JP3459478B2 - Thread for airbag - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thread for an airbag which can obtain an airbag base fabric having excellent mechanical properties and flexibility. 2. Description of the Related Art At present, airbags used as safety devices for automobiles are mainly formed of a base fabric obtained by coating a synthetic fiber woven fabric using nylon 66 with rubbers. [0003] Airbags, together with shock absorption, are usually
In order to store it in a very small place, it is required to have excellent flexibility. [0004] However, the base fabric in which the synthetic fiber woven fabric is covered with rubber can improve heat resistance and airtightness by covering with rubber, but the base fabric is hardened, so that the storage property is poor. There's a problem. [0005] In order to solve this problem and reduce the manufacturing cost, a non-coated type airbag which is not coated with rubber has recently been developed.
The use of a polyester that is less expensive than 6 and has good heat resistance has been studied. [0006] However, polyester is nylon 6
6 has a drawback of lacking flexibility when woven into a base fabric, especially when woven at high density to increase airtightness, it is more difficult to store compactly. Problem arises. Japanese Patent Application Laid-Open No. Hei 3-167312 proposes a fiber having improved toughness and knot strength as a polyester fiber for an airbag, and an airbag base fabric obtained from this fiber has improved impact resistance and durability. It has excellent properties and the flatness of the base fabric is also improved. [0008] However, the base fabric obtained from these fibers has a drawback that the flexibility is not sufficient, and if the fabric is woven at a high density in order to increase the airtightness, the storability is poor. As described above, it is not easy to impart flexibility to the polyester yarn while maintaining strength and durability, and it is possible to obtain a flexible airbag base fabric which is excellent in strength and durability and at the same time. Polyester yarn has not yet been developed. [0010] The present invention solves the above-mentioned problems and provides an airbag capable of obtaining a base cloth having both the mechanical properties and flexibility required for an airbag base cloth. An object of the present invention is to provide a bag thread. The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, the inner layer portion and the surface layer portion of the fiber cross section have a difference in orientation. Was found to be a fiber having a degree of orientation lower than that of the inner layer portion and to reduce the rigidity in the bending direction, thereby obtaining a yarn having high strength and soft flexibility against bending, and reached the present invention. That is, the present invention comprises polyethylene terephthalate having an intrinsic viscosity of 0.8 or more, a single fiber fineness of 1 to 2.5 d, a total fineness of 200 to 500 d, and a tensile strength of 8 g.
/ D, the breaking elongation is 15% or more, the birefringence distribution of the cross section of the single yarn satisfies the expression (1), and the bending rigidity is in the range of the expression (2). . (1) Δnc−Δns ≧ 0.015, Δnc ≧ 0.170 Δnc: Average value of the birefringence of 70% in the radial direction from the center of the single yarn Δns: Radius from the surface of the single yarn Average value of birefringence of a portion up to 30% in the direction (2) B ≦ 6.0 × 10 ⁻⁶ × TD B: Flexural rigidity (g · cm ² / thread) TD: Total fineness (d) Hereinafter, the present invention Will be described in detail. The yarn in the present invention is made of polyethylene terephthalate (PET), but the PET is mixed with a third component such as a heat-resistant agent, a flame retardant, and a matting agent to the extent that the intrinsic properties of polyester are not impaired. It may be. Further, the intrinsic viscosity of PET needs to be 0.8 or more. Here, the intrinsic viscosity is measured at 20 ° C. using an equal weight mixed solvent of phenol and tetrachloroethane. If the intrinsic viscosity is less than 0.8, the yarn becomes poor in strength and durability, which is not preferable. Although the upper limit of the intrinsic viscosity is not particularly limited, it is preferable that the range of the intrinsic viscosity be 0.8 to 1.1 for spinning with good operability. In the fiber according to the present invention, the inner layer portion and the surface layer portion of the fiber cross section have a difference in orientation, the orientation of the surface layer portion is lower than that of the inner layer portion, and the rigidity of the fiber in the bending direction is reduced. Thus, the fiber has flexibility while having high strength. Specifically, the birefringence measured by dividing the fiber in the radial direction at a ratio of 7/3 is (1)
It is necessary to satisfy the expression. By having a birefringence distribution that satisfies the expression (1), the energy required for inner compression when the fiber is bent is small, the bending rigidity is small, and the inner layer portion of the fiber is highly oriented. Therefore, high strength can be maintained in the fiber axis direction. The fineness of the single yarn must be 1 to 2.5 d. If the single-fiber fineness is larger than 2.5 d, the bending rigidity of the fiber becomes large, and the obtained fabric is not flexible. On the other hand, if it is smaller than 1 d, the strength is inferior.
It is difficult to provide a distribution satisfying the expression (1). The total fineness must be in the range of 200 to 500 d. When the total fineness is larger than 500 d, when weaving at high density, the base fabric lacks flexibility.
It becomes a base fabric with weak tear strength. The value of the bending rigidity of the yarn varies depending on the fineness of the single yarn and the number of filaments. In the present invention, it is necessary to satisfy the expression (2) in order to impart sufficient flexibility to the knitted and woven fabric. is there. Further, it is necessary that the tensile strength be 8 g / d or more and the breaking elongation be 15% or more. 8g tensile strength
If it is less than / d, it will be a base fabric with low tear strength, and if the elongation at break is less than 15%, it will not be possible to obtain a base fabric having impact resistance to withstand the impact during airbag operation. Next, an example of a method for producing the yarn of the present invention will be described. In general, when a single component polymer is spun by a usual melt spinning method, the orientation of the surface layer tends to be promoted more than the inner layer due to a difference in cooling rate. The orientation of the portion needs to be lower than the orientation of the inner layer portion. Therefore, in the present invention, the above-described orientation difference is provided by causing a difference in melt viscosity between the inner and outer layers at the time when the polymer is discharged. That is, the polymer supplied to the surface layer portion and the inner layer portion is temperature-controlled by independent extruders, and both components are joined and discharged by a core-sheath type spinneret, thereby causing a difference in melt viscosity. First, the temperature of the extruder was set to 305 to 31 on the surface side.
5 ℃, inner layer side 290 ~ 300 ℃, discharge temperature 295 ~ 30
The spinning is performed at a temperature of 5 ° C., and the supply ratio of the polymer is 3/7 to 5/5 for the surface layer / inner layer by weight. Next, the spun yarn is passed through a heating zone at a temperature of 350 to 450 ° C. higher than the discharge temperature in order to maintain a difference in melt viscosity, and then cooled and solidified. After passing through the heating zone, the yarn is cooled by blowing cooling air from the outside to the center of the yarn, and the oil is applied immediately after solidification to bundle the yarn. After the collected yarn is taken out, the yarn is stretched to obtain a yarn having a tensile strength of 8 g / d or more. However, in order to improve the productivity, the stretching process should be performed continuously after the spinning. Preferably, the take-up speed is in the range of 400 to 600 m / min, and a heating steam having a temperature of 200 ° C. or more is sprayed or heated using a heat plate or the like so as to reduce the stress applied to the fiber surface layer during drawing. While stretching ratio 4.5
Stretch by 5.5 times. After stretching, the film is subjected to a relaxation treatment of 5% or less and wound up. At this time, if the stretching is performed in multiple stages or the relaxation ratio is increased, the difference in orientation between the surface layer and the inner layer of the fiber becomes small, which is not preferable. Next, the present invention will be described in detail with reference to examples. In addition, the measuring method of the characteristic value in this invention is as follows. (A) High elongation Using an autograph S-100 manufactured by Shimadzu Corporation, sample length 25c
m, and a tensile speed of 30 cm / min. (B) The birefringent interference microscope was used to measure each of the portions obtained by dividing the cross section of the fiber into 10 equal parts in the radial direction, and the average value was calculated for three places on the surface layer and seven places on the inner layer side. (C) Flexural rigidity The flexural rigidity was measured using a pure bending tester KES-FB2 manufactured by Kato Tech. (D) Flexibility JIS L-1096 6.19.1A method (45 ° cantilever method)
Was measured. The flexibility sufficient as a base fabric for an air bag is 60 mm or less. Examples 1-2, Comparative Examples 1-3 PET chips having an intrinsic viscosity of 0.9 were extruded into two extruders.
Each of them was supplied to the equipped composite melt spinning machine, and was spun from a core-sheath type spinneret having the number of filaments shown in Table 1.
At that time, the supply ratio between the surface layer and the inner layer was 4/6 by weight, the control temperature of the extruder on the surface layer was 315 ° C, the control temperature of the extruder on the inner layer was 300 ° C, and the discharge temperature was 305 ° C. did. The spun yarn is passed through a 10 cm long heating cylinder maintained at an ambient temperature of 400 ° C., and then cooled at a temperature of 20 ° C. and a speed of 30 m / min by a cylindrical cooling air blowing device. After blowing the wind to cool and solidify and applying the oil, the speed is 48
It was taken off by a take-off roller of 0 m / min. Subsequently, the paper is sent to a drawing roller having a surface temperature of 220 ° C., and 400 mm is applied to the yarn between the drawing roller and the drawing roller.
Sprayed with heated steam at a temperature of 5.2 ° C (Comparative Example 3).
The film was stretched at 5.6 times), subjected to a 3% relaxation heat treatment with a relaxation roller having a surface temperature of 160 ° C., and wound up by a winder. Table 1 shows the values of single fiber fineness, tensile strength, elongation at break, birefringence, and flexural rigidity of the obtained yarn. Each of the yarns obtained in Examples 1 and 2 had a low bending rigidity, and both the strength and the elongation were sufficient for an airbag yarn. On the other hand, the yarn obtained in Comparative Example 1 has a large single-fiber fineness and therefore has a high bending rigidity, and the yarn obtained in Comparative Example 2 has a low single-fiber fineness and thus lacks strength. Since the obtained yarn was excessively stretched, it had a low elongation, a small difference in orientation between the surface layer and the inner layer, and a high flexural rigidity. Comparative Example 4 Example 1 was repeated except that a PET chip having an intrinsic viscosity of 0.9 was fed to a melt spinning machine equipped with a single extruder, and the control temperature of the extruder was 310 ° C. and the discharge temperature was 305 ° C. Spinning-drawing was performed in the same manner as in 1. Table 1 shows the values of single fiber fineness, tensile strength, elongation at break, birefringence, and flexural rigidity of the obtained yarn. The yarn obtained in Comparative Example 4 had high flexural rigidity because the orientation of the fiber surface layer was higher than that of the inner layer. [Table 1] Example 3, Comparative Example 5 Using the yarns of Example 1 and Comparative Example 4, a woven fabric having a flat structure with a warp and weft density of 60 yarns / 2.54 cm was measured, and the flexibility was measured. Table 2 shows the measured values of the flexibility of the obtained woven fabric. [Table 2] The woven fabric obtained in Example 3 was excellent in flexibility, but the woven fabric obtained in Comparative Example 5 was inferior in flexibility and was insufficiently storable as a base fabric for an airbag. It was something. The yarn for an airbag according to the present invention, when knitted and woven, has a mechanical property of strength and elongation required as an airbag base fabric, and a fabric having flexibility. Becomes possible. [0050]

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-5-311513 (JP, A) JP-A-61-207619 (JP, A) JP-A-3-167312 (JP, A) JP-A-6-206 306728 (JP, A) JP-A-7-186858 (JP, A) JP-A-60-88120 (JP, A) JP-A-2-289115 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) D01F 6/62 301-308 D01F 8/14 B60R 21/16

Claims (1)

(57) [Claims 1] A polyethylene terephthalate having an intrinsic viscosity of 0.8 or more, a single fiber fineness of 1 to 2.5 d, a total fineness of 200 to 500 d, and a tensile strength of 8 g / d or more. An airbag yarn having a breaking elongation of 15% or more, a birefringence distribution of a cross section of a single yarn satisfying the expression (1), and a bending rigidity in a range of the expression (2). (1) Δnc−Δns ≧ 0.015, Δnc ≧ 0.170 Δnc: Average value of the birefringence of 70% in the radial direction from the center of the single yarn Δns: 30 in the radial direction from the surface of the single yarn % (2) B ≦ 6.0 × 10 ⁻⁶ × TD B: Flexural rigidity (g · cm ² / thread) TD: Total fineness (d)