Process for preparing poly (trimethylene terephthalate) yarns

Abstract: Poly(trimethylene terephthalate) is formed into a bulk continuous filament yarn by a process comprising melt-spinning poly(trimethylene terephthalate) to produce a plurality of spun filaments; forming the spun filaments into a yarn; and drawing the yarn in a two-stage drawing process wherein the second stage draw is at a significantly higher draw ratio than the first draw ratio.

Description: This invention relates to the spinning of poly(trimethylene terephthalate) into yarn suitable for carpets. Polyesters prepared by condensation polymerization of the reaction product of a diol with a dicarboxylic acid can be spun into yarn suitable for carpet fabric. U.S. 3,998,042 describes a process for preparing poly(ethylene terephthalate) yarn in which the extruded fiber is drawn at high temperature (160°C) with a steam jet assist, or at a lower temperature (95°C) with a hot water assist. Poly(ethylene terephthalate) can be spun into bulk continuous filament (BCF) yarn in a two-stage drawing process in which the first stage draw is at a significantly higher draw ratio than the second stage draw. U.S. 4,877,572 describes a process for preparing poly(butylene terephthalate) BCF yarn in which the extruded fiber is drawn in one stage, the feed roller being heated to a temperature 30°C above or below the Tg of the polymer and the draw roller being at least 100°C higher than the feed roll. However, the application of conventional polyester spinning processes to prepare poly(trimethylene terephthalate) BCF results in yarn which is of low quality and poor consistency. It has now been found that poly(trimethylene) terephthalate can be melt-spun into high quality BCF yarn by using a two-stage drawing process in which the second stage draw is at a significantly higher draw ratio than the first stage. The present invention therefore provides a process for preparing bulk continuous fiber yarn from poly(trimethylene terephthalate) comprising: (a) melt-spinning poly(trimethylene terephthalate), suitably at a temperature within the range of 250 to 280°C, to produce a plurality of spun filaments; (b) cooling the spun filaments; (c) converging the spun filaments into a yarn; (d) drawing the yarn at a first draw ratio within the range of 1.05 to 2 in a first drawing stage defined by at least one feed roller and at least one first draw roller, each feed roller being heated to a temperature less than 100°C and each draw roller being heated to a temperature greater than the temperature of said feed roller and within the range of 80 to 150°C; (e) subsequently drawing the yarn at a second draw ratio of at least 2.2 times that of the first draw ratio in a second drawing stage defined by said first draw roller and at least one second draw roller, each second draw roller being heated to a temperature greater than said first draw roller and within the range of 100 to 200°C; and (f) winding the drawn yarn. The process may optionally include texturing the drawn yarn prior to or after winding step (f). The fiber-spinning process is designed specifically for poly(trimethylene terephthalate), the product of the condensation polymerization of the reaction product of trimethylene diol (also called "1,3-propane diol") and a terephthalic acid or an ester thereof, such as terephthalic acid and dimethyl terephthalate. The poly(trimethylene terephthalate) may also include minor amounts of the derivatives of other monomers such as ethane diol and butane diol as well as minor amounts of the derivatives of other diacids or diesters such as isophthalic acid. Poly(trimethylene terephthalate) having an intrinsic viscosity (i.v.) within the range of 0.8 to 1.0 dl/g, preferably 0.86 to 0.96 dl/g (as measured in a 50/50 mixture of methylene chloride and trifluoroacetic acid at 30°C) and a melting point within the range of 215 to 230°C is particularly suitable. The moisture content of the poly(trimethylene terephthalate) should be less than 0.005% prior to extrusion. Such a moisture level can be achieved by, for example, drying polymer pellets in a dryer at 150-180°C until the desired dryness has been achieved. One embodiment of the invention process can be described by reference to Figure 1. Molten poly(trimethylene terephthalate) which has been extruded through a spinneret into a plurality of continuous filaments 1 at a temperature within the range of 240 to 280°C, preferably 250 to 270°C, and then cooled rapidly, preferably by contact with cold air, is converged into a multifilament yarn and the yarn is passed in contact with a spin finish applicator, shown here as kiss roll 2. Yarn 3 is passed around denier control rolls 4 and 5 and then to a first drawing stage defined by feed roll 7 and draw roll 9. Between rolls 7 and 9, yarn 8 is drawn at a relatively low draw ratio, within the range of 1.05 to 2, preferably 1.10 to 1.35. Roller 7 is maintained at a temperature less than about 100°C, preferably within the range of 40 to 85°C. Roller 9 is maintained at a temperature within the range of 80 to 150°C, preferably 90 to 140°C. Drawn yarn 10 is passed to a second drawing stage, defined by draw rolls 9 and 11. The second-stage draw is carried out at a draw ratio at least 2.2 times that of the first stage draw ratio, preferably at a draw ratio within the range of 2.2 to 3.4 times that of the first stage. Roller 11 is maintained at a temperature within the range of 100 to 200°C. In general, the three rollers will be sequentially higher in temperature. The selected temperature will depend upon other process variables, such as whether the BCF is made with separate drawing and texturing steps or in a continuous draw/texturing process, the effective heat transfer of the rolls used, residence time on the roll, and whether there is a second heated roll upstream of the texturing jet. Drawn fiber 12 is passed in contact with optional relax roller 13 for stabilization of the drawn yarn. Stabilized yarn 14 is passed to optional winder 15 or is sent directly to the texturing process. The drawn yarn is bulked by suitable means such as a hot air texturing jet. The preferred feed roll temperature for texturing is within the range of 150 to 200°C. The texturing air jet temperature is generally within the range of 150 to 210°C, and the texturing jet pressure is generally within the range of 340 to 825 kPa to provide a high-bulk BCF yarn. Wet or superheated steam can be substituted for hot air as the bulking medium. Figure 2 shows an embodiment of the two-stage drawing process which includes texturing steps downstream of the drawing zone. Molten poly(trimethylene terephthalate) is extruded through spinneret 21 into a plurality of continuous filaments 22 and is then quenched by, for example, contact with cold air. The filaments are converged into yarn 24 to which spin finish is applied at 23. Yarn 27 is advanced to the two-stage draw zone via non-heated rolls 25 and 26. In the first draw stage, yarn 31 is drawn between feed roll 28 and draw roll 29 at a draw ratio within the range of 1.05 and 2. Drawn yarn 32 is then subjected to a second draw at a draw ratio at least 2.2 times the first draw ratio, preferably a draw ratio within the range of 2.2 to 3.4 times that of the first draw. The temperature of roll 28 is less than 100°C. The temperature of draw roll 29 is within the range of 80 to 150°C. The temperature of draw roll 30 is within the range of 100 to 200°C. Drawn yarn 33 is advanced to heated rolls 34 and 35 to preheat the yarn for texturing. Yarn 36 is passed through texturing air jet 37 for bulk enhancement and then to jet screen cooling drum 38. Textured yarn 39 is passed through tension control 40, 41 and 42 and then via idler 43 to optional entangler 44 for yarn entanglement if desired for better processing downstream. Entangled yarn 45 is then advanced via idler 46 to an optional spin finish applicator 47 and is then wound onto winder 48. The yarn can then be processed by twisting, texturing and heat-setting as desired and tufted into carpet as is known in the art of synthetic carpet manufacture. Poly(trimethylene terephthalate) yarn prepared by the invention process has high bulk (generally within the range of 20 to 45%, preferably within the range of 26 to 35%), resilience and elastic recovery, and is useful in the manufacture of carpet, including cut-pile, loop-pile and combination-type carpets, mats and rugs. Poly(trimethylene terephthalate) carpet has been found to exhibit good resiliency, stain resistance and dyability with disperse dyes at atmospheric boil with optional carrier. Example 1 Effect of Intrinsic Viscosity on Poly(trimethylene terephthalate) Fiber Drawing Four poly(trimethylene terephthalate) polymers having intrinsic viscosities of 0.69, 0.76, 0.84 and 0.88 dl/g, respectively, were each spun into 70 filaments with trilobal cross-sections using a spinning machine having a take-up and drawing configuration as shown in Figure 1. Roll 1 (see detail below) was a double denier control roll; roll 2 ran at a slightly higher speed to maintain a tension and act as a feed roll for drawing. First stage drawing took place between rolls 2 and 3, and second-stage drawing took place between rolls 3 and 4. The drawn yarn contacted relax roll 5 prior to wind-up. The spin finish was a 15% Lurol PF 4358-15 solution from G.A. Goulston Company applied with a kiss roll. Fiber extrusion and drawing conditions for each polymer were as follows: Extrusion Conditions Polymer IV (dl/g): 0.84, 0.88 0.69, 0.76 Units Extruder Temp. Profile: Zone 1 °C 230 225 Zone 2 °C 250 235 Zone 3 °C 250 235 Zone 4 °C 250 235 Melt Temp. °C 255 240 Extrusion Pack Pressure kPa 12710-19700 3500-9000 Denier Control Roll Speed m/min. 225 220 Fiber Drawing Conditions Polymer IV (dl/g) 0.88 0.84 00.76 0.69 Roll Temp.: °C Roll 2 80 80 80 80 Roll 3 95 95 95 95 Roll 4 155 155 155 155 Roll 5 RT RT RT RT Roll Speeds: m/min. Roll 2 230 230 230 230 Roll 3 310 310 404 404 Roll 4 1020 1165 1089 1089 Roll 5 1035 1102 1075 1075 First Stage Draw Ratio 1.35 1.35 1.76 1.76 Second Stage Draw Ratio 3.29 3.29 2.70 2.70 Fiber tensile properties are shown in Table 1. Run I.V. (dl/g) Yarn Count (den.) Tenacity (g/den.) % Elongation 1 0.69 131.3 (1182 den.) 13.59 (1.51 g/den.) 70.7 2 0.76 127.3 (1146 den.) 14.31 (1.59 g/den.) 79.7 3 0.84 129.7 (1167 den.) 18.27 (2.03 g/den.) 89.0 4 0.88 133.1 (1198 den.) 20.16 (2.24 g/den.) 67.5 Poly(trimethylene terephthalate) of intrinsic viscosities 0.69 and 0.76 (Runs 1 and 2) have a second stage draw ratio only 1.53 greater than that of the first stage draw ratio, i.e. below the 2.2 minimum ratio of the present invention, and are included for comparative purpose. These comparative runs gave yarn of inferior tensile properties compared with the yarn of Runs 3 and 4 (which illustrate the invention). These polymers were re-spun at a lower extruder temperature profile. Although they could be spun and drawn, the fibers had high die swell. When the fiber cross-sections were examined with an optical microscope, the 0.69 i.v. fibers swelled to a point that they were no longer trilobal in shape and resembled delta cross-sections. They also had relatively low tenacity. Example 2 Two-Stage Drawing of PTT Fibers 0.88 i.v. poly(trimethylene terephthalate) was extruded into 72 filaments having trilobal cross-section using a fiber-spinning machine having take-up and drawing configurations as in Example 1. Spin finish was applied as in Example 1. Extrusion and drawing conditions were as follows. Extrusion Conditions Extruder Temperature Profile: Units Zone 1 °C 230 Zone 2 °C 260 Zone 3 °C 260 Zone 4 °C 260 Melt Temp. °C 265 Denier Control Roll Speed m/min. 230 It was observed during spinning and drawing that, when the first-stage draw ratio (between rolls 2 and 3) was less than about 1.5, and the second stage draw ratio was 2.63 greater than that of the first stage draw ratio (i.e. in conformity with the present invention), as in Runs 5 and 6, there were fewer broken filaments and the tenacities of the filaments were generally higher than when first-stage draw was higher than 1.5. When the first-stage draw was increased to greater than 3 and the second stage draw ratio was less than that of the first stage (i.e. illustrative of prior art spinning processes, and therefore included for comparative purposes; Runs 7, 8, 9, 10, and 11), it was observed that the fibers had a white streaky appearance, the threadlines were loopy, and there were frequent filament wraps on the draw rolls. The process was frequently interrupted with fiber breaks. Example 3 Spinning, Drawing and Texturing Poly(trimethylene terephthalate) BCF to High Bulk The extrusion conditions in this experiment were the same as in Example 2. The fibers were spun, drawn and wound as in Example 1. They were then textured by heating the fibers on a feed roll and exposing the fibers to a hot air jet. The textured fibers were collected as a continuous plug on a jet-screen cooling drum. Partial vacuum was applied to the drum to pull the ambient air to cool the yarns and keep them on the drum until they were wound. The yarns were air entangled between the drum and the winder. The feed roll and texturizer air jet temperatures were kept constant, and the air jet pressure was varied from 350 to 700 kPa to prepare poly(trimethylene terephthalate) BCF of various bulk levels. Drawing and texturing conditions were as follows. Drawing Conditions Rolls Temperature, C Speed, m/min. Roll 1 RT 225 Roll 2 80 230 Roll 3 95 264 Roll 4 90 1058 Roll 5 110 1042 Texturing Conditions Feed Roll Temperature, °C 180 Feed Roll Speed, m/min. 980 Air Jet Temperature, °C 180 Interlacing Pressure, kPa 70 Yarn bulk and shrinkage were measured by taking 18 wraps of the textured yarn in a denier creel and tying it into a skein. The initial length L 0 of the skein was 560 mm in English unit creel. A 1g weight was attached to the skein and it was hung in a hot-air oven at 130°C for 5 minutes. The skein was removed and allowed to cool for 3 minutes. A 50g weight was then attached and the length L 1 was measured after 30 seconds. The 50g weight was removed, a 4.5 kg weight was attached, and the length L 2 was measured after 30 seconds. Percent bulk was calculated as (L 0 - L 1 )/L 0 x 100% and shrinkage was calculated as (L 0 - L 2 )/L 0 x 100%. Results are shown in Table 2. Package No. Yarn Count, den. % Bulk % Shrinkage T50 159.7 (1437 den.) 32.6 3.6 T60 156.2 (1406 den.) 35.7 2.7 T70 161.7 (1455 den.) 39.4 3.2 T80 166.7 (1500 den.) 38.0 3.6 T90 169.4 (1525 den.) 37.6 4.1 T100 167.4 (1507 den.) 38.0 3.6 The experiment showed that poly(trimethylene terephthalate) BCF can be textured to high bulk with a hot air texturizer. Example 4 Carpet Resiliency Comparison Poly(trimethylene terephthalate) BCF yarns were made in two separate steps: (1) spinning and drawing set-up as in-Example 1 and (2) texturing. Extrusion, drawing and texturing conditions for the poly(trimethylene terephthalate) yarns were as follows. Extrusion Conditions Extruder Temperature Units Zone 1 °C 240 Zone 2 °C 255 Zone 3 °C 255 Zone 4 °C 255 Melt Temperature °C 260 Pack Pressure kPa 12800 Drawing Conditions Units Roll 1 Temp./Speed °C/m/min. RT/223 Roll 2 Temp./Speed °C/m/min. 80/230 Roll 3 Temp./Speed °C/m/min. 95/288 Roll 4 Temp./Speed °C/m/min. 150/1088 Roll 5 Temp./Speed °C/m/min. TY/1000 Texturing Conditions Units Feed Roll Temp. °C 180 Feed Roll Speed m/min. 980 Air Jet Temp. °C 180 Air Jet Pressure kPa 630 Interlacing Pressure kPa 70 The yarn produced was 127.8 tex (1150 denier) with 22.95 g/tex (2.55 g/den) tenacity and 63% elongation. The textured yarn was twisted, heat set as indicated, and tufted into carpets. Performances of the poly(trimethylene terephthalate) carpets were compared with a commercial 122.2 tex (1100 denier) nylon 66 yarn. Results are shown in Table 3. The heat-set yarns were tufted into 680 g cut-pile Saxony carpets in 3.2 mm gauge, 14.3 mm pile height, and dyed with disperse blue 56 (without a carrier) at atmospheric boil into medium blue color carpets. Visual inspection of the finished carpets disclosed that the poly(trimethylene terephthalate) carpets (Runs 12, 13 and 14) had high bulk and excellent coverage which were equal to or better than the nylon controls (Runs 15 and 16). Carpet resiliency was tested in accelerated floor trafficking with 20,000 footsteps. The appearance retention was rated 1 (severe change in appearance), 2 (significant change), 3 (moderate change), 4 (slight change) and 5 (no change). As can be seen in Table 3, the poly(trimethylene terephthalate) carpets were equal to or better than the nylon 66 controls in the accelerated walk tests and in percent thickness loss. Example 5 One-Step Processing of Poly(trimethylene terephthalate) BCF Yarn from Spinning to Texturing Poly(trimethylene terephthalate) (i.v. 0.90) was extruded into 72 trilobal cross-section filaments. The filaments were processed on a line as shown in Figure 2 having two cold rolls, three draw rolls and double yarn feed rolls prior to texturing. The yarns were textured with hot air, cooled in a rotating jet screen drum and wound up with a winder. Lurol NF 3278 CS (G.A. Goulston Co.) was used as the spin finish. Texturing conditions were varied to make poly(trimethylene terephthalate) BCF yarns having different bulk levels. Extrusion, drawing, texturing and winding conditions were as follows. Extrusion Conditions Extruder Temperature Profiles Units Zone 1 °C 240 Zone 2 °C 260 Zone 3 °C 260 Zone 4 °C 265 Melt Temperature °C 265 Pump Pressure kPa 25500 Drawing Conditions Temperature °C Speed, m/min. Cold Roll 1 RT 211 Cold Roll 2 RT 264 Draw Roll 1 50 290 Draw Roll 2 90 330 Draw Roll 3 110 1100 The yarns were twisted, heat set and tufted into carpets for performance evaluation. Results are shown in Table 4. Example 6 Effects of Draw Ratio and Roll Temperature on Yarn Properties Poly(trimethylene terephthalate) (0.90 i.v.) was spun into 72 filaments with trilobal cross-sections using a machine as described in Example 5. Extrusion conditions were as follows. Extrusion Conditions Extruder Temperature Profiles Units Zone 1 °C 240 Zone 2 °C 260 Zone 3 °C 260 Zone 4 °C 260 Melt Temperature °C 260 The poly(trimethylene terephthalate) BCF yarns and commercial nylon 6 and 66 yarns were tufted into 900 g. 5/32 gauge cut-pile Saxony carpets having 16 mm pile height. They were walk-tested with 20,000 footsteps accelerated floor trafficking for resiliency and appearance retention comparisons. Roll conditions and results are shown in Table 5.

Claims: A process for preparing bulk continuous fiber yarn from poly(trimethylene terephthalate) comprising: (a) melt-spinning poly(trimethylene terephthalate) to produce a plurality of spun filaments; (b) cooling the spun filaments; (c) converging the spun filaments into a yarn; (d) drawing the yarn at a first draw ratio within the range of 1.05 to 2 in a first drawing stage defined by at least one feed roller and at least one first draw roller, each feed roller being heated to a temperature less than 100°C and each draw roller being heated to a temperature greater than the temperature of said feed roller and within the range of 80 to 150°C; (e) subsequently drawing the yarn at a second draw ratio of at least 2.2 times that of the first draw ratio in a second drawing stage defined by (the last of) said first draw roller(s) and at least one second draw roller, each second draw roller being heated to a temperature greater than said (last) first draw roller and within the range of 100 to 200°C; and (f) winding the drawn yarn. The process as claimed in claim 1 in which each feed roller is heated to a temperature within the range of 40 to 85°C. The process as claimed in claim 1 or 2 in which the first draw ratio is within the range of 1.10 to 1.35. The process as claimed in claim 1, 2 or 3 in which the second draw ratio is within the range of 2.2 to 3.4 times the first draw ratio. The process as claimed in any one of the preceding claims in which the poly(trimethylene terephthalate) has an intrinsic viscosity within the range of about 0.80 to about 1.0 dl/g. Process as claimed in any one of the preceding claims wherein the drawn yarn is submitted to a texturising treatment. The process as claimed in claim 6 in which texturing is carried out with an air jet at a pressure within the range of 340 to 825 kPa. The process as claimed in claim 6 or 7 in which the texturing step is carried out at a temperature within the range of 150 to 210°C. A carpet the fibers of which consist essentially of poly(trimethylene terephthalate) yarn having a bulk greater than 20 percent and prepared by a process as claimed in any one of the preceding claims.

Inventors: CHUAH HOE HIN, CHUAH, HOE HIN
Applicants: SHELL INTERNATIONALE RES BR MI, SHELL INTERNATIONALE RESEARCH<BR>MAATSCHAPPIJ B.V.
Application year: 1996
Main classification: D02J1
IPC codes: D01D5, D02G1, D03D27, A47G27, D02J1, D01F6