Generally, a fixing device mounted in an image forming apparatus employs a lamp that emits infrared rays, e.g., a halogen lamp, as a heat source, or employs a method of heating with Joule heat by electromagnetic induction.
In general, fixing devices include a heating roller or a fixing belt coupled to a plurality of rollers and a press roller. It is necessary to reduce the heat capacity of each component as much as possible and to further concentrate heating areas of the fixing device in order to maximize overall thermal efficiency.
Furthermore, typical heating widths are wide, thus making it difficult to intensively provide widely distributed thermal energy to a nip portion.
In addition, fixing quality within the fixing device for an electronic photograph is affected if heat generated unevenness is present in a paper transport direction and in a perpendicular direction thereto. Particularly, with respect to color printing, heating unevenness produces differences in color developing and can generate a gloss-like appearance.
Additionally, in a fixing device in which heat capacity is extremely reduced, additional problems with respect to speed irregularity, warp or deterioration of the belt, and/or expansion of the transport roller exist in that the temperature of parts of the fixing device through which paper does not pass is increased dramatically. Due to energy conservation concerns, heating of such areas is not preferable. As such, due to environmental concerns, an apparatus or method that provides energy to the nip portion which heats only the passing area of the paper or the image forming area in the paper has become an area of focus in the field.
Furthermore, the area adjacent to the image forming area (referred to as an intermediate area) and the area inside the lateral width of the paper is in contact with the image forming area. As such, the heating of such areas affects the heating of the image forming area and the like. It is preferable that the intermediate heating area should have a low temperature in order to conserve energy, but the paper is heated during printing, and the paper typically expands and contracts due to heat. Differences in temperature at the border of the paper result in wrinkling. In addition, a diameter of the press roller (for pressing the paper from a rear surface thereof) changes depending on the temperature. Accordingly, the border between the intermediate area and the image forming area has an uneven shape thus reducing the overall print quality of the paper.