Method of fixing toner on recording medium

A method of fixing on a recording medium an unfixed toner image that is held on the recording medium by using a fixing unit, wherein the fixing unit includes

• a first fixing member that faces a surface of a recording medium on which an unfixed toner layer is held;
• a second fixing member that is in a pressurized contact with the first fixing member so as to form a fixing nip theirbetween;
• and
• a heating unit that heats the unfixed toner layer from a side of the first fixing member so as to fix the unfixed toner layer on the recording medium, wherein
• if a difference between a lower limit temperature TMIN for fixing of a surface of the first fixing member that satisfies a fixity and a minimum temperature TOFF of the surface of the first fixing member at which a hot offset occurs at an exit of the fixing nip when a fixing time, in seconds, that is obtained by dividing a width, in meters, of the fixing nip by a velocity, in m/s, of carrying the recording medium through the fixing nip is set to 1 second is let to be T0, following conditions are satisfied:
• (1) 2.4×103×d/(TC×t)<T0, where d is a thickness of the unfixed toner layer in meters, TC is a thermal conductivity of toner in W/mK, and t is the fixing time in seconds,
• (2) a temperature Ttop of a topmost layer of the toner layer is not greater than the minimum temperature TOFF at which the hot offset of the surface of the first fixing member occurs when the fixing time is set to 1 seconds, and
• (3) a temperature Tbot of a bottommost layer of the toner layer that is in contact with the recording medium is not less than the lower limit temperature TMIN for fixing of the surface of the first fixing member when the fixing time is set to 1 second.

An image forming apparatus comprising:

• an image carrier that holds a latent image;
• a charging unit that charges a surface of the image carrier;
• a latent-image forming unit that forms a latent image on the surface of the image carrier that is charged;
• a developing unit that develops the latent image with a toner and forms an image;
• a transferring unit that transfers the image on a recording medium;
• and
• a fixing unit that forms a fixed image by fixing an unfixed toner that is transferred to the recording medium, wherein the fixing unit includes
• a first fixing member that faces a surface of a recording medium on which an unfixed toner layer is held;
• a second fixing member that is in a pressurized contact with the first fixing member so as to form a fixing nip theirbetween;
• and
• a heating unit that heats the unfixed toner layer from a side of the first fixing member so as to fix the unfixed toner layer on the recording medium, wherein
• if a difference between a lower limit temperature TMIN for fixing of a surface of the first fixing member that satisfies a fixity and a minimum temperature TOFF of the surface of the first fixing member at which a hot offset occurs at an exit of the fixing nip when a fixing time, in seconds, that is obtained by dividing a width, in meters, of the fixing nip by a velocity, in m/s, of carrying the recording medium through the fixing nip is set to 1 second is let to be T0, following conditions are satisfied:
• (1) 2.4×103×d/(TC×t)<T0, where d is a thickness of the unfixed toner layer in meters, TC is a thermal conductivity of toner in W/mK, and t is the fixing time in seconds,
• (2) a temperature Ttop of a topmost layer of the toner layer is not greater than the minimum temperature TOFF at which the hot offset of the surface of the first fixing member occurs when the fixing time is set to 1 seconds, and
• (3) a temperature Tbot of a bottommost layer of the toner layer that is in contact with the recording medium is not less than the lower limit temperature TMIN for fixing of the surface of the first fixing member when the fixing time is set to 1 second.