JP2023102441A - Addition curing type liquid silicone rubber composition for air bag, production method thereof, and air bag - Google Patents

Abstract

To provide: an addition curing type liquid silicone rubber composition for air bag, which has an excellent low combustion rate property and emits little mount of VOC at a high temperature; and an air bag.SOLUTION: Provided is an addition curing type liquid silicone rubber composition for air bag, comprising as essential components: (A) a linear organopolysiloxane having a degree of polymerization of 50-2,000, which contains 2 or more alkenyl groups bound to silicon atoms in a molecule; (B) an organohydrogenpolysiloxane which contains at least 2 hydrogen atoms (hydrosilyl groups) bound to silicon atoms in a molecule; (C) surface-treated silica fine powder having a BET method specific surface area of 50 m2/g or more, which does not contain a triorganosiloxy unit (M unit) on a surface of the surface-treated silica fine powder; (D) a catalyst for a hydrosilylation reaction; (E) and an organosilicon compound containing adhesiveness providing functional groups.SELECTED DRAWING: None

Description

The present invention relates to an addition-curable liquid silicone rubber composition for airbags, an airbag having this cured coating, and a method for producing the addition-curable liquid silicone rubber composition for airbags.

Conventionally, silicone rubber compositions for airbags have been proposed for the purpose of forming a rubber film on the fiber surface. Airbags having a silicone rubber coating are excellent in internal pressure retention and low burning rate, and are therefore suitably used as airbags for automobiles and the like.

Examples of such addition-curable liquid silicone rubber compositions for airbags include a combination of a cross-linking agent having hydrosilyl groups at both molecular chain terminals and a cross-linking agent having hydrosilyl groups in side chains (Patent Document 1). This addition-curable liquid silicone rubber composition for air bags is characterized by excellent internal pressure retention. Also known is a method of producing an addition-curable liquid silicone rubber composition for airbags by pre-mixing a resinous polysiloxane with a siloxane component together with silica, a surface treatment agent and water (Patent Document 2). By coating the surface of the fiber with this composition, an airbag fabric excellent in low burning rate property can be obtained. Furthermore, an addition-curable liquid silicone rubber composition for airbags is disclosed which uses an organohydrogenpolysiloxane containing T units or Q units as a cross-linking agent (Patent Document 3). A coated base fabric coated with this composition is characterized by excellent strength. Further, an addition-curable liquid silicone rubber composition for airbags is disclosed in which a silicone resin containing M, D, and Q units and having a crosslinkable functional group only in the D unit is compounded as a flame retardant (Patent Document 4). An airbag coated with this composition is characterized by excellent low burning rate properties.

However, for the purpose of weight reduction and space saving, the coating amount of the silicone rubber composition coated on the base fabric for airbags tends to decrease. Therefore, there is a demand for a silicone rubber composition that can maintain conventional properties even at a low coating weight.

In recent years, air pollution caused by volatile organic compounds (VOC) generated from adhesives and paints used in houses and furniture has caused health hazards such as sick building syndrome and environmental damage such as photochemical smog. On the other hand, regulations on VOCs are progressing in various countries, and automobile interiors are no exception. Compared to a house, the interior of an automobile has a smaller interior volume, and on the other hand, the interior temperature is often high. Therefore, it is an environment where VOCs easily diffuse from automobile parts, etc., and it is necessary to reduce the amount of VOC emissions from each part used in automobiles.

As for a silicone-coated base fabric for airbags that emits a small amount of VOCs, the following patents relating to the manufacturing method are disclosed (Patent Document 5). First, an addition-curing liquid silicone rubber containing a volatile adhesive is coated on a base fabric for an air bag, and cured by heating. Next, an addition-curable liquid silicone rubber containing no volatile compound is coated and cured by heating. As a result, it is possible to obtain a silicone-coated airbag fabric which has excellent adhesion to the airbag fabric and which emits a small amount of VOCs at high temperatures.

However, in this method, the silicone rubber layer on the airbag base fabric is two layers, so the coating base fabric becomes thick. Therefore, the foldability of the coated base fabric is poor, and the volume of the airbag module becomes large, which presses on the room space inside the vehicle when it is stored. Moreover, in this method, the coating amount of the silicone rubber layer is increased, so that the overall weight of the airbag module is increased, resulting in a decrease in fuel efficiency.

Japanese Patent Application Publication No. 2013-531695 JP 2013-209517 A Japanese Patent Application Publication No. 2019-513907 WO2018/168315 Japanese Patent Publication No. 2021-508619

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and aims to provide an addition-curable liquid silicone rubber composition for airbags that provides a cured coating that has an excellent low burning rate and low VOC emissions at high temperatures, an airbag having a cured coating of the composition, and a method for producing the addition-curable liquid silicone rubber composition for airbags.

In order to solve the above problems, in the present invention,
An addition-curable liquid silicone rubber composition for an air bag,
(A) a linear organopolysiloxane containing two or more silicon-bonded alkenyl groups in one molecule and having a weight-average degree of polymerization of 50 to 2,000: 100 parts by mass;
(B) an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms (hydrosilyl groups) per molecule: the amount of hydrosilyl groups contained in the composition is from 1 to 10 moles per mole of the total silicon-bonded alkenyl groups contained in the composition;
(C) a surface-treated fine silica powder having a BET specific surface area of 50 m ² /g or more, wherein the surface of the surface-treated fine silica powder does not contain triorganosiloxy units (M units): 1 to 30 parts by mass;
(D) catalyst for hydrosilylation reaction: 1 to 500 ppm in terms of mass of the catalytic metal element with respect to the total mass of (A) to (C);
(E) An organosilicon compound containing an adhesion imparting functional group: 0.1 to 10 parts by mass is provided as an essential component of an addition-curable liquid silicone rubber composition for airbags.

Such an addition-curable liquid silicone rubber composition provides a cured film with excellent low burning rate (flame retardancy), and the air bag silicone-coated base fabric produced therefrom emits a small amount of VOCs at high temperatures.

Further, in the present invention, the component (C) is preferably treated with dichlorodimethylsilane.

With such an addition-curable liquid silicone rubber composition, the silicone-coated base fabric for airbags produced therefrom will emit less VOCs at high temperatures.

（式中、Ｒ^１は独立して炭素数１～１２の１価飽和脂肪族炭化水素基又は炭素数６～１２の１価芳香族炭化水素基であり、Ｒ^２は独立して水素原子又は炭素数１～６のアルキル基であり、ｎは１～１００の整数である） In the present invention, it is also preferable that the component (C) is treated with an organosilicon compound represented by the following general formula (1).

(In the formula, R ¹ is independently a monovalent saturated aliphatic hydrocarbon group having 1 to 12 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 12 carbon atoms, R ² is independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 100.)

With such an addition-curable liquid silicone rubber composition, the silicone-coated base fabric for airbags produced therefrom will emit less VOCs at high temperatures.

Further, in the present invention, it is preferable that 0.1 to 5 parts by mass of at least one condensation catalyst selected from organic titanium compounds, organic zirconium compounds, and organic aluminum compounds be added as component (F) with respect to 100 parts by mass of component (A).

With such an addition-curable liquid silicone rubber composition, the silicone rubber layer formed therefrom has better adhesion to the base fabric for airbags.

Further, in the present invention, it is preferable that 0.1 to 100 parts by mass of a powdery three-dimensional network organopolysiloxane resin is contained as component (G) with respect to 100 parts by mass of component (A).

With such an addition-curable liquid silicone rubber composition, the silicone-coated base fabric for airbags produced therefrom will be more excellent in flame retardancy.

The present invention also provides an airbag comprising a base fabric for an airbag and a cured film of the addition-curable liquid silicone rubber composition for an airbag on the base fabric.

Such an airbag is excellent in low combustion rate and emits less VOC at high temperatures.

The present invention also provides a method for producing an addition-curable liquid silicone rubber composition for air bags, which comprises the step of mixing the components (A) to (E) with other optional components, and uses fine silica powder surface-treated with a surface-treating agent containing no triorganosiloxy units as the component (C).

Such a production method enables efficient production of the addition-curable liquid silicone rubber composition for airbags.

（式中、Ｒ^１は独立して炭素数１～１２の１価飽和脂肪族炭化水素基又は炭素数６～１２の１価芳香族炭化水素基であり、Ｒ^２は独立して水素原子又は炭素数１～６のアルキル基であり、ｎは１～１００の整数である） In this case, it is preferable to use one selected from dichlorodimethylsilane and an organosilicon compound represented by the following general formula (1) as the surface treatment agent.

(In the formula, R ¹ is independently a monovalent saturated aliphatic hydrocarbon group having 1 to 12 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 12 carbon atoms, R ² is independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 100.)

By using such a surface treatment agent, it is possible to improve the low burning rate property of the manufactured airbag silicone-coated base fabric and to further reduce the amount of VOC emissions at high temperatures.

As described above, according to the present invention, it is possible to provide an addition-curable liquid silicone rubber composition for airbags that provides a cured film that exhibits excellent low burning speed (that is, excellent flame retardancy) and that emits a small amount of VOCs at high temperatures, an airbag having the cured film, and a method for producing the addition-curable liquid silicone rubber composition for airbags.

There has been a demand for an addition-curable liquid silicone rubber composition for airbags that provides a cured film with excellent low burning rate (hereinafter also referred to as "flame retardancy") and low VOC emissions at high temperatures.

The inventors of the present invention have made intensive studies to achieve the above objects, and as a result, found that the above problems can be solved by using a surface-treated fine silica powder that does not contain triorganosiloxy units (M units) as a component of an addition-curable liquid silicone rubber composition for air bags, and have completed the present invention.

Incorporation of a surface-treated fine silica powder having no such triorganosiloxy units (M units) on its surface into an air bag composition has not been considered at all.

That is, the present invention
An addition-curable liquid silicone rubber composition for an air bag,
(A) a linear organopolysiloxane containing two or more silicon-bonded alkenyl groups in one molecule and having a weight-average degree of polymerization of 50 to 2,000: 100 parts by mass;
(B) an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms (hydrosilyl groups) per molecule: the amount of hydrosilyl groups contained in the composition is from 1 to 10 moles per mole of the total silicon-bonded alkenyl groups contained in the composition;
(C) a surface-treated fine silica powder having a BET specific surface area of 50 m ² /g or more, wherein the surface of the surface-treated fine silica powder does not contain triorganosiloxy units (M units): 1 to 30 parts by mass;
(D) catalyst for hydrosilylation reaction: 1 to 500 ppm in terms of mass of the catalytic metal element with respect to the total mass of (A) to (C);
(E) Organosilicon compound containing an adhesiveness imparting functional group: An addition-curable liquid silicone rubber composition for airbags comprising 0.1 to 10 parts by mass as an essential component.

Although the present invention will be described in detail below, the present invention is not limited thereto.

In the present specification, viscosity is a value measured at 25° C. using a rotational viscometer according to the method described in JIS K 7117-1:1999. The weight average degree of polymerization is a value obtained as a weight average degree of polymerization (weight average molecular weight) in terms of polystyrene by GPC (gel permeation chromatography) analysis using toluene as a developing solvent measured under the following conditions.
[Measurement condition]
Developing solvent: toluene Flow rate: 0.35 mL/min
Detector: Differential Refractive Index Detector (RI)
Column: TSK Guard column SuperH-L
TSKgel Super H4000 (6.0 mm I.D. x 15 cm x 1)
TSKgel Super H3000 (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)

In this specification, "flame retardancy" is a characteristic evaluated in a burning rate test based on FMVSS-302, and if the burning rate is 102 mm/min or less, it is considered to have flame retardancy. In addition, the “VOC emission amount at high temperature” specifically refers to the amount of VOCs detected when the sample is kept at 120° C. for 5 hours and then measured by headspace gas chromatography (GC), and “the amount of VOCs emitted is low” means that the amount of VOCs detected is 100 ppm or less.

<Addition-curable liquid silicone rubber composition for air bags>
The addition-curable liquid silicone rubber composition for airbags of the present invention is
(A) a linear organopolysiloxane containing two or more silicon-bonded alkenyl groups in one molecule and having a weight-average degree of polymerization of 50 to 2,000: 100 parts by mass;
(B) an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms (hydrosilyl groups) per molecule: the amount of hydrosilyl groups contained in the composition is from 1 to 10 moles per mole of the total silicon-bonded alkenyl groups contained in the composition;
(C) a surface-treated fine silica powder having a BET specific surface area of 50 m ² /g or more, wherein the surface of the surface-treated fine silica powder does not contain triorganosiloxy units (M units): 1 to 30 parts by mass;
(D) catalyst for hydrosilylation reaction: 1 to 500 ppm in terms of mass of the catalytic metal element with respect to the total mass of (A) to (C);
(E) an organosilicon compound containing an adhesion imparting functional group: 0.1 to 10 parts by mass,
as an essential component, and is liquid at room temperature (25°C).

Each component will be described in detail below.

[(A) component]
The linear organopolysiloxane of component (A) is an organopolysiloxane containing two or more silicon-bonded alkenyl groups per molecule and having a weight average degree of polymerization of 50 to 2,000, and is the base polymer (main component) of the composition according to the present invention.

The molecular structure of component (A) is preferably a diorganopolysiloxane having a linear main chain basically consisting of repeating diorganosiloxane units and having both ends of the molecular chain blocked with triorganosiloxy groups. In addition, the position of the silicon atom to which the alkenyl group is bonded in the molecule of the straight-chain organopolysiloxane of component (A) may be either or both of the terminal of the molecular chain (i.e., triorganosiloxy group) and the middle of the molecular chain (i.e., the bifunctional diorganosiloxane unit located at the non-terminal of the molecular chain). A particularly preferred component (A) is a linear diorganopolysiloxane containing at least alkenyl groups bonded to silicon atoms at both ends of the molecular chain.

Examples of the silicon-bonded alkenyl group in component (A) generally include those having 2 to 8 carbon atoms, preferably 2 to 4 carbon atoms. Specific examples thereof include vinyl group, allyl group, propenyl group, butenyl group, pentenyl group, hexenyl group, cyclohexenyl group, heptenyl group and the like, and vinyl group is particularly preferred.

The content of silicon-bonded alkenyl groups in component (A) is preferably 0.05 to 10 mol%, particularly preferably about 0.1 to 5 mol%, based on the total silicon-bonded monovalent organic groups (that is, unsubstituted or substituted monovalent hydrocarbon groups) in the organopolysiloxane.

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

The weight average degree of polymerization of component (A) is 50 to 2,000, preferably 100 to 1,500, and more preferably 120 to 1,000. If the weight-average degree of polymerization is lower than 50, the resulting silicone rubber may have poor mechanical properties.

The component (A) may be liquid at 25°C, and the viscosity of the component (A) at 25°C is preferably 50 to 200,000 mPa·s, more preferably 100 to 150,000 mPa·s, still more preferably 400 to 100,000 mPa·s. If the viscosity of component (A) is higher than 50 mPa·s, the mechanical properties of the resulting silicone rubber will not deteriorate.

Specific examples of the above component (A) organopolysiloxane include dimethylsiloxane/methylvinylsiloxane copolymer with both molecular chain terminals blocked with trimethylsiloxy groups, methylvinylpolysiloxane with both molecular chain terminals with trimethylsiloxy groups blocked, dimethylsiloxane/methylvinylsiloxane/methylphenylsiloxane copolymer with both molecular chain terminals blocked with trimethylsiloxy groups, dimethylpolysiloxane with both molecular chain terminals blocked with dimethylvinylsiloxy groups, methylvinylpolysiloxane with both molecular chain terminals blocked with dimethylvinylsiloxy groups, and dimethylvinylsiloxy group-blocked with both molecular chain terminals. siloxane-methylvinylsiloxane copolymer, dimethylsiloxane-methylvinylsiloxy-group-blocked dimethylsiloxane-methylvinylsiloxane-methylphenylsiloxane copolymer, dimethylpolysiloxane-blocked at both molecular chain ends, divinylmethylsiloxy-blocked dimethylpolysiloxane at both molecular chain ends, dimethylsiloxane-methylvinylsiloxane copolymer-blocked at both molecular chain ends with trivinylsiloxy groups, dimethylpolysiloxane-blocked at both molecular chain ends with trivinylsiloxy groups, dimethylsiloxane-methylvinylsiloxane copolymer with both molecular chain ends-blocked, and a mixture of two or more of these organopolysiloxanes. things are mentioned.

The organopolysiloxane of component (A) may be used alone or in combination of two or more.

[(B) component]
The organohydrogenpolysiloxane containing two or more silicon-bonded hydrogen atoms (hydrosilyl groups) per molecule of component (B) mainly undergoes a hydrosilylation addition reaction with the alkenyl groups in component (A) to act as a cross-linking agent (curing agent).

The molecular structure of component (B) includes, for example, linear, cyclic, branched, three-dimensional network (resinous) structures, and the like. It is necessary to have 2 or more, preferably 3 or more silicon-bonded hydrogen atoms (hydrosilyl groups) in one molecule, and it is desirable to have usually 2 to 300, preferably 3 to 200, more preferably 3 to 100 hydrosilyl groups, and it is preferable to use one that is liquid at 25°C. Such hydrosilyl groups may be located either at the end of the molecular chain, in the middle of the molecular chain, or both.

As this organohydrogenpolysiloxane, one represented by the following average compositional formula (2) can be used.

In the average composition formula (2), R ³ is preferably independently a monovalent hydrocarbon group having 1 to 10 carbon atoms. For example, alkyl groups such as methyl group, ethyl group, propyl group, isopropyl group, butyl group, isobutyl group, tert-butyl group, pentyl group, neopentyl group, hexyl group, cyclohexyl group, octyl group, nonyl group and decyl group; aryl groups such as phenyl group, tolyl group, xylyl group and naphthyl group; aralkyl groups such as benzyl group, phenylethyl group and phenylpropyl group; Those substituted with a halogen atom, such as a chloromethyl group, a chloropropyl group, a bromoethyl group, a trifluoropropyl group and the like can be mentioned. ^R3 is more preferably an alkyl group or an aryl group, and even more preferably a methyl group. R ³ excludes aliphatic unsaturated hydrocarbon groups such as alkenyl groups. In addition, it is preferable that a is 0.7 to 2.1, b is 0.001 to 1.0, and a + b is a positive number satisfying 0.8 to 3.0, more preferably a is 1.0 to 2.0, b is 0.01 to 1.0, and a + b is a positive number satisfying 1.5 to 2.5.

Examples of the organohydrogenpolysiloxane 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 with both molecular chain ends blocked with trimethylsiloxy groups, dimethylsiloxane methylhydrogensiloxane with both molecular chain ends blocked with trimethylsiloxy groups. Siloxane copolymer, trimethylsiloxy group-blocked dimethylsiloxane/methylhydrogensiloxane/methylphenylsiloxane copolymer at both molecular chain ends, dimethylsiloxane/methylhydrogensiloxane/diphenylsiloxane copolymer with trimethylsiloxy group-blocked at both molecular chain ends, methylhydrogenpolysiloxane with dimethylhydrogensiloxy group-blocked at both molecular chain ends, dimethylpolysiloxane with dimethylhydrogensiloxy group-blocked at both molecular chain ends, dimethylsiloxane/methylhydrogensiloxane copolymer with dimethylhydrogensiloxy group-blocked at both molecular chain ends, dimethylhydrogensiloxy group-blocked at both molecular chain ends Group-blocked dimethylsiloxane/methylphenylsiloxane copolymer, dimethylsiloxane/diphenylsiloxane copolymer blocked with dimethylhydrogensiloxy groups at both ends of the molecular chain, methylphenylpolysiloxane blocked with dimethylhydrogensiloxy groups at both ends of the molecular chain, diphenylpolysiloxane blocked with dimethylhydrogensiloxy groups at both ends of the molecular chain, and in each of these exemplified compounds, some or all of the methyl groups are substituted with other alkyl groups such as ethyl groups and propyl groups, the formula: R³ ₃SiO_1/2A siloxane unit represented by the formula: R³ ₂HSiO_1/2A siloxane unit represented by the formula: SiO_4/2An organosiloxane copolymer consisting of siloxane units represented by the formula: R³ ₂HSiO_1/2A siloxane unit represented by the formula: SiO_4/2An organosiloxane copolymer consisting of siloxane units represented by the formula: R³HSiO_2/2A siloxane unit represented by the formula: R³SiO_3/2A siloxane unit or formula represented by: HSiO_3/2and mixtures of two or more of these organopolysiloxanes.

The amount of component (B) is such that the amount of hydrosilyl groups contained in the composition containing component (B) is 1 to 10 moles (or units), preferably 1.2 to 9 moles (or units), more preferably 1.5 to 8 moles (or units), per 1 mole (or units) of silicon-bonded alkenyl groups in total in the addition-curable liquid silicone rubber composition for airbags containing component (A). If the composition containing component (B) contains less than 1 mol of hydrosilyl groups per mole of silicon-bonded alkenyl groups contained in the composition containing component (A), the composition will not be sufficiently cured.

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

[(C) component]
The BET specific surface area of component (C) is 50 m ² /g or more, and the surface-treated fine silica powder containing no triorganosiloxy units (M units) on the surface acts as a reinforcing filler. That is, it imparts strength to the silicone rubber cured product obtained from the composition according to the present invention, and the surface-treated silica fine powder is used as a reinforcing filler to form a coating film that satisfies the strength required for the present invention. In addition, by using surface-treated silica fine powder containing no M units, cracking of M units directly bonded to Q units of silica is prevented, and generation of triorganosilanol is suppressed. Since triorganosilanol has high reaction activity and induces cracking of siloxane, the reduction of VOC at high temperatures is achieved by suppressing the cracking. In addition, for the same reason, a low burning rate is achieved by preventing the generation of combustible triorganosilanol during combustion and reducing the generation of combustible low-molecular-weight siloxane due to siloxane cracking.

In the present invention, the method for quantifying the siloxane units present on the surface of the surface-treated fine silica powder is measured by ²⁹ Si solid-state NMR as described below. In addition, "does not contain M units" refers to a state in which M units are not detected by the above measurement.

< ²⁹ Si solid state NMR method>
When the sample was powder, it was filled in a sample tube for solid-state NMR measurement, and ²⁹ Si solid-state NMR was measured under the following conditions.
Apparatus: Solid NMR JNM ECA-600 manufactured by JEOL Ltd.
Measurement nucleus: 29Si
Measurement mode: CP/MAS method Sample rotation speed: 5.2 kHz
Accumulated times: 16,000 times

In the case of the surface-treated fine silica powder treated with a surface-treating agent in the component (A) at the time of preparation of the base compound, the following pretreatment was carried out. First, the base compound is dissolved in toluene, and silica is filtered off with filter paper. After repeatedly washing the silica with toluene, the sample was air-dried at 25° C. for 24 hours or longer to obtain a sample for evaluation. ²⁹ Si solid state NMR was measured using the evaluation sample.

The surface-treated fine silica powder is, for example, a surface-treated fine silica powder whose surface has been hydrophobized with a surface-treating agent such as a (usually hydrolyzable) organosilicon compound such as chlorosilane, alkoxysilane, or organosilazane, and does not contain a triorganosiloxy group (M unit) on the surface. These surface-treated silica fine powders may be powdered in advance and directly surface-hydrophobicized with a surface-treating agent, or may be surface-hydrophobicized by adding a surface-treating agent during kneading with silicone oil (for example, the alkenyl group-containing organopolysiloxane of component (A)).

The organosiloxy group on the surface-treated fine silica powder refers to the organosiloxy group derived from the organosilicon compound, which is the surface treatment agent.

Such surface-treated silica fine powder has a specific surface area of 50 m ² /g or more, preferably 50 to 400 m ² /g, more preferably 100 to 300 m ² /g, as determined by the BET method. If the specific surface area is less than 50 m ² /g, it is not possible to impart mechanical strength characteristics that are satisfactory as an air bag coating agent.

Such surface-treated silica fine powders may be those conventionally used as a reinforcing filler for silicone rubber, and examples thereof include fine powders such as fumed silica (fumed silica) and precipitated silica (wet silica) that have been surface-treated.

As the surface treatment method for component (C), a surface treatment can be carried out by a known technique. For example, untreated fine silica powder and a surface treatment agent are placed in a mechanical kneading device or fluidized bed sealed at normal pressure, and mixed at room temperature (25° C.) or under heat treatment (heating) in the presence of an inert gas as necessary. Optionally, water or catalysts (such as hydrolysis accelerators) may be used to facilitate the surface treatment. Surface-treated silica fine powder can be produced by drying after kneading. The amount of the surface treatment agent to be blended may be at least the amount calculated from the coverage area of the surface treatment agent.

（式中、Ｒ^１は独立して炭素数１～１２の１価飽和脂肪族炭化水素基又は炭素数６～１２の１価芳香族炭化水素基であり、Ｒ^２は独立して水素原子又は炭素数１～６のアルキル基であり、ｎは１～１００の整数である） The surface treatment agent is not particularly limited as long as it does not contain a triorganosiloxy unit (M unit). Specific examples include alkoxysilanes such as methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, dimethyldimethoxysilane, diethyldimethoxysilane, vinyltriethoxysilane, vinyltrimethoxysilane, vinyltris(methoxyethoxy)silane, divinyldimethoxysilane and chloropropyltrimethoxysilane, chlorosilanes such as dimethyldichlorosilane and methyltrichlorosilane, and organohydrosilanes. Genpolysiloxane, diorganosiloxypolysiloxane whose terminals are each blocked with a group selected from diorganoalkoxysilyl groups or diorganohydroxysilyl groups represented by the following formula (1), and the like, can be surface-treated with these and used as hydrophobic surface-treated fine silica powder. Dichlorodimethylsilane or dimethylpolysiloxane having both terminal silanol groups (in the following formula (1), R ¹ is a methyl group and R ² is a hydrogen atom) is particularly preferable as the surface treatment agent.

(In the formula, R ¹ is independently a monovalent saturated aliphatic hydrocarbon group having 1 to 12 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 12 carbon atoms, R ² is independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 100.)

Component (C) is added in an amount of 1 to 30 parts by mass, preferably 2 to 25 parts by mass, and more preferably 3 to 20 parts by mass, per 100 parts by mass of the organopolysiloxane of component (A). If the blending amount is less than 1 part by mass, the strength required for the present invention cannot be obtained, and if the blending amount exceeds 30 parts by mass, the viscosity of the resulting silicone rubber composition will be high, fluidity will be reduced, and coating work will be deteriorated.

The silica fine powder of component (C) may be used alone or in combination of two or more.

[(D) component]
Component (D), the hydrosilylation reaction catalyst, mainly promotes the addition reaction between the silicon-bonded alkenyl groups in component (A) and the hydrosilyl groups in component (B). The hydrosilylation reaction catalyst is not particularly limited, and examples thereof include platinum group metals such as platinum, palladium and rhodium; chloroplatinic acid; alcohol-modified chloroplatinic acid; coordination compounds of chloroplatinic acid and olefins, vinylsiloxane or acetylene compounds;

The blending amount of component (D) is 1 to 500 ppm, preferably 5 to 100 ppm, in terms of the mass of the catalytic metal element per 100 parts by mass of components (A) to (C). If the amount is less than 1 ppm, the addition reaction will be significantly slowed down, and the composition will not cure. If the amount exceeds 500 ppm, the heat resistance of the cured product may decrease.

The addition reaction catalyst of component (D) may be used alone or in combination of two or more.

[(E) component]
Component (E) is an organosilicon compound containing an adhesion-imparting functional group. Examples of the adhesion-imparting functional group include one or more groups selected from an epoxy group, a silicon-bonded alkoxy group (alkoxysilyl group), a hydrosilyl group, an isocyanate group, an acrylic group, and a methacrylic group.

As the organosilicon compound, any organosilicon compound can be used as long as it has such an adhesion-imparting functional group. However, an organosilicon compound having one or more epoxy groups and one or more silicon-bonded alkoxy groups in one molecule is preferable. From the viewpoint of adhesion development, an organosilicon compound having at least one epoxy group and at least one silicon-bonded alkoxy group (e.g., trialkoxysilyl group, organodialkoxysilyl group, etc.), e.g., organosilane, or having 1 to 1 silicon atoms. 00, preferably 1 to 50, cyclic or linear organosiloxanes having at least one epoxy group and at least two silicon-bonded alkoxy groups are more preferred.

The epoxy group is preferably bonded to a silicon atom in the form of, for example, a glycidoxyalkyl group such as a glycidoxypropyl group; an epoxy-containing cyclohexylalkyl group such as a 2,3-epoxycyclohexylethyl group or a 3,4-epoxycyclohexylethyl group.

The silicon-bonded alkoxy group is bonded to the silicon atom to form, for example, a trialkoxysilyl group such as a trimethoxysilyl group and a triethoxysilyl group;

In addition, the component (E) may have at least one functional group selected from the group consisting of alkenyl groups such as vinyl groups, acryl groups, (meth)acryloxy groups, isocyanate groups, and hydrosilyl groups as functional groups other than epoxy groups and silicon-bonded alkoxy groups in one molecule.

Examples of the organosilicon compound of component (E) include γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, (3,4-epoxycyclohexylethyl)trimethoxysilane, (3,4-epoxycyclohexylethyl)triethoxysilane, (3,4-epoxycyclohexylethyl)methyldimethoxysilane, (3,4-epoxycyclohexylethyl)methyldiethoxysilane, Epoxy group-containing silane coupling agents (i.e., epoxy functional group-containing organoalkoxysilanes) such as (2,3-epoxycyclohexylethyl)triethoxysilane, (2,3-epoxycyclohexylethyl)methyldimethoxysilane, (2,3-epoxycyclohexylethyl)methyldiethoxysilane; or vinyl group-containing silane coupling agents such as vinyltrimethoxysilane; acrylic group-containing silane coupling agents such as 3-acryloxypropyltrimethoxysilane; In addition to silane coupling agents such as cyanate group-containing silane coupling agents and methoxysilyl-modified triallyl isocyanurate, cyclic organopolysiloxanes represented by the following chemical formulas, or organic silicon compounds such as linear organopolysiloxanes, mixtures of two or more of these, or partial hydrolysis condensates of one or more of these.

Main examples are given below.

（式中、ｈは１～１０の整数、ｋは０～４０の整数、好ましくは０～２０の整数、ｐは１～４０の整数、好ましくは１～２０の整数、ｑは１～１０の整数である。）

(Wherein, h is an integer of 1 to 10, k is an integer of 0 to 40, preferably an integer of 0 to 20, p is an integer of 1 to 40, preferably an integer of 1 to 20, and q is an integer of 1 to 10.)

Component (E) is added in an amount of 0.1 to 10 parts by mass, preferably 0.25 to 5 parts by mass, per 100 parts by mass of organopolysiloxane as component (A). If the amount is less than 0.1 part by mass, the resulting composition may not exhibit sufficient adhesive strength. If the blending amount exceeds 10 parts by mass, the thixotropy of the composition may be increased, the fluidity may be lowered, and the coating workability may be deteriorated.

When the component (E) contains alkenyl groups and/or hydrosilyl groups, the total number of hydrosilyl groups contained in the composition containing the component (B) and the component (E) is 1 to 10 mol (or units), preferably 1.2 to 9 mol (or units), more preferably 1.2 to 9 mol (or units), per 1 mol (or units) of silicon-bonded alkenyl groups contained in the composition containing the components (A) and (E). is an amount that is 1.5 to 8 moles (or pieces).

This is because if the amount of hydrosilyl groups is less than 1 mol per 1 mol of silicon-bonded alkenyl groups in the composition, the composition may not sufficiently cure and may not develop sufficient adhesive strength.

The component (E) may be used alone or in combination of two or more.

[Other ingredients]
In addition to the above components (A) to (E), the composition according to the present invention may contain other optional components depending on the purpose of the present invention. Specific examples thereof include the following. Each of these other components may be used alone or in combination of two or more.

[(F) Component]
The condensation catalyst of component (F) is at least one selected from an organic titanium compound, an organic zirconium compound, and an organic aluminum compound, and acts as a condensation catalyst for the adhesion imparting functional groups in component (E) to promote adhesion.

Specific examples of the above component (F) include titanium-based condensation catalysts (titanium compounds) such as organic titanate esters such as titanium tetraisopropoxide, titanium tetra-normal butoxide and titanium tetra-2-ethylhexoxide; organic titanium chelate compounds such as titanium diisopropoxybis(acetylacetonate), titanium diisopropoxybis(ethylacetoacetate) and titanium tetraacetylacetonate; Zirconium-based condensation catalysts (zirconium compounds) such as organic zirconium esters such as oxides, organic zirconium chelate compounds such as zirconium tributoxy monoacetylacetonate, zirconium monobutoxyacetylacetonate bis(ethylacetoacetate), zirconium tetraacetylacetonate; organic aluminum acid esters such as aluminum secondary butoxide; and aluminum-based condensation catalysts (aluminum compounds) such as compounds.

The organotitanium compound, organozirconium compound, and organoaluminum compound of component (F) are optional components that are blended as needed, and the blending amount thereof is preferably 0.1 to 5 parts by mass, more preferably 0.2 to 4 parts by mass, based on 100 parts by mass of component (A). When the blending amount is within the range of 0.1 to 5 parts by mass, the obtained cured product has excellent adhesion to the base fabric for airbags.

The component (F) may be used alone or in combination of two or more.

[(G) component]
Component (G) is an organopolysiloxane resin characterized by a powdery three-dimensional network (resin-like) structure. Suitably, it consists essentially of one or more branched siloxane units selected from trifunctional R ⁵ SiO _3/2 units and tetrafunctional SiO _4/2 units, optionally containing monofunctional R ⁵ ₃ SiO _1/2 units and/or difunctional R ⁵ ₂ SiO _2/2 units. This component acts as a flame retardant improver. However, this organopolysiloxane resin may contain alkenyl groups in its molecule, but does not contain silicon-bonded hydrogen atoms (hydrosilyl groups). In addition, since this organopolysiloxane resin has a three-dimensional network (resin-like) structure and is powdery at 25°C, it is clearly differentiated from component (A), which basically has a linear structure and may be liquid at 25°C.

R in the above formula⁵is independently a monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms, and includes the same alkenyl groups and monovalent organic groups as exemplified in the above component (A). Specifically, alkenyl groups such as vinyl, allyl, propenyl, butenyl, pentenyl, hexenyl, cyclohexenyl and heptenyl; methyl, ethyl, propyl, butyl, pentyl and hexyl. Aryl groups such as phenyl group, tolyl group, xylyl group and naphthyl group; Aralkyl groups such as benzyl group and phenethyl group; Halogen-substituted alkyl groups such as chloromethyl group, 3-chloropropyl group and 3,3,3-trifluoropropyl group;

The content of silicon-bonded alkenyl groups in component (G) is preferably 0 to 10 mol%, more preferably about 2 to 8 mol%, based on the total silicon-bonded substituents.

The organopolysiloxane resin of component (G) preferably contains R ⁵ SiO _3/2 units and/or SiO _4/2 units, and the total amount thereof is preferably 20 to 75 mol %, particularly preferably 30 to 60 mol %, of the organopolysiloxane resin of component (G).

Here, as described above, the organopolysiloxane resin of component (G) may optionally contain R ⁵ ₃ SiO _1/2 units and/or R ⁵ ₂ SiO _2/2 units.

When the total amount of R ⁵ SiO _3/2 units and/or SiO _4/2 units in the organopolysiloxane resin of component (G) is within the range of 20 to 75 mol %, a sufficient flame retardancy improving effect can be obtained, which is preferable.

The polystyrene-equivalent weight-average molecular weight of the organopolysiloxane resin of component (G) in GPC (gel permeation chromatography) analysis using toluene as a developing solvent is preferably in the range of 2,000 to 50,000, particularly preferably 4,000 to 20,000. When the weight-average molecular weight is in the range of 2,000 to 50,000, a sufficient flame retardancy improving effect is obtained, and the viscosity of the liquid silicone rubber coating agent composition has good coating workability. This weight average molecular weight is a value determined by GPC analysis under the same conditions as those used for determining the weight average degree of polymerization of the component (A).

A specific example of the organopolysiloxane resin of component (G) is represented by the formula: R'₃SiO_1/2A siloxane unit represented by the formula: R '₂R"SiO_1/2A siloxane unit represented by the formula: R '₂SiO_2/2A siloxane unit represented by the formula: SiO_4/2An organosiloxane copolymer consisting of a siloxane unit represented by the formula: R '₃SiO_1/2A siloxane unit represented by the formula: R '₂R"SiO_1/2A siloxane unit represented by the formula: SiO_4/2An organosiloxane copolymer consisting of a siloxane unit represented by the formula: R '₂R"SiO_1/2A siloxane unit represented by the formula: R '₂SiO_2/2A siloxane unit represented by the formula: SiO_4/2Organosiloxane copolymer consisting of a siloxane unit represented by the formula: R'R"SiO_2/2A siloxane unit represented by the formula: R'SiO_3/2A siloxane unit or formula: R″SiO_3/2and a mixture of two or more of these organopolysiloxanes.

In the above formula, R 'is the same or different unsubstituted or substituted monovalent hydrocarbon group having 1 to 10 carbon atoms, preferably 1 to 8 carbon atoms other than alkenyl group, examples thereof include alkyl groups such as methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, cyclohexyl group and heptyl group; aryl groups such as phenyl group, tolyl group, xylyl group and naphthyl group; aralkyl groups such as benzyl group and phenethyl group; and halogenated alkyl groups such as 3-chloropropyl group and 3,3,3-trifluoropropyl group, and methyl group is particularly preferred. R″ in the above formula is an alkenyl group, examples of which include vinyl, allyl, butenyl, pentenyl, hexenyl, and heptenyl groups, with vinyl being particularly preferred.

The amount of component (G) is preferably 0.1 to 100 parts by mass, more preferably 1 to 90 parts by mass, and particularly preferably 2 to 80 parts by mass, based on 100 parts by mass of the organopolysiloxane of component (A). When the blending amount is in the range of 0.1 to 100 parts by mass, a sufficient flame retardancy improving effect is obtained, and the cost effectiveness is excellent.

When the component (G) contains an alkenyl group, the amount of all hydrosilyl groups contained in the composition is 1 to 10 mol per 1 mol of all silicon-bonded alkenyl groups contained in the composition. For example, the amount of component (G) can be such that the amount of hydrosilyl groups contained in component (B) and component (E) is 1 to 10 mol (or units), preferably 1.2 to 9 mol (or units), more preferably 1.5 to 8 mol (or units), per 1 mol of silicon-bonded alkenyl groups contained in component (A), component (E), and component (G) in the composition. If the total amount of hydrosilyl groups is less than 1 mol with respect to 1 mol of silicon-bonded alkenyl groups in the composition, the composition may not sufficiently cure and may not exhibit sufficient adhesive strength.

Thus, in the present invention, each component is blended so that the total number of moles of hydrosilyl groups per 1 mole of alkenyl groups of each component contained in the addition-curable liquid silicone rubber composition for air bags is 1 to 10 moles.

The three-dimensional network organopolysiloxane resin, component (G), may be used alone or in combination of two or more.

Reaction Control Agent The reaction control agent is not particularly limited as long as it is a compound having a curing inhibitory effect on the catalyst for hydrosilylation reaction of component (D), and known ones can be used. Specific examples thereof include phosphorus-containing compounds such as triphenylphosphine; nitrogen-containing compounds such as tributylamine, tetramethylethylenediamine and benzotriazole; sulfur-containing compounds; acetylenic compounds such as acetylene alcohols; compounds containing two or more alkenyl groups;

Since the degree of curing inhibitory effect of the reaction control agent varies depending on the chemical structure of the reaction control agent, the amount of the reaction control agent to be added is preferably adjusted to the optimum amount for each reaction control agent used. By adding an optimum amount of the reaction control agent, the composition has excellent long-term storage stability and curability at room temperature.

・Non-reinforcing filler
As a filler other than the surface-treated silica fine powder of component (C), for example, crystalline silica (for example, BET specific surface area of 50 m²/ g of silica powder), organic resin hollow filler, polymethylsilsesquioxane fine particles (so-called silicone resin powder), fumed titanium dioxide, magnesium oxide, zinc oxide, iron oxide, aluminum hydroxide, magnesium carbonate, calcium carbonate, zinc carbonate, carbon black, diatomaceous earth, talc, kaolinite, glass fiber, etc. Fillers; surface hydrophobic treatment of these fillers with organosilicon compounds such as organoalkoxysilane compounds, organochlorosilane compounds, organosilazane compounds, low-molecular weight siloxane compounds, etc. filler; silicone rubber powder; and silicone resin powder other than component (G).

・Other components In addition, for example, an organopolysiloxane containing one silicon-bonded hydrogen atom in one molecule and no other functional groups, an organopolysiloxane containing one silicon-bonded alkenyl group in one molecule and no other functional groups, a non-functional organopolysiloxane (so-called dimethyl silicone oil) containing no silicon-bonded hydrogen atoms, silicon-bonded alkenyl groups, or other functional groups, organic solvents, creep hardening inhibitors, and permissible A plasticizer, a thixotropic agent, a pigment, a dye, an antifungal agent, etc. can be blended.

<Preparation of addition-curable liquid silicone rubber composition>
In addition to the above components (A) to (E), the addition-curable liquid silicone rubber composition can be prepared by uniformly mixing the above components (F), (G), and other components that are blended as necessary.

The addition-curable liquid silicone rubber composition thus obtained is a composition that is liquid at 25°C, and has a viscosity at 25°C of preferably 1 to 1,000 Pa·s, more preferably 2 to 500 Pa·s, and even more preferably 5 to 300 Pa·s. If the viscosity is within the above range at 25° C., it can be preferably used because unevenness in coating and insufficient adhesion to the base fabric after curing are less likely to occur when it is applied to the base fabric for an air bag.

The addition-curable liquid silicone rubber composition for airbags of the present invention includes a step of mixing components (A) to (E) above with other optional components, and can be produced by using, as component (C), fine silica powder surface-treated with a surface treatment agent that does not contain triorganosiloxy units.

As the surface treatment agent, those described in the explanation of the component (C) can be used, and it is preferable to include one selected from dichlorodimethylsilane and an organosilicon compound represented by the general formula (1).

<Air bag base fabric>
In general, known airbag base fabrics (base materials made of fiber fabrics) on which a silicone rubber layer is formed are used, and specific examples thereof include woven fabrics of various synthetic fibers such as various polyamide fibers such as 6,6-nylon, 6-nylon, and aramid fibers, and various polyester fibers such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT).

<Airbag>
The airbag of the present invention comprises a base fabric for an airbag and a cured film of the addition-curable liquid silicone rubber composition for an airbag on the base fabric.

<Method for manufacturing airbag>
The addition-curable liquid silicone rubber composition for airbags can be applied to one side or both sides, particularly only one side, of an airbag base fabric (base material made of fiber fabric), and then heat-cured in a drying oven or the like to form a silicone rubber layer (cured coating). An air bag can be manufactured using the silicone rubber coated base fabric for an air bag thus obtained.

Here, as a method for coating the air bag addition-curable liquid silicone rubber composition on the air bag base fabric, a conventional method can be employed, but coating with a knife coater is preferable. The thickness (or surface coating amount) of the coating layer can be generally 5 to 100 g/m ² , preferably 8 to 90 g/m ² , more preferably 10 to 80 g/m ² .

The curing method of the addition-curable liquid silicone rubber composition for airbags is not particularly limited, and it can be cured by a known curing method under known curing conditions. Specifically, for example, the composition can be cured by heating at 100 to 200° C. for 1 to 30 minutes.

When processing the air bag base fabric having a silicone rubber layer on one or both sides thus produced into an air bag, there is a method in which the outer peripheral portions of two pieces of the above silicone rubber-coated air bag base fabric are adhered together with an adhesive, and then the adhesive layers are stitched together with the surface coated with silicone rubber as the inner surface. In addition, as described above, the addition-curable liquid silicone rubber composition may be coated in a predetermined coating amount on both outer sides of the airbag base fabric that has been prepared by hollow weaving in advance, and the coating may be cured under predetermined curing conditions. As the adhesive used here, a known adhesive can be used, but a silicone-based adhesive called a seam sealant is preferable from the standpoint of adhesive strength and adhesive durability.

Preparation Examples, Examples, and Comparative Examples are shown below to specifically describe the present invention, but the present invention is not limited to the following Examples. In the following examples, M units are R ₃ SiO _1/2 units, D units are R ₂ SiO _2/2 units, Q units are SiO _4/2 units, and R represents an organic group. Also, the weight average degree of polymerization and viscosity were measured by the above methods.

[Example 1]
分子鎖両末端がビニルジメチルシロキシ基で封鎖され重量平均重合度が４５０の直鎖状ジメチルポリシロキサン（Ａ１）１４７質量部、（ＣＨ _３ ） _３ ＳｉＯ _１／２単位３９．５モル％と（ＣＨ _３ ） _２ （ＣＨ _２ ＝ＣＨ）ＳｉＯ _１／２単位６．５モル％とＳｉＯ _２単位５４モル％とからなる三次元網状構造のオルガノポリシロキサンレジン（Ｇ）（重量平均分子量：６，０００）２７．５質量部、比表面積がＢＥＴ法で１１０ｍ ^２ ／ｇであるジメチルジクロロシランで処理されたシリカ微粉末（Ｃ１）（商品名：Ａｅｒｏｓｉｌ Ｒ－９７２、日本アエロジル株式会社製、 ^２９ Ｓｉ固体ＮＭＲでＤ単位とＱ単位以外は検出されない）１０質量部、架橋剤として２５℃における粘度が８ｍＰａ・ｓであり、分子鎖側鎖にケイ素原子に結合した水素原子を有する分子鎖両末端トリメチルシロキシ基封鎖直鎖状ジメチルシロキサン・メチルハイドロジェンシロキサン共重合体（Ｂ）（ケイ素原子結合水素原子含有量＝０．００９２ｍｏｌ／ｇ、上記式（２）中でａ＝１．５６，ｂ＝０．５６、Ｒ ^３ ＝メチル基に相当）１７質量部、γ－グリシドキシプロピルトリメトキシシラン（Ｅ）０．５０質量部、１－エチニルシクロヘキサノール０．０７質量部、塩化白金酸／１，３－ジビニルテトラメチルジシロキサン錯体を白金原子含有量として１質量％含有するジメチルポリシロキサン溶液（Ｄ）０．３２質量部、テトラオクチルチタネート（Ｆ）０．６０質量部を１時間混合して、組成物Ａ（組成物全体において、ヒドロシリル基／ビニル基＝５．２ｍｏｌ／ｍｏｌ、粘度１２Ｐａ・ｓ）を調製した。

<Flame retardant test method>
The above composition A was coated on a 66 nylon base fabric (210 denier) for air bags with a knife coater so that the surface coating amount was 25 to 30 g/m ² , and then heat-cured in a dryer at 200 ° C. for 1 minute to prepare an air bag base fabric coated with a silicone rubber cured product (cured film). The prepared silicone rubber-coated air bag base fabric was evaluated for flame retardancy by the method described in FMVSS-302 (Federal Motor Vehicle Safety Standard-302). The silicone rubber-coated surface of the base cloth (width 10 cm x length 35 cm), which is a test piece, was placed upward, and the burning distance and burning time until the flame disappeared when burned by the method described in FMVSS-302 were measured at N = 10. The burning speed was calculated from this burning distance and burning time, and those with a burning speed of 102 mm/min or less were accepted, those that passed all N = 10 tests were passed, and those that failed at least one were evaluated as unacceptable. In addition, when the burning distance was 50 mm or less and the burning time was 60 seconds or less, it was determined as "self-extinguishing", and Table 1 shows the self-extinguishing rate when tested with N=10.

<Measurement method of headspace GC (gas chromatography)>
The above composition A was coated on a 66 nylon base fabric (210 denier) for air bags with a knife coater so that the surface coating amount was 25 to 30 g/m ² , and then heat-cured in a dryer at 200 ° C. for 1 minute to prepare an air bag base fabric coated with a silicone rubber cured product (cured film). This airbag silicone-coated base fabric was cut into pieces having a weight of 15 to 25 mg, and dried in a desiccator for 24 hours using calcium chloride as a desiccant. Thereafter, a sample cut to 2.0000±0.001 g was weighed into a 20 mL vial for headspace GC, and sealed with a lid dedicated to headspace GC vials. Headspace GC (Nexis GC-2030 and HS-20 manufactured by Shimadzu Corporation) was measured for the samples thus prepared under the following conditions.

[Measurement condition]
Oven temperature: 120°C
Vial heat retention time: 5 hours Column oven temperature: 50°C (3 minutes) → 12°C/min temperature increase → 200°C (4 minutes)
Detector: FID
Column used: Capillary column (product name: SH-Stabilwax, manufactured by Shimadzu Corporation)
Column length: 30m
Split ratio: 20:1

<How to create a calibration curve>
Seven acetone-butanol solutions of 0.1 g/L, 0.5 g/L, 1.0 g/L, 5.0 g/L, 10.0 g/L, 50.0 g/L, and 100.0 g/L were used as standard solutions, and the headspace GC of each standard solution was measured under the following conditions.
[Measurement condition]
Sample volume: 4 μL
Oven temperature: 120°C
Vial heat retention time: 1 hour Column oven temperature: 50°C (3 minutes) → 12°C/min temperature increase → 200°C (4 minutes)
Detector: FID
Column used: Capillary column (product name: SH-Stabilwax, manufactured by Shimadzu Corporation)
Column length: 30m
Split ratio: 20:1
Next, plotting the acetone concentration on the horizontal axis and the GC peak area of acetone on the vertical axis, a calibration curve was drawn by the least squares method, and the slope was taken as the coefficient K.

<Method for calculating total VOC>
Total VOC [ppm] was calculated as a semi-quantitative value using acetone as a standard from the following formula.

Total VOC [ppm] = GC peak area of all compounds/coefficient K x 2 calculated from the calibration curve

Table 1 shows the median value of the total VOC [ppm] calculated from the above equation by measuring the headspace GC three times.

[Example 2]
実施例１の比表面積がＢＥＴ法で１１０ｍ ^２ ／ｇであるジメチルジクロロシランで処理されたシリカ微粉末（Ｃ１）（商品名：Ａｅｒｏｓｉｌ Ｒ－９７２ 日本アエロジル株式会社製）を比表面積がＢＥＴ法で１７０ｍ ^２ ／ｇであるジメチルジクロロシランで処理されたシリカ微粉末（Ｃ２）（商品名：Ａｅｒｏｓｉｌ Ｒ－９７４ 日本アエロジル株式会社製、 ^２９ Ｓｉ固体ＮＭＲでＤ単位とＱ単位以外検出されない）に同質量部で置き換えたこと以外は同様にして組成物Ｂ（組成物全体において、ヒドロシリル基／ビニル基＝５．２ｍｏｌ／ｍｏｌ、粘度１５Ｐａ・ｓ）を調製し、実施例１と同様に難燃性とトータルＶＯＣを評価した結果を表１に示す。

[Example 3]
A composition C (hydrosilyl group/vinyl group = 5.2 mol/mol, viscosity 25 Pa s in the entire composition) was prepared in the same manner as in Example 1, except that 10 parts by mass of the dimethyldichlorosilane-treated silica fine powder (C1) (trade name: Aerosil R-972, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 110 m ² /g by the BET method in Example 1 was replaced with 15 parts by mass. Table 1 shows the results of evaluating VOC.

[Comparative Example 1]
Composition D (hydrosilyl group/vinyl group = 5.2 mol/mol, viscosity 3 Pa s in the entire composition) was prepared in the same manner as in Example 1 except that the dimethyldichlorosilane-treated silica fine powder (C1) (trade name: Aerosil R-972, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 110 m ² /g by the BET method was not blended. Table 1 shows.

[Comparative Example 2]
実施例１の比表面積がＢＥＴ法で１１０ｍ ^２ ／ｇであるジメチルジクロロシランで処理されたシリカ微粉末（Ｃ１）（商品名：Ａｅｒｏｓｉｌ Ｒ－９７２ 日本アエロジル株式会社製）を比表面積がＢＥＴ法で１７０ｍ ^２ ／ｇであるヘキサメチルジシランで処理されたシリカ微粉末（商品名：Ｍｕｓｉｌ １２０Ａ 信越化学工業株式会社製、 ^２９ Ｓｉ固体ＮＭＲでＭ単位とＱ単位以外検出されない）に同質量部で置き換えたこと以外は同様にして組成物Ｅ（組成物全体において、ヒドロシリル基／ビニル基＝５．２ｍｏｌ／ｍｏｌ、粘度８Ｐａ・ｓ）を調製し、実施例１と同様に難燃性とトータルＶＯＣを評価した結果を表１に示す。

[Comparative Example 3]
Composition F (hydrosilyl group/vinyl group = 5 in the entire composition) was prepared in the same manner as in Example 1 except that the dimethyldichlorosilane-treated silica fine powder (C1) (trade name: Aerosil R-972, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 110 m ² /g by the BET method was replaced with talc fine powder (Micro Ace K-1, manufactured by Nippon Talc Co., Ltd.) having a specific surface area of 7.0 m ² /g. .2 mol/mol, viscosity 5 Pa·s) was prepared, and flame retardancy and total VOC were evaluated in the same manner as in Example 1. Table 1 shows the results.

[Preparation Example 1]
60 parts by mass of dimethylpolysiloxane (A2) having a viscosity at 25° C. of 30,000 mPa s and a weight average degree of polymerization of 750, 4 parts by mass of polydimethylsiloxane having silanol groups at both ends represented by the following formula (3), 0.1 part by mass of aqueous ammonia (28%), and untreated silica fine powder (C3) having a specific surface area of 130 m ² /g by the BET method (trade name: 40 parts by mass of Aerosil 130 (manufactured by Nippon Aerosil Co., Ltd.) was put into a kneader and mixed at 25° C. for 1 hour. The temperature was then raised to 150° C. followed by mixing for 2 hours. Thereafter, the mixture was cooled to 25°C, and 30 parts by mass of dimethylpolysiloxane (A2) having both ends of the molecular chain blocked with vinyldimethylsiloxy groups and having a viscosity of 30,000 mPa s at 25°C was added and mixed until uniform to obtain a base compound (1). When the ²⁹ Si solid-state NMR of this base compound was measured, no units other than D units and Q units were detected.

[Preparation Example 2]
60 parts by mass of dimethylpolysiloxane (A2) having both ends of the molecular chain blocked with vinyldimethylsiloxy groups, a viscosity of 30,000 mPa s at 25°C and a weight average degree of polymerization of 750, 4 parts by mass of polydimethylsiloxane having silanol groups at both ends represented by the above formula (3), 3.0 parts by mass of hexamethyldisilazane, and untreated fine silica powder (C3) having a specific surface area of 130 m ² /g by the BET method (trade name: A erosil 130 (manufactured by Nippon Aerosil Co., Ltd.) was put into a kneader and mixed at 25° C. for 1 hour. The temperature was then raised to 150° C. followed by mixing for 2 hours. After that, the mixture was cooled to 25°C, and 30 parts by mass of dimethylpolysiloxane (A2) having both molecular chain ends blocked with vinyldimethylsiloxy groups and having a viscosity of 30,000 mPa s at 25°C was added and mixed until uniform to obtain a base compound (2). ^{A 29} Si solid state NMR measurement of this base compound (2) showed that 72% of the organosiloxy groups were D units and 28% were M units.

[Preparation Example 3]
60 parts by mass of dimethylpolysiloxane (A2) having a viscosity of 30,000 mPa s at 25°C and a weight-average degree of polymerization of 750, 5.0 parts by mass of hexamethyldisilazane, and 40 parts by mass of untreated silica fine powder (trade name: Aerosil 200, manufactured by Nippon Aerosil Co., Ltd.) having a specific surface area of 200 m ² /g by the BET method were charged into a kneader; Mixed for 1 hour at 25°C. The temperature was then raised to 150° C. followed by mixing for 2 hours. Thereafter, the mixture was cooled to 25°C, and 30 parts by mass of dimethylpolysiloxane (A2) having both ends of the molecular chain blocked with vinyldimethylsiloxy groups and having a viscosity of 30,000 mPa s at 25°C was added and mixed until uniform to obtain a base compound (3). ²⁹ Si solid-state NMR of this base compound (3) detected only M units and Q units.

[Example 4]
調製例１で調製したベースコンパウンド（１）７０質量部、２５℃での粘度が１，０００ｍＰａ・ｓであり、重量平均重合度が２００である分子鎖両末端ビニルジメチルシロキシ基封鎖ジメチルポリシロキサン（Ａ３）６１．６質量部、分子鎖両末端がビニルジメチルシロキシ基で封鎖され重量平均重合度が４５０のジメチルポリシロキサン（Ａ１）２７．５質量部、（ＣＨ _３ ） _３ ＳｉＯ _１／２単位３９．５モル％と（ＣＨ _３ ） _２ （ＣＨ _２ ＝ＣＨ）ＳｉＯ _１／２単位６．５モル％とＳｉＯ _２単位５４モル％とからなる三次元網状構造のオルガノポリシロキサンレジン（Ｇ）（重量平均分子量：６，０００）２７．５質量部、架橋剤として２５℃における粘度が８ｍＰａ・ｓであり、分子鎖側鎖にケイ素原子に結合した水素原子を有する分子鎖両末端トリメチルシロキシ基封鎖ジメチルシロキサン・メチルハイドロジェンシロキサン共重合体（Ｂ）（ケイ素原子結合水素原子含有量＝０．００９２ｍｏｌ／ｇ、上記式（２）中でａ＝１．５６，ｂ＝０．５６、Ｒ ^３ ＝メチル基に相当）１６質量部、γ－グリシドキシプロピルトリメトキシシラン（Ｅ）０．５０質量部、１－エチニルシクロヘキサノール０．０７質量部、塩化白金酸／１，３－ジビニルテトラメチルジシロキサン錯体を白金原子含有量として１質量％含有するジメチルポリシロキサン溶液（Ｄ）０．３２質量部、テトラオクチルチタネート（Ｆ）０．６０質量部を１時間混合して、組成物Ｇ（組成物全体において、ヒドロシリル基／ビニル基＝４．６ｍｏｌ／ｍｏｌ、粘度５９Ｐａ・ｓ）を調製した。 Table 2 shows the results of evaluating the flame retardancy and total VOC of the prepared composition G in the same manner as in Example 1.

[Example 5]
Composition H (in the entire composition, hydrosilyl group/vinyl group = 4.3 mol/mol, viscosity 30 Pa s) was prepared in the same manner except that 70 parts by mass of the base compound (1) of Example 4 was replaced with 50 parts by mass, and 61.6 parts by mass of vinyldimethylsiloxy group-blocked dimethylpolysiloxane (A3) having a weight average degree of polymerization of 200 was replaced with 81.6 parts by mass. Table 2 shows the evaluation results.

[Comparative Example 4]
Composition I (hydrosilyl group/vinyl group in the entire composition = 4.6 mol/mol, viscosity 54 Pa s) was prepared in the same manner except that base compound (1) of Example 4 was replaced with base compound (2) prepared in Preparation Example 2 by the same parts by weight, and flame retardancy and total VOC were evaluated in the same manner as in Example 1. Table 2 shows the results.

[Comparative Example 5]
Composition J (hydrosilyl group/vinyl group in the entire composition = 4.6 mol/mol, viscosity 13 Pa s) was prepared in the same manner except that base compound (1) of Example 4 was replaced with base compound (3) prepared in Preparation Example 3 at the same parts by weight, and flame retardancy and total VOC were evaluated in the same manner as in Example 1. Table 2 shows the results.

As can be seen from Tables 1 and 2, Examples 1 to 5 using the addition-curable liquid silicone rubber composition for air bags of the present invention exhibited excellent flame retardancy and low VOC emissions at high temperatures.

On the other hand, Comparative Examples 1 to 5, which did not use the addition-curable liquid silicone rubber composition for airbags of the present invention, could not achieve both flame retardancy and low VOC emissions.

In addition, this invention is not limited to the said embodiment. The above embodiment is an example, and any device having substantially the same configuration as the technical idea described in the claims of the present invention and having similar effects is included in the technical scope of the present invention.

Claims (9)

An addition-curable liquid silicone rubber composition for an air bag,
(A) a linear organopolysiloxane containing two or more silicon-bonded alkenyl groups in one molecule and having a weight-average degree of polymerization of 50 to 2,000: 100 parts by mass;
(B) an organohydrogenpolysiloxane containing at least two silicon-bonded hydrogen atoms (hydrosilyl groups) per molecule: the amount of hydrosilyl groups contained in the composition is from 1 to 10 moles per mole of the total silicon-bonded alkenyl groups contained in the composition;
(C) a surface-treated fine silica powder having a BET specific surface area of 50 m ² /g or more, wherein the surface of the surface-treated fine silica powder does not contain triorganosiloxy units (M units): 1 to 30 parts by mass;
(D) catalyst for hydrosilylation reaction: 1 to 500 ppm in terms of mass of the catalytic metal element with respect to the total mass of (A) to (C);
(E) An addition-curable liquid silicone rubber composition for airbags, comprising 0.1 to 10 parts by mass of an organosilicon compound containing an adhesion imparting functional group as an essential component. 2. The addition-curing liquid silicone rubber composition for airbags according to claim 1, wherein said component (C) is treated with dichlorodimethylsilane. 2. The addition-curable liquid silicone rubber composition for airbags according to claim 1, wherein the component (C) is treated with an organic silicon compound represented by the following general formula (1).

(In the formula, R ¹ is independently a monovalent saturated aliphatic hydrocarbon group having 1 to 12 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 12 carbon atoms, R ² is independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 100.) The addition-curable liquid silicone rubber composition for airbags according to any one of claims 1 to 3, further comprising, as component (F), 0.1 to 5 parts by mass of at least one condensation catalyst selected from an organic titanium compound, an organic zirconium compound, and an organic aluminum compound per 100 parts by mass of component (A). 5. The addition-curable liquid silicone rubber composition for airbags according to any one of claims 1 to 4, further comprising, as component (G), 0.1 to 100 parts by mass of a powdery three-dimensional network organopolysiloxane resin per 100 parts by mass of component (A). An air bag comprising a base fabric for air bag and a cured film of the addition-curable liquid silicone rubber composition for air bag according to any one of claims 1 to 5 on the base fabric. 6. The method for producing an addition-curable liquid silicone rubber composition for air bags according to any one of claims 1 to 5, which comprises the step of mixing components (A) to (E) with other optional components, and using fine silica powder surface-treated with a surface-treating agent containing no triorganosiloxy units as component (C). 8. The method for producing an addition-curable liquid silicone rubber composition for airbags according to claim 7, wherein dichlorodimethylsilane is used as the surface treatment agent. 8. The method for producing an addition-curable liquid silicone rubber composition for an air bag according to claim 7, wherein the surface treatment agent is selected from organosilicon compounds represented by the following general formula (1).

(In the formula, R ¹ is independently a monovalent saturated aliphatic hydrocarbon group having 1 to 12 carbon atoms or a monovalent aromatic hydrocarbon group having 6 to 12 carbon atoms, R ² is independently a hydrogen atom or an alkyl group having 1 to 6 carbon atoms, and n is an integer of 1 to 100.)