NONWOVEN FABRICS1 RAYMOND 1. SPAHR Chicopee Manufacturing Corporation, Milltown, New Jersey
DURING the past several years nonwoven fabrics have received considerable publicity both in the daily press and in trade publications. As a consequence, several questions have been repeatedly asked by readers: "What is a nonwoven fabric?" "How does it differ from woven fabrics?" "Where is it used?" One purpose of this paper is to answer these and related questions. I n simple terms, a nonwoven fabric can be defined as a structure made from textile fibers without spinning the fibers into yarns and weaving the yams. However, this definition means many things to many people, and in its broadest sense it encompasses felts, knit goods, glazed waddings, and webs bonded with an adhesive. Felts are considered to he the oldest man-made textile, predating woven cloth. Thousands of years before Christ, desert nomads stuffed sheep shearings into their boots to keep their feet warm, and the combined action of moisture from perspiration and pressure of the feet brought about a reaction which caused the fibers t o interlock (1). To make felting possible, a fiber must possess a surface-scale structure which results in the interlocking of fibers, ease of deformation, and the ability to recover from deformation. Fibers which possess these properties are generally of animal origin, e . g., wool, hair, fur, etc. Depending upon the grade and staple length of the felting fiber, i t is possible to make pressed felts which contain a medium or high percentage of nonfelting fibers such as cotton, rayon, and other synthetics. During recent years i t has been found possible to cause cotton fibers to interlock and felt by processing under specified conditions with given concentrations of caustic soda solution ( 2 ) . I n making knit fabrics, textile fibers are spun into yarns, and the yarns are knitted either by hand or by mechanical devices. I n its simplest form, knitting consists of forming loops of yarn with the aid of thin pointed shafts and drawing other new loops through those previously formed. This "interlocking" and the contin-
uous formation of more loops into each other produces the knitted fabric structure. One of the early patents pertaining to glazed cotton wadding appeared in 1860 (3). Waddings are made with either bleached or unbleached cotton by applying a surface coating of starch to each face of a carded web. Cotton waddings are limited in materials of construction, and they are deficient in many properties such as tensile strength, tear resistance, softness, and the like, hut even these handicaps have not prevented the development of substantial markets for these products. This paper is not concerned with felts or glazed waddings or knit goods, hut rather with that type of nonwoven fahric which is defined by the Joint D-13 Committee of American Society for Testing Materials and the American Association of Textile Chemists and Colorists in the following terms: "A nonwoven fabric is a structure consisting of a mass of fibers held together by a bonding agent." This type of fabric differs from those previously mentioned in that it can be made with any type of textile fiber, with any type of bonding agent, in a wide range of weights, and it can be treated with a variety of chemical finishes. Nonwoven fabrics are generally compared with woven fabrics. The same types of textile fibers are used in the manufacture of both types of fahric, and the initial stages of manufacture are practically identical. I n each case, fiber, synthetic or natural, is converted into what the trade calls a "picker lap" which is then converted into a so-called "carded web." From this point on the two processes differ. I n the manufacture of nonwovens, a number of fiber webs are plied together, adhesively bonded, and then dried or calendered depending upon the type of adhesive. For many applications, the nonwoven fabric is then ready for the trade. I n the case of a woven fabric, the web is twisted to form a yarn, and the spun yarn is then woven on looms. The various steps employed in these two processes can be more readily understood by studying the data in Table 1. 1 Presented st the 17th Summer Conference of the New England Association of Chemistry Teachers a t Tufts University, This chart indicates the difference in the amount of processing equipment used in making these fabrics. Medford, Massachusetts, August, 1955.
VOLUME 33, NO. 4, APRIL, 1956
Although the difference in man power required to make a yard of cloth is not indicated on the chart, one can readily surmise that a nonwoven process requires less man power per unit of cloth produced than the woven process. The chart also does not show the differences in the amount of cloth produced per hour, but it can safely be said that a nonwoven processing line operates a t a much higher speed than a loom. The nonwoven fabrics, as dealt with in this paper, are relatively new. Their development was the cousequence of the desire of a manufacturer of surgical dressings to produce a low-cost replacement for surgical gauze. From this work there resulted a segmentally bonded nonwoven fabric (4) which was characterized by high absorbency, excellent surface softness, and low flexural resistance. Late in 1930, consumer products using segmentally bonded nonwovens appeared on the American market in such applications as covers for sanitary napkins, in dental towels, and in facings for disposable diapers. Progress was slowed somewhat during World War 11, but one important war-time development, a t a time when woven fabrics were in critically short supply, was camouflage cloth for the Marine Corps. Since the war, considerable progress has been made, and today a number of substantial manufacturers produce several different types of nonwoven fabrics which find an ever increasing number of applications, ranging from disposable diapers to linings for burial caskets. As one wit puts it, nonwovens serve mankind from the cradle to the grave. The two principal raw materials used in nonwoven construction are textile fibers and synthetic or natural bonding agents. Some of the more important fibers in common use are cotton, viscose rayon staple, acetate staple, vinyon, nylon, and dacron. Fibers are received from the supplier in the form of tightly compressed bales or cartons. I n this form the fibers are matted together, and, for proper processing of the stock, it is necessary to reduce fiber entanglement. One important function of a "picker" is to reduce the amount of this fiber entanglement, i. e., to open the stock. Fibers vary in the ease with which they can be opened. Bleached absorbent cotton is difficult to open, whereas viscose rayon staple is rather easily disentangled. A second function of a picker is to arrange the fibers in the form of a thick, uniform mass of fibers which can he fed continuously to a "card." Two important functions of a card are: (1) to bring about a separation of fiber tufts into individual fibers, and (2) to convert the individual fibers into a lightweight uniform fibrous web. In this form, the structure is truly a cobweb. Whereas the fibers run in all directions in a picker lap, carding produces a web in which the fibers are essentially parallel to one another. Consequently, fabrics made with card webs have high strength in one direction, the longitudinal or machine direction, whereas the strength in the cross direction is contributed almost solely by the adhesive bond developed between the fibers and the bonding agent. Many commercial applications have been found for
TABLE 1 S t e p Employed in Production of Nonwoven and Woven Fabrics Nonwoven fabrics Woven fabrics Picking
Picking
+. Cardmg
Carding
4. I
Bindmg Drying
+
Inspection
I 1 1st Drawing I
2nd Drawing
+
.
Intefmed~ateroving
Warping Slashing Entering
, Filling winding
I
t Inspection
fabrics using carded webs, and a high proportion of present production employs this type of structure. In many applications, particularly in industrial uses, fabrics with two-way strength are required. Webs having strength in two directions are produced by the following methods: the cross-lay method, in which parallel webs are laid in the transverse direction, resulting in a fabric having a more balanced strength in both the longitudinal and the cross directions; and the random web method, in which webs are produced by an aerodynamic process (6). The latter method consists in individualizing the fibers, throwing the individualized fibers into an air stream, and collecting the fibers on a moving or condensing screen. The resultant webs produce fabrics which are essentially isotropic, i. e., have equal strengths in all directions. The other major component of nonwoven fabrics is the bonding agent. Many of the physical properties of nonwoven fabrics, e. g., tensile strength, tear strength, wet abrasion resistance, etc., are to a major degree dependent upon the adhesive bond developed between the fibers and the bonding agent. More fundamental information will have to be developed TABLE 2 Binders Emdoved in Manufacture of Nonwoven Fabrics Miscellamua Melmnin+formldehyde Cellulose Polystyrene Urea-formaldehyde xanthate Polyacrylate Cellulose acePolyvinylidene chloride tate (fiber) Polyvinyl chloride Polyvinjl acetate Vinyon (fiber) Polyvinyl butyrate Starch Natural rubber latex Butadiene aerylonitrile Butsdiene styrene Polyvinyl alcohol resins
yesins
JOURNAL OF CHEMICAL EDUCATION
We will now show how these materials are combined with one another. There are currently available three different types of nonwoven fabrics which are arbitrarily designated as follows: Type 1. This class of fabric is made by depositing the binder uniformly throughout the entire fabric structure. Horirontsl nip Type 2. These fabrics are made by a segmental application of the binder to the web. Type 3. Nonwovens of this kind are produced by hot calendering a web consisting of a blend of heat-reactive and non-heat-reactive fibers. The methods employed in activating the heat-reactive fibers in fabrics of Type Segmental banding 3 have already been covered. In making fabrics of Type 1, the bonding agent can be applied to the web by one of several methods: before it is possible to predict fabric properties from (1) By spraying the binder onto the web and then a knowledge of the chemical composition of the fibers passing the wet web through a set of squeeze rolls to and the bonding agent. provide a uniform distribution of the adhesive. Some of the common binders employed in nonwoven(2) By impregnating the web by carrying it through fabric manufacture are to be found in Table 2. Poly- a bath of resin dispersion. This requires that the web mer disperisons of the thermoplastic and thermosetting be supported, usually by a screen. types are used most. Solvent-soluble resins are seldom (3) The most commonly used method is to apply used, since their use necessitates a solvent-recovery the binder a t the nip of a set of squeeze rolls. When system and presents a fire hazard. One large producer vertical squeeze rolls are used, the binder dispersion is uses cellulose xanthate which on regeneration with sul- maintained in a supply pan, and the bottom roll rofuric acid gives a strong fabric. Somewhat similar tates in the dispersion and feeds it to the web. The fabrics can be produced by parchmentizing a web of amount of adhesive applied to the web is regulated by either cotton or rayon, or a blend of these fibers, with the solids content of the dispersion and the amount of .sulfuric acid. Another means for bonding a non- pressure applied a t the nip. When horizontal squeeze woven fabric is to employ a web containing a propor- rolls are used, i t is common practice to provide a pond tion of heat-reactive fibers (6). The heat-sensitive of dispersion between the squeeze rolls. The web is fed fiber in a composite web of heat-reactive and non-heat- directly through the dispersion pond to the squeeze reactive fibers can be made active by passing the web rolls. The method of controlling pick-up is similar to over hot cans to soften the thermoplastic fibers, or by that used for the vertical nip. passing the web between hot calender rolls. Any In the manufacture of fabrics of Type 2, the b i d e r is heat-reactive fiber can be nsed if its softening tem- applied segmentally to the web. This can be accomperature is reasonably low. Plasticized cellulose ace- plished in several ways. but the most commonly emtate and vinyon are the fibers normally employed. ployed methods are the gravure and the positive printThe end-use requirements of a fabric dictate the type ing methods. In either case, the binder is applied to of adhesive to be employed in its construction. If one the web in predetermined designs which can vary from requirement is wet strength, binders such as polyvinyl a straight line to a doughnut design. In Type 2 alcohol and starch must be avoided. If rapid absorp- fabrics, the physical properties can be varied within tion of liquid is important, as for example, in a diaper wide limits by the proper selection of binder pattern. facing, natural and certain synthetic rubbers should not Types of equipment employed in applying resin dispersions to fibrous webs are shown in Figure 1. be used. Thus far we have concerned ourselves with the basic The moisture present in the dispersions employed in raw materials and the equipment employed in making making Types 1 and 2 is removed from the treated web the fibrous webs nsed in nonwoven fabric production. by means of a series of dry cans or hot air drying over a
TI-
2.
Reduction Unit for M m u M u r i n g Nonro-n
(1) Card, (2) neb, (3) impremator.
Fabrics
(4) dryer. and (5) batcher.
187
VOLUME 33, NO. 4, APRIL, 1956
bank of infrared lights. Combinations of these various drying methods is sometimes used. When a thermosetting resin is used and curing is required, it is necessary to use temperatures of 30&350°F., and in this case it is somewhat common practice to use a hotair oven. After drying, the fabric is wound in mill rolls, inspected, and slit to desired widths, if reqnired. A typical production unit for making nonwoven fabrics of Types 1 and 2 is illustrated in Figure 2. Fabrics of Tvne ". 3 reauire no drvinn. The type of fiber,"the fiber-lay, the binder, and the manner in which the binder is distributed in the fabric all influence the physical properties of a nonwoven fabric. Fabrics of each type possess some desirable properties and undesirable shortcomings. The largescale volume uses found for nonwoven fabrics are due to one or several of the properties listed in Table 3. Mu& of today's nonwoven fabric production is sold in "unfinished" form, but during recent years new markets have been created by finishing. The earliest types of finishing used on nonwovens were printing and dyeing, but today i t is possible to obtain these fabrics with almost any type of chemical finish. Drapery fabrics are available which have been treated with a fireretardent finish and then printed in attractive patterns. Dusting cloths are treated with special oils. They deposit a very fine film of oil which tends to repel dust particles. Sanitary facings for disposable diapers and incontinent pads are treated with bactericides and deodorants to minimize diaper rash and odor development. Glass Dolishin!i! cloths are treated with silicone resins whichieadily remove dust, lint, and grime from spectacles, glasses, goblets, and like objects, leaving a film of resin which repels these contaminants. Dyed fabrics are available for a varietv of a~nlications. raneine &. from oil-field tane to table cl&hs. Printed fabrics-are used in household items such as napkins and towels, as well as in certain items 'of clothing. Finishes which protect silverware from tarnishing are now being applied to nonwoven fabrics.
TABLE 3 Properties Obtainable in Nonwoven Fabrics High absorptive capacity Drape Porosity Close formation in lightweight fabrics Absence of raveling Smooth surface Softness, surface, and flexural Ahrasion resistsnee
Wet strength Resistance to distortion on dry cleaning and laundering Ease of sewing Loft with lightweight Solvent resistance Rapid absorbency Heahealing Cling
Diverse applications have been found for nonwoven fabrics and a partial list of these are found in Table 4. In conclusion, I would like to make a few comments about the future of this small, but industry, Every now and then someone asks me whether we will be able to make a fabric which can replace the wool fabric in a man's overcoat. Others ask whether we will be able to replace shirtings, Actually I do not foresee either of these developments taking place in the immediate near future. It would be imprudent a guess as to where our industry will be even to years or an even longer span of time, in years or Many of the important producers have well-staffed, well-equipped laboratories, which are aggressively furthering the horizon of nonwoven fabrics. It is safe to predict that our future progress will be measured in terms of the following: (1) the development of new and improved fabrics, (2) the development of new and improved processes and nrocessine eaui~ment.and (3) the contributions of the chemical industry in terms of improving- bonding-agents, fibers, and finishes. . -
A
.
LITERATURE CITED (1) DAYIDSON, W. A. B., Tertile Age, 19.6 (June, 1955). (2) S E C R IH. ~ , A., U. S. Patent 2,528,793 (November 7,1950). (3) FWZZARD, W., U. S. Patent 28,745 (June 19, 1860). (4) GOLDMAN, J, H., U, S, Patent 2,039,312 (May 5, 1936), (5) BUEESH. F. M.. U. S. patent 2.451.915 (October 19. 1948). (6j REED,R. E., U,S. Patent 2,277,049 ( ~ i r c 24, h 1942)
TABLE 4 Usea of Nonwoven Fabrics
Industrial
Household
Pattern-marking cloth Burial-casket lining Filter cloths Cheese press cloth Desiccant bags Laminated plastics Coated fabrics Oil-field tape Bowling-dley cloths Restaurant cloths Lithographic wipes
Towels Napkins Shoe cloths Table cloths Dust cloths Eye-glass wipes Auto wipes Wet wiping cloths Draperies Ironing-board covers Ribbons Anti-tariah cloth Hot-dish mita Handkerchiefs
Surpkzl andsanitary Eye P@S Incontment pads Obstetrioal pads Hospital oaps Dental bibs Disposable diapers Hospital wipes Diaper liners Hospital wwash cloths Breast pads Burn dressing Sanitary napkins
Apparel Wai~tbands Shoulder pads Bouffant skirts Bow ties Lapel linings Shoe linings Dress shields Swim suits Quilting
