Colloid systems and wetting agents; subcombinations thereof; pro – Continuous liquid or supercritical phase: colloid systems;... – Aqueous continuous liquid phase and discontinuous phase...
Reexamination Certificate
2003-01-16
2004-05-18
Moore, Margaret G. (Department: 1712)
Colloid systems and wetting agents; subcombinations thereof; pro
Continuous liquid or supercritical phase: colloid systems;...
Aqueous continuous liquid phase and discontinuous phase...
C524S588000
Reexamination Certificate
active
06737444
ABSTRACT:
FIELD OF THE INVENTION
Silicone MQ resins or silicone MQ resin/silicone polymer blends containing high levels of an MQ resin are known in the art to be difficult to emulsify by direct emulsification using high shear or by inversion. This invention is directed to a method of emulsifying silicone MQ resin/polydiorganosiloxane blends by employing, what is referred to herein, as an inversion assisting polymer. In particular, the inversion assisting polymer comprises a silicone polymer or a silicone copolymer containing polar functional groups. Some examples of suitable polar functional groups are amino groups, epoxidized amino groups, quaternary ammonium groups, glycidyl groups, mercapto groups, carboxyl groups, polyoxyethylene oxypropylene groups, or combinations thereof. The inversion assisting polymer can be incorporated at levels as low as 4 percent by weight based on the total amount of silicone content. When incorporated, silicone MQ resin/polydiorganosiloxane blends at a resin:polymer ratio of 25:75 to 70:30 can be readily inverted by a mechanism known in the art as catastrophic inversion. This enables oil-in-water (O/W) silicone resin emulsions to be obtained using most conventional nonionic surfactants in a conventional mixer. The method provides aqueous silicone resin emulsions that have been heretofore not been obtainable otherwise.
BACKGROUND OF THE INVENTION
Water-based delivery of silicone resin materials is desired in many applications. However, the emulsification of silicone resins of the structural type MQ, and blends of MQ silicone resins and silicone polymers, with high levels of MQ resins, i.e., containing 20-90 percent by weight based on the total silicone content, and forming oil-in-water emulsions by conventional means is known to be difficult. For example, while conventional techniques such as direct emulsification using high shear are suitable for low viscosity blends, and emulsification by catastrophic inversion is suitable for high viscosity blends, neither is suitable when MQ resins are present. In particular, the presence of a high level of silicone MQ resins in a silicone resin/silicone polymer blend significantly increases the oil phase viscosity, such that a direct emulsification using high shear fails to yield the particle size most desired for emulsion stability. In addition, the presence of a significant amount of silicone MQ resin also makes the oil phase resistant to inversion, to the extent that often the oil phase remains non-inverted at any water-to-oil ratio.
While mixing a volatile silicone fluid, a volatile organic fluid, or a low molecular weight diluent, with a high silicone resin content oil phase can ease the process of emulsification, such volatile compositions or low molecular weight fluids may not be desired in a given formulation, such that successful emulsification of a silicone MQ resin containing material is limited. In contrast, the present invention provides an effective way of emulsifying materials containing high levels of silicone MQ resins. This is enabled according to the present method by using a small amount of a secondary silicone polymer, referred to herein as the inversion assisting polymer. Its function is to ease the inversion process during emulsification. It has been found that the presence of the inversion assisting polymer does not adversely affect performance of the final formulation. In fact, the inversion assisting polymer can contribute to the final formulation some desirable attributes of its own.
SUMMARY OF THE INVENTION
This invention relates to a method of making aqueous silicone resin emulsions containing silicone particles having a particle size in range of 100 nanometer to 5,000 nanometer (0.1 to 5.0 micron). According to the method, the silicone resin emulsions can be obtained by (i) mixing a silicone resin or a blend of a silicone resin and a non-resinous silicone polymer with an inversion assisting polymer, and forming a homogeneous oil phase.
In the second step of the method, (ii) one or more surfactants are mixed with the homogenous oil phase in (i) to form a mixture. By (iii) adding sufficient water to the mixture formed in (ii), inversion of the continuous phase and the dispersed phase is caused to occur resulting in an oil-in-water emulsion. In step (iv), the oil-in-water emulsion formed in (iii) is diluted by the addition of more water; and (v) an oil-in-water emulsion containing silicone particles with sizes in range of 100 nanometer to 5,000 nanometer (0.1 to 5.0 micron) is recovered.
The inversion assisting polymer can be silicon functional or organofunctional. The polysiloxane contains in its molecule at least one functional group. Some representative functional groups include hydroxyl groups, alkoxy groups, amino groups, epoxidized amino groups, glycidyl groups, polyoxyethylene oxypropylene groups, carboxyl groups, mercapto groups, quaternary ammonium groups, or combinations of such groups.
The contribution of the present invention to the state of the art is that it enables those skilled in the art to use inversion processing techniques for making aqueous emulsions containing silicone resins. These and other features of the invention will become apparent from a consideration of the detailed description.
DETAILED DESCRIPTION OF THE INVENTION
A phase inversion generally occurs when the continuous phase of a dispersion becomes the dispersed phase, or vice versa. Phase inversions in liquid/liquid dispersions are categorized as either catastrophic inversions or transitional inversions. Catastrophic inversions can be caused by simply changing the phase ratio until there is such a high ratio of the dispersed phase that it becomes the continuous phase. In contrast, transitional inversions occur when the affinity of the surfactant for the two phases is altered in order to bring about the inversion. For purposes of the present invention, inversion as used herein is intended to mean a catastrophic inversion.
The acronym MQ as used herein is derived from four symbols M, D, T, and Q, which represent the functionality of structural units present in organosilicon compounds containing siloxane units joined by ≡Si—O—Si≡ bonds. The monofunctional (M) unit represents (CH
3
)
3
SiO
1/2
; the difunctional (D) unit represents (CH
3
)
2
SiO
2/2
; the trifunctional (T) unit represents CH
3
SiO
3/2
and results in the formation of branched linear siloxanes; and the tetrafunctional (Q) unit represents SiO
4/2
which results in the formation of crosslinked and resinous compositions. Hence, MQ is used when the siloxane contains all monofunctional M units and tetrafunctional Q units, or a high percentage of M and Q units such as to render it resinous.
The oil phase of the emulsion according to the present invention therefore consists of a blend of a silicone MQ resin and a non-resinous silicone polymer, as well as a small amount of a secondary silicone polymer hereafter referred to as the “inversion assisting polymer”.
The silicone resin is a non-linear siloxane resin with a glass transition temperature (Tg ) above 0° C. The glass transition temperature is the temperature at which an amorphous material such as a higher polymer changes from a brittle vitreous state to a plastic state. The silicone resin used herein otherwise has the general formula R′
a
SiO
(4-a)/2
wherein R′ is a monovalent hydrocarbon group with 1-6 carbon atoms or R′ can be a functionally substituted hydrocarbon group with 1-6 carbon atoms, and a has an average value of 1-1.8. The resin preferably consists of monovalent trihydrocarbonsiloxy (M) groups R″
3
SiO
1/2
and tetrafunctional (Q) groups SiO
4/2
, in which R″ is a monovalent hydrocarbon group having 1-6 carbon atoms. R″ is most preferably a methyl group. The number ratio of M groups to Q groups is in the range of 0.5:1 to 1.2:1, so as to provide an equivalent wherein a in the formula R′
a
SiO
(4-a)/2
has an average value of 1.0-1.63. Preferably, the number ratio is 0.6:1 to 0.9:1. If desired, the silicone resin may also contain 1-5
DeCesare Jim L.
Dow Corning Corporation
Moore Margaret G.
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