CA1323184C - Blend of textile staple fiber - Google Patents

Abstract

ABSTRACT
BLEND OF TEXTILE STAPLE FIBER

Textile staple fiber, especially of polyester, and precursor continuous filament tows, and downstream textile articles, such as spun yarns, fabrics and garments, made from such staple fiber and blends thereof, wherein the staple fiber is of intentionally mixed denier, the higher denier being about twice the lower denier. A preferred process for preparing such staple fiber and precursor tows, by spinning filaments of different deniers, and collecting them in the same filament bundle on the same spinning machine, from orifices/capillaries of different diameters and/or throughputs.

Description

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TITLE
BLl~D OF TE~TIL~3 STAPL~
TECHNICAL FIELD
This invention concerns improvements in and relating to textile staple fiber of the polyester type, such as is commonly referred to as polyester staple fiber, and including precursor polyester tows that are cut or otherwise converted to staple fiber, and to textile articles such as spun yarns prepared from such staple, and fabrics and garments containing such yarn or fiber, and to processes for obtaining the same.
BACKGROUND OF THE INVENTION
Synthetic polyester yarns have been known and used commercially for several decades, having been first suggested by W.~I. Carothers, U.S. Patent No. 2,071,251, and then by Whinfield and Dickson, U.~. Patent No. 2,465,319. In particular, polyester staple fiber has been an industrial commodity that has been manufactured and used in such textile yarns on a very large scale, primarily in blends with natural fibers, especially cotton, such blends having been spun (twisted) into spun yams that have been made into textile fabrics, and eventually into garments and other textiles. A typical textile yarn is of cotton count 25, containing a cross-section of about 140 fibers of 1-1/2 denier and 1-1/2 inches cut length, for example, but the denier and cut length can vary up to about 3 and down to about 1. Because of the sophistication of the textile industry, both ~f the polyester fiber manufacturing industry and of downstream consum~rs of textiles, and because of the commercial interest in providing apparel and fabrics that will perform well during actual use by the ultimate consumer (wearer), much attention has been devoted to analyzing appropriate requirements. Many technical papers, for example, have been published on various aspects, and patents have been issued with the objective ~' ~3~3~

of improving the "comfort" that can be obtained from textile articles, and their constituent , and the literature ha6 been replete with these ~uggestions for 6ev~ral years. so it ha~ long been considered desirable to improve the ~omfort properti~e~ obtainable from textile~
prepared from yarns of polyester staple fiber, and much effort has been devoted in the textile indu~try toward6 this objective.
An important objective of my invention i6 to provide such polyester staple f:iber, or its precur~or tow, in a new form ~uch that it can be formed into spun yarns, which can then be formed into fabric~ and garments that can show i~proved comfort properties, as discus6ed hereinafter.
Polye6ter 6taple fiber ha6 generally been manufactured commercially by a process of ~elt ~pinning ~i.e. extruding molten polyester polymer) into ~ bundle of ~ilaments, collecting such filament~ into a tow, which can be relatively small and converted directly, e.g. by stretch-breaking, into a spun yarn, but has ~ore often been extremely large, amounting to many thou6and ~nd even ~ome million(s) of ilaments, and thi~ tow has then been processed by drawinq, and possibly ~nnealing, and crimping, before the crimped filaments have been converted into ~tapl~ fiber by cutting, or otherwi6e, to the de6ired lenqth~. AS indicated, most polye~ter çtaple flber has then been blended, e.g. with cotton, and converted into yarn, which is generally referred to as ~ ~pun yarn, to distinguish it from a continuous filament yarn. ~he natural fiber~, such a~ cotton, with whish the polyester staple has been blended have not been uniform. For instance, they vary in 6ize, ~hape and surface properties to some extent. The natural characteristic~ of cotton have long been believed to be responsible for the ~ttractive qualities of the spun yarn~, and of the articles, such as fabrics and garment~, prepared -31~

therefrom, and much effort has been devoted to duplicating various characteristics of cotton. Nevertheless, 60 far as I know, polyester staple has been sold commerci~lly as of uniform nominal denier (denier being the weight in grams of 900 meters of a 6taple fiber, continuou~ il~ment or yarn, ~nd thus being a measure in effect of the thickness of the fiber, filament or yarn; in fact, since 6taple fiber is, by definition, of short cut length, about 1 to 3 inches, the denier must be calculated by extrapolation or mu~t be measured on the precur~or tow or, more precisely, on random extracts of ~ ~pecified number of continuous filaments from the tow). When one refers to uniform denier, the nominal denier, i.e. averaye denier, i6 referred to, since there is inevitable variation along-end and end-to-end. ~owever for co~modity fibers, as opposed to some specialty fibers, it har. generally been the objective of fiber producers to achieve a~ much uniformity as possible when melt-spinning and drawing, and thus to minimize variations between individual filaments (i.e. end-to-end) and along the individual filaments (i.e.
along-end), so as to produce a polyester fiber product of as uniform denier as practical. This is the pre6ent commercial practice. Polyester fiber producer~ 6ell tow or staple fiber of various nominal deniers. ~t would have been pos~ible for anyone to buy polyester staple fiber (or tow) of various different denier~, and to blend them together, if desired with natural fiber , ~uch as cotton.
I do not know that anyone has actually done thi~, but it would have been ~uite possible. I believe that polyester staple fiber of intentionally ~ixed denier ha6 not previously been ~old ~ an article o~ commerce.
By way of contrast, there has certainly been a ~uggection that continuous filament yarns be prepared of mixed filament denier, e.g. by Jamieson and Reese, U.S.
Patent No. 2,980,492, and there ~ay have been other ~uggestions and, indeed, continuous filament polyester _4_ yarns of mixed filament denier ~ay po~sibly have been sold. The objectiv~ of Jamieson and Reese was to prepare a bulky yarn by making 6uch continuou6 filament yarn of mixed shrinkage. In other words, the component ilament6 of the mixed filament yarn have indiv~dually different ~hrinkages, ~o that upon ~ub~ecting the yarns, preferably in fabric or garment for~, to conditions under which the yarns will ~hrink, the ~omponent filament~ will ~hrink to differing extents with the result that the high ~hrinkage filaments will become load-bearing filament6 in the resultiny articles or yarns, and consequently the lower shrinkage filament6 will become longer than the higher shrinkage filaments and so impart a bulky texture. ~his i6 an entirely different objective from the objective of the present invention, which is to provide textile articles from fitaple fiber having improved comfort properties. This invention i~ not concerned with continuous filament yarns, but with ~pun yarn~ from staple fiber. However, all 6ynthetic fiber is prepared initially in the form of extruded filaments, and 60 all synthetic 6taple fiber is formed from precursor ilament~ in bundles which are referred to 2s tow~, as opposed to ~arn~.
SUM~RY OF THE INVENTION
According to the present invention, there are provided new blends, or inst~nce in the ~orm of bales of such blends, of polye~ter ~taple fiber of larger denier and o~ ~maller denier, the larger denier being about twice the 6maller denier, and of cut length about 1 to about 3 inches ~nd of average denier up to about 3, ~uch ac are suitable for conversion into epun yarn, ~nd spun yarns prepared ~rom such new blends, optionally with other fibers, And textile fabricc and garments consisting wholly or partially of ~uch yarn~. In other words, the yarns (and precursors thereof and textile~ therefrom) are characterized by the mixed denier of the ~taple ~iber, i.e. the polyester ~taple is intentionally not of uniform . . :

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nominal denier, but is intentionally of ~ixed denier, larger and ~maller.
It is believed that it is thi6 mixed denier of the 6taple fiber in the new art;icle~ of the invention that provides ~dvantage6 over articles from polyester staple fiber that h~s been available heretofore commercially.
Only comparisons in fabrics or gar~ent~ are considered truly meaningful, and these will be di6cussed hereinafter.
As indicated in the Examples, the mixed denier staple fiber and the precursor tows were obtained by a preferred process sf melt 6pinning filament~ Df mixed denier on the same ~pinning machine. In other word6, filament6 of different denier~ were 6pun from the 6ame spinning machine ~nd were collected and mixed together in the same bundle, ~s cvntrasted with mixing 6eparate batches of uniform fibers (i.e. o the ca~e 6ingle denier) made by ~pinning on different maehines and collecting into ceparate bundles and processing ~eparately before they are 6ubsequently mixed.
Accordingly, there i6 provided also, according to the invention, a proce~s for preparing a blend of polyester staple fiber of different denier~, wherein a bundle of filaments of deniers that differ by the desired ratio i~ prepared by 6pinning through capillarie~ of differing size and/or throughput on the ~ame ~pinning machine, and the~e filament6 of different denier~ are collected together in the same bundle, and ~uch bundles are then converted into staple ~iber. According to present conventional technology for preparing polyester staple fibers, generally ~everal ~uch bundles will be collected toyether ~nd ~ubjected to the ~tep~ of drawing, and po~sibly annealing, before crimping and conver~ion to 6taple fiber. ~owever, it has been 6ugge~ted and is known to be possible to prepare polyester filament~ directly by winding at high ~peeds (of the order of several km/~in.
and thereby avoid the need for drawing. A~ explained, ~5--~32~

however, the filament~ are preferably mixed by ~nitially spinning the filaments of different deniers on the ~ame spinning machine, than by spinning ~eparately filaments of the same 6ingle denier followed by later mixing cut fibers of different deniers. Furtherlmore, although thi~ i8 not yet certain, there may be ~ttendant advantages in the properties of the actual filamlents by co~pinning the ~ame ¦ bundle in the 6ame cell or 6pimning position through I capillaries of different diameter~ and/or throughput, and advancing this bundle of intimately mixed ~ilaments of ; different deniers together from the ~ame cell.
~ccordingly, there i~ al60 provided, according to the present invention, a proeess for preparing a blend of polyester ~taple fiber of different denier6, wherein bundles of filament6 of denier6 that differ by the desired ratio are prepared by co pinning each bundle rom the same spinneret through capillaries of differing ~ize ~nd/or throughput at the same spinning position, whereby the6e ; filaments of different deniers are collected and mixed together in the same bundle, and such bundles are then converted into 6taple fiber.
The precur~or polyester tow~ of intimately mixed filament6 of different deniers are ~lso believed new, ~6 are the processe6 for their preparation. Accordingly, there is also provided, according to the pre~ent invention, a process for preparing a tow of polye~ter filaments for conversion into polyester ~taple fiber, wherein the tow is a mixture of polyester filament~ of different deniers, ~uch proce6~ comprising the 6tep of forming bundles of filament~ of denier~ that differ by the de6ired ratio by ~pinning through capillarie6 of differing size and/or throughput on the same ~pinning machine, and such filaments of different denier are collected together in the ~ame bundle, optionally combining together 6uch bundle~ into a larger tow, and optionally subjecting the '~, " ' , . ' ~3~ ~

filament~ to drawing, annealing and/or crimping operations in the form of such tow.
Furthermore, there is provided a proces~ for preparing a tow of polyester filaments for conver~i~n into polyester staple fiber, ~herein the t~w is a ~ixture of polyester filament~ of different deniers, such proc~ss comprising the ~tep of forming bundles of fil~ment~ of denler that differ by the desired ratio by co~pinning each bundle from the same spinneret through capillaries of differing size and/or throughput into the same 6pinning position, whereby such filaments of different denier are collected and mixed together in the ~ame bundle, optionally combining together such bundles into a larger tow, and optionally ~ubjectiny the filaments to drawing, annealing and/or crimping operation6 in the for~ of such tow.
The textile yarns, fabrics and gar~ents containing fiber of mixed denier referred to herein are also believed new, according to the invention.
BRIEF DSSC~IPTION OF DRAWINGS
FIGURES 1 and 2 show, in cross-section, ~ssemblie6 of ~ome 140 fibers to demonstrate the difference between how the fiber6 pack together in a mixed denier yarn in contr~st to a unifor~ denier yarn, as explained hereinafter.
FIGURE 3 is a block diagram to ~how typical process teps by which a 6taple fiber blend of the invention ~ay be prepared.
FIGURE 4 6hows schematically a part of a spinning machine with a piddler can, whereby a bundle of filaments of mixed denier according to the invention may be prepared.
FIGURE 5 6hows denier histograms for yarns, as explained hereinafter.
DETAILED DESCRIPTION OF INVENTION
Assemblies of 140 fibers are shown as circles in Figures 1 and 2, to represent ~chematically the difference .

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between the packing together of fibers in a 6pun yarn consisting of an intimate mixture of fibers of tw~
different denier~, i.e. according to the inv~ntion, as shown in cross-section in Figure 1, ~nd a ~imilar as~embly but of uniform denier, a~ shown in cross-~ectlon in Figure 2, i.e. accordin~ to the prior ~rt. It will be noted that, in Figure 2, the filaments of uniform denier are closely packed, and that this does not permit ~uch ~pace between the filament~. In cGntr~st, in Figure 1, defipite the random arrangement ~i.e. the filaments are not arranged in a uniformly alternating pattern), ~ignificantly larger ~paces are provided between the filament I believe that this ~ay be a signific~nt factor in increa6ing the comfort of fabrics and garments incorporating polyecter fibers of mixed denier according to the present invention, although this may not explain all the advantages of the invention, as will be apparent, hereinafter.
The degree of mixing of the fibers of mixed denier in the cross-section of ~uch yarn as represented in Figure 1 can be measured by a DFI test. DFI means degree of filament intermingling, and i~ described, in relation to continuous filament yarns (referred to as heather yarns) in Reese U.S. Patent No. 3,593,513. The same general technique, i.e. measurement of intermingling, i6 applicable herein to polyester staple fiber in a ~pun yarn. However, unlike heather continuou~ filament yarn~, for which the filaments must be colored to distinguish them, the DFI relates to the degree of intermingling of fibers of differing deniers. Sin~e the ~iber of 6maller denier i~ distinctly smaller (about half the size) of the fiber of larger denier, the difference will be immediately apparent, and there is no need to cclor the fiber6. As will be appreciated from looking ~t Figure 1, even a comparatively random degree of mixing provides a significant increase in the interstitial ~pa~es, because .... _ _ . . .. . . ". ~ . .. . ... .. . . .

.

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g the presence of fibers of ~ignificantly differing deniers prevents close packing, even if the fibers of one denier tend to pack together to some extent. What i~ ~o~t ~ignificant i6 that the use of iEiber~ of mixed denier has S shown a perceptible increase in comfort propertie~ in wholly polyester fabric~. Po6sibly, the improvement may be because of the inevitable packing tsgether of the prior 3rt polyester fibers, of uniforDn denier, especially when they are subjected to the later~ pressure~ involved in spinning (twisting) into yarn~, and in ~ubsequent fabric formation.
~he advantaqes of using the intimate ~ixture6 of polyester ~taple fiberfi acc~rding to the invention are better described hereinafter in relation to the Examples.
These advant~ges ~hown hitherto ~re significantly ~urprising, especially if such advantages can be confirmed by perceived comfort improvements in fabrics prepared from yarns prepared from blends with cotton.
Because cotton i5 a natural product, cotton is it~elf a variable product, in the sense that there i6 no uniform length, diameter, or sur ace, and in this respect, quite apart from chemical differences, there are ~ignificant physical differenc~ between a natural ~iber, such as cotton, ~nd a ~ynthetic fiber, where every effort has generally been made by a ~ynthetic fiber manufacturer to achieve uniformity to the extent ~f practical identity between different fibers. Because of the 6ignificant content of cotton (which is nece~sarily of varying dimension~) it would be extremely ~urpri~ing if garments formed ~rom yarns of blends of cotton with mixed denier polyester staple according to the ~nvention 6hould provide confirmed comfort advantages, ~s compared with garments prepared from prior art blends, involving only single nominal denier polyester staple fiber.
Although the reasons for these advantages are not fully understood, and the invention is not limited by _g_ .. . .. . .. . .. . . . . ..... . ..

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any theory of operation, the following ~peculations may be of assistance. Conventionally, most polyester staple has been of round cros~ ~sction. This is becau~e a round cross ~ection ha~ proven, ~o far, to be the most economical tc produce, and cost ha6 been an extremely important consideration in the manufacture o~ polyester staple fiber, which has long been ~ comm~dity, and has been ~vailable in ~bundant quantities (~enerally in exce~s of demand) in many industrial countries, and ha6 been easily transportable at relatively low cost6 from countries where costs of manufacture are already low, and are often 6ubsidized ~o a~ to facilitate the export of polyester staple fiber ~nd imprDve the balance of trade of the country of manufacture 85 part of that country' 5 government policy. As already indicated, conventionally, polyester staple fiber i~ manufactured from polye~ter filament tow which, in turn, is generally prepared by assembly from individual bundles of polye~ter continuous filaments formed by spinning in individual cell6, in a manner comparable to that conventionally u~ed for polyester continuous filament yarns. These bundle~ of filaments are ~ssembled into a tow, which may amount to ~ome ~illion or 50 polyester filament~. The filament~ in these bundles ~ay have 60me oohesion, depending on their hi6tory and mode of preparation, possibly resulting from the applic~tion of ini~h to the freshly-6pun bundle, from any other r~ason for the filaments in the initial bundle to stick together, and from any ~light degree of twist that may be introduced as the filament bundle is advanced past various rolls and guides. Consequently, depending on the particular history of making the individual bundles and the tow, and on the particular conditions of mixin~, any 6uch ~ubsequent mixing or blending operation may appear to achieve intimate admixture with cotton, but may not achieve a degree of mixing of the individual fibers as great as can be obtained by cospinning or 6pinning on the .

.

.. ' '. . . . . , , ' .
., ' . , ' .
. .

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same machine according to the preferred proce~s of the invention. If filaments of the 6ame denier and round cross section are closely packed into small bundles, it is believed that certain results may follow, such as reduced air permeability between the fibers, difficultie~ in dyeing, reduced moisture transport (wicking ~ction) and other characteristics that may, in retrospect, also be attributable to the close packing of the individual filament~. In contrast, if the filaments ~re of distinctly different deniers, this close packing arrange~ent become~ more difficult, if not impossible, and probably account~ for improved air permeability, ease of access of dye molecules, ~oisture tran~port, for example, and alco an ability of the filaments to move past each other readily and take up different positions, which could be of great advantage in a comfort sen~e and in improving processability of the staple fibers and possibly even of precursor tows. These results and consequent advantayes may be enhanced by varying the cross ~ection of the individual filaments, in addition to varying the denier, and this i~ why, from technical considerations, different cross sections for the polyester ~taple fiber and precursor filaments may be preferred, as well a6 ~ixed deniers. However, 60me cro~s-6ections (~uch as ~ertain trilobal filament~) may tend to give a harsher feel in fabric~, whereas ~ ~calloped-oval cros~-~ection or other les~ harsh configuration may be preferred.
For convenience, the discussion herein is directed to mixtures of fibers of two different deniers, with the perceived objective being to minimize the possibility of close packing, and maximize the spaces between adjacent fibers. Taking this simple combination of two different deniers, from theoretical considerations, we have calculated that the percentage of space between such elosely packed fibers increases through a maximum, at a ratio of small to large diameters of about 0.7, .. , .. .... .. _ _ _ . .... . . .. . . .

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corresponding to a small to large denier ratio of about O.S. It will be understood that essentially the same effect can, however, be obtained with different diameter or denier ratios within a range on either side of this approximate optimum. For instance, almost as much 5 beneflt can be obtained when the small to large flber diameter ratio is from 0.5 to 0.9, corresponding to a denier ratio of 0.25 to 0.8. In other words, it is believed possible to obtain essentially as much advantage by providing m;xed denier staple of such small to large denier ratios, and it is not necessary to provide mixed denier fibers only in the exact 0.5 ratio of small to large denier. The above calculations have been made on the basis that essentially 10 only 2 fiber diameters are involved, which would be the case in a wholly polyester yarn of only 2 deniers mixed together. When blended with cotton, however, assuming that the polyester blend is of, for example, 1-1/2 nominal denier, i.e., the lower denier fibers are of average denier about 1, and the higher denier fibers are of average denier about 2, and that the polyester is blended with cotton also of matching average denier 1-1/2, then the resulting 15 yarn will involve such cotton hbers of this intermediate average denier, which may have the effect of reducing the void content, so that it may be advantageous to further widen the difference between the average deniers of the polyester fibers, so as to increase the void content in the resulting blend, because it is this blend with cotton, rather than the polyester blend of mixed deniers, that will be used in the yarns, and so in the ultimate garments and 20 fabrics that must be worn.
For conven;ence, about equal numbers of small and large denier fibers have been used, but this is not essential, especially if mixed cross-sections are used in addition to mixed deniers, bearing in mind the perceived objective of maximizing spaces between fibers, and minimizing close packing. Indeed, from a theoretical ~5 . ~ . . , , ' . - '.
,, . ' " . ' ' ' ' ' ' ' . '''', ~ "'' ~-13~ ~3~3~

stan~point, in a yarn of some 140 fibers in cross-section, a major improvement in loose packing can be ~btained, in theory, from arran~ing only a relatively 5~all number of fibers of different denier, provided they are 5 strategically located ~o as to ~aximize the packing dislocation, i.e. prevent clo~e packing. ~ow~ver, the u6e of minimally 6mall proportions of fibers of di~ferent denier will not necessarily achieve uni~orm ~dvantageç, and so it is pre$erred to use more equal proportions and obtain more reliable re6ult~. This will al60 depend on the number of fibers, 6ince ~he u~e of mixed denier~ will probably provide little difference in the packing of fibers in yarns having only a very ~mall number of fibers in each cross-section.
A process or preparing the blends according to the invention will be described with reference to Figure 3, which is a block diagram showing a typical processing sequence th~t may be used. Thus, the fir6t 6tage i~ to - melt spin the filaments of higher denier ~nd the filament~
of lower denier and form them into a bundle of filaments of mixed denier, and this will be descr~bed in further detail. However, in other respects, the preparation of the staple fiber may be conventional. The preci~e de~ails will generally depend on the intended use of the polyester fiber and, accordingly, the prspertie~ desired. For $nst~nce~ for textile processing, e~pecially spin~ing (twisting) to form 6pun yarns, polyester tow6 are conventionally crimped mechanically, e.g. by a ~tufer-box. ~or some purposes, especially where 6trength is desirable, the tows are annealed. At present, it is believed that all polyecter ~taple fiber or textile u6e is prepared from filaments that have been withdrawn from the spinneret at relatively low speeds, followed by a drawing operation to increase the orientation and 3~ crystallinity. ~owever, it has been known for many years, e.g. as disclosed by Hebeler, U.S. Patent No. 2,604,667, .

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that 60mewhat similar properties can be obtained, without drawing, merely by withdrawing polyester filament~ at extremely high speeds, although ~uch a process requires high capital investment. Conventionally, ~n appropriate finish is applied to the polyester filaments to facilitate further proce~sing, and the particular finish selected will depend on the 0nd use intended. For some end u~e applicati~ns, a tran~ient finish is desired, i.e. one that is easily re~oved, e.g. by washing. For other applications, it ~ay be de~ir~ble to apply a permanent finish, or a combination of a plermanent and transient ~inish, according to the desired end u~e.
The preparation of an intimate mixture of filaments of mixed denier in the same bundle by 6pinning on the ~ame spinning machine will now be desçribed in greater det~il with reference to Figure 4, which represents part of ~ conventional 6pinning ~achine prov~ding a bundle of polyester continuous filaments which are collected in a piddler can, Dnd which can be adapted for preparing a tow of filaments of mixed denier for use according to the pre~ent invention. The piddler can 1 is 6hown on the left and is ~ed with a l~rge bundle ~ of filament~ obtained fro~ the ~pinning ~achine 3 on the right of the Figure. ~t the top are ~hown a ~eries of spinneret~ 4, ~tretching away to the right, it being under~tood that only part of the cpinning machine 16 6hown, with only two of the spinneret~, but it being conventional ts arrange a much larger number of ~pinnerets in a bank on either &ide of the spinning machine, only one side of which is shown in the Figure. Molten polymer i5 ~pun through orifices in each ~pinneret 4 to form filaments 5 which are cooled by air conventionally by means not ~hown, ~nd are converged by passing between guides 6, before the solid filaments pass a ~ini~h applicator, 6hown as a roll 7, before contacting feed rolls 8, which are driven at a speed (the withdrawal -~4-: .
,. '~ . .
.

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speed, ~r ~pinning speed) which deter~ines the orientation of the freshly-extruded filaments. Thereafter, each filament bundle 9 rom each individual ~jpinneret ~, or ~pinnin~ po~ition, or ~pinning cell, is advanced by rolling guides 10 ~nd combined ~ith bundles from the other ~pinning position~ to form larger bundle 11 that emerge6 from the front of the spinning machine and i~ co~bined with a ~imilar bundle 11' that has been provided from cpinnerets and spinning positions (not shown) on the ~ack of the spinning ~achine and advanced by rolling guides 10~. Thus the larger bundles 13 and 11' are ~upeeimposed and so combined into large bundle 2 which i6 further advanced by rolling guide or guides 10'' ~nd fed into air jet 12 and through lay-down ~pout 13 into piddler can 1, which i5 used for transporting the freshly-spun ~ilaments in large bundle 2 to the next ~tage. The next ~tage is conventionally a drawing machine, assuming that large bundle 2 consists of conventional undrawn polyester filaments, which are subjected to the conventional ~teps of drawing, annealing if desired, crimping, relaxing and converting to staple fiber. Hitherto, the process described has been conventional.
Such a process can easily be adapted for preparing the mixed denier products of tbe invention in several ways. It is believed that the most uniform mixing can be achieved by co~pinning, i.e. by spinning mixed denier filaments from the same ~pinneret 4 through capillaries of differing size and/or throu~hput into the ~ame spinning cell, or ~pinning position, and sollecting these filaments of different deniers into the ~ame bundle 9 at the bottom of each spinning position, and then collecting several such bundles of mixed denier filaments forwarding and processing them appropriately. Such a process may be particularly desirable if the bundles 9 are provided with 6ignificant bundle integrity, e.g. by application of twist and/or such amount and/or type of -16- ~323~

finish, or for ~mall tows, e.g. for conversion by stretch-breahing.
~ owever, provided precauti~ns ~re taken, we have found that very ~ati~factory re~iults have been obtained by spinning filaments of uniform denier from each 6pinneret 4 and collecting them in the ~ame bundle 9 at the b~ttom of each ~pinning position, and then combining 6uch bundle 9 of filament6 of unifDrm denier with other bundles of filaments of different denier into a large bundle of filaments of mixed denier. In other words, different spinning poæitions on the ~a~e spinning machine will each spin bundles 9 of filaments of uniform denier, but because the different ~pinnerets 4 Dre spinning filaments of different denier, the final bundle 2, and possibly the larger bundles 11 and 11', contain filaments of ~ixed denier. It i~ important to Avoid the individual bundles 9 having too much bundle integrity Guch as will inhibit for~ing an intimate ~ixture of mixed denier during later processing. Thus, it is important to ~void excessive interlacing, or bundle twist, Ot exces~ive coating of finish, as will inhibit later intimate mixing.
If the ab~ve theory is correct, namely that mixed denier fibers provide more comfort in garments because they do not pack ~o closely in ~pun yarns as single denier fiberc, then thi6 advantage will be obtained, regardless of the time of mixing proYided the distribution of fibers of different denier6 is achieved ~e.g. by obtaining a preferred DFI of at lea~t about 90~) in the spun yarns in the ultimate garment~. Thu~, in order to obtain thi~ objective, it may not prove necessary to mix the filament~ in the precursor tows, a~ described above for the preferred proces6. Neverthele6s, thi~
process is preferred because of its effectivenes6 and it~
economy. However, alternatively, ~ixing could be achieved during proce6E;ing of the staple fiber, preferably by cutter blending tows containing filaments of different -~7- ~323~

deniers so a6 to produee a mixed denier ~taple, or ~t a convenient later stage. It will be understood that the normal staple operations are intended to ~ix the various fibers together, and to improve the degree 9f mixing of whatever materials are fed. For instance, if slivers o~
fibers of differing denier are fed into an e~rly stage of a multi-stage drafting operation, considerable mixing will be achieved in the l~ter stages and in the resulting spun yarns. The drafting conditions should not be ~uch as to 6egregate the different deniers to an undesirable extent.
The fibers in ~pun yarns must be twi6ted tightly together in order to ~aintain the integrity of the yarn.
In contrast in filament yarns, close packing i~ not necessary to maintain the inteqrity of the yarns. So it can be understood that the need for interstitial voids between closely packed fibers is correspondingly greater if, indeed, such inter~titial voids or pas6age~ promote greater comfort for the wearer of the garment6. Thus, it is believed that the garment from spun yarn~ containing mixed denier fibers are ~ofter and provide more comfort because of the open space and loose ends, which are believed to provide soft, dry, cool, and airy ~esthetics, and more breathability. It i~ p~ssible that the mixture of deniers also gives better aesthetics for reasons that are not connected (or only indirectly connected) with the grsater inters~itial spacing, ~or ~nstance the loose ends that inevitably protrude from the ~urface of a ~pun yarn and garment thereof may provide a more pleasant texture, because of the mixture of denier~. The inter~titial spacing may, however, be responsible for a greater ability of the fibers to move and flex, and this could be responsible, in part, for ~ny greater feeling of comfort in the garments.
The invention is further illustrated in tbe following Exa~p~e.

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EXAMPLE
An intimate mixture of appr~ximately equal numbers of low pilling polyester staple fiber (relative viscosity 15.4, LRV 11.5) of about 1 and about 2 dpf was obtained by a proce6s, as described with reference to Figure 4, involving conventionally ~elt-spinning to ~orm a bundle of filaments, combining 6everal bundles to form a large bundle, i.e. ~ small tow, drawing/annealing and crimping the tow, and converting the tow to 6taple ~iber by cutting, except that the large bundle (tow) contained intimately mixed filaments of different dpf made by ~pinning through orifices and capillaries with different throughput on the same ~pinning machine. The orifices were circular to provide filaments of round cro~ ~ection.
The smaller filaments (spun denier 2.72, natural draw ratio 1~68) were ~pun on one ~ide, on 18 po6ition5, ~ach having 2400 orifices of diameter 15 x 30 ~il (about 0.38 x 76 mm) under a pack pressure of 1500 psig at a throughput of 0.0625 lbs. per hour. The larger filaments (spun denier 4.89, natural draw ratio 1.69) were ~pun through similar orifice6, but under a pack pressure of 1900 psig at a throughput of 0.1195 lbs. per hour, on the other side, on 24 po6itions, each having 1590 orifices.
~ll these filamen~ were 6pun ~t a withdrawal ~peed o~
1,800 ypm. The tow, ~mounting to ~bout 80,000 filaments, was drawn at a draw ratio of 3.1X, cr~mped to give drawn filaments of 9 crimps per inch and crimp take-up 31.5, and cut to a cut length of 1-1~2 inches, to give taple ~iber with tenacity of 3.4 g/d and a dry heat shrinkage of about 5.5% and a fini6h level of 0.07% by weight of the filament~. The nominal denier was 1.5, but about half the filaments were of 1 denier and the other half of 2 denier.
It wa~ ~urprising that it was possible to spin on the same ~pinning machine undrawn filaments of different denler that could be assembled into a tow and then be drawn satisfactorily at the same draw ratio in the ... . . ... .. . . . . .

1~23~ ~

~ame t~w, i.e. to give ~atisfactory drawn filament~ and eventually cut fiber (of intentionally ~ignificantly different denier). ln other words, it was ~urprising that it was possible to spin undrawn filaments of 6ubstantially S the same natural draw ratio, but of ~ignificantly different denier, on the ~ame ~pinning ~achine. These filament~ and cut fiber have alEio ~hown good processability through to spun yarns, and eventually fabric~ and garments, which ~ay be 2 re~ult of their relatively sharply deined denie!r distribution, as shown hereinafter in Figure 5 for Yarn A. The tensile properties of the drawn filaments (and cut ~iber~) were ~ignificantly different, the tenacities of the 6~aller denier filaments being significantly higher than those of the filaments Df higer denier.
The staple fiber was formod into yarns of singles tcotton) count 16 (corresponding to ~bout 330 denier, or about 220 fibers of nominal denier 1-1/2) and knit by an outside evaluator into fabrics which were tested in comparison with co~parable fabrics, except from a competitive co~mercial polyester 6taple fiber (Fabric K). The details are shown in Table 1.

--lg--... . .. , . . . " , .

~323~ ~

Yarn Types Par~meter A R
Fabric Wt., oz./sq. yd. 4.93 5.36 ~abric Count, w x c 25x27 26x26 Fabric Thickness, mil 19.0 20.0 Moisture Vapor, gm./sq.m./24 hrs.987.3 953.0 Air Permeability-Dry, cu . ft ./sq . ft./min. 576.4 479.3 Air Permeability-Wet, cu.ft./sq.ft./min.613.0 50~.5 Random Pilling, 0 min.4.9 4.9 3 min.4.3 2.9 5 min.3.1 l.9 10 ~in.2.1 1.3 20 min.1.5 1.0 30 ~in.1.2 l.0 Cover/Thickness 4.53 4.40 Tenacity, gm/den 1.75 2.39 Elongation, ~ 17.30 27.50 ~/S ~ 460 nm 0.0061 0.0053 ~ -20-... .. . .. .. .. . . . .. . .

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Fabric A prepared fro~l staple fiber of the invention showed the foll~wing differences, which translate into a ~ignificant sverall ~dvantage, ~s rated by the outside evaluator;
1. 17% deeper dyed in competitive dyeing;
2. 20~ higher air-permeability in dry fabric, and 12% higher in wet fabric;
3. 4% higher moisture vapor tran6port;

4. 27% lower tenacit:y;

5. 37% lower elongat:ion;

6. ~ignificantly 6uperior pilling performance;

7. 3% higher cover per thickne6s.
The i~proved results obtained with the polyester ~taple fiber of the invention prepared in thi~ Example over the prior art fiber are believed to result from the ~ixed denier feature, which may provide ~ore open ~pace between the tightly packed fibers, and possibly other advantages, which cannot yet be fully explained,, and are not yet therefore under6tood.
The distribution of the denier~ in representative samples of ~taple fiber compri lng yarns A
and R was counted, by taking 200 ~uch staple fibers from each yarn, measuring their deniers and plotting the frequency of such denier~ as histograms that are ~hown in Figure 5 of the accompanying drawings. Thus, the histogram for yarn R, at the bottom, is typical in that it it monomodal, i.e. ha~ a distribution about a single peak at the nominal denier of about 1.5, whereas the histogram for yarn ~ is bimodal, i.e. has distribution about two ~eparate peaks at the approximate nominal deniers of the two component fibers of about 1 and about 2.
These histograms seem to indicate that the significant advantages in fabrics of mixed denier yarn A
over yarn K may not result entirely or directly only from ~he fact that fibers of mixed denier do not pack together so olosely, because the variation in denier for the fibers .

.
.

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6ampled fro~ yarn ~ ~fro~ a ~in~mum of abo~t l dpf t~
maximum of more th~n 2 dpf) ~ ~ignificant ~ough ln theory to allow for 1006e packinq unle6~ the f~ber6 o 6imilar denier ~n yarn ~ happen to or tend to conqeqrAte together in practice.
A further comp~rison i~ ~Dde by ~king spun y~rn of 27/1 cc from 1003 of the same mixed denier y~rn A, and from 50/50 polyester/cotton blonds, and knitting 18-cut $nterl~ck fabric6 therefrom an~d comp~ring with ~lm1lar fabric~ ~r~ a commerclal ~taple flber ~ (of the ~ame polymer as used for yarn A) anld from a c~mercial competiti~e ~taple fiber C, both of un$form den~er 1.5 .
The fabrics were ~ll Jawatex 6coured at 205F, pressure dyed, dried, Tubetex~6teamed tw~ce and he~t set at 350Dr for l minute. No re~ins or 60ftener6 were u6ed. ~he breathability of these fabric6 w~c tested by mea~ur$ng their air permeability ~n cfm ~average cubic ~eet per ~inute), for both the lO0~ polye~t~r and the blends. The results are ~hown in ~ble 2.
TAaLE 2 Sample A ~ C
Air Permeability in CFM
100% Polye~ter 393 3~1 363 50f50 Blend 300 291 237 These re6ult6 6how an lmprove~ent ln alr permeab$1ity for Sample A (~ixed den~er ~t~ple of ~y invention) over two commercial flber~ of the ~a~e nomin~l denier, but of uni~orm denier. The ~mprovement 18 ~ignificant, and is ~hown b~th for 100~ polyester and for 50/50 blends with ootton. Intere6tingly, the ~ir permeability for the blends i~ in~erisr to that ~or the lO0~ polyester, ~nd the difference ~r A ~nd C, ~t least, is far gre~ter in the blend than ~or the lO0~ polye~ter, which ~eems to indic~te that any 6peculation based on ~heoretical calculations o~ 6pacinq between fiberE ~ay not ; * denotes trade mark ' ' . . .

' ' .

-23- 13~3~

be sufficient to account for the differences obtained in practice.
Si~ilar yarns of other cotton counts can be made, and formed into fabrics and garments, from 100%
polyester and/or blends containing variou~ percentages of other fibers, ~uch ~s cotton. An advantage of the perception that the mixed denier staple fiber provides better perceived comfort, is that the proportion of polyester in such blends can be improved over that preferred today by the wearer, e.g. back to 60/40 polyester-cotton, or sven higher, e.g. to 75/25, or 80/20 or 100% polyester. The cut length of the polyester has generally been 1-1/2 inches to match the average length of the cotton. Conventionally, cut lengths range from about 1 to ~bout 3 inche~. The denier of the polyester 6taple has conventionally matched the cut length ~pproximately, i.e. a 1-1/2 nominal denier for a ~ut length of 1-1/2 inches. Vsing mixed denier poly~ster staple according to the invention, therefore, a mixed denier (1 and 2 denier) blend would match 1-1/2 inches in cut length, as in the Example, although use of the mixed deniers may enable some variation in this hitherto-accepted rule of thumb. Thus nominal deniers of up to about 3 (mixed deniers of about 2 and about 4 denier) and generally down to ~bout 1 (~ixed deniers to about ~/4 and ab~ut 1-1/2) ~an be expected to be used, althouqh there has been a tendency to use finer deniers in recent years, and thi~ could be of advantage, e.g. in pilling performance. Furthermore, as indicated, especially when blending with cotton, there ~ay be an advantage in widening the difference between the average denier6 of the polyester fibers beyond the value~
indicated.
The invention has been described hereinbefore with particular reference to yarns and other articles consisting of polyester staple fiber of ~ixed denier prepared from poly~ethylene terephthalate), which i6 u~ed . . ~ . . - ~

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commercially on a very large ~cale. Other polyester polymer may be used alternatively, or in addition, of course, e.g. cationic-dyeable polyesters, ~uch as are already used commercially, or other copolymer~ that are mentioned in the literature. IE desired, the polyester may include ingredients and/or additives, a6 i6 conventional, e.g. a content of delustrant, r~uch as titanium dioxide, and/or be treated so ~s to modify the surface or other characteristic~s, as desired, to improve the properties of the ~ubstrate polyester during filament formation or subsequently, e.g. in fabric form. Such changes or modifications in the nature of the polyester polymer do not affect the essence of the invention, which is ba~ed on the intentional u~e of mixed denier ~taple $nstead of uniform denier staple to form the ~pun yarns.
.

Claims (18)

1. An intimate blend of polyester staple fiber of uniformly the same color, of uniform cut length about 1 to about 3 inches, and of average denier up to about 3, such as is suitable for spinning into spun yarn, wherein the blend consists essentially of polyester fiber of larger denier randomly and uniformly mixed with polyester fiber of smaller denier, the larger denier being about twice the smaller denier, and the degree of filament intermingling (DFI) being at least about 90%.

2. The blend of Claim 1 in which the polyester staple fiber has a dry heat shrinkage (DHS) of about 5.5%.

3. A blend of fibers of different denier according to Claim 1, wherein the fibers are also of mixed cross-sections.

4. A bale of polyester staple fiber consisting essentially of a blend according to any one of Claim 1, Claim 2 or Claim 3.

5. A process for preparing a blend of polyester staple fiber of low shrinkage and of intentionally different deniers, wherein bundles of filaments of deniers that differ by the desired ratio are prepared by cospinning each bundle from the same spinneret through capillaries of differing size and/or throughput at the same spinning position, whereby these filaments of different deniers are collected and mixed together in the same bundle, and such bundles are processed to reduce their shrinkage, and then converted into staple fiber.

6. A process for preparing a blend of polyester staple fiber of low shrinkage ofintentionally different deniers, wherein bundles of filaments of deniers that differ by the desired ratio are prepared by spinning through capillaries of differing size and/or throughput on the same spinning machine, and these filaments of different deniers are collected together into the same tow, and such tow is processed to reduce the filament shrinkage, and is then converted into staple fiber.

7. A process for preparing a tow of polyester filaments for conversion into polyester staple fiber, wherein the tow is a mixture of polyester filaments of intentionally different deniers, such process comprising the step of forming bundles of filaments of denier that differ by the desired ratio by cospinning each bundle from the same spinneret through capillaries of differing size and/or throughput at the same spinning position, whereby such filaments of different denier are collected and mixed together in the same bundle.

8. The process of Claim 7 in which the bundles are combined together.

9. The process of Claim 7 or Claim 8 in which the filaments are subjected to drawing, annealing and/or crimping operations in the form of such tow.

10. A process for preparing a tow of polyester filaments for conversion into polyester staple fiber, wherein the tow is a mixture of polyester filaments of intentionally different deniers, such process comprising the steps of forming bundles of filaments of denier that differ by the desired ratio by spinning through capillaries of different size and/or throughput on the same spinning machine, and such filaments of different denier are collected together in the same bundle, optionally combining together such bundles into a larger tow, and optionally subjecting the filaments to drawing, annealing and/or crimping operations in the form of such tow.

11. A tow of polyester filaments for conversion into polyester staple fiber, being a mixture of filaments of larger denier and of smaller denier, the larger denier being about twice the smaller denier, and of average denier up to about 3.

12. A tow according to Claim 11, wherein the filaments are of mixed cross-sections.

13. A spun textile yarn consisting essentially of a blend of intimately mixed polyester staple fibers of low shrinkage, wherein the polyester fibers are uniformly the same color, of boil-off shrinkage about 1% or less, of uniform cut length about 1 to 3 inches, and of average denier up to about 3 but consisting essentially of polyester fibers of larger denier randomly mixed with polyester fibrs of smaller denier, the degree of filament intermingling (DFI) being at least about 90%, the larger denier being about twice the smaller denier.

14. A spun textile yarn consisting essentially of an intimately mixed blend of polyester staple fibers with fibers other than polyester fibers, wherein the polyester fibers are uniformly the same color, of boil-off shrinkage about 1% or less, of uniform cut length about 1 to about 3 inches, and of average denier up to about 3 but consisting essentially of polyester fibers of larger denier randomly mixed with polyester fibers of smaller denier, the degree of filament intermingling (DFI) being at least about 90%, the larger denier being about twice the smaller denier.

15. A spun textile yam consisting essentially of an intimately mixed blend of polyester staple fibers with cotton fibers, wherein the polyester fibers are uniformly the same color, of boil-off shrinkage about 1% or less, of cut length about 1 to about 3 inches, and of average denier up to about 3 but consisting essentially of polyester fibers of larger denier randomly mixed with polyester fibers of smaller denier, the degree of filament intermingling (DFI) being at least about 90%, the larger denier being about twice the smaller denier.

16. A textile fabric consisting wholly or partially of spun yarns according to any one of Claims 13 to 15.

17. A garment consisting wholly or partially of spun yarns according to any one of Claims 13 to 15.

18. The spun textile yarn of any one of Claims 13 to 15 in which the polyester staple fiber has a dry heat shrinkage (DHS) of about 5.5%.