US3384536A - Process for forming fibrous sheets containing limited penetration of additaments within the sheet and sheets thereof - Google Patents

Description

y 1968 R. w. SANDBERG ET AL 3, 84, 36

PROCESS FOR FORMING FIBROUS SHEETS CONTAINING LIMITED PENETRATION OF ADDITAMENTS WITHIN THE SHEET AND SHEETS THEREOF 2 Sheets-Sheet 1 Filed March 24, 1965 INVENTORS ROBERT W. SANDBERG BRUCE W. BROCKETT a DONALD B. CLARK THEIR ATTORNEYS 2 Sheets-Sheet 2 kmmIO M25042 max-S R. W. SANDBERG ET AL PENETRATION OF ADDITAMENTS WITHIN THE SHEET AND SHEETS THEREOF $5 3 m z wom H mm L INVENTORS ROBERT W. SANDBERG BRUCE W. BROCKETT 8 DONALD B. CLARK THEIR ATTORNEYS PROCESS FOR FORMING FIBROUS SHEETS CONTAINING LIMITED May 21, 1968 Filed March 24, 1965 United States Patent "ice PROCESS FOR FORMING FIBROUS SHEETS CONTAINING LllVlITED PENETRATION 0F ADDITAMENTS WITHIN THE SHEET AND SHEETS THEREOF Robert W. Sandberg, New Lebanon, and Bruce W. Brockett and Donald B. Clark, Dayton, Ohio, assignors to The National Cash Register Company, Dayton, Ohio, a corporation of Maryland Filed Mar. 24, 1965, Ser. No. 442,352 9 Claims. (Cl. 162-175) ABSTRACT OF THE DISCLOSURE A process for limiting the penetration of particulate material within an embryonic fibrous web by effecting a phase separation of a wall-forming polymeric mater al (coacervate phase) within the web in the presence of the particulate material; the coacervate phase being formed by applying one or more of the components essential to the phase separation to one side of the embryonic web and the products therefrom.

This invention rel-ates to a system for limiting the penetration of particulate material through the thickness of a fibrous sheet material, and to the novel product produced thereby.

In its preferred embodiment, though not limited thereto, the novel system is capable of limiting the penetration of particulate material into a fibrous sheet, as the sheet is being formed, so that the particles are substantially concentrated adjacent one surface thereof in a firm, well defined stratum of binder material.

It has been found, and applicants have taken advantage of the finding to provide the novel sheet (of paper) made by the process of this invention, that a liquid solution of a film-forming polymeric material, under certain changes in conditions, usually the presence of another material, will undergo a change such that a phase separation occurs which produces, as the binder material, a relatively viscous, liquid phase comprising a liquid solution of the film-forming polymeric material (coacervate phase), and a phase comprising a film-forming polymer-poor liquid phase (equilibrium phase) and that the above-referred-to phase separation can be made to occur in the case of embryonic paper sheet (web) within a limited thickness, measured toward the center line of the web, upon application of one or more of the components essential to the phase separation to one side of the said embryonic paper web. In one form, when a liquid slurry of paper fibers, treated with one of the components essential to phase separation, is laid down as a soggy web, and a solution of other component(s) essential to the phase separation is applied to said web, all components being present in sufficient amount and under conditions appropriate to the formation of a coacervate, the components thus brought together cause the phase separation and the emergence of the binder material to occur substantially immediately, with the result that the viscous phase is formed within the web in a well defined stratum substantially adjacent the surface of the side of the embryonic web to which the solution was applied. Moreover, the viscous phase of binder material Wets and adheres to the fibers within its immediate vicinity, and, further, the viscous phase envelops and forms a matrix for any particulate material within the zone of thickness in which the phase separation occurs.

Patented May 21, 1968 The binder stratum is generated in situ in the fiber mat comprising the wet web. Preferably, at least one essential component is present in the Wet web when the other essential component(s) and particulate material are applied to and penetrate into the wet web. The instant generation of the viscous polymeric material phase (coacervate), which constitutes the binder, causes it to stall for the most part, preventing it and the retained particles from proceeding farther into the web. This occurs with respect to the thickness of the sheet, much before the center line of the sheet is reached, most being retained in the first ten to twenty percent of the sheet thickness.

In one form of practicing the invention, a slurry of paper fibers having present therein a phase-separation-inducing material, such as, for example, a polymer of one polarity, is allowed to form a wet, soggy web on a papermaking machine, and, while the web has a substantial liquid content (ninety-five percent, for example), there is introduced evenly to the top side of the web a solution of polymeric material of opposite polarity, in which is dispersed finely-divided particulate material of a size which could, in part, penetrate completely through the soggy web. Surprisingly, it has been found that, upon contact of the introduced polymeric material solution with the web, a viscous liquid phase binder material is formed, which phase develops the particulate material and attaches to the contiguously-disposed fibers, leaving the residual liquid free to drain away. The separated viscous phase of polymeric binder material which forms is stalled at once on and among the topmost fibers. This formation of the viscous phase of polymeric material around the fibers is made to occur before the introduced solution has had a chance to penetrate more than a fraction of the thickness of the web, and said viscous phase maintains its limited penetration during the subsequent pressing and drying operations involved in producing the finished sheet. The liquid viscous binder material, when dried of liquid, is a firm material subject to deformation. This finished sheet' has, buried in the top fraction of its thickness, substantially all of the particulate matter added, held within a matrix of the dried polymer-fiber complex.

The primary aspect of this invention relates to a system (and the product thereof) for limiting the penetration of particulate mark-forming components into markforming sheet record material, during the formation of said record material, to thereby impart a one-sidedness to the sheet material as regards such components; i.e., the sheet material in a cross-section through its thickness has the particulate material essential to the mark formation disposed, for example, substantially to one side of the center-line of said thickness.

Pressure-sensitive mark-forming sheet material generally has two forms; namely, the self-contained form, wherein all of the necessary mark-forming components are present in a single sheet in contiguous juxtaposition to each other, and the transfer form, which utilizes two or more sheets wherein one or more of the mark-forming components physically move from one sheet to another sheet. In the transfer form, said one sheet is generally considered as the transfer sheet, and said other sheet is commonly referred to as the receiving sheet, said receiving sheet, if necessary, containing one or more mark-forming components which cooperate with the transferred markforming components to produce a mark on the receiving sheet.

The one-sidedness" is particularly desirable in record material, since it confines the mark or mark-producing material to one side thereof to produce a more commercially acceptable record material. In the case of the selfcontained type, the one-sidedness and retention of the mark-forming material adjacent one surface also mean that, for given marking characteristics, a smaller amount of mark-forming material may be required than when the mark-forming material is incorporated throughout the thickness of the record material, since it is only those marks which are adjacent the surface which can be seen from the outside of the record material, and those marks which are formed deep down in the body of the sheet are not necessary. In the case of the transfer type, the one-sidcdness and retention of the mark-forming material adjacent one surface enable a more efiicient transfer of the mark-forming material from that surface than would be possible if the same amount of mark-forming material were distributed throughout the thickness of the record. material. In both types of record material, therefore, the retention of the mark-forming material adjacent one surface of the record material requires less marleforming material to be used to produce commercially acceptable marking than when the markforming material is dispersed throughout the record material and thus enables a saving to be effected in the manufacture of such record material. Moreover, in the usual case, at least one of the mark-forming components is present as the potentially mobile internal contents of a minute pressure-rupturable capsule (said capsules being used in large quantities numerically and being the particulate material in one form of this invention), so that, upon application of pressure to the sheet material, the capsule is ruptured and, in the case of self-contained sheet material, the inner contents is released to eoact with the other mark-forming components disposed within said sheet to produce a mark, and, in the case of the transfer system, the inner contents is released to transfer or move from the transfer sheet to the receiving sheet for forming marks on the receiving sheet, in both instances the mark being formed according to the pressure pattern.

By pressure-sensitive mark-forming sheet material, or similar phraseology, is meant that type of material which, upon the application of mark-forming pressure against the sheet material (for example, pressure of a stylus, a type face such as that carried by a typewriter lever, raised type printing plates, or the like) and without any intervening agency such as a ribbon, carbon, ink, or mating impression sheet, or other agency other than the sheet material itself, the configuration of the area receiving the pressure is reproduced on the sheet material as a visible, distinctive mark by mark-forming components in the material itself.

Mark-forming sheet materials embodying minute capsules, such as those described in US. Letters Patent Nos. 2,730,456 and 2,730,457, issued to Barrett K. Green and Lowell Schleicher on Jan. 10, 1956, and assigned to the assignee herein, have proven commercially successful and have been the practices art in what is often referred to as carbonless carbon-paper systems. In said patents, pressure-rupturable microcapsules containing one of the mark-forming components are coated onto a sheet material, such as finished paper, to provide, as the case may be, either a self-contained sheet material or a transfer sheet material, said sheet material, in the instance of the self-contained system, also containing at least one other reactive mark-forming component, so that, upon application of marking pressure to the system, a mark is produced either on the sheet bearing the capsules, in the case of the self-contained unit, or on the receiving sheet, in the case of the transfer system. In the prior systems referred to above, coating of fibrous sheet material, such as finished paper, with the capsules results in a substantial portion of the capsules being retained on the surface of the sheet, though a minor and significant portion of the capsules migrates within the sheet material. Having the capsules on the surface of the sheet renders the sheet material somewhat hypersensitive to pressure having a vector parallel to the plane of the sheet, and thus to a degree subject to undesirable smudging. Further, the capsular surface imparts a certain degree of roughness to the feel of the sheet relative to the smooth finish obtainable with an uncoated sheet. Moreover, the presence of the capsules on the surface produces a moderate amount of pick-up by printing mechanisms during overprinting operations on said sheet material.

An obvious and well-known expedient to overcoming the aforementioned difiiculties attending the presence of mark-forming capsules on the surface of the sheet material, such as paper, for example, is to mix the capsules with the pulp prior to the formation of the sheet, or to otherwise generally distribute the capsules through the body of the sheet. With such a technique in paper manufacture, the capsules would hopefully and at best be distributed throughout the pulp. However, efforts to form the sheet material by mixing the capsules and the pulp, without more, have been unsatisfactory due to the enormous percentage of escape and loss of capsules through drainage from the embryonic paper web and the disposition of the remaining capsules in the sheet in sedimentary patterns which are non-uniform because of dependence on gravitational and suction forces, the relative size of the capsules, and the interstitial spaces between fibers.

The subject invention provides a system for limiting the penetration of capsular material applied to a wet fibrous sheet, or, more broadly, any particulate material so applied, which affords the advantages inherent in having said particulate material disposed within the body of the sheet material and yet accomplishes this end without concomitant intolerable loss of the particulate material, by burying or total escape, to achieve it. Also of considerable significance is that the present invention provides a system and materials that have resulted in particulate material being retained within 10% to 20% of the thickness of the finished sheet as measured from one surface.

Broadly stated, the subject invention comprises a system (and the product produced ther from) for limiting the penetration of applied particulate material through the thickness of a fibrous sheet material wherein an embryonic web of sheet material is formed on a support member, and the particulate material, preferably in the form of a liquid suspension thereof, is applied to said embryonic web while still wet and draining, and at the same time, or substantially simultaneously, upon appli- Cation of the particulate material, there is caused to emerge or form within the embryonic Web, but adjacent the entering surface, a relatively viscous liquid binder phase stratum capable of wetting the particulate material and the fibers of said web that are in contact proximity to the viscous liquid phase; the viscous liquid enveloping the particulate entities and binding itself and the particulate material to the proximate fibers, yet allowing the residual liquid within the web to drain therefrom. Ordinarily, without the practice of this invention, a substantial amount of any micro-fine particulate material applied to one surface of an embryonic web as a liquid slurry will pass through said web, being entrained with the drainage liquid. The problem of retaining particulate material becomes more difiicult as the particle size decreases. By the practice of this invention, there is minimal, if any, loss of particulate material through the embryonic sheet, no mat ter how small its size. Thus, a myriad of particles of material of microscopic size can be contained in a droplet of the slurry and in a corresponding amount of the dried stratum, and such fineness and multiplicity of particles positioned in a sheet exactly where wanted near one surface has been attained.

Otherwise stated, the subject invention provides a conrol or limitation of the penetration of a particulate solid or liquid through a fibrous web by effecting the formation or generation, in a portion of the cross-sectional thickness of the web, of a relatively viscous liquid phase of binder material, which phase wets both the particulate material and the fibers of the web, holding them together. The formed liquid phase is a relatively viscous solution of a film-forming polymeric material which has been induced to separate as such from a solution thereof by introducing into the environment of the fibers one of many known change of condition agents, whether they be of chemical and/or physical nature, to cause said separation. The phenomenon of phase separation to produce a relatively viscous liquid solution of a film-forming polymer from a homogeneous liquid solution thereof is referred to as ccacervation, and tie separated or generated relatively viscous liquid phase consequently is referred to as a coacervate or a coacervate solution Coacervation and various techniques or procedures for effecting it are generally described by H. G. Bungenberg and H. R. Kruyt in Proceedings of the Academy of Sciences of Amsterdam, volume 32, pp. 849 to 856 (1929), and Colloid Science II, by H. R. Kruyt, published by Elsevier Publishing Company, Inc., New York, N.Y., in chapters VIII and XI. Specific techniques and procedures for effecting and using the emergence of a coacervate phase from a solution of polymeric material are further discussed and described in United States Letters Patent No. 2,800,457, issued to Barrett K. Green and Lowell Schleicher on July 23, 1957, and United States Letters Patent No. 2,800,458, issued to Barrett K. Green on July 23, 1957, both assigned to the assignee herein,

which patents relate to the making of minute capsules. The procedures set forth in British Patents Nos. 907,284 and 920,866, both assigned to the assignee herein, also produce such a phase separation with a more viscous solution as the separated phase.

An emergent coacervate phase seems to appear as droplets which if left alone will coalesce on moving together by gravity or other forces. In the making of paper, the agitation of the materials is such that any coalescence is interfered with; hence these emer ent droplets, while closely positioned, may be separate.

By the use of so-called complex coacervation, wherein polymeric materials of opposite electric charge coact under appropriate conditions to cause the generation and emergence of a relatively viscous solution of the polymeric materials in discontinuous state, it has been found that penetration of particulate material in the form of microcapsules, having as their internal contents a markforming component dissolved in an oil, into an embryonic paper web while wet can be limited by disposing in the web a polymeric material of one electric charge and then passing onto said wet web a solution of an oppositelycharged polymeric material to generate a complex of the polymeric materials, said solution having dispersed therein, as a separate particulate phase, the microcapsules. Thus, upon contact of the added polymer molecules of the solution and the polymer molecules of opposite charge on the web, a relatively viscous liquid solution phase separates, which, being capable of Wetting the capsules and the fibers, binds the capsules to the fibers so wetted and precludes further penetration into the web by said capsules.

In general, any known technique for effecting a phase separation of a viscous liquid phase and wherein the separated viscous liquid phase will form substantially on contact with the fibers of the embryonic web is satisfactory. Preferably, the separated phase forms instantly upon contact with the fibers of the web so as to maintain substantially all of the applied particulate material within the web as a subsurface stratum or layer adjacent the surface of entry. Other techniques for inducing an emergent coacervate phase of film-forming polymeric material are referred to in the literature cited above, including, without limitation, the following:

(a) Simple c0acervation.A procedure wherein a homogeneous wall-forming polymeric material solution phase comprising a single polymer is caused to separate by the addition of a microionic agent or by a change induced by a physical agent, such as temperature, to bring the original polymer solution into the coacervate state, comprising the viscous emergent phase and the non-viscous phase, which mostly is the solvent;

(b) Introduced incompatible polymeric material.A procedure wherein the addition of an incompatible polymeric material decreases the solubility of a polymer in homogeneous solution to thereby effect a phase separation and emergence of a coacervate phase of the polymeric material originally as a viscous solution; and

(c) Introduction of a non-solvent for polymeric material.A procedure wherein the addition of a non-solvent liquid for the wall-forming polymer in homogeneous solution effects a separation of a viscous coacervate solution of said polymeric material.

In all procedures, the necessary concentrations and conditions to bring about the emergence of the enveloping phase may be predetermined and the formation of the em bryonic fibrous sheet material conducted in such a manner that at the time the several components essential to Y causing the emergent phase separation are brought into operational proximity to each other, the appropriate concentrations and conditions will be present within the limits of that portion of the cross-sectional thickness of the fibrous sheet material to which it is desired to restrict the penetration of the particulate material.

While, as noted above, any particulate material, solid or liquid, dispersable as a separate phase in a liquid medium, may be added to the embryonic web of sheet material, for convenience of description, and with the desire to delineate and illustrate various aspects of the invention, the specification hereafter will emphasize the application of the invention to a system and product thereof useful in the preparation of pressure-sensitive markforming sheet material employing minute capsules as the particles. Before proceeding to such discussion, however, it seems provident to set out some broad requirements of the system of this invention at the time of emergence of the separated viscous phase, particularly as regards the nature of the essential components with respect to each other.

Essentially, the system at the initiation of the particle capture on and among the fibers may be characterized as follows:

It comprises the following three phases, characterized first of all by being mutually incompatible in the sense that each phase is an identifiable phase, and further characterized respectively, as follows:

(a) A continuous liquid phase vehicle Within the web material,

(b) A discontinous phase of a myriad of minute entitles of particulate matter, either solid or liquid, dispersed in the discontinuous phase (c), and

(c) A discontinuous phase of minute, mobile entities of film-forming emergent polymeric material dispersed in the vehicle and having dispersed therein minute entities of particulate matter (b), and said mobile liquid entities of emergent polymeric material being bound to the fibers, the location of the fibers in the sheet to which the mobile entities are bound determining the degree of penetration of the associated particulate matter.

In the instance where the particulate material is a solid, drying of the web alone provides a sheet material wherein the particulate material has a limited penetration. In the instance where the particulate material is wholly liquid, more can be done to retain it in the captured position, such as the hardening by chemical action (or other means) of the viscous emergent wall-forming polymer solution surrounding said liquid particulate material (in effect hardening of embryonic walls), and the drying of the web to provide a finished sheet material having limited penetration of particulate material.

It is within the scope of this invention to add part or all of the components essential to the formation of the separated phase at one or more points in the formation of the embryonic web of sheet material subsequent to the initial laying down of the fibers on the supporting member, it being kept in mind, however, that all materials should be added to the web while said web is normally penetrable by liquid and particulate material in the absence of the agency of this invention; provided further, however, that the particulate material should be added substantially simultaneously with the occurrence of the change in condition that produces the emergence of the relatively viscous polymeric material coacervate binder phase.

A primary objective of the invention is to provide a paper sheet with limited penetration of liquid-containing capsules as the particles that, because of their position in the sheet, when mptured by forces applied to the sheet, release the contained liquid at or near the surface of one side of the sheet only. This objective is accomplished by forming a sheet of paper with the capsules embedded in it only near that one surface, so that liquid released is available at or just beneath that surface only. The amount of capsules applied should be related to the final sheet thickness and the amount of encapsulated liquid necessary or desirable to be provided.

Such onesidedness is independent of the presence of one or more other sets of capsules throughout the thickness of the sheet or on the outside of the sheet, and it does not preclude the presence of other material, particulate or other, present in, on the outside of, or otherwise associated with the sheet, to cooperate, or not, with the set of capsules positioned in the sheet by the practice of this invention, cumulatively or countervailing, which produce the one-sidedness, or to serve another purpose. There may be two or more sets of capsules in the sheet, one of which brings about the one-sidedness by its distribution from one side towards the center, and the other being confined or not confined to the other side, or spread throughout the thickness of the sheet. Another objective of this invention is to provide a novel sheet which combines the advantages of one-sidedness and the particle (capsule) physical protection from touch and sight found in sheets where such are distributed throughout the thickness of the sheet. To the end that the particles (capsules) may be confined within the sheet, they are of necessity much smaller in their average diameter size than the sheet thickness and preferably are of such size, and present in such quantity, that they are protectively nested in the interstitial spaces between the felted fibers of the paper support sheet, in addition to being adherent to the fiber, even if calendered, without disturbing, from a users viewpoint, the normal physical structure of such a sheet made Without them.

If the particles are capsules, they are subject to rupture by pressure, indentation of the sheet, or pounding, to release the liquid locally to perform the function, which will be evident only Where the capsules are located.

It is contemplated that the embedded particles (cap sules) need not be of uniform substance, content, and size. When the particles are capsules, they may be a mixture as to size and Wall material, or of difierent content or origin, to serve one or more utilitarian purposes in behavior, or, if capsules, to have walls of varying resistance to rupture or fracture, or to be different in any other aspect of structure or performance (such as resistance to heat or solvents, resistance or non-resistance to electric currents) or different in any organic sense characteristics as to odor or color-or sensitive to magnetic flux in one way or anotheror to be sensitive to heat, light, or other radiation-or to contain chemical reactants, medicines, perfumes, or marking materials which are already colored or which color on release of the contents of the capsule to react with adjacent materials or with materials attached to the capsule walls on the outsideor to contain poisons, food, cosmetics, radiating molecules or atoms, or adsorbents or absorbentsto be different in reflectance or absorption of light, as between the fractured and unfractured state or in either stateor to be affected by other forms of energy in various manners which will be evident to those skilled in the art. Each of the capsules may be self-contained, in that each, upon rupture, creates a color mark, as disclosed in Example II, to follow. The particulate liquid may contain either liquid or solid solute material dissolved therein, or have such materials dispersed therein in any physical state, and may contain materials which may be subject to growth, metamorphosis, or degeneration, all to the purpose of making a paper sheet having utility by being one-sided.

To obtain disuniformity among capsules if such are used, they may be manufactured in separate batches according to the characteristics of the capsules as to origin, size, contents, or wall material and structure, and thereafter blended in the desired proportions for introduction into the paper as a single applied slurry. This is important where more than one kind of capsule contents (solid or fluid) is to be made use of either by rupture of the capsules or by their characteristics in the unruptured state. It is within the province of this invention to provide capsules having different thicknesses of walls or different strengths of walls, to the end that they may be differentially fractured by variations in pressure, so that some capsules may be ruptured by one pressure and the rupture of other capsules will follow in response to application of a greater pressure.

Considering now the application of the subject invention to the production of pressure-rupturable mark-forming sheet material, the preferred system comprises laying down a wet web of fibrous material on a supporting member to form an embryonic sheet, said web having disposed therein a suitable agent to effect phase separation or emergence of a relatively viscous liquid solution of film-forming polymeric material from a less viscous homogeneous solution of applied polymeric material, and applying to said web the less viscous solution of the said film-forming polymeric material having dispersed in it the aforementioned minute capsules, the contents of which capsules comprise a mark-forming component material, whereupon on contact of the agent and the less viscous solution the viscous liquid binder phase emerges and binds the capsules to the proximate fibers.

The applied solution is of low viscosity and is easily flowed uniformly onto the wet sheet. The viscous separated phase, in part, by reason of its viscosity, does not penetrate through the sheet, and, because of its exceptional wetting characteristics, clings to the proximate fibers to become bound thereto.

Suitable fibrous sheet material can be readily formed from a liquid slurry, generally an aqueous slurry, or wet stock of any paper-forming fibers which forms a substantially unified fibrous web, the most common fibers being cellulose rag and wood pulp fibers, which are ordinarily used to form papers. Other discontinuous randomly or otherwise oriented fibers, including what are commonly referred to as fibrils, mica and synthetic mica platelets, or other filament-forming solids (e.g. fibers of polyacrylonitriles, polyesters, and polyamids, that can be deposited from a slurry on a paper-making machine to form a unified paper or paper-like web having interstitial voids on a paper-making machine) can be used.

Suitable capsular material containing at least one of the mark-forming components are described in the aforementioned United States Patents Nos. 2,730,456 and 2,730,457.

The figures of the drawings illustrate a manufacturing procedure and apparatus suitable for carrying out the subject invention, more particularly the manufacture of pressure-rupturable mark-forming sheet material on a Fourdrinier paper machine. FIGS. 1 and 2 are schematic diagrams showing the various components of the Fourdrinier paper machine, and apparatus for introducing the materials used in the practice of this invention.

In FIG. 1, the headbox contains the aqueous slurry of paper pulp, which is passed onto the Fourdrinier wire 11, table rolls 12 and suction boxes 13 being shown. Particulate material, the penetration of which is to be limited, is added to an embryonic web being formed on the Fourdrinier wire 11, as at a dandy roll 14. After leaving the wire 11 at the couch roll 15, the web W passes through a series of presses 16, 17, and 18 and from there through a series of drying drums 19 (shown in fragmented section) to a wind-up roll 20.

FIG. 2 represents a more detailed schematic view showing storage of sheet-forming materials, and distribution to and recirculation from the Fourdrinier wire section to the storing vessels of such materials, and application of the liquid slurry to the dandy roll.

In FIG. 2, the stock and the size are introduced into a mixer 20 and then to a machine chest 21, wherein they are blended with white water from the couch pit 22 through the conduit 23. The resulting slurry may be diluted further by introduction of water through a conduit 24, after which the mass is passed through at Jones refiner 25 and conveyed through a pump 26 and then a conduit 27 to the inlet storage vessel 28, whereat a material that takes part in the subsequently occuring phase separation, such as a cationic starch sol, is added. The resulting slurry is metered through a Bird screen 29 via a conduit 30 to the headbox 31 and thence to the Fourdrinier Wire 32, thus forming an embryonic web (W). The embryonic web moves toward the dandy roll 33, the screen of which in turn is being supplied by a slurry comprising the particular matter dispersed in an aqueous sol of, for example, Karaya gum.

It should be understood that the foregoing description of FIGS. 1 and 2 is merely illustrative. It is within the scope of this invention to add the capsules or other particulate material by means other than the dandy roll and at any point in the web formation, provided that the web at the time of addition of the particulate material is sufficiently wet and penetrable, either by reason of undrained liquid or because the particulate material was added as a liquid slurry, to permit emergence of a relatively viscous liquid solution of polymeric material and its fixation on the fibers. Thus, while the preferred procedure, as shown in FIGS. 1 and 2, calls for the addition of the capsules at the dandy roll, where under normal paper-making procedure the moisture content of the embryonic web of sheet material is of the order of 92% to 98% by weight of water, the capsular slurry might be added at another point, again provided that the web of sheet material allowed 'suflicient penetration of the capsular material into the web,

and provided that there are within the web appropriate conditions and concentrations of the components necessary to the formation of a viscous liquid solution of polymeric material.

Following are examples of systems that produce a controlled penetration of capsules within a paper web.

EXAMPLE I The following is a description of the preferred embodiment of the invention as carried out using the process steps and apparatus shown in FIGS. 1 and 2, wherein minute capsules were added to a wet web of fibrous paper on a Fourdrinier paper-making machine. Karaya gum was present in the capsular slurry, and cationic starch was present in the pulp, these materials, Karaya gum and cationic starch, acting in concert to cause the emergence, within the sheet of wet fibers, of a relatively viscous liquid phase, which in its emergent form is present as a plurality of entities. The emergent liquid phase becomes less in volume and, in contracting from the original volume occupied by the solution, breaks up into entities carrying with them the associated capsules, which are thus enveloped. The entities themselves, when formed among the topmost fibers, wet them and entangle with them and clothe them, thus in eii'ect securing and binding the capsules against migration through the sheet, thereby forming a stratum.

The majority of entities and associated capsules are caught in the top ten to twenty percent of the sheet, measured from the entering surface. Substantially no capsules migrate beyond the center line of the sheet. When this wet web is pressed and dried, the entities shrink by loss of solvent, leaving the dried polymeric binder material, and the capsules remain in place relatively with respect to sheet thickness. The apparatus and the procedure for adding the various components were as shown in FIGS. 1 and 2. Several runs were made under varying conditions, and the conditions and the characteristics of the paper which was produced are tabulated in Table I.

The Karaya gum solution and the cationic starch solution were prepared in the following manner:

Concentrated Karaya gum 's0lnti0n.4.5 pounds of dry Karaya gum powder was stirred into 50 gallons of water, using a suitable mixer. Five minutes after all the powder had been added, the mixer was turned off. The Karaya gum solution was allowed to sit for two hours, and then the mixer was turned on for live minutes. After sitting for two additional hours, which periods enabled the Karaya gum to hydrate, 2.7 pounds of 29% aqueous ammonia was added, with stirring to deacetylate the Karaya gum. After five minutes, the mixer was turned off, and the 55- gallon drum was covered. Just prior to combining the Karaya gum solution and the capsular slurry, 50 gallons of Karaya gum solution was diluted with water to 542 gallons, or 0.1% Karaya gum on a solids basis.

Cationic starch s0lnti0n.--The cationic starch (Q-TAC 3891, manufactured by Corn Products, Inc., and described in Corn Products Technical Bulletin No. QT-27-002 as a cationic derivative of corn starch produced by the reaction of starch with a quaternary amine) solution was prepared by heating a surry of the starch at degrees Fahrenheit for a minimum of fifteen minutes to provide a 1%, by weight, starch-in-water solution.

Preparation of capsular slurry.Both acid and basic slurries were prepared.

Acid slnrry.-Benzoyl leuco methylene blue (BLMB) and crystal violet actone (CVL) were dissolved in chlorinated diphenyl and kerosene. The resulting oil was dispersed as a liquid phase in an aqueous gelatin sol. To this dispersion were added gum arabic and polyvinyl methyl maleic anhydride (PVM/MA), which, upon lowering of pH with acetic acid at the proper dilution, effects the formation of a coacervate solution of the gelatin, said coacervate forming embryonic capsule walls of coacervate solution about the dispersed oil droplets. Subsequently, the embryonic walls were set, by cooling, and hardened with glutaraldchyde. The weight ratio of oil to gelatin was on the order of 10:1, and average diameter of the resulting aggregate of individual droplets was on the order of 8 to 12 microns.

The capsule preparation described above is more fully described in United States Letters Patent No. 3,041,289, issued to Bernard Katchen and Robert E. Miller on June 26, 1962.

Basic slurry.Benzoyl leuco methylene blue (BLMB) and crystal violet lactone (CVL) were dissolved in chlorinated biphenyl and kerosene. The resulting oil was dispersed as a liquid phase in an aqueous gelatin sol. To this dispersion were added gum arabic and polyvinyl methyl maleic anhydride (PVM/ MA), which, upon lowering of pH with acetic acid at the proper dilution, effects the formation of a coacervate solution of the gelatin, said coacervate forming embryonic capsule walls of coacervate solution about the dispersed oil droplets. Subsequently, the embryonic walls were hardened with glutaraldehyde. PVM/ MA was added, and the pH was raised to 10 with 20% caustic soda. The weight ratio of oil to gelatin was on the order of 10: 1, and average diameter of the resulting aggregate of individual droplets was on the order of 8 to 12 microns.

Additions to aqueous capsular slurry.In certain of the runs, the acid slurry was used, and in other runs the basic 12 slurry, 50 gallons of Karaya gum solution was diluted with water to 542 gallons, or 0.1% Karaya gum on a solids basis.

I to 1:11 Dr Wei lat VctWci ill; U a r y g g Preparation of capsular slurry-Benzoyl leuco methyl- Capsules, Acid Slurry 455. 2, 100 Kamya Gum solution 2' 28 2,280 ene blue BLMB) and crystal violet lactone (CVL) were dissolved in chlorinated biphenyl and kerosene. The re- Total 41630 sulting oil was dispersed as a liquid phase in an aqueous 9,75% solids gelatin sol. To this dispersion were added gum arabic and gfl gglf gg g i ggg 4 polyvinyl methyl maleic anhydride (PVM/ MA), which,

upon lowering of pH with acetic acid at the proper dilu- 4 80d tion, effected the formation of a coacervate solution of the 9.5% solids gelatin, said coacervate forming embryonic capsule walls of coacervate solution about the dispersed oil droplets.

u e n. i g gz g fi g 5 2223 z f gg g 5 Subsequently, the embryonic Walls were set by cooling and g; svlgr g throw cougidrmin g thfingddirf the hardened with glutaraldehyde, and the coacervate solution gg Gvm zolutiojatfhe dand tank g was treated wtih colloidal silica (United States Letters T112; ul used in etc'ri of the uns re orted in Table I Pamnt issued to Bruce Brockett on p p p April 20, 1965, and assigned to the assignee herein). The was 75% bleached kraft and bleached sulfite, re-

weight ratio of 011 to gelatin was on the order of 3.5 to 1, fined to a nominal Jordan freeness of 250 cc. Canadian so and the average diameter of the resulting aggregate of Standard at degrees cenmgrade' The pulp was Sued individual droplets was on the order of 8 to 12 microns with 1.2% rosin and 2.4% alum based on the pulp. No pH adjustment was made.

The operating conditions are described in Table I.

TABLE I Run No 1 2 3 4 5 9 t 8 9 10 11 Machine Speed, ft. min 700 700 700 700 700 700 700 700 700 500 565 Alum Concentration, Percent (Dry Pulp Solids) 2. 4 2. 4 2. 4 2. 4 2. 4 2. 4 2. 4 2. 4 2. 4t 2. 4 2. 4 Rosin Concentration, Percent (Dry Pulp Solids). 1. 2 1. 2 1.2 1. 2 1. 2 1. 2 1. 2 1. 2 1. 2 1. 2 1. 2 Percent Weight Capsules in Capsular Slurry:

Acid 2.85 1.30 1. 96 1. 36 3.0 3.0 3.0 1. 95 2.6 Basic 1.74 Cationic Starch Solids. Percent (Solid Stare Solution 0.99 0.90 0.97 0.00 0.06 1.0 1.0 1.0 0.9 1.5 Cationic Starch Applied at Hcadbox, Percent on pul 2.9 2.6 2.9 0 2.8 2.8 4.3 4.3 4.3 3.3 4.4 Jordan Consistency, percent 2. 00 2.50 2. 54 2. 4 2. 46 2.56 2.00 2. 84 2. 84 2. 54 2.60 Jordan Frecness, cc 265 252 224 239 240 274 385 420 420 455 272 Headbox Consistency, percent .54 .60 .48 .58 .56 .53 0.58 0,49 Hcadbox Fi'ceness, cc 125 132 94 131 129 127 79 Minutes Running Time.. 10 10 10 l5 20 10 1O 30 10 Beams ofPaper/minfl 1.92 1.92 r. 92 1.92 1.92 1.92 1.92 1.92 1. 92 1. 37 1. Moisture of Web at Dandy Rolhperccut 92-93 92-93 92-93 92-93 92-93 92-93 92-93 95-96 97-98 96-97 95-96 Typewriter Intensity 3 66 61 50 50 57 67 48 57 54 62 Smudge Resistance 3 98 98 96 95 92 92 99 99 99 98 98 Capsule Weight, lbs/ream (25 x 38/500) 2. 1 2. 3 3.0 3.1 2. 8 2. 3 2. 2 3.0 2. 5 2. 8 2. 9

1 The starch content was not ascertained, but starch was present as residual amount in the re-uscd white water from the previous runs.

1 Calculated on the basis of 108 inches wet web width. 1 Described hercaitcr.

EXAMPLE 11 The following is a description of a series of runs wherein minute capsules and other particulate matter were added to a wet web of fibrous paper on a Fourdrinier papermaking machine to make a self-contained record material.

Karaya gum, colloidal silica, and kaolin clay were present in a modified capsular slurry, and the cationic starch was present in the pulp, the Karaya gum and the cationic starch acting in concert to cause the emergence, Within the sheet of wet fibers, of a relatievly viscous liquid phase, as in Example I. The Karaya-clay-modified capsular slurry was added at the dandy roll, as shown in FIG. 1.

The Karaya gum and cationic starch solutions were prepared in the following manner:

Concentrated Karaya gum s0lu-ti0n.4.5 pounds of dry Karaya gum powder was stirred into 50 gallons of water, using a suitable mixer. Five minutes after all the powder had been added, the mixer was turned off. The Karaya gum solution was allowed to sit for two hours, and then the mixer was turned on for five minutes. The solution was allowed to sit for two additional hours, which periods enabled the Karaya gum to hydrate, and 2.7 pounds of 29% aqueous ammonia was added, with stirring to deacetylate the Karaya gum. After five minutes, the mixer was turned off, and the SS-gallon drum was covered. Just prior to combining the Karaya gum solution and the capsular The resulting capsular slurry was modified in the following manner:

Percent Total Solids 21. Capsule Solids as Percent of Total Solids 5-1.5.

The above modified capsular slurry was prepared by first mixing the kaolin clay and the capsular slurry, and then passing this mixture through a colloid mill. Then the oxidized potato starch, the colloidal silica, and the ZnCl were stirred in. The Karaya gum solution was added last, just prior to use.

Cationic starch solution.The cationic starch (Q-TAC 3891 Corn Products) solution was prepared by heating a slurry of the starch at 195 degrees Fahrenheit for a mini mum of fifteen minutes to provide a 1%, by weight, starch-in-water solution.

The pulp used was bleached kraft and 25% bleached sulfite, refined to a nominal Jordan freeness of 420 cc. Canadian Standard at 30 degrees Centigrade. The pulp was sized with 1.2% rosin and 2.4% alum based on the pulp. Concentrated sulfuric acid was added to the 1 3 machine chest to control pH. The operating data and results for these runs are set forth in Table H.

TABLE 11 Run No 1 2 3 4 5 Machine Speed, feet/minute 500 500 500 500 500 Alum Concentration, percent 2. 4 2. 4 2. 4 2. 4 2. 4 Rosin Concentration, percent 1. 2 1. 2 1. 2 1. 2 1. 2 Weight Solids in Modified Capsular Slurry, percent 4. 35 4. 35 4. 35 4. 35 5.0 Minutes Running Time- 7 3 27 10 42 Reams of Paper/minute 1. 37 1. 37 1. 37 1. 37 1. 37 Cationic Starch Solids, perceu 0. 94 0. 94 0.94 0. 94 0. 94 Cationic Starch Applied at Head ox,

percent on pulp 1. 96 2. 68 3. 72 4. 76 4. 76 Jordan Consistency, percent. 2. 22 2. 22 2. 22 2. 22 2. 33 Jordan Freeness, cc 418 414 410 405 485 Jordan pH 3. 5 3. 4 3. 8 3. 2 3. 8 Headbox Consistency, percent. 0.37 0.36 0. 36 0.35 0. 40 Headbox Freeness, cc 164 165 167 168 199 Headbox pH 4. 5 4. 3 4. 2 4. 1 4. 5 Tray pH 4. 3 4. 2 4. 2 4. 1 4. 5 Moisture of Web at Dandy Roll, percent 96 95-96 95-96 95-06 97-98 Typewriter Intensity 2 46 46 43 56 46 Smudge Resistance 2 85 89 89 96 88 Capsule Weight lbs/R 1 Calculated on the basis of 108 inches wet web width. 2 Described hereafter.

Once the embryonic sheet has the particles fixed in it in a stratum, or layer, predominately just beneath one surface, from which position they cannot migrate, subsequent operations may be performed on the web. Any other applications of materials may be made to the web, while wet, either while being pressed, while being dried, or in off-the-machine conversion of the finished sheet, as may be desired in view of the ultimate use for it.

In this respect, one or more coatings of mate-rial may subsequently be placed on either surface or on both surfaces .as may be desired.

Of particular interest in this respect are coatings containing minute capsules or particles which are applied to the side opposite said one surface, making the sheet useful as one of a stack of such sheets for making multiple copies by pressure. Other coatings may be applied to make the sheet sensitive to light, heat, or other energy application, or to give it magnetic or radiation properties, coloration, luminescence, or to make it photoelectrically or photoconductively responsive or non-responsive, or modified as may be desired in any pattern or mode of response not inconsistent with the presence of the novel stratum of particles.

EXAMPLE III Other combinations of materials useful to effect a phase separation within a fibrous sheet material are shown in Table III. In each case, an embryonic hand sheet was formed, and the indicated materials were .applied in the manner described hereafter.

For each of the combinations reported, the capsular slurry and the pulp used were the same. Table 111 gives a tabulation of the modifying agents used and .an indication of the response characteristics of the sheets.

The procedure used in preparing the sheets was as follows:

Preparation of aqueous capsular slurry.Benzoyl .leuco methylene blue (BLMB) and crystal violet lactone (CVL) were dissolved in chlorinated biphenyl and kerosene. The resulting oil was dispersed as a liquid phase in an aqueous gelatin sol. To this dispersion were added gu-m ar-abic and polyvinyl methyl maleic anhydride (PVM/MA), which, upon lowering of pH with acetic acid at the proper dilution, effected the formation of a coacervate solution of the gelatin, said coacerv-ate forming embryonic capsule walls of coacervate solution about the dispersed oil droplets. Subsequently, the embryonic Walls were set "by cooling and hardened with glutaraldehyde. The capsule-making process is described in the Katchen et a1. United States Patent No. 3,041,289, of which mention has been made. The weight ratio of oil to gelatin was on the order of 10:1, and average diameter of the resulting aggregate of individual droplets was on the order of 8 to r12 microns.

Additions to aqueous capsular slurry.The aqueous slurry of capsules described above had the various agents indicated in Table III below added thereto. The agents were added as an aqueous sol (solution) to give a modified slurry which contained capsules in an amount of 8% by Weight of the total slurry.

Preparation of puIp.-The pulp, consisting of kraft and 25% bleached sulfite, was beaten to a Canadian Standard 'Freeness of approximately 250 cc. at 30 degrees centigrade. The pulp was sized with 1.2% rosin .and 2.4% papermakers alum, both 'by weight on the dry fiber. The sized pulp was used at 0.5% solids.

Modification of sized pulp.-T0 600 cc. of the sized pulp described above were added the agents in the amounts indicated in Table III, based on the dry fiber weight. The agents were added as a sol (solution) or, in the case where the agent is insoluble in water, as an aqueous dispersion.

Preparation of sheet.-The modified sized pulp was placed in six liters of water in a sheet mould, and the liquid was .allowed to drain through the screen in said mold to form a wet web having approximately 96% moisture. The screen having the wet web thereon was transferred to a coating table, whereat the modified aqueous capsular slurry was drawn down across the top side of the wet web, using a No. 22 Meyer rod, being careful not to disturb the wet web. Subsequently, the sheet was couched from the screen, using TAPP'I standard blotter stock (TAPPI Standard No. T20 5 M58 Apparatus Item 9), and both surfaces were encased in TAP-PI blotters. This sandwich was pressed in a Williams hydraulic press for thirty seconds at 50 pounds per square inch gauge. The pressed sheet, at approximately 75% moisture, was removed from the blotters and dried on a rotary sheet dryer at degrees Fahrenheit for three minutes.

Table III, below, shows various agents and amounts thereof that were added to the capsular slurry and the pulp, respectively, and also shows the dry capsule weight per ream (DOW/R), ream size being 25" x 38"/500 sheets, and the typewriter intensity (TI) (more fully described below).

TABLE III Chart of Comparative Performance As To Print Intensity Reaction of Sheets Having:

A. Capsules Coated On Surface-Standmd N C. R. Commercial Product B. Capsules Appl ed To Wet Web Without Use 01 Phase-Separating Agents (Control Sheet) C. Capsules Applied 'Io Wet Web With With Use 0! Various Phase-Separating Agents.

Typewriter Amount of Intensity Agent Applied to Paper Fibers Agent Applied to Wet Web Capsules by Typewriter Corrected to With Capsules as Slurry Weight/Ream Intensity 3 Pounds in Pounds Coating,

Weight/Ream A (None) (None) 3 44 44 B (%onc) (None) 3 78 78 1. 5%Q-TAC (quaternary amine derivative 0.5% Karaya gum 3.1 49 50 cationic starch 2 0.2% Karaya gum, 2.0% Q-TAC do 3. 4 52 54 3. 0.5% Polymin P (polyetliylenimine). do i. 3.0 44 44 4. 0.8% Polymin P do 3. 4 40 42 5. 5% Colloidal Alumina do 2. 7 52 50 6. 0.2% Karaya, 1.0% Colloidal Alumina do 2. 9 52 51 i F i a 1i 6 Typewriter Amount 01 Intensity Agent Applied to Paper Fibers Agent Applied to Wet Web Capsules by Typewriter Corrected to With Capsules as Slurry Weight/Ream Intensity 3 Pounds in Pounds Coating,

Weight, Ream 3.0% Polymin P. 2.9 55 54 3.0% organic polyelcctrolyte (cationic 2. 2 55 50 amine). 5% Polyvinyl methyl malelc anhydride 3. 59 50 PVM [M A) 10. 3% Polymin P 2. 8 59 58 11. 2% gelatin (pH 4 0).. 3. 1 61 61 12. 5% gum tragaeanth 1. 5 85 73 13. 3% copolymer of polyethylene maleic 3. 4 55 59 anhydlide. 14. 0.3% DX-81 copolymer of polyethylene 5% Q IAC 2. 6 75 70 mnleic anhydride. 15. 0.5% Arquad 18-50 Quaternary am- 0.5% Karaya gum 3.0 61 61 monium salt. 16. Q-TAC 3% gelatin (pH 9.5) 1. 7 75 60 17. 3% casein (N11 cut)" 2. 2 79 7 l8. 3% methyl cellulose- 1. 0 70 67 10. 5% PVA 72-60 2. 2 80 74 20. 0.1% Separan NP-lO (Polyacrylamid L. 2. 6 62 58 21. 3% Polymin P 2. 2 61 55 22. 0.5% Separan AP 3.1 49 50 23. 0.1% Locust Bean Gu 2.1 66 59 24. 0.1% Guar gum 2. 7 59 57 c 0.1% Karaya gum- 2. 6 53 50 0.1% PVM/AIA 2.4 61 55 0.1% 1. 8 71 59 0.1% 2. 2 65 58 0.1% Karaya guru- 3. 1 46 47 0.1% Karaya gum. 3. 5 53 56 t (Free alum) 0.1% PVM/MA 3.5 57 60 (Free alum). 0.1% Locust Bean Gum 2. 5 61 56 S {Free a1um) 0.1% Guar gum 8.5 55 57 34. 0.3% Karaya gum, l u 0.1% Karaya gum. 3. 2 45 46 35. 0.3% Karaya gum, 10% Urea do 3. 3 52 54 36. 0.1% Knraya gum. 5% colloidal alumina. 3. 5 43 47 7. 5% CATO 8 (tertiary amine derivative 3.1 48 49 of corn starch). B8. 5% Cationic starch 3. 2 48 49 TAC 2. 9 47 46 3. 6 48 53 2. 2 58 51 2. 9 6'2 61 4. 6 48 54 3% Carboxyme 2. 9 63 62 5% Peniord Gum 250 Starch 2. 9 70 69 3% OMG 7L 2.0 76 66 3% PVM/MA 2. 2 70 63 5% Stayco M Stare 3. 1 62 63 0.5% Karaya gum 3. 0 62 62 50. 5% )Organic polyeleetrolyte (cationic .do 2. 8 54 52 amine 51. 0.8% Polymin P 0.1% g iglslehytle starch plus 15% 3. 9 48 49 a n 3 52. 0.3% Polyrnin P 0.4350% Karaya gum, 0.05% Separan AP- 3.0 43 43 1 Alum rosin sized pulp, free alum acting in presence of agent added to capsular slurry to cause emergent phase.

Set forth below is further information regarding the trade names appearing in Table III.

Q-TAC is as described on page 23.

Polymin P is manufactured by Badischc Anilin-E' Soda-Fabrik AG and is described in their bulletin No. MlllSe, 80950 (610) FKi, dated July 1961, as an aqueous solution of 'polyethyleniminc (50% solids), molecular weight 2030,000.

Arquad 18-50 is manufactured by Armour Chemical Company, described in their technical bulletin on Fatty Acid Derivatives, and Industrial Oils, dated 1957, is a quaternary ammonium chloride salt.

PVA 72-60 is manufactured by Du Font and described in their technical bulletin entitled Elvanol, polyvinyl alcohol, third edition, 1961, as a completely hydrolyzed, high viscosity grade of polyvinyl alcohol.

Separan NP-1O is manufactured by Dow Chemical Company and is described in Dows technical booklet No. 125-28442, entitled Separan, dated 1961, as .a high molecular weight polyacrylamide.

Separan AP-30, manufactured by Dow Chemical Company, is described as a high molecular weight polyacrylamide in their technical booklet No.125-284-62, entitled Soparan, dated 1961.

CATO-8 is manufactured by National Starch & Chemical Corporation and is described in their Technical Service Bulletin No. 20S rev., and further described in US. Patent No. 2,917,506.

Stayco M is manufactured by A. E. Staley Manufacturing Co. and described in their bulletin Calender starches, dated 1959 as a sodium hypochlorite oxidized corn starch of low viscosity.

Pen'ford Gum 250 Starch is manufactured by Penick & Ford, Ltd. and is described in the Corn Refining Divisions technical letter No. 87, dated February 2, 19611, as a hydroxy ethyl ether derivative of corn starch.

CMC-7L, manufactured by Hercules is described in their technical bulletin Sodium Carb'oxymethylcellulose, dated 1963, as a sodium carboxymethyl cellulose gum having a degree of substitution range of 0.65 to 0.85 and a low viscosity in the range of 30 to 50 cps. for a 2% solution.

As to the examples of Table III, in all instances except in the case of the control shcct, separation of a relatively viscous liquid phase occurred in the web upon addition of the capsular slurry.

Limitation of penetration of the capsules within the paper sheet material was tested for each of the samples reported in Examples I, II, and III by disposing each surface, in turn, of the sample sheet against a standard commercial N.C.R. receiving sheet (that is, a sheet containing attapulgite clay) and applying a pressure mark. In all samples, when the top surface of the sample sheet was adjacent the receiving sheet and pressure was applied, a distinctive mark was produced on the receiving sheet. In contradistinction, when the screen side of the sample sheet, except in the instance of the control sheet, Was placed adjacent the receiving sheet and pressure was ap plied, a mark was not formed on the receiving sheet. In the case of the control sample, a distinctive mark was produced on the receiving sheet when the screen side of the sample sheet was placed adjacent the receiving sheet and pressure was applied. This test clearly established that penetration of the capsules was limited to a depth less than the thickness of the paper. Had the capsules penetrated entirely through the paper, as was the case with the control sheet, a mark would have been produced on the receiving sheet, regardless of which side of the sample sheet was placed adjacent the receiving sheet.

Lest it be thought that burying of the capsules within the sheet makes it less effective as a pressure-responsive mark-forming sheet material, evidence to the contrary is found in the reported typewriter intensity and smudge resistance values obtained when using sheets made according to the teachings of this invention.

In determining typewriter intensity, a standard mark is prepared by taking a sheet having the dye-containing capsules coated on its outer surface, and placing said surface against the surface of a coated second sheet having the other mark-forming component, whereupon a pressure is brought to bear on the two sheets over an area of the sheet to produce a marked area, by transfer of the ruptured capsule contents to the second sheet. The reflectances of incident light from the unmarked area and the marked area after a period of time (twenty minutes) are then measured and compared. The typewriter intensity is the ratio of the reflectance of the marked area to the unmarked areaxlOO, the lower said ratio value the more intense the mark. The values of reflectance given are relative numbers only, but show the variance from the values obtained from standard coated sheets and from sheets in which the capsules were distributed through the body of fibers (the control sheet).

In many instances where a comparable weight of capsular material was contained in the paper, the typewriter intensity value was similar to or compared favorably with that of the present standard commercial paper coated with capsules.

The smudge resistance is a measure of the frictional smudge properties of a sheet material and is determined in general by disposing a sheet containing a complementary mark-forming reactant which completes the markforming reaction onto the sample sheet, so that the colorreactant-bearing surfaces of the two sheets are in contact, placing on said pair of sheets a standard weight, and drawing the top sheet across the under (sample) sheet for a fixed distance, both in a machine direction and in a cross-machine direction of the paper. Thereafter, the reflectance of the area of the top sheet which was under the weight is measured. Smudge resistance, as reported, is the ratio of the reflectance of the weighted area to the background area l00.

By the practice of this invention, sheet material, more particularly a microcapsule-containing paper, has been obtained wherein the major portion of the capsules are present in the top quarter of the thickness of the paper. Utilizing the so-called split test, wherein the paper sheet to be tested is soaked in water and then passed between two polished rolls, said rolls having a surface temperature below freezing (say, about 28 degrees Fahrenheit), the sample sheet is split in a plane through its thickness. A sample sheet prepared according to Run No. 3 of Table I was successively split as described above to yield sliver sections corresponding to the top /2, A, and A; of the thicknesses of the sample sheet. Determination of the capsule weight in each enumerated sliver showed that 59% of the capsules were present in the top /8 sliver, 87% of the capsules in the A sliver, and 96% of the capsules in the top /2 sliver.

Considering that the overall thickness of the sample was about 4 mils and the particle size of the capsules was about 4 to microns, it was beyond reasonable expectation and highly gratifying to find that the major portion of the capsules resided in the upper quarter of the paper. This was particularly surprising when considera- 18 tion is given to the pull through" forces that exist on a paper-making machine due to gravity, liquid entrainment, and suction.

EXAMPLE IV In this example, the particulate matter, whose penetration into a wet fibrous web is to be limited, is an oilsoluble dye, Azo Blue Black B.

Preparation of aqueous particulate slurry.-Microfine titanium dioxide was dispersed in water, using sodium silicate and Triton N- as the dispersing agents. To this dispersion was added the solid Azo Blue Black B in powdered form, and the entire mixture was blended in a Waring Blendor. After blending and just prior to use, dilute (0.1%) Karaya gum was stirred in. Octauol was added as a foam killer. The formulation for this slurry is as follows:

Material Dry Weight, Wet Weight,

E grams Titanox T102 20 20 5% NaiSiO4 0.5 10 Triton N-100 5 Water 300 A20 Blue Black B 5 5 0.1% Karaya gum solution.-- 025 25 Total 25. 525 365 4 drops Octauol Preparation of the pulp.The pulp, consisting of 75% bleached kraft and 25% bleached sulfite, was beaten to a Canadian Standard Freeness of approximately 250 cc. at 30 degrees centigrade. The pulp Was sized with 1.2% rosin and 2.4% papermakers alum, both by weight, on the dry fiber. The sized pulp at 0.5% solids was modified by the addition of 5% cationic starch (Q-TAC 3891) based on the dry fiber weight. The cationic starch was added as a 1% aqueous sol (solution).

Preparation of sheet.600 mls. of modified sized pulp was placed in six liters of water in a sheet mould, and the liquid was allowed to drain through the screen in said mould to form a wet web having approximately 96% moisture. The screen, having the wet web disposed thereon, was transferred to a coating table, whereat the aqueous particulate slurry was drawn down across the top side of the wet web, using a No. 22 Meyer Rod, being careful not to disturb the wet web. Subsequently, the sheet was couched from the screen, using TAPPI standard blotter stock (TAPPI Standards, T205, M-58, Apparatus, Item 9), and both surfaces were encased in such TAPPI blotters. This sandwich was pressed in a Williams hydraulic press for thirty seconds at fifty pounds per square inch on the gauge. The pressed sheet, at approximately 75 moisture, was removed from the blotters and dried on a rotary sheet dryer at degrees Fahrenheit for three minutes.

Emergence of the expected relatively viscous liquid phase occurred when the aqueous particulate slurry was drawn across the top of the cationic-starch-treated web. The web was then pressed and dried.

Limitation of penetration of the particulate matter within the paper sheet material was tested by disposing each surface of the sample sheet adjacent to the coated side of a specially-prepared capsule-coated sheet (conversion coated), said capsules containing oil only, no dye, and applying a pressure mark. When the top surface of the sample sheet was adjacent to the speciallyprepared capsule-coated sheet and pressure was applied, a distinctive mark was produced on the sample sheet. In contradistinction, when the screen side of the sample sheet was placed adjacent to the specially-prepared capsule coated sheet and pressure was applied, a mark was not produced on the sample sheet. This test clearly established that penetration of the particulate matter (the A10 Blue Black B dye) was limited to a depth within the thickness of the paper. Had the particulate matter penetrated entirely through the paper, a mark would have been produced on the sample sheet regardless of which side of the sample sheet was placed adjacent to the coated side of the specially-prepared capsule-coated sheet.

A further aspect of the subject invention concerns the nature of the fibrous sheet material resulting from carrying out the process of this invention. The sheet of the invention differs from earlier fibrous sheets in that the penetration of the particulate material is substantially uniform. In the usual fibrous sheet, though attempts are made to achieve a uniform laydown of fiber, this is generally difficult to obtain, and, for this reason, penetration of particulate material in a uniform stratum is impossible of attainment without the agency of this invention. In the subject invention, it has been found that the particulate matter penetrates over the area applied, to a substantially uniform degree through a limited thickness of the web.

It has been noted in the practice of this invention as applied to the formation of paper containing capsules as the particulate material that care should be exercised in the amount of the emergent viscous phase that is generated. It is believed that excess addition of the components essential to the formation of the viscous phase will produce a mass of coacervate that precludes or substantially reduces the capability of the embryonic web to sufiiciently rid itself of associated water and thereby to acquire sufiicient strength to maintain its integrity during the drying operation of the paper-making process. Moreover, it is uneconomical to add capsules and other materials beyond the needed amount. It has been found that a capsule addition of two to six pounds of cap sules/ream is satisfactory. However, the carrying out of this invention in a manner to avoid said excess, should this be the desired end, is well within the skill of the art having the benefit of the subject teaching.

What is claimed is:

1. A process for limiting the penetration of particulate material within an embryonic fibrous sheet, comprising forming a wet web of the fibrous material on a suitable support member, said wet web being sufficiently free to allow drainage of associated liquid and micro-size particulate material therethrough; While the web is in said state of freeness, applying particulate material to one surface of said web, and then substantially simultaneously with the application of said particulate material, forming a coacervate solution of a film-forming polymeric material within a limited thickness of the sheet, said coacervate solution enveloping the particulate material and wetting the fiber(s) in proximate relation thereto to thereby bind the particulate material to the fiber(s).

2. The product produced according to the process of claim 1.

3. A process for limiting the penetration of particulate material within a fibrous sheet, comprising and forming a wet web of fibrous material having a coacervate phaseenducing agent present therein on a suitable support member, said web being sufficiently free to allow drainage of liquid and particulate material therethrough, and then applying particulate material in the form of a liquid suspension to said wet web, said suspension containing in solution a film-forming polymeric coacervatable material to form a coacervate solution of film-forming polymeric material within a limited thickness of the sheet which envelopes the particulate material and simultaneously adheres to the proximate fibers thereby to atfix the particulate material to the fibers.

4-. The process of claim 3 wherein the particulate material is pressure-rupturable microcapsules each having a mark-forming component therein, the coacervate-phaseinducing agent is a cationic starch, and the film-forming polymeric material is ammonia-treated Karaya gum.

5. The process of claim 3 wherein the wet web comprises paper fibers and associated aqueous liquid and wherein the particulate material is applied when the wet web comprises from 92% to 98% water.

6. The process of claim 3 wherein the particulate material is pressure-rupturable microcapsules each having a mark-forming component therein, the coacervate-phaseinducing agent is a cationic starch, and the film-forming polymeric material is ammonia-treated Karaya gum.

7. The process of claim 3 wherein the phase-inducing agent and the film-forming polymeric material are of opposite polarity.

8. The process of claim 3, wherein the particulate material is pressure-rupturable capsules.

9. The product produced according to the process of claim 8.

References Cited UNITED STATES PATENTS 2,730,456 1/1956 Green et al. 11736.l 2,730,457 1/1956 Green 1l7-36.8 3,041,288 6/1962 Anthony 162158 X 3,137,631 6/1964 Soloway 162-158 X 3,257,267 6/1966 Hay 162183 X S. LEON BASHORE, Primary Examiner.

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