|Publication number||US3910793 A|
|Publication date||Oct 7, 1975|
|Filing date||Oct 5, 1970|
|Priority date||Jul 21, 1967|
|Publication number||US 3910793 A, US 3910793A, US-A-3910793, US3910793 A, US3910793A|
|Inventors||Joel M Peisach|
|Original Assignee||Polaroid Corp|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Referenced by (5), Classifications (9)|
|External Links: USPTO, USPTO Assignment, Espacenet|
novel photosensitive elements wherein a silver halide emulsion and an X-ray intensifier screen are combined into a single layer, and this single layer is used in conjunction with a reflecting layer.
Other objects of the invention will in part be obvious and will in part appear hereinafter.
For a fuller understanding of the nature and objects of the invention. reference should be had to the following detailed description taken in connection with the accompanying drawing wherein;
HO. 1 illustrates in diagrammatic enlarged crosssectional view, an embodiment of this invention wherein a support 15 bears on its surface a reflcctant dispersed in a suitable matrix I4, which in turn bears on its surface a layer 13 of a silver halide emulsion containing particles of a luminophor dispersed therein.
This layer 13 is overcoated with an opaqui ng layer which optionally may serve as an antiabrasion coating;
FIG. 2 is a diagrammatic enlarged cross-sectional view showing the novel product of this invention adapted for use in diffusion transfer photography. prior to the application of the processing composition, the
thickness of the various materials being gerated for purposes of illustration;
FIG. 3 illustrates another embodiment of the -invention adapted for use in diffusion transfer photography wherein the image-receiving layer 12 is loosely bonded greatly exag-.
to the photosensitive layer 13, and said layers are seps rated from each other by spreading of the processing 45,
composition contained in pod .16; and
FIG. 4 illustrates a badge. wall plaque or other suitable container designed to hold a photosensitive product within this invention prior to processing when the product is used as a radiation detection means.
it is known to prepare radiographs by diffusion transfer processes. U.S. Pat. No. 2,565,378, issued to Edwin H. Land on Aug. 21, l95i, discloses such a'diffusion transfer process for preparingX-ray images, as does US. Pat. No. 3,l85.84 I .aiso issued to Edwin H. Land, on May 25, l965. U.S. Pat. No..2,887,37 9, issued to Blake et al on May I9. 1959, disclosesa filmstructure containing an intensifier screen,'which may be utilized in diffusion transfer processes for obtaining X-ray images. 1 g
The use of intensifier screens inradiography is wellknown. As is understood in the art. suchscreensare employed primarily to reduce the amount of exposure to X-ray or other radioactive waves necessary to form a latent image. Use of such screens also gives a more desirable, i.e., longer, contrast range curve. The advantages to be obtained by subjecting living organisms to lesser amounts of radiation are well-known to those familiar with the radiographic art. Accordingly, it has become quite common to employ such screens in radiography.
The generic tenn luminophor is subclassified into two categories; namely, fluorophors. i.e., fluorescent materials. and phosphors, i.e., phosphorescent materials. A luminophor has the property of being able to convert a part of the energy absorbed from activation by exposure to particular wavelengths of the spectrum. e.g., X-rays, into emitted radiation of a lower energy than the absorbed radiation, e.g., visible light, the lower energy radiation being in excess of associated'thermal radiation. Fluorescent materials continue to emit radiation essentially only during the period of excitation. There is a minimal afterglow. Phosphorescent materials, on the other hand, will continue to emit energy upon the cessation of the excitation of the luminophor. A phosphorescent material is said topossess an afterglow, i.e., continuance of emission after cessation of excitation, longer than about lO' seconds for optical photons, whereas for fluorescent materials the afterglow is less than IO" seconds. The basis for the demarcation at l0 seconds between fluorescence and phosphorescence is explained in detail in An Introduction !0 Luminescence of Solids by Humboldt W. Leverenz, published by John Wiley and Sons. lnc., i950, at page 149, et seq.
in general operation. a penetrable ionizing radiation package is exposed to, for example, X-ray radiation. The silver halide stratum possesses low stopping power for X-ray radiation. Thus, it permits the radiation to penetrate through it to theluminophor of the intensifier screemThe luminophor, upon absorbing X-ray radiation, will emit quanta in a particular segment of the quantai'namely, directly by the X rays, and indirectly from the yisibie light emitted by the luminophor. it therefore follows that the use of an intensifier screen results in a lowering of the exposure dosage and/or the amount of radiation necessary to form the latent image.
The radiographic element of the present invention comprises the use of a dual function intensifier-silver halide emulsion layer used in conjunction with a superposed reflecting'layer. The dual function layer can be prepared by admixing particles of a luminophor which is activatable substantially only by invisible radiation directly into the photosensitivesiiver halide emulsion material and layingthis combination down as one layer.
preferably. upon a reflecting layer.
Thecombined intensifier-emulsion'of the present invention utilizes thesame principles to obtain exposure of thesilverhaiide present as in the prior art X-ray packages previously discussed. Whereasthe prior art utilized a physically distinct separate,intensifier layer (coated in intimate contact with the emulsion or else a separate intensifier screen that is placed in a superposed coextensive planar relationship with the emulsion). the present invention uses but a single layer that contains particles of luminophor as well as particles of silver halide within the binding agent. Here the quanta 3 of X-ray radiation penetrate into the binding agent. strike the particles of luminophor which are in turn excited and are thus induced to emit light. primarily in the visible part of the spectrum. to expose the grains of silver halide present.
The advantages to be gained from a utilization of an integral system of the present configuration are several fold. ln the first instance, only one coating operation is involved as opposed to the multiplicity of coatings in previous integral systems. i
The close proximity of the luminophor particles to particles of emulsion given rise to a more efficient utlllzation of the excited lumlnophorlc material. it is seen therefore that the flow of visible light emitted from each particle of luminophor has less chance of being impeded by another particle of luminophor prior to striking a silver halide grain. This better utilization of the luminophor gives rise to an increase in package efficiency" over the conventional separate screen and separate silver halide emulsion.
Package efficieney as used herein is the total efi'icicncy of all of the components of a photographic system in its ability to translate high energy invisible radiation into a high quality, high contrast photographic image. it is the sum of the inherent photosensitivity of the negative, the efficiency of the diffusion transfer processing composition in its ability to amplify a latent image, the ability of the luminophor to convert essentially invisible ionizing radiation to visible light. and the ability of receiving material to deposit positive silver in such a manner that maximum covering power is obtained. v t
it was also found that as a result of this close proximity of the luminophor to the silver halide that diffusion transfer images of a higher resolution were obtained than were obtained from the diffusion transfer separate intensifier screen system utilizing similar kilovoltdosmg/sq. foot of silver and utilizes a 20:l ratio of luminophor to binder would contain 3 to 5 grams of luminophor per square foot. When this amount of luminophor was coated upon a transparent support for the purposes of conducting alight transmission test. it was found that only about 25-40 percent of the incident light striking the test panel was transmitted. The amount transmitted by a silver halide emulsion containing this amount of luminophor would be approximately 50 percent less. (Measurements were made on a transmission densitometer having a 30 watt tungsten source. manufactured by the Macbeth Corp. Newburgh. N.Y.) Satisfactory prints could not be obtained from such a negative as a practical matter because of this exceedingly low light transmission.
in contradistinction to a wet developed negative of the type just discussed, diffusion transfer radiographic images are fonned in a different layer and their optical properties are essentially independent of the quantity of luminophor in the silver halide emulsion. The amount of luminophor that can be added to the silver halide emulsion in accordance with this invention is governed by the'physical volume available for packing" luminophor into the binder. This amount is independent of the translucency factor but is, of course, dc-
pendent upon the mean particle size of the luminophor.
' in accordance with the present invention may best be understood by referring to the drawing.
FIG. 1 illustrates one embodiment of this invention wherein the several layers are coated upon each other.
' FIGJ Z illustrates an embodiment of the invention spe- As is known,,when the luminophoric particles are'a'ctivated by penetrating ionizing radiation, the light quanta emitted travel omnidirectionally. it has beenfound that about 54 percent of this emitted light quanta is transmitted out of the intensifieremul'sion layer. it has been found that by using a "back-scattering or reflecting layer, an increased efficiency of 30-50 percent isobtaincd in the use of this emitted lightasa result'of. its a cifically adapted for diffusion transfer processing employing the element of FIG. 1. A rupturable container of processing solution, such as thatdisclosed in US. Pat. No. 2,565,378, 'is provided between the intensifiere mulsion layer l3 and the receiving layer 12. A suitable support 15, such as those of a nature to be described below, is provided for both the receiving layer and the processing composition spread in a uniform layer between'the emulsion layer containing the latent image and the receiving layer.
'At some time subsequent to exposure, luminophoremulsion layer. containing the latent imageis contacted with a processing composition preferably applied as a relatively viscous layer by rupture of pod 16.
The processing composition may be any of those known 'in the art,e.g..a film-forming processing composition such as those disclosed in U.S. Pat. Nos.
emulsion. Only exceedingly small ratios of luminophor to silver, no greater than 5:1 or 6:1 may be employed since negatives which, contain higher amounts of luminophor will not readily transmit light. A conventlonal negative that contains between L500 and 2.000
'2,543,l8i and 2.565.378. it may comprise, for examethyl cellulose or sodium carboxymethyl cellulose.
Various other additives such as accelerating developing agents, preservatives, antifogging agents, and the like may-also be included. All of these'materials are prefer:
liquid prior to the spreading thereof, but one or more of them may be in part or wholly located in the film element and dissolved into the applied processing composition.
When the embodiment set forth in FIG. 2 is processed through a pair of rollers'or other spread system in conformance with the well-known diffusion transfer processing techniques, the ingredients of the processing composition help to maintain an intimate contact between the receiving material and the photosensitive element during imbibition. After processing. the imagereceiving material is stripped from the integral emulsion-intensifier screen unit and the latter is discarded.
it is also within the scope of this invention to coat the image-receiving'layer over the dual function intensifier-emulsion layer; and to maintain said layers as an integral unit after processing. The luminophor effectively masks the developed silver in that layer. lnaddition, the luminophor remains activatable by ultraviolet light;
placing the integral unit in a source of ultraviolet. light will result in increased light being reflected throughthe,
silver transfer image to the observer, thereby increasing the effective contrast scale of the image. FIG. 3 illustrates yet another embodiment of the inphotosensitive element can comprise if desired. a single layer film which contains both a'luminophor and the silver halide. Optionally, one may incorporate the desired opacifying and reflecting layers into the film badge holder instead of placing such layers inthe photosensitive element itself. it will be appreciated, however, that the reflecting layer will be less effective if incorporated into the holder instead of being part of the photosensitive element.
FIG. 4 is a perspective view of a badge or wall plaque adapted to hold a photosensitive element such as the embodiment of FIG. I when such is to be used as a radiation detection system. The badge comprises any suitable holder 20 having a retaining means for a radiosensitive element, an inlet portion 22 for the insertion and removal of said element, and means (not shown in this view) for adhering the holder to an article of clothing. or to a solid surface such as a wall, a portion of said badge opposite said element 21 being capable of penetration byionizing radiation. The holder may be of any known plastic or metal known in the art as useful for substance such as polyethylene. Upon removal from i the holder, the exposed photosensitive element may be vention utilizing a preformed laminate? film fom'lat of the type shown in FIG. 10 of U.S. Pat. NO. 3,053,659.
in this embodiment, the element containing the imagereceiving layer 12 is bound in place to the element containing the luminophor-emulsion layer 13, a stripping layer [7 being positioned between 'said layers. The
for such a stripping layer is cellulose acetate hydrogen a phthalate. it shouldalsqbe noted that the rupturable" container or l6 thatholds the processing composition is positioned so'as to discharge its contents tween the stripping layer and the luminophor-emulsion layer. i
it will be recognized that the novel photosensitive elements of this invention may be'utilized to advantage, by virtue' of their[ increased efficiency torecordinciprocessed in the same manner as the embodiment of FIG. 2.
'. Support 15 is either opaque to visible radiation and transparent to X-rays and other radioactive rays, or, comprises a transparent base material, preferably a plastic, for. example, a cellulosic ester such as cellulose acetate, or a synthetic polymer such as polyvinyl chloride, polyvinyl acetate, polystyrene, and polyethylene 'jtrephthalate, etc. Where the support is transparent, it
will be apparent that it must be' provided with a lightopaque backing, such as a'black dye dispersed in a suitable medium, (e.g., gelatin as is known in the art, or thejfilm unit must otherwise be encased in a lightopaque material to prevent exposure to visible light.
Y ered as a separate entity can be translucent or o aque to visible light. Means for preparing such reflecting lay- .ers are well-known in the art; note, for example, the
dent invisible radiatior pto detect other invisibie radia t, tion besidesix raygegy, alpha,-beta, and low..level' gamma particles. The'systemfof this invention snows; for a highly sensitive autoradi'ographic image recording medium. Typical areas where'such monitoring is neces i sary include dentists offices, research laboratories;
atomic power plants, etc. and anywhere else thathu-fi mans and animals might be exposed to sources of penetratingionizing'radiation.
aforementioned LLS. Pat. No. 3,053,659. In a preferred embodiment, this layercontains sufficient reflectant so as .to act as an opaq'uin giayer for the juxtaposed intensifie'r-emulsion layer.
TheJurninOphQrs used in the intensifier-emulsion layer may compr'is efany phosphorescent or luminescent luminophor known in theart, which is susceptible to excitation substantially only from penetrating ionizing radiation, e.g., X-ray radiation. Particularly satisfactory Film badges as such forradiation'detectlon, i.e., dosimeters, are not new in the art. Examples of film badges can be found, for example, in US. Pat. Nos.
2,483,991 and 2,659,013. However, the badge embodiment of the present invention comprises thefirstisuch badge wherein a luminophor is found in the same layer as the silver halide, and the first such badge wherein the l. ZnS Ag 2.- ZnMgF Mn 3.-ZnCdS Cu 4. ZnO. :-Zn 5. MgF 6. ZnS- Cu 7. ZnCdS Ag Particularly satisfactory results may also be obtained utilizing the following luminescent materials as they luminophor:
l. ZnS Ag ZnS 0. Mg
. ZnO 2n ZnS Cu ZnCdS Ag CdS Ag CaZnPO CdBO l0. BaTlPO ll. CaSiO Mg i2. Ygoa Eu l4. ZnSiO, Mn
l5. KMgF; Mn
l6. ZnSe Cu i 7. CaWO l8. ZnS Mn 19. LaBaO 20. CaMgSiO Ce- Members of this class of luminophors emit light in the rangefrom 375 to 620 millimicrons,or essentially, throughout the whole visible spectrum, and are activated only by radiation within the range of about 200 to about 360 millimicrons.
it has been found that satisfactoryradiographic iniages can be obtained by use of a luminophor'to silver ratio of 1:1 to :1 and a gelatin to silver ratio of 2:]
package would result in exposure in the previously unexposed areas should one attempt to move the film while phosphorescence isstill occurring. in the present invention. there is a continuous point-to-point relationship between the silver halide and the. luminophor due to the dual function of the single layer. This positioning of the intensifier material in relation to the silver halide is such that the problem of ghost images which could arise from the utilization of a phosphorescent intensifier cannot arise in the process of the present invention. Thus it is seen that movement of the intensifier. since it is in flxed relationship to the silver halide, l.e.. it is all in one layer. will have no detrimental effect upon the latent image.
if a phosphorescent luminophor is utilized, it should be noted that said phosphorescent luminophor is not quenched by the processing composition but rather the silver halide solvent of the diffusion transfer processing composition complexes the unexposed silver halide and starts theimbibition process. The developing agent in the processing composition reduces the exposed silver halide to silver. The silver halide which was not exposed, by the incident radiation and/or the radiation emitted from the luminophor, is complexed and transquenching had taken place, whereas with a luminescent to l5:l. This intensifier-emulsion is coated upon the luminophor can prevent'white light striking the surface of the intensifier-emulsion"layer from exposing'siiver halide grains within the layer. However, since the luminophor can be activated by ultraviolet light which is to be found in sunlight as well as incandescent and fluorescent light sources, exposure to such ultraviolet light will causethe luminophor to emit radiation which will fog the grains. 'l'heuse of an "opacifying layer 11 which is penetrable only by ionizing radiation is recom mended for placement on the exposed surface to prevent such undesired indirect fogging. Thisopaquing layer will also prevent directfogging by white light sources of those grains which by a statistical basis happen to be on the surface of the layer. Such an opacifying layer may comprise, for example, carbon black or a black dye in a suitable matrix, such as gelatin. The opacifying layer must be permeable to the alkaline processing composition so that it will not interfere with the luminophor. when such is used, "the quenching need never arises since excitation ceases at the cessationof radiation exposure.
The image-receiving layer 12 may be any of those useful in photographic diffusion transfer processes. in a preferred embodiment, image-receiving layer 12 comprises an-image-receiving layer containing deacetylated chitin. which is described andclaimed in the U.S. Pat. No. 3,087,8l5, issued to.Ryan et al.
- The emulsion material may be any suitable photosensitive silver halide emulsion known in the art Particularly satisfactory results were obtained when a standard termined that there was substantiallyno chemical interaction between t he's ilver halide and the luminophor.
When theembodim'ents of the, invention are utilized for-diagnostic:radiographie imaging, the use of higher X-ray' voltages is facilitatedisince the actual exposure time may beof'a shorterduration than that commonly required with the use of a separate: screen and separate emulsion of a non-integral system Satisfactory results have been obtained utilizing a kilovolt range 'of 40to .l30 kv.. the choice being depenformation of the desired silver transferimage. The
o acifying layer may alsobe utilized as an antiabrasion layer, as is conventional with anti-halatlon layers.
l n the X-ray systems of the present invention, it is not necessary to quench the phosphor prior. todeveloping the image. The failure to quench a phosphorescent luminophor when such is used in a non-integral X-ray.
dent upon abiiityof a particular luminophor to absorb theionizing radiation as well as on the nature of the subject;
; The use of the higher" voltages insuresminimal absorption of ionizing radiation by'the subject; This is true because the higher the voltage the less the absorption, dueto the greater proportion of "hard" X-rays which are hthe deeppenetrating short wave length X- rays. These rays are least absorbed by the human body.
The dangerrthat arises fromthe soft X-rays isthe fact .thatupon'abso'rption by the body. they give rise to an EXAMPLE I 22 cc. of i percent gelatin were mixed with cc. of a standard silver halide emulsion and with Li cc. of Triton X-IOO. a non-ionic isooctylphenylpolyethoxyethanol dispersing agent. trade name of and marketed by Rohm and Haas Company, Philadelphia, Pa. l0 grams of luminescent zinc sulfide were added and stirred for several seconds to insure a uniform mixture. This still liquid mixture was put into a syringe and sprayed onto a suitable support, and stroked with a Myrod a steel wire bound rod to insure a smooth layer. The cast layer was allowed to air dry.
EXAMPLE ll A base comprising paper overcoated with TiO, dispersed in polyethylene was coated with a layer of luminescent zinc sulfide, activated with copper, dispersed in i an X-ray type emulsion containing 97 percent silver bromide and 3 percent iodide. The coating was of a coverage of L7 grams of luminophor per square foot of base, and the silver concentration was 100 mg. per square foot of base. The gelatin to silver ratio was 4: l.
An emulsion containing particles of intensifier screen material was thereby formed on the reflecting base after drying. A black dye in a gelatin matrix as an opaquing and anti-abrasion layer was then overcoated onto the emulsion-intensifier layer.
EXAMPLE iii A sheet of the photographicfilm prepared as in Example 2 was given a 30 second unscreened X-ray expo- ,sure at 68 k.v.p., 100 MA. 40-inch distance through an aluminum step wedge. A positive transfer image was then obtained, in accordance with conventional diffusion transfer techniques, by imbibing the X-ray exposed film for 30 seconds through the permeable black dye layer with a developing composition similar to the one used in Polaroid Type 47 Land film. The positive image was revealed by stripping the silver receiving layer from the silver halide emulsion layer.
EXAMPLE IV A conventional system employing a separate intensifier screen and separate superposed emulsion. wherein the intensifier screen comprises the same luminophor with the same coverage per unit area, was similarly exposed to X-ray radiation of the same kilovoltage. Time duration, distance, etc. were held constant. A control system comprising emulsion only without the presence of any luminophoric material was exposed inthe same manner. Both of these radiographically exposed elements were processed in the same manner as was the sheet prepared in Example 1. Both samples that utilized a luminophor displayed a greater efficiency as to the utilization of invisible radiation to form a visible image.
The system of the presentjinvention required 25 per-- obtain similar images. The material of Example i re-.
quired 50 percent less radiation than the conventional separate screen-separate emulsion system to obtain the same sensitometric results.
For convenience,the expression X-ray" has been used in the specification and in the claims and is intended to cover all photographically useful radioactive rays'such as those emanating from an X-ray tube, radium, or radioactive isotopes.
Since certain changes may be made in the above product and process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense. The invention accordingly comprises the products possessing the features, properties and relation of components. and the processes involving the several steps and the relation and order of one or more of such steps with respect to each of the others which are exemplified in the foregoing detailed disclosure, and the scope of the application of which will be indicated in theclaims.
1. An integral photographic product for providing diffusion transfer image patterns comprising:
a. an intensifier-emulsion layer which contains a particulate luminophor and a photosensitive silver halide system, the amount of particulate luminophor being sufficient to render said intensifier-emulsion layer substantially opaque and b. a receiving layer arranged to receive a diffusion transfer image pattern from said intensifier emulsion layer.
2. A product of claim 1 wherein the ratio of particulate luminophor to silver is from about 7:l to about 20:1.
3. A product of claim I further including a reflecting layer superposed on a support transparent to radioactive radiation and arranged so that said reflecting layer is interposed between said intensifier-emulsion layer and said support.
4. A product of claim 1 further including means for preventing visible light from striking the intensifieremulsion layer.
5. A product of claim 4 wherein the means for preventing said visible light comprises a black dye which is'alkali permeable and opaque to visible light but transparent to radioactiveradiation and wherein the dye is coated on said intensifier emulsion layer.
6. A product of claim I further including an integral rupturable-container confining anaqueous alkaline processing composition and wherein the container is integrated with the product so that upon-rupture. the processing composition can. be distributed between the intensifier-emulsion layer and the receiving layer.
7. A product of claim I wherein the particulate lumlnophor comprises zinc sulfide.
8. An integral photographic product which comprises:
a. a first support transparent to radioactive radiation and having thereupon a reflecting layer; and an intensifier-emulsion layer superposed on the re fleeting layer, saidinternsifier emulsion layer comprising a particulate luminophor and a photosensitive silver halide system and wherein the amount of luminophor is sufficient to render the intensifieremulsion layer substantially opaque;
b. a second support carrying a receiving layer arranged with respect to the intensifier-emulsion 9. A product of claim 8 wherein the ratio of particulate luminophor to silver is from about 7:1 to about 20:l.
10. A product of claim Swherein the particulate luminophor comprises zinc sulflte.
ll. A product of claim 8 wherein said first support comprises a base material opaque to visible light.
* i i i l
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|U.S. Classification||430/227, 430/967|
|International Classification||G03C8/06, G03C5/17|
|Cooperative Classification||Y10S430/168, G03C5/17, G03C8/06|
|European Classification||G03C8/06, G03C5/17|