US3515855A

US3515855A - Xerographic fusing apparatus

Info

Publication number: US3515855A
Application number: US775615A
Authority: US
Inventors: Arthur L Mix Jr
Original assignee: International Business Machines Corp
Current assignee: International Business Machines Corp
Priority date: 1968-11-14
Filing date: 1968-11-14
Publication date: 1970-06-02
Anticipated expiration: 1987-06-02
Also published as: NL6915488A; CA976226A; ES373067A1; SE350135B; CH494986A; BE739611A; FR2023231A1; DE1955850A1

Description

A.L. MIX. JR

'XEROGRAPHIC FUSING APPARATUS June 2, 1970 2 Sheets-Sheet 1 Filed Nov. 14 1968 DEVELOPMENT O S A n RN [L T UHW NrE 2 me 2 U F FIG. 1

a VAUUM as V 86 FIG. 2b

INVENTOR ARTHUR L. MIX JR.

BY J76 fuzwl- AGENT June 2, 1970 A. L.1.IMIX. JR 3,515,855

XEROGRAPHIC FUSING APPARATUS Filed Nov. 14 1968 2 Sheets-$heet 2 102i o POWDER IMAGE WED) 100 FROM Q TRANSFER smnom 4 I I 112 114 FIG. 30

P WDER IMAGE SUPP0RTl26 I VACUUM 124 !O) X 7; 0 VACUUM 13a 0 122 A 120 Q .Ti.'IT,Z '34 136 1513 T) 1s2-v 150 FIG. 3b

TEMP 30R. U 1] SENSING PHASE ELEMENT CONTROL E 1 150 FIG. 4

AC. SOURCE United States Patent 015cc 3,515,855 Patented June 2, 1970 3,515,855 XEROGRAPHIC FUSING APPARATUS Arthur L. Mix, Jr., Lexington, Ky., assignor to International Business Machines Corporation, Armonk, N.Y.,

a corporation of New York Filed Nov. 14, 1968, Ser. No. 775,615 Int. Cl. F27b 9/06 US. Cl. 219-388 12 Claims ABSTRACT OF THE DISCLOSURE A fusing apparatus for fixing a xerographic powder image on a support member. The support member is passed through a heated, low melting point liquid which is nonwetting to the image and its support member. The nonwetting liquid is maintained at a temperature sufficient to fix the powder image, but less than that which would cause damage to the support member.

BACKGROUND OF THE INVENTION This invention relates to xerographic fusing apparatus, and more particularly to such a fusing apparatus which utilizes a nonwetting liquid both as a heat storage medium and as a heat transfer medium.

Description of the prior art A conventional xerographic reproduction machine includes a xerographic plate having a photoconductive layer or light-receiving surface on a conductive backing and formed in the shape of a drum. The drum is rotatable and sequentially passes a plurality of xerographic processing stations, such as a charging station, an exposure station, a developing station, a transfer station, and a drum cleaning station.

At the charging station a uniform electrostatic charge is deposited on the photoconductive layer of the drum. At the exposure station, an image of the copy to be reproduced is projected onto the drum surface in order to dissipate the drum charge in the exposed areas. Consequently, a latent electrostatic image of the copy to be reproduced is formed on the drum surface. At the developing station xerographic development material is spread over the drum surface. This development material includes toner particles which have an electrostatic charge opposite to that of the electrostatic latent image. The toner particles adhere to the electrostatic latent image and form a xerographic powder image in the configuration of the copy being reproduced. At the transfer station the xerographic powder is electrostatically transferred from the drum surface to a transfer material or support surface. The drum cleaning station is one at which the drum surface is brushed to remove residual toner particles which remain on the drum after image transfer.

In the conventional xerographic machine the image transfer step is generally realized by transferring the xerographic powder onto a sheet of copy paper which is brought into contact with the drum when the developed image on the drum surface arrives at the transfer station. Electrostatic transfer of the image from the drum surface to the copy sheet can be achieved by means of transfer corona, which is well known in the prior art. The electrostatic field created by the corona transfer device is sufficiently strong to actually tack the support member electrostatically to the drum surface. The support member will then move synchronously with the drum. The resulting electric field is also effective to attract the powder particles from the drum surface and cause them to adhere electrostatically to the surface of the copy sheet. The support member, having a powder image thereon, is then conveyed to the fuser station where the powder is heated to its melting point for causing adherence of the powder particles to the surface of the copy sheet.

Conventionally, two methods of fixing a powder im age have been developed. These are: (1) a heat fixing method, and (2.) a vapor fixing method. In the heat fixing method, heat is applied to the powder image. Here, the developing powder or its support must be formed of a thermo-responsive material which will flow without serious image distortion when heated. It must coalesce when later cooled to ambient temperature. The vapor fixing method involves passing the image-bearing support member through an atmosphere of the vapor of a solvent for the developing powder. This causes the powder image to become tacky and cohesive while in the presence of the solvent vapor atmosphere. The support is then removed to ambient air where the solvent evaporates. This leaves the developing powder bonded to the support, thus forming a copy of the latent image.

Both of these methods have certain disadvantages, al-

though both have been and are employed in automatic copying machines. As with all heat-type fusing methods, the heat applied must be less than that which would cause charring of the support member. The powder must be made of a material which becomes adhesive at a temperature below that which would cause damage to the support member. A further disadvantage of the heat fixing apparatus is that of fire hazard. With this type of fuser, it is difficult to overcome the possibility of fire hazard and yet have short warm-up time, low power dissipation, and uniform heat distribution.

Although vapor fixing of powder images produces more dark images than those produced by heat fixing, this method also has disadvantages, chief of which is the production of annoying and often dangerous fumes, which may be toxic. This disadvantage is especially pronounced where there is a large volume of reproduction required.

The present invention is a heat fusing apparatus which utilizes a nonwetting liquid for the storage of heat energy and also for the transfer of heat energy. The support member carrying the powder image to be fixed is passed through the nonwetting liquid or across the surface of the liquid. During the heat transfer process, the liquid bath does not dislodge and float away the powder image from its support member. Even though fusing has been a problem in the xerographic art for many years, no one has heretofore suggested this particular technique.

Previous xerographic fusing apparatuses have had problems with respect to the very large electrical current required during the actual fusing operation. This resulted because prior machines had no heat storage capability and had poor thermo-coupling. Another problem with prior art fusing apparatus is that high temperatures are required to maintain the heat station; this creates a fire hazard. A further disadvantage with prior art means is that heat transfer is not efficient, due to the fact that the heat source is not in direct contact with the image and its support member. A still further problem with existing xerographic fusing apparatus is that a constant, high electric current is required to main tain proper temperatures in the fusing station. Due to conduction and radiation, there is a great deal of heat loss within these prior machines.

Accordingly, it is a primary object of the present invention to provide an improved xerographic heat fusing apparatus in which very low power is required to maintain the proper temperature for fixing a xerographic image.

It is another object of the present invention to provide an improved xerographic fusing apparatus in which the energy required for fixing a xerographic image is stored as heat, rather than as electrical energy or chemical energy or mechanical energy.

Another object of the present invention is to provide an improved xerographic fusing apparatus in which there is a high effieiency of heat transfer between the heat storage medium and the support member carrying a xerographic powder image.

A further object of this invention is to provide an improved xerographic fusing apparatus having a minimum danger of fire hazard.

It is a still further object of this invention to provide an improved Xerographic fusing apparatus that is easily maintainable within a desired temperature range.

Another object of the present invention is to provide an improved xerographic fusing apparatus having a minimal space requirement,

The foregoing and other objects, features, and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention as illustrated in the accompanying drawings.

SUMMARY OF THE INVENTION In the present invention, the heat fusing technique is employed for fixing xerographic powder images. The apparatus includes a conveying means for conveying a powder image-bearing support member, such as a com tinuous web or individual sheets, to the heat exchange portion of the apparatus and through it. The conveying means can be of any type, such as a perforated belt, through which a vacuum is applied to secure the support member. Another suitable means is a series of drive and guide rollers for operating supply and take-up reels.

Also included is a heat storage and transfer medium, which is a nonwetting liquid across which or through which the support member travels. The liquid is contained in a tank, and is preferably a low melting point substance which has high heat capacity, and is nonwetting to the powder image and support member. In addition, it is desirable to have the liquid density be small, since then the likelihood of floating away the powder image is reduced. Metallic alloys which are noutoxic and of low vapor pressure are suitable. The nonwetting liquid is maintained within a temperature range that is sufiicient to fix the powder image but not so high as to cause damage to the support member.

Heat supplying means is provided for supplying heat to the heat storage and transfer medium above described. A suitable heater is an electrical immersion heater which is located in the nonwetting liquid medium. Consequent- 1y, there is very efficient heat transfer to the nonwetting liquid, as no heat is lost to the surrounding environment. The low heat loss means that the temperature of the nonwetting liquid is very easy to maintain, without high input power.

Control means is provided to activate and deactivate the heat supplying means in order to maintain the temperature of the nonwetting liquid within the desired temperature range. The control means can be of any con ventional type, such as a thermistor sensing element, amplifier, and S.C.R. phase control circuit which is connected to the resistance heating elements of the heat supplying means.

In operation, the powder image-bearing support means is transported through the heat exchange portion of the fusing apparatus by the conveying means, such that the support member passes across or through the nonwetting liquid. The heat transfer from the nonwetting liquid to the powder image is very efiicient and causes the thermoresponsive powder material to be fixed. During heat transfer to the powder image, the powder is not dislodged from the support member by the nonwetting liquid.

In another aspect of the invention, means is provided for positioning the heat storage and transfer medium in order to contact the support member which has a thermoresponsive powder image thereon. Heat transfer through the support member to the powder image fixes the image, without danger of the powder being floated away. While many different positioning means are suitable for raising the level of the nonwetting liquid, a revolving cylinder is illustrated. The cylinder draws the nonwetting liquid around its periphery as it revolves thereby raising the liquid so that it will contact the underside of an imagebearing support member passing over the tank containing the nonwetting liquid.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of a xerographic machine employing the inventive fusing apparatus.

FIG. 2a is an illustration of a xerographic fusing apparatus having conveying means suitable for handling a support member that is a continuous web, in which powder images are fixed upon passage through the heat exchange portion of the fusing apparatus.

FIG. 2b is an illustration of a xerographic fusing apparatus having conveying means suitable for handling support members that are individual sheets, in which the powder images are fixed upon passage through the heat exchange portion of the fusing apparatus.

FIG. 3a is an illustration of a xerographic fusing apparatus having conveying means for handling a continuous web, in which the heat storage medium is physically brought into contact with the continuous web in order to fix images positioned thereon.

FIG. 3b is an illustration of a xerographic fusing apparatus for handling individual sheets bearing xerographic powder images thereon, in which the heat storage medium is physically brought into contact with the individual sheets in order to fix images positioned theron.

FIG. 4 is an illustration of a suitable control means for maintaining the temperature of the fusing apparatus within certain limits.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 is a schematic diagram of a conventional xerographic machine which utilizes the subject fusing apparatus. In this case, the xerographic image is transferred to a web of material which is wound onto a take-up reel. Of course, it is to be understood that the web may be passed directly out to a cutter or the like in which the web is cut into separate lengths.

A light image of the material to be reproduced impinges upon the xerographic plate 20. This plate is coated on a drum which is rotatable about the axis 12. The xerographic drum is driven in a clockwise direction at a constant rate that is proportional to the transport rate of the copy to be reproduced, so that the peripheral rate of the drum surface is identical to the rate of movement of the incident light image. The drum surface 10 comprises a layer of photoconductive material on a conductive backing that is sensitized prior to exposure by means of a corona generating device which is energized from a suitable high potential source.

The exposure of the drum to the light image discharges the photoconductive layer in the areas struck by light, so that a latent electrostatic image in image configuration corresponding to the light image projected from the copy to be reproduced, is obtained on the drum surface 10.

As the drum surface continues its clockwise movement, the electrostatic latent image passes through a developing station at which a developing material, in this case a thermo-responsive powder, is deposited on the drum surface 10 by means of a developing apparatus not shown. The developing apparatus is conventional and well known in the prior art.

After developing, the xerographic powder image on the drum surface passes through an image transfer station at which the powder image is electrostatically transferred to a support surface web 14 by means of another corona generating device 16.

The support surface 14 to which the powder image is transferred may be paper, film, card stock, etc. The support surface is obtained from supply roll 18 and is fed 'over guide and

tensioning rollers

20 and 22, and over tensioning rolls being directed into surface contact with the xerographic drum in the immediate vicinity of transfer corona generating device 16.

After transfer, the support surface 14 is separated from the drum surface and is guided over guide rolls 24, 26 and through the fusing apparatus 28. The powder image is permanently affixed to the support surface when the support surface passes through the heat exchange portion of the 'xerographic fuser. The temperature range of the heat exchange portion is regulated by the control means portion of the fusing apparatus. After passing through the fusing apparatus, the support surface is fed over a further system of guide and tensioning rolls (not shown) and is then Wound upon a take-up roll 30 that is driven by motor 32. Of course, the support surface web 14 may be passed directly to a cutter in which the web is cut into severed lengths.

After separation of the support web from the dru surface 10, another corona generating device directs electrostatic charge to the residual powder image on the drum surface. After this, the xerographic drum surface passes through a cleaning station where residual developing powder remaining on the drum is removed. The drum surface then passes through a charging station at which uniform charge is applied to the drum surface.

Referring to FIG. 2a, a suitable embodiment of the subject fusing apparatus 28 is shown. In this figure, the support member 40 is a continuous web. The conveying means for the Web 40 is a suitable combination of tensioning, drive, and guide rolls 42, 44, 46 which cause the guide web 40 to move from the transfer station through the heat exchange and storage medium 48. As mentioned above, the heat storage and transfer medium 48 is a nonwetting liquid that is maintained at a temperature sufficient to fix the thermo-responsive powder image 50 on the support member 40 while at the same time not harming the image or the support surface.

In more detail, a tank 52, preferably made of heat insulating material, contains a nonwetting liquid 48 which is the heat storage and transfer medium. Suitable nonwetting liquids are molten alloys of various metals, which have high heat capacity. Generally speaking, it is preferable that the alloy not contain lead in order to avoid the toxic properties of lead solutions. A suitable eutectic alloy is one which is comprised of 53.9% bismuth, 25.9% tin, and 20.2% cadmium. Its melting point is 216.5" F. A suitable temperature range for most thermoresponsive material is 200 F. to 250 F. Within this range, the xerographic powder image will be fixed and no damage will occur to the support member.

The support surface, or web blank 40, travels from the transfer station to the fusing apparatus as shown generally in FIG. 1. The web 40 travels around guide roller 46 and then enters the nonwetting liquid 48 which acts as the heat storage and transfer medium. Within the liquid bath heat transfer to the powder image occurs and the xerographic power image is fixed. The small projections 50 on the outer surface of the web 40 are schematic representations of the powder images on the support surface. The web is wound around the roller 46in such a manner that the nonfixed powder images are not contacted by the guide roller. The tank 52 is trough-shaped and contains the heat storage and transfer medium 48. Tank 52 is made of insulating material as are the bafiies 54 and guide roller 56. After passage through the liquid 48, the web passes between the drive and pinch rollers 44 and 42, respectively, and then is either stored on a take-up roll or is severed by a cutter.

Located within the liquid bath 48 are electrical resistance heater elements 58 which are supplied with current from a separate source (not shown). This is a conventional type immersion heater and need not be explained further. Also located within the liquid bath 48 is a tem perature sensing element 60-, such as a thermistor, which is part of the control circuitry that maintains the temperature of the liquid bath within the desired range. The control circuitry will be explained more fully in the discussion of FIG. 4.

In operation, the support surface 40', having xerographic powder images thereon, passes through the nonwetting liquid 48 and heat transfer between the liquid and the powder images 50 occurs, thereby fixing the xerographic powder images. Even though a small oxidation scale might form on the surface, of a molten metallic alloy 48, this is not a disadvantage. The support member 40 is usually paper and there is very little heat absorption by it so that it is unlikely that oxidation scale will adhere to the support surface as it passed through the molten bath 48. Also, preheating and postheating of the support surface before and after it enters and leaves the molten bath is unnecessary, as the chance of metal particles adhering to the support surface is minimal.

Even though the support surface travels through the molten metal, there is not appreciable floating away of the powder so that the images are not distorted. The density of the molten metallic alloy is preferably low so that the chance of disloding powder material will be minimized.

Referring to FIG. 2, an apparatus is shown in which the support member is a single sheet, rather than a continuous web. The rest of the fusing apparatus is similar to that illustrated in FIG. 2a, and the same considerations apply with respect to the chartacteristics of the nonwetting liquid, the heater elements, and the temperature sensing element.

FIG. 2b shows a fusing apparatus in which the support members are individual sheets, rather than a contnuous web, as with the case in FIG. 2a. The individual support members 80, having powder images 81 thereon, are transported to the heat storage and transfer medium by various roller-driven endless perforated belts. A source of vacuum is applied to the underside of the belts.

A tank 70', made of insulating material, contains a nonwetting liquid 72 which is the heat storage and transfer medium. This medium is usually a molten metal alloy, and the considerations discussed with respect to the liquid employed in the apparatus of FIG. 2a apply here also. Heat is applied to the nonwetting liquid 72 by the heater elements 74, which are electrical resistance heating units immersed in the molten bath 72. Also contained within the nonwetting liquid is a temperature sensing element 76 which is used in the control circuitry that regulates the temperature range of the nonwetting liquid 72.

A revolving cylinder 78, which is partially above the level of the nonwetting liquid, is also located within the tank. This cylinder revolves in the direction shown (clockwise) and serves to aid the travel of the individual support members 80 across the width of the tank 70. In order to ease the movement of a support member across the width of the tank, the exit wall 82 of the tank is ininclined so that support members 80 can easily slide up the wall and onto the vacuum belt 84.

On the exit side of the tank 70 is located a perforated belt 84 which is driven by roller 86. Applied to the underside of this perforated belt is a vacuum from the source 88. Support members 80 which have passed through the heat exchange and storage medium 72 are propelled onto the vacuum belt 84 which then carries them away from the heat fusing apparatus. On the entrance side of the tank 70 is located a similar vacuum belt drive means which takes the support members from the transfer station and delivers them to the heat transfer medium 72. A perforated belt is driven by a roller 92. Vacuum is applied to the support member 80 through the perforated belt 90, by a source 94.

In operation, a support member 80 is transported by peforated belt 90 to the tank containing the heat storage and transfer medium 72. The support member is then aided in its movement across the width of the tank by the revolving cylinder 78. The support member will ride substantially on the surface of the nonwetting liquid in its travel across the Width of the tank. Upon reaching the inclined region 82 of the exit portion of the tank, the support member will move upward and out of the tank 70 onto a second perforated belt 84. This belt, being driven in a clockwise direction by the roller 86, holds the support member 80 and moves it away from the heat exchange portion of the fusing apparatus. The powder image on the surface of the support member receives heat from the nonwetting liquid 72 and is fixed by the action of this heat.

FIG. 3a shows a heat fusing apparatus in which a web support member is carried across the surface of a heat storage and exchange medium that is raised to contact the underside of the continuous web.

The continuous web 100 having powder images 101 thereon, is transported by a conveying means consisting of a drive roller 102, a pinch roller 104, and a guide roller 106. If desired, the combination of the drive roller 102 and the pinch roller 104 could be replaced by a perforated belt having vacuum applied beneath it so that the continuous web is moved and held in contact with the perforated belt by the applied vacuum. This would be desirable if the action of the pinch roller were harmful to the powder image on the surface of the continuous web 100. However, the chance of this is minimal, as the powder image is fixed by the time the drive roller contacts it. The direction of movement of the web support member is shown by the arrows.

A tank 108, made of insulation material, contains within it a heat storage and transfer medium 110 which is a nonwetting liquid. As before, the liquid is usually a molten metallic alloy and was described previously with respect to the structure in FIGURE 2a. Heating elements 112 are located within the nonwetting liquid and a temperature sensing element 114 is also located within the liquid. The temperature sensing element 114 is connected to a control circuit which regulates the temperature range of a nonwetting liquid.

Also located within the tank boundaries is a means 116 for positioning the heat storage and transfer medium 110.

This latter means 116 is a means for raising the level of the nonwetting liquid so that it will contact the underside of the support member 100. The means for raising the level of the nonwetting liquid is in this case a revolving cylinder which draws the nonwetting liquid around it when it revolves in a clockwise direction. This lifts the nonwetting liquid into contact with the underside of the support means 100, so that there is a heat transfer from the nonwetting liquid to the support member and then to the powder image thereon. It is to be understood that any means for bringing the nonwetting liquid 110 into contact with the underside of the web support 100 would be sufficient to provide heat transfer from the liquid to the support member.

In operation, the continuous web 100 travels from the transfer station on the xerographic drum to the heat exchange portion of the fusing apparatus by means of the drive roller 102, pinch roller 104 and guide roller 106. The direction of the travel of the web support is indicated by the arrows. Upon passing over the tank 108 containing the heat storage and transfer medium 110', this medium is raised to contact the underside of the web support. Heat is transferred to the support member and then to the thermo-responsive powder image located on the upper surface of the support member. Consequently, the powder image is fixed and the web then continues beyond the fusing apparatus. Subsequently, the web can be severed by a cutter or stored on a reel.

FIG. 3b shows a heat fusing apparatus similar to that in FIGURE 3a; however, the support members are individual sheets rather than a continuous web. Perforated belts are used to transport these sheets across a tank containing the heat storage and transfer medium.

The perforated belt is driven by a driving roller 122 which causes the endless belt 120 to travel in a clockwise direction. Vacuum is applied to the underside of the perforated belt by the vacuum source 124. Consequently, individual support members 126 having xerographic powder images 128 thereon, are conveyed from the transfer station on the xerographic drum across the tank 130 which contains the liquid heat storage and transfer medium 132. Upon passage over the tank 130, the support members 126 are picked up by the perforated belt 134, which is driven by roller 136. Vacuum is applied to the underside of this belt by the vacuum source 138.

Tank 130 contains the liquid heat storage and transfer medium 132, which is usually a low melting point metallic alloy. Suitable liquids have been described above. Located within the heat storage and transfer medium 132 is a temperature sensing element and various heater elements 142. The temperature sensing element 140 is connected to a control circuit which regulates the temperature of the molten metal bath 132 and keeps it within the desired range. This range is such that the heat exchange to the powder image 128 will be sufficient to fix the image but not excessive to the extent that damage will occur to the image and its support 126. The temperature at which damage occurs to the image or the support is defined as the scorch point of the support member.

A means for positioning the liquid heat storage and transfer medium is a revolving cylinder 144 made of insulating material. This cylinder draws the nonwetting liquid upwards around its periphery when it revolves, raising the level of the nonwetting liquid so that it will contact the underside of a support member 126 passing over the tank 130.

In operation, the individual support members 126 are transported from the transfer station of the xerographic drum by the perforated belt 120. Their direction of travel is indicated by the arrow above the support member. Upon passage over the surface of the tank 130, the heat storage and exchange medium 132 is raised by the action of the revolving cylinder 144. The nonwetting liquid is brought into contact with the underside of the support member passing overhead, so that heat transfer occurs from the liquid 132 to the support member 126. This fixes the powder image 128 on the surface of the support member. After passing across the width of the tank, the support members 126 are held by the perforated belt 134 and are transported away from the fusing apparatus.

FIG. 4 shows the control circuitry that regulates the temperature of the liquid heat storage and exchange medium so that the powder images will be fixed without damage to the image or the support member. The control means regulates the flow of electrical energy to the heater elements, and in this way maintains the temperature of the heat storage and exchange medium within the desired limits. Usually, this is the range of approximately 200 F. to 250 F. However, it is to be understood that the range can be difierent than this if the support members and the thermo-responsive powder material are chosen differently. It is only sufficient that the thermo-responsive powder image be properly fixed and that no harm be done to the image or its support member.

A temperature sensing element is located within the nonwetting liquid which serves as the heat storage and exchange medium. This temperature sensing element can be a thermocouple, whose voltage output varies with temperature of a thermistor whose electrical resistance varies with temperature. If a thermistor is used, a circuit is used with it to provide an electrical output that varies with temperature. The output of the temperature sensing element 150 is applied to an amplifier 152 where it is amplified and passed to a silicon control rectifier phase control unit 154. The'input to the S.C.R. phase unit 154 is an AC 9 signal of approximately 115 V. The output ofthe 'S.C.'R. phase control unit 154 is shown diagrammatically; This output is applied to the heater elements 156 that are locatedwithin the nonwetting liquid vamp.

The upper and lower limits of the temperature range are fixed and the output of the temperature sensing element 150 is usedto activate the S.C.R. phase control unit 154 such that the current to the heater elements will be increased or decreased depending upon whether the liquid temperature is above or below the desired temperature range. This is a conventional type of circuitry and any control circuitry that would maintain the temperature bounds within the desired range would be suitable.

A heat fusing apparatus for fixing thermo-responsive xerographic powder images has been described. This fusing apparatus has many advantages, chief of which is the very high efficiency of heat exchange between the heat storage and transfer medium and the image to be fixed. In this invention, heat is stored in the form of heat, rather than as electricity or mechanical energy. That is, the energy which is stored is heat energy rather than electrical or mechanical energy. This is achieved by using a nonwetting liquid as the heat storage and transfer medium. Rather than storging energy electrically or mechanically and then converting this energy to heat which is applied to the thermo-responsive powder image, energy is stored directly as heat and supplied to the therrno-responsive powder images, without an added conversion step. The liquid medium has both a coupling and a storage function.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention.

What is claimed is:

1. A fusing apparatus for fixing a Zerographic image of thermo-responsive powder located on a support member comprising:

a heat exchange portion having a heat storage and transfer medium, said medium further comprising a heated liquid which is nonwetting to the support member and the image, said liquid heated to a temperature greater than the fusing temperature of the thermo-responsive powder and less than the scorch point of the support member;

container means for containing said liquid;

heating means for heating said liquid;

conveying means for conveying the support member with the xerographic powder image thereon through said heat exchange portion, whereby the xerographic powder images are fixed by heat transfer from said heat storage and transfer medium to the support member and the powder images.

2. The apparatus of claim 1, wherein said nonwetting liquid is a molten metallic alloy.

3. The apparatus of claim 2, wherein said molten metallic alloy is comprised of bismuth, tin, and cadmium.

4. The apparatus of claim 1, wherein said heating means includes control means for maintaining said temperature of said liquid within said temperature range.

5. A fusing apparatus for fixing a xerographic image of thermo-responsive powder located on a support member comprising:

a heat storage and transfer medium for storing heat energy and for transferring heat energy to the support member having the xerographic powder image thereon, said medium being a heated liquid that is non-wetting to the support member and the powder image, said liquid heated to'a temperature greater than the fusing temperature of the thermo-responsive powder and less than the scorch point of the support member;

container means for containing said liquid;

conveying means for conveying the support member across and in contact with the surface of said heat storage and transfer medium; and

heat supply means for supplying heat energy to said nonwetting liquid, said nonwetting liquid retaining said heat energy as heat energy, wherein heat transfer from said nonwetting liquid to the support member and the powder image fixes the powder image.

6. The apparatus of claim 5, wherein said nonwetting liquid is a molten metallic alloy.

7. The apparatus of claim 6, including means for positioning said nonwetting liquid for contacting said support member to provide heat to said support member, as it passes across said heat storage and transfer medium.

8. The apparatus of claim 6 including means positioning the support member and said molten metallic alloy to be in contact with each other, thereby effecting heat transfer to the support member.

'9. The apparatus of claim 8 wherein said positioning means is a revolving cylinder partially submerged in said molten alloy.

10. The apparatus of claim 5, wherein said heat supplying means further comprises control means to maintain said non-wetting liquid within said temperature range.

11. A fusing apparatus for fixing xerographic powder images located on a support member comprising:

a heat storage and transfer medium further comprising a molten metallic alloy which is non-wetting to the support member and the powder image, said metallic alloy consisting of 53.9% bismuth, 25.9% tin, and 20.2% cadmium;

container means for containing said molten metallic alloy;

conveying means for conveying the support member to, across, in contact with, and away from said molten metallic alloy;

heat supplying means for heating said alloy to a temperature above the fusing temperature of the thermo-responsive powder and below the scorch point of the support member, said heat supplying means including control means to maintain said alloy with in said temperature limits; and

means for positioning said alloy for contacting the support member to provide heat to the support member and the powder image, said positioning means being a revolving cylinder partially submerged in said molten alloy to draw said molten alloy up to and into contact with the support member, thereby effecting heat transfer to the support member and the powder image causing fusing of the image to the support member.

12. A fusing apparatus for fixing a xerographic image of thermo-responsive powder located on a support member comprising:

a heat exchange portion having a heat storage and transfer medium, said medium comprising a heated liquid which is nonwetting to the support member and the image, said liquid heated to a temperature greater than the fusing temperature of the thermoresponsive powder and less than the scorch point of the support member;

container means for containing said liquid;

heating means for heating said liquid;

conveying means for conveying the support member with the xerographic powder image thereon into contact with said heat transfer and storage medium, whereby the xerographic powder images are fixed by heat transfer from said heat storage and transfer medium to the support member and the powder image.

(References on following page) References Cited UNITED STATES PATENTS Famworth et a1. 263-3 Codichini 263-3 X Carlson 34-77 Sturgeon 165-104 X Andrus et a1 219-388 12 1 3,445,626 5/1969 Michaels 219-216 3,093,051 6/1963 Ritzerfeld et a1. 95-89 VOLODYMYR Y. MAYEWSKY, Primary Examiner 5 U.S. c1. X.R.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 51 5 5 Dated June 2 a 1970 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

In the Specification Column 6, line 30 Change "FIG. 2," to --FIG. 2b,-

(SEAL) Attest:

mm 3. Edwmi u n h commissioner of Patents Attesting Officer