US3329755A

US3329755A - Process of treating polycarbonate fibrous structures

Info

Publication number: US3329755A
Application number: US398397A
Authority: US
Inventors: Reichardt Manfred; Reichle Alfred; Rellensmann Wolfgang
Original assignee: Bayer AG
Current assignee: Bayer AG
Priority date: 1963-09-25
Filing date: 1964-09-22
Publication date: 1967-07-04
Anticipated expiration: 1984-07-04
Also published as: BE653490A; DE1435459A1; DE1303448B; BE653489A; GB1077507A; GB1066187A; DE1303448C2; BE653491A; GB1077506A

Description

3,329,755 PROCESS OF TREATING POLYCARBONATE FIBROUS TRUCTURES Manfred Reichardt, Bla von Falkai, Alfred Reichle, and Wolfgang Rellensmann, Dormagen, Germany, assignors to Farbenfabriken Bayer Aktiengesellschaft, Leverkusen, Germany, a German corporation No Drawing. Filed Sept. 22, 1964, Ser. No. 398,397 Claims priority, application Germany, Sept. 25, 1963,

F 40,831, F 40,832, F 40,833 v 6 Claims. (Cl. 264-210) This invention relates to improvements in the manufacture of synthetic fibers, films, yarns, woven and knitted fabrics and the like from high molecular weight polycarbonates.

More particularly, this invention relates to methods for treating polycarbonate fibers, films, yarns, fabrics and the like to improve their physical characteristics.

In one aspect this invention is addressed to the elevated temperature stretching of initially stretched fibers, films, yarns, fabrics, etc., obtained from polycarbonates.

A further aspect of the invention is the treatment of polycarbonate structures, such as threads, films, woven and knitted fabrics, yarns and the like, whereby the same are provided with a uniform and stable crimp.

Still a further aspect of the invention is the fixation by application of heat of polycarbonate structures, such as fibers, threads, films, woven and knitted fabrics and the like, for imparting thereto dimensional stability.

It is known that the mechanical, physical, and textile technologically important properties of crystallizable, thermoplastic, synthetic, high molecular weight polymeric structures, such as fibers, films, yarns, foils, bands, and wires can be considerably improved by stretching. It is further known that stretching may generally be carried out at a temperature which lies between the freezing and the melting point of such crystallizable, thermoplastic, synthetic high molecular weight polymeric material. The optimum temperature for stretching within this Wide temperature range falls, for polycarbonates, within the same narrow temperature interval in which the tangent of the dielectric loss angle attains a maximum. Polycarbonate structures drawn or stretched by 1:3 to 1:5 generally have imparted thereto tensile strengths of between 3.2 and 4.2 g./den. at elongations at break of 25 to 35%, when this stretching temperature is employed. The tensile strength and elongation attained are largely determined by the type of polycarbonate and, in particular the molecular weight of the initial material, the degree of polymerization and molecular weight distribution thereof.

In accordance with the invention it has now been discovered that in the production of fibers, films, yarns, tapes, fabrics and the like from polycarbonates, having a molecular Weight of about 20,000 to about 100,000 preferably 60,000 to 80,000, particularly those based on the di monohydroxy-diarylalkanes, -sulphones, -sulphoxides, -sulphides or ethers or mixtures of these dihydroxy compounds with each other, products which are superior in such desired mechanical and textile technological properties as elastic modulus, tensile strength,

3,329,755 1C6 Patented July 4, 19 7 etc., can be obtained by subjecting the stretched fibers or films to an after-stretching in the temperature range at which the tangents of the dielectric loss angle of the stretched material has its first subsidiary maximum. This characteristic quantity can be determined experimentally by the method described by F. Krum and F. H. Miiller (K-olloid-Zeitschrift 164 (1959) pages 81-107). For measuring the loss angle of fibrous structures, it is preferable to employ as measuring condenser cell the cell described by Hearle in the book by Morton and Hearle Physical Properties of Textile Fibres (1962) page 440.

The process of the invention is particularly applicable to the after-stretching of fibrous structures of improved crystallinity such as are obtained by the methods described in US. patent applications Ser. No. 356,052, Ser. No. 356,076, both filed Mar. 21, 1964, and Ser. No. 356,- 053, filed Mar. 31, 1964, and now US. Pat. No. 3,287,316, all having a common assignee. The after-stretching can best be carried out continuously following a pre-stretching of the starting material employing the same heating and stretching apparatus as are conventionally used in the initial stretching processes composed of the usual elements, i.e., the heating rollers, heating irons, heating plates, heating rods, nozzles and pipes fed with hot air or hot inert gases, hot air chambers, heating baths, etc. Filaments can be after-stretched in accordance with the invention to a total titer of about 1,000 den. using heating irons and heating rollers, and thicker endless bands can be after-stretched to titers of up to about 10 den., using therefor heating plates.

The extent of the after-stretching is dependent on the type of the polycarbonate, the molecular weight thereof, the molecular weight distribution, and also and particularly on the conditions selected for the spinning and stretching.

The extent of the after-stretching advantageously should be for crystalline spun fibers and films initially stretched with a stretching ratio of 1:3 to 1:6 between 5 and 100% and, preferably, 20 and 50% for fibers which have been stretched at ratio of 1:4 to 1:5. The after-stretched fibers and films obtained in accordance with the invention have tensile strengths of up to 5.8 g./ den. at elongations at break of 10 to 20%.

The after-stretching, in addition to the improvement in the tensile strengths, considerably improves the other properties of the fibrous material and, in particular, the elastic properties thereof. Thus, the usual values for the E-modulus (200 to 400 kp./mm. of polycarbonate fibers and films which have only been stretched once can be increased to 500 to 700 kp./mm. by after-stretching The degree of elasticity when loaded with of the breaking load increases from 55% in fibers and films stretched but once (only initially) to in the afterstretched structures (complete elasticity).

Further, the after-stretched structures according to the invention are distinguished by greater resistance to solvents owing to their improved crystallinity.

The optimum temperature for effecting the afterstretching is determined by measuring the tangent of the dielectric loss angle (tg 6) of the stretched structure prior to carrying out the after-stretch and should be chosen between 5 C. above and 5 C. below the maximum. The temperature position and absolute value of the subsidiary maximum which has been termed by F. Krum and F. H. Miiller the stretching dispersion region differs for each formed structure and for each polycarbonate according to the frequency employed and also depends on the chemical structure, the molecular weight, the morphological structure and, in particular, on the selected stretching ratio. Whereas this stretching dispersion region of F. Krum and F. H. Miiller falls within the temperature range of between 40 and 120 C. (maximum 75 C.) for a film which has been stretched by 90% at 25 C. at a frequency of 1 kilocycle per second, this dispersion region for fibers which have been stretched hot by 500% falls within the temperature range between 50 and 165 C.

According to a further feature of this invention, it has now been found that threads, fibers, yarns, twists, woven and knitted materials and the like, prepared from polycarbonates based on dimonohydroxy-diarylallcanes, -sulphones, -sulphoxides, -sulphides, or -ethers or mixtures of these dihydroxy compounds with each other, can be provided with a crimp of optimum uniformity and stability by heating the material during the crimping process to a temperature which corresponds to ':5 C. of the maximum position of the tangent of the dielectric loss angle in the first subsidiary maximum. This characteristic quality can be determined experimentally by the method described by F. Krum and F. H. Miiller (Kolloid-Zeitschrift 164 (1959) pages 81-107). For measuring the loss angle of fibrous structures, it is preferable to employ as measuring condenser cell the cell described by Hearle in the book by Morton and Hearle Physical Properties of Textile Fibres (1962) page 440.

In the process of this invention, it is particularly advantageous to employ a compression crimping process using in that connection a compression chamber which can be heated with accuracy to at least within :2.5 C. The material to be crimped, as for example a bundle of fibers, is preferably preheated to the required temperature before the same enters into the compression chamher.

The optimum crimping temperature for use in accordance with this feature of the invention is determined by measuring the tangent of the dielectric loss angle (tg 6) of the stretched structure and should be chosen between C. above and 5 C. below the first subsidiary maximum (stretching dispersion region). At constant frequency, the temperature and absolute value of this maximum depend, in the main, on the starting material used and on the conditions employed in the spinning and stretching. The crimped fibrous structures obtained in accordance with the invention are characterized not only by the above set out uniformity and stability of crimp but additionally by excellent crease-resistance.

When the crimping is carried out at temperatures below the optimum temperature, then the crimp which is obtained is unstable on application of mechanical stress. When crimping temperatures above the optimum are employed, the stability of the crimp obtained is comparable to that obtained with the optimum temperature, but a marked damage to the individual fibers occurs. It has further been found in accordance with another aspect of the invention that in the production of polycarbonate structures such as threads, films, yarns, woven knitted fabrics and the like, based on the dimonohydroxy-diarylalkanes, -sulphones, -s ulphoxides, -sulphides or -ethers or mixtures of these dihydroxy compounds with each other, products which are superior in their dimensional stability, are obtained by heat fixation employing for the fixation a temperature which corresponds by the 12.5 C. exactly to the maximum position of the tangent of the dielectric loss angle in the first subsidiary maximum (stretching dispersion region).

This characteristic quantity can be determined ex- 4 perimentally by the method described by F. Krum and F. H. Miiller, as set out above, preferably employing for the measuring of the loss angle of the fibrous structure a measure condenser cell described by Hearle in the publication similarly set out above.

In the process of this invention, the heat fixation of endless filaments, threads, and bands of polycarbonates is carried out using apparatus, as for example an intersecting roller drier providing a constancy of temperature of at least -1.5 C. and which has a variable inlet and outlet speed. Fixing can thus be carried out under suitable stretching conditions.

Woven and knitted fabrics prepared on the basis of polycarbonates may be fixed using therefor tenter frames under corresponding conditions.

In accordance wit-h the invention, the fixing temperature is determined by measuring the tangent of the dielectric loss angle (tg 6) of the stretched starting material and should be chosen so that the same lies between 2.5 C. above and 2.5 C. below the first subsidiary maximum (stretching dispersion region). The temperature for the fixation and the absolute value of this maximum depend, at constant frequency, in the main on the starting material employed.

By reason of the above treatment, the fibrous and film structures of polycarbonate obtained in accordance with the invention are distinguished by improvements in properties and, in particular, by very high creaseresistance, low shrinkage and outstanding dimensional stability.

When the fixing is carried out at a temperature below the optimum temperature, no significant improvement is observed as to these properties and, where it is carried out at temperatures above the temperature herein disclosed, marked damage of the resulting material is observed.

The following examples illustrate but do not limit the invention:

Example 1 A polycarbonate base-d on 2:2-(4:4'-di0xydiphenyl)- propane having an average molecular weight of 32,000 was melted using a usual melt spinning process at temperatures of 290 to 300 C. and was then spun from spinnerets having an aperture diameter of 0.25 mm. The fibers, which were solidified by blowing air into the spinning shaft, were wound at a speed of 320 meters per minute. The unstretched polycarbonate silk which was thus obtained was stretched with a stretching ratio of 1:3.5 at the optimum temperature of 175 C. The tensile strength of the stretched material was 2.95 g./ den. with an elongation at break of 34%, the modulus of elasticity was 250 kp./mm. and the degree of elasticity under a load which is of the breaking load was 65%. On the basis of measurements of tg 6 at 1 kilocycle per second, the temperature interval of the stretching dispersion region was found to lie between 50 and 135 C. with its maximum at C. With an afterstretching of 25% and after-stretching temperatures between 100 and C., a maximum value for the tensile strength was found to be 3.62 g./den. at an elongation at break of 21%. The modulus of elasticity rose to 530 kp./mm. the degree of elasticity under a load which is 90% of the breaking load rose to 93%. When after-stretching was carried out at temperatures below or above this range of 10 C., the technological properties of the product obtained were greatly inferior.

Example 2 Polycarbonate having a molecular weight of 75,000 and prepared from 4:4'-dihydroxydiphenyl-2:2-propane and phosgene, was dissolved to a 20.5% solution in methylene chloride, pressed through a filter press and thereafter spun into a heated shaft through spinnerets having aperture diameters of 0.1 mm. The bundles of fibers drawn off by rollers at a speed of 1 50 m./min. were deposited in canisters. The unstretched polycarbonate band was then stretched with a stretching ratio of 124.25 at the optimum temperature of 183 C. The tensile strength of the stretched material was 3.19 g./ den. at an elongation at break of 36%, the modulus of elastici-ty was 290 kp./mm. and the degree of elasticity under a load which is 90% of the breaking load was 72%. On the basis of measurements of tg 5 at 1 kilocycle per second, the temperature interval of the stretching dispersion region was found to lie between 7-0 and 155 C. with its maximum at 130 C. With an after-stretching of 30% and an after-stretching temperature between 125 and 135 C., a maximum value for the tensile strength of 4.3 -g./den. was obtained at an elongation at break of 17%. The modulus of elasticity increased to 570 kp./mm. the degree of elasticity under a load of 90% of the breaking load increased to 96%. If the afterstretching was carried out at temperatures below or above this region limited to C., the resulting technological properties of the stretched material were greatly inferior.

Example 3 Polycarbonate based on 4:4'-dihy-droxydiphenyl-2:2- propane and having a molecular weight of 68,000- was dissolved to a 22% solution in methylene chloride, pressed through a filter press and conveyed into a mixing apparatus. There were also injected into this mixing apparatus a mixture of methyl-glycol-acetate and methylene chloride in such a ratio and in such quantities that a 17.5% polycarbonate solution containing 42% methylglycol-acetate calculated on the polycarbonate was obtained. The polycarbonate solution which was thus intensively mixed with the additional components was then spun into a heated shaft through spinnerets having aperture diameters of 0.12 mm. The fibers that were drawn off by rollers at a speed of 1 60 m./min. were wound. The fibers stretched in the ratio of 1:5.8 at the optimum stretching temperature 190 C. had the following proper-ties:

Tensile strength g./den 4.26 Elongation at break percent 38.5 Modulus of elasticity kp./mm. 3 30 Degree of elasticity (under a load of 90% of the breaking load) percent 45 Tensile strength g./den

Elongation at break percent 14.5

Modulus of elasticity kp./mm. 650 Degree of elasticity (under a load of 90% of the breaking load) percent 100 If after-stretching was carried out at temperatures below or above this region limited to 10 C., the technological properties of the resulting silk were greatly inferior and the silk had a ragged and stripy appearance owing to internal tears.

Example 4 A carbonate melt based on 4:4-dihydroxydiphenylsulphide and having an average molecular weight of 48,000 was melted according to a conventional melt spinning process at temperatures of 260 to 270 C. and spun' from spinnerets having an aperture diameter of 0.3 mm. The cooled and solidified fibers Were then wound at a speed of 550 m./min. The fibers stretched in the ratio of 1:3.7 at an optimum stretching temperature of 118 C. had the following properties:

Tensile strength g./den 2.1 Elongation at break percent 36 Modulus of elasticity kp./mm. 240 Degree of elasticity (under a load of of the breaking load) percent 55 Tensile strength g./den 2.6 Elongation at break percent 18 Modulus of elasticity kp./mm. 420 Degree of elasticity (under a load of 90% of the breaking load) percent 88 Fibers after-stretched outside of this narrow temperature range of 75:5 C. had inferior textile technological properties.

Example 5 Fibers were produced by the dry spinning process from a solution of a polycarbonate based on 2:2-(4:4- dioxydiphenyl)-propane (having a mean molecular weight of 75,000) and were then stretched.

On the basis of tg 6 measurements at a frequency of 1 kilocycle per second of a sample of stretched material, the stretching dispersion region was found to lie in the temperature range between 75 and 150 C. with a maximum at C. This temperature of 125 C.i5 C. was thus the optimum crimp temperature according to the invention for the stretched material.

A bundle of fibers of the above-described material having a total titer of about 100,000 den. was preheated by a preheater to a temperature of 125 C. to a degree of accuracy of $2.5 C. and then carried to the compression crimping chamber under a constant tension (of about 0.05 g./den.) at an inlet speed of 40 m./min. The compression crimping chamber was also maintained at 125 C. with a degree of accuracy of 11.5 C. by means of circulating oil heating. The compression crimping pressure was controlled pneumatically so that a mean duration of dwell of 12 seconds resulted. The crimped band was tested with respect to the stability of its crimp. In the present experiment, a value of 85% was obtained for the crimp stability. (Determination according to A. Zart Die Untersuchung der Faserkrauselung Melliand Textil- Berichte (1947), page 329). The fiber material produced from the crimped band (60 mm. staple length) was further tested for the uniformity and fineness of the crimp and the resistance to creasing according to the procedure described by Herzog, Zart and Rees (E. Wagner Mech.- technologische Textilprufungen, 7th edition, pages 107108 (1957) The following values were obtained:

Uniformity (coefficient of variation of the length of A comparison with these values was made using temperatures for preheating the band and for the crimping chamber. The results of the comparison are set out in the following table:

Measurements Temperature, C.

On the band On the fiber Uniformity (coefii- Crimped Crimp Tensile cient of variation of Fineness (mean Resistance to Preheater band stability strength, length of arc) in length of arc) in creasing in in percent gJden. percent mm. percent 50 50 49 3. 2 6.8 1. 85 50 so so 57 3. 2 7. 4 1. 78 52 100 100 70 3. 2 6.9 1.83 51 120 120 81 3.1 7.1 1.82 65 125 125 85 3.1 7. 2 1. 80 74 130 130 83 3. 1 7. 1.78 72 140 140 80 2. 9 7. 7 1. 73 73 150 150 73 2. 7 10. 5 1. 73 69 160 160 68 2. 7 17 1. 61 68 170 170 61 2. 4 52 1. 21 60 130 180 58 1. 9 s4 0. 95 58 On comparing the data in the table, it is clear that the optimum crimp temperature is 125 C. This corre- Grease gnglein accor ing to sponds with the value determined by the dielectric meas Tear shrink DIN 53890 Crease test urements. Fixing strength, age 1 in after 60 min. according to E l 6 temperature kg. percent release Lake and Veer 2 A solution of polycarbonate based on 2:2-(4:4-dihy In th I the droxyphenyD-propane having an average molecular E weight of 78,000 in methylene chloride was formed by the dry spinning process into fibers having an individual titer 591 L5 74 82 5 of 16 den. On the basis of tg B-measurements at a fre- 127 130 5 57.4 0.4 127 131 4 quency of 1 kilocycle per second of the material stretched 5&8 [L2 140 143 3 by 124.2, the stretching dispersion region in the temperature range of 75 to 155 C. was found to have a maxi- Fabric partly damaged mum at 138 C. This temperature of 138 C.i2.5 C.

was thus taken according to the invention as the optimum fixing temperature for the stretched material.

The stretched fibers were combined into a fiber bundle having a total titer of about 75,000 den. and delivered to a crossed roller drier (manufactured by Kiefer) which was accurately adjusted to the optimum temperature of 138 C.i1.5 C.

Following a duration of dwell of 5 minutes and an outlet speed of 5% less than the inlet speed, the heat shrinkage at 140 C. and 30 minutes was found to be 2.8%. If fixation was carried out for example at 6 C. below the determined optimum temperature range then the heat shrinkage measured at 140 C. and 30 minutes was already as much as 4.3% and at a fixing temperature of 125 C. it was 11.7%. At a fixing temperature of 144 C., however, the fibrous material had a tear strength reduced by 12% at a heat shrinkage of 2% at 140 C., 30 minutes.

Example 7 A solution of polycarbonate based on 2:2-(4:4'-dihydroxyphenyl)-propane having an average molecular weight of 72,000 in methylene chloride was formed by the dry spinning process into crystalline fibers having an individual titer of 11 den. stretched by a ratio of 115.5 and worked up into a woven fabric having a weight per unit area of 180 g./m

For this fabric, the optimum fixing temperature based on tg e-measurements in the stretching dispersion region was 150 C.

Fabrics which are fixed at this temperature for a period of seconds on a tenter frame which ensured a temperature constancy of 1.5 C. had the following improved qualities as compared with fabrics which were not fixed according to the invention.

Aecording t0 the method of Spuhr (E. Wagner Meek.- iiechsnogpgische 'lextilprofungen, 7th edition, page Tex-t. Inst. Conference of Sept. 7 to 12, 1961.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that we do not limit ourselves to the specific embodiments thereof except as defined in the appended claims.

We claim:

1. In a process for treating fibers, films, filaments, tapes, ribbons and the like comprising high molecular weight linear crystallizable polycarbonates to impart thereto improved mechanical and textile technological properties, the step which comprises subjecting such a polycarbonate material after it has been pre-drawn to from 3 to 6 times its initial length at a temperature in the range from 5 C. below to 5 C. above that temperature at which the tangent of the dielectric loss angle attains a maximum to a further drawing at a drawing temperature within the range of 5 C. above and 5 C. below the temperature at which the tangent of the dielectric loss angle of the pre-drawn polycarbonate material has its first subsidiary maximum, said second drawing being effected to an extent of from 5 to 100%.

2. Process according to claim 1 wherein said drawing is effected to an extent of from 20 to 50%.

3. A process for treating fibers to impart thereto improved mechanical and textile technological properties, which comprises melt-spinning a high molecular weight linear crystallizable polycarbonate based on 2:2-(4:4- dioxydiphenyl)-propane, solidifying the spun polycarbonate fibers thus obtained, drawing the solidified polycarbonate fibers with a drawing ratio of 1:3.5 at the optimum temperature of said polycarbonate of C. and

thereafter drawing the drawn polycarbonate fibers to cause a increase in the length of said fibers at a temperature within the range of and C. at which temperature the tangent of the dielectric loss angle of the pre-drawn material has its first subsidiary maximum.

4. A process for treating fiber-s to impart thereto improved mechanical and textile technological properties, which comprises solution-spinning a high molecular weight linear crystallizable polycarbonate prepared from 4:4'-dihydroxy di-phenyl-2z2-propane and phosgene, solidifying the spun polycarbonate fibers thus obtained, drawing the solidified polycarbonate fibers with a drawing ratio of 1:425 at the optimum temperature of said polycarbonate of 183 C. and thereafter drawing the drawn polycarbonate fibers to cause a 30% increase in the length of said fibers at a temperature within the range of and C. at which temperature the tangent of the dielectric loss angle of the pre-drawn material has its first subsidiary maximum.

5. A process for treating fibers to impart there-to improved mechanical and textile technological properties, which comprises solution-spinning a high molecular weight linear crystallizable polycarbonate prepared from 4:4-dihydroxydiphenyl-2:2-propane, solidifying the spun polycarbonate fibers thus obtained, drawing the solidified polycarbonate fibers with a drawing ratio of 1:5.8 at the optimum drawing temperature for said polycarbonate and thereafter drawing the drawn polycarbonate fibers to cause a 45% increase in the length of said fibers at a temperature within the range of and C. at which temperature the tangent of the dielectric loss angle of the pre-drawn material has its first subsidiary maximum.

6. A process for treating fibers to impart thereto improved mechanical and textile technological properties, which comprises melt-spinning a high molecular weight linear crystallizable polycarbonate prepared from 4:4'-dihydroxydiphenyl sulfide, solidifying the spun polycarbonate fibers thus obtained, drawing the solidified polycarbonate fibers with a drafing ratio of 1:3.7 at the optimum temperature of said polycarbonate of 118 C. and thereafter drawing the drawn polycarbonate fibers to cause a 25% increase in the length of said fibers at a temperature within the range of 70 and 80 C. at which temperature the tangent of the dielectric loss angle .of the predrawn material has its first subsidiary maximum.

References Cited UNITED STATES PATENTS 2,556,295 6/ 1951 Pace 264290 2,794,700 6/1957 Cheney 264-346 2,942,325 6/1960 Spellrnan 264290 3,005,236 10/ 1961 Reichle et a1. 264290 3,022,545 2/1962 Wylde et a1 19-66 3,101,245 8/1963 Fuitita et al 264-346 ALEXANDER H. BRODMERKEL,

Primary Examiner.

ROBERT F. WHITE, Examiner.

A. L. LEAVITI, F. S. WHISENHUNT, D. J. ARNOLD,

Assistant Examiners.

Claims

1. IN A PROCESS FOR TREATING FIBERS, FILMS, FILAMENTS, TAPES, RIBBONS AND THE LIKE COMPRISING HIGH MOLECULAR WEIGHT LINEAR CRYSTALLIZABLE POLYCARBONATES TO IMPART THERETO IMPROVED MECHANICAL AND TEXTILE TECHNOLOGICAL PROPERTIES, THE STEP WHICH COMPRISES SUBJECTING SUCH A POLYCARBONATE MATERIAL AFTER IT HAS BEEN PRE-DRAWN TO FROM 3 TO 6 TIMES ITS INITIAL LENGTH AT A TEMPERATURE IN THE RANGE FROM 5*C. BELOW TO 5*C. ABOVE THAT TEMPERATURE AT WHICH THE TANGENT OF THE DIELECTRIC LOS ANGLE ATTAINS A MAXIMUM TO A FURTHER DRAWING AT A DRAWING TEMPERATURE WITHIN THE RANGE OF 5*C. ABOVE AND 5*C. BELOW THE TEMPERATURE AT WHICH THE TANGENT OF THE DIELECTRIC LOSS ANGLE OF THE PRE-DRAWN POLYCARBONATE MATERIAL HAS ITS FIRST SUBSIDIARY MAXIMUM, SAID SECOND DRAWING BEING EFFECTED TO AN EXTEND OF FROM 5 TO 100%.