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Free sample for testing and checking. Quick response for all kinds of problems. The individual crimped filaments thus differ markedly from filaments of conventional polyester tow produced, for instance, with the aid of a stuffer box crimper, which exhibit a relatively sharp, saw-tooth, two dimensional crimped form. The staple fiber product of the invention is readily cut rfrom the tow by conventional methods. The staple fiber product of the invention is also readily distinguishable from asymmetrically birefringent staple fibers which have been produced without the aid of a mechanical crimper, since the latter bers exhibit a three-dimensional crimp having substantially a reversing helical form.
Such fibers are already relatively bulky, hence have a correspondingly much lower shipping density. The term tow, as used herein, refers to a large number of continuous, substantially parallel, synthetic filaments without difinite twist collected in a loose, ribbonlike or rope-like form. Generally speaking, the minimum number of filaments to which the term tow is considered applicable is on the order of about one thousand, and normally there are 10, or more filaments.
While there is no fixed maximum number, tows containing on the order of 1,, filaments are frequently encountered, and there may be occasions to employ tows of l0,- , filaments or even more. The nature of the invention will be more readily under- I stood by reference to the following description taken in conjunction with the accompanying drawings in which FIGURE l is a schematic illustration of the process of the invention and apparatus which may be used in carrying out the process of the invention,.
FIGURE 2 is a view of a portion of the drawn, mechanically crimped, asymmetrically birefringent polyester tow bundle of the invention,. FIGURE 3 is a view of a drawn, asymmetrically birefringent polyester tow bundle of the prior art which has not been subjected to mechanical crimping. FIGURE 4 is an enlarged view of conventional, mechanically crimped polyester staple fibers of the prior art which are not asymmetrically birefringent,.
FIGURE 5 is an enlarged view of mechanically crimped, asymmetrically birefringent staple fibers of the invention, and. FIGURE 6 is an enlarged view of asymmetrically birefringent polyester fibers possessing a three-dimensional or reversing helical crimp, produced without the aid of a mechanical crimper. Referring now to FIGURE 1, tow 9 comprises a large number of polyester filaments which have been melt extruded and jet quenched in an asymmetric manner, e.
The tow is drawn by being passed from feed rolls 1 through 8, respectively, maintained at a given uniform peripheral speed and then around draw rolls 11 through 18, respectively, having a uniform peripheral speed considerably higher than that of the feed rolls.
Between rolls 4 and 5 the tow passes through a pre-wetting vessel 10, which contains an aqueous bath which may be at room temperature or which may be heated to a temperature in the range C. Additional quantities of the aqueous bath used in pre-wetting bath 10 are usually sprayed onto or otherwise supplied to rolls 5, 6, 7 and 8.
Between rolls 8 and 11 the tow passes under spray nozzles 19, from which hot liquid spray is directed upon the moving tow, whereupon the tow is drawn to a length several times its original length in response to the tension imposed by the draw rolls.
Preferably, the hot spray supplied to the tow is at a temperature equal to or higher than the secondorder transition temperature, Tg, of the polyester of which the filaments are made.
After leaving the draw section, the tow is passed around puller rolls 20 and into a stufer ybox crimper 21, cornprising -oppositely driven feed rolls 22, shoe plates 23, defining channel 24, and gate 25 mounted at one side of the channel at its exit.
The gate impedes to a predetermined extent the free fiow of the tow to the restricting channel and causes the yarn to fold back upon itself into the upper portions of the channel, thus forming a crimp or crinkle in the filaments comprising the tow bundle. The crimped tow is passed through a traversing funnel 26 which lays the tow down on a conveyor 27, upon which the tow is passed through drying chamber The dry tow may then either be packed as tow or cut to staple.
As previously described, in the absence of a mechanical crimper the asymmetrically birefringent filaments in the tow assume a three-dimensional helical crimp to a marked degree upon release of the tension of drawing. Upon employing a mechanical crimper in accordance with the process of the invention, the asymmetrically birefringent filaments are not released from the tension of drawing until imposition of the mechanical crimping step.
It is believed that the tendency of the asymmetrically birefringent filaments to assume three-dimensional crimp simultaneously with the imposition of the mechanical crimp produces the disclosed novel sinusoidal crimp, as contrasted with either a three-dimensional crimp or a conventional saw-tooth mechanical crimp.
In a preferred embodiment of the process, a conventional stuffer box crimper is employed. However, a gear crimper or other mechanical crimping apparatus which imposes a two-dimensional crimp may also 'be employed. FIGURES 2 and 3 illustrate the over-all appearance of two bundles of drawn asymmetrically birefringent polyester filaments. As shown in FIGURE 2, mechanically crimped tow 30 has the appearance of a single ribbonlike bundle having a fine wavy or crinkled configuration with most of the filaments being substantially parallel throughout the bundle at most points, so that the troughs and crests of the fine waves 31 appear to run transversely across the width of the tow bundle, giving it the appearance of a fiat ribbon.
The gross appearance of the tow bundle is very similar to that of a tow bundle of conventional mechanically crimped polyester filaments. As shown in FIGURE 3, the tow 32 comprised of drawn asymmetrically ybirefringent polyester filaments which have not been mechanically crimped has the appearance of a loose collection of small bundles 33 of filaments.
The small bundles possess three-dimensional crimp and the filaments within these small bundles are substantially parallel to one another, but the bundles of filaments are not parallel with one another, giving the tow the appearance of a fluffy rope. FIGURE 4 shows the saw-tooth crimp 35 of conventional mechanically-crimped polyester staple fiber 34 having a substantially symmetric birefringence differential across its diameter.
FIGURE 5 shows mechanically-crimped asymmetrically birefringent polyester staple fiber 36 prepared in accordance with the invention, having the characteristic sinusoidal crimp 37, which is substantially two dimensional. FIGURE 6 illustrates asymmetrically birefringent polyester staple fiber 38 which has not been mechanically crimped.
It possesses a reversing helical crimp which lacks definite infiection points in its curvature and is three dimensional in form. In general, the invention is applicable to any crystallizable, linear condensation polyester. These comprise linear polyester containing in the polymer chain carbonyloxy linking radicals,. Polymers containing oxycarbonyloxy radicals are comprehended within this group. The polymers should be of fiber-forming molecular weight; usually, this implies a relative viscosity of about or higher as conventionally measured in solution in a solvent for the polymers.
A good solvent for most of the linear condensation polyesters is a mixture of Copolyesters, terpolyesters, and the like are intended to be comprehended within the term polyesters. Preferably, the polyester of which the tow and staple fibers of the invention are formed is a linear glycol terephthalate polyester. By this is meant a linear condensation polyester derived from a glycol and an organic acid in which the glycol component is comprised substantially of a dihydroxy compound of a divalent saturated hydrocarbon radical containing from 2 to 10 carbon atoms and the acid component is at least about 75 mol percent terephthalic acid.
The expression second-order transition temperature, designated herein by the symbol Tg, is defined as the temperature at which a discontinuity occurs in the curve of a first derivative thermodynamic qu-antity with temperature.
It is correlated with yield temperature and polymer fluidity and can be observed from a plot of density, specific volume, specific heat, sonic modulus or index of refraction against temperature. Tgr is sometimes also known as the glass transition temperature because it is the temperature below which the polymer exhibits glass-:like behavior; above 'I'g the polymer is somewhat more rubber-like. A convenient method for determining Tg for a given sample of polymer is given by Pace in his U.
Patent 2,, col. Tg for this polymer is approximately 76 C. Approximately , of the spun filaments are combined to form a tow bundle which is drawn -at a draw ratio of 3 from a feed section comprising 8 feed rolls and a pre-wetting bath, maintained at approximately 50 C. The filaments in the drawn tow have a denier per filament of 3. A conventional finish was applied to provide a finish level on the fiber of 0 0. The tow was collected in a conventional tow box and sent to a mill for downstream processing, blending with wool, and yarn conversion.
Successful mill processing of tow including cutting to form a continuous sliver, dyeing, and pin drafting, gilling, etc. I was surprised that processing the tow and resulting sliver from the present example with fibers of mixed-denier, scalloped-oval cross-section was significantly superior to processing of tow that was similar, except that it contained fibers of round cross-section and of unmixed dpf , and I believe that the latter were possibly hard to process due to the effect of unacceptably high levels of fiber-to-fiber and fiber-to-metal friction during various pin drafting operations.
The friction characteristics of the two types are shown and compared in FIGS. Filaments of similar scalloped-oval cross-section were spun in approximately equal amounts by weight of lower denier 3. Twenty-four positions, with 12 positions on each side of the machine, produced lower denier filaments. Similarly, 24 positions, with 12 positions on each side of the machine, produced higher denier filaments. The smaller filaments were spun from spinnerets containing capillaries while the larger filaments were spun from spinneret containing capillaries.
The total denier of the spun tow collected in a can was approximately , As-spun properties are indicated in Table 2A. Mod Ten. Fourteen cans of spun supply were combined together to provide a tow with a total denier of approximately 2. Conventional finish was applied, as in Example I.
I was surprised that the tow of this Example processed well through various mill processing stages involving crush cutting to a specified length, dyeing and pin drafting because a tow consisting of 2 dpf unmixed dpf round fiber geometry did not process acceptably but caused productivity, efficiency, and quality problems.
In Example VII hereinafter, a tow of even lower dpf filaments was made and processed successfully. These tows and their slivers demonstrated good downstream processing characteristics.
Data is tabulated in Table 3. In Table 4, data are summarized for fibers spun essentially as described for Table 3, but for filaments prepared by a procedure essentially as described in Example II, and wherein the relative proportions and denier were varied.
Filaments of poly ethylene terephthalate of 3. Filaments of 7. Three bobbins of 3. The tow was drawn at a draw ratio of 2.
Conventional finish was applied as in Example I. The tow was collected in a conventional tow box and sent to a mill for downstream processing, blending with wool for yarn conversion and then into fabrics.
How a tow and the resulting sliver processes in a mill is critical for commercial viability. To estimate product performance in the mill, sliver cohesion tests, a measure of fiber-to-fiber friction, were performed both before and after dyeing. Sliver cohesion tests consist of carding to make a sliver 12 inches long, hanging the sliver vertically and adding weights at the bottom until a load-bearing limit is reached i.
Such tests reflect the magnitude of the frictional property change between items before and after dyeing. For comparison, sliver cohesion tests were performed on slivers of 3.
The results of the sliver cohesion tests are given in Table 5C. These may explain in retrospect why the tow of the invention and its resulting sliver processed much better. In Table 6, data are summarized for tows of mixed dpf filaments prepared essentially as described for Example V, but wherein the relative concentration of lower and higher deniers and their respective deniers are varied.
As explained before, the denier is varied by changing polymer throughput rate through the capillary, while the relative concentration in the blend is varied by changing the number of bobbins of a given denier in the blend prior to drawing.
The spun tow collected in a can had a total denier of approximately , As-spun properties are indicated in Table 7A.
Average stress-strain curves as for Examples 1 and 2 are shown in FIG. Fifteen cans of spun supply were combined together for a total tow denier of approximately 2. The tow was collected in a conventional tow box and sent to a mill for downstream processing, including stretch-breaking, followed by blending with wool, yarn conversion, and fabric making.
Mixed dpf tows spun essentially as described in Example III, Item 1, were processed, including being drawn at different draw ratios DR so the final product could be scrutinized for product quality defect level, as indicated hereinafter in Table 8. Both defects must be longer than 0. Samples are processed through a roller top type card. The sliver is dyed light blue and examined visually under a lighted magnifying glass. Each type of defect is reported as number of defects per 0.
Splinters are oversized fibers or clumps of fibers. To be classified as a splinter, this defect must be longer than 0. Splinters are concentrated in the flat strip waste when a staple sample is processed through a flat card. The flat strip waste is visually examined against a black background. Splinters are removed, classified by size, counted, and expressed on a weight of sample basis.
In other words, the product quality was not adversely impacted by varying the draw ratio over such a draw range, and these various draw ratios did not give rise to observable fiber defects. In addition, throughput of the draw machine was not reduced by broken filaments or roll wraps.
Tow made essentially as described in Example II was treated with durable silicone elastomer finish prior to blending with wool. The tow was processed at a rate of 8 lbs. The resultant silicone level on the fiber was 0. Application of this silicone improved the softness and resiliency of the resulting fabrics, because it reduced the fiber-to-fiber and yarn-to-yarn friction, so gave better aesthetics somewhat similar to previous experience with applying silicone slickener to fiberfill for use in filled articles.
Filaments of 3. Filaments of Eleven bobbins of 3. This tow was drawn, crimped, and relaxed as described in Example V to give a final tow size of approximately 50, denier of an intimate blend containing light-, medium-, and heavy-denier filaments. A conventional finish was applied as in Example I. Accordingly, this Example shows the invention is not limited to tows containing only two different dpfs, but more than two may be included in such tows, and their corresponding slivers and downstream products.
The Examples have demonstrated how filament tows of the invention may be prepared and processed, including their sliver processing, and subsequent processing into yarns, fabrics and garments.
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