ACIDIC LIQUID COMPOSITION AND PROCESS FOR CLEANING ALUMINUM

Abstract: The stability of an acidic liquid cleaner for aluminum comprising mineral acid, oxidant, polyvalent metal ions, and surfactant is substantially improved by the presence in the cleaner of from 0.05 to 5 g/l of a component selected from the group of glycols containing from 2 to 10 carbon atoms per molecule and mixtures of such glycols. The effectiveness of the cleaner for primary cleaning and desmutting of aluminum and its alloys is not impaired and may even be improved by the addition of the glycol component.

Description: ACIDIC LIQUID COMPOSITION AND PROCESS FOR CLEANING ALUMINUM TECHNICAL FIELD The present invention relates to an acidic liquid cleaner for articles, such as sheets, strips, containers, and the like, that are made of aluminum or of aluminum al- loys that are predominantly aluminum (both hereinafter des¬ ignated briefly as "aluminum", unless the context requires otherwise) . The cleaner is very effective in maintaining its etching capacity and in removing the smut produced by the etching of an aluminum surface as well as in general cleaning. BACKGROUND ART Due to problems with waste water treatment, acidic li¬ quid cleaners for aluminum are currently being converted from the fluorine-based cleaners used heretofore to fluor- ine-free, chromium-free cleaners. The acidic liquid aluminum cleaners disclosed in, for example, (a) Japanese Patent Application Laid Open [Kokai] Number 61-106783 [106,783/86], (b) Japanese Patent Applica¬ tion Laid Open Number 61-231188 [231,188/86], and (c) Japa- nese Patent Application Laid Open Number 63-223798 [223,798/88] are examples of prior art fluorine-free, chromium-free cleaners. The liquid cleaners disclosed in (a) and (b) are sulfuric acid-based acidic liquid cleaners for aluminum. In addition to sulfuric acid, nitric acid, and surfactant, these also contain ferric ion (etching ac¬ celerator) and an oxidant (stabilizer for the ferric ion) . These compositions are heated to 50 to 80 ° C for use in cleaning. The liquid cleaner in (c) is a phosphoric acid- based acidic liquid cleaner for aluminum. In addition to phosphoric acid, sulfuric acid, and surfactant, it contains small amounts of ferric ion (in order to inhibit corrosion of the cleaning equipment) and an oxidant which acts as a stabilizer for the ferric ion. It is heated to 50 to 80 ° C for use in cleaning. DESCRIPTION OF THE INVENTION Problem to Be Solved by the Invention These prior art examples are all acidic liquid alumi¬ num cleaners composed of mineral acid, ferric ion, oxidant, and surfactant, and as such they suffer from common prob¬ lems. Thus, because they are fluorine-free, chromium-free cleaners, their treatment temperatures are higher than for fluorine-based cleaners. Moreover, because they contain oxidant and metal ion, surfactant decomposition occurs to a substantial extent. Not only does this increase consump¬ tion of the surfactant, but decomposition product remaining in the treatment bath impairs its degreasing performance. As a consequence, these cleaners lack a robust, durable cleaning activity. Summary of the Invention The present invention seeks to introduce a concrete means for solving the problems outlined hereinbefore for acidic liquid aluminum cleaners comprising mineral acid, oxidant, polyvalent metal ions, and surfactant. It has been found that the problems observed with such cleaners in the prior art are largely or entirely avoided by addition to such an acidic liquid cleaner of 0.05 to 5 grams per liter (hereinafter "g/L") of a component selected from the group of C_ to C- 0 glycols. Details of Preferred Embodiments of the Invention In more specific terms, a preferred acidic liquid aluminum cleaner with a robust, durable cleaning activity can be obtained by preparing the acidic liquid aluminum cleaner as follows: - the aforesaid mineral acid comprises at least one selection from phosphoric acid, sulfuric acid, and nitric acid; the concentrations of phosphoric acid and sulfuric acid do not exceed 20 g/L; and the nitric acid concentration does not exceed 10 g/L; - the aforesaid oxidant is hydrogen peroxide or a ni¬ trite, and its concentration is in the range from 0.02 to 3.0 g/L; the aforesaid polyvalent metal ion is ferric ion, and the ferric ion content is 0.02 to 5 g/L; the aforesaid surfactant is nonionic, and the surfac- tant content is in the range from to 0.1 to 5 g/L; there is additionally present at least 1 selection from the C_ to C glycols such as propylene glycol, ethylene glycol, diethylene glycol, and triethylene glycol; and - the pH of this acidic liquid cleaner does not exceed 2.0. The simultaneous presence of surfactant, polyvalent metal ion (for example, ferric ion) , and oxidant in the acidic liquid aluminum cleaner according to the present invention is essential for the effective maintenance of a degreasing capacity and aluminum etchability. In addition, the presence of such compounds also functions to inhibit corrosion of the cleaning equipment. The mineral acid is exemplified by sulfuric acid, ni- trie acid, phosphoric acid, and the like, and at least one selection therefrom should be added. The preferable con¬ centrations are as follows: not more than 20 g/L for phos¬ phoric acid, not more than 20 g/L for sulfuric acid, and not more than 10 g/L for nitric acid. This mineral acid may take the form of a single acid or may comprise a com¬ bination 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. Through the use of these mineral acids, the pH pref¬ erably does not exceed 2.0 and more preferably is 0.6 to 2. When the pH exceeds 2, the aluminum etching rate is reduced and a satisfactory surface cleaning usually cannot be ob¬ tained. No particular restriction is placed on the lower pH limit. No specific restriction is placed on the polyvalent metal ion, this component being exemplified by Fe ions, Co ions, Sn ions, Ce ions, and the like. However, this com- ponent most preferably comprises, or more preferably con¬ sists essentially or, most preferably, entirely of, 0.02 to 5 g/L ferric ion (Fe +3) , which can be furnished, for example, by ferric sulfate or ferric nitrate. Moreover, ferrous ions (e.g., from ferrous sulfate or ferrous ni- trate) may be added to the acidic liquid cleaner and then oxidized to ferric ions by the oxidant. No particular limitation is placed on the oxidant, but it is preferably H O or NO ~ present at 0.02 to 3.0 g/L. The surfactant component should be nonionic surfac- tants, as exemplified by hydrocarbon derivatives, abietic acid derivatives, ethoxylated primary alcohols, and modi¬ fied polyethoxylated alcohols, and these may be used singly or in combinations of two or more. The preferable concen¬ tration is 0.1 to 10 g/L and more preferably 0.5 to 3 g/L. With regard to the glycol which is used in order to inhibit surfactant decomposition, propylene glycol is ef¬ fective in this regard, but ethylene glycol, diethylene glycol, triethylene glycol, etc., are also effective. At least one of these or other glycols with 2 - 10 carbon atoms per molecule is used, suitably at 0.05 to 5 g/L and preferably at 0.2 to 2 g/L, referred to the treat¬ ment composition. The C to C 1Q glycol present in the acidic liquid aluminum cleaner according to the present invention sub- stantially inhibits decomposition of the surfactant by the polyvalent metal ions and oxidant and thus improves the durability of the cleaning activity. 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, a chelating agent which sequesters the aluminum ions may also be present. Chelating agents useable for this purpose are exemp¬ lified by citric acid, oxalic acid, tartaric acid, gluconic acid, and the like. The acidic liquid aluminum cleaner prepared according to the present invention is highly effective for the remov¬ al of smut and scale from aluminum and aluminum alloy as well as for the etching of same. The practice of the invention may be further appreci- ated from the following working and comparison examples. Examples The following general conditions applied to all the examples, unless otherwise noted: 1. Test material: Container fabricated by the drawing and ironing (hereinafter "DI") of 3004 alloy aluminum sheet and carrying normal DI lubricating oil and smut. 2. Preparation of the test baths: Five cleaners in total were prepared as examples, and their compositions are reported in Table 1. The four surfactants identified by number in Table 1 had the following chemical characteris¬ tics: nonionic (1) : nonylphenol/EO (20 moles) adduct (hydrocarbon derivative) nonionic (2): higher alcohol/EO (5 moles)-PO (10 moles) adduct (hydrocarbon derivative) nonionic (3) : nonylphenol/EO (14 moles) adduct (hydrocarbon derivative) nonionic (4): higher alcohol/EO (5 moles)-PO (15 moles) adduct (hydrocarbon derivative) Five test baths were also prepared by the omission of the C to C 1Q glycol from Examples 1 to 5, and these are reported in Table 2 as comparison examples 1 to 5 respec¬ tively. Table 1. (Continued below) Table 2. (Continued below) 3. Test methods (a) Comparison of the maintenance of the surfactant concentration in the acidic liquid cleaners The test baths (Examples 1 to 5 from Table 1 and Com¬ parison Examples 1 to 5 from Table 2) were maintained quiescent at 75 + 1 ° C while replenishing the decom¬ posed H_0_ in order to maintain the E O content in the bath at 0.5 g/L. The quantity of residual surfac¬ tant under quiescent acidic bath conditions was mea¬ sured every 24 hours for three 24-hour intervals. The results are reported in Table 3. (b) Comparison of the cleaning activitv for aluminum can (water-wetting test) The test baths (Examples 1 to 5 from Table 1 and Com¬ parison Examples 1 to 5 from Table 2) were maintained quiescent at 75 + 1 ° C while replenishing the decom¬ posed -- 2 °2 in order to maintain the H_0 content in the bath at 0.5 g/L. A container as described above under the heading "Test material" was sprayed for 50 seconds at 75 + 1 ° C using the test bath after stand¬ ing for zero, 24, 48, or 72 hours. This was followed by a spray rinse for 10 seconds with tap water and standing for 30 seconds. The water-wetted area (%) was then visually evaluated. The results for this evaluation are reported in Table 4. Considering the test results first as they relate to surfactant decomposition, the results reported in Table 3 show that it was possible to obtain an approximately 42 to 75% inhibition of surfactant decomposition. With regard to the maintenance of the cleaning activity, the results re¬ ported in Table 4 also show superior results obtained in the examples in all cases.

Claims: CLAIMS 1. An acidic liquid cleaner for aluminum comprising min¬ eral acid, oxidant, polyvalent metal ions, and surfactant, characterized in that it also comprises from 0.05 to 5 g/L of a component selected from the group of glycols contain¬ ing from 2 to 10 carbon atoms per molecule and mixtures thereof. 2. An acidic liquid cleaner for aluminum as claimed in claim 1, wherein the mineral acid is selected from the group consisting of phosphoric acid, sulfuric acid, nitric acid, and mixtures thereof and the concentrations of phos¬ phoric acid and sulfuric acid do not exceed 20 g/L each and the concentration of nitric acid does not exceed 10 g/L. 3. An acidic liquid cleaner for aluminum as claimed in claim 1, wherein the oxidant component is nitrite ions or hydrogen peroxide, in a concentration of from 0.02 to 3.0 g/L. 4. An acidic liquid cleaner for aluminum as claimed in claim 1, wherein the polyvalent metal ions are ferric ions and are present at a concentration of form 0.02 to 5 g/L. 5. An acidic liquid cleaner for aluminum as claimed in claim 1, wherein the surfactant is a nonionic surfactant and is present at a concentration of from 0.1 to 5 g/L. 6. An acidic liquid cleaner for aluminum as claimed in claim 5, wherein the surfactant concentration is from 0.5 to 3 g/L. 7. An acidic liquid cleaner for aluminum as claimed in claim 1, wherein the glycol component comprises propylene glycol, ethylene glycol, diethylene glycol, or triethylene glycol. 8. An acidic liquid cleaner for aluminum as claimed in claim 7, wherein the pH does not exceed 2.0 and preferably is between 0.6 and 2.0. 9. An acidic liquid cleaner for aluminum as claimed in claim 6, wherein the pH does not exceed 2.0 and preferably is between 0.6 and 2.0. 10. An acidic liquid cleaner for aluminum as claimed in claim 5, wherein the pH does not exceed 2.0 and preferably is between 0.6 and 2.0. 11. An acidic liquid cleaner for aluminum as claimed in claim 4, wherein the pH does not exceed 2.0 and preferably is between 0.6 and 2.0. 12. An acidic liquid cleaner for aluminum as claimed in claim 3 , wherein the pH does not exceed 2.0 and preferably is between 0.6 and 2.0. 13. An acidic liquid cleaner for aluminum as claimed in claim 2, wherein the pH does not exceed 2.0 and preferably is between 0.6 and 2.0. 14. An acidic liquid cleaner for aluminum as claimed in claim 1, wherein the pH does not exceed 2.0 and preferably is between 0.6 and 2.0. 15. A process for cleaning aluminum, comprising contacting the aluminum with a composition as claimed in any of claims 1 - 14.

Inventors: AOKI TOMOYUKI, ASAI SHINICHIRO, IINO YASUO, ONO YOJI, AOKI, TOMOYUKI, ASAI, SHINICHIRO, IINO, YASUO, ONO, YOJI
Applicants: HENKEL CORP, HENKEL CORPORATION
Application year: 1991
Main classification: C23G1
IPC codes: C11D10, C23G1