External additive particles including a polymer containing a sulfur atom and a nitrogen atom, wherein the polymer includes a vinyl polymer moiety and a siloxane moiety, relative to a total number of carbon atoms, oxygen atoms, and silicon atoms constituting the external additive particles, a ratio of a number of the silicon atoms constituting the external additive particles is 4.0% or more and 25.0% or less, and in surfaces of the external additive particles analyzed by X-ray photoelectron spectroscopy, relative to a total number of carbon atoms, nitrogen atoms, oxygen atoms, silicon atoms, and sulfur atoms, a ratio of a number of the nitrogen atoms is 0.40% or more and 2.50% or less, and a ratio of a number of the sulfur atoms is 0.05% or more and 0.25% or less.

A toner includes toner particles. The toner particles each include a toner mother particle and an external additive attached to the surface of the toner mother particle. The external additive includes specific resin particles. The specific resin particles contains a specific resin having an alkoxysilyl group. The specific resin may include a first repeating unit derived from a specific monomer having the alkoxysilyl group and a (meth)acryloyl group.

A toner set capable of eliminating unclearness in a color boundary of an image in which a color image and a black image are printed side by side. The toner set includes at least: a black toner for forming a black image; and a color toner for forming a color toner image. The black toner is a toner comprising a black toner particle containing a black colorant formed of carbon black or iron oxide, a binder resin, and a releasing agent, and an external additive. The color toner is a toner comprising a color toner particle containing a color organic colorant, a binder resin, and a releasing agent. A ratio in surface roughness (Sa) between the toners is 1.30≤ surface roughness Sa(C) of color toner/surface roughness Sa(Bk) of black toner ≤4.00. The surface roughness Sa(C) of the color toner is 10 nm to 30 nm.

A developing apparatus comprising a toner and a toner bearing member for bearing the toner, wherein the volume resistivity of the toner is from 1.0×10.sup.10 Ω.Math.cm to 1.0×10.sup.14 Ω.Math.cm, a toner bearing member exhibits multiple elementary processes, the volume resistance value Rdr per unit area of the toner bearing member is from 5.0×10.sup.5 Ω/cm.sup.2 to 2.0×10.sup.8 Ω/cm.sup.2, the capacitance Cdr per unit area of the toner bearing member is from 300 pF/cm.sup.2 to 900 pF/cm.sup.2, and the capacitance per unit area and volume resistance value of the toner as converted by a parallel plate capacitor model at a thickness of 1.5 times the weight-average particle diameter of the toner are in specific relationships.

The present disclosure provides a fine particle containing silicon, wherein the fine particle has a number-average particle diameter of a primary particle of 0.05 μm or more and 0.20 μm or less, wherein the fine particle contains a silicon atom at a ratio of 20% or more with respect to all elements in measurement by X-ray fluorescence.

An electrophotographic apparatus comprising an electrophotographic photosensitive member, a charging unit, and a developing unit, wherein the charging unit has a conductive member contactable with the electrophotographic photosensitive member, and a conductive layer of the conductive member has a matrix-domain structure; at least some of the domains are exposed at the outer surface; a volume resistivity R1 of the matrix and a volume resistivity R2 of the domains satisfy specific relationship; Martens hardness G1 of the matrix and Martens hardness G2 of the domains satisfy relationship G1<G2; the surface roughness Ra of the conductive member is not more than 2.00 μm; the toner has an external additive having a shape factor SF-1 of not more than 115; and A<Dms is satisfied where A is the number-average diameter of the external additive and Dms is a distance between adjacent walls between the domains.

An external additive particle includes a sulfur-containing polymer. The polymer includes a vinyl polymer moiety and a siloxane moiety. The proportion of the number of silicon atoms to the sum of the number of carbon atoms, the number of oxygen atoms, and the number of silicon atoms in the external additive particle is 4.0% or more and 25.0% or less, and sulfur atoms are contained in the surface of the external additive particle as detected by X-ray photoelectron spectroscopy.

A toner comprising a toner particle comprising a binder resin, wherein the toner particle comprises a condensation product of an organosilicon compound, in time-of-flight secondary ion mass spectrometry of the toner particle, a normalized intensity of silicon ions derived from the condensation product of the organosilicon compound is from 7.00×10.sup.−4 to 3.00×10.sup.−2, a normalized intensity of silicon ions after sputtering the toner particle under a specific condition is 6.99×10.sup.−4 or lower, the toner comprises a fine particle on the surface of the toner particle, and the fine particle has at least one selected from the group consisting of a specific fine particle of a polyhydric acid metal salt, a strontium titanate fine particle, a titanium oxide fine particle and an aluminum oxide fine particles.

A toner comprising a toner particle, wherein the toner particle comprises a binder resin, a resin A, and a resin B, the resin A comprises a substituted or unsubstituted silyl group in a molecule, a substituent of the substituted silyl group is at least one selected from the group consisting of an alkyl group having 1 or more carbon atoms, an alkoxy group having 1 or more carbon atoms, a hydroxy group, a halogen atom, and an aryl group having 6 or more carbon atoms, and the resin B comprises an azo group in a molecule.

A toner containing a toner particle, wherein, when a dielectric loss tangent measured at a frequency of 10 kHz in an impedance measurement on the toner in an environment having a temperature of 50° C. and a relative humidity of 50% RH is designated by tan δ50° C.(1), and a dielectric loss tangent measured at a frequency of 10 kHz in an impedance measurement on the toner in an environment having a temperature of 30° C. and a relative humidity of 50% RH after the impedance measurement on the toner in an environment having a temperature of 50° C. and a relative humidity of 50% RH is designated by tan δ30° C.(2), tan δ50° C.(1) is from 0.015 to 0.050, the relationship tan δ50° C.(1)>tan δ30° C.(2) is satisfied, and tan δ30° C.(2)/tan δ50° C.(1) is from 0.25 to 0.66.