US 2776907 A
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METHOD OF FIXING ELECTROSTATIC POWDER IMAGE Filed July 18, 1952 Jan. 8, 1957 c. F. CARLSON s Sheets-Sheet 1 INVENTOR M w Jan. 8, 1957 c, c so 2,7?6,907
METHOD OF FIXING ELECTROSTATIC POWDER IMAGE Filed July 18, 1952 3 Sheets-Sheet 2 FIG. 6
ABSORBENT $OLVENT\ ABSORBENT 111: 1 11 1111111111/1/1/11111 IIIlIIII/IIIII/ I NVENTOR c. F. CARLSON 2,776,907
METHOD OF FIXING ELECTROSTATIC POWDER IMAGE 5 Sheets-Sheet 5 Jan. 8, 1957 Filed July 18, 1952 FIG.8
SOLVENT ABSORBENT FIG. 9
COLD SOLVENT SOLVENT ABSORBED 3kg? VAPOR m T IMAGE HEAT HEAT coLo FIXING ABSORBENT FROM BATH ROOM ROOM SOLVENT I RECLAIMING COLD SOLVENT SPENT SOLVENT VAPOR J ABSORBENT HOT HEAT ABSORBENT HEAT HEAT
INVENTOR Ueited ita sPa s f 2,776,907 METHOD 10F #FlXlNG ELEC EROSZIATIC .POWD-ER .IMAGE 'Ghest'er rucanson, ilittsford, "N. -Y., assignor to -"-The Battelle Development Corporation, Columbus, Ohioya icorporation of Delaware Application July 18,11952, Serial No. 299,673
6 Claims. "(CL 1 17-1715) This invention-relates 'to iniage fixing methods, particu- 7 lar ly' *rnethods of fixing powder images.
'iThepresent application is -'a -continuati'on in-part-ofco- .pe'n'din'g application, "Serial No. 1579883, filed April -25, *19'50.
l ert'ain electrostatic recording =processes,='such as the let photographic, xerographic and electric printi'ng pr oces'ses described in my Patents 2,221,776;123292691 and l 7-809, and the-process "of graphic recording deser ib'ed -in my ap lieation' se'rial No. 15 58252, .fil'ed Oc- *tober -111, I944, n'ow Patent '2;624,'652, an "electrostatic image is developed by depositing a powder on a surface to p'r'oduc'e a powder image. The powder irnage is then affixed ie the surface upon which it has been deposited or on 1 another surface to which it 'has been trans'fe'rred. 'f leretotora' the =u'sual methodof fixing has" been bys the proces'sof he'at 'iusin'gg-in which ease the powder i'ma'ge muse be torm'ed of a thermo-adhesive material, such.ias a fu'sible re'sin, which becomes adhesive wheruheate'd.
wliile' heat iusing h'a's been put to 'pra'cticalwuse, cer- --tain diiiictilties 'have been encountered. "Where the im'age i's to 'be fus'e'd' topape'r orother organic base, as is' usually *the 'c'ase,-the powder irlu'st bemade of material which becomesedhesive at a temperature= below that whioh *-will"cause"'damage to the organic base. llhissimposes "limitations on the choice-of *resins which make it difiictilt ie-meet other desirable characteristics in the powder "com osition. 'Moreover, it has been 'difiicult to reach'an entirely satisfactory design of heat' fuser with regard to 'shor't' w'arm-up '-"time, low electriccurrent requirements,
adequate heat instila'ti'o'n and uniform heat distribution.
Fixing-of pow der ima'ges by-condensinga liquid solvent 'ontothe"imagesurface-from a h'eated solvent vaporyas described, forexairi'ple, in my above-mentioned applicatibhsfSeiizihNo. 558,252 and 157,883, has'been' success- "ftillyu's'ed andjoifersthe'advantages of a broadened-choice off powtier materials, lower power requirements, and elimination 'ofh'eat damage to the base sheet.
Thepres'ent invention contemplates. a further improvem'ent-in solvent vapor fixing of powder images which ,.liniinates all, or most electricfpower requirements, sim- ,plifieslthe. design of equipment, materially reduces the consumption of solvent and the loss of solvent vapor, and -.-eliniinates-,.all delays. due to warm-up time. 'This is accomplished'byhmethods and apparatus which .introduce -;the.-powder-im-age into an atmosphere of 'solvent'vapor -whichis at substantially the same temperature as the ipowder-image,- or even at a lower temperature than the image. The=vaporatrnosphere is held, at a vapor con- --centration-=sufl"1cient. to produce absorption offsolvent vapor by thepowderrimage and consequentfusing of the aiirn'age; butithere is-uothermal condensation .onthe paper orrother base-which supports-the powder image. The base material consequently-remains dry.
aOthet-ieatures-ofgthe-invention willbe broughtout and i exemplified in the -disclosurerhereinafter ,set; forth, .mrlcludinig zthezillustrations in the drawings.
auteur In the drawings: Figure 1 illustrates a manually operated cold vapor fixing devi'ce for fixing powder images onto sheet-ma terials by theamethod of the present invention;
Figure b :illustrates a modification in 'Which a solvent absorbent chamber is added, the section 'beingsimilar to thatof Figure 4;
Figure 7 shows -a form of vapor fuser and solvent ab- :soitptiort .unitiortstraight-through'operation;
Figure 8 =is-azdiagram of a inset-absorber for hightp'roduction': speeds; and
vFigurecQ is a diagram of the process steps which. can
Elbe usedaiwiih'the apparatus of. Figures 6, '7 and 8.
The vaporfixing device of Figuresrl aud2 is "a hand aoperated unit which-maybe used tor'fixinglpowder images -.:intoi individual sheets --.ofpaper, :cloth, metal, 'plasticor .theulike, :and even onto the surfaces 0f electrophoto- ,egraphicaplates. It comprises a woodenwbox orihousing v10 storming avwide fiat and deep enclosureihaving its mouthorentrance at one end. 1A :pair of :triangular legs '.:"1-1-supportthe:housing at an incline :of about-30-degrees :Withthe horizontal supporting :surface; the mouth forming -.;ahorizontal opening 2 at the upper front end.
"The-housing l0 is lined with a sheet metal lining -12 rwhichis welded or soldered to provide a liquid-tight ,.-vapor chamber'-13. The openend "of -.liningv12 projects a-.short=distance out ot the mouth of wood housinglO, as izshowng at 14, the sheet rnetal- 'being' doubled- Eback and -bent;= out to provide flanges: '15 which fit againstthe @end of the wood housing-and which may be .attached to the ==wo'od-housing. 'Aislide member 16 of sheet metalis arrangedrto be-movedinto and out of'vapor chamber 1'3Zby 40:
its awooden end-piece 17 :which is tprovided withr ahandle 1 18. Endpiece 17 is provided with agroove which'fits "over-the projecting edges 14 of'the lining 12, so thatz when "the, slidewis inserted in the i chamber the -block"17:provides taught-closure for the vapor chamber. :Slide-16-rests=flat Qagainshthe sloping-lower wall of -the chamber and is -turned :up and back. at its inner end to provide a' channel ;.p'ortion-=liliin whieh the lower end of a-copy; sheetcarrybring a powder image :may be inserted for positioning-and support during fixing.
iAwsol vent wick 20 formed of felt, cloth' or blotting ;,paper..-isnsupported against the sloping :ceiling of the vapor chamber--13 by aseriestof stifi' sheet metal -ribs -21 wvhichtare secured at their outer, ends to the: ceiling near themouthiof the chamber and'extend along close to-the =ceiling and then benddown to form n-feet which rest-on thebottom and-bear against the rearend of the-.chamber. .The lowertend of wick 2il is rolled into a wad-22 atthe bottom ot the chamber.
The :fixing device is prepared for operation by pouring a quantity of a liquid solvent into the chamber-suiticienhtorsaturate thewick .20. The "slide "is inserted so that'the end'piece 17 closesthechamber-andthe device isallowed toystand until'the'solven-t is drawn'up-along "the ceiling of the chamber by the wick and the vapor space 13 becomes saturated with solvent vapor. The choice of solvent will depend upon the composition'of "the powder images to be fixed. With powders 'formed of pigmented rosin, copal, asphalt and other natural "resinsas well as several synthetic resins and plastics, such as ethyl cellulose, adesirable solvent is trich-loroethylene. Amyl acetate or butyl acetatecan likewise be used with many resins. Butyl alcohol and perchlorethylene are also useful, particularly in hot Weather, as they are somewhat less volatile.
Powder images can be fused in the device as soon as a saturated vapor atmosphere has been genera-ted. Once the wick has become wet with solvent over its entire area the necessary vapor atmosphere is quickly produced. The operator can then fix copies by simply grasping handle 18, withdrawing slide 16, placing a sheet bearing a powder image on the slide, inserting the slide in the chamber 13 for a few seconds, withdrawing the slide and removing the copy.
Although the solvent and solvent vapor are at the same temperature as the copy sheet and powder image, namely, at room temperature, fusion of the image takes place, provided the powder is soluble in the solvent. The powder absorbs solvent from the vapor phase until it becomes adhesive. In some instance the powder image will absorb enough solvent to completely liquify it. It has been found, however, that serious spreading of the image does not take place on paper base material unless the copy is allowed to remain in the fixing device much longer than the few seconds needed for fusing. The fusing time is not critical, whereas it is with heat fusing.
As soon as the fused copy is removed from the vapor chamber the solvent begins to evaporate from the image and the image solidifies and becomes permanently bonded or fixed onto the base material in a few seconds.
Since the solvent vapor has a density greater than that of air it tends to remain in the vapor space 13 as the slide is removed and reinserted. The small loss of vapor due to absorption by the powder image and drag-out by the slide is quickly regenerated from the wick 20 so that copies can be fused in rapid succession. On the other hand, when not in demand, the device stands ready for use at any moment since the vapor atmosphere is maintained in the space 13 at all times. Recharging with solvent is necessary only at infrequent intervals and with moderate use one charge of a few cubic centimeters of liquid solvent may last several days.
This method of operation, in which the vapor is at the same temperature as the copy, is much more economical of solvent than vapor fixing methods in which the solvent is heated, as with cold vapor there is no condensation on the paper base unless it carries a resin or material soluble in the solvent used. In most cases the powder image is the only part of the copy which absorbs the solvent and its requirements are very small. With unheated solvent the loss due to vapor leakage from openings in the vapor space is practically negligible since the vapor is kept denser than air and no vapor pressure is built up to drive solvent out of the chamber.
The advantages of the present invention are most fully realized in the fixing of powder images to paper using the vapor of a non-aqueous solvent such as the organic solvents and chlorinated organic solvents, where the economy of solvent consumption is an important factor, and the evaporation of excessive quantities of solvent into the room may be objectionable. Moreover, these solvent vapors at the same temperature as the copy to be fixed are not noticeably absorbed by the paper base and do not produce any dimensional change or buckling in the base.
Aqueous solvents are not useful, of course, infixing most resin or plastic images as these materials are not water-soluble. Where water-soluble image forming materials are used, some spreading and loss of sharpness may frequently take place due to the humidification of the cellulose fibres of the paper during fusing.
For effective fusing of a powder image to take place the solvent vapor is held at a great enough concentration in the vapor fixing chamber to produce absorption of solvent vapor by the powder until the powder becomes adhesive. This means that the partial pressure of the solvent vapor shall exceed the vapor pressure of a $0111- tion of the powder (or the soluble constituents of the powder) which contains suflicient absorbed solvent to be adhesive. A concentrated vapor atmosphere is insured by providing a reservoir of liquid solvent in contact with the vapor space, particularly if the solvent is brought to the upper part of the vapor space by a wick or other means so that the higher density vapor will settle and fill the space. The air in the chamber is thus saturated with vapor, and the concentration is maintained in excess of the minimum requirements even with frequent use.
While the advantages of the process are greatest where base materials, such as paper, which are not soluble in the solvent are used, the method may sometimes be used to affix powder images to plastic films and to plastic coated paper, in which the plastic may be made adhesive by the solvent and the powder may or may not be affected by the solvent. In the case of films, the fusing time must, of course, be controlled to obtain only a surface adhesion without undue softening the entire plastic layer.
Figures 3, 4 and 5 show a vapor fixing device for fusing a continuous web of copy issuing from an electrostatic powder printing machine or a continuous electrophotographic copying machine. Paper web 30 carrying the unfixed powder images 31 enters in a horizontal plane from a powder printing or copying machine located at the left, as viewed in Figures 3 and 4, and passes over a horizontal roller 32 mounted in bearings on supports 33 and extending obliquely or diagonally across the web.
The web then passes obliquely downward for a substantial distance to a point where it passes around and under a horizontal roller 34 mounted in bearings parallel to roller 32 and directly beneath it. The web then passes diagonally upward and around and over roller 32 again,
this time at a spaced position on the length of roller 32 as clearly seen in the drawings, from which point it passes to a take-up reel 44 driven by motor 45 through constant tension clutch 46. It will be noted that the powder images are always kept on the outside of the web as it passes around rollers 32 and 34 so that no surface is brought into contact with the images.
A vapor tank 35 encloses roller 34 and the major part of the web between rollers 32 and 34. The tank provides a saturated vapor space 36 which is lined with a porous wicking of fibreboard, fabric or blotting paper and a solvent fountain bottle 37 maintains a shallow layer of liquid solvent 39 in the bottom of the tank by supply tube 40 to keep the wicking saturated.
The top of the tank is closed in part by a central guide bar or plate 41 which is in contact with the inside face of the web entering and leaving the tank. A pair of adjustable plates 42 are mounted along the upper edges of the tank by screws 43 so that the inner edges of these plates can be adjusted to keep the entering and leaving slots at the minimum necessary to avoid contact with the image and still prevent excessive drag-out of vapor.
In operation of the fusing device of Figures 3, 4 and 5 the web 30 carrying the powder images is drawn through the device by the take-up reel 44, the web being kept under tension by the take-up reel and by a braking member on the supply reel in the printing or copying machine. As the web enters the vapor space 36 the powder image absorbs solvent vapor and becomes adhesive.
When the web emerges the absorbed solvent rapidly evaporates and the images reach the take-up reel in dry condition. For high production machines a ventilating system may be provided to remove vapor from the room.
Since substantially the only solvent consumed is that carried out of the tank by the resin image the fuser is very economical of solvent consumption and very little vapor is released into the room. An average powder image of text matter contains about one-twentieth of a gram or less of resin powder per square foot and an equal weight of solvent is sufficient to cause fusion. It is obvious that the rate of solvent consumption, using cold vapor fusing, is low. This has a marked advantag'e lowerszthe temperature of the walls one or two degrees below room temperature causing the walls to absorb heat t-rom..the air around the tank. I
Figure 6 shows a modification applicable to the apparatus of Figures 3, 4 :and 5 which provides the added feature of capture and absorption of solvent evaporated from the fused images. In this embodiment the fusing tank 35 is enclosed in anabsorption tank 61 through which the web passes on entering and leaving tank 35.
Absorption tank 61 is provided with a removable cover 62 having a web opening :provided with a guide bar 63 and side plates 64 similar to those in the top of the .fusing tank. A liquid absorbent 65 the space in tank 61 around the sides of inner tank 35 and an overflowpipe 66 and drain valve67 are provided and tapped .into the side of absorbent tank 61 near its bottom. The open end of overflow pipe 66 is below the .level of the top of inner tank 35 and insures that the absorbent liquid will not rise to ,a height where it cantflow into the inner tank.
An absorbent liquid 65 is used which itself has low vapor pressure and which will readily absorb or dissolve large quantities of the solvent vapor used in inner tank 35 before the solvent vapor pressure from the mixture rises to a very high value. Thus, when trich'olorethylene is used as a fusing solvent, the absorbent may be a high boiling petroleurnfraction such as pa'raffin oil, new or used lubricating oils, and even oils containing a high percentage of dissolved waxes or tars, or crude petroleum with the volatile fractions removed. Suitable absorbent liquids for the volatile esters and alcohols inblade the higher boiling esters, alcohols, aliphatic oils, and some hydrocarbons.
In operation of Figure 6 the vapors space inside tank 35 is kept saturated with solvent vapor as previously described, while the 'spa'ce'68 above the absorbent liquid in outer tank 61 contains air in which the solvent vapor concentration is kept very low by the absorbent. As the web passes through inner tank 35 the powder images are fused with solvent vapor as previously described. Then as the ascending portion 69 of the web passes through air space 68 the solvent evaporates from the images so that they leave tank 61 in substantially dry and fixed condition. The solvent vapor released into space 68 is rapidly absorbed by the absorbent liquid 65 thus keeping the vapor pressure of solvent in space 68 at a very low value which is most effective for drying the images. Absorption of solvent vapor by liquid 65 will gradually increase its volume and the liquid level will rise in the outer tank. Should the level accidentally exceed the height of standpipe 66 the liquid will overflow through the pipe and prevent further rise of the level which might flood liquid over into inner tank 35. As solvent vapor is absorbed the concentration of dissolved solvent in the absorbent liquid 65 increases and consequently the vapor pressure of solvent in space 68 will gradually rise and decrease the thoroughness of the evaporation from the images. When the elfectiveness of the absorbent liquid has been lowered to the point where adequate drying of the images no longer occurs it is replaced with fresh absorbent.
Figure 7 illustrates another fixing device in which the web 30 is fed straight through in a horizontal plane. The web enters fusing tank 70 through a horizontal slot defined by guide bar 71 and adjustable plate 72 and is provided with solvent vapor by solvent liquid 39 and -i-ng air is blown along its surface. generated .in tank-86 containing liquid solvent 39 and wic k member 73 insidethewtank. tSolvent tanlr 10 is mounted. inside :the cover :74 -o-rectangulair absorbent tank 75 :and as the web 30 ;leaves the solvent it passes through a long shallow slot 76 into thea'siris'pabe above absorbent liquid. Here the webpass'es between a pair of closely spaced horizontal electric hotplates :or strip heaters 77 and 78 surrounded by "layerszof iti's'ulation 79 and :80 'on all sides except the shallow space between them through which the paper web. passes. The web and the fused images it carries are heated slightly by these plates to drive ofi the solvent more rapidly. The travelof the Web sets a circulation of airin the absorption chamber, as indicated by the arrows, which carries the slightly warm solvent vapor driven ofi from the webdown- -over the surface of the -absorbent liquid which rapidly takes up the solvent. The Web leaves the absorption tank through an air tseal comprising a soft rubber flap 81 which slides onthe top surface of the web as the web rides over the horizontal guide flange 82-011 leaving the tank. Tank 75 may be provided with cooling fins, suchas83, to keep the absorbent liquid near to room temperature. Most of the heatgenera-ted by the .hotplates is carried out by the paper web.
Figure 8 shows another form of straight-through fixing device especially suitable for high production speeds. As the web 30 passes horizontally from left to right, asshown, it passes first under a fusing head '84 where solvent vapor is blown against -and-along the web, and then the web passes under a drying head 85 where dry- Solventvapor is having wicks 87 lining its walls. The vapor is drawn from the lower part of the vapor space through conduit 88 to the intake opening of blower 89 driven by e1ectric motor .90. The output oft-he blower passes into .a chamber 91 of the head "84 from which chamber it emerges through sloping slot 92 which projects the vapor stream against the top of the web '30. The vapor stream passes along the web to return slot 93 through which it passes into a chamber .94 and then through conduit 95 back to the top of tank 86. By providinga forced circulation of vapor the fusing process is accelerated.
A similar system is provided for circulating drying air from absorption tank 96 through drying head 85. Air from the upper part of tank 96 is drawn under the horizontal flange 97 of floating intake nozzle 98 which is supported on floats 99 in order to route the air close to the surface of the absorbent liquid 65. The air passes up through conduit 100 to the intake part of blower 101 driven by motor 90. From the blower the air enters chamber 102 in head 85, then passes out of slot 103 and against the web, then along the web, through slot 104, chamber 105 and conduit 106 back to tank 96. A heater 107 mounted above the web in the air passage may be energized if desired to heat the Web and hasten evaporation during drying.
Figure 9 is a diagram of a process cycle which may be used with Figures 6, 7 and 8, and an optional reclaiming cycle in which the solvent and absorbent are reclaimed by distillation of the spent absorbent bath. Where it is uneconomic to reclaim the materials the distillation steps can be eliminated and the spent absorbent liquid is thrown away. The heat introduced in the generation of the cold vapor is preferably obtained from the surroundings and is sufiicient only for vaporization of the solvent to produce a vapor at room temperature. The heat introduced in drying the web may come from the drying air at room temperature or may be supplied in part by an electric heater as described in connection with Figures 7 and 8. The temperature of the absorbent bath is raised slightly during operation and the heat passes out through the tank walls into the room, aided, if necessary, by added cooling surfaces on the tank in order that the bath temperature shall be held as low as possible.
While the present invention, as to its objects and advantages, has been described herein as carried out in specific embodiments thereof, it is not desired to be limited thereby, but it is intended to cover the invention broadly within the spirit .and scope of the appended claims. 1
What is claimed is:
1. In a process wherein an electrostatic image corresponding to a pattern of light and shadow to be reproduced is made visible by depositing powder on a surface in conformity with said electrostatic image and afiixing said powder in image conformation to a support material, the improvement comprising afiixing said powder in image conformation by introducing said support material into the vapor of an organic liquid solvent for an adhesive constituent of at least one of the materials from which said powder image and said support material from which said powder image and said support material are formed, said vapor and said support material being at ambient temperature and said vapor being at a partial pressure exceeding the vapor pressure of solvent from a tacky solution of said adhesive constituent, and then removing said support material from said vapor after said adhesive has become tacky, and removing said solvent from said adhesive to permanently bond said image to said support material.
2. The method of claim 1 in which said powder image is formed of a pigmented resin and said solvent is a solvent for said resin.
3. In a process wherein an electrostatic image corresponding to a pattern of light and shadow to be reproduced is made visible by depositing resin powder on a surface in conformity with said electrostatic image and afiixing said powder in image conformation to paper, the improvement comprising afiixing said powder in image conformation by introducing said paper surface carrying said powder image into a chamber containing the vapor of a volatile solvent for said resin, said paper, powder image and vapor all being at ambient temperature, and then after said resin-base powder has become K adhesive through absorption of solvent removing said paper and image from said chamber to permit evaporation of solvent whereby said resin-base image becomes permanently bonded to said paper surface.
4. The method of claim 3 in which said resin powder is insoluble in water and said solvent is an organic solvent in which said resin becomes tacky.
5. The method of claim 3 in which said resin-base powder is formed of a resin and a pigment suspended therein, and said solvent is an organic solvent in which said resin is soluble.
6. In a process wherein an electrostatic image corresponding to a pattern of light and shadow to be re produced is made visible by depositing dry colored resin powder onto the surface of a sheet upon which it is loosely supported in conformity with said electrostatic image and afiixing said powder in image conformation to said sheet, the improvement comprising introducing said sheet and powder image into an enclosed space containing the vapor of a solvent for said resin, said vapor and said sheet being at ambient temperature and said vapor being at a partial pressure exceeding the solvent vapor pressure of a tacky solution of said resin therein to tackify said resin powder whereby said image is permanently afiixed to said sheet without impairing the resolution and clarity of said image and then, transferring said sheet with the tacky image into an air space in which the solvent vapor pressure is below the solvent vapor pressure of a tacky solution of said resin, to evaporate solvent from said resin solution and leave the resin image affixed to said surface.
References Cited in the file of this patent UNITED STATES PATENTS 921,229 Gleason May 11, 1909 1,141,224 Wawrziniok June 1, 1915 1,339,529 Verhoogen May 11, 1920 1,569,048 Stock Jan. 12, 1926 1,811,107 Barnebey June 23, 1931 2,034,008 Taylor Mar. 17, 1936 2,097,885 Koppe Nov. 2, 1937 2,138,578 Hershberger Nov. 29, 1938 2,221,776 Carlson Nov. 19, 1940 2,250,925 Babcock July 29, 1941 2,297,691 Carlson Oct. 6, 1942 2,361,350 Keep et al Oct. 24, 1944 FOREIGN PATENTS 7,402 Great Britain of 1906