Process For The Preparation Of Polyethylene Terephthalate Filaments

Abstract

A continuous spin-draw process is disclosed for preparing highly drawn polyethylene terephthalate filaments drawn at speeds greater than 1,800 meters per minute using only one heated draw roll system without the use of any other heating device. Feed and draw rolls are provided with a surface roughness which allows a slipping of the filaments along a number of turns before they leave the feed rolls and after they arrive at the draw rolls. The filaments are partially drawn at the lower temperature of the feed rolls, drawing continues between the feed and draw rolls, and is completed at the higher temperature of the draw rolls with a total draw ratio between 5 and 8.

Description

This invention relates to a continuous process for the preparation of highly drawn polyethylene terephthalate filaments by melt-spinning of the polymer followed immediately by drawing of the spun filaments without prior winding up. As used herein, polyethylene terephthalate means a fiber-forming long chain synthetic polymer composed of at least 85 percent by weight of an ester of ethylene glycol and terephthalic acid.

It is well known that filaments useful for textile and industrial purposes can be prepared by extruding molten polyethylene terephthalate through a spinnerette and winding up the quenched filaments. It is further known that, to obtain their optimal properties, the filaments must be drawn to several times their original length to produce orientation along the fiber axis. This is usually done by winding off the spun filaments and by passing them over sets of rolls driven at different speeds and eventually heating the filaments by various means to facilitate drawing.

It would obviously be of advantage to eliminate the step of winding up the undrawn quenched filaments and to wind them off again for the purpose of drawing. Such processes have already been proposed. Thus, U.S. Pat. No. 2,604,667 proposes to produce oriented polyethylene terephthalate fibers by withdrawing melt-spun fibers from the spinnerette at high speeds of 4,700 meters and more per minute. Another method is described by U.S. Pat. No. 3,002,804 for passing melt-spun quenched filaments through a liquid drag bath. British Pat. No. 1,168,767 proposes to pass such filaments over a drag pin aggregate at a defined distance from the spinnerette and to withdraw the filaments at a low tension.

It is a disadvantage of all these processes that they generally do not allow freely to select and to predetermine the draw ratios. The processes also do not permit high draw ratios which are necessary, for example, to produce filaments of low elongation. It is known that draw ratios of at least about 5 are required to realize this aim. Such highly drawn polyethylene terephthalate filaments of good uniformity are only obtainable, if drawing is done by the use of feed and draw roll systems in which the rolls have exactly specified speeds.

To obtain filaments of very high draw ratios, it is essential to heat the filaments during drawing, and various devices are used for this purpose. Thus, U.S. Pat. No. 3,216,187 describes, inter alia, a continuous one-step process for the preparation of high-strength polyethylene terephthalate filaments, in which the filaments are heated by passing through a steam jet while moving from the feed rolls to the draw rolls. As the passage of the filaments through the steam occurs only during a very short period, the temperature of the steam must be very high to transfer sufficient heat to the filaments. Temperatures of 350.degree.-450.degree. C. are used, i.e., temperatures which are 100.degree.-200.degree. C. above the melting point of the polymer.

Another well-known method is to pass the filaments to be drawn over heated pins or plates. However, at the high winding up speeds employed at present, the period of contact between the filaments and such heating devices is very short, as the size of the pins and plates is limited by the overall dimensions of the machine. These methods therefore also require the use of rather high temperatures in order to transfer the necessary amount of heat during the short period of contact. Similar to the method using a steam jet, the temperature gradient along the diameter of the filaments during drawing is therefore rather high. A much better way to heat the filaments is the use of heated feed and draw rolls. As the filaments can pass over such rolls several times, they may have a considerably longer period of contact with the heating device than when using hot plates or steam jets. For transfer of the same amount of heat, the temperature of the heated rolls can therefore be kept considerably lower than that of the other practicable heating devices described above. The temperature of the rolls will always remain below the melting point of the filaments, and the temperature gradient along the diameter of the filaments will be quite moderate. The use of heated rolls is therefore a very safe and effective way of heating the filaments for the purpose of drawing. The amount of heat transferred depends on the size and temperature of the rolls, the number of filament turns around the rolls, and the speed of the filaments.

If freshly spun polyethylene terephthalate filaments, which are practically non-crystalline, are for the purpose of being highly drawn, rapidly heated to temperatures of about 180.degree. C., they suddenly start to crystallize and become sticky during a short period of time. It has also been observed that the temperature at which the filaments become sticky depends, inter alia, on the speed with which the filaments are heated. If therefore filaments pass from a conventional polished feed roll to a polished draw roll, such filaments having a temperature of at least 180.degree. C., which was found by the inventors to be the minimum temperature to obtain high draw ratios at speeds of 1,800 meters per minute or more, a sticky mass of filaments is wrapped around the draw roll, and the filaments cannot proceed and cannot be wound up.

However, if the spun filaments pass from a polished feed roll to a polished draw roll having a temperature substantially below 180.degree. C., and are partially drawn and oriented, they can easily proceed to a second polished draw roll having a substantially higher temperature, without showing any adhesive properties. By a second drawing, filaments of a high total draw ratio can be obtained. Accordingly, the already cited U.S. Pat. No. 3,216,187 also describes such a two-stage drawing process, in which freshly spun polyethylene terephthalate filaments pass, without prior winding-up, from a feed roll having a temperature of slightly over 100.degree. C. to a first draw roll heated to 150.degree.-155.degree. C. and then to a second draw roll heated to about 225.degree. C.

The use of only one heated draw roll system would, of course, represent an essential improvement of existing processes and would be of considerable technical and economic advantage. British Pat. No. 1,176,164 describes such a process of drawing polyethylene terephthalate filaments by using only one draw roll system heated to 220.degree. C, said draw roll system having a modified surface showing tiny protuberances of equal height which are regularly or irregularly distributed, preferably forming a series of microridges parallel to the roll axis. It is the aim of this device to allow a steady decrease of the tension of the filaments during their last turns around the draw roll. It is also stated that a roll surface having unequal protuberances is not suitable for this purpose.

However, to achieve draw ratios of 5.3-5.4, British Pat. No. 1,176,164 requires the use of an additional hot plate between feed and draw roll, and the wind-up speed is only 152 meters per minute. The process is therefore not suitable to obtain high draw ratios at the high wind-up speeds required for spin-drawing polyethylene terephthalate filaments.

It is the object of this invention to provide a continuous spin-draw process for the preparation of highly drawn polyethylene terephthalate filaments drawn at high speeds by the use of only one heated draw roll system and without the use of any heating device other than heated rolls.

The process according to the present invention comprises extruding molten polyethylene terephthalate through a spinnerette to form filaments, quenching the filaments, applying to the filaments a lubricating finish, passing the filaments successively over a feed roll system and a draw roll system, each system comprising at least two cylindrical rolls, each roll having a surface roughness of a roughness height, as defined by ASA B 46.1 - 1962, of 0.5-2.2 microns, allowing a slipping of the filaments around the feed roll system and the draw roll system of one to five turns, at least one feed roll and one draw roll being motor-driven. The axis of the feed roll from which the filaments leave the feed roll system and the axis of the draw roll at which the filaments arrive at the draw roll system are parallel, while the axes of the feed rolls and the draw rolls, respectively, are skewed. The process includes gradually drawing the filaments in a manner so that starting the drawing occurs while the filaments pass around the last one to five turns before leaving the feed rolls which have a surface temperature of 75.degree.-130.degree. C, and completing the drawing while the filaments pass around the first one to five turns after arrival on the draw rolls which have a surface temperature of 180.degree.-240.degree. C, drawing the filaments at a total draw ratio of not less than 5,0, and finally winding up the drawn filaments at a speed of not less than 1,800 meters per minute.

Both the feed roll system and the draw roll system shall consist of at least two rolls of equal or different size, and at least one feed roll and one draw roll shall be driven by a motor. The use of a motor for the additional rolls depends on whether or not they can be moved without difficulty by the drawing force of the passing filaments. At least one of the feed rolls shall be heated to 75.degree.-130.degree. C, and preferably to 80.degree.-90.degree. C, and at least one of the draw rolls shall be heated to 180.degree.-240.degree. C, and preferably to 210.degree.-230.degree. C. How many rolls are to be heated is determined by the aim that the filaments assume the same temperature as the heated rolls of the system over which they pass. No other heating device for the purpose of drawing the filaments is provided. The examples describe the use of two heated motor-driven feed rolls and two heated motor-driven draw rolls, all rolls having the same size with a diameter of 180 millimeters.

The filaments pass several times both over the feed rolls and the draw rolls, before they are finally wound up. The high draw ratios used according to the invention correspond to very high tensions of the filaments during drawing, and, at the temperatures employed, these tensions may be as high as one-third of the breaking strength of the filaments. The high tensions require a special position of the feed and draw rolls, such a position being used in all the examples. All feed and draw rolls should be cylindrical, and as shown in FIG. 4 the axis of the feed roll from which the filaments leave the feed roll system and the axis of the draw roll at which the filaments arrive at the draw roll system shall be parallel. In this connection, it has also to be considered that the filaments passing from the feed roll to the draw roll system, will form an angle of 90.degree. to the axis of the feed roll from which they leave and to the axis of the draw roll at which they arrive (see FIG. 4), if the use of filament guides is to be avoided. If these conditions are not implemented, the filaments coming from the feed rolls will run off from the draw rolls and will go astray. In addition, within the feed and draw roll systems, the axes of the two feed rolls and the axes of the two draw rolls, respectively, are skew set (see FIG. 4) to effect a correct separation of the passing filaments. The speed of the feed and draw rolls shall be such as to obtain a draw ratio of not less than 5.0. The draw ratio is defined as the ratio between the surface speed of the draw rolls and the surface speed of the feed rolls. The filaments shall perform at least so many turns around the respective rolls, that the surface speed of the rolls corresponds to the speed of the filaments at a point about half-way between the points of entry to, and exit from, the respective rolls. At otherwise equal conditions, the draw ratio also depends on the spinning speed of the filaments, higher spinning speeds producing a lower draw ratio. According to the invention, the wind-up speed shall be not less than 1,800 meters per minute. The upper limit of the wind-up speed is given by limitations of performance and equipment and may be as high as 6,000 meters per minute. The optimal draw ratio obtainable also depends on the melt viscosity of the filaments, a lower melt viscosity producing a lower orientation of the spun filaments and therefore permitting a higher draw ratio.

It is essential for the successful realization of the objects of this drawing process that the feed and draw rolls have a surface roughness, which will allow a slipping of the filaments along a number of turns before they leave the feed rolls and after they arrive at the draw rolls. As stated above, polyethyleneterephthalate filaments temporarily become sticky, when, for the purpose of drawing, they are quickly heated to temperatures of about 180.degree. C, so that they wrap up around the draw rolls and cannot properly pass on. The slipping of the filaments allowed by the surface roughness of the rolls makes it possible that the filaments are gradually drawn along their way from the last few turns around the feed rolls up to the first few turns around the draw rolls.

This means that the filaments are partially drawn and oriented at the lower temperatures of the feed rolls, that the drawing continues between the feed and draw rolls, and that the drawing is completed at the higher temperatures of the draw rolls, finally reaching a high total draw ratio of not less than 5.0. As already explained above, when describing a conventional two-stage drawing process, filaments already partially drawn and oriented at lower temperatures on a first draw roll system, can proceed to a second draw roll system having substantially higher temperatures without showing any adhesive properties. By the use of feed and draw rolls with a rough surface which allows a limited slipping of the filaments, the process according to the invention applies a gradual drawing of the filaments on and between one feed roll system and one draw roll system heated to different temperatures, and thereby saves the use of a second heated draw roll system.

How the slipping allowed by the rough surface of the rolls makes it possible to start the drawing of the filaments already on the feed rolls, is demonstrated by the following Table showing the speed of the filaments measured at different turns before leaving the feed rolls.

Turns Before Filaments Leave Filament Speed Feed Rolls (meters/minute) __________________________________________________________________________ 41/4 364 31/4 365 21/4 371 13/4 858 11/4 1505 1/4 1798 __________________________________________________________________________

In this experiment, the surface speed of the feed rolls was 364 meters per minute, and the surface speed of the draw rolls was 2,171 meters per minute. The Table shows, how, under the pull from the rapidly moving draw rolls, the speed of the filaments increases during their last turns around the feed rolls indicating that the drawing of the filaments has begun. A still more complete picture of a drawing performance of filaments according to the invention, is given in Example I, Table 1 a, showing the tension of the filaments along their whole way around the feed and draw rolls.

To allow a slipping of the filaments over one to five turns of the rolls, the nature of the roughness of the roll surface is of great importance. Preferably, the roll surface shall consist of a coherent, non-porous coating of tiny, smooth-topped elevations of defined unequal height and defined irregular distribution in all directions of the surface. The description and definition of such a surface can only be made by use of statistical terms introducing averages from a great number of single figures having considerable fluctuations. For evaluation of these figures, use is made of a surface profile which is the contour of a surface taken, in any direction, in a plane perpendicular to the surface.

FIG. 3 shows such a profile of a roll surface according to the invention. The profile was measured with a "Talysurf" instrument made by Taylor-Hobson Co., England. One centimeter of the vertical scale represents 0.45 microns, and 1 centimeter of the horizontal scale represents 19.8 microns. The evaluation of the profile is made about the "center line" which is the line parallel to the general direction of the profile, such that the sums of the areas contained between the center line and those parts of the profile which lie on either side of it are equal (ASA B 46.1 - 1962). The evaluation was carried out by use of a digital computer permitting an accuracy corresponding to distances of the measured profile of .+-. 0.01 microns in vertical direction and of .+-. 1.0 microns in horizontal direction.

Terms suitable to describe and define surface roughness are given by American and German Standards, and additional terms have been introduced to meet the special requirements of the invention. The most important term is the "roughness height" which is the arithmetical average deviation expressed in microns measured normal to the center line (ASA B 46.1 - 1962). The roughness height of the surfaces according to the invention shall be 0.5 - 2.2 microns.

Other suitable terms to define the surface roughness according to the invention are:

"Roughness range" which is the distance between the highest and the lowest point of the surface texture measured normal to the center line ("Rauhtiefe" according to DIN 4762). The roughness range of the surface according to the invention shall be 4.5 -8.0 microns.

"Average Roughness Range" which is the distance between the average height of the peaks and the average depth of the bottoms of the surface texture measured normal to the center line. The average roughness range of the the surfaces according to the invention shall be 1.6 - 3.0 microns.

"Peak Distance" which is the distance between successive peaks. The peak distance of the surfaces according to the invention shall not exceed 140 microns.

"Average Peak Distance" which is the average distance between two successive peaks. The average peak distance of the surfaces according to the invention shall be 40 - 60 microns.

"Profile Curvature" which is the reciprocal radius of curvature at any point of the profile. The profile curvature of surfaces according to the invention shall not exceed 0.030 microns.sup..sup.-1 to exclude any sharp peaks or bends of the profile.

It should be noted that the terms adopted to describe and define the surface roughness according to the invention do not include the term "roughness width" which is the distance between successive peaks which constitute the predominant pattern of the roughness (ASA B 46.1 - 1962). This term, which is somewhat similar to that of a wavelength is only applicable to patterns of a predominantly periodic lateral surface texture, different from the surfaces according to the invention with their great fluctuations of peak distance values.

A roll surface according to the invention can be produced by several methods, for example by sandblasting under controlled conditions followed by galvanic metal coating, by depositing metals in crystallized form from a gaseous phase, or by affixing small metallic globules of different size. It should be noted that sandblasting alone without a subsequent metal coating would produce elevations having too sharp peaks. It is emphasized that the elevations shall form a non-porous, coherent coating which is abrasion-resistant and impermeable.

As lubricating finish for the filaments a composition is preferred which does not contain more than 10 per cent by weight of water. As shown in the examples, such a finish facilitates producing filaments of considerably higher draw ratios and higher tenacities than a finish having a high water content or an emulsion-type finish. One of the reasons for the advantage of the finish according to the invention is probably that it does not consume any substantial amount of heat from the heated rolls for the purpose of evaporation of water.

A possible modification of the inventive process is characterized by the use of an additional pre-tension roll system comprising at least one unheated motor-driven roll and a separator roll, over which the filaments pass on their way from the spinnerette to the feed rolls. The motor-driven pre-tension roll and the separator roll have, of course, the same surface speed, and this speed shall be slightly lower than the surface speed of the feed rolls, the speed difference not to exceed 2 percent. This speed difference will produce some tension of the filaments, which is well within the range of reversible elastic elongation of the undrawn filaments. The advantage of such a pre-tension roll system is that the filaments run very quietly over the feed rolls and do not show any undesired sideway movements. Further advantages are described in detail in Example IV.

FIG. 1 is a diagrammatic illustration of apparatus in accordance with one embodiment of the invention.

FIG. 2 is a diagrammatic illustration of apparatus in accordance with another embodiment of the invention.

FIG. 3 is a profile of a roll surface in accordance with the invention.

FIG. 4 is a simplified perspective view of the apparatus illustrated in FIG. 1, and specifically indicating the surface roughness of the feed and draw rolls, as well as the skew sets within the feed roll system and the draw roll system, respectively.

FIGS. 1 and 4 show schematically one embodiment of an arrangement suitable for preparing spin-drawn filaments according to the invention. The filaments 2 extruded for spinnerette 1 are exposed to transversely directed stream of air 3, and are passed over a guiding device 4 and roll 5 applying a lubricating finish. Thereafter, the filaments pass around heated feed rolls 6 and heated draw rolls 7. The drawn filaments are wound-up as usual on bobbin 8. Such an arrangement is used in Examples I, II, and III.

FIG. 2 shows schematically another possible embodiment of an arrangement which comprises the same elements as shown in FIG. 1, but, in addition, contains a pre-tension roll 9 with separator roll 10 arranged before the feed rolls. Two relaxation rolls 11 are arranged between draw rolls 7 and windup bobbin 8. Such an arrangement is used in Examples IV, V and VI. The following examples will show details as to the performance of the process and the properties of the filaments obtained. The tenacities of the filaments were determined by the use of an INSTRON Tester and refer to the filament denier at zero elongation. The tension of the filaments passing around the various rolls were measured by a ROTHSCHILD ELECTRONIC TENSIOMETER. The intrinsic viscosity [.psi.] is defined by the following equation:

wherein .psi.spec. means the specific viscosity at 25.degree. C of a solution of 0.5000 grams of polyethylene terephthalate in 100 milliliters of a mixture of equal parts by weight of phenol and tetrachloroethane.

EXAMPLE I

This example shows the dependence of filament tenacity, elongation, and shrinkage upon the draw ratio. It further shows, at a fixed draw ratio, the filament tensions existing at various positions in relation to the feed and draw rolls.

The polyethylene terephthalate filaments leaving the spinnerette were quenched by transverse air, passed over a convergence guide, and were treated with a lubricating finish. Where a preparation based on isooctyl stearate containing 6-7 weight percent water is the lubricating finish, a suitable temperature for the lubricating finish treatment is 80.degree. C.

A wide variety of lubricating finishes may be used in the subject invention, and such lubricating finishes and their operative temperatures, per se, form no part of the present invention. Examples of suitable lubricating finishes are set forth hereinafter in Example VI.

The filaments passed over two motor-driven rolls, acting simultaneously as withdrawal rolls for the spun filaments and as feed rolls for the drawing process, and then over two motor-driven draw rolls, whereafter the drawn filaments were wound up. All rolls had a diameter of 180 millimeters, and their axes were in a position as prescribed by the specification. The rolls had a surface roughness as roll surface type E of Example V.

The two feed rolls were heated to 85.degree. C, and the filaments passed around the feed rolls in 12 turns. Different draw ratios were obtained by variation of the surface speed of the feed rolls between 327 and 372 m/min. The two draw rolls were heated to 210.degree. C, the surface speed of the draw rolls was 2,180 meters per minute, and the filaments also passed around the draw rolls in 12 turns. To effect some relaxation, the filaments were wound up at a speed of 2,000 meters per minute, i.e., at a speed slightly less than the speed of the draw rolls.

The spun, undrawn filaments had an intrinsic viscosity of 0.75 and, at a withdrawal speed of 372 meters per minute, a birefringence of 0.6 - 0.7 .times. 10.sup..sup.-3. The drawn filaments had a total denier of 1,000/192 and a finish content of 0.5 - 0.6 percent. Table 1 gives the figures for tenacity and break elongation of the drawn filaments at different draw-ratios:

TABLE

1 Break Tenacity Elongation Draw Ratio (g/denier) (%) 5.9 7.6 18 6.1 7.7 17 6.3 8.0 16 6.5 8.2 16 6.7 8.5 14 __________________________________________________________________________

As Table 1 shows, the filaments obtained according to the inventive process have been drawn at a high draw-ratio and possess a high tenacity and a medium break elongation.

Table 1 a shows, at a constant draw ratio of 6.1, the tension of the filaments measured before and after contact with, and at various turns around the feed and draw rolls:

TABLE 1

a Filament Filament Tension (in mg/denier of the Position wound-up filament) Feed Rolls Draw Rolls __________________________________________________________________________ Before contact 40 2500 1 turn 20 2000 2 turns 15 1500 3 turns 15 1300 4 turns 10 1200 5 turns 10 1300 6 turns 10 1300 7 turns 0 1300 8 turns 0 1000 9 turns 200 950 10 turns 250 150 11 turns 400 100 12 turns 1600 50 After contact 2500 15 __________________________________________________________________________

As Table 1 a shows, the filament tension on the feed rolls decreases over the first eight turns. The reason is that the length of the filaments increases when they are heated above their glass transition temperature which is about 70.degree. C. The strong increase of the filament tension during the last four turns around the feed rolls indicates that the pull from the draw rolls has become effective, and that the gradual drawing of the filaments has begun. As explained above, this gradual drawing is made possible by the slipping effect due to the special rough surface of the rolls. The slipping effect is also the cause of the decrease of the filament tension while passing around the first four turns around the draw rolls. Table 1 a also shows that at a position about four turns after arrival on, and before departure from, both the feed and draw rolls, the respective filament tensions remain constant within a rather small range. It was also found that, at these positions, the filament speeds coincided with the respective surface speeds of the rolls.

The low filament tension at the central turns around the feed rolls may cause undesirable sideway movements of the filaments. This can be prevented by the insertion of an additional unheated pre-tension roll between the spinnerette and the feed rolls, as described in Example IV.

EXAMPLE II

This example describes the properties of the filaments at different temperatures of feed and draw rolls. The filaments were spun and drawn as described in Example I, with the following differences: The feed rolls had a surface speed of 374 meters per minute, and were passed by the filaments in nine turns. The draw rolls had a surface speed of 2,180 meters per minute and were passed by the filaments in 14 turns. To effect some relaxation, the filaments were wound up at a speed of 2,002 meters per minute, i.e., at a speed slightly less than the speed of the draw rolls. The drawn filaments had a total denier of 250/48.

When the feed roll temperature was 68.degree. C, the filaments obtained had poor uniformity and showed a bottleneck structure. Fabrics made from such incompletely drawn filaments showed streaks and were irregularly dyed. Feed roll temperatures above 135.degree. C produced filaments of substantially decreased tenacity, and at still higher temperatures, the filaments began to stick to the feed rolls.

Table 2 shows the filament properties at different temperatures of the draw rolls:

TABLE 2

Break Draw Roll Tenacity Elonga- Shrinkage Temperature (.degree.C) g/denier tion (%) % at 165.degree. C in Air __________________________________________________________________________ 180 7.9 18 3.5 200 7.8 19 2.3 225 7.9 18 1.6 __________________________________________________________________________

Table 2 shows that, at increased draw roll temperature, the tenacity and elongation of the filaments remain substantially constant, while their shrinkage is reduced. Such low-denier, low-shrinking filaments are, for example, suitable for making sewing threads. At draw roll temperatures below 180.degree. C, the filaments obtained had a considerably lower tenacity.

EXAMPLE III

The filaments were spun and drawn as described in Example I, with the following differences: A polymer of higher viscosity was used, so that the spun undrawn filaments had an intrinsic viscosity of 0.95. At a surface speed of the feed rolls of 365 meters per minute, the birefringence of the spun filaments was 1.0 .times. 10.sup.-.sup.3. By variation of the speed of the feed rolls, various draw ratios were obtained, while the surface speed of the draw rolls was kept constant at 2,160 meters per minute. To effect some relaxation, the filaments were wound up at a speed of 2,000 meters per minute, i.e., at a speed slightly less than the speed of the draw rolls. The total denier of the drawn filaments was 1,000/192.

Table 3 shows the filament properties at various draw ratios:

TABLE 3

Tenacity Elongation Draw Ratio (g/denier) (%) __________________________________________________________________________ 5.9 8.8 16 6.0 9.0 15 6.1 9.1 14.5 6.2 9.2 14 __________________________________________________________________________

As can be seen in comparison with Example I, Table 1, the higher filament viscosity reduces the upper limit of the draw ratio obtainable, but permits, at equal draw ratios, to obtain filaments of higher tenacities. The filaments are partially shrunk and are suitable for making tire cord yarn.

EXAMPLE IV

This example describes the use of an additional pretension roll system between spinnerette and feed rolls and the use of additional relaxation rolls between draw rolls and windup device. The example further shows the working of the inventive process at different speeds.

The filaments were spun and drawn as described in Example I with the following differences: A polymer of higher viscosity was used, so that the spun undrawn filaments had an intrinsic viscosity of about 0.92. The filaments were withdrawn from a spinnerette of 192 holes by means of an unheated motor-driven roll and separator roll, serving as pre-tension rolls and placed between spinnerette and feed rolls. From the draw rolls the filaments passed over another two motor-driven rolls heated to a higher temperature than the draw rolls and serving for the purpose of relaxation and stabilization. The axes of the two pre-tension rolls and the two relaxation rolls are skew set.

The feed and draw rolls had a surface roughness as roll surface type E of Example V. The diameter of the motor-driven pre-tension roll was such that its surface speed was about 1.5 percent lower than the surface speed of the feed rolls. As explained above, this speed difference produces some tension of the filaments which is well within their range of reversible elastic elongation and prevents undesired sideway movements of the filaments on the feed rolls as described in Example I.

Filaments were spun and drawn at different speeds of the rolls. The rate of polymer extruded through the spinnerette was so adjusted that, in all cases, the filaments finally obtained had a total denier of 1,000/192. Table 4 shows the surface temperature of the heated rolls, the number of turns around each roll system, and the speed of the rolls:

TABLE 4

Surface Speed in Meters Per Minute Number Rolls Temp. of turns A B C __________________________________________________________________________ Feed Rolls 90.degree. C 5 358 465 550 Draw Rolls 220.degree. C 11 2160 2690 2900 Relaxation Rolls 235.degree. C 8 2000 2500 2695 Wind-Up Roll 2002 2503 2700 __________________________________________________________________________

The heating of the relaxation rolls results in the filaments being wound-up in a rather hot condition, which decreases their initial modulus and produces a stable build-up of the yarn package.

Table 4a compares the withdrawal speed and birefringence of the spun filaments with the draw-ratio, tenacity, and break elongation of the drawn filaments:

TABLE 4a

Spun Filaments Drawn Filaments withdrawal Tenacity Break Speed Birefri- Draw g/denier Elonga- (m/min) ngence Ratio tion (%) __________________________________________________________________________ A 358 1.5.times. 10.sup.-.sup.3 6.0 8.9 15 B 465 2.2.times. 10.sup.-.sup.3 5.6 9.1 14 C 550 3.2.times. 10.sup.-3 5.3 9.0 15 __________________________________________________________________________

table 4a shows that the birefringence of the spun, undrawn filaments depends on their withdrawal speed. The filaments spun at a higher speed have a higher orientation and therefore a higher birefringence. Table 4a also shows that the higher spin-oriented filaments withdrawn at higher speed and drawn at a draw-ratio of 5.3 and lower spin-oriented filaments withdrawn at a lower speed and drawn at a draw-ratio of 6.0 produce drawn filaments of about the same tenacity of about 9 grams per denier and the same elongation at break of about 15 percent.

Table 4b compares filaments spun and drawn according to A in Table 4a, but with and without the use of a pre-tension roll:

TABLE 4b

Filament Number of Filament Sideway Tension Turns around Feed Movements of before contact Rolls Required for the Filaments on the of feed rolls Satisfactory Run Feed Rolls __________________________________________________________________________ with pre- Tension 0.16 g/denier 5 .+-. 0.5 mm Roll Without 0.04 g/denier 8 .+-. 4.0 mm Pre- Tension Roll __________________________________________________________________________

As Table 4b shows, the filaments spun with the use of pre-tension rolls had a considerably higher tension than the filaments spun without such rolls. As a result of this tension, the filaments are in closer contact with the feed rolls and show considerably less sideway movements than the filaments spun without pre-tension roll. As a further result of the closer contact, the pre-tensioned filaments are heated more rapidly and therefore require fewer turns than the un-tensioned filaments. Thus, as Table 4b shows, the tensioned filaments needed only five turns around the feed rolls, while the un-tensioned filaments required eight turns to obtain a satisfactory run.

EXAMPLE V

This example describes how the nature of the surface of the feed and draw rolls affects the performance of the process and the qualities of the filaments obtained. Filaments were spun and drawn as described in Example IV, selecting the following roll surface speeds: Draw rolls -- 2,160 m/min., relaxation rolls -- 2,000 m/min., and wind-up roll -- 2,002 m/min. The draw ratio was varied by variation of the surface speed of the feed rolls. The surface speed of the pre-tension rolls was about 1.5 percent lower than the surface speed of the feed rolls. The temperature of the heated rolls and the number of filament turns around the rolls were the same as described in Example IV, Table 4. The drawn filaments had a total denier of 1,000/192.

In comparing rolls of different surface roughness, the following roughness terms, as defined in the Specification, were determined:

Roughness Terms Prescribed Limits __________________________________________________________________________ (1) Roughness height 0.5 - 2.2 microns (2) Roughness range 4.5 - 8.0 microns (3) Average roughness range 1.6 - 3.0 microns (4) Peak distance Max. 140 microns (5) Average peak distance 40 - 60 microns (6) Profile curvature Max. 0.030 microns.sup.-.sup.1 __________________________________________________________________________

Filaments were spun and drawn using rolls having a conventional polished surface and rolls of different surface roughness complying with all or any of the prescribed limits. For each type of roll surface, the maximum possible draw ratio of the filaments was determined, i.e., the draw ratio at which a correct drawing without occurrence of filament stickiness or of filament fracture could be accomplished.

Roll surface type A in Table 5 represents a conventional polished roll, while surface types B to H represent surfaces of different roughness, B being the smoothest and H the coarsest type. All rolls of types B to H are within the limits prescribed as regards roughness height (1), but only rolls of types E and F comply with the prescribed limits of all the terms (1) to (6).

Table 5 shows the results of the measurements of the surface roughness of the rolls used. Table 5a indicates, by + and - signs, whether or not the various roll surface types complied with the prescribed limits of the roughness terms, and Table 5b shows the qualities of the corresponding drawn filaments obtained;

TABLE 5

Roll Roughness Terms surface (1) (2) (3) (4) (5) (6) microns mic- mic- mic- mic- microns.sup.-.sup.1 type rons rons rons rons __________________________________________________________________________ A Polished 0.04 0.2 -- -- -- -- B Too smooth 0.53 4.0 1.3 130 47 0.022 C Too smooth 0.58 4.0 1.5 110 44 0.021 D Too smooth 0.65 4.5 1.5 140 59 0.018 E satisfactory 0.78 5.6 2.1 110 55 0.026 F satisfactory 0.69 4.7 1.6 120 45 0.024 G Too coarse 1.85 13 4.8 160 70 0.032 H Too coarse 1.77 11 4.8 180 78 0.031 __________________________________________________________________________

TABLE 5a

Roll Surface Roughness Terms Type (1) (2) (3) (4) (5) (6) __________________________________________________________________________ A - - B + - - + + + C + - - + + + D + + - + + + E + + + + + + F + + + + + + G + + + - - - H + + + - - - __________________________________________________________________________

TABLE 5b

Roll Drawn Filaments Surface Maximum Draw Tenacity Elonga- Type Description Ratio g/denier tion (%) __________________________________________________________________________ A Polished -- -- -- B Too smooth 5.8 8.4 16 C Too smooth 5.9 8.5 15 D Too smooth 6.0 8.8 14.5 E Satisfactory 6.4 9.2 14.5 F Satisfactory 6.5 9.3 14 G Too coarse 6.4 8.2 12 H Too coarse 6.2 8.2 13.5 __________________________________________________________________________

With polished rolls (A), the filaments could not be drawn at all, because they became sticky and adhered to the draw rolls. Rolls (B), (C), and (D) had a surface which was still too smooth to allow such slipping as to effect a sufficient preliminary drawing of the filaments when passing over the feed rolls. As a result, the maximum possible draw ratio of the filaments was substantially below the draw ratio obtained with satisfactory rolls (E) and (F). When it was tried to apply higher draw ratios, the filaments became sticky when contacting the draw rolls and were wrapped around them.

With rolls (G) and (H) having a surface which was too coarse, the filaments were partially damaged. This is shown by the fact that their tenacity and their elongation are substantially lower than the tenacity and their elongation are substantially lower than the tenacity and elongation of satisfactory filaments (E) and (F) drawn at about the same draw ratio. Rolls (E) and (F) having a surface roughness complying with all prescribed limits, produced very satisfactory filaments which showed no stickiness and which were not damaged. At a draw ratio of 6.4 - 6.5 these filaments had a high tenacity of 9.2 - 9.3 grams per denier and an elongation of about 14 percent.

EXAMPLE VI

This example describes the effects of the composition of the lubricating finish. Filaments were spun as described in Example V with roll surface (F), but varying the draw ratio of the filaments by variation of the speed of the feed rolls. The following lubricating finishes were used:

a. Neutral emulsion of a mixture of an ethoxylated fatty acid ester and a sulphonated fatty alcohol, the emulsion containing 75 percent by weight of water.

b. Conventional emulsion of a mixture of 40 percent emulsifying, antistatic, and sizing agents and 60 percent mineral oil, the emulsion containing 80 percent by weight of water.

c. Finish as (b), but containing 15% by weight of water.

d. Water-insoluble ethylene glycol derivate.

e. Lubricating finish based on isooctyl stearate, containing 5 - 7 percent by weight of water.

f. Mixture of equal parts by weight of (d) and (e), containing 2.5 - 3.5 percent by weight of water.

g. Ready-made mixture of isooctyl stearate and an ethoxylated emulsifying agent, containing 2 - 5 percent by weight of water.

Table 6 shows the results of the tests. The temperature indicated is the temperature of the finish as applied to the filaments. The content of finish in the filaments was determined by extraction and refers to water-free finish.

TABLE 6

Con- tent in Finish fil- Filaments ame- draw Water nts rat- Tenacity Elonga- Type Content Temp. % tio g/denier tion (%) __________________________________________________________________________ a 73% 25.degree. C 0.7 5.0 4.1 28 b 80% 25.degree. C 0.9 5.2 4.1 30 c 15% 60.degree. C 1.2 5.4 6.0 16 d -- 40.degree. C 1.1 6.0 8.2 16 e 6% 80.degree. C 0.6 6.0 8.8 15 f 3% 80.degree. C 0.9 6.0 8.5 15 g 4% 30.degree. C 0.3 6.0 8.8 15 __________________________________________________________________________

the draw ratio indicated for finishes (a), (b), and (c), containing more than 10 percent of water, is the maximum draw ratio at which filaments could still be spun and drawn. As Table 5 shows, this draw ratio is substantially lower than the draw ratio obtainable with finishes (d), (e), (f), and (g) the water content of which did not exceed 10 percent as prescribed. Accordingly, the tenacities of 8.2 - 8.8 grams per denier of the filaments prepared with the preferred lubricating finish considerably exceed the tenacities of 4.1 - 6.0 grams per denier of the filaments made with finishes of a high water content.

The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification as indicating the scope of the invention.

Claims

We claim:

1. Continuous process for the preparation of highly drawn polyethylene terephthalate filaments which comprises extruding molten polyethylene terephthalate through a spinnerette to form filaments, quenching the filaments, applying to the filaments a lubricating finish, passing the filaments successively over a feed roll system and a draw roll system, each system comprising at least two cylindrical rolls with each roll having a surface roughness with a roughness height as defined by ASA B 46.1 - 1962 of 0.5-2.2 microns, allowing a slipping of the filaments around the feed roll system and the draw roll system of one to five turns, driving at least one feed roll and one draw roll by a motor, arranging said systems so that the axis of the feed roll from which the filaments leave the feed roll system and the axis of the draw roll at which the filaments arrive at the draw roll system are parallel while the axes of at least two of the feed rolls of the feed roll system are skew set to each other and the axes of at least two of the draw rolls of the draw roll system are skew set to each other, gradually drawing the filaments, starting the drawing while the filaments pass around the last one to five turns before leaving the feed rolls which have a surface temperature of 75.degree. - 130.degree. C., and completing the drawing while the filaments pass around the first one to five turns after arrival on the draw rolls which have a surface temperature of 180.degree. - 240.degree. C. and a surface speed at least five times that of the feed rolls, drawing the filaments at a total draw ratio of not less than 5.0, and finally winding up the drawn filaments at a speed of not less than 1,800 meters per minute.

2. Process as set forth in claim 1 including using a lubricating finish which contains not more than 10 percent by weight of water.

3. Process as set forth in claim 1, wherein the spun filaments before arriving at the feed roll system, pass over a pre-tension roll system comprising at least one unheated motor-driven roll, using a surface speed of the pre-tension unheated roll which is lower than the surface speed of the feed rolls with the speed difference not exceeding 2 percent.

4. Process as set forth in claim 1 including providing said rolls with a surface roughness range, as defined by DIN 4762, of 4.5 - 8.0 microns, a peak distance of not more than 140 microns, an average peak distance of 40 - 60 microns, and a profile curvature of not more than 0.030 microns.sup.-.sup.1.

5. Process as set forth in claim 4 including providing said rolls with an average roughness range of 1.6 - 3.0 microns.

6. Process as set forth in claim 1 including providing said rolls with a peak distance of not more than 140 microns.

7. Process in accordance with claim 6 including providing said rolls with an average peak distance of 40 - 60 microns.

8. Process in accordance with claim 1 including providing said rolls with a profile curvature of not more than 0.030 microns.sup.-.sup.1.

9. Continuous process for the preparation of highly-drawn polyethylene terephthalate filaments which comprises extruding molten polyethylene terephthalate through a spinnerette to form filaments, quenching the filaments, applying to the filaments a lubricating finish, passing the filaments over feed rolls and draw rolls which have a surface roughness which allows slipping of from one to five turns before the filaments leave the feed rolls and after the filaments arrive at the draw rolls, the feed rolls having a surface temperature of 75.degree. - 130.degree. C, and the draw rolls having a surface temperature of 180.degree. - 240.degree. C and a surface speed at least five times that of the feed rolls, partially drawing the filaments at the lower temperature of the feed rolls, continuing to draw the filaments between the feed rolls and the draw rolls, and completing the drawing of the filaments at the higher temperature of the draw rolls to attain a total draw ratio of 5 to 8, and winding up the drawn filaments at a speed of 1,800 to 6,000 meters per minute.

10. A process as set forth in claim 9 wherein the temperature of the feed rolls is 80.degree. - 90.degree. C, and the temperature of the draw rolls is 210.degree. - 230.degree. C.

11. Process as set forth in claim 9 including using a lubricating finish which contains not more than 10 percent by weight of water.

12. A process as set forth in claim 9 wherein said surface roughness consists of a coherent, non-porous, abrasion-resistant, impermeable coating of tiny, smooth-topped elevations of unequal height and irregular distribution in all directions on the surface of said rolls.

13. A process as set forth in claim 12 wherein said coating is a metal.