US3019507A

US3019507A - Method of making bulky continuous filament yarns of isotactic polyolefins

Info

Publication number: US3019507A
Application number: US727398A
Authority: US
Inventors: Maragliano Domenico; Denti Francesco
Original assignee: Montedison SpA
Current assignee: Montedison SpA
Priority date: 1959-02-18
Filing date: 1958-04-09
Publication date: 1962-02-06
Anticipated expiration: 1979-02-06
Also published as: FR1194370A; GB882329A; NL248500A; US3137989A; DE1302793C2; CH376220A; BE587716A; ES255841A2; DE1302793B

Description

Feb. 6, 1962 D. MARAGLIANO ETAL METHOD OF MAKING BULKY CONTINUOUS FILAMENT YARNS OF ISOTACTIC POLYOLEFINS Filed. April 9, 195a iii;

INVENTORS DOMEN/CO MPAG'LH/VO FRANCESCO DENT/ ATTORNEYS 3,tl19,507 METHOD OF MAKING BULKY CGNTHNUOUS FILAMENT YE; F ISOTACTEC POLY- OLEFKNS Domenico Maragliano and Francesco Denti, Milan, Italy,

assignors to Montecatini Societa Generale per llndustria Mineraria e Chimica, Milan, Italy Filed Apr. 9, 1953, Ser. No. 727,398 Claims priority, application ltaly Apr. 11, 1957 7 tClaims. (Cl. 28--72) This invention relates to yarns and to processes for making the same.

Yarns formed from continuous filaments of synthetic polymers are generally not adapted to use for purposes requiring a soft, light yarn having high covering power. When yarns meeting those needs are required, it is conventional to use a spun yarn, i.e., a yarn formed from short or staple fibers of the synthetic polymers, by the process normally used in making yarns from natural fibers such as cotton, wool, etc. For that reason, continuous filaments formed from synthetic polymers and synthetic resins generally have not been fabricated as such in practice but have been cut or otherwise disrupted to staple fibers and the mass of short fibers thus obtained has then been converted into a spun yarn, as such or in a blend with natural fibers.

There is a great need in the art for a yarn formed from continuous synthetic polymer filaments but having the softness, light Weight, and marked covering power of the yarns spun from staple fibers, and for a method of making such yarns, so that the operations involved in producing spun yarns, i.e., the crimping and cutting and the expensive after-treatments, can be eliminated.

Heretofore, no satisfactory process for making bulky, voluminous yarns from continuous filaments of the synthetic fiber-forming polymers has been available. In fact, some of the processes proposed for accomplishing that objective have been based on complex working cycles which are so expensive that the yarns obtained are neither entirely satisfactory nor competitive with spun yarns. Other less complex methods that have been suggested for producing continuous filament yarns of increased bulk yield yarns the bul"iness of which is not permanent, or which have poor mechanical characteristics the values for which are substantially no better than, and practically the same as, the values for the mechanical properties of unstretc'ned yarns.

One object of this invention is to provide new yarns formed from continuous synthetic polymer filaments and having a bulk equal to or higher than that of staple yarn.

Another object is to provide bulky yarns of the continuous synthetic polymer filaments which have a tenacity much higher than the tenacity normally possessed by yarns spun from staple synthetic fibers.

An additional advantage is to provide a multi-filament yarn which is light and voluminous like a staple yarn, but which does not tend to lose its hairiness.

A further object is to provide a method for making light, voluminous yarns of continuous filaments of synthetic polymers.

These and other objects are accomplished by the present invention in accordance with which continuous filament yarns are made from synthetic polymers of higher alpha-olefins consisting prevailingly of isotactic macromolecules, particularly such polymers of propylene.

G. Natta and his co-worlters have disclosed (e.g., in two papers entitled, respectively, A New Class of Alpha- Olefin Polymers Having Exceptional Uniformity of Structure and The Crystalline Structure of a New Type of Polypropylene, presented at a meeting of Accadernia amass? Patented Feb. 6, 1952 Nazionale Dei Lincei on December 11, 1954 and published in the Proceedings of the Accademia on January 27, 1955), entirely new polymers of the alpha-olefins CH =CHR in which R is an alkyl radical containing 1 to 16 carbon atoms. The polymers are linear, regular head-to-tail, contain substantially no branches longer than R, and possess different steric structures which Natta has termed isotactic and atactic.

The isotactic structure is characterized in that, assuming the macromolecular main chain to be fully extended in a plane, the R groups bound to the tertiary asymmetric carbon atoms of adjacent monomeric units occur, on the same chain section, on one side of the plane, and the hy drogen atoms bound to those carbon atoms occur, on said chain section, on the opposite side or" the plane.

In the atactic polymers, on the other hand, again assuming the macromolecular main chain to be fully eX- tended in a plane, the R groups and hydrogen atoms bound to the asymmetric tertiary carbon atoms of adjacent monomeric units are randomly distributed on the two sides of the plane.

As Natta et al. have shown, the sterically difierent polymers may be produced in admixture when the alphaolefin is polymerized by means of certain organometallic catalysts, and may be separated on the basis of the difference in their steric structure by selective organic solvents. Natta et al. have also disclosed that, using specific organometallic catalysts, the polymerization of the alpha-olefin can be oriented to the direct production of a polymerizate which consists prevailingly to substantially of isotactic macromolecules, that is, of macromolecules having substantially the isotactic structure, or which consists prevailingly to substantially of linear, regularly head-to-tail atactic macromolecules.

The yarns of the present invention are made from the Natta et al. poly(a1pha-olefins) which consist prevailingly (for our purposes over 60%) of isotactic macromolecules.

In practicing the invention, continuous filaments of the prevailingly to substantially isotactic poly(alpha-olefin) and especially filaments of such polymers of propylene, are formed into a yarn, and the yarn is stretched under special conditions resulting in the introduction into the individual filaments of internal strains which are non uniformly distributed along the filament length. The stretched yarn is then immersed abruptly into a hot medium in which it is heated rapidly to cause rapid shrinkage of the internally strained filaments. The rapid shrinkage of the irregularly strained filaments causes the formation of waves or crimps in the individual filaments resulting in a yarn which is crimped in a specific manner. The crimp is distributed irregularly along the filaments and yarn, with the loops disposed in different planes. The crimps serve to separate the individual filaments in the yarns from each other, so that air spaces are formed between the crimps. The air spaces contribute to the bulk, lightness, and insulating capacity of the yarn, and the crimps render the yarn highly elastic because they can stretch under tensile stress and then resume their initial shape as soon as the stress is removed. Moreover, the filaments and yarn obtained as described, are permanently crimped as shown by the tests illustrated hereinbelow.

The factors at the stretchin stage which are determinative so far as obtaining our results is concerned are the rate at which the yarn is stretched, i.e. the rate at which the yarn is fed through the stretching zone, and the stretching temperature. For optimum results, the yarns are stretched at the maximum safe rate for the given temperature, the limit being the point at which the filaments break under the given conditions. In general, the

3 yarns are subjected to a high rate of stretching at a relatively low temperature.

The term isotactic defines the particular steric structure and is not synonymous with crystalline, since the isotactic structure exists independently of whether the polymer is crystalline or not under the given conditions. However, the isotactic polymers are crystallizable and under appropriate conditions are crystalline.

Stretching of the filaments results in orientation of the crystals in the direction of the filament axis. It is an important feature of the present method that the orientation of the crystals in the filaments is not destroyed by the processing producing the crimping, and that the final crimped yarn which is obtained has the high tensile strength which is a characteristic of oriented crystalline yarns.

This is in contrast to the results obtained by processes dependent on strong shrinking of the yarns, during which most of the orientation of the crystals is destroyed, and which yield a final yarn the tenacity of which is no better than the tenacity of the unstretched yarn.

In general, as is known, yarns of synthetic resins are stretched at a rate of to meters/minute and at a temperature between 80 C. and 145 C.

Those conditions, which are conventional, do not result in the present bulky continuous filament yarns.

On the contrary, our bulky, voluminous final yarns are obtained by feeding the yarn formed from continuous filaments of the at least prevailingly isotactic poly(alphaolefin) through the stretching zone at a rate of to 150 meters/minute and at a temperature between 20 C. and 80 C.

The stretching ratio can vary between 1:25 and 1:55.

Release of the irregularly distributed internal strains introduced by the stretching, and the resulting crimping of the yarn, are effected at a temperature between 50 C. and the melting point of the poly(alpha-olefin), i.e., at between 50 C. and about 170 C. in the case of the polypropylene.

The specific conditions, and combination of conditions, can be varied within the ranges stated, depending on the molecular weight of the poly(alpha-olefin) and the titre of the yarn, both of which can influence the results obtained. by the stretching. The ranges given, however, are generally operative for yarns having widely varying titres and for poly(alpha-olefins) of widely different average molecular weight, so that regardless of the yarn titre and molecular weight of the polymer, values in the ranges given for the stretching rate, stretching temperature, and relaxing temperature can be used in combination to produce the optimum results.

In the accompanying drawing,

FIGURES 1-A and 1-B illustrate the eifects obtained by crimping a continuous IS-filament yarn of polypropylene by the present method; the yarn has on the average 12 to 15 crimps per inch.

FIGURE 2 shows the bulk effect obtained by the present method in the case of a twisted 6-filament yarn (see Example 2 below) having a titre of the same order as conventional wool yarns;

In FIGURES l-A and 1-13, the yarn is shown enlarged approximately 15 times, while in FIGURE 2 the enlargement is 8 times.

The properties of a continuous-filament bulky polypropylene yarn (A) produced according to the invention are compared in the table below, with those of a normal yarn (B) formed from continuous filaments of the polypropylene, and of a yarn (C) spun from staple fibers of the polypropylene.

The volume of the yarn was established by winding a given constant amount of the three different yarn types on reels, under constant tension, and then determining the volume geometrically.

Tests performed with an Instron dynamometer have shown that when our bulky continuous filament yarns are subjected to deformation cycles equivalent to those to which the yarns are subjected in textile operations, they do no change in shape, voluminosity, or in the frequence of loops per unit of length, and that the crimp is permanent.

A particularly bulky yarn can be obtained by crimping a continuous filament yarn by our method as described herein, disrupting the crimped yarn to obtain staple or short fibers, and then spinning the staple fibers into a yarn.

The embodiment of our invention described above consists of the two stages (1) stretching the yarn under the particular conditions, and (2) rapidly heating the stretched yarn to release the nonuniformly distributed internal strains introduced into the filaments by the stretching.

In an alternative embodiment within the scope of our invention, the yarns, after being subjected to stages (1) and (2), are coupled and twisted with yarns which have passed through stage 1) only, and the yarn resulting from the coupling and twisting operation is then subjected to the thermal treatment of stage (2).

In still another modification, the continuous filament yarn which has passed through stage (1) above, is coupled with a normal yarn formed from continuous filaments of a poly(alpha-olefin) and the coupled yarns are allowed to shrink at high temperatures.

By normal continuous filament yarn as used herein is meant yarns formed from continuous filaments of the polymers which may be stretched under the usual or conventional conditions for orientation of the crystals but which are not processed according to this invention, that is, yarnswhich are not stretched under the present special conditions and then abruptly heated to relax the internal strains.

The bulky yarns of the invention are adapted for use in the production of soft, bulky fabrics which have a high covering power and high thermal insulating capacity. The fabrics are made by the usual processes, using the bulky voluminous yarns for both the warp and the weft. Fabrics can also be constructed in which the bulky voluminous yarns of the invention are used for the weft, and the web consists of a normal continuous yarn or of a staple fiber yarn. Also, the normal continuous yarn or the staple fiber yarn can be used for the weft, while the new bulky continuous yarn is used for the web. In another, specific embodiment, a fabric is made in which the weft, the warp, or both consists (consist) of a continuous filament yarn whichhas been stretched under our particular conditions, and the fabric is then subjected to the thermal treatment of stage (2) of our method, to relax the strains and develop the crimp in the filaments and yarns in situ in the fabric.

In addition to providing satisfactory entirely acceptable and desirable bulky continuous filament yarns of the synthetic polymers, the invention has the advantage that the yarns are obtained by a method involving an essentially normal working cycle using conventional equipment, and with changes only in specific conditions.

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

Example 1 A prevailingly isotactic polypropylene having an intrinsic viscosity of 0.9 determined in tetrahydronaphthalene at 135 C. is melt-extruded to form filaments through a spinneret having holes of 0.4 mm. diameter. The single extruded filaments have a titre of den.

Eighteen of the filaments are combined to form a yarn which is stretched on a warm plate (temperature of the plate: 70 C.) at a rate of 50 meters/minute, with a stretching ratio of 1:4.

After stretching, the yarn (in the form of a skein) is placed in an autoclave into which steam at 120 C. is introduced. The yarn shrinks immediately, and assumes a crimped condition; the heating, shrinking and crimping are completed in five minutes.

The characteristics of the yarn (A) thus obtained are tabulated below and compared with those of a normal continuous yarn (B) of the same polypropylene, i.e., an 18-filament yarn which was not subjected to stages (1) and (2) of the present process.

Filaments are obtained by melt-extrusion of a prevailingly isotactic polypropylene having an intrinsic viscosity of 1.1, and 18 of the filaments are formed into a yarn which is stretched at 55 C. on a Warm plate with a stretching ratio of 113.5, and at an outlet rate of 175 meters/min. Six ends of the resulting yarn are coupled and twisted at 40 turns/meter.

The yarn, in the form of skeins, is treated in an autoclave at 115 C. for 5 minutes.

A very bulky yarn, shown in FIGURE 3 of the drawing (enlarged 8 times) and having the following characteristics is obtained:

Example 3 A fabric of bee hive weave was constructed using as the warp a normal yarn having a titre of 320 den. and formed of continuous filaments of highly isotactic poly propylene having an intrinsic viscosity of 1.3, and as weft a yarn of the continuous polypropylene filaments having a count of 350 den. and which was stretched (stage 1 of the present process) but not subjected to the thermal treatment (stage 2).

The fabric was treated in an autoclave at 115 C. for 5 minutes. A soft, particularly voluminous fabric was obtained.

The characteristics of the final fabric (A) are summarized below, and compared to those of the fabric (13) before the thermal treatment. The thickness given was determined according to ASTM D 76/49.

Fabric Type Thickness, Weight, Volume,

mm. g./meter calg.

fabric, but below the melting temperature for the synthetic polymer.

Various changes in details may be made in practicing the invention without departing from the spirit thereof. Therefore, we intend to include in the scope of the appended claims all such variations and modifications as may be apparent to those skilled in the art.

What is claimed is:

1. The process comprising the steps of forming a yarn of smooth, continuous melt-extruded filaments of a fiberiorming polymeric higher alpha-olefin consisting prevailingly of isotactic, crystallizable macromolecules, heating the yarn at a temperature between 20 C. and C. while stretching it at the maximum safe rate for the given temperature between 20 C. and 80 C. by feeding it through a stretching zone at the rate of 30 to 150 meters/minute and stretching it with a stretch ratio between 1:2.5 and 1:55 to introduce into the individual filaments of the yarn internal strains which are irregularly distributed along the lengths of the individual filaments, abruptly introducing the yarn of stretched, irregularly strained filaments into a medium in which it is heated rapidly, without the application of tension thereto, to a temperature between 50 C. and the melting point of the polymeric alpha-olefin and selected in dependence on the stretching temperature to release the strains introduced into the filaments by the stretching, the release of the irregularly-distributed internal strains resulting in the formation of crimps in the individual filaments which crimps are irregularly distributed along the length of the filaments with their loops disposed in different planes, and the crimps in the different filaments serving to separate the individual filaments of the yarn from each other and provide air spaces between the crimps which contribute to the bulkiness, lightness and insulating capacity of the yarn, the bulky yarn being further characterized in that the orientation of the crystallites of the polymeric alphaolefin resulting from stretching of the smooth continuous filaments is substantially retained in the crimped filaments, and the yarn consisting of the crimped filaments has substantially the same tensile strength as the stretched and oriented yarn prior to the relaxation of the strains and crimping.

2. The process according to claim 1, characterized in that smooth, continuous melt-extruded filaments of a fiberforming polypropylene consisting prevailingly of isotactic macromolecules are formed into a yarn which is stretched and then abruptly heated in relaxed condition to release the irregularly distributed strains introduced into the individual filaments during the stretching.

3. The process according to claim 2, characterized in that smooth, continuous melt-extruded filaments of a fiber-forming polypropylene consisting prevailingly of isotactic macromolecules are formed into a yarn and, after the stretching, the yarn is introduced abruptly into a medium in which it is heated rapidly, without the application of tension thereto, to a temperature between 80 C. and C.

4. The process according to claim 2, characterized in that the stretched yarn formed of the polypropylene filaments is introduced abruptly into a chamber in which it is treated, in relaxed condition, with superheated steam.

5. The process according to claim 2, characterized in that a plurality of ends of the stretched yarn formed of the polypropylene filaments are coupled and twisted, and the twisted yarns are then introduced abruptly into a chamber in which they are treated, in relaxed condition, with superheated steam.

6. The process acwrding to claim 2, characterized in that the stretched yarns consisting of the irregularly strained polypropylene filaments are incorporated in a fabric and the fabric is then heated rapidly, without the application of tension thereto, to release the strains irregularly distributed in the polypropylene filaments and efiect the crimping of said filaments in situ in the fabric.

7. The process according to claim 2, characterized in that the bulky yarns comprising the polypropylene filamerits having the crimps irregularly distributed along the lengths of the individual fibers are disrupted to obtain a mass of discontinuous crimped fibers.

References Cited in the file of this patent UNITED STATES PATENTS 8 lngersoll July 27, Heymann Feb. 13, Stevenson et a1. Nov. 19, Rugeley et al. May 13, Kulp et a1 Apr. 20, Sisson Apr. 20, Hebeler July 29, White June 19, Hasler -1; Jan. 22, Griset Oct. 1,

Natta et a1. Apr. 14,

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,019,507 February 6 1962 Domenico Maragliano et a1.

- It is hereby certified that error appears in the above numbered pat ent requiring correction and that the said Letters Patent should read as corrected below.

Column 5, line 35 for "FIQURE 3" read FIGURE 2 Signed and sealed this 4th day of September 1962:.

( SEA L) Attest:

DAVID L. LADD ERNEST W SWIDEB.

Commissioner of Patents Attesting Officer

Claims

1. THE PROCESS COMPRISING THE STEPS OF FORMING A YARN OF SMOOTH, CONTINUOUS MELT-EXTRUDED FILAMENTS OF A FIBERFORMING POLYMERIC HIGHER ALPHA-OLEFIN CONSISTING PREVAILINGLY OF ISOTACTIC, CRYSTALLIZABLE MACROMOLECULES, HEATING THE YARN AT A TEMPERATURE BETWEEN 20* C. AND 80* C. WHILE STRETCHING IT AT THE MAXIMUN SAFE RATE FOR THE GIVEN TEMPERATURE BETWEEN 20* C. ASND 80* C. BY FEEDING IT THOUGH A STRETCHING ZONE AT THE RATE OF 30 TO 150 METRES/MINUTE AND STRETCHING IT WITH A STRETCH RATIO BETWEEN 1:2.5 AND 1:5.5 TO INTRODUCE INTO THE INDIVIDUAL FILAMENTS OF THE YARN INTERNAL STRAINS WHICH ARE IREEGULARLY DISTRIBUTED ALONG THE LENGTHS OF THE INDIVIDUAL FILAMENTS, ABURPTLY INTRODUCING THE YARN OF STRETCHES, IRREGULARLY STRAINED FILAMENTS INTO A MEDIUM IN WHICH IT IS HEATED RAPIDLY, WITHOUT THE APPLICATION OF TENSION THERETO, TO A TEMPERATURE BETWEEN 50* C. AND THE , MELTING POINT OF THE POLYMERIC ALPHA-OLEFIN AND SELECTED IN DEPENDANCE OF THE STRETCHING TEMPERATURE TO RELEASE THE STRAINS INTRODUCED INTO THE FILAMENTS BY THE STRETCHING, THE RELEASE OF THE IRREGULARLY-DISTRIBUTED INTERNAL STRAINS RFESULTING IN THE FORMATION OF CRIMPS IN THE INDIVIDUAL FILAMENTS WHICH CRIMPS ARE IRREGULARLY DISTRIBUTED ALONG THE LENGTH OF THE FILAMENTS WITH THEIR LOOPS DISPOSED IN DIFFERNET PLANES, AND THE CRIMPS IN THE DIFFERENT FILAMENTS SERVING TO SEPARATE THE INDIVIDUAL FILAMENTS OF THE YARN FROM EACH OTHER AND PROVIDE AIR SPACES BETWEEN THE CRIMPS WHICH CONTRIBUTE TO THE BULKINESS, LIGHTNESS AND INSULTING CAPACITY OF THE YARN, THE BULKY YARN BEING FURTHER CHARACTERIZED IN THAT THE ORIENTATION OF THE CRYSTALLITES OF THE POLYMERIC ALPHAOLEFIN RESULTING FROM STRETCHING OF THE SMOOTH CONTINUOUS FILAMENTS IS SUBSTANTIALLY RETAINED IN THE CRIMPED FILAMENTS, AND THE YARN CONSISTING OF THE CRIMPED FILAMENTS HAS SUBSTANTIALLY THE SAME TENSILE STRENGTH AS THE STRENGTH AND ORIENTED YARN PRIOR TO THE RELAXATION OF THE STRAINS AND CRIMPING.