US3793057A - Process for impregnating nonwovens with alkyl acrylate-carboxyl latices - Google Patents

Abstract

A process for obtaining nonwoven materials having improved physical properties, especially internal bond strength or delamination resistance and wet tensile strength, is provided. The nonwoven fabrics and papers are impregnated with an alkyl acrylate copolymer latex containing carboxyl functionality and exposed to ammonia or amine vapors prior to the drying and curing operations to obtain the improved properties. Papers treated in this manner have shown up to a two-fold increase in internal bond strength.

Description

United States Patent 1191 Wheelock Feb. 19, 1974 [5 PROCESS FOR IMPREGNATING 2,983,623 5 1961 Coates 117/62.2 NONWOVENS WITH ALKYL 3,085,897 4/ 1963 Priest et al.... 117/62.2 2,429,698 10/1947 Schneider 117/106 R ACRYLATE-CARBOXYL LATICES 3,168,415 2/1965 Goldstein et a1.. 117/62 [75] Inventor: George L. Wheelock, Avon Lake, 3,318,722 5/1967 Ullman 117/62 Ohio 3,404,022 10/1968 Chance et aL 1l7/62.2 3,472,611 10/1969 Langwell 117/62.1 Asslgneei The Goodrich p y, New 3,483,014 12/1969 lssacs et a1 117/62 York, NY. [22] Filed; July 14, 1972 Primary Examiner-william D. Martin Assistant ExaminerM. Sofocleous PP N04 271,972 Attorney, Agent, or Firm-J. Hughes Powell, Jr.

Related US. Application Data [63] Continuation-impart of Ser. No. 725,152, April 29, [57] ABSTRACT 1968, abandoned. A process for obtaining nonwoven materials having I improved physical properties, especially internal bond [52] US. Cl. l17/62.2, 117/106 R, 117/140 A, strength or delamination resistance and wet tensile 117/155 UA strength, is provided. The nonwoven fabrics and pa- [51] Int. Cl B44d l/44, 844d l/48, B32b 29/00 pers are impregnated with an alkyl acrylate copolymer [53] Field of Search 117/62, 62.1, 62.2, 106 R, latex containing carboxyl functionality and exposed to 117/140 A, 155 UA; 161/170 ammonia or amine vapors prior to the drying and curing operations to obtain the improved properties. Pa- [56] References Cited pers treated in this manner have shown up to a twofold increase in internal bond strength.

10 Claims, No Drawings PROCESS FOR IMPREGNATING NONWOVENS WITH ALKYL ACRYLATE-CARBOXYL LATICES CROSS REFERENCE TO RELATED APPLICATION This is a continuation-in-part of my copending application Ser. No. 725,152, filed Apr. 29, 1968, now abandoned.

BACKGROUND OF THE INVENTION Nonwoven fibrous materials, typically formed by randomly depositing individual fibers to form a web and then impregnating the web with a binder to hold the individual fibers together, are recognized as possessing many advantages over conventional woven materials. Such advantages include absence of raveling, smoother surfaces, increased softness, improved hand, greater absorbency, higher loft, and others. Underlying these advantages is the fact that, unlike woven materials which owe their physical characteristics primarily to the construction of the weave and are thereby limited for a given fiber, the properties and characteristics of the nonwoven fabrics may be varied over a wide range with the same fiber simply by varying the bonding agent (binder).

Although the particular fiber/binder combination and web-type will govern the ultimate physical properties achievable in a nonwoven fabric, the amount of binder taken up by the nonwoven substrate and the uniformity with which the binding agent is dispersed throughout the nonwoven will also be important factors in achieving the optimum properties. If the nonwoven substrate as a whole is deficient in bonding agent or if localized areas are deficient, the physical properties such as wet and dry tensile strengths and especially the internal bond strength (resistance to delamination or splitting) are markedly reduced, in fact, the nonwoven is often rendered useless. This problem of obtaining adequate binder content throughout the nonwoven material is especially significant when using the aqueous emulsion binder systems. These are probably the single most important class of binder because they not only provide nonwoven fabrics having excellent physical properties and wear endurance but also, as a practical matter, they are easily applied to the nonwoven substrate by the use of conventional saturation and spraying techniques. It is sometimes so difficult with these emulsion systems to incorporate sufficient binder to obtain the desired level of physical properties for certain nonwoven applications, that it becomes necessary to resaturate the nonwoven with latex after drying the first binder solution; but this is not a desirable method.

Efforts to overcome the problem of achieving an acceptable binder content has led to much work, primarily directed to obtaining more efficient latices, that is, improved latex binder systems which permit the use of less bonding agent to develop optimum physical properties in the nonwoven material. Typically, these improved latex binders contain reactive monomers, capable of reacting upon the application of heat, catalysis or other chemical reagents, to form cross-linked polymers.

This approach is not completely satisfactory either since the binders, even though more efficient, are still susceptible to migration through the nonwoven material. During the drying operation, polymeric binder can migrate to the surface of the nonwoven material with the water and emulsifying agent resulting in a nonuniform distribution of the binder and lowered physical properties. The viscosity of the binder latex can be increased prior to saturation by the addition of thickening agents such as natural gums and pastes, polyvinyl alcohol, and the like, to reduce the tendency of the binder to migrate within the nonwoven material, however, this technique is only partially effective and makes it impossible to achieve uniform saturation of the nonwoven.

SUMMARY OF THE INVENTION I have now developed a process whereby nonwoven materials having markedly improved internal bond strength and resistance to delamination are obtained. In most instances the wet tensile strength of the nonwoven will also be noticeably increased. To obtain these improved properties, the nonwoven web or mat is impregnated with an alkyl acrylate polymer latex containing carboxyl functionality which for the purposes of the present invention can be obtained by interpolymerizin g or overpolymerizing a carboxyl-containing monomer, preferably an afi-olefinically unsaturated carboxylic acid, with the alkyl acrylate. The saturated fabric or paper is then exposed to vapors of ammonia or an amine prior to the drying operation.

The nonwoven materials, both fabrics and papers, 0- tained by the present process will have markedly increased internal bond strength and delamination resistance over conventionally prepared nonwovens without the ammonia or amine exposure. Resistance to delamination has been increased as much as 100 percent for some papers. The present process enables us to achieve a more uniform distribution of the binder within the finished nonwoven due to the ammonia or amine exposure prior to heat treatment. It is felt that the in situ thickening of the latex binder prior to the drying step reduces the migration of the polymer toward the surface of the nonwoven as the water is removed during drying.

DETAILED DESCRIPTION The process of the present invention is applicable to any nonwoven material, that is, the particular fiber used in the make-up of the nonwoven and the thickness of the nonwoven does not limit the application of the present process. This is not to say that certain fibers are not more useful for certain nonwoven applications than others, but only that if a fiber has the required specifications to be formed into a nonwoven web or mat then the nonwoven so formed may be treated according to the present process.

Natural fibers such as cotton, wool, silk, sisal, cantala, henequen, hemp, jute, kenaf, sunn and ramie may be used to form the nonwoven web or mat as well as synthetic fibers or filaments. Useful synthetic fibers in clude: rayon (viscose); cellulose esters such as cellulose acetate and cellulose triacetate; proteinaceous fibers such as those manufactured from casein; polyamides (nylons) such as those derived from the condensation of adipic acid and hexamethylenediamine or the selfcondensation of caprolactam; polyesters such as polyethylene glycol terephthalate; acrylic fibers containing a minimum of about percent acrylonitrile with vinyl chloride, vinyl acetate, vinyl pyridene, methacrylonitrile or the like and the so-called modacrylic fibers containing smaller amounts of acrylonitrile; fibers of copolymers of vinyl chloride with vinyl acetate or vinylidene chloride; fibers obtained from the formal derivatives of polyvinyl alcohol; olefin fibers such as polyethylene and polypropylene; and the like.

The process of the present invention is particularly advantageous for use with specialty papers which require the saturation of the paper mat with binders in order to modify the structural properties of the paper. Papers obtained from bleached or nonbleached pulp may be employed; also, those obtained by the unbleached sulfite, bleached sulfite, unbleached sulfate (kraft), semibleached and bleached sulfate processes. Papers prepared wholly from synthetic fibers and those obtained from blends of natural cellulose and synthetic fibers also may be used.

The nonwoven mat or web may be formed by conventional techniques. For example, for papers they will be formed on a moving fine wire screen from an aqueous suspension of the fibers. When other fibers are to be formed into a nonwoven, depending on the particular fiber or fiber blend being used, whether the fibers are to be orientated or deposited at random, the thickness of the nonwoven, etc., the fibrous web can be formed by carding, garnetting, deposition from an air stream, deposition from solution, deposition from a melt, wet-laying, or the like.

The binders employed for the process of the present invention are aqueous carboxyl-containing dispersions of lower alkyl acrylate polymers. The required carboxyl functionality may be either chemically bound to the alkyl acrylate polymer, that is, one or more a,B-olefinically unsaturated carboxylic acid monomers will be interpolymerized with the alkyl acrylate monomers or overpolymerized or grafted on the alkyl acrylate base polymer; or physically admixed with the alkyl acrylate polymer, for example, by the addition of a polymeric carboxylcontaining thickening agent to the alkyl acrylate polymer latex. In either case the carboxyl group will constitute from about 0.05 to about 25 percent by weight of the total make-up of the polymeric binder.

The alkyl acrylate polymer binder latices employed are obtained by polymerizing esters of a,B-olefinically unsaturated carboxylic acids having the structural formula wherein R is hydrogen, methyl or ethyl group and R represents a hydrocarbon radical containing from one to 12 carbon atoms. Representative monomers of the foregoing type include methyl acrylate, ethyl acrylate, the propyl acrylates, the butyl acrylates, the amyl acrylates, the hexyl acrylates, cyclohexyl acrylate, phenyl acrylate, 2-methylhexyl acrylate, n -octy1 acrylate, 2- ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-octyl methacrylate, dodecyl methacrylate and the like. Most preferred are the lower alkyl esters of acrylic and methacrylic acid containing from four to carbon atoms.

The polymeric acrylate binders may contain one or more other polymerizable comonomers, preferably vinylidene monomers containing at least one terminal group, interpolymerized with the alkyl acrylate monomers. Such polymerizable comonomers may constitute up to about 49.95 percent by weight of the polymer. Such polymerizable comonomers include the conjugated dienes such as butadiene and isoprene; a-olefins such as ethylene, propylene and isobutylene', vinyl aromatics such as styrene, a-methyl styrene, chlorostyrene, vinyl toluene and vinyl naphthalene, vinyl halides such as vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride and vinylidene fluoride; vinyl esters such as vinyl acetate; alkyl vinyl ethers such as methyl vinyl ether, isopropyl vinyl ether, n-butyl vinyl ether, isopropyl vinyl ether and haloalkyl vinyl ethers as 2- chloroethyl vinyl ether; nitriles as acrylonitrile or methacrylonitrile; vinyl ketones and haloalkyl vinyl ketones; a,B-olefinically unsaturated amides such as acrylamide, N-methyl acrylamide, N-t-butyl acrylamide, N- cyclohexyl acrylamide, methacrylamide, N-ethyl methacrylamide and diacetone acrylamide; a,B-olefinically unsaturated N-alkylol amides having the structural formula wherein R is a hydrogen or an alkyl group containing from one to four carbon atoms and x is a number from l to 4, such as N-methylol acrylamide, N-ethanol acrylamide, N-propanol .acrylamide, N-methylol methacrylamide, and N-ethylol methacrylamide; polyunsaturated compounds such as methylene-bis-acrylamide, ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl pentaerithritol and divinyl benzene; alkoxyalkyl acrylates as ethoxyethyl acrylate, haloalkyl and cyanoalkyl acrylates, excluding aminoacrylates and methacrylates; allyl chloroacetate, vinyl chloroacetate; and the like as is known by those skilled in the art.

The carboxyl functionality present in the polymeric acrylate latex binders useful in this invention is introduced by the use of one or more a,B-olefinically unsaturated carboxylic acid monomers containing from three to 10 carbon atoms. Representative examples of such acid monomers include acrylic acid, methacrylic acid, ethacrylic acid, a-chloroacrylic acid, a-cyanoacrylic acid, crotonic acid, B-acryloxy propionic acid, hydrosorbic acid, sorbic acid, a-chlorosorbic acid, cinnamic acid, ,B-styrylacrylic acid, itaconic acid, citraconic acid, maleic acid, fuman'c acid, mesaconic acid, glutaconic acid, aconitic acid and the like. The preferred acid monomers are the a,B-monoolefinically unsaturated monocarboxylic acids such as acrylic acid and methacrylic acid. Mixtures of one or more of the above-mentioned carboxylic monomers may be employed if desired. As was previously mentioned, the

The carboxyl-containing polyacrylate binders which contain carboxyl-containing monomers interpolymerized may be prepared by any of the conventional emulsion polymerization techniques. About 50 to 99.95 percent of one or more of the above-mentioned alkyl esters of a,B-olefinically unsaturated carboxylic acids will be interpolymerized with about 0.05 to 25 percent by weight of the a,B-olefinically unsaturated carboxylic acid monomer to constitute the polyacrylate latices. In addition, up to about 49.5 percent by weight of other polymerizable vinylidene comonomers free of amine groups can be interpolymerized therewith. The preferred polyacrylate binders useful for the present process will contain about 70 to 95 percent by weight of the acrylate ester, about 0.1 to percent by weight of the carboxyl-containing monomers and about 5 to 29 percent by weight of other polymerizable comonomers.

The aqueous medium may be emulsifier free or it may contain a surface active agent. When an emulsifier is used to prepare the polyacrylate binders it may range from as low as about 0.01 up to about 6 percent or more as 8 to 10 percent by weight based on the total monomers. The emulsifier may be charged at the outset of the polymerization or may be added incrementally or by proportioning throughout the run. Any of the general types of anionic or nonionic emulsifiers may be employed, however, best results are generally obtained when anionic emulsifiers are used. Typical anionic emulsifiers which may be used include the alkali metal or ammonium salts of the sulfates of alcohols containing from eight to 18 carbon atoms such as, for example, sodium lauryl sulfate; alkali metal and ammonium salts of sulfonated petroleum or paraffin oils; sodium salts of aromatic sulfonic acids such as dodecane-l-sulfonic acid and octadiene-l-sulfonic acid; aralkyl sulfonates such as sodium isopropyl benzene sulfonate and sodium dodecyl benzene sulfonate; alkali metal and ammonium salts of sulfonated dicarboxylic acid esters such as sodium dioctyl sulfosuccinate and disodium N- octadecyl sulfosuccinamate; alkali metal or ammonium salts of the free acids of complex organic monoand diphosphate esters; and the like. So-called nonionic emulsifiers are octylor nonylphenyl polyethoxyethanol and the like. Preferred as emulsifiers are the alkali metal salts of the aromatic sulfonic acids and the sodium salts of the aralkyl sulfonates of the formula wherein R is alkyl or alkenyl, having eight to 20 carbon atoms such as octyl, decyl, dodecyl, alkoxy or ethoxy groups, or aryl, such as a phenyl radical of the formula wherein R is H or an aliphatic radical containing one to 16 carbon atoms as the butyl, decyl, dodecyl and like alkyl or alkenyl radicals, y is CH or O, and naphthyl Ar is benzyl or naphthyl and M is an alkali metal or NH In addition to the above-mentioned emulsifiers it may be desirable and advantageous to add post-polymerization emulsifiers and stabilizers to the polymeric latex binders in order to improve the latex stability if it is to be stored for prolonged periods prior to use. Such post-polymerization emulsifiers may be the same as, or different than, the emulsifier employed in conducting the polymerization, preferably anionic or nonionic agents.

To initiate the polymerization free radical catalysts are employed. The use of such catalysts, although in certain systems not absolutely essential, insure a more uniform and controllable polymerization and a satisfactory polymerization rate. Commonly used free radical initiators include the various peroxygen compounds such as the persulfates, benzoyl peroxide, t-butyl hydroperoxide, and l-hydroxycyclohexyl hydroperoxide; azo compounds such as azodiisobutyronitrile, and dimethyl azodiisobutyrate; and the like. Especially useful as polymerization initiators are the water-soluble peroxygen compounds such as hydrogen peroxide and the sodium, potassium and ammonium persulfates.

The alkali metal and ammonium persulfate catalysts may be employed by themselves or in activated redox systems. Typical redox systems include the persulfates in combination with: a reducing substance such as a polyhydroxyl phenol and an oxidizable sulfur compound such as sodium sulfite or sodium bisulfite, a reducing sugar, a diazomercapto compound, a ferricyanide compound, dimethylaminopropionitrile and the like. Heavy metal ions such as silver, cupric, iron, cobalt, nickel and others may also be used to activate persulfate catalyzed polymerizations. In general the amount of free radical initiator employed will range between about 0.1 to 5 percent based on the weight of the total monomers. The initiator is generally completely charged at the start of the polymerization, however, incremental addition or proportioning of the initiator throughout the polymerization is often desirable.

In conducting the polymerization for the preparation of the acrylate binder latices of the present invention the monomers are typically charged into the polymerization reactor which contains the water and the emulsifying agent. The reactor and its contents are then heated and the polymerization initiator added. The temperature at which the polymerization is conducted is not critical and may range from about 30 C. to about 100 C. or higher. Excellent results, however, have been obtained when the polymerization temperature is maintained between 0 and C. A pH below 7 is generally maintained throughout the polymerization. Polymerization modifiers such as the primary, secondary and tertiary mercaptans, buffers, electrolytes and the like may also be included in the polymerization.

Preferred carboxyl-containing polyacrylate latices which have proved particularly advantageous as binders for treatment by the process of the present invention are those having about 0.1 to 10 percent by weight of the a,B-olefinically unsaturated carboxylic acid monomer overpolymerized on an alkyl acrylate base polymer. The base polymers will typically contain about 50 to 99.9 percent by weight based on the total monomers of an ester of an a,B-olefinically unsaturated carboxylic acid and from about zero to 49 percent by weight of one or more other aminefree polymerizable comonomers, preferably from about 0.5 to 15 percent by weight of an a,,B-olef1nically unsaturated N-alkylol amide or 0.5 to 35 percent by weight of an acrylic amide or nitrile such as'acrylamide, methacrylamide, acrylonitrile or methacrylonitrile.

These preferred and highly efficient overpolymerized polyacrylate latices are obtained with slight modification of the conventional polymerization techniques described above. The acrylate base polymer is in fact formed using these conventional techniques.

In conducting the overpolymerization certain changes must be made. Generally, the carboxyl containing monomer may be overpolymerized by itself, or other polymerizable monomers can be combined with the carboxyl-containing monomer. Useful polymers are obtained when the other polyrnerizable monomers are vinylidene monomers employed in amounts so that the weight ratio of the vinylidene comonomer to the acid monomer is less than about 5:1. Excellent overpolymerizations are obtained when the vinylidene comonomer to acid monomer weight ratio is maintained at 1:1 or below.

The same monomers interpolymerized to form the polyacrylate base polymer, also serve as useful comonomers with the acid monomer in the overpolymerization step. Small amounts of alkyl acrylates, such as ethyl acrylate and methyl acrylate, have been found especially useful comonomers to be overpolymerized with the acid monomers. In addition to the usual vinylidene comonomers, small amounts of polyfunctional compounds such as methylene-bis-acrylamide, ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl pentaerythritol, divinyl benzene and the like may also be included in the overpolymerization. By including these vinylidene monomers and polyfunctional compounds capable of cross-linking with the acid monomers during the overpolymerization, latices having excellent stability and capable of developing extremely high viscosities are obtained, which when employed as binders for nonwovens according to the present process, provide nonwovens having much improved internal bond strength or delamination resistance.

The overpolymerization or grafting of the acid monomers is commenced when the polymerization of the base polymer is complete or essentially so. More conveniently it is begun after about 50 percent conversion of the base monomers has been achieved. Preferably, the overpolymerization is delayed until about 70 percent or more of the monomers comprising the base polymer are polymerized. The technique of combining other monomers with the carboxylic monomer is especially useful to obtain stable overpolymerizations and latices when the overpolymerization is delayed until high conversions of the base monomers is achieved.

The present process consists of exposing the nonwoven material which has been saturated with one of the above-mentioned carboxyl-containing polymeric latex binders to the vapors of ammonia or amines. By such exposure, the latex binder is thickened in situ, thereby reducing the migration of the polymeric binder from the interior regions of the nonwoven toward the surface as the water is removed during the drying operation. Thus, a more uniform distribution of the polymeric binder throughout the nonwoven than was previously possible is achieved. The net result of such treatment is a noticeable improvement in the physical properties of the nonwoven material. The internal bond strength or delamination resistance and generally the tensile strength, especially the wet tensile strength, of the nonwovens are increased by employing the process of the present invention.

To achieve the maximum advantage of this invention, the pH of the carboxyl-containing polymer latices must be maintained below specific limits during the saturation or impregnation. This insures the complete penetration and uniformity of the binder latex throughout the nonwoven material which is essential to obtain the improved physical properties. Although the pH requirement will vary from one latex to another, depending on the monomers employed and the carboxyl content, to be acceptable for impregnation the pH should preferably be maintained on the acid-side. A neutral or slightly basic latex will give acceptable results in most instances, however. In general, the pH of the carboxylcontaining alkyl acrylate polymer latex will be maintained at about 7.5 or below and more preferably between about 6.5 and 2.5. Excellent results are achieved when latices at the higher pH limits are acidified prior to saturation to achieve a more desirable pH and viscosity. To facilitate the saturation of the nonwoven, the total solids of the latex binder is generally maintained below about 50 percent and excellent results are obtained with latices containing about 15 to 35 percent total solids.

A critical feature of the present invention is the exposure of the saturated nonwoven material to ammonia or amine vapors. Although ammonia is generally preferred due to its ready availability, gaseous nature and excellent solubility in the binder latices at the temperatures employed, primary, secondary or tertiary aliphatic monoamines may also be employed to give excellent results. Typical amines which can be used may contain up to 12 carbon atoms, however, amines containing up to six carbon atoms are generally preferred. Gaseous amines such as methyl amine, ethyl amine, dimethyl amine and trimethyl amine have produced excellent results. The higher molecular weight amines which are normally liquids at room temperature, such as primary amines containing from three to l 1 carbon atoms and the lower secondary and tertiary amines,

' which will normally exert an appreciable vapor pressure at room temperature, or slightly above, and are readily soluble in water may also be employed. Generally, the amines useful in the present process should have boiling points less than about 150 C. and more preferably less than C. The ready solubility of the ammonia and amines in water insures that binder latex even in the innermost regions of the nonwoven will be uniformly acted on, thus rendering in situ thickening of the latex to minimize subsequent binder migration. It is the ability of the ammonia and amines to be instantaneously, or essentially so, taken up by the saturated nonwoven and contact both the interior and surface regions with the same effectiveness, which renders the present process so useful and permits the development of superior physical properties in the nonwovens treated in accordance with the present invention.

Attempts to achieve thisuniform treatment of saturated nonwovens using other techniques were unsuccessful. Either the binder could not uniformly penetrate the nonwoven in the cases where thickening of the binder latex prior to saturation was employed, or when post-thickening of the binder latex was attempted with agents other than the ammonia or amines of this invention, the initial thickening occurring at the surface of the nonwoven is so pronounced and so rapid that it impedes further penetration of the thickening agent to the interior regions of the nonwoven and consequently EXAMPLE I To demonstrate the process of the present invention, a latex of an alkyl acrylate polymer having a carboxylthese interior regions are subject to migration of the containing monomer owl-polymerized was prepared hinder P y for use as a binder for nonwoven materials. The poly- Exposure of the saturated nonwoven material to the met latex was prepared by emulsion polymerizing in 4 ammonia of amine Vapors will depending on the parts water containing 0.26 part ammonium persulfate particular latex binder and thickening agent employed. and l ifi an l ifi d monomer mixture Contact times will generally be less than about 80 min- 10 prising 32 parts water, 35 parts ethyl acrylate, 2 7 utes, preferably they will range between about 2 secparts l iu-il 1 8 n l id d 1 3 parts onds and 5 minutes. With ammonia and the more vola- N ;h l 1 l id Th polymerization was tile amines, contact times between 5 seconds and l d d at 80 C, b metering th monomer ixt re into minute have been Successfully p y and found to the polymerizer for a period of about 1 hour. Near the impart maximum Properties to the cured nonwoven completion of the metering a mixture of 2.6 parts methmaterial. Once maximum thickening of the binder latex li id 25 parts h l l ()3 part th l is achieved, additional exposure to the ammonia or methacrylate d ()()5 part h l -bi l id amines will Produce he further improvement in the was charged to the reactor. The polymerization was hehwoveh p Neither will any detrimental then maintained at 80 C. until essentially complete feets be realized from Prolonged exposure to the conversion was achieved. The total amount of water mehia amine Vapors, heweverand sodium lauryl sulfate emulsifier present in the final Exposure to the ammehla 0T amme ls conveniently latex was 98 parts and 0.3 part respectively. The final brought about in a chamber maintained at room temlatex contained about 50 percent w] lid Pemture or above, Such as a g y Oven, wherein a A saturation bath was prepared by diluting the sufficient concentration Of the ammonia Oi amine vaearboxy]-eontaining acrylate latex to percent iota] P can he maintained for Contact with the Saturated solids with water. 10 mils uncoated flat paper (Paterson nonwoven. Although the exposure ovens can be mainparchment C h i a i i fib i0 fib tained at elevated temperatures, these temperatures Contact d supported i hi a Dacron marquisene should generally not exceed 212 F particularly if long velope was then saturated by submerging the paper in I expesure times are p y Because of the Short the latex bath. The excess binder latex was removed by contact times possible with the present process, the satpassing the paper between padde queeze rolls main- "fated nonwoven y be continuously Passed through tained at 20 pounds pressure. The saturated paper was the gaseous ammonia or amine to facilitate the expoh v d fr m the mar isetre envelope. sure step. Such a continuous process would be highly Papers saturated in this manner were then exposed to desirable for large-scale commercial operations. nia vapors f r varying time intervals by placing After exposure and thickening with the ammonia or th papers i a warm (60-80 C.) ammonia gravity amine, the nonwoven material is then dried and cured. oven A fresh 20 p rcent solution of ammonium hy- The drying step is normally conducted by passing the droxide was placed in a pan on the floor of the oven nonwoven material through one or more ovens or heatprior to treating the papers. Immediately after exposure ing chambers maintained at a temperature between t th am i the papers were dried and cured in a about 200 and 325 F. The preferred drying tempera- 275 F. air oven for 5 minutes. Physical properties of ture will be in the range between about 225 and 275 th se cured papers were then determined and com- F. The drying ovens may be maintained at subatmopared against those obtained with identically saturated spheric pressure to facilitate the removal of water if so papers which were not exposed to ammonia. Table I desired. The dried nonwoven is then typically passed sets forth the test results. through one or more ovens maintained at higher tem- Tensile (breaking) strengths and elongation of the peratures to effect the cure of the binders employed nonwoven material were determined in accordance and develop the ultimate physical characteristics of the with the ASTM D1 1 17-63 Cut-Strip Method. Specinonwoven. Such curing ovens are maintained at temmens for use in determining the wet tensile strength peratures between about 250 and 325 F. preferably were soaked in water at room temperature for 16 hours between 275 and 300 F. In either the drying operation immediately prior to the testing. Solvent tensile or the curing step the nonwoven material may be strengths were obtained after immersion of the nonwopassed through the heating chamber once or it may be ven in perchloroethylene for 20 minutes at room temrecycled for as many times as required. The drying and perature. Samples (1 inch X 6 inch) of the nonwoven curing need not be distinct steps, depending on the were sandwiched between two 1% inch X 6 inch pieces temperature requirements of the binder it may be desirof Bondex T-7 tape and sealed with the weight of an able to combine them in one operation. iron at 275 F. for 30 seconds on a heated plate. The

The following Examples serve to illustrate the invenresistance to delamination for fabrics or internal bond tion more fully; however, they are not intended to limit strength for papers was then reported as the force its scope. in these Examples all parts and percentages (ounces/inch) required to peel the tapes apart when are given on a weight basis unless otherwise indicated. pulled at a rate of 12 inches per minute.

TABLE 1 Paper Properties Ammonia Exposure Time None 5 Seconds l Minute 3 Minutes 60 Minutes Dry Tensile Strength (pounds/inch) 61 2 Wet Tensile Strength (pounds/inch) 16 25 32 30 3! 1 Qn. uc. i

v a llaper Properties v Q I v v I Ammonia Exposure Time I i None'. 5 Seconds l Minute 3 Minutes 60 Minutes Solvent Tensile Strength (pounds/inch) 37 I I 39 Dry Elongation (9%) '9 9 .lnternalBond Strength (ounces/inch) 20 42 ,39

Reported the average obtained for three samples. Oven maintained at 118F. I

Paper's exposed 3 minutes at 178 F. prior to curing, i.e., having an identical heat history. with the samples exposed for 3 ,minutes in Table l,.developed only about one-half the internal bond strength of samples. treated with ammonia. In other words, by treating the nonwoven materialsimpregnated with acrylate binder latices containing carboxyl functionality with ammonia vapors, l have been able to obtain nonwoven materials having twice the resistance to delamination as conventionalsaturated nonwovens. t t I Q f When the abovelatex wasused to saturate a nonwoven polyester fabric andthe saturated polyester cured for 5 minutes at 275 C.,the unexposedpolyester had a resistance to delamination of 21 ounces/inch. The polyester sample which was exposed to ammonia for 3 lamination, in fact,. ,the cohesion within the polyester was greater than the adhesion of the Bondex Tape to the polyestersaturated fabric and. the fabric pulled. 30

' ple l and diluted to 25' percent total solids-was used to saturate 10 mil flat papers. The procedures employed for saturation and testing were identical to those previ-.

ously described T-he-papers were exposed to dietl'iylpercent T'.S. )of Example lll containing about 1 part minutes prior to the cure had a greater resistance to deaminevapors from a 10 percent aqueous solutionof-the amine for:3' .minutesand 10 minutes prior to the standard 275 -,F. cure'for 5 minutes. Internal bond strengths are reported-in Table II and compared withthose 'obtained without exposure to-diethylamine and an unsaturated -paper,control.-,1;

" "TABLEII" Paper Sample J Internal Bond Strength Unsaturated Control- I -5 Unexposed to diethylamine Saturated Control Unexposed 20 to diethylamine 3 minute exposure to 32 diethylamine 10 minute exposure to 34 diethylamine 7 EXAMPLE III I 'trile and N-methylol acrylamide. The polymer latex I after dilution with water to about 25 percent total solids was-used as a saturant for paper samples in accors/inch'and internal bond strengths of l4 ounces/inch. The paper samples which were exposed for 3 minutes in an ammonia oven after saturation and before the cureshowed a 10 percent increase in wet tensile strengths and over percent increase in the internal bond strengths. The internal bond strength was 22 ounces/inch- EXAMPLE IV About 100' partsof the acrylate polymer latex (25 interpolymerized acrylic acid was blended with 2.5 parts of a water-soluble salt of a copolymer of about 70 percentalkyl acrylates and about '30 percent methacrylic acid to'increase the overall c'arboxyl content of the resulting latex. After 3 minutes exposure to ammonia at 178F. and curing at 275 F..for 5'minut'es the wet breaking strength and internal bond strengths were 34. pounds/inch and 35 ounces/inch respectively.

Theiabove Examples illustrate the utility of the present process clearly showing the nonwoven materials saturated with the carboxyl-containing alkyl acrylate polymer latices and exposed to ammonia or amine vapors have markedly improved internal bond strengths or resistance to delamination and also improved wet tensile strengths. Thatthe present process is applicable to both papers and nonwoven fabrics is also shown. The

process is-especially attractive in that only short exposure ,toammonia or amine will renderthese improvements. it is demonstrated that the exposure tov ammonia or 'amine is critical :to obtain the improved properties.

The Examples demonstrate'that the present process dance with the procedure described in Example I. The I saturated unexposed control papers cured for 5 minutes at275 F. had wet breaking strengths of 27 poundmay be employed with alkyl acrylate binder latices containing 'chemicallyboundcarboxyl functionality or alkyl acrylate latex binders which are blended with other carboxyl-containing latices to achieve the carboxyl functionality.

' strength in paper and nonwoven fabric comprising (1 impregnating a nonwoven web with an aqueous carboxyl-containing alkyl acrylate copolymer latex, said copolymer consisting essentially of from about 50 to 99.95 percent by weight of (a) one or more esters of an a,B-olefinically unsaturated carboxylic acid having the structural formula wherein R is hydrogen or methyl and R is a hydrocarbon radical containing from one to 12 carbon atoms polymerized, with up to about 40 percent by weight (b) of one ormore copolymerizable vinylidene monomers having at least one terminal HZIC groupand being free of amine groups and (c a,B-olefinically unsaturated carboxylic acids containing from three to 10 carbon atoms to provide about 0.05 percent to about 25 percent by weight of carboxyl groups, said latex containing up to about 6 percent by weight, based on the total weight of monomers, of emulsifiers selected from the group consisting of anionic or nonionic emulsifiers; (2) reacting the impregnated nonwoven web with ammonia or an aliphatic monoamine containing from one to six carbon atoms, at a temperature less than 212 F., for about 1 second to less than 80 minutes; and (3) heating the impregnated nonwoven web at a temperature between about 200 and 325 F.

. 2. A process of claim 1 wherein R is an alkyl radical containing two to eight carbon atoms, in (b) the vinylidene comonomer is selected from the group consiting of a vinyl aromatic, a vinyl or vinylidene halide, a vinyl ester, an a,B-unsaturated nitrile, and an :,B-unsaturated amide, and (c) is selected from the group consisting of acrylic and methacrylic acids, in amounts of about 0.1 percent to about percent by weight of carboxyl groups.

3. A process of claim 2 wherein the latex is maintained at a pH below 7.5 during impregnation, in (2) the reaction time is from about 2 seconds to less than 5 minutes and in (3) the heating temperature is between 200 and 300 F.

4. A process of claim 3 wherein R is an alkyl radical containing from four to eight carbon atoms, present in (a) in amount from about to percent by weight and about 5 to 29 percent by weight of (b) vinylidene monomer. 5. A process of claim 4 wherein (b) is at least one of acrylonitrile, methacrylonitrile, acrylamide, methacrylamide and N-methylol acrylamide.

6. A process of claim 3 wherein in (a) there is greater than 70 percent by weight of ethyl acrylate, and (b) is about 0.5 to 10 percent of acrylonitrile and 0.5 to 15 percent weight total of acrylamide, methacrylarnide and N-methylol acrylamide.

7. A process of claim 1 wherein the copolymer contains about 0.1 to 10 percent by weight of a,B-olefinically unsaturated carboxylic acid is polymerized in the presence of the base polymer containing from about 50 to 99.9 percent by weight of (a).

methylol acrylamide.

Claims (9)

1. 2. A process of claim 1 wherein R1 is an alkyl radical containing two to eight carbon atoms, in (b) the vinylidene comonomer is selected from the group consiting of a vinyl aromatic, a vinyl or vinylidene halide, a vinyl ester, an Alpha , Beta -unsaturated nitrile, and an Alpha , Beta -unsaturated amide, and (c) is selected from the group consisting of acrylic and methacrylic acids, in amounts of about 0.1 percent to about 10 percent by weight of carboxyl groups.
2. 3. A process of claim 2 wherein the latex is maintained at a pH below 7.5 during impregnation, in (2) the reaction time is from about 2 seconds to less than 5 minutes and in (3) the heating temperature is between 200* and 300* F.
3. 4. A process of claim 3 wherein R1 is an alkyl radical containing from four to eight carbon atoms, present in (a) in amount from about 70 to 95 percent by weight and about 5 to 29 percent by weight of (b) vinylidene monomer.
4. 5. A process of claim 4 wherein (b) is at least one of acrylonitrile, methacrylonitrile, acrylamide, methacrylamide and N-methylol acrylamide.
5. 6. A process of claim 3 wherein in (a) there is greater than 70 percent by weight of ethyl acrylate, and (b) is about 0.5 to 10 percent of acrylonitrile and 0.5 to 15 percent weight total of acrylamide, methacrylamide and N-methylol acrylamide.
6. 7. A process of claim 1 wherein the copolymer contains about 0.1 to 10 percent by weight of Alpha , Beta -olefinically unsaturated carboxylic acid is polymerized in the presence of the base polymer containing from about 50 to 99.9 percent by weight of (a).
7. 8. A process of claim 7 wherein the carboxylic acid is acrylic or methacrylic acid and the base copolymer contains 70 to 95 percent by weight of (a) wherein R1 contains two to eight carbon atoms.
8. 9. A process of claim 8 wherein (b) is at least one acrylonitrile, methacrylonitrile, acrylamide, methacrylamide and N-methylol acrylamide.
9. 10. A process of claim 9 wherein in (a) R1 is ethyl, and (b) is about 0.5 to 15 percent by weight of N-methylol acrylamide.