Coating processes – With post-treatment of coating or coating material – Heating or drying
Reexamination Certificate
2002-11-18
2004-07-20
Cameron, Erma (Department: 1762)
Coating processes
With post-treatment of coating or coating material
Heating or drying
C427S421100
Reexamination Certificate
active
06764717
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the use of antimisting additives for reducing the formation of aerosol in crosslinkable silicone coating compositions.
2. Background Art
A trend within the silicone coating industry is to increase machine speed in order to raise productivity. Where silicone coatings are applied to a substrate at relatively high speeds, for example at speeds of of more than 300 m/min, fine spray mists of the silicone coating system may be formed. This aerosol is formed at the silicone applicator unit. The formation of this spray mist has proven to be a serious problem in the context of further increasing the coating speed. The formation of this spray mist can be reduced by adding what are known in the industry as antimisting additives to the silicone coating system.
EP-A 716 115 (Dow Corning Corp.) describes antimisting additives obtained by reacting an organosilicon compound, a compound containing oxyalkylene groups, and a catalyst. The addition of these oxyalkylene-functional reaction products to crosslinkable silicone coating systems reduces the formation of aerosol in rapid coating processes.
U.S. Pat. No. 6,265,497 (Wacker-Chemie GmbH) describes alkenyl functional siloxane copolymers which are branched and whose organopolysiloxane blocks are linked by hydrocarbon bridges.
It would be desirable to provide antimisting additives for silicone coating compositions which reduce the formation of aerosol in rapid coating processes, which are readily miscible with the silicone coating compositions, and which do not impair the silicone coating compositions.
SUMMARY OF THE INVENTION
The present invention provides efficient antimisting additives for use in silicone coating processes prepared by hydrosilylation of an at least tris(alkenyl)-substituted hydrocarbon radical with an organopolysiloxane bearing terminal SiH groups, wherein the SiH groups of the organopolysiloxane are in stoichiometric excess with respect to alkenyl groups, followed by reaction of the SiH-functional product with a stoichiometric excess of an &agr;,&ohgr;-dialkenylsiloxane polymer. The alkenyl-functional product and/or the SiH-functional intermediate product may optionally be equilibrated with further functional or non-functional organopolysiloxanes.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
The invention provides for the use of antimisting additives in crosslinkable silicone coating compositions for reducing the formation of aerosol, comprising employing as antimisting additives, alkenyl-functional siloxane copolymers prepared, in a first step, by reacting a compound (1) containing at least three aliphatic double bonds, of the general formula
R
2
(CR
3
═CH
2
)
x
(I)
where R
2
is a trivalent or tetravalent hydrocarbon radical having preferably from 1 to 25 carbon atoms per radical, and which can contain one or more non-adjacent heteroatoms selected from oxygen, silicon, and titanium, R
3
is a hydrogen atom or an alkyl radical having from 1 to 6 carbon atoms per radical, and x is 3 or 4, with an organosiloxane (2) having terminal Si-bonded hydrogen atoms, in the presence of a catalyst (3) which promotes the addition of Si-bonded hydrogen onto aliphatic double bonds, the ratio of Si-bonded hydrogen in the organosiloxane (2) to aliphatic double bond in the compound (1) being from 1.3 to 10, preferably from 1.5 to 5; and in a second step, reacting the resulting hydrocarbon-siloxane copolymers, containing Si-bonded hydrogen atoms, with &agr;,&ohgr;-dialkenylsiloxane polymer (4) in the presence of a catalyst (3) which promotes the addition of Si-bonded hydrogen onto aliphatic double bonds, the ratio of aliphatic double bond in the &agr;,&ohgr;-dialkenylsiloxane polymer (4) to Si-bonded hydrogen in the siloxane copolymers being from 1.2 to 10, preferably from 1.5 to 5; and optionally in a third step, equilibrating the resulting alkenyl-functional siloxane copolymers with organopolysiloxane (5), selected from among linear organopolysiloxanes containing terminal triorganosiloxy groups, linear organopolysiloxanes containing terminal hydroxyl groups, branched organopolysiloxanes optionally containing hydroxyl groups, cyclic organopolysiloxanes, and copolymers comprising diorganosiloxane and monoorganosiloxane units.
The alkenyl-functional siloxane copolymers may be prepared employing techniques now known to the art, for example as described in U.S. Pat. No. 6,265,497, incorporated herein by reference.
The alkenyl-functional siloxane copolymers antimisting additives of the invention have the advantage that they not only reduce the formation of aerosol formed by crosslinkable silicone coating compositions in rapid coating systems, but also, in particular, can be homogeneously mixed in any desired proportions, with the crosslinkable silicone coating compositions, unlike the antimisting additives containing polyglycol groups from the above-cited EP-A 716 115. Moreover, the antimisting additives of the invention have no inhibiting effect on the cure of the coatings.
In the alkenyl-functional siloxane copolymers of the invention the siloxane blocks are preferably connected to one another by way of hydrocarbon bridges, resulting in a hydrocarbon-siloxane block structure. The alkenyl-functional siloxane copolymers preferably have a viscosity of from 0.05 to 500,000 Pa.s at 25° C., more preferably from 0.1 to 100,000 Pa.s at 25° C., and most preferably, from 0.2 to 10 000 Pa.s at 25° C.
One preferred embodiment in the case of very viscous siloxane copolymers is the preparation of the alkenyl-functional siloxane copolymers of the invention in solvents, preferably hydrocarbons having a boiling point preferably below 150° C., such as toluene, xylene, n-hexane, n-octane, isooctane, and petroleum fractions, preferably in a concentration of from 20-60% by weight siloxane content, although higher or lower concentrations may be used as well.
In the first process step it is possible to use a single compound (1) or multiple compounds (1). As compound (1) in the first process step it is preferred to use compounds in which R
2
is a trivalent hydrocarbon radical, preferably having from 1 to 25 carbon atoms per radical, where x is 3.
The organosiloxane (2) used in the first process step preferably contains two Si-bonded hydrogen atoms per molecule. In the first process step it is possible to use a single organosiloxane (2) or different organosiloxanes (2). It is preferred to use, a organosiloxane (2) an organosiloxane of the general formula
HR
2
SiO(SiR
2
O)
n
SiR
2
H (II)
where preferably each R is an identical or different, unhalogenated or halogenated (“optionally halogenated”) hydrocarbon radical having from 1 to 6 carbon atoms per radical, and n is 0 or an integer, preferably an integer from 7 to 2000, with each integer between 0 and 2000 considered to have been explicitly disclosed herein.
In the second process step it is possible to use one kind of &agr;,&ohgr;-dialkenylsiloxane polymer (4) or different kinds of &agr;,&ohgr;dialkenylsiloxane polymer (4). As the &agr;,&ohgr;-dialkenylsiloxane polymer (4) in the second process step it is preferred to use a polymer of the general formula
R
4
a
R
3−a
SiO(R
2
Si—R
1
—SiR
2
O)
m
(R
2
SiO)
k
SiR
4
a
R
3−a
(III)
where R is as defined above, R
1
is a divalent hydrocarbon radical, preferably an alkylene radical, and more preferably an alkylene radical having from 2 to 10 carbon atoms per radical, or is a divalent silane or siloxane radical, having from 2 to 10 Si units,
R
4
is a terminally olefinically unsaturated radical having from 2 to 10 carbon atoms,
a can be identical or different and is 0 or 1, preferably, on average from 0.7 to 1.0,
m is 0 or an integer from 1 to 10, preferably 0, and k is 0 or an integer from 1 to 1000, preferably from 20 to 1000, and more preferably from 50 to 500.
Examples of radicals R are alkyl radicals, such as the methyl, ethyl, n-propyl, isopropyl, 1-n-butyl, 2-n-butyl, isobutyl, tert-butyl, n-amyl, and n-hexyl radicals. The methyl radica
Bloechl Martina
Herzig Christian
Lautenschlager Hans
Brooks & Kushman P.C.
Cameron Erma
Wacker-Chemie GmbH
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