EA001176B1 - Process formaking high tenacity aramid fibers - Google Patents

Abstract

1. A process for making yarn of poly(p-phenylene terephthalamide) having a tenacity of at least 28 grams per denier (31 grams per dtex) comprising the steps of: (a) extruding filaments of an acid solution containing at least 30 grams of poly(p-phenylene terephthalamide) having an inherent viscosity of at least 4 per 100 milliliters of acid, out of a spinneret (10) and through a layer of inert noncoagulating fluid into a coagulating bath (1) and then through a spin tube (14) along with overflowing coagulating liquid; (b) jetting additional coagulating liquid symmetrically about the filaments in a downward direction forming an angle of 0 to 85 degrees with respect to the filaments within 2.0 milliseconds from the time the filaments enter the spin tube (14), (i) maintaining a ratio of the mass flow rate of combined overflowing and jetted coagulating liquid to mass flow rate of the filaments of greater than 250, (ii) maintaining an average linear velocity of combined overflowing and jetted coagulating liquid in the spin tube (14)which is less than the velocity of the filaments exiting from the spin tube (14), and (iii) maintaining constant the flow rates of both the jetted and the overflowing coagulating liquids; and (c) drying the filaments, the improvement comprising employing a spinneret (10) having capillaries with diameters of up to 0.051 mm (2 mils) and drying the filaments under a tension of at least 3.0 grams per denier (3,33 grams per dtex). 2. The process of claim 1 wherein the ratio of the mass flow rate of combined overflowing and jetted coagulating liquid to mass flow rate of the filaments is greater than 300. 3. The process of claim 1 wherein the diameter of the spinneret capillaries is 0.025 mm (1 mil) to 0.051 mm (2 mils). 4. The process of claim 1 wherein the filaments are dried under a tension of 3.0 grams per denier (3,33 grams per dtex) to 7.0 grams per denier (7,77 grams per dtex).

Description

FIELD OF THE INVENTION

This invention relates to a method for manufacturing aramid fibers of particularly high tensile strength by combining process elements, including the specific capillary size of a multi-channel mouthpiece, specific coagulation conditions, and specific tension during drying.

Description of the Related Art

In US patent No. 4965033, issued October 23, 1990 according to the application of Chiou (Soy), a method for forming fibers of an aromatic polyamide using a large mass flow rate of a coagulating liquid pumped by a jet is described.

US Pat. No. 3,767,756, issued Oct. 23, 1973. according to the application of Blades (B1a6e§), and No. 5173236, issued on December 22, 1992 at the request of Young (Uapd). - describes the formation of fibers of aromatic polyamide using multichannel mouthpieces having capillaries from 0.025 to 0.25 mm (1 to 10 mil) and less than 0.064 mm (2.5 mil), respectively, and drying such fibers with strains of the order of 0.3 grams denier (g / d).

In US patent No. 4726922, issued February 23, 1988. according to the application of Kohren (Sosygap) and Young, the formation of aromatic polyamide fibers and their drying under tension of 3-7 grams in denier (g / d) are described to increase the strength of the fibers.

Summary of the invention

A method has been developed for the production of poly (p-phenylene terephthalamide) filaments having a tensile strength of at least 28 g / d, which consists in the following: (a) filaments are extruded from an acid solution containing at least 30 g poly (p-phenylene terephthalamide) having an intrinsic viscosity of at least 4 per 1,00 ml of acid from a multi-channel mouthpiece and through a layer of inert non-coagulating fluid into a coagulation bath, and then through a forming tube together with flowing coagulating fluid; (b) provide injection of a stream of additional coagulating fluid symmetrically around the filaments in the downstream direction, forming an angle of 0 ° -85 ° relative to the filaments, for about 2.0 ms the moment when the filaments fall into the forming tube, (ί) maintain the ratio of the mass flow rate of the total overflowing and injected jet of coagulating liquid to the mass flow rate of elementary filaments in excess of about 250, (ίί) maintain the average linear velocity of the total overflow and pump second jet of the coagulating liquid in the spin tube is less than the velocity of the filaments, you walking from the forming tube, and (u) are kept constant as the costs jetted and flowing coagulating liquids; and (c) the filaments are dried, the improvement being that a multi-channel mouthpiece having capillaries with diameters of up to 0.051 millimeters (2 mil) is used, and the filaments are dried with at least 3.0 grams denier ( g / d).

Brief Description of the Drawing

The drawing shows a cross section of a device that can be used in the implementation of the method of manufacturing fibers used in this invention.

DETAILED DESCRIPTION OF THE INVENTION

A lot of effort has been put into the development of threads and fabrics with increased strength. Each increase is difficult and very important, because even small increases give significant benefits.

The filaments referred to in the present invention have a tensile strength of at least 28 g / d and can be made using the device shown in FIG. 1. These threads are made mainly in accordance with the process described in US patent No. 3767756, using poly (rphenylene terephthalamide) (PPPTA) having an intrinsic viscosity of at least 4.0, dissolved in sulfuric acid having a concentration at least 98%. The PPPTA solution is extruded from a multi-channel mouthpiece through an air gap into a coagulation bath. The multi-channel mouthpiece has capillaries with a diameter of 0.051 mm (2.0 mil) or less. It was found that capillaries with a diameter of more than 0.051 mm (2.0 mils) produce filaments of fibers that are considered to have a deteriorated molecular orientation, which is manifested in reduced strength and therefore not as strong as those made using capillaries of smaller diameter. In practice, it is difficult to use capillaries of less than about 0.025 mm (1 mil), and they do not produce fiber fibers of acceptable quality.

In FIG. 1 is a cross-sectional view of a preferred coagulation bath 1. Bath 1 has a circular structure consisting of an insert disk 2 mounted in a supporting structure 3. The supporting structure 3 includes an inlet channel 4 for introducing quenching liquid 5 under pressure into a distribution ring 6, which contains filler 7, suitable for improving the uniform supply of quenching fluid around the periphery of the coagulation bath 1.

The introduction of the coagulating fluid into the bath may occur from a peripheral collector containing partitions or packing to ensure uniform distribution and non-turbulent flow of the coagulating fluid to the outlet. In the case of a round bath, a collector may surround the bath. In the case of a rectangular bath with a slotted outlet, the collector can also surround the bath, but coagulating liquid should be supplied only on the sides of the bath, which are parallel to the gap. It is only necessary that the flow of coagulating fluid to the outlet be non-turbulent near the outlet. Thus, the filler 7 may be glass beads, a series of screens, a cellular structure, sintered metal plates or other similar device.

After passing through the filler 7, the quenching fluid 5 passes through a perforated plate or screen and flows uniformly without noticeable turbulence to the center of the bath 1, where the quenching fluid 5 comes into contact with filaments 9 extruded from the multi-channel mouthpiece 10, due to which the quenching fluid 5 and filaments 9 pass together through the outlet 11 in the downstream direction into the forming tube 14.

The bottom of the bath can be contoured in the form of zones indicated by the letters A and B to facilitate uniform non-turbulent flow to the outlet 11. The area around the outlet can also taper towards the outlet. Preferably, the depth of the coagulating bath is not more than 20% of the width of the bath in the zone of non-turbulent flow.

For spinning in small quantities, such as 20 filaments, a suitable bath width is about 6.35 cm (2.5 inches) in combination with an outlet opening having a diameter of 3.1 mm, which has a tapering feed channel having an initial diameter of about 1 2 mm. For forming in a larger quantity, for example, 1,000 filaments, a suitable bath width is about 23 cm in combination with an outlet diameter of 9 mm, which may have a tapering inlet channel having an initial diameter of about 28 mm.

The insert disk 2 includes a circular ink element 1 2 that operates similarly to the ink element described in US Pat. No. 4,298,565. The inlet 11 preferably has an edge 13, i.e. the outlet has a slightly smaller diameter than the forming tube 1 to 4 to prevent adhesion of the filaments 9 to the walls of the outlet 11 and the forming tube 14. The quenching liquid 5 is introduced through the hole 1 5 through the passage 1 6 into one or more holes 17 for the jet due to which the quenching fluid 5 passes together with the filaments 9 and another quenching fluid 5 in the downstream direction through the forming tube to the outlet 1 8 to a conveying device (not shown). In accordance with known procedures, filaments are washed and / or neutralized and dried before winding yarns obtained in this way.

It is preferable that the angle of the liquid direction of the holes 1 7 for the jet relative to the filaments formed an angle (θ) in the range from 0 to 85 °. At the same time, satisfactory results are also obtained for 090 °, however, this choice of theta makes the process very dependent on control, and therefore undesirable when working in industry. An angle of 30 ° is practically suitable for use in an industrial process. The jet openings 17 are located adjacent to the outlet 11 and direct the coagulating fluid injected by the jet downstream to the filaments for about 2 milliseconds from the moment the filaments enter the forming tube.

The method provides the greatest improvement when the multichannel mouthpiece, the forming outlet, the jet and any length of the forming tube are carefully oriented along the same axis and when the inkjet elements are carefully designed and oriented in order to ensure perfectly symmetrical injection of the stream around the thread lines. Any misorientation of the inkjet elements or jamming of any solid particles in the jet openings in violation of symmetry can reduce or eliminate improvements. Such symmetry can be achieved by two or more jet outlets or by slots symmetrically spaced relative to the line of threads.

In accordance with the method, the flow rates of the overflowing coagulating fluid ^) and the injected jet of coagulating fluid (Ω ₂ ) are controlled and kept constant to achieve an improvement in accordance with the present invention. The mass flow ratio (B) for the mass flow rate of the combined flowing and pumped jet of coagulating liquid to the mass flow rate of the filaments is controlled so that it exceeds about 250. Preferably, the mass flow ratio (B) exceeds about 300.

In carrying out the invention, the mass flow rate (Οι) of the flowing coagulating fluid is controlled by adjusting the depth of the bath above the outlet 11 (size 11) by metering the inflow into the bath, but this mass flow also depends on the diameter of the forming tube 14. Size 1 is usually less than one inch (2.5 cm) and preferably is 0.5 inches (1.3 cm). If 11 is too small, the air will be sucked into the forming tube 14 by the pumping action of the filaments moving forward, and this is harmful both for the tension properties and for the mechanical quality of the produced thread. Thus, 1 must be large enough to ensure that no gas bubbles penetrate. The above considerations lead to the calculation of a suitable diameter of the forming tube 14.

Due to the fact that the flow rate (Οι) when the quenching fluid flows through the outlet is largely dependent on the line of threads moving through the same outlet, this effect must also be taken into account. For example, flow rate when flowing through an outlet with a diameter of 9.5 mm (0.375 in) with a hydrostatic head of 15.9 mm (0.625 in) is approximately 1.5 l / min (0.4 gallon / min) in the absence of a line of moving threads and 8.7 l / min (2.3 gallons / min) in the presence of a line of threads of 1,000 filaments with a parameter of 1.5 denier per filament, moving at a speed of 686 m / min. This is usually inherent in the pumping effect of filaments moving through a liquid layer due to the boundary layer phenomenon. To compensate for this effect, the size of the outlet, i.e., the diameter of the cross-sectional area, is appropriately selected.

The flow rate (O ₂ ) of the coagulating fluid pumped by the jet is preferably controlled by metered pumping through a jet opening of a selected size. The smallest cross-sectional size of the jet (i.e., the diameter of the hole or the width of the stream) is usually in the range of 0.05-2.5 mm (2-100 mil). It is desirable that the mass flow rate and the opening for the jet be such that the axial velocity of the coagulating liquid injected by the jet exceeds at least 50% the speed of the processed thread, and preferably should exceed the speed of the thread by at least 80% to prevent slow displacement of the line of threads, which leads to a decrease in tensile strength. However, the axial speed of the coagulating fluid injected by the jet should not significantly exceed 200% of the speed of the processed thread, and preferably does not exceed about 1 50% of the speed of the thread, in order to prevent buffering of the thread line, which can lead to a decrease in the measured tensile strength of the threads. Therefore, it is necessary to use a suitable mass flow rate of the fluid injected by the jet and openings or slots for the jet, which provide a mass flow ratio of the combined coagulating fluid to the mass of filaments in excess of about 250, preferably greater than about 300, and a ratio of the momentum of the pumped fluid and the flowing coagulating fluids, greater than about 6.0, which also provides a suitable velocity for the coagulating fluid pumped by the jet relative to the speed of the nit and.

In the method of the invention, the average linear velocity of the combined coagulating liquids in the spinning tube is maintained at a speed level lower than the speed of the filaments exiting the spinning tube. This prevents loss of tensile strength of the filament due to looping of filaments in filaments and possible problems of process continuity arising from the lack of sufficient tension in front of the feed rollers.

The present invention can be used in a wide range of molding speeds and, in particular, can be used for molding speeds of at least 300 m / min, and preferably at least about 350 m / min, although higher molding speeds result lower tensile strength compared to lower molding speeds. Although the advantages of tensile strength obtained by the method of the invention continue to increase with increasing mass flow rate (K.) and mass momentum ratio (φ), and therefore can compensate for lower tensile strength due to continued increases in molding speed , it is assumed that the ratio (K) of mass expenditures over 5000 and the ratio (φ) of quantities of movement over 50 will not give any additional significant improvement and will not be economically attractive for industry production, especially at high denier values, for example, 1500 denier.

The fibers that have just been formed and passed through the coagulation bath are washed and dried to complete production. The fibers should be thoroughly washed to remove all traces of acid and to prevent deterioration in the quality of the fibers associated with the acid. For washing the fibers, you can use one water or a combination of water and alkaline solutions. A convenient way to rinse is to spray the line of filaments when it leaves the coagulating bath through rollers, aqueous alkaline solutions (for example saturated with No. ₁ HCO ₃ , or 0.05 with 5 normal альнымαΟΗ) to reduce the acid content to about 0.01% (in dry fibers) )

Fibers can be conveniently dried on heated rollers (for example, at a temperature of 160 ° C). The preferred washing method for this invention is to wash the fibers with a spray liquid and continuously pass them to the rollers of the dryer, maintained at a temperature of about 150 ° C.

One important element of the process of this invention involves drying the fibers under high tension of about 3.0-7.0 g denier (g / d). Tensions during drying of less than about 3.0 g / d result in fibers that have a reduced molecular orientation, resulting in reduced strength, and tension during drying above 7.0 g / d causes an excessive break in the thread line and the associated technological difficulties . Particularly preferred are drying tensions of about 3.0-5.0 g / d.

Test methods

Tensile properties

Tensile strength is called tensile strength divided by linear density. The module is called the slope of the initial stress / strain curve, converted to the same units as the tensile strength. Elongation is the percentage increase in length at break. Both the tensile strength and the modulus are first calculated in units of g / denier, which after multiplying by 0.8826 gives units dN / tex. Each dimension referred to is an average of 10 breaks.

Denier is the mass in grams of 9,000 m, dtex is the mass in grams of 1,000,000 m of filament or filament.

The tensile properties for the threads are measured at 24 ° C and a relative humidity of 55% after exposure to the test conditions for at least 1 to 4 hours. Before testing, each thread is twisted until a twist coefficient of 1.1 is reached (for example, a thread with a nominal value of 1,500 denier is twisted approximately up to 0.8 turns per centimeter). Each twisted sample has a test length of 25.4 cm and is extended by 50% per minute (based on the initial length in unstretched condition) using a typical stress / strain registration device.

The twist coefficient (QC) of the thread is defined as (r / in) (Denier) ^1/2 (r / cm) (dtex) ^1.2

QC = --------------------------- = -------------------- , zo, z where rpm = rpm, and rpm = rpm.

The tensile properties for filaments differ from the tensile properties for individual filaments and below them, and such values for filaments cannot be successfully and accurately estimated based on the values for filaments.

The ratio (φ) of the momentum

The ratio of momentum is defined as the ratio of momentum (M ₂ ) along the direction of the line of threads for the coagulating fluid pumped by the jet to the amount of motion (M ₁ ) of the flowing coagulating fluid, i.e. φ = M ₂ / M ₁ . The momentum is defined as the product of mass flow and flow velocity. The calculation of the ratio of the moments of momentum is described in the aforementioned US patent No. 4298565 and in the examples is determined from the expression

Oh x 41 ² so50

4C1 ² x 4 ₂ (Φ + cbcsoO) where

P ₁ - flow rate of the flowing fluid;

C) ₂ - flow rate of the fluid pumped by the jet;

b ₁ - the inner diameter of the forming tube;

ά ₂ - smaller size of the hole for the jet;

θ is the acute angle between the fluid pumped by the jet and the thread line.

Since b ₁ and ά ₂ and O | and О ₂ are expressed in identical units, the ratio θ does not depend on the selected units.

Mass Cost Ratio (K)

This is the ratio of the mass flow rate of the total coagulating fluid to the mass flow rate of filaments (in terms of dry state). The basic unit of flow rate O fluid is gal / min.

C) x 3899 = mass flow rate in g / min.

For the thread, the main units are speed (Υ) in yards per minute and denier (Ό) in g / 9000 m.

ΥΏ x (0.9144 / 9000) = mass flow rate in g / min.

Then the mass flow rate takes the form (,) ΥΙ) x 3.8376 x 10 ⁷ .

In this equality, it is assumed that the density of the coagulating fluid is approximately 1.03 g / ml.

Examples

In the following examples, poly (paraphenylene terephthalamide) (PPPTA) having an intrinsic viscosity of about 6.3 dl / g before dissolving and about 5.5 dl / g in fiber form was fed to the device illustrated in US Pat. No. 4,340,559 using tray O The diameter of the forming tube was 0.76 cm (0.3 in.), And jets with a diameter of 0.21 and 0.42 mm (8 and 1 6 mils) were used with an angle of 30 ° between the flow pumped by the jet and the thread line. The solution used in the manufacture of the molding additive was approximately 1 00.1% sulfuric acid, and the polymer concentration in the molding additive was approximately 19.4 wt.%.

As shown in tables I and II, multichannel mouthpieces with capillaries of 0.051 and 0.064 mm (2.0 and 2.5 mil) were used. The number of capillaries used multichannel mouthpieces included 133, 266, 400, 500, 560 and 666 capillaries. Air gap i.e. the distance of movement of the filaments from the exit surface of the multi-channel mouthpiece to the first contact with the coagulating liquid was approximately 0.635 cm (0.25 inches). The coagulating liquid was maintained at a temperature of about 3 ° C. In all the examples described below, yarn tensions of about 1.0 g / d were used during washing and neutralization.

In embodiments of the invention, a mass flow ratio (I) of 325-1680 was used along with multichannel mouthpieces with 0.051 mm capillaries. The yarns were dried with a tension of more than 2 g per denier, and the yarns had linear densities of 160-1500 denier

In the comparative examples, the same polymer and the same molding device were used under the same conditions, except that the ratios of mass flow rates, ratios of momentum, tension during drying and capillary sizes of multichannel mouthpieces were different, as shown in table 1.

TableI

Invention Comparative examples Conditions one 2 BUT IN FROM Ό E E Capillary Diameter (Mils) 2.0 2.0 2,5 2.0 2,5 2,5 2,5 2,5 (mm) 0.051 0.051 0,064 0.051 0,064 0,064 0,064 0,064 Number of ale. threads 266 400 133 133 266 500 560 666 Drying tension (g / d) 3,5 3,5 0.7 0.3 2.0 2.1 2.1 2.1 Jet Width (mils) sixteen sixteen 8 sixteen 8 8 8 8 (mm) 0.42 0.42 0.21 0.42 0.21 0.21 0.21 0.21 Οι (gpm) 1.32 1.32 1,6 1.3 1.4 1.7 1.7 1.7 (l / min) 4.96 4.96 6.01 4.88 5.26 6.38 6.38 6.38 0; (gpm) 1.65 1.65 1,1 2.0 0.9 0.9 0.9 0.9 (l / min) 6.20 6.20 4.13 7.51 3.38 3.38 3.38 3.38 Speed (yard / min) 400 400 750 500 400 400 400 400 (m / min) 366 366 686 458 366 366 366 366 φ (momentum) 6.1 6.1 3.8 9.2 3.3 2.2 2.2 2.2 I (Mass) 712 475 690 1266 552 332 297 249 Thread Properties Denier threads Den./ Elem. a thread 400 600 200 200 400 750 840 1000 Tensile strength (g / d) 28.5 28,2 23 27 27 26.5 27 26.5 Elongation(%) 3.2 3.2 3.0 3,5 3.3 3.3 3.4 3.4 Module (g / d) 830 800 750 700 760 740 760 740

In the following examples, NNFTA of the same quality as that used above was molded using the same device and molding conditions as used above for the exceptionally channel mouthpieces and changed some other conditions, as shown in Table II. Table II also shows the properties of the yarn for these examples.

The fact that they used a variety of Table II

Invention Comparative examples Conditions one 2 3 4 5 6 7 BUT IN Capillary diameter (mil) 2.0 2.0 2.0 2.0 2.0 2.0 2.0 2,5 2,5 (mm) 0.051 0.051 0.051 0.051 0.051 0.051 0.051 0,064 0,064 Number of ale. threads 270 270 270 270 270 1000 1000 1000 1000 Drying tension (g / d) -..................... 3.0 - 3.5 -------------------- 2,3 0.8 Jet Width (mils) sixteen sixteen sixteen sixteen sixteen sixteen sixteen 8 8 (mm) 0.42 0.42 0.42 0.42 0.42 0.42 0.42 0.21 0.21 01 (gpm) 0 ₂ (gpm) Speed (yard / min) 350 350 350 350 350 350 350 350 775 (m / min) 320 320 320 320 320 320 320 320 691

φ (momentum) K (Mass) | 1075 | 1075 | | 1275 | 1680 | 1,785 | | 370 1,325 1 199 | 140 Thread Properties Denier threads 270 270 216 162 400 1000 1200 1500 1500 Den./ Elem. a thread 1,0 1,0 0.8 0.6 1.5 1,0 1,2 1,5 1,5 Tensile strength (g / d) 31.3 30.9 31,0 30,2 29.5 28.7 28.6 26.5 23.5 Elongation (%) 3.4 3.4 3.4 3.3 3,5 3.6 3.6 3.0 3.6 Module (g / d) 934 887 862 819 850 820 810 760 570

CLAIM

Claims (4)

1. A method of manufacturing a yarn of poly (rphenylene terephthalamide) having a tensile strength of at least 28 grams per denier (31 grams per dtex), which consists in the fact that: (a) the strands are extruded from an acid solution containing at least 30 grams of poly (p-phenylene terephthalamide) having an intrinsic viscosity of at least 4 per 100 milliliters of acid from a multi-channel mouthpiece (10) and through layers of an inert non-coagulating fluid into a coagulation bath (1), and then through the forming tube (14) together with p flowing coagulating fluid; (b) ensure that the jet of additional coagulating liquid is injected symmetrically around the filaments in the downstream direction, forming an angle of 0-85 degrees relative to the filaments, for about 2.0 milliseconds from the moment when the filaments fall into the forming tube (14), (1) maintain the ratio of the mass flow rate of the total flowing and injected jet of coagulating liquid to the mass flow rate of elementary threads exceeding 250, (and) maintain the average linear velocity of the total flowing and the coagulating fluid injected by the jet in the forming tube (14) is less than the speed of the filaments leaving the forming tube (14), and (w) the mass flow rates of both the injected jet and the flowing coagulating fluids are kept constant; and (c) drying the filaments, characterized in that they use a multi-channel mouthpiece (10) having capillaries with diameters of up to 0.051 millimeters (2 mil), and the filaments are dried under tension of at least 3.0 grams in denier (3 , 33 grams per dtex). 2. The method according to claim 1, characterized in that the ratio of the mass flow rate of the total flowing and pumped jet of coagulating liquid to the mass flow rate of elementary threads exceeds 300. 3. The method according to claim 1, characterized in that the diameter of the capillaries of the multi-channel mouthpiece is 0.025 mm (1 mil) - 0.051 mm (2 mil). 4. The method according to claim 1, characterized in that the filaments are dried under tension of 3.0 grams per denier (3.33 grams per dtex) - 7.0 grams per denier (7.77 grams per dtex).