Note: Descriptions are shown in the official language in which they were submitted.
~065096
BACKGROUND OF THE INVENTION
Field of the Invention
This invention relates to certain adhesive and
sealant compositions having improved strength prop~rties at
elevated temperatures and improved resistance to thermal
degradation.
; Prior Art
Adhesive and sealant compositions based on acrylate
- and methacrylate monomers polymerizable by free-radical
initiation are known in the art. Likewise, anaerobic com- -
positions are known in the art (see, for example U.S. patents
2,895,950, 3,043,820, and 3,218,305). Anaerobic compositions
` are characterized by their ability to remain liquid in the ~
presence of air, but cure to a strong adhesive bond when air -
is excluded, as by assembling a mated nut and bolt to which
the composition has been applied.
` While serving many useful purposes, both standard
acrylate compositions as well as anaerobic-type acrylate
compositions have been limited in applicability due to degrad-
ation of adhesive strength at elevated temperatures, e.g.,
250F or more.
SUMMARY OF THE INVENTION
According to the present invention there is provided
an adhesive and sealant composition having significantly
improved strength at elevated temperatures and improved re-
; sistance to thermal degradation. This composition comprises
a mixture of
ta) a monomçr selected from the group consisting ofethoxylated bisphenol A diacrylate, ethoxylated bisphenol A
dimethacrylate, and an acrylate ester corresponding to the
- 1 - ~ ,
106S~96
: formula
2)mtC ¦ C_o3~C-c=
R' R'' R R'
p
.~,
.
wherein R represents a radical selected from the group con- ~ .
sisting of hydrogen, lower alkyl of 1-4 carbon atoms,
inclusive, hydroxy alkyl of 1-4 carbon atoms inclusive, and : .
O
-cH2-o-c-c=cH2
R' .
~ R' is a radical selected from the group consisting of hydrogen, :~
halogen, and lower alkyl of 1-4 carbon atoms; R" is a radical -
:` selected from the group consisting of hydrogen, - OH and
:.~
; ,, :
` 10 -O-C-C=CH2 :
: m is an integer equal to at least 1, e.g., from 1 to 8 or
higher, for instance, from 1 to about 4 inclusive; n is an
` integer equal to at least 1, for example, 1 to 20 or more; `
` and p is 0 or 1;
(b) about 1 to about 50 percent by weight of the
; total composition of an additive selected from the group
~ consisting of
:
.. 2
~065~9~
o o o
¢ > N--R ¢ ~N--R'--N < ?
-. O :
\ N-R o o
~ > N-R'-N <
O O
wherein R and R' are selected from the group consisting of
alkyl, cycloalkyl, aralkyl, alkaryl.
The invention further relates to a process for seal-
ing or adhering surfaces comprising applying a composition of
this invention to surfaces ~o be sealed or.adhered,placing the ~- surfaces in abutting relationship and allowing the composition .
to cure.
DETAILED DESCRIPTION OF THE INVENTION
. . .
One class of monomers suited for use in this in-
vention comprises acrylate esters having the following general
formula:
,
'.
'
., ~
.: . - . . .. . . .
: . , , . . ,. , ~ :,
\ \
~()65096
...
..
¦/ R \ R O
H2C=C-C-O tt R" J R - C-C=CH2
P n
wherein R represents a radical selected from the group consisting
of hydrogen, lower alkyl of 1-4 carbon atoms, inclusive, hydroxy
alkyl of 1-4 carbon atoms inclusive, and
.' o
..
2 , 2
R' is a radical selected from the group consisting of hydrogen,
halogen, and lower alkyl of 1-4 carbon atoms; R" is a radical -~
selected from the group consisting of hydrogen, - OH and
" O
.~ , .. .
-O-C-C=CH
R
m is an integer equal to at least 1, e.g., from 1 to 8 or higher,
for instance, from 1 to 4 inclusive; n is an integer equal to at
least 1, for example, 1 to 20 or more; and p is one of the
. following: O,l.
~: The polymerizable polyacrylate esters utilized in
accordance with the invention and corresponding to the above
general formula are exemplified by, but not restricted to, the
following materials: diethylene glycol dimethacrylate, tri-
ethylene glycol dimethacrylate, tetraethylene glycol dimeth- ~ :
acrylate, dipropylene glycol dimethacrylate, di-(pentamethylene
~ 20 glycol) dimethacrylate, tetraethylene diglycerol diacrylate,
.. :
- 4 - ;
,, .
.. ... , , . ~ :
, . :
..
' ' ' : ' . , - : . ' ' , '
: .. . - . ~ : .
1065~9~
diglycerol tetramethacrylate, tetramethylene dimethacrylate,
ethylene dimethacrylate, neopentyl glycol diacrylate and tri-
methylol propane triacrylate. Of t~ese, the preferred monomers
are triethylene glycol dimethacrylate and polyethylene glycol
dimethacrylate.
The most preferred class of monomers for use in
this invention, however, is ethoxylated bisphenol A dimeth-
acrylate, which has the following structural formula:
(C33)2-CL ~-o-c32-C32--C-c-c~2
The ocher critical component of the composition is
an additive which conforms to any of the following structures:
.' '"
, O O O
J~- R¢'~ N--R '--N ~ 3
: o . o o
. .
.. o o o
- ¢~>N-R OE~ ~N--R' -N )3
O O
The nature of R and R' iS not critical for purposes
of this invention and may be any organic radical which does not
contain any group which will adversely affect the composition
- for purposes disclosed herein. Most commonly, R and R' are
selected from the group consisting of alkyl, cycloalkyl, aralkyl,
alkaryl, any of which may be exceptionally large radicals, e.g.,
containing up to about 200 carbon atoms or more; preferably they
- will contain from 6 to about 100 carbon atoms, most preferably,
. .
. ~ .
- . ~ .. . : . . .
1065096
6 to about 50 carbon atoms.
It has been found that resistance to thermal oxi-
dative degradation is improved if R or R' are aromatic; however,
this is not required for the general improvement of this in-
vention to be realized. It will, of course, be understood that
both R and R' can consist of relatively complicated moieties,
provided only that they do not contain functionality which
interferes with the performance of the additive for its intended
purposes. The useful concentration range for this additive is
10 about 1 to about 50, preferably about 5 to about 35, percent by
~; weight of the total composition.
~ In general, these compositions are readily curable by
; application of moderate heat.
` The compositions may also be rendered anaerobic and
curable at room temperature by inclusion of a peroxy initiator
of free-radical polymerization, which is a preferred embodiment
of this invention. A number of such initiators are well known
. ~ . .
in-the anaeEobic art, e.g.j hydroperoxides, such as cumene hydro-
peroxide, paramenthane hydroperoxide, tertiary butyl hydroper-
.
- 20 oxide, and peresters which hydrolyze to peroxides such as
- tertiary butyl perbenzoate, and the like. The amount of such
peroxy compounds may vary from about 0.1 to about 10, preferably
- about 1 to about 5, percent by weight of the total composition.
, Accelerators of anaerobic polymerization may also be -
advantageously included. Such accelerators include a variety of
secondary and tertiary organic amines as well as sulfimides
(e.g., benzoic sulfimide) which are also known in the art. These
- may be used at a concentration range of about 0.1 to about 5,
preferably about 1 to about 2, percent by weight of the total
composition.
:
'
.. . . . . . .. . . . . .
.. ~ , . . .
.. . . .
1065096
Other agents such as thickeners, plasticizers, etc.,
are also known in the art and may advantageously ~e incorporated
where functionally desirable, provided only that they do not
interfere with the functioning of the additive for its intended
purpose. This, of course, can be determined by simple
experimentation.
The additives of this invention tend to improve at
least three properties of the cured composition, the extent and
nature of the improvement appearing to depend on the specific
monomer involved. These improvements comprise greater re-
sistance to degradation of an adhesive bond caused by oxidative
~ effects incurred at elevated temperatures, greater strength of
; the bond or seal at elevated temperatures, and often also an
improvement of the cure strength obtained under room temperature
curing conditions. The precise nature of the improvement
mechanism is not well understood. Without wishing to be bound
by any particular theory, it appears that the additives of this
invention tend to copolymerize with the monomers, thereby tend-
ing to terminate the molecular "unzipping" effect which appears
to characterize thermal degradation. The improvement of hot
strength is believed due to the increase in glass transition
temperature brought about by such copolymerization.
The following examples illustrate but in no way limit
the invention. Percentages are by weight based on the total
composition.
EXAMPLE 1 -
~::
Anaerobic compositions were prepared by mixing into
bisphenol A dimethacrylate the following materials:
i
..
1065096
5% bisphenol A fumarate (suspending agent)
3~ cumene hydroperoxide
1.5~ benzoic sulfimide
1~ diethyl paratoluidene
0.5~ dimethyl orthotoluidene
25~ additive of this invention as shown in the Table 1.
These compositions were applied to steel pins and collars,
which were then assembled and allowed to cure for 24 hours at
room temperature until bond strength had fully developed. The
samples were then aged at 450F for the periods shown in Table
1. They were then allowed to cool to room temperature and the
pins were pressed from the collars using an Instron tester.
Table 1 reports the results in pounds per square inch of shear
strength and shows the desirable improvement in thermal aging
strength retention.
TABLE 1
Weeks at 450F 1 2 4 8 11 15 26
N-phenylmaleimi-de 3900 3350 2000 1200 -- -- 0
m-phenylene di-
maleimide 4300 5000 5000 5000 ~000 -- 0
"Kerimide 601"* 4500 4600 4700 4300 4300 2200 700
Control-no additive 3500 1100 0
*Sold by Rhodia Corp., New York, N. Y. A reaction product of a
bismaleimide with a diamine.
EXAMPLE ll
Formulations were prepared similar to those of
Example 1 except that only Keramid 601[Trade Mark] was employed
as the additive and the monomer was polyethylene glycol dimeth-
acrylate, having a molecular weight of about 330. The formula-
tions in Table 11 were used to adhere 1/4-20 steel nuts and
bolts together. The samples were aged at 400F for the times
shown, but were tested at room temperature, as before. Table
11 shows "break/prevail" strength in foot-pounds. "Break"
strength is the torque required to cause the first movement
between nut and bolt. "Prevail" strength is the torque re-
quired to unwind the nut 180 beyond the break point.
- 8 -
"
~, .
~0~;5096
TABLE 11
Time at 400F One Day One Week Two Weeks
10% additive142/400 93/340 ` 33/145
30% additive172/390 178/465 165/445
Control-no additive 48/330 7/18 0J2
EXAMPLE 111
A sample corresponding to the 30% additive level in
Table 11 was tested after two weeks' aging at 400F. The test
: was performed at 400 with the following break/prevail results:
180/235.
Example 11 again illustrates the improved resistance
to thermal degradation and Example 111 illustrates the improved
strength at high temperature which characterize the formulations
of this invention. :
''' ~
', ~- ,.
:: - 9 -
., . ~ . .
