Image fusing unit of liquid electrophotographic printer

Information

  • Patent Grant
  • 6618568
  • Patent Number
    6,618,568
  • Date Filed
    Friday, February 22, 2002
    22 years ago
  • Date Issued
    Tuesday, September 9, 2003
    21 years ago
Abstract
An image fusing unit of a liquid electrophotographic unit for fusing an image developed by a developer which is a mixture of toner particles and liquid solvent and transferred onto a sheet of paper includes a charging portion installed on a transfer path of the paper for applying electric potential in a direction in which the toner is in close contact with the paper, a drying portion for drying the image by directly contacting and heating the paper, and a fusing portion for fixing the image to the paper by heating and pressing the paper. Thus, the efficiency of heat can be improved by drying in the direct contact method. Also, by closely pressing the toner against the paper prior to drying, the disadvantage according to the contact type drying method, that is, the toner adheres to a contact member, can be solved.
Description




BACKGROUND OF THE INVENTION




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 C


1


is transferred in a non-contact manner, and a fusing portion


2


for fusing the image C


1


by heating and pressing the paper C. The drying portion


1


includes a first roller R


1


where a heater H


1


is built in, a drying belt B circulating between the first roller R


1


and a second roller R


2


. The fusing portion


2


includes the second roller R


2


and a third roller R


3


where a heater H


2


is built in and rotating in contact with the second roller R


2


.




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 H


1


of the first roller R


1


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 C


1


on the paper C and the solvent included in the image C


1


is vaporized and thus removed. Then, the paper C is heated and pressed as it passes between the second roller R


2


and third roller R


3


of the fusing portion


2


, so that the image C


1


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 H


1


, 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 H


1


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.




SUMMARY OF THE INVENTION




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.











BRIEF DESCRIPTION OF THE DRAWINGS




The above aspects and advantages of the present invention will become more apparent by describing in detail illustrative, non-limiting embodiments thereof with reference to the attached drawings, in which:





FIG. 1

is a view of an image fusing unit of a conventional liquid electrophotographic printer; and





FIG. 2

is a view of an image fusing unit of a liquid electrophotographic printer according to the present invention.











DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION




Referring to

FIG. 2

, an image fusing unit of a liquid electrophotographic printer according to an illustrative, non-limiting embodiment of the present invention includes a charging portion


10


, a contact type drying portion


20


, and a fusing portion


30


. The charging portion


10


includes a charger


11


for forming electric potential on a path along which a sheet of paper C passes. The charger


11


forms an electric potential in a direction in which an image C


1


of a developer transferred onto the paper C is pressed against the paper C. That is, since toner in the developer is typically charged to plus (+), as shown in the drawing, the surface of the paper C where the image C


1


is transferred is charged to be relatively higher than the opposite surface thereof so that the toner is in close contact with the paper C by an electric force. This corresponds to a preliminary pressing step to prevent the toner from adhering to a drying belt


21


when the paper C passes through a contact type drying portion


20


which is described below.




The drying portion


20


includes the drying belt


21


endlessly circulating between a drying roller


22


and a support roller


23


, a backup roller


24


rotating by being in close contact with the drying belt


21


, a heater


22




a


included in the drying roller


22


, and a regeneration roller


25


including another heater


25




a


for vaporizing solvent absorbed in the drying belt


21


by contacting the drying belt


21


. Thus, the paper C passing the charging portion


10


passes between the drying belt


21


and the backup roller


24


and dried by directly contacting the drying belt


21


heated by the heater


22




a


of the drying roller


22


. In this case, part of the solvent included in the image formed on the paper C is vaporized by receiving the heat from the drying belt


21


and part thereof is removed by being absorbed by the drying belt


21


. For this purpose, the drying belt


21


is preferably, but not necessarily, formed by coating silicon on a metallic substrate so that the solvent can be easily absorbed by the coating layer. The drying roller


22


and the regeneration roller


25


can be formed to be an aluminum roller coated with silicon. The backup roller


24


can be formed to be a silicon foamed conductive roller.




The fusing portion


30


includes a fusing roller


31


having a built-in heater


31




a,


and a backup roller


32


rotating in close contact with the fusing roller


31


and passing the paper C therebetween. Thus, the paper C passing through the drying portion


20


is heated and pressed while passing between the fusing roller


31


and the backup roller


32


and the image C


1


is completely fixed to the paper C. The fusing roller


31


may be an aluminum roller coated with TEFLON and the backup roller


32


may be a silicon foamed conductive roller.




Reference numeral


41


denotes a drive roller for driving the drying roller


22


. reference numeral


43


denotes a driven roller for driving the fusing roller


31


by receiving power of the drive roller


41


via a power transfer belt


42


.




When a print job is performed, the paper C where the image C


1


is transferred enters the image fusing unit after the developing and transferring steps. First, when the paper C enters the charging portion


10


, the toner forming the image C


1


is forced to contact the paper C more closely by the electric potential of the charger


11


.




Next, the paper C passes between the drying belt


21


and the backup roller


24


of the drying portion


20


. At this stage, the solvent included in the image C


1


is absorbed by the drying belt


21


and part of the solvent is vaporized by the heat generated from the heater


22




a


of the drying roller


22


. That is, since the drying work is performed by directly contacting the paper C, the efficiency of transfer of heat to the paper C is superior and an effect of removing through absorption can be achieved. As the toner is pressed more closely to the paper C in the charging portion


10


, a phenomenon in which the toner adheres to the drying belt


21


is restricted. Also, the solvent absorbed by the drying belt


21


is heated by the heater


25




a


of the regeneration roller


25


and vaporized. Thus, the drying belt


21


continues to absorb the solvent.




The paper C dried as described above finally passes through the fusing portion


30


. At this stage, the paper C is heated and pressed between the fusing roller


31


and the backup roller


32


so that the image C


1


is completely fixed to the paper C. The paper C where the image C


1


is fixed is exhausted through an outlet (not shown) of the printer along a predetermined path. Thus, the image fusing unit can provide a superior efficiency of heating as heat is applied in a state of directly contacting the paper in the drying portion, and an effect of removing solvent by absorption. Also, since the toner is pressed closer to the paper in the charging portion, the toner is prevented from adhering to the drying belt during the drying step although it is a contact type drying method.




As described above, in the image fusing unit of a liquid electrophotographic printer according to the present invention, the efficiency of heat can be improved by drying in the direct contact method. Also, by closely pressing the toner against the paper prior to drying, the disadvantage according to the contact type drying method, that is, the toner adheres to a contact member, can be solved.




It is contemplated that numerous modifications may be made to the image fusing unit of a liquid electrophotographic printer of the present invention without departing from the spirit and scope of the invention as defined in the following claims.



Claims
  • 1. 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 comprising: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.
  • 2. The image fusing unit as claimed in claim 1, wherein the drying portion comprises:a drying belt arranged on the transfer path of the paper to contact the paper and supported by a plurality of rollers to circulate in an endless path; a heater for heating which is included in at least one of the rollers for supporting the drying belt; and a backup roller rotating in contact with the drying belt and allowing the paper to pass between the backup roller and the drying belt.
  • 3. The image fusing unit as claimed in claim 2, wherein the drying portion further comprises a regeneration roller including a heater and rotating in contact with the drying belt to vaporize the liquid solvent absorbed therein.
  • 4. The image fusing unit as claimed in claim 2, wherein the drying belt comprises silicon coated on a metallic substrate.
  • 5. The image fusing unit as claimed in claim 1, wherein the fusing portion comprises:a pair of rollers rotating in contact with each other and allowing the paper to pass between the rollers; and a heater for heating which is included in at least one of the rollers.
  • 6. The image fusing unit as claimed in claim 2, further comprising a drive roller which drives one of the rollers for supporting the drying belt.
  • 7. The image fusing unit as claimed in claim 6, further comprising a power transfer belt and a driven roller, wherein the fusing portion includes a heated fusing roller which is driven by the driven roller by receiving power from the drive roller via the power transfer belt.
Priority Claims (1)
Number Date Country Kind
2001-49315 Aug 2001 KR
US Referenced Citations (9)
Number Name Date Kind
4780742 Takahashi et al. Oct 1988 A
4903082 Dyer et al. Feb 1990 A
5025292 Steele Jun 1991 A
5150161 Bujese Sep 1992 A
5164782 Nagayama et al. Nov 1992 A
5495324 Kopp Feb 1996 A
5983048 Moser Nov 1999 A
6418289 Kleckner et al. Jul 2002 B1
20010043821 Okamoto Nov 2001 A1