Corrosion protection for metallic substrates

Abstract

To provide a tiecoat coating composition for a metallic substrate.SOLUTION: There is disclosed a tiecoat coating composition for use in a coating system for a metallic substrate comprising at least three coating layers. The system has a primer coating layer which overlies the metallic substrate, a tiecoat coating layer which overlies the primer coating layer, and a finish coating layer which overlies the tiecoat coating layer. The primer coating layer is formed from a primer composition, the tiecoat coating layer is formed from a tiecoat composition, and the finish coating layer is formed from a finish composition. The primer composition comprises a primer carrier medium and a primer corrosion inhibitor in which the primer inhibitor has a galvanic cathodic mechanism. The finish composition is formulated to give a predetermined surface texture and appearance. The tiecoat composition comprises a tiecoat carrier medium and a tiecoat corrosion inhibitor. The tiecoat corrosion inhibitor has a barrier mechanism.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to corrosion protection for metal substrates. More particularly, the present application relates to corrosion protection for metal substrates. [Background technology]

[0002] Corrosion of metals is estimated to cost approximately 3% of global Gross Domestic Product (GDP) and constitutes an important aspect of the global economy. There is considerable interest in the development of new and improved corrosion protection techniques and, in particular, protective coatings. Protective coatings are generally classified according to the mechanism by which they act. Commonly used mechanisms are barrier protection, inhibition or passivation of the substrate and galvanic cathodic protection.

[0003] Coatings that use a barrier mechanism, so-called barrier coatings, can and often are used on structures that are submerged underwater or underground. Barrier coatings are typified by the use of inert pigmented coatings such as micaceous iron oxide, glass flake, and lamellar aluminum. These systems are typically used as high pigment volume concentration (PVC) systems, giving a dense coating with significantly reduced permeability to water and other aggressive chemical species. The level of protection is highly dependent on the coating thickness and number of coats, with coating thicknesses reported to provide the highest performance when built up from several thin coats.

[0004] The most common pigment used in barrier coatings is micaceous iron oxide. Optimum performance is obtained with PVC in the range of 0.5% to 1.5%. When lamellar aluminum is used as a pigment, it is typically a leafing grade. Aluminum-based paints or coatings need to be applied as the first coat to affect cathodic delamination. Aluminum can corrode at high and low pH as well, and therefore by reaction with hydroxyl radicals generated at the cathode of any electrochemical cell that are formed at the metal substrate / coating interface. The use of glass flakes is typically limited to very thick coatings due to the large size of the flakes (100 μm to 1000 μm).

[0005] Coatings that use an inhibition or passivation mechanism, so-called inhibition coatings, function by reaction of the coating components / pigments with the metal substrate and are therefore primarily applied as primers. These coatings are preferentially used when the substrate is exposed to atmospheric corrosion and not when it is submerged in water or soil. The inhibition mechanism relies on the passivation of the metal and the building up of a layer of metal complexes as a result of the passivation reaction. The metal complexes are formed by the reaction of Cl - Or H + It prevents the transport of aggressive species, such as ions or dissolved oxygen, to the metal of the substrate.

[0006] The active components / pigments of inhibitor coatings are typically slightly water soluble and generate cations upon dissolution. Phosphates are commonly used, but chromates, molybdates, nitrates, borates and silicates are also used. The choice of active ingredient is increasingly subject to regulatory pressure due to increasing environmental and health and safety concerns.

[0007] Current regulations limit the substances that can be used in inhibitor coatings. Chrome(VI) compounds are subject to authorisation under REACH (Annex XIV, 2008). Other legislation regarding anti-corrosion pigments includes the ELV (Enc of Life Vehicle) Directive, which has seen the phasing out of lead pigments since 2003 and Chromium(VI) in primers and pre-treatments since 2007. Other regulations include the WEEE (Waste Electrical and Electronic Equipment Directive 2006), which restricted the use of Cr(VI) in white goods, and the RoHS (Restriction of Hazardous Substances Directive 2002). In the US, OSHA (Occupational Safety and health Administration regulation 2006) limits the permissible employee exposure to Cr(VI) to 52 μg / m 3 to 5 μg / m 3 to 100 mg / kg. Zinc phosphate is also of increasing concern because it is toxic to aquatic organisms and can produce long-term adverse effects in the aquatic environment. Accidental ingestion of this material can be harmful to an individual's health. Soluble zinc salts cause painful irritation and wasting of the digestive tract, as well as vomiting. Therefore, it would be beneficial to reduce or eliminate such materials from anticorrosive coatings.

[0008] The mechanism of inhibitory pigments is based on partial dissolution of the pigment by water diffusing into the coating. At the surface of the metal substrate, the dissolved ions react with the metal and generate reaction products that passivate the surface. It is essential that the inhibitory pigment is soluble enough to release ions for reaction. However, too high a solubility can result in blistering at the metal substrate / coating interface. An ideal inhibitory coating should form a barrier against water and harmful ions while simultaneously releasing a sufficient amount of inhibitor ions. These two requirements are in principle contradictory, and inhibitory coatings require a balance between the barrier properties of the coating (the lower the permeability, the better the barrier) and the ability of the pigment to solvate and migrate the created ions to the coating-substrate interface (the higher the permeability, the greater the solvation and migration of ions). Pigments used in inhibitory coatings are sometimes classified according to their effect on the anodic and cathodic reactions of the electrochemical cell formed at the metal substrate / coating interface.

[0009] Galvanic cathodic inhibitors, typically with high levels of zinc (often called "zinc rich") or inorganic salts of magnesium and manganese, inhibit corrosion at the cathode by reacting with hydroxyl ions to form insoluble deposits that increase the cathodic resistance to polarization. Anodic inhibitors similarly slow the rate of corrosion by increasing the anodic polarization at the anode. Summary of the Invention [Means for solving the problem]

[0010] In accordance with the present invention, there is provided a tie coat coating composition for use in a coating system including at least three coating layers for a metal substrate, the coating layer being a primer coating layer on the metal substrate, the tie coat coating layer being on the primer coating layer, and the finish coating layer being on the tie coat coating layer, the primer coating layer being formed from a primer composition, the tie coat coating layer being formed from a tie coat composition, and the finish coating layer being formed from a finish composition, the primer composition comprising a primer carrier medium and a primer corrosion inhibitor, the primer corrosion inhibitor having a galvanic cathode mechanism, and the finish composition being formulated to impart a predetermined surface texture and / or appearance, the tie coat coating composition comprising a tie coat carrier medium and a tie coat corrosion inhibitor, and the tie coat corrosion inhibitor having a barrier mechanism.

[0011] According to the present invention, there is also provided a coating system for a metal substrate comprising at least three coating layers, a primer coating layer on the metal substrate, a tie coat coating layer on the primer coating layer, and a finish coating layer on the tie coat coating layer, wherein the primer coating layer is formed from a primer composition, the tie coat coating layer is formed from a tie coat composition according to the above paragraph, and the finish coating layer is formed from a finish composition, the primer composition comprising a primer carrier medium and a primer corrosion inhibitor, the primer corrosion inhibitor having a galvanic cathode mechanism, and the finish composition is formulated to impart a predetermined surface texture and / or appearance.

[0012] For a better understanding of various embodiments which are helpful in understanding the detailed description, reference is made by way of example only to the accompanying drawings in which: [Brief description of the drawings]

[0013] [Figure 1] The results of a test for water vapor transmission rate are illustrated. [Diagram 2] 4 illustrates the progression of impedance modulus for a single coated sample. [Diagram 3] 4 illustrates the impedance modulus evolution for a three-coat system sample. [Figure 4(a)] 1 illustrates a selection of Bode plots of phase shift for the 3-coat control sample. [Figure 4(b)] 1 illustrates a phase angle Bode plot for a high impedance sample. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Detailed Description An embodiment of the present disclosure provides a tie coat coating composition for use in a coating system for a metal substrate, the coating system including at least three coating layers, in which a primer coating layer (i.e., a first primer coating layer) is disposed on the metal substrate, a tie coat coating layer (i.e., a second tie coat coating layer) is disposed on the primer coating layer, and a finish coating layer (i.e., a third finish coating layer) is disposed on the tie coat coating layer.

[0015] The primer coating layer is formed from a primer composition (i.e., a first primer composition). The tie coat coating layer is formed from a tie coat composition (i.e., a second tie coat composition). The finish coating layer is formed from a finish composition (i.e., a third finish composition). The primer composition includes a primer carrier medium (i.e., a first primer carrier medium) and a primer corrosion inhibitor (i.e., a first primer corrosion inhibitor). The primer corrosion inhibitor has a galvanic cathode mechanism. The finish composition is formulated to impart a predetermined surface texture and / or appearance. The tie coat composition includes a tie coat carrier medium (i.e., a second tie coat carrier medium) and a tie coat corrosion inhibitor (i.e., a second tie coat corrosion inhibitor). The tie coat corrosion inhibitor has a barrier mechanism.

[0016] Tie Coat corrosion inhibitors are water and Cl - or H + It creates a barrier that reduces the access of corrosive ions such as arsenic, nitric acid, and phosphate to the metal substrate. The level of protection depends on the integrity of the tie coat coating, its hydrophobicity, affinity for water and the thickness of the coating.

[0017] In some embodiments of the invention, the tie coat corrosion inhibitor is present in the range of 0.05% to 1.0%, 0.05% to 0.8%, 0.05% to 0.6%, or 0.1% to 0.5% by weight of the tie coat composition. In some embodiments of the invention, the tie coat corrosion inhibitor is present in the range of 0.1% or 0.5% by weight of the tie coat composition.

[0018] In some embodiments of the invention, the tie coat corrosion inhibitor comprises one or a mixture of graphene nanoplates, graphene oxide nanoplates, reduced graphene oxide nanoplates, bilayer graphene nanoplates, bilayer graphene oxide nanoplates, bilayer reduced graphene oxide nanoplates, few layer graphene nanoplates, few layer graphene oxide nanoplates, few layer reduced graphene oxide nanoplates, graphene / graphite nanoplates of 6-14 layers of carbon atoms, graphite flakes having at least one nanoscale dimension and up to 40 layers of carbon atoms, graphite flakes having at least one nanoscale dimension and 25-30 layers of carbon atoms, graphite flakes having at least one nanoscale dimension and 20-35 layers of carbon atoms, or graphite flakes having at least one nanoscale dimension and 20-40 layers of carbon atoms.

[0019] Graphene nanoplates, graphene oxide nanoplates, reduced graphene oxide nanoplates, bilayer graphene nanoplates, bilayer graphene oxide nanoplates, bilayer reduced graphene oxide nanoplates, few layer graphene nanoplates, few layer graphene oxide nanoplates, few layer reduced graphene oxide nanoplates, graphene / graphite nanoplates with 6-14 carbon atom layers, graphite flakes with nanoscale dimensions and up to 40 carbon atom layers, graphite flakes with nanoscale dimensions and 25-30 carbon atom layers, graphite flakes with nanoscale dimensions and 20-35 carbon atom layers, or graphite flakes with nanoscale dimensions and 20-40 carbon atom layers are hereinafter collectively referred to as "graphene / graphite platelets." Graphene, graphene oxide, and / or reduced graphene oxide nanoplates typically have 1-10 carbon atom layers, thicknesses typically between 0.3 nm and 3 nm, and in-plane dimensions in the range of roughly 100 nm to 100 μm.

[0020] In some embodiments of the present invention, the tie coat corrosion inhibitor comprises nanoplates of one or a mixture of 2D and / or layered 2D materials.

[0021] 2D materials (sometimes called monolayer materials) are crystalline materials consisting of a single layer of atoms. Layered 2D materials consist of layers of 2D materials that are weakly stacked or bound together to form a three-dimensional structure. 2D materials and nanoplates of layered 2D materials have thicknesses in the sub-nanoscale range, with the other two dimensions generally being at a scale greater than the nanoscale.

[0022] The 2D material used in the compositions of the invention can be graphene, graphene oxide, reduced graphene oxide, hexagonal boron nitride (hBN), molybdenum disulfide (MoS2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), graphene (C), borophene (B), phosphorene (P), or a 2D in-plane heterostructure of two or more of the aforementioned materials.

[0023] The layered 2D materials can be multiple layers of graphene (C), graphene oxide, reduced graphene oxide, hexagonal boron nitride (hBN), molybdenum disulfide (MoS2), tungsten diselenide (WSe2), silicene (Si), germanene (Ge), graphene (C), borophene (B), phosphorene (P), or 2D vertical heterostructures of two or more of the aforementioned materials.

[0024] The use of graphene / graphite platelets and / or nanoplates of 2D materials as tie coat corrosion inhibitors in a tie coat composition according to the invention will result in multiple layers of graphene / graphite platelets and / or nanoplates of 2D materials in the tie coat layer depending on the concentration of incorporation of the graphene / graphite platelets and / or nanoplates of 2D materials and the applied dry film thickness. Each platelet or nanoplate is potentially several atomic layers thick. The presence of multiple layers of graphene platelets in the tie coat layer will provide a barrier against water, any dissolved oxygen and / or Cl carried by the water. - or H +The labyrinth-like pathway provides a complex and tortuous (labyrinth-like) pathway for the ingress of any aggressive ions such as argon, ...

[0025] Graphene / graphite platelets typically have thicknesses between 0.3 nm and 12 nm and in-plane dimensions in the range of roughly 100 nm to 100 μm. As a result, and due to the high lateral and surface area of ​​graphene / graphite platelets, coatings comprised of tie coat compositions according to the present invention can be significantly thinner than comparable coatings that include other barrier mechanism materials / pigments, such as micaceous iron oxide, glass flakes, and / or aluminum flakes. Furthermore, it has been found that the use of graphene platelets results in coatings with good adhesive strength and mechanical properties. In some embodiments of the present invention, the graphene / graphite platelets and or nanoplatelets of 2D materials have a D50 particle size of less than 45 μm, less than 30 μm, or less than 15 μm as measured by a Mastersizer 3000.

[0026] In some embodiments of the present invention, the primer corrosion inhibitor is one or a mixture of inorganic salts of zinc, magnesium and / or manganese.

[0027] Anticorrosive coating systems may include the compositions according to the present invention. Such coatings are within the scope of the present invention. Such coatings may further include other components known to be used in the formulation and / or manufacture of anticorrosive coatings.

[0028] In some embodiments of the invention, the tie coat composition further comprises an additional tie coat corrosion inhibitor, the additional tie coat corrosion inhibitor having a galvanic cathodic or passivation mechanism. In some embodiments of the invention, the additional tie coat corrosion inhibitor is present in the range of 0.05% to 1.0%, 0.05% to 0.8%, 0.05% to 0.6%, or 0.1% to 0.5% by weight of the tie coat composition. In some embodiments of the invention, the additional tie coat corrosion inhibitor is present in a proportion of 0.1% or 0.5% by weight of the second composition (i.e., the tie coat composition).

[0029] In some embodiments of the present invention, the additional tie coat corrosion inhibitor comprises at least one of ion exchanged pigments, silica, calcium exchanged silica, magnesium oxyaminophosphate, and / or a mixture of organic amines, phosphoric acid and / or inorganic phosphates and metal oxides and / or metal hydroxides.

[0030] Ion-exchanged pigments, silica, calcium-exchanged silica, and magnesium oxyaminophosphates are all generally considered to be non-hazardous materials. Mixtures of organic amines, phosphoric acids and / or inorganic phosphates and metal oxides and / or hydroxides are generally considered to be non-hazardous materials depending on the metals used. Such materials are therefore beneficial in that they pose far fewer environmental concerns than previously used corrosion inhibitors.

[0031] In some embodiments of the invention, the additional tie coat corrosion inhibitor, i.e., the third tie coat corrosion inhibitor, is selected from the group consisting of zinc chromate, zinc molybdate, zinc tungstate, zinc vanadate, zinc phosphite, zinc polyphosphate, zinc borate, zinc metaborate, magnesium chromate, magnesium molybdate, magnesium tungstate, magnesium vanadate, magnesium phosphate, magnesium phosphite, magnesium polyphosphate, magnesium borate, magnesium metaborate, calcium chromate, calcium molybdate, calcium tungstate, calcium vanadate, calcium phosphate, calcium phosphite, calcium polyphosphate, calcium borate, calcium ... The additives may include one or more of strontium bromate, strontium molybdate, strontium tungstate, strontium vanadate, strontium phosphate, strontium phosphite, strontium polyphosphate, borates, strontium metaborate, barium chromate, barium molybdate, barium tungstate, barium vanadate, barium phosphate, barium phosphite, barium polyphosphate, barium borate, barium metaborate, aluminum chromate, aluminum molybdate, aluminum tungstate, aluminum vanadate, aluminum phosphate, aluminum phosphite, aluminum polyphosphate, aluminum borate, and / or aluminum metaborate.

[0032] In some embodiments of the present invention, the carrier medium of the primer and / or tie coat composition is an epoxy resin. Thus, in such embodiments, the tie coat carrier medium comprises a curable resin, which may be a liquid curable resin. Thus, in such embodiments, the primer carrier medium comprises a curable resin, which may be a liquid curable resin.

[0033] As a result, coatings formed from primer and / or tie coat compositions according to some embodiments of the present invention will be comprised of an epoxy resin in which a first and / or second corrosion inhibitor (i.e., a primer corrosion inhibitor and / or a tie coat corrosion inhibitor) is loaded. Thus, in such embodiments, the primer corrosion inhibitor is loaded in the primer carrier medium of the primer coating layer formed from the primer composition. In such embodiments, the primer corrosion inhibitor is substantially uniformly dispersed throughout the primer coating layer.

[0034] Thus, in such embodiments, the tie coat corrosion inhibitor is disposed in the tie coat carrier medium of the tie coat coating layer formed from the tie coat composition, hi such embodiments, the tie coat corrosion inhibitor is substantially uniformly dispersed throughout the tie coat coating layer.

[0035] In embodiments where the tie coat composition includes an additional tie coat corrosion inhibitor, the additional tie coat corrosion inhibitor is disposed in the tie coat carrier medium of the tie coat coating layer formed from the tie coat composition, hi such embodiments, the additional tie coat corrosion inhibitor is substantially uniformly dispersed throughout the tie coat coating layer.

[0036] In some embodiments of the present invention, the carrier medium of the primer and / or tie coat composition is comprised of one or more suitable crosslinkable resins, non-crosslinkable resins, thermosetting acrylics, amino resins, urethanes, carbamates, polyesters, alkyd epoxies, silicones, polyureas, silicates, polydimethylsiloxanes, vinyl esters, unsaturated polyesters, and mixtures or combinations thereof.

[0037] Epoxy resins and other materials suitable for use as the carrier medium for the primer composition tend to release Cl from water and / or dissolved oxygen and / or sodium chloride after relatively short periods of exposure to water or moisture. -or H from water + The coating will become saturated with dissolved ions such as ions. If water, oxygen and / or dissolved ions reach the interface between the primer coating and the metal substrate, they can cause the creation of an electrochemical cell, followed by wet corrosion of the metal substrate. The mechanisms of such corrosion are well known and need not be discussed herein.

[0038] Use of a tie coat layer according to the present invention has the advantage that the barrier to permeation of water, oxygen and / or dissolved ions as a result of the tie coat corrosion inhibitor inhibits or delays the water, oxygen and / or dissolved ions from reaching the surface of the primer layer remote from the metal substrate, thus inhibiting or delaying saturation of the primer layer with water, oxygen and / or dissolved ions.

[0039] Graphene comes in many forms, and the growth of films by CVD (chemical vapor deposition) is well understood and can result in graphene films of 1-3 atomic layers. Such films are often used in experiments related to graphene. Such techniques have limited practical applicability since they only allow relatively small areas of films to be produced or substrates to be coated. In practical applications, graphene is more typically used in the form of graphene nanoplatelets. Graphene nanoplatelets may be produced either by exfoliation of graphite or via synthetic solvothermal processes. Such graphene nanoplatelets vary in number of atomic layers, surface area, functional groups and sp 2The content can vary considerably. Such variation affects the physical properties of graphene, such as the conductivity of the graphene. Similarly, graphite flakes having nanoscale dimensions and 40 or fewer layers of carbon atoms, graphite flakes having nanoscale dimensions and 25-30 layers of carbon atoms, graphite flakes having nanoscale dimensions and 20-35 layers of carbon atoms, or graphite flakes having nanoscale dimensions and 20-40 layers of carbon atoms may be produced either by graphite exfoliation or via synthetic solvothermal processes.

[0040] Graphene / graphite platelets typically have a thickness between 0.3 nm and 12 nm and in-plane dimensions in the range of roughly 100 nm to 100 μm. As a result, and due to the high lateral and surface area of ​​graphene / graphite platelets, coatings comprised of compositions according to the present invention can be significantly thinner than comparable coatings that include other barrier mechanism materials / pigments, such as micaceous iron oxide, glass flakes, and / or aluminum flakes. Furthermore, it has been found that the use of graphene platelets results in coatings with good adhesive strength and mechanical properties. In some embodiments of the present invention, the graphene platelets have a D50 particle size of less than 45 μm, less than 30 μm, or less than 15 μm as measured by a Mastersizer 3000.

[0041] It is well known that metals, particularly steel, can be protected from the deteriorating effects of rapid corrosion by applying a coating of metallic zinc to the steel. The coating may be by immersing the steel in molten zinc (galvanizing), but this is not always possible. A second, and often more practical, approach is to coat the steel with a zinc-rich coating.

[0042] Galvanizing protects steel because zinc is much more durable than steel under most conditions, so the zinc coating forms a barrier on the steel surface that shields the steel from corrosive agents while corroding very slowly.

[0043] The corrosion protection afforded to steel by zinc-rich coatings is provided in several ways.

[0044] The use of zinc-rich coatings protects steel by the electrochemical or sacrificial action of zinc. This effect occurs when the steel and zinc particles of the coating are electrically bonded and in contact with a conductive aqueous solution. In such a case, the steel is protected at the expense of zinc because the potential of zinc is sufficiently higher than that of the steel (iron) that the flow of electrons is directed towards the steel, maintaining a negative charge on the steel surface and preventing the formation of ferrous ions that can lead to iron(III) oxide (rust). This effect results in the formation of zinc hydroxide on the zinc, which in turn reacts with chlorine or carbon dioxide in the surrounding environment to form basic zinc salts. These basic zinc salts are deposited on the steel surface. The zinc salts form a protective coating that provides good barrier protection for the steel. When this effect is exerted, the metallic zinc in the zinc-rich coating has been consumed by salt formation.

[0045] It is known that cathodic protection only occurs up to the point where electrical contact between the zinc particles and the steel is lost following dissolution of the zinc and the formation of zinc hydroxide and zinc oxide. Thus, the efficiency of zinc-rich primers is low and involves leaching of zinc compounds, creating environmental problems.

[0046] It is known to incorporate conductive carbon black into zinc-rich coatings to improve the electrical connectivity between the zinc particles and the steel, thus allowing for lower zinc metal retention and improved film performance. Several alternatives to conductive carbon black (carbon nanotubes, graphene) have been evaluated with varying levels of success.

[0047] Without being bound by theory, it is believed that the barrier activity of the graphene / graphite platelets and or nanoplates of 2D material encapsulated in a carrier medium of a second composition (i.e., tie coat composition), such as an epoxy resin, and applied as a second coating layer (i.e., tie coat coating layer) to a first coating layer (i.e., primer coating layer) comprising a zinc-rich primer and beneath a third coating layer (i.e., top coating layer) acts as a highly efficient barrier that reduces the rate of water absorption by the first coating layer (i.e., primer coating layer) and, consequently, the reaction rate of the zinc-rich primer.

[0048] Thus, there are several advantages that accrue from the use of the composition of the first aspect of the invention as a tie coat coating layer (i.e., the second coating layer) in a three coating layer coating system. These include: a. Increased life of the coating system as a whole b. Potential to reduce thickness of zinc-rich primer c. A reduction in the amount of zinc lost through leaching from the membrane resulting in improved environmental performance It is.

[0049] In a composition (i.e., a tie coat composition) according to the present invention, the inclusion of at least one third corrosion inhibitor (i.e., an additional tie coat corrosion inhibitor) having a passivation mechanism helps to prevent corrosion or inhibit initiated corrosion.

[0050] In some embodiments of the present invention, the additional tie coat corrosion inhibitor comprises at least one ion exchange pigment (IEP). Ion exchange pigments include, but are not limited to, compositions comprising silica, calcium exchanged silica, and alumina. Ion exchange pigments are a relatively new class of pigments that are corrosion inhibitors with a passivation mechanism. These compounds are inorganic oxides with a large surface area that support ionic corrosion inhibitors by ion exchange with surface hydroxyl groups. The oxides are chosen for their acid or base properties to provide either cation or anion exchangers (silica is used as the cation carrier and alumina for the anion carrier). The corrosion protection behavior of the primer corrosion inhibitor is governed by the rate of ion release caused by dissolution of the ion exchange pigment.

[0051] Calcium exchanged silica ion-exchange pigments offer an environmentally friendly alternative to chromium and zinc based systems. Calcium exchanged silica works by controlled diffusion as water and aggressive ions penetrate the coating. The ions released by the ion-exchange pigment react with the metal substrate in a known manner associated with passivation. There are both anodic and cathodic reactions. Depending on the pH in the coating, the silica of the ion-exchange pigment can dissolve as silicate ions. When the metal substrate is an iron alloy such as low or medium or high unalloyed carbon steel or low or high alloy steel. This soluble fraction of the pigment, the silicate ions, can react with ferric ions. This results in the formation of a protective layer at the surface of the metal substrate. In parallel with this reaction, calcium cations or other metal cations on the silica surface are released and form a calcium silicate film in the alkaline areas on the metal surface by reaction with the soluble silica. This, together with the iron silicate, helps to strengthen the protective film by the formation of a mixed oxide layer on the metal surface. At the same time, calcium or other metal cations are released and the silica captures the aggressive cations that enter the calcium silicate film. These processes of film and compound formation result in the inhibition of the corrosion reaction by a dual passivation mechanism: adsorption of aggressive ions on the metal substrate and the formation of a protective layer.

[0052] In some embodiments of the present invention, the additional tie coat corrosion inhibitor comprises at least one magnesium oxyaminophosphate. The magnesium oxyaminophosphate constitutes an alternative environmentally friendly anti-corrosion material. Upon exposure of the magnesium oxyaminophosphate to moisture, the amines of the salt passivate the metal surface by a known passivation mechanism. As a result of the passivation, a protective layer composed mainly of magnesium oxide and having a thickness of approximately 25-50 nm is deposited on the surface of the metal substrate. When the metal substrate is steel, the protective layer keeps the metal surface passive by providing anodic inhibition. When the metal substrate is aluminum or an aluminum alloy, the magnesium oxide layer keeps the potential higher than the corrosion potential of the aluminum or aluminum alloy, thus providing cathodic inhibition.

[0053] Electrochemical impedance spectroscopy (EIS) measurements show that while graphene has a high level of conductivity in its native state, this conductivity is significantly reduced when incorporated as platelets into epoxy resins (which are generally good insulators). This is especially true when the epoxy resin contains other amorphous or crystalline additives such as pigments and fillers, creating a homogeneous but highly disordered matrix. In such a matrix, the graphene platelets do not exhibit any significant conductivity and therefore do not provide any cathodic protection or benefit to the corrosion potential at the surface of the metal substrate.

[0054] The advantage of the tie coat composition according to the invention is that the tie coat and the additional tie coat corrosion inhibitor act synergistically with each other. In particular, the combination of the tie coat and the additional tie coat corrosion inhibitor in the same carrier medium has the advantage of increasing the service life of the tie coat layer made of the tie coat composition according to the invention. The enhancement can be significant and can exceed the service life of known anticorrosive coatings by two, three or four times. In this context, the service life should be understood to be the period between the application of the coating and the need to reapply the coating due to the degradation of the originally applied coating. In the terminology of the International Organization for Standardization standard 4628-3:2005, the service life is the period between the application of the coating and the occurrence of a rust rating of grade Ri3.

[0055] A further advantage of the compositions according to the first aspect of the invention (i.e. the tie coat compositions) and the coating systems according to the second aspect of the invention is that the tie coat coating layer of the first aspect enhances the adhesion strength of the primer coating layer to the top coating layer compared to known systems.

[0056] Without wishing to be bound by theory, it is believed that the increased useful life of the coating is realized for the following reasons. The primer corrosion inhibitor is substantially uniformly mixed in the primer carrier medium so that a portion of the first corrosion inhibitor is proximate the interface between the primer coating layer and the metal substrate. The tie coat corrosion inhibitor is substantially uniformly mixed in the tie coat carrier medium which are applied together as a tie coat coating layer. - The optional additional tie coat corrosion inhibitor is substantially uniformly mixed in the tie coat carrier medium carrying the tie coat corrosion inhibitors together applied as a tie coat coating layer. Metals in the vicinity of the primer corrosion inhibitor can dissociate from moisture experienced during application of the primer coating layer and eventual exposure during use to form zinc hydroxide and zinc hydroxide when the primer corrosion inhibitor is zinc. The graphene / graphite platelets and / or nanoplates of the 2D material distributed by the tie-coat carrier medium create labyrinth-like pathways between the surface of the tie-coat coating layer away from the metal substrate and the surface of the tie-coat coating layer adjacent to the primer coating layer. The labyrinth-like pathways created by the graphene / graphite platelets and / or nanoplates of the 2D material inhibit the diffusion of water, dissolved oxygen, and / or dissolved ions from a surface of the tie-coat coating layer away from the metal substrate to a surface of the tie-coat coating layer adjacent to the primer coating layer. Once water, dissolved oxygen, and dissolved ions diffuse through the labyrinth of pathways in the tie coat coating layer, they enter the primer coating layer and encounter the primer corrosion inhibitor, causing the primer corrosion inhibitor (i.e., the first corrosion inhibitor) to dissolve and react. The slow diffusion of water, dissolved oxygen, and / or dissolved ions along the labyrinthine pathways of the tie coat coating layer (i.e., the second coating layer) has the effect that it takes a significant amount of time for the primer corrosion inhibitor (i.e., the first corrosion inhibitor) in the primer coating layer to completely dissolve, so that there is a very long period of time before the primer corrosion inhibitor in the primer coating layer is exhausted and the benefits of the primer corrosion inhibitor cease, which period is longer than in the case of known anticorrosive coatings, and therefore the primer coating layer has an increased useful life.

[0057] Increasing the service life of coatings comprising the tie coat compositions according to the present invention has significant economic advantages since application of corrosive coatings is expensive in terms of both labor and material costs, as well as significant ecological advantages since less coating is used and, as noted above, the coating content can be ecologically better than known coatings.

[0058] experiment A graphene-free epoxy prototype base coating (part A) was first prepared and formulated to be representative of a standard practical intermediate coating layer, as outlined in Table 1.

[0059] [Table 1]

[0060] D3 includes an additional tie coat corrosion inhibitor. In the above example, the additional tie coat corrosion inhibitor is a calcium oxide modified silica product (Inhibisil; see Table 2 for further details). In other examples, the additional tie coat corrosion inhibitor may be an ion-exchanged pigment or other passivated pigment. In the above example, the additional tie coat corrosion inhibitor, Inhibisil, is present at 1% by weight of the tie coat composition.

[0061] The preparation steps were as follows:

[0062] Components 1-6 were placed in a high speed overhead mixer and mixed for 10 minutes at 2000 rpm. The resulting gel was inspected to see if it was uniform and free of particles. If not, mixing was continued until the gel was uniform and free of particles.

[0063] Components 7 and 8 were added to the mixer and mixed at 2000 rpm for 15 minutes or until the grind (maximum particle size) was less than 25 μm. This is known as the grinding stage of the production.

[0064] Component 9 was added and mixed at 1000 rpm for 15 minutes. This is known as the letdown stage of the process.

[0065] By adding amine slow curing agent 11 at 10 wt%, the composition was ready for application to a primer coating layer (i.e., first coating layer) to form a tie coat coating layer (i.e., second coating layer) having barrier properties.

[0066] As shown in Table 1 above, three compositions D1, D2 and D3 according to the invention were then prepared using the same initial preparation route as for the epoxy prototype base, by replacing the epoxy in the last step (formulation component 10) with a commercial GNP-containing dispersing additive (formulation component 9).

[0067] The graphene dispersion additives detailed in Table 2 were effectively treated as masterbatches and added in various amounts according to their graphene content and the final graphene content specified in the end coating (Table 1, i.e., GNP loading).

[0068] [Table 2]

[0069] The graphene dispersion additives used (e.g., graphene / graphite platelets) were commercially available from Applied Graphene UK Limited, UK as A-GNP10 or Genable™ 1000, having 25-35 layers of carbon atoms, A-GNP35 or Genable™ 1200, having 6-14 layers of carbon atoms, and Genable™ 3000, a mixture of A-GNP10 and Inhibisil™. Inhibisil is a calcium oxide modified silica product commercially available from PPG Industries Ohio, Inc., USA.

[0070] Prior to coating application, all substrates were degreased with acetone. Each first coat was applied using a conventional spray gun to grit blasted mild steel CR4 grade panels of dimensions 150 x 100 x 2 mm (commercially available from Impress North East Ltd). For multi-coat samples, the overcoat interval was 3 hours and all panels were given a final cure period of 7 days at 23°C (± 2°C).

[0071] The dry film thickness of the prepared coatings ranged from 50-60μ for single-coated samples and 120-180μ for multi-coated samples. All the details of the prepared coating systems can be seen in Table 3.

[0072] [Table 3]

[0073] All substrates were back-stiffened and edged prior to testing. The zinc-rich primer and polyurethane topcoat used were standard commercial primer and topcoat, respectively.

[0074] Neutral Salt Spray (NSS) Test

[0075] ISO 12944 identifies three test methods (see Table 4, an excerpt from ISO 12944) that demonstrate performance at C4 and C5 atmospheric conditions.

[0076] [Table 4]

[0077] These include moisture condensation, neutral salt spray and cyclic aging tests. As a preliminary step to identify systems with the potential to provide extended service life, neutral salt spray was selected as the initial screening method. Moisture condensation and cyclic aging tests will be performed on graphene formulations that performed as well or better than zinc-rich epoxy primers.

[0078] Panels were placed in a corrosion chamber to ISO 9227 for up to 720 hours. The test method consists of a continuous salt spray mist at a temperature of 35°C. At 10 days (240 hour intervals) the panels were evaluated for signs of blistering, corrosion and corrosion creep according to ISO 4628. These evaluations were supplemented with electrochemical measurements performed at the same intervals.

[0079] Electrochemical measurements

[0080] Prior to electrochemical / NSS testing, a small amount of panel back stiffener material was removed with a knife blade to provide an electrical contact for the working electrode connector. After completion of electrochemical testing, the section where the back stiffener material was removed was covered with electrical tape to reduce the possibility of any corrosion while the sample was under NSS conditions. An additional preliminary step was to mark the test area with a permanent marker to aid in repositioning the test area for subsequent electrochemical measurements.

[0081] All electrochemical measurements were recorded using a Gamry 1000E potentiostat with a Gamry ECM8 multiplexer to allow for simultaneous testing of up to eight samples per run. Each individual channel was connected to a Gamry PCT-1 paint test cell, specifically designed for the electrochemical testing of coated metal substrates.

[0082] Within each paint test cell, a conventional three-electrode system was used, with the coated steel specimen representing the working electrode, a graphite rod as the counter electrode, and a saturated calomel electrode (SCE) as the reference electrode. The test area of ​​the working electrode was 14.6 cm 2 All tests were performed using 3.5 wt% NaCl electrolyte. For all samples, electrochemical tests were performed using corrosion potential measurements (E corr ), consisted of an experimental cycle consisting of electrochemical AC impedance spectroscopy (EIS) measurements.

[0083] AC EIS and E corr The measurements allow the quantitative determination of several properties related to the corrosion resistance of the samples without lengthy tests requiring artificial weathering.

[0084] E corr- Electrochemical corrosion potential (ECP) is the voltage difference between a metal immersed in a given environment and a suitable standard reference electrode (SRE) or electrode with a stable and known electrode potential. Electrochemical corrosion potential is also known as rest potential, open circuit potential or free corrosion potential and is expressed in the equation: E corr It is represented by E corr A higher value indicates a lower corrosion rate and a lower value indicates a higher corrosion rate.

[0085] During all EIS experiments, an AC voltage of 10 mV was applied to the sample with 0 volts DC bias over the frequency range of 1 MHz to 0.05 Hz. Ten measurements were recorded for every 10 divisions of frequency. An integration time of 1 second was used per measurement, with a delay time of 0.2 seconds between each measurement. Equivalent circuit fitting to the acquired data was performed using the proprietary Gamry Echem Analyst software package.

[0086] In the first case, the samples listed in Table 3 above were tested before being placed under the NSS. Then, every 10 days, the samples were removed from the NSS and electrochemical measurements were performed.

[0087] Results and Discussion

[0088] Single layer coat

[0089] Water absorption in organic coatings can be measured and quantified using a variety of different methods, including more traditional gravimetric and capacitance methods. Capacitive methods rely on the creation of a capacitor over time due to water absorption in the organic coating. Water has a dielectric constant around 30 times that of most organic coatings, and the change in capacitance as water enters the coated substrate correlates with the level of water absorption. Such dielectric type capacitance information can also be derived from EIS data, but there are several additional advantages to using EIS.

[0090] When applied to the study of organic-based protective anticorrosive coatings, impedance values ​​provide an indication of the corrosion protection in its original form. Such values ​​may be used as an initial screen for coating barrier-type performance. Furthermore, by appropriate equivalent circuit modeling of EIS data, additional important information can be obtained, such as interfacial properties when the coating is breached, e.g., pore resistance and coating capacitance along with double layer capacitance.

[0091] The main contribution of the coating to the impedance occurs in the lower frequency range, at frequencies close to 0.1 Hz. This feature is sometimes used as a kind of screening method in the selection of suitable organic coatings. In a review on the performance of fast-curing epoxies for pipe and tank linings, O'Donoghue et al. (Journal of Protective Coatings and Linings (1998), pp. 36-51) describe the use of EIS as such a screening tool [references], where the coating impedance measured at a frequency of 0.1 Hz can be used to screen materials. O'Donoghue et al. 4 Ωcm 2 The impedance value of poor quality coating is 10 10 Ωcm 2 Between these values, relatively good coatings are assigned impedance values ​​of 10 8 Ωcm 2 and the barrier protection is assigned an impedance value on the order of 10 6 Ωcm 2 This barrier performance impedance diagram is shown in Figure 5 of the O'Donoghue et al. paper. Since the O'Donoghue paper, several other papers have also used this screening method to measure coating performance.

[0092] FIG. 2 shows the progression of impedance modulus for single-coated samples measured at 0.1 Hz, during which all samples were subjected to NSS test conditions. It is noted that the impedance values ​​are generally relatively low since these are single-coated samples and therefore of very low thickness (50-60μ range) compared to the thicker multi-layer systems. Performance is judged based on relative values ​​and not on overall impedance values. The commercially equivalent coatings show relatively low impedance values ​​indicating poor barrier properties. Adding any of the commercially available graphene-containing dispersions to the commercially equivalent coating formulations (prototypes) increases the impedance values ​​by various amounts, indicating that in all cases the inclusion of graphene nanoplatelets acts to increase the barrier performance properties of the base coating (prototypes).

[0093] The NSS ratings of the single coats at 720 hours are shown in Table 5.

[0094] [Table 5]

[0095] 3-coat system

[0096] FIG. 3 shows the evolution of impedance modulus for a three-coat system sample measured at 0.1 Hz over time that the sample was subjected to NSS conditions. The initial impedance value (recorded at t=0) was 10 8 ~10 10 Ωcm 2In general, these values ​​are higher than the initial values ​​observed in the single layer sample. This is expected due to the increased thickness of the three-coat system. The control sample consisting of the zinc-rich primer coat, the commercial equivalent layer, and the polyurethane top coat displays the lowest overall impedance value in addition to one of the higher rates of impedance decrease from the t=0 point. When tested as a single entity, the commercial equivalent coat also provided the lowest impedance throughout the duration of the test. It was also observed when incorporated into a full coating system. With the introduction of graphene nanoparticles in the intermediate layer, the impedance modulus increased by various amounts over the course of the experiment, again suggesting that the inclusion of graphene nanoparticles acts to increase the barrier performance properties of the system as a whole. The smallest increase in overall impedance was observed when the D1 dispersion was incorporated into the intermediate layer, and this was also the case when D1 was tested as a single-coat entity. In the case of the D1 intermediate layer, the impedance is roughly an order of magnitude higher than the control when tested as part of a three-coat system, similar to the observations of D1 as a single-coat entity. In single coat tests, dispersions D2 and D3 provided roughly the same level of impedance rise relative to the control sample. When these dispersions were incorporated into the interlayer of a three coat system, the D3 interlayer provided a final rise nearly two orders of magnitude higher than the control, and the D2 interlayer provided a final rise five orders of magnitude higher than the control. Furthermore, the sample incorporating D2 (ZRP / D2 / PUTC) showed little change in impedance compared to the other samples over the course of the experiment. This suggests that the D2 interlayer sample provided good to excellent barrier performance throughout the experiment with the control finishing just above the poor region.

[0097] A relatively high thickness coating with excellent barrier properties, such as those designed for use in C4 / C5 type environments, will typically be high impedance both at the onset of exposure and, ideally, after the coating has been exposed to the harsh environment for an extended period of time. Lower performing coatings due to thinner applications or poorer barrier properties will also display high impedance if only for a relatively short period of time.

[0098] The EIS response of such high impedance coatings at the very beginning of exposure to harsh C4 / C5 type environments is dominated by capacitive behavior. The coatings essentially behave as ideal or non-ideal dielectric type capacitors. Indeed, due to their very nature, complex multi-layer coatings are very likely to exhibit non-ideal type capacitance. Looking at the phase angle plots from the EIS data, values ​​approaching -90° (or close to, in the case of non-ideal) indicate the presence of pure capacitive type behavior. After exposure to harsh environments, water can enter the coating. Depending on the specific properties of the coating, the dielectric constant of water is in the region of 20 times that of the coating, leading to an increase in capacitance as water enters the coating. This change in capacitance is therefore related to water absorption in the coating.

[0099] Further deviations from pure capacitive behavior can occur when water or corrosive species penetrate into the coating pores, grow ionic pathways, and create a resistive contribution (pore resistance) to the total impedance of the system. Figure 4(a) shows a selection of phase shift Bode plots for the 3-coat control sample before and after 720 hours of NSS exposure. The T=0 measurements show values ​​close to -90° at high frequencies, but can drift away from this value at low frequencies, suggesting some water absorption even at this early stage. From 72 hours onwards, measurements at subsequent times show phase change values ​​that are relatively much further away from the ideal capacitor value. The measurements after 72 hours are reasonably well-aligned, suggesting that the coating is approaching its saturation point. In contrast, the phase angle Bode plot for the high impedance sample, ZRP / D2 / PUTC, as shown in Figure 4(b), shows a relatively small deviation from near the -90° point, consistent with the coating absorbing relatively little water. As discussed previously, the fact that the phase angle is not exactly at -90° is due to the non-ideal capacitive behavior of the system. Some increasing deviation is observed in the low frequency domain, indicating that the system is never fully saturated, but water is beginning to enter the system.

[0100] Water absorption in the coating as volume percent %v is

[0101]

number

[0102] where C0 is the non-ideal coating capacitance at T=0 and C X is the non-ideal coating capacitance at T=72, 240, 480 and 720 hours. Table 6 shows the water absorption values ​​for the 3-coat system.

[0103] [Table 6]

[0104] The NSS ratings of the multiple coats at 720 hours are shown in Table 7.

[0105] [Table 7]

Claims

1. 1. A tie coat coating composition for use in a coating system including at least three coating layers for a metal substrate, the coating system including a primer coating layer on the metal substrate, a tie coat coating layer on the primer coating layer, and a finish coating layer on the tie coat coating layer, the primer coating layer being formed from a primer composition, the tie coat coating layer being formed from a tie coat composition, and the finish coating layer being formed from a finish composition, the primer composition including a primer carrier medium and a primer corrosion inhibitor, the primer corrosion inhibitor having a galvanic cathode mechanism, and the finish composition being formulated to provide a predetermined surface texture and / or appearance, the tie coat coating composition including a tie coat carrier medium and a tie coat corrosion inhibitor, and the tie coat corrosion inhibitor having a barrier mechanism.

2. 10. The tie coat composition of claim 1, wherein the tie coat corrosion inhibitor comprises one or a mixture of graphene nanoplates, graphene oxide nanoplates, reduced graphene oxide nanoplates, bilayer graphene nanoplates, bilayer graphene oxide nanoplates, bilayer reduced graphene oxide nanoplates, few layer graphene nanoplates, few layer graphene oxide nanoplates, few layer reduced graphene oxide nanoplates, graphene / graphite nanoplates of 6-14 layers of carbon atoms, graphite flakes having at least one nanoscale dimension and up to 40 layers of carbon atoms, graphite flakes having at least one nanoscale dimension and 25-30 layers of carbon atoms, graphite flakes having at least one nanoscale dimension and 20-35 layers of carbon atoms, or graphite flakes having at least one nanoscale dimension and 20-40 layers of carbon atoms.

3. 3. The tie coat composition of claim 1 or 2, wherein the tie coat corrosion inhibitor comprises nanoplates of one or a mixture of 2D materials and / or layered 2D materials, the 2D materials being one or a mixture of graphene, graphene oxide, reduced graphene oxide, hexagonal boron nitride, molybdenum disulfide, tungsten diselenide, silicene, germanene, graphene, borophene, phosphorene, or 2D in-plane heterostructures of two or more of the materials, and the layered 2D materials being one or a mixture of graphene, graphene oxide, reduced graphene oxide, hexagonal boron nitride, molybdenum disulfide, tungsten diselenide, silicene, germanene, graphene, borophene, phosphorene, or 2D vertical heterostructures of two or more of the materials.

4. 4. The tie coat composition of any one of claims 1 to 3, wherein the tie coat corrosion inhibitor comprises graphene / graphite platelets and / or nanoplates of 2D material having a D50 particle size of less than 45 μm.

5. 5. The tie coat composition of any one of claims 1 to 4, wherein the tie coat corrosion inhibitor comprises graphene / graphite platelets and / or nanoplates of 2D material having a D50 particle size of less than 30 μm.

6. 6. The tie coat composition of any one of claims 1 to 5, wherein the tie coat corrosion inhibitor comprises graphene / graphite platelets and / or nanoplates of 2D material having a D50 particle size of less than 15 μm.

7. The tie coat composition of any one of claims 1 to 6, wherein the tie coat corrosion inhibitor is present in the range of 0.05% to 1.0% by weight of the tie coat composition.

8. The tie coat composition of any one of claims 1 to 7, wherein the tie coat corrosion inhibitor is present in the range of 0.05% to 0.6% by weight of the tie coat composition.

9. The tie coat composition of any one of claims 1 to 8, wherein the tie coat corrosion inhibitor is present in the range of 0.1% to 0.5% by weight of the tie coat composition.

10. The tie coat composition of any one of claims 1 to 9, wherein the tie coat corrosion inhibitor is present at 0.1% or 0.5% by weight of the tie coat composition.

11. The tie coat composition of any one of claims 1 to 10, wherein the tie coat corrosion inhibitor is present in an amount of 0.1% by weight of the tie coat composition.

12. The tie coat composition of any one of claims 1 to 11, wherein the tie coat composition further comprises an additional tie coat corrosion inhibitor, the additional tie coat corrosion inhibitor having a passivation mechanism.

13. The tie coat composition of claim 12, wherein the additional tie coat corrosion inhibitor is present in the range of 0.05% to 1.0% by weight of the tie coat composition.

14. The tie coat composition of claim 12 or 13, wherein the additional tie coat corrosion inhibitor is present in the range of 0.05% to 0.8% by weight of the tie coat composition.

15. The tie coat composition of any one of claims 12 to 14, wherein the additional tie coat corrosion inhibitor is present in the range of 0.05% to 0.6% by weight of the tie coat composition.

16. The tie coat composition of any one of claims 12 to 15, wherein the additional tie coat corrosion inhibitor is present in the range of 0.1% to 0.5% by weight of the tie coat composition.

17. The tie coat composition of any one of claims 12 to 16, wherein the additional tie coat corrosion inhibitor is present in the range of 0.1% or 0.5% by weight of the tie coat composition.

18. The tie coat composition of any one of claims 12 to 17, wherein the additional tie coat corrosion inhibitor is present in an amount of 0.1% by weight of the tie coat composition.

19. The additional tie coat corrosion inhibitors may be selected from the group consisting of ion exchanged pigments, silica, calcium exchanged silica, magnesium oxyaminophosphates, and / or organic amines, phosphoric acid and / or inorganic phosphates, and metal oxides, metal hydroxides, zinc chromate, zinc molybdate, zinc tungstate, zinc vanadate, zinc phosphite, zinc polyphosphate, zinc borate, zinc metaborate, magnesium chromate, magnesium molybdate, magnesium tungstate, magnesium vanadate, magnesium phosphate, magnesium phosphite, magnesium polyphosphate, magnesium borate, magnesium metaborate, calcium chromate, calcium molybdate, calcium tungstate, calcium vanadate, calcium phosphate, calcium phosphite, calcium polyphosphate, calcium borate, calcium metaborate, calcium chromate, calcium molybdate, calcium tungstate, calcium vanadate, calcium phosphate, calcium phosphite, calcium polyphosphate, calcium borate, 19. The tie coat composition of any one of claims 12 or 18, comprising at least one of mixtures of calcium tungstate, strontium chromate, strontium molybdate, strontium tungstate, strontium vanadate, strontium phosphate, strontium phosphite, strontium polyphosphate, borates, strontium metaborate, barium chromate, barium molybdate, barium tungstate, barium vanadate, barium phosphate, barium phosphite, barium polyphosphate, barium borate, barium metaborate, aluminum chromate, aluminum molybdate, aluminum tungstate, aluminum vanadate, aluminum phosphate, aluminum phosphite, aluminum polyphosphate, aluminum borate and / or aluminum metaborate.

20. The tie coat composition of any one of claims 12 to 19, wherein the additional tie coat corrosion inhibitor is a composition comprising silica.

21. 21. The tie coat composition of any one of claims 1 to 20, wherein the tie coat carrier medium comprises at least one of epoxy resins, crosslinkable resins, non-crosslinkable resins, thermosetting acrylics, aminoplasts, urethanes, carbamates, polyesters, alkyd epoxies, silicones, polyureas, silicates, polydimethylsiloxanes, vinyl esters, unsaturated polyesters, and mixtures and / or combinations thereof.

22. The tie coat composition of any one of claims 1 to 21, wherein the tie coat carrier medium comprises a curable resin.

23. 23. The tie coat composition of claim 22, wherein the curable resin comprises an epoxy resin.

24. 24. The tie coat composition of claim 22 or 23, wherein the curable resin comprises a liquid curable resin.

25. 25. A coating system for a metal substrate comprising at least three coating layers, the coating layer being a primer coating layer on the metal substrate, the coating layer being a tie coat coating layer on the primer coating layer, and the coating layer being a finish coating layer on the tie coat coating layer, the primer coating layer being formed from a primer composition, the tie coat coating layer being formed from the tie coat composition of any one of claims 1 to 24, the finish coating layer being formed from a finish composition, the primer composition comprising a primer carrier medium and a primer corrosion inhibitor having a galvanic cathode mechanism, the finish composition being formulated to impart a predetermined surface texture and / or appearance.

26. 26. The coating system of claim 25, wherein the primer corrosion inhibitor is one or a mixture of inorganic salts of zinc, magnesium and / or manganese.

27. 27. The coating system of claim 25 or 26, wherein the primer composition is a zinc-rich composition.

28. The coating system of any one of claims 25 to 27, wherein the primer carrier medium of the primer composition comprises a curable resin.

29. 30. The coating system of claim 28, wherein the hardenable resin comprises an epoxy resin.

30. 30. The coating system of claim 28 or 29, wherein the curable resin comprises a liquid curable resin.

31. The coating system of any one of claims 25 to 30, wherein the finishing composition is a polyurethane.

32. The coating system of any one of claims 25 to 31, wherein the primer corrosion inhibitor is carried in the primer carrier medium of the primer coating layer formed from the primer composition.

33. The coating system of any one of claims 25 to 32, wherein the primer corrosion inhibitor is substantially uniformly dispersed throughout the primer coating layer.

34. 34. The coating system of any one of claims 25 to 33, wherein the tie coat corrosion inhibitor is carried in the tie coat carrier medium of the tie coat coating layer formed from the tie coat composition.

35. The coating system of any one of claims 25 to 34, wherein the tie coat corrosion inhibitor is substantially uniformly dispersed throughout the tie coat coating layer.

36. 36. The coating system of any one of claims 25 to 35, wherein the tie coat composition comprises an additional tie coat corrosion inhibitor, the additional tie coat corrosion inhibitor having a passivation mechanism, and the additional tie coat corrosion inhibitor is entrained in the tie coat carrier medium of the tie coat coating layer formed from the tie coat composition.

37. 37. The coating system of any one of claims 25 to 36, wherein the tie coat composition comprises an additional tie coat corrosion inhibitor, the additional tie coat corrosion inhibitor having a passivation mechanism, and the additional tie coat corrosion inhibitor is substantially uniformly dispersed throughout the tie coat coating layer.

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