US2262822A - Safety paper and the manufacture thereof - Google Patents

Description

' Patented Nov. 18, 1941 SAFETY PAPER AND THE MANUFACTURE THEREOF Francis L. Simons, Montclair, N. J., assignor to George La Monte & Son, Nutley, N; 3., a corporation of New Jersey No Drawing. Application September 2a, 1938, Serial No. 232,082

21 Claims.

This invention relates to safety paper including fraud-preventing writing material made of paper or other substance or composition adapted for printing or lithographing or for the inscription of writing thereon and for use, for example,

.in the manufacture of checks, drafts, bonds,

stock certificates or other instruments which it is desired to have protected against fraudulent alteration. This invention also relates to methods of making such paper.

There are many chemical substances which are known and which have the property, when incorporated with paper during the manufacture thereof or by impregnation therein or superficial application thereto, of developing a disfiguring stain upon the application of a chemical ink eradicator thereto by changing from a colorless to a colored substance, by becoming more intensely colored or by change in color or the like when the chemical ink eradicator is applied to the paper. The developed stain that results upon application of a chemical ink eradicator to the paper makes obvious any attempt by means of a chemical ink eradicator to alter or tamper with the paper. Some chemicals such as manganese sulphate, iodides, etc., change color when a bleaching agent is applied thereto but can readily be converted back to their original condition by application of a reducing agent. Other chemicals, however, such as the chemicals specifically .mentioned hereinbelow after having their color changed by the application of a chemical ink eradicator thereto cannot be readily reduced to their e original color and afford a record of attempted alteration of the paper that and 1,535,863 the use of primary amines such as benzidine, tolidin, dianisidine, and diphe'nylamine. and their derivatives is described. In Patent No. 1,839,995 aryl substances referred to therein as guanidine substances," e. g., diphenylguanidine, are described as stain-producing substances for use in safety paper. In Patent No. 2,061,632, there is disclosed a large number of amino-aryl-thiazoles, reference being made particularly to l-amino-aryl-thiazoles in which the v amino-nitrogen is directly bonded to the carbon 55 coloration.

of the thiazole ring and has at least one free amino-hydrogen and in which the aryl'group contains at most two benzene rings.

It is a purpose of this invention to incorporate stain-producing substances such as the stain-producing amines in safety paper in such a way that thorough impregnation is facilitated while at the same time eifecting a very permanent incorporation of the substance in the Paper. It is a further purpose of this invention to incorporate in safety paper acidic derivatives of stainproducing amine substances without adversely affecting the quality and ageing characteristics of the paper. It is a further purpose of this invention to incorporate stain-producing amine substances in safety paper in conjunction with ferrocyanide as an ink-fixingsubstance in such a way that the ferrocyanide does not decompose prematurely and discolor the paper.

Ferrocyanides, when incorporated in safety paper have the property of forming with iron compounds in ink certain deeply-colored compounds known as Prussian blue, the exact chemical nature of which is not certain and may vary to some extent, depending upon the proportions and character of the reacting substances. Prussian blue is highly resistant to ink eradicators in general use at the present time. The most commonly used ink eradicators have a chlorine bleach as a .basis. Another type of eradictor has potassium permanganate as a basis. The latter eradicator is normally followed in actual use by the application of some reducing agent such as sodium bisulphite to clean up the manganese dioxide deposited during the application of the permanganate. The Prussian blue formed by by writing with ordinary iron-containing ink on safety paper prepared with a ferrocyanide is resistant to the action of either of the eradicators referred to. The Prussian blue is especially resistant to the potassium permanganate type of eradicator. While the Prussian blue is also resistant to a chlorine bleach type of eradicator when the color has been developed to a relatively pronounced degree, faint coloration such as that produced when a very small amount of ferrocyanide is incorporated with safety paper can be affected to some extent by the chlorine bleachtype of ink eradicator.

The stain-producing amine substances mentioned above react merely with ,the chlorine bleach type of eradicator to produce disfiguring stains. They do not react with the potassium permanganate type of eradicator to produce dis- The stain-producing amine substances which have been mentioned above are commonly used in a Water-insoluble condition. The stain-pro ducing amine substances when so used are generally incorporated with the pulp in the beater during the manufacture of the safety paper. This method of incorporating the chemical in the safety paper is not altogether satisfactory inasmuch as there is considerable loss of the safety chemical during the formation of the paper from the pulp. Moreover, it is frequently desirable to treat paper that has already been manufactured so as to make it sensitive to chemical ink eradicators and this is difi'icult when'a waterinsoluble chemical is to be used.

There are water-soluble forms of stain-producing amine substances, the water soluble acid salts of such substances being the most common,

presence of li ht and tend to decompose so as to prematurely discolor the safety paper; Moreover, the water-solubility of such substances makes it possible to wash such substances out of the safety .pamr, thus destroying the effectiveness of the safety paper. The fact that stainproducing amine substances can be successfully washed out of safety paper is a serious drawback to the 'eiiectiveness or the protection afiorded by these materials.

According to one of the features of this invention a stain-producing substance such as a stain-producing amine is incorporated in safety paper while in a water-soluble acidic form and is converted into a water-insoluble form while incorporated in the safety paper by neutralizing the acidity of the substance. For example, a stain producing amine substance is incorporated in the safety paper in the form of a watersoluble acid salt and, while -it is incorporated in the safety paper, is treated to transform it into a water-insoluble stain-producing amine substance by neutralizing the acidity of the acid salt added to the safety paper. Other stainproducing substances such as stain-producing.

thioureas and their amino-derivatives may be incorporated in a similar way. .It is another feature of this invention that caustic alkali, neutralization in this manner is regarded as much less desirable than neutralizathe neutralization of a water-soluble acid salt of a stain-producing amine substance is accomplished while it is incorporated in the, safety paper by means of a buffer mixture. The. buffer is efiective to overcome the acidity of the stainproducing substance and has the greatadvantage of not being injurious in any way to the paper;

This invention may be illustrated, for example, in connection with the substance l-amino-5- chloro-benzo-thiazole. This substance while insoluble in water, is water-soluble when in the form of the hydrochloride. According to this invention 1-amino-5-chloro-benzo-thiazole hydrochloride in aqueous solution is added to safety paper and then is-transformedto insoluble form.

"For example, the hydrochloride is added to safety paper which contains a bufler such as a mixture aaeaeaa of mono-sodium phosphate and di-sodium phosphate or a mixture of borax or boric acid, or is added to the paper first, the paper thereafter being treated with the buffer. In either event the. 1- amino- 5 -chl0ro-benzo-thiazole-hydrochloride while incorporated in the safety paper is transformed by the louder from the water-soluble acid salt to a water-insoluble form. This is of advantage for the reason mentioned above, namely, that while the water-soluble hydrochloride is readily incorporated in the safety paper, it is rendered insoluble so, that it is very dificult to remove the stain-producing substance from the paper by washing the paper with water. It is of even greater practical importance that the aging quality of the paper is improved. When the l-amino-E-chloro-benzot mole-hydrochloride is applied to the paper,

it includes the hydrochloric acid forming partof the molecule and in addition 50?.19 free-hydrochloric acid which is necessary for the purpose of keeping this substance in solution. The solution as applied to the paper usually has a pH value below 4 and usually has a pH value of about 3. This causes the paper which is normally somewhat acid anyway to be removed from the bath in a distinctly acid condition. This additional acidity of the paper has a tendering effect upon the paper. The age resistance of the paper can be improved by increasing the pH value to about 5.5 and even a lesser degree of acidity than this is to be preferred for papers designed for long life.

The neutralization by means of a bufier of the acidity imparted to safety paper as a r'esultof the addition to the paper of an acid salt of a stain-producing amine substance is distinctly preferable according to this invention. By causing the acid salt to react with the buffer, it is not necessary to make the paper distinctly alkaline at any time or to treat the paper with strongly alkaline substances, nor is it necessary to run the danger of underor over-neutralizing the paper. While it is within the scope of this invention to neutralize the acidity of an acid salt of a stain-producing amine substance while the substance is incorporated in the paper by means of an alkali such as soda ash or a dilute tion accomplished by a bufier mixture. When a straight alkali is used, it is injurious to many types of paper and is essentially injurious to Paper which has been sized with the usual rosin sizing. Moreover, care has to be exercised in controlling the amount of alkali that is-used.

I have iound that a ferrocyanide may be successfully incorporated in safety paper together with a stain-producing amine substance. Ferrocyanides tend to be unstable standing by themselves or in the presence of an acid when applied to safety paper, with the result that the ferrocyanide decomposes so as to cause prematurediscoloration of l the paper. In my Patent No. 2,037,937, the stabilization of ferrocyanides incorporated in safety paper is described. The acidity of an acid salt of a stain-producing amine substance tends to cause premature decomposition of ierrocyanide applied to safety paper. I have found, however, that by incorporating a bufi'er with safety paper it is possible .to makea stable safety paper which has been treated both with a water-soluble acid salt of .a stainproducing amine and with a ferrocyanide.

T e use of a buffer containing alkali metal minor proportion of monosodium phosphate, it

is apparent that the disodium phosphate may be used by itself as a bufl'er to counteract the acidic eflect of an acid salt of a-stain-producing amine. Tri sodium phosphate may also be used but is normally less desirable than the disodium phosphate due to its greater degree of alkalinity.

A safety paper that contains a stain-producing amine substance and a ferrocyanide is extremely effective against all types of chemical ink eradicators'that may be applied thereto. While the stain-producing amine does not react with the permanganate type of ink eradicator, the inkflxing efiect resulting from the reaction of the ferrocyanide with ink containing iron such as the ordinary blue-black iron 'gallotanate writing ink is extremely resistant to the permanganate type of ink eradicator and afiords very effective protection, even when the ferrocyanide is present in only a relatively small amount. If the chlorine bleach type of ink eradicator is applied to the safety paper, the stain-producing amine substance immediately produces a discoloration or stain of a permanent character that shows that the paper has been tampered with and in addition the ink-fixing action of the ferrocyanide affords added protection when this type of ink eradicator is used. Therefore, a high degree of protection is afforded against both the permanregarded as being particularly efiective and are relatively inexpensive.

A further understanding of the preparation of safety paper according to this invention will be apparent from the following specific example which is illustrative of the practice of this invention. The paper is first treated with an aqueous solution of a water-soluble acid salt of a stain-producing amine substance, e. g., 1- amino-5-chloro-benzo-thiazole-hydrochloride. A solution of about 4% to 2% concentration of this substance is suitable for the purpose. The paper then may be dried or merely passed between squeeze rolls so as to press out its excess moisture and so as to make the surface of the paper free of the solution. If the paper is not completely dried it is preferable to'not only pass the paper between the squeeze rolls but also over a drying drum so that the surface of the paper may be free of excess solution of acidic character. The paper is then passed through a bath containing about 5% of sodium ferrocyanide, about 12% of disodium phosphate, and about 1% of monosodium phosphate. treating the paper withthis second bath, the paper is passed between squeeze rolls so as to remove excess solution and then is dried. The paper is then ready for use although further finishing, printing or ornamentation as desired may be applied to the paper. The finished paper preferably has a pH of about 6.0 to about 7.0 although satisfactory results are also obtained when the pH value is about 6.2 to about 7.3; but

these limits are not to be regarded as absolutely ganate type and against the chlorine bleach type of chemical ink eradicator. Moreover, due to the presence of the acid-alkali buffer in the paper, the stain-producing amine substance occurs in a water-insoluble condition and cannot be washed out of the paper.

It is also of great practical importance that the paper cannot be treated so as to wash out the safety chemicals. It has been mentioned above that stainyproducing amine substances can be washed out of safety paper containing such substances in water-soluble form by washing the paper with water. Even when these substances are in water-insoluble form they can be washed out of safety paper by using dilute acid. For example, substances such as benzidine or 1-amino-5-chlor-benzo-thiazole are soluble in dilute hydrochloric acid and substances such as guanidine substances are soluble in dilute acetic acid. When, however, a ferrocyanide stabilized by a buifer is present in addition to the stain-v producing substance, it is impossible to wash out the stain-producing substance. If the paper is washed with a dilute acid, the acid immediately causes the ferrocyanide to turn dark blue and to reveal the" attempt to alter the'paper. Therefore, the new paper of this invention, due to the combination of safety chemicals used, not only is effective against the different types of chemical ink eradicators which might be used, but also is effective against attempts to remove the safety chemicals from the paper and affords much more effective protection than that which has been regarded as possible heretofore.

In the practice of the invention using ferrocyanides, the soluble ferrocyanides are preferable,

namely, the ferrocyanides of the alkali metals (including ammonium) and of alkaline earths. The ferrocyanides of sodium and potassium are essential to the practice of the invention. In the foregoing example, the proportions given are based on the weight of the fully hydrated commercial salts that are added to the bath. The

bath containing ferrocyanide and monoand disodium phosphates has a pH value of about 7.0 to 7.4 when made up.

The sequence of operations mentioned above is regarded as preferable from the point of view of effectiveness and economy although the order in which the chemicals are added to the paper may vary. For example, the ferrocyanide and phosphate may be added to the paper prior to the treatment of the paper with the acid salt of the stain-producing amine substance. In such case,

the acidity of the acid salt is neutralized as the salt becomes incorporated with the paper and while the salt is within the paper.

sheet in the manner above described, the solu-- tion can. of course, be applied in any other manner as by spraying the sheet with thesolution, applying the solution locally by printing or otherwise, or in any other suitable manner. Whether the substances are applied through the paper or at the surface, the same are to be regarded as incorporated with the safety paper.

A stain-producing am ne substance can be incorporated at the time the paper is tub sized by mixing th substance with the sizing bath. This substance can also be included in a .dye bath and incorporated with the paper during the application of the dye to the paper.

After Further in this connection. the treatment of the-paper with a buffer may be performed as a separate step at have in the safety paper an'amount of alkali metalphosphate or other bufier material corresponding to about 50% to about 300% of the combined ferrocyanide and amine substance in the paper. The amount of ferrocyanide that is incorporated in the paper may be increased to about 5%, the maximum amount that the paper retains when impregnated with a saturated solution of a ferrocyanide. The proportion of stainproducing amine that is used may also be increased considerably, e. g., to about 1.0% by applying a more concentrated-solution thereof to the paper. In general the more ferrocyanide or stain-producing substance that is used, the more vigorous will be the ink-fixing property of the ferrocyanideand the stain-producing property of the amine substance. For purposes of economy it is preferable to use amounts such as those cyanide in the paper, the ferrocyanide may be omitted. In such case the procedure mentioned in the foregoing example may be followed, using the disodium phosphate and mono-sodium phosphate mixture to convert the l-amino-S-chloro benzo-thiazole-hydrochloride to an insoluble form. When the ferrocyanide is omitted, however, the advantages which result from the combined presence of stain-producing substance and ferrocyanide and which have been referred to above, are also omitted. While it is preferable to introduce the stain-producing substance in water-soluble form and convert it while incorporated with the paper to a water-insoluble formand combine the stain-producing compound in insoluble form with a ferrocyanide, the stain-producing compound in insoluble form may be in-' corporated with the paper, as by mixing it with the pulp in the beaters, and thereafter adding the ferrocyanide to the paper to' achieve the advantages that result from the combined presence of a stain-producing substance and. a ferrocyanide in the finished paper.

While this invention has been described in Y connection with specific examples, it is to be un- 1. A method of making safety paper which comprises incorporating with paper 3 a watersoluble acid salt of an organic aryl e adapted ,to react with a chlorine bleach to produce a stain and converting said substanceto a waterinsoluble' form by neutralizing the acidity ,of said salt: a

being in the presence of said buffer when said organic amine is contacted therewith.

3. A method of making safety paper which comprises incorporating in paper a solution of a we.- ter-soluble acid salt of a stain-producing amino.- aryl-thiazole substance and neutralizing the acidity of said substance to convert it into a water-insoluble form while said substance is incorporated with said paper.

4. A method of making safety paper which comprises incorporating a solution of awater-soluble acid salt'of a stain-producing amino-aryl-tln'azole in paper containing a bufier.

5. A method of making safety paper which comprises incorporating in paper a solution of a water-soluble acid salt of a stain-producing aminoaryl-thiazole and then treating the paper containing said incorporated acid salt with a solution containing a bufier.

6. A method of making safety paper which comprises incorporating in paper a solution of a water-soluble acid salt of a stain-producing amino-aryl-thiazole and then treating the paper containing said incorporated acid salt with a solution containing a bufier and a water-soluble ferrocyanide.

7. A method of making safety paper which comprises incorporating in paper a solution of a water-soluble acid salt derivative of benzidlne andneutralizing the acidity of said salt to convert it into a water-insoluble form while the substance is incorporated in said paper.

8. A method of making safety paper which comprises incorporating in safety paper a hydro-.

chloride of an organic aryl amine adapted to react with chlorine bleach to produce a stain, a ferrocyanide and a buffer, said hydrochloride being neutralized by action of said buffer while incorporated in said paper and said ferrocyanide being in the presence of said bufier when said hydrochloride is contacted therewith.

9. A method of making safety paper which comprises incorporating in safety paper l-amino- 5-chloro-benzo-thia'zole hydrochloride, an alkali metal phosphate and aferrocyanide.

10. A safety paper having incorporated therewith a water-insoluble organic aryl amine adapted to react with a chlorine bleach to produce a stain, a ferrocyanide, and a buffer, the pH-value of the paper being between about 6.2 and about 7.3. 11. A safety paper having incorporated therewith a water-insoluble organic and amine adapted to react with a chlorine bleach to produce a stain, a ferrocyanid and a buffer.

12. A safety paper having incorporated therewith a water-insoluble organic aryl amine adapted to react with a chlorine bleach to pro- 2. A methodof making safety pape'r'which comprises treating paper with a water-soluble acid-salt of an organic arylamine adapted to react with a chlorine bleach to'produce a stain, a ferrocyanide and a bufier, said acid salt being neutralized by the action of said bufier while incorporated in said paper and thereby converted into water-insoluble form anolsaid ferrocyanide --duce a stain, a ferrocyanide, and an alkali xfnetal with a stain-producing amino-aryI-thiazole, a

ferrocyanide, and an alkali metal phosphate.

15. A safety/paper having incorporated 1- amino-5-chloro-benzo-thiazole in insoluble form in the presence of a bufier and a soluble ferrocyanide.

162A safety paper having incorporated lamino-5-chloro-benzo-thiazole in insoluble form in the presence of an acid-alkali buffer and a soluble ferrocyanide, the pH value of the paper .being about 6.2 and about 7.3.

17. A safety paper having incorporated therein a substance adapted to react with a chlorine bleach to produce a stain, said substance being selected from the group consisting of anilin, anilin chloride, benzidine and its derivatives that contain the benzidine nucleus, tolidin and its derivatives that contain the tolidin nucleus, dianisidine and its derivatives that contain the dianisidine nucleus, diphenylamine and its derivatives that contain the diphenylamine nucleus, aryl guan'idine substances, and l-amino-arylthiazoles in which the amino-nitrogen is directly bonded to the carbon of the thiazole ring and has at least one free amino-hydrogen and in which the aryl group contains at most two benzene rings; and also having incorporated therein a ferrocyanide and a buffer.

18. A safety paper having incorporated therein benzidine, a water-soluble ferrocyanide, and a butler, the pH value of the paper being between about 6.2 and about 7.3.

19. A method of making safety paper which comprises incorporating with paper' in watersoluble acidic form a substance adapted to react with achlorine bleach to produce a stain,

said substance being selected from the group consisting of anilin, anilin chloride, benzidine and its derivatives that contain the benzidine nucleus, tolidin and its derivatives that contain the tolidin nucleus, dianisidine and its derivatives that contain the dianisidine nucleus, diphenylamine and its derivatives that contain the diphenylamine nucleus, aryl guanidine substances, and l-amino-aryl-thiazoles in which the amino-nitrogen is directly bonded to the carbon of the thiazole ring and has at least one free amino-hydrogen and in which the aryl group contains at most two benzene rings; and converting said substance to a water-insoluble form while the substance is incorporated with the safety paper by neutralizing the acidity of the substance.

20. A safety paper having incorporated therein'diphenylamine, a Water-soluble ferrocyanide, 4

and a buffer, the pH value of the paper being between about 6.2 and about 7.3.

21. A method of making safety paper which comprises incorporating in papera solution of a water soluble acid salt derivative of diphenylamine and neutralizing the acidity of said salt to convert it into a water-insoluble form while the substance "is incorporated in said paper.

FRANCIS L. SIMONS.

CERTIFICATE OF comes-non. PatentNo. 2,262,822. November 1 19in.

FRANCIS L. sInoN's.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 1, first column, line 1414., for the patent number "1,556,861" read --l,555,861-"- and second column, line 56, strike out "by"; page 2, second column, line 2, for orax or" read --borax and-; page 14., second column, line 56, claim 8, insert "a" before "chlorine" page5, first column, line 5 claim 16, after "being" insert -betweenq and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the' case in the Patent Office.

Signed and sealed this 25rd day of December, A, D. 19l1l.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.