Method of preparing polyester fiber for seat belt

Abstract

Disclosed is a high strength polyester fiber for a seat belt, and in particular, a polyester fiber for a seat belt, which has intrinsic viscosity of 0.8 to 1.5 dl/g, tensile strength of 8.8 g/d or more, and total fineness of 400 to 1800 denier. A method of preparing the fiber is disclosed. The polyester fiber includes filaments having high strength, low modulus, and high elongation to significantly lower shrinkage, while securing excellent mechanical properties, it is possible to manufacture a seat belt having excellent impact absorption and significantly improved abrasion resistance and heat resistant strength retention, even with a woven density of 260 yarns/inch or less.

Claims

1. A method of preparing a polyester fiber for a seat belt: melt spinning a polyester polymer having intrinsic viscosity of 0.8 dl/g or more at 270 to 310° C. to produce undrawn polyester yarn; and drawing the undrawn polyester yarn; wherein the drawing process is carried out after passing the undrawn yarn through a godet roller so that an oil pickup amount is 0.3% to 0.7%; a first draw ratio is 3.5 to 4.5 and a second draw ratio is 0.9 to 1.8 in the drawing process; and a first godet roller is operated at a temperature of 60 to 80° C. at a speed of 500 to 540 m/min, a second godet roller is operated at a temperature of 80 to 100° C. at a speed of 550 to 590 m/min, a third godet roller is operated at a temperature of 110 to 130° C. at a speed of 1800 to 2000 m/min, and a fourth godet roller is operated at a temperature of 160 to 180° C. at a speed of 2800 to 3000 m/min, in the drawing process.

2. The method according to claim 1, wherein the oil pickup amount is 0.35% to 0.7%.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a process chart schematically representing a preparation process of polyester fiber for a seat belt, according to one exemplary embodiment of the invention.

(2) FIG. 2 shows an example of a load-elongation curve for calculating impact energy absorption on a seat belt including the polyester fiber according to one exemplary embodiment of the invention.

(3) FIG. 3 is a schematic diagram of a device used for evaluation of abrasion resistance of a seat belt including the polyester fiber according to one exemplary embodiment of the invention by a hexagonal bar.

EXAMPLES

(4) Hereinafter, preferred examples are presented in order to help better understanding of the present invention, however the following examples are only illustrative of the present invention, and do not limit the scope of the present invention.

Examples 1-5

(5) After preparing undrawn polyester yarn in a manner of melt spinning and cooling a polyester polymer having predetermined intrinsic viscosity, the undrawn yarn was subjected to heat treatment while being drawn at a predetermined draw ratio, thereby preparing polyester fiber. Herein, the drawing process was carried out after passing the undrawn yarn through a godet roller so that an oil pickup amount was in an optimized range as shown in Table 1 below, using a paraffin-based lubricant.

(6) Meanwhile, the intrinsic viscosity of the polyester polymer, the spinning speed, spinning tension, and spinning temperature condition of the melt spinning process, a draw ratio, and a heat treatment temperature were as shown in Table 1 below, and the remaining conditions followed a general condition for preparing a polyester fiber.

(7) TABLE-US-00001 TABLE 1 Example Example Example Example Example 1 2 3 4 5 Intrinsic viscosity of 0.95 0.98 1.13 1.15 1.2 chip (dl/g) Spinning temperature 285 290 293 295 295 (° C.) Oil pickup amount 0.7 0.6 0.5 0.4 0.3 (%) Total draw ratio 5.9 5.7 5.6 5.5 5.5 First draw ratio 3.6 3.6 3.7 3.7 3.7 Second draw ratio 1.6 1.5 1.5 1.5 1.5 First godet roller 60 65 70 75 80 temperature (° C.) First godet roller 500 510 520 530 540 speed (m/min) Second godet roller 80 85 90 95 100 temperature (° C.) Second godet roller 550 560 570 580 590 speed (m/min) Third godet roller 110 115 120 125 130 temperature (° C.) Third godet roller 1800 1850 1900 1950 2000 speed (m/min) Fourth godet roller 160 165 170 175 180 temperature (° C.) Fourth godet roller 2800 2850 2900 2950 3000 speed (m/min) Heat treatment 240 235 235 235 240 temperature (° C.)

(8) For the polyester fiber prepared according to Examples 1-5, physical properties were measured by the following methods, and the results are summarized in the following Table 2.

(9) 1) Tensile Strength and Elongation at Break

(10) The tensile strength and elongation at break of the polyester yarn were measured using a Universal Testing Machine (Instron), with the length of the sample of 250 mm, tensile speed of 300 mm/min, and an initial load of 0.05 g/d.

(11) Further, in the strength-elongation curve according to tensile strength and elongation measured above, an elongation value (%) corresponding to each tensile strength (0.8 g/d, 5.0 g/d, and 8.8 g/d) was confirmed, and also maximum strength (g/d) and elongation (%) of the yarn at maximum strength point were confirmed.

(12) 2) Initial Modulus

(13) Modulus (Young's modulus), and strength and elongation, were measured by a method according to the American Society for Testing and Materials ASTM D 885 method, and each modulus at 1% and 2% elongation, that is, at the point of being stretched by 1% and 2%, are shown in the following Table 2.

(14) 3) Dry Heat Shrinkage

(15) The measurement of dry heat shrinkage was carried out after maintaining the fiber in an oven at 150° C. for 30 minutes.

(16) 4) Crystallinity

(17) The density ρ of the polyester fiber was measured at 25° C. according to a density gradient column method using n-heptane and carbon tetrachloride. Then, the crystallinity was calculated according to the following Calculation Formula 1.

(18) $\begin{array}{cc}{X}_c\left(\mathrm{Crystallinity}\right)=\frac{{\rho }_c\left(\rho -{\rho }_a\right)}{\rho \left({\rho }_c-{\rho }_a\right)}& \left[\mathrm{Calculation}\mathrm{Formula}1\right]\end{array}$

(19) wherein ρ is the density of the fiber, ρ.sub.c is the density of a crystal for the fiber (ρ.sub.c=1.457 g/cm.sup.3 for PET), and ρ.sub.a is the density of amorphism for the fiber (ρ.sub.a=1.336 g/cm.sup.3 for PET).

(20) 5) Intrinsic Viscosity

(21) First, an emulsion was extracted from the fiber sample using carbon tetrachloride and dissolved in OCP (ortho-chlorophenol) at 160±2° C. Then, the viscosity of the fiber sample was measured from the OCP solution in a viscosity tube using an automatic viscometer (Skyvis-4000) under the condition of 25° C. The intrinsic viscosity (IV) of the polyester fiber was calculated according to the following Calculation Formula 2.
Intrinsic viscosity (IV)={(0.0242×Rel)+0.2634}×F  [Calculation Formula 2]

(22) wherein

(23) $\mathrm{Rel}=\frac{\begin{array}{c}\mathrm{seconds}\mathrm{of}\mathrm{solution}\times \mathrm{specific}\mathrm{gravity}\mathrm{of}\mathrm{solution}\times \\ \mathrm{viscosity}\mathrm{coefficient}\end{array}}{\mathrm{OCP}\mathrm{viscosity}},\mathrm{and}$$F=\frac{\mathrm{IV}\mathrm{of}\mathrm{standard}\mathrm{chip}}{\begin{array}{c}\mathrm{average}\mathrm{of}\mathrm{three}\mathrm{IV}\text{'}s\mathrm{measured}\mathrm{from}\\ \mathrm{standard}\mathrm{chip}\mathrm{with}\mathrm{standard}\mathrm{action}\end{array}}.$

(24) 6) Total Fineness and Single Yarn Fineness

(25) Total fineness of the fiber was measured by taking 9000 m of yarn using a reel, and weighing the yarn (denier). Then, single yarn fineness was calculated by dividing the total fineness by the number of filaments, as denier per filament.

(26) TABLE-US-00002 TABLE 2 Intrinsic vis- Initial Tensile Elongation Dry heat Single yarn Total Crystallinity cosity of yarn modulus strength at break shrinkage fineness fineness (%) (dl/g) (g/d) (g/d) (%) (%) (DPF) (de) Example 1 48.2 0.94 92 9.8 14 9.3 10.21 1500 Example 2 47.3 0.95 89 9.8 15 9.5 10.23 1500 Example 3 47.4 0.93 78 9.9 14 10.3 10.11 1500 Example 4 48.5 0.96 74 9.8 13 10.6 10.31 1500 Example 5 47.8 1.0 65 9.9 14 10.5 10.52 1500

Comparative Examples 1-5

(27) Polyester fiber of Comparative Examples 1-5 was prepared in the same manner as Examples 1-5, except for the conditions described in the following Table 3.

(28) TABLE-US-00003 TABLE 3 Comparative Comparative Comparative Comparative Comparative Example Example Example Example Example 1 2 3 4 5 Intrinsic viscosity of chip (dl/g) 0.80 0.85 0.90 0.93 0.97 Spinning temperature (° C.) 311 312 313 314 315 Oil pickup amount (%) 0.75 0.75 0.8 0.8 0.75 Total draw ratio 6.02 6.01 5.94 5.92 5.86 First draw ratio 3.6 3.6 3.7 3.7 3.7 Second draw ratio 1.6 1.5 1.5 1.5 1.5 First godet roller temperature 60 65 70 75 80 (° C.) First godet roller speed (m/min) 500 510 520 530 540 Second godet roller 80 85 90 95 100 temperature (° C.) Second godet roller speed 550 560 570 580 590 (m/min) Third godet roller temperature 110 115 120 125 130 (° C.) Third godet roller speed 1800 1850 1900 1950 2000 (m/min) Fourth godet roller temperature 160 165 170 175 180 (° C.) Fourth godet roller speed 2800 2850 2900 2950 3000 (m/min) Heat treatment temperature 220 220 220 210 210 (° C.)

(29) For the polyester fiber prepared according to Comparative Examples 1-5, physical properties were measured by the above-described method, and the results are summarized in the following Table 4.

(30) TABLE-US-00004 TABLE 4 Intrinsic vis- Initial Tensile Elongation Dry heat Single yarn Total Crystallinity cosity of yarn modulus strength at break shrinkage fineness fineness (%) (dl/g) (g/d) (g/d) (%) (%) (DPF) (de) Comparative 42.2 0.60 111 9.0 12 9.4 12.3 1500 Example 1 Comparative 42.8 0.65 106 9.5 12 9.1 12.4 1500 Example 2 Comparative 42.3 0.70 104 9.3 13 9.2 12.4 1500 Example 3 Comparative 42.1 0.75 102 9.2 13 9.4 12.3 1500 Example 4 Comparative 42.1 0.78 100 9.3 13 9.3 12.2 1500 Example 5

Preparation Example

(31) A webbing having warp density of 250 yarns/inch and weft density of 5.65 yarns/inch as woven density was manufactured through a narrow width weaving machine using the polyester fiber prepared according to Examples 1-5 and Comparative Examples 1-5. The webbing was subjected to a dyeing process to manufacture a specimen of a seat belt, and the physical properties were measured by the following method.

(32) a) Average Thickness of a Seat Belt

(33) The average thickness of a seat belt was measured by the method according to the Korean Parts and Materials Reliability Standards RS K 0005: 2007 method (webbing for a vehicle safety belt).

(34) b) Tensile Strength of a Seat Belt

(35) The tensile strength of a seat belt was measured by the method according to the Korean Parts and Materials Reliability Standards RS K 0005: 2007 method (webbing for a vehicle safety belt).

(36) c) Elongation of a Seat Belt

(37) The elongation of a seat belt was measured by the method according to the Korean Parts and Materials Reliability Standards RS K 0005: 2007 method (webbing for a vehicle safety belt).

(38) d) Evaluation of Energy Absorption Rate

(39) The energy absorption rate of the seat belt specimen, that is, the work ratio, was measured and evaluated by the following method.

(40) First, an energy absorption rate test was carried out by applying a tensile load by an elongation measurement method, when the load reached 11.1 kN, removing the load immediately at the same speed as the tension, and recovering the load to initial load, thereby obtaining a load-elongation curve as shown in FIG. 2. Work area (ΔABD) was measured from the area produced below the curve AB under the tensile load from the initial load to the maximum load. The work area (ΔABC) was measured from the area surrounded by the curve AB under the tensile load and the curve BC upon removal of the load. The energy absorption rate, that is, the work ratio, was calculated according to the following Calculation Formula 3.
Work ratio=(ΔABC/ΔABD)×100  [Calculation Formula 3]

(41) e) Evaluation of Abrasion Resistance by Hexagonal Bar

(42) Abrasion resistance of the seat belt specimen by a hexagonal bar was measured by the following method.

(43) First, the seat belt specimen (webbing) was attached to the testing device of FIG. 3, a weight of 2.35±0.05 kg was suspended on one end of the specimen, and the other end was fixed to a vibration drum (diameter of 400 mm) across the hexagonal bar. The drum was driven through a crank arm, a crank, and the like. The specimen was rubbed back and forth 2500 times at two angles of the hexagonal bar at 30±1 times every minute and a distance of 330±30 mm, and then strength retention and tensile strength of the specimen were measured using the Universal Testing Machine (Instron). Herein, the angle of the hexagonal bar used once was not used again as it was.

(44) Particularly, the strength retention of the seat belt specimen was measured by the method according to the American Society for Testing and Materials ASTM D 2256 method. The tensile strength of the specimen was obtained by leaving the specimen at a temperature of 20±2° C. and relative humidity of 65±2% for 24 hours, carrying out installation so that the distance between two clamps was 200±20 mm, applying a load so that tensile speed was 100 mm per minute, and pulling the specimen until being broken, thereby measuring tensile strength at break.

(45) The measurement results of the physical properties of the seat belts manufactured using the polyester fiber prepared according to Examples 1-5 and Comparative Examples 1-5 are shown in the following Table 5.

(46) TABLE-US-00005 TABLE 5 Impact Evaluation of abrasion resistance Average Tensile Elongation absorption Tensile thickness strength (%) rate/work ratio Strength strength (mm) (kgf) (%) (%) retention (kgf) Example 1 1.3 3005 15.8 70 95.1 2858 Example 2 1.4 3012 16.2 68 95.3 2870 Example 3 1.3 3030 16.3 70 95.3 2887 Example 4 1.3 3008 16.1 71 95.6 2877 Example 5 1.4 3015 15.9 72 95.8 2887 Comparative 1.5 2989 14.2 62 78.2 2337 Example 1 Comparative 1.6 2980 14.3 58 79.8 2378 Example 2 Comparative 1.5 2996 14.2 61 80.5 2413 Example 3 Comparative 1.5 2988 14.5 62 79.8 2385 Example 4 Comparative 1.6 2984 14.3 60 81.5 2432 Example 5

(47) As shown in the above Table 5, the seat belts manufactured from the polyester fiber having high intrinsic viscosity and elongation, low initial modulus, and the like according to Examples 1-5 had strength retention after evaluation of abrasion resistance of 95.1% to 95.8%, and tensile strength of 2870 to 2887 kgf, and thus had excellent properties. At the same time, the seat belts manufactured from the polyester fiber of Examples 1-5 had impact absorption rates of 68% to 72%, which is the property of an excellent seat belt. Thus, it is appreciated that it had excellent impact resistance absorption, strength retention, and the like. Further, though the seat belts from the polyester fiber of Examples 1-5 were weight lightened to an average thickness of 1.3 mm to 1.4 mm, their strength retention was 3005 kgf to 3030 kgf, and thus it is appreciated that they had excellent properties.

(48) On the contrary, it is appreciated that the seat belts manufactured using the polyester fiber of Comparative Examples 1-5 did not satisfy such properties. Particularly, the seat belts manufactured with the polyester fiber of Comparative Examples 1-5 had strength retention after evaluation of abrasion resistance of only 78.2% to 81.5%, and significantly low tensile strength of 2337 to 2432 kgf. At the same time, it is appreciated that the seat belts from the polyester fiber of Comparative Examples 1-5 had significantly low impact absorption rates of 58% to 62%, and in such case, such low impact absorption rate may cause injury to a passenger upon an accident. As described above, the seat belts of Comparative Examples 1-5 had significantly low strength retention, and thus, upon a long-term use, physical properties may be rapidly degraded to the state where a passenger may not be protected upon an accident. Further, though the seat belts from the polyester fiber of Comparative Examples 1-5 were thicker, having an average thickness of 1.5 mm to 1.6 mm, they had strength of 2980 kgf to 2996 kgf, which is significantly lower than that of Examples 1-5.