Method for recycling airbag base fabric and liquid for peeling silicone coating layer

Abstract

To provide a method for easily peeling a silicone coating layer in order to enable recycling of an air bag base fabric having the silicone coating layer on the surface, and to provide a silicone coating layer peeling liquid therefor SOLUTION: A method for recycling an airbag base fabric, the method including an immersion step of immersing an airbag base fabric in a silicone coating layer peeling liquid that is an aqueous solution containing 2% by weight to 30% by weight of an alkali component, 0.05% by weight to 20% by weight of a surfactant, and 1% by weight to 30% by weight of an alcohol component, and a peeling step of peeling the silicone coating layer from the airbag base fabric after the immersion, wherein an ash content of the airbag base fabric after the peeling step is 0.01% to 0.45%.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for recycling an airbag base fabric and a silicone coating layer stripping solution. [Background technology]

[0002] In recent years, vehicles have been equipped with various airbags to ensure the safety of occupants in the event of a vehicle collision, thereby enhancing the protective function for occupants. Airbags are generally manufactured by preparing a base fabric by applying a silicone resin or the like to a synthetic fiber woven fabric to improve properties such as heat resistance, flame retardancy, and air barrier properties, and then cutting this base fabric and sewing it into a bag body.

[0003] In order to improve the recyclability of airbags, development is also underway on uncoated airbags, which are made by weaving synthetic resin filament yarns at a high density without coating them with silicone resin or other materials. However, due to the complexity of the structure required to ensure sufficient airtightness as an airbag and issues with durability, silicone-coated airbags are currently the mainstream.

[0004] In order to recycle silicone-coated airbags, the silicone coating layer must be removed and separated from the resin base material. However, industrial technology for removing the silicone coating layer has not yet been established, and recycling airbag base fabrics as raw materials for various molded products without fully removing the silicone coating layer can result in problems such as a deterioration in mechanical properties and contamination of molds. As a result, a large number of airbags are currently discarded without being recycled.

[0005] As a method for removing a silicone coating layer from an airbag base fabric, Patent Document 1 discloses a method for removing the silicone coating layer by dissolving it in a solvent containing a tetraalkylammonium salt and an organic solvent.

[0006] Meanwhile, as a relatively low-cost method, Patent Document 2 discloses a method in which airbag scrap fabric is immersed in an alkaline solution, dehydrated, and the scrap fabric is agitated and rubbed against itself in a container to peel off the silicone layer. Patent Document 3 and Patent Document 4 disclose methods in which the silicone layer is peeled off by immersing the fabric in an alkaline solution containing a surfactant and agitating the resulting solution, respectively. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2024-020989 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-180413 [Patent Document 3] Japanese Patent Application Publication No. 2023-125970 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-299242 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the method described in Patent Document 1, the silicone layer is dissolved in a chemical, so the amount of silicone remaining in the recovered airbag base fabric is very small and high quality, but the use of chemicals increases costs and the use of organic solvents increases the environmental impact.

[0009] Furthermore, in the method described in Patent Document 2, only the airbag scrap fabric is agitated in a container after being immersed in an alkaline solution and dehydrated. This requires sufficient agitation so that the fabrics come into contact with each other, and there is also the risk of the peeled silicone layer re-adhering.

[0010] Furthermore, in the methods described in Patent Documents 3 and 4, the peeling of the silicone layer is at a level that can be visually observed and the resin can be used as a recycled resin raw material, but the quality is not sufficient to withstand use in applications that require strict quality standards.

[0011] The present invention has been made in view of the above circumstances, and aims to provide a method for easily removing a silicone coating layer and a silicone coating layer removing solution for the method, in order to enable the recycling of an airbag base fabric having a silicone coating layer on its surface. [Means for solving the problem]

[0012] As a result of extensive research conducted by the inventors to achieve the above object, they discovered a method for efficiently peeling off a silicone coating layer by immersing an airbag base fabric in a stripping solution containing an alkaline component, a surfactant, and an alcohol component in a specific blending ratio.

[0013] That is, the present invention comprises the following configurations. (1) A method for recycling airbag base fabrics by peeling off a silicone coating layer from a silicone-coated airbag base fabric, the method comprising: an immersion step of immersing the airbag base fabric in a silicone coating layer peeling solution, which is an aqueous solution containing 2% by weight to 30% by weight of an alkaline component, 0.05% by weight to 20% by weight of a surfactant, and 1% by weight to 30% by weight of an alcohol component; and a peeling step of peeling off the silicone coating layer from the airbag base fabric after immersion, wherein the ash content of the airbag base fabric after the peeling step is 0.01% to 0.45%. (2) A method for recycling airbag base fabrics by peeling off a silicone coating layer from a silicone-coated airbag base fabric, the method comprising: an immersion step of immersing the airbag base fabric in a silicone coating layer peeling liquid, which is an aqueous solution containing 2% by weight to 30% by weight of an alkaline component and 0.05% by weight to 20% by weight of a surfactant; and a peeling step of peeling off the silicone coating layer from the airbag base fabric after immersion, the peeling step comprising a step of specific gravity separation using a liquid having a specific gravity of 1.01 to 1.10, and the ash content of the airbag base fabric after the peeling step is 0.01% to 0.45%. (3) The method for recycling an airbag base fabric according to (2) above, wherein the silicone coating layer stripping solution is an aqueous solution further containing 1% by weight to 30% by weight of an alcohol component. (4) The method for recycling an airbag base fabric according to any one of (1) to (3) above, wherein the alkaline component includes sodium hydroxide, potassium hydroxide, or both. (5) The method for recycling an airbag base fabric according to (1) or (3) above, wherein the surfactant comprises a polyoxyalkylene alkyl ether-based nonionic surfactant having a hydrophobic moiety composed of an aliphatic alkyl group having an HLB value of 16.0 or more and 20.0 or less. (6) The method for recycling an airbag fabric according to any one of (1) to (3) above, wherein the surfactant includes an anionic surfactant, a nonionic surfactant, or both. (7) The method for recycling an airbag base fabric according to any one of (1), (3), and (4) above, wherein the alcohol component includes a water-soluble lower alcohol, a glycol, or both. (8) The method for recycling an airbag base fabric according to any one of (1) to (3) above, further comprising the step of rinsing the airbag base fabric with water after immersion in the silicone coating layer stripping solution. (9) The method for recycling an airbag base fabric according to any one of (1) to (3) above, wherein the synthetic fiber woven material constituting the airbag base fabric is a polyamide fiber. (10) The method for recycling an airbag base fabric according to (2) above, wherein the liquid used for gravity separation is an aqueous solution in which the specific gravity has been adjusted by dissolving salts. (11) A silicone coating layer remover liquid used to remove a silicone coating layer from a silicone-coated airbag base fabric, the silicone coating layer remover liquid being an aqueous solution containing 2% by weight to 30% by weight of an alkaline component, 0.05% by weight to 20% by weight of a surfactant, and 1% by weight to 30% by weight of an alcohol component. (12) The silicone coating layer remover according to (11) above, wherein the alcohol component comprises a water-soluble lower alcohol or glycol. [Effects of the Invention]

[0014] According to the present invention, compared to conventional methods for peeling a silicone coating layer, the peeled silicone coating layer has good cohesion and can be easily peeled from the base fabric, and an airbag base fabric with a reduced amount of residual silicone can be recovered. Therefore, by melting and pelletizing the airbag base fabric obtained by the present invention, it can be applied to various molded products as a high-quality recycled resin material with few impurities. DETAILED DESCRIPTION OF THE INVENTION

[0015] The present invention will be described in further detail below with reference to embodiments.

[0016] A first aspect of the airbag base fabric recycling method of the present invention is a method for recycling airbag base fabric, which involves peeling a silicone coating layer from a silicone-coated airbag base fabric, and includes an immersion step of immersing the airbag base fabric in a silicone coating layer peeling solution, which is an aqueous solution containing 1% by weight to 30% by weight of an alkaline component, 0.05% by weight to 20% by weight of a surfactant, and 1% by weight to 30% by weight of an alcohol component, and a peeling step of peeling the silicone coating layer from the airbag base fabric after immersion, and the ash content of the airbag base fabric after the peeling step is 0.01% to 0.45%.

[0017] A second aspect of the airbag fabric recycling method of the present invention is a method for removing a silicone coating layer from a silicone-coated airbag fabric, comprising an immersion step of immersing the airbag fabric in a silicone coating layer removal solution, which is an aqueous solution containing 1% by weight to 30% by weight of an alkaline component and 0.05% by weight to 20% by weight of a surfactant, and a removal step of removing the silicone coating layer from the airbag fabric after immersion, wherein the removal step comprises a step of specific gravity separation using a solution with a specific gravity of 1.01 to 1.10, and the ash content of the airbag fabric after the removal step is 0.01% to 0.45%.

[0018] The airbag base fabric to be treated in the present invention may be either offcuts generated in the airbag manufacturing process or offcuts removed from automobiles.

[0019] In the present invention, the airbag base fabric refers to a synthetic fiber fabric base coated with silicone, and includes a fabric in which part of the silicone coating layer remains after the silicone coating layer is peeled off.

[0020] Examples of the synthetic fiber woven material constituting the airbag base fabric include polyamide-based fibers, polyester-based fibers, aramid-based fibers, rayon-based fibers, polysulfone-based fibers, and ultra-high molecular weight polyethylene-based fibers. Among these, from the viewpoint of excellent mass productivity and economy, it is preferable that the synthetic fiber woven material constituting the airbag base fabric is polyamide-based fibers or polyester-based fibers, and polyamide-based fibers are more preferable.

[0021] Examples of polyamide fibers include fibers made of nylon 6, nylon 66, nylon 12, nylon 46, copolymer polyamides of nylon 6 and nylon 66, and copolymer polyamides obtained by copolymerizing nylon 6 with polyalkylene glycol, dicarboxylic acid, amine, etc. Among these, fibers made of nylon 66 are preferred from the viewpoints of heat resistance and flexibility.

[0022] As described above, the method for recycling airbag fabrics of the present invention includes an immersion step of immersing the airbag fabric in a silicone coating layer stripping solution and a peeling step of peeling the silicone coating layer from the airbag fabric after immersion. Depending on the size of the airbag fabric to be treated, the method may further include a cutting step of adjusting the airbag fabric to an appropriate size.

[0023] In the airbag fabric recycling method of the present invention, the silicone coating layer peeled from the airbag fabric can be peeled off in clumps. Conventional peeling techniques using alkaline solutions peeled off the silicone coating layer in the form of fine debris, some of which dissolved in the stripping solution. Therefore, although it appeared to have peeled off from the silicone coating layer to the naked eye, the silicone debris became entangled in the gaps in the weave of the synthetic fiber woven airbag fabric or in the fibers at the edges of the cut airbag fabric, making it difficult to remove. In contrast, the airbag fabric recycling method of the present invention not only peels the silicone coating layer evenly from the airbag fabric, but also easily gathers the peeled silicone coating layer into clumps, making it less likely for silicone residue to reattach during the water washing process. The recovered airbag fabric has an ash content of 0.01 to 0.45%, resulting in a high-quality product with few impurities. Furthermore, because the peeled silicone coating layer is easily recovered, it can be separately depolymerized to form monomers and reused as a silicone resin raw material, contributing to economic efficiency and reducing environmental impact.

[0024] <Cutting process> As described above, the airbag fabric recycling method of the present invention may further include a cutting step of adjusting the airbag fabric to an appropriate size. The timing of the cutting step is not particularly limited, but it is preferably performed before the immersion step or after the peeling step.

[0025] In the cutting process, the airbag fabric is preferably cut into a size of 5 mm or more and 500 mm or less, more preferably 15 mm or more and 300 mm or less, and particularly preferably 30 mm or more and 100 mm or less. A size of 5 mm or more reduces the edge surface of the airbag fabric, making it easier to prevent the airbag fabric from unraveling. Furthermore, a size of 500 mm or less provides excellent handling when the airbag fabric obtained by the airbag fabric recycling method of the present invention is melted and pelletized.

[0026] If the airbag base fabric to be treated is of an appropriate size without being cut, such as scraps generated in the airbag manufacturing process, it is not necessary to include a cutting step. The device used for cutting is not particularly limited, but examples include a cutter, a grinder, and a cutting machine.

[0027] <Soaking process> As described above, the airbag fabric recycling method of the present invention includes a dipping step in which the airbag fabric is dipped in a silicone coating layer peeling solution. The dipping step loosens the bonds of the silicone coating layer, making it easier to peel the silicone coating layer from the airbag in the peeling step described below. Furthermore, in the present invention, the partial decomposition of the silicone causes the peeled silicone coating layer to aggregate, making it easy to separate from the airbag fabric.

[0028] In the first embodiment of the airbag fabric recycling method of the present invention and the silicone coating layer stripping liquid of the present invention, the silicone coating layer stripping liquid is an aqueous solution containing an alkaline component, a surfactant, and an alcohol component. In the second embodiment of the airbag fabric recycling method of the present invention, the silicone coating layer stripping liquid is an aqueous solution containing at least an alkaline component and a surfactant, preferably an aqueous solution containing an alcohol component.

[0029] In the present invention, the alkaline component preferably contains a strongly alkaline inorganic alkaline component, more preferably contains sodium hydroxide, potassium hydroxide, or both, and further preferably contains sodium hydroxide from the standpoints of handleability and cost.

[0030] In the present invention, the content of the alkaline component in the silicone coating layer remover solution is 2% by weight to 30% by weight. The content of the alkaline component is more preferably 4% by weight to 25% by weight, and even more preferably 5% by weight to 20% by weight. If the content of the alkaline component is less than 2% by weight, hydrolysis between the silicone layer and the resin substrate does not proceed sufficiently, and the silicone layer remains on the substrate. On the other hand, if the alkaline concentration is more than 30% by weight, the alkaline strength is too high, increasing the risk of handling and the chemical costs are high, making it economically disadvantageous and difficult to apply.

[0031] In the present invention, the silicone coating layer remover liquid has a low dissolution rate of silicone and the removed silicone layer can be easily removed from the remover liquid, allowing for repeated use, thereby reducing the burden on the environment.

[0032] In the present invention, the silicone coating layer remover solution contains a surfactant, and the type of surfactant may be any of commonly used nonionic surfactants, anionic surfactants, cationic surfactants, and amphoteric surfactants.

[0033] For example, the nonionic surfactant is not particularly limited, but specific examples include polyoxyethylene nonylphenyl ether, polyoxyethylene octylphenyl ether, polyoxyethylene alkyl ether, polyoxyethylene lauryl ether, polyoxyethylene oleyl ether, polyoxyethylene tridecyl ether, polyoxyethylene cetyl ether, polyoxyethylene stearyl ether, polyoxyethylene alkylamine, aminopolyoxyethylene, sorbitan fatty acid ester, polyoxyethylene sorbitan laurate, polyoxyethylene sorbitan palmitate, polyoxyethylene sorbitan stearate, polyoxyethylene sorbitan oleate, naphthol ethylene oxide adduct, acetylene glycol ethylene oxide adduct, bisphenol A ethylene oxide adduct, oxyethylene oxypropylene block polymer, sorbitan fatty acid ester, polyoxyethylene sorbitan fatty acid ester, polyoxyethylene sorbitol fatty acid ester, glycerin fatty acid ester, polyoxyethylene fatty acid ester, polyoxyethylene alkylamine, and the like.

[0034] Furthermore, in the present invention, when the silicone coating layer remover solution contains an alcohol component, a polyoxyalkylene alkyl ether-based nonionic surfactant having a hydrophobic moiety composed of an aliphatic alkyl group and an HLB value of 13.0 to 20.0 can also be preferably used as the surfactant. The HLB value is a physical property that indicates the degree of hydrophilicity or hydrophobicity (lipophilicity) of a surfactant, and ranges from 0 to 20. The closer the HLB value is to 0, the higher the hydrophobicity, and the closer it is to 20, the higher the hydrophilicity. The HLB value is determined experimentally, but can also be calculated simply from the structure. Commonly known methods for calculating the HLB value include the Griffin method, the Kawakami method, and the Davis method. The HLB value of the surfactant used herein is the value determined by the Griffin method. The HLB value according to the Griffin method is calculated based on the formula: HLB value = 20 × (formula weight of the hydrophilic group of the surfactant) / (molecular weight of the surfactant).

[0035] In addition, two or more polyoxyalkylene alkyl ether nonionic surfactants having a hydrophobic moiety consisting of an aliphatic alkyl group can be used in combination, in which case the HLB value is the sum of the weight fractions of the HLB values ​​of each component.

[0036] In the present invention, when the silicone coating layer stripping solution contains an alcohol component, the surfactant preferably contains a polyoxyalkylene alkyl ether-based nonionic surfactant having a hydrophobic moiety composed of an aliphatic alkyl group with an HLB value of 16.0 to 20.0. The HLB value is more preferably 16.5 to 20.0. Having an HLB value within this range improves the penetration of the stripping solution into the substrate, and alkaline hydrolysis at the interface between the substrate and the silicone layer facilitates more uniform separation of the silicone layer from the substrate. Furthermore, because it has excellent affinity with the silicone layer, it prevents the separated silicone layer from reattaching to the substrate, making it easier to recover a higher-quality airbag base fabric. Furthermore, because the separated silicone coating layer is also easier to recover, it can be separately depolymerized to form silicone monomers, making it easier to reuse as a silicone resin raw material, contributing to economic efficiency and reduced environmental impact.

[0037] Furthermore, by setting the HLB value to 16 or higher, the hydrophobicity is not too strong, so when combined with an alcohol component, the silicone layer is less likely to dissolve in the stripping solution, making it easier for the silicone layer to separate uniformly from the substrate and less likely to remain on the substrate. Furthermore, the silicone decomposition products are less likely to dissolve in the stripping solution, making it easier to reuse the stripping solution and reducing the effort and cost required to dispose of the stripping solution.

[0038] Examples of anionic surfactants include fatty acid salts, alkyl sulfate ester salts, alkylbenzene sulfonates, alkylnaphthalene sulfonates, alkyl sulfosuccinates, alkyldiphenyl ether disulfonates, alkyl phosphates, polyoxyethylene alkyl sulfate ester salts, polyoxyethylene alkylaryl sulfate ester salts, alkanesulfonates, naphthalenesulfonate-formalin condensates, polyoxyethylene alkyl phosphate esters, N-methyl-N-oleoyl taurate, and α-olefin sulfonates.

[0039] Cationic surfactants and amphoteric surfactants include alkylamine salts, quaternary ammonium salts, alkylbetaines, and aminoxides.

[0040] In particular, in the present invention, the surfactant preferably contains an anionic surfactant, a nonionic surfactant, or both, because it has excellent permeability into resin fibers such as polyamide that constitute the airbag base fabric. It is even more preferable to use an anionic surfactant and a nonionic surfactant in combination.

[0041] The surfactant content in the silicone coating layer remover solution is 0.05% to 20% by weight. The surfactant content is more preferably 0.1% to 10% by weight. If the surfactant content is less than 0.05% by weight, sufficient penetration into the resin fibers will not be achieved, and if it is more than 20% by weight, excessive foaming may occur, which may result in poor operability.

[0042] In the first embodiment of the airbag fabric recycling method of the present invention and the silicone coating layer stripping solution of the present invention, the silicone coating layer stripping solution contains 1 wt % to 30 wt % of an alcohol component. Furthermore, in the second embodiment of the airbag fabric recycling method of the present invention, the silicone coating layer stripping solution preferably further contains 1 wt % to 30 wt % of an alcohol component. By including an alcohol component of 1 wt % or more, the stripping solution can easily penetrate into the airbag fabric, making it easier to reduce residual silicone. Furthermore, by keeping the alcohol component at 30 wt % or less, the stripped silicone layer moderately aggregates, improving its separability from the airbag fabric and making it less likely to remain on the fabric.

[0043] Examples of the alcohol component include water-soluble lower alcohols such as methanol, ethanol, n-propanol, and isopropanol; glycols such as ethylene glycol and propylene glycol; and glycol ethers such as diethylene glycol, dipropylene glycol, ethylene glycol monobutyl ether, and polyethylene glycol.

[0044] In the present invention, the alcohol component preferably contains water-soluble lower alcohols, glycols, or both, and more preferably contains water-soluble lower alcohols. Here, "water-soluble" in the context of water-soluble lower alcohols means that 1 g or more of the alcohol dissolves in 100 g of water at 20° C. Furthermore, "lower alcohol" refers to an alcohol having 5 or fewer carbon atoms.

[0045] The role of the alcohol component in the present invention is speculative, but it is believed that the presence of a hydroxyl group improves the penetration of the silicone coating layer stripping solution into the airbag base fabric, and also has the effect of agglomerating the silicone coating layer stripped from the airbag base fabric surface by hydrolysis with the alkaline component, preventing it from dispersing too much in the silicone coating layer stripping solution. In this case, if an alcohol component without an ether bond is used, the stripped silicone coating layer is more likely to form clumps. This is speculative, but it is believed that the presence of an ether bond increases the affinity with the stripped silicone coating layer around the ether group, resulting in a slight dispersion / dissolution effect of the silicone coating layer. Therefore, in the present invention, it is preferable that the alcohol component contains a water-soluble lower alcohol, a glycol, or both that does not contain an ether bond.

[0046] In the immersion step, the immersion time is appropriately adjusted depending on the immersion temperature. For example, when the immersion temperature is 50°C or lower, the hydrolysis reaction caused by the alkaline component proceeds slowly, making a long immersion time appropriate. Specifically, the immersion time is preferably 1 hour to 72 hours, more preferably 2 hours to 48 hours, and particularly preferably 4 hours to 24 hours. Furthermore, when the immersion temperature is higher than 50°C, the hydrolysis caused by the alkaline component proceeds quickly, making a short immersion time appropriate. Specifically, the immersion time is preferably 0.5 hours to 24 hours, more preferably 1 hour to 16 hours, and particularly preferably 2 hours to 12 hours. By setting the immersion temperature and immersion time within the above ranges, the silicone coating layer can be uniformly peeled from the airbag, and the peeled silicone coating layer can be easily aggregated into clumps. Furthermore, the silicone coating layer can be easily peeled sufficiently, reducing the amount of silicone dissolved in the silicone coating layer peeling solution and making silicone recovery easier.

[0047] The bath ratio of the silicone coating layer release liquid in the immersion step is preferably 0.5 to 100, more preferably 2 to 50, and particularly preferably 5 to 20. A bath ratio of 0.5 or greater allows the silicone coating layer to be sufficiently impregnated with the silicone coating layer release liquid. Furthermore, a bath ratio of 20 or less reduces the amount of release liquid used and reduces the recycling cost of the airbag base fabric. The bath ratio of the silicone coating layer release liquid refers to the weight ratio of the silicone coating layer release liquid to the weight of the airbag base fabric introduced into the immersion step (weight of silicone coating layer release liquid (g) / weight of airbag base fabric (g)).

[0048] <Peeling process> As described above, the method for recycling an airbag fabric of the present invention includes a peeling step in which the silicone coating layer is peeled off from the airbag fabric after immersion. In the method for recycling an airbag fabric of the present invention, the bond between the silicone coating layer and the airbag fabric is loosened in the immersion step, and then the silicone coating layer is peeled off by applying physical force in the peeling step.

[0049] A specific example of the peeling process, in a small scale such as in a laboratory or for trial production, is to remove the silicone coating layer from the airbag fabric by rubbing the surface with a hand or a jig after the immersion process. Examples of industrial methods include placing the airbag in a tank filled with liquid and subjecting it to stirring using a stirring blade, stirring using a water flow, stimulation by bubbles using a bubble generator, or ultrasonic vibration using an ultrasonic generator.

[0050] In particular, when these industrial methods are used, a method for separating the peeled silicone coating layer and the airbag base fabric can be used, for example, to utilize the difference in specific gravity between the silicone coating layer and the airbag base fabric and separate them in liquid. A method can be used.

[0051] In a first embodiment of the method for recycling an airbag fabric of the present invention, the peeling step preferably includes a step of performing specific gravity separation using a liquid with a specific gravity of 1.01 to 1.10. Furthermore, in a second embodiment of the method for recycling an airbag fabric of the present invention, the peeling step includes a step of performing specific gravity separation using a liquid with a specific gravity of 1.01 to 1.10. The specific gravity is more preferably 1.02 to 1.08. By setting the specific gravity to 1.01 or more, the silicone coating layer can be floated. Furthermore, by setting the specific gravity to 1.10 or less, the airbag fabric can be sunk. The liquid used for specific gravity separation is not particularly limited, but is preferably an aqueous solution in which the specific gravity has been adjusted by dissolving salts. Examples of salts used to adjust the specific gravity include sodium carbonate, sodium bicarbonate, sodium chloride, potassium chloride, and magnesium chloride.

[0052] The bath ratio in the gravity separation step is preferably 10 to 500, more preferably 20 to 300, and particularly preferably 50 to 200. A bath ratio of 10 or more eliminates overlapping of airbag fabrics and prevents the silicone coating layer from being held between the airbag fabrics. Furthermore, a bath ratio of 500 or less reduces the volume of the equipment. The bath ratio refers to the weight (g) of gravity-adjusted water relative to the weight (g) of airbag fabric placed in the gravity-adjusted water.

[0053] In the peeling process, it is preferable to minimize the force applied to the airbag base fabric to peel off the silicone. The greater the force applied to the airbag base fabric, the easier it is to peel off the silicone layer, but this may cause the airbag base fabric to defibrate, and the peeled silicone layer may become entangled with the defibrated fibers, making separation difficult. Furthermore, when stirring using a stirring blade, it is preferable to improve the flow state in the tank to reduce the power per unit liquid volume and the blade tip speed.

[0054] When stirring using a stirring blade in the peeling process, the type of stirring blade is not particularly limited, but it is preferable to use a large blade or a propeller blade or paddle blade with three or more stages. Examples of large blades include Maxblend, Fullzone, Supermix, home base blade, and large paddle blade. By using a large blade, the airbag base fabric is mixed up and down, making it easier to eliminate overlaps between the airbag base fabrics, thereby reducing the stirring power required to peel off the silicone layer. Furthermore, compared to using a small blade such as a propeller blade, the rotation speed can be reduced, and the blade tip speed can be reduced.

[0055] The ease with which the silicone coating layer peels during the peeling process is affected by the composition of the stripping solution, the immersion time, and the immersion temperature during the immersion process. When the stripping solution contains alcohol, the silicone coating layer peels more easily than when it does not. The longer the immersion time, the easier the silicone coating layer peels, and the higher the immersion temperature, the easier the silicone coating layer peels. If the stripping process is performed after immersion under conditions that make the silicone coating layer more easily peelable, the force applied to the airbag base fabric for peeling will be smaller, making it easier to prevent the airbag base fabric from unraveling. However, since adding alcohol, lengthening the immersion time, and increasing the immersion temperature all increase processing costs, it is desirable to use conditions that reduce costs within a range that allows for unraveling of the airbag base fabric.

[0056] The peeling step may include a washing step of washing the airbag base fabric. By including the washing step, the silicone coating layer peeling liquid impregnated in the airbag base fabric and the silicone coating layer adhering to the surface can be further removed. Examples of the washing step include stirring in a stirring tank filled with water or an organic solvent, and shower washing.

[0057] The peeling step may also include a drying step of drying the collected airbag fabric. By drying the airbag fabric, it becomes easier to obtain a high-quality airbag fabric with almost no silicone coating layer remaining. As the drying method, for example, vibration drying, hot air drying, vacuum drying, or other known drying methods can be used.

[0058] In the airbag fabric recovery method of the present invention, the ash content of the airbag fabric is used as an index for quantitatively evaluating the quality of the recovered airbag fabric. The ash content of the airbag fabric is measured as follows: The airbag fabric after the peeling process is dried under reduced pressure at 80°C for 2 hours, and the dry weight (A) of the airbag fabric is recorded. The dried airbag fabric is placed in a platinum crucible and fired in an electric furnace set at 800°C for 2 hours, and the weight (B) of the airbag fabric residue is recorded. The platinum crucible used here is one that has been fired in advance in an electric furnace set at 800°C for at least 2 hours. The airbag fabric after the peeling process refers to an airbag fabric that has undergone all operations of the peeling process. For example, if the peeling process includes a cleaning process and a drying process and ends with the drying process, the airbag fabric that has undergone the drying process is defined as the airbag fabric after the peeling process. The ash content of the airbag fabric is calculated as B / A x 100. Since the majority of the residue that does not burn is silica produced from the silicon in the silicone coating layer, the ash content is a quantitative indicator of the silicone component remaining in the airbag base fabric.

[0059] In the method for recycling airbag fabrics of the present invention, the silicone layer can be efficiently removed by the immersion step and peeling step, so the ash content of the airbag fabric after the peeling step is 0.01% to 0.45%. Although a lower ash content is preferable, a range of 0.05% to 0.45% can be indicated as a preferable range in terms of balancing practicality and cost.

[0060] The airbag base fabric obtained by the airbag base fabric recycling method of the present invention can be melted and pelletized to become a high-quality recycled resin that can be used as a raw material for various molded products. [Example]

[0061] The effects of the present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0062] [Ash content measurement] The ash content in each of the examples and comparative examples was evaluated by the following method.

[0063] The dried airbag fabric obtained in each case was weighed, placed in a pre-dried platinum crucible, and fired for two hours in an electric furnace set at 800°C to obtain an airbag fabric residue. This residue was weighed and divided by the sample weight before firing to obtain the ash content as a percentage.

[0064] [Airbag base fabric] Airbag base fabric A was used, which was a woven fabric made of nylon 66 fiber coated with a silicone layer at 15 g / m², and cut into 50 mm square pieces. Ten pieces of this base fabric were used for each experiment. The ash content of airbag base fabric A before treatment was measured using the above method and found to be 3.3%. Similarly, a base material made of only non-silicone-coated nylon 66 fiber fabric was measured and found to be less than 0.01%.

[0065] [Surface observation of airbag fabric] The surface of the airbag base fabric after the silicone coating layer was peeled off was measured using an optical microscope (Leica Microsystems Digital Microscope DVM6) at 300x magnification to observe the remaining condition of the silicone coating layer.

[0066] [Example 1] The silicone coating layer stripper consisted of 10 wt% sodium hydroxide, 1.3 wt% (0.52 wt% surfactant) commercially available laundry detergent containing linear alkylbenzene sulfonate and 40% polyoxyethylene alkyl ether as surfactants, and 1 wt% isopropanol dissolved in ion-exchange water. The silicone-coated airbag fabric was cut into 50 mm squares, and 10 pieces were weighed and placed in a beaker with 20 times the weight of the stripper solution and left to stand at room temperature (25°C). After 4 hours, the airbag fabric was washed in a beaker containing 300 ml of water. The airbag fabric was removed and the state of the silicone layer on the surface was observed. When lightly touched with a finger, the silicone coating layer peeled off in a single rubber-like lump. The treated airbag fabric was then dried under reduced pressure at 80°C and the ash content was measured using the method described above. The ash content was 0.23%. Furthermore, when the surface of the airbag fabric was observed with an optical microscope, no silicone coating was observed on the surface.

[0067] [Example 2 and Comparative Examples 1, 2, and 3] The peeling state of the silicone coating layer was observed and the ash content was measured in the same manner as in Example 1, except that the isopropanol concentration was 0 wt% (Comparative Example 1), 0.6 wt% (Comparative Example 2), 5 wt% (Example 2), and 50 wt% (Comparative Example 3). As a result, in Comparative Example 1, the silicone coating layer only partially peeled off when the base fabric was rubbed, and the peeled silicone coating layer did not clump together but instead became crumb-like. In Comparative Example 2, the silicone coating layer peeled off in chunks when rubbed lightly, but the ash content was 0.48%. Furthermore, observation with an optical microscope revealed that a thin layer of the silicone coating layer remained on the entire surface of the base fabric. In Example 2, peeling occurred similarly to Example 1, and the ash content was 0.38%. On the other hand, in Comparative Example 3, where the isopropanol concentration was 50 wt%, the silicone coating layer peeled off easily, but the ash content was 0.58%, and microscopic observation revealed that aggregates of the silicone coating layer remained in the gaps between the fiber woven fabric of the airbag base fabric.

[0068] [Example 3] The peeling state of the silicone coating layer was observed and the ash content was measured in the same manner as in Example 2, except that ethylene glycol monobutyl ether was used instead of isopropanol as the alcohol component. As a result, compared to Example 2, it was difficult to hold together some of the peeled silicone coating layer. The ash content of this sample was measured and found to be 0.30%.

[0069] [Example 4 and Comparative Example 4] The peeling state of the silicone coating layer was observed and the ash content was measured in the same manner as in Example 1, except that the sodium hydroxide concentration was 5 wt% (Example 4) and 1 wt% (Comparative Example 4). As a result, in Example 4, the silicone coating peeled off in chunks when the base fabric was lightly rubbed, and the ash content was 0.42%. On the other hand, in Comparative Example 4, the silicone coating did not peel off at all, even when the airbag base fabric was rubbed hard.

[0070] Comparative Example 5 A stripping solution for the silicone coating layer was prepared with the following blending ratio: sodium hydroxide concentration 1 wt%, surfactants 1 wt% sodium lauryl sulfate, 1 wt% sodium dioctyl sulfosuccinate, and 5 wt% polyoxyethylene polyoxypropylene alkyl ether, and alcohol component 3 wt% ethylene glycol monobutyl ether. Ten sheets of airbag fabric were placed in the stripping solution and immersed at 50°C for 1 hour while stirring. The conditions other than those described were the same as in Example 1. As a result, the silicone coating layer did not peel off at all, even when the airbag fabric was rubbed hard.

[0071] The results of Comparative Examples 4 and 5 show that if the alkali concentration is too low, the releasability of the silicone coating layer deteriorates significantly, and therefore the alkali concentration must be 5% by weight or more.

[0072] Comparative Example 6 Except for not adding a surfactant, the peeling state of the silicone coating layer was observed in the same manner as in Example 1. As a result, in Comparative Example 6, the silicone coating layer did not peel off at all even when the airbag base fabric was rubbed hard.

[0073] [Example 5] A commercially available laundry detergent containing 10% by weight of sodium hydroxide, 40% linear alkylbenzene sulfonate, and 40% polyoxyethylene alkyl ether as a silicone coating layer stripper was dissolved in ion-exchange water to a concentration of 2.5% by weight (1.04% by weight of surfactant). The silicone-coated airbag fabric was cut into 50 mm squares, and 20.0 g was weighed out. This was then placed in a beaker with 5 times the weight of the stripper and allowed to stand at room temperature (25°C). After 72 hours, the airbag fabric was placed in a beaker (JAN: 4977642001954) containing 2000 ml of 5.0% by weight sodium chloride aqueous solution and stirred for 15 minutes using a large paddle blade (stirring blade diameter: 60 mm, stirring blade width: 100 mm). The temperature of the aqueous solution at this time was 25°C, and the specific gravity was 1.03. After stirring, the solution was left to stand for 1 minute, and the silicone layer floating on the water surface was removed, and the airbag fabric was recovered. The collected airbags were placed in a beaker containing 2000 mL of ion-exchanged water and stirred for one minute. After discarding the ion-exchanged water, the airbag fabric was washed by placing it in a new 2000 mL beaker of ion-exchanged water and stirring for one minute. The treated airbag fabric was then dried under reduced pressure at 80°C and the ash content was measured using the method described above. The ash content was found to be 0.24%. By adjusting the specific gravity to a high level, the buoyancy of the silicone coating increased, and no silicone coating layer sunk to the bottom, allowing it to be easily separated from the airbag fabric.

[0074] [Example 6] The silicone layer was removed in the same manner as in Example 5, except that the airbag fabric was immersed for 24 hours in a stripping solution prepared by dissolving 2.5 wt% of a commercially available laundry detergent containing 10 wt% sodium hydroxide, 40% linear alkylbenzene sulfonate surfactants, and polyoxyethylene alkyl ether (1.04 wt% surfactant), and 10 wt% isopropanol in ion-exchange water. The ash content of the resulting airbag fabric was 0.22%. As in Example 5, the airbag fabric and the silicone coating layer were successfully separated by adjusting the specific gravity of the solution to a high level and performing gravity separation. Furthermore, the addition of isopropanol to the stripping solution improved the permeability of the stripping solution into the airbag fabric, enabling the silicone layer to be removed with a shorter immersion time.

[0075] [Example 7] The silicone layer was removed in the same manner as in Example 6, except that ion-exchanged water was used instead of the 5.0 wt% sodium chloride aqueous solution. The water temperature was 25°C, and the specific gravity of the water was 1.00. If an appropriate remover was used, removal was possible regardless of the specific gravity, and the ash content of the recovered airbag base fabric was 0.26%.

[0076] [Example 8] The silicone coating layer was peeled off in the same manner as in Example 6, except that a 7.0 wt% aqueous solution of sodium chloride was used. The temperature of the aqueous solution was 25°C, and the specific gravity was 1.05. The airbag fabric and the silicone coating layer were successfully separated, and the ash content of the recovered airbag fabric was 0.21%.

[0077] [Example 9] The silicone coating layer was peeled off in the same manner as in Example 6, except that a 12.0 wt% aqueous solution of sodium chloride was used. The temperature of the aqueous solution was 25°C, and the specific gravity was 1.08. The airbag fabric and the silicone coating layer were successfully separated, and the ash content of the recovered airbag fabric was 0.21%.

[0078] [Example 10] The silicone coating layer was removed in the same manner as in Example 6, except that a 20.0 wt% aqueous sodium chloride solution was used. The temperature of the aqueous solution was 25°C, and the specific gravity was 1.11. If an appropriate remover solution was used, removal was possible regardless of the specific gravity, and the ash content of the recovered airbag base fabric was 0.25%.

[0079] [Example 11 and Comparative Example 7] The peeling state of the silicone coating layer and the ash content were observed and measured in the same manner as in Example 1 (Example 11), except that a polyoxyalkylene alkyl ether-based nonionic surfactant with an HLB value of 18.4 was used, and in the same manner as in Example 11, except that no isopropanol was added (Comparative Example 7). As a result, in Example 11, the silicone layer was observed to peel off from the airbag base fabric in sheet form and float to the water surface during stirring. The ash content of the recovered airbag base fabric was 0.1%. On the other hand, in Comparative Example 7, the silicone coating layer did not peel off at all, even when the airbag base fabric was rubbed hard.

[0080] [Comparative Example 8] The peeling state of the silicone coating layer was observed and the ash content was measured in the same manner as in Example 1, except that a polyoxyalkylene alkyl ether-based nonionic surfactant with an HLB value of 13.4 was used. As a result, part of the silicone layer dissolved in the stripping solution and remained on the base fabric. The ash content of the recovered airbag base fabric was 0.46%. [Industrial Applicability]

[0081] According to the present invention, it is possible to efficiently remove the silicone coating layer coated on the airbag base fabric. Therefore, by melting and pelletizing the airbag base fabric obtained by the present invention, it is possible to apply it to various molded products as a high-quality recycled resin raw material with few impurities.

Claims

1. The method for recycling airbag base fabric involves peeling off a silicone coating layer from a silicone-coated airbag base fabric, and includes an immersion step of immersing the airbag base fabric in a silicone coating layer peeling liquid, which is an aqueous solution containing 2% by weight to 30% by weight of an alkaline component, 0.05% by weight to 20% by weight of a surfactant, and 1% by weight to 30% by weight of an alcohol component, and a peeling step of peeling off the silicone coating layer from the airbag base fabric after immersion, wherein the ash content of the airbag base fabric after the peeling step is 0.01% to 0.45%.

2. A method for recycling airbag base fabrics, in which a silicone coating layer is peeled off from a silicone-coated airbag base fabric, includes an immersion step of immersing the airbag base fabric in a silicone coating layer peeling liquid, which is an aqueous solution containing 2% by weight to 30% by weight of an alkaline component and 0.05% by weight to 20% by weight of a surfactant, and a peeling step of peeling off the silicone coating layer from the airbag base fabric after immersion, wherein the peeling step comprises a step of specific gravity separation using a liquid having a specific gravity of 1.01 to 1.10, and the ash content of the airbag base fabric after the peeling step is 0.01% to 0.45%.

3. The method for recycling an airbag base fabric according to claim 2, wherein the silicone coating layer stripping liquid is an aqueous solution further containing 1% by weight to 30% by weight of an alcohol component.

4. The method for recycling an airbag base fabric according to any one of claims 1 to 3, wherein the alkaline component includes sodium hydroxide, potassium hydroxide, or both.

5. The method for recycling an airbag base fabric according to claim 1 or 3, wherein the surfactant comprises a polyoxyalkylene alkyl ether-based nonionic surfactant having a hydrophobic moiety composed of an aliphatic alkyl group having an HLB value of 16.0 or more and 20.0 or less.

6. The method for recycling an airbag base fabric according to any one of claims 1 to 3, wherein the surfactant comprises an anionic surfactant, a nonionic surfactant, or both.

7. The method for recycling an airbag base fabric according to claim 1 or 3, wherein the alcohol component comprises a water-soluble lower alcohol, a glycol, or both.

8. The method for recycling an airbag base fabric according to any one of claims 1 to 3, further comprising a step of rinsing the airbag base fabric with water after immersion in the silicone coating layer peeling liquid.

9. The method for recycling an airbag base fabric according to any one of claims 1 to 3, wherein the synthetic fiber woven material constituting the airbag base fabric is a polyamide fiber.

10. The method for recycling an airbag base fabric according to claim 2, wherein the liquid used for specific gravity separation is an aqueous solution in which a salt is dissolved to adjust the specific gravity.

11. A silicone coating layer remover liquid used to remove a silicone coating layer from a silicone-coated airbag base fabric, the silicone coating layer remover liquid being an aqueous solution containing 2% by weight to 30% by weight of an alkali component, 0.05% by weight to 20% by weight of a surfactant, and 1% by weight to 30% by weight of an alcohol component.

12. The silicone coating layer remover according to claim 11, wherein the alcohol component comprises a water-soluble lower alcohol or a glycol.