Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2000-08-24
2002-05-14
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C428S413000, C428S480000, C428S474400, C524S265000, C524S731000, C524S266000, C524S858000
Reexamination Certificate
active
06387520
ABSTRACT:
This invention relates to a solventless (or solvent free) liquid silicone rubber coating composition, and more particularly, to a liquid silicone rubber composition which is effectively coated without a need for solvent and suitable as an air bag coating that is resistant to the impact by inflation, especially high temperature inflation. It also relates to an air bag fabric.
BACKGROUND OF THE INVENTION
Air bags are currently installed in many automobiles as the vehicle passenger safety device. The air bags are constructed of base fabric in the form of nylon fabric coated with chloroprene rubber.
The base fabric coated with chloroprene rubber, however, has the drawbacks that weight reduction is difficult and especially, physical properties deteriorate with the lapse of time. JP-A 63-78744, JP-A 3-243442 and Japanese Patent No. 2,571,986 disclose air bag base fabrics coated with silicone rubber compositions. These silicone rubber-coated air bag base fabrics advantageously have improved high-temperature properties. Nevertheless, these silicone rubber compositions have the drawback that upon application to air bag-forming base fabric of synthetic fibers such as nylon 66, an organic solvent for dilution must be used in order to achieve uniform thin coating and a sufficient bond strength to the base fabric. More particularly, to ensure thin film coating and infiltration into the base fabric, the silicone rubber compositions must be diluted with organic solvents such as toluene and xylene.
As a solution to this problem, Japanese Patent No. 2,571,986 discloses a solventless liquid composition comprising a silicone resin having SiO
4
units. JP-A 7-90777 corresponding to U.S. Pat. No. 5,401,566 discloses the use of hydrophobic silica as the filler. These proposals still have a problem. When a bonding component is added to the silicone composition in order to provide a firm bond to the base fabric, the silicone composition becomes so thixotropic that it may become difficult to achieve a coating thickness of about 40 &mgr;m or less, especially about 20 &mgr;m or less, which is currently desired from the standpoints of cost reduction and compactness.
SUMMARY OF THE INVENTION
An object of the invention is to provide a solventless (or solvent free) liquid silicone rubber coating composition which has improved infiltration and adhesion abilities and can be thinly coated, without a need for solvent, to form a coating film having minimized surface tack, and which is especially suited for coating on air bag-forming synthetic fiber fabric. Another object is to provide an air bag fabric having a coating film of the composition.
The invention pertains to a liquid silicone rubber coating composition comprising an organopolysiloxane containing at least two alkenyl groups in a molecule, an organohydrogenpolysiloxane having at least two hydrogen atoms each attached to a silicon atom (that is, at least two SiH groups) in a molecule, wet silica, an adhesive agent, and a platinum group catalyst. It has been found that when a wet silica having a specific surface area of 150 to 250 m
2
/g on average as measured by the BET method, a mean particle size (secondary particles) of up to 20 &mgr;m, and a sodium ion content of up to 0.35% by weight calculated as Na
2
O is used as the wet silica, the composition has good infiltration and thin film coating abilities to air bag-forming synthetic fiber fabrics, even in the absence of solvent, and forms a coating having minimized surface tack and a high bond strength.
According to the invention, there is provided a solventless (or solvent free,) liquid silicone rubber coating composition comprising
(A) an organopolysiloxane containing at least two alkenyl groups in a molecule,
(B) an organohydrogenpolysiloxane having at least two hydrogen atoms each attached to a silicon atom in a molecule,
(C) wet silica having a specific surface area of 150 to 250 m
2
/g on average as measured by the BET method, a mean particle size of up to 20 &mgr;m, and a sodium ion content of up to 0.35% by weight calculated as Na
2
O,
(D) a bonding component, and
(E) a platinum group catalyst.
An air bag fabric having formed thereon a coating film of the composition is also contemplated.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The organopolysiloxane (A) is a base component (or base polymer) of the composition. It must have at least two alkenyl groups attached to silicon atoms in a molecule in order that the composition form a silicone rubber coating film having rubbery elasticity upon curing.
Preferred is an organopolysiloxane having on the average at least two alkenyl groups attached to silicon atoms in a molecule, represented by the following average compositional formula (1):
R
1
a
SiO
(4−a)/2
(1)
wherein R
1
is a substituted or unsubstituted monovalent hydrocarbon group, 0.01 to 10 mol % of R
1
being preferably alkenyl groups, and “a” is a positive number of 1.9 to 2.4.
R
1
stands for substituted or unsubstituted monovalent hydrocarbon groups of 1 to 12 carbon atoms, especially 1 to 8 carbon atoms, attached to silicon atoms. Examples include alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, neopentyl, hexyl heptyl, octyl, nonyl, decyl and dodecyl; cycloalkyl groups such as cyclopentyl, cyclohexyl and cycloheptyl; alkenyl groups such as vinyl, allyl, propenyl, isopropenyl, butenyl, isobutenyl, hexenyl and cyclohexenyl; aryl groups such as phenyl, tolyl, xylyl, naphthyl and biphenyl; aralkyl groups such as benzyl, phenylethyl, phenylpropyl and methylbenzyl; and substituted ones of the foregoing groups in which some or all of the hydrogen atoms are replaced by halogen atoms (e.g., F, Cl and Br) or cyano groups, such as chloromethyl, 2-bromoethyl, 3,3,3-trifluoropropyl, 3-chloropropyl and cyanoethyl.
The organopolysiloxane favors that methyl accounts for at least 90 mol % (usually 90 to 90.99 mol %, preferably 95 to 99.98 mol %) of the substituted or unsubstituted monovalent hydrocarbon groups represented by R
1
. Also, at least two groups of the entire R
1
groups on the average should be alkenyl groups. It is preferred that 0.01 to 10 mol % and more preferably 0.02 to 5 mol % of the entire R
1
groups be alkenyl groups. Outside the range, a lower proportion of alkenyl may result in a composition which is poorly curable whereas a high proportion of alkenyl may result in a composition having poor physical properties including tensile strength, tear strength and elongation after curing. The alkenyl group may be attached to a silicon atom either at the end or at an intermediate of a molecular chain or both. The preferred alkenyl group is vinyl. The preferred groups other than methyl and vinyl groups are phenyl and 3,3,3-trifluoropropyl.
In formula (1), “a” is a positive number of 1.9 to 2.4 and preferably 1.95 to 2.05. The molecular structure of the organopolysiloxane is preferably a linear one consisting essentially of recurring diorgnosiloxane units (i.e., R
1
2
SiO
2/2
unit) and further preferably, having alkenyl groups at both ends of the molecular chain although a branched structure partially containing R
1
SiO,
3/2
units or SiO
4/2
units is acceptable. It is noted that the organopolysiloxane is preferably end-blocked with a triorganosiloxy group (i.e., R
1
3
SiO
1/2
group) such as trivinylsiloxy, methyldivinylsiloxy, dimethylvinylsiloxy or trimethylsiloxy.
The organopolysiloxane preferably has a viscosity of at least about 100 centipoise at 25° C., and typically about 100 to 50,000centipoise at 25° C. When the strength of a silicone rubber coating film and ease of blending operation are taken into account, the more preferred viscosity is about 400 to 10,000 centipoise at 25° C., and especially about 500 to 5,000 centipoise at 25° C.
Illustrative examples of the organopolysiloxane (A) are both end dimethylvinylsiloxy blocked dimethylpolysiloxane, both end dimethylvinylsiloxy blocked dimethylsiloxane-methylvinylsiloxane copolymers, and both end dimethylvinylsiloxy blocked dimethylsiloxane-methylphenylsiloxane copolymers.
In th
Fujiki Hironao
Harada Yoshifumi
Ikeno Masayuki
Inoue Yoshifumi
Miyao Takeshi
Birch & Stewart Kolasch & Birch, LLP
Dawson Robert
Feely Michael J.
Shin-Etsu Chemical Co. , Ltd.
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