Methods and Compositions for Acid Treatment of a Metal Surface

Abstract

The invention relates to compositions and methods that are useful in etching a metal surface. In particular, the invention relates to novel acid compositions and methods of using such compositions in etching a metal surface, preferably an aluminum surface prior to anodizing to dissolve impurities, imperfections, scale, and oxide. The compositions are effective in maintaining their etching capacity and in removing smut produced by the etching of a surface as well as in general cleaning.

Claims

1. (canceled)

2. A composition consisting essentially of: (a) one or more fluoride ion compounds; and (b) one or more grain refiners.

3. The composition according to claim 2, consisting essentially of ammonium bifluoride and diammonium phosphate.

4. The composition according to claim 2, consisting essentially of ammonium bifluoride and a mixture of ammonium phosphate and diammonium phosphate.

5. A composition consisting essentially of: (a) about 20 to about 80 grams per liter of ammonium bifluoride; and (b) about 1 to about 50 grams per liter of diammonium phosphate or a mixture of ammonium phosphate and diammonium phosphate.

6. The composition according to claim 5, which has a pH of about 2 to about 5.

7. The composition according to claim 5, consisting essentially of about 5 to about 30 grams per liter of diammonium phosphate or a mixture of ammonium phosphate and diammonium phosphate.

8. The composition according to claim 7, consisting essentially of about 10 to about 20 grams per liter of diammonium phosphate or a mixture of ammonium phosphate and diammonium phosphate.

9. The composition according to claim 5, consisting essentially of about 60 to 70 grams per liter of ammonium bifluoride.

10. The composition according to claim 5, consisting essentially of: (a) about 20 to about 80 grams per liter of ammonium bifluoride; and (b) about 1 to about 50 grams per liter of diammonium phosphate.

11. The composition according to claim 10, which has a pH of about 2 to about 5.

12. The composition according to claim 10, consisting essentially of about 5 to about 30 grams per liter of diammonium phosphate.

13. The composition according to claim 12, consisting essentially of about 10 to about 20 grams per liter of diammonium phosphate.

14. The composition according to claim 10, consisting essentially of about 60 to 70 grams per liter of ammonium bifluoride.

15. A composition consisting essentially of: (a) about 20 to about 80 grams per liter of ammonium bifluoride; (b) about 1 to about 50 grams per liter of diammonium phosphate or a mixture of ammonium phosphate and diammonium phosphate; and (c) water.

16. The composition according to claim 5, consisting essentially of: (a) about 20 to about 80 grams per liter of ammonium bifluoride; (b) about 1 to about 50 grams per liter of diammonium phosphate; and (c) water.

17. The composition according to claim 15, which has a pH of about 2 to about 5.

18. The composition according to claim 15, consisting essentially of about 5 to about 30 grams per liter of diammonium phosphate.

19. The composition according to claim 18, consisting essentially of about 10 to about 20 grams per liter of diammonium phosphate.

20. The composition according to claim 15, consisting essentially of about 60 to 70 grams per liter of ammonium bifluoride.

Description

DETAILED DESCRIPTION OF THE INVENTION

Definitions

[0022] As used herein and unless otherwise indicated, the term “alkyl” or “alkyl group” means a saturated, monovalent, unbranched (i.e., linear) or branched hydrocarbon chain. An “alkyl group” further means a monovalent group selected from (C.sub.1-C.sub.8)alkyl, (C.sub.2-C.sub.8)alkenyl, and (C.sub.2-C.sub.8)alkynyl, optionally substituted with one or two suitable substituents. Preferably, the hydrocarbon chain of a hydrocarbon group is from 1 to 6 carbon atoms in length, referred to herein as “(C.sub.1-C.sub.6)hydrocarbon.” Examples of alkyl groups or hydrocarbon groups include, but are not limited to, (C.sub.1-C.sub.6)alkyl groups, such as methyl, ethyl, propyl, isopropyl, 2-methyl-1-propyl, 2-methyl-2-propyl, 2-methyl-1-butyl, 3-methyl-1-butyl, 2-methyl-3-butyl, 2,2-dimethyl-1-propyl, 2-methyl-1-pentyl, 3-methyl-1-pentyl, 4-methyl-1-pentyl, 2-methyl-2-pentyl, 3-methyl-2-pentyl, 4-methyl-2-pentyl, 2,2-dimethyl-1-butyl, 3,3-dimethyl-1-butyl, 2-ethyl-1-butyl, butyl, isobutyl, t-butyl, pentyl, isopentyl, neopentyl, and hexyl, and longer alkyl groups, such as heptyl, and octyl. An alkyl group can be unsubstituted or substituted with one or two suitable substituents.

[0023] As used herein and unless otherwise indicated, the term “aryl” refers to a monovalent aromatic hydrocarbon group derived by the removal of one hydrogen atom from a single carbon atom of a parent aromatic ring system (e.g., removal of a H atom from benzene). Typical aryl groups include, but are not limited to, groups derived from aceanthrylene, acenaphthylene, acephenanthrylene, anthracene, azulene, benzene, chrysene, coronene, fluoranthene, fluorene, hexacene, hexaphene, hexalene, as-indacene, s-indacene, indane, indene, naphthalene, octacene, octaphene, octalene, ovalene, penta-2,4-diene, pentacene, pentalene, pentaphene, perylene, phenalene, phenanthrene, picene, pleiadene, pyrene, pyranthrene, rubicene, triphenylene, trinaphthalene and the like. Preferably, an aryl group comprises from 6 to 24 carbon atoms.

[0024] As used herein and unless otherwise indicated, the term “etching” or “etch” will be understood by persons of ordinary skill in the art to include, but not be limited to cleaning of an aluminum or aluminum alloy surface; dissolving impurities, imperfections, scale or oxide from an aluminum or aluminum alloy surface.

[0025] As used herein and unless otherwise indicated, the term “fluoride salt(s)” and “fluoride ion compounds” are used interchangeably and will be understood by persons of ordinary skill in the art to include, but not be limited to, fluoride salts and bifluoride salts including metal salts, ammonium salts and quaternary ammonium salts. Illustrative examples of the fluoride metal salts include those which have high solubility, such as potassium fluorides, sodium fluoride, potassium hydrogen fluoride, sodium hydrogen fluoride and the like. Examples of the ammonium salts encompassed by the invention include, but are not limited to, ammonium fluoride and ammonium hydrogen fluoride (ammonium hydrogen fluoride). Examples of the quaternary ammonium salts encompassed by the invention include, but are not limited to, tetramethyl-ammonium fluoride, methylamine hydrofluoride, 2-hydroxyethyltrimethyl-ammonium fluoride, tetramethylammonium hydrogen fluoride.

[0026] As used herein and unless otherwise indicated, the term “grain refiner” refers to any material that is added to a metal or alloy because of its high melting temperature that enhances the physical properties of the metal or alloy. Illustrative examples of grain refiners include, but are not limited to, sodium, potassium, or ammonium salts. Particular examples of grain refiners include, but are not limited to sodium phosphate, ammonium phosphate, or diammonium phosphate or mixtures thereof.

[0027] As used herein and unless otherwise indicated, the term “organic acid” includes, but is not limited to, acetic acid, propionic acid, butyric acid, isobutyric, valeric acid, caproic acid, caprylic acid, monochloroacetic acid, dichloroacetic acid, trichloroacetic acid, monofluoroacetic acid, difluoroacetic acid, trifluoroacetic acid, α-chlorobutyric acid, β-chlorobutyric acid, γ-chlorobutyric acid, lactic acid, glycolic acid, pyruvic acid, glyoxalic acid, acrylic acid and like monocarboxylic acids, methanesulfonic acid, toluenesulfonic acid and like sulfonic acids, oxalic acid, succinic acid, adipic acid, tartaric acid, citric acid and like polycarboxylic acids.

Compositions

[0028] In one embodiment the invention encompasses novel aqueous acidic compositions for treating the surface of a metal. In an illustrative embodiment, the compositions are useful for treating a surface prior to anodizing the surface. In another embodiment, the compositions are useful for etching a surface to dissolve impurities, imperfections, scale and/or oxide from the metal surface. In a preferred embodiment, the metal surface is an aluminum or aluminum alloy surface. The compositions are also useful for removing or minimizing extrusion line to produce a uniform texture and better appearance for the finished surface.

[0029] In another embodiment, the compositions of the invention comprise one or more fluoride ion compounds, one or more organic acids, and one or more surfactants or combinations thereof. The composition optionally comprises one or more grain refiners and/or one or more mineral acids.

[0030] Another embodiment of the invention encompasses an aqueous, acidic solution comprising one or more grain refiners, one or more fluoride ion compounds, such as for example a fluoride salt, one or more grain refiners, and one or more surfactants. The composition optionally comprises one or more organic acids and/or one or more mineral acids.

[0031] In another embodiment, the compositions of the invention have a pH from about 2.0 to about 5.0, preferably from about 3.0 to about 4.0. In an illustrative embodiment, the compositions overcome limitations of alkaline etch solutions.

[0032] In another illustrative embodiment, the organic acid of the invention includes, but is not limited to, oxalic acid or glycolic acid or mixtures thereof. Preferably, the organic acid is present in an amount from about 1 to about 30 grams per liter, more preferably from about 2.5 to about 25 grams per liter, and even more preferably from about 5 to about 20 grams per liter.

[0033] In another illustrative embodiment, the surfactant of the invention includes, but is not limited to, nonionic surfactant, an amphoteric surfactant, or a synergistic surfactant. Preferably, the surfactant comprises salts of alkyl aryl sulfonates, alkyl sulfonates, alkyl ether sulfates, alkyl sulfates, alkyl taurates, alkyl sulfosuccinates, hydrocarbon derivatives, abietic acid derivatives, ethoxylated primary alcohols, and modified polyethoxylated alcohols, individually or in combinations of two or more. Preferably, the surfactant is present in an amount from about 1 to about 3 grams per liter.

[0034] In another illustrative embodiment, the fluoride ion compound of the invention includes, but is not limited to, hydrofluoric acid, hydrofluorosilic acid, or fluoroboric acid or mixtures thereof. In another preferred embodiment, the fluoride ion compound is a fluoride salt. Preferred fluoride salts include, but are not limited to, sodium fluoride, potassium fluoride, ammonium bifluoride or mixtures thereof. Preferably, the fluoride ion compound is present in an amount from about 5 to about 225 grams per liter, preferably from about 10 to about 200 grams per liter, more preferably from about 20 to about 80 grams per liter, and even more preferably from about 60 to about 70 grams per liter.

[0035] In another illustrative embodiment, the grain refiner of the invention includes, but is not limited to, sodium phosphate, ammonium phosphate, or diammonium phosphate or a mixture thereof. In an illustrative embodiment, the composition comprises a single grain refiner. In another illustrative embodiment, the composition comprises combinations of two or more grain refiners. In an illustrative embodiment, the grain refiner is present in an amount of from about 1 to about 50 grams per liter, preferably from about 5 to about 30 grams per liter, and more preferably from about 10 to about 20 grams per liter.

[0036] In another illustrative embodiment, the mineral acid of the invention is hydrofluoric acid, nitric acid, sulfuric acid, or phosphoric acid or mixtures thereof. Preferably, the mineral acid is present in an amount from about 20 to about 100 grams per liter, more preferably from about 30 to about 90 grams per liter and even more preferably from about 40 to about 80 grams per liter.

[0037] In a particular embodiment, the invention encompasses a composition for etching aluminum or aluminum alloy, comprising ammonium bifluoride, hydrofluoric acid, glycolic acid, and surfactant.

Methods

[0038] Another embodiment of the invention encompasses a method of treating the surface of a metal, preferably aluminum or aluminum allow, which comprises treating the metal (preferably aluminum or aluminum allow) with a composition comprising a one or more fluoride ion compounds, one or more mineral acids, one or more organic acids and one or more surfactants.

[0039] In an illustrative embodiment, the treatment is done at a solution temperature of about 60° F. to about 200° F., preferably at a solution temperature of about 70° F. to about 150° F., and more preferably at a solution temperature of about 100° F. to about 120° F. Preferably, the treatment is done from about 0.5 to about 15 minutes, preferably from about 1 to about 10 minutes, and more preferably from about 3 to about 5 minutes.

[0040] In one embodiment the invention encompasses a novel method for treating the surface of a metal comprising contacting the surface of the metal with an aqueous acidic composition. In an illustrative embodiment, the methods are useful for treating a surface prior to anodizing the surface. In another embodiment, the methods are useful for etching a surface to dissolve impurities, imperfections, scale and/or oxide from the metal surface. In a preferred embodiment, the metal surface is an aluminum or aluminum alloy surface. The methods are also useful for removing or minimizing extrusion line to produce a uniform texture and better appearance for the finished surface.

[0041] In another embodiment, the methods of the invention comprise contacting a metal surface, preferably aluminum or aluminum alloy, with one or more fluoride ion compounds, one or more organic acids, and one or more surfactants or combinations thereof. The methods optionally comprise contacting the metal surface with one or more grain refiners and/or one or more mineral acids.

[0042] Another embodiment of the invention encompasses a method for treating a metal surface, preferably aluminum or aluminum alloy comprising contacting the metal surface with one or more grain refiners, one or more fluoride ion compounds, such as for example a fluoride salt, one or more grain refiners, and one or more surfactants. The method optionally comprises treating a metal surface with one or more organic acids and/or one or more mineral acids.

[0043] In another embodiment, the methods of the invention encompass contacting a metal surface with a composition of the invention having a pH from about 2.0 to about 5.0, preferably from about 3.0 to about 4.0. In an illustrative embodiment, the methods overcome limitations of alkaline etch solutions.

[0044] In another illustrative embodiment, the organic acid encompassed by the method for treating a metal surface, preferably aluminum or aluminum alloy, include, but are not limited to, oxalic acid or glycolic acid or mixtures thereof. Preferably, the organic acid is present in an amount from about 1 to about 30 grams per liter, more preferably from about 2.5 to about 25 grams per liter, and even more preferably from about 5 to about 20 grams per liter.

[0045] In another illustrative embodiment, the surfactants encompassed by the method for treating a metal surface, preferably aluminum or aluminum alloy, include, but are not limited to, a nonionic surfactant, an amphoteric surfactant, or a synergistic surfactant. Preferably, the surfactant comprises salts of alkyl aryl sulfonates, alkyl sulfonates, alkyl ether sulfates, alkyl sulfates, alkyl taurates, alkyl sulfosuccinates, hydrocarbon derivatives, abietic acid derivatives, ethoxylated primary alcohols, and modified polyethoxylated alcohols, individually or in combinations of two or more. Preferably, the surfactant is present in an amount from about 1 to about 3 grams per liter.

[0046] In another illustrative embodiment, the fluoride ions encompassed by the method for treating a metal surface, preferably aluminum or aluminum alloy, include, but are not limited to, hydrofluoric acid, hydrofluorosilic acid, or fluoroboric acid or mixtures thereof. In another preferred embodiment, the fluoride ion compound is a fluoride salt. Preferred fluoride salts include, but are not limited to, sodium fluoride, potassium fluoride, ammonium bifluoride or mixtures thereof. Preferably, the fluoride ion compound is present in an amount from about 5 to about 225 grams per liter, preferably from about 10 to about 200 grams per liter, more preferably from about 20 to about 80 grams per liter, and even more preferably from about 60 to about 70 grams per liter.

[0047] In another illustrative embodiment, the grain refiners encompassed by the method for treating a metal surface, preferably aluminum or aluminum alloy, include, but are not limited to, sodium phosphate, ammonium phosphate, or diammonium phosphate or a mixture thereof. In an illustrative embodiment, the method comprises a single grain refiner. In another illustrative embodiment, the method comprises combinations of two or more grain refiners. In an illustrative embodiment, the grain refiner is present in an amount of from about 1 to about 50 grams per liter, preferably from about 5 to about 30 grams per liter, and more preferably from about 10 to about 20 grams per liter.

[0048] In another illustrative embodiment, the mineral acid encompassed by the method for treating a metal surface, preferably aluminum or aluminum alloy, include, but are not limited to, hydrofluoric acid, nitric acid, sulfuric acid, or phosphoric acid or mixtures thereof. Preferably, the mineral acid is present in an amount from about 20 to about 100 grams per liter, more preferably from about 30 to about 90 grams per liter and even more preferably from about 40 to about 80 grams per liter.

[0049] In a particular embodiment, the invention encompasses a method for etching aluminum or aluminum alloy, comprising contacting the aluminum or aluminum alloy with ammonium bifluoride, hydrofluoric acid, glycolic acid, and surfactant.

[0050] An illustrative acidic liquid aluminum etching agent with a robust, durable cleaning activity can be obtained by preparing the acidic liquid aluminum cleaner as follows:

[0051] A mineral acid is exemplified by sulfuric acid, nitric acid, phosphoric acid, and the like, and at least one selection therefrom should be added. The preferable concentrations are as follows: about 80 g/L for phosphoric acid, about 80 g/L for sulfuric acid, and about 80 g/L for nitric acid. The mineral acid may take the form of a single acid or may comprise a combination of two or more acids, which is freely selected within a range, which does not adversely affect the surface cleaning performance. Such mixed acids are exemplified by tricomponent mixed acids of 3 to 10 g/L phosphoric acid, 5 to 15 g/L sulfuric acid, and 0.5 to 2 g/L nitric acid, and by bicomponent mixed acids of 10 to 20 g/L sulfuric acid and 0.5 to 2 g/L nitric acid.

[0052] Through the use of these mineral acids, the pH preferably does not exceed 2.0 and more preferably is 0.6 to 2. Preferably, no particular restriction is placed on the lower pH limit.

[0053] The surfactant component preferably is a hydrocarbon derivative, abietic acid derivatives, ethoxylated primary alcohols, and modified polyethoxylated alcohols, and these may be used singly or in combinations of two or more. The preferable concentration is 0.1 to 10 g/L and more preferably 0.5 to 3 g/L.

[0054] In addition, aluminum ions are eluted during cleaning with the acidic liquid cleaner according to the present invention, and this may reduce its cleaning efficiency. Accordingly, as a countermeasure in response to this, optionally a chelating agent, which sequesters the aluminum ions may also be present. Chelating agents useable for this purpose are exemplified by citric acid, oxalic acid, tartaric acid, gluconic acid, and the like.

[0055] The acidic liquid aluminum cleaner prepared according to the present invention is highly effective for the removal of smut and scale from aluminum and aluminum alloy as well as for the etching of same.

[0056] The practice of the invention may be further appreciated from the following working and comparison examples, which are meant to provide illustrative embodiments and are in no way intended to limit the scope of the invention.

EXAMPLES

Example 1

[0057] Aluminum test specimens of 6063-T5 aluminum alloy were cleaned in acid cleaner, rinse then etched in the following acid etch composition of Table 1:

TABLE-US-00001 TABLE 1 Hydrofluoric Acid 49%  7.5 g/L Fluoroboric Acid 49%  5.0 g/L Ammonium Bifluoride 60.0 g/L Sodium Phosphate 15.0 g/L Surfactant  1.0 g/L The Solution pH was adjusted to 3.4.

[0058] Test samples were etched in the above solution for 1.0, 3.0 and 5.0 minutes respectively. The etched samples were subjected to rinse, deox, rinse, dry off and weight loss taken before and after etch were performed on all test samples to determine the aluminum dissolution or removal rate. For comparison, a controlled aluminum specimen was acid cleaned, rinse then etched in aqueous alkaline etch bath for 5.0 and 10.0 minutes respectively at a temperature of 145°-150° F.

[0059] The etch bath contained 90.0 g/L sodium hydroxide, 100.00 g/L dissolved aluminum and 2.0% volume of Houghton no-dump/long life etchant additives. As with the acid etched samples, all alkaline etched samples were subjected to rinse, deox, rinse, dry off and weight loss taken before and after etch.

[0060] All acid and alkaline etched samples were anodized as noted in Table 2:

TABLE-US-00002 TABLE 2 1. Rinse Room Temperature 2. Deox Houghto Deox ™ A-1745 at 7.0% volume for 1.0 min. 3. Rinse Room Temperature 4. Anodizing Sulfuric Acid 180 g/L Aluminum  10 g/L Current Density 18 amps per sq. ft. Bath Temperature 72° F. Anodizing Time 30 min. Coating Thickness 0.7 mil 5. Rinse Room Temperature 6. Houghto Safe ® A-620 Seal (Houghton Mid-Temp. Seal) 3% volume at 180° F. for 10.0 min. 7. Rinse 8. Dry off

[0061] Results from illustrative embodiments of the invention compared to a base alkaline etch are described in Table 3.

[0062] Aluminum removal is measured in grams per square foot of aluminum removal (i.e., g/ft.sup.2). All anodized samples were carefully evaluated for the quality of the etch by visual examinations and by the gloss reading using reflectometer at 60° angle.

TABLE-US-00003 TABLE 3 Al Temp. Removed Time Etch Bath (° F.) (g/ft.sup.2) (min.) Gloss Acid 115 0.70 1.0 6.2 Acid 115 1.17 3.0 5.9 Acid 115 1.42 5.0 4.9 Alkaline 145 5.4 5.0 18.1 Alkaline 145 10.5 10.0 9.4

Example 2

[0063] Aluminum test specimens of 6063-T.sub.5 aluminum alloy were etched in the following acid bath (Table 4).

TABLE-US-00004 TABLE 4 Hydrofluoric acid 49%  10.0 g/L Ammonium bifluoride  80.0 g/L Diammonium phosphate  30.0 g/L Surfactant 200.0 ppm pH 3.4-3.6

[0064] Aluminum removal rate was performed as in Example (1). All samples were anodized the same as Example (1) and the finished samples were evaluated using same method as in Example (1). Results from Example 2 are described in Table 5.

TABLE-US-00005 TABLE 5 Al Temp. Removed Time Etch Bath (° F.) (g/ft.sup.2) (min.) Gloss Acid 110 0.85 2.0 6.0 Acid 110 1.51 6.0 4.8 Acid 110 1.53 10.0 4.2

Example 3

[0065] Aluminum test specimens of 6063-T.sub.5 aluminum alloy that contained high zinc content at 0.1% in its alloy were etched separately in the following etch baths (Table 6).

TABLE-US-00006 TABLE 6 Acid Etch Bath: Bath composition same as in example (2) Bath temperature   110° F. Etch time  5.0 minutes Alkaline Etch Bath: Sodium Hydroxide 8.0 oz/gal Aluminum 100.0 g/L Temperature 145.0° F. Etch Time 10.0 minutes

[0066] After etch all samples were subjected to rinse, deox, rinse, dry off and carefully evaluated.

[0067] Results:

[0068] Alkaline etched samples had very rough or galvanizing problem while acid etched parts had uniform matt finish.

Test Results:

[0069] 1. The compositions and methods of the invention comprising the acid etch compositions produce excellent uniform matte finish.

[0070] 2. The compositions and methods of the invention comprising the acid etch compositions are more effective than alkaline etch in hiding extrusion lines, scratches or defects than alkaline etch.

[0071] 3. The compositions and methods of the invention comprising the acid etch compositions produce lower gloss reading than alkaline etch.

[0072] 4. The compositions and methods of the invention comprising the acid etch compositions operates at lower bath temperature and unlike alkaline etch does not require cooling.

[0073] 5. The compositions and methods of the invention comprising the acid etch compositions reduces etch time to 3.0-5.0 minutes compared to 9-15 minutes in case of alkaline etch

[0074] 6. The compositions and methods of the invention comprising the acid etch compositions produce less aluminum removal 0.5-1.5 gr/ft.sup.2 vs 9.0-13.0 gr/ft.sup.2 in case of alkaline etch.

[0075] 7. The compositions and methods of the invention comprising the acid etch compositions reduce waste. Due to the fact that 1.0 lb. of aluminum is removed in the etch process results in 20.0 lbs. of waste sludge, therefore acid etch presents significant waste sludge reduction.

[0076] 8. The compositions and methods of the invention comprising the acid etch compositions parts are easy to rinse and require less rinse tanks than alkaline etch. This presents less water consumption.

[0077] 9. The compositions and methods of the invention comprising the acid etch compositions are more effective in preventing pitting prior to anodizing.

[0078] 10. The compositions and methods of the invention comprising the acid etch compositions are not sensitive to zinc content in the aluminum alloy as in the case of alkaline etch. High zinc content results in a rough finish or galvanizing defect.

[0079] The invention described and claimed herein is not to be limited in scope by the specific embodiments herein disclosed, since these embodiments are intended as illustrations of several aspects of the invention. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the appended claims.