Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2002-10-02
2004-06-15
Robertson, Jeffrey B. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S492000, C524S493000, C524S588000
Reexamination Certificate
active
06750273
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a filled silicone composition and more particularly to a filled silicone composition containing a hydrophobic partially aggregated colloidal silica. The present invention also relates to a cured silicone product formed from the composition.
BACKGROUND OF THE INVENTION
Silicones are useful in a variety of applications by virtue of their unique combination of properties, including high thermal stability, good moisture resistance, excellent flexibility, high ionic purity, low alpha particle emissions, and good adhesion to various substrates. In particular, silicones containing a reinforcing filler, such as treated silica, are commonly employed in applications requiring exceptional mechanical properties. For example, filled silicones are widely used in the automotive, electronic, construction, appliance, and aerospace industries.
Silicone compositions containing hydrophobic non-aggregated colloidal silica are known in the art. For example, Kwan et al. disclose a silicone composition containing a vinyl-terminated polydimethylsiloxane, and Si—H functional crosslinker, a hydrophobic colloidal silica, and a platinum catalyst. (156
th
ACS Rubber Division Meeting, Orlando, Fla., September 1999, paper 96).
U.S. Pat. No. 6,051,672 to Burns et al. discloses a silicone rubber composition comprising hydrophobic non-aggregated colloidal silica prepared by a method comprising reacting an aqueous suspension of a hydrophilic non-aggregated colloidal silica having an average particle diameter greater than about 4 nm with a silicon compound selected from the group consisting of organosilanes and organosiloxanes at a pH less than about pH 4 in the presence of a sufficient quantity of a water-miscible organic solvent to facilitate contact of the hydrophilic non-aggregated colloidal silica with the silicon compound at a temperature within a range of about 20 C to 25 C for a time period sufficient to form a hydrophobic non-aggregated colloidal silica.
Although, the aforementioned silicone compositions cure to form silicone products having a wide range of mechanical properties, high concentrations, for example, 60% w/w, of hydrophobic non-aggregated colloidal silica are typically required to achieve superior mechanical properties. Consequently, there is a need for a filled silicone composition containing a low concentration of a hydrophobic colloidal silica that cures to form a silicone product having excellent mechanical properties.
SUMMARY OF THE INVENTION
The present invention is directed to a filled silicone composition comprising:
(A) a curable silicone composition; and
(B) 5 to 60% (w/w) of a hydrophobic partially aggregated colloidal silica.
The present invention is also directed to a cured silicone product comprising a reaction product of the above-described filled silicone composition.
The filled silicone composition of the present invention has numerous advantages including low VOC (volatile organic compound) content and good flow. Moreover, the filled silicone composition cures to form a cured silicone product having excellent mechanical properties, such as durometer hardness, tensile strength, elongation, modulus, and tear strength, at relatively low concentrations compared with a similar silicone composition lacking the hydrophobic partially aggregated colloidal silica. The potential advantages of low filler concentrations include shorter formulation time, lower cost, and lower viscosity.
The filled silicone composition of the present invention has numerous uses including adhesives, sealants, encapsulants, and molded articles, such as o-rings.
These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DETAILED DESCRIPTION OF THE INVENTION
A filled silicone composition according to the present invention comprises:
(A) a curable silicone composition; and
(B) 5 to 60% (w/w) of a hydrophobic partially aggregated colloidal silica.
Component (A) is a curable silicone composition. Curable silicone compositions and methods for their preparation are well known in the art. Examples of curable silicone compositions include, but are not limited to, hydrosilylation-curable silicone compositions, peroxide curable silicone compositions, condensation-curable silicone compositions, epoxy-curable silicone compositions; ultraviolet radiation-curable silicone compositions, and high-energy radiation-curable silicone compositions. For example, a suitable hydrosilylation-curable silicone composition typically comprises (i) an organopolysiloxane containing an average of at least two silicon-bonded alkenyl groups per molecule, (ii) an organohydrogensiloxane containing an average of at least two silicon-bonded hydrogen atoms per molecule in an amount sufficient to cure the composition, and (iii) a hydrosilylation catalyst. The hydrosilylation catalyst can be any of the well known hydrosilylation catalysts comprising a platinum group metal, a compound containing a platinum group metal, or a microencapsulated platinum group metal-containing catalyst. Platinum group metals include platinum, rhodium, ruthenium, palladium, osmium and iridium. Preferably, the platinum group metal is platinum, based on its high activity in hydrosilylation reactions.
The hydrosilylation-curable silicone composition can be a one-part composition or a multi-part composition comprising the components in two or more parts. Room-temperature vulcanizable (RTV) compositions typically comprise two parts, one part containing the organopolysiloxane and catalyst and another part containing the organohydrogensiloxane and any optional ingredients. Hydrosilylation-curable silicone compositions that cure at elevated temperatures can be formulated as one-part or multi-part compositions. For example, liquid silicone rubber (LSR) compositions are typically formulated as two-part systems. One-part compositions typically contain a platinum catalyst inhibitor to ensure adequate shelf life.
A suitable peroxide-curable silicone composition typically comprises (i) an organopolysiloxane and (ii) an organic peroxide. Examples of organic peroxides include, diaroyl peroxides such as dibenzoyl peroxide, di-p-chlorobenzoyl peroxide, and bis-2,4-dichlorobenzoyl peroxide; dialkyl peroxides such as di-t-butyl peroxide and 2,5-dimethyl-2,5-di-(t-butylperoxy)hexane; diaralkyl peroxides such as dicumyl peroxide; alkyl aralkyl peroxides such as t-butyl cumyl peroxide and 1,4-bis(t-butylperoxyisopropyl)benzene; and alkyl aroyl peroxides such as t-butyl perbenzoate, t-butyl peracetate, and t-butyl peroctoate.
A condensation-curable silicone composition typically comprises (i) an organopolysiloxane containing an average of at least two hydroxy groups per molecule; and (ii) a tri- or tetra-functional silane containing hydrolysable Si—O or Si—N bonds. Examples of silanes include alkoxysilanes such as CH
3
Si(OCH
3
)
3
, CH
3
Si(OCH
2
CH
3
)
3
, CH
3
Si(OCH
2
CH
2
CH
3
)
3
, CH
3
Si[O(CH
2
)
3
CH
3
]
3
, CH
3
CH
2
Si(OCH
2
CH
3
)
3
, C
6
H
5
Si(OCH
3
)
3
, C
6
H
5
CH
2
Si(OCH
3
)
3
, C
6
H
5
Si(OCH
2
CH
3
)
3
, CH
2
═CHSi(OCH
3
)
3
, CH
2
═CHCH
2
Si(OCH
3
)
3
, CF
3
CH
2
CH
2
Si(OCH
3
)
3
, CH
3
Si(OCH
2
CH
2
OCH
3
)
3
, CF
3
CH
2
CH
2
Si(OCH
2
CH
2
OCH
3
)
3
, CH
2
═CHSi(OCH
2
CH
2
OCH
3
)
3
, CH
2
═CHCH
2
Si(OCH
2
CH
2
OCH
3
)
3
, C
6
H
5
Si(OCH
2
CH
2
OCH
3
)
3
, Si(OCH
3
)
4
, Si(OC
2
H
5
)
4
, and Si(OC
3
H
7
)
4
; organoacetoxysilanes such as CH
3
Si(OCOCH
3
)
3
, CH
3
CH
2
Si(OCOCH
3
)
3
, and CH
2
═CHSi(OCOCH
3
)
3
; organoiminooxysilanes such as CH
3
Si[O—N═C(CH
3
)CH
2
CH
3
]
3
, Si[O—N═C(CH
3
)CH
2
CH
3
]
4
, and CH
2
═CHSi[O—N═C(CH
3
)CH
2
CH
3
]
3
; organoacetamidosilanes such as CH
3
Si[NHC(═O)CH
3
]
3
and C
6
H
5
Si[NHC(═O)CH
3
]
3
; aminosilanes such as CH
3
Si[NH(s-C
4
H
9
)]
3
and CH
3
Si(NHC
6
H
11
)
3
; and organoaminooxysilanes.
A condensation-curable silicone compositi
DeCesare Jim L.
Dow Corning Corporation
Robertson Jeffrey B.
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