US 3560238 A
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Feb. 2, 1971 RQTHERY V 3,560,238
METHOD FOR PRINTING VISIBLE CHARACTERS WITH NARROW BAND FLUORESCENT INKS Filed May 26, 1967 DARK COLORED INTERFACE 4\ WHITE COAT 7 2 .F N B N /y////////3(// //2 PAPER BA SE INVENTOR. JOHN L. ROTHERY ATTORNEY United States Patent 3,560,238 METHOD FOR PRINTING VISIBLE CHARACTERS WITH NARROW BAND FLUORESCENT INKS John L. Rothery, Concord, Mass., assignor, by mesne assignments, to American Cyanamid Company, Stamford, Conn., a corporation of Maine Filed May 26, 1967, Ser. No. 641,606 Int. Cl. C09d 11/00, 11/16 US. Cl. 117-12 2 Claims ABSTRACT OF THE DISCLOSURE Information, such as typewritten symbols, is made both in visibly readable form and in a code in which one or more narrow-band fluorescent materials are present in inks for particular symbols, the presence or absence of the components being detectable by ultraviolet illuminationand detection of the particular fluorescent radiation produced.
Paper or other substrate is coated with a material which is capable of reacting with color forming components in the inks to form visible color images. The ink is transparent so that ultraviolet light which is used for the determination of the code can pass into it without being absorbed or attenuated by colored pigments. The visual component for optical reading forms a boundary under the fluorescent ink next to the paper and can be observed through the transparent ink. All of the advantages of sensitive response to ultraviolet light for code reading and the capability of visual reading are retained without offsetting disadvantages.
BACKGROUND OF THE INVENTION The use of inks having components which fluoresce in diflerent colors, and particularly inks containing components which are of extremely narrow band fluorescence, such as chelates of lanthanide ions having an atomic number greater than 57, has made possible coding of symbols either without the possibility of visual reading or in addition thereto and without showing that there is a special code present which requires reading out under ultraviolet or similar shortwave radiation. These inks are usually referred to as coded inks and form the subject matter of an application of Freeman and Halverson, Ser. No. 596,366, now Pat. 3,473,027 filed Oct. 14,- 1966, which is a continuation-in-part of an earlier application .Ser. No. 437,866, filed Mar. 8, 1965, and now abandoned. The Freeman and Halverson applications are assigned to the assignee of the present application. When such coded inks are used, it is possible to encode a number of symbols on a presence or absence basis equal to (2 )l, where n is the number of components present. For example, six components permit 63 symbols, which is suflicient for ordinary alpha-numeric representation, or seven if it is desired to have both upper and lower case letters. It is also possible to have a larger number of symbols from a given number of components by having various levels of concentration, for example, none, a moderate amount, and twice as much. In such a case, of course, the number of symbols possible is (3)1. The larger number of symbols is obtained at the expense of lowered precision in code reading, which is sometimes considered as analogous to signal to noise ratio in an electronic circuit.
In the Freeman and Halverson application the preferred coded components are complexes of lanthanide ions, as referred to above, the complexes being formed with suitable organic or inorganic ligands, and are frequently associated with certain synergic agents which minimize transformation of electronic states excited by ultraviolet radia- 3,560,238 Patented Feb. 2, 1971 tion into a lower state of excitation without emitting radiation.
The coded inks are for the most part transparent as far as their code components are concerned and may be used with or without pigments which permit the symbols or messages to be read visually without requiring code reading by ultraviolet illumination. Various other modifications have been described, for example, in which an ordinary symbol is typed and then small areas of the different coded inks superimposed onto it or adjacent to it. The advantages of having a visible symbol as well as a coded one are very great in many cases, for example account numbers on bank checks and the like, and so in the past it has been common either to incorporate coloring matter in the various coded inks or to type or otherwise imprint a colored symbol which is then overprinted or associated with small areas of the different coded inks. The presence of color in the ink results in strong absorption of ultraviolet radiation. This either requires extremely high intensity ultraviolet radiation for reading or reduces the accuracy and precision with which the code can be read. In other words, the great practical advantage of having symbols or messages imprinted on a substrate such as paper both in visual form and in code is obtained only at the price of some masking or attenuation of the fluorescent response when it is desired to read out the code. This has certain disadvantages, the obvious one being the requirement for intense ultraviolet radiation, and also it restricts the choice of different coded components fluorescing in a narrow band. In other words, only complexes of lanthanide ions which are very eflicient transformers of ultraviolet radiation into longer wavelength radiation can be used, and this restricts to some extent the choice of components; and where a large number of components are needed, as for example seven in the case of alphanumeric representation with upper and lower case letters, this can be a serious problem, though not so serious that coded inks are not practically useful.
SUMMARY OF THE INVENTION The present invention permits representation of symbols which can be visually read and at the same time encoded in coded inks. Essentially, in the present invention the ink which contains the coded components for each particular symbol is uncolored or transparent, so that ultraviolet and visible light can penetrate deeply and a very efficient fluorescence of the coded ink coding components is obtained. The coded inks contain an additional colorless component which is capable of reacting with other components to produce color.
Paper or other substrate is used with a coating which is either transparent or very light colored, for example white, and which contains the second component that reacts with the component in the coded ink to produce a colored image. This image is at the interface with the substrate, such as the paper base, and does not extend throughout the thin film of the coded ink itself. In other words, as far as the ink film is concerned ultraviolet light can penetrate readily and so high efficiency in readout is made possible. It should be noted that the colored image is only formed where the printed symbol is present, and the rest of the light or transparent coating above it permits ultraviolet light to enter freely. On the other hand, if the coloring material is in the coded ink itself ultraviolet light has to pass through this film, with the problems presented by attenuation, which have been discussed above in connection with the prior art.
The particular color-forming components form no part of the present invention, and any pairs of components which are transparent to ultraviolet light, at least as far as the component in the coded ink is concerned, may be used. The present invention has not developed new com 3 ponents which react to form color, as this is a very common thing in color photography and a number'of processes for reproducing documents. Some of the component pairs are colorless chemicals which react together to form azo dyes.
It should be noted that there is a slight distinction between color photography and the present invention because in many color photographic processes one of the components has to be in a form in which it will not react but only does so when reduced by silver formed in the photographic image. Thus, for example, certain nitroso compounds can be used which in contact with the silver of the photographic image are transformed into diazo compounds which are capable of reacting with the other component, which is usually a dye coupler that forms an azo dye of the particular color desired in the colored photograph. In the present invention, of course, there is no photographic process, and therefore the component I in the ink may be a component in the form in which it reacts directly with the other component in the coating on the paper or other substrate.
This is not to say that the component in the ink may not be similar to the components used in color photography, but in such a case, if it is not already in reactive form with the color coupler, there must be present in the coating on the paper a third component, such as a reducing agent, which transforms the component in the ink into a form in which it will react with the other component in the coating. Of course the situation may be reversed, that is to say, the two components may be in the ink and the material which on reduction or other chemical change reacts with one of the components may be in the coating on the paper. Ordinarily it is preferable to have only a single component in the ink, but the invention is in no sense limited thereto.
It should be noted that the present invention permits a variant which is sometimes of importance. For example, if it is desired to imprint the message only in coded ink form so that it cannot be read visually, all that is necessary is to use ordinary paper or other substrate instead of the coated paper which has the other component which is capable of forming a colored image in contact with the imprinted symbol in the coded ink. This is an advantage of the invention, but it should be understood that the combination of the invention requires both a coated substrate, such as paper, and the coded ink itself if it is desired to produce visually readable images.
BRIEF DESCRIPTION OF THE DRAWING The drawing is a section through coated paper on which a symbol has been printed in coded ink.
DESCRIPTION OF THE PREFERRED EMBODIMENTS In the drawing the paper base is shown at 1 with a white or colorless coating 2 which contains a compound capable of reacting to produce color. The symbol imprinted in colorless coded ink is shown at 3, and since the ink contains the other chemical or chemicals which form the colored image, a dark or colored image is formed at the interface between the ink film of the symbol and the white coating. Needless to say, the thicknesses of the various coatings in the drawing are greatly exaggerated for clarity.
As a typical example of the present invention, paper is 5 coated with a white compound having a small amount of a color coupler, ferric sulfate or'ferric ammonium alum, and the coded ink with the necessary components which form the code for the particular symbol imprinted contains another chemical, tetra'butyl ammonium thiocyanate, which reacts with the chemical in the white coating to produce the colored image 4. It should be noted that the narrow band fluorescing ink and its chemical component which reacts to form a color are transparent or substantially so to ultraviolet light so that on ultraviolet irradiation strong fluorescence in the colors corresponding to the code is produced. As has been pointed out above, particular coded inks are not per se the feature of the present invention. Thus, as a typical illustration, in the drawing the coded ink may have two components, one of them yttrium vanadate doped with dysprosium, which luminesces in the yellow, and the other yttrium vanadate doped with europium, which luminesces in the red. This is an illustration of a symbol which required for its code the presence of these two components. Other symbols, of course, would have different components.
I claim: 1. A symbol printed on a substrate in a coded ink corresponding to the symbol and comprising at least one complex of a lanthanide ion having an atomic number greater than 57 and an additional compound of a pair of color forming chemicals which react together to form a colored image, all of the constituents of the ink being substantially transparent to ultraviolet radiation, the substrate having a coating on its surface of the other compound of the color forming pair, whereby when the symbol is printed on the substrate the two compounds of the color forming pair react to form a colored image of the symbol.
2. A symbol printed on a substrate according to claim 1 in which the coded ink comprises a plurality of lanthanide ions having an atomic number greater than 57, each one fluorescing in a separate and unique color different from the other components.
ALFRED L. LEAVITT, Primary Examiner ALAN GRIMALDI, Assistant Examiner us. 01. X.R. 106-21; 117-335; 252-3013