Primer composition

Primer composition comprising a silane coupling agent, an alkoxysilylated NCO-containing urethane prepolymer which is prepared by reacting a polyisocyanate with a diol to give an NCO-containing urethane prepolymer, and reacting the resulting NCO-containing urethane prepolymer with a trialkoxysilane having a functional group active to NCO group wherein a part of whole of the remaining NCO groups of the high molecular weight polyisocyanate are reacted with the silane. Said primer composition has excellent plasticizer resistance, solvent resistance and film-forming properties and further improved adhesin properties to glass, metals, ceramics, and is useful as a primer for various adhesives, particularly for applying to glass, metals, and ceramics.

DETAILED DESCRIPTION OF THE INVENTION 
The primer composition of this invention comprises a silane coupling agent 
and an alkoxysilylated NCO-containing urethane prepolymer which is 
prepared by reacting a polyisocyanate with a diol to give an 
NCO-containing urethane prepolymer, followed by reacting with a 
trialkoxysilane having a functional group active to NCO group wherein a 
part or whole of the remaining NCO groups of the NCO-containing urethane 
prepolymer are reacted with the silane. 
The silane coupling agent used in this invention includes epoxysilanes 
[e.g. .gamma.-glycidoxypropyltrimethoxysilane, 
.gamma.-glycidoxypropylmethyldimethoxysilane, 
3,4-epoxycyclohexylethyltrimethoxysilane, 
3,4-epoxycyclohexylethylmethyldimethoxysilane, etc.], aminosilanes [e.g. 
aminomethyltriethoxysilane, 
N-(.beta.-aminoethyl)aminomethyl-trimethoxysilane, 
aminomethyldiethoxysilane, N-(.beta.-aminoethyl)methyltributoxysilane, 
.gamma.-aminopropyltriethoxysilane, 
.gamma.-aminopropylmethyldiethoxysilane, 
.gamma.-aminoisobutyltrimethoxysilane, 
N-bis(.beta.-hydroxyethyl)-.gamma.-aminopropyltriethoxysilane, 
N-(.beta.-aminoethyl)-.gamma.-aminopropyltrimethoxysilane, 
N-(.beta.-aminoethyl)-.gamma.-aminopropylmethyldimethoxysilane, 
N-(.beta.-aminoethyl)-.gamma.-amino-.beta.-methylpropyltrimethoxysilane, 
etc.], mercaptosilanes [e.g. .gamma.-mercaptopropylmethyldimethoxysilane, 
.gamma.-mercaptopropyltrimethoxysilane, 
.gamma.-mercaptopropylmethyldiethoxysilane, 
.gamma.-mercaptopropyltriethoxysilane, 
.gamma.-mercaptopropylethyldimethoxysilane, 
.gamma.-mercaptopropylethyldiethoxysilane, 
.beta.-mercaptopropyldimethylmethoxysilane, 
.beta.-mercaptoethylmethyldimethoxysilane, 
.beta.-mercaptoethyltriethoxysilane, etc.], and modified silanes which are 
prepared by reacting 1 mole of the above epoxysilane with 0.1 to 1 mole of 
the above aminosilane or mercaptosilane having a functional group active 
to epoxy group (e.g. hydroxyl group, amino group, imino group, or mercapto 
group). 
The alkoxysilylated NCO-containing urethane prepolymer can be prepared by 
reacting a polyisocyanate with a diol in an appropriate organic solvent 
(preferably a solvent as used in the preparation of a primer composition 
as mentioned hereinafter) wherein the reaction proceeds in a ratio of 
NCO/OH=2-3, followed by reacting with a trialkoxysilane having a 
functional group active to NCO group such as hydroxyl group, amino group, 
imino group, mercapto group, wherein a part or whole of the NCO groups 
remained in the polyisocyanate thus reacted is reacted with the 
NCO-reactive silane. It is assumed that the alkoxysilylated NCO-containing 
urethane prepolymer will be a mixture of dimers, trimers and pentamers, 
but the mixture can be used as it stands without isolating. It is 
preferable that less than 30%, more preferably less than 10%, of the NCO 
groups of the polyisocyanate are remained in the free form in the final 
alkoxysilylated compound. The above reaction proceeds in two stages, but 
the reaction can be carried out in a single vessel by adding the diol and 
the NCO-reactive silane to a polyisocyanate. 
The polyisocyanate used in tne above reaction includes aliphatic, alicyclic 
or aromatic polyisocyanates, and further hydrogenated products of these 
polyisocyanates, and adducts thereof. Preferred examples of the 
polyisocyanate are hydrogenated xylylenediisocyanate, trimethylolpropane 
adduct of hydrogenated xylylenediisocyanate, hydrogenated 
diphenylmethanediisocyanate, hexamethylenediisocyanate, 
isophoronediisocyanate adduct of hexamethylenediisocyanate (a commercial 
product, Duranate W3330-75E, manufactured by Asahi Chemical Industry Co., 
Ltd.), trimethylhexamethylenediisocyanate, tolylenediisocyanate adduct of 
hexamethylenediisocyanate (a commercial product, Desmodur HL, manufactured 
by Bayer A.G.), tolylenediisocyanate adduct (a commercial product, Sumidur 
IL, manufactured by Sumitomo Bayer Urethane K.K.). 
The diol used above is glycols having a straight chain of 2 to 6 carbon 
atoms [e.g. ethylene glycol (molecular weight: 62, OH number: 1810), 
1,4-butanediol (molecular weight: 90, OH number: 1247), 1,6-hexanediol 
(molecualr weight: 118, OH number: 1122), etc.], and compounds having a 
C.sub.1 -C.sub.4 alkyl side chain on the above glycols [e.g. 
2,2,4-trimethyl-1,3-pentanediol (molecular weight: 146, OH number: 768), 
2-ethyl-1,3-hexanediol (molecular weight: 146, OH number: 768), 
2,2-diethyl-1,3-propanediol (molecular weight: 132, OH number: 850), 
2-n-butyl-2-ethyl-1,3-propanediol (molecular weight: 159, OH number: 706), 
etc.]. The OH number is calculated by the following equation: 
##EQU1## 
wherein f is average number of hydroxy groups per molecule of the diol, 
and M. W. is average molecular weight of the diol. 
The glycols having a straight chain of 7 or more carbon atoms are expensive 
and further tend disadvantageously to induce increased viscosity of the 
primer composition and hence is not preferable in view of less 
workability. Preferred diols have a molecular weight of not more than 150 
and the OH number of more than 700, more preferably more than 1000, 
because when the diols have a higher molecular weight, the final 
composition shows inferior film-forming properties (that is, gives merely 
soft film but can not give hard film), and further when the diols have a 
lower OH number, for example less than 700, the final composition shows 
too high viscosity and can not applied to smoothly, and further the diols 
having lower OH number have lower alkoxysilyl content which gives 
disadvantageously a final composition having less adhesion, and moreover, 
the final composition becomes soft like a sealing composition and hence 
can not be used as a primer. Thus, the preferred diols are glycols having 
a straight chain of 2 to 6 carbon atoms as mentioned above. 
The trialkoxysilane used in the above reaction includes, for example, 
aminotrialkoxysilanes such as aminomethyltriethoxysilane, 
N-(.beta.-aminoethyl)aminomethyltrimethoxysilane, 
N-(.beta.-aminoethyl)methyltributoxysilane, 
.gamma.-aminopropyltriethoxysilane, 
N-bis(.beta.-hydroxyethyl)-.gamma.-aminopropyltriethoxysilane, 
N-(.gamma.-aminoethyl)-.beta.-aminopropyltrimethoxysilane, 
N-(.beta.-aminoethyl)-.gamma.-amino-.beta.-methylpropyltrimethoxysilane, 
etc., and mercaptotrialkoxysilanes such as 
.gamma.-mercaptopropyltrimethoxysilane, 
.beta.-mercaptopropyltriethoxysilane, 
.gamma.-mercaptoethyltrimethoxysilane, 
.beta.-mercaptoethyltriethoxysilane, etc. 
The primer composition of this invention is prepared by dissolving the 
above silane coupling agent and the alkoxysilylated NCO-containing 
urethane prepolymer in a ratio of 1/50 to 5/1 by weight in an appropriate 
organic solvent, such as ketones (e.g. methyl ethyl ketone, acetone, 
etc.), esters (e.g. ethyl acetate, butyl acetate, etc.), ethers (e.g. 
diethyl ether, tetrahydrofuran, dioxane, etc.), aromatic hydrocarbons 
(e.g. toluene, xylene, benzene, etc.), and the like. The solvent is 
contained in an amount of 10 to 90 parts by weight, preferably 30 to 60 
parts by weight, based on the whole weight of the composition. When the 
primer composition is used for applying to glass, the composition may also 
be incorporated with carbon black (preferably acidic carbon black having 
pH 2.5-4 because of its extremely high weatherability), inorganic 
pigments, organic dyes, ultraviolet absorbers, and the like in order to 
prevent effectively from ultraviolet. The primer composition may also be 
incorporated with thickening agents, dehydrating agents, plasticizers, and 
the like. 
This invention is illustrated by the following Examples, but should not be 
construed to be limited thereto. 
EXAMPLE 1 
Trimethylolpropane adduct of hydrogenated xylylenediisocyanate (Takenate 
D-120N, manufactured by Takeda Chemical Industries, Ltd.) (27 g) is 
dissolved with stirring in methyl ethyl ketone (MEK) (60 g) under N.sub.2 
gas, and thereto are added 1,4-butanediol (1 g) and 
.gamma.-mercaptopropyltrimethoxysilane (KBM-803, manufactured by Shin-Etsu 
Chemical Co., Ltd.) (9 g), and the mixture is reacted with stirring at 
room temperature for 10 minutes and further under refluxing of MEK (at 
about 60.degree. C.) for 24 hours to give an alkoxysilylated 
NCO-containing urethane prepolymer. 
To the alkoxysilylated NCO-containing urethane prepolymer (30 g) are added 
as a silane coupling agent a reaction product (3 g) of 
N-(.beta.-aminoethyl)-.gamma.-aminopropyltrimethoxysilane (KBM-603, 
manufactured by Shin-Etsu Chemical Co., Ltd.) and 
.gamma.-glycidoxypropyltrimethoxysilane (KBM-403, manufactured by 
Shin-Etsu Chemical Co., Ltd.), carbon black (6 g) and MEK (11 g), and the 
mixture is dispersed with a ball mill to give a primer composition. 
The primer composition was applied to a glass plate and immediately a 
plasticizer [i.e. di(2-ethylhexyl) phthalate] or a solvent (toluene) was 
added thereto, but the film of the primer was not dissolved. 
Test of film forming property 
The primer composition prepared in the above (1) was applied to a glass 
plate in a thickness of 5-10 .mu.m and allowed to stand at 20.degree. C., 
65% relative humidity (RH), and the time till being dried (dryness in 
touch with finger) was measured. The result is shown in Table 1 together 
with the result in Reference Example. 
Test of weatherability 
The above primer composition was applied to a glass plate and allowed to 
stand at room temperature for 5 minutes, and thereto was applied a 
urethane sealant (Penguinseal #551, manufactured by Sunstar Giken K.K.), 
and the resultant was allowed to stand at room temperature for 5 days to 
cure the composition. The resultant glass plate was irradiated with a 
sunshine weatheromether for 2,000 or 4,000 hours, and thereafter, 
subjected to a test for adhesion by a knife-cut peeling test at 
180.degree.. The result is shown in Table 1 together with the result in 
Reference Example, wherein "CF" means cohesive failure of the sealant, and 
"AF" means interfacial failure between the glass and the primer film. 
TABLE 1 
______________________________________ 
Example 1 
Reference Example* 
______________________________________ 
Film-forming property 
less than 5 
50-60 minutes 
minutes 
Weatherability 
for 2,000 hours 
CF AF 
for 4,000 hours 
CF AF 
______________________________________ 
*In Reference Example, there was used a primer composition prepared as 
follows: 
In the same manner as described in Example 1, an alkoxysilylated 
NCOcontaining urethane prepolymer (30 g) prepared by reacting a 
polyisocyanate (Takenate D120N) with a mercaptosilane (KBM803) is mixed 
with a reaction product (3 g) of an aminosilane (KBM603) and an 
epoxysilane (KBN403), carbon black (6 g), MEK (11 g) and an acrylic resin 
(5 g), and the mixture is dispersed with a ball mill for 24 hours to give 
a primer composition. 
In the same manner as described in Example 1, an alkoxysilylated 
NCO-containing urethane prepolymer (30 g) prepared by reacting a 
polyisocyanate (Takenate D-120N) with a mercaptosilane (KBM-803) is mixed 
with a reaction product (3 g) of an aminosilane (KBM-603) and an 
epoxysilane (KBN-403), carbon black (6 g), MEK (11 g) and an acrylic resin 
(5 g), and the mixture is dispersed with a ball mill for 24 hours to give 
a primer composition. 
EXAMPLE 2 
Tolylenediisocyanate adduct (Sumidur IL, manufactured by Sumitomo Bayer 
Urethane K.K.) (30 g) is dissolved with stirring in MEK (60 g) under 
N.sub.2 gas, and thereto are added 50% (w/w) solution (4 g) of 
2,2,4-trimethyl-1,3-pentanediol (CS-8, manufactured by Chisso Petroleum 
Co., Ltd.) in MEK and .gamma.-mercaptopropyltrimethoxysilane (KBM-803) (10 
g), and the mixture is reacted with stirring at room temperature for 10 
minutes and further under refluxing of MEK for 24 hours to give an 
alkoxysilylated compound of a high molecular weight polyisocyanate. 
To the alkoxysilylated NCO-containing urethane prepolymer thus obtained (20 
g) are added .gamma.-glycidoxypropyltrimethoxysilane (KBM-403) (2 g) and 
MEK (18 g), and the mixture is stirred for 1 hour to give a primer 
composition. 
The primer composition was subjected to the tests of plasticizer resistance 
and solvent resistance like in Example 1, but the primer film was not 
dissolved. 
Test of moisture resistance 
The above primer composition was applied to a stainless steel plate and 
allowed to stand at room temperature for 5 minutes, and thereto was 
applied a urethane sealant (Penguinseal #551), and the resultant was 
allowed to stand at room temperature for 5 days to cure the composition. 
The resultant plate was kept at 50.degree. C.., 90% RH for 30 or 60 days, 
and thereafter, subjected to a test for adhesion by a knife-cut peeling 
test at 180.degree. like in Example 1. The result is shown in Table 2 
together with the result in Reference Example (the same as in Example 1). 
TABLE 2 
______________________________________ 
Mositure resistance: 
Example 2 Reference Example 
______________________________________ 
for 30 days CF 5% AF 
for 60 days CF 50% AF 
______________________________________