Polyamide fiber for airbag and method for producing the same

Abstract

The present invention provides a polyamide fiber which can achieve suppression of fabric wrinkles after heat shrinkage processing of a fabric for an airbag and suppression of deviation in air permeability characteristics based on improvement in uniformity. The present invention relates to a polyamide fiber for an airbag and a method for manufacturing the polyamide fiber for an airbag. The polyamide fiber for an airbag is characterized in that the fineness of the fiber is 200 dtex or more and 800 dtex or less, and the stress retention rate obtained by a predetermined step is 3.0% or more. The method for manufacturing the polyamide fiber for an airbag is characterized in that, in a heat setting step and a relaxation step, the contact time between a roll reaching 190°C or more and a filament is 30 msec or more and less than 110 msec, the temperature of the heat setting roll is 190°C or more and 205°C or less, the temperature of the relaxation roll exceeds 100°C and is less than 190°C, and the speed ratio of the relaxation roll to the heat setting roll satisfies the following formula: 1.00 < relaxation roll speed / heat setting roll speed < 1.10.

Description

Technical Field

[0001] The present invention relates to polyamide fibers for airbags and a method for manufacturing the same. Background Art

[0002] Polyamide fibers have various material uses by forming high-density fabrics. Among them, the airbag use is important.

[0003] An airbag device is a safety device that restrains an occupant in a collision accident of a vehicle. The airbag device includes a collision sensor, an inflator as a gas generator, and an airbag. The airbag is composed of a fabric of polyamide fibers, which withstands the heat in the reaction of the propellant of the inflator and unfolds within several tens of milliseconds, and functions to absorb the intrusion energy of the occupant by the expanding gas of the unfolded airbag. For this function, a smaller air permeability of the fabric constituting the bag is required. In addition, for the purpose of improving occupant restraint, the airbag expands and unfolds, and in order to maintain the internal pressure of the airbag above a certain value when receiving the occupant, the requirement for preventing gas leakage from the fabric when the internal pressure increases becomes higher.

[0004] It is known that for a fabric for an airbag, after weaving is performed at a high density, the fabric is heated in a post-weaving processing step to shrink it, thereby increasing the density of the fabric and reducing the air permeability.

[0005] In Patent Document 1 below, a method is disclosed in which the physical properties of the fibers used for the fabric are adjusted to improve the weft insertion stability and the physical property uniformity of the fabric.

[0006] In Patent Document 2 below, a fabric having excellent anti-seam properties and burst resistance is disclosed by controlling the heat shrinkage behavior of the fibers.

[0007] Prior Art Documents

[0008] Patent Documents

[0009] Patent Document 1: Japanese Patent No. 5253685

[0010] Patent Document 2: Japanese Patent No. 5969999 Summary of the Invention

[0011] Problems to be Solved by the Invention

[0012] In the processing steps of the woven fabric, regarding the behavior of the fibers constituting the fabric, the fibers are heated to generate shrinkage stress, causing the fabric to shrink. Subsequently, the heating is stopped and the fibers return to room temperature, reducing the shrinkage stress and making the fabric loose. At this time, due to the fabric being loose, the tension is not uniformly transmitted across the entire fabric, and wrinkles may form on the fabric surface. Additionally, due to the reduced fabric uniformity, there may be deviations in the air permeability performance. Therefore, there is a need for further improvement in suppressing fabric wrinkles and enhancing uniformity after the processing steps.

[0013] In Patent Document 1, no research has been conducted on suppressing the reduction in fabric uniformity during the post-weaving heat treatment process. Additionally, regarding air permeability, no research has been carried out on suppressing the change in air permeability during internal pressure changes, which is required to be higher from the perspective of occupant protection using the air permeability under a certain specific pressure condition as an index, leaving room for improvement.

[0014] In Patent Document 2, during the processing steps, processing at a relatively low temperature such as 120°C is assumed, and no research has been conducted on the thermal shrinkage behavior in the temperature range of the processing steps where the fabric shrinks at high temperatures, which has been studied in the present invention. Additionally, no research has been carried out on improving the fabric uniformity after the heat shrinkage processing and suppressing the change in air permeability during internal pressure changes, leaving room for improvement.

[0015] In view of this technical level, the problem to be solved by the present invention is to provide a polyamide fiber for airbags that can suppress fabric wrinkles after heat shrinkage processing of airbag fabrics and suppress deviations in air permeability characteristics based on improved uniformity.

[0016] Means for Solving the Problem

[0017] The inventors of the present invention conducted in-depth research to solve the above problems and found that by making the thermal shrinkage behavior of the yarns constituting the fabric during and after heating a specific value, the wrinkles and uniformity of the fabric can be improved, thus completing the present invention.

[0018] That is, the present invention is as follows.

[0019] [1] A polyamide fiber for airbags, characterized in that

[0020] The fineness of the fiber is 200 dtex or more and 800 dtex or less, and the stress retention rate obtained through the following steps 1) to 6) is 3.0% or more:

[0021] 1) Immerse the fiber in water at 20°C for 5 seconds. After taking it out, fix it on a thermal shrinkage stress measuring machine under the state of applying an initial load of 0.4 mN / dtex to the fiber.

[0022] 2) Set the heating furnace to 130 °C, insert the fiber into the heating furnace and heat for 5 min;

[0023] 3) Take out the fiber from the heating furnace, set the temperature of the heating furnace to 190 °C and raise the temperature. During this period, hold the fiber firmly without releasing it and maintain a fixed length;

[0024] 4) After the device is heated to 190 °C, insert the fiber into the heating furnace and heat for 3 min, and measure the shrinkage stress at the moment 3 min after heating;

[0025] 5) Take out the fiber from the heating furnace and measure the shrinkage stress at the moment 3 min after taking it out; and

[0026] 6) Set the value obtained by subtracting the value of the initial load given in step 1) from the shrinkage stress obtained in step 4) as [shrinkage stress in step 4)]. In addition, set the value obtained by subtracting the value of the initial load given in step 1) from the shrinkage stress obtained in step 5) as [residual stress in step 5)]. Calculate the stress retention rate by the following formula:

[0027] Stress retention rate (%) = {[Residual stress in step 5)] / [Shrinkage stress in step 4)]} × 100.

[0028] [2] The polyamide fiber for airbag according to [1] above, wherein the stress retention rate is 5.0% or more.

[0029] [3] The polyamide fiber for airbag according to [1] or [2] above, wherein the tensile strength is 7.5 cN / dtex or more.

[0030] [4] The polyamide fiber for airbag according to any one of [1] to [3] above, wherein the fineness is 340 dtex or more and 500 dtex or less.

[0031] [5] The polyamide fiber for airbag according to any one of [1] to [4] above, wherein the fineness of a single filament is 1.0 dtex or more and 7.0 dtex or less.

[0032] [6] The polyamide fiber for airbag according to any one of [1] to [5] above, wherein the polyamide fiber for airbag is polyamide 6,6 fiber.

[0033] [7] An airbag fabric, wherein the airbag fabric comprises the polyamide fiber for airbag according to any one of [1] to [6] above.

[0034] [8] A method for manufacturing a polyamide fiber for airbag, the polyamide fiber for airbag being the polyamide fiber for airbag according to any one of [1] to [6] above, characterized in that

[0035] The manufacturing method of the airbag polyamide fiber comprises the following steps:

[0036] A step of performing thermal stretching after applying an aqueous sizing agent to the filaments spun from a spinneret;

[0037] A stretching step;

[0038] A heat setting step; and

[0039] A relaxation step,

[0040] In this heat setting step and this relaxation step, the contact time between the roll at 190 °C or higher and the filaments is 30 msec or more and less than 110 msec, the temperature of the heat setting roll in this heat setting step is 190 °C or higher and 205 °C or lower, the temperature of the relaxation roll in this relaxation step exceeds 100 °C and is lower than 190 °C, and the speed ratio of this relaxation roll to this heat setting roll satisfies the following formula:

[0041] 1.00 < relaxation roll speed / heat setting roll speed < 1.10.

[0042] Effects of the Invention

[0043] By using the airbag polyamide fiber of the present invention, it is possible to provide a fabric for airbags with excellent suppression and uniformity of fabric wrinkles. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 is an example of the manufacturing equipment for the airbag polyamide fiber of this embodiment (three-stage stretching process). DETAILED DESCRIPTION OF THE INVENTION

[0045] Hereinafter, embodiments of the present invention will be described in detail.

[0046] An embodiment of the present invention is an airbag polyamide fiber, characterized in that the fineness of the fiber is 200 dtex or more and 800 dtex or less, and the stress retention rate obtained by the following steps 1) to 6) is 3.0% or more:

[0047] 1) Immerse the fiber in water at 20 °C for 5 seconds, and after taking it out, fix it on a heat shrinkage stress measuring machine under the state of applying an initial load of 0.4 mN / dtex to the fiber;

[0048] 2) Set the heating furnace to 130 °C, insert the fiber into the heating furnace and heat it for 5 min;

[0049] 3) Take out the fiber from the heating furnace, set the temperature of the heating furnace to 190 °C and raise the temperature. During this period, keep the fixation of the fiber without being released and maintain a constant length;

[0050] 4) After the device is heated to 190 °C, insert the fiber into the heating furnace and heat it for 3 min, and measure the shrinkage stress at the moment 3 min after the start of heating;

[0051] 5) Take out the fiber from the heating furnace and measure the shrinkage stress at the moment 3 min after taking it out; and

[0052] 6) Set the value obtained by subtracting the value of the initial load applied in step 1) from the shrinkage stress obtained in step 4) as [the shrinkage stress in step 4)]. In addition, set the value obtained by subtracting the value of the initial load applied in step 1) from the shrinkage stress obtained in step 5) as [the residual stress in step 5)], and calculate the stress retention rate by the following formula:

[0053] Stress retention rate (%) = {[residual stress in step 5)] / [shrinkage stress in step 4)]} × 100.

[0054] Examples of the polymer constituting the polyamide fiber of the present embodiment include polyamide 6, polyamide 6,6, polyamide 11, polyamide 12, polyamide 6,10, polyamide 6,12, polyamide 4,6, copolymers thereof, and polymers formed from mixtures thereof. Among them, polyamide 6,6 polymers are preferred, and polyamide 6,6 fibers mainly contain polyhexamethylene adipamide fibers. Polyhexamethylene adipamide fiber refers to a polyamide fiber composed of 100% of 1,6-hexanediamine and adipic acid with a melting point of 250 °C or higher, but polyamide 6,6 fibers can also be copolymerized or blended with polyamide 6, polyamide 6,I, polyamide 6,10, polyamide 6,T, etc. within the range where the melting point is not lower than 250 °C. In addition, various additives commonly used to improve the productivity or properties in the manufacturing process and processing process of the raw yarn can be included in the fiber. For example, it can contain heat stabilizers, antioxidants, light stabilizers, lubricants, antistatic agents, plasticizers, thickeners, pigments, flame retardants, etc.

[0055] The total fineness of the polyamide fiber is preferably in the range of 200 dtex or more and 800 dtex or less, more preferably 200 dtex or more and 700 dtex or less, further preferably 300 dtex or more and 600 dtex or less, and particularly preferably 340 dtex or more and 500 dtex or less. When the total fineness is 200 dtex or more and the larger it is, the more sufficient the mechanical strength is. When it is 800 dtex or less and the smaller it is, the better the accommodation performance is.

[0056] As the single filament fineness, it is preferably in the range of 1 dtex or more and 7 dtex or less, more preferably 1.5 dtex or more and 6.0 dtex or less, further preferably 2.5 dtex or more and 5.7 dtex or less, and particularly preferably 3.3 dtex or more and 4.9 dtex or less. If the single filament fineness is 1 dtex or more, there are no problems with the productivity of the filament, and the weavability is appropriate. The smaller the single filament fineness is within the range of 7 dtex or less, the softer the resulting fabric is, it can be folded compactly with improved accommodation, and it is easy to obtain low air permeability even under a high pressure difference such as when deploying an airbag.

[0057] In the present embodiment, the polyamide fiber is preferably woven and used for the airbag fabric. As the airbag fabric, a high-density fabric is preferred in terms of mechanical properties and low air permeability. To produce a high-density fabric, there are methods to increase the weaving density during weaving and methods to densify the fabric by shrinking it during the heat treatment in the weaving process. When the weaving density during weaving becomes high, it may cause poor weavability due to friction between warp threads and poor productivity due to an increase in the number of weft thread insertions per unit length. Therefore, in order to achieve a fabric that combines weavability, productivity, and high density, densification formed by heat shrinkage in the post-weaving processing step is effective.

[0058] In the post-weaving processing step, for the fabric, first, scouring using water is performed, and then, after passing through a drying process using a hot air dryer, a heat roller heating machine, etc., the fabric is sent to a heat setting process using a heat roller heating machine, a stenter, etc., and finally wound up. At this time, regarding the thermal behavior of the yarns constituting the fabric, after immersing them in water, they are temporarily heated in the drying process, naturally cooled, and then heated again using the heat setting process, and then naturally cooled. At this time, the yarns are in a constrained state due to being formed into a fabric. As an index of the thermal behavior of the yarns in this processing step, the thermal shrinkage stress of the fibers is measured using the following steps 1) to 6).

[0059] Step 1): Immerse the fiber in water at 20 °C for 5 seconds. After taking it out, fix it on a thermal shrinkage stress measuring machine in a state where an initial load of 0.4 mN / dtex is applied to the fiber.

[0060] Step 2): Set the heating furnace to 130 °C, insert the fiber into the heating furnace, and heat for 5 min.

[0061] Step 3): Take out the fiber from the heating furnace, set the temperature of the heating furnace to 190 °C and raise the temperature. During this period, hold the fixation of the fiber without being released and maintain a constant length.

[0062] Step 4) After the apparatus is heated to 190°C, insert the fiber into the heating furnace and heat for 3 min, and measure the shrinkage stress at the moment 3 min after the start of heating;

[0063] Step 5) Take out the fiber from the heating furnace and measure the shrinkage stress at the moment 3 min after taking it out; and

[0064] Step 6) Set the value obtained by subtracting the value of the initial load applied in Step 1) from the shrinkage stress obtained in Step 4) as [shrinkage stress in Step 4)]. In addition, set the value obtained by subtracting the value of the initial load applied in Step 1) from the shrinkage stress obtained in Step 5) as [residual stress in Step 5)], and calculate the stress retention rate by the following formula:

[0065] Stress retention rate (%) = {[residual stress in Step 5)] / [shrinkage stress in Step 4)]} × 100. In addition, measure the shrinkage stress in Step 4) in the heating furnace.

[0066] The above Step 4) corresponds to the heating in the heat setting process, and is a process in which the fabric is densified by thermal shrinkage. In addition, the above Step 5) corresponds to the natural cooling process to the winding process after the heat setting process, and relaxation occurs corresponding to the stress reduction.

[0067] Here, the present inventors found that the stress retention rate (%) shown in Step 6) is related to the appearance and uniformity of the processed fabric.

[0068] That is, the stress retention rate represents the ratio of the residual stress after natural cooling to the thermal shrinkage stress generated in the heat setting process. The stress retention rate of the polyamide fiber in the present embodiment is 3% or more, preferably 5% or more. If the stress retention rate is 3% or more, the relaxation of the fabric after the heat shrinkage process is small, and the tightened state of the fabric can be maintained. Therefore, the air permeability physical properties of the fabric are made uniform, the tension applied to the constituent yarns becomes uniform, and the generation of wrinkles can be suppressed. In addition, the upper limit of the stress retention rate is not particularly limited, and can be 30% or less, 20% or less, or 10% or less.

[0069] The (tensile) strength of the polyamide fiber is preferably in the range of 7.5 cN / dtex or more and 11.5 cN / dtex or less, more preferably 8.0 cN / dtex or more and 11.5 cN / dtex or less, and particularly preferably 8.2 cN / dtex or more and 11.5 cN / dtex or less. If the strength is 7.5 cN / dtex or more, desired mechanical properties can be obtained, and it is sufficient as a fiber for industrial materials. In addition, if the strength is 11.5 cN / dtex or less, the fiber quality is excellent. For example, the occurrence frequency of fuzzing is also small, and it does not cause a decrease in the spinning yield or lead to weaving failures in post-processing.

[0070] The polyamide fiber of the present embodiment can be manufactured by the melt spinning method. Figure 1 As an example of the apparatus for manufacturing polyamide fiber, a three-stage drawing process is shown.

[0071] Another embodiment of the present invention is a method for manufacturing the polyamide fiber for an airbag, characterized in that the manufacturing method includes the following steps:

[0072] A step of performing hot drawing after applying an aqueous sizing agent to the filaments spun from the spinneret;

[0073] A drawing step;

[0074] A heat setting step; and

[0075] A relaxation step,

[0076] In this heat setting step and this relaxation step, the contact time between the roll at 190 °C or higher and the filaments is 30 msec or more and less than 110 msec, the temperature of the heat setting roll in this heat setting step is 190 °C or higher and 205 °C or lower, the temperature of the relaxation roll in this relaxation step exceeds 100 °C and is lower than 190 °C, and the speed ratio of the relaxation roll to the heat setting roll satisfies the following formula:

[0077] 1.00 < relaxation roll speed / heat setting roll speed < 1.10.

[0078] Hereinafter, each step will be described in detail.

[0079] The filaments spun from the spinneret assembly 2 provided in the melt spinning machine are directly cooled and solidified by the cold air at 0.5 m / sec or more and 1.5 m / sec or less supplied from the cold air cylinder 3.

[0080] Next, after applying an oil agent of 0.5% or more and 2.0% or less using the oil supply device 4, it is wound around the drawing roller 5 and drawn. The oil agent applied by the oil supply device is preferably an aqueous emulsion (aqueous oil agent). From the viewpoints of filament quality and industrial material use, a filament having excellent smoothness and heat resistance is preferred so that the drawing of the filament in the silk reeling process can be carried out smoothly. As an oil agent composition satisfying this property, for example, an oil agent mainly composed of a divalent fatty acid ester compound, a divalent fatty acid ester compound containing an alkylene oxide, a polyol alkylene oxide adduct, and a polyol alkylene oxide adduct containing an alkylene oxide is preferably used. In the melt spinning process, the polyamide spun from the spinneret is cooled and crystallized. During this crystallization process, if water molecules are present in the polymer, the amino group in the polyamide and the water molecules exhibit an interaction through hydrogen bonds, and crystallization is formed starting from the water molecules, promoting crystallization. In the above spinning process, by adding an aqueous emulsion oil agent to the filament spun from the spinneret 2, water molecules enter the filament, promoting the crystallization of the surface of the monofilaments forming the filament. As a result, a layer with a higher degree of crystallinity is formed on the fiber surface.

[0081] In addition, by allowing water molecules to enter the amorphous part of the polyamide fiber, the hydrogen bonds between the polyamides are cut off, increasing the mobility of the amorphous part. In the post-weaving processing step, after performing refining using water and then performing a drying step, since heat treatment is performed in a state where water molecules have entered the amorphous part of the fiber in a large amount, shrinkage of the fiber accompanied by strain relaxation of the amorphous part occurs. As a result, strain relaxation inside the fiber is carried out, reducing the strain inside the fiber, and thus reducing the shrinkage stress (residual stress) after heat treatment. At this time, since the fiber using the aqueous emulsion oil agent has a layer with a higher degree of crystallinity in the fiber surface layer part, in the post-weaving processing step, when immersed in water, the entry of water molecules into the fiber interior can be suppressed, thereby suppressing the strain relaxation caused by heat treatment, and the residual stress after heat treatment can be maintained at a relatively high level.

[0082] In this embodiment, the production of fibers was carried out using a conventional roll-to-roll production apparatus. In the roll-to-roll apparatus, the target physical properties are exhibited by the speed difference between the rolls and heat imparted based on heating. Each roll has a function, including a stretching roll for stretching the fibers, a heat setting roll for achieving structural fixation by relaxation of molecular strain and promotion of crystallization within the fibers, and a slack roll for adjusting the tension during product winding. The fibers spun from the spinneret and imparted with an oil agent by the oil supply device are pulled by the pulling roll 5 and continuously supplied to the stretching process without being temporarily wound up. The stretching process is a process of stretching the fibers by more than 20% by the speed difference between the rolls. That is, when comparing the speeds of this roll and the roll at the next position, when the speed of the roll at the next position is a value more than 20% higher than the speed of this roll, this roll is defined as the stretching roll. The stretching process preferably employs a multi-stage stretching method. Regarding the stretching of the spun filaments, preferably, with respect to the total stretching ratio required to obtain the necessary tensile strength, first, the pre-stage stretching is carried out at a low temperature below 150 °C, then the post-stage stretching is carried out at a high temperature above 150 °C, and finally, after heat setting for structural fixation and relaxation treatment to relieve the tension, winding is performed. The pre-stage stretching and the post-stage stretching can each be multi-stage stretching. There is no particular limitation on the number of stretching stages, and a two-stage stretching process is preferably used, and a three-stage stretching process is more preferably used. The illustrated stretching process includes: a first stretching roll 6, a second stretching roll 7, a third stretching roll 8, a heat setting roll 9, and a slack roll 10. The filaments are wound around each roll in sequence to carry out stretching heat treatment, etc., in order to obtain the desired physical properties. First, a slight tension is maintained between the pulling roll and the first stretching roll. The preferred stretching rate between the rolls is in the range of 0.5% or more and 5% or less. The surface temperature of the pulling roll is preferably 20 °C or more and 50 °C or less. Next, since the pre-stage stretching process is carried out in a low-temperature region below 150 °C, the temperature of the first stretching roll is preferably 40 °C or more and less than 150 °C, and the temperature of the second stretching roll is preferably above the stretching temperature of the first roll and less than 150 °C. The temperature of the third stretching roll for the post-stage stretching, which is carried out in a high-temperature region, is 150 °C or more and 190 °C or less.

[0083] The silk quilt after the stretching process is continuously supplied to the heat setting process. The heat setting process is a process of applying heat to the fibers on a roller after the stretching process in order to fix the structure of the fibers. In the present invention, it is important that there is a heat setting roller between the stretching roller and the relaxation roller. The temperature of the heat setting roller is 190 °C or higher and 205 °C or lower. In the heat setting process, the movement of the amorphous part in the fibers increases due to heat, causing strain relaxation and crystallization. If the temperature of the heat setting roller is 190 °C or higher, the crystal layer formed in the outer layer part of the fibers grows sufficiently, and during the processing steps in the weaving process, the entry of water molecules into the interior of the fibers can be suppressed, thereby suppressing strain relaxation and increasing the residual stress. In addition, if it is 205 °C or lower, the relaxation of the strain inside the fibers is small, and the residual stress becomes large after heat treatment is performed during the processing steps in the weaving process.

[0084] The silk quilt after the heat setting process is continuously supplied to the relaxation process. The relaxation process is a process of causing the fibers to contract, relaxing the strain inside the fibers, and adjusting the tension during winding. In order to cause the fibers to contract, the speed ratio between the rollers or the speed ratio between the roller and the winder needs to be less than 1. That is, when the speed of the roller or the winder at the next position is slower than the speed of this roller, this roller is defined as a relaxation roller. It is important that the temperature of the relaxation roller exceeds 100 °C and is lower than 190 °C. The temperature of the relaxation roller is more preferably more than 155 °C and less than 187 °C, and further preferably more than 170 °C and less than 187 °C. If the temperature of the relaxation roller is 190 °C or higher, the strain inside the fibers is relaxed by performing relaxation treatment at a high temperature, and the value of the residual stress after weaving becomes small, and the stress retention rate decreases. In addition, if it is 100 °C or lower, the relaxation of the strain inside the fibers is insufficient, and the dimensional stability decreases.

[0085] In the present embodiment, it is important that the contact time between the silk strand and the roller at 190 °C or higher is 30 msec or more and less than 110 msec during the heat setting treatment and the relaxation treatment. The contact time is more preferably 40 msec or more and 100 msec or less, and further preferably 50 msec or more and 95 msec or less. During the heat setting treatment and the relaxation treatment, the fibers are heated to promote the movement of the polymers inside the fibers and eliminate the strain inside the fibers. At this time, if the contact time between the silk strand and the roller reaching 190 °C or higher is 110 msec or less, the relaxation of the strain inside the fibers can be suppressed, and during the post-weaving heat treatment process, the strain remaining when heated becomes large, and the residual stress after the heat treatment becomes large. On the other hand, if it is 30 msec or more, the crystal layer formed in the surface layer part of the fibers grows sufficiently, suppressing the entry of water molecules during the weaving process, thereby suppressing the strain relaxation during the heat treatment and increasing the residual stress.

[0086] In the present embodiment, the speed ratio of the heat setting roll to the relaxation roll preferably satisfies the following formula:

[0087] 1 < relaxation roll speed / heat setting roll speed < 1.10.

[0088] The speed ratio is more preferably more than 1.01 and less than 1.09. If the speed ratio is greater than 1, the fiber is pulled between the heat setting roll and the relaxation roll, so that the molecules are in a tensioned state, and the strain relaxation in this section is suppressed. Therefore, it is possible to suppress the reduction of the residual stress after the heat treatment process during processing and improve the stress retention rate. On the other hand, if the speed ratio is less than 1.10, the structural change accompanied by stretching can be suppressed, and the crystal layer grown in the heat setting process remains undamaged. Therefore, in the processing process after weaving, it is possible to suppress the entry of water molecules into the fiber interior, suppress strain relaxation, and thus the residual stress becomes larger and the stress retention rate increases. For the above reasons, conditions for maximizing the stress retention rate can be found in the range where the speed ratio is more than 1 and less than 1.10.

[0089] The filament after the relaxation treatment is wound up by the winder 12. In order to prevent the filament from loosening during the weaving process, high-pressure fluid can be blown onto the filament between the relaxation roll and the winder to impart interlacing to the filament, so as to bundle the filament, while winding up. For the device for imparting interlacing to the filament, a known interlacing imparting device 11 can be appropriately used.

[0090] In the present embodiment, in order to adjust the stress retention rate to a predetermined range, it is important to use an aqueous sizing agent, and in the heat setting treatment process and the relaxation treatment process, the contact time between the roll at 190 °C or higher and the filament is 30 msec or more and less than 110 msec, the temperature of the heat setting roll is 190 °C or higher and 205 °C or lower, the temperature of the relaxation roll is more than 100 °C and less than 190 °C, and the relaxation roll speed / heat setting roll speed as the speed ratio of the relaxation roll to the heat setting roll is more than 1.00 and less than 1.10.

[0091] Examples

[0092] Hereinafter, the present invention will be specifically described by way of examples and comparative examples, but the present invention is not limited to these examples. In addition, each measured value in the examples was measured by the following method.

[0093] (1) Formic acid relative viscosity (VR)

[0094] 4.5 g of the sample was fully dissolved in 90% formic acid to make the concentration 8.4 wt%, and then the dropping time of the solution was measured using an Ubbelohde viscometer after standing for 10 minutes in an environment with a water temperature of 25 °C. The dropping time of the solvent was evaluated by the same method, and VR was calculated according to the following formula:

[0095] VR = Falling time of the sample solution (seconds) / Falling time of the solvent (seconds)

[0096] (2) Fuzzing quality

[0097] The obtained fibers were encapsulated and rewound at a speed of 450 m / min. A laser detector "LV - H62" manufactured by KEYENCE Corporation was set at a position 2 mm away from the filament being rewound. The total number of fuzzes detected was converted to the number per 100,000 m. When the value was 0 - 1, it was evaluated as ◎; when the value was 2 - 3, it was evaluated as ○; when the value was 4 - 9, it was evaluated as △; when the value was 10 or more, it was evaluated as ×. Additionally, the total number of fuzzes is the number of times the laser was blocked during the measurement by the laser detector.

[0098] (3) Total fineness (dtex)

[0099] Measured using the method described in JIS L 1017 8.3 of Japanese Industrial Standards.

[0100] (4) Filament fineness (dtex)

[0101] Obtained by dividing the total fineness obtained using the method described in JIS L 1017 8.3 of Japanese Industrial Standards by the number of single filaments constituting the filament.

[0102] (5) (Tensile) strength (cN / dtex), Tensile fracture elongation rate (%)

[0103] Obtained by dividing the tensile strength measured using the method described in JIS L 1017 8.5 of Japanese Industrial Standards by the total fineness. Additionally, the elongation rate at break was determined.

[0104] (6) Thermal shrinkage stress (mN / dtex)

[0105] For a 70 - cm measurement fiber sample, using a thermal shrinkage stress measuring machine (manufactured by Lenzing Instruments, Thermal Shrinkage Tester: TST510), a weight was attached to the end of the fiber. Thus, it was fixed in a state where an initial load of 0.4 mN / dtex was applied to the fiber sample, and the shrinkage stress during heating was measured.

[0106] (7) Stress retention rate (%)

[0107] Measured using the above - mentioned thermal shrinkage stress measuring machine through the following steps 1) - 6).

[0108] Step 1) Immerse the fiber in water at 20°C for 5 seconds. After taking it out, fix it on a heat shrinkage stress measuring machine under the state of applying an initial load of 0.4 mN / dtex to the fiber.

[0109] Step 2) Set the heating furnace to 130°C, insert the fiber into the heating furnace and heat for 5 min.

[0110] Step 3) Take out the fiber from the heating furnace, set the temperature of the heating furnace to 190°C and raise the temperature. During this period, hold the fixation of the fiber without being released and maintain a constant length.

[0111] Step 4) After the device is heated to 190°C, insert the fiber into the heating furnace and heat for 3 min, and measure the shrinkage stress at the moment 3 min after heating starts.

[0112] Step 5) Take out the fiber from the heating furnace and measure the shrinkage stress at the moment 3 min after taking it out; and

[0113] Step 6) Set the value obtained by subtracting the value of the initial load applied in Step 1) from the shrinkage stress obtained in Step 4) as [the shrinkage stress in Step 4)]. In addition, set the value obtained by subtracting the value of the initial load applied in Step 1) from the shrinkage stress obtained in Step 5) as [the residual stress in Step 5)]. Calculate the stress retention rate by the following formula:

[0114] Stress retention rate (%) = {[residual stress in Step 5)] / [shrinkage stress in Step 4)]} × 100.

[0115] Perform these measurement steps 1) to 6) 5 times, and use the average value as the stress retention rate.

[0116] (8) Folds after processing

[0117] For the obtained polyamide fiber, a plain fabric was obtained using a water jet loom without twisting or sizing. Then, the fabric was washed at 50°C for 1 minute in a stretched state, drum-dried at 130°C, and then, using a pin tenter, heated at 190°C for 1 minute and then rapidly cooled. An appearance inspection was carried out on the obtained rolled-up fabric after heat treatment. As a result, in the length direction of 500 m, the number of folds with a length of 50 cm or more was evaluated according to the following criteria:

[0118] ×: 10 or more

[0119] △: 2 - 9

[0120] ○: 0 - 1.

[0121] (9) Dynamic air permeability curve index

[0122] Measurements were carried out based on ASTM D6476.

[0123] Using the airbag special air permeability tester FX3350 from TEXTEST company, with a test head of 200 cm 3 In addition, the pressure of the compressed air (START PRESSURE) filled in the test head was adjusted so that the maximum pressure applied to the fabric reached 100 ± 5 kPa. The compressed air filled in the test head was released to contact the specimen of the fabric, and the pressure and air permeability were measured over time. According to the obtained pressure-dynamic air permeability curve, the dynamic air permeability curve index (Exponent) was calculated by FX3350.

[0124] (10) CV value (%) of dynamic air permeability curve index

[0125] Taking the length in the width direction of the base fabric as 100%, the dynamic air permeability curve indices at positions 25%, 50%, and 75% from the end were measured using the above method. For this measurement, 10 times were carried out every 10 m in the length direction. Based on the measurement data of a total of 30 points and using the following formula, the CV value (%) of the dynamic air permeability curve index was calculated:

[0126] CV value (%) of dynamic air permeability curve index = {(standard deviation of dynamic air permeability curve index) / (average value of dynamic air permeability curve index)} × 100.

[0127] [Example 1]

[0128] Through Figure 1 the device shown, a polyamide 6,6 polymer with a relative viscosity of 85 in 90% formic acid obtained by a polymerization method through common methods was melted at 300 °C. Then, the temperature was made uniform using a rotating head (1), and it was ejected from a spinneret (2) with 136 holes, and directly wound up using a spinning and drawing process to manufacture polyamide 6,6 fibers of 470 dtex and 136 filaments. That is, the ejected polyamide 6,6 polymer was cooled and solidified in a cold air chamber (3) to form a filament. Then, the filament passed through an oil supply device (4), a traction roller (5), a first drawing roller (6), a third drawing roller (8), a heat setting roller (9), and a relaxation roller (10) in sequence, and the filament was given interlacing using an interlacing imparting device (11) and wound up.

[0129] Regarding the temperature of each roll, the drawing roll (5) is not heated, the first drawing roll (6) is at 65°C, the second drawing roll (7) is at 140°C, the third drawing roll (8) is at 190°C, the heat setting roll (9) is at 190°C, and the relaxation roll (10) is at 185°C. The contact time between the filament and the heat setting roll is 93 msec. For the drawing distribution, the speed ratio of the first drawing roll to the drawing roll is 1.01, the speed ratio of the second drawing roll to the first drawing roll is 2.34, the speed ratio of the third drawing roll to the second drawing roll is 1.50, and the speed ratio of the heat setting roll to the third drawing roll is 1.30. In the heat setting process and the relaxation treatment process, winding is carried out in such a way that the speed ratio of the relaxation roll to the heat setting roll becomes 1.03 and the speed ratio of the winder to the relaxation roll becomes 0.93. The speed of the winder is 3000 m / min. Regarding the number of windings of the filament on each roll, the first drawing roll is 3 times, the second drawing roll is 3 times, the third drawing roll is 3 times, the heat setting roll is 7 times, and the relaxation roll is 4.5 times. An aqueous sizing agent with an adhesion amount of 1.0% by weight and 80% by weight of water in the composition is used. The physical properties of the obtained polyamide 6,6 fiber are shown in Table 1 below.

[0130] For the obtained polyamide 6.6 fiber, a plain fabric was obtained using a water jet loom without twisting or sizing. Then, the fabric was washed at 50°C for 1 minute in a stretched state, drum dried at 130°C, and then heat set by heating at 190°C for 1 minute using a pin tenter and then rapidly cooled, obtaining a fabric for airbags with a warp and weft density of 53 threads / 2.54 cm. Regarding this fabric, the generation of wrinkles was confirmed and the dynamic air permeability was measured, and the evaluation results are shown in Table 1 below.

[0131] [Example 2]

[0132] The number of holes in the spinneret used during spinning was made 72, and otherwise, it was carried out in the same manner as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric, etc. are shown in Table 1 below.

[0133] [Example 3]

[0134] The fineness of the fiber after spinning was made 350 dtex, and the warp and weft densities of the fabric after weaving were both made 60 threads / 2.54 cm, and otherwise, it was carried out in the same manner as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric, etc. are shown in Table 1 below.

[0135] [Example 4]

[0136] The winding number of the heat setting roll was made 4 times, and the contact time between the filament and the heat setting roll was made 53 msec. Otherwise, it was carried out in the same manner as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 1 below.

[0137] [Example 5]

[0138] The temperature of the heat setting roll was made 200 °C. Otherwise, it was carried out in the same manner as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 1 below.

[0139] [Example 6]

[0140] The speed ratio of the relaxation roll / heat setting roll was made 1.08. Otherwise, it was carried out in the same manner as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 1 below.

[0141] [Table 1]

[0142]

[0143] [Comparative Example 1]

[0144] The temperature of the relaxation roll was made 195 °C, and the total contact time with the heat setting roll and the relaxation roll was made 151 msec. Otherwise, it was carried out in the same manner as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below. In the heat setting process and the relaxation process, the contact time between the obtained fiber and the roll reaching 190 °C or higher was long, and since the temperature of the relaxation roll was high, relaxation treatment was carried out at a high temperature, thereby relaxing the strain inside the fiber and lowering the stress retention rate. The fabric using this fiber had more wrinkles and larger unevenness in air permeability. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below.

[0145] [Comparative Example 2]

[0146] The winding number of the heat setting roll was made twice, and the contact time between the filament and the heat setting roll was made 26 msec. Otherwise, it was carried out in the same manner as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below. In the heat setting process, the contact time between the obtained fiber and the roll reaching 190°C or higher was short, and the crystals inside the fiber did not grow sufficiently. Therefore, the crystal layer formed in the outer layer of the fiber was less, and it was in a state where water molecules could easily enter the fiber interior. As a result, the strain relaxation caused by heating after impregnation in water was large, and the stress retention rate was low. The fabric using this fiber had more wrinkles and larger unevenness in air permeability. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below.

[0147] [Comparative Example 3]

[0148] The winding number of the heat setting roll was made 9 times, and the contact time between the filament and the heat setting roll was made 119 msec. Otherwise, it was carried out in the same manner as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below. In the heat setting process, the contact time between the obtained fiber and the roll reaching 190°C or higher was long, thereby relaxing the strain inside the fiber, and the stress retention rate was low. The fabric using this fiber had more wrinkles and larger unevenness in air permeability. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below.

[0149] [Comparative Example 4]

[0150] The speed ratio of the relaxation roll / heat setting roll was made 1.13. Otherwise, it was carried out in the same manner as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below. The obtained fiber was crystallized in the heat setting process and then stretched at a high draw ratio. As a result, the fiber broke from the crystal part that was difficult to follow the deformation, and fuzzing occurred more frequently. In addition, since the crystal layer was destroyed by stretching, it was in a state where water molecules could easily enter the fiber interior. The strain relaxation caused by heating after impregnation in water was large, and the stress retention rate was low. The fabric using this fiber had wrinkles, and the unevenness in air permeability was also large. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below.

[0151] [Comparative Example 5]

[0152] The temperature of the heat setting roller was set at 210 °C, and the procedure was otherwise the same as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below. For the obtained fiber, in the heat setting process, the temperature of the heat setting roller was increased to 210 °C, thereby relaxing the strain inside the fiber and reducing the stress retention rate. The fabric made from this fiber had more wrinkles and greater non-uniformity in air permeability. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below.

[0153] [Comparative Example 6]

[0154] The temperature of the heat setting roller was set at 170 °C, and the procedure was otherwise the same as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below. For the obtained fiber, in the heat setting process, the temperature of the heat setting roller was lowered to 170 °C, resulting in insufficient growth of the crystals inside the fiber. Therefore, fewer crystal layers were formed in the outer layer of the fiber, creating a state where water molecules could easily enter the fiber interior. Consequently, the strain relaxation caused by heating after immersion in water was greater, and the stress retention rate was reduced. The fabric made from this fiber had more wrinkles and greater non-uniformity in air permeability. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below.

[0155] [Comparative Example 7]

[0156] The speed ratio of the relaxation roller / heat setting roller was set at 1.00, and the procedure was otherwise the same as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below. For the obtained fiber, the tension state of the fiber between the heat setting roller and the relaxation roller was insufficient, and strain relaxation inside the fiber was carried out based on the temperature of the heat setting roller, resulting in a reduced stress retention rate. The fabric made from this fiber developed wrinkles and had greater non-uniformity in air permeability. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below.

[0157] [Comparative Example 8]

[0158] The spinning oil used was a water-free non-aqueous oil, and the procedure was otherwise the same as in Example 1. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below. The obtained fiber did not fully form the crystal layer in the fiber surface layer and was in a state where water molecules could easily enter the fiber interior. Therefore, the strain relaxation caused by heating after immersion in water was greater, and the stress retention rate was reduced. The fabric made from this fiber had more wrinkles and greater non-uniformity in air permeability. The physical properties of the obtained polyamide 6.6 fiber and the evaluation results of the fabric are shown in Table 2 below.

[0159] [Comparative Example 9]

[0160] The spinning finish used during spinning was a non-aqueous finish that did not contain water. Otherwise, the procedure was carried out in the same manner as in Example 2. The physical properties of the obtained polyamide 6.6 fibers and the evaluation results of the fabric, etc. are shown in Table 2 below. The obtained fibers did not sufficiently form a crystalline layer in the fiber surface layer portion and were in a state where water molecules could easily enter the fiber interior. Therefore, the strain relaxation caused by heating after immersion in water was relatively large, and the stress retention rate was low. The fabric made from these fibers had more wrinkles and a greater unevenness in air permeability. The physical properties of the obtained polyamide 6.6 fibers and the evaluation results of the fabric, etc. are shown in Table 2 below.

[0161] [Comparative Example 10]

[0162] The spinning finish used during spinning was a non-aqueous finish that did not contain water. Otherwise, the procedure was carried out in the same manner as in Example 3. The physical properties of the obtained polyamide 6.6 fibers and the evaluation results of the fabric, etc. are shown in Table 2 below. The obtained fibers did not sufficiently form a crystalline layer in the fiber surface layer portion and were in a state where water molecules could easily enter the fiber interior. Therefore, the strain relaxation caused by heating after immersion in water was relatively large, and the stress retention rate was low. The fabric made from these fibers had more wrinkles and a greater unevenness in air permeability. The physical properties of the obtained polyamide 6.6 fibers and the evaluation results of the fabric, etc. are shown in Table 2 below.

[0163] [Table 2]

[0164]

[0165] Industrial Applicability

[0166] The polyamide fibers of the present invention are suitable for weaving high-density fabrics. With polyamide filaments having a relatively high stress retention rate, the shrinkage of the fibers after weaving processing becomes good and uniform, which can improve the process passability and the deviation of the dynamic air permeability curve index, and can preferably be used as a fabric for airbags with low air permeability.

[0167] Explanation of Reference Numerals

[0168] 1, rotating head; 2, spinneret; 3, cold air chamber; 4, oil supply device; 5, draw roll; 6, first drawing roll; 7, second drawing roll; 8, third drawing roll; 9, heat setting roll; 10, relaxation roll; 11, interlacing device; 12, winder.

Claims

1. A method for manufacturing polyamide fiber for airbag, characterized in that, the method for manufacturing polyamide fiber for airbag includes the following steps: a step of performing hot drawing after applying an aqueous sizing agent to the filaments spun from a spinneret; a drawing step; a heat setting step; and a relaxation step, in this heat setting step and this relaxation step, the contact time between the roller reaching 190 °C or higher and the filaments is 30 msec or more and less than 110 msec, the temperature of the heat setting roller in this heat setting step is 190 °C or higher and 205 °C or lower, the temperature of the relaxation roller in this relaxation step exceeds 100 °C and is lower than 190 °C, and the speed ratio of this relaxation roller to this heat setting roller satisfies the following formula: 1.00 < relaxation roller speed / heat setting roller speed < 1.

10.

2. The method for manufacturing polyamide fiber for airbag according to claim 1, characterized in that, the drawing step includes: performing pre-stage drawing at a low temperature below 150 °C and performing post-stage drawing at a high temperature above 150 °C.

3. The method for manufacturing polyamide fiber for airbag according to claim 2, characterized in that, the pre-stage drawing and the post-stage drawing are respectively multi-stage drawing.

4. The method for manufacturing polyamide fiber for airbag according to claim 1, characterized in that, the temperature of the relaxation roller exceeds 155 °C and is lower than 187 °C.

5. The method for manufacturing polyamide fiber for airbag according to claim 4, characterized in that, the temperature of the relaxation roller exceeds 170 °C and is lower than 187 °C.

6. The method for manufacturing polyamide fiber for airbag according to claim 1, characterized in that, the contact time is 40 msec or more and 100 msec or less.

7. The method for manufacturing polyamide fiber for airbag according to claim 6, characterized in that, the contact time is 50 msec or more and 95 msec or less.

8. A polyamide fiber for airbag, characterized in that, this polyamide fiber for airbag is obtained by the method for manufacturing polyamide fiber for airbag according to any one of claims 1 to 7, the fineness of this fiber is 200 dtex or more and 800 dtex or less, and the stress retention rate obtained by the following steps 1) to 6) is 3.0% or more: 1) Immerse the fiber in water at 20 °C for 5 seconds, and after taking it out, fix it on a heat shrinkage stress measuring machine in a state where an initial load of 0.4 mN / dtex is applied to this fiber; 2) Set the heating furnace to 130 °C, insert the fiber into the heating furnace and heat for 5 min; 3) Take out the fiber from the heating furnace, set the temperature of the heating furnace to 190 °C and raise the temperature. During this period, hold the fixation of the fiber without being released and maintain a constant length; 4) After the device is heated to 190 °C, insert the fiber into the heating furnace and heat for 3 min, and measure the shrinkage stress at the moment 3 min after the start of heating; 5) Take out the fiber from the heating furnace and measure the shrinkage stress at the moment 3 min after taking it out; and 6) The value obtained by subtracting the value of the initial load imparted in step 1) from the shrinkage stress obtained in step 4) is set as the [shrinkage stress in step 4)]. Additionally, the value obtained by subtracting the value of the initial load imparted in step 1) from the shrinkage stress obtained in step 5) is set as the [residual stress in step 5)]. The stress retention rate is calculated by the following formula: Stress retention rate (%) = {[Residual stress in step 5)] / [Shrinkage stress in step 4)]} × 100.

9. The polyamide fiber for airbag according to claim 8, wherein, The stress retention rate is 5.0% or more.

10. The polyamide fiber for airbag according to claim 8 or 9, wherein, The tensile strength of the polyamide fiber for airbag is 7.5 cN / dtex or more.

11. The polyamide fiber for airbag according to claim 8 or 9, wherein, The fineness of the polyamide fiber for airbag is 340 dtex or more and 500 dtex or less.

12. The polyamide fiber for airbag according to claim 8 or 9, wherein, The fineness of a single filament of the polyamide fiber for airbag is 1.0 dtex or more and 7.0 dtex or less.

13. The polyamide fiber for airbag according to claim 8 or 9, wherein, The polyamide fiber for airbag is polyamide 6,6 fiber.

14. The polyamide fiber for airbag according to claim 8, wherein, The stress retention rate is 30% or less.

15. The polyamide fiber for airbag according to claim 14, wherein, The stress retention rate is 20% or less.

16. The polyamide fiber for airbag according to claim 15, wherein, The stress retention rate is 10% or less.

17. The polyamide fiber for airbag according to claim 16, wherein, The stress retention rate is 6.3% or more and 8.7% or less.

18. The polyamide fiber for airbag according to claim 10, wherein, The tensile strength is 7.5 cN / dtex or more and 11.5 cN / dtex or less.

19. The polyamide fiber for airbag according to claim 18, wherein, The tensile strength is 8.0 cN / dtex or more and 11.5 cN / dtex or less.

20. The polyamide fiber for airbag according to claim 19, wherein, The tensile strength is 8.2 cN / dtex or more and 11.5 cN / dtex or less.

21. The polyamide fiber for airbag according to claim 12, wherein, The fineness of a single filament is 1.5 dtex or more and 6.0 dtex or less.

22. The polyamide fiber for airbag according to claim 21, wherein, The fineness of a single filament is 2.5 dtex or more and 5.7 dtex or less.

23. The polyamide fiber for airbag according to claim 22, wherein, The fineness of a single filament is 3.3 dtex or more and 4.9 dtex or less.

24. A fabric for airbag, wherein, The fabric for airbag comprises the polyamide fiber for airbag according to any one of claims 8 to 23.

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