US2859352A - Electroradiography - Google Patents

Description

Nov. 4, 1958 Filed June 25, 1955 M. L. SUGARMAN, JR

ELECTRORADIOGRAPHY 2 Sheets-Sheet 1 INVENTOR #im l. 60m/mmf, Je.

Nov. 4, 1958 M. L. SUGARMAN, JR

ELECTRORADIOGRAPHY 2 Sheets-Sheet 2 Filed June 23, 1955 No" M mm., n

L Y on ELEC''RGRAPHY Meyer L. Sugarrnan, Jr., Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware` Y v Application .inne 23, 1955, SeriaiNo. 517,476 Claims. (Cl. Z50-65) This invention relates to improved methods and means ior making radiographs (graphic recordings of X-ray images) electrophotographically. More particularly, the invention relates to improved eleetrophotographic methods and means for electroradiography employing a novel X-ray sensitive photoconduetivel material.V Y

Previously radiographs or X-ray prints have normally been made on chemically developed iilm. X-ray processes using such lm are expensive and time consuming. Furthermore, the methods using iilm require wet processes for developing and making prints. Often it is necessary to wait several hours before a usableprint is obtained. Normally, in order to save time in obtaining usable results, the exposed negative is examined directly.- The black-for-white reversed image involved is much more diii'lcult to interpret than a direct positive image,

United States Patent such as that normally provided according to this inve'ntion.

It is therefore an object of this invention to provide improved methods and means for electroradiography.

A further object .of the invention is to provide im. proved methods and means for producing usable radio-` graphic prints directly upon an expendable X-.ray sensi.

tive material without the necessity of an intermediate dry or Wet transfer step.

Another object of the invention is to provide improved methods and means for directly producing usable radiographic prints quickly and economically.

Still another object of the invention is to provide proved methods and means for directly producing a usable radiographic print on the object itself which is being inspected by X-rays. i

Another object of the invention is to provide improved methods and means for directly producing usable radiographic prints within a few seconds after exposure withf out the necessity of an intermediate transfer step.

Yet another object of the invention is to provide proved methods and means for directly and continuously producing usable radiographic prints of a series of objects.

These and other objects and advantages of ythe invention are realized by a rapid dry process for directly making immediately usable radiographs. No transfer steps are necessary. In contrast to other dry electroradiograph systems using photoconductive selenium plates, for exam-v ple, the X-ray sensitive material of the present invention does not require a transfer step, and does not require a special master plate Which must be exposed over and over again, and cleaned between successive usages. In accordance with the invention, X-ray sensitive photoconductor-resin mixtures may be coated on paper, plastic, or metal sheets, for example, or directly upon the object to be examined. An example of such a material is'tinely divided ZnO dispersed in a silicone resin binder.. An X-ray image of an object when formed on such a coating results in an electrostatic image corresponding to the X-ray image. The electrostatic image may be developed with a iinely divided developer powder and fixed, as by f. to light, are also sensitive Y 2,859,352 Patented Nov-v 44. 9.5.3,

ICC

2 #me f SPfaYiilS .with a quick-divins adhesivo sfiato.- r1

The invention will beV described in greater detail yby reference to the accompanying drawing wherein: i y' Figure 1 is a diagram illustrating the steps of onevmethod for carrying out the processes of the invention; A Figure 2 is a` sectional, elevational Vview of one embodiment of apparatus in accordance with the invention for producing an X-ray image of an object on an X-ray sensitive photoconductive coating according to the invention; Figure 3a is an elevational viewv of a completely as sembled (potted) junction transistor whose internal struc'- ture is not visible to the unaidedeye; l Figure 3b is a sectional, elevational view of apparatus for forming an X-ray image on anu X-ray` sensitive photo'- conductive'eoating of the internal lstructure of a transistor such `as shown in Figure 3a; 1

Figure 3c represents a developed electroradiograph ofthe internal structure ot the transistor shovvn in Figure 3a;

Figure 4 is a sectional, elevational' view of anotherembodiment of the invention for producing an' X51-.ay image on aphotoconductive coating according'tothe invention;

Figure 5a is an elevational view of another embodi1 ment ,of the invention wherein an X-ray image of the bone structure of the human arm is formed on an Xfray sensitive photoconductive coating directly upon .the outer skin .ofthe arm being X-rayedg Figure 5b shows a developed electroradiographi print of the bone structure of the human -arm shownin Figure 5a; Y A .v

Figure 6 is a partially schematic, elevational Nien! .of another embodiment oi the invention .for Daisies radiographs of objects in a continuous process wherein the objects themselves are carried by an X-ray sensitive photoconductiveqcoated conveyor sheet; V

Figure 7 is a lpartially schematic, elevational vieu oi another embodiment of the invention lfor making r 'ographs in a continuous process on `an X-ray tive photoconductive-coated conveyor sheet; and

Figure 8 is a partially schematic, `elevational view oi' still another embodiment of the invention for rn ing radiographs in a cQntinuQuS PIOPSSS .IQIY 211.1951. objects being inspected. t.

.Similar reference characters are applied vto, similiar elements throughout the draw-ing. l

It is known .that fcertain photoooaoiifivs materiels may be employed to proxluce Visible images by iokii! dY tage of the ,electrical response of ouah Het i. *i diations such es visible light. Sugli materials may ,e

charged electrostatically so as to hold a uniform eleetric conductive at these points. Thus, a latent *ellec/tro charge pattern orresponding to the incident light e' al charge yin diesem portions of the #here Paitiio is are: portions to the intensity of the liebt fesait/.osi different portions of the light image. .in yi 'bl l nt eleotrostatio .charge Pattern .maville rendered visiti developing with an o losiiisaily .Charged sleoirosoooio row: der which is attracted to and held by the chargepattern. This powder may be permanently iixed to the coatin by heating, Solvent action., supplementary adhesivos, ,or ,other techniques.

The photooonduoiivo ,Coating-according to .the intenti comprises a finely divided photoconductive material y parsed in an electrically-insulating film-forming Yoh .o- It has been found that the materials acjcordingjto ventilos, in addition t9 being sisaiosteiisallyrs P to X-rays and mayf,

onsive sr. Q

ployed to excellent -advantage'for almost instantaneously providing radiographs. photoconductive material may be coated on paper sheets orvrolls, metalor plastic films, glass plates or any other mechanically suitable surfaces to which 'the' coatingwill. adhere. Because of its cheapneSS, paper is preferred.V s another important feature of the invention, the X-ray sensiv e photoconductive material maybecoated `directly upon the object to be inspected radiographically. The mixture used to produce the photoconductive coatmg may include a solvent or the mixture may be thermoplastic. I'he mixture may be coated by any convenient coating method, for example, Ibyl rolling on with a roller, by screening with a silk or metal screen, by brushing, by v vhirling,` by spraying, or lby stamping. After the mixture is coated, it is dried, for example by evaporation 'of the solvent, or by coolingif themixture is thermoplastic. Where the :coating is dried by evaporation, heat may be applied togaccelerate the dryingprocess. Similarly, the

' coating may be chilled where the mixture is thermoplastic and is applied hot; Y

When the photoconductive .coating is produced-on a resistivity plastics, the backing may be treated so, as to render its surface electrically conducting. This furnishes a plane immediately below the coating capable of being placed at ground or other desired potential in order to facilitate charging with a blanket electrostatic charge bef fore exposure. 'Ihis plane may be oating (isolated in potential) during all stages of image production 'other than charging. Preferably a double corona discharge is employed to provide ions of opposite charge on opposite sides of the coated insulating base so 'as to obviate the necessity of rendering Va surface of the insulating base conductive.

` y X-RAY SENSITIVE PHOTOCONDUCTIVE MATERIALS Examples of suitable mixtures for producing an X-ray sensitive photoconductive coating are as follows:

Example 1.-A mixture of 80 grams of a 60% solution in xylene of silicone resin GE-SR-SZ, marketed bythe General Electric Company, Silicone Products Division, Waterford, New York, 106 grams of toluene and 120 grams 'of photoconductive white zinc oxide is ball-milled for about three hours and then applied to the fixed form as described above. lExample 2.-A mixture comprising 100 grams .of powdered photoconductive lead iodide, 100 millilitersof toluene and 60 milliliters, of `a 60% solution of asilicone resin (SR-SZ, source as above) in xylene is `ballmilled until the lead viodide is thoroughly dispersed in-the` plastic-solvent mix and is coated as described above.

` Example 3,-A mixture comprising 100 grams'of finely ground photoconductive cadmium sulfide and 150 grams of a 35% polystyrene solution in toluene is `thoroughly mixed for about minutes in a high speed blender and coated as described above.

Example 4.-A mixturecomprising 60 grams of a 35% solution of polyvinyl acetate resin in methanol, '40 grams of CP dry process white zinc oxide and 20 liters of acetone is ball-milled for about one hour and then coated as described-above. Y

Example 5 .--Equal parts by weight of CP photoconductive white zinc oxide and `melted paratiin areintimately mixed and then the molten mixture applied as described' above and then allowed to cool.

Example 6.--A mixture of three parts by'weight'bf' CP` photoconductive white zinc oxide and one part by weight of carnauba wax are melted` together and then coated as described above and then allowed to cool.

Example 7 .-Three parts by weight of CP photocondu tive white zinc oxide and one part by weight of carnauba wax are dissolved in toluene and then coated as described According to the invention, the

1 polymer resin in acetone.

;. of this solution is mixed with 50 grams .of CP photocon- Example 8 .-Two parts by weight of CP photoconducf tive white zinc oxide and one part by weight of methyl cellulose are `dispersed in f a suitable solvent and then coated as described above. Y

Example 9.--Seven parts by weight of CP photoconduc--V tive white zinc oxide are dispersed in ten parts by weightV of a 10% solution yof a vinyl chloride, vinyl lacetate coductive white zinc oxide and then coated'asV described above.

It w-as found that a mixture of zinc oxide and lead iodide had a greater sensitivity to X-rays than either maf I terial alone according to the examples above, described.

Vbacking of highly insulating material such as glass or high This mixture comprised about l0 grams of vPblz` to 90 grams of ZuO in the-mixture.

FILM-FORMING VEHICLES -I The electrically-insulating, hlm-forming vehicle essential part of the composition and may be chosen from any one of a number Vof substances. A preferred ilmfV forming vehicle has a high dielectric constant and a high.

dielectric strength. These materials may be naturalor synthetic -resins or waxes. are the vinyl resins, silicone resins, phenol-formaldehyde compositions, cellulose esters and cellulose others. Shellac is an example of a naturalmaterial. Examples of suitf able waxes are paran, carnauba wax and beeswax. In;

'il organic binders such as sodium silicate mayalso be used.

Mixtures including one or more vehicles may be used;4

The photoconductor may be suspended in the vehicle in any of several ways. A simpleway is to dissolve the film-forming vehicle in an organic solventcapable of` effecting the solution and then dispersing the powdered photoconductorthereon. Alternatively the photoconductor maybe dry blended by kneading with the lm'-form ing vehicle heated'to a sufficiently high temperature to be rendered plastic. In this case of waxes they may be melted.

and the photoconductor mixed with the melt.

The proportion of powdered photoconductor to {ilmforming vehicle in the nal coating may vary over a wide range. The preferred rangesare 50 to 90% of photoconductor and 50 to 1,0% of film-forming vehicle. The (2ptimum proportions will be based upon the nature ofthe photoconductor, the lmfforming vehicle andthe results desired. Y

The speed of response of the photoconductive coating is partially dependent upon the nature of the photocon-,

i" ductor material, the nature of the film-forming vehicle-y and the ratio by weight of the film-forming vehicle to that of the photoconductor. Sincethe speed of response de: pends on a balance of characteristics of these factors, al'

most any desired response may be obtained by a proper selection of materials and compositions. t

A'proper selection of materials and compositions will also designate how long an electrostatic image may bei stored, since storage of the electrostatic image `depends at least in part upon the resistivity of the coating. Gen'-r erally the higher the resistivity of the coating the longer the storage time.

DEVELOPER MATERIALS AND APrLrCAriori"` The developer powder may be appliedin any of a` number of ways such as by spraying, dusting, orr-brush-j ing. For application by brushing a convenient brush;

comprises a mixture of magnetic Vcarrier particles,.-forj example, powdered iron and the developer powder.` The mixture is secured in a magnetic iield'to form ardeveloper;

" brush. This method lof development is more completely described by H. G. Greig in U.'S. Patent applicati o n;,V

Serial No. 344,123, tiled March 23,1 1953. V'A carnels hair,A

The mixture is thinned with v Examples of vsuitable resins or other brush comprised ,of bristles having suitable tijboelectric properties VVto impart the desired charge to theV powder may also be used.

A preferred carrier material for the developer mix in thev magnetic developer system consists of alcoholized iron, that is, iron particles free from grease and other impurities soluble in alcohol. These iron particles are preferably relatively small in size, being preferably in their largest dimension about .002" minimum to .008 maximum. Satisfactory results are also obtained using a carrier consisting of iron particles of a somewhat wider range of sizes up to about .001 to .020.

Other developing techniques are available and may be employed to advantage in any of the embodiments of the invention described. One method in particular may actually be preferred because of the sharply outlined images produced thereby. This technique is termedk cascade development and is fully described by Robert C. Mc- Master in an article entitled New Developments in Xeroradiography published in the Journal of the Society for Nondestructive Testing Summer Number, 1951. ln this technique the developing powders, consisting of a mixture of line pigment particles and a coarse granular carrier material, are cascaded over the surface of the exposed plate in a rocking developing tray, for example. The images produced by this technique are high-contrast, sharp-line types rather than those of large areas of nearly constant density. Such images, of course, are highly desirable for some applications in radiography. This is particularly true where it is desired to accentuate small, but abrupt, changes in image density.

Another method which may be employed to develop the latent electrostatic images is placing the exposed photoconductor in an environment consisting of a cloud of electrically charged particles of powder. This technique is also described in the aforementional article by McMaster.

A preferred developer powder may be prepared as follows: A mixture comprising 200 grams of 200 mesh Piccolastic resin 4358 (an elastic thermoplastic resin composed of polymers of styrene, substituted styrene and its homologs) marketed by the Pennsylvania Industrial Co., Clairton, Pa., l2 grams of Car-bon Black 6, marketed by the Eimer and Amend Co., New York, N. Y., l2 grams of spirit Nigrosine S. S. B., marketed by the Allied Chemical and Dye Co., New York, N. Y., and S grams of Iosol Black, marketed by the Allied Chemical and Dye Co., New York, N. Y., are thoroughly mixed in a stainless steel beaker at about 200 C. The mixing and heating should be done in as short a time as possible. The melt is poured onto a brass tray and allowed to cool and harden, The hardened mix is then broken up and ballmilled for about 20 hours. The melted powder is screened through a 200 mesh screen and is then ready for use as a developer powder. TlLs powder takes on a positive electrostatic charge when mixed with glass beads or iron powder. It therefore develops an electrostatic image coinposed of negative charges. 2-.4 grams of the developer powder and 100 grams of the magnetic cer-tier material are blended together giving the completed developer Other ratios may be used.

The developer powder may be chosen from a large class of materials. The developer powder is preferably electrically charged to aid in the development of the electrostatic latent image. The powder may be electric ally charged because the powder (l) is electroscopic, or

(2) has interacted with other particles with which it is triboelectrically active, or (3) has been charged from an electric source such as a corona discharge. Examples of other suitable developer powders are sulphur, natural and synthetic resins or mixtures thereof.

THE ELECTRORADIOGRAPHIC PROCESS Referring to Figure 1, the Steps .of .the method. .of the invention comprise the formation of an X-.rav image of an `object to be examined on a blanket-.charged phgtpconductivecoating. This .coatingmay benna suitable basking Such as Paper cellophane motel. or glass. or upon the object itself. The X-ray image causes the, photoconductive coating to become more conductive at the points receiving the radiation so that the charge 'at these points leaks off. Thus, the charges remainingifi. e., the dark areas not receiving X-rays) constitute a latent electrostatic image on the coating corresponding to the intensities in the X-ray image. This electrostatic image is then developed by applying a finely divided tone powder thereto. The powder deposits in densities proportional to Athe, charge pattern, and may be fixed in place by a suitable method, such as by heating.

ELECTRORADOGRAPHIC APPARATUS Referring to Figure 2, an object 2 which is to be, inspected ,is shown as being located between the X-.ray apparatus l and the photoconductive plate A4. The X-rayapparatus is adapted to irradiate the object 2 with X-rays and to project an X-ray image thus formed upon the X-.ray sensitive photoconductive coating 3 which has previously been charged with a uniform electrostatic charge. As is well known in radiography the precise distance of the object with respect to the X-ray source is not critical for focusing purposes if the X-ray source is a substantiallyI point source as preferred in this and other embodiments. of the invention. In general the distance of the object from the point source of X-rays and from the image plane determines only the enlargement of the image of the object from impingement of u nabsorbed radiation from the X-ray source. Hence, the object 2 may be irradiated with X-rays whether spaced between the X-ra-y source 1 and the photoconductively coated plate 4 or placed directly on the plate as shown by dotted lines.

The ysensitivity of the photoconduetive coating may be appreciably improved by employing a metallic backing plate or intensifying screen just as in present radiography practice. The intensity of radiation is increased by such a plate due to the secondary emission of X-rays reflected back to the X-ray sensitive coating.

A latent electrostatic image is formed 0n the photoconductive coating 3 which corresponds to the X-ray image. After exposure the plate may then be removed and brushed, for example, with a finely divided devoloper as previously described to render the electrostatic image visible.

Referring to Figures 3a, 3b, and 3c, a typical use of the invention is illustrated. Figure 3a depicts the normally visual appearance of a potted junction transistor. Such devices are normally encased or potted in a small metallic cylinder or can or in a solid opaque block of a plastic such as a polymerized epoxy resin. The internal contents und structure thereof, of course, cannot be visually examined after the device is so potted. Usually such completed articles, if inoperative or defective, must be ldis-assembled to determine the defect. According to .the invention, a transistor such as shown in Figure 3a may be radiographed as shown in Figure 3b. In this embodiment the transistor 6 is shown as lying upon the Charged X-ray sensitive photoconductive coating 3. After irradiation with X-rays and the development and fixing of the electrostatic image of the internal contents of the transistor formed thereby, a radiographic print is obtained as illustrated in Figure 3c. The total time involved in obtainingto the invention, and the easy and rapid processing in,-

7 volved, it is'fea'sble for the rst time .to make radiographic prints of each completed transistor or other artlcles of manufacture at the end of an assembly line production to detect posisble defects su-ch as thus described.

ELECTRORADIOGRAPHIC PRINTING ON X-RAYED OBJECTS Figure 4 illustrates an important embodiment of the invention wherein the object 2 to be inspected by X-rays from the X-ray apparatus 1 is coated itself with the photoconductive material 3. Since the radiograph of the object 2 is to be formed actually on the object itself, the coating of photoconductive material is applied to the side of theV Y 8 paints may be employed.' The X-ray image on the photoconductive coating results in an electrostatic' image which may be developed and fixed directly upon thev arm itselfv or upon the cast.

radiograph 5 is thus obtained directly upon the memberV As shown in Figure 5b a X-rayed showing not only the extent .of the fracture 'but also its direction and location. Such a print is available within seconds after Vexposure to` the X-rays. desired to keep the area available for further radiographs,

the fixing step may be omitted and after the fracture has been set the photoconductive coating with its visible image may be removed as by blowing off, by erasing with a magnetic brush after light exposure, or by washing with water or alcohol. Tor make later radiographs either on the the coating re-used immediately or at a future time by ice-charging, re-exposing with X-rays or visible light, and re-developing. Additional images may also be added by incidence of additional images of suitable spectral characteristics on non-image portions of the coated area.

By using the method of coating the object as illustrated in Figure 4, many advantages heretofore unobtainable with any previously known X-ray process may be realized. A radiograph of the contents of any opaque container may thus be printed upon the surface of the container showing not only the structure therein but also the shape, size, and position. This embodiment of the invention may be practiced to advantage in other applications such as in detecting flaws in metals which have been cast or machined. Here a radiograph showing the aws may be printed directly upon the metal itself where the flaw occurs. As pointed out in connection'with Figures 3a, 3b, and 3c the internal structure of devices such as a transistor showing size, position and defects, if any, can be printed directly upon the opaque casing in an assembly line technique.

Another important use of the embodiment wherein the X-ray sensitive photoconductive coating is applied directly to the object to be radiographed is in the eld of medicine. Referring particularly to Figure 5a, a human arm is depicted which may have a bone fracture, for example. Heretofore prior to the setting of the bones it was necessary to X-ray the arm using chemically-developed lilm. After development of the film, which may consume several hours, the bone could properly be set by referring to the film. Furthermore, it is often desirable to have an indication on the limb itself representing the direction and location of the fracture. By prior methods this was accomplished by referring to the X-ray film in order to manually draw with an indelible pencil the approximate location and direction of the fracture. Finally, after the fractured arm or leg has been set, a cast is often placed thereon.

As` shown in Figure 5a, the photoconductive coating may be applied directly onto the arm or to the outside of the cast on the side opposite the side to be exposed to X-rays. In order to charge the photoconductive coating 3 it is necessary to provide a conducting path to ground immediately `below the photoconductive coating. The skin itself may be suiciently conductive to provide this ground. Other additional grounding means may be easily and cheaply provided by first coating the skin surface with a thin lm 7 of a colloidal graphite dispension such as one of the Dag dispensions marketed by the Acheson Colloid'Company, Port Huron, Michigan. Likewise'silver platelet suspensions or otherv conducting tures thereof. An alternative indicia marking means;

arm or a cast it is only necessary to re-charge vthe photo-.2 .Y

conductive material and re-expose andV develop.

ELECTRORADIOGRAPrnC CONTINUOUS PROCESSES Referring now to Figure 6, a continuous process of l electroradiography is shown for printing radiographs of a' continuous series of objects 10 directlyV upon anAX-'ray' Y sensitive photoconductive tape 12 which carries the objects.

The paper which is coated with X-ray sensitive photo-.wV

This

conductive material is supplied by the roll 14. paper may comprise any grade of paper of reasonable strength. The coating comprises a nely divided photo-y conductive material dispersed in an electrically-insulating film-forming vehicle such as previously described.

The iirst operation is that of depositing a blanket electro- 'i static charge upon the photoconductive coating by means of the corona discharge apparatus 20 and a grounded metal plate 22. The paper passes between the corona discharge. apparatus 20 and the grounded metal plate 22 which is necessary to aid in establishing the electricl lield necessary to produce a corona discharge. A grounded conductive roller may be used instead of the plate 22. The corona discharge apparatus may comprise three .003" diameter wires placed about 0.5" apart and-A about 0.5 from the'surface to be charged.

The objects 10 to be electroradiographed are then placed on the charged photoconductive surface of the paper 12 and as the objects and the paper pass beneath the X-ray source 1 they are irradiated thereby. The

X-ray image of the objects thus formed on the X-ray sensitive photoconductive coating in turn forms a latentk electrostatic image corresponding thereto.

After exposure to the X-rays the objects may then be removed while thepaper continues to travel to the,

developing station. The latent electrostatic images formed on the coating are brushed with a'rotary mag-1 netic brush 24. The magnetic brush may comprise a rotatable, circular magnet having attached thereto a mixture of finely divided magnetic carrier particles and linely divided developer particles. As the brush contacts the electrostatic images, the developer powder particles adhere thereto in a pattern corresponding to the electrostatic image. scribed developer mix which includes a thermoplastic developer powder. Y

After development the paper with its developed images thereon passes a heat source 26 which `applies heat to the developed images, fusing the images and causing Y them to adhere to the photoconductive coating, thereby fixing the developed images to the paper 12. The heat source 26 may comprise a resistance heater or an infrared lamp. Thereafter the paper is wound upon a take-up reel 28.

A permanent radiographic record thus is obtained ofl each object coming oif an assembly line production-type process, for example. In order to identify each object with its respective radiograph, X-ray opaque indicia may be placed on the objects so as to not obscure the strucfhus fer-md" If it isY It is preferred to use the previously deassegna' terial is also light-sensitive.' Thus the index information may be added by exposing the photoconductive coating atsome convenient point to a visible light imageV using a `suitable optical arrangement.

VAnother embodiment of theinvention is shown in Figure 7 wherein aV continuous series of objects 10 may be electroradiogra-phed upon an X-ray sensitive photoconductive tape 12. In this embodiment the objects are not carried upon the X-ray sensitive tape itself but are transported by means of an X-ray transparent belt 30. Thus as the objects 10 are carried past the X-ray source 1, the X-ray images formed thereby are focused upon the X-ray sensitive paper which is being transported directly beneath the X-ray transparent-belt 30. As before the X-ray sensitive paper 12 may be supplied already coated from the reel 14; Alternatively the paper may be fed uncoated past a coating-application-trough 16 and coated thereby and then dried as it passes the heating source 18. Either an infrared lampV or an electrical resistance element may comprise the heating source 18. Other rapid drying means may beemployed. Charging may be accomplished by means of a'grounded metal roller 22 instead of but for the same purpose as the grounded plate described in connection with Figure 6. After the formation of the latent electrostatic image corresponding to the X-ray images, the paper is transported past the developer 24 and the fixer 26. This embodiment is especially advantageous where the weight of the objects to be electroradiographed is too great to be supported by the X-ray sensitive paperitself. In order to form sharp X-ray images of the objects upon the X-ray sensitive paper, the travel speed of both the conveyor belt 30 and the paper 12 must be substantially the same. Otherwise due to the movement of the objects 10 at a dierent rate with respect to the movement of the paper 12 during image formation blurring would occur. The synchronization of the belt conveyor 30 and the X-ray Sensitive paper 12 may be accomplished by driving both the conveyor and the paper from the same motor 32 by like-diameter pulleys on the same motor shaft, and like-diameter pulleys on the paper take-up reel 28 and the conveyor belt driver 34. The X-ray transparent belt 30 may be made from any suitable X-ray transparent material having sufficient strength to support objects of given weights. An example of such a material is plasticised plastic-laminated fiberglass or cloth, or a thin Valuminum or stainless steel belt. A suflicient intensity of X-rays to penetrate the belt completely should be employed.

In this embodiment a permanent radiographic print of each object is obtained. As explained before, the identication of a particular object with its image may be accomplished by placing X-ray opaque indicia upon the objects in some convenient location so as to not obscure any of the structure of the objects or by exposing to a Visible light image of the indexing information.

Referring to Figure 8, a continuous process is shown for printing radiographs directly upon the objects to be examined by X-rays. The objects 10 are carried upon a continuous X'ray transparent conveyor 30 which may be made of any suitable X-ray transparent material sufficiently strong enough to support the objects. The conveyor 30 first carries the objects past a spray nozzle 16 which sprays the photoconductive coating completely over the upper surface of the objects. This coating comprises a nely divided photoconductive material dispersed in electrically-insulating hlm-forming vehicle such as previously described.

The photoconductive coated objects are then fed past an infrared lamp 18 or other heating means where the coating is dried. The next operation is that of depositing a blanket electrostatic charge upon the photoconductive coating on each object by means of the corona discharge apparatus and 22 such as described previously. If the objects themselves are electrically conduct- 1,0 ing, a single corona discharge is suificient. lilowevei',` the objects are relatively-thinandvflat but not electrically conductive, a -second corona apparatus 22 furnishing Aa blanket charge of lopposite electrical sign on thereverse side of the object may be aligned opposite the corona unit 20. The objects thus pass between thel corona discharge apparatus 20 and the corona discharge apparatus 22 which is necessary to aid in'establishing the electrical eld necessary to produce a uniform surface charge.

The objects are thereafter passed over the X-ray source 1 and irradiated with X-rays therefrom. The X-ray image of the objects are thus formed on the X-ray sensi,-` tive coating on the objects themselvesand these Xray` images in turn form latent electrostatic .images corresponding thereto on the photoconductive coating on the objects.

rI he latent electrostatic images formed on the coatings on each object are then brushed with a rotarymagneft'ic brush 24, or developed by other suitable v means"such as have been described. The magnetic brush (which may comprise a rotatable cylindrical magnet having attached thereto a mixture of finely divided magnetic carrier Vparticles and finely divided developer particles) contactsthe electrostatic images on the objects. The developer powder particles adhere to the images in a pattern corresponding thereto. Preferably a developer may be employed which includes a thermoplastic developer powder.

The last operation is performed as the conveyor 30 carries the objects with their developed images thereon past an infrared lamp 26 which fuses the images and causes them to adhere to the photoconductive coating on each object. The developed images are thereby permanently xed to the objects themselves.

It has been found that the exposure time for the X-ray sensitive photoconductive materials such as zinc oxide or lead iodide is of the same order of magnitude as the exposure time of industrial X-ray lm (type M, such as supplied by Eastman Kodak Co., Rochester, New York, for example).

It should be understood that the various charging techniques described are interchangeable and are primarily dependent upon the electrical characteristics of the material which is coated photoconductively. In general if the objects to be radiographed according to the invention are thin but not electrically conductive the double corona discharge apparatus described in connection with Figure 8 is to be preferred.

There thus has been described economically inexpensive methods and means for making radiographic prints either on a separate recording medium or upon an object being inspected radiographically. Many modifications of the invention may be made, as has been demonstrated, without departing from the scope of the invention. Because of the demonstrated versatility of the novel X-ray sensitive material according to the invention,

many uses heretofore impossible or impractical may be realized. The instant specication has representatively illustrated the range of possible applications of the instant invention.

v What is claimed is:

l. A method of electroradiography comprising the steps of: exposing an electrostatically charged object to be electroradiographed having an X-ray sensitive coating thereon to an X-ray image of said object, said coating consisting at least of a finely-divided photoconductive material dispersed in an electrically-insulating film-forming vehicle, and developing said electrostatic image.

2. A method of electroradiography comprising the steps of: coating at least one side of an object to be electroradographed with a finely-divided photoconductive material dispersed in an electrically-insulating filmforming vehicle, providing said coating with a blanket electrostatic charge, irradiating the side of said object which is uncoated and opposite said coated side with X- rays whereby the X-ray image of said object which is electroradiogra'phed, means adjacent said conveyor for coating at least one side of each of said objects on said conveyor with a finely-divided photocondctive materiall dispersed in an electrically-insulating` hlm-'forming vehicle, means adjacent said conveyor for electrostatically charging 'said coating on said objects, X-ray means adjacent said conveyor for kforming an X-ray image of each' of said objects on said coating of each object as'said objects are carried thereby, each ofv said X-ray images forming on said coating of each of said objects a latent electrostatic image correspondingrto said X-ray image thereon, and means adjacent said conveyor for developing said electrostatic images as said conveyor passes thereby.

,g 4,.',Electroradiograph apparatus comprising'an X-ray transparent conveyor adapted to transport objects to be electroradiographed, meansV adjacent said conveyor for coating at least Vone side of'each of said objects on said conveyor with a Iinely-divid'ed photoconductive material, means adjacent said conveyor for electrostatically chargelectro#V static image corresponding to said X-ray image, and de` ing said'c'oating'on' said objects, X-ray means adjacentV said conveyor for yforming an X-ray imagev of eaclzfof' saidV objects on said'co'atingof eachY object as said obj; jects are ycarried thereby,` each 4ofsaid X-ray inag'es' formingon saidcoating of each of said objects a latentVV electrostatic'irnage corresponding to said X'ray image thereon', means adjacent said conveyor `for developing said electrostatic images with a finely-divided developer as said conveyor passes thereby, and means for iiXingvsaidy developed images. Y

5. The'method of claim 2 wherein said photoconductive' material is zincoxide.`

References Cited inthe iile of this patent UNITED'srATES PATENTS 2,221,776 Carlson Nov.

2,666,144 Schatert et al. ..,Jan. V12,` 1954;. 2,701,764 ,Carlsonr Feb. 8, 1955; 2,728,021

ciety of America, August 1955, vol. 45,V No.V 8, pages Y.

6474650 especially p. 647. Y

Claims (1)

1. 2. A METHOD OF ELECTRORADIOGRAPHY COMPRISING THE STEPS OF: COATING AT LEAST ONE SIDE OF AN OBJECT TO BE ELECTRORADIOGRAPHED WITH A FINELY-DIVIDED PHOTOCONDUCTIVE MATERIAL DISPERSED IN AN ELECTRICALLY-INSULATING FILM FORMING VEHICLE, PROVINDING SAID COATING WITH A BLANKET ELECTROSTATIC CHARGE, IRRADIATING THE SIDE OF SAID OBJECT WHICH IS UNCOATED AND OPPOSITE SAID COATED SIDE WITH XRAYS WHEREBY THE X-RAY IMAGE OF SAID OBJECT WHICH IS THEREBY FORMED ON SAID COATING PRODUCES A LATENT ELECTROSTATIC IMAGE CORRESPONDING TO SAID X-RAY IMAGE, AND DEVELOPING SAID ELECTROSTATIC IMAGE.

Images