in the thickness direction at each position P3, when the elastic moduli in the first region from the outer surface of the elastic layer to a depth of 0.1 μm are E11, E12, and E13, respectively, Applicable E11, Applicable E12 and Applicable All E13s are 500 MPa or higher. the law of nature, In the cross section in the thickness direction of the elastic layer at each of the positions P1, P2, and P3, The elastic moduli of a second region at a depth of 0.5 μm or more and 0.6 μm or less from the outer surface of the elastic layer are defined as E21, E22, and E23, respectively; When the elastic moduli of the third region at a depth of 1.0 μm or more and 1.1 μm or less from the outer surface of the elastic layer are E31, E32, and E33, respectively, The E11, the E12, the E13, the E21, the E22, the E23, the E31, the E32, and the E33 satisfy any of the following formulae (1) to (3): E11≧E21≧E31 (1) E12≧E22≧E32 (2) E13≧E23≧E33 (3) When the elastic moduli of a fourth region at a depth of 5.0 μm or more and 5.1 μm or less from the outer surface of the elastic layer in the cross section in the thickness direction of the elastic layer at each of the positions P1, P2, and P3 are E41, E42, and E43, respectively, The E41, E42 and E43 are all 100 MPa or less. Characterized by A developer roller is provided.

[0006] According to another aspect of the present disclosure, there is provided a process cartridge configured to be detachably mountable to a main body of an electrophotographic image forming apparatus, comprising: The process cartridge is The developing roller according to the above aspect 、 Characterized by A process cartridge is provided.

[0007] Furthermore, according to another aspect of the present disclosure, there is provided a toner image forming apparatus including at least an image carrier, a charging device, a developing device, and a transfer device for transferring the formed image onto recording paper. An electrophotographic image forming apparatus , The developing device has the developing roller according to the above aspect. 、 Characterized by An electrophotographic imaging apparatus is provided. [Effects of the Invention]

[0008] According to one aspect of the present disclosure, it is possible to provide a developing roller capable of suppressing the occurrence of density unevenness even when printing a large number of sheets in a low-temperature, low-humidity environment. Also, according to another aspect of the present disclosure, it is possible to provide an electrophotographic process cartridge and an electrophotographic image forming apparatus having the developing roller. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic cross-sectional view of a developing roller according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic diagram illustrating a development roller according to one aspect of the present disclosure. [Figure 3] 3 is a schematic cross-sectional view showing a measurement position of the elastic modulus of the elastic layer of the developing roller according to one embodiment of the present disclosure. FIG. [Figure 4] 1 is a schematic diagram illustrating an electrophotographic process cartridge according to one embodiment of the present disclosure. [Figure 5] 1 is a schematic diagram illustrating an electrophotographic image forming apparatus according to one aspect of the present disclosure. [Figure 6] FIG. 1 is a schematic diagram showing a dielectric relaxation measurement device used to measure surface potential unevenness in the present disclosure. [Figure 7] 10 is a schematic view showing an electron beam treatment device used in manufacturing a developing roller according to Comparative Example 3. FIG. [Figure 8] 10A and 10B are explanatory diagrams illustrating a method for measuring a current value of a developing roller according to an actual example and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present inventors conducted extensive research to determine the cause of density unevenness in electrophotographic images caused by long-term use in a low-temperature, low-humidity environment of a developing roller having a single-layer conductive elastic layer containing a diene rubber and having a crown shape. During this research, they discovered that when an electrophotographic image having density unevenness was formed on the developing roller, the electrical resistance measured on the surface varied along its axial direction. Based on this finding, the inventors deduced that this phenomenon of differing electrical resistance along the axial direction was due to the crown shape. That is, in a crown-shaped elastic layer, the amount of compression of the elastic layer at the nip portion varied along its axial direction. Specifically, for example, the amount of compression at the center in the axial direction is greater than the amount of compression at the end portions. This difference in compression amount results in a difference in the electrical resistance of the elastic layer at the nip portion. This causes a difference in the amount of current flowing through the elastic layer along its axial direction. Over long-term use, the difference in the amount of current flowing through the diene rubber gradually increases along the axial direction of the elastic layer, and as a result, the degree of deterioration of the diene rubber varies along the axial direction. As a result, it is believed that the electrical resistance of the elastic layer varies in the axial direction. The present inventors have conducted further studies to solve the above-mentioned problems caused by the conductive elastic layer having a crown shape, and have found that making the region near the very surface of the elastic layer, specifically the region up to a depth of 0.1 μm from the outer surface, less susceptible to distortion even in the nip portion can contribute to solving the above-mentioned problems. Specifically, when the thickness of the elastic layer is 0.30 mm or more, the length of the elastic layer in the longitudinal direction is L, and positions P1, P2, and P3 from one end of the elastic layer to the other in the longitudinal direction are (1 / 10)L, (1 / 2)L, and (9 / 10)L, respectively, and the moduli of elasticity in a first region from the outer surface of the elastic layer to a depth of 0.1 μm in the cross section in the thickness direction at each of positions P1, P2, and P3 are E11, E12, and E13, respectively, E11, E12, and E13 are all 500 MPa or more. It has been found that a developing roller having such an elastic layer is less likely to cause density unevenness in electrophotographic images even when used for forming electrophotographic images over a long period of time in a low-temperature, low-humidity environment.

[0011] <Developing roller> A schematic cross-sectional view of a developing roller 10 according to one embodiment of the present disclosure is shown in FIG. 1, but the shape of the developing roller is not limited to this. FIG. 1(a) is a circumferential cross-sectional view of a developing roller 10a having a solid conductive substrate 11a and an elastic layer 12 provided on the outer periphery of the substrate 11a. FIG. 1(b) is a circumferential cross-sectional view of a developing roller 10b having a hollow cylindrical conductive substrate 11b and an elastic layer 12 provided on the outer periphery of the substrate 11b. The hollow cylindrical substrate 11b has a hollow portion, which reduces weight and makes it suitable for developing rollers with larger outer diameters. In the following description, the developing roller will be referred to as 10 and the conductive substrate as 11.

[0012] [Conductive substrate] The conductive substrate 11 (11a, 11b) can be a cylindrical or hollow cylindrical conductive mandrel, or one in which a single or multiple conductive intermediate layers are further provided on the outer periphery of such a mandrel. The mandrel has a cylindrical or hollow cylindrical shape and is made of the following conductive materials: metals or alloys such as aluminum, copper alloys, and stainless steel; iron plated with chromium or nickel; and conductive synthetic resins. A known adhesive may be applied to the surface of the mandrel as needed to improve adhesion to the intermediate layer or surface layer on the outer periphery of the mandrel.

[0013] [Elastic layer] The elastic layer 12 contains a diene rubber and is provided as a single layer on the outer periphery of the conductive substrate 11. Examples of diene rubber include natural rubber, isoprene rubber (IR), acrylonitrile-butadiene rubber (NBR), styrene-butadiene rubber (SBR), butadiene rubber (BR), chloroprene rubber (CR), and modified versions of these rubbers. One or a mixture of two or more of these rubbers may be used. Among the diene rubbers, NBR is particularly suitable due to its excellent mechanical strength and impact resilience. The properties of NBR can be adjusted by the acrylonitrile content (AN content), allowing for appropriate selection and use. Specifically, the higher the AN content, the better the mechanical strength, but the harder the rubber becomes. An excessively high AN content tends to reduce the stability of nip formation with the contacting member. Therefore, it is preferable to select an AN content below a certain level. On the other hand, an excessively low AN content tends to reduce the polarity of the material, approaching that of butadiene rubber. Furthermore, this reduces the impregnation of the treatment solution in the surface treatment described below. Therefore, the AN content of NBR is preferably in the range of 10% to 50% by mass, and more preferably in the range of 15% to 42% by mass. NBR with an AN content within this range achieves an excellent balance between mechanical strength and flexibility and has moderate polarity, allowing for appropriate control of the impregnation of the treatment solution in the surface treatment described below. Furthermore, the elastic layer 12 may contain a rubber other than the diene rubber as long as the effects of the present disclosure are not lost. If necessary, various additives such as resin particles, conductive agents, plasticizers, fillers, extenders, crosslinking agents, crosslinking accelerators, vulcanization aids, crosslinking aids, acid acceptors, cure inhibitors, antioxidants, and antioxidants may be contained in the elastic layer 12. The additives may be blended in amounts that do not impair the features of the present disclosure.

[0014] In order to be used as a developing roller, the elastic layer 12 has conductivity that allows it to receive a potential from the conductive substrate 11 and carry toner on its surface. The volume resistivity of the elastic layer 12 is preferably 10 3 Ωcm or more 10 11 Ωcm or less, more preferably 10 4 Ωcm or more 10 10 It is adjusted to Ωcm or less. To impart conductivity to the elastic layer, a conductivity-imparting agent (conductive agent) such as an electronically conductive substance or an ionic conductive substance can be blended. Examples of electronically conductive substances include the following: conductive carbon, e.g., carbon black such as Ketjenblack EC and acetylene black; rubber carbon such as SAF (Super Abrasion Furnace), ISAF (Intermediate SAF), HAF (High Abrasion Furnace), FEF (Fast Extruding Furnace), GPF (General Purpose Furnace), SRF (Semi-Reinforcing Furnace), FT (Fine Thermal), and MT (Medium Thermal); oxidation-treated carbon for color (ink); and metals and their metal oxides such as copper, silver, and germanium. Among these, conductive carbon is preferred, as it is easy to control conductivity with a small amount. Examples of ionic conductive substances include the following: Inorganic ion-conductive substances such as sodium perchlorate, lithium perchlorate, calcium perchlorate, and lithium chloride; and organic ion-conductive substances such as modified aliphatic dimethylammonium ethosulfate and stearylammonium acetate.

[0015] The crosslinking agent may be a sulfur-based crosslinking agent (vulcanizing agent), such as powdered sulfur, oil-treated powdered sulfur, precipitated sulfur, colloidal sulfur, or dispersible sulfur, or an organic sulfur-containing compound such as tetramethylthiuram disulfide or N,N-dithiobismorpholine. In order to impart good rubber properties, the proportion of the vulcanizing agent is preferably 0.5 to 2.0 parts by mass of sulfur per 100 parts by mass of the total rubber. Also, when an organic sulfur-containing compound is used as a crosslinking agent, the proportion is preferably adjusted so that the amount of sulfur in the molecule is within the above range.

[0016] Examples of crosslinking accelerators for accelerating crosslinking include thiuram accelerators, thiazole accelerators, thiourea accelerators, guanidine accelerators, sulfenamide accelerators, and dithiocarbamate accelerators.

[0017] Examples of the crosslinking aid include known crosslinking aids such as metal compounds such as zinc oxide, stearic acid, oleic acid, and fatty acids. The proportion of the crosslinking aid is preferably 0.1 parts by mass or more and 7.0 parts by mass or less per 100 parts by mass of the total amount of rubber.

[0018] As the acid acceptor, various substances that act as acid acceptors can be used, but hydrotalcites, which have excellent dispersibility, are particularly preferred.

[0019] Examples of fillers that can be used include silica, carbon black, talc, calcium carbonate, magnesium carbonate, and aluminum hydroxide. By blending these fillers, it is expected that the mechanical strength of the resin will be improved. Furthermore, by using conductive carbon black as a filler, which functions as an electronic conductive agent, it is possible to impart electronic conductivity to the elastic layer in addition to the effect as a filler.

[0020] The thickness of the elastic layer 12 can be adjusted as needed, but it may have a region with an elastic modulus of 500 MPa or more near the surface, 0.1 μm from the surface, and is set to 0.30 mm or more to ensure a uniform nip width in the axial direction. The upper limit is not particularly limited, but is, for example, 3.00 mm or less. Therefore, the preferred thickness of the elastic layer is 0.30 mm or more and 3.00 mm or less, particularly 0.50 mm or more and 3.00 mm or less.

[0021] The elastic layer 12 has a crown shape in which the outer diameter of the central portion in the longitudinal direction along the axis of the substrate is larger than the outer diameter of both ends in the longitudinal direction. The difference between the outer diameter of the central portion of the elastic layer 12 and the outer diameter of both ends is the crown amount. There are no particular restrictions on the crown amount, and it may be set appropriately within a range that allows a stable formation of a nip with the contact member. For example, to make the contact width more uniform, the crown amount is preferably 1% to 30% of the thickness of the elastic layer in the central portion, and more preferably 3% to 25%. If the crown amount is insufficient, the developing roller will bend when the end is gripped and brought into contact with another member, preventing proper formation of a contact nip with the image carrier near the center of the developing roller's length, resulting in improper development. This results in blank areas at the center of the output image. On the other hand, if the crown amount is too large, the developing roller will not properly form a contact nip near the end, resulting in blank areas at the end of the image. Therefore, if blank areas occur in the center of the image, the crown amount should be increased, and if blank areas occur at the end of the image, the crown amount should be decreased.

[0022] Furthermore, if the overall macroscopic hardness of the elastic layer 12 is high, it is disadvantageous for forming a nip and white spots are more likely to occur. The macroscopic hardness can be confirmed, for example, by a durometer hardness test. Therefore, in order to suppress white spots, it is sufficient to design the durometer hardness of the elastic layer 12 to be low within an appropriate range; for example, it is preferable that the type A durometer hardness is 90 or less.

[0023] The crown shape can be formed, for example, by a traverse grinding method or a plunge-cut grinding method in which a grinding wheel wider than the length of the developing roller 10 is moved back and forth while rotating the base 11 around its axis. Of these, the plunge-cut grinding method is preferable because it has the advantage of being able to grind the entire longitudinal width of the elastic layer 12 at once and is suitable for continuous production because it shortens the processing time.

[0024] [Surface treatment] As shown in FIG. 2, the overall length of the elastic layer 12 of the developing roller 10 is L, and positions (1 / 10)L, (1 / 2)L, and (9 / 10)L from one end of the elastic layer 12 to the other end in the longitudinal direction are designated P1, P2, and P3, respectively. Position P2 corresponds to the longitudinal center of the conductive layer. As shown in FIG. 3, in the thickness direction cross section at positions P1, P2, and P3, the elastic moduli of the first region 31 extending from the outer surface of the elastic layer 12 to a depth of 0.1 μm are designated E11, E12, and E13, respectively. In the developing roller 10 of the present disclosure, E11, E12, and E13 are all 500 MPa or greater. To achieve the elastic moduli within the above ranges, a surface treatment method is selected. Common surface treatment methods include ultraviolet treatment and electron beam treatment. Among these methods, a method that preferentially increases the elastic modulus of the elastic layer 12 near the outermost surface of the developing roller 10 is selected. For example, a treatment method in which a treatment liquid containing a polymerizable monomer and a polymerization initiator is impregnated into the surface of the elastic layer 12 and polymerized by ultraviolet irradiation can preferentially increase the elastic modulus near the outermost surface of the elastic layer 12. Furthermore, this method is preferable because it allows control of the elastic modulus and the depth at which the elastic modulus increases.

[0025] [Processing liquid] The treatment liquid contains a polymerizable monomer, a polymerization initiator, and, if necessary, a solvent. An acrylic monomer is preferred as the polymerizable monomer. There are no limitations on the type of acrylic monomer, as long as it has one or more acryloyl or methacryloyl groups in one molecule. In particular, an acrylic monomer having one or two acryloyl or methacryloyl groups in one molecule is preferred because it easily penetrates into the network structure of the diene rubber in the elastic layer and can effectively modify the outermost surface of the elastic layer of the developing roller. A mixture of multiple types of acrylic monomers may also be used. The molecular weight of the acrylic monomer is preferably in the range of 200 to 750. By using a monomer with a molecular weight in this range, the monomer can be easily absorbed into gaps in the network structure of the diene rubber during the impregnation treatment of the elastic layer surface, and the elastic modulus or hardness of the elastic layer surface can be effectively improved. As described above, the acrylic monomer is impregnated into the elastic layer containing the diene rubber. To achieve this, the acrylic monomer must have an appropriate viscosity. That is, if the viscosity is high, impregnation is difficult, and if the viscosity is low, it is difficult to control the impregnation state. Therefore, the viscosity of the acrylic monomer at 25°C is preferably 5.0 mPa·s or more and 140 mPa·s or less.

[0026] The polymerization method of the acrylic monomer is not particularly limited, and known methods can be used. Specific examples include ultraviolet irradiation. For each polymerization method, known radical polymerization initiators or ionic polymerization initiators can be used as the polymerization initiator. Examples of photopolymerization initiators for photopolymerization by irradiation with ultraviolet light include 2,2-dimethoxy-1,2-diphenylethan-1-one, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenylpropan-1-one, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one, and 2-hydroxy-1-{4-[4-(2-hydroxy-2-methyl-propionyl)-benzyl]-phenyl}-2-methylpropane. -1-one, 2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropan-1-one, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one, 2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one, bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide. These photopolymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator is preferably 0.5 parts by mass or more and 10 parts by mass or less, when the total amount of the acrylic monomers is 100 parts by mass, from the viewpoint of efficiently progressing the reaction.

[0027] It is also preferable to blend a solvent into the treatment liquid. By blending a solvent, the acrylic monomer and polymerization initiator can be easily impregnated into the surface of the elastic layer of the developing roller. The solvent is not particularly limited, but an organic solvent that can swell the diene rubber used in the elastic layer and dissolve the acrylic monomer and polymerization initiator in the treatment liquid is preferred. For example, one or more solvents that are compatible with other materials can be used, such as alcohols such as methanol, ethanol, and n-propanol; ketones such as acetone, methyl ethyl ketone, and methyl isobutyl ketone; and esters such as methyl acetate and ethyl acetate.

[0028] The surface of the elastic layer is impregnated with a treatment liquid prepared by mixing the above materials. The method for impregnating the surface with the treatment liquid is not particularly limited, but any of dip coating, ring coating, spray coating, and roll coating can be used. After the impregnation treatment, the acrylic monomer is polymerized and cured. However, if the solvent swelled by the impregnation treatment remains in the elastic layer, the curing reaction may not proceed smoothly. Therefore, it is preferable to dry the elastic layer to remove the remaining solvent before the curing reaction. The solvent that has soaked into the elastic layer is trapped in the rubber network structure and its molecular motion is restricted, so it is difficult to volatilize when air-dried at room temperature and is likely to remain in the elastic layer. Therefore, a heating method is preferable as a drying method. In particular, it is preferable to dry at a temperature higher than the boiling point of the solvent contained in the treatment liquid.

[0029] After removing the solvent by drying, the acrylic monomer is polymerized and cured, thereby increasing the hardness of the outermost surface of the elastic layer. The polymerization and curing method is not particularly limited, and known methods can be used. Specific examples include heat curing and ultraviolet irradiation. In particular, ultraviolet irradiation is preferred because it allows preferential treatment of the outermost surface. Known devices for ultraviolet irradiation can be used as appropriate. Examples of light sources that can be used for ultraviolet irradiation include LED lamps, high-pressure mercury lamps, metal halide lamps, xenon lamps, and low-pressure mercury lamps. The ultraviolet irradiation conditions during polymerization can be adjusted as appropriate depending on the type and amount of materials used. However, if the amount of ultraviolet irradiation is insufficient, the curing reaction will be insufficient and a sufficient elastic modulus will not be imparted to the outermost surface (first region) of the elastic layer. The cumulative light dose can be used as an indicator of UV treatment. The cumulative light dose is expressed as cumulative light dose (mJ) = illuminance (mW) x time (s), and the greater the cumulative light dose, the stronger the treatment intensity. Although it depends on the reaction speed of the material used, the cumulative light dose is preferably 15,000 mJ or more, and particularly preferably 30,000 mJ or more. Furthermore, when performing curing by ultraviolet treatment, it is preferable to maintain the surface temperature of the elastic layer of the developing roller being treated at a certain level or higher, as this increases the reaction rate of the curing reaction on the surface of the elastic layer, thereby effectively increasing the elastic modulus of the outermost surface of the elastic layer. Specifically, it is preferable to start irradiation when the surface temperature of the elastic layer is 50°C or higher. Methods for controlling the surface temperature include temperature control within the ultraviolet treatment device, and preheating the workpiece by heating before ultraviolet treatment.

[0030] By carrying out the above impregnation and curing treatments, the elastic moduli E11, E12, and E13 at positions P1, P2, and P3 of the first region 31 shown in Fig. 3 can be set to 500 MPa or more. Note that the elastic moduli at the outermost first region 31 are the elastic moduli at the three measurement points mentioned above, but the elastic modulus is substantially 500 MPa or more over the entire first region 31. In this way, by increasing the hardness of the outermost surface of the elastic layer, it is possible to suppress density unevenness due to resistance unevenness, even when durable printing of 300,000 sheets or more is performed in a low-temperature, low-humidity environment.

[0031] The present inventors speculate as follows as to whether the developing roller according to the present disclosure can suppress density unevenness due to resistance unevenness even when endurance printing is performed in a low-temperature, low-humidity environment.

[0032] First, the mechanism by which uneven resistance occurs on the surface of the developing roller will be described. During the image formation process in an electrophotographic image forming apparatus, a potential difference between the elastic layer of the developing roller and another member in contact with it, such as an image carrier, generates a current between the surface of the elastic layer of the developing roller and the other member in contact with it. The generation of electric current causes deterioration of the diene rubber in the elastic layer of the developing roller, resulting in an increase in resistance. The deterioration here refers to the increase in resistance caused by the oxidation of the remaining double bonds in the diene rubber due to the application of electric current. The increase in resistance is correlated with the amount of current flowing, and the greater the current, the greater the tendency for resistance to increase. Therefore, when printing a large number of pages, the cumulative amount of current flowing through the developing roller also increases, and the resistance of the surface of the elastic layer tends to increase. In other words, if there is a difference in the amount of current flowing, there will be a difference in the increase in resistance due to rubber deterioration, which will ultimately lead to uneven resistance.

[0033] The apparent resistance of conductive rubber fluctuates with strain. Specifically, when rubber is strained by compression, the greater the strain, the smaller the apparent resistance. Conventionally, developing rollers using a single layer of diene rubber have typically been formed into a crown shape, with the elastic layer being thicker at the center than at the ends of the roller, in order to make the nip width with the image carrier uniform in the longitudinal direction. When a crown-shaped developing roller is brought into contact with an image carrier to create a nip of uniform width, the amount of strain in the elastic layer varies depending on the longitudinal position of the developing roller. This is because the elastic layer, which has a different outer diameter in the longitudinal direction, is compressed to the point where the nip width becomes the same, so the amount of strain, which is the amount of deformation relative to the original rubber thickness, differs depending on the longitudinal position of the developing roller. As mentioned above, the apparent resistance of the conductive rubber varies depending on the amount of strain. Therefore, when a crown-shaped developing roller is in contact with an image carrier to form a uniform nip width in the longitudinal direction, the unevenness in the amount of strain that occurs in the longitudinal direction causes local resistance values ​​to vary in the longitudinal direction. As a result, the unevenness in local resistance in the longitudinal direction causes the amount of current that flows locally to vary depending on the position in the longitudinal direction.

[0034] Furthermore, as mentioned above, if there is a difference in the amount of current, the amount of resistance increase due to rubber degradation will also differ. This mechanism causes resistance unevenness in the longitudinal direction on the outermost surface of the elastic layer of the developing roller. If there is resistance unevenness on the outermost surface of the elastic layer, resulting in locally high resistance areas, charge will accumulate in the high resistance areas when a bias is applied during the development process. As a result, a difference in apparent potential will occur between the high resistance areas and the low resistance areas. Typically, in the electrophotographic development process, a development bias is applied to move the developer from the developing roller toward the image carrier. As mentioned above, if a difference in apparent potential occurs between the high resistance areas and the low resistance areas, a corresponding difference will occur in the apparent development bias, resulting in a difference in the amount of developer developed. This is thought to manifest as density unevenness when an image is printed.

[0035] In the past, when printing a limited number of sheets, the total current was small and the resulting resistance unevenness was small, so it did not lead to image defects such as uneven density. However, in the case of printing an extremely large number of sheets, as will be required in future products, the total current will increase and the range of resistance unevenness will also increase. Furthermore, in a low-temperature, low-humidity environment, charges tend to accumulate in high-resistance areas more easily than in a high-temperature, high-humidity environment, and this is thought to result in more pronounced density unevenness in printed images. In other words, this phenomenon of uneven density is thought to occur only when a crown-shaped diene rubber developing roller is used in a low-temperature, low-humidity environment to print an extremely large number of sheets, which was not previously anticipated, and the total amount of current becomes large.

[0036] Next, the inventors will discuss below the reason why the development roller of the present disclosure can suppress the occurrence of uneven density in an image due to uneven resistance as described above. In the developing roller of the present disclosure, the first region 31, which is the outermost surface of the elastic layer 12, has an elastic modulus of 500 MPa or more at each of points P1, P2, and P3 in FIG. 3 . This elastic modulus reduces strain associated with nip formation near the outermost surface of the elastic layer 12, and also reduces unevenness in strain in the longitudinal direction. As a result, the aforementioned variation in apparent resistance associated with uneven strain is reduced at the outermost surface of the elastic layer 12, resulting in uniform resistance. This reduces unevenness in the local amount of current at the outermost surface of the elastic layer 12 depending on the position in the longitudinal direction. Therefore, it is believed that unevenness in the increase in resistance associated with deterioration of the diene rubber due to current flow can be reduced, thereby reducing density unevenness when printing a large number of sheets.

[0037] Furthermore, in the developing roller of the present disclosure, as shown in Figure 3, in the cross section in the thickness direction at positions P1, P2, and P3, the elastic moduli in a second region 32 at a depth of 0.5 μm to 0.6 μm from the outer surface are defined as E21, E22, and E23, respectively. Furthermore, the elastic moduli in a third region 33 at a depth of 1.0 μm to 1.1 μm from the outer surface are defined as E31, E32, and E33, respectively. In this case, it is preferable that E11, E12, E13, E21, E22, E23, E31, E32, and E33 satisfy the following formulas (1) to (3): E11 ≥ E21 ≥ E31 (1), E12 ≥ E22 ≥ E32 (2), E13 ≥ E23 ≥ E33 (3). Furthermore, it is more preferable that the following formulae (1') to (3') are satisfied: E11>E21>E31 (1'), E12>E22>E32 (2'), E13>E23>E33 (3').

[0038] If the modulus of elasticity of the elastic layer 12 decreases with increasing depth from the surface in the longitudinal direction of the developing roller 10, as shown in the above formula, the inside of the elastic layer 12 is distorted preferentially when forming a nip. Therefore, the distortion of the outermost surface of the elastic layer 12 is relatively reduced. For this reason, the modulus of elasticity of the inside of the elastic layer 12 is highly effective in suppressing density unevenness caused by resistance unevenness.

[0039] Furthermore, in the developing roller 10 of the present disclosure, as shown in FIG. 3 , a fourth region 34 is defined as a region having a depth of 5.0 μm to 5.1 μm from the outer surface in the cross section in the thickness direction at positions P1, P2, and P3. When the elastic moduli of the fourth region 34 are E41, E42, and E43, respectively, E41, E42, and E43 are preferably 100 MPa or less. When the elastic moduli are within the above ranges, the interior of the elastic layer is preferentially distorted during nip formation, thereby suppressing distortion of the outermost surface of the elastic layer. Therefore, the relationship between the elastic moduli is highly effective in suppressing density unevenness caused by resistance unevenness.

[0040] As mentioned above, the higher the macroscopic hardness of the entire elastic layer, the more disadvantageous the formation of a nip. Therefore, when increasing the hardness of the outermost surface of the elastic layer, it is preferable to minimize the effect on the macroscopic hardness. To achieve this, it is preferable to preferentially increase the hardness only in the region close to the outermost surface. In other words, it is preferable that E11, E31, and E41, as well as E12, E32, and E42, and E13, E33, and E43 satisfy the following formulas (4) to (6). This makes it possible to achieve both a good nip and suppression of density unevenness caused by resistance unevenness at a high level: (E31-E11) / (E41-E11)≧0.50 (4), (E32-E12) / (E42-E12)≧0.50 (5), (E33-E13) / (E43-E13)≧0.50 (6).

[0041] <Process cartridge> A process cartridge according to one aspect of the present disclosure includes at least a developing device, the developing device including the developing roller according to the present disclosure, and is supported by a housing (not shown) and configured to be detachably mountable to an electrophotographic image forming apparatus.

[0042] 4 shows a process cartridge according to one embodiment of the present disclosure. The process cartridge 100 has an image carrier (photosensitive member) 101, a charging member (charging roller) 102, and a developing member 103 (developing roller 10). It also incorporates a toner supplying member 105 that contacts the developing member 103 and a toner regulating member 106 as a developing device. Furthermore, a cleaning member (cleaning blade) 104 is disposed upstream of the charging member 102.

[0043] <Electrophotographic image forming apparatus> An electrophotographic image forming apparatus according to one aspect of the present disclosure includes at least an image carrier, a charging device, a developing device, and a transfer device that transfers the formed image onto recording paper, and the developing device includes a developing roller according to the present disclosure. 5 shows a schematic configuration diagram of an electrophotographic image forming apparatus 200 according to an embodiment of the present disclosure, in which the process cartridge shown in FIG. 4 is installed as four cartridges containing toners of different colors, making the apparatus full-color compatible. The image forming apparatus is an intermediate transfer type, in which the toner images of each color formed on the image carrier 101 are combined into a full-color image on an intermediate transfer member (intermediate transfer belt 202) and transferred to recording paper 205. The image carrier 101 is uniformly charged (primary charging) by a charging member 102 connected to a bias power supply (not shown). Next, exposure light 201 for writing an electrostatic latent image onto the image carrier 101 is irradiated from an exposure device (not shown), and an electrostatic latent image is formed on the surface of the image carrier 101. Either LED light or laser light can be used as the exposure light. Next, negatively charged toner is applied to the electrostatic latent image by the developing member 103, forming a toner image on the image carrier 101 and converting the electrostatic latent image into a visible image (development). At this time, a voltage is applied to the developing member 103 by a bias power supply (not shown). The developing member 103 is in contact with the image carrier 101 with a certain nip width. The toner image developed on the image carrier 101 is primarily transferred to an intermediate transfer belt 202, which is a transfer device. The transfer device includes a primary transfer member 203 that contacts the back surface of the intermediate transfer belt 202, and by applying a voltage to the primary transfer member 203, a negative polarity toner image is primarily transferred from the image carrier 101 to the intermediate transfer belt 202. The primary transfer member 203 may be in the form of a roller as shown in the figure, or in another blade shape.

[0044] When the electrophotographic image forming apparatus 200 is a full-color image forming apparatus, typically, the above-mentioned processes of charging, exposing, developing, and primary transfer are performed for each of the colors yellow, cyan, magenta, and black. Therefore, the electrophotographic image forming apparatus 200 shown in FIG. 5 has a total of four process cartridges 100, one for each color, built-in, detachably mounted in the main body of the electrophotographic image forming apparatus 200. The above-mentioned processes of charging, exposing, developing, and primary transfer are performed sequentially with a predetermined time difference, and a state in which four color toner images are superimposed on the intermediate transfer belt 202 to represent a full-color image is created. As the intermediate transfer belt 202 rotates, the toner image on the intermediate transfer belt 202 is transported to a position facing a secondary transfer member 204. Recording paper 205 is transported along a transport route between the intermediate transfer belt 202 and the secondary transfer member 204 at a predetermined timing, and the toner image on the intermediate transfer belt 202 is transferred to the recording paper 205 by applying a secondary transfer bias to the secondary transfer member 204. The secondary transfer member 204 is also included in the transfer device. The recording paper 205 onto which the toner image has been transferred by the secondary transfer member 204 is transported to a fixing device (not shown). The fixing device melts and fixes the toner image on the recording paper 205, and then the recording paper 205 is discharged outside the electrophotographic image forming apparatus 200, thereby completing the printing operation. The intermediate transfer belt 202 is stretched between the secondary transfer member 204 and an opposing roller 206 that faces the intermediate transfer belt, and a predetermined potential is applied to the opposing roller 206. The image transfer surface of the intermediate transfer belt 202 is kept clean by a cleaning member (not shown). Although the transfer device has been described above as having an intermediate transfer belt, the invention is not limited to this and may be a direct transfer type transfer device in which an image is transferred directly from an image carrier to a recording sheet. [Example]

[0045] The present disclosure will be specifically described below using examples, but the present disclosure is not limited to these examples. Table 1 shows the materials used in the examples and comparative examples.

[0046] [Table 1]

[0047] [Example 1] <Manufacturing of developing rollers> (Formation of elastic layer) As the first mixture, the materials for the elastic layer 2 shown in Table 2 below were mixed for 16 minutes using a 6-liter pressure kneader (product name: TD6-15MDX, manufactured by Toshin Co., Ltd.) at a filling rate of 70 vol% and a blade rotation speed of 30 rpm.

[0048] [Table 2]

[0049] Next, as the second mixture, the materials shown in Table 3 below were further added to the above mixture, and the mixture was turned left and right a total of 20 times using an open roll with a roll diameter of 12 inches (0.30 m) at a front roll rotation speed of 10 rpm, a rear roll rotation speed of 8 rpm, and a roll gap of 2 mm. After that, the roll gap was set to 0.5 mm and thin-threading was performed 10 times to obtain Mixture 1.

[0050] [Table 3]

[0051] A stainless steel (SUS304) mandrel with an outer diameter of 6 mm and a length of 270 mm was prepared, and a conductive vulcanizing adhesive (product name: Metalock U-20, manufactured by Toyo Kagaku Kenkyusho) was applied to the circumferential surface of the mandrel and baked to produce a substrate. Next, Mixture 1 was extruded using a crosshead to form a cylindrical shape coaxially with the substrate, while simultaneously extruding it with the substrate, to form a layer of Mixture 1 on the outer circumferential surface of the substrate. An extruder with a cylinder diameter of 45 mm (Φ45) and L / D=20 was used, and the temperatures during extrusion were controlled to 90°C for the head, 90°C for the cylinder, and 90°C for the screw. Both longitudinal ends of the base of the layer of mixture 1 were cut to make the length of the base of the layer of mixture 1 in the longitudinal direction 237 mm. The mixture was then heated in an electric furnace at 160°C for 40 minutes to vulcanize the layer of Mixture 1, forming a vulcanized part. The surface of the vulcanized part was then polished using a plunge-cut grinding machine. The outer diameter was measured using a laser length measuring device (product name: Conto Component LS-7000, sensor head LS-7030R, manufactured by KEYENCE Corporation). Measurements were taken at 10 mm intervals along the length, and the difference between the outer diameter 10 mm from the end of the part and the outer diameter at the center of the part was taken as the crown amount. The outer diameter of the finished part's end was 11.958 mm, and the outer diameter at the center was 12.048 mm. This resulted in a polished roller with an elastic layer thickness of approximately 3.0 mm at the center and a crown amount of 90 μm. The surface of the resulting polishing roller was subjected to the following treatment.

[0052] (Surface treatment) The materials shown in Table 4 below were dissolved and mixed to form Impregnation Treatment Solution No. 1 for treatment. A polishing roller was immersed in this Impregnation Treatment Solution No. 1 for 2 seconds to obtain an impregnated roller impregnated with the acrylic monomer component. The roller was then air-dried at room temperature for 30 minutes and then dried at 90°C for 1 hour to volatilize the solvent and preheat the impregnated roller.

[0053] [Table 4]

[0054] After the preheating, the surface of the impregnated roller was irradiated with ultraviolet light to cure the acrylic monomer. The UV irradiation was performed using an ultraviolet irradiation device consisting of a mechanism for gripping and rotating the impregnated roller and an ultraviolet lamp placed parallel to the impregnated roller. The surface treatment was performed by irradiating the impregnated roller with ultraviolet light while rotating it at a rotation speed of 20 rpm. The ultraviolet lamp used was a high-pressure mercury lamp (manufactured by iGraphics Co., Ltd.) The irradiance of 365 nm wavelength at the surface of the impregnated roller was measured using an ultraviolet integrating actinometer (main body: UIT-250, light receiving part: UVD-S365, both Ushio Inc. product names), and the lamp output and distance were adjusted to obtain an irradiance of 150 mW. The dried and preheated impregnated roller was set in this ultraviolet irradiation device, and ultraviolet irradiation was carried out for 200 seconds so that the integrated light amount was approximately 30,000 mJ. The surface temperature of the elastic layer of the impregnated roller at the start of ultraviolet irradiation was 60°C, and at the end of ultraviolet irradiation the surface temperature of the elastic layer was 90°C. In this manner, developing roller No. 1 was manufactured.

[0055] The resulting developing roller was evaluated as follows. <Evaluation method> (Measurement of current value of developing roller) As shown in FIG. 8 , a developing roller 801 to be evaluated was brought into contact with a cylindrical electrode 803 made of stainless steel (SUS304) and having a diameter of 40 mm, with a load of 500 g applied to each end of the exposed portion of the mandrel of the developing roller. By rotating the cylindrical electrode 803 in this state, the developing roller 801 was driven to rotate at a rotational speed of 24 rpm. In this state, a DC voltage of 50 V was applied between the mandrel and the cylindrical electrode 803 from a DC power supply 805, and the current value per rotation of the developing roller 801 was measured with an ammeter 807. This evaluation was performed in an environment with a temperature of 20°C and a relative humidity of 50%. The average current values ​​thus obtained were then calculated and listed in Table 8.

[0056] (Evaluation of elastic modulus) The cross-sectional area of ​​the developing roller to be measured was cut into thin sections using a cryomicrotome (product name: EMFC6, manufactured by Leica Microsystems) while kept at -110°C, using a diamond knife to prepare flakes measuring 100 μm square and 100 μm wide in the depth direction. The obtained thin sections were placed on a smooth silicon wafer and left in an environment of room temperature 25°C and humidity 50% for 24 hours, after which the elastic modulus was measured in the same environment. In this disclosure, the elastic modulus was measured in each of the first, second, third, and fourth regions at positions P1, P2, and P3 shown in Figure 3. For the measurements, a scanning probe microscope (SPM) (product name: MFP-3D-Origin, manufactured by Oxford Instruments) and a silicon probe (product name: OMCL-AC160, manufactured by Olympus, tip curvature radius: 8 nm) were used. The spring constant and proportionality constant of the probe were confirmed to be 22 nN / nm and 82.59 nm / V, respectively, using the thermal noise method with the SPM. At this time, the force curve was measured 10 times, and the arithmetic mean of 8 points excluding the highest and lowest values ​​was calculated, and the elastic modulus was calculated according to Hertz's theory.

[0057] (White area evaluation) The developing roller manufactured as described above was incorporated into a laser printer (product name: HP Color LaserJet Enterprise M652dn, manufactured by HP) and a cyan cartridge for the laser printer (product name: HP 656X High Yield Cyan Original LaserJet Toner Cartridge, manufactured by HP) in a low-temperature, low-humidity environment of a temperature of 15°C and a relative humidity of 10%, and left to stand in the above environment for 48 hours to allow for sufficient aging. After aging, a solid black image was printed at a coverage rate of 100%, and the presence or absence of white spots on the image was confirmed. The evaluation of white spots was carried out by measuring the image density using a spectrodensitometer (product name: 508, manufactured by X-Rite Corporation), and the image density difference within the image area was calculated to evaluate the density unevenness. The image density difference was measured at three points at each end and center of the image area, and the absolute value of the difference in image density between the end and center was taken as the image density difference, and white spots were evaluated according to the following criteria: The end of the image area refers to a position 10 mm inward from the image edge. Evaluation criteria Rank A: Image density difference of solid black image is less than 0.20 Rank B: Image density difference of solid black image is 0.20 or more and less than 0.30 Rank C: Image density difference of solid black image is 0.30 or more and less than 0.50 Rank D: Image density difference of solid black image is 0.50 or more

[0058] (Evaluation of uneven density) After evaluating the white spots, two images with a print rate adjusted to 0.5% were printed repeatedly for a total of 30,000 sheets. Then, the cyan cartridge was disassembled, the developing roller was removed, and the developing roller was reassembled into another new cyan cartridge, and 30,000 sheets were printed in the same manner. This was repeated for 10 cyan cartridges, printing a total of 300,000 pages. Thereafter, density unevenness was checked. To evaluate density unevenness, a halftone image was printed using the cyan cartridge installed after the above 300,000 sheets had been printed. The halftone image was an image in which horizontal lines with a width of 1 dot extending perpendicular to the direction of rotation of the image carrier were drawn at intervals of 1 dot in the direction of rotation. After printing, the image density was measured using a spectrodensitometer (product name: 508, manufactured by X-Rite Corporation), and the difference in image density within the image area was calculated to evaluate density unevenness. The image density difference was measured at three points at each end and center of the image area, and the absolute value of the difference in image density between the end and center was taken as the image density difference, and density unevenness was evaluated according to the following criteria: The end of the image area refers to a position 10 mm inward from the image edge. Evaluation criteria Rank A: Halftone image density difference is less than 0.05 Rank B: Halftone image density difference is 0.05 or more and less than 0.10 Rank C: Halftone image density difference is 0.10 or more and less than 0.30 Rank D: Halftone image density difference is 0.30 or more

[0059] (Evaluation of resistance unevenness ΔV on the outermost surface of the elastic layer in a low-temperature, low-humidity environment) If there is uneven resistance on the top surface of the developing roller, charge-up occurs in areas where the resistance is high. This causes a deviation in the development bias between the developing roller and the image carrier, resulting in density differences. Therefore, uneven resistance on the top surface of the developing roller leads to density unevenness. In order to quantify the unevenness in the surface resistance of the developing roller, an electric charge was emitted onto the surface of the developing roller using a corona discharger 41, and the residual electric charge was measured using a surface potentiometer to calculate the unevenness in surface potential (ΔV). The reason for using this evaluation method is as follows. Methods commonly used to measure resistance include, for example, volume resistivity and surface resistivity as specified in JIS K6911. In actuality, uneven density of images printed in electrophotographic processes is influenced by uneven resistance on the outermost surface of the developing roller. However, the results obtained using the general resistance measurement method described above are macroscopic resistance values ​​that include information on the resistance of not only the outermost surface but also the internal resistance. Therefore, it is not possible to obtain information on the resistance of only the outermost surface of the developing roller, which is directly related to density unevenness in images printed in the electrophotographic process. Therefore, in this embodiment, a method of measuring the residual charge after corona discharge is used. In the method using corona discharge, corona discharge is performed from the surface side of the elastic layer, so it is possible to evaluate the resistance unevenness on the outermost surface of the developing roller as described above, regardless of the internal resistance.

[0060] The portion of the outermost surface of the developing roller with high resistance has a relatively large amount of residual charge after corona discharge, and therefore the measured surface potential value is high. Therefore, by checking the unevenness of the surface potential of the outermost surface of the developing roller, it is possible to check the unevenness of the resistance of the outermost surface of the developing roller. The surface potential of the entire surface of the elastic layer of the developing roller was measured, and ΔV was calculated using the surface potential data obtained for the entire surface. The specific method is described below.

[0061] The evaluation device used was a dielectric relaxation measurement device 40 (trade name: DRA-2000L, manufactured by QEA) as shown in Fig. 6. The dielectric relaxation measurement device 40 will be outlined with reference to Fig. 6. The device 40 is equipped with a head 43 in which a corona discharger 41 and a surface potential meter probe 42 are integrated. In addition, since the distance from the position where discharge occurs by the corona discharger 41 in the head 43 to the center of the probe 42 of the surface electrometer is 25 mm, a delay time occurs between the end of discharge and measurement depending on the movement speed of the head 43. The head 43 can move parallel to the longitudinal direction of the installed developing roller 10. In addition, the charge generated by the corona discharger 41 is radiated toward the surface of the elastic layer 12 of the developing roller 10.

[0062] The head 43 moves while corona discharge is being performed, and the following measurements are made. 1) The corona discharger 41 radiates electric charges onto the surface of the elastic layer 12 of the developing roller 10 . 2) During the delay time until the probe 42 of the surface electrometer reaches the measurement position, the charge on the surface of the elastic layer 12 escapes to the ground through the conductive substrate 11. 3) The amount of residual charge on the surface of the elastic layer 12 is measured as potential using an electrometer.

[0063] The dielectric relaxation measuring device 40 and the developing roller 10 were left in a low temperature and low humidity (15° C. / 10% RH) environment for 24 hours or more to be sufficiently aged. A master made of stainless steel (SUS304) and having the same outer diameter as the developing roller 10 is placed in the dielectric relaxation measurement device 40, and this master is short-circuited to earth. Next, the distance between the master surface and the probe of the surface potentiometer is adjusted to 0.76 mm, and the surface potentiometer is calibrated to zero. After the above calibration, the master is removed, and the developing roller 10 to be measured is placed in the dielectric relaxation measuring device 40 . The measurement conditions were a bias setting of 8 kV for the corona discharger 41, a scanner movement speed of 400 mm / sec, and a sampling interval of 0.5 mm or less, and measurements were taken in the longitudinal direction of the developing roller 10. The range for data collection was (8 / 10)L, where L is the longitudinal length of the elastic layer 12 of the developing roller 10, excluding the areas up to (1 / 10)L from both ends. Furthermore, measurements were taken in the longitudinal direction every time the developing roller was rotated in 10° increments in the rotation direction, and this was repeated 36 times to obtain surface potential data for one rotation of the roller.

[0064] The potential data obtained in this way is expressed as an m-row, 36-column matrix, with the potential values ​​obtained at each longitudinal position in the vertical direction and the potential values ​​obtained at each phase in 10° increments in the horizontal direction as elements. The value of m is determined by the sampling interval. ΔV is calculated from this surface potential data. ΔV is obtained by dividing the above (8 / 10)L range in the longitudinal direction of the elastic layer of the developing roller into five areas, calculating the average value of the surface potential for each area, and then calculating the ratio of the maximum value to the minimum value of the average surface potential for the five areas obtained. Specifically, first, the m-row, 36-column matrix obtained above is divided into five equal parts, each with m / 5 rows. For each of the five divided matrices, the arithmetic mean of all elements, i.e., the (m / 5) × 36 element values, is calculated, and the obtained value is used as the average surface potential for each area. Of the five average surface potentials, the maximum value is set to Vmax and the minimum value is set to Vmin, and the value obtained by calculating ΔV = Vmax - Vmin is used as the surface potential unevenness of the developing roller.

[0065] [Examples 2 to 5, Examples 7 to 12] The materials listed in Table 5 were used to prepare the polishing rollers, and the materials listed in Table 6 were used to prepare the treatment liquid used for surface treatment. Except for this, the polishing rollers and impregnation treatment liquids were combined as shown in Table 7 in the same manner as in Example 1 to prepare developing rollers Nos. 2 to 5 and 7 to 12, and evaluations were performed in the same manner as in Example 1. The evaluation results are shown in Tables 7 and 8. It should be noted that Examples 11 and 12 should be read as Reference Examples 11 and 12, respectively.

[0066] [Example 6] The materials listed in Table 5 were used to prepare the polishing roller, and the impregnation treatment solution No. 4 listed in Table 6 was used for the surface treatment. Furthermore, the cumulative amount of ultraviolet light was set to 50,000 mJ / cm. 2 Other than that, developing roller No. 6 was produced in the same manner as in Example 1, and evaluations were carried out in the same manner as in Example 1. The evaluation results are shown in Tables 7 and 8.

[0067] [Example 13] <Manufacturing of developing rollers> (Preparation of the substrate) An aluminum cylindrical tube ground to an outer diameter of 10 mm was prepared as the conductive substrate 1 . The substrate was surface-treated by immersing it in a cleaning bath adjusted to pH 12.0 for 3 minutes. Next, for the convenience of subsequent processing to shape the end face, further surface treatment was performed. Specifically, to simplify the removal of the layer formed within 0.5 mm from both ends of the cylindrical tube, a 0.01% citric acid solution was applied to the entire circumferential surface up to 0.5 mm inside both ends to prepare a cylindrical tube substrate.

[0068] (Formation of elastic layer) Mixture 1 was prepared in the same manner as in Example 1. Next, the above mixture 1 was extruded using a crosshead to form a cylindrical shape coaxially with the cylindrical tubular substrate at the center, while simultaneously extruding the mixture 1 with the cylindrical tubular substrate, to form a layer of mixture 1 on the outer peripheral surface of the cylindrical tubular substrate. An extruder with a cylinder diameter of 45 mm (Φ45) and L / D=20 was used, and the temperatures during extrusion were controlled to a head temperature of 90°C, a cylinder temperature of 90°C, and a screw temperature of 90°C. Both longitudinal ends of the cylindrical tubular substrate carrying the layer of mixture 1 were cut. The mixture was then heated in an electric furnace at 160°C for 40 minutes to vulcanize the layer of Mixture 1, forming a vulcanized component. The surface of the vulcanized component was then polished using a plunge-cut grinding machine. The outer diameter was measured using a laser length measuring device (product name: Conto Component LS-7000, sensor head LS-7030R, manufactured by KEYENCE Corporation). Measurements were taken at 10 mm intervals along the length, and the difference between the outer diameter 10 mm from the end of the component and the outer diameter at the center of the component was taken as the crown amount. The outer diameter of the finished component end was 10.600 mm, and the outer diameter at the center was 10.650 mm, resulting in a polished roller with an elastic layer thickness of 0.30 mm and a crown amount of 50 μm. The surface of the resulting polished roller was then subjected to the following treatment.

[0069] (Surface treatment) The obtained polished roller was subjected to surface treatment in the same manner as in Example 1 to obtain developing roller No. 13. The elastic modulus of the first to fourth regions of developing roller No. 13 was evaluated in the same manner as in Example 1.

[0070] <Evaluation method> (White area evaluation) The evaluation was carried out in the same manner as in Example 1, except that a color laser printer (product name: HP LaserJet Pro M102w Printer, manufactured by HP) and a black cartridge for the color laser printer (product name: HP 17A (CF217A) Black Original LaserJet Toner Cartridge, manufactured by HP) were used as the printers for evaluation.

[0071] (Evaluation of uneven density) After evaluating whiteout, two images with a print rate adjusted to 0.5% were printed repeatedly, for a total of 3,000 prints. The cartridge was then disassembled, the developing roller removed, and the developing roller reassembled into another new cyan cartridge. 30,000 prints were similarly performed with this cartridge. This process was repeated until a total of 300,000 prints were performed. Density unevenness was then checked. To evaluate density unevenness, a halftone image was printed using the cartridge installed after the 20,000 prints had been completed. The halftone image consisted of horizontal lines, each 1 dot wide, extending perpendicular to the rotation direction of the image carrier, spaced 1 dot apart in the rotation direction. After printing, the image density was measured using a spectrodensitometer (product name: 508, manufactured by X-Rite), and the difference in image density within the image area was calculated to evaluate density unevenness.

[0072] The image density difference was measured at three points at each end and center of the image area, and the absolute value of the difference in image density between the end and center was taken as the image density difference, and density unevenness was evaluated according to the following criteria: The end of the image area refers to a position 10 mm inward from the image edge. Evaluation criteria Rank A: Halftone image density difference is less than 0.05 Rank B: Halftone image density difference is 0.05 or more and less than 0.10 Rank C: Halftone image density difference is 0.10 or more and less than 0.30 Rank D: Halftone image density difference is 0.30 or more

[0073] [Comparative Example 1] The cumulative amount of ultraviolet light is 3000mJ / cm2 Developing roller No. 14 was produced in the same manner as in Example 1, except that the setting was made so that the temperature was 100°C or more, and the same evaluation as in Example 1 was carried out.

[0074] Comparative Example 2 Developing roller No. 15 was produced using the materials listed in Table 5 for producing the polishing roller and impregnation treatment liquid No. 4 in Table 6 as the treatment liquid used for the surface treatment. In the surface treatment of developing roller No. 15, the roller was immersed in the treatment liquid for 10 seconds, and the drying conditions after immersion were 25°C for 10 minutes. After that, the roller was irradiated with ultraviolet light with an integrated dose of 3000 mJ / cm. 2 When irradiation was started when the surface temperature of the elastic layer of the polishing roller was 25° C., the surface temperature after ultraviolet irradiation was 40° C. The developed roller No. 15 thus produced was evaluated in the same manner as in Example 1.

[0075] Comparative Example 3 A polishing roller was obtained in the same manner as in Example 1. This polishing roller was not subjected to the surface treatment of Example 1, but instead was subjected to treatment with electron beams. Fig. 7 shows a schematic diagram of an electron beam irradiation device 50. This electron beam irradiation device 50 is an apparatus that can irradiate an electron beam onto a surface of a member while rotating a polishing roller 58, and as shown in Fig. 7, it is equipped with an electron beam generation unit 51, an irradiation chamber 52, and an irradiation port 53. The electron beam generating unit 51 has a terminal 54 that generates an electron beam and an acceleration tube 55 that accelerates the electron beam generated by the terminal 54 in a vacuum space (acceleration space). The inside of the electron beam generating unit is evacuated by a vacuum pump (not shown) or the like to prevent the electrons from colliding with gas molecules and losing energy. -3 Pa or more 10 -6The filament 56 is maintained at a vacuum of less than 1 Pa. When a current is passed through the filament 56 from a power source (not shown) to heat it, the filament 56 emits thermoelectrons, and only those of the thermoelectrons that pass through the terminal 54 are effectively extracted as an electron beam. The electrons are then accelerated in the acceleration space within the acceleration tube 55 by the electron beam acceleration voltage, and then pass through the irradiation port foil 57 to be irradiated onto the polishing roller 58 transported within the irradiation chamber 52 below the irradiation port 53. When the polishing roller 58 is irradiated with an electron beam, the inside of the irradiation chamber 52 can be filled with a nitrogen atmosphere. Using the above electron beam processing device 50, the polishing roller 58 was processed at an acceleration voltage of 50 kV for a time period that resulted in a dose of 200 kGy, thereby obtaining developing roller No. 16. The developing roller No. 16 was evaluated in the same manner as in Example 1.

[0076] Comparative Example 4 As a surface treatment for the polishing roller, only 10,000 mJ of ultraviolet light was irradiated without immersion in a treatment liquid and drying. Except for this, developing roller No. 17 was produced in the same manner as in Example 1, and the same evaluations as in Example 1 were carried out.

[0077] Comparative Example 5 As a surface treatment for the polishing roller, only 10,000 mJ of ultraviolet light was irradiated without immersion in a treatment liquid and drying. Except for this, developing roller No. 18 was produced in the same manner as in Example 13, and the same evaluations as in Example 13 were carried out.

[0078] [Table 5]

[0079] [Table 6]

[0080] [Table 7]

[0081] [Table 8]

[0082] In Examples 1 to 13, E11, E12, and E13 were all 500 MPa or higher. As a result, even after printing a large number of sheets, ΔV could be suppressed to 9V or lower, and images of good quality, with density unevenness ranked A or B, could be obtained. In particular, in Examples 1 to 10 and 13, E41, E42, and E43 were 100 MPa or lower, which were lower ΔV values ​​than Examples 11 and 12, which exceeded 100 MPa. Furthermore, in Examples 1 to 6, 8 to 10, and 13, the left side of equation (4): (E31-E11) / (E41-E11), the left side of equation (5): (E32-E12) / (E42-E12), and the left side of equation (6): (E33-E13) / (E43-E13), were all 0.50 or higher. As a result, ΔV could be suppressed to 4V or less, and an image of better quality was obtained, with an A rank in density unevenness.

[0083] On the other hand, in Comparative Example 2, drying after the impregnation treatment was performed at room temperature, and the surface temperature of the elastic layer during ultraviolet irradiation was also 50°C or lower, so the monomer was not cured sufficiently, and E11, E12, and E13 were less than 500 MPa. As a result, the density unevenness was ranked D. In Comparative Example 1, it is thought that the integrated amount of ultraviolet light was insufficient, so the monomer was not cured sufficiently, and E11, E12, and E13 were less than 500 MPa, resulting in the density unevenness being ranked D. In Comparative Examples 4 and 5, the impregnation step in the treatment liquid was not performed, and only the ultraviolet treatment step was performed. Therefore, it is thought that the first region of the developing rollers according to these Comparative Examples did not contain a cured product of an acrylic monomer, and E11, E12, and E13 were less than 500 MPa, and the evaluation result for density unevenness was ranked D. In Comparative Example 3, electron beam irradiation was performed as the surface treatment. Because the electron beam penetrates deeper from the irradiated surface, the elastic modulus of the elastic layer in the portion deeper than the first region is also increased. Therefore, it is believed that the first region of the elastic layer is preferentially distorted, resulting in a large ΔV and a D rank evaluation result for density unevenness. The evaluation result for white spots was also D rank. This is believed to be due to the higher elastic modulus of the elastic layer in the portion deeper than the first region, which resulted in an uneven nip with the image carrier.

[0084] The present disclosure includes the following configurations. [Configuration 1] a conductive substrate; a conductive elastic layer consisting of a single layer on the outer periphery of the substrate; A developing roller having the elastic layer contains a diene rubber, the elastic layer has a crown shape in which the outer diameter of a central portion in a longitudinal direction along the axis of the base is larger than the outer diameters of both end portions in the longitudinal direction; The thickness of the elastic layer is 0.30 mm or more, The length of the elastic layer in the longitudinal direction is defined as L, and positions P1, P2, and P3 are defined as (1 / 10)L, (1 / 2)L, and (9 / 10)L, respectively, from one end of the elastic layer to the other end in the longitudinal direction, In a cross section in the thickness direction at each of the positions P1, P2, and P3, when the elastic moduli in a first region from the outer surface of the elastic layer to a depth of 0.1 μm are E11, E12, and E13, respectively, the developing roller characterized in that E11, E12, and E13 are all 500 MPa or more. [Configuration 2] The developing roller according to [Configuration 1], wherein the thickness of the elastic layer is at least 0.30 mm or more and 3.00 mm or less. [Configuration 3] In the cross section in the thickness direction of the elastic layer at each of the positions P1, P2 and P3, The elastic moduli of a second region at a depth of 0.5 μm or more and 0.6 μm or less from the outer surface of the elastic layer are defined as E21, E22, and E23, respectively; When the elastic moduli of the third region at a depth of 1.0 μm or more and 1.1 μm or less from the outer surface of the elastic layer are E31, E32, and E33, respectively, E11, E12, E13, E21, E22, E23, E31, E32 and E33 are represented by the following formulas (1) to (3): E11≧E21≧E31 (1) E12≧E22≧E32 (2) E13≧E23≧E33 (3) The developing roller according to [Configuration 1] or [Configuration 2] satisfies the above. [Configuration 4] When the elastic moduli of a fourth region at a depth of 5.0 μm or more and 5.1 μm or less from the outer surface of the elastic layer in the cross section in the thickness direction of the elastic layer at each of the positions P1, P2, and P3 are E41, E42, and E43, respectively, The developing roller according to [Configuration 3], wherein E41, E42 and E43 are all 100 MPa or less. [Configuration 5] The elastic moduli E11, E31, E41, E12, E32, E42, and E13, E33, and E43 of the first region, the third region, and the fourth region at the positions P1, P2, and P3 are expressed by the following formulas (4) to (6): (E31-E11) / (E41-E11)≧0.50 (4) (E32-E12) / (E42-E12)≧0.50 (5) (E33-E13) / (E43-E13)≧0.50 (6) The developing roller according to [Configuration 4] satisfies the above. [Configuration 6] The developing roller according to any one of [Configuration 1] to [Configuration 5], wherein the diene rubber is acrylonitrile-butadiene rubber. [Configuration 7] The developing roller according to [Configuration 6], wherein the amount of acrylonitrile in the acrylonitrile-butadiene rubber is 15% by mass or more and 42% by mass or less. [Configuration 8] The developing roller according to any one of [Configuration 1] to [Configuration 7], wherein the elastic layer contains a conductive agent. [Configuration 9] The developing roller according to [Configuration 8], wherein the conductive agent is carbon black. [Configuration 10] The volume resistivity of the elastic layer is 10 3 Ωcm or more 10 11 The developing roller according to any one of [Configuration 1] to [Configuration 9], wherein the resistivity is in the range of Ωcm or less. [Configuration 11] A process cartridge configured to be detachably mounted in a main body of an electrophotographic image forming apparatus, A process cartridge comprising the developing roller according to any one of [Configuration 1] to [Configuration 10]. [Configuration 12] An electrophotographic image forming apparatus comprising at least an image carrier, a charging device, a developing device, and a transfer device that transfers a formed image onto recording paper, wherein the developing device has the developing roller according to any one of [Configuration 1] to [Configuration 10].

[0085] 10 Developing roller 11 Conductive substrate 12 Elastic layer 31 First area 32 Second area 33 Third area 34 4th area 100 Process cartridge 101 Image carrier 102 Charging member 103 Developing material 200 Electrophotographic image forming apparatus

Claims

1. a conductive substrate; a conductive elastic layer consisting of a single layer on the outer periphery of the substrate; A developing roller having the elastic layer contains a diene rubber, the elastic layer has a crown shape in which the outer diameter of a central portion in a longitudinal direction along the axis of the base is larger than the outer diameters of both end portions in the longitudinal direction; The thickness of the elastic layer is 0.30 mm or more, The length of the elastic layer in the longitudinal direction is defined as L, and positions of (1 / 10)L, (1 / 2)L, and (9 / 10)L from one end of the elastic layer to the other end in the longitudinal direction are defined as P1, P2, and P3, respectively; In the cross section in the thickness direction at each of the positions P1, P2, and P3, when the elastic moduli in the first region from the outer surface of the elastic layer to a depth of 0.1 μm are E11, E12, and E13, respectively, The E11, the E12, and the E13 are all 500 MPa or more, In the cross section in the thickness direction of the elastic layer at each of the positions P1, P2, and P3, The elastic moduli of a second region at a depth of 0.5 μm or more and 0.6 μm or less from the outer surface of the elastic layer are defined as E21, E22, and E23, respectively; When the elastic moduli of the third region at a depth of 1.0 μm or more and 1.1 μm or less from the outer surface of the elastic layer are E31, E32, and E33, respectively, The E11, the E12, the E13, the E21, the E22, the E23, the E31, the E32, and the E33 satisfy any of the following formulas (1) to (3): E11 ≧ E21 ≧ E31 (1) E12 ≧ E22 ≧ E32 (2) E13 ≧ E23 ≧ E33 (3) When the elastic moduli of a fourth region at a depth of 5.0 μm or more and 5.1 μm or less from the outer surface of the elastic layer in the cross section in the thickness direction of the elastic layer at each of the positions P1, P2, and P3 are E41, E42, and E43, respectively, E41, E42 and E43 are all 100 MPa or less; A developing roller characterized by:

2. 2. The developing roller according to claim 1, wherein the elastic layer has a thickness of 0.30 mm or more and 3.00 mm or less.

3. The E11, the E31 and the E41, the E12, the E32 and the E42, and the E13, the E33 and the E43 satisfy any of the following formulas (4) to (6): (E31-E11) / (E41-E11)≧0.50 (4) (E32-E12) / (E42-E12)≧0.50 (5) (E33-E13) / (E43-E13)≧0.50 (6) 2. The developing roller according to claim 1.

4. 2. The developing roller according to claim 1, wherein the diene rubber is an acrylonitrile-butadiene rubber.

5. 5. The developing roller according to claim 4, wherein the amount of acrylonitrile in the acrylonitrile-butadiene rubber is 15% by mass or more and 42% by mass or less.

6. The developer roller of claim 1 , wherein the elastic layer comprises a conductive agent.

7. 7. The developer roller of claim 6, wherein the conductive agent is carbon black.

8. The volume resistivity of the elastic layer is 10 ３ Ωcm or more 10 １１ 2. The developing roller according to claim 1, wherein the surface roughness is in the range of Ωcm or less.

9. A process cartridge configured to be detachably mounted in a main body of an electrophotographic image forming apparatus, The process cartridge has the developing roller according to any one of claims 1 to 8. A process cartridge characterized by:

10. An electrophotographic image forming apparatus comprising at least an image carrier, a charging device, a developing device, and a transfer device for transferring a formed image onto a recording sheet, The developing device has the developing roller according to any one of claims 1 to 8. Electrophotographic image forming apparatus characterized in that:

Images