Acrylic modified silicone resin

A polymeric mixture comprising a graft copolymer of silicone resin is useful as a polymeric binder in paint coatings and particularly powder coatings. The polymeric mixtures are produced by copolymerizing ethylenically unsaturated monomers including glycidyl monomers in the presence of silicone resin to produce the graft silicone resins.

This invention pertains to acrylic modified silicone resin useful in powder 
coatings and particularly to a process and composition based on in-situ 
copolymerization of monomers including glycidyl monomers in the presence 
of silicone resin. 
Acrylic resins containing glycidyl groups are useful in powder coatings and 
are known to exhibit good weathering properties if the acrylic copolymer 
does not contain appreciable amounts of copolymerized styrene. Acrylic 
copolymers of silicone resin should provide substantially improved 
weathering properties as well as offset some of the deficiencies with 
silicone resins. However, attempting to coreact hydroxyl containing 
acrylic copolymers with silicone resins is difficult to achieve in 
practice since the reaction is difficult to control and often results in 
cross-linked polymer known as gels. The reaction is difficult to control 
due to hydroxyl groups or other functional groups on the acrylic polymer 
as well as the preponderance of hydroxyl groups or alkyl ether groups on 
silicone resins, which coreact to cause a gel either during synthesis or 
subsequently during a solvent stripping step. 
It now has been found that glycidyl acrylic copolymers in combination with 
silicone resins can be produced by in-situ copolymerization of ethylenic 
monomers, including glycidyl monomers, in the presence of silicone resins 
containing hydroxyl and/or alkyl ether groups to provide a fluid 
non-gelled copolymer mixture, believed to be a graft copolymer of 
silicone, useful as a polymeric binder in powder coatings. Such powder 
coating exhibits superior weathering properties and similarly improved 
film integrity properties. In this invention, hydroxyl and carboxyl 
containing monomers are not necessary and preferably avoided to avoid 
gellation. In accordance with this invention, glycidyl containing monomers 
are copolymerized with other ethylenic monomers in the presence of 
silicone resin to produce a graft silicone polymer. These and other 
advantages of this invention will become more apparent by referring to the 
detailed description of the invention and the illustrative examples. 
SUMMARY OF THE INVENTION 
Briefly, the invention pertains to a process and resulting composition 
produced by in-situ copolymerization of ethylenically unsaturated 
monomers, including acrylic monomers and glycidyl monomers, in the 
presence of silicone resin containing hydroxyl or lower alkyl ether groups 
to produce a stabilized, non-gelled acrylic-silicone copolymer mixture. 
The in-situ polymerization process in the presence of silicone can be in 
bulk (solvent-free) or in the presence of organic solvent which can be 
subsequently stripped from the resulting polymer mixture. The polymer can 
be combined with other components to produce a clear or pigmented binder 
system for powder coatings.

DETAILED DESCRIPTION OF THE INVENTION 
The process and composition of this invention pertain to the in-situ 
copolymerization of ethylenically unsaturated monomers, including acrylic 
monomers and glycidyl monomers, in the presence of silicone resin. 
Referring first to the ethylenically unsaturated monomers, ethylenic 
monomers contain carbon-to-carbon unsaturation and include vinyl monomers, 
acrylic monomers, allylic monomers, acrylamide monomers, and mono- and 
dicarboxylic unsaturated acids. Vinyl monomers include vinyl esters, vinyl 
acetate, vinyl propionate, vinyl butyrates, vinyl benzoates, vinyl 
isopropyl acetates and similar vinyl esters; vinyl halides such as vinyl 
chloride, vinyl fluoride, and vinylidene chloride; vinyl aromatic 
hydrocarbons such as styrene, methyl styrenes and similar lower alkyl 
styrenes, chlorostyrene, vinyl toluene, vinyl naphthalenes, divinyl 
benzoate, and cyclohexene; vinyl aliphatic hydrocarbon monomers such as 
alpha olefins such as ethylene, propylene, isobutylene, and cyclohex as 
well as conjugated dienes such as 1,3 butadiene, methyl-2-butadiene, 
1,3-piperylene, 2,3 dimethyl butadiene, isoprene, cyclopentadiene, and 
dicyclopentadiene; and vinyl alkyl ethers such as methyl vinyl ether, 
isopropyl vinyl ether, n-butyl viyl ether, and isobutyl vinyl ether. 
Acrylic monomers include monomers such as lower alkyl esters of acrylic or 
methacrylic acid having an alkyl ester portion containing between 1 to 12 
carbon atoms as well as aromatic derivatives of acrylic and methacrylic 
acid. Useful acrylic monomers include, for example, acrylic and 
methacrylic acid, methyl acrylate and methacrylate, ethyl acrylate and 
methacrylate, butyl acrylate and methacrylate, propyl acrylate and 
methacrylate, 2-ethyl hexyl acrylate and methacrylate, cyclohexyl acrylate 
and methacrylate, decyl acrylate and methacrylate, isodecylacrylate and 
methacrylate, benzyl acrylate and methacrylate, and various reaction 
products such as butyl, phenyl, and cresyl glycidyl ethers reacted with 
acrylic and methacrylic acids, hydroxyl alkyl acrylates and methacrylates 
such as hydroxyethyl and hydroxypropyl acrylates and methacrylate. Acrylic 
acids include acrylic and methacrylic acid, ethacrylic acid, 
alpha-chloroacrylic acid, alpha-cycanoacrylic acid, crotonic acid, 
beta-acryloxy propionic acid, and beta-styrl acrylic acid. N-alkylol 
amides are acrylamides or methacrylamides such as N-methylol acrylamide, 
N-ethanol acrylamide, N-propanol acrylamide, N-methylol methacrylamide, 
N-ethanol methacrylamide, and similar alkyl acrylamide or methacrylamide 
monomers containing methyl, ethyl, propyl, n-butyl or iso-butyl alkyl 
groups. Hydroxyl functional monomers are hydroxy containing ethylenically 
unsaturated monomers including hydroxyl alkyl acrylates such as 2-hydroxyl 
ethyl acrylate and methacrylate, 2-hydroxypropyl acrylate and 
methacrylate, and similar hydroxy alkyl acrylates, although hydroxy 
containing monomers are not preferred and advantageously avoided. 
In accordance with this invention, glycidyl monomers are oxirane monomers 
characteristically containing oxirane functionality: 
##STR1## 
in addition to pendant ethylenic double bond unsaturation. Glycidyl 
monomers include for instance acrylic, methacrylic, or vinyl monomer 
derivatives of glycidyl and include, for example glycidyl acrylate, 
glycidyl methacrylate and similar lower alkyl acrylates, and allyl 
glycidyl ether. The glycidyl monomers can be copolymerized with the other 
ethylenically unsaturated monomers in the presence of silicone resin in 
accordance with this invention. 
In accordance with this invention, the acrylic monomers comprise by weight 
based on monomers copolymerized, between 30% and 95% acrylic monomers, 
between 1% and 50% glycidyl monomer, with the balance being other 
ethylenic monomers. 
Referring now to the silicone resins useful in this invention, silicon 
resins are based on a chemical backbone structure comprise alternate 
silicon and oxygen atoms, where methyl groups primarily or other lower 
alkyl groups or phenyl groups are attached to the silicon atoms, provided 
that hydroxyl groups (silanol groups) or lower alkyl ether (methoxy silane 
groups) are available and attached to silicon atoms for curing purposes. 
Silicone resins are prepared from organochlorosilanes such as 
methyltrichlorosilane, phenyltrichlorosilane, and dimethyldichlorosilane, 
which can be coreacted with an organic halide such as methyl chloride or 
chlorobenzene in the presence of silicon and copper catalyst to produce 
chlorobenzene in the presence of silicon and copper catalyst to produce 
chlorosilanes which can be further reacted with water to form 
hydroxysilanes and dehydrolysis to eventually organopolysiloxanes 
(silicones). Silcone resins have the generalized structure: 
##STR2## 
wherein most commercial silicones the R=methyl, but can include lower 
alkyl, fluoroalkyl, phenyl, vinyl and as part of the silicone resin 
polymer can include hydrogen, chlorine, alkoxyl, ocyloxy, or alkylamino 
groups; and where n represents monofunctional, difunctional, 
trifunctional, and quadrafunctional monomer units in the silicone polymer. 
Useful silicone resins in accordance with this invention have a number 
average molecular weight above 500 , preferably between 600 and 8000 and 
have more than 1, preferably at least 2 hydroxyl (silanol) groups and/or 
alkyl ether (methoxy silane) groups per Si atom and preferably between 2 
and 3 silanol and/or methoxy silanol groups (including fractions) per Si 
atom. Molecular weights can be determined by gel permeation chromatography 
(GPC) in accordance with ASTM D3016-72, ASTM D3536-76, ASTM D3593-80, 
and/or ASTM 3016-78. 
A preferred siloxane component is a cyclic silanol having at least two SIOH 
groups per molecule and wherein some of the non-hydroxy valence bonds of 
the silanol contribute to the cyclic structure. Preferred polyfunctional 
silicones include those set forth in U.S. Pat. Nos. 3,912,670 and 
4,107,148, both incorporated herein by reference. The most preferred 
hydroxy functional silicone is Z-6018 (Dow Corning) which is a hydroxy 
functional, low molecular weight, silicone having a molecular weight of 
about 600 and a theoretical formula: 
##STR3## 
where R is independently lower alkyl or phenyl groups and particularly 
methyl, ethyl, and phenyl groups. Physical properties of Z-6018 are as 
follows: 
______________________________________ 
Appearance Flaked solid 
Theoretical Silicone Content, wt. percent 
96.6 
Nonvolatile Content, percent 
98.0 
Volatility, 1.5 gms for 3 hrs at 
4.5 
482 F. (250 C.), percent 
Hydroxyl Content 
weight percent total 6.4 
hydroxy no. 211 
weight percent free 0.5 
Specific Gravity at 77 F. (25 C.) 
1.23 
Durran Melting Point, degrees 
185 F (85 C.) 
______________________________________ 
The desired crystallinity, tack temperatures and flow properties are 
derived from a rigid diacid, a multifunctional glycol and 
hydroxy-functional cyclic siloxanes. It is believed, without being bound 
thereto, that the advantageous properties of the instant powder coatings 
result in part from a controlled linearity resulting from the use of rigid 
diorganic acids and the inherent structure provided by the cyclic 
siloxanes having a terminal hydroxyl groups Si(R)--OH functionality and in 
part from the contribution of a high silicon content. The preferred 
siloxane is Z-6018 and self-condensation products thereof. Such products 
may contain up to twelve units of the above-identified siloxane and have 
molecular weights of from about 600 to about 8,000. 
The in-situ composition of this invention comprises on a polymeric weight 
basis between 30% and 90% copolymerized monomers (including acrylic and 
glycidyl monomer) with the balance being silicone resin. 
In accordance with the process of this invention, silicone resin is 
dispersed into an organic solvent such as aromatic hydrocarbons including 
xylene, toluene, benzene, or aliphatic hydrocarbons or derivatives thereof 
such as chlorinated hydrocarbons, esters or ketones. To provide solubility 
for the subsequent addition of ethylenic monomers the aliphatic or 
aromatic hydrocarbons can be mixed with alkyl alcohols such as methanol, 
ethanol, propanol, butanol as well as other solvents such as ethylene 
glycol monobutyl ether, ethylene glycol monobutyl ether acetate, and 
hexane. 
The solvated silicone resin is then heated to temperatures preferably 
between about 50.degree. C. and 150.degree. C., depending on the solvents 
and monomers as well as the polymerization initiator and the stage of the 
copolymerization of monomers. The ethylenically unsaturated monomers are 
then added to the heated solvated silicone resin over a period of time to 
effect in-situ copolymerization of the monomers in the presence of 
silicone resin. Suitable initiators for promoting copolymerization of the 
monomers include, for example, hydrogen peroxide, ammonium persulfate, 
sodium persulfate, or potassium persulfate. The peroxide catalyst is 
effectively coupled with a reducing agent such as an alkali metal, 
sulfite, bisulfite, or metabisulfite, or hydrosulfite or hydrazine. Other 
suitable initiators include organic or inorganic azo catalysts, such as 
azodiisobutyronitrile, azodiisobutyramide, or diethyl azodiisobutyrate. 
Example of other suitable azo catalysts include dimethyl or dibutyl 
azodiisobutyrate, azobis(alpha,v-dimethylvaleronitrile), 
azobis(alpha-methylbutyronitrile), azo-bis(alpha-methylvaleronitrile), 
dimethyl or diethyl azobismethylvalerate, and the like. Preferred such 
initiators comprise the persulfates, such as potassium persulfate, sodium 
persulfate, ammonium persulfate, and the like. Another useful class of 
initiators comprises percarbonates, such as diisopropyl percarbonate, and 
the like. Another useful class of initiators for this in situ 
polymerization comprises organic peroxides. One group of suitable 
peroxides comprises diacyl peroxides, such as benzoyl peroxide, lauroyl 
peroxide, acetyl peroxide, caproylperoxide, butyl perbenzoate, 
2,4-dichloro benzoyl peroxide, p-chlorobenzoyl peroxide, and the like. 
Another group comprises ketone peroxides, such as methyl ethyl ketone 
peroxide and the like. Another group comprises alkyl hydroperoxides such 
as t-butyl hydroperoxide, and the like. 
After the copolymerization of the monomers is completed, the in-situ formed 
polymer mixture comprises acrylic copolymer and silicone resin, believed 
to include graft copolymer of silicone resin. The solvent can be stripped 
off without causing gellation and provides an exceptionally good binder 
useful in powder coatings. The resulting polymer can be cured or 
cross-linked in use to form a fully cured protective film exhibiting 
superior weatherability and similar film integrity properties. The 
polymeric composition can be cured with the addition of a diacid or 
polyfunctional acid. Diacids for example can include aliphatic having 1-18 
or more carbon atoms, aromatic, dimer fatty acids, or unsaturated diacids. 
Saturated diacids include dodecanoic, succinic, glutaric, adipic, pimetic, 
suberic, azelaic, and sebacic acids. Aromatic acids include anhydride 
forms including the o-, p-, m- phthalic isomers, isophthalic, terephthalic 
tetrahydrophthalic, hexahydrophthalic, and trimellitic acid, as well as 
diphenyl or higher dicarboxylic acids such as p,p-diphenylether 
dicarboxylic acid, diphenyl lower alkyl dicarboxylic acid such as methyl, 
ethyl, propyl, bis A, and similar diphenyl or aromatic diacids. 
The acrylic-silicone binder of this invention can be thoroughly and 
uniformly mixed with raw batch ingredients by homogenizing the binder, 
pigmentary solids, plasticizers and other components to uniformly blend 
the resinous binder with the pigmentary solids. Pigments can ordinarily 
include opacifying pigments such as titanium dioxide, zinc oxide, leaded 
zinc oxide, titanium calcium, as well as tinting pigment such as carbon 
black, yellow oxides, brown oxides, tan oxides, raw and burnt sienna or 
umber, chromium oxide green, phthalocyanine green, phthalonitrile blue, 
ultramarine blue, cadmium pigments, chromium pigments, and the like. 
Filler pigments such as clay, silica, talc, mica, woolastonite, wood 
flower and the like can be added. The raw batch ingredients can be 
thoroughly mixed in a high intensity mixer such as a frustroconical 
agitator whereby the materials are discharged in a uniform mixture. The 
high intensity mixer discharges the batch components to a heated screw 
extruder. The extrudate emerges from the extruder as a ribbon of less than 
abut 1/16 inch thickness which passes onto a water cooled stainless steel 
conveyor belt whereby the plastic ribbon extrudate fully hardens. The 
cooled extrudate then passes through a mechanical commuter discharged at 
the end of the cooled stainless steel belt to efficiently break the 
fragile brittle ribbon into very small flakes. The small flakes are then 
discharged onto a cooled mill, such as a hammer mill, to grind the small 
particles onto powder paint of less than 325 mesh and preferably passing a 
200 mesh U.S. Standard sieve screen whereupon the powder can be further 
classified into particle size if desired. 
The powder paints in accordance with this invention can be applied to a 
steel panel substrate and moderately heated between temperatures of abut 
80.degree. C. and 100.degree. C. to obtain desirable flow out. 
The foregoing describes the in-situ copolymerization of ethylenically 
unsaturated monomers, including acrylic and glycidyl monomers, in the 
presence of siicone resin to form an interpenetrating network of polymers 
believed to be an acrylic graft of silicone resin. The polymeric mixture 
is useful as a binder system in powder coatings as further illustrated in 
the following examples wherein percentages are by weight and temperatures 
are in .degree.C., unless otherwise indicated. 
EXAMPLE 1 
Preparation of Glycidylmethacrylate Containing Acrylic Powder Resin 
Into a 5-liter roundbottom 4 necked flask was charged 750 g. of toluene. 
Through the 4 necks were placed a monomer addition funnel, a water cooled 
condenser, an air driven stirring motor and nitrogen inlet. The toluene 
was heated to 108.degree. C. with a nitrogen banket and a monomer 
composition of the following: 
______________________________________ 
Grams 
______________________________________ 
glycidyl methacrylate 
294 
methyl methacrylate 
570 
butyl acrylate 172 
styrene 127 
methacrylic acid 12 
mercapto ethanol 12 
VAZO 64 23 
______________________________________ 
was slowly added to the following toluene in 3 hours. At the end of the 
monomer addition the temperature rose to 114.degree. C. The reaction 
mixture was held for 3 hours at 114.degree.-116.degree. C. and then cooled 
for the night. The next morning, the reaction mixture was heated to 
90.degree. C. and a vacuum of 23" of Hg was applied to strip off the 
solvent. When most of the solvent was stripped off, the resin was poured 
out onto aluminum foil. Viscosity of the resin on a ICI Cone and Plate 
viscometer at 200.degree. C. was 25 poise, tack temperature of resin was 
177.degree. F. Weight average molecular weight from gel permeation 
chromatography (GPC) was 33600 and the number average molecular weight was 
4670. 
EXAMPLE 2 
Preparation of Silicone-Glycidyl Methacrylate Graft Acrylic Powder Resin 
Into a 5-liter round bottom 4-necked flask was charged 750 g. of toluene 
and heated to 99.degree. C. with a nitrogen blanket. 379 g. of a solid 
silicone resin Z6018 (from Dow Corning Company, Midland, Mich.), a hydroxy 
functional low molecular weight, silicone having a hydroxyl No. of 211, 
was added and dissolved in toluene. 
A monomer mixture consisting of the following: 
______________________________________ 
Grams 
______________________________________ 
glycidyl methacrylate 294 
methyl methacrylate 570 
butyl acrylate 178 
styrene 133 
mercapto ethanol 12 
Azobis polymerization initiator (VAZO 64) 
23 
______________________________________ 
was added to the silicone resin solution at 109.degree.-117.degree. C. The 
monomer addition took about three hours, and 5.2 ml of water was 
collected. The reaction mixture was held at 117.degree. C. for three hours 
and then let cool overnight. The next morning the grafted reaction mixture 
was heated to about 108.degree. C. with 23" of vacuum, and most of the 
solvent was stripped off. The hot resin was then poured onto a sheet of 
aluminum foil. The tack temperature of the resin is 192.degree. F., ICI 
cone and plate viscosity is 28 poise at 200.degree. C., the nonvolatile is 
100%. 
EXAMPLE 3 
Preparation of silicone-glycidyl methacrylate graft acrylic power resin 
Into a 5-liter round bottom 4 necked flask was charged 750 g. of toluene 
and heated to 90.degree. C. with a nitrogen blanket. Then 379 g. of a 
solid silicone resin Z-6018 (from Dow Corning) was added and dissolved in 
toluene. The structure of the silicone resin is believed to be of the 
following as shown above. 
A monomer mixture consisting of the following: 
______________________________________ 
Grams 
______________________________________ 
glycidyl methacrylate 
294 
methyl methacrylate 
570 
butyl acrylate 172 
styrene 127 
methyacrylic acid 12 
VAZO 64 23 
______________________________________ 
was added to the silicone resin solution at 106.degree. C. in 3 hours and 
the reaction mixture held at 114.degree.-116.degree. C. for 3 more hours, 
and then let cool over night. The next morning the grafted reaction 
mixture was heated to 100.degree. C. and a vacuum was applied to strip off 
solvent. The resin was quite thick. The viscosity of the resin on the ICI 
Cone and Plate viscometer at 200.degree. C. was erratic. The tack 
temperature of the resin was 220.degree. F. The color of the graft 
copolymer is of a milky opalescent color vs. clear for the acrylic 
copolymer by itself. 
The foregoing detailed description and illustrative examples indicate the 
principles of this invention based on in-situ copolymerization of 
ethylenic monomers including glycidyl monomers in the presence of silicone 
resin to produce an in-situ formed graft copolymer mixture, but is not 
intended to be limiting except by the appended claims.