WO1998007801A1

WO1998007801A1 - Cyanoacrylate compositions with improved thermal and glass bonding performance

Info

Publication number: WO1998007801A1
Application number: PCT/IE1997/000059
Authority: WO
Inventors: Bernard Ryan; Gerard Mccann
Original assignee: Loctite (Ireland) Limited
Priority date: 1996-08-16
Filing date: 1997-08-15
Publication date: 1998-02-26
Also published as: KR20000068165A; AU726418B2; JP2000516289A; CA2263313A1; AU3861697A; EP0918831A1; BR9711196A

Abstract

A one-part cyanoacrylate adhesive composition including a cyanoacrylate monomer and at least one salt of a cation which is a hard Lewis acid with an anion of low nucleophilicity. The cation is suitably a metal cation optionally selected from: Li?+, Na+, K+, Be2+, Mg2+, Ca2+, Cr3+, Al3+, Fe2+, Co2+, Ni2+, Cu2+, Zn2+ or Pb2+¿. The anion may be selected from BF-4, PF-6, SbF-6, SbC1-4, AsF-6, SbCl-6, SnCl-6, FeCl-4, CF-3SO3 or C1O-4. The salt may be present in an amount from 0.001 % to 6 % by weight of the composition or the monomer.

Description

CYANOACRYLATE COMPOSITIONS WITH IMPROVED THERMAL AND GLASS BONDING PERFORMANCE

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. However 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. This limitation of cyanoacrylate adhesives has persisted for over four decades since the materials were originally invented. Commercially 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, SnCl₂.6H₂0, and FeCl₃.6H₂0. Other metal halide salts mentioned (but not used in the Examples) include LiF, LiI.3H_?0, LiI.H_?0 and MgCl₂- 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-0 080 269) 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 cation M and an anion A. The pKa relating to cation M in the equilibrium is defined by

M(H₂0)⁺*^=i M0H+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. + + + The cation M is disclosed in Robins to be K , Na , Ca ,

Li⁺, Ba ⁺, Ca ⁺, Mg , Mn , 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, methyl sulfonate, trifluoroacetate, tetrafluoroborate, periodate, triflate, hexafluorophosphate, hexafluoroantimonate and hexafluoroarsenate. In the working examples (Table III) the accelerator compounds include lithium triflate (CF^SO^Li), lithium bromide (LiBr) and magnesium bromide (MgBr,-,) .

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 is 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 phosphoniu salts. The salts are solids and are stated not to have adverse effects on the curing of 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 2 228 943A Loctite (Ireland) Limited describes one-part cyanoacrylate adhesive compositions suitable for bonding porous or non-active surfaces containing a phase transfer catalyst of the formula

cV

wherein C is a cation other than sulfonium, e.g. ammonium, a quaternary chlorometallate, pyrilliu , thiopyryll ium, iodoniu , phosphoniu , metalloceniu , 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 = ally! cyanoacrylate

ECA = ethyl cyanoacrylate

RT = room temperature LTFB = LiBF. = lithium tetrafluoroborate

LHFP = LiPF_fi = lithium hexafluorophosphate

LHFA = LiSbF_c = lithium hexafluorantimonate o MTFB = Mg (BF = magnesium tetrafluoroborate

ZTFB = Zn(BF.)_? = zinc tetrafluoroborate

TBAHFP = tetrabutyl ammonium 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 bonding 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 Drawings

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 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. Figure 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 GBMS bonded with ACA formulations containing 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 GBMS laps bonded with ethyl CA. Figure 15 shows the effect of LTFB which has been washed repeatedly with diethyl ether on the heat-aged shear strength (120°C, 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 aciid thus includes Li⁺ , Na⁺

Be²⁺, Mg²⁺, , Ca²⁺, Cr³⁺, Al³⁺, H , Fe²⁺, Co²⁺, Ni ⁺,r

Cu²⁺, Zn²⁺ and Pb ⁺.

The cation is desirably a metal cation. Suitably the metal

+ + 2+ 2+ 2+ cation is selected from Li , K , Mg , Ni and Zn

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 , Mg and Zn .

The anion may suitably be selected from

BF~, PFg, SbF~, SbCl^, AsF^", SbCl^", SnClg, FeCl^, CF-^SO^ or ClO^j

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 BF ^" , PF- , SbF₆ or AsF^" .

Compositions according to the invention have been found to have 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 GBMS (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 Mg ⁺ and Zn cations are relatively small and have a high charge density. The ionic radii of some metal ions are listed below in nanometers (nm): Li Zn Ma 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 larger cations, such as tetrabutyl ammonium, sodium or potassium, are not as effective as those with smaller cations e.g. cations with an ionic radius less than 0.095πm. 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

+ 2+ compound) which can form a complex with Li or Mg , 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 πiay 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) for steel are:

0.1 - 0.2 LHFP

0.1 - 0.5 LTFB 0.1 - 0.5 MTFB

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. 4,460,759 (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 BF , PF , AsFj, SbFl do not destablize CA formulations. These ions undergo reversible hydrolysis with water yielding hydrofluoric acid e.g.

BF^~ + H₂0 ^ BF₃0H^" + HF

The equilibrium constant for the reaction of pure water with BFl indicates that approximately half of the BFl anions undergo hydrolysis releasing HF. Polar substrates such as metal and most glasses are basic, and are coated in tightly bound water onolayers. While the present invention is not limited by any theory, it is considered that small cations and fluorinated anions should function as water-activated, surface-active, latent acid additives for CA polar substrate bonding applications. "Surface-active" in this context means that the latent acid binds to the substrate surface, resulting in much higher concentrations of acid at the adhesive/substrate 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. Examples

In the following examples, bond strengths (shear strengths) were 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.

The 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, Gilingha , Dorset SP8 4XT, England).

Example 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.

Table 1

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 2 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 90 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 (LTFB) concentrations is illustrated in Fig.l. 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, that even after 2 weeks at 120 C, glass bonds made with formulations which contained 0.2% LTFB remained clear and colourless.

(b) 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 LTFB formulations which remained colourless.

Example 3

Effect of Magnesium Salts on Thermal Performance

Tetrafluoroborate

The ionic radius of Mg is similar to that of Li⁺, and the intense electrostatic field 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. 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 Table 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 quoted 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 GBMS were not heavily dependent on the volume of applied adhesive. Table 2.1

The effect of lithium and magnesium salts on the fixture time (seconds) of ethyl CA on soda glass

C Coonnee %%ww// L LTTFFBB L LHHFFPP 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 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 (GBMS)

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. Table 2.2

Fixture times (seconds) of GBMS laps bonded with ethyl CA which contained lithium and magnesium fluorinated anion salts

Cone % w/w LTFI LHFP MTFB

0 30 30 30

OJ 75 150 -

0.2 90 - 390

0.5 105 180 >1000

1.0 150

These results show, inter a1 i a . 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 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 strength is noted for similar bonds on heat ageing where the ECA contains approximately 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. 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 tetrabutyl ammonium 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 Cone %w/w Fixture Times (S)

Control (no salt) 0 30

LTFB 0.1 75

LHFP 0.1 150

MTFB 0.2 390

MPC 0.1 30

MTRIF 0.1 30

TBAHFP 0.1 30

II 2.0 30

M 10.0 30

L = lithium, M - magnesium, TBA = tetrabutyl ammonium, TFB = tetrafluoroborate, HFP = hexafluorophosphate, PC = perchlorate, TRIF triflate. Example 9

Deactivating Effect of Calixarene on LTFB

Fig. 9 shows the effect of added lithium-sequestering calixarene on the thermal performance of GBMS bonds made with ethyl CA formulations which contained LTFB. Clearly, the calixarene completely deactivates the beneficial effect of the LTFB. The properties of calixarenes as ion-sequestering agents are well known. US patent No. ^■1, 882, 49 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 recrystal 1 ized 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 10 shows the effects on the fixture times of varying 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 Aαeinα at 150°C of Al 1 vi CA bonded GBMS Effect of LTFB and CHP

The short and long term effects of LTFB on the room temperature bond strength of GBMS 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 containing CHP.

As shown in Figure 13 the corresponding hot shear strengths of GBMS bonds at 150°C show small but significant 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 significantly 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, Gilingha , Dorset SP8 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 FIRELIGHT 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 respective ethyl CA bonds not containing any LTFB. 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 recrystall ization of the nickel salt or double recrystall ization of the sodium salt from hot solutions of the respective salts in 75% (w/w) ethanol/25% (w/w) water.

Industrial Applicability

This invention provides articles of manufacture, namely adhesive compositions.

Claims

WHAT IS CLAIMED IS

1. Λ one-part cyanoacrylate adhesive composition comprising a cyanoacrylate monomer and at least one salt of a cation which is a hard Lewis acid with an anion of low nucleophilicity.

2. A composition according to Claim 1 wherein the cation is a metal cation.

3. A composition according to Claim 2 wherein the metal is selected from t Al³⁺,

4. A composition according to claim 1 wherein the cation has an ionic radius equal to or less than 0.095 nm.

5. A composition according to claim 2 wherein the cation is at least one of lithium, magnesium or zinc.

6. A composition according to claim 1 wherein the anion is selected from the group consisting of

BF^, PF^~, SbFg, SbCl^", AsF~, SbClg, SnCl^" FeCl^, CF^~S0₃ and ClO^j.

7. A composition according to Claim 6 wherein the anion is a fluorinated anion selected from the group consisting of BF7, PFg, SbFg and AsF~.

8. A composition according to claim 1 wherein the salt is present in an amount from 0.001% to 6% by weight of the composition.

9. A composition according to claim 1 wherein the salt is present in an amount from 0.001% to 6% by weight of the cyanoacrylate monomer.

10. A composition according to Claim 1 wherein the salt is present in an amount from 0.001% to 1% by weight of the composition.

11. A composition according to Claim 1 wherein the salt is present in an amount from 0.001% to 1% by weight of the cyanoacrylate monomer

12. A method of bonding two substrates, which comprises the step of applying a one-part composition according to Claim 1 to at least one of the substrates and bringing the substrates together.