WO1995013196A1

WO1995013196A1 - Coded indentification card and other standardized documents

Info

Publication number: WO1995013196A1
Application number: PCT/US1994/012708
Authority: WO
Inventors: Jack A. Soules; Bryan D. Carpenter
Original assignee: Technical Systems Corp.
Priority date: 1993-11-09
Filing date: 1994-11-03
Publication date: 1995-05-18

Abstract

A document such as an indentification card (10) is constructed as a laminate within which is a code (16) is concealed from human view. The document is read by an electro-optic reader means, if the reader uses a beam of light in the wavelength absorbed by the material with which the coded indicia is produced, but reflected by the background against which the coded indicia is 'seen' by the beam. The card is a laminate of an upper lamina (11) and a lower lamina (12), each made of a synthetic resin which is printed with a person's identification (14) with an ink which is visible to the human eye but substantially transparent to wavelengths outside the visible range. Typically, both the upper and the lower laminae, are opaque to visible light, but the face through which the coded indicia is to be read by the reader, is transparent to the reader's beam.

Description

CODED IDENTIFICATION CARD AND OTHER STANDARDIZED DOCUMENTS

BACKGROUND OF THE INVENTION

This application is a continuation-in-part application of Serial No. 07/983,973 filed December 1, 1992 which in turn is a divisional of Ser. No. 07/501,148 filed March 29, 1990 issued as U.S. Patent No. 5,067,713 on November 26, 1991.

This invention relates to an internally coded laminated standardized document such as an identification card, label or other document unrelated to any card game, and of no value in playing cards, as is the playing card of the parent case, though the inventions are conceptually related. The coded document of this invention is coded underneath its surface with an arbitrarily chosen machine-readable indicia not visible to the human eye (termed "human-invis¬ ible"), because the code is physically, literally "covered up" with an opaque, or nearly opaque sheet. Typically, if it were not for the "cover sheet" or "upper lamina" the machine-readable code would also be clearly visible to the human eye. The upper surface or "face" of the coded document usually carries a legend, drawing or photograph which is meant to be read by the human eye ("human- visible"), on the same area (field) as the machine readable indicia, or on different areas.

By "identification card" we refer - any card or label which carries inform¬ ation as to the identity of the carrier oi the card, e.g. an ID card for an employ¬ ee of a company or for a student at a university, or a driver's license; a bank, or gasoline credit card; or, a label which identifies an article of arbitrary size and shape, such as packing cartons, or merchandise to which the card is attached.

Labels are currently identified with human and machine readable insignia as des¬ cribed for example in U.S. Patent No. 4,889,367 to Miller, and in the references cited therein.

Other documents to which this invention is directed are larger cards, that is, larger than a conventional ID card which is typically about 5.5 cm x 8.75 cm, such as a card which carries information about the codes for locks on an auto- mobile, or identifications of various parts used in its construction; or, a card which carries information as to the model of a vehicle for sale, some of which information is meant to be hidden from the prospective purchaser, e.g. the actual price the seller has paid, the origin of the vehicle, the conditions under which it was purchased by the seller, etc.

Still other documents are certificates of registration, documents relating to insurance carried, to the blood type of an insured, medical history, executed original contract, wills, warranty deeds, bearer bonds, passports, etc., all of which may now be coded to contain information meant for only a particular party to whom that information is to be made available, and to no other party not equip¬ ped to read the coded information. For the sake of convenience and brevity any such standardized document coded as taught in this invention is generically refer¬ red to hereinafter as "document".

In each embodiment, no change is made to the information carried on the document's face, and the document appears to be identical to one which does not carry the human-invisible coded information. The coded information is stor¬ ed in a unique pattern visible only in the infrared (IR) or ultraviolet (UV) regions, without being visibly defaced. The coded document is an otherwise con¬ ventional identification card formed from either a single non-laminated sheet of flexible material ("card stock"), such as paper, preferably coated with a cured latex of an acrylate-containing polymer; or, a laminate of printed card stock sandwiched between sheets of thin light permeable synthetic resinous material (plastic) coextensive with the card stock, and designed to protect the card as well as provide it with stiffness. Typically a document such as an ID card will have a photograph of the owner of the card adhesively secured to the card before it is laminated between the plastic sheets, as schematically illustrated in Fig 1 herein. The laminated document is coded in a reflective region between an upper lamina and a lower lamina, at least one of which, typically the upper, is opaque to the human eye but permeable to an IR or UV laser beam of predetermined wavelength. The reflective region lies in an intermediate zone between the upper and lower laminae, and the code to be read contrasts with the reflective region in a manner such that an electronic device can access whatever information the code may have been devised to reveal. Of course, in addition, the document con¬ veys information which is visible to the human eye. The reflective region typically includes a surface which will reflect the IR or UV laser beam and is imprinted with letters or a picture ("insignia") in inks which are permeable to the wave- length of light used to read the covered code or figure which absorbs that wave¬ length.

In a specific embodiment, the code indicates to an electronic "reader" the hidden fingerprint of the owner of the ID card, foiling the use of that card by someone who does not own that fingerprint. When the ID card is presented to a reader adapted to read both the fingerprint covered in the card, and a person's fingerprint, and the reader compares the fingerprints it reads against one another, the mismatch is discovered.

As one skilled in the art will readily appreciate, coding a document with a human-visible fingerprint, or a standard Hollerith pattern or "bar code", by which each document is uniquely identified, is a routine task. To code a document with the code being covered with an opaque sheet, whether that code is visible to the human eye or not, so that the document may be read by a machine viewing only the face of the ID card which traverses the reading means of a machine, is not a routine task. It is not a routine task even if all the information, both human- visible and machine-readable is carried on the surface of the document. The diff¬ iculty is increased in either case, because the document must be read without defacing it, and essentially without regard for its orientation in the plane in which the code is machine-read; that is, a lateral plane when the document trav¬ erses the reading means in that plane, and a vertical plane when the document traverses the reading means in the vertical plane.

Coded playing cards coded as disclosed in U.S. Patent No. 4,534,562 to Cuff et al, were conventionally marked with a binary code along its opposite edges so that the code could be seen by the human eye (read by light in the range of visible wavelengths). Since there was no concern about hiding the fact that the cards were coded the necessity of overprinting the faces of the cards did not arise, and the cards were marked on the side edges.

In Miller '367, the surface of a package of corn chips provided the subs- trate which was marked with machine readable information overprinted on human-readable symbology, each with a different type of ink. It is essential that the machine-readable ink be essentially invisible to the human eye; that is, the human-readable ink absorbs energy in the visible but insufficient energy in an- other wavelength range to prevent a bar-code reading machine ("reader") from reading the bar code. However, because the two inks of the human-visible and machine readable information overlap, in practice the images printed in human- visible ink suffer from the dilution of the machine-readable ink. Since the degree of dilution is different in different areas of the field, depending upon the amount of interaction between the two inks, the inevitable result is an uneven appear¬ ance of the image on the surface.

Further, knowing how difficult it is to find infrared or ultraviolet-absorp¬ tive inks which do not absorb in the visible region, that is, have essentially no color, it must be accepted that it is even more difficult to find two inks which do not, when mixed, noticeably interfere with each other. Though inks having very specific energy absorption and reflection characteristics are commercially avail¬ able, if only on special order, no suggestion or illustrative example of an infrared or ultraviolet absorbing ink which does not substantially absorb in the visible region, is provided in the '562 or '367 patents. Thus the "invisible" bar code of the '367 patent, in practice, is limited to use on colored substrates, such as a mustard color on a bag of chips, or the brown or blue of other snack foods.

Such a two-ink printing of a bar code on a substrate was well-suited for coding an article where its appearance is of relatively minor concern, for example, an inventory and shipping label on a carton. But the appearance of the document is of the utmost concern in a document such as an identification card which carries a photograph of a person.

Moreover, the Miller '367 coding overlapped with human-visible insignia is printed in only one orientation. This allows a package to be read when passed across a grocery store counter where the laser reading the bar code rotates until it can read the code. However, since the orientation of the bar code is fixed on each of the foregoing substrates in the '367 and '562 patents, the code can only be read in one direction by a reader having a fixed light source. Still further, there is no suggestion in the prior art as to what kind of contrast is required between the infrared "ink" and the background against which it is printed to enable the code to be read without being scattered by the human- visible ink. Our coded document uses an essentially invisible bar code, typically only because the bar code is covered under the surface of the conventionally printed document. A "covered up" code which can be read only by an electro-optical reading means using light in the IR region is described in greater detail hereinbelow, though, in addition it may have a human-visible bar code as illustrated in Fig 2 herein.

The unexpected result of being able to code only the "covered up" or hid¬ den reflective region of a document essentially invisibly, is that the reflective surface may be imprinted, that is, marked or printed, textured or etched with the code either singly or repetitively and in multiple orientations, depending upon the figure to be read and recognized, thus enabling the document to be read in any generally lateral orientation whatsoever, as long as the document traverses, that is, passes over the machine which reads it, preferably in contact with it. Of course, the document may also be marked with the code in such a manner that the reader will read the code in any generally fixed direction (say along the horizontal x-axis), whether the document is introduced to the reader from either end along the axis.

For example, the particular advantage of coding the ubiquitous "plastic card" according to this invention, is that the code hidden within the card is essen¬ tially non-susceptible to wear because the code is covered with and protected by the upper and lower laminae which have specified optical properties, described in greater detail herebelow. The upper and lower laminae are self-supporting sheets of material which serve as the top and base layers, respectively, of the laminated card.

The term "lamina" is used to emphasize the fact that the sheet is self- supporting and of appreciable thickness, at least about 0.5 mil (0.0005 inch) thick. The terms "top layer" or "upper layer" and "base layer" or "lower layer" are used synonymously with "upper lamina" and "lower lamina" herein only because the former terms are less awkward and more familiar than the latter. The term "intermediate layer" or reflective surface refers either to a selectively reflective non-self-supporting layer typically less than about 0.5 mil thick, or a combination of the non-self-supporting layer with a supporting layer the optical properties of which are immaterial.

A non-self-supporting layer, typically consisting essentially of solid part¬ icles from OJμm - 5μm (micrometer) may be sputter-coated or vacuum deposit¬ ed; particles up to 44μm in average size may be conventionally deposited; while films less than 0.5 mils (0.0005") thick, say from 10μm to about 13μm, may be formed by known means. A non-self-supporting intermediate layer less than 0.0005" thick may consist of only the particles which define the code, or such particles supported on a thin film of material, preferably a polymeric film.

The face of the upper layer of the standardized document carries the human-readable insignia and comprises an upper lamina which provides a select- ively reflective background, substantially fully light-reflective in the visible, and substantially transparent (light-permeable) in the infrared or ultraviolet regions. The electrical conductivity of the upper layer is irrelevant, as is that of the base layer, provided such conductivity, if present, does not interfere with operation of the device used to read the coded intermediate layer of the laminated card. Though the principles upon which the interaction of the components of the laminated standardized document, are well known in optical physics, the choice of the components with a view to their desired interaction is unique.

SUMMARY OF THE INVENTION A laminated standardized document of no value in a game, is imprinted on an intermediate layer, with concealed, machine-readable coding indicia, either as a single set of coding indicia (say, a fingerprint, bar code, or a photograph composed of a multiplicity of dots each no smaller than the width of a beam with which the photograph is to be read) readable from either of two generally axially opposed directions; or, as multiple coding indicia (plural sets of bar codes, say) readable from any arbitrary direction so long as the document is presented to the reader with its IR or UN-light permeable face directly facing the reader. Partic¬ ular such documents are ID cards, bank and other credit cards, and the like. The coding indicia may also be imprinted along each margin of the intermediate layer, or, the entire surface of the intermediate layer.

The code is imprinted so that it is read by the reader in the same direc¬ tion as a human would read the human-visible information on the principal side of the document, referred to herein as the "face" of the document. In an ID card the face of the document typically carries a photograph of the owner of the card. If the code is imprinted unidirectionally, say in the direction of the longi¬ tudinal axis of the document, then the document will be read as long as a por¬ tion of the document carrying the imprinted code passes transversely (that is, not parallel to the direction in which lines of the indicia are marked on the docu¬ ment) over an electro-optical reading means which identifies the document and can read the coded information it conceals. The code read is then used for what¬ soever purpose it was provided.

It is a specific object of this invention to provide a laminated document having (1) an upper lamina or top layer which is entirely selectively light- permeable to light in the IR or UV regions, but not in the visible region, and the upper face of the top layer is imprinted with human-visible indicia conveying human-readable information (2) a lower lamina or base layer which serves as a supporting layer for (3) an intermediate, selectively light-reflective coded layer which is sandwiched between the upper and lower laminae, so that the code on the intermediate coded layer, which may or may not be visible to the human eye, is readily machine-readable. The code is read by a device using light in a predet¬ ermined wavelength to which the upper lamina is permeable, and which predet¬ ermined wavelength is selectively reflected/absorbed by the intermediate layer and coding indicia thereon, so as to provide sufficient contrast to be read by a

"reader". The reader most preferably is an electro-optical reading means sensitive to light in the wavelength range above about 7000 A Angstroms (700 nm) but below about 2.2x10^ A, preferably in the infra-red range from about 800 - 10^ nm, more preferably 800 - 2000 nm (near infrared). The document may be read laterally, either substantially unidirectionally, from either end but face down; or, without regard for the document's face-downwards lateral orientation.

It is a specific object of this invention to provide a laminated label or other standardized document the upper (top) layer of which is made of non- fibrous material which is substantially reflective in the visible spectrum and is marked with visible indicia in black or colored inks, but the material and inks are both permeable to IR or UV light; the intermediate layer is light-reflective and substantially coextensive with the document. The intermediate layer has a code imprinted thereupon which absorbs light in a predetermined wavelength range, the intermediate layer being sandwiched between the upper layer and a base layer which supports the intermediate layer. The optical properties of the base layer are immaterial to the information-transmitting function of the code in the document.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and additional objects and advantages of the invention will best be understood by reference to the following detailed description, accomp¬ anied with schematic illustrations of preferred embodiments of the invention, in which illustrations like reference numerals refer to like elements, and in which: Figure 1 is a schematic exploded representation of an ID card displaying conventional human-visible insignia on the upper layer or face of the card, imp¬ rinted with IR-permeable ink, and showing a sputter-coated fingerprint, or one made by a person whose finger was first coated with ordinary human-visible and IR-absorbing India ink. The fingerprint is placed in the intermediate zone, against a reflective, preferably metallized surface, on the lower lamina or base layer. Only a single fingerprint is necessary since the reader will recognize the pattern irrespective of the orientation in which it is presented.

Figure 2 is a diagrammatic exploded representation of a conventional label used on merchandise showing a human-visible and machine-readable first bar code, under the legend giving the price of the item on sale, both imprinted in substantially IR-permeable ink, except that the label is used as the upper lamina of a laminate in which a second bar code is imprinted on the lower lamina. Again, the second bar code is printed with conventional printing ink containing colloidal carbon, which ink is both human-visible and IR-absorbing, but because the second bar code is covered with the upper lamina, the second bar code is not human-visible. The second bar code gives data such as the price paid for the item by the seller, the source of the item, the day it was acquired by the seller, etc., none of which information is meant for the prospective purchaser.

Figure 3 is a schematic representation of a laminated plastic ID card which appears conventional except that it has a photographic likeness of the owner of the card imprinted on a thin sheet of machine-invisible synthetic resin which may be either non-self-supporting or self-supporting, and the thin sheet is bonded to a metallized surface on the lower lamina.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Though it is most preferred to use a code imprinted in an ink which absorbs both in the visible and the IR region, the code may also be provided without using an ink, that is, inklessly. The code may be provided by depositing microscopic particles of powder, such as crystals from a solution of an inorganic salt such as barium sulfate, or a solution of an organic salt such as sodium acetate. The particles are chosen for their absorptivity of the wavelength of light used by the reader. Alternatively, the code may be obtained by etching or textur¬ ing the surface of the card with an abrasive powder or by mechanical means so as to produce a code of contrasting textures, the bars being dull (that is, infrared absorptive) and leaving the spaces between the bars, and the background shiny (that is, infrared reflective); or, less preferably, vice versa. In either case, whether produced by a solution or by etching or texturing, a card is encoded with the bar code without using an ink, i. e. inklessly.

In another embodiment, a dispersion or solution of inorganic or organic particles used to produce the bar code may be chosen to fluoresce in the visible or infrared when illuminated by an appropriate UV light source, contrasting with the spaces and background.

In general, a clandestine bar code, namely one which cannot be read by the naked eye, may be textured into any surface which already bears visible indicia, for example, a garment label, a ticket to a ball game, stock certificates, legal documents, bank drafts, checks and bank notes. When the code is textured, it will be readable by either an infrared or ultraviolet detection system, that is, in a range outside the visible. When the surface to be coded is smooth, one has the option of providing either a textured bar code, or a code with an invisible dispersion of dye or microscopic powder.

In the particular instance of conveying printed information in a predeter¬ mined limited area, for example a printed page of text, the use of invisible solutions readable in the infrared or ultraviolet may be used to increase the den- sity of text several fold. For example, a laminated sheet of conventionally printed text, printed in ink which to the eye appears jet black, may be overlaid and bonded to a second sheet imprinted with an invisible solution which is readable in the infrared, and again overprinted with an invisible solution which is readable in the ultraviolet. Thus, the number of forms of text is limited only by the optical wavelength band width of the detectors, the band width of the exciting radiation, and the responsivity of the inks or solutions, whether absorbers or fluorescers. In some instances, the inks or solutions may not be overprinted one on top of the other, but within unprinted or blank spaces such as interlinearly in a page of conventional text. Referring to each of the documents illustrated in Figs 1-3, the upper lamina of each is made from material which reflects substantially all light in the visible spectrum, that is, the top layer is opaque or nearly opaque. For the specific embodiment of the invention described in detail below, a 905 nm IR beam, focussed to a spot size in the range from about 10 μm to about 200 μm is used. Such a beam directed upon an IR absorbing figure shows high contrast between the area occupied by the figure and the IR-reflecting background. Such a reflecting background is provided by a silver, aluminum or gold substrate any of which are highly reflecting at 905 nm. A broad area detector collects IR light reflected from and scattered by the reflecting background. Referring, for example, to Fig 1, there is shown an ID laminated card in¬ dicated generally by reference numeral 10, having an opaque upper lamina 11 and an opaque lower lamina 12. The face of the upper lamina 11 presents an opaque background against which is printed the desired human-visible insignia 13. A photograph 14 is thermally bonded or adhesively secured to the face of the upper lamina 11. The insignia 13 are printed with inks which may be black or in color, and though these inks are transparent to the IR beam, they reflect subs¬ tantially all hght in the visible spectrum, so they are human-visible. By "subs- tantially all light" we refer to at least about 80% of the light in the visible spectrum being reflected, the remaining 20% or less being transmitted.

A coded intermediate layer 15 which is substantially coextensive with the document, preferably reflects substantially all the IR light (chosen for the reader) and this layer is provided with a fingerprint 16 of the owner of the card in IR- absorbing ink readable by the reader. When the laminae are bonded together, whether thermally, sonically or adhesively, and the document is held up and viewed against a bright light in the visible spectrum, there is no visible trace of the fingerprint 16 carried within the document. Only the insignia carried on the face of the document can be read by a human because the fingerprint is covered. Viewed from the rear, only the insignia (not shown) carried on the rear face of the lower lamina 12 can be read by a human. The optical properties of the lower lamina, whether it is permeable to light of any wavelength or not, is not material to its function herein if the ID card is to be read face-against the reader. More specifically, Table I lists the various combinations of sources, appro¬ priate detectors and the optical response which is monitored.

TABLE I

Source Detectc Optical response

IR IR Differential reflectivity or long wavelength fluorescence

Visible IR fluorescence

UV Visible fluorescence

UV UV reflectivity

The difference in reflectivity read by the reading means determines whether the space read contains a bit. The reading means can only distinguish between reflective and non-reflective portions in the wavelength range visible to the reading means. The reading means therefore can use any wavelength range which is either in the IR or in the UV, the former being preferred.

The preferred document reader is of the type conventionally used and functions by scanning the IR laser over the surface of the document in a regular manner, analogous to the raster scan in a television tube. The response of the detector is recorded and displayed, for example, on an oscilloscope which is synchronized with the scanning motions, all of which is well known in the art. To operate with a low power IR beam the thickness of each lamina is in the range from about 1 mil to about 10 mils, the thicker the lamina, the more the unde¬ sirable back scattering of the IR radiation. Most preferred are laminae about 5 mils thick.

The upper lamina 11 which is overlaid on the lower lamina with the inter¬ mediate layer carrying the code therebetween, is preferably a pigmented synthe¬ tic resinous material which, without the pigment would be light permeable. When the pigment particles are smaller than the wavelength of the IR beam, the beam passes through what appears to be an opaque sheet. Though a white pigment is typically chosen, the pigment could be red, either providing enough back scatter¬ ing in the visible to appear opaque also. Since permeability depends both on the particle size and their absorption function, it will be evident that small particles of the same size as the red ones will absorb too much of the infrared to be effective. Therefore pigments of any other color but white or red will not be suitable with a 905 nm IR beam. However, the surface of the upper lamina may be printed with an ink of arbitrary color provided the ink is IR-transparent.

Alternatively, a sheet of substantially crystalline, semicrystalline or amorphous polymer may be used, provided the substituent groups (if any) on each repeating unit, and the morphology of the polymer are such that it is opaque to human-visible hght but permeable to the 905 nm IR beam. Though there is no known predictable manner for detei-nining the correlation between polymer structure and permeability of hght through that polymer structure, a suitable polymer may be found with routine trial and error. Commonly available poly(vinyl chloride) "shelf paper" used in kitchens, is suitable. Paper and other fibrous laminae are unsuitable because they scatter a much larger fraction of the IR hght back to the detector, reducing the contrast.

Referring now to Fig 2 there is shown a sales tag 20 to be laminated from upper and lower laminae 21 and 22 in a manner analogous to that described hereinabove. As before the upper lamina 21 carries on its face, a human-visible code 23. An IR-absorbing powder of an organic or inorganic material is deposit¬ ed in a bar code 26 on the front surface 25. The powder used for the bar code is human-visible until it is covered by the upper lamina, when it is not visible against the surface of the lower lamina 22 but absorbs in the IR so as to be read by the reader. The intermediate layer is therefore only the powder.

Only a single bar code of multiple repetitively imprinted codes on the re- flective upper surface of the lower lamina is shown. A single bar code, as shown, is readable in both directions by a stationary reader means, and readable in any orientation by a rotating reader means. For a fixed reader means, it is desirable that the bar code be readable in any orientation, and accordingly, multiple im¬ prints of the bar code are provided in each of at least two directions, one perpendicular to the other, and preferably at least three if not four directions, the third and fourth directions being at 45° to the first two directions.

Referring now to Fig 3, there is shown still another embodiment of an ID card 30 having upper and lower laminae 31 and 32 respectively and the upper lamina carries human-readable insignia 33. A thin self-supporting sheet of a synthetic resinous material about 0.5 mil thick has imprinted on it a photograph which identifies the owner of the card. The photograph is preferably printed in "half-tone" form with individual dots about 0.002" (2 mils) in diameter, which is small enough to provide contrast when scanned by the laser which is absorbed by the dots. The thin sheet with the photograph on it is then bonded to the upper lace of the lower lamina 22 which has been coated with a highly reflective gold foil.

The intermediate layer 35 is thus provided by a thin metal (aluminum or gold) or metallized film which reflects essentially all the hght falling upon it. Such a metallized intermediate layer may be provided by any conventional tech- nique for applying a thin film coating, for example, by vacuum deposition, sput¬ tering or electrolytic deposition. By "thin film" we refer to a thickness which is sufficient to reflect substantially all infrared and visible light falling upon it. A preferred metallized layer is provided by sputtering or vacuum depositing alum¬ inum, nickel, tin, copper and the like. Most preferred is gold because of its high reflectivity for IR radiation, lower initial optical transmissivity and its resistance to oxidation. The conductivity of the metallized layer is immaterial for the purpose of this invention, as the intermediate layer is substantially electrically insulated by the upper and lower laminae, and each of which is typically formed from insulating materials. An appropriate choice of a metal for the reflective intermediate layer may be made by reference to the teachings in the text "Physics of Thin Films" by J. L. Vossen Vol 9, Academic Press, New York (1977). The photograph or any other writing, for example, coded information on a last will and testament, is preferably provided with colloidal carbon as before, requiring that the laminae be thick enough to provide opacity. If the code is provided in a "white" powder which is not visible against the normally reflective white surface of the base sheet, the writing is hidden from view even when the document is held up and viewed against a strong light. It will now be evident that any coded document, coded as disclosed herein, can make it essentially tamper-proof, avoiding costly legal battles.

To avoid using an infrared-permeable ink, the auxiliary layer of spread- able medium may be a thin layer of visible-light-scattering particles. Such particles are microspheres necessarily having a diameter in the range from about 0.5μm to O.όμm (micrometers) commercially available under the Scotch-Lite^® brand from 3M Company. Such a thin layer of microspheres may be deposited from a suspension in a suitable liquid. The specific size range of the micro- spheres is required to scatter visible light which is reflected from the inter- mediate layer, and to allow infrared hght having a wavelength in the range of about 0.8μm or higher, to be transmitted so as to increase the contrast of the code read.

When so scattered, the visible hght cannot be seen by the reading means in the reader, and the contrast between the reflected infrared hght (substantially all of which is transmitted through the spreadable medium) and that absorbed by the bar code is increased.

It should be noted that Scotch-Lite microspheres are routinely used in the paper industry to reflect substantially all the visible light which falls upon paper containing them. In such a use (as a reflective material) the sizes of the micro- spheres are randomly scattered over a wide range with the specific intent of per¬ forming a mirror-function, that is, not transmitting any hght, irrespective of its wavelength. The high reflectivity of the intermediate layer provides from 50% to 90% contrast on the bar code pattern in the IR region, depending upon the reflectiv¬ ity of the metallized layer and the effectiveness of absorption or scatter of the infrared permeable auxiliary layer, whether ink, paint, dye, or microspheres. The components of the laminated card are preferably adhesively bonded together with an adhesive which is essentially permeable to infrared light. Such an adhesive is commonly available rubber cement, or the glue in a commercially available solid glue stick. Most preferred is an infrared transmitting epoxy resin such as Epon 828 from Shell Chemical. When the intermediate layer is support- ed on a thin sheet of thermoplastic synthetic resin, for example poly (vinyl chloride), the thin sheet may be thermally bonded to the base layer and to the upper layer dispensing with the use of an adhesive. In another embodiment, the rear surface of the top sheet and the front surface of the base sheet may each be coated with a thermally bondable resin which is essentially transparent to the wavelength absorbed by the indicia of the code.

It will now be evident that the best mode for producing a coded document which provides no clue that it is coded, will depend in large part upon the econ¬ omics of manufacturing the document, particularly with respect to the imprinting of the code within it, and more particularly when the code is a textured code. Having thus provided a general discussion, described the coded document in detail, and having illustrated specific embodiments with examples of the best mode of making and using it, it will be evident that the invention has provided an effective and economical solution to a difficult problem. It is therefore to be understood that no undue restrictions are to be imposed by reason of the specific embodiments illustrated and discussed, except as provided by the following claims.

Claims

1. A laminated document comprising, an essentially opaque upper lamina or top layer having an upper or front surface imprinted with insignia with ink which absorbs and reflects wavelengths in the range from 4000A to 7000A, said upper lamina and ink being permeable to a preselected wavelength in the range of infrared or ultraviolet regions; a lower lamina or base layer having an upper reflective surface which reflects said preselected wavelength, and a lower surface; coding insignia adapted to be read by a device using light in said predetermined wavelength, and concealed from human view in an intermediate zone between said lower surface of said upper lamina and said upper surface of said lower lamina, said coding indicia being fixedly imprinted in said zone with material which absorbs said preselected wavelength; whereby said coding indicia is adapted to be read with said predetermined wavelength by a reader mans sensitive to the contrast between signals from said coding indicia and said reflective surface.

2. The document of claim 1 wherein said document is an identification card, said preselected wavelength is provided by an infrared beam.

3. The document of claim 2 wherein said coding indicia is a fingerprint.

4. The document of claim 2 wherein said coding indicia is a bar code.

5. The document of claim 1 wherein said coding indicia is a photographic likeness imprinted in dots having a diameter of at least 905 nm.

6. The document of claim 1 wherein said coding indicia is defined with an inkless material which absorbs in the infrared region.

7. The document of claim 6 wherein said inkless material is selected from the group consisting of microscopic particles of powder defining said indicia and an organic pigment each of which is visible to the human eye before said document is laminated.

8. A standardized document comprising an intermediate layer which is substantially light-reflective and substantially coextensive with said document, said intermediate layer having a code imprinted thereupon which absorbs light in the infrared region, said intermediate layer being sandwiched between an upper lamina and a base lamina, said upper lamina printed with an ink which absorbs in the visible wavelength but is transparent to light in said infrared region, said ink is printed on said upper lamina of card stock which reflects substantially all hght in the visible spectrum, and transmits rather than reflects substantially all infrared hght used to read said code, and said intermediate layer is imprinted with coding indicia which will absorb infrared light and reflect substantially all hght not incident upon said coding indicia.