1. Field of the Invention
An apparatus consistent with the present invention relates to an image fusing unit of a liquid electrophotographic printer.
2. Description of the Related Art
In a typical liquid electrophotographic printer such as a color laser printer, a desired image is developed on a photosensitive medium with a developer liquid mixture of charged toner particles and solvent, and then, the developed image is transferred to a sheet of print paper.
However, since the image transferred onto the print paper includes a large amount of solvent, an image fusing unit is needed to dry the image after transfer and completely fuse it on the print paper.
FIG. 1 shows a conventional image fusing unit for drying and fusing which is disclosed in U.S. Pat. No. 5,465,146. As shown in the drawing, the image fusing unit includes a drying portion 1 for drying a sheet of paper C where an image C1 is transferred in a non-contact manner, and a fusing portion 2 for fusing the image C1 by heating and pressing the paper C. The drying portion 1 includes a first roller R1 where a heater H1 is built in, a drying belt B circulating between the first roller R1 and a second roller R2. The fusing portion 2 includes the second roller R2 and a third roller R3 where a heater H2 is built in and rotating in contact with the second roller R2.
In the above structure, the paper C transferred to the image fusing unit through a transfer belt T is heated and dried while passing through the drying portion 1. That is, heat generated from the heater H1 of the first roller R1 heats the drying belt B and the paper C passing under the drying belt B receives radiant heat of the heated drying belt B. This heat dries the image C1 on the paper C and the solvent included in the image C1 is vaporized and thus removed. Then, the paper C is heated and pressed as it passes between the second roller R2 and third roller R3 of the fusing portion 2, so that the image C1 which is previously dried is completely fused on the paper C.
However, in the image fusing unit having the above structure, since the drying portion 1 is configured in a non-contact heating manner, the efficiency of heat in the drying work is low. That is, since the paper C is heated in a non-contact manner through the radiant heat of the drying belt B heated by the heater H1, even when the temperature of the surface of the drying belt B is high, the temperature of the surface of the paper C heated thereby is quite low as compared to that of the drying belt B. Thus, in order to obtain a desired degree of dryness by increasing the temperature of the paper C to a predetermined level, since the temperature of the heater H1 must be much higher than the predetermined level, much energy is consumed accordingly. To solve the problem, the paper C is preferably dried in a contact manner. In this case, however, since an image which is not sufficiently dried needs to be contacted, the image may be damaged during a drying step. Therefore, an image fusing unit having an improved structure to solve the above problem is required.
To solve the above-described problems, it is an aspect of the present invention to provide an improved image fusing unit of a liquid electrophotographic printer which can restrict damage to an image while increasing the efficiency of heat during image drying.
To achieve the above aspect, there is provided an image fusing unit of a liquid electrophotographic unit for fusing an image developed by a developer, which is a mixture of a toner and a liquid solvent, and transferred onto a sheet of paper, the image fusing unit comprises a charging portion installed on a transfer path of the paper and which applies electric potential in a direction in which the toner is in close contact with the paper, a drying portion which dries the image by directly contacting and heating the paper, and a fusing portion which fixes the image to the paper by heating and pressing the paper.