Note: Descriptions are shown in the official language in which they were submitted.
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ONE COMPONENT ACID-SCAVENGED REV
BONDING SILICONE RUBBER COMPOSITIONS
Background of the Invention
The present invention relates to one-component
REV silicone rubber compositions and more particularly
the present invention relates -to one-component silicone
rubber compositions with good bond:iIlcJ proprieties even
at hi.cJh humidity conditions.
One-component REV silicone rubber compositions
(REV stands for room temperature vulcanizable) are well
known. Examples of such coy positions are for instance
disclosed in US. Patent 3',38 , issued May 7, 1968
to Beers, and US. Patent 3,296,195, issued January 3,
1967 to Gauziness. Those compositions comprise
as the basic ingredient a sullenly terminated
diorganopolysi].oxane polymer having a viscosity
varying from 100 to 1,000,000 centipoise at 25C.,
an acyloxy functional Eros slinking agent and a
metal salt of a carboxylic acid as a curing promoter.
The composition may contain fillers, self-bondlng
additives, f1.ame-retardant additives and other
ingredients that are necessary. The most common
acyloxy functional cross-linking agent is methyl,
triacetoxysilane. The most common and the most
desirable curing promoter is a tin soap. The most common
types of fillers are fumed silica or precipitated
silica treated or untreated with various types of
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extending fillers such as crushed quartz, diatomaceous
earth etc. A preferred self-bonding additive for such
a composition is disclosed in Kulpa, US. Patent 3,296,151
issued January 3, 1967.
Irrespective of what ingredients are utilized,
such compositions are packaged in a single package
in the substantial absence of moisture and stored as
such. When it is- desired to cure the composition
seal on the package is broken and the composition is
applied to cross-link and cure by exposure to atoms-
phonic moisture to a silicone elastomers with final
cure taking place in a period of time varying anywhere
frown 24 to 72 hours. Other types of one-co~lponent
REV compositions are also known with various types
of cross-linking agents such as alkoxy functional
cross-linking agents such as are disclosed in Beers
US. Patent 4,100,129, issued July 11, 1978.
The Aztecs functional REV systems are desirable
; in that they are relatively simple and inexpensive to
produce. However, such compositions had one major
drawback and that is that they gave off acetic acid
; upon curing which was corrosive in some applications and had a
pungent odor. Nevertheless, such Aztecs functional
REV systems were utilized as sealants and gasket
2; forming materials in the automotive industry as early
as 1971 for various purposes. It was found that these
Aztecs functional REV systems Audi acceptable bonding
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........ .. .,.. , .. ... . .. ,. . .. ,. _, .. ,,, I,.. . ............
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proper en to thy substrates eve: at high humidity
conditions that is, at a Relative Humidity of 80% or
more. However, as stated, such Aztecs systems were
corrosive and the acid that was released tended to
5 discolor the metal to which it was applied. Since
that time, the use of REV in the automotive industry
has increased and it has been desirable to find a
gasket sealant for automotive applications which
would have good bonding properties to the steel or
metal substrate. Accordingly, it was highly desirable
to find a one component REV system which was relatively
non-corrosive and which could be utilized as a
casketing material in the automotive industry, and
which further did not have a pungent odor. It should
he noted that the alkoxy functional REV of Beers
US. Patent 4,100,129 did have these properties,
that is it was not corrosive and did not give off a
pungent odor, but unfortunately such systems cured
too slowly for automotive applications in most cases.
Z0 Accordingly, it was highly desirable to develop a one-
component REV system that was relatively non-corrosive
and did not give off a pungent odor and which ha high
. temperature thermal properties and could he utilized
. satisfactorily as a casketing sealant in automotive
. 25 applications.
An example of such a sealant is disclosed in Beers,
US. Patent 4,257,g32. Such sealant which was acyloxy
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functional differed from the traditional Aztecs
functional REV systems in that the acyloxy group
in the cross-linking agent had from 5 to 30 carbon
atoms and was most preferably methyl iris (2-ethyl
hexanoxy) Solon. There was incorporated into such
a composition a plasticizer and an adhesion promoter
which generally comprised a fluid polysiloxane having
a high degree of tri-functionality or twitter-
functionality as disclosed in the foregoing patent,
fumed silica as the filler, a tin soap and preferably
iron oxide as a thermal stabilizer for the composition.
It was disclosed in this pa-tent -there may be preferably
incorporated ion -the composition as -the self-bonding
agent a sill isocyanurate. Thor modifications of
this system are for instance, disclosed in Smith et at,
United States Patent Number 4,247,445, issued
January 27, 1981. Another modification of this
system was the utilization as disclosed in Mitchell,
et at, United States Patent Number 4,273,698,
issued June 16, 1981, the incorporation therein
of sill Maltese, sill numerates and sill
succinates as self-bonding additives. The foregoing
sill Maltese, sill numerates and sill succinates
of the foregoing Mitchell et at US. patent was
preferable to the isocyanurates as adhesion promoters
since they gave better bonding properties -to the
foregoing RUT systems of United States Patent
Number 4,257,932, issued March 24, 1981.
Another modification of such a system was
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the pre-reacting of the cross-linking agent with the
acyloxy functional Solon cross-linking agent and
preferably also the tin soap so as to yield more shelf
stable compositions, as disclosed in US. Patent No.
4,308,372, issued December 29, 1981 to Dziark et at.
All of these patents disclose improvements over the
basic composition of US. Patent No. 4,257,932, issued
March 24, 1981 to Beers, which result in an improved
composition. Elowever, the improvements disclosed in
the foregoing Mitchell, et at. patent and the Dziark
et alp patent were especially desirable in the
application of the 2-ethyl hexanoxy functional REV
system in the automotive industry.
However, it was found that such compositions had
a problem when applied as a casketing material. At
environments of up to 50g Relative Humidity, most of
the time the composition had acceptable bonding
properties. However, it was noted that such systems did
create a brown film on the steel substrate. However,
what was more noticeable was that in the area of
70, 80 and more percent Relative Humidity the
liberated acid upon the cure of the 2-ethyl hexanoxy
system would react with the iron in the steel to
form iron octet which would cause a brown
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oil deposit on the steel and which acted as a release
agent destroying the self-bonding properties of the
composition. Although there was some loss of adhesion with
the Aztecs systems, it was much more noticeable with 2-
ethyl hexanoxy REV systems.
Accordingly, it was highly desirable to find a
scavenger which wound lock up the acid as it was no-
leased in the REV system such that the self-bonding pro-
parties of the system would be maintained. It should be
noted that self-bonding properties are highly desirable
in REV systems, otherwise a primer has to he utilized
which requires additional material and labor; thus in-
creasing the cost of producing the silicone gasket,
Accordingly, it was highly desirable to solve this
problem 50 that the 2-ethyl hexanoxy REV system would
have good self-bonding properties to metal substrates,
and other substrates even at hick percent Relative
Humidity of 70, 80 or more.
It is one object of the present invention to
provide for a hexanoxy functional REV system with good
self-bonding properties even at high percent Relative
Humidity.
It is yet another object of the present invention
to provide for a hexanoxy functional REV system that does
not discolor the underlying metal to which it is Apple en'
- which has good self-bonding properties to the underlying,
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swig
metal substrate.
It lo yet an additional object of the present
invention to provide fur an acid scavenger for Alex
functional REV systems so as to maintain the self-
S bonding properties of the composition even at high percent relative humidity.
It is yet also an additional object of the preset
invention to provide a process for forming a silicone
gasket in the automotive industry from an ac~loxy lung-
tonal REV system in wish the system contains an acid
scavenger.
It is yet still an additional object of the
present invention to provide a process for forming a
. silicone gasket against a metal substrate for auto-
motive applications in which the silicone gasket has
good self-bonding properties even at elevated percent
Relative Humidity, is relatively non-corrosive, does
not discolor toll metallic substrate and does not have
a pungent odor.
It is still an additional object of the present
invention to provide for an improved silicone gasket
. for top automotive industry which has good self-bonding
properties to metallic substrates.
. These and other objects of the present invention are
25 accomplished by means of the disclosures set forth here
. below
.
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Summary o-f the -Invention
In accordance with the above objects,
there is provided by the present invention a
one-component REV silicone rubber composition with
good bonding properties even at high humidity conditions
comprising (A) 100 parts by weight of a sullenly
end-stopped diorganopolysiloxane polymer having a
viscosity varying from 100 to 1,000,000 centipoise
at 25C. where the organ groups are monovalent
hydrocarbon radicals and (B) from .1 to 10 parts
by weight of an acyloxy cross-linking agent owe
the formula r
RmSi (OR em
where R is a monovalent hydrocarbon radical of
1 to 8 carbon atoms and Al is an acyloxy radical
of 2 to 30 carbon atoms, m is 0 or 1; (C) from .01
to 10 parts by weight of a curing promoter which
is a metal salt of carboxylic acid; and
(D) an effective amount of acid scavenger selected
from the class consisting of zinc materials,
magnesium materials, aluminum materials and
mixtures thereof
The most preferred materials within
the above group are the metals, the oxides and
the carboxylic acid salts. It should be noted
further that the oxides must be utilized at a
smaller concentration than the salts. If the
oxides are utilized at somewhat above their
ranges disclosed below, then what happens is that they
inhibit the cure of the composition and the composition
will cure slowly if at all, depending on how much
of the materials has been placed in the composition.
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Accordingly while zinc oxide and possibly even aluminum
oxide are- disclosed as fillers for acyloxy functional one-
component REV systems, nevertheless if they are utilized
in the 2-ethylhexanoxy system at above the concentration
S limits disclosed in the ranges below, then they will in-
habit the cure of the composition. Accordingly, we will
now proceed to a more detailed description of the invent
Shea.
Description of Preferred Embodiment
it must be noted that preferably there is utilized
the foregoing materials of zinc, aluminum end magnesium
as acid scavengers in the instant composition The car-
boxlike acid salts of zinc and magnesium, operate in the
present invention and the oxides of these metals should
15 also operate within the scope of the present invention as
acid scavengers.
Accordingly, only slightly basic or amphoteric
metals would be desirable as acid scavengers in the
instant composition. If the material it slightly ask
20 or amphoteric it will absorb the acid that is riven off
during the hydrolysis to form an innocuous salt without
detracting from the final cured properties of the compost-
lion. Accordingly, zinc, magnesium and aluminum compounds
will function effectively in the instant case even as
- 25 zinc and magnesium metals.
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Aluminum metal might also function effect lively as an
acid scavenger. There does not appear any reason why
this metal powder cannot function effectively as acid
scavengers in acyloxy-functional Al systems.
on addition, it is not known whether this lack or
decrease in the self-bonding properties of a composition
takes place with compositions other than acyloxy-
. functional REV systems at high humidity conditions. How-
ever, if the REV system gives off an acid during cure,
and the composition is applied to metallic substrate,
then conceivably the same type of phenomenon would be
encountered and the same scavengers as utilized in the
instant invention would be suitable to prevent loss of
self-bonding properties.
It should be noted that the functions of the acid
scavengers of the instant case are twofold one, to
prevent or tie up the acids that are given off so as to
decrease or eliminate the formation of an oily residue
at the interface of the silicone rubber composition and
the metallic substrate which would cause a decrease in
self-bonding properties of the composition and the other
is to prevent the acid given off from attacking the
; metallic substrate and resulting in discoloration of
the substrate. It would also appear that other types ox
compounds of zinc, aluminum and magnesium can be utilized
'.
.
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. ....................... ... . .. ,.. .... ,. .,.,.. , ,.,.,.. ,,~,.. ,.. _
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as acid scavengers other thy the carbolic acid salts or the oxides
or the eta powder. However, these other expounds would have to
be neutral, or slightly basic. Further, although surety salts are
preferred, any carbcxylic acid salts can be utilized in the instant
invention as acid scavengers, other than aluminum carboxylic acid
salts, and particularly carboxylic acid salts that average from 6 to
30 carbon atoms. There may ye utilized individual salts, Oxides,
and metal powers or there may be utilized mixtures thereof depend-
in on the type of ingredients that are used.
Further, zinc oxide is a scavenger in the instant case although
not as effective as My and My. The most effective scavengers are
the magnesium materials.
Aluminum car~oxylic acid salts such as an aluminum Stewart are
not effective scavengers. Hkhever, other aluminum compounds and toe
metal, although not as effective as the zinc and magnesium
materials, should function to some extent as scavengers.
In this respect, there is a broad range in which
the foregoing materials may be utilized in the system.
That is, the amount of material that will be used in
the system will depend on the type of material it is.
Thus, broadly, there may be utilized an effective amount
- of zinc, aluminum or magnesium material or mixtures thereof
up to generally 6 part by weight of the material
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per 100 parts of the sullenly terminated diorganopoly-
selection base polymer. If more than 6 parts are
utilized, then the material would inhibit the cure of the
dcyloxy-functional REV system in which it is incorvoratec.
Preferably the oxides and the metal powders are utilize
in a concentration of anywhere from 0.05 - 2.0 parts by
weight while the carboxylic acid salts are utilized in a
concentration of anywhere from 3.0 to 6.0 parts by weigh-
per 100 parts of the sullenly base polymer. As stated,
it more than the specified amount of material is utilize
in the composition, the cure of the composition will be
inhibited, that is, it may not cure for weeks, for months,
or not at all, or it may remain tickles to the touch for a
long period of time or if too much of the oxides are use-,
they may cause gellation of the composition before it
cures completely and obtains its optimum physical roper-
ties. In this respect, it should be noted that income
cure results in poor physical properties of the compost on
as well as making it very tacky to the touch This is
highly undesirable in a silicone elastomers As indicate
above and as shown in the examples below, the amount of
concentration of the ingredient that is utilized will
depend upon the ingredient that is used. Its optimum
concentration will have to be determined by experimental an.
;' , .
.
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The acid scavenger material is not utilized as a
filler in the instant composition. That is, fillers are
normally used in the composition to Pitter cheapen the cost
of the composition - for instance extending fillers -
or to increase the physical properties of the composition or give preferred select properties to the composition.
Most fillers such as fumed silica are utilized in the
composition to increase its physical properties such as
Tear, Hardness, and Tensile Strength. This is to be
distinguished in the present composition in which
oxides such as aluminum oxide, magnesium oxide and
zinc oxide are utilized to absorb the acid that is
formed from the cross-linkin~ agent when it hydrolyzes
upon cure of the system. It should be noted that zinc
oxide, and magnesium oxide have been disclosed as
extending fillers for acyloxy-functional REV systems.
However, these ingredients when utilized as a filler
are used not only at higher concentrations than the
acid scavengers of the instant case, but they are also
utilized in the traditional sense of fillers and not
for absorption of acids formed by the hydrolysis
of a cross-linking agent so as to preserve the self-
bonding properties of the composition as is the case with
the instant case.
.
13
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............ , ...... ... ,.. ..................... -; ;-.. .....
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It must also be appreciated that the present
phenomenon is noted to some extent with Aztecs
functional Revs that is, with a cross-linking agent
such as methyltriacetoxysilane. However, in those
cases, while the acid does attack and discolor the
metal substrate, the liberation and forming of a non-oily
roused at the surface does not affect the self-bondin~
properties ox the acetoxy-functional composition
anywhere near as great as is the case for the
2-ethylhe~anoxy functional REV system. Accordingly, the
acid scavengers of the instant case can he utilized
wit those systems not depending on how desirable
it is to improve the self-bonding properties. However,
the acid scavengers of to instant case are effective
in preventing the discoloration of the metallic substrate
by the acetic acid that it given off when the Aztecs
system cures. Accordingly, the acid scavengers of the
present invention are especially effective in preventions
discoloration of metallic substrates of all types of
acyloxy functional REV systems, and are most effective
in preventing the decrease in self-bonding properties
of one-component acyloxy functional REV systems where
the acyloxy group has from 5 to 30 carbon atoms. It
should also be noted that the discoloration of the
; 25 metallic surface, that is the discoloration of the
substrate as well as the loss of sel,-bonding properties,
is most noticeable with metallic substrates such as
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. .. I...... ................... ... .. ..........
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zinc and iron substrates. It is not noticeable and it
is not the case with plastic, glass, and ceramic sub-
striates. Accordingly, the acid scavengers of the present
case find most use in acyloxy-~unctional REV systems where
the acyloxy group has from 5 to 30 carbon atoms, where the
REV system is to be applied to metallic substrates, such
as steel.
It is postulated that this phenomenon also occurs to
some extent with a masonry or concrete substrate, that is
the discoloration of the substrate around the sealant,
and the possible loss of self-bonding properties. Accord-
tingly, the acid scavengers of the present case would wind
utility as ingredients to stop the loss of sel-bonding
properties o. acvloxy functional REV systems where the
REV system is to be applied to masonry substrates such as
concrete as well as when it is applied to metallic sub-
striates such as steel, but not stainless steel. An oily
residue is not formed on stainless steel. As noted above,
the acid scavengers absorb the acid and turn it into
an innocuous salt without detracting from the physical
properties of the cured composition.
This is especially important where the cured sift-
cone elastomers is to be applied as a gasket in combo-
session for automotive applications. Thus the composition
is applied by machines or other means such as in
. a layer between metallic substrates on which there
. is applied another metallic layer there over to form a
gasket between two metallic substrates in which
--it-- , -
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.... ....... ........... . . ... . . ... . ......
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the cured silicone elastomeric gasket acts as a seal.
Such silicone elastomeric gaskets must have quick curing
I- properties, be fairly non-corrosive, not have an
objection Al odor, and have good oil resistance as
5 well as good thermal and weathering properties at high
temperatures. Especially important is that such silicone
elastomers gaskets have good self-bonding adhesion to the
metallic substrate. Primers can be utilized to enhance
adhesion. However, the use of primers increases the
lo cost of applying or forming the silicone gasket.
Accordingly it is desirable to have a silicone elastom~ric
composition with good self-bonding properties which the
present invention accomplishes.
It must also be noted that within the above broad
15 definitions of concentrations of oxides and salts that
there can be utilized a combination of a salt and oxide
at a concentration within the preferred ranges
disclosed above. However, the optimum levels whether
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oxides or natal polymers are used my themselves or
in combination with metal salts, must be determined by
experimentation and depend to some extent on the other
ingredients of the composition. Accordingly, it is left
to a worker skilled in the art to determine the best
Go optimum concentration of metal salts or oxides in
the composition to achieve the optimum acid scavenger
function in an acyloxy-functional one-component REV
. system.
It should be noted that generally iris are
utilized at a concentration of 10 parts or more by weight
per 100 parts by weight of sullenly terminated diorgano-
polysiloxane base polymer, and that the present acid
~czvengers are utilized in concentrations considerably
below those levels.
With respect to the instant invention, it is now
necessary to proceed to a brief description of toe archways
components that may be present in the composition. us
has been noted above, the basic polymer of the composition
comprises a sullenly terminated diorganopolysiloxane
.. . .. .. ..... . .. ... . .
. - .
-I .
_ _ _ _ _ _ _ ... _ . _ _ _ _ _ _ ... . . . .. . . . . . .
~zz~9~
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polymer hazing a viscosity varying from 100 - 1,000,000
centipoise at Corey the organ group is a monovalent
hydrocarbon radical. The monovalent hydrocarbon radical
can be any monovalent hydrocarbon radical such as alkyd
radicals of 1 - 8 carbon atoms as methyl,ethyl,propyl,
etc., cycloalkyl radicals such as cyclohexyl, cycloheptyl,
etc.; mononuclear aureole radicals such as phenol, methylphenyl,
ethylphenyl, etc.; alkenyl radicals such as vowel, alveoli, etc.;
and fluoroalkyl radicals of 3 - 8 carbon atoms such as
3, 3, 3, trifluoropropyl, to Preferably, the sullenly
based polymer has the formula,
HESS i o 1
1 I
I s
where R3 and R4 are independently selected monovalent
hydrocarbon radicals and the value of s is such that the
viscosity of the polymer varies from 100 to 1,000,000
centipoise at SKYE. and more preferably varies from 100
to 100,000 centipoise at 25C. Tile radicals R3 and R4
- can be any of the monovalent hydrocarbon radicals pro-
piously identified for the organ group for the term
- "organ" in the sullenly terminated diorganopolysiloxane
polymer. Per 100 pats of such polymer that may be
I; present from .1 to 10 parts by weight of an acyloxy
- functional cross-linXing agent of the formula,
R S, (OR )
m 4-m
-
, -18-
. . .
.
.. .. , .. .... ,. _ .. _. _~_.__.. _.. ,___~__,,,.,,,, ,,,,,,,,,,, ,,,_,,,, ,,,,,; , ............... ..
~2Z3~98
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where R is a monovalent hydrocarbon radical of 1 - 8
carbon atoms and R is an acyloxy radical of 2 - 30
carbon atoms, m is 0 or 1. Preferably R is methyl and
Al is benzoxy or 2-ethylhexanoxy. The symbol Al can also
5 be Aztecs Accordingly, the three most preferred acyloxy
functional cross-linking agents is methyl-triace~oxysilane,
methyl-tris benzoxysilane, and methyl-tris 2-ethylhexanoxy
Solon.
Although the improvement of the present invention will
apply in any acid-functional one-component REV system, it
is most preferably applied to acyloxy functional REV systems,
specifically those in which the acyloxy group varies prom
5 - 30 carbon atoms. Finally, there may be present from
0.01 - 10 parts by weight of a curing promoter which is a
metal salt of a carboxylic acid. Preferably the metal
salt of a carboxylic acid that is a curing promoter is
a tin salt. The most preferred tin salts are, for instance,
dibutyl tin dilaurate, dibutyltindiacetate, dibutyl tin
oxide, and dim ethyl tin bis-neodecanoate. In a case where
the cross-linking agent is 2-ethylhexanoxy, then preferably
the tin salts are dibutyl tin diacetate, dibutyl tin oxide
and dim ethyl tin bis-neodecanoate disclosed in the fore-
- going Beers Us Patent 4,257,9~2. There may also be used
as disclosed in the foregoing patent from 1 - 10 parts by
weight per 10~ parts of the sullenly polymer of an iron
oxide thermal stabilizer.
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There may also be used anywhere from 10 Jo 200 parts
by weight of a filler. The filler, if it is a rein-
forcing filler, it is preferably present at a concern-
triune of lo to lo parts by weight. Examples of
reinforcing fillers are for instance fumed silica and
precipitated silica. These fillers may be present,
treated, or untreated, but preferably are treated with
cyclopolysiloxane such as disclosed in Lucas US.
Patent 2,938,009, Lichtenwalner, US. Patent 3,004,859
lo and or soullessness as disclosed in Smith, US. Patent
3,635,743. Such patents are exemplary of such
treatment technology. Preferably the reinforcing
type of fillers are treated so that the filler will
not unduly increase the viscosity of the composition
in the uncured state. The rest of the filler may
be a reinforcing or extending filler. All of the
filler or some of the filler can be an extending
filler. Examples of extending fillers, are for
instance, titanium dioxide lithopone, ~e-exidc
zirconium silicate, silica argyle, irk
diatomaceous earth, fibers, calcium carbonate,
chronic oxide, zirconium oxide, alpha quartz, calcined
clay, carbon black graphite, cotton, synthetic fibers,
etc.
It should be noted that these extending fillers
are utilized preferably in addition to the reinforcing
fillers for various purposes. Most notably, they may
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make the composition paintable, or they may
increase or reinforce the properties of the
composition without unduly increasing the uncured
viscosity of the composition. However they are
not anywhere near as effective as the fumed silica
and precipitated silica in increasing the cured
physical properties of the silicone rubber
composition.
Per 100 parts of the sullenly terminated
polymer on the base polymer of the instant
composition, there may also be present from 1 to
10 parts of iron oxide as a terminal stabilizer
as disclosed in -the ~oregoincJ US. Patent 4,257,932,
issued March 24, :L981 to Beers.
There is also disclosed in the foregoing
patent, that there may also be present from
2 to 20 parts by weight of a fluid polysiloxane
containing a high degree of tri-functionality,
~étra-functionality or a mixture of in- and
tetra-functionality, comprising
(i) from 25 to 60 mole percent of moo-
alkylsiloxy units; sulks units or a
mixture of such units;
(ii) from 1 to 6 mole percent of in-
alkylsiloxy units;
(iii) from 34 to 74 mole percent of
dialkylsiloxy units, said polysiloxane
containing from about .1 to 2% by weight
of a silicone bonded hydroxyl groups.
For more information in-to such fluids, one is
referred Jo the foregoing USE Patent 4,257,932
and US. Patent 3,382,205, issued May 7, 1968
to Beers.
- 21 -
1 2Z 30~8 SUE
It is generally advantageous in such compositions to
decrease the amount of fumed silica in the composition
so that the composition has the desirable properties
of the cured state but does not have an undesirably
5 high viscosity in the uncured state. Accordingly, when
the concentration of fumed silica is reduced below a
certain point, the uncured silicone rubber composition
does not have a sag control. That is, it is not
thixotropic. Accordingly, a sag control agent may be
incorporated into the composition which is a small
amount ox a polyether as disclosed iII Wright et alp
United States Patent ~,261,758, issued April 14, 1981.
Accordingly, per 100 parts of the sullenly terminated
diorganopolysiloxane polymer, there may be incorporated
into the composition from .03 to 2.0 parts by weight Ox
a l~olyether selected from a class consisting of
A -- O -- CXH 2 x ) B
and (A - O - ~CXH2xO) I
wherein A and B represent radicals selected from the
20 class consisting of hydrogen, alkyd radicals containing
from 1 Jo 12 carbon atoms, cycloalkyl radicals containing
5 Jo 7 carbons in the ring, mononuclear and binocular
aureole radicals and mononuclear aureole lower alkyd groups
attached to the aromatic nucleus contain a total of no
more than 5 carbon atoms;
O
RZ _ ¦ _ o
- -22-
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I Z~3~9~3
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where R is alkyd containing from 1 Jo 11 carbon atoms,
Q is a residue of a polyhydric initiator radical containing
at least two hydroxyl radicals selected from the class
consisting of ethylene, glycol, glycerol, trim ethyl-
polypropane~ and other polyhydric alcohols having from to 6 hydroxyl groups, a is a number having a value of
from 4 to 2000; x is a number having a value of 2 to 4;
y has a value of from 2 to 10 and z has a value of prom
1 to 5; the polyether having a molecular weight of from
about 300 to about 200,000. There may also be present
in the composition from .1 Jo 3 parts by weight of a
self-bonding agent. The self-bonding agent may be a
isocyanurate as disclosed in the foregoing Biers US.
Patent No. 4,257,932. If the self-bonding agent is an
isocyanurate, it is preferably 1, 3, Tracy trimethoxy-
silylpropyl isocyanurate. Most preferably, such additive
is preferably selected from sill Maltese, sill
numerates and sill succinates as well as selection Maltese
and mixtures thereof. Examples of such self-bonding
additives which are preferred for the composition of
the instant invention are for instance disclosed in
the foregoing Mitchell et Allis, Patent A ,273,698
issued June 16, 1981.
Preferably the cross-linking agent is reacted with
a self-bonding additive prior to being incorporated into
the composition. The cross-linking agent, that is the
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I
awry functional cross-linking agent and the self-
bonding additive are prereacted prior to being
incorporated into the composition. This is especially
true if the 2-ethylhexanoxy junctional Solon cross-
linking agent is utilized and also a self bonding additive selected from sill Maltese, sill fumarates,
and sill succinates. This prereacted self-bonding
additive and cross linking agent is disclosed in the
US. Patent of Dziark et at, Patent No. 4,308,372,
issued December 29, lg81. The most preexred Scholl-
bonding additive is for instance bis-trimethoxypropyl
fumarate or alternatively bis-trimethoxypropyl
Malta. There may be other additives in the
composition as desired, such as flame-retardant
additives, further heat agent additives, plasticizers,
etc. These additional additives will not affect the
efficiency and suitability of the acid scavengers in
carrying out their function.
The foregoing acid scavengers will not affect the
uncured properties of the composition as far as is
known. These acid scavengers may be incorporated in
the composition in any manner which may be desired.
That is, generally they may be added to the catalyst
component and mixed with the other ingredients as desired.
The entire mixture is made substantially an hydrous and
packaged as such. To cure the composition, the seal
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....... . , ., , ,--
~223~9~ SUE
on the package is broken, and the composition applied
whereupon on exposure to atmospheric moisture the come
position cures to a silicone elastomers with final cure
taking place in 24 - 72 hours. It must be appreciated
that it is necessary to have a curing promoter in the
composition if the composition is to cure to a full cure
in the 24 - 72 hour period. Without a curing promoter,
the cure may take a longer period of time and may not be
as complete.
In the instant composition, the magnesium materials
the aluminum materials, and zinc materials junction as
acid scavengers. That is, they absorb and react with the
acid that is given up during the cure of the composition
and the hydrolysis of the cross-linking agent so as to
prevent such acids and salts detracting from the physical
properties of the composition and will not affect
deleteriously the self-bonding properties of the compost-
lion. One function of the acid scavengers is to improve
the self-bonding properties of the composition or rather
to prevent the acid that is liberated at a high percent
relative humidity from detracting from the sel-bonding
properties of the composition and the other is to
prevent the acid that is liberated from attacking and
discoloring the metal substrate on which the silicone
rubber composition is applied. As can be seen from
the examples below the acid scavengers of the instant
case perform their function very well. It should also be
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issue 605I-499
noted that the various constituents of the compositions
of the instant case which haze bee described and which
are well known have not been described in great detail
since workers skilled in the art may be referred to the
foregoing patents and patent applications referred to
herein for further information on the subject.
The examples below are given for the purpose of
illustrating the present invention. They are not given
for the purpose of illustrating limits and boundaries to
the instant invention. All parts are by weight.
okay no
In the -ego examples there was utilized a
Sealant A. Sealant A comprised 66.423 by weight ox
a blend of sullenly terminated dimethylpolysiloxane
polymers having a blend viscosity of 4500 centipoise
at 25C., 3.98% of iron oxide, 6.64% by weight of a
tri-functional fluid containing 3 mole percent trim ethyl-
sulks mono-functional units, 40 mole percent of
monomethylsiloxy tri-functional units, 57 mole percent
ox dimethylsiloxy, di-functional sulks units and .5
percent hydroxy groups. The composition also contains
I weight of U KIWI which is a polyether sold
by the Union Carbide Corporation, Connecticut. To
this mixture was added 15.94% by weight of octamethyl-
cyclotetrapolysiloxane treated fumed silica, 4.70% by
weight of methyl iris ~-ethylhexanoxy Solon 2.03%
by weight of bis-trimetnoxypropyl fumarate, and .1% by
weight of dimethyltin bis-neodecanoate.
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Such a sealant which was tested with various types
of acid scavengers in it was compared with the following
Aztecs Sealant B. Sealant B comprised 71.63% by
weight of a sullenly terminated dimethylpolysiloxane
having 6000 centipoise viscosity at 25C., 2.16% of
iron oxide, 7.88% of tri-func~ional fluid containing 3
mole percent of trimethylsiloxy monofunctional units,
20 mole percent methyl trifunctional sulks units, 77
mole percent of dimethylsiloxy di-functional units and
lo approximately .5 weight percent of sullenly to this
mixture of Sealant B there was added 14.32~ ox' octame-thyl~
cyclotetrapolysiloxane treated fumed silica, 3.19~ of
methyltriacetoxysilane, .79% by weight of di-tertiary-
butoxydiacetoxysilane and .03% of dibutyltindilaurate.
Example l
There was prepared and tested in Sealant A and a
Sealant B containing no acid scavengers in them. This
data was compared with a composition containing 3.66
weight percent zinc Stewart and .46% by weight of
magnesium oxide.
All of the compositions were tested after cure
for five days at 77% and 80% relative humidity.
There were samples of Sealant with the acid
scavenger, which were further exposed to 4 hours at
250F. to simulate the temperature increase encountered
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~ZZ3~
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in d starting automobile engine. results are set forth
in Table I below. The shear adhesion in psi and percent
cohesive failure was measured as follows:
The substrate and screen were both cleaned by
first immersing in Tulane and then scrubbing and
drying with laboratory tissue.
The typical shear adhesion test specimen was
prepared using previously cleaned 1 inch by 4 inch by
a 0.040 inch cold-rolled steel substrate. This substrate
was clamped into place by means of a steel bar bolted
over one end to a 1/2 inch thick rigid machined steel jig.
The jig was so designed as to leave one square inch of
exposed surface area. The sealant was applied to the
exposed surface. A 1 by 4 inch 20 mesh piece of stainless
steel screen was then embedded into the sealant at a
bond line thickness of 0.010 to 0.015 inches. The excess
sealant was removed from the top and sides of the
specimen by means of a spatula. The resulting specimen
-was then allowed to cure in the environments described
in the examples.
; After completion of cure the specimens were
pulled apart at the rate of 0.5 inches per minute using
a Monsanto Extensiometer.
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.
.
.
.
isle SUE
TABLE I
Shear Adhesion Performance after Five Days
at 77F. and go Relative Humidity
Sex t B Sealant A lank A with
on S rate and Moo
4 his 4 hut 4 his
Into 250~F.~ vial 250~F.Initial 250F.
Shapiro
adhesion psi 142 12943 27 135 198
cohesive
Failure 7 3 0 0 80 lo
As the results indicate, the adhesion performance of
the zinc Stewart, magnesium oxide in Sealant A was
superior to the other two specimens. In addition, this
specimen exhibited no discoloration of the steel sub-
tryout whereas the Aztecs specimen had a bright brown
discoloration at the sealant, metal interface and the
other Sealant A specimen had a dark brown oily deposit`
in the sealant steel interface.
Example 2
Sealant A and Sealant B were tested for shear
adhesion with various levels of magnesium oxide. These
runs were made with a direct comparison with Sealant B
which contained no scavenger. Again the samples were
prepared as set forth in Example 1 and exposed to 80%
relative humidity for five days at 77F. At the end of
that period they were tested for shear adhesion both in
psi and percent. cohesive failure and also after four
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hours at 25UF. The results are set forth in Table II
below: Sealant A and Sealant B are the same sealant
as defined previously
TABLE II
The Effect of Magnesium Oxide on the
Adhesion Performance of Sealant A at
80% Relative Humidity and 77F.
Sealant A Sealant B
MgOShear Adhesion no Scavenger)
: 10 Level(psi/% OF (psiJ%C.F.)
~wt.%)Initial 4 hrs.!250~FInitial 4 hrs.l250F.
0.35263/90 217/70 95/0 1~7/0
O 35 (1) 202/75 180/85 71/0 6~0
0 15182/55 215/65 71/n 6~/0
. 15 (1) This was a repeat of the preceding experiment using
another newly prepared formulation.
As the results of Table II indicate, there is obtained
a superior self-bonding composition with Sealant A with
an acid scavenger as compared with Sealant B. It should
be noted that the optimum level of acid scavenger, that
is, of magnesium oxide alone appeared to be .35% by
weight. Again similar tests were run utilizing zinc
Stewart as the acid scavenger in Sealant A as compared
to Sealant B utilizing no acid scavenger in the composition
- 25 Gwen, after the shear adhesion specimens were prepared, the
- samples were exposed to 80% Relative Humidity for five
. . .
.
.
-
.
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. .
... .
I.
~L~;23~98
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days at 77 F. At the end of that period, samples were
tested for shear adhesion and percent cohesive failure.
Other samples were further exposed for four hours at
250F. before being tested for shear adhesion and
percent cohesive failure. The results for the zinc
Stewart and zinc oxide at various levels are indicated
in Table III below. As noted previously, Sealant B
was the formulation as identified previously and
wherein the Sealant B samples had no acid scavenger in
I them.
TALE III
The Effect of Zinc Stewart on the
Adhesion Performance of Sealant A
at 80% Relative Humidity and '77 F.
Sealant A Sealant B
Zinc Stewart Shear Adhesion (No Scavenger)
Level (White) (psi./% OF (psi./% OF
Initial 4 hrs./250 Initial 4 hrs./250 F.
3.8125/75 210/100 157/3 153/100
Z~0 Level
(wt.%) _
0.35128/10 191/95 71/0 64/0
0.70189/40 291/100 71/0 64/~
It should be noted that in the above experiment the
zinc oxide containing sealant samples exhibited some sun-
face tack after curing for five days at 50% RHO but not
after the 80% RHO cure or exposure to 250F. for four hours.
As the results in Table III show, both zinc Stewart and
zinc oxide are effective acid scavengers for the Sealant A
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system, Although, the levels at which each on was
effective differed markedly as explained above
Example 3
There was prepared a Sealant C similar to Sealant
A comprising the following composition: 66.42% by
weight of a sullenly terminated dimethylpolysiloxane
polymer blend having a viscosity of 4500 centipoise
plus or minus 500 centipoise at 25C., 3.98~ of
iron oxide; various levels of acid scavengers; 6.64
lo by weight ox a tri-functional fluid of Sealant A;
.13% by weight of a polyether which sold under the
name of Pluracol-7, a polyether sold under the above
trade name by the Wyandotte Chemicals Corporation;
15.94% of octamethacyclotetrasiloxane treated fumed
silica filler; 4.70% of methyl iris 2-ethylhexanoxy
Solon; 2.09~ by weight of bis-tri-methoxy propel
numerate (or Malta) and .10% of dim ethyl tin bus-
neodecanoate. These samples were prepared as in
Example 1 which were exposed to 80% Relative tumidity,
80 F. for five days. The samples were also part
baked for four hours at 250F. to simulate engine
heat up. The shear adhesion and % cohesion
failure results of Sealant C mixed with various
levels of zinc Stewart and magnesium oxide under
the foregoing conditions are listed in Table IV.
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...... , _, _ _ . .......... _ _ . .... . . _ . _ _ . _ .. _ _ . .............................................. _ .. _
122309~3 swig
TABLE IVY
Effect of Zinc Stewart - Magnesium
Oxide Combinations on the Adhesion
Performance of Sealant C at: 80F/
. 80% RHO
Zinc Stewart level, White % 10.8 3.6 2.6 O
Magnesium Oxide. Wt. % 103 0.5 0.3
Shear Adhesion, PsV% OF 35/90~2) Lowe ~.12/100 30-65/0
(11 Samples were also post-baked for 4 hours.J250F
to simulate engine heat-up. For quality control
purposes, this is for 8 hrs./150F.
(2) Inhibition of Cure Noted at 10.8 Wit Zinc
Stewart.
Example 4.
Into Sealant C which was prepared as in
Example 3 there were incorporated various amounts
of zinc Stewart by itself as an excellent scavenger
was compared to Sealant C without any acid scavenger
as a control. The composition was the save in each case
except there was utilized tune various levels of zinc
Stewart as indicated in Table V below. The results
are set forth in Table V.
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TABLE V
Effect of Zinc Stewart on
Sealant C Adhesion Performance
at 8QF~aO% RHO
cure Times 5 Days)
zinc Stewart Level, ~t.%10.8* 3.8 2.6 1.3 0
shear Asian psi/% C~F.35190 210/lt)0 45/0 6~.5 30~65/0
(Steel Substrate
*Cure butted
lo Moo included
The results of Tale V were samples which were aged for five
days at 803 Relative Humidity and 80F. Each sample was
then post-baked for four hours at 250F. to simulate engine
heat-up. As the results in Table V indicate, zinc
15 Stewart was a very effective acid scavenger and self-
bonding improver at a level of 3.8% by weight. Similar
tests on the same Sealant C composition but with various
levels of magnesium oxide showed similar improvements in
self-bonding properties of the Sealant C composition after
20 the sample was aged at 80% Relative Humidity and 80F.
` for five days and then post-baked for four hours at 250F.
- Each sample was subjected to this procedure. The result-
in shear adhesion tests which were curried out in the same
manner as set forth in Example 1 are set forth in Table
25 VI below.
Jo -
-
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BLUE VI
The Effect of Magnesium Oxide on
Sealant C Adhesion Performance at
80~F/80% RHO * (Cure Time 5 Days)
Magnesium 1.4 a .5 Owe 0~23 0.16 Owe Owe
Oxide Level
(Maglite D)
Adhesion, 45/0 130/30 165/85 215/~ 291/100 215/70 248/100 3~-6~/0
s~xked hours.J250F.
As the results of Table VI show magnesium oxide appeared
to be very effective as an acid scavenger to improve the
sel~-bondLng properties of the sealant C composition at
levels of ~16% by weight or somewhat less. The results
of both Tables V and VI show that zinc Stewart and
magnesium oxide were effective self-bonding improvements
for the 2-ethylhexanoxy functional REV systems. It
should be noted that the magnesium oxide utilized in
these tests was sold unsex the name Magllte-D, a trade-
name of Merck Chemical Corporation, of New Jersey.
As the results above indicate, there is obtained
advantageous improvement in self-bonding properties of
acyloxy-functional REV systems and especially those in
which the cross-linking agent is 2-ethylhexanoxy
functional at 80~ Relative Humidity even when the cured
composition is exposed to 80% Relative Humidity for
extended periods of time. The most effective acid
scavensersfor accomplishing this purpose have been found
Jo be zinc Stewart, zinc oxide, magnesium oxide and museum metal
However, other materials, that is other metal salts of
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~Z~3~ SUE
carboxylic acids other than the foregoing metals of
zinc and magnesium should be just as effective as the
zinc Stewart. Preferably the carboxylic acid group
carbon content varies from 6 to 30 carbon atoms. In
addition, all the oxides should also function effectively
although at lower levels as the foregoing magnesium oxide
and zinc oxide, as well as the metal powders. No format
lion of gas was noted with the magnesium and zinc powders.
Further, although the present system was devised when the
acyloxy REV system is to be applied to a metallic sub-
striate, it can be appreciated that similar advantages
will also be found in the utilization of such acid
scavengers when the acyloxy-functional REV system is
applied to other types of substrates.
Example 5
In Examples - 9, the shear adhesion specimens
were first cured for five days under the conditions desk
cried and then post-baked for four hours at 250~F. In
each experiment the conditions for the control were 77F~
and 50% Relative Humidity. The elevated humidity environ-
mint was maintained at 80F. and 80 percent Relative
tumidity. In each case, in Examples 5 - 9, the composition
was the same as Sealant A on page 26 except for the type
and amount of the scavenger defined below. The Control
.;,~.
composition was the same as Sealant With the same amount
of scavenger and cured under normal conditions.
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A composition the same as Sealant A was prepared into
which aluminum Stewart was incorporated at a concentra-
lion of 2.78 weight percent. The control sealant con-
twined the same amount of scavenger.
Shear Adhesion Results:
1 Control: the sample was cured 5 days at phoned 50% Relative Humidity followed
by a post-bake of four hours at 250F.
Shear Adhesion = 247 psi at 100%
cohesive failure.
2. Elevated Humidity: The sample was cured five
days at 80F. and 80% Relative
Humidity followed by a post bake of
four hours at 250F. Shear Adhesion
= 3 psi at 0%
cohesive failure.
Conclusion
Aluminum Stewart does not function as a
scavenger.
Example 6
Alumina (aluminum oxide was incorporated in the
Sealant A composition at a concentration of 0.5 weight
percent. The control sealant contained the same amount of
scavenger.
1. Control
Shear Adhesion = 292 psi at 100%
cohesive failure.
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... ,.. ,......... ,....... . _ . _ ., .. . ... = , _ _ , .,, ,,, ,, =, ,_ I,
~Z~3~9~3
swig
2. Elevated Humidity
Shear Adhesion - 39 psi at I
- cohesive failure.
Thy test conditions were the same as in Example 5.
Conclusion
Aluminum oxide has a low degree of scavenger
activity in comparison with the control shown
in Example 9.
Exile 7
Powdered magnesium metal ox a particle size of 70 -
80 mesh was incorporated into Sealant A composition at
a concentration of 0.71 weight percent. Top control
sealant contained the same amount of scavenger.
lo 1. Control
Shear Adhesion = 190 psi at 90%
cohesive failure.
2. Elevated Humidity
Shear Adhesion - 212 psi at 96~
cohesive failure.
The test conditions were the same as in Example 5.
. . .
.
Magnesium metal is an excellent scavenger.
I. ,
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.
Example 8
Powdered zinc metal of a particle size of about 20
mesh was incorporated in the Sealant A composition at a
concentration of 0.71 weight percent. The Control con-
twined the same amount of scavenger.
1, Control
Shear Adhesion = 18~ psi at 100%
cohesive failure.
2. Elevated Humidity
Shear Adhesion - 105 psi at 0%
cohesive failure.
The test conditions were the same as in Example 5.
Conclusion
zinc metal is a mildly active scavenger.
Example
No test scavenger was used in this example. The
composition was the same as Sealant A. This is the
experimental control.
1. standard Conditions
Shear Adhesion = 288 psi at 97%
cohesive failure.
2. Elevated Humidity
Shear Adhesion = 11 psi at I
cohesive failure.
Alumina, magnesium metal and zinc have varying degrees
of activity as scavengers as indicated above.
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