Gloss imparting method, image forming method, fixing apparatus and image forming apparatus

1. A gloss-imparting method comprising:

(a) applying heat and pressure to one side of a recording material having an image of toner formed on both sides, and fixing the image to the one side of the recording material;

(b) cooling the one side of the recording material on which the image was fixed in the step (a);

(c) applying heat and pressure to the other side of the recording material cooled in the step (b), and fixing the image to the other side of the recording material; and

(d) cooling the other side of the recording material on which the image was fixed in the step (c),

in the step (a), the fixing being performed such that a value of exp(−T·tan δ 0 ) will be approximately 0.85 or less, where tan δ 0 is a loss tangent of the toner when measured by dynamic viscoelastic measurement at a frequency of approximately 1 rad/sec at approximately the same temperature as a fixing temperature of the step (a), and T is a fixing time in the step (a).

2. An image forming method comprising:

(a) forming an image of toner on both sides of a recording material;

(b) applying heat and pressure to one side of the recording material having the image formed on both sides, and fixing the image to the one side of the recording material;

(c) cooling the one side of the recording material on which the image was fixed in the step (b);

(d) applying heat and pressure to the other side of the recording material cooled in the step (c), and fixing the image to the other side of the recording material; and

(e) cooling the other side of the recording material on which the image was fixed in the step (d),

in the step (b), the fixing being performed such that a value of exp(−T·tan δ 0 ) will be approximately 0.85 or less, where tan δ 0 is a loss tangent of the toner when measured by dynamic viscoelastic measurement at a frequency of approximately 1 rad/sec at approximately the same temperature as a fixing temperature of the step (b), and T is a fixing time in the step (b).

3. A fixing apparatus comprising:

a first fixing part that applies heat and pressure to one side of a recording material having an image of toner formed on both sides, and fixes the image to the one side of the recording material;

a first cooling part that cools the one side of the recording material on which the image was fixed by the first fixing part;

a second fixing part that applies heat and pressure to the other side of the recording material cooled by the first cooling part, and fixes the image to the other side of the recording material; and

a second cooling part that cools the other side of the recording material on which the image was fixed by the second fixing part,

a value of exp(−T·tan δ 0 ) being approximately 0.85 or less, where tan δ 0 is a loss tangent of the toner when measured by dynamic viscoelastic measurement at a frequency of approximately 1 rad/sec at approximately the same temperature as a fixing temperature of the first fixing part, and T is a fixing time of the first fixing part.

4. The fixing apparatus according to claim 3 , further comprising a third cooling part that cools the one side of the recording material during a period from the fixing by the second fixing part to the cooling by the second cooling part.

5. An image forming apparatus comprising:

an image forming part that forms an image of toner on both sides of a recording material;

a first fixing part that applies heat and pressure to one side of the recording material having the image formed on both sides by the image forming part, and fixes the image to the one side of the recording material;

a first cooling part that cools the one side of the recording material on which the image was fixed by the first fixing part;

a second fixing part that applies heat and pressure to the other side of the recording material cooled by the first cooling part, and fixes the image to the other side of the recording material; and

a second cooling part that cools the other side of the recording material on which the image was fixed by the second fixing part,

a value of exp(−T·tan δ 0 ) being approximately 0.85 or less, where tan δ 0 is a loss tangent of the toner when measured by dynamic viscoelastic measurement at a frequency of approximately 1 rad/sec at approximately the same temperature as a fixing temperature of the first fixing part, and T is a fixing time of the first fixing part.

6. The image forming apparatus according to claim 5 ,

wherein the image forming part forms images of toner of a plurality of colors in layers on the recording material, and

at least the uppermost toner layered on the recording material has a storage elastic modulus of approximately 2×10 3 Pa or less and a loss tangent tan δ 0 of approximately 2 or more, when measured by dynamic viscoelastic measurement at a frequency of approximately 1 rad/sec at approximately the same temperature as a fixing temperature of the first fixing part.

7. The image forming apparatus according to claim 5 , wherein at least the uppermost toner layered on the recording material is configured to include a crystalline linear aliphatic polyester resin and one or more amorphous resins.

8. The image forming apparatus according to claim 5 , wherein the image forming part forms a layer of colorless toner so as to cover an entire surface of the recording material and the image of toner formed thereon.