WO2013026153A1

WO2013026153A1 - Nano-particle polymer composite

Info

Publication number: WO2013026153A1
Application number: PCT/CA2012/050551
Authority: WO
Inventors: Nazila Dadvand; Xianyao LI
Original assignee: Monnaie Royale Canadienne / Royal Canadian Mint
Priority date: 2011-08-23
Filing date: 2012-08-14
Publication date: 2013-02-28
Also published as: WO2013026153A8

Abstract

A coating for a metal or metal alloy, the coating including an adhesive layer covalently bonded to the metal or metal alloy; and a layer of a nanoparticle polymer composite, the nanoparticle polymer composite comprising nanoparticles covalently bonded to a polymer matrix.

Description

NANO-P ARTICLE POLYMER COMPOSITE

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/526,462 filed August 23, 201 1 , which is incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates generally to nanoparticle polymer composite coatings, for instance for coating metal or metal alloys.

BACKGROUND

[0003] Coatings can be used to provide protection to a surface of an underlying substrate. For example, coatings can be used to provide protection from corrosion, wear, ultraviolet light, and other environmental conditions that may damage the substrate. Coatings can be used to change the appearance of an underlying substrate. For example, coatings can be used to change the colour, tint, reflectance, or other visual characteristics of the underlying substrate.

[0004] Coatings may be used to provide protection to, change the appearance of, or both provide protection to and change the appearance of, metals, metal alloys, plastics, polymers, paints, glass, printed material, cloth, or other materials.

[0005] In one particular situation, circulation coins, made from a metal or metal alloy, are damaged over time, where the damage may be due to corrosion and/or wear of alloy or plated material. Yellow circulation coins are made using copper alloys, for example copper-zinc, copper-tin or copper-zinc-tin, as the top layer.

[0006] The rate of damage to a coin depends on the environment to which the coin is subjected. For example, the rate of wear depends on the physical forces applied to the coin (e.g. sliding and abrasive forces due to coins contacting each other). The rate of corrosion of the coin depends on the conditions to which the coin is exposed (e.g.

humidity, temperature, UV exposure, chemical exposure). Protecting the surface of the coin can increase the life span of the coin by reducing the rate of damage to the coin.

[0007] Wear is often due to scratches caused by contact with other objects, including other coins. It is desirable to reduce the rate of wear by applying a protective coating on the metal or metal alloy surfaces of the coin. Corrosion can be concentrated locally (resulting in the formation of pits or cracks) or can corrode across the surface of the coin. It is desirable to reduce the rate of corrosion by coating the coin's metal or metal alloy surface with a corrosion-resistant coating.

[0008] Known coatings for metals or metal alloys include: chromate-conversion coatings, vanadium-conversion coatings, and phosphate-conversion coatings. Physical vapour deposition and chemical vapour deposition have been used to coat metals or metal alloys. The purpose of such coatings is to provide a durable surface between the environment and the metal or metal alloy surface in order to reduce the rate of damage due to wear and/or corrosion.

[0009] Coatings often contain defects or failures. Defects or failures in the coatings can be due to poor adhesion of the coating to the metal or metal alloy surface. Poor adhesion may be due to contamination of the surface and/or inadequate preparation of the surface before coating. The defects may allow moisture to reach the metal or metal alloy surface, thereby resulting in corrosion. The defect or failure, coupled with osmotic transfer of moisture to the metal or metal alloy surface, may result in blistering and/or delamination of the coatings.

[0010] It is desirable to provide a coating for a material, where the coating provides protection to, changes the appearance of, or both provides protection to and changes the appearance of the material.

[0011] It is desirable to provide a coating for a metal or metal alloy, where the coating provides resistance to damage.

[0012] It is desirable to provide a method for applying a coating to a material, for example a metal or metal alloy.

SUMMARY

[0013] In a first aspect, the present disclosure provides a coating for a metal or metal alloy. The coating includes: an adhesive layer bonded to the metal or metal alloy; and a layer of a nanoparticle polymer composite, the nanoparticle polymer composite comprising nanoparticles covalently bonded to a polymer matrix. The covalent bond between the nanoparticle and the polymer matrix is a product of the reaction between a - SH group on the nanoparticle and a -SH group on the polymer matrix so that the covalent bond between the nanoparticle and the polymer matrix is -S-S-.

[0014] At least a portion of the nanoparticles may include a linker covalently bound to the surfaces of the nanoparticles; where the linker is a product of the reaction between the surfaces of the nanoparticles and a linking compound having the general formula (R 0)_xSi-((CH₂)_n(CHSH)(CH₂)_oH)_y, where R is a methyl or ethyl group; the sum of "n" and "o" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4.

[0015] In examples of some coatings, "n" is 2, "o" is 0, "x" is 3 and "y" is 1.

[0016] The nanoparticles may be silica, aluminum oxide nanoparticles, or a combination thereof.

[0017] The adhesive layer may be a monolayer. The adhesive layer and the metal or metal alloy may be covalently bonded together by the reaction of the metal or metal alloy with a first functional group on an adhesive compound. The first functional group on the adhesive compound may be -NH₂ or -SH and the resulting covalent bond may be - S-Ag, -NH-Cu, or -S-Cu. Alternatively, the adhesive layer and the metal or metal alloy may be bonded together using an adhesion promoter, such as a fluoro-modified polysiloxane.

[0018] The adhesive layer may be covalently bonded to the layer of the nanoparticle polymer composite, where the covalent bond between the adhesive layer and the nanoparticle polymer composite is a product of the reaction between a second functional group on the adhesive compound and a functional group on the nanoparticle polymer composite. The functional group on the nanoparticle polymer composite which reacts with the second functional group on the adhesive compound may be a functional group on the nanoparticle. The functional group on the nanoparticle polymer composite which reacts with the second functional group on the adhesive compound may be -SH.

[0019] The adhesive compound may be a molecule of the general formula:

(R²)(R³)C=C(R⁴)(R⁵) wherein at least one of R², R³, R⁴ and R⁵ is ((CH₂)_p(CHSH)(CH₂)_qH) wherein the sum of "p" and "q" is between 0 and 10; and the others are independently: H; an alkyl group; an aryl group; halogen; substituted ketone; or heteroatom; and the -SH group corresponds to the first functional group on the adhesive compound; or (R^sO)_xSi- ((CH₂)_r(CHSH)(CH₂)_sH)_y, where R⁶ is methyl or ethyl; the sum of "r" and "s" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4; and the -SH group corresponds to the first functional group on the adhesive compound.

[0020] In examples of adhesive compounds, R² is nitro, R³ is H, and R⁴ and R⁵ are independently ((CH₂)_p(CHSH)(CH₂)_qH) where "p" is 0 or 1 , and "q" is 0. In other examples of adhesive compounds, "r" is 2, "s" is 0 or 1 , "x" is 3, and "y" is 1.

[0021] In another aspect, the current description provides a metal or metal alloy coated with a composition described above.

[0022] In yet another aspect, there is provided a nanoparticle monomer composite compound having: a polymerizable monomer covalently bound to a surface of a nanoparticle, where the surface of the nanoparticle is modified with a compound of the general formula (R 0)_xSi-((CH₂)_n(CHSH)(CH₂)₀H)_y, where R is methyl or ethyl; the sum of "n" and "o" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4; and where the covalent bond is a product of the reaction between the -SH group on the surface of the nanoparticle and a -SH group on the polymerizable monomer so that the covalent bond between the nanoparticle and the polymerizable monomer is -S-S-.

[0023] The surface of the nanoparticle may be modified with a compound of formula (R 0)₃Si-(CH₂)₃SH. The nanoparticle may be a silica or an aluminum oxide nanoparticle.

[0024] In yet another aspect, there is provided a nanoparticle polymer composite having: nanoparticles covalently bonded to a polymer matrix, where the nanoparticles are modified with a compound of the general formula (R 0)_xSi-((CH₂)_n(CHSH)(CH₂)₀H)_y, where R is methyl or ethyl; the sum of "n" and "o" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4; and where the covalent bond is a product of reaction between the -SH group on the nanoparticles and a -SH group on the polymer matrix so that the covalent bond between the nanoparticles and the polymer matrix is -S- S-.

[0025] The nanoparticles may be modified with a compound of formula (R 0)₃Si-

(CH₂)₃SH.

[0026] The nanoparticles may be silica nanoparticles, aluminum oxide nanoparticles, or a combination thereof.

[0027] In yet another aspect, there is provided a method that includes:

synthesizing a nanoparticle comprising -SH; and reacting the nanoparticle comprising - SH with a polymer matrix comprising -SH so that the covalent bond between the nanoparticle and the polymer matrix is -S-S-.

[0028] Synthesizing the nanoparticle comprising -SH may include synthesizing an unmodified nanoparticle; and reacting the unmodified nanoparticle with a linking compound comprising -SH.

[0029] The linking compound may be a molecule having the general formula (R 0)_xSi-((CH₂)_n(CHSH)(CH₂)₀H)_y, where R is an methyl or ethyl; the sum of "n" and "o" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4.

[0030] In examples of the linking compound, "n" is 2, "o" is 0, "x" is 3 and "y" is 1.

[0031] The method may also include: coating a surface of a metal or metal alloy with an adhesive compound to form an adhesive layer bound to the surface of the metal or metal alloy; coating the adhesive layer with a polymerizable solution, wherein the polymenzable solution comprises the nanoparticles comprising -SH; and polymerizing the polymenzable solution to form a layer of a nanoparticle polymer composite on the adhesive layer, the nanoparticle polymer composite comprising the nanoparticles covalently bonded to the resulting polymer matrix by the -S-S- bond.

[0032] The method may further include cleaning the surface of the metal or metal alloy with an alkaline soap cleaner prior to coating with the adhesive compound.

[0033] Polymerizing the polymerizable solution may include forming a covalent bond between the adhesive layer and the nanoparticle polymer composite.

[0034] The adhesive compound may be a molecule of the general formula: (R²)(R³)C=C(R⁴)(R⁵) wherein at least one of R², R³, R⁴ and R⁵ is ((CH₂)_p(CHSH)(CH₂)_qH) wherein the sum of "p" and "q" is between 0 and 10; and the others are independently: H; an alkyl group; an aryl group; halogen; substituted ketone; or heteroatom, and the -SH group corresponds to the first functional group on the adhesive compound; or (R^sO)_xSi- ((CH₂)r(CHSH)(CH₂)sH)_y, where R⁶ is methyl or ethyl; the sum of "r" and "s" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4; and the -SH group corresponds to the first functional group on the adhesive compound.

[0035] In specific examples of the adhesive compound, R² is nitro, R³ is H, and R⁴ and R⁵ are independently ((CH₂)_p(CHSH)(CH₂)_qH) where "p" is 0 or 1 , and "q" is 0. In other examples of the adhesive compound "r" is 2, "s" is 0 or 1 , "x" is 3, and "y" is 1.

[0036] In yet another aspect, there is provided a use of an adhesive compound for forming an adhesive layer bonded to a surface of a metal or metal alloy, the adhesive layer for adhering the surface of the metal or metal alloy to a layer of a nanoparticle polymer composite, the nanoparticle polymer composite comprising nanoparticles covalently bonded to a polymer matrix wherein the covalent bond between the nanoparticle and the polymer matrix is a product of the reaction between a -SH group on the nanoparticle and a -SH group on the polymer matrix so that the covalent bond between the nanoparticle and the polymer matrix is -S-S-.

[0037] In yet another aspect, there is provided a use of a nanoparticle monomer composite compound and a polymerizable solution for forming a coating of a nanoparticle polymer composite on a surface, the nanoparticle polymer composite comprising nanoparticles covalently bonded to a polymer matrix, wherein the nanoparticle monomer composite compound comprises a polymerizable monomer covalently bound to a surface of a nanoparticle wherein the covalent bond between the nanoparticle and the polymerizable monomer is a product of the reaction between a -SH group on the nanoparticle and a -SH group on the polymerizable monomer so that the covalent bond between the nanoparticle and the polymerizable monomer is -S-S-.

[0038] In yet another aspect, there is provided a use of a nanoparticle polymer composite for coating a surface of a metal or metal alloy, the surface of the metal or metal alloy comprising an adhesive layer which is bonded to the surface of a metal or metal alloy, the nanoparticle polymer composite comprising nanoparticles covalently bonded to a polymer matrix wherein the covalent bond between the nanoparticle and the polymer matrix is a product of the reaction between a -SH group on the nanoparticle and a -SH group on the polymer matrix so that the covalent bond between the nanoparticle and the polymer matrix is -S-S-.

[0039] Other aspects and features of the present disclosure will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments in conjunction with the accompanying figures. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Embodiments of the present disclosure will now be described, by way of example only, with reference to the attached Figures.

[0041] FIGs. 1 A to 1 D are photomicrographs of scratches on tokens (simulation coins with no circulation value) coated with an acrylic polymer.

[0042] FIGs. 2A to 2D are photomicrographs of scratches on tokens coated with a nanoparticle polymer composite.

[0043] FIGs. 3 and 4 are photographs of wear-tested tokens, which were previously coated with a nanoparticle polymer composite.

[0044] FIG. 5 is a photograph of a wear-tested, non-coated token.

[0045] FIG. 6 is a photograph of a wear-tested token, which was previously coated with acrylic polymer.

[0046] FIG. 7 is a photograph of a steam-tested, non-coated token.

[0047] FIG. 8A are photographs of steam-tested tokens, which were previously coated with a nanoparticle polymer composite and wear tested.

[0048] FIG. 8B are photographs of steam-tested, non-coated tokens, which were previously wear-tested.

[0049] FIG. 8C are photographs of both sides of an uncoated control after the steam test. DETAILED DESCRIPTION

[0050] This application relates to coatings for materials, for example metals or metal alloys. For the purposes of explanation, coatings will be discussed with respect to coatings for coins or tokens, but it is to be understood that the coatings could alternatively be used to coat other materials.

[0051] Generally, the present disclosure provides a coating for a material, where the coating is a nanoparticle polymer composite. The nanoparticle polymer composite includes a nanoparticle and a polymer matrix which have been covalently bonded together. When the nanoparticle polymer composite is used to coat a metal, it is adhered to the surface of the material with a layer of adhesive compound. The adhesive compound may be covalently bonded to the surface of the substrate, or may be bonded to the surface of the substrate using an adhesion promoter, such as a fluoro-modified polysiloxane. The adhesive compound may be covalently bonded to the nanoparticle polymer composite. The adhesive compound may be a mixture of different chemicals.

[0052] The coating may further include an adhesion promoter which may be applied directly to the surface of the material and which improves the adhesion of the adhesive layer.

[0053] The material may be, for example, a metal, metal alloy, plastic, polymer, coating of paint, glass, printed material, cloth, or other solid material. The coating may, for example, provide protection to the material, change the appearance of the material, change the properties of the material, or any combination thereof.

[0054] Foam may be formed during the coating process. Foams are defined as a fine distribution of a gas in a liquid phase where the gas bubbles rise through the liquid to reach the surface. The foams may result in coatings with surface defects. Such surface defects may result, for example, in optical disturbances, reduction in protective function of the coating, or both. Reduction in protective function of the coating may include reduction in the strength of the coating, the adhesion of the coating, the wear resistance of the coating, or any combination thereof. In order to reduce surface defects, additional coating material may be used. However, using additional coating material results in increased costs. In order to reduce the formation of foam, the coating formulation may include a de- foamer. Use of a de-foamer may, accordingly, reduce surface defects and/or reduce costs. Nanoparticle Polymer Composites

[0055] The nanoparticle and polymer matrix may be covalently bonded together by reacting a first functional group on the nanoparticle with a second functional group on the polymer matrix. The first functional group is -SH group and the second functional group is an -SH group so that the resulting bond is -S-S-.

[0056] The first functional group may be introduced to a surface of a modified or an unmodified nanoparticle after the nanoparticle has been synthesized by reacting, for example, a linking compound having the first functional group with a surface of the nanoparticle. The surface of the nanoparticle may be chemically modified, modified using plasma treatment, or modified using ion bombardment in order to generate a surface which can bind with the linking compound. The modified or unmodified surface of the nanoparticles may be chemically reacted with the linking compound in order to attach the first functional group to the nanoparticle.

[0057] Chemical reaction to introduce the first functional group onto the surface of a nanoparticle may be achieved by, for example, reacting a linking compound, which incorporates the first functional group, with an unmodified nanoparticle or with a nanoparticle which has been otherwise modified post-synthesis. This linking compound may be used as an end-capping group during the synthesis of the nanoparticle. Since the linking compound includes the first functional group, the resulting nanoparticle with the linking compound may be subsequently reacted with the second functional group.

[0058] One example of a linking compound which can be used to add the first functional group to a surface of a nanoparticle is a chemical compound of the general formula (R 0)_xSi-((CH₂)_n(CHSH)(CH₂)_oH)_y, where R is methyl or ethyl; the sum of "n" and "o" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4; and the -SH group corresponds to the first functional group. In particular embodiments, "n" is 2, "o" is 0 or 1 , "x" is 3, and "y" is 1. Specific examples of linking compounds include: 3- mercapropropyl trimethoxysilane, 3-mercaptopropyl triethoxysilane, 3-mercaptobutyl triethoxysilane and 4-mercaptobutyl triethoxysilane.

[0059] In one specific example of reacting a linking compound with a

nanoparticle, (3-mercaptopropyl)trimethoxysilane (MPTMS) may be used to end-cap silica nanoparticles, where the nanoparticles are prepared by a sol-gel process using tetramethoxysilane (TMOS) as a monomer precursor. The 3-mercaptopropyl side chain of MPTMS can be reacted, for example, with a second functional group which is a part of a monomer during polymer matrix polymerization to form a covalent linkage. [0060] Depending on what the nanoparticle polymer composite is used for, it may be desirable for the nanoparticle polymer composite to have an elasticity of >88%, have good yield strength, have good hardness, have the ability to self-heal, be scratch resistant, be curable by UV, stable under UV, or any combination thereof. Vinyl-based polymers, for example acrylic-based polymers, are one example of polymer matrixes which can be used to form a nanocomposite polymeric material according to the application. Vinyl-based polymers are polymers or copolymers derived from compounds with vinyl groups. Acrylic-based polymers are one example of vinyl-based polymers and are thermoplastic polymers or copolymers, for example polymers or co-polymers derived from an arylic acid based monomer, a methacrylic acid based monomer, a

methylmethacrylate based monomer, or their esters or amides.

[0061] The nanoparticles were selected to protect the substrate; It may also change the electric characteristics of the coating; magnetic characteristics of the coating; or any combination thereof. Changing characteristics such as these may enhance security features of, for example, coins, bills or the like.

[0062] Depending on what the nanoparticle polymer composite is used for, it may be desirable for the nanoparticles to be no larger than 100 nm since larger nanoparticles may result in coloured or translucent nanoparticle polymer composite coatings.

[0063] Examples of nanoparticles which can be used to form a nanoparticle polymer composite according to the application include silica nanoparticles and aluminum oxide nanoparticles.

Coating Materials with Nanoparticle Polymer Composites

[0064] When using nanoparticles to coat a metal or metal alloy, it may be desirable to provide an adhesive layer between the nanoparticle polymer composite and the metal or metal alloy. The adhesive layer may be a monolayer formed through the reaction between the metal or metal alloy and an adhesive compound. The adhesive compound may be a mixture of different chemicals.

[0065] Adhesive compounds have a first functional group that reacts with the metal or metal alloy to form a stable bond, for example a covalent bond. For example, the first functional group on the adhesive compound may be -NH₂, or -SH and the resulting stable covalent bond may be, for example, -S-Ag, -NH-Cu, or -S-Cu. Alternatively, the adhesive compound may be bonded to the surface of the substrate using an adhesion promoter, such as a fluoro-modified polysiloxane, where the adhesion promoter interacts with the substrate and the adhesive compound interacts with the adhesion promoter. [0066] Adhesive compounds may have a second functional group that reacts with a functional group on the nanoparticle polymer composite. For example, the second functional group of the adhesive compound may react with a functional group on: a nanoparticle, or a modified nanoparticle. The functional group on the nanoparticle polymer composite which reacts with the second functional group of the adhesive compound may be the second functional group of the nanoparticle composite.

[0067] In one example, the adhesive compound is a molecule having the formula

(R²)(R³)C=C(R⁴)(R⁵) where at least one of R², R³ R⁴ and R⁵ is ((CH₂)_p(CHSH)(CH₂)_qH) where the sum of " p" and "q" is between 0 and 10; and the others are independently: H; alkyl group, as defined herein; aryl group, as defined herein; halogen, for example: fluoro, chloro, bromo or iodo; substituted ketone; or heteroatom, for example: oxygen, nitrogen (for example nitrile, amine, or nitro), or sulfur. In particular embodiments, R² is nitro, R³ is H, and R⁴ and R⁵ are independently ((CH₂)_p(CHSH)(CH₂)_qH) where "p" is 0 or 1 , and "q" is 0.

[0068] The term "alkyl" refers to a substituted or un-substituted carbon radical which is straight, branched or cyclic. The term "alkyl" includes hetero- and non-heteroalkyl groups. The term "aryl" refers to a substituted or un-substituted, aromatic or

heteroaromatic ring radical containing 5 to 14 ring atoms. Examples of an un-substituted aryl group include phenyl, naphthyl, furan, and pyrrole.

[0069] The term "substituted" indicates that at least one hydrogen atom of the functional group is replaced by a non-hydrogen substituent or group. When a functional group is "substituted", it may have up to the full valence of substituents; for example, a methyl group may be substituted by 1 , 2 or 3 substituents. Substituents on a functional group may be the same or different. Contemplated substituents include, for example: alkyl groups, as defined herein; aryl groups, as defined herein; halogens, for example: fluoro, chloro, bromo or iodo; ketones; heteroatoms, for example: oxygen, nitrogen (for example nitrile, amine, or nitro), and sulfur.

[0070] In another example, the adhesive compound is a molecule having the general formula (R⁶0)_xSi-((CH₂)_r(CHSH)(CH₂)_sH)_y, where R⁶ is methyl or ethyl; the sum of "r" and "s" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4; and the -SH group corresponds to the first functional group. In particular embodiments, "r" is 2, "s" is 0 or 1 , "x" is 3, and "y" is 1.

[0071] Examples of adhesive compounds include 3-mercaptopropyl

trimethoxysilane (MPT MS), and 1 , 1 -bis(methylthio)-2-nitroethylene. In these exemplary adhesive compounds, the thiol functional groups react with the metal or metal alloy, for example the copper in the copper-zinc alloy, copper-tin alloy, copper-zinc-tin alloy, or other type of copper alloy used in the top layer of a coin. With regard to 3-mercaptopropyl trimethoxysilane, the second functional group is the trimethoxysilane, which may be reacted with the nanoparticle to form a covalent bond. With regard to 1 , 1 -bis(methylthio)- 2-nitroethylene, the second functional group is the 2-nitroethylene, which may be reacted with a functional group which is a part of the nanoparticle particle composite.

[0072] Other chemicals which may be used in combination with MPTMS to form an adhesive compound include, for example: polyisocyanates and modified acrylic resins. Properties of Nanoparticle Polymer Composites

[0073] The properties of the nanoparticle polymer composite (for example, the chemical, mechanical, electronic, optical properties) may be altered by changing the nanoparticle and/or the polymeric matrix. Changing the nanoparticles, for example by changing the size of the nanoparticle or changing the interfacial property between the nanoparticle and the polymer, or both, may result in different nanoparticle polymer composites with different properties.

Testing of Nanoparticle Polymer Composites

[0074] Wear resistance of coins may be measured in a metallurgical laboratory by using various wear testing methods, such as using pin-on-disc, block-on-block, or scratch test, according to ASTM standards. A tumbler test has been developed to evaluate wear performance, simulating circulation environment of coins. The tumbler is a metal drum lined with a cloth and with a smooth hump which randomly upsets and rotates the coins, creating coin-coin contact. The wear test is carried out at a specified rotation speed for days in order to correlate and simulate multiple years of circulation life of the coins.

[0075] This kind of wear test may be used to evaluate coating performance of coated coins. Scratches, dents and/or delaminations or breakage may develop on the coating for coins subjected to the tumbler wear test. Visual damage of the coating, and subsequent tarnishing or corrosion tests may be carried out to evaluate the coverage and integrity of the coating. If cracks, breakage or delamination occur in the coating, the coated coins will show discoloration in the tarnish test or corrosion test.

[0076] The hardness of nanoparticle polymer composites may be similar to the hardness of polymer matrix that does not have nanoparticles. However, the critical load at which cracking is initiated in nanoparticle polymer composites has been measured to be greater than that of the polymer matrix that does not have nanoparticles. Examples

Example 1 - Coating a metal alloy

[0077] Silica nanoparticles were synthesized using tetramethoxysilane (TMOS) as a precursor mixed in a commercially available polymer solution. Briefly, deionized (Dl) water containing a mixture of ammonium hydroxide and hydrochloric acid at pH 4.7 was added to iso-propanol. Tetramethoxysilane (TMOS), a precursor of the silica nanoparticles, was added into the solution water / isopropanol solution. The solution was agitated for about 5 min, then refluxed at 80 °C for at least one hour in order to grow the synthesized silica nanoparticles. The size of the synthesized silica particles is determined by the reaction time. It is desirable to limit the reaction time to time periods during which nanoparticles are produced. Longer reaction time may lead to production of particles of micron size, which may agglomerate and precipitate.

[0078] An acidified solution of a co-solvent, for example acetone, was then added into the water / isopropanol solution in order to reduce agglomeration. Subsequently, (3- mercaptopropyl)trimethoxysilane was added to the reaction solution. A small quantity of NanoDur™-AI, suspended in 1 ,2-propanediolmonomethylether acetate, was added into the reaction solution. The reaction solution was then refluxed for 1 hr at 84 °C, allowing the MPTMS to react with the silica to cap the nanoparticle. The resulting solution has nanoparticles with a linking compound comprising a first functional group.

[0079] The solution with the nanoparticles having the first functional group was then mixed with polymerizable material used for the polymerization of the polymer matrix.

[0080] Copper alloy tokens (simulation coins with no circulation value) were cleaned using an alkaline soap cleaner and subsequently reacted with MPTMS to provide a monolayer of adhesive compound. The solution containing the nanoparticles with the polymerizable material was then used to coat the copper alloy tokens having the monolayer of adhesive compound using micropipette. The coated copper alloy tokens were subjected to UV irradiation in order to induce polymerization. Example 2 - Coating a metal alloy

[0081] Silica nanoparticles were synthesized using tetramethoxysilane (TMOS) as a precursor mixed in a commercially available polymer solution. Briefly, deionized (Dl) water containing a mixture of ammonium hydroxide and hydrochloric acid at pH 4.7 was added to iso-propanol. Tetramethoxysilane (TMOS), a precursor of the silica nanoparticles, was added into the solution water / isopropanol solution. The solution was agitated for about 5 min, then refluxed at 80 °C for at least one hour in order to growth the synthesized silica nanoparticles. The size of the synthesized silica particles is determined by the reaction time. It is desirable to limit the reaction time to time periods during which nanoparticles are produced. Longer reaction time may lead to production of particles of micron size, which may agglomerate and precipitate.

[0082] An acidified solution of a co-solvent, for example acetone, was then added into the water / isopropanol solution in order to reduce agglomeration. Subsequently, (3- mercaptopropyl)trimethoxysilane was added to the reaction solution. A small quantity of NanoDur™-AI, suspended in 1 ,2-propanediolmonomethylether acetate, was added into the reaction solution. The reaction solution was then refluxed for 1 hr at 84 °C, allowing the MPTMS to react with the silica to cap the nanoparticle. The resulting solution has nanoparticles with a linking compound comprising a first functional group.

[0083] The solution with the nanoparticles having the first functional group was then mixed with polymerizable material used for the polymerization of the polymer matrix.

[0084] Copper alloy tokens (simulation coins with no circulation value) were treated with an adhesion promoter, and subsequently reacted with MPTMS to provide a monolayer of adhesive compound. The solution containing the nanoparticles with the polymerizable material was then used to coat the copper alloy tokens having the monolayer of adhesive compound using micropipette. The coated copper alloy tokens were subjected to UV irradiation in order to induce polymerization.

Example 3 - Coating a metal alloy

[0085] Silica nanoparticles were synthesized using tetramethoxysilane (TMOS) as a precursor mixed in a commercially available polymer solution. Briefly, deionized (Dl) water containing a mixture of ammonium hydroxide and hydrochloric acid at pH 4.7 was added to iso-propanol. Tetramethoxysilane (TMOS), a precursor of the silica nanoparticles, was added into the solution water / isopropanol solution. The solution was agitated for about 5 min, then refluxed at 80 °C for at least one hour in order to growth the synthesized silica nanoparticles. The size of the synthesized silica particles is determined by the reaction time. It is desirable to limit the reaction time to time periods during which nanoparticles are produced. Longer reaction time may lead to production of particles of micron size, which may agglomerate and precipitate.

[0086] An acidified solution of a co-solvent, for example acetone, was then added into the water / isopropanol solution in order to reduce agglomeration. Subsequently, (3- mercaptopropyl)trimethoxysilane was added to the reaction solution. A small quantity of NanoDur™-AI, suspended in 1 ,2-propanediolmonomethylether acetate, was added into the reaction solution. The reaction solution was then refluxed for 1 hr at 84 °C, allowing the MPTMS to react with the silica to cap the nanoparticle. The resulting solution has nanoparticles with a linking compound comprising a first functional group.

[0087] The solution with the nanoparticles having the first functional group was then mixed with polymerizable material used for the polymerization of the polymer matrix.

[0088] Copper alloy tokens (simulation coins with no circulation value) were treated with an adhesion promoter, and subsequently reacted with a mixture of MPTMS and a polyisocyanate to provide a monolayer of adhesive compound. The solution containing the nanoparticles with the polymerizable material was then used to coat the copper alloy tokens having the monolayer of adhesive compound using micropipette. The coated copper alloy tokens were subjected to UV irradiation in order to induce polymerization. Example 4 - Coating a metal alloy

[0089] Silica nanoparticles were synthesized using tetramethoxysilane (TMOS) as a precursor mixed in a commercially available polymer solution. Briefly, deionized (Dl) water containing a mixture of ammonium hydroxide and hydrochloric acid at pH 4.7 was added to iso-propanol. Tetramethoxysilane (TMOS), a precursor of the silica nanoparticles, was added into the solution water / isopropanol solution. The solution was agitated for about 5 min, then refluxed at 80 °C for at least one hour in order to growth the synthesized silica nanoparticles. The size of the synthesized silica particles is determined by the reaction time. It is desirable to limit the reaction time to time periods during which nanoparticles are produced. Longer reaction time may lead to production of particles of micron size, which may agglomerate and precipitate.

[0090] An acidified solution of a co-solvent, for example acetone, was then added into the water / isopropanol solution in order to reduce agglomeration. Subsequently, (3- mercaptopropyl)trimethoxysilane was added to the reaction solution. A small quantity of NanoDur™-AI, suspended in 1 ,2-propanediolmonomethylether acetate, was added into the reaction solution. The reaction solution was then refluxed for 1 hr at 84 °C, allowing the MPTMS to react with the silica to cap the nanoparticle. The resulting solution has nanoparticles with a linking compound comprising a first functional group.

[0091] The solution with the nanoparticles having the first functional group was then mixed with polymerizable material used for the polymerization of the polymer matrix. [0092] Copper alloy tokens (simulation coins with no circulation value) were treated with an adhesion promoter, and subsequently reacted with a mixture of MPTMS and a defoamer to provide a monolayer of adhesive compound. The solution containing the nanoparticles with the polymerizable material was then used to coat the copper alloy tokens having the monolayer of adhesive compound using micropipette. The coated copper alloy tokens were subjected to UV irradiation in order to induce polymerization.

Example 5 - Scratch Testing

[0093] Coated tokens according to Example 1 were scratch tested using a CSM Micro Scratch Tester. Scratch tests were performed as a quick and efficient way to test the mechanical properties of films to determine whether or not they would be suitable and should be continued on to a long term tumbler wear test. A diamond Rockwell tip was used to apply a progressively increasing load along a line. The surface profile, penetration depth, and residual depths were all measured along the resulting scratch paths.

[0094] For wear resistant protective coatings on tokens, a material with a high hardness and toughness is desired, for example a Vickers hardness of greater than 19 GPa. A coating with high toughness will be able to undergo a great deal of deformation before failure of the coating occurs in the form of cracking and delamination. After designating the scratch path, the instrument was completely automated. The scratch performed three passes. The first pass used a light load of 30mN to measure the surface profile of the area to be scratched. The second pass applied the designated load to the surface using the diamond tip, while measuring the penetration depth of the scratch as it progresses. The third pass once again used a low load of 30mN to measure the surface profile along the scratch track. This final pass measured the residual depth along the scratch track.

[0095] By comparing the penetration depth under the applied load to the residual depth, the recovery of the material was examined. The percentage of material recovery provides information on its elasticity. If the applied load results in solely elastic deformation, then the coating will recover completely and the final pass over the coating will yield a surface profile identical to the initial surface profile. However, surfaces which are plastically deformed lose their ability to recover. The magnitude of the plastic deformation can be seen from the residual depth and recovery of the material.

[0096] Coated copper alloy tokens were scratch tested using a progressive load from 30mN to 4000mN along a scratch path 4mm long. Images of the scratch track were taken with an optical microscope so that the onset of plastic deformation, as well as any cracking or delamination of the coating, could be seen. FIGS. 1 and 2 are

photomicrographs taken of scratches that were created with the Micro Scratch Tester on tokens coated with an acrylic polymer and with a nanoparticle polymer composite;

respectively.

[0097] FIGS. 1 A and 1 B are photomicrographs of 2mm track length scratches formed with a progressive load of 30-2000 mN on tokens coated with an acrylic polymer.

[0098] FIGS. 1 C and 1 D are photomicrographs of 4mm track length scratches formed with a progressive load of 30-4000 mN on tokens coated with an acrylic polymer.

[0099] FIGS. 2A and 2B are photomicrographs of 2mm track length scratches formed with a progressive load of 30-2000 mN on tokens coated with a nanoparticle polymer composite.

[00100] FIGS. 2C and 2D are photomicrographs of 4mm track length scratches formed with a progressive load of 30-4000 mN on tokens coated with a nanoparticle polymer composite.

Example 6 - Tumbler Wear Testing

[00101] Tokens coated with an acrylic polymer and tokens coated with a nanoparticle polymer composite according to Example 1 were tested in a tumbler wear test. This wear test used a Motorized Rotary Tumbler to rotate a cloth-lined barrel, containing the coated tokens, for varying periods of time.

[00102] Previous studies have been performed using a similar setup to simulate wear of coins in a circulation environment. Higher number of coins in rotation, faster rotation rate, longer time spent in the tumbler, and smaller tumbler diameter all resulted in a higher weight loss percentage. The higher the weight loss percentage, the greater amount of wear. This is because all of these conditions contribute to a greater number of collisions between coins in the tumbler, resulting in more wear. To maintain consistency, and to allow for comparison between multiple tests, all of the above parameters were kept constant for the tumbler wear testing reported below.

[00103] Coated tokens were placed in a barrel along with sufficient uncoated tokens to bring the total number of tokens up to 20. The barrel was rotated at 26 rpm.

[00104] The coated tokens were subjected to the tumbler wear testing for 80hrs. Coated tokens were periodically removed and observed to view the change in the quality of the coating over time. Coatings that could withstand 80 hrs of tumbling, without undergoing delamination, were considered to be of acceptable quality. [00105] FIGS. 3 and 4 show photos taken from the surface of three tokens coated with a nanoparticle polymer composite after treatment in the tumbler for about 1 1 and 82 hours; respectively. FIG. 5 shows a photo taken from the non-coated token after treatment in the tumbler for about 2 hrs. FIG. 6 shows a photo taken from a token coated with the acrylic polymer after treatment in the tumbler for about 1 1 hrs. These results show that the performance of nano-particle composite out-performed samples with no nano-particle polymer matrix and samples with no coating at all.

Example 7 - Steam Testing

[00106] Wear tested coated tokens from Example 6 which showed no delamination were steam tested in a Parr™ 4838 Bench-top Reactor. The steam test was used to determine if the coatings maintained enough of a seal to prevent the penetration of moisture through the coating at high temperature and pressure. Scratches in the token's surface that are deep enough to penetrate the entire coating layer allow moisture to penetrate the coating, resulting in undesirable tarnishing of the token's surface due to corrosion in that specific region.

[00107] Wear tested coated tokens from Example 6 were placed in the reactor with enough water to fill roughly half of the reactor volume, but not so much as to come in contact with the tray of tokens. The reactor was then sealed and heated to a temperature between 1 15 °C and 120 °C and kept at this temperature for 1 hour. At a temperature of 1 15 °C, the sealed chamber reaches a pressure of 25 psi. After 1 hour, the pressure in the chamber was released and the heater was shut off and allowed to cool.

[00108] The steamed tokens were removed and examined in comparison to uncoated tokens that were also steam tested. This process was repeated for up to 3 steam tests, or until tarnishing was visible on the token's surface under the transparent layer of the coating.

[00109] FIG. 7 shows a photograph of a non-coated token after exposure to steam at 1 10 °C for 1 hour under a pressure of 25 psi. As it can be seen, the token is tarnished and the discolouration of the token's surface is clearly visible.

[00110] FIG. 8A are photographs taken of tokens coated with the nanoparticle polymer composite of Example 1 after exposure to steam at 1 15 °C for 1 hour under a pressure of 25 psi. The coated tokens show no tarnishing on their coated sides. FIG. 8B are photographs which show some brown tarnishing on the uncoated sides of the tokens from FIG. 8A. FIG. 8C are photographs which show extensive greenish blue tarnishing on both sides of an uncoated control after the steam test. [00111] In the preceding description, for purposes of explanation, numerous details are set forth in order to provide a thorough understanding of the examples. However, it will be apparent to one skilled in the art that these specific details are not required and that the above-described examples are intended to be illustrative only. Alterations, modifications and variations can be effected to the particular examples by those of skill in the art without departing from the scope, which is defined solely by the claims appended hereto.

Claims

WHAT IS CLAIMED IS:

1. A coating for a metal or metal alloy, the coating comprising:

an adhesive layer bonded to the metal or metal alloy; and

a layer of a nanoparticle polymer composite, the nanoparticle polymer composite comprising nanoparticles covalently bonded to a polymer matrix;

wherein the covalent bond between the nanoparticle and the polymer matrix is a product of the reaction between a -SH group on the nanoparticle and a -SH group on the polymer matrix so that the covalent bond between the nanoparticle and the polymer matrix is -S-S-.

2. The coating according to claim 1 wherein at least a portion of the nanoparticles comprise a linker covalently bound to the surfaces of the nanoparticles; the linker being a product of the reaction between the surfaces of the nanoparticles and a linking compound having the general formula (R 0)_xSi-((CH₂)_n(CHSH)(CH₂)_oH)_y, where R is a methyl or ethyl group; the sum of "n" and "o" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4.

3. The coating according to claim 2 wherein "n" is 2, "o" is 0, "x" is 3 and "y" is 1.

4. The coating according to any one of claims 1 to 3 wherein the nanoparticles are silica, aluminum oxide nanoparticles, or a combination thereof.

5. The coating according to any one of claims 1 to 4, wherein the adhesive layer is a monolayer.

6. The coating according to any one of claims 1 to 5, wherein the bond between the adhesive layer and the metal or metal alloy is a covalent bond which is formed by the reaction of the metal or metal alloy with a first functional group on an adhesive compound.

7. The coating according to claim 6, wherein the first functional group on the adhesive compound is -NH₂ or -SH and the resulting covalent bond is -S-Ag, -NH-Cu, or -S-Cu.

8. The coating according to any one of claims 1 to 5, further comprising an adhesion promoter between the adhesive layer and the metal or metal alloy, where the adhesion promoter is bonded to the substrate and the adhesive compound is bonded to the adhesion promoter.

9. The coating according to claim 8 wherein the adhesion promoter is a fluoro- modified polysiloxane.

10. The coating according to any one of claims 6 to 9, wherein the adhesive layer is covalently bonded to the layer of the nanoparticle polymer composite, wherein the covalent bond between the adhesive layer and the nanoparticle polymer composite is a product of the reaction between a second functional group on the adhesive compound and a functional group on the nanoparticle polymer composite.

1 1. The coating according to claim 10, wherein the functional group on the nanoparticle polymer composite which reacts with the second functional group on the adhesive compound is a functional group on the nanoparticles.

12. The coating according to claim 10 or 11 , wherein the functional group on the nanoparticle polymer composite which reacts with the second functional group on the adhesive compound is -SH.

13. The coating according to any one of claims 6 to 12, wherein the adhesive compound is a molecule of the general formula:

(R²)(R³)C=C(R⁴)(R⁵) wherein at least one of R², R³, R⁴ and R⁵ is

((CH₂)_p(CHSH)(CH₂)_qH) wherein the sum of "p" and "q" is between 0 and 10; and the others are independently: H; an alkyl group; an aryl group; halogen; substituted ketone; or heteroatom; and the -SH group corresponds to the first functional group on the adhesive compound; or

(R⁶0)_xSi-((CH₂)_r(CHSH)(CH₂)_sH)_y, where R⁶ is methyl or ethyl; the sum of "r" and

"s" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4; and the -SH group corresponds to the first functional group on the adhesive compound.

14. The coating according to claim 13 wherein R² is nitro, R³ is H, and R⁴ and R⁵ are independently ((CH₂)_p(CHSH)(CH₂)_qH) where "p" is 0 or 1 , and "q" is 0.

15. The coating according to claim 13 wherein "r" is 2, "s" is 0 or 1 , "x" is 3, and "y" is 1.

16. A metal or metal alloy coated with the composition according to any one of claims 1 to 15.

17. A nanoparticle monomer composite compound comprising:

a polymerizable monomer covalently bound to a surface of a nanoparticle, wherein the surface of the nanoparticle is modified with a compound of the general formula (R 0)_xSi-((CH₂)_n(CHSH)(CH₂)₀H)_y, where R is methyl or ethyl; the sum of "n" and "o" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4; and

wherein the covalent bond is a product of the reaction between the -SH group on the surface of the nanoparticle and a -SH group on the polymerizable monomer so that the covalent bond between the nanoparticle and the polymerizable monomer is -S-S-.

18. The nanoparticle monomer composite compound according to claim 17, wherein the surface of the nanoparticle is modified with a compound of formula (R 0)₃Si- (CH₂)₃SH.

19. The nanoparticle monomer composite compound according to 17 or 18, wherein the nanoparticle is a silica or an aluminum oxide nanoparticle.

20. A nanoparticle polymer composite comprising:

nanoparticles covalently bonded to a polymer matrix,

wherein the nanoparticles are modified with a compound of the general formula (R 0)_xSi-((CH₂)_n(CHSH)(CH₂)₀H)_y, where R is methyl or ethyl; the sum of "n" and "o" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4; and

wherein the covalent bond is a product of reaction between the -SH group on the nanoparticles and a -SH group on the polymer matrix so that the covalent bond between the nanoparticles and the polymer matrix is -S-S-.

21. The nanoparticle polymer composite according to claim 20, wherein the nanoparticles are modified with a compound of formula (R 0)₃Si-(CH₂)₃SH.

22. The nanoparticle polymer composite according to 20 or 21 , wherein the nanoparticles are silica nanoparticles, aluminum oxide nanoparticles, or a combination thereof.

23. A method comprising:

synthesizing a nanoparticle comprising -SH; and

reacting the nanoparticle comprising -SH with a polymer matrix comprising -SH so that the covalent bond between the nanoparticle and the polymer matrix is -S-S-.

24. The method according to claim 23 wherein synthesizing the nanoparticle comprising -SH comprises:

synthesizing an unmodified nanoparticle; and

reacting the unmodified nanoparticle with a linking compound comprising -SH.

25. The method according to claim 24, wherein the linking compound is a molecule having the general formula (R 0)_xSi-((CH₂)_n(CHSH)(CH₂)_oH)_y, where R is an methyl or ethyl; the sum of "n" and "o" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4.

26. The method according to claim 25 wherein "n" is 2, "o" is 0, "x" is 3 and "y" is 1.

27. The method according to any one of claims 24 to 26, further comprising:

coating a surface of a metal or metal alloy with an adhesive compound to form an adhesive layer bound to the surface of the metal or metal alloy;

coating the adhesive layer with a polymerizable solution, wherein the

polymerizable solution comprises the nanoparticles comprising -SH; and

polymerizing the polymerizable solution to form a layer of a nanoparticle polymer composite on the adhesive layer, the nanoparticle polymer composite comprising the nanoparticles covalently bonded to the resulting polymer matrix by the -S-S- bond.

28. The method according to claim 27 further comprising cleaning the surface of the metal or metal alloy with an alkaline soap cleaner prior to coating with the adhesive compound.

29. The method according to claim 27 further comprising coating the surface of the metal or metal alloy with an adhesion promoter prior to coating with the adhesive compound.

30. The method according to claim 29 wherein the adhesion promoter is a fluoro- modified polysiloxane.

31. The method according to any one of claims 27 to 30 wherein polymerizing the polymerizable solution comprises forming a covalent bond between the adhesive layer and the nanoparticle polymer composite.

32. The method according to any one of claims 27 to 31 wherein the adhesive compound is a molecule of the general formula:

(R²)(R³)C=C(R⁴)(R⁵) wherein at least one of R², R³, R⁴ and R⁵ is

((CH₂)_p(CHSH)(CH₂)_qH) wherein the sum of "p" and "q" is between 0 and 10; and the others are independently: H; an alkyl group; an aryl group; halogen; substituted ketone; or heteroatom, and the -SH group corresponds to the first functional group on the adhesive compound; or

(R⁶0)_xSi-((CH₂)r(CHSH)(CH₂)sH)_y, where R⁶ is methyl or ethyl; the sum of "r" and "s" is between 0 and 3; "x" and "y" are both at least 1 ; the sum of "x" and "y" are 4; and the -SH group corresponds to the first functional group on the adhesive compound.

33. The method according to claim 32 wherein R² is nitro, R³ is H, and R⁴ and R⁵ are independently ((CH₂)_p(CHSH)(CH₂)_qH) where "p" is 0 or 1 , and "q" is 0.

34. The method according to claim 32 wherein "r" is 2, "s" is 0 or 1 , "x" is 3, and "y" is 1.

35. Use of an adhesive compound for forming an adhesive layer bonded to a surface of a metal or metal alloy, the adhesive layer for adhering the surface of the metal or metal alloy to a layer of a nanoparticle polymer composite, the nanoparticle polymer composite comprising nanoparticles covalently bonded to a polymer matrix wherein the covalent bond between the nanoparticle and the polymer matrix is a product of the reaction between a -SH group on the nanoparticle and a -SH group on the polymer matrix so that the covalent bond between the nanoparticle and the polymer matrix is -S-S-.

36. Use of a nanoparticle monomer composite compound and a polymerizable solution for forming a coating of a nanoparticle polymer composite on a surface, the nanoparticle polymer composite comprising nanoparticles covalently bonded to a polymer matrix, wherein the nanoparticle monomer composite compound comprises a polymerizable monomer covalently bound to a surface of a nanoparticle wherein the covalent bond between the nanoparticle and the polymerizable monomer is a product of the reaction between a -SH group on the nanoparticle and a -SH group on the polymerizable monomer so that the covalent bond between the nanoparticle and the polymerizable monomer is -S-S-.

37. Use of a nanoparticle polymer composite for coating a surface of a metal or metal alloy, the surface of the metal or metal alloy comprising an adhesive layer which is bonded to the surface of a metal or metal alloy, the nanoparticle polymer composite comprising nanoparticles covalently bonded to a polymer matrix wherein the covalent bond between the nanoparticle and the polymer matrix is a product of the reaction between a -SH group on the nanoparticle and a -SH group on the polymer matrix so that the covalent bond between the nanoparticle and the polymer matrix is -S-S-.