Toner for electrophotography, image forming apparatus, and toner manufacturing method

An image forming apparatus comprising:

• an image carrier on which a latent image is formed;
• a developing unit that forms a toner image by supplying a toner to the latent image formed on the image carrier;
• and
• a transfer unit including an intermediate transfer member unit on which of the toner image is transferred from the image carrier, wherein
• the toner is a toner for electrophotography satisfying a relation
• Ft/Dt≦3.0 [nN/μm]
• where Ft is an inter-toner non-electrostatic adhesion force and Dt is a diameter of a toner particle,
• the inter-toner non-electrostatic adhesion force Ft is obtained by measuring a tensile rupture stress St [nN/μm2] and substituting measured tensile rupture stress into Rumpf's equation Ft=St×Dt2×ε/(1−ε), where ε is a toner-layer gap ratio, and
• the tensile rupture stress St is measured, with a temperature inside a cell of 25 degrees Celsius, by filling the toner in a cell having a diameter of 15 millimeters, which can be divided vertically in two, up to a height corresponding to 90 percent of a height of the cell, applying a compressive stress ranged from 0.7×10−2 [N/m2] to 1.5×10−2 [N/m2] by placing down a plate member on the cell at a speed of 0.1 millimeter per second, maintaining a compressed state for about 60 seconds, pulling the cell vertically at a speed of 0.2 millimeter per second, and measuring a tensile rupture stress required for dividing the cell.

A method of manufacturing a toner for electrophotography that is used in an image formation in which a toner image is formed by supplying the toner to a latent image formed on an image carrier, and the toner image is transferred onto a recording medium by using a transfer unit including an intermediate transfer member that on which the toner image is transferred from the image carrier, the toner satisfying a relation Ft/Dt≦3.0 [nN/μm], where Ft is an inter-toner non-electrostatic adhesion force and Dt is a diameter of a toner particle, the inter-toner non-electrostatic adhesion force Ft being obtained by measuring a tensile rupture stress St [nN/μm2] and substituting measured tensile rupture stress into Rumpf's equation Ft=St×Dt2×ε/(1−ε), where ε is a toner-layer gap ratio, the tensile rupture stress St being measured, with a temperature inside a cell of 25 degrees Celsius, by filling the toner in a cell having a diameter of 15 millimeters, which can be divided vertically in two, up to a height corresponding to 90 percent of a height of the cell, applying a compressive stress ranged from 0.7×10−2 [N/m2] to 1.5×10−2 [N/m2] by placing down a plate member on the cell at a speed of 0.1 millimeter per second, maintaining a compressed state for about 60 seconds, pulling the cell vertically at a speed of 0.2 millimeter per second, and measuring a tensile rupture stress required for dividing the cell, the toner including a first toner manufactured so that an average value of the circularity is larger than a predetermined value and a second toner manufactured so that an average value of the circularity is smaller than the predetermined value, the method comprising:

• mixing the first toner and the second toner in a container at a time of shipping.