There is a decolorable toner having a characteristic of decoloring a color at a certain temperature (hereinafter referred to as a “decoloring temperature”). In response to the growing social awareness of environmental protection in recent years, an apparatus, which serves as both an image forming apparatus and an image decoloring apparatus and is capable of reusing paper printed with decolorable toner, has been developed. Moreover, the development of the hybrid type apparatus, which serves as both an image forming apparatus and an image decoloring apparatus and can print an image with one or both of the decolorable toner and the toner that cannot be decolored, has been developed. Hereinafter, the toner that cannot be decolored is described as a non-decolorable toner.
Incidentally, the image forming apparatus includes a fixing device for fixing toner on a sheet. The fixing device fixes the toner on the sheet by heating and pressing the sheet to which the toner is transferred. The fixing device, which includes rollers for heating and pressing the sheet, heats the rollers to a temperature (hereinafter referred to as a “set temperature”) required for fixing the toner on the sheet. Generally, it is necessary to raise the set temperature required for the fixing process with the increase in the amount of the toner fixed on the sheet. In addition, when the binder resin to be used in the non-decolorable toner and the decolorable toner are different from each other according to the difference of the pigment, there is also a case where the fixing temperature of the non-decolorable toner is higher than that of the decolorable toner. As a result, in a printing process after fixing the decolorable toner and the non-decolorable toner on a single sheet at the same time, the set temperature is increased to be close to the decoloring temperature of the decolorable toner, and therefore, the color of the decolorable toner may be decolored. In addition, if the set temperature is set to be lower to avoid the decoloring of the toner, there is a possibility that the fixing failure of the toner is generated.
Further, in a color printing of the decolorable toner or a color printing of the non-decolorable toner, other than in the case in which the decolorable toner and the non-decolorable toner are fixed on the sheet at the same time, the set temperature is also set to be higher. In this way, after setting the set temperature to be higher and having finished the color printing, in a case of desiring to print with a monochrome decolorable toner, similar to the case described above, there is a problem that the color of the decolorable toner will be decolored.