US2331575A - Safety paper and method of making same - Google Patents

Description

`SAFETY PAPER AND METHOD OF MAKING SAME Filed Aug. s, 1940 y llNvlaN-roR w BY Y . ATTORNEYS Patented Oct. 12, 1943 UNITED STATES lPrzrlawr OFFICE -Francis L. Simons, Montclair, N. J., assignor -to George La Monte & Son, Nutley, N. J., a corporation o t New Jersey attempted erasure.

Application August 3, 1940, Serial No .350,:123 I 13 Claims. (Cl. 117-1) This invention relates to safety paper and method of making same.

It is a purpose of this invention to afford a safety paper that has the capacity to reveal attempts to erase by mechanical erasure legends Written thereon. It is a special advantage of safety paper embodying thisinvention that it i adapted to evidence attempted alteration of leg# ends written'thereon in pencil.

'Ordinary pencil markings or legends that have been applied to paper as byharfdwriting in pencil thereon are readily erasable by mechanical erasure, there being a varietyl of erasing com.- positions, generally made up in arrubber base, that are suitable for erasing pencil markings.

' Most writing pencils are made up withv a small eraser of this type at the end thereof.

Attempts haveheretofore been made'to make pencil legends more difficult to erase by providing so-called indelible pencils that include a by dining checl which after the figures giving' lead containing a coloring material that strikes 'sure so that the attemptedalteration of the pasiderable mechanical erasure is required to re-` move the lpencil legend and so that removal of the pencil legend by mechanical erasure will also remove the coloring material to a very pronounced degree.

The advantages of a safety paper of the characted described are several. It is often desirable to use a pencil instead of pen and ink in making notations and legends on paper, which legends should be protected from attempted alteration. An example of this character is afforded the amount d ue have been filled in are used by the waiter in making change to be returned by the-waiter tothe customer. Such dining checks, if-of the ordinary type that can readily be altered can be used by dishonest waiters in a fraudulent way. It is highly desirable that such dining checks be adapted to reveal any attempted alterations of pencil legends inscribed thereon. Use of pencil safety paper for dining checks is only one of many uses to which safety paper Y emboiving thisinvention may be put.

dye is carried by the surface of the coating without penetrating therethrough. The material of the coating is of 'any suitable color, preferably white or nearly so, and the color of the coloring material is of a contrasting color. The coating material while carrying the color of the Acoloring material at the surface therefor comprises `a substantial portion that is uncolored by said coloring material. v

When a paper constituted as above described is written upon with a pencil, the pencil forms a clearlyV inscribed legend of the usualcharacter. If attempt is made to erase the pencil legend by mechanical' erasure, however, the mechanical erasure tends to rub off the dye or othercoloring matter that is supercially carried by the coating so that wherever the mechanical erasure occurs kthe contrasting color of the underlying body of the coating material e.' g. white, becomes more prominent thereby clearly evidencing the It is very dimcult if not impossible to replace color of the coloring material that4 has been removed by the mechanical eras- For'the purpose of illustrating the practice of this invention and affording a better understanding thereof it will be described in connection with certain specific examples thereof and in connection with the accompanying drawing, wherein Fig. 1 is a cross section of a portion of a sheet l of safety paper embodying this invention on a very greatly enlarged scale,

Fig. 2 is a plan view of a sheet of safety paper embodying this invention, illustrating the effect of mechanical erasure thereon, and

Fig. 3 is a largely diagrammatic sectional elevation of suitable means for applying the coloring material.

In Fig. 1 the pencil safety paper comprises a sheet 'I0 of paper of any desired type and thickness. Usually the paper runs from about .002 to .025 inch in thickness, i. e. from paper .A

that is quite thin to paper having suillcient body to be somewhat boardy in character. 'I'he paper may be writing paper, book paper, tag board,

'box board, card board, bristol board or the like and is preferably not a highly absorptive type of Somewhat more generally the term paterial of the character aforesaid or other similar or equivalent sheet material suitable for inscription of legends in pencil thereon when treated casein together with a minor proportion of some alkaline material such as tri-sodium phosphate, sodium carbonate or the like to render the casein waten soluble. An exemplary formula for a suitable coating composition and a description of the manner of application of the coating will be given more in detail below. The coating is preferably applied so as to be uniformly of substantial thickness and so as to have a matte or eggshell surface.

Overlying the coating Il is a layer I2 of a suitable coloring material such as Methylene Blue, for example, the color of which is diierent from the color, e. g. white, of the underlying coating material. The dye adheres to the outside surface of the coating as a very thin deposit. In this connection the layers shown in Fig. 1 are not drawn to scale inasmuch as the relative thickness of the layer- I2 has been exaggerated for clarity in the showing in the drawing. As amatter of fact the layer I2 of coloring material is an extremely thin supercial deposit.

The layer I2 of coloring material may be cieposited uniformlyover the entire surface of the coating II or non-uniformly. In Fig. 2 the coloringv I2 is shown in -the form of a. plurality of parallel lines of dye separated by undyed portions. Alternatively the lines could be separated by intervening areas which are of less color intensity. In Fig. 2, the effect of a mechanical erasure is illustrated. On the-face of the pencil safety paper the legend 1 2 3 4 5 6 '7 appears and is to be regarded as having been placed thereon by pencil handwriting. If attempt is made to erase the gures 6 and 7 from the legend the effect of the erasure is that shown in Fig. 2. At and adjacent the figures 6 and 'I of the legend the coloring material I2 has been rubbed oil? so that instead of the blue colored linesvor other surface coloring of the paper a white area. appears that is in sharp contrast to the color of the remainder of the paper and clearly indicates the attempted alteration. .The faint o utline of the figures 6 and' 7 may still be visibie as shown in Fig. 2. This is in accordance with the normalA action of the pencil safety paper. The action of the pencil in inscribing the legend in the safety paper tends to abrade the surface coating somewhat and colored material from the lead pencil tends to work into the coating so that it is quite diflicult to remove by mechanical erasure. Thus, upon attempt to remove a pencil legend from the face of the safety paper, a faint outline of the original legend usually remains in the local area from which coloring material has been removed thereby enhancing the tell-tale evidence of attempted alteration.

The manufacture of the paper may be exemplied as follows. An aqueous binder solution may be made up containing 100 pounds of casein, 5 pounds of borax, 6.5 pounds of tri-sodium phosphate and 2 gallons of 26 ammonia together with water to form 100 gallons. The binder component, namely the casein, therefore is present in such amount that each gallon of solution contains 1 pound of casein. English china, clay is incorporated in the binder solution, about 100 pounds of the clay being employed for each pounds of casein. This coating mixture is applied to a paperl sheet or web so that the paper will carry about 5 to 8 pounds of the casein and clay 5 mixture (dry weight) per ream of paper measuring 17 x 22 inches.

The application of the coating may be made in a varietyvof different ways. For example the coating can be applied by a brush coater. an application of the coating composition carried by the paper web being spread uniformly by a plurality of oscillating brushes. Alternatively the coating can be applied by a roll coater, an application of the coating composition carried by l5 the paper web'being spread uniformly by rapidly rotating rolls between which the paper passes.

4United States patents, Nos. 1,597,218 and 1,597,-

219,.v may be cited as illustrative, of a suitable roll coater. An air brush coater may also be 20 used, an application of the coating composition carried by the paper being spread uniformly by a blast of air. United States Patent No.` 1,980,923

is illustrativeof an air brush coater. The coating may also be applied by a cast coating operation wherein the coating material is dried while in contact with a smooth surface as described in United States Patent No. 1,719,166. The coating material may also be applied during the manufacture of the paper. Thus paper from a paper machine, after it has been partially dried may be passed through a roll coater, the drying of the paper being completed thereafter. United States patents, Nos. 1,707,333; 1,921,369; and 2,044,281

- illustrate the application of coatings in this Way. Alternatively the coating may be applied while the paper is still on the screen of a Fourdrinier machine, the paper thereafter being made up and finished in the usual way, and for such an operation reference may be made to United States Patent No. 2,079,846. A still .further method of application consists merely in passing paper during 'the manufacture thereof through a tub-size bath, the paper carrying the coating composition being finished in the usual Way.

After the coating material has been applied in any of the ways mentioned above by Way of ex'- ample, the paper is subjected in subsequent treatments only to light calendering which leaves the coating with a light matte or eggshell finish. Preferably the coated paper is passed through a super-calender and whose rolls are entirely unweighted.

The paper which has been coated as above de- 1 scribed is then passed through a bath of coloring D5 material e. g. a dye bath. In its simplest form this can be done merely by passing a web of the paper carrying the superficial coating through a dye bath, removing excess solution and drying the paper thus treated.

In Fig. 3 is shown a simple type of apparatus that may be used to apply the coloring material. The dye solution II3 is contained in a tank Il. A web IB of the paper that has been coated and dried is taken from thev roll I5 and is subu merged in the bath I3 by causing it to pass under the roller I1. The web carrying the dye solution is then passed between pressure rolls I8 and I9. The roll I8 may be embossed with a suitable design while roll I9 may be plain. The paper web is subjected to pressure e. g. about pounds to about 250 pounds per inch of line contact between the rolls, and since the recesses 20 on the surface of roll I8 prevent paper underlying the recesses from being compressed, p0rtions only of the web are subjected to the pressure. The portions of the web subjected to the pressure take up more of the dye in the dye bath than the other portions of the surface of theweb. After being subjected to pressure between rolls I8 andy I9 the web is again submerged` in the bath I3 by causing it to pass under roller 2l and upon emerging from the bath is passed between the wringer rolls 22. The paper web thereafter is passed to a plurality of drying rolls 23 which may be heated and is subjected to drying until it contains about 6% of moisture.

The result of the foregoing operation is to `color the surface of the coating material that overlies the surface of the paper. The coating material is of high white color substantially throughout and the dye occurs only at the surover the entire surface of the coating but wherever the pressure isl applied by the embossed roll I8 the coloration is more pronounced sov that the surface of the paper is coloredwith two shades of the samecolor. The vpattern of the two shades is determined by the embossing on the roll I8. The pattern may be in the form of parallel lines, reticulated lines, portions in the form of aseal, etc. as may be desired. The occurrence of the dye in an overall pattern or design of different shades of the same color applied to the surface of the coating is to be preferred in thepractice of this invention.

In the above described apparatus rolls I8 and I9 may be omitted so that the coated paper may merely be immersed in the dye bath and then passed between wringer rolls 22 to remove excess of the dye solution before the paper is dried. In such case the coating will receive an overall application of dye that is of substantially uniform colo;` intensity throughout.

In addition to the foregoing any other means f for applying the dye to the coated paper as a thin application or laye; deposited on the surface of the coating may be employed such as spray application, printing operation, calender staining or the like.-

Referring'to the specific coating composition above described other alkaline materials may be used with'thecasein binder such as triethanolamine, sodium silicate, lime, caustic soda or the like adapted to cause the casein to occur in soluble form. l v i V l In addition to casein other binder materials may be vused for the coating. For example one pound of glue dissolved in one gallon of water affords a suitable binder 4solution which can 3 that it be nigh white in color and of'mmcient degree of nneness to be free from grit and also be well washed so as to be' freei'rom impurities such as soluble electrolytes or iron.

Another example of a satisfactory ller is satin white which is amixture of precipitated calcium sulphate and aluminum hydroxide. Blanc iixe, which is a mixture of precipitated barium sulphate and aluminum hydroxide, is also desirable. Other examples of suitable illlers are preg cipitated chalk (calcium carbonate). titanum diavoiding any excess of binder. on the other hand; i

be used with a ller such as china clay. Likev wise starch made up with 1 pound per gallon of water affords a desirable binder solution. Shellac may also be used 1 pound being dissolved per gallon of water .with the aid of a little borax or ammonia. Albumene. g. egg albumen may also be used as a binder. Such binders are either white or substantially colorless or are only lightly colored so that in combination with white or light colored pigments, a coating composition that is white or nearly so is produced. By reference to a coating, composition, ller, pigment or the like as being lightv colored, any material which is white or approximately white is intended.

The ller that is used may likewise be varied.-

oxide, zinc sulphide, asbestine, lithopone, etc.

While the foregoing filler materials may be` used separately they may be mixed together and it is usually preferable to do so as a better coating composition is afforded thereby. For example English china clay mixed in about equal 'proportions with satin white or blanc ilxe affords a very desirable filler.

yIn addition to the foregoing other iller ma` terials may' also be used. The foregoing fillers have' a high white color and are desirable for this reason inasmuch as it is usually desirable to have the coating that is-carried by the paper as white as possible. If the coating maybe of some other color than white then illlers having colors other than white may be employed. In

this connection many clays, especially of a. rea-v lac or the like is'preferably about 15 to 40 parts of the binder for each parts of filler. The optimum amount in any case will depend upon the filler Aselected and type of binder material. A

filler such as china clay can be used in relatively high proportion e. g. about 100 parts. of china clay to about; l5 parts of binder. When satin white is used it is usually desirable to employ more of the binder, e.'g. about 35 parts ot binder to-100 parts of the satin white. In general it is desirable to employ enough binder to hold the filler in place so that it will not easily rub olf,

that would impart excessive glossiness to the coating material as applied.- Depending upon the ller and binder being used, and upon the mechanical coating method, the final coating mixture may require more or less thinning with water so as to obtain a good working consistency.

In applying the coating composition by immersion in a size-tub it is desirable to keep the ller material in suspension so that the coating will will in itseli act as a protective colloid. Other protective colloid materials may also beincorporated in the suspension'oi' filler such as methyl cellulose, pectin, etc.

In order to promote the occurrence of the filler I in a state of suspension in the composition it is also 4desirable to employ a wetting agent of which many are' known such as sulphonated lauryl alcohol, sulphonated cetyl alcohol, certain sulfonium compounds. e. g. those described in United States Patent No. 2,192,906, various diamides,

e. g. those described in UnitedStates Patent No. 2,193,963 or the like. The presence of the wetting agent is not essential but is desirable in achievinguniformity of application of the coating composition in the practice of this invention.

colored pencils. The only limitation in this regard is that the color of the coloring material applied to the surface of the coating should be different in color or color intensity from the color of the pencil so that the legend will show up when inscribed on the paper. v

The coating material is applied to the paper so that preferably about to 8 pounds of the coating composition by dry weight per ream of sheets 17 x 22 inches will be deposited upon the papel'. not regarded as desirable to have deposited on the paper less than 2 pounds per ream of sheets 17 x 22 inches. While the coating can be appliedso that it will be in excess of 8 pounds per ream of sheets 17 x 22 inches the additional thickness of coating material ordinarily serves no useful purposes according to this invention I and may make the paper excessively bulky.

The amount of the coating composition that vis employed'is of considerable importance inasmuch as the coating composition serves to cover the bers of the paper sheet (e. g. the sheet i0 in the foregoing example) so that when the dye material is applied the dye will not strike through to the fibers. Heretofore it has been the practice in applying a dye to a sheet 0f paper to cause the dye to penetrate to substantial depth and special liquid vehicles and wetting agents have been used for this purpose. By way of contrast according to the present invention suiilcient coeting material is. caused to overlie the paper s0 that the dye'in the dye bath is prevented from,

contacting the fibers of the paper and preferably the dye from the dye bath merely adheres to the. surface of the coating composition. Penetration of the coating by the dye is reduced to a minimum and preferably does not occur to any substantial extent. The coating material carryingadyeorthelikeonlyatthesurfaceistobe distinguished from a coating material that is' colored throughout the thickness thereof.

The texture of the coating composition is such thatitwillreadilyrecelvelegendsinscribedin pencil thereon. To thisend the mineral filler materials especially hard abrasive filler materials have a somewhat abrasive action on pencil lead causingthepartilesofleadabraded fromthe 'penciltobe receivedbythecoating composition and become embeddedtherein. Moreovenbyprovidingthecoatingwithamatteoreggsh'ellnnish insteadofaglossysurfacethereceptionoflegends applied by a lead Apencil is facilitated. .A8 aforesaid the lead from a lead pencill appears toworkintothecting'soastobequitedimcult tommove. Fromthispointofview-itisdeslrable thatthecolormgmatetlalbeesreadilyremovablebymeehanicalensm'efremthepaper coating-spezielllegendathatniaybeinscribcd' thereon. Preferably, thle coloring material is more readily removable by mechanical erasure fromthe coating composition than an! pencil inscriptions applied to the coating composition .sothattheremovaloftheeoloringmaterldwill be veryapperentupon mechanical erasure sumcienttoresultinanysubstsntialremovelofa pmcillegendins'lbedmthepaper.

'lhepmeilthatisnsedininscrlbine aleend entire-pencil saletypapermaybeanordina!! leadpencilwhiehprodusse.grveyornenrlyblackv marking depending uponwhether'the pencil is hurra-sett Thepmcllsafebpeperisalso While lesser amounts may be used it While this invention has been described here.

inabove primarily from the point of view aiording a safety paper that is adapted to evidence attempted mechanical erasure of legends written thereon in pencil, it is apparent that safety paper embodying this invention is likewise adapted to evidence attempted mechanical erasure of legends written on the paper in other ways. Thus, for example, safety paper embodying this invention is adapted to reveal attempted mechanical erasure of legends written thereon by typewriter.

' The safety paper of this invention is likewise adapted to reveal attempted mechanical erasure of legends in the form of so-called carbon copies produced by writing with a pencil, a. typewriter or the like on a first sheet and transmitting the writing to an underlying sheet by means of car.- bon paper or the like interposed between the first sheet and the underlying sheet on which the carbon copy is produced. With regard to legends written in writing lnk on safety paper embodying this invention, the superflcially colored coating material comprising a filler and a binder readily receives'ink, and the ink when applied is very diiiic'ult to remove either by mechanical or chemical erasure and any attempted mechanical erasure will, be evidence in the manner above.

described.

The coloring matter or dye that is used in the coloring bath may vary widely depending primarily upon the color desired. For most purposes, basic dyes are regarded as preferable. Ex-

amples of such dyes are Methylene Blue, Methyl Violet, Malachite Green, Bismarck Brown, Saffranine, Rhodamine, etc. 5

Acid dyes may also be used, such as Buffalo 'Blue Black, Blue Black SX, Acid Green LX, Acid Violet, Croceine Scarlet, etc.

- to chemical ink eradicators, are Naphthol Green,

Palatine Fast Yellow, Palatine Fast Orange, and

New Red B. Dyes such as these are mentioned in order to illustrate the fact that the paper of this invention is designed primarily as a pencil safety paper without regard to whether or not the coloring matter that isused is sensitive to chemical ink eadicators.l When it is saidherein and in theclaimsthatadyeiscarriedbythesurface of, the coating of coating material that in turn is `adherent to a'paper base sheet. it is to be understood thatA the dye is carried superiicially as a stain on the surface of the coating,-.andthat no binder vehicle for the dye is present. As is the practice'in the dyeing or staining of materials. the dye is applied .in an aqueous solution that does not contain a binder vehicle. and this is to be distinguished from the formulation` of paints, lacquers, printing inks and the like, which safetycharacteristics in the practice of the invention.

Moreover, it is to be understood that the specific embodiments of this invention herein described have been set forth merely for the purpose of exemplifying the practice of this invention and that the exemplary embodiments may be varied considerably within the scope of this invention as defined in the following claims.

I claim: v

l. A safety paper adapted to evidence mechanical erasure of a legend written thereon, saidsafety paper comprising a base sheet, a coating of substantially white coating material which comprises substantially white mineral filler pigment and binder material that bonds said filler pigment to said base sheet as an adherent coating and which coating material is applied substantially uniformly to a surface of said base sheet so as to weigh at least about 2 pounds per ream yof sheets 17 x 22 inches, and a dye that is superflcially carried by the outer surface of said coating material without a binder .vehicle and that'does not penetrate through said coating material to said paper and that is readily removable by mechanical erasure to render more prominent the white color of said coating material.`

2. A safety paper according to claim 1 wherein said dye is a basic dye.

3. A safety paper adapted to evidence mechanicalerasure of a legend written thereon, which safety paper comprises a paper base sheet, a coating of light colored coating material applied to a surface o f said base `sheet so as to weigh about 2 to approximately 8 pounds per ream of sheets 17` x 22 inches, said coating material consisting essentially of inorganic filler sufliciently finely-divided not to impart grittiness to the coating and a binder that bonds said filler to said base sheet as an adherent coating adapted for the inscription of a legend thereon and containing about to about 40 pounds of said binder for each 100 pounds of said filler, and a dyeV that is carried by the surface of said coating as a' stain deposited from solution without a binder vehicle and that -does not penetrate said coating to subcoating material comprising a finely-divided mineral filler anda binder adapted to bondV said filler to said surface to form a coating vweighing at least 2 pounds per ream of sheets 17 x 22 inches and suitable for the inscription of a legend thereon, and applying an aqueous solution of a dye to the surface of the coating, the paper being subjected to pressure in local areas of predetermined design to cause the dye solution to be absorbed to greater degree'where said pressure is .,applied, thereby producingy a paper4 having a design distinguished by areas of different intensity of the same color, the dye solution not penetrating through the coating in any of said areas and not containing a binder vehicle and said dye as thus applied to the surface of said coating being readily removable by mechanical erasure to expose underlying coating `material uncolored by said dye.

5. A safety paper adapted to evidence mechanical erasure of a legend written thereon, which safety paper comprises a paper base sheet, a coating that is superciallyapplied to surface of said base sheet and that comprises a finelydivided inorganic ller pigment and a binder that bonds said filler pigment to said base sheet as an adherent coating suitable for the inscription ofa legend thereon, said coating material being applied substantially uniformly to said base sheet so as to weigh at least about 2 pounds per ream of sheets 17 x 22 inches, a dye that is carried by the outer surface of said coating without a binder vehicle and that vdoes not penetrate said coating to substantial depth, said dye being of a substantially different color from the color of said coating and being readily removable from the surface of said coating upon mechanical erasure'so as to expose' the contrasting color of said coating.

6. A safety paper according to claim 5 wherein said dye is fugitive dye adapted to be decolorized by a chemical ink eradicator, thereby affording a safety paper that is adapted to evidence attempted erasure either by mechanical erasure or by use of a chemical ink eradicator.

7. A safety paper adapted to evidence mechanical erasure |of a `legend written thereon, which safety paper comprises a paper base sheet, a coating of substantial thickness of coating material that is applied so as to overlie a. surface of said base vsheet and that comprises inorganic Ifiller which is sufficiently finely-divided not to impart grittiness to the coating and which imparts tothe coating a matte upper surface and a binder which bonds said inorganic iiller to said base sheet as an adherent coating adapted for the inscription of a legend thereon, said coating material being applied substantially uniformly to said base sheet so as to weigh at least 2 pounds per ream of sheets 17 x 22 inches, and a dye that is supercially carried by said coating without a binder vehicle and that does not penetrate substantially into said coating or to said base sheet, said 'dye being of a substantially different color from Vthe color of said coating material and being readily removable by mechanical erasure to render more prominent the color of said coating material..

8. -A safety paper according to claim 7 wherein said dye is 'applied so as to form a predetermined overall pattern deflned by areas of different color intensity.

9.A A safety paper adapted to evidence mechanical erasure of a legend written thereon, which safety paper comprises a paper base sheet, a coating of light-colored coating material that is adapted for the inscription of a legend lthereon and that is applied substantially iformly to a surface of said'base sheet so as to weigh at least about 5 pounds per ream of sheets 17 x 22 inches,

and a binder which bonds said inorganic filler to said surface of said base sheet as an adherent d coating and a d ye thatcontrasts with the light color ofsaid coating material and` that is carried by the surface of said coating without a binder vehicle and that does not penetrate substantially into said coating material, said dye being readily removable from the surface of said coating by mechanical erasure, so as'to expose the light color of said coating material. y

10. A method of making safety paper which comprises applying to the surface of paper a coating material comprising a nely-divlded mineral ller and a binder adapted to bond said iiller to said surface to form a coating weighing at least 2 pounds per ream of sheets 17 x 22 inches and suitable for the inscription of a legend thereon, and applying to the surface of the coating an aqueous solution of a dye having a color diierent from the color of said coating, the dye solution not penetrating through-the coating and not containing a binder vehicle, and said dye thus applied to the surface of said coating being readily removable by mechanical erasure to expose underlying coating material uncolored by said dye.

11. A method according to claim 10 'wherein said coating after application to said paper is subjected to light calendering to provide a matte surface.

12. A method according to claim 10 wherein said coating material comprising said ller and said binder is applied to said paper in the form of an aqueous composition containing a wetting agent.

13. A method according to claim 10 wherein said coating material comprising said filler and said binder is applied to said paper in the form of an aqueous composition containing a protective colloid.

FRANCIS L. SIMONS.

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