 |
Description  |
|
|
The present invention relates to primer compositions and more particularly
to primer compositions for bonding silicone elastomers to porous,
nonmetallic substrates.
Heretofore, silicone elastomers have been bonded under heat and pressure to
various substrates by coating the substrates with various silanes, such as
alkyacyloxysilanes, alkyalkoxysilanes, alkoxyacyloxsilanes or
vinyltriacyloxysilanes prior to the application of the silicone elastomer.
Among the silanes which have been used as primers are tetraethoxysilane,
t-butoxytriethoxsilane, methyltriethoxysilane, methyltriacetoxysilanes,
ethyltriacetoxysilane, propyltriacetoxysilane, and the like.
Although the primers known heretofore exhibit good adhesion to metallic
substrates, they do not exhibit good adhesive properties when applied to
porous substrates which are subject to high humidity or where they are in
direct contact with water.
Therefore, it is an object of this invention to provide unique primer
compositions. Another object of this invention is to provide primer
compositions for silicone elastomers. Still another object of this
invention is to provide primer compositions which are resistant to water.
A further object of this invention is to provide a method for bonding room
temperature vulcanizable organopolysiloxanes to substrates which are in
contact with water.
The foregoing objects and others which will become apparent from the
following description are accomplished in accordance with this invention,
generally speaking, by providing compositions which may be used for
bonding silicone elastomers to porous nonmetallic substrates. These primer
compositions are obtained by reacting an acrylate with an
acryloxyalkylalkoxysilane in the presence of a free radical initiator and
an organic solvent at a temperature of from about room temperature up to
the reflux temperature of the solvent.
The acrylate or substituted acrylate which may be employed in this
invention may be represented by the following formula
##STR1##
where R is a monovalent hydrocarbon radical having from one to ten carbon
atoms or hydrogen, R' is a monovalent hydrocarbon radical or a divalent
hydrocarbon radical having up to 10 carbon atoms and m is a number of from
1 to 4. When m is 1 then R' is a monovalent hydrocarbon radical and when m
is 2 to 4, R' is a divalent hydrocarbon radical.
The acryloxyalkylalkoxysilane or substituted acryloxyalkylsilane employed
in this invention may be represented by the following formula
##STR2##
in which R is the same as above and R" is a monovalent hydrocarbon radical
having from 1 to 10 carbon atoms, R"' is a divalent hydrocarbon radical
having from 2 to 10 carbon atoms and n is a number of from 1 to 3.
Examples of suitable monovalent hydrocarbon radicals represented by R, R'
and R" above are alkyl radicals such as methyl ethyl, propyl, butyl,
pentyl, hexyl, octyl, and decyl; aryl radicals such as the phenyl and
naphthyl radicals; alkaryl radicals such as tolyl, xylyl, cumenyl and
ethylphenyl and aralkyl radicals such as benzyl, .alpha.-phenylethyl,
B-phenylethyl, .alpha.-phenylbutyl and the like. Examples of suitable
divalent hydrocarbon radicals represented by R' and R"' are ethylene,
trimethylene, tetramethylene, hexylmethylene, octamethylene, and the like.
Examples of suitable acrylates which may be employed are methyl acrylate,
ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, methyl
methacrylate, ethyl methacrylate, butyl methacrylate, isobutyl
methacrylate, lauryl methacrylate, stearyl methacrylate, 1,3-butylene
dimethylacrylate, and the like.
Suitable examples of polyfunctional acrylates, i.e., acrylates having at
least two nonconjugated olefinic linkages are allyl methacrylate, allyl
acrylate, methallyl acrylate, methallyl methacrylate, vinyl acrylate,
vinyl methacrylate, ethylene dimethacrylate, tetramethylene diacrylate,
1,3-butylene dimethacrylate, and the like.
Examples of suitable acryloxyalkylalkoxysilanes which may be employed are
methacryloxyethyltrimethoxysilane, methacryloxypropyltrimethoxysilane,
methacryloxybutyltrimethoxysilane, methacryloxhexyltrimethoxysilane,
methacryloxyethyltriethoxysilane, methacryloxyethyltributoxysilane,
methacryloxyethyldimethoxybutoxysilane,
methacryloxyethyldibutoxymethoxysilane and the like.
The compositions of this invention are prepared by reacting an acrylate or
substituted acrylate with an acryloxyalkylalkoxysilane or substituted
acryloxyalkylalkoxysilane in the presence of a free radical initiator and
an organic solvent at a temperature of from about room temperature up to
the reflux temperature of the solvent and more preferably at a temperature
of from about 50.degree. to 150.degree. C.
Suitable free radical initiators which may be employed are organic
peroxides and certain azo-compounds in which both the nitrogen atoms of
the azo linkage are attached to a tertiary carbon atom and the remaining
valences of the tertiary carbon atom are satisfied by nitrile, carboxy,
cycloalkylene or alkyl radicals, preferable having from 1 to 18 carbon
atoms.
Examples of suitable peroxide initiators are compounds of the formula
R.sub.1 OOH, R.sub.1 OOR.sub.1, R.sub.1 COOOR.sub.1, or (R.sub.1
COO).sub.2 in which R.sub.1 is an organic radical. Specific examples of
peroxides which are operative in this invention are hydroperoxides such as
t-butyl hydroperoxide, cumene hydroperoxide, and decalin hydroperoxide;
dialkyl peroxides such as di-t-butyl and dicumyl peroxide; diacyl
peroxides such as benzoyl peroxide; cyclic peroxides such as ascaridole;
diperoxides such as 2,5-dimethyl-2,5-di-t-butyl peroxyhexane; peresters
such as t-butyl perbenzoate, t-butylperoxy isopropyl carbonate and t-butyl
peroctoate; keto peroxides such as acetone peroxide and cyclohexanone
peroxides.
The amount of free radical initiator employed is not critical. Thus, any
amount capable of producing a perceptible degree of fine radicals is
suitable. Generally, amounts as low as 0.05 percent of the more reactive
peroxide initiator based on the weight of the reactants is adequate in
most cases. When the initiator is added in small increments, the total
amount required may be as little as 0.01 percent based on the weight of
the reactants, although amounts up to about 1 percent may be employed.
Under certain circumstances it may be desirable to dilute the initiator
with an inert solvent especially when a normally solid initiator is
employed. In such cases the concentration of initiator may be as low as 1
percent or less, but it is preferably in the range of from about 5 to
about 20 percent. Any solvent with low chain transfer activity may be
used. Examples of suitable solvents include benzene, toluene, xylene,
chlorobenzene, cyclohexane, and ethyl acetate.
Several considerations determine the choice of temperature to be used in
the reaction, although generally speaking, temperatures in the range of
from room temperature up to the reflux temperature of the solvent and more
preferable from about 50.degree. to 150.degree. will be found suitable.
For best results and convenient reaction times, the temperature and
initiator should be chosen so that the half-life is between about 15
minutes and 10 hours and more preferably between about one hour and six
hours. Table I shows the optimum temperature ranges for various free
radical initiators.
TABLE I
______________________________________
Four-hour Preferred
half-life temperature
Temperature, range,
Initiator .degree. C. .degree. C.
______________________________________
2,4-dichlorobenzoyl
peroxide 61 60-75
Azobisisobutyronitrile
73 70-85
Benzoyl peroxide
79 75-90
t-butyl peroctoate
80 75-90
1,1-di-t-butylperoxy-
3,3,5-trimethylcyclo-
hexane 101 100-110
t-butylperoxy
isopropyl carbonate
107 105-115
t-butyl perbenzoate
113 110-125
Di-t-butyl peroxide
135 130-145
______________________________________
Examples of suitable organic solvents which may be employed are aromatic
hydrocarbons such as benzene, toluene, xylene, and the like; halogenated
aromatic hydrocarbons such as chlorobenzene; aliphatic hydrocarbons such
as pentane, hexane, octane, decane and halogenated aliphatic hydrocarbons
such as methylene chloride, carbon tetrachloride, perchloroethylene and
the like. Other organic solvents which may be employed are the ketones
such as methyl ethyl ketone; esters such as ethyl acetate; ethers such as
diethyl ether, dibutyl ether and the like. It is preferred that the
solvent employed be sufficiently volatile to evaporate under the coating
conditions.
The amount of acrylate and acryloxyalkylalkoxysilane employed in the primer
composition is not critical and may range from a mol ratio of from 1 to 99
percent to 99 to 1 percent and more preferably from about 5 to 95 percent
to 95 to 5 percent.
Surprisingly, it was found that the stability of the primer composition is
substantially improved if one or more of the alkoxy groups of the
acryloxyalkylalkoxysilane contain at least 3 carbon atoms.
It is preferred that the primer composition be applied as a solution which
contains from about 5 to about 60 percent by weight of the product
obtained from the reaction of the acrylate or substituted acrylate and the
acryloxyalkylalkoxysilane or substituted acryloxyalkylalkoxysilane and
more preferably from about 10 to about 50 percent by weight based on the
total weight of the reaction product and the solvent. It has been found
that with increased porosity of the substrate, a higher concentrated
solution is necessary in order to provide good adhesion.
The primer compositions of this invention may be applied to any porous,
nonmetallic substrate by spraying, dipping, brushing, wiping and the like
and thereafter dried at any temperature from about room temperature up to
the boiling point of the solvent. Where higher temperatures are used, the
primer may be dried in about 10 seconds while lower temperatures may
require relatively longer drying times.
These compositions may be applied as primers to any porous, nonmetallic
substrates such as masonry materials. Other substrates which may be
employed are carbon, plastic, ceramic, cellulosic materials, such as
paper, wood and the like.
These compositions are primers for any one- or two-component
organopolysiloxane compositions which are curable at ambient temperature.
Examples of suitable one component organopolysiloxane compositions are
those which are endblocked with groups that are hydrolyzable in ambient
moisture. These compositions may be represented by the general formula
##STR3##
in which R"" is a monovalent hydrocarbon radical or halogenated monovalent
hydrocarbon radical having from 1 to 18 carbon atoms, or a cyanoalkyl
radical, Q is a siloxane unit of the formula
##STR4##
or a modified siloxane of the formula
##STR5##
in which R'" and R"" are the same as above, A is a polymeric organic
radical linked to R'" by a carbon-to-carbon linkage, Z represents a
hydroxyl group or a group hydrolyzable in ambient moisture, x is a number
of from 0 to 20,000 and y is a number of from 1 to 500.
The modified organopolysiloxane is prepared by graft polymerizing an
organopolysiloxane of the formula
##STR6##
wherein R"" and x are the same as above with a polymerizable organic
monomer having aliphatic unsaturation in the presence of a free radical
initiator. The modified organopolysiloxanes and their methods of
preparation are described in U.S. Pat. Nos. 3,555,109, 3,627,836 and
3,776,875 to Getson; U.S. Pat. No. 3,631,087 to Lewis et al and U.S. Pat.
No. 3,694,478 to Adams et al, which references are made a part of the
disclosure of the present invention. These modified organopolysiloxanes
consist of organopolysiloxane polymers having attached thereto at least
one or more side chains or branches consisting of a carbon-to-carbon chain
polymer. In the formation of these polymers, hydrogen is abstracted from
the organopolysiloxane polymer by a free radical initiator to form an
active site for grafting the organic monomer and/or polymer thereto.
Various cross-linking agents may be combined with the organopolysiloxane to
form curable elastomers. Examples of suitable cross-linking agents are
silanes and siloxanes containing at least three hydrolyzable groups as
well as organohydrogenpolysiloxanes of the formula
##EQU1##
in which R"" is the same as above and w is a number less than 2, but
greater than zero.
A one-component room temperature vulcanizable composition may be prepared
by mixing a hydroxyl-terminated organopolysiloxane or modified
organopolysiloxane with a silane of the general formula
X.sub.4-t SiY.sub.t
wherein X is a relative inert group such as an alkyl or aryl group; Y is a
group hydrolyzable in ambient moisture, e.g., an acyloxy, oximo, alkoxy,
aminoxy, amido, amino, halogen or phosphato group and t is a number of
from 3 to 4.
Examples of suitable silanes are methyltriacetoxysilane,
isopropoxytriacetoxysilane, methyltriacetoximosilane,
methyltris(diethylphosphatos)silane and the like.
The silanes are added to the hydroxyl-terminated organopolysiloxanes and
cured by merely exposing them to atmospheric moisture with or without any
additional water vapor.
Generally, the amount of silane cross-linking agent may range from about
0.5 to about 10 percent and more preferably from about 1 to 5 percent by
weight based on the weight of the organopolysiloxane.
In the two component system, hydroxyl terminated organopolysiloxanes or
modified organopolysiloxanes are mixed with cross-linking agents such as
polyalkoxysilanes of the formula
(X'O).sub.z Si(Y').sub.4-z
or polyalkoxysiloxanes in which the silicon atoms are linked through
Si-O-Si linkages and the remaining valences of the silicon atom are
satisfied by X'O and/or Y' to form compositions which are curable at room
temperature. In the above formula the groups represented by X' are
monovalent hydrocarbon radicals having up to 8 carbon atoms while those
represented by Y' are monovalent hydrocarbon radicals or halogenated
monovalent hydrocarbon radicals having up to 8 carbon atoms and z has a
value of from 3 to 4.
Examples of suitable monovalent hydrocarbon radicals represented by X' are
methyl, ethyl propyl, butyl, hexyl, octyl, phenyl, vinyl, allyl,
ethylallyl, and the like. Radicals represented by Y' may be the same as
the radicals represented by X' above as well as the corresponding
halogenated groups such as chloromethyl, 2-bromo-4,6-diiodophenyl,
1,2-fluorovinyl, 6-chlorohexyl and the like. The polyalkoxysilanes used
herein include monoorganotrihydrocarbonoxy silanes, tetrahydrocarbonoxy
silanes and partial hydrolysates thereof. Examples of suitable polyalkoxy
compounds are alkyl silicates, polysilicates or partially hydrolyzed
silicates, such as ethylsilicate "40". Other cross-linking agents are
ethyl trimethoxysilane, methylbutoxydiethoxysilane,
propyltripropoxysilane, methyltriethoxysilane, ethyltriethoxysilane,
tetraethylorthosilicate and n-butyl orthosilicate. Example of alkyl
polysilicates are ethylpolysilicates, isopropylpolysilicates,
butylpolysilicates; siloxanes such as dimethyltetraethoxydisiloxane,
trimethylpentabutoxydisiloxane, trimethylpentabutoxytrisiloxane and the
like.
The polyalkoxysilanes and polyalkoxysiloxanes employed herein may be used
either alone or in combination. They should be used in an amount of from
about 0.5 to about 20 percent or more preferably from about 1 to 10
percent by weight based on the weight of the organopolysiloxane.
The two-component organopolysiloxane compositions are cured by mixing the
hydroxyl-terminated organopolysiloxanes with the polyalkoxysilane or
polyalkoxysiloxane cross-linking agents in the presence of a curing
catalyst. Examples of suitable catalysts are metallic salts of carboxylic
acids, in which the metals are lead, tin, zirconium, iron, cadmium,
titanium, calcium and maganese. It is preferred that the carboxylic acid
salts of the above metals be characterized by the properties that the
carboxylic acid radical contain up to 18 carbon atoms and more preferably
up to about 16 carbon atoms. Likewise, it is preferred that the salts be
soluble in the organopolysiloxane.
Examples of suitable matallic salts are tin naphthenate, leat octoate, tin
octoate, iron stearate, tin oleate, antimony octoate, tin butyrate and the
like. Other tin catalysts which may be employed include dibutyltin
butoxychloride, dibutyltin dilaurate, bis-(dibutylphenyltin)oxide,
bis-(acetoxdibutyltin)oxide, bis(tributyltin)oxide, dibutoxydibutyltin,
t-butyltin hydroxide, triethyltin hydroxide, diamyldipropoxytin,
dioctyltin dilaurate, diphenyloctyltin acetate, dodecyldiethyltin acetate,
trioctyltin acetate, triphenyltin acetate, tridecyltin laurate and the
like. These catalysts may be dispersed in a solvent and then added to the
hydroxyl-terminated organopolysiloxane composition or they may be
dispersed in a suitable filler or additive and thereafter milled with the
organopolysiloxane composition.
Examples of suitable hydrocarbon solvents which may be employed to disperse
the catalysts are benzene, toluene, xylene and the like. Also, halogenated
hydrocarbons such a tetrachloroethylene or chlorobenzene; organic ethers
such as diethyl ether, dibutyl ether and hydroxyl free fluid polysiloxanes
may be used as solvents. It is preferred that the solvent be sufficiently
volatile to evaporate off at room temperature.
The amount of catalyst used in these curing systems may range from about
0.05 to about 2 percent by weight and more preferably from about 0.1 to
about 1 percent by weight based on the weight of the composition. A
mixture of two or more of the catalysts mentioned above may be used, if
desired.
Although not essential, fillers may be incorporated in these curable
organopolysiloxane compositions to further improve the physical properties
for some commercial applications. Examples of suitable fillers are fumed
silicas, high surface area precipitated silicas, silica aerogels as well
as coarser silicas such as diatomaceous earth, crushed quartz and the
like. Other fillers which may be used are metallic oxides such as titanium
oxide, ferric oxide, zinc oxide; fibrous fillers such as asbestos, fibrous
glass and the like. Other additives such as pigments, antioxidants,
ultraviolet absorbers and the like may be included in these compositions.
This invention can be used to produce a wide range of products including
silicone rubber coated substrates which may be used as dampers in sonar
devices and as protective coatings where silicone rubber is applied to
plastic sheets and films. In addition porous substrates such as masonry
and cellulosic materials may be coated with silicone rubber and subjected
to a water environment and still maintain its adhesive properties.
The embodiments of this invention are further illustrated by the following
examples which all parts are be weight unless otherwise specified.
EXAMPLE 1
A composition is prepared by adding over a period of about 6 hours a
mixture containing 9.7 parts of methacryloxypropyltrimethoxysilane, 81
parts of ethyl acrylate and 1.2 parts of di-t-butylperoxide to a reactor
containing 90 toluene heated to reflux temperature and thereafter refluxed
for an additional hour. An opaque viscous product is obtained which is
brush applied to a porous masonry substrate and dried at room temperature.
A room temperature vulcanizable organopolysiloxane composition containing
100 parts of a hydroxyl terminated dimethylpolysiloxane having a viscosity
of about 4000 cs. at 25.degree. C., 5 parts of methyltriacetoxysilane and
8 parts of Cab-O-Sil is applied to the dried substrate and cured in the
presence of atmospheric moisture for 48 hours. The coated masonry
substrate is then immersed in water for 7 days, after which the bond is
tested by trying to remove the silicone elastomer from the primed
substrate. Excellent adhesion between the silicone elastomer and the
masonry substrate is observed.
EXAMPLE 2
Four primer compositions are prepared in accordance with the procedure of
Example 1 in which 13 parts of methacryloxypropyltrimethoxysilane are
reacted with 48 parts of ethyl methacrylate in the presence of
di-t-butylperoxide and varying amounts of toluene. The resultant
compositions are each applied as a film to porous masonry substrates,
dried and thereafter the room temperature vulcanizable organopolysiloxane
composition described in Example 1 is applied thereto. The coated masonry
substrates are each immersed in water for 7 days after which the bond is
tested by trying to remove the silicone rubber from the primed substrate.
The results of these tests are illustrated in the following table as
Examples 2(a) to 2(d).
In a comparative test a porous masonry substrate is treated with a
composition containing 30 parts of vinyltriacetoxysilane and 70 parts of
toluene, dried and thereafter the room temperature vulcanizable
organopolysiloxane composition described in Example 1 is applied thereto.
The coated masonry substrate is immersed in water for 7 days after which
the bond is tested by trying to remove the silicone rubber from the primed
substrate. The results are illustrated in Table II as Example 2(e).
In another comparative test a porous masonry substrate is coated with a
composition containing 30 parts of vinyltriethoxysilane and 70 parts of
toluene, dried and thereafter the room temperature vulcanizable
organopolysiloxane composition described in Example 1 is applied thereto.
After curing for 48 hours at room temperature the coated masonry substrate
is immersed in water for 7 days after which the bond is tested in
accordance with the procedure described above. The result is illustrated
in Table II as Example 2(f).
In a similar test, the room temperature vulcanizable organopolysiloxane
composition described in Example 1 is applied to an unprimed porous
masonry substrate. After curing for 48 hours at room temperature the
coated substrate is immersed in water for 7 days after which the bond is
tested by removing the rubber from the primed substrate. The result is
illustrated in Table II as Example 2(g).
TABLE II
______________________________________
Ethyl Methacryloxy
Methyl- Propyltrim-
Example acrylate,
ethoxysilane,
Toluene,
No. Parts Parts Parts Adhesion
______________________________________
2(a) 48 13 122 Excellent
2(b) 48 13 244 Good
2(c) 48 13 549 Fair
2(d) 48 13 1159 Poor
Comparison
Examples
2(e) 30* 0 70 None
2(f) 30** 0 70 None
2(g) 0 0 0 None
______________________________________
*vinyltriacetoxysilane
**vinyltriethoxysilane
EXAMPLE 3
A composition prepared in accordance with Example 2(a) is applied to a
porous masonry substrate and dried. A room temperature vulcanizable
organopolysiloxane composition which is prepared by mixing 100 parts of a
hydroxyl-terminated dimethylpolysiloxane having a viscosity of about
10,000 cs. at 25.degree. C. with 8 parts of
methyltris(cyclohexylamino)silane, 50 parts of a trimethylsiloxy
endblocked dimethylpolysiloxane having a viscosity of 50 cs. at 25.degree.
C. and 17 parts of diatomaceous earth is applied to the coated masonry
substrate and exposed to atmospheric moisture for 48 hours. The coated
substrate is then immersed in water for 7 days after which the bond is
tested by removing the rubber from the primed substrate. Excellent
adhesion between the silicone elastomer and substrate is observed.
EXAMPLE 4
A primer composition is prepared by adding a mixture containing 62 parts of
butyl acrylate, 13 parts of methacryloxypropyltrimethoxysilane and 0.7
part of di-t-butylperoxide to a reactor containing 75 parts of toluene.
The reaction mass is heated to reflux temperature and maintained at this
temperature for 6 hours. The resultant product is cooled to room
temperature after which 100 parts of toluene are added. The product is
then applied by brushing onto a porous masonry substrate and dried at room
temperature. The room temperature vulcanizable organopolysiloxane
composition described in Example 1 is applied thereto and cured at room
temperature for 48 hours. The coated masonry substrate is immersed in
water for 7 days after which the bond between the primed substrate and the
silicone elastomer is tested. Good adhesion between the silicone rubber
and the primed substrate is observed.
EXAMPLE 5
A primer composition is prepared in accordance with Example 4, except that
100 parts of tetramethylene diacrylate is substituted for the butyl
acrylate and 190 parts of tolune are employed. The reaction product is
applied to a concrete substrate and dried. The room temperature
vulcanizable organopolysiloxane composition of Example 1 is applied to the
coated substrate and cured at room temperature. The coated substrate is
immersed in water for 7 days, after which time the adhesive bond is
determined. Excellent adhesion between the silicone rubber and the coated
substrate is observed.
EXAMPLE 6
(a) A modified organopolysiloxane composition is prepared by heating a
mixture containing 80 parts of a hydroxyl-terminated dimethylpolysiloxane
(400 cs. at 25.degree. C.), 54 parts of butyl acrylate and 66 parts of
styrene to 150.degree. C. with agitation. A solution containing 0.4 part
of t-butylperbenzoate in 6 parts of toluene is added in increments of 0.3
part at intervals of 20 minutes. When the addition is complete, the
reaction mass is heated at 150.degree. C. for an additional 30 minutes.
About 100 parts of the modified organopolysiloxane prepared above is mixed
with 5 parts of ethyl silicate "40" and 0.5 part of dibutyltin
butoxychloride and applied to a porous substrate coated with the
composition of Example 1 and dried. The modified organopolysiloxane
composition is cured at room temperature for 48 hours and then immersed in
water for 7 days. Excellent adhesion between the modified
organopolysiloxane composition and the porous substrate is observed.
(b) The procedure of Example 6 (a) is repeated except that a room
temperature curable organopolysiloxane composition containing 5 parts of
methyltriacetoxysilane, about 100 parts of the modified organopolysiloxane
prepared in accordance with Example 6 (a) and about 8 parts of Cab-O-Sil
is applied to the coated substrate. The organopolysiloxane composition is
cured for 48 hours after which time the coated substrate is immersed in
water for 7 days.
Excellent adhesion between the silicone elastomer and the porous substrate
is observed.
EXAMPLE 7
A porous masonry substrate is primed with the composition of Example 1,
dried and thereafter a room temperature vulcanizable organopolysiloxane
composition containing 5 parts of ethyl silicate "40", about 100 parts of
a hydroxyl-terminated dimethylpolysiloxane having a viscosity of about
2000 cs. at 25.degree. C., about 0.5 part of dibutyltin dilaurate and 60
parts of iron oxide is applied thereto.
The room temperature vulcanizable organopolysiloxane composition is cured
at room temperature for 48 hours, after which time the masonry substrate
is immersed in water for 7 days. Excellent adhesion between the silicone
rubber and the primed substrate is observed.
EXAMPLE 8
In a comparative test, a composition is prepared by adding dropwise over a
period of 30 minutes a mixture containing 90 parts of
methacryloxypropyltrimethoxysilane and 0.9 part of di-tertiary butyl
peroxide to a reactor containing 180 parts of toluene at reflux
temperature. The reactants are refluxed for an additional 5 hours, cooled
and then applied to a concrete substrate. After drying overnight, the room
temperature vulcanizable composition prepared in accordance with Example 1
is applied and cured in the presence of atmospheric moisture for 48 hours.
The coated substrate is then immersed in water for 7 days, after which
time the adhesive bond between the silicone elastomer and the primed
substrate is determined. Only slight adhesion between the silicone
elastomer and the primed substrate is observed.
EXAMPLE 9
In a comparison test, a composition is prepared by refluxing 50 parts of
ethyl methacrylate, 0.5 part of tertiary butylperoxy isopropyl carbonate
and 100 parts of toluene in a reactor for about 6.5 hours. The reaction
mass is cooled and applied to a concrete substrate. After drying, a room
temperature vulcanizable composition prepared in accordance with Example 1
is applied to the dried substrate and cured in the presence of atmospheric
moisture for 48 hours. The coated substrate is immersed in water for 7
days, after which time the adhesive bond between the silicone elastomer
and the primed substrate is determined. No adhesion between the silicone
elastomer and the primed substrate is observed.
EXAMPLE 10
When room temperature vulcanizable silicone elastomers are applied to other
substrates such as wood, vinyl, ceramic and carbon black surfaces that
have been primed with the primer composition of Example 1, excellent
adhesion of the silicone elastomers is observed even after being immersed
in water for several days.
It is to be understood that this invention is not limited to the specific
examples set forth herein and that modifications may be made without
departure from the spirit and scope of the appended claims.
* * * * *
|
|
 |
|
 |
Description |
|
