A charging roller includes a conductive shaft, an elastic body layer formed on an outer periphery of the conductive shaft, and a surface layer formed on an outer periphery of the elastic body layer. The surface layer contains a binder resin and conductive particles. The binder resin contains only a thermoplastic resin. The thermoplastic resin has a water contact angle of not less than 40 but less than 180. The conductive particles contain first conductive particles and second conductive particles. The first conductive particles are metal oxide particles. A content of the first conductive particles in the surface layer is not less than 10.0% by mass but not more than 55.0% by mass. A particle size distribution of the conductive particles has at least one peak within a range of not less than 0.01 m but not more than 1.00 m.

A charging roller includes a conductive shaft, an elastic body layer formed on an outer periphery of the conductive shaft, and a surface layer formed on an outer periphery of the elastic body layer. The surface layer contains a binder resin and conductive particles. The binder resin contains only a thermoplastic resin. The thermoplastic resin has a water contact angle of not less than 40 but less than 180. The conductive particles contain first conductive particles and second conductive particles. The first conductive particles are metal oxide particles. A content of the first conductive particles in the surface layer is not less than 10.0% by mass but not more than 55.0% by mass. A particle size distribution of the conductive particles has at least one peak within a range of not less than 0.01 m but not more than 1.00 m.

A charging roller includes a conductive shaft, an elastic body layer formed on an outer periphery of the conductive shaft, and a surface layer formed on an outer periphery of the elastic body layer. The surface layer contains a binder resin and conductive particles. The binder resin contains only a thermoplastic resin. The conductive particles contain first conductive particles and second conductive particles. The first conductive particles are carbon black particles. A particle size distribution of the conductive particles has at least one peak within a range of not less than 0.01 m but not more than 1 m. A water contact angle x of the thermoplastic resin and a content y of the first conductive particles in the conductive particles satisfy the following expressions: 40y, y(800/27)x+(280/9), and y8x+200.

A charging roller includes a conductive shaft, an elastic body layer formed on an outer periphery of the conductive shaft, and a surface layer formed on an outer periphery of the elastic body layer. The surface layer contains a binder resin and conductive particles. The binder resin contains only a thermoplastic resin. The conductive particles contain first conductive particles and second conductive particles. The first conductive particles are carbon black particles. A particle size distribution of the conductive particles has at least one peak within a range of not less than 0.01 m but not more than 1 m. A water contact angle x of the thermoplastic resin and a content y of the first conductive particles in the conductive particles satisfy the following expressions: 40y, y(800/27)x+(280/9), and y8x+200.

A charging roller includes a conductive shaft, an elastic body layer formed on an outer periphery of the conductive shaft, and a surface layer formed on an outer periphery of the elastic body layer. The surface layer contains a binder resin and conductive particles. The binder resin contains only a thermoplastic resin. The conductive particles contain first conductive particles and second conductive particles. The first conductive particles are carbon black particles. A particle size distribution of the conductive particles has at least one peak within a range of not less than 0.01 m but not more than 1 m. A water contact angle y of the thermoplastic resin and a ratio x of a surface area of the first conductive particles with respect to a surface area of the entire conductive particles satisfy the following expressions: 40y<180, y(800/13)x+(408/13), and y400x+3440.

A charging roller includes a conductive shaft, an elastic body layer formed on an outer periphery of the conductive shaft, and a surface layer formed on an outer periphery of the elastic body layer. The surface layer contains a binder resin and conductive particles. The binder resin contains only a thermoplastic resin. The conductive particles contain first conductive particles and second conductive particles. The first conductive particles are carbon black particles. A particle size distribution of the conductive particles has at least one peak within a range of not less than 0.01 m but not more than 1 m. A water contact angle y of the thermoplastic resin and a ratio x of a surface area of the first conductive particles with respect to a surface area of the entire conductive particles satisfy the following expressions: 40y<180, y(800/13)x+(408/13), and y400x+3440.

A developing apparatus including: a toner configured to have toner particle and external additive; a toner carrying member configured to carry the toner; and an charge injection member configured to inject electric charge into the toner, in which the external additive contain titanium atom-containing fine particles containing a compound containing titanium atoms, a presence ratio of the titanium atoms is 0.05 to 4.00 atomic % when a surface of the toner is measured using X-ray photoelectron spectroscopy, the toner carrying member is a developing roller having a substrate having a conductive outer surface and a resin layer on the outer surface of the substrate, impedance of the developing roller measured under specific conditions is 1.0010.sup.6 or more, and a maximum value of a surface potential measured under specific conditions is less than 20.0 V.

A developing apparatus including: a toner configured to have toner particle and external additive; a toner carrying member configured to carry the toner; and an charge injection member configured to inject electric charge into the toner, in which the external additive contain titanium atom-containing fine particles containing a compound containing titanium atoms, a presence ratio of the titanium atoms is 0.05 to 4.00 atomic % when a surface of the toner is measured using X-ray photoelectron spectroscopy, the toner carrying member is a developing roller having a substrate having a conductive outer surface and a resin layer on the outer surface of the substrate, impedance of the developing roller measured under specific conditions is 1.0010.sup.6 or more, and a maximum value of a surface potential measured under specific conditions is less than 20.0 V.

An electrophotographic photoreceptor includes a conductive substrate, a first undercoat layer that is provided on the conductive substrate, a second undercoat layer that is provided on the first undercoat layer, and a photosensitive layer that is provided on the second undercoat layer, in which the first undercoat layer contains at least one electron transport material selected from the group consisting of a compound represented by Formula (1), a compound represented Formula (2), and a compound represented by Formula (3), and a binder resin, and a content of silica particles in the first undercoat layer is 0% by mass or 5% by mass or less, and the second undercoat layer contains at least one electron transport material selected from the group consisting of the compound represented by Formula (1), the compound represented Formula (2), and the compound represented by Formula (3), silica particles, and a binder resin, and a content of the silica particles in the second undercoat layer is larger than the content of the silica particles in the first undercoat layer.

##STR00001##

In Formula (1), R.sup.11, R.sup.12, R.sup.13, R.sup.14, R.sup.15, R.sup.16, R.sup.17, and R.sup.18 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom, R.sup.11 and R.sup.12, R.sup.12 and R.sup.13, or R.sup.13 and R.sup.14 may be each independently linked to each other to form a ring, and R.sup.15 and R.sup.16, R.sup.16 and R.sup.17, or R.sup.17 and R.sup.18 may be each independently linked to each other to form a ring.

In Formula (2), R.sup.21, R.sup.22, R.sup.23, R.sup.24, R.sup.25, R.sup.26, R.sup.27, and R.sup.28 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom, R.sup.21 and R.sup.22, R.sup.22 and R.sup.23, or R.sup.23 and R.sup.24 may be each independently linked to each other to form a ring, and R.sup.25 and R.sup.26, R.sup.26 and R.sup.27, or R.sup.27 and R.sup.28 may be each independently linked to each other to form a ring.

In Formula (3), R.sup.31, R.sup.32, R.sup.33, R.sup.34, R.sup.35, R.sup.36, R.sup.37, and R.sup.38 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an alkoxycarbonyl group, or a halogen atom.

An electrophotographic photoreceptor includes a conductive substrate, a first undercoat layer that is provided on the conductive substrate, a second undercoat layer that is provided on the first undercoat layer, and a photosensitive layer that is provided on the second undercoat layer, in which the first undercoat layer contains at least one electron transport material selected from the group consisting of a compound represented by Formula (1), a compound represented Formula (2), and a compound represented by Formula (3), and a binder resin, and a content of silica particles in the first undercoat layer is 0% by mass or 5% by mass or less, and the second undercoat layer contains at least one electron transport material selected from the group consisting of the compound represented by Formula (1), the compound represented Formula (2), and the compound represented by Formula (3), silica particles, and a binder resin, and a content of the silica particles in the second undercoat layer is larger than the content of the silica particles in the first undercoat layer.

##STR00001##

In Formula (1), R.sup.11, R.sup.12, R.sup.13, R.sup.14, R.sup.15, R.sup.16, R.sup.17, and R.sup.18 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom, R.sup.11 and R.sup.12, R.sup.12 and R.sup.13, or R.sup.13 and R.sup.14 may be each independently linked to each other to form a ring, and R.sup.15 and R.sup.16, R.sup.16 and R.sup.17, or R.sup.17 and R.sup.18 may be each independently linked to each other to form a ring.

In Formula (2), R.sup.21, R.sup.22, R.sup.23, R.sup.24, R.sup.25, R.sup.26, R.sup.27, and R.sup.28 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an aryloxy group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkoxycarbonylalkyl group, an aryloxycarbonylalkyl group, or a halogen atom, R.sup.21 and R.sup.22, R.sup.22 and R.sup.23, or R.sup.23 and R.sup.24 may be each independently linked to each other to form a ring, and R.sup.25 and R.sup.26, R.sup.26 and R.sup.27, or R.sup.27 and R.sup.28 may be each independently linked to each other to form a ring.

In Formula (3), R.sup.31, R.sup.32, R.sup.33, R.sup.34, R.sup.35, R.sup.36, R.sup.37, and R.sup.38 each independently represent a hydrogen atom, an alkyl group, an alkoxy group, an aralkyl group, an aryl group, an alkoxycarbonyl group, or a halogen atom.