NONWOVEN FABRICS
i
The Rando-Webber feeder 1.
Opener and tuft former 2. Elevating apron 3. Stripper apron 4. Air bridge 5. Feed material condenser screen 6. Roller conveyor 7. Air bridge fan 8. Trash chamber 9. Feed roll 10. Lickerin
not necessary with the double wire type, and in addition the double wire machine provides positive web control through the saturating operation. Another web stabilization system is the bonding method in which the binder is applied with an automatic horizontal reciprocating spraying machines. Fabrics made in this manner are characterized by resilience and very low density or high volume to weight ratio. This product is accepted for cushioning, padding, innerlinings, comforter, and filter materials, replacing conventional glazed waddings or garnetted batts in many applications. After saturation of the web or application of the binder by spraying the wet
11. 12.
13. 14. 15. 16.
17. 1 a. 19. 20.
Saber tube Condenser for forming Rando-web Adiustable duct cover Rando-web Webber fan Humidifier Creeping delivery apron Delivery conveyor Venturi Dust collection
web is dried and in case of a compounded binder is cured at an elevated temperature. Dry cans are used for drying the fabrics. The newer installations incorporate tunnel-type ovens of one, two, or three passes. The ovens are heated by steam, gas, oil, or electricity. Some resin cures may require temperatures as high as 350' to 400' F. Spray bonded webs are dried by radiant heat either from electric units or gas fired ceramic burners. Webs to be bonded with thermoplastic binders in powder or fiber form may be subjected to heat sufficient to melt the resin. Pressure may or may not be used concurrently with the application of heat.
Winders, slitters, and allied equipment may be installed downstream along with calenders and packaging facilities. How are these new and improved fabrics to be produced? In the selection of fiber content there is a wide range of fiber lengths and deniers, fiber types: natural and synthetic, cellulosic, acrylic, polyamide, polyester, polyethylene, etc., fibers with high and low melting points, hydrophobic and hydrophilic, high and low chemical resistance, etc., and more new fibers in the offing. Certainly there is a large number of fibers to choose from and to use in fabric design. There are many binder types available on the market today-powders, fibers, solutions and emulsions, all of which have some desirable performance characteristics. Some systems other than water based may provide performance superior to that now obtainable. In web formation, new or modified fiber working machines may be developed to produce improved webs at higher production rates. Saturating units of the future will probably be designed to handle efficiently the expected bonding systems. The same applies to the drying equipment in that modifications might be required to handle toxic or hazardous vapors. I t is possible that existing finishing equipment might be used as installed, although there might be changes in settings or operational cycles. However, it is also possible that new finishing techniques may evolve concurrently with fabric development in order to exploit the unique properties of these materials. 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.
WILLARD E. CARLSON and KENNETH A. ARNOLD St. Regis Paper Co., Carthage, N. Y.
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Nonwoven Fabrics Their Growing Importance to the Paper Industry T
1 HE types of paper produced by the paper industry may be divided into production grades, which are usually of high volume and low unit profit, and into specialty grades, which are generally of much lower volume. Profits on pro-
duction grades are related closely to wood costs, paper machine speeds, and customer acceptability, coupled with efficient and sound business practices. Profits on specialty grades, however, are more closely related to the research and
development efforts that serve as the basis for the specialty, the equipment modifications, and know-how associated with production of uniform quality and customer acceptance. As specialty grades are usually premium priced, raw VOL. 51, NO. 8
AUGUST 1959
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This dumbbell appearance is undesirable in the finished product. These dense areas d o not dry as readily as the body of the web and may pick out during drying, forming a major defect in the fabric
materials costs and machine speeds do not play dominant roles in a mill’s survival as is the case with production grades. The paper industry has expanded tremendously in the South during the past 20 years because of the more favorable raw materials costs. The stimulus for development of profitable specialties for northern mills has been widespread in the paper industry as more and more production grades are transferred South. The limitations of cellulose are generally recognized and they become more acute in some specialty papers. Hence, synthetic or man-made fibers as a new material have been considered to obtain specific properties unobtainable with the usual papermaking fibers. These synthetic papers ale available commercially in trace quantities only. The major obstacle to the commercial production of synthetic paper in substantial quantities is the relatively high cost -a price of $1.50 or more per pound. From a papermaking standpoint, production of synthetic paper and a nonwoven fabric are related. and attention is directed to nonwovens because of the more favorable price structure. At the St. Regis Paper Co., a synthetic paper is designed to replace a paper substance, while a nonwoven or bonded fabric is designed to replace a textile material. Also, the term “bonded fabric” is preferable to nonwoven, as bonded implies a web treatment used to impart strength and other
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properties and fabric denotes the end use. The range of speed in the papermaking or wet process is determined by the weight and type of paper being produced and the physical condition of the paper machine. Today a paper machine running 600 feet per minute in the North on a production grade like kraft shipping sack or a ground-wood printing grade makes little, if any, profit for a company. However, this same machine on a specialty grade might be expected to produce substantial profit at this speed. If a paper machine of 120-inch trim was modified to produce bonded fabric a t 600 feet per minute, it would have a production rate of 6000 pounds per hour of a 2.4 ounces per square yard fabric. Data on the conventional nonwoven textile machines of 60-inch trim are listed as having production rates of 200 pounds per hour at a speed of 30 feet per minute on an equivalent fabric weight (2). A new paper machine, incorporating recent developments, might be expected to produce bonded fabric of such a weight in excess of 1200 feet per minute. Because of the difference in speeds between the two types of equipment, the production rates of paper machines are perhaps 20 to 80 times the production rates of present dry nonwoven units. While the greater production rates of the wet process over the dry process may have a more favorable fiber to fabric conversion cost, a market problem exists because of the high production. A medium size (120-inch trim) bonded fabric machine of the wet type operating on the lower end of its speed range ivould have a rated capacity of about 86,000,000 pounds per year. The 1958 volume of nonwoven fabrics has been estimated at 90,000,000 to 100,000,000 pounds. Consequently, markets for bonded fabrics must be developed before high production units will be built by the paper industry. In order that a fiber be adaptable to the wet process, it must be dispersible in water and it must be treated so that some prebond dry web strength is attained; otherwise the web will disintegrate at the high operating speeds. At present, it appears that when the ratio of fiber length to diameter is greater than 500 to 1, uniform dispersion of the fiber becomes a major problem. The need for fiber dispersion limits the fiber length to less than ‘/z inch in the 1- to 3-denier range; therefore, cotton and man-made fibers must be cut. Wood fibers usually encountered in papermaking do not exceed ‘/4 inch with a length over diameter ratio of about 100. A problem in cutting of fiber for the wet process is the elimination of trace quantities of overlength fiber (11/2 inches or longer). At the dilute consistencies and turbulence as-
INDUSTRIAL AND ENGINEERING CHEMISTRY
sociated with this process, an overlength fiber may result in forming a pair of fiber bundles connected by the fiber. This formation i s referred to as a durnbell (Figure 1).
Research I s Advancing
Building Specific Nonwoven Struo tures. These structures are built within the limitations of the wet process. Besides the fiber dispersion and prebond strength requirements, the binder and method of incorporating the binder in the web are very important, and in some cases a limitation. The continuing search for improved binders with improved aging characteristics, at lower cost, and especially binders having approval of the Food and Drug Administration for food packaging, may improve these limitations. Hydraulic Studies of Fiber Dispersion. The goal of this work is to prevent the flocculation by controlled turbulence and additives, so that the fibers are evenly distributed on the forming wire. Studies of this type related to wood fibers have been made (7, 4, 5 ) , but they must be extended to include man-made fibers of various lengths and deniers. Hydraulic Studies for Commercial Application. Once the fiber water slurry has been dispersed, it must then be introduced onto a forming wire where the water removal is begun. Fiber orientation, filtration resistance, mat stability, and dynamic drainage of the newly formed web must be determined and controlled for commercial application ( 3 ) . With the growing importance of nonwoven fabrics to the paper industry emphasis is placed on the raw material economics. the high production rates obtainable, and the research and development work. The penetration of the textile markets by bonded fabric produced by the wet proccss will depend to a great extent upon the research accomplishments of the individual paper companies.
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literature Cited (1) Baines, W. D., Tappi 40, No. 6, 407-11 (June 1957). (2) Buresh, F. M., Textile Bull. 84, 48-51
(April 1958).
(3) Goodwillie, J. E., T a j j i 41, No. 12,
202A-4A (December 1958). (4) Robertson, A. A,, Mason, S. G., Pulp &? Paper M a g . of Can. 55, NO. 3, 263-9 (1954). (5) Roos, A. J. de, Tajji 41, No. 7, 354-8 (July 19%).
RECEIVED for review February 18, 1959 ACCEPTEDMay 1, 1959 Division of Industrial and Engineering Chemistry, Symposium on Nonwoven Fabrics, 135th Meeting, ACS, Boston, Mass., April 1959.
