The present invention provides a curable polymethylsilsesquioxane composition that uses polymethylsilsesquioxane obtained from inexpensive precursors and that provides a hard, scratch-resistant, highly corrosion-resistant, water-repellent, and transparent cured film. The curable polymethylsilsesquioxane composition of the invention includes a polymethylsilsesquioxane having the general formula EQU (CH.sub.3 SiO.sub.3/2).sub.n (CH.sub.3 Si(OH)O.sub.2/2).sub.m and a predetermined number-average molecular weight, Mn, from 380 to 2,000, wherein m and n are positive numbers that provide the predetermined Mn, with the proviso that the value of m/(m+n) is less than or equal to 0.152/(Mn.times.10.sup.-3)+0.10 and greater than or equal to 0.034/(Mn.times.10.sup.-3) and 10 to 250 weight parts colloidal silica.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to generally to curable coating compositions 
and more particularly to a curable polymethylsilsesquioxane composition 
that provides a highly water-repellent and strongly corrosion-resistant 
cured film. 
2. Description of the Prior Art 
Silicone resins that contain 1.5 oxygen atoms per silicon atom are 
generically known as polysilsesquioxanes. The polysilsesquioxanes are 
highly heat resistant and exhibit good electrical insulation properties 
and flame retardancy. Because of these properties, polysilsesquioxanes 
have been used as resist materials and interlayer dielectric films in 
semiconductor fabrication (see, among others, "Shirikoon Handobukku" 
(English title: Silicone Handbook), edited by Kunio Itoh, published by 
Nikkan Kogyo Shinbunsha (1990)). 
Methods are already known for the synthesis of polymethylsilsesquioxane. 
For example, polymethylsilsesquioxane can be synthesized by dissolving 
methyltrichlorosilane in the presence of amine in a single solvent or 
mixture of solvents selected from ketones and ethers, adding water to this 
system dropwise to effect hydrolysis, and then heating to effect 
condensation (see Japanese Patent Publication (Kokoku) Numbers Sho 
60-17214 (17,214/1985) and Hei 1-43773 (43,773/1989) and U.S. Pat. No. 
4,399,266). Another synthesis example is taught in EP 0 406 911 A1. This 
reference teaches the dissolution of a trifunctional methylsilane in 
organic solvent; 
then hydrolysis by the dropwise addition of water to this solution at a 
temperature from -20.degree. C. to -50.degree. C. under an inert gas 
pressure of 1,000 to 3,000 Pa; and thereafter condensation by heating. Yet 
another synthesis example is disclosed in Japanese Patent Application Laid 
Open (Kokai or Unexamined) Number Hei 3- 20331 (20,331/1991). This 
reference teaches the reaction in organic solvent of 
methyltriacetoxysilane with an equivalent amount of alcohol and/or water 
to synthesize the alkoxyacetoxysilane; polycondensation of the 
alkoxyacetoxysilane in organic solvent in the presence of sodium 
bicarbonate to give a prepolymer; and condensation of this prepolymer by 
heating in the presence of at least 1 catalyst selected from the alkali 
metal hydroxides, alkaline-earth metal hydroxides, alkali metal fluorides, 
alkaline-earth metal fluorides, and triethylamine. Yet another synthesis 
example is found in Japanese Patent Application Laid Open (Kokai or 
Unexamined) Number Hei 3-227321 (227,321/1991). This reference teaches the 
dissolution of alkali metal carboxylate and lower alcohol in a mixed 
liquid system that forms two phases (water and hydrocarbon solvent); the 
dropwise addition of methyltrihalosilane into this system to effect 
hydrolysis; and condensation by heating. 
The polymethylsilsesquioxanes afforded by these methods share a 
characteristic feature: they are hard but brittle. Some of the preceding 
references even include tactics for addressing this problem. Japanese 
Patent Publication (Kokoku) Number Hei 1-43773 instructs regulating the 
fraction with molecular weight.ltoreq.20,000 (molecular weight as 
determined by gel permeation chromatography (GPC) calibrated with 
polystyrene standards) to 15 to 30 weight % of the 
polymethylsilsesquioxane. However, even this does no more than enable the 
preparation of coatings with thicknesses of about 1.8 to 2.0 .mu.m. 
Similarly, the technology in EP 0 406 911 A1 can only provide films with 
maximum thicknesses of 3 to 3.5 .mu.m without cracking. At larger film 
thicknesses cracking occurs, and of course the flexibility that would 
permit the fabrication of an independent film is absent. 
We have already discovered (see Japanese Patent Application Numbers Hei 
7-208087 (208,087/1995) and Hei 7-208143 (208,143/1995)) that a coating 
that combines flexibility with high heat resistance is provided by the 
cure of a polymethylsilsesquioxane having a molecular weight and hydroxyl 
content in specific ranges and preferably prepared by a special method. 
Japanese Patent Application Laid Open (Kokai or Unexamined) Number Sho 
51-2736 (2,736/1976) discloses the dispersion of waterborne colloidal 
silica in a water-lower aliphatic alcohol solution of the partial 
condensate of RSi(OH).sub.3. However, this cannot be applied to steel 
sheet, etc., due to its acidity (pH=3 to 6). Moreover, the water 
repellency of the corresponding cured film is not high enough, as will be 
shown below in a comparative example. 
Japanese Patent Publication (Kokoku) Number Sho 62-55554 (55,554/1987) 
discloses a waterborne coating composition with a pH of 7.1 to 7.8. This 
is a dispersion of waterborne colloidal silica in a water-aliphatic 
alcohol solution of the partial condensate of RSi(OH).sub.3. However, this 
reference makes no mention of the water repellency. 
A coating originating from a composition containing organotrialkoxysilane 
and acidic colloidal silica (waterborne) is disclosed in Japanese Patent 
Application Laid Open (Kokai or Unexamined) Number Hei 5-163463 
(163,463/1993). Other essential components in this composition are 
additional organotrialkoxysilane, alcohol, and pigment. While this coating 
is reported to have an excellent hardness, water resistance, resistance to 
staining, aging resistance, and so forth, its water repellency (contact 
angle versus water) and processability (flexibility) are not elucidated 
and of course it is not transparent since it contains pigment. 
Highly water-repellent coatings can be obtained by providing the coating 
surface with a microfine irregularity or roughness through the addition of 
relatively large particles with diameters in excess of 1 .mu.m, as 
disclosed in, for example, Japanese Patent Application Laid Open (Kokai or 
Unexamined) Number Hei 3-244679 (244,679/1991). However, due to the 
presence of large particles whose size exceeds the thickness of the film 
itself, the physical properties of the film, such as hardness and 
processability, are poor, and of course the film is again not transparent. 
Fluorocarbon resins do provide transparent and water-repellent films, but 
these films generally have a low surface hardness and thus do not always 
have a good staining resistance. These resins are also expensive. 
SUMMARY OF THE INVENTION 
The object of the present invention is to provide a curable 
polymethylsilsesquioxane composition that uses polymethylsilsesquioxane 
obtained from inexpensive precursors and that provides a highly 
corrosion-resistant, highly water-repellent, and transparent cured film 
and does so while maintaining the physical properties required of a 
coating, such as surface hardness and processability. 
The present inventors have discovered that the combination of colloidal 
silica (wherein primary particle diameter is approximately 10 nm) and 
polymethylsilsesquioxane, with a molecular weight and hydroxyl content in 
specific ranges--and preferably prepared by a special method--yields a 
highly corrosion-resistant, highly water-repellent, and transparent cured 
film and does so while maintaining the physical properties required of a 
coating, such as surface hardness and processability. 
The polymethylsilsesquioxane of the present invention has a predetermined 
number-average molecular weight, Mn, from 380 to 2,000, as determined by 
gel permeation chromatography calibrated with polystyrene standards. The 
polymethylsilsesquioxane of the invention is represented by the general 
formula 
EQU (CH.sub.3 SiO.sub.3/2).sub.n (CH.sub.3 Si(OH)O.sub.2/2).sub.m 
wherein m and n are positive numbers that provide the predetermined Mn, 
with the proviso that the value of m/(m+n) is less than or equal to 
0.152/(Mn.times.10.sup.-3)+0.10 and greater than or equal to 
0.034/(Mn.times.10.sup.-3). Hence, the boundary conditions for the 
polymethylsilsesquioxane of the invention can be graphically illustrated 
with equations (1) through (4), as set forth in FIG. 1.

DETAILED DESRIPTION OF THE INVENTION 
The curable polymethylsilsesquioxane of the invention comprises the 
combination of a polymethylsilsesquioxane of the general formula (CH.sub.3 
SiO.sub.3/2).sub.n (CH.sub.3 Si(OH)O.sub.2/2).sub.m and colloidal silica 
in an amount from 5 to 250 weight parts per 100 weight parts of the said 
polymethylsilsesquioxane. 
When the number average molecular weight, Mn, of the 
polymethylsilsesquioxane falls outside the range given above, or when the 
silanol content (CH.sub.3 Si(OH)O.sub.2/2).sub.m exceeds the upper limit 
given above, cracking readily occurs in the cured product. When the 
silanol content falls below the lower limit given above, the curability of 
the product is inadequate. 
The polymethylsilsesquioxane used in the formulation of the present 
invention has a molecular weight and silanol content in the 
above-specified ranges. It is preferably prepared by hydrolyzing a 
methyltrihalosilane MeSiX.sub.3 (wherein Me is methyl and X is a halogen 
atom selected from the group consisting of F, Cl, Br, and I) and 
condensing the resulting hydrolysis product, wherein the preparation is 
run in a two-phase system of water and solvent selected from the group 
consisting of 
(a) oxygenated organic solvents and 
(b) a mixture of oxygenated organic solvent and at least one hydrocarbon 
solvent, provided that the mixture contains no more than 50 volume % of 
the hydrocarbon solvent. 
The curable polymethylsilsesquioxane of the invention cures into a product 
that has an excellent flexibility, heat resistance, water repellency, and 
corrosion resistance. 
The type of colloidal silica used in the formulation of the present 
invention is not critical as long as it exhibits the specified effects 
when used in the curable polymethylsilsesquioxane composition according to 
the present invention. An organic solvent-borne colloid having a particle 
diameter of 10 to 50 nanometers will generally be used. Suitable 
dispersing solvents are exemplified by isopropyl alcohol, ethylene glycol 
mono-n-propyl ether, methyl ethyl ketone (MEK), xylene/n-butanol, and 
methyl isobutyl ketone (MIBK). 
The colloidal silica is preferably used at from 5 to 250 weight parts per 
100 weight parts polymethylsilsesquioxane. The use of less fails to 
provide a definite effect from its addition, while the use of more causes 
the cured film to become brittle. A solution of the composition according 
to the present invention can be prepared through the use of organic 
solvent-borne colloidal silica since the polymethylsilsesquioxane used in 
the present invention is soluble in aromatic hydrocarbon solvents such as 
benzene, toluene, and xylene; ether solvents such as diethyl ether and 
tetrahydrofuran; alcohol solvents such as isopropyl alcohol, butanol, and 
hexanol; ketone solvents such as acetone, methyl ethyl ketone, and methyl 
isobutyl ketone; ester solvents such as ethyl acetate and butyl acetate; 
and halohydrocarbon solvents such as chloroform, trichloroethylene, and 
carbon tetrachloride. Even when a waterborne colloidal silica is used, the 
invention composition can still be prepared through the co-use of an 
organic solvent such as isopropyl alcohol and so forth. However, the use 
of an organic solvent-borne colloidal silica is preferred because it 
affords a better compatibility between the polymethylsilsesquioxane and 
silica. 
The solids concentration in solutions of the present composition is not 
critical. While the optimal solids concentration will vary as a function 
of the thickness of the dried film and the coating method, values from 0.5 
to 60 volume % are suitable in practice. 
Cure of the composition according to the present invention can be effected 
using an optional catalyst or optional crosslinker or by simply heating. 
When a catalyst or crosslinker is used, the solution of the composition is 
combined with the catalyst or crosslinker and curing is then effected with 
heating. In the case of cure by heating alone, cure is effected at 
50.degree. C. to 350.degree. C. and preferably at 80.degree. C. to 
250.degree. C. The reaction does not proceed at temperatures below 
50.degree. C., while temperatures higher than 350.degree. C. run the risk 
of siloxane decomposition. 
Suitable curing catalysts are exemplified by tin compounds such as tin 
diacetate, tin dioctylate, tin dilaurate, tin tetraacetate, dibutyltin 
diacetate, dibutyltin dioctylate, dibutyltin dilaurate, dibutyltin 
dioleate, dimethoxydibutyltin, dibutyltin oxide, dibutyltin benzylmaleate, 
bis(triethoxysiloxy)dibutyltin, and diphenyltin diacetate; titanium 
compounds such as tetramethoxytitanium, tetraethoxytitanium, 
tetra-n-propoxytitanium, tetraisopropoxytitanium, tetra-n-butoxytitanium, 
tetraisobutoxytitanium, tetrakis(2-ethylhexoxy)titanium, 
di--isopropoxybis(ethyl acetoacetate)titanium, 
dipropoxybis(acetylacetonato)titanium, 
diisopropoxybis(acetylacetonato)titanium, 
dibutoxybis(acetylacetonato)titanium, triisopropoxyallylacetate titanium, 
titanium isopropoxyoctylene glycol, and bis(acetylacetonato)titanium 
oxide; metal/fatty acid salts such as lead diacetate, lead 
bis(2-ethylhexanoate), lead dineodecanoate, lead tetraacetate, lead 
tetrakis(n-propionate), zinc diacetate, zinc bis(2-ethylhexanoate), zinc 
dineodecanoate, zinc diundecenoate, zinc dimethacrylate, iron diacetate, 
zirconium tetrakis(2-ethylhexanoate), zirconium tetrakis(methacrylate), 
and cobalt diacetate; and amino-containing compounds such as 
aminopropyltrimethoxysilane, 
N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, tetramethylguanidine, 
tetramethylguanidylpropyltrimethoxysilane, 
tetramethylguanidylpropyldimethoxysilane, 
tetramethylguanidylpropyltris(trimethylsiloxy)silane, and 
1,8-diazabicyclo(5.4.0.)-7-undecene. These curing catalysts will generally 
be used at from 0.01 to 10 weight parts per 100 weight parts of the 
polymethylsilsesquioxane and are preferably used at from 0.1 to 5 weight 
parts per 100 weight parts of the polymethylsilsesquioxane. 
Suitable crosslinkers are exemplified by the following compounds 
EQU CH.sub.3 Si(OCH.sub.3).sub.3 
EQU CH.sub.2 .dbd.CHSi(OCH.sub.3).sub.3 
EQU Si(OC.sub.2 H.sub.5).sub.4 
##STR1## 
EQU Si(OCH.sub.2 CH.sub.2 CH.sub.3).sub.4 
EQU CH.sub.3 Si(OC(.dbd.O)CH.sub.3).sub.3 
EQU C.sub.2 H.sub.5 Si(OC(.dbd.O)CH.sub.3).sub.3 
EQU CH.sub.2 .dbd.CHSi(OC(.dbd.O)CH.sub.3).sub.3 
EQU CH.sub.3 Si(ON.dbd.C(CH.sub.3)(C.sub.2 H.sub.5)).sub.3 
EQU CH.sub.2 .dbd.CHSi(ON.dbd.C(CH.sub.3)(C.sub.2 H.sub.5)).sub.3 
EQU Si(ON.dbd.C(CH.sub.3)(C.sub.2 H.sub.5)).sub.4 
EQU (CH.sub.3).sub.2 Si(N(CH.sub.3)C(.dbd.O)CH.sub.3).sub.2 
##STR2## 
The crosslinker will be used generally at from 0.1 to 80 weight parts and 
preferably at from 1 to 70 weight parts, in each case per 100 weight parts 
of the polymethylsilsesquioxane. The curing temperature for use of either 
a catalyst or crosslinker will be from 20.degree. C. to 350.degree. C. and 
preferably from 20.degree. C. to 250.degree. C. Curing temperatures in 
excess of 350.degree. C. run the risk of siloxane decomposition. 
Optimal methods for synthesizing polymethylsilsesquioxane having a 
molecular weight and hydroxyl content in the above-specified ranges are 
exemplified by the following: 
(1) forming a two-phase system of water and solvent, wherein the solvent is 
selected from the group consisting of 
(a) an oxygenated organic solvent or 
(b) a mixture of oxygenated organic solvent and hydrocarbon solvent that 
contains no more than 50 volume % of the hydrocarbon solvent, 
adding the below-described (A) or (B) dropwise to this system to hydrolyze 
the (A) methyltrihalosilane, and effecting condensation of the resulting 
hydrolysis product, wherein 
(A) is the methyltrihalosilane MeSiX.sub.3 (Me=methyl and X is a halogen 
atom selected from F, Cl, Br, and I) and 
(B) is the solution afforded by dissolving such a methyltrihalosilane in 
solvent selected from the group consisting of 
(a) an oxygenated organic solvent or 
(b) a mixture of an oxygenated organic solvent and hydrocarbon solvent that 
contains no more than 50 volume % of the hydrocarbon solvent; 
(2) the same method as described under (1), but in this case effecting 
reaction in the two-phase system resulting from the dropwise addition of 
the solution described in (B)-(1) to only water; 
(3) the same method as described under (1), but in this case effecting 
reaction in the two-phase system resulting from the simultaneous dropwise 
addition of water and the solution described in (B)-(1) to an empty 
reactor. 
X in the subject methyltrihalosilane (A) is preferably bromine or chlorine 
and more preferably is chlorine. As used herein, the formation of a 
two-phase system of water and organic solvent refers to a state in which 
the water and organic solvent are not miscible and hence will not form a 
homogeneous solution. This includes the maintenance of a layered state by 
the organic layer and water layer through the use of slow-speed stirring 
as well as the generation of a suspension by vigorous stirring. Below 
these phenomena are referred to as the "formation of two layers". 
The organic solvent used in the subject preparative methods is an 
oxygenated organic solvent that can dissolve the methyltrihalosilane and, 
although possibly evidencing some solubility in water, can nevertheless 
form a two-phase system with water. The organic solvent can contain up to 
50 volume % hydrocarbon solvent. The use of more than 50 volume % 
hydrocarbon solvent is impractical because this causes gel production to 
increase at the expense of the yield of the target product. Even an 
organic solvent with an unlimited solubility in water can be used when 
such a solvent is capable of forming two phases with the aqueous solution 
of a water-soluble inorganic base or with the aqueous solution of a weak 
acid salt with a buffering capacity. 
Suitable oxygenated organic solvents are exemplified by--but not limited 
to--ketone solvents such as methyl ethyl ketone, diethyl ketone, methyl 
isobutyl ketone, acetylacetone, cyclohexanone, and so forth; ether 
solvents such as diethyl ether, di-n-propyl ether, dioxane, the dimethyl 
ether of diethylene glycol, tetrahydrofuran, and so forth; ester solvents 
such as ethyl acetate, butyl acetate, butyl propionate, and so forth; and 
alcohol solvents such as n-butanol, hexanol, and so forth. The ketone, 
ether, and alcohol solvents are particularly preferred among the 
preceding. The oxygenated organic solvent may also take the form of a 
mixture of two or more selections from the preceding. Suitable hydrocarbon 
solvents are exemplified by--but again not limited to--aromatic 
hydrocarbon solvents such as benzene, toluene, xylene, and so forth; 
aliphatic hydrocarbon solvents such as hexane, heptane, and so forth; and 
halogenated hydrocarbon solvents such as chloroform, trichloroethylene, 
carbon tetrachloride, and so forth. 
The quantity of the organic solvent which is used is not critical, but 
preferably is in the range from 50 to 2,000 weight parts per 100 weight 
parts of the methyltrihalosilane. The use of less than 50 weight parts 
organic solvent per 100 weight parts methyltrihalosilane is inadequate for 
dissolving the polymethylsilsesquioxane product and, depending on the 
circumstances, will not give polymethylsilsesquioxane in the desired 
molecular weight range due to an overly high molecular weight. The use of 
more than 2,000 weight parts organic solvent can lead to slow development 
of the hydrolysis and condensation of the methyltrihalosilane and hence to 
the failure to obtain polymethylsilsesquioxane in the desired molecular 
weight range. 
While the quantity of water used is not critical, the water is preferably 
used at from 10 to 3,000 weight parts per 100 weight parts 
methyltrihalosilane. 
Reaction is possible even with the use of water entirely free of additives 
as the aqueous phase; however, such a system will give a 
polymethylsilsesquioxane product with an elevated molecular weight since 
the reaction is accelerated by the hydrogen chloride evolved from the 
chlorosilane. Polymethylsilsesquioxane with a relatively lower molecular 
weight can therefore be synthesized through the addition of water-soluble 
inorganic base capable of controlling the acidity or a weak acid salt with 
a buffering capacity. 
Such water-soluble inorganic bases are exemplified by water-soluble alkalis 
such as the lithium, sodium, potassium, calcium, and magnesium hydroxides. 
The subject weak acid salt with a buffering capacity is exemplified 
by--but not limited to--carbonates such as the sodium, potassium, calcium, 
and magnesium carbonates; bicarbonates such as the sodium and potassium 
bicarbonates; oxalates such as potassium trihydrogen bis(oxalate); 
carboxylates such as potassium hydrogen phthalate and sodium acetate; 
phosphates such as disodium hydrogen phosphate and potassium dihydrogen 
phosphate; and borates such as sodium tetraborate. These are preferably 
used at .ltoreq.1.8 gram-equivalents per 1 mole halogen atom from the 
trihalosilane molecule. In other words, these are preferably used at up to 
1.8-times the quantity that just neutralizes the hydrogen halide that is 
produced when the halosilane is completely hydrolyzed. The use of larger 
amounts facilitates the production of insoluble gel. Mixtures of two or 
more of the water-soluble inorganic bases and mixtures of two or more of 
the buffering weak acid salts can be used as long as the above-specified 
quantity range is obeyed. 
The methyltrihalosilane hydrolysis reaction bath can be stirred slowly at a 
rate that maintains two layers (aqueous phase and organic solvent) or can 
be strongly stirred so as to give a suspension. The reaction temperature 
is suitably in the range from ambient (20.degree. C.) temperature to 
120.degree. C. and is preferably from about 40.degree. C. to 100.degree. 
C. 
The curable polymethylsilsesquioxane according to the present invention may 
contain small amounts of units not specifically included in the claimed 
structure that originate from impurities that may be present in the 
precursors. These units are exemplified by units bearing non-methyl lower 
alkyl, monofunctional units as represented by R.sub.3 SiO.sub.1/2 (where R 
is the lower alkyl), difunctional units as represented by R.sub.2 
SiO.sub.2/2 (where R is the lower alkyl), and tetrafunctional units as 
represented by SiO.sub.4/2. The curable polymethylsilsesquioxane under 
consideration contains the OH group and has the structure specified by the 
structural formula given above; however, its structure may also contain 
very small levels of OH-functional units other than that in the specified 
structural formula. Thus, the curable polymethylsilsesquioxane according 
to the present invention has the structure represented by the chemical 
formula provided above, but may contain structural units produced by the 
mechanisms outlined above insofar as the effects of the present invention 
are not adversely effected. 
EXAMPLES 
The present invention is explained in greater detail in the following 
through working and comparative examples, but is not limited to these 
examples. 
Substrates 
Steel sheet: JIS G-3141 (SPCC-SB), 0.3 mm.times.50 mm.times.150 mm 
Aluminum sheet: JIS H-4000 (Al050P), 0.3 mm.times.50 mm.times.150 mm 
Glass plate: JIS R-3202 (float glass plate), 2.0 mm.times.50 mm.times.50 mm 
Film test methods 
Using a multipurpose film thickness meter (LZ-200 from Ketto Kagaku 
Kenkyusho), the film thickness was measured electromagnetically on the 
steel sheet substrate and was measured by a high-frequency method on the 
aluminum sheet and glass plate substrates. 
The pencil hardness was measured using pencils for pencil scratch testing 
that had been validated by Nippon Toryo Kensa Kyokai. Testing was carried 
out by the manual scratch method of JIS K-5400: scratching was effected by 
pressing the pencil down with the greatest force that would not crumble 
the lead, and the hardness symbol is reported for the pencil that did not 
cause any film scratching. The softness of the substrate in the case of 
the aluminum sheet caused lower apparent values due to indention of the 
substrate by this method. 
The adherence was evaluated using the crosshatch tape test described in JIS 
K-5400, in which a score of 10 is the best possible score. 
The flexural resistance was evaluated using the flexure tester described in 
JIS K-5400. Cracking and debonding were evaluated using a 2 mm diameter 
mandrel on a scale in which a score of 10 is the best possible score. 
The contact angle versus water was measured using a contact angle meter 
(Model CA-D from Kyowa Kaimen Kagaku). 
The salt-spray test used the apparatus described in JIS K-5400. A 5 weight 
% aqueous sodium chloride solution was sprayed at 35.degree.C. For the 
steel sheet substrate the test time required for the rust area to reach 
50% is reported. For the aluminum sheet substrate the test time required 
for the production of rust is reported. 
Reference Example 1 
63.5 g (0.60 mol) sodium carbonate and 400 mL water were introduced into a 
reactor equipped with a reflux condenser, addition funnel, and stirrer. 
400 mL methyl isobutyl ketone was added while stirring. The stirring rate 
was sufficiently slow that the organic layer and aqueous layer remained 
intact. Into this was gradually added 74.7 g (0.5 mol) 
methyltrichlorosilane dropwise from the addition funnel. During this 
period the temperature of the reaction mixture rose to 50.degree. C. The 
reaction mixture was then heated and stirred on an oil bath at 60.degree. 
C. for an additional 24 hours. After completion of the reaction, the 
organic layer was washed with water until the wash water reached 
neutrality and was then dried over a drying agent. The drying agent was 
subsequently removed and the solvent was distilled off at reduced 
pressure. Drying overnight in a vacuum then gave polymethylsilsesquioxane 
as a white solid. The following results were obtained when the molecular 
weight distribution of this polymethylsilsesquioxane was measured by GPC 
calibrated with polystyrene standards (solvent=chloroform, 
columns=2.times.TSKgelGMH.sub.HR -L (brand name) from Tosoh, 
instrument=HLC-8020 from Tosoh): weight-average molecular weight=3,270; 
number-average molecular weight=920. The hydroxyl group content as 
determined from the .sup.29 Si-NMR spectrum (measured with an ACP-300 from 
Bruker) was 0.22 per silicon atom (this 0.22 corresponded to the value of 
m/(m+n)). 
Reference Example 2 
While stirring 2 L water and 1.5 L methyl isobutyl ketone in a reactor as 
described in Reference Example 1 with sufficient vigor that 2 layers did 
not form, 745 g (5.0 mol) methyltrichlorosilane dissolved in 0.5 L methyl 
isobutyl ketone was gradually added dropwise at a rate such that the 
temperature of the reaction mixture did not exceed 50.degree. C. The 
reaction mixture was then additionally stirred and heated for 2 hours on 
an oil bath at 50.degree. C. Work up as in Reference Example 1 gave 
polymethylsilsesquioxane as a white solid. Analysis of the molecular 
weight distribution of this polymethylsilsesquioxane as in Reference 
Example 1 gave the following results: weight-average molecular 
weight=9,180; number-average molecular weight=1,060. 0.22 hydroxyl per 
silicon atom was determined. 
Reference Example 3 
A reactor was set up with a reflux condenser, two addition funnels, and a 
stirrer. A mixed solution of 40 mL methyl isobutyl ketone and 14.9 g (0.1 
mol) methyltrichlorosilane was placed in one addition funnel, while 40 mL 
water was placed in the other addition funnel. The contents of the two 
addition funnels were simultaneously added dropwise to the empty reactor 
while the reactor was cooled on an ice bath. Stirring was carried out with 
sufficient vigor that two layers did not form. After completion of the 
addition, the reaction mixture was heated and stirred for 2 hours in an 
oil bath at 50.degree. C. After completion of the reaction, the reaction 
was worked up as in Reference Example 1 to give polymethylsilsesquioxane 
as a white solid. Analysis of the molecular weight distribution of this 
polymethylsilsesquioxane as in Reference Example 1 gave the following 
results: weight-average molecular weight=1,320; number-average molecular 
weight=600. 0.24 hydroxyl per silicon atom was determined. 
Example 1 
To 100 weight parts of the polymethylsilsesquioxane of Reference Example 1 
were added 333 weight parts of a dispersion of colloidal silica in methyl 
ethyl ketone (MEK-ST from Nissan Kagaku Kogyo, 30 weight % solids) and 124 
weight parts methyl ethyl ketone (solids=25 volume % assuming a specific 
gravity of 1 for the polymethylsilsesquioxane; 100 weight parts silica per 
100 weight parts polymethylsilsesquioxane). A coating composition was then 
prepared by the addition of 0.25 weight part tin dioctylate as catalyst. 
This coating composition was applied to the steel sheet using a bar coater 
and then cured in a 200.degree. C. oven for 1.5 hours to give a 6 
.mu.m-thick film. The test results for this film are reported in Table 1. 
Example 2 
A coating composition was prepared as in Example 1, but in this case 
starting from the polymethylsilsesquioxane of Reference Example 2. This 
coating composition was applied to the aluminum sheet and cured as in 
Example 1 to give a 6 .mu.m-thick film. The test results for this film are 
reported in Table 1. 
Example 3 
The coating composition prepared in Example 1 was coated on the glass plate 
and cured as in Example 1 to give a 6 .mu.m-thick film. The test results 
for this film are reported in Table 1. 
Example 4 
A coating composition was prepared as in Example 1, but in this case using 
150 weight parts silica per 100 weight parts polymethylsilsesquioxane. 
This coating composition was applied to the steel sheet and cured as in 
Example 1 to give a 6 .mu.m-thick film. The test results for this film are 
reported in Table 1. 
Example 5 
The coating composition described in Example 1 was coated on the aluminum 
sheet and cured as in Example 1 to give a 6 .mu.m-thick film. The test 
results for this film are reported in Table 1. 
Example 6 
The coating composition described in Example 1 was coated on the aluminum 
sheet and cured as in Example 1 to give a 1 .mu.m-thick film. The test 
results for this film are reported in Table 1. 
Example 7 
A coating composition was prepared as in Example 1, but in this case 
starting from the polymethylsilsesquioxane of Reference Example 3. This 
coating composition was applied to the steel sheet and cured as in Example 
1 to give a 6 .mu.m-thick film. The test results for this film are 
reported in Table 1. 
Comparative Example 1 
To 100 weight parts of the polymethylsilsesquioxane of Reference Example 1 
was added 186 weight parts methyl ethyl ketone (solids=30 volume % 
assuming a specific gravity of 1 for the polymethylsilsesquioxane). A 
coating composition was then prepared by the addition of 0.25 weight part 
tin dioctylate as catalyst. This coating composition was applied and cured 
onto the steel sheet as in Example 1 to give a 6 .mu.m-thick film. The 
test results for this film are reported in Table 1. The contact angle 
versus water and the corrosion resistance of this film were both inferior 
to the corresponding values for the films in the working examples. 
Comparative Example 2 
A coating agent as described in Example 1 of Japanese Patent Application 
Laid Open (Kokai or Unexamined) Number Sho 51-2736 was applied to the 
steel sheet using a bar coater and then cured in a 150.degree. C. oven for 
30 minutes. However, a sample suitable for testing could not be prepared 
because rust appeared on the steel sheet and the coating cracked and 
debonded. 
Comparative Example 3 
The coating agent described in Comparative Example 2 was coated on the 
aluminum sheet and cured in a 150.degree. C. oven for 30 minutes to give a 
6 .mu.m-thick film. The test results for this film are reported in Table 
1. This film had a poor adherence and also gave poorer results for the 
contact angle versus water and the corrosion resistance. 
Reference Example 4 
Polymethylsilsesquioxane was prepared by the HCl-mediated hydrolysis and 
condensation of methyltrimethoxysilane using a literature method (S. 
Nakahama, et al., Contemp. Top. Polym. Sci., 1984, Volume 4, page 105; Y. 
Abe, et al., J. Polym. Sci. Part A Polym. Chem., 1995, Volume 33, page 
751). Analysis of the molecular weight distribution of the 
polymethylsilsesquioxane by the method described in Reference Example 1 
gave the following results: weight-average molecular weight=2,150; 
number-average molecular weight=660. This polymethylsilsesquioxane 
contained both hydroxyl and methoxy. The hydroxyl and methoxy contents as 
determined from the .sup.29 Si-NMR and .sup.1 H-NMR spectra were 0.216 and 
0.057, respectively, per silicon atom. 
Comparative Example 4 
A silica-free coating composition was prepared as in Comparative Example 1 
using the polymethylsilsesquioxane prepared in Reference Example 4. This 
coating composition was applied and cured onto the steel sheet as in 
Example 1 to provide a 6 .mu.m-thick film. The test results for this film 
are reported in Table 1. The contact angle versus water and the corrosion 
resistance for this film were both inferior to those of the films in the 
working examples. 
Comparative Example 5 
A silica-containing coating composition was prepared as in Example 1 using 
the polymethylsilsesquioxane of Reference Example 4 and a methyl isobutyl 
ketone dispersion of colloidal silica (MIBK-ST, 30 weight % solids, from 
Nissan Kagaku Kogyo Kabushiki Kaisha). MIBK-ST exhibited a better 
compatibility with this polymethylsilsesquioxane resin than did MEK-ST. 
This coating composition was then applied and cured onto the steel sheet 
as in Example 1 to give a 6 .mu.m-thick film. The test results for this 
film are reported in Table 1. No increase in the contact angle versus 
water was observed as a result of the addition of the colloidal silica. 
Comparative Example 6 
A silica-free coating composition was prepared as in Comparative Example 1 
using SR2400 methylsilicone resin from Dow Corning Toray Silicone Company, 
Limited. This coating composition was applied and cured onto the steel 
sheet as in Example 1 to give a 6 .mu.m-thick film. The test results for 
this film are reported in Table 1. The pencil hardness, contact angle 
versus water, and corrosion resistance for this film were all inferior to 
those of the films in the working examples. 
Comparative Example 7 
A silica-containing coating composition was prepared as in Example 1 using 
the SR2400 referenced in Comparative Example 6 and MIBK-ST, which was more 
compatible with this resin than the MEK-ST. This coating composition was 
applied and cured onto the steel sheet as in Example 1 to give a 6 
.mu.m-thick film. The test results for this film are reported in Table 1. 
This film was white and had a very low pencil hardness due to its brittle 
character. It also had a poor adherence. 
Comparative Example 8 
To a mixture of 100 weight parts of the polymethylsilsesquioxane described 
in Reference Example 1, 100 weight parts fumed silica R972 from Nippon 
Aerosil Kabushiki Kaisha, and 760 weight parts methyl isobutyl ketone 
(13.3 volume % solids assuming the specific gravity of the 
polymethylsilsesquioxane is 1; 100 weight parts silica per 100 weight 
parts of the polymethylsilsesquioxane) was added 800 weight parts glass 
beads, and the silica was dispersed by stirring. Addition of the same 
catalyst as in Example 1 then gave a coating composition. This coating 
composition was applied and cured onto the steel sheet as in Example 1 to 
give a 6 .mu.m-thick film. The test results for this film are reported in 
Table 1. This film was white and had a very low pencil hardness due to its 
brittle nature. Its adherence and corrosion resistance were also poor. 
TABLE 1 
__________________________________________________________________________ 
contact 
angle 
salt- 
film versus 
spray 
Example thickness pencil flexural 
water 
test 
number 
substrate 
(.mu.m) 
appearance 
hardness 
adherence 
resistance 
(degrees) 
(hours) 
__________________________________________________________________________ 
Example 1 
steel 
6 transparent 
4H 10 10 119.2 
&gt;216 
sheet 
Example 2 
Al sheet 
6 transparent 
H 10 10 120.5 
&gt;216 
Example 3 
glass 
6 transparent 
4H 10 --.sup.a 
121.2 
--.sup.a 
plate 
Example 4 
steel 
6 transparent 
4H 10 10 115.4 
&gt;216 
sheet 
Example 5 
Al sheet 
6 transparent 
H 10 10 122.2 
&gt;216 
Example 6 
Al sheet 
1 transparent 
H 10 10 118.4 
&gt;216 
Example 7 
steel 
6 transparent 
4H 10 10 120.2 
&gt;216 
sheet 
Comp. 
steel 
6 transparent 
4H 10 10 97.2 24 
Example 1 
sheet 
Comp. 
steel 
--.sup.b 
red rust 
--.sup.b 
--.sup.b 
--.sup.b 
--.sup.b 
--.sup.b 
Example 2 
sheet color and 
debonding 
Comp. 
Al sheet 
6 transparent 
H 4 10 93.0 24 
Example 3 
Comp. 
steel 
6 transparent 
4H 10 10 96.2 48 
Example 4 
sheet 
Comp. 
steel 
6 transparent 
4H 10 10 98.7 &gt;216 
Example 5 
sheet 
Comp. 
steel 
6 transparent 
HB 10 10 100.7 
168 
Example 6 
sheet 
Comp. 
steel 
6 white &lt;6B 8 10 128.3 
&gt;216 
Example 7 
sheet 
Comp. 
steel 
6 white &lt;6B 2 10 141.7 
24 
Example 8 
sheet 
__________________________________________________________________________ 
.sup.a not measured 
.sup.b could not be measured 
This invention provides a curable polymethylsilsesquioxane composition 
whose cured polymethylsilsesquioxane product is sufficiently flexible that 
it can be used as an independent film or thick film not heretofore 
accessible by the prior art. Moreover, this curable 
polymethylsilsesquioxane composition provides a highly water-repellent and 
strongly corrosion-resistant cured film and does so without a loss of 
transparency or a decline in the physical properties required of a 
coating, such as surface hardness and processability. These properties 
make possible the use of the cured film in a wide range of applications. 
The curable polymethylsilsesquioxane coating compositions of the present 
invention have utility for forming water-repellent, corrosion-resistant 
and scratch-resistant films and coatings. 
Although various features and advantages of the present invention have been 
described herein and illustrated by way of example, the scope of the 
present invention is not limited thereto and should be judged solely in 
accordance with the following claims and equivalents thereof.