Black toner with defined loss tangent
To provide a black toner having excellent charging property and transferring property against a severe environmental change. The black toner includes toner particle containing at least a binder resin, carbon black and a releasing agent, wherein: the toner particles have a weight-average particle diameter of 3.5 to 8.0 μm; total amount of acid value and hydroxyl value of the toner is 30 to 75 mgKOH/g; average circularity of particles contained in the toner having circle-equivalent diameter of 2 μm or more is 0.915 to 0.960; loss tangent tan δ (10 3 to 10 4 Hz) of the toner is represented by the following expression: tan δ(10 3 to 10 4 Hz)≦0.0060 where the loss tangent tan δ is represented by ∈″/∈′ where ∈″ denotes dielectric loss factor and ∈′ denotes dielectric constant, and tan δ (10 3 to 10 4 Hz) denotes the loss tangent in a frequency range of 10 3 to 10 4 Hz; and a ratio of tan δ (10 5 Hz) to tan δ (5×10 4 Hz) is represented by the following expression: 1.05≦tan δ(10 5 Hz)/tan δ(5×10 4 Hz)≦1.40 where tan δ (10 5 Hz) denotes loss tangent at the frequency of 10 5 Hz and tan δ (5×10 4 Hz) denotes loss tangent at the frequency of 5×10 4 Hz.
1. A black toner comprising toner particles containing at least a binder resin, carbon black and a releasing agent, wherein:
the toner particle has weight-average particle diameter of 3.5 to 8.0 μm;
total value of acid value and hydroxyl value of the toner is 30 to 75 mgKOH/g;
average circularity of particles contained in the toner having circle-equivalent diameter of 2 μm or more is 0.915 to 0.960;
loss tangent tan δ (10 3 to 10 4 Hz) of the toner is represented by the following expression:
tan δ(10 3 to 10 4 Hz)≦0.0060
where the loss tangent tan δ is represented by ∈″/∈′ where ∈″ denotes dielectric loss factor and ∈′ denotes dielectric constant, and tan δ (10 3 to 10 4 Hz) denotes the loss tangent in a frequency range of 10 3 to 10 4 Hz;
a ratio of tan δ (10 5 Hz) to tan δ (5×10 4 Hz) is represented by the following expression:
1.05≦tan δ(10 5 Hz)/tan δ(5×10 4 Hz)≦1.40
where tan δ (10 5 Hz) denotes loss tangent at the frequency of 10 5 Hz and tan δ (5×10 4 Hz) denotes loss tangent at the frequency of 5×10 4 Hz; and
wherein the toner has molecular weight distribution whose main peak is in a range of 3,000 to 40,000 in gel permeation chromatography (GPC) of tetrahydrofuran (THF) extraction, and has Mw/Mn of 70 or more where Mw denotes weight-average molecular weight and Mn denotes number-average molecular weight.
2. The black toner according to claim 1 , wherein the toner has a peak temperature of maximum endothermic peak of 60 to 95° C. in a temperature range of 30 to 200° C. of an endothermic curve of differential scanning calorimetry (DSC) measurement.