US3495295A - Apparatus for drawing thermoplastic filamentary yarns - Google Patents

Description

Feb. 17, 1970 T, FARRAND ETAL 3,495,295

APPARATUS FOR DRAWING THERMOPLASTIC FILAMENTARY YARNS Filed April 19, 1967 I 2 Sheets-Sheet 1 ATTORNEYS Feb. 17,1970 T, H, gm-ND EI'AL 3,495,295

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US. Cl. 18-1 6 Claims ABSTRACT OF THE DISCLOSURE Thermoplastic yarn drawing apparatus including feed and draw rolls, the peripheral surface of at least the latter consisting of microprotrusions of round, elongated or ridge form and of substantially equal heights. The apparatus may be of the spin-drawing or batch-drawing type and may include snubbing or heat treating surfaces between the feed and draw rolls.

This invention relates to an apparatus for drawing filamentary yarns composed of synthetic, thermoplastic, linear polymers.

Fibres and filaments of synthetic thermoplastic polymers are produced by extrusion of the molten polymer or as a solution thereof in a volatile solvent, in continuous filamentary form, which usually possesses only a small amount of longitudinal orientation. Such filaments have a low strength and are highly extensible, most of which extensibility is irreversible. Such filaments are of limited use and are converted into more useful filaments by the process of drawing, wherein the filaments are elongated, with or without the addition of heat, between feed and draw means, as for example two sets of rolls operating at different peripheral speeds. The elongation may be facilitated by localising the drawing tension in the filaments by contacting them with a surface of high friction, which has the effect of localising the region wherein most of the elongation occurs. The drawing may be carried out using separate drawing apparatus and temporarily collecting the extruded filaments, usually and hereinafter referred to as spun yarn, which provides the starting material for the drawing machines. Alternatively, the processes of extrusion (melt or solution-spinning) and drawing may be integrated in a unitary apparatus, frequently and here inafter referred as spin-draw apparatus, wherein the spun yarn is taken directly around a feed roll, which may be heated, and then around a draw roll rotating at a higher peripheral speed than the feed roll, the yarn which is thus drawn being collected in a suitable package by winding means as in a two-stage process of spinning and drawing.

Tensions applied to filaments in drawing are of a high order and such tensions may lead to filament breakage, particularly on the faster rotating draw roll around which a sufficient number of turns of drawn filamentary yarn must be wound to prevent slippage of the yarn which would lead to irregular drawing. Filament breakage is manifested in the form of wraps or laps of broken filaments around the draw roll, which can cause yarn breakdown or as accretions or neps in the drawn yarn both of which effects are undesirable in terms of reduced productivity and drawn yarn quality.

Draw rolls having their peripheral surfaces treated to produce various types of surface finish have been proposed heretofore, as for example, by roughening and then polishing the surface or by applying a rough ceramic surface which is afterwards partially smoothed by brushing or tumbling procedures. Rolls having circumferential- 3,495,295 Patented Feb. 17, 1970 ice 1y alternating smooth and rough sections on the periphery have also been proposed. While all these methods have improved the drawing performance somewhat there is still room for improvement, particularly in terms of productivity and yarn quality.

According to the present invention we provide apparatus for drawing filamentary yarn composed of a synthetic, thermoplastic, linear polymeric substance including a feed roll and draw roll rotatable at a higher peripheral speed than said feed roll, characterised in that the peripheral surface of at least the draw roll which contacts the filamentary yarn is composed of metallic round or elongated microprotrusions of substantially equal height.

Drawing apparatus according to the invention may optionally include stationary or rotatable heated or unheated snubbing means between the feed and draw rolls. Also optionally the feed roll and/ or draw roll may be heated.

In drawing thermoplastic filamentary yarn it is very desirable to control the variation of the tension to which the yarn is subjected from beginning to end of its passage over the draw roll. This is most readily achieved using apparatus according to the invention, for the profiled surface of the draw roll provides the necessary control, maintaining the tension substantially constant at the drawing tension in approximately the first 20-50% of the total yarn/ roll contact length and thereafter allowing a steady decrease in tension with increasing contact length to a value just before the yarn leaves the roll which is very close to the winding tension exterted by the yarn collecting means.

This behaviour is illustrated in the accompanying drawings as hereinafter designated and is compared with the behaviour of commonly used known surfaces consisting of a polished metal surface or a rough metal surface having unequal protrusions produced by sand-blasting and then chromium plating the surface of a steel roll. The latter type of roll is hereinafter referred to as a matt roll.

In drawing thermoplastic filamentary yarn it is usual to associate each roll with an idler roll and to take the yarn around the roll/idler roll combination. The axis of the idler roll is skewed slightly in relation to the roll axis which has the effect of spacing the individual turns of yarn axially along the roll. Tension in the yarn passing around the draw roll is then conveniently measured by insertion of the sensing head of a suitable tensiometer, as for example a Rothschild Electronic Tensiometer made by Rothschild Elektronische Mess-and Steuergerate of Traubenstrasse 3, Zurich, Switzerland, under each turn of yarn about the draw/idler roll combination.

Methods for producing rough surfaces simply by roughening, for example, by sand blasting or by the steps of roughening the surface or coating thereon and thereafter removing some of the roughness by a polishing, brushing or plating processes, all produce surface asperities which are both irregular in shape and in height. Roughening of surfaces for use in the present invention, wherein substantiall equal heights of the surface protrusions are required, may be readily accomplished by photoetching methods which are adapted to the production of surfaces of controlled form.

One form of roll surface according to the invention consists of a series of microridges on the roll periphery which are parallel to each other and the roll axis. These microridges are of equal height and may be spaced at equal or unequal intervals around the roll circumference and preferably are of about the same length as the roll. This form of roll surface is preferred for the ease with which it may be produced by a photo-etching process involving preparation of a simple ruled mask by wellknown photo-reduction methods. Depending upon how the etching stage of the process is carried out microridges FIGURE 2 is a profile of a surface similar to that shown in FIGURE 1 but with larger ridges.

FIGURES 3 and 4 are profiles of rnicroridged surfaces wherein the microridges are approximately rectangular in cross-section and FIGURE 5 comprises graphs of tension against number of turns of yarn around the draw rolls of FIGURE 1 and FIGURE 2 together with the graphs for a polished roll and for a mat roll illustrate, by way of example, the form of four draw roil surfaces according to the invention and the behaviour of two of these (FIGURES 1 and 2) in drawing a multifilamentary yarn composed of polyethylene terephthalate having a drawn denier of 975 and containing 192 filaments which is wound around the draw roll five times. In both cases the draw rolls were of 5 inches (12.7 cm.) diameter. From FIGURE 5 it can be seen that with the surface ha 'ing unequal protrusions, that is the matt roll, the yarn tension drops steadily throughout the passage of the yarn around the draw roll, whereas with a surface according to the invention the tension at first remains high and substantially constant and then steadily falls to a value close to the winding tension. With a roll having a polished surface the yarn tension remains high until nearly the end of the yarn passage and then suddenly falls to a lower value which is still appreciably higher than the winding tension.

FIGURES 1-4 are of course highly magnified profiles, 1 cm. of the vertical scale representing 5 microns and 1 cm. of the horizontal scale representing 50 microns. These profiles were measured using a Talysurf (registered trademark: of Taylor Hobson Co., England) instrument. The mean profile heights in FIGURES 1-4 are 4, 5', 18 and 8 microns respectively and the mean peak spacings are 130, 165, 180 and 255 microns respectively.

In addition to being of substantially equal height protrusions on surfaces for use in the invention may also be irregularly or equally spaced apart on the surface and may be of various shapes such as ridges or hills of circular or other geometrical shape. It is essential that the peaks of the protrusions should not be sharp but should be of flat or rounded form and a photo-etching process by its very nature is adapted to produce such protrusions. We have referred to the protrusions on the surfaces to be used in the invention as micro-protrusions and by this is meant protrusions which are measurable only by special techniques and which are larger than the protrusions of a highly polished surface which protrusions are of the order 10 micro inches (0.254 micron) or less in height.

Drawing of synthetic thermoplastic filamentary yarn with apparatus according to this invention leads to a marked reduction in the number of laps or neps formed by filament breakage at least when compared with the frequently-used polished, chromium plated, steel draw roll. In drawing synthetic filamentary yarn a number of turns of yarn are taken around the draw roll to prevent slippage and it is found that with a draw roll surface according to the invention it is possible to use a fewer number of turns of yarn therearound, compared with a matt roll while still preventing overall slippage of the yarn.

Thus in FIGURE 5 is can be seen, from the yarn tension changes, that five turns of yarn around the draw roll are sufiicient to prevent overall slippage of the yarn on a draw roll surface according to the invention but insufficient to prevent such slippage on a matt draw roll sur face of the same size. The yarn in its drawn condition is therefore subjected to less abrasion in passing through the drawing apparatus which in turn further reduces the likelihood of filament breakage.

The actual shape, height and spacing of protrusions on roll surfaces which gives the best drawing efficiency of a particular kind or size of synthetic thermoplastic filamentary yarn according to the invention, will depend to some extent on the nature of the polymeric substance, the denier of the filaments in the yarn and the degree of drawing, that is to say the draw ratio, to which it is subjected as well as other factors such as the presence of lubricant on the yarn.

The following examples illustrate the improved drawing achieved by means of the invention in terms of the markedly reduced number of laps which occur during drawing of nylon 66 and polyethylene terephthalate yarn in spindraw and two-stage processes.

EXAMPLES l4 Spun polyethylene terephthalate yarn was drawn using a multiposition drawframe, each position of which comprises a single feed roll and a draw roll (5 inches; 12.7 cm.) diameter having a peripheral surface of the FIGURE 1 or FIGURE 2 type, a stationary hot. plate between the rolls to heat treat the yarn and to complete the last 510% of drawing, and a ring-rail type collecting spindle; each roll having an idler roll associated therewith. For comparison the same yarn was drawn using a highly polished draw roll of equal diameter in place of those according to the invention. In Table 1 results for the three types of draw roll are given when the draw roll is unheated (surface temperature approx. 40 C.) and in Table 2 when the draw roll is heated to 220 C. Other drawing conditions are as follows.

Spun yarns of birefringence 4X 10- and intrinsic viscosity 0.915 (measured in o-chlorophenol at 25 0.), treated with a lubricating finish is supplied to the drawframe the feed rolls of which are heated to 75 C. and in which a draw ratio of 5.43:1 is applied. The hot plate temperature is 215 C. and the drawspeed is 500 ft. per

minute (152 metres per minute). Five turns of yarn were taken around the draw roll and its associated idler roll.

TABLE Weight Drawn of yarn Draw roll yarn, drawn Draw roll Example surface denier (kg.) laps TABLE 2 Weight Drawn of yarn Draw roll yarn, drawn Draw roll Example surface denier (kg) laps 3 Fig. 1 960 10.9 0 4 Fig. 950 10. 9 0 Comparative B Polished 954 10. 9 18 The properties of yarn drawn using the profiled draw rolls of the invention were substantially identical with those of yarn drawn with the conventional polished draw roll. In particular the free shrinkage at C. of yarns drawn using a heated draw roll was the same in all cases, showing that heat transfer from the draw roll surface to the yarn passing therearound was unaffected by profiling the surface according to the invention.

In these examples the level of lap occurrence was artificially raised by using a higher draw ratio than that required to produce substantially fully drawn yarn that is to say the drawing process was operated in the region of incipient threadline breakdown where filament breakage would be at its highest level.

EXAMPLE 5 Example 4 and comparative Example B were repeated using a draw ratio of 5.34:1, just below the incipient threadline breakdown level, to draw a large quantity,

180 kilo., of the same yarn.

Only 2 draw roll laps were formed during the run with the profiled draw roll compared with 23 for the polished draw roll.

EXAMPLES 6-7 Spun nylon 66 yarn having 140 filaments of total denier 4200 was drawn using a multi-position drawframe two positions of which comprised a single feed roll a draw roll having a peripheral surface of the FIGURE 1 or 2 type, each roll having an idler roll adjacent thereto, a stationary unheated chromium snubbing pin and a 15 cm. hot plate (187 C.) between the rolls and a ring-rail type collecting spindle. Feed and draw rolls were unheated and their peripheral speeds were 60.5 metres/minute and 320 metres/minute respectively, thus applying a draw ratio of 5.28:1 to the spun yarn. Six turns of yarn "were taken around the draw roll and its associated idler roll.

Table 3 shows the results obtained together with a comparative result using a polished draw roll to process the same yarn in the same way.

TABLE 3 Drawn Y denier Draw roll Draw r011 surface laps EXAMPLE 8 Nylon 66 polymer was melt extruded into filaments which were air-quenched, converged, steam conditioned and lubricated in conventional manner and then drawn with spin-drawing apparatus comprising a feed roll, an intermediate roll the peripheral speed of which is 1% greater than that of .the feed roll, a chromium plated snubbing pin, a draw roll having a peripheral surface of the FIGURE 3 type rotating at 790 metres/minute (applied total draw ratio 3.7: 1) and a surface driven yarn winder. Each roll had an idler roll associated therewith. The denier of the spun yarn having 204 filaments was 10,800 and the denier of the drawn yarn was 3,120.

For comparison the same yarn was drawn using the same apparatus equipped with a polished draw roll in place of the profiled roll and the same spin-drawing conditions.

In each case 18 kg. of yarn were drawn and when using the profiled draw roll of the invention no laps occurred but using the polished draw roll 24 laps occurred during the run necessitating restarting the drawing several times by taking the yarn around the rolls again (stringing-up).

In addition it was unnecessary to lower the speed of any rolls during the stringing-up operation when a profiled draw roll was used. Such reduced speed stringing-up was necessary when using a polished draw roll.

What we claim is:

1. Apparatus for drawing filamentary yarn composed of a synthetic, thermoplastic linear polymeric substance including a feed roll and a draw roll rotatable at a higher peripheral speed than said feed roll, characterised in that the peripheral surface of at least the draw roll which contacts the filamentary yarn is composed of a metallic round or elongated microprotrusions of substantially equal height.

2. Apparatus according to claim 1 wherein the microprotrusions are ridges parallel to each other and to the roll axis.

3. Apparatus according to claim 2 wherein the microridges are equally spaced around the roll circumference.

4. Apparatus according to claim 2 wherein the microridges are spaced at irregular intervals around the roll circumference.

5. Apparatus according to claim 1 wherein the cross sections of the microridges are triangular the apex of the microridges being rounded or flattened.

6. Apparatus according to claim 1 wherein the cross sections of the microridges are square or rectangular.

References Cited UNITED STATES PATENTS 3,009,231 11/1961 Kleekamni et al. 3,020,621 2/1962 Sacks 2871 3,212,158 10/1965 Kasey 28713 XR WILLIAM J. STEPHENSON, Primary Examiner US. Cl. X.R. 188, 47; 2871.3

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