High elastic modulus bandage

#FIG. 1 is a schematic representation showing the manufacture of the elastic sheet material.

#FIG. 2 is a representation in plan view of a portion of the product.

#As shown in FIG. 1, elastic yarns 10 from a beam 11 are unwound under tension controlled by driven press roll 12 and through comb 14. Thin non-woven fibrous webs 15 and 17, from supply drums 16 and 18, respectively, or directly from the forming machine, if desired, are brought into contact with the yarns and with each other between rubber-covered squeeze roll 19 and knurled steel squeeze roll 20, the latter dipping into a pan 21 containing a fluid binder mixture 22 and depositing the binder mixture throughout the web 17. The composite web passes directly into a drying oven 24 and thence between pull drums 25 and 26. The web next passes around roll 27, between heating platens 28 and 29, around idler rolls 31 and surface winder roll 30, and is wound up to form stock roll 32.

#Squeeze rolls 19 and 20 rotate at a considerably greater surface speed than does beam 11, and the yarns 10 are accordingly stretched a corresponding amount. This stretch is maintained by operating pull drums 25 and 26 and turn-around drum 27 at approximately the same speed compared with rollers 19 and 20. Surface winder roll 30 and wind-up drum 32, however, are again operated at a slower speed to permit shrinkage of the web as it passes between the heater platens 28 and 29. The composite web 34, which is smooth as it reaches the roll 27, becomes increasingly puckered or shirred as it passes through the heating zone, the result being further indicated in FIG. 2.

#The heat supplied by the platens 28 and 29 is sufficient to cause considerable fuming of the sheet material and to relax the structure sufficiently to permit the elastomeric yarns to retract and produce the desired degree of puckering or shirring as controlled by the speed of the surface winder roll. The temperature may be regulated by adjusting both the energy input to the platens and the distance between the platens and the web. In a typical installation for producing a finished web, the electrically heated platens are each 48 inches high, and are spaced between six and nine inches from the web. The platens are operated 600.degree. F. at idle and 525.degree. F. when the web is running. The duration of the heat treatment may be regulated, for a given length of platen, by adjusting the speed of travel of the web, sufficient time being provided to permit retraction of the web to the desired degree. The platens are maintained at a temperature sufficient to keep the web taut during the shrinking operation between rolls 27 and 30 at the speed indicated but not so high as to cause deterioration of the web as evidenced by excessive fuming and discoloration thereof. The length of the relaxed web after retraction will be within the range of about one-third to about two-thirds the fully extended length. The elastic yarns are initially stretched to a length of about three to five times (and preferably three to three and one-half times) their fully relaxed length (the ratio of stretched length to relaxed length of the yarns is referred to as the draw ratio), and are permitted to relax only partially during the puckering step. Nevertheless, the shirred product is dimensionally stable, the heat treatment serving to provide an effective degree of heat-setting or stabilizing, and neither shrinks nor expands when allowed to stand at normal temperatures and under no external stress; and it returns to such dimensions when first stretched and then permitted to retract.