Method and means for protecting documents

Abstract

A safety paper composition is provided for protective documents in which a stabilized dye in the colloidal size range is dispersed. The dye which is substantially masked from view is sensitive to liquid ink eradicators such as bleach solutions and organic solvents in which the dye is soluble. A dye formulation is also provided, the dye being alcohol-soluble but which is stabilized with an alkaline agent, e.g., caustic soda, to render it water insensitive so that it can be easily dispersed together with either potassium iodide or manganese sulfate in a paper pulp slurry without dissolving away in the water and without coloring the paper to any substantial degree.

Description

This invention relates to safety paper and to a dye formulation therefor, including a method of utilizing said formulation in producing safety paper for protective documents.

Many methods have been devised for producing protective documents, such as checks, negotiable instruments, drafts, bonds, stock certificates or other instruments, to prevent such documents from being tampered with. Some means which have been proposed involved application to the paper of a special design which is affected by any attempt at alteration. Other means include the printing of various layers of ink on the paper, often with one of the layers being printed in invisible ink, such that any attempt at alteration causes a predetermined design to appear on the paper.

The use of other methods and formulations based on different chemical compounds in the production of safety paper are also known but generally such formulations are complicated and costly. For example, a product formed of three layers of paper is known, in which the middle layer is sensitized. Another method is to add a sensitizing agent to a paper pulp slurry so that the papers produced therefrom will react to certain types of ink eradicators. In many instances, such agents are dyes which tend to color the paper and also which tend to be water sensitive. Such papers, therefore, should be kept in a relatively dry environment.

It is thus the object of my invention to provide a novel dye formulation in which the dye is stabilized to the extent it will not prematurely color the paper into which the dye is dispersed.

Another object is to provide a safety paper composition characterized by the presence of a colloidal dispersion of an alcohol-soluble dye throughout the matrix of the paper, which dye is hidden until such time that an attempt is made to alter the paper by the addition thereto of a liquid ink eradicator, such as a bleaching agent (e.g., a hypochlorite solution) or an organic solvent which is capable of releasing said dye.

These and other objects of the invention will more clearly appear when taken in conjunction with the following disclosure, the appended claims and the accompanying drawing which is a schematic representation of a paper making process of the present invention.

Stating it broadly, one aspect of the invention resides in a safety paper composition characterized by colloidal dispersion therethrough (i.e., throughout the matrix thereof) consisting essentially of a small but effective amount of an alcohol-soluble dye of Azul Victoria B (generally known as Victoria Blue B designated as Color Index 44045), stabilized with an alkaline agent, for example, an alkaline agent selected from the group consisting of carbonates and hydroxides of ammonia and alkali metals, preferably caustic soda (NaOH).

As stated above, the stabilized dye should be colloidal in size. Such dyes can be reduced to colloidal size in a colloid mill consisting of a series of closely spaced discs, each rotating at a very high speed in a direction opposite to that of its immediate neighbors. The liquid dispersion medium, together with the substance to be dispersed, and the stabilizing agent are passed through the mill and, after a period of time, a colloidal suspension results. The foregoing method is well known in the art.

Thus, in preparing the dispersion, the dye Victoria Blue B (C.I. 44045), is subjected to the action of a colloid mill to produce particles that may have an average size ranging from about 0.01 to 0.2.mu. (micron). The dye is reacted with a solution of an inorganic alkaline reagent of pH over 9, and preferably at least about 11, for example, alkaline agents selected from the group consisting of carbonates and hydroxides of ammonia and alkali metals (Na, K, Li), whereby the dye is stabilized. An aqueous dispersion thereof together with potassium iodide or manganese sulfate provides a solution that can be readily applied to or absorbed by the paper near the finishing stages of paper making. Sodium hydroxide is preferred as the stabilizing agent for said dye and may be added to the colloid mill.

The amount of dye dispersion added to the paper composition is small but effective to provide a telltale stain or color when the paper is contacted by a bleaching agent (e.g., hypochlorite solution) or an organic solvent, such as ethyl alcohol, methyl alcohol, ether, acetone, and other organic solvents specific to the dye. A range of composition in the paper with respect to the stabilized dye is about 0.02 to 0.5 percent by weight of said dye, a preferred range being about 0.05 to 0.2 percent, for example 0.1 percent. The potassium iodide or manganese sulfate in the paper may range from about 0.02 to 0.5 percent by weight.

Where the dye is absorbed into the paper during the finishing stages of paper making, it is preferred that the dye formulation comprise said Victoria Blue B (C.I. 44045) dispersed in an aqueous solution containing caustic soda and potassium iodide. This provides a solution which is substantially colorless and which assures a uniform paper with the color substantially masked from view.

A typical solution formulation for applying to or for absorption into the paper is one comprising about 0.5 to 5 percent or 1 to 3 percent by weight of said colloidal dye, about 1 to 5 percent or 1 to 3 percent by weight of the dye-stabilizing alkaline reagent, about 1 to 6 percent or 1 to 3 percent potassium iodide or manganese sulfate as a reinforcing agent, and the balance essentially water.

It may be desirable to add 1 or 2 percent starch to the solution to thicken the mixture where this is desired.

A specific aqueous composition found particularly useful is one containing by weight about 2 percent of the dye, 2 percent caustic soda, 2 percent potassiun iodide and the balance essentially water.

When the foregoing solution is used, it is stirred rapidly to assure a uniform suspension. The solution may be applied uniformly to one side or both sides of the paper near the finishing stage before the drying rolls and dried or it can be actually added to the cellulose slurry during the paper making process with the potassium iodide omitted, the potassium iodide being thereafter applied to the paper near the finishing stage of the paper making process.

The art of paper making is well known and need not be discussed here. For example, a typical paper making process is the Fourdrinier system using an endless wire screen or belt upon which the paper pulp slurry is deposited. In this connection, reference is made to the book Manual of Industrial Chemistry by Allen Rogers (pages 1,050 to 1,065; published by D. Van Nostrand Co., 1926).

For example, during the making of the wet cellulose mix in the vat in the well known manner, a solution containing 2 parts by weight of Victoria Blue B, 2 parts by weight of the stabilizing agent NaOH and the balance water is added to the vat in a proportion to produce a cellulose slurry or paper pulp mix containing by weight 1 part of the dye, 1 part of NaOH and 998 parts of cellulose determined on the screen-dried basis. The mixture is passed through a shredder which provides a homogeneous pulp or slurry for delivery to another mixer which then feeds the uniformly mixed material onto an endless drying screen. The material is layed down to provide a continuous uniform sheet which is dried on the screen and the sheet then passed through and between an arrangement of contacting drying rolls which are heated. The dried paper is then fed into a tank containing a solution of potassium iodide, a typical solution being one containing 3% KI and the balance essentially water. The treated paper sheet is again passed through a series of drying rolls at the finishing stage and then rooled up as paper stock.

The foregoing process is shown schematically in the drawing. A vat 10 is shown comprising stirrer 11, into which vat a wet cellulose mix is added (wet paper pulp) and after preliminary mixing the wet cellulose is passed through shredder 12. The details as to the chemistry are given in the book mentioned hereinabove. Means are provided to add water as shown when needed and the shredded material then collected into mixer 13. The uniformly mixed pulp is then discharged to endless dry screen 14 to provide a continuous matrix of paper 15 which is then passed between drying rolls 16, following which the paper is fed between rolls 17 into coating or absorption tank 18 to be described later. Following this treatment, the paper is passed between drying rolls 19 and the dried paper coiled at coiler 20.

In the one embodiment described hereinbefore, an aqueous colloidal dye dispersion containing by weight, for example, 2 percent Victoria Blue B, 2 percent sodium hydroxide and the balance essentially water is added to the cellulose either to vat 10 or mixer 13, the amount being such as to provide a paper composition taken on the dry basis comprising 1 part by weight of dye, 1 part by weight of sodium hydroxide and 998 parts by weight of cellulose. That is to say, the final paper product will contain approximately 0.1 percent of the stabilized dye. After the laying down of the pulp on drying screen 14, the paper 15 with the dispersed dye is passed between finishing drying rolls 16 and then led into coating or absorption tank 18 via rolls 17, the tank containing an aqueous solution containing about 3 percent by weight of potassium iodide, the tank being located at the finishing stage of the paper making process. The potassium iodide treated paper is then passed between drying rolls 19 and then wound up on coiler 20.

In the alternative, instead of adding the dye to the pulp, all of the constituents can be applied to the paper during the finishing stage of the process by passing the paper without the dye from drying rolls 16 into tank 18 which contains an aqueous dye dispersion comprising by weight 2 percent colloidal Victoria Blue B, 2 percent sodium hydroxide, 2 percent potassium iodide and the balance essentially water.

As stated above, the advantage of stabilizing the dye with the caustic soda or other inorganic alkaline agent is that the colloidally dispersed dye can be carried through the aqueous media of the paper making machine without being taken up by the water. The advantage of working with colloidal dye particles is that the dye can be dispersed uniformly in the paper product either by adding it to the pulp during paper making or applying it to the paper itself near the finishing operation.

Thus, the paper need contain only a small but effective amount of the stabilized dye and the alkaline reagent and a small but effective amount of potassium iodide. These materials can be present in the paper in amounts by weight ranging from about 0.02 to 0.5 percent (preferably 0.05 to 0.2 percent) Victoria Blue B, about 0.02 to 0.5 percent or 0.05 to 0.2 percent alkaline reagent (e.g., NaOH) and 0.02 to 0.5 percent (preferably 0.05 to 0.2 percent) of KI and the balance essentially the paper matrix.

Summarizing the foregoing, dye formulation for use in manufacturing the safety paper may comprise an aqueous dispersion of colloidal particles of Victoria Blue B (C.I. 44045) in an amount ranging by weight from about 0.5 to 5 percent stabilized with about 1 to 5 percent of the alkaline dye-stabilizing agent and containing 1 to 6 percent of potassium iodide or manganese sulfate, and the balance water. The foregoing can be applied to the paper as stated hereinbefore. A more preferred solution is one containing about 1 to 3 percent of the dye Victoria Blue B stabilized with about 1 to 3 percent sodium hyrdoxide, and also containing about 1 to 3 percent potassium iodide and the balance essentially water.

Broadly speaking, one method aspect of the invention comprises preparing a dye formulation comprising a colloidal dispersion of about 0.5 to 5 percent by weight of said alcohol-soluble dye (Victoria Blue B, C.I. 44045) stabilized with about 1 to 5 percent by weight of a dye-stabilizing alkaline agent. The pH of the solution should be over 9 and preferably at least about 11. The alkaline agent may be selected from the group consisting of carbonates and hydroxides of ammonia and alkali metals, and the balance essentially water. The additional steps include providing a paper pulp slurry, adding to said slurry an amount of said dye formulation such that the amount of said dye in the slurry based upon the dry weight of said paper pulp ranges from about 0.02 to 0.5 percent, and then forming a paper product in the usual manner with a dispersion of said stabilized colloidal dye therein. After the paper product has passed through the drying rolls, it is then contacted with a solution of potassium iodide which is absorbed into the paper and the paper then dried by passage through the drying rolls. The latter solution may contain 1 to 6 percent potassium iodide or manganese sulfate. The dye in the formulation preferably ranges in particle size from about 0.01 to 0.2.mu..

As stated hereinbefore, in the alternative, the solution containing by weight about 0.5 to 5 percent of the dye, about 1 to 5 percent of the alkaline reagent, about 1 to 6 percent potassium iodide or manganese sulfate and the balance essentially water, may be applied to the surface of the paper or absorbed into it at or near the finishing stage of the paper making process and the paper thereafter dried.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and the appended claims.

Claims

1. As an article of manufacture a safety paper composition characterized by a colloidal dispersion therethrough of a small but effective amount of an alcohol-soluble dye consisting essentially of Victoria Blue B stabilized with an alkaline agent selected from the group consisting of carbonates and hydroxides of ammonia and alkali metals, the paper also containing a small but effective amount of one of the reinforcing compounds potassium iodode and manganese sulfate such that the stabilized dye is uniformly masked and rendered water insensitive and such that when a selected portion of said paper is contacted by an ink eradicator selected from the group consisting of a bleaching agent and an organic solvent for said dye, the dye is caused permanently to strain said paper at said selected

2. The safety paper of claim 1, wherein the average colloidal size of said stabilized dye ranges from about 0.01 to 0.2 micron and wherein the amount of dye in said paper ranges from about 0.02 to 0.5 percent by weight of

3. The safety paper of claim 2, wherein said dye is sodium hydroxide-stabilized and wherein the amount of dye in said paper ranges

4. The safety paper of claim 1, wherein said stabilized dye has an average colloidal size ranging from about 0.01 to 0.2.mu., wherein the amount of stabilized dye ranges by weight from about 0.02 to 0.5 percent, and wherein said reinforcing compound is potassium iodide ranging by weight

5. In a method of producing safety paper, the improvement which comprises, uniformly dispersing through said paper a small but effective amount of a colloidal alcohol-soluble dye consisting essentially of Victoria Blue B stabilized with an alkaline agent selected from the group consisting of carbonates and hydroxides of ammonia and alkali metals, said paper also having added thereto a small but effective amount of one of the reinforcing compounds potassium iodide and manganese sulfate such that the stabilized dye is uniformly masked and rendered water insensitive and such that when a selected portion of said paper is contacted by an ink eradicator selected from the group consisting of a bleaching agent and an organic solvent for said dye, the dye is caused permanently to stain said

6. The method of claim 5, wherein the amount of dye dispersed in said paper ranges by weight from about 0.02 to 0.5 percent and wherein said reinforcing compound is potassium iodide ranging by weight from about 0.02

7. A method of producing safety paper which comprises:

preparing a dye formulation comprising an aqueous colloidal dispersion of about 0.5 to 5 percent by weight of an alcohol-soluble dye consisting essentially of Victoria Blue B stabilized with about 1 to 5 percent by weight of a dye-stabilizing alkaline agent selected from the group consisting of carbonates and hydroxides of ammonia and alkali metals, and the balance essentially water, the pH of said solution being over 9,

preparing a paper pulp slurry,

adding to said slurry in amount of said dye formulation such that the amount of Victoria Blue B dye in said slurry based upon the dry weight of said paper pulp ranges from about 0.02 to 0.5 percent,

forming a paper product in the usual manner with a uniform dispersion of said stabilized colloidal dye therein,

contacting said paper product with a solution containing 1 to 6 percent by weight of one of the reinforcing compounds potassium iodide and manganese sulfate,

and then drying said paper,

whereby a safety paper is provided such that when a selected portion of said paper is contacted with an ink eradicator selected from the group consisting of a bleaching agent and an organic solvent for said dye, a

8. The method of claim 7, wherein said alkaline agent is sodium hydroxide and wherein said colloidal dye ranges in average size from about 0.01 to

9. A method of producing safety paper which comprises:

preparing a dye formulation comprising an aqueous colloidal dispersion of about 0.5 to 5 percent by weight of an alcohol-soluble dye consisting essentially of Victoria Blue B, about 1 to 5 percent by weight of a dye-stabilizing alkaline agent selected from the group consisting of carbonates and hydroxides selected from the group consisting of ammonia and alkali metals, and about 1 to 6 percent by weight of one of the reinforcing compounds potassium iodide and manganese sulfate dissolved therein,

said aqueous dispersion having a pH of over 9,

preparing a paper pulp slurry,

forming a paper product from said slurry in the usual manner up to the finishing stage thereof including passing said paper product between heated rolls,

uniformly contacting said paper product with said foregoing aqueous dispersion thereby absorbing said dispersion therein,

and then drying said paper,

whereby a safety paper is provided such that when a selected portion of said paper is contacted with an ink eradicator selected from the group consisting of a bleaching agent and an organic solvent for said dye, a

10. The method of claim 9, wherein the alkaline agent is sodium hydroxide, wherein the aqueous dispersion has a pH of at least about 11 and contains by weight from about 1 to 3 percent Victoria Blue B, about 1 to 3 percent sodium hydroxide and about 1 to 3 percent potassium iodide, and wherein said colloidal dye has an average particle size ranging from about 0.01 to

11. A dye formulation for use in manufacturing safety paper which comprises:

an aqueous dispersion of colloidal particles of an alcohol-soluble dye of Victoria Blue B in an amount ranging from about 0.5 to 5 percent by weight stabilized with about 1 to 5 percent by weight of a dye-stabilizing alkaline agent selected from the group consisting of carbonates and hydroxides of ammonia and alkali metals, and also containing dissolved therein about 1 to 6 percent by weight of one of the reinforcing compounds potassium iodide and manganese sulfate,

and the balance essentially water, the pH of said aqueous dispersion being over 9,

said formulation being characterized such that when said stabilized dye is uniformly dispersed in a paper product, the dye in the paper is masked until contacted by a liquid ink eradicator, whereby said dye causes a

12. A dye formulation for use in manufacturing safety paper which comprises:

a dispersion of colloidal particles of an alcohol-soluble dye in an average size range of about 0.0l to 0.2 micron consisting essentially of Victoria Blue B in an amount ranging by weight from about 1 to 3 percent, about 1 to about 3 percent of sodium hydroxide, about 1 to 3 percent by weight of potassium iodide and the balance essentially water, the pH of said dispersion being at least about 11,

said formulation being characterized such that when said stabilized dye is uniformly dispersed in a paper product, the dye in the paper is masked until contacted by a liquid ink eradicator, whereby said dye causes a permanent stain to appear.