EP0760799B1

EP0760799B1 - Spandex supply package

Info

Publication number: EP0760799B1
Application number: EP95920648A
Authority: EP
Inventors: Takamasa Uchida; Kazue Oka
Original assignee: Du Pont Toray Co Ltd
Current assignee: Du Pont Toray Co Ltd
Priority date: 1994-05-24
Filing date: 1995-05-24
Publication date: 1998-08-12
Anticipated expiration: 2015-05-24
Also published as: DE69504062D1; EP0760799A1; DE69504062T2; WO1995032140A1

Description

Field of the Invention

This invention relates to a spandex supply package intended for passive feeding of the spandex to various types of textile equipment. More particularly, the invention concerns an improved spandex supply package, in the form of a bobbin, cake or the like, which permits more uniform feeding of the spandex elastic yarn with fewer yarn breaks. The invention also provides a method for preparing the improved spandex supply package.

Description of the Prior Art

Spandex elastic yarn is well known and widely used in the manufacture of knitwear, see FR-A-1 585 265. The term "spandex", as used herein, has its conventional meaning, namely a manufactured fiber or filament in which the fiber-forming substance is a long chain synthetic elastomer comprised of at least 85% by weight of a segmented polyurethane. In the process of knitting fabrics with spandex, the spandex is forwarded from a supply package to a knitting machine by means of an active or a passive feeding device. The spandex supply package comprises spandex wound on a cylindrical tube. Typically, an active feeding device removes the spandex from the package while the package is rotated by a surface-contacting driven roller or by driven rotation of the tube on which the spandex is wound. A passive feeding device removes the spandex from the supply package by pulling the spandex over one end of the supply package (i.e., "over-end take-off") or by pulling the spandex yarn tangentially from the surface of the supply package while the package is free to rotate on its tubular axis. Passive feeding devices are more economical than active feeding devices. However, when a spandex supply package is used with a passive feeding device, non-uniform unwinding often is encountered. In knitting operations, the nonuniform unwinding can cause uneven knitting, variations in fabric size (i.e., dimensions) and fabric of low quality.

A conventional method for decreasing the problems associated with non-uniform unwinding of spandex yarns with passive feeding devices, is disclosed, for example, in Japanese Patents Kokai Sho 51-127229, Kokoku Sho 62-21714, and Kokai Hei 1-226669. In the conventional method, cylindrical supply packages which were formed by directly winding up spandex on a tubular core as the spandex emerged from a dry spinning process are completely rewound to form a new package. The rewound spandex supply packages have less tackiness and fewer non-uniformities in subsequent knitting operations. However, rewinding of spandex supply packages is time-consuming, labor intensive and expensive. Furthermore, even when spandex yarn is fed from a rewound supply package to a knitting machine by a passive feeding device, undesirable thread breaks and fabric non-uniformities still are encountered, although at a somewhat lower frequency than with spandex supply packages that were not rewound.

In view of the above-described problems with spandex supply packages, an object of the present invention is to provide an improved spandex supply package that requires no rewinding and provides passive feeding characteristics that are superior to those of currently known spandex supply packages.

SUMMARY OF THE INVENTION

The present invention provides a spandex supply package. The supply package which is formed by winding spandex obtained directly from a spandex dry-spinning process onto a cylindrical core is characterized by a maximum percent package relaxation value and a minimum percent package relaxation value that differ by no more than 2 percentage points, preferably by no more than 1.5 percentage points. The percent package relaxation value, %R, in any segment of length along the wound-up spandex of the supply package is calculated by the equation %R = 100(Lr/Ls) where, in any segment of yarn unwound from the package, L_s is the stretched length that the unwound segment had while it was still wound in the package and L_r is the difference between the stretched length L_s and the relaxed length of the unwound segment. %R, L_r and L_s are determined by the "package relaxation value" test described hereinafter.

The invention further provides a process for making the spandex supply package. The process includes the steps of dry spinning spandex, forwarding the spandex from an exit of the dry-spinning spin shaft via feed rolls to a windup on a cylindrical core to form the spandex supply package. The process is characterized in that the spandex is wound at a speed that is varied in multiple stages from the start of the winding of the supply package to the completion of the winding of the package. Preferably, the winding speed in each stage, S_x, is pre-set at a speed that is determined from the corresponding percent package relaxation value, R_o, measured in a corresponding stage of a package of the same spandex that was wound up at constant speed, S_o and from the desired percent package relaxation value, R_x, in accordance with equation (II), as follows Sx = So (100 - Ro)/(100 - Rx) Typically, R_x is selected to be in the range of 1 to 10%, butpreferably in the range of 4 to 8%.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood by reference to the drawings, in which:

Fig. 1 is a graph of the winding speed as a function of the percent of the total amount of spandex wound in the spandex supply package prepared according to the invention by the procedures of the Example below, and

Fig. 2 is schematic side view of the apparatus used to measure the percent package relaxation values reported herein for spandex supply packages.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The invention is further explained in greater detail with particular reference to a preferred spandex supply package of the invention. The description of a preferred embodiment is included for the purpose of illustration and is not intended to limit the scope of the invention, which is defined by the appended claims.

In accordance with the present invention, spandex is wound up as cylindrical tube to form a spandex supply package for feeding via a passive feeding device to further textile operations, such as knitting, yarn covering, air-jet entangling, etc. The spandex is wound on the cake or bobbin under some tension. The tension causes the spandex to be in an extended state in the package. The percent package relaxation value, %R, of any segment of the length of spandex wound in the supply package is a measure of the extension of the spandex in that segment and is defined by equation (I), %R = 100(Lr/Lt) where in any segment of yarn unwound (i.e., removed) from the package, L_r is the relaxed length of the unwound segment, and L_s is the stretched length of the unwound segment as it would have been while still wound and under tension in the supply package.

Spandex elastic yarn in a conventional spandex supply package (i.e., bobbins or cakes or the like) is wound up at a constant windup speed from the start to the end of the winding of the supply package. As a result of the constant windup speed, the spandex in the supply package has percent package relaxation values that vary from a large value in the outside layer of the wound up package to a small value in the middle layer of the package and then to a large value again in the innermost layer nearest the core of the package.

In contrast to the conventional spandex supply package, the spandex supply package of the invention is characterized by a maximum and a minimum percent package relaxation value that differs by less than 2 percentage points, preferably by less than 1.5 percentage points. As a result of this characteristic, the spandex supply package of the invention does not require rewinding, even when the spandex was wound up directly from the spinning process. As described herein, directly wound up means that the spandex filaments were removed by feed rolls from the exit of the spinning shaft of a dry spinning apparatus and then forwarded immediately by the feed rolls to a windup apparatus that formed the spandex supply package. When the spandex supply package of the invention is used in a knitting process with a passive feeding apparatus, more stable knitting, fewer spandex breaks and a more even, consistent knit fabric size are obtained as compared to that obtained from conventional spandex supply packages, including conventional packages that had been rewound.

If the difference between the maximum and minimum of the percent package relaxation values within a spandex supply package exceeds 2 percentage units, when spandex from such a supply package is passively fed to a knitting process, a stable product size often cannot be obtained and the number of broken filaments can become a serious problem.

In a conventional spandex supply packages prepared with a constant windup speed, the percent package relaxation values typically differ considerably throughout the package and the maximum and minimum package relaxation values can differ by several percentage points. Usually, the package relaxation value of the conventional spandex supply package is large at the outside layer and inner layer of the wound up package, but small in the middle layer. The package can be divided into segments according to the order of unwinding and for each segment, a percent package relaxation value, %R, can be determined. For convenience, to determine the maximum and minimum percent package relaxation values in any given supply package, the whole length of the wound up spandex in the package can be divided evenly into three or more segments and the largest value of the average %R values in the segments is designated the maximum %R and the smallest average %R for any segment is designated the %R. The number of the segments used in a supply package for this determination of maximum and minimum % R should be at least three, preferably five or more. However, no matter how many segments are used, the outermost, the middle and the innermost layers should be sampled for this determination, because the %R always large in the outermost and innermost layers and smallest in the middle layer.

A spandex supply package of the invention can be prepared conveniently as follows.

First, in order to determine a desired package average relaxation value in the supply package of the invention, the package relaxation values of sampled segments of a conventional supply package, are determined. The spandex of the conventional package is made of the same composition by the same spinning process, under the same conditions and at the same feed roll speed as the spandex to be formed into the supply package of the invention. However, the conventional supply package is formed at a constant windup speed (e.g., 1,300 meters/min) from the starting point to the ending point of the package.

Any value between the maximum and minimum percent package relaxation values of the conventional constant-speed-wound package can be used for the desired percent package relaxation value of the spandex supply package of the invention. Typically, the desired percent package relaxation value is in the range of 1 to 10%, preferably in the range of 4 to 8%. For example, when the total length of the spandex of the conventional supply package was divided evenly into six segments, and the average percent package relaxation values of each segment was determined, the present inventors found that the %R of the first segment from the outside of the package was 9%; of the second segment, 7%; of the third segment, 5%; of the fourth segment, 6%; of the fifth segment, 7%; and of the sixth (innermost) segment, 8%. The maximum %R was 9% and the minimum %R was 5%, or a difference of 4 percentage units. Thus, the conventional spandex supply package in which the spandex was wound up at a constant speed, had a large variation of package relaxation values along the length of the spandex.

To overcome the disadvantages of a wide spread in percent relaxation values, and to achieve more equal values the segments of the spandex length, in accordance with the invention, the total length of the spandex is divided evenly into same number of segments as the conventional corresponding spandex supply package was divided, and the speed for each segment is set based on the location of the segment in the package. For example, in the illustration given above, the conventional spandex supply package was divided into six equal segments and the maximum and minimum percent package relaxation values were respectively 9 and 5 %. Thus, a suitable desired package relaxation value for the supply package of the invention could be set at 7% (i.e., selected to be between the maximum and minimum values of the conventional package). Then, by use of Equation II above, the desired windup speed for each corresponding segment of the spandex supply package of the invention could be calculated and pre-set. In the illustration just given, this results in the pre-set windup speeds in the first and sixth segments of the supply package of the invention being decreased compared to the windup speed used to prepare the conventional spandex supply package. The pre-set windup speeds in the second and fifth segments of the supply package of the invention would be the same as the windup speed of the conventional spandex supply package. The pre-set winding speeds in the third and fourth segments of the supply package of the invention would be higher than the windup speeds of the conventional package. It is preferred that in the proceeding from the speed in one segment to another speed in the next segment, the transition be accomplished smoothly. The speed change can be linear or a curve.

The spandex of the supply package of the invention be prepared from any fiber-forming long chain synthetic elastomer comprising at least 85% segmented polyurethane. The spandex can contain additives which are included for various purposes. Among typical suitable additives are, for example, hindered amines, hindered phenols, UV absorbents, tertiary amines, gas discoloration inhibitors, metal soaps, such as magnesium stearate, calcium stearate, lithium stearate, zirconium stearate, etc., pigments, such as titanium dioxide, etc. The polymer is typically dry spun from solution of the polymer in an inert organic solvent (e.g., dimethyl acetaminde) through spinnerets into a spin shaft heated with gas at 300-460°C, preferably at 350-440°C. The surface of the dry-spun filaments are coated with an oiling agent. A typical oiling agent contains as a major component, an organopolysiloxane such as dimethylpolysiloxane or polysiloxanes modified with amino group, hydroxyl group, etc. The amount of oiling agent coated is 1-20%, preferably 3-15%, more preferably 4-12%. The filaments are removed from the spin shaft by feed rolls which forward the filaments to a windup that forms the filaments into a spandex supply package.

Test Procedures

Various parameters mentioned in the preceding discussion and reported in the Example below are determined by the following methods.

1. Percent package relaxation value (%R)

The "percent package relaxation value test" is carried out with the apparatus depicted in the schematic side view of Figure 2 and %R is then calculated from the test results by application of Equation I. Figure 2 shows a sample spandex supply package 10, comprising spandex 12 wound on tube 14 which is mounted on package holder 20. the package holder is rotatable by crank 22 with handle 24. The surface of package 10 is contacted by the surface of roll 30 which permits a specimen length 40 of spandex to be forwarded to a scale 50. The end of specimen 40 is held with clip 55 at a zero point on scale 50. At the start of the measurement, only enough spandex is forwarded from the supply package to permit the end of the specimen to be precisely positioned at the zero point of the scale. The scale can be moved up or down to adjust the position of the zero point. Then by rotating the crank spandex can be released from the package without any tension. The released spandex forms a narrow U-shaped loop hanging on the scale. The length of the loop (2H, in Fig. 2) is of insufficient weight to cause sagging of the loop and no tension is applied to the loop. The number of rotations N of the spandex package, the length "H", and the outer diameter D_x of the spandex package during the determination are precisely measured. Then, L_s, the stretched length that the unwound segment had while it was still wound in the package and L_r, the difference between the stretched length L_s and the relaxed length of the unwound segment, and %R, the percentage package relaxation value are calculated from III and IV below and from Equation I: Lr = πDx N - 2H Ls = πDx N %R = 100 (Lr/Ls) Alternatively, equation I can be written as %R = 100 (1 - 2H/L_s).

2. Waistband size

A panty hose waistband is knitted with Nagata KTS-4 knitting machine. The knitting is carried out at a rate of 545 rpm using four feed yarn inlets, with a 30-denier (33-dtex) nylon thread and a spandex elastic yarn being fed to the first inlet, 30-den nylon threads being fed to the second and third inlets and a 15-den (17-dtex) nylon thread being fed to the fourth outlet. The pantyhose waistband is set at 35 cm in the circular knitting. "Waistband size" is the measured width of the relaxed circular knit waistband after the waistband was released from tension.

EXAMPLE

This example shows the clear advantage of the spandex supply packages of the invention over conventionally prepared, rewound supply packages of the same spandex. The supply packages of the invention had a lower range of package relaxation values and in a 14-day knitting test exhibited a broken thread rate that was one-twentieth the broken thread rate experienced with the rewound conventional spandex supply packages.

A 12-filament and 140-denier (160-dtex) spandex yarn was prepared by extruding 500 grams/hour of a solution of a polyetherurethane-urea in N,N-dimethylacetamide solvent through spinnerets into a the nitrogen atmosphere of a spin shaft that heated with nitrogen gas at 430°C. The polymer was made by reacting polytetramethyleneether diol with 4,4-diphenylmethane diisocyanate to form an isocyanate-capped polymer that was chain extended with ethylenediamine. A lubricating agent containing dimethylpolysiloxane as the major component was applied to the surface of the spandex. The lubricating agent amounted to 7.5 %. of the total weight of the spandex.

A conventional bobbin of the thusly prepared spandex yarn was then wound up with a constant winding speed of 1300 m/min on a core tube of 5-cm diameter, at a helix angle of 17 degrees to form a supply package with an outer diameter of 17 cm. The spandex wound on the conventional bobbin was divided into five equal segments and the percent package relaxation value of each segment was measured. The maximum and the minimum package relaxation values were 10.9% and 6.8%, respectively.

A desired percent package relaxation value for the preparation of corresponding spandex supply bobbins was set according to the invention at 7.0%, a value that was between the maximum and the minimum values of the percent package relaxation values of the conventional spandex bobbin. Then, with the desired 7% for the percent relaxation value for the spandex supply package of the invention, and the %R values measured for the various segments of the corresponding conventionally prepared spandex supply package wound up at the constant windup speed, S_o, of 1,300 meters per minute, the following windup speeds were calculated by Equation II and preset for the preparation of the spandex supply packages of the invention. The spandex windup speeds for each package were changed in five stages. Table 1 summarizes the amounts of spandex wound on the bobbin during each windup stage, from beginning of the winding to the end of the winding of the bobbin, and Figure 1 shows the windup speed changes graphically.

Cumulative % of total spandex wound on bobbin	Windup speed meters/min
0	1,286
32	1,300
49	1,314
66	1,328
83	1,300
100	1.272

The 0% wound corresponds to the innermost segment of the spandex wound on the bobbin. The 100% wound corresponds to the outermost segment of the spandex wound on the bobbin.

The percent package relaxation values, %R, of the various segments of the wound-up spandex supply bobbins of the invention made in this example and the results of pantyhose waistband knitting tests with the spandex from the bobbins are compared in Table 2 to the %R values and waist band knitting results obtained with corresponding segments from rewound conventional spandex supply packages.

Amount wound, %	Package of invention	Rewound conventional
	%R	Size, cm	%R	Size, cm
100	7.6	10.5	6.8	11.0
83	7.3	10.9	5.1	11.1
66	7.0	11.1	4.0	11.2
49	6.9	11.1	3.5	11.1
32	6.7	11.0	4.5	11.2
15	6.3	11.1	6.5	11.1

As shown in Table 2, the difference between the maximum and minimum package relaxation values in the spandex supply packages of the invention was 1.3%. In contrast, the corresponding difference was 3.3% in the spandex of the rewound conventional spandex supply packages. Note that the size variation in the width of the knit waistbands prepared with spandex supply packages according to the invention was 0.6 cm. Although this value was larger than the 0.2-cm size variation of waistbands that were knit with the conventional rewound spandex supply bobbins, for practical use, the allowed size variation in such waistbands is usually within 1 cm. Therefore, the variation in size exhibited by waistbands made with supply packages of the invention will not cause any problems.

A 14-day continuous knitting test with five Nagata KTS-4 knitting machines was then performed to compare the efficiency of producing knit pantyhose with of spandex passively fed from the supply bobbins prepared according to the invention versus from rewound conventionally prepared supply bobbins. In the knitting test, the number of thread breaks per knitting machine per day were recorded as a measure of production efficiency. The spandex supply bobbins of the invention were clearly superior to the conventional rewound spandex supply bobbins. The frequency of breaks with spandex supplied from the conventional rewound bobbins (0.80 breaks per machine per day) was 20 times greater than that experienced with spandex supplied from bobbins prepared according to the invention (0.04 breaks per machine per day).

Claims

A spandex supply package (10) formed by winding spandex (12) obtained directly from a dry-spinning process onto a cylindrical core (14) characterized by a maximum percent package relaxation value and a minimum percent package relaxation value that differ by no more than 2 percentage points, the percent package relaxation value, %R, in any segment of length along the wound-up spandex of the supply package being calculated by the equation %R = 100(Lr/Ls) where, in any segment of yarn unwound from the package, L_s is the stretched length that the unwound segment had while it was still wound in the package and L_r is the difference between the stretched length L_s and the relaxed length of the unwound segment, and %R, L_r and L_s are measured by the package relaxation value test described in the description.
A spandex supply package (10) according to claim 1 wherein the maximum percent package relaxation value and a minimum percent package relaxation value differ by no more than 1.5 percentage points.
A process for making a spandex supply package (10), the process including the steps of dry spinning the spandex, forwarding the spandex from an exit of a dry-spinning shaft via feed rolls to a windup on a cylindrical core (14) to form the spandex supply package (10), characterized in that the spandex (12) is wound at a speed that is varied in multiple stages from the start of the winding of the supply package to the completion of the winding of the package, the winding speed in each stage, S_x, being pre-set at a speed that is determined from the corresponding percent package relaxation value, R_o, measured in a corresponding stage of a package of the same spandex that was wound up at a constant speed, S_o, and the desired percent package relaxation value, R_x, in accordance with the equation Sx=So (100 - Ro)/(100 - Rx).
A process according to claim 3 wherein R_x is in the range of 1-10%.
A process according to claim 3 wherein R_x is in the range of 4 to 8%.