Stencil duplicating inks

Patented June 12, 1951

2,556,902

UNITED STATES PATENT OFFICE

2,556,902

STENCIL DUPLICATING INKS

Thomas Seal Chambers and Robert Thompson Florence, Chicago, JUL, assignors to A. B. Dick Company, Chicago,DI·, a corporation of Illinois

No Drawing. Application April 16,1949, ' Serial No. 88,043

Claims. (Cl. 260—29.3)

This invention relates to-water base stencil du.plicating inks for use with rotary stencil duplicating machines or for use-in other stencilling Operations wherein ink is transferred through-a stencil to an impression -medium. 5

In a steneil duplicating -machine of the rotary type, ink is supplied in-continuous f ashion-to -an ink pad, other like reservoir or distributing medium. After uniform distribution therein, ink is transmitted ..through the openings of a-stencil to 10 the impression medium, -chiefly in response - to forces developed- at-the point of contact between a rotating cylinder and -the impression roller. For the most part, drying of the-applied-ink occurs'by absorption of'the vehicle-or carrier «into 15 the pores of the impression-medium or -/into the interstices .between the fibers of which - the¹ i-m pression medium may be formed.

The characteristics desirable in a stencil duplicating ink are manifold and, in many respects, 20 non-analogous to ink compositions commonly used for printing or writing. 'For example, in-order to function properly in the duplicating -machine, the ink. should have sufficient apparent body'to-minimizeTeakage from the cylinder and 25 the ink pad and to prevent-flooding of the-stencil. On the,other hand, to produce, uniform and good copy, it should have sufficient flow of a Desired.Character to.effect satisfactory transmission through :the stencil to the - impression medium 30 and’to enable uniform and rapid distribution ;of the: ink throughout the ink pad. Thejnk should be .sufficiently slow-dry ing. while in the machine to, minimize premature hardening .on- the ink -pad or clogging of .the stencil openings. At the same 35 time,: it should be quick drying when: applied-to the: impression medium; otherwise, it would -be necessary to resort'to special devices and costly practices in order to handle copy within a reasonable time and eliminate setoff. The ink-should 40 dry-without-feathering, without giving an-oily- or colored letter outline or “halo,” and it should not give “show-through,” which may be defined as visibility'from the opposite side of -the-impression-medium. -The ink -should also be stable and 45 non-corrosive to¹ the* machine parts with- which it might-come in -contact. Upon- drying, it should be-resistant to moisure, the common solvents, and other -substances - with - which the - copy -might come in-contact.

<To ihe best of our -knowledge,- stencil duplicating -inks -heretofore -produced fail to meet these requirements. - Such failure -may. -be attributed in part to the formulation of stencil duplicating inks with large amounts of oil, the greater portion of which is of the non-drying type, such as castor oil, palm oil, cocoanut oil, and the like. Oils in. such large proportion and of a non-drying character permit a highly objectionable degree of setoff and smear unless special devices are used in handling the copy. The commonest device to. cope with , this problem is the costly and awkward practice of slip-sheeting; that is, the insertion of interlayer sheets between successive copies as they are duplicated. The problem may be, alleviated to a limited extent by using, as the impression medium, highly absorbent paper stock which rapidly distributes the vehicle but then the use of highly absorbent impression medium makes-it practically impossible to. obtain sharply defined copy because of “feathering” of the ink.

High oil content is directly responsible for the presence of objectionable “oily letter” outline or “halo” in copy prepared with, oil base inks. /Stencil duplication with oil base ink is further burdened by the fact that its use is limited to impression media of a highly absorbent nature and is not used successfully, with hard or highly filled paper, such as card, ledger, bond, or enamel stock.

. Oil base^emulsion inks are formulated with; less oil to relieve some of the objectionable features of the non-emulsion inks, but many of the limitations inherent in the oils still remain. -Emulsion inks present other operating problems because they have-less stability and often separate at some stage prior, to transmission through, the stencil,, whereby; the ink pad or the stencil or both become clogged and prevent uniform ink distribution to complicate the production of good copy. In .addition, the inner phase, of the . ink. emulsion frequently contains sulfonated glycerides, that are corrosive, to. machine, parts or other elements with which the ink might be associated.

It -is an object of this invention to produce a stencil duplicating ink that is not subject to the objections to prior duplicating inks.

More specifically, it is an object of this invention to .-produce a .stencil duplicating ink that ds substantially free of oil and is thereby not limited by. the restrictions imposed by the use of oily substances.

Another object is to produce ..a stencil duplicating ink that is substantially free -of oil, yet has-flow of the desired character and in proper balance to operate successfully in stencil dupli2,556,902 eating machines and in the production of copy of good quality.

A further object is to produce an oil-free stencil duplicating ink which has the desired balance of slow drying while in the stencil duplicating machine and quick drying upon transmission to the impression medium·.

A still further object is to produce a stencil duplicating ink which may be used for duplication on hard, filled, or highly finished impression media, stocks upon which stencil duplication without slip-sheeting was practically impossible with stencil duplicating oil base inks heretofore used.

Another object is to produce a stencil duplicating ink which is quick drying to permit handling of the copy almost immediately after duplicating without fear of setoff or smearing, and which, upon drying, becomes substantially impervious to moisture, many hydrocarbons and solvents with which the copy might come in contact.

A still further object is to produce a stencil duplicating ink which is substantially non-corrosive, non-flammable, stable, safe and easy to manufacture and handle.

A very important object of this invention is to formulate a water base stencil duplicating ink without oils. We achieve these characteristics .with a formulation constituted with water as the major diluent and the vehicle for the tinctorial agent. The term “water base” is used because water is present as a major constituent; often the water content is as high as 75 or 85 percent.

Body or flow of the desired character is derived primarily from the incorporation into the ink composition of high molecular weight substances which are soluble in water or dilute aqueous alkaline solutions. The high molecular weight substance, in reality, serves two separate functions. It serves as the bodying agent in the ink composition; and it serves, subsequently, as an adherent base upon drying.

Suitable water base stencil duplicating inks embodying features of our invention have a measurable viscosity that is much lower than the viscosity of oil base inks or oil emulsion inks operable unjler corresponding conditions. Viscosity can be used as a measure for certain flow characteristics; yet, we find it impractical presently to define the desired flow characteristics rigidly and exclusively in terms of viscosity. When measured by a Stormer Viscosimeter operating under a 200 gram load at 20° C. with a standard cup having a thermometer well and a center baffle, suitable water base inks may give a reading between 35 and 150 seconds; whereas, many oil base inks give a reading between 400-500 seconds, and many oil emulsion inks give a reading between 325 and 400 seconds. The lower viscosity permissible with water base inks of the type produced by this invention favors more rapid and uniform distribution of the ink throughout the ink pad and greater ease of operation in the duplicating process.

As the high molecular weight substance, use may be made of organic materials capable of increasing the viscosity or body of the aqueous medium in which it is dissolved. Ordinarily, such characteristics are secured by the use of organic compounds and polymers having at least 30 carbon atoms, mostly in chainlike arrangement; more often, suitable compounds are measured by their average molecular weight which ordinarily is greater than 1000. Representative of suitable bodying agents of high molecular weight are the hydroxy resinous materials, such as polyvinyl alcohols; hydroxylated cellulose ether derivatives, including hydroxy ethyl cellulose, partially alkylated cellulose derivatives, such as methyl cellulose and ethyl cellulose having about one-third of the hydroxy groups alkylated, or water soluble salts of carboxy methyl cellulose or ammonium carboxy celluloses. Use may also be made of other relatively water soluble high molecular weight compounds, such as the carbohydrates, including starches, and certain sugars, dextrin, and the like; proteins, including gelatin, glue, casein and the like; polyethylene glycols; and resin forming material reacted to an intermediate stage of polymeric growth, such as the water soluble “A-stage” phenol-aldehyde resins wherein the phenolic component is of the type phenol, cresol, xylenol and resorcinol and the aldehyde is of the type formaldehyde, the intermediate being constituted primarily of phenol alcohols; or nitrogenous resin forming materials such as urea, melamine and guanidine reacted with an aldehyde to an intermediate stage of polymeric growth to provide water soluble substances such as methylol ureas. Characteristic of many of these materials are the free hydroxy and/or amino groups which influence water solubility and enable subsequent insolubilization by reaction with such materials as glyoxal.

Proper concentration of the high molecular weight substance in the ink composition required to impart the desired flow characteristics depends on its average molecular weight, the arrangement and type of constituent groups of which the molecule is formed, and the materials with which the high molecular weight material is associated in solution. As previously pointed out, it is convenient to define the concentration of high molecular weight material by that amount capable of giving a viscosity equivalent to 35-150 seconds measured with a Stormer viscosimeter under the described conditions. In actual practice, the desired viscosity may be secured with about 3-20 percent polyvinyl alcohol (depending on the molecular weight of the original polyvinyl acetate and the degree of hydrolysis thereof), 2-15 percent hydroxy ethyl cellulose, 1-10 percent methyl cellulose (depending on the degree of alkylation) 20-50 percent urea or phenol formaldehyde resin forming material, or 30-60 percent polyethylene glycol, depending on the molecular weight. The viscosity range is not to be taken as a strict limitation because flow requirements change according to changes made in duplicating machines in the course of developments, and the amount of bodying agent may change accordingly without departing from the spirit of the invention.

As tinctorial agents, dyes or pigments soluble or dispersible in the largely aqueous vehicle may be used. Representative of the class of dyes having the desired solubility characteristics are the nigrosine, triphenylmethane, rhodamine, thioflavine, auramine, quinone-imide, xanthane, sulphonated triphenylmethane, and nitro dyes. These include acid dyes, such as refer to the mono-, di-, and tri-sodium sulphonates of the nitro, azo, pyrazoline, quinoline, triphenylmethyl, diphenylnaphthyl methane, azine, xanthane, and anthraquinone groups. Suitable pigments include water-dispersible blacks such as carbon black; white pigments, such as zinc oxide or

2,556,802 &

titanium oxides; or colored pigments, such as malachite green, iron blue, cadmium yellow, and the like. When pigments are used, they usually are dispersed as the discontinuous phase in suitable carriers, such as water, resin solutions and 5 the like.

The amount of dye in the ink formulation depends on the chemical nature of the coloring material used. Some dyes, even when used in small quantities, are capable of imparting sufficient 10 color to lend legibility to the copy. With others, it is necessary to use higher concentrations Of dye to secure the desired effect. The lower limit of the dye concentration, therefore, is determined by its tinctorial strength which varies 15 widely from compound to compound, The upper limit often is influenced by the solubility factors or by the effect of the dye on other ingredients of the ink composition, aS, for example, in causing gelation of the resinous material. We have found 20 that 3 to 7 percent nigrosine WSJ is suitable for water base stencil duplicating inks. Other dyes may be used in corresponding ratio although more or less may be used according to their characteristics, as pointed out above. When pigments are 25 used, it is often desirable to use concentrations above 3 percent by weight with the upper limit in the region of 15 percent by weight or even more in some instances.

An important feature of our invention resides 30 in the possibility of insolubilizing the bodying, agent upon drying to render the copy resistant to moisture and many of the hydrocarbons, chemicals and solvents, including oils, greases, alcohols, and other materials with which the copy 35 might come in contact, insolubilization may be effected by reaction of the hydroxy or amino groups to form acetals, hemiacetals, cross-linked polymers, or condensation reaction products by the addition of aldehydes having latent reactivity 40 and incapable of activation while ih dilute solution. Excellent results have been obtained with carbonyl compounds of the type glyoxai. Glyoxal, for example, is soluble in water and it is latent while in dilute water solution. When used 45 in amounts ranging up to 5 percent by weight of the ink composition or about 5 to 20 percent by weight based upon the amount of the molecular weight substances, glyoxal is able to insolubilize the high molecular weight substance to resist go water, moisture, and many solvents, oils, greases, waxes, and other hydrocarbons which might come in contact with the copy. More rapid insolubilization may be secured by the use of more than 5 percent by weight glyoxal, and excellent _5Sresults are secured by the use of amounts ranging from 0.5 to 2 percent. Pyruvic aldehyde is illustrative of another suitable insolubilizing. _:agent but it is less reactive than glyoxal and may be used in higher concentration to accomplish go a degree of insolubilization.

In order to increase the penetrability ..into the . impression paper and in order to improve the characteristics of the ink with respect to distri- . bution through the ink pad and stencil, a wetting gg agent may be added to the composition. A suit- . able wetting agent may be selected from materials, such as the dioctyl esters of sodium sulfosuccinate (Aerosols), quaternary ammonium salts (Duponols), dibutylphenol sodium disulfonates 70 (Areskelene) .sulfonated ethers (Tensol), and the like. Less than 2 percent but more than 0.2 percent of the wetting agent ordinarily is sufficientto impart the desired Wetting characteristic, although more may be used when desired. 75

Another importafit feature of our new stencil duplicating ink composition comprises the addition of a humectant which reduces the (evaporating rate of the water diluent and is compatible with the aqueous solution of the substance of high molecular weight. More important, the added humectant has the characteristic of modifying certain flow properties of the ink composition. Such modification is not necessarily measurable by viscosimeters operating at high rates of shear but exists, in fact, to the extent that leakage of the ink pad is greatly minimized and duplicator operation is substantially simplified. Under high shear, such as the forces developed by the Stormer Viscosimeter of the shearing forces operating while the ink is being forced through the stencil during duplication, the modified flow properties are not apparent and the ink flows as a liquid having little additional viscosity. Polyhydric alcohols, such as ethylene glycol, diethylene glycol, triethylene glycol, polyethylene glycols, glycerine, polyglycols and polyalkylglycols and alkylolamines such as diethanolamine, triethanolamine, N-aCetyl ethanolamine, N-formyl ethanolamine, monoethanolamine sulphamate, monoisopropanolamine sulphamate and the like exhibit these characteristics, especially with solutions containing hydroxy celluloses. Polyhydric alcohols are not readily volatilized and they remain after the water has been removed to flexibilize the adherent base. In a specific application, 1 to 25 percent by weight may be used with hydroxy ethyl cellulose of medium viscosity while amounts up to 40 to 50 percent by weight may be used with the same material of higher viscosity grade. Corresponding amounts of other polyhydric alcohols with hydroxy ethyl cellulose or other high molecular weight substances may be used, the upper limit of concentration being that at which instability results. When more is used, there is a tendency to disturb the structure and stability of the colloid composition.

We prefer to use a polyhydric alcohol and a latent insolubilizing agent, such as an aldehyde, in the same formulation. When so formulated, the aldehydric substance is able to react with the polyhydric alcohol and the high molecular weight compound when constituted with hydroxyl ' or amino groups, the reaction being in the nature of condensation or acetalization to form acetals, hemiacetals, and cross-linked polymers or copolymers. Our invention also contemplates the use of one without the other. When the aldehyde is omitted, the ink still has some degree of water resistance because the polyhydric alcohol is capable of functioning as a protective agent.

Without limiting our invention to any particular composition, the following examples, given in parts by weight, will serve to illustrate suitable stencil duplicating inks embodying features of our invention:

Example I

<td> Percentage</td><td> Material</td>

<td> 5.0</td><td> Nigrosine WSJ.</td>

<td> 15.0</td><td> Polyvinyl alcohol (low viscosity grade) (4-6 cp. in 4%</td>

<td></td><td> water solution at 20° C.).</td>

<td> 1.0</td><td> Dioctyl ester of sodium sillfosuccinate (Aerosol OT).</td>

<td> 10.0</td><td> Ethylene glycol.</td>

<td> 1.5</td><td> Glyoxal (in 30 percent solution).</td>

<td> 67.5</td><td> Water,</td>

<td> 100,0</td><td></td>

Viscosity, 120-130 Stormer seconds.

2,556,003

Example II

Example VIII

<td> Percentage</td><td> Material</td>

<td> 15.0</td><td> Carbon black in 40 percent aqueous dispersion (Aquablack M).</td>

<td> 1.0</td><td> Alkyl aryl sulfonate.</td>

<td> 10.0</td><td> Diethylene glycol.</td>

<td> 1.0</td><td> Glyoxal (in 30 percent solution).</td>

<td> 7.0</td><td> Polyvinyl alcohol (medium viscosity grade) (20-25 cp. in 4 percent water solution at 20° C.).</td>

<td> 66.0 100.0</td><td> Water.</td>

Viscosity, 110-120 Stormer seconds.

<td> Percentage</td><td colspan="2"> Material</td>

<td> 5.0</td><td> Nigrosine WSJ.</td><td></td>

<td> 1.0</td><td> Wetting agent.</td><td></td>

<td> - 45.0</td><td> Urea-formaldehyde</td><td rowspan="2"> water soluble resin methylol</td>

<td></td><td> ureas).</td>

<td> 2.0</td><td> Glyoxal.</td><td></td>

<td> 47.0</td><td> Water.</td><td></td>

<td> 100.0</td><td></td><td></td>

Viscosity, 100-120 Stormer seconds.

Example IX

Example III

<td> Percentage</td><td> Material</td>

<td> 5.0</td><td> Nigrosine WST (water soluble dye).</td>

<td> 6.0</td><td> Hydroxyethyl cellulose (75-125 cp. in 5 percent water</td>

<td></td><td> solution at 20° C.).</td>

<td> 1.0</td><td> Dioctvl ester of sodium sulfosuccinate (Aerosol OT).</td>

<td> 10.0</td><td> Ethylene glycol.</td>

<td> 0.5</td><td> Glyoxal (in 30 percent solution).</td>

<td> 77.5</td><td> Water.</td>

<td> 100.0</td><td></td>

Viscosity, 100-120 Stormer seconds.

Example IV

<td> Percentage</td><td> Material</td>

<td> 15.0</td><td> Carbon black (Aqua black M).</td>

<td> 3.0</td><td> Pyruvic aldehyde (in 30 percent solution).</td>

<td> 1.0</td><td> Dioctvl ester of sodium sulfosuccinate.</td>

<td> 10.0</td><td> Diethylene glycol.</td>

<td> 1.5</td><td> Methyl cellulose (400 c. p. in 10 percent water solution</td>

<td></td><td> at 20° C.).</td>

<td> 69.5</td><td> Water.</td>

<td> 100.0</td><td></td>

Viscosity, 140-150 Stormer seconds.

Example V

<td> Percentage</td><td> Material</td>

<td> 6.0</td><td> Calcocid Scarlet MOO (water soluble dye).</td>

<td> 1.0</td><td> Wetting agent (dioctyl ester of sodium sulfosuccinate).</td>

<td> 1.5</td><td> Glyoxal (in 30 percent solution).</td>

<td> 3.0</td><td> Gelatin.</td>

<td> 3.0</td><td> Urea.</td>

<td> 40.0</td><td> Ethylene glycol.</td>

<td> 45.5</td><td> Water.</td>

<td> 100.0</td><td></td>

Example VI

<td> Percentage</td><td> Material</td>

<td> 5.0</td><td> Nigrosine WSJ.</td>

<td> 1.0</td><td> Wetting agent (sodium lauryl sulphate).</td>

<td> 1.5</td><td> Glyoxal (in 30 percent solution).</td>

<td> 30.0</td><td> Ethylene glycol.</td>

<td> 4.5</td><td> Hydroxy ethyl cellulose (400-600 cp. in 5 percent water</td>

<td></td><td> solution at 20° C.).</td>

<td> 58.0</td><td> Water.</td>

<td> 100.0</td><td></td>

Viscosity, 140-150 Stormer seconds.

Example VII

<td> Percentage</td><td> Material</td>

<td> 15.0</td><td> Carbon black in aqueous dispersion.</td>

<td> 1.0</td><td> V, etting agent (dioctyl ester of sodium sulfo succinate).</td>

<td> 24.0</td><td> Phenol-formaldehyde water soluble “A Stage” resin</td>

<td> 60.0</td><td> (Amberlite PR-14). Water.</td>

<td> 100.0</td><td></td>

<td colspan="2"> Viscosity, 90-120 Stormer seconds.</td>

<td> Percentage</td><td> Material</td>

<td> 5.0</td><td> Nigrosine WSJ.</td>

<td> 47.0</td><td> Polyethylene glycol (6000 M. W.).</td>

<td> 3.0</td><td> Glyoxal (in 30 percent solution).</td>

<td> 1.0</td><td> Wetting agent.</td>

<td> 44.0</td><td> Water.</td>

<td> 100.0</td><td></td>

<td colspan="2"> Viscosity, 100-140 Stormer seconds.</td>

Glyoxal and pyruvic aldehyde are normally incorporated in a water solution containing 30 percent aldehyde; however, the amounts designated in the examples refer to dry weight of the free aldehyde. These materials may be combined in any order since they are generally miscible one with the other, but it is preferable first to combine the high molecular weight substance or bodying agent and water and then incorporate the other ingredients. When a pigment dispersion is used, it may be incorporated into the formulation with stirring to distribute the dispersed pigments uniformly in the ink composition.

By the use of our new and improved stencil duplicating ink, drying takes place at a speed which is beyond that heretofore comtemplated for stencil duplicating inks, making it possible to handle the copy immediately. It is possible to eliminate setoff without the costly and cumbersome technique of slip-sheeting. It is possible to duplicate on hard stocks and highly finished impression media and still handle the work immediately. The ink produced by this invention dries rapidly on bond, ledger, card, or enamel stock, papers which have heretofore not been suitable for widespread use with stencil duplicating machines, and it may be formulated to become insolubilized substantially immediately upon drying.

There are no materials present in such quantity to cause undesirable “show through” or “halo.” This is because the present carrier and diluent is water which may be completely eliminated from the impression medium and is not resident as are the oils of prior duplicating inks.

It will be evident that other important advantages are derived from the use of water base stencil inks including the elimination of possible separation of the ink in use or prior to use because the ink composition is stable; simplifica-, tion in the processes of cleaning the machine and stencil by the use of a simple water rinse as effected by a dip or spray because the ink composition before transfer to the impression medium is readily soluble in water and many of the common solvents; self-sealing characteristics derived from the use of the polyhydric alcohol and a high molecular weight bodying agent to reduce the tendency of the inks to drip coupled with flow properties so related to rate of shear that inadvertent flow in the cylinder is eliminated without impairing the ability of the ink to

2,556,902 pass through the stencil openings in the duplicating operation; and simplicity in ink manufacture because preparation is effected by solution which eliminates grinding or other tedious means for incorporating the colors and resinous material.

It will be understood that the basic substances may be prepared for marketing in concentrated or dry form to be diluted at the station of use with water before filling the ink container. It will further be understood that other miscible solvents may be partially substituted for the water as the diluent or diluting substance, such, for example, as the lower glycols, alcohols and the like. In addition, it will be understood that numerous substitutions may be made in the materials and their amounts without departing from the spirit of the invention, especially as defined in the following claims.