US 3105491 A
Abstract available in
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Description (OCR text may contain errors)
Oct. 1, 1963 K. J. HARWOOD 3, 05, 9
' COMPOSITE MACROFIBERS AND ABSORBENT PADS MADE THEREFROM Filed June 22, 1960 s Sheets-Sheet 1 Oct. 1, 1963 K. J. HARWOOD 3,105,491
COMPOSITE MACROFIBERS AND ABSORBENT PADS MADE TI-IEREFROM 3 Sheets-Sheet 2 Filed June 22, 1960 Oct. 1, 1963 K. J. HARWOOD COMPOSITE MACROFIBERS AND ABSORBENT PADS MADE THEREFROM H 3 Sheets-Sheet 3 Filed June 22, 1960 3,105,491 COMPOSITE MACRGFIBERS AND ABSORBENT PADS MADE TI-EREFROM Kenneth J. Harwood, Neenah, Wis, assignor to Kimherly-Ciarir Corporation, Neenah, Wis., a corporation of Deiaware Filed June 22, 196i), Ser. No. 37,901 11 Claims. (Cl. 128-2%) This invention relates to fibers of composite structure.
A major object of the invention is to provide composite macrofibers with physical characteristics superior to the characteristics of the conventional small fibers which compose the macrofiber structure.
Another object is to provide composite fibers for use in pads of improved bulk, resilience and absorbency.
A further object is to provide absorbent pads made from composite macrofibers.
An additional object is to provide a method and apparatus for producing composite macrofibers.
Other objectives and advantages will become apparent from the drawings and description as will various modifications and adaptations of the described structure without departure from the inventive concept as defined in the appended claims.
FIG. 1 is an enlarged representation of about 30X magnification showing typical individual fibers which make up the composite fibers of this invention.
FIG. 2 is a similarly enlarged representation showing a typical composite fiber or macrofiber.
FIG. 3 is a sectional elevational diagram of a device suitable for making composite fibers.
FIG. 4 is a sectional View taken through line 44 of the treatment chamber shown in FIG. 3.
FIGS. 5a and 5b are plan views of a pad of conventional fibers and a pad of macrofibers respectively, showing relative effect of fluids absorbed by each.
FIGS. 6a and 6b show in section, test tubes containing conventional fibers and macrofibers respectively and the relative absorbent effect when fluid is added to each.
FIG. 7 is a perspective view partially cut away and with the wrapper partially open, to show an absorbent bandage including in its structure an element comprised of macrofibers.
In absorbent pads generally, the body portion, or a large portion thereof, often consists of an unfelted or loosely felted pad of wood pulp or similar fibrous materials. The individual fibers =in such pads are relatively short and heterogeneously arranged in the pads to give a soft, fluffy, absorbent structure which is readily disintegrated in Water. Although pads of this construction have a potentially high absorptive capacity, this potential is never fully realized because of the way the pads perform in actual use. When fluid strikes, the pads have a tendency to mat down in localized areas, thus losing bulk and allowing the fluid to strike through with com parative ease, while large areas of the pad remain unused. The short fibers, while highly absorbent in themselves apparently do not readily transfer fluids transversely from one fiber to another and hence the fluid does not spread out in available absorbent areas of the pad satisfactorily. Thus local areas become saturated easily and pools of liquid tend to build up in these areas while some of the immediately adjacent areas remain unused and free of liquid.
The highly absorbent composite macrofibers taught herein promote the rapid flow of fluids therethrough and when assembled in pads, result in a strong highly resilient structure which resists matting, even when wetted. The composite structure of the fibers acts to spread the fluid readily throughout the pad, permitting substantially all of the pad area to exercise its absorptive properties before absorptive capacity is exceeded in any localized area thereof.
The composite fibers fabricated as herein taught comprise a multiplicity of mechanically intertwined relatively short component fibers of the type most commonly associated with papermaking, although longer individual fibers may also be used. The individual short component fibers shown in magnified form in FIG. 1, are aligned and twisted together in substantial parallel relationship, to produce composite fibers of greatly increased length, width, and diameter as shown in the enlarged representation of FIG. 2.
Several advantages accrue from the new fiber structure. The speed of fluid absorbency is increased because the many small short fibers which form the macrofibers are in intimate contact and apparently provide interconnected capillary channels which promote directional migration of absorbed fluid through individual macrofibers and from one macrofiber to another throughout the pad. These interconnected capillary channels within individual macrofibers obviously are not present in the individual relatively small component fibers. While short fibers of pads assembled in a conventional manner promote to a limited extent lateral migration of fluids from areas of fluid concentration, the increased dispersion rate attendant the use of macrofibers tends to eliminate localized fluid con centration and resulting fluid strike-through. In addition to their ability to absorb and rapidly spread fluids, it has been found that a pad of macrofibers is stronger and more resilient than a pad constructed only of the short fibers from which macrofibers are formed, hence has more ability to resist deformation and thus retain its body or bulk during use. Various additives such as adhesives, resins, waxes, starch, etc. can also be incorporated in the fibers at the time of manufacture to modify resiliency, strength, absorbency and the like.
Fibers suitable for processing into composite macrofibers include short vegetable fibers conventionally used in papermaking, such as wood fibers obtained by mechanical or chemical means, cotton fibers including linters, and the various currently available synthetic fibers of papermaking length such as rayon, polyethylenes, polyamides, polyesters, and mixtures thereof. Adhesives such as polyvinyl acetate, polyvinyl alcohol, natural and synthetic glues, etc., may be added to facilitate the building up of some of the latter hydrophobic fibers.
Wood pulp fibers from coniferous trees average from between about 1 to 5 millimeters in length, while those from deciduous trees average from between about 0.5 to about 2 millimeters in length. Individual lengths range from very fine short fibers of 0.1 millimeter to comparatively long fibers of about 5 millimeters. Diameters of wood fibers are extremely variable depending upon their source and the method of obtaining them,
but roughly fall between 0.010 and 0.025 millimeter. Material which has been defibrated in hammerrnills or the like fall in the lower side of the above range and in addition contain large amounts of smaller sized material known as fines or wood flour.
Cotton fibers normally have an average length of between 16 and 56 millimeters and an average width or diameter of between 0.012 and 0.025 millimeter, but when refined for papermaking use, the maximum length for cotton is usually. no more than a few millimeters.
The composite fibers produced by methods of this invention have a potentially wide range of sizes depending upon the duration, and type of treatment used. Composite fibers made from component short fibers have been produced measuring from 6 to about 38 millimeters in length with a diameter of 0.5 to about 4 millimeters. The composite fiber therefore has a unit volume which is from about 100 to over 5,000 times the unit volume of the individual component fibers.
The fibrous pulp material used in making the composite fibers must first be conditioned to a moisture content of about 30-80% moisture by weight, with a range of 55-65% moisture preferred. If the starting material is too dry, the individual fibers remain too stiff to intertwine and composite fibers are not readily formed. Higher moisture content in the pulp causes the fibers to adhere to the cylinder walls, thus minimizing the effect of the rolling and twisting action induced by the rotating impeller and attendant air currents. Excess moisture also causes pulp fibers to ball up into nodular form rather than in the long fibrous configuration desired. Not enough moisture negates potential intertwining action between individual fibers so that substantially no macrofibers are formed.
To produce macrofibers, fibrous pulp material having a moisture content within the specified range is introduced into a treatment chamber in the form of small pieces where it is acted upon by an impeller blade rotating at high speeds. Within 5 to 30 seconds the pulp pieces are broken up into the individual fibers shown in FIG. 1, and almost simultaneously reformed by a twisting, intermingling action into the comparatively long composite fibrous structures shown in FIG. 2.
Cutting action, such as occurs in refiners or beaters commonly associated with papermaking is avoided in the treatment chamber since it is essential that the individual fibers be worked together without reduction in unit size. As indicated previously, it is equally important that the moisture level be kept within the preferred ranges.
FIGS. 3 and 4 illustrate details of a high speed impeller type mixing device wherein relatively short wood fibers or the like are converted into macrofibers. A cylindrical chamber is provided with a throat 12 through which suitable short fibers are introduced into the chamber. An agitator or impeller 14 is fixed to the end of a rotatable shaft 16 suitably journalled at 17 in a wall of the chamber to be rotatably driven, by means not shown, at about 4000 rpm. or more. Chamber 10 comprises a cylindrical wall 18 enclosed by end walls 20 and 22. Impeller 14 is preferably centered in the cylindrical chamber and terminates in a pair of paddle-like blades of a width substantially less than the axial dimension of the chamber. The inner surface of cylindrical wall 1 8 is preferably provided with a plurality of axially extending and circumferentially spaced rib-like projections 24 to aid in providing the turbulence to which short fibers must be subjected in forming macrofibers. Impeller 14 is of a longitudinal dimension substantially less than the interior diameter of chamber 10' insuring sufficient clearance between the blade-like end thereof and the cylindrical chamber wall to avoid mutilation of the macrofibers formed therein. A clearance of at least one-eighth inch between the ends of the impeller and the cylinder has been found suitable, although a somewhat larger clearance is preferred.
The clearance between the sides of the impeller blades and walls 20 and 22 is preferably somewhat greater than the above mentioned end clearance. It is important that substantial rubbing or pressing action be avoided between the impeller blades and all interior surfaces of the chamber to prevent the fibrillation of individual fibers while subjecting the fibers to forces which efiect a twisting action and cause intertwinement therebetween and the resulting composite formation of macrofibers. Apparently, the high impeller speed establishes a vorticular air circulation within chamber 10, the forces of which when imposed on individual short fibers retain them within the chamber while subjecting the fibers to a complex movement of generally circular orbit which twists, spins, and tumbles the fibers with resultant accumulation into intertwined groups or bunches of the type illustrated in FIG. 2, to form composite macrofibers. As the short fibers accumulate in this manner to form macrofibers the Weight of the latter (many times the weight of the individual fibers) increases sufiiciently to overcome the inwardly directed force components of the air currents, and the macrofibers thus move progressively outwardly to the cylinder wall eventually to escape under gravity pull through an outlet port 26 and onto an endless conveyor belt 28 for conveyance to a remote position.
The interior walls of the cylindrical chamber may be smooth but it is preferred to provide the walls with raised elements 24 as shown in FIG. 3 of the drawings to insure the rolling and twisting of the fibers by the combined action of the impeller blade and resulting air currents. Various other interior surfaces may be used in the cylinder, including abrasive coated surfaces, wire screens, raised projections, foam lining and the like. The interior wall surface may rotate or be fixed, with varying results. The cylinder wall may be rotated in the same or opposite direction as the impeller. The impeller blades may also have various shapes other than that shown.
Fibrous material introduced into the apparatus should have a moisture content of between 3080% and may be supplied in loose form, or as small sheets, flakes, pellets, wet lap pulp, or the like. When introduced into the chamber in one of the latter forms, the high speed impeller breaks up the starting material into individual fibers, while the simultaneously generated air currents roll and twist the individual fibers together into larger composite fibers. The latter as shown in the enlarged view of FIG. 2 roughly may be compared in appearance to irregular lengths cut from twisted slivers or rovings used in spinning yarn except that the macrofibers are usually tapered on each end. Another difference is that the fibers making up the composite fibers are not continuous as are rovings. Still another difference is that the individual fibers used to form the larger composite fibers are shorter than normal staple fibers used for spinning yarn. The extremely small particles known as fines, which are usually present in papermaking pulp, are caught up in substantial amounts in the voids of the composite fibers during the process and subsequent dusting out is greatly reduced or substantially eliminated.
The appanatus shown also can be used in a batch process by feeding a supply of fibers into the chamber, closing it and running the impeller at high speed for from 5-30 seconds. However, the previously described continuous method is preferred. In this method, the insufliciently built-up fibers rotate with air currents generated by the impeller blade Within the chamber until they build up to a size sufiicient in body and weight to be deposited through the bottom opening onto a screen for subsequent treatment and drying.
Most cellulose fibers have a high natural absorbency. This invention increases the effective absorbency of the individual fibers by interlinking them in a manner to form long fibers having interconnected channels through which absorbed fluid travels freely. Thus speed of absorption within the composite fibers themselves as well as in pads assembled therefrom is increased by capillary action. At the same time the absorptive action of the pad is extended rapidly over a larger transverse area than in a pad made up of haphazardly assembled fibers of conventional size. The rate of absorbency is increased to such an extent that more efficient use is made of the available absorptive capacity of a pad having 'a given cubic area. Fluid spreading action and efiicient use of available absorptive capacity of pads made from macrofibers may be further increased by the use of judiciously placed baffles within the pad.
The improved absorption characteristics of macrofibers are demonstratable in several ways. For example, when water is dropped on an absorbent pad made up of ordinary fibers, it will be absorbed quickly but will saturate the immediate area of contact and will not spread over an extended area. As more fluid is added, small puddles often form on the surface in saturated areas. When water is dropped on an absorbent pad made up of macrofibers, it is absorbed much more quickly and spreads over a larger area than in conventional pads. Thus more water or fluid may be added at a given point before saturation occurs. The immediate area of contact in the improved pad is not saturated easily and the eflective capacity is thus improved considerably. Even when fluid is added after the entire macrofiber pad is wetted, puddles do not appear on the surface. Thus the pad tends always to maintain a dry appearance even in the resence of large quantities of absorbed fluid.
FIGS. 5a and 5b and 6a and 6b demonstrate the marked difierence in absorbency characteristics of macrofibers as compared with conventional fibers.
Pad 3%, of FIG. 5a, is made of sulfite pulp flufi fibers While the pad 32, of FIG. 5b, is made of sulfite pulp macrofibers. '10 cc. of a colored aqueous solution was dropped in the center of each pad. In the conventional iiufi pad 30 the fiuid spread out in an area 31, equal to less than half the diameter of the pad, and had a wet shiny appearance on its surface. In the macrofiber pad 32, the fluid spread out in an area 33, which almost encompassed the entire pad area and had a dull dry appearance. The colored fluid spread out over the larger areas of absorption 33 shown in the macrofiber pad 32 in a fraction of the time required to spread over the smaller area of absorption 31 in the conventional flufi pad 30.
Test tube 34, of FIG. 6a, was filled with 1 gram of sulfite flufi 35 while test tube 37, of FIG. 6b, was filled with 1 gram of macrofibers 38. A colored solution was titrated into the top of each tube. The fluff in tube 34 would accept only 3 cc. of fluid before becoming saturated thus forcing any subsequently added fluid to run over at the top of the tube. The fluid only penetrated to the depth indicated at 36. The tube containing macrofibers accepted 10 cc. of fluid which penetrated rapidly to the bottom as shown. The macrofibers themselves, although colored by the fluid, appeared dry and accepted large additional amounts of fluid before saturation.
Another method of measuring 1 e improved absorption characteristics of the macrofibers over conventional fibers is to measure absorption speed by means of what is called a sink test. In this test, when a pad of fibers is dropped into water, it sinks when completely saturated. The time elapsed between dropping the fiber pad into the water and subsequent sinking is measured. This sink time varies directly with the rapidity of absorption. Pads made up of the composite fibers of this invention absorb water almost instantaneously, thus sink much more rapidly than pads made of fibrous material from a similar source but where the fibers in the pad have not been made into This is demonstrated as Ordinary Composite Fiber Pad, Macrofiber Type of Fiber Sink Time Pad, Sink in Seconds Time in Seconds Cotton Linters 1.0 0. 10 Sulfate Pulp"-.- 2.0 0. 40 Sulfite Pulp 3.0 1.0
In every case, the sink time of an absorbent pad made from the new composite fibers was only a fraction of the sink time for the corresponding absorbent pad made from conventional short fibers.
The absorbent bandage of FIG. 7 represents a sanitary napkin of a construction in which part of the absorbent pad contained therein comprises microfibers. A wrapper 42 of fluid pervious material encloses a body portion comprising outer layers 44 of cellulose wadding, intermediate layers 46 of macrofibers and a central layer 48 of Waxed tissue or the like to serve as a bafiie. Numerous variations in the illustrated arrangements of component elements within the pad will be apparent to those skilled in the art.
The composite fibers of this invention may be further processed into sheet products by airlaying or water-laying techniques. The resulting products have open porous structures for which many potential end uses are immediately apparent. When formed into sheets by waterlaying means it will be noted that the composite fibers due to their self-sustaining macrostructure have a higher freeness than conventional fibers.
When the composite fibers are formed into relatively thick pads, they may be employed as absorbent elements in products such as sanitary napkins, diapens, surgical sponges, surgical compresses and bandages, packaging materials, cushioning, adding, filters, and the like. Formed into thinner sheets, they find use in bibs, diapers, polishing cloths, filters, saturated base sheets, wipes and the like.
Various changes may be made in the processes and products described herein as the preferred embodiments, without departing from the principles and scope of the invention as defined in the appended claims.
What is claimed is:
1. Composite macrofibers comprising individually selfsustaining elongate fibrous structures of irregular length substantially tapered at each end and consisting of a multiplicity of twisted and intertwined relatively short component fibers, the unit volume of said individual macrofiber structures being in the range of from about to 5,000 times the unit volume of the short component fibers.
2. Composite macrofibers comprising individually selfsustaining structures substantially tapered at each end and composed of a multiplicity of substantially parallellyaligned and intertwined relatively short component fibers, the unit volume of said individual macrofiber structures being in the range of from about 100 to 5,000 times the unit volume of the short component fibers, the length of said individual macrofiber structures being substantially greater than their width.
3. A composite highly absorbent cellulosic macnofiber comprising a self-sustaining unitary structure composed of an assembly of closely intertwined discrete papermaking fibers, said unitary structure being relatively bulky at the center and tapered at the ends and having a thread-like configuration of finite length wherein said length is relatively great in proportion to its width.
'4. Composite macrofibers having substantially tapered ends, each macrofiber comprising a multiplicity of intertwined papermaking fibers, the unit volume of each of said macrofibers being in the range of from about 100 to 5,000 times the unit volume of the individual component papermaking fibers, the length of each of said macrofibers being substantially greater than the width, a substantial portion of said intertwined component fibers extending in a common direction.
5. A composite macrofiber comprising a unitary selfsustaining assembly of a multiplicity of predominantly parallelly-aligned and mechanically intertwined short component fibers, said short component fibers ranging between about 0.5 to millimeters in length and about 0.010 to 0.025 millimeters in diameter, said self-sustaining macrofibers ranging between about 6 to 38 millimeters in length and about 0.5 to 4 millimeters in diameter and being substantially tapered at each end.
6. An absorbent pad comprising an assembly of individually self-sustaining, resilient, highly absorbent macrofibers, said individual macrofibers comprising a plurality of individual short fibers, twisted and intertwined into a unitary substantially self-sustaining fibrous macrostruc ture of generally elongate configuration and tapered at each end.
7. An absorbent pad comprising an assembly of individually self-sustaining, resilient, highly absorbent composite macrofibers substantially tapered at each end, said macrofibers comprising a plurality of short, discrete cellulosic fibers twisted and intertwined into a unitary selfsustaining fibrous macrostructure, said unitary macrostructure being of generally elongate configuration and ranging in size from about 100 to 5,000 times the size of the individual component fibers.
8. The device of claim 7 wherein said absorbent pad is enclosed in a fluid pervious wrapper.
9. A sanitary napkin comprising an absorbent pad enclosed in a fluid pervious Wrapper, said absorbent pad comprised of a plurality of absorbent elements, at least one of said elements containing absorbent individually self-sustaining macrofibers consisting of a plurality of individual short absorbent component fibers, twisted and intertwined into a substantially self-sustaining unitary macrostructure of generally elongate configuration substantially tapered at each end.
10. An absorbent pad comprising an assembly of individually self-sustaining, resilient, highly absorbent composite macrofibers substantially tapered at each end, said macrofibers comprising a plurality of short discrete cellulosic component fibers twisted and intertwined into a unitary self-sustaining fibrous macrostructure, said composite macrofibers being of generally elongate configuration and ranging in size from about to 5,000 times the size of the individual component fibers, said composite macrofibers ranging between about 6 to 38 millimeters in length and about 0.5 to 4 millimeters in diameter, said component fibers ranging between about 0.5 to 5 millimeters in length and about 0.010 to 0.025 millimeters in diameter.
11. A sanitary napkin comprising an absorbent pad enclosed in a fluid pervious wrapper, said absorbent pad comprised of a plurality of absorbent elements, at least one of said elements comprised of unitary absorbent individually self-sustaining composite macrofibers composed of an assembly of a plurality of individual short absorbent component fibers twisted and intertwined into a unitary macrostructure of generally elongate configuration substantially tapered at each end, said composite macrofibers ranging in size from about 100 to 5000 times the size of the individual component fibers, said composite macrofibers ranging between about 6 to 38 millimeters in length and about 0.5 to 4 millimeters in diameter, said short component fibers ranging between 0.5 to 5 millimeters in length and from about 0.010 to 0.025 millimeters in diameter.
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