Curable resin and composition containing the same

The curable resin having a number average molecular weight of 600 to 6000 and at least two hydrolyzable silyl groups which is prepared by reacting an aliphatic polyester resin having acryloyl group and alcoholic hydroxyl group with an isocyanate silane compound: ##STR1## reacting the obtained reaction product with an aminosilane compound: ##STR2## and reacting the obtained reaction product with a monofunctional isocyanate: OCN-R.sup.5 and/or a polyfunctional isocyanate; and the composition containing the resin. The curable resin and the composition are excellent in acid resistance such as acid resin resistance, scratch resistance, solvent resistance, flexibility, and the like.

BACKGROUND OF THE INVENTION 
The present invention relates to a curable resin and a composition 
containing the same, and more particularly to a curable resin whose main 
chain consists essentially of an aliphatic polyester chain and which has 
on the polymer chain end at least two hydrolyzable silyl groups, and the 
composition containing the same. 
The present invention provides a curable resin which is excellent in 
flexibility, solvent resistance, resistance to acid rain (acid rain 
resistance), resistance to scratch (scratch resistance), and is low in 
viscosity, and a composition containing the above-mentioned resin. The 
curable resin of the present invention is suitable for use as a base resin 
used in coatings, adhesives, sealing agents and potting agents, or as a 
polymer to be blended with a cellulose such as nitrocellulose or cellulose 
acetate butyrate, another polymer such as an epoxy resin, a polyester, an 
alkyd resin or an acrylic polyol, particularly a hydrolyzable silyl 
group-containing vinyl resin disclosed in, for instance, Japanese 
Unexamined Patent Publication No. 54-36395, and the like. 
In a field that a curable resin is used in the state of a solution, 
particularly in a field of a coating, it is desired to prepare a high 
solid coating material which can be conformed to effluent regulations to 
solvents, for instance, prescribed in VOC Regulation provided in United 
States of America. 
On the other hand, as to qualities to top coatings required in a market, 
particularly as to qualities of coatings for automobiles, it is desired to 
obtain an improved appearance due to intentions by user that goods of high 
grade are desired, it is desired to improve a scratch resistance, namely 
outside parts of an automobile are not scratched in a car washer, or it is 
desired to improve an acid rain resistance, derived from the environmental 
pollution. 
As to melamine coatings which are generally used at the present time, in 
order to obtain a high solid coating, some efforts have been exerted. 
However, when a mixing ratio of a melamine resin component having a low 
viscosity is increased in the coating composition for obtaining a high 
solid coating, an acid resistance and a scratch resistance are further 
lowered. Also, an acid resistance and a scratch resistance of a regular 
solid coating are not necessarily attained to a satisfactory level. 
An object of the present invention is to provide a curable resin which is 
improved in flexibility, solvent resistance, acid rain resistance and 
scratch resistance and is low in viscosity, and which is suitable for use 
of a blend with another resin. 
A further object of the present invention is to provide a composition 
containing the above-mentioned resin which is improved in flexibility, 
solvent resistance, acid rain resistance and scratch resistance. 
These and other objects of the present invention will become apparent from 
the description hereinafter. 
SUMMARY OF THE INVENTION 
It has now been found that a resin whose main chain comprises an aliphatic 
polyester and which has on the polymer chain end a hydrolyzable silyl 
group is low in viscosity and a cured product thereof is excellent in 
scratch resistance, flexibility, solvent resistance and acid rain 
resistance. 
In accordance with the present invention, there is provided a curable resin 
having a number average molecular weight of 600 to 6000 and at least two 
hydrolyzable silyl groups in one molecule, which is prepared by 
(i) reacting an aliphatic polyester resin (A) having, in one molecule, both 
acryloyl group and alcoholic hydroxyl group on the polymer ends with an 
isocyanate silane compound (B) having the formula (I): 
##STR3## 
wherein R.sup.1 is a bivalent hydrocarbon group having 1 to 10 carbon 
atoms selected from an alkylene group, an arylene group and an aralkylene 
group, R.sup.2 is an alkyl group having 1 to 10 carbon atoms, each X.sup.1 
is a hydrolyzable group and m is 1, 2 or 3 to give a reaction product (i); 
(ii) reacting the obtained reaction product (i) with an aminosilane 
compound (C) having the formula (II): 
##STR4## 
wherein R.sup.3 is a bivalent hydrocarbon group having 1 to 10 carbon 
atoms selected from an alkylene group, an arylene group and an aralkylene 
group, R.sup.4 is an alkyl group having 1 to 10 carbon atoms, each X.sup.2 
is a hydrolyzable group and n is 1, 2 or 3 to give an aminosilane-modified 
resin (ii), and 
(iii) reacting the aminosilane-modified resin (ii) with a monofunctional 
organic isocyanate compound (D-1) having the formula (III): 
EQU OCN--R.sup.5 (III) 
wherein R.sup.5 is a monovalent hydrocarbon group having 1 to 25 carbon 
atoms selected from an alkyl group, an aryl group and an aralkyl group, a 
group of the formula: (CH.sub.3 O).sub.3 Si--(CH.sub.2).sub.3 or a group 
of the formula: (C.sub.2 H.sub.5 O).sub.3 Si--(CH.sub.2).sub.3 and/or a 
polyfunctional organic isocyanate compound (D-2) in the substantial 
absence of water. 
Also, in accordance with the present invention, there is provided a 
composition comprising the above-mentioned curable resin (b) and a silyl 
group-containing vinyl polymer (a) having, in one molecule, at least one 
silyl group having the formula (IV): 
##STR5## 
wherein R.sup.6 and R.sup.7 are the same or different and each is a 
hydrogen atom or a monovalent hydrocarbon group having 1 to 10 carbon 
atoms selected from an alkyl group, an aryl group and aralkyl group, each 
Y is a halogen atom, an alkoxy group, an acyloxy group, an aminoxy group, 
a phenoxy group, a thioalkoxy group or an amino group, and at least one Y 
is an alkoxy group or a phenoxy group, and a is 1, 2 or 3.

DETAILED DESCRIPTION 
In the present invention, firstly, the aliphatic polyester resin (A) having 
both acryloyl group and alcoholic hydroxyl group in one molecule is 
reacted with the isocyanate silane compound (B). 
In the present invention, any aliphatic polyester resins can be used as the 
component (A) without any limitation, so long as the aliphatic polyester 
resin has both acryloyl group and alcoholic hydroxyl group at the polymer 
ends and has a number average molecular weight of 200 to 5,000, preferably 
from 300 to 3,000. 
Examples of the polyester chain of the aliphatic polyester resin (A) are, 
for instance, a polyester such as polyethylene adipate, polydiethylene 
adipate, polypropylene adipate, polytetramethylene adipate, 
polyneopentylene adipate, polymethylpentanediol adipate, 
poly-.epsilon.-caprolactone or polymethylvalerolactone, a copolyester, a 
polyhexamethylene carbonate, and the like. Among them, 
poly-.epsilon.-caprolactone and polymethylvalerolactone are preferable 
from the viewpoint of weatherability, and polymethylvalerolactone is 
preferable from the viewpoint of acid rain resistance. Examples of the 
aliphatic polyester resin (A) are, for instance, 
poly-.epsilon.-caprolactone acrylates such as "Placcel FA-1" commercially 
available from Daicel Chemical Industries, Ltd., "Placcel FA-2", "Placcel 
FA-3", "Placcel FA-4", "Placcel FA-8", polymethylvalerolactone acrylates 
commercially available from Kabushiki Kaisha Kuraray, and the like. 
The isocyanate silane compound (B) has the formula (I): 
##STR6## 
In the formula (I), R.sup.1 is a bivalent hydrocarbon group having 1 to 10 
carbon atoms, concretely, an alkylene group having 1 to 10 carbon atoms 
such as trimethylene group, hexamethylene group, including a cycloalkylene 
group having 6 to 10 carbon atoms such as cyclohexylene group, in addition 
to the linear or branched alkylene group, an arylene group having 6 to 10 
carbon atoms such as phenylene group or an aralkylene group having 7 to 10 
carbon atoms such as xylylene group, R.sup.2 is an alkyl group having 1 to 
10 carbon atoms such as methyl group or ethyl group, each X.sup.1 is a 
hydrolyzable group, and m is 1, 2 or 3. Examples of the hydrolyzable group 
X.sup.1 are, for instance, a halogen atom, an alkoxy group such as methoxy 
group, ethoxy group or butoxy group, an acyloxy group such as acetoxy 
group, an aminoxy group, a phenoxy group, a thioalkoxy group, an amino 
group, and the like. Among them, the alkoxy group and the acyloxy group 
are preferable from the viewpoints of the safety and smelling. 
Examples of the isocyanate silane compound (B) are, for instance, 
3-isocyanatepropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, 
3-isocyanatepropylmethyldimethoxysilane, and the like. 
It is preferable that the isocyanate silane compound (B) is reacted with 
the aliphatic polyester resin (A) in an amount of 0.3 to 1.0 mole, more 
preferably from 0.6 to 1.0 mole, per mole of the alcoholic hydroxyl group 
in the aliphatic polyester resin (A). When the amount of the isocyanate 
silane compound (B) is less than 0.3 mole per mole of the alcoholic 
hydroxyl group in the polyester resin (A), the non-reacted hydroxyl groups 
numerously remain, thus the storage stability tends to lower. On the other 
hand, when the amount of isocyanate silane compound (B) is more than 1.0 
mole, there is a tendency that the non-reacted isocyanate silane compound 
(B) remains. 
The reaction of the aliphatic polyester resin (A) and the isocyanate silane 
compound (B) can be conducted at a temperature of room temperature to 
200.degree. C. for 0.5 to 5 hours in the substantial absence of water, and 
the reaction can easily proceed under the above-mentioned reaction 
conditions. 
In the above-mentioned reaction, as a catalyst, an organotin catalyst such 
as dibutyltin dilaurate, tin octoate or stannous octoate can be used. 
Also, in order to inhibit the radical polymerization of acryloyl group in 
the aliphatic polyester resin (A) during the reaction, it is preferable to 
add a polymerization inhibitor such as hydroquinone, hydroquinone 
monomethyl ether or 2,6-ditert-butyl-4-methylphenol (BHT) prior to the 
reaction. 
Thus, the reaction product (i) having urethane bond formed by the reaction 
of hydroxyl group in the component (A) with isocyanato group in the 
component (B) can be obtained (urethane bond formation). 
Subsequently, the reaction product (i) is reacted with the aminosilane 
compound (C) having the formula (II): 
##STR7## 
In the reaction, acryloyl group in the reaction product (i) is reacted 
with amino group in the aminosilane compound (C). 
In the formula (II), R.sup.3 is a bivalent hydrocarbon group having 1 to 10 
carbon atoms, concretely, is an alkylene group having 1 to 10 carbon atoms 
such as trimethylene group or hexamethylene group, including a 
cycloalkylene group having 6 to 10 carbon atoms such as cyclohexylene 
group, in addition to the linear or branched alkylene group, an arylene 
group having 6 to 10 carbon atoms such as phenylene group or an aralkylene 
group having 7 to 10 carbon atoms such as xylylene group, R.sup.4 is an 
alkyl group having 1 to 10 carbon atoms such as methyl group or ethyl 
group, each X.sup.2 is a hydrolyzable group, and n is 1, 2 or 3. Examples 
of the hydrolyzable group X.sup.2 are, for instance, a halogen atom, an 
alkoxy group such as methoxy group, ethoxy group or butoxy group, an 
acyloxy group such as acetoxy group, an aminoxy group, a phenoxy group, a 
thioalkoxy group, an amino group, and the like. Among them, the alkoxy 
group and the acyloxy group are preferable from the viewpoints of the 
safety and smelling. 
Examples of the aminosilane compound (C) are, for instance 
3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 
3-aminopropylmethyldimethoxysilane, and the like. 
It is preferable that the aminosilane compound (C) is reacted with the 
reaction product (i) in an amount of 0.7 to 1 mole, more preferably from 
0.8 to 1 mole, per mole of acryloyl group in the reaction product (i). 
When the amount of the aminosilane compound (C) is less than 0.7 mole per 
mole of acryloyl group in the reaction product (i), the non-reacted 
acryloyl groups remain, thus the curability of the curable resin tends to 
lower. On the other hand, when the amount of the aminosilane compound (C) 
is more than 1 mole, there is a tendency that the non-reacted aminosilane 
compound remains. 
The reaction is conducted, for instance, at a temperature of 10.degree. to 
100.degree. C. for 0.5 to 2 hours. 
In the above-mentioned reaction, 5 to 90% by mole of the aminosilane 
compound (C) can be replaced by a mercaptosilane compound such as 
.gamma.-mercaptopropyltrimethoxysilane. 
Thus, the aminosilane-modified resin (ii) is obtained by the addition 
reaction of amino group in the component (C) to acryloyl group in the 
reaction product (i) (Michael addition reaction). 
Finally, amino group in the thus obtained reaction product, namely, the 
aminosilane-modified resin (ii) is reacted with the monofunctional organic 
isocyanate compound (D-1) and/or the polyfunctional organic isocyanate 
compound (D-2). 
The monofunctional organic isocyanate compound (D-1) has the formula (III): 
EQU OCN--R.sup.5 (III) 
In the formula (III), R.sup.5 is an alkyl group having 1 to 25 carbon atoms 
such as hexyl group, octyl group, dodecyl group or stearyl group, 
including a cycloalkyl group having 6 to 25 carbon atoms such as 
cyclohexyl group, in addition to the linear or branched alkyl group, an 
aryl group having 6 to 25 carbon atoms such as phenyl group, an aralkyl 
group having 6 to 25 carbon atoms such as benzyl group, the group of the 
formula: (CH.sub.3 O).sub.3 Si (CH.sub.2).sub.3 or the group of the 
formula: (C.sub.2 H.sub.5 O).sub.3 Si (CH.sub.2).sub.3. 
Examples of the monofunctional isocyanate compound (D-1) are, for instance, 
n-butyl isocyanate, n-dodecyl isocyanate, stearyl isocyanate, cyclohexyl 
isocyanate, phenyl isocyanate, benzyl isocyanate, 
3-isocyanatepropyltrimethoxysilane, 3-isocyanatepropyltriethoxysilane, 
3-isocyanatepropylmethyldimethoxysilane, and the like. 
Any polyfunctional organic isocyanate compound (D-2) can be used without 
particular limitations so long as the isocyanate compound (D-2) has at 
least two isocyanato groups in one molecule. The preferable polyfunctional 
isocyanate compounds (D-2) are isocyanate compound having 2 to 3 
isocyanato groups in the molecule. 
Typical examples of the polyfunctional organic isocyanate compound (D-2) 
are, for instance, hexamethylene diisocyanate, isophorone diisocyanate, 
2,4-toluene diisocyanate, diphenylmethane-4,4'-diisocyanate, 
dicyclohexylmethane-4,4'-diisocyanate, xylylene diisocyanate, lysine 
methyl ester diisocyanate, 
##STR8## 
a trimer of isophorone diisocyanate (isocyanurate), and the like. 
When the curable resin of the present invention is used in exterior 
coatings, the use of the aliphatic isocyanate or alicyclic isocyanate is 
preferable to the use of the aromatic isocyanate, from the viewpoints of 
the weatherability and yellowing resistance. When a hydrolyzable silyl 
group-containing monofunctional isocyanate such as 
3-isocyanatepropyltrimethoxysilane is used as the component (D-1), one of 
the hydrolyzable silyl group is further introduced into the curable resin. 
Also, when the polyfunctional organic isocyanate compound (D-2) such as a 
difunctional isocyanate is used, two molecules of the aminosilane-modified 
resins (ii) can be bonded. Accordingly, the monofunctional organic 
isocyanate compound (D-1) and the polyfunctional organic isocyanate 
compound (D-2) can be suitably used alone or as a mixture thereof 
depending on the purposes. 
It is preferable that the isocyanate compound (D-1) or (D-2) is reacted 
with the aminosilane-modified resin (ii) in an amount of 0.7 to 1 
gram-equivalent, more preferably from 0.8 to 1 gram-equivalent, of active 
hydrogen of amino group in the aminosilane-modified resin (ii). When the 
amount of the isocyanate compound is less than 0.7 gram-equivalent of 
active hydrogen of amino group in the aminosilane-modified resin (ii), the 
storage stability (the increase of viscosity due to moisture) and the 
yellowing resistance tend to lower. On the other hand, when the amount of 
the isocyanate compound is more than 1.0 gram-equivalent, there is 
tendency that the free isocyanate remains. 
The reaction is conducted in the substantial absence of water, and it can 
easily and exothermically proceed by only adding the monofunctional 
isocyanate (D-1) and/or the polyfunctional isocyanate (D-2) to the 
aminosilane-modified resin (ii) or a solution containing the resin (ii) at 
a temperature of room temperature to 60.degree. C. 
As mentioned above, the curable resin of the present invention is prepared 
by a series of addition reactions (urethane bond formation.fwdarw.Michael 
addition reaction.fwdarw.urea bond formation). It is not required to 
remove the eliminated product in each addition reaction from the reaction 
mixture, and the desired curable resin can be easily obtained by 
controlling the amounts of the reactants and the reaction temperature. 
In the above-mentioned reactions, it is not necessary to use a solvent. In 
order to control the reaction temperature or the viscosity, a solvent can 
be used. As the solvent, a solvent having no active hydrogen such as 
heptane, toluene, xylene, butyl acetate or methyl ethyl ketone is used. 
Particularly, if a raw material contains water, it is possible to 
previously remove water according to azeotropic dehydration, using heptane 
or toluene. 
The thus obtained curable resin has, in one molecule, the aliphatic 
polyester chain, at least one, preferably from 1 to 3, urethane bond and 
at least one, preferably from 1 to 3, N,N,N'-3-substituted urea bond in 
its backbone and has at least two, preferable from 2 to 6, more preferably 
from 2 to 4, hydrolyzable silyl groups at the polymer ends. 
The curable resin has the number average molecular weight of 600 to 6000, 
preferably from 700 to 4000. When the number average molecular weight is 
less than 600, the flexibility becomes poor. On the other hand, when the 
number average molecular weight is more than 6000, the acid resistance and 
the scratch resistance become poor. 
The curable resin of the present invention is excellent in flexibility due 
to the aliphatic polyester chain, is excellent in solvent resistance due 
to the urethane bond and the N,N,N'-3-substituted urea bond, is low in 
resin viscosity though it has the bonds with high cohesion, and is 
excellent in compatibility with another polymer. Accordingly, the curable 
resin of the present invention is most useful as a high solid top coating 
used for automobiles. Also the top coating containing the curable resin of 
the present invention is more excellent in acid rain resistance and 
scratch resistance, which have recently been desired to more improve in 
the use of top coatings for automobiles, than the acrylic-melamine 
coatings which has been generally and widely used. 
It could be considered that the reason why the curable resin of the present 
invention is excellent in acid rain resistance is that the coating film of 
the curable resin of the present invention is not cured (crosslinked) by 
the formation of ether bond alike in the case of the acrylic-melamine 
coatings, but cured by the formation of siloxane bond which is excellent 
in chemical resistance. Also, though the cause that the scratch resistance 
can be given to the curable resin is not clear, the cause could be 
considered that the backbone of the curable resin is excellent in elastic 
restoration. 
The composition of the present invention comprises the vinyl polymer (a) 
containing in one molecule at least one, preferably from 2 to 10, silyl 
group having the formula (IV): 
##STR9## 
and the curable resin (b) as mentioned above. 
In the formula (IV), R.sup.6 and R.sup.7 are the same or different and each 
is a hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms 
selected from an alkyl group such as methyl group or ethyl group, an aryl 
group such as phenyl group and an aralkyl group such as benzyl group; each 
Y is a halogen atom or a group selected from an alkoxy group such as 
methoxy group, ethoxy group or butoxy group, an acyloxy group such as 
acetoxy group, a thioalkoxy group such as aminoxy group or phenoxy group 
and an amino group, and at least one Y is an alkoxy group os phenoxy 
group; and a is 1, 2 or 3. 
Examples of the vinyl monomer, for instance, a methacrylic monomer such as 
methyl methacrylate, n-butyl methacrylate or iso-butyl methacrylate, an 
acrylic monomer such as n-butyl acrylate or 2-ethylhexyl acrylate, a 
hydrolyzable silyl group-containing vinyl monomer such as 
.gamma.-trimethoxysilylpropyl methacrylate, styrene, acrylamide, and the 
like. 
The vinyl polymer having at least one silyl group (a) can be prepared in a 
manner, for instance, described in Japanese Unexamined Patent Publication 
No. 54-36395, or the like. 
The composition of the present invention comprises 5 to 95 parts by weight, 
preferably from 10 to 70 parts by weight, of the vinyl polymer (a) and 95 
to 5 parts by weight, preferably from 30 to 90 parts by weight, of the 
curable resin (b), the total amount of the curable resin (b) and the vinyl 
polymer (a) being 100 parts by weight. When the amount of the vinyl 
polymer is less than 5 parts by weight, it tends to lower the effect for 
improving the acid resistance. On the other hand, when the amount of the 
vinyl polymer (a) is more than 95 parts by weight, it tends to lower the 
effect for improving the scratch resistance. 
When the silyl group-containing vinyl polymer (a) is blended with the 
curable resin (b), the obtained composition can be improved in acid rain 
resistance and hardness. 
The composition of the present invention can further contain other resins 
and other coatings. For instance, when an epoxy resin, a polyester alkyd 
resin or an acrylic polyol resin is blended with the composition of the 
present invention, the obtained composition can be improved in flexibility 
and solvent resistance. Also, when a melamine-alkyd coating or a 
melamine-acrylic coating is blended with the composition of the present 
invention, the obtained composition can be improved in acid rain 
resistance and scratch resistance. 
It is preferable that the other component is blended with the composition 
of the present invention in an amount of not more than 50 parts by weight, 
based on 100 parts by weight of the total resin solids from the viewpoints 
of the characteristic physical properties of the composition of the 
present invention. 
The composition of the present invention can further contain a known 
additive such as a solvent, dehydrating agent, antoxidant, leveling agent 
or pigment. 
The curable resin or the composition containing the resin of the present 
invention can be cured by using a known curing catalyst. Examples of the 
curing catalyst are, for instance, an organotin compound such as 
dibutyltin dilurate or tin octoate, and acid compound such as 
p-toluenesulfonic acid or an acid phosphoric ester, an amine compound such 
as ethylene diamine, isophorone diamine or N,N-dimethyldodecylamine, and 
the like. 
It is preferable that the amount of the curing catalyst is from 0.005 to 10 
parts by weight, more preferably from 0.1 to 8 parts by weight, based on 
100 parts by weight of the curable resin (a). The curing of the curable 
resin (a) can proceed rapidly at room temperature without using the curing 
catalyst. It is possible that the curable resin (a) can be cured further 
rapidly by heating to 80.degree. to 160.degree. C. 
The curable resin (a) or the composition of the present invention is 
excellent in acid rain resistance, scratch resistance, flexibility, 
weatherability, and the like, and is suitable for use as, particularly 
exterior coating agents. 
The present invention is more specifically described and explained by means 
of the following Examples in which all percents and parts are by weight 
unless otherwise noted. It is to be understood that the present invention 
is not limited to the Examples, and various changes and modifications may 
be made in the invention without departing from the spirit and scope 
thereof. 
REFERENCE EXAMPLE 1 
Preparation of hydrolyzable silyl group-containing acrylic copolymer 
A reactor equipped with a stirrer, a thermometer, a nitrogen inlet tube and 
a condenser was charged with 200 g of "Solvess 100" commercially available 
from Exxon Company and the temperature was elevated to 110.degree. C. 
Then, a mixture of 177 g of n-butyl methacrylate, 177 g of methyl 
methacrylate, 240 g of trimethoxysilylpropyl methacrylate, 6 g of 
acrylamide, 32 g azobisisobutyronitrile and 64 g of xylene was 
continuously added to the reactor for 5 hours with stirring under nitrogen 
gas. Then, a mixture of 4 g of azobisisobutyronitrile and 40 g of xylene 
was continuously added for 2 hours, and the post-polymerization was 
conducted for 1 hour. 
The obtained reaction mixture was diluted with xylene to give a 
hydrolyzable silyl group-containing acrylic copolymer solution (1) having 
a solid concentration of 60%. The obtained silyl group-containing acrylic 
copolymer had a number average molecular weight of 3,000 and a solution 
viscosity of 200 cps (at 23.degree. C.). 
EXAMPLE 1 
A reactor equipped with a stirrer, a thermometer, a nitrogen inlet tube and 
a condenser was charged with 284 g of Placcel FA-3 (commercially available 
from Daicel Chemical Industries, Ltd., polycaprolactone acrylate, Mn: 
458), 127 g of 3-isocyanatepropyltrimethoxysilane and 200 g of xylene and 
the mixture was reacted at 100.degree. C. for 2 hours with stirring under 
nitrogen gas. 
In the infrared absorption spectrum (IR) of the obtained product (i), the 
absorption based on NCO (2270 cm.sup.-1) disappeared completely and the 
absorption based on urethane bond (1540 cm.sup.-1) was seen. Also, the 
absorption based on acryloyl group (1630 to 1640 cm.sup.-1) remained. The 
chart of IR spectrum of the reaction product (i) is shown in FIG. 1. 
Then, after the reaction temperature was dropped to 30.degree. C., 116 g of 
3-aminopropyltrimethoxysilane was added to the reactor and the reaction 
was conducted for 1 hour, and was further continued at 60.degree. C. for 
30 minutes. 
In IR of the reaction product (ii), the absorption based on acryloyl group 
(1630 to 1640 cm.sup.-1) disappeared. The chart of IR spectrum of the 
reaction product (ii) is shown in FIG. 2. 
Subsequently, after the reaction temperature was dropped to 30.degree. C., 
73 g of cyclohexyl isocyanate was gradually added through a dropping 
funnel, and the reaction was conducted at 60.degree. C. for 30 minutes 
after completing the addition. The reaction product diluted with xylene to 
give a curable resin solution (1) having a solid concentration of 60%. 
In the IR of the obtained curable resin, the absorption based on urea bond 
(1640 cm.sup.-1) was seen. The chart of IR spectrum of the curable resin 
is shown in FIG. 3. The curable resin has a number average molecular 
weight of 1000, measured by gel permeation chromatography (GPC). 
There was mixed 100 parts of the curable resin solution (1) (solid 
concentration: 60%) with 0.5 part of dibutyltin dilaurate, and the mixture 
was diluted with "Solvesso 100" to give a clear coating having a suitable 
viscosity for using as a coating. 
A black melamine-acrylic enamel was spray-coated on a plate (30 cm.times.10 
cm.times.0.08 mm) coated with an electrodeposition intermediate coating so 
as to give a dry film thickness of 10 to 15 .mu.m, the film was allowed to 
stand for 1 minute, then the clear coating was spray-coated on the film so 
as to give a dry film thickness of 40 to 50 .mu.m. The film was allowed to 
stand for 5 minutes, it was baked at 140.degree. C. for 30 minutes, and it 
was allowed to stand at room temperature for one day. 
As to the obtained test piece or the curable resin solution (1), the 
following physical properties were estimated. 
Solution viscosity 
A viscosity of the curable resin solution having a solid concentration of 
60% was measured at 23.degree. C. by using a Brookfield viscometer. 
Pencil hardness 
The pencil hardness of the film is measured according to Japanese 
Industrial Standards (JIS) K 5400. 
Acid resistance 
A 20.degree.-gloss of the film is measured. The test piece was dipped in a 
1% solution of sulfuric acid for 24 hours, and then a 20.degree.-gloss of 
the film is measured. The gloss retention is characterized by the 
following equation: 
##EQU1## 
The higher the gloss retention, the more excellent the acid resistance. 
Scratch resistance 
The test piece is horizontally set, an abrasive of 1.2% of a loam having an 
abrasive grain size of #8 provided in JIS, 1.2% of a loam having an 
abrasive grain size of #11 provided in JIS, 0.6% of kaoline, 1.0% of a 
neutral detergent and 96.0% of water was coated on the film of the test 
piece, with which a kraft paper is covered (a diameter of contact area: 5 
cm, a load: 22 g/cm.sup.2). The kraft paper was stroked on the film. The 
lightness of the film which is not stroked, the lightness of the film 
which is stroked 12 times, and the lightness of the film which is stroked 
100 times are measured by using differential colorimeter. The scratch 
resistance is estimated according to the difference (.DELTA.L) between the 
lightness of the film which is not stroked and the lightness of the film 
which is stroked 12 times or 100 times. The smaller the .DELTA.L, the more 
excellent the scratch resistance. 
Bending by mandrel 
A test piece (30 cm.times.10 cm.times.0.08 mm) is prepared by coating a 
mild steel plate with the curable resin or composition so as to get a dry 
film thickness of 50 .mu.m. The test piece is bended by using a mandrel 
tester commercially available from Ericksen Corp. and a length (cm) of 
crack is measured. 
The results are shown in Table 1. 
EXAMPLE 2 
The procedure of Example 1 was repeated except that 49 g of hexamethylene 
diisocyanate was used instead of 73 g of cyclohexyl isocyanate to give a 
curable resin solution (2) containing a solid concentration of 60%. 
In the IR of the curable resin, the absorption based on urea bond (1640 
cm.sup.-1) was seen. The curable resin had a number average molecular 
weight of 1500 measured by GPC. 
The physical properties of the curable resin solution (2) and the film were 
measured in the same manner as in Example 1. 
The results are shown in Table 1. 
EXAMPLE 3 
The procedure of Example 1 was repeated except that 98 g of 
tri(6-isocyanatehexyl)isocyanurate was used instead of 73 g of cyclohexyl 
isocyanate to give a curable resin solution (3) having a solid 
concentration of 60%. 
In the IR of the obtained curable resin, the absorption based on urea bond 
(1640 cm.sup.-1) was seen. The curable resin has a number average 
molecular weight of 3,000 measured by GPC. 
The test piece was prepared in the same manner as in Example 1. 
As to the obtained film and the resin solution (3) the physical properties 
were measured in the same manner as in Example 1. 
The results are shown in Table 1. 
EXAMPLE 4 
A reactor equipped with a stirrer, a thermometer, a nitrogen inlet tube and 
a condenser was charged with 407.2 g of polymethylvalerolactone acrylate 
(commercially available from Kabushiki Kaisha Kuraray, Mn=1080), 77.3 g of 
3-isocyanatepropyltrimethoxysilane and 200 g of xylene, and the reaction 
was conducted at 100.degree. C. for 2 hours with stirring under nitrogen 
gas. 
In the IR of the reaction product, the absorption based on --NCO (2270 
cm.sup.-1) completely disappeared, the absorption based on urethane bond 
was seen, and the absorption based on acryloyl group (1630 to 1640 
cm.sup.-1) remained. 
Then, the reaction temperature was dropped to 30.degree. C., to which 70.9 
g of 3-aminopropyltrimethoxysilane was added, and the reaction was 
conducted for 1 hour and then was continued at 60.degree. C. for 30 
minutes. 
In the IR of the reaction product, the absorption based on acryloyl group 
(1630 to 1640 cm.sup.-1) disappeared. 
Then, the reaction temperatures was dropped to 30.degree. C., and 44.6 g of 
cyclohexylisocyanate was gradually added through a dropping funnel to the 
reaction system. After completing the addition, the reaction was conducted 
at 60.degree. C. for 30 minutes and the reaction product was diluted with 
xylene to give a curable resin solution (4) having a solid concentration 
of 60%. 
In the IR of the obtained curable resin, the absorption based on urea bond 
(1640 cm.sup.-1) was seen. The curable resin has a number average 
molecular weight of 1600 measured by GPC. 
The test piece was prepared in the same manner as in Example 1. 
The physical properties of the film and the curable resin solution (4) were 
measured in the same manner as in Example 1. 
The results are shown in Table 1. 
COMATIVE EXAMPLE 1 
A test price was prepared in the same manner as in Example 1 except that a 
commercial melamine-acrylic clear coating was used instead of the clear 
coating obtained in Example 1. 
The physical properties of the film were measured in the same manner as in 
Example 1. 
The results are shown in Table 1. 
TABLE 1 
__________________________________________________________________________ 
Solution 
viscosity Acid Bending by 
(60%) Pencil 
resistance 
Scratch resistance 
mandrel 
Ex. No. 
(cps) 
hardness 
(Gross retention) 
20 times 
100 times 
(cm) 
__________________________________________________________________________ 
1 40 HB 80 0.1 1.3 0 
2 70 HB 85 0.1 1.0 0 
3 100 HB 90 0.1 0.8 0 
4 60 2B 95 0.3 1.5 0 
Com. Ex. 1 
-- H 20 5.0 11.0 10 
__________________________________________________________________________ 
EXAMPLES 5 TO 7 AND COMATIVE EXAMPLE 2 
The curable resin solution (1) was mixed with the hydrolyzable silyl 
group-containing acrylic copolymer obtained in Reference Example 1 in 
amounts shown in Table 2 to give a composition. 
The test piece was prepared in the same manner as in Example 1 except that 
the obtained composition was used instead of the curable resin. 
The physical properties of the film and the resin solution were measured in 
the same manner as in Example 1. 
The results are shown in Table 2. 
TABLE 2 
__________________________________________________________________________ 
Hydrolyzable silyl 
group-containing 
Solution 
Curable resin 
acrylic copolymer 
viscosity Acid Bending by 
Ex. solution (1) 
solution (1) 
(60%) 
Pencil 
resistance 
Scratch resistance 
mandrel 
No. (part) (part) (cps) 
hardness 
(Gross retention) 
20 times 
100 times 
(cm) 
__________________________________________________________________________ 
5 75 25 50 F 90 0.5 2.2 0 
6 50 50 70 H 100 2.3 4.1 0 
7 25 75 100 H 100 3.5 7.0 1 
Com. 
0 100 200 H 100 4.0 9.5 10 
Ex. 2 
__________________________________________________________________________ 
In addition to the ingredients used in the Examples, other ingredients can 
be used in the Examples as set forth in the specification to obtain 
substantially the same results.