US2221776A - Electron photography - Google Patents

Description

Nov. 19, 1940. c. F. CARLSON ELECTRON PHOTOGRAPHY Filed Sept. 8, 1938 2 Sheets-Sheet l u INVENTOR Nov. 19, 1940. c. F. CARLSONy ELECTRON PHOTOGRAPHY Filed Sept. 8, 19.38 2 Sheets-Sheet 2 lNV'ENTOR Patented Nov. 19, 1940 UNITED STATES PATENT OFFICE 11 Claimsf This invention relates to photography. An object of the invention is to improve photographic processes and devices.

Other objects of the invention will be apparent from the following description and accompanying drawings taken in connection with the appended claims. The invention comprises the features of construction, combina-tion of elements, arrangement of parts, and methods of manufacture and operation referred to above or which will be brought out and exemplified in the disclosure hereinafter set forth, including the illustrationsfin the drawings.

In the drawings: Figure 1 is a sectional eleva-tion of an electrophotographic device;

Figure 2 is a section on the line 2-2 of Figure 1; Figure 3 shows a modied part;

Figure 4 shows part of a modified device suitable for contact printing;

Figure 5 illustrates part of an X-ray electrophoto arrangement; Figure 6 shows a modified arrangement for developing the electric latent image; and

Figures 7 and 8 illustrate another photographic procedure.

My invention contemplates the use of a photoemissive material, that is, material which emits electrons when exposed to radiation such as light, ultra-violet rays, X-rays or the like. According to the invention a layer or surface having photoemissive qualities is exposed -to radiation (having a desired image or pattern, for example) to produce a corresponding emission of electrons in the areas receiving the radiation. The electric charge pattern (electrostatic latent image) thus produced on the photoemissive layer or on an adjacent layer of insulation is then developed or rendered visible by depositing a suitable material, such as powder, under influence of the charge pattern.

This may preferably be done automatically immediately after the electric latent image is produced and I have devised certain automatic devices for depositing a iinely divided material to develop the image and for fixing the material after deposition. My invention therefore provides an automatic photographing machine comprising a single piece of apparatus for producing a finished print.

While a preferred embodiment of the invention is described herein, it is contemplated that considerable variation may be made in the method of procedure and the construction of parts without departing from .the spirit of the invention. In the following description and in the claims, .parts will be identified by specific names for convenience, but they are intended to be as generic in their application to similar parts as the ant will permit.

Referring to the drawings, Figure 1 shows a device particularly adapted for making photographic reproductions of printed or typewritten matter, drawings, pictures and the like although it may also be used in some cases for general photography. The sheet III bearing the printing or drawing to be reproduced is laid on a table and the apparatus is suitably suspended above it with camera portion I I disposed directly over the sheet I0. Lens I2 is positioned in the lower end of the camera so as to focus the image of the sheet III on a photo-electric layer I4 deposited upon a sheet I5 of transparent material supported in the upper part of the camera. Shutter I3 controls the entry of light into the camera. The photoelectric layer I4 is preferably conductive or provided with a contiguous conductor such as a transparent thin metal film deposited upon the sheet I6 before the photoelectric material, or a fine wire screen secured Ato the surface of sheet I5. A current collecting margin strip I 6 of highly conductive material is also provided near the edges of sheet I5 and this is connected to a battery Il by an insulated conductor I8 and switch A plane metal electrode I9 is also supported within the camera behind photo-emissive layer I4 and lparallel -to it. Electrode I9 is connected to the opposite terminal of battery II by conductor 2li and switch 31. Battery II is a high voltage battery, preferably above 1000 volts or even several thousand volts although the voltage should not vbe suiiicient to start or to maintain a discharge between the surfaces of layers I4 and I9, other than that which is incidental to the photoelectric effect.

A spool or mandrel `2 I, mounted at the left end of the back part of the camera (as seen in Figure 1) carries a roll of sheet insulating material 22 upon which the .photographs are to be produced.

Sheet 22 is of material of high insulating value under the conditions present in the camera and is transparent or translucent. Suitable materials are unplasticized and dehydrated Cellophane, cellulose acetate, translucent paper, transparent sheet resins, polystyrene sheet, paper or Cellophane impregnated with polystyrene, ethyl cellulose sheet. Celluloid or the like. The end of the sheet 22. as it is unrolled from the spool 2i passes between two smooth metal rollers 2l which are grounded through conductor 2l. These roll- 5 ers serve to remove any electric charge accidentally present on the surface of the sheet 22 as it leaves the roll.

The rolls 2l are positioned to hold the sheet 22 in a plane approximately mid-way between l0 layers il and I9. The sheet 22 passes between layers Il and it without touching them and passes between rolls 2l near the right end of the back of the camera (as seen in Figure l). The sheet is further supported in proper position by guide slots 2l along the two sides of the plates as illustrated in the section shown in Figure 2. This figure also shows how plates Il and II are mounted. Spool 2i is free to rotate but has a friction brake (not shown) to apply a tension to sheet 22. Rolls 25a and 25h are all geared together and are driven by a hand crank or an electric motor whenever it is desired to move the sheet 22 ahead.

A series of chambers 21, adjacent the camera 26 chamber Il, contain a hygroscopic material 22,

such as calcium chloride. to maintain a dry atmosphere in the camera. These chambers also help to keep dust out of camera parts.

A dusting chamber 28 is also disposed beneath 80 the sheet 22 and has its open upper end closely adjacent the under surface of the sheet. A rotary vane wheel or propeller 30 is supported within the chamber and connected with a drive motor to rotate it when desired. It may be geared to rollers 25 so as to rotate whenever they are pulling sheet 22 ahead. Chamber 29 contains a charge of very ilne powder or dut ll for application to the sheet 22, as will be described. The powder may be nely powdered dye, pigment.

carbon or other black or colored substance or in some cases a white powder such as zinc oxide. titanium dioxide or lycopodium. Likewise mixtures of powders such as a mixture of nnely powdered sulfur and finely powdered minimum may be used.

A spool 32 is mounted adJacent rolls 2lb and carries a roll of sheet material I8 of approximately the same width as sheet 22. Sheet il is led up over rolls 2lb so as to be rolled against I0 sheet 22 andbecarriedalongwithittotheend of the camera where the two sheets emerge throughslit Mandmaybecutoifinanydeaired length bypaperknife Il. Sheetmaybepaper or other similar material. If the powder 2l is black or coloredthesheetll maypreferablybe white while if the powder is white or light-coloredthesheetcanbeblackordarklycoldred.

Either sheet 22 or sheet Il (or both) is provided with a surface coating of thermosoftening adhe- 00 sive on the side which comes in contact with the other sheet. Such material may be. for example, a resin such as shellac or rosin. one of the various thermosoftening synthetic resins, rubber compounds. such as rubber hydrochloride, a gum 05 orawax. Ifusedonsheet22itshouldforma smooth, non-tacky and preferably glossy surface. Rolls 2l are provided with internal electric heating coils which soften the coating as the sheets pass between the rolls thereby causing` the 7 sheets to adhere together after they emerge from the rolls.

Switch Il is arranged to connect conductor 2l. to ground when it is closed. Switches l1 and Il connect the terminals of battery i1 to conductors 1I nanars. witntnetnreeswucnesmtnepositionsshowninligurelplate Ilisconnected to the .positive terminal of the battery amleto ground and photoelectric layer Il to the negative terminal.

A `otogralph'is produced by the above-des scribed device in the following manner. Shutter l2 ia opened and lens I2 focuses the image of sheet Il onto the photoelectrlc layer I4. The areas of layer il illuminated by the light areas of the image will emit electrons into the ldlal0 cent air space between layer Il and sheet 22. Theareascorrespondingtothedarkpartsof the image will be only poorly illuminated or will receive practically no light at all and hence will emit fewer electrons per unit area, or practically ll none.

The layers Il and i0 being connected to opposite terminals of the high voltage source are oppositely charged and an intense electric field exists between them tending to draw any free eleoa0 trons rapidly toward sheet 22. Although electrons will be emitted from layer il at all angles the iield is strong enough to draw all the emitted electrons onto the surface of sheet 22, which is closely spaced from layer Il, before there is any z5 substantial spreading of the electrons away from their points of origin. Any slight ionization of the air by the stream of electrons will be insufflcient to interfere materially with the electron deposition. an

The shutter Il is kept open for sumcient length of time to allow the emitted electrons to build up a considerable electric charge on sheet 22 in the form of an electrostatic latent image or charge image. g5

As soon as the charge image is formed, rollers 2l are rotated to draw sheet 22 toward the right (as seen in Figure 1) and vane wheel Il is rotated to bring the powder particles Il into suspension in the air of chamber 2l. As the o charged surface of sheet 22 is drawn over chamber 2l the particles are attracted to the surface of the sheet by the charges and adhere to it where the charge density is suiiicient, thereby producing a pattern corresponding to the electrostatic latent image. Deposition of the particles is facilitated. if desired. by connecting vane wheel 3l to the positive terminal of a high voltage battery Il to impart podtive charges to the particlel. o

As sheet 22 proceeds past chamber 2l, therefore. it picks up powder particles which develop the electric latent image and render it visible. The sheet 22 then pases between heated rollers 28a and 2lb in contact with sheet 22 and the two u sheets are stuck together by the thermoaoftening adhesive on the surface of one or both. When sheet 22 carries the thermosoftening surface it may be preferable to preset the powder in the surface of the sheet by passing the sheet adia- .o cent a heating element 4l before it comes in contact with sheet 3l. In some cases sheet Il may be dispensed with.

The finished prints emerge through slot Il and are cut oi! by knife 25. g5

According to a modification in the above dev scribed apparatus the plate II is provided with a surface of photoemissive material and layer il 'is merely a transparent metal iilm electrode or a fine wire screen. In operation the switches 7 I1 and 3l are reversed to connect layer II to the negative and layer Il to the positive terminal of the Ahigh voltage source I'l. Ihe image is focused by lens I2 onto the surface of laver il and the electrostatic latent image is built up on the 'l5 upper surface of transparent sheet 22. In developing the image the charges attract the powder particles through dielectric layer 22, the powder being deposited on the under surface of the sheet as before. y

Figure 3 shows a une wire screen III stretched on a metal frame IIII supported in an insulating frame |02. 'I'his screen may be used in place of plate I5 and its surface layer in the arrangement just described. Likewise, if screen l is of photoelectric metal or has a coating of ,photoelectric material it may be used as the photoemis-v sive layer in the arrangement rst described or in arrangements to be subsequently mentioned. A With further reference to the nature of the photoemissive layer, this will depend upon the wave length of the radiation to be recorded. The composition must, of course, be capable of exposure to air for at least a short time without destroying its photoelectric properties. One series of compounds which are suitable are the Lenard phosphors. For radiation in the blueviolet part of the visible spectrum and in the near ultra-violet the preferred material is the phosphor usually designated as Ca Bi S. This consists essentially of pure calcium sulilde to which a flux and a trace of bismuth have ben added and the whole fused together. With such amaterial the usual sources of light (containing the effective wave lengths) and lens systems can be used to advantage.` The phosphor may preferably be deposited in a very thin layer I4 on top of a thin transparent metal film previously deposited on transparent plate I5. Or it may be held in the interstlces of avery iine wire screen secured to the surface of plate I5. In the modification described the phosphor layer may be deposited on plate I9. It will be appreciated that in my invention the photoelectric effect of the phosphors are used, and not the fluorescence which is usually associated with the use of these materials. In fact, the fluorescent excitation of the phosphors appears to diminish the photoelectric emission. To overcome this I provide a small infra-red lamp 4I within the camera chamber II, connected to battery 42 `through switch 43. 'I'he infrared light has a quenching action on the fluorescence. By energizing lamp 4I during exposure of the phosphor layer its photoelectric activity is maintained throughout the exposure period. 'I'he lamp is limited to infra-red radiation suitable for quenching the fluorescence and emits none of the shorter wave lengths which produce photoemission.

Other photoelectric materials may be used in carrying out the invention where they possess photoemissive properties at the wave lengths desired to be recorded. For ultra-violet radiation,

for example, freshly prepared metal surfaces may alreadymentioned are suitable, including most oi the metals.

In some cases printing,.drawings, typewriting and the like may be reproduced by a contact printing process in which the original is placed adjacent the photoelectric layer and illuminated so as to throw the shadow of the printing or drawing onto the photoelectric layer. Figure 4 shows an original sheet 45 of transparent material carrying indicia 45 to be reproduced. Sheet 45 is placed adjacent to or in contact with a layer of sheet insulating material 41 unrolled from roll 4l. Sheet material 41, such as translucent paper or transparent regenerated sheet cellulose carries a thin layer 48 on its under surfaceV of photoemissive material. A metal plate electrode 50 is spacedvfrom this surfaceand is maintained at a high positive voltage by battery 5I. The superposed sheets are illuminated from above by a suitable source of radiation such as arc 52. 'I'he parts of the photlectric layer unprotected by the indicia will emit electrons to plate 50 thereby leaving the surface of sheet 41 with a positive charge distributed over the unshaded areas. The positive latent charge image is developed by dusting as heretofore described.

'Ihis method has the advantage of requiring no lenses which cut oil! part of the 'ultra-violet. spectrum.' Hence photoelectric materials which are sensitive only to the shorter ultra-violet waves can be used. For example layer 49 may be a layer of shellac or other resin which is photoelectrically active when illuminated by short ultra violet. Also very thin layers of metals Awhich are'photoelectrically active in this region may be used, the metal being deposited in small discrete areas to prevent lateral conductivity in the layer. The contact printing process can also` be used withA the electrode arrangements of Figure 1, by replacing the lens systemby a source of radiation and placing the original to be copied against plate I5.

Figure 5 shows an arrangement for making X- ray shadowgraphs utilizing the invention. The top of the apparatus comprises a plate of insulating material 53 carrying a thin layer 54 of material which emits electrons when exposed to X-rays. Metal plate 55 is spaced slightly below layer 54 and insulating sheet 22 passes between the two.V Layer 54 is connected to the negative terminal of battery 51 and plate 55 to its positive termina-l. The negative terminal may preferably be grounded by switch`58.

The subject ss to be x-rayed is 1am on plate 53 and X-ray tube is positioned above it. The electrons ejected from layer 54 by the X-rays are drawn to sheet 22 forming an electrostatic latent image thereon, which is developed as already described.

In Figure 6 is shown a modified powder deposition apparatus in which a rotating tube 6I of very fine wire screen, silk cloth or the like is positioned above the path of sheet 22 and contains a charge of powder 3| to be deposited on it. The sheet then passes around insulating roller 62 whereupon excess powder not held onto the sheet by the electric charges falls oil'. 'I'he sheet then passes in contact with an electrically heated plate 55 to permanently fix the adherentk powder to the sheet. In this arrangement the surface of sheet 22 may be of heat softenable material or the powder itself may be capable of softening by i heat. Finely powdered rosin carrying a dye or el.l 2,221,770

Figures 7 and 8 illustrate dlagrammaticaliy another method which can be used. According to this method the photoelectric material I4 is of an insulating variety and is coated on insulating plate Il. It is illuminated with the image as shown in Figure 'I with collecting grids 0l podtioned adjacent the surface to collect the ejected electrons, the grids being charged positively by battery 61. A positive charge latent image is 10 thereby formed on the surface of layer il. The surface is dusted by sprinkling with powder and shaking of! the excess. The dust image is then transferred to a sheet having a slightly tacky surface B9 by rolling the sheet against the plate with sofi rubber roner n.

In the description and drawings the source of high voltage has been indicated as a battery. However, other suitable means of obtaining a high voltage charge are also contemplated as n coming within the scope of the invention. Fior example, various types of electrostatic generators can be used such as the Van de Graaf generator using a rapidly moving silk ribbon belt to carry the charges. Also high voltage power packs using u transformer and rectiner may be used. It will be appreciated that almost no current is used in the photographic process and hence only a very minute current capacity is required of the voltage source.

3 rn addition to the powder deposition methods described it is also possible to develop the picture by producing a fine mist of ink with an atomizer, the ink droplets being attracted to the charged areas of the insulating sheet where they deposit and produce the visible picture.

'I'he present invention, in addition to being applicable to general photography and for the reproduction of printing, typewritten matter and drawings, is suitable for graph work wherein a o point of light is focused on the photoelectric layer as the insulating sheet travels by, and the graph thus traced is promptly rendered visible by the powder development.

It will also be appreciated that the different s parts of the various apparatus described can be combined in different ways, the special combinations illustrated being examples of only a few of the suggested combinations. It will likewise be recognized that any of the well known 5 types of optical systems and camera arrangements, as well as projecting systems for X-rays, ultra-violet radiation and the like can be used to project the image desired upon the photoelectric layer.

This application is a continuaticn-in-part of my co-pending application, Serial Number 169,630, filed Oct. 18, 1937.

While the present invention. as to its objects and advantages, has been described herein as w carried out inI specic 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.

What is claimed is:

gg l. A device for photography comprising a layer of photoemissive material, a conductive layer in spaced parallel relation thereto, a sheet of insulating material between said layers and spaced therefrom by air gaps. means for projecting an image on said photoemissive layer and means for applying an accelerating electric eld between said photoemissive layer and said conductive layer.

2. A device for developing and thereby rendering visible an electric charge image upon the surface of sheet material which comprises a chamber containing finely divided material and an agitator therein for bringing said material intosuspensionintheairofsaidchamberand means for supporting said sheet material across g the top of said chamber with the charged surface thereof facing downwardly and in contact with the air suspension in said chamber.

3. 'Ihe method of producing a permanent visible picture from an electrostatic image on the 10 face of a member which comprises bringing finely divided electrostatically attractable material adjacent said face whereby to form an electrostatic deposit thereon. then engaging said facs and deposit with a sheet of material having a is thermoscftening adhesive surface and applying heat and pressure to the assembly.

4. The method of electrophotography which comprises placing a layer having an insulating surface in spaced parallel relation to a photozo emissive layer, with an air space therebetween, applying an electron accelerating electric field across the air space between the photoemissive layer and said insulating surface, and projecting an image on said photoemissive layer whereby 25 electrons will be emitted therefrom and drawn to said insulating surface by said held thereby producing an electrostatic latent image on said insulating surface, then depositing a finely divided material on said insulating surface to develop said image.

5. An electrophoto device comprising a photoemissive layer, a layer of insulating material and means supporting said insulating layer in spaced parallel relation to said photoemissive layer with 35 an air gap therebetween, means for applying an electric ileld between said layers to drive electrons ejected from said photoemissive layer to said insulating layer, means for projecting radiation onto said photoemissive layer in an image (n to be reproduced, said radiation causing photoemission of electrons from said layer. means for depositing a finely divided material on said insulating layer, and means for moving said insulating layer into a position to receive said finely divided material.

6. A device for developing an electrostatic latent image on the surface of an insulating layer which comprises a chamber having one side open to the surface of said layer, an agitator for the n air of said chamber and any powder particles carried thereby, means to support said insulating layer over the open side of said chamber. and means to move said layer along in a direction parallel to its own surface whereby successive lg portions of said surface may be brought over the open side of said chamber.

7. A device for developing an electrostatic latent image on an insulating sheet surface which comprises mains for applying dust tosaid surface. Q means for heating the surface to soften any ther. mosoftening material on said dusted surface and fix said dust thereto, and means to move said surface along in a direction parallel to itself firstpastsaiddustingmnsandthenpastsaid heating means.

8. In combination, means for moving an insulating layer having an electrostatic charge image on its surface along in a direction parallel to its surface, means to apply dust to said surface. 70 means to subsequently roll a sheet of flexible sheet material against said surface and means for applying heat to said sheet.

9. In combination, means for Flying dust tothesurface ofaninsulatinglayenmeam for subsequently rolling a sheet of flexible material against said surface and means for heating said sheet.

10. In combination, means for moving an insulating sheet along in a direction parallel to its surface, means for applying an electric charge image to said sheet, means for dusting said sheeJ and means for xing the dust in the configuration in which it has been deposited, said three last named means being sequentially arranged along the path of movement of said insulating sheet in the order named.

11. In combination, means for moving an insulating sheet along in a direction parallel to its surface, means for applying an electric charge image to said sheet, means for dusting said sheet and means for rolling a flexible sheet against the dusted surface of said insulating sheet and for heating said flexible sheet, said three last named means being sequentially arranged along the path of movement o-f said insulating sheet in the order named.

CI-ES'I'ER F. CARLSON.

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