Magnetic toner
To provide a magnetic toner which: enables a stable image density to be obtained irrespective of a use environment; and exhibits excellent low-temperature fixability, little image deterioration upon fixation, high coloring power, and a reduced toner consumption. The present invention relates to a magnetic toner containing at least: a binder resin; and a magnetic body. The binder resin contains a polyester unit. The toner has a weight average particle size of 5.0 to 9.0 μm, a true specific gravity of 1.3 to 1.7 g/cm 3 , and a saturated magnetization of 20 to 35 Am 2 /kg in a magnetic field of 796 kA/m. The dielectric loss tangent (tan δ) of the toner satisfies (tan δ H −tan δ L )/tan δ L ≦0.20 at 100 kHz.
1. A magnetic toner comprising magnetic toner base particles each containing at least a binder resin and magnetic iron oxide, wherein:
(i) the binder resin contains a polyester unit;
(ii) the toner has a weight average particle size (D4) of 5.0 to 9.0 μm;
(iii) the toner has a true specific gravity of 1.34 to 1.56 g/cm 3 ;
(iv) the toner has a saturated magnetization of 20 to 35 Am 2 /kg in a magnetic field of 796 kA/m;
(v) the toner contains 60 number % or more of toner having a circularity of 0.93 or more; and
(vi) a dielectric loss tangent (tan δ) of the toner at 100 kHz satisfies the following formula (I):
(tan δ H −tan δ L )/tan δ L <0.20 (1)
wherein tan δ H represents a dielectric loss tangent of the toner at a glass transition temperature (° C.)+10° C. and tan δ L represents a dielectric loss tangent of the toner at the glass transition temperature (° C.)−10° C.
2. A magnetic toner according to claim 1 , wherein the toner contains 75 number % or more of toner having a circularity of 0.95 or more.
3. A magnetic toner according to claim 1 or 2 , wherein a dielectric loss tangent (tan δ) of the toner at 100 kHz and 40° C. is 2×10 −3 to 1×10 −2 .
4. A magnetic toner according to claim 1 or 2 , wherein a dielectric constant of the toner at 100 kHz and 40° C. is 15 to 40 (pF/m).
5. A magnetic toner according to claim 1 or 2 , wherein the magnetic iron oxide has a number average particle size of 0.08 to 0.30 μm.
6. A magnetic toner according to claim 1 or 2 , further comprising 30 mass % or more of a component having a molecular weight of 10,000 or less in a molecular weight distribution of the toner.
7. A magnetic toner according to claim 1 or 2 , wherein the binder resin contains two or more kinds of resins different from each other in softening point.