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
2001-01-03
2002-08-20
Moore, Margaret G. (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...
C528S018000, C523S435000, C523S204000, C523S209000, C524S588000, C524S589000, C524S506000, C524S731000, C525S100000, C525S106000, C525S476000, C525S477000, C525S464000, C525S453000, C525S452000, C525S431000, C428S403000, C428S405000
Reexamination Certificate
active
06437042
ABSTRACT:
FIELD OF THE INVENTION
This invention is directed to a method for crosslinking a condensation crosslinkable silicone composition to produce crosslinked silicone particles. In particular, it relates to a method for efficiently producing crosslinked silicone particles with a lower mean particle diameter and better dispersion in organic resins.
BACKGROUND OF THE INVENTION
In Japanese Unexamined Patent Applications Kokai No. 63-202658/EP 350 519 (Jan. 17, 1990), Kokai No. 64-70558/EP 304 946 (Mar. 1, 1989), and Kokai No. 10-36674, methods are described for producing crosslinked silicone particles, in which a condensation crosslinkable silicone composition containing an organopolysiloxane with at least two silanol groups per molecule, a crosslinker, and a condensation catalyst, is crosslinked while emulsified in water using a surfactant.
However, when such a condensation crosslinkable silicone composition is emulsified in water with a surfactant, the crosslinker and condensation catalyst are mixed as a separately blended silicone composition is cooled. Unless the silicone composition mixed in this manner is emulsified in cold water, problems occur such that the composition continues to undergo crosslinking while emulsified, making it impossible to achieve a homogenous emulsion. Crosslinked silicone particles also have a large mean particle diameter.
These Kokai applications provide that the condensation crosslinkable silicone composition can be emulsified in water and then crosslinked by addition of the condensation catalyst, but after the condensation crosslinkable silicone composition without the condensation catalyst has been first emulsified in water using a surfactant.
BRIEF SUMMARY OF THE INVENTION
It is therefore an object of the present invention is to provide a method for crosslinking a condensation crosslinkable silicone composition to efficiently produce crosslinked silicone particles with a lower mean particle diameter, and with a better dispersion in organic resins.
Thus, the invention relates to a method for producing crosslinked silicone particles with a mean particle diameter of 0.1-500 &mgr;m, in which a condensation crosslinkable silicone composition containing (A) an organopolysiloxane having at least two silanol groups per molecule, and (B) a crosslinker, but without a (C) condensation catalyst, is first emulsified in water using a surfactant. An emulsion containing a tin (II) salt of an organic acid with no more than 10 carbon atoms is emulsified in water using a surfactant, and is added as component (C) to the emulsion of the condensation crosslinkable silicone composition. This crosslinks the emulsified condensation crosslinkable silicone composition.
These and other features of the invention will become apparent from a consideration of the detailed description.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
Not applicable.
DETAILED DESCRIPTION OF THE INVENTION
In the method of the present invention, a condensation crosslinkable silicone composition containing (A) an organopolysiloxane having at least two silanol groups per molecule and (B) a crosslinker, but no (C) condensation catalyst, is first emulsified in water with a surfactant.
Organopolysiloxane (A) is the primary component of the condensation crosslinkable silicone composition, and should have at least two silanol groups in its molecule. The silanol groups in organopolysiloxane (A) are preferably at the terminals of the molecular chain. Examples of silicon atom bonded organic groups which can also be present in organopolysiloxane (A) include alkyl groups such as methyl, ethyl, propyl, and butyl; alkenyl groups such as vinyl and allyl; aryl groups such as phenyl; aralkyl groups such as benzyl and phenethyl; cycloalkyl groups such as cyclopentyl and cyclohexyl ; and substituted monovalent hydrocarbon groups such as 3-chloropropyl, 3,3,3-trifluoropropyl, and other such halogenated alkyl groups.
The molecular structure of organopolysiloxane (A) may be linear, linear with some branching, branched, or reticulated. While the viscosity of organopolysiloxane (A) at 25 ° C. is not particularly limited, it is preferably 5-1,000,000 mPa·s, more preferably 5-10,000 mPa·s, and even more preferably 5-1,000 mPa·s. This is because the physical properties of the crosslinked silicone particles tend to suffer when the viscosity of organopolysiloxane (A) at 25° C. is lower than the minimum of the range, whereas a viscosity over the maximum of the range makes it more difficult to emulsify the composition in water.
A crosslinker (B) is used to crosslink the condensation crosslinkable silicone composition by condensation with the silanol groups in organopolysiloxane (A). Examples of suitable crosslinkers (B) include (i) silanes having at least three silicon atom bonded hydrolysable groups or partially hydrolyzed condensates thereof, and (ii) organosiloxanes having at least three silicon atom bonded hydrogen atoms per molecule.
The silicon atom bonded hydrolysable groups which may be present in silanes of crosslinker (B)(i) include alkoxy groups such as methoxy, ethoxy, and methoxyethoxy; oxime groups such as methyl ethyl ketoxime; acetoxy groups; and aminoxy groups. Examples of silanes or siloxanes of crosslinker (B)(i) include alkoxysilanes such as methyltrimethoxysilane, ethyl trimethoxysilane, methyltris(methoxy ethoxy)silane, tetramethoxysilane, tetraethoxysilane, and partially hydrolyzed condensates thereof; oxime silanes such as methyltris(methyl ethyl ketoxime)silane, ethyltris(methyl ethyl ketoxime)silane, tetra(methyl ethyl ketoxime)silane, and partially hydrolyzed condensates thereof; acetoxysilanes such as methyltriacetoxysilane ethyltriacetoxysilane, tetracetoxysilane, and partially hydrolyzed condensates thereof; and aminoxysilanes such as methyltris(trimethyl aminoxy)silane, ethyltris(trimethyl aminoxy)silane, tetra(trimethyl aminoxy)silane, and partially hydrolyzed condensates thereof. Alkoxysilanes and partially hydrolyzed condensates thereof are preferred, while alkyl polysilicates which are partially hydrolyzed condensates of tetralkoxysilanes are particularly preferred.
Examples of silicon atom bonded organic groups which may be present in crosslinker (B)(ii) include alkyl groups such as methyl, ethyl, propyl, and butyl; alkenyl groups such as vinyl and allyl; aryl groups such as phenyl; aralkyl groups such as benzyl and phenethyl; cycloalkyl groups such as cyclopentyl and cyclohexyl; and substituted monovalent hydrocarbon groups such as 3-chloropropyl, 3,3,3-trifluoropropyl, and other such halogenated alkyl groups.
The molecular structure of crosslinker (B)(ii) may be linear, linear with some branching, branched, reticulated, and cyclic. Some examples of organopolysiloxanes of crosslinker (B)(ii) include methylhydridopolysiloxanes with trimethylsiloxy groups at both ends of the molecular chain, dimethylsiloxane methylhydridosiloxane copolymers with trimethylsiloxane groups at both ends of the molecular chain, dimethylsiloxane methylhydridosiloxane copolymers with dimethylhydridosiloxy groups at both ends of the molecular chain, cyclic methylhydridopolysiloxanes, and organopolysiloxanes with part or all methyl groups in the siloxane substituted by alkyl groups such as ethyl or aryl groups such as phenyl.
The condensation crosslinkable silicone composition contains crosslinker (B) in an amount sufficient to crosslink the condensation crosslinkable silicone composition. Specifically, the amount crosslinker (B) should be 0.1-50 weight parts per 100 weight parts of organopolysiloxane (A). The reason is that an amount of crosslinker (B) less than the minimum range can result in insufficient crosslinking, whereas an amount more than the maximum range can result in crosslinked silicone particles with diminished physical properties.
The condensation crosslinkable silicone composition may contain other optional components such as (D) organoalkoxysilanes containing groups such as C
5
or greater alkyl groups, (meth)acrylic groups, epoxy groups, mercapto groups, amino groups, alkenyl groups, or partially hy
Kobayashi Kazuo
Morita Yoshitsugu
Tanaka Ken
Brown Catherine U.
De Cesare Jim L.
Dow Corning Toray Silicone Co. Ltd.
Moore Margaret G.
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