DE19747895A1 - Metal treatment liquid for the neutral pH range - Google Patents

Abstract

A metal processing liquid with a pH value ranging from 6-9, containing a combination of one or several carboxylic acids and one or several nitrogen compounds selected from organic amines or heterocycles containing nitrogen, whereby the nitrogen compounds have a pKS value for at least one proteolysis step ranging from 6-9, with a weight ratio of 10:1 to 10:20.

Description

The invention relates to metal treatment fluids such as Cooling lubricants, cleaners and anti-corrosive emulsions, which due to a new corrosion inhibitor combination in the pH range of about 6 to about 9, especially up to about 8.5 can be used. The Corrosion inhibitor combination of carboxylic acids and nitrogen compounds has a good buffer effect in addition to the good corrosion protection effect. This allows the lying in the neutral range pH of the Metal treatment fluid despite a possible acid entry and / or maintain microbiological acidity for a longer period of time become.

The protection of corrosion-prone metals such as iron, aluminum, Zinc, copper or their alloys from corrosion is a wide-ranging technical task. It arises in particular when the metal parts due to their processing status or due to their field of application not or not yet with a permanent corrosion protective coating such as For example, a varnish are covered. Examples include metal parts during technical processing stages such as cutting or non-cutting Shaping or cleaning as well as finished metal components such as  Heat exchangers or pipelines that are corrosive during their function aqueous media come into contact. To prevent corrosion during or between the individual processing fonts or during the To prevent or curb normal use, you bring the Metal surfaces with corrosion inhibitors in contact with a temporary Corrosion protection effect. It is often for technical reasons required, for example in aqueous cooling or heating circuits, or off Environmental protection desirable, for example during or after an aqueous cleaning of the metal surfaces, that the corrosion inhibitors in aqueous phase can be brought into contact with the metal surfaces. Therefore, it is a desirable property of corrosion inhibitors, water-soluble or at least dispersible in water.

As water-soluble or water-dispersible corrosion inhibitors are a Variety of inorganic and organic compounds known. inorganic Corrosion inhibitors can be used, for example, on chromates, nitrites or However, phosphates can be built up, however, from toxicological and ecological Reasons are more or less disadvantageous. Organic corrosion inhibitors are often based on carboxylates, amines, amides or on nitrogenous heterocyclic compounds. Carboxylic acids prove in practice, however as not sufficiently long-term effective, if by an acid entry into the Inhibitor baths or by microbiological processes commonly used in alkaline pH range is lowered so far that the carboxylic acids instead of being in the salt form in the less effective acid form.

The use of carboxylic acids as corrosion inhibitors in at For example, coolants, cleaners and anti-corrosive emulsions are available in the State of the art disseminated. For example, DE-A-42 29 848 describes a Coolant emulsion, its corrosion protection system on a combination long-chain fatty acids, short-chain fatty acids, dimer fatty acids as well as  aromatic carboxylic acids such as benzoic acid or salicylic acid based. In this case, the carboxylic acids are neutralized with potassium hydroxide. This System is alkaline.

DE-A-43 23 909 teaches two-component agents for the cleaning and / or passivation of metal surfaces, one component containing the anticorrosive agents. The corrosion inhibitor active ingredients are selected from

• i) at least one carboxylic acid of the general formula (I):
  R-COOY (I)
  where R is a straight-chain or branched, saturated or unsaturated alkyl or alkenyl radical having 5 to 21 C atoms or a radical of the general formula (II)
  with R ¹ = saturated, straight-chain or branched alkyl radical having 6 to 18 C atoms and Y is hydrogen, an alkali metal ion equivalent or an ammonium ion,
• ii) substituted benzoic acids,
• iii) benzenesulfonamidocarboxylic acids,
• iiii) aliphatic dicarboxylic acids having 2 to 36 carbon atoms, and
• iiiii) the salts of the acids mentioned under i) to iiii) and mixtures thereof.

Also this system unfolds its effect in the alkaline area and includes no buffer components for stabilizing the alkaline pH in this case Value for acid entry or acid formation.

Finally, it can be seen from EP-A-556 087 that Mo Nocarboxylic acids with an odd number of carbon atoms, in particular heptanoic acid, nonanoic acid and undecanoic acid, particularly effective cor represent rosioninhibitorsen.

DE-A-44 44 878 discloses nitrogen-free corrosion inhibitors with good buffer action, which have a pH in the range from 7 to 11 at the application concentration. As a corrosion protection component containing carboxylic acid anions having 6 to 44 C atoms and, as buffer component aromatic hydroxy compounds with a pK _s value for the hydroxy group is in the range 7 to 11

Because of the good corrosion protection effect have conventional Corrosion inhibitor in application concentration usually one alkaline pH in the range of about 9 to about 10. When disposing These solutions must be neutralized, so that an additional substance consumption and a sewage pollution with salts occurs. Furthermore, the alkaline Medium endanger the user, for example, by splashes in the eyes. Therefore There is a need for effective anticorrosive agents which are available in the neutral pH range. Range between about 6 and about 9, preferably between about 6 and about 8.5 and in particular between about 6 and about 8 can be used. These Funds are more safe to use and easier to dispose of than the conventional ones Medium. They should also have a certain buffer capacity, so that the Approximately neutral pH despite possible acid entry and / or maintain microbiological acidity for a longer period of time can be.  

From EP-A-520 108 neutral corrosion inhibitors for aerosol spray cans are known, which consist of certain ammonium salts of carboxylic acids. These cause corrosion inhibition in the approximately neutral pH range. Since such aerosol spray cans are closed systems, decomposition of the corrosion-inhibiting liquid by microorganisms is not to be expected. Therefore, in this closed system, there can be no pH shift due to biological processes, so that the liquid does not have to be stabilized against a shift in pH. Accordingly, the corrosion inhibitor combination need not have a buffer action and the pK _S - values of the nitrogen compounds may be located in any area. In fact, the pK _s values of the nitrogen compounds to be used according to EP 520 108 are all above 9.

The present invention, on the other hand, has as its object a corrosion protection system for the pH range between about 6 and about 9 available against acidification due to biological decomposition processes is stabilized. The corrosion protection system must therefore have a certain buffer effect in have this pH range.

The invention is a metal processing liquid with a pH in the range of 6 to 9, comprising a combination of one or more carboxylic acids and one or several nitrogen compounds selected from organic amines or nitrogen-containing heterocycles, wherein the nitrogen compounds have a _pK a value for at least one Protolysis stage in the range of 6 to 9, in a weight ratio of 10: 1 to 10: 20.

The pH is preferably in the range of 6 to 8.5 and especially in the range 6 to 8 show Accordingly, the nitrogen compounds preference as a _pKa in the range of 6 to 8.5 and especially in the range from 6 to 8 on.

When this is the case of carboxylic acids, this means that the acids can be used as such or in the form of their water-soluble in application concentration salts. Depending on the pK _S value of the acids, a pH-dependent equilibrium of acid anions and undissociated acid is established. Accordingly, this applies to the balance between the free nitrogen base and its protonated form.

Preferably, the weight ratio is carboxylic acids: nitrogen compounds ranging from about 10: 2 to about 10: 10.

The carboxylic acid is preferably selected from mono- or polybasic, saturated or unsaturated, linear or branched aliphatic Carboxylic acids with 6 to 14 carbon atoms and from carboxylic acids in the Carbon chain inserted heteroatoms containing between 6 and 26 atoms in having the carbon heteroatom chain. Examples of such carboxylic acids are the unbranched saturated carboxylic acids n-hexanoic acid, n-octanoic acid, n-decanoic acid and n-dodecanoic acid and in particular those according to the teaching of EP-A-556 087 preferably used monocarboxylic acids having an odd number of carbon atoms, in particular n-heptanoic acid, n-nonanoic acid and n-undecanoic acid. Special technical advantages also offer branched saturated Carboxylic acids, in particular 2-ethylhexanoic acid, 3,5,5-trimethylhexanoic acid (= Isononanoic acid) and 2,2-dimethyloctanoic acid. An example of a dicarboxylic acid is the 1,8-octanedicarboxylic acid. A preferably usable example of an unsaturated short-chain carboxylic acid is 1,4-hexadienoic acid (sorbic acid).

Preferred carboxylic acids with heteroatoms inserted into the carbon chain are preferably ether carboxylic acids of the general formula R- (OC ₂ H ₄ ) _n -OCH ₂ COOH, where R is a linear or branched, saturated or unsaturated alkyl radical having 6 to 16 C atoms, n represents a number in the range of 1 to 5 and R and n are to be matched to one another such that the sum of the C and O atoms is not greater than 25, neglecting the carboxyl group. The ether carboxylic acids may be technical mixtures of molecules with different radicals R and different values for n. An example of this is the technical lauryl ether carboxylic acid in which R stands for a mixture of linear, saturated alkyl groups having 12 and 14 C atoms and n is about 2.

Furthermore, as carboxylic acids are nitro-containing aromatic carboxylic acids suitable. An example of such an acid is 3-nitrobenzoic acid.

In addition to the carboxylic acid components whose corrosion inhibiting effect in The prior art is already known, which additionally acts as a buffer Nitrogen compound of particular importance to the metal treatment liquid to stabilize against acid entry or acid formation and thus without further Caring for a prolonged compared to unbuffered systems Period to be usable. Preferably, one chooses such Nitrogen compounds having a buffer capacity of about 1 to about 4. To determine this value, dilute 50 mg of the nitrogen compound with 50 ml of demineralized water. If the nitrogen compound is insufficient for this is water soluble, it is first dissolved with 10 ml of isopropanol and then diluted to 50 ml with demineralized water. Is the pH value this solution below 6.0, titrated with 0.1 N sodium hydroxide solution. Has the aqueous solution of the nitrogen compound has a pH of above 7.5, so tritrated with 0.1 N hydrochloric acid. The consumption of 0.1 N lye or acid in ml, to change the pH from 6.0 to 7.5 or from 7.5 to 6.0 is referred to as Buffer capacity defined. Is the pH of the solution inherent in the area? between 6.0 and 7.5, it is first set with lye to a value of  above 7.5 and then titrated with 0.1 N acid until the pH is 7.5 lowered to 6.0.

Sufficient buffer capacity in the neutral pH range frequently have such nitrogen compounds, which have a _pK a value in the range of about 6 to about 9, wherein nitrogen compounds having pK _s in the range of about 6 to about 8.5 and especially from about 6 to about 8 are preferred.

The _pK a value is known to be the negative decadic logarithm of the acid constants, K _S, which is commonly known as thermodynamic quantity and a measure of the completeness of the proton transfer reaction of the acid to water and thus represents the acid strength. Details can be found in textbooks of general chemistry. HRChristen is mentioned as an example: "Fundamentals of General and Inorganic Chemistry", Verlag Sauerländer, Aarau and Disterweg.Salle, Frankfurt, 4th edition 1973, pp. 353-372. the purposes of this invention, the _pKa refers to the conjugate acid of the nitrogenous base, ie to the protonated nitrogen compound. Thus, the acid constant for the equilibrium reaction of the protonated nitrogen base with water is selected for the free nitrogen base and an oxonium cation. Have the nitrogen compounds more nitrogen atoms, it is sufficient according to the invention when the _pKa is for the protolysis in the desired range. The _pK a values for a range of nitrogen compounds can for example be taken from DD Perrin: "Dissociation Constants of Organic Bases in Aqueous Solutions", International Union of Pure and Applied Chemistry, Butterworths (London)., 1965

The nitrogen compounds may for example be selected from linear or cyclic alkylenediamines, alkylene triamines and alkylene tetraamines. Examples of such compounds are ethylenediamine, propylenediamine (especially 1,2-propylenediamine), butylenediamine, diethylenetriamine,  Dipropylenetriamine, triethylenetetraamine and tripropylenetetraamine. ethylenediamine is preferred. Another example is guanidinium salts with suitable anions, in particular guanidinium carbonate.

Also well suited are those nitrogen compounds which are selected from 5- or 6-membered aromatic organic heterocycles having 1 or 2 nitrogen atoms, which may also be present as parts of benzo-fused ring systems. A preferred example of such heterocycles is imidazole with a pK _s value of about 7.

Metal treatment fluids according to the present invention, which for example as water-soluble cooling lubricants, as water-mixed Coolant emulsions, as cleaners or as anti-corrosive emulsions can be used, usually come as concentrates in the trade and are used by the user on site with water to the application concentration diluted. Such concentrates of the metal treatment fluids are used the carboxylic acid in amounts between about 5 and about 30 wt .-%, preferably from about 8 to about 20 weight percent, the nitrogen compound in amounts between about 0.5 to about 40% by weight, preferably about 2 to about 10% by weight.

From such concentrates by dilution with water ready-to-use solutions or oil-in-water emulsions. These ready-to-use metal treatment liquids are usually prepared in this way that they contain from about 2% to about 10% by weight of the concentrate in water. Of course you can also such metal treatment liquids in the Make way that the individual components in the desired Concentration in water dissolves or disperses. Here one is from the Manufacturability of concentrates independently and has a larger Formulation latitude. Such a method is not common in practice, wherein however, individual components in an otherwise ready to use  Metal treatment fluid can be replenished if necessary. Lying the Metal treatment fluids as ready-to-use aqueous solution or as ready for use oil-in-water emulsion, they contain about 0.1 to about 3 Wt .-%, preferably about 0.2 to about 2 wt .-% of the carboxylic acid and about 0.01 to about 6 wt .-%, preferably about 0.04 to 2 wt .-% of Nitrogen compound.

When in the context of this invention of "carboxylic acid" or "Nitrogen compound" is mentioned, so here are also mixtures different carboxylic acids or nitrogen compounds understood.

In a further aspect, the invention relates to the use of a combination of one or more carboxylic acids and one or more nitrogen compounds selected from organic amines or nitrogen-containing heterocycles in a weight ratio of 10: 1 to 10: 20 as corrosion inhibitors in the metal treatment liquids having a pH in the range of 6 to 9, wherein the nitrogen compounds have a pK _s value for at least one protolysis step in the range of 6 to 9. Preferably, the pH of the metal treatment is liquid in the range of about 6 to about 8.5 and especially from about 6 to about 8. Accordingly, it is preferred that the nitrogen compounds have a _pK a value for at least one protolysis in the range from 6 to 8.5 and in particular in the range of 6 to 8 have.

Preferably, the weight ratio is carboxylic acids: Stickstoffverbindun about 10: 2 to about 10: 10. For the use in this preferred to be used carboxylic acids and nitrogen compounds are the above further explanations.

Typical metal treatment liquids for the pH range between about 6 and about 9, the inventive combination of carboxylic acids and Contain nitrogen compounds are coolants or Coolant emulsions and neutral cleaners or their concentrates.  

For example, the metal treatment liquid may be an oil-in-solution. Water emulsion having an oil content of about 0.2 to 4 wt .-% act as Emulsifiers contains nonionic surfactants. Here come as nonionic Surfactants such as ethoxylates or propoxylates of fatty alcohols into consideration. Such oil-in-water emulsions are usually made by offsetting Concentrates prepared with water. As essential components contain these Concentrates usually about 30 to 50 wt .-% of an oil components such as For example, mineral oil, about 10 to 20 wt .-% emulsifiers, about 20 to 50 Wt .-% of the inventive combination of carboxylic acids and Nitrogen compounds and the remainder water and / or other auxiliaries.

Furthermore, the inventive combination of carboxylic acids and Nitrogen compounds oil-free cooling lubricant solutions such as Be added to grinding waters. Such abrasive waters are commonly referred to as Concentrates marketed and user-supplied with water Diluted application concentration. The application concentration is in the Usually about 2 to about 8, especially about 4 to about 6 wt .-% concentrate in Water. These concentrates usually contain about 6 to about 30% by weight of the inventive combination of carboxylic acids and nitrogen compounds.

Furthermore, the grinding water concentrates usually contain non-ferrous metal inhibitors in amounts between about 0.05 and about 0.3% by weight. Examples of Non-ferrous metal inhibitors are triazines, triazoles or thiazoles. For example, called be benzotriazole, tolyltriazole or benzothiazole derivatives.

Optional components of grinding water concentrates are, for example Boric acid in amounts of about 5 to about 15 wt .-% and complexing agents such as For example, nitrilotriacetic acid in amounts of about 0.01 to about 0.2 wt .-%. To improve the drying behavior of the processed pieces you set the concentrates of the grinding waters advantageously polyhydric alcohols,  such as glycerol too. For example, a concentrate between about Contain 10 to about 30 wt .-% glycerol.

embodiments

The following amines were used in the practice of the invention: 1,2-diaminoethane (ethylenediamine) having a buffering capacity determined as described above of 4.4, imidazole having a buffering capacity of 2.0 and guanidinium carbonate having a buffering capacity of 2.4 , Diaminoethane has protolysis in the second at 20 ° C has a _pK a value of 7, imidazole at 20 ° C has a _pK a value of 7.2. Further suitable examples are 1,2-diaminopropane with a pK _s value in the second protolysis stage at 25 ° C. of 7,1, 1,3-diaminopropane with a pK _s value at 20.degree. C. of 8.6, or diethylenetriamine with a pK _s value of the second protolysis stage at 20.degree. C. of 8.9. Other suitable examples of nitrogen compounds having pK _S values in accordance with the invention the desired range can be taken from the table work by DD Perrin cited above.

The carboxylic acids used were heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid and lauryl ether carboxylic acid R- (OC ₂ H ₄ ) _2,5 -CH ₂ COOH with R = C _12/14 -alkyl.

The corrosion protection effect was tested in a coolant concentrate of the following composition diluted with water to application concentration:

ingredients weighing Enepar 301 (paraffinic mineral oil) 609.3 g rapeseed oil fatty acid 71.1 g Oleic acid (technical) 47.5 g Oleyl / cetyl alcohol + 5 ethylene oxide 114.1 g diglycol 19.0 g least. water 20.0 g sulfonated fatty acid 47.5 g benzotriazole 10.2 g total quantity 938.7 g

To test the corrosion protection effect, the concentrate was additionally with the added in Table 1 amounts of corrosion inhibitor combination. The% data given in Table 1 refer to Components on the total amount of concentrate after mixing with the Inhibitor combination. For corrosion protection test were from the concentrates water-mixed coolant emulsions with the in Table 1 percentages of concentrate produced. The determination of Corrosion protection properties of the ready-to-use water-mixed Coolant emulsions were made by the chip / filter paper method in accordance with German standard DIN 51 360, Part 2. For this test Cast iron chips on a round filter wetted with the coolant lubricant emulsion, 2 Exposed for hours in a Petri dish to room temperature and then visually assess the round filter for corrosion marks. A degree of corrosion 0 means no signs of corrosion, a degree of corrosion 4 strong traces of corrosion. The test results for application concentrations of 5 to 8% by weight Concentrate in water according to DIN 51 360 are given in Table 1. (The  Water according to DIN 51 360 is prepared in the following way: One prepares one Solution A, by adding 39 g of calcium chloride hexahydrate with demineralized water dissolves to a volume of one liter. Furthermore, you prepare a solution B, by adding 44 g of magnesium sulfate heptahydrate with demineralized water to a Volume of one liter triggers. Take 17 ml of solution A and 3 ml of Solution B and mixed with 980 ml of deionized water). Additionally contains the table shows the pH of the 5% cooling lubricant emulsion, the if necessary adjusted to the stated value with lye or acid.

With some of the water-mixed metal treatment fluids was added the anticorrosive effect was carried out after a plate climatic test. For this were steel sheets of quality ST 1405 with the dimensions 5 cm × 10 cm with brushed an aqueous surfactant solution, rinsed with water and alcohol and dried. Thereafter, the sheets were dipped in the application solution, drain and place in a climatic chamber at 22 ° C and a relative Humidity of 76% stored. For the production of the tested Application solutions were first prepared concentrates, the 20 wt .-% Heptanoic acid, 5% by weight of nitrogen compound and 75% of demineralized water contained. As nitrogen compounds were respectively ethylenediamine, imidazole and Guanidinium carbonate selected. 2 parts by weight of concentrate were used with 98 Parts by weight of water to the application solution for the Plattenklimatest to obtain. If necessary, the pH of the emulsion was adjusted to 7 with potassium hydroxide solution set. In all 3 trials, the required corrosion protection (less as 30% corrosion after 40 days of test).  

Claims (11)

1. Metal treatment liquid having a pH in the range of 6 to 9, comprising a combination of one or more carboxylic acids and one or several nitrogen compounds selected from organic amines or nitrogen-containing heterocycles, wherein the nitrogen compounds have a _pK a - value for at least a protolysis in the range from 6 to 9, in a weight ratio of 10: 1 to 10: 20. 2. Metal treatment liquid according to claim 1, characterized in that it has a pH in the range of 6 to 8.5. 3. Metal treatment liquid according to one or both of claims 1 and 2, characterized in that the weight ratio of carboxylic acids to Nitrogen compounds in the range of 10: 2 to 10: 10. 4. Metal treatment liquid according to one or more of claims 1 to 3, characterized in that the carboxylic acids are selected from on or polybasic, saturated or unsaturated, linear or branched aliphatic carboxylic acids having 6 to 14 carbon atoms and from linear Carboxylic acids with inserted into the carbon chain heteroatoms, the have between 6 and 24 atoms in the carbon heteroatom chain. 5. Metal treatment liquid according to claim 4, characterized in that the carboxylic acids are selected from n-hexanoic acid, n-heptanoic acid, n-octanoic acid, n-nonanoic acid, n-decanoic acid, n-undecanoic acid, n-dodecanoic acid, 2-ethylhexanoic acid, 3,5,5-trimethylhexanoic acids 2,2-dimethyloctanoic acid, 1,8-octanedicarboxylic acid, sorbic acid and from ether carboxylic acids. 6. Metal treatment fluid according to one or more of claims 1 to 5, characterized in that the nitrogen compounds are selected from linear or cyclic alkylenediamines, alkylene triamines and Alkylentetraaminen. 7. Metal treatment liquid according to one or more of claims 1 to 5, characterized in that the nitrogen compounds is selected from 5- or 6-membered aromatic organic heterocycles having one or two  Nitrogen atoms. 8. Metal treatment liquid according to one or more of claims 1 to 7, characterized in that it is present as a concentrate and 5 to 30 wt .-% the carboxylic acid and 0.5 to 40 wt .-% of the nitrogen compound. 9. Metal treatment liquid according to one or more of claims 1 to 7, characterized in that they are as ready-to-use aqueous solution or as ready-to-use oil-in-water emulsion is present and 0.1 to 3 wt .-% of Containing carboxylic acid and 0.01 to 6 wt .-% of the nitrogen compound. 10. Use of a combination of one or more carboxylic acids and one or more nitrogen compounds selected from organic amines or nitrogen-containing heterocycles in a weight ratio of 10: 1 to 10: 20 as corrosion inhibitors in the metal treatment liquids having a pH in the range of 6 to 9, wherein the nitrogen compounds have a pK _s value for at least one protolysis step in the range of 6 to 9. 11. Use according to claim 10, characterized in that the nitrogen compounds for at least have a _pK a protolysis stage is in the range of 6 to 8.5.