HK1191360B - Coating compositions with anticorrosion properties - Google Patents

Abstract

Anticorrosive coating compositions comprise a binding polymer and an amorphous aluminum phosphate corrosion inhibiting pigment dispersed therein. The coating composition comprises 1 to 25 percent by weight aluminum phosphate. The binding polymer can include solvent-borne polymers, water-borne polymers, solventless polymers, and combinations thereof. The aluminum phosphate is made by combining an aluminum source with a phosphorous source to form an amorphous aluminum phosphate solid condensate. The coating composition is specially engineered to provide a controlled delivery of phosphate anions of 50 to 500 ppm, and has a total solubles content of less than 1500 ppm. The amorphous aluminum phosphate is preferably free of alkali metals and alkaline earth metals. The amorphous aluminum phosphate has an oil absorption of less than 50, and a surface area of less than about 20 m2/g, The coating composition has a water adsorption potential of up to 25% by weight water.

Description

Coating composition with anti-corrosion properties

Technical Field

The present invention relates to coating compositions having anticorrosion properties, and, more particularly, to coating compositions specifically formulated to contain amorphous aluminum phosphate corrosion inhibiting pigments and methods for their preparation.

Background

Such coating compositions are known in the art: formulated to contain one or more substances to provide corrosion protection for forming a thin film layer on the surface of a metal substrate. Such coating compositions utilize known materials to provide a degree of corrosion protection by one of three different mechanisms.

The first mechanism of corrosion control in the coating composition is: in the formulation, the binder composition, in which the moisture and water are prevented from diffusing to a high degree into the resulting cured film, is combined with a pigment or solid component that enhances the barrier properties of the film composition, thereby providing a physical barrier to any water that enters the cured coating film to prevent corrosion of the underlying metal substrate surface. Pigments or solid ingredients useful in this regard include aluminum, iron oxides, mica, talc, calcium silicate, and particulate and/or flaked barium sulfate.

The second mechanism of corrosion control in coating compositions is: the desired substance is placed in proximity to the surface of the metal substrate selected to produce sacrificial corrosion upon contact with any water or oxygen that enters the cured paint film, thereby producing sacrificial corrosion to cathodically protect and prevent corrosion of the underlying metal substrate. Zinc metal is an example of a material useful in this regard and may be provided on the substrate surface as a component in a coating composition or may be provided separately.

The third mechanism of corrosion control is: coating compositions utilize corrosion inhibiting materials, e.g., corrosion inhibiting pigments, wherein such materials, upon contact with water and oxygen, release a material that diffuses to the surface of the substrate and adsorbs onto the substrate to form a water impervious layer or form a reaction product with the surface of the metallic substrate, thereby preventing its reaction with water, oxygen, or other corrosive materials. This passivates the substrate surface, thereby preventing corrosion thereof. Materials known to be useful in this regard include calcium zinc phosphomolybdate, aluminum triphosphate, zinc phosphate, zinc iron phosphate, strontium zinc phosphosilicate, calcium phosphosilicate, aluminum zinc phosphate, lead-containing materials, and chromate-containing materials.

Anticorrosion coating compositions known in the art, which may rely on substances that present a risk/hazard to the environment and/or a health or safety hazard to humans, and for which reason the use of such coating compositions has been or is being completely restricted or prohibited, provide a degree of protection against unwanted corrosion. Furthermore, while such known coating compositions provide a degree of corrosion protection, they do not provide a desired or required level of corrosion control sufficient to meet the needs of certain end-use applications.

Therefore, there is a need for anticorrosion coating compositions formulated in such a manner: provide a desired degree of corrosion control/resistance without the use of materials that are regulated or known to present a hazard/risk to the environment and/or present a health or safety concern to humans. Such anticorrosion coating compositions need to be prepared in this way: provide desirable better corrosion resistance than known coating compositions, thereby meeting the needs of certain end-use applications. There is a further need for such anticorrosion coating compositions formulated from existing materials, and/or prepared according to such processes: the process facilitates the manufacture of the coating composition in a manner that does not require the use of unusual equipment, is not overly labor intensive, and is economically viable.

Documents US 2008/085965 a1, GB 2221684 a and DE 3233092C 1 disclose coating compositions for corrosion protection.

Disclosure of Invention

The anticorrosion coating composition disclosed herein comprises a binding polymer and aluminum phosphate dispersed within the binding polymer. The binder polymer may be selected from the group consisting of: polyurethanes, polyesters, solvent-borne epoxies, solventless epoxies, water-soluble epoxies, epoxy copolymers, acrylics, acrylic copolymers, silicones, silicone copolymers, polysiloxanes, polysiloxane copolymers, alkyds, and combinations thereof. The aluminum phosphate includes amorphous aluminum phosphate. In a preferred embodiment, the aluminum phosphate is amorphous aluminum phosphate when combined with the binding polymer and the coating composition is applied to the surface of a metal substrate. The coating composition contains aluminum phosphate in a range of about 1 to 25 weight percent.

In embodiments, the coating composition controls phosphate delivery, e.g., phosphate anion, in the range of about 50 to 500ppm, and preferably in the range of about 100 to 200 ppm. In embodiments, the coating composition has a total solubles content of less than about 1500ppm, less than 800ppm, preferably less than about 400ppm, more preferably from about 100 to 250 ppm. The amorphous aluminum phosphate is preferably substantially free of alkali and alkaline earth metals.

An anticorrosion coating composition is formed by combining a starting material comprising an aluminum source with a phosphorus source and reacting the combined starting materials to form a solution comprising an amorphous aluminum phosphate solid condensate. The aluminium source may be selected from: sodium aluminate, aluminum hydroxide, aluminum sulfate, and combinations thereof, and the phosphorus source can be phosphoric acid or a phosphate salt. In the examples, the aluminum phosphate production process is specifically controlled to produce amorphous aluminum phosphate having desirable engineering properties: controlled phosphate anion release and has reduced/low levels of solubles content.

The amorphous aluminum phosphate has a low oil absorption of less than about 50 and less than about 20 m²Low surface area per gram. Further, in a preferred embodiment, amorphous aluminum phosphate is produced that is free of alkali and alkaline earth metals and is dried at a temperature of less than about 200 ℃. Thereafter, the amorphous aluminum phosphate is mixed with a binding polymer to form an anticorrosion coating composition.

Such anti-corrosion compositions may be used as primer, intermediate, and/or topcoat coatings depending on the particular formulation and/or end-use application. Anticorrosion coating compositions can be applied to a metal substrate and allowed to dry to form a fully cured film. In this event, the binder polymer is solvent-borne, and the amorphous aluminum phosphate in the cured film controls the corrosion of the underlying substrate by absorbing and/or adsorbing water into the film and providing passivating phosphate anion.

The anticorrosion coating compositions described herein are prepared in a manner that provides a desired degree of corrosion control/resistance to corrosion without the use of materials that are regulated or known to present a hazard/danger to the environment and/or a health or safety concern to humans. Further, this anticorrosion coating composition is prepared in such a manner that: provide the desired better corrosion resistance than known coating compositions, thereby meeting the needs of certain end-use applications. Such anticorrosion coating compositions are prepared from existing materials and are produced by a process which comprises: the process facilitates the manufacture of the coating composition in a manner that does not require the use of unusual equipment, is not overly labor intensive, and is economically viable.

Detailed Description

Disclosed herein are anticorrosion coating compositions and methods of making the same. Such anticorrosion coating compositions contain a desired amount of an amorphous aluminum phosphate corrosion inhibiting pigment specifically designed to provide a controlled release/delivery of an optimal amount of passivating ion, e.g., phosphate anion, to inhibit corrosion, and a desired combination of characteristics of a controlled amount of total solubles. At the same time, these features enable the anticorrosion coating composition to provide better corrosion resistance to the underlying metal substrate without compromising the integrity and stability of the film and composite material, as compared to conventional anticorrosion coating compositions, thereby providing such improved corrosion resistance for extended service life. Conventional anticorrosion coating compositions do not allow control of the rate of release of passivating ions nor the amount of total solubles.

The amorphous aluminum sulfates used in the anticorrosion coating compositions disclosed herein are also specifically designed to have a high level of compatibility with a variety of different binding polymers or binding polymer systems useful in forming such coating compositions, thereby providing a high degree of flexibility and choice in preparing anticorrosion coating compositions to meet the needs and conditions of a variety of end-use applications of many different end-use industries.

Anticorrosion coating compositions contain a desired binding polymer that can be selected depending on the end use application and other factors. Examples of binder polymers include those currently used in the preparation of known anticorrosion coating compositions and may be selected from water-soluble polymers, solvent-based polymers, and combinations thereof. Examples of water-soluble polymers useful for preparing anticorrosion coating compositions include acrylic and acrylic copolymers, alkyds, epoxies, polyurethanes, and silicones, as well as polysiloxane polymers. Solvent-borne and/or non-water soluble polymers useful for preparing anticorrosion coating compositions include acrylic and acrylic copolymers, epoxies, polyurethanes, silicones, polysiloxanes, polyesters, and alkyds. Preferred binder polymers include acrylic copolymer emulsions, alkyds, polyurethanes, and epoxy polymers.

In an embodiment, the anticorrosion coating composition comprises in the range of about 15% to 75% by weight, preferably in the range of about 20% to 60% by weight, more preferably in the range of about 20% to 35% by weight of the binder polymer, based on the total weight of the coating composition. An anticorrosion coating composition comprising less than about 15 weight percent of the binding polymer may comprise more corrosion inhibiting pigment than is required to provide a desired degree of corrosion resistance. Anticorrosion coating compositions containing greater than about 75 weight percent of the binding polymer may include corrosion inhibiting pigments in an amount sufficient to provide a desired degree of corrosion resistance. While a certain amount of binder polymer has been provided, it will be appreciated that, depending on these factors: such as the type of binder polymer used, the type and/or amount of inhibiting pigment used, and/or the particular end use application, e.g., the substrate to be coated and the corrosive environment expected for the substrate, the exact amount of binder polymer used to prepare the anticorrosion coating composition will vary.

Corrosion inhibiting pigments useful for preparing anticorrosion coating compositions include phosphate-containing compounds. The preferred phosphate-containing compound is aluminum phosphate. Aluminum phosphates useful in this regard include amorphous aluminum phosphates, crystalline aluminum phosphates, and combinations thereof. The preferred aluminum phosphate is amorphous aluminum phosphate, and the most preferred aluminum phosphate is amorphous aluminum orthophosphate. Amorphous aluminum phosphates are preferred because amorphous aluminum phosphates have been shown to release phosphate anions in amounts sufficient to provide passivation to the metal substrate when diffused water contacts the pigment in the coating. Specifically, the anticorrosion coatings disclosed herein are specifically designed to control the rate of phosphate anion release for this purpose.

Further, it has been found that amorphous aluminum phosphate compositions can be prepared having a sufficiently low level of soluble material such that solubles do not cause osmotic blistering of the cured film when such film is contacted with water. Thus, amorphous aluminum phosphates for use in anticorrosion coating compositions are specifically useful for controlling the release or delivery of passivating anions, e.g., phosphate anions, to inhibit corrosion, and have low total solubles content to avoid osmotic blistering.

In an embodiment, the amorphous aluminum phosphate is amorphous aluminum hydroxyphosphate. Amorphous aluminum hydroxyphosphates are preferred because they provide uniform dispersion properties within the composition and the dispersion remains stable over the shelf life of the formulation. The hydroxyl component of the amorphous aluminum hydroxyphosphate provides matrix stability by forming hydrogen bonds with suitable groups of the binder polymer in the formulation, such as carboxyl groups, amino groups, hydroxyl groups, acidic groups, and the like. This feature is characteristic of amorphous aluminum hydroxyphosphates and is not present in crystalline or other types of amorphous phosphates. By adjusting the ratio of Al-OH to Al-OP in the composite, the release of secondary components contained in the material can be modulated during concentration. This secondary component may contain sodium phosphate salts resulting from the synthesis reaction.

Anticorrosion coating compositions contain a specific amount of an inhibiting pigment intended to provide a sufficient amount of a passivating anion when placed in an end-use application to inhibit corrosion. In an embodiment, the anticorrosion coating composition comprises in the range of about 3 to 25 weight percent, preferably in the range of about 5 to 15 weight percent, and more preferably in the range of about 8 to 12 weight percent amorphous aluminum phosphate, based on the total weight of the coating composition dry film. Anticorrosion coating compositions comprising less than about 3 percent by weight amorphous aluminum phosphate may contain insufficient amounts to provide the desired degree of corrosion resistance. Anticorrosion coating compositions comprising greater than about 25 weight percent amorphous aluminum phosphate may contain more than is necessary to provide the desired degree of corrosion resistance, and such additional amounts may impair the long-term stability and/or integrity of the cured coating film. While certain amounts of amorphous aluminum phosphate have been provided, it is understood that, depending on these factors: the exact amount of binder polymer used to prepare the anticorrosion coating composition will vary, such as the type and/or amount of binder polymer used, and/or the particular end use, e.g., the substrate to be coated and the corrosive environment expected for the substrate.

As briefly described above, amorphous aluminum phosphates are specifically designed to provide controlled release or delivery of one or more passivating anions upon contact with water and oxygen when the coating composition is applied to the surface of a metallic substrate, formed into a cured film, and placed in a corrosive environment. Over time, water/moisture migrates or diffuses into the applied coating film, and the water comes into contact with the existing phosphoric acid constituents in the film. This contact with water facilitates the release/delivery of phosphate anion from the amorphous aluminum phosphate in a controlled manner. These phosphate anions react with the iron species on the metal surface or on the surface of the underlying oxide of the metal substrate itself to form a passive film on the metal substrate that serves to form a barrier against corrosion of the underlying metal surface.

The amorphous aluminum phosphate used to prepare these anticorrosion coating compositions is characterized by its ability to release/deliver a controlled amount of phosphate anion. In particular, for releasing/delivering phosphate anions in an amount that provides an optimum level of corrosion protection without sacrificing other coating cured membrane properties that may compromise the effective service life of the membrane.

In embodiments, the amorphous aluminum phosphate releases about 50 to 500ppm, and preferably in the range of 100 to 200ppm, of passivating phosphate anion when the cured film is placed in an end use application. The amount of passivating anion delivered depends on many different factors, such as the weight or amount of amorphous aluminum phosphate used to prepare the corrosion protection composition, the type of binding polymer used, the type of metallic substrate being protected, and the type of corrosive environment present in the end-use application. In the preferred embodiment, wherein the metallic substrate being protected comprises iron and the corrosive environment comprises water, oxygen, and other corrosive salts, the amorphous aluminum phosphate releases about 160ppm of the passivating phosphate anion.

Amorphous aluminum phosphates having a controlled release of less than about 50ppm of passivating anion may not provide a sufficient amount of passivating anion to inhibit corrosion. Amorphous aluminum phosphates having a controlled release of greater than about 500ppm of passivating anion, when provided at a level sufficient to inhibit corrosion, may provide too much passivating anion, which may cause blistering or other undesirable effects in the cured film, which may impair its long-term integrity and stability, which may reduce the effective service life of the coating.

Anticorrosion coating compositions have a controlled or minimal level of solubles. As used herein, the terms "solubles" and "nonpassivating solubles" are used interchangeably to refer to materials that: are commonly produced as a by-product of the preparation of amorphous aluminum phosphate and can include alkali metals such as sodium, potassium, and lithium, and such anions as sulfate, chloride, and nitrate; and it should be understood that the passivating anion present in the amorphous aluminum phosphate is not included. In a preferred embodiment, the amount of non-passivating solubles is zero. The maximum amount of non-deactivated solubles was 250 ppm.

It has been found that the presence of such solubles, if not controlled, can impair the stability and/or integrity of the anticorrosion coating composition and/or a cured film formed from the coating composition, thereby adversely affecting its life expectancy. For example, it has been found that the presence of these solubles, when exposed to certain corrosive environments, can lead to unwanted blistering, peeling from the substrate, corrosion of the carrier film and other types of unwanted film failure that render the film unprotected by not exposing the underlying metal substrate surface.

In embodiments, it is desirable that the anticorrosion coating composition comprises less than about 1% (or less than 10000 ppm) of such total solubles, i.e., solubles containing passivating phosphate anion, preferably less than about 1500ppm total solubles, and preferably less than about 400ppm total solubles. In embodiments, the anticorrosion coating composition comprises in the range of about 50 to 800ppm total solubles, and preferably in the range of about 100 to 250ppm total solubles. Anticorrosion coating compositions comprising less than about 1500ppm total solubles produce a cured film: when exposed to the corrosive environment of the end use application, does not exhibit blistering or other undesirable film events, thereby increasing useful service life. Thus, anticorrosion coating compositions are characterized by having a reduced amount of total solubles specifically designed to ensure an expected service life, in addition to controlling the release of passivating anions.

Secondary concentration preparation method

Typically, amorphous aluminum phosphates are phosphate complexes in which the nucleating cation is aluminum alone or in combination with other multivalent cations, such as calcium, magnesium, barium, and the like. In an embodiment, the desired amorphous aluminum sulfate is prepared by a process comprising: to produce amorphous aluminum phosphate free of all other metal cations, particularly free of alkali metal cations. As disclosed herein, depending on the particular aluminum salt used to form the aluminum phosphate, the phosphate complex is prepared by combining suitable aluminum salts, such as aluminum hydroxide, aluminum sulfate, and phosphoric acid or phosphate analogs. The resulting concentrated solid composition depends on the ratio of metal to phosphate anion. The nature of the resulting complex, i.e., amorphous aluminum phosphate, depends on the processing parameters employed for the concentration reaction, including the selection of the aluminum salt, the temperature, the order of addition of the reactants, the rate of addition of the reactants, the degree and duration of stirring, and the pretreatment of one or more of the reactants.

One surprising result is that the resulting concentrated solids, even after milling, have very low oil absorption properties and low surface area (as measured by BET) when compared to aluminum phosphate prepared by other known methods. Oil absorption is defined as the amount (grams or pounds) of linseed oil required to wet out and fill the voids around the pigment ASTM-D-281-84, which is a measure of the binder demand or amount of binder resin that the pigment can absorb given a formulation. High binder requirements increase formulation costs and can affect certain barrier properties of the dry film. This is all the more surprising because the aluminum phosphate produced by the double concentration process disclosed herein exhibits the controlled release and water adsorption properties typically associated with high surface area particles.

In embodiments, the concentrated aluminum phosphate prepared herein has an oil absorption of less than about 50, preferably in the range of about 10 to 40, more preferably in the range of about 20 to 30. In contrast, aluminum phosphates prepared by other methods have oil absorptions greater than about 50, and generally range from about 50 to 110.

In an embodiment, the concentrated aluminum phosphate prepared herein has less than about 20 m²Per g, and preferably less than about 10 m²Surface area in g. In embodiments, the surface area ranges from 2 to 8 m²Between/g, and more preferably, in the range of about 3 to 5 m²Between/g. In contrast, aluminum phosphates prepared by other methods have greater than 20 m²In g, e.g. about 30 to 135 m²Surface area in g.

Thus, the amorphous aluminum phosphate included in the anticorrosion coating composition is prepared as a secondary concentrated product by combining selected starting materials, including an aluminum source and a phosphorus source, under specific conditions of controlled material delivery, temperature and agitation. Suitable starting materials and process conditions are selected to produce amorphous aluminum phosphate: the material composition and chemical structure of the amorphous aluminum phosphate enable the amorphous aluminum phosphate to have the combined engineering characteristics as follows: desirable passivating anion content, controlled delivery/release of passivating anion, and desirable reduced total solubles and high water adsorption.

Aluminum sources useful for forming amorphous aluminum phosphate by concentration include aluminum salts,such as aluminum chloride, aluminum nitrate, aluminum phosphate and the like. Preferred aluminum salts include aluminum hydroxide and aluminum sulfate. Phosphorus sources useful for forming amorphous aluminum phosphate by concentration include phosphoric acid, as well as phosphorus salts that are orthophosphates or polyphosphates. One source of phosphorus is fertilizer grade phosphoric acid from any source that has been cleaned and decolorized. For example, containing about 54% P₂O₅Can be chemically treated and/or diluted with treated water to produce a concentration of about 20% P₂。

Amorphous aluminum phosphates can be prepared by selective incorporation of the foregoing. The following selected methods of preparation are provided as examples and it should be understood that other methods of preparation may be used in addition to those specifically disclosed.

Example 1

In an embodiment, amorphous aluminum phosphate having the above-described engineering characteristics is prepared by: by reacting phosphoric acid H₃PO₄With aluminium hydroxide Al (OH)₃And combine at room temperature to form the desired amorphous aluminum phosphate. After adding Al (OH)₃Diluting H with water before neutralization₃PO₄And before addition, Al (OH)₃Not wet with water. The preparation method is therefore characterized in that it does not involve an increase in free water after the reactants have been combined and is carried out at room temperature without heating. In the examples, H₃P0₄85wt% aqueous solution supplied by Sigma-Aldrich, and Al (OH)₃Is reagent grade, 50-57%, supplied by Sigma-Aldrich. Specifically, in the presence of Al (OH)₃Diluted with 50g of water to about 57.3 g H before combination₃P0₄. About 39g Al (OH)₃Add quickly to the solution and stir the mixture slowly at room temperature to wet the powder. The amorphous aluminum phosphate concentrating solid is formed and present as dispersed solid particles in solution. In the presence of Al (OH)₃Dilution H before addition₃PO₄Are believed to contribute to the formation of only amorphous aluminum phosphate, e.g., wherein no crystalline form is produced. Filtration suspensionTo isolate amorphous aluminum phosphate particles. The particles are washed and dried under cryogenic conditions, e.g., below about 130 ℃. Another feature of the amorphous aluminum phosphate so formed is that it can be used in combination with a desired binding polymer to form an anticorrosion coating composition without the need for further heat treatment, tempering, or calcining, e.g., heating at temperatures above 200 ℃, which is undesirable because such heat treatment causes the desired amorphous form of the aluminum phosphate to transform into an undesired crystalline form.

Example 2

In another embodiment, amorphous aluminum phosphate having the above-described engineered properties is prepared by: by reacting H₃PO₄And Al (OH)₃Combine to form the desired amorphous aluminum phosphate. In contrast to example 1, Al (OH) was added₃Before neutralization, H is not diluted₃PO₄. However, prior to bonding, H is heated₃PO₄. In addition, in the reaction with H₃PO₄Before bonding, the Al (OH) is soaked in water₃. The preparation method is characterized in that the method does not include an increase in free water after the reactants are combined. In the examples, H₃P0₄85wt% aqueous solution supplied by Sigma-Aldrich, and Al (OH)₃Is reagent grade, 50-57%, supplied by Sigma-Aldrich. Specifically, about 57.6g H₃PO₄Heated to a temperature of about 80 ℃. About 39g of Al (OH) was wetted with about 2g of water₃And rapidly combining the wet Al (OH) with rapid mechanical agitation₃Is added to H₃P0₄In (1). The amorphous aluminum phosphate solids formed were doughy balls, removed at room temperature and stored. The amorphous aluminum phosphate so formed does not require further processing in the form of filtration and washing to isolate and obtain the desired amorphous aluminum phosphate. As with example 1, this amorphous aluminum phosphate (once dried and formed to the desired particle size) is combined with a desired binding polymer to form an anticorrosion coating composition without the need for further heat treatment, tempering, or calcining, e.g., at 200 ℃Heating at the above temperature.

In these example processes, the chemical reaction results in amorphous aluminum orthophosphate or orthophosphate (A1)₂(HP0₄)₃Or A1 (H)₂P0₄)₃) Is performed. The reaction is carried out by mixing the two starting materials. The reagents are added to a reactor equipped with a stirring device and are capable of reacting in a short time, e.g., less than about 10 minutes.

As noted above, a feature of the amorphous aluminum phosphate prepared herein and included in an anticorrosion coating composition is that it has a reduced/low total solubles content. In this preparation process, the desired low total solubles content is inherent in that no by-products, for example, other metal cations such as alkali metal cations or the like, are produced from the reaction other than water. Thus, an advantage of this two-shot concentration process for making amorphous aluminum phosphate is that it eliminates the need for any subsequent solubles removal treatment, thereby reducing manufacturing costs and time. In contrast, amorphous aluminum phosphate formed by the concentration reaction can be separated from solution by conventional methods, such as by a filter press or by separating the liquid phase (sometimes also referred to as a "liquor") from the solid (sometimes also referred to as a "cake"). In one or more steps, the wet cake, containing about 35% to 45% solids, may be optionally washed, if desired. The resulting isolated amorphous aluminum phosphate can be dried using conventional drying equipment, such as a "turbo dryer" or the like, at a temperature of less than about 200 ℃, preferably at a temperature of about 40 to 140 ℃, and more preferably at a temperature of less than about 130 ℃. The resulting dried amorphous aluminum phosphate product has a final moisture content of between about 10% and 20% by weight water. Although specific drying techniques are disclosed, it should be understood that other types of drying techniques may be used.

Amorphous aluminum phosphates prepared by the above process have a P to Al ratio of about 0.5: 1 to 1.5: 1. The P to Al ratio of the amorphous aluminum hydroxyphosphate is desirably within this range because it provides a suitable range of particle morphology and properties compatible with the chemistry of the target coating formulation. Also, the phosphorus release rate of such solids within this range provides the desired level of passivation for corrosion protection.

After forming the amorphous aluminum phosphate concentrated solid, the solid is processed into a white powder having the desired particle size and particle distribution. The particle size will depend on such factors as the binder polymer, the particular end use application, and the method of applying the coating composition. In an embodiment, the amorphous aluminum phosphate has a particle size distribution D50 of about 0.5 to 8 microns. In the examples, the P: an Al ratio of about 0.9 to 1 and a particle size distribution D50 of about 1 micron with D90 less than about 4 microns is desirable. For use in anticorrosion coating compositions, the amorphous aluminum phosphate has a particle size less than about 20 micrometers, and preferably in the range of about 0.5 to 10 micrometers, and more preferably in the range of about 1 to 8 micrometers. Particle sizes less than about 0.5 microns can affect processing of the coating formulation and adversely affect film performance due to increased binder resin adsorption.

Enhanced control over the amorphous aluminum phosphate's intrinsic characteristics is achieved by controlling the aluminum source concentration and adjusting and fine tuning the P to Al ratio to achieve the desired amount of amorphous aluminum phosphate described above, thereby promoting the formation of amorphous aluminum phosphate that provides the desired controlled delivery of passivating anion. In addition, the above-described methods provide an inherent process of controlling the content of unwanted solubles, such as solubles are not a by-product of the formation reaction, thereby facilitating the formation of a coating composition having the desired film stability and integrity.

The amorphous aluminum phosphates prepared as described above are preferably not subjected to high temperature drying or other heat treatment for the purpose of maintaining the amorphous structure and avoiding transformation into a crystalline structure. It has been found that amorphous aluminum phosphates formed in this manner retain the desired amorphous structure even after low temperature drying, and that this structure provides distinct advantages/features as a corrosion inhibiting pigment. These amorphous aluminum phosphates exhibit a significantly increased water adsorption potential or degree of rehydration when compared to crystalline aluminum phosphates, which enables the aluminum phosphates, once dehydrated by drying, to be rehydrated to contain about 25% water by weight. This feature is particularly useful when amorphous aluminum phosphate is used with anticorrosion coating compositions containing water insoluble binding polymers. In these coating compositions, in addition to acting as a corrosion inhibiting pigment, the amorphous aluminum phosphate also acts as a moisture scavenger to slow water intrusion into the cured film and limit water diffusion through the cured film. Thus, this water adsorption feature provides another moisture barrier mechanism for corrosion control. This effect has been demonstrated by using an Electrical Impedance Spectroscopy (EIS).

Anticorrosion coating compositions are prepared by combining the selected binding polymer with the amorphous aluminum phosphate in the amounts described above. The amorphous aluminum phosphate can be provided to the composition formulation as a dry powder or as a slurry or suspension, depending on the formulation circumstances or preferences.

Table 1 gives examples of anticorrosion coating composition formulations in the form of epoxy-polyamide primer compositions prepared in the manner disclosed herein for reference purposes.

TABLE 1 epoxy based anticorrosion coating composition

In this example, the first epoxy resin is based on a diglycidyl ether or bisphenol a such as EPON 828 (Hexion chemical), the additive is a polymer that promotes outflow in film formation (Cytec), the pigment dispersant is an additive such as Anti-terra U (byk chemie), the solvent 1 is an aromatic solvent such as toluene or xylene, the solvent 2 is a glycol ether, the Anti-settling additive is a thixotrope (thixatrope) such as bentonite SD, the underlying color pigment is iron oxide red, the Anti-corrosion pigment is amorphous aluminum phosphate prepared by the preparation method disclosed herein and is provided in the form of a dry powder, the extender pigment 1 is barium sulfate, the extender pigment 2 is magnesium silicate, the extender pigment 3 is mica, the second epoxy resin is the same as the first additive, the third solvent is xylene, and the curing agent is a polyamide resin such as EPIKURE 3175 (Hexion). The amorphous aluminum phosphate is present in an amount of about 10% by weight based on the total weight of the composition. In addition, variations of the formulation of this example were prepared at amorphous aluminum phosphate weight levels of 5 weight percent and 15 weight percent.

Epoxy-based example samples were studied using Electrical Impedance Spectroscopy (EIS). One unexpected result from EIS testing was: incorporation of up to 15% by weight amorphous aluminum phosphate was observed in the epoxy-based samples, which demonstrated an increase in the impedance of the epoxy film compared to the reference due to the number of steps to a certain level. This result has been found in 5% and 15% by weight amorphous aluminum phosphate in epoxy resins. This result indicates that the amorphous aluminum phosphate in these samples removes diffused water from the matrix by acting as a water scavenger to enhance the barrier properties of the epoxy adhesive polymer.

As the water penetrates into the film, it adsorbs to and accumulates on the amorphous aluminum phosphate particles present in the film. Water is preferentially adsorbed by the amorphous aluminum phosphate and is adsorbed except at the film only after local particle saturation has occurred. When this occurs, the next layer of amorphous aluminum phosphate will absorb water. The adsorption of water by the amorphous aluminum phosphate significantly slows the diffusion of water through the film and thus increases the useful life of the film. Further, the presence of water around the saturated aluminum phosphate particles, which are again bound to water, causes phosphate anions to be released into the moving water. Thus, even if the service life is long enough to allow water to diffuse through the film to the substrate, the aqueous solution that reaches the substrate will contain passivating phosphate anions, thereby preventing corrosion of the steel substrate. Further, the ability of the amorphous aluminum phosphate to release an amount of inhibitory phosphate anion can provide corrosion inhibition at sites of physical defects or film failure.

As noted above, despite the unique morphological properties of the solid (low oil adsorption and low surface area), the aluminum phosphate produced by secondary concentration is effective as a water scavenger. Further, amorphous aluminum phosphate prepared by this process has a low oil absorption measurement, indicating that it has a low binder requirement when added to a coating composition. This ensures that the addition of amorphous aluminum phosphate by this method does not add to the cost of the formulation or interfere with the color change or gloss appearance properties of the resulting dry film.

This discovery enables amorphous aluminum phosphate to be physically incorporated into the middle and top layers as a barrier enhancer, rather than just the bottom layer. Conventional inhibitive pigments are only of value in the underlayer, as they only provide a passivation mechanism for corrosion control. The amorphous aluminum phosphate and coating compositions containing amorphous aluminum phosphate disclosed herein prevent corrosion by a dual mechanism of water adsorption enhancing the barrier properties of the coating and releasing passivating anions.

Table 2 sets forth examples of anticorrosion coating composition formulations in the form of acrylic latex basecoat compositions prepared in the manner disclosed herein for reference purposes.

TABLE 2 acrylic emulsion based anticorrosion coating composition

In this example, the pigment dispersant was Surfynol CT-131, the corrosion inhibiting pigment was amorphous aluminum phosphate prepared by the process disclosed above and provided in the form of a powder, the defoamer was Drewplus L-475, coalescent 1 was Eastman EB, coalescent 2 was Dowanol DPnB, coalescent 3 was a tridecyl ester, the dispersant/surfactant was Surfynol DF210, the plasticizer was plasticizer 160, the flash rust inhibitor was ammonium benzoate, and the HASE thickener was Acrysol TT 615. The weight of the amorphous aluminum phosphate in the formulation is about 4.6 weight percent based on the total weight of the composition.

As indicated above, embodiments of the present invention provide novel anticorrosion coating compositions comprising amorphous aluminum phosphate. While the invention has been described with respect to a limited number of embodiments, the specific features of one embodiment should not be attributed to other embodiments of the invention. A single embodiment may not represent all aspects of the invention. In some embodiments, the composition or method may include a number of compounds or steps not mentioned herein. In other embodiments, the composition or method does not include, or is substantially free of, any compounds or steps not recited herein.

For example, if desired, anticorrosion coating compositions can be prepared: in addition to the amorphous aluminum phosphate, one or more elements known to have corrosion protection value are included, for example, cations such as zinc, calcium, strontium, chromates, borates, barium, magnesium, molybdenum, and combinations thereof. The addition of these other elements may increase or supplement the corrosion protection effect of the coating composition.

Further, while the corrosion protection coating compositions described herein include aluminum phosphate in amorphous form, it should be understood that the corrosion protection compositions described herein may include aluminum phosphate in known crystalline forms. For example, such crystalline aluminum phosphate can be present in an amount that does not adversely affect or impair the designed corrosion protection mechanism and/or performance of the coating composition.

There are various variations and modifications of the above-described embodiments. The method of making the coating composition and/or amorphous aluminum phosphate is described as comprising several acts or steps. The steps or acts may be performed in any order or sequence unless otherwise indicated. Finally, any number described herein should be construed as an approximation regardless of whether the number is described in terms of "about" or "approximately. It is intended that the appended claims shall indicate all such modifications or variations as falling within the scope of the present invention.

Claims (47)

1. An anticorrosion coating composition comprising:

a binder polymer selected from the group consisting of solvent-based polymers, water-soluble polymers, and combinations thereof;

an aluminum phosphate corrosion inhibiting pigment consisting of a condensed amorphous aluminum hydroxy orthophosphate dispersed in a binder polymer, wherein the condensed amorphous aluminum hydroxy orthophosphate has an oil absorption of less than 50; and is

Wherein the coating composition contains 1 to 25wt% amorphous aluminum hydroxy orthophosphate, and wherein the coating composition provides controlled delivery of phosphate anion in the range of 50 to 500ppm when the coating composition is in the form of a cured film, and wherein the total solubles content in the coating composition is in the range of 50 to 800ppm, wherein the total solubles comprise passivating phosphate anion.

2. The coating composition as claimed in claim 1, characterized by having a total solubles content of less than 400 ppm.

3. The coating composition of claim 1, having a total solubles content of 100 to 250 ppm.

4. The coating composition of claim 1, wherein the controlled delivery of phosphate anion is between 100 and 200 ppm.

5. The coating composition of claim 1, additionally comprising a zinc-containing material.

6. The coating composition as recited in claim 1 wherein the amorphous aluminum hydroxy orthophosphate has a water adsorption potential of up to 25 percent by weight water.

7. A primer formed from the coating composition of claim 1, wherein the primer is disposed on a metal substrate.

8. The middle or top layer of a coating system formed from the coating composition of claim 1, wherein the middle or top layer contacts the metal substrate or the primer layer is disposed on the metal substrate.

9. The coating composition of claim 1, wherein the binder polymer is selected from the group consisting of polyurethanes, polyesters, solvent-based epoxies, solventless epoxies, water-soluble epoxies, epoxy copolymers, acrylics, acrylic copolymers, silicones, silicone copolymers, polysiloxanes, polysiloxane copolymers, alkyds, and combinations thereof.

10. A system for providing corrosion protection comprising the coating composition of claim 1 applied to a metal substrate and capable of curing to form a film.

11. The system of claim 10, comprising a passivation film interposed between the coating composition and the surface of the metal substrate, wherein the passivation film is a reaction product formed between phosphate anions and the metal substrate.

12. The system as recited in claim 10 wherein the binder polymer comprises an epoxy resin and the amorphous aluminum hydroxy orthophosphate adsorbs up to 25 weight percent of water entering the cured film.

13. The system as recited in claim 10 wherein the coating composition has a total solubles content of less than 400 ppm.

14. The system as recited in claim 10 wherein the coating composition has a total solubles content of 100 to 250 ppm.

15. The system as recited in claim 10 wherein the amorphous aluminum hydroxy orthophosphate is free of alkali metals.

16. The system as recited in claim 10 wherein the amorphous aluminum hydroxy orthophosphate has a water adsorption potential of up to 25 weight percent.

17. The system of claim 10, wherein the coating composition is a primer coating applied to the metal substrate.

18. The system of claim 10, wherein the coating composition is a mid-coat or top-coat coating applied to the metallic substrate, or a bottom-coat coating applied to the metallic substrate.

19. The system of claim 10, wherein the coating composition has a controlled release of phosphate anion of between 100 and 200 ppm.

20. A method of making an anticorrosion coating composition comprising the steps of:

preparing an amorphous aluminum phosphate corrosion inhibiting pigment by combining a starting material comprising an aluminum source with a phosphorus source and reacting the combined starting materials at room temperature to form a solution comprising condensed aluminum phosphate;

drying the condensed aluminum phosphate at a temperature of less than 200 ℃, wherein the dried condensed aluminum phosphate comprises amorphous aluminum hydroxy orthophosphate; and is

Mixing amorphous aluminum hydroxy orthophosphate with a binder polymer selected from solvent borne polymers, water soluble polymers and combinations thereof to form a coating composition, wherein the coating composition comprises less than 25 percent by weight of aluminum hydroxy orthophosphate based on the total weight of the coating composition, wherein the amorphous aluminum hydroxy orthophosphate has an oil absorption of less than 50, and wherein the coating composition provides controlled delivery of phosphate anion in the range of 50 to 500ppm when applied to a metallic substrate and when the coating composition is contacted with moisture and water in the form of a cured film, and wherein the total solubles content in the coating composition is in the range of 50 to 800 ppm.

21. The method of claim 20, wherein the solvent does not contain any alkali or alkaline earth metals.

22. The method of claim 20, wherein the coating composition further comprises a zinc-containing material.

23. The method of claim 20 wherein the aluminum source is selected from the group consisting of aluminum hydroxide, aluminum sulfate, and combinations thereof.

24. The method of claim 20, wherein the phosphorus source is phosphoric acid.

25. The method as recited in claim 20 wherein the amorphous aluminum hydroxy orthophosphate has a total solubles content of less than 400 ppm.

26. The method as recited in claim 20 wherein the coating composition has a controlled release of phosphate anion of between 100 and 200 ppm.

27. The method of claim 20 wherein the phosphorus source is diluted with water prior to combining the aluminum source.

28. The method of claim 20 wherein the source of aluminum is not diluted with water prior to combining the source of phosphorus.

29. The method as recited in claim 20 wherein the amorphous aluminum phosphate has a water adsorption potential of up to 25 percent by weight water after the drying step.

30. The method as recited in claim 20 further comprising the step of applying an anticorrosion coating composition to the metal substrate and allowing the applied coating composition to form an integral cured film, wherein the binder polymer is solvent-based and wherein the amorphous aluminum hydroxy orthophosphate in the cured film controls corrosion of the underlying substrate by absorbing and/or adsorbing water into the film and providing passivating phosphate anion.

31. The method of claim 20, wherein the adhesive polymer comprises an epoxy resin.

32. The method of claim 20, wherein during the mixing step, the binder polymer is selected from the group consisting of: polyurethanes, polyesters, solvent-borne epoxies, solventless epoxies, water-soluble epoxies, epoxy copolymers, acrylics, acrylic copolymers, silicones, silicone copolymers, polysiloxanes, polysiloxane copolymers, alkyds, and combinations thereof.

33. A primer coating formed from an anticorrosion coating composition prepared according to claim 20, wherein the primer coating is applied to a metal substrate.

34. A mid-coat or top-coat paint formed from an anticorrosion coating composition prepared according to claim 20, wherein the mid-coat or top-coat paint is applied to a metallic substrate or to a primer layer applied to a metallic substrate.

35. The method as recited in claim 20 wherein the amorphous aluminum hydroxy-orthophosphate is not heat treated above 200 ℃ prior to the step of mixing.

36. The method of claim 20, wherein no free water is added to the process after combining the starting materials.

37. The method of claim 20, comprising the steps of: preparing an amorphous aluminum phosphate corrosion inhibiting pigment by combining a starting material comprising aluminum hydroxide with phosphoric acid to form a solution comprising condensed aluminum phosphate;

drying the condensed aluminum phosphate at a temperature of less than 200 ℃, wherein the dried condensed aluminum phosphate consists of amorphous aluminum hydroxy orthophosphate;

(ii) providing a particle size range of dried amorphous aluminum hydroxy orthophosphate from 0.01 to 25 microns; and

amorphous aluminum hydroxy orthophosphate is mixed with a binder polymer to form a coating composition.

38. The method of claim 37, wherein the solution does not contain any alkali or alkaline earth metals.

39. The method of claim 37 further including mixing a zinc-containing substance with the binder polymer.

40. The method as recited in claim 37 wherein the coating composition has a controlled release of phosphate anion of between 100 and 200 ppm.

41. The method as recited in claim 37 wherein the binding polymer comprises a solvent-based polymer and the anticorrosion coating composition is applied to a metal substrate and allowed to dry to form an integral cured film wherein the amorphous aluminum hydroxy orthophosphate controls corrosion by absorbing and/or adsorbing water into the film and generating passivating anions.

42. The method of claim 37, wherein the adhesive polymer comprises an epoxy polymer.

43. The method of claim 37, wherein the preparing step is performed without heating.

44. The method as recited in claim 37 wherein the amorphous aluminum phosphate is not heat treated above 200 ℃ prior to the step of mixing.

45. The method of claim 37, wherein the phosphoric acid is diluted with water prior to the combining step.

46. The method of claim 37, wherein the phosphoric acid is not diluted with water prior to the combining step.

47. The method of claim 37, wherein during the mixing step, the binder polymer is selected from the group consisting of: polyurethanes, polyesters, solvent-borne epoxies, solventless epoxies, water-soluble epoxies, epoxy copolymers, acrylics, acrylic copolymers, silicones, silicone copolymers, polysiloxanes, polysiloxane copolymers, alkyds, and combinations thereof.