Patent Description:
Cyanoacrylate adhesive compositions are well known, and widely used as quick setting, instant adhesives with a wide variety of uses. See also <NPL>).

<CIT>) pioneered rubber toughened cyanoacrylate compositions through the use of certain organic polymers as toughening additives that are elastomeric, i.e., rubbery, in nature. The '<NUM> patent is thus directed to and claims a curable adhesive comprising a substantially solvent-free mixture of: (a) a cyanoacrylate ester, and (b) about <NUM>% to about <NUM>% by weight of an elastomeric polymer. The elastomeric polymer is selected from elastomeric copolymers of a lower alkene monomer and (i) acrylic acid esters, (ii) methacrylic acid esters or (iii) vinyl acetate. More specifically, the '<NUM> patent notes that as toughening additives for cyanoacrylates, acrylic rubbers; polyester urethanes; ethylene-vinyl acetates; fluorinated rubbers; isoprene-acrylonitrile polymers; chlorosulfinated polyethylenes; and homopolymers of polyvinyl acetate were found to be particularly useful.

The elastomeric polymers are described in the '<NUM> patent as either homopolymers of alkyl esters of acrylic acid; copolymers of another polymerizable monomer, such as lower alkenes, with an alkyl or alkoxy ester of acrylic acid; and copolymers of alkyl or alkoxy esters of acrylic acid. Other unsaturated monomers which may be copolymerized with the alkyl and alkoxy esters of acrylic include dienes, reactive halogen-containing unsaturated compounds and other acrylic monomers such as acrylamides.

One group of elastomeric polymers are copolymers of methyl acrylate and ethylene, manufactured by DuPont, under the name of VAMAC, such as VAMAC N123 and VAMAC B-<NUM>. VAMAC N123 and VAMAC B-<NUM> are reported by DuPont to be a master batch of ethylene/acrylic elastomer.

Henkel Corporation (as the successor to Loctite Corporation) has sold for a number of years since the filing of the '<NUM> patent rubber toughened cyanoacrylate adhesive products under the tradename BLACK MAX, which employ as the rubber toughening component the DuPont materials called VAMAC B-<NUM> and N123. In addition, Henkel has sold in the past clear and substantially colorless rubber toughened cyanoacrylate adhesive products, namely, LOCTITE <NUM>, <NUM> and <NUM>, which employ as the rubber toughening component the DuPont material, VAMAC G. While VAMAC G contains no fillers to provide color or stabilizers, it does contain processing aids.

And in an effort to improve moisture and thermal resistance of cyanoacrylates applied to substrates constructed with nitrogen- or sulfur-containing compounds, such as synthetic rubbers like chloroprene rubber and EPDM, and Bakelite, <CIT> discloses a cyanoacrylate adhesive composition which comprises (a) a cyanoacrylate and (b) at least one di- or higher functional ester, such as tri- or higher acrylates or methacrylates, having an alcohol residue and having an acid residue, where the alcohol residue is a residue of dipentaerythritol and the acid residue is a residue of an acrylic or methacrylic acid. More specifically, the di- or higher functional ester is reported as (i) an ester of a dipentaerythritol with an acrylic acid or a methacrylic acid, (ii) an ester of a modified alcohol with an acrylic acid or a methacrylic acid, where the modified alcohol is a dipentaerythritol modified by addition of a lactone, and (iii) a combination of an ester of a dipentaerythritol with an acrylic acid or a methacrylic acid and an ester of the modified alcohol with an acrylic acid or a methacrylic acid.

<CIT> discloses cyanoacrylate compositions that include a cyanoacrylate component and a rubber toughening component which is a reaction product of ethylene, methyl acrylate and monomers having carboxylic acid cure sites.

Notwithstanding the state-of-the-technology, it would be desirable to provide a cyanoacrylate composition, reaction products of which demonstrate improved thermal degradation resistance compared to known cyanoacrylate compositions.

Provided herein are cyanoacrylate compositions that include an allyl-<NUM>-cyanoacrylate, a rubber toughening component and a component functionalized with at least two blocked hydroxyl groups. These cyanoacrylate compositions demonstrate improved thermal degradation resistance compared to known cyanoacrylate compositions.

The rubber toughening component has (a) reaction products of the combination of ethylene, methyl acrylate and monomers having carboxylic acid cure sites, (b) dipolymers of ethylene and methyl acrylate, and combinations of (a) and (b).

The component functionalized with at least two (meth)acrylate groups is hexane diol diacrylate.

This invention is also directed to a method of bonding together two substrates, which method includes applying to at least one of the substrates a composition as described above, and thereafter mating together the substrates.

In addition, the present invention is directed to reaction products of the inventive compositions.

Also, the invention is directed to a method of preparing the inventive compositions.

The invention will be more fully understood by a reading of the section entitled "Detailed Description", which follows.

As noted above, provided herein are cyanoacrylate compositions that include an allyl-<NUM>-cyanoacrylate, a rubber toughening component and a component functionalized with at least two blocked hydroxyl groups.

The rubber toughening component comprises (a) reaction products of the combination of ethylene, methyl acrylate and monomers having carboxylic acid cure sites, (b) dipolymers of ethylene and methyl acrylate, and combinations of (a) and (b).

Examples of the rubber toughening component include those materials sold under the VAMAC trade name, including G, B-<NUM>, VMX (such as VMX <NUM>), VCS (such as VCS <NUM> or <NUM>), and N123, all of which being available from DuPont, Wilmington, DE.

VAMAC N123 and VAMAC B-<NUM> are reported by DuPont to be a master batch of ethylene/acrylic elastomer. The DuPont material VAMAC G is a similar copolymer, but contains no fillers to provide colour or stabilizers. VAMAC VCS rubber appears to be the base rubber, from which the remaining members of the VAMAC product line are compounded. VAMAC VCS (also known as VAMAC MR) is a reaction product of the combination of ethylene, methyl acrylate and monomers having carboxylic acid cure sites, which once formed is then substantially free of processing aids such as the release agents octadecyl amine, complex organic phosphate esters and/or stearic acid, and anti-oxidants, such as substituted diphenyl amine.

Recently, DuPont has provided to the market under the trade designation VAMAC VMX <NUM> and VCD <NUM>, which are rubbers made from ethylene and methyl acrylate. It is believed that the VAMAC VMX <NUM> rubber possesses little to no carboxylic acid in the polymer backbone. Like the VAMAC VCS rubber, the VAMAC VMX <NUM> and VCD <NUM> rubbers are substantially free of processing aids such as the release agents octadecyl amine, complex organic phosphate esters and/or stearic acid, and anti-oxidants, such as substituted diphenyl amine, noted above. All of these VAMAC elastomeric polymers are useful herein.

The rubber toughening component should be present in a concentration of about <NUM>% to about <NUM>% by weight, such as about <NUM>% to about <NUM>% by weight, with about <NUM>% to about <NUM>% being particularly desirable.

The component functionalized with at least two blocked hydroxyl groups is hexane diol diacrylate.

It has been found that the presence of many of the underlying components having at least two hydroxyl functional groups show an adverse impact on the shelf life stability of the cyanoacrylate composition to which they have been added. Blocking the hydroxyl groups has alleviated the observed shelf life stability issues.

The component should be present in a concentration of about <NUM>% to about <NUM>% by weight, such as about <NUM>% to about <NUM>% by weight, with about <NUM>% to about <NUM>% by weight being particularly desirable.

In addition to the allyl-<NUM>-cyanoacrylate may be included a cyanoacrylate component selected from cyanoacrylate monomers having a raft of substituents, such as those represented by H<NUM>C=C(CN)-COOR, where R is selected from C<NUM>-<NUM> alkyl, alkoxyalkyl, cycloalkyl, alkenyl, aralkyl, aryl, and haloalkyl groups. Desirably, the cyanoacrylate monomer is selected from methyl cyanoacrylate, ethyl-<NUM>-cyanoacrylate, propyl cyanoacrylates, butyl cyanoacrylates (such as n-butyl-<NUM>-cyanoacrylate), octyl cyanoacrylates, ß-methoxyethyl cyanoacrylate and combinations thereof. A particularly desirable one is ethyl-<NUM>-cyanoacrylate.

The additional cyanoacrylate component should be included in the compositions in an amount within the range of from about <NUM>% to about <NUM>% by weight, with the range of about <NUM>% to about <NUM>% by weight being desirable, and about <NUM> to about <NUM>% by weight of the total composition being particularly desirable.

Thermal resistance conferring agents may also be added. Included among such agents are certain sulfur-containing compounds, such as sulfonates, sulfinates, sulfates and sulfites as set forth in <CIT>).

Maleimide components may also be added, either alone or in combination with other thermal resistance conferring agents.

Suitable maleimides include those having the following structures:
<CHM>.

For example, R<NUM> may be represented by the following structure:
<CHM>
Where the phenyl groups are optionally substituted at one or more positions with linear, branched or cyclic alkyl, alkenyl, alkynyl, alkoxy or aryl groups having from <NUM> to about <NUM> carbon atoms, with or without substitution by halogen, hydroxyl, nitrile, ester, amide or sulfate and Y may represent O, S, carbonyl, sulfone or primary or secondary methylene groups optionally substituted with linear, branched or cyclic alkyl, alkenyl, alkynyl, alkoxy or aryl groups having from about <NUM> to about <NUM> carbon atoms, with or without substitution by halogen, hydroxyl, nitrile, ester, amide or sulfate.

Desirable maleimides include the following:
<CHM>
<CHM>
<CHM>.

Suitably the maleimide component comprises one or more of N-phenyl maleimide, N,N'-m-phenylene bismaleimide, N,N'-(<NUM>,<NUM>'-methylene diphenylene)bismaleimide, bis-(<NUM>-ethyl-<NUM>-methyl-<NUM>-maleimidephenyl)methane, or [<NUM>,<NUM>'-bis[<NUM>-(<NUM>'maleimidediphenoxy)phenyl]propane.

Compositions of the invention may optionally comprise additives which confer thermal resistance properties such as <NUM>-sulfobenzoic acid anhydride, triethylene glycol di(p-toluene sulfonate), trifluoroethyl p-toluene sulfonate, dimethyl dioxolen-<NUM>-ylmethyl p-toluene sulfonate, p-toluene sulfonic anhydride, methanesulfonic anhydride, <NUM>,<NUM> propylene sulfite, dioxathiolene dioxide, <NUM>,<NUM>-naphthosultone, sultone <NUM>,<NUM>-propane, sultone <NUM>,<NUM>-butene, allyl phenyl sulfone, <NUM>-fluorophenyl sulfone, dibenzothiophene sulfone, bis(<NUM>-fluorophenyl) sulfone, ethyl p-toluenesulfonate, trifluoromethanesulfonic anhydride, tetrafluoroisophthalonitrile and combinations thereof.

When used, the thermal resistance conferring additives may be included in the compositions in an amount within the range of from about <NUM>% to about <NUM>% by weight, with the range of about <NUM> to about <NUM>% by weight being desirable, and about <NUM>% by weight of the total composition being particularly desirable.

Suitably, the thermal resistance conferring additives may include a maleimide component and tetrafluoroisophthalonitrile.

Accelerators may also be included in the inventive rubber toughened cyanoacrylate compositions, such as any one or more selected from calixarenes and oxacalixarenes, silacrowns, crown ethers, cyclodextrins, poly(ethyleneglycol) di(meth)acrylates, ethoxylated hydric compounds and combinations thereof.

Of the calixarenes and oxacalixarenes, many are known, and are reported in the patent literature. See e.g. <CIT><CIT><CIT><CIT><CIT>, and <CIT>.

For instance, as regards calixarenes, those within the following structure are useful herein:
<CHM>
where R<NUM> is alkyl, alkoxy, substituted alkyl or substituted alkoxy; R<NUM> is H or alkyl; and n is <NUM>, <NUM> or <NUM>.

One particularly desirable calixarene is tetrabutyl tetra[<NUM>-ethoxy-<NUM>-oxoethoxy]calix-<NUM>-arene.

A host of crown ethers are known. For instance, examples which may be used herein either individually or in combination, or in combination with other first accelerator
<CHM>
include <NUM>-crown-<NUM>, <NUM>-crown-<NUM>, dibenzo-<NUM>-crown-<NUM>, benzo-<NUM>-crown-<NUM>-dibenzo-<NUM>-crown-<NUM>, dibenzo-<NUM>-crown-<NUM>, tribenzo-<NUM>-crown-<NUM>, asym-dibenzo-<NUM>-crown-<NUM>, dibenzo-<NUM>-crown-<NUM>, dicyclohexyl-<NUM>-crown-<NUM>, dicyclohexyl-<NUM>-crown-<NUM>, cyclohexyl-<NUM>-crown-<NUM>, <NUM>,<NUM>-decalyl-<NUM>-crown-<NUM>, <NUM>,<NUM>-naphtho-<NUM>-crown-<NUM>, <NUM>,<NUM>,<NUM>-naphtyl-<NUM>-crown-<NUM>, <NUM>,<NUM>-methyl-benzo-<NUM>-crown-<NUM>, <NUM>,<NUM>-methylbenzo-<NUM>, <NUM>-methylbenzo-<NUM>-crown-<NUM>, <NUM>,<NUM>-t-butyl-<NUM>-crown-<NUM>, <NUM>,<NUM>-vinylbenzo-<NUM>-crown-<NUM>, <NUM>,<NUM>-vinylbenzo-<NUM>-crown-<NUM>, <NUM>,<NUM>-t-butyl-cyclohexyl-<NUM>-crown-<NUM>, asym-dibenzo-<NUM>-crown-<NUM> and <NUM>,<NUM>-benzo-<NUM>,<NUM>-benzo-<NUM>-oxygen-<NUM>-crown-<NUM>. See <CIT>).

Of the silacrowns, again many are known, and are reported in the literature. For instance, a typical silacrown may be represented within the following structure:
where R<NUM> and R<NUM> are organo groups which do not themselves cause polymerization of the cyanoacrylate monomer, R<NUM> is H or CH<NUM> and n is an integer of between <NUM> and <NUM>. Examples of suitable R<NUM> and R<NUM> groups are R groups, alkoxy groups, such as methoxy, and aryloxy groups, such as phenoxy. The R<NUM> and R<NUM> groups may contain halogen or other substituents, an example being trifluoropropyl. However, groups not suitable as R<NUM> and R<NUM> groups are basic groups, such as amino, substituted amino and alkylamino.

Specific examples of silacrown compounds useful in the inventive compositions include:
<CHM>
dimethylsila-<NUM>-crown-<NUM>;
<CHM>
dimethylsila-<NUM>-crown-<NUM>;
<CHM>
and dimethylsila-<NUM>-crown-<NUM>. See e.g. <CIT>).

Many cyclodextrins may be used in connection with the present invention. For instance, those described and claimed in <CIT>, as hydroxyl group derivatives of an α, β or γ-cyclodextrin which is at least partly soluble in the cyanoacrylate would be appropriate choices for use herein as the first accelerator component.

For instance, poly(ethylene glycol) di(meth)acrylates suitable for use herein include those within the following structure:
<CHM>
where n is greater than <NUM>, such as within the range of <NUM> to <NUM>, with n being <NUM> as particularly desirable. More specific examples include PEG <NUM> DMA, (where n is about <NUM>) PEG <NUM> DMA (where n is about <NUM>), PEG <NUM> DMA (where n is about <NUM>), and PEG <NUM> DMA (where n is about <NUM>), where the number (e.g., <NUM>) represents the average molecular weight of the glycol portion of the molecule, excluding the two methacrylate groups, expressed as grams/mole (i.e., <NUM>/mol). A particularly desirable PEG DMA is PEG <NUM> DMA.

And of the ethoxylated hydric compounds (or ethoxylated fatty alcohols that may be employed), appropriate ones may be chosen from those within the following structure:
<CHM>
where Cm can be a linear or branched alkyl or alkenyl chain, m is an integer between <NUM> to <NUM>, such as from <NUM> to <NUM>, n is an integer between <NUM> to <NUM>, such as from <NUM> to <NUM>, and R may be H or alkyl, such as C<NUM>-<NUM> alkyl.

Commercially available examples of materials within the above structure include those offered under the DEHYDOL tradename from Henkel KGaA, Dusseldorf, Germany, such as DEHYDOL <NUM>.

When used, the accelerator embraced by the above structures should be included in the compositions in an amount within the range of from about <NUM>% to about <NUM>% by weight, with the range of about <NUM> to about <NUM>% by weight being desirable, and about <NUM>% by weight of the total composition being particularly desirable.

A stabilizer package is also ordinarily found in cyanoacrylate compositions. The stabilizer package may include one or more free radical stabilizers and anionic stabilizers, each of the identity and amount of which are well known to those of ordinary skill in the art. See e.g. <CIT> and<CIT>.

Other additives may be included to confer additional physical properties, such as improved shock resistance, thickness (for instance, polymethyl methacrylate), thixotropy (for instance fumed silica), and color. Such additives therefore may be selected from certain acidic materials (like citric acid), thixotropy or gelling agents, thickeners, dyes, and combinations thereof.

These other additives may be used in the inventive compositions individually in an amount from about <NUM>% to about <NUM>%, such as about <NUM>% to <NUM>%, desirably <NUM>% to <NUM>% by weight, depending of course on the identity of the additive. For instance, and more specifically, citric acid may be used in the inventive compositions in an amount of <NUM> to <NUM> ppm, desirably <NUM> to <NUM> ppm.

In another aspect, there is provided a method of bonding together two substrates, which method includes applying to at least one of the substrates a composition as described above, and thereafter mating together the substrates for a time sufficient to permit the adhesive to fixture. For many applications, the substrate should become fixed by the compositions in less than about <NUM> seconds, and depending on the substrate as little as about <NUM> seconds. In addition, the composition should develop shear strength on the substrates between which they have been applied, as well as side impact strength and fracture toughness.

In yet another aspect, there is provided reaction products of the so-described compositions.

In still another aspect, there is provided a method of preparing the so-described compositions. The method includes providing an allyl-<NUM>-cyanoacrylate component, a rubber toughening agent, and a component containing at least two (meth)acrylate functional groups, and mixing to form the cyanoacrylate composition.

These aspects of the invention will be further illustrated by the examples which follow.

A number of samples comprising an allyl-<NUM>-cyanoacrylate component, a rubber toughening agent and a component functionalized with at least two blocked hydroxyl groups were prepared as provided in Table <NUM>.

The rubber toughening agent is comprised of:
(a) reaction products of the combination of ethylene, methyl acrylate and monomers having carboxylic acid cure sites, (b) dipolymers of ethylene and methyl acrylate, and combinations of (a) and (b).

The control sample does not comprise a component functionalized with at least two blocked hydroxyl groups. Examples <NUM>-<NUM> of Table <NUM> do not belong to the invention.

The initial tensile strengths of control and test compositions were evaluated on grit blasted mild steel (GBMS). The results are provided in Table <NUM>.

Tensile strengths were determined according to Henkel STM <NUM> for the determination of shear strength of adhesives using lap shear specimens.

Hexanediol dimethacrylate, di-trimethylolpropane tetracrylate (SR355), hexane diol bis cyanoacrylate (Bis CA), pentaerythritol triaacrylate (PETriA) and pentaerythritol tetracrylate (PETetraA) were also screened in this study. The effect of allyl and ethyl CA as well as the level of the rubber toughening agent (Vamac) were also looked at.

Formulations <NUM> to <NUM> have varying concentrations of cyanoacrylate monomers. The <NUM>% allyl-<NUM>-cyanoacrylate formulation (No. <NUM>) gives good results overall even without an additive, particularly after heat ageing on GBMS at <NUM>.

A <NUM>/<NUM> mix (No. <NUM>) of the allyl cyanoacrylate/ethyl cyanoacrylate gives good results after heat ageing on GBMS at <NUM> and <NUM>, but when heat aged at <NUM> the tensile strengths obtained were significantly lower.

The formulation comprising ethyl cyanoacrylate as the sole cyanoacrylte component (No. <NUM>), as expected demonstrated poor tensile strengths after heat ageing at all temperatures tested.

The level of rubber toughening agent (Vamac) in the formulation also proved important. Comparing formulations <NUM> and <NUM> the results are much lower for the formulation with the lower level of rubber toughening agent (Vamac), typically half the performance with half the rubber toughening agent.

Overall the formulation comprising hexanediol dimethacrylate (formulation <NUM>) gives the best performance of the various additives investigated, a slight drop off after <NUM> weeks at <NUM> being the only slight negative.

The formulation comprising hexanediol bis cyanoacrylate (BisCA) (formulation <NUM>) again showed excellent tensile strength results after heat ageing at <NUM>. Comparable results were obtained when tensile strengths were measured after heat ageing at <NUM>; however, when assessed after heat aging at <NUM> the tensile strengths for formulation <NUM> on GBMS were considerably lower.

The tensile strength determined for formulation <NUM> which comprises di-trimethylolpropane tetracrylate (SR355) after heat ageing at <NUM> for <NUM> weeks on GMBS was approximately <NUM> MPa. This dropped slightly to approximately <NUM> MPa after heat ageing at <NUM> for <NUM> weeks.

Similarly, the tensile strength determined for formulations <NUM>, <NUM> and <NUM> was over <NUM> MPa after heat ageing at <NUM> for <NUM> weeks, but the tensile strength for each formulation dropped off after heat ageing for a further <NUM> weeks (to a total of <NUM> weeks). The formulation comprising hexandiol diacrylate (formulation <NUM>) delivered a tensile strength after heat ageing for <NUM> weeks at <NUM> of approximately <NUM> MPa, whereas the tensile strength determined for formulations <NUM> and <NUM> after the same ageing conditions was approximately <NUM> MPa for each formulation.

The effect of varying levels of hexanediol and the rubber toughening agent on tensile strengths was subsequently assessed.

Formulations <NUM> to <NUM> were prepared as provided in Table <NUM>
Each of formulations <NUM> to <NUM> were evaluated for thermal performace by determining the tensile strength for each formulation on mild steel (MS) substrate, after heat ageing for <NUM>, <NUM> or <NUM> weeks.

The perforamce of formulations <NUM> to <NUM> under humid conditions was also evaluated.

Formulation <NUM> is the control formulation which comprises <NUM> wt% ethyl cyanoacrylate, <NUM> wt% allyl cyanoacrylate, <NUM> wt% stabilizer and <NUM> wt% rubber toughening agent.

The level of hexane diol diacrylate, and the effect of including additives on tensile strength performance is assessed in the formulations of Table <NUM>. Examples <NUM> and <NUM> of Table <NUM> do not belong to the invention.

Initial tensile strengths were assessed after curing for <NUM> hours on mild steel (MS), aluminium (Al), polycarbonate (PC) and polyvinlychloride (PVC) substrates.

In addition, tensile strength was assessed for each formulation on GBMS substrate, after ageing for <NUM>, <NUM> or <NUM> weeks at room temperature, <NUM>, <NUM>, <NUM>, <NUM> and <NUM>.

The tensile strength of formulation <NUM> on MS substrate after heat ageing for <NUM>, <NUM> or <NUM> weeks at each of <NUM>, <NUM>, <NUM>, <NUM> and <NUM> was greater than that of the control formulation.

In addition to comprising <NUM> wt% hexanediol diacrylate formulation <NUM> further comprises <NUM> wt% of tert-butyl peroxybenzoate.

The initial tensile strength of formulation <NUM> was lower than that for control formulation <NUM> and the tensile strength of formulation <NUM> after heat ageing also proved inferior to the control at all time points for all temperatures tested. Thus the addition of ter-butyl peroxybenzoate had a negative effect on tensile strength performance.

Formulation <NUM> which comprises <NUM> wt% di-trimethylolpropane tetracrylate (SR355) demonstrated similar properties to control formulation <NUM>: comparable tensile strengths were observed after heat ageing at <NUM>, <NUM>, <NUM>, and <NUM>, but superior tensile strength was observed after heat ageing at <NUM>. Formulation <NUM> also outperformed control formulation <NUM> when aged humidity testing was assessed. Excellent fixture time was also observed for formulation <NUM>. Thus di-trimethylolpropane tetracrylate (SR355) proved to enhance the thermal performance of cyanoacrylate compositions comprising allyl-<NUM>-cyanoacrylate and a rubber toughening agent.

Formulations <NUM> to <NUM> look at the effect of different levels of hexanediol diacrylate (HDDA) and rubber toughening agent. Higher levels of rubber toughening agent (for example, Vamac) give improved thermal properties at <NUM>.

Lower levels of HDDA (Formulation <NUM>) show excellent thermal properties at <NUM> but with inferior aging at <NUM> and <NUM>.

Thus low levels of a component functionalized with at least two blocked hydroxyl groups, such as HDDA, enhanced thermal ageing properties at <NUM> whereas higher levels of said component enhance thermal performance of cyanoacrylate compositions comprising allyl-<NUM>-cyanoacrylate and a rubber toughening agent at higher temperatures (i.e. temperatures above <NUM>).

Formulations <NUM> and <NUM> which comprise <NUM>% HDDA had poor initial tensile strengths. Formulation <NUM> which comprised <NUM> wt% of rubber toughening agent (Vamac) and <NUM> wt% HDDA exhibits excellent tensile strength after heat ageing at <NUM> but again has poor initial tensile strength.

Formulation <NUM> looks at the effect of naphthosultone and ethylene sulfite. Thermal properties at <NUM> and initially at <NUM>/<NUM>/<NUM> are excellent.

Figures <NUM> to <NUM> show the percentage tensile strength retention after formulations <NUM> to <NUM> on mild steel substrate after heat ageing for <NUM>, <NUM> and <NUM> weeks.

The effect of both naphthosultone and ethylene sulphite on heat ageing performance of allyl cyanoacrylate formulations was also investigated (see Table <NUM>).

The control formulation (<NUM>) contains <NUM>% by weight of the rubber toughening agent and <NUM>% by weight of hexanediol diacrylate. Formulations <NUM> to <NUM> comprise the following additives in varying amounts: tetrahydrophthalic anhydride, ethylene sulphite and naphthosultone. The level of each additive is varied as provided in Table <NUM>. The level of stabilizer present in the formulations of Table <NUM> is <NUM>% by weight of the total composition.

The initial tensile strength values on mild steel substrate are generally in the range of <NUM> to <NUM> MPa with the exception of formulation <NUM>, whose cyanoacrylate component is entirely allyl cyanoacrylate. Formulations <NUM> and <NUM> which comprise higher levels of rubber toughening agent and higher levels of hexane diol diacrylate had initial tensile strengths of about <NUM> to <NUM> MPa. Encouragingly the tensile strengths generally increase over time over a <NUM> week period at room temperature.

The results at <NUM> are excellent. All formulations of the invention show exceptional strength retention, with an increase in tensile strength being observed in all cases after up to <NUM> weeks of heat ageing. At the <NUM> week mark the control formulation (formulation <NUM>) is the only formulation which shows a significant drop off in tensile strength value. The influence of the additives for long term ageing at <NUM> is clear. Ethylene sulphite and naphthosultone markedly improve the heat ageing performance of cyanoacrylate compositions comprising an allyl cyanoacrylate component.

The strength retention for formulations <NUM>, <NUM>, <NUM> and <NUM> are excellent after heat ageing at <NUM> up to about the <NUM> week mark. Without the additives present at a concentration of <NUM>% by weight of the total composition, or in the case of the composition comprising solely allyl <NUM>-cyanoacrylate as the cyanoacrylate component, the tensile strength performance dropped off after heat ageing at <NUM>. Disappointingly, after <NUM> weeks, the tensile strength observed for each of the formulations tested fell between <NUM> to <NUM> MPa, with a recovery to about <NUM> MPa after <NUM> weeks. Formulations with higher loadings of rubber toughening agent had tensile stength values of <NUM> to <NUM> MPa after <NUM> weeks.

Previous results for the ageing of allyl cyanoacrylate compositions have shown a dip in tensile strength performance after heat ageing at <NUM> due to the fact that allyl cyanoacrylate is unable to thermally corsslink across the allyl group at this relatively low temperature. However, the addition of naphthosultone and ethylene sulphite have been demonstrated herein to eliminate this phenomenon.

<FIG> shows the heat ageing performance of formulations <NUM> and <NUM> on GBMS at <NUM>. The tensile strength performance of formulation <NUM> which comprises <NUM>% by weight (of the total composition) of each of the additives naphthosultone and ethylene sulphite performed significantly better than control formulation <NUM>, absent said additives.

Excellent strength retention was observed after heat ageing at <NUM>. The addition of the additives naphthosultone and ethylene sulphite eliminate the dip associated with heat ageing of allyl cyanoacrylate compositions. In general an increase in tensile strength was observed after <NUM> weeks.

The bond strength associated with formulation <NUM> is seen to increase over time at <NUM>.

The harsh conditions of aging at <NUM> are reflected in a large drop in performance, albeit formulation <NUM>, which comprises only allyl cyanoacrylate as the cyanoacrylate demonstrates good tensile strength up to the <NUM> week mark.

All formulations demonstrated good tensile strength retention in the highly humid conditions.

Table <NUM> provides compositions comprising varying levels of allyl cyanoacrylate and additive components. Examples <NUM> and <NUM> do not belong to the invention.

The thermal performance of the compositions of table <NUM> and comparative examples <NUM> and <NUM> was assessed (see <FIG>). Comparative examples <NUM> and <NUM> are general purpose instant adhesive formulations based on ethyl CA. Comparative example <NUM> comprises ethyl CA and PMMA, whereas comparative example <NUM> comprises ethyl CA and Vamac.

<FIG> shows the tensile strength performance of the formulations of Table <NUM> and comparative examples <NUM> and <NUM> on GBMS substrate after heat ageing at <NUM> over a <NUM> week period.

Formulation <NUM> demonstrated excellent tensile strength performance with bond strengthes exceeding <NUM> MPa after heat ageing at the prescribed temperature for <NUM> hours.

At <NUM> formulation <NUM> shows excellent retention of bond strength out to <NUM> hours and then falls to around <NUM> MPa after <NUM> hours. Formulation <NUM> again shows excellent strength retention after <NUM> hours but falls to <NUM> MPa after <NUM> hours before rebuilding its strength back to <NUM> MPa after <NUM> hours (see <FIG>).

At <NUM> and <NUM> formulation <NUM> and formulation <NUM> behave in a very similar manner with approximately <NUM>% retention of strength being observed for formulation <NUM> at both temperatures (See <FIG> and <FIG>).

At <NUM> only formulation <NUM> which comprises solely allyl cyanoacrylate as the cyanoacrylate component shows any appreciable strength retention. (See <FIG>).

The performance of formulations <NUM> - <NUM>, and that of comparative examples <NUM> and <NUM> after heat ageing at <NUM> in <NUM>% relative humidity, is shown in <FIG>.

Overall, the addition of a component functionalized with at least two blocked hydroxyl groups, such as hexane diol diacrylate, to a cyanoacrylate formulation comprising allyl cyanoacrylate and a rubber toughening agent provides a composition having excellent thermal ageing properties. The combination excels at <NUM> and shows <NUM>% tensile strength retention after <NUM> hours at <NUM> and <NUM>. At <NUM> good tensile strength performance is demonstrated up to the <NUM> hour mark, with a dip in performance being witnessed thereafter, before the tensile strength recovers to about <NUM> MPa.

The effect of thermal resistance conferring additives on the compositions of the invention was also investigated. Table <NUM> provides compositions with varying levels of components and additives. Examples <NUM> and <NUM> do not belong to the invention.

Formulations <NUM> and <NUM> comprise varying levels of ethyl CA and allyl CA. Both formulations comprise <NUM> wt% tetrafluoroisophthalonitrile. The initial tensile strength and thermal performance of said compositions proved excellent.

The thermal performance of formulations of table <NUM>, was also assessed. Therein, the benefit of thermal resistance conferring additives in allyl cyanoacrylate formulations was examined.

As seen above, and as further outlined in Table <NUM>, formulations of the invention further comprising phthalic anhydride and tetrafluoroisophthalonitrile demonstrated excellent thermal performance when aged for <NUM> weeks at elevated temperatures of from <NUM> to <NUM>. The effect of varying the level of tetrafluoroisophthalonitrile and hexane diol diacrylate is shown in Table <NUM>. The benefit of including a maleimide component, was also examined, and as seen in formulations <NUM> and <NUM>, this led to further enhancement of initial tensile strength performance and thermal aged perforamance.

Formulations <NUM> and <NUM> which comprise phthalic anhydride, tetrafluoroisophthalonitrile and a bismaleimide additive, specifically, bis-(<NUM>-ethyl-<NUM>-methyl-<NUM>-maleimidephenyl)methane, (available from K-I Chemical Industry Co. Ltd under the tradename BMI-<NUM>) demonstrated excellent thermal resistance from <NUM> to <NUM>. The heat ageing performance of allyl cyanoacrylate formulations were particularly improved in the <NUM> to <NUM> range. For example, formulation <NUM> had a <NUM>% retention of tensile strength after heat ageing at <NUM> for <NUM> hours (<NUM> weeks).

Table <NUM> compares the performance of formulation <NUM> which comprises allyl cyanoacrylate as the sole cyanoacrylate component, with formulation <NUM> which comprises both allyl cyanoacrylate and ethyl cyanoacrylate. The tensile strength performance of both formulations which have been a range of temperatures for <NUM> hours is tested, as is their performance under humid conditions. While heat ageing formulation <NUM> at <NUM> and <NUM>, led to an increase in tensile strength performance, formulation <NUM> retained about <NUM>% of its tensile strength when aged at <NUM> for <NUM> hours, and furthermore, retained about <NUM>% of its initial tensile strength after heat ageing at <NUM> for <NUM> hours.

As can be seen in Table <NUM>, the combination of hexanediol diacrylate, phthalic anhydride, tetrafluoroisophthalonitrile and bis-(<NUM>-ethyl-<NUM>-methyl-<NUM>-maleimidephenyl)methane significantly enhances the thermal performance, and humid ageing performance of allyl cyanoacrylate formulations.

The words "comprises/comprising" and the words "having/including" when used herein with reference to the present invention are used to specify the presence of stated features, integers, steps or components but do not preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

Claim 1:
A cyanoacrylate composition, comprising:
(a) allyl-<NUM>-cyanoacrylate,
(b) a rubber toughening agent comprised of i) reaction products of the combination of ethylene, methyl acrylate and monomers having carboxylic acid cure sites, ii) dipolymers of ethylene and methyl acrylate, and combinations of i) and ii) and
(c) a component functionalized with at least two blocked hydroxyl groups, wherein the component functionalized with at least two blocked hydroxyl groups is hexane diol diacrylate.