US 3308827 A
Description (OCR text may contain errors)
March 14, 1967 J. GROSS NAPK-IN FABRICS 3 Sheets-Sheet 1 Filed Sept. 5, 1963 BAQ3 BA Z
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NAPKIN FABRICS Filed Sept. 5, 1963 3 Sheets-Sheet 3 United States Patent 3,308,827 NAPKIN FABRICS John Gross, Charlotte, NC, assignor to Celanese Corporation, a corporation of Delaware Filed Sept. 3, 1963, Ser. No. 306,244 9 Claims. (Cl. 128290) The present invention relates to novel fabrics and their use, especially as coverings for sanitary napkins.
Copending applications Ser. Nos. 795,858, now US. Patent No. 3,208,451 issued September 28, 1965 and 830,771 filed in the names of Stephen L. Porter, Calvin Au-ville and Allen R. Winch disclose novel fabrics warp knit of continuous filament yarns which are suited for sanitary napkin coverings because of their low weight, high strength and desirable physical properties such as hydrophobicity.
It is an object of the present invention to provide novel fabrics of even lighter weight which nonetheless possess the other desirable properties of the Porter et al. fabrics.
A further object of the invention is to provide a fabric which can be produced rapidly on conventional equipment.
Another object of the invention is to provide a balanced fabric which will lie fiat without any tendency to curl, thereby to facilitate its use as a wrapper for articles.
Still another object of the invention is to provide a novel process and apparatus for producing a multiplicity of fabrics simultaneously on a single machine.
Other objects and advantages of the invention will become apparent from the following detailed description and claims taken in conjunction with the accompanying drawings wherein:
FIG. 1 is a schematic elevation of an apparatus for collecting and cutting fabric knit in accordance wtih the invention;
FIG. 2 is a sectional view through a cutting blade illustrating its mounting on its shaft, shown in full;
FIG. 3 is a schematic illustration of the stitches knit by the individual yarns of a three bar warp knitting machine;
FIG. 4 is a schematic illustration of a preferred fabric construction; and
FIG. 5 is a side elevation, partly cut-away, of a sanitary napkin carrying a fabric wrapper.
In accordance with one aspect of the invention a flat undistorted fabric is produced by the warp knitting of three sets of warp yarns on a machine such as a Raschel machine. One set of warp yarns is formed into chains extending longitudinally. Each of the other sets of warp yarns, supplied by a respective bar of the knitting machine, extends tranversely of the chains and unites adjacent chains into a fabric structure. Each transverse yarn may span only two adjacent chains or the stitch pattern may be such that it spans several chain-s.
Because each chain is united to any one neighboring chain by at least two transverse yarns, should one transverse yarn break the fabric will not separate or unzip even if the transverse yarns individually are not knotted to the chain yarns, i.e. even if each transverse yarn is in a zip stitch construction relative to a chain yarn rather than a lock stitch construction.
As a result, fabrics will be quite strong even at extremely low weight per unit area. This is especially useful when the fabrics are used as covers for sanitary napkins because of their longitudinal stability and ability to stretch laterally to conform to the pad. In such end use it is desirable to have a high yield, i.e. low weight per square yard, both for economy and in order for the fabric to be sufficiently open so as not to interfere with passage 'of fluid therethrough to the absorptive pad therebelow.
At the same time the cover fabric must be sufiiciently 0.5 ounce per square yard.
The foregoing figures are based on cellulose acetate multifilament ya-rns which have a tenacity of about 1.3 grams per denierand a density of about 1.3 grams per cubic centimeter. If other yarns are substituted and their densities and/or tenacities differ appreciably from the cellulose acetate reference there will be corresponding difierences in the fabric yield required to give any particular pinning strength. Representative other yarns include cellulose triacetate, esters of cellulose other than the acetate, polyamides such as nylon, polyesters, polymers and/or copolymers of vinylidene compounds such as ethylene, propylene, acrylonitrile, vinylidene cyanide, vinyl chloride, vinylidene chloride, and the like. Not only synthetic yarns, but even natural yarns such as silk may be employed. The foregoing are preferred for sanitary napkin cover fabrics because of their hydrophobicity which keeps them from losing strength when wet but hydrophilic fibers such as rayon or cotton or the like may be used if desired, especially if they have been treated to render them more hydrophobic. The yarns may b spun from staple fibers but preferably comprise continuous multifilaments since this gives greater strength per unit weight and is more compact so as to leave larger openings in the fabric for passage of fluids. With cellulose acetate multifilament yarn, for example,it is possible to achieve the requisite strength at deniers of or less, e.g. 55, which contributes to the high fabric yield with open structure. 7 I
In accordance with another aspect of the invention, desirably the stitch patterns of the transverse yarns engaging any one chain are approximately balanced in op posite directions. This is in contrast with certain constructions, e.g. in which the transverse yarn stitch patterns are such that each transverse yarn jogs only to one side of a chain or in which the sum of the torques to one side of any chain are greater than those in opposite direction. Balance can be achieved by equalizing the torques on any chain yarn. With two bars of transverse yarns this may be effected, for example, by having one transverse yarn of one bar jogging to the left of a partic- -ular chain while a transverse yarn of the other bar jogs to the right, with their stitch patterns offsetting one another. Advantageously their stitch patterns not only are counter balanced but are exactly opposite, i.e. any loop or stitch of a chain contacting a left-directed transverse yarn of one bar also contacts a right-directed transverse yarn of the other bar.
While a knitting machine may be capable of knitting fabrics as wide as 168 inches or more, for certain end uses much narrower fabrics are needed, e.g. about 7 inches for a sanitary napkin cover fabric. Rather than utilize only 7 inches of the available'machine width, it has been proposed to knit several fabrics in side-by-side relation simultaneously on a single machine. This has been done by knitting in full width and then cutting the fabric as formed or by selecting a stitch pattern which permits the fabric to be unzipped at predetermined wales to give a multiplicity of narrower bands of fabric which are taken up simultaneously. Certain disadvantages attend either of these techniques and the present invention provides an improved process.
In accordance with this aspect of the invention a fabric is warp knit in substantially the full machine width. At locations spaced from one another by a predetermined lateral distance, e.g. 7 inches, the fabric construction is such that only a few and preferably only a single yarn end extends transversely between two adjacent chains or wales. As knit the fabric is taken up on a roll in full width and is continuously slit on the roll by blades positioned along the roll at locations spaced apart by distances equal to the spacing between such single end chain connectors, the blades being located at such single end positions and thereby cutting the rolled up fabric into 7 inch widths. Because the cutting of the fabric takes place just prior to the fabric storage roll the narrow rolls of fabric have fiat faces which facilitates their use on wrapping equipment in subsequent operations. By contrast, if cutting is performed at a substantial distance from Where the fabric is rolled up the faces of the narrow rolls may not always be flat, being distorted by corresponding distortions in the narrow bands which are not exhibited when rolling up is effected in full width. Similarly, if severance into narrower bands is effected by unzipping of stitches without cutting this would be done before wind up so that, again, the edges of the narrow bands might not be flat. In addition, severance by unzipping places somewhat of a strain upon the yarn (ends) near the split so as to Weaken them and also to produce strains in them.
When the narrow bands are to be produced by cutting between two chains it has proven effective to employ a stitch pattern which results in selvages on both sides of the cut. This selvage, or zone or relatively dense stitch construction, strengthens the fabric against transverse tearing. As noted, the selvages are provided for a special purpose and have a dense construction and, moreover, appear on the outside or non-absorbing face of the sanitary napkin. Accordingly the fluid permeabl stitch constructions described hereinabove refer to the body of the fabric rather than to such selvages.
Referring now more particularly to the drawing, in FIG. 1 there is shown a knitting machine 11 such as a Raschel machine having three bars for knitting warps into a fabric 12. The fabric is pulled from the machine by rolls 13, 14, 15, 16 and 17 of which 13, 15 and 16 are driven with 14 and 17 serving as guide rolls. The fabric 12 next passes over a driven roll 18 which through friction surface drives a storage roll 19 on which the fabric is collected. Roll 20 connects the axes of rolls 18 and 19 in conventional manner to permit the axis of roll 19 to move away from that of roll 18 as the fabric package increases in diameter. A cutter 21, of non-circular contour for better cutting action, is positioned adjacent roll 19 to slit the fabric thereon into narrower bands.
As shown in FIG. 2 the cutter 21 comprises a rotating shaft 22 on which there are keyed one or more collars 23 connected to a blade 24. The collar 23 is provided with a tapped hole 25 which can receive a set screw (not shown) so that the blade can be locked in predetermined position along the shaft 22 for cutting the fabric into bands of predetermined width.
In FIGS. 3 and 4 there is shown a preferred fabric construction knit on a Raschel machine from three warps supplied from three bars. As seen in FIG. 3 the first bar knits chains 26 of 2/2() stitch construction. The second bar knits transverse yarns 27 of O0/44/ -10/4-4 stitch construction and the third b-ar knits transverse yarns 28 of 1010/66/00/66 stitch construction. To produce fabric bands 6.5 inches wide in relaxed condition, only half the guides or 9 guides per led are utilized. The first bar is threaded 68 in-l out, the second bar is threaded [(2 out-2 in)xl7]1 out and the third bar is threaded 1 in-l out-[(2 in-2 out)x 1-2 in-l out1 in-l out1 in-l out. The warping ratio for the front and rear beam is 1:1. In this manner the fabric knit on a 100 inch machine can be slit into 13 bands of the desired width.
The fabric has the appearance shown in FIG. 4 which, by suitable omission of chain 26 and transverse yarns 27, includes a zone 29 which is traversed laterally by a single transverse yarn 28. Slitting in this zone 29 produced the narrow bands which are bounded by selvages 30, 31.
By changing the threading of the first bar to 88 in-1 out, that of the second bar to [(2 out-2 in)x22]1 out and that of the third bar to l in-l out-[(2 in2 out)x2()]2 in1 out-1 in-l out-1 in-l out there can be produced 10 fabric bands each 8.5 inches wide.
At a setting of 18 courses per inch the resulting fabric knit of 5S denier cellulose acetate yarn of 22 filaments has a yield of 38.8 square yards per pound. Its pinning strength exceeds 2.5 pounds, determined as follows:
I One end of a fabric sample is clamped between a pair of jaws mounted at a fixed location on a rod. Another pair of jaws is mounted on a carriage capable of sliding along the rod; the second pair of jaws has two L-sh aped pins projecting therefrom and spaced one-half inch laterally from one another. The pins xtend toward the first pair of jaws and then stick up through the fabric. A weight is mounted on the second pair of jaws and the rod is tilted to vary the tension on the fabric, the fabric. wales running parallel to the rod. The pinning strength is the vector of the weight acting along the rod when the pins tear the fabric. Any other tensile testing machine meeting ASTM D76-53 requirements, suitably modified with pins, can be similarly employed.
A fabric prepared in accordance with this invention is shown wrapped conventionally about a sanitary napkin absorbent pad in FIG. 5. Thus, the fabric 32 completely surrounds the absorbent pad 33 and extends beyond the end of the padto form attaching tabs 34.
The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.
1. A sanitary napkin comprising a longitudinally extending absorbent pad, and a flat undistorted wrapper surrounding said pad, said cover fabric including tabs projecting longitudinally beyond said pad for attachment to a support, said wrapper comprising a warp knit fabric comprising three sets of warp yarns, a first set of warp yarns being formed into longitudinally extending chains and the sec-0nd and third sets of warp yarns extending transversely of said chains in generally opposite direc! tions, each of said second and third sets of warp knit yarns. being interlaced with at least one other of said sets of yarns to form a unitary fabric.
2. A sanitary napkin according to claim 1, said fabric having a yield in excess of about 30 yards per pound and a pinning strength in longitudinal direction in excess of about 2 pounds.
3. A sanitary napkin according to claim 1, said fabric including selvages knit into the fabric at both edges and in pairs in the body of the fabric.
4. A sanitary napkin according toclaim 1, wherein each pair of selvagesin the body of the fabric are joined. by a singl yarn extending transversely back and forth between said selvages.
5. A sanitary napkin according to claim 1, wherein said yarns comprise continuous filaments.
6. A sanitary napkin according to claim 1, wherein said yarns are of less than about denier each and comprise continuous synthetic hydrophobic filaments.
7. A sanitary napkin comprising a longitudinally extending absorbent pad, and a flat undistorted warp knit cover fabric surrounding said pad, said cover fabric including tabs projecting longitudinally beyond said pad for attachment to a support, said fabric comprising three sets of warp yarns, a first set of warp yarns being formed into longitudinally extending chains and the second and third sets of Warp yarns extending transversely of saidchains in opposite directions and in balanced approximately opposite stitch patterns, each of said second and third sets of warp knit yarns being interlaced with at least one other of said-sets of yarns to (form a unitary fabric;
8. A sanitary napkin according to claim 7, wherein the stitch patterns of said second and third sets of warp yarns are exactly opposite, any given stitch of a chain of said first set of yarns which meshes with a yarn of said second set also meshing with a yarn of said third set.
9. A sanitary napkin comprising a longitudinally extending absorbent pad, and a flat undistorted warp knit cover fabric surrounding said pad, said cover fabric including tabs projecting longitudinally beyond said pad for attachment to a support, said fabric having a yield in excess of about 30 yards per pound and a pinning strength in longitudinal direction in excess of about 2 pounds, said fabric comprising three sets of continuous synthetic hydrophobic filament warp yarns of less than about 75 denier each, a first set of warp yarns being formed into longitudinally extending chains and the second and third sets of warp yarns extending transversely of said chains in opposite directions and in exactly opposite stitch patterns, each of said second and third sets of warp yarns being interlaced with at least one other of said sets of yarns to form a unitary fabric any given stitch of a chain References Cited by the Examiner v UNITED STATES PATENTS 2,439,300 4/1948 Huber 66147 2,964,041 12/1960 Ashton et al 128290 3,041,861 7/1962 Kasey 66195 3,068,676 12/1962 Bolton 66195 3,208,451 9/1965 Porter et a1, 128-290 3,209,559 10/1965 Sharp et a1 66-147 RICHARD A. GAUDET, Primary Examiner.
20 C. F. ROSENBAUM, Assistant Examiner.