Oil resistant silicone sealants containing a metal acetate

The invention relates to a RTV silicone composition having increased hot oil resistance upon curing. The RTV silicone composition comprises a polydiorganosiloxane, an acyloxy-functional crosslinker, a metal salt of a carboxylic acid catalyst, a filler, and a metal acetate. In a preferred embodiment a metal acetylacetonate is also added.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to room temperature vulcanizing (RTV) silicone 
compositions, curable in the presence of moisture, comprising 
polydiorganosiloxanes, acyloxy-functional crosslinkers and additives such 
as metal acetates and metal acetylacetonates which provide oil resistance 
to the cured composition. 
2. Background Information 
The use of room temperature vulcanizing (RTV) silicone sealants for 
creating formed-in-place gaskets is well known in both original equipment 
manufacture and in repair and maintenance. A problem with certain 
conventional silicone sealants is their tendency in the presence of hot 
oil to lose structural integrity leading to seal failure. Therefore, it is 
desirable to have silicone sealants providing increased oil resistance as 
demonstrated by increased tensile strength in the presence of hot oil. 
Getson, et al., U.S. Pat. No. 4,123,472, describe oil resistant 
organopolysiloxane compositions prepared by polymerizing an acrylic ester 
and an acrylic nitrile in the presence of an organopolysiloxane and a free 
radical initiator at an elevated temperature. This modified polysiloxane 
when mixed with a crosslinking agent, such as an acyloxy-functional 
silane, and exposed to moisture and heat aging, cures to an oil resistant 
composition. 
Beers, U.S. Pat. No. 4,680,363, describes a process for forming a one 
component RTV silicone rubber composition with good bonding properties at 
high humidity conditions, and Beers, U.S. Pat. No. 4,758,611, describes 
the RTV silicone composition comprising a silanol-endblocked 
diorganopolysiloxane, an acyloxy-functional crosslinking agent, a curing 
promoter which is a salt of a carboxylic acid, and a magnesium or zinc 
salt of a carboxylic acid as an acid scavenger. 
Beers, U.S. Pat. No 4,833,037, describes a laminated article comprising a 
plurality of metal substrates, wherein between the metal substrates there 
is a layer of a one component RTV silicone rubber composition with good 
bonding properties at high humidity conditions, comprising a 
silanol-endblocked diorganopolysiloxane, an acyloxy-functional 
crosslinking agent, a curing promoter which is a salt of a carboxylic 
acid, and an acid scavenger selected from magnesium or zinc oxide, 
magnesium, aluminum or zinc metal, magnesium or zinc salt of a carboxylic 
acid, or mixtures thereof. 
Beers, U.S. Pat. No. 4,257,932 describes a self-bonding silicone RTV 
comprising a silanol endstopped polydiorganosiloxane; a fluid polysiloxane 
having a high degree of tri or tetrafunctionality; a silica filler; a 
crosslinking silane evolving relatively low volatility carboxylic acid 
fragments on hydrolysis; and a tin catalyst. Beers, also discloses the 
improvement of high temperature performance with the addition of an iron 
oxide thermal stabilizer. 
Letoffe, et al., U.S. Pat. No. 4,797,462, describe organopolysiloxanes 
curable into elastomeric state and well adapted as sealing materials for a 
variety of substrates, comprising a polyhydroxylated polysiloxane, a 
polyacyloxysilane crosslinking agent and an effective amount of at least 
one of calcium oxide, strontium oxide and/or barium oxide cure accelerator 
therefor. 
The present inventors have unexpectedly determined that the addition of a 
metal acetate, preferably along with a metal acetylacetonate, to a RTV 
silicone composition comprising a polydiorganosiloxane, acyloxy-functional 
crosslinker, filler, and tin catalyst results in a cured composition 
having increased hot oil resistance. In addition, these compositions may 
find use when cured as sealants, adhesives, gaskets, coatings, molding and 
potting compounds, and gels. 
The objective of this invention is to provide a RTV silicone composition 
having increased hot oil resistance upon curing. 
SUMMARY OF THE INVENTION 
The present invention is a RTV silicone composition having increased hot 
oil resistance when cured. The RTV silicone composition which is curable 
in the presence of moisture comprises a polydiorganosiloxane, an 
acyloxy-functional crosslinker, a metal salt of a carboxylic acid 
catalyst, a filler, a metal acetate, and optionally a metal 
acetylacetonate. 
DETAILED DESCRIPTION OF THE INVENTION 
This invention is a RTV silicone composition which is curable in the 
presence of moisture and has increased hot oil resistance upon curing 
comprising: 
(A) 100 parts by weight of a polydiorganosiloxane in which the terminal 
groups are selected from the group consisting of silanol and 
triorganosilyl groups, provided at least 60 mole percent of the terminal 
groups are silanol groups; 
(B) 1 to 15 parts by weight of an acyloxy-functional crosslinking agent 
described by the formula 
EQU R.sub.m Si(OCOR').sub.4-m 
where R is a monovalent hydrocarbon radical comprising from 1 to about 12 
carbon atoms, each R' is an independently selected monovalent hydrocarbon 
radical comprising from 1 to about 12 carbon atoms, and m is 0 or 1; 
(C) 0.001 to 1 part by weight of a metal salt of a carboxylic acid 
catalyst; 
(D) 5 to 150 parts by weight of a filler; 
(E) an effective amount of a metal acetate; and 
(F) optionally, an effective amount of a metal acetylacetonate. 
Component (A) is a polydiorganosiloxane having terminal groups selected 
from the group consisting of silanol and triorganosilyl groups, provided 
at least 60 mole percent of the terminal groups are silanol groups. The 
polydiorganosiloxane may be one type of polymer or a mixture of different 
polymers. The polydiorganosiloxanes may have a linear structure and may be 
homopolymers or copolymers. In addition, the organic groups linked to any 
particular silicon atom may be the same or different. The organic groups 
of the polydiorganosiloxane can include any monovalent hydrocarbon group 
or any monovalent halohydrocarbon group comprising 1 to about 18 carbon 
atoms. Preferred organic groups are methyl, ethyl, propyl, phenyl, vinyl, 
and 3,3,3-trifluoropropyl, with methyl being most preferred. 
The terminal groups of the polydiorganosiloxane are selected from the group 
consisting of silanol and triorganosilyl groups. The organic substituent 
of the triorganosilyl groups can include any monovalent hydrocarbon group 
or any monovalent halohydrocarbon group comprising 1 to about 18 carbon 
atoms. The preferred organic substituent of the triorganosilyl groups are 
methyl, ethyl, propyl, phenyl, vinyl, and 3,3,3-trifluoropropyl, with 
methyl being most preferred. 
Although the terminal groups are selected from silanol and triorganosilyl 
groups, it is required that at least 60 mole percent of the terminal 
groups be silanol groups in order to obtain the desired properties of the 
composition when cured. Preferably, 80 to 100 mole percent of the terminal 
groups of the polydiorganosiloxane are silanol groups. 
The viscosity of the polydiorganosiloxane may be from about 1 to 150 Pa.s 
at 25.degree. C. The preferred viscosity of the polydiorganosiloxane is 
from about 5 to 100 Pa.s at 25.degree. C. 
The methods of manufacture of the silanol terminated polydiorganosiloxanes 
are well known in the art. One common method is based upon the hydrolysis 
of diorganodichlorosilane, the separation of a diorganotetrasiloxane 
cyclic material from the hydrolysis mixture, and the subsequent 
polymerization of the cyclic material to the polydiorganosiloxane through 
the use of an alkaline catalyst. The triorganosilyl terminated 
polydiorganosiloxanes are also prepared by known methods, such as 
described in Dupree, U.S. Pat. No. 3,274,145, which is hereby incorporated 
by reference. 
Component (B) is an acyloxy-functional crosslinking agent described by the 
formula 
EQU R.sub.m Si(OCOR').sub.4-m 
where R is a monovalent hydrocarbon radical comprising from 1 to about 12 
carbon atoms, each R' is an independently selected monovalent hydrocarbon 
radical comprising from 1 to about 12 carbon atoms, and m is 0 or 1. 
R is a monovalent hydrocarbon radical comprising from 1 to about 12 carbon 
atoms. The monovalent hydrocarbon radicals represented by R may be linear 
or branched and can include alkyl radicals such as methyl, ethyl, 
isopropyl, or hexyl; alkenyl radicals such as vinyl, allyl or hexenyl; 
alkynal radicals such as propargyl; cycloaliphatic radicals such as 
cyclopentyl, cyclohexyl or cyclohexenyl; aromatic radicals such as phenyl 
or tolyl; and aralkyl radicals such as benzyl or beta-phenylethyl. R is 
preferably methyl or ethyl. 
Each R' is an independently selected monovalent hydrocarbon radical 
comprising from 1 to about 12 carbon atoms. Examples of R' include those 
provided for R. R' is preferably methyl or ethyl, with methyl being most 
preferred. 
The acyloxy-functional crosslinker may have trifunctionality, as occurs 
when m is 1 or tetrafunctionality, as occurs when m is 0. It is preferred 
that m be 1. 
Examples of preferred acyloxy-functional crosslinkers include 
methyltriacetoxysilane, ethyltriacetoxysilane, methyl-tris-benzoxysilane, 
vinyltriacetoxysilane and methyl-tris-2-ethylhexanoxy silane. 
The acyloxy-functional crosslinker can be present in the present 
composition in amounts from 1 to 15 parts by weight based on 100 parts by 
weight of the polydiorganosiloxane, and preferably from 2 to 10 parts by 
weight on the same basis. The acyloxy-functional crosslinker may be added 
as a single species or as a mixture of two or more species. 
Component (C) is a metal salt of a carboxylic acid catalyst. The metal 
component of the catalyst is preferably tin, but may be for example, lead, 
chromium, antimony, iron, cadmium, barium, titanium, bismuth, or 
magnesium. Examples of suitable metal salts of carboxylic acids include 
tin naphthenate, lead octoate, tin octoate, iron stearate, tin oleate, 
dibutyltindilaurate, dibutyltindiacetate, dibutyl tin oxide, and dimethyl 
tin bis-neodecanoate. Preferred catalysts are dibutyltindilaurate, 
dibutyltindiacetate, and dimethyl tin bis-neodecanoate. The most preferred 
catalysts are dibutyltindilaurate and dibutyltindiacetate. 
The catalyst can be present in the present composition in amounts from 
0.001 to 1 part by weight based on 100 parts by weight of the 
polydiorganosiloxane, and preferably from 0.01 to 0.3 part by weight on 
the same basis. It is most preferred to have 0.01 to 0.2 part by weight 
catalyst present in the composition on the same basis. The catalyst may be 
added as a single species or as a mixture of two or more species. 
In order to obtain the desired physical properties of the present 
composition when cured, a filler (component (D)) is added to the 
composition. This filler may include reinforcing fillers, semi-reinforcing 
fillers, or non-reinforcing fillers also called extending fillers, or any 
combination thereof. One or more of each type of filler is also 
acceptable. 
Reinforcing fillers include any finely divided form of silica which can be 
prepared by precipitation or a pyrogenic process and may be treated or 
untreated. Generally, methods of treating the silica can include mixing 
the silica with polycyclosiloxane such as disclosed in Lucas U.S. Pat. No. 
2,938,009, and Lichtenwalner U.S. Pat. No. 3,004,859, or silazanes as 
disclosed in Smith U.S. Pat. No. 3,635,743, which are incorporated herein 
by reference. The treating agents may also include liquid 
hydroxyl-terminated polydiorganosiloxanes which can contain an average of 
about 2 to 20 repeating units and can contain at least one alkenyl unit. 
The treating agent may also be an alkylhalosilane, such as 
dimethyldichlorosilane or an alkoxysilane. Carbon black is also useful as 
a reinforcing filler in this invention. Semi-reinforcing fillers include 
barium sulfate and crystalline silica. Non-reinforcing or extending 
fillers include glass spheres, wollastonite, diatomaceous earths, clay, 
and talc. The preferred fillers are untreated fumed silica and treated 
fumed silica. 
The filler can be present in the present composition in amounts from 5 to 
150 parts by weight based on 100 parts by weight of the 
polydiorganosiloxane, and preferably from 5 to 30 parts by weight on the 
same basis. The filler may be added as a single species or as a mixture of 
two or more species. 
Component (E) comprises an effective amount of a metal acetate. The 
inventors have unexpectedly determined that the addition of a metal 
acetate to an RTV silicone composition provides the composition upon 
curing with increased hot oil resistance. 
The metal portion of the metal acetate may be selected from the group 
consisting of calcium, zinc, magnesium, aluminum, zirconium, barium, 
titanium, strontium, and copper. Examples of the metal acetate include 
calcium acetate, zinc acetate, magnesium acetate, aluminum acetate, 
zirconium acetate, barium acetate, titanium IV acetate, strontium acetate 
and copper II acetate. The metal portion of the metal acetate is 
preferably calcium or strontium and most preferably calcium. 
An effective amount of the metal acetate is an amount which provides 
increased hot oil resistance to the RTV silicone composition upon curing. 
Typically, about 0.01 to 10 parts by weight metal acetate based on 100 
parts by weight of the polydiorganosiloxane is effective. It is preferable 
to add about 0.01 to 1.5 parts by weight metal acetate on the same basis, 
with amounts from about 0.01 to 1 part by weight on the same basis being 
most preferred. The metal acetate may be added as a single species or as a 
mixture of two or more species. 
In a preferred embodiment, an effective amount of Component (F) a metal 
acetylacetonate, is also added to the RTV silicone composition. The metal 
portion of the metal acetylacetonate is preferably copper, iron or 
zirconium, with copper being most preferable, but may be selected from the 
group consisting of copper, chromium, iron, aluminum, zinc, titanium, and 
zirconium. Examples of the metal acetylacetonate include copper II 
acetylacetonate, ferric acetylacetonate, chromium III acetylacetonate, and 
zinc acetylacetonate. The addition of a metal acetylacetonate to the 
present RTV silicone composition without a metal acetate also provides the 
composition upon curing with increased hot oil resistance. 
Although the addition of the metal acetylacetonate is optional, in a 
preferred embodiment, an effective amount of the metal acetylacetonate is 
added to the present composition. An effective amount is an amount which 
provides increased hot oil resistance to the RTV silicone composition upon 
curing. Typically, an effective amount of the metal acetylacetonate is 
from about 0.01 to 5 parts by weight based on 100 parts by weight of the 
polydiorganosiloxane. Preferably, the metal acetylacetonate is present in 
amounts from about 0.05 to 1.5 parts by weight on the same basis, with 
amounts from about 0.1 to 0.6 part by weight metal acetylacetonate on the 
same basis being most preferred. The metal acetylacetonate may be added as 
a single species or as a mixture of two or more species. 
In preferred embodiments, the present composition can also optionally 
include up to about 2 parts by weight of an adhesion promoter based on 100 
parts by weight of the polydiorganosiloxane. Examples of useful adhesion 
promoters include ethylpolysilicate and glycidoxypropyltrimethoxysilane. 
In addition to the above ingredients, the present composition may include 
additives which impart or enhance certain properties of the cured 
composition or facilitate processing of the curable composition. Typical 
additives include, but are not limited to: plasticizers, functional and 
non-functional diluents, pigments, dyes, heat and/or ultraviolet light 
stabilizers, flame-retardant agents, thickeners, rheology modifiers, and 
preservatives. The effect of any such additives should be evaluated as to 
their result and impact on other properties of the composition. 
The RTV silicone composition of this invention may be prepared by mixing 
all the ingredients together in amounts as specified to provide a 
composition which is stable in the absence of moisture and which cures to 
an elastomeric material when exposed to moisture. 
These compositions are preferably prepared by mixing all the ingredients 
under anhydrous conditions. This means that the amounts of moisture or 
water in the ingredients used should be minimized and the conditions of 
mixing should minimize the amounts of moisture or water allowed into the 
system. Excess moisture or water may have deleterious effects on the 
composition, such as causing curing in the storage package or reduced 
cured properties. 
The present compositions may be prepared as either a one package system or 
a two (or multi) package system. With a one package system, all the 
ingredients are mixed together and stored in an anhydrous state. With a 
two or multi package system the ingredients may be stored separately and 
then mixed prior to use. For example, it is often convenient to form a 
"base" blend comprising a polydiorganosiloxane, a filler and, if needed, a 
plasticizer (I). Another blend comprising curing agents such as the 
crosslinker and catalyst may also be mixed together (II) and still another 
blend comprising additional ingredients including Components (E) and (F) 
may also be mixed together (III). As described above, the components 
comprising (I), (II) and (III) may be mixed together or separately. If 
mixed and stored together a one part sealant results. Obviously a two or 
multi package system is possible if (I), (II), and (III) are mixed and 
packaged separately. It is also possible to mix and store two of the 
components together, ie., (I) and (III) and later mix in (II). In a 
preferred embodiment of the present invention it is preferred to mix and 
store (I) and (II) together and then later mix in (III) as required. 
The present RTV silicone compositions may be used, for example, as gasket 
materials for sealing gaps or seams in a given substrate or for sealing 
between substrates. Due to the oil resistance of the present RTV silicone 
compositions when cured these compositions are preferably used for sealing 
gaps or substrates having surfaces exposed to oil or hot oil. However, 
these RTV silicone compositions may also be used to seal gaps or 
substrates which may not have surfaces exposed to oil or hot oil. 
A method for sealing using the present composition comprises for example, 
(i) providing at least two substrates having a plurality of surfaces; (ii) 
applying a layer of a RTV silicone composition which is curable in the 
presence of moisture, to at least a portion of at least one of the 
surfaces of at least one of the substrates, the RTV silicone composition 
comprising Components (A)-(E) and preferably also Component (F), as 
described above; (iii) bringing at least two of the substrates, where at 
least one of the substrates has the RTV silicone composition applied 
thereto, into proximity so as to form a gasket of the RTV silicone 
composition therebetween; and (iv) exposing the gasket of step (iii) to 
moisture to effect curing of the RTV silicone composition. 
The substrates useful for this preferred embodiment can be metal materials, 
composites or certain plastic materials. Preferably the substrates are 
metal materials.