US2917779A - Process for preparing improved thin shaped structures, such as filaments or foils, from linear polyesters - Google Patents

Description

Dec. 22, 1959 H. KURZKE ETAL PROCESS FOR PREPARING IMPROVED THIN SHAPED STRUCTURES, SUCH AS FILAMENTS OR FOILS. FROM LINEAR POLYESTERS Filed May 8, 1956 INVENTORS Herbert Kurzlte Hermut SoiHLer mmuwgqmd ATTORNEY 5 United States Patent PROCESS FOR PREPARING IMPROVED THIN SHAPED STRUCTURES, SUCH AS F ILAMENTS 0R 1F OILS, FROM LINEAR POLYESTERS Herbert Kurzke and Helmut Sattler, Bobingen, near Augsburg, Germany, assignors to Farbwerke Hoechst Aktiengesellschaft vormals Meister Lucius 8: Bruning, Frankfurt am Main, Germany, a corporation of Germany Application May 8, 1956, Serial No. 583,380

Claims priority, application Germany May 13, 1955 13 Claims. (Cl. 18-48) The present invention relates to a process for preparing improved thin shaped structures, such as filaments or foils, from linear polyesters.

In the manufacture of shaped structures from highmelting linear polyesters, especially terephthalic acid polyesters, the polymerization products in the fused mass or in solution are converted into the shaped structures. In this manner filaments are obtained by forcing the material through a nozzle provided with holes, and foils are produced by forcing the material through a nozzle provided with a slit. These preshaped structures are drawn off the nozzles by means of which they have been produced, and collected on bobbins, rollers or the like. Subsequently, the products are stretched, using appropriate devices at room temperature or at a raised temperature, to a multiple of their original dimensions, thus imparting to the products a lasting molecular orientation and consequently a high strength.

The above mentioned process becomes considerably less economical when particularly thin shaped structures from linear polyesters are to be produced, for example thin filaments, ribbons or foils. The rate at which the articles are produced cannot be simply accelerated beyond an upper limit, which in the case of filaments, for example, generally amounts to about 1000 m./min., so that a considerably greater number of manufacturing devices working at the same time, for example spinning devices, is required.

The shaped structures obtained by the known processes display over their entire length uniform cross sections of a very simple form. Filaments from polyesters possess circular cross sections, and foils from polyesters are of uniform thickness. In numerous cases it is of advantage in industry to use structures from linear polyesters the cross sections of which differ from the normal form. There may be desired, for example, cross sections which are uniform in the longitudinal d'mension of the shaped structures but not round nor of uniform thickness. There are also required structures having cross sections which vary periodically or aperiodically in form and/or area, for example certain effect threads.

Shaped structures from linear polyesters the cross sections of wh ch differ from the normal ones have hitherto been obtained by forcing the fused mass through nozzles provided with noncircular holes or not plane parallel slits. Varying cross sections are obtained by periodically influencing the formation of the structures, for example by provoking variations in spinning pressure or using mechanically oscillating spinneret plates.

All these processes are beset with great disadvantages. For example, it is difficult, if not even practically impossible, to manufacture nozzles with noncircular holes for sp nning very thin structures. When the formation process is periodically influenced, only long periodicities in the form of the cross sections are obtained due to the 2,917,779 Patented Dec. 22, 1959 very high speed at which the shaped structures are generally drawn off, or very high frequencies of the periodic influencing of the formation process must be used in order to obtain essential effects on the structures. In view of the already complicated technique of melt extrusion, such processes can scarcely be carried out in an economic manner.

It is an object of the invention to obtain drawn structures from linear polyesters such as filaments, fibers or foils, by plasticizing the non-stretched structures and subjecting them in the plastic state to permanent plastic deformation and subsequently subjecting them to molecular orientation by drawing.

The invention further provides a simple process for the preparation of thin shaped structures from linear polyesters in which thick shaped structures are converted into thinner ones, thus substantially reducing the number of shaping devices required per unit of quantity of structures to be produced. Since as starting material thick shaped structures are used, shaping devices of simpler construction which can be handled more easily can be used. Furthermore, such a process enables thick structureswhich have been obtained in any desired way, for example small ribbons, shaped foils or the like, to be converted into thin structures of similar shape.

It is another object of the invention to obtain in a simple manner structures from linear high melting polyesters which are especially formed vertically to the direction of producing. According to the invention the shaped non-stretched structures are plasticized, additionally deformed in the plastic state without molecular orientation and subsequently subjected in the usual manner in the non-plastic state to orienting drawing while maintaining the add tional formation.

It is known from US. Patent 2,578,899 to convert nonstretched shaped structures from linear polyesters into the plastic state. According to said patent newly prepared structures from linear polyesters can be converted into the plastic state at temperatures 20-60 above the apparent minimum crystallization temperature and permanently stretched or deformed in this state to a mult ple of their initial dimensions without molecular orientation. The permanently stretched structures are subsequently oriented by drawing in the usual manner at a temperature between the second order transition point of the polyester and 30' above its apparent minimum crystallization temperature. By apparent minimum crystallization temperature is meant the lowest temperature at which an essential crystallization of the polyester takes place; in the case of most of the high melting polyesters coming into consideration for the production of fibers, said temperature is at about C. The second order transition point is the temperature at which nonuniformities in the dependency of thermodynamic values on the temperature occur. Said temperature is generally with n the range from 65 C. to 70 C. The plastic stretching by which no molecular orientation is imparted is thus carried out according to the process of the above US. application at temperatures above C. and below C.

Deforming the structures in the plastic state according to the process described in the above US. patent involves the following disadvantages:

(1) The plastic non-orientating stretching must be carried out with newly shaped structures.

(2) The plasticizing temperature is between 120 C. and 160 C., that is to say above 100 C., and can therefore only be obtained by means of hot air, s ecial liquid baths or hot contact surfaces. Large quantities of material which are to be treated simultaneously cannot be easily heated with hot air or hot surfaces. When liquid baths are used the removal of the remainders of the liquid 3 of the bath from the final products involves additional inconvenience.

(3) It is an essential disadvantage of the plasticizing process that the structures so obtained possess only a relatively small strength. Filaments obtained from linear polyesters according to the examples of said patent display values of only up to 2.4 grams/denier. These strength values are far below those of the structures obtained without previous plastic stretching.

We have found, and this being surprising, that shaped non-stretched structures from linear polyesters become plastic at a temperature between the second order transition point and the apparent minimum crystallization point by means of water or steam and in this plastic state can be subjected to plastic deformation in at least one dimension Without molecular orientation. After plastic deformation without molecular orientation according to the process of the invention the structures can be oriented by drawing in the non-plastic state, while cold or hot, and yield final products which, as regards their strength values, are equal or even superior to those obtained in known manner. The structures are automatically reconverted from the plastic state into the normal non-plastic state as soon as at least one of the two requirements necessary for producing the plastic state no longer prevails, for example when the temperature of the structure drops below the second order transition point.

it is a special object of the invention plastically to stretch the structures in at least one dimension to a multiple of their original dimensions at a temperature between the second order transition point and the apparent minimum crystallization point by means of water or steam as plasticizer and subsequently to draw them in the nonplastic state thus imparting to them a molecular orientation.

The process of the invention further provides a process for the manufacture of one or two dimensional structures from linear polyesters in which the shaped structures are drawn oh the shaping device, wound up if desired, and then subjected to orienting drawing. After being drawn off the shaping device the shaped structures are plasticized in the non-stretched state at a temperature between the second order transition point and the apparent minimum crystallization point by means of water or steam as plasticizer. in the plastic state the structures are plastically deformed by mechanical means without molecular orientation in a direction deviating from the longitudinal dimension f the structures and subsequently drawn in the non-plastic state, whereby the molecules are oriented. In the direction of the manufacture the additional plastic deformation may be uniform or vary periodically. it is, however, also possible plasticallyto deform the-structures not only in a direction deviating from the direction of motion but also simultaneously or immediately thereafter in the direction of motion.

As compared with the known art the process of the invention offers considerable advantages. For example, it is no longer necessary to use newly manufactured struc ures. Several months old structures can also be plae deformed. The plastic non-orienting deformation is carried out at a temperature between 70 and 100 C., which temperature .can be easily obtained. It is of special importance that the final products possess a strength usual in common structures from linear polyesters which have been obtained without plasticizing deformation. In the case of filaments from polyethylene terephthalate, for example, the strength amounts to 5-6 g./ denier. The procedure of permanent plastic deformation is determined by the residence time of the material in the hot medium. After a sufficient long time of stay plastic deformation takes place without molecular orientation of the structure. There even occurs removal of or at least a considerable decrease in the molecular preorientation resulting from the manufacturing process of the structures. A

When the deforming procedure is carried out after a relatively short time of stay in the plasticizer, the latter has not yet completely penetrated into the structure and during deformation a molecular orientation takes place in the interior part of the structures which orientation decreases towards the exterior of the structures. Such structures which display layers of different degree of molecular orientation cannot of course be oriented by a drawing process in the same degree as completely nonoriented ones. They are particularly suited for specialized uses. They differ from the structures of the same chemical composition obtained by the known process, for example, with respect to their dye receptivity which as is known depends to a great extent on the orientation of the exterior part of the structures.

Whether non-orienting plastic stretching or partially orientaing drawing takes place depends on the time of stay in the plasticizer, its nature and temperature. In a filament having a titer of 50 deniers a drawing to 2.5 times the original length associated with 2 seconds of stay in water at C. results, for example, in a marked laminated orientation, while with a drawing to 4.2 times the original length and a time of stay of 15 seconds in steam no orientation occurs. When proceeding at a lower temperature of the plasticizer a longer time of stay is required for the non-orienting deformation. Since it is of advantage to proceed at a fairly short time to stay, the temperature of plasticizer must be near the apparent minimum crystallization point.

Furthermore, it is not necessary that the small mechanical force required for the deformation proper acts upon the structure during its whole time of stay in the plasticizer. A residence time without mechanical influence suffices and the deforming procedure can be carried out in the plasticizer at the end of said time of stay.

The non-stretched structures are plasticized as follows: The structures such'as filaments and foils are obtained in the usual manner by means of appropriate devices, generally nozzles, drawn off said devices and, if desired, wound on to the storage bobbins or rollers. In accordance with the invention the structures are then introduced into steam or water of a temperature above 70 C., preferably 95 C., and plastically deformed in at least one dimension without molecular orientation after a predetermined time of stay. If steam is used as plasticizer the structures may be previously treated with a wetting agent. If the plasticizer is water, the latter may contain a wetting agent. The plastic deforming process can be carried out continuously due to the relatively short time of stay. The structures are subsequentially subjected to a molecular orientation by drawing as usual.

The plastic deformation may be a plastic stretching or may be effected by mechanical means, both taking place in a direction deviating from the longitudinal dimensions of the structures. In the first-named case stretching without orientation in the plasticizer may be carried out to almost any enlargement of the longitudinal dimensions of the structures, in filaments, for example, to 15-20 times the original length.

By the plastic stretching according to the invention thin shaped structures can be obtained from thicker ones. A smaller number of shaping devices is required than in the known processes or if an equal number of shaping devices is used the capacity is increased in accordance with the ratio of plastic stretch without orientation. Furthermore, the shaping devices can be constructed in a considerably simpler manner since only relatively thick structures are to be produced. It is a further essential advantage of the process of the invention that it facilitates the production of thin structures of special form such as small ribbons, filaments of noncircular cross section, foils of varying thickness, etc. Such elfects can be obtained with thicker structures in a relatively easy way, for example by noncircular or profile nozzles, whereas thin structures exhibiting such effects can scarcely be obtained directly. The special form of the shaped starting material is not destroyed by the plastic deformation.

The plastic deformation of the structures in a direction deviating from the direction of preparation or longitudinal direction, which procedure is carried out before the molecular orientation, is efiected, for example, by

squeezing, embossing or shoving the structures. Several modes of executing the process of the invention can be used for realizing said deformation.

The accompanying drawing illustrates apparatus suitable for use in carrying out the process of this invention.

Fig. 1 is a side elevation partially in section of one such apparatus; and

Fig. 2 illustrates a modification of Fig. 1.

Fig. 1 illustrates a device for the plastic deformation of a filament between smooth rolls. Case 1 is filled with a plasticizer, such as steam. The case contains two smooth rolls 2 and 3 which turn in opposite directions, thus conveying between them filament 4 which enters the case by opening 5 and leaves it by opening 6. The distance between the surfaces of the rolls 2 and 3 is smaller than the diameter of the filament entering the case. Due to the action of the plasticizer contained in the case the filament becomes plastic and it is pressed together by the two rolls to form a ribbon.

Pig. 2 shows a device for the plastic formation of a filament between grooved rolls. Case 14 is filled with a plasticizer, such as steam. The case contains two rolls 7 and 8 whose convex surfaces are provided with notches 9, which are parallel with the axis. The rolls turn in opposite directions thus conveying filament 10 which enters the case by opening 13and leaves it by opening 11. The distance between the projecting parts of the convex surfaces of the two rolls is smaller than the diameter of the non-shaped filament. When passing between the rolls, the filament is provided at certain intervals with notches 12 which are preserved even after the filament has been stretched with orientation.

When after a suificient time of stay in the plasticizer filaments from linear high-melting polyesters are passed within the plasticizer between unruffied rolls, uniform 'small ribbons are obtained having cross sections the form of which is not destroyed by orienting drawing.

When filaments from polyesters are passed within the plasticizer between rotating grooved rolls, short-period variations in the cross sections of the filaments are obtained. By subsequent orienting drawing, the length of the periods only increases according to .the draw ratio.

Instead by means of rolls, plastic deformation can also be effected by any other mechanical periodic transverse compression of the plastic filament, for example by means of a hammer mill or a similar device.

By the process of the invention there can also be obtained filaments from linear polyesters the titers of which vary periodically or aperiodically. To this end the plasticized filament which continuously passes through the plasticizer must be stretched periodically, for example by periodically lengthening or shortening the passage of the filament in the plasticizer between two pairs of rolls, for example by means of an oscillating guiding pin. The periodic variations in titer thus produced are not destroyed by subsequent orienting drawing.

When several filaments are to be subjected simultaneously to plastic deformation according to one of the modes of execution described above, it is of advantage to introduce a number of continuous filaments simultaneously and side by side into the plasticizer and to pass them within the plasticizer through shaping de- 6 vices of the above kind, the shaping devices being of the same type and being arranged one beside the other. When foils from linear polyesters are passed within the plasticizer between pairs of appropriate grooved rolls,

foils'of irregular or varying thickness are obtained. By

means of grooved or fluted rolls, foils can beprepared that display optical effects which are interesting with a view to proceising. In combination with or immediately after the additional uniform or periodically varying deformation in a direction vertical to the longitudinal direction as described above, the structures can be plastically stretched according to another mode of executing the process of the invention in longitudinal direction without molecular orientation, in the plasticizer and prior to the orienting drawing. By doing so, particularly thin, additionally shaped structures are obtained. 1

The process of the invention is of special importance for shaping filaments from polymethyleneterephthalates, particularly polyethtylene terephthalate. The process is, however, also applicable to all fiber-forming synthetic linear polyesters, including those containing small portions of other modifying substances. For preparing, for example, terephthalates there can be used instead of a small quantity of ethylene glycol, another glycol such as 1,4-b'utanediol or hexamethylene glycol or another dicarboxylicacid such as adipic acid, sebacic acid, naphthalene-2,7-dicarboxylic acid, or isophthalic acid. The

process of the invention may further be used for preparing filaments or foils from polyesters obtained from hydroxycarboxylic acids such as para-w-hydroxybutoxybenzoic acid or hydroxypivalic acid.

The following examples serve to illustrate the invention but they are not intended to limit it thereto:

Example 1 Example 2 A non-stretched filament from polyethylene terephthalate consisting of 18 individual filaments and having a total titer of 200 deniers is continuously stretched without orientation to four times it original length in a water bath at 95 C. On spinning or drawing oil the nozzle, a pre-orientation is imparted to the rayon characterized by a double refraction of 3.8x l0 By plastic formation the double refraction decreases to 1.5 X10- and the preorientation decreases accordingly. The stretched filament is drawn in the cold to four times its original length, thus being oriented. In this manner a filament is obtained having a final titer of 12.5 deniers and consisting of 18 individual filaments, i.e. possessing an individual titer of 0.7 denier. The product shows a strength of 6 grams/denier.

Example 3 A non-stretched monofil from polyethylene terephthalate having a titer of 50 deniers is plasticallystretched to 2.5 times its original length in a water bath at 95 C. The stretching is carried out so rapidly as to be finished after a time of stay of 2 seconds in the plasticizer. Subat the exterior of the filament and to l7 10- in the interior of the filament, whereas the double refraction of the non-treated filament is 2.5 l0- throughout.

7 Exqmple 4 A tow from polyethylene terepththalate having a total titer of 350,000 deniers (titer of the individual filaments=44 deniers), is treated with a 2 percent solution of marseilles soap. The material is then continuously introuced at a rate of 2 m./min. into a steam chamber which is 1 m. long and into which saturated steam is continuously introduced. After having been plastically stretched in said steam chamber without orientation to about 4.5 times its length, the tow is drawn oif said steam chamber at a rate of 9.1 m./min. via 4 rolls. Subsequently the cable is oriented by continuously drawing, also in a steam bath, to 4.1 times its length. After this procedure the individual filaments of the tow possess a titer of 2.3 deniers, an elongation at break of 38 percent and a tensile breaking strength of 5.2 grams/ denier.

Example 5 A tow from polyethylene terephthalate having a total titer of 120,000 deniers (titer of the individual filaments=50 deniers) is introduced at a rate of l m./min. into the steam bath described in Example 4 and stretched therein plastically and without orientation to 15.6 times its original length. The tow is subsequently subjected to normal orienting drawing with steam, the draw ratio being 1:3. After said procedure the individual filaments of the tow possess a titer of 1.1 deniers, an elongation at break of 23 percent and a tensile strength of 5.1 grams/ denier.

Example 6 A tow from polyethylene terephthalate having a total titer of 3,000 deniers (titer of the individual filaments =50 deniers) is introduced at a rate of 3 rn./rnin. into the steam chamber described in Example 4 where it is plastically stretched without orientation to 4.2 times its length. The tow is subsequently oriented by drawing in the usual manner in a ratio of 1:4.2. After this procedure the individual filaments of the tow possess a final titer of 2.8 deniers, an elongation at break of 28 percent and a tensile breaking strength of 6.4 grams/ denier.

Example 7 A non-stretched monofil of 50 deniers from polyethylene terephthalate is plasticized in a water bath at 95 C. with a time stay of 20 seconds and conveyed in the plasticizing bath by means of unrufiled rolls. The filament is subsequently subjected to orienting drawing. In this manner a small ribbon is obtained having a titer of deniers and a tensile strength of 4 grams/ denier. The ribbon has a cross section the breadth of which is to the thickness as 5:1.

Example 8 A non-stretched monofil of 50 deniers from polyethylene terephthalate is plasticized in a water bath at 95 C. with a time of stay of 20 seconds, the material being conveyed in the bath between unruffied rolls. Subsequently the monofil is permanently stretched in the plasticizing bath Without molecular orientation in the ratio of 1:2.5 by being drawn oil the unrufi'led rolls. The filament is subsequently oriented by drawing. A filament having the form of a small ribbon is obtained which possesses a titer of 4 deniers, an elongation at break of 4 grams/denier and a cross section profile of 1:5.

Example 9 A non-stretched monofil of 50 deniers from polyethylene terephthalate is p lasticized in a water bath of 95 C., the material being conveyed in the water bath by means of fluted rolls. After orienting drawing, the titer of the filament displays short periodic variations in the ratio of 1:2.

We claim:

1. In'the process for producing improved filaments,

yarns, films and like structures of synthetic, linear, polyesters, in which process the structures are drawn off a shaping device and then subjected to a molecular orienting drawing, the step which comprises plasticizing the nonstretched structures by means of steam as plasticizer at a temperature between the second order transition point of the amorphous polyester in the nonplas'ticized state and its apparent minimum crystallization point, subjecting the structures in the plastic state to permanent plastic deformation in at least one direction without molecular orientation, and subsequently subjecting the structures in a non-plastic state to a molecular orienting drawing.

2. In the process for producing improved filaments, yarns, films, and like structures of synthetic, linear polyesters, in which process the structures are drawn oil a shaping device and then subjected to a molecular orienting drawing, the step which comprises plasticizing the nonstretched structures by means of water as plasticizer at a temperature between the second order transition point of the amorphous polyester in the non-plasticized state and its apparent minimum crystallization point, subjecting the structures in the plastic state to permanent plastic deformation in at least one direction without molecular orientation, and subsequently subjecting the structures in a non-plastic state to a molecular orienting drawing.

3. In the process for producing improved filaments, yarns, films, and like structures of synthetic, linear polyesters, in which process the structures are drawn off a shaping device, wound on to a bobbin and then subjected to a molecular orienting drawing, the step which comprises plasticizing the non-stretched structures by means of steam as plasticizer at a temperature between the second order transition point of the amorphous polyester in the non-plasticized state and its apparent minimum crystallization point, subjecting the structures in the plastic state to permanent plastic deformation in at least one direction without molecular orientation, and subsequently subjecting the structures in a non-plastic state to a molecular orienting drawing.

4. In the process for producing improved filaments, yarns, films and like structures of synthetic, linear polyesters, in which process the structures are drawn off a shaping device and then subjected to a molecular orienting drawing, the step which comprises plasticizing the nonstretched structures by means of steam as plasticizer at a temperature between the second order transition point of the amorphous polyester in the non-plasticized state and its apparent minimum crystallization point, subjecting the structures in the plastic state to a plastic stretching in at least one direction without molecular orientation, and subsequently subjecting the structures in a non-plastic state to a molecular orienting drawing.

5. In the process for producing improved filaments, yarns, films, and like structures of synthetic, linear polyesters, in which process the structures are drawn off a shaping device and then subjected to a molecular orienting drawing, the step which comprises plasticizing the non-stretched structures by means of steam as plasticizer at a temperature between the second order transition point of the amorphous polyester in a non-plasticized state and its apparent minimum crystallization point, subjecting the structures in the plastic state to a plastic deformation by mechanical action, without molecular orientation, in a direction deviating from the longitudinal direction of the structures and subsequently subjecting the structures in a non-plastic state to a molecular orienting drawing.

6. In the process for producing improved filaments, yarns, films, and like structures of synthetic, linear polyesters, in which process the structures are drawn off a shaping device and then subjected to a molecular orienting drawing, the step which comprises plasticizing the non-stretched structures by means of steam as plasticizer at a temperature between the second order transition point of the amorphous polyester in the non-plasticized state and its apparent minimum crystallization point, subjecting the structures in the' plastic state, without molecular orientation, to a plastic stretching in their longitudinal direction and simultaneously to a plastic deformation, without molecular orientation, in a direction deviating from the longitudinal direction of the structures and subsequently subjecting the structures in a non-plastic state to a molecular orienting drawing.

7. In the process for producing improved filaments, yarns, films, and like structures of synthetic, linear polyesters, in which process the structures are drawn off a shaping device and then subjected to a molecular orienting drawing, the step which comprises plasticizing the non-stretched structures by means of steam as plasticizer at a temperature between the second order transition point of the amorphous polyester in the non-plasticized state and its apparent minimum crystallization point, subjecting the structures in the plastic state, without molecular orientation, to a plastic stretching in their longitudinal direction, and in any desired succession to a plastic deformation, without molecular orientation, in a direction deviating from the longitudinal direction of the structures and subsequently subjecting the structures in a non-plastic state to a molecular orienting drawing.

8. The process according to claim 1 wherein the nonstretched structures remain in the plasticizing medium for such a short period that the plasticizing medium is permitted to penetrate only the outer portion of the structure, whereby a partial permanent molecular orientation is set up within the interior portion of the nonstretched structure when being deformed.

9. The process according to claim 5, wherein the nonstretched structures are conducted within the plasticizing medium between rotating unruffled rollers.

10. The process according to claim 5, wherein the non-stretched structures are conducted within the plasticizer between rotating grooved rollers.

11. The process according to claim 1, wherein the plasticizer is water at a temperature within the range from C. to C.

12. The process of claim 1, wherein the synthetic linear polyesters are polymethylene terephthalates.

13. The process of claim 1, wherein the synthetic linear polyester is polyethylene terephthalate.

References Cited in the file of this patent UNITED STATES PATENTS 2,556,295 Pace June 12, 1951 2,578,899 Pace Dec. 18, 1951 2,734,794 Calton Feb. 14, 1956 FOREIGN PATENTS 712,950 Great Britain Aug. 4, 1954

Images