Uncoated polyester base fabric for airbags

Abstract

The present invention addresses the problem of providing a polyester base fabric for airbags using polyester fibers capable of attaining a cost reduction, the polyester base fabric being characterized by retaining the mechanical properties required of fabric for airbags, retaining said performances on a high level over a prolonged period, and meeting the standards for FMVSS No. 302 flammability test.　This non-coated polyester base fabric for airbags is characterized by having an increase in acid value of 150% or less and having a solvent-extractable content of 0.1% or less.

Description

[Technical Field]

[0001] The present invention relates to a polyester base fabric for airbags. More specifically, the present invention relates to a polyester base fabric for airbags that maintains high levels of mechanical properties as an airbag even when subjected to aging. [Background technology]

[0002] In recent years, airbags have become widely used as occupant safety protection devices in automobiles, and their installation locations have expanded to include driver's seat, passenger seat, thigh protection airbags built into the seat, and curtain airbags that deploy along the side windows, resulting in an increasing amount of airbag fabric used per automobile. The fabrics currently used for airbags are primarily made of polyamide fibers, particularly nylon 6,6 fibers, which have properties suitable for airbag fabrics. However, nylon 6,6 fibers are relatively expensive, and the cost burden is increasing as airbags become more widespread. Therefore, there is a demand for fabrics made of polyester fibers, which have lower raw yarn costs than nylon 6,6 fibers.

[0003] Airbag fabrics are required to maintain sufficient performance even in accelerated aging tests that simulate the environment in which they will be used. It is known that polyester fibers are susceptible to deterioration in humid and hot environments. To meet this requirement, for example, Patent Document 1 proposes polyester fibers intended to use a catalyst other than an antimony compound.

[0004] However, such fibers have the problem of being slightly inferior in thermal stability. While such fibers have been used in industrial materials such as films, they have not been used in airbags, which are life-threatening applications. They have not been studied as uncoated base fabrics for airbags, and have not been substantially disclosed as uncoated base fabrics made of polyester, which have excellent hydrolysis resistance. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-242043 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide a polyester base fabric for airbags that uses polyester fibers and maintains high levels of mechanical properties even with aging, and at the same time has excellent thermal stability. An object of the present invention is to provide a polyester base fabric for airbags that maintains high levels of mechanical properties even with aging, and at the same time has excellent thermal stability. [Means for solving the problem]

[0007] The present inventors have conducted extensive research to solve the above problems and have finally completed the present invention.

[0008] (1) An uncoated polyester base fabric for airbags, characterized by satisfying the requirement that the acid value increase rate after 24 hours at 121°C and 100% relative humidity is 150% or less, and conforming to the standard of the combustion test for automotive interior materials, FMVSS No. 302. The acid number increase rate (AR) after 24 hours at 121°C and 100% relative humidity is calculated using the following formula: AR (%) = AE / AI x 100 Here, AE (eq / ton) is the acid value of the uncoated polyester base fabric for airbags after 24 hours at 121°C and 100% relative humidity. AI (eq / ton) indicates the initial acid value of the polyester base fabric for uncoated airbags. (2) A polyester base fabric for uncoated airbags, characterized in that the solvent extraction rate of the base fabric is 0.1% or less. (3) A polyester base fabric for uncoated airbags, characterized in that the phosphorus catalyst content is 10 ppm or more. (4) A polyester base fabric for uncoated airbags, characterized in that the aluminum catalyst content is 5 ppm or more. [Effects of the Invention]

[0009] According to the present invention, even if a base fabric uses a relatively inexpensive polyester fiber, the performance can be maintained at a high level even if it changes over time when used in an airbag, and at the same time, it has excellent thermal stability and conforms to the standards for combustion tests. It is possible to provide a polyester base fabric for airbags. DETAILED DESCRIPTION OF THE INVENTION

[0010] The technical concept of the present invention is mainly comprised of the following elements: the increase in acid value after 24 hours of aging treatment at 121°C and 100% relative humidity is 150% or less. Note that the pressure in a 121°C, 100% RH environment is 2 atmospheres, which is the saturated vapor pressure.

[0011] The acid number increase rate (AR) after 24 hours at 121°C and 100% relative humidity was defined by the following formula: AR(%)=AE / AI×100 An oxidation increase rate (AR) of 100% indicates no change in oxidation, and an AR greater than 100% indicates increased oxidation. Here, AE (eq / ton) indicates the acid value of the uncoated airbag polyester fabric after 24 hours at 121°C and 100% relative humidity, and AI (eq / ton) indicates the initial acid value of the uncoated airbag polyester fabric.

[0012] The present inventors conducted a detailed analysis of polyester fabrics and found that, as long as the acid value increase rate after 24 hours at 121°C and 100% relative humidity is 150% or less, a polyester fabric can be used to obtain an airbag fabric that is comparable in resistance to aging to polyamide fabrics. A more preferred acid value increase rate after 24 hours at 121°C and 100% relative humidity is 140% or less. There is no particular lower limit for the acid value increase rate.

[0013] On the other hand, the tensile strength retention rate of the base fabric after 3,000 hours of treatment at 80°C and 95% relative humidity, which is one of the aging treatment conditions used by automobile manufacturers, is considered to be an important factor in indicating aging resistance.

[0014] Detailed analysis by the inventors revealed that there is a strong correlation between the tensile strength retention rate after 3,000 hours of treatment at 80°C and 95% relative humidity and the acid number increase rate after 24 hours of treatment at 121°C and 100% relative humidity. It was confirmed that the acid number increase rate after 24 hours of treatment at 121°C and 100% relative humidity can be an important indicator of hydrolysis resistance. In the present invention, the relative value of the tensile strength after treatment, when the tensile strength before treatment is taken as 100%, is defined as the tensile strength retention after treatment. The tensile strength retention after treatment for 3000 hours at 80°C and a relative humidity of 95% is preferably 80% or more, and more preferably 90% or more.

[0015] Treatment at 121°C and 100% relative humidity for 24 hours is a common treatment condition for polyester film. By treating under this environment, the treatment time can be more rapidly shortened than under an environment of 80°C and 95% relative humidity for 3,000 hours.

[0016] In the present invention, the main factor in achieving an acid value increase rate of 150% or less after 24 hours at 121°C and 100% relative humidity is the following: polyester fiber using a catalyst other than a general-purpose antimony compound.

[0017] The catalyst other than an antimony compound is a polyester polymerization catalyst composed of an aluminum compound and a phosphorus compound or a phenolic compound, particularly a phosphorus compound having a phenol moiety in the same molecule, as cited in JP 2002-242043 A. Use of this catalyst makes it possible to suppress the generation of foreign matter due to metal precipitation, contributing to hydrolysis resistance.

[0018] The catalyst concentration of the aluminum compound is 5 ppm or more to exhibit catalytic effects. A more preferred catalyst concentration is 10 ppm or more. Furthermore, since a catalyst concentration of the aluminum compound that is too high may lead to the generation of foreign matter, a concentration of 25 ppm or less is preferred.

[0019] The catalyst concentration of the phosphorus compound is 10 ppm or more to exhibit catalytic effects. A more preferred catalyst concentration is 20 ppm or more. Furthermore, since a too high catalyst concentration of the phosphorus compound may lead to the generation of foreign matter, a concentration of 50 ppm or less is preferred.

[0020] However, the use of such catalysts results in slightly lower thermal stability compared to polyester fibers using antimony catalysts. While there is a flammability standard for automobile interior materials (FMVSS No. 302), polyester fibers using such catalysts do not meet the standard.

[0021] After extensive research, the present inventors have found that the key to overcoming these problems is to reduce the amount of residual organic matter derived from the spinning oil, i.e., to reduce the solvent extraction rate. The solvent extraction rate of the present invention was calculated as a ratio of the mass of the extract extracted using the test method specified in ASTM D 2257-98 to the mass of the polyester base fabric before treatment.

[0022] In particular, when the acid value increase rate is reduced, organic matter tends to remain, and conventional manufacturing methods have not been able to reduce the solvent extraction rate, so it has been thought that it is difficult to achieve both a reduced acid value increase rate and flammability at the same time.

[0023] The present inventors conducted a detailed analysis of polyester fabrics using a polyester polymerization catalyst comprising an aluminum compound and a phosphorus compound or a phenolic compound, particularly a phosphorus compound having a phenol moiety in the same molecule, and found that if the solvent extraction rate of the polyester fabric is 0.1% or less, a polyester airbag fabric that complies with the standard of the flammability test specified in FMVSS No. 302 (Federal Motor Vehicle safety Standards No. 302) can be obtained. A more preferable solvent extraction rate is 0.05% or less. The lower limit of the solvent extraction rate is preferably 0.01% or more in consideration of the tear strength of the airbag base fabric.

[0024] The inventors have found two main methods for reducing the solvent extraction rate to 0.1% or less: immersion in hot water with a bath temperature of 90°C or higher, followed by vacuum suction at a pressure of 30 kPa or higher. While baths have been used in the past for shrinking airbag fabrics, the bath temperature and vacuum pressure were not set to control the solvent extraction rate. Through detailed investigation, the inventors have found that the solvent extraction rate can be effectively reduced by suctioning the solvent-containing water with a high vacuum pressure following treatment in a high-temperature bath.

[0025] The bath temperature during fabric processing, i.e., the temperature of the hot water, is preferably 90°C or higher, more preferably 95°C or higher, and even more preferably 98°C or higher. At 90°C or higher, the amount of fatty acid esters, the main remaining component, can be reduced, thereby lowering the solvent extraction rate of the polyester fabric. The upper limit of the bath temperature is 100°C, the boiling point of water.

[0026] As a result of extensive research, the inventors have found that if the vacuum pressure after the hot water bath during fabric processing is 30 kPa or more, the solvent contained in the fibers can be reduced, thereby lowering the solvent extraction rate of the polyester fabric. A more preferred vacuum pressure is 35 kPa or more. The upper limit of the vacuum pressure is preferably 45 kPa or less from the viewpoint of operability during fabric processing.

[0027] The polyester airbag fabric of the present invention is preferably composed of polyester fibers with a total fineness of 200 to 555 dtex. Polyester fibers tend to have higher rigidity than nylon 6,6 fibers, resulting in reduced packability. However, if the total fineness is 200 dtex or more, there is no need to increase the weave density excessively, which prevents an excessive increase in the binding force between the warp and weft yarns and helps to keep packability in the airbag module within an appropriate range. Furthermore, if the total fineness is 555 dtex or less, it is easier to prevent an excessive increase in the rigidity of the woven yarns themselves.

[0028] The polyester base fabric for airbags of the present invention is preferably composed of polyester fibers having a single yarn fineness of 6.0 dtex or less. If the single yarn fineness is 6.0 dtex or less, spinning operability and storability of the airbag can be ensured.

[0029] Examples of polyester fibers used in the polyester base fabric for airbags of the present invention include polyethylene terephthalate and polybutylene terephthalate, and may also be fibers made of copolymerized polyesters in which polyethylene terephthalate or polybutylene terephthalate is copolymerized with an aliphatic dicarboxylic acid such as isophthalic acid, 5-sodium sulfoisophthalic acid, or adipic acid as an acid component.

[0030] The polyester base fabric for airbags of the present invention preferably has a weave density of 40 threads / 2.54 cm or more in both the warp and weft directions, more preferably 46 threads / 2.54 cm or more. A weave density of 46 threads / 2.54 cm or more can prevent the base fabric structure from collapsing during weaving. There is no particular upper limit to the weave density, but due to restrictions on weft insertion during weaving, it is preferably 70 threads / 2.54 cm or less.

[0031] In the present invention, the weave density is measured according to JIS L1096 (2010) 8.6.1. Specifically, the sample is placed on a flat table, and unnatural wrinkles and tension are removed. Then, the number of warp and weft threads in 2.54 cm sections is counted at five different locations, and the average value for each unit length is calculated to determine the weave density.

[0032] The tensile strength of the polyester airbag fabric of the present invention is preferably 500 N / cm or more, more preferably 550 N / cm or more, from the viewpoint of mechanical properties. There is no particular upper limit to the tensile strength, but in view of the relationship between the total fineness and tensile strength of the polyester multifilaments used and the weave density of the airbag fabric, it is preferably 1000 N / cm or less, more preferably 900 N / cm or less.

[0033] In the present invention, the tensile strength of the base fabric is measured according to JIS L1096 (2010) 8.14.1 A (labeled strip method). Specifically, a test piece is gripped with a tensile tester under an initial load, and the test is performed under the conditions of a test piece width of 50 mm, grip spacing of 200 mm, and a pulling speed of 200 m / min, and the strength at break (N) is measured. However, specimens that break within 10 mm from the grip or abnormal breaks are excluded.

[0034] A typical method for producing the polyester base fabric for uncoated airbags of the present invention can be summarized as follows, but the method is not limited to this method as long as it produces the same effects as the present invention. This method for producing a polyester base fabric for uncoated airbags involves weaving polyester multifilament yarn spun from a polymer containing an aluminum compound and a phosphorus compound, passing the yarn through a hot water bath at 90°C or higher, applying a vacuum pressure of 30 kPa or higher, and then drying the weaved yarn. It is desirable to carry out "passing through a hot water bath at 90°C or higher" and "suction at a vacuum pressure of 30 kPa or higher" consecutively. Furthermore, in the manufacturing method of the present invention, there is no problem if a heat setting treatment, such as a pin tenter, is added to the above manufacturing method.

[0035] The uncoated airbag polyester base fabric of the present invention has excellent properties, such as heat resistance and resistance to deterioration of mechanical strength over time, and can therefore be suitably used as a base fabric when coating is applied to one or both sides. In this case, elastomer resins are preferred as the coating resin, with silicone-based resins being the most effective. Conventional, well-known methods can be used to apply the resin, but knife coating, particularly knife-on-air coating, is most preferred in terms of ease of adjusting the coating amount and the impact of foreign matter (protrusions) being mixed in. Airbags using the uncoated airbag polyester base fabric of the present invention and the coated airbag polyester base fabric to which the above-mentioned coating has been added are suitable for use in, for example, driver's seat airbags, passenger seat airbags, curtain airbags, side airbags, knee airbags, seat airbags, reinforcing fabrics, etc. The uncoated airbag polyester base fabric of the present invention and the coated airbag polyester base fabric to which the above coating has been added also have particularly excellent storage capacity, making them suitable for use in airbags that require particularly high storage capacity. Specifically, the present invention can be used for driver's airbags, passenger's airbags, curtain airbags, side airbags, and knee airbags. [Example]

[0036] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to the following examples, and it is of course possible to carry out the present invention with appropriate modifications within the scope of the above and below-mentioned aims, and all such modifications are included within the technical scope of the present invention. The test methods for various properties used in the following examples are as follows.

[0037] <Acid value of polyester base fabric> A 0.2 g sample (polyester base fabric) dried at 70°C for 16 hours was weighed out. 10 ml of benzyl alcohol and the weighed sample were added to a test tube, which was then immersed in an oil bath heated to 205°C. The sample was dissolved using a magnetic stirrer while stirring with a glass rod for 5 minutes. The titration was performed using 0.04 mol / L potassium hydroxide solution (ethanol solution), using phenol red as the indicator. The end point was the change from yellow-green to pale pink, and the amount of carboxyl end groups in the esterification reaction product was measured and expressed as eq / ton of polyester base fabric.

[0038] <Weave density of base fabric> Measurements were made based on JIS L1096 (2010) 8.6.1. The sample was placed on a flat table, and after removing any unnatural wrinkles or tension, the number of warp and weft threads in 2.54 cm sections was counted at five different locations, and the average value for each unit length was calculated to determine the density.

[0039] <Tensile strength and elongation at break of base fabric> Measurements were made based on JIS L1096 (2010) 8.14.1 A (Labeled Strip Method). Test pieces were gripped with a tensile testing machine under an initial load, and the test was conducted under the following conditions: test piece width 50 mm, grip spacing 200 mm, and tensile speed 200 m / min. The strength (N) and elongation (mm) at break were measured. However, specimens that broke within 10 mm of the grip or abnormally broken specimens were excluded.

[0040] <Total fineness of raw yarn> Measurement was performed in accordance with JIS L1013 (2010) 8.3.1. Specifically, an initial load was applied to a sample exactly 90 cm long, and its bone dry mass was measured. The corrected fineness (dtex) was calculated based on the following formula (7), and the average value of five measurements was taken as the total fineness. F0=1000×m / 0.9×+(100+R0) / 100 ···(7) F0: normal fineness (dtex), L: length of sample (m), m: bone dry mass of sample (g), R0: official moisture content (%)

[0041] <Aluminum and phosphorus catalyst content> Metal concentrations were quantified by ICP optical emission spectrometry. The measurement device used was a SPECTRO BLUE TI (manufactured by SPECTRO). The measurement conditions were as follows: plasma power: 1400 W, plasma gas flow rate: 12 L / min, nebulizer gas flow rate: 1.0 L / min, auxiliary gas flow rate: 1.0 L / min. The conditions for quantifying aluminum and phosphorus are as follows: an yttrium nitrate solution is added to approximately 0.5 g of sample, and after hydrolysis, the residue is dissolved in 1.2 N hydrochloric acid, and the resulting sample is measured. The conditions for quantifying aluminum are also as follows: approximately 0.5 g of sample is carbonized and incinerated, and the residue is dissolved in 1.2 N hydrochloric acid, and the resulting sample is measured. The concentrations (by weight) of aluminum and phosphorus obtained in this measurement are defined as the concentrations of aluminum and phosphorus contained in the catalyst of the present invention.

[0042] Example 1: 555 dtex / 144 f polyester multifilament yarns (single yarn cross section is round) were used for the warp and weft, spun from a polymer containing an aluminum compound and a phosphorus compound. The warp and weft were woven in a plain weave using a water jet loom with a set weave density of 51 threads / 2.54 cm. The fabric was then passed through a 98°C hot water shrinkage bath without drying, subjected to a vacuum pressure of 35 kPa, and then passed through a 160°C heating oven to obtain an uncoated base fabric. The production conditions and the physical properties of the obtained uncoated base fabric are shown in Table 1. In Table 1, 24 hours at 121°C and 100% relative humidity is expressed as 121°C 100% RH 24H. Ta.

[0043] Example 2: 555 dtex / 144 f polyester multifilament yarns (single yarn cross section is round) were used for the warp and weft, spun from a polymer containing an aluminum compound and a phosphorus compound. The warp and weft were woven in a plain weave using a water jet loom with a set weave density of 51 threads / 2.54 cm. The fabric was then passed through a 98°C hot water shrinkage bath without drying, subjected to a vacuum pressure of 40 kPa, and then passed through a 160°C heating oven to obtain an uncoated base fabric. The production conditions and the physical properties of the obtained uncoated base fabric are shown in Table 1.

[0044] Example 3: 555 dtex / 144 f polyester multifilament yarns (single yarn cross section is round) were used for the warp and weft, spun from a polymer containing an aluminum compound and a phosphorus compound. The warp and weft were woven in a plain weave using a water jet loom with a set weave density of 51 threads / 2.54 cm. The fabric was then passed through a 90°C hot water shrinkage bath without drying, subjected to a vacuum pressure of 30 kPa, and then passed through a 160°C heating oven to obtain an uncoated base fabric. The production conditions and the physical properties of the obtained uncoated base fabric are shown in Table 1.

[0045] Example 4: 470 dtex / 96 f polyester multifilament yarns (single yarn cross section is round) were used for the warp and weft, spun from a polymer containing an aluminum compound and a phosphorus compound. The warp and weft were woven in a plain weave using a water jet loom with a set weave density of 56 threads / 2.54 cm. The fabric was then passed through a 98°C hot water shrinkage bath without drying, subjected to a vacuum pressure of 35 kPa, and then passed through a 160°C heating oven to obtain an uncoated base fabric. The production conditions and the physical properties of the obtained uncoated base fabric are shown in Table 1.

[0046] Comparative Example 1: 555 dtex / 144 f polyester multifilament yarns (round single yarn cross section) were used for the warp and weft, spun from a polymer containing an aluminum compound and a phosphorus compound. The warp and weft were woven in a plain weave using a water jet loom with a set weave density of 51 threads / 2.54 cm. The fabric was then passed through a 50°C hot water shrinkage bath without drying, subjected to a vacuum pressure of 20 kPa, and then passed through a 160°C heating oven to obtain an uncoated base fabric. The production conditions and the physical properties of the resulting uncoated base fabric are shown in Table 1.

[0047] Comparative Example 2: 555 dtex / 144 f polyester multifilament yarns (round single yarn cross section) were used for the warp and weft, spun from a polymer containing an antimony compound. The warp and weft were woven in a plain weave using a water jet loom with a set weave density of 51 threads / 2.54 cm. The fabric was then passed through a 50°C hot water shrinkage bath without drying, subjected to a vacuum pressure of 20 kPa, and then passed through a 160°C heating oven to obtain an uncoated base fabric. The production conditions and the physical properties of the resulting uncoated base fabric are shown in Table 1.

[0048] [Table 1] [Industrial Applicability]

[0049] The present invention provides a polyester base fabric for airbags that has high restraint performance for receiving an occupant when deployed while maintaining the mechanical properties of an airbag, and further maintains this performance at a high level even with aging. Therefore, it is possible to popularize relatively low-cost polyester airbags, which will greatly contribute to the development of the industry.

Claims

1. An uncoated polyester base fabric for airbags, the base fabric using polyester fibers, the polyester containing an aluminum compound and a phosphorus compound or a phenolic compound as catalysts, the base fabric having a solvent extraction rate of 0.1% or less, an acid value increase rate of 150% or less after 24 hours at 121°C and a relative humidity of 100%, and conforming to the standard of the combustion test for automotive interior materials, FMVSS No. 302 combustion test.

2. 2. The polyester base fabric for uncoated airbags according to claim 1, wherein the phosphorus catalyst concentration is 10 ppm or more.

3. 3. The polyester base fabric for uncoated airbags according to claim 1, wherein the aluminum catalyst concentration is 5 ppm or more.

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