US2075538A - Safety paper - Google Patents

Description

v Patented Mar. 30, 1937 UNITED STATES;

PATENT OFFICE SAFETY PAPER No Drawing. Application August 2, 1932, Serial No. 627,300

4 Claims.

This invention relates to safety .paper for checks, commercial paper, bonds, and other documents in which it is desired that the making of alterations shall be revealed, and it relates more 5 particularly to that class of safety paper wherein the paper carries substances applied thereto .or incorporated therein and adapted to change conspicuously in color when an attempt is made to alter with an ink eradicating agent writing in ink that appears on the paper.

Safety paper carrying, by reason of being incorporated therein or applied thereto, certain chemical substances or materials capable of causing a change of color on or in the paper as a result of the action of oxidizing or bleaching agents contained in ink eradicators has been known in the prior art. In some cases these chemicals have constituted an ingredient of an ink used for printing a design upon the paper, and in other cases they have been incorporated in the paper during the making thereof.

The substances heretofore known and used in safety paper have possessed disadvantages which render their use undesirable or ineffective. For example, certain of the substances previously employed lack stability and have a tendency to change in color gradually on exposure to air or to light, or a tendency to lose their effectiveness by lapse of time even when protected from air and light. Certain of the substances previously employed are too feeble in their reaction with ink eradicators, in that they develop so slight a change of color upon treatment with ink eradicators as to give an unsatisfactory indication of an attempted alteration. Certain of the substances previously employed possess such high inherent coloration that an effectively concentrated 'or dense distribution of the substances on or in the paper, and especially when they are distributed on the surface of the paper by a-pririting operation, necessitates an over-printing orcovering; and in the making of white or substantially white papers or lightly-tinted papers, only very small quantities of such substances of high inherent color can be used and such small quantity is incapable of giving a 'sufncient color change to indicate clearly a fraudulent alteration. Certain of the substances previously employed are initially .colorless, but such ,of those substances as are capable of developing a sufliciently conspicuous color change upon treatment with eradicators and are sufiiciently stable to retain their initial colorlessness, are in many instances too expensive and require great effort and care in distributing them on or in the paper.

(Cl. ill-67.95)

Another disadvantage in the use of substances heretofore known is that each of them is reactive (i. e., will change color) only when an oxidizing agent is applied to the paper and not when a reducing agent is used; or is reactive only when a reducing agent is applied and not when an oxidizing agent is used. As is well known, most ordinary ink eradicators are bleaches, that is, they 7 are oxidizing in character because the principal constituents of most writing inks will be de-colorized by oxidation. But there are some ink constituents which are not bleached by oxidizing agents, and can be de-colorized only by reducing agents. Therefore a safety paper which is to be capable of protecting all ink writings, whether the ink be formed wholly of one orwholly of the other of these constituents, must be adapted to discolor when either an oxidizing or a reducing agent is applied to the paper as an ink eradicator.

The general object of this invention is to provide a safety paper which will develop, when attacked with an ink eradicating agent, a conspicuous and ineradicable stain constituting a change of appearance which is so permanent and prominent as to warn others into whose hands the paper may come that the same has been tampered with. j A feature of this invention is that the production of safety paper is accomplished by providing the paper with one or more chemical substances which have the property (hereinafter referred to as sensitivity") of causing .a permanent stain or change of color or deepeningof color to occur in those parts of the paper which may be attacked with an ink eradicator. It is immaterial to the present invention whether the safety paper made in accordance therewith is white,is lightlytinted, or (as by the use of neutral colors and dyes) has any desired degree of coloration, but it is one feature of this invention that, if desired, a relatively white or colorless paper may be made having substantial and useful sensitivity to ink eradicating agents. Moreover, it is immaterial to the present invention whether the safety paper made in accordance therewith carries the chemical substances which possess such sensitivity, .on the surface of the paper as a result of printing or within the body of the paper as a result of being incorporated therein; but it is one feature of this invention that, if desired, the chemical substance may be distributed upon paper by including it in an ink made from crystal varnish and then printing upon the surface of the paper with such ink.

A further feature of this invention is that the substances possessing such sensitivity, and which 2 5 a,o7s,sss

are employed for the purpose of giving an indication of an attempt to alter the paper, are relatively inexpensive and are readily applied to or incorporated in thepaper in effective condition 6 and with-a concentration or density eflective to' colorless and the substances are not readily dis- Iv cernible thereon, and the paper nevertheless posl5 sesses sufficient sensitivity to .the action of eradicating agenta- Accordingly, it is a feature of myinvention that the chemical substances employed for the purpose of indicating the use of eradicating agents upon the paper, while inher- 20 ently colored, nevertheless possess such sensitivity that substantially white or lightly-tinted papers carrying such substances may be produced. It is to be understood, however, that any use of the substances herein referred to falls within the 25 spirit of the invention although color may be imparted to the paper by use of neutral dyes or pigments and although decorative overprinting may be applied.

It is a feature of this invention that the stain 30 or discoloration resulting from the attack by ink eradicators upon safety paper made in accordance with this invention, cannot be removed from the paper except with strong acids which would destroy the paper.

35 It is a further object of thepresent invention provide a safety paper having the foregoing characteristics, which may be sensitive both to oxidizlng agents and to reducing agents, or may be sensitive. only to oxidizing agents, or only to re- 40 ducing agents.

This application is a continuation in part of my co-pending application 8. N. 463,365 filed June 23, 1930, in which I have disclosed safety paper carrying substances, of which the conspicu- 45 ous examples named therein are dehydrothiopara-toluidine which is yellow in color and cobalt ferrocyanide which is greenish gray in color, and which are capable of deepening or changing in color upon application of ink eradicating agents,

so and which are applied to the paper in such manner as to be normally substantially non-discemible thereon, either by being incorporated in the paper orby being included in a crystal varnish of light consistency which is printed upon the paper 55 as an ink. Also, in said application there is disclosed the distribution of such chemicals in or on the paper in such -manner that an attack with an ink eradicating agent causes a symbol or symbols to appear which convey a warning that th 5 paper has been tampered with.

Further objects and features of this invention will appear from the more detailed description herein, it being understood that various changes may be made, within the scope of this invention by those skilled in the art.

In accordance with this invention the substances which possess sensitivity are distributed throughout the entire area of the paper or throughout such portions thereof as may be at- 70 tacked, either by incorporating the substances in the paper during the making thereof, or by incorporating the substances in the paper after partial or full completion thereof, or by applying I the substances to the surface of the paper. In 75 the incorporation of the substa ces in. th p p during the making thereof they may be introduced in divided form or in complete or partial solution or in suspension in a liquid to the watery pulpprior to the introduction thereof into the Fourdrinier or other paper-making machine, or they may be'added to the pulp or to the paper at any suitable point in the process of manufacture of the paper so long as the pulp or web is suf- .flcien'tly moist to permit the chemical substance added to penetrate to a sufficient degree therev in. In such case the chemical substances dry on and with the paper during the drying thereof.

Also, the solution or partial solution or suspension of the chemical substance may be applied to the paper after the completion thereof in any manner which will result in an incorporation of 'the chemical substance in the paper. Obviously,

if one of the substances added to the paper is soluble in water and another substance so added isnot soluble, the insoluble substance may be suspended in the solution of the soluble substance.

In the application to the surface of the paper of the chemical substances possessing sensitivity, the substances are embodied in ink suitable for use on lithographic or regular printing presses. example of the production of such ink consists in mixing the chemical substances in a crystal varnish medium of light consistency such as No.

1, No. 0 or No. 00 varnish. Substances insoluble in varnish are introduced thereto in finely divided form' in suitable proportions such as one part of the chemical to three parts of varnish by weight. When incorporated in such an ink, chemical substances herein referred to which are insoluble in varnish, lose theiropacity and be- '35 come substantially transparent, and an effectively dense concentration of the substances on the paper can be effected by application of such proportions of the ink that the ink is not readily discernible on the paper. In fact, the embodiment 40 of the sensitive chemicals in such a varnish enables the use of many chemicals which could not otherwise be used because oftheir high inherent color.

I have found that the thionated condensation products of para-toluidine have a high degree of sensitivity (as defined above) to ink eradicators which are bleaching or oxidizing in character. The simplest thionated condensationproduct of para-toluidine is the substance which contains twp benzene rings and is called dehydro-thioparijtoluidine and is yellow. Higher members of The same series, containing three or four or more benzene rings, may also be used for the purposes of the present invention. Preferably, though not necessarily, the salts of the sulphonic acids of each of the foregoing substances may be used, such for example as the sodium or ammonium salt. A useful member of this .series is the sodium salt of the sulphonic acid of the member having four benzene rings, which is called primuline and is yellow. In addition, I have found that cobalt ferrocyanide which is greenish gray may likewise be used for the purpose here described. These substances are relatively inexpensive and are inherently colored and are highly sensitive (as herein defined) to oxidizing or bleaching agents. As a result these substances may be distributed upon or in the paper in such low concentration or density, or so thinly or lightly, that the substance carried by the paper imparts substantially no color thereto and is substantially not discernible, while at'the same time it is present in such quantity. as to give a conspicuous indication of attack by ink eradicat- One 25 ing agents. The substances mentioned in this paragraph are sometimes hereinafter referred to as substances in the first group.

I have also found that mercurous chloride, copper sulphate or oxalate, and bismuth tri-nitrate have a high degree of sensitivity to ink eradicators which are reducing in character. These substances are either colorless or are of such light inherent coloration, when present in effective quantities and concentrations here contemplated, as to be useful in substantially white papers. They are sometimes hereinafter referred to as substances in the second group.

If it is desired to make the paper sensitive to oxidizing or bleaching agents, any one of the chemical substances named in the first group above maybe incorporated.

If it is desired to make the paper sensitive to reducing agents, any one of the chemical substances named in the second group above may be incorporated.

It is intended that any of the substances named in the first group may be used in safety paper, with or without the incorporation of a substance of the second group; and any of the substances in the second group may be used with or without the incorporation of a substance in the first group. It is a useful feature of my invention, however, that any substance selected from one of these groups may be combined in safety paper with any substance from the other group to give a safety paper which is doubly protected, that is, reactive either to oxidizing or reducing agents. But the invention is not limited to such double protection, as a highly useful and satisfactory safety paper may be formed by the incorporation of a substance selected from either group (and especially from the first group) without the addition of a substance from the other group, as for example a paper containing dehydro-thio-para-toluidine.

If it is desired to make the paper sensitive both to oxidizing and reducing agents, any one of the chemicals in one group may be incor- F porated in the paper together with any one of the chemicals in the other group. I have found that the chemicals named are compatible in the same paper, do not destroy their respective sensitivity to ink eradicators and combine to provide a doubly protected safety paper.

The density or concentration with which chemical substances possessing sensitivity may be incorporated and distributed in the paper by adding them to the pulp or to the incomplete or complete paper may be varied within considerable limits. Also the density or concentration with which those substances may be applied to and distributed upon the paper by printing thereon with varnish containing the substances may be varied within considerable limits. Certain of the chemical substances named above are inherently colorless, as for example, mercurous chloride. Others have inherent coloration, as for example, dehydro-thio-para-toluidine, which is light yellow in color. In the case of the substances which are colorless, or substantially colorless, it is only necessary to incorporate in the paper a sufficient quantity to make the paper adequately sensitive. For example 1% by weight of mercurous chloride, on the weight of the paper pulp, will give a white paper sensitive to reducing agents. And, in the case of such colorless substances any suitable amount of ink containing them may be employed. In the case of substances named above which have inherent coloration, an amount of the substances should be incorporated in the paper or a quantity of ink containing the substances should be applied to the paper, which will give adequate sensitivity thereto, and at the same time will impart to thepaper a color within permissible limits of coloration. One particular useful feature of the substances mentioned above, especially the thionated condensation products of para-toluidine, is that they will produce an extremely sensitive safety paper when present in or upon the paper in such small amounts as to permit the making of a paper which is nearly, or substantially, white in color.

In this characteristic these substances represent a substantial advance over substances heretofore used or known for this purpose, since such prior substances, in order to obtain the desired degree of sensitivity, must be incorporated in or applied upon the paper in such quantities as substantially to discolor it. Such discoloration is especially inherentin the use of benzidine, which is suggested in the Sammet Patent No. 1,535,861.

Accordingly, the proportion and amounts of the slightly colored chemical substance disclosed hereinabove to be used in each case must be left to selection, depending upon the desired degree of sensitivity of the paper, the amount of coloration tolerated or desired therein, and the character of sensitivity which it is desired to have therein (whether sensitive to reducing agents, to oxidizing agents, or to both).

By way of example only, 1% of primuline (by weight on the weight of the paper fibres in the pulp) will produce a safety paper of light coloration which is sensitive to oxidizing agents.

Certain of the chemical substances mentioned in each group above are relatively insoluble in water solution. In one form of the invention I take advantage of this fact by incorporating one of these chemical substances in and throughout the paper pulp, before it goes upon the wire. in the form of a finely divided suspension. The minute and relatively insoluble particles are deposited upon the fibres and remain deposited thereon as the water is extracted and, as the paper dries out and hardens, these minute particles of the chemical substance remain incorporated in, and a part of, the finished paper.

Others of the chemical substances mentioned above (as for example, copper sulphate) are relatively soluble in neutral or basic solution, and others of said substances (as for example, the ammonium salt of the sulphonic acid of dehydrothio-para-toluidine) are somewhat soluble in acid solution. If desired these substances may be added to the paper pulp in solution, or in a saturated solution with an excess thereof added in the form of a suspension.

There is included within the scope of this invention the addition or incorporation of any of the chemicals named, in or within the paper at any convenient stage of the manufacture thereof, and in such quantities and/or amounts as shall be best adapted to produce a satisfactory safety paper; and also the use of the chemical substance herein named, in and as a part of substantially colorless inks which are printed upon the paper. It is intended in this application to cover the use of these substances in and as ingredients of washes or sizes which may be applied to the paper either during the period of drying or after drying has been completed.

The description hereinbefore given has been set forth in order to illustrate and describe one form or manner of application of the inven- 3. A safety paper having a light, normally substantially imperceptible s'irface application comprising a thionated condensation product of para-toluidine. 4. A safety paper having a light surface ap-" plication comprising a thionated condensation product of para-toluidlne mixed with a crystal Y varnish of light consistency.

JOHN WALLACE NEFF.