Image forming apparatus which includes a colorless toner image forming device

1. An image forming apparatus comprising:

a color toner image forming device to form a toner image on a recording medium with a color toner;

a fixing device to heat the toner image on the recording medium to fix the toner image on the recording medium;

a cooling device to cool the fixed toner image;

a colorless toner image forming device to form a toner image on the recording medium with a colorless toner having a storage elastic modulus of 100 or less and a loss tangent of 10 or greater at a heating temperature of the fixing device; and

a control device to control cooling power of the cooling device based on whether or not the colorless toner image forming device forms the toner image.

2. The image forming apparatus according to claim 1 , wherein the control device controls the cooling power of the cooling device by increasing the cooling power of the cooling device when the colorless toner image forming device forms the toner image and not increasing the cooling power of the cooling device when the colorless toner image forming device does not form the toner image.

3. The image forming apparatus according to claim 2 , wherein, when the colorless toner image forming device forms the toner image, the control device increases the cooling power of the cooling device to reduce a temperature of the toner image to be equal to or lower than an offset resistance critical temperature.

4. The image forming apparatus according to claim 3 , wherein the offset resistance critical temperature is obtained by a tape peel test.

5. The image forming apparatus according to claim 1 , wherein the colorless toner employed in the colorless toner image forming device is an oilless fixing toner.

6. The image forming apparatus according to claim 1 , wherein the cooling device includes a contact-type cooling unit that directly contacts and cools the toner image on the recording medium.

7. The image forming apparatus according to claim 6 , wherein the cooling device further includes an auxiliary cooling unit that assists the cooling of the toner image by the contact-type cooling unit, and

wherein the control device changes cooling power of the contact-type cooling unit by using the auxiliary cooling unit.

8. The image forming apparatus according to claim 7 , wherein the auxiliary cooling unit is disposed to cool a rear surface of the recording medium being transported while in contact with the contact-type cooling unit.

9. The image forming apparatus according to claim 1 , wherein the control device changes a transport speed of the recording medium when the recording medium is transported through the cooling device to change the cooling power of the cooling device.

10. The image forming apparatus according to claim 9 , wherein the control device changes the transport speed of the recording medium at a position downstream of the fixing device in a recording medium transport direction.

11. The image forming apparatus according to claim 9 , wherein the change of the transport speed of the recording medium satisfies a relationship V>V′>B/(A+B)×V in which V represents a normal speed for transporting the recording medium when the colorless toner image forming device does not form the toner image, V′ represents a reduced speed for transporting the recording medium when the colorless toner image forming device forms the toner image, A represents a length of a space between adjacent recording media located upstream of the fixing device in a recording medium transport direction, and B represents a length of each of the recording media in the recording medium transport direction.

12. The image forming apparatus according to claim 1 , wherein the control device determines whether or not the colorless toner image forming device forms the toner image based on input setting.