EP2288665A1

EP2288665A1 - Surface-promoted cure of one-part cationically curable compositions

Info

Publication number: EP2288665A1
Application number: EP09749934A
Authority: EP
Inventors: David Farrell; Ciaran Mcardle; Michael Doherty; Emilie Barriau; Rainer Schoenfeld
Original assignee: Henkel AG and Co KGaA; Henkel Loctite Ireland Ltd
Current assignee: Henkel IP and Holding GmbH
Priority date: 2008-05-23
Filing date: 2009-05-22
Publication date: 2011-03-02
Also published as: WO2009141444A1; KR20110021917A; CN102083918A; JP2011523670A

Abstract

The present invention relates to cationically curable compositions for curing on a surface comprising a cationically curable component, and an initiator component capable of initiating cure of the cationically curable component. The initiator comprises at least one metal salt, which is chosen so that it is reduced at the surface, wherein the standard reduction potential of the initiator component is greater than the standard reduction potential of the surface, and further wherein when the composition is placed in contact with the surface, the metal salt of the initiator component of the composition is reduced at the surface, thereby initiating cure of the cationically curable component of the composition. No catalytic component is required in the composition for efficient cure.

Description

Title

Surface-Promoted Cure of One-Part Cationically Curable Compositions

Field of the Invention

[0001] The present invention relates to stable one-part cationically curable compositions for curing on a surface, and uses there for.

Discussion of Background Art

Reduction-Oxidation (RedOx) Cationic Polymerisation

[0002] RedOx cationic polymerizations involve oxidation and reduction processes [Holtzclaw, H. F.; Robinson, W.R.; Odom, J. D.; General Chemistry 1991 , 9^th Ed., Heath (Pub.), p. 44]. When an atom, either free or in a molecule or ion, loses an electron or electrons, it is oxidised and its oxidation number increases. When an atom, either free or in a molecule or ion, gains an electron or electrons, it is reduced and its oxidation number decreases. Oxidation and reduction always occur simultaneously, as if one atom gains electrons then another atom must provide the electrons and be oxidised. In a RedOx couple, one species acts as a reducing agent, the other as an oxidizing agent. When a RedOx reaction occurs the reducing agent gives up or donates electrons to another reactant, which it causes to be reduced. Therefore the reducing agent is itself oxidised because it has lost electrons. The oxidising agent accepts or gains electrons and causes the reducing agent to be oxidised while it is itself reduced. A comparison of the relative oxidising or reducing strengths of strength of the two reagents in a redox couple permits determination of which one is the reducing agent and which one is the oxidising agent. The strength of reducing or oxidising agents can be determined from their standard reduction (E_reό°) or oxidation (E_0x ⁰) potentials. [0003] Onium salts have been widely used in cationically curable formulations. Extensive investigation into the use of onium salts as photoinitiators for cationic polymerisation led to the realisation that during the course of the photochemical reaction the onium cation undergoes photochemical reduction. In particular, diaryliodonium salts have been used in cationically curable formulations. Extensive investigation into the use of diaryliodonium salts (1) as photoinitiators for cationic polymerisation led to the realisation that during the course of the photochemical reaction iodine undergoes a reduction in oxidation state from +3 to +1.

[0004] Crivello et al. (J.V. Crivello and J. H. W. Lam, J. Polym. Sci. 1981 , 19, 539 - 548) propose that the action of light on the diaryliodonium salt liberates radical intermediates, see Scheme 1. A resulting cascading series of reactions results in reduction of the oxidation state of iodine in the diaryliodonium salt. The aryliodine cation radicals generated during the photolysis process are extremely reactive species and react with solvents, monomers, or impurities (denoted SH in the scheme) to produce a protonic acid. The protonic acid in turn reacts with the cationically curable monomer resulting in polymerisation.

₊ - hv + - _t

Ar₂I X *- [ Ar₂I X ]

[ Ar₂I⁺ X ] ^* *-Ar— h + Ar - + X ^~

⁺ +

Ar-I ^■ + SH *-Ar — I H + S ■

+

Ar-I H *- Ar-I + H ⁺

H ⁺ + X ^" ^ HX

Scheme 1

[0005] Diaryliodonium salts as initiators of cationic polymerisation via RedOx type chemistry have also been the subject of investigation. The general premise here was that, in the presence of a chemical reducing agent, the iodine component of the diaryliodonium salt could be reduced resulting in the generation of the protonic acid species HX, as shown in Scheme 2 (below), which will in turn initiate cationic polymerisation.

ArJ ⁺ X - + R-M -» Ad •*^■ Ar* + R* *^■ MX Scheme 2 [0006] Crivello and co-workers developed diaryliodonium salt/reducing agent couples incorporating ascorbic acid (J. V. Crivello and J. H. W. Lam, J. Polym. Sci. 1981 , 19, 539 - 548), benzoin (J.V. Crivello and J. L. Lee, J. Polym. Sci. 1983, 21 , 1097 - 1110), and tin (J.V. Crivello and J. L. Lee, Makromol. Chem. 1983, 184, 463 - 473). Direct reduction of the iodonium salt (an onium salt) by the reducing agent is inefficient. Consequently, there is the need to incorporate a copper catalyst in order to achieve efficient polymerization. Thus, such RedOx cationic initiation packages are effectively three component systems - the salt, the reducing agent and the catalyst. [0007] These Crivello RedOx systems thus suffer from the drawback that direct reduction of the "onium" salt by the reducing agent is highly inefficient. Copper salts were required for efficient electron transfer. However, even in the absence of a catalyst very slow electron transfer between the reducing agent and the onium salt is observable rendering compositions having reducing agent and onium salt together in a composition inappropriate for long-term storage. There is thus still an unsatisfied need for suitable curable formulations which provide alternatives to the conventional onium formulations set out above.

Lewis Acid Metallic Salts as Initiators for Cationic Polymerisation: [0008] Lewis acids in the form of metal salts have been used as initiators of cationic polymerization (Collomb, J. et al.; Eur. Poly. J. 1980, 16, 1135-1144; Collomb, J.; Gandini, A.; Cheradamme, H.; Macromol. Chem. Rapid Commun. 1980, 1 , 489-491 ). Many strong Lewis acid initiators have been shown to function by the direct initiation of the monomer (Scheme 3) (Collomb, J.; Gandini, A.; Cheradamme, H.; Macromol. Chem. Rapid Commun. 1980, 1 , 489-491 ). The stronger the Lewis acid the more pronounced is its initiating power.

M(XJn + P=C *- (X)_n-iM— C— C⁺ X^"

Scheme 3

[0009] Not all Lewis acid metal salts react with cationically polymerizable monomers. Many can be formulated as the initiating component in storage stable one-component cationically polymerisable systems (Castell, P. et al.; Polymer2000, 41 (24), 8465-8474). In these instances decomposition of the initiator and activation of polymerization is typically achieved by thermal or electromagnetic radiation curing processes (Castell, P. et al.\ Polymer2000, 41 (24), 8465-8474).

[0010] There is thus still an unsatisfied need for suitable curable formulations which provide alternatives to the conventional Lewis acid metal salt formulations set out above, which will cure in the absence of thermal or electromagnetic radiation curing processes.

Existing Coating Technologies

[0011] E-Coating (Electrocoating / Electrodeposition coating) is a method of painting which uses electrical current to deposit the paint. The process works on the principal of "Opposites Attract". This process is also known as electrodeposition. The fundamental physical principle of electrocoat is that materials with opposite electrical charges attract each other. An electrocoat system applies a DC charge to a metal part immersed in a bath of oppositely charged paint particles. The paint particles are drawn to the metal part and paint is deposited on the part, forming an even, continuous film over every surface, in every crevice and corner, until the electrocoat reaches the desired thickness. At that thickness, the film insulates the part, so attraction stops and the electrocoat process is complete. Depending on the polarity of the charge, electrocoat is classified as either anodic or cathodic. A major disadvantage of this technology is that it suffers from the Faraday Cage effect and so cannot coat inside metallic tubes, etc. It is necessary to bake the material in order to cross-link and cure the paint film. [0012] The present inventors aim to utilise Redox chemistry as an alternative coating technology.

Summary of the Invention

[0013] In one aspect the present invention provides a stable one-part cationically curable composition for curing on a surface comprising: (i) a cationically curable component; and (ii) an initiator component comprising at least one metal salt;

wherein the standard reduction potential of the initiator component is greater than the standard reduction potential of the surface, and wherein when the composition is placed in contact with the surface, the metal salt of the initiator component of the composition is reduced at the surface, thereby initiating cure of the cationically curable component of the composition. [0014] References to standard reduction potentials in this specification indicate the tendency of a species to acquire electrons and thereby be reduced. Standard reduction potentials are measured under standard conditions: 25 ⁰C, 1 M concentration, a pressure of 1 atm and elements in their pure state.

[0015] Desirably, the metal salt of the composition comprises a transition metal cation. Suitable metals include silver, copper and combinations thereof. The metal salt may be substituted with a ligand. The metal salt counterions may be chosen from the group consisting Of CIO₄ ^", BF₄ ^", PF₆ ^", SbF₆ ^",AsF₆ ^", (C₆F₅)₄B anion, (C₆F₅)₄Ga anion, Carborane anion, triflimide (trifluoromethanesulfonate) anion, bis-triflimide anion, anions based thereon and combinations thereof. Further desirably, the metal salt counterions may be chosen from the group consisting Of CIO₄ ^", BF₄ ^", PF₆ ^", SbF₆ ^" and combinations thereof. [0016] The solubility of the metal salt may be modified by changing the counterion, the addition and/or substitution of ligands to the metal of the metal salt and combinations thereof. This will allow for efficient electron transfer between the surface and the metal salt to be observed as appropriate solubility is achieved.

[0017] The cationically curable component desirably has at least one functional group selected from the group consisting of epoxy, vinyl, oxetane, thioxetane, episulfide, tetrahydrofuran, oxazoline, oxazine, lactone, trioxane, dioxane, styrene with combinations thereof also being embraced by the present invention. Further desirably, the cationically curable component has at least one functional group selected from the group consisting of epoxy, episulfide, oxetane, thioxetane, and combinations thereof. Preferably, the cationically curable component has at least one functional group selected from the group consisting of epoxy, oxetane and combinations thereof. [0018] Desirably, the surfaces to which the compositions of the present invention are applied may comprise a metal, metal oxide or metal alloy. Further desirably, the surface may comprise a metal or metal oxide. Preferably, the surface may comprise a metal. Suitable surfaces can be selected from the group consisting of iron, steel, mild steel, gritblasted mild steel, aluminium, aluminium oxide, copper, zinc, zinc oxide, zinc bichromate, and stainless steel. References to aluminium and aluminium oxide include alclad aluminium (low copper content), and oxide removed alclad aluminium (low copper content) respectively. Desirably, the surface can be selected from the group consisting of steel and aluminium. Metal salts suitable for use in compositions for curing on steel or aluminium surfaces may be chosen from the group consisting of silver salts, copper salts and combinations thereof, and wherein the counterions of the silver and copper salts may be chosen from the group consisting of CIO4 , BF₄ , PF₆ , SbF₆ and combinations thereof.

[0019] In general, the inventive compositions disclosed herein can cure on oxidised metal surfaces without the need for additional etchant or oxide remover. However, the compositions of the invention may optionally include an oxide remover. For example, including an etchant or oxide remover, such as those comprising chloride ions and/or a zinc (II) salt, in formulations of the invention may allow etching of any oxide layer. This will in turn expose the (zero-oxidation state) metal below, which is then sufficiently active to allow reduction of the transition metal salt.

[0020] The RedOx cationic systems discussed herein do not require any additional reducing agent. They are stable until applied to a substrate which is capable of participating in a RedOx reaction, thus fulfilling the role of a conventional reducing agent component. The compositions of the present invention can thus be utilized in any application in which curing on a metal surface is required. The compositions of the invention are storage stable even as a one-part composition and require no special packaging unlike prior art compositions, which tend to be multi-component compositions. [0021] The compositions of the present invention do not require an additional catalyst for efficient curing. The present invention utilizes appropriate selection of the initiator component relative to the surface on which the composition is to be applied and cured. Thus surface promoted RedOx chemistry can be utilized to initiate cure in cationically curable compositions. However, it will be appreciated that compositions according to the invention may optionally comprise a catalyst to effect electron transfer between the surface and the metal salt of the composition. This may be useful where even greater cure speeds are required. Suitable catalysts include transition metal salts. [0022] The inventive compositions described herein will generally be useful as adhesives, sealants or coatings, and can be used in a wide range of industrial applications including metal bonding, thread-locking, flange sealing, and structural bonding amongst others.

[0023] The inventive compositions may be encapsulated if it is desired to do so. Suitable encapsulation techniques comprise, but are not limited to, coacervation, softgel and co-extrusion.

[0024] Alternatively, the inventive compositions may be used in a pre-applied format. It will be appreciated that the term pre-applied is to be construed as taking the material in an encapsulated form (typically but not necessarily micro-encapsulated) and dispersing said capsules in a liquid binder system that can be dried (e.g. thermal removal of water or an organic solvent, or by photo-curing the binder) on the desired substrate. A film of material remains which contains the curable composition (for example adhesive liquid for example in the form of filled capsules). The curable composition can be released for cure by physically rupturing the material (for example capsules) when the user wishes to activate the composition, e.g. in pre-applied threadlocking adhesives the coated screw threaded part is activated by screwing together with its reciprocally threaded part for example a threaded receiver or nut.

[0025] The invention further extends to a process for bonding two substrates together comprising the steps of:

(i) applying a composition comprising: i) a cationically curable component; and ii) an initiator component comprising at least one metal; to at least one substrate, and

(ii) mating the first and second substrates so as to form a bond with the composition, where the standard reduction potential of the initiator component is greater than the standard reduction potential of at least one of the substrates. [0026] In one particular embodiment, both substrates comprise a metal. Where the second substrate comprises a different metal substrate to the first metal substrate the composition of the invention may comprise more than one type of metal salt. Thus, the invention also provides for curable compositions wherein the inclusion of more than one type of metal salt can be used to bond different metal substrates together. [0027] Desirably, the metal of the metal salt of the inventive compositions of the present invention is lower in the reactivity series than the metal surface on which it is to be cured. [0028] Metallic substrates can also be bonded to non-metallic substrates. For instance mild steel may be bonded to e-coated steel (e-coat is an organic paint which is electrodeposited, with an electrical current, to a metallic surface, such as steel). [0029] Moreover, the inventive compositions of the present invention can be utilised to form (polymer) coatings on parts such as metallic parts. [0030] The invention also relates to a pack comprising: a) a container; and b) a cationically curable composition according to the present invention, wherein the container may be air permeable. Alternatively, the container may not air permeable.

[0031] In a further aspect, the present invention provides for a stable one-part cationically curable composition for curing on a surface comprising:

(i) a cationically curable component;

(ii) an accelerator species comprising at least one vinyl ether functional group; and

(iii) an initiator component comprising at least one metal salt;

wherein the standard reduction potential of the initiator component is greater than the standard reduction potential of the surface, and wherein when the composition is placed in contact with the surface, the metal salt of the initiator component of the composition is reduced at the surface, thereby initiating cure of the cationically curable component of the composition. [0032] References to standard reduction potentials in this specification indicate the tendency of a species to acquire electrons and thereby be reduced. Standard reduction potentials are measured under standard conditions: 25 ⁰C, 1 M concentration, a pressure of 1 atm and elements in their pure state.

[0033] The accelerator species comprising at least one vinyl ether functional group greatly enhances the rate of cure. The accelerator species may embrace the following structures:

wherein m can be 0 or 1 ; n can be 0 - 5;

Ri, R₂, and R₃ can be the same or different and can be selected from the group consisting of hydrogen, Ci-C₂oalkyl chain (linear, branched or cyclic) and C₅-C₂O aryl moiety, and combinations thereof;

X can be a CrC₃O saturated or unsaturated, cyclic or acyclic moiety; and Ri, R₂, R₃ and X may or may not independently contain ether linkages, sulfur linkages, carboxyl groups, and carbonyl groups. [0034] It will be appreciated by a person skilled in the art that X, Ri, R₂, and Ra in the above formulae may comprise substituted variants and derivatives thereof, e.g. halogen substituted, heteroatom substituted, etc. without substantially altering the function of the molecules.

[0035] Desirably, the vinyl ether component is selected from the group consisting of 1 ,4- Butanediol divinyl ether, 1 ,4-Butanediol vinyl ether, bis-(4-vinyl oxy butyl) adipate, Ethyl- 1-propenyl ether, bis-(4-vinyl oxy butyl) isophthalate, Bis[4-(vinyloxy)butyl] succinate, Bis[4-(vinyloxy)butyl] terephthalate, Bis[[4-[(vinyloxy)methyl]cyclohexyl]methyl] isophthalate, Bis[[4-[(vinyloxy)methyl]cyclohexyl]methyl] glutarate, Tris(4- vinyloxybutyl)trimellitate, VEctomer™ 2020 (CAS no. 143477-70-7), and combinations thereof.

[0036] The accelerator component comprising the at least one vinyl ether functional group greatly accelerates the rate of cationic polymerization. The accelerator component may be present in 5-98% w/w of the total composition, for example 5-50% w/w of the total composition, desirably from 5-30% w/w of the total composition. [0037] Desirably, the metal salt of the composition comprises a transition metal cation. Suitable metals include silver, copper and combinations thereof. The metal salt may be substituted with a ligand. The metal salt counterions may be chosen from the group consisting Of CIO₄ ^", BF₄ ^", PF₆ ^", SbF₆ ^",AsF₆ ^", (C₆F₅)₄B anion, (C₆F₅)₄Ga anion, Carborane anion, triflimide (trifluoromethanesulfonate) anion, bis-triflimide anion, anions based thereon and combinations thereof. Further desirably, the metal salt counterions may be chosen from the group consisting Of CIO₄ ^", BF₄ ^", PF₆ ^", SbF₆ ^" and combinations thereof. [0038] The solubility of the metal salt may be modified by changing the counterion, the addition and/or substitution of ligands to the metal of the metal salt and combinations thereof. This will allow for efficient electron transfer between the surface and the metal salt to be observed as appropriate solubility is achieved.

[0039] The cationically curable component desirably has at least one functional group selected from the group consisting of epoxy, vinyl, oxetane, thioxetane, episulfide, tetrahydrofuran, oxazoline, oxazine, lactone, trioxane, dioxane, styrene with combinations thereof also being embraced by the present invention. Further desirably, the cationically curable component has at least one functional group selected from the group consisting of epoxy, episulfide, oxetane, thioxetane, and combinations thereof. Preferably, the cationically curable component has at least one functional group selected from the group consisting of epoxy, oxetane and combinations thereof. [0040] Desirably, the surfaces to which the compositions of the present invention are applied may comprise a metal, metal oxide or metal alloy. Further desirably, the surface may comprise a metal or metal oxide. Preferably, the surface may comprise a metal. Suitable surfaces can be selected from the group consisting of iron, steel, mild steel, gritblasted mild steel, aluminium, aluminium oxide, copper, zinc, zinc oxide, zinc bichromate, and stainless steel. References to aluminium and aluminium oxide include alclad aluminium (low copper content), and oxide removed alclad aluminium (low copper content) respectively. Desirably, the surface can be selected from the group consisting of steel and aluminium. Metal salts suitable for use in compositions for curing on steel or aluminium surfaces may be chosen from the group consisting of silver salts, copper salts and combinations thereof, and wherein the counterions of the silver and copper salts may be chosen from the group consisting of CIO₄ ^", BF₄ ^", PF₆ ^", SbF₆ ^" and combinations thereof.

[0041] The RedOx cationic systems discussed herein do not require any additional reducing agent. They are stable until applied to a substrate which is capable of participating in a RedOx reaction, thus fulfilling the role of a conventional reducing agent component. The compositions of the present invention can thus be utilized in any application in which curing on a metal surface is required. The compositions of the invention are storage stable even as a one-part composition and require no special packaging unlike prior art compositions, which tend to be multi-component compositions. [0042] The compositions of the present invention do not require an additional catalyst for efficient curing. The present invention utilizes appropriate selection of the initiator component relative to the surface on which the composition is to be applied and cured. Thus surface promoted RedOx chemistry can be utilized to initiate cure in cationically curable compositions. However, it will be appreciated that compositions according to the invention may optionally comprise a catalyst to effect electron transfer between the surface and the metal salt of the composition. This may be useful where even greater cure speeds are required. Suitable catalysts include transition metal salts. [0043] The inventive compositions described herein will generally be useful as adhesives, sealants or coatings, and can be used in a wide range of industrial applications including metal bonding, thread-locking, flange sealing, and structural bonding amongst others. [0044] The inventive compositions may be encapsulated if it is desired to do so. Suitable encapsulation techniques comprise, but are not limited to, coacervation, softgel and co-extrusion.

[0045] Alternatively, the inventive compositions may be used in a pre-applied format. It will be appreciated that the term pre-applied is to be construed as taking the material in an encapsulated form (typically but not necessarily micro-encapsulated) and dispersing said capsules in a liquid binder system that can be dried (e.g. thermal removal of water or an organic solvent, or by photo-curing the binder) on the desired substrate. A film of material remains which contains the curable composition (for example adhesive liquid for example in the form of filled capsules). The curable composition can be released for cure by physically rupturing the material (for example capsules) when the user wishes to activate the composition, e.g. in pre-applied threadlocking adhesives the coated screw threaded part is activated by screwing together with its reciprocally threaded part for example a threaded receiver or nut.

[0046] The invention further extends to a process for bonding two substrates together comprising the steps of:

(i) applying a composition comprising: i) a cationically curable component; ii) an accelerator species comprising at least one vinyl ether functional group; and iii) an initiator component comprising at least one metal salt; to at least one substrate, and (ii) mating the first and second substrates so as to form a bond with the composition, where the standard reduction potential of the initiator component is greater than the standard reduction potential of at least one of the substrates. [0047] In one particular embodiment, both substrates comprise a metal. Where the second substrate comprises a different metal substrate to the first metal substrate the composition of the invention may comprise more than one type of metal salt. Thus, the invention also provides for curable compositions wherein the inclusion of more than one type of metal salt can be used to bond different metal substrates together. [0048] Desirably, the metal of the metal salt of the inventive compositions of the present invention is lower in the reactivity series than the metal surface on which it is to be cured. [0049] Metallic substrates can also be bonded to non-metallic substrates. For instance mild steel may be bonded to e-coated steel (e-coat is an organic paint which is electrodeposited, with an electrical current, to a metallic surface, such as steel). [0050] Moreover, the inventive compositions of the present invention can be utilised to form (polymeric) coatings on parts, for example on metallic parts. [0051] The invention also relates to a pack comprising: a) a container; and b) a cationically curable composition, comprising an accelerator species comprising at least one vinyl ether functional group; wherein the container may be air permeable. Alternatively, the container may not air permeable.

[0052] In yet a further aspect, the present invention provides for a composition for and a method of coating surfaces. It is envisaged that cross-linking and cure can be achieved directly on the surface, thus eliminating the necessity for an additional baking step.

Moreover, it is envisaged that the coating method will allow coating of inside of surfaces, for example surfaces that can exhibit a Faraday Cage effect preventing coating inside tubes, etc.

[0053] The invention provides a stable one-part cationically curable coating composition for coating a surface comprising:

(i) a cationically curable component; and

(ii) an initiator component comprising at least one metal salt; wherein the standard reduction potential of the initiator component is greater than the standard reduction potential of the surface, and wherein when the composition is placed in contact with the surface, the metal salt of the initiator component of the composition is reduced at the surface, thereby initiating cure of the cationically curable component of the composition. [0054] References to standard reduction potentials in this specification indicate the tendency of a species to acquire electrons and thereby be reduced. Standard reduction potentials are measured under standard conditions: 25 ⁰C, 1 M concentration, a pressure of 1 atm and elements in their pure state.

[0055] Desirably, the metal salt of the cationically curable coating composition comprises a transition metal cation. Suitable metals include silver, copper and combinations thereof. The metal salt may be substituted with a ligand. The metal salt counterions may be chosen from the group consisting Of CIO₄ ^", BF₄ ^", PF₆ ^", SbF₆ ^",AsF₆ ^", (C₆F₅)₄B anion, (CeFs)₄Ga anion, Carborane anion, triflimide (trifluoromethanesulfonate) anion, bis-triflimide anion, anions based thereon and combinations thereof. Further desirably, the metal salt counterions may be chosen from the group consisting of CIO₄ ^", BF₄ ^", PF₆ ^", SbF₆ ^" and combinations thereof.

[0056] The cationically curable component of the coating composition desirably has at least one functional group selected from the group consisting of epoxy, vinyl, vinyl ether, oxetane, thioxetane, episulfide, tetrahydrofuran, oxazoline, oxazine, lactone, trioxane, dioxane, styrene with combinations thereof also being embraced by the present invention. Further desirably, the cationically curable component has at least one functional group selected from the group consisting of vinyl ether, epoxy, oxetane, thioxetane, episulfide and combinations thereof. Preferably, the cationically curable component has at least one functional group selected from the group consisting of vinyl ether, epoxy, oxetane and combinations thereof.

[0057] In a preferred embodiment the cationically curable component will comprise a vinyl ether and a least one other cationically curable component selected from the group consisting of epoxy, vinyl, oxetane, thioxetane, episulfide, tetrahydrofuran, oxazoline, oxazine, lactone, trioxane, dioxane, styrene and combinations thereof. The vinyl ether functional group and the at least one other cationically curable functional group may be on the same molecule/monomer.

[0058] It will be appreciated that the cationically curable coating compositions of the present invention may optionally contain fillers, dyes, pigments, and lubricating elements. Furthermore, the cationically curable monomer may be adapted to be provide curable hydrophobic monomers, bifunctional monomers and secondarily curable components, including vulcanising agents, curatives, etc. Modification of the curable monomer can be utilised to modulate the properties of the deposited film, facilitating the control of: surface tension and polarity, lubriciousness, tacticity, colour hardness, scratch resistance, surface reactivity to subsequent coatings and or adhesives, and reactivity towards light, heat, moisture to promote further reaction within the surface deposited film itself or between the surface deposited film and a material in contact with same. [0059] The solubility of the metal salt in the cationically curable coating compositions may be modified by changing the counterion, the addition and/or substitution of ligands to the metal of the metal salt and combinations thereof. This will allow for efficient electron transfer between the surface and the metal salt to be observed as appropriate solubility is achieved. [0060] Desirably, the surfaces to which the coating compositions of the present invention are applied may comprise a metal, metal oxide or metal alloy. Further desirably, the surface may comprise a metal or metal oxide. Preferably, the surface may comprise a metal. Suitable surfaces can be selected from the group consisting of iron, steel, mild steel, gritblasted mild steel, aluminium, aluminium oxide, copper, zinc, zinc oxide, zinc bichromate, and stainless steel. References to aluminium and aluminium oxide include alclad aluminium (low copper content), and oxide removed alclad aluminium (low copper content) respectively. Desirably, the surface can be selected from the group consisting of steel and aluminium.

[0061] Metal salts suitable for use in cationic coating compositions for coating on steel or aluminium surfaces may be chosen from the group consisting of silver salts, copper salts and combinations thereof, and wherein the counterions of the silver and copper salts may be chosen from the group consisting of CICU^", BF₄ ^", PF₆ ^", SbF₆ ^" and combinations thereof.

[0062] Further desirably, the metal of the metal salt of the inventive coating compositions of the present invention is lower in the reactivity series than the metal surface on which it is to be cured. Thus, the inventive compositions of the present invention allow for coating on a number of different metal surfaces. [0063] All references to the term "coating" in this specification shall be interpreted to comprise a polymeric film or coating on a surface. In addition, all references to a functionalized polymeric films or coatings below apply to both cross-linked and non cross-linked coatings.

[0064] It will be appreciated that the curable component can be functionalized to confer desirable properties on the polymerised film. The monomer can be modified to control the following characteristics of the coatings; surface tension and polarity, lubriciousness, tacticity, colour hardness, scratch resistance, and reactivity to subsequent coatings and/or adhesives. Moreover, the functionalized coating could be subjected to stimuli such as light, heat, moisture, etc. to encourage further reaction within the surface deposited coating itself or between the surface deposited coating and a material in contact with same.

[0065] For example, a cationically curable monomer functionalized with a radically curable monomer to create a dual curable system; a cationically curable monomer functionalized with secondary curable components, including vulcanising agents, curatives, etc., a coating functionalized for control of surface tension and polarity, lubriciousness, tacticity, colour hardness, scratch resistance, reactivity to subsequent coatings and/or adhesives, reactivity towards light, heat, moisture, etc. to promote further reaction within the surface deposited film itself or between the surface deposited film and a material in contact with same.

[0066] The RedOx cationically curable coating compositions discussed herein do not require any additional reducing agent. They are stable until contacted with a metallic substrate which is capable of participating in a RedOx reaction (or other surface capable of participating in a RedOx reaction), thus fulfilling the role of a conventional reducing agent component. The RedOx cationically curable coating compositions of the invention are storage stable as a one-part composition and require no special packaging unlike prior art compositions, which tend to be multi-component compositions. [0067] The coating compositions of the present invention do not require an additional catalyst for efficient curing. The present invention utilizes appropriate selection of the metal salt component relative to the surface on which the coating composition is to be applied and cured. However, it will be appreciated that coating compositions according to the invention may optionally comprise a catalyst to effect electron transfer between the surface and the metal salt of the composition. This may be useful where even greater cure speeds are required. Suitable catalysts include transition metal salts. [0068] The kinetics of polymerisation/film formation is proportional to the difference in standard reduction potential between the surface and the metal salt in the composition. Cross-linking is achieved directly on the surface. However, it will be appreciated that a post polymerisation baking step can be applied.

[0069] The invention further extends to a method of coating a substrate comprising applying a coating composition comprising: i) a cationically curable component; and ii) an initiator component comprising at least one metal salt; to the substrate, wherein the standard reduction potential of the initiator component is greater than the standard reduction potential of the surface.

[0070] It will be appreciated that the method of coating a substrate may further comprise the steps of: i) cleaning the substrate prior to application of the coating composition; ii) dipping the substrate into said coating composition of the present invention or an emulsion of said coating composition; and iii) rinsing the coated substrate when polymerisation is complete. [0071] The step of cleaning the substrate may comprise washing with acid, base, detergent, aqueous solutions, water, deionised water, organic solvents and combinations thereof. The emulsion of the coating composition of the present invention, referred to in step (ii) may comprise an aqueous or an organic emulsion. The step of rinsing the coated substrate may comprise rinsing with water and/or rinsing with a rinsing solution beneficial to the properties of the coating/film. [0072] The invention also relates to a pack comprising: a) a container; and b) a cationically curable coating composition according to the present invention.

The container may be air permeable. Alternatively, the container may not air permeable.

[0073] The invention further extends to a coating applied to a substrate utilising the methods discussed above. The substrate may be metallic.

[0074] In a further aspect, the invention extends to a coated article comprising a coating applied to a substrate utilising the methods discussed above. The substrate may be metallic. The invention further provides for a coated article comprising a coating applied to a substrate. The substrate may comprise a metallic component. [0075] Furthermore, the coated article may have a curable composition applied thereto. Thus, facilitating mating with a second substrate. The coated article may have a second substrate adhered thereto.

[0076] As will be appreciated by a person skilled in the art, the metal salt in the compositions of the present invention will be chosen such that the anion of the metal salt will not result in quenching of the polymerization/cure process.

[0077] Where suitable, it will be appreciated that all optional and/or additional features of one embodiment of the invention may be combined with optional and/or additional features of another/other embodiment(s) of the invention.

Brief Description of the Drawings:

[0078] Additional features and advantages of the present invention are described in, and will be apparent from, the detailed description of the invention and from the drawings in which: [0079] Figure 1 is a plot of the Exotherm of Polymerisation of a two-part system comprising the RedOx couple ascorbyl-θ-palmitateidiphenyliodonium hexafluorophosphate in an epoxy resin as a function of time (in days) at a temperature of

25 ⁰C.

[0080] Figure 2 is a FTIR-ATR spectra (3100 cm^"1 to 600 cm^"1) of surface promoted epoxy polymerisation on grit blasted mild steel at 25 ^°C.

[0081] Figure 3 is a FTIR-ATR spectra (1 190 cm^"1 to 760 cm^"1) of surface promoted epoxy polymerisation on grit blasted mild steel at 25 ^°C.

[0082] Figure 4 is a plot of percentage polymerisation versus time for the cationically curable coating composition depicted in Figures 2 and 3.

Detailed Description of the Invention:

[0083] It was found that by using a commercially available copper priming aerosol applied to the cycloaliphatic epoxy resin Cyracure 6110 containing the Crivello-type redox couple "Ascorbyl-6-hexadecanoate:Diphenyliodonium Hexafluorophosphate" polymerization at room temperature to give usable cure strengths on a reasonable timescale (<24 hr) was achievable.

[0084] Of the Crivello-type redox couples, the Ascorbyl-6-hexadecanoate: Diphenyliodonium Hexafluorophosphate was the least stable and not usable in a reliable two-component configuration. Polymerization did not occur without copper primer being applied to the substrate. All other possible redox couples based upon this and alternative onium-type salts were ineffective as surface curing adhesives even when the substrate was primed with copper. In Crivello's paper (Crivello, J.V.; Lee, J. L.; J. Polym. Sci. Part A: PoIm. Chem. 1983, 21 , 1097-11 10) the suggestion was made that a two-part configuration of these redox cationic system components may be possible. Our investigations have shown this to be unlikely as any combination of these three components in a two-part configuration is storage unstable on a practical timescale (see Figure 1 ).

[0085] Figure 1 is a graphical representation of the stability of a two-part system comprising the Ascorbyl-6-palmitate:Diphenyliodonium Hexafluorophosphate redox couple in the epoxy resin Cyracure 6110, monitored by the Exotherm of Polymerisation of 10 g samples. The stability of the composition was evaluated by measuring the Exotherm of Polymerisation of 10 g samples of the above two-part system stored over varying periods of time. The graph clearly shows an inverse relationship between heat liberated and the number of days the system was stored prior to use. After 112 days a significant reduction in the measured exotherm of polymerisation was observable indicating considerably reduced reactivity of the composition. Additionally, there was a significant increase in the formulation viscosity so the formulation was difficult to dispense and work with.

[0086] The electrochemical series is a measure of the oxidising and reducing power of a substance based on its standard potential. The standard potential of a substance is measure relative to the hydrogen electrode. A metal with a negative standard (reduction) potential has a thermodynamic tendency to reduce hydrogen ions in solution, whereas the ions of a metal with a positive standard potential have a tendency to be reduced by hydrogen gas. The reactivity series, shown in Scheme 4 (below), is an extension of the electrochemical series.

Most Reactive

Least Reactive

Scheme 4

[0087] Ordinarily, only a metal or element positioned higher in the reactivity series can reduce another metal or element that is lower down in the reactivity series, e.g. Iron can reduce Tin but not Potassium. It is appreciated that the order of the reactivity series can be (changed) inverted from that shown in Scheme 4. The terms "higher" and "lower" will be understood however as referring to a reactivity series having at the most reactive at the top and the least reactive at the bottom in the sequence shown in Scheme 4. In any event in the context of the present invention it will be appreciated that the metal of the metal salt is chosen so that it is reducible at the surface to which it is applied.

Examples:

[0088] All preparations discussed below were carried out in the dark as these salts are known to be photosensitive. All formulations were mixed thoroughly for a period of 16 hr prior to use to ensure homogeneity.

General Procedure for Testing Formulations:

[0089] A standard test method was followed for testing all adhesive formulations based on ASTM E177 and ASTM E6.

Apparatus

Tension testing machine, equipped with a suitable load cell.

Test Specimens

Lap-shear specimens, as specified in the quality specification, product or test program.

Assembly procedure

1. Five test specimens were used for each test.

2. Specimen surface was prepared where necessary, e.g. mild steel lap-shears are grit blasted with silicon carbide.

3. Test specimens were cleaned by wiping with acetone or isopropanol before assembly.

4. Bond area on each lap-shear was 322.6 mm² or 0.5 in². This is marked before applying the adhesive sample.

5. A sufficient quantity of adhesive was applied to the prepared surface of one lap- shear.

6. A second lap-shear was placed onto the adhesive and the assembly was clamped on each side of the bond area. Test Procedure

After allowing for cure as specified in test program the shear strength was determined as follows:

1. The test specimen was placed in the grips of the testing machine so that the outer 25.4 mm (1 in.) of each end were grasped by the jaws. The long axis of the test specimen coincided with the direction of the applied tensile force through the centre line of the grip assembly.

2. The assembly was tested at a crosshead speed of 2.0 mm/min or 0.05 in./min, unless otherwise specified.

3. The load at failure was recorded.

The following information was recorded:

1. Identification of the adhesive including name or number, and lot number.

2. Identification of the test specimens used including substrate and dimensions.

3. Surface preparation used to prepare the test specimens.

4. Cure conditions (Typically ambient room temperature only, 20 - 25°C).

5. Test Conditions (Standard Temperature and Pressure, i.e. Room temperature).

6. Environmental conditioning, if any (None, all substrates to be bonded are freshly prepared before use).

7. Number of specimens tested, if other than 5 (Typically an average of 5 results for each quoted result).

8. Results for each specimen.

9. Average shear strength for all replicates.

10. Failure mode for each specimen when required by the quality specification, product profile, or test program.

11. Any deviation from this method.

RedOx Cationic Systems without vinyl ether component::

General Procedure for Preparation of Formulations

[0090] To monomer (10 g) was added a quantity of initiator salt. The salt was thoroughly dissolved in the monomer by continuous stirring (16 hours) at room temperature. All samples were kept covered to exclude light during preparation and while in storage. Example 1 :

(Diphenyliodonium)PF₆ (0.20 g) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 61 10, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (10 g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: No Cure

Glass Lapshears: No Cure Example 2:

[Ag(Cyclohexen)₂]SbF₆ (0.19 g, 0.47 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (10 g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 3.5 N/mm² Example 3:

[Ag(Cyclododecene)₂]SbF6 (0.27 g, 0.47 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (10 g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 4 N/mm² Example 4:

[Ag(Hexadien)n]SbF₆ (0.19 g, 0.47 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (10 g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 2.5 N/mm² Example 5:

[Ag(1 ,9-Decadiene)n]SbF₆ (0.24 g, 0.47 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (10 g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 2.5 N/mm² Example 6: [Ag(1 ,7-octadiene)_n]SbF₆ (0.21 g, 0.47 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (10 g).

Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 3.5 N/mm² Example 7:

[Ag(15-Crown-5)]SbF₆ (0.32 g, 0.47 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (10 g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 5.5 N/mm² Example 8:

[Ag(1 ,5-Cyclooctadien)₂]SbF₆ (0.24 g, 0.47 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (10 g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 5.5 N/mm²

Aluminum: 3.5 N/mm²

Aluminium (Alclad - Low Copper): 2.0 N/mm²

Aluminium (Scratched to remove oxide): 5.0 N/mm²

Stainless steel: 3.0 N/mm²

RedOx Cationic Systems with vinyl ether component: General Procedure for Preparation of Formulations

[0030] To a quantity of monomer was added a quantity of initiator salt and a quantity of accelerator. The salt was thoroughly dissolved in the monomer by continuous stirring (16 hours) at room temperature. All samples were kept covered to exclude light during preparation and while in storage. Example 1 [Control A]:

Diphenyliodonium PF₆ (0.2Og, 0.43mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

99 Grit Blasted Mild Steel Lapshears: No Cure

Glass Lapshears: No Cure Example 2 [Control B]:

[Ag(1 ,5-Cyclooctadiene)2] SbF₆ (0.24 g, 0.43 mmol) was dissolved in the cycloaliphatic monomer Cyracure 61 10 (1O g, 40 mmol). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 4 N/mm² Example 3:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24 g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm²

Plain Mild Steel Lapshears: 7 N/mm²

Alclad Aluminium (Low Copper Content) 2.5 N/mm²

Alclad Aluminium (Oxide Removed) 5.0 N/mm²

Standard Aluminium 10 N/mm²

Copper 5.2 N/mm²

Stainless Steel 6.2 N/mm²

Zinc Bichromate 5.0 N/mm²

E-Coated Steel to Grit Blasted Mild Steel Lapshears: 20 N/mm²

Glass Lapshears: No Cure

Adhesive performance following 4 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 9 N/mm² Example 3a:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.12 g, 0.215 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Adhesive performance following 4 hr at 25 ⁰C on: Grit Blasted Mild Steel Lapshears: 9 N/mm2

Accelerators & Accelerator Concentrations Example 4:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol vinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 5 N/mm² Example 5:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator 1 ,4-Butanediol vinyl ether (0.5g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 6:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator VEctomer™ 4060: bis-(4-vinyl oxy butyl) adipate {CAS # 135876-36-7} (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 12 N/mm² Example 7:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator VEctomer™ 4060: bis-(4-vinyl oxy butyl) adipate {CAS # 135876-36-7} (0.5g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 15 N/mm² Example 8: [Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the accelerator VEctomer™ 4060: bis-(4-vinyl oxy butyl) adipate {CAS # 135876-36- 7} (10.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 7 N/mm² Example 9:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 10:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator 1 ,4-Butanediol divinyl ether (0.5g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 11 :

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator Ethyl-1-propenyl ether, mixture of cis and trans (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 18 N/mm² Example 12:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator Ethyl-1-propenyl ether, mixture of cis and trans (0.5g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 18 N/mm² Example 13: [Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator VEctomer™ 4010: bis-(4-vinyl oxy butyl) isophthalate {CAS # 130066-57-8} (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 9 N/mm² Example 14:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator VEctomer™ 4010: bis-(4-vinyl oxy butyl) isophthalate {CAS # 130066-57-8} (0.5g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 18 N/mm² Example 15:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the accelerator VEctomer™ 4010: bis-(4-vinyl oxy butyl) isophthalate {CAS # 130066-57-8} (10.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 15 N/mm² Example 16:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator VEctomer™ 4030: Bis[4-(vinyloxy)butyl] succinate {CAS # 135876-32-3} (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 23 N/mm² Example 17:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator VEctomer™ 4030: Bis[4-(vinyloxy)butyl] succinate {CAS # 135876-32-3} (0.5g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 11 N/mm² Example 18: [[Ag(1 , 5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the accelerator VEctomer™ 4030: Bis[4-(vinyloxy)butyl] succinate {CAS # 135876- 32-3} (10.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 10 N/mm² Example 19:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator VEctomer™ 4050: Bis[4-(vinyloxy)butyl]terephthalate {CAS # 117397-31-6} (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 11 N/mm² Example 20:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator VEctomer™ 4050: Bis[4-(vinyloxy)butyl]terephthalate {CAS # 117397-31-6} (0.5g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 12 N/mm² Example 21 :

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ 6 (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator VEctomer™ 4040: Bis[[4-[(vinyloxy)methyl]cyclohexyl]methyl] isophthalate {CAS # 119581-93-0} (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 2 N/mm² Example 22:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator VEctomer™ 4040: Bis[[4-[(vinyloxy)methyl]cyclohexyl]methyl] isophthalate {CAS # 119581-93-0} (0.5g). Adhesive performance following 24 hr at 25 ⁰C on: Grit Blasted Mild Steel Lapshears: 4 N/mm² Example 23:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator VEctomer™ 4020: Bis[4-(vinyloxymethyl)cyclohexylmethyl] glutarate {CAS # 131132-77-9} (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 3 N/mm² Example 24:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator VEctomer™ 4020: Bis[4-(vinyloxymethyl)cyclohexylmethyl] glutarate {CAS # 131132-77-9} (0.5g). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 5 N/mm² Example 25:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the accelerator VEctomer™ 4020: Bis[4-(vinyloxymethyl)cyclohexylmethyl] glutarate {CAS # 131132-77-9} (10.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 13 N/mm² Example 26:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator VEctomer™ 5015: Tris(4-vinyloxybutyl)trimellitate {CAS # 196109-17-8} (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 16 N/mm² Example 27:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator VEctomer™ 5015: Tris(4-vinyloxybutyl)trimellitate {CAS # 196109-17-8} (0.5g). Adhesive performance following 24 hr at 25 ⁰C on: Grit Blasted Mild Steel Lapshears: 12 N/mm² Example 28:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the accelerator VEctomer™ 5015: Tris(4-vinyloxybutyl)trimellitate {CAS # 196109-17- 8} (10.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 12 N/mm² Example 29:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (9.5g) and the accelerator VEctomer™ 2020: Aliphatic urethane divinyl ether oligomer {CAS # 143477-70-7} (0.5g). Adhesive performance following 72 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 6 N/mm²

Monomer Component Example 30:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic resin Bis (3,4 Epoxy Cyclohexyl Methyl) Adipate Cyracure UVR 6128, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 31 :

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the alicyclic epoxy resin Cyracure UCB CAT-002, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 32:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic resin PC 1000 (from PolySet), (8.Og) and the accelerator 1 ,4- Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on: Grit Blasted Mild Steel Lapshears: 9.0 N/mm² Example 33:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24g, 0.43 mmol) was dissolved in Epichlorohydrin-4,4'-isopropylidine diphenol resin, Araldite GY 266, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 26 N/mm² Example 34:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24 g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (6.Og), OXT-101 , 3-Ethyl-3-hydroxymethyl- oxetane (2.Og), and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 35:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24 g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (6.Og), OXT-121 , 1 ,4-Bis[3-ethyl-3- oxetanylmethoxy)methyl]benzene (2.Og), and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 36:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24 g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (6.Og), OXT-221 , 3,3'- [oxybis(methylene)]bis(3-ethyl-Oxetane) (2.Og), and the accelerator 1 ,4- Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 37:

[Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.24 g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (6.Og), OXT-212, 3-Ethyl-3-[(2- ethylhexyloxy)methyl]oxetane (2.Og), and the accelerator 1 ,4-Butanediol divinyl ether (2.Og).

Adhesive performance following 24 hr at 25 ⁰C on: Grit Blasted Mild Steel Lapshears: 20 N/mm²

Metal Salts, Concentrations & Combinations of Metal Salts

Example 38:

[Ag(1 ,5-Hexadiene)₂] SbF6 (0.22g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-

3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og).

Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 39:

[Ag(1 ,9-Decadiene)₂] SbF6 (0.26g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 40:

[Ag(1 ,7-octadiene)2] SbFβ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 41 :

[Ag(1 ,7-octadiene)2] PF6 (0.2Og, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on: Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 42:

[Ag(1 ,7-octadiene)2] BF4 (0.18g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 43: [Ag(1 ,7-octadiene)2] CIO4 (0.18g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 44:

[Ag(15-Crown-5)] SbF₆ (0.24g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 61 10, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 45:

[Ag(15-Crown-5)] SbF₆ (0.2Og, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 46:

[Ag(15-Crown-5)] BF₄ (0.18g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 47:

[Ag(1 ,5-Cyclooctadiene)₂] PF₆ (0.22g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 48:

[Ag(1 ,5-Cyclooctadiene)2] BF₄ (0.18g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 49:

[Ag(1 ,5-Cyclooctadiene)₂] CIO₄ (0.18g, 0.43 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy- 3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 24 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 20 N/mm² Example 50:

[Cu(1 ,5-Cyclooctadiene)₂] BF₄ (0.026g, 0.07 mmol) and [Ag(1 ,5- Cyclooctadiene)₂] SbF₆ (0.2Og, 0.35 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 4 hr at 25 ⁰C on:

Grit Blasted Mild Steel Lapshears: 14 N/mm² Example 51 :

[Cu(1 ,5-Cyclooctadiene)₂] BF₄ (0.052g, 0.14 mmol) and [Ag(1 ,5- Cyclooctadiene)₂] SbF₆ (0.16g, 0.28 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og).

Adhesive performance following 4 hr at 25 ⁰C on: Grit Blasted Mild Steel Lapshears: 13 N/mm² Example 52:

[Cu(1 ,5-Cyclooctadiene)₂] BF₄ (O.Oδg, 0.21 mmol) and [Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.12g, 0.21 mmol) was dissolved in the cycloaliphatic diepoxide monomer Cyracure 6110, 3,4-epoxycyclohexylmethy-3,4- epoxycyclohexane carboxylate, (8.Og) and the accelerator 1 ,4-Butanediol divinyl ether (2.Og). Adhesive performance following 4 hr at 25 ⁰C on: Grit Blasted Mild Steel Lapshears: 11.5 N/mm²

Coating Examples

[0091] 100 ml. quantities of the cationically curable formulations of the invention were prepared. The formulations were placed in a suitably sized bath.

Typical Cationic Formulation: a. 3,4-Epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate (77.6%); b. 1 ,4-Butanediol-Divinyl Ether (20%); and c. Silver(1 ,5-Cyclooctadiene) Hexafluoroantimonate (2.4%) [0092] It will be appreciated by a person skilled in the art that the above coating formulation is only a representative formulation given for the purpose of example. The coating formulation can be modified in terms of monomer, metal salt, concentration, etc. suitable to the end use of the coating formulation.

[0093] Metal substrates (10 x 2.5 cm) were cleaned by wiping with acetone and dipped into the formulations. The metal substrates were submerged in the baths containing the formulations. The duration of immersion was proportional to the difference in standard potential between the surface and the metal salt in the composition, and the thickness of the desired coating - if required to be less than the self-limiting thickness. When coating/polymerisation was complete, residual monomer was removed by washing. The films formed were analysed by FTIR-ATR.

[0094] Figure 2 is a FTIR-ATR spectra of surface promoted epoxide coating on grit blasted mild steel at 25 ^°C. The epoxide monomer has a characteristic IR stretch at 700 cm^"1. The desired polyether coating has a characteristic IR stretch at 1080 cm^"1. Iterative scanning of the sample over intervals of 10 mins illustrates increasing polyether concentration over time, substantiating the formation of a polymeric coating on the surface of the grit blasted mild steel.

[0095] An expanded view of the important 1190 cm^"1 to 760 cm^"1 region in Figure 2 is given in Figure 3. The IR spectrum clearly demonstrates that as polyether concentration increases over time the epoxide monomer concentration decreases. [0096] A percentage polymerisation versus time plot for a cationically curable coating composition is given in Figure 4. The coating composition comprises Cyracure 6110 (3,4-Epoxycyclohexylmethyl-3,4-Epoxycyclohexane Carboxylate) (8.Og), 1 ,4- Butanediodivinyl Ether (2.Og) and [Ag(1 ,5-Cyclooctadiene)₂] SbF₆ (0.25 mmol) using Grit Blasted Mild Steel as the Substrate at 20 ⁰C. The extent of polymerisation was determined utilising FTIR-ATR as per Figures 1 and 2 (vide supra). The change in peak intensity in the spectrum over time at 1080 cm^"1 is indicative of polyether formation, and thus polymerisation. The plot illustrates that the initial rate of polymerisation is quick and linear up to approximately 30 mins, whereupon the onset of a plateau is gradually observed.

[0097] 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. [0098] It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination.

Claims

Claims:

1. A cationically curable composition for curing on a surface comprising:

(i) a cationically curable component; and

(ii) an initiator component comprising at least one metal salt;

wherein the standard reduction potential of the initiator component is greater than the standard reduction potential of the surface, and wherein when the composition is placed in contact with the surface, the metal salt of the initiator component of the composition is reduced at the surface, thereby initiating cure of the cationically curable component of the composition.

2. A curable composition according to Claim 1 , wherein the metal salt comprises a transition metal cation.

3. A curable composition according to Claim 2, wherein the transition metal cation is selected from silver, copper and combinations thereof.

4. A curable composition according to Claim 1 , wherein the metal salt includes a counterion chosen from the group consisting of CICU^", BF₄ ^", PF₆ ^", SbF₆ ^",AsF₆ ^" ,(C₆F₅^B, (C₆F₅^Ga, carborane, triflimide, bis-triflimide, and combinations thereof.

5. A curable composition according to Claim 1 , wherein the cationically curable component has at least one functional group selected from the group consisting of epoxy, vinyl, oxetane, thioxetane, episulfide, tetrahydrofuran, oxazoline, oxazine, lactone, trioxane, dioxane, styrene and combinations thereof.

6. A curable composition according to Claim 1 , wherein the surface comprises a metal, metal oxide or metal alloy.

7. A curable composition according to Claim 1 , wherein the surface is selected from the group consisting of iron, steel, mild steel, gritblasted mild steel, aluminium, aluminium oxide, copper, zinc, zinc oxide, zinc bichromate, and stainless steel.

8. A curable composition according to Claim 1 , further comprising a metal oxide removal agent.

9. A curable composition according to Claim 8, wherein the metal oxide removal agent is selected from the group consisting of chloride ions, zinc (II) salts and combinations thereof.

10. A curable composition according to Claim 1 further comprising a catalyst to effect electron transfer between the surface and the metal salt.

11. A curable composition according to Claim 1 for adhering a first metallic substrate to another substrate.

12. A curable composition according to Claim 1 for sealing.

13. Use of the composition of Claim 1 in thread locking, flange sealing, structural bonding and/or metal bonding.

14. Use of at least one metal salt for initiating cure of a cationically curable composition on a surface, wherein the standard reduction potential of the metal salt is greater than the standard reduction potential of the surface.

15. A process for bonding two substrates together comprising the steps of:

(i) applying a composition comprising: i) a cationically curable component; and ii) an initiator component comprising at least one metal salt; to at least one substrate, and

(ii) mating the first and second substrates so as to form a bond with the composition, where the standard reduction potential of the initiator component is greater than the standard reduction potential of at least one of the substrates.

16. A process according to Claim 15 wherein at least one substrate comprises a metal, metal oxide or metal alloy.

17. A process according to Claim 16 wherein at least one substrate comprises a metal.

18. A pack comprising: i) a container; and ii) a cationically curable composition according to Claim 1.

19. A pack according to Claim 18, wherein the container is air permeable.

20. A pack according to Claim 19, wherein the container is not air permeable.

21. A cationically curable composition for curing on surface comprising: i) a cationically curable component; ii) an accelerator species comprising at least one vinyl ether functional group; and iii) an initiator component comprising at least one metal salt; wherein the standard reduction potential of the initiator component is greater than the standard reduction potential of the surface, and wherein when the composition is placed in contact with the surface, the metal salt of the initiator component of the composition is reduced at the surface, thereby initiating cure of the cationically curable component of the composition.

22. A curable composition according to Claim 21 , wherein the metal salt comprises a transition metal cation.

23. A curable composition according to Claim 22, wherein the transition metal cation is selected from silver, copper and combinations thereof.

24. A curable composition according to Claim 21 , wherein a the metal salt includes a counterion chosen from the group CIO₄ ^", BF₄ ^", PF₆ ^", SbF₆ ^",AsF₆ ^",(C₆F₅)₄B, (C₆F₅)₄Ga, carborane, triflimide, bis-triflimide, and combinations thereof.

25. A curable composition according to Claim 21 , wherein the accelerator species comprising at least one vinyl ether functional group is of the general structure:

wherein m can be O or 1 ;

Ri, R₂, and R₃ can be the same or different and can be selected from the group consisting of hydrogen, C₁-C₂₀ alkyl chain (linear, branched or cyclic) and C₅-C₂₀ aryl moiety, and combinations thereof; and

X can be a C₁-C₃₀ saturated or unsaturated, cyclic or acyclic moiety; and

R₁, R₂, R₃ and X may or may not independently contain ether linkages, sulfur linkages, carboxyl groups, and carbonyl groups.

26. A curable composition according to Claim 21 , wherein the accelerator species comprising at least one vinyl ether functional group is of the general structure:

wherein m can be O or 1 ; n can be O - 5;

R₃ can be selected from the group consisting of hydrogen, C₁-C₂₀ alkyl chain (linear, branched or cyclic) and Cs-C₂₀ aryl moiety and combinations thereof; and

X can be a C₁-C₃₀ saturated or unsaturated, cyclic or acyclic moiety; and R₃ and X may or may not independently contain ether linkages, amine linkages, sulfur linkages, carboxyl groups, and carbonyl groups.

27. A curable composition according to Claim 21 , wherein the accelerator species comprising at least one vinyl ether functional group component is selected from the group consisting of 1 ,4-Butanediol divinyl ether, 1 ,4-Butanediol vinyl ether, bis-(4-vinyl oxy butyl) adipate, Ethyl-1-propenyl ether, bis-(4-vinyl oxy butyl) isophthalate, Bis[4-(vinyloxy)butyl] succinate, Bis[4-(vinyloxy)butyl] terephthalate, Bis[[4-[(vinyloxy)methyl]cyclohexyl]methyl] isophthalate, Bis[[4- [(vinyloxy)methyl]cyclohexyl]methyl] glutarate, Tris(4-vinyloxybutyl)trimellitate, VEctomer™ 2020, and combinations thereof.

28. A curable composition according to Claim 21 , wherein the accelerator species comprising at least one vinyl ether functional group is present in 2-98% w/w of the total composition.

29. A curable composition according to Claim 21 , wherein the accelerator species comprising at least one vinyl ether functional group is present in 5-50% w/w of the total composition.

30. A curable composition according to Claim 21 , wherein the accelerator species comprising at least one vinyl ether functional group is present in 5-30% w/w of the total composition.

31. A curable composition according to Claim 21 , wherein the cationically curable component has at least one functional group selected from the group consisting of epoxy, vinyl, oxetane, thioxetane, episulfide, tetrahydrofuran, oxazoline, oxazine, lactone, trioxane, dioxane, styrene and combinations thereof.

32. A curable composition according to Claim 21 , wherein the surface comprises a metal, metal oxide or metal alloy.

33. A curable composition according to Claim 21 , wherein the surface is selected from the group consisting of iron, steel, mild steel, gritblasted mild steel, aluminium, aluminium oxide, copper, zinc, zinc oxide, zinc bichromate, and stainless steel.

34. A curable composition according to Claim 21 applied to a metal, metal oxide or metal alloy.

35. A curable composition according to Claim 21 further comprising a catalyst to effect electron transfer between the metal surface and the metal salt.

36. A curable composition according to Claim 21 for adhering a first metallic substrate to another substrate.

37. A curable composition according to Claim 21 for sealing.

38. Use of the composition defined in Claim 21 in thread locking, flange sealing, structural bonding and/or metal bonding.

39. An initiator package for initiating cure of a cationically curable component comprising: i) a metal salt; and ii) an accelerator species comprising at least one vinyl ether functional group.

40. A process for bonding two substrates together comprising the steps of: i) applying a composition comprising: a) a cationically curable component; b) an accelerator species comprising at least one vinyl ether functional group; and c) an initiator component comprising at least one metal salt; to at least one substrate, and ii) mating the first and second substrates so as to form a bond with the composition, wherein the standard reduction potential of the initiator component is greater than the standard reduction potential of at least one of the substrates.

41. A process according to Claim 40 wherein at least one substrate comprises a metal, metal oxide or metal alloy.

42. A process according to Claim 40 wherein at least one substrate comprises a metal.

43. A pack comprising: i) a container; and ii) a cationically curable composition according to Claim 21.

44. A pack according to Claim 43, wherein the container is air permeable.

45. A pack according to Claim 43, wherein the container is not air permeable.

46. A curable coating composition for coating a surface comprising: i) a cationically curable component; and ii) an initiator component comprising at least one metal salt;

47. A coating composition according to Claim 46, wherein the metal salt comprises a transition metal cation.

48. A coating composition according to Claim 47, wherein the transition metal cation is selected from silver, copper and combinations thereof.

49. A coating composition according to Claim 46, wherein the metal salt includes a counterion chosen from the group CIO₄ ^", BF₄ ^", PF₆ ^", SbF₆ ^",AsF₆ ^",(C₆F₅)₄B, (C₆F₅)₄Ga, carborane, triflimide, bis-triflimide, and combinations thereof.

50. A coating composition according to Claim 46, wherein the surface comprises a metal, metal oxide, or metal alloy.

51. A coating composition according to Claim 46, wherein the surface is selected from the group consisting of iron, steel, mild steel, gritblasted mild steel, aluminium, aluminium oxide, copper, zinc, zinc oxide, zinc bichromate, and stainless steel.

52. A coating composition according to Claim 46, wherein the cationically curable component has at least one functional group selected from the group consisting of epoxy, vinyl, vinyl ether, oxetane, thioxetane, episulfide, tetrahydrofuran, oxazoline, oxazine, lactone, trioxane, dioxane, styrene and combinations thereof.

53. A coating composition according to Claim 46 wherein the cationically curable component comprises a vinyl ether component and at least one other cationically curable component selected from the group consisting of epoxy, vinyl, oxetane, thioxetane, episulfide, tetrahydrofuran, oxazoline, oxazine, lactone, trioxane, dioxane, and styrene.

54. A method of coating a substrate comprising applying a coating composition comprising: i) a cationically curable component; and ii) an initiator component comprising at least one metal salt; to the substrate, where the standard reduction potential of the initiator component is greater than the standard reduction potential of the surface.

55. A coating applied to a substrate utilising the method of Claim 54.

56. A coated article comprising: i) a coating according to Claim 55; and ii) a substrate.

57. A coated article according to Claim 56 having a curable composition applied thereto.

58. A coated article according to Claim 56 mated with a second substrate.

59. A coated article according to Claim 56 having a second substrate adhered thereto.

60. A pack comprising: i) a container; and ii) a cationically curable coating composition according to Claim 46.

61. A pack according to Claim 60, wherein the container is air permeable.

62. A pack according to Claim 60, wherein the container is not air permeable.