Nylon sewing thread for safety air bag and preparation method of nylon sewing thread

Abstract

The invention relates to the technical field of chinlon sewing threads, and discloses a chinlon sewing thread for an air bag restraint system and a preparation method thereof.The chinlon sewing thread for the air bag restraint system comprises a core layer and a sheath layer which are integrally formed through a sheath-core composite spinning technology; the core layer comprises a chinlon matrix and nano particles uniformly dispersed in the chinlon matrix, and the nano particles account for 0.5-10wt% of the mass of the core layer; the sheath layer is a chinlon layer, and the mass ratio of the core layer to the sheath layer is 30: 70-70: 30; the surface of the sewing thread is coated with an intelligent response type coating, the intelligent response type coating comprises thermal expansion microspheres and heat-resistant resin, the thermal expansion microspheres account for 5-40 wt% of the solid content of the intelligent response type coating, and the initial expansion temperature of the thermal expansion microspheres ranges from 120 DEG C to 180 DEG C. According to the invention, 5-10wt% of surface modified nanoparticles (such as amino silane grafted SiO2) are added into the core layer, and the interface bonding force is enhanced through covalent bonds, so that the strength retention rate at 180 DEG C is greater than 85% (only 55% of a traditional product), and the risk of high-temperature fusing of chinlon is solved.

Description

Technical Field

[0001] The invention relates to the technical field of nylon sewing threads, in particular to a nylon sewing thread for an airbag and a preparation method thereof. Background Art

[0002] Automobile airbags must withstand high temperatures of 150-200°C and high-pressure gas impacts at the moment of deployment. Therefore, sewing threads must meet requirements such as ultra-high strength (≥8.0 cN / dtex), high-temperature strength retention (>80%@180°C), excellent airtightness (leakage at the seam <5 L / min@2 bar), low sewing damage (base fabric strength loss rate <10%), and stable sewing processability (friction coefficient <0.25).

[0003] Traditional nylon sewing thread contains a large number of amide bonds (-NH-CO-) in its molecular chain. At 180°C, the hydrogen bond network collapses, the molecular chain slip intensifies, and the crystalline region de-sequences, which leads to a 40-50% drop in strength under high temperature conditions. At the same time, the coating of existing nylon sewing thread generally uses conventional silicone oil or wax coating. However, the viscosity of silicone oil will drop sharply from 5000cP to 10cP at 180°C, and the coating will turn from gel state to liquid state and flow from the fiber surface. The melting point of paraffin is 70-100°C, and it completely liquefies and falls off at 160°C. Long-term heat exposure causes molecular cracking, generating small olefin molecules and coking, which blocks the spinneret holes and makes the existing coating ineffective under high temperature conditions. Summary of the Invention

[0004] The object of the present invention is to provide a nylon sewing thread for airbags and a preparation method thereof, so as to solve the problems raised in the background technology.

[0005] To achieve the above-mentioned object, the present invention provides the following technical solution: a nylon sewing thread for airbags, comprising: a core layer and a sheath layer integrally formed by a sheath-core composite spinning process; The core layer comprises a nylon matrix and nanoparticles uniformly dispersed therein, wherein the nanoparticles account for 0.5-10 wt% of the core layer mass; The sheath layer is a nylon layer, and the mass ratio of the core layer to the sheath layer is 30:70 to 70:30; The surface of the sewing thread is coated with an intelligent responsive coating, which contains heat-expandable microspheres and a heat-resistant resin. The heat-expandable microspheres account for 5-40 wt% of the solid content of the intelligent responsive coating, and the initial expansion temperature is 120-180°C. The intelligent responsive coating has a friction coefficient of ≤0.25 at room temperature, providing lubricity, and expands or cross-links at ≥150°C to achieve self-sealing.

[0006] Furthermore, the nanoparticles are at least one of nano-silicon dioxide, nano-aluminum oxide, and carbon nanotubes whose surfaces are modified with a silane coupling agent, and have a particle size range of 10-200 nm.

[0007] Furthermore, the heat-resistant resin is at least one of modified silicone resin, fluorocarbon resin or polyurethane acrylate.

[0008] Furthermore, the heat-expandable microspheres are acrylonitrile copolymer microcapsules.

[0009] Furthermore, the surface modification treatment comprises the following steps: Particle pretreatment: Nanoparticles were activated in acid solution at 60-80°C for 1-2 hours; Coupling agent grafting: react the activated particles with a silane coupling agent in an ethanol aqueous solution at a temperature of 70-90°C for 2-4 hours; Washing and drying: After centrifugal separation, drying is performed to obtain modified particles with surface grafted active groups.

[0010] A method for preparing nylon sewing thread for airbags comprises the following steps: S1. Preparation of core layer spinning solution: nylon chips and nanoparticles are melt-blended via a twin-screw extruder to obtain a core layer spinning melt; S2. Preparation of sheath spinning solution: Melting nylon chips and nanoparticles to prepare sheath spinning melt; S3, composite spinning: the core layer spinning melt and the sheath layer spinning melt are extruded through a core-skin composite spinning assembly, wherein: The diameter of the core layer spinning melt flow channel Dc (mm) and the annular gap width of the sheath layer spinning melt flow channel Ws (mm) satisfy: Ws = 0.2 × Dc; The flow ratio of the core layer spinning melt and the sheath layer spinning melt is 30:70 to 70:30; After extrusion, it undergoes three-stage gradient cooling, three-stage hot drawing, and heat setting to form a core-sheath composite fiber monofilament; S4, twisting: twisting and plying multiple core-sheath composite fibers to form a sewing thread; S5. Plasma treatment: Under an inert gas atmosphere, the sewing thread is subjected to low-temperature plasma surface treatment; S6. Coating treatment: evenly apply the intelligent responsive coating emulsion to the treated surface of the sewing thread, and dry and solidify it to form a coating.

[0011] Furthermore, in step S3: the drawing adopts a three-stage hot drawing process, wherein: Primary drawing temperature: 80-100°C, drawing ratio 1.5-2.5; Secondary drawing temperature: 120-150°C, drawing ratio 2.0-3.0; The third-stage drawing temperature is 160-190°C, and the drawing ratio is 0.8-1.2.

[0012] Furthermore, in step S5: the power of the low-temperature plasma treatment is 100-500 W, the treatment time is 10-60 s, and the treatment atmosphere is argon or nitrogen.

[0013] Furthermore, in step S6: the drying and curing is a gradient temperature rising process: Stage 1: drying at 60-80°C for 1-2 minutes; Second stage: 100-120°C curing for 2-5 minutes; The third stage: heat treatment at 150-180°C for 0.5-1 min.

[0014] Furthermore, in step S3: the combined pressure of the core layer spinning melt and the sheath layer spinning melt in the spinning assembly is 8-15 MPa.

[0015] Compared with the prior art, the present invention provides a nylon sewing thread for airbags and a preparation method thereof, which has the following beneficial effects: The present invention adds 5-10 wt% surface-modified nanoparticles (such as aminosilane-grafted SiO2) to the core layer to enhance the interfacial bonding force through covalent bonds, so that the 180°C strength retention rate is greater than 85% (traditional products are only 55%), thus solving the risk of nylon high-temperature melting. The coating contains 5-40 wt% thermal expansion microspheres (such as Expancel® 951DU), which trigger a volume expansion of 300-500% at 150°C, blocking the micropores in the sutures and achieving an airtightness of 1.5 L / min@2 bar (the national standard requires <5 L / min), overcoming the problem of gas leakage; the sheath maintains pure nylon, combined with plasma treatment to optimize coating adhesion, the friction coefficient is reduced to 0.18-0.22, the base fabric damage rate is <8% (traditional>15%), and the spinning breakage rate is <5%; sheath-core spinning integration (core-sheath ratio 30:70-70:30) and three-stage drawing process (140-180℃ crystal zone reorganization) ensure product batch consistency, and the mass production qualification rate is >98%. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is a schematic three-dimensional cross-sectional view of the nylon sewing thread for the airbag of the present invention; Figure 2 This is a schematic diagram of the planar cross-section structure of the nylon sewing thread for the airbag of the present invention; Figure 3 This is the raw material ratio table in structural embodiment 1 of the present invention; Figure 4This is a table of parameters for preparing the nylon sewing thread for the airbag of the present invention; Figure 5 This is the raw material ratio table in structural embodiment 2 of the present invention; Figure 6 This is the raw material ratio table in structural embodiment 3 of the present invention; Figure 7 This is the raw material ratio table in structural embodiment 4 of the present invention; Figure 8 The following is a performance comparison table of the finished sewing threads of Examples 1-4 of the present invention and traditional nylon threads.

[0017] In the figure: 1. Core layer; 2. Sheath layer; 3. Smart responsive coating. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. Example 1

[0019] The formula of core layer 1 is as follows: nylon matrix: 95 parts by weight of nylon 66 chips (relative viscosity 2.4), nanoparticles: 5 parts by weight of nano-silica modified with a silane coupling agent (particle size 50 nm, amino grafting rate ≥12%); The formula of sheath layer 2 is as follows: Nylon layer: 100 parts by weight of nylon 66 chips (relative viscosity 2.4); The formula of the intelligent responsive coating 3 is: 70 parts by weight of modified silicone resin, 29.5 parts by weight of acrylonitrile copolymer microcapsules, and 0.5 parts by weight of a wetting agent.

[0020] Nanoparticle surface modification steps: Particle pretreatment: Nanoparticles were activated in acid at 70 °C for 1.5 h; Coupling agent grafting: The activated particles were reacted with a silane coupling agent in an ethanol aqueous solution at a temperature of 80°C for 3 hours; Washing and drying: After centrifugal separation, drying is performed to obtain modified particles with surface grafted active groups.

[0021] Nylon sewing thread for airbags is prepared by the following steps: Preparation of the spinning solution of the core layer 1: the core layer 1 is melt-blended by a twin-screw extruder to obtain a spinning melt of the core layer 1; Preparation of sheath layer 2 spinning solution: melting sheath layer 2 to obtain sheath layer 2 spinning melt; The core layer 1 spinning solution and the sheath layer 2 spinning solution were extruded through a core-skin composite spinning assembly, wherein the core-skin composite spinning assembly temperature was 285°C, the core layer 1 spinning melt flow channel diameter was 0.5 mm, and the sheath layer 2 spinning melt flow channel annular gap width was 0.1 mm; The flow ratio of the core layer 1 spinning melt and the sheath layer 1 spinning melt is 50:50, and the compounding pressure is 12 MPa; After extrusion, it undergoes three-stage gradient cooling and three-stage hot drawing, with the first-stage drawing temperature at 90°C and a drawing ratio of 2.0, the second-stage drawing temperature at 140°C and a drawing ratio of 2.5, and the third-stage drawing temperature at 180°C and a drawing ratio of 1.0; and heat setting to form a core-sheath composite fiber monofilament. Twisting and plying a plurality of core-sheath composite fibers into a raw sewing thread; In an argon inert gas atmosphere, the sewing thread is subjected to low-temperature plasma surface treatment; the power is 300W and the treatment time is 30S; The smart responsive coating 3 emulsion is evenly coated on the treated sewing thread surface and dried and cured to form a coating. The drying and curing is a gradient temperature rising process: the first stage: temperature 70°C, time 1.5 minutes, the second stage: temperature 110°C, time 3 minutes, and the third stage: temperature 170°C, time 0.8 minutes.

[0022] Among them, the finished sewing thread breaking strength (cN / dtex): 9.2, 180℃ strength retention rate: 88%, air tightness (L / min@2bar): 1.5, base fabric damage rate: 5.7%, spinning breakage rate: 3%. Example 2

[0023] The difference between Example 2 and Example 1 is that the formula of the core layer 1 is as follows: nylon matrix: 99.5 parts by weight of nylon 66 chips (relative viscosity 2.4), nanoparticles: 0.5 parts by weight of nano-silicon dioxide modified with a silane coupling agent (particle size 50 nm, amino grafting rate ≥12%); The formula of the intelligent responsive coating 3 is: 95 parts by weight of modified silicone resin, 4.5 parts by weight of acrylonitrile copolymer microcapsules, and 0.5 parts by weight of a wetting agent.

[0024] Among them, the finished sewing thread breaking strength (cN / dtex): 8.5, 180℃ strength retention rate: 81%, air tightness (L / min@2bar): 4.2, base fabric damage rate: 7.2%, spinning breakage rate: 2%. Example 3

[0025] The difference between Example 3 and Example 1 is that the formula of core layer 1 is: nylon matrix: 90 parts by weight of nylon 66 chips (relative viscosity 2.4), nanoparticles: 10 parts by weight of nano-alumina modified with silane coupling agent (particle size 80 nm, epoxy modified).

[0026] Among them, the finished sewing thread breaking strength (cN / dtex): 9.8, 180℃ strength retention rate: 85%, air tightness (L / min@2bar): 1.8, base fabric damage rate: 6.1%, spinning breakage rate: 12%. Example 4

[0027] The difference between Example 4 and Example 1 is that the formula of the core layer 1 is as follows: nylon matrix: nylon 66 chips are 29.7 parts by weight (relative viscosity 2.4), nanoparticles: carbon nanotubes modified with a silane coupling agent are 0.3 parts by weight (diameter 20 nm, aspect ratio 80); The formula of sheath layer 2 is as follows: Nylon layer: 70 parts by weight of nylon 66 chips (relative viscosity 2.4); The formula of the intelligent responsive coating 3 is: 60 parts by weight of fluorocarbon resin, 39.5 parts by weight of acrylonitrile copolymer microcapsules, and 0.5 parts by weight of a wetting agent.

[0028] Among them, the finished sewing thread breaking strength (cN / dtex): 8.1, 180℃ strength retention rate: 80%, air tightness (L / min@2bar): 0.9, base fabric damage rate: 8%, spinning breakage rate: 4%.

[0029] Traditional nylon sewing thread breaking strength (cN / dtex): 7.8, 180℃ strength retention rate: 55%, air tightness (L / min@2bar): >10, base fabric damage rate: 15.2%, spinning breakage rate: 5% While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A nylon sewing thread for airbags, characterized in that: include: A core layer (1) and a sheath layer (2) integrally formed by a core-skin composite spinning process; The core layer (1) comprises a nylon matrix and nanoparticles uniformly dispersed therein, wherein the nanoparticles account for 0.5-10 wt% of the mass of the core layer; The sheath layer (2) is a nylon layer, and the mass ratio of the core layer (1) to the sheath layer (2) is 30:70 to 70:30; The surface of the sewing thread is coated with an intelligent responsive coating (3), which contains heat-expandable microspheres and a heat-resistant resin. The heat-expandable microspheres account for 5-40 wt% of the solid content of the intelligent responsive coating (3), and the initial expansion temperature thereof is 120-180°C. The intelligent responsive coating (3) has a friction coefficient of ≤0.25 at room temperature, provides lubricity, and expands or cross-links at ≥150°C to achieve self-sealing.

2. The nylon sewing thread for airbags according to claim 1, characterized in that: The nanoparticles are at least one of nano-silicon dioxide, nano-aluminum oxide and carbon nanotubes whose surfaces are modified with a silane coupling agent, and the particle size ranges from 10 to 200 nm.

3. The nylon sewing thread for airbag according to claim 1, characterized in that: The heat-resistant resin is at least one of modified silicone resin, fluorocarbon resin or polyurethane acrylate.

4. The nylon sewing thread for airbags according to claim 1, characterized in that: The heat-expandable microspheres are acrylonitrile copolymer microcapsules.

5. The nylon sewing thread for airbag according to claim 2, characterized in that: The surface modification treatment comprises the following steps: Particle pretreatment: Nanoparticles were activated in acid solution at 60-80°C for 1-2 hours; Coupling agent grafting: react the activated particles with a silane coupling agent in an ethanol aqueous solution at a temperature of 70-90°C for 2-4 hours; Washing and drying: After centrifugal separation, drying is performed to obtain modified particles with surface grafted active groups.

6. A method for preparing the nylon sewing thread for airbags according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1. Preparation of the core layer (1) spinning solution: nylon chips and nanoparticles are melt-blended via a twin-screw extruder to obtain a core layer (1) spinning melt; S2, sheath (2) spinning solution preparation: nylon chips and nanoparticles are melted to prepare sheath spinning melt; S3, composite spinning: the core layer (1) spinning melt and the sheath layer (2) spinning melt are extruded through a core-skin composite spinning assembly, wherein: The diameter of the spinning melt flow channel of the core layer (1) Dc (mm) and the annular gap width of the spinning melt flow channel of the sheath layer (2) Ws (mm) satisfy: Ws = 0.2 × Dc; The flow ratio of the core layer (1) spinning melt and the sheath layer (2) spinning melt is 30:70 to 70:30; After extrusion, it undergoes three-stage gradient cooling, three-stage hot drawing, and heat setting to form a core-sheath composite fiber monofilament; S4, twisting: twisting and plying multiple core-sheath composite fibers to form a sewing thread; S5. Plasma treatment: Under an inert gas atmosphere, the sewing thread is subjected to low-temperature plasma surface treatment; S6. Coating treatment: evenly apply the intelligent responsive coating (3) emulsion to the treated surface of the sewing thread, and dry and solidify it to form a coating.

7. The method for preparing nylon sewing thread for airbag according to claim 6, characterized in that: In step S3: the drawing adopts a three-stage hot drawing process, wherein: Primary drawing temperature: 80-100°C, drawing ratio 1.5-2.5; Secondary drawing temperature: 120-150°C, drawing ratio 2.0-3.0; The third-stage drawing temperature is 160-190°C, and the drawing ratio is 0.8-1.

2.

8. The method for preparing nylon sewing thread for airbags according to claim 6, characterized in that: In step S5: the power of the low-temperature plasma treatment is 100-500 W, the treatment time is 10-60 s, and the treatment atmosphere is argon or nitrogen.

9. The method for preparing nylon sewing thread for airbag according to claim 6, characterized in that: In step S6: the drying and curing is a gradient temperature rising process: Stage 1: drying at 60-80°C for 1-2 minutes; Second stage: 100-120°C curing for 2-5 minutes; The third stage: heat treatment at 150-180°C for 0.5-1 min.

10. The method for preparing nylon sewing thread for airbag according to claim 6, characterized in that: In step S3: the composite pressure of the core layer (1) spinning melt and the sheath layer (2) spinning melt in the spinning assembly is 8-15 MPa.

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