DK152056B - STABILIZED OIL-IN-WATER DISPERSIONS AND THEIR USE AS METAL WORKING LIQUID - Google Patents

Description

DK 152056B

The invention relates to stabilized oil-in-water dispersions comprising an emulsifier selected from anionic and non-ionic agents and mixtures thereof which provide electronegativity for the oil phase of the dispersion. The invention further relates to the use of such dispersions as metal working fluid.

Metalworking fluids are well known in the art where they serve to lubricate and cool various metal surfaces during metalworking operations such as cutting, milling, turning, drilling, grinding, quenching and the like. To date, metalworking fluids have not exhibited long functional life. Eg. the oil and water emulsions or dispersions are degraded by use usually for a limited period of time, even as short as some 2

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A few weeks', The degradation of the emulsions has been attributed to a number of causes associated with metalworking operations, including the introduction of foreign material such as abrasive dust or dirt, metal particles, polyvalent metal ions and bacteria, and metal working conditions including pressure and temperature, etc.

The lack of extended stability in metalworking fluids has therefore led to serious direct and indirect disadvantages of their use in metalworking operations. Eg. Increases the short life of metalworking fluids increases the work and material costs associated with handling and using the fluids in metalworking systems. Furthermore, the degradation of such fluids increases the wear of the metalworking machines themselves and reduces the tool life due to failure of the metalworking fluids. Among other effects of metalworking liquids decomposition are increased disposal of workpieces, reduced production and increased costs associated with downtime, expensive collection of discarded liquids, work and health problems related to their use and environmental pollution. Therefore, the provision of metal working fluids with increased service life and stabilized against degradation due to metal working conditions among other desirable properties is very important not only for the industry in which they are used, but also for the environment in which we live.

Various attempts have been made in the past to improve metalworking fluids and to overcome or mitigate the direct and indirect disadvantages associated with the use of such metalworking fluids. Patents representative of the prior art in the art are U.S. Patents Nos. 2,688,146, 3,240,701, 3,244,630, and 3,365,397. These patents and the efforts of others have mainly been directed to overcoming the factors , which helps in the breakdown of emulsions. Suffice it to say that the results of these efforts have been less than satisfactory and that improved metalworking fluids are needed which will yield new results and overcome the current problems and disadvantages.

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As disclosed in Danish Patent Application No. 3601/77, the antimicrobial activity of certain metal complexes, e.g. the dialkali metal monocobes (II) citrates, have been determined by their toxic and growth inhibitory action against a number of microorganisms in oil emulsions used as refrigerants in various processing operations. The efficiency of metal complexes in industrial coolants was established in such fluids, where a number of microorganisms were found to multiply. As also stated in the aforementioned patent application, it was found in particular that the metal complexes were remarkably effective at alkaline pH values occurring under metalworking conditions.

The present invention further extends the aforementioned findings regarding the stabilization of oil-in-water dispersions by the addition of an effective stabilizing amount of a metal complex of a metal ion and a polyfunctional organic ligand.

These metal complexes are listed in the above application.

The stabilizing metal complex has been found to have a very unexpected proton-induced dissociation ability in water which results in controlled release of metal ion into the oil-in-water dispersions and provides metalworking stability to them. This dissociation ability is represented by an S-shaped curve on a right-angled coordinate plot of the negative logarithm of the metal ion concentration versus the negative logarithm of the hydrogen ion concentration, ie. a pM pH diagram. Accordingly, the stabilized oil-in-water dispersions of the invention are characterized by the characterizing part of claim 1.

Unexpectedly, it has been found that the dispersions of the invention, when used as metal working liquids, can be stabilized against attack and degradation for various reasons.

Eg. For example, the metal complexes in question, as set forth in the above application, are effective as antimicrobial agents in metalworking emulsions. It has further been demonstrated that these metal complexes provide other stabilizing properties to the metalworking fluids and bring improvements and advantages which 4

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has not yet been achieved with metal working fluids. This stability is not only achieved against bacteria, but the liquids are stabilized against degradation for physical, chemical and physical-chemical reasons associated with metalworking conditions, including heat, pressure and changes in the composition of the metalworking environment due to metalworking particles, polyvalent ions, etc. According to the invention, metal working fluids have been greatly improved. Eg. the life of liquids as industrial refrigerants has been extended from e.g. a few weeks to almost a year or more, and current results suggest that life can be extended almost indefinitely. The metal complex stabilizers are themselves very stable at relatively high alkaline pHs of the order of 9 or 10 to about 12. However, the stabilizing complexes in an alkaline pH range of from about 7 to about 9, where metal working fluids are to function, are very advantageous stabilizing effects on the metalworking fluids. In this connection, it has also been found that metal working fluids containing very small amounts of stabilizing metal complex can be provided, i.e. amounts which may be below those which would exert biocidal activity and that such metalworking fluids may nevertheless be stabilized against degradation from all factors in the metalworking environment.

Thus, the invention is directed to providing stability to otherwise degradable oil-in-water dispersions which are subject to degradation for a variety of reasons. Eg. For example, the dispersions can be added to biostability by introducing the metal complexes even in amounts less than previously used biocidal amounts. On the other hand, general emulsion stability can be achieved by introducing amounts of metal complexes which stabilize the emulsions against degradation from foreign sources, such as metal particles, polyvalent metal ions and the like. Furthermore, the dispersions can be given extremely high resistance to pressure and heat by using the stabilizers in question. According to another aspect of the invention, the chemical effect of other groups is reduced on the emulsified particles which would otherwise tend to decrease stability. These and other advantages of the invention will be explained in more detail in the following description.

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The theories or the underlying causes of the rather unexpected activities of the metal complex stabilizers in question have been explored. Although applicants do not wish to be limited by theoretical considerations, it is believed that they may assist in a deeper understanding of the benefits and unexpected results obtained by the invention. It is believed that oil-in-water dispersions can be biodegradable, chemically degradable due to chemicals in the liquid media, physically degradable due to conditions such as mechanical forces, or degradable due to combinations of two or more such factors. As is known, such oil-in-water dispersions contain emulsifiers, and these emulsifiers are typically of the "anionic" and / or "nonionic" type. Due to their hydrophilic-hydrophobic nature, the emulsifiers allow the suspension of the oil particles in a continuous phase of the liquid. Electronegative groupings, e.g. carboxyl and sulfonate groups in the emulsifier provide electronegative oil droplet charges. The combined electronegativity of such an emulsified particle is commonly referred to as the zeta potential. Essentially, the zeta potential is associated with the force and distance over which the emulsified particles can repel each other and thus prevent flocculation. This is, of course, an oversimplification of such oil-in-water dispersions. Nevertheless, one might have expected that introduction of a highly charged divalent metal cation or similar grouping into the stabilizing metal complexes would impair the stability of the emulsion and perhaps cause flocculation due to of neutralizing the highly electronegative nature of the emulsion droplets.

Thus, in a broader sense, the invention provides for the stabilization of oil-in-water dispersions by the addition of a polyvalent metal ion which forms a coordinate bond with the electronegative emulsifier. The stabilizing effects of such coordination are realized because the electronegativity still exists to prevent demulsification, while the other susceptible sites in the emulsifier are now 6

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blocked to enzymatic degradation * and to transfer the metal ion as an interface lubricant to the interface between tool and workpiece ', This stabilization is attributed to the highly electronegative nature of the emulsified droplet, which either generates or contributes to the dissociation of the metal complex and allows for the coordination of the metal with the metal ion. units in the emulsified droplets, e.g. the carboxyl groups, the sulfonate groups or the alcoholic hydroxy groups in the emulsifiers. This blocking of these bio-sensitive or functional groups prevents the enzymatic degradation of these structures, which are commonly associated with microbial metabolism. However, it is quite unexpected that the introduction of the metal complexes or the introduction of such metal ions has been found not to produce demulsification of the electronically charged emission droplets. This is because the amount of positively charged ions that connect to the electronegative surface of the oil droplet, although sufficient to provide biostability, is not sufficient to reduce the electronegativity of the particle to the demulsification point. Therefore, the formation of co-ordinating structures with emulsifiers is a novel method of stabilizing emulsions.

It has also been found that the introduction of the metal complex stabilizers in question gives rise to extremely high heat and pressure resistance of the emulsion during metalworking procedures. Such high heat and pressure resistance is produced by the coordinate structures of metal ions and emulsifiers in the stabilized dispersions of the invention. These properties are exhibited by the metal cation or metal complex which is transported to and then associated with the electronegative groupings in the emulsified droplets as mentioned above. The emulsified droplets are continuously brought into intimate contact with the interfaces between the tool and workpiece during metalworking procedures. Eg. For example, copper associated with the emulsified droplets at the interface undergoes the heat and pressure of the metalworking process in an oxidation-reduction process which serves to lubricate the metal surfaces, but without degrading the emulsion to a useless state. Furthermore, the dispersion becomes in practice, perhaps due to the formation of 7

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highly reactive cations at the tool-workpiece interface in any machining operation involving metallic substrates, charged with metal ions which, upon replacement, tend to replace the cations in the metal complex and further allow them to migrate and bond with electronegative structures in the emulsified particle, thus actually coating the one with cation.

Although the chemical nature of the metal complex stabilizer is such that it is highly soluble in aqueous systems, it is readily dissociated due to its unique proton dissociation ability at the pH of the metalworking conditions, so that the metal ion is transported to the oil phase of the emulsion from the aqueous phase. This surprising phenomenon has been demonstrated by two-phase extraction of an oil-in-water emulsion system treated with the metal complex at concentrations well below those found to be biocidal in nature. More specifically, emulsions treated with disodium monocobes (ii) citrate have been investigated at a concentration of from about 50 to about 100 mg Cu ++ per day. liter of emulsion, e.g. 1/10 - 1/5 of the biocidal dosage in a particular medium. Examination of the mixture of metal complex and emulsion by two-phase extraction using chloroform or other chlorinated hydrocarbons reveals that the copper is present in the organic phase. However, although the exact mechanism of this reaction has not been precisely elucidated, the biostability, chemical stability and physicochemical stability afforded by the treatment of emulsions with the metal complexes in question have been empirically observed. Furthermore, the biostability supplied by less than biocidal or biostatic amounts of the metal complexes in question must be considered particularly remarkable and must be associated with the reaction of organic phase groupings which render them insensitive to bacterial attack as opposed to a direct cation reaction with microorganism units associated with the aqueous phase.

It has been previously noted that polyvalent metal cations can be formed in metal working fluids by the machining process, such as cations of iron, aluminum and the like. On the other hand, other such polyvalent metal cations, such as calcium and mag

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nesium, be present in the aqueous medium used in metal working fluids. These ions can be referred to as "generated ions", ie. those formed by machining operations, or "native ions", i.e. those present from the start in the aqueous media of the metalworking fluids. These polyvalent cations usually damage the metalworking processes and further contribute to the instability of the emulsified particles. However, it has been empirically established that the present stabilizers make the emulsions stable to the action of such polyvalent metal ions. Thus, the stabilizing components of the oil-in-water dispersions of the invention tend to post-dissociate not only stability to the emulsified particles due to their association with them, but also to complex undesirable polyvalent ions in the media.

The metal complexes used as stabilizers in the dispersions of the invention release large amounts of metal ion from their coordinate structures at a pH of from about 4 to about 9 and most preferably at a pH of from about 7 to about 9 or 10. , ie the values usually met in metalworking fluids. Because of their unique dissociation ability as demonstrated by an S-shaped curve on a pM pH diagram, these agents provide, as needed, a controlled release of metal ions at a pH compatible with metalworking conditions. Furthermore, due to the organic ligand nature of the metal complexes, as pointed out above, the activity of other polyvalent metal cations or other foreign groupings present in metalworking liquids and which could otherwise adversely affect the stability of the metalworking emulsions is inhibited.

Therefore, the metal complex stabilizers in question must be distinguished from other metal complexes in which metal cations have been complexed with organic ligands represented by ethylenediaminetetraacetic acid (EDTA), diethylenetriamine pentaacetic acid (DTPA) or other amino acids or the like having relatively high stability or chemical content and provides the metal ion in quantities which coordinate with the electronegative emulsifiers to a significant degree and therefore cannot provide stability to the emulsion.

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Also, such known complexes do not provide a controlled release of metal ion or a dissociation ability represented by an S-shaped curve in a pM pH diagram. Rather, such known metal complexes, due to their stability and chemical inertia, tend to dissociate to a lesser extent in a rather linear fashion. Furthermore, the invention provides complexes which are soluble in water at high concentrations due to their ionic nature and yet remain in their stable form. This solubility, especially in alkaline media such as in this case, allows the preparation of concentrates capable of producing, as needed, the metal ion that provides the emulsion with metal working stability. Such solubility can be distinguished from the known metal compounds consisting of metal cationic and anionic components which are practically insoluble in such media, and from the metal complexes which, although soluble, bind the metal ion in such a complex state that it is only weakly dissociated and therefore hardly available for release of metal ion for coordination with the emulsified particle.

The term "metalworking fluids" in this specification, as in the art, is generally understood to mean the fluids used to lubricate, cool, cleanse, and inhibit degradation of metal surfaces during the metalworking process. These fluids are well known to those skilled in the metalworking art. There are two basic metalworking areas, namely mechanical operations relating to cutting, drilling, grinding, turning, milling, escaping, grinding etc. along with forming, bending, rolling, drawing and the like, and non-mechanical operations, relating to washing, quenching after heat treatment and the like.

It is generally accepted that metal working fluids perform mechanical, lubricating, cooling, cleaning, and rust-inhibiting functions in mechanical operations, while in non-mechanical operations, they perform primarily cleansing, rust-inhibiting, and cooling functions.

The stabilized dispersions of the invention are as mentioned by

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oil-in-water type. These dispersions have generally been referred to as oil emulsions or soluble oils in the art. Such fluids are mainly characterized by two phases, viz. a liquid-in-liquid system wherein there is a dispersed phase and a continuous phase. Where the particle size of the dispersed phase is of a magnitude greater than 0.1 µm, they have been classically termed "emulsions". Where the particle size is in a colloidal range of about 1 nm to about 0.1 µm, the dispersion may be of colloidal nature. Thus, whether to characterize them as coarse emulsions or colloidal suspensions, the liquids consist mainly of organic and aqueous phases, ie. of a two-phase system consisting of one liquid in another liquid, with which the first liquid is immiscible. Furthermore, the term "oil" in this specification is used to identify a large class of substances, whether of mineral, vegetable, animal or ether origin. However, the oils used for metalworking purposes are usually derived from the class of mineral oils, either petroleum or petroleum derivative and especially from the lubricant class. These dispersions include emulsifiers, typically of the anionic or nonionic type. In the case of the anionic agents, the anion moiety has the molar character required to produce the desired surfactant effects and provides electronegativity to the suspended oil droplets or particles. In the case of the nonionic agents, the oil particle is given electronegativity due to a high density of inherent electronegativity. Most commonly, the emulsifiers used in the metalworking emulsions are anionic and / or nonionic surfactants. The anionic surfactants contain a negatively charged ionic moiety and an oil dispersible or oleophilic moiety in the molecule. The surfactant may belong to (1) the group of saponified fatty acids or soaps or (2) the group of saponified petroleum oils, such as sodium salts or organic sulfonates or sulfates or (3) the group of saponified esters, alcohols or glycols, the latter of which are well known as anionic synthetic surfactants. Examples of these anionic surfactants include the alkylarylsulfonates or amine salts such as sulfonates of dodecylbenzene or diethanolamine salts of dodecylbenzenesulfonic acid, the sulfates of

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chained primary alcohols or fatty alcohols which are products of the Oxo process (i.e. sodium lauryl sulfate). A presumed light petroleum oil such as sulfonated petroleum distillation residue (eg mahogany oil) is common. Generally, the majority of the surfactants or emulsifiers are of the "anionic". type: alkali metal or amine salts of organic acids. Sulfonic acids are frequently used where the structure of the organic part is not well known, as in the case of the "petro-sulfonates" family. Most of these sulfonates contain many chemical groups. The class name given to most of them is "alkylarylsulfonate". This simply means that an alcanic hydrocarbon is bonded to an aromatic hydrocarbon core (usually benzene or naphthalene) and the aromatic moiety has been sulfonated. Examples of saponified fatty acids (Cg-C2 are the sodium or potassium salts of myristic acid, palmitic acid, stearic acid, oleic acid or linoleic acid or mixtures thereof. Also, in this class of anionic surfactants, the alkali metal and alkaline earth metal salts of neutral phosphoric acid esters are higher). Examples are the potassium and sodium salts of phosphate esters of isodecyl alcohol-ethylene oxide addition products. Thus, anionic surfactants or emulsifiers in this specification include soaps or synthetic surfactants from the class of alkali metal, ammonium metal and alkaline earth metal the organic sulfonates, phosphates or sulfates.

The suitable nonionic surfactants generally have hydrophilic moieties or side chains, usually of a polyoxyalkylene type. The oil-soluble or dispersible portion of the molecule | is derived from fatty acids, alcohols, amides or amines. By appropriately selecting the starting materials and controlling the length of the polyoxyalkylene chain, the surfactant portions of nonionic surfactants can be varied as is well known. Suitable examples of nonionic surfactants include alkylphenoxy-polyoxyethylene glycols, e.g. ethylene oxide addition products of octyl, nonyl, or tridecylphenol and the like. These said nonionic surfactants are usually prepared by

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12 reaction of alkyl phenol with ethylene oxide. Other specific examples of nonionic surfactants include glycerol monooleate, oleyl monoisopropanolamide, sorbitol dioleate, alkylolamides prepared by reaction of alkanolamides such as monoisopropanolamine, diethanolamine or monobutanolamine with fatty acids such as oleic acid, pelargonic acid, lauric acid and lauric acid.

The metal working fluids are typically composed as is well known in the art by a combination of a lubricating oil, such as a solvent-refined paraffin or napthenic oil, an emulsifier of the aforementioned anionic type and special additives, including generally anti-rusting agents and the like. In the industry, such mixtures containing the additives are commonly called "neat oil" and the oil mixture is then mixed with sufficient water to give an emulsion. The volume of water will vary depending on the various factors. Eg. For example, the oil phase may vary over wide ranges of from about 1 to about 95% by weight or more, the remainder being aqueous phase and other amounts of emulsifiers and additives. Usually, the amount of emulsifier may be in the range of from about 5 to about 50% by weight. In lubricating and cutting oils, the oil mixture is mixed with a sufficient volume of water to give an emulsion containing from about 90 to about 99% water, and from about 100 to about 1 volume of oil mixture. The ingredients in the neat oil mixture are usually from about 30 to about 90% of lubricating oil, from about 10 to about 25% of emulsifier and the rest optionally additives of the above type.

The stabilizing metal ion is present in the lubricating oil mixture in an effective amount to provide metalworking stability.

This effective amount can vary depending on a number of factors including the particular metal being processed, the pH, the contaminants and the amounts of oil and water phase, emulsifying agent, metal working cations, the particular metal complex and the like. Generally, the stabilizing metal ion is contained e.g. in an emulsion formed from the "neat oil" mixture

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13 as mentioned above, within a range of from about 10 to about 500 mg of metal ion per day. liter of oil phase. The metal complex which supplies the metal ion is added to the aqueous phase. After such addition, the metal ion, as explained above, migrates to form coordinative bonds with the emulsifier and establishes an equilibrium between the oil and water phases. As the metal ion depletes from one or the other phase during the metalworking, more complex is added to maintain the effective stabilizing amount. Specifically, in a cutting or lubricating oil emulsion for use in machining iron and containing about 97 volumes! water and about 3 volumes! oil as mentioned above by about 10-15! emulsifier, and where disodium monocobal (II) citrate is used as a stabilizer, with 500 mg of copper per a liter of aqueous phase achieves a toxic effect against bacteria. However, as mentioned above, the emulsion can be added to metalworking stability with as little as 10-100 mg of the copper cation per minute. liter of aqueous phase or well below the toxicity level. With 500 mg of copper per a liter of aqueous phase achieves a toxic effect against bacteria. However, amounts of metal complex outside these areas can also be used.

The stabilizers used according to the invention can be applied to the emulsion in a number of ways. Eg. For example, the stabilizing metal complex may be added to the aqueous phase of the emulsion prior to preparation, after which the "neat oil" mixture containing the oil, emulsifier and additives may be added to form the emulsion, optionally with some stirring. On the other hand, the emulsion can be formed first and the stabilizing metal complex thereafter added to the emulsion formed. The emulsion is formed so that the metal complex does not degrade. Especially in the case of metal complexes of zinc, nickel and copper citrate, these are relatively stable under alkaline conditions up to about pH 12, but still provide the desired stabilizing effect to the metalworking emulsion at an alkaline pH of up to about 9 or 10. Thus For example, the pH value on the alkaline side is adjusted from about 7 to about 10 in the liquids so that the metal complex is not first degraded, so that a pH value is reached in the middle of about 8.5.

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In a presently preferred embodiment, the stabilized dispersions of the invention contain a monometal complex of a divalent metal ion and a polyfunctional organic ligand in a metal-to-ligand ratio of 1: 1, which complex has a dissociation ability represented by an S-shaped curve on a pM -Ph-diagram. A specific example of the metal complex is dialkali metal monocobes (II) citrate such as disodium, dipotassium or dilithium monocobes (II) citrate. These dialkali metal monocobes (II) citrates have a dissociation ability represented by S-shaped curve, whereby the two-direction curve meets at a point within the pH range from about 7 to about 9. It has been shown that these monocobes (II) Complexes are very stable in basic media with a pH of the order of about 9 to about 12, i.e. has an effective stability 12 constant, of the order of about 10 to about 1013. However, for these monocobal (II) citrate complexes at a pH of about 7-8 of the order of about 5 to about 10 to about 10 . Therefore, at a pH of about 7-8, the effective stability constant of the monocobic (II) citrate complex is significantly lower (from one thousand to several hundred thousand times lower) and a substantial concentration of free Cu ++ is available for toxic or stabilizing activity. Eg. about 10% of the copper in the complex is in the ionized state at about pH 7, while approximately 0.1% of the copper is ionized at about pH 9. This would not be the case for an EDTA or polyamine complex of a polyvalent metal, such as copper, since its stability constant (10 ^ - 10 ^) would vary only slightly within the normal pH range from 7 to 9. Such EDTA complexes exhibit a pH effect on the stability constant, but it is represented by a smooth monotonous curve which reaching a limiting effect of proton-induced dissociation at pH values of from about 7 to about 9 and yielding only from about 0.001% ions at about pH 7 to as little as 0.00001% ions at about pH 9. It should be understood that the stabilizing or antimicrobial complexes will operate over a pH range from about 3 to about 12. Above approx. At pH 12, the complexes tend to be degraded by the alkaline media as they precipitate from the media as water-containing media.

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dense metal oxides. Below approx. pH 6, i.e. from about 3 to about 6, the instability of the metal complex results in a high concentration of the free Cu ++ in solution which will affect the biostability and other stabilizing functions mentioned above. In the middle range of about 7 to about 9, the controlled release is most effective. Thus, these complexes provide controlled release of metal ion from about 10% to about 0.1% of the complexed metal in the pH range from about 7 to about 9, so that the metal ion is then available for coordination and for antimicrobial and stabilizing functions.

It is clear that other metal complexes of polyfunctional organic ligands will correspond to the model of the invention when exhibiting the dissociation ability described, characterized by an S-shaped curve on a standard pM pH chart. Eg. For example, the preferred monometal-polyfunctional-organic-ligand complex for use in the dispersions of the invention may be based on other monovalent or polyvalent metal ions, especially divalent and polyvalent cations such as zinc, nickel, chromium, bismuth, mercury, silver, cobalt and others. similar metal or heavy metal cations. The complexes of heavier metals are believed to be more toxic than the complexes of the lighter metals. Other polyfunctional organic ligands may be used in place of citric acid exemplified by the preferred embodiment of the invention. Other polyfunctional ligands include the wider class of α- or β-hydroxypolycarboxylic acids within which the citric acid falls. Other functionally substituted acids, such as oxo or β-amino acids, sulfhydro acids, phosphinolic acids, etc. can also be used in the molecular model of the metal complexes in question, whereby similar results can be obtained. Generally from a metal complex formula point of view, the metal and citric acid monometric complex corresponds to a complex formula represented by one of the following structural formulas (A) and (B).

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(Λ) · —Ο α / "\ \ - ru J \ .Η η ο 'Α i

-ϋ CIU-C-O

* \\ ο (Β) V ° \ / “> ° \ - CH // CU-H20. / Ch2 - C - <Γ 2 - ° CH- I 2 C = 0 0_

Form (A) is assumed to touch the preferred form from free energy considerations. A single proton introduced into the complex structure of the form (A) or (B) prevents the formation of stable 5- or 6-membered coordinate rings. Upon introduction of a proton, only T'-linked rings can be formed by coordination of the acetate electron donors, and such 7-membered ring structures are unstable. Therefore, the complex molecule is dissociated and releases the metal ion to its toxic or stabilizing effects. In comparison, metal complexes of EDTA or other polyamines require four or more protons, and therefore greater acidity, to dissociate the complex. This explains this small pH effect exhibited by such complexes in a pM pH diagram.

The structural forms (A) and (B) can be more generally reproduced by the following models:

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17 (MODEL Λ)

M

(R) --- X:

. Y

ly (MODEL B) - Z (

(R 1 - X: M

(R) In the above models, the fully drawn lines represent a chemical bond between elements in the skeletal structure of the molecule, X, Y and Z represent electron pair donors, (R) represent any element or molecule year or group, M- represents a metal, and the proton affinity of X is greater than that of Z, Y or R. It will therefore be appreciated that other Lewis base proton pairs and other metal ions can be introduced into these structural models instead of oxygen, divalent copper or, for that matter, the carbon atoms to obtain a molecule model that will similarly dissociate following the introduction of a proton or groupings that behave similarly as shown by the S-shaped curve on a pM pH diagram. Thus, the molecular models are alternative terms for the antimicrobial or stabilizers according to the invention.

The invention and its various embodiments and advantages will be elucidated in the following detailed description and drawings which illustrate the preparation of the complexes and their activity.

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PREPARATION OF COMPLEXES

A. Dilithium Monocobes (II) Citrate 10 mmol of lithium citrate was dissolved in 10 ml of water. To this solution was gradually added, with stirring, 10 mmol of copper (II) chloride (CuClp * 2HpO). A deep blue solution formed. This was neutralized to a pH of about 7 with 10 mmol of lithium hydroxide (LiOH'HpO). Upon evaporation to dryness, this solution gave a deep blue, semi-crystalline solid. This solid was ground to a fine powder and the lithium chloride was extracted with 50 ml of dry methanol, five times at 35 ° C. The remaining blue solid was vacuum treated to remove methanol and dried. An attempt was made to crystallize the salt from the water and organic solvent system, but apparently due to the highly hygroscopic nature of the salt and the high negative charge of the ionized molecule, the solid obtained was microcrystalline to amorphous. The following formula is proposed for the 1: 1 complex of copper and citrate, based on the clarification of the structure and analyzes described below:

Li2CuC6H407 'XH? 0

Depending on the degree of hydration, the following formula weights (FV) and corresponding copper content are suggested:

LigCuCgH ^ cyXHgO

FV: 265.51 for X = 0,% Cu = 23.93 FV: 283.55 for X = 1,% Cu = 22.41 FV: 301.54 for X = 2,% Cu = 21, 07 FV: 319.56 for X = 3,% Cu = 19.88

The observed copper content of variously dried samples of the solid complex ranged from 20 to 23 $. The compound (solid 1: 1 complex) was highly soluble in water. A solution as strong as two molars could easily be prepared. 0o to a pK value of 11.5, there was no effect on the solubility of the compound in water. In addition to this pH, the complex was decomposed to a greenish brown precipitate, probably aqueous copper oxides. That

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solid 1: 1 complex can be used as antimicrobial or stabilizing agent with or without removal of the lithium chloride formed during manufacture.

B. Disodium Monocobes (II / Citrate (1)) Equimolar solutions of copper chloride and sodium citrate were dissolved in water as under A above to obtain a deep blue solution having a pH of about 5 * A 50 ml aliquot of this solution was placed An equal volume of anhydrous acetone was added and the funnel was shaken to mix the phases. On standing, a two-phase system was separated. A blue liquid phase rested on the bottom of the funnel in a reduced volume of approximately 25 ml. while the top layer (approximately 75 ml) was slightly cloudy and colorless, while crystal clear before shaking, the blue liquid (oily, viscous) was removed from the funnel through the stopcock and collected in another separating funnel. evaporated to dryness over a steam bath, about 25 ml of anhydrous acetone was added to the second separating funnel, forming almost immediately a plastic-like mass on the bottom n of the hopper unlike the oily liquid that was there before. The plastic mass supernatant was placed in another beaker and labeled supernatant 2. The addition of distilled water to the plastic-like mass resulted in immediate re-dissolution of the material. The total volume of the redissolved substance was adjusted to 25 ml, which in turn resulted in the formation of a viscous oily liquid. After evaporation of supernatant 1 to dryness, microscopic examination of the dry residue showed the presence of precipitated copious amounts of sodium chloride crystals. Evaporation of supernatant 2 gave a very finely divided powdery residue containing a small number of clear sodium chloride crystals. Analysis of the twice-extracted blue oily solution for copper content showed that the solution contained approximately 125 mg of copper per liter. and thus represented a concentrate of the metal complex, which originally contained approximately 65 mg per ml. ml. The large reduction in the amount of sodium chloride in supernatant 2 showed that the major amount of the contaminating salt by-product had been removed; A portion of the concentrate was evaporated and crystalline material was observed.

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(2) The procedures in the previous section (1) were repeated except that there was a pH adjustment of the first blue solution formed from about pH 5 to about pH 7 with KOH solution to neutralize the resulting HCl. After extraction and evaporation as above, a concentrate of the metal complex was obtained which, after evaporation, gave the crystalline material.

(5) Equimolar amounts of copper sulfate and sodium citrate as in section (1) were combined followed by pH adjustment to about pH 7 with NaOH. Extraction and evaporation of the resulting blue solution as described above gave an amorphous powder which had no visually discernible crystalline structure.

The following formula is proposed for it in section (1). - (3) disodium monocobes (II) citrate prepared above, based on the structure and assays described hereinafter: 2CuC6H207-XH20 C. Disodium monozinc citrate

Using the following ingredients, a zinc complex was prepared analogous to the copper complex under B above: 50 ml of cold water 29.4 g of trisodium citrate dihydrate 13 »6 g of zinc chloride (ZnCl2) concentrated HCl

NaOH-pellets

The zinc chloride was ground to fine particles in a mortar and then dissolved in water. The pH was adjusted to between 0.5 and 1.0 with hydrochloric acid. The sodium citrate was added slowly with the addition of hydrochloric acid to keep the pH below 1.0. After all the material was dissolved, the solution was slowly neutralized with NaOH pills. The material which remained in solution at pH 7.2 was decanted, adjusted to a pH of 8.5-9.0 and then extracted with a double volume of a 50:50 methane / acetone solution. The material was collected on a Biichner funnel using Whatman No. 42 filter paper. Alternatively, the solution may be vacuum dried at. 70 ° C.

21

DK 152056B

Do Disodium Mononickel Citrate.

A nickel complex was prepared using them. the following ingredients: 40 ml cold water 38.4 g anhydrous citric acid 47.5 g nickel chloride (NiCl?), finely ground

NaOH flakes

The citric acid was dissolved in the water. The nickel salt was added slowly with constant pH adjustment. After all the material was in solution, the NaOH flakes were added slowly (to reduce the heat generation) to adjust the pH to between 4.0-5.0. The yield was about 100 ml containing about 117 mg / ml Ni ++.

E. Disodium mono-mercury silver citrate.

A mercury complex was prepared using the following ingredients: 40 ml of water

V

2.2 g mercury oxide (HgO) 1.9 g anhydrous citric acid

NaOH-pellets

The citric acid was dissolved in the water and the solution heated to a maximum of 50 ° C. The mercury oxide was added slowly with vigorous stirring and allowed to react until the solution was clear. The pE value was adjusted to 8.5-9.0 with NaOH pills, ensuring that the temperature did not exceed 50 ° C. The material was crystallized by one of the methods described for the zinc complex under C above.

DETERMINATION OF METAL COMPLEX DISSOCIATION

The dissociation ability of the 1: 1 copper-cltrate complex prepared above was determined over a pK range of 3-12 using

22 DK 152056 B

of a copper (II) ion specific electrode (Orion Copper (II) Specific Electrode). Samples of 50 ml of 1: 1 copper-citrate solution (0.0068 molar) were adjusted to pH 3> 4, 5> 6, 7, 8, 9, 10, 11 and 12, then the concentration of free copper ion each time was determined using the copper ion specific electrode. The following values for free copper ion concentrations were obtained at the indicated pH values and the negative logarithms of the copper ion concentrations were calculated.

TABLE

pH Cu * + 1- pH

3 '3.2 X 10 "3 2.495 4 9.0 X 10" 4 3,046 5 2.5 X 10 ~ 4 3,602 6' 5.3 X 10 "5 4,276 7 1.0 X 10 ~ 5 5,000 8 8, 0 X 10 ~ 8 7,097 9 8.8 X 10 "12 11,055 10 9, · 6 X 10" 13 12,018 11 3.3 X 10 "13 12,482 12 1.34 X 10 ~ 13 12,873

23 DK 152056 B

From this data, a pH curve was constructed to indicate the dependence between the free Cu 2 ion concentration and the pH value as shown in the drawing. The drawing is a Cartesian coordinate plot (met drawn black line) of the negative logarithm of the metal ion concentration (pM) versus the negative logarithm of the hydrogen ion concentration (pH) at the points listed in the above table. This image is an S-shaped curve representative of the proton-induced dissociation ability of the metal complex. In the pH range from about 9 to about 12, the complex is very stable and the concentration of free Cu ++ is low. At a pH of about 7, the complex is relatively unstable and the dissociation to free Cu ++ is considerable, enabling antimicrobial or stabilizing function. In the range of about 7 to about 9, the Cu ++ ion is available for controlled release, which occurs from about 10% to about 0.1 $ dissociation of Cu ++ from the complex. This unexpected dissociation / pH behavior makes the complexes extremely effective as antimicrobial agents or stabilizers for metalworking fluids.

In comparison, a Cu ++ EDTA complex curve is represented by the dotted line in the drawing as reported by a. Ringbom, "Complexation in Analytical Chemistry", J. Wiley & Sons, NY, 1963, page 360. As shown, the pH effect is represented. on the Cu-EDTA complex by a smooth, monotonous curve, which reaches a limiting effect by proton-induced dissociation at about pH 7-9, for example, providing only from about 0.001 $ to about 0.00001 $ ionized metal .

Compounds in the ratio of 1 mole of metal: 1 mole of citrate may have been proposed to exist in dilute solutions in M, Bobtelsky and J. Jordan, J.Amer Chem. Soc., Vol. 67 (1945). however, no one has reported the remarkable antimicrobial or emulsion-stabilizing activities of these derivatives or their ability to form coordinate structures with emulsified droplets. Furthermore, according to the invention, further unique advantages of such complexes in metal working liquids have been found as explained below.

24 DK 152056 B

Further, according to the invention, solid metal complexes of the dialkali metal monocobes (II) citrates have been prepared, and such solid forms are surprising and unexpected. It has also been found possible to prepare highly concentrated solutions of such metal complexes. The nature of these complexes has been definitively determined using analytical criteria, namely: (1) the molar ratio method introduced by Yoe and Jones (Yoe, JH, & Jones, AL: in Chern. Anal. Edition 16; 111 , (1944); (2) the continuous variation method attributed to Job and modified by Vosburgh and Cooper (Vosburg, WC & Cooper, GR: j. Am. Chem.

Soc., 63; 437, (1941); (3) the dependence of the complex on pH and (4) the determination of the apparent stability constant of the complex. Spectrophotometric studies, including visible and ultraviolet microscopy, pH determinations as well as infrared spectroscopic measurements were used as an additional means to confirm the aforementioned findings regarding the formation and molecular composition of the 1: 1 copper (II) citrate complex.

The 1: 1 copper-citrate complexes used here are highly soluble, showing that such complexes are ionic in nature.

This is further supported by the observation that the color band of a solution of the complex migrated toward the anode (the positive electrode) by electrophoresis experiments. Visible and UV spectra show formation of 1: 1 compound. The overall reaction for the complex formation with the structural form (3) appears to be:

DK 152056B

+. + + ~ CN i * »- · * · o 0 u

CM

tc O u

N \ j-U

/ \ o o \ / 3

L _ ^ _ In

«A

V

CM

- Oh

1 CM r— O W i — i t “^ O fi co n

o * I · I

CM J * P -P

K f — 1 tf r-ι rC

O cm p cm U

is / I -P I -P

rj -P -H -P -H

/ \ <d u cd, υ, O K 0) -y Ο Μ -Η π · Η J—, I i πί o cm u ίΓ 4. o * - * P P P 3 *! ^^^^ CM 4 * + 3 +

O Μ It II

tn u-i - - Λ 44 i— (CM 3 0) v— '

DK 152056 B

26 Thus, instead of complexing the -C00 groups, it is seen that the alcohol alone, -OH and is involved in the coordination.

This forms a stable 5-membered and probably β-membered ring. Thus, the reaction is pulled to the right (stabilized) by OH ”(base) as the product H + is thereby removed as the reaction proceeds. This results in the very high effective stability constant Keff * Keff ior such a reaction is ρΗ-dependent, but associated with the absolute stability constant K ^ by the equations: _ ICu-citrate 1 eff (Pu ++ 1 Citrate

K _ {Cu-citrate J Ch + J

abS | Cu ++ I [citrate-3]

Kabs = Kef £ 'lK +>

It has been found that the K for the 1: 1 complex has a constant value of 1 * 2 8.DS * of about 10 (a strong complex) over a pH range from about S to about 12. The apparent value of K ^ decreases sharply at pH 7-9, and at pH values below ca. 7 there is a further decrease, which shows that the complex exists in final concentrations even at pH 3-7.

27

DK 152056B

Another important feature of the present complexes is believed to be to enable them to function as highly effective bactericides. This is exemplified where bacteria grow in a medium having a pH of e.g. from about 9 to about 11, and a diaicalimetal monocobes (II) citrate complex is introduced. As explained above, the alkaline pH environment makes the monocobal (II) citrate complex very stable.

It is hypothesized that due to its direct association with the cell surface, the free copper ion cannot be expected to be transported through the cell membrane at all or at best not as easily as the complex form. On the other hand, the complex is readily transported through the cell membrane, possibly due to (1) its organic nature, which could serve as a metabolic substrate upon which bacterial growth or propagation depends, or (2) the low dianionic mixture density of the complex which increases permeability through the bacterial cell wall. . After transport through the cell membrane, the complex is expected to be exposed to a pH environment of the order of about 7.

Therefore, the particular complex after transport is very unstable and labile and the copper ion is liberated abundantly and rapidly to denature cell protein or other metabolic effect on the intracellular biochemical reactions, thereby causing cell death. In contrast, other known complexes, where they can be transported under such circumstances, are fairly stable and kinetically inert and will not be effective because the copper is too tightly bound, even at the intracellular pH of about 7 highly toxic.

The metal complexes at issue here have unique antimicrobial properties as compared to the known compounds.

Eg. the formation of heavy metal salts by carboxylic acids is quite common. However, with the exception of low molecular weight salts, these are usually insoluble in water. This is demonstrated by the dicobs (1l) citrate, (Cu2citrate) 2 · 5H2O indicated in the literature. This compound is formed by heating a strongly basic solution of sodium citrate with Cu ++. The di-copper citrate (a ratio of 2 copper atoms to 1 citration) is precipitated by the solution. This

28 DK 152056 B

dicobber citrate has the following properties: (1) water insolubility ψ · | · (with the total net charge of the compound being 0? 2Cu and ci - 4 trat)? the reaction is: 2Cu ++ + citrate ^^ CU2Citrate Ί '+ H + and offset to completion by reaction of the product H * with 0H "in basic media, (2) light green solid color and (3) elemental analysis of essentially 2Cu to 1 citrate. The insolubility of the dicob citrate ether has also limited the efficacy of this compound as a bactericide and, although previously suggested for pharmaceutical applications, its use has been limited.

Metalworking fluids can be composed, as explained above, from many different types of ingredients. the aforementioned patents and "American Society of Tool Engineers - Tool Engineer's Handbook", First Edition, 1953, page 357 et seq.

The following embodiments serve to illustrate the invention in more detail.

Example 1

A cutting oil is prepared by mixing the following ingredients on a volume basis: 1% Sodium xylene sulfonate 9% Naphthenesulfonate 90% Mineral oil, approx. 300 fish.

This mixture is then used to prepare a 3 volume% emulsion by mixing with water and the pH is adjusted to 8.5-8.9 by the addition of acid. Then, disodium monocobic (II) citrate is added to the emulsion to obtain 100 µmg / liter Cu ++ in the aqueous phase. When such a metalworking fluid is used in metal cutting operations, it has been found that all the advantages mentioned above can be obtained.

29

DK 152056B

Example 2

An abrasive liquid is prepared using the same steps as in Example 1 with similar results except that the emulsion ingredients were replaced by 50% naphthenesulfonate, 15% mineral oil (about 100 vis) and 35% tall oil.

In order to demonstrate the coordination of metal ions with the emulsified droplets to achieve the stabilization activities mentioned earlier, the following experiments were performed.

Experiment 1

Relation of the copper concentration in the oil and water phases to the percentage of oil in the emulsion and to the initial concentration of metal complex._

methods:

Emulsions containing 2.5, 5.0 and 10.0% oil in water were prepared. 10 ml of each emulsion was pipetted into 16 x 100 ml test tubes. Samples of 1 ml of each were taken. Disodium mono-copper (II) citrate (hereinafter referred to as "metal complex") was added to each of these test tubes to give final concentrations of 50, 100 and 150 ppm Cii ++. Samples of 1 ml were taken immediately after the metal complex and the emulsions were mixed.

Samples were sampled again after 1 hour of mixing occasionally during this time.

The oil samples were extracted by adding an equal volume of dichloroethane and 1 drop of saturated potassium chloride solution, mixing and centrifuging for 5 min. at top speed of a table centrifuge. 0.5 ml of the organic (bottom) layer and 0.1 ml of the aqueous layer were transferred to different test tubes and 4.9 ml of water was added to the aqueous sample. 0 ^ 2 ml of Copper Reagent # 1 was added to each test tube under mixing and then 0.2 ml of Reagent # 2 was added. All the tubes were well shaken and 30 ml.

DK 152056B

5.0 ml of water was added to the vials containing the organic extract. The glasses containing the organic phase were again shaken and the organic material was allowed to settle. Absorbances of the glasses were read at 700 nm against the relevant blank samples (organic or aqueous extract of emulsions without added metal complex).

Results and conclusions

The test results are summarized in the table below. The percentage of copper in each phase was determined by correcting AyQQ for volume differences between the organic and aqueous extracts and adding the A ^ qq values for each phase. The percentage of "total A ^ qq" in each phase was estimated to be directly proportional to the percentage of total copper in each phase:

Table 1

Percent total copper in each phase as a function of time τ (minutes), the percentage of oil and the original copper concentration.

50 ppm metal complex as Cu ++% total Cu ++

Organic phase Aqueous phase% oil TQ Tg0 TQ Tg0 2.5 0.9 0.0 99.1 100.0 5.0 13.0 22.7 87.0 77.5 10.0_19.2 25.9_80.8 74.1 31

DK 152056B

100 ppm metal complex as Cu ++% total Cu ++ _% oil Organic phase Aqueous phase T0 T60 T0 T60 2.5 0.8 3.6 99.2 96.4 5.0 10.6 12.2 89.4 87.8 10.0 12, 7 15.6 87.5 86.4 150 ppm metal complex as Cu ++% total Cu +, f_% oil Organic phase Aqueous phase T0 T60 T0 T60 2.5 1.0 1.0 99.0 99.0 5.0 8.4 11.7 91.6 88.3 10.0 11.9 12.6 88.1 87.4

The results clearly showed that at any metal complex concentration, the percentage of total copper in the organic phase increased slowly over time. This effect was most pronounced in the samples containing 5.0% oil in the emulsion. The adsorption of Cu ++ in the oil layer appears to be of first order in enzymological terminology with respect to both oil and metal complex concentration, with the concentration of copper in the oil leveling off. the saturation point of the oil.

A Michaelis-Menten curve is expected for the transfer rate of Cu * 4 'to the oil phase as explained below.

At a given time and metal complex concentration, the percentage of total copper in the organic phase was directly proportional to the percentage of oil in the emulsion. The correlation was most evident in the samples

DK 152056 B

32 with 50 ppm metal complex. The amount of copper in the organic phase was dependent on the concentration of oil in the sample, showing that the copper was bound or coordinated directly to the surface of the oil particles.

As the metal complex concentration was increased, there was no corresponding increase in the percentage of Cu ++ in the organic phase. This phenomenon suggests several different mechanisms of Cu ++ transfer to the oil. The size of the oil particles in the emulsion is certainly not uniform. Therefore, the total surface area of oil particles in the 10.0% oil emulsion was not four times as large as the surface area in the 2.5% oil emulsion. The variation in particle size affects the amount of copper that can be transferred to the organic layer. An equilibrium may exist between copper in the oil and water phases. The "equilibrium constants" for transfer in both directions can be determined by concentrations of metal complex in the aqueous phase, i.e. the reactant concentration, and concentrations of organic copper and citrate salts. The transfer of metal complex can be described as follows: k-. Jl3_v

Metal Complex ^ Cu ++ + Nacitrate = ~ Λ Cu + t. Oil = χ +++ citrate *

2 4 U H

Cu ++ oil = X +++ + citrate "where X +++ is any simple or complex cation carrying three positive charges, k- ^ is determined by the dissociation constant of metal complex at pH 9> and k ^ by the adsorption rate of copper inside the oil phase and the affinity of nitrate and - and trivalent cations for each other. Apparently k ^ k and k ^ k4, since with greatly increased time and displacement almost all copper has been found in the organic phase. -like curves.

33

DK 152056B

Experiment 2

Relation of copper concentration in the oil and water phases to comminution of oil particles.

methods;

A 50% oil concentrate was comminuted by passing three times through a homogenizer at 55 MPa. The oil particles were found to be below 0.1 µm in diameter. The same concentrate, homogenized, was found to have a wide range of oil particle size of 0.8-3 µm, with the average diameter being approximately 1.5 µm.

The two concentrates were mixed with tap water to obtain 10% oil-in-water emulsions, as this percentage of oil emulsion in the previous experiment was found to give the highest adsorption rate of Cu ++ into the oil phase. A sample of 2 ml of each emulsion was taken and centrifuged to remove all large particulate matter. Each emulsion was added to a metal complex corresponding to a content of 100 ppm Cu ++, and samples of 2 ml were taken and centrifuged immediately. Aliquots of 1 ml of the supernatants were taken and tested as described in Experiment 1. The emulsions were shaken gently for one hour and 2 ml samples were taken and treated as described above after 10, 30 and 60 minutes.

results;

The test results are summarized in the table below. The percentage of copper in each phase was determined as described in Experiment 1.

34

DK 152056 B

-P

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cO

a 'h -p o ω to bo S3 -P -Hø ø ø xi ω _

CQ Ol 3 H LT \ S (S O

ø H ro S ~ 1

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+5 above 00 00 S S

u o ø + x a> t1 2, 3 SØ Λ

OH

H ft h a 3 ø o

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, 0 OH

fit -P 0 -P

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EH And H

+ J 3 O ft 3 IA ro O) H

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fit 0 ΚΛ CO LCO S

φ bO Η Η CM CM

* i ο Λ 3

Xj Η Ο Ο Ο Ο

Η a Η to VO

+) w 35

DK 152056B

A comparison of these results with the results of Experiment 1 showed that significantly more copper had been adsorbed in the organic phase of the homogenized material and somewhat more in the organic phase of the homogenized material. If the concentration of metal complex added to these samples, especially to the homogenized material, had been increased, a higher copper content in the organic layer would be expected. In a circulating metalworking coolant with high concentrations of divalent cation such as Mg "*" * "and Ca" * "" * \ competing for the citrate portion, the reaction rate of copper adsorption (k- ^ and k ^) should be higher.

The results of this experiment show quite well the validity of a Michaelis-Menten copper adsorption rate analysis. The greatest uptake rate of copper in the organic phase of the homogenized sample occurs in the first 10 minutes after the metal complex has been added to the coolant. From 10 to 60 minutes a lower copper adsorption rate is noted. More has been absorbed by the homogenized than by the unhomogenized oil particles.

In the homogenized oil sample, a much higher initial rate of copper adsorption is seen due to the enormous surface area of the oil particles. These effects confirm that copper adsorption to oil is also a surface phenomenon, ie. that the copper binds to the surface of the oil particles rather than being incorporated into them.

Claims (10)

1. Stabilized oil-in-water dispersions comprising an emulsifier selected from anionic and nonionic agents and mixtures thereof which give electronegativity to the oil phase of the dispersion, characterized in that the dispersions also contain a metal complex of a polyvalent metal ion and a polyfunctional organic ligand. which has a proton-induced dissociation ability in water represented by an S-shaped curve on a right-angled coordinate plot of the negative logarithm of the metal ion concentration versus the negative logarithm of the hydrogen ion concentration to produce a controlled release of metal ion which provides stability to the dispersion. Dispersions according to claim 1, characterized in that they have an alkaline pH of up to about 12. Dispersions according to claim 1, characterized in that they have an alkaline pH within the range of from about 7 to about 9. Dispersions according to claim 1, characterized in that the controlled release of metal ion is such that from about 10 to about 0.1% by weight of the metal ion in the complex is released over a pH range from about 7 to about 9. Dispersions according to claim 1, characterized in that the metal complex is a complex of a divalent metal ion and a polyfunctional organic ligand in a ratio of 1: 1. Dispersions according to claim 5, characterized in that the metal is selected from copper, nickel and mercury and that the ligand is citric acid. DK 152056B Dispersions according to claim 5, characterized in that the organic ligand is an α-hydroxypolycarboxylic acid. Dispersions according to claim 1, characterized in that the metal complex is a dialkali metal monocobes (II) citrate. Dispersions according to claim 1, characterized in that the metal complex is contained in an amount which provides from about 10 to about 500 mg of metal ion per minute. liter of aqueous phase. Use of stabilized oil-in-water dispersions according to any one of the preceding claims as a metal working fluid.