Note: Descriptions are shown in the official language in which they were submitted.
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CYANOACRYLATE COMPOSITIONS WITH IMPROVED THERMAL AND GLASS BONDING
P~RFORMANCE
Background of the Invention
Technical Field
This invention relates to one part cyanoacrylate adhesive
compositions having improved bonding and/or thermal bonding
performance and which are particularly useful for bonding polar
surfaces, such as glass and metal surfaces, and other high energy
surfaces, such as ceramics, quartz and certain plastics, especially
flame-treated plastics and engineering plastics such as those of
polycarbonates, polysulfones, polyimides, polyetheretherketones (PEEK)
or phenolic-type or epoxy-based plastics.
Bried Description of Related Technology
Cyanoacrylate adhesive compositions are noted for their rapid
bonding activity i.e very low fixture times. ~owever if their
usefulness for bonding some surfaces, in particular polar surfaces, is
to be increased, the bond strength performance needs to be improved.
On glass, the bond strength retention is unsatisfactory at room
temperature as well as at elevated temperatures. On metal surfaces
such as mild steel the bond strength performance tends to deteriorate
at elevated temperatures.
While this invention is not limited by any theory, the
deficiency of cyanoacrylate adhesives in glass bonding is likely to be
related to the extremely rapid speed at which these adhesives cure on
glass, aided by the basic nature of the surface. High stresses are
believed to be generated in the bond line immediately adjacent to the
glass, at a molecular level. These stresses make the polymer in the
bond line susceptible to chemical or physical degradation, for example
as a response to contraction and expansion of the joint with changes
in room temperature or to hydrolytic attack by atmospheric moisture.
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This limitation of cyanoacrylate adhesives has persisted for
over four decades since the materials were originally invented.
Commercial1y available cyanoacrylate products generally have a limited
usefulness in connection with the bonding of glass.
U.S. Patent No. 5,290,825 (Lazar) describes cyanoacrylate
compositions that are temporarily inhibited from polymerizing and
curing even in the presence of activating substances, such as metals,
the inhibition-stabilization being accomplished by an
inhibitor-stabilizer including an organic carboxylic acid, and a
hydrated or anhydrous metal chloride, fluoride, bromide or iodide.
The metal halide salts used in the working examples of Lazar are
MgBr.6H20, SnC12.6H20, and FeC13.6H20. Other metal halide
salts mentioned (but not used in the Examples) include LiF,
LiI.3H20, LiI.H20 and MgC12. However, metal halide salts are
too reactive for the purposes of the present invention. Accordingly,
Lazar reports a solution different from that taught herein.
U.S. Patent No. 4,460,759 (and EP-A-O 080 269) Robins describes
a two-part adhesive system wherein one part includes an
alpha-cyanoacrylate monomer with a stabilizer and the other part is a
weakly acidic or weakly basic ionic accelerator compound including a
z5 cation M and an anion A. The pKa relating to cation M in the
equilibrium is defined by
M(H20) = MOH+H
and is at least about 10. The pKa relating to anion A in the
equilibrium is defined by
HA = A +H
and is less than or equal to about 0. The nucleophilicity constant of
anion A is less than about 2 when cation M is an onium cation
comprising more than 8 carbons, with the nucleophilicity constant
being determined relative to methyl iodide.
~ , .. . . . .... ... . .. ......
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The cation M is disclosed in Robins to be K , Na , Ca ,
Li , Ba2 , Ca2 , Mg2+, Mn2 , or an onium cation such as a
quaternary ammonium cation e.g. tetraethyl ammonium cation,
tetrapropyl ammonium cation, tetrabutyl ammonium cation,
trimethylethyl ammonium cation, dimethyldiethyl ammonium cation, and
trimethylbutyl ammonium cation. Examples given of anion A are
perchlorate, iodide, bromide, chloride, chlorate, thiocyanate,
nitrate, phenylsulfonate, methyl phenyl sulfonate, methylsulfonate,
trifluoroacetate, tetrafluoroborate, periodate, triflate,
hexafluorophosphate, hexafluoroantimonate and hexafluoroarsenate. In
the working examples (Table III) the accelerator compounds include
lithium triflate (CF3S03Li), lithium bromide (LiBr) and magnesium
bromide (MgBr2).
This two-part adhesive system is said to exhibit suitable cure
rates when employed on wooden substrates. In particular the problem
that Robins set out to solve was the slow curing of cyanoacrylate
adhesive on wooden substrates. The objective therefore ;s to
compensate for the slow curing (due to the acidic nature of wooden
substrates) by using a suitable accelerator to enhance cure speeds.
The salts listed in the Robins patent are said to increase the cure
speed of the cyanoacrylate adhesive, acting as accelerators to the
curing process. The alternative use of the composition on other
substrates such as on glass, metal and plastics is mentioned.
No examples of the use of the Robins compositions relate to
substrates other than wooden substrates and there is no teaching about
polar or high energy surface substrates. Robins is silent with
respect to one-part cyanoacrylate adhesive compositions.
FR 2,187,870 discloses a stable adhesive of a substituted
olefinic monomer, which polymerises easily by anionic polymerisation,
in particular which may be polymerised by weak Lewis bases. The
adhesives are stabilised on storage and during processing by the
addition of an effective amount of an onium-type salt. The
stabilisers may alternatively be phosphonium salts. The salts are
solids and are stated not to have adverse effects on the curing of
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cyanoacrylate. The inventors were thus seeking salts which would
stabilise the adhesive composition on storage but which would not slow
down the rate of cure of the adhesive.
GB ~ 228 943A Loctite (Ire1and) Limited describes one-part
cyanoacrylate adhesive compositions suitable for bonding porous or
non-active surfaces containing a phase transfer catalyst of the formula
I0 C A
wherein C is a cation other than sulfonium, e.g. ammonium, a
quaternary chlorometallate, pyrillium, thiopyryllium, iodonium,
phosphonium, metallocenium, or diazonium;
and A is an anion of relatively low nucleophilicity which
does not initiate polymerization of the cyanoacrylate monomer.
The specification suggests that upon contact with a surface such
as paper or wood the anion A is exchanged for a more nucleophilic
anion present on the surface to be bonded. As this other anion is
transferred into the composition it initiates anionic polymerization
of the monomer which leads to bonding. The bonding of polar surfaces
or highly energy surfaces presents different problems.
None of the above documents discusses the longstanding problem
of the poor performance of cyanoacrylate adhesive compositions on
polar substrates such as glass. They do not solve problems overcome
by the present invention e.g. to provide cyanoacrylate bonds,
particularly on polar substrates, which have enhanced thermal
durability. A one-part adhesive composition is highly desirable,
compared to a two-part composition because of its convenience in use.
The abbreviations given below are used in the following text :
CA = cyanoacrylate
ACA = allyl cyanoacrylate
ECA = ethyl cyanoacrylate
RT = room temperature
, . .. , .-- --.. .. . . . .... ... . ... .
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LTFB = LiBF4 = lithium tetrafluoroborate
LHFP = LiPF6 = lithium hexafluorophosphate
LHFA = LiSbF6 = lithium hexafluorantimonate
MTFB = Mg (BF4)2 = magnesium tetrafluoroborate
ZTFB = Zn(BF4)2 = zinc tetrafluoroborate
TBAHFP = tetrabutylammonium hexafluorophosphate
LPC = lithium perchlorate
GBMS = grit blasted mild steel (lapshears)
Cx = calixarene
CHP = cumene hydroperoxide
DOS = dioctyl sebacate
CNA - cyanoacetic acid
Summary of the Invention
The present invention overcomes the problems noted above, and
provides cyanoacrylate compositions having improved ~onding and/or
thermal bonding performance, particularly on polar substrates and
other high energy surfaces. That is, provides a one-part
cyanoacrylate adhesive composition including a cyanoacrylate monomer
and a salt of a cation which is a hard Lewis acid with an anion of low
nucleophilicity which does not initiate polymerization of the
cyanoacrylate monomer. This invention will be more readily
appreciated by a reading of the detailed description of the invention
in conjunction with the examples and with reference to the figures.
Brief Description of Drawin~s
Figure 1 is a graph of shear strength (mPa) against salt
concentration (% w/w) which shows shear strength performance (RT
pulled) after heat ageing at 120~C of soda glass bonded with ethyl
CA containing a range of LTFB concentrations.
Figure 2 shows shear strength performance (RT pulled) after heat
ageing for 24 hours at 120~C of soda glass laps bonded with ethyl CA
containing very low salt levels of LHFP.
Figure 3 shows shear strength performance (RT pulled) after heat
ageing at 120~C of soda glass bonded with ethyl CA containing LTFB
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or MTFB.
Figure 4 is a graph of fixture time (seconds) against
formulation ageing time (weeks) and shows the effect of LTFB on the
fixture times of soda glass laps which were bonded with ethyl CA
formulations had been subjected to accelerated ageing at 55~C. The
control formulation "set-up" after nine weeks.
Figure 4a is a similar graph showing the effect of LTFB on the
fixture times (minutes) of GBMS lapshears which were bonded with ethyl
CA formulations which had been subjected to accelerated ageing at
55~C. The control formulation "set up" after three weeks.
Figure 5 is a graph of shear strength (mPa) against ageing time
(weeks~ and shows the effect of LTFB on the heat aged (120~C) shear
strength (RT pulled) of GBMS laps bonded with ethyl CA.
Fiyure 6 shows the effect of LHFP on the heat aged (120~C)
shear strength (RT pulled) of GBMS laps bonded with ethyl CA.
Figure 7 shows the effect of MTFB on the heat aged (120~C)
shear strength ~RT pulled) of GBMS laps bonded with ethyl CA.
Figure 8 is a shear strength diagram and shows the separate and
combined effects of the lithium cation and the hexafluorophosphate
anion on the shear strength of ethyl CA bonded GBMS laps which were
heat aged at 120~C and pulled at RT.
Figure 9 shows the effect of 0.5% w/w calixarene (Cx) on the
shear strength (RT pulled) of heat aged (120~C) GBMS laps bonded
with ethyl CA containing 0.1% w/w LTFB.
Figure 10 shows the effect of LHFP on the fixture times of soda
glass and GBMS bonded with ethyl CA.
Figure 11 shows the short term effect of LTFB and CHP on heat
ageing (RT pulled) of G8MS bonded with ACA formulations containing
- 30 LTFB and/or CHP.
Figure 12 shows the long term effects of LTFB and CHP on heat
ageing (RT pulled) of GBMS bonded with ACA formulations containing
LTFB and/or CHP.
Figure 13 shows heat aged hot strength at 150~C of GBMS bonded
with Allyl CA formulations containing 0.5% w/w LTFB and/or 1% w/w
CHP.
Figure 14 shows the effect of ZTFB on the heat aged (120~C) RT
pulled bond strength of G8MS laps bonded with ethyl CA.
.. . . . .. . . . .
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Figure 15 shows the effect of LTFB which has been washed
repeatedly with diethyl ether on the heat-aged shear strength
(120~Ct RT pulled) of GBMS bonded with ethyl CA
Figure 16 shows the effect of LTFB on heat aged shear strength
(120~C, RT pulled) of FIRELITE (glass ceramic) and stained glass
(20% w/w lead oxide content) bonded with ethyl CA.
Detailed Description of the Invention
As noted above, the present invention provides a one-part
cyanoacrylate adhesive composition including a cyanoacrylate monomer
and a salt of a cation which is a hard Lewis acid with an anion of low
nucleophilicity which does not initiate polymerization of the
cyanoacrylate monomer.
The term "hard" Lewis acid as used herein refers to those acids
which are classified as "hard" or "borderline" in Chapter 5 (Table
5.4) p.213 of "Inorganic Chemistry" by Shriver, Atkins and Langford
(second edition) published by Oxford University Press (1994). The
definition of "hard" Lewis acid thus includes Li , Na , K ,
Be , Mg , Ca2+, Cr3+, Al3+ H+ Fe2+ C 2~ Nj2+
C 2+ zn2+ a d Pb2+
The cation is desirably a metal cation. Suitably the metal
cation is selected from Li , K , Mg2 , Nj2 and zn2 .
Particularly suitable cations are metal ions having an ionic radius of
less than about 0.095 nm and especially less than 0.090 nm. A
selected group of cations are Li , M92 and zn2 .
The anion may suitably be selected fro~
BF4, PF6, SbF6, SbCl4, AsF6, SbCl6,
SnCl6, FeCl4, CF3S03, or ClO4
The anion is desirably a fluorinated or chlorinated anion which
releases a fluorine or chlorine anion and an acidic species e.g. on
hydrolysis. A selected group of anions are fluorinated anions such as
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BF4, PF6, SbF6 or AsF6.
Compositions according to the invention have been found to have
5 improved bonding performance as compared to compositions without the
above-defined salts.
Retarding the speed of cure is desirable in improving bond
strength on high energy surfaces such as glass.
As shown in the Examples herein, lithium salts with the above
selected anions have been found to stabilize cyanoacrylate (CA)
compositions without substantial loss of activity apart from causing
slower fixture on polar surfaces. On glass it is desirable to reduce
the speed of bonding e.g. to a fixture time greater than 5 seconds.
The presence of one of the above-noted salts which increases fixture
time in the composition allows more time to position the components to
be bonded, before bonding takes place. The slower cure allows time
for accurate positioning of the glass substrates. On metal, such as
~BMS (grit blasted mild steel), the addition of the above-noted salts
has been shown to improve the heat ageing properties of ethyl CA
compositions and to reduce bond weakening during thermal ageing of an
allyl CA composition.
It is significant that Li and M92 and zn2 cations are
relatively small and have a high charge density. The ionic radii of
some metal ions are listed below in nanometers (nm):
Lj zn2 M92+ Na K
0.068 0.074 0.082 0.097 0.133
(The ionic radii listed are taken from "Inorganic Chemistry" by
Shriver, Atkins and Langford (second edition) published by Oxford
University Press (1994)).
The present inventors have found that salts with laryer cations,
such as tetrabutylammonium, sodium or potassium, are not as effective
as those with smaller cations e.g. cations with an ionic radius less
than O.Og5nm.
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Lithium is a hard Lewis acid in accordance with the above
definition. It is believed that the above-noted salts undergo phase
transfer adsorption onto polar surfaces. If adsorption/phase transfer
is restricted by adding a chelating agent (such as a calixarene
compound) which can form a complex with Li or Mg2 , the effect of
the invention is lost. The composition should therefore not contain a
chelating agent which complexes with the cation species.
A further advantage of certain compositions of the invention is
that they form a colourless bond with glass which remains optically
clear even after heating. Previous CA compositions suffered from
yellowing after heating.
The compositions of the invention contain the above-defined salt
in amounts effective to improve bonding and/or thermal bonding
performance which may be very small quantities, suitably not more than
6%, and more suitably not more than 1% by weight of the composition,
and most suitably in the range 0.001% to 0.5%. The amount of the salt
may also be determined with reference to the CA monomer so that the
salt is present in an amount not more than 6% by weight of the monomer
and more suitably not more than 1% by weight of the monomer and most
suitably in the range 0.001% to 0.5%. Unless otherwise stated all
percentages are calculated on a weight by weight basis.
A selected group of salts for compositions of the invention are
LHFP, LTFB, LHFA, MTFB and ZTFB
Particularly suitable salt concentrations which may be based on
the weight of the monomer or on the weight of the composition (% w/w)
for glass bonding applications are:
0.001 - 0.01 LHPF
0.01 - 0.2 LTFB
0.01 - 0.2 MTFB
0.01 - 0.6 LHFA
1.0 - 6.0 LPC
Particularly suitable salt concentrations which may be based on
the weight of the monomer or on the weight of the composition (% w/w)
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- 10 -
for steel are:
0.1 - 0.2 LHFP
0.1 - 0.5 LTFB
0.1 - 0.5 MTF~
It will be understood that the CA adhesive composition may
contain an anionic polymerization inhibitor and/or free radical
polymerization inhibitor in conventional amounts [see U.S. Patent No.
4,960,759 (Robins)]. Cyanoacrylate compositions already including
such inhibitors to which the salts of the invention may be added are
sold by Loctite Corporation, Hartford CT, USA under the trade mark
Quick-Tite and by Loctite (Ireland) Limited, Dublin 24, Ireland under
the trade mark Super-Attak. The non-gel version of these products
should be used.
It has been found that lithium or magnesium salts with
fluorinated anions such as BF4, PF6, AsF6, SbF6 do
not destablize CA formulations. These ions undergo reversible
hydrolysis with water yielding hydrofluoric ac;d e.g.
BF4 ~ H20 ~ ' BF30H + HF
The equilibrium constant for the reaction of pure water with
BF4 indicates that approximately half of the BF4 anions
undergo hydrolysis releasing HF. Polar substrates such as metal and
most glasses are basic, and are coated in tightly bound water
monolayers. While the present invention is not limited by any theory,
it is considered that small cations and fluorinated anions should
function as water-activatedt surface-active, latent acid additives for
CA polar substrate bonding app)ications. ''Surface-active" in this
context means that the latent acid binds to the substrate surface,
resulting in much higher concentrations of acid at the
adhesivelsubstrate interface than in the bulk bondline adhesive.
The lithium, magnesium, or zinc cations could also function as
acidic species by lessening the reactivity of surface base, owing to
the ability of these ions to coordinate with basic species.
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Examples
In the following examples, bond strengths (shear strengths) were
5 measured in mPa by conventional methods using INSTRON apparatus. An
average was taken of 3 results for each test. Unless otherwise
stated, where experiments were performed on glass, 6mm soda glass was
used. All concentrations given in the Examples are in % w/w based on
the total weight of the monomer.
~ he cyanoacrylate formulations used in the Examples contain
inhibitors in accordance with conventional practice in the art. Of a
number of purification methods tested for lithium tetrafluoroborate
repeated washing with diethyl ether was one of the simplest and more
effective methods.
The lithium tetrafluoroborate salt used in bonding soda glass as
detailed in the Examples below was purified by washing with diethyl
ether. Except where otherwise stated the lithium tetrafluoroborate,
used in bonding GBMS was used as supplied (Aldrich Chemical Company,
Gilingham, Dorset SP8 4XT, England).
Exam~le 1
Effect of LTFB. LHFP on Room Temperature Glass Bonding
The effect of cure speed on the long term performance of ethyl
CA bonded soda glass laps which were aged under ordinary indoor
conditions (20~C, 50-60% relative humidity) is summarized in Table 1.
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Table ~
Effect of LTFB, LHFP, LPC and CNA on the RT soda
glass bonding performance of ethyl CA
Formulation/ Fixture
Test Conditions Time (Sec) Effect
ECA control < 3 fell apart after 1 month
ECA+0.05% CNA 30 fell apart after Z months
ECA+0.2% LTFB 30 substrate failure after 44
weeks in shear test, no
damage after greater than
1.5 years
ECA~0.005% LHFP gO no damage after
7 months
ECA + 5% LPC 195 bond strength was 4.2 MPa
after 12 weeks
While the formulation containing CNA had the same fixture time
as the LTFB formulation, the glass bonding performance of the CNA
formulation was much poorer. The formulations containing LTFB, LHFP
and LPC show improved glass bonding performance and increased fixture
times over the control ECA formulation.
Example 2
Effect of Lithium Salts on the Thermal Performance of Soda Glass
Bonded with Ethyl CA formulations
(a) Tetrafluoroborate
The thermal ageing performance (120~C~ of soda glass laps
which were bonded with ethyl CA formulations containing a range of
lithium tetrafluoroborate (LTFg) concentrations is illustrated in
Fig.1. Samples were heat aged for 1 day , 4 days, 7 days and 14 days
respectively and then pulled at room temperature .'S.F.' indicates
substrate failure. It is evident that the salt produces a very
significant improvement in the high temperature glass bonding
performance of ethyl CA. An important feature of these results was,
. ~ .. ... ~ .~
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that even after 2 weeks at 12~~C, glass bonds made with formulations
which contained 0.2% LTFB remained clear and colourless.
(bj Hexafluorophosphate
The effect of lithium hexafluorophosphate (LHFP) on heat aged
glass bonding performance is illustrated in Fig 2. This salt was
effective even at very low concentrations.
(c) Hexafluoroantimonate (HFA)
Soda glass having a thickness of 4mm bonded with ethyl CA
containing 0.52% w/w LHFA and heat aged at 120~C for six weeks
underwent substrate failure (rather than bond failure) in room
temperature shear strength tests. The associated fixture time was 45
seconds. Control ethyl CA glass bonds heat aged at 120~C fell apart
after 36 hours.
These results with LHFA indicate that it is an extremely
effective ethyl CA glass bonding additive. It imparted a red
colouration to ethyl CA formulations, unlike equivalent LTF~
formulations which remained colourless.
Example 3
Effect of Magnesium Salts on Thermal Performance
Tetrafluoroborate
The ionic radius of M92 is similar to that of Li , and the
intense electrostatic fie1d associated with the magnesium ion ensures
it has a high affinity for polar substrates. The thermal glass
bonding performance of ethyl CA formulations containing magnesium
tetrafluoroborate (MTFB) were comparable with equivalent LTFB
formulations as shown in Fig 3.
,
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Example 4
Soda Glass Fixture Times
Test results have shown that the fixture times for all of the
ethyl CA formulations which contained small cation fluorinated anion
salts increased when increasing volume of adhesive was applied to the
glass prior to bonding. The fixture times quoted in Tahle 2.1 and
Fig. 4 refer to an adhesive volume of 7-10 microlitres applied to a
bond overlap area of 3.2cm ~0.5 square inches). The bond was
considered to have fixtured when it supported a 3 Kg mass hung
vertically from the bonded laps, giving a bond loading of 0.091 MPa.
If larger volumes of adhesive were applied, lower salt concentrations
were required to maintain the ~uoted fixture times. It is believed
that this phenomenon may be due to migration of the salt towards the
glass surfaces, thus providing the necessary concentration at the
adhesive/glass interface. Fixture times on CBMS were not heavily
dependent on the volume of applied adhesive.
Ta~le 2.1
The effect of lithium and magnesium salts on the
fixture time (seconds) of ethyl CA on soda glass
25Conc %w/w LTFB LHFP MTFB LHFA
0 < 3 < 3 - -
0.0010 - 3-5
0.0025 - 25-30
0.0050 - 60
0.0100 10 600
0.0250 20
0.0500 20
0.1000 20 >24 hours
0.1500 25
0.2000 30 - 105
0.5200 - 45
. , . . .. . , . ~ ..... . ..
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A remarkable feature of the results summarized in Table 2.1 was
the large increase in glass fixture times caused by even very low
concentrations of LHFP. For example, ethyl CA formulations containing
0.1% LHFP did not bond glass but readily bonded GBMS (Table 2.2 ).
The potent effect of LHFP on glass fixture times mirrored its
effect on thermal performance of glass bonds (Fig. 2).
Example 5
Accelerated Adhesive Ageing Fixture Times
The fixture times of soda glass laps bonded with ethyl CA
formulations which were subjected to accelerated ageing at 55~C are
illustrated in Fig. 4. Remarkably, the fixture times of the LTFB
containing formulations were constant at 30 seconds even after eleven
weeks ageing. In contrast, the fixture times of ethyl CA which did not
contain LTFB gradually increased from < 3 seconds to 30 seconds after
nine weeks of ageing.
A similar formulation with 0.2% w/w LTFB and 5% w/w dioctyl
sebacate added thereto had seven weeks stability at 55~C compared to
three weeks stability for an equivalent formulation which did not
contain LTFB.
The fixture times of GBMS lapshears bonded with ethyl CA
formulations which were subjected to accelerated ageing at 55~C are
illustrated in Figure 4a.
Example 6
Effect of Li and Mg Salts on the Thermal Performance of Ethyl CA Bonded
Grit Blasted Mild Steel rGBMS)
The thermal ageing performance (120~C) of GBMS laps which were
bonded with ethyl CA formulations which contained LTFB, LHFP or MTFB
are shown in Figs. 5, 6 and 7 respectively. Corresponding fixture
times for the respective formulations are given in Table 2.2.
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- 16 -
Table 2.2
Fixture times (seconds) of GBMS laps bonded
with ethyl Ch which contained lithium and magnesium
fluorinated anion salts
i
Conc ~ w/w LTFB LHFP MTFB
0 . ~ 75 1 50
0 . ~ gQ - 390
0.5 105 180>1000
1.0 150 - -
These results show, inter alia, that LHFP at greater than or
equal to 0.1% w/w bonds GBMS satisfactorily, whereas the results in
Example 4 show that LHFP at this level will not bond glass. This has
potential advantages for selective bonding applications involving
glass.
Example 7
The Separate Effects of Lithium and HexafluoroPhosphate on Thermal
25 Performance
ECA formulations bonding GBMS show improved shear strength on
heat ageing when LHFP is present in the formulation as shown in Fig.8.
No overall increase in shear stren~th is noted for similar bonds
on heat ageing where the ECA contains approxi~ately equimolar
concentrations of TBAHFP or LPC.
The results shown in Fig 8 suggest that appreciably increased
shear strengths on heat-ageing are obtained when both the lithium
anion and HFP cation are present as compared to salts in which either
of these ions is present individually.
.. ., . . . . ... , . ., ~ . . ..
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Example 8
The activity of the lithium or magnesium fluorinated anion salts
was also reflected by their effect on the fixture times of ethyl CA
bonded GBMS laps. Only those salts listed in Table 2.3 which
contained Li or Mg cations and fluorinated anions increased fixture
times. Remarkably, even 10% w/w levels of tetrabutylammonium
hexafluorophosphate in ethyl CA had no effect on GBMS fixture times
(Table 2.3).
Table 2.3
Separate and combined effects of lithium or magnesium and
fluorinated anion salts on the fixture times
of ethyl CA bonded GBMS lap shears
Salt Conc %w/w Fixture Times
(S)
Control (no salt) 0 30
LTFB 0.1 75
L~FP 0.1 150
MTFB 0.2 390
MPC 0.1 30
MTRIF 0.1 30
TBAHFP 0.1 30
" 2.0 30
" 10.0 30
L = lithium, M = magnesium, TBA = tetrabutyl ammonium, TFB -
tetrafluoroborate, HFP = hexafluorophosphate, PC = perchlorate, TRIF =
triflate.
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Example 9
~eactivatinq Effect of Calixarene on LTFB
Fig. 9 shows the effect of added lithium-sequestering calixarene
on the thermal performance of ~BMS bonds made with ethyl CA
formulations which contained LTFB. Clearly, the calixarene completely
deactivates the beneficial effect of the LTFB. The properties of
lQ calixarenes as ion-sequestering agents are well known. US patent No.
4,882,449 of Harris describes calixarene derivatives which are useful
for sequestration of transition metals. US patent No. 5,210,216,
Harris et al. describes similar compounds. Chang et al. Chemistry
Letters pages 477-478, 1984 also describes the properties of
calixarene. It should be noted that the LTFB was recrystallized twice
(from a 75% ethanol, 25% water solvent) prior to performing the above
experiment in order to eliminate any possible effect from acidic
impurities.
Example 10
Figure lO shows the effects on the fixture times of varyin~
concentrations of LHFP on ECA bonded soda glass and GBMS. Relatively
small increases in the concentrations of LHFP show large increases in
the fixture times on soda glass. Smaller increases in fixture time
occur with GBMS.
Example 11
Thermal Aqeinq at 150~C of Allvl CA bonded GBMS Effect of LTFB and
CHP
The short and long term effects of LTFB on the room temperature
bond strength of ~BMS laps that were heat aged (150~C) and which
were bonded with either allyl CA or allyl CA/CHP formulations are
shown in Figs. 11 and 12 respectively. It is evident that LTFB
produces a small but significant increase in the thermal bonding
performance of allyl CA formulations and allyl CA formulations
, . . , .. , ., , ~.. . . . ... ..
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containing CHP.
As shown in Figure 13 the corresponding hot shear strengths of
GBMS bonds at 150~C show smal1 but signi~icant increases in the heat
aged performance of the formulation containing LTFB only. The bond
formed with the formulation containing CHP only has relatively high
initial hot strength. The bond formed with the formulation containing
both CHP and LTFB shows high initial hot strength and sign;ficantly
increased shear strengths on heat ageing.
Example 12
As shown in Figure 14 the heat-aged performance of GBMS bonds
made with ethyl CA containing 0.1% w/w ZTFB shows substantially
increased shear strengths as compared to control ethyl CA bonds not
containing any ZTFB.
Example 13
As shown in Figure 15 the heat-aged performance of GBMS bonds
made with ethyl CA containing 0.5% w/w of LTFB, which has been
purified by repeated washings with diethyl ether, shows substantially
increased shear strengths as compared to ethyl CA bonds not containing
any LTFB. The LTFB thus washed also shows improved heat-aged
performance over identical bonds formed using LTFB as supplied
(Aldrich Chemical Company, Gilingham, Dorset SP~ 4XT, England)
particularly when the bonds are heat-aged at 120~C for periods
greater than approximately 7 weeks (cf. Figure 5, and Example 5).
Example 14
As shown in Figure 16 the heat aged performance of FIRELIG~T
glass and stained glass (20% w/w lead oxide) each bonded with ethyl CA
containing 0.2% w/w LTFB show substantially increased shear strengths
as compared to their respecti~e ethy1 CA bonds not containing any LTFB.
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Example 15
Salts That Destabilized Ethyl CA Formulations
Nickel tetrafluoroborate and sodium tetrafluoroborate (both
supplied by Aldrich) destabilized ethyl CA. No improvement in
stability was obtained following single recrystal1ization of the
nickel salt or double recrystallization of the sodium salt from hot
solutions of the respective salts in 75~ (w/w) ethanol/25% (w/w) water.
~ndustrial Applicability
This invention provides articles of manufacture, namely adhesive
compositions.
