RU2653028C2 - Method for treating a ferrous metal substrate - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: invention relates to the removal of iron from a pretreatment bath withdrawn from operation. Variants of a method for removing iron from a pretreatment bath are proposed, substantially free of phosphate ions during its functioning, which are carried out in the absence of an article, which is to be coated with said pre-treatment composition. In a first variant of the method for removing iron from a pretreatment bath, containing composition for pretreatment, containing Group IIIB metal and / or Group IVB, (a) reducing the pH of said pretreatment bath to at least 0.2; (b) adding phosphate ions to said pretreatment bath from step (a); (c) increasing the pH of said pretreatment bath from step (b) to at least 0.2; and (d) removing the insoluble precipitate that is formed in the bath of step (c). In a second variant of the process, an acid is added to said pretreatment bath (a) to reduce the pH of said pre-treatment composition to less than 4.0; (b) adding phosphate ions to said pretreatment bath from step (a); (c) increasing the pH of said pre-treatment bath from step (b) to 4-5.5; and (d) removing the insoluble precipitate.

EFFECT: removal of iron.

19 cl, 5 dwg, 4 tbl, 8 ex

Description

This application is a partial continuation of the application for US patent reg. No. 13/313473 (filing date 12/07/2011). This application, in turn, is a continuation of application for US patent No. 12/237770 (filing date 09/25/2008), which is published as patent document US 8097093 B2 and which claims the priority of provisional patent application US reg. No. 60/975957 (filing date September 28, 2007). All of these applications are incorporated into this description by reference.

FIELD OF THE INVENTION

The present invention relates to methods for treating a ferrous metal substrate such as cold rolled steel, hot rolled steel and electroplated steel. The present invention also relates to coated ferrous metal substrates. The invention also relates to methods for removing iron from a pretreatment bath if said pretreatment bath is on the production line, both in the presence of an article to be coated using the pretreatment composition and when said pretreatment bath is taken out of operation.

State of the art

The use of protective coatings on metal substrates to improve their corrosion resistance and the adhesion of coatings is common in the art. A common method for coating such substrates involves pretreating the metal substrate using a phosphate conversion coating and chromium-containing washing solutions. Conventional phosphate conversion coatings perform their functions in the region of at least 1000 parts per million (ppm) of phosphate, which leads to the need to solve the problems of the neutralization and disposal of processing waste. Therefore, the use of such phosphate and / or chromium-containing compositions makes it necessary to take into account the problems associated with the protection of health and the environment.

As a result, pre-treatment compositions are developed that do not contain chromates and phosphates. Such compositions are usually based on mixtures of chemical compounds that in some way react with the surface of the substrate and attach to it to form a protective layer. As an example, compositions for pretreatment based on a metal compound of Group IIIB or IVB of the Periodic Table have recently become more common.

However, when treating ferrous metal substrates with a pretreatment composition based on a Group IIIB or IVB metal compound, the concentration of ferric iron (Fe ⁺³ ) in the bath with the pretreatment composition increases over time as more iron-based metal is processed . In this case, soluble iron (Fe ⁺² ) from the substrate becomes insoluble iron (Fe ⁺³ ) due to an increase in the concentration (Fe ⁺² ), oxidation, and subsequent reaction with oxygen and water. The resulting insoluble rust, i.e. hydrated iron (III) oxide (Fe ₂ O ₃ ⋅H ₂ O) and / or iron (III) oxide-hydroxide (FeO (OH)) forms flakes, and the deposition of insoluble rust particles is difficult in the process of weak mixing that occurs when processing parts . As a result, insoluble rust particles can adhere to the precipitate or settle on it and can be transferred to subsequent processing steps (in particular, if there is no filtration equipment), in particular, to the electrodeposition coating bath located downstream of the processing line used for organic coating deposition. Such cross-contamination may adversely affect the performance of such subsequent electrodeposition coatings.

As a result, the practice commonly used in industrial plants consists, as a preventive measure, in periodically diluting the pre-treatment bath to reduce the concentration of soluble iron and in adding a replenishment to the pre-treatment bath, designed to replenish the amount of ingredients in the bath and restore the covering ability of the composition. In some cases, for the implementation of processes for removing rust from the bath, the pre-treatment bath must be removed from the process. As an alternative, the pre-treatment bath needs to be unloaded once every two weeks and a fresh bath should be prepared. Each of these applied methods is expensive due to significant losses of the composition used, waste treatment and inconvenience.

As a result, it would be desirable to provide improved methods for treating a ferrous metal substrate and removing soluble iron that provide a solution to at least some of the above problems.

Disclosure of invention

In certain aspects, the present invention relates to methods for coating a ferrous metal substrate.

In certain aspects, a method of coating a ferrous metal substrate includes: (a) contacting the ferrous metal substrate with an aqueous pretreatment composition having a pH of from 4 to 5.5 and comprising: (a) a compound of a metal of Group IIIB and / or IVB ; (b) phosphate ions; and (c) water, wherein said Group IIIB and / or IVB metal compound is present in the pretreatment composition in an amount of from 10 to 500 ppm (parts per million) of metal, and a weight ratio of Group IIIB and / or IVB metal to phosphate ions in the pretreatment composition is at least 0.8: 1; wherein said phosphate ions are maintained in a bath with a pretreatment composition in an amount of: (i) sufficient to substantially prevent the formation of insoluble rust in the bath; (ii) insufficient to prevent the deposition of a Group IIIB and / or IVB metal film with a coating density of at least 10 mg / m ² on said ferrous metal substrate; and (iii) leading to a mass ratio of phosphate to ferric ions of 1: 1 to 1.8: 1; and then (b) contacting said substrate with a coating composition comprising a film-forming resin to form a coated metal substrate that exhibits anti-corrosion properties.

In certain other aspects, a method of coating a ferrous metal substrate includes: a) contacting the ferrous metal substrate with an aqueous pretreatment composition having a pH of from 4 to 5.5 and containing: (a) a compound of a metal of Group IIIB and / or IVB ; (b) phosphate ions; and (c) water, wherein said compound of a metal of Group BW and / or IVB is present in the composition for pretreatment in an amount of from 10 to 500 ppm of metal, and a mass ratio of the metal of Group IIIB and / or IVB to phosphate ions in the composition for pretreatment is at least 0.8: 1; wherein said phosphate ions are maintained in a bath with a pretreatment composition in an amount of: (i) sufficient to substantially prevent the formation of insoluble rust in the bath; (ii) insufficient to prevent the deposition of a Group IIIB and / or IVB metal film with a coating density of at least 10 mg / m on said ferrous metal substrate; and (iii) leading to a mass ratio of phosphate to additional soluble iron in the state of ferric iron in the range from 1.8: 1 to 10: 1; and then (b) contacting said substrate with a coating composition comprising a film-forming resin to form a coated metal substrate that exhibits anti-corrosion properties.

In certain other aspects, the present invention is directed to providing methods for removing iron from a pretreatment bath, comprising the steps that take place when the pretreatment bath is removed from the processing line.

In certain aspects, methods for removing a bath from a processing line for removing iron from a pretreatment bath containing a pretreatment composition containing Group IIIB and / or IVB metal include: (a) reducing the pH in the pretreatment bath by at least 0 , 2; (b) adding phosphate ions to the pretreatment bath from step (a); and (c) raising the pH of the pretreatment bath from step (b) by at least 0.2.

In certain aspects, methods for removing a bath from a process to remove iron from said pretreatment bath containing a pretreatment composition containing Group IIIB and / or IVB metal include: (a) adding acid to the pretreatment bath to lower the pH of the composition pretreatment to values less than 4.0; (b) adding phosphate ions to the pretreatment bath from step (a); and (c) increasing the pH of the pretreatment bath from step (b) to at least 4.0 to 5.5.

The present invention also provides substrates treated and coated in this manner.

Brief Description of the Drawings

FIG. 1 and FIG. 2 is a graphical representation of the experimental data of Example 3.

FIG. 3 is a graphical representation of the experimental data of Example 4.

FIG. 4 is a graphical representation of the experimental data of Example 5.

FIG. 5 is a graphical representation of the experimental data of Example 6.

The implementation of the invention

In the framework of the following detailed description of the invention, it should be understood that the invention may provide various alternatives and sequence steps of the method, unless specifically indicated otherwise. In addition, in addition to any of the embodiments, or unless otherwise specified, all numerical values expressing, for example, the amounts of ingredients used in the description and claims, should be understood as changeable in all cases using the term “approximately”. Accordingly, except as otherwise indicated, the quantitative parameters set forth in the following description and the attached claims are approximations that may vary depending on the desired characteristics obtained by using the present invention.

At least not as a limitation on the application of the doctrine of equivalents to the scope of the invention, each numerical parameter should at least be construed in light of the number of indicated significant digits and using conventional rounding methods.

Although the numerical ranges and parameters describing the scope of the invention are approximations, the numerical values given in the specific examples are indicated as accurately as possible. However, any numerical value certainly contains certain errors, obviously obtained as a result of standard deviations detected in the corresponding measurements during the test.

In addition, it should be understood that any numerical range indicated herein includes all sub-ranges. For example, the interval “from 1 to 10” implies the inclusion of all sub-intervals between the specified minimum value of 1 and the specified maximum value of 10 (and including these values), i.e. having a minimum value equal to or greater than 1 and a maximum value equal to or less than 10.

In this application, the use of the singular includes the plural, and the plural encompasses the singular unless otherwise indicated. In addition, in this application, the use of “or” means “and / or”, unless otherwise expressly agreed, even if “and / or” can be directly used in certain cases.

In this application, the term “withdrawn from the process” means that the product to be coated using the pre-treatment composition is not in the pre-treatment bath, but does not mean that this bath is necessarily removed from the production line.

In this application, the term “total iron” or “total Fe” means the total amount of iron in the pretreatment bath, including but not limited to ferrous iron (Fe ^{+ 2} ) and ferric iron (Fe ⁺³ ).

In the present description, unless otherwise specified otherwise, when it is indicated that the pretreatment composition is “substantially free” of a particular component, this means that the material in question is present in the composition, if at all, as a random impurity. In other words, such a material is not intentionally added to the composition, but may be present in insignificant or insignificant amounts, since it was introduced as an impurity as part of a component of said composition. In addition, when it is indicated that the composition for pre-treatment is “completely free” of a particular component, this means that the material in question is not contained in the composition at all.

As noted above, certain embodiments of the present invention relate to methods for treating a ferrous metal substrate. Suitable ferrous metal substrates for use in the present invention include those that are often used in automobile body structures, automobile parts, and other products, for example metal parts, including fasteners, i.e. nuts, bolts, screws, studs, pins, clamps, pins and the like. Specific examples of suitable ferrous metal substrates include, but are not limited to, substrates of cold rolled steel, hot rolled steel, zinc coated steel, zinc compounds or zinc based alloys, for example, galvanized steel, hot dip galvanized steel annealed galvanized steel and zinc alloy plated steel. In addition, the ferrous metal substrate processed by the methods of the present invention may be a trimmed edge of the substrate that has already been otherwise processed and / or coated on the rest of the surface. The ferrous metal substrate coated in accordance with the methods of the present invention may, for example, be in the form of a sheet of metal or a fabricated part.

The ferrous metal substrate to be treated in accordance with the methods of the present invention can be pre-cleaned to remove fatty substances, dirt and other foreign substances. This is in most cases accomplished by using mild or strong alkaline cleaners, such as are commercially available and are commonly used in metal pretreatment processes. Examples of alkaline cleaners suitable for use in the present invention include Chemkleen ™ 163, 177, 61 1L and 490MX, all of which are manufactured by PPG Industries, Inc. After using such cleaners and / or before using them, water rinsing is often carried out.

As noted above, certain embodiments of the present invention relate to methods for treating a metal substrate, which comprise contacting the metal substrate with a pretreatment composition comprising a Group IIIB and / or IVB metal. As used herein, the term “pretreatment composition” refers to a composition that, when contacted with a substrate, chemically reacts with the surface of the substrate, chemically changes this surface and adheres to it to form a protective layer.

In many cases, the pretreatment composition contains a carrier, in most cases an aqueous medium, so that the composition may be in the form of a solution or dispersion of a Group IIIB and / or IVB metal compound in the carrier. In these embodiments, the solution or dispersion can be brought into contact with the substrate using any of a variety of known methods, for example, dipping or dipping, spraying, batch spraying, dipping followed by spraying, spraying followed by dipping, brushing or roller coating. In certain embodiments, the solution or dispersion when applied to a metal substrate is at a temperature in the range of 50 to 150 ° F. (10 to 65 ° C.). The contact time is often from 2 seconds to five minutes, in particular from 30 seconds to 2 minutes.

As used herein, the term “Group IIIB and / or IVB metal” refers to a chemical element in Group IIIB and / or IVB of the Periodic Table of Chemical Elements, such as, for example, Handbook of Chemistry and Physics, 63 ^rd edition (1983).

Where applicable, the metal itself may be used. In certain embodiments, a Group IIIB and / or IVB metal compound is used. As used herein, the term “Group IIIB and / or IVB metal compound” refers to chemical compounds that contain at least one element from Group IIIB or Group IVB of the Periodic Table of the Chemical Elements.

In certain embodiments, the Group IIIB and / or IVB metal compound used in the pretreatment composition may be a zirconium, titanium, hafnium compound, or a mixture thereof. Suitable zirconium compounds include, but are not limited to, hexafluorozirconic acid and its alkali metal or ammonium salts, zirconium ammonium carbonate, zirconium basic carbonate, zirconyl nitrate, zirconium carboxylates, and zirconium hydroxycarboxylates, in particular zirconium hydrofluorocarbonium zirconium oxalate, zirconium-ammonium glycolate, zirconium-ammonium lactate, zirconium-ammonium citrate and mixtures thereof. Suitable titanium compounds include, but are not limited to, fluorotitanic acid and its salts. Suitable hafnium compounds include, but are not limited to, hafnium nitrate.

In certain embodiments, the Group IIIB and / or IVB metal compound is present in the bath with the pretreatment composition in an amount of at least 10 ppm metal, in particular at least 20 ppm metal, at least 30 ppm metal or in some cases at least 50 ppm metal (measured based on elemental metal). In certain embodiments, the Group IIIB and / or IVB metal compound is present in the bath with the pretreatment composition in an amount of not more than 500 ppm metal, in particular not more than 150 ppm metal, or in some cases not more than 80 ppm million metal (measured per elemental metal). The amount of Group IIIB and / or IVB metal in the pretreatment composition may vary in the range of any combination of the listed values, including, but not limited to, the listed values.

As noted above, pretreatment compositions used in certain embodiments of the methods of the present invention contain phosphate ions. In certain embodiments, the source of phosphate ions is phosphoric acid, in particular phosphoric acid at a concentration of 75%, although other sources of phosphate ions, such as, for example, monosodium phosphate or disodium phosphate, are also considered as possible in the present invention. In certain embodiments, pretreatment compositions according to the methods of the present invention are substantially free of phosphate ions.

As noted above, in certain embodiments of the methods of the present invention, phosphate ions are maintained in a bath with a pretreatment composition in an amount sufficient to substantially prevent the formation of insoluble rust in the bath. As used herein, the term “maintained” means that the amount of phosphate ions is controlled and, if necessary, set to substantially prevent the formation of insoluble rust in the bath. As used herein, the phrase “substantially prevents the formation of insoluble rust” means that the formation of insoluble rust in the bath, i.e. containing, but not limited to, hydrated oxide (Fe ₂ O ₃ ⋅nH ₂ O) iron (III) and / or oxide-hydroxide (FeO (OH)) iron (III) is prevented to such an extent that the appearance in the bath orange or red-brown in color, indicating the formation of such compounds, is not visible to the naked eye.

In certain embodiments of the present invention, it is sometimes preferred that the phosphate ions are maintained in the bath in an amount sufficient to complex with soluble iron etched from the surface of the ferrous metal substrate to be formed to form iron (III) phosphate (FePO ₄ ) in the bath, resulting in the bath is light in color, not orange or reddish brown due to the presence of rust. This leads to the formation of an insoluble precipitate that can be removed from the bath using conventional filtration equipment. Certain embodiments of the present invention, therefore, limit the amount of ferric iron (Fe ⁺³ ) (separated from a ferrous metal substrate) that can become insoluble rust that can precipitate on the substrate and can be transferred to subsequent process equipment, for example, to downstream nozzles, pumps, flushing baths and bathtubs intended for electrodeposition of organic coating. As noted above, such cross-contamination can have a detrimental effect on the performance of subsequent deposited coatings.

In certain embodiments of the methods of the present invention, phosphate ions are also maintained in a bath with a pretreatment composition in an amount insufficient to inhibit the precipitation of a Group IIIB or IVB metal film having a coating density (total film weight) of at least 10 mg / m ² , in particular at least 100 mg / m ^2, or in some cases from 100 to 500 mg / m ² , on a ferrous metal substrate. It was found that, in particular, at the pH of the bath used in the present invention, there is an unstable equilibrium between phosphate ions forming complexes with soluble iron etched from a ferrous metal substrate to form iron phosphate, which is desirable, and forming complexes with a Group IIIB or IVB metal in the bath, which is undesirable as this will prevent the deposition of a sufficient film of Group IIIB or IVB metal on a ferrous metal substrate.

It was found that the presence of phosphate ions in an amount of from 1 to 1.8, in particular, from 1.2 to 1.6 mass parts for each 1 mass part of ferric ions (Fe ⁺³ ) in the composition is sufficient to to substantially prevent the formation of insoluble rust, and at the same time, it is not enough to prevent the deposition of a film of a metal of Group IIIB or IVB having a coating density of at least 10 mg / m ² , for example at least 100 mg / m ² , ferrous metal substrate. As a result, in certain embodiments of the methods of the present invention, phosphate ions are maintained in the bath at a level that results in a mass ratio of phosphate ions to ferric ions of from 1: 1 to 1.8: 1, in some cases from 1.2: 1 up to 1.6: 1. If the mass ratio of phosphate ions to ferric ions is less than 1: 1, then there may be too little phosphate in the bath to substantially prevent the formation of insoluble rust in the bath as described above. If the mass ratio of phosphate ions to ferric ions is more than 1.8: 1, then the amount of phosphate ions may be sufficient to prevent the necessary amount of Group IIIB or IVB metal film from being deposited on a ferrous metal substrate. The specified ratio between the amounts of phosphate ions and ferric ions in the pretreatment composition may vary in the range including any combination of the above values, including including the indicated values.

In addition, in certain embodiments of the methods of the present invention, the amount of phosphate ions in the bath is maintained at a level that results in a mass ratio of Group IIIB and / or IVB metal to phosphate ions in the bath of at least 50: 1, some cases at least 25: 1, in some cases at least 12.5: 1, in some cases at least 3: 1, and in some cases at least 2: 1. If the mass ratio of Group IIIB and / or IVB metal to phosphate ions is less than 2: 1, then too much phosphate may be in the bath, which will adversely affect the ability to deposit enough film of Group IIIB or IVB metal on the substrate from ferrous metal.

As can be seen, due to the fact that the pretreatment compositions in accordance with the present invention contain in some cases from 20 to 500 ppm of Group IIIB or IVB metal, in particular from 30 to 150 ppm, or in some cases from 30 to 80 ppm metal of Group IIIB or IVB metal, in certain embodiments of the methods of the present invention, the bath in many cases contains a relatively small amount of phosphate ions, since in certain embodiments the phosphate ions are maintained in the bath at a level that leads to a mass ratio the crosslinking of a Group IIIB and / or IVB metal to phosphate ions in a bath of at least 2: 1, in some cases at least 3: 1. As a result, in certain embodiments, such a bath contains fofsfate ions in amounts of not more than 30 ppm, in particular from 10 to 30 ppm. It was shown that the presence of a small amount of phosphate ions has a strong effect on the duration of normal operation of the bath by preventing the formation of insoluble rust in the pre-treatment bath for a period of time up to months and years in certain embodiments, in particular due to the removal of iron from the pretreatment bath.

As described above, when treating a ferrous metal substrate using a pretreatment composition based on a Group IIIB metal compound and / or IVB, the concentration of ferric iron (Fe ⁺³ ) in the bath with the pretreatment composition increases over time as more and more iron-based metal. As a result, such a bath accumulates insoluble rust, which can be deposited on the substrate to be treated and can thus be transferred to subsequent process steps. To avoid this, such a bath often needs to be replaced periodically, in some cases once a week. However, it was unexpectedly discovered that the presence of the above small amounts of phosphate can prevent the formation of insoluble rust without preventing the formation of the necessary Group IIIB and / or IVB metal film so that the bath can function without replacement for several months, possibly for an indefinitely long time. . The fact that such a small amount of phosphate can extend the life of the bath to a large extent was surprising and unexpected. In addition, the presence of phosphate ions in such small amounts leads to the formation of a minimum amount of solid precipitate, which is more compensated by preventing the formation of insoluble rust. As a result, the problems of disposal and disposal of industrial waste are not an important issue that needs to be resolved.

In certain embodiments, the pretreatment composition further comprises an electropositive metal. As used herein, the term “electropositive metal” refers to metals that are more electropositive than the substrate metal. This means that for the purposes of the present invention, the term "electropositive metal" encompasses metals that are less readily oxidized than the metal of the metal substrate to be treated. A person skilled in the art will understand that the tendency of a metal to oxidize is called the oxidation potential, expressed in volts and measured with respect to a standard hydrogen electrode, which is conditionally associated with an oxidation potential of zero. The oxidizing potential for various elements is shown in the table below. An element is less easily oxidized compared to another element if it has a potential value E * in the table below, which is greater than that of the element with which it is compared.

Thus, it is understood that if the metal substrate contains ferrous metal, as in the case of the present invention, suitable electropositive metals for use in the pretreatment composition include, for example, nickel, tin, copper, silver and gold, as well as mixtures thereof.

In certain embodiments, the source of the electropositive metal in the pretreatment composition is a water soluble metal salt. In certain embodiments of the present invention, the water-soluble metal salt is a water-soluble copper compound. Specific examples of water-soluble copper compounds suitable for use in the present invention include, but are not limited to, copper cyanide, potassium cyanide, copper sulfate, copper nitrate, copper pyrophosphate, copper thiocyanate, disodium tetrahydrate of copper ethylene diamine tetraacetate, copper bromide, copper oxide, copper hydroxide, copper chloride, copper fluoride, copper gluconate, copper citrate, copper lauryl sarcosinate, copper formate, copper acetate, copper propionate, copper butyrate, copper lactate, copper oxalate, copper phytate, copper tartrate, copper malate, copper succinate one, copper malonate, copper maleate, copper benzoate, copper salicylate, copper aspartate, copper glutamate, copper fumarate, copper glycerophosphate, sodium copper chlorophylline, copper fluorosilicate, copper fluoroborate and copper iodate, as well as copper salts of carboxylic acids in homological series from formic acid to decanoic acid, copper salts of polybasic acids ranging from oxalic acid to suberic acid and copper salts of hydroxycarboxylic acids, including glycolic, lactic, tartaric, malic and citric acids.

When copper ions from the above water-soluble copper compounds precipitate as impurities in the form of copper sulfate, copper oxide, etc., it may be preferable to add a complexing agent that inhibits the deposition of copper ions and thus stabilizes them in the form of a copper complex in solution.

In some embodiments, the copper compound is added as a complex salt of copper, such as K ₃ Cu (CN) ₄ or Cu-EDTA (ethylenediaminetetraacetic acid), which may itself be stably present in the pretreatment composition. It also seems possible to form a copper complex, which can be stably present in the pretreatment composition by combining a complexing agent with a compound that is itself sparingly soluble. Examples of such formation include a complex compound of copper cyanide formed by a combination of CuCN and KCN or a combination of CuSCN and KSCN or KCN, and a complex compound Cu-EDTA formed by a combination of CuSO ₄ and EDTA⋅2Na.

As a complexing agent, a compound can be used that can form a complex compound with copper ions; examples of this include polyphosphates, in particular sodium tripolyphosphate and hexametaphosphoric acid; aminocarboxylic acids such as ethylenediaminetetraacetic acid, gadroxyethylethylenediamine triacetic acid, and nitrilotriacetic acid; hydroxycarboxylic acids, such as tartaric acid, citric acid, gluconic acid and salts of these acids; amino alcohols such as triethanolamine; sulfur compounds, in particular thioglycolic acid and thiourea, and phosphonic acids such as nitrilotrimethylene phosphonic acid, ethylenediamine tetramethylene phosphonic acid and hydroxyethylidene diphosphonic acid.

In certain embodiments, an electropositive metal, in particular copper, is included in the pretreatment compositions in an amount of at least 1 ppm, in particular at least 5 ppm, or in some cases at least 10 ppm of the total metal (measured per elemental metal). In certain embodiments, an electropositive metal is included in such pretreatment compositions in an amount of not more than 500 ppm, in particular not more than 100 ppm, or in some cases not more than 50 ppm of the total amount of metal (measured based on elemental metal). The amount of electropositive metal in the pretreatment composition may be in the range including any combination of the above values, including the indicated values themselves.

As noted above, the working pH values of the pretreatment composition used in the methods of the present invention are in the range from 4.0 to 5.5, in some cases from 4.0 to 5.0, from 4.5 to 5 , 5 or in other cases from 4.5 to 5.0. The pH of the pretreatment composition can, if necessary, be adjusted using, for example, any acid or base.

In addition to the above components, the pre-treatment compositions used in the methods of the present invention may contain a number of additional optional components. For example, in certain embodiments, the pre-treatment compositions used in the methods of the present invention comprise a polyhydroxy-functional cyclic compound, such as described in US Pat. No. 6,805,756, from column 3, line 9 to column 4, line 32 (cited portion of said document is included in the present description by reference). However, in other embodiments, the pre-treatment compositions used in the methods of the present invention are substantially free or, in some cases, completely free of any such polyhydroxy-functional cyclic compound.

In certain embodiments, the pretreatment compositions used in the methods of the present invention comprise an oxidizing agent, such as those described in US Pat. No. 6,805,756, column 4, line 52 to column 5, line 13, and in US Pat. No. 6193815, column 4, line 62 to column 5, line 39 (cited portions of these documents are incorporated herein by reference). In other embodiments, in contrast, the pretreatment compositions are substantially free or, in some cases, completely free of any such oxidizing accelerator.

In certain embodiments, the pretreatment composition comprises a film-forming resin, such as, for example, a reaction product of an alkanolamine and an epoxy-functional material containing at least two epoxy groups, such as described in patent document US 5653823; a resin containing beta-hydroxy ester, imide or sulfide functionality, introduced by using dimethylolpropionic acid, phthalimide, or mercaptoglycerol as an additional reagent to obtain said resin; the reaction product of diglycidyl ester of bisphenol A (marketed by the Shell Chemical Company under the name EPON 880), dimethylol propionic acid and diethanolamine in a molar ratio of 0.6 to 5.0: 0.05 to 5.5: 1; water-soluble and water-dispersible polyacrylic acids described in patent documents US 3912548 and US 5328525; phenol formaldehyde resins described in patent document US 5662746; water-soluble polyamides, such as those described in international application WO 95/33869; copolymers of maleic or acrylic acid with allyl ether described in Canadian Patent Application No. 2,087,352; and water-soluble and water-dispersible resins, including epoxies, aminos, phenol-formaldehyde resins, tannins and polyvinyl phenols described in US Pat. No. 5,449,415. In other embodiments, in contrast, the pretreatment compositions are substantially free or, in some cases, completely free of any organic film-forming resin, for example, one or more of the above resins.

In certain embodiments, the pretreatment compositions used in the methods of the present invention comprise a fluoride ion, such as described in US Pat. No. 6,805,756, column 7, lines 7-23 (a cited portion of this document is incorporated herein by reference). In certain embodiments, the fluoride ion is introduced into the composition by a Group IIIB and / or IVB metal compound. In certain embodiments, the pretreatment compositions are free or, in some cases, completely free of any fluoride ion introduced into said pretreatment composition from a source other than a Group IIIB and / or IVB metal compound.

In certain embodiments, the pretreatment compositions used in the methods of the present invention comprise a polysaccharide, such as described in US Pat. No. 6,805,756, column 6, lines 53-64 (a cited portion of this document is incorporated herein by reference) and internationally WO 2005/001158, p. 3, lines 17-23. In other embodiments, in contrast, the pretreatment compositions are substantially free or, in some cases, completely free of any such polysaccharide.

In certain embodiments, the pretreatment compositions used in the methods of the present invention comprise a phosphate ester, a water soluble ester of polyethylene glycol and a fatty acid, and / or nitric acid, as described in US Pat. No. 5,139,586, column 5, lines 31-63 (cited part of this document is incorporated into this description by reference). In other embodiments, in contrast, the pretreatment compositions are substantially free or, in some cases, completely free of phosphate ester, water soluble polyethylene glycol ester and fatty acid and / or nitric acid.

In certain embodiments, the pretreatment compositions used in the methods of the present invention comprise vanadium and / or cerium ions, such as those described in US Pat. included in the present description by reference), and in the application for US patent No. 2007/0068602. In other embodiments, in contrast, the pretreatment compositions are substantially free or, in some cases, completely free of vanadium and / or cerium ions.

In certain embodiments, the pretreatment compositions used in the methods of the present invention comprise phosphoric acid, hypophosphoric acid and / or their salts, such as those described in US Pat. No. 5,728,233, column 4, lines 24-37 (cited portion of this document is included in the present description by reference). In other embodiments, in contrast, the pretreatment compositions are substantially free or, in some cases, completely free of phosphoric acid, hypophosphoric acid and / or their salts.

In certain embodiments, the pretreatment compositions used in the methods of the present invention comprise a Group IIA metal, such as described in US Pat. No. 5,380,374, column 3, lines 25-33, and / or Group IA metal, such as described in the patent document US 5441580, from column 2, line 66 to column 3, line 4 (cited portions of these patent documents are incorporated into this description by reference). In other embodiments, in contrast, the pretreatment compositions are substantially free or, in some cases, completely free of any Group IIA metal and / or Group IA metal.

In certain embodiments, the pretreatment compositions used in the methods of the present invention comprise a molybdenum compound, such as described in GB Patent Application GB 2259920 A. In other embodiments, in contrast, the pretreatment compositions are substantially free or, in some cases, are completely free of molybdenum compounds.

In certain embodiments, the pretreatment compositions used in the methods of the present invention comprise one or more metal ions selected from the group consisting of scandium, yttrium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium and lutetium, as described in patent document US 5104577, from column 2, line 60 to column 3, line 26 (the cited part of this document is incorporated into this description by reference). In other embodiments, in contrast, the pretreatment compositions are substantially free or, in some cases, completely free of any metal ions selected from the group consisting of scandium, yttrium, lanthanum, praseodymium, neodymium, samarium, europium, gadolinium, terbium, dysprosium , holmium, erbium, thulium, ytterbium and lutetium.

The pretreatment composition may optionally contain other materials, such as a nonionic surfactant and auxiliary additives commonly used in the prior art for pretreatment. In the aqueous medium, water-dispersible organic solvents may be present, for example, alcohols containing up to 8 carbon atoms, such as methanol, isopropanol, and the like, or glycol ethers, for example, monoalkyl ethers of ethylene glycol, diethylene glycol or propylene glycol, and the like.

Water-dispersible organic solvents, if present in the composition, are typically used in amounts up to about 10 vol. %, based on the total volume of the aquatic environment.

Other optional materials used include surfactants that function as anti-foaming agents or as wetting agents for the substrate.

In certain embodiments, the pretreatment compositions further comprise a filler, for example, a silicon-containing filler. Non-limiting examples of suitable fillers include silica, mica, montmorillonite, kaolinite, asbestos, talc, diatomite, vermiculite, natural and synthetic zeolites, cement, calcium silicate, aluminum silicate, sodium aluminosilicate, aluminum polysilicate, aluminosilicates and glass particles. In addition, in addition to silicon-based fillers, other finely divided, substantially water-insoluble fillers can also be used. Examples of such fillers used if necessary include carbon black, coal, graphite, titanium oxide, iron oxide, copper oxide, zinc oxide, antimony oxide, zirconium dioxide, magnesium oxide, aluminum oxide, molybdenum disulfide, zinc sulfide, barium sulfate, strontium sulfate, calcium carbonate and magnesium carbonate. In other embodiments, in contrast, the pretreatment compositions are substantially free or, in some cases, completely free of any such filler.

In certain embodiments, the pretreatment composition is substantially free or, in some cases, completely free of heavy metal chromate and / or phosphate, such as zinc phosphate. As used herein, the term “substantially free” when used, indicating the absence of chromate and / or heavy metal phosphate in the pretreatment composition, means that these substances are not present in the composition to such an extent that they cause environmental pollution. As used herein, the term "completely free" when used, indicating the absence of chromate and / or phosphate of heavy metal, means that chromate and / or phosphate of heavy metal is generally absent in the composition.

It is understood that in certain embodiments, the pretreatment composition used in the methods of the present invention consists of, or in some cases consists of: (a) a Group IIIB and / or IVB metal compound, for example, a zirconium compound; (b) a source of phosphate ions, for example phosphoric acid; and (c) water. In certain other embodiments, the pretreatment composition used in the methods of the present invention essentially consists of, or in some cases consists of: (a) a Group IIIB and / or IVB metal compound, for example, a zirconium compound; and (c) water. In certain embodiments, such a pretreatment composition comprises fluoride ions introduced into the pretreatment composition by combining a Group IIIB and / or IVB metal. As used herein, the term “essentially consists of” means that the composition does not contain any other components that could have a significant effect on the main and new characteristic (s) of the invention. In the context of the present invention, this means that the pre-treatment composition does not contain any components that could significantly affect the ability of the composition to be successfully used in the methods of the present invention.

In certain embodiments, the density of the film (total film weight) formed from the deposited pre-treatment coating composition is at least 10 mg / m ² , in particular from 100 to 500 mg / m ² , or in some cases at least 50 mg / m ² . The thickness of the coating deposited during the pre-treatment can vary, but usually the coating is very thin and often has a thickness of less than 1 micron, in some cases the coating thickness is in the range from 1 to 500 nanometers, and in other cases in the range of 10 up to 300 nanometers, for example, from 20 to 100 nanometers.

In certain embodiments, a method for withdrawing a bath from a process is used to remove soluble iron from the pre-treatment bath so that this pre-treatment bath is substantially free of iron upon completion of the process withdrawing from the process, thereby substantially preventing formation of insoluble rust in a functioning bath with a composition for pre-treatment. As used herein, the term “substantially free” when used with respect to iron in a working bath with a pretreatment composition means that the total amount of iron is present in an amount of less than 10 ppm.

As indicated above, in certain embodiments, the bath with the pretreatment composition is substantially free of phosphate ions when operating in a composition of the pretreatment system in which the presence of phosphate in the pretreatment bath can adversely affect the deposition on the substrate of the composition pretreatment. In such embodiments, a method for removing iron from a pretreatment bath to remove the bath from the process may be particularly suitable for pretreatment systems that are substantially free of phosphate ions, as a method of substantially preventing the formation of insoluble rust in the bath pretreatment. In addition, as indicated above, in certain other embodiments, the pretreatment bath contains phosphate ions as a method that substantially prevents the formation of insoluble rust in the pretreatment bath. In such embodiments, the method for removing iron from the pre-treatment bath, carried out with the removal of the bath from the process, may be particularly suitable as an additional or auxiliary method, essentially preventing the formation of insoluble rust in the pre-treatment bath.

In accordance with the foregoing, in certain embodiments, the working pH of the composition in the pretreatment bath is more than 4.0, in particular in the range from 4.2 to 5.5, preferably from 4.5 to 5.0, and most preferably is 4.8. In certain embodiments, the first step in a method for removing iron from a pretreatment bath, carried out to remove the bath from the process, involves reducing the pH in the pretreatment bath by at least 0.2, for example, at least 0.5 or at least at least 1.0, so that the pH of the pretreatment bath is reduced to a value in the range from 1.0 to 3.8 and preferably from 2.5 to 3.3. In certain embodiments, the pH of the pretreatment bath is reduced by adding acid to the pretreatment bath, including, but not limited to, acid containing fluorine and a Group IVB metal, for example, hexafluorozirconic acid and hexafluorotitanic acid, phosphoric acid, sulfuric acid, sulfamic acid, nitric acid and mixtures thereof.

In certain embodiments of the method for removing iron from the pre-treatment bath, carried out with the removal of the bath from the process, the first step in reducing the pH in the pre-treatment bath is by adding acid to the pre-treatment bath in an amount sufficient to lower the pH in the above manner.

In certain embodiments of a method for removing iron from a pretreatment bath carried out to remove the bath from the process, the second step comprises adding phosphate ions to the pretreatment bath. In certain embodiments, the sources of phosphate ines may be alkali metal or ammonium orthophosphates present as a monohydro type or dihydro type compound, including, for example, monosodium phosphate, disodium phosphate, and mixtures thereof. In specific cases, Zircobond Additive P, a monosodium phosphate solution marketed by PPG Industries, Inc., Euclid, Ohio, is used as a source of phosphate ions.

In certain embodiments of a method for removing iron from a pretreatment bath carried out to remove the bath from the process, the third step comprises adding an oxidizing agent to the pretreatment bath. In such embodiments, the oxidizing agent is a peroxide compound, air, sodium nitrite, sodium bromate, and mixtures thereof. In a preferred embodiment, the peroxide compound is hydrogen peroxide.

In certain embodiments of a method for removing iron from a pretreatment bath to remove the bath from the process, a phosphate ion source and an oxidizing agent are each added in amounts that are sufficient to make the pretreatment bath substantially free of iron.

In certain embodiments of a method for removing iron from a pre-treatment bath, carried out with the removal of the bath from the process, the fourth stage of the method includes increasing the pH in the pre-treatment bath by at least 0.2. In embodiments, the pH is increased to greater than 4.0, for example, in the range of 4.2 to 4.5, 4.5 to 5.0, and 4.8. In certain embodiments, the pH is increased by adding a sufficient amount of an alkali metal compound to the pretreatment bath, including but not limited to caustic soda, potassium hydroxide, and sodium hydroxide. In embodiments, a slightly alkaline Chemfil Buffer, commercially available from PPG Industries, Inc., Euclid, Ohio, in an amount sufficient to achieve the desired operating pH can be used as the alkali metal compound.

In certain embodiments of the method of the present invention carried out with the removal of the bath from the process, the phosphate ions are added to the pretreatment bath in an amount sufficient to form a complex with soluble iron etched from the surface of the processed ferrous metal substrate to form phosphate in the bath (FePO ₄ ) iron (III), as a result of which the bath becomes light in color, not orange or reddish brown due to the presence of rust. The formation of this phosphate results in the formation of a precipitate that can be removed from the bath using conventional filtration equipment. In certain embodiments of the method of removing the bath from the process, the fifth step includes filtering the pre-treatment bath using such conventional filtration equipment to remove solids from the pre-treatment bath, i.e. iron phosphate, iron oxides, iron hydroxides or any other insoluble precipitate that forms in the bath for pre-treatment. In certain embodiments, the filtration step may be carried out immediately after increasing the pH of the pretreatment bath by at least 0.2. In certain other embodiments, the filtration step can be carried out immediately after the equilibrium period during which this insoluble precipitate is deposited on the bottom of the pretreatment bath, for example, from 1 to 10 hours after increasing the pH in the pretreatment bath.

Thus, the method corresponding to the present invention, carried out with the removal of the bath from the process, removes soluble iron in the bath (from the ferrous metal substrate), which can be converted into insoluble rust, which can be deposited on the substrate and can be transferred to the subsequent process equipment, such as downstream nozzles, pumps, rinsing baths, and bathtubs intended for electrodeposition coverings. As indicated above, such cross-contamination can adversely affect the properties of subsequent deposited coatings. However, it was unexpectedly discovered that lowering the pH in the pre-treatment bath below the working pH and then adding the above-mentioned small amounts of phosphate and, at the discretion of the oxidizing agent, can essentially remove the iron contained in the bath, thereby preventing the formation of insoluble rust in the pre-treatment bath, not while preventing the formation of the required quality of a film of a metal of Group IIIB and / or IVB after raising the pH to working levels so that the bath can function for not how many months, possibly for an indefinitely long period of time, without replacement. The discovered possibility of increasing the duration of the bath's functioning to such a large extent due to the carrying out of the indicated stages of the method was surprising and unexpected.

After contacting with the pretreatment solution, the substrate may be washed with water and dried.

In certain embodiments of the method of the present invention, after the substrate is contacted with the pretreatment composition, it is then contacted with a coating composition containing a film-forming resin. Any suitable method can be used to make the substrate contact with such a coating composition, including, for example, brushing, dipping, spray coating, spraying, and the like. However, in certain embodiments described in more detail below, such contacting involves the step of electrodepositing, wherein the electrodepositing composition is deposited on a metal substrate by electrodeposition.

As used herein, the term “film-forming resin” refers to resins that can form a self-supporting continuous film on at least the horizontal surface of the substrate after removing any diluents or carriers present in the composition, or after curing at ambient or elevated temperature. Conventional film-forming resins that can be used include, without limitation, those commonly used in automotive component coating (OEM) compositions, automotive repair compositions, industrial coating compositions, architectural coating compositions, coating compositions rolled products, aerospace coating compositions, among others.

In certain embodiments, the coating composition comprises a thermoset film-forming resin. The term “thermoset” as used herein refers to resins that undergo irreversible “cure” upon hardening or crosslinking, in which the polymer chains of the polymer components are joined together by covalent bonds. This property is usually associated with the crosslinking reaction of the components of the composition, often initiated by heat or radiation. Curing or crosslinking reactions can be carried out under ambient conditions. After curing or crosslinking, the thermosetting resin will not melt when heat is applied and will be insoluble in solvents. In other embodiments, the coating composition comprises a thermoplastic film-forming resin. As used herein, the term “thermoplastic” refers to resins comprising polymer components that are not covalently bonded and therefore, when heated, can become fluid and soluble in solvents.

As noted above, in certain embodiments, the substrate is in contact with a coating composition comprising a film-forming resin, in an electrodeposition coating step, in which an electrodepositable composition is deposited onto a metal substrate by electrodeposition. During the electrodeposition process, the treated metal substrate serving as the electrode and the electrically conductive counter electrode are placed in contact with the ionic electrodepositable composition. With the passage of electric current between the specified electrode and the counter electrode when they are in contact with the electrodepositable composition, a tight-fitting film of the electrodepositable composition will be substantially continuously deposited on the metal substrate.

Electroplating is usually carried out at a constant voltage in the range from 1 volt to several thousand volts, usually from 50 to 500 volts. The current density is usually in the range of 1.0 to 15 amperes per square foot (10 to 161.5 amperes per square meter) and tends to decrease rapidly during the electrodeposition process, which indicates the formation of a continuous self-insulating film.

The electrodepositable composition used in certain embodiments of the present invention in many cases contains a resinous phase dispersed in an aqueous medium, wherein said resinous phase contains: (a) an ionic electrodepositable resin containing active hydrogen groups, (b) a functional rejecting agent groups reactive with groups from (a) containing active hydrogen

In certain embodiments, electrodepositable compositions used in certain embodiments of the present invention comprise, as a base film-forming polymer, an active hydrogen containing ionic, often cationic, electrodepositable resin. A wide variety of electrodepositable film-forming resins are known and can be used in the present invention, provided that these polymers are "water dispersible", i.e. made with the ability to be dissolved, dispersed or emulsified in water. A water dispersible polymer is ionic in nature, i.e. this polymer will contain anionic functional groups to impart a negative charge or, which is often preferred, cationic functional groups to impart a positive charge.

Examples of film-forming resins suitable for use in anionic electrodepositable compositions are base solubilized polymers containing carboxylic acid, such as a reaction product or an adduct of quick-drying oil or a quick-drying ester of a complex fatty acid with dibasic carboxylic acid or anhydride; and a reaction product of an ester of a fatty acid, an unsaturated acid or anhydride, and any further unsaturated modifying substances that have further reacted with a polyhydric alcohol. In addition, at least partially neutralized interpolymers of hydroxyalkyl ethers of unsaturated carboxylic acids, unsaturated carboxylic acid and at least one other ethylenically unsaturated monomer are suitable. Another suitable electrodepositable film-forming resin comprises an alkyd-aminoplast binder, i.e. a binder containing an alkyd resin and an amine aldehyde resin. Another composition of anionic electrodepositable resin contains a mixture of esters of resinous polyhydric alcohol, as described in patent document US 3749657, from column 9, lines 1-75, to column 10, lines 1-13 (a cited part of this document is included in this description as links). Other polymers with acidic functional groups, such as phosphated polyepoxide or phosphated polyacrylates, which are known to those skilled in the art, may also be used.

As noted above, it is often desirable that the ionic electrodepositable resin (a) containing active hydrogen is cationic and capable of being deposited onto the cathode. Examples of such cationic film-forming resins include resins containing amine salt groups, such as the acid-solubilized reaction products of polyepoxides and primary or secondary amines described in US Pat. No. 3,663,389; US 3984299; US 3947338 and US 3947339. Often these resins containing amine salt groups are used in combination with a curing agent containing blocked isocyanate. The isocyanate can be completely blocked, as described in US Pat. No. 3,984,299, or the isocyanate can be partially blocked and can react with the main chain of the resin, as described in US Pat. No. 3,947,338. In addition, single-component compositions can be used as the film-forming resin. described in documents US 4134866 and DE-OS 2707405. In addition to the amino-epoxy reaction products, film-forming resins can be selected from cationic acrylic resins, such as described in patent documents US 3455806 and US 3928157.

In addition to resins containing an amine salt group, resins containing a quaternary ammonium salt group can also be used, for example, from those formed by the reaction of an organic polyepoxide with a tertiary amine salt, as described in patent documents US 3962165, US 3975346 and US 4001101. Examples of other cationic resins are resins containing a tertiary sulfonium salt group and resins containing a quaternary phosphonium salt group, such as those described in US Pat. No. 3,793,278 and US Pat. No. 3,984,922, respectively. In addition, film-forming resins that can be cured by transesterification, as described, for example, in European Patent Application No. 12463, can be used. In addition, cationic compositions prepared from Mannich bases, such as those described in US Pat. No. 4,134,932, can be used.

In certain embodiments, the resins present in the electrodepositable compositions are positively charged resins that contain groups of primary and / or secondary amines, such as those described in US Pat. No. 3,663,389; US 3947339 and US 4116900. In the document US 3947339 polyketimine derivative of a polyamine, such as diethylene triamine or triethylenetetraamine, reacts with polyepoxide. When the reaction product is neutralized with acid and dispersed in water, free primary amine groups are formed. In addition, equivalent products are formed by chemically reacting the polyepoxide with an excess of polyamines, such as diethylene triamine or triethylenetetraamine, and an excess of polyamines is evaporated under vacuum from the reaction mixture, as described in patent documents US 3663389 and US 4116900.

In certain embodiments, an ionic electrodepositable resin containing active hydrogen is present in the composition in an amount of from 1 to 60 wt. %, for example, from 5 to 25 wt. % based on the weight of the plating bath.

As noted, the resinous phase of the electrodepositable composition often further comprises a curing agent capable of reacting with active hydrogen groups of the ionic electrodepositable resin. For example, curing agents containing both a blocked organic polyisocyanite and an aminoplast are suitable for use in the present invention, although blocked isocyanites are in many cases preferred for cathodic electrodeposition.

Aminoplasts, which are often preferred curing agents for anionic electrodeposition, are the condensation products of amines or amides with aldehydes. Examples of suitable amines or amides are melamine, benzoguanamine, urea, and the like. A commonly used aldehyde is formaldehyde, although products can be obtained from other aldehydes such as acetaldehyde and furfural. The condensation products contain methylol groups or similar alkylol groups, depending on the particular aldehyde used. In many cases, these methylol groups are esterified by reaction with an alcohol, such as a monohydric alcohol containing from 1 to 4 carbon atoms, for example, methanol, ethanol, isopropanol and n-butanol. Aminos are marketed by American Cyanamid Co. under the trade name CYMEL and Monsanto Chemical Co. under the trade name RESIMENE.

Amino-plastic-containing curing agents are often used together with an anionic electrodepositable resin containing active hydrogen in amounts ranging from 5 wt. % up to 60 wt. %, in particular, from 20 wt. % up to 40 wt. %, based on the total mass of the solid phase of the resin in the electrodepositable composition.

As noted above, in cathodic electrodeposition compositions, blocked organic polyisocyanates are often used as a curing agent. Polyisocyanates can be completely blocked, as described in US Pat. No. 3,982,299, from column 1, lines 1-68, column 2 and column 3, lines 1-15, or partially blocked and react with the polymer backbone as described in US 3947338 , column 2, lines 65-68, column 3 and column 4, lines 1-30 (cited portions of these documents are incorporated herein by reference). The term “blocked” means that the isocyanate groups reacted with the compound so that the resulting blocked isocyanate group is resistant to active hydrogens at ambient temperature, but reacts with active hydrogens in a film-forming polymer at elevated temperatures, usually in the range of 90 ° C. to 200 ° FROM.

Suitable polyisocyanates include aromatic and aliphatic polyisocyanates, including cycloaliphatic polyisocyanates, and representative examples include diphenylmethane-4,4'-diisocyanate (MDI), 2,4- or 2,6-toluene diisocyanate (TDI), including mixtures thereof, p-phenylenediisocyanate, tetramethylene and hexamethylene diisocyanates, dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate, a mixture of phenylmethane-4,4'-diisocyanate and polymethylene polyphenyl isocyanate. Higher polyisocyanates, such as triisocyanates, may be used. One example may include triphenylmethane-4,4 ', 4ʺ-triisocyanate. In addition, isocyanate prepolymers with polyhydric alcohols such as neopentyl glycol and trimethylolpropane and with polymeric polyhydric alcohols such as polycaprolactone diols and triols (equivalent NCO / OH ratio of more than 1) can be used.

Polyisocyanate curing agents are usually used together with a cationic electrodepositable resin containing active hydrogen, in amounts ranging from 5 wt. % up to 60 wt. %, in particular, from 20 wt. % up to 50 wt. %, based on the total mass of the solid phase of the resin in the electrodepositable composition.

In certain embodiments, coating compositions comprising a film-forming resin further comprise yttrium. In certain embodiments, yttrium is present in such compositions in an amount of from 10 to 10,000 ppm, for example, not more than 5,000 ppm and, in some cases, not more than 1,000 ppm of the total amount of yttrium (measured as elemental yttrium).

As a source of yttrium, both soluble and insoluble yttrium compounds can be used. Examples of yttrium sources suitable for use in lead-free electrodepositable coatings are soluble organic and inorganic yttrium salts, for example, yttrium acetate, yttrium chloride, yttrium format, yttrium carbonate, yttrium sulfamate, yttrium lactate and yttrium nitrate. If yttrium is added as an aqueous solution to the electrodeposition bath, then yttrium nitrate is the preferred source of yttrium, i.e. readily available yttrium compound. Other yttrium compounds suitable for use in electrodepositable compositions are organic and inorganic yttrium compounds such as yttrium oxide, yttrium bromide, yttrium hydroxide, yttrium molybdate, yttrium sulfate, yttrium silicate and yttrium oxalate. Organo-yttrium complexes and metallic yttrium may also be used. If there is a need to introduce yttrium into the electrodeposition bath as a component in the pigment paste composition, yttrium oxide is often the preferred source of yttrium.

The electrodepositable compositions described herein are in the form of an aqueous dispersion. The term “dispersion” is believed to mean a two-phase transparent, translucent, or opaque resinous system in which the resin is in the dispersed phase and the water is in the continuous dispersion phase. The average particle size of the resinous phase is generally less than 1.0 and usually less than 0.5 microns, often less than 0.15 microns.

The concentration of the resinous phase in the aqueous medium is often at least 1 wt. %, for example from 2 to 60 wt. % relative to the total weight of the aqueous dispersion. When such compositions exist in the form of resin concentrates, they generally have a resin solids content of from 20 to 60 wt. % relative to the weight of the aqueous dispersion.

The electrodepositable compositions described herein are typically supplied in the form of two components: (1) a pure resin feedstock that typically contains an electrodepositable ionic resin containing active hydrogen, i.e. a base film-forming polymer, a curing agent and any additional water-dispersible unpainted components; and (2) a pigment paste, which usually contains one or more coloring agents (listed below), a water-dispersible pulverized resin, which may be the same or may differ from the main film-forming polymer, and optionally contains additives such as wetting agents or dispersing excipients.

In certain embodiments, the two-component electrodepositable composition is embodied as an electrodeposition bath, as is well known to those skilled in the art in which the components (1) and (2) of the bath are dispersed in an aqueous medium containing water and, as a rule, coalescing solvents. An advantage of the methods of the present invention, as noted above, is that they can prevent rust in such bathtubs, even in the absence of filtration equipment.

As indicated above, in addition to water, the aqueous medium may contain a coalescing solvent. Suitable coalescing solvents include, for example, hydrocarbons, alcohols, esters, ethers and ketones. Preferred coalescing solvents in many cases are alcohols, polyols and ketones. Representative coalescing solvents include isopropanol, butanol, 2-ethylhexanol, isophorone, 2-methoxypentanone, ethylene and propylene glycols and monoethyl, monobutyl and monohexyl ethers of ethylene glycol. The amount of coalescing solvent is, in general, from 0.01 to 25%, for example, from 0.05 to 5 wt. % in relation to the total mass of the aquatic environment.

In addition, a coloring agent and, if desired, various additives such as surfactants, wetting agents, or a catalyst may be included in the coating composition containing the film-forming resin. As used herein, the term “colorant” means any substance that gives the composition a color and / or other opacity and / or other visual effect. The coloring agent may be added to the coating in any suitable form, such as discrete particles, dispersions, solutions and / or flakes. A single coloring material or a mixture of two or more coloring materials may be used.

Examples of coloring agents include pigments, dyes, and tinting agents, such as those used in the dye industry and / or listed on the Dry Color Manifacturers Association (DCMA), as well as compositions for creating special effects. The colorant may, for example, be a finely divided powder of a solid material that is insoluble but wettable under conditions of use. The colorant may be organic or inorganic and may be agglomerated or non-agglomerated. Coloring agents can be introduced using dispersant carriers, such as acrylic dispersant carrier, the use of which is known to specialists in this field.

Examples of pigments and / or pigment compositions include, but are not limited to, carbazole-dioxazine crude pigment, azo-, monoazo-, disazo-, naphthol AS, salt-type pigments (varnishes), benzimidazolone, condensed, metal complexes, isoindolinone, isoindoline and polycyclic phthalocyanine, quinacridone, perylene, perinone, diketopyrrolopyrrole, thioindigooid, anthraquinone, indatronic, anthrapyrimidine, flavantrone, pyrantron, anthantrone, dioxazine, triarylcarbonium quintile and quinophthalone pigments, diketopyrrolopyrrole red (“DPPBO red”), titanium dioxide, carbon black and mixtures thereof. The terms “pigment” and “colored filler” may be used interchangeably.

Examples of dyes include, but are not limited to, those which are water based or solvent based, for example phthalo green or blue, iron oxide, bismuth vanadate, anthraquinone, perylene, aluminum, and quinacridone.

Examples of tinting agents include, but are not limited to, pigments dispersed in water-based carriers or water-miscible carriers, such as AQUA-CHEM 896, marketed by Degussa, Inc., as well as CHARISMA COLORANTS and MAXITONER INDUSTRIAL COLORANTS, marketed by Accurate Dispersions division of Eastman Chemical, Inc ..

As noted above, the colorant may be in the form of a dispersion, including, but not limited to, a dispersion of nanoparticles. Nanoparticle dispersions may contain one or more highly dispersed coloring agents in the form of nanoparticles and / or coloring agent particles that impart the desired visible color and / or opacity and / or visual effect. Nanoparticle dispersions may contain coloring agents, such as pigments or dyes, with a particle size of less than 150 nm, for example, less than 70 nm or less than 30 nm. Nanoparticles can be obtained by grinding finished organic or inorganic pigments using a grinding medium having a particle size of less than 0.5 mm. Examples of dispersions of nanoparticles and methods for their manufacture are given in patent document US 6875800, which is incorporated into this description by reference. Dispersions of nanoparticles can also be obtained by crystallization, precipitation, gas phase condensation, and chemical attrition (i.e., partial dissolution). To minimize re-agglomeration of nanoparticles within the coating, a dispersion of resin coated nanoparticles can be used. The term “resin coated nanoparticle dispersion” as used herein refers to a continuous phase in which discrete “composite microparticles” are dispersed that contain a nanoparticle and a resinous coating on the nanoparticle. Examples of dispersions coated with resin nanoparticles and methods for their preparation are given in patent documents: application for US patent 2005-0287348 A1 (filing date - 06/24/2004), provisional application US 60/482167 (filing date - 07/24/2003) and application for US patent No. 11/337062 (filing date - 01/20/2006), which are also incorporated into this description by reference.

Examples of compositions with special effects that can be used include pigments and / or compositions that produce one or more appearance effects, such as reflectivity, pearlescent effect, metallic luster, phosphorescence, fluorescence, photochromia, photosensitivity, thermochromia, goniochrome and / or discoloration. Compositions with additional special effects may provide other notable properties, such as opacity or texture. In certain embodiments, compositions with special effects can produce a color change, so that the color of the coating changes when viewing the coating from different angles. Examples of compositions with color effects are given in US Pat. No. 6,894,086, incorporated herein by reference. Compositions with additional color effects may include transparent mica and / or synthetic coated mica, coated silica, coated alumina, transparent liquid crystal pigment, liquid crystal coating and / or any composition in which chromatographic interference results from differences in refractive indices within material, and not a consequence of the difference in refractive indices between the surface of the material and air.

In certain embodiments, a photosensitive and / or photochromic composition can be used that reversibly changes color when irradiated with one or more light sources. Photosensitive and / or photochromic compositions can be activated by radiation of a specific wavelength. When the composition is in an excited state, the molecular structure changes, and the changed structure has a new color that differs from the original color of the composition. When the radiation source is removed, the photosensitive and / or photochromic composition may return to an undisturbed state in which the original color of the composition returns. In certain embodiments, the photosensitive and / or photochromic composition may be colorless in an unexcited state and has a specific color in an excited state. A complete color change can occur within milliseconds or several minutes, for example, in the range from 20 seconds to 60 seconds. Examples of photosensitive and / or photochromic compositions include photochromic dyes.

In certain embodiments, the photosensitive composition and / or photochromic composition may be attached and / or at least partially linked, for example, by covalent bonding, to the polymer and / or polymer material of the polymerizable component. Unlike some coatings in which the photosensitive composition can migrate from the coating and crystallize into the substrate, the photosensitive composition and / or photochromic composition, attached and / or at least partially associated with the polymer and / or polymerizable component in accordance with certain embodiments of the present invention are characterized by minimal migration from the coating. Examples of photosensitive compositions and / or photochromic compositions and methods for their preparation are disclosed in US patent application No. 10/892919 (filing date July 16, 2004), incorporated herein by reference.

In general, the colorant may be present in the coating composition in any amount sufficient to create the desired visual and / or color effect. The coloring matter may be from 3 to 40 wt. % or from 5 to 35 wt. % based on the total weight of the composition.

After deposition, the coating is in most cases heated to cure the deposited composition. The heating or curing operation is often carried out at a temperature in the range from 120 to 250 ° C., for example, from 120 to 190 ° C., for a period of time in the range from 10 to 60 minutes. In certain embodiments, the thickness of the resulting film is from 10 to 50 microns.

From the above description, it is understood that certain embodiments of the present invention also relate to methods for preventing rust contamination of coating equipment, even in the absence of filtration equipment in a process in which the coating of a ferrous metal substrate is carried out. In certain embodiments, such methods include the use of a pretreatment composition having a pH of from 4 to 5.5 and containing, or, in some cases, essentially consisting of: a) a Group IIIB and / or IVB metal compound; b) phosphate ions; and c) water. In such embodiments of the methods of the invention, the phosphate ions are maintained in a bath with a pretreatment composition in an amount of: (i) sufficient to substantially prevent the formation of insoluble rust in the bath; and (ii) and insufficient to prevent the deposition of a Group IIIB and / or IVB metal film having a coating density of at least 10 mg / m ² on the surface of the ferrous metal substrate. In certain other embodiments, such methods include a method for removing iron from a pretreatment bath (removing the bath from the process) containing Group IIIB and / or Group IVB metal, which, in certain embodiments, is substantially free of phosphate ions during operation, and in certain other embodiments, contains phosphate ions. The specified method with the removal of the bath from the process includes the steps of: (a) reducing the pH of the pre-treatment bath by at least 0.2; (b) adding phosphate ions to the pretreatment bath from step (a); (c) adding an oxidizing agent to the pretreatment bath from step (b); and (d) increasing the pH of the pretreatment bath from step (c) by at least 0.2. In such methods for removing iron from a pretreatment bath, removing the bath from the process, insoluble rust can be substantially removed from the pretreatment bath. In certain embodiments, a method for removing a bath from a process includes the step of filtering the pre-treatment bath using filtration equipment.

From the above description, it is also understood that the present invention further relates to methods for coating a ferrous metal substrate. In certain embodiments, such methods include: (a) contacting a ferrous metal substrate with an aqueous pretreatment composition having a pH of from 4 to 5.5 and containing, or, in some cases, essentially consisting of: (i) a metal compound Groups IIIB and / or IVB; (ii) phosphate ions; and (iii) water, the phosphate ions being maintained in the bath with the pretreatment composition in an amount sufficient to substantially prevent the formation of insoluble rust in the bath; and then (b) contacting the substrate with a coating composition comprising a film-forming resin to form a coated metal substrate that exhibits anti-corrosion properties. In other specific cases, such methods include: (a) removing iron from the pre-treatment bath, carried out with the removal of the bath from the process; and then (b) contacting the ferrous metal substrate with an aqueous pretreatment composition having a pH of from 4 to 5.5 and containing, or, in some cases essentially consisting of: (i) a Group IIIB metal compound and / or IVB; and (ii) water, wherein said pretreatment composition in certain embodiments is substantially free of phosphate ions; and then (c) contacting the substrate with a coating composition comprising a film-forming resin to form a coated metal substrate that exhibits anti-corrosion properties. In such methods, the step of removing iron from the pretreatment bath when the bath is removed from the process includes, or in some cases essentially consists of: reducing the pH of the pretreatment bath by at least 0.2; (b) adding phosphate ions to the pretreatment bath from step (a); (c) adding an oxidizing agent to the pretreatment bath from step (b); and (d) increasing the pH of the pretreatment bath from step (c) by at least 0.2. As used herein, the term “anti-corrosion properties” refers to experimental research and measurements regarding the quantification of corrosion prevention on a metal substrate by testing as described in ASTM B117 (salt spray tests). In these tests, the coated substrate is scribed with a cutting tool (incisions are formed) so that the bare metal substrate is tested in accordance with ASTM D 1654-92. The scribed substrate is placed in a test chamber, where an aqueous salt solution is continuously sprayed onto the substrate. A constant temperature is maintained in the chamber. The coated substrate is subjected to salt spray conditions for a certain period of time, for example, 250, 500 or 1000 hours. After the indicated salt spray exposure, the coated substrate is removed from the test chamber and the degree of corrosion along the notch is evaluated. Corrosion is evaluated by a “scribe defect,” which is defined as the total distance, measured in millimeters, over which corrosion extends in the direction across the notch. When it is said that the substrate “exhibits anti-corrosion properties”, this means that the notch defect on the ferrous metal substrate is not more than 3 mm after tests carried out in accordance with ASTM Bl 17 for 500 hours under salt spray conditions when the substrate is coated with polyester resin powder supplied by PPG Industries, Inc. under the name PCT79111 in accordance with the manufacturer's instructions.

The invention is illustrated by the following examples, which should not be construed as limiting the invention to the details of these examples. In the examples, as well as throughout the description, all parts and percentages are indicated by weight unless otherwise specified.

Examples

Example 1

In one experiment, five clean steel plates were placed in an aqueous solution having a pH value of approximately 1.8-2.4 containing fluorozirconic acid and phosphoric acid (90 ppm Zr and 10 ppm PO ₄ ^-3 ). After increasing the ferrous iron content to approximately 30 ppm, the plates were removed from the clear solution and the solution was divided into parts of one gallon volume (3.78 liters).

The first gallon was further divided into 700 ml parts to which phosphoric acid was added (75 wt.%), Resulting in a series of baths containing 10, 25, 50, 75 and 100 ppm phosphate ions. The same sequences of phosphate levels were repeated for zirconium with a content of 125, 150 and 200 ppm.

The pH value in all bath samples was set to 5.0. These baths, containing 30 ppm ferrous iron and varying amounts of zirconium and phosphate ions, were left to stand at rest for two days. After two days, the appearance of the individual baths was recorded. The results summarized in table 1 below show that in this example a zirconium bath containing 30 ppm total iron will change the appearance (color) from brown to white in the presence of phosphate ions in the range from 25 to 50 ppm . The brown color of the bath indicates the formation of iron oxide or iron oxyhydroxide.

A matrix of the results showed that all baths containing 10 ppm PO ₄ ^-3 had equally rust-colored water and mainly a brown precipitate, moreover, regardless of the Zr content. In subsequent light-colored baths, the concentration of PO ₄ ^-3 was 25 ppm and, in addition, the precipitate had a lighter color. All baths with a concentration of PO ₄ ^{-3 of} 50 ppm had almost no color and contained a precipitate with a structure similar to crystalline, which was barely noticeable white with a grayish tint. Bath concentration PO ₄ 75 ^-3 and 100 parts / million were all colorless and contained a white crystalline precipitate. The white precipitate was iron phosphate, often with small amounts of zirconium compounds.

This example shows that a mass ratio of phosphate and ferrous iron of at least 1: 1, for example at least 1.2: 1, in particular from 1 to 1.8: 1, is sufficient to substantially prevent the formation of insoluble rust in a pretreatment bath containing a metal of Group ШВ and / or IVB, when used for processing a substrate of ferrous metal.

Example 2

The steel plates were cleaned using ordinary alkaline solution, washed twice with tap water, treated in baths containing zirconium with a concentration in the range of 10 to 150 ppm and phosphate with a concentration of 10 to 100 ppm, and then washed sequentially with tap water. The treated steel plates were painted using an electrodepositable coating of cationic epoxy resin P590 or a coating of powder material containing triglycidyl isocyanurate and polyester PCT79111. Both of these coating compositions are marketed by PPG Industries Inc. Corrosion properties were determined by turning the panels painted and processed using zirconium to neutral salt fog in accordance with ASTM B117 for the time periods given in Table 2. As a result, an acceptable anticorrosion characteristic of the electrodeposited cationic epoxy coating was obtained when exposed to neutral salt fog in this experiment for 1000 hours, namely 4.0-5.0 mm, defined as 1/2 of the width of the corrosion propagation zone in the direction transverse to the notch. An acceptable coating characteristic of a powder material containing triglycidyl isocyanurate (TGIC) and polyester when exposed to neutral salt mist in this experiment for 500 hours was 2.0-3.0 mm (also defined as 1/2 of the width of the corrosion propagation zone in the direction across the notch). The data below show that acceptable anticorrosion characteristics can be obtained when phosphate ions are added to the treatment bath containing zirconium. As shown in example 1, at a low concentration of phosphate ions, the treatment bath turns brown, indicating the presence of iron oxide or iron oxyhydroxide.

Example 3

A pretreatment solution was prepared in which increasing amounts of hexafluorozirconic acid were added. Before coating the cold-rolled steel plates, the pH of the bath was adjusted to 4.7. The plates obtained from ACT Labs (Hillsdale, MI) were first blasted in an alkaline solution (PPG Industries Chemkleen 611L solution, concentration 2% and temperature 140-150 ° F) and then twice before being sent to the pretreatment zone flushing carried out. In a zirconium bath, a coating layer was applied to the steel plates for 60 seconds at a pressure of 9 psi. Then the plates were washed with tap water and finally with deionized water before carrying out the drying stage by infrared radiation.

Samples in the form of plates were obtained at zirconium concentrations in the bath of 0, 10, 15, 20, 50, and 80 ppm. The sections of each plate were analyzed using XPS (X-ray photoelectron spectroscopy) to determine the thickness of the zirconium layer in the coatings. The thickness, in nanometers, of the zirconium layer was determined at which a reverse transition down to the level of 10 atomic percent occurred on the graph of the graphical dependence. The resulting table with the thicknesses was presented as a graphical dependence of the thicknesses on the concentration of zirconium in the bath shown in FIG. one.

Three plates of the same batch were coated with an anionic acrylic electrodepositable coating marketed by PPG Industries, Inc. under the trade name Powercron 395, at each concentration level before corrosion testing, in accordance with ASTM B117 and D1654-92. The test results are shown in FIG. 2. These results confirm that a good degree of corrosion protection is achieved, which coincides with the achievement of a minimum thickness, i.e. for a bath containing 20 ppm zirconium.

Example 4

In practice, baths heavily contaminated with rust are opaque, brownish-red with a previous appearance of translucent orange-colored solutions, which indicates the initial conversion of insoluble complexes of ferric iron. In one experiment, steel plates were sprayed with ten gallons of a low pH (about 2.7) bath composition containing 100 ppm zirconium for several hours until a total iron content of 50 ppm was reached. The ferrous iron content was approximately 40 ppm. Although the bath contained 10 ppm soluble ferric iron ions, it was transparent and colorless. A large sample was divided into parts to which phosphate was added with an increasing concentration to determine a concentration that could prevent the bath from starting to discolor after increasing the pH to 5. For a phosphate-free control sample, the concentration of ferric iron increased to 24 ppm just before the change colors. The results of this experiment are shown in table 3.

With an increase in the PO ₄ content, the color change takes a longer time and was not as intense as in the case of aging at zero phosphate level. In addition, after one night of storage, the pH decreased to the levels shown in the table, indicating the completion of the oxidation and precipitation stages. The pH decreased to a lesser extent with an increase in the amount of phosphate used. After reaching a certain level of phosphate content, the pH remained constant, showing an excess in relation to the amount required for ferric iron. After two days, the quality of the precipitate was pronounced, such as shown in table 3. If there is not enough phosphate in the system, the precipitate forms as a flocculent brown oxide, resulting in a significant decrease in pH. In the case of a sufficient amount of phosphate, the precipitate was white and had a density that facilitated the removal of iron before it could be moved downstream.

In addition, control measurements of zirconium were performed to determine the effect of any excess phosphate. FIG. 3 shows that although some zirconium was consumed in the system, the losses were not significant. When phosphate converts the soluble complex of ferric iron into insoluble iron phosphate, the point of the corresponding equivalent addition of phosphate to ferric iron can be determined in the gentle plot of the graph for pH. This occurred at approximately a phosphate concentration of 35-40 ppm for a ferric concentration of 24 ppm.

So, in a working bath, only 25-35 ppm of phosphate per 24 ppm of ferric iron may be sufficient to inhibit the development of a reddish-brown bath only with a slight depletion of zirconium. The life of the bath for this example can be significantly longer than usually observed in comparative industrial baths also based on a metal of Group IIIB and / or IVB, but not containing phosphate ions. The ratio of phosphate and ferric iron is in the range from 1: 1 to 1.8: 1 by weight. At higher ratios, too much zirconium may be consumed.

Example 5

The iron-containing concentrate was obtained by hanging clean steel plates for two days in a solution of hexafluorozirconic acid in deionized water that does not contain phosphate. The final concentration of ferrous iron was approximately 900 ppm, and the concentration of ferrous iron was 33 ppm. The indicated concentration was then diluted with tap water to obtain approximately 20 ppm of ferrous iron and 3 ppm of ferric iron. Various amounts of phosphoric acid were added, followed by a sufficient amount of hydrogen peroxide to convert all ferrous iron to ferric. Then, for each bath, the pH value was set at 4.7. After standing at rest for one day, a bath analysis was performed to determine the concentration of phosphate and zirconium. The results are graphically presented in FIG. 4. As can be seen, approximately 30 ppm of phosphate may be sufficient to remove 20 ppm of ferrous iron while maintaining most of the 65 ppm of zirconium in solution.

Example 6

Example 6 was carried out in order to demonstrate the feasibility of removing ferric iron (Fe ⁺³ ) from a pretreatment bath. An initial (base) solution was prepared from three liters of tap water and 1.2 g of a solution of fluorozirconic acid (45%). The initial solution had a predetermined Zr level of 85 ppm. To do this, 0.28 ml of ferric sulfate (50% solution) was added and an initial solution containing 20 ppm ferric ions was obtained. The stock solution had a pH of 2.9.

The stock solution was divided into Baths AD, each of which contained 900 ml of stock solution. As described in more detail below, in this example, an NASH concentration meter was used to measure the concentration of ferrous iron (Fe ^{+ 2} ) and the total iron concentration at various points in time. If it is necessary to obtain data on the concentration of ferric iron (Fe ⁺³ ) in a particular bath, the concentration of ferric iron was calculated as the difference between the total concentration of iron and the concentration of ferrous iron. In the considered Example 6, none of the Baths AD during the measurement at any time did not contain any amount of ferrous iron (Fe ⁺² ).

Bath A served as a control, with which ferric iron concentrations (Fe ⁺³ ) and total iron concentrations (ppm) in Baths B, C, and D (processed as described below) were compared.

To control bath A, 0.1 g of an alkaline solution of Chemfil Buffer, marketed by PPG Industries, Inc., was added as a source of alkalinity to obtain a pH of 3.4. As shown in FIG. 5, the concentration (ppm) of ferric iron (Fe ⁺³ ) in Bath A was approximately 18.6 ppm during the experiment period of 72 hours. In Bath A, a barely noticeable precipitate was formed that was rusty in color. These data confirm that ferric iron (Fe ⁺³ ) is extremely stable at pHs of approximately 3.4.

In 900 mg of the stock solution in Bath B, 0.5 g of Chemfil Buffer solution was added to increase the pH of this bath to 4.8. The indicated pH was within the typical operating range for a pretreatment bath containing the composition described herein. As shown in FIG. 5, the concentration of ferric iron (Fe ⁺³ ) in Bath B decreased from an initial concentration of approximately 21 ppm to a concentration of approximately 2 ppm within 2 hours after increasing the pH in the pretreatment bath to 4.8. These data show that most of the soluble ferric iron was converted to rust or iron oxide, which is insoluble in the pretreatment composition. A rust colored precipitate was visible in Bath B for 2 hours after increasing the pH.

0.09 g of monosodium phosphate solution was added to the 900 ml bath solution of C as a Zircobond Additive P additive supplied by PPG Industries, Inc., Euclid, OH (45 wt.%). Bath C contained phosphate with a concentration of 14 ppm and had a pH value of 2.9, which was maintained for 72 hours during the experiment. As shown in FIG. 5, the concentration of ferric iron (Fe ⁺³ ) in Bath C decreased from about 18 ppm to about 12 ppm in the first 2 hours of the experiment and then continued to gradually decrease over the course of 72 hours of the experiment to a final concentration of 7 ppm . In the first hours of the experiment in Bath C, a white precipitate was visible, and at the end of the experiment a slightly reddish-brown precipitate formed, indicating that, in the case of a pH below the normal operating level, the removal of ferric iron was gradual and incomplete.

0.09 g of monosodium phosphate solution (45% by weight) was added to 900 ml of the original Bath D solution as a Zircobond Additive P additive supplied by PPG Industries, Inc., Euclid, OH. Bath D contained phosphate at a concentration of 34 ppm. As shown in FIG. 5, the concentration of ferric iron (Fe ⁺³ ) in Bath D was 20 ppm. To increase the pH to 4.75, a 0.5 g Chemfil Buffer solution was added to Bath D, and the Bath immediately became cloudy. After creating conditions for the deposition of crystals, the sample from the bath was filtered through a syringe filter with a pore size of 5 μm, and the obtained filtrate was subjected to a control measurement to determine the total concentration of iron. The concentration of ferric iron in Bath D was 2 ppm, and after 2 hours (at the end of the experiment), 1.9 ppm. The bath was transparent with a little white sediment.

The data of example 6 show that the addition of phosphate to the pretreatment bath removes a significant portion of ferric iron at low pH and essentially all ferric iron in a shorter period of time after increasing the pH again to the operating range. These data confirm that ferric iron can be removed from the pretreatment bath if the bath is removed from the processing line.

Example 7

The data presented in FIG. 5 and described in Example 6 show that ferric iron was removed from the pretreatment bath by adding phosphate to the pretreatment bath at low pH. However, in practice, the pretreatment baths that were used to treat the substrate contain ferrous iron, which is to be converted to ferric iron and then removed from the bath. Example 7 and the obtained data, presented in table 4 and described here, show that the addition of an oxidizing agent to the pre-treatment bath improves the removal of iron, which was originally in the form of ferrous iron.

An initial (base) solution was prepared from three liters of tap water and 1.2 g of a solution of fluorozirconic acid (45%). The initial solution had a predetermined Zr concentration level of 85 ppm. 0.32 ml of ferrous sulfate heptahydrate was added to obtain a stock solution containing 20 ppm of ferric ions and 23 ppm of the total amount of iron. The initial solution had a pH value of 3.1.

The stock solution was divided into EG Baths, each of which contained 900 ml of stock solution. Bath E served as a control, with which the concentrations of ferrous iron (Fe ^{+ 2} ) and total iron concentrations (ppm) in Baths F and G (processed as described below) were compared. Using a concentration meter from NASH, the concentration of ferrous iron in each bath was continuously monitored at periodic intervals for 44 hours of the experiments.

Bath E served as a control and had an initial pH of 3.1. A few drops of Chemfil Buffer solution were added to the bath to increase the pH to 3.5, which, as can be seen from Table 4, remained stable during the experiment. In addition, as shown in Table 4, the total iron concentration (ppm) in bath E drops from the initial value of 22.8 ppm to 22.1 ppm at the end of the experiment, which lasted 44 hours. The concentration of ferrous iron (Fe ^{+ 2} ) was initially 19.8 ppm and dropped to 15.7 ppm at the end of the experiment, which lasted 44 hours. During the experiment, the bath remained transparent, without becoming red. These data show that all the iron in the bath remained in solution in the form of ferrous iron, and there was only a slight conversion of ferrous iron to ferric iron. The data obtained show that at low pH (i.e., the pH is less than the working pH), only a minimal conversion of ferrous iron to ferric iron takes place.

0.093 g of monosodium phosphate (45% solution) was added to Bath F to prepare a solution containing 43 ppm phosphate and the ratio of PO _{4 to} total iron was approximately 1.8: 1. Then, 0.5 g of a Chemfil Buffer solution was added to this bath to obtain a pH of 4.7. The pH in Bath F was slightly reduced during the experiment, and after 44 hours was 4.38. As Table 4 shows, the total iron concentration in Bath F was reduced from the initial value of 22.8 ppm to 18.5 ppm after 30 minutes and was 14.7 ppm at the end of the experiment lasting 44 hours. The concentration of ferrous iron at first was equal to 19.8 ppm, decreased to 17.2 ppm after 30 minutes, and corresponded to 12.4 ppm at the end of the experiment lasting 44 hours. During the experiment, a certain amount of white precipitate formed in the bath, which indicated the formation of ferrous phosphate. These data show that the addition of phosphate, followed by an increase in pH to a value in the range from 4.38 to 4.7, allows only a certain amount of soluble iron to be removed as ferric phosphate, since, irrespective of any particular theory, the oxidation of ferrous iron in by increasing the pH only, it was relatively slow and limited by the pH value corresponding to the equilibrium state.

As can be seen from table 4, Bath G first has a pH = 3.0, a total iron concentration of 22.8 ppm and a concentration of ferrous iron of 19.8 ppm. Immediately before the addition of 0.32 g of hydrogen peroxide (solution concentration of 3 wt.%), 0.1 g of monosodium phosphate (solution of 45%) was added. 15 minutes after the addition of hydrogen peroxide, the total iron concentration was reduced to 10.2 ppm, the concentration of ferrous iron was reduced to 0.4 ppm and the pH was 2.6. A certain amount of white precipitate formed in the bath, indicating a partial formation of a phosphate complex of iron. Then, the pH of the bath was increased to 4.7 by adding 0.6 g of a Chemfil Buffer solution, and within 15 minutes after that (i.e., 46 minutes after the start of the experiment) almost all of the iron was removed, with a total iron concentration of 5 ppm and the concentration of ferrous iron was 0.1 ppm At the end of this experiment (i.e., 44 hours after the start), the pH of the bath was 4.6, the total iron concentration was 0.24 ppm, and the concentration of ferrous iron was 0.02 ppm. These data show that the addition of phosphate and hydrogen peroxide to the bath significantly improved the removal of iron from the bath at a working pH.

Example 8

In this Example, a functioning pretreatment bath was obtained by adding 3.60 g of hexafluorozirconic acid to three liters of water to obtain a solution containing 240 ppm zirconium. A sufficient amount of Chemfil Buffer was added to increase the pH of the solution to 4.5. To obtain 20 ppm of ferrous iron, 0.31 g of ferrous sulfate heptahydrate was added. To prevent the formation of rust particles, approximately 14 drops of hexafluorozirconic acid were directly added to reduce the pH to 3.3. The bath was transparent. Using a NASH meter, a total iron concentration of 23.2 ppm was measured, with a ferrous concentration of 19.5 ppm.

Phosphate was added to the bath so that the molar ratio of phosphate to total iron concentration to be precipitated was approximately 1: 1 (or the mass ratio was 1.8: 1). 41.5 ppm of phosphate from 0.175 g of phosphoric acid solution (75% by weight) was added to this bath so that the excess was approximately 8-9 ppm. After mixing for 1 min, 1.27 g of hydrogen peroxide solution (3 wt.%) Was added, based on a 1: 1 molar ratio to ferrous iron (with a slight excess). Ferrous iron was converted to ferric iron in less than 1 minute.

To precipitate all ferric iron as ferric phosphate (III), the pH of the bath was increased to 4.75 by adding dropwise a solution of Chemfil Buffer. If the pH increase occurred too quickly, some rust-free iron (III) oxide insoluble in the form of rust may form instead of ferrous iron (II) phosphate. With an increase in pH, a white haze occurs in the bath, which eventually becomes flakes, completely precipitated within 10 minutes to obtain a clear bath. The resulting final solution contained 0.2 ppm total iron in the absence of a noticeable concentration of ferrous iron. The concentration of residual phosphate was 8.5 ppm, which corresponds to the mass balance calculations.

Those skilled in the art will appreciate that changes may be made to the embodiments described above without departing from the scope of the inventive concept. It should be appreciated that the invention is not limited to the specific embodiments described above, but encompasses modifications that are within the scope and spirit of the invention as defined by the appended claims.

Claims (29)

1. A method of removing iron from a pretreatment bath containing a pretreatment composition containing a metal of Group IIIB and / or Group IVB, in which: (a) reducing the pH of said pretreatment bath by at least 0.2; (b) adding phosphate ions to said pretreatment bath from step (a); (c) increase the pH of said pretreatment bath from step (b) by at least 0.2; and (d) removing the insoluble precipitate that forms in the bath from step c); moreover, the removal of iron is carried out in the absence of the product to be coated with the specified composition for pre-treatment, and the specified pre-treatment bath is essentially free of phosphate ions during its operation. 2. The method of claim 1, wherein the pH of said pretreatment bath is reduced by at least 1.0. 3. The method of claim 1, wherein said pH reduction comprises adding acid to said pretreatment bath. 4. The method of claim 3, wherein said acid is selected from an acid containing fluorine and a Group IVB metal, phosphoric acid, sulfuric acid, sulfamic acid, nitric acid, and mixtures thereof. 5. The method of claim 3, wherein said acid is hexafluorozirconic acid. 6. The method of claim 1, wherein the source of said phosphate ions comprises alkali metal orthophosphates, ammonium orthophosphates, and mixtures thereof. 7. The method of claim 1, wherein the source of said phosphate ions comprises monosodium phosphate. 8. The method of claim 1, wherein said pretreatment bath in step (c) is substantially free of iron. 9. The method of claim 1, wherein an oxidizing agent is further added to said pretreatment bath in step (b). 10. The method of claim 9, wherein said oxidizing agent comprises peroxide compounds. 11. The method according to p. 1, in which the removal of insoluble precipitate is carried out by filtration. 12. The method of claim 1, wherein said Group IIIB and / or Group IVB metal is zirconium. 13. A method of removing iron from a pretreatment bath containing a pretreatment composition containing a metal of Group IIIB and / or Group IVB, in which: (a) add acid to said pretreatment bath to reduce the pH of said pretreatment composition to less than 4.0; (b) adding phosphate ions to said pretreatment bath from step (a); (c) increase the pH of said pretreatment bath from step (b) to 4-5.5; and (d) removing the insoluble precipitate that forms in the bath from step c); moreover, the removal of iron is carried out in the absence of the product to be coated with the specified composition for pre-treatment, and the specified pre-treatment bath is essentially free of phosphate ions during its operation. 14. The method of claim 13, wherein said acid is hexafluorozirconic acid. 15. The method of claim 13, wherein the source of said phosphate ions is monosodium phosphate. 16. The method of claim 13, wherein the oxidizing agent is further added to said pretreatment bath in step (b). 17. The method of claim 16, wherein said oxidizing agent comprises peroxide compounds. 18. The method according to p. 13, in which the removal of insoluble precipitate is carried out by filtration. 19. The method according to p. 13, in which the specified composition for pre-treatment in the specified pre-treatment bath after stage (C) has a mass ratio of phosphate to ferric ions in the range from 1: 1 to 1.7: 1 mass parts.

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