Treating fabrics
FIELD OF THE INVENTION 
     The present invention relates to a method and apparatus for the treatment of cotton fabrics, and is applicable to knit fabrics having a cotton content of between 40-100%. It is particularly effective for the treatment of insulating fabrics known as thermal knits. 
     BACKGROUND OF THE INVENTION 
     The conventional techniques for treating knitted fabrics in tubular form prior to cutting and sewing the fabrics into garments provides fabrics having residual shrinkage in the range of 25%. When the fabric is formed into garments and sold to the public, the fabric is normally oversized to some degree and as the garment is subjected to normal wear and washing, it shrinks. A tubular knit fabric is designed to stretch to conform to the body of the wearer, and the fact of cotton fabric shrinkage has been an accepted characteristic which the public must tolerate when seeking the advantage of cotton knit fabrics. 
     To control shrinkage, resins are applied to the fabric either during the fabric finishing operation or during the yarn preparation phase of the operation. Such treatment is expensive and eventually adversely affects the longevity of the fabric and detracts from the soft &#34;hand&#34; of the fabric. Furthermore, most resins contain formaldehyde which is deemed unsafe at certain levels in the workplace and on the product. 
     During the preparation of the knitting yarn and during the knitting operation, lubricants and waxes are used and other foreign matter may become entrapped in the fabrics which preferably should be removed before the fabric is made into garments. Commonly the fabric is separated into batches which are washed and dried individually in tumble washers and dryers. The handling of the batches of fabric while wet tends to impart stresses and strains to the fabric tubes, which strains may or may not be relieved during subsequent processing operations, and the resulting fabrics are characterized by shrinkage which is not uniform and which may vary in residual shrinkage from as low as 10% to as high as 25%. 
     In the case of thermal knit fabrics, the fabric is characterized by air-entrapping cells or pockets on one or both sides which provide dead air spaces in the fabric. These cells are produced by the knit construction during knitting of the fabric and are disposed in longitudinal and transverse rows. Known as &#34;waffle knit&#34; fabric, the development of thermal knit fabric since 1951 is briefly described in U.S. Pat. No. 4,678,693, the disclosure of which is incorporated herein by reference. 
     In a common type of thermal fabric, the knit construction provides in the neighborhood of 5.25 cells per inch in both the lengthwise and transverse direction and a typical density in the range of 51/2 ounces per square yard. To counteract the effect of the residual shrinkage, the fabric has typically been subjected to compaction and setting with formaldehyde resin treatment. 
     In efforts to obtain more uniformity, the batch treatment has been replaced by continuous treatment, but it has been found that the conventional continuous treatment has resulted in residual shrinkage in the range of 25%. Attempts to reduce the shrinkage without chemical treatment of the fabric have previously been directed to the final stages of the finishing operations, specifically during the drying operation following the washing and scouring and other chemical treatment of the fabric after it comes from the knitting machines. Although such treatments reduce the residual shrinkage to some degree, none has proved entirely satisfactory. 
     SUMMARY OF THE PRESENT INVENTION 
     The present invention provides an improved method and a novel combination of apparatus which provide a finished fabric having a uniformly low residual shrinkage in the range of approximately 5-8%. 
     The method of the present invention contemplates the treatment of a continuous length of tubular knit fabric in substantially continuous operations of washing, rinsing, and drying in two stages with moisture control of the fabric prior to and during the final drying stage, all under controlled conditions of fabric relaxation. 
     More specifically, the present invention contemplates in the washing and rinsing operation handling of the fabric with a minimized application of tension or other stress to the fabric so as to subject the fabric to agitation in a bath of liquid without substantial tension or other stress to enable thorough relaxation of the fibers and yarns of the fabric to maximize shrinkage of the fabric while it is saturated in a liquid bath. 
     The saturated fabric is removed from the liquid bath with minimum application of tension and is flattened while still saturated with free and bound liquid so that it may thereafter be subjected to extraction in open tubular width to remove the free liquid. The fabric is then submitted to two stages of the drying, the first stage being air drying in open tubular width and the second stage being tumble-drying in open tubular width with a positive control of the moisture content of the fabric as it enters the tumble-drying stage and throughout the tumble-drying stage of the two-stage drying operation. 
     Specifically, in the tumble-drying stage of the operation, the fabric is introduced into the tumble dryer at 40% moisture content and the heat and moisture content of the drying medium is controlled throughout the tumble drying operation so as to reduce the moisture content of the fabric in controlled steps as the fabric advances through the tumble-drying operation, so that it is discharged at a moisture content of approximately 5% with residual shrinkage less than 8%. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects of the invention are more fully set forth hereinafter in the following description taken in conjunction with the attached drawings, wherein: 
     FIG. 1 is a diagram of the processing steps embodied in the method of the present invention; 
     FIG. 2 is a drawing of apparatus for saturating the fabric and introducing it into the first washing stage; 
     FIG. 3 is a fragmentary view of a relaxing and washing range showing the transfer of the fabric from one washing stage to the next; 
     FIG. 4 is a fragmentary view illustrating the removal of the fabric from the final washing stage and the depositing of the fabric in a carrier for transport to a next station for flattening; 
     FIG. 5 is a fragmentary plan view of the station showing a padder in which the fabric tube is flattened and squeeze-dried; 
     FIG. 6 is a schematic view of the first stage of the drying; 
     FIG. 7 is a view of apparatus intermediate the first and second stages of the drying for controlling the moisture content of the fabric, and specifically for uniformly restoring the fabric to a 40% moisture content; and 
     FIG. 8 is a diagrammatic view of the tumble dryer, with a portion magnified to illustrate the tumbling effect achieved in the apparatus. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to the drawings, FIG. 1 is a block diagram of the operational steps embodied in the method of the present invention. As described more fully hereinafter, the fabric from the knitting machine is first saturated and then caused to flow through a sequence of baths in a relaxing and washing range. In each bath the fabric is consolidated and caused to flow through the bath with the liquid so as to be immersed in the liquid throughout its travel. There is a longitudinal flow of liquid in the baths which assists the fabric to advance from the entrance end to the exit end of each bath. In its travel in the baths, the fabric is pushed through the bath rather than pulled through the bath, and, accordingly, the fabric tends to fold up upon itself in a series of laps which are folded back against themselves as they are carried through the bath in the liquid medium. 
     At the exit end of each bath, the fabric is allowed to unfold, and as it is drawn from the bath it may open out and be withdrawn from the bath and fed to the next bath in the sequence in a somewhat open state, and when it is fed into the next bath it is again caused to double up on itself. 
     In passing through a sequence of baths, the baths preferably also perform the function of scouring the fabric to remove any wax and lubricants applied during the previous operations in which the cotton fibers are formed into yarns and the yarns are formed into fabrics. The initial baths in the sequence include scouring compositions which are effective to scour the fabric. Suitable fabric softeners and wetting agents may be applied separately or incorporated in the scouring compositions to enhance the scouring operation and also to enhance the ability of the fibers in the fabric to completely relax. Removal of the waxes and lubricants, and any other foreign matter entrained in the yarns assists in the relaxation of the fabric by removing the impediments to relaxation which the foreign matter may represent. 
     During the scouring treatment, the cotton fibers become saturated and swell, becoming shorter to assist in the relief of residual stresses which may be in the fabric as a result of the previous processing operations. During the immersion of the fabric in the liquid flow, the fabric achieves maximum shrinkage and relaxation. The relaxed fabric is then advanced to the next operation with care being taken to minimize imparting stresses to the fabric as would result from stretching. Of course, any handling of the fabric imparts stresses to it, but the transport of the fabric to the next stage is accomplished in a gentle fashion to avoid prolonged exposure to stretching or stress. 
     In the next operation, the fabric tube is flattened and opened to its full width without stretching, although some degree of transverse stretching must occur in order to achieve the full opening of the fabric tube. During the flattening, the fabric is maintained saturated with liquid so as to facilitate the flattening of the fabric with minimum application of stress. The flattened fabric is then put through apparatus to express free moisture from the fabric. The extraction of the free moisture in the tube may be performed by hydraulic, centrifugal, bubble or hydro extraction. In the present case, the apparatus comprises a padder with squeeze rolls. The rate of feed of the fabric through the squeeze rolls is coordinated with the rate of travel of the feed rolls to avoid application of longitudinal stress to the fabric as it is squeezed. The longitudinal stitch count at the exit end of the padder approximates the longitudinal stitch count at the entrance end, evidencing the absence of stretching in this operation. 
     By extracting the excess moisture from the fabric, the weight of the free moisture is removed from the fabric so that it may be fed into the next stage, the hot air drying stage, with minimum stretching. The hot air drying is accomplished between a pair of foraminous conveyors which support the fabric as it is subjected to the hot air in a fashion to assure freedom to contract and shrink at the same time to remove a large percentage of the moisture content to a condition of dryness where the moisture content is substantially less than 40%, for example approximately 20%. The dried fabric is then fed into a tumble dryer through a humidfying apparatus which stabilizes the moisture content of the fabric to approximately 40%, which has been found to be appropriate for achieving maximum effectiveness of fabric treatment in the tumble drying operation. 
     In the tumble drying operation illustrated in FIG. 8, the fabric is carried on a conveyor and is subjected to forceful jets of air which cause the fabric to impinge against an overlying baffle. In the present instance, as described more fully hereinafter, the tumble dryer is compartmentalized into sequential sections and the heat and moisture content of the air supplied to each section is precisely controlled to obtain a moderate reduction in the moisture content of the fabric tube from the initial 40% moisture content at the entrance end of the tumble dryer to a final moisture content in the neighborhood of 5-8%. By gradually reducing the moisture content, the residual stresses in the fabric are released and relieved so that the fabric exiting from the tumble dryer may be collected in a fully relaxed state which is not subject to any substantial further shrinking. 
     In the treatment of the fabric, the fabric from the knitting machines is brought to the first station as shown in FIG. 2, for example in a carrier 21, from which it is withdrawn by pull rolls 22 and a feed reel 23 into the upright receiving leg of a J-box 24 having a liquid level, as indicated at 25. The J-box is filled with liquid, for example by a spray 26, preferably including a wetting agent, to insure saturation of the tubular fabric introduced from the feed reel 23. The tubular fabric accumulates in the curved bottom of the J-box as indicated at 20a and is discharged through an orifice 28 into a receiving tank 29 at the feed end of a relaxing and washing range designated generally at 31. 
     In the illustrated embodiment of the invention, the relaxing and washing range is modeled after a unit manufactured in West Germany by Machinenfabrik Max Goller and identified as Model SV. The Model SV apparatus has been modified in substantial respects in order to perform the necessary operations found to be desirable to obtain maximum shrinkage of the fabric during the first stage without subjecting the fabric to stresses and strains which detract from the desired fabric treatment as set forth herein. 
     In setting up the operation of the washing range 31, the tubular fabric is allowed to accumulate in the receiving tank 29 so as to insure a dwell time of the fabric in the J-box which assures thorough penetration of the wetting agent into the fabric and saturation of the tubular fabric. The fabric is supplied in open-width folds, and care is exercised to avoid twisting the fabric tube as it passes through the J-Box 24 into the receiving tank 29. When a sufficient length of tubular fabric has accumulated in the bottom of the J-box and in the receiving tank 29, the leading end of the fabric is drawn up through a guide loop 32 over a feed pulley 33 and a knot detector 34 into feed rolls 35, the nip of which is regulated by a pressure controller 36 to control the amount of slippage between the fabric tube and the feed rollers. The tubular fabric is not twisted, and the guide loop 32 is sufficiently above the surface of the liquid in the receiving tank 29 so that the tube inherently balloons out as it leaves the tank and passes through the guide loop 32 in opened-out condition. The feed pulley 33 and feed rolls 35 flatten the opened-out tube and compact it, thereby providing a gentle &#34;working&#34; of the fabric to relieve stress. The controller 36 is responsive to the accumulation of material in the receiving tank 29 so as to maintain the desired quantity of material between the pull rolls 22 and the feed rolls 35. 
     From the feed rolls 35 the compacted tube of material, indicated at 20b, is introduced into the entrance portal 41 of a tubular conduit 42 extending from the feed rolls 35 to the entrance end of the first bath section 43 of the range. The entrance portal 41 of the conduit 42 has an annular jet insert 45 and a liquid inlet 46 to introduce a carrier liquid into the portal 41 surrounding the annular jet 46 at a sufficient pressure to cause the liquid to be directed inwardly toward the center of the conduit 43 and to flow longitudinally into the conduit 42. The flow in the conduit 42 has a rate of flow greater than the rate of feed of the tubular material at 20b from the feed rolls 35 into the portal. The effluent from the incoming annular jets entrains the compacted fabric tube 20b and carries it into the conduit 42 in a flow of liquid. The flow resistance in the conduit is sufficient to insure that there is a flowing body of liquid within the conduit through which the fabric tube passes. The operation of the feed rolls 35 is such as to push the fabric into the flow of liquid and cause the fabric to be advanced by the pushing by the fabric following it rather than by pulling. In this fashion, the fabric tube is compressed and compacted while saturated in the body of liquid, thereby further &#34;working&#34; the fabric to facilitate the release of any stresses or strains which may have been built into the fabric during the previous operations. 
     At the opposite end of the range 31, the conduit 42 empties into a bath 43, and the liquid flowing through the conduit carries with it the fabric tube. In start-up, the fabric in the bath 43 is held against withdrawal so that the fabric bunches up upon itself in overlapping folds as indicated at 20c in FIG. 2. In order to maintain the material 20c beneath the surface of the bath 43, longitudinal guide rods 48 are placed in the bath subjacent the surface, and these guide rods are preferably comprised of polytetrafluoroethylene (Teflon™) and oscillated longitudinally so as to facilitate and assist in the migration of the folds of material 20c leftward toward the exit end of the bath 43. The liquid flowing through the conduit 42 into the entrance end of the bath 43 provides a leftward flow of liquid within the bath, as seen in FIG. 2, which assists in the migration of the fabric from the entrance end at 47 to the exit end. The exit end of the bath 43 is shown in FIG. 3, and the fabric is advanced at the exit end into a tank 49 similar to the receiving tank 29. 
     At the exit end, the tank 49 also serves as the entrance end for a succeeding section of the washing range. To this end, there is a guide loop 32a through which the fabric tube is drawn upwardly by feed pulleys 33a through a knot detector 34a, feed rolls 35a, which are controlled at 36a to advance the material into the portal 41a of the next section of the machine. Care is exercised to avoid twisting the tubular fabric, so that it may balloon out as it is drawn out of the tank 49 through the loop 32a. 
     In the preferred embodiment of the invention, the washing range 31 has eight baths, each within a separate section of the machine so that the fabric tube is caused to travel sequentially through all eight baths. In the initial bath, the liquid bath includes washing and scouring components which serve to thoroughly cleanse the fabric tube and cause the removal of any waxes, lubricants or other foreign matter which may be entrained in the fabric. Preferably, the scouring bath is controlled to a resident temperature of 200° F. As shown in FIG. 3, water is withdrawn from the tank 49 through a drain indicated at 51 and is directed rearwardly through a conduit 52 to a pump 53, a mixing control 54, a filter 55 and a steam heat exchanger 56 to feed the inlet 46 of the inlet portal 41 for the conduit 42. Thus, the liquid in the bath in each section is recirculated and may be replenished and/or enriched through the mixing control 54. The mixing control 54 may introduce fresh water or fresh cleansing components into the recirculating flow, and may also use washing or rinsing liquid from subsequent sections in lieu of fresh water in order to conserve water and energy. The liquid levels in the apparatus are maintained by discharge of a similar quantity of liquid, preferably from the receiving tank 29. In this way, there is an overall countercurrent flow of treating liquid within the washing range. 
     FIG. 4 illustrates the arrangement for withdrawing the fabric from the washing range 31. To this end, the final bath 43x discharges the fabric, as indicated at 20e, from under the guide bars 48x into a scray 49x. From the scray 49x, the fabric is withdrawn through a guide loop 32x, around a feed pulley 33x, through feed rollers 35x and around the upper nip roller 36x of the feed rollers 35x through a knot detector 34x over a feed pulley 58 around feed reels 59 into a carrier 61, the fabric, as indicated at 20f, being fully saturated. To facilitate folding, a swinging plaiter 62 may be used below the feed reels 59 to deposit the fabric into the carrier 61. 
     The fabric in the carrier 61 has been thoroughly scoured and rinsed, and if chemical additives are required in the fabric, they may be added in one of the baths through which the fabric is passed. The temperature and the composition of the liquid in each of the baths is monitored and adjusted to insure maximum efficiency in the scouring and rinsing operations so that the fabric in the carrier 61 is subjected to its maximum shrinkage and is relaxed to introduction of stress or strains in the fabric. It should be noted that in the tanks 29 and 49, the fabric is free to open out. As the fabric is drawn up through the loops 32 and 32a, it tends to balloon below the loops so as to provide further &#34;working&#34; of the fabric as it is transferred from one bath to the next and from one section of the range to the next. 
     In the present instance, there is a series of eight separate baths. The accumulation of the fabric in each of the baths of the several sections of the washing range 31 provides a dwell time on the order of 20 minutes in each of the first four baths, and 10 minutes in each of the final four baths. The dwell time is set up during the initial loading of the range 31, with twice the length of fabric in the first four sections than in the final four sections. In the present case, all sections are of the same length, so that the fabric is more densely packed into the first four baths than in the final four baths. In other words, any segment of the fabric 20 introduced into the washing liquid at 20a will exit the washing range at 20e approximately 120 minutes later. 
     Since the fabric shrinks as it travels through the range 31, the feed rolls 35 accommodate to the shrinkage by releasing the pressure through the controller 36. The shrinkage in the relaxing and washing range will normally approximate 20%, i.e. if the longitudinal cell count of the thermal fabric at 20 is 5.25 cells per inch, the cell count increases to 5.75 after the first bath and gradually increases to over 6.00 as the foreign matter is scoured from the fabric and the fabric is subjected to soft rinsing in final baths. The crosswise cell count may increase to some degree as the fabric travels through the series of baths, but the lateral contractile forces in the knitted tube are not as dominant as the longitudinal contractile forces. 
     The fabric 20f in the carrier 61 is transferred to the next station where it is flattened in open tubular width and squeeze dried. As shown in FIG. 5, the fabric 20f is fed through a padder which is operated at a rate to avoid application of longitudinal tension to the fabric tube. The fabric tube is fed over a floating shoe 63 which is positioned between counter-rotating rolls 64 which advance the fabric over the shoe at a rate which does not stretch it longitudinally. Beyond the shoe, the fabric at 20g is sprayed with a liquid by a spray manifold 65 to restore full saturation to the fabric in advance of the squeeze rolls 66 which deposit the fabric on a slow moving conveyor 67 in overlapping folds for ultimate depositing in a carrier 68 (not shown in FIG. 5). The squeeze rolls 66 extract the free water from the fabric so that the fabric deposited on the conveyor 67 is saturated, but without substantial free water therein. The tubular fabric in the carrier 68 is flattened so that the fabric consists of the two layers of the tube in open tubular width. 
     The carrier 68 transfers the fabric to the entrance end of an air dryer 71, as shown in FIG. 6. The fabric is withdrawn from the carrier 68 as shown at 20h and is deposited on the lower belt 73 of the air dryer. A hold-down belt 74 overlies the belt 73 and travels concurrently with the belt 73 to advance the fabric loosely deposited on the belt through the air dryer housing in which air is impinged against the fabric on the carrier belt 73 from both sides and is discharged laterally so as to evaporate the moisture contained in the fabric. 
     The air dryer 71 is designed to receive a plurality of flattened tubes side by side so as to treat the tubes concurrently and reduce their moisture content to the range of 20-40%, preferably drying the tubes to about 20% moisture content. The conveyors 73 and 74 deposit the fabric tubes on a cooling belt 75. The apparatus shown in FIG. 6 is a dryer made in Switzerland by Santex AG and which has been modified to minimize the longitudinal tension applied to the tubes by the dryer at the entrance and exit ends. 
     From the cooling belt 75, the dried fabric at 20j is fed into a steam chest 81 on a foraminous conveyor 82 (FIG. 7). The tube 20j is deposited on the conveyor in loose folds and is carried through the steam chest 81 where it is subjected to steam and water sprays at 83 which are designed to stabilize the moisture content of the fabric exiting the steam chamber at 20k at a uniform moisture content of approximately 40% moisture content. The sprays 83 are very very fine so as to create a mist enveloping the fabric on the top and bottom. Steam coils 85 within the chest 81 generate a steam atmosphere which restores the moisture content of the fabric to the desired level. A fabric of this moisture content is capable of further relaxation and shrinkage when subjected to agitation under dry heat. In this condition, the fabric from the steam chamber at 20k is deposited on a perforated tray conveyor 92 of a tumble dryer apparatus 91. 
     The fabric 20k is deposited in overlapping folds on the conveyor 92 so that the fabric is free to be tumbled on the conveyor as it is conveyed through the several sections of the tumble dryer 91. The tumble dryer 91 has a plurality of sections through which the conveyor 92 carries the fabric. In each section of the dryer 91, as shown in the enlarged portion of FIG. 8, jets of air are directed upwardly through the conveyor to impinge against the underside of the fabric 20m  reposed on the conveyor 92. Overlying the path of the conveyor there is a saw-tooth perforated baffle plate 93 which is sufficiently close to the conveyor 92 that the air jets directed upwardly through the conveyor cause the fabric 20m to impinge against the undersurface of the baffles 93 and the saw-tooth configurations of the baffles bounce the fabric down against the conveyor 92 so as to effect a tumbling action on the fabric as it is conveyed through the dryer in a continuous length. 
     Each section of the dryer has the humidity and temperature in the air jets controlled so that the drying effect of each section is likewise controlled to provide a low gradient in the drying effect as the fabric tube is conveyed through the successive sections. As a result, the dryer achieves a uniform gradual drying of the several fabric tubes traveling through the dryer side-by-side. Since the fabric tubes entering the dryer are uniformly stabilized at a 40% moisture content, the fabric tubes exiting the dryer are uniformly dried to the desired final moisture content for subsequent operations. The fabric exiting the dryer at 20p exhibits the fully pre-shrunk characteristics which have been found desirable for fabrication into garments which do not need to be further shrunk for distribution and sale. 
     From the foregoing, it is apparent that the present invention provides a method for treating a knitted tube in a continuous length so as to achieve a uniformly controlled shrinkage of the fabric which permits the fabric to be made into garments which may be designated &#34;pre-shrunk&#34;, without actually exposing the finished garments to shrinkage. 
     While a particular embodiment of the present invention has been herein illustrated and described, it is not intended to limit the invention to such disclosure but changes and modifications may be made therein and thereto within the scope of the following claims.