Note: Descriptions are shown in the official language in which they were submitted.
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Background Of The Injection
1. Fiend of the Invention
This invention relates to certain liquid adhesive and
sealant compositions which, upon cure, have improved
structural strength properties at elevated temperatures and
improved resistance to thermal degradation.
2. Prior Art
Adhesive and sealant compositions based on cyanoacrylate
monomers are known in the art. Typical examples of patents
relating to cyanoacrylate adhesives are US. Patents 2,784,215
to Junior 2~794/788 to Cover et aloe and British Patent
1,196,069 to O'Sullivan. Cyanoacrylate adhesive compositions
are extremely sensitive, and great care must be exercised in
their formulation. Cure (polymerization) is generally
considered to be initiated by an anionic mechanism, with
water being a sufficiently strong base to initiate the cure
under most circumstances. The adhesives remain shelf-stable
items of commerce as long as they are suitably packaged, but
when placed on a substrate to be bonded and exposed to
atmospheric and surface moisture, cure generally is
instituted in a relatively short period of tome, generally
less than one (1) minute and on many surfaces, within a
matter of seconds. This exceptional cure speed offers
numerous advantages, particularly to those who use adhesive
bonding in production line applications. However, a major
shortcoming which has heretofore limited the areas of
applicability of cyanoacrylate adhesives has been the
relatively low thermal resistance of the cured bonds. Bonded
assemblies frequently are exposed to continuous operating temperatures
substantially above normal room temperature, and adhesive assemblies must
retain reasonable strength for substantial periods of time at these
elevated to azures to retain their usefulness.
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In addition to strength retention by the adhesive at
elevated temperatures (i.e., hot strength?, the adhesive bonds
must not be unduly affected by continuous or repeated
exposure to elevated temperatures (resistance to heat
degradation). In the prior art it has not been possible to
prepare a cyanoacrylate adhesive composition which produced
substantial cross-linking on cure, even when ostensively
difunctional cyanoacrylate monomers were used. Further t
because of the extreme reactivity of the cyanoacrylate monomer,
there have been substantial limitations upon addition of other
ingredients, such as cross-linking agents or co-monomers, in
order to improve the above-described thermal properties.
In US. Patent 3,832,3~4, the problem of thermal
resistance was solved by the addition of malefic androids and
their substitution products. Additionally, it has been known
in the prior art to include cross-linking agents such as ally-
2-cyanoacrylate or polymerizable acrylate esters to improve
thermal properties. However, none of the prior art has shown
the improved thermal properties at 250F that the instant
invention is able to demonstrate. Thus, the need for such a
useful adhesive is evident and would prove useful in many
applications.
SUMMARY OF THE INVENTION
mere is provided an adhesive and sealant composition, which is
normally liquid in toe uncured state, and upon cure exhibits a
significantly improved hot strength at elevated erasures and
improved resistance to they'll degradation. This position
comprises (a) at least one polymerizable
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cyanoacrylate, (b) about 0.1~ to about 10~ by weight of the
composition of at least one difunctional or monofunctional
polymerizable acrylate ester, I about 0.1% to about 20% by
weight of the composition of an additive selected from the
group consisting-of the following compounds:
O O
if if if
¢ N-R7 _R8 N 3
,. .. ..
O O O
o
N-R7
O O
I ..
N-R -
O O
wherein R7 and R8 are selected from the group consisting of
alkyd, cycloalkyl, aralkyl, alkaryl, (d) an anionic
polymerization inhibitor; and (e) optionally a free-radical
polymerization inhibitor.
The instant invention solves the problems of the prior art adhesives,
particularly their Liability to retain their structural integrity at
elevated twitters (hot strength, as well as their low resistance to
they'll degradation through heat aging. me compositions disallowed herein
are useful in a variety of surfaces, particle steel, aluminum, phenolics,
epoxies, and th~plastic materials. The shelf e stability of cure
speed are excellent as well.
DETAILED DESCRIPTION OF THE INVENTION
_ AND PREFERRED EMBODIMENTS
The cyanoacrylate monomers useful in this invention
are represented by the general formula:
I ON
CH2=C-COOR
wherein R is Clue alkyd, cycloalkyl~ alkenyl, cycloal-
Kenya, phenol or heterocyclic radical. The preferred
monomer which conforms to the general formula is ethyl
cyanoacrylate, but a mixture of the above can be useful
The polymerizable acrylate ester monomers useful in
this invention may be moo- or polyfunctional, or a mix-
lure of both, and conform to the general formulas:
CH2=C-COOR2
II I
wherein Al is H, SHEA or lower alkyd, R is H, alkyd,
alkoxy, cycloalkyl, alkenyl, aryalkyl, alkaryl or airlocks
group;
or
R13~ R3
R o ( 2~mt R4J~ C OUR
wherein R3 is H, Of 4 alkyd or hydroxyalkyl or R50CH2-;
R6 is H, halogen or Of 4 alkyd; R4 is H, OH or R50-; R5
is CH2=CR6C=O; m is an integer, preferably 1 to 8; k is an
integer, preferably 1 to 20; and p is O or 1.
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There must be at least one acrylate ester monomer present
in the instant composition, generally in the amount of about
0.1~ to about 10% by weight of the total composition. The
preferred amount is about 1 to about 5%, most preferably about
1% by weight.
Among the monofunctional polymerizable acrylate ester
monomers (formula II) useful, are hydroxyethyl methacrylate,
hydroxypropyl methacrylate, isobornyl methacrylate, methyl
methacrylate, tetrahydrofurfuryl methacrylate, and bottle
methacrylate; hydroxyethyl, hydroxypropyl and methyl
methacrylate and alkyd methacrylate being prefarrPd.
The polymerizable polyacrylate ester utilized in accordance
with the inventioll and corresponding to the above general
formula III are exemplified by, but not restricted to, the
following materials diethylene glycol dimethacrylate,
triethylene glycol dimethacrylate, tetraethylene glycol
dimethacrylate, dipropylene glycol dimethacrylate, dip
(pentamethylene glycol) dimethacrylate, tatraethylene diglyceroldiacrylate, diglycerol tetramethacrylate, tetramethylene
dimethacrylate, ethylene dimethacrylate, neopentyl glycol
diacrylate and trimethyol propane triacrylate. Of these,
the preferred monomers are triethylene glycol dimethacrylate and
polyethylene glycol dimethacrylate.
Another ingredient essential to the instant invention is
an additive selected from the group consisting of any of the
following structures:
I
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O O
Jo No ~N-R7
O O
O O
I NUB
O O o
the nature of R7 and R8 jot critical for purposes of
this invention end may ye any organic radical which does not
Contain any group which will adversely affect the composition
for purposes disclosed herein Most commonly, R7 aloud I are
S selected from the group consisting of alkyd, çycloalkyl,
aralkyl, alkaryl, aureole, airlocks, alkoxy, any of which may be
, exceptionally large radicals; e.g., containing up to about 200
carbon atom or more; preferably they will contain from 6 to
Jo bout 100 carbon atoms, most preferably, 6 to about 50 carbon
atoms.
It has been found that resistance to thermal oxidative
degradation is improved if I or I is aromatic; however, this
; is not required for the general improvement of this invention
I to be realized. It will of course, be understood that both R7
and R8 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.
j The useful concentrations range for this additive is about 0.1
: 1!1 to about 20%, preferably about 1 to about 5% by weight of the
total composition and more preferably about 2%.
ii Without wishing to be bound by any one theory, it is be
lived that the improved hot strength properties obtained from
the instant composition are a result of the unique combination
I; of the above maleimides with the polymerizable acrylate esters,
!
j both of which are vital constituents in the cyanoacrylate
adhesive composition, Theoretically, the maleimide additive
reacts with the cyanoacrylate monomer during polymerization.
The maleimide ring opens to participate in thyroxine and
grafts to the cyanoacrylate chain during its polymerization.
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I
Without intending to be bound to any particular chemical
theory, it is believed that as the cyanoacrylate cures, the
maleimide is incorporated into the cyanoacrylate chain.
Subsequent elevated temperatures are believed to induce a
second stage of polymerization between the grafted maleimides,
which have unsaturated cites, and the acrylic ester monomer.
Cross-linkages are thus formed. The superior ability to
maintain structural properties, such as tensile strength, at
temperatures of 250F or more for long periods of time, as
well as to resist the general effects of thermal aging, is
attributed to this unique interaction.
Generally, the amount of the maleimide additive to be
used is about 0~1 to about 20% by weight of the composition,
but the preferred amount is about 1 to about 5% t the most
preferred amount being about 2%. Amounts of about 2% or less
readily dissolve at room temperature into the cyanoacrylate
and acrylic ester monomer. Above this amount, the additive
may remain in suspension in the liquid composition, still
serving its function and producing the desired properties,
however.
Among the maleimide additives preferred is the following
structure:
O O J'
_R8_
no
O O
where R8 is a phenol group. This compound is manufactured
by E. I. Dupont de Numerous & Co., under the trade mark HA.
I. .
It is important to maintain proper stability of the
composition without losing the advantage of fast cure.
The stability can be controlled by the use of known
inhibitors of anionic polymerization.
Standard acidic gases, such as sulfur dioxide, sulfur
trioxides and nitric oxide, can be incorporated as convent
tonal inhibitors of anionic polymerization. However, it
is preferred that a combination of sulfur dioxide and an
acid selected from the group of sulfonic acids, phosphorus
acids, phosphoric acids, and carboxylic acids, with a Pea
range of about negative twelve) to about 7 (seven) be
used. This inhibiting system is disclosed in Canadian
Patent 1,1~2,5620 The most preferred components of the
combination are sulfur dioxide with methane sulfonic acid,
both present in the range of about 0.005 to about 10% by
weight of the composition, but most preferably in the
range of about 0.005 to about 0.1~. The preferred pro-
portion ox SO to methane sulfonic acid is 20:50.
It is optional, but recommended, that an inhibitor of
free-radical polymerization, selected from the group con-
sitting of hydroquinones, benzoquinones, naphthoquinones,
phenanthraquinones, anthraquinones, and a substituted come
pound of any of the foregoing, be incorporated into the
adhesive as well. Hydroquinone is the most preferred.
Generally, the amount of such inhibitors is about
0.17 to about 10~ by weight of the composition, 0.17
to 5% being preferred, and 0.95% being most preferred.
Other agents such as thickeners, plasticizers,
delineates, etc. are also known in the art and may
pa advantageously be incorporated where functionally
desirable, provided only that they
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do not interfere with the functioning of the vital additives
for their intended purposes. The instant compositions exhibit
good shelf-life stability, e.g., they normally remain liquid
at room temperature in the uncured state. This, of course,
can be determined by simple experimentation.
In the drawings illustrating the invention,
Figures 1 and 2 are thermograms of the present invention and
the prior art, respectively.
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I
. EXAMPLES
The flying examples are given to demonstrate the
compositions within the scope of the inventicm disclosed
herein. These examples are not intended to be limitations on
the scope of the invention.
Below it a table ox the ingredients in each of the c~mpo-
Chinese used in the examples. ~11 percentages are by weight
based on the amount of ethyl cyanoacrylate. which comprises the
: rest of the adhesive composition.
table I
Compositor
Additives control) (control) (controls)
% by weight _ A _ ED C D E F G
HA __ __ 2 2 _ 4 Jo 2
Lowe eighth-
acrylate - __ 1% 1% I __ 1 I
.. inhibitors 0.2~ 0.2~ 0.24 0~2~ 0.2% 0.2~l 0.2%
!! * Compositions I) had approximately I ~hickeninq .
;, agents to increase their Brook field viscosity to 200 ens at
25C, using a No. 2 spindle
Example 1
Not strengths of control compositions A and B from
Table I were measured it 250 . Grit-blasted and solvent washed
steel lops were used to prepare lap shear samples with these
1. compositions end the samples were then aged end tested at ~50~.
he lap shear mules were allowed Jo cure or 24 hours at room
emper~ture before heat g.
. After 1 hour, the lop err tensile length ox ~omposi-
Zion was 1300 psi. After US hour, the length propped to
: . 700 pi, an after 4B o'er thy trying way 650 Paid
121~i~9
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Composition B was similarly tested and the results are
tabulated in the table below:
Table II
HOT STRENGTH AFTER AGING AT 250F
Tested at:250F --psi/% strength retention
. . .. _
. room tempt 24 48 72 96 1 2 3 4
position control HO HIS HIS HIS HIS WACO WAS WOKS WOKS
B 3250/1120/ 690/ 650/ 670/ 400 740 700~ 500/ 520/
100%34~ 21~ 20~ 21~ 12% 23% 22~ 17% 16%
As noted from the data above, there is a significant
decrease in the hot strength properties as measured by lap
shear tensile at 250F beginning with the first hours of aging
and continuously declining until there is little structural
integrity at the bond line.
These compositions are ones typical of the prior art and
clearly demonstrate the degradation of tensile strength at
elevated temperature. This example is for the purpose of
comparison with the compositions of the instant invention
(see Examples 2 and 3).
Example 2
Compositions C and D from Table I were used to prepare
grit-blasted steel lap shears, which were subsequently aged
and tested at 250F. The results are tabulated in the table
below:
a aye
a
1 'O ox L _
owe r
o o UP 3 2 o
a
8 Jo
a
L
¦ I . x I . /
example 3
. ,
,: Lap shear specimen were prepared as in the previous
examples using compositions E end P and I.
TABLE IV
HOT STRENGTH AFTER AGING AT 250F
.._
I (P s I)
LAP SHEARS TESTED AT 250~F
1 6
Composition HO HIS_ DAY _ DAYS
E 720 540B90 1050
F . 950 9201200 1140
; C 895 ' 96013~3 1610
I ,
As indicated in Table I, composition E is fiimilax to the
I! control composition A, except that E has ally methacrylate as
an additional ingredient. Composition is also similar to thy
control composition A, except it contains the additional in-
gradient HA. Composition C is an embodiment of the instant
I, invention.
The results of the above Table IV indicate that the use of
EVA or an acrylic ester additive in the adhesive composition by
themselves produce very similar hot length results. The
j composition of the instant invention demonstrates an improved
: hot strength, particularly after 6 days at elevated temperature;
i-
Jo
I Al this example demonstrates the improved heat resistance
properties of the Nanette ~ompositi~n~ steel l a p shears were
prepaid with compos~tlons I, P, pa G in the tame manner I
14
! :
. .. . ... . . . . .. .. . .. ...
~2J
before, end heat aged at 2~00F for up to five (5) days. The
lap shears were then allowed to cool to room temperature and
pulled. The results are shown below:
TABLE V
S HEAT RESISTANCE
(PSI )
Room Days exposure at 2500F
Composition Temp. 1 2 I 4 5
A (control) 1600613 550 -- Jo Jo
F 2025 1017 917 900
i 16421775 18001913 1592
As evidenced by the above table, composition G of the
instant invention us superior in its heat resistance capability
' than those compositions of the prior art. Composition A was a
typical prior art cyanoacrylate adhesive composition, and
composition F had HA in its formulation (see Tale I). This
jig example clearly illustrates that the instant compositions yield
' improved heat resistance characteristics over the prior art
compositions.
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This last example shows results from a thermal stability
i test (thermogram). This test involves heating a sample of the
if cured composition and measuring its weight loss. The weight
¦, loss is proportional to degradation of the polymer. The analysis
was performed using a Perking Elmer US using the following
if conditions:
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Temperature range 40C - 400C
Heating range 20C/min.
Sample size approx. 9mg.
Purge gas air at 40cc/min. flow
Chart speed 10 mm/min.
The results in the chart below indicate composition G
of the instant invention retains nearly 50% of its weight at
280% and 40% of its weight Attica. It is apparent from the
table below and figures 1&2, that the compositions of this
invention have two steps of decomposition, one which starts at
ICKY and represents 48~ of the total sample, and another
which starts at 280C and represents 42% of the sample weight.
Contrast this with one step decomposition of the prior art.
The prior art composition (control A) shows total degradation,
98.8% weight loss at 260C.
TABLE VI
% Weight Lost at TIC
Cup. 120 140 160_180 200 220_ 740 2~0 280 3~0 ~320 360 80 400
. .. . . ... .
G 0 0 0.2 0.5 1.7 7.8 25. 46.8 53.8 59.8 72 86 89 90.2
A 0 0.2 0.3 0.8 2.2 13.0 78 98.8 99.3
