Electrostatic latent image developing toner
A composite core of a toner particle is a composite of a toner core containing a polyester resin and a plurality of resin particles each containing a first resin. A shell layer partially covering a surface of the composite core is a film containing a second resin. The first resin has a glass transition point that is 10° C. or more higher than a glass transition point of the second resin. The plurality of resin particles each have a particle diameter that is 1.5 times or more greater than a thickness of the shell layer. An amount of the resin particles is at least 0.3 parts by mass and no greater than 2.0 parts by mass relative to 100 parts by mass of the toner cores. The resin particles have a positive zeta potential at pH 4.
1. An electrostatic latent image developing toner comprising:
a plurality of toner particles each including a composite core and a shell layer partially covering a surface of the composite core, wherein
the composite core is a composite of a toner core containing a polyester resin and a plurality of resin particles each containing a first resin,
the plurality of resin particles each adhere to a surface of the toner core,
the shell layer is a film containing a second resin,
the first resin has a glass transition point that is 10° C. or more higher than a glass transition point of the second resin,
the plurality of resin particles each have a particle diameter that is 1.5 times or more greater than a thickness of the shell layer,
an amount of the resin particles is at least 0.3 parts by mass and no greater than 2.0 parts by mass relative to 100 parts by mass of the toner cores,
the resin particles have a positive zeta potential at pH 4 measured by laser Doppler electrophoresis,
the resin particles each include a top portion, a middle portion, and a bottom portion,
the top portion of each resin particle protrudes from a surface of the shell layer,
the middle portion of each resin particle is in contact with the shell layer, and
the bottom portion of each resin particle is embedded in the toner core.
2. The electrostatic latent image developing toner according to claim 1 , wherein
the shell layer selectively covers a surface region of the composite core where the resin particles are not present.
3. The electrostatic latent image developing toner according to claim 1 , wherein
the toner particles each include: a toner mother particle including the composite core and the shell layer; and an external additive adhering to a surface of the toner mother particle,
the external additive includes a powder of inorganic particles adhering to the surface of the toner mother particle mainly by Van der Waals force or electrostatic force, and
the powder of the inorganic particles has a number average primary particle diameter of at least 10 nm and no greater than 30 nm.
4. The electrostatic latent image developing toner according to claim 1 , wherein
the thickness of the shell layer is at least 10 nm and no greater than 40 nm, and
the particle diameter of each of the plurality of resin particles is at least 30 nm and no greater than 100 nm.
5. The electrostatic latent image developing toner according to claim 4 , wherein
the second resin is a thermoplastic resin,
the shell layer is a film substantially formed from the thermoplastic resin,
the first resin is more readily positively chargeable than the second resin, and
the second resin is more hydrophobic than the first resin.
6. The electrostatic latent image developing toner according to claim 5 , wherein
the shell layer covers at least 70% and no greater than 95% of a surface area of the toner core.
7. The electrostatic latent image developing toner according to claim 1 , wherein
the first resin is a polymer of monomers including a (meth)acryloyl group-containing quaternary ammonium compound, and
the second resin is a polymer of monomers including a styrene-based monomer and a (meth)acrylic acid alkyl ester.
8. The electrostatic latent image developing toner according to claim 1 , wherein
the first resin is a polymer of monomers including a (meth)acrylamidoalkyltrimethylammonium salt and an acrylic acid-based monomer, and
the second resin is a polymer of monomers including a styrene-based monomer and a (meth)acrylic acid alkyl ester.
9. The electrostatic latent image developing toner according to claim 1 , wherein
the first resin includes a repeating unit represented by formula (1) shown below and a repeating unit represented by formula (2) shown below,
a quaternary ammonium cation in the repeating unit represented by formula (1) forms a salt through ionic bonding to chlorine, and
the second resin includes a repeating unit represented by formula (3) shown below,
where in formula (1),
R 11 and R 12 each represent, independently of one another, a hydrogen atom, a halogen atom, or an optionally substituted alkyl group,
R 21 , R 22 , and R 23 each represent, independently of one another, a hydrogen atom, an optionally substituted alkyl group, or an optionally substituted alkoxy group, and
R 2 represents an optionally substituted alkylene group,
in formula (2),
R 31 and R 32 each represent, independently of one another, a hydrogen atom, a halogen atom, or an optionally substituted alkyl group, and
R 33 represents a hydrogen atom or an optionally substituted alkyl group,
in formula (3),
R 41 to R 45 each represent, independently of one another, a hydrogen atom, a halogen atom, a hydroxyl group, an optionally substituted alkyl group, an optionally substituted alkoxy group, or an optionally substituted aryl group, and
R 46 and R 47 each represent, independently of one another, a hydrogen atom, a halogen atom, or an optionally substituted alkyl group.