WO2007145472A1

WO2007145472A1 - Electro photographic type image forming apparatus

Info

Publication number: WO2007145472A1
Application number: PCT/KR2007/002872
Authority: WO
Inventors: Hyung Woo Kim
Original assignee: Hyung Woo Kim
Priority date: 2006-06-14
Filing date: 2007-06-14
Publication date: 2007-12-21

Abstract

Provided is an electro photographic type image forming apparatus including a conveyor- driven pressurization driving unit having a driving belt; a guide member installed above the pres- surization driving unit, the guide member having a horizontal surface formed in parallel to a horizontal transfer section of the driving belt; a heating unit stacked on the opposite surface to the horizontal surface of the guide member, the heating unit generating heat by using a thin-film heater; and a sleeve mounted to cover the outer surface of the guide member so as to receive the generated heat, frictionally driven while facing the horizontal transfer section of the pressurization driving unit, and transferring a printing medium supplied between the friction surfaces such that toner on the printing medium is thermally fixed.

Description

ELECTRO PHOTOGRAPHIC TYPE IMAGE FORMING

APPARATUS

Technical Field

[1] The present invention relates to an electro photographic type image forming apparatus, in which a heating unit including a thin-film heater is formed on the top surface of a guide member such that the entire surface of the guide member is utilized as a heating plate, and the structure of a pressurization driving unit is conveyor-driven. The electro photographic type image forming apparatus can sufficiently secure a heated area and heating time so as to perform high-speed printing. Background Art

[2] In general, fixing devices used in laser printers and digital photocopiers, which serve to fix toner particles transferred on a printing medium, have a structure shown in Fig. 1.

[3] Fig. 1 is a schematic cross-sectional view of a conventional image forming apparatus using a halogen lamp.

[4] The conventional image forming apparatus includes a heating section composed of a cylindrical metal tube 12 and a halogen lamp 11 installed in the inner central portion of the cylindrical metal tube 12. The cylindrical metal tube 12 has a coating layer 13 formed of Teflon or the like.

[5] The halogen lamp 11 inside the cylindrical metal tube 12 of the heating section generates radiant heat so as to indirectly heat the cylindrical metal tube 12.

[6] Under the cylindrical metal tube 12, a pressing roller 14 is positioned with a printing medium 14 interposed therebetween.

[7] The pressing roller 15 presses the printing medium 14 with a constant force by using a compression spring 16.

[8] Accordingly, powder-type toner 17 is fixed on the printing medium by the heat generated by the heating section such that an image is formed on the printing medium.

[9] In the conventional fixing device, when a printer or digital photocopier is turned on/ off, a preheating time of more than several seconds is required for increasing the temperature of the cylindrical metal tube 12 to a temperature at which the toner 17 can be fixed.

[10] In the conventional fixing device, the heat of the heating section is transmitted as radiant heat to the printing medium through the air or the cylindrical metal tube 12 (indirect heating). Further, when the wait mode is switched into the operation mode, more than several seconds are required for increasing the temperature of the cylindrical metal tube 12 to the fixing temperature. Therefore, the wait time of users increases.

[11] Further, initial power used for operating the halogen lamp of the conventional fixing device is as high as 1.0 to 3kW, which means that the power consumption of the fixing device is considerably large.

[12] Japanese Unexamined Patent Application Publication Nos. 63-212182, 2-157878,

4-44075, 4-44083, 4-204980, and 4-204984 disclose heating fixing devices which adopt a film heating system.

[13] The heating fixing device is closely attached to a heating member (hereinafter, referred to as a heating body) such as a ceramic heater, which is fixed and disposed by a pressurization driving unit or a pressing member, a heat-resistant film (hereinafter, referred to as a fixing film or sleeve) serving as a rotating member for heating. The heating fixing device slidably rotates the fixing film.

[14] Then, a printing medium on which a toner image is formed is introduced into a fixing nip section serving as a pressure contact nip section, in which the fixing film is disposed between the heating body and the pressurization driving unit. The introduced printing medium is carried with the fixing film such that the toner image is permanently fixed on the surface of the printing medium by the pressure of the fixing nip section and the heat applied from the heating body through the fixing film.

[15] In the heating fixing device adopting the film heating system, a linear heating body with a small heat capacity such as a ceramic heater or the like can be used as the heating body. Further, a thin film with a small heat capacity can be used as the fixing film. Accordingly, power can be saved, and wait time can be reduced. Additionally, a method in which a driving roller is provided on the inner surface of the fixing film and a method in which the pressurization driving unit is used as a driving roller and the fixing film is driven by a frictional force between the driving roller and the pressurization driving section are known as a fixing film driving system which is to be used in the heating fixing device adopting the film heating system.

[16] Fig. 2 is a schematic cross-sectional view of a conventional image forming apparatus using a plate-shaped heater, showing an example of the heating fixing device adopting the film heating system.

[17] In Fig. 2, reference numeral 20 represents a heating assembly, and reference numeral 22 represents an elastic pressurization driving unit serving as a pressing member. The elastic pressurization driving unit 22 and the heating assembly 20 disposed in parallel to each other in a vertical direction come in contact with each other, thereby forming a fixing nip portion N.

[18] The heating assembly 20 includes a heater 23 serving as a heating member, a film guide 25 serving as a guide member supporting the heater 23, a cylindrical fixing film 21 serving as a flexible rotating body which is inwardly contacted with the heater 23 and having the film guide 25, and a flange member 26 supporting the fixing film 21 through both ends thereof and inserted into the film guide 25.

[19] The heater 23 is a rectangular ceramic heater which is longitudinally thin and formed to extend along a direction perpendicular to a conveyance direction of a printing medium P. The heater 23 has a small heat capacity as a whole and generates heat by receiving power.

[20] The film guide 25 is a rectangular member having a cross-section formed in a semi- arc, and the side portion thereof extends in the direction perpendicular to the conveyance direction of the printing medium P. The film guide 25 is formed of phenol thermosetting resin. The heater 23 is inserted into a heater insertion groove formed in the central portion of the bottom surface of the film guide 25 in a vertical direction. Accordingly, the heater 23 is fixedly supported.

[21] The cylindrical fixing film 21 is loosely attached to the outside of the film guide 25 into which the heater is inserted.

[22] The flange member 26 includes a collar washer portion 26, which adjusts the movement of the fixing film in an axial direction thereof with the ends of the cylindrical fixing film 21 held, and a sliding portion 26b which is inserted into the inside of the ends of the cylindrical fixing film 21, the sliding portion 26b supporting the ends of the fixing film and having a cross-section formed in a circular arc.

[23] The elastic pressurization driving unit 22 is rotatably bearing- supported between side covers (not shown) of the heating fixing device. The heating assembly 20 has the heater 23 formed in lower portion thereof and is disposed in parallel above the elastic pressurization driving unit 22. The heating assembly 20 and the elastic pressurization driving unit 22 are pressed against each other by a pressing unit (not shown) with respect to the elasticity of the elastic pressurization unit 22. Accordingly, the heater 23 and the elastic pressurization driving unit 22 are contacted with each other by the pressure of the pressing unit. Then, the fixing film 21 is disposed between the heater 23 and the pressurization driving unit 22, and the fixing nip portion N serving as a pressure contact nip portion with a predetermined width is formed by the elastic deformation of the pressurization driving unit 22.

[24] The elastic pressurization driving unit 22 is rotationally driven in a counterclockwise direction by a driving unit (not shown), as indicated by an arrow of Fig. 2. As the elastic pressurization driving unit 22 is rotationally driven, the torque is applied to the fixing film 21 from the fixing nip portion N by a frictional force between the elastic pressurization unit 22 and the fixing film 21. Then, the inner surface of the fixing film 21 comes in close contact with the bottom surface of the heater 23 at the fixing nip portion N such that the fixing film 22 slides along the surface. Accordingly, the fixing film 22 is rotated around the circumference of the film guide 25 at a circum- ferential speed corresponding to that of the elastic pressurization driving unit 22 in a clockwise direction, as indicated by an arrow of Fig. 2.

[25] The movement of the fixing film 21 in the axial direction thereof is adjusted by the collar washer member 26a of the flange member 26. The inside of the end of the fixing film 21 is supported by the sliding portion 26b of the flange member 26 and is rotatably guided.

[26] Then, the fixing film 21 is rotatably driven by the elastic pressurization driving unit

22. In a state where the temperature approaches a predetermined value due to the convection of the heater 23, a non-fixed toner image T is formed. When the printing medium P having the non-fixed toner image T is introduced between the elastic pressurization driving unit 22 and the fixing film 21 at the fixing nip portion P from an image forming unit (not shown), the printing medium P passes through the fixing nip portion N with the fixing film 21 while coming in close contact with the outer surface of the fixing film 21.

[27] While the printing medium P passes through the fixing nip portion N, the heat energy of the heater 23 is applied to the printing medium P through the fixing film 21 such that the non-fixed toner image T of the printing medium P is heated and fixed. Then, the printing medium P passing through the fixing nip portion N is separated from the surface of the fixing film 21 at a separation point A and is then discharged.

[28] Recently, there is a demand for an increase in printing speed. In the conventional image forming apparatus constructed in such a manner, however, when the printing medium is passed at high speed during the heating and fixing operation, the fixing operation is not reliably performed because the heating area of the heater is limited and the heating time is not sufficient.

[29] Further, since the heater is formed on the bottom surface of the film guide, the pressure caused by the pressurization driving unit is applied to the heater, and simultaneously, the heater continuously comes in frictional contact with the sleeve. Therefore, the lifespan of the heater is reduced.

[30] In addition, it takes a long time for the preheating of the heater such that the operation wait time is lengthened.

[31] Furthermore, since a ceramic substrate with low heat conductance is used as the substrate on the heater, an excessive temperature difference occurs between the passage region and non-passage region of the printing medium P. Since expensive Ag/ Pd paste is used as the heater, the manufacturing cost increases. Disclosure of Invention Technical Problem

[32] An advantage of the invention is that it provides an electro photographic type image forming apparatus, in which a heating unit including a thin-film heater is formed on the top surface of a guide member such that the entire surface of the guide member is utilized as a heating plate.

[33] Another advantage of the invention is that it provides a conveyor- structure electro photographic type image forming apparatus in which a pressurization driving unit has more than two rotating shafts.

[34] A further advantage of the invention is that it provides an electro photographic type image forming apparatus having a heating unit which can rapidly generate heat such that preheating time can be reduced.

[35] A still further advantage of the invention is that it provides an electro photographic type image forming apparatus having a pair of heating units formed on and under a guide member. Technical Solution

[36] According to an aspect of the present invention, an electro photographic type image forming apparatus comprises a conveyor-driven pressurization driving unit having a driving belt; a guide member installed above the pressurization driving unit, the guide member having a horizontal surface formed in parallel to a horizontal transfer section of the driving belt; a heating unit stacked on the opposite surface to the horizontal surface of the guide member, the heating unit generating heat by using a thin-film heater; and a sleeve mounted to cover the outer surface of the guide member so as to receive the generated heat, frictionally driven while facing the horizontal transfer section of the pressurization driving unit, and transferring a printing medium supplied between the friction surfaces such that toner on the printing medium is thermally fixed.

[37] Preferably, the heating unit includes a thin-film heater deposited on the outer surface of the guide member so as to be instantly heated by supplied power; and an electrode forming an electrical connection pattern such that power is uniformly supplied to the thin-film heater.

[38] Preferably, the heating unit includes an insulation film deposited on the outer surface of the guide member so as to provide an electric insulation property and a heat conductance property; a thin-film heater deposited on the outer surface of the insulation film so as to be instantly heated by supplied power; and an electrode forming an electrical connection pattern such that power is uniformly supplied to the thin-film heater.

[39] Preferably, the heating unit includes an electrode forming an electrical connection pattern such that power is uniformly supplied to the outer surface of the guide member; and a thin-film heater deposited on the electrode and the guide member so as to be instantly heated by supplied power. [40] Preferably, the heating unit includes an insulation film deposited on the outer surface of the guide member so as to provide an electric insulation property and a heat conductance property; an electrode forming an electrical connection pattern such that power is uniformly supplied to the outer surface of the insulation film; and a thin-film heater deposited on the electrode and the guide member so as to be instantly heated by supplied power.

[41] Preferably, the electrode is formed by a thermal bonding method or a vacuum sintering method.

Advantageous Effects

[42] According to the invention, the heating unit including the thin-film heater is formed on the guide member such that the entire surface of the guide member is utilized as a heating plate, and the structure of a pressurization driving unit is conveyor-driven. Therefore, the electro photographic type image forming apparatus can sufficiently secure a heated area and heating time so as to perform high-speed printing.

[43] Further, as the conveyor-type pressurization driving unit is provided, the apparatus can be reduced in size, and operation-wait time (preheating time) can be reduced due to a high-speed heating characteristic using the thin-film heater.

[44] Furthermore, when the heating unit is formed on and under the guide member, the heating temperature can be significantly increased, and the preheating time can be reduced, compared with when only one heating unit is used. In addition, as an amount of current supplied to each of the heating units is adjusted, problems caused by overload can be prevented, so that the lifespan of the heating units can be expanded. Brief Description of the Drawings

[45] Fig. 1 is a schematic cross-sectional view of a conventional image forming apparatus using a halogen lamp.

[46] Fig. 2 is a schematic cross-sectional view of a conventional image forming apparatus using a plate-shaped heater.

[47] Fig. 3 is a schematic cross-sectional view of an image forming apparatus using a thin-film heater according to a first embodiment of the invention.

[48] Fig. 4 is an expanded view of a portion 'A' of Fig. 3.

[49] Fig. 5 is a schematic view of another example of the pressurization driving unit according to the first embodiment of the invention.

[50] Fig. 6 is an expanded cross-sectional view of a heating unit according to the invention.

[51] Fig. 7 is an expanded cross-sectional view of a modification of the heating unit according to the first embodiment of the invention.

[52] Figs. 8 to 10 illustrate various examples of conductive patterns formed on a thin- film heater according to the invention.

[53] Figs. 11 and 12 illustrate various disposition patterns of an electrode and a thin-film heater according to the invention.

[54] Fig. 13 is a schematic view of a test piece for experimenting the heating unit according to the invention.

[55] Fig. 14 is a graph showing a result that a temperature change is measured in accordance with time in a state where a constant current (50W) is applied to the test piece.

[56] Fig. 15 is a graph showing a result that a temperature change is measured in accordance with a change in amount of current applied to the test piece for a predetermined time (10 seconds).

[57] Fig. 16 is a cross-sectional view of an image forming apparatus using a thin-film heater according to a second embodiment of the invention.

[58] Fig. 17 is an expanded view of a portion "B" of Fig. 16.

[59] Fig. 18 is an expanded view of a portion "C" of Fig. 16.

[60] Fig. 19 is an expanded cross-sectional view of a modification of the heating unit according to the second embodiment of the invention.

[61] Fig. 20 is an expanded cross-sectional view of another modification of the heating unit according to the second embodiment of the invention.

[62] Fig. 21 is a schematic cross-sectional view of an image forming apparatus using a thin-film heater according to a third embodiment of the invention.

[63] Fig. 22 is a schematic cross-sectional view of an image forming apparatus using a thin-film heater according to a fourth embodiment of the invention. Best Mode for Carrying Out the Invention

[64] Hereinafter, preferred embodiments of the invention will be described in detail with reference to the accompanying drawings.

[65] Fig. 3 is a schematic cross-sectional view of an image forming apparatus using a thin-film heater according to a first embodiment of the invention, and Fig. 4 is an expanded view of a portion 'A' of Fig. 3.

[66] As shown in Figs. 3 and 4, the image forming apparatus according to the invention includes a pressurization driving unit 100, a guide member 130, a heating unit 120, and a sleeve 140. The pressurization driving unit 100 is conveyor-driven by a pair of driving wheels 111 which are installed to be spaced at a predetermined distance from each other and are connected through a driving belt 113. The guide member 130 is installed above the pressurization driving unit 110 and has a horizontal surface 131 formed in parallel to a horizontal transfer section 113a of the driving belt 113. The heating unit 120 is stacked on the opposite surface of the horizontal surface 131 of the guide member 130 so as to generate heat by using a thin-film heater 123. The sleeve 140 is mounted to cover the outer surface of the guide member 130 such that the generated heat is received. Further, the sleeve 140 is frictionally driven in a state where it faces a transfer surface of the pressurization driving unit 110, so that a printing medium put therebetween is transferred and toner on the printing medium is thermally fixed.

[67] The pressurization driving unit 110 includes the pair of driving wheels 111 for transmitting power, the driving belt 113 installed to cover the outer circumferences of the driving wheels 111, and a pressing plate 115 which is installed inside the driving belt 113 so as to press the upper surface of the driving belt 113 toward the guide member 130.

[68] Preferably, the pressing plate 115 is elastically supported by a separate elastic member (such as a compression spring or the like) and may be formed of a metal bearing.

[69] As for the driving belt 113, an elastic pressurizing belt can be used, which is formed of a rubber material with a high surface friction coefficient.

[70] To reinforce the strength of the driving belt 113, a plurality of reinforcement pins

113b may be installed in a lateral direction of the elastic rubber plate.

[71] The reinforcement pins 113b can be connected through a link 113c. Depending on products, the number, the thickness, and the material of the reinforcement pins 113b may differ.

[72] The pressing plate 115 has both ends formed in a semi-circle. A pressing-plate sleeve 119 is movably coupled to the outer circumference of the pressing plate 115 and serves to help the driving belt 13 to rotate.

[73] Next, the front surface of the guide member 130 is heated by the heating unit 120 stacked thereon so as to provide a heat source to the sleeve 140 such that toner on a printing medium P is thermally fixed. The guide member 130 includes the horizontal surface 131 on which the heating unit 120 is stacked and a wing portion 133 which is formed to extend from at least one of the left and right ends of the horizontal surface 131.

[74] The wing portion 133 serves to preheat the sleeve 140 before the horizontal surface

131. The wing portion 133 may be formed to have a larger or smaller length and may be formed in various shapes depending on the characteristics of products.

[75] The guide member 130 should have excellent heat conductivity. Further, the guide member 130 should have such excellent mechanical strength as to endure the pressure of the pressurization driving unit 110.

[76] Therefore, it is preferable that the guide member 130 is formed of conductive metal such as aluminum or stainless steel of which the heat conductivity is excellent. However, if the guide member 130 satisfies the above-described condition, it may be formed of a nonmetallic and non-conductive material.

[77] Further, the guide member 130 may have a flange member 150 coupled to either side thereof, the flange member 150 preventing the sleeve 140 from coming off and guiding a driving locus of the sleeve 140.

[78] The heating unit 120 includes a thin-film heater 123 which can be driven by low power (for example, 500W). The thin-film heater 123 is rapidly heated when external power is supplied. Therefore, the thin-film heater 123 can reduce operation- wait time for preheating in a printer or photocopier.

[79] Since the heating unit 120 is deposited with a very small thickness, various office appliances using the electro-photographic scheme can be reduced in size.

[80] The sleeve 140 is formed of thermosetting resin and is mounted to be loosely put on the outside of the guide member 130. The sleeve 140 directly heats and fixes toner T on a printing medium P.

[81] The flange member 150 includes a collar washer 151 which adjusts the movement of the sleeve 140 in an axial direction of the sleeve 140 and a sliding portion 153 which is coupled to both ends of the guide member 130 so as to come in sliding contact with the end of the sleeve 140.

[82] Fig. 5 is a schematic view of another example of the pressurization driving unit according to the first embodiment of the invention. As shown in Fig. 5, the pressurization driving unit 110 according to the invention may have a tension adjusting roller 117 installed between the pair of driving wheels 111, the tension adjusting roller 117 adjusting the tension of the driving belt 113.

[83] As the tension adjusting roller 117 is fixed in such a state that a rotating shaft thereof can move in the vertical direction, it adjusts the tension of the driving belt 113.

[84] Fig. 6 is an expanded cross-sectional view of the heating unit according to the invention, showing a state where the heating unit 120 is installed on the guide member 130 formed of a non-conductive material.

[85] As shown in Fig. 6, the heating unit 120 is installed on the guide member 130 formed of a non-conductive material. The heating unit 120 includes the thin-film heater 123 which is mounted on the outer surface of the guide member 130 and receives power from outside to instantly generate high-temperature heat through instant heating caused by its electric resistor, an electrode 125 which is electrically connected to the thin-film heater 123 and has a specific pattern such that the power supplied from outside can be uniformly applied on the entire surface of the thin-film heater 123, and a protective layer 127 which is coated with a predetermined thickness such that the electrode 125 and the thin-film heater 123 can be protected from the external environment. [86] The guide member 130 may be formed of a non-conductive material such as tempered plastic, heat resistant resin, ceramic, glass, stone and the like, which can endure high temperature of more than 25O⁰C.

[87] Fig. 7 is an expanded cross-sectional view of a modification of the heating unit according to the invention, showing a state where the heating unit 120 is installed on the guide member 130 formed of a conductive material.

[88] As shown in Fig. 7, the heating unit 120 is installed on the guide member 130 formed of a conductive material. The heating unit 120 includes an insulation film 122 which is coated with a predetermined thickness on the inner surface of the guide member 130 such that an electric insulation characteristic and an excellent heat- conduction characteristic are provided, a thin-film heater 123 which is mounted on the insulation film 122 and receives power from outside to instantly generate high- temperature heat through instant heating caused by its electric resistor, an electrode 125 which is electrically connected to the thin-film heater 123 and has a specific pattern such that the power supplied from outside can be uniformly applied on the entire surface of the thin-film heater 123, and a protective layer 127 which is coated with a predetermined thickness such that the electrode 125 and the thin-film heater 123 can be protected from the external environment.

[89] Preferably, the guide member 130 is formed to have a thickness of 1 to 3mm and may be formed of metal such as aluminum or stainless steel.

[90] As shown in Figs. 6 and 7, a plurality of conductive patterns 124 are formed on the thin-film heater 123 so as to help current supply. Therefore, a current applied through the electrode 125 is uniformly supplied onto the entire surface of the thin-film heater 123, and a heating characteristic can be stabilized.

[91] Hereinafter, the properties and constitutional conditions of the respective components such as the insulation film 122, the thin-film heater 123, the conductive patterns 124, the electrode 125, and the protective film 127, which compose the heating unit 120 of the invention, will be described in more detail.

[92] The insulation film 122 is formed to have a thickness as small as possible, so that heat generated from the thin-film heater 123 can be quickly transmitted to the guide member 130. Further, the insulation film 122 is formed of a ceramic material, such as alumina (aluminum oxide, Al O ) or magnesia (magnesium oxide, MgO), a polymer material, or a compound composed of the materials such that the guide member 130 and the thin-metal film 123 can be electrically insulated from each other.

[93] Preferably, the thickness of the insulation film 122 ranges from 0.5 to 500D, more preferably, from 0.5 to 200D. Depending on the materials, the thickness of the insulation film 122 may differ.

[94] The constitutional condition of the insulation film 122 is as follows. [95] The insulation film 122 should electrically insulate the guide member 130 from the thin-film heater 123. When a voltage of 1000V is applied to the thin-film heater 123, the insulation film 122 should be prevented from being destroyed, in order to electrically isolate the thin-film heater 123 receiving external power. Further, the leakage current of the insulation film 122 should be maintained at less than 2OD.

[96] In addition, when high-temperature heat is generated from the thin-film heater 123, the adhesion between the insulation film 122 and the guide member 130 and the adhesion between the insulation film 122 and the thin-film heater 123 should be excellent so that the insulation film 122 is not detached from the guide member 130 and the thin-film heater 123, respectively.

[97] When high-temperature heat is generated from the thin-film heater 123, the insulation film 122 should not chemically react with the guide member 130 and the thin-film heater 123, respectively. Further, the surface roughness of the insulation film 122 should be excellent.

[98] That is, when the surface roughness of the insulation film 122 is not excellent, the insulation film 122 has an effect upon a specific resistance characteristic of the thin- film heater 123. Therefore, it is preferable that the insulation film 122 has such a surface roughness as not to have an effect on a specific resistance characteristic of the thin-film heater 123.

[99] To satisfy the above-described condition, the insulation film 122 is formed of an oxide insulation film obtained by oxidizing the surface of the guide member 130 composed of a metallic material such as aluminum or stainless steel through arc, an insulation film obtained by coating the surface of the guide member 130 with ceramic, glass or the like, a polymer insulation film obtained by coating the surface of the guide member 130 with a polymer-based material such as polyimide, polyamide, Teflon, or Polyethylene Terephthalate (PET), or a double insulation film obtained by forming one or more insulation films on the surface of the guide member 130.

[100] The oxide insulation film is formed by the following method.

[101] First, electric energy such as arc is applied from outside onto the surface of the guide member 130 soaked in an alkali electrolyte, the guide member 130 being formed of a metallic material such as Al, Be, Ti, or stainless steel. Then, metallic atoms on the guide member 130 electrically and chemically react with external oxygen such that the surface of the guide member 130 is converted into an oxide film.

[102] As for the oxide insulation film, Al O , ZrO , Y O and the like are used. Further, the oxide insulation film can be formed on the guide member 130 by a plasma spray coating method or the like.

[103] Hereinafter, the process of forming the oxide insulation film on the guide member will be described as follows. [104] First, the concentration of an alkali electrolyte filled in a bath is evaluated. In a state where a conducting wire is connected to the guide member 130 formed of aluminum such that external power can be supplied to the guide member 130, the guide member 130 is soaked into the alkali electrolyte in the bath. Then, external power is supplied to the guide member 130 such that the surface of the guide member 130 is oxidized.

[105] Next, as strong power such as a high-frequency alternating current is applied to the guide member 130, arc is momentarily generated on the surface of the guide member 130. Accordingly, an oxide insulation film, of which the oxidation is prominent and the pinhole concentration is very low, is formed on the guide member 130.

[106] Through the oxide-insulation-film formation process, aluminum oxide can be formed on the surface of the guide member 130 formed of aluminum, titanium oxide can be formed on the surface of the guide member 130 formed of titanium, or beryllium oxide can be formed on the surface of the guide member 130 formed of beryllium.

[107] Meanwhile, the polymer insulation film is formed by coating the surface of the guide member 130 with a polymer-based material, which can secure an insulation property, at a uniform thickness.

[108] In particular, when the thin-film heater 123 generates heat, the polymer insulation film should be prevented from being thermally deformed. Further, the adhesion of the polymer insulation film with the guide member 130 and the thin-film heater 123 should be excellent so as not to be detached from the guide member 130 and the thin- film heater 123, respectively. In addition, the polymer insulation film should not chemically react with the guide member 130 and the thin-film heater 123 and should have an excellent surface roughness.

[109] The polymer insulation film is formed by the following process.

[110] First, the polymer insulation film is formed of liquid organic polymer material. The surface of the guide member 130 is coated with the liquid organic material at a uniform thickness.

[I l l] As for the coating method, a spring coating method, a spring coating method, a dipping coating method, a screen printing method and the like are used.

[112] As for the polymer-based material, a polyimide-based material, a poly amide-based material, a Teflon-based material, a paint-based material, silver-stone, tefzel-s, epoxy, rubber and the like are used. Alternately, a material photosensitive to ultraviolet rays (UV) may be also used.

[113] For example, the process of forming a polyimide-based material on the guide member by using the spray coating method is performed as follows.

[114] First, the guide member 130 is organically washed using acetone or Isopropyl

Alcohol (IPA). Then, while the guide member 130 is rotated on its own axis at high speed (for example, 2000rpm), the polyimide-based material is sprayed onto the guide member 130 and is then heat-treated.

[115] Through the polymer- insulation-film formation process using the spray coating method, a polymer insulation film, which has excellent thermal stability and of which the glassy temperature (GT) is more than 300⁰C, is formed on the surface of the guide member 130.

[116] Further, as the polyimide-based material is slowly cooled in the heat- treatment process, the adhesion between the polymer insulation film and the guide member 130 becomes excellent. As the surface of the guide member 130 is coated with the polymer-based material in the spray coating process, the thickness uniformity of the polymer insulation film becomes excellent, and the pinhole concentration of the polymer insulation film becomes so low that leakage current does not occur.

[117] Meanwhile, the double insulation film composed of the oxide insulation film and the polymer insulation film is formed by the following method. The oxide insulation film is formed on the surface of the guide member 130 composed of metal, and a polymer-based material is then coated on the oxide insulation film at a uniform thickness. Alternately, a polymer-based material is first coated on the surface of the guide member 130, and the oxide insulation film is then formed on the guide member 130 coated with the polymer-based material.

[118] The overall thickness of the double insulation film composed of the oxide insulation film and the polymer insulation film may be smaller than the sum total of the thickness of the oxide insulation film, which is independently formed on the surface of the guide member 130, and the thickness of the polymer insulation film which is independently formed on the surface of the guide member 130. The double insulation film can minimize dielectric breakdown, compared with when only one of the oxide insulation film and the polymer insulation film is independently formed.

[119] The dielectric breakdown of the oxide insulation film may occur when external power supplied to the thin-film heater 123 is transmitted into the pinholes formed in the oxide insulation film.

[120] Further, when liquid photoresist (PR) is coated during the formation of the polymer insulation film, bubbles may be generated. In this case, after the polymer insulation film is solidified, the dielectric breakdown of the polymer insulation film may occur in the portions where the bubbles were present.

[121] Therefore, it is preferable that the occurrence of the dielectric breakdown in the oxide insulation film or the polymer insulation film is suppressed by the double insulation film of the oxide insulation film and the polymer insulation film.

[122] Preferably, for the enhancement of heat efficiency, the thickness of the insulation film 122 ranges from 0.5 to 500D, or more preferably, 0.5 to 200D (the thickness differs depending on materials). The breakdown voltage of the insulation film 122 is more than 1000V, and the leakage current of the insulation film 122 is less than 2OD at a voltage of 100V. When heat is generated from the thin-film heater 123, the insulation film 122 should not be separated from the guide member 130 and the thin-film heater 123, respectively.

[123] The insulation film 122 can be formed of self-curing or thermosetting ceramic by a thick- film coating method. The insulation film 122 formed of ceramic enhances a withstanding voltage characteristic.

[124] Preferably, the withstanding voltage is set to be more than 2kV.

[125] The thin-film heater 123 is mounted on the insulation film 122 in the form of a thin film having a thickness of 0.05 to several D (for example, 0.05 to 2D). When external power (DC power or AC power) is supplied from outside through the electrode 125, the thin-film heater 123 generates Joule heat through its electric resistor.

[126] Since the thin-film heater 123 has a small thickness and a small volume, heating speed and cooling speed are very high. The temperature of heat generated by the thin- film heater 123 through its electric resistor may exceed 500⁰C. Further, compared with conventional heaters, the temperature of the thin-film heater 123 rapidly increases.

[127] The constitutional condition of the thin-film heater 123 is as follows.

[128] First, due to the thin-film characteristic of the thin-film heater 123, the temperature t hereof rapidly increases, compared with conventional heaters. However, since a current flux or the like may increase due to the thin-film characteristic, the thin-film heater 123 requires electric, thermal, and chemical resistances.

[129] That is, the thin-film heater 123 should have high heater strength. When the thin- film heater 123 has high resistance to energy which is continuously applied through the electrode 125, the lifespan of the thin-film heater 123 can last for a long term.

[130] The thin-film heater 123 is mounted on the insulation film 122. The thin-film heater

123 should be prevented from being detached by the generated heat, and the guide member 130 and the thin-film heater 122 should be prevented from being separated from each other.

[131] Further, a thermal impact is continuously applied to the thin-film heater 123. A considerable increase in resistance change of the thin-film heater 123 due to the thermal impact should be prevented from occurring.

[132] The thin-film heater 123 may generate high-temperature heat in a state where it is exposed to the air (oxygen). In this case, a considerable increase in resistance change of the thin-film heater 123 due to the oxidation should be prevented from occurring.

[133] As for materials of the thin-film heater 123 which can satisfy the above-described conditions, there are provided a single metal such as Ta, W, Pt, Ru, Hf, Mo, Zr, Ti or the like with a high fusion point, a binary-system metal alloy such as TaW or the like obtained by combining the metals, a binary-system metal-nitride material such as WN, MoN, ZrN or the like obtained by combining metal nitrides, and a binary-system metal suicide material such as TaSi, WSi, or the like obtained by combining metal suicides.

[134] Further, the thin-film heater 123 is set to have a thickness of less than several D (for example, 0.05 to 2D). The thickness differs depending on the materials.

[135] To instantly increase the temperature of the thin-film heater 123, that is, to minimize the time required until the thin-film heater 123 is heated, the thin-film heater 123 is set to have an extremely small heat capacity.

[136] The heat capacity of the thin-film heater 123 is expressed by a function in which the thickness of the thin-film heater 123 is set to a parameter. As the thickness is reduced, the heat capacity decreases. On the contrary, the lifespan of the thin-film heater may be reduced, as the thickness is reduced.

[137] Therefore, to satisfy two conditions for instantly increasing the temperature of the thin-film heater 123 and expanding the lifespan of the thin-film heater 123, the optimal thickness range of the thin-film heater 123 can be derived through various simulations and experiments. Meanwhile, a slight difference may occur depending on the materials of the thin-film heater 123. However, the difference is insignificant.

[138] That is, the optimal thickness of the thin-film heater 123 is derived on the basis of

Equation 1.

[139] [Equation 1]

[140] p = Rsxt

[141] Here, p represents a specific resistance of the material of the thin-film heater 123,

Rs represents a sheet resistance of the thin-film heater 123, and t represents the thickness of the thin-film heater 123. As expressed in Equation 1, the thickness is proportional to the specific resistance.

[142] Therefore, when a simulation using the above-described parameters as input data is performed in consideration of the specific resistance range of the material of the thin- film heater 123, the optimal thickness range of the thin-film heater 123 is derived depending on the materials (for example, 0.05 to 2D).

[143] The thin-film heater 123 is formed on the insulation film 122 by a vacuum deposition method. As for the vacuum deposition method, a Physical Vapor Deposition (PVD) method such as sputtering, reactive sputtering, co-sputtering, evaporation, E- beam or the like and a Chemical Vapor Deposition (CVD) method such as low- pressure CVD or plasma-enhanced CVD are used.

[144] Figs. 8 to 10 illustrate various examples of the conductive patterns formed on the thin-film heater according to the invention. As shown in the drawings, the conductive patterns 124 having lower electric resistance and higher heat conductivity than the thin-film heater 123 are formed on the thin-film heater 123. The conductive patterns may be formed in various shapes.

[145] If a thin-film heater having no conductive pattern is used, a temperature difference between an electrode introduction portion and the central portion of the thin-film heater occurs at the initial stage of power supply. Then, temperature distribution is not uniformly achieved on the entire surface of the thin-film heater or heat is excessively generated in a portion of the thin-film heater such that the thin-film heater or the insulation film 122 may suffer fatal damage (degradation) or the lifespan of the thin- film heater may be extremely reduced.

[146] That is, to uniformly generate heat on the entire surface of the thin-film heater 123 within a short time at the initial stage of power supply, the conductive patterns 124 are formed on the thin-film heater 123, as shown in Figs. 8 to 10.

[147] As such, when the conductive patterns 124 are formed on the thin-film heater 123, the production yield of the thin-film heater 123 can be increased rather than that of the thin-film heater having no conductive pattern. In the thin-film heater having no conductive pattern, when a minute thickness difference of a portion of the thin film heater occurs or the thin-film heater is partially damaged by scratch or the like, the quality of the entire resistor is reduced.

[148] The electrode 125 is mounted on the thin-film heater 123 and serves to uniformly supply power to the thin-film heater 123, the power being supplied from outside. Preferably, the electrode 125 is installed so as to be uniformly grounded to the entire surface of the thin-film heater 123 such that the thin-film heater 123 can have constant current density on the entire surface thereof.

[149] In particular, in order for the constant current density on the entire surface of the thin-film heater 123, it is preferable that the width (thickness) of the electrode 125 is set to be larger than or equal to that of the thin-film heater 123.

[150] Figs. 11 and 12 illustrate various disposition patterns of the electrode and the thin- film heater according to the invention. As shown in Figs. 11 and 12, the electrode 125 may be formed in a pattern having various positions, shapes, and sizes such that a plurality of heat-generating thin-film cells are formed.

[151] The thin-film cells are formed so as to prevent the connected portions between the electrode 125 and the thin-film heater 123 from being thermally destroyed when a large amount of power is supplied at once. Further, the heat-generating region is divided into a plurality of regions such that the resistance of each region can be controlled so as to control partially-generated heat.

[152] As for the material of the electrode 125, metal such as Al, Au, W, Pt, Ag, Ta, Mo,

Ti, H, Cu or the like can be used. Then, when heat is generated by the thin-film heater 123, the stability of the electrode 125 with respect to the temperature is secured, an increase in resistance due to oxidation is prevented, and the electrode 125 is prevented from being detached from the thin-film heater 123.

[153] The protective layer 127 is mounted on the thin-film heater 123 and the electrode

125 so as to electrically and chemically protect the thin-film heater 123 and the electrode 125 from the external environment. As for the material of the protective film 127, SiNx, SiOx, AlOx, polymer, polyimide, Teflon or the like may be used. The thickness of the protective layer 127 is determined depending on the materials. Preferably, the optimal thickness of the protective film for heat conductivity and an excellent protection function ranges from 0.1 to 2OD.

[154] The protective layer 127 may be formed on both the thin-film heater 123 having the conductive patters 124 formed thereon and the thin-film heater having no conductive pattern.

[155] Fig. 13 is a schematic view of a test piece for experimenting the heating unit according to the invention. Fig. 14 is a graph showing a result that a temperature change is measured in accordance with time in a state where a constant current (50W) is applied to the test piece. Fig. 15 is a graph showing a result that a temperature change is measured in accordance with a change in amount of current applied to the test piece for a predetermined time (10 seconds).

[156] In Figs. 13 to 15, the measured temperature may differ depending on the resistances, thicknesses, and materials of the respective components such as the thin-film heater 123, the conductive patterns 124, the insulation film 122, the electrode 125, and the guide member 130.

[157] As shown in Fig. 14, it can be found that when power of 5OW is applied, saturation occurs at 287⁰C after a predetermined time passes.

[158] As shown in Fig. 15, it can be found that a change in surface temperature, which increases for 10 seconds in accordance with a power change, has a linear increase characteristic.

[159] In the above-described heating unit 120 according to the invention, when the resistances, thicknesses, and materials of the respective components such as the thin-film heater, the conductive patterns, the insulation film, the electrode, the thin-film cells, and the guide member are differently applied from each other, the surface-temperature reaching time and the power consumption can be reduced in accordance with a product characteristic such that an optimal product can be manufactured.

[160] Fig. 16 is a cross-sectional view of an image forming apparatus using a thin-film heater according to a second embodiment of the invention. Fig. 17 is an expanded view of a portion "B" of Fig. 16. Fig. 18 is an expanded view of a portion "C" of Fig. 16.

[161] In the second embodiment of the invention, the heating unit 120 and the guide member 130 are constructed in a different manner from those of the first embodiment.

[162] Therefore, the descriptions of the other components except for the heating unit 120 and the guide member 130 will be omitted, and like reference numerals are attached to the same components as those of the first embodiment.

[163] The guide member 130 has a horizontal surface 131, on which the heating unit 120 for heating and fixing toner on a printing medium P is stacked, and a wing portion 133 which is formed to extend from at least one of the left and right ends of the horizontal surface 131. The wing portion 133 serves to preheat the sleeve 140 before the printing medium P is introduced onto the horizontal surface 131.

[164] On and under the guide member 130, the pair of upper and lower heating units 120 are installed respectively.

[165] According to the second embodiment of the invention, the upper and lower heating units 120 generate heat at the same time. Therefore, compared with when only one heating unit 120 generates heat, the preheating time can be reduced, and high- temperature heat can be generated.

[166] The upper and lower heating unit 120 can separately receive power supply. Accordingly, the power supply to each of the heating units 120 is adjusted so that the load on the heating units 120 can be dispersed. Therefore, the heating units 120 are stably driven, and the lifespan thereof can last for a long time.

[167] In addition, the heating units 120 may be formed on the guide member 130 and the pressing plate 115, respectively, so as to heat the top and bottom surfaces of the printing medium P at the same time.

[168] As for the guide member 130, a conductive material with high conductivity or a non-conductive material can be used. As for the conductive material, metal such as aluminum, stainless steel, or an alloy of aluminum and stainless steel can be used. As for the non-conductive material, polymer synthetic resin and ceramic can be used.

[169] In the lower opposite side to the guide member 130, the pressurization driving unit

110 for transferring the printing medium P is installed. The pressurization driving unit 110 includes a driving belt 113, a pressing plate 115 installed inside the driving belt 113 so as to press the upper surface of the driving belt 113 toward the guide member 130, and a driving wheel 111 formed in one side of the pressing plate 115 so as to drive the driving belt 113.

[170] Preferably, the pressing plate 115 is elastically supported by a separate elastic member (such as a compression spring).

[171] The pressing plate 115 includes a plane portion 115a corresponding to the horizontal surface 131 of the guide member 130 and a guide wing 115b formed in the other side thereof, where the driving wheel 111 is not formed, the guide wing 115b guiding the driving belt 113.

[172] Fig. 19 is an expanded cross-sectional view of a modification of the heating units

120 according to the second embodiment of the invention. [173] Referring to Fig. 19, the case will be described, where the pair of heating units 120 are simultaneously formed on and under the guide member 130 formed of a non- conductive material.

[174] In the heating units 120 of the invention, a pair of thin-film heaters 123 are formed on and under the guide member 130, a pair of electrodes 125 for supplying external power to the surfaces of the thin-film heaters 123 are formed on the upper and lower thin-film heaters 123, respectively, and a pair of protective layers 127 with a predetermined thickness are formed on the upper and lower thin-film heaters 123, respectively.

[175] That is, the pair of heating units 120 are symmetrically formed by reference to the guide member 130.

[176] On the upper and lower thin-film heaters 123, a plurality of conductive patterns 124 may be further formed so that power supply from the electrodes 125 can be uniformly distributed on the entire surfaces of the thin-film heaters 123. As for the conductive patters 124, various patterns which electrically connect the electrode 125 to the electrode 125 may be used.

[177] Preferably, the thickness of the lower protective layer 127 connected to the sleeve

140 is set to be larger than that of the upper protective layer 127.

[178] As for a material of the guide member 130, tempered plastic, heat resistant resin, ceramic, glass, stone or the like can be used.

[179] The guide member 130 may be formed of a conductive material. In this case, the thin-film heater 123 is not immediately deposited on the guide member 130, but the insulation film 122 is first formed as shown in Fig. 6. Then, the thin-film heater 123 is deposited on the insulation film 122.

[180] Fig. 20 is an expanded cross-sectional view of another modification of the heating unit according to the second embodiment of the invention.

[181] In the heating unit 120 according to the modification of the invention, the electrode

125 is thermally bonded before the thin-film heater 123 is deposited on the guide member 130 formed of a non-conductive material, as shown in Fig. 20.

[182] The electrode 125 can be thermally bonded by a vacuum sintering method in which after paste electrode is coated on the guide member 130, it is solidified in a vacuum chamber by removing a solvent.

[183] When the electrode 125 is formed by the above-described method, it is possible to prevent such a problem that the electrode 125 is burned away due to overload current capacity.

[184] At this time, the conductive patterns connecting the electrode 125 to the electrode

125 may be formed so as to uniformly supply power to the thin-film heater 123.

[185] On the guide member 130 where the electrode 125 and the conductive patterns 124 are formed, the thin-film heater 123 is deposited in such a shape as to cover the electrode 125 and the conductive patterns 124.

[186] On the surface of the thin-film heater 123, the protective layer 127 with a predetermined thickness is formed to protect the thin-film heater 123 from the external environment.

[187] The guide member 130 is formed of a non-conductive material. As for the non- conductive material, tempered plastic, heat resistant resin, ceramic, glass, stone or the like can be used, which can endure a temperature of at least more than 25O⁰C.

[188] The guide member 130 may be formed of a conductive material. In this case, the thin-film heater 123 is not immediately deposited on the guide member 130, but the insulation film 122 is first formed as shown in Fig. 6. Then, the thin-film heater 123 is deposited on the insulation film 122.

[189] The heating unit 120 according to the modification of the invention may be installed on the top and bottom surfaces of the guide member 130, respectively.

[190] Fig. 21 is a schematic cross-sectional view of an image forming apparatus using a thin-film heater according to a third embodiment of the invention. Fig. 22 is a schematic cross-sectional view of an image forming apparatus using a thin-film heater according to a fourth embodiment of the invention.

[191] In the third embodiment of the invention, a driving wheel 111 is installed in either side under a pressing plate 115. In the fourth embodiment of the invention, a driving wheel 111 is installed in the central portion under a pressing plate 115.

[192] As shown in Figs. 21 and 22, the pressing plate 115 includes a plane portion 115a corresponding to the horizontal surface 131 of the guide member 130 and a guide wing 115b which is formed at either end of the plane portion 115a so as to guide the driving belt 113.

[193] In this case, the pressing plate 115 may be coupled to a support 115 such that the strength of the pressing plate 115 can be reinforced.

[194] Further, a position changing unit 160 may be installed in one side of the pressing plate 115 so as to change the position of at least any one of the pressing plate 115 and the guide member 130. The position changing unit 160 moves the pressing plate 115 at the initial stage of preheating of the heating unit 120 such that the guide member 130 and the pressing plate 115 are spaced at a predetermined distance from each other.

[195] As for the position changing unit 160, various mechanisms such as a hydraulic cylinder, a solenoid valve, or a cam structure can be used.

[196] If the heat generated from the heating unit 120 at the initial stage of preheating is transmitted to the pressing plate 115, the preheating time may be lengthened. Therefore, the position changing unit 160 serves to prevent the heat from being transmitted to the pressing plate 115. [197] At the initial stage where the image forming apparatus is driven, the position changing unit 160 moves the pressurizing unit 115 such that the guide member 130 and the pressurizing unit 115 are spaced at a predetermined distance from each other. When the temperature of the heat generated from the heating unit 120 approaches predetermined temperature (for example, 18O⁰C), the position changing unit 160 moves the pressurizing unit 115 to press the guide member 130.

[198] Now, the operation of the image forming apparatus according to the invention constructed in such a manner will be described.

[199] First, when power is applied to the image forming apparatus, the power is supplied to the electrode 125 of the heating unit 120. Then, the power is uniformly supplied to the entire area of the thin-film heater 123 such that the thin-film heater 123 generates heat.

[200] The horizontal surface 131 of the guide member 130 and the wing portion 133 are heated by the heat generated from the thin-film heater 123. The heated guide member 130 heats the sleeve 140 covering the outer surface of the guide member 130, the sleeve 140 being formed of thermosetting resin.

[201] At this time, since the sleeve 140 comes in contact with the guide member 130 across the horizontal surface 131 and the wing portion 133, a sufficient heated area and heating time can be secured.

[202] While the pressurization driving unit 110 coming in contact with the sleeve 140 is rotated, a printing medium P is supplied and transferred therebetween.

[203] At this time, toner powder sprayed on the surface of the printing medium P is thermally fixed while the printing medium P passes onto the horizontal surface 131 of the guide member 130. Then, the printing medium P is discharged from the image forming apparatus.

[204] The thin-film heater 123 is rapidly heated even by low external power. When power of 500W is applied, the thin-film heater 123 is rapidly heated to more than 14O⁰C within 20 seconds (the result may differ depending on the size of the guide member). Therefore, the operation- wait time required for preheating can be reduced.

[205] While the present invention has been described with reference to exemplary embodiments thereof, it will be understood by those skilled in the art that various changes and modifications in form and detail may be made therein without departing from the scope of the present invention as defined by the following claims.

Claims

[1] An electro photographic type image forming apparatus comprising: a conveyor-driven pressurization driving unit having a driving belt; a guide member installed above the pressurization driving unit, the guide member having a horizontal surface formed in parallel to a horizontal transfer section of the driving belt; a heating unit stacked on the opposite surface to the horizontal surface of the guide member, the heating unit generating heat by using a thin-film heater; and a sleeve mounted to cover the outer surface of the guide member so as to receive the generated heat, frictionally driven while facing the horizontal transfer section of the pressurization driving unit, and transferring a printing medium supplied between the friction surfaces such that toner on the printing medium is thermally fixed.

[2] The electro photographic type image forming apparatus according to claim 1, wherein the heating unit includes: a thin-film heater deposited on the outer surface of the guide member so as to be instantly heated by supplied power; and an electrode forming an electrical connection pattern such that power is uniformly supplied to the thin-film heater.

[3] The electro photographic type image forming apparatus according to claim 1, wherein the heating unit includes: an insulation film deposited on the outer surface of the guide member so as to provide an electric insulation property and a heat conductance property; a thin-film heater deposited on the outer surface of the insulation film so as to be instantly heated by supplied power; and an electrode forming an electrical connection pattern such that power is uniformly supplied to the thin-film heater.

[4] The electro photographic type image forming apparatus according to claim 1, wherein the heating unit includes: an electrode forming an electrical connection pattern such that power is uniformly supplied to the outer surface of the guide member; and a thin-film heater deposited on the electrode and the guide member so as to be instantly heated by supplied power.

[5] The electro photographic type image forming apparatus according to claim 1, wherein the heating unit includes: an insulation film deposited on the outer surface of the guide member so as to provide an electric insulation property and a heat conductance property; an electrode forming an electrical connection pattern such that power is uniformly supplied to the outer surface of the insulation film; and a thin-film heater deposited on the electrode and the guide member so as to be instantly heated by supplied power.

[6] The electro photographic type image forming apparatus according to claim 4 or

5, wherein the electrode is formed by a thermal bonding method or a vacuum sintering method.

[7] The electro photographic type image forming apparatus according to any one of claims 1 to 5, wherein the pressurization driving unit includes: a pressing plate installed to face the bottom surface of the guide member; a driving belt installed to cover the outer circumference of the pressing plate; and a driving wheel for transmitting power to the driving belt.

[8] The electro photographic type image forming apparatus according to claim 7, wherein the driving wheel is installed in the left and right sides of the pressing plate, respectively.

[9] The electro photographic type image forming apparatus according to 7, wherein the driving wheel is installed in only one side of the pressing plate.

[10] The electro photographic type image forming apparatus according to 9, wherein the pressing plate includes a plane portion corresponding to the horizontal surface of the guide member and a guide wing formed on the other side of the pressing plate, where the driving wheel is not installed, the guide wing guiding the driving belt.

[11] The electro photographic type image forming apparatus according to claim 7, wherein the driving wheel is installed in either side under the pressing plate.

[12] The electro photographic type image forming apparatus according to claim 7, wherein the driving wheel is formed only in the central portion under the pressing plate.

[13] The electro photographic type image forming apparatus according to claim 11 or

12, wherein the pressing plate 115 includes a plane portion corresponding to the horizontal surface of the guide member and a pair of guide wings formed to extend from the right and left ends of the plane portion, respectively, the guide wings guiding the driving belt.

[14] The electro photographic type image forming apparatus according to claim 13, wherein the pressing plate is coupled to a support for reinforcing the strength thereof.

[15] The electro photographic type image forming apparatus according to any one of claims 1 to 5, wherein the heating unit is formed on the guide member and the pressing plate, respectively.

[16] The electro photographic type image forming apparatus according to any one of claim 1 to 5, wherein the entire horizontal surface of the guide member is heated by the heating unit stacked on the guide member, and the guide member includes a wing portion formed to extend to at least any one of the left and right ends of the horizontal surface.

[17] The electro photographic type image forming apparatus according to claim 16, wherein the guide member is coupled to a support for reinforcing the strength thereof.

[18] The electro photographic type image forming apparatus according to claim 2 or

4, wherein the guide member is formed of a non-conductive material such as tempered plastic, heat resistant resin, ceramic, glass, stone or the like, which is capable of enduring a temperature of at least more than 25O⁰C.

[19] The electro photographic type image forming apparatus according to claim 3 or

5, wherein the guide member is formed of at least any one of conductive metals including aluminum, stainless steel, and an alloy of aluminum and stainless steel, which have excellent heat conductance.

[20] The electro photographic type image forming apparatus according to any one of claims 1 to 5, wherein the heating unit is formed on the top surface of the guide member.

[21] The electro photographic type image forming apparatus according to any one of claims 1 to 5, wherein the heating unit is formed on the bottom surface of the guide member.

[22] The electro photographic type image forming apparatus according to any one of claims 1 to 5, wherein the heating unit is formed on the top and bottom surfaces of the guide member, respectively.

[23] The electro photographic type image forming apparatus according to any one of claims 1 to 5, the apparatus further comprising: a position changing unit formed in one side of the pressing unit, the position changing unit changing the position of at least any one of the pressing plate and the guide member, wherein the guide member and the pressing unit are spaced at a predetermined distance from each other by the position changing unit at the initial stage of preheating.

[24] The electro photographic type image forming apparatus according to any one of claims 2 to 5, wherein the heating unit includes a plurality of conductive patterns for connecting the electrode to the electrode such that power is uniformly supplied to the entire surface of the thin-film heater.

[25] The electro photographic type image forming apparatus according to any one of claims 2 to 5, wherein the thin-film heater is formed of any one of a single metal, a binary-system metal alloy obtained by combining the single metals, a binary- system metal-nitride material obtained by combining metal nitrides, a binary- system metal-silicide material obtained by combining metal suicides, and thick- film conductive paste.

[26] The electro photographic type image forming apparatus according to any one of claims 2 to 5, wherein the electrode is set to have a larger or equal width than or to that of the thin-film heater such that power is supplied to the thin-film heater at a uniform current density and is formed of any one of Al, Au, W, Pt, Ag, Ta, Mo, Ti and the like, which are stable with respect to the temperature, when heat is generated, and prevent an increase in resistance caused by oxidation and physical separation.

[27] The electro photographic type image forming apparatus according to claim 3 or

5, wherein the insulation film is formed of self-curing or thermosetting ceramic by a thick-film coating method.

[28] The electro photographic type image forming apparatus according to claim 3 or

5, wherein the insulation film is any one of an oxide insulation film obtained by oxidizing the surface of the guide member through arc, a polymer insulation film obtained by coating polymer on the surface of the guide member, and a double insulation film obtained by forming the oxide insulation film and the polymer insulation film on the surface of the guide member.

[29] The electro photographic type image forming apparatus according to claim 28, wherein the oxide insulation film is any one of metal oxides including aluminum oxide, beryllium oxide, and titanium oxide, and the polymer of the polymer insulation film is any one of polyimide, polyamide, Teflon, paint, silver-stone, tefzel-s, epoxy, and rubber.

[30] The electro photographic type image forming apparatus according to any one of claims 1 to 5, wherein the heating unit further includes a protective film coated with a predetermined thickness such that the surface of the heating unit can be protected from the external environment.