Pressure-sensitive Sheet Material

Abstract

This invention relates to paper, or like sheet material, sensitized with a coating of liquid-containing pressure-rupturable capsules of both minute and a little larger dimensions arranged in interspersion and in close juxtaposition. In the preferred embodiment, the larger capsules contain a nonsignificant diluent, and the smaller capsules contain a concentrated liquid marking substance or other significant material. The capsules, large and small, are rupturable individually, are interspersed as to size, and are closely spaced on the sheet, so that an intentional impact directed on a small area of the coating will smash all of the capsules in the area and result in the expression of diluted liquid marking or other significant material, whereas a hit-or-miss applied pressure will rupture only a few of the larger capsules of the area, releasing a small amount of harmless diluent. Each capsule is a unit containing a cluster of droplets and, when the cluster is encapsulated, forms an irregular botryoid minute mass. The larger and protruding bosses of the diluent capsules represent outside droplets acting to guard the smaller capsule units beside them. The marking or other significant material may be an inherently colored dye, a colorless chromogenic color reactant, or an odorous, obscurant, or active material, and the capsules on a sheet may be associated with other materials on the sheet or be used to express their contents onto another sheet in contact therewith.

Description

DESCRIPTION OF PRIOR ART

The prior art discloses sheet material sensitized with liquid-containing pressure-rupturable capsules protected from accidental damage by being interspersed with solid particulate material which yields no diluent liquid and which undesirably soaks up part of any capsule-yielding liquid by interstitial or porous capillary action. The diluent contents of the large capsules of this invention may have evaporative properties and, once having performed its function of acting as capsule contents to hold the buffering capsules in a rotund condition and its function, when released, of increasing mobility of the concentrated released marking fluid, disappears by evaporation.

A great drawback of the use of particulate solid stilt material now in commercial use is that too much of it in the system interferes with the liquid flow of released marking or other significant material, and too little of it does not prevent smudge. The upper limit of diluent-supplied capsules provided by the construction of this invention is not a critical one and does not require close proportional control against oversupply of it in the coating composition. Moreover, casual loss of the contents of a smaller number of buffering capsules by accident will not be noticeable in the allover abundance of diluent that remains encapsulated in adjacent capsules. To put it another way, the use of diluent capsules as stilts aids in transfer of liquid material expressed from the small capsules, and this is a remarkable technological advance.

The compromise of using just enough stilt material without limiting transfer efficiency of released marking liquid is no longer quantitatively critical when this invention is practiced.

If an occasional marking material small capsule alone is intentionally ruptured, it releases a concentrated iota of smudge of small dimensions and mobility and may be disregarded.

The use of solid stilt material in the old practice always involves a balance between the frictional smudge resistance and the liquid transfer efficiency factors, the addition of more stilt material tending to increase the former at the expense of the latter.

By the provision of this invention, the more liquid-containing capsule stilt used, the greater the smudge resistance and the greater the transfer efficiency.

Thus, it is the chief object of the invention to provide liquid-yielding smudge-resisting stilt material in a sheet coated with sensitizing capsules, wherein pressure-sensitive small capsules are yielding the significant liquid of use and are physically buffered by larger capsules, the contents of which is of use as a diluent and which, additionally, may be evaporable.

Another object of the invention is to provide the diluent capsules with either an evaporable liquid or a relatively nonevaporable liquid.

THE DRAWING

Both views are enlarged and out-of-proportion views of aspects of the invention showing the irregular conformation of both kinds of capsule units, large and small.

FIG. 1 shows the capsules disposed on a support sheet, and

FIG. 2 is a section through a capsule unit.

The reference numeral 20 designates one of the small capsules containing the concentrated liquid to be protected from accidental release by an adjacent large capsule 21 (FIG. 1). The irregular shape of both the large and small capsules is due to the fact that the deposit of polymeric matrix material follows the contour of the capsule cluster, which clusters assume a botryoid shape in the making of both sizes of capsule. FIG. 2 is a section through a diluent large capsule 21 but also is typical of the construction of one of the smaller capsules 20. The supporting sheet material 23 (FIG. 1) is shown as fibrous material, such as paper, although it might well be film material. The contours of the large capsules will protect the smaller adjacent capsules by overhang or by bridging the accidentally applied pressures.

The specific examples to follow will give a rough measure of acceptable amounts of diluent which may be used with a given amount of the encapsulated marking fluid.

The size of the capsule units depicted in the coating has been exaggerated, relative to the thickness of the supporting web. Generally, if the web is paper, the thickness of the supporting web material, counted in units of mils, is many times the average cross-sectional diameters of the capsule units. The thickness of the supporting web material is of minor consequence; the average cross-sectional diameter of the smaller, protected, capsule units should be in the range of about 1 to 12 microns, and the larger, protecting, capsule units should be at least about 1 to 3 microns larger, in the range of about 2 to 15 microns. The capsules should be randomly interspersed, as shown, in close juxtaposition, so that the released diluent reaches the released marking liquid.

FIG. 2, the stylized view of the preferred kind of capsule unit for use in this invention, shows aggregated, thin-walled droplet clusters further encapsulated in an outer wall matrix of the type disclosed in U.S. Pat. No. 3,041,289, which issued June 26, 1962, on the application of Bernard Katchen and Robert E. Miller. When such capsular aggregates are used, capsular diameter for selection of larger and smaller capsule units is the diameter of the overall capsular aggregate. FIG. 2 shows each capsule as sectioned in elevation, although in actuality a section through a walled cluster of capsules would show some in full elevation in the background and others sectioned at various planes.

Only that part of the construction which is considered novel is shown in FIG. 1, as it is to be understood that solid particulate materials, such as materials reactive toward the encapsulated liquid marking agent, may be coated on the paper and situated under, on top of, or coincidentally with the layer of capsules shown, to make an autogenous sheet needing no transfer of material to a second sheet. Alternatively, the coated paper sheet shown may be superimposed coated side against a second sheet of paper coated with necessary reactive materials, so that rupture of the marking agent capsules on the first sheet causes the transfer of the liquid agent to the second sheet, with the aid of the released diluent, where a chemical reaction, such as color development in a colorless, chromogenic compound, may take place. There are many such constructions, particularly in the field of record sheet material manufacture. The invention is applicable to other than record systems where pressure is used to bring two liquids together for blending or reaction that are not of significance for marking, but which are to be kept apart until used by application of pressure.

SUMMARY OF THE INVENTION

There is provided by this invention a method and construction of protecting minute, liquid-containing pressure-rupturable capsule units, coated on a supporting web, from accidental rupture due to pressures such as those encountered in the handling and storage of the coated web. The supporting web, as said, may be, and usually is, a sheet of paper, and the capsule contents may be chosen from a number of significant materials for pressure release; for example, an odorant, or obscurant, a colored dye, or a colorless chromogenic material suitable for causing the appearance of marks on a record sheet when the capsules are ruptured by pressure from a printing member. The method consists of including, in a capsule coating for a web, other liquid-containing capsules which are larger than the capsules to be protected, so as to give an interspersion of the two kinds of capsules, closely juxtaposed. The liquid contained in the larger capsules which is an insignificant liquid except for its diluent property, so that its accidental release does not appreciably affect the supporting web or the walls of the neighboring smaller capsules. Thus, if odor is one of the significant effects to be noted upon release of the liquid reactant in the smaller capsule units, the contents of the larger, protecting, capsules may be odorless. Similarly, if a significant property of the liquid reactant is its color, the protecting capsules may have colorless contents, odorless or not, and, if the smaller capsule units contain a colorless, chromogenic material, the larger capsules should contain neither such a potential dye nor any material capable of generating color with the contents of the smaller capsules.

The advantage in using this provided novel method of protecting capsules containing an agent to be preserved against accidental release is that the surface texture of the coated web is not qualitatively changed by the addition of the physical buffer capsule units, and, more important, when the significant liquid agent is released by the intentional rupture of its enclosing walls, its transfer as a flowing material to the desired place is not impeded by its pressure protector but rather is aided by the simultaneous release of diluent from the protector capsules.

DETAILED DESCRIPTION OF THE INVENTION

As has been pointed out in the preceding sections of this disclosure, the invention provides a method of using larger expendable liquid-containing capsules to shield closely adjacent smaller liquid-containing capsules that should not be prematurely broken. As stated, the protected capsule contents could be any liquid or liquid dispersion which a practitioner might wish and be able to encapsulate and coat on a surface of a supporting web. There are many examples of such materials used in commerce and published in the literature. The superiority of this invention is particularly marked in record systems where a back-coated first sheet comprises small capsules containing a liquid dispersion of a chemically reactive colorless, chromogenic material and the coating of a front-coated underlying second sheet comprises a solid coreactant designed to convert the colorless, chromogenic material to a distinctively colored product. Such back- and front-coated sheets are also used in multiple sheet record unit forms as the top and bottom sheets of a stack, respectively, intermediate sheets of which stack are coated both on the front and on the back to give transfer and copy-receiving properties. The material and economic advantages of using the capsular units of this invention over using previously known capsule coatings in such sheets is as pronounced as in the case of capsule-coated sheets in a two-sheet system. In all these cases, the transfer efficiency of the system is very important and is adversely affected if absorbent stilt material in the capsular back coating of the sheets is present. When the absorbent stilt is replaced with liquid-containing capsule buffers, as in this invention, the transfer efficiency is enchanced, and more intense marks are developed on the second sheet.

When the liquid content of the small capsules to be protected is a liquid solution of a solid agent, the liquid content of the buffer capsules may well be the same liquid solvent used to make the agent-containing solution, or some inert liquid, miscible with the solvent for the solid agent.

The concentration of the agent in the liquid of the smaller capsules and the relative weight proportions of the two kinds of capsules may be varied at will. The concentration of the agents and the parts by weight to be used of the two kinds of capsules is simply chosen so that the delivered agent solution will be at the desired concentration after the capsules are ruptured and the two liquids are thereby mixed together.

With reference to capsular wall materials, this invention is dependent not on any particular kind of capsule unit wall material but on the relative size and content of the capsules, except that the large buffering capsules may be overcoated with a harder polymeric material. Minute liquid-containing capsule units of any kind of content in a paper coating may be protected by other larger capsules that contain an inert liquid diluent miscible with the contents of the protected capsules.

Miscibility of the two kinds of liquids is not absolutely required, because the larger capsules would protect the smaller capsules even if the liquid contents of the two were not miscible, and some help in transfer of the agent liquid would result from the washing effect of the released liquid of the larger capsules even if it were not miscible with the agent liquid. However, miscibility of the two liquids is preferred. Such liquids may be chosen from among common organic liquids, the choice not being critical to this invention.

When the protected encapsulated liquid is to be a dispersion of a dye for use in making marks by color reaction, it may be of the colorless, chromogenic kind, such as crystal violet lactone along or mixed with benzoyl leuco methylene blue, as in example 3 to follow, or any of many colorless chromogenic materials known in the art, many of which are noted in an application for U.S. Letters Patent, Ser. No. 392,404, filed Aug. 27, 1964, by Robert E. Miller and Paul S. Phillips, Jr., now abandoned, but the substance of which is published in British Pat. No. 1,053,935 (1966), corresponding thereto, and which is disclosed in continuation U.S. Pat. application, Ser. No. 744,601, filed June 17, 1968. The dye could also be already colored to form a printing ink solution or dispersion, such as a dispersion of carbon black or a blackish oil-soluble dye in an organic oil, such a system not requiring a sensitized transfer receiving sheet.

"Dispersion" as used in this disclosure does not exclude solutions which are viewed herein as extremely fine dispersions or, in reality, molecular dispersions.

In the following examples, the preferred embodiment of this invention is example 5. All solution concentrations are given as percent by weight. The water used in all encapsulation procedures (examples 1, 2, and 3) is deionized water.

EXAMPLE 1

Buffer capsule units having gelatin-gum-arabic-urea-formaldehyde wall material: An emulsion of the following formulation was prepared in a Waring "Blendor":

92.5 grams of an 11 percent aqueous solution of pigskin gelatin at 55.degree. C. and pH of 6.5 (adjusted with 20 percent sodium hydroxide)

50.7 grams of water

112.5 grams of xylene as the intended capsule contents The "Blendor" was set for moderate agitation, and stirring was continued until emulsion droplets of 3 to 6 microns were obtained.

To the above solution were added 62.5 grams of an 11 percent aqueous solution of gum arabic, 8.1 grams of a 5 percent aqueous solution (pH adjusted to 8 with 20 percent sodium hydroxide) of poly(methyl vinyl ether-maleic anhydride) copolymer such as a "Gantrez AN" copolymer with a specific viscosity (1 gram of copolymer in 100 milliliters of butanone and determined at 25.degree. C.) of 0.9 to 1.0 poise, as supplied by General Aniline and Film Corporation, New York, N.Y. United States of America, and 444.5 grams of hot (approximately 65.degree. C.) water. At this point, the temperature of the mixture was adjusted to 55.degree. C., and the pH was again adjusted to 9. Then, with the warm mixture under continuous agitation, the following steps were taken:

1. 9.1 millimeters of 14 percent, by weight, aqueous acetic acid was added dropwise over a 15-minute period, and then

2. the mixture was cooled to 12.degree. C. and treated with 5.1 milliliters of 25 percent, by weight, aqueous glutaraldehyde and stirred for one hour to harden the now-formed capsules. Clustering of the droplets into botryoid units occurs just after the emergent phase of coacervate material first deposits on the droplets individually.

While the capsular suspension, prepared above, was being stirred, a solution of 107 grams of 37 percent aqueous formaldehyde and 47 grams of urea, with the pH of the solution adjusted to 10 with 20 percent sodium hydroxide, was prepared and stirred for one hour at 70.degree. C.

The urea-formaldehyde mixture was then added slowly to the agitated capsular suspension, and initiated the formation of a rigid and hard outer wall to the capsule units as the pH was lowered. The reaction mixture was adjusted with 10 percent aqueous sulfuric acid to a pH of 3.0 and stirred overnight.

The pH was finally adjusted to 10 with 20 percent aqueous sodium hydroxide to give a capsular suspension suitable for use as an aqueous paper-coating slurry of buffer capsule units. The capsule units may be isolated from the reaction mixture by decantation, filtration, or centrifugation if isolation is desired, but it is not necessary. Isolated capsule units may be washed and dried by conventional means.

EXAMPLE 2

Buffer capsule units having walls of poly(vinyl alcohol) impregnated with phenolic-formaldehyde resin: An emulsion of the following formulation was prepared in a Waring "Blendor":

166 milliliters of 18.5 percent aqueous gum arabic solution.

140 milliliters of toluene as the intended capsule "oily" contents.

The emulsion was agitated until the oil-phase droplets were 2 to 3 microns in diameter as determined by optical transmission readings or by direct microscopic observation, through a reticle, of small samples of emulsion removed from the stirred mixture. With 490 milliliters of water as a transfer aid to rinse the vessel, the emulsion was transferred to a stirred beaker of 224 milliliters of 5 percent, by weight, aqueous poly(vinyl alcohol) solution. The poly(vinyl alcohol) solution was prepared as follows: 2.1 grams of about 86,000-molecular weight poly(vinyl alcohol) characterized by having a viscosity of about 28 to about 32 centipoises in a 4 percent, by weight, aqueous solution at 20.degree. C. and by being 99 percent to 100 percent hydrolyzed (such as the material) designated "Elvanol 71-30" sold by E. I. du Pont de Nemours and Company, Wilmington, Delaware, United States of America), and 9.1 grams of about 125,000-molecular weight poly vinyl alcohol) characterized by having a viscosity of about 35 to 45 centipoises in a 4 percent, by weight, aqueous solution at 20.degree. C. and by being 87 percent to 89 percent hydrolyzed (such as the material designated "Elvanol 50-42" sold by the aforementioned E. I. du Pont de Nemours and Company) were dissolved in enough water to yield a total volume of 160 milliliters of solution. The contents of the beaker was stirred throughout the following steps and additions: (1) The mixture was cooled to 15.degree. C. and treated by the dropwise introduction, over a 15-minute period, of a solution made up of 280 milliliters of 5 percent aqueous resorcinol plus 5.6 milliliters of 10 percent aqueous urea; (2) after 15 minutes more of stirring, 140 milliliters of 2 percent aqueous sodium sulfate was added, dropwise, over a 15-minute period; (3) stirring was continued for 15 minutes, and 84 milliliters of 37 percent aqueous formaldehyde was added from a separatory funnel over the period; (4) again at a moderate rate, spread over the ensuing stirring period, 140 milliliters of 10 percent aqueous sulfuric acid was added and stirred for 45 minutes; (5) 50.4 milliliters of 10 percent aqueous urea was added slowly, at a similar rate; and (6) the mixture was stirred overnight, about 16 hours.

As discussed in example 1, the capsule units may be isolated, washed, and dried, or used directly in the preparative vehicle as an aqueous coating slurry.

EXAMPLE 3

Marking-material-bearing gelatin-gum arabic capsule units: An aqueous emulsion having oil droplets of 1 to 2 microns diameter was prepared by stirring in a Waring "Blendor" the following materials at 55.degree. C.

208 grams of a 2:1 mixture of "Aroclor 1242" and "Magnaflux" oil, having dissolved therein 3 percent crystal violet lactone and 2.5 percent benzoyl leuco methylene blue as the capsule contents.

135 grams of 11 percent aqueous gelatin (isoelectric point at pH 8).

74 grams of water.

"Aroclor 1242" is a liquid chlorinated biphenyl substantially nonevaporable solvent, supplied by Monsanto Chemical Company, Saint Louis, Missouri, United States of America, and "Magnaflux" oil is a hydrocarbon oil with a distillation range of 370.degree. to 500.degree. F., supplied by Magnaflux Corporation, Chicago, Illinois, United States of America.

The emulsion was placed in a beaker with continual stirring, and the pH of the stirred emulsion was adjusted to 9 with a 20 percent, by weight, aqueous solution of sodium hydroxide. To the stirred emulsion were then added 11 grams of a 5 percent, by weight, aqueous solution (pH adjusted to 8 with 20 percent sodium hydroxide) of poly(methyl vinyl ether-maleic anhydride) copolymer such as a "Gantrez AN" copolymer with a specific viscosity (1 gram of copolymer in 100 milliliters of butanone and determined at 25.degree. C.) of 0.9 to 1.0 poise as supplied by General Aniline and Film Corporation, New York, N.Y., United States of America, 91 grams of an 11 percent, by weight, aqueous solution of gum arabic, and 655 grams of hot (approximately 65.degree. C.) water. At this point, the temperature of the mixture was adjusted to 55.degree. C., and the pH was again adjusted to 9. Then, with the mixture under continuous agitation, the following steps were taken: (1) 13.5 milliliters of 14 percent, by weight, aqueous acetic acid was added dropwise, (2) the mixture was cooled to 12.degree. C. and treated with 7.5 milliliters of 25 percent by weight, aqueous glutaraldehyde, (3) one hour later, 15 milliliters of a 5 percent, by weight, aqueous solution of poly(methyl vinyl ether-maleic anhydride) copolymer (at pH 8) was added dropwise, and finally (4) one-half hour after the preceding addition was complete, the pH was raised to 10 with 20 percent sodium hydroxide solution.

The now-completed capsule units thus prepared may be isolated from the vehicle by decantation, centrifugation, or filtration, washed, and dried, or more conveniently used without isolation as a suspension in the aqueous manufacturing vehicle.

In this example, the isolated marking material is suspended in a substantially nonevaporable solvent subject to dilution with the contents of associated buffering capsules among which they may be disposed. The diluent may be evaporable, and marks made by the diluted marking material are completed by drying and imbibition in the paper, if paper is the web material.

EXAMPLE 4

Capsule-coated paper was produced by mixing the product of examples 2 and 3 to form a composition. The aqueous suspension of buffer capsule units prepared in example 2 was used without recovery of the capsule units from the manufacturing vehicle. Similarly, the dye-bearing aqueous suspension of capsules of example 3 was used without isolation from the manufacturing vehicle. The combination coating slurry was prepared according to the following formulation:

Dry Weight Solids Wet Weight (grams) (%) (grams) __________________________________________________________________________ Dye capsule unit suspension of example 3 741 18.5 4,000 Buffer capsule unit suspension of example 2 1,000 25.0 4,000 Starch (aqueous).sup.1 148 20.0 741 Water -- -- 2,400

The coating slurry was applied to paper with an air knife coater to give a coating weight of 4.0 pounds per ream of 3,300 square feet after the paper was oven dried at 200.degree. F.

EXAMPLE 5

Capsule-coated paper was made by mixing the product of examples 1 and 3. The aqueous suspension of capsule units prepared in example 1 was used as buffer capsules without isolation of the capsule units from the manufacturing vehicle. Similarly, the dye-containing capsules of example 3 were used without isolation from the manufacturing vehicle. The coating mixture was prepared according to the following formulation:

Dry Weight Solids Wet Weight (grams) (%) (grams) __________________________________________________________________________ Dye capsule unit suspension of example 3 814 18.5 4,400 Buffer capsule unit suspension of example 1 400 10 4,000 Elvanol 71-30 130 10 1,300 Water -- -- 500

The coating slurry was applied to paper with an air knife coater to give a coating weight of 3.8 pounds per ream of 3,000 square feet after the paper was oven dried at 200.degree. F.

The dried coating of examples 4 and 5 consisted of interspersed capsules of diluent and concentrated marking material, the diluent-containing capsules being sufficiently larger than those containing marking material to act as physical stilts to protect the latter.

By the method of manufacture, the capsule wall material in each kind of capsule deposited on the internally held droplet cluster to reveal the conformation of the cluster as a botryoid inclusion, which is evidenced by the diagrammatic irregularity shown in the two views of the drawing. This botryoid form of the capsule entities or units favors the protective role of the larger buffer capsule units while they are intact.

Claims

What is claimed is:

1. A record sheet consisting of a sheet of paper and a coating on a surface of the sheet comprising minute, pressure-rupturable, liquid capsule units of two kinds, one kind containing a concentrated marking liquid and a second kind, being at least about 1 to 3 microns larger in diameter than the first kind and containing a nonmarking diluent liquid, the second kind of capsules being randomly interspersed in the coating with the first kind to serve as a protective buffer for the first kind prior to marking pressure rupture of the capsules, the diluent liquid mixing with the marking liquid at the time of marking-pressure rupture of the capsules to give a free-flowing dilute marking liquid when and where capsules are ruptured by marking pressures.

2. A coated sheet which releases liquid confined in capsules coated on the sheet when and where subject to pressure, characterized by the capsules being coated on the sheet in close juxtaposition and of individual size too small to be seen by the unaided eye, yet being of two kinds in random interspersion, a first kind being of two kinds in random interspersion, a first kind being smaller than the second kind and containing droplets of concentrated liquid selected from the group consisting of marking liquids and odorant liquids, and wherein said liquid droplets are protected from pressure release except by direct intentionally applied pressure, and the other kind being at least about 1 to 3 microns larger in diameter, and containing droplets of liquid which is a diluent for and which does dilute in use the liquid contained in the first kind of capsules, and which does not contribute to the odorant or marking properties of the liquid in the first kind of capsules and which larger capsules act as a physical buffer to prevent rupture and release of liquid from the first kind of capsules by less than the direct intentionally applied pressure.

3. A sheet of record material comprising a sheet of support material; and a coating, on the sheet, of an interspersed mixture of two kinds of minute liquid-droplet-containing capsules in close juxtaposition, both kinds of capsules being pressure rupturable to release the droplets and being of botryoid outer conformation, the inner construction of each capsule consisting of a cluster of droplets held in a matrix of deposited polymeric material, the botryoid conformation resulting from the matrix material following the cluster contours, one kind of capsule being smaller than the second kind and containing droplets of concentrated marking liquid material, which droplets are to be protected against premature release, and the second kind of capsule being at least about 1 to 3 microns larger in diameter than the smaller kind, and the larger kind of capsule containing droplets of liquid useful as a diluent for the droplets of the marking liquid in the smaller kind of capsule.

4. The product of claim 3 wherein the sheet material is paper.

5. The product of claim 2 wherein the droplets of the smaller capsules are of a marking material.

6. The product of claim 3 wherein the droplets of the smaller capsules comprise a colorless marking material.

7. The product of claim 3 in which the larger kind of capsule has an outer coating of a more rigid material than the matrix material.

8. The product of claim 3 wherein the diluent droplets of the larger capsules are at least in part a readily evaporable liquid.

9. The product of claim 3 wherein the diluent droplets are a readily evaporable liquid.