JP4983691B2 - Polyester fiber for seat belt - Google Patents

Description

  The present invention relates to a polyester fiber for seat belts. Specifically, it is a polyester fiber suitable for obtaining a seat belt webbing that combines high strength, high toughness, and high quality, and relates to a polyester fiber that can be produced at low cost without requiring special equipment and facilities. It is.

  The seat belt device is indispensable as a device for ensuring the safety of passengers who have boarded vehicles such as automobiles, airplanes, rockets, and roller coasters, and is installed in many vehicles. The seat belt device is composed of a webbing portion formed by weaving fibers and a winding device called a retractor, and the webbing portion plays a role of directly holding and restraining the human body at the time of impact. The properties required for webbing include, firstly, high strength that does not easily break, and excellent energy absorption performance that reduces impact on the human body. In particular, in recent years, the required characteristics have become more severe due to the increase in safety awareness. In addition, the retractability to the retractor is important, and by using a webbing with a thin thickness and appropriate rigidity, the retractor can be smoothly wound and the safety reliability is further increased. . Seat belt webbing is not only technically demanding, but also strongly demands how to reduce manufacturing costs, and there is a continuing demand for a webbing that combines all the characteristics in a well-balanced manner without increasing costs. .

  Many techniques related to seat belt webbing have been proposed so far. In order to increase the strength of the webbing, there is a method using so-called ultra-high strength fibers. Patent Document 1 discloses a method using aramid fibers and Patent Document 2 uses wholly aromatic polyester fibers. By using the fiber described in Patent Document 1 or Patent Document 2, the breaking strength of the webbing is certainly greatly increased and the level required in recent years can be easily cleared, but the elongation of the fiber itself is small. As a result, the results of the webbing's energy absorption performance are insufficient, and the rigidity of the webbing is too high so that the retractor cannot be wound smoothly and sometimes does not function as a seat belt. Was a concern.

  In this regard, polyester fiber, especially polyethylene terephthalate fiber, has high strength, high toughness, moderate rigidity, and excellent dimensional stability, and is considered to be the most suitable material as a fiber material for seat belt webbing. Has been used for some time.

  There are Patent Documents 3 and 4 as techniques for enhancing the strength of a seat belt webbing using a polyester fiber.

  Patent Document 3 discloses a method of stretching a polymer having a high degree of polymerization at a high magnification in order to increase the strength of the polyester fiber. However, it is difficult to produce polyester fibers with high-quality drawing with high quality, and many practical problems remain such as inducing all yarn breakage and single yarn breakage. Moreover, even if the breaking strength of the polyester fiber itself is simply increased by high-strength drawing, the strength of the webbing using the polyester fiber does not necessarily reach a sufficient level, and is a suitable polyester for obtaining a high-strength webbing. From the fiber standpoint, challenges remained.

  Patent Document 4 is expected to increase the strength of the webbing by increasing the number of polyester fibers used for webbing. By flattening the cross-sectional shape of the single yarn of the fiber, the increase in webbing thickness due to the increased number of fibers is suppressed. Have been disclosed. According to the technique described in Patent Document 4, although a high-strength and thin webbing can be obtained, the fibers have a close-packed structure in the cross-section of the webbing, and the webbing rigidity becomes too high. There was a risk of loss of takeability. Further, flat cross-sectional yarns are not cooled and heated uniformly in the production process, and may cause variations in quality and deterioration of yarn-making properties, leaving uneasy as fibers used in safety devices.

As described above, various characteristics required for seat belt webbing, specifically, high breaking strength, excellent energy absorption performance, thin and moderate rigidity, and it is easy to obtain a seat belt webbing with a good balance at a low cost. Rather, its realization was desired from many perspectives.
JP 62-104938 A (Claims) JP-A-8-72668 (Claims) JP-A-6-17313 (Claims) JP 2004-315984 A (Claims)

  The present invention has been achieved as a result of paying attention to and examining the load-elongation curves of the polyester fibers constituting the webbing for various problems that could not be solved by the prior art as described above. That is, it is to provide a polyester fiber particularly suitable as a seat belt by appropriately controlling a load-elongation curve, that is, by using the polyester fiber of the present invention, a high strength that has not existed so far. In addition, a seat belt webbing having excellent energy absorption ability and maintaining appropriate rigidity without increasing the thickness can be obtained. Moreover, the polyester fiber of the present invention and the webbing made thereof can be manufactured without requiring special equipment and devices, and can be said to be an extremely advantageous technique in terms of cost.

In order to achieve the above object, the present invention mainly has the following configuration. That is, the breaking strength in the fiber load-elongation curve is 7.5 to 9.5 cN / dtex, and the terminal modulus is 5 to 20 cN / dtex. Furthermore, it is preferable that the polyester fiber for seat belts of the present invention satisfies any one of the following (a) to (d) or a combination thereof, and further excellent effects can be expected.
(A) The elongation at break in the fiber load-elongation curve is 12 to 16%, and the elongation at 4.0 cN / dtex is 5.0 to 6.5%.
(B) a dry heat shrinkage _{S (100)} in the dry heat 100 ° C. of fiber, dry heat shrinkage _{S (120)} in dry heat 120 ° C., and the difference ΔS to satisfy the following characteristics.
S ₍₁₀₀₎ = 0.6-1.5%
S ₍₁₂₀₎ = 2.0-3.5%
ΔS = 1.0-2.5%
(C) shrinkage stress at dry heat ₁₀₀ ℃ _{F (100),} contraction stress _{F (180)} in dry heat 180 ° C., and the temperature _T of the time giving the maximum shrinkage stress _(max) to satisfy the following characteristics.
F ₍₁₀₀₎ = 0.10 to 0.25 cN / dtex
F ₍₁₈₀₎ = 0.18-0.40 cN / dtex
T _(max) = 200 to 230 ° C.

  The polyester fiber of the present invention has a load-elongation curve appropriately controlled and can be suitably used as a webbing for a seat belt. In other words, by using the polyester fiber of the present invention, it is possible to obtain a seat belt webbing that has high strength, excellent energy absorption ability that has not existed so far, and that retains moderate rigidity without increasing thickness. . Moreover, since a unique apparatus is not required for producing polyester fiber and webbing, it is a very advantageous technique in terms of cost.

  The present invention is described in detail below.

  In order to obtain high strength, high toughness, high dimensional stability and the like, the polyester fiber for seat belts of the present invention uses a polymer having ethylene terephthalate as a repeating unit substantially. However, acid components such as isophthalic acid, adipic acid, sebacic acid, 2,6-naphthalenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, butanediol, hexanediol, diethylene glycol are included in a part of the polymer as long as such characteristics are not impaired. , Neopentyl glycol, 1,4 cyclohexanediol and other diol components may be copolymerized. In addition, for polymers, the main purpose is matte, inorganic substances such as titanium oxide, calcium carbonate, kaolin and clay, benzophenone and benzotriazole UV absorbers, antioxidants, radical scavenging for the purpose of improving weather resistance. There is no problem even if it contains an agent. Furthermore, the polymer may contain a colorant. Examples of the colorant include inorganic colorants such as carbon black, zinc oxide, and iron oxide, and organic colorants such as cyanine, phthalocyanine, anthraquinone, azo, perinone, styrene, and quinacdrine. By using a polymer containing these colorants, colored polyester fibers can be obtained, and the dyeing step in the seat belt webbing manufacturing step can be omitted.

  The degree of polymerization of polyethylene terephthalate or a copolymer thereof used for obtaining high strength and high toughness fibers is better. Specifically, the intrinsic viscosity is 0.8 or more, preferably 0.9 or more, more preferably 1.0 or more.

  High-strength and high-toughness fibers can be obtained by melt spinning and stretching the above-mentioned polyethylene terephthalate having an intrinsic viscosity of 0.8 or more or a copolymer thereof, and its breaking strength is 7.5 to 9.5 cN / dtex, preferably Is 8 to 9.5 cN / dtex. If the breaking strength of the fiber is less than 7.5 cN / dtex, the strength of the seat belt webbing made of polyester fiber is insufficient even if the load-elongation curve up to the breaking strength is properly controlled as will be described later. As a result, the required level may not be reached in recent years. On the other hand, those whose breaking strength exceeds 9.5 cN / dtex are difficult to manufacture in the first place, and forcibly stretching results in inducing complete yarn breakage or single yarn breakage, and stably obtaining high-quality polyester fibers. Can not be.

  The greatest and important feature of the polyester fiber for seat belts of the present invention is to control the load-elongation curve of the fiber, the inclination at the breaking point of the fiber, the so-called terminal modulus is 5 to 20 cN / dtex, 8 More preferably, it is -15 cN / dtex. In order to increase the webbing strength so far, it has been thought that it is only necessary to increase the breaking strength of the fiber used as described in Patent Document 3, for example. It has been found that reducing the modulus near the breaking point is a particularly effective requirement for obtaining a high strength webbing.

  The seat belt webbing is formed by driving about 300 polyester fibers of 1670 dtex, for example. However, the webbing strength is not the sum of the breaking strengths of 300 fibers, and is usually lower than the sum. FIG. 1 shows an example of a fiber load-elongation curve. Curve (a) shows the case where the slope at the break point of the fiber, so-called terminal modulus is large, and curve (b) shows the case where the slope at the break point of fiber, so-called terminal modulus is small. In the seat belt webbing, there is a length variation in the fibers constituting the webbing. Therefore, when a load is applied to the seat belt webbing, a large load is applied to some fibers and a small load is applied to some fibers. That is, when a load is applied to the entire seat belt webbing, not all of the fibers constituting the webbing are subjected to a constant load, but there is a variation in the load. For this reason, the fiber with a large load breaks first, and as a result, sufficient physical properties as a seat belt webbing cannot be maintained.

  In the case of curve (a), since the terminal modulus is large, when the fiber (small length) subjected to a large load breaks, the fiber (large length) subjected to a small load does not stretch until it breaks. A fiber having a margin and a small load is not fully utilizing the physical properties of the fiber. On the other hand, in the case of curve (b), since the terminal modulus is small, when the fiber (small length) under heavy load breaks, the fiber (long length) under heavy load stretches until it breaks. This means that the physical properties of the fibers subjected to a small load are sufficiently utilized.

  That is, the conventional fiber has a large load at break as shown by the curve (a), but when used in a seat belt webbing, the original characteristics of the fiber constituting the webbing were not utilized. Although the fiber is inferior in load at break as shown by curve (b), the terminal modulus is small, so that the original characteristics of the fiber constituting the webbing are utilized. As a result, even if the load at the time of breaking one fiber is small, when it is used as a seat belt webbing, it will exhibit characteristics superior to those of a fiber exhibiting a load-elongation curve such as curve (a). .

  Actually, when a fiber having a load-elongation curve such as curve (a) is used, the value obtained by dividing the webbing strength by the sum of the breaking strengths of the fibers constituting the webbing, the so-called strength utilization rate is at most 75 to 80%. Degree.

  The terminal modulus of the polyester fiber of the present invention is 5 to 20 cN / dtex. By using a polyester fiber having a terminal modulus in such a range, the strength of each fiber can be maximized as described above, and high strength as a webbing can be achieved. In addition, when the strong utilization factor is calculated with the seat belt webbing composed of the polyester fiber of the present invention, the value exceeds 80%. A fiber having a terminal modulus of less than 5 cN / dtex often has a low breaking strength in the first place, and is not suitable as a fiber for a seat belt. On the other hand, in the case of a conventional polyester fiber having a terminal modulus exceeding 20 cN / dtex, no matter how much the fiber strength is increased, the effect of improving the webbing strength is small and the strength level required in recent years may not be reached.

  Next, the breaking elongation of the polyester fiber for seat belts of the present invention is preferably 12 to 16%, and more preferably 13 to 15%. The seat belt webbing is required to have high strength and high toughness, and by using a polyester fiber having an elongation characteristic in such a range, a webbing excellent in energy absorption performance can be easily obtained. The elongation at 4.0 cN / dtex is preferably 5.0 to 6.5%, more preferably 5.5 to 6.5%. By setting the elongation rate within this range, it is possible to reduce the load applied to the human body immediately after the collision, and it becomes easy to obtain a webbing excellent in safety.

  Up to now, as a method to increase the strength of the seat belt webbing, a method of reducing the terminal modulus of the polyester fiber, that is, the breaking strength of each fiber on the premise that there is variation in the fiber length constituting the webbing in the webbing However, it is expected that the strength of the webbing can be increased by reducing the length variation of each fiber in the webbing.

And when the cause of the length variation of each fiber in the webbing was examined, it was found that the heat shrinkage behavior of the fiber was related. In other words, the seat belt webbing is subjected to dyeing and heat setting processes after weaving and weaving hundreds of fibers, but when the amount of heat received for each webbing site is different, a difference occurs in the shrinkage behavior of each fiber, It has been found that it appears to contribute to the length variation in the webbing. In consideration of this point, it is preferable that the polyester fiber for seat belts of the present invention has a low shrinkage rate and a small change in shrinkage rate due to heat. That is, the polyester fiber shrinkage of the present invention is preferably 0.6 to 1.5%, more preferably 0.8 to 1.3% in terms of dry heat shrinkage S ₍₁₀₀₎ at 100 ° C. preferable. Further, the dry heat shrinkage S ₍₁₂₀₎ at 120 ° C. is preferably 2.0 to 3.5%, more preferably 2.3 to 3%. Further, the difference ΔS between S ₍₁₀₀₎ and S ₍₁₂₀₎ is preferably 1.0 to 2.5%, and more preferably 1.3 to 2%. A webbing made of polyester fiber having a shrinkage in such a range is particularly preferable because high strength is easily obtained. In the initial stage of the dyeing process, the seat belt webbing is estimated to reach approximately 100 to 120 ° C.

The polyester fiber of the present invention preferably has a lower heat shrinkage stress, and the shrinkage stress F _{(100) at} 100 ° C. dry heat is preferably 0.10 to 0.25 cN / dtex, and 0.12 to 0.22 cN / d. More preferably, it is dtex. Further, the shrinkage stress F _{(180) at} a dry heat of 180 ° C. is preferably 0.18 to 0.40 cN / dtex, and more preferably 0.25 to 0.35 cN / dtex. Moreover, it is preferable that temperature T _(max) when giving a maximum shrinkage stress is 200-230 degreeC. By setting the heat shrinkage stress in such a range, as described above, in the webbing manufacturing process, the dimensional change of each fiber constituting the webbing is suppressed, and the length variation of the fiber in the webbing can be reduced. Can be expected to increase.

  Further, as described above, by setting the dry heat shrinkage rate and the heat shrinkage stress of the polyester fiber to a specific range, the effect of stabilizing the dyeing process of the seat belt webbing and obtaining a high-quality colored webbing is also exhibited. The effects of fiber shrinkage and shrinkage stress on the webbing dyeing process have not been analyzed strictly, and there is no confirmation of the mechanism by which the dyeing process is stabilized by making it within the scope of the present invention. As a result of the reduction in fiber length variation in the webbing as well as improvement, it is thought that the flow path and moving speed of the dye solution in the webbing may be made uniform.

  Next, a method for obtaining the polyester fiber for seat belt of the present invention will be described. The seat belt fiber of the present invention has an appropriately controlled load-elongation curve, but may be based on a normal method for producing industrial high-strength polyester fiber without using special equipment or equipment. .

  First, a polyethylene terephthalate chip having an intrinsic viscosity of 0.8 or more is melted and filtered and then spun from the die pores. Next, the spun yarn is passed through an atmosphere heated to a temperature equal to or higher than the melting point of the polymer, for example, 270 to 350 ° C., and then cooled and solidified with cooling air of 50 ° C. or lower. By passing through such a temperature history, it becomes possible to manufacture high-strength and high-toughness polyester fibers with good quality. The cooled yarn is provided with an oil and wound around a take-up roller that rotates at a predetermined rotation speed. Subsequently, the film is stretched by winding around a roller that rotates at high speed sequentially. The drawing is preferably carried out in two to three stages at a magnification of 4.5 to 6.5 times, and high strength fibers having a breaking strength of 7.5 to 9.5 cN / dtex can be obtained stably with high quality. It becomes easy to be done.

  The stretched yarn is subjected to heat setting and relaxation treatment, and this process is important for obtaining the polyester fiber of the present invention, that is, a polyester fiber exhibiting a load-elongation behavior extremely suitable for a seat belt.

  In the conventional polyester fiber for seat belts, in order to avoid a decrease in strength after stretching, the temperature of the final stretching roller subjected to heat setting is not set too high, and the relaxation rate is the speed difference between the final stretching roller and the relaxation roller. Was set as low as possible. On the other hand, the polyester fiber of the present invention is as high as possible within the range in which the temperature of the final drawing roller does not cause a problem such as fusion, and is set to, for example, 235 ° C. to 255 ° C. It is obtained by adopting 5%. In fact, although the strength of the polyester fiber itself tends to decrease due to high-temperature heat setting and high-relaxation treatment, the strength of utilization is reduced by decreasing the slope of the load-elongation curve at the breaking point described above, that is, the terminal modulus. Further, since the length variation in the webbing is reduced due to the decrease in the dry heat shrinkage rate and the heat shrinkage stress, the webbing using the fiber has excellent strength.

  The yarn after the heat setting / relaxation treatment is preferably subjected to an entanglement treatment by injecting high-pressure air. It is desirable that the entanglement applied to the yarn is large and uniform, and the number of entanglements (CF value) per 1 m of fiber length is sufficient if it is 15-30. By performing the entanglement process on the yarn, processability such as webbing weaving is improved, and a high-quality seat belt webbing can be obtained in a high yield.

  Even when a seat belt webbing is produced using the polyester fiber for seat belts of the present invention, a specific method is not required, and a conventional method can be employed. For example, weaving may be performed using a needle type loom, and the warp yarn tension may be controlled to about 0.05 to 1.5 cN / dtex, and the weft yarn may be controlled to about 0.05 to 1.5 cN / dtex. In the subsequent dyeing process, the webbing obtained in the weaving process may be immersed in a dyeing solution containing a known disperse dye for polyester and an auxiliary agent, and then sequentially processed in a color developing tank, a washing tank, and a heat setting tank.

  The seat belt webbing obtained in this way has high strength and high toughness, and is thin and has an appropriate rigidity, so that it has excellent winding performance. In addition, the polyester fiber of the present invention and the webbing made of the polyester fiber can be manufactured without requiring special equipment and apparatus, and are extremely advantageous in terms of cost.

  Hereinafter, the present invention will be described specifically by way of examples. Various physical properties were calculated by the following methods.

[Intrinsic viscosity of polymer (IV)]:
The relative viscosity ηr of a solution obtained by adding 100 ml of orthochlorophenol to 8.0 g of a sample and heating and dissolving at 160 ° C. for 10 minutes was measured using an Ostwald viscometer, and calculated according to the following approximate expression.
IV = 0.0242ηr + 0.02634

[Total fineness]:
JIS L-1013 (1999) 8.3.1 Positive fineness a) Measured according to method A at a predetermined load of 5 mN / tex × number of displayed tex and a predetermined yarn length of 90 m.

[Breaking strength, breaking strength, breaking elongation, terminal modulus]:
The constants shown in the JIS L-1013 (1999) 8.5.1 standard test with a “TENSILON” UCT-100 manufactured by Orientec Co., Ltd. in a temperature control room where the temperature is 20 ° C. and the humidity is 65%. Measured under fast extension conditions. At this time, the holding interval was 25 cm, the tensile speed was 30 cm / min, and the number of tests was 10. The elongation at break was determined from the elongation at the point showing the maximum strength in the load-elongation curve. The terminal modulus was obtained from the slope of the tangent line drawn from the breaking point (the point showing the maximum strength) toward the zero point.

[Elongation at 4.0 cN / dtex]:
The elongation (%) at 4.0 cN / dtex was read from the load-elongation curve obtained by the above measurement of [breaking strength, breaking strength, breaking elongation, terminal modulus].

[Dry heat shrinkage]:
JIS L-1013 (1999) 8.18.2 Dry heat shrinkage rate a) According to skein shrinkage rate (Method A), predetermined load 5 mN / tex at the time of sample sampling × displayed tex number, predetermined load 200 kN / S ₍₁₀₀₎ was obtained at a treatment temperature of 100 ° C, and S ₍₁₂₀₎ was obtained at a treatment temperature of 120 ° C. The difference ΔS was obtained from the following equation.
ΔS = S ₍₁₂₀₎ −S ₍₁₀₀₎

[Temperature T _(max) when applying shrinkage stress and maximum shrinkage stress]:
The sample was attached to a Toyo Baldwin SS-207D-UE strain measuring machine, and a temperature-heat shrinkage stress curve was drawn while raising the temperature using a Toyo Baldwin TKC-IIIS heating furnace. The temperature at which stress was applied was read. The sample length at this time was 25 cm, and an initial load of 0.045 cN / dtex was applied. The measurement temperature range was 25 ° C. to 260 ° C., and the temperature increase rate was set to 5 ° C./min. Each sample was measured twice to obtain an average value.

[Number of confounding (CF value)]:
In accordance with JIS L-1013 (1999) 8.15, the weight of the weight is 0.22 mN / tex × display tex number, the predetermined load display tex number / filament number × 1.09 mN at the other end of the hook, the descending speed is 1 to 2 cm / It descended at sec and calculated by the following formula.
CF value = 100 (cm) / Descent distance (cm)

[Tensile strength of webbing / elongation at 11.1 kN]:
It measured according to JIS D-4604 (1995) 7.4. The distance between the clamps at this time was 220 mm, the tensile speed was 10 cm / min, and the number of tests was 5. The elongation at 11.1 kN was obtained from the elongation when a load of 11.1 kN was shown in the load-elongation curve.

[Strong utilization rate]:
The webbing tensile strength was calculated by dividing the webbing tensile strength by the product of the breaking strength of the polyester fiber constituting the webbing and the number of fibers used as shown in the following formula.
Strength utilization rate (%) = (Webbing tensile strength (N)) × 100 / (Fracture strength of fiber (N) × Number of driven (number))

[Webbing thickness]:
Using a Mitutoyo thickness measuring device 156-101, both ends (the left end and the right end) and the center of the webbing were measured three times for a total of nine times to obtain an average value.

[Webbing rigidity]:
According to the method of JIS L-1096 8.20.1, a sample having a length of 38.1 mm and a width of 12.7 mm was collected and measured using a Gurley type stiffness tester manufactured by Tester Sangyo Co., Ltd.

[Example 1]
A polyethylene terephthalate resin composition containing 0.1 part by weight of titanium oxide is melted by an extruder type spinning machine with respect to 100 parts by weight of polyethylene terephthalate having an intrinsic viscosity of 1.2, and the discharge rate is 468 g / min with a metering pump. Then, the mixture was filtered in a spinning pack and spun from a spinneret. The temperatures of the extruder, spin block, and spin pack were adjusted so that the melt polymer temperature was 300 ° C. A spinneret having a hole number of 144 and a circular hole type was used.

  The spun yarn was passed through a heating tube having a temperature of 320 ° C. and a length of 300 mm, and then a cooling air of 20 ° C. was blown onto the yarn at a wind speed of 30 m / min to be cooled and solidified. Next, an oil agent is applied to the cooling yarn, taken up by a take-up roller set at 70 ° C., and then rotated at a lower speed than the heated supply roller, the first drawing roller, the final drawing roller, and the final drawing roller, which are sequentially rotated at a high speed. The film was wound around a relaxation roller and subjected to stretching, heat setting, and relaxation treatment.

  Here, the surface temperature of the supply roller was set to 110 ° C., and the surface temperature of the first stretching roller was set to 120 ° C. Further, the first stage magnification represented by the speed difference between the supply roller and the first stretching roller was set to 3.6 times. Table 1 shows the stretching ratio represented by the speed difference between the final stretching roller and the take-off roller, the relaxation rate represented by the speed difference between the final stretching roller and the relaxation roller, and the set temperature of the final stretching roller.

  The yarn after the relaxation treatment was subjected to entanglement treatment by injecting high-pressure air and wound up with a winder to produce polyester fibers for seat belt warp yarn of 1670 dtex-144 filament. The properties of the obtained polyester fiber are shown in Table 2.

  Separately, a polyethylene terephthalate resin composition containing 0.1 parts by weight of titanium oxide with respect to 100 parts by weight of an intrinsic viscosity of 1.2 polyethylene terephthalate was melted with an extruder-type spinning machine, and a discharge rate of 232 g / min with a metering pump. Then, the mixture was filtered in a spinning pack and spun from a spinneret. The temperatures of the extruder, spin block, and spin pack were adjusted so that the melt polymer temperature was 300 ° C. As the spinneret, a circular hole type with 96 holes was used.

  The spun yarn was passed through a heating cylinder having a temperature of 300 ° C. and a length of 150 mm, and then a cooling air of 20 ° C. was blown onto the yarn at a wind speed of 30 m / min to be cooled and solidified. Next, an oil agent is applied to the cooling yarn, taken up by a take-up roller set at 70 ° C., and then rotated at a lower speed than the heated supply roller, the first drawing roller, the final drawing roller, and the final drawing roller, which are sequentially rotated at a high speed. The film was wound around a relaxation roller and subjected to stretching, heat setting, and relaxation treatment. Here, the surface temperature of the supply roller was set to 110 ° C., the surface temperature of the first stretching roller was set to 120 ° C., and the surface temperature of the final stretching roller was set to 210 ° C. Also, the first stage magnification expressed by the speed difference between the supply roller and the first stretching roller is 3.4 times, and the total stretching ratio expressed by the speed difference between the take-off roller and the final stretching roller is 5.3 times, and the final stretching. The relaxation rate represented by the speed difference between the roller and the relaxation roller was set to 2%. The yarn after the relaxation treatment is entangled by injecting high-pressure air and wound with a winder, 830 dtex-96 filament, strength 63 (N), strength 7.6 (cN / dtex), elongation 20 % Of polyester fiber for seat belt weft.

  Subsequently, 280 polyester fibers for seat belt warp yarn obtained were aligned and directly led to a needle-type loom, and woven under 2up2down conditions to obtain a webbing having a width of 50 mm. The warp yarn tension during weaving was adjusted to 0.5 cN / dtex. In addition, the obtained 830 dtex-96 filament polyester fiber was used for the weft, and it was driven by adjusting it to 20 strands / inch under a tension condition of 0.5 cN / dtex. Next, the obtained webbing was immersed in a disperse dye bath, preliminarily dried with an infrared heater, and developed in a 200 ° C. coloring tank. Subsequently, the excess dye liquor was removed by washing in a water washing tank, and heat treatment was carried out for 1 minute under dry heat at 150 ° C. to produce a seat belt webbing. The characteristics of the obtained seat belt webbing are also shown in Table 2.

[Examples 2 and 3, Comparative Examples 1 to 3]
Except that the draw ratio represented by the speed difference between the take-up roller and the final draw roller, the relaxation rate represented by the speed difference between the final draw roller and the relax roller, and the surface temperature of the final draw roller were set to the values shown in Table 1. Same as Example 1. Table 2 shows the characteristics of the obtained polyester fiber and the characteristics of the obtained seat belt webbing.

[Examples 4 and 5]
A polyester fiber of 1100 dtex-72 filaments was produced in the same manner as in Example 1 except that a spinneret having a round hole shape of 72 holes was used and the discharge rate was adjusted to 330 g / min. The characteristic properties of the obtained polyester fiber are shown in Table 2.

  Subsequently, 430 polyester fibers obtained were aligned, and a seat belt webbing was produced in the same manner as in Example 1. Table 2 shows the characteristics of the obtained seat belt webbing.

  As is apparent from Table 2, the polyester fiber for seat belts of the present invention has high strength, but has a low terminal modulus at the breaking point in the load-elongation curve, and the webbing made therefrom is used for seat belts. It has all the required characteristics in a well-balanced manner. Specifically, a webbing having high strength and high energy absorption, a thin thickness and appropriate rigidity has been obtained. Moreover, the polyester fiber and seat belt webbing of the present invention can be manufactured without requiring special equipment and devices, and can be said to be extremely advantageous in terms of cost. On the other hand, since the polyester fiber of Comparative Example 1 has a high terminal modulus, no matter how much the breaking strength of the fiber itself is increased, the strength of the webbing made of the fiber does not increase and the reliability as a safety device is impaired. It was. Conversely, in Comparative Example 2, since the breaking strength of the fiber itself is low, even if the terminal modulus near the breaking point is kept relatively low, the obtained webbing is insufficient in strength. Further, the strength of the webbing made of the polyester fiber of Comparative Example 3 which is outside the scope of the present invention in terms of both breaking strength and terminal modulus is greatly reduced, and does not serve as a seat belt.

  The polyester fiber of the present invention is a fiber having an appropriately controlled load-elongation curve, and is suitably used as a webbing for a seat belt. In other words, by using the polyester fiber of the present invention, it is possible to obtain for the first time a seat belt webbing that has high strength that has not existed so far, excellent energy absorption ability, and that retains moderate rigidity without increasing thickness. It will be possible. Moreover, since a unique apparatus is not required for producing polyester fiber and webbing, it can be said to be a very advantageous technique in terms of cost.

It is a figure which shows the example of the load-elongation curve of a fiber.

Explanation of symbols

(A): Curve when the terminal modulus is large (b): Curve when the terminal modulus is small

Claims (4)

    A polyester fiber for a seat belt having a breaking strength in a load-elongation curve of the fiber of 7.5 to 9.5 cN / dtex and a terminal modulus of 5 to 20 cN / dtex.   The seat belt according to claim 1, wherein the elongation at break in the fiber load-elongation curve is 12 to 16%, and the elongation at 4.0 cN / dtex is 5.0 to 6.5%. Polyester fiber. Dry heat shrinkage _S in dry heat 100 ° C. fibers _(100), a dry heat shrinkage _{S (120)} in dry heat 120 ° C., and claim 1 or 2, the difference ΔS is characterized by satisfying the following characteristics A polyester fiber for seat belts according to 1.
S ₍₁₀₀₎ = 0.6-1.5%
S ₍₁₂₀₎ = 2.0-3.5%
ΔS = 1.0-2.5% Dry heat shrinkage stress _{F (100)} at 100 ° C., shrinkage stress _{F (180)} in dry heat 180 ° C., and claim 1, the temperature _T of the time giving the maximum shrinkage stress _(max) to satisfy the following characteristics The polyester fiber for seat belts according to any one of -3.
F ₍₁₀₀₎ = 0.10 to 0.25 cN / dtex
F ₍₁₈₀₎ = 0.18-0.40 cN / dtex
T _(max) = 200 to 230 ° C.

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