HIGH STRENGTH POLYAMIDE YARN

Abstract

The invention relates to a Yarn comprising a copolyamide in an amount of at least 90 wt % with respect to the total weight of the yarn, which copolyamide comprises a) at least 95 wt % with respect to the total weight of copolyamide, monomeric units derived from epsilon-caprolactam and b1) cyclic monomeric units derived from a diamine X, and cyclic monomeric units derived from a diacid Y, and/or b2) cyclic monomeric units derived from an amino acid Z, in which the summed amount of monomeric units derived from X,Y and Z is between 0.1 to 4.5 wt % with respect to the total weight of the copolyamide and wherein the yarn has a tensile strength of at least 80 cN/tex as measured according to ASTM D885-04. The invention also relates to a process for preparing the yarn.

Claims

1. Yarn comprising a copolyamide in an amount of at least 90 wt % with respect to the total weight of the yarn, which copolyamide comprises a) at least 95 wt % with respect to the total weight of copolyamide, monomeric units derived from epsilon-caprolactam and b1) cyclic monomeric units derived from a diamine X, and cyclic monomeric units derived from a diacid Y, and/or b2) cyclic monomeric units derived from an amino acid Z, in which the summed amount of monomeric units derived from X,Y and Z is between 0.1 to 4.5 wt % with respect to the total weight of the copolyamide and wherein the yarn has a tensile strength of at least 80 cN/tex as measured according to ASTM D885-04.

2. Yarn according to claim 1, comprising at least 95 wt % of the copolyamide with respect to the total weight of the yarn.

3. Yarn according to claim 1, in which X and Y are present in essentially equal molar amounts.

4. Yarn according to claim 1, in which the yarn has a tensile strength of at least 85 cN/tex.

5. Yarn according to claim 1, in which the summed amount of monomeric units derived from X, Y and Z is between 0.5 to 4.0 wt % with respect to the total weight of the copolyamide.

6. Yarn according to claim 1, in which the diamine X is isophorone diamine and the diacid Y is chosen from the group of isophthalic acid and terephthalic acid.

7. Yarn according to claim 1, in which the hot air shrinkage is between 1.0 to 8.0% as measured according to ASTM D4974-04 at 177 C. for 2 minutes.

8. Yarn according to claim 1, in which the yarn has a titer of between 200 to 700 dtex.

9. Yarn according to claim 1, in which the yarn has a titer of between 300 dtex and 500 dtex and a tenacity of at least 85 cN/tex.

10. Yarn according to claim 1, in which the yarn has a HAS of at most 8.0% and a tenacity of at least 85 cN/tex, and a titer of between 300 dtex and 400 dtex.

11. Process for preparing a yarn according to claim 1, in which the process comprises the following steps: Providing a composition comprising a copolyamide to an extruder and melting it, optionally mixing with additives, such as stabilizer or pigment, to obtain a molten composition; The molten composition is extruded through a spinneret to form filaments, which are subsequently stretched, cooled and combined to form at least one yarn; The at least one yarn is subsequently subjected to a drawing process at a temperature between 25 C. and 220 C. to a draw ratio of between 4 and 6; After drawing, the yarn is relaxed by from 4% to 10% in at least three stages while being kept in a temperature range of 205 C. to 215 C.; The at least one yarn is wound up.

12. Process according to claim 11, in which the drawing process is carried out at a temperature between 50 C. and 170 C.

13. Air bag fabric, comprising a yarn according to claim 1.

Description

[0055] List of numbers for FIG. 1 and FIG. 2:

[0056] (01) Extruder

[0057] (03) Spinneret

[0058] (05) Filaments

[0059] (07) Take up rolls

[0060] (11) First rolls pair

[0061] (21) Second rolls pair

[0062] (31) Third rolls pair

[0063] (41) Fourth rolls pair

[0064] (51) Fifth rolls pair

[0065] (91) Reel device

[0066] (12) First drawing step

[0067] (22) Second drawing step

[0068] (32) First relaxation step

[0069] (42) Second relaxation step

[0070] (52) Third relaxation step

[0071] An example of the apparatus to perform the process A is illustrated in Error! Reference source not found.

[0072] The composition is molten and, if necessary, mixed with additives such as for example stabilizers, pigments, in an extruder (01) and further extruded through a spinneret (03) to form filaments. The filaments (05) are cooled, drawn and combined to at least one yarn between the spinneret (03) and take up rolls (07). Further a two stage drawing of the yarn is performed. First, the yarn is heated up by a pair of rolls (11) to a temperature between 50 C. and 80 C. and drawn 2 to 3 times in air gap (12) between pairs of rolls (11) and (21). Then, the yarn is heated up by a pair of rolls (21) to a temperature between 120 C. and 200 C. and drawn 1.35 to 3 times in air gap (22), between pairs of rolls (21) and (31), resulting in a draw ratio between 4 and 6. The drawing steps are followed by heat setting and relaxation: the yarn is heated up to the temperatures of 170 C. to 200 C. by a pair of rolls (31) and relaxed by 0% to 10% in the air gap (32) between the pairs of rolls (31) and (41). Finally, the yarn is wound up on a bobbin by a reel device (91).

[0073] The yarn according to the invention is preferably made by a process, hereafter referred to as process B, which comprises the following steps:

[0074] Providing a composition comprising a copolyamide to an extruder and melting it, optionally mixing with additives, such as stabilizer or pigment, to obtain a molten composition;

[0075] The molten composition is extruded through a spinneret to form filaments, which are subsequently stretched, cooled and combined to form at least one yarn;

[0076] The at least one yarn is subsequently subjected to a drawing process at a temperature between 25 C. and 220 C. to a draw ratio of between 4 and 6. Preferably the drawing is carried out at a temperature between 50 C. and 170 C. The drawing may be performed, e.g., by means of pairs of heated draw rolls, heated hot air ovens, etc.

[0077] After drawing, the yarn is relaxed by from 4% to 10% in at least three stages while being kept in a temperature range of 205 C. to 215 C.

[0078] The at least one yarn is wound up. Preferably, the at least one yarn is wound up on a bobbin.

[0079] Preferably, the temperature during relaxation is higher than the highest temperature during drawing. This has the advantage that the relaxation is more effective. More preferably, the temperature during relaxation is increased in each subsequent stage. This has the advantage that sufficient yarn tension is maintained between the relaxation rolls, which avoids breaking of the yarn.

[0080] The advantage of process B is that it yields yarns with a lower hot air shrinkage as compared to process A.

[0081] An example of the apparatus to perform process B is illustrated in Error! Reference source not found. The difference between FIG. 2 and the process described in Error! Reference source not found. is that five heated roll pairs (11), (21), (31), (41), (51) are employed, instead of four. The extrusion (01), the spinneret (03), the air gap (05), the take up rolls (07) as well as the first two roll pairs (11), (21) conditions can be chosen in the same way as in the process A, as illustrated in Error! Reference source not found. To achieve low HAS values, rolls (31),(41) and (51) have to be set to a temperature of between 205 C. and 215 C., the yarn being relaxed by from 4% to 10% in the at least three stages (32), (42), (52). The yarn is subsequently wound up on a reel device (91).

[0082] Applications for the yarn according to the invention include air bag fabric such as air bags for driver, passenger, knee, curtain airbags. Other applications include ropes, tire cords.

EXAMPLE 1 (EX 1)

[0083] A yarn consisting of 72 filaments was prepared from a copolyamide PA6/IPDT according to process A. The copolyamide was synthesized from a mixture of epsilon-caprolactam, isophorondiamine (IPD), and terephthalic acid (T). The monomeric unit derived from IPD was 0.5 wt % with respect to the copolyamide and the monomeric unit derived from T was 0.5 wt % with respect to the copolyamide. The remainder of the copolyamide were monomeric units derived from epsilon-caprolactam, thus 99 wt %. The synthesized copolyamide had a relative viscosity of 3.2 as measured in 90% formic acid HCOOH.

[0084] Using the apparatus as illustrated in Error! Reference source not found., operated at the process conditions specified in the Ex 1 column in Table 1. After take up, the yarn was drawn in a two-step process to a draw ratio of 5.0. After hot drawing, relaxation of in total 6% has been applied between the 3.sup.rd and the 4.sup.th rolls pair and between the 4.sup.th rolls pair and the reeling device.

[0085] The yarn thus obtained had a tenacity of 93cN/tex, elongation at break of 20%, titer of 354dtex, and hot air shrinkage, as measured at 177 C. 2 min, of 8.9%.

EXAMPLE 2 (EX 2)

[0086] The same copolyamide has been used as in the Example 1 and the yarn was prepared according to process A.

[0087] Using the apparatus as illustrated in Error! Reference source not found., operated at the process conditions specified in the Ex 2 column in Table 1. After take up, the yarn was drawn in a two-step process to a draw ratio of 5.0. After hot drawing, relaxation of in total 4% has been applied between the 3.sup.rd and the 4.sup.th rolls pair and between the 4.sup.th rolls pair and the reeling device.

[0088] The yarn thus obtained had a tenacity of 94cN/tex, elongation at break of 20%, titer of 473dtex, and hot air shrinkage, as measured at 177 C. 2 min, of 9.0%.

EXAMPLE 3 (EX 3)

[0089] The same copolyamide has been used as in the Example 1. The yarn was prepared according to process B.

[0090] Using the apparatus as illustrated in Error! Reference source not found., operated at the process conditions specified in the Ex 3 column in Table 1. After take up, the yarn was drawn in a two-step process to a draw ratio of 4.9. After hot drawing, three-step relaxation process of in total 10% has been applied between the 3.sup.rd and the 4.sup.th rolls pair, between the 4.sup.rd and the 5.sup.th rolls pair and between the 5.sup.th rolls pair and the reeling device.

[0091] The yarn thus obtained had a tenacity of 90cN/tex, elongation at break of 22%, titer of 356dtex, and hot air shrinkage, as measured at 177 C. 2 min, of 6.1%.

Comparative Example A (Comp A)

[0092] A yarn consisting of 72 filaments was prepared from a homopolyamide PA6 according to process A. The homopolymer was synthesized from epsilon-caprolactam contributing 100 wt % of the monomers. The synthesized PA6 had a relative viscosity of 3.2 as measured in 90% formic acid HCOOH.

[0093] Using the apparatus as illustrated in Error! Reference source not found., operated at the process conditions specified in the Comp A column in Table 1. After take up, the yarn was drawn in a two-step draw process to a draw ratio of 4.5. Higher draw ratios were not achievable as they led to spinline breakages.

[0094] After hot drawing, relaxation of in total 6% has been applied between the 3.sup.rd and the 4.sup.th rolls pair and between the 4.sup.th rolls pair and the reeling device.

[0095] The yarn thus obtained had a tenacity of 85cN/tex, elongation at break of 18%, titer of 356dtex, and hot air shrinkage, as measured at 177 C. 2 min, of 8.8%.

Comparative Example B (Comp B)

[0096] The same homopolyamide PA6 has been used as in the Comparative Example A and the yarn was prepared according to process B.

[0097] Using the apparatus as illustrated in Error! Reference source not found., operated at the process conditions specified in the Comp B column in Table 1. After take up, the yarn was drawn in a two-step process to a draw ratio of 4.3. After hot drawing, three-step relaxation process of in total 10% has been applied between the 3.sup.rd and the 4.sup.th rolls pair, between the 4.sup.rd and the 5.sup.th rolls pair and between the 5.sup.th rolls pair and the reeling device.

[0098] The yarn thus obtained had a tenacity of 81cNitex, elongation at break of 25%, titer of 469dtex, and hot air shrinkage, as measured at 177 C. 2 min, of 4.6%.

TABLE-US-00001 TABLE 1 Example number Ex 1 Ex2 Ex3 Comp A Comp B Material Copolyamide PA6/IPDT Homopolymer PA6 PROCESS CONDITIONS: Temperature at the C. 290 290 290 290 290 spinneret Take up rolls speed m/min 681 679 689 758 793 1.sup.st rolls Speed m/min 702 705 711 780 817 pair Temperature C. 70 70 70 70 70 2.sup.nd rolls Speed m/min 1800 1800 1800 2000 2368 pair Temperature C. 155 155 155 155 155 3.sup.rd rolls Speed m/min 3409 3409 3409 3409 3409 pair Temperature C. 200 200 210 200 210 4.sup.th rolls Speed m/min 3272 3272 3272 3272 3272 pair Temperature C. 170 170 215 170 215 5.sup.th rolls Speed m/min 3150 3150 pair Temperature C. 215 215 Reel device speed m/min 3201 3194 3098 3108 3110 Drawing ratio 5.0 5.0 4.9 4.5 4.3 TEST RESULTS: Titer dtex 354 473 356 356 469 Number of filaments 72 140 72 72 140 Tenacity cN/tex 93 94 90 85 81 Elongation at break % 20 20 22 18 25 HAS 177 C. 2 min % 8.9 9.0 6.1 8.8 4.6

[0099] The examples as shown in Table 1 show the advantages of the yarn according to the invention as compared to a yarn prepared from a homopolyamide.

[0100] As Example 1 shows, the yarn according to the invention could be drawn to a draw ratio of 5.0 and reached tenacity of 93cNitex. Similar properties could also be reached with yarn with a higher titer as well, as shown in the Example 2.

[0101] As Comparative example A shows, a homopolyamide of the same relative viscosity being spun at very similar conditions could be drawn only 4.5 times resulting in a yarn with tenacity of 85cN/tex, which is approximately 10% lower than the yarn made with the copolyamide from the Example 1.

[0102] Example 3 illustrates that if a process B is employed yarns with a tenacity of 90cN/tex and low hot air shrinkage could be obtained by employing the copolyamide.

[0103] If a homopolyamide is used in a process B as shown in the Comparative example B, then the yarn tenacity reached only 81cN/tex, which is approximately 10% lower than the yarn obtained from the copolyamide in Example 3.