US3106442A - Method of producing dimensionally stable polypropylene fibers - Google Patents

Description

1963 M. COMPOSTELLA ETAL 3,106,442

METHOD OF PRODUCING DIMENSIONALLY STABLE POLYPROPYLENE FIBERS Filed July 11, 1957 INVENTORS MARIO COMPOSTELLA Fnguco DENT/ a BY ATTORNEY$ United States Patent This invention relates to textile fibers and more particularly to textile fibers of high polymers of propylene composed of, or containing a predominant proportion of, isotactic macromolecules as defined by Natta et al., and to processes for producing such fibers.

Entirely new polymers of the alpha-olefines CH :CHR

having substantially no branches longer than R have recently been described by G. Natta and his co-workers, and have been defined, by G. Natta in the Journal of Polymer Science, April 1955, vol. XIV, issue No. 82, pages 143-154, as linear, head-to-tail polymers composed of isotactic macromolecules. Isotactic macromolecules as defined by Natta et al. are macromolecules in which,

at least for long portions of the main chain or for substantially the main chain, the tertiary asymmetric carbon atoms have, on the same chain section, the same steric configuration, and the main chain of which, if fully extended in a plane, shows all of the R groups bound to the tertiary carbon atoms of the monomeric units making up said chain section on one side of the plane and all of the H atoms bound to said tertiary carbon atoms on the opposite side of the plane. The isotactic macromolecules, which are crystallizable or crystalline, have a stereoregular structure of the kind shown in the model below:

(Model of a pontion of the main chain of an isotactic macromolecule of an alpha-olefin polymer according to Natta et al., arbitrarily fully extended in a plane, in which the R substituerrts on the tertiary C atoms of adjacent monomeric units are above, and their H atoms are below, the plane of the chain.)

ice

paring the elastic properties of nylon yarn with those of a comparable yarn of polypropylene (RF. in the table):

TABLE Elongation 8% 15% Fiber Nylon P.P. Nylon Pl. Instantaneous Elastic Recovery, 100 100 Delayed Elastic Recovery, 98 100 81 95 The instantaneous elastic recovery is measured by subjecting the fiber to elongating stress, releasing the stress immediately, and measuring the elastic recovery of the fiber after 60 seconds. measured by subjecting the fiber to the elongation stress, maintaining the stress for 60 seconds, and determining the elastic recovery of the fiber after 60 seconds.

The high elastic recovery of our polypropylene fibers is, for many purposes, a very valuable characteristic. However, it results in certain difficulties during processing of the fibers and, in addition, the yarn tends to shrink strongly when placed in hot water. This tendency to shrink is troublesome during further processing of the yarn and, also, under certain conditions of use of the fibers. Thus, shrinkage of the stretched polypropylene yarns which we produced earlier is even troublesome in the first winding up. The filament proceeding from the stretching stage, having a high elasticity and being under tension, can be wound up on a bobbin but shrinks thereon so that the inner windings are compressed by the outer windings and the filament or yarn is, as a consequence, differentially strained and has different residual shrinkage capacities along the length thereof which are expended during further processing, e.g., dyeing, and result in uneven effects, such as uneven or non'le-vel dyeing.

The existence of the different strains in the fibers and yarns also causes frequent rupture of the yarn when it is unwound from the bobbin under a constant tension. Moreover, the individual filaments of the yarns are electrized by rubbing and tend to separate from each other, so that the winding tends to be irregular, increasing the danger of rupture of the unwinding yarn, as well as of yarn still on the bobbin, during the unwinding operation.

An object of this present invention is to provide filaments and yarns of isotactic polypropylene which are less susceptible to heat-shrinkage (more heat-stable), may have modified elastic characteristics, and which have, in general, better mechanical characteristics than is normally the case.

This and other objects are accomplished by the practice of this invention in accordance with which the fibers or yarns are heat-treated under special conditions, after stretching thereof, the heat-treatment being performed, at least in part, before the fibers or yarns are twisted and Wound up. The stretched fibers or yarns are stabilized against excessive shrinkage by heating them at a temperature which may be somewhat higher than the stretching temperature and while they are held under a tension The delayed elastic recovery is such that they are not free to shrink or can shrink to only a controlled extent not greater than 15% of the initial length. In order to insure maximum relaxation of the strains introduced into the fibers and yarns during the earlier processing thereof, the heat-treatment must be carried out at a temperature as close as possible to the first order transition temperature for the isotactic polypropylene, which is about 169170 C.

In practice, the stabilization can be carried out continuously. For example, the yarn can be stretched at temperatures between 80 C. and 140 C. and then held under conditions of non-shrinkage or of controlled shrinkage at a temperature between 80 C. and 160 C., preferably between 135-145 C., i.e., at a temperature which is the same as or only slightly than the stretching temperature, for a time varying from a fraction of a second to a few seconds, e.g., about 5 seconds.

The invention will be more readily understood by reference to the accompanying drawing, in which FIGURE 1 is a diagrammatic showing of apparatus suitable for use in stretching and annealing the yarns of isotactic polypropylene.

FIGURE 2 is a fragmentary view of one element of the apparatus.

Referring to FIGURE 1, there is shown a roll 2, a heater 3, a second roll 4, a second heater 5, a roll 6 and a winding system 7 of the ring type.

In practice, the yarn (l in the drawing) passes over roll 2 into the heater 3 and thence over roll 4, being stretched between rolls 2 and 4 which are rotated at different peripheral speeds to effect stretching of the yarn to the predetermined extent. For example, roll 2 may be rotated at a peripheral speed of 415 m./minute, and roll 4 may be rotated at a peripheral speed of 20 to 100 m./minute, to impart the desired stretch to the yarn as it proceeds through heater 3. The stretched yarn then passes from roll 4 into the heater 5 and over roll 6 to the wind-up. The peripheral speed of roll 6 may be lower (15%) than, the same as, or somewhat higher than that of roll 4, so that the yarn passing through heater is held against shrinkage or shrinks to a controlled extent. Rolls 2, and 6 may be driven by means of continuous speed-variators to adjust the stretching ratios. The rate of feed of the yarn to the heaters and the heating times are correlated so that at the selected stretching and stabilizing temperatures, the desired objectives are accomplished.

Heaters 3 and 5 may be heated in any suitable manner, for example by hot air, may have a length of, for instance 30 centimeters (for peripheral speeds of the rolls within the ranges already stated), and are provided with inlet and outlet openings as shown in FIGURE 2 for entry and exit of the yarn.

The heaters may be opened as shown at 8 in order to facilitate the introduction of the yarn.

They can be obviously substituted by any equivalent heating medium as for exampie a warm plate.

Alternatively, the stretched yarn may be stabilized against excessive heat-shrinkage in two stages. Thus, the fibers or yarns may be heat-treated under conditions of controlled shrinkage between 0 and twisted, wound on bobbins, and then given a further heat-treatment on the bobbin, the second heat-treatment being preferably performed at a temperature somewhat higher than the first heat-treatment.

In practicing the latter embodiment, the heating time on the bobbin (second heat-stabilizing step) may be a few seconds or it may be increased to about 60 minutes. The stabilized yarn obtained by completing the heattreatment on the bobbin has substantially the same characteristics as the yarn which is stretched and annealed continuously in what may be regarded as essentially a single-stage process.

The stretched and heat-stabilized yarn can be wound up without diificulty, has satisfactory dimensional stability, and has improved mechanical characteristics, as compared to the yarns which are not annealed under heating and conditions of controlled shrinking.

As mentioned above, and disclosed in the pending Natta et al. applications, 514,097, 514,098 and 514,099, filed June 8, 1955, the isotactic polypropylene produced by polymerizing propylene with the aid of the catalysts prepared from the transition metal compounds and the metal alkyls, may contain some atactic polypropylene. Such products may be used in making fibers and yarns provided the content of atactic polypropylene is not in excess of about 30%.

A close relationship exists between the residual shrinkage capacity of the stretched, stabilized yarns obtained by the present process and the amount of atactie polymer contained in the starting polypropylene from which the fibers are formed. If the atactic polymer is 15% or less, stretched, annealed yarns which shrink only 01% in water at C. are usually obtained, whereas at higher atactic polymer contents, residual shrinkage of 34% may be regarded as a good result of the heattreatment.

The extent to which the yarn is allowed to shrink between the limits of zero to 15 during the heat-stabilization is determined by the final characteristics desired for the yarn. Thermal treatment of the yarn under controlled shrinkage, which favors the return to a certain disorder or irregularity of the molecular structure, results in a slight decrease in the elastic characteristics of the yarn, a phenomenon which is useful for certain applications of the yarn. On the other hand, when the thermal treatment of the stretched yarn is carried out under conditions such that the yarn is not free to shrink, or is even held under a slight tension, the heattreatment fixes the orientation of the molecules effected by the stretching and the elastic properties of the yarn are not substantially altered as a result of the heat-stabilization. This is generally advantageous for most purposes for which the yarn is to be used, but the yarn tends to shrink to a somewhat higher extent in water at 100 C. than when the yarn is allowed to shrink to the limited controlled extent during the heat-treatment, other conditions being equal.

In any event, the high elastic characteristics normally possessed by the isotactic polypropylene fibers and yarns are at most only slightly reduced. The final yarn therefore is not only dimensionally stable, and easy to wind, unwind, process and fabricate, but such stability is achieved without any substantial sacrifice of the desirable elastic properties.

Whether the stretched yarn is free to shrink up to 15 during the heat-treatment, or is prevented from shrinking, the residual shrinkage capacity is uniform along the length of the yarn and is not greater than 34% as a maximum, which is acceptable and permits preparation of the cops and subsequent weaving operations to be carried out smoothly, without breaking of the yarn, and in the most satisfactory manner.

As noted, the extent to which the yarn shrinks during the heat-stabilization may be between zero and 15%. Increase in the percent shrinkage, within that range and up to the limit of 15 generally results in an increased elongation at break, the tenacity remaining almost constant.

The following examples are given to illustrate the invention, it being understood that these examples are not intended as limitative.

Example 1 Using the apparatus shown in FIGURE 1, yarn of polypropylene having an intrinsic viscosity of 0.9 and consisting of isotactic polypropylene mixed with about 15% of atactic polypropylene, and having a titer of 100 den. were processed in diiferent ways with the results shown in the table below, items 1-8. The yarns were- Stretched on a warm plate (yarns of items l3) After-stretched and stabilized under controlled shrinkage (yarns of items 4-6) Stretched and stabilized while prevented from shrinking (yarn of item 7) and Stretched-and stabilized under'tension (yarn of item 8) Mechanical Character Alter Stretching and Mechanical Oharac. after immersion in Setting boiling Water for 30 min. at free shrinking Rel. Tens. No V1 V2 V3 RS. Per- Per- T T Td cent cent I II Shrin. Shrin.

R,g./ Elong. Percent R.E.I. R.E.R. M.E. R,g./ Elong. Percent R.E.I. R.E.R. den. Percent in H20 Percent Percent den. Percent in H2O Percent Percent M.E.

V =speed of roll 2 (m./min.).

Vi=speed of roll 4 (m./min.).

Va=speed of roll 6 (UL/111111.).

R.S. =stretcl1ing ratio. I

Rel. Percent=relaxation between rolls 4 and 6.

Tons. Percent=tension between rolls 4 and 6.

'1 I=temperature of the stretching medium.

'1 II=temperature oi the stretching medium between rolls 4 and 6. Td. =titer denier.

R=ultimete strength, gJden.

Elong. Percent=percent elongation at break.

Shrin. =shrinkage.

R.E.R. percent=perccnt recovery after a 10% strain of 5 minutes. R.E.I. percent=percent recovery after a 10% strain of 5 seconds. M.E.=elastic modulus, gJden.

Example 2 The yarn processed had a tenacityof 0.7 g./den., an elongation of 580%, and a titer of 300 denier, and was obtained by melt-spinning an isotactic polypropylene having an intrinsic viscosity of 0.8 and containing about 12% of atactic polypropylene. Apparatus asshown in FIG- URE 1 was used.

The yarn was stretched between roll 2 (peripheral speed 4.5 m./min.) and roll 4 (peripheral speed 27 m./min.) while passing through the warm air heater 8, having a length of 300 mm, and maintained at 130 C. The stretched yarn was passed from roll 4 into warm air heater 5 (300 mm. long) maintained at 140 C., and thence to roll 6 rotating at a peripheral speed of 24.8 m./min. The yarn was thus allowed to shrink 8% during travel thereof between rolls 4 and 6. i

From roll 6 the shrunk, heat-stabilized yarn was passed to the twisting and winding device 7. The cop thus prepared was very regular and could be unwound without diflic-ulty. The final heat-stabilzed yarn had a tenacity of 5.3 g./den., an elongation of 19%, and a titer of 30 deniers. It shrank 3% when immersed in water at 100 C. for 30 minutes.

Example 3 The yarn processed had a tenacity of 0.8 g./den., an elongation of 610%, and a titer of 300 deniers. it was obtained by melt-spinning a crystallizable polypropylene having an intrinsic viscosity of 0.95 and containing about 12% of atactic polypropylene. Using apparatus as shown in FIGURE 1, the yarn was stretched between roll 2 (peripheral speed 4 m;/min.) and roll 4 (peripheral speed 2 6 m./min.) While passing through heater 3 having a length of 300 mm. and maintained at 130 C. by hot air circulating therein.

From roll 4, the stretched yarn was passed to roll 6 (peripheral speed 23.4 m./min.) thruogh the heater 5 maintained at 145 C. and 300 mm. in length. The yarn was thus allowed to shrink 10% during the second heattreatment.

The shrunk, heat-stabilized yarn was taken up on the dominant proportion of isotactic macromolecules and which is melt-spun to the fibers that can be processed by the present method may have, in general and preferably, an intrinsic viscosity of 0.3 to 2.0. Such a polypropylene may be obtained by separation from the polymerizate resulting from polymerization of propylene with the catalysts aforesaid, by direct polymerization, or by heat-degradation of an isotactic polypropylene having a higher intrinsic viscosity.

Fibers formed by other methods, such as wetand dryspinning techniques, may also be stretched and heat-stabi lized against subsequent excessive shrinkage by the present process, and either continuously or in successive stages.

Since some changes and variations may be made in the method as specifically exemplified herein without departing from the spirit and scope of the invention it is to be understood that it is intended to include as part of this invention'such changes and variations as may be apparent to those skilled in the art.

What isv claimed is: In the manufacture of fibers of polypropylene comprising crystal-lizable isotactic macromolecules and up to 15% of amorphous, atactic, non-crystallizable macromolecules,

the method of orienting the fibers and then setting them in the oriented condition while rendering them dimensionally stable without any substantial reduction in their elastic properties, which method consists of the stepsof 1) passing the unor-iented fibers through a heating and stretching-for-orientation zone in which they are oriented by being stretched 5 to 10 times their initial length while being heated, in the absence of applied pressure, at a temperature of about C. without effecting any heatsetting of the fibers in said zone and (2.) thereafter introducing the oriented fibers into an annealing zone in which, while being maintained under a tension such that shrinkage thereof, if any, is held to a maximum of 15%, the oriented fibers are heated at a temperature of from to C., and thereby set in the oriented condition, the annealing of the fibers being performed, at least in part, prior to any twisting or winding up of the fibers.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Ingersoll July 27, 1943 Stevenson Nov. 19, 1946 Kline et a1. "May 27, 1947 Sisson Apr. 20, 1948 Hitt Nov. 30, 1948 'Miles May 30, 1950 8 Merion et a1. Aug. 8, 1950 Averns et a1 Feb. 5, 1952 Keen Feb. 16, 1954 Hasler Ian. 22, 1957 Natta et a1 Apr. 14, 1959 Hunt et a1 Sept. 20, 1960 FOREIGN PATENTS Belgium Dec. 6, 1955

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