RU2142522C1 - Method for obtaining filaments from optically anisotropic spinning solution - Google Patents

Abstract

FIELD: production of specific filaments. SUBSTANCE: method involves extruding spinning solution through spinning openings concentrated in at least one spinning section; directing extrudates in succession through inert gas and coagulating bath. Ratio of spinning opening spacing to spinning section width is in the excess of 0.15 and below 0.7. Width of spinning section is less than 5 mm. Method allows filaments with good physical characteristics and free from spread blocking to be produced. EFFECT: increased efficiency by increased spinning speed and improved physical qualities of filaments by reduced concentration of acid in coagulant and absence of blocked parts. 7 cl, 4 dwg, 1 tbl, 1 ex

Description

 The present invention relates to a method for producing fibers from an optically anisotropic spinning solution, in which the spinning solution is extruded through the spinning holes grouped into at least one spinning section, and in which the extrudates pass sequentially through an inert gas and a coagulation bath.

 This method is known from Japanese Laid-open Application No. 1986-239012, which describes a method for forming filaments of poly (paraphenylene terephthalamide) (PPTA), where the filaments that are formed using spinning holes are grouped to form a rectangle. The ratio of the lengths of the long side of the rectangle and its short side should be at least 4. A hole is also provided in the coagulation bath, also rectangular, under the spinning section. Since both the spinning section and the hole in the coagulation bath are rectangular, the bundle of threads is also rectangular. As a result of this rectangular beam shape, very few vortices are formed in the coagulant, some of which come out of the coagulation bath with the threads. This leads to a significant reduction in the formation of filaments in the coagulation bath (where the filaments are not yet fully coagulated) and makes it possible to increase the spinning speed.

 In the examples, yarns with good strength are obtained from the description of said Japanese patent. This strength is attributed primarily to low concentrations of sulfuric acid (0 and 10%) in the coagulant and the large average distance between the spinning holes (the so-called step). The low concentration of acid, which can only be maintained by treating the coagulant and replacing it, and the large step that makes it necessary to use large equipment in relation to the number of strands obtained makes the described method expensive with a very large waste stream.

 In addition, at high molding speeds, it is necessary to have a pressure close to atmospheric below the coagulation bath, this is necessary in order to further increase the speed of the coagulant and thus reduce the tension in the threads.

 If, in the method described in Japanese Patent, the pitch of the spinning holes is reduced in the order of increasing their number (and thus the number of threads) per unit area, the threads in the coagulation bath stick together with each other at the spinning speeds discussed above, resulting in an end product unsuitable for intended applications requiring high quality (e.g. woven materials or composite reinforcement).

 An object of the present invention is to provide a method that enables high-speed spinning (≥300 m / min) of a plurality of threads having physical properties from good to very good.

 This technical problem is solved due to the fact that in the method for producing threads from an optically anisotropic spinning solution, in which the spinning solution is extruded through the spinning holes grouped in at least one spinning section, and the extrudates pass sequentially through an inert gas and a coagulation bath, according to of the invention, the ratio of the distance between the spinning holes to the width of the spinning section is greater than 0.15 and less than 0.7, and the width of the spinning section is less than 5 mm.

 In this case, the spinning holes may be grouped in more than one spinning section, and the spinning section or spinning sections may be rectangular.

 In addition, the spinning sections may be arranged in a circle, and the longitudinal direction of each of the spinning sections may coincide with the radius.

 The bottom of the coagulation bath can be provided, for each spinning section, with a rectangular hole that is longer than the spinning section and is narrower in width.

 The bottom of the coagulation bath may be provided with at least two openings, and the adjacent edges of adjacent openings are at different levels.

 The distance traveled by filamentous extrudates through an inert gas medium may be more than 0.5 mm, and less than 8 mm.

 Preferably, the specified ratio of the distance between the spinning holes to the width of the spinning section (which is easily calculated by dividing the pitch in millimeters by the length of the spinning section, also in millimeters) is in the range from 0.20 to 0.55, the spinning section has a width in the range from 1 5 to 4 mm, and the pitch is in the range of 0.3 to 0.7 mm. In addition, the spinning section is preferably rectangular.

 It was unexpectedly found that the use of this method makes it possible to produce fibers having good physical properties, with a small step (and therefore, with a large number of fibers per unit area), with a relatively high concentration of acid in the coagulation bath, which results in an economical method with a small stream of effluents. As can be seen from the example, the number of adhesions occurring during the implementation of the method (from fibers having contact before this, there is sufficient coagulation of the outer shell) is low.

 The method of the present invention makes it possible to use relatively compact spinning equipment or supply existing spinning equipment with multi-channel mouthpieces with a higher number of spinning holes. For example, production on existing spinning equipment can be increased from 1,000 to 2,000 or 3,000 fibers per spinning position.

 Favorable results are most likely due to the low resistance that the coagulant encounters when it flows into the interior of the fiber bundle (alternatively, this may be referred to as high permeability of the fiber bundle). The resistance depends on the method of broaching, that is, on half the width of the fiber bundle and the distance between the different threads (step).

 Preferably, the spinning holes are grouped into more than one spinning section. The different sections are then placed one opposite the other so as to provide the smallest possible resistance to the incoming coagulant flow and the most complete possible elimination of disturbances in the coagulation bath.

 In addition, the individual spinning sections are preferably positioned so that the maximum distance between the outer strands is relatively low at the time of extrusion from the spinning holes of the various spinning sections, so that the convergence, say, to the guide may be low.

 One of the most effective ways of arranging rectangular spinning sections is to form spinning sections that are distributed at the same distance from each other in a circle, with the longitudinal direction of each of the spinning sections coinciding with the radius. This arrangement greatly (or completely) slows down the incoming coagulant flow and gives low convergence for each of the fiber bundles.

 To further reduce convergence in the fiber bundle or fiber bundles, it is preferable to create a rectangular hole at the bottom of the coagulation bath for each spinning section, which is longer than the spinning section and is somewhat narrower in width. In this case, neither the length nor the width of the hole in the bottom of the coagulation bath leads to the convergence of the bundle of threads, and the threads are protected from being pressed against each other or from damage from friction against the edge of the hole.

 The physical properties of the filaments obtained by the method of the present invention can be further enhanced by selecting the range of distances traveled by filamentary extrudates through an inert gas medium (gas gap) greater than 0.5 mm and less than 8 mm.

 When using very small air gaps (say, smaller than 2 mm), there is a risk that the coagulant, which always exhibits some movement under the influence of a bundle of filaments (vibrations, small waves and the like), will come into contact with a multi-channel mouthpiece. When this happens, the harmful effect on the process can reach such an extent that its suspension is required. Therefore, if the use of very small air gaps is required, the main thing is to have as calm a surface of the coagulation bath as possible. It was unexpectedly found that the extent to which the surface of the coagulation bath is in motion is highly dependent on the geometry of the bottom of the coagulation bath. If more than two spinning sections are used and the corresponding number of outlet openings in the bottom of the coagulation bath, the degree to which movement on the surface of the coagulant is carried out can be significantly reduced by introducing changes in height or at the bottom. A very simple and effective implementation of this is where the edges of adjacent holes are at different heights ("at different levels"). A possible explanation of this phenomenon is given below.

 At the edges of the outlets, the liquid that is brought in by the outgoing bundle of threads stops or is subjected to friction. Due to inertia, the fluid retains (partially) its speed and flows parallel to the bottom in the direction of the adjacent outlet. However, the incoming coagulant flow also takes direction from this adjacent outlet, which gives a collision of flows flowing in opposite directions. As a result, the fluid is pushed out, and the surface of the coagulation bath rises above this stagnation point. Obviously, the difficulty in the flow of the coagulant is a significant limitation when choosing an air gap; after all, it is necessary to prevent the coagulant from coming into contact with the multi-channel mouthpiece.

 When the flows discussed above converge at different levels, the described flow difficulty does not occur. On the contrary, since the speed of one of the flows (i.e., flowing from the lower edge) already has a component directed towards the surface of the liquid, there is absorption, and the surface of the liquid remains calm.

 If the coagulation bath has a depth greater than 10 mm and less than 20 mm (preferably less than 15 mm), on the one hand, the filaments meet only a small resistance in the bath and the consumption of the coagulant is low, and on the other hand, the residence time in the coagulation the bath is long enough to achieve the desired coagulation.

 It should be noted that European patent 172001 describes a method for forming aramid yarn, which provides for the use of rectangular spinning sections with a small width and a small pitch. However, this process is significantly different from the process of the present invention, since the coagulant is not contained in the bath, but is supplied in the form of a waterfall. Due to the strong flow in the waterfall and a small number of rows of threads, the resistance encountered by the coagulant in the bundle of threads does not constitute a noticeable part.

 The method according to European patent 172001 involves a very high consumption of coagulant. Moreover, only water (0% sulfuric acid) is used in the examples. As a result, the (very large) coagulant stream must undergo costly post-processing and / or neutralization.

 It should also be noted that Japanese Patent Application Laid-Open No. 1985-065110 describes a method in which multi-channel mouthpieces having 20 spinning sections are used, each with 50 spinning holes. The pitch is 1.5 mm, which gives a low number of threads per unit area.

 The coagulant used in the method under discussion is water containing 0% or 10% sulfuric acid, so this method is likely to be associated with a large stream of effluents.

 It is noted that French patent A-1102056 (filing date June 16, 1947) describes a very small multi-channel mouthpiece with a large number of spinning holes. Such multi-channel mouthpieces can only be used in truly wet spinning processes, that is, in processes that do not include an air gap (e.g., forming viscose), and in which the extruded strands directly come into contact with the coagulant and coagulate. Truly wet spinning processes for this reason do not encounter sticking together of threads and problems associated with the free surface of the coagulant. In addition, the publication requires that the spinning holes be grouped into spinning sections, and the width of the groups should not exceed two holes, although the invention allows the use of a larger width.

 European patent A-0168879 relates to a method comprising the use of two or more separate, spinning sections separated from each other. The sections of European Patent A-0168879 are rather large, and the resulting yarns leave much to be desired with respect to the mechanical properties and uniformity of the yarn, especially if the process is carried out at high speed.

 Within the scope of the present invention, the term “step” is used to mean the average distance between the centers of the spinning holes at adjacent spinning holes.

 The present invention will be further illustrated with reference to an example and figures. Needless to say, the present invention is illustrated, but not limited to this example.

 FIG. 1 is a bottom view of a multi-channel mouthpiece of the present invention provided with eight rectangular spinning sections.

 FIG. 2 shows in more detail two of the eight spinning sections of the multi-channel mouthpiece of FIG. 1.

 FIG. 3 is a bottom view of a multi-channel mouthpiece serving as a comparative example.

 FIG. 4 shows in more detail one of the spinning sections of the multi-channel mouthpiece of FIG. 3.

Example
In a similar manner to that described in Example 6 of US Pat. No. 4,308,374, poly (paraphenylene terephthalamide) was prepared using a mixture of N-methylpyrrolidone and calcium chloride. After neutralization, washing and drying, a polymer having an initial viscosity of 5.4 is obtained.

 The polymer was dissolved in sulfuric acid at a 99.8% concentration according to the method described in Example 3 of US Pat. No. 4,320,081. The spinning solution thus obtained had a polymer concentration of 19.4%.

 The spinning solution is formed using various multi-channel mouthpieces.

 The first circular multi-channel mouthpiece 1 shown in FIG. 1 and 2, having an outer diameter of 57 mm (in the table, this multi-channel mouthpiece is marked with the symbol S1), is equipped with eight rectangular spinning sections 2 (2.58 mm wide, designated 3 in Fig. 1, and 9 mm long), each , 125 spinning holes 4. Spinning holes 4 have a diameter of 65 μm and a distance from one to the other (pitch) 5 of 0.5 cm (the ratio of pitch 5 to the width of the spinning section is thus 0.2).

 The second circular multi-channel mouthpiece 6, indicated in FIG. 3 and 4 (in the table, this mouthpiece is indicated by S2), which serves as a comparative example, has an outer diameter of 57 mm and is equipped with four spinning sections 8 (having a constant width of 7 to 9.5 mm) that track each circle curve of a circular multi-channel mouthpiece, and including, each, 250 spinning holes. The spinning holes have a diameter of 65 μm and the distance from one to the other 9 is 1.0 mm (the ratio of the pitch 9 to the width 7 of the spinning section 8 is thus 0.11).

 The spinning solution is passed through an air gap, as shown in the table. A coagulation bath with a bottom of one level or a flat bottom (having a depth of 10 mm) is provided with eight or four holes, respectively (S1: rectangular 2.0 mm x 15 mm; S2: circular with a diameter of 5 mm), each located directly under the spinning section.

The coagulant is obtained from water having a sulfuric acid concentration of 20% and a temperature of 10 ^o C. The molding speed and the degree of drawing are indicated in the table. Physical properties are determined according to ASTM D 885.

 The term fluff is used to denote various heterogeneities (arising from tears, threading of threads on rolls and the like) in the yarn produced.

 The degree of adhesion is determined visually. 1 means that there is no or little adhesion (less than 1% of the threads are sticky), 5 means a very strong degree of adhesion (more than 25% of the threads are sticky).

 Threads made using S1 have significantly greater strength than threads made using S2. In addition, the number of adhesions is also much smaller. Further, due to the availability of space, the number of spinning sections in a multi-channel mouthpiece, such as S1, can be increased, say, to 12 or 16, while S2 does not allow this.

 A third circular multi-channel mouthpiece (S3; this multi-channel mouthpiece, unless otherwise specified, corresponds to S1), having an outer diameter of 75 mm, is provided with eight rectangular spinning sections (2.58 mm wide and 18 mm long), each having 250 spinning holes giving a total of 2000 threads. Spinning yarns have a diameter of 65 μm and are separated from each other by 0.5 mm.

 The S3 multi-channel mouthpiece is used to spin the dope described above (under conditions that, unless otherwise indicated, correspond to the conditions described above) using an air gap of 6 mm and a molding speed of 300 m / min. The resulting yarn has a strength of 2202 mn / tex. The number of fluffs in 15 minutes is 4, and they do not stick together.

Claims (7)

 1. A method for producing filaments from an optically anisotropic spinning solution, in which the spinning solution is extruded through the spinning holes grouped in at least one spinning section, and the extrudates sequentially pass through an inert gas and a coagulation bath, characterized in that the distance between the spinning holes to the width of the spinning section is greater than 0.15 and less than 0.7 and the width of the spinning section is less than 5 mm.  2. The method according to claim 1, characterized in that the spinning holes are grouped in more than one spinning section.  3. The method according to any one of the preceding paragraphs, characterized in that the spinning section or spinning sections are rectangular.  4. The method according to claim 3, characterized in that the spinning sections are arranged in a circle and the longitudinal direction of each of the spinning sections coincides with the radius.  5. The method according to claim 3 or 4, characterized in that the bottom of the coagulation bath is provided for each spinning section with a rectangular hole, which has a length greater than the spinning section, and is narrower in width.  6. The method according to claim 5, characterized in that the bottom of the coagulation bath is provided with at least two holes and the neighboring edges of the neighboring holes are at different levels.  7. The method according to any one of the preceding paragraphs, characterized in that the distance traveled by the filamentary extrudates through an inert gas medium is more than 0.5 mm and less than 8 mm.

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