JP7770745B2 - Photocurable silicone rubber coating composition, coated airbag fabric and method for producing same - Google Patents

Description

The present invention relates to a photocurable silicone rubber coating composition and a method for producing a silicone-coated base fabric for airbags that is coated with a cured film of the composition.

Conventionally, base fabrics coated with curable silicone rubber to form a cured silicone rubber film on the surface have been ideally used as base fabrics for automotive airbags due to their excellent heat resistance, airtightness, weather resistance, and flame retardancy. However, because airbags are stored in a folded state, such as inside pillars, undesirable adhesion (blocking) can occur between coating materials on the surface of the base fabric. If this blocking occurs or if the cured coating surface has high friction, the airbag may not deploy properly in a vehicle collision, potentially preventing it from fulfilling its role of preventing injury or death to passengers. Furthermore, if the coating has high friction, passengers may suffer abrasions from contact with the airbag surface when the airbag deploys. Therefore, there is a need for coating materials that do not cause blocking and have a low surface friction coefficient. Furthermore, when an airbag base fabric is folded and stored in a pillar or the like inside a vehicle, if the base fabric has low flexibility, the volume of the airbag base fabric when folded increases, compressing the passenger compartment space. Therefore, there is a demand for airbag base fabrics with high flexibility.

As a countermeasure to this problem, a low-friction silicone coating composition containing an addition-curable silicone rubber composition, inorganic fillers such as alumina, talc, and silica, and an organic solvent, and a method for forming a silicone rubber coating film using the composition have been disclosed (Patent Document 1). In this method, the organic solvent in the composition is volatilized during heat curing, exposing a portion of the inorganic filler to the surface of the coating film, achieving low friction and allowing the production of a silicone rubber coating film with low friction and high surface roughness. However, in recent years, concerns have arisen about reducing _CO2 emissions and the health hazards caused by volatile organic compounds (VOCs), making methods that use large amounts of organic solvent undesirable.

A heat-curable silicone coating composition containing a polysiloxane with vinyl groups only on the side chains, a polysiloxane with hydrosilyl groups, and talc has been disclosed as a silicone coating agent for airbag base fabrics (Patent Document 2). This composition produces airbag base fabrics with low friction and excellent blocking resistance. However, because the silicone coating layer is hard, there are concerns that the coated base fabrics lack flexibility and have poor foldability.

Another coating material for airbag fabrics is disclosed in Patent Document 3, which discloses an anti-blocking coating containing a blend of fluoropolymer, talc, alumina, aqueous aliphatic polyurethane, a surfactant, and an adhesive. This coating material produces a coated fabric with excellent blocking resistance and flame retardancy. However, the only specific example of a resin used to form the coating layer on the fabric is a urethane resin containing an ethylene-vinyl acetate copolymer. Urethane resins generally have poor heat resistance and moist heat resistance, raising concerns about durability in high-temperature, humid environments such as the interior of a car in the summer. Additionally, Patent Document 4 discloses an aqueous coating composition in which talc, chlorite, and other solid lubricants are dispersed in an aqueous solution of sodium polyacrylate, a water-soluble organic polymer. This aqueous coating composition can produce a coating with low friction and excellent blocking resistance. However, because it uses a water-soluble organic polymer, the coating swells in humid environments due to moisture, raising concerns about an increase in the coefficient of friction and a decrease in blocking resistance and adhesion.

JP 2016-098319 A JP 2010-083946 A JP 2016-005953 A Special table 2013-516522 publication

The present invention therefore aims to provide a photocurable silicone rubber coating composition that, when applied to a base fabric, produces a cured coating that is resistant to blocking, has a low surface friction, is highly flexible, and can be compacted for storage, without using large amounts of organic solvents. It also aims to provide a method for producing a silicone-coated base fabric for airbags that is coated with a cured coating of the silicone rubber coating composition.

As a result of extensive research into achieving the above object, the present inventors discovered that the above problems could be solved by the photocurable silicone rubber coating composition described below, which led to the creation of the present invention.
[1]
(A) 100 parts by mass of a linear organopolysiloxane containing two or more silicon-bonded alkenyl groups per molecule and having a number-average degree of polymerization of 10 to 1,000;
(B) an organohydrogenpolysiloxane containing two or more silicon-bonded hydrogen atoms per molecule: an amount such that the number of silicon-bonded hydrogen atoms contained per molecule of this component is 0.4 to 5 per total number of silicon-bonded alkenyl groups in component (A);
(C) 50 to 150 parts by mass of fine talc powder having a median diameter (D50) of 0.5 to 20 μm, and (D) an effective amount of a platinum group compound catalyst that is activated by light with a wavelength of 200 to 500 nm as a hydrosilylation reaction catalyst,
A photocurable silicone rubber coating composition comprising:
[2]
The photocurable silicone rubber coating composition according to [1], wherein the component (D) is bis(acetylacetonato)platinum(II) or (trimethyl)methylcyclopentadienylplatinum(IV).
[3]
The photocurable silicone rubber coating composition according to [1] or [2], wherein component (A) is an organopolysiloxane having vinyl groups only at both molecular chain terminals.
[4]
The photocurable silicone rubber coating composition according to any one of [1] to [3], wherein component (A) is an organopolysiloxane in which 0.1 to 15 mol % of all substituents bonded to silicon atoms are alkenyl groups having 2 to 8 carbon atoms.
[5]
A coated airbag fabric having a cured product layer of the photocurable silicone rubber coating composition according to any one of [1] to [4] as the outermost layer.
[6]
A method for producing a coated airbag fabric, comprising the steps of: applying the photocurable silicone rubber coating composition according to any one of [1] to [4] to the outermost layer of an airbag fabric; and irradiating the surface coated with the photocurable silicone rubber coating composition with light at a dose of 100 to 10,000 mJ/ ^cm2 .
[7]
[6] A method for producing a silicone rubber-coated airbag fabric according to [6], which comprises a curing acceleration step at 40 to 120°C for 5 to 120 seconds following the light irradiation step.

The photocurable silicone rubber coating composition of the present invention, when coated on the outermost layer of a base fabric, does not require the use of large amounts of organic solvents and provides a cured coating (cured product layer) that is resistant to blocking, has a low surface friction, is highly flexible, and can be compacted for storage. Therefore, particularly in the production of airbags, using a base fabric coated with this composition can prevent poor deployment of the airbag and abrasions caused by contact between the airbag surface and the occupant. Furthermore, the airbag can be easily folded and stored in a compact size inside the vehicle.

The photocurable silicone rubber coating composition of the present invention comprises the following components (A) to (D):
(A) 100 parts by mass of a linear organopolysiloxane containing two or more silicon-bonded alkenyl groups per molecule and having a number-average degree of polymerization of 10 to 1,000;
(B) an organohydrogenpolysiloxane containing two or more silicon-bonded hydrogen atoms per molecule: an amount such that the number of silicon-bonded hydrogen atoms contained per molecule of this component is 0.4 to 5 per total number of silicon-bonded alkenyl groups in component (A);
(C) 50 to 150 parts by mass of fine talc powder having a median diameter (D50) of 0.5 to 20 μm, and (D) an effective amount of a platinum group compound catalyst that is activated by light with a wavelength of 200 to 500 nm as a hydrosilylation reaction catalyst,
Each component is described in detail below.

[Component (A)]
The linear organopolysiloxane of component (A) is an organopolysiloxane containing two or more silicon-bonded alkenyl groups per molecule and having a number-average degree of polymerization of 10 to 1,000, and is the base polymer (main component) of the composition of the present invention.

The molecular structure of component (A) is a linear main chain consisting essentially of repeating diorganosiloxane units, and diorganopolysiloxanes in which both molecular chain terminals are blocked with triorganosiloxy groups are particularly preferred. Furthermore, the position of the silicon atom to which the alkenyl group is bonded in the molecule of component (A) may be either or both at the molecular chain terminal (i.e., triorganosiloxy group) and/or in the middle of the molecular chain (i.e., difunctional diorganosiloxane units located at non-terminal positions).

The alkenyl group bonded to the silicon atom in component (A) typically has 2 to 8 carbon atoms, and preferably 2 to 4 carbon atoms. Specific examples include vinyl, allyl, propenyl, butenyl, pentenyl, hexenyl, cyclohexenyl, and heptenyl groups, with vinyl groups being particularly preferred.

The content of alkenyl groups bonded to silicon atoms in component (A) is preferably 0.1 to 15 mol %, more preferably 0.5 to 13 mol %, and even more preferably 1.0 to 11 mol %, of all substituents bonded to silicon atoms in the organopolysiloxane. If the alkenyl group content is less than 0.1 mol % of all substituents bonded to silicon atoms, the resulting cured coating may not have sufficiently low friction, while if it exceeds 15 mol %, the resulting cured product may be brittle.

The monovalent organic group bonded to the silicon atom other than the alkenyl group in component (A) is preferably a monovalent hydrocarbon group having 1 to 12 carbon atoms, and more preferably a monovalent hydrocarbon group having 1 to 10 carbon atoms. Specific examples of monovalent hydrocarbon groups include alkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl, cyclohexyl, and heptyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl and phenethyl; and halogen-substituted alkyl groups such as chloromethyl, 3-chloropropyl, and 3,3,3-trifluoropropyl. Methyl is particularly preferred.

The number-average degree of polymerization of component (A) is 10 to 1,000, preferably 20 to 800, and more preferably 50 to 500. If the number-average degree of polymerization is lower than 10, the mechanical properties of the resulting silicone rubber may deteriorate. Furthermore, if the number-average degree of polymerization is higher than 1,000, the viscosity of the resulting silicone rubber coating composition may increase, resulting in poor coating workability.

In this specification, the number average degree of polymerization is a value calculated as the number average degree of polymerization from the value of the number average molecular weight obtained by GPC (gel permeation chromatography) analysis using toluene as a developing solvent under the following conditions, converted into polystyrene:
[Measurement conditions]
Developing solvent: toluene Flow rate: 0.35 mL/min
Detector: Refractive index detector (RI)
Column: TSK Guard column Super H-L
TSKgel SuperH4000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH3000 (6.0mm I.D. x 15cm x 1)
TSKgel SuperH2000 (6.0mm I.D. x 15cm x 2)
(Both manufactured by Tosoh Corporation)
Column temperature: 40°C
Sample injection volume: 10 μL (toluene solution with a concentration of 0.5% by mass)

The above-mentioned component (A) may be liquid at 25°C, and the viscosity of the above-mentioned component (A) at 25°C is preferably 10 to 100,000 mPa·s, more preferably 20 to 30,000 mPa·s, and even more preferably 40 to 10,000 mPa·s. If the viscosity of component (A) is below 10 mPa·s, the mechanical properties of the resulting silicone rubber may deteriorate, while if it exceeds 100,000 mPa·s, the viscosity of the resulting silicone rubber coating composition may increase, resulting in poor coating workability.

In this specification, viscosity is a value measured at 25°C using a rotational viscometer according to the method described in JIS K 7117-1:1999.

Specific examples of the organopolysiloxane of component (A) include a dimethylsiloxane-methylvinylsiloxane copolymer capped at both molecular chain terminals with trimethylsiloxy groups, a methylvinylpolysiloxane capped at both molecular chain terminals with trimethylsiloxy groups, a dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer capped at both molecular chain terminals with trimethylsiloxy groups, a dimethylpolysiloxane capped at both molecular chain terminals with dimethylvinylsiloxy groups, a methylvinylpolysiloxane capped at both molecular chain terminals with dimethylvinylsiloxy groups, and a dimethylsiloxane-methylpolysiloxane capped at both molecular chain terminals with dimethylvinylsiloxy groups. Examples of organopolysiloxanes include vinylsiloxane copolymers, dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymers terminally blocked with dimethylvinylsiloxy groups, dimethylpolysiloxanes terminally blocked with divinylmethylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers terminally blocked with divinylmethylsiloxy groups, dimethylpolysiloxanes terminally blocked with trivinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymers terminally blocked with trivinylsiloxy groups, and mixtures of two or more of these organopolysiloxanes.
When the organopolysiloxane of component (A) is an organopolysiloxane having vinyl groups only at both molecular chain ends, such as a dimethylpolysiloxane terminated at both molecular chain ends with dimethylvinylsiloxy groups, the hardness of the resulting cured coating is reduced, and air bag fabrics having such cured coatings have excellent flexibility.

The organopolysiloxane of component (A) may use either a single compound or a combination of two or more different compounds.
In the composition of the present invention, the content of component (A) is preferably 20 to 80% by mass, and more preferably 30 to 70% by mass.

[(B) Component]
Component (B), an organohydrogenpolysiloxane containing two or more silicon-bonded hydrogen atoms (hydrosilyl groups) per molecule, primarily undergoes a hydrosilylation addition reaction with the alkenyl groups in component (A) above, and acts as a crosslinking agent (curing agent).

The molecular structure of component (B) can be, for example, linear, cyclic, branched, or three-dimensional network (resinous) structure, but is preferably liquid at 25°C. It is characterized by having two or more hydrogen atoms (hydrosilyl groups) bonded to silicon atoms per molecule, and preferably three or more. More specifically, it typically has 2 to 300, preferably 3 to 200, and more preferably 3 to 100 hydrosilyl groups. Such hydrosilyl groups may be located at either the terminal or midway along the molecular chain, or both.

As this organohydrogenpolysiloxane, one having the average composition formula represented by the following formula (1) can be used.

In the above formula (1), R is independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, such as alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl, cyclohexyl, octyl, nonyl, and decyl; aryl groups such as phenyl, tolyl, xylyl, and naphthyl; aralkyl groups such as benzyl, phenylethyl, and phenylpropyl; and groups in which some or all of the hydrogen atoms have been substituted with halogen atoms such as fluorine, bromine, or chlorine, such as chloromethyl, chloropropyl, bromoethyl, and trifluoropropyl. R is more preferably an alkyl group or an aryl group, and even more preferably a methyl group. R does not include aliphatic unsaturated hydrocarbon groups such as alkenyl groups. Furthermore, it is preferable that a is a positive number between 0.7 and 2.1, b is a positive number between 0.001 and 1.0, and a+b is a positive number between 0.8 and 3.0; more preferably, a is a positive number between 1.0 and 2.0, b is a positive number between 0.01 and 1.0, and a+b is a positive number between 1.5 and 2.5.

Examples of component (B) include 1,1,3,3-tetramethyldisiloxane, 1,3,5,7-tetramethylcyclotetrasiloxane, tris(hydrogendimethylsiloxy)methylsilane, tris(hydrogendimethylsiloxy)phenylsilane, methylhydrogencyclopolysiloxane, methylhydrogensiloxane-dimethylsiloxane cyclic copolymer, methylhydrogenpolysiloxane terminated at both molecular chain ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane copolymer terminated at both molecular chain ends with trimethylsiloxy groups, dimethylsiloxane-methylhydrogensiloxane-methylphenylsiloxane copolymer terminated at both molecular chain ends with trimethylsiloxy groups, and dimethylsiloxane-methylhydrogensiloxane-diphenylsiloxane copolymer terminated at both molecular chain ends with trimethylsiloxy groups. and compounds of the formula: R Organosiloxane copolymers consisting of siloxane units represented by the formula: R ₃ SiO _1/2 and siloxane units represented by the formula: R ₂ HSiO _1/2 and siloxane units represented by the formula: SiO _4/2 ; organosiloxane copolymers consisting of siloxane units represented by the formula: R ₂ HSiO _1/2 and siloxane units represented by the formula: SiO _4/2 ; siloxane units represented by the formula: RHSiO _2/2 and siloxane units represented by the formula: RSiO _3/2 or siloxane units represented by the formula: HSiO _3/2的硅氧烷基的硅氧烷共聚物，但优选为基氧烷烷、基氧烷烷共聚物组合 ...

The amount of component (B) to be blended is such that the number of silicon-bonded hydrogen atoms (hydrosilyl groups) in component (B) is 0.4 to 5 moles (or units), preferably 0.8 to 4 moles (or units), and more preferably 1.2 to 3 moles (or units) per mole of silicon-bonded alkenyl groups in component (A). If the number of hydrosilyl groups in component (B) is less than 0.4 moles per mole of silicon-bonded alkenyl groups in component (A), the composition will not cure sufficiently, and if it exceeds 5 moles, the heat resistance of the resulting silicone rubber cured product may deteriorate significantly.
In addition, when the photocurable silicone rubber coating composition of the present invention contains a component other than component (A) that has an alkenyl group bonded to a silicon atom and/or when the photocurable silicone rubber coating composition contains a component other than component (B) that has a hydrogen atom bonded to a silicon atom (hydrosilyl group), it is preferable to adjust the amount of each component so that the number of silicon-bonded hydrogen atoms (hydrosilyl groups) in the entire composition is 0.4 to 5 moles (or units) per mole (or units) of silicon-bonded alkenyl groups in the entire composition.

The organohydrogenpolysiloxane of component (B) above may be used alone or in combination of two or more types.

[(C) Component]
Component (C) is a fine talc powder having a median diameter (D50) of 0.5 to 20 μm, and is added to the composition of the present invention as an inorganic filler to impart low friction to the surface of the resulting cured coating.

The talc fine powder of component (C) has a median diameter of 0.5 to 20 μm, preferably 1 to 15 μm, and more preferably 2 to 10 μm. The median diameter is measured by laser diffraction. If the median diameter is greater than 20 μm, the surface of the resulting cured coating will be rough, resulting in increased frictional resistance and the desired properties may not be achieved. If the median diameter is less than 0.5 μm, the viscosity of the composition will be high, which may reduce coating workability.

The amount of component (C) blended is 50 to 150 parts by mass, preferably 60 to 120 parts by mass, and particularly preferably 70 to 100 parts by mass, per 100 parts by mass of component (A). If the amount of component (C) blended is less than 50 parts by mass, the surface of the resulting cured coating may not exhibit low friction, while if it is more than 150 parts by mass, the viscosity of the resulting composition may increase, resulting in poor coating workability.

[(D) Component]
Component (D) is a platinum group compound catalyst that is activated by light with a wavelength of 200 to 500 nm and is a hydrosilylation catalyst. It is inactive in the absence of light and is activated by irradiation with light with a wavelength of 200 to 500 nm, preferably 300 to 450 nm, to promote the hydrosilylation reaction between the alkenyl groups in component (A) and the silicon-bonded hydrogen atoms in component (B). Here, "activation" of the catalyst refers to a state in which, in the presence of alkenyl groups, silicon-bonded hydrogen atoms, and the catalyst, the hydrosilylation reaction proceeds at room temperature (25°C) or higher.

Examples of such component (D) include β-diketonato platinum complex compounds, (η ⁵ -cyclopentadienyl)trialkyl platinum complex compounds, and derivatives thereof. Specific examples include trimethyl(acetylacetonato)platinum(IV), trimethyl(3,5-heptanedionato)platinum(IV), trimethyl(methylacetoacetate)platinum(IV), bis(acetylacetonato)platinum(II), bis(2,4-pentanedionato)platinum(II), bis(2,4-hexanedionato)platinum(II), bis(2,4-heptanedionato)platinum(II), bis(3,5-heptanedionato)platinum(II), bis(1-phenyl-1,3-butanedionato)platinum(II), bis(1,3-diphenyl-1,3-propanedionato)platinum(II), bis(hexafluoroacetylacetonato)platinum(II), and bis(hexafluoroacetylacetonato)platinum(II). (methylcyclopentadienyl)trimethylplatinum(IV), (cyclopentadienyl)trimethylplatinum(IV), (1,2,3,4,5-pentamethylcyclopentadienyl)trimethylplatinum(IV), (cyclopentadienyl)dimethylethylplatinum(IV), (cyclopentadienyl)dimethylacetylplatinum(IV), (trimethylsilylcyclopentadienyl)trimethylplatinum(IV), (methoxycarbonylcyclopentadienyl)trimethylplatinum(IV), (dimethylphenylsilylcyclopentadienyl)trimethylcyclopentadienylplatinum(IV), and the like. Of these, particularly preferred are bis(acetylacetonato)platinum(II) and derivatives in which the hydrogen atom bonded to the carbon atom of the acetylacetonato group is substituted with an alkyl group, and (cyclopentadienyl)trimethylplatinum(IV) and derivatives in which the hydrogen atom bonded to the carbon atom of the cyclopentadienyl group is substituted with an alkyl group, with bis(acetylacetonato)platinum(II) or (trimethyl)methylcyclopentadienylplatinum(IV) being particularly preferred.

When using these catalysts, if they are solid catalysts they can be used in solid form, but to obtain a more uniform cured product it is preferable to use them dissolved in an appropriate solvent.

The amount of component (D) added should be an effective amount as an addition reaction catalyst, and is preferably in the range of typically 0.5 to 1,000 ppm, preferably 1 to 500 ppm, and more preferably 10 to 100 ppm, calculated as the mass of platinum group metal element relative to the total mass of components (A) and (B). By adjusting this amount, the addition reaction can proceed more efficiently after light irradiation.

[Other ingredients]
In addition to the above components (A) to (D), other components may be blended into the composition of the present invention as required.

[Fine silica powder]
To reinforce the cured coating, the composition of the present invention may contain a fine silica powder having a specific surface area of at least 50 m ² /g as measured by the BET method. Such a fine silica powder has a specific surface area of at least 50 m ² /g, preferably 50 to 400 m ² /g, and more preferably 100 to 300 m ² /g, as measured by the BET method.

Such fine silica powder may be any known material that has traditionally been used as a reinforcing filler for cured silicone rubber, provided that its specific surface area falls within the above range, such as fumed silica and precipitated silica (wet silica).

The silica fine powder may be one whose surface has been hydrophobized with a surface treatment agent, such as a (typically hydrolyzable) organosilicon compound, such as chlorosilane, alkoxysilane, or organosilazane. In this case, the silica fine powder may be one whose surface has been hydrophobized directly with a surface treatment agent while still in powder form. Alternatively, the silica fine powder may be one whose surface has been hydrophobized by adding a surface treatment agent during kneading with silicone oil (for example, the alkenyl-containing organopolysiloxane of component (A) above).

The surface of silica fine powder can be hydrophobized using known techniques. For example, the untreated silica fine powder and a surface treatment agent are placed in a mechanical mixer or fluidized bed sealed at atmospheric pressure, and mixed at room temperature (25°C) or under heat treatment (heating), optionally in the presence of an inert gas. In some cases, water or a catalyst (such as a hydrolysis promoter) may be used to accelerate the surface treatment. After mixing, the mixture is dried to produce surface-treated silica fine powder. The amount of surface treatment agent added should be equal to or greater than the amount calculated from the surface area covered by the surface treatment agent.

Specific examples of surface treatment agents include silazanes such as hexamethyldisilazane; silane coupling agents such as methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, trimethylmethoxysilane, triethylmethoxysilane, vinyltris(methoxyethoxy)silane, trimethylchlorosilane, dimethyldichlorosilane, divinyldimethoxysilane, and chloropropyltrimethoxysilane; polymethylsiloxane; and organohydrogenpolysiloxane. Surface treatment with these agents can be used to produce hydrophobic silica fine powder. Silane coupling agents or silazanes are particularly preferred as surface treatment agents.

The amount of silica fine powder added is preferably 0.1 to 20 parts by mass, more preferably 0.5 to 15 parts by mass, and even more preferably 1 to 10 parts by mass per 100 parts by mass of the organopolysiloxane of component (A).

[Adhesion imparting agent]
If it is necessary to further improve the adhesiveness of the composition of the present invention, an adhesion promoter can be added. Examples of adhesion promoters include epoxy group-containing organopolysiloxanes such as epoxy group-containing organopolysiloxanes having alkoxy groups and vinyl groups, epoxy group-containing organopolysiloxanes having silicon-bonded hydrogen atoms, and epoxy group-containing organopolysiloxanes having silicon-bonded hydrogen atoms and alkoxy groups; alkoxy group-containing organopolysiloxanes having silicon-bonded hydrogen atoms; and silane coupling agents such as γ-glycidoxypropyltrimethoxysilane, 3,4-epoxycyclohexylethyltrimethoxysilane, and vinyltrimethoxysilane.

When an adhesion promoter is added to the composition of the present invention, the amount added is preferably 0.1 to 20 parts by mass, and more preferably 0.2 to 10 parts by mass, per 100 parts by mass of component (A).

[Heat resistance improver]
When it is necessary to further improve the heat resistance of the composition of the present invention, it is preferable to add a heat resistance improver to the composition, such as carbon, iron oxide, titanium oxide, or cerium oxide.

When a heat resistance improver is added, the amount added is preferably 0.1 to 30 parts by mass, and more preferably 0.3 to 10 parts by mass, per 100 parts by mass of component (A).

[Hydrosilylation Reaction Inhibitor]
In addition to the above components, the composition of the present invention may also contain a hydrosilylation reaction inhibitor, if necessary. Specific examples of the hydrosilylation reaction inhibitor include triallyl isocyanurate and acetylene alcohols such as 1-ethynylcyclohexanol.

[Other ingredients]
In addition, the composition of the present invention may contain, for example, organopolysiloxanes containing one silicon-bonded hydrogen atom per molecule and no other functional groups, organopolysiloxanes containing one silicon-bonded alkenyl group per molecule and no other functional groups, non-functional organopolysiloxanes containing no silicon-bonded hydrogen atoms, silicon-bonded alkenyl groups, or other functional groups (so-called dimethylsilicone oil), organic solvents, creep-hardening inhibitors, plasticizers, thixotropy-imparting agents, pigments, dyes, anti-fungal agents, and the like.

[Coat airbag base fabric and manufacturing method thereof]
The coated airbag fabric of the present invention has, as its outermost layer, a cured layer of the photocurable silicone rubber coating composition of the present invention. In a preferred embodiment, the coated airbag fabric of the present invention has a cured layer of a base coating agent formed by applying a silicone rubber coating composition or the like as a base coating agent to the surface of a known airbag fabric, and also has a cured layer of a top coating agent formed by applying the photocurable silicone rubber coating composition of the present invention as a top coating agent on the surface of the cured layer of the base coating agent.
The coated airbag fabric of the present invention can be produced, for example, by a method comprising the steps of applying the photocurable silicone rubber coating composition of the present invention to the outermost layer of an airbag fabric, and irradiating the surface coated with the photocurable silicone rubber coating composition with light at a dose of 100 to 10,000 mJ/cm ^2. In particular, the coated airbag fabric of the present invention is preferably produced by a method comprising the steps of applying a silicone rubber coating composition or the like as a base coat agent to the surface of a known airbag fabric, curing the composition to form a cured layer of the base coat agent, applying the photocurable silicone rubber coating composition of the present invention as a top coat agent to the surface of the cured layer of the base coat agent, and irradiating the surface coated with the photocurable silicone rubber coating composition with light at a dose of 100 to 10,000 mJ/cm ² .

Coating process: Known airbag fabrics can be used, and specific examples include woven fabrics of various synthetic fibers such as 6,6-nylon (PA66), 6-nylon (PA6), aramid fiber, various polyamide fibers, and various polyester fibers. A PA66 base fabric or a PET base fabric is preferred.
The airbag fabric may be formed into a bag shape in advance by sewing or the like, depending on the embodiment.

Base Coating Agent The base coating agent applied to the surface of a known airbag fabric is a composition different from the photocurable silicone rubber coating composition of the present invention, particularly a silicone rubber coating composition, and known compositions used for airbag fabrics can be used. Examples include heat-addition-curing liquid silicone rubber coating compositions containing a silicone oil having a vinyl group, a silicone oil having a hydrosilyl group, a platinum catalyst, reinforcing silica, an adhesion aid, etc., an ultraviolet-curing liquid silicone rubber coating composition in which the platinum catalyst is replaced with a platinum catalyst activated by light of a specific wavelength, and an organic peroxide-curing silicone rubber coating composition in which an organic peroxide is added instead of the platinum catalyst (for example, JP 2019-019196 A, JP 2018-003194 A, etc.).
The silicone rubber coating composition used as a base coat agent does not contain the talc fine powder that is component (C) of the photocurable silicone rubber coating composition of the present invention, and is different from the photocurable silicone rubber coating composition of the present invention, but the main organopolysiloxane component (silicone oil having a vinyl group, silicone oil having a hydrosilyl group, etc.) contained in the silicone rubber coating composition of the base coat agent can be exemplified by the same as the components (A) and (B) described above for the photocurable silicone rubber coating composition of the present invention. In order to improve the airtightness and flame retardancy of the airbag base fabric, it is preferable that the silicone rubber coating composition used as a base coat agent contains reinforcing silica and an adhesion aid.

The silicone rubber coating composition of the base coat agent can be applied to both sides of the airbag base fabric by a known method such as knife coating, and the thickness (or surface application amount) of the above-mentioned silicone rubber coating material for airbags is preferably 30 to 200 g/ ^m2 , more preferably 40 to 150 g/ ^m2 , and even more preferably 50 to 100 g/ ^m2 .
After applying the silicone rubber coating composition of the base coat agent to the base fabric for an airbag, the silicone rubber coating composition of the base coat agent is cured by heating or irradiating with light in a conventional manner in accordance with the curing type of the silicone rubber coating composition of the base coat agent, thereby forming a cured layer of the silicone rubber coating composition of the base coat agent.

Next, the photocurable silicone rubber coating composition of the present invention is applied to each of the cured layers of the silicone rubber coating composition of the base coat agent formed on both sides of the airbag fabric by a conventional method such as knife coating. The coating amount (thickness) of the photocurable silicone rubber coating composition is preferably 1 to 30 g/ ^m2 , more preferably 3 to 25 g/ ^m2 , and even more preferably 5 to ²⁰ g/m2.

Light Irradiation Step After the coating step, the coated surfaces of the photocurable silicone rubber coating composition formed on the cured layer of the silicone rubber coating composition of the base coat agent formed on both sides of the airbag base fabric are irradiated with light.
Light sources useful for curing the photocurable silicone rubber coating composition of the present invention include conventional mercury vapor lamps, metal halide lamps, and light-emitting diode (LED) elements designed to emit light energy in various wavelength bands. For example, a useful light wavelength range is 200 to 500 nm, preferably 300 to 450 nm. The light irradiation dose useful for curing is not particularly limited as long as it is sufficient for curing, but is preferably 100 to 10,000 mJ/ ^cm² , more preferably 200 to 5,000 mJ/ ^cm² , and even more preferably 300 to 3,000 mJ/ ^cm² . This light irradiation step can be carried out in air or in an inert gas atmosphere. However, an inert gas atmosphere is preferred, as curing is less inhibited by oxygen, and a nitrogen or argon gas atmosphere is more preferred.

Curing Acceleration Step: The photocurable silicone rubber coating composition of the present invention can be cured by irradiating it with light even at room temperature (25°C). However, curing can be further accelerated by heating in a drying oven or the like after light irradiation. The method for producing a coated airbag fabric of the present invention may optionally include a curing acceleration step. The acceleration temperature is preferably 40 to 120°C, more preferably 60 to 100°C, and the acceleration time is preferably 5 to 120 seconds, more preferably 10 to 90 seconds. If the acceleration temperature is too high, wrinkles may form in the airbag fabric due to the difference in thermal shrinkage between the cured coating of the photocurable silicone rubber coating composition, the cured layer of the silicone rubber coating composition of the base coat agent, and the airbag fabric.

The present invention will be explained in detail below using preparation examples, examples, and comparative examples, but the present invention is not limited to the following examples.

The following components were used as component (A):
(A-1): A linear dimethylpolysiloxane (alkenyl group: 1.30 mol%) having both molecular chain terminals blocked with vinyldimethylsiloxy groups, a number average degree of polymerization of 75, and a viscosity of 100 mPa·s.
(A-2): A linear dimethyl-vinylmethylpolysiloxane (alkenyl group: 10.8 mol%) whose molecular chain is terminally blocked with trimethylsiloxy groups, has a number-average degree of polymerization of 170, a viscosity of 650 mPa s, and contains 20 mol% vinylmethylsiloxane units and 80 mol% dimethylsiloxane units among the bifunctional diorganosiloxane units that make up the main chain.

The following components were used as component (B):
(B-1): A linear methylhydrogenpolysiloxane (in the formula (1) above, a = 1.10, b = 0.95, R = CH ₃ ) having a number average degree of polymerization of 40 and a viscosity of 20 mPa·s, both molecular chain terminals of which are blocked with trimethylsiloxy groups.
(B-2): A linear dimethylsiloxane-methylhydrogensiloxane copolymer (in the formula (1) above, a = 1.33, b = 0.70, R = _CH3 ) having a number average degree of polymerization of 64 and a viscosity of 45 mPa·s, both molecular chain terminals of which are blocked with trimethylsiloxy groups.

The following components were used as component (C):
(C): Talc fine powder having a median diameter of 8.0 μm (product name: MicroAce K-1, manufactured by Nippon Talc Co., Ltd.)

The following components were used as component (D):
(D-1): A toluene solution containing 0.5% by mass of bis(acetylacetonato)platinum(II) as a platinum atom content. (D-2): A toluene solution containing 0.5% by mass of (trimethyl)methylcyclopentadienylplatinum as a platinum atom content. (D-3): A dimethylpolysiloxane solution containing 1% by mass of a chloroplatinic acid/1,3-divinyltetramethyldisiloxane complex as a platinum atom content (a platinum group compound catalyst that is not activated by light with a wavelength of 200 to 500 nm, for use as a comparative example).

The following components were used as reaction inhibitors:
(Reaction inhibitor): 1-ethynylcyclohexanol

The following components were used as the reinforcing silica fine powder.
(Fine silica powder): R-974 (manufactured by Nippon Aerosil Co., Ltd., BET specific surface area: 170 g/m ² )

[Examples and Comparative Examples]
The components in the amounts shown in Tables 1 and 2 were mixed in a mixer at room temperature (25°C) for 30 minutes to prepare silicone rubber coating compositions.

<Dynamic friction coefficient>
To evaluate the friction properties of the cured coating surface, the dynamic friction coefficient of the cured coating surface was measured in accordance with JIS P8147:2010. Specifically, the silicone rubber coating composition was coated onto a PET film at a thickness of 20 g/ ^m² , and then cured under the conditions listed in Tables 1 and 2 to prepare measurement samples bearing a cured coating of the silicone rubber coating composition on their surfaces. A UV-LED irradiator, model HLUV-504UV365 (manufactured by CCS Inc., wavelength 365 nm), was used for light irradiation. The dynamic friction coefficient of the resulting samples was measured under a load of 100 g using an automatic friction and wear analyzer, model TSF-503 (manufactured by Kyowa Interface Science Co., Ltd.). Measurements were performed on five samples, and the median values are shown in Tables 1 and 2.

<Blocking resistance>
To evaluate the blocking resistance of the cured coating surface, the following test was conducted in accordance with JIS K 6404-3:2020. First, a sample having a cured coating of silicone rubber coating composition on its surface was prepared, similar to the sample for measuring the dynamic friction coefficient described above. Two 150 mm x 150 mm pieces were cut from this sample having a cured coating on its surface. The cured coatings on the two pieces were then bonded together and sandwiched between smooth plates (metal, glass, etc.) of the same size. A 5 kgf weight was placed on the sample so that a uniform force was applied to the cured coating. The sample was then left to stand in an oven at 70°C for 3 hours, after which the weight was removed, the sample was removed from the oven, and the sample was allowed to cool naturally, yielding a sample having PET films on the top and bottom, with two layers of cured coating bonded together between them. Thereafter, a region of the sample extending parallel to one side and extending about 20 mm therefrom was manually peeled off together with the PET film so that the bonded surfaces of the cured coatings were peeled off. One end of the peeled PET film on one side of the sample was fixed during peeling, and a 50 gf weight was hung from the other end of the PET film to measure the time until the entire bonded surface peeled off. Cases in which the time until peeling was within 30 seconds (including cases in which peeling had already occurred before measurement) were evaluated as passing, and cases in which it exceeded 30 seconds were evaluated as failing.

[Preparation Example 1]
60 parts by mass of dimethylpolysiloxane, both molecular chain terminals of which are capped with vinyldimethylsiloxy groups, with a viscosity of 30,000 mPa·s at 25°C and an average degree of polymerization of 750, 8 parts by mass of hexamethyldisilazane, 2 parts by mass of water, and 40 parts by mass of silica fine powder (Aerosil 300, manufactured by Nippon Aerosil Co., Ltd.) with a specific surface area of 300 ^m2 /g measured by the BET method, were added to a kneader and mixed at room temperature for 1 hour. Subsequently, 8 parts by mass of hexamethyldisilazane were further added to the mixture and mixed at room temperature for 1 hour. The mixing temperature of the mixture was then raised to 150°C, and the mixture was mixed for a further 2 hours. The mixture was then cooled to room temperature, and 30 parts by mass of dimethylpolysiloxane, both molecular chain terminals of which were capped with vinyldimethylsiloxy groups and had a viscosity of 30,000 mPa·s at 25°C, was added and mixed until homogeneous, thereby preparing a base compound.
To 128 parts by mass of the obtained base compound, 50 parts by mass of dimethylpolysiloxane having a viscosity of 30,000 mPa·s and an average degree of polymerization of 750, 4.1 parts by mass of dimethylsiloxane-methylhydrogensiloxane copolymer (average degree of polymerization: 16, SiH group amount: 0.0031 mol/g) in which both molecular chain terminals are blocked with dimethylhydrogensiloxy groups and which has an average of 2 hydrogen atoms bonded to silicon atoms in the molecular chain side chains, and methylhydrogenpolysiloxane (average polymerization: 16, SiH group amount: 0.0031 mol/g) in which both molecular chain terminals are blocked with trimethylsiloxy groups and which has an average of 38 hydrogen atoms bonded to silicon atoms in the molecular chain side chains, were added. A silicone rubber coating composition for air bags was prepared by mixing for one hour 0.25 parts by mass of γ-glycidoxypropyltrimethoxysilane, 0.3 parts by mass of a titanium tetraacetylacetonate isopropanol solution (trade name: TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.), 0.36 parts by mass of a titanium tetraacetylacetonate isopropanol solution, 0.05 parts by mass of 1-ethynylcyclohexanol as a reaction inhibitor, and 0.2 parts by mass of a dimethylpolysiloxane solution containing chloroplatinic acid/1,3-divinyltetramethyldisiloxane complex with a platinum atom content of 1% by mass.

<Base fabric stiffness test>
To evaluate the stiffness of the airbag fabrics, the following test was conducted in accordance with ASTM D4032. Specifically, the silicone rubber coating composition for airbags prepared in Preparation Example 1 was knife-coated onto a 210-denier PA66 base fabric at a base coating rate of 80 g/ ^m² . The base coating was then cured in a 200°C oven for 1 minute. The cured base coating was then knife-coated onto the surface of the cured base coating at a top coating rate of 15 g/ ^m² with each of the silicone rubber coating compositions listed in Tables 1 and 2, and cured under the conditions listed in Tables 1 and 2. Each of the resulting coated airbag fabrics was cut to a size of 102 mm x 204 mm, and stiffness was tested using a SASD-672-1 stiffness tester (manufactured by J.A. KING) with N = 3. The median values are shown in Tables 1 and 2.

As can be seen from Table 1, in Examples 1 to 8, which used the photocurable silicone rubber coating composition of the present invention, the cured coating had a low coefficient of dynamic friction, excellent blocking resistance, and the coated airbag base fabric also had low stiffness and flexibility.

On the other hand, as can be seen from Table 2, Comparative Examples 1 to 7, which did not use the photocurable silicone rubber coating composition of the present invention, were either uncured or had a cured coating with a higher dynamic friction coefficient than the Examples, poorer blocking resistance, and the stiffness and flexibility of the coated airbag fabric were also high.

Claims (7)

A photocurable silicone rubber coating composition used to form a cured layer on the outermost surface of a coated airbag fabric, comprising:
(A) 100 parts by mass of a linear organopolysiloxane containing two or more silicon-bonded alkenyl groups per molecule and having a number-average degree of polymerization of 10 to 1,000;
(B) an organohydrogenpolysiloxane containing two or more silicon-bonded hydrogen atoms per molecule: an amount such that the number of silicon-bonded hydrogen atoms contained per molecule of this component is 0.4 to 5 per total number of silicon-bonded alkenyl groups in component (A);
(C) 50 to 150 parts by mass of fine talc powder having a median diameter (D50) of 0.5 to 20 μm, and (D) an effective amount of a platinum group compound catalyst that is activated by light with a wavelength of 200 to 500 nm as a hydrosilylation reaction catalyst,
A photocurable silicone rubber coating composition comprising: The photocurable silicone rubber coating composition according to claim 1, wherein component (D) is bis(acetylacetonato)platinum(II) or (trimethyl)methylcyclopentadienylplatinum(IV). The photocurable silicone rubber coating composition according to claim 1, wherein component (A) is an organopolysiloxane having vinyl groups only at both ends of the molecular chain. The photocurable silicone rubber coating composition according to claim 1, wherein component (A) is an organopolysiloxane in which 0.1 to 15 mol % of all substituents bonded to silicon atoms are alkenyl groups having 2 to 8 carbon atoms. A coated airbag fabric having, as its outermost layer, a cured layer of the photocurable silicone rubber coating composition described in any one of claims 1 to 4. A method for producing a coated airbag fabric, comprising the steps of: applying the photocurable silicone rubber coating composition according to any one of claims 1 to 4 to the outermost surface of an airbag fabric; and irradiating the surface coated with the photocurable silicone rubber coating composition with light at a dose of 100 to 10,000 mJ/ ^cm2 . The method for producing a coated airbag fabric according to claim 6, further comprising a curing acceleration step at 40 to 120 ° C. for 5 to 120 seconds following the light irradiation step.