阅读说明：本技术 用于保持预处理浴的系统和方法 (System and method for maintaining pretreatment baths ) 是由 K·T·西尔维斯特 N·J·西尔弗奈尔 于 2020-04-14 设计创作，主要内容包括：公开了一种用于保持预处理浴的系统,所述预处理浴含有包括IVB族金属的预处理。所述系统包括水性还原剂,所述水性还原剂包括金属阳离子和潜在的硫酸盐来源,所述金属阳离子和所述潜在的硫酸盐来源在与所述预处理浴中的污染物反应时形成金属硫酸盐。所述污染物包括亚硝酸盐来源。所述金属硫酸盐在25℃的温度下的pKsp为4.5到11。还公开了一种用于保持预处理浴的方法,所述预处理浴含有包括IVB族金属的预处理组合物。所述方法包括向所述预处理浴供应足以将所述预处理浴的污染比降低到小于1:1的量的所述还原剂。还公开了使用根据所述系统和方法保持的预处理浴的基材。(A system for maintaining a pretreatment bath containing a pretreatment comprising a group IVB metal is disclosed. The system includes an aqueous reducing agent including metal cations and a potential sulfate source that form metal sulfates upon reaction with contaminants in the pretreatment bath. The contaminant includes a source of nitrite. The metal sulfate has a pKsp of 4.5 to 11 at a temperature of 25 ℃. Also disclosed is a method for maintaining a pretreatment bath containing a pretreatment composition comprising a group IVB metal. The method includes supplying the reducing agent to the pretreatment bath in an amount sufficient to reduce a contamination ratio of the pretreatment bath to less than 1:1. Also disclosed are substrates using a pretreatment bath maintained in accordance with the system and method.)

1. A system for maintaining a pretreatment bath, the system comprising:

an aqueous reducing agent comprising metal cations and a potential source of sulfate that, upon reaction with contaminants in the pretreatment bath, form metal sulfates;

wherein the contaminant comprises a source of nitrite; and is

Wherein the metal sulfate has a pKsp from 4.5 to 11 at a temperature of 25 ℃.

2. The system of claim 1, wherein the metal cation comprises a cation of calcium, strontium, barium, radium, lead (II), and/or silver (I).

3. The system of claim 1, the reducing agent further comprising an anion capable of forming a salt with the metal cation.

4. The system of claim 3, wherein the anion comprises a hydroxide, a carbonate, or a combination thereof.

5. The system of claim 1, wherein the pH of the reducing agent is less than 7.

6. The system of claim 1, further comprising a pretreatment composition comprising a group IVB metal.

7. The system of claim 6, wherein the group IVB metal comprises zirconium.

8. The system of claim 6, wherein the pretreatment composition further comprises free fluoride ions, an electropositive metal, and/or a binder.

9. The system of claim 1, further comprising a pH adjuster.

10. A substrate treated with a pretreatment bath maintained by the system of claim 1.

11. The substrate of claim 10, wherein the film formed on the surface of the substrate has at least a 33% increase in zirconium coating weight as compared to a film formed on a surface of a substrate treated with a pretreatment bath not maintained by the system of claim 1.

12. A method for maintaining a pretreatment bath containing a pretreatment composition comprising a group IVB metal, the method comprising:

supplying an aqueous reducing agent to the pretreatment bath in an amount sufficient to reduce a contamination ratio of the pretreatment bath to less than 1: 1;

wherein the reducing agent comprises metal cations and a potential source of sulfate that form metal sulfate upon reaction with contaminants in the pretreatment bath;

wherein the contaminant comprises a source of nitrite; and is

Wherein the metal sulfate has a pKsp from 4.5 to 11 at a temperature of 25 ℃.

13. The method of claim 12, wherein the metal cation comprises a cation of calcium, strontium, barium, radium, lead (II), and/or silver (I).

14. The method of claim 12, wherein the reducing agent further comprises an anion capable of forming a salt with the metal cation.

15. The method of claim 14, wherein the anion comprises a hydroxide, a carbonate, or a combination thereof.

16. The method of claim 12, wherein the pH of the reducing agent is less than 7.

17. The method of claim 12, further comprising supplying a pH adjuster to the pretreatment bath.

18. The method of claim 12, wherein the contamination ratio of the pretreatment bath is greater than 1:1 prior to supplying the reducing agent.

19. The method of claim 12, wherein the reducing agent is supplied to the pretreatment bath in an amount sufficient to render the pretreatment bath substantially free of nitrite.

20. The method of claim 12, wherein the reducing agent is supplied to the pretreatment bath in an amount sufficient to render the pretreatment bath completely free of nitrite.

21. The method of claim 12, wherein the supplying the reductant is performed during non-shift hours.

22. The method of claim 12, wherein the supplying the reductant is performed on a shift.

23. A substrate treated according to the method of claim 12.

24. The substrate of claim 23, wherein the film formed on the surface of the substrate has at least a 33% increase in zirconium coating weight as compared to a film formed on the surface of a substrate not treated with the method of claim 12.

Background

It is common to use protective coatings on metal surfaces to improve corrosion and paint adhesion. Conventional techniques for coating such substrates include techniques involving pretreatment of the metal substrate with a phosphate conversion coating and a chromium-containing rinse. However, the use of such phosphate and/or chromate containing compositions can present environmental and health concerns. Accordingly, either chromate and/or phosphate free pretreatment compositions or pretreatment compositions containing sufficiently low levels of phosphate to avoid environmental and health problems caused by conventional coating techniques have been developed. Such compositions are typically based on chemical mixtures that react with the substrate surface and bond therewith to form a protective layer. For example, pretreatment compositions based on group IVB metal compounds have recently become more prevalent.

Disclosure of Invention

In accordance with the present invention, disclosed herein is a system for maintaining a pretreatment bath, the system comprising an aqueous reducing agent comprising metal cations and a potential source of sulfate that form metal sulfate upon reaction with contaminants in the pretreatment bath; wherein the contaminant comprises a source of nitrite; and wherein the metal sulfate has a pKsp of 4.5 to 11 at a temperature of 25 ℃.

Also disclosed is a method for maintaining a pretreatment bath containing a pretreatment composition comprising a group IVB metal, the method comprising supplying an aqueous reducing agent to the pretreatment bath in an amount sufficient to reduce a contamination ratio of the pretreatment bath to less than 1: 1; wherein the reducing agent comprises metal cations and a potential source of sulfate that form metal sulfate upon reaction with contaminants in the pretreatment bath; wherein the contaminant comprises a source of nitrite; and wherein the metal sulfate has a pKsp of 4.5 to 11 at a temperature of 25 ℃.

Also disclosed is a substrate treated with a pretreatment bath maintained by the system or method of the invention, wherein the weight percent zirconium of the film formed on the surface of the substrate is increased by at least 33% as compared to a film formed on a surface of a substrate not treated with the system or method of the invention or with a pretreatment bath not maintained by any maintenance system or method as measured by X-ray fluorescence.

Detailed Description

For the purposes of the following detailed description, it is to be understood that the invention may assume various alternative variations and step sequences, except where expressly specified to the contrary. Moreover, except in any operating examples, or where otherwise indicated, all numbers such as those expressing values, amounts, percentages, ranges, subranges, or fractions, may be read as if prefaced by the word "about", even if the term does not expressly appear. Accordingly, unless indicated to the contrary, the numerical parameters set forth in the following specification and attached claims are approximations that may vary depending upon the desired properties to be obtained by the present invention. At the very least, and not as an attempt to limit the application of the doctrine of equivalents to the scope of the claims, each numerical parameter should at least be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Where closed or open numerical ranges are described herein, all numbers, values, amounts, percentages, subranges and fractions within or encompassed by such numerical ranges are to be considered as specifically encompassed within the original disclosure of the present application and as if such numbers, values, amounts, percentages, subranges and fractions were explicitly written out in their entirety.

Notwithstanding that the numerical ranges and parameters setting forth the broad scope of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as possible. Any numerical value, however, inherently contains certain errors necessarily resulting from the standard deviation found in their respective testing measurements.

As used herein, unless otherwise specified, plural terms may encompass their singular counterparts and vice versa, unless otherwise specified. For example, although reference is made herein to "a" reducing agent and "an" group IVB metal, combinations of these components (i.e., a plurality of these components) may be used. In addition, in this application, the use of "or" means "and/or" unless specifically stated otherwise, even though "and/or" may be explicitly used in some cases.

As used herein, "comprising," "including," and similar terms, are understood in the context of this application to be synonymous with "including" and thus open-ended and do not exclude the presence of additional unrecited and/or unrecited elements, materials, ingredients, and/or method steps. As used herein, "consisting of …" is understood in the context of the present application to exclude the presence of any unspecified elements, ingredients and/or method steps. As used herein, "consisting essentially of …" is understood in the context of the present application to include the named elements, materials, ingredients, and/or method steps "as well as those elements, materials, ingredients, or method steps that do not materially affect the basic characteristics and novel characteristics of the described content.

As used herein, the terms "on …", "onto …", "applied on …", "applied on …", "formed on …", "deposited on …", "deposited on …" mean formed, covered, deposited and/or provided on but not necessarily in contact with a surface. For example, a coating layer "formed over" a substrate does not preclude the presence of one or more other intermediate coating layers of the same or different composition positioned between the formed coating layer and the substrate.

Unless otherwise disclosed herein, the term "substantially free," when used in reference to the absence of a particular material, means that such material, if present in a composition, a bath containing the composition, and/or a layer formed from and including the composition, may be present only in trace amounts of 5ppm or less, based on the total weight of the composition, bath, and/or layer, as the case may be. Unless otherwise disclosed herein, the term "essentially free," when used in relation to the absence of a particular material, means that such material, if present in a composition, a bath containing the composition, and/or a layer formed from the composition, may be present only in trace amounts of 1ppm or less, based on the total weight of the composition, bath, and/or layer, as the case may be. Unless otherwise disclosed herein, the term "completely free," when used in reference to the absence of a particular material, means that such material is not present in a composition, a bath containing the composition, and/or a layer formed from the composition (i.e., the composition, the bath containing the composition, and/or the layer formed from the composition contains 0ppm of such material), if such material is present in the composition, the bath containing the composition, and/or the layer formed from the composition. When a composition, a bath containing the composition, and/or a layer formed therefrom is substantially free, essentially free, or completely free of a particular material, this means that such material is excluded except that the material may be present as a result of carryover from a pretreatment bath in solution, for example, from a processing line, municipal water source, substrate, and/or equipment.

As used herein, "salt" refers to an ionic compound consisting of a metal cation and a non-metal monoatomic or polyatomic anion and having zero overall charge. The salt may be hydrated or anhydrous.

As used herein, "aqueous composition" refers to a solution or dispersion in a medium that primarily includes water. For example, the aqueous medium may comprise water in an amount of more than 50 wt.%, or more than 70 wt.%, or more than 80 wt.%, or more than 90 wt.%, or more than 95 wt.%, calculated on the total weight of the medium. The aqueous medium may, for example, consist essentially of water.

As used herein, "nitrite" or "NO₂ ^-By "or" nitrite ion "or" nitrite anion "is meant Nitrate (NO) from contact with the metal substrate in the pretreatment bath₃ ^-) Reduction to NO₂ ^-And the total amount of nitrite (bound and free, including nitrite electrostatically attached to or bound to the metal surface) produced.

As used herein, the term "group IA metal" refers to an element in group IA of the CAS version of the periodic table of the elements, as shown, for example, in Handbook of Chemistry and Physics, 63 rd edition (1983), which group IA corresponds to group 1 in the actual IUPAC numbering.

As used herein, the term "group IA metal compound" refers to a compound comprising at least one element from group IA of the CAS version of the periodic table of elements.

As used herein, the term "group IIA metal" refers to an element in group IIA of the CAS version of the periodic table of elements, which group IIA corresponds to group 2 in the actual IUPAC numbering, for example as shown in handbook of chemistry and physics, 63 rd edition (1983).

As used herein, the term "group IIA metal compound" refers to a compound that includes at least one element in group IIA of the CAS version of the periodic table of elements.

As used herein, the term "group IVB metal" refers to an element in group IVB of the CAS version of the periodic table of the elements, corresponding to group 4 in the actual IUPAC numbering, such as shown in the handbook of chemistry and physics, 63 rd edition (1983).

As used herein, the term "group IVB metal compound" refers to a compound comprising at least one element from group IVB of the CAS version of the periodic table of elements.

As used herein, the term "group IVA metal" refers to an element in group IVA of the CAS version of the periodic table of the elements, corresponding to group 14 in the actual IUPAC numbering, such as shown in the handbook of chemistry and physics, 63 rd edition (1983). Examples of group IVA include lead (II).

As used herein, the term "group IV metal compound" refers to a compound comprising at least one element from group IVA of the CAS version of the periodic table of elements. An example of a group IVA compound includes lead (II) sulfate.

As used herein, the term "group IB metal" refers to an element in group IB of the CAS version of the periodic table of the elements, as shown, for example, in the handbook of chemistry and physics, 63 rd edition (1983), which group IB corresponds to group 11 in the actual IUPAC numbering. An example of a group IB metal is silver.

As used herein, the term "group IB metal compound" refers to a compound comprising at least one element from group IB of the CAS version of the periodic table of elements. An example of a group IB compound is silver (I) sulfate.

As used herein, "pretreatment composition" refers to a composition, such as a solution or dispersion, that is capable of reacting with and chemically altering the surface of a substrate to form a film that provides corrosion protection.

As used herein, "pretreatment bath" refers to an aqueous bath formed from a pretreatment composition (concentrated or diluted composition) comprising a group IVB metal.

As used herein, a "fresh" pretreatment bath refers to a pretreatment bath that is not exposed to the articles to be treated thereby.

As used herein, a "spent" pretreatment bath refers to a pretreatment bath that has been exposed to the articles to be treated thereby. A "spent" pretreatment bath may be artificially produced (as in the example) by adding known contaminants that build up in the bath as a result of the pretreatment process. For example, nitrite and zinc are often byproducts that accumulate in the pretreatment bath during part processing. Sodium nitrite may be used to supply the former contaminant and soluble zinc salts such as zinc chloride may be used to supply the latter contaminant.

As used herein, "shift-on" means that the article to be treated with the pretreatment composition is present in the pretreatment bath.

As used herein, "non-shift" means that the article to be treated by the pretreatment composition is not present in the pretreatment bath, but does not mean that the pretreatment bath must be removed from the production line.

As used herein, the term "contamination ratio" refers to the millimolar ratio of nitrite to zirconium in the pretreatment bath based on the total volume of the pretreatment composition. As the magnitude of the contamination ratio increases, the millimolar concentration of nitrite (contaminant) in the pretreatment bath increases.

As used herein, unless otherwise disclosed herein, the terms "total weight of composition", "total weight of bath", "total weight of composition", "total weight of treatment bath" or similar terms refer to the total weight of all ingredients present in the respective composition or bath, including any carriers and solvents.

According to the present invention, the pretreatment bath contains a pretreatment composition that can be used to pretreat metal substrates, such as those often used to assemble automotive bodies, automotive parts, and other articles such as small metal parts that include fasteners (i.e., nuts, bolts, screws, pins, nails, clamps, buttons, etc.). Specific examples of suitable metal substrates include, but are not limited to, cold rolled steel, hot rolled steel, steel coated with zinc metal, zinc compounds, or zinc alloys, such as electrogalvanized steel, hot-dip galvanized steel, galvanealed steel, and steel coated with zinc alloys. Also, aluminum alloys, aluminum-plated steels, and aluminum-alloy-plated steel substrates may be used. Other suitable non-ferrous metals include copper and magnesium and alloys of these materials. According to the present invention, the metal substrate treated with the pretreatment composition can be a cut edge of the substrate that is otherwise treated and/or coated over the remainder of its surface. According to the invention, the metal substrate can be in the form of, for example, a metal sheet or a manufactured part.

The introduction of the reducing metal, metal oxide or metal salt is a common method of supplying the metal to the pretreatment bath containing the pretreatment composition, including, for example, the addition of metal nitrate. Because all nitrates are water soluble, these species provide the easiest way to supply metal cations to an aqueous pretreatment composition. For example, electropositive metals such as copper or nickel are typically added as nitrates to group IVB pretreatment compositions. However, under acidic pretreatment conditions, nitrate can be reduced to Nitrite (NO)₂ ^1-) Or nitrous acid (HNO)₂). Due to E^* _{Battery with a battery cell}Is positive, so this reduction occurs spontaneously in the presence of a substrate such as steel. As the nitrite concentration increases, this species may react with the substrate surface, resulting in the formation of mixed iron oxides on the substrate surface, which may interfere with the deposition of the pretreatment composition onto steel substrates, thereby interfering with the corrosion protection of such substrates. Relative to the group consisting of IVBThe above iron oxide mixture, which may be formed on the surface of a steel substrate, may be poor in the film formed by the pretreatment composition of (1).

Table 1: oxidation reduction reaction

(1) Calculation of E Using the conversion of iron (0) to iron (II) as the Oxidation half-cell reaction^* _{Battery with a battery cell}The value was + 0.45V.

In accordance with the present invention, disclosed herein is a system for maintaining a pretreatment bath containing a pretreatment composition comprising or consisting essentially of a group IVB metal. According to the present invention, the system may comprise, consist essentially of, or consist of an aqueous reducing agent comprising metal cations and a potential source of sulfates that form metal sulfates upon reaction with contaminants in the pretreatment bath; wherein the contaminant comprises a source of nitrite; and wherein the metal sulfate has a pKsp of 4.5 to 11 at a temperature of 25 ℃. According to the present invention, the method for maintaining a pretreatment bath containing a pretreatment composition comprising, consisting essentially of, or consisting of a group IVB metal may comprise or consist of supplying to the pretreatment bath an amount of aqueous reducing agent sufficient to reduce the contamination ratio of the pretreatment bath to less than 1: 1; wherein the reducing agent comprises metal cations and a potential source of sulfate that form metal sulfate upon reaction with contaminants in the pretreatment bath; wherein the contaminant comprises a source of nitrite; and wherein the metal sulfate has a pKsp of 4.5 to 11 at a temperature of 25 ℃.

Suitable metal sulfates (which are reducing agents andreaction products of contaminants) and their corresponding pKsp are shown in table 3 below. As used herein, "maintaining" a pretreatment bath refers to maintaining certain parameters of the pretreatment bath, including concentrations of certain components, relative concentrations of certain components (as may be defined by the concentration ratio of one component to another component in the pretreatment bath), and/or pH of the pretreatment bath within a desired range. As described in more detail below, this may be accomplished by adding a reducing agent to the treatment bath on a shift and/or off-shift basis. The reducing agents described herein can be supplied to a spent pretreatment bath containing a pretreatment composition to chemically control nitrite levels therein, for example, by reducing the oxidation state of nitrogen in the nitrite (formed during substrate processing). Examples of nitrogen compounds having an oxidation state lower than that of nitrite include N₂、NO、N₂O、NH₃And the like. Thus, as noted above, the methods of the present invention may comprise, consist of, or consist essentially of supplying a reducing agent to a pretreatment bath. In other words, the reducing agent may react with the nitrite present in the spent pretreatment bath such that the oxidation state of the nitrogen in the nitrite is reduced from + 3. The oxidation states of the various nitrogen compounds are shown in Table 2.

Table 2: selecting the oxidation state of nitrogen in nitrogen compounds

Name of Compound	Molecular formula	Nitrogen oxide state
			Ammonia	NH3	-3
Hydrazine	N2H4	-2
			Elemental nitrogen	N2	0
Nitrous oxide	N2O	+1
			Nitric oxide	NO	+2
Nitrous acid or nitrite salt	HNO2Or NO2 1-	+3
			Nitrogen dioxide	NO2	+4
Nitric acid or nitrate salts	HNO3Or NO3 1-	+5

Table 3: the pKsp values of suitable metal sulfates

According to the present invention, the systems and methods of the present invention may include (i) adding materials different from those used to formulate the pretreatment composition to a pretreatment bath formed from the pretreatment composition, and optionally (ii) adding the same materials as those used to formulate the pretreatment composition to a pretreatment bath formed from the pretreatment composition. For example, while the method of maintaining a pretreatment bath containing a pretreatment composition can include adding a reducing agent as described herein to the pretreatment bath, the pretreatment composition can be formulated using a group IVB metal. Thus, the systems and methods of the present invention do not involve simply adding more pretreatment composition to the pretreatment bath to maintain the bath. In contrast, as noted above, the systems and methods of the present invention involve supplying reducing agent to the pretreatment bath in an amount sufficient to reduce the contamination ratio of the pretreatment bath to less than 1:1 millimolar parts, based on the total volume of the bath. Optionally, the systems and methods of the present invention may further comprise supplying the same materials to the pretreatment bath as are used to formulate the pretreatment composition. For example and as described in more detail below, the pretreatment composition may be formulated using a group IVB metal, and the system for maintaining the bath may further comprise adding a composition comprising a group IVB metal to the pretreatment bath, such as in an amount sufficient to supplement the amount of ingredients in the spent pretreatment bath to the amount present in the fresh pretreatment bath by at least 80% (as described below), such as at least 90%, such as at least 95%, such as at least 97%, based on the total weight of the pretreatment composition. The contamination ratio in the pretreatment bath may be at least 1:1 millimolar parts based on the total volume of the bath prior to supplying the reducing agent.

The reducing agent may include metal cations that form metal sulfates when reacted with contaminants in the pretreatment bath, such as nitrites. The metal sulfate may have a pKsp of 4.5 to 11 at a temperature of 25 ℃. Suitable examples of metals that may be used in the reducing agent include alkaline earth metals such as calcium, barium, strontium, radium, and combinations thereof, late transition metals such as lead, and/or transition metals such as silver, and combinations thereof. For example, the reducing agent may include barium sulfamate. The reducing agent may include a potential source of sulfate that may be formed or released upon reaction of the reducing agent with the contaminant (i.e., nitrite) in the pretreatment bath. Examples of potential sulfate sources include sulfamic acid and sulfamates. For example, sulfamic acid and sulfamates may release sulfate as sulfuric acid or bisulfate salt when reacted with nitrous acid or nitrite anion:

HSO₃NH₂+HNO₂→N₂+H₂SO₄+H₂O

other non-limiting examples of potential sulfate sources include Sulfite (SO)₃ ²-), bisulfite (HSO)₃ ^1-) Thiosulfates (S)₂O₃ ^2-) Dithionate (S)₂O₆ ^2-) Dithionite (S)₂O₄ ^2-) Acids and metal salts of (a). In such examples, sulfates may be released from these chemicals by the action of contaminants (i.e., nitrites) through the oxidation of sulfur. For example, in sulfurous acid (H)₂SO₃) The sulfur in (b) is in the 4+ oxidation state and when exposed to nitrite salts can form sulfates with sulfur present in the 6+ oxidation state.

The reducing agent may be prepared by adding discrete metal salts such as barium sulfamate. Alternatively, the reducing agent may be prepared by adding the metal cation in soluble form and a separate source of potential sulfate. For example, a reducing agent comprising barium sulfamate may be prepared by adding a mixture of barium hydroxide and sulfamic acid to a carrier such as water. In such examples, barium sulfamate provides a soluble source of barium, and sulfamic acid provides a potential source of sulfate. When this mixture is contacted with the contaminant (i.e., nitrite) after addition to the pretreatment composition, barium sulfate precipitates and nitrogen gas gradually forms as described above.

The reducing agent may further comprise an additional metal, which may be present in the reducing agent in the form of a salt, for example, a hydroxide, sulfamate, carbonate, halide, sulfate, phosphate, silicate (e.g., orthosilicate or metasilicate), or a combination thereof. For example, the reducing agent can further include ascorbic acid, sulfanilic acid, titanium (III) chloride, tin (II) chloride, or a combination thereof.

According to the invention, the sulfate forming metal may have a pKsp at 25 ℃ of at least 4.5, such as at least 5.5, such as at least 6.0, such as at least 6.5, and a pKsp at 25 ℃ of only 11, such as only 10.5, such as only 10.25, such as only 10.0. According to the invention, the sulphate-forming metal may have a pKsp at 25 ℃ of from 4.5 to 11, such as from 5.5 to 10.5, such as from 6.0 to 10.25, such as from 6.25 to 10.0.

The reducing agent typically includes an aqueous medium as a carrier. The reducing agent may thus be in the form of an aqueous solution and/or dispersion of the metal or metal cation which forms the sulphate in the carrier. For example, the reducing agent may further include water, and in some cases, water may be used to dilute the reducing agent. Any suitable amount of water may be present in the reducing agent to provide the desired concentration of the other component.

According to the present invention, the reducing agent may be prepared by combining the sulfate-forming metal with water to form a first pre-blend. Once the ingredients are combined with each other, the ingredients of the first preblend may be stirred under mild agitation. The reducing agent may be prepared at ambient conditions, such as about 70 ° f to 80 ° f (21 ℃ to 26 ℃), or at a temperature slightly below and/or slightly above ambient conditions, such as about 50 ° f to 140 ° f (10 ℃ to 60 ℃), such as 60 ° f to 105 ° f (16 ℃ to 41 ℃).

The pH of the reducing agent may be adjusted to any desired value as needed using, for example, any acid or base, prior to supplying the reducing agent to the spent pretreatment bath. According to the present invention, the pH of the reducing agent may be adjusted, for example, to less than 7, such as less than 5, such as less than 3, and may be adjusted by including an acidic material comprising a water dispersible acid, such as sulfuric acid, sulfamic acid, hydrohalic acid, fluorozirconic acid, fluorotitanic acid, hydrofluoric acid, an alkyl sulfonic acid, an organic carboxylic acid such as formic acid or acetic acid, perchloric acid, or combinations thereof. According to the present invention, the pH of the composition may be adjusted by including a basic material comprising a water soluble and/or water dispersible base such as sodium hydroxide, sodium carbonate, potassium hydroxide, ammonium hydroxide, ammonia, and/or an amine such as triethylamine, methylethylamine, or mixtures thereof.

According to the present invention, the reducing agent may be added to the pretreatment bath in an amount sufficient to reduce the contamination ratio to less than 1.0:1.0, such as less than 0.75:1.0, such as less than 0.5:1.0, such as less than 0.3: 1.0.

The method of maintaining the treatment bath according to the present invention may further comprise adjusting the pH of the treatment bath, as required by adding any acid and/or base. According to the present invention, the treatment bath may be maintained by including an acidic material comprising a water-soluble and/or water-dispersible acid, such as nitric acid, sulfuric acid, and/or phosphoric acid. According to the present invention, the pH of the treatment bath may be maintained by including a basic material comprising a water soluble and/or water dispersible base, such as a group I carbonate, a group II carbonate, a hydroxide, such as sodium hydroxide, potassium hydroxide, lithium hydroxide, ammonium hydroxide, ammonia, an amine, such as triethylamine, methylethylamine, or mixtures thereof.

The method of maintaining a treatment bath of the present invention may further comprise monitoring the pH of the treatment bath using a pH meter and probe appropriate for the size of the bath containing the pretreatment composition. Examples of suitable pH meters and probes include, but are not limited to, Accumet AB15 (available from Fischer Technology) and single junction electrodes (Ag/AgCl reference; Fischer Technology).

According to the present invention, the pretreatment composition used to prepare the pretreatment bath may comprise or may consist essentially of a group IVB metal. According to the present invention, the pretreatment composition and the fresh pretreatment bath may be substantially free of nitrite or may be completely free of nitrite.

Optionally, according to the present invention, the method may further comprise the step of adjusting the pH of the pretreatment bath to a pH of less than 7, such as a pH of less than 5, such as a pH of less than 3, by adding any of the acidic materials described above, prior to the step of supplying the reducing agent to the pretreatment bath. The methods disclosed herein optionally may further comprise adjusting the pH of the pretreatment bath after supplying the reducing agent to the bath. The pH of the pretreatment bath may be adjusted to within the standard operating range of the pretreatment composition, such as 2 to 6.5, such as 3.0 to 6.0, such as 4 to 5.5. The pH of the pretreatment bath may be adjusted as desired using, for example, any acid or base. For example, the pH of the solution may be maintained by the inclusion of a basic material comprising a water-soluble and/or water-dispersible base, such as sodium hydroxide, sodium carbonate, potassium hydroxide, ammonium hydroxide, ammonia, and/or an amine, such as triethylamine, methylethylamine, or mixtures thereof.

As noted above, in an example, the methods disclosed herein involve supplying a reductant to a spent pretreatment bath to control nitrite levels in the spent pretreatment bath. As described above, the pretreatment bath may contain a pretreatment composition. According to the invention, the reducing agent may be added to the bath at the time of pre-treatment of the bath shift or non-shift.

As the substrate is treated in the pretreatment bath, the contamination ratio may increase such that the contamination ratio of the pretreatment bath may be 1.0:1.0 or greater, such as 2.0:1.0, such as 5.0:1.0, such as 10.0:1.0, such as 100.0:1.0, such as 500.0: 1.0. According to the present invention, a reducing agent may be added to the pretreatment bath to reduce the contamination ratio of the pretreatment bath to less than 1.0:1.0, such as less than 0.75:1.0, such as less than 0.5:1.0, such as less than 0.3: 1.0. For example, the reducing agent may be added to the pretreatment bath in an amount sufficient to render the pretreatment bath substantially free or completely free of nitrite.

The reducing agent may be added to the pretreatment bath with or without agitation, followed by agitation of the material. The reducing agent may be added to the pretreatment bath when the pretreatment bath is at ambient temperature, such as about 70 ° f to 80 ° f (21 ℃ to 26 ℃), and when the pretreatment bath is at a temperature slightly below and/or slightly above ambient temperature, such as about 50 ° f to 140 ° f (10 ℃ to 60 ℃), such as 60 ° f to 105 ° f (16 ℃ to 41 ℃).

As discussed above, the pretreatment composition can include a group IVB metal. The group IVB metal may include zirconium, titanium, hafnium, or combinations thereof. For example, zirconium, titanium, hafnium or mixtures thereof may be used in the pretreatment composition. Suitable zirconium compounds include, but are not limited to, hexafluorozirconic acid, alkali metal and ammonium salts thereof, ammonium zirconium carbonate, zirconyl nitrate, zirconyl sulfate, zirconium carboxylates such as zirconium acetate, zirconium oxalate, ammonium zirconium glycolate, ammonium zirconium lactate, ammonium zirconium citrate, zirconium hydroxy carboxylates, zirconium basic carbonate, and mixtures thereof. Suitable titanium compounds include, but are not limited to, fluotitanic acid and salts thereof. Suitable hafnium compounds include, but are not limited to, hafnium nitrate.

According to the present invention, the group IVB metal can be present in the pretreatment composition in a total amount of at least 20ppm metal (calculated as metal), such as at least 50ppm metal, or in some cases at least 70ppm metal, based on the total weight of the pretreatment composition. According to the present invention, the group IVB metal may be present in the pretreatment composition in a total amount of only 1000ppm metal (calculated as metal), such as only 600ppm metal, or in some cases only 300ppm metal, based on the total weight of the pretreatment composition. According to the present invention, the group IVB metal may be present in the pretreatment composition in a total amount of from 20ppm metal to 1000ppm metal (calculated as metal), such as from 50ppm metal to 600ppm metal, such as from 70ppm metal to 300ppm metal, based on the total weight of the pretreatment composition. As used herein, the term "total amount" when used in relation to the amount of group IVB metal means the sum of all group IVB metals present in the pretreatment composition.

According to the present invention, the pretreatment composition may further comprise anions that may be suitable for forming salts with cations of group IVB metals, such as halogens, sulfates, silicates (orthosilicate and metasilicate), carbonates, hydroxides, and the like. According to the present invention, the pretreatment composition may further include an electropositive metal ion. As used herein, the term "electropositive metal ion" refers to a metal ion that will be reduced by the metal substrate being treated when the pretreatment solution contacts the surface of the metal substrate. As will be understood by those skilled in the art, the tendency of a chemical to be reduced is referred to as the reduction potential, expressed in volts, and is measured relative to a standard hydrogen electrode, which is arbitrarily assigned a reduction potential of zero. Table 4 below showsThe reduction potentials of several elements are listed (according to CRC 82 th edition, 2001-. If an element or ion is in the voltage value E in the table below^*More positive than the element or ion it is compared to, the element or ion is more easily reduced than another element or ion.

Table 4: reduction potential

Thus, it is apparent that when the metal substrate comprises one of the materials listed above, such as cold rolled steel, hot rolled steel, steel coated with zinc metal, zinc compounds or zinc alloys, hot dip galvanized steel, galvannealed steel, steel coated with zinc alloys, aluminum plated steel, aluminum alloyed steel, magnesium and magnesium alloys, suitable electropositive metal ions for deposition on the metal substrate comprise, for example, nickel, copper, silver and gold, and mixtures thereof.

According to the present invention, when the electropositive metal ions include copper, both soluble and insoluble compounds may serve as a source of copper ions in the pretreatment composition. For example, the source of supply of copper ions in the pretreatment composition can be a water soluble copper compound. Specific examples of such compounds include, but are not limited to, copper sulfate, copper nitrate, cuprous thiocyanate, disodium copper ethylenediaminetetraacetate tetrahydrate (sodium ethylene diaminetetraacetate tetrahydrate), copper bromide, copper oxide, copper hydroxide, copper chloride, copper fluoride, copper gluconate, copper citrate, copper lauroyl sarcosinate, copper lactate, copper oxalate, copper tartrate, copper malate, copper succinate, copper malonate, copper maleate, copper benzoate, copper salicylate, copper amino acid complex, copper fumarate, copper glycerophosphate, sodium copper chlorophyll, copper fluorosilicate, copper fluoroborate and copper iodate, and copper salts of carboxylic acids, such as copper salts of the polybasic acids in the formic acid to capric acid series, and in the oxalic acid to suberic acid series.

When copper ions supplied from such a water-soluble copper compound precipitate as impurities in the form of copper sulfate, copper oxide, or the like, it may be desirable to add a complexing agent that inhibits the precipitation of copper ions, thereby stabilizing the copper ions as a copper complex in the composition.

According to the present invention, the copper compound may be added in the form of a copper complex salt such as Cu-EDTA, which may be stably present in the pretreatment composition itself, but may also be combined with a compound that is difficult to dissolve itself to form a copper complex that may be stably present in the pretreatment composition. Examples include compounds derived from CuSO₄A Cu-EDTA complex formed by combining EDTA-2 Na.

According to the present invention, the electropositive metal ion may be present in the pretreatment composition in an amount of at least 2ppm (calculated as metal ion), such as at least 4ppm, such as at least 6ppm, such as at least 8ppm, such as at least 10ppm, etc., based on the total weight of the pretreatment composition. According to the present invention, the electropositive metal ion may be present in the pretreatment composition in an amount of only 100ppm (calculated as metal ion), such as only 80ppm, such as only 60ppm, such as only 40ppm, such as only 20ppm, etc., based on the total weight of the pretreatment composition. According to the present invention, the electropositive metal ion may be present in the pretreatment composition in an amount of, for example, from 4ppm to 80ppm, such as from 6ppm to 60ppm, such as from 8ppm to 40ppm, and the like, from 2ppm to 100ppm (calculated as the metal ion) based on the total weight of the pretreatment composition. The amount of electropositive metal ion in the pretreatment composition can range between and including the recited values.

According to the present invention, a source of fluoride ions may be present in the pretreatment composition. As used herein, the amount of fluoride ion disclosed or reported in the pretreatment composition is referred to as "free fluoride ion," i.e., fluoride ion present in the pretreatment composition that is not bound to metal ions or hydrogen ions, as measured in parts per million of fluoride ion. Free fluoride is defined herein as being able to use fluoride ions such as those provided with available from seemer science and technology (Thermoscientific)Sub-selective electrodes ("ISE"), supplied by VWR International (VWR International)The measurement is carried out by an Orion Dual Star two-channel table-type measuring instrument of a fluorine ion selective combined electrode or a similar electrode.See, e.g.Light and Cappuccino, the use of ion-selective electrodes to determine fluoride ion in toothpaste (Determination of fluoride in toothpaste using an-selective electrode), journal of chemical education (J.chem.Educ.), 52:4, 247-. The fluoride ion ISE may be normalized by immersing the electrodes in a solution of known fluoride ion concentration and recording readings in millivolts and then plotting these millivolt readings in a log plot. The millivolt reading of the unknown sample can then be compared to this calibration map and the concentration of fluoride ion determined. Alternatively, the fluoride ion ISE may be used with a meter that will perform calibration calculations internally, and thus after calibration, the concentration of the unknown sample may be read directly.

Fluoride ions are small negative ions with high charge density, and therefore in aqueous solutions, fluoride ions are often complexed with metal ions or hydrogen ions with high positive charge density. The fluorine ion in solution that is covalently bound to the metal cation or hydrogen ion or the anion is defined herein as "bound fluorine ion". The fluoride ions so complexed cannot be measured with fluoride ion ISE unless the solution in which they are present is mixed with an ionic strength-adjusting buffer (e.g. citrate anion or EDTA) that releases fluoride ions from such complexes. At that time, (all) fluorine ions can be measured by the fluorine ion ISE, and the measurement result is referred to as "total fluorine ions". The sum of the concentrations of bound and free fluoride ions equals the total fluoride ions, which can be determined as described herein.

The total fluoride ion in the pretreatment composition may be supplied from hydrofluoric acid and alkali metal and ammonium fluoride or hydrogen fluoride. Alternatively, the total fluoride ions in the pretreatment composition can be derived from the group IVB metal present in the pretreatment composition comprising, for example, hexafluorozirconic acid or hexafluorotitanic acid. Such as H₂SiF₆Or HBF₄And other complex fluorides may be added to the pretreatment composition to supply total fluoride ions. The skilled person will appreciate that the presence of free fluoride ions in the pretreatment bath may affect the pretreatment deposition and etching of the substrate, and therefore measuring this bath parameter is of vital importance. The level of free fluoride ion will depend on the pH of the pretreatment bath and the addition of chelating agents in the pretreatment bath and indicates the degree of correlation of fluoride ion with the metal ions/protons present in the pretreatment bath. For example, a pretreatment composition of the same total fluoride level may have different levels of free fluoride that will be affected by the pH of the pretreatment solution and the presence of the chelating agent in the pretreatment solution.

According to the present invention, the free fluoride of the pretreatment composition may be present in an amount of at least 15ppm, such as at least 50ppm free fluoride, such as at least 100ppm free fluoride, such as at least 200ppm free fluoride, based on the total weight of the pretreatment composition. According to the present invention, the free fluoride of the pretreatment composition may be present in an amount of only 2500ppm, such as only 1000ppm free fluoride, such as only 500ppm free fluoride, such as 250ppm free fluoride, based on the total weight of the pretreatment composition. According to the present invention, the free fluoride of the pretreatment composition may be present in an amount of from 15ppm free fluoride to 2500ppm free fluoride, such as from 50ppm fluoride to 1000ppm, such as from only 200ppm free fluoride to 500ppm free fluoride, such as from only 100ppm free fluoride to 250ppm free fluoride, based on the total weight of the pretreatment composition.

According to the present invention, in some cases, the pretreatment composition may include an adhesion promoter. As used herein, the term "adhesion promoter" refers to a chemical species having at least two binding sites (bifunctional) for promoting interaction (whether electrostatic, covalent, or adsorptive) between the pretreated surface and a subsequent coating, or enhancing cohesive bonding within the pretreated layer by co-deposition during pretreatment film deposition. Non-limiting examples of adhesion promoters include carboxylates, phosphonates, silanes, sulfonates, anhydrides, titanates, zirconates, unsaturated fatty acids, functionalized amines, phosphonic acids, functionalized thiols, carboxylic acids, polycarboxylic acids, bisphosphonic acids, poly (acrylic) acids, or combinations thereof. According to the invention, the molecular weight of the adhesion promoter may be from 200 to 20,000, such as from 500 to 5000, such as from 1000 to 3000. Commercially available products include, for example, Acumer 1510 (available from Dow) and Dispex Ultra 4585, 4580 and 4550 (available from BASF). In accordance with the present invention, the adhesion promoter may be present in the pretreatment composition in an amount of from 10ppm to 10,000ppm, such as from 15ppm to 1500ppm, such as from 20ppm to 1000ppm, such as from 25 to 500 ppm.

According to the present invention, the pretreatment composition may not comprise chromium or chromium-containing compounds. As used herein, the term "chromium-containing compound" refers to a material comprising trivalent and/or hexavalent chromium. Non-limiting examples of such materials include chromic acid, chromium trioxide, chromic acid anhydrides, dichromates such as ammonium dichromate, sodium dichromate, potassium dichromate, calcium dichromate, barium dichromate, magnesium dichromate, zinc dichromate, cadmium dichromate, strontium dichromate, chromium (III) sulfate, chromium (III) chloride, and chromium (III) nitrate. When the pretreatment composition and/or the coating or layer formed therefrom, respectively, is substantially free, essentially free, or completely free of chromium, this includes any form of chromium, such as, but not limited to, the trivalent and hexavalent chromium-containing compounds listed above.

Thus optionally, according to the present invention, the pretreatment composition of the present invention and/or the coating or layer deposited therefrom, respectively, may be substantially free, may be essentially free and/or may be completely free of one or more of any of the elements or compounds listed in the preceding paragraphs. A pretreatment composition and/or a coating or layer respectively formed therefrom that is substantially free of chromium or derivatives thereof means that chromium or derivatives thereof are not intentionally added, but may be present in trace amounts, such as due to impurities or unavoidable environmental contamination. In other words, the amount of material is so small that it does not affect the properties of the pretreatment composition; in the case of chromium, this may further comprise elements or compounds thereof not being present in the pretreatment composition and/or the coating or layer formed therefrom, respectively, at such levels as to place a burden on the environment. The term "substantially free" means that the coating or layer formed from the pretreatment composition and/or from the coating or layer, respectively, contains less than 10ppm of any or all of the elements or compounds listed in the preceding paragraph, if any, based on the total weight of the composition or coating, respectively. The term "essentially free" means that the coating or layer formed from the pretreatment composition and/or from it, respectively, contains less than 1ppm of any or all of the elements or compounds listed in the preceding paragraph, if any. The term "completely free" means that the coating or layer formed from the pretreatment composition and/or from it, respectively, contains less than 1ppb of any or all of the elements or compounds listed in the preceding paragraph, if any.

In accordance with the present invention, in some cases, the pretreatment composition may not contain phosphate ions or phosphate-containing compounds and/or the formation of sludge, such as aluminum phosphate, iron phosphate, and/or zinc phosphate, formed with zinc phosphate-based treating agents. As used herein, "phosphate-containing compound" includes phosphorus-containing compounds such as orthophosphates, pyrophosphates, metaphosphates, tripolyphosphates, organophosphonates, and the like, and may include, but is not limited to, monovalent, divalent, or trivalent cations such as: sodium, potassium, calcium, zinc, nickel, manganese, aluminum and/or iron. When the composition and/or the layer or coating comprising said composition is substantially free, essentially free or completely free of phosphate, this comprises phosphate ions or a compound containing phosphate in any form.

Thus, in accordance with the present invention, the pretreatment composition and/or the layer deposited therefrom may be substantially free, or in some cases may be essentially free, or in some cases may be completely free of one or more of any of the ions or compounds listed in the preceding paragraph. By a substantially phosphate-free pretreatment composition and/or layer deposited therefrom is meant that phosphate ions or phosphate-containing compounds are not intentionally added, but may be present in trace amounts, such as due to impurities or unavoidable environmental contamination. In other words, the amount of material is so small that it does not affect the properties of the composition; this may further comprise that phosphate is not present in the pretreatment composition and/or the layer deposited therefrom at such levels as to burden the environment. The term "substantially free" means that the pretreatment composition and/or the layer deposited therefrom, respectively, contains less than 5ppm of any or all of the phosphate anions or compounds listed in the preceding paragraph, if any, based on the total weight of the composition or layer. The term "essentially free" means that the pretreatment composition and/or the layer comprising the composition contains less than 1ppm of any or all of the phosphate anions or compounds listed in the preceding paragraph. The term "completely free" means that the pretreatment composition and/or the layer comprising the composition contains less than 1ppb of any or all of the phosphate anions or compounds listed in the preceding paragraph, if any.

Optionally, according to the present invention, the pretreatment composition may further comprise a source of phosphate ions. For clarity, when used herein, "phosphate ions" refers to phosphate ions derived or derived from inorganic phosphate compounds. For example, in some cases, the phosphate ion can be present in an amount greater than 5ppm, such as 10ppm, such as 20ppm, based on the total weight of the pretreatment composition. In some cases, the phosphate ion can be present in an amount of only 60ppm, such as only 40ppm, such as only 30ppm, based on the total weight of the pretreatment composition. In some cases, the phosphate ion can be present in an amount of 5ppm to 60ppm, such as 10ppm to 40ppm, such as 20ppm to 30ppm, based on the total weight of the pretreatment composition.

According to the invention, the pH of the pretreatment composition may be 6.5 or less, such as 6.0 or less, such as 5.5 or less, such as 4.0 or less, such as 3.0 or less. According to the present invention, in some cases, the pH of the pretreatment composition may be 2.0 to 6.5, such as 3.0 to 6.0, such as 4.0 to 5.5, and may be adjusted as desired using, for example, any acid and/or base. According to the present invention, the pH of the pretreatment composition may be maintained by the inclusion of an acidic material comprising a water-soluble and/or water-dispersible acid, such as nitric acid, sulfuric acid, and/or phosphoric acid. According to the present invention, the pH of the composition may be maintained by the inclusion of a basic material comprising a water soluble and/or water dispersible base, such as sodium hydroxide, sodium carbonate, potassium hydroxide, ammonium hydroxide, ammonia and/or an amine, such as triethylamine, methylethylamine or mixtures thereof.

According to the present invention, the pretreatment composition may further include a resin binder. Suitable resins include the reaction product of one or more alkanolamines and an epoxy-functional material containing at least two epoxy groups, such as the reaction product disclosed in U.S. Pat. No. 5,653,823. In some cases, such resins contain beta hydroxy ester, imide, or sulfide functionality that is incorporated by using dimethylolpropionic acid, phthalimide, or thioglycerol (mercaptoglycerol) as an additional reactant in the resin preparation. Alternatively, the reaction product may be, for example, the reaction product of diglycidyl ether of bisphenol a (commercially available as EPON 880, e.g., from Shell Chemical Company), dimethylolpropionic acid and diethanolamine in a molar ratio of 0.6 to 5.0:0.05 to 5.5: 1. Other suitable resin binders include water soluble and water dispersible polyacrylic acids such as those disclosed in U.S. patent nos. 3,912,548 and 5,328,525; phenol-formaldehyde resins such as those described in U.S. patent No. 5,662,746; water soluble polyamides, such as the water soluble polyamides disclosed in WO 95/33869; copolymers of maleic or acrylic acid with allyl ethers, such as the copolymers described in canadian patent application No. 2,087,352; and water soluble and dispersible resins including epoxy resins, aminoplasts, phenol-formaldehyde resins, tannins, and polyvinylphenols, such as the water soluble and dispersible resins discussed in U.S. patent No. 5,449,415.

According to the present invention, the resinous binder may generally be present in the pretreatment composition in an amount of from 0.005% to 30% by weight, such as from 0.5% to 3% by weight, based on the total weight of the composition. Alternatively, in accordance with the present invention, the pretreatment composition may be substantially free or, in some cases, completely free of any resin binder. As used herein, the term "substantially free" when used with reference to the absence of resin binder in the pretreatment composition means that any resin binder, if present, is present in the pretreatment composition in a trace amount of less than 0.005 wt.%, based on the total weight of the composition. As used herein, the term "completely free" means that there is no resin binder at all in the pretreatment composition.

The pretreatment composition may include an aqueous medium, and may optionally contain other materials such as nonionic surfactants and adjuvants conventionally used in the art of pretreatment compositions. In the aqueous medium, a water dispersible organic solvent may be present, for example, an alcohol having up to about 8 carbon atoms, such as methanol, isopropanol, and the like; or glycol ethers such as monoalkyl ethers of ethylene glycol, diethylene glycol or propylene glycol, and the like. When present, the water-dispersible organic solvent is generally used in an amount up to about 10 volume percent, based on the total volume of the aqueous medium.

Other optional materials include surfactants that act as defoamers or substrate wetting agents. Anionic, cationic, amphoteric and/or nonionic surfactants may be used. The antifoaming surfactant may optionally be present at a level of up to 1 wt.%, such as up to 0.1 wt.%, and the wetting agent is typically present at a level of up to 2 wt.%, such as up to 0.5 wt.%, based on the total weight of the pretreatment composition.

Optionally, in accordance with the present invention, the pretreatment composition and/or a film deposited or formed therefrom may further comprise a silicon-containing compound, such as a silane, silica, silicate, and the like, in an amount of at least 10ppm, such as at least 20ppm, such as at least 50ppm, and the like, based on the total weight of the pretreatment composition. In accordance with the present invention, the pretreatment composition and/or films deposited or formed therefrom can include silicon in an amount of less than 500ppm, such as less than 250ppm, such as less than 100ppm, based on the total weight of the pretreatment composition. In accordance with the present invention, the pretreatment composition and/or films deposited or formed therefrom may include silicon in an amount of from 10ppm to 500ppm, such as from 20ppm to 250ppm, such as from 50ppm to 100ppm, based on the total weight of the pretreatment composition. Alternatively, the pretreatment compositions of the present invention and/or films deposited or formed therefrom can be substantially free of silicon, or in some cases completely free of silicon.

The pretreatment composition may include a carrier, which is typically an aqueous medium, such that the composition is in the form of a solution or dispersion of the group IVB metal in the carrier. According to the present invention, the solution or dispersion may be contacted with the substrate by any of a variety of known techniques, such as dipping or immersion, spraying, intermittent spraying, spraying after dipping, dipping after spraying, brushing, or rolling. In accordance with the present invention, the temperature of the solution or dispersion when applied to a metal substrate ranges from 40F to 185F, such as 60F to 110F, such as 70F to 90F. For example, the pretreatment process may be performed at ambient or room temperature. The contact time is typically from 5 seconds to 15 minutes, such as from 10 seconds to 10 minutes, such as from 15 seconds to 3 minutes, such as from 30 seconds to 2 minutes.

As discussed above, elevated nitrite levels in the pretreatment bath interfere with the deposition of group IVB metals on the metal substrate being treated in the pretreatment bath, thereby resulting in diminished corrosion protection. It has been surprisingly found that the method of controlling nitrite levels in a pretreatment bath disclosed herein avoids the disadvantages associated with elevated nitrite levels in the bath by providing a method of chemically controlling nitrite levels on the process line, thereby avoiding the need for replacement or overflow baths.

In view of the foregoing description, the present invention thus specifically relates to, but is not limited to, the following aspects 1-26:

aspect(s)

1. A system for maintaining a pretreatment bath, the system comprising: an aqueous reducing agent comprising metal cations and a potential source of sulfate that, upon reaction with contaminants in the pretreatment bath, form metal sulfates; wherein the contaminant comprises a source of nitrite; and wherein the metal sulfate has a pKsp of 4.5 to 11 at a temperature of 25 ℃.

2. The system of aspect 1, wherein the metal cation comprises a cation of calcium, strontium, barium, radium, lead (II), and/or silver (I).

3. The system of aspect 1 or aspect 2, the reducing agent further comprising an anion capable of forming a salt with the metal cation.

4. The system of aspect 3, wherein the anion comprises a hydroxide, a carbonate, or a combination thereof.

5. The system of any one of aspects 1-4, wherein the pH of the reducing agent is less than 7.

6. The system of any one of aspects 1-5, further comprising a pretreatment composition comprising a group IVB metal.

7. The system of aspect 6, wherein the group IVB metal comprises zirconium.

8. The system of aspect 6 or aspect 7, wherein the pretreatment composition further comprises free fluoride ions, an electropositive metal, and/or a binder.

9. The system of any one of aspects 1-8, further comprising a pH adjuster.

10. A substrate treated with a pretreatment bath maintained by the system of aspects 1 through 9.

11. The substrate of aspect 10, wherein the film formed on the surface of the substrate has at least a 33% increase in zirconium coating weight as compared to a film formed on a surface of a substrate treated with a pretreatment bath not maintained by the system of any of aspects 1-9.

12. A method for maintaining a pretreatment bath containing a pretreatment composition comprising a group IVB metal, the method comprising: supplying an aqueous reducing agent to the pretreatment bath in an amount sufficient to reduce a contamination ratio of the pretreatment bath to less than 1: 1; wherein the reducing agent comprises metal cations and a potential source of sulfate that form metal sulfate upon reaction with contaminants in the pretreatment bath; wherein the contaminant comprises a source of nitrite; and wherein the metal sulfate has a pKsp of 4.5 to 11 at a temperature of 25 ℃.

13. The method of aspect 12, wherein the metal cation comprises a cation of calcium, strontium, barium, radium, lead (II), and/or silver (I).

14. The method of aspect 12 or aspect 13, wherein the reducing agent further comprises an anion capable of forming a salt with the metal cation.

15. The method of aspect 14, wherein the anion comprises a hydroxide, a carbonate, or a combination thereof.

16. The method of any one of aspects 12-15, wherein the pH of the reducing agent is less than 7.

17. The method of any one of aspects 12-16, further comprising supplying a pH adjuster to the pretreatment bath.

18. The method of any one of aspects 12-17, wherein the contamination ratio of the pretreatment bath is greater than 1:1 prior to supplying the reducing agent.

19. The method of any one of aspects 12-18, wherein the reducing agent is supplied to the pretreatment bath in an amount sufficient to render the pretreatment bath substantially free of nitrite.

20. The method of any one of aspects 12-19, wherein the reducing agent is supplied to the pretreatment bath in an amount sufficient to render the pretreatment bath completely free of nitrite.

21. The method of any one of aspects 12-20, wherein the supplying the reductant is performed non-shift.

22. The method of any one of aspects 12-21, wherein the supplying the reductant is performed on a shift.

23. The method according to any one of aspects 12 to 22, wherein the reducing agent is the reducing agent described according to any one of aspects 1 to 5, and/or the pretreatment bath comprises the pretreatment composition described according to any one of aspects 6 to 8.

24. A substrate treated according to the method of any one of aspects 12-23.

25. The substrate of aspect 24, wherein the film formed on the surface of the substrate has at least a 33% increase in zirconium coating weight as compared to a film formed on a surface of a substrate not treated with the method of any of aspects 12-23.

26. Use of the reducing agent described in any one of aspects 1 to 5 for holding the pretreatment bath described in any one of aspects 6 to 8.

The following examples illustrate the invention and should not be construed as limiting the invention to the details thereof. All parts and percentages in the examples, as well as throughout the specification, are by weight unless otherwise indicated.

Examples of the invention

In all of the examples described herein, the amount of nitrite in the solution was measured using a fermentation tube according to the protocol described in the technical data sheet for Chemfos liquid additive (available from PPG Industries, inc., Cleveland, OH) of Cleveland, ohio. In each of the examples below, the fermentation tube was filled with 70mL of the pretreatment bath sample to reach just below the orifice. Two (2.0) g sulfamic acid was added to the tube and the tube was inverted to mix sulfamic acid and pretreatment solution. Gas evolution occurred, which displaced the liquid at the top of the fermenter, and the water level was read and recorded. The water level corresponds to the point of gas measured in milliliters of solution.

Table 5: calculation of contamination ratio of pretreatment bath

Example 1

Cold rolled steel test panels (105 mm. times.190 mm) were obtained from Kenturtel (Chemetall) (Gardobond MBS 21; Frankfurt, Germany) (referred to herein as "Steel C"). These panels were cut into 4 "x 6" prior to cleaning and pretreatment of all of the following examples.

A 10 gallon bath of the cleaner composition was prepared in deionized water at a concentration of 1.25% v/v Chemkleen 2010LP (phosphate-free alkaline cleaner available from PPG industries) and 0.125% Chemkleen 181ALP (phosphate-free blended surfactant additive available from PPG industries).

Pretreatment composition a was prepared by adding 11.0g of fluorozirconic acid (45 wt.% in water), available from Honeywell International, Inc (Morristown, Nj), 12.0g of Chemfos AFL (a partially neutralized aqueous ammonium bifluoride solution, commercially available from PPG industries), and 22.1g of a copper nitrate solution (a 2 wt.% Cu solution, prepared by diluting a copper nitrate solution (18 wt.% Cu in water), available from Shepherd Chemical Company, Cincinnati, OH). The bath pH was measured using a Sammer scientific Orion Dual Star pH/ISE bench reader attached to the Accumet catalog number 13-620-221pH probe and the pH was adjusted to 4.7 with Chemfil buffer (an alkaline buffer commercially available from PPG industries, Inc.).

Pretreatment bath A contained 200ppm zirconium (calculated), 38ppm copper (calculated), and 110ppm free fluoride (using a fluoride ion selective electrode ("ISE") equipped with a material available from Sammer technology, supplied by VWR International Inc.)Orion Dual Star two-channel bench gauge measurement of fluoride ion selective combination electrodes). The nitrite concentration in pretreatment bath a was measured as described above. No gas spots were detected in the fermenter, indicating that the nitrite concentration in the solution was less than 1 ppm. The contamination ratio in pretreatment bath a was 0.01:1.0 (see table 5).

A steel C panel was cleaned/degreased by immersion in a bath containing the cleaner composition described above (heated to 48.9 ℃ or 125 ° f) for 2 minutes, then rinsed with a deionized water spray for 30 seconds using a Melnor real-Trigger 7-Pattern nozzle set to a shower mode (available from Home Depot).

Next, the panels were immersed in pretreatment bath A for 2 minutes (ambient temperature (27 ℃ or 80 ℃ F.) and then rinsed with a deionized water spray for 30 seconds, as described above(model 078302-300-000) a high speed hand held blower that dried the panel with warm air at a high temperature setting of 50-55 deg.C (122-131 deg.F) until dry (1-5 minutes).

The weight percentages of zirconium and copper in the untreated steel C panel and in the film formed on the substrate surface after immersion in pretreatment bath a were measured using an Axios Max-Advance X-ray fluorescence (XRF) spectrophotometer (PANanytical, almento, the Netherlands). Table 6 shows the weight percentages of zirconium and copper on untreated steel C panels and in panels immersed in pretreatment bath a. Both zirconium and copper are deposited on the surface of the steel C panel immersed in the pretreatment bath a.

Example 2

To form a bath containing elevated nitrite levels (as may occur instantaneously as the substrate passes through the bath containing the pretreatment composition), pretreatment bath B was made by adding 2.0g of sodium nitrite (Fisher Scientific International, inc., Hampton, NH) to pretreatment bath a (the entire volume). The pH of pretreatment bath B was measured as described in example 1, and adjusted to 4.7 with nitric acid (fisher scientific international).

Pretreatment bath B contained 200ppm zirconium (calculated), 38ppm copper (calculated), and 110ppm free fluoride (measured as described in example 1). Using the technique described above, the gas point of pretreatment bath B was measured with a fermentation tube to be 3.0. The concentration of nitrite in the solution was 84 ppm. The contamination ratio was 0.82:1.0 (see table 5).

One panel of the steel C panel was cleaned/degreased as described in example 1. The panels were then immersed in pretreatment bath B at ambient temperature (27 ℃ or 80 ° f) for 2 minutes, and then rinsed and dried as described in example 1.

The weight percentages of zirconium and copper in the film formed on the substrate after immersion in pretreatment bath B were measured as described in example 1. As shown in table 6, the weight% of zirconium deposited on the surface of the steel C panel immersed in the pretreatment bath B was reduced by 32% compared to the panel immersed in the pretreatment bath a. These data indicate that the presence of nitrite in the pretreatment bath compromises the deposition of zirconium on steel C. That is, as the contamination ratio increases, the deposition of zirconium on the surface of the substrate decreases.

Example 3

To form a bath containing elevated nitrite levels (as may occur instantaneously as the substrate passes through the bath containing the pretreatment composition), pretreatment bath C was prepared by adding an additional 2.67g of sodium nitrite (new hampton, jejun hampton feishell scientific international) to pretreatment bath B (yielding a total of 4.67g of sodium nitrite). The pH of pretreatment bath B was measured as described in example 1, and adjusted to 4.7 with nitric acid (fisher scientific international).

Pretreatment bath C contained 200ppm zirconium (calculated), 38ppm copper (calculated), and 108ppm free fluoride (measured as described in example 1). Using the technique described above, the gas point of the pretreatment bath C was measured with a fermentation tube to be 7.0. The concentration of nitrite in the solution was 196 ppm. The contamination ratio was 2.0: 1.0.

Steel C panels were cleaned/degreased as described in example 1. The panels were then immersed in a pretreatment bath C (ambient temperature (27 ℃)) for 2 minutes, and then rinsed and dried as described in example 1.

The weight percentages of zirconium and copper in the film formed on the substrate after immersion in the pretreatment bath C were measured as described in example 1. As shown in table 6, the weight% of zirconium deposited on the surface of the steel C panel immersed in the pretreatment bath C was reduced by 98% compared to the panel immersed in the pretreatment bath a. The weight percentage of copper in the film formed on the substrate surface after immersion in the pretreatment bath C was reduced by 24%.

These data indicate that the presence of increased nitrite levels compared to zirconium in pretreatment bath B impairs the deposition of zirconium even further and reduces the deposition of copper on steel C. That is, as the contamination ratio increases, the deposition of zirconium and copper on the surface of the substrate decreases.

Example 4

To form a bath containing elevated nitrite levels (as may occur instantaneously as the substrate passes through the bath containing the pretreatment composition), pretreatment bath D was made by adding an additional 2.0g of sodium nitrite (new hampton, jejun hampton feishell international) to pretreatment bath C (yielding a total of 6.67g of sodium nitrite). The pH of pretreatment bath D was measured as described in example 1, and adjusted to 4.7 with nitric acid (fisher scientific international).

Pretreatment bath D contained 200ppm zirconium (calculated), 38ppm copper (calculated), and 110ppm free fluoride (measured as described in example 1). Using the technique described above, the gas point of pretreatment bath B was measured with a fermentation tube to be 10.0. The concentration of nitrite in the solution was 281 ppm. The contamination ratio was 2.8:1.0 (see table 5).

A steel C panel was cleaned/degreased as described in example 1. The panels were then immersed in pretreatment bath C at ambient temperature (27 ℃ or 80 ° f) for 2 minutes, and then rinsed and dried as described in example 1.

The weight percentages of zirconium and copper in the film formed on the substrate after immersion in the pretreatment bath D were measured as described in example 1. As shown in table 6, the weight% of zirconium deposited on the surface of the steel C panel immersed in the pretreatment bath D was reduced by 98% compared to the panel immersed in the pretreatment bath a. The weight percentage of copper in the film formed on the substrate surface after immersion in the pretreatment bath D was reduced by 75%. These data indicate that the presence of increased nitrite levels compared to nitrate in the pretreatment bath D impairs the deposition of zirconium and copper on steel C even further.

Example 5

To remove nitrites from pretreatment bath D, pretreatment bath E WAs prepared by adding a barium sulfamate solution (prepared by adding 30.6g barium hydroxide octahydrate (feishell scientific international) and 11.3g sulfamic acid (from Univar, Redmond, WA)) to 200mL deionized water) to pretreatment bath D. Within 5 minutes of the addition of the barium sulfamate solution, the pH of pretreatment bath E (measured as described in example 1) dropped to 2.6. Pretreatment bath E was circulated at room temperature (26.7 ℃, 80 ° f) for 1 hour using a submerged heater set to a high agitation mode (Polyscience Sous Vide Professional, model #7306AC1B5, available from Polyscience, Niles, Illinois). After addition of the barium sulfamate solution, gas gradually formed and a large amount of off-white precipitate formed, which was analyzed by Inductively Coupled Plasma (ICP) and identified as barium sulfate. Specifically, ICP analysis found less than 2ppm of soluble barium in bath E. The solid material contained 111ppm insoluble barium and 20ppm sulfur, which corresponds to the molecular composition of barium sulfate. The pH of the pretreatment bath E was measured again as described in example 1 and adjusted to 4.7 with nitric acid (fisher scientific international).

Pretreatment bath E contained 197ppm zirconium (calculated), 38ppm copper (calculated), and 110ppm free fluoride (measured as described in example 1). Using the technique described above, the gas point of pretreatment bath E was measured with a fermentation tube to be 0.0, which confirmed that all nitrite was consumed by the addition of barium sulfamate. Ion Chromatography (IC) analysis found less than 1ppm nitrite in bath E. The contamination ratio of bath E was less than 0.1: 1.0. No evidence of barium incorporation into the film was observed by XRF.

A steel C panel was cleaned/degreased as described in example 1. The panels were then immersed in a pretreatment bath E (ambient temperature (27 ℃)) for 2 minutes, and then rinsed and dried as described in example 1.

The weight percentages of zirconium and copper in the film formed on the substrate after immersion in the pretreatment bath E were measured as described in example 1. As shown in table 6, the weight% of zirconium deposited on the surface of the steel C panel immersed in the pretreatment bath E was partially restored, with a reduction of only 10% compared to the panel immersed in the pretreatment bath a, and compared to the 98% reduction seen in the pretreatment bath D (i.e. before the addition of barium sulfamate to the bath). Furthermore, as shown in table 6, the weight% of copper deposited on the surface of the steel C panel immersed in the pretreatment bath E was partially recovered, with a reduction of only 20% compared to the panel immersed in the pretreatment bath a, and compared to the 75% reduction seen in the pretreatment bath D (i.e. before the addition of barium sulfamate to the bath). These data indicate that the consumption of nitrite (i.e., reduction in the contamination ratio) by barium sulfamate at least partially restores the deposition of zirconium and copper onto the substrate surface.

Table 6: XRF measurements of control (untreated panel) and steel C panels treated in pretreatment baths A-E

Example 6

Pretreatment composition F was prepared by adding 11.0g of fluorozirconic acid (45 wt.% in water) (available from honeywell international, morris town, nj.), 12.0g of Chemfos AFL (commercially available from PPG industries), and 22.1g of copper nitrate solution (2 wt.% Cu solution, prepared by diluting copper nitrate solution (18 wt.% Cu in water), available from shepherd chemical, inc (cincinnati, oh)), and 6.7g of sodium nitrite (feishel scientific international), to 11.4L of deionized water. The pH of the bath was measured and adjusted to 4.7 as described in example 1.

Pretreatment bath F contained 200ppm zirconium (calculated), 36ppm copper (calculated), and 108ppm free fluoride (using a fluoride ion selective electrode ("ISE") equipped with a material available from Samer technology, supplied by VWR International Inc.)Orion Dual Star two-channel bench gauge measurement of fluoride ion selective combination electrodes). The gas point in pretreatment bath F (as described above) was measured to be 10.0. Pretreatment bath F contained 281ppm nitrite. The contamination ratio of the pretreatment bath F was 2.8: 1.0.

A steel C panel was cleaned/degreased as described in example 1, then immersed in pretreatment bath F at ambient temperature (27 ℃ or 80 ° F) for 2 minutes, and then rinsed and dried as described in example 1.

The weight percentages of zirconium and copper in the film formed on the substrate after immersion in the pretreatment bath F were measured as described in example 1. As shown in table 7, the weight% of zirconium deposited on the surface of the steel C panel immersed in the pretreatment bath F was 0.014 weight%. The weight% of copper in the film formed on the surface of the steel C panel immersed in the pretreatment bath F was 4.7 weight%.

Example 7

To remove nitrites from the pretreatment bath F, a pretreatment bath G was prepared by adding a strontium sulfamate solution (prepared by adding 25.4G of strontium hydroxide octahydrate (feishell scientific international) and 11.3G of sulfamic acid (redmond ewingier, washington) to 200mL of deionized water) to the pretreatment bath F. After addition of the strontium sulfamate solution, the pH of pretreatment bath G (measured as described in example 1) dropped to 2.6. Pretreatment bath G was circulated at room temperature (26.7 ℃, 80 ° f) for 1 hour using a submerged heater set to a high agitation mode (Polyscience Sous Vide Professional, model #7306AC1B5, available from nels scientific, illinois). After addition of the strontium sulfamate solution, gas gradually formed and a small amount of fluffy white precipitate formed. After 1 hour bath circulation, the pH was measured as described in example 1 and Chemfil buffer (PPG industries) adjusted the pH to 4.7.

Pretreatment bath G contained 160ppm zirconium (calculated), 38ppm copper (calculated), and 100ppm free fluoride (measured as described in example 1). The zirconium concentration and free fluoride concentration were adjusted to 200ppm and 108ppm, respectively, by adding fluorozirconic acid and Chemfos AFL (PPG industries, inc.) to the bath. IC analysis found less than 1ppm nitrite in bath F. The contamination ratio in the pretreatment bath G was less than 0.01: 1.0. No evidence of strontium incorporation into the film was observed by XRF.

A steel C panel was cleaned/degreased as described in example 1, then the panel (ambient temperature (27 ℃ or 80 ° f)) was immersed in a pretreatment bath G for 2 minutes, and then rinsed and dried as described in example 1.

The weight percentages of zirconium and copper in the film formed on the substrate after immersion in the pretreatment bath G were measured as described in example 1. As shown in table 7, the weight% of zirconium deposited on the surface of the steel C panel immersed in the pretreatment bath G was partially recovered, with a reduction of only 10% compared to the panel immersed in the pretreatment bath a, and compared to the 98% reduction seen in the pretreatment bath F (i.e. before the addition of strontium sulfamate to the bath). Furthermore, as shown in table 7, the weight% of copper deposited on the surface of the steel C panel immersed in the pretreatment bath G was partially recovered. These data indicate that the consumption of nitrite by strontium sulfamate restores the deposition of zirconium and copper onto the surface of steel C.

Table 7: XRF measurements of steel C panels treated in pretreatment baths F and G

Example 8

The pretreatment baths were prepared as described above, except on a 5 gallon scale (see table 8). After the sulfamate source was added to pretreatment baths F and G, the baths were stirred as described above for 1 hour, at which time the bath parameters were measured and determined to return to normal operating parameters (pH 4.7, 200ppm Zr, 35ppm Cu, 100ppm free fluoride). The panels were processed as described above and operated in quadruplicate.

Table 8: pretreatment conditions (example 8)

After drying, electrophoretic coating was performed with ED7000Z electrocoat available from PPG. The electrocoat was applied to a target 0.60 mil thick. The rectifier (Xantrex model XFR600-2) is set to a "coulomb control" setting. The conditions were set at 24 coulombs and 180V with a ramp time of 30 seconds. The electrocoat was held at 90 ℃ F. with a stirring speed of 340 rpms. After the electrocoat was applied, the panels were baked in an oven (Despatch LFD-1-42 type) at 177 deg.C (350F.) for 25 minutes. The coating thickness was measured using a film thickness gauge (Fischer Technologies) model FMP 40C.

The electrophoretically coated panel was drawn down the middle of the panel to the metal substrate with a 10.2cm vertical line. The panels were also subjected to scribe creep (scriber creep) blistering test using GM cycle corrosion test GMW14872 for 25 days. At the end of 25 days, the panel was removed and allowed to dry until the surface was free of visible water (about 1 hour at 25 ℃). Scotch 898 filament tape (commercially available from 3M company) was used to remove poorly adhering paint. Scribe creep (rust, darkened area or exposed metal substrate with coating lifted from the surface) measured from the affected paint on the left side of the scribe line to the affected paint on the right side of the scribe line is measured per cm along the scribe line forming a total of 10 measurement points. Thus, the average score creep reported in table 9 below was calculated using the average values of the panels. The measurements were made by using a Fowler Sylvac model S235 digital caliper.

Table 9: corrosion performance

Pretreatment examples/baths	Average scribe creep (mm)	Standard deviation of
			8/A	4.0	0.2
8/B	4.0	0.5
			8/C	12.41	0.7
8/D	15.82	1.9
			8/E	15.13	4.1
8/F	5.4	1.1
			8/G	4.0	0.3

¹Severe delamination.

²Significant edge corrosion and severe surface blistering.

³Significant edge corrosion.

The data in table 9 show that elevated nitrite levels (i.e., increased fouling ratio) in baths containing zirconium-based pretreatment compositions negatively impact the corrosion performance of steel C. The addition of the alkali metal sulfamate chemically reduces nitrite levels in the pretreatment bath (i.e., reduces the fouling ratio) and restores zirconium deposition and corrosion performance.

It will be appreciated by those skilled in the art that changes could be made to the embodiments described above without departing from the broad inventive concept thereof. It is understood, therefore, that this disclosure is not limited to the particular embodiments disclosed, but it is intended to cover modifications within the spirit and scope of the disclosed methods as defined by the appended claims.