Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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ANAEROBIC SEALANT UNAFFECTED BY WATER CONTAMINATION
Background of the Invention
Composite articles manufactured from fiber reinforced
thermoset resins frequently have some degree of porosity. Low
to moderate performance composites with high resin to fiber
ratios (e.g. 50% or more resin), such as sheet molding
compounds will cure with small bubbles entrained throughout
the article. Because cured resin surrounds these bubbles in
the interior of the matrix, they usually do not cause
lo performance problems. However, at the surface the bubbles are
exposed. In industries such as automobile manufacture,
articles formulated from sheet molding compound are frequently
used in areas where they must be painted. This can be very
difficult because surface porosities can blow unsightly holes
! 15 in the paint finish during a paint bake cycle.
Much higher performance composite articles, such as
wound fiber reinforced piping or pressure vessels for high
pressure gas or chemicals, engines for solid fuel rockets and
military hardware or ammunition, utilize very high fiber
contents (typically as much as 85%). In such low resin
content articles, the presene of porosity may provide
significan leak paths for gases or liquids, especially
~- corrosive hot gases such as those provided by an ignited
rocket engine. The consequence of a leak during use of such
- 25 articles can, of course, be catastrophic. It is therefore
;~ been proposed to seal porosities in cured fiber reinforced
composite materials with an anaerobic curing impregnant. Such
impregnants are frequently used to seal porous metal parts
such as metal castings and sintered metal articles.
Descriptions of such impregnants may be found in U.S. Patents
3,672,942; 3,969,552; 4,069,378 and EP 0101367.
In the impregnation of metal parts, the anaerobic sealant
will usually contain a copper salt or complex at a level in
excess of 1 ppm, typically 3-10 ppm as an accelerator of
anaerobic cure. Copper at these levels in conjunction with
the hydroperoxide catalyst and, usually, a saccharin
coaccelerator, will give the sealant an unaerated pot-life, at
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ambient temperatures, of about 3 minutes to about an hour,
which is usually sufficient to permit a vacuum or pressure
cycle to force the sealant into the porosities of the article
to be completed and aeration resumed before the pot begins to
ge.
In commercial impregnation processes for small metal
parts and the like, however, it is often the case that
substantial quantities of moisture will be introduced into the
sealant vat. This may come from condensation when
refrigerated tanks are opened to air on humid days, from parts ?
baskets which have been dipped in aqueous rinse baths, etc.
It has been found that typical anaerobic impregnants which
include copper salt accelerators can be severely inhibited by
water. Although the repeated vacuum cycles to which an
impregnation bath is subjected will help to get rid of water
contamination, it would be desirable to have an anaerobic
acceleration system which is less sensitive to moisture since
use levels vary and less frequently evacuated baths may
accumulate high moistures of wet level between uses. Also, if
pressure rather than vacuum is used in the impregnation
process there is no mechanism for removing water.
; Furthermore, when composite materials are impregnated, it
- is often more difficult to force the sealant into the article
and consequently a longer pot life sealant is desirable.
Also, depending on the article, it may be desirable to
minimize catalyst levels so as to avoid undesirable reactions
due to residual oxidizing catalyst in the composite. However,
when copper-content is dropped below the 1 ppm leve, it has
been found that the cure sensitivity to moisture becomes
critical. Any significant moisture content can prevent curing
altogether even in the microscopic porosities of the
impregnated article.
It has been found that many composite articles have a
tendency to absorb substantial quantities of moisture (as much
as several weight %) from the atmosphere. This is believed to
be due to the presence of hydrophilic groups, such as
hydroxyl, amine or amide in the cured resin (typically
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polyepoxides or polyamides), or in reinfrocing fibers such as
KevlarR .
Accordingly, there is a need for an anaerobic sealant
which will reliably cure upon deprivation of oxygen even in
the presence of moisture. In particular, it is desirable that
such a sealant be capable of curing in the microscopic
porosities of a thermoset resin/fiber composite articles at or
near ambient temperatures and have a copper content below
-1 ppm.
Summary of the Invention
The present invention pertains to a novel anarobic
sealant material comprising an acrylate or methacrylate
monomer, a hydroperoxide or perester initiator, an accelerator
having -SO2NHCO- functionality, and a transition metal
coaccelerator, wherein the transition metal coaccelerator
comprises: a copper salt or complex at the level of
0.1-10 ppm copper, preferably 0.4-1.0 ppm copper, based on
composition weight; and an iron salt or complex at the level
; of .5~60 ppm Fe, based on composition weight, preferably
10-20 ppm Fe.
The inventive sealants display greatly reduced sensitiviy
to water and while maintaining the long term stability with
aeration.
Detailed Description of the Invention
Generally, the anaerobic sealant compositions of the
invention contain monoacrylic and di- or polyacrylic monomers
(that is acrylate and/or methacrylate functional compounds);
peroxy initiators, typically hydroperoxide or perester
compounds; accelerators such as saccharin or other compounds
with -S02HNCO- functionality such as described in U.S. Patent
4,513,127; and a source of transition metal ion. Free radical
stabilizers are also typically included. Such compositions
are well known in the art and are described in detail in the
previously mentioned U.S. Patents 3,672,9~2 and 3,969,552.
Suitably the compositions may also employ surfactants or
surfactant monomers such as described in U.S. 4,069,378 and EP
9191267.
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The distinctive feature of the inventive compositions is
that the composition includes both source of copper ion, in an
amount equivalent to 0.1-10 ppm Cu, and a source of iron,
which may be present as ionic iron or as a ferrocenyl
5 compound, in an amount equivalent to 0.5-60 ppm iron.
Preferably the iron compound is present as ferrocene in the
range of 10-20 ppm iron and the copper is present at a level
of 0.4-1.0 ppm. Also, it has generally been observed that the
amount of copper should be less in parts by weight than the
10 amount of iron. Preferably the iron is present at a level of
2-30 times that of the copper.
This novel combination of iron and copper gives an
anaerobic sealant which is uni~uely storage stable and
insensitive to moisture content. The sealant is especially
; 15 suitable for sealing composite materials, especially porous
high performance composites. The sealant is also
advantageously employed in other impregnation processes
; susceptible to contamination of the sealant with water.
The invention is illustrated by the following non-
20 limiting examples.
Example 1
An impregnant formulation was made up as follows:
Triethylene glycol dimethacrylate 70.1%
Lauryl methacrylate 25.96%
Cumene hydroperoxide 1.0%
Dyes and surfactants 2.6%
Stabilizer solution* 0.4%
Saccharin 0.3%
* 5% benzoquinone and 0.5%
1,2-bis(6-methyl-2'-pyridylmethyleneamino)-
ethane in polyethylene glycol dimethacrylate.
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To the formulation was added the levels of copper ion and iron
shown in Table I as solutions in trichloroethane of copper
ethylhexanoate (0.2% Cu) and ferrocene (1.0% Fe),
respectively. These compositions are aerated for one hour and
then gel times determined at 50C in glass test tubes
(10 x 75 mm). The results demonstrate that iron at levels
which give gel times comparable to a 0.6 ppm copper catalyzed
system is not a practial system because of the instability of
the composition with aeration.
TABLE I
:
cu(ppm) Fe(ppm)(min) Comments
I
Control 0.6 _ 23 Stable
Indefinately
With Aeration l
_ I
A _ 30 >48 hrs. _ l
_ 9 0 ~
_ __
C _ 300 _ Set up before
gel time taken
D _ 630 120 min.
E _ 840 22 Set up in 3
hrs. with
aeration
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Example 2
; To the sealant formulation of Example 1 was added copper
and iron solutions as in the previous example, equivalent to
0.6 ppm copper and 15 ppm iron. This composition was
designated composition F. A control composition using just
0.6 ppm copper was also prepared. The compositions were
aerated 1 hour and then water added as indicated in Table II.
Gel times were determined at 60C. The results which are set
forth in Table II demonstrate that the combination of iron and
copper gives much reduced moisture sensitivity while
maintaining the desired dry gel times of the opper accelerated
systems. Both compositions are stable for many months with
aeration.
. . .
TABLE II
60 Gel Times (min)
,
Cu Fe % Added Water
(ppm) (ppm) o% .5% 2% 3% 6% 8%
_ _
Control 0 6 _ 6 12 ~1-3138-41 70-84 1156
F 0.6 15 6.5 9- 14 20 20-33 23-26
_ _ _ _
Example 3
To another batch of a formulation as set forth in Example
1 was added 0.6 ppm copper. The sample was divided with one
portion maintained as a control. To another portion was added
15 ppm iron as ferrocene and this composition was designated
as composition G. To a third portion was added 16 ppm iron as
iron octanoate. Samples were aerated for one hour and 60 gel
times determined on dry and added water samples, as shown in
Table III. The results demonstrate that ionic iron is less
beneficial than ferrocene but does confirm significant
improvement in performance at water levels above ~3%.
TABLE III
60 Gel Times (min)
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Cu Fe % Added Water
(ppm) (ppm) o% .5% 2% 3% 6% 8%
Control 0.6_ 8 15 43 85 165 165+
G 0.6 15 8 11 27 32 33 35
H 0.6 16 14 17 47 72 68 58
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Example 4
Another 0.6 ppm copper control ~ormulation was prepared
as in the previous examples. A formulation, designated
composition I was prepared as in the control except that the
copper level was 0.3 ppm and iron was added at a level of
0.6 ppm. The sample was aerated for 24 hours and 60 gel
times determined on samples to which 3%, 6% and 8% water had
been added. Room temperature gel times were also determined
on the samples in capillary tubes. The results in Table IV,
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demonstrate that the benefits of the invention are present
even at levels of iron and copper of less than 1.0 ppm.
TABLE IV
60 Gel Times (min)
_
Cu(ppm)Fe(ppm) % Added Water
, I _ 3% _ 6% 8%
Control 0.6 _ 82 280 290
I 0.3 0.6 19 20 40
RT Gel Times _ _
_ , r
Control l5 days ¦6 days 6 days
. I I
I l 7 hrs. 7hrs. 7 hrs.
_ . _
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