US 3784401 A
A process for obtaining nonwoven materials having improved physical properties, especially internal bond strength and resistance to delamination is provided. Nonwoven fabrics and papers impregnated with carboxyl-containing butadiene polymer latices, especially carboxylated butadienestyrene and carboxylated butadiene-acrylonitrile copolymer, are 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 a marked increase in internal bond strength.
Description (OCR text may contain errors)
United States Patent [191 Wheelock 1 Jan. 8, 1974  PROCESS FOR IMPREGNATING 3,085,897 4/1963 Priest et al.. 117/62.2 NON WOVENS'WITH BUTADIENE 2,429,698 10/1947 Schneider 117/106 R 3,168,415 2/1965 Goldstein et al.... 117/62 CARBOXYL POLYMER LATICES 3,318,722 5/1967 Ullman ll7/62  Inventor: George L. Wheelock, Avon Lake, 3,404,022 0/ 6 a e et a1 1 17/622 Ohio 3,472,611 10/1969 Langwel1...... 1'l7/62.1 3,483,014 12/1969 lssacs et a1 117/62  Assignee: The B. F. Goodrich Company, New
York Primary Examiner-Murray Katz  Filed: July 14, 1972 Assistant Examiner-M. Sofocleous [211 pp No: 272,006 Attarney-J. Hughes Powell, Jr. et a1.
Related US. Application Data Continuation-in-part ofSer. No. 739,584, May 20, 1968, abandoned.
US. Cl ll7/62.2, 117/106 R, 117/140 A, 117/155 UA, 34/36 Int. Cl B44d 1/48 Field of Search 117/62, 62.1, 62.2, 117/106 R, 140 A, 155 UA; 161/170, 34/36 References Cited UNITED STATES PATENTS 2/1961 Berke et a1. l17/62.2 5/1961 Coates 117/62.Z
 ABSTRACT A process for obtaining nonwoven materials having improved physical properties, especially internal bond strength and resistance to delamination is provided. Nonwoven fabrics and papers impregnated with carboxyl-containing butadiene polymer latices, especially carboxylated butadienestyrene and carboxylated butadiene-acrylonitrile copolymer, are 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 a marked increase in internal bond strength.
10 Claims, No Drawings 1 PROCESS FOR IMPREGNATING NON-WOVENS WITH BUTADIENE CARBOXYL POLYMER LATICES CROSS REFERENCE TO RELATED APPLICATION This is a continuation in part of my copending application Ser. No. 739,584 now abandoned, filed May 20, 1968.
BACKGROUND OF THE INVENTION Polymer latices have been used for many years for coating and impregnating papers and more recently in the manufacture of nonwoven fabrics. Typically, the paper or non-woven is saturated with the latex and then the water removed leaving the polymer behind to bond the fibers in the finished nonwoven. Aside from the type of binder employed, one of the more important factors governing the ultimate physical properties achievable with a nonwoven is the amount of binder present in the nonwoven and also the uniformity with which the binder is dispersed throughout the substrate. If the non-woven on a whole is deficient in bonding agent or if localized areas are deficient, the physical properties of the nonwoven, especially the internal bond strength and the resistance to delamination, are quite low and often the nonwoven is rendered unsuitable for many applications.
The'problem of obtaining adequate and uniform binder throughout the nonwoven material is especially significant when using the latex binder systems. With these latex systems it is sometimes so difficult to incorporate sufficient binder to obtain the desired level of physical properties that it becomes necessary to resatu rate the nonwoven with the latex a second time after drying the first binder solution. This, however, is a time-consuming and costly operation and therefore not generally desirable.
Efforts to overcome the problem of achieving an acceptable binder content has led to much work primarily in the field of developing improved latex binder systems. Typically, the improved latex binder systems developed to date contain monomers capable of reacting.
upon the application of heat, chemical reagents or catalysis to form cross-linked polymers having improved physical properties. This approach is not completely satisfactory, however, since the binders, even though more efficient, are susceptible to migration through the nonwoven material. This migration occurs during the drying or curing of the nonwoven. As the water is removed the polymeric binder is carried toward the surface of the nonwoven material creating a nonuniform distribution of the binder throughout the nonwoven and consequently poor physical properties.
The viscosity of the binder latex can be increased prior to saturation of the nonwoven by the addition of thickening agents such as natural gums and pastes, polyvinyl alcohol and the like. This technique, however, is only partially effective to reduce the migration within the nonwoven material since it creates the additional problem of achieving uniform initial saturation of the nonwoven due to the poor penetrability and the difficulty of application of the thickened latices.
Butadiene-based polymer latices, especially butadiene-acrylonitrile and butadiene-styrene latices, are an important class of binders for use with papers and nonwoven fabrics. They provide nonwoven fabrics having an acceptable balance of physical properties and wear endurance. The butadiene-acrylonitrile copolymer latices are especially important for nonwoven applications since they provide nonwovens having good fiber adhesion, superior aging and resistance to oils.
SUMMARY OF THE INVENTION I have now developed a process whereby nonwoven materials having markedly improved internal bond strength and resistance to delamiination are obtained when the nonwoven is saturated with a carboxylated butadiene polymer anionic latex and then exposed to ammonia or amine vapors prior to drying or curing. To obtain these improved properties the nonwoven web or mat is impregnated with the carboxylated butadiene polymer latex which for the purposes of the present invention can be obtained by interpolymerizing one or more carboxyl-containing monomers, preferably a,B-olefinically unsaturated carboxylic acid monomers, with, for example, the butadiene and styrene or acrylonitrile.
The nonwoven materials treated in accordance with the present process have improved internal bond strength and resistance to delamination overtnonwovens prepared conventionally, that is, without the am monia or amine exposure. The present process is equally applicable to both fabricsand papers. It provides a means for achieving a more uniform distribution of the polymeric binder within the finished nonwoven as a result of the in situ thickening of the latex binder prior to the drying step. This in situ thickening reduces the migration of the polymer toward the surface of the nonwoven as the water is removed after a uniform initial saturation has been obtained.
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 with the butadiene binder latices 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 include: 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 self-condensation of caprolactam; polyesters such as polyethylene glycol terephthalate; acrylic fibers containing a minimum of about percent acrylonitrile with vinyl chloride, vinyl acetate, vinyl pyridine, 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 presentinvention is particularly advantageous for use with specialty papers which require specific 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), semi-bleached 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 latex binders employed for the process of the present invention are aqueous carboxyl-containing butadienebased polymer latices containing an anionic surface active agent. The required carboxyl functionality is chemically bound to the butadiene polymer, that is, one or more a,B-olefinically unsaturated carboxylic acid monomers will be polymerized with the butadiene and other comonomers. The carboxyl group present in the butadiene latex will constitute from about 0.5 to about 25 percent by weight based on the total polymer.
The butadiene polymer latices useful in the present invention are obtained by polymerizing from about 29.5 to 99.5 percent by weight butadiene, preferably with up to about 70 percent by weight styrene or up to about 50 percent by weight acrylonitrile. In addition to these monomers, up to about 40 percent by weight of one or more other polymerizable comonomers may be interpolymerized therewith. Typically, these polymerizable comonomers will be vinylidene monomers having at least one terminal group. Polymerizable comonomers useful in the present invention include: other vinyl aromatics as a-methyl styrene and. chlorostyrene; oz-olefins such as ethylene, propylene and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide, vinyl fluoride, vinylidene chloride, and vinylidene fluoride; vinyl esters such as vinyl acetate; other a,B-olefinically unsaturated nitriles as methacrylonitrile; 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; esters of a,B-olefinically unsaturated carboxylic acids such as methyl acrylate, ethyl acrylate, the propyl acrylates, the butyl acrylates,
the amyl acrylates, cyclohexyl acrylate, Z-methyl hexyl acrylate, n-octyl acrylate, 2-ethyl hexyl acrylate, methyl methacrylate, ethyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, methyl ethacrylate, ethyl ethacrylate, haloalkyl acrylates as chloropropyl acrylate but excluding amino-acrylates and methacrylates and the like; vinyl ketones; vinyl pyridine, a,B-olefinically unsaturated amides such as acrylamide, N-. methyl acrylamide, N-t-butyl acrylamide, N-cyclohexylj acrylamide, diacetone acrylamide, methacrylamide, and N-ethyl methacrylamide; a,fl-olefinically unsatu-; rated N-alkylol amides having the structural formula wherein R is a hydrogen or an alkyl group containing from 1 to 4 carbon atoms and x is a number from 1 to 4, such as N-methylol acrylamide, N-ethanol acrylamide, N-propanol acrylamide, N-methylol methacrylam ide, and N-ethylol methacrylamide; polyfunctional compounds such as methylene-bis-acrylamide, ethylene glycol dimethacrylate, diethylene glycol diacrylate, allyl pentaerithrito] and divinyl benzene; and the like, as are known to those skilled in the art.
The carboxyl functionality necessary for the present process is chemically bound in the butadiene polymer of the latices and is introduced by polymerizing one or more a,B-olefinically unsaturated carboxylic acid monomers containing from 3 to 10 carbon atoms with the butadiene and any other comonomers which may be present. 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, fumaric 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. The carboxyl-containing monomers may be chamically bonded to the butadiene polymers through interpolymerization, which includes overpolymerization, graft or block polymerization or the like, to obtain the carboxyl functionality necessary for this invention. Generally, the butadiene polymers will contain about 0.5 to 15 percent by weight of the a,B-olefinically unsaturated carboxylic monomer interpolymerized. An especially useful polymer latex for the purposes of the present invention contains about 50 to percent by weight butadiene, 20 to 45 percent by weight styrene or acrylonitrile, l to 5 percent acrylic or methacrylic acid and up to about 20 percent by weight other polymerizable vinylidene comonomers free of amine groups interpolymerized. The styrene and acrylonitrile may be present individually or in combination in the butadiene latices. Useful nonwovens have been obtained when the butadiene latex contained about equal parts of styrene and acrylonitrile interpolymerized.
The carboxyl-containing butadiene polymer latices wherein the carboxyl functionality is interpolymerized with the butadiene and styrene or acrylonitrile may be prepared using any of the conventional polymerization techniques. The aqueous medium may contain a surface active agent. When an emulsifier or dispersing agent is used to prepare the polybutadiene binders they may range from about 0.1 percent, as 0.5 percent, up to about 6 percent or more, as 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 those types known to those skilled in the art, for example, as disclosed beginning on page 102 in J. Van Alphens Rubber Chemicals, Elsevier, 1956, for example, the alkali metal or ammonium salts of the sulfates of alcohols containing from 8 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 mono and diphosphate esters; and the like. So-called nonionic "emulsifiers are octylor nonyl phenyl 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 8 to 20 carbon atoms such as octyl, decyl, dodecyl, alkoxy or ethoxy groups, or aryl, such as a phenyl radical of the formula 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-polym erization emulsifiers and stabilizers to the polymeric anionic 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 but preferably are anionic or nonionic surface active 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 hy droperoxide, l-hydroxycyclohexyl hydroperoxide; azo compounds such as azodiisobutyronitrile, and dimethyl azodiisobutyrate; and the like. Especially useful as polymerization initiators are the watersoluble 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 polyhydroxy phenol and an oxidizable sulfur compound such as sodium sulfite or sodium bisulfite, a re ducing 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.l 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 butadiene 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 0 C. to about C. or higher. Excellent results, however, have been obtained when the polymerization temperature is maintained between 5 C. and 60 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.
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 isthickened in situ, thereby inhibiting 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 butadiene 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 6 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 3 to 1 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 100 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 this uniform 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 penetrationof the thickening agent to the interior regions of the nonwoven and consequently these interior regions are subject to migration of the binder upon drying.
Exposure of the saturated nonwoven material to the ammonia or amine vapors will vary depending on the particular latex binder and thickening agent employed. Contact times will generally be from 1 second to less than about 80 minutes, preferably they will range between about 2 seconds and 5 minutes. With ammonia and the more volatile amines, contact times between 5 seconds and 1 minute have been successfully employed and found to impart maximum properties to the cured nonwoven material. Once maximum thickening of the binder latex is achieved, additional exposure to the ammonia or amines will produce no further improvement in the nonwoven properties. Neither will any detrimental effects be realized from prolonged exposure to the ammonia or amine vapors.
Exposure to the ammonia or amine is conveniently brought about in a chamber maintained at room temperature or above, such as a gravity oven, where in a sufficient concentration of the ammonia or amine vapors can be maintained for contact with the saturated nonwoven. Although the exposure ovens can be maintained at elevated temperatures, these temperatures should generally not exceed 212 F., particularly if long exposure times are employed. Because of the short contact times possible with the present process, the saturated nonwoven may be continuously passed through the gaseous ammonia or amine to facilitate the exposure step. Such a continuous process would be highly desirable for large-scale commercial operations.
After exposure and thickening with the ammonia or amine, the nonwoven material is then dried and cured. The drying step is normally conducted by passing the nonwoven material through one or more ovens or heating chambers maintained at a temperature between about 200 and 325 F. The preferred drying temperature will be in the range between about 225 and 275 F. The drying ovens may be maintained at subatmospheric pressure to facilitate the removal of water if so desired. The dried nonwoven is then typically passed through one or more ovens maintained at higher temperatures to effect the cure of the binders employed and develop the ultimate physical characteristics of the nonwoven. Such curing ovens are maintained at temperatures between about 250 and 325 F., preferably between 275 and 300 F. ln either the drying operation or the curing step the nonwoven material may be passed through the heating chamber once or it may be recycled for as many times as required. The drying and curing need not be distinct steps, depending on the temperature requirements of the particular binder latex employed.
The following Examples will illustrate the invention more fully. They are not intended to limit its scope however. All parts and percentages set forth in the Examples are given on a weight basis unless otherwise indicated.
EXAMPLE I To demonstrate the process of the present invention a butadiene polymer latex containing interpolymerized carboxyl functionality was prepared for use as a binder. The latex was prepared by emulsion polymerizing 52 parts butadiene, 45 parts styrene and about 1.5 parts each of acrylic acid and methacrylic acid in 95 parts water containing 3 parts of an alkyl benzene sulfonate emulsifier. The polymerization was initiated with 0.15 part of a potassium persulfate catalyst. The polymerization was maintained at about 50 C. until essentially complete conversion was achieved. The resulting butadiene copolymer latex contained about 50 percent total solids.
A saturation bath was prepared by diluting the latex obtained to 25 percent total solids with distilled water. Ten mil uncoated flat paper (Patterson Parchment Company) having a minimum fiber to fiber contact and placed in a Dacron marquisette envelope was then saturated by submerging the paper in the latex bath. The excess binder latex was then removed by passing the paper between padder squeeze rolls maintained at about 20 pounds pressure. The saturated paper was then removed from the marquisette envelope.
The paper saturated in' the above manner was then exposed to ammonia vapors for three minutes by placing the papers in warm (60 to C.) gravity oven containing ammonia vapors. The ammonia atmosphere was achieved by placing a fresy 20 percent solution of ammonium hydroxide in a pan on the floor of the oven prior to inserting the papers. Immediately after expo- I sure to the ammonia the papers were dried and cured in a 275 F. air oven for five minutes.
Physical properties of the cured papers were then determined and compared against those obtained with identically saturated papers but not exposed to ammonia. Tensile (breaking) strengths of the nonwoven ma terials were determined in accordance with ASTM D1l17-63 cut-strip method. Samples used for determining the wet tensile strength were soaked in water at room temperature for 16 hours immediately prior to testing. Resistance to delamination for fibers and internal bond strength for papers was determined by sandwiching a 1 X 6 inch sample of the nonwoven between two l-% X 6 inch pieces of Bondex T-7 tape, sealing with the weight of an iron at 275 F. for 30 seconds on a heated plate and peeling the tapes apart at a rate of 12 inches per minute. The forces required to pull the tapes apart is reported in ounces/inch.
Papers saturated with the above-described butadiene binder latex and dried and cured in the conventional manner had a wet breaking strength of 2.1 pounds/inch and an internal bond strength 'of 14.4 ounces/inch. Identical paper samples exposed to ammonia vapors after saturation and prior to drying and curing in accordance with the process of the present invention had wet breaking strengths of 3.1 pounds/inch and internal bond strength of 16.5 ounces/inch.
When the above butadiene latex is used to saturate fabrics rather than papers similar improved properties are obtained. Also, the improved properties of both papers and fabrics saturated with these carboxylated butadiene latices are improved when exposure times less than three minutes are used. Exposure times as low as seconds are effective. Exposure to diethylamine instead of ammonia gives comparable improvement in the wet tensile strength and internal bond strengths.
EXAMPLEVII The butadiene latex prepared in Example I was diluted to 25 percent total solids and the pH adjusted to 3.5 by the addition of 10 percent acetic acid. 2.5 parts of a water-soluble salt of a copolymer of about 70 percent alkyl acrylates and about 30 percent methacrylic acid was blended with the latex to increase the overall carboxyl content of the resulting butadiene binder la tex. Papers saturated using the procedure described in Example 1, exposed to ammonia for 3 minutes at 178 F. and cured at 275 F. for five minutes had wet breaking strengths of 4.4 pounds/inch internal bond strengths 19.2 ounces/inch.
EXAMPLE III A latex was prepared using the described emulsion polymerization techniques containing 55 percent butadiene, 20 percent acrylonitrile, 20 percent methyl methacrylate and 5 percent methacrylic acid. The latex was used to saturate 10 mil flat paper and tested for internal bond strength and wet tensile strength. After exposure for 3 minutes to ammonia at 178 F. the wet tensile strength was 4.7 lbs/in. and the internal bond strength was 6.1 ounces/inch.
The above Examples clearly point out the utility of the present invention. They demonstrate that nonwoven materials saturated with carboxyl-containing butadiene polymer latices exposed to ammonia have improved internal bond strength and generally improved wet tensile strength. Carboxylated'butadiene-styrene 10 and butadiene-acrylonitrile latices, which may contain one or more other polymerizable comonomers, are useful for the present process.
l. A process for obtaining increased internal bond strength in paper and nonwoven fabric comprising (1) impregnating a nonwoven webwith an aqueous carboxyl-containing butadiene copolymer latex, said copolymer consisting essentiallyof (a) from about 29.5 to 99.5 percent by weight of butadiene, (b) up to about percent by weight of a styrene or up to about 50 percent by weight of an acrylonitrile, (c) up to about 40 percent by weight of one or more polymerizable vinylidene comoiiomers having at leastone terminal group and being free of amine groups, and (d) 05B ,olefinically unsaturated carboxylic acids containing from 3 to 10 carbon atoms providing about 0.5 to iabout 25.0 percent by weight of carboxyl groups said Elatex containing from about 0.1 up to about 6 percent by weight, based on the total weight of monomers, of an emulsifier selected from the group consisting es- ;sentially of anionic and nonionic emulsifiers, (2) reiacting the impregnated nonwoven web with ammonia for an aliphatic monoamine containing from 1 to 6 icarbon atoms at a temperature less than 212 F. for [about 1 second to less than minutes; and (3) heatling the impregnated nonwoven web at a temperature !between about 220 and 325 F.
2. A process of claim 1 wherein the vinylidene comonomer (c) is selected from the group consisting of a vinyl aromatic, a vinyl or vinylidene halide, a vinyl cster, an a,B-unsaturated nitrile, and an a,B-unsaturated amide, and (d) is selected from the group consisting of acrylic and methacrylic acid in amount of about 0.1 to about 10 percent by weight of of carboxy groups.
3. The 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. The process of claim 3 wherein (a) is from about 50 to 70 percent by weight butadiene, (b) is from about 20 to 45 percent by weight acrylonitrile, there is up to about 40 percentby weight Ofvinylidene comonomer and about 1 to 5 weight percent (d). V 5. The process of claim 3 wherein'(a) is from about 50 to 70 percent by weight butadiene, (b) is from about 20 to 45 percent by weight styrene, there is up to about 40 percent by weight of vinylidene comonomer and about 1 to 5 weight percent (d).
6. The ptocess of claim 4 wherein (c) is methyl meth- ,acrylate.
7. The process of claim 4 wherein there is about 0.1 to 5 percent by weight of an acrylamide, methacrylamide or a,B-ole-finically unsaturated N'alkylol amide of .the formula wfi'efi R is hydrogen or alkyl containing 1 to 4 carbon contains about 55 percent by weight butadien'e, about 20 percent by weight acrylonitrile, about 20 percent by weight methyl methacrylate'and about 5 percent by weight methacrylic acid.