JPH0748717A - Polyester fiber for base fabric for air bag - Google Patents

Abstract

PURPOSE:To obtain a polyester fiber suitable as a base fabric for uncoated air bags good in impact resistance and airtightness, capable of being compactly housed. CONSTITUTION:This polyester fiber for air bags is an ethylene terephthalate- based polyester fiber satisfying characteristics of >=0.8 intrinsic viscosity, 1-3 denier single filament size, 0.38-1.39g/cm<3> density, 90-120g/d initial modulus, >=9/d breaking strength, a knot strength of >=0.5 based on the breaking strength and >=10% dry shrinkage factor (180 deg.C).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyester fiber for an air bag base cloth for ensuring safety. More specifically, the present invention relates to a polyester fiber suitable for an uncoated airbag base cloth which is not coated.

[0002]

2. Description of the Related Art In recent years, improvements in inflators for operating airbags have made it possible to lower the temperature of high-pressure gas that expands momentarily, and to store it in a more compact manner. Airtight fabrics for bag base fabrics (non-coated airbag base fabrics) have begun to be put into practical use.

The characteristics required of such a non-coated airbag base fabric are that it has a high permeability of high-pressure gas even if the base fabric is thin, and has impact resistance and durability capable of withstanding momentary expansion. I can mention.

However, since nylon fibers, which have been widely used in the past, have an insufficient initial modulus, the fibers are likely to be stretched under a momentary expansion by high-pressure gas, which causes a serious problem for non-coated airbag base fabric. I have it.
On the other hand, polyester fibers have a high initial modulus, but have a low knot strength, and therefore have a problem in impact resistance, and thus a thin base fabric cannot be obtained.

To solve the problem of impact resistance, JP-A-3-167312 proposes a polyester fiber having a toughness of 120 or more and a knot strength of 4.1 g / d or more. However, as clearly shown in the specification, this fiber is a fiber for an air bag in which rubber or the like is laminated in a post-process, and when it is not coated, it has a ventilation blocking property and a storage property. At the same time it was difficult to satisfy.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the problems of the above polyester fiber, to provide a non-coated airbag base cloth which has good impact resistance and air-permeability and can be stored compactly. It is to provide a polyester fiber that can be preferably used.

[0007]

The above object is to provide a polyester fiber for an air bag base fabric, which comprises polyester in which 90 mol% or more of repeating units are ethylene terephthalate, and the fiber has the following requirements (a) to (g). Is achieved at the same time by the polyester fiber for an air bag base fabric. (A) Intrinsic viscosity IV: IV ≧ 0.80 (b) Single fiber fineness D (denier): 1.0 ≦ D ≦ 3.0 (c) Density ρ (g / cm ³ ): 1.38 ≦ ρ ≦ 1.39 (d) Initial modulus Y (g / d): 90 ≦ Y ≦ 120 (e) Breaking strength S (g / d): S ≧ 9.0 (f) Knot strength K (g / d): K ≧ 0.5 × S (g) 180 ° C. dry heat shrinkage SH (%): SH ≧ 10

In the polyester constituting the polyester fiber of the present invention, 90% or more of the repeating units of the polyester must be ethylene terephthalate, and preferably 95% or more. The copolymerizable component may be any conventionally known acid component or glycol component. Among them, the copolymerization of a bifunctional phosphorus compound may improve the flame retardancy of the obtained airbag. It is preferable because it improves. In this case, the copolymerization amount is appropriately in the range of 0.3 to 1.5% by weight, preferably 0.6 to 1.1% by weight, as the amount of elemental phosphorus. Phosphorus element amount is 0.
If it is less than 3% by weight, the flame retardancy becomes insufficient, while if it exceeds 1.5% by weight, the strength of the fiber decreases.

Examples of preferably used bifunctional phosphorus compounds include phosphonic acid derivatives or phosphinic acid derivatives represented by the following formula (I) or (II).

[0010]

[Chemical 1]

In the formula, R ₁ represents a hydrocarbon group having 1 to 18 carbon atoms, R ₂ and R ₃ are the same or different groups and represent a hydrogen atom or a hydrocarbon group, and R ₄ is a divalent group. Represents an organic group, and X represents a carboxyl group or an ester thereof. Specifically, dimethyl phenylphosphonate,
(2-Carboxylethyl) methylphosphinic acid and the like are preferably used.

Next, by setting the intrinsic viscosity of the polyester fiber of the present invention to 0.80 or more, the strength and durability of the airbag are improved, and the shock absorbing property when the airbag is momentarily inflated is improved. can do. When the intrinsic viscosity is less than 0.80, the strength and the toughness represented by √ (elongation) cannot be increased, and the impact resistance becomes insufficient.

The single fiber fineness is required to be 3.0 denier or less, preferably 2.0 denier or less. When it exceeds 3.0 denier, the air permeability (0.20 cc / cm ² / sec /
0.5 inch Aq. Below, preferably 0.15 cc /
cm ² /sec/0.5 inch Aq. ) Is difficult to achieve, and the bulkiness when formed into an air bag is increased and the storability is reduced. On the other hand, if it is less than 1 denier, single yarn breakage is likely to occur during spinning, making yarn production difficult, which is not preferable.

Next, the density of the polyester fiber of the present invention must be in the range of 1.38 to 1.39 g / cm ³ . If it is out of this range, it becomes difficult to obtain a fiber having high breaking strength and high knot strength at the same time, and the object of the present invention cannot be achieved.

When the initial modulus of the polyester fiber is too low, the fiber is easily stretched by the impact of high pressure gas, and the burst strength is improved but the air permeability becomes too large. On the other hand, if it is too high, stress concentration occurs when the high-pressure gas receives an impact, and the stress is likely to tear and rupture at the stress concentration point. Therefore, in order to achieve both impact resistance and low air permeability, the initial modulus needs to be in the range of 90 to 120 g / d.

In order to satisfy excellent impact resistance, in addition to the requirement of initial modulus, the breaking strength (tensile strength) of the fiber is large and the knot strength is 50% or more of the breaking strength.
It is important to have a strength of preferably 5.5% or more. That is, when the breaking strength is low, it is necessary to increase the basis weight of the base cloth in order to increase the strength of the airbag, and the storability is deteriorated. Further, even if the breaking strength is sufficiently large, if the knot strength does not have a magnitude corresponding to the breaking strength, tearing easily occurs from the sewn portion due to the impact when the airbag is operated. Therefore, the breaking strength (S) of the fiber needs to be 9.0 g / d or more, and it is important that the knot strength K is 50% or more of the breaking strength.

In addition to the above characteristics, the polyester fiber of the present invention must have a 180 ° C. dry heat shrinkage SH of 10% or more. When it is less than 10%, it is difficult to obtain a high-density woven fabric with low air permeability required for a non-coated base fabric for airbags, even if shrinkage heat treatment is performed after sewing, which is not preferable.

To obtain the polyester fiber of the present invention described above, for example, the following method is used. That is,
Polyester whose intrinsic viscosity is increased by solid-state polymerization, usually 0.85 or higher polymer, is melted and discharged at about 300 ° C., passed through a heating region of 300 ° C. or higher, cooled and solidified, and after applying an oil agent, 500 Wind up at a take-up speed of ~ 1000 m / min. Next, the undrawn yarn obtained is first rotated by a roller heated to a temperature of not less than 90 ° C. and not lower than the glass transition temperature,
After being stretched at a step stretching ratio of 2.5 to 4.0, in order to increase both the breaking strength and the knot strength, a second non-contact type heating atmosphere at 150 to 230 ° C. is passed for 0.5 seconds or more.
Stretching is carried out at a stage draw ratio of 1.5 to 3.0 and then 5 to 10 while being passed through a heating atmosphere of 200 ° C. or lower for 0.5 seconds or more.
% Relaxation shrinkage can be obtained by heat treatment.
In other words, it is important to heat-stretch and relax heat-treat in a lower temperature atmosphere for a longer time than before, so that fibers with high orientation and low crystallinity can be obtained. When the heating roller of No. 2 is used, the roller needs to be heated to a high temperature because it is a heat transfer heating method, and the obtained drawn yarn has a highly oriented and highly crystalline structure, and the knot strength tends to be insufficient.

The total fineness of the drawn yarn is suitably in the range of 210 to 840 denier. The obtained drawn yarn is warped in the untwisted or twisted state, and woven so that the value of woven density (books / inch) × √ (thread fineness) is in the range of 920 to 1025,
After scouring and heat setting, calendering is carried out using a roller heated to 130 to 200 ° C. to further fabricate a high density fabric. At that time, it is preferable to apply tension by a pin tenter or the like so that the fabric is not wrinkled.

[0020]

Since the polyester fiber of the present invention has a low monofilament fineness and a large heat shrinkage ratio, a high density woven fabric having a high airtightness can be easily obtained. In addition, since the modulus is in an appropriate range, the airtightness is not deteriorated by being stretched at the time of inflation, and the rupture of the base cloth due to stress concentration is less likely to occur. Further, since the knot strength and the breaking strength are large in balance, the base cloth having sufficient burst strength can be obtained even if the basis weight of the base cloth is reduced.

Therefore, according to the polyester fiber of the present invention, it is possible to provide a non-coated base fabric for an air bag which is less likely to cause perforation due to inflation and lowers in airtightness and has a good storability.

[0022]

The present invention will be described in more detail with reference to the following examples. Each measurement item was as follows. Intrinsic viscosity It was determined from the solution viscosity measured at 35 ° C. using offochlorophenol as a solvent. Amount of phosphorus element It is a value measured in accordance with "Polymer analysis by instrument (1) Quantification of phosphorus in polymer polymerization" published by Hirokawa Shoten in 1964. Flame retardance A value measured according to JIS L-1091 (D). Air permeability This is a value measured by the JIS L-1096 Frazier method. Burst pressure Ito Seiki Co., Ltd. High-speed burst tester equipped with an airbag bag with an internal volume of 60 liters, and nitrogen gas compressed to 40 kg / cm ² G was instantaneously introduced for 20 to 40 msec.
Burst with, and make the pressure value at that time burst pressure.

[0023]

Example 1 100 parts of dimethyl terephthalate, 54 parts of ethylene glycol, 0.063 parts of calcium acetate and 0.013 parts of cobalt acetate were charged into an autoclave,
Gradually raise the temperature to distill the generated methanol out of the system.
Gradually raise the temperature to 5 ° C and increase the reaction system pressure to 1 mmH.
The temperature was maintained at g and the temperature and the degree of reduced pressure were maintained until the intrinsic viscosity reached 0.70 to carry out the reaction.

When imparting a flame retardant function, after the temperature in the system reaches 220 ° C., (2-carboxyethyl) methylphosphinic acid as a phosphorus compound and ethylene glycol are heated and reacted at a 1: 1 weight ratio. The products obtained are shown in Table 1.
The mixture was added at the ratio shown and the temperature was gradually raised from 220 ° C to 285 ° C, and the pressure of the reaction system was adjusted to 1 mmHg. After that, the reaction was carried out while maintaining this temperature and the degree of reduced pressure until the intrinsic viscosity reached 0.70.

The obtained polymer was dried at 1 mmHg for 8 hours and then the solid phase polymerization time was adjusted at 230 ° C. under a reduced pressure of 0.5 mmHg or less to change the intrinsic viscosity. This solid-state polymerized polymer chip was melt-transported at about 300 ° C. and the hole diameter × the number of holes was 0.35 mm × 250 holes, 0.35 mm × 14.
After discharging using a spinneret of either 0 hole or 0.35 mm × 105 hole, after passing through a heating area of 30 cm from 300 ° C. to 400 ° C., solidifying with cooling air and applying an oil agent with an oiling roller I wound up. This unstretched fiber was fed to a feed roll heated to 85 ° C., and first-stage stretched between the first roll and the first roll at a draw ratio DR ₁ , and then passed through a heated gas bath for 0.8 seconds to draw a draw ratio DR. ₂ performs the second stage stretching, turning the second roll, subsequently 120 ° C. relaxed state of using subsequently heated gas bath perform relaxing DR ₃ DR ₄ between the heating roll (third roll) of Was subjected to a heat treatment for 1 second, wound on a cooling roll (fourth roll), and wound up at 300 m / min to obtain a drawn yarn of 420 denier. The conditions of DR _{1 to} DR _4, stretching temperature and relaxation heat setting temperature are shown in Table 1. The denier was adjusted to 420 by adjusting the discharge amount.

The obtained multifilament has 150 T /
m was twisted, woven into a plain weave, scoured, and heat set. Next, using a pair of metal / elastic roll calenders having a metal roll temperature of 180 ° C. and a linear pressure of 200 kg /
Heat treatment was performed at a speed of 6 cm / min. The obtained woven fabric had a warp density of 55 warps / inch, weft 50 threads / inch, and a thickness of 0.22 mm.

Table 1 shows the fiber properties and the woven fabric properties of the obtained Examples and Comparative Examples.

[0028]

[Table 1]

Claims (2)

[Claims] 1. A polyester fiber for an airbag base fabric, which comprises polyester in which 90 mol% or more of repeating units are ethylene terephthalate, wherein the fiber simultaneously satisfies the following requirements (a) to (g): Polyester fiber for airbag base fabric. (A) Intrinsic viscosity IV: IV ≧ 0.80 (b) Single fiber fineness D (denier): 1.0 ≦ D ≦ 3.0 (c) Density ρ (g / cm ³ ): 1.38 ≦ ρ ≦ 1.39 (d) Initial modulus Y (g / d): 90 ≦ Y ≦ 120 (e) Breaking strength S (g / d): S ≧ 9.0 (f) Knot strength K (g / d): K ≧ 0.5 × S (g) 180 ° C. dry heat shrinkage SH (%): SH ≧ 10 2. The polyester fiber for an airbag base cloth according to claim 1, wherein the polyester contains a bifunctional phosphorus compound in an amount of 0.3 to 1.5% by weight as a phosphorus element amount.