Note: Descriptions are shown in the official language in which they were submitted.
-1- 60SI-732
SILICONE gELEASE CO~TINGS AND INHIBITORS
BACKGROUND OF THE INVENTTON
The present invention relates to silicone release coating
compositions and inhibitors therefor. More particular].y, the
present invention relates to a blend of a dialkyl carboxylic
ester having carbon to carbon unsaturation and an olefinic
carboxylic acid ester of an aliphatic alcohol as an inhibitor
for precious metal catalyzed polysiloxane compositions ~hich
are particularly well suited for solventless silicone release
coating compositions.
Silicone compositions have long been used for rendering
surfaces nonadherent to materials which would normally adhere
thereto. For a long time it was necessary that these silicone
coatings be applied as a dispersion within a solvent in order
to control the ~iscosity of the coating material so as to be
suitable for coating applications. However, although the
solvent aids in the application of the coating, it is a highly
inefficient process inasmuch as the solvent must thereafter be
evaporated The evaporation of solvents requires large
expenditures of energy, and additional].y, pollution control
requirements mandate that solvent vapors be prevented from
escaping into the environment. Thus, removal and recovery of
solvents entails considerable expenditures for apparatus and energy.
Consequently, solventless release coating compositions,
sometimes referred to as 100% solids release compositions, have
been developed. The absence of a solvent in such compositions
.
-
-~4~7~ (
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1 both lowess the amount of energy requiret to effect curing and
eliminates ~he need for expensive pollution contsol equip-
mene. However, a problem associated with such silicone release
coatings relating to premature gelation must be overcome.
Since a typical composition is made up of a vinyl chain-stopped
base polymer, a crosa-linking agent and a plstinum metal
catalyst, premature curing or gelation may occur in a short
period of time, thus resul~ing in a prsduct with an
unsatisfactory pot-life. When the composition is ready for use
it is desirable that the catalyzed polymer composition have a
sufficiently long pot-life to enable the end-user to carry out
the coating application. Accordingly, the coating composition
is provided with an inhibitor which effectively retard~ the
hydrosilation addition cure reaction of the composition at
ambient temperature, but does not retard the cure at elevated
temperatures. Examples of inhibitors which have been utilized
in prior art solventless release compositions include vinyl
acetate, diallylmaleate and triallylisocyanurste tTAIC).
Eckberg in U.S. Patent No. 4,256,870 discloses a silicone
composition comprising a base polymer such as a vinyl chain-
stopped polydialkyl-alkyl~inyl polys.loxane base copolymer snd
a methylhydrogen cros~-linking $1uid. This composition is
catalyzed by platinum or a platinum met61 complex which will
initiate an addition cure reaction. An inhibitor selected from
organic esters of maleic acid is added to the composition in
order to selectively retard the cure reaction so as to provide
a workable pot-life $or the costing composition.
7~
- 3 - 60SI-732
Eckberg in U.S. Patent No. 4,262,107, issued
April 14, 1981 discloses a silicone rubber composition
with good pot-life and fast curing at elevated
temperatures comprising a silanol end-stopped
diorganopolysiloxane polymer, a silicone hydride
crosslinker and a rhodium complex catalyst in
combination with an inhibitor compound selected from
low molecular weight silanol end-stopped
diorganopolysiloxanes, certain acetylenic compounds,
lo olefinic carboxylic acid esters of aliphatic alcohols
such as vinyl acetate, alkenyl isocyanurates and
mixtures of such inhibitor compounds.
Eckberg in U.S. Patent No. 4,347,346, issued
August 31, 19~ discloses a solventless platinum or
rhodium catalyzed addition curable polyorganosiloxane
release coating composition containing a
dialkylacetylenedicarboxylate inhibitor for preventing
premature gelation at ambient temperatures but which
will cure at elevated temperature via a hydrosilation
reaction to form a coating capable of releasing
materials from substrates which would normally adhere
thereto.
A novel multi-component solventless silicone
release system is disclosed in Grenoble and
Eckberg in Canadian Application Serial Number
447,719, filed February 17, 1984, assi~ned to the
same assignee as the present invention. Therein
it is disclosed that prior art two-component
systems, one part of which comprises a vinyl
silicone fluid, precious metal catalyst and an
inhibitor, and the other part a polymethyl-
hydrogensiloxane crosslinker, unduly limit the
flexibility of the end-user to formulate solvent-free
605I-732
1 silicone release coatings which more precisely meet their
performance and cost requirements. Accordingly,~ there i8
provided a multi-component system wherein the ingredients are
provided the end-user in three or more separate part6 to
provide such flexibility. While such a multi-component system
substantially eliminates the proble~ of premature gelation over
an extended period of ti~e, it is also desirable to further
increase the useful pot-life of release coating compositions to
extend the period of time during which the end-user can carry
out the coating application.
Thus, there is provided by the present invention a
solventless silicone release coating composition containing a
two-part inhibitor which not only exhibits more effective
inhibition than similar concentrations of the individual
ingredients, but also improves the solubility of such~inhibitor
in silicone fluids. Hence the present invention provides a
significant improvement over prior art release coating composi-
tions containing a one-part inhibitor.
It is therefore a primary object of the present invention
to provide a solventless composition which will render surfaces
non-adherent to materials which ~ould normally adhere thereto.
Another object of the present invention is to provide a
solventless coating composition which will cure to a coating
having satisfactory smear, rub-off, migration and release
characteristics.
'
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1 A further object of ~he presen~ invention i6 to provide a
solventless coating composition which has ~ satisfactory
pot-life or baeh-life in its catalyzed for~ when it is ready
for use.
Still another object of the present invention i8 to
provide a method of rendering materials nonadherent to other
materials which would normally adhere thereto.
It is still a further object of the present invention to
provide a release coating composition having a two-part
inhibitor which effectively retards the catalyzed cross-linking
reaction at temperatures below the heat cure te~perature of
these compositions and to provide solventless silicone
compositions which are particularly well suited for paper
release applications.
These and other objects will become apparent to those
skilled in the art upon consideration of the present descrip-
tion, examples and cl8ims.
Summar~ of the Invention
The present invention provides 8 ~ilicone release coating
composition containing a two-part inhibitor comprised of
blend of a dialkyl casboxylic ester having carbon to carbon
unsaturation and an olefinic carboxylic acit ester of an
aliphatic alcohol ~hich ic eEfe~tive for retardiDg a precioDs
.
-
- 6 - 60SI-732
metal catalyzed addition cure hydrosilation
reaction at room temperature but which does not
interfere with curing at elevated temperatures.
Such two-part inhibitor is especially effective
for use with release coating baths containing high
concentration and in the multi-component system
described by Grenoble and Eckberg in Canadian
Patent Application Serial Number 447,719, filed
February 14, 1984 and assigned to the same
assignee as the present invention. The cured
composition provides a silicone coating which will
tenaciously adhere to a substrate, such as paper,
to which it is applied, but will render such
substrate substantially nonadherent to materials,
such as pressure sensitive adhesives, which would
normally adhere thereto.
The release coating composition containing a
two-part inhibitor as provided by the present
invention can be a two-component system or, more
preferably, is a multi-component system of the
type disclosed in Grenoble and Eckberg, Canadian
Serial Mo. 447,719. Generally, the release
coating composition of the present invention
comprises:
(a) an olefinorganopolysiloxane having
structural units of the formula:
a b (4-a-b) (I)
or a silanol end-stopped organopolysiloxane
having the general formula:
605I-732
1 H0 t lio ~ B (Ia)
-
(b) an organohydrogenpolysiloxane having structural units
- of the formuls:
Ra~bSi(4-a-b) (Il)
-
S wherein R is an organic radical attached to silicon
by a C-Si linkage and is selected from the group
consisting of monovalent hydrocarbon radicals,
halogen~tet monovalent hydrocarbon radicals and
cyanoalkyl rsdicals; ~enerally R contains from 1 to
30 carbon ato,.,s, either in branched or linear chains,
- preferably from 1 to 12 carbon atoms and most
preferably from 1 to 8 carbon atoms; R is an
olefinic hydrocarbon radical attached to silicon by a
C-Si linkage and generally contains 1 to 20 aliphatic
carbon atoms, either in branched or linear chain6,
and preferably l to 12 carbon atoms, linked by
multiple bonds (e.g. vinyl, allyl, methallyl,
butenyl, pentenyl, ethenyl and the like); a has a
value of 0 to 3 inclusive, and preferably from about
0.5 to about 2 inclusive; b has a value from about
~7~
60SI-732
1 0.005 to about 2.0 inclusive, and the 8um uf a snd b
equals from 0.8 to 3 inclusive; and wherein the
release coating composition is a fluid at rc,om
temperature having a viscosity of approximately lO to
5000 centipoise and preferably 30~ to l~00 centipoi~e
at 25C;
(c) a cstalytic amount of a precious metal catalyst,
preferably a platinum or rhodium compound, to effect
the co-reaction of (a) &nd (b); and
(d) an amount of a blend of a dialkyl carboxylic ester
having carbon to carbon unsaturation and an olefinic
carboxylic acid ester of an aliphatic alcohol effec-
tive for inhibiting an addition cure hydrosilation
reaction between said olefinorganopolysiloxane and
said organohydrog2npolysiloxane at room temperature
but is not present in an amount sufficient to prevent
curing of said coating composition at elevated
temperatures.
Description of the Invention
In accordance with the presene invention there is provided
8 composition particularly well ~uited for rendering material6
nonadherent to other normally adhèrent materialfi ~uch 85 glue,
adhesivell a=d the like. Additicnally the cD=position ca= be
- 9 - 60SI-732
applied directly to a substrate without the need
for a solvent, thereby avoiding the problems
associated with solvent-based release compositions
as described above.
The addition curable composition of the
present invention can be provided as a mixture of
several components wherein at least one component
contains more than one ingredient as taught in the
prior art. An example of such a system is
described in U.S. Patent No. 4,256,870 wherein one
part includes a vinyl silicone fluid, a precious
metal catalyst and an inhibitor, and a second part
comprises a polymethylhydrogensiloxane
cross-linker. In such a composition the inhibitor
of the present invention exhibits improved
solubility, and if the composition has a high
platinum content further effects improved bath
life. ~owever, it is preferable that the coating
composition be provided as a four part system such
as that described in Canadian Serial Number
447,719 filed February 17, 1984 to Grenoble and
Eckberg and assigned to the same assignee as the
present invention, teaches that shelf-life is
substantially improved for release coating
compositions when the individual ingredients are
stored separately, and that low temperature cure
performance comparable to that of prior art high
platinum content two part systems can be provided
with significantly reduced catalyst concentrations
as a result of more effective use of the catalyst.
The release coating composition is made up of the above-
mentioned ingredients which will thermally cure on the
~:4~7~ (
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--10--
1 substrate upon which it is coated and render the substrate
substantially nonadherent. More particularly, the olefinor-
ganopolysiloxanes having structural units represented by
Formula I hereinabove are iDtended to broadly cover low
viscosity fluid organopolysiloxanes suitable for coating which
preferably, but not necessarily, are free of silanic hydrogen
and contain olefinic unsaturation by means of double or triple
bonds between two adjacent aliphatic csrbon atoms. Among the
radicals which R represents in Formula I hereinabove are
included alkyl, such as methyl, ethyl, propyl, isopropyl,
butyl, octyl, dodecyl and the like; cycloalkyl, such as
cyclopentyl, cyclohexyl, cycloheptyl and the like; aryl, such
as phenyl, naphthyl, tolyl, xylyl, and the like; aralkyl such
as phenylethyl, phenylpropyl and the like; halogenated
derivatives of the aforesaid radicals including chloromethyl,
trifluoromethyl, chloropropyl, chlorophenyl, dibromophenyl,
tetrachlorophenyl, difluorophenyl and the like; and cvanoalkyl,
such as beta-cyanoethyl, ga~a-cyanopropyl, beta-cyanopropyl
and the ~ike. Preferably R is ~ethyl. Furthermore, Formula I
is intended to encompass those materials wherein R is a mixture
of the aforesaid radicals.
Among the radicals represented by R in Formula I are
included alkenyl, such as vinyl, allyl, ~ethallyl, butenyl,
pentenyl and the like; snd nlkynyl, such as ethynyl, propynyl,
butynyl, pentynyl and the like. Preferably R is vinyl or
allyl and ~ost preferably R is vinyl.
77~ (
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--11--
The olefinorganopolysiloxanes encompassed within the scope
of Formula I are well known in the art, for exa~ple, as d;s-
1 closed in U.S. Patent ~o. 3,344,111 to Chalk and U.S. Patent
: No. 3,436,366 to Modic, Simllarly, their pre~aration andcommercial availability are also well known. Ihe
olefinorganopolysiloxanes o~ Formula I can be characterized
as copolymers of (1) siloxane units havin~ the
formul~:
RCRdsi~_C_d) (IV)
where R and Rl are as defined above and c has a value of from
0 to 2 inclusive and the average sum of c and d is equal to
from 0.8 to 3.0 inclusive, and (2) organopolysiloxane units
having the structural formula:
(R)nSiO4-n (V)
where R is as defined above and n has a value of from 0.8 to
2.5 inclusive. Thus, where the olefinorganopolysiloxane
employed herein is a copolymer of units within the scope of
Formula IV and an organopolysiloxane having an average formula
within the scope of Formula V, the copolymer generally contains
from 0.5 to 99.5 mole percent of the unit~ of Formula IV and
from 0.5 to 99.5 mole percent of unit6 within the scope of
Formula V. The preparation of these copolymers i6 well known
to those skilled in the art.
A major proportion of the composition is typieally 8 vinyl
chain-stopped polysiloxane having the general formula:
o
60SI-732
/ R ~ ~ R
R t i ~ Rl~ I
wberein R is a monovalent hydroc rbon radical free of
unsaturation. Suitsble radicals for R include, for example,
methyl, ethyl, propyl, butyl and other similar unsaturated
hydrocarbons, but ordinarily wDuld not include phenyl groups
for paper release purposes. R i8 a hydrocarbon radical
having alkenyl unsaturation. Typically Rl represents vinyl
groups but may also represent Qllylic or cycloalkenyl uns~tu-
rated groups; x and y are positive integers such that the vinyl
chain-stopped polysiloxane has up to approximately 20% by
weight of Rl groups. The viscosity of such a polysiloxane
ranges from approximately 50 to approximately 100,000
centipoise at 25C. Preferably the vinyl chain-stopped
polysiloxane has up to approximately 20~ by weight of vinyl
groups and the vîscosity ranges from approximately 300 to
approximately 550 centipoise at 25DC. Ihe preferred vinyl
chain-stopped polysiloxane has the general formula:
1 ~ l \ ~ l
CH3 t CH3 ~x si ~ s CH ~ CH
whesein x and y are as described ove.
7Q C
60SI-732
.
-13-
1 The silanol chain-6topped linear polydiorganosiloxane of
Formula Ia can be used with, or in place of, ~the vinyl-
containing copolymer of Formula I. Such 6ilanol end~6topped
polysiloxanes are preparet by equilibration of cyclic poly-
siloxane6 in the presence of sn alksli metal hydroxide
catalyst. The desired viscoGity is obtained by ~ontrolling the
amount of water added to the reaction. These procedures are
described in the literature and are well known to those skilled
in the art. Furthermore, silanol chain-6topped polydimethyl-
methylvinylsiloxane copolymers can be envisioned which are al50
within the scope of the present invention.
Methylhydrogen fluid is often used by those 3killed in the
silicone srt as a cross-linking agent for addition-cured
tilicone systems. Particularly useful as a cross-linking agent
for the present invention is a trimethyl chain-stopped
polymethylhydrogen siloxane fluid having from approximately 10~
to approximately lOO~o SiH groups, any re~2ining groups being
dimethylsiloxy units, and having a viscosity in the range o~
&pproximately 15 to approximately 1000 centipoise at 25C.
The organohydrogenpolysiloxanes having structural units
represented by For~uls II hereinabove are intended to broadly
cover fluid organopolysiloxanes which are preferably, but not
necessarily, free of olefinic unsaturation, but which do
contain silanic hydrogen. The organohydrogenpolysiloxanes
represented by Formuls II are also well known in the art, for
example, as described in ~.S. Patent No. 3,344,111 and V.S.
Patent No. 3,436,366.
C
60SI-732
-14-
Among the radicals iocluded within R of Formula II are
alkyl, such as methyl, ethyl, propyl, isopropyl, butyl, octyl
snd the like; cycloalkyl, such as cyclopentyl, cyclohexyl,
cycloheptyl and the like; aryl, such a8 phenyl, naphthyl,
tolyl, xylyl and the like; sralkyl, such as phenylethyl,
phenylpropyl and ehe like; halogenated derivatives of the above
radicals, including chloromethyl, trifluoromethyl, chloropro-
pyl, chlorophenyl, dibrGmophenyl, tetrachlorophenyl,
difluorophenyl and the like; and cyanoalkyl, such as beta-
cyanoethyl, gamma-cyanopropyl, beta-cyanopropyl and the like.
Also intended to be included within the scope of Formula II are
those materials where R is a mixture of the aforesaid
radicals. Preferably the R group of For~ula II is methyl.
Materials specifically encompassed within Formula II
hereinabove include 1,3-dimethyldisiloxane and 1,1,3,3-tetra-
methyldisiloxane, as well as higher polymers containing up to
100,000 or more silicon atoms per molecule. Also included
within the scope of Formula II are cyclic materials such as
cyclic polymers of methylhydrogen siloxane having the general
formula:
¦ CH3\
-L iio- _
\~ x
wherein x is a whole number equal to from 3 to 10 or more.
Particularly included is sym-tetramethylcyclotetrasiloxane.
~2~
60SI-732
-15-
The organohydrogenpolysiloxanes emp;oyed in the practice
of the present invention can also be char~cteri~ed ~8
copolymers containing at least one unit per molecule having the
formulR
S
RCHd Sio(4-c-d) (VI)
with the remaining siloxsne units of the organopolysiloxane
being within the scope of Formula V hereinabove, where R, c, d,
and n are as defined above.
Within the scope of FormulA VI are siloxane units such as
hydrogen siloxane units (HSiO~l 5, methyl hydrogen siloxane
units (HSiCH30), dimethyl hydrogen siloxane units
(H Si¦CH3]20~, and dihydrogen siloxane units (H25iO). In
these copolymers, the siloxane units of For~ulae V and VI are
present in proportions so as to form a hydrogenpolysiloxane
within the scope of Formula II hereinabove. In general such
copolymers coiltain from 0.5 to 99.5 mole percent of siloxane
units of Formula V and from 0.5 to 99.5 mole percent of
siloxane units of Formula VI.
Ordinarily for release coating purposes it i8 preferred
that the organohydrogenpoly6il0xsne cro6slinker be essentially
a trimethyl chain-stopped methylhydrogenpolysiloxane fluit
having a viscosity of approximately 10 to 500 centipoise at
25C and a hydrogen content of from approximstely 0.1 to 1.67
percent by weight.
60SI-732
-16-
The precious metal catalyst component utilized in compositions
of the present invention incl~des all of the well known platinum
and rhodium catalysts which are effective for catalyzing the
reaction between silicon-bonded hydrogen atoms and silicon-
bonded olefinic groups, and which are freely miscible insolvent-free silicone polymers. These materials especially
include the platinum hydrocarbon complexes described in U.S.
Patent No. 3,159,601 issued December 1, 196~ to Ashby and
U.S. Patent No. 3,159,662, issued Decem~er 1, 1964 to Ashby,
and the platinum alcoholate catalysts described in U.S. Patent
No. 3,220,970, issued November 30, 1965 to Lamoreaux, as well
as the platinum catalysts of U.S. Patent ~o. 3,814,730, issued
June 4, 1974 to Karstedt. Additionally, the platinum chloride-
olefin complexes described in U.S. Patent ~o. 3,516,946, issued
June 23, 1970 to Modic are also useful herein.
The curing reaction which takes place between the vinyl-
functional polysiloxanes and the polymethylhydrogensiloxane
fluid cross-linking agent is an addition cure xeaction, also
known as hydrosilation. The composition of the present
invention may be the mally cured by means of a platinum
catalyzed cross-linking reaction between pendant vinyl groups
of a dialkylvinyl chain-stopped polydialkyl-alkylvinylsiloxane
copolymer and a trimethyl chain-stopped polymethylhydrogen fluid.
A particularly use~ul catalyst ~or facilitatin~ the
hydrosilation reaction is the Karstedt catalyst described in
U.S. Patent No 3,814,730. Other platinum metal catalysts can
be utilized in the practice of the present invention, however,
{ ~ ~L~ ~77~ ~
60SI-732
-17-
their Eelection depends upon ~uch factos6 85 the required
seaceion rate, expense, useful pot-life and the temperature at
which the cure reacti~n is to take place. Other metal
catalysts useful in the present invention include those which
are silicone soluble complexes of the metals rhodium,
: ruthenium, palladium, osmium, iridium and platinum. For
coat;ng compositions of the present invention, the amount of
catalyst ranges from approximately 10 to approximately 500 ppm
~as weight of metal atoms), again depending on Euch factors as
Epeed of reaction and c06t requirements. Preferably, the
amount of catalyse is approximately 10 to 150 ppm of the
precious metal.
In order to substantially eliminate the problem of
premature curing or gelation it is desirable to include an
inhibitor in the coating composition package. It has surpris-
ingly been found that an inhibitor comprising a blend of a
dialkyl carboxylic ester having carbon to carbon unsaturation
and an olefinic carboxylic acid ester of an aliphatic alcohol
is more effective as an inhibitor ehan similar amounts of the
individual ingredients utilized alone, especially in high
platinum content (i.e. low cure temperature) Eystems. By a
high platinum content or low cure temperature sy6tem, it is
meant thst the catalyzed bath contains more than 50 ppm of
precious metal catalyst, and typically may be more than lOO ppm
of precious metal catalyst. Such two-part inhibitor is al60
especially useful in the multi-component packaging sy6tem of
; Grenoble et al., Can. Serial No. y y ~ ~7~9 as it affords
the end-user with the cspability of formulating re~ease coating
76)
60SI-732
-18-
1 bath compositions suited to his specific need~. Furthermore,
the inhibitor of the present invention is used more~advantage-
ously in low tempersture curing release coating sy6tem6 than
prior art one-part inhibitors since, for exsmple, diallyl-
maleste i6 a polar substance which i6 not very soluble in
silicone fluids at concentration6 above about 0.3 weight
percent. However, in the instant invention vinyl acetate
function~ both as sn inhibitor and as a mutual 601vent for
diallylmaleate and silicone fluid, snd accordingly, ~ore
preferred concentrations of inhibitor can be utilized which
would otherwise be impractical.
Eckberg in U.S. Patent No. 4,256,870 discloses that an
amount of dialkyl carboxylic ester containing carbon to carbon
unsaturation is effective to inhibit the precious metal
catslyzed hydrosilation cure reaction at temperatures below the
heat cure temperature of the release coating composition. Most
preferably such dialkyl carboxylic ester is diallylmaleate
which has the formuls: 8 H
~ ~C /
CH2 ~ CHCH2 - O - C l l 2CH CH2
O O
and ordinarily i8 utilized in A ran8e of from spproximstely
O.lX to approxi~ately 0.5X by weight. Other preferred
diallylic carboxylic e~ters which are preferred include
diallylphthalate and diallylsuccinate. Also, satur~ted dialkyl
esters of maleic acid, ~uch as diethyl and dimethyl maleate,
60SI-732
~ 247770
and ~ixed esters such as butylallylmaleate or methylethyl-
maleate are useful as hydrosilation inh;bitors for solventless
release coating compositions. Other useful inhibitors can also
be found in the Eckberg patent.
The use of ari olefinic carboxylïc acid ester of an
aliphatic alcohol is disclosed in Eckberg as an inhibitor for
rhodium catalyzed silicone rubber compositions in U.S. Patent
No. 4,262,107. Therein it is taught that such compositions can
be utilized at low concentration, such as from 0.1 to 2 parts
per 100 parts of the silanol base polymer, but preferably
should be utilized in a concentration of 0.5 to 5 parts per 10C
parts of the silanol base polymer. The preferred inhibitor
compound is vinyl acetate, however, those olefinic carboxylic
acid esters of an aliphatic alcohol wherein the alcohol has
from 1 to 4 carbon atom and the olefinic carboxylic acid has
from 2 to 10 carbon atoms are within the scope of the
disclosed.
The present invention is based on the surprising discovery
that a blend of a dialkyl carboxylic ester containing carbon to
carbon unsaturation and an olefinic carboxylic acid ester of an
aliphatic alcohol results in a blend which is a more effective
inhibitor than utilizing similar amounts of the individual
compounds, that is, a synergistic effect is obtained by such a
blend of inhibitors.
Iq
7~ C-
.
60SI-732
-20-
The most preferred dialkyl carboxylic e~ter containing
carbon to carbon unsaturation is diallylmaleate, however, any
of the inhibitor composit;ons within the scope of V.S. Patent
No. 4,256,870 can also be utilized in the present invention.
Among the preferred inhibitor compositions which also can be
utilized are butylallylmaleate, diallylsuccinate,
dimethylmaleate, diethylmaleate and 6ilylmaleates such as
bis- ~ -propyltris (methoxy) silylmaleate which has the
formula: ~ H
~ f 1 / \ ~ ~
~i(OCH3)3 C C CH2 si (OCH3)3
The most preferred olefinic carboxylic acid ester of an
aliphatic alcohol is vinyl acetate, however, any inhibitor
compound within the scope of U.S. Patent No. 4,262,107 may also
be utilized. More particularly, such compounds are those
derived from an aliphatic alcohol having l to 4 carbon atoms
and an olefinic carboxylic acit having from 2 to 10 carbon
atoms.
The dialkyl carboxylic ester having carbon to carbon
unsaturation, preferably diallylmaleate or butylallylmaleate,
is blended with the olefinic carboxylic acid ester of an
aliphatic slcohol, preferably vinyl acetate, in a r.atio ranging
from approximately i:24 to l:l, but most preferably i6 blended
77~ c
605I-732
-21-
l in approximately a 1:3 ratio. Accordingly, the most preferred
inhibitor for the release coating composition of t~e present
invention is a blend comprising 1 pare diallyl~aleate snd 3
I:-rt6 vinyl acetate.
I~ has been discovered that small amounts of such 8 two-
par~ inhibitor permit exceptionally long catalyzed pot-life
without sacrifice of cure perfo~ance, especially in co~po-
sitions having a high platinum content. Ordinarily the
effective smount of inhibitor ranges from approximately 0.05 to
approximately 2% by weight, and preferably fro~ 0.1 to 1.5% by
weight. Use of the present invention results in improved
pot-life yet the composition rapidly cures to a smear-free and
migration-free nonadherent surface when thermally cured.
1~
The improved inhibitor of the present invention can be
provided in a conventional two package system, that is, it can
be stored in one container which includes the inhibitor blend,
a vinyl silicone fluid and a precious metal cat~lyst, while the
polymethylhydrogensiloxane cross-linking agent is stored in a
separate container. It is preferred, however, that a three or
more component package system as disclosed in Grenoble
et al., Can. Serial No. ~ ;7~ ~, be utilized. Thus, it is
preferable that each of the ingredients be 6tored ;n separste
contfliner6 ~o that in addition to the i~proved pot-life
provided by the inhibitor blend of the prebent invention, very
long shelf-life is also obtained.
In addition to the foregoing ingredients, it is within the
scope of the present invention that other ingredients can be
included. One of the preferred additional ingredients is a
'~ ~L~ ~ 7 7 0
60SI-732
-22-
vinyl-gum cure accelerator of the type disclosed by Eckberg in
V.S. Patent No. 4,340,647, issued July 20, 1~82, which is
assigned to the same assignee as the present invention. Therein
it is disclosed that a dimethylvinyl chain-stopped
polydimethylmethylvinylsiloxane polymer gum will accelerate
the hydrosilation cure reaction at a relatively low
temperature without sacrificing performance. Such vinyl gum may
be packaged alone or preferably with the base polymer.
In order that those skilled in the art might be better able
to practice the present invention, the following examples are
given by way of illustration ana not by way of limitation.
Description of the Preferred Em'oodiments
Examples 1 to 14
In the following examples, release coating compositions
were prepared from the following ingredients:
(A) a mixture consisting of 100 parts of a linear
dimethylvinyl chain-stopped polyaimethylsiloxane fluid
having a viscosity of 120 cps at 25 C and 5 parts of a
dimethylvinyl chain-stopped linear polydimethyl~ethyl-
vinylsiloxane copolymer gum having a molecular weight
of approximately 300,000 and containing 0.2 mols
percent methylvinyl siloxane units, such mixture
having a viscosity of approximately 400 cps at 25 C;
r ~ f~"~L~jL777Q
60SI-732
--23--
(B) a solution of a platinum catalyst in a dimethylvinyl
end-stopped polydi~eehylsiloxane fluid ~ hsving a
viscosity of 300 cps nt 25C, there being sufficient
catalyse present to afford 1800 ppm platinu~ (as
metal~ in the solution;
- (C) a trimethylsiloxy chain-stopped linear
polymethylhydrogensiloxane fluid having 8 viscosity of
approximately 20 to 40 cps at 25C as a cross-linking
agent; and
(D) a blend of 3 parts vinyl acetate to 1 part of
diallylmaleate.
Initial experiements were performed by preparing release
coating composition baths 8S described in Table 1.
7~
C
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Tsble I
Bath _ xample 1 Example 2 Example 3 Ex~mple 4
Ingredient A150.0g 150.0g 150.0g 150.0g
Ingredient B 2.1 4.17 8.33 12.51
Ingredient C 6.0 6.0 6.0 6.0
Ingredient D 0.3 0.6 1.2 1.8
ppm Pt 24.0 47.0 91.0 134.0
Total Inhibieor, X 0.2 0.39 0.75 1.10
ViOAc, X 0.15 0.29 0.5S 0.82
DAM, X 0.05 0.10 0.19 0.28
7~
60SI-732
The viscositie6 of the four release coating baths were
monitored as a function of time under still condition6 at 25C
over a seven hour period. The results set forth i~ Table II
illustrate that the two-part inhibitor of the present in~ention
provides a release coating bath havin a satisfactory pot-life.
Note that for purposes of these experiments, the cross-linking
agent W8S added at time zero.
Table II
Bath Example 1 Example 2 Example 3 Example 4
lS Initial 500 cps 495 cps 465 cps 460 cps
2 hours 525 525 490 480
4 hours 530 525 505 480
7 hours 540 550 525 495
Thus it can be seen thae varying a~ounts of the diallyl-
maleate/vinyl acetate inhibitor gsve satisfsctory pot-life while
effectively controlling the percentage vi6cosity increase of the
catalyzed baths regardless of the absolute level of catsly6t.
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Examples 5 and 6
In the following examples tWD baths were prepared
identically to that of Example 1 with the exception that each
contained only one of the inhibitors of the blend utilized in
Example 1. The composition of these release coating baths is
shown in Table III.
~able III
Bath Example 5 Example 6
Ingredient A 150.0 g 150.0 g
Ingredient B 2.1 2.1
Ingredient C 6.0 6.0
2~
ViOAc 0.23 (0.15Z) Not present
DAM Not present 0.08 (0.05Z)
ppm Pt 24 24
The viscositie6 of the two release coating bathfi were again
monitored as a function of time under still conditions at 25C
over a seven hour period. The results are set forth in Table IV.
... . ... .. ....... _ . ... .
~L~7~ (
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Table IV
- Bath Exa~ple 5 ExamDle 6
Initial 360 cps 36S cps
2 hours 500 525
4 hours 570 7S0
7 hours 1025 4000
Although the ~iscosity of each bath doubled in approximately
four hours, the results are un erarkable in the sense that the
total inhibitor concentration in the bath of Example 1 exceeds the
total inhibitor load in the bath of either Example 5 or Example 6.
Examples 7 to 9
Experiments were then run to determine the effectiveness of
the individual inhibitors at levels comparable to the level of
two-part inhibitor utilized in Example 1. The :co~position of
these release coating baths is sho~n in Table V.
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.
Table V
S
Bath Example 7 Example 8
Ingredient A 150.0 g 150.0 g
Ingredient B 2.1 2.1
Ingredient C 6.0 6.0
VioAc 0.31 (0.2X) Not present
DAM Not present 0.31 ~0.2%)
ppm Pt 24.0 24.0
The viscosities of the release coating baths were once again
monitored as a function of time undes still conditions at 25C
over a seven hour period. The result6 are illustrsted in Tsble VI.
C f~ 7~ C
60SI-732
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1 Table VI
Bath _ Example 7 Example 8
Initial 335 cps 355 cps
2 hours 480 370
4 hours 620 375
7 hours 900 380
These results sho~ that the combined diallylmaleate/vinyl
acetate inhibitor significantly improves upon the inhibitory
15effect of vinyl acetate alone. While the bath composition of
Example 8 has a satisfactory bath life, i~ is not useful for a low
temperature cure applications, such as those of the bath in
Example 4. Moreover, even in those compositions ~hich require
high temperature curing, the inhibitor blend of the present
20invention exhibits improved solubility thus enabling more
preferred concentrations of inhibitor to be utili2ed~ Next, a
release coating bath having a high platinum content, that is,
comparsble to that of Example 4, was prepared to determine the
effectiveness of diallylmaleate in such A bath. The composition
of this bath is set forth in Table VII,
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Table VII
Bath Example 9
Ingredient A 150.0 g
Ingredient B 12.5
Ingredient C 6.0
DAM 0.49 (0.3%)
ppm Pt 134
The viscosity of the bath was monitored as a function of time
under still conditions at 25C over a seven hour period, the
results being shown in Table VIII.
Table VIII
Bath Example 9
Initial 350 CpB
2 hours 590
4 hours 1200
7 hours GEL
~4~77C:~ ~
605I-732
1 Thus it can be ~een that diallylmaleate slone i8 not
effecti~e for use in high platinum content release coating
co~position baths, whereas a bath which inste&d utilizes the two
part inhibitor of the present invention pro~ide~ a useful pot-life
of 7 hour6 or more.
While the examples and claim~ cited in U.S. Patent No.
4,256,870 in lude references to silicone comp~sitions in which
diailylmalea~e alone inhibits premature curing in the presence of
high levels of platinum, it should be understood that the cataly6t
specified therein is the ~ameroux caealyst of U.S. Patent No.
3,220,972~ The Lameroux catalyst has been found to be ineffective
for promoting commercially useful cure rates at temperstures below
250~F, even at platinum concentrations as high a8 200 ppm. For
example, U.S. Patent ~o. 4,256,870 discloses that a composition
which include~ 200 ppm Lameroux catalyst and O.5X diallylmaleate
requires 40 seconds to cure at 250DF. Use of the Rarstedt or
As~by type catalysts, on the other hand, permits curing in less
than 30 seconds at temperatures as low 88 200F and in the
presence of 100 to 200 ppm platinum catalyst. High concentrations
( ~ 3000 ppm) of diallylmaleate by itself i6 incompatible with
high concentrations of Karstedt or Ashby platinu~ cntaly6t
(i.e. ;~ 100 ppm Pt), and causes rapid precipitation of insoluble
plstinum residues. Thu6, further sesearch has cbown that
diallylmaleate alone i8 not suitnble a~ an inhibitor for high
~5 platinum content compositions nor for the multi~component system
described by Grenoble and Eckberg in Can. Serial No. 4~
