CA1159991A - Silicone resin coating composition - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
Silicone resin coating compositions, which when applied to a solid substrate provide an abrasion resistant coating thereto, are disclosed herein. The coating compositions have a basic pH in the range of from 7.1 - 7.8 and are prepared by hydrolyzing an alkyltrialkoxysilane or aryltrialkoxysilane in an aqueous colloidal silica dispersion. Linear, functionally terminated oligomeric siloxanes may be added to the coating compositions to render the compositions crack resistant. In addition the use of thickening agents may further enhance the coatings abrasion resistance.

Description

5~ 9 91 1 Background of the Invention 3 This invention relates to a protective coating compo-4 sition. More particularly, it relates to a silicone resin coating composition which, when applied to a substrate, forms a 6 protective, abrasion-resistant coatin~ thereon.

8 Recently, the substitution of glass glazing with 9 transparent materials which do not shatter or are more resistant to shattering than glass, has become widespread. For exam~le, 11 transparent glazing made from synthetic organic polymers is now 12; utilized in public transportation vehicles, such as trains, 13 , buses, taxis and airplanes. Lenses, such as for eye glasses 14 and other optical instru~ents, as well as glazing for large 15,l buildings, also employ shatter-resistant transparent plastics.
16,~ The lighter weight of these plastics in comparison to glass is 17 , a further advantage, especially'in the transportation industry 18'~ whexe the weight of the vehicle is a major factor in its fuel 19~¦ economY-20~
21 !ll While transparent plastics provide the major advantage ¦22 1! Of being more resistant to shattering and lighter than glass, a 23jl serious drawback lies in the ease with which the5e plastics mar 24~1 and scratch, due to everyday contact with abrasives, such as 25¦j dust, cleaning equipment and/or ordinary weathering. Continu- ¦
26,j ous scratching and marring results in impaired visibility and 271~ poor aesthetics, and oftentimes requires replacement of the 28~t glazing or lens or the like.
29, 3 ;~ One of thè most promising and widely used transparent ;l ` i; 60 SI 222 i9~1 !! I
~' I
1 ! plastics for glazing is polycarbonate, such as that known as

2~ Lexan~, sold by General Electric Company. It is a tough mate- !

3 ¦I rial, having high impact strength, high heat deflection te~per~- I

4 ¦¦ ture, good dimensional stability, as well as bein~ self-extin-, ¦

5 1I guishing, and is easily fabricated.

7 ¦1 Attempts have been made to improve the abrasion resis-8 ~! tance of transparent plastics. For example, scratch-resistant 9 jZ coatings formed from mixtures of silica, such as colloidal sil- ~
10.~ ica or silica gel, and hydrolyzable silanes in a hydrolysis mP- ¦
11~i dium, such as alcohol and water, are known. U.S. Patents 12 ¦1 3,708,225, 3,986,997 and 3,976,497, for example, describe such 13l; compositions.
14i1 While these afore-mentioned coating formulations have 16 been found acceptable, there still remains room for improvement.
17 For example, the coating compositions of this in~ention provide 18 coatings having improved resistance to moisture and humidity and 19 ~ ultraviolet light, in comparison with those coatings provided in 20 ¦ accordance with U.~. 3,9~6,997. Moreover, it has been found 21 !¦ herein that in direct contrast to the teachings of U.S.
2211 3,986,997, the basic coating com?ositions of this invention hav-23 ing a pH in the range of from 7.1-7.8, do not immediately gel 24 ~nd provide excellent coatings having good properties on solid 25 ¦ substrates.

27 ~ Protective coatings for metals, bright or dull, are 281 also needed. For example, bright metallized plastics, wherein 29¦1 small a~ounts of metal are vacuum sputtered or vacuum metallized 3~!1 over the plastic, now popular with the auto industry because , .,, l of their light weight, need protective layers to prevent s~ratch~
2 ing and marring of the brilliant surface. Metal wheel covers 3 (hub caps) also require protective coatings for their preserva-' 4 tion and lasting beauty. I
t

6`; Summary of the Invention

7 ,

8 Accordingly, it is one obj~ct of the present invention

9 to provide a new protective coating resin for solid substrates

10 ' '

11 Another object of this invention is to provide a coat-

12 ing resin for solid substrstes which, when applied to the sub-13l strate, will provide an abrasion-resistant surface thereto.
14~
lS , Still another object of the present invention is to 16jl provide a coating composition, especially well suited for pro-17i~ viding an abrasion resistant co~ting surface to transparent 18 ¦I substrates. `
191~ 1 20j A further object of this invention is to provide a 21 ¦I protectîve coating resin which is readily applicable to a sub- ll 2~ I strate and which, when applied, provides an im~roved coating I
23 I h2ving especially superior resistance to moisture,- humidity and i 24 ~ traviolet light than prior art coatings. ~
25 l i 26 1 A still further object of the present invention is to 27 I provide a coating resin composition also well suitable as a , 28 I protective coating for metals and metallized surfaces.

30 ~ _ 3 _ ., , ,. . I

1~ 11~9 ~ 1 60 SI 222 il ~ . These and other objects are accomplished herein by a 2 ¦I coating composition comprising a dispersion of colloidal silica 3 li in an aliphatic alcohol-water solution of the partial condensate 4 ¦! of a silanol of the formula RSi(OH)3, wherein R is selected fram 5 !~ ~e group consisting of alkyl having from 1 to 3 carbon atoms 6 ~ and aryl, at least 70 weight percent of the silanol being CH3-7 ~I Si~O~)3, said composition containing 10 to 50 weight percent 8 ll solids, said solids consisting essentially of 10 to 70 weight 9 l~ percent colloidal silica and 30 to 90 weight percent of the par-o !I tial condensate, said co~,position having a pH from 7.1 to about ~ 7.8.
12 ll

13 1! Detailed Description of the Invention `14 ~1 15 li The coating compositions of this invention are pre-16 ,¦ pared by hydrolyzing a trialkoxysilane or a mixture of trial-17 Ij koxysilanes of the formula RSi~OR)3, wherein R is alkyl of froml 18 !¦ 1 to 3 carbons or aryl, such as phenyl, in an aqueous dispersion¦
19 i~ of colloidal silica.
20 ,! .
21 ¦ In the practice of the present invention, suitable 22 ! aqueous eolloidal silica dispersions generally have a particle 23 ~ size of from 5 to 150 millimicrons in diameter. These silica 24 dispersions are well known in the art and commercially available 25 1 ones include, for example, those sold ~der the trademarks of 26 1 Ludox (duPont) and Nalcoag (NALC0 Chemical Co.). Such col-27 ¦ loidal silicas are available as both acidic and basic hydro- ;

28 1 ~ols. For the purpose of this invention, wherein the pH of the 29 ~ coating compositions is on the basic side, basic colloidal sil-30 ,'. ica sols are preferred. However, acidic colloidal silicas, I

, 60 SI 222 1 wh`erein the pH is adjusted to a basic level, are also contem-2 ` plated. In addition, it has been found that colloidal silicas 3 !i having a low alkali content (e.g., Na2O) yield a more stable 4 ' coating composition. Thus, colloidal silicas having an alkali ~
S ' content of less than 0.35% (calculated as Na2O) have been found ¦
6 1 to be preferable. Moreover, colloidal silicas having average 7 i, particle size of from 10 to 30 millimicrons are also preerred.
8 A particularly preferred aqueous colloidal silica dispersion for ¦
9 the purposes herein is known as Ludox LS, sold by duPont Company.
10 ,' ' 11 l, Xn accordance with this invention, the aqueous col-12 li loidal silica dispersion is added to a solution of a small 13 ¦1 amount of alkyltriacetoxysilane in aIk~ltrialkoxysilane or

14 ,l aryltrialkoxysilane. For the purposes herein, from about 0.07

15 ¦I parts by weight to about 0.1 parts by weight, based on 100 parts

16 ll by weight of the total composition, of the alkyltriacetoxy-

17 sil~ne is used. The temperature o~ the reaction mixture is

18 , maintained at about 20~C to about 40C, preferably 20~C to abou~

19 ¦ 30C, and most prefe~ably below 25~C. It has been found that

20 ¦~ in about six to eight hours sufficient trialkoxysilane has hy-

21 l~ drolyzed so as to reduce the initial two phase liquid mixture to 2~ ¦ one liquid phase in ~hich the now treated silica (i.e., treated 23 ~ by its admixture with the alkyltrialkoxysilane or aryltrialkoxy-2~ ¦ silane) is dispersed. In general, the hydrolysis reaction is I allowed to continue for a total of about 24 to 48 hours, de-26 ~I pending upon the desired viscosity of the final product. I
27 !I The more ti~e the hydrolysis reaction is perm~tted to continue Z8 li the higher will be the viscosity of the product. After the ~9 hydrolysis has been completed to the desired extent, the sol-' ids content is adjusted by the addition of alcohol, preferably 31 l~ isobutanol, to the reaction mixture. Other suitable i!
1.

" ~ 6 0 S I 2 2 2 .. ` ~ I

l alcohols for the purposes herein include iower aliphatic alco-2 hols such as methanol, ethanol, propanol, isopropanol, n-butyl 3 alcohol and t-butyl alcohol. Mixtures of such alcohols can be 4 ' used, too. The solvent system should contain from about 20 to 75 weight percent alcohol to ensure solubility of the partial 6 condensate (siloxanol). Optionally, additional water-miscible 7 ' polar solvents, such as acetone, butyl cellosolve and the like 8 in minor amounts, like no more than 20 weight pereent of the co-9 , solvent system can also be used. The solids content of the ' coating compositions of this invention is generally preferred 11 I to be in the range of from about 18 to 25%, most preferably, 12 ! about 20%, by weight of the total composition. The pH of the 13 ,j resultant coating cDmposition is in the range of from about 7.1 ¦
14 to about 7.8, preferably higher than 7.2. If necessary, dilute 1, 15 ~ base, such as ammonium hydroxide or weak acid, such as acetic 16 ~ acid, can be added to the composition to adjust the final pH to 17 , this desired range. At these b~asic pH's, the compositions are 18 il translucent liquids which are stablè at room temperature for at 19 li least several weeks. When stored at temperatures below about 20 ¦ 5~C (40F) the period of stability is increased further.
21 ~ Additives and other modifying agents, such as thick-

22 1 eners, pigments, dyes, and the like, m~y be added to the compo-

23 1 sition at this tlme. A particùlarly desirable additive to the

24 ¦ coating compositions of this invention has been found to be a I small amount of a polysiloxane polyether copolymer. It has 26 been found, and is the subject of another invention disclosed in 27~ ~ a Cdn. Appl. S.N- 33æ 5~ e~titled 'Improved Silicone Resin 28 I Coating Com~osition" filed ~Vo~en~b~,~ 9,~79 by Robert 29 ' Bruce Frye, that these polysiloxane polyether copolymers prevent the occurrence of undesirable flowmarks and dirtmarks which some-!1 !

times occur with the application of the coating composition onto the substrate. A particularly useful polysiloxane polyether copolymer for the purposes herein is known as SF-106~ and is available from the General Electric Company. The preparation, further description and structural formulae for these polysiloxane polyether copolymers are found in U.S. Patent No. 3,629,165, issued December 21, 1971.
The alkyltriacetoxysilane is used to buffer the basicity of the initial two liquid phase reaction mixture and thereby also temper the hydrolysis rate. While the use of alkyltriacetoxy-silane is preferred herein, glacial acetic acid may be used in its place, as well as other acids such as organic acids like propionic, butyric, citric, benzoic, formic, oxalic and the like. Alkyl-triacetoxysilanes wherein the alkyl group contains from 1 to 6 carbon atoms can be used, alkyl groups having from 1 to 3 carbon atoms being preferred. Methyltriacetoxysilane is most preferred for the purposes herein.
The silanetriols, RSi(OH)3, hereinbefore mentioned, are formed in situ as a result of the admixture of the corresponding trialkoxysilanes with the aqueous medium, i.e., the aqueous dis-persion of colloidal silica. Exemplary trialkoxysilanes are those containing methoxy, ethoxy, isopropoxy and n-butoxy substituents which, upon hydrolysis, generate the silanetriol and further liberate the corresponding alcohol. In this way, at least, a portion of the alcohol content present in the final coating composition is provided. Of course, if a mixture of trialkoxysilanes is employed, as provided for hereinabove, a mixture of different silanetriols, as well as different alcohols, is generated. Upon the generation of the silanetriol or mixtures of silanetriols in the basic aqueous medium, condensation of the hydroxyl substituents to form -Si-O-Si- bonding occurs. This condensation takes place ~ ,. .
~:~ - 7 -. l'' 1 over a period of time and is not an exhaustive condensation but 2 rather the siloxane retains an appreciable quantity of silicon-3 bonded hydroxyl groups which render the polymer soluble in the 4 alcohol-water cosolvent. This soluble partial condensate can be characterized as a siloxanol polymer having at least one silicon-6 bonded hydroxyl ~roup per every three -SiO- units. ', 8 The non-volatile solids portion of the coating compo-9 sition herein is a mixture of colloidal silica and the partial condensate (or siloxanol) of a silanol. The major portion or 11 all of the partial condensate or siloxanol is obtained fro~ the ~l 12 condensation of CH3Si(OH)3 and, depending upon the input of in-13 gredients to the hydrolysis reaction, minor portions of partial 14 condensate can be obtained, for example, from the conden~ation ll Of CH3Si~OH)3 with C2HsSi(OH)3 or C3H7Si(OH)3; CH3Si(OH)3 16 jl with C6H5Si(OH)3, or even mixtures of the foregoing. For opti-17 ll mum results in the cured coating it is preferred to use all 18 1¦ methyltrimethoxysilane (thus generating all monomethylsilane-19 ¦ triol)in preparing the coating compositions herein. In the 20 ll preferred coating co~positions herein the partial condensate is 21 l~ present in an amount of from about 55 to 75 weight percent of 22 ~I the total solids in a cosolvent o alcohol and water, the alco-~3 ii hol comprising from about 50% to 95% by weight of the cosolvent.

25 ~I The coating compositions of this invention will cure

26 on a substrate at temperatures of, for exampie, 120C without

27 the aid of an added curing catalyst. However, in order to em-

28 ploy more desirable milder curing conditions, buffered latent

29 , condensati~n catalysts can be added. Included in this class 3~ l of catalysts are alkali metal salts of carboxylic acids, such ~1 .

~ 9~ 6~ SI 222 ` I :

1 as so~dium acetate, potassium formate and the like. Amine car- !
2 , boxylates, such as dimethylamine acetate, ethanolamine aceta$e, ¦
3 I dimethylaniline formate and the like, quaternary ammonium car- ~!¦
4 '~ boxylates such as tetramethylammonium ace~ate. benzyltrimethyl-. I
ammonium acetate, metal carboxylates, like tin octoate and !
6 l amines such as triethylamine, triethanolamine, pyridine and the ¦
7 i' like are also contemplated curing catalysts herein. Alkali i~
8 !'` hydroxides, like sodium hydroxide and ammonium hydroxide can ;j 9 also be used as curing catalysts herein. ~oreover, typical i commercially available colloidal silica, especially those hav- l ll , ing a basic pH, contain free alkali metal base and alkali metal I
12 , carboxylate catalysts will be genera~ed in situ during the hy-13 ~I drolysis reaction herein. 1~14 1l The amount of curing catalyst can be varied within a ¦
15 ! wi~e range, depending upon the desired curing conditions.
16 i! However, in general, catalyst in the amounts of from about 0.05 17 to about 0.5 weight percent, preferably about 0.1 weight per-18 ,I cent, of the composition can be used. Compositions con~ainingl9 il catalysts in these amounts`can be cured on a solid substrate in !~ a relatively short time at temperatures in the range of from 21 ¦1 about 75~-150~C to provide a transparent abrasion resistant sur-22 l! facecoating~

24 1~ The coating compositions of the present invention can !I be applied to a variety of solid substrates by conventional ! .:
26 ¦! methods, such as flowing, spraying or dipping, to form a con-27 1~ .

30 '' I
ii ' I :
_ g _ 1159~91 60sI 222 , 1 tinuo~s surface film. Substrates which are especially contem-2 plated herein are transparent, as well as non-transparent~plas- .
3 , tics and metals. More particularly, these plastics are syn-4 thetic organic polymeric substrates such as acrylic polymers, like poly(methylmethacrylate), polyesters, such as poly(ethylene 6 terephthalate), poly(butylene terephthalate), etc., polyamides, 7 ~, polyimides, acrylonitrile-styrene copolymers, styrene-acrylo-8 nitrile~butadiene copolymers, polyvinyl.chloride, butyrates, I
9 polyethylene and the like. As noted above, the coating compo- !
sitions of this invention are especially useful as coatings for 11 polycarbonates, such as those polycarbonates known as Lexan~, i 12 ~ sold by General Electric Company. The metal substrates on 13 l which the present protective coatings are utilized include brightj 14 1 and dull metals like aluminum and bright metallized sur~aces likei 1, sputtered chromium alloy. Other solid substrates contemplated 16 ~' herein include wood, painted surfaces, leather, glass, ceramics 17 and textiles .

19 I By choice of the proper formulation, application con-¦ ditions and pretreatment, including the use of primers, of the 21 j substrate, the coatings can be adhered to substantially all 22 ~ solid substrates. A hard coating having all of the aforemen-23 ! tioned characteristics and advantages is obtained by the remo~al 24 I of the solvent and volatile materials. The coating composition ¦ will air-dry to a tack-free condition, but heating in the range 26 .. of 75~C to 200C is necessary to obtain condensation of residual 27 ~ silanols in the partial condensate.. This final cure results in 28 ¦. the formation of silsesq~ioxane (RSiO3/2) In the finished 29 ~ cured coating the ratio of RSiO3/2 units to SiO2 will range from 3~ , about 0.43 to about 9.0, preferably 1 to 3 A cured coating l' !

115~1 60 SI 222 having a ratio of RSiO3/2 to SiO2, where R is methyl, of 2 is most preferred. The coating thickness can be varied by means of the particular application technique, but coatings of about 0.5 to 20 microns, preferably 2-10 micron thickness are generally utilized.
In order that those skilled in the art may better understand how to practice the present invention, the following examples are given by wa~ of illustration and not by way of limitation.
Example 1 22.1 parts by weight of Ludox LS, silica sol (aqueous dispersion of colloidal silica, average particle size of 12 millimicrons, pH of 8.2, sold by duPont) is added to a solution of 0.1 parts by weight of methytriacetoxysilane in 26.8 parts by weight of methyltrimethoxysilane. The temperature of the reaction mixture is maintained at 20C to 30C, preferably below 25C. The hydrolysis is allowed to continue for 24 hours.
The solids content of the resultant reaction mixture is 40.5% and is diluted to about 20% solids with the addi-tion of isobutanol thereto. The pH of the product is about 7.2.
This composition is flow-coated onto a trans-parten Lexan ~ coated (poly)bisphenol-A carbonate)) panel primed with a thermosetting acrylic emulsion.
~fter air drying for 30 minutes the panel is cured for one hour at 120C. After 500 Taber Abraser cycles (500 g. load, CS-lOF wheels) (ANSI-Z26.1-1977 section 5.17) the change in percent haze ( ~%H) is 1.8. The sample passes the cross-hatched adhesion test (DIN-53-151) after 7 days in 65C water. It also passes the cross-hatched adhesion test (DIN-53-151) after 1000 hours under il~9~91 60 SI 222 R-S Lamp exposure on a rotating platform 10" from the faces of an array of 6 lamps arranged at 120 from one another. The platform rotates at about 3 RPM.
Example 2 300 grams of a 30% aqueous colloidal silica dispersion having an average particle size of 20 milli-microns and pH of 9.2 (prepared by dilution of Nalcoag 1050, a product of NALCO Chemical Company) is added to a solution of 0.9 grams glacial acetic acid and 366 grams of methyltrimethoxysilane. The temperature of the reaction mixture is maintained below 30C. The hydrolysis is allowed to continue for 3 days. The solids content of the resultant reaction mixture is 40.5% and is diluted with 419 grams of isopropanol to a final dilution of 25% solids. The pH of the final composition is about 7.5.
This composition (containing 3% of a 3%
solution of tetramethylammonium acetate) is flow-coated on a transparent Lexan ~ panel primed with an ethanol-isobutanol solution containing 1.5 weight percent of gamma-aminopropyltriethoxysilane and 1.5 wt. % of a preformed reaction product of gamma-aminopropyltri-ethoxysilane and maleic anhydride as disclosed in United States Patent 4,246,038 issued January 20, 1981 to Holub and Vaughn. After air drying for 30 minutes the panel is cured for 1 hour at 120C. After 500 Taber Abraser cycles the change in percent haze ( ~ %H) is 1.15.
Example 3 17.9 grams of LudoxTM LS is added to a solution of 0.06 grams of glacial acetic acid in 27.2 grams of methyltrimethoxysilane. The temperature of the reaction ~ 60 SI 222 mixture is maintained below 30C. The hydrolysis is allowed to continue for 6 hours. The solids content is 41.6% and is diluted with 30 grams of isobutanol to a final solids content of 25%. The pH is about 7.2.
The compsoition (containing 3% of a 3% solution of tetramethylammonium acetate) is flow-coated on a transparent Lexan ~ panel primed as in Example 2. After curing, the (~ ~H) of the panel is 1.6.
Obviously, other modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that changes may be made in the particular embodiments described above which are within the full intended scope of the invention as defined in the appended claims.

1~9~1 60 SI 222 Supplementary Disclosure It has further been discovered that the addition of blocks of linear, functionally terminated oligomeric siloxane to the coating compositions of the present invention enhances the crack resistance of the cured coating composition by imparting a greater degree of flexibility to the final, cured resin structure.
Linear, functionally terminated oligomeric siloxanes useful in the practice of the present invention are those represented by the general formula R' ~ R'~ R' t . t ( I) R~ \ R ~n R"
y wherein X is hydroxy, alkoxy, or -N-Y wherein Y is hydrogen or alkyl, R' and R" may be the same or different and are selected from the group consisting of alkyl, haloalkyl, cyanoalkyl and alkenyl and n is from about 1 to about 18, at least 70 weight percent of the silanol being CH3Si(OH)3, said composition containing 10 to 50 weight percent solids, said solids consisting essentially of 10 to 70 weight percent colloidal silica, 30 to 90 weight percent of the partial condensate and 0.5 to 5 weight percent of the functionally terminated oligosiloxane, said composition having a pH from 7.1 to about 7.8.
Typical linear functionally terminated oligosiloxanes useful in the practice of the present invention and encompassed by Formula I hereinabove, include, for example, hydroxy-terminated poly(dimethylsiloxane), methoxy-terminated poly(dimethysiloxane), isopropyl amino-terminated poly(dimethyl-siloxane), hydroxy-terminated poly(methyltrifluoropropyl)siloxane and the like.
The use of these linear functionally terminated oligosiloxanes in amounts of from about 0.5% to about 5% by weight of the total solids content of the coating composition resin will greatly improve the cured resin's crack resistance.
Tests have shown that if the oligomer is cohydrolyzed into the resin, lesser amounts than if the oligomer is blended into the resin, are necessary to provide the improved cracking resistance. In any event, these amounts are within the range described hereinbefore.
Thus, in accordance with the present invention, the aqueous colloidal silica dispersion is added to a solution of a small amount of glacial acetic acid (or an alkyltriacetoxy-silane) in an alkyltrialkoxysilane or aryl trialkoxysilane.
The glacial acetic acid or the alkyltriacetoxysilane is used to buffer the basicity of the initially two liquid phase reaction mixture and thereby also temper the hydrolysis rate.
For the purposes herein, from about 0.07 parts by weight to about 0.1 parts by weight, based on 100 parts by weight of the total composition, of glacial acetic acid or alkyltriacetoxy silane is used. While the use of glacial acetic used or alkyltriacetoxysilane is preferred, other organic acids like propionic, butyric, citric, benzoic, formic, oxalic and the like may be used. Alkyltriacetoxysiloxanes wherein the alkyl group contains from 1 to 6 carbon atoms can be used, alkyl groups having from 1 to 3 carbon atoms being preferred. The temperature of the reaction mixture is maintained at about 20C to about 40C, preferably 20C to about 30C, and most preferably below 25C. In about six to eight hours sufficient ~rialkoxysilane has hydrolyzed so as to reduce the initially two phase liquid mixture to one liquid phase in which the now treated silica (i.e., treated by its admixture with the alkyltrialkoxysilane or aryltrialkoxysilane) is dispersed.
In general, the hydrolysis reaction is allowed to continue for a total of about 12 to 48 hours, preferably about 16 B; - 15 -J

~ i 60 SI 222 hours, depending upon the desired viscosity of the final product.
The more time the hydrolysis reaction is permitted to continue, the higher will be the viscosity of the product. After the h,ydrolysis has been completed to the desired extent, the solids content is adjusted by the addition of alcohol, preferably iso-butanol, to the reaction mixture. The linear functionally terminated oligosiloxane hereinbefore described, is then added to this resin mixture and thoroughly mixed therewith. On the other hand, the oligosiloxane may be added to the hydrolysis mixture before dilution with alcohol or even simultaneously with dilution. To facilitate mixing, the oligosiloxane may be added in solution in alcohol, i.e., generally the same alcohol used to adjust the solids content of the resin. Other suitable alcohols for the purposes herein include lower aliphatic alcohols such as methanol, ethanol, propanol, isopropanol, n-butyl alcohol and t-butyl alcohol. Mixtures of such alcohols can be used, too. The solvent system should contain from about 20 to 75 weight percent alcohol to ensure solubility of the partial condensate (siloxanol). Optionally, additional water-miscible polar solvents, such as acetone, butyl cellosolve and the like in amounts, like up to about 50 weight percent of the co-solvent system can also be used. The solids content of the coating compositions of this invention is generally preferred to be in the range of from about 10 to 25%, most preferably, from about 13 to 22%, by weight of the total composition. The pH of the resultant coating composition is in the range of from about 7.1 to about 7.8, preferably higher than 7.2. If necessary, dilute base, such as ammonium hydroxide ox weak acid, such as acetic acid, can be added to the composition to adjust the final pH to this desired range. At these basic pH's, the compositions are translucent liquids which are stable at room temperature for at least several weeks. When stored at temperatures below about 5C (40F) the period of stability is increased further.
~.~

6~ SI 222 ~5~91 As indicated hereinbefore, the linear functionally terminated oligosiloxane may be incorporated into the resin composition herein by cohydrolyzing the oligomer and the tri-alkoxysilane in the aqueous colloidal silica dispersion. The procedure is generally carried out by adding the aqueous colloidal silica dispersion to a solution of a small amount of glacial acetic acid (or alkyltriacetoxysilane) in the trialkoxy-silane. The hydrolysis conditions used in this embodiment are the same as those described hereinabove.
10The following examples are illustrative only and should not be construed as limiting the scope of the present invention in any manner.
Example 4 The following four formulations are prepared by first blending the silane, the oligomer and acetic acid.
Then the silica sol is added to that solution with good agitation. Theisobutanol is added 24 hours after the silica addition to dilute the reaction mixture to 20~ solids. Amounts of materials are in parts by weight.
Table I

_ B C D
Methyltrimethoxysilane240.6 242.0 240.6 242.0 Glacial Acetic Acid 0.72 0.720.72 0.72 30~ Nalcoag 1050 200 200 200 200 Hydroxyterminated poly-(dimethylsiloxane)* 2.0 1.0 Methoxystopped poly-~imethylsiloxane)** 2.0 1.0 Isobutanol 459 457 459 457 30* degree of polymerization 6-7 (n=4-5) ** degree of polymerization 9.8 to 16.1 (n= 7.8 to 14.1) Each of the above resin solutions is coated and cured on two 9~31 , ~ transparent polycarbonate plaques, one primed with ~ Rhoplex AC-658, thermosetting acrylic emulsion, and the other with 4%
Rhoplex AC-658. The primer is dried at room temperature and cure for 30 minutes at 120C. The silicone resins are dried at room temperature and cured for one hour at 120C. There are no cracks in the cured films. The plaques have a more slippery feel to them than those coated with unmodified resin.
The abrasion resistance is determined by measuring the change in haze with a Gardner haze meter after abrading for 500 cycles on a Taber Abrazer with CS-lOF wheels with a 500g load on each wheel. The change in percent haze is tabulated below.
Table I (Cont'd) /\ % Haze Sample 2% Primer 4% Primer A 4.45 4.2 B 3.0 3.9 C 4.5 4.7 D 4.0 4.2 Control --- 3.95 Rhoplex AC-658 is a product of Rohm & Haas, and is a copolymer of n-butylmethacrylate and methylmethacrylate having hydroxy functionality crosslinked with a substituted melamine, diluted herein to 4% solids by using a mixture of 875 parts by weight distilled water, 470 parts by weight 2-butoxyethanol and 125 parts by weight Rhoplex AC-658. 2% solids is achieved by similar further dilution.
Example 5 A series of 4 coating resins is prepared using the amounts of reactants listed in Table II below. The reactions are conducted by adding the colloidal silica to a stirring solution of the methyltrimethoxysilane, methyltri-acetoxysilane and varying polysiloxane oligomers (when used).
After stirring at ambient temperature for 24 hours, the reaction ~ 991 60 SI 222 mi~ture is diluted with isobutanol to obtain a final solution containing approximately 20% solids by weight. Amounts of materials are in parts by weight.
Table II
A B C D
methyltrimethoxysilane203.4g 202.8g 201.4g 201.lg methyltriacetoxysilane0.74 0.74 0.74 0.74 Ludox LS (12 millimicrons) 166.8 166.8 166.8 166.8 Isobutanol 380 380 380 380 hydroxy terminated poly-(dimethylsiloxane) (n=4-5) 0 0.6 2.0 0.0 methoxy stopped poly(di-methylsiloxane) (n=7.8 to 14.V 0 0.0 0.0 2.0 RS Lamp Induced micro-cracking '~167hrs.~167hrs ~288hrs ~452hrs 120C Oven induced microcracking ~41hrs ~41hrs <166hrs ~177hrs Recoated 2 wks.~ later Abrasion Resistance (~ % lIaze, 500 cycles) 1.7 1.4 1.8 2.3 RS Sunlamp Cracks ~430hrs~ 291hrs ~V485hrs ~v598hrs 120C Oven Cracks rv99hrs~ 99hrs ~V99hrs r~99hrs After standing at room temperature for 3 days, the coatings are filtered and flowcGated (without a flow control agent) onto glass panels. B and C produced smooth coats; D
exhibited some flow marks.
Three weeks later, a flow control agent (SF-1066) is added at 4% by weight of solids and the 4 coatings are applied by flowcoating to 6" x 8" x 1/4" plaques of transparent Lexan~
polycarbonate sheet previously primed with the same thermo-setting acrylic emulsion described in Example 4.
The coated plaques are subject to both a 120C
thermal soak test (in a convection oven) and an accelerated D~ - 19 -sunlight test (exposure to General Electric RS Lamps). All of the test plaques are thoroughly examined several times a week for the first signs of microcracking (using an illuminated magnifier) or loss of scribed adhesion. The data are tabulated above in Table II. Two weeks later, the formulations are coated again as above and retested. In addition, the coatings' abrasion resistance is evaluated. These data also appear in the table.
These experiments demonstrate that cohydrolysis of hydroxy terminated poly(dimethylsiloxane) or methoxy terminated poly(dimethylsiloxane) at 1% of the methyltrimethoxysilane significantly improves crack resistance to RS lamp exposure and the improvement is retained even after 5 weeks of room temperature storage. No adhesion loss occurred during these tests, and the abrasion resistance is excellent.
Example 6 A coating composition containing the same ingredients as the control composition (i.e., that notcontaining the oligosiloxane) in Example 5, and prepared similarly thereto has a tendency to crack slightly when coated and cured on primed Lexa ~ transparent polycarbonate. To a portion of this coating composition is added hydroxy terminated poly(dimethyl-siloxane), n=4-5 at 5~ by weight of solids, and thoroughly blended therewith. The treated and untreated coating compositions are coated as above, cured and examined: the untreated coating produces 1/2" long cracks at the bottom of the placque, the treated coating is crack-free.
The crack-free specimer is subjected to the same tests used in Example 5. It has ~ % H500=~.8, it does not show microcracking till 540 hours of RS lamp exposure, and it remains crack-free after 1220 hours of thermal soak in a 120C oven.
One week later, the same crack-prone resin is treated with various concentrations of hydroxy terminated poly(dimethyl-; ~

siloxane) and tested as before. These results are tabulated below. No adhesion loss is seen during the tests.
Table III
A B C D
*~ligosiloxane 0 1.3~ 2.5% 5.0 as percent of coating solids Appearance 2-3"cracks 1/2"cracks (after cure) crack-free crack-free Microcracking from RS lamps after............... 139 hrs. 293 hrs. 293 hrs. 379 hrs.
Microcracking from 120C
Oven after~......... 43 hrs. 43 hrs. 43 hrs. 888 hrs.

These results demonstrate that adding oligosiloxane to the finished resin at 5% by weight of solids significantly retards the onset of cracking from thermal or sunlamp exposure and prevents initial cracking during cure.
* hydroxyterminated poly(dimethylsiloxane) n=4-5.
Example 7 The same crack prone coating composition as that used in Example 6 is applied to a large panel of Lexa ~ transparent polycarbonate (4'xl'xl/4") primed as in Example 4. Inspection of cured topcoat revealed some cracks in the lower 2' of the panel (it is flow-coated with the 4' dimension as the vertical).
A second panel coated identically except that hydroxy terminated poly(dimethylsiloxane), n=4-5, is added to the resin at 4% the weight of solids (added as a solution in isobutanol to facilitate efficient mixing) is crack-free after cure. Thus, it is seen that the additive can upgrade crack-prone coatings to permit application to even large substrates (where wedging effects can promote cracking).
It has also been discovered that the addition of a thickening agent to the compositions of the present invention s-wi11 realize improved abrasion resistance in cured coating films having coating thicknesses of 3-10 microns, and especially improved abrasion resistance in coatings of about 5 microns thickness. Surprisingly the addition of the thickening agent entails no penalty in loss of the shelf life of the present compositions.
The thickening agent may be added to the coating composition either during hydrolysis or after adjustment of the solids content with alcohol as described hereinbefore in relation to production of the coating composition.
Generally any thickening agent will serve the purpose note herein.
Preferred thickening agents include hydroxypropyl guar gum and hydroxypropyl cellulose. Amounts contemplated are from about 0.1 to about 1%, preferably from about 0.1 to about 0.5% by weight of the total composition.
At low solids content, such as about 13%, it has been found that the polysiloxane polyether copolymers may be employed in the thickened compositions of this invention as flow control additives which assist in the prevention of flowmarks, dirtmarks and the like on the surface of the substrate which is coated. Generally, these polysiloxane polyether copolymers may be employed in amounts of from about 2.5 to about 15% by weight of the total solids of the composition.
In order that those skilled in the art may better understand how to practice the present invention, the following examples are given by way of illustration and not by way of limitation.
Examples 8 - 12 80.1 lbs. of Ludox LS (aqueous colloidal silica dispersion, average particle size of 12 millimicrons, pH 8.2 sold by duPont) is added, over a period of one-half hour, to a solution of 135g of methyltriacetoxysilane in 97.6 lbs. of ~ 60 SI 222 methyltrimethoxysilane. The temperature of the reaction mixture is maintained between 20C and 30C. The hydrolysis is allowed to proceed over a period of sixteen hours. At this time the reaction mixture is diluted wity 182 lbs. of isopropanol.
Aliquots of 500 g. are taken from the resultant diluted reaction mixture resin and to each is added 1.5 g of a thickener. The thickeners are hydroxypropyl cellulose (Klucel M, Types G, H, and J, sold by Hercules Inc.) and hydroxypropyl guar gum. The thickness are added in small portions ~ the well-agitated resin samples. The viscosities of the resins are determined using a calibrated Cannon-FenskeTM
routine type viscometer. The pH of all resins is determined using a CorningTM Model 10 pH meter fitted with a combination pH electrode. The viscosities and pH's are shown in Table IV.
Table IV
Example ThickenerViscosity pH
8 (control -- 5.3 Centistokes 7.4 9 Klucel, Type G14.8 Centistokes 7.35 Klucel, Type H74.2 Centistokes 7.5 11 Klucel, Type J8.8 Centistokes 7.5 12 Hydroxypropyl guar gum20.2 Centistokes 7.4 Plaques of Acrylite FF (extruded transparent acrylic sheet manufactured by Cyro Industries) are dip coated in these five resins at four inches per minute. A sixth acrylic plaque is dip coated in the resin of Example 10 at two inches per minute. All the plaques are allowed to air dry for one-half hour and are then cured at 85C for three hours. The thickness of the cured films is measured by masking the coated plaque with pressure sensitive adhesive tape that is resistant to hydrofluoric acid and the coating is etched away in an unmasked area using hydrofluoric acid. The plaque is rinsed with water. The masking tape is removed and the thickness of the film is ~B-~ 23 ~ 91 60 SI 222 measured using a TalysurfTM surface profile measuring device.
The results are shown in Table V.
Table V
Example Acrylite FF
4"/Min. 2"/Min.
8 (control) 60X10 6 in. --9 9OX10 6 in. --260X10 6 in. 210X10 6 in.
11 6OX10 6 in. --12 120X10 6 in. --Example 13 Pieces of transparent Lexan ~ tpoly(bisphenol-A
carbonate) are primed with a thermosetting acrylic emulsion (Rhoplex 658, sold by Rohm & Haas, a copolymer of n-butyl-methacrylate and methylmethacrylate having hydroxy functionality crosslinked with a substituted melamine, diluted to 4~ solids by using a mixture of 875 parts by weight distilled water, 470 parts by weight 2-butoxyethanol and 125 parts by weight Rhoplex AC 658) allowed to air dry and cured for one-half hour at 120C. They are dip coated in the composition of Example 10 at two and ~ur inches per minute, allowed to dry for one-half hour and cured one hour at 120C. The cured coating thicknesses are measured in the same fashion as described above. The results appear ln Table VI.
Table VI
Primed LexanR Sheet Coated with the composi*ion of Example 10 '4"/Min. 2"/Min.
280X10 6 in. 240X10 6 in.
Other primers may be used such as Rhoplex 1230, also a thermosetting acrylic emulsion sold by Rhom & Haas, or an ethanol-isobutanol solution containing 1.5 weight percent of 5~

1~9~ 60 SI 222 a preformed reaction product of gamma-aminopropyltriethoxysilane and maleic anhydride.
Example 14 Pieces of Acrylite FF are dip coated in the resin compositions of Examples 8, 9 and 10 above at a withdrawal rate of four inches per minute. They are allowed to dry and then cured 2 hours at 90C. These plaques are abraded on a falling sand abraser using 250 ml. of 20-30 mesh silica sand. Per cent haze is measured using a GardnerTM Hazemeter. The change in per cent haze after abrasion is shown in Table VII.
Table VII
Acrylite FF coated with the composition of Example ~ % Haze 8 17.2 9 10.5 5.5 An uncoated sheet of Acrylite FF abraded in the same way has a % haze of 39Ø
Obviously, other modifications and variations of the present invention are possible in the light of the above teachings. For example, additives and other modifying agents, such as pigments, dyes and the like, may be added to the compositions of this invention. It is to be understood, however, that changes may be made in the particular embodiments described above which are within the full intended scope of the invention as defined in the appended claims.

'13

Claims (83)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:

1. An aqueous coating composition comprising a dispersion of colloidal silica in an aliphatic alcohol-water solution of the partial condensate of a silanol of the formula RSi(OH)3, wherein R is selected from the group consisting of alkyl having from 1 to 3 carbon atoms and aryl, at least 70 weight percent of the silanol being CH3Si(OH)3, said composition containing 10 to 50 weight percent solids consisting essentially of 10 to 70 weight percent colloidal silica and 30 to 90 weight percent of the partial condensate, said composition having a pH of 7.1 to about 7.8.

2. A coating composition as defined in Claim 1 wherein the aliphatic alcohol is a mixture of methanol and isobutanol.

3. A coating composition as defined in Claim 1, wherein said partial condensate is of CH3Si(OH)3.

4. A coating composition as defined in Claim 1 containing from about 0.05 to about 0.5 weight percent of a buffered latent silanol condensation catalyst.

5. A coating composition as defined in Claim 4 wherein said catalyst is sodium acetate.

6. A coating composition as defined in Claim 4 wherein said catalyst is tetramethylammonium acetate.

7. A coating composition as defined in Claim 1 wherein the pH is about 7.2 to 7.8.

8. A coating composition as defined in Claim 1 wherein the composition contains from about 18 to 25 weight percent solids consisting essentially of 25-45 weight percent colloidal silica and 55-75 weight percent of the partial condensate.

9. A coating composition as defined in Claim 8 wherein the partial condensate is of CH3Si(OH)3.

10. A coating composition as defined in Claim 1 wherein the composition contains about 20% solids, the partial condensate is of CH3Si(OH)3 and the aliphatic alcohol is a mixture of methanol and isobutanol.

11. An aqueous coating composition prepared by admixing an aqueous colloidal silica dispersion with a solution of an alkyl-triacetoxy silane in an alkyltrialkoxysilane, maintaining the temperature of the admixture at from about 20°C to about 30°C
for a sufficient time to reduce the reaction mixture to one liquid phase, maintaining the pH of the composition in the range of from about 7.1 to about 7.8 , and adjusting the solids content of the reaction mixture by the addition of an aliphatic alcohol thereto.

12. An aqueous coating composition as defined in Claim 11 wherein said alkyltrialkoxysilane is methyltrimethoxysilane, said alkyl(triacetoxy)silane is methyl(triacetoxy)silane and said aliphatic alcohol is isobutanol.

13. An aqueous coating composition as defined in Claim 12 wherein said aqueous colloidal silica dispersion has a basic pH, an average particle size of about 12 microns and an alkali con-tent of about 0.10%.

14. A solid substrate having at least one surface coated with the aqueous coating composition of Claim 1.

15. An article as defined in Claim 14 wherein the solid substrate is comprised of a synthetic organic polymer.

16. An article as defined in Claim 14 wherein said solid substrate is a metal.

17. An article as defined in Claim 14 wherein said solid substrate is a synthetic organic polymer having a metallized surface.

18. An article as defined in Claim 15 wherein said polymer is a transparent polymer,

19. An article as defined in Claim 18 wherein said polymer is a polycarbonate.

20. An article as defined in Claim 19 wherein said poly-carbonate is transparent.

21. An article as defined in Claim 19 wherein said poly-carbonate is a poly(bisphenol-A carbonate).

22. An article as defined in claim 14 wherein the aqueous coating composition has been cured on said surface of said solid substrate.

23. An article as defined in claim 14 wherein said surface of said solid substrate has been primed with a primer composition prior to having been coated with the aqueous coating composition of claim 1

24. An article as defined in claim 23 wherein said primer composition is comprised of a thermosetting acrylic emulsion.

25. An article as defined in claim 23 wherein said primer composition is comprised of an ethanol isobutanol solution containing 1.5 weight percent of gamma-aminopropyltriethoxysilane and 1.5 weight percent of a preformed reaction product of gamma-aminopropyltriethoxysilane and maleic anhydride.

26. An aqueous coating composition comprising a dispersion of colloidal silica, having a particle size of from about 5 to about 150 millimicrons in diameter, in a lower aliphatic alcohol-water solution of the partial condensate of a silanol of the formula RSi(OH)3, wherein R is selected from the group consisting of alkyl having from 1 to 3 carbon atoms and phenyl, at least 70 weight percent of the silanol being CH3Si(OH)3, said composition containing 10 to 50 weight percent solids consisting essentially of 10 to 70 weight percent colloidal silica and 30 to 90 weight percent of the partial condensate, said composition having a pH of 7.1 to about 7.8.

27. An aqueous coating composition as defined in claim 26 wherein the partial condensate is of CH3Si(OH)3 and the lower aliphatic alcohol is a mixture of methanol and isobutanol.

Claims Supported by the Supplementary Disclosure

28. An aqueous coating composition comprising a mixture of colloidal silica, an aliphatic alcohol-water solution of the partial condensate of a silanol of the formula RSi(OH)3, wherein R is selected from the group consisting of alkyl having from 1 to 3 carbon atoms and aryl, and a flexibilizing amount of a linear functionally terminated oligosiloxane having the general formula, wherein X is selected from the group consisting of hydroxy, y alkoxy, and -N-Y wherein Y is hydrogen or alkyl, R' and R" may be the same or different and are selected from the group consisting of alkyl, haloalkyl, cyanoalkyl and alkenyl and n is a number from about 1 to about 18, at least 70 weight percent of the silanol being CH3Si(OH)3, said composition containing 10 to 50 weight percent solids consisting essentially of 10 to 70 weight percent colloidal silica, 30 to 90 weight percent of the partial condensate, and 0.5 to 5 weight percent of said linear functionally terminated oligosiloxane, said composition having a pH of 7.1 to about 7.8.

29. A coating composition as defined in claim 28 wherein the aliphatic alcohol is a mixture of methanol and isobutanol.

30. A coating composition as defined in claim 28 wherein said partial condensate is of CH3Si(OH)3.

31. A coating composition as defined in claim 28 wherein the pH is about 7.2 to 7.8.

32. A coating composition as defined in claim 28 wherein the linear functionally terminated oligosiloxane is selected from the group consisting of hydroxy terminated poly-(dimethylsiloxane) and methoxy terminated poly(dimethylsiloxane).

33. A coating composition as defined in claim 32 wherein the degree of polymerization of the hydroxy terminated poly(dimethylsiloxane) is 6 to 7 and the degree of polymerization of the methoxy terminated poly(dimethylsiloxane) is 9.8 to 16.1.

34. A coating composition as defined in claim 28 wherein the linear functionally terminated oligosiloxane is present in an amount comprising from about 1% to about 5% by weight of the total solids content of the composition.

35. A coating composition as defined in claim 28, wherein the composition contains about 20% solids,the partial condensate is of CH3Si(OH)3, the aliphatic alcohol is a mixture of methanol and isobutanol and the linear functionally terminated oligosiloxane is selected from the group consisting of hydroxy terminated poly(dimethysiloxane) and methoxy terminated poly(dimethysiloxane).

36. An aqueous coating composition prepared by admixing an aqueous colloidal silica dispersion with a solution of alkyltriacetoxysilane or glacial acetic acid in an alkyl-trialkoxysilane, maintaining the temperature of the admixture at from about 20°C to about 30°C for a sufficient time to reduce the reaction mixture to one liquid phase, maintaining the pH
of the composition in the range of from about 7.1 to about 7.8 and to the resultant product thoroughly admixing a flexibilizing amount of a linear functionally terminated oligosiloxane having the general formula.

wherein X isyselected from the group consisting of hydroxy, alkoxy and -N-Y wherein Y is hydrogen or alkyl, R' and R" may be the same or different and are selected from the group consist-ing of alkyl, haloalkyl, cyanoalkyl and alkenyl and n is from about 1 to 18.

37. An aqueous coating composition as defined in claim 36 wherein the solids content of the reaction mixture is adjusted prior to the addition of said oligosiloxane.

38. An aqueous coating composition as defined in claim 36, wherein said linear functionally terminated oligosiloxane is selected from the group consisting of hydroxy terminated poly(dimethylsiloxane) and methoxy terminated poly(dimethylsiloxane).

39. An aqueous coating composition prepared by admixing an aqueous colloidal silica dispersion with a solution of an alkyltriacetoxysilane or glacial acetic acid, a trialkoxysilane and a flexibilizing amount of a linear functionally terminated oligosiloxane having the general formula, wherein X is selected from the group consisting of hydroxy, alkoxy, and -N-Y wherein Y is hydrogen or alkyl, R' and R" may be the same or different and are selected from the group consisting of alkyl, haloalkyl, cyanoalkyl and alkenyl, and n is a number from 1 to 18, maintaining the temperature of the admixture at from about 20°C to about 30°C for a sufficient time to reduce the reaction mixture to one liquid phase, maintaining the pH of the composition in the range of from about 7.1 to 7.8, and adjusting the solids content of the reaction mixture by the addition of an aliphatic alcohol thereto.

40. An aqueous coating composition as defined in claim 39 wherein said trialkoxysilane is an alkyltrialkoxysilane.

41. An aqueous coating composition as defined in claim 39 wherein said linear functionally terminated oligosiloxane is a hydroxy terminated poly(dimethylsiloxane) or a methoxy terminated poly(dimethylsiloxane).

42. A coating composition as defined in claim 41 wherein the degree of polymerization of the hydroxy terminated poly(di-methylsiloxane) is 6 to 7 and the degree of polymerization of the methoxy terminated poly(dimethylsiloxane) is 9.8 to 16.1.

43. A solid substrate having at least one surface coated with the aqueous coating composition of claim 28.

44. An article as defined in claim 43 wherein the solid substrate is comprised of a synthetic organic polymer.

45. An article as defined in claim 43 wherein said solid substrate is a metal.

46. An article as defined in claim 43 wherein said solid substrate is a synthetic organic polymer having a metallized surface.

47. An article as defined in claim 44 wherein said polymer is a transparent polymer.

48. An article as defined in claim 47 wherein said polymer is a polycarbonate.

49. An article as defined in claim 48 wherein said polycarbonate is transparent.

50. An article as defined in claim 48 wherein said polycarbonate is a poly(bisphenol-A carbonate).

51. An article as defined in claim 43 wherein the aqueous coating composition has been cured on said surface of said solid substrate.

52. An article as defined in claim 43 wherein said surface of said solid substrate has been primed with a primer composition prior to having been coated with said aqueous coating composition.

53. An article as defined in claim 52 wherein said primer composition is comprised of a thermosetting acrylic emulsion.

54. An article as definedin claim 44 wherein said polymer is polymethylmethacrylate.

55. An aqueous coating composition comprising a mixture of colloidal silica, an aliphatic alcohol-water solution of the partial condensate of a silanol of the formula RSi(OH)3, wherein R is selected from the group consisting of alkyl having from l to 3 carbon atoms and phenyl, and flexibilizing amount of a linear functionally terminated oligosiloxane having the general formula, wherein X is selected from the group consisting of hydroxy, alkoxy, and -N-Y wherein Y is hydrogen or alkyl, R' and R"
may be the same or different and are selected from the group consisting of alkyl, haloalkyl, cyanoalkyl and alkenyl and n is a number from about l to about 16, at least 70 weight percent of the silanol being CH3Si(OH)3, said composition containing 10 to 50 weight percent solids consisting essentially of 10 to 70 weight percent colloidal silica of from 5 to 150 microns in diameter, 30 to 90 weight percent of the partial condensate, and 0.5 to 5 weight percent of said linear functionally terminated oligosiloxane, said composition having a pH of 7.1 to about 7.8, said aliphatic alcohol being selected from methanol, ethanol, propanol, isopropanol, n-butyl alcohol, t-butyl alcohol or a mixture thereof.

56. An aqueous coating composition prepared by admixing an aqueous colloidal silica dispersion of from 5 to 150 microns in diameter with a solution of alkyltriacetoxysilane or glacial acetic acid in an alkyltrialkoxysilane, wherein alkyl is from 1 to 3 carbon atoms, maintaining the temperature of the admixture at from about 20°C to about 30°C for a sufficient time to reduce the reaction mixture to one liquid phase, maintaining the pH of the composition in the range of from about 7.1 to about 7.8 and to the resultant product thoroughly admixing a flexibilizing amount of a linear functionally terminated oligosiloxane having the general formula, wherein X is selected from the group consisting of hydroxy, alkoxy, and -N-Y wherein Y is hydrogen or alkyl, R' and R" may be the same or different and are selected from the group consisting of alkyl, haloalkyl, cyanoalkyl and alkenyl and n is from about 1 to 18 in an amount at least sufficient to impart enough flexibility to the composition when applied as a coating and cured to resist cracking.

57. An aqueous coating composition prepared by admixing an aqueous colloidal silica dispersion of 5 to 150 microns in diameter with a solution of an alkyltriacetoxysilane, wherein alkyl is from 1 to 3 carbon atoms or glacial acetic acid, a trialkoxysilane wherein alkyl is from 1 to 3 carbon atoms and a flexibilizing amount of a linear functionally terminated oligosiloxane having the general formula, wherein X is selected from the group consisting of hydroxy, alkoxy, and -N-Y wherein Y is hydrogen or alkyl, R' and R"
may be the same or different and are selected from the group consisting of alkyl, haloalkyl, cyanoalkyl and alkenyl, and n is a number from 1 to 18, maintaining the temperature of the admixture at from about 20°C to about 30°C for a sufficient time to reduce the reaction mixture to one liquid phase, maintaining the pH of the composition in the range of from about 7.1 to 7.8, and adjusting the solids content of the reaction mixture by the addition of a lower aliphatic alcohol thereto.

58. An aqueous coating composition comprising a dispersion of colloidal silica in an aliphatic alcohol-water solution of the partial condensate of a silanol of the formula RSi(OH)3, wherein R is selected from the group consisting of alkyl having from 1 to 3 carbon atoms and aryl, at least 70 weight percent of the silanol being CH3Si(OH)3, said composition containing 10 to 50 weight percent solids consisting essentially of 10 to 70 weight percent colloidal silica and 30 to 90 weight percent of the partial condensate, the composition further containing from about 0.1 to about 1 percent by weight of a thickening agent, said composition having a pH of 7.1 to about 7.8.

59. A coating composition as defined in claim 58 wherein said thickening agent is selected from the group consisting of hydroxypropyl guar gum.

60. A coating composition as defined in claim 58, wherein the aliphatic alcohol is a mixture of methanol and isopropanol.

61. A coating composition as defined in claim 58, wherein said partial condensate is of CH3Si(OH)3.

62. A coating composition as defined in claim 58 containing from about 0.05 to about 0.5 weight percent of a buffered latent silanol condensation catalyst.

63. A coating composition as defined in claim 62, wherein said catalyst is sodium acetate.

64. A coating composition as defined in claim 62, wherein said catalyst is tetramethylammonium acetate.

65. A coating composition as defined in claim 58, wherein the pH is 7.2 to about 7.8.

66. A coating composition as defined in claim 58 wherein the composition contains from about 10 to about 25 weight percent solids consisting essentially of 25-45 weight percent colloidal silica and 55-75 weight percent of the partial condensate.

67. A coating composition as defined in claim 66 wherein the partial condensate is of CH3Si(OH)3.

68. A coating composition as defined in claim 58 wherein the composition contains about 20% solids, the partial condensate is of CH3Si(OH)3, the aliphatic alcohol is a mixture of methanol and isopropanol and said thickening agent is selected from the group consisting of hydroxypropyl cellulose and hydroxypropyl guar gum.

69. An aqueous coating composition prepared by admixing an aqueous colloidal silica dispersion with a solution of an alkyltriacetoxysilane in an alkyltrialkoxysilane, maintaining the temperature of the admixture at from about 20°C to about 30°C for a sufficient time to reduce the reaction mixture to one liquid phase maintaining the pH of the composition in the range of from about 7.1 to about 7.8, adjusting the solids content of the reaction mixture by the addition of an aliphatic alcohol thereto and adding a thickening agent to the admixture.

70. An aqueous coating composition as defined in claim 69 wherein said alkyltrialkoxysilane is methyltrimethoxy-silane, said alkyl(triacetoxy)silane is methyl(triacetoxy)silane and said aliphatic alcohol is isopropanol.

71. An aqueous coating composition as defined in claim 70 wherein said aqueous colloidal silica dispersion has a basic pH, an average particle size of about 12 millimicrons and an alkali content of about 0.10%.

72. A solid substrate having at least one surface coated with the aqueous coating composition of claim 58.

73. An article as defined in claim 72 wherein the solid substrate is comprised of a synthetic organic polymer.

74. An article as defined in claim 73 wherein said polymer is a transparent polymer.

75. An article as defined in claim 74 wherein said polymer is a polycarbonate.

76. An article as defined in claim 75 wherein said polycarbonate is transparent.

77. An article as defined in claim 75 wherein said polycarbonate is a poly(bisphenol-A carbonate).

78. An article as defined in claim 73 wherein said polymer is a polymethylmethacrylate.

79. An article as defined in claim 78 wherein said polymethylmethacrylate is transparent.

80. An article as defined in claim 72 wherein the aqueous coating composition has been cured on said surface of said solid substrate.

81. An article as defined in claim 72 wherein said surface of said solid substrate has been primed with a primer composition prior to having been coated with said aqueous coating composition.

82. An article as defined in claim 81 wherein said primer composition is comprised of a thermosetting acrylic emulsion.

83. An article as defined in claim 81 wherein said primer composition is comprised of an ethanol-isobutanol solution containing 1.5 weight percent of gamma-aminopropyltriethoxysilane and 1.5 weight percent of a preformed reaction product of gamma-aminopropyltriethoxysilane and maleic anhydride.