Silyl-polyacrylates for polycarbonate substrates

Heat curable hard coat compositions are provided of aqueous colloidal silica and copolymer of an alkylacrylate and a polyalkoxysilylacrylate or a mixture of an alkylacrylate-acrylic acid copolymer and an epoxyalkoxysilane. The heat curable hardcoat composition can be applied onto various substrates, for example, a polycarbonate substrate, and thereafter heat cured to produce coated articles having adherent and abrasion resistant coatings.

CROSS REFERENCE TO RELATED APPLICATIONS 
Reference is made to copending application Ser. No. 269,122, filed June 1, 
1981, for Daniel R. Olson et al., for UV Curable Hardcoat Compositions, 
Coated Articles and Method, assigned to the same assignee as the present 
invention. 
BACKGROUND OF THE INVENTION 
Prior to the present invention, thermoplastic substrates, for example, 
polycarbonate articles, were treated with a photocurable acrylic coating 
composition, as shown in Moore et al., U.S. Pat. No. 4,198,465, assigned 
to the same assignee as the present invention. Although the use of acrylic 
resins provide durable mar resistant and chemical resistant coatings, the 
ability of such cured polyacrylates to serve as a protective coating for a 
thermoplastic substrate, often did not satisfy the abrasion resistant 
standards required in many applications. 
As shown by Clark, U.S. Pat. No. 4,027,073, an acidic dispersion of 
colloidal silica in a hydroxylated silsesquioxane can provide heat curable 
mixtures which result in valuable transparent abrasion resistant coatings 
on a variety of thermoplastic substrates. It was found, however, that the 
cure of the hydroxylated silsesquioxane binder resin often requires 
several hours, or even days to achieve acceptable mar resistant 
properties. In addition, a major drawback found with abrasion resistant 
coatings made in accordance with the aforementioned Clark patent is that 
the silsesquioxane colloidal silica coating does not adhere well to 
polycarbonate surfaces unless specialized surface treatments, for example 
primers, are used. 
In the aforesaid copending application Ser. No. 269,122, valuable results 
were obtained by utilizing a UV curable mixture of a 
polyalkoxysilylacrylate, aqueous colloidal silica and polyfunctional 
acrylic monomer. The mixture was convertible to an adherent 
organopolysiloxane hardcoat in several seconds or less during radiation 
curing. 
I have now discovered that highly abrasion resistant coatings for various 
thermoplastic substrates, for example, polycarbonate, exhibiting good 
optical quality and weatherability, also can be obtained from heat curable 
compositions containing colloidal silica and silyl-containing 
polyacrylate. The silyl-containing polyacrylate can either be, for 
example, a methylmethacrylate/.gamma.-methacryloxypropyltrimethoxysilane 
copolymer or a mixture of methylmethacryate/methacrylic acid copolymer and 
an epoxy silane. The aforementioned heat curable compositions can be 
applied onto various thermoplastic substrates and thereafter heated to 
effect the separation of volatiles, followed by curing of the resulting 
residue to produce a weather resistant coating having good optical quality 
and abrasion resistance. 
STATEMENT OF THE INVENTION 
There is provided by the present invention, heat curable hardcoat 
compositions comprising the product obtained by mixing together the 
following essential ingredients by weight, 
(A) 20 to 80% of colloidal silica utilized as an aqueous dispersion having 
at least 10% by weight of colloidal silica solids, 
(B) 80 to 20% of a silyl-containing polyacrylate selected from the class 
consisting of 
(i) an alkylacrylate-acryloxyalkyl polyalkoxysilane copolymer or 
(ii) a mixture of a carboxy containing polyacrylate and an epoxy silane 
and, 
(C) 1% to 20% of a UV absorber, based on the weight of (A), (B) and (C). 
One of the ingredients of the hardcoat compositions of the present 
invention is colloidal silica. Colloidal silica is generally available as 
a dispersion of submicron-sized silica (SiO.sub.2) particles in an aqueous 
medium which may contain an organic solvent such as isopropanol. It 
provides the hardcoat composition with hardness and integrity along with 
many of the advantages inherent in silicone products such as a 
wide-ranging resistance to environmental extremes. 
Aqueous dispersions of colloidal silica are available from chemical 
manufacturers such as DuPont and Nalco Chemical Company. Colloidal silica 
is available in either acidic or basic form. However, for purposes of the 
present invention it is preferable that the acidic form be utilized and 
that there is present at least 10% by weight of colloidal silica solids. 
It has been found that superior hardcoat properties can be achieved with 
acidic colloidal silica (i.e. dispersions with low sodium content). 
Alkaline colloidal silica also may be converted to acidic colloidal silica 
with additions of acids such as HCl or H.sub.2 SO.sub.4 along with high 
agitation. 
An example of a satisfactory colloidal silica for use in these coating 
compositions is Nalcoag 1034A, Available from Nalco Chemical Company, 
Chicago, Ill. Nalcoag 1034A is a high purity, acidic pH aqueous colloidal 
silica dispersion having a low Na.sub.2 O content, a pH of approximately 
3.1 and an SiO.sub.2 content of approximately 34% by weight. In the 
examples given below, the weight in grams of parts by weight of the 
colloidal silica includes its aqueous medium. Thus, for example, 520 grams 
of Nalcoag 1034A colloidal silica represents, approximately, 177 grams of 
SiO.sub.2 by weight. 
The term colloidal silica is intended to represent a wide variety of finely 
divided SiO.sub.2 forms which can be utilized to form the hardcoat 
compositions of the present invention without the necessity of undue 
experimentation. Further description can be found in U.S. Pat. No. 
4,027,073. 
The heat curable hardcoat compositions of the present invention can be made 
by combining aqueous colloidal silica with the silyl-containing 
polyacrylate and the UV absorber. The order of mixing the various 
ingredients is not critical. The silyl-containing polyacrylate can be in 
the form of a copolymer of an acrylic monomer and an 
acryloxyalkylalkoxysilane defined below. The silyl-containing polyacrylate 
also can be a mixture of a carboxy-containing acrylic copolymer and an 
epoxyalkoxysilane. Temperatures in the range of about 
25.degree.-50.degree. C. can be employed to mix the various ingredients. 
Preferably, the acryloxyalkylalkoxysilanes which can be copolymerized with 
acrylic monomer to form the silyl-containing polyacrylate are included 
within the formula, 
##STR1## 
where R is a C.sub.(1-13) monovalent radical, R.sup.1 is a C.sub.(1-8) 
alkyl radical, R.sup.2 is selected from hydrogen and R radicals and 
mixtures thereof, R.sup.3 is a divalent C.sub.(1-8) alkylene radical, 
R.sup.4 is selected from hydrogen or methyl, a is a whole number equal to 
0 to 2 inclusive, b is an integer equal to 1-3 inclusive, and the sum of 
a+b is equal to 1 to 3 inclusive. 
Another form of the silyl-containing polyacrylate used in making the heat 
curable hardcoat compositions of the present invention is a mixture of a 
carboxy-containing polyacrylate and an epoxyalkoxy silane of the formula, 
EQU ((R.sup.5).sub.c Si(OR.sup.6).sub.4-c ( 2) 
where R.sup.5 is a C.sub.(3-12) oxirane containing organic radical, R.sup.6 
is a C.sub.(1-8) alkyl radical and c is an integer equal to 1 or 2. 
Radicals which are included by R of formula (1), are for example, 
C.sub.(1-8) alkyl radicals, for example, methyl, ethyl, propyl, butyl, 
etc.; C.sub.(6-13) aryl radicals, for example, phenyl, tolyl, xylyl; 
aralkyl radicals, for example, benzyl, phenylethyl, etc.; halogenated 
derivatives thereof. R.sup.1 is C.sub.(1-8) alkyl radical such as methyl, 
ethyl, propyl, butyl, etc.; R.sup.3 can be methylene, ethylene, 
trimethylene, etc.; R.sup.5 is selected from radicals, such as 
##STR2## 
and R.sup.6 is selected from R.sup.1 radicals. 
Some of the acrylic monomers which can be used in the practice of the 
present invention to form silylpolyacrylates by copolymerization with the 
silylacrylates of formula (1) are, for example, methyl methacrylate, 
methyl acrylate, ethyl methacrylate, ethyl acrylate, butyl methacrylate, 
butyl acrylate, etc. In addition, functionalized acrylic monomers, for 
example, 
##STR3## 
also can be used in amounts at up to about 50% by weight of the 
aforementioned acrylic monomer. Copolymerization can be achieved by using 
1 to 49 parts of acrylic monomer per part of the silylacrylate of formula 
(1) at a temperature in the range of from 50.degree. C. to 120.degree. C., 
preferably at 85.degree. C..+-.15.degree. C. and in the presence of an 
effective amount of an organo peroxide or other free-radical initiator, 
such as azobisisobutyronitrile. There can be used organic solvents such as 
an aliphatic alcohol, for example, butoxyethanol, methanol, etc., to 
facilitate the copolymerization which is preferably achieved by agitating 
the ingredients under an inert atmosphere, for example, nitrogen, for a 
period of 1 to 48 hours. 
The carboxy-containing polyacrylate can be made by copolymerizing an 
acrylic ester monomer, for example, methyl methacrylate, ethyl 
methacrylate, butyl methacrylate, methyl acrylate, etc., with an acrylic 
acid monomer, such as methacrylic acid or acrylic acid. 
There can be utilized from about 1 to 50 parts by weight of the acrylic 
acid monomer, and preferably from about 5 to 30 parts by weight, per 100 
parts by weight of the acrylic ester monomer, to form the 
carboxy-containing polyacrylate which can be formed by agitating a mixture 
of the aforementioned monomeric acrylic reactants at a temperature of from 
50.degree. C. to 120.degree. C., preferably 85.degree. C..+-.15.degree. C. 
in an inert atmosphere, for example under nitrogen, in the presence of an 
organic solvent, such as butoxyethanol. 
A typical procedure is to combine 0.5 to 2 milimoles of alkoxysilane per 
gram of colloidal silica which can be used with the carboxy-containing 
polyacrylate. Experience has shown that the amount of alkoxysilane used 
depends on the amount of SiO.sub.2 in the formulation. 
Included among the polyalkoxysilanes of formula (2) which can be used in 
the practice of the present invention are compounds having the formulas, 
##STR4## 
In addition to the aforementioned ingredients of colloidal silica and 
silyl-containing polyacrylate, an effective amount of a UV absorber can be 
utilized. Typical UV absorbers are, for example, hydroxybenzophenones, 
benzotriazoles, cyanoacrylates, benzylidene malonates, salicylates and 
silane-functional UV absorbers such as 
##STR5## 
Some of the polyalkoxysilanes which can be used in the practice of the 
present invention are compounds having the formulas, 
EQU CH.sub.2 .dbd.CCH.sub.3 CO.sub.2 --CH.sub.2 CH.sub.2 --Si(OCH.sub.2 
CH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CHCO.sub.2 --CH.sub.2 CH.sub.2 --Si(OCH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CCH.sub.3 CO.sub.2 --CH.sub.2 CH.sub.2 CH.sub.2 
--Si(OCH.sub.2 CH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CHCO.sub.2 --CH.sub.2 CH.sub.2 --Si(OCH.sub.2 
CH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CCH.sub.3 CO.sub.2 --CH.sub.2 CH.sub.2 CH.sub.2 
--Si(OCH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CHCO.sub.2 --CH.sub.2 CH.sub.2 CH.sub.2 
--Si(OCH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CCH.sub.3 CO.sub.2 --CH.sub.2 CH.sub.2 CH.sub.2 
--Si(OCH.sub.2 CH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CHCO.sub.2 --CH.sub.2 CH.sub.2 CH.sub.2 --Si(OCH.sub.2 
CH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CCH.sub.3 CO.sub.2 --CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 
--Si(OCH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CHCO.sub.2 --CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 
--Si(OCH.sub.2 CH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CCH.sub.3 CO.sub.2 --CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 
--Si(OCH.sub.2 CH.sub.3).sub.3, 
EQU CH.sub.2 .dbd.CHCO.sub.2 --CH.sub.2 CH.sub.2 CH.sub.2 CH.sub.2 
--Si(OCH.sub.2 CH.sub.3).sub.3, 
The coating compositions of the present invention may also optionally 
contain various flatting agents, surface active agents, thixotropic 
agents, UV light stabilizers, antioxidants, quenchers, catalysts and dyes. 
It has been found that optically clear coatings can be obtained by 
utilizing a surface active agent in effective amounts, for example, 0.01 
to 2 parts of the surface active agent per 100 part of the coating 
mixture. 
Among the surface active agents which can be used are, for example, those 
shown in Frye U.S. Pat. No. 4,277,287, assigned to the same assignee as 
the present invention. 
The various surface-active agents, including anionic, cationic and nonionic 
surface-active agents are described in Kirk-Otmer Encyclopedia of Chemical 
Technology, Vol. 19, Interscience Publishers, New York, 1969, pp. 507-593, 
and Encyclopedia of Polymer Science and Technology, Vol. 13, Interscience 
Publishers, New York, 1970, pp. 477-486, both of which are incorporated 
herein by reference. 
Various substrates can be treated in the practice of the present invention 
with the heat curable hardcoat compositions to produce shaped 
thermoplastic articles having enhanced abrasion resistance. The heat 
curable hardcoat compositions can be applied onto the substrate by flow 
coating, painting, etc. After application, the treated substrate can be 
heated to a temperature in the range of 85.degree. C. to 140.degree. C. to 
effect the cure of the hardcoat composition. Substrates which can be 
treated include Lexan polycarbonate, Valox polyester, Ultem 
polyetherimide, PPO polyphenyleneoxide, polymethylmethacrylate, metals 
such as steel, aluminum, metallized thermoplastics, etc. Those skilled in 
the art also know that certain of the aforementioned substrates can be 
primed if desired prior to being treated in accordance with the invention, 
such as priming a polycarbonate substrate with a polyacrylic coating.

In order that those skilled in the art will be better able to practice the 
invention, the following examples are given by way of illustration and not 
by way of limitation. All parts are by weight. 
EXAMPLE 1 
A coating formulation was made by combining at ambient temperatures, 25.92 
parts of an 85:15 copolymer of methylmethacrylate and 
.gamma.-methacryloxypropyltrimethoxysilane (MAPTMS) with 9.54 parts of 
methanol, 54.04 parts of diacetone alcohol and 43.2 parts of Nalcoag 
1034A, which is manufactured by the Nalco Chemical Company, Chicago, Ill. 
The resulting solids in the formulation contained 60% colloidal silica. In 
addition, 0.1 part of BYK-300 surfactant manufactured by the Mallinckrodt 
Chemical Company, was added to the formulation. The above mixture was flow 
coated onto a Lexan polycarbonate panel, drained 15 minutes and cured for 
1 hour at 125.degree. C. An additional mixture was made using 10 parts of 
the coating formulation to 0.1 part of Uvinul N-539, a UV absorber 
manufactured by the General Aniline and Film Corporation. 
The above coated substrates were evaluated for abrasion resistance using a 
Taber Abraser and the following results were obtained: 
______________________________________ 
Initial 
% Abrasion Resistance.sup.a 
Coating Haze (.DELTA.%H).sup.50 
(.DELTA.%H).sup.100 
(.DELTA.%H).sup.300 
______________________________________ 
40% 85 MMA/15 
0.4 4 4 6 
MAPTMS copolymer 
+ 60 SiO.sub.2 
colloidal SiO.sub.2 
40% 85 MMA/15 
0.4 4 4 6 
MAPTMS copolymer 
+ 60 SiO.sub.2 
colloidal SiO.sub.2 
+ 5% Uvinul .RTM. 
0.4 6 7 9 
N539 
40% 85 MMA/15 
0.4 4 4 6 
MAPTMS copolymer 
+ 60 SiO.sub.2 
colloidal SiO.sub.2 
+ 14% Uvinul N539 
0.3 10 11 12 
MARGARD .TM. 0.4 -- 1.5 5 
polycarbonate sheet 
______________________________________ 
.sup.a Change in haze after Taber Abraser Testing. The superscripts after 
the H indicate the number of Taber cycles. 
In the above table, abrasion resistance was determined by measuring the 
change in percent haze (.DELTA.%H) using a Gardner model UX10 haze meter 
before and after 300 cycles of abrasing on a model 174 Taber Abraser 
equipped with CS10F wheels and 500 gram weights. Margard polycarbonate 
sheet is manufactured by the General Electric Company and is a 
commercially available transparent material consisting of a polycarbonate 
sheet coated with a silicone hardcoat. 
The above results show that a hardcoat made in accordance with the practice 
of the present invention provides satisfactory abrasion resistance to a 
polycarbonate substrate when compared to a commercially available 
material, such as Margard polycarbonate sheet. 
EXAMPLE 2 
A coating formulation was made by combining 0.75 part of 
glycidoxypropyltrimethoxysilane, 8.58 parts of Nalcoag 1034A and 13.2 
parts of a methylmethacrylate/methacrylic acid copolymer. The copolymer 
was made by combining 200 ml of butoxyethanol, 40 ml of 
methylmethacrylate, 10 ml of methacrylic acid, 0.1 gram of dodecanethiol 
and 0.4 gram of azobisisobutyronitrile. The copolymer mixture was stirred 
at 70.degree. C..+-.10.degree. C. in a nitrogen atmosphere for 18 hours. 
There was then added 10 ml of diacetone alcohol to solublize the 
copolymer. 
The above coating formulation was applied onto a polycarbonate panel and 
cured for 1 hour. The coated sample had an initial haze of 0.5%. After 
Taber abrasing for 50, 100 and 300 cycles as shown in Example 1, the 
change in haze was 4, 6 and 9%, respectively. 
It was further found that a polycarbonate panel coated with a lacquer of 
polymethylmethacrylate having a molecule weight of 37,000, LS-123, of the 
Bee Chemical Company of Chicago, Ill. exhibited a 20% increase in haze 
after 50 cycles using the above-described Taber Abraser technique. A 26% 
increase in haze was experienced by the treated polycarbonate panel after 
1000 Taber cycles. An improvement in abrasion resistance was shown with 
polycarbonate panels treated with a coating mixture of 50% by weight of 
the polymethylmethacrylate lacquer and 50% of colloidal silica. For 
Example, after 50 Taber Abraser cycles, a 14% increase in haze was found. 
This compares favorably with the 20% increase shown for the 
polymethylmethacrylate lacquer free of colloidal silica. However, as shown 
by the Table of Example 1, a substantial increase in abrasion resistance 
was further realized beyond that shown for the mixture of the 
polymethylmethacrylate lacquer and colloidal silica when the silylacrylate 
was used in the coating composition either as a silylalkoxy acrylate, or a 
mixture of a carboxycontaining polyacrylate and alkoxysilane in accordance 
with the practice of the present invention. 
Although the above examples are directed to only a few of the very many 
variables which can be utilized in the practice of the present invention, 
it should be understood that the present invention is directed to a much 
broader variety of coating formulations, coated articles and methods of 
making such materials as set forth in the description preceding these 
examples.