Toner and two-component developer
Provided are a toner and a two-component developer each of which: shows a small fluctuation in charge quantity and a small fluctuation in image density even under a high-temperature and high-humidity environment; and does not cause any member contamination even after endurance and hence can stably output an image. The toner and the two-component developer each have a feature in that positively chargeable strontium titanate fine particles are added to toner particles having fixed thereto negatively chargeable silica fine particles.
1. A toner, comprising:
toner particles each containing a binder resin, a wax, and a coloring agent; and
silica fine particles A and strontium titanate fine particles B present on surfaces of the toner particles,
wherein:
the silica fine particles A have a number-average particle diameter (D1) of 60 nm or more and 300 nm or less;
when
a coverage rate of the surfaces of the toner particles with the silica fine particles A is defined as a coverage rate X (%) and
a coverage rate with the silica fine particles A fixed to the surfaces of the toner particles is defined as a coverage rate Y (%),
the coverage rate X is 20% or more and 95% or less, and
a ratio [coverage rate Y/coverage rate X] of the coverage rate Y to the coverage rate X is 0.75 or more;
the strontium titanate fine particles B have a fixing rate, measured as indicated in the description, of 0.10 or more and 0.60 or less;
the silica fine particles A are negatively chargeable;
the strontium titanate fine particles B are positively chargeable;
an amount of the silica fine particles A is 2.0 parts by mass or more and 10.0 parts by mass or less when an amount of the toner particles is set to 100 parts by mass; and
an amount of the strontium titanate fine particles B is 0.2 part by mass or more and 1.0 part by mass or less when an amount of the toner particles is set to 100 parts by mass.
2. A toner according to claim 1 , wherein:
surfaces of the silica fine particles A are treated with one of hexamethyldisilazane and a silicone oil; and
surfaces of the strontium titanate fine particles B are treated with one of a fatty acid and a fatty acid metal salt.
3. A toner according to claim 1 , wherein:
primary particles of the strontium titanate fine particles B have a number-average particle diameter of 30 nm or more and 300 nm or less; and
the strontium titanate fine particles B each have a perovskite crystal, and particle shapes of the strontium titanate fine particles B each have one of a cubic shape, a rectangular parallelepiped shape, and a mixture thereof.
4. A toner according to claim 1 , wherein the silica fine particles A have a number-average particle diameter (D1) of 70 nm or more and 280 nm or less.
5. A two-component developer, comprising:
a toner; and
a magnetic carrier,
wherein:
the toner comprises the toner according to claim 1 ; and
the magnetic carrier has a carrier core, and a surface of the carrier core is covered with a copolymer containing, as copolymerization components, a monomer having a structure represented by the following formula (1) and a macromonomer having a structure represented by the following formula (2):
in the formula, R 1 represents a hydrocarbon group having 4 or more carbon atoms, and R 2 represents H or CH 3 ;
in the formula, A represents an alicyclic hydrocarbon group having 5 or more and 10 or less carbon atoms, or a polymer using, as a polymerization component, at least one kind of compound selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, styrene, and acrylonitrile, and R 3 represents H or CH 3 .