Note: Descriptions are shown in the official language in which they were submitted.
T~is invention relates to silicone elastomers, particularly to
paintable silicone elastomers and more particularly to a process for pre-
paring silicone elastomers having paintable surfaces.
Heretofore, silicone elastomers having a paintable surface have
been prepared by adding silane additives to organopolysiloxane compositions
prior to crosslinking. Schulz discloses in U.S. Patent N0 3,812,164
issued May 21, 1974 to J.R. Schulz adding an amide silane of the formula
O
(CH30)3 Si(C~12)3 S CH2 CH2 CNH2
to an organopolysiloxane composition containing a hydroxyl endblocked poly-
dimethylsiloxane,~an ethyl orthosilicate and a metallic salt of a carboxyl-
ic acid. The resultant composition vulcanizes at room temperature to form
an elastomer whose surface is paintable.
Also Schulz discloses in U.S. Patent No. 3,836,502 issued Sept.
17, 1974 to J.R. Schulz a composition containing (a~ hydroxyl endblocked
polydimethylsiloxàne, (b) an alkoxy compound, e.g. ethyl orghosilicate,
(c~ a metallic salt and (d) a silane of the formula
n
(C~30)3 si(C112) S~C>
(CH3) u
which is vulcanizable at room temperature to form an elastomer whose sur-
face is paintable.
U.S. Patent No. 3,836,503 issued Sept. 17, 1974 to J.R. Schulz
discloses the addition of a silane of the formula
(CH30)3 Si ch2 CH2 SCH6H5
. ,~
to a room temperature vulcanizable composition to Eorm an elastomer having
a paintable surfaca.
-la-
~;
z~
Young, discloses applying a silane to an aqueous based paint or caulking
shortly after its applicatlon to a substrate. Also, U.S. Patent N0. 4,038,
293 issued July 26, 1977 to Smith et al disclose quinonoid dyes containing
organosiloxane units which are used as painting materials.
A room temperature vulcaniæable organopolysiloxane composition
con~taining a silane having at least one amino substituent bonded to silicon
through Si-C bonding or alkoxyhydrocarbonoxy radical bonded to silicon
through silicon-oxygen linkage is disclosed in U.S. Patent N0. 3,678,003
issued July 18, 1972 to W. Kaiser et al. Even though the resultant elasto-
mer exhibits improved adhesion to a substrate, the pressure of the silane
in the room temperature vulcanizable organopolysiloxane composition does not
improve the paintability of the elastomer.
Therefore, an object of this invention is to provide a process for
imparting paintable surfaces to silicone elastomers which are obtained from
vulcanizable organopolysiloxane compositions.
In accordance with an aspect of this invention, a process is pro-
vided for coating a crosslinked organopolysiloxane elastomer with a paint
composition which comprises applying at least one silane having at least
one amino group bonded to a silicon atom via carbon and at least one mono-
valent hydrocarbon radical which is bonded to silicon via oxygen and which
may be substituted with an amino or an alkoxy group and/or partial hydroly-
zates thereof to a crosslinked organopolysiloxane elastomer; and there-
after applying a paint selected from the group consisting of lacquers,
aqueous dispersions or varnishes based on nitrocellulose, polyvinyl chlor-
ide, polyvinyl acetate, copolymers of pGlyvinyl acetate and copolymers of
styrene.
In another embodiment of this in~iention, the silane may be ad-
mixed
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~28~
with the paint snd the resultant mixture is then applied to the crosslinked
organopolysiloxane elastomer.
By a variant thereof, the monovalent hydrocarbon radical is sub-
stituted with a group selected from the class consisting of amino groups,
alkoxy groups, and mixtures thereof.
By another variant, the silane is represented by the formula
[R22N(CH2)mYa(CH2)m~bsi(oR )c 4-b-c
where R i6 selected from the group consisting of monovalent hydrocarbon
radicals and substituted monovalent hydrocarbon radicals, R2 is selected
from the group consisting of hydrogen, monovalent hydrocarbon radicals and
substituted monovalent hydrocarbon radicals, R3 is selected from the group
consisting of monovalent hydrocarbon radicals, amino substituted monovalent
hydrocarbon radicals and alkoxy substituted monovalent hydrocarbon radicals,
Y is selected from the group consisting of oxygen and NR , a is 0 or 1, b
and c each represent integèrs of 1, 2 or 3, with the proviso that the sum
of b + c may not exceed 4, and m is an integer of from 1 to 10.
By other variants, the catalyst selected from the group consisting
of a condensation catalyst and a hydrolysis catalyst is applied to the
crosslinked organopolysiloxane; or a catalyst selected from the group con-
sisting of a condensation catalyst and a hydrolysis catalyst is mixed withthe organosilicon compound.
Compared to Ithe processes described heretofore,for preparing
paintable organopolysiloxanes, the process of aspects of this invention has
several advantages over the prior art. For example, the process of aspects
of this invention is applicable for several different types of crosslin~ed
organopolysiloxanes and/or paints. Moreover, readily available organosili-
con compositions may be used in the process of aspects of this invention.
Although any crosslinkable organopolysiloxane may be used in the
process of aspects of this invention, it is preferred that diorganopoly-
-- 3 --
silo~ane-based compositions which may be stored under anhydrous conditions
but when exposed to atmospheric moisture, crosslink (cure) at room tempera-
ture to form elastomers, be employed.
The diorganopolysiloxane-based compositions which may be stored
under anhydrous conditions but which crosslink to form elastomers when ex-
posed to atmospheric moisture at room temperature, may be prepared from
the same constituents and quantities of constituents which have been used
heretofore to form silicone elastomers at room temperature. These diorgano-
polysiloxane-based compositions are prepared by mixing at least one silicon
compound containing at least 3 silicon-bonded hydrolyzable groups with an
organopolysiloxane containing terminal condensable groups and other mater-
ials, e.g. fillers, e.g., silicon dioxide which is pyrogenically produced in
the gaseous phase~ or calcium carbonate, condensation catalysts, e.g. di-
butyltin dilaurate, emollients, e.g. dimethylpolysiloxanes which are liquid
at room temperature and which are endblocked by trimethylsiloxy groups, and
polyoxyalkylene glycols.
Examples of silicon compounds having at least 3 hydrolyzable
groups which are bonded to silicon and which may be used in the preparation
of the compositions are silanes having the general formula:
a 4-a '
wherein R represents the same or different monovalent hydrocarbon radicals
or substituted monovalent hydrocarbon radicals, Z represents the same or
different hydrolyzable groups, and a is zero or 1, and partial hydrolysates
thereof containing from 2 to 10 silicon atoms per molecule.
Examples of hydrocarbon radicals represented by R are alkyl radi-
cals, e.g. thé methyl, ethyl, n-propyl, and isopropyl radicals as well as
octadecyl radicals; alkenyl radicals e.g. the vinyl and allyl radicals;
cycloaliphatic hydrocarbon radicals, e.g. the cyclopentyl and cyclohexyl
radicals, as well as methylcyclohexyl and cyclohexenyl radicals; aryl radi-
cals e.g. the phenyl radical and xenyl radical; aralkyl radicals, e.g.
benzyl, beta-phenylethyl and the beta-phenylpropyl radicals; as well as
alkaryl radicals e.g. the tolyl radical.
Exa~ples of substituted hydrocarbon radicals represented by R
are the haloaryl radicals, e.~. chlorophenyl and bromophenyl radicals, as
well as cyanoalkyl radicals, e.g. the beta-cyanoethyl radical.
The methyl radical is the preferred R radical since it
is readily available.
Examples of hydrolyzable groups represented by Z are
acyloxy radicals (-OOCRl), hydrocarbonoxy radicals (-ORl) and
substituted hydrocarbonoxy radicals, aminoxy radicals (-ONR2),
amino radicals (-NR21), acylamino radicals (-NRlC0Rl), oxime
radicals (-ON=CR2) and phosphate radicals [-OP(OR ) ~
In the above formulas R represents the same or dif-
ferent, monovalent hydrocarbon radicals or substituted mono-
valent hydrocarbon radicals. In some of the formulas described
abov~, at least one of the Rl radicals may also represent
hydrogen.
Examples of acyloxy radicals are the formyloxy and the
acetoxy radicals.
Examples of hydrocarbonoxy radicals are the methoxy,
20ethoxy and the isopropenyloxy radicals.
An example of a substituted hydrocarbonoxy radical
- ls the methoxyethyleneoxy radical.
Examples of aminoxy radicals are the dimethylaminoxy
and diethylaminoxy radicals.
Examples of amino radicals are the n-butylamino, sec-
butylamino and the cyclohexylamino radicals.
An example of an acylamino radical is the benzoyl-
amino radical,
Examples of oxime radicals are the acetaldoxime,
acetonoxime and the 2-butanonoxime radicals.
An example of a phosphate radical is the di-n-butyl-
phosphate radical.
~ 5 --
B~
Addittonal examples of cross:Linked organopolysiloxanes which may
be coated using the process of aspects of this invention are elastomers or
resin-like products of the so-called "two-component system". The "two-
component system" comprises a dimethylpolysiloxane having an Si-bonded hy-
droxyl group in each ot i-~s terminal groups and filler in one package, and
a mixture of a polyethylsilicate and a catalyst 9 e.g. dibutyltin dilaurate
in a~other package. When the components of these two packages are mixed,
they crosslink to form elastomers.
Other examples of crosslinked organopolysiloxanes which may be
coated using the process~of aspects of this invention are elastomers or
resin-like products which are obtained from the condensation or from the
free radical formation of organopolysiloxanes in the presence of, for ex-
ample dicumyl peroxide and at elevated temperatures, for example at tempera-
tures in excesæ of 100C.
Examples of crosslinked organopolysiloxanes which may be coated
using the process of aspects of this invention are elastomers or resln-like
products which are obtained by the addition of organopolysiloxanes contain-
ing Si-bonded hydrogen atoms, to organopolysiloxanes containing aliphatic
multiple bonds in the presence of a catalyst~ e.g. platinum compound which
promotes the addition of Si-bonded hydrogen atoms to aliphatic multiple
bonds.
Silanes having at least one amino group per molecule which is
bonded to carbon via silicon and which contain at least one monovàlent hydro-
carbon radical which is bonded to silicon via oxygen, or substituted by an
amino or an alkoxy group
are the preferred silanes. These compounds may be represented
by the general formula: -
[R22N(CH2)mYa(cH23m]bsi(oR )c 4-b-c
in which R and a are the same as above; R2 represents hydrogen
and/or the same or different monovalent hydrocarbon radicals; R3
represents the same or different monovalent hydrocarbon radicals,
or radicals substituted by an amino or an alkoxy group; Y is
oxygen or NR ; b and c each represent the integers 1, 2 or 3,
with the proviso that the sum of b ~ c may not be more than 4;
and m represents the same or different lntegers in the range of
from 1 to 10.
Except for the vin~l radical, the examples cited above
for the hydrocarbon radicals R are equally applicable to the
hydrocarbon radicals represented by R . Additional examples of
'hydrocarbon radicals represented by R2 are the n-butyl, tert-
i butyl, 3,5,5-trimethylcyclohexyl and the ~,3,4-triethylcyclo-
10 hexyl radicals. It is, however, preferred that at least one R2
be hydrogen.
Other examples of R radicals are alkyl radicals having from
1 to 6 carbon atoms, e.g. the methyl, ethyl and n-butyl radicals as well as
the sec,- and tert,-butyl radicals; amino-alkyl radicals, e~g. the beta-
aminoethyl radical; alkoxy-alkyl radicals, e.g. the beta-methoxyethyl radi-
cal; cycloalkyl radicals, e.g. the cyclohexyl radical, aryl radicals e.g.
the phenyl radical and aralkyl radicals such as the benzyl radical.
Further examples of silanes represented by the above
formula are the following:
CH3Si(OCH2CH2NH2)2(CH2)3O(CH2)2 2
(cH3o)3si(cH2)3NH(cH2)2NH2
H2N(cH2)2o(cH2)3si(ocH2cH2NH2)3
H2N(CH2)20(CH2)3Si(oc2H5)3
Additional examples of these silanes are
N-beta-aminoethyl-gamma-amlnopropyltriethozysilane,
beta-aminoethyltriethoxysilane, N-beta-aminoethyl-delta-amino-
butyltriethoxysilane, gamma-aminopropyltriethoxysilane,
2~
aminomethyltrimethoxysilane, N-beta-aminoethyl-gam~a-amino-
propyltris-(methoxyethyleneoxy)- silane, and delta-aminobutyl-
triethoxysilane.
It is preferred that a silane be used which has for
each molecule at least one amino group bonded to silicon via
carbon and at least one monovalent hydrocarbon radical which i$
bonded to silicon vla oxygen and which may be substituted by an
amino or an alkoxy group, rather than the partial hydrolysates
of such a silane.
However, when a partial hydrolysate of a silane is
used which has for each molecule at least one amino group
bonded to silicon via carbon and at least one monovalent hydro~
carbon radical which may be substituted by an amino or an
alkoxy group, then it is preferred that such a partial hydroly-
sate contain no more than - 10 silicon atoms per molecule.
It is however poss'ible to use mixtures of various
~silanes having for each molecule at least one amino group which
is bonded to silicon via carbon and at least one hydrocarbon
radical or substituted hydrocarbon radical which is bonded to
silicon via oxygen. ,
It is preferred that the organosilicon compound having
at least one amino group bonded to silicon via carbon be applied
to the crosslinked organopolysiloxane prior to the application
of paint rather than being mixed with the paint. When the
crosslinked organopolysiloxane is coated with the organosilicon
compound rather than being mixed with the paint, a smaller
amount of organosilicon compound is required in order to improve
-the,adhesion o paint to the crosslinked organopolysiloxane.
When the organosilicon compound is applied as a coating, it is
preferred that the silane contain for each molecule at least one
amino group which is bonded to silicon via carbon and have at
least one monovalent hydrocarbon radical bonded to silicon via
oxygen and which may be substituted by an amino or an alkoxy
group, and/or partial hydrolysates of such silal~es, be diluted
with a solvent,.,,Examples of suitable solvents are aliphatic
hydrocarbons,e.g. ,~~-alkanes having boiling points in the
range of from 120 to!l80C at 1 bar, aromatic hydrocarbons, e.g.
toluene and xylene; ketones, e-g. \ methyl ethyl ketone;
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alcohols, e.g. methanol or isopropanol and/or chlorinated hydrocarbons, e.g.
trichloroethylene~ The organosilicon compounds having at least one amino
group bonded to silicon via carbon used in accordance with the process of
aspects of this invention may be present in an amount of from 1 to 90 per-
cent by weight baæed on the total wieght of the organosilicon compound and
the solvent.
The organosilicon compound used in accordance with the process of
aspects of thls invention to improve the adhesion of paint on crosslinked
. ~
organopolysiloxanes, may be applied to the organopolysiloxanes by spraying,
brushing, rolling or immersion~ Condensation or hydrolysis catalysts may
be applied to the surface of the crosslinked organopolysiloxane which is to
be painted prior to the application, r or simultaneously with the application,
and/or subsequent to the application of or mixed with the organosilicon
compound containing at least one amino group.
Examples of condensation or hydrolysis catalysts which may be em-
ployed are metal carboxylic acid salts or organometallic carboxylic acid
salts of metals forming the electromotive series from lead to manganese
tcf. Handbook of Chemistry and Physics, 31st Edition, Cleveland, Ohio, 1949,
page 1465), especially t~ose of tin, e.g. dibutyltin dilaurate, dibutyltin
diacetate, mixtures of dibutyltin diacylates, where the acylates are de-
rived from carboxylic acids contalning from 9 to 11 carbon atoms per mole-
cule and the carboxyl group is bonded to a tertiary carbon atom in at least
90 percent by weight of the acids; dibutyltin dioctoate, distannoxanes,
e.g. diacetoxytetrabutyldistannoxane and dioleyoltetramethyldistannoxane.
Other catalysts are iron octoate, lead octoate, lead laurate and cobalt
naphthenate; titanium esters, e.g. tetrabutyltitanate; amines,e.g. n-hexyl-
amine; and amine salts, e.g. n-hexylamine hydrochloride and n-butylamine
acetate.
The paints used in the process of aspects of this invention may
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consist of lacquers, aqueous dispersions or varnishes, for example those
based on alkyd resins, polyurethane or raw materials for polyurethane,
nitrocellulose, epoxide, polyester or polyvinyl chloride or copolymers of
polyvinyl chloride which are generally dissolved in an organic solvent.
Other materials which may be used are those based on acrylic resin, poly-
vinyl acetate or copolymers of polyvinyl acetate and/or styrene, for ex-
ample polystyrene acrylate, which are generally used in the form of aque-
ous dispersions.
When the organosilicon compound having at least one amino group
which is bonded to silicon via carbon which is used in accordance with
the process of an aspect of this invention to improve the adhesion of paint
on crosslinked organopolysiloxanes, is added to the paint, it is preferred
that the amount of organosilicon compound be from 0.1 to lO percent by
weight based on the total weight of paint and organosilicon compound.
The silicone elastomers may be used as sealing and caulking com-
positiuns on substrates9 e.g. wood su~strates where it is desirable that
they be painted~ Also these compositions may be used to seal around win-
dow frames and fissures on decks of sh:ips where they are subsequently
painted.
In the following examples all parts and percentages
are by weight unless otherwise specified.
The organopolysiloxane elastomers used in the follow-
ing examples were prepared in the following manner:
Elastomer A
A mixture containing 120 parts of a dimethypolysilox-
ane having an Si-bonded hydroxyl group in each of its terminal
units and a viscosity of 80,000 mPas at 25C, 80 parts of a
dimethyl-trimethylsiloxy terminated dimethylpolysiloxane
having a viscosity of 35 mPas at 25C and 8 parts of a polyoxy-
alkylene glycol containing ~0 percent by weight of ethylene
A' .
_ g _
oxide and 60 percent by weight propylene oxide and having an
average molecular weight of 3,400, were mixed with 28 parts of
a mixture consisting of 2 moles of methyltris-(butanone-2-oxime)-
silane and 1 mole of methyltris-(cyclohexylamino)-silane and
then with 2.4 parts of a silane of the formula:
~CH30)3Si(cH2)3NH(cH2)2N 2
, 180 parts of calcium carbonate whose particles
are coated with 3 percent of stearic acid are first added to
the resultant mixture, then 16 parts of pyrogenically prepared
silicon dioxide having a surface area of 150 m2/g, and then 0.4
part of dibutyltin dilaurate are added to the mixture.
,
A 5mm thick layer of the composition thus obtained,
is placed on a flat base and e~posed to atmospheric moisture.
The resultant composition is crosslinked to form an elastomer
and then used 7 days later.
Elastomer ~
~~ ~ 100 parts of a diorganopolysiloxane end-blocked
with trimethylsilox~ groups and consisting of 99.93 mol per-
cent of dimethylsiloxane units and 0.07 mol percent of vinyl-
methylsiloxane units and having a viscosity of ~ ~ 5 ~1o6
mPas at 25C, are mixed first wi-th 7 parts of a dimethylpoly-
siloxane navlng an ~i-bonded hydroxyl group in each of its
terminal units and a viscosity of 40 mPas at 25C and 40
parts of pyrogenically produced silicon dioxide having a
surface area of 200 m /g and then with 1 part of 95 percent
dicumyl peroxide. The resultant composition is shaped and
heated ~or 15 minutes to 165C and thereafter heated for 4 hours
'at 200C to form an elastomer.
Exampla 1
A portion of the surface of Elastomer A is brushed
with a solution containing 50 parts by weight of a silane of the
formula:
(cH3o)3si(cH2)3NH(cH2)2 2 '
60 parts of toluene and 5 parts of tetra-n-butyltitanate. The
coating is allowed to dry at room temperature for one hour.
The section of the surface of Elastomer A which was coated with
-- 10 --
alkyd resin base, [that known by the registered trademark,
DUCOLUX, Glanzcolor gray DG 704, manufactured by the Hermann
Wiederhold Company; 4010 Hilden], identified as Paint No. l.
Another section of the surface of Elatomer A which was coated
with the silane is coated with a commercially available wood
varnish based on alkyd resin [Tixoton wood varnish, nut brown,
"Meisterpreis" (the terms "TIXOTON" and "MEISTERPREIS" are
trade marks of the Spangenberg Company; 4010 Hilden)], iden-
tified as Paint No. 2. A third section of the coated Elastomer
A is coated with a commercially available two-component poly-
urethane lacquer ~Efdedur KRO-423 ~ Efdedur HU 7 in a ratio
~'o~: 9:1. "EFDEDUR" is a trade mark of the Emil Frei Company;
~15 Braunlingen-Doggin-
.
- 10 a -
gen), identified as Paint.No. 3. A fourth section of Elastomer
which was previously coated with the silane is coated with
a commercially available white paint consisting of an aqueous
dispersion of a copolymer of styrene and vinyl-acetate
(available from Wacker-Chemie GmbH; Munich), identified as
Paint No. 4. All four paints completely covered the surface and
did not migrate from the surface.
Example 2
The process described in Example 1 is repeated,
exclept that elastomer B is substituted for elastomer A. The
paint spread evenly on the surface of the elastomer without
migrating.
Comparison Example (a?
The process described in Example 1 is repeated, except
that the paint migrated on the surface of the untreated
,elastomer.
Comparison Example (b?
The process described in Example 2 is repeated, ex-
cept that the untreated surface of the elastomer is coated
with the paint. The paint migrated on the surface of the
elastomer.
~ fter one month, a 2.54 cm square is subdivided on
each painted area with the aid of a :razor blade into 100 equal
squares having an area of 6.45 mm . A pressure sensitive
adhesive tape is placed on the grid thus formed and then slowly
removed at a 30 angle. The number of small squares remaining
on the elastomer indicates the percentage of paint retained.
Retention factors of at least 95 percent indicate an excellent
adhesion, retention factors of no more than 65 percent indicate
poor adhesion. The following table shows the average results
of various measurements.
~ ~ , " ,- , .,",,.,~ ~"- ,,~ , ,", -,, '~ - :
3'L8
TABLE
__
~xample Percentage o~ paint retained
1 2 3 -4
1 95 100 99 99
2 ' . '100 100 100 100
. Comparison
. Examples 2 2 O O
(b) 4 O 5 O
. . .
' ' ' .
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