EP0854905A1

EP0854905A1 - Improved water soluble metal working fluids

Info

Publication number: EP0854905A1
Application number: EP96928010A
Authority: EP
Inventors: Dennis J. Kalota; David A. Martin; David C. Silverman
Original assignee: Monsanto Co
Current assignee: Solutia Inc
Priority date: 1995-07-20
Filing date: 1996-07-19
Publication date: 1998-07-29
Also published as: KR19990029090A; AU6762596A; JP2002503260A; CN1196079A; CA2227330A1; NO980239D0; NO980239L; PL324550A1; EP0854905A4; WO1997004052A1; BR9610062A

Abstract

There are disclosed improved water-soluble metal working fluids comprising polyaspartic acid, amides and salts thereof, a corrosion inhibitor(s) and a basic additive said additive having sufficient basicity and buffering power to maintain the pH of the composition above about 8.5 and preferably above about 9. Such compositions are useful as lubricants in processes to cut, bend, grind and shape both ferrous and non-ferrous metals and tend to maintain higher pH values due to the incorporation of a basic additive. The polyaspartic acid and salts thereof are particularly advantageous in that the fluids can be easily disposed of after use without special treatment because polyaspartic acid and salts thereof are readily biodegradable.

Description

IMPROVED WATER SOLUBLE METAL WORKING FLUIDS This invention relates to novel water soluble metal working fluids which are biodegradable and do not require reclaiming. More particularly, this invention relates to an improved formulation containing polyamino acid, salts and amides useful in cutting, grinding, shaping and other metal working operations which require a metal working fluid. The disclosed polyamino acid compounds have improved anticorrosive properties and are environmentally more acceptable than current oil containing fluids. BACKGROUND OF THE INVENTION Because of the concern for environmental factors, previously known oil-containing metal working fluids require reclaiming or disposal by means other than by discharging them to common sewage treatment systems. In some cases the cost of disposal has become a major cost in that the cost of disposal approaches the initial cost of the fluid. Metal working fluids fulfill numerous functions in various metal working applications. Typically, such functions include removal of heat from the work piece and tool (cooling), reduction of friction among chips, tool and work piece (lubrication), removal of metal debris produced by the work, reduction or inhibition of corrosion and prevention or reduction of build-up on edges as between the work piece and the tool. This combination of functions usually requires a formulation or combination of ingredients in the fluid to accomplish the best attributes required for a particular metal working operation.

Various fluids have been recently proposed to be substituted for oil-containing metal-working fluids such as primary amides, ethylenediamine tetraacetic acid, fatty acid esters, and alkanolamine salts. Such compounds can be replenished during use by dissolving tablets containing such compounds during the useful life of the fluid. See U.S. Patent 4,144,188 to Sato. Amines have also been found useful in cutting oils as antibacterial agents. Such amines include anilinoamines and arylalkylamine such a p-benzylaminophenol. See EPO 90-400732 to Noda et al. As noted above, one of the problems occurring in industry is the proper disposal of metal working fluids. The above mentioned amines are removed from the fluids by biodegradation, requiring facilities such as settling tanks, treatment tanks and sludge treatment tanks. Such a system is disclosed in Japanese Patent 03181395. Other methods of waste disposal and oil removal systems are employed to comply with environmental standards.

Worker sanitation is always an issue with presently employed oil-containing water soluble metal- working fluids. Such fluids unavoidably come in contact with workers using the fluids in cutting, bending, threading and other metal- working applications. Such oil-containing fluids create a mist at the site of the work piece being operated on and such mist travels through the air in the vicinity of the machine and the operator thereof. Some attempts have been made to reduce the mist problem as is noted in British Patent 2,252,103. There is disclosed therein a polymeric thickener comprising a copolymer of acrylamide, sodium acrylate and N-n-octyl acrylamide. The copolymer is formulated with water soluble and water insoluble monomer.

Because of the misting and drift thereof in the workplace employing the commonly employed water-soluble metal-working fluids, there is usually associated with such work place a distinctive odor which permeates the entire area. Usually such odor is unpleasant and is tolerated as a condition which is unavoidable.

There is needed a highly biodegradable, odorless, non-misting, water soluble metal working fluid, particularly useful in cutting operations. Such a fluid would dispense with the need for disposal costs, and provide the work place with a more sanitary and acceptable atmosphere in which to work.

Various methods have been discovered to catalyze the polymerization of a dry mixture of aspartic acid to form polysuccinimide. The preferred catalyst to perform in the dry environment is phosphoric acid. While phosphoric acid has been known for many years to be an excellent catalyst for the thermal condensation of aspartic acid, it has traditionally been employed in large quantities so as to form a liquid or pasty mixture. However the use of relatively small amounts so as to maintain a substantially flowable powder is also known. For example, it is disclosed in U.S 5,142,062 to Knebel et al., that a weight ratio of aspartic/catalyst ratio in the range of from 1:0.1 to 1:2, can be employed. Also, Fox and Harada have published processes for thermal polycondensation of α-amino acids in a publication entitled "Analytical

Methods of Protein Chemistry" wherein a procedure is described employing a mole ratio of aspartic/- catalyst of 1 :0.07. Also, Fox and Harada disclose the use of polyphosphoric acid as a very effective catalyst for the polycondensation reaction of amino acids and indicate that temperatures below that required when o-phosphoric acid is employed are possible.

In U.S. Patent 5,401,428 to Kalota et al., there is disclosed a utility of polyaspartic acid, salts and amides in metal working. Although such salts are known from U.S. Patent 4,971,724 to Kalota et al. as being useful in aqueous systems as a corrosion inhibitor for ferrous metals, surprisingly, it has been found that the metal working fluids disclosed in U.S. 5,401,428 are required to contain a corrosion inhibitor. Exposure of the liquids to air over time results in a fluid which reacts corrosively with metals thereby necessitating the inclusion of a corrosion inhibitor. Even with a corrosion inhibitor present there is observed some degradation of the fluids due to aeration which occurs throughout normal use in metal working applications. There is needed a formulation of the metal working fluids of Kalota et al which will resist becoming corrosive upon continued exposure to air.

BRIEF DESCRIPTION OF THE INVENTION

There has now been discovered a new metal working fluid formulation comprising polyaspartic acids, salts and amides which are highly biodegradable, odorless and non-misting and a stabilizing amount of a basic additive, said additive having sufficient basicity and buffering power to maintain the pH of the composition above about 8.5 and preferably above about 9. Such compositions have been found to be resistant to degradation due to aeration during metal working functions and to remain non-corrosive over extended periods of time. When diluted in water, such compositions provide a highly desirable water-based metal-working fluid useful in such operations as cutting, threading, bending, grinding, broaching, tapping, planing, gear shaping, reaming, deep hole drilling/gundrilling, drilling, boring, hobbing, milling, turning, sawing and shaping of various ferrous and non-ferrous metals. After reading this specification, those of skill in the art will recognize that such diverse metal working operations and materials optimally will require different dilutions of the metal working fluids and different concentration ratios of the various formulation components. BRIEF DESCRIPTION OF THE DRAWING

Figure 1 is a graphical representation of data obtained in an experiment showing the effect on pH of carbon dioxide on an aqueous solution of sodium polyaspartate containing a small amount of sodium phosphate and benzotriazole. DETAILED DESCRIPTION OF THE INVENTION

Typically, the metal-working fluids of this invention comprise an effective amount of polyaspartic acid or a salt or an amide thereof or any compound which provides an effective amount of the same in solution, preferably in concentrations in the range of from about 0.5% to about 70%, by weight in water. This very broad range covers both the composition as used in metal working applications (working fluid) and as typically packaged commercially as a concentrate adapted for dilution prior to actual use as a working fluid. It has been found convenient to provide a working fluid by dilution of the commercial composition in a ratio of about 10: 1 although other ratios may be employed. Other concentrations and dilution ratios will be apparent to those skilled in the art.

Preferred compositions of this invention comprise from about 3% to about 25% polyaspartic acid, and preferably from about 5% to about 20% salt or amide in water as the concentrate. The working fluid would contain from about 0.15% to about 20% of the polymer upon dilution to form a working fluid although greater or lesser amounts may be employed. Any number of basic compounds can be used as additives to produce polyaspartic compositions having improved stability in accordance with this invention. It is preferred that the basic additive be at least somewhat soluble in water. Because of the small amount in solution actually required to impart stability, the basic compounds need only be soluble to a relatively small extent to be effective. The basic additive should have sufficiently high basicity and buffering power to effectively maintain the pH of the polymer solution (measured as at 10% or below aqueous solution at normal room temperature) above about 8.5 to about 11 and more preferably from about 9 to about 10.5. However, at effective levels, it should preferably not result in a pH of the polymer solution greater than about 11 because it might render the fluid more hazardous for use, particularly with respect to machine operators.

Examples of suitable basic additives include alkali metal carbonates, alkali metal orthophosphate, alkali metal polyphosphates, alkali metal silicates, alkali metal borates and the like, including mixtures thereof.

Alkali metal carbonates are preferred in view of their low cost, appropriate basicity, solubility characteristics and availability. The term "alkali metal" as employed herein means lithium, sodium, potassium, rubidium and cesium and mixtures thereof. Preferably, the alkali metal employed in this invention is potassium. It has been found that potassium salts, as employed in this invention, result in metal working fluids having greater solubility in water and, more importantly, depress the freezing point of the composition below that of other commonly available and inexpensive alkali metals such as sodium. Accordingly, it is preferred to employ the potassium ion in all of the steps employed to prepare compositions of this invention That is, hydrolysis of the polysuccinimide intermediate, such hydrolysis being known in the art, is preferably performed with potassium hydroxide rather than the usual sodium hydroxide. The alkali metal basic additive is preferably potassium salt, particularly, potassium carbonate. However, some benefit is provided by employing at least a portion of the alkali metal as potassium and the remainder being another alkali metal such as sodium. For example, when the hydrolysis of the polysuccinimide is performed by employing the commonly used sodium hydroxide, the basic additive may be a potassium salt such as potassium carbonate. The amount of basic additive employed to form a stabilized polyaspartic metal working fluid can vary widely with good results and the minimum effective level can be determined for any selected additive by routine experimentation in view of the present description, keeping in mind the above noted preferred pH ranges. In the use of sodium carbonate the preferred range is, by weight, from about 0.02% and up in a working fluid and up to about 7% by weight of the sodium carbonate in a concentrate while a range of from 0.02% to about 4% and preferably from about 1% to about 3% by weight of the sodium carbonate is especially preferred in a concentrate.

The basic additive of this invention is mixed with the polyaspartic solution by any typical and suitable mixing or blending means. In the typical manufacture of polyaspartic metal working fluids, polysuccinimide is usually first produced which is a solid material. This material is hydrolyzed by any typical known means, usually with an aqueous solution of a base, which renders the material in a liquid form. The basic additive is typically added to the liquid during the formulation step. Since only small amounts are employed the blending of the basic additive may be performed during the final stages of preparation and packaging of the fluid. No special means of procedures are required so long as adequate mixing to obtain a uniformly constituted formulation is achieved. With respect to the basic additive, sodium carbonate, any amount up to the solubility limit, may be employed. Because solubility of the potassium salt is higher in such aqueous solutions, slightly higher amounts than sodium salts can be employed as for example 9% by weight in a concentrated solution of the polyamide. However, the polyaspartic metal working fluid of this invention is typically prepared as a concentrate containing in the range from about 2% to about 70% by weight or up to the solubility limit of polyaspartic acid, salt or amide. When added to a concentrate of this invention, the amount of sodium carbonate present may be in the range of from about 0.2% to about 7% by weight of the total mixture. In diluted form for use in common metal working equipment a concentrate of this invention is typically diluted to about 0.7% with respect to the polyaspartate polymer and from about 0.02% to about the solubility limit of sodium carbonate perhaps about 7% whichever is higher, or from about 0.03% to about 10% and preferably from about 0.08% to about 0.8% of potassium carbonate.

Various other additives may be employed in compositions of this invention to enhance or contribute properties which enable broader functions with respect to the use of the compositions in metal working applications. The types of additives include boundary lubricants, corrosion inhibitors, oxidation inhibitors, detergents and dispersant, viscosity index improves, emulsion modifiers, antiwear and antifriction agents and foam depressors.

For example, additives may be employed to enhance boundary lubrication such as wear inhibitors, lubricity agents, extreme pressure agents, friction modifiers and the like. Typical examples of such additives are metal dialkyl dithiophosphates, metal diaryl dithiophosphates, alkyl phosphates, alkali metal phosphates, tricresyl phosphate, 2-alkyl-4-mercapto-l,3,4-thiadiazole, metal dialkyldithiocarbonates, metal dialkyl phosphorodithioates wherein the metal is typically zinc, molybdenum, tungsten or other metals, phosphorized fats and olefins, sulfurized or chlorinated fats and olefins and paraffins, fatty acids, carboxylic acids and their salts, esters of fatty acids, organic molybdenum compounds, molybdenum disulfide, graphite and borate dispersions. Such boundary lubrication additives are well known in the art. Other additives useful herein include detergents and dispersant which provide cleaning functions.

Although the polyaspartic acid compounds of this invention function as corrosion inhibitors in a certain range of pH, corrosion inhibitors may be employed in compositions of this invention which will function in a pH range in which the polyaspartic acid, salt or amide may not function as a corrosion inhibitor. Typical but not limiting examples of corrosion inhibitors known in the art and useful herein include zinc chromate, dithiophosphates such as zinc dithiophosphate, metal sulfonates wherein the metal is an alkali metal, alkanolamines such as ethanolamine and substituted alkanolamines wherein the backbone of the alkyl group is substituted to provide various properties, alkyl amines such as hexylamine and triethanol amine, borate compounds such as sodium borate and mixtures of borates with amines, carboxylic acids including polyaspartic acid at high pH (10 and above)and alkyl amino carboxylic acids particularly useful in hard water, sodium molybdate, boric acid ester such as monobenzyl borate and boric acid with various ethanol amines (also acting as a biostat), benzoic acid, nitro derivatives of benzoic acid, ammonium benzoate, hydroxybenzoic acid, sodium benzoate, triethanolamine salts of carboxylic acids with a carboxymethyl thin group such as l-l-(carboxymethylthio)undecanoic acid triethanol amine salt, benzotriazole, tolyltriazole and other C,-C₄ alkylbenzotriazoles.

A more thorough review of corrosion inhibitors are provided by Aruna Bahadur in a publication entitled "Chromate Substitutes For Corrosion Inhibitors in Cooling Water Systems" appearing in Corrosion Reviews, 11(1- 2), pp. 105-122, 1993 which is incorporated herein by reference.

In particular, an alkali metal phosphate, preferably potassium or sodium orthophosphate, is preferred and is advantageously included in compositions of this invention to complement the corrosion inhibitor. Thus compositions of this invention comprise, in a preferred embodiment a corrosion inhibitor and a complementary corrosion inhibitor comprising an alkali metal orthophosphate. The complementary alkali metal orthophosphate is employed in amounts depending on the metal working operation in the range of from about 0.1% to about 10% by weight in the working fluid. Other concentrations will be apparent to those of ordinary skill in the art as the amount of polyamino polymer is adjusted in concentrate as well as working fluid embodiments. The term "corrosion inhibitor" as employed herein include those chemicals which when employed with other components of compositions of this invention exhibit corrosion inhibition.

Typical concentrate compositions of this invention, in parts by weight, adapted for dilution to prepare a working fluid, is shown below in

Table I. The compositions in Table I are shown in parts by weight.

Atypical concentrate composition of this invention is an aqueous solution containing from about 3% to about 30%, by weight, of the salt or amide of polyaspartic acid together with about 1% to about 10% by weight corrosion inhibitor and from about 200 ppm to about 5% by weight of the solution of a basic additive.

TABLE I

10

15

The composition of this invention may also contain minor amounts of catalyst employed in the thermal condensation reaction of L- aspartic acid whereby the polymer was made. Typically such catalyst is an acid such as phosphoric acid which is converted to the corresponding salt and salts of the pyrophosphate by-product during hydrolysis of the succinimide polymer.

Typical oxidation inhibitors may also be incorporated into the compositions of this invention and include for example zinc and other metal dithiophosphates, hindered phenols, metal phenol sulfides, metal-free phenol sulfides, aromatic amines as well as mixtures thereof. Because many operations in which compositions of this invention are employed create particulates that must be carried away from metal surface, there are employed in compositions of this invention detergents and dispersant. Typical dispersant(s) include polyamine succinimides, alkaline oxides, hydroxy benzyl polyamines, polyhydroxy succinic esters and polyamine amide imidazolines and mixtures thereof. Typical detergents include metal sulfonates, overbased metal sulfonates, metal phenate sulfides, overbased metal phenate sulfides, metal salicylates and metal thiophosphonates and mixtures thereof.

Therefore, compositions of this invention may also include surfactants, extreme pressure agents, buffers, thickeners, antimicrobial agents and other adjuvants commonly employed in such compositions and mixtures thereof.

Concentrate compositions of this invention most conveniently employed commercially and adapted for dilution prior to use will preferably contain potassium salts of the various components in varying ranges of concentration but typically comprising by weight from about 0.5% potassium polyaspartate, or up to its solubility limit, from about 0.1% to about 10% potassium orthophosphate dibasic as a complementary corrosion inhibitor, from about 0.02% to about its solubility limit perhaps about 9.5%, of potassium carbonate, and from about 200 ppm to about 3% by weight of a corrosion inhibitor. As noted above the preferred corrosion inhibitor is tolyltriazole which comprises by weight about 40 to about 0% 4-methyl-lH-benzotriazole and about 60% to about 100% 5-methyl-lH-benzotriazole. Those of skill in the art will recognize that the solubility limits of components will be effected by the pressure of other components. Other useful corrosion inhibitors include alkylbenzotriazoles, such as C,-C₄ alkylbenzotriazoles and butylbenzotriazole.

The polyaspartic acid of this invention is preferably provided by the thermal condensation of aspartic acid. Polyaspartic acid can also be prepared by the polymerization of other monomers such as mono -or diammonium maleate, mono -or diammonium fumarate, and maleamic acid. Many different processes are known for such purpose. For example, there has recently been discovered a continuous process employing a tray dryer wherein the aspartic acid is introduced into the top level of trays which cyclically travel in the horizontal plane to deliver the reacting material to the next adjacent lower level of trays. The residence time in the dryer is controlled by the number of tray levels, the tray rotation rate, circulation of heated gas, such as air, through the dryer, and temperature. The temperature in such a device is usually in the range of from about 180°C to about 350°C with a residence time in the range of from about 0.5 to about 6 hours. A typical tray dryer is commercially available from the Wyssmont Company, Incorporated, Fort Lee, New Jersey.

Another tray dryer which may be employed in such process is a tray dryer commercially produced by Krauss Maffei of Florence, Kentucky. In the Krauss Maffei tray dryer, heated trays are stationary and the reactant is moved across each plate by axially rotating plows or shovels. The reactant alternatively falls from one tray level to the next at the internal or external edge of the tray. The reactant is directly heated by the trays.

While there are several isomers of aspartic acid which may be employed to prepare polyaspartic acid, such as D-, L- or DL-aspartic acid, it is preferred herein to employ L-aspartic acid. If a catalyst is employed the reaction, residence time in the dryer may be less, in the range of from about 30 minutes to about 2 hours, depending upon other factors noted above. It has recently been discovered that carbon dioxide in the circulating gas catalyzes the thermal condensation when present in amounts of at least about 5%, by volume. Amounts of carbon dioxide in the circulated gas is usually about 10%, by volume. Various other reactors can be employed to produce the polyaspartic acid of this invention. Typical reactors include the List reactor commercially available from Aerni, A.G. Augst, Switzerland and the Littleford Reactor such as the model FM 130 Laboratory Mixer and larger production models available from the Littleford Bros. Inc., Florence, KY. The Littleford mixer provides sufficient agitation to produce a fluid bed condition and may be equipped with a chopper to break up any lumps or clumps of particles that develop and to provide additional shear forces to the fluid bed. The agitation provided by the mixer is sufficient to maintain the particles in a substantially free-flowing state throughout the time period of the reaction. Typically, the Littleford mixer is operated at a temperature of at least about 180°C and is capable of maintaining the heated bed at a temperature in the range of about 180°C to about 250 °C or higher for a time sufficient to polymerize the aspartic acid. The mixer is desirably equipped to provide a purge gas stream through the reactor. In accordance with this invention the gas stream is provided with sufficient amounts of carbon dioxide so as to catalyze the condensation reaction, thus greatly reducing the amount of time to reach complete polymerization of the aspartic acid.

The usual thermal condensation reaction of aspartic acid produces the polysuccinimide intermediate. The intermediate is easily hydrolyzed by alkaline solution to polyaspartic acid salt. Examples of an alkaline solutions are alkali metal hydroxides, triethanolamine (TEA) and the like, ammonium hydroxide, and the like.

Any water-soluble salts of polyaspartic acid including those which can be produced by the thermal condensation of L-aspartic acid may be employed in the metal-working composition of this invention. Typical water soluble salts include alkali metal salts, ammonium, organic ammonium and mixtures thereof. The term "alkali metal" encompasses lithium, sodium, potassium, cesium and rubidium and mixtures thereof. The organic ammonium salts useful herein include those prepared from the low molecular weight organic amines, i.e. having a molecular weight below about 270. Organic amines useful herein include the alkyl amines, alkylene amines, alkanol amines.

Typical organic amines include propylamine, isopropylamine, ethylamine, isobutylamine, n-amylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, undeclyamine, dodecylamine,hexadecylamine, heptadecylamine, ocatdecylamine, and basic amino acids such as lysine. No matter which reactor is employed, the polyaspartic acid or salt thereof produced by the thermal condensation of L-aspartic acid, is useful in this invention. It has been discovered that this polymer provides sufficient lubrication to permit metal working operations on ferrous and non-ferrous metals. Any molecular weight of polyaspartic acid may be usefully employed herein.

Polyaspartic acid derived from other sources are also useful in the compositions and method of this invention. For example, polyaspartic acid can be derived from the polycondensation processes employing maleic acid or derivatives thereof such as are known from U.S. Patents 3,846,380 to Fujimoto et al., U.S. 4,839,461 to Boehmke, U.S. 4,696,981 to Harada et al, all of which are incorporated herein by reference. While not preferred, copolymers of amino acids can also be employed in the process of this invention such as copolymers prepared according to U.S. Patent 4,590,260 to Harada et al. The water based metal-working fluids of this invention are particularly advantageous in that there is essentially no odor associated with water solutions of polyaspartic acid or salts or amines thereof. Further, it has been observed that the fluid dramatically reduces any mist around the tool working area as is common with water-based oil containing fluids. Because of the virtual lack of mist formation the work area is maintained virtually free of deflected fluid leaving the machinery and worker substantially free of contamination by the metal working fluid impracticing this invention. The water-based metal-working fluids of this invention are most advantageous in that the active ingredient, polyaspartic acid or salts have been found to have a rapid rate of biodegradation. The biodegradability of the metal working fluids of this invention allows their disposal through normal means such as by discharge into a sewage treatment system. The cost advantages of such a fluid of this invention are obvious in view of the environmental concerns resulting in alternative means of disposal.

Tests with non-ferrous metals such as brass and copper indicate that not only is the work place relatively free of contamination but that the workpiece remains relatively free of discoloring deposits. In fact, it has been observed that the aqueous solutions of the salts of polyaspartic acid are corrosion inhibitors as indicated by U.S. Patent 4,971,724 to Kalota et al. Therefore, metals, particularly ferrous metals, are free of harmful deposits and are, in fact protected from corrosion by the metal-working fluids of this invention. However the corrosion inhibiting effect of aqueous solutions of polyaspartic acid extend to those solutions having a pH in the range of from about 8.5 and above. If the formulation employed with the polyaspartic acid or derivative of this invention results in an aqueous solution having a pH of about 10 or below it is recommended that additional anti-corrosion inhibitors be incorporated into the formulation of the metal-working fluid of this invention. However, it has been shown in Figure 1 that during extended use of the fluids in actual practice, the pH of the polyaspartic compositions of this invention tend to decrease due to contact with acidifying agents such as the carbon dioxide from the atmosphere. Therefore, it is common practice to include additional corrosion inhibitor(s) in compositions of this invention. The amount of corrosion inhibitor can vary widely depending upon the particular inhibitor and the environment in which the fluid is employed. For example, if zinc chromate is the corrosion inhibitor effective amounts range upwards from as little as 50 ppm in the working fluid. The metal-working fluids of this invention are useful in the various metal-working applications such as were noted above with any number of types of metals. In particular they are useful in working ferrous metals and alloys such as iron, steel (carbon steel and low alloy carbon steel), cast iron, stainless steels, nickel-based alloys, and cobalt-containing alloys and the like.

Non-ferrous metals and alloys which can be worked with fluids of this invention are copper, brass, titanium, aluminum, bronze, and magnesium and the like. Such metals are safely worked with lubricity supplied by the water based fluids of this invention. A particularly important function of a metal working fluid of this invention in cutting operations is the function of cooling so as to maintain lower temperature of the tool as well as the work temperature. Such control aids in minimizing tool wear and distortion of the workpiece. Another function of the metal working fluid of this invention is lubrication which reduces friction as between the tool and chips produced during the cutting operation as well as reduction of the friction between the tool and the workpiece. In cutting operations of various types there are typically produced chips of small pieces of metal which are advantageously carried away from the workpiece as soon as possible so that they do not jam the cutting tool. DESCRIPTION OF THE PREFERRED EMBODIMENTS

EXAMPLE 1 In the following example, a laboratory model of a tray dryer was employed having two trays which passed the reactant material from one to the other thereby simulating the conditions of a commercially available tray dryer referred to above. The reactant material was passed from one tray to the other so as to equal the desired number of tray levels of the commercial model. The tray dryer, simulating the Wyssmont Turbo Dryer, available from the Wyssmont Company, Fort Lee, NJ was operated with the addition of 1 kg of L-aspartic acid per tray level at a depth of 2.5 cm on the trays. A total of 28 tray levels was employed. Circulated air temperature through the dryer of

305 °C was maintained throughout the experiment. Air velocity was maintained at 114.3 meters per minute and tray rotation was set at 3 minutes per revolution. An amount of carbon dioxide was fed into the air supply to provide a total amount of 10 percent, by volume, carbon dioxide in the air contacting the material on the trays. Samples were taken from the trays at various reaction times and analyzed for the amount of conversion to polymer, pH, color (JAPHA), and molecular weight. The data obtained appears in Table π below.

TABLE II

EXAMPLE 2 An experiment was conducted to show the effect of carbon dioxide on the pH of the polyaspartic metal working fluids of this invention. A 1% aqueous solution of sodium polyaspartate containing residual (1500 ppm as PO₄) sodium phosphate was subjected to aeration with a gaseous mixture of 2.5% carbon dioxide by volume in nitrogen as well as pure nitrogen. The data is present in Figure 1 wherein Curve A is the data obtained with pure nitrogen and Curve B is the data obtained with the blend of carbon dioxide and nitrogen. The rapid decline in pH as shown by Curve B indicates the influence of carbon dioxide on pH of the solution. As shown in Fig. 1, the solution aerated with gas containing carbon dioxide quickly (within a few hours) indicated a pH of about 7 while the pH of the solution aerated with only nitrogen remained essentially unchanged. EXAMPLE 3 An accelerated test was performed to show the effect of a basic additive on the stability of the pH of a metal working fluid and thus the tendency of the fluid to become corrosive to metals. Samples of polysuccinimide prepared by various means were hydrolyzed and formulated for use as metal working fluids. One set of samples was prepared from catalyst free aspartic acid (Sample A) and another set was prepared from polyaspartic produced in the presence of phosphoric acid at 7.5% by weight of the aspartic acid (Sample B). Samples were prepared having the following formulation and adjusted to equal pH by addition of acid or base as required:

A third sample, tap water, (Sample C) adjusted to a pH of 9.6 with sodium hydroxide was used as a control. Ambient air, typically containing 0.033% carbon dioxide, was entrained through the liquid samples at a constant rate of greater than 200cc/min at ambient room temperature and pressure. The pH of each solution was measured once per day for six days. Amounts of sodium carbonate from 250 ppm to 1000 ppm were added to each sample at the beginning of the test. The results of the test is shown below in Table III. TABLE m

From the above data it is noted that sodium carbonate was effective at all levels in maintaining higher pH levels than found in the tap water. Also, at 1000 ppm level the pH reached an equilibrium at 9 or above after 2 days. It is known that at a pH of 9 or above corrosion levels are reduced to an insignificant level. The addition of the basic additive stabilizes the pH at an acceptable level in the accelerated test which indicates that the working fluid would not degrade by normal use for a relatively long period of time

EXAMPLE 4

Polyaspartic acid, sodium salt, was prepared by means of a Wyssmont Turbo Dryer in the presence of 7.5% phosphoric acid catalyst. The acid polymer was hydrolysed with sodium hydroxide and diluted to a 1% by weight aqueous solution. Two batches of the polyaspartic polymer were formulated with benzotriazole, which has a pKa of 8.3. Any effect on pH in this test is not affected by the benzotriazole since the pKa is below the pH of the test solutions. In one batch, containing 200 ppm benzotriazole, no sodium carbonate was added and in the other batch containing 950 ppm benzotriazole, sodium carbonate was added at a concentration of 1000 ppm. Each batch of cutting fluid was employed as the cutting fluid in a Okuma LB 10 cutting machine. The pH of each batch of cutting fluid was measured initially, after 1 day and after 5 days. Each batch was used to cut 300 pieces of 1018 steel down from 2.54 cm to 0.934 cm using a Mitsubishi DMN G432MA insert. The parting tool was a Manchester M50. The results of periodic pH tests from the periodic pH measurement of the polyaspartic polymer cutting fluid are shown below in Table IV.

TABLE IV

The results indicate that a level of 1000 ppm sodium carbonate stabilized the pH of the polyaspartic polymer cutting fluid while the pH of the cutting fluid without a basic additive declined below the desired pH level of 9 to 9.5.

EXAMPLE 5

Typically, a preferred composition of this invention can be prepared by polymerizing L-aspartic acid as described in Example 4 and then hydroiyzing the resulting polysuccinimide by charging a suitable vessel with the following amounts in parts by weight shown in Table V below:

TABLE V

To the potassium polyaspartate produced by the above described hydrolysis procedure there is then added 21 parts of dipotassium phosphate, 17.7 parts of potassium carbonate and 13.5 parts of tolyltriazole. The tolyltriazole is comprised of a mixture containing 40% 4-methyl-lH- benzotriazole and 60% 5-methyl-lH-benzotriazole. In the use of tolyltriazole, it is desirable to maintain the level above about 900 ppm in the working fluid for best results.

EXAMPLE 6 To demonstrate the depression of the freezing point in compositions of this invention achieved by incorporation of the potassium ion instead of the sodium ion, the three compositions described in Table I above were tested by subjecting them to cooling while noting the visual observation of the composition with respect to homogeneity and freezing point. The results appear in Table VI below. The composition, in percent by weight were as follows:

TABLE VI

From the above data it is evident that the potassium salt is highly advantageous in that it has a significantly reduced freezing temperature. As significant at the reduced freezing temperature is the fact that no precipitate was observed, even at the freezing temperature indicating that no separation of the solution into different phases occurred. Therefore, the effect of freezing the potassium salt mixture is not as deleterious as either the sodium salt or mixed salt compositions which would require further mixing to redistribute the separated phases of the composition due to the occurrence of freezing temperatures.

Although the invention has been described in terms of specific embodiments which are set forth in considerable detail, it should be understood that this description is by way of illustration only of effective compositions and of effective amounts of components and that the invention is not necessarily limited thereto, since alternative embodiments and operating techniques will become apparent to those skilled in the art (in view of the disclosure.) Accordingly, modifications are contemplated which can be made without departing from the spirit and scope of the described invention.

Claims

WHAT IS CLAIMED IS:

1. In a method of metal working wherein a lubricant is provided for said metal, the improvement which comprises providing an aqueous solution of a polyaspartic polymer selected from the group consisting of the acid, salt or amide thereof, a corrosion inhibitor and a stabilizing amount of a basic additive, said basic additive having sufficient basicity and buffering power to maintain the pH of the composition above about 8.5.

2. The method of Claim 1, wherein said pH is maintained above about 9.

3. The method of Claim 1 wherein the polyaspartic polymer is potassium polyaspartate, the basic additive is an alkali metal salt or amine salt or ammonium salt and the corrosion inhibitor is tolyltriazole or benzotriazole or an alkylbenzotriazole.

4. The method of Claim 3, wherein said alkali metal salt is a potassium salt and the corrosion inhibitor is tolyltriazole.

5. The method of Claim 3 wherein the tolyltriazole or benzotriazole is present in amount of at least about 100 ppm and preferably about 900 ppm.

6. The method of Claim 5 wherein the tolyltriazole or benzotriazole is present as a mixture comprising about zero to about 40% 4- methyl-lH-benzotriazole and about 60% to about 100% 5-methyl-lH- benzotriazole

7. The method of Claim 1 wherein the solution contains from about 0.05% to about 70%, and preferably from about 0.5% to about 2% by weight, of said polymer, wherein the corrosion inhibitor is tolyltriazole or benzotriazole or an alkylbenzotriazole and wherein the basic additive is potassium carbonate.

8. The method of Claim 7 wherein the solution contains from about 0.05% to about 70% by weight of said polymer and wherein the basic additive is present in the range of from 0.02% to about 8% by weight of said solution.

9. The method of claim 1 wherein the metal working is a cutting operation selected from the group consisting of threading, grinding, shaping, turning, milling or drilling and the like.

10. The method of Claim 1 wherein the metal working is bending.

11. The method of Claim 1 wherein the metal is a ferrous metal or alloy selected from the group consisting of iron, steel (carbon steel and low alloy steel), cast iron stainless steels, nickel based alloys, cobalt containing alloys, and the like.

12. The method of Claim 1 wherein the metal is a non-ferrous metal or alloy selected from the group consisting of copper, bronze, brass, titanium, alumminum, magnesium and the like.

13. A metal working composition comprising an aqueous solution of a polyaspartic polymer selected from the group consisting of the acid, salt or amide thereof wherein the concentration of said polymer is in the range of from about 0.05% to about 70%, a corrosion inhibit or(s) and a stabilizing amount of a basic additive, said basic additive having sufficient basicity and buffering power to maintain the pH of the composition above about 8.5.

14. The composition of Claim 13, whereby said pH is maintained above about 9.

15. The composition of Claim 13 wherein said corrosion inhibitor(s) is present in the range of from about 50 ppm to about 15 percent by weight and wherein said basic additive maintains a pH in the range of from about 8.5 to about 11.

16. The composition of Claim 15 wherein the basic additive is potassium carbonate and the corrosion inhibitor is tolyltriazole.

17. The composition of Claim 16 wherein the tolyltriazole is present as a mixture comprising from about zero to about 40% 4-methyl-lH-benzotriazole and from about 100% to about 60% 5-methyl- lH-benzotriazole.

18. The composition of Claim 16 wherein the tolyltriazole is present as a mixture comprising about 100% 5-methyl- lH-benzotriazole.

19. The composition of Claim 13 wherein the concentration of the polyaspartic polymer is at least about 0.05% by weight of the solution, the corrosion inhibitor is tolyltriazole and is present in an amount in the range of from about 0.01% to about 2% by weight together with a complementary corrosion inhibitor comprising a water soluble alkali metal or ammonium phosphate in the range of from about 0.1% to about 10% by weight.

20. The composition of Claim 19 wherein the alkali metal phosphate is selected from the group consisting of sodium or potassium orthophosphate.

21. The composition of Claim 20 wherein the polymer is an alkali metal salt.

22. The composition of Claim 21 wherein the salt is a potassium salt.

23. The composition of Claim 22 wherein the polymer is an amide.

24. A metal working composition concentrate adapted for dilution to prepare a working fluid comprising an aqueous solution of potassium polyaspartate, a basic additive, said basic additive having sufficient basicity and buffering power to maintain the pH of the composition above about 8.5, a corrosion inhibitor and from about 1% to about 10%, by weight, of a complementary corrosion inhibitor comprising potassium orthophosphate.

25. The composition of Claim 24, wherein the pH is maintained above about 9 and the basic additive is potassium carbonate.

26. A metal working composition of Claim 24 wherein the potassium polyaspartate is present in the range of from about 0.5% up to about its solubility limit and the corrosion inhibitor is tolyltriazole wherein said tolyltriazole comprises from about zero to about 40% 4-methyl-lH- benzotriazole and from about 100% to about 60% 5-methyl- IH-benzotriazole, by weight.

27. A metal working composition of Claim 26 wherein the tolyltriazole is present in the range of from about 0.1% to about 2% by weight.

28. A metal working composition of Claim 24 wherein the corrosion inhibitor is a salt of benzoic acid.

29. A metal working composition of Claim 24 wherein the corrosion inhibitor is selected from the group consisting of sodium benzoate and ammonium benzoate.

30. A metal working composition concentrate adapted for dilution comprising by weight from about 0.5% to its solubility limit of potassium polyaspartate, from about 0.2% to about 9% potassium carbonate, about 0.3% to about 2% of a corrosion inhibitor and a complementary corrosion inhibitor comprising from about 1% to about 10% potassium orthophosphate.

31. A composition of Claim 30 wherein the corrosion inhibitor is tolyltriazole.

32. A composition of Claim 31 wherein said tolyltriazole comprises from about zero to about 40% 4-methyl- IH-benzotriazole and from about 100% to about 60% 5-methyl- IH-benzotriazole, by weight.

33. The method of Claim 32 wherein the solution contains from about 0.5% to about 70%, by weight, of said polymer, wherein the corrosion inhibitor is alkylbenzotriazole or tolyltriazole or benzotriazole and wherein the basic additive is sodium carbonate.

34. The method of Claim 33 wherein the solution contains from about 0.5% or up to its solubility limit by weight, of said polymer and wherein the sodium carbonate is present up to about 7% by weight of said solution.

35. The method of Claim 33 wherein the metal working is a cutting selected from the group consisting of threading, grinding, shaping, turning, drilling and milling.

36. The method of Claim 33 wherein the metal working is bending.

37. The method of Claim 33 wherein the metal is a ferrous metal or alloy selected from the group consisting of iron, steel (carbon steel and low alloy steel), cast iron, stainless steels, nickel based alloys, cobalt containing alloys.

38. The method of Claim 33 wherein the metal is a non-ferrous metal or alloy selected from the group consisting of copper, bronze, brass, titanium, aluminum and magnesium.

39. The composition of Claim 33 wherein the basic additive is a mixture of sodium and potassium carbonates and the corrosion inhibitor is benzotriazole or tolyltriazole or an alkylbenzotriazole.

40. The composition of Claim 39 wherein the concentration of the corrosion inhibitor is in the range of from about 50 ppm to about 15% by weight.

41. The composition of Claim 1 further containing a minor amount of sodium orthophosphate retained from the polymerization process to obtain said polyaspartic polymer.

42. The composition of Claim 1 wherein the polymer is an alkali metal salt.

43. The composition of Claim 1 wherein the polymer is an ammonium salt or amine salt.

44. The composition of Claim 1 wherein the polymer is an amide.

45. A metal working composition comprising an aqueous solution of sodium polyaspartate, a basic additive, said additive having sufficient basicity and buffering power to maintain the pH of the composition above about 8.5, a minor amount of sodium orthophosphate and a corrosion inhibitor and potassium othrophosphate.

46. A metal working composition of Claim 45 wherein the sodium polyaspartate is present in the range of from about 0.5% to about its solubility limit and the corrosion inhibitor is benzotriazole or alkylbenzotriazole or tolytriazole.

47. A metal working composition of Claim 45 wherein the corrosion inhibitor additives are present in the range of from about 50 ppm to

15% by weight.

48. The method of Claim 1 wherein the solution contains from about 0.5% to about 70%, by weight, of said polymer, wherein the corrosion inhibitor is benzotriazole and wherein the basic additive is sodium carbonate.

49. The method ofColaim 2 wherein the solution contains from about 5% to about 15% by weight, of said polymer and wherein the sodium carbonate is present up to abut 7% by weight of said solution.

50. The method of claim 2 wherein the metal working is a cutting selected from the group consisting of threading, grinding and shaping.