BACKGROUND OF THE INVENTION

The use and manufacture of metalworking fluids (MWFs) represent a major cost-factor in the industrial processing of metals. MWFs play a significant role in processes like drilling, forming, grinding, or cutting of metals. Besides their lubricating capabilities, in these applications MWFs are used as coolants. This is achieved by conducting and dissipating accruing heat and reducing friction between a work piece and the tool and, therefore, influence the heat generation, MWFs are not only used for iron and steel but also for processing light metals, such as aluminum, magnesium, and their alloys, and are crucial in order to avoid thermal damage of the material of the work piece and to reduce wear on the tool.

MWFs can be divided in three groups: Oil-based, water-based, and emulsions. Water-based formulations may be composed in form of fairly complicated solutions containing up to 300 different additives. One important group of such additives are acidic corrosion inhibitors including but not limited to sulfonates, organic boron compounds, fatty acids, carboxylates, and phosphonates. For their use in neutral or alkaline media they are usually composed of an acid and a base to neutralize the acid. Typically, amino alcohols are used for such a neutralization. Besides 2-Amino-2-methylpropanol (AMP) and 1 -Aminopropan-2-ol (MIPA), Triethanolamine (TEA) is one of the predominantly used bases for this purpose. However, despite its comprehensive usage TEA has some major downsides. In the past it has been linked to allergic contact dermatitis, seawater ecotoxicity, and carcinogenic activity. Additionally, it is listed on the “EU Control List of Dual-Use Items”, which entails farther regulation and higher expenses. Thus, there is a general need for the replacement of commonly used amino alcohols like TEA with more environmentally friendly and less toxic bases for the neutralization of acidic corrosion inhibitors to be used as components of MWFs, While some attempts to utilize simple amino acids as “green” acidic corrosion inhibitors may have been made, salts of amino acids as neutralizing agents for acidic corrosion inhibitors have not been used so far, Proteinogenic as well as other amino acids are - unlike TEA and other commercially used organic amines and amino alcohols - nontoxic and non-hazardous. Additionally, they are easily available from renewable sources.

DETAILED DESCRIPTION OF THE INVENTION

With the present invention it has been found that the salts of bases with readily available amino acids (including proteinogenic amino carboxylic acids, such as methionine, cysteine, glutamic acid, arginine, and glycine, analogues and derivatives thereof, such as aminocaproic acid, as well as amines with other acid functionalities like a sulfonic acid group, a phosphonic acid group, or a phosphoric acid group, such as taurine) and dipeptides (such as N-(L-α-aspartyl)-L- phenylalanine or its 1 -methyl ester), which are nontoxic, nonvolatile, and available in big tonnages from bio-renewables, can be used as highly efficient green neutralizing agents for corrosion inhibition in alkaline media - replacing (fully, wherein the amino acid represents the only neutralizing component, or in part) environmentally problematic TEA and similar organic amines that are each, for several reasons, environmentally problematic.

With the present invention it was surprisingly found that the use of amino acids (such as methionine, cysteine, glycine, glutamic acid, serine, arginine, histidine, alanine, lysine, aminocaproic acid, or taurine; each used in their deprotonated form - e.g. in form of solutions of their sodium, potassium, or lithium salts) - wherein the amino acid is monomeric or in form of a dipeptide or wherein the amino acid is a derivative of a monomeric amino acid or of a dipeptide - in the neutralization of acidic corrosion inhibitors leads to very effective anticorrosive systems that are, in view the aforementioned problems of commonly used bases, highly advantageous. In comparison to mixtures of the same acidic corrosion inhibitors with the standard neutralizing agent triethanolamine (TEA), the amino acids of the present invention provide at least similar - in several cases increased - efficacies. The amino acids can be formulated with a broad range of acidic corrosion inhibitors including aliphatic, cycloaliphatic, and aromatic carboxylic acids, sulfonates, phosphonic and phosphoric acids, boric acid, tall oil derived acids, and others. Typical examples of acidic corrosion inhibitors to be used with the present invention are azelaic, sebacic, undecanoic, and dodecanoic acid, triazintriyltriiminotrihexanoic acid (TC ^® ) arylsulfonamido carboxylic acid (ASCplus ^® ), 11-phosphonoundecanoic acid (PUDA), phosphonobutanetricarboxylic acid (PBTC), amino - tris(methylenephosphonic acid)-N-oxide ( ATMP -N -Oxide) , or hexamethylenediaminetetra (methy lenephosphoni c acid) (HDTMP) but also phosphonic acid derivatives of terpenes and fatty acids, such as phosphonic acids derived from geraniol, citronellol, or pinene.

Preferably the amino acid comprises a primary amino-function. The preferred amino acids of the present invention are proteinogenic amino acids, β-alanine, y-aminobutyric acid, aminocaproic acid and taurine; most preferred are glycine, alanine, lysine, methionine, taurine, and aminocaproic acid (AC A).

In view of the aforementioned advantages of amino acids, which are non-toxic and available from renewable sources, and in view of their surprising efficacy in mixtures with acidic corrosion inhibitors, the present invention provides highly advantageous anticorrosive additives for MWFs that can be used in the industrial processing of numerous metals. It was well noted that neutralized amino acids and acidic corrosion inhibitors can easily be formulated into stable solutions in water, which can be stored at room temperature for months. In addition, it is remarkable that highly concentrated compositions can be formulated, such as, for example, 98 g of TC ^® , 80 g of amino caproic acid, and 24,4 g ofNaOH in 100 ml of water or 84,6 g of TC ^® , 39,1 g of glycine, and 22, lg ofNaOH in 100 ml of water

Comparisons of the commonly used neutralizing agent, TEA, with the neutralizing agents in accordance of the present invention, amino acids, which are used in deprotonated form (in form of their salts or in equimolar mixtures with, e.g., NaOH), showed that the latter may further increase the efficacy of the employed acidic corrosion inhibitors. As known from the art, simple inorganic bases, such as NaOH, that are used to neutralize acidic corrosion inhibitors do not result in efficient anti-corrosion systems, and while we do not want to be bound to this theory, it is expected that the amino acids interfere with the metal surfaces on their own and, thus, stabilize the layer formed by the primary acidic corrosion inhibitor. In particular, glycine, taurine, and ACA lead to highly efficient anticorrosive systems. While the amino acids are already effective at low concentrations (such as one molar equivalent, relative to the amount of the acidic corrosion inhibitor and the number of acid functions in the acidic corrosion inhibitor) and while the amino adds may be used also in higher concentrations, the preferred molar ratios of the amino acid (with one equivalent of base, such as NaOH or KOH) and the anticorrosive acid is 1/1 - 3/1 per acid group of the anticorrosive acid; preferably, the ratio is 1.5/1 per acid group of the anticorrosive acid. E.g., in the case of TC containing three carboxylic acids, the preferred ratio is 4.5 equivalents of the amino acid and NaOH - thus, the absolute molar ratio of the components (amino add/NaOH/TC) is 4.5/4,5/1.

As demonstrated in the Chip-Filter-Test, the amino acids of the present invention provide highly effective anti-corrosion systems for steel. In addition, in Leaching- Tests with Co, Cu, and Ni it was demonstrated that the amino acids in accordance with the present invention prevent or, at least, limit the undesired leaching of alloy elements and that they can be used successfully when handling, for example, Co-, Cu-, and/or Ni-containing steel-alloys; in particular, ACA shows impressive results outperforming even the current gold- standard for low Go-leaching applications, MIPA. Therefore, the amino acid-additives of the present invention allow to reduce the undesired leaching of certain elements (such as Co, Cu, and Ni) from an alloy, which is regularly observed when a corresponding workpiece is processed in the presence of a common metalworking fluid that comprises, e.g., TEA as basifying component.

Corrosion inhibition is not only important when handling iron or steel, it is also important when processing light metal alloys of, e.g., aluminum or magnesium. While commonly used carboxylic acid additives like TC are not capable of preventing corrosion or staining on light metal alloys, mixtures of octylphosphonic acid (OPA) and TEA provide some corrosion inhibition on aluminum. In the corresponding tests (with a copper containing hardened Al-alloy used in aerospace applications, AL 5083. an aluminum-alloy mostly used for welding and marine applications, AL 2024, and a standard wrought magnesium-alloy containing 3% aluminum and 1 % zinc used for example in automotive industry, MG AZ31 ), it was surprisingly found that the amino acids of the present invention (such as glycine or ACA, each with an equimolar amount of NaOH) can act as full and extremely valuable substitutions of the environmentally problematic TEA. In case of AL 5083 and MG AZ31, the amino acids of the present invention showed some effect even with TC and the mixtures of the present invention outperformed those of the prior art. Additionally, in view of the results achieved with aluminum and magnesium, it can plausibly be expected that the amino acids of the present invention can also be used to neutralize acidic corrosion inhibitors, when formulating efficacious anticorrosive systems for the processing of other metals and alloys, such as titanium, beryllium, and zirconium.

With the present invention it has been demonstrated that in combinations with acidic corrosion inhibitors, amino acids, which are highly beneficial due to their general bio compatibility, cost effectiveness, and nontoxicity, allow to replace harmful and problematic TEA - in applications on steel, aluminum, and magnesium. ,

The amino acids of the present invention are compatible with a range of acidic corrosion inhibitors, such as phosphonic and/or carboxylic acids commercially used for steel and aluminum. These new systems achieve corrosion scores as good as or even better than the corresponding TEA based additives of the prior art. Additionally, with the present invention anticorrosive systems entirely based on renewable resources become available - e.g., by using the amino acids of the present invention as neutralizing agents for natural product-derived acidic corrosion inhibitors, such as geranylphosphonic acid, pinene derived phosphonic acid (PDPA), or 11 -phosphonoundecanoic acid (PUDA). These fully renewable mixtures are highly efficient anticorrosives and can be utilized in the processing of steel, aluminum, and even magnesium. The corrosion inhibitors of the present invention fit the ongoing need of green chemistry to develop technologies and materials that are intrinsically nontoxic to living organisms and the environment and that minimize harmful waste.

EXPERIMENTAL SECTION

Syntheses

11 -Phosphonoundecanoic acid (PUDA) may be synthesized from undecylenic acid via palladium-catalyzed hydrophosphorylation with H ₃ PO ₂ . Geranylphosphonic acid can be synthesized via palladium catalyzed dehydrative ally lie substitution with H3PO2 and geraniol and subsequent oxidation with iodine and DMSO. PDPA may be obtained via radical addition of ammonium hypophosphite with triethyiborane to b-pinene and subsequent oxidation with iodine and DMSO (scheme 1).

Scheme 1, Possible syntheses of the natural product-derived phosphonic acids.

Chip-Filter-Test The evaluation of the rust preventive properties of water-miscible coolants was conducted with 2 mL 3 w.-% solutions (calculated to the acid) and 2,0 g sieved grey cast 25 chips for 2 h according to DIN 51360-02-A. Table 1: Results of the Chip-Filter- Test of TC (3 w.-%) neutralized with TEA or amino acids of the present invention (in form of their sodium salt).

*Used as disodium salt.

Table 2. Conditions and corrosion scores of Chip-Filter-Tests of various acidic corrosion inhibitors (acid, each in a concentration of 3 w.-%) in combination with TEA or an amino acid for neutralization.

* Used as Sodium salt, ** 4.5 eq of amino acid and 4 eq of NaOH. ***after 16 h at 60°C.

Staining Assay. The evaluation of corrosion inhibition for light metal alloys was conducted with 2.5 mL of an aqueous solution containing up to 4 weight % of the acidic corrosion inhibitor and 1*3 cm plates of aluminum or magnesium alloys for 24 h at 40°C. The plates were placed in a small glass vessel with half of their surface being covered by the test medium. Subsequently, the staining was rated on a scale from 0 (No Staining) to 4 (strong staining). The optical assessment of staining was performed in accordance to Watanabe et al. (S. Watanabe, J Oleo Sci, 2008, 57, 1-10),

Table 3. Conditions and scoring of TC, PUDA, PDPA and OPA in combination with TEA, Glycine and AC A on Al 2024, Performed in hardw'ater (10° dH) at 40°C for 24h.

Table 4. Conditions and scoring of TC, PUDA, PDPA and OPA in combination with TEA,

Glycine and AC A on A1 5083. Performed in hardwater (10° dH) at 40°C for 24h. Tabic 5. Conditions and scoring of TC, PUDA, PDPA and OPA in combination with TEA,

Glycine and AC A on Mg AZ31. Performed in hard water (10° dH) at 40°C for 24h.

Leaching Another parameter to consider for the industrial usage of metal working fluid is their leaching characteristics for important alloy metals such as Co, Ni or Cu. AMP and MIPA are marketed as low leaching additives. Several amino acids were examined. For realistic results, the solution was pH-adjusted to match the pH value of the mixture in the Chip-Filter- Assay. 225 mg Co, Ni or Cu-Powder ( < 150 μm, 99.9% trace metal basis) was suspended in 15 ml of a 1 w.-% aqueous solution of the amine (in case of the amino acids and taurine, the pH value was adjusted with sodium hydroxide) and heated under reflux for 24 hours. The suspension was cooled to room temperature, filtered and the metal -concentration (either Co, Ni or Cu) of the filtrated was measured directly via F-AAS. Table 6. Detected Co, Ni and Cu-concentrations and pH values for each tested amine. The concentration was measured from the filtrate via F-AAS

*Used as sodium salt.