N O N W O V E N FABRICS felt constructions in current use (72)mechanically interlocked fibers alone and in combination with woven fabrics; mechanically interlocked fibers plus chemical felting; and any one of these three containing fibers that can be made cohesive or adhesive. The use of the first of these types parallels that of the low density wool pad felts. The second type is used in applications beyond the range of the high density thin gage mechanical roll felts, whereas the third type is most generally suited for potentially extending felt applications. The four class is experimental at this time, but will undoubtedly enable modified versions of the other types to be produced for special uses. The manufacturing procedure for the mechanically interlocked and chemically felted class are briefly outlined. In order for this structure to be achieved, a synthetic fiber which not only can be mechanically interlocked, but also under certain combinations of heat, moisture, and chemical action can be made to reorient or shrink along its lengthwise axis must be available. Shrinkage along the individual fiber length must be about 5070 to obtain the felting power that is necessary for this class of felt to result. With fibers of this type it is possible to produce synthetic fiber felts with percentages of nonshrinkable synthetic fibers in the blend. These new materials are not replacements for wool felt. Rather, they are finding greatest applications in industrial process equipment where wool felt
I
has not been utilized. For example, in the mining of taconite, polyester fiber felts used on reverse air jet dust collectors have overcome one of the major process stumbling-blocks in using this ore. Other developmental types of industrial applications are currently under way. These new synthetic fiber fabrics in lighter weights and in colors have aroused interest in the fields of apparel and decoration. Natural protein fibers form basic building blocks for nonwoven felt materials over a wide range of types, grades, weights, and thicknesses. The materials are proved, established, and standardized. New synthetic fiber felts are being developed to extend felt applications and use beyond the limitations of natural fiber felts.
References (1) Alexander, P., Am. Dyestuff Rep&. 39, 420 (1950). (2) Alexander, P., Hudson, R. F., “Wool, Its Chemistry and Physics,” chap. 11, Reinhold, New York, 1954. (3) Am. SOC.Testing Materials, Philadelphia, Pa., ASTM Standards on Textile Materials, 1957. (4) Boeddinghaus, H., Think Mag., pp. 7-8 IBM publication (July 1952). (5) Bogaty, H., Sookne, A., Harris, M., Textile Research J . 21, 822 (1951). (6) Bohm, L., J . SOC.Dyers Colourists 61, 278-83 (1945). (7) Colwell, W., Products Fznishing (Felt Association reprint) 5 (January 1952). (8) Ditzell, Deut. Wollen-Gewerbe 23, No. 1 (1891). (9) Dusenbury, J. H., Menkart, J., Proc.
Intern. Wool Textile Research Conf., Australia, 1955. (10) Felt Association Inc., The, New York, N. Y . , “Felt-Wool,” 1952. (11) Gillick, T. J., Elec. Mfg.61, 126-31 (1958). (12) Gillick, T. J., Magnant, F. J., Prod. Eng. 28, 478-82 (July 1957). (13) Harris, M., Am. Dyestuff Reptr. 37, 72 (1945). (14) Horio, M., Kodo, T., Textile Research J . 23, 373 (1953). (15) Kaswell, E. R., “Fibers, Yarns, and Fabrics,” chap. 18, Reinhold, New York, 1953. (16) Kent, R. T., Iron Age 135, 124-8 11095\ \----,.
(17) Lauderbach, H., Textile Research J . 25, No. 2 (February 1955). (18) Lehmberg, W. H., Mech. Eng. 67,93-9 (February 1945). (19) Martin, A. J. P.. J . SOG. Dvers Colourists 60, 325 (1944). ’ (20) Menkart, J., Speakman, J. B., Nature 159, 640 (1947). (21) Moncrieff, R. W., “Wool Shrinkage and Its Prevention,” p. 147, Chemical Publ. Co., New York, 1954. (22) Rile M. W., Materials @ Methods 43, 89-93 &ecember 1956). (23) SAE Handbook, SOC. Automotive Inc., New York, p. 387, 1957. (2%; eakman, J. B., Stott, E., J . Textzle Research Inst. 22, T339 (1931). (25) U. S. Dept. of Commerce, Washington 25, D. C., Commercial Standard 18552, 1952. (26) U.S. Govt. Printing Office, Washington 25, D. C., Federal Specification C-F206a, 1954. (27) Wakelin, J. H., Textile Research Institute, Princeton, N. J., Ann. Rept. 1953-54, p. 41. (28) Williams, M. C., Natl. Geograjhic M a g . 61, No. 3, “First Over the Roof of the World.” (29) Wrotnowski, A. C., Chcm. Eng. Progr. 53, NO,7, 313-19 (1957).
NEIL H. SHERWOOD Products Application Laboratory, B. F. Goodrich Chemical Co., Avon Lake, Ohio
Binders for Nonwoven Fabrics the past I O years, progress in technology of nonwoven fdbrics has been much slower than for the nonwoven fabrics industry because there has been a ready market for products which can be made rather simply on comparatively inexpensive equipment. A nonwoven fabric is a textilelike product in which the fibers are held together by a bonding material. A nonwoven fabric has two parts-fiber and binder. Hence, the choice of the binder is equally as important as the choice of the fiber. Each construction must be judged separately on the basis of its end use. For certain uses many DURING
binders may be used with many different fibers and web construction. The vario-us binders are summarized with some of their defects and benefits. I
Binder Systems
No attempt is made to list all of the binders used for nonwoven fabrics. Binders may be separated, by their physical state a t the time of application, into the two broad classifications of dry or wet binders. 1. The dry systems are made up of thermoplastic fibers or powders,
2. Wet systems include solutions, of both aqueous and solvent types, as well as polymer dispersions or emulsions. Dry Binders. Attempts have been made to use thermoplastic polymers in powder form for binding nonwoven fabrics. Although some have been prepared commercially, the practice is very limited. The thermoplastic powders are satisfactory for binding, but the problems of distributing the powder into the web and keeping it where it can bind the fibers efficiently make this process unattractive a t the present time. O n the other hand, the use of thermoplastic fibers is practicable and is in VOL. 51, NO. 8
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commercial usage. This method provides a more uniform distribution of the binder throughout the web, because the binder is itself a fiber which can be incorporated into a fiber blend. The actual bonding may be achieved by passing the web containing the bonding fiber between heated smooth or patterned rolls, depending on the type of end product desired and the amount of bonding fiber present. Infrared or hot air heating may also be used for bonding. Theoretically, any fiber which softens and flows at a temperature lower than that of the remainder of the web can be used as a thermoplastic fiber. In actual practice fibers of poly(viny1 chloride), polyethylene, or vinylidene polymers and copolymers, polyamides or polyesters or acetate of very low softening points are some of the types used. Thermoplastic fibers offer a number of advantages as binders for nonwoven fabrics. The exact amount of binder used can be determined exactly as it is part of the web blend. The distribution of the binding fiber can be controlled very well depending upon the type of web forming equipment used. No special impregnating system is required as the binder was part of original web. Thermoplastic fibers may also serve in heat sealing the product to other materials. However, thermoplastic fibers have not gained much prominence as nonwoven binders probably because of the nature of the fibers themselves. To have a low melt temperature the polymers are usually of low molecular weight and thus have inherently low strength. Such fibers generally are not suitable where high strength, at minimum binder weight, is required. There is also less flexibility in operations and in the type of product than when latex binders are used. Wet Binders. Only a few nonwoven fabrics are made using solvent solutions as binders. Although the efficiency of the process and the end product are both good, the major problem comes from the use of solvents. Unless recovery systems, which are very expensive, are available the use of solvents is costly. Furthermore, there is the ever present hazard of solvents, both by fire and toxicity. Water solutions of natural gums, proteins, starches, and some synthetic water soluble polymers are limited in use as binders. None of these are used as the primary binder for quality items except where stiffness can be tolerated as in cheaper decorative fabrics. In some cases these materials are used as a prebond before other treatments. The water-based emulsion systems, which include the polymer latices, are the most versatile and popular of the nonwoven binders. Their ease of handling and genera1 freedom from hazard
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make them attractive. Until recently the literature was lacking in reference to nonwoven binder systems.
Literature Background for Nonwoven Fabrics Subject
Ref
Survey of cotton in industry Fibers and equipment used in manufacturing A s a new textile material Bonded fabrics and its industry Production and utilization Technology New bonding techniques New type Cellulosic fibers Binders Chemical and processing techniques Nonwoven filter media Properties of thermoplastic fiberbonded fabrics
(0
I
(3)
(3)
(4, 9) (6)
(6) (7) (8)
(10, 1 0 (la) (13) (14) (16)
Discussion Many latices are available today. Behavior and preference of some of the classes of latices are discussed. Some of the basic properties of nonwoven fabrics are shown for several basic latex binder classes. Variations can be obtained by changing the character of the latex itself-for example, acrylics may vary from soft and tacky to hard and brittle. However, only normal polymers, suitable for nonwoven binding have been used in table.
runs well on the engraved print rolls and still does not spread when printed onto the web. One of the large industrial uses for nonwoven fabrics is in automotive upholstery. A typical door panel assembly consists of a hardboard base, a layer of resilient nonwoven fabric, and an outer covering of vinyl film (or sheeting). This construction has been plied up and electronically sealed into a single unit in one operation using a die which produces a quilted sealing pattern. The resilient nonwoven fabric, which provides softness and also provides the medium which seals film to the board and padding to the panel, has been produced by spray bonding a thick web of fibers with a heat sealable latex. As the web is about l/Z-inch thick and must not be compressed during bonding, the latex binder is sprayed onto the surface of the web as it moves into a drying tunnel. If desired the dried web may be inverted and run through again spraying on the other side. The latex for heat sealing applications is usually a poly(viny1 chloride) latex alone or blended with a nitrile (butadiene/acrylonitrile copolymer) latex. In this case the nitrile latex softens the normally stiff vinyl latex without reducing the sealing properties. In many cases nitrile latices are necessary to achieve the resiliency required. A heat-sealable nonwoven fabric can be produced by the same application using a thermoplastic fiber bound web.
Properties of Saturated Nonwoven Fabric' Showing t h e influence of Latex Binder Type Latex Type Resilient Butadiene/acrylonitrile Eb Butadiene/styrene E F Acrylic Poly(viny1 chloride) P Poly(viny1 acetate) P Polychloroprene E E Natural
D~~ Colorfastness Heat Yealable Softness Washfast Cleanable HeaB Light E E E B F G E G F B F P G G G E E P F G G 0 E E P P G E E F E E P P P P E G P F F P
a Average properbies obtained by saturating a random web of acetate/cotton blend with Code E = excellent; G = good; F = fair; P = poor. normallatexto 100% polymerpickup.
The method of application also has a profound effect on the final properties. Saturation was used in the example as a large percentage of nonwovens are prepared in this manner. In manufacturing sanitary products from nonwoven fabrics it is necessary to have a construction which is well bonded but is still soft and highly absorbent. One method is to bind a thin, oriented web of cellulosic fibers using a printed pattern of vinyl latex which covers only 5 to 10% of the web surface. Although relatively stiff in itself, the latex covers such a small area that it still gives a soft product. In addition the viscosity and flow properties are such that the latex
INDUSTRIAL AND ENGINEERING CHEMISTRY
However, to date the latex bound web is more common. In the same door panel construction the vinyl film may be backed by a thin, dense nonwoven fabric. Here the nonwoven produced by a saturation process would probably contain the same or similar latex system. Where upholstery fabrics are to be used without sealing, a number of latex binders such as nitriles, vinyls, SB-R types or acrylates, could be used. In many cases the choice might be controlled by cost and compatability. Another type of a specialized nonwoven fabric is used for apparel interliners. Here the product must have a high degree of crease-resistance with
NONWOVEN FABRICS instant recovery, must also withstand laundering and dry cleaning, and if possible, not discolor under heat and light aging. Nitrile latices have come closest to meeting all of the requirements. I n particular, carboxylic nitrile latex blended with a small amount ( 5 to 10%) of a methylated methylol melamine resin give outstanding results. Acrylate latices, although very resistant to heat and light, were not as wash fast or as resilient. Recent advances in polymer techniques have resulted in new acrylic latices which show promise in this application.
Problems General applications of nonwoven fabrics are now used successfully, but these products are by no means perfect. A number of very serious problems must be solved if nonwoven fabrics are to continue to grow as predicted. Unfortunately, many of these problems are directly associated with the binder. Binder Efficiency. Although production rates for nonwovens are faster than for comparable woven goods (by weight) the costs are not lower in many cases because large amounts of relatively expensive binders are needed to achieve strength properties. In most applications, from the print bound absorbent material to the saturated interliner fabric, the final product usually contains almost an equal weight of fiber and binder. Before new fields can be opened application techniques or binder modification must be developed to reduce the amount of binder needed to produce a useful product. In this regard nonwoven producers hope to make high quality outer garments from nonwoven fabrics. However, they must have a good hand and a good drape. Where strength has been built into present nonwovens the drape is exceedingly poor. Strength. Although tear strength equal to woven fabric (weight to weight basis) can be built into nonwovens the tensile strength is poorer. While tensile strength in woven goods can be improved by changing fiber composition, the same has little or no effect in nonwovens. The substitution of nylon for cotton has only a small influence on the tensile strength of a nonwoven construction. Low strength of the binder itself is not always the cause of low strength nonwoven fabrics. In many cases it is a failure of the adhesive bond between the polymer and fiber. In the polymerization of latices emulsifiers, dispersants, and electrolytes must be used to prevent agglomeration of the latex particles. However, they may act as a two-edged sword. When latex is dried everything
remains behind with the polymer for only water is driven off. In many cases these materials, which worked so well keeping the particles apart, tend to prevent the particles from adhering to the fibers. There is also a tendency for polymer particles to attract each other rather than foreign substances. This causes comparatively large lumps of polymer to form when, for adhesive purposes, exceedingly thin layers of binder polymer are desirable. Solvent Solutions. Solvent solutions of polymers would probably make superior binders. Most dry polymers have extraneous polymerization materials removed during their processing. Thus a solution should contain only pure binder. Solvents have numerous drawbacks in cost and hazards. Also, high strength polymers have high molecular weight which lowers their solubility. Thus only dilute solutions are possible. Solvent solutions normally wet too easily and deposit polymer over too much fiber area. This field is one which offers some promise for improved binders and work is being done on improved solvent techniques. Many fabrics are prepared by saturation techniques wherein the fiber web is run through a latex bath. Excess latex is removed by squeeze rolls or by vacuum slots and the saturated web is dried in a tunnel drier or on hot cans. For an ideal fabric of high strength with a minimum weight, the binder should remain at fiber junctions with none along the open fiber length. This has not been possible. There is always a large percentage of the binder on the exposed fiber. However, this condition is desirable in some cases. If the nonwoven fabric is to be heat sealed to another material, the “extra” binder is useful in providing points for sealing. Although these ideal situations are easier to discuss than to produce, certain principles are of value when working with either solutions or emulsions. Binders which have poor wetting properties tend to draw up into droplets and are more likely to end up at fiber junctions. Conversely, those binders which wet readily are more likely to leave binder along the entire fiber lengths in addition to the junction points. Other Problems. In the production of thick, dense nonwoven fabrics the latex polymer tends to migrate to the fabric surface as the water slides it along the fiber during drying. This produces a two-faced construction which delaminates very easily. This is not limited to thick sections alone but it is easier to control in the thinner webs. A numbev of remedies have been tried and used under certain conditions. The best method utilizes heat sensitization of the
latex. In this process a nonionic soap of low cloud point is added to the latex along with a coagulating agent. As the temperature is raised the nonionic soap loses its protective ability and the coagulant sets the latex particles before they can migrate. Here rapid application of heat is necessary. Where heat sensitization is not practical, it is usually better to heat the saturated web more slowly. Here the rapid application of heat causes the water to drive the polymer to the surface faster. As rapid water removal promotes migration it is frequently helpful to use high bath solids. Thus there is less water to be removed and less of polymer movement in the web. Color Retention. In the decorative and apparel types of nonwoven fabric, color retention is another problem. So far no one polymer has all of the desirable characteristics of a universal nonwoven binder. Nitrile latices provide strength with softness, are resistant to drycleaning and washing, yet they tend to discolor when subjected to extended heat and light aging. Considerable progress has been made on new versions of nitrile latices available with greatly improved aging characteristics, but they still are not perfect. Discoloration problems exist to even a greater degree, with the SB-R and polychloroprene latices. A fair degree of colorfastness can be obtained in SB-R latex by leaving out some antioxidant and by proper compounding. However, on aging they become stiff and lose binding properties. Poly(viny1 chloride) and poly(viny1 acetate) latices provide polymers which are generally resistant to color change. These materials are basically stiff and less resilient and must be plasticized to achieve softness. Increased plasticization results in progressive loss of strength and the plasticizers may not be resistant to cleaning. Acrylic latices appear to be the answer to the color problem. Usually they are completely saturated and therefore completely resistant to discoloration on aging. One major drawback is that they basically lack resiliency and are less resistent to washing and drycleaning. Polymer structure has been improved by incorporating reactive groups that have produced polymers which can react with themselves or with certain thermosetting resins to provide binders with very useful properties. Washfastness is improved and the thermosetting resins make up for some of the resiliency that is lacking. The research and development groups of both the nonwoven manufacturers and the binder producers are continuing to work toward the solution of these problems. VOL. 51,
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literature Cited (1) Am. Dyestuff Reptr. 38, 582 (1949). (2) Brennan, W. E., Zbid., 46, 583 (1957). (3) Coke, C. E., Can. Textile J . 73, 51-5 (June 29, 1956). (4) Coke, C. E., Textile Mf7. 77, 12-14 (January 1951). (5) Leventhal, H. L., A n . Dyestuff Reptr. 44,464-6 (1955). ( 6 ) Lovin, L. G., Wenzell, L. P., Ibid., 46, 326 (1957).
17) Moffett, R. P., Modern Textiles M a g . 37.62-5 (1956). ( 8 ) Ryan, 3. F.; A m . Dyestuj' Reptr. 40, 262 (1951). 19) Seymour, R. B., Zbid., 38, 453 (1949). (10) Shearer, H. E., Zbid., 41, 429 (1952). (11) Shearer, H. E., Symposium on Non-
woven Fabrics, Textile Sect., New York Board of Trade, January 28,1958. (12) Sherwood, N. H., A m . Dyestuj Reptr.
46, 323 (1957). (13) Taylor, J. T., Zbid.,46,437 11957).
(14) Wrotnowski, A. C., Chem. Eng. Progr. 53, 313 (1957). (15) Wrotnowski, A. C., Textile Research J.7,480 (1952).
RECEIVED for review February 18, 1959 ACCEPTED May 1, 1959 Division of Industrial and Engineering Chemistry, Symposium on Nonwoven Fabrics, 135th Meeting, ACS, Boston, Mass.. April 1959.
D. C. NICELY The Chemstrand Corp., Decatur, Ala.
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Nonwoven Fabrics Their Growing Importance to the Textile Industry
NONWOVEN
fabrics were pioneered by a few mills of the textile industry, and those mills are now among the leaders in the growing list of nonwoven producers. I n the first few years production of nonwovens was entirely in the hands of the textile industry, but today only about 35y0of the productive capacity for nonwoven fabrics is owned or controlled by companies whose interest is the conventional textile industry. About 307, of the productive capacity is controlled by companies whose major interest is something other than textile business. Almost 20% of the capacity is owned by independent interests. The textile industry has apparently relinquished leadership in the nonwoven field to others. In general the first nonwoven products were made of carded mill wastes held together with simple binders and were designed for disposable or nondurable end uses such as wiping cloths, sanitary products, etc. However, as quality standards were raised, more and more virgin fiber was consumed. This has been the trend in fiber consumption from almost exclusive mill wastes to virgin staple cellulosics and to considerable poundage of the higher priced synthetics : acrylics, polyamides, and polyesters. Similarly, as new binders with interesting characteristics emerged from the chemical laboratories, new fabrics have become realities, and the emphasis in development of new products has been pointed toward the durable type of product. There has been a change from simulated woven goods to engineered, bonded fiber sheets. Recently there has been development of bulky, lofty, resilient bonded fiber batts for specialized end uses. These new concepts are materials for which there is no counter part in woven or knitted goods. When apparel fabrics and home furnishing fabrics reach fruition in nonwoven form, finishing techniques now
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employed in the textile industry or modifications required for specific cases will be of prime importance. Dyeing, brushing, napping, shearing, printing, and the variety of secondary treatments given to woven goods will undoubtedly be major factors in preparing nonwoven fabrics for the consumer market. Laboratory and development samples of skirting fabrics, blankets, jacket linings, and the like show promise of commercialization of these materials. However, the finest fabric produced will not yield profits unless it is styled and merchandised, and certainly the well organized merchandising departments of existing related textile companies may well be one of the keys to market acceptance of the new nonwoven fabrics. Certain properties of fabrics such as hand and drape are difficult to define and measure because of the intangible nature. They play a very important role in the commercial success of all fabrics. The trained operators in the textile business evaluate these properties and the st)lists are aware of the problems and demands of the market. The nonwoven producers affiliated with textile companies may utilize the functions of these merchandising groups. Textile fiber consumption in this country is about 6.5-billion pounds per year or some 35 to 40 pounds per capita. O n the basis of an estimated 90-million pounds per year of fiber used in nonwoven fabrics this represents a total usage of only about l1/,Y0 of all textile fibers consumed. In five years nonwovens might consume 370 of all textile fibers, and ultimately 5% of the fiber will go into nonwovens. Impact o n Textile industry
In many cases, the nonwoven products will complement orthodox textiles in the high-loft bonded fabrics which cannot be produced on conventional textile
INDUSTRIAL AND ENGINEERING CHEMISTRY
equipment, and other engineered fabrics tailored for specialized end uses. However, some volume might be lost from woven goods to the new nonwoven apparel, blanket, and home furnishing fabrics, on the basis of price or performance. Some synthetic fiber felts are available commercially and volume use is expected in the future. Nonwoven carpet constructions will be an interesting development. Aside from the normal growth curve of nonwovens expected, accelerated growth will result from technological breakthroughs in binder, fibers, web formation, and finishing. In the early days of nonwoven production, the basic line consisted of a series of cotton cards placed in tandem from w-hich a sandwich of full width webs was assembled for passage through a roll padder or discontinuous print bonding followed by dry cans and a windup. Later several organizations developed systems for the production of randomly oriented webs. About 60 of the mills in this country now use the random web process. One machine, Rando-Webber (Curlator Corp.), is commercially available. Garnetts with cross-lay equipment are in use as well as woolen cards for web production. Fibrous webs may be made in a wide range of weights, from an extremely fine gauzy web up to batts of two inches or more in thickness. A carded web has no appreciable strength or dimensional stability, and the binder added to the fiber imparts strength and other characteristics to the final fabric. In the initial phases of development nonwoven production lines were equipped with two-roll padders or resin printing devices. Now, the trend is to use wire screen saturators of either a single wire and drum type or the two double screen saturator. The single wire type is usually operated with a vacuum extraction system for removal of excess bonding liquor. Vacuum extraction is
