Technical Field

This invention relates to liquid alkaline degreasers for aluminum and its alloys. More particularly, this invention relates to a liquid alkaline degreaser that (i) thoroughly removes oil and contaminants adhering on the surface of aluminum and its alloys; (ii) exhibits a good degreasing performance even when loaded with oil in an amount three times, that of the pure degreasing component (combined weight of inorganic builder and surfactant); (iii) is free of phosphorus, a cause of the eutrophication of rivers, lakes, and wetlands; and (iv) has a low chemical oxygen demand (hereinafter usually abbreviated as "COD") and thereby facilitates effluent treatment. Background Art

In order to support their cleaning action, degreasers for aluminum and its alloys typically contain an inorganic builder whose main component is phosphate or condensed phosphate. These degreasers also contain other components in the form of chelating agent and surfactant. Within the realm of phosphorus-free alkaline degreasers, Japanese Patent Application Laid Open [Kokai or Unexamined] Number Hei 6-116768 [116,768/1994] teaches a phosphorus-free alkaline degreaser for the low-temperature cleaning of metals. This alkaline degreaser contains: (A) inorganic builder consisting of 0.05 to 0.30 weight %, measured as its stoichiometric equivalent as SiO ₂ , of silicate and 0.4 to 3.0 weight % of at least one selection from sodium hydroxide, sodium carbonate, and sodi¬ um bicarbonate; (B) organic builder consisting of 0.01 to 0.5 weight % of at least one selection from ethylenediaminetetraacetate salts and nitrilotriacetate salts and 0.1 to 0.5 weight % of at least one selection from polyacrylic acid salts, cyclo- pentanetetracarboxylic acid salts, polycarboxylic acid salts, hydroxycar- boxylic acid salts, and urethanated polyvinyl alcohol; and

(C) 0.2 to 0.6 weight % of surfactant.

It is taught therein that this phosphorus-free alkaline degreaser, even when used continuously at low temperatures of 35°C to 45°C, exercises an excellent cleaning activity on metal surfaces and provides metals with highly conversion- treatable surfaces. At the same time, however, the use of a high-COD surfactant is required in order to provide a good detergency.

Moreover, the regulatory situation with regard to the effluent from plants in the chemical, electrical, and manufacturing sectors has become increasingly severe in association with the recent heightened global attention to environment- al protection. This has led to a requirement for aluminum degreasers that have a low COD and are phosphorus-free in order to prevent the eutrophication of rivers, lakes, and wetlands. In addition, in order to reduce treatment line costs, there is also demand for a degreasing liquid composition, often hereinafter called a "bath" for brevity even if it is not used by immersion, that requires minimal renewal, i.e., there is demand for a long bath-life degreaser that is able to maintain an excellent detergency even when loaded with large amounts of oil. Finally, processability considerations make a degreaser supplied in liquid form preferable to one supplied in powdered form.

However, a liquid degreaser for aluminum and its alloys that satisfies these requirements has yet to appear. More particularly, no such degreaser has appeared that is able to provide an excellent cleaning performance and at the same time has a lowered COD and is resistant to oil loading. Disclosure of the Invention

Problems to Be Solved bv the Invention The present invention, which was pursued in order to solve the problems described above in the prior art, will therefore be directed to the introduction of a liquid alkaline degreaser for aluminum and its alloys that can be used to clean the surface of aluminum and its alloys but which is nevertheless able to maintain an excellent degreasing performance even when loaded with large amounts of oil through continuous use, for example, even when loaded with three times as much oil as active degreasing component (combined weight of inorganic builder and surfactant). Furthermore, such a liquid alkaline degreaser should be free of

phosphorus and the degreaser's COD, which is also a problem for effluent treatment, should be kept low.

Summary of the Invention It has been discovered that these problems can be solved through the use of a liquid alkaline degreaser that comprises water and surfactant with a par¬ ticular chemical nature and that uses specific amounts of alkali metal silicate as its inorganic builder. The present invention was achieved based on this discovery.

In specific terms, the present invention introduces a liquid alkaline de- greaser concentrate for aluminum and aluminum alloys that characteristically comprises, preferably consists essentially of, or more preferably consists of the following as its main components:

(A) as inorganic builder, 1.5 to 5.0 weight %, measured as its stoichiometric equivalent as SiO ₂ , of alkali metal silicate; (B) as nonionic surfactant, 10 to 25 weight % of at least one selection from trialkylamine oxides and di(hydroxyethyl)monoalkylamine oxides with formula (I)

R ²

, I® θ R ¹ -N-O (I).

R ² wherein R ¹ is a C ₁₀ to C^ alkyl group and R ² is methyl, ethyl, or hydroxy- ethyl; and (C) water.

Details of Invention. Including Preferred Embodiments The aluminum and aluminum alloy that are substrates for the present in¬ vention comprise aluminum metal itself and alloys whose main component is aluminum, and may be in any physical shape or form, for example, sheet, die castings, and the like. Unless the context requires otherwise, the term "aluminum" when used below is intended to include such alloys as well as the pure metal.

The alkali metal silicate used as inorganic builder in the present invention

is added in order to improve the degreasing activity. Its functions are to inhibit the redeposition of contaminants on the workpiece, to saponify acidic substances and thereby promote the solubility of oil components, and the like.

Commercially available sodium metasilicate, sodium orthosilicate, and the like, can be used, for example, as the silicate builder, as can corresponding potassium and lithium salts. Commercially available sodium silicate takes the form of the anhydride and various hydrates, and its blending concentration is given in terms of the stoichiometric equivalent as SiO ₂ in the sodium silicate. The suitable range for the silicate is 1.5 to 5.0 weight % (as SiO ₂ ) of the total weight of the liquid alkaline degreaser. The particularly preferred range for the silicate is 2.0 to 3.0 weight % on the same basis. At concentrations below 1.5 weight % the resulting liquid alkaline degreaser will not usually have a satisfactory degreasing performance. While concentrations in excess of 5.0 weight % do retain a satisfactory degreasing performance, no additional benefits accrue to these higher concentrations, which are thus economically undesirable.

The nonionic surfactant used in the present invention consists of at least one selection from trialkyl amine oxides and di(hydroxyethyl) monoalkyl amine oxides with formula (I):

R ²

, *Θ Θ

R ¹ -N-O (I),

I

R ² wherein R ¹ is a C ₁₀ to C ₂₂ alkyl group and R ² is methyl, ethyl, or hydroxyethyl. A poor degreasing performance is usually obtained when R in formula (I) has fewer than 10 or more than 22 carbons. Moreover, the COD has a strong tendency to increase at more than 22 carbons. R ² is preferably methyl, ethyl, or hydroxyethyl, and groups other than these do not usually give both a good degreasing performance and a low COD. Nonionic surfactants with the structure given above have COD's that are much lower than the usual type of nonionic surfactants, for example, the polyoxy- ethylene nonylphenol ethers. The former therefore impose little burden on ef¬ fluent treatment facilities and have little impact on the environment.

Amine oxides usable in the present invention are exemplified by dimethyl- caproylamine oxide, dimethyllaurylamine oxide, dimethyimyristylamine oxide, di- methylpalmitylamine oxide, dimethyl stearyl amine oxide, dimethyl behenyl amine oxide, diethyl lauryl amine oxide, diethyl stearyl amine oxide, di(hydroxyethyl)- lauryl amine oxide, and di(hydroxyethyl)myristyl amine oxide. Compounds containing branched structures can be used as long as R ¹ has 10 to 22 carbons. Among subject nonionic surfactants, the use of dimethyl lauryl amine oxide, diethyl lauryl amine oxide, and di(hydroxyethyl) lauryl amine oxide, in which R ¹ contains 12 carbons, is particularly preferred.

The suitable concentration range for subject nonionic surfactant in the present invention is 10 to 25 weight % as the straight or undiluted nonionic sur¬ factant component. 15 to 20 weight % is a more preferred range. The degreas¬ ing performance may be poor at concentrations below 10 weight %, and in particular the degreasing performance at these concentrations will decline when oil becomes admixed. A good degreasing is still obtained, even in the presence of oil, at concentrations in excess of 25 weight %, but such concentrations raise the COD of the degreaser and for this reason often should be avoided. Moreover, additions in excess of 25 weight % also impair the storage stability of the degreaser. At present it is unclear why use of the particular nonionic surfactant spec¬ ified for the present invention affords a good degreasing performance and does so even at high oil loads. One hypothesis is as follows: While the nonionic surfactant specified for the present invention is nonionic in the degreasing bath, in the oil-enveloping micellar state the presence of the strongly polar moiety in the surfactant molecule causes the micelle surface to carry a moderate anionic charge. This prevents redeposition of the oil particle on the surface of the workpiece, which also carries an anionic charge, and thereby provides the basis for the excellent degreasing performance.

A defoamer may be added to the liquid alkaline degreaser according to the present invention in order to suppress the adverse effects of foaming during the cleaning operation. This defoamer can be selected as appropriate from those defoamers in common use.

The liquid alkaline degreaser according to the present invention is prefer¬ ably used diluted about 10 to 100 times with water, in correspondence to the spe¬ cific surface conditions of the workpiece (load of oil, dust, etc.). Dilutions of 20 to 50 times are particularly preferred. The temperature, duration, and technique for treating aluminum and its al¬ loys with the liquid alkaline degreaser according to the present invention can not be rigorously specified because these conditions vary with the specific surface conditions of the workpiece (load of oil, dust, etc.). However, based on con¬ siderations with regard to foaming, an immersion treatment is typically carried out at 60°C to 80°C for 20 to 120 seconds.

The invention will be illustrated below in specific terms by reference to working and comparative examples.

Examples 1 to 8 and Comparative Examples 1 to 5 Preparation of the test liquid alkaline degreasers Liquid alkaline degreasers were prepared in Examples 1 to 8 and Compar¬ ative Examples 1 to 5 by diluting with water the inorganic builder and nonionic surfactant compositions reported in Table 1. In each case the concentration of the prepared degreaser was brought to 50 g/L by dilution with water, thus yielding the corresponding test liquid alkaline degreasers. Specimens

(a) aluminum alloy (Japanese Industrial Standard A 5052): dimensions: 50 mm x 100 mm sheet thickness: 1.0 mm

(b) fin stock (Japanese Industrial Standard A 3000): dimensions: 50 mm x 100 mm sheet thickness: 0.3 mm Measurement of the COD

The Chemical Oxygen Demand value of the test liquid alkaline degreasers in parts per million by weight was measured according to the method of Jap- anese Industrial Standard K 0102-17.

Table 1

COMPOSITIONS AND COD VALUES OF THE CONCENTRATED ALKALINE

DEGREASERS

Ingredient Type and Percent by Weight of Ingredient in:

Chemical Nature

E l E 2 E3 E 4 E 5 E 6 E 7 E 8

Inorganic Builders

SiO ₂ from Sodium Metasilicate 2.83 4.25 0.00 2.83 2.83 2.83 2.26 2.83 Pentahydrate

SiO ₂ from

Anhydrous Sodium 0.00 0.00 3.26 1.63 0.00 0.00 0.65 0.00

Orthosilicate

Anhydrous Sodium 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Tripolyphosphate

Sodium Tetraborate

Decahydrate (Also 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00

Called "Borax")

N onionic Surfactants

Dimethyl lauryl 17.5 0.0 10.0 17.5 15.0 10.0 20.0 0.0 amine oxide

Di(hydroxyethyl) 0.0 17.5 0.0 2.5 0.0 0.0 0.0 15.0 lauryl amine oxide

Diethyl stearyl amine 0.0 0.0 5.0 0.0 0.0 2.0 0.0 0.0 oxide

Polyoxyethylene (11

EO) nonylphenol 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 ether

Polyoxyethylene (12

EO) secondary 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 alcohol ether

Water Bal. Bal. Bal. Bal. Bal. Bal. Bal. Bal.

COD, ppm in: 600 620 550 690 520 430 680 520

Table I is continued on the next page .

Ingredient Type and Percent by Weight of Ingredient in:

Chemical Nature

CE 1 CE 2 CE 3 CE 4 CE 5

Inorganic Builders

SiO ₂ from Sodium Metasilicate 1.13 2.83 2.83 2.83 0.00 Pentahydrate

SiO ₂ from

Anhydrous Sodium 0.00 0.00 1.63 0.00 0.00

Orthosilicate

Anhydrous Sodium 0.0 0.0 0.0 0.0 12.0 Tripolyphosphate

Sodium Tetraborate

Decahydrate (Also 0.0 0.0 0.0 0.0 25.0

Called "Borax")

N onionic Surfactants

Dimethyl lauryl 17.5 0.0 5.0 0.0 0.0 amine oxide

Di(hydroxy ethyl) 0.0 8.75 0.0 0.0 0.0 lauryl amine oxide

Diethyl stearyl amine 0.0 0.0 0.0 0.0 0.0 oxide

Polyoxyethylene (11

EO) nonylphenol 0.0 0.0 0.0 17.5 0.0 ether

Polyoxyethylene (12

EO) secondary 0.0 0.0 0.0 0.0 17.5 alcohol ether

Water Bal. Bal. Bal. Bal. Bal.

COD, ppm in: 600 290 170 9450 6300

Abbreviations for Table 1

E = Example According to the Invention; CE = Comparison Example; (11 EO) = with an average of 11 molecules of ethylene oxide per molecule of phenol/alcohol; (12 EO) = with an average of 12 molecules of ethylene oxide per molecule of phenol/alcohol; Bal. = Balance; ppm = parts per million by weight.

Method for testing the deoreasino performance

For each of duplicate specimens of types (a) and (b), in which type (a) was aluminum alloy sheet and type (b) was aluminum fin stock as specified un¬ der the heading "Specimens" above, the surface was first cleaned with 1 ,1 ,1-trichloroethane vapor and then coated with a 1:1 mixture by volume of press oil (G-634B from Nippon Kosakuyu Kabushiki Kaisha) and machine oil (Spindle Oil #1 from Nippon Oil Co., Ltd.). This 1:1 mixture was applied with a roll coater to an add-on mass per unit area of approximately 2 grams per square meter (hereinafter usually abbreviated as "g/m ² "). The specimen was then allowed to stand for 2 days, at which point it was designated as the test spec¬ imen.

To test the degreasing performance, baths were respectively prepared by adding 10 parts per thousand by weight (hereinafter usually abbreviated as " ppt"), 20 ppt, or 50 ppt of the above-described oil mixture to the test degreaser. The test was also carried out using test degreaser to which the oil mixture had not been added. Each degreasing bath was heated to and held at 60°C ± 2°C, and the two test specimens (a) and (b) were immersed therein for 60 seconds without touching each other. This was followed by rinsing with a 30-second spray of water; setting the test specimens up vertically; holding for 60 seconds in a chamber; and immediately measuring the percentage of the area of the two test specimens that was water-wetted.

The results are reported in Table 2.

The following can be concluded from the results for Examples 1 to 8 and Comparative Examples 1 to 5. (1) Low COD values and excellent degreasing results were obtained in Ex¬ amples 1 to 8, which employed liquid alkaline degreasers according to the present invention. (2) Unsatisfactory degreasing results were obtained in Comparative Example 1 (deficient addition of inorganic builder on SiO ₂ basis) and in Compar- ative Examples 2 and 3 (deficient addition of nonionic surfactant accord¬ ing to the present invention) even in the absence of oil addition. The degreasing performance in each case was substantially reduced when oil

Table 2

DEGREASING PERFORMANCE OF THE ALKALINE DEGREASERS IN EXAMPLES 1 TO 8 AND COMPARATIVE EXAMPLES 1 TO 5

OilAddition in Specimen PercentofAreaWater-Wetted in:

PartsPer Designa¬

Thousand by tion El E2 E3 E4 E5 E6 E7 E8

Weight

100 100 100 100 100 100 100 100

(a) 100 100 100 100 100 100 100 100

0

100 100 100 100 100 100 100 100

(b) 100 100 100 100 100 100 100 100

100 100 100 100 100 100 100 100

(a) 100 100 100 100 100 100 100 100

10

100 100 100 100 100 100 100 100

(b) 100 100 100 100 100 100 100 100

100 100 100 100 100 100 100 100

(a) 100 100 100 100 100 100 100 100

20

100 100 100 100 100 100 100 100

(b) 100 100 100 100 100 100 100 95

100 95 100 100 95 95 100 90

(a) 100 95 100 100 100 90 100 90

50

100 100 100 90 100 85

(b) 95 100 100 90 100 100 95 90 100 90

Table 2 is continued on the next page ...

Abbreviations for Table 2 E = Example According to the Invention; CE = Comparison Example.

was admixed. (3) Comparative Example 4 (use of nonionic surfactant outside the scope of the present invention) and Comparative Example 5 (use of nonionic sur¬ factant and inorganic builder that are both outside the scope of the pres- ent invention) each gave degreasing results in the absence of oil addition approximately equal to those of products according to the present inven¬ tion. However, these comparative products suffered from a sharp decline in degreasing performance at an oil addition of 20 ppt or more. In addi¬ tion, their fairly high COD values would make effluent treatment difficult. Benefits of the Invention

As described hereinabove, the liquid alkaline degreaser according to the present invention is able to maintain an excellent degreasing performance with respect to the surface of aluminum and its alloys, and is able to do so even when, through continuous use, it has become loaded with three times as much oil as pure degreasing component (combined weight of inorganic builder and sur¬ factant). Moreover, liquid alkaline degreaser according to the present invention has a long life and is free of phosphorus. Its COD, which can be a problem for effluent treatment, is also low. These features and characteristics make subject liquid alkaline degreaser very valuable to the concerned industries.