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`IPR of U.S. Pat. No. 9,109,309
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`U.S. Patent
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`Oct. 10, 2006
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`US 7,117,695 B2
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`U.S. Patent
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`US 7,117,695 B2
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`1
`METHOD TO MAKE CIRCULAR-KNIT
`ELASTIC FABRIC COMPRISING SPANDEX
`AND HARD YARNS
`
`CROSS REFERENCE TO RELATED
`APPLICATIONS
`
`This application is a continuation of International Appli-
`cation PCT/US2004/017364 designated in the United States
`and filed Jun. 1, 2004, which PCT application claims benefit
`under 35 U.S.C. §365(c) as a continuation of U.S. applica-
`tion Ser. No. 10/454,746, filed Jun. 2, 2003, now U.S. Pat.
`No. 6,776,014, issued Aug. 17, 2004; the entire contents of
`both of which are hereby expressly incorporated herein by
`reference in their entirety.
`
`FIELD OF INVENTION
`
`This invention relates to circular knitting yarns into
`fabrics, and specifically to elastic single-knit jersey fabrics
`comprising both spun and/or continuous filament hard yarns,
`and bare spandex yams.
`
`BACKGROUND OF THE INVENTION
`
`Single-knit jersey fabrics are broadly used to make under-
`wear and top-weight garments, such as T-shirts. Compared
`to woven structures, the knit fabric can more easily deform,
`or stretch, by compressing or elongating the individual knit
`stitches (comprised of interconnected loops) that form the
`knit fabric. This ability to stretch by stitch rearrangement
`adds to the wearing comfort of garments made from knit
`fabrics. Even when knit fabrics are constructed of 100%
`
`hard yarns, such as cotton, polyester, nylon, acrylics or wool,
`for example, there is some recovery of the knit stitches to
`original dimensions after imposed forces are removed. How-
`ever, this recovery by knit stitch rearrangement generally is
`not complete because hard yams, which are not elastomeric,
`do not provide a recovery force to rearrange the knit stitches.
`As a consequence, single-knit fabrics may experience per-
`manent deformations or ‘bagging’ in certain garment areas,
`such as at the elbows of shirt sleeves, where more stretching
`occurs.
`
`To improve the recovery performance of circular, single-
`knit fabrics, it is now common to co-knit a small amount of
`spandex fiber with the companion hard yarn. As used herein,
`“spandex” means a manufactured fiber in which the fiber-
`forming substance is a long-chain synthetic polymer com-
`prised of at least 85% of a segmented polyurethane. The
`polyurethane is prepared from a polyether glycol, a mixture
`of diisocyanates, and a chain extender and then melt-spun,
`dry-spun or wet-spun to form the spandex fiber.
`For jersey knit constructions in circular knit machines, the
`process of co-knitting spandex is called “plating.” With
`plating, the hard yarn and the bare spandex yam are knitted
`parallel, side-by-side relation, with the spandex yam always
`kept on one side of the hard yarn, and hence on one side of
`the knitted fabric. FIG. 1 is a schematic illustration of plated
`knit stitches 10 wherein the knitted yam comprises spandex
`12 and a multi-filament hard yam 14. When spandex is
`plated with hard yarn to form a knit fabric, additional
`processing costs are incurred beyond the added cost of the
`spandex fiber. For example, fabric stretching and heat setting
`usually are required in the finishing steps when making
`elastic knit jersey fabrics.
`By “circular knitting” is meant a form of weft knitting in
`which the knitting needles are organized into a circular
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`knitting bed. Generally, a cylinder rotates and interacts with
`a cam to move the needles reciprocally for knitting action.
`The yarns to be knitted are fed from packages to a carrier
`plate that directs the yarn strands to the needles. The circular
`knit fabric emerges from the knitting needles in a tubular
`form through the center of the cylinder.
`The steps for making elastic circular-knit fabrics accord-
`ing to one known process 40 are outlined in FIG. 4.
`Although process variations exist for different fabric knit
`constructions and fabric end uses, the steps shown in FIG. 4
`are representative for making jersey knit elastic fabrics with
`spun hard yarns, such as cotton. The fabric is first circular
`knit 42 at conditions of high spandex draft and feed tensions.
`For example, for single-knit jersey fabrics made with bare
`spandex plated in every knit course,
`the prior-art feed
`tension range is 2 to 4 cN for 22 dtex spandex; 3 to 5 cN for
`33 dtex; and 4 to 6 cN for 44 dtex (DuPont Technical
`Bulletin L410). The fabric is knit in the form of a tube,
`which is collected under the knitting machine either on a
`rotating mandrel as a flattened tube, or in a box after it is
`loosely folded back and forth.
`In open-width finishing, the knitted tube is then slit open
`44 and laid flat. The open fabric is subsequently relaxed 46,
`either by subjecting it to steam, or by wetting it by dipping
`and squeezing (padding). The relaxed fabric is then applied
`to a tenter frame and heated (for heat setting 46) in an oven.
`The tenter frame holds the fabric on the edges by pins, and
`stretches it in both the length and width directions in order
`to return the fabric to desired dimensions and basis weight.
`This heat setting is accomplished before subsequent wet
`processing steps and, consequently, heat setting is often
`referred to as “pre-setting” in the trade. At the oven exit, the
`flat fabric is released from the stretcher and then tacked 48
`
`(sewed) back into a tubular shape. The fabric then is
`processed in tubular form through wet processes 50 of
`cleaning (scouring) and optional bleaching/dyeing, e.g., by
`soft-flow jet equipment, and then dewatered 52, e.g., by
`squeeze rolls or in a centrifuge. The fabric is then “de-
`tacked” 54 by removing the sewing thread and re-opening
`the fabric into a flat sheet. The flat, still wet, fabric is then
`dried 56 in a tenter-frame oven under conditions of fabric
`
`overfeed (opposite of stretching) so that the fabric is under
`no tension in the length (machine) direction while being
`dried at temperatures below heat-setting temperatures. The
`fabric is slightly tensioned in the width direction in order to
`flatten any potential wrinkling. An optional fabric finish,
`such as a softener, may be applied just prior to the drying
`operation 56. In some cases a fabric finish is applied after the
`fabric is first dried by a belt or tenter-frame oven, so that the
`finish is taken up uniformly by fibers that are equally dry.
`This extra step involves re-wetting the dried fabric with a
`finish, and then drying the fabric again in a tenter-frame
`oven.
`
`Heat setting “sets” spandex in an elongated form. This is
`also known as redeniering, wherein a spandex of higher
`denier is drafted, or stretched, to a lower denier, and then
`heated to a sufficiently high temperature, for a sufficient
`time,
`to stabilize the spandex at the lower denier. Heat
`setting therefore means that
`the spandex permanently
`changes at a molecular level so that recovery tension in the
`stretched spandex is mostly relieved and the spandex
`becomes stable at a new and lower denier. Heat setting
`temperatures for spandex are generally in the range of 175
`to 200° C. For the prior art process 40 shown in FIG. 4, the
`heat setting 46 commonly is for about 45 seconds or more
`at about 190° C.
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`If heat-setting is not used to “set” the spandex, after the
`fabric is knitted and released from the constraints of the
`
`circular knitting machine, the stretched spandex in the fabric
`will retract to compress the fabric stitches so that the fabric
`is reduced in dimensions compared to what those dimen-
`sions would be if the spandex were not present. Compres-
`sion of the stitches in the knitted fabric has three major
`effects that are directly related to elastic knit fabric proper-
`ties, and thereby usually renders the fabric inappropriate for
`subsequent cut and sew operations.
`First, stitch compression reduces fabric dimensions and
`increases fabric basis weight (g/m2) beyond desired ranges
`for single jersey knit fabrics for use in garments. As a result,
`the traditional
`finishing process for elastic circular-knit
`fabric includes a fabric stretching and heating step, at
`sufficiently high temperatures and sufiiciently long residence
`time, so that the spandex yarn in the knit will “set” at desired
`stretched dimensions. After heat setting, the spandex yarn
`will either not retract, or will retract only modestly below its
`heat-set dimension. Thus, the heat-set spandex yarn will not
`significantly compress the knit stitches from the heat-set
`dimensions. Stretching and heat setting parameters are cho-
`sen to yield the desired fabric basis weight and elongation,
`within relatively tight limits. For a typical cotton-jersey
`elastic single-knit, the desired elongation is at least 60%, and
`the basis weight ranges from about 140 to about 240 g/m2.
`Second, the more severe the stitch compression, the more
`the fabric will elongate on a percentage basis,
`thus far
`exceeding minimum standards and practical needs. When a
`plated knit with elastic yarn is compared with a fabric knit
`without elastic yarn, it is common for the plated elastic knit
`fabric to be 50% shorter (more compressed) than the fabric
`without elastic yarn. The plated knit is able to stretch in
`length 150% or more from this compressed state, and such
`excessive elongation is generally undesirable in jersey knits
`for cut and sew applications. This length is in the warp
`direction of the fabric. Fabrics with high elongation in length
`(stretch) are more likely to be cut irregularly, and are also
`more likely to shrink excessively upon washing. Similarly,
`stitches are compressed by spandex in the width direction, so
`that fabric width is reduced about 50% as well, far beyond
`the 15 to 20% as-knit width reduction normally encountered
`with rigid (non-elastic) fabrics.
`Third, the compressed stitches in the finished fabric are at
`an equilibrium condition between spandex recovery forces
`and resistance to stitch compression by the companion hard
`yarn. Washing and drying of the fabric can reduce the
`hard-yarn resistance, probably in part because of agitation of
`the fabric. Thus, washing and drying may permit the span-
`dex recovery forces to further compress the knit stitches,
`which can result in unacceptable levels of fabric shrinkage.
`Heat-setting the knit fabric serves to relax the spandex and
`reduce the spandex recovery force. The heat setting opera-
`tion therefore improves the stability of the fabric, and
`reduces the amount that the fabric will shrink after repeated
`washings.
`Heat setting is not used for all varieties of weft knit elastic
`fabrics. In some cases a heavy knit will be desired, such as
`in double knits/ribs and flat sweater knits. In these cases,
`some stitch compression by the spandex is acceptable. In
`other cases, the bare spandex fiber is covered with natural or
`synthetic fibers in a core-spinning or spindle-covering
`operation, so that the recovery of the spandex and resultant
`stitch compression is restrained by the covering. In still other
`cases, bare or covered spandex is plated only on every
`second or third knit course, thereby limiting the total recov-
`ery forces that compress the knit stitches.
`In seamless
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`knitting, a process wherein tubular knits are shaped for
`direct use while being knitted on special machines, the fabric
`is not heat set because dense, stretchy fabrics are intended.
`For circular-knit jersey elastic fabrics made for cutting and
`sewing, however, wherein bare spandex is plated in every
`course, heat setting is almost always required.
`Heat setting has disadvantages. Heat setting is an extra
`cost to finish knit elastic fabrics that contain spandex, versus
`fabrics that are not elastic (rigid fabrics). Moreover, high
`spandex heat-setting temperatures can adversely affect sen-
`sitive companion hard yarns, e.g., yellowing of cotton,
`thereby requiring more aggressive subsequent
`finishing
`operations, such as bleaching. Aggressive bleaching can
`negatively affect fabric tactile properties, such as “hand,”
`and usually requires the manufacturer to include fabric
`softener to counteract bleaching. Also, heat-sensitive hard
`yarns, such as those from polyacryonitrile, wool and acetate,
`carmot be used in high-temperature spandex heat-setting
`steps, because the high heat-setting temperatures will
`adversely affect such heat-sensitive yarns.
`The disadvantages of heat setting have long been recog-
`nized, and, as a result, spandex compositions that heat-set at
`somewhat lower temperatures have been identified (U.S.
`Pat. Nos. 5,948,875 and 6,472,494 B2). For example, the
`spandex defined in U.S. Pat. No. 6,472,494 B2 has a heat set
`efiiciency greater than or equal to 85% at approximately
`175—190° C. The heat set efiiciency value of 85% is con-
`sidered a minimum value for effective heat setting. It is
`measured by laboratory tests comparing the length of
`stretched spandex before and after heat setting to the before-
`stretched spandex length. While such lower heat setting
`spandex compositions provide an improvement, heat setting
`is still required, and the costs associated with it have not
`been significantly reduced.
`The traditional practice of making and heat setting circu-
`lar-knit fabrics has further disadvantages. The knit fabric
`emerges from a circular knitting machine in the form of a
`continuous tube. As the tube is formed in knitting, it is either
`rolled under tension onto a mandrel, or it is collected as a flat
`tube under the knitting machine by plaiting, or loose folding.
`In either case, the fabric establishes two permanent creases
`where the fabric tube has been folded or flattened. Although
`the fabric is “opened” by slitting the fabric tube along one
`of the creases, subsequent use and cutting of the fabric
`usually must avoid the remaining crease. This reduces the
`fabric yield (or the amount of knit fabric that can be further
`processed into garments).
`New methods are sought for making circular-knit, elastic,
`single-knit jersey fabrics that have bare spandex plated in
`every knit course, and that avoid the costs and disadvantages
`associated with heat setting.
`
`SUMMARY OF THE INVENTION
`
`We have surprisingly found that a circular knit, elastic,
`single jersey fabric that includes bare spandex plated with
`spun and/or continuous filament hard yarns can be manu-
`factured with commercially acceptable properties without a
`need for in-fabric spandex heat setting if: (1) the spandex
`draft is limited during the knitting process; and (2) certain
`desired single knit jersey fabric parameters are maintained.
`“Hard yarns” include spun staple yarns, spun staple and
`continuous filament yarns and continuous filament yarns.
`The first aspect of the invention is a method for making
`a circular knit, single jersey fabric in which bare spandex
`yarn from 17 to 33 dtex, preferably from 22 to 33 dtex, is
`plated with a hard yarn of spun and/or continuous filament
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`5
`yarn, or blends thereof, with yarn count (Nm) from 35 to 85,
`preferably from 44 to 68, most preferably from 47 to 54.
`Preferably, hard yarn is spun staple yarn of cotton or cotton
`blended with synthetic fibers or yarn. Other natural and
`synthetic fibers may be selected for the hard yarn, including
`nylon, polyester, acrylics and wool, for example.
`The spandex and the hard yam are plated in every knit
`course. The circular knit, single jersey fabric produced by
`this knitting method has a cover factor of from 1.3 to 1.9.
`During the knitting, the draft on the spandex feed is con-
`trolled so that the spandex yarn is drafted no more than 2><
`its original length when knit to form the circular knit, single
`jersey fabric.
`In addition, the knit fabric is finished and dried without
`heat setting the fabric or the spandex within the fabric. Thus,
`the fabric is dried at temperatures below the heat setting
`temperature of the spandex. Finishing may comprise one or
`more steps, such as cleaning, bleaching, dyeing, drying, and
`compacting, and any combination of such steps. Preferably,
`the finishing and drying are carried out at one or more
`temperatures below 160° C. Drying or compacting is carried
`out while the knit fabric is in an overfeed condition in the
`
`warp direction.
`The resulting circular knit, elastic, single jersey knit fabric
`preferably has a spandex content of from 3.5% to 14% by
`weight based on the total fabric weight per square meter,
`more preferably from 5% to 10% by weight based on the
`total fabric weight per square meter. In addition, such fabric
`preferably has a cover factor of 1.4.
`The second and third aspects of the invention are the
`circular knit, elastic, single jersey fabrics made according to
`the inventive method, and garments constructed from such
`fabrics. The fabric produced by the inventive method pref-
`erably is formed with hard yarns of cotton or cotton blends
`and has a basis weight of 140 to 240 g/m2 most preferably
`of 170 to 220 g/m2. The fabric preferably also has an
`elongation of 60% or more, preferably from 60% to 130%
`in the length (warp) direction, and a shrinkage after washing
`and drying of about 7% or less, preferably less than 7% in
`both length and width. Garments may include underwear,
`T-shirts, and top-weight garments.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 illustrates plated knit stitches comprising a hard
`yarn and spandex;
`FIG. 2 is a schematic diagram of a portion of a circular
`knitting machine fed with a spandex feed and a hard yarn
`feed;
`FIG. 3 illustrates a series of single jersey knit stitches and
`highlights one stitch of stitch length “L”;
`FIG. 3A shows the single stitch of FIG. 3 straightened to
`illustrate stitch length “L”;
`FIG. 4 is a flow chart showing prior art process steps for
`making circular-knit, elastic, single-knit jersey fabrics that
`have bare spandex plated in every knit course; and
`FIG. 5 is a flow chart showing the inventive process steps
`for making circular-knit, elastic, single-knit jersey fabrics
`that have bare spandex plated in every knit course.
`While the invention will be described in connection with
`
`preferred embodiments below, it is to be understood that the
`invention is in no way intended to be limited by such
`description. On the contrary,
`it
`is intended to cover all
`alternatives, modifications and equivalents as may be
`included within the true spirit and scope of the invention as
`defined by the claims appended hereto.
`
`6
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`is circular knitting, and in
`The subject of this patent
`particular the manufacture of specific knit elastic fabrics for
`subsequent ‘cut and sew’ use. Regarding circular knitting,
`FIG. 2 shows in schematic form one feed position 20 of a
`circular knitting machine having a series of knitting needles
`22 that move reciprocally as indicated by the arrow 24 in
`response to a cam (not shown) below a rotating cylinder (not
`shown) that holds the needles. In a circular knitting machine,
`there are multiple numbers of these feed positions arranged
`in a circle, so as to feed individual knitting positions as the
`knitting needles, carried by the moving cylinder, are rotated
`past the positions.
`For plating knit operations, a spandex yam 12 and a hard
`yarn 14 are delivered to the knitting needles 22 by a carrier
`plate 26. The carrier plate 26 simultaneously directs both
`yarns to the knitting position. The spandex yam 12 and hard
`yarn 14 are introduced to the knitting needles 22 at the same
`or at a similar rate to form a single jersey knit stitch 10 like
`that shown in FIG. 1.
`
`The hard yam 14 is delivered from a wound yam package
`28 to an accumulator 30 that meters the yarn to the carrier
`plate 26 and knitting needles 22. The hard yam 14 passes
`over a feed roll 32 and through a guide hole 34 in the carrier
`plate 26. Optionally, more than one hard yarn may be
`delivered to the knitting needles via different guide holes in
`the carrier plate 26.
`The spandex 12 is delivered from a surface driven pack-
`age 36 and past a broken end detector 39 and change of
`direction roll(s) 37 to a guide slot 38 within the carrier plate
`26. The feed tension of the spandex 12 is measured between
`the detector 39 and drive roll 37, or alternatively between the
`surface driven package 36 and roll 37 if the broken end
`detector is not used. The guide hole 34 and guide slot 38 are
`separated from one another in the carrier plate 26 so as to
`present the hard yarn 14 and spandex 12 to the knitting
`needles 22 in side by side, generally parallel
`relation
`(plated).
`The spandex preferably is a commercially available elas-
`tane product for circular knitting, such as Lycra® types
`T162, T169, and T562.
`The spandex stretches (drafts) when it is delivered from
`the supply package to the carrier plate and in mm to the knit
`stitch due to the difference between the stitch use rate and
`
`the feed rate from the spandex supply package. The ratio of
`the hard yam supply rate (meters/min) to the spandex supply
`rate is normally 2.5 to 4 times (2.5>< to 4x) greater, and is
`known as the machine draft. This corresponds to spandex
`elongation of 150% to 300%, or more. The feed tension in
`the spandex yarn is directly related to the draft (elongation)
`of the spandex yarn. This feed tension is typically main-
`tained at values consistent with high machine drafts for the
`spandex.
`We have found that improved results are obtained when
`the total spandex draft, as measured in the fabric, is kept to
`about 2x or less. This draft value is the total draft of the
`
`spandex, which includes any drafting or drawing of the
`spandex that is included in the supply package of as-spun
`yarn. The value of residual draft from spinning is termed
`package relaxation, “PR”, and it typically ranges from 0.05
`to 0.15 for the spandex used in circular knit, elastic, single
`jersey fabrics. The total draft of the spandex in the fabric is
`therefore MD*(1+PR), where “MD” is the knitting machine
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`draft. The knitting machine draft is the ratio of hard yarn
`feed rate to spandex feed rate, both from their respective
`supply packages.
`Because of its stress-strain properties, spandex yarn drafts
`(draws) more as
`the tension applied to the spandex
`increases; conversely, the more that the spandex is drafted,
`the higher the tension in the yarn. A typical spandex yarn
`path, in a circular knitting machine, is schematically shown
`in FIG. 2. The spandex yarn 12 is metered from the supply
`package 36, over or through a broken end detector 39, over
`one or more change-of-direction rolls 37, and then to the
`carrier plate 26, which guides the spandex to the knitting
`needles 22 and into the stitch. There is a build-up of tension
`in the spandex yarn as it passes from the supply package and
`over each device or roller, due to frictional forces imparted
`by each device or roller that touches the spandex. The total
`draft of the spandex at the stitch is therefore related to the
`sum of the tensions throughout the spandex path.
`The spandex feed tension is measured between the broken
`end detector 39 and the roll 37 shown in FIG. 2. Altema-
`
`tively, the spandex feed tension is measured between the
`surface driven package 36 and roll 37 if the broken end
`detector 39 is not used. The higher this tension is set and
`controlled, the greater the spandex draft will be in the fabric,
`and vice versa. The prior art teaches that this feed tension
`should range from 2—4 cN for 22 dtex spandex, and from 4—6
`cN for 44 dtex spandex in commercial circular knitting
`machines. With these feed tension settings and the additional
`tensions imposed by subsequent yarn-path friction, the span-
`dex in commercial knitting machines will be drafted sig-
`nificantly more than 2><.
`the ways that
`This invention does not anticipate all
`spandex friction can be minimized between the supply
`package and the knit stitch. The method requires, however,
`that friction be minimized to keep the spandex feed tensions
`sufiiciently high for reliable spandex feeding when the
`spandex draft is 2x or less.
`After knitting a circular knit, elastic, single jersey fabric
`of plated spandex with hard yarn per the method of this
`invention, the fabric is finished in either of the alternate
`processes 60 illustrated diagrammatically in FIG. 5. Drying
`operations can be carried out on circular knit fabric 62 in the
`form of an open width web (top row of diagram, path 6311),
`or as a tube (bottom row of diagram, path 63b). For either
`of these paths, wet finishing process steps 64 (such as
`scouring, bleaching and/or dyeing) are carried out on the
`fabric while it is in tubular form. One form of dyeing, called
`soft-flow jet dyeing, usually imparts tension and some
`length deformation in the fabric. Care should be taken to
`minimize any additional tension applied during fabric pro-
`cessing and transport from wet finishing to the dryer, and
`also enable the fabric to relax and recover from such
`
`wet-finishing and transport tensions during drying.
`Following wet finishing process steps 64, the fabric is
`dewatered 66, such as by squeezing or centrifuging. In
`process path 6311, the tubular fabric is then slit open 68
`before it is delivered to a finish/dry step 70 for optional
`finish application (e.g., softener by padding) and subsequent
`drying in a tenter-frame oven under conditions of fabric
`length overfeed. In process path 63b, the tubular fabric is not
`slit open, but is sent as a tube to the finish/dry step 70.
`Finish, such as softener, can be optionally applied by pad-
`ding. The tubular fabric is sent through a drying oven, e.g.,
`laid on a belt, and then to a compactor to separately provide
`fabric overfeed. A compactor commonly uses rolls to trans-
`port the fabric, usually in a steam atmosphere. The first
`roll(s) is driven at a faster speed of rotation than the second
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`65
`
`8
`roll(s) so that the fabric has an overfeed. Generally, the
`steam does not “re-wet” the fabric so that no additional
`
`drying is required after compacting.
`The drying step 70 (path 6311) or the compacting step 72
`(path 63b), is operated with controlled, high fabric overfeed
`in the length (machine) direction so that the fabric stitches
`are free to move and rearrange without tension. A flat,
`non-wrinkled or non-buckled fabric emerges after drying.
`These techniques are familiar to those skilled in the art. For
`open width fabrics, a tenter-frame is used to provide fabric
`overfeed during drying. For tubular fabrics, forced overfeed
`is typically provided in a compactor 72, after belt drying. In
`either open-width or tubular fabric processing, the fabric
`drying temperature and residence time are set below the
`values required to heat set the spandex.
`The structural design of a circular knit fabric can be
`characterized in part by the “openness” of each knit stitch.
`This “openness” is related to the percentage of the area that
`is open versus that which is covered by the yarn in each
`stitch (see, e.g., FIGS. 1 and 3), and is thus related to fabric
`basis weight and elongation potential. For rigid, non-elastic
`weft knit fabrics, the Cover Factor (“Cf”) is well known as
`a relative measure of openness. The Cover Factor is a ratio
`and is defined as:
`
`Cf:% (tex))L
`
`where tex is the grams weight of 1000 meters of the hard
`yarn, and L is the stitch length in millimeters. FIG. 3 is a
`schematic of a single knit jersey stitch pattern. One of the
`stitches in the pattern has been highlighted to show how the
`stitch length, “L” is defined. For yarns of metric count Nm,
`the tex is 1000)Nm, and the Cover Factor is alternatively
`expressed as follows:
`c,e%(1ooo/Nm))L.
`
`We have found that commercially useful circular knit,
`elastic, single jersey fabrics plated from bare spandex and a
`hard yarn can be made without heat setting if the spandex
`draft is kept about 2x or less, and if the knit fabric is
`designed and manufactured within the following preferred
`limits:
`
`The Cover Factor, which characterizes the openness of the
`knit structure, is between 1.3 and 1.9, and is preferably
`1.4;
`The hard yarn count, Nm, is from 35 to 85, preferably
`from 44 to 68, and most preferably from 47 to 54;
`The spandex has 17 to 33 dtex, preferably 22 to 33 dtex;
`Preferably, the content of spandex in the fabric, on a %
`weight basis, is from 3.5% to 14%, and is most pref-
`erably from 5% to 10%;
`The knit fabric so formed has a shrinkage after washing
`and drying of about 7% or less, preferably less than 7%
`in both the length and width directions;
`The knit fabric has an elongation of 60% or more,
`preferably from 60% to 130%,
`in the length (warp)
`direction; and
`Preferably, the hard yarn is spun staple yarn of cotton or
`cotton blended with synthetic fibers or yarns.
`While not wishing to be bound by any one theory, it is
`believed that the hard yarn in the knit structure resists the
`spandex force that acts to compress the knit stitch. The
`effectiveness of this resistance is related to the knit structure,
`as defined by the Cover Factor. For a given hard yarn count,
`Nm, the Cover Factor is inversely proportional to the stitch
`length, L. This length is adjustable on the knitting machine,
`and is therefore a key variable for control.
`
`OOOOO9
`
`000009
`
`

`
`US 7,117,695 B2
`
`9
`Because the spandex is not heat set in the process of the
`invention,
`the spandex draft should be the same in the
`circular knit, elastic, single jersey as-knit fabric, the finished
`fabric, or at fabric-processing steps in-between, within the
`limits of measurement error.
`
`For circular knit, elastic, single jersey fabric, the appro-
`priate gauge of knitting machine is selected according to
`prior art relationships between hard yarn count and knitting
`machine gauge. Choice of gauge can be used to optimize
`circular knit, elastic, single jersey basis weight, for example.
`The benefits of this invention are evident when the prior
`art process shown diagrammatically in FIG. 4, is compared
`with the inventive process shown diagrammatically in FIG.
`5. Traditional knitting and finishing require more process
`steps, more equipment, and more labor-intensive operations
`than does either alternative method of the invention shown
`
`in FIG. 5. Further, by eliminating high-temperature heat set
`previously required (see FIG. 4),
`the inventive process
`reduces heat damage to fibers like cotton, requires less or no
`bleaching, and thus improves the ‘hand’ of the finished
`fabric. As a further benefit, heat sensitive hard yarns can be
`used in the invention process to make circular knit, elastic,
`single jersey fabrics, thus increasing the possibilities for
`different and improved products.
`The use of a softener is optional, but commonly a softener
`will be applied to the knit fabric to further improve fabric
`hand, and to increase mobility of the knit stitches during
`drying. Softeners such as SURESOFT or SANDOPERM
`SEI are typical. The fabric may be passed through a trough
`containing a liquid softener composition, and then through
`the nip between a pair a pressure rollers (padding rollers) to
`squeeze excess liquid from the fabric.
`Also surprisingly, circular knit, elastic, single jersey fab-
`rics knitted by the method of the invention and collected by
`folding (plaiting), do not crease to the same extent as prior
`art circular knit single jersey fabrics. Fewer or less visible
`fold creases in the finished fabric can result in an increased
`
`yield for cutting and sewing the fabric into garments. Also
`unexpectedly, the circular knit, elastic, single jersey fabrics
`of the invention have significantly reduced skew during
`process in either open-width or tubular finishing processes,
`compared to prior art fabrics. With excess skew or spirality,
`fabrics are diagonally deformed and courses are “on the
`bias”, and are unacceptable. Garments made with skewed
`fabric will twist on the body.
`The following examples demonstrate the invention and its
`benefits. The invention is capable of other and different
`embodiments, and its several details are capable of modifi-
`cations in various apparent respects, without departing from
`the scope and spirit of the present invention. Accordingly,
`the examples are to be regarded as illustrative in nature and
`not as restrictive.
`
`EXAMPLES
`
`Fabric Knitting and Finishing
`
`Circular knit elastic single jersey fabrics with bare span-
`dex plated with hard yarn for the examples were knit on Pai
`Lung Circular Knitting Machines,
`ei