US3720562A - A method of bonding non woven fabrics - Google Patents

Abstract

Bonded fibrous nonwoven textile fabrics having excellent strength and textile-like softness, drape and hand which are intermittently bonded with synthetic resins in predetermined print patterns of binder areas having a relatively high, uniform concentration of from about 50 percent to about 120 percent by weight of resin binder in the binder areas, based on the weight of the fibers therein, said binder areas having very sharply defined borders or edges with a minimum of binder feathering thereat whereby the optical density of the bonded fibrous nonwoven textile fabric very sharply increases from substantially zero to a maximum of at least from about 0.6 to about 1.0 or greater in a distance of less than about 1 mm. (0.04 inch), and methods of depositing such synthetic resins from colloidal aqueous dispersions thereof into wet fibrous webs to form the bonded fibrous nonwoven textile fabrics, comprising the use of (1) metal complex coordination compounds and (2) synthetic resins and/or surfactants, at least one of which contains a specific coordinating ligand capable of being affected by ions or said metals to control the total migration of the resin binder during such deposition.

Description

United States Patent {191 Dreliclt M IMarch 13, 1973 A METHOD OF BONDING NON WOVEN FABRICS [75] Inventor: Arthur H. Drellch, Plainfield, NJ.

[73] Assignee: Johnson 8: Johnson [22] Filed: Aug. 21,1970

[211 Appl. No.: 65,880

Related 0.8. Application Data [63] Continuation'in-part of Ser. No. 800,265, Feb. 18, 1969, Pat. No. 3,649,330, which is a continuation-im part of Ser. No. 618,317, Feb. 24, 1967, abandoned, and a continuation-in-part of Ser. Nos. 623,797, March 10, 1967, Pat. No. 3,536,518, and Ser. No. 2,955, Jan. 14, 1970, abandoned, and Ser. No. 817,177, April 17, 1969, which is a continuation-inpart of Ser. No. 639,01 1, May 17, 1967, abandoned.

[52] U.S.Cl ..156/291,l17/98,117/11l R, 117/140, 117/143, 117/148, 117/161 R,

117/161 UZ, 117/161 UN, 117/161 UC,

[51] 1nt.Cl. ..B32b 7/14 [58] Field of Search 156/277, 290, 291; 117/143, 117/144, 145, 148,161 UZ, 161 UD,161

UN, 161 UC, 162,163, 98; 260/308, 296

SQ, 29.6 R, 128, 29.6 BM; 161/150,157

[56] References Cited UNITED STATES PATENTS 3,001,957 9/1961 Kray etal ..117/161UZ Attorney-Alexander T. Kardos and Robert L. Minier [57] ABSTRACT Bonded fibrous nonwoven textile fabrics having excellent strength and textile-like softness, drape and hand which are intermittently bonded with synthetic resins in predetermined print patterns of binder areas having a relatively high, uniform concentration of from about 50 percent to about 120 percent by weight of resin binder in the binder areas, based on the weight of the fibers therein, said binder areas having very sharply defined borders or edges with a minimum of binder feathering thereat whereby the optical density of the bonded fibrous nonwoven textile fabric very sharply increases from substantially zero to a maximum of at least from about 0.6 to about 1.0 or greater in a distance of less than about 1 mm. (0.04 inch), and methods of depositing such synthetic resins from colloidal aqueous dispersions thereof into wet fibrous webs to form the bonded fibrous nonwoven textile fabrics, comprising the use of 1) metal complex coordination compounds and (2) synthetic resins and/or surfactants, at least one of which contains a specific coordinating ligand capable of being affected by ions or said metals to control the total migration of the resin binder during such deposition.

15 Claims, 14 Drawing Figures PATENTEUNAR 1 3:975

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304/050 fies/vs ATTORNEY PATENTEUHARI 3127a dmm 7- W4 ATTORNEY METHOD OF BONDING NON WOVEN FABRICS This patent application is a continuation-in-part of my earlier-filed, co-pending patent application Ser. No. 800,265, filed Feb. 18, 1969 now U.S. Pat. 3,649,330, which is a continuation-in-part of my earlier-filed patent application Ser. No. 618,317, filed Feb. 24, 1967, now abandoned. It is also a continuation-in-part of my earlier-filed, co-pending patent application Ser. No. 623,797, filed Mar. 10, 1967, now U.S. Pat. No. 3,536,518, and my earlier-filed, co-pending patent application Ser. No. 2,955, filed Jan. 14, 1970, now abandoned. And, it is also a continuation-in-part of my earlier-filed, co-pending patent application Ser. No. 817,177, filed Apr. 17, 1969 which is a continuationin-part of my earlier-filed patent application Ser. No. 639,01 I, filed May 17, 1967, now abandoned.

The present invention relates to porous, absorbent, fibrous sheet materials and to their methods of manufacture. More particularly, the present invention is concerned with the so-called bonded, "nonwoven" textile fabrics, i.e., fabrics produced from textile fibers without the use of conventional spinning, weaving, knitting or felting operations. Although not limited thereto, the invention is of primary importance in connection with nonwoven fabrics derived from oriented" or carded fibrous webs composed of textile-length fibers, the major proportion of which are oriented predominantly in one direction.

Typical of such fabrics are the so-called MASS- LlNN" nonwoven fabrics, some of which are described in greater particularity in U. S. Pat. Nos. 2,705,687 and 2,705,688, issued Apr. 5, 1955, to D. R. Petterson et al. and l. S. Ness et al., respectively.

Another aspect of the present invention is its application to nonwoven fabrics wherein the textile-length fibers were originally predominantly oriented in one direction but have been reorganized and rearranged in predetermined designs and patterns of fabric openings and fiber bundles. Typical of such latter fabrics are the so called KEYBAK" bundled nonwoven fabrics, some of which are described in particularity in U. S. Pat. Nos. 2,862,251 and 3,033,721, issued Dec. 2, 1958 and May 8, 1962, respectively, to F. Kalwaites.

Still another aspect of the present invention is its application to nonwoven fabrics wherein the textile length fibers are disposed at random by air-laying techniques and are not predominantly oriented in any one direction. Typical nonwoven fabrics made by such procedures are termed isotropic" nonwoven fabrics and are described, for example, in U. S. Pat. Nos. 2,676,363 and 2,676,364, issued Apr. 27, 1954, to C. H. Plummer et al.

And, still another aspect of the present invention is its application to nonwoven fabrics which comprise textile length fibers and which are made basically by conventional or modified aqueous papermaking techniques such as are described in greater particularity in pending patent application, Ser. No. 4,405, filed Jan. 20, 1970 now abandoned, by P. R. Glor and A. H. Drelich. Such fabrics are also basically isotropic" and generally have like properties in all directions.

The conventional base starting material for the majority of these nonwoven fabrics is usually a fibrous web comprising any of the common textile-length fibers, or mixtures thereof, the fibers varying in average length from approximately 56 inch to about 2% inches. Exemplary of such fibers are the natural fibers such as cotton and wool and the synthetic or man-made cellulosic fibers, notably rayon or regenerated cellulose.

Other textile length fibers of a synthetic or manmade origin may be used in various proportions to replace either partially or perhaps even entirely the previously-named fibers. Such other fibers include: polyamide fibers such as nylon 6, nylon 66, nylon 610, etc.; polyester fibers such as "Dacron", FortreP' and Kodel"; acrylic fibers such as Acrilan", Orlon" and Creslan"; modacrylic fibers such as Verel" and Dynel"; polyolefinic fibers derived from polyethylene and polypropylene; cellulose ester fibers such as Arnel" and "Acele; polyvinyl alcohol fibers; etc.

These textile length fibers may be substituted either partially or entirely by fibers having an average length of less than about 16 inch and down to about A inch. These fibers, or mixtures thereof, are customarily processed through any suitable textile machinery (e.g., a conventional cotton card, a Rando-Webber", a papermaking machine, or other fibrous web producing apparatus) to form a web or sheet of loosely associated fibers, weighing from about grains to about 2000 grains per square yard or even higher.

If desired, even shorter fibers, such as wood pulp fibers or cotton linters, may be used in varying proportions, even up to 100 percent, where such shorter length fibers can be handled and processed by available apparatus. Such shorter fibers have lengths less than 54 inch.

The resulting fibrous web or sheet, regardless of its method of production, is then subjected to at least one of several types of bonding operations to anchor the individual fibers together to form a self-sustaining web. One method is to impregnate the fibrous web over its entire surface area with various well-known bonding agents, such as natural or synthetic resins. Such over-all impregnation produces a nonwoven fabric of good longitudinal and cross strength, acceptable durability and washability, and satisfactory abrasion resistance. However, the non-woven fabric tends to be somewhat stiff and boardlike, possessing more of the properties and characteristics of paper or board than those of a woven or knitted textile fabric. Consequently, although such over-all impregnated nonwoven fabrics are satisfactory for many uses, they are still basically unsatisfactory as general purpose textile fabrics.

Another well-known bonding method is to print the fibrous webs with intermittent or continuous straight or wavy lines, or areas of binder extending generally transversely or diagonally across the web and additionally, if desired, along the fibrous web. The resulting nonwoven fabric, as exemplified by a product disclosed in the Goldman U.S. Pat. No. 2,039,312 and sold under the trademark MASSLINN", is far more satisfactory as a textile fabric than over-all impregnated webs in that the softness, drape and hand of the resulting nonwoven fabric more nearly approach those of a woven or knitted textile fabric.

The printing of the resin binder on these non-woven webs is usually in the form of relatively narrow lines, or elongated rectangular, triangular or square areas, or annular, circular, or elliptical binder areas which are spaced apart a predetermined distance which, at its maximum, is preferably slightly less than the average fiber length of the fibers constituting the web. This is based on the theory that the individual fibers of the fibrous web should be bound together in as few places as possible.

The nominal surface coverage of such binder lines or areas will vary widely depending upon the precise properties and characteristics of softness, drape, hand and strength which are desired in the final bonded product. In practice, the nominal surface coverage can be designed so that it falls within the range of from about percent to about 50 percent of the total surface of the final product. Within the more commercial aspects of the present invention, however, nominal surface coverages of from about l5 percent to about 40 percent are preferable.

Such bonding increases the strength of the nonwoven fabric and retains substantially complete freedom of movement for the individual fibers whereby the desirable softness, drape and hand are obtained. This spacing of the binder lines and areas has been accepted by the industry and it has been deemed necessarily so, if the stiff and board-like appearance, drape and hand of the over-all impregnated nonwoven fabrics are to be avoided.

The nonwoven fabrics bonded with such line and area binder patterns have had the desired softness, drape and hand and have not been undesirably stiff or board-like. However, such nonwoven fabrics have also possessed some disadvantages.

For example, the relatively narrow binder lines and relatively small binder areas of the applicator (usually an engraved print roll) which are laid down on the fibrous web possesses specified physical dimensions and inter-spatial relationships as they are initially laid down. Unfortunately, after the binder is laid down on the wet fibrous web and before it hardens or becomes fixed in position, it tends to spread, diffuse or migrate whereby its physical dimensions are increased and its inter-spatial relationships decreased. And, at the same time, the binder concentration in the binder area is lowered and rendered less uniform by the migration of the binder into adjacent fibrous areas. One of the results of such migration is to make the surface coverage of the binder areas increase whereby the effect of the intermittent bonding approaches the effect of the over-all bonding. As a result, some of the desired softness, drape and hand are lost and some of the undesired properties of harshness, stiffness and boardiness are increased.

Various methods have been proposed to prevent or to at least limit such spreading, difiusing or' migration tendencies of such intermittent binder techniques.

For example, U. S. Pat. No. 3,009,822, issued Nov. 21, |96l to A. H. Drelich et al. discloses the use of a non-migratory regenerated cellulose viscose binder which is applied in intermittent fashion to fibrous webs under conditions wherein migration is low and the concentration of the binder in the binder area is as high as 35 percent by weight, based on the weight of the fibers in these binder areas. Such viscose binder possesses inherently reduced spreading, diffusing and migrating tendencies, thereby increasing the desired softness, drape and hand of the resulting nonwoven fabric. This viscose binder has found acceptance in the industry but the use of other more versatile binders has always been sought.

Resins, or polymers as they are often referred to herein as interchangeable terms, are high molecular weight organic compounds and, as used herein, are of a synthetic or man-made origin. These synthetic or manrnade polymers have a chemical structure which usually can be represented by a regularly repeating small unit, referred as a mer, and are formed usually either by an addition or a condensation polymerization of one or more monomers. Examples of addition polymers are the polyvinyl chlorides, the polyvinyl acetates, the polyacrylic resins, the polyolefins, the synthetic rubbers, etc. Examples of condensation polymers are the polyurethanes, the polyamides, the polyesters, etc.

Of all the various techniques employed in carrying out polymerization reactions, emulsion polymerization is one of the most commonly used. Emulsion polymerized resins, notably polyvinyl chlorides, polyvinyl acetates, and polyacrylic resins, are widely used throughout many industries. Such resins are generally produced by emulsifying the monomers, stabilizing the monomer emulsion by the use of various surfactant systems, and then polymerizing the monomers in the emulsified state to form a stabilized resin polymer. The resin polymer is usually dispersed in an aqueous medium as discrete particles of colloidal dimensions (1 to 2 microns diameter or smaller) and is generally termed throughout the industry as a resin dispersion, or a resin emulsion" or latex".

Generally, however, the average particle size in the resin dispersion is in the range of about 0.1 micron (or micrometer) diameter, with individual particles ranging up to l or 2 microns in diameter and occasionally up to as high as about 3 or 5 microns in size. The particle sizes of such colloidal resin dispersions vary a great deal, not only from one resin dispersion to another but even within one resin dispersion itself.

The amount of resin binder solids in the resin colloidal aqueous dispersion varies from about 1/ l0 percent solids by weight up to about 60 percent by weight or even higher solids, generally dependent upon the nature of the monomers used, the nature of the resulting polymer resin, the surfactant system employed, and the conditions under which the polymerization was carried out.

These resin colloidal dispersions, or resin emulsions, or latexes, may be anionic, non-ionic, or even polyionic and stable dispersions are available at pl-l's of from about 2.5 to about 10.5.

The amount of resin which is applied to the porous or absorbent material varies within relatively wide limits, depending upon the resin itself, and nature and character of the porous or absorbent materials to which the resins are being applied, its intended use, etc. A general range of from about 4 percent by weight up to about 50 percent by weight, based on the weight of the porous or absorbent material, is satisfactory under substantially all uses. Within the more commercial limits, however, a range of from about 10 percent to about 30 percent by weight, based on the weight of the porous or absorbent material, is preferred.

Such resins have found use in the coating industries for the coating of woven fabrics, paper and other materials. The resins are also used as adhesives for laminating materials or for bonding fibrous webs. These resins have also found wide use as additives in the manufacture of paper, the printing industry, the decorative printing of textiles, and in other industries.

In most instances, the resin is colloidally dispersed in water and, when applied from the aqueous medium to a wet porous or absorbent sheet material which contains additional water, is carried by the water until the water is evaporated or otherwise driven off. if it is desired to place the resin only on the surface of the wet porous or absorbent sheet material and not to have the resin penetrate into the porous or absorbent sheet material, such is usually not possible inasmuch as diffusion takes place between the aqueous colloidal resin and the water in the porous material. in this way the colloidal resin tends to spread into and throughout the porous material and does not remain merely on its surface.

Or, if it is desired to deposit the resin in a specific intermittent print pattern, such as is used in bonding nonwoven fabrics, the aqueous colloid tends to diffuse and to wick along the individual fibers and to carry the resin beyond the confines of the nominal intermittent print pattern. As a result, although initially placed on the nonwoven fabric in a specific intermittent print pattern, the ultimate pattern goes far beyond that due to the spreading or migration which takes place due to the diffusion of the water and the resin, until the water is evaporated or otherwise driven off.

I have discovered new resin binder compositions containing polymers colloidally dispersed in aqueous media and new methods of applying such resin binder compositions to porous or absorbent fibrous materials, whereby the resins are applied in a controlled relatively non-migrating manner. If it is desired that the resin be placed only on the surface of the porous or absorbent material, my compositions and methods will allow this to be done. Furthermore, if it is desired that the resin be impregnated throughout the material, from one surface to the other surface, again, my composition and method will allow this to be done.

In patent application Ser. Nos. 618,3]7 and 800,265, filed Feb. 24, 1967 and Feb. I8, 1969, respectively, there are disclosed improved methods of using emulsion polymerized resins which are so prepared as to be stable under acid conditions, i.e., an environment with a pH below 7.

In accordance with the invention disclosed in these patent applications, the resin dispersion comprises from about 0.1 percent to about 60 percent by weight of emulsion polymerized resin solids and from about 0.0l percent to about 10 percent by weight of the resin solids of a water soluble metal salt. The metal ion of the salt has a valence of at least +3 and the metal salt is capable of forming an insoluble oxide, hydroxide, or hydrated oxide under alkaline conditions.

If such a resin composition is utilized in applying resins to fibrous materials, the deposition of the resin and its migration or spreading tendencies on such fibrous materials may be controlled by applying the acid-stable resin dispersion to the fibrous material while substantially simultaneously raising the pH of the dispersion to a value greater than 7. For example, if it is desired to apply the resin merely to the surface of the fibrous material, the pH of the fibrous material is raised to greater than 7 and the acid-stable dispersion having a pH less than 7 is applied to the fibrous materials by spraying techniques or by other methods which apply the resin dispersion basically only on the surface of the fibrous materials. Microscopic inspection of the fibrous materials and the resin which has been sprayed thereon will reveal that the resin has not penetrated into the fibrous material to any appreciable degree. This, of course, is due to the fact that the resin dispersion is stable as long as its pH remains on the acid side, that is, below 7. However, upon contacting the fibrous material having a pH greater than 7, the pH of the resin dispersion is raised to greater than 7, its stability vanishes, and it figuratively freezes" in position whereby any migration or penetration inwardly from the point of initial deposition by the resin dispersion is instantly stopped.

Further, if the application of the resin employs a conventional rotogravure process using a conventional engraved-roll wherein a pattern is impressed and printed on the material, the resin print pattern will penetrate through the material completely due to the normal pressure of the print roll and will then coagulate and be fixed in place with minimal migration or lateral spread. Microscopic inspection of the material and the resin thereon will reveal that the resin has penetrated directly and completely through to the other surface of the material but with controlled and minimal migration or lateral spread from the point of initial deposition.

0n the other hand, if the fibrous material has or is given a pH of less than 7 and the resin dispersion which, of course, also has a pH of less than 7 is applied by a conventional engraved print roll in a rotogravure process, the acid stable dispersion will retain its stability after deposition and its tendency to migrate or spread laterally will continue to exist. Therefore, the fibrous material and the resin dispersion must be substantially immediately treated to raise the pH to greater than 7. The resin will then be deposited through the fibrous material from the top surface to the bottom in the print patterns of the engraved print roll but the substantially immediate conversion to a system having a pH greater than 7 will immediately control migration or lateral side spread from the point of initial deposition.

The principles of the invention described in these patent applications also find application in impregnation or "over-all" bonding processes, wherein a fibrous material is passed into and through an impregnating bath of the acid-stable resin dispersion. It has been noted that the resin dispersion which substantially completely impregnates the fibrous material has a tendency to migrate to the surfaces thereof, particularly during the drying process, leaving the center with a lesser concentration of resin solids, and creating a socalled soft-center" which is often not desired. If the over-all bonded and impregnated material is treated with an alkali to raise the pH to above 7, before the drying step is initiated, then the impregnating resin dispersion is again "frozen in place and there is substantially no tendency of the resin dispersion to migrate to the surfaces and create a "soft-center" during the drying operation. Other variations will, of course, be readily apparent to one skilled in the art.

In the dispersion of the emulsion polymerized, colloidal resin particles, there exists around each particle,

an electrokinetic charge generally called the Zeta Potential. In most colloids this charge is negative and tends to cause the particles to repel each other and hence, stay in the dispersed form. It is believed that the addition of the salts, as described above, to the colloidal resin dispersion allows this Zeta Potential to be controlled by controlling the pH of the dispersion. When the pH of the dispersion is brought to above about 7 in the presence of the appropriate metal salt, the Zeta Potential of the colloidal resin particles is reduced to substantially zero and the individual particles no longer repel each other. The dispersion becomes unstable and the deposition of the resin on other substances may be controlled. This, of course, is only one suspected theory as to why my new composition allows for controlled resin deposition.

The salts used in accordance with the invention described in these patent applications are the salts of metals, wherein, the cation has a positive valence of 3 or higher. Suitable examples of such metals are zirconium, thorium, aluminum, iron, chromium, etc. The salt may be sulfate, acetate, nitrate, chloride, etc., or virtually any salt so long as the metal ion has a positive valence of 3 or greater. The salt must be capable of forming an insoluable oxide, hydroxide or hydrated oxide under alkaline conditions.

The amount of salt used will vary in accordance with the resin used and with the degree of control of the resin deposition that is desired. From about 0.01 percent to percent or even higher by weight of the amount of resin solids present of metal salt may be used in accordance with the invention described in these patent applications. The control at the lower percentages of salt may be difficult in some instances and it is preferred to keep this lower limit above about 0.1 percent. It is uneconomical to use the higher amounts of salts especially in view of the relative cost of some of the salts compared to the resin and hence, it is preferred to keep the upper limit at 2 percent or less.

The resins which may be used in the method of the present invention are the emulsion polymerized resins which are in the form of solid resin particles dispersed in a liquid which is usually water. These resin dispersions or resin emulsions as they are called, are stabilized by various types of surfactant systems and the dispersion is stable under acid conditions. Suitable examples would be the polyvinyl chlorides, polyvinyl acetates, polyacrylic resins, etc. Materials such as natural rubber or synthetic rubber are unsuitable for use in accordance with the invention described in these patent applications as they have oleates or soaps present which appear to disrupt the mechanism of the present invention.

The resin emulsion may be anionic or non-ionic or in fact may be polyionic so long as it is stable under the acid conditions. By being stable under acid conditions it is meant that the resin dispersion will remain in the dispersed state at pHs of from 7 or slightly less than 7 down to the very acid pH's such as 2 or 3.

Generally, the particle size in the resin dispersions will vary from about 1/10 of a micron or smaller to 3 to 5 microns in size. And the amount of resin solids in the dispersion will vary from l/l0 of a percent solids up to 60 percent or even higher solids, generally dependent upon the resin used, the surfactant system used and the conditions under which the resin is polymerized.

The salt may be added to the resin dispersion either in its solid form or it may be initially dissolved in water and the salt solution added to the resin dispersion.

The resin dispersion is stable as long as the pH is less than 7, however, once the pH is raised to greater than 7, it appears that the Zeta Potential of the resin particles is reduced and possibly brought to zero which causes the resin particles to conglomerate or coagulate. If the surface ofa fibrous web contains an alkali and the composition of resin and metal salt as previously described is placed on the web, the particles will immediately be attracted to the fibers and coagulate on the surface of the fibers.

The pH may be raised by any of the known alkalies such as ammonium hydroxide, sodium hydroxide, potassium hydroxide, lithium hydroxide, sodium car bonate or any other material which will give a pH of greater than 7. The alkali and amount of alkali used is controlled by economics and by the effect the alkali may have on the other material, for example, sodium hydroxide can do great damage to cotton fibers and will interfere with the curing of many resins. It will be readily apparent to one skilled in the art that suitable alkalies and concentrations may be chosen dependent on the material to be treated.

In some instances the resin may contain active crosslinking co-monomers, such as the acrylic resins having N-methylol acrylamide or other type groups. When such resins are used in the presence of certain metal salts, especially zirconium salts, the zirconium may cross-link and form various complexes with these resins which in turn improves the binding properties of the resin. it appears to be immaterial whether the metal salt cross-links or does not cross-link the resin as far as controlling the deposition of the resin in accordance with the present invention.

in patent applications Ser. Nos. 623,797 and 2,955, filed Mar. 10, 1967 and Jan. 14, 1970, respectively, there are disclosed other improved methods of using emulsion polymerized resins which are so prepared as to be stable under alkaline conditions, i.e., pHs of 7 to 9 or higher.

In accordance with the invention disclosed in these latter two patent applications, there is utilized a stable emulsion polymerized resin dispersion having a pH of from about 7 to 9 and an anionic surfactant selected from the class consisting of alkyl aromatic sulfonic acids, alkyl sulfonic acid and carboxylic acids. The dispersion comprises from about 0.] to percent by weight of emulsion polymerized resin solids, from about 0.1 to 5 percent by weight of the resin solids of an anionic surfactant selected from the class consisting of alkyl aromatic sulfonic acids, alkyl sulfonic acids and carboxylic acids and from about 0.01 to 2 percent by weight of the resin solids ofa metal chelate compound.

If the resin composition described in these patent applications is applied to porous materials, its deposition may be controlled by applying it to the porous material while substantially simultaneously lowering its pH to a value less than 7. For example, if it is desired to apply the resin merely to the surface of the porous material, the pH of the porous material is lowered to less than 7 and the dispersion, in accordance with the present invention, then applied to the porous material. The resin will be deposited substantially only on the surface of the porous material. On the other hand, if the porous material is given a pH of greater than 7 and the resin applied and then the porous material substantially immediately treated to lower its pH to less than 7, the resin will be deposited throughout the porous material. Other variations will, of course, be readily apparent to one skilled in the art.

It is believed that the anionic surfactant in the resin dispersion system maintains the colloidal dispersion of solid particles in a stable dispersed form. When a potentially strong cation such as is present in a chelate compound is introduced in the resin dispersion and the resin dispersion made acid forming the cation, the cation destroys the surfactant system precipitating the resin particles and allowing for control of the deposition of the resin on other substances. This, of course, is only one suspected theory as to why my new composi tion allows for controlled resin deposition.

The metal chelate compounds suitable for use with the invention disclosed in these patent applications are compounds in which atoms of the same chelate molecule are coordinated with a metal ion. Suitable metals in the chelate compound are calcium, magnesium, iron, zinc, copper, tin, etc. Suitable chelate compounds are the metal chelates of ethylenediaminetetraacetic acid, the metal chelates of salicylaldehyde imine, the metal chelates of condensed phosphates, the metal chelates of ammonium triacetic acid, etc.

The amount of metal chelate compound used will vary in accordance with the resin used and with the degree of control of the resin deposition that is desired. From about 0.0l to 2 percent or even higher by weight of the amount of resin solids present of the metal chelate compound may be used in accordance with the present invention. It is uneconomical to use the higher amounts of chelates especially in view of the relative cost of some of the chelates compared to the resin and hence, it is preferred to keep the upper limit at 2 percent or less.

The resins which may be used in the method of the present invention are the emulsion polymerized resins which are in the form of solid resin particles dispersed in a liquid which is usually water. These resin dispersions or resin emulsions as they are called, are stabilized by an anionic surfactant system and the dispersion is stable at pl-ls of 7 to 9. Suitable examples are the polyvinyl chlorides, polyvinyl acetates, polyacrylic resins, synthetic rubber latexes, etc.

Generally, the particle sizes in the resin dispersions vary from about l/l of a micron or smaller to 3 to 5 microns in size. And the amount of resin solids in the dispersion varies from l/lO of a percent solids up to 60 percent or even higher solids, generally dependent upon the resin used, the surfactant system and the conditions under which the polymerization was carried out.

The surfactant system used must be anionic and the anionic surfactant must be capable of precipitation by a cation. Suitable anionic surfactants are the alkyl aromatic sulfonic acids, alkyl sulfonic acids and the carboxylic acids, such as dodecyl benzene sulfonate, oetyl benzene sulfonate, hexyl benzene sulfonate, octadecyl benzene sulfonate, cetyl sulfonate, hexyl sulfonate, dodecyl sulfonate, octadecyl sulfonate, and the sodium and potassium fatty acid soaps containing from five to 18 carbon atoms. Other anionic surfactants include sodium p-l-methyl alkyl benzene sulfonates in which the alkyl group contains from l0 to 16 carbon atoms, the sodium di-n-alkyl sulfosuccinates in which the alkyl groups contain from four to l2 carbon atoms, the potassium n-alkyl malonates in which the alkyl group contains from eight to [8 carbon atoms, the potassium alkyl tricarboxylates in which the alkyl group contains from six to [4 carbon atoms, the alkyl betaines in which the alkyl group contains from six to l4 carbon atoms, the ether alcohol sulfates, sodium n-alkyl sulfates, containing from six to 18 carbon atoms, etc.

The amount of surfactant used may vary from about 0.1 percent to 5 percent by weight of the resin solids dependent on the type resin being polymerized and the conditions under which it is polymerized.

The resin dispersion containing the metal chelate compound is stable as long as the pH is from about 7 to 9. However, once the pH is lowered below about 7, it appears that the metal cation is released and attacks the anionic surfactant system in the resin dispersion causing the resin particles to agglomerate or coagulate. If the surface of a fibrous web contains a dilute acid and the composition of resin and metal chelate compound as previously described is placed on the web, the particles will immediately coagulate on the surface of the fibers.

The pH may be lowered by any of the known dilute acids such as acetic acid, or any other material which will give a pH of less than 7. The dilute acid and amount of acid used is controlled by economics and by the effect the acid may have on the other material. it will be readily apparent to one skilled in the art that suitable acids and concentrations may be chosen de pendent on the material to be treated.

In patent applications Ser. Nos. 639,01 1 and 8l7,l77, filed May l7, 1967 and Apr. 17, 1969, respectively, there are disclosed still other improved methods of using emulsion polymerized resins which are stable under moderately acid or alkaline conditions, i.e., pHs of from about 2.5 to about 10.5.

In accordance with the invention disclosed in these latter two patent applications, the deposition of emul sion polymerized resins on absorbent materials may be controlled by first treating the absorbent material with an aqueous solution containing from about 0.02 to l percent of a high molecular weight polyelectrolyte polymer having cationic constituents containing nitrogen in the form of amines, amine salts, imines, amides, etc., and applying the emulsion polymerized resin to the treated absorbent material. Unexpectedly, the diffusion of the resin in the absorbent material is greatly inhibited even in the presence of large amounts of water.

in the dispersion of the emulsion polymerized, colloidal resin particles, there exists around each particle, an electrokinetic charge called the Zeta Potential. in most colloids this charge is negative and tends to cause the particles to repel each other and stay in the dispersed form. It is believed that a polyelectrolyte polymer containing certain cationic constituents reduces the Zeta Potential of the resin particles and by so doing inhibits the particle from diffusing in its water carrier. This, of course, is one suspected theory as to why my new methods allow for the control of the deposition of resins on absorbent materials.

The desired binder migration control resulting from the pretreatment of the absorbent material with the aqueous polyelectrolyte solution and the subsequent printing of the impregnated absorbent material with the desired pattern of polymeric resin binder, however, is realized fully only if the printing with the polymeric resin binder takes place while the absorbent material is still wet with the polyelectrolyte solution. Under such circumstances, the penetration of the polymeric resin binder into the absorbent material rapidly takes place under controlled conditions and resin bonding takes place completely through the absorbent material from the top surface to the bottom surface substantially instantaneously.

Such a bonded absorbent material with a suitable binder is capable of withstanding laundering and/or dry cleaning; it withstands relatively rough usage and has good abrasion resistance.

However, if drying of the absorbent material were permitted subsequent to the impregnation with the polyelectrolyte solution and the polymeric resin binder were to be applied to the dried absorbent material, there would be very little penetration of the polymeric resin binder into the absorbent material and there would merely be a surface deposition of polymeric resin binder on the top surface of the absorbent material. As a result, the absorbent material, being unbonded on the back side, would not be acceptable as a uniformly or adequately bonded product, for example, in the nonwoven fabric industry. It would be incapable of withstanding laundering; it would fall apart in use; and the unbonded back surface would be incapable of resisting abrasion.

The polyelectrolyte compounds suitable for use are the high molecular weight polymers which are water soluble or colloidally dispersible and have a repeating cationic constituent on the polymer backbone. The cationic substituents suitable for use in accordance with the invention are those groups containing nitrogen having a positive charge as are well known in the art, it includes the amines, amine salts, imines, amides, etc.

The amount of polyelectrolyte compound used will vary in accordance with its cationic activity, the resin used and the degree of control of resin deposition that is desired. From about 0.1 to percent of polyelectrolyte by weight of the resin to be deposited on the absorbent surface may be used in accordance with the invention disclosed in these patent applications. It is uneconomical to use the higher amounts of polyelectrolytes especially in view of the relative cost of some of these compounds compared to the resin and hence, it is preferred to keep the upper limit at 5 percent or less.

The resins which may be used in the method of the invention disclosed in these patent applications are the emulsion polymerized resins which are in the form of solid resin particles dispersed in a liquid which is usually water. These resin dispersions or resin emulsions as they are called, may be anionic, non-ionic or even polyionic and the dispersion is stable at pl'l's of 2.5 to 10.5. Suitable examples are the polyvinyl chlorides, polyvinyl acetates, polyacrylic resins, etc.

Generally, the particle size in the resin dispersions will vary from about 1/10 ofa micron or smaller to 3 to 5 microns in size. The amount of resin solids in the dispersion will vary from l/IO of a percent solids up to 75 percent or even higher solids, generally dependent upon the resin used, the surfactant system and the conditions under which the polymerization was carried out.

The amount of resin which is applied to the absobent material varies within relatively wide limits, depending upon the resin binder itself, the nature and character of the absorbent material being bonded, its intended use, etc. A range of from about 4 percent by weight to about 50 percent by weight, based on the weight of the absorbent material, is satisfactory under substantially all uses. Within the more commercial limits, however, a range of from about 5 percent by weight to about 30 percent by weight, based on the weight of the absorbent material, is preferred.

ln carrying the invention disclosed in these patent applications into practice, the polyelectrolyte is dissolved or dispersed in an aqueous medium and the aqueous medium containing the polyelectrolyte applied to the absorbent material to be treated with resin. The medium containing the polyelectrolyte may be sprayed or padded onto the absorbent material as desired. The resin dispersion is applied to the treated absorbent material by printing the resin dispersion on the material or by padding, spraying, impregnating or other techniques for applying emulsion polymerized resins to absorbent materials.

I have now discovered still another improved method of controllably depositing colloidal resin compositions on porous or absorbent materials whereby spreading, diffusing, and migration of the resin are controlled and are markedly reduced and wherein the concentration of the resin in the resin binder area reaches exceptionally high values. When applied to fibrous webs in the manufacture of nonwoven fabrics, excellent strength is obtained in the resulting fabrics along with desirable textile-like softness, hand and drape.

The improved method involves the use of an aqueous resin dispersion which comprises from about 0.1 percent to about 60 percent by weight on a solids basis of a colloidal resin containing a coordinating ligand, said resin dispersion being stable at pHs of about 7 and greater but which is unstable at pl-l's of below 7 when in the presence of heavy metal ions such as zirconium, chromium, nickel, cobalt, cadmium, zinc, vanadium, titanium, copper and aluminum.

The coordinating ligand is normally an acidic or proton donor group, especially those containing terminal hydroxy groups. Examples of hydroxy-containing coordinating ligands are: hydroxy 0H; carboxy COOH; sulfino SO(OH); sulfo SO,(Ol-l); sulfonoamino NHSO,(0H); aci-nitro=NO(0l-l); hydroxyamino NHOH; hydroxyimino NOH', etc. it is to be observed that these hydroxy-containing radicals contain a hydrogen atom which is capable of dissociating to form an H ion or proton.

The colloidal resins possessing a hydroxy-containing coordinating ligand are obtained by copolymerizing from about 92 percent by weight to about 99 percent by weight of a monomer or a mixture of monomers of the group comprising vinyl halide, vinyl ester, or vinyl ether monomers including, for example, vinyl chloride, vinyl acetate and vinyl ethyl ether; olefins such as ethylene and propylene; acrylic and methacrylic monomers including, for example, ethyl acrylate, ethyl hexyl acrylate, methyl acrylate, propyl acrylate, butyl acrylate, hydroxyethyl acrylate, dimethyl amino ethyl acrylate, methyl methacrylate, ethyl methacrylate,

isopropyl methacrylate, butyl methacrylate, acrylonitrile methacrylonitrile, acrylamide, N- isopropyl acrylamide, N-methylol acrylamide,

methacrylamide; vinylidene monomers such as vinylidene chloride; diene monomers including, for example, 1,2-butadiene l,3-butadiene, 2-ethyl-l,3-butadiene; styrene monomers including, for example, styrene, Z-methyl styrene, 3-methyl styrene, 4-methyl styrene, 4-ethyl styrene, 4-butyl styrene; and other polymerizable monomers, with a relatively small amount, on the order of from about 1 percent by weight to about 8 percent by weight of an unsaturated acid containing a terminal hydroxy group such as the a,B-unsaturated carboxylic acids including acrylic acid, methacrylic acid, fumaric acid, maleic acid, itaconic acid, crotonic acid, isocrotonic acid, angelic acid, tiglic acid, etc. Anhydrides which exist of these acids are also of use. Other a,fl-unsaturated acids are of use and include 2-sulfoethy] methacrylate, styrene sulfonic acid, vinyl phosphonic acid, etc.

It is to be appreciated that more than one monomer may be included in the polymerization with the a,B-unsaturated acid containing a terminal hydroxy group. An outstanding example of the use of more than one monomer is the polymerization of butadiene and styrene with an a,fi-unsaturated acid such as acrylic acid, methacrylic acid, fumaric acid, maleic acid, or itaconic acid. Anhydrides, for example, maleic anhydride, are also of use.

To the resulting emulsion polymerized composition containing the colloidal resin with its coordinating ligand is added a small amount of from about 0.1 percent by weight to about 3 percent by weight, based on the weight of the synthetic resin solids, of a coordination metal complex compound wherein the central metallic atom is zirconium, chromium, nickel, cobalt, cadmium, zinc, vanadium, titanium, copper or aluminum.

Examples of such coordination compounds are:

ammonium carbonate zirconate (NH,),a8[Zr OH (CO,),]-H,0

sodium tetraoxalato zirconate Na,[Zr(C,0 ]-3H,0

ammonium heptafluoro zirconate (NH ),a8[ZrF-,]

ammonium tetrathiocyanato diammine chromate NH,[Cr(NCS),(NH,),-H,0

sodium pentacarbonyl chromate Na,[Cr(CO hexammine chromium chloride [Cr(NH,),]Cl,-H,0

hexa urea chromium fluosilicate [Cr(CON,H,),[,'(SiF,),-3H,0

chloro pentammine chromium chloride hexammine nickel chloride sodium tetracyano nickelate Na,[Ni(CN ]3H,0

hexammine nickel bromide sioi s hexammine nickel chlorate a)e]( a)z hexammine nickel iodide I K QAL hexammine nickel nitrate tetra pyridine nickel fluosilicate i s 5 )4] a tetrammine zinc carbonate l s)c] a tetrammine zinc sulfate potassium tetracyano zincate sodium tetrahydroxo zincate diammine zinc chloride a):i z

tetrapyridine zinc fluosilicate s a )4] c sodium tetrahydroxo aluminate Na,[Al(OH potassium trioxalato aluminate a[ 1 s)a] tetrapyridine cadmium fluosilicate l ms s hl s hexammine cobalt chloride s)s] s hexammine cobalt iodide hexammine cobalt nitrate i i a)n]( a) hexammine cobalt sulfate hexammine cobalt bromide l t slul z dinitro tetrammine cobalt nitrate [Co(NH,),(NO,),(NO,)

diammine copper acetate l a)z]( s z)2 tetrammine copper sulfate [Cu(NH ),]SO-H,O

tetrapyridine copper fluosilicate [Cu(C .,I-l,N) ]SiF As defined herein, a metal complex coordination compound is one of a number of types of metal complex compounds, usually made by addition of organic or inorganic atoms or groups to simple inorganic compounds containing the metal atom. Coordination compounds are therefore essentially compounds to which atoms or groups are added beyond the number possible of explanation on the basis of electrovalent linkages, or the usual covalent linkages, wherein each of the two atoms linked donate one electron to form the duplet. In the cases of the coordination compounds, the coordinated atoms or groups are linked to the atoms of the coordination compound, usually by coordinate valences, in which both the electrons in the bond are furnished by the linked atoms of the coordinated group.

The emulsion polymerized, ligand-containing resin and the coordination compound exist together in a stable emulsion form and normally do not agglomerate, coagulate or precipitate, as long as the pH remains at about 7 or above. Ammonia, alkali hydroxides and carbonates, or other alkaline compounds may be used in order to insure such neutral or alkaline pH range. In some cases, excess Nl-LOH must be present in the mixture for stability.

Subsequently, when the emulsion is acidified to an acid pH below 7, the resin immediately coagulates and agglomerates in place with substantially no further spreading, diffusion or migration.

It is believed that, when the pH is reduced to below 7, the metal cation is released from the coordination compound and immediately attacks or reacts with the ligand-containing resin causing the resin particles to agglom erate or coagulate.

[t is also to be appreciated that, when the pH is reduced to below 7, the metal cation which is released from the coordination compound also is capable of at tacking or reacting with any other chemical compounds which are present and which possess anionic groups, particularly those containing terminal hydroxy groups such as hydroxy, carboxy, sulfino, sulfo, and like acid groups.

For example, the metal cation by is released im mediately attacks a surfactant system which is anionic and contains surfactants such as alkyl aromatic sulfonic acids, alkyl sulfonic acids, the carboxylic acids, and other anionic surfactants described hereinbefore and in greater particularlity in patent applications Ser. Nos. 623,797 and 2,955. Such anionic surfactants are present in the colloidal dispersion in amounts of from about 0.0] percent to about 2 percent ky weight, based on the weight of the synthetic resin solids.

The specific surfactant which is selected for use in the resin composition does not relate to the essence of the invention. It is merely necessary that it possess the necessary properties and characteristics to carry out its indicated function of stabilizing the resin composition prior to the time that coagulation and precipitation of the resin is required. Additionally, in the event that it is desired that the surfactant assist in or promote the coagulation and precipitation function, then it must possess the necessary anionic groups, as described hereinbefore, which are capable of reaction due to the presence of the metal cations released from the metal complex coordination compound.

The mechanism of instant controlled agglomeration, coagulation and precipitation of the colloidal resin binder may therefore be triggered by reaction of the metal cation which is released and reacts with either the colloidal resin, or the anionic surfactant, or both.

The pH may be lowered in different ways in order to activate the reaction mechanism. For example, the porous or absorbent fibrous material may be pretreated by being pre-wet with a sufficient quantity of an acidic material such as acetic acid, whereby the alkaline colloidal resin composition immediately becomes acid upon contact therewith. Or, if desired, the alkaline colloidal resin composition may be first printed on the alkaline or neutral porous or absorbent fibrous material and then substantially immediately treated with the acidic material, such as acetic acid, to reduce the pH to below 7 whereupon the colloidal resin particles substantially immediately controllably agglomerate or coagulate in place with no further spreading, diffusion or migration.

The acid which is used to acidify the colloidal resin composition is preferably a weak acid such as acetic acid, citric acid, phosphoric acid, lactic acid, tartaric acid, oxalic acid, etc., or an acid salt such as alum.

The pH may be lowered in other ways in order to activate the reaction mechanism. For example, in a case wherein the pH is created or affected by the presence of a volatile material such as ammonia, for example, heating to expel the volatile material will bring about the desired change in pH to activate the reaction mechanism.

When printed on a fibrous web during the manufac ture of nonwoven fabrics, the controlled total migration of the resin binder solids may be reduced to as little as about 50 percent beyond the originally deposited area. In some instances, the migration is relatively negligible. Normally, however, the total controlled migrational increase in area of the resin binder solids, even under the most adverse conditions does not materially exceed about 200 percent. Such values are to be compared to increases in binder migration of at least about 300 percent and up to about 800 percent when emulsion polymerized resins are applied to fibrous porous absorbent sheet materials, unaided by the principles referred to or disclosed herein.

The concentration of the binder resin solids in the binder area is correspondingly increased and is in the range of from about 50 percent by weight to about 120 percent by weight, and more normally from about 60 percent to about 80 percent by weight, based on the weight of the fibers in the binder area.

The excellent migration control exercised over the resin binder is illustrated in the drawings in which:

FIG. 1 is an enlarged, idealized cross-sectional view of a bonded nonwoven fabric illustrating the principles of the present invention;

FIG. 2 is an enlarged, idealized cross-sectional view of a bonded nonwoven fabric, not utilizing the principles of the present invention;

FIG. 3A is a further enlarged, idealized cross-sectional view of the nonwoven fabrics of FIGS. I and 2, taken on the line 3-3 thereof, before any resin binder has been applied to the fibrous web;

FIG. 3B is a further enlarged, idealized cross-sectional view of the nonwoven fabrics of FIGS. 1 and 2, taken on the line 3-3 thereof, at the moment the resin binder is applied to the fibrous web; it is also an enlarged, idealized cross-sectional view of the invention nonwoven fabric of FIG. 1, taken on the line 3-3 thereof, after the resin binder has set;

FIG. 3C is a further enlarged idealized, cross-sectional view of the fibrous web of FIG. 2 taken on the line 3-3 thereof, after the resin binder has set;

FIG. 4A is a further enlarged, idealized cross-sectional view of the nonwoven fabrics of FIGS. 1 and 2, taken on the line 4-4 thereof, before any resin binder has been applied to the fibrous web;

FIG. 4B is a further enlarged, idealized cross-sectional view of the nonwoven fabrics of FIGS. 1 and 2, taken on the line 4-4 thereof, at the moment the resin binder is applied to the fibrous web; it is also an enlarged idealized cross-sectional view of the invention nonwoven fabric of FIG. 1, taken on the line 4-4 thereof, after the resin binder has set;

FIG. 4C is a further enlarged, idealized cross-sectional view of the nonwoven fabric of FIG. 2, taken on the line 4-4 thereof, after the resin binder has set;

FIG. 5A is an idealized graph or histogram showing the surface overage and the concentration of an ideal binder on a nonwoven fabric;

FIG. 5B is a graph or histogram showing the surface coverage and the concentration of a binder placed on a nonwoven fabric in accordance with the principles of the present invention;

FIG. 5C is a graph or histogram showing the surface coverage and the concentration of a binder placed on a nonwoven fabric but not in accordance with the principles of the present invention;

FIG. 6 shows a graph or histogram of the critical bonded areas of FIGS. 5A, 5B, and SC in superimposed fashion to accentuate their differences and similarities;

FIG. 7 is a pair of superimposed graphs or histograms of the binder concentrations on nonwoven fabrics showing their differences.

FIG. 8 is another graph or histogram of a binder deposition of a nonwoven fabric showing surface coverage and concentration of binder in the binder area;

FIG. 9 is another graph or histogram of a binder deposition on a nonwoven fabric showing the surface coverage and concentration of binder in the binder area; and

FIG 10 is still another graph or histogram of a binder deposition on a nonwoven fabric showing the surface coverage and concentration of binder in the binder area.

With reference to the drawings and with particular reference to FIG. 1 thereof, there is shown a bonded nonwoven fabric 10 which has been bonded according to the principles of the present invention. The bonded nonwoven fabric 10 comprises fibrous areas 12 of unbonded overlapping, intersecting fibers l4 and bonded areas 16 containing bonded fibers l8 and a resin binder 19. As shown, the bonded areas I6 extend completely through the bonded non-woven fabric 10 from one surface to the other surface and possesses relatively straight, sharp, distinct edges or boundary lines.

The sharpness and distinctness of the edges or boun dary lines which exist between the bonded areas 16 and the unbonded areas 12 is attested to by the fact that the optical density of the bonded nonwoven fabric 10 increases from about 0.0 optical density to as much as from about 0.6 to about 1.0 optical density in merely moving a distance of about 1 mm. (0.04 inch) or less, lengthwise of the nonwoven fabric from the unbonded area into the bonded area. This feature will be described in greater detail hereinafter.

As defined herein, optical density varies generally proportionately to the concentration of binder and is equal to the logarithm (base 10) of the ratio of (I the intensity of an incident ray (1,) falling upon a trans parent or a translucent medium to (2) the intensity of a transmitted ray (1,) which passes through the transparent or translucent medium. This quantity (log IJL) is therefore a measure of the degree of ability of light to pass through the medium. When the fibers are made transparent and the binder is made opaque, the optical density is a measure of the intensity or the concentration of the binder on the nonwoven fabric. Since it is frequently not possible to make the fibers transparent, an alternate procedure, based on differential staining of fiber and binder, measuring light reflectance may also be used.

Inasmuch as the optical density is a logarithmic function and difficult to compare directly, optical transparency will also be used in this description of the invention. As defined herein, optical transparency is equal to IJL, or it is the direct ratio of the intensity of the transmitted light (1,) to the intensity of the incident light (I Such a term is more easily employed for direct comparison purposes.

It is important to describe the procedures which are used for determining l the sharpness and the distinctness of the boundary lines which exist between the bonded areas and the unbonded areas; (2) the border or edge feathering and total surface coverage of the binder; (3) the optical densities and transparencies of various points in the bonded areas; (4) the concentration of the binder in the bonded areas; etc.

It has long been known that the actual width of a bond on a nonwoven fabric is greater than the nominal width of the engraved line on the print roll which applied the binder to the fibrous web during the making of a bonded nonwoven fabric. The difference between the two widths is, of course, the binder migration.

It is relatively easy to measure the nominal width of the engraved line on the print roll. However, a problem has always existed as to the best method for accurately measuring the actual bond width on the bonded nonwoven fabric. Incorporating a dye or pigment in a resin binder and measuring the resultant colored binder area is misleading. It is now known that the binder spreads much farther in the fibrous web than the pigment or dye because of a chromatographic phenomenon among the fibers. As a result, a subjective viewing of a resin bonded nonwoven fabric will merely reveal the width of the pigmented or dyed area which is considerably less than that of the bonded area covered by the binder.

Incorporating a pigment or dye in a viscose binder, as compared to a resin binder, and measuring the resulting colored binder area may also be misleading, although it is believed that in the case of bonding with viscose, as differentiated from bonding with a resin binder, the binder stays more closely with the pigment or dye. in any event, however, the pigmented or dyed areas are probably less than the bonded fabric areas which are covered with a viscose binder.

in the case of practically all the resins used for binder purposes, differential staining techniques may be employed so that the rayon fibers are unstained and remain practically white while the resin binder becomes stained and takes on an intense color. Under magnification, the colored resin binder is discernible and distinguishable from the rayon fibers. Such differentially stained nonwoven fabrics have then been studied under relatively low power microscopes and the width of the actual binder line has been subjectively estimated by comparison to a standard scale, usually in the microscope eyepiece. The binder edge, especially in the case of a migrated print line, gradually fades to zero or substantially zero, and the visual estimation of the binder width is therefore a difficult, subjective procedure. lt is now known that prior efforts to estimate binder widths have led to low estimates inasmuch as the extremes of the binder-feathering have been neglected.

The improvements brought about by the present invention are determined by measuring actual bond widths and relative binder content across a bond stripe by an objective method using an analytical instrument for the actual measurements. These improved methods will be described in greater detail hereinafter.

It has been observed that it is characteristic of migrated print bonded patterns to show a binder feathering near the bond edges. On the other hand, when migration is controlled, binder feathering is nonexistent and the line of demarcation between bonded area and non-bonded area is sharp. The feathering, however, in a migrated binder reflects the diffusion of binder into the water of the wet web and also the capillary absorption ofliquid binder by the web structure. In contrast, when binder has been coagulated to control migration, diffusion, capillarity and feathering near the edge of the bond are essentially nonexistent.

An unusual feature of the feathering phenomenon is the fact that it is more pronounced on one side of the bonded area. It is believed that this is caused by the fact that the binder, as it is applied by an engraved print roll, tends to smear and migrate more on the trailing side of the applied binder. The leading edge, that is, the edge first contacted by the print roll, is usually cleaner with less smearing and less migration.

When binder migration is controlled, the total amount of binder applied may be selected to be the same but the binder is restricted to a smaller area within the web. Hence, binder concentration within the bond area is higher and the line of demarcation between bond and free-fiber areas is much sharper in controlled nonwoven fabrics. In fact, it is believed that the feathered edge of the bond area deleteriously affects nonwoven properties for the following reasons:

I. The low binder content in the feathered areas is sufficient to cause stiffness, but not sufficient to impart good strength.

. The highest concentration of binder attainable in the bond area in non-controlled print areas is not sufficient to make bonds as strong as the fibers. On the other hand, when binder migration is controlled, the binder content is high enough to equal fiber strengths, but not so high that the bond feels nubby. Furthermore, the high concentration of binder in the bonded areas in a controlled printed fabric approaches (but does not reach) a continuous binder film. Therefore, a better carry-through of binder properties in the web is obtained, especially strength and resilience.

Several new concepts, and unexpected results are believed to be embodied in the controlled migration fabrics which have been made. A laboratory method for giving numerical values to the fiber-bond transition area has been developed, based on the staining properties of binder, and the optical characteristics of a stained bond area. By this method, the nonwoven fabric is stained with the proper dye or chemical reagent and the reflected light from the surface of the various areas of the fabric is measured. The intensity of staining across a bond is measured by means of its magnified image on the ground glass of a camera. The microscope image of the surface of the stained fabric on the camera ground glass is scanned with a light sensing instrument and a graph of the intensity of reflected light (as "Optical Density") versus location across a bond is made.

In order for this procedure to be quantitative and reproducible, it is necessary to specify many of the details, as follows. The print-bonded nonwoven fabric is differentially stained in a 1 percent solution of Celliton Fast Violet 68A (manufactured by General Aniline and Film), by immersion for one minute in boiling solution and rinsing in cool water until the cellulosic fibers become white. This dye will stain all of the common types of binders including acrylics, vinyl acetates, butadiene-styrene rubbers, vinyl chloride polymers, etc. Other dyes may be used as long as the base fibers are essentially undyed, and the resin itself is dyed an intense color. The fabrics are air-dried and mounted on a flat white surface. The mounted sample is placed on a graduated mechanical stage under a ground glass camera using lenses and distances to enlarge the image 20.0X by methods well known in the photographic and microscopic arts. This specimen is illuminated by two small spot lights mounted at about 45 above the specimen and at from each other, that is, opposite each other in a straight line.

The probe of an optical densitometer is fixed at the focusing plane (the ground glass) of the camera. It is convenient to use a reflex housing so that the specimen can be examined visually or the reflected image can be measured simply by turning a mirror to deflect the light for observation or for measurement, respectively. The

size of the probe is set at a 4X4 millimeter square.

The two lights illuminating the specimen are carefully placed to minimize the formation of shadows. An area of the test specimen which is completely free of binder is moved underneath the sensing area, and by means of the controls on the densitometer, the needle reading is set at Optical Density.

The stage micrometer is manipulated to move the specimen in definite intervals of 0.] mm., only along the axis perpendicular to the bond line. As the magnified image is traversed stepwise across the probe, light reflectivity readings are taken. Light reflectivity is measured as Optical Density". As mentioned above, the actual size of the light sensing probe is 4X4 millimeters and is fixed to the screen where a 20.0X magnified image is projected. At an actual movement of 0.] mil limeter, the apparent movement is magnified to 2.0 millimeters at X magnification, hence, the probe of 4X4 mm. dimension reads an overlapping area with each consecutive reading. The purpose of choosing this probe size and obtaining overlap is to tend towards smoothing the curve. Otherwise, an erratic reading is obtained.

In other words, the differentially stained test sample, under constant illumination, is traversed across the field while a fixed lightsensing probe measures the light reflectance of its magnified image, hence, the comparative binder content across a single bond unit.

The intensity of the reflected light, in units ofOptical Density yields a comparative measure of binder content across a binder pattern unit.

This procedure can be used on any nonwoven fabric so long as the rayon fibers or other fibers are white and are not colored significantly by the dye which stains the binder.

Such procedures establish that:

l. The binder content within the binder area is higher in controlled migration samples, and is in the range of about 50-l20 percent binder content (based on fiber weight in the same area).

2. The binder penetrates essentially throughout the entire thickness of the web. This is in sharp contrast to the products of dry printing where the binder stays on one side of the web.

. The binder content across the binder area is more uniform in the controlled sample, that is, there is a virtual absence of feathering and practically no transition area between clean fiber and bond area.

Inasmuch as it can be arranged that the total amount of binder material in each bond unit ofa controlled and an uncontrolled migrational sample of a nonwoven fabric is the same, as determined by chemical analysis, the areas under the curves in the histograms of these samples will denote the same amount of binder. However, as an artifact of the test procedures, based on the saturation color of the binder stain, the raw data taken by the hereindescribed procedures usually shows an apparently appreciable higher area under the curve for the migrated samples.

Hence, it is therefore necessary that the raw data be normalized by multiplying it by a factor less than one to bring the area under its curve to that of the controlled migration binder area. In this way, the controlled and uncontrolled migration bond areas can be examined and compared. This normalization has been done for FIGS. 7 through 10, but further refinement thereof may be necessary in some cases.

It is to be appreciated that regardless of whether raw data or normalized data is used, the zero points and the distances required to go from zero binder content to maximum binder content or to go from zero to maximum Optical Density are unchanged. On the other hand, however, the slopes of the curves and the apparent peak optical densities are changed.

In FIG. 2, there is illustrated another bonded nonwoven fabric 20 which has not been bonded according to the principles of the present invention. The bonded non-woven fabric 20 comprises fibrous areas 22 of unbonded overlapping, intersecting fibers 24 and bonded areas 26 containing bonded fibers 28 and a resin binder 29. It is to be observed that the bonded areas 26, although they were as small as the bonded areas 16 of FIG. 1, when originally applied to the fibrous web, are very much larger in the finished fabric and have much greater actual surface coverage. Also, it is to be noted that the boundary lines of the binder areas are not relatively straight, nor are they sharp and distinct, and that the resin binder is concentrated in the center and feathers and gradually thins out as the binder edges are approached.

The lack of sharpness or distinctness of the boundary lines which exist between the bonded areas 26 and the unbonded areas 22 is attested to by the fact that the optical density of the bonded nonwoven fabric 20 increases from about 0.0 to only about 0.35 and that such is accomplished in moving a much greater distance of 2 or 3 millimeters lengthwise of the nonwoven fabric from the unbonded area into the bonded area.

In other words, the present invention provides for greater increases of intensity or concentrations of binder in shorter lengthwise distances of the bonded nonwoven fabric. As a result, the concentration of the binder in the binder areas is much greater which is, of course, very desirable. Also, the surface coverage of the bonded nonwoven fabrics by the binders of the present invention is very much decreased whereby strength and softness characteristics and properties are greatly improved.

FIG. 3A is an enlarged, idealized cross-sectional view of the fibers of the fibrous webs 10 and 20 before any resin binder has been applied thereto. These fibers are, of course, as yet unbonded. FIG. 3B is an enlarged, idealized cross-sectional view of the fibers of the fibrous webs l0 and 20 at the precise moment that the resin binder is applied thereto and before it has an opportunity to spread, migrate or diffuse. The resin dispersion is illustrated as droplets added to the water already present in the pre-wet fibrous web.

Application of the principles of the present invention causes the colloidally dispersed resin to agglomerate, coagulate and precipitate instantly whereby they exist in the final bonded nonwoven fabric substantially as shown in FIG. 3B.

In FIG. 3C, however, there is illustrated the effect of the migration, diffusion and spreading of the resin binder which takes place in the absence of instantaneous agglomeration, coagulation and precipitation after the binder is deposited on the fibrous web and before it has time to harden or set. It is to be observed that the resin binder has shifted to a position within a group of fibers and does not completely surround many fibers. The changes that have taken place in the transition from FIG. 38 to FIG. 3C are worthy of note.

FIG. 4A is an enlarged, idealized cross-sectional view of the fibers of the fibrous web 10 and 12 before any resin binder has been applied thereto. These fibers are, of course, as yet unbonded. FIG. 4B is an enlarged, idealized cross-sectional view of the fibrous webs l and 20 at the precise moment that the resin binder is applied thereto and before it has an opportunity to spread, diffuse or migrate. The resin is illustrated as droplets added to the water already present in the prewet fibrous web.

Application of the principles of the present invention causes the colloidally dispersed resin to agglomerate, coagulate and precipitate instantly whereby they exist in the final bonded nonwoven fabric substantially as shown in FIG. 4B.

In FIG. 4C, however, there is illustrated the effect of the migration, diffusion and spreading of the resin binder which takes place in the absence of instantaneous agglomeration, coagulation and precipitation after the binder is deposited on the fibrous web and before it has time to harden or set. It is to be observed that the resin binder has shifted to a position within a group of fibers and does not completely surround many fibers. The changes that have taken place in the transition from FIG. 48 to FIG. 4C are worthy of note.

One very important feature of the present invention, as mentioned previously, is the sharpness and definiteness of the edges or boundaries of the binder areas. In FIG. A, there is illustrated a graph or histogram depicting the change in the concentration of the binder in the bonded fabric as measurements are taken, progressively lengthwise thereof, passing through bonded areas and non-bonded areas. The ideal situation (FIG. SA) shows no binder whatsoever in the unbonded area and a steep 90 rise at the beginning of the binder area to a maximum flat plateau of high optical density and high uniform binder concentration in the bonded area, followed by a steep 90 drop to zero binder concentration and zero Optical Density" at the end of the bonded area. Such 90 slopes are, of course, ideal.

The variation in the concentration of the binder content with respect to the bonded fabric in the case of the present invention is shown in FIG. 5B. The slopes of the leading and trailing edges or boundaries of the binder areas are very close to 90 and are in the range of from about 75 to about 90". As a result of such steep slopes, the maximum flat plateau is practically at the same level or very slightly lower than the maximum flat plateau of the ideal binder concentration as that set forth in FIG. 5A.

On the other hand, when the principles of the present invention are not followed, the slopes of the leading and trailing edges of the binder areas fall to a much lower range and are in the range of from about 30 to about 55". This is shown in FIG. 5C. As a result, the maximum flat plateau falls considerably and is in the range of from only about 30 percent to about 55 percent of the maximum flat plateau of the ideal set forth in FIG. 5A.

Another very important feature of the present invention is the ability to control or confine the total coverage of the binder areas on the bonded fabric. This is shown in FIG. 6 wherein the curves or histograms of three typical binder areas are superimposed. The solid line shows the ideal binder area with 90 slopes, maximum binder concentration in the binder area and minimum non-woven fabric coverage. The dash line shows the present invention binder with slopes of about and a flat plateau of about 92 percent of the ideal binder concentration. The dot-dash line shows binder applied not utilizing the present invention. The slopes are only about 45 and the flat plateau is only about 50 percent of the ideal binder concentration.

The migration of the ideal binder is 0 percent; the controlled total migration of the invention binder is less than about 200 percent, based on the ideal binder area, whereas the migration of non-invention binder is in excess of about 300 percent and up to about 800% based on the ideal binder area, all of such values including feathered areas.

FIG. 7 discloses graphs or histograms actually prepared from two samples of bonded nonwoven fabrics; one utilizing the principles of the present invention and the other not utilizing the principles of the present invention.

The average maximum level of the concentration of binder of the invention fabric has a relatively high peak relative Optical Density value of about 0.64 with a realitively low peak relative optical transparency value of about 0.23. These values are reached in less than 0.7 mm. (0.028 inch). The average level of the concentration of binder of the non-invention fabric has a relative ly low peak relative Optical Density value of only about 0.35 with a relatively high peak relative optical transparency value of about 0.45. These values are reached in more than L6 mm. (0.064 inch).

The slopes of the invention binder curves are approximately 84 and 86 whereas the slopes of non-inven tion binder curves are approximately only 45 and 49". The effective base of both binder areas, as originally laid down, is approximately 0.024 inch in width. The effective base of the invention binder curve in the final product is approximately 0.056 inch in width which equals a controlled total migration of 133 percent. The effective base of the non-invention binder in the final product is approximately 0.159 inch in width which equals a migration of over 560 percent due primarily to the large amount of feathering.

The same amount of binder is applied in both samples and the areas under each curve are the same. For a percentage add-on of binder of 24 percent applied in a six (0.024 inch) horizontal wavy line print pattern, this equals (for the invention binder) a surface coverage of 33.6 percent and a concentration of binder of 72 percent in the invention binder area. For the non-invention binder, the surface coverage is 95.4 percent and the average concentration of binder in the binder area is only 25.2 percent due to loss of binder which migrates into the feathered areas.

The invention binder fabric is strong and has textilelilte softness, drape and hand. The other binder fabric is stiff and boardy.

The invention will be further illustrated in greater detail by the following specific examples. It should be

Claims (14)

1. A method of applying a synthetic resin binder to a fibrous web of overlapping, intersecting fibers and controlling its migration thereon which comprises: applying to a fibrous web of overlapping, intersecting fibers a stable, alkaline, colloidal aqueous dispersion comprising: (1) a synthetic resin; (2) a surfactant, at least one of said resin and surfactant components having a hydroxy-containing coordinating ligand; and (3) a metal complex coordination compound, said metal being selected from the group consisting of zirconium, chromium, nickel, cobalt, cadmium, zinc, vanadium, copper and aluminum, said dispersion being applied to said fibrous web in a predetermined, intermittent print pattern oF spaced areas; and substantially immediately acidifying said dispersion whereby a metal cation is released from said metal complex coordination compound to substantially immediately destroy the stability of said dispersion and coagulate said resin in said spaced areas with a minimum of migration therefrom.

2. A method as defined in claim 1, wherein the metal complex coordination compound is sodium tetrahydroxo zincate.

3. A method as defined in claim 1, wherein the metal complex coordination compound is sodium tetrahydroxo aluminate.

4. A method as defined in claim 1, wherein the metal complex coordination compound is ammonium zirconyl carbonate.

5. A method as defined in claim 1, wherein said aqueous dispersion comprises: from about 0.1 percent to about 60 percent by weight of said synthetic resin; from about 0.01 percent to about 2 percent by weight, based on the weight of said resin, of said surfactant; and from about 0.1 percent to about 3 percent by weight, based on the weight of said resin, of said metal complex coordination compound.

6. A method as defined in claim 1 wherein the synthetic resin has said hydroxy-containing coordinating ligand.

7. A method as defined in claim 1 wherein the surfactant has said hydroxy-containing coordinating ligand.

8. A method as defined in claim 1 wherein the metal complex coordination compound is zinc tetrammine sulfate.

9. A method as defined in claim 1 wherein the metal complex coordination compound is zinc tetrammine carbonate.

10. A method as defined in claim 1 wherein the surfactant is an anionic surfactant.

11. A method as defined in claim 1 wherein the surfactant is a non-ionic surfactant.

12. A method of applying a stable synthetic resin composition to porous materials and controlling the migration thereon which comprises: applying to porous materials a stable, alkaline, colloidal aqueous dispersion comprising: (1) a synthetic resin; (2) a surfactant; at least one of said resin and surfactant components having a hydroxy-containing coordinating ligand; and (3) a metal complex coordination compound; said metal being selected from the group consisting of zirconium, chromium, nickel, cobalt, cadmium, zinc, vanadium, titanium, copper, and aluminum and substantially immediately acidifying said dispersion to substantially immediately destroy the stability of said dispersion and coagulate said resin whereby the migration of said resin on said porous materials is controlled.

13. A method as defined in claim 12 wherein the surfactant is an anionic surfactant.

14. A method as defined in claim 12 wherein the surfactant is a non-ionic surfactant.

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