Hard coating compositions

A hard coating composition comprising an organic silicon compound and inorganic submicron particles such as silica sol and antimony oxide sol is improved in curing properties and shelf stability by blending aluminum perchlorate as the curing catalyst.

This invention relates to hard coating compositions suitable for forming a 
coating layer having mar resistance, high hardness, and chemical 
resistance, that is, a hard coating film on plastic articles, typically 
optical articles such as plastic lens. 
BACKGROUND OF THE INVENTION 
Plastic optical articles are generally characterized by light weight, ease 
of processing and impact resistance. In the prior art, various coatings 
were used on such plastic optical articles for the purpose of imparting 
mar resistance and solvent resistance thereto. One such coating is 
proposed in Japanese Patent Publication No. 2735/1982 as a composition 
comprising an epoxy group-containing silicon compound, colloidal silica, 
and aluminum chelate. This composition has a problem that the coating film 
can be colored upon curing at high temperatures of 110.degree. C. or 
higher since the amount of aluminum chelate added is as large as 5 to 10% 
by weight based on the resin solids. In addition, boiling immersion causes 
the coating film to lower its hardness and sometimes peel away from the 
substrate. 
Another coating composition is disclosed in Japanese Patent Publication No. 
9266/1987 as comprising an epoxy group-containing silicon compound, 
colloidal silica, and ammonium perchlorate. This coating liquid is 
unstable and prone to a color change. 
Japanese Patent Application Kokai Nos. 30361/1978 and 46502/1985 disclose 
the use of perchloric acid and magnesium perchlorate as the curing 
catalyst for similar coating compositions. The strong acidity of these 
catalysts causes the coating liquids to show a substantial change with the 
lapse of time. The silanol resulting from hydrolysis of an epoxy 
group-containing silicon compound can undergo poly-condensation in the 
presence of these acidic catalysts to soften the cured coating. 
Still further coating compositions may be prepared from acidic colloidal 
silica and an organic silicon compound. The compositions may be cured with 
phosphoric acid, organic carboxylic acids, chromic acid, bromic acid, 
perchloric acid, aluminic acid, thiosulfuric acid or salts thereof. These 
coating liquids are too acidic as pH 1 or 2 and unstable. 
SUMMARY OF THE INVENTION 
Therefore, an object of the present invention is to provide a hard coating 
composition which has improved curing properties and shelf stability and 
which can form a hard coating film having high hardness, mar resistance, 
solvent resistance, and improved adherence without coloring upon curing. 
According to the present invention, there is provided a hard coating 
composition comprising in admixture, 
(A) an organic silicon compound of the formula: 
EQU R.sup.1.sub.a Si(OR.sup.2).sub.4-a ( 1) 
wherein R.sup.1 is selected from the class consisting of epoxy containing 
organic groups having 2 to 8 carbon atoms, alkyl groups having 1 to 6 
carbon atoms, alkenyl groups having 2 to 6 carbon atoms, halo-alkyl groups 
having 1 to 6 carbon atoms, and aryl groups having 6 to 10 carbon atoms, 
R.sup.2 is selected from the class consisting of hydrogen, alkyl groups 
having 1 to 4 carbon atoms, alkoxyalkyl groups having 2 to 8 carbon atoms, 
and acyl groups, and 
letter a is equal to 1, 2 or 3, or a partial hydrolysate thereof, 
(B) inorganic submicron particles, and 
(C) aluminum perchlorate. 
The inventors have found that by blending aluminum perchlorate in a hard 
coating composition comprising an organic silicon compound of formula (1) 
or a partial hydrolysate thereof and inorganic submicron particles such as 
antimony oxide sol, silica sol, titania sol, and alumina sol, curing of 
the organic silicon compound can be significantly promoted while 
minimizing coloring upon curing. The resulting coating film has high 
hardness, mar resistance, and solvent resistance, that is, improved 
properties as hard coatings. Particularly when a colloidal oxide which has 
been treated with a basic material or stabilized under basic conditions as 
the preferred inorganic submicron particles is reacted with the organic 
silicon compound, the resulting coating liquid can be neutralized to pH 2 
to 6.5 with acidic aluminum perchlorate having high curing ability. The 
coating liquid is then improved in shelf stability. 
DETAILED DESCRIPTION OF THE INVENTION 
Component (A) constructing the hard coating composition of the invention is 
a component contributing to film formation and adsorption of organic dyes. 
It is an organic silicon compound of the formula: 
EQU R.sup.1.sub.a Si(OR.sup.2).sub.4-a ( 1) 
wherein R.sup.1 is selected from the class consisting of epoxy containing 
organic groups having 2 to 8 carbon atoms, alkyl groups having 1 to 6 
carbon atoms, alkenyl groups having 2 to 6 carbon atoms, halo-alkyl groups 
having 1 to 6 carbon atoms, and aryl groups having 6 to 10 carbon atoms; 
R.sup.2 is selected from the class consisting of hydrogen, alkyl groups 
having 1 to 4 carbon atoms, alkoxyalkyl groups having 2 to 8 carbon atoms, 
preferably 2 to 6 carbon atoms, and acyl groups; and letter a is equal to 
1, 2 or 3, or a partial hydrolysate thereof. The alkoxyalkyl group 
represented by R.sup.2 has the formula: R.sup.3 OR.sup.4 -- wherein 
R.sup.3 is an alkyl group having 1 to 4 carbon atoms and R.sup.4 is an 
alkylene group having 1 to 4 carbon atoms, for example, CH.sub.3 OC.sub.2 
H.sub.4, C.sub.2 H.sub.5 OC.sub.2 H.sub.4, C.sub.3 H.sub.7 OC.sub.2 
H.sub.4, and CH.sub.3 OC.sub.3 H.sub.6. 
Examples of the substituent represented by R.sup.1 in formula (1) include 
glycidoxypropyl, epoxycyclohexylethyl, methyl, ethyl, propyl, 
3-chloropropyl, 3,3,3-trifluoropropyl, vinyl, allyl, butyl, and phenyl 
groups. Examples of the substituent represented by R.sup.2 include a 
hydrogen atom, methyl, ethyl, propyl, butyl, methoxymethyl, methoxyethyl, 
ethoxyethyl, acetyl, and propionyl groups. 
Illustrative, non-limiting examples of the organic silicon compound of 
formula (1) include: 
3-glycidoxypropyltrimethoxysilane, 
3-glycidoxypropyltriethoxysilane, 
3-glycidoxypropylmethyldimethoxysilane, 
3-glycidoxypropylmethyldiethoxysilane, 
2-(3',4'-epoxycyclohexyl)ethyltrimethoxysilane, 
2-(3',4'-epoxycyclohexyl)ethyltriethoxysilane, 
methyltrimethoxysilane, 
methyltriethoxysilane, 
vinyltrimethoxysilane, 
vinyltriethoxysilane, 
dimethyldimethoxysilane, 
dimethyldiethoxysilane, 
vinyltris(2-ethoxyethoxy)silane, 
vinylmethyldimethoxysilane, 
vinylmethyldiethoxysilane, 
phenyltrimethoxysilane, 
phenyltriethoxysilane, 
phenylmethyldimethoxysilane, 
phenylmethyldiethoxysilane, 
phenylvinyldimethoxysilane, 
phenylvinyldiethoxysilane, 
diphenyldimethoxysilane, 
diphenyldiethoxysilane, etc. 
The organic silicon compounds may be used alone or in admixture of two or 
more. 
The organic silicon compound may be used as such although it may be 
previously hydrolyzed into a partial hydrolysate which is more preferred 
as component (A). 
Component (A) as described above is generally dissolved in an organic 
solvent to form a coating composition. Examples of the suitable organic 
solvent include alcohols such as methanol, ethanol, isopropyl alcohol, 
(iso)butanol, and diacetone alcohol, ketones such as acetone, methyl ethyl 
ketone, and methyl isobutyl ketone, esters such as ethyl acetate, 
(iso)propyl acetate, and (iso)butyl acetate, and cellosolves such as 
methyl cellosolve, ethyl cellosolve, cellosolve acetate, propyl 
cellosolve, and butyl cellosolve. 
The hard coating composition of the invention may contain an optional 
component in addition to component (A). The optional component may include 
3-methacryloxypropyl trimethoxysilane, 
3-methacryloxypropylmethyldimethoxysilane, 
3-mercaptopropyltrimethoxysilane, methyl silicate, ethyl silicate, and the 
like. The optional component may be added in any desired amount, 
preferably less than 100 parts by weight per 100 parts by weight of the 
silane of formula (1) or a partial hydrolysate thereof. 
Component (B) constructing the hard coating composition of the invention is 
a submicron particulate inorganic material which contributes to the 
hardness of the resulting coating film. The submicron particulate 
inorganic material is preferably selected from antimony oxide sol, silica 
sol, titania sol, alumina sol, and a mixture of two or more of them. The 
particles preferably have a particle size of from about 1 to about 200 
m.mu., more preferably from about 5 to about 100 m.mu.. Inorganic 
particles of smaller than 1 m.mu. in size would be less effective in 
increasing the surface hardness of the coating film whereas particles of 
larger than 200 m.mu. would detract from the clarity of the coating film. 
The refractive index of the coating film can be adjusted in the range 
between 1.50 and 1.65 so as to match with that of the substrate when 
antimony oxide sol or titania sol is used as component (B). 
For the inorganic submicron particles, commercially available colloidal 
solutions having inorganic submicron particles dispersed in water or 
organic solvents may be used. The organic solvents used herein include 
alcohols such as methanol, ethanol, propanol, isopropyl alcohol, butanol, 
isobutanol, and diacetone alcohol, cellosolves such as methyl cellosolve, 
ethyl cellosolve, and butyl cellosolve, and amides such as 
N,N-dimethylformamide. 
Preferably the inorganic submicron particles have been treated with a basic 
material or stabilized under basic conditions because the coating 
composition becomes more stable. The basic materials used herein include 
sodium hydroxide, sodium oxide, potassium hydroxide, sodium carbonate, 
sodium hydrogen carbonate, triethylamine, tributylamine, ammonia, 
triethanolamine, tributanolamine and the like. These treatments may be 
effected by adjusting the pH of the sol solution to the range between 6 
and 9. These treatments include neutralizing commercially available 
ordinary hydrochloric acid-acidified sols (pH 2-5) with the 
above-mentioned basic materials; hydrolyzing metal alkoxides in the 
presence of acidic catalysts such as hydrochloric acid, phosphoric acid, 
acetic acid, methanesulfonic acid, p-toluenesulfonic acid, and sulfuric 
acid and neutralizing the resulting sols with the above-mentioned basic 
materials to pH 6-9; and neutralizing sodium salts (e.g., sodium silicate) 
with hydrochloric acid to form metal oxide sols stable at pH 6-9. Examples 
of the inorganic submicron particles which have been treated with a basic 
material or stabilized under basic conditions include an antimony oxide 
sol obtained by treating sodium antimonate with hydrochloric acid and 
neutralizing the resulting agglomerate with triethanol amine, as well as a 
silica sol which is stabilized to a weak basicity with residual sodium 
oxide. More particularly, the antimony oxide sol is obtained by treating 
sodium antimonate (Na.sub.2 O.Sb.sub.2 O.sub.5.6H.sub.2 O) with 
hydrochloric acid at pH 1 or lower, adding water and triethanolamine to 
the resulting slurry, and heating the slurry into a colloidal sol which is 
stable at pH 6-8. 
The amount of component (B) blended preferably ranges from 5 to 200 parts 
by weight, more preferably from 20 to 150 parts by weight per 100 parts by 
weight of component (A), provided that component (B) is calculated as 
inorganic submicron particle solids. Less than 5 parts by weight of 
component (B) is less desirable in forming a fully hard coating whereas 
more than 200 parts by weight of component (B) is likely to form a brittle 
coating having a poor covering power. 
Component (C) is a curing catalyst for curing a mixture of components (A) 
and (B). According to the present invention, aluminum perchlorate is used 
for the stability of the coating composition as well as the hardness, 
anti-yellowing, moisture resistance, and curing properties of the 
resulting hard coating film. The aluminum perchlorate may be selected from 
commercially available ones in any desired form including hydrate and 
partial hydroxide forms. One preferred form is the hexahydrate 
Al(ClO.sub.4).sub.3.6H.sub.2 O. 
The amount of component (C) or aluminum perchlorate added is an effective 
amount to adjust the coating composition to pH 2 to 6.5, more preferably 3 
to 5 so that the composition may be improved in shelf stability. 
Preferably Al(ClO.sub.4).sub.3.6H.sub.2 O is added in such an amount as to 
adjust the coating composition to pH 2.5 to 5.5 because the silanol is 
stabilized. The effective amount preferably ranges from 0.1 to 10 parts by 
weight, more preferably from 0.2 to 5 parts by weight per 100 parts by 
weight of component (A). Less than 0.1 part by weight of aluminum 
perchlorate would be too small to promote the curing of a coating 
composition whereas the presence of more than 10 parts by weight of 
aluminum perchlorate would render the coating composition too acidic to 
below pH 2 to maintain the composition stable. 
Any of various well-known additives may be added to the hard coating 
composition of the invention for the purposes of increasing the adhesion 
of the composition to substrates such as plastics and improving the 
weatherability, applicability, and glare protection of the composition. 
Examples of the useful additives which can be blended in the hard coating 
composition include epoxy resins, for example, polyolefinic epoxy resins, 
cyclohexene oxide, polyglycidyl esters, polycondensates of epichlorohydrin 
and bisphenol-A, and copolymers of glycidyl methacrylate and an acrylic 
compound in amounts of up to 30 parts by weight per 100 parts by weight of 
component (A). Addition of more than 30 parts of epoxy resin will result 
in a soft coating having substantially reduced weatherability. UV 
absorbers such as benzophenones, benzotriazoles, and phenols may be 
blended in the composition in amounts of up to 20 parts by weight per 100 
parts by weight of component (A). Addition of more than 20 parts of UV 
absorbers will reduce the hardness of the coating. Various surface-active 
agents may also be blended in the composition in amounts of up to 10 parts 
by weight per 100 parts by weight of component (A) for the purpose of 
improving the applicability thereof, for example, block and graft 
copolymers of dimethylsiloxane and polyether, and fluoride surface-active 
agents. Addition of more than 10 parts of surface-active agent will 
adversely affect the adherence of the coating to a substrate. 
The hard coating composition of the invention may be prepared by mixing 
components (A) and (B) and an optional additive or additives, aging the 
mixture, and then adding component (C) to the mixture. Particularly when 
it is desired to use a partial hydrolysate of an organic silicon compound 
as component (A), the composition is prepared by first adding pure water 
or an acidic aqueous solution of hydrochloric acid or acetic acid to 
monomeric component (A) in admixture with an optional additive or 
additives for hydrolysis, and then adding components (B) and (C) to the 
partial hydrolysate. It is also possible to utilize the basic material 
often available along with component (B) for the hydrolysis of component 
(A). 
The hard coating composition of the invention may be based on a solvent, 
for example, alcohols, ketones, esters, and cellosolves, preferably lower 
alcohols such as methanol, ethanol, isopropanol, butanol, isobutanol, and 
diacetone alcohol, and cellosolves such as methyl cellosolve, ethyl 
cellosolve, cellosolve acetate, and butyl cellosolve. Also useful are 
mixtures of these solvents with other ester, ketone, and aromatic 
solvents. Examples of the ester solvent include ethyl acetate, (iso)propyl 
acetate, and (iso)butyl acetate, examples of the ketone solvent include 
acetone, methyl ethyl ketone, and methyl isobutyl ketone, and examples of 
the aromatic solvent include benzene, toluene, xylene, and ethylbenzene. 
The hard coating composition of the invention may be advantageously applied 
to various plastic materials as well as other substrates. The plastic 
materials to which the composition is applicable are not particularly 
limited. Better results are obtained when it is applied to polymethyl 
methacrylate, polycarbonate, polystyrene, polyesters, modified acrylic 
resins, diethylene glycol bisallylcarbonate (trade name: CR-39), and 
urethane resins, to name a few. The hard coating composition of the 
invention may be applied to a plastic material substrate, typically 
plastic optical article and heat treated into a protective coating film 
having a high hardness. It may be applied by any desired conventional 
techniques including brush coating, roll coating, spray coating, flow 
coating, dipping, and spin coating. The curing conditions will vary with 
the amount of curing catalyst blended and other factors. Usually, a cured 
coating film can be obtained by heating the coating to a temperature below 
the softening point of the plastic substrate, typically 80.degree. to 
150.degree. C. for about 1/2 to about 5 hours. 
The cured coating film resulting from the composition of the invention may 
be dyed with disperse dyes. For a particular disperse dye, dyeing 
conditions including the concentration, temperature, and time may be 
determined without undue experimentation. In general, the coating film is 
dyed by immersing in a dye bath containing about 0.1 to 1% by weight of a 
dye in water at about 80.degree. to 100.degree. C. for about 5 to 15 
minutes.

EXAMPLE 
Examples of the present invention are given below by way of illustration 
and not by way of limitation. 
EXAMPLES 1-3 
Into a flask were admitted 100 grams of 3-glycidoxypropyltrimethoxysilane, 
125 grams of 3-glycidoxypropylmethyldiethoxysilane, and 80 grams of 
isobutyl alcohol. With stirring under ice cooling, 38 grams of 0.05N 
dilute hydrochloric acid water was added dropwise over 30 minutes. After 
300 grams of inorganic submicron particles shown in Table 1 (a water or 
methanol dispersion having 30% by weight of non-volatile values) were 
added to the mixture, the mixture was aged for 16 hours at 20.degree. C. 
Then 50 grams of ethanol and 70 grams of ethyl cellosolve were added to 
the mixture, and aluminum perchlorate hexahydrate was finally added in the 
amount shown in Table 1, obtaining a coating liquid. This coating liquid 
was applied to an alkali treated plastic lens of CR-39 by dipping and then 
cured at 120.degree. C. for 60 minutes. 
For comparison purposes, coating liquids were prepared by the same 
procedure as above except that aluminum acetyl acetonate and ammonium 
perchlorate were used instead of the aluminum perchlorate. They were 
applied and cured to plastic lens by the same procedure as above. 
The hard coating films obtained were examined by the following methods. 
Separately, the respective coating liquids were examined for shelf 
stability by the following method. 
Shelf Stability 
The coating liquid was shelf stored for one month at 25.degree. C. The 
shelf stability was evaluated in terms of a change of viscosity before and 
after shelf storage. 
Mar Resistance 
The coating was rubbed 10 strokes with #000 steel wool under a load of 500 
grams and visually examined for mars. 
Adhesion 
A scribed adhesion test was carried out according to JIS K-5400, item 6.15. 
The coating was scribed with a knife to form a grid of 11 horizontal cuts 
and 11 vertical cuts all spaced 1 mm. An adhesive tape (manufactured by 
Nichiban K.K.) was applied and stripped to and from the scribed area. The 
number of remaining sections was counted. 
Solvent Resistance 
The coating was lightly wiped 100 times with acetone-impregnated absorbent 
cotton and visually examined for clarity. 
Coloring 
The cured coating was visually examined for color. 
Dyeability 
The CR-39 lens having the coating applied thereon was immersed for 5 
minutes in an aqueous solution containing 0.2% by weight of disperse dye 
Brown D (manufactured by Seiko K.K.) at 86.degree. C. The light 
transmittance of the lens was measured. 
Dyeability After Aging 
The coating liquid was shelf stored for one month at 25.degree. C. before 
it was applied and cured to CR-39 lens. The coated lens was tested in the 
same manner as the "Dyeability" test. 
TABLE 1 
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Comparative 
Comparative 
Example 1 
Example 2 
Example 3 
Example 1 
Example 2 
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Components 
Submicron particles 
Sb.sub.2 O.sub.5 *.sup.1 
Sb.sub.2 O.sub.5 *.sup.1 
SiO.sub.2 *.sup.2 
SiO.sub.2 *.sup.3 
SiO.sub.2 *.sup.3 
Curing catalyst 
Al(ClO.sub.4).sub.3.6H.sub.2 O 
Al(acac).sub.3 *.sup.4 
NH.sub.4 ClO.sub.4 
Amount (g) 8 2 8 15 3 
Coating Liquid 
pH 3.0 6.0 3.0 3.5 3.0 
Shelf stability 
no change 
no change 
no change 
slightly 
slightly 
thickened 
thickened 
Coating Film 
Refractive index @ 25.degree. C. 
1.58 1.58 1.48 1.48 1.48 
Mar resistance 
OK OK OK OK OK 
Adhesion 100/100 
100/100 
100/100 
100/100 
100/100 
Solvent resistance 
OK OK OK OK OK 
Coloring OK OK OK yellowed 
yellowed 
Dyeability (%) 
88 85 82 85 89 
Dyeability 83 76 56 71 68 
after aging (%) 
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*.sup.1 sol treated with 2% by weight of triethanol amine (methanol 
solution) 
*.sup.2 sol having 0.3% by weight of Na.sub.2 O left therein (aqueous 
solution at pH 9) 
*.sup.3 acidic methanol silica sol (methanol solution at pH 3) 
*.sup.4 aluminum acetylacetonate 
There has been described a hard coating composition which has improved 
curing properties and shelf stability. The composition is cured into a 
hard coating film having high hardness, mar resistance, and solvent 
resistance. The film firmly bonds to the underlying material and undergoes 
no yellowing. The refractive index of the coating film can be adjusted in 
the range between 1.50 and 1.65 so as to match with that of the substrate 
when antimony oxide sol or titania sol is used as component (B), allowing 
the coating film to cover various substrates having different refractive 
indexes without producing an interference band. 
Although some preferred embodiments have been described, many modifications 
and variations may be made thereto in the light of the above teachings. It 
is therefore to be understood that within the scope of the appended 
claims, the invention may be practiced otherwise than as specifically 
described.