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Description  |
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BACKGROUND OF THE INVENTION
The present invention relates to coating compositions based upon hydroxyl
containing acrylic polymers and organopolysiloxanes.
U.S. Pat. No. 4,283,387 to Young et al is directed to a reversibly
crosslinkable coating composition designed for the controlled release of
bioactive agents, more particularly to the controlled release of
pesticides. The coating composition comprises a mixture of a carbinol
containing polymer, crosslinking agents for said polymer consisting
essentially of a hydrolyzable silane or an organopolysiloxane containing
hydrolyzable silane groups, and a hydrolyzable organic titanium compound
and a pesticide. Since these coating compositions are reversibly
crosslinked, the crosslinking is capable of breaking down to release the
bioactive agent. Moreover, the amount of organopolysiloxane and carbinol
containing polymer is such that the organopolysiloxane is present in
relatively small amounts as compared to the carbinol containing polymer.
U.S. Pat. No. 4,103,065 to Gagnon is directed to improved coating
compositions for polycarbonate or acrylic articles. The improvement in the
composition of the Gagnon invention resides in the addition of constituent
(c) to constituents (a) and (b) which are organopolysiloxane partial
condensate product resin and an alkylated melamine formaldehyde partial
condensate resin, respectively. The additional constituent (c) is a
composition containing specified percentages of linear diol, thermosetting
acrylic and crosslinking agent. The Gagnon composition specifically
requires that the thermosetting acrylic contain from about 4 to about 10
percent by weight of the acrylic of a hydroxyalkyl ester of an
alpha,beta-unsaturated carboxylic acid.
The art recognized compositions such as those of Gagnon which have been
detailed above have been deficient in that they have been unable to
provide the proper balance of flexibility and durability. Coating
compositions based predominantly upon the type of polysiloxanes which are
detailed in Gagnon tend to be much too brittle. Attempts to flexibilize
these compositions has tended to make them less brittle, although not as
durable as might be desired.
In contrast to the above, the coating compositions provided by the present
invention show unexpected advantages both in flexibility and durability.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a coating
composition comprising a blend of: (a) from about 5 percent by weight to
about 35 percent by weight of a hydroxyl functional vinyl polymer having
at least 2 percent by weight of hydroxyl groups based on the total weight
of the vinyl polymer; and (b) from about 65 percent by weight to about 95
percent by weight of an organopolysiloxane containing hydrolyzable groups
prepared by the partial hydrolysis of a compound or mixture of compounds
represented by the structural formula R.sub.a SiX.sub.(4-a) wherein:
R is hydrogen, alkyl, aryl, alkylaryl, arylalkyl, aryloxyalkyl or
haloalkyl;
X is halogen, OR.sup.1,
##STR2##
or the monohydroxy or cyclic C.sub.2 to C.sub.3 residue of a 1,2- or
1,3-glycol, wherein:
R.sup.1 is C.sub.1 -C.sub.3 alkyl,
R.sup.2 is hydrogen or C.sub.1 -C.sub.4 alkyl,
R.sup.3 and R.sup.4 independently are hydrogen, C.sub.1 -C.sub.4 alkyl or
C.sub.6 -C.sub.8 aryl,
R.sup.5 is C.sub.4 -C.sub.7 alkylene, and
a is an integer ranging from 1 to 2,
the percentage of (a) and (b) being based on the total weight of (a) and
(b).
Also provided in accordance with the present invention is a method of
providing a substrate with a protective coating, comprising:
I. applying to the surface of a substrate a coating composition comprising
a blend of
(a) from about 5 percent by weight to about 35 percent by weight of a
hydroxyl functional vinyl polymer having at least 2 percent by weight of
hydroxyl groups based on the total weight of the vinyl polymer; and
(b) from about 65 percent by weight to about 95 percent by weight of an
organopolysiloxane containing hydrolyzable groups prepared by the partial
hydrolysis of a compound or mixture of compounds represented by the
structural formula R.sub.a SiX.sub.(4-a) wherein:
R is hydrogen, alkyl, aryl, alkylaryl, arylalkyl, aryloxyalkyl or
haloalkyl;
X is halogen, OR.sup.1,
##STR3##
or the monohydroxy or cyclic C.sub.2 to C.sub.3 residue of a 1,2- or
1,3-glycol, wherein:
R.sup.1 is C.sub.1 -C.sub.3 alkyl,
R.sup.2 is hydrogen or C.sub.1 -C.sub.4 alkyl,
R.sup.3 and R.sup.4 independently are hydrogen, C.sub.1 -C.sub.4 alkyl or
C.sub.6 -C.sub.8 aryl,
R.sup.5 is C.sub.4 -C.sub.7 alkylene, and
a is an integer ranging from 1 to 2,
the percentage of (a) and (b) being based on the total weight of (a) and
(b);
II. at least partially curing the coating composition of step (I).
There is also provided a coated article prepared in accordance with the
aforesaid method.
DETAILED DESCRIPTION OF THE INVENTION
The coating compositions of the present invention comprise a blend of two
principle constituents. The first component is a hydroxyl functional vinyl
polymer having at least 2 percent by weight of hydroxyl groups based on
the total weight of the vinyl polymer. Preferably the vinyl polymer
contains from about 2.5 percent by weight to about 15 percent by weight of
hydroxyl groups based on the total weight of the vinyl polymer. The vinyl
polymer is present in the coating composition in an amount ranging from
about 5 percent by weight to about 35 percent by weight, preferably from
about 5 percent by weight to about 20 percent by weight. The percentage of
the hydroxyl functional vinyl polymer in the coating composition is based
on the total weight of the hydroxyl functional vinyl polymer and the
organopolysiloxane component which is described below.
A very important aspect of the claimed invention is the hydroxyl content of
the vinyl polymer component of the coating composition. As has been stated
above, the vinyl polymer contains at least 2 percent by weight of hydroxyl
groups based on the total weight of the vinyl polymer. This is very
important in providing the requisite flexibility of the claimed coating
compositions. The percent by weight of hydroxyl groups contained in the
vinyl polymer can be determined by dividing the gram molecular weight of a
hydroxyl group (17 grams) by the hydroxyl equivalent weight of the vinyl
polymer.
In an embodiment wherein the hydroxyl functional vinyl polymer is a
hydroxyl functional acrylic polymer the percent by weight of hydroxyl
groups based on the total weight of the acrylic polymer can be correlated
to the amount, in percent, of hydroxyl functional vinyl monomer which is
used in the preparation of the hydroxyl functional acrylic polymer. If one
speaks in terms of the amount of hydroxyl functional vinyl monomer
utilized in the preparation of a hydroxyl functional acrylic polymer, the
vinyl monomer component should comprise at least 20 percent by weight,
based on the total weight of the vinyl monomer component, of a
hydroxyalkyl acrylate or methacrylate. Preferably the vinyl monomer
component comprises from about 30 percent to about 40 percent by weight,
based on the total weight of the vinyl monomer component, of a
hydroxyalkyl acrylate or methacrylate. Coatings prepared from acrylic
polymers having less than the required amount of hydroxyl functional vinyl
monomer are too brittle for the applications contemplated by the present
invention.
The hydroxyl functional vinyl polymer which is a principle component of the
claimed coating compositions, can be of several types which can be
prepared in a number of different ways. A preferred vinyl polymer for use
in the present invention is a hydroxyl functional acrylic polymer or
acrylic polyol.
Acrylic polyols include but are not limited to the known hydroxyl
functional addition polymers and copolymers of acrylic and methacrylic
acids and their ester derivatives including but not limited to their
hydroxyl functional ester derivatives, acrylamide and methacrylamide, and
unsaturated nitriles such as acrylonitrile and methacrylonitrile.
Additional examples of acrylic monomers which can be addition polymerized
to form acrylic polyols include hydroxyethyl(meth)acrylate,
hydroxypropyl(meth)acrylate, methyl(meth)acrylate, ethyl(meth)acrylate,
propyl(meth)acrylate, isopropyl(meth)acrylate butyl(meth)acrylate,
t-butyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, n-hexyl(meth)acrylate,
cyclohexyl(meth)acrylate, 3,3,5-trimethylcyclohexyl(meth)acrylate,
decyl(meth)acrylate, isodecyl(meth)acrylate, lauryl(meth)acrylate,
stearyl(meth)acrylate, phenyl(meth)acrylate, and isobornyl(meth)acrylate.
Additional examples of compounds which may be employed in the preparation
of hydroxyl functional acrylic polymers include: compounds produced by the
reaction of lactones such as caprolactone with hydroxyl functional acrylic
esters such as hydroxyethyl acrylate and hydroxyl propyl acrylate; and
epoxy-esters produced by the reaction of fatty acids, especially
monocarboxylic fatty acids, with ethylenically unsaturated epoxides such
as glycidyl acrylate.
Where desired, various other unsaturated monomers can be employed in the
preparation of hydroxyl functional acrylic polymers examples of which
include: vinyl aromatic hydrocarbons such as styrene, alpha-methyl
styrene, and vinyl toluene; vinyl acetate; vinyl chloride; and unsaturated
epoxy functional monomers such as glycidyl(meth)acrylate. For convenience,
the term "(meth)acrylate" has been used herein to denote either or both of
the respective acrylate compound and the respective methacrylate compound.
Suitable acrylic polyols have number average molecular weights ranging
from 500 to 100,000, preferably 1,000 to 20,000, more preferably 1,000 to
10,000 determined by gel permeation chromatography using a polystyrene
standard. Moreover, suitable acrylic polyols of the invention have a
hydroxyl equivalent weight of from 116 to 867.
In addition to the copolymerization of hydroxyl containing monomers
including allyl alcohol, alloxy ethanol, and the like, a route to hydroxyl
containing polymers includes the use of hydroxyl containing catalysts or
catalysts convertible to hydroxyl groups.
The hydrolysis of poly(allyl acetate), poly(vinyl acetate), and copolymers
of allyl acetate or vinyl acetate or other allyl or vinyl esters yields
polymers with hydroxyl groups. Partial hydrolysis of these homopolymers or
copolymers yields copolymers containing hydroxyl groups and residual
unhydrolyzed functionality. The hydrolyzed polymers may be reacted with
aldehydes such as formaldehyde, butyraldehyde, and benzaldehyde to yield
formals and acetals containing residual hydroxyl groups. Oxyalkylation of
the hydrolyzed polymers yields crosslinkable hydroxyalkyl derivatives.
The above examples of hydroxyl functional vinyl polymers should be
considered illustrative and not limiting of materials suitable for use in
the present invention. As has been set forth above, the polymer should
have at least 2 percent by weight of hydroxyl groups based on the total
weight of the polymer.
The second principle constituent of the claimed coating compositions
comprises an organopolysiloxane containing hydrolyzable groups. The
organopolysiloxane is present in the claimed coating compositions in an
amount ranging from about 65 percent by weight to about 95 percent by
weight, the percentages based on the total weight of organopolysiloxane
and hydroxyl functional vinyl polymer.
The organopolysiloxane is prepared by the hydrolysis or partial hydrolysis
of an organosilane compound or mixture of compounds represented by the
structural formula R.sub.a SiX.sub.(4-a) wherein:
R is hydrogen, alkyl, aryl, alkylaryl, arylalkyl, aryloxyalkyl or
haloalkyl;
X is halogen, OR.sup.1,
##STR4##
or the monohydroxy and/or cyclic C.sub.2 to C.sub.3 residue of a 1,2- or
1,3-glycol, wherein:
R.sup.1 is C.sub.1 -C.sub.3 alkyl,
R.sup.2 is hydrogen or C.sub.1 -C.sub.4 alkyl,
R.sup.3 and R.sup.4 independently are hydrogen, C.sub.1 -C.sub.4 alkyl or
C.sub.6 -C.sub.8 aryl,
R.sup.5 is C.sub.4 -C.sub.7 alkylene, and
a is an integer ranging from 1 to 2.
Preferably the organopolysiloxane is prepared by the partial hydrolysis of
a compound of the formula CH.sub.3 Si(OR.sup.1).sub.3 wherein R.sup.1 is
C.sub.1 to C.sub.3 alkyl. This type of material is commercially available
from Owen-Illinois as OI 650.
Exemplary of organosilane compounds which can be subjected to partial
hydrolysis to prepare the organopolysiloxane include but are not limited
to methyl trimethoxy silane, phenyl trimethoxy silane, dimethyl dimethoxy
silane, methyl triethoxy silane, dimethyl diethoxy silane, dimethoxy
diphenyl silane, dimethoxy methyl phenyl silane, diethoxy dipropyl silane,
dimethoxy dipropyl silane, chloropropyltrimethoxysilane, and
chloropropyltriethoxysilane.
The preparation of a partial hydrolysis product involves the use of a
specific amount of water. Typically the hydrolysis product will be
prepared utilizing a ratio of moles of organosilane to moles of water
ranging from 1:0.4 to 1:3.0, preferably 1:1 to 1:3.0.
The organopolysiloxane comprises one or more siloxane linkages represented
by the formula:
##STR5##
It should be understood that depending upon the ratio of organosilane to
water and the reaction conditions the organopolysiloxane comprises a
mixture of products that may include some low molecular weight compounds
which contain residual easily hydrolyzable groups. The partial hydrolysis
product is preferably free of such low molecular weight species; however,
always will contain some residual easily hydrolyzable groups to permit
crosslinking of the product through reaction with ambient moisture and/or
reaction with hydroxyl groups of the aforedescribed hydroxyl functional
vinyl polymers.
The hydrolysis of the compounds set forth above is conducted in the
presence of a catalyst. Generally from about 0.0003 to about 20 percent by
weight of the catalyst is utilized. Examples of suitable catalysts include
gamma-aminopropyltriethoxy silane; isophorone diamine;
2-amino-2-methyl-1-propanol; protonic acids such as hydrochloric acid,
formic acid, acetic acid, sulfuric acid; or various tin catalysts such as
dibutylin dilaurate or the like. Preferably the acidic catalysts mentioned
above are utilized. The percent by weight of catalyst is based upon the
total weight of the material to be hydrolyzed.
It should be noted that the organopolysiloxane and hydroxyl functional
vinyl polymer should be selected so that they are compatible. By
"compatible" is meant that the two components mix freely to form a
homogeneous mixture which does not separate upon standing. Moreover when
the mixture of components is applied as a film and cured the cured film
does not exhibit evidence of phase separation of the components such as
excessive cratering or dewetting.
The coating compositions of the present invention are prepared by blending
component (a) and component (b) together with mild agitation. By "blend"
is meant that the components are simply mixed together prior to
application and the coating composition is essentially free of any
pre-reaction of the components. The coating compositions of the present
invention can be prepared as a one-package or two-package composition. For
the preparation of a two-package composition each of the components (a)
and (b) is prepared separately and then introduced together immediately
prior to use. The hydroxyl functional vinyl polymer is present in one
package and the organopolysiloxane is present in a second package. It
should be understood that other components can be present in the
composition and can be added to either package as desired as is
appreciated by those skilled in the art. When the claimed coating
compositions are prepared as one-package compositions they are relatively
package stable at ambient temperature for several months.
It should be noted that, if desired, other optional resinous ingredients
can be added to the coating compositions of the present invention so long
as they are compatible with the hydroxyl functional vinyl polymer and the
organopolysiloxane and do not detract from the physical properties of the
cured coating composition. For example, in one embodiment, the coating
compositions can additionally contain an aminoplast crosslinking agent.
These materials are described more fully below.
Aminoplast resins are based on the addition products of formaldehyde, with
an amino- or amido-group carrying substance. Condensation products
obtained from the reaction of alcohols and formaldehyde with melamine,
urea or benzoguanamine are most common and preferred herein. These
condensation products can be monomeric or polymeric. Condensation products
of other amines and amides can also be employed, for example, aldehyde
condensates of triazines, diazines, triazoles, guanadines, guanamines and
alkyl- and aryl-substituted ureas and alkyl- and aryl-substituted
melamines. Some examples of such compounds are N,N'-dimethyl urea,
benzourea, dicyandiamide, formaguanamine, acetoguanamine, glycoluril,
ammelin 2-chloro-4,6-diamino-1,3,5-triazine,
6-methyl-2,4-diamino-1,3,5-triazine, 3,5-diaminotrizole,
triaminopyrimidine, 2-mercapto-4,6-diaminopyrimidine,
3,4,6-tris(ethylamino)-1,3,5-triazine, and the like.
While the aldehyde employed is most often formaldehyde, other similar
condensation products can be made from other aldehydes, such as
acetaldehyde, crotonaldehyde, acrolein, benzaldehyde, furfural, glyoxal
and the like.
The aminoplast resins contain methylol or similar alkylol groups, and in
most instances at least a portion of these alkylol groups are etherified
by a reaction with an alcohol to provide organic solvent-soluble resins.
Any monohydric alcohol can be employed for this purpose, including such
alcohols as methanol, ethanol, propanol, butanol, pentanol, hexanol,
heptanol and others, as well as benzyl alcohol and other aromatic
alcohols, cyclic alcohol such as cyclohexanol, monoethers, of glycols such
as CELLOSOLVES and CARBITOLS, and halogen-substituted or other substituted
alcohols, such as 3-chloropropanol and butoxyethanol. The preferred
aminoplast resins are substantially alkylated with methanol or butanol.
The coating compositions of the present invention can be pigmented or
unpigmented and can be utilized in the presence of various generally known
additives such as flow control agents, surfactants, leveling agents,
fungicides, mildewcides and the like. Examples of pigments include any of
the generally known pigments including extender pigments used in the
coatings and resins industry such as mica, titanium dioxide, magnesium
carbonate, talc, zinc oxide, magnesium oxide, iron oxides red and black,
carbon black, metallic flake pigments such as aluminum flakes, and in
addition organic pigments can also be utilized. Mixtures of pigments can
also be employed.
The coating compositions of the present invention are typically formulated
in an amount of organic solvent ranging from about 30 percent to about 60
percent. Examples of suitable solvents include alcohols, such as methanol,
ethanol, butanol and the like; the mono- and di-alkyl ethers of ethylene
and propylene glycol such as ethylene glycol monoethyl ether, ethylene
glycol monobutyl ether, ethylene glycol dibutyl ether, ethylene glycol
monoethyl ether acetate, and propylene glycol dibutyl ether; the mono- and
di-alkyl ethers of diethylene glycol such as diethylene glycol monoethyl
ether, diethylene glycol diethyl ether and diethylene glycol monobutyl
ether acetate; ketones such as methylethyl ketone; esters such as butyl
acetate; hydrocarbons such as xylene and toluene; N-methyl-2-pyrrolidone;
and mixtures thereof.
The claimed coating compositions can be applied to a variety of substrates
using any suitable technique such as brushing, dipping, spraying, roll
coating and curtain coating.
In accordance with the present invention there is also provided a method of
providing a substrate with a protective coating. The method comprises the
steps of
I. applying to the surface of a substrate a coating composition comprising
a blend of:
(a) from about 5 percent by weight to about 35 percent by weight of a
hydroxyl functional vinyl polymer having at least 2 percent by weight of
hydroxyl groups based on the total weight of the vinyl polymer; and
(b) from about 65 percent by weight to about 95 percent by weight of an
organopolysiloxane containing hydrolyzable groups, the percentage of (a)
and (b) being based on the total weight of (a) and (b);
II. at least partially curing the coating composition of step I.
Preferably the substrate utilized in the claimed method is a metal
substrate. In one embodiment of the claimed method a metal substrate is
primed with a suitable primer coating composition prior to application of
the claimed coating composition which has been described above. The primer
coating composition can be selected from a wide variety of available
materials. One particularly suitable primer coating composition is a
fluorocarbon based primer coating composition. This composition comprises
broadly from about 10 percent to about 15 percent of a polyepoxide resin;
from about 30 percent to about 45 percent of a thermoplastic acrylic
resin; and from about 40 percent to about 55 percent of fluorocarbon
polymer. This primer coating composition typically has a resin solids
content of from about 15 percent to about 35 percent. This fluoropolymer
based primer coating composition is described in detail in U.S. Pat. No.
4,379,885 to Miller et al, said patent being incorporated by reference
herein. Another suitable primer coating composition for use in the claimed
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