Tamper Proof Laminations Having Silver Image

Abstract

Laminar structures comprising a photographic image in silver, the image-bearing surface of which is laminated to a transparent layer comprising a hydroxylated polymer via an intermediate layer consisting essentially of a mixture of polyvinyl alcohol and a methyl vinyl ether-maleic acid copolymer or a partial lower alkyl ester of such a copolymer.

Description

This invention relates to a novel and improved card that serves to identify its holder.

It is one object of the present invention to provide an identification card, or the like, which comprises a photographic likeness of its holder.

A further object of the present invention is to provide an identification card, or the like, which bears a photographic likeness of its holder and which will automatically be defaced by or will automatically reveal any attempt to change or alter said photographic likeness.

A further object of the present invention is to provide an identification card of the type described above which is durable and which will provide a long and useful service life.

A further object of the present invention is to provide novel laminations comprising photographic likenesses which cannot be separated without destroying or defacing said photographic likenesses.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties, and relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims, 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:

FIG. 1 is a cross section, greatly magnified, of one stage in the preparation of a lamination made in accordance with this invention;

FIG. 2 is a cross section, greatly magnified, of a completed lamination made in accordance with this invention;

FIG. 3 is an illustration of one method of preparing the laminations of this invention;

FIG. 4 represents a plan view of one stage in the preparation of one embodiment of the laminations of this invention;

FIG. 5 represents a section taken along line 5-5 of FIG. 4;

FIG. 6 represents a section of the embodiment shown in FIGS. 4 and 5 when complete; and

FIG. 7 is a cross section, greatly magnified, of still another lamination made in accordance with this invention.

Numerous cards have been proposed which are designed to identify their holders to others. Typical examples are the so-called "Credit Cards" provided by various commercial enterprises, such as department stores, service stations, and the like, automobile drivers' licenses, and identification badges, such as those used to identify the personnel of plants or buildings where employees are limited in their right of access to predetermined portions of the plant or building. In such instances, it is of great importance to provide persons with an identification card or badge which is difficult or impossible to counterfeit and which immediately identifies its holder or wearer, preferably by containing a photographic likeness of him. In particular, it is highly desirable to provide a card or badge which comprises a photographic likeness of its holder together with any other desired identifying indicia, which card or badge is laminated to a transparent rigid or semirigid film by way of a so-called "security seal," that is, a seal which cannot be broken or tampered with without immediately clearly rendering obvious the intrusion by destroying or defacing the photographic likeness.

Where the identification card contains a photographic likeness of its holder, it is desirable, in the interest of speed and efficiency, to provide a rapid means of obtaining such a likeness. Of particular advantage in this respect are silver transfer images of the type which may be produced by applying a processing composition containing a silver halide developing agent and a silver halide solvent to a photoexposed photosensitive silver halide element and an image-receptive element that are in superposed relation. The processing composition acts to reduce exposed silver halide to silver, to react with unreduced silver halide to form a water soluble, complex silver salt, and to transfer it to the image-receptive element, and there, reduced it to silver. Examples of photographic materials useful in the production of the foregoing type of photographic silver images are described in detail in U.S. Pat. No. 2,543,181 issued in the name of Edwin H. Land on Feb. 27, 1951, and in U.S. Pat. No. 2,647,056 issued in the name of Edwin H. Land on July 28, 1953. In a typical process employing such materials a processing composition containing a viscous aqueous solution of a silver halide developing agent, a silver halide solvent and an alkali is spread in a uniformly thin layer between the superposed surfaces of the photoexposed gelatino silver halide stratum of a photosensitive element and the sliver-receptive stratum of an image-receptive element. The elements are maintained in superposed relation for a predetermined period ordinarily of approximately 10 to 120 seconds in duration, during which exposed silver halide is reduced to silver and unreduced silver halide forms a water soluble, complex silver salt which diffuses through the layer of composition to the image-receptive stratum, where, upon being reduced to silver, it forms a silver print. At the end of this period, the photosensitive element, preferably together with the solidified layer of processing composition, is stripped from the image-receptive element.

Image-receptive strata of the foregoing type include silver precipitating nuclei dispersed in a macroscopically continuous vehicle comprising submacroscopic agglomerates of minute particles of a water insoluble inorganic, preferably siliceous material such as silica aerogel. Silver grains precipitated in the foregoing manner are concentrated primarily at the surface of the stratum. This stratum, both before and after receiving these precipitated silver grains, is extremely thin, preferably being approximately 1 to 8 microns thick. Materials of the foregoing type are specifically described in U.S. Pat. No. 2,698,237 and 2,698,245 issued to Edwin H. Land on Dec. 28, 1954.

The foregoing process is particularly adapted for use in a polaroid Land camera made by Polaroid Corporation, Cambridge, Massachussetts 02139, or a similar camera structure such for example, as the camera forming the subject matter of U.S. Pat. No. 2,435,717, issued to Edwin H. Land on Feb. 10, 1948.

Where photographic likenesses of individuals are desired for identification card purposes, the forgoing process when used in cameras of the aforementioned type renders it possible to obtain such likenesses immediately upon making the photographic exposure, and obviates the necessity of the usual waiting period required for conventional photographic processes wherein a negative must be photoexposed and developed in a separate subsequent operation. However, owing to the nature of the image-receptive element as described above, it has been found that where it is sought to laminate the final silver transfer image to any conventional transparent supporting material, the image layer tends to separate, or be easily separable from, the transparent overlay. This was found to be particularly true when laminations were sought to be made between the silver transfer image and various transparent supports using pressure-sensitive adhesives.

Copending application Ser. No. 562,767, filed July 5, 1966 now Pat. no. 3,498,788 in the name of Howard C. Haas discloses the provision of security seals for silver transfer images of the aforementioned type by laminating such images to transparent layers which comprise a hydroxylated polymer, preferably a polyvinyl alcohol, modified polyvinyl alcohol, or hydrolyzed cellulose ester, which layer may have a suitable transparent backing if desired, via an intermediate layer constituting essentially of a methyl vinyl ether/maleic acid copolymer.

It has now been found that more uniformly durable security seals may be achieved in laminations of the aforementioned type by providing an intermediate adhesive layer substantially identical to that disclosed in Ser. No. 562, 767 referred to above, except that about half of the methyl vinyl ether/maleic acid copolymer is replaced by polyvinyl alcohol.

As examples of hydroxylated polymers which may be used as transparent layers for bonding to silver transfer images to form the laminations of this invention, mention may be made of polyvinyl alcohol; oriented, light polarizing polyvinyl alcohol-polyvinylene, oriented polyvinyl alcohol containing dichroic dyes, vinyl alcohol-containing copolymers such as partially hydrolyzed polyvinyl acetate; partially hydrolyzed vinyl acetate-vinyl chloride copolymers; polyvinyl alcohol with various subcoats such as cellulose nitrate and/or cellulose esters, and hydrolyzed cellulose esters such as hydrolyzed cellulose acetate.

The methyl vinyl ether/maleic acid copolymer-polyvinyl alcohol mixture is preferably coated upon the support from solution, following which the coating is permitted to dry. In the dried state the coated material is stable and may be stored for extending periods of time prior to its actual use in a lamination with a silver transfer image.

In preparing coating solutions for the laminations of this invention, the copolymer is simply dissolved in a suitable solvent, either in the form of methyl vinyl ether/maleic acid copolymer, or alternatively, in the form of methyl vinyl ether/maleic anhydride copolymer; where the latter form is used, the solvent should be one in which upon being dissolved, the anhydride is converted to the free acid. An aqueous solution of polyvinyl alcohol is then combined with the copolymer solution thus prepared.

It has been found convenient to use a 6 to 12 percent by weight aqueous solution comprising about half poly (methyl vinyl ether/maleic acid) and half polyvinyl alcohol as the coating solution, for the reason that at such a concentration, the materials are both readily soluble in water; further, the solutions thus formed provide a layer of adequate thickness to give a good bond in a single coating operation without being unduly viscous. If desired, however, stronger or weaker concentrations may be employed, limited only by the ultimate solubilities of the copolymer material and polyvinyl alcohol.

The optimum ratio of poly (methyl vinyl ether/maleic acid) to polyvinyl alcohol is about 1 to 1 by weight. If the mixture were to comprise substantially more polyvinyl alcohol, the effectiveness of the security seal is considerably diminished. Of course, at lesser polyvinyl alcohol concentrations, highly satisfactory security seals may be achieved, as was disclosed in copending application Ser. No. 562,767, referred to previously. In fact, laminations prepared in accordance with the teachings of Ser. No. 562,767 are slightly more water resistant over extended periods of time than those prepared in accordance wit the instant invention. However, in many practical applications, particularly where the final lamination is intended to be kept or sealed in a protective pouch or envelope, the seal is not exposed to high moisture content over long periods; and it is thus more desirable to provide a security seal which is consistent and uniform throughout, such as may be realized by the practice of the instant invention. And in any event, where the adhesive layer comprises at least about half poly (methyl vinyl ether/maleic acid), the final laminations cannot be said to be water sensitive.

While in the preferred embodiment the poly (methyl vinyl ether/maleic acid) or poly (methyl vinyl ether/maleic anhydride)-polyvinyl alcohol mixture is coated from aqueous solution, it is also within the scope of this invention to employ a solution of the material in an organic solvent in which both polyvinyl alcohol and the copolymer in the acid form are soluble such as lower alcohols, e.g., methanol and ethanol. There is no criticality in the thickness of the final poly (methyl vinyl ether/maleic acid)-polyvinyl alcohol layer, other than it be sufficient to provide a secure bond to both the hydroxylated polymeric overlay and the silver transfer image. Materials which have been found to be particularly efficacious in providing the copolymer material referred to above are the series of resins commercially available from General Aniline & Film Corporation, New York 14, New York, under the trade name Gantrez AN, and may be designated as copolymers of methyl vinyl ether and maleic anhydride, and the partial lower-alkyl esters thereof. Poly(methyl vinyl ether/maleic anhydride) may be represented by the formula: ##SPC1## when dissolved in a suitable solvent, the copolymer takes the form of the free acid. ##SPC2## Partial esters of the above copolymer are also useful in providing the laminations of this invention; these compounds may be represented by the formula: ##SPC3## wherein one of R and R' is a lower alkyl radical, such as methyl, ethyl, isobutyl, etc., and the remaining R or R' moiety is hydrogen. It is also within the scope of this invention to employ mixtures of the diacid copolymer of formula (B) with the partial esters thereof, represented by formula (C).

It is to be noted that in general, coatings comprising mixtures of poly(methyl vinyl ether/maleic acid) and polyvinyl alcohol are hard and free of tackiness when dried. However, where certain of the partial lower alkyl esters of the copolymer are employed, such as the 45percent partial methyl ester, the coating, even when completely dried, is slightly tacky to the touch. This has no effect upon the security seal ultimately formed and hence, need be considered only in those instances where it is desired to prepare coated hydroxylated polymeric overlays and store such materials for a finite period prior to their use in a security seal lamination.

As was stated previously, the coatings prepared as just described consist essentially of mixtures of a poly (methyl vinyl ether/maleic acid) and polyvinyl alcohol in a weight ratio of about 1 to 1. It will be understood that such a layer may also include minor amounts of modifying substances, such as plasticizers and the like, with which the polyvinyl alcohol and the copolymer are compatible.

When it is desired to prepare the final lamination with the silver transfer image, the dried poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol coating must be activated with water. This can be achieved either by wetting the coated surface, or by wetting the silver transfer print surface. Finally, the silver transfer print and coated surface are placed in face-to-face relationship and pressed together. High pressures are not necessary to achieve the security bond, but may aid in the exclusion or expulsion of any air which may be trapped between the layers. While as stated above, water alone may be used to activate the poly(methyl vinyl ethyl/maleic acid)-polyvinyl alcohol mixture in some instances it has been found helpful to include a trace of a swelling agent, such as N-methyl pyrrolidone, ethanol, propanol, or dioxane, in the activating solution. This has been found not to alter the nature of the security bond, but may tend to decrease the bond setting time.

Extremely thin photographic silver images of the foregoing types have been observed to retain traces of the photographic reagents wit which they have been processed, and the continued presence of which has been found to adversely affect their stability. Thus, in the past, it has been found desirable to physically wash such prints and coat them with a protective film-forming material. In the practice of this invention, it is still preferable that the silver transfer print be washed prior to its lamination. However, it has been found that if the lamination is achieved by feeding the print to be laminated along with the coated transparent material and a drop of activating solution between two rolls ordinarily known as "V-ing rolls," a bead of activating solution forms at the nip which effectively washes the silver transfer image. After the aqueous bead has passed over the surfaces being laminated, it is ultimately extruded, carrying with it the underside residue of the developing composition and thus, a separate washing step is not necessary. However, where the silver transfer print and the coated transparent hydroxylated polymeric overlay are simply placed in face-to-face relationship and pressure applied directly, it is preferred that the silver transfer image first be washed with water. Where the silver transfer print is washed immediately prior to lamination, it need not be dried; the aqueous washing fluid remaining on the surface of the print in such instances may then also provide the activating solution for the poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol coating.

An alternate procedure may be used for washing and laminating silver transfer images of the aforementioned type, which procedure is particularly adapted to those instances where it is unnecessary or inexpedient to prepare the transparent hydroxylated polymer overlay in advance by coating it with the poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol mixture and allowing the coating to dry. In this alternate procedure, an aqueous solution of the poly(methyl vinyl ether/maleic acid) and polyvinyl alcohol is used to simultaneously coat and wash the silver transfer image, and while the coating thus applied is still fresh and wet, the print is pressed directly against the transparent hydroxylated polymer overlay. Suitable devices and processes for simultaneously washing and coating silver transfer prints are described in U.S. Pat. No. 2,768,403 issued Oct. 30, 1956 to Charles A. Govatsos, and in U.S. Pat. No. 2,963,953, issued Dec. 13, 1960, to Donald R. Bishop et al. While the bonds between the silver transfer prints and transparent overlays are equally satisfactory to those prepared by the first-described procedure, the latter procedure necessitates the availability, not simply of water, but rather, of aqueous solutions of the polymeric coating materials. Where the laminating technique is desired for use as a relatively simple means for the production of tamperproof identification cards or badges, the disadvantage of the latter procedure are obvious.

The use of poly(methyl vinyl ether/maleic anhydride) in composition for washing and protecting silver transfer images is disclosed in the copending U.S. Pat. application of Edwin H. Land and Meroe M. Morse, Ser. No. 487,598, filed Sept. 15, 1965.

An additional suitable method for simultaneously providing the poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol coating, washing the silver transfer print, and laminating the print to an overlay is described in u.s. Pat. No. 2,798,021, issued July 2, 1957 to Edwin H. Land. In this procedure, the coating material is contained in a sealed, rupturable container which when ruptured by a suitable pressure-applying means such as pressure-applying rollers, discharges its contents; means are provided for spreading the contents between the surfaces being laminated. It is to be noted that the procedure described in the last-mentioned patent can also be employed in the lamination of silver transfer prints to hydroxylated polymer surfaces which have previously been coated with poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol mixtures as described above. In such a case, the rupturable container contains only activating solution (e.g., water) rather than a poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol solution.

Where the transparent hydroxylated polymeric overlay comprises a light-polarizing material, a second security feature is added to the final laminated photographic image, in addition to that provided by the security bond. Any attempt to tamper with or otherwise alter the surface of the laminate, e.g., by cutting into the material or heating it, affects the light-polarizing properties of the surface to the extent that the attempted alteration or intrusion can be readily detected with a suitable light-polarizing analyzer. The use of transparent light-polarizing sheets as a security feature for laminates is described and claimed in U.S. Pat. application of Robert Malster, Ser. No. 451,895, filed Apr. 29, 1965 now U.S. Pat. No. 3,313,052.

Additionally, if desired, the overlay may include a pattern, such as a stripe, comprising a mixture of dichroic dyes in an oriented polymeric substrate, such as a mixture of a positive dichroic dye of a first color and a negative dichroic dye of a second, distinct color; when viewed through a light-polarizing device, laminations of this type exhibit the original colors of the dyes comprising the mixture, as well as that of the mixture itself, thereby conferring an additional security feature upon the lamination as a whole. The use of the mixtures of dichroic dyes to provide security features for information-bearing surfaces is disclosed and claimed in the copending application of Howard C. Haas and Harold O. Buzzell, Ser. No. 513,046, filed Oct. 1, 1965 now U.S. Pat. No. 3,391,479.

Where it is sought to provide a card or similar laminate which is suitable for embossing, it is necessary that the outermost surface of the laminate comprise a transparent, relatively rigid polymeric material of the type which is capable of permanently maintaining raised or embossed letters. Of particular efficacy are those polymeric films known commercially as "rigid vinyls," which generally comprise a high chloride content vinyl acetate-vinyl chloride polymers or "semirigid vinyl," which are similar to rigid vinyl films except that they include a small amount of a suitable plasticizer. In order to provide a hydroxylated surface on such vinyl films so that they can form a security bond with the poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol layers described above, it is preferred that the rigid or semirigid vinyl film be subcoated with a layer of a vinyl acetate-vinyl chloride copolymer, having a ratio of from about 7:3 to 1:1 vinyl acetate: vinyl chloride; thereafter, the outer surface of the vinyl acetate-vinyl chloride layer is at least partially hydrolyzed so as to provide hydroxyl groups to which the poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol mixture can adhere.

The use of security-sealed laminations comprising rigid and semirigid embossable films with other image-bearing strata is disclosed and claimed in copending U.S. application of Pheobe F. Jordan and Harold O. Buzzell, Ser. No. 513,046, filed Oct. 1, 1965.

Referring now to the drawing, FIG. 1 represents the layers as described above immediately prior to laminations, comprising a silver transfer image layer 8, a transparent hydroxylated polymer overlay 10 on which a layer 9 of poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol mixture has been coated and allowed to dry. A drop of aqueous activating solution 11 has been placed between silver transfer image layer 8 and layer 9 which, when spread between the layers, activates layer 9, enabling it to adhere to the silver transfer image layer 8 in a security bond.

FIG. 2 represents the structure shown in FIG. 1, in which the activating solution has been spread, and the respective layers pressed together to form security bond 18, thus completing the lamination.

FIG. 3 is a cross section greatly magnified of a laminated transfer image being prepared by one of the methods described previously. As shown, the sheet materials, comprising the silver transfer image 8, and hydroxylated polymer sheet 10 with its poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol layer 9, are fed between two "V-ing rolls" 12 and 13 rotatably mounted and suitably driven in directions indicated by the arrows on the rolls. Rolls 12 and 13 are adjustable with respect to the distances between centers so that a suitable pressure may be brought to bear upon the contacting surfaces of the sheets. Numeral 11 designates an aqueous bead of activating solution maintained at the nip between the two sheets of material undergoing lamination adjacent to the point of contact. AS described previously, as the aqueous bead 11 is forced by the rotation of rolls 12 and 13 over the surfaces of the layers being laminated and is extruded from between the layers at the completion of the lamination, it not only activates the poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol coating 9 but also effects a washing of the silver transfer image 8. As the completed lamination passes from rolls 12 and 13, it is characterized by the presence of security bond 18 which is formed between layers 8 and 9.

FIGS. 4 through 6 represent a special embodiment of this invention, which may be characterized as an envelope or pouch comprising a silver transfer image laminated to one of its inner surfaces in a security bond.

FIG. 4 is a plan view of an envelope or pouch which has been prepared for providing the aforementioned embodiment, prior to lamination. The envelope or pouch comprises wall 15, which is made up of a transparent hydroxylated polymeric overlay, coated with a poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol mixture on its inner surface as described previously. Wall 15 is heat solvent, or adhesive sealed around a portion of its periphery 16 to a nonadhesive backing 14, which is preferably flexible, leaving the remainder of the periphery open for insertion of the silver transfer print.

FIG. 5 is a section taken along lines 5-5 of FIG. 4, and shows the relationship of transparent hydroxylated polymeric layer 10 which its dried coating 9 of poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol, both of which when taken together comprise the front wall 15 of the envelope, heat sealed at its periphery 16 to backing 14. Where poly(methyl vinyl ether/maleic acid) is employed or where the particular poly(methyl vinyl ether/maleic ester) employed is one which at least in combination with polyvinyl alcohol, dries free of tackiness, the envelope or pouch so prepared may be stored for extended periods of time prior to its use in making silver transfer print laminations; in the absence of water, layer 9 will exhibit no tendency to adhere to nonadhesive backing 14.

Envelope or pouches so prepared provide ready structures for lamination to silver transfer prints. The print is preferably first washed with water to remove the residue of developing composition as described above, and to provide a thin film of water to activate the poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol coating. Thereafter, the print is inserted into the pouch or envelope by way of its open end, in such a way that the image- bearing siliceous surface of the silver transfer print is immediately adjacent to the coated front wall. Thereafter, the entire envelope is subjected to pressure, such as by passing it between "V-ing rolls" as described above, to provide the security bond. (The use of V-ing rolls to provide the necessary pressure gives the additional advantage that any excess activating solution can be forced out of the envelope by way of its open end.) Preferably, the envelope is then heat sealed along its remaining open side.

FIG. 6 is a section similar to that of FIG. 5, showing the relationship of all of the elements when completed laminate is prepared as just described. The final structure is an envelope or pouch comprising a transparent front wall 15, made up of an outer layer 10 of transparent hydroxylated polymer having a coating 9 on its inner surface of poly(methyl vinyl ether/maleic anhydride)-polyvinyl alcohol, to which is bonded the face of a silver transfer print 8 in a security bond 16. Front wall 15 is heat, solvent, or adhesive sealed at its periphery 16, and heat sealed at its periphery 17 to nonadhesive backing 14, to provide a tamperproof lamination having a security seal 18.

FIG. 7 is a cross section, greatly magnified, of a silver transfer image which is security laminated in such a manner as to provide an embossable structure. The laminate as shown comprises a transparent rigid or semirigid embossable overlay 20, having a subcoat 19 comprising a vinyl acetate-vinyl chloride copolymer, the lower surface 21 of which has been at least partially hydrolyzed, coated with a layer 9 of poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol, and bonded to the image-bearing surface of a silver transfer print 8. It will be appreciated that such an embossable structure could readily comprise the front wall and bonded silver transfer image of the embodiment described as FIGS. 4 through 6 above. Thus, referring to FIGS. 5 and 6, the transparent hydroxylated polymer layer 10 could comprise a rigid or semirigid embossable vinyl overlay, having on its underside a subcoat of a surface-hydrolyzed vinyl acetate-vinyl chloride copolymer. The layer of poly(methyl vinyl ether/maleic acid)-polyvinyl alcohol 9 is then coated onto the hydrolyzed surface of the subcoat. This envelope or pouch so prepared would then be characterized, not only as comprising a security-sealed silver transfer print but also as having an outer front surface which can be embossed with any desired indicia.

The following nonlimiting example illustrates the preparation of adhesive solutions for use in laminations with the scope of this invention:

EXAMPLE I

A first mixture, consisting of 90 parts of water and 10 parts of a medium molecular weight poly(methyl vinyl ether/maleic anhydride), commercially available from General Aniline & Film Corporation, New York 14, New York under the trade name Gantrez AN-139, was heated and mechanically stirred until a rather viscous gelatinous composition was obtained. (The term "medium viscosity" as will be appreciated by those skilled in the art, is used to designate a copolymer having a specific viscosity of 1.0--1.4, as determined on a 1 percent solution of the copolymer in methyl ethyl ketone at 25.degree. C.) The mixture was then removed from heat, and was placed in a cold water bath until the viscosity had dropped and the solution was clear of bubbles.

A second mixture consisting of 90 parts of water and 10 parts of 88 percent hydrolyzed polyvinyl alcohol, commercially available from E. I. du Pont de Nemours & Co. (Inc.), Wilmington, Delaware, under the trade name Elvanol 52-22, was heated and mechanically stirred until all of the polyvinyl alcohol had gone into solution. The solution thus formed was removed from heat and allowed to cool until it was clear of bubbles.

Equal parts of the first and second solutions were mixed, to provide the final adhesive solution.

The following nonlimiting examples further illustrate the present invention:

EXAMPLE II

A linear dichroic polyvinylene-polyvinyl alcohol light polarizing sheet having a cellulose acetate butyrate backing, commercially available from Polaroid Corporation, Cambridge, Massachusetts 02139, and designated as Product No. 950 was given a single coating of the solution prepared in example I, which coating was allowed to dry until all tackiness had disappeared. A silver transfer photographic print was made, using a Polaroid 3000 speed Land Film Pack, Type 107. Two drops of water were placed along one side of the print, and the print was then passed through V-ing rolls along with the prepared polarizer sheet in such a way that the print surface was pressed firmly against the coated surface of the polarizer, forcing the water across the facing of the print between the surfaces being pressed together. After a period of about 5 minutes an attempt was made to separate the print from its overlay; it was found that the image adhered firmly to the overlay and could not be pulled away, even with the aid of a razor blade.

EXAMPLE III

The procedure of example II was followed, using a silver transfer photographic print prepared from a film assembly similar to that of example II, but having an A.S.A. equivalent speed of 75. The lamination obtained was substantially identical in physical characteristics to that of example II.

EXAMPLE IV

A sheet comprising a cellulose acetate butyrate support, subcoated with cellulose nitrate, followed by a layer of cellulose nitrate and hydrolyzed polyvinyl acetate, and lastly a layer of polyvinyl alcohol, was coated on its polyvinyl surface and laminated to a silver transfer print exactly as in example II. The security bond formed was substantially identical to that formed in the forgoing examples.

Cellulose acetate butyrate films having subcoats as described above may be prepared in accordance with the teachings contained in U.S. Pat. No. 2,362,580, issued Nov. 14, 1944, to Gale F. Nadeau and Clemens B. Starck; U.S. Pat. No. 2,541,478, issued Feb. 13, 1951, to the same inventors and U.S. Pat. No. 2,835,609, issued May 20, 1958, to Clemens B. Starck, Gale F. Nadeau, and Carl F. Smith.

EXAMPLE V

The hydrolyzed surface of a sheet of cellulose triacetate was laminated to a silver transfer print prepared from a Polaroid 3000 speed Land Film Pack, Type 107 following the procedure of example II; a substantially identical security bond was formed.

Surface-hydrolyzed cellulose triacetate film may be prepared in accordance with the teachings contained in u.s. pat. No. 3,078,178 issued Feb. 19, 1963, to Bertil E. Ostberg.

After initial attempts to separate the laminations of each of the foregoing examples proved unsuccessful, the laminations were subjected to the following test conditions:

1. Stored at 140.degree. C. for 16 hours.

2. Packed in Dry Ice for 2 hours.

3. Suspended for 10 days over a hot, saturated sodium chloride solution.

4. Refrigerated overnight.

5. Stored at 100.degree. F. and 80 percent relative humidity for 10 days.

6. Subjected to dry air at 90.degree. C. for about 1 hour.

None of the forgoing tests were found to have any effect upon the security bond. In test (2), in which the laminates were packed in Dry Ice, the laminates readily shattered; the image could still not be separated from the rest of the laminate, even in a fragmented condition. It was also observed that the laminated silver transfer print exhibited no tendency to fade, even when subjected to sulfur and to accelerated agining conditions.

It will be appreciated that the term "image" as used in the foregoing discussion is intended to include not only photographic likenesses of given individuals, but also, especially when applied to identification cards and the like, includes a photographically recorded indicia which may form a part of the final picture.

Since certain changes may be made in the above process and products 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.

Claims

What I claim is:

1. A laminar structure comprising a first transparent layer at least one surface of which comprises a transparent hydroxylated polymer, a second layer adjacent to said hydroxylated polymer surface consisting essentially of an approximately 1 to 1 parts by weight homogeneous mixture of polyvinyl alcohol and a material selected from the group consisting of methyl vinyl ether-maleic acid copolymers and the partial lower alkyl esters thereof, and a third layer comprising a silver image, the surface of which is bonded to said second layer.

2. A laminar structure as defined in claim 1 wherein said transparent hydroxylated polymer is polyvinyl alcohol.

3. A laminar structure as defined in claim 1 wherein said transparent hydroxylated polymer is a molecularly oriented light-polarizing polyvinyl alcohol.

4. A laminar structure as defined in claim 1 wherein said transparent hydroxylated polymer is a partially hydrolyzed vinyl acetate-vinyl chloride copolymer.

5. A laminar structure as defined in claim 1 wherein said transparent hydroxylated polymer is hydrolyzed cellulose acetate.

6. A laminar structure as defined in claim 1 wherein said first transparent layer comprises a cellulose acetate butyrate support having a first subcoat comprising cellulose nitrate, a second subcoat comprising cellulose nitrate and hydrolyzed polyvinyl acetate, and a third subcoat comprising polyvinyl alcohol.

7. A laminar structure as defined in claim 1 wherein said first transparent layer comprises a vinyl acetate-vinyl chloride embossable film having a subcoat comprising a vinyl acetate-vinyl chloride copolymer having a vinyl acetate to vinyl chloride ratio of from about 7:3 to 1:1, the surface of said subcoat away from said embossable film being at least partially hydrolyzed.

8. A tamperproof identification card comprising a laminar structure as defined in claim 1.