WO2000039357A1

WO2000039357A1 - Composition and process for heavy zinc phosphating

Info

Publication number: WO2000039357A1
Application number: PCT/US1999/027956
Authority: WO
Inventors: Richard J. Church
Original assignee: Henkel Corporation
Priority date: 1998-12-23
Filing date: 1999-12-21
Publication date: 2000-07-06
Also published as: AU2348500A

Abstract

Addition of fluoride to a prior art heavy zinc phosphatizing composition that contains hydroxylamine yields a composition that will form high quality lubricant carrier phosphate conversion coatings at a lower temperature than does the prior art composition. A preferred working phosphatizing composition according to the invention comprises water, from 1.50 to 3.3 % of dissolved zinc cations; from 1.90 to 3.5 % of dissolved phosphate anions, from 2.10 to 4.0 % of nitrate anions, a source of from 0.020 to 0.07 % of hydroxylamine, from 0.14 to 0.32 % of dissolved fluoride, from 25 to 45 total acid points, and from 0.012 to 0.025 % of dissolved nickel cations.

Description

COMPOSITION AND PROCESS FOR HEAVY ZINC PHOSPHATING

BACKGROUND OF THE INVENTION

This invention relates to compositions and processes for forming, on a metallic substrate, a well known type of conversion coating called a "heavy zinc phosphate" coating, that is particularly suited to carrying a solid or liquid lubricant to facilitate cold working of the underlying metal by a process that requires relative motion of the lubricant-bearing conversion coating on the metal substrate with respect to a tool surface. More particularly, the invention relates to such processes and compositions that give satisfactory results at lower temperatures than are conventionally used in the prior art to form heavy zinc phosphate conversion coatings. One preferred embodiment of the prior art utilizes an aqueous phosphatizing liquid composition that contains at least 20 grams per liter (this unit of concentration being hereinafter usually abbreviated as "g/\") of zinc cations, at least 25 g/l of phosphate anions, at least 25 g/l of nitrate anions, at least 0.30 g/l of hydroxylamine or a source thereof, and at least 35 "points" of Total Acid (as defined later herein). Preferably, this type of phosphatizing composition also contains a relatively small concentration of nickel cations. An aqueous phosphatizing liquid composition of this type is conventionally maintained at a temperature of at least 76 °C during its contact with the substrate to be phosphatized and when so used provides a technically satisfactory heavy zinc phosphate layer to carry lubricant for cold working. However, the cost of this embodiment of the prior art is relatively high, in large part because of the energy cost of maintaining the high temperature required for its satisfactory use.

Accordingly, a major object of the present invention is to provide a satisfactory composition and process for heavy zinc phosphating to produce a good lubricant carrier coating at a lower temperature than the prior art method described immediately above. Except in the claims and the operating examples, or where otherwise expressly indicated, all numerical quantities in this description indicating amounts of material or conditions of reaction and/or use are to be understood as modified by the word "about" in describing the broadest scope of the invention. Practice within the numerical limits stated is generally preferred, however. Also, throughout the description, unless express- ly stated to the contrary: percent, "parts of", and ratio values are by weight or mass; the term "polymer" includes "oligomer", "copolymer", "terpolymer" and the like; the description of a group or class of materials as suitable or preferred for a given purpose in connection with the invention implies that mixtures of any two or more of the members of the group or class are equally suitable or preferred; description of constituents in chemical terms refers to the constituents at the time of addition to any combination specified in the description or of generation in situ within the composition by chemical reaction(s) noted in the specification between one or more newly added constituents and one or more constituents already present in the composition when the other constituents are added, and does not necessarily preclude unspecified chemical interactions among the constituents of a mixture once mixed; specification of constituents in ionic form additionally implies the presence of sufficient counterions to produce electrical neutrality for the composition as a whole and for any substance added to the composition; any counterions thus implicitly specified preferably are selected from among other constituents explicitly specified in ionic form, to the extent possible; otherwise such counterions may be freely selected, except for avoiding counterions that act adversely to an object of the invention; the word "mole" means "gram mole", and the word itself and all of its grammatical variations may by used for any chemical species defined by all of the types and numbers of atoms present in it, irrespective of whether the species is ionic, neutral, unstable, hypothetical, or in fact a stable neutral substance with well defined molecules; and the terms "solution", "soluble", "homogeneous", and the like are to be understood as including not only true equilibrium solutions or homogeneity but also dispersions that show no visually detectable tendency toward phase separation over a period of observation of at least 100, or preferably at least 1000, hours during which the material is mechanically undisturbed and the temperature of the material is maintained within the range of 18 - 25 °C. BRIEF SUMMARY OF THE INVENTION

It has surprisingly been found that an aqueous phosphatizing liquid composition that includes fluoride along with other conventional ingredients as described above, most of them preferably in smaller than conventional concentrations but with nickel preferably at higher than conventional concentrations, produces satisfactory heavy zinc conversion coatings at substantially lower temperatures than those conventionally used and in some instances also produces less sludge. DETAILED DESCRIPTION OF THE INVENTION Embodiments of the invention include processes for forming a phosphate conversion coating suitable for lubricant carrying; extended processes including other operations that may be conventional in themselves, before and/or after formation of a phosphate conversion coating according to the invention; working compositions for use in a process according to the invention; make-up concentrate compositions from which fresh working compositions may be obtained by mixing with water, and, optionally, other concentrate compositions; and replenisher compositions (usually concentrated) that are suitable for adding to used working compositions to restore their optimum concentrations of constituents initially present that are consumed during use by being incorporated into the conversion coatings formed and/or into sludge precipitating from the liquid working composition as a solid phase, or simply by decomposing. (Some compositions according to the invention may be any two or all of working, replenisher, or concentrate compositions according to this definition.)

Dissolved zinc cations are a necessary component of any composition according to the invention. These cations may be provided to a composition by mixing with water any water soluble source of zinc cations, such as a salt of zinc or, for a liquid water solu- tion also containing acid, zinc oxide or zinc hydroxide, which react to form a solution of a zinc salt. In view of the other necessary constituents of a composition according to the invention, preferred sources for the zinc cations are zinc salts of orthophosphoric acid, either added as such or prepared in situ by adding zinc oxide or hydroxide to a precursor solution already containing water and phosphoric acid. (For purposes of this description, unless explicitly noted or necessarily implied by the context to the contrary, the stoichiometric equivalent as orthophosphoric acid of any other oxyacid of phosphorus in which the phosphorus is in its +5 valance state is to be considered to be orthophosphoric acid. This applies for example to condensed phosphoric acids such as pyrophosphoric and tripolyphosphoric acids and to metaphosphoric acid. Also, all of these acids themselves and any anions that can be produced by total or partial neutralization of any of these acids are to be considered, to the extent of their stoichiometric equivalent as PO₄ ^-3, as "phosphate anions" as specified further below, irrespective of the actual degree of ioniza- tion and neutralization that may prevail in a particular liquid composition.)

In a working composition according to the invention, the concentration of zinc cations preferably is at least, with increasing preference in the order given, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.50, 1.60, 1.70, 1.80, 1.90, 1.95, or 2.00 percent of the total working composition and independently preferably is not more than, with increasing preference in the order given, 10, 8, 6.0, 5.0, 4.7, 4.4, 4.1 , 3.8, 3.5, 3.3, 3.1 , 2.9, 2.7, 2.5, 2.3, 2.20, 2.10, or 2.05 percent of the total working composition. A second necessary component of a composition according to the invention is dissolved orthophosphate anions, including the stoichiometric equivalent(s) as orthophosphate anions of orthophosphoric acid itself, any other oxyacid in which phosphorus is in its +5 valence state, and all wholly or partially neutralized salts of all such acids as already described in detail above. At least for economy, the phosphate anions are preferably provided to an aqueous phosphatizing liquid composition according to the invention by mixing with water and, optionally, other dissolved ingredients, orthophosphoric acid and/or one or more salts thereof. In a working aqueous phosphatizing liquid composition according to the invention, the concentration of orthophosphate anions and their stoichiometric equivalents as described above preferably is at least, with increasing preference in the order given, 0.3, 0.6, 0.9, 1.2, 1.5, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, or 2.60 percent of the total working composition and independently preferably is not more than, with increasing preference in the order given, 12, 10, 8, 7.0, 6.0, 5.0, 4.5, 4.0, 3.5, 3.3, 3.1 , 3.00, 2.90, 2.80, or 2.70 percent of the total working composition. Furthermore, independently of their actual concentrations, in a composition according to the invention the ratio of the concentration of these phosphate anions to the concentration of zinc cations, both being expressed in the same units, preferably is at least, with increasing preference in the order given, 0.50:1.00, 0.60:1.00, 0.70:1.00, 0.80:1.00, 0.90:1.00, 1.00:1.00, 1.10:1.00, 1.15:1.00, 1.20:1.00, or 1.25:1.00 and independently preferably is not more than, with increasing preference in the order given, 8.0:1.00, 5.0:1.00, 4.0:1.00, 3.0:1.00, 2.6:1.00, 2.4:1.00, or 2.2:1.00.

A third necessary component of an aqueous phosphatizing liquid composition according to this invention is dissolved nitrate anions, which are assumed to be present to their stoichiometric equivalent amount after dissolution in an aqueous phosphatizing liquid composition, or a precursor composition therefor, of nitric acid or any soluble nitrate salt. At least for economy, the nitrate anions are preferably supplied by nitric acid, except to whatever extent they may be alternatively supplied as counterions to other necessary or optional cations present in the same aqueous phosphatizing liquid composition. The total concentration of nitrate anions from all sources in a working aqueous phosphatizing liquid composition according to the invention preferably is at least, with increasing preference in the order given, 0.3, 0.6, 0.9, 1.2, 1.5, 1.70, 1.80, 1.90, 2.00, 2.10, 2.20, 2.30, 2.40, 2.50, 2.60, or 2.65 percent of the total working composition and independently preferably is not more than, with increasing preference in the order given, 12, 10, 8, 7.0, 6.0, 5.0, 4.5, 4.0, 3.5, 3.3, 3.1 , 3.00, 2.90, 2.80, or 2.70 percent of the total working composition. Furthermore, independently of their actual concentrations, in a composition according to the invention the ratio of the mass of nitrate anions to the mass of phosphate anions, both being expressed in the same units, preferably is at least, with increasing preference in the order given, 0.50:1.00, 0.60:1.00, 0.70:1.00, 0.80:1.00, 0.90:1.00, 0.94:1.00, 0.97:1.00, 1.00:1.00, or 1.02:1.00 and independently preferably is not more than, with increasing preference in the order given, 4.0:1.00, 3.0:1.00, 2.6:1.00, 2.4:1.00, 2.2:1.00, 2.0:1.00, 1.8:1.00, 1.6:1.00, 1.4:1.00, 1.20:1.00, 1.10:1.00, or 1.05:1.00. A fourth necessary component of a working aqueous phosphatizing liquid composition according to the invention is a dissolved source of hydroxylamine. Pure hydroxylamine itself is preferably not used as this source, although permissible, because it is often unstable because of spontaneous decomposition. A preferred source is a compound, 5 such as a hydroxylamine salt or complex, that provides hydroxylamine to the compositions in which it is dissolved, by dissociation to produce a relatively small concentration of free hydroxylamine in equilibrium with the hydroxylamine source. As free hydroxylamine is consumed by the chemical reactions that help to produce the desired phosphate coating on the treated metal substrates or even simply by spontaneous

10 decomposition, additional free hydroxylamine is then released to the solution by further dissociation of the hydroxylamine source(s). Suitable examples of hydroxylamine sources more stable than pure hydroxylamine itself include hydroxylamine phosphate, hydroxylamine nitrate, and hydroxylamine sulfate and oximes that hydrolyze readily in solution to produce hydroxylamine. At least for economy, hydroxylamine sulfate with the

15 chemical formula (NH₂OH)₂ ^»H₂SO₄, a compound readily available commercially, is the most preferred source and hereinafter is usually abbreviated as "HAS". Whatever the source, its stoichiometric equivalent as hydroxylamine preferably has a concentration in a working aqueous phosphatizing liquid composition according to the invention that is at least, with increasing preference in the order given, 0.0010, 0.0030, 0.0050, 0.0070,

20 0.0090, 0.010, 0.015, 0.020, 0.025, 0.030, or 0.035 percent of the total working composition and independently preferably is not more than, with increasing preference in the order given, 1.0, 0.80, 0.60, 0.50, 0.40, 0.30, 0.20, 0.17, 0.14, 0.11 , 0.09, 0.07, 0.05, or 0.040 percent of the total working composition.

A fifth necessary component of an aqueous phosphatizing liquid composition ac-

25 cording to the invention is dissolved fluoride. The fluoride component preferably is sourced to the composition by at least one of hydrofluoric acid, tetrafluoroboric acid,¹ hexafluorosilicic acid, and the water soluble salts, including partially neutralized salts, of all of these acids. In the immediately preceding list, the acids are in order of increasing preference, although there is relatively little preference between fluoroboric and fluorosil-

30 icic acids. For each particular acid, the acid itself and its salts produce substantially the same results, provided that the overall acidity of the compositions is properly adjusted as independently preferred. Dissolved fluoride anions are presumed to be present in their full stoichiometric equivalent amount in an aqueous phosphatizing liquid

'Acids such as trifluorohydroxy- and difluorodihydroxy-boric acids are considered equivalent to tetrafluoroboric acid but are less preferred because of their greater cost. composition whenever one or more of the above-noted acid or salt sources of fluoride anions are mixed with water and optionally other ingredients into a homogenous liquid composition, irrespective of the actual extent of ionization, neutralization, dissociation, or other reaction that may prevail in the liquid composition (unless, of course, after having been introduced into a liquid composition, such ingredients have been removed by some physical or chemical means such as ion-exchange, precipitation, or the like). For a composition to be used at about 60 °C as is generally preferred, the most preferred sources for the fluoride are alkali metal salts, or a combination of the acids corresponding to these anions with sufficient alkali metal base to at least partially neutralize the acids in situ. At substantially lower operating temperatures, however, manganese and ammonium salts produce higher quality coatings than alkali metal salts. When a combination of fluorine containing acid and an alkali metal base is used, the alkali metal base is preferably a carbonate, for economy and avoidance of the introduction of possibly problematic anions as would occur with most other salts, and avoidance of the disturbances in the FA and/or TA values that would be expected from introducing a stronger alkali metal base such as an alkali metal hydroxide into a composition according to the invention.

The concentration of fluoride in a working aqueous phosphatizing liquid composition according to the invention preferably is at least, with increasing preference in the order given, 0.020, 0.040, 0.060, 0.080, 0.10, 0.12, 0.14, 0.16, 0.18, or 0.20 percent of the total working composition and independently preferably is not more than, with increasing preference in the order given, 1.00, 0.70, 0.60, 0.50, 0.43, 0.37, 0.32, 0.28, 0.25, 0.23, or 0.21 percent of the total working composition.

The final necessary component in a composition according to the invention is a source of acid. As is customary in the art, concentrations of acid in a liquid composition according to the invention are measured in "points", which are defined in this instance as equal to the number of milliliters of 0.1 N strong hydroxide solution required to titrate a 5.00 milliliter sample of the composition to an end point of pH 8.2 for a value called "Total Acid", hereinafter usually abbreviated as 'TA", and to an end point of pH 3.8 for a value called "Free Acid", hereinafter usually abbreviated as "FA". (These end points may be measured with indicators or a pH meter, as known to those skilled in the art.) A working aqueous phosphatizing liquid composition according to this invention preferably has a TA value that is at least, with increasing preference in the order given, 5, 10, 15, 20, 25, 30, or 35 points and independently preferably is not more than, with increasing preference in the order given, 50, 45, or 40 points. Further and independently, in a working aqueous phosphatizing liquid composition according to the invention, there is a ratio between TA points and FA points that is at least, with increasing preference in the order given, 4.0:1.00, 5.0:1.00, 6.0:1.00, 6.5:1.00, 6.7:1.00, 6.90:1.00, or 7.00:1.00 and independently preferably is not more than, with increasing preference in the order given, 20:1.00, 15:1.00, 13:1.00, 11 :1.00, 10.0:1.00, 9.5:1.00, 5 9.0:1.00, or 8.5:1.00. Preferred sources of acid for compositions according to the invention are a combination of nitric acid and zinc dihydrogen phosphate, which supply other components (nitrate ions and zinc cations respectively) that are also needed in the compositions.

An optional component that is usually preferred in a composition according to the o invention is nickel(ll) cations. Any soluble nickel salt may be used as a source of these cations, which are presumed to be present to their full stoichiometrically possible extent from any salt of nickel(ll) cations dissolved in the composition, irrespective of the actual extent of ionization, complex formation, or the like that may prevail in the particular composition. The concentration of nickel cations in a working aqueous phosphatizing 5 liquid composition according to the invention preferably is at least, with increasing preference in the order given, 0.002, 0.004, 0.006, 0.008, 0.010, 0.012, or 0.014 percent of the total working composition and independently, particularly for economy and to reduce pollution and/or pollution abatement costs, preferably is not more than, with increasing preference in the order given, 0.10, 0.08, 0.06, 0.04, 0.03, 0.025, 0.020, or o 0.016 percent of the total working composition.

An optional component, which is almost always present after even a few minutes of use when a working aqueous phosphatizing liquid composition according to the invention is used to phosphatize a ferriferous metal surface, is dissolved iron cations. In this as in other phosphatizing compositions and processes, this optional component is a tol- 5 erated rather than preferred component in principle, but because its eventual presence is inevitable, a small amount of it is sometimes added at the beginning so that the initial coating characteristics will be more nearly identical to those that prevail later. A working aqueous phosphatizing liquid composition according to this invention can tolerate as much as 1 percent of the total working composition of dissolved iron cations without any serious loss of coating quality, more than would be expected for otherwise similar compositions without the fluorometallate component. Ordinarily, under practical conditions, dragout and precipitation of solid sludge containing some iron will keep the concentration of dissolved iron well below this level.

Another optionally tolerated component of an aqueous phosphatizing liquid com- position according to the invention is sulfate, which is generally regarded as an unfavorable constituent of any phosphatizing composition. However, because of the use of HAS as the preferred source of hydroxylamine, some accumulation of sulfate in a used aqueous phosphatizing liquid composition according to the invention is usual, and at least 0.5 percent of the total working composition of sulfate may be present in a working aqueous phosphatizing liquid composition according to this invention without causing any harm. A concentrate make-up composition according to the invention preferably contains all of the necessary ingredients of a working aqueous phosphatizing liquid composition according to the invention and nickel cations if the presence of that optional constituent is desired in the working aqueous phosphatizing liquid composition. Such a one-component concentrate, in order to achieve maximum economy in shipping costs compatible with storage stability, preferably contains each ingredient, for which a preferred value for its percentage in a total working composition is specified above, in a concentration in the concentrate composition that is at least, with increasing preference in the order given, 2, 4.0, 5.0, 6.0, 7.0, 8.0, or 9.0 times as great as the specification for the same degree of preference in a working aqueous phosphatizing liquid composition and independently preferably is not more than 12 times as great as the specification for the same degree of preference in a working aqueous phosphatizing liquid composition. A process according to the invention for forming a phosphate conversion coating does not require and normally preferably does not include any use of an externally imposed electromotive force such as would be used in plating or anodizing. Instead, con- tact between a working composition according to the invention and a substrate on which a phosphate conversion coating is to be formed is sufficient for the coating forming reaction to begin. During coating formation, the temperature of the aqueous phosphatizing liquid composition in contact with the substrate preferably is at least, with increasing preference in the order given, 49, 51 , 53, 55, 57, or 59 °C and independently preferably is not more than, with increasing preference in the order given, 74, 72, 70, 68, 66, 64, 62, or 60 °C.

The quality of a phosphate conversion coating for carrying lubricant for metal cold working depends primarily on the lubricant absorptivity and ductility of the coating and on the uniformity of these characteristics of the coating over its entire extent. Any non- uniformity of the coating that is readily perceptible on close examination with unaided normal human vision is normally disadvantageous and often entirely unsatisfactory for the most demanding uses. A minimum level of mass of the coating per unit area of substrate is required to obtain the best quality, and for this reason a zinc phosphate conversion coating produced in a process according to the invention preferably has a mass per unit area of substrate surface coated (a characteristic often called "coating weight" for brevity) that is at least, with increasing preference in the order given, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 10, or 12 grams of coating per square meter of substrate coated (hereinafter usually abbreviated as "g/m²). Considerably higher coating weights than this are, in principle, wasteful and unpreferred for that reason, but in many instances it has proved to be more economical in practice to accept somewhat higher average coating weights rather than risk having some parts of the substrate with too little coating for the best lubricity. Very high coating weights, however, can reduce technical effectiveness of the coatings as lubricant carriers, inasmuch as they may have inferior morphological characteristics of the outer part of the coating which carries most of the lubricant. Therefore, the coating weight produced in a process according to the invention independently preferably is not more than, with increasing preference in the order given, 200, 120, 80, 60, 45, or 35 g/m², and for economy still more preferably is not more than 29 g/m². The coating weight may be measured by means well known in the art, for example, by mass difference of a coated substrate sample before and after a coating stripping treatment in a solution containing 200 grams of CrO₃ per liter in water. The time of contact between the aqueous phosphatizing liquid composition and the substrate being coated in a process according to the invention is less important to the quality of coating achieved than are the temperature and coating weight, but as a general guideline, this contact time preferably is at least, with increasing preference in the order given, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, or 4.5 minutes (hereinafter usually abbreviated as "min") and independently preferably is not more than, with increasing preference in the order given, 60, 40, 20, or 10 min.

As a freshly prepared aqueous phosphatizing liquid composition according to the invention is used, at least its contents of zinc cations and phosphate anions are depleted to form the conversion coating, and these and other constituents of the composition may also be depleted for various other reasons such as physical loss by dragout on coated substrates, spontaneous decomposition, and the like. Continued operation eventually requires replenishment of these lost materials in order for the process to continue to produce conversion coatings at all, and optimum results are promoted by frequent replenishment, carefully adjusted to maintain the favorable initial characteristics of a freshly prepared aqueous phosphatizing liquid composition according to the invention as closely as possible. Under most operating conditions, all or nearly all of the replacement ingredients needed can be and preferably are supplied in a single liquid replenisher concentrate composition. The exact optimum concentrations for the replenisher concentrate will vary slightly with operating conditions of a process according to the invention, but for most conditions using a working composition according to the invention in which (i) the fluoride component is exclusively sourced from fluorosilicic acid and (ii) there is a concentration of 0.015 % of nickel cations, a preferred replenisher concentrate liquid preferably comprises, more preferably consists essentially of, or still more preferably consists of, water and:

(A) zinc cations in a concentration of at least, with increasing preference in the order given, 20, 40, 60, 80, 90, 100, or 110 parts per thousand of the total replenisher concentrate;

(B) orthophosphoric acid in a concentration that is at least, with increasing preference in the order given, 50, 80, 110, 140, 170, 200, 220, 230, 250, 260, 270, 280, or 290 parts per thousand of the total replenisher concentrate; (C) nitric acid in a concentration that is at least, with increasing preference in the order given, 10, 20, 30, 40, 50, 55, 60, 65, 70, 75, 80, 85, or 90 parts per thousand of the total replenisher concentrate;

(D) a hydroxylamine source in a concentration corresponding stoichiometrically to at least, with increasing preference in the order given, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 parts per thousand of the total replenisher concentrate of HAS;

(E) fluorosilicic acid in a concentration that is at least, with increasing preference in the order given, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, 9.0, 9.5, 10.0, 10.5, or 11.0 parts per thousand of the total replenisher concentrate; and

(F) nickel cations in a concentration that is at least, with increasing preference in the order given, 0.03, 0.05, 0.07, 0.09, 0.11 , 0.13, 0.15, 0.17, 0.19, or 0.21 parts per thousand of the total replenisher concentrate; and, optionally,

(G) an alkali metal base in an amount sufficient to neutralize completely at least, with increasing preference in the order given, 5, 10, 5, 20, 25, 30, or 35 % of the fluorosilicic acid contained in the total replenisher concentrate. If other fluoride sources are used instead of or in addition to fluorosilicic acid, these preferences should be adjusted so that the same concentrations of fluoride will be present as with the explicit numbers above for fluorosilicic acid as the only fluoride source. Independently, if the aqueous phosphatizing liquid composition being replenished does not contain nickel cations, the replenisher used for it also preferably does not contain nickel cations. Otherwise, the preferences given last above also apply to replenisher concentrates for these types of working compositions according to the invention.

Single package replenisher concentrates as described above are preferred primarily for convenience, and it is technically satisfactory to supply individual components needed for replenishment, or to combine some of the components into two or more dis- tinct concentrates for use together in replenishing.

This invention may be applied to any substrate that is suitable for phosphatizing, including most alloys that are predominantly constituted of any one or more of iron, zinc, and aluminum. However, it is most preferably applied to cold rolled steel.

The invention and its benefits compared with prior art may be further appreciated from the following working examples and comparison examples. EXAMPLE AND COMPARISON EXAMPLE GROUP 1

In this group, conditions of commercial operation were simulated in a laboratory by processing cold rolled steel panel substrates through a working aqueous phosphatizing liquid composition at a certain rate of substrate surface area/volume of phosphatizing composition/hour, with replenishment of the bath at regular intervals. Two types of substrates were used, Types 1008 and 4130 cold rolled steel, both in the form of conventional rectangular test sheets with dimensions 10 x 15 centimeters. For substrates, called "one-pass substrates", on which the characteristics of the coating were to be carefully evaluated, the following process sequence was used:

1. Clean by immersion in a cleaning solution in water containing 30 grams of PARCO® Cleaner 2077X (a commercial product of the Henkel Surface Technologies

Div. of Henkel Corporation, Madison Heights, Michigan) per liter of solution, the cleaning solution being maintained during its use at a temperature of 88 °C and immersion being continued for 10 min.

2. Rinse with hot tap water for 0.50 min. 3. Pickle by immersion in a solution containing 10 % by volume of concentrated sulfuric acid in water, the pickling solution being maintained during pickling at a temperature of 71 °C and pickling being continued for 5 min.

4. Rinse with cold tap water for 0.50 min.

5. Form phosphate coating, according to details as given further below. 6. Rinse with cold tap water for 0.50 min.

7. Blow dry with compressed air.

The one-pass substrates were processed in sets, each of which consisted of two 1008 alloy panels and one 4130 alloy panel, all held on a rack and run simultaneously.

In addition to the one-pass substrates, other substrate panels called "multiple- pass substrates" were processed simply to simulate extensive use of the aqueous phosphatizing liquid composition. Each set of multiple-pass substrates consisted of a rack of three 1008 alloy panels. The same rack and panels were cycled through the composition several times. The first time through, each set of multiple-pass substrates was processed according to the first six steps of the process for one-pass substrates as described above and set aside until the next use. In subsequent cycles of the multiple- pass substrates, only steps 3 through 5 as defined above were performed, and the time for pickling step 3 was reduced to 0.50 min.

The first set of substrate panels to be processed through each freshly prepared aqueous phosphatizing liquid composition was a set of one-pass substrates. This was followed by 19 sequences of processing multiple-pass substrates. Processing was timed so that one rack of panels would be phosphated every 20 minutes. Each rack held substrates having a total area of 9.3 square decimeters (hereinafter usually abbreviated as "dm²") and there were 4.0 liters of aqueous phosphatizing liquid composition, so that there was a throughput rate of approximately 7.4 dm² of substrate surface per liter of composition per hour of operation in this manner. After 20 racks of substrate samples had been phosphatized, the aqueous phosphatizing liquid composition was replenished to a preselected target value for TA points, using one or more replenisher concentrates as described in detail further below. A small sample of the aqueous phosphatizing liquid composition was then taken for analysis of its contents of zinc cations, nickel cations, phosphate anions, nitrate anions, sulfate an- ions, sodium cations, iron cations, silicon, fluorine, and hydroxylamine. The remainder of the replenished aqueous phosphatizing liquid composition was then used to phospha- tize 20 additional rack loads of substrate samples as before: first a rack of single pass substrate samples and then one rack of new multi-pass substrate samples passed through the same volume of aqueous phosphatizing liquid composition 19 successive times.

This sequence was repeated until a total of 100 rack loads of substrate samples had been passed through the volume of aqueous phosphatizing liquid composition and the volume had been replenished after phosphatizing the 100th rack load. One more rack, the 101 st, of one-pass substrates was then processed. After this, further phospha- tizing with this particular aqueous phosphatizing liquid composition was discontinued. The volume of sludge in each container for a particular aqueous phosphatizing liquid composition was then recorded and the containers set aside to stand for at least 24 hours. The volume of sludge was then again recorded to determine whether it had compacted spontaneously during this period. The sludge was then collected by gravity filtration through qualitative filter paper. The collected sludge was rinsed with deionized water and dried for 24 hours at 49 °C, weighed, and analyzed for its contents of zinc, iron, phosphate, and fluorosilicate.

Three working compositions, the first of which is a comparison example, were prepared from zinc dihydrogen phosphate, concentrated nitric acid, zinc nitrate solution, nickel nitrate solution, hydroxylamine sulfate, and, where indicated, fluorosilicic acid and sodium carbonate, to have the characteristics shown in Table 1 below. Comparison 1 was used at 82 °C for 6 min, Example 1 was used at 49 °C for 10 min, and Example 2 was used at 60 °C for 10 min for each phosphating step. The constituents of the replenisher concentrates used with each working composition are shown in Table 2 below. In both Tables 1 and 2, the balance not shown was water and, for Table 1 only, counterions.

Analyses from the aging study are shown in Tables 3, 4, and 5 for Comparison 1 , Example 1 , and Example 2 respectively. (The entry "n.m." in these tables means "not measured".) The coating weights obtained on Type 1008 and Type 4130 substrates are shown in Tables 6 and 7 respectively. All of the coatings reported in these two Tables appeared to be complete and uniformly dense on examination with unaided normal human vision, except where noted to the contrary in a footnote to the Tables. (Explanations of footnotes for both Tables are given as part of Table 6.) Sludge quantities and analyses are shown in Table 8.

One additional comparison and one additional example according to the invention were performed after the 101 st rack load had been processed for Comparison 1 and Example 1 : The temperature of each composition was changed to 60 °C, and one more rack load of one-pass substrates was processed, with the resulting coating weights determined and visual observations made. At this temperature, Comparison 1 produced a coating weight of 11 g/m² on Type 1008 steel substrates and a coating weight of only 0.65 g/m² on Type 4130 steel substrates. The first of these coatings was visibly non-uniform in crystal density and the second one had numerous void areas. In contrast, Example 1 produced coatings with visual uniformity at this temperature, considerably better than it had at a lower temperature. The coating weights from Example 1 at 60 °C were 16.8 g/m² on Type 1008 steel substrates and 13.1 g/m² on Type 4130 steel substrates.

Table 1

Table 2

Footnotes for Table 2

^♦'Contained 14.7 % of Zn *²Containedl4.0%ofNi

Table 3: ANALYSES FOR COMPARISON 1 AGING

Table 4: ANALYSES FOR EXAMPLE 1 AGING

Table 5: ANALYSES FOR EXAMPLE 2 AGING

Table 6: COATING WEIGHTS ON TYPE 1008

Footnotes for Tables 6 and 7

*These surfaces had areas of non-uniform crystal density, giving the appearance of waves or wisps, visible on examination with unaided normal human vision.

**These surfaces had uncoated areas apparent on visual examination with normal unaided human vision. Table 7: COATING WEIGHTS ON TYPE 4130

Table 8

Table 9

GROUP 2

In this group the substrates were cold rolled steel. The processing sequence consisted of the following steps: 1. Clean by immersion in a cleaning solution in water containing 30 grams of PARCO® Cleaner 2077X (a commercial product of the Henkel Surface Technologies Div. of Henkel Corporation, Madison Heights, Michigan) per liter of solution, the cleaning solution being maintained during its use at a temperature of 88 °C and immersion being

5 continued for 5 min.

2. Rinse with hot tap water for 0.50 min.

3. Pickle by immersion in a solution containing 10 % by volume of concentrated sul- furic acid in water, the pickling solution being maintained during pickling at a temperature of 71 °C and pickling being continued for 5 min. ιo 4. Rinse with cold tap water for 0.50 min.

5. Form phosphate coating, by immersion for 5 min, with other composition and process characteristics as given further below.

6. Rinse with cold tap water for 0.50 min.

7. Blow dry with compressed air.

15 The working phosphatizing compositions used contained ingredients as shown in Table 10 below. (In Table 10, "Comp. No." means "Composition Number".) The cations and anions shown as ingredients in Table 10 were supplied from the same sources as in Group 1. The compositions shown in Table 10 were used in phosphatizing as described in more detail in Table 11 , which also shows the coating weights and visually rated sur-

20 face quality of the coatings formed. It is clear that the coatings are of higher quality when the fluorosilicate salts are present.

GROUP 3

These tests were performed in the same manner as for Group 1 , except as noted below. Only one principal replenisher composition and one working phosphatizing composition were used. Their ingredients, except for water which formed the unspecified balance of each composition, are shown in Table 12 below. Table 12

Footnotes for Table 12

^♦'Contained 14.7 % of Zn *²Contained 14.0 % of Ni

*These ingredients were not added specifically to the working composition, but were present in the make-up concentrate that was added. (Nickel nitrate solution was present in the make-up concentrate and was also added separately to increase its concentration in the working composition.)

The contact time for phosphating was 5 min and the temperature of the working phosphatizing composition during phosphating was maintained at 60 °C. The phosphatizing composition was replenished by adding 3 milliliters of the above replenisher after every rack of panels. After 20 rack loads had been processed, it was observed that the total acid was rising. Therefore, the replenishment with 3 milliliters of the replenisher concentrate shown above was supplemented with 1.0 gram of a 4.1 % solution of sodium carbonate in water. (This amount of soda ash is stoichiometrically just sufficient to neutralize the hydrofluorosilicic acid in 3 milliliters of replenisher.) After 60 rack loads had been processed, it was observed that the total acid was falling and the ratio rising; thereafter, the amount of soda ash solution added per replenishment was reduced to 0.5 gram.

Results for total acid, acid ratio, % iron, % HAS, and coating weights for both 1008 and 4130 alloy panels are given in Table 13 below. Coatings in all cases were complete and uniformly dense with the exception of the starting panels, which had a somewhat wispy appearance.

GROUP 4

In this group the substrates were Type 1008 cold rolled steel. The processing sequence consisted of the following steps:

1. Clean by immersion in a cleaning solution in water containing 45 grams of PARCO® Cleaner 2077X (a commercial product of the Henkel Surface Technologies Division of Henkel Corporation, Madison Heights, Michigan) per liter of solution, the cleaning solution being maintained during its use at a temperature of 88 °C and immersion being continued for 5 min.

2. Rinse with hot tap water for 0.50 min. 3. Pickle by immersion in a solution containing 10 % by volume of concentrated sul- furic acid in water, the pickling solution being maintained during pickling at a temperature of 71 °C and pickling being continued for 5 min.

4. Rinse with cold tap water for 0.50 min.

5. Form phosphate coating, by immersion for 5 min at 60 °C, with other composition and process characteristics as given further below.

6. Rinse with cold tap water for 0.50 min.

7. Blow dry with compressed air.

Two starting working compositions, each with a volume of 3.8 liters, were prepared. These were not compositions according to the invention, but a part of each of them was made into several compositions according to the invention by additions of fluoride later. The starting working compositions had the ingredients shown in Table 14, in addition to water as the otherwise unspecified balance. In Table 14, "Make-Up Concentrate 3" had the same ingredients as are given in Table 12.

Each of starting working compositions 4.1 and 4.2 was used as the first working composition for a phosphatizing operation on a rack of three panel substrates with a total substrate surface area of 9.3 dm². After one rack had been phosphated, a sufficient amount of sodium fluoride solution in water (prepared by adding to commercial 48 % HF

Table 14

Footnote for Table 14

*Contained l4.0 % of Ni solution in water an amount of sodium carbonate that was just sufficient stoichiometrically to neutralize the HF) to make the fluoride content in the working phosphatizing composition 0.10 grams per liter was added to each starting working composition to make a new working composition, after which another rack of substrates was phosphatized. This process was continued, phosphatizing one rack of substrates for each altered concentration of fluoride, to produce the phosphatized panels described in Table 15.

Table 15

Key to Appearance Ratings "X" means "Non-uniform crystal density, with a wispy appearance but no blush". "+" means "Complete, uniformly dense coating, with no blush or void". "X +" means "Complete and almost uniformly dense coating, with a very slightly wispy appearance."

Claims

1. An acidic aqueous liquid composition that is suitable, either directly or after dilution with water, to phosphatize a metal surface by spontaneous chemical reaction therewith, said composition comprising water and:

(A) at least 0.4 % of dissolved zinc cations;

(B) at least 0.9 % of dissolved phosphate anions;

(C) at least 0.9 % of dissolved nitrate anions;

(D) a dissolved source of at least 0.003 % of hydroxylamine; and (E) at least 0.060 % of dissolved fluoride.

2. A liquid composition according to claim 2, wherein: there is a concentration of dissolved zinc cations that is from 0.8 to 6.0 %; there is a concentration of dissolved phosphate anions that is from 1.2 to 6.0 %; there is a concentration of nitrate anions that is from 1.5 to 6.0 %; - there is a dissolved source of from 0.010 to 0.30 % of hydroxylamine; and there is a concentration of dissolved fluoride that is from 0.080 to 0.60 %.

3. A liquid composition according to claim 2, wherein: there is a ratio of the percent concentration of dissolved phosphate anions to the percent concentration of dissolved zinc cations that is from 0.70:1.00 to 5.0:1.00; - there is a ratio of the percent concentration of dissolved nitrate anions to the percent concentration of dissolved phosphate anions that is from 0.50:1.00 to 2.4:1.00; and the composition has from 5 to 50 total acid points and has a ratio of total acid points to free acid points that is from 4.0:1.00 to 20:1.00.

4. A liquid composition according to claim 3, wherein there is a concentration of dissolved nickel cations that is from 0.006 to 0.10 % of the total composition.

5. A liquid composition according to claim 4, wherein: there is a concentration of dissolved zinc cations that is from 1.50 to 3.3 %; there is a concentration of dissolved phosphate anions that is from 1.90 to 3.5 %; there is a concentration of nitrate anions that is from 2.10 to 4.0 %; there is a dissolved source of from 0.020 to 0.07 % of hydroxylamine; there is a concentration of dissolved fluoride that is from 0.14 to 0.32 %; there is a ratio of the percent concentration of dissolved phosphate anions to the percent concentration of dissolved zinc cations that is from 1.20:1 .00 to 2.2:1.00; there is a ratio of the percent concentration of dissolved nitrate anions to the percent concentration of dissolved phosphate anions that is from 0.90:1.00 to 1.4:1.00; the composition has from 25 to 45 total acid points and has a ratio of total acid points to free acid points that is from 6.0:1.00 to 9.0:1.00; there is a concentration of dissolved nickel cations that is from 0.012 to 0.025 % of the total composition.

6. A liquid composition according to claim 1 that is suitable after dilution with water to phosphatize a metal surface by spontaneous chemical reaction therewith, wherein: - there is a concentration of dissolved zinc cations that is at least 8.9 %; there is a concentration of dissolved phosphate anions that is at least 11.3 %; there is a concentration of nitrate anions that is at least 12.5 %; there is a dissolved source of at least 0.12 % of hydroxylamine; there is a concentration of dissolved fluoride that is at least 0.83 %; - there is a ratio of the percent concentration of dissolved phosphate anions to the percent concentration of dissolved zinc cations that is from 1.20:1.00 to 2.2:1.00; there is a ratio of the percent concentration of dissolved nitrate anions to the percent concentration of dissolved phosphate anions that is from 0.90:1.00 to

1.4:1.00; and - there is a concentration of dissolved nickel cations that is at least 0.108 % of the total composition.

7. A liquid composition according to claim 1 that is a replenisher concentrate, said replenisher concentrate comprising water and:

(A) dissolved zinc cations in a concentration of at least 90 parts per thousand of the total replenisher concentrate;

(B) orthophosphoric acid in a concentration that is at least 220 parts per thousand of the total replenisher concentrate;

(C) nitric acid in a concentration that is at least 60 parts per thousand of the total replenisher concentrate; (D) a hydroxylamine source in a concentration corresponding stoichiometrically to at least 35 parts per thousand of the total replenisher concentrate of HAS;

(E) fluorosilicic acid in a concentration that is at least, with increasing preference in the order given, 7.0 parts per thousand of the total replenisher concentrate; and

(F) nickel cations in a concentration that is at least 0.13 parts per thousand of the total replenisher concentrate; and, optionally, (G) an alkali metal base in an amount sufficient to neutralize completely at least 25 % of the fluorosilicic acid contained in the total replenisher concentrate.

8. An acidic aqueous liquid composition that is suitable either directly or after dilution with water to phosphatize a metal surface by spontaneous chemical reaction therewith, said composition having been made by mixing with water at least the following components:

(A) a source of zinc cations that provided to the acidic aqueous liquid composition at least 0.4 % of dissolved zinc cations;

(B) a source of phosphate anions that provided to the acidic aqueous liquid composi- tion at least 0.9 % of dissolved phosphate anions;

(C) a source of nitrate anions that provided to the acidic aqueous liquid composition at least 0.9 % of dissolved nitrate anions;

(D) a source of hydroxylamine that provided to the acidic aqueous liquid composition at least 0.003 % of dissolved hydroxylamine; and (E) a source of fluoride anions that provided to the acidic aqueous liquid composition at least 0.060 % of dissolved fluoride anions.

9. A liquid composition according to claim 8, wherein, at the time of mixing to make the composition: all sources of zinc cations that were mixed with water to make the composition provided dissolved zinc cations in an amount that was from 0.8 to 6.0 % of the total composition; all sources of phosphate anions that were mixed with water to make the composition provided dissolved phosphate anions in an amount that was from 1.2 to 6.0 % of the total composition; - all sources of nitrate anions that were mixed with water to make the composition provided dissolved nitrate anions in an amount that was from 1 .5 to 6.0 % of the total composition; all sources of hydroxylamine that were mixed with water to make the composition provided hydroxylamine in an amount that was from 0.010 to 0.30 % of the total composition; and all sources of dissolved fluoride that were mixed with water to make the composition provided fluoride anions in an amount that was from 0.080 to 0.60 % of the total composition.

10. A liquid composition according to claim 9, wherein the amounts of all of the sources of zinc cations, phosphate anions, nitrate anions, and acid mixed with water to make the composition were such that, at the time of mixing: there was a ratio of the mass of dissolved phosphate anions provided to said composition to the mass of dissolved zinc cations provided to said composition that was from 0.70:1.00 to 5.0:1.00; - there was a ratio of the mass of dissolved nitrate anions provided to said composition to the mass of dissolved phosphate anions provided to said composition that was from 0.50:1.00 to 2.4:1.00; and the composition had from 5 to 50 total acid points and had a ratio of total acid points to free acid points that was from 4.0:1 .00 to 20:1.00.

1 1 . A liquid composition according to claim 10, wherein there was additionally mixed to make said composition one or more sources of nickel cations, all of such sources having provided to the composition a concentration of dissolved nickel cations that was from 0.006 to 0.10 % of the total composition.

12. A liquid composition according to claim 1 1 , wherein, at the time of mixing to make the composition: all sources of zinc cations that were mixed with water to make the composition provided dissolved zinc cations in an amount that was from 1 .50 to 3.3 % of the total composition; all sources of phosphate anions that were mixed with water to make the compo- sition provided dissolved phosphate anions in an amount that was from 1 .90 to

3.5 % of the total composition; all sources of nitrate anions that were mixed with water to make the composition provided dissolved nitrate anions in an amount that was from 2.10 to 4.0 % of the total composition; - all water-soluble sources of hydroxylamine that were mixed to make the composition provided to the composition an amount of hydroxylamine that was from 0.020 to 0.07 % of the total liquid composition; all sources of fluoride that were mixed with water to make the composition provided dissolved fluoride anions in an amount that was from 0.14 to 0.32 % of the total composition; the amounts of all of the sources of zinc cations, phosphate anions, nitrate anions, and acid mixed with water to make the composition were such that, at the time of mixing: there was a ratio of the mass of dissolved phosphate anions provided to the composition to the mass of dissolved zinc cations provided to the composition that was from 1.20:1.00 to 2.2:1.00; there was a ratio of the percent concentration of dissolved nitrate anions to the percent concentration of dissolved phosphate anions that was from 0.90:1.00 to 1.4:1.00; ~ the composition had from 25 to 45 total acid points and had a ratio of total acid points to free acid points that was from 6.0:1 .00 to 9.0:1.00; all sources of dissolved nickel cations that were mixed with water to make the composition provided dissolved nickel cations in an amount that was from 0.012 to 0.025 % of the total composition.

13. A liquid composition according to claim 8 that is suitable after dilution with water to phosphatize a metal surface by spontaneous chemical reaction therewith, wherein, at the time of mixing to make the composition: all sources of zinc cations that were mixed with water to make the composition provided dissolved zinc cations in an amount that was at least 8.9 % of the total composition; all sources of phosphate anions that were mixed with water to make the composition provided dissolved phosphate anions in an amount that was at least 1 1 .3 % of the total composition; all sources of nitrate anions that were mixed with water to make the composition provided dissolved nitrate anions in an amount that was at least 12.5 % of the total composition; all water-soluble sources of hydroxylamine that were mixed to make the composition provided to the composition an amount of hydroxylamine that was at least 0.12 % of the total liquid composition; - all sources of fluoride that were mixed with water to make the composition provided dissolved fluoride anions in an amount that was at least 0.83 % of the total composition; the amounts of all of the sources of zinc cations, phosphate anions, and nitrate anions mixed with water to make the composition were such that, at the time of mixing: there was a ratio of the mass of dissolved phosphate anions provided to the composition to the mass of dissolved zinc cations provided to the composition that was from 1.20:1.00 to 2.2:1 .00; there was a ratio of the percent concentration of dissolved nitrate anions to the percent concentration of dissolved phosphate anions that was from

0.90:1.00 to 1 .4:1.00; all sources of dissolved nickel cations that were mixed with water to make the composition provided dissolved nickel cations in an amount that was at least 0.072 % of the total composition.

14. A liquid composition according to claim 8 that is a replenisher concentrate, wherein, at the time of mixing to make the replenisher concentrate, there were mixed with water:

(A) one or more sources of zinc cations in an amount sufficient to supply dissolved zinc cations in a concentration of at least 90 parts per thousand of the total replenisher concentrate; (B) orthophosphoric acid to constitute at least 220 parts per thousand of the total replenisher concentrate;

(C) nitric acid to constitute at least 60 parts per thousand of the total replenisher concentrate;

(D) a water soluble hydroxylamine source in a concentration corresponding stoichio- metrically to at least 35 parts per thousand of the total replenisher concentrate of HAS;

(E) fluorosilicic acid to constitute at least 7.0 parts per thousand of the total replenisher concentrate; and, optionally, one or both of the following components:

(F) one or more water soluble sources of nickel cations to provide to the replenisher concentrate a concentration of dissolved nickel ions that is at least 0.13 parts per thousand of the total replenisher concentrate; and

(G) an alkali metal base in an amount sufficient to neutralize completely at least 25 % of the fluorosilicic acid supplied to the total replenisher concentrate.

15. A process of phosphatizing a metal substrate, said process comprising an opera- tion of contacting said metal substrate with a phosphatizing composition according to any one of claims 1 through 5 and 8 through 12, while the phosphatizing composition is maintained during said contacting at a temperature of at least 49 °C.

16. A process according to claim 15, wherein a phosphate conversion coating having a coating weight of at least 8.0 g/m² is formed on the metal substrate by the end of the process.

17. A process according to claim 16, wherein the phosphatizing composition is maintained during said contacting at a temperature that is from 55 to 70 °C.

18. A process according to claim 15, wherein the phosphatizing composition is maintained during said contacting at a temperature that is from 55 to 70 °C.