Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-11-27
2003-08-05
Dawson, Robert (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S588000, C525S477000, C428S402000, C428S405000
Reexamination Certificate
active
06602945
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not applicable.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
REFERENCE TO A MICROFICHE APPENDIX
Not applicable.
FIELD OF THE INVENTION
This invention relates to a vibration damping silicone composition and particularly to a vibration damping silicone composition that has excellent long-term storage stability.
BACKGROUND OF THE INVENTION
A large number of vibration damping compositions comprising a viscous fluid and solid powder have already been proposed. For example, Japanese Patent Application Publication Number Sho 63-308241 (308,241/1988) describes a vibration damping composition comprising a viscous fluid (e.g., silicone oil) and a solid powder such as silica powder, glass powder, or silicone resin powder. Japanese Patent Application Publication Number Hei 10-251517 (251,517/1998) describes a vibration damping composition comprising a silicone resin powder and a viscous fluid such as silicone oil. Japanese Patent Application Publication Number Hei 10-281202 (281,202/1998) describes a viscous fluid blend comprising silsesquioxane powder and non-surface-treated wet-process silica micropowder in silicone oil. Japanese Patent Application Publication Number Hei 11-182624 (182,624/1999) describes a viscous fluid blend of silsesquioxane powder, wet-process silica micropowder, and silanol-terminated dimethylsiloxane in silicone oil.
However, these compositions typically undergo changes when stored and/or used over extended periods of time, resulting in a deterioration in their vibration damping properties.
DETAILED DESCRIPTION OF THE INVENTION
This invention relates to a vibration damping silicone composition comprising:
A. a silicone oil,
B. a silicone resin which is solid at room temperature, and
C. a surface-hydrophobic silica powder having a pH of greater than 6 and less than 9.
In a preferred composition there is provided
A. 100 parts by weight of silicone oil,
B. 10 to 300 parts by weight of a silicone resin powder which is solid at room temperature, and
C. 0.1 to 10 parts by weight of a surface-hydrophobic silica powder having a pH of greater than 6 and less than 9.
Component A, the Silicone oil, functions as the matrix component in which components B and C are dispersed. The silicone oil is an organopolysiloxane, comprising substantially of units of the formula R′
2
SiO
2/2
and is a liquid at room temperature. The R′ groups bonded to the silicon atoms may be the same or different and are typically monovalent hydrocarbon groups, for example alkyl groups such as methyl, ethyl, propyl and octyl groups; alkenyl groups such as vinyl, allyl, and butenyl groups and aryl groups such as phenyl and tolyl groups. Halogenated alkyl groups such as 3,3,3-trifluoropropyl may also be used. Small amounts of these hydrocarbon groups may be replaced by hydroxyl groups, or alkoxy groups such as methoxy, and ethoxy groups. Preferably most R′ groups are alkyl groups, most preferably methyl groups. Alkyl groups are preferred because the composition in accordance with the present invention containing such silicone oils has a low degree of change of viscosity with respect to temperature and excellent storage stability.
Component A may be a linear, partially branched linear, branched, or cyclic. A linear structure is preferred. Component A should have a kinematic viscosity at 25° C. of from 100 to 1,000,000 mm
2
/s, preferably from 500 to 500,000 mm
2
/s. When the kinematic viscosity at 25° C. is less than 100 mm
2
/s, it is difficult to maintain components B and C in a uniformly dispersed state in component A. When the viscosity of component A exceeds 1,000,000 mm
2
/s, handling properties deteriorate, and components B and C are difficult to disperse in component A. Component A may be exemplified by trimethylsiloxy-endblocked dimethylpolysiloxanes, dimethylvinylsiloxy-endblocked dimethylpolysiloxanes, trimethylsiloxy-endblocked methyloctylpolysiloxanes, silanol-endblocked dimethylpolysiloxanes, and trimethylsiloxy-endblocked dimethylsiloxane-methylphenylsiloxane copolymers.
Component B, the Silicone resin powder, is a solid at room temperature and is utilised to enhance the vibration damping performance of the composition in accordance with the invention. Component B may be an organopolysiloxane containing RSiO
3/2
units and/or SiO
4/2
units in the main skeleton structure. Component B may also contain R
2
SiO
2/2
units and/or R
3
SiO
1/2
units. An organopolysilsesquioxane powder containing substantially only RSiO
3/2
units is most preferred. Preferably R is a monovalent hydrocarbon group for example alkyl groups such as methyl, ethyl, and propyl; alkenyl groups such as vinyl, allyl, and butenyl; and aryl groups such as phenyl and tolyl. R may also be a halogenated alkyl group such as 3,3,3-trifluoropropyl. In addition, some of these groups may be substituted by hydroxyl groups or alkoxy groups such as methoxy and ethoxy groups. Alkyl groups are preferred as the resulting composition in accordance with the invention containing such resins has only a low degree of change of viscosity with respect to temperature and excellent storage stability. Each R may be the same or different, but it is preferred that at least 50 percent of the R groups are alkyl groups, most preferably methyl groups.
A small number of hydroxyl groups, halogen groups such as chlorine and/or alkoxy groups such as methoxy and ethoxy groups may be present at terminal ends in the molecular chain of the silicone resin powder. Component B may have an average particle size of from 0.1 to 100 &mgr;m, preferably from 10 to 40 &mgr;m. The shape of the particles may be spherical, oblate, or irregular. The amount of component B to be added per 100 parts by weight of component A may be in the range of from 10 to 300 parts by weight, preferably from 20 to 200 parts by weight. When the amount of component B is less than 10 parts by weight, the vibration damping properties of the composition according to the present invention tend to deteriorate, and when the amount of component B exceeds 300 parts by weight, the operating properties composition in accordance with the present invention deteriorate.
Component C, the surface-hydrophobic silica powder, functions in the composition according to the present invention as a means of improving both the storage stability and vibration damping performance of the composition. The pH of component C must be greater than 6 but less than 9 and is preferably in the range of from 6.5 to 8.5. Properties such as the thermal stability and storage stability undergo a decline at a pH of 6 or below and at a pH of 9 or above. For example component A may depolymerise in a more acidic environment than pH 6 or a more alkaline environment than pH 9. For the purposes of this invention, the pH values are all measured using a glass electrode pH meter, and each sample tested is an ethanol/water suspension of a surface-treated silica powder prepared by wetting 2 g of the surface-treated silica powder with 25 ml ethanol followed by dispersion of the ethanolic silica in 25 ml water whose pH has been adjusted to 7.0. Both wet-process and dry-process silicas may be used as the silica powder of component C. The silica used will generally have a BET specific surface area in the range of from 40 to 500 m
2
/g. Wet-process silica powder with a BET specific surface area in the range of from 50 to 400 m
2
/g is preferred. An organopolysiloxane with a low degree of polymerisation (DP) is generally used to surface treat the silica of component C to render it hydrophobic. The kinematic viscosity of the organopolysiloxane used to surface treat the silica is preferably from 0.5 to 100 mm
2
/s and the DP is preferably from 2 to about 90. Examples of the organopolysiloxane, which may be used to surface treat the silica of component C, include trimethylsiloxy- and dimethylsiloxy-endblocked dimethylpolysiloxanes, methylhydrogenpolysiloxanes, and dimethylsiloxane-methylhydrogensiloxane copolymers. The surface treatment of the silica powder with org
Hayashi Masayuki
Kobayashi Hideki
Dawson Robert
Dow Corning Toray Silicone Company Limited
McKellar Robert L.
McKellar Stevens
Zimmer Marc S.
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