DESCRIPTION

Field of invention

The present invention relates to a metalworking fluid with a low impact on health, safety in workplace and environment, as well as the method of treating the related exhausted emulsion. More specifically, the invention con cerns an emulsifiable metalworking fluid for mechanical processing (cutting oil), specifically designed to reduce operating costs and minimize the HSE (Health, Safety, Environment) impact during the entire life cycle thereof, from the selection of raw materials to its use and the final treatment of the exhaust ed emulsion. This product is formulated in line with the principles of circular economy, to bring added value throughout its life cycle.

Background of the invention

Metalworking operations require the use of metalworking fluids to dissi pate the heat produced during processing and minimize friction between the tool and the workpiece. Additional features required are the protection of parts and machine tools from corrosion, resistance to bacterial attack and minimiza tion of the HSE impact, with particular attention to the risks for workers.

The vast majority of cutting oils available on the market contain mineral, synthetic or semi-synthetic base oils, as well as numerous additives, such as surfactants, anticorrosives, extreme pressure additives (EP), antiwear addi tives (AW) and biocides. The cutting oils can be used as such, as whole oils, or mixed with water to form stable emulsions, with a metalworking fluid con tent of 3-10% by weight.

The useful life of metalworking fluids can vary from 4-8 weeks up to more than a year, depending on the case. There are two systems for the ap plication of metalworking fluid: small and medium-sized factories usually use machine tools with a dedicated system, which requires the presence of a col- lection tank and an independent recirculation system for each machine. Large plants, on the other hand, have a centralized system with a single emulsion tank and a distribution system that reaches all the machines inside the plant.

Both distribution and application systems provide for regular drainage and make up with fresh emulsion, in order to preserve the efficiency and per formance of the emulsion. These operations are performed on a daily basis, while the emulsion in the tank must be completely replaced on average after 6-18 months.

The drained exhausted emulsion is collected in storage tanks and sent to the treatment facility inside the industrial plant, or given to specialized com panies for treatment in another site.

The treatment of the exhausted emulsion is complex and expensive, both in terms of energy and in terms of the chemicals used and the volumes of sludge produced. The treatment basically consists of two basic phases:

1. breaking of the emulsion, performed by one or more operations as pH adjustment, addition of chemical de-emulsifying agents, ultra filtration and evaporation;

2. treatment of the oily and aqueous phases: typically, the oily phase is concentrated to remove excess water, and subsequently burned to produce energy, or distilled/refined to be reused; the aqueous phase must be treated to bring the content of polluting components below the legal limits.

Conventional products release large quantities of surfactants in the aqueous phase downstream of the emulsion breaking, and the related waste products have COD (Chemical Oxygen Demand) values in the order of sever al thousands or tens of thousands mg of oxygen per litre. The pollutants con tained in the water phase are complex and expensive to be eliminated. For this reason a physico-chemical treatment is necessary, followed by a biologi cal or oxidative treatment (Fenton-like reaction) and the use of filters with acti vated carbon. It is known that all these processes generate considerable quantities of sludge and materials to be disposed of, and, moreover, the in- creasingly strict environmental regulations require a more extensive use of pu rification technologies, increasing treatment costs.

The cost to conferring an exhausted metalworking fluid emulsion for treatment to specialized companies is between € 150 and € 300. Considering that the exhausted emulsion contains about 95% of water and 5% of metal working fluid (50 litres in 1 m ³ ), the cost of treating a litre of metalworking fluid is about 3-6 €, which is a figure comparable with the purchase cost. In the case of in situ treatment, the costs are approximately halved, but still remain extremely high, without considering the environmental aspects.

The conventional products available on the market are formulated to ensure excellent performance during processing. However, they generally form very stable emulsions and release large concentrations of pollutants into the aqueous phase. These characteristics result in these products being not in line with the principles of circular economy.

A valid alternative to conventional products would be constituted by a metalworking fluid that has performance characteristics similar to the products of the prior art during use, but allows to minimize the costs of treatment of the emulsion at the end of its life, reduce toxicity and risks for the workers in volved and, furthermore, minimize the environmental impact of the related ef fluent.

The known art has already taken into consideration compositions for water-based metalworking fluids in which the oily component is not a mineral, synthetic or semi-synthetic oil, but an oil of animal or vegetable origin. In spite of the advantages of the raw material costs and safety at work (for example, due to the reduced flammability), such a choice entails at least a considerable increase in the stability problems of the metalworking fluid, due to the microbi al attack to which animal and vegetable oils are subject. Therefore, products of plant or animal origin to be used in cutting oils must contain effective amounts of antimicrobial agents or biocides, which are adequate to protect the oil phase throughout the useful life of the product.

An example of a metalworking fluid composition based on an oil-in water emulsion in which the oily component consists of a vegetable oil (specif- ically, soybean oil) is described in the international patent application W003/020855 (United Soy Bean Board). According to the document, the veg etable oil is associated with a non-chlorinated additive of the "extreme pres sure" (EP) type, which in turn can be assisted by a coupling agent, with the aim of increasing its stability.

European patent EP 3061804 B1 (Indian Oil Corporation Limited and Steel Authority of India Limited) is another example of a metalworking fluid formulation consisting of an oil-in-water dispersion in which the oil is of animal or vegetable origin. The document describes a product for the hot rolling of steel in which the oily component is combined with 1-12% by weight of an "ex treme pressure" type additive, consisting of a sulphurised fatty oil.

In both documents mentioned above no reference is made to the prob lem of disposing of the corresponding products at the end of their life cycle.

It is therefore an object of the present invention to develop a metalwork ing fluid which possesses lubricating efficacy, ability to dissipate the heat gen erated and resistance to corrosion comparable to the products currently in use, but which at the end of its life, allows for a simple treatment, drastically reducing the costs of in situ treatment or transfer of the exhausted emulsion. The simplified treatment of the exhausted emulsion would allow significant economic savings in terms of energy consumption, chemical reagents and sludge production.

Summary of the invention

According to the present invention, the aim was to provide a cutting oil formulation with the same functions and performance as the products of the prior art, but in which the oil-in-water emulsion constituting the fluid in use is a metastable emulsion. Such metastable emulsion does not contain, among the additives, any substances which, as a result of the demixing occurring when the exhausted fluid is to be discarded, may remain dissolved or suspended in the aqueous phase, without being transferred to the aqueous phase.

To achieve this object, among the raw materials that can be used for a metalworking fluid composition, only the materials free (or substantially free) from non-ionic surfactants were used, which materials, following the breaking of the emulsion, remain in the oily phase without affecting the content of pollu tants of the aqueous phase.

Another criterion used is to avoid the use of low-boiling raw materials, which end up in the aqueous condensate following the evaporation process (technology widely used for the treatment of exhaust emulsions).

An eco-sustainable metalworking fluid has therefore been formulated according to the present invention, using oils of natural origin from renewable sources, which has performance characteristics similar to the products cur rently in use, but which can be treated in a simple and cheap way at the end of its life cycle, generating an oily phase to be used as a secondary raw mate rial and an aqueous phase which can be disposed of according to legal limits, or which can be reused in the production process. At the end of its life cycle the exhausted emulsion, in addition to presenting advantages in terms of ease of treatment and reuse of the starting materials, can also be given to special ized companies as a non-hazardous waste downstream of a simple pH ad justment, with the result of significantly reducing disposal costs.

To obtain the cutting fluid of the invention, some substances normally used in the formulation of conventional metalworking fluids are precluded, such as oil mineral bases (if not in minimal proportions), boron-based com pounds, chlorine-based compounds, formaldehyde. Further, coupling agents (generally consisting of propylene glycol, glycerol, etc. or, much more fre quently, glycol-ethers, which allow stable mixtures of non-polar substances, such as mineral bases, with polar substances, such as anti-corrosives), non ionic surfactants and amine-based buffers are excluded as well. On the other hand, anionic surfactants can be present in very small quantities.

A remarkable aspect of the invention is the possibility of easily treating the exhaust emulsion. The fresh emulsion initially has a metal content close to 0 mg/I. The concentration of metals increases during use, due to the solubili sation of metal ions from the machined surfaces. In addition, the emulsion with use becomes enriched with pollutants from the hydraulic oil and the oil from the guide slides used in machine tools. In order to carry out the treatment of the emulsion according to the in vention when it is exhausted, it is thus necessary to carry out a first treatment with an acid de-emulsifying agent based on a mixture of inorganic acids and salts, such as for example phosphoric acid + sulphamic acid. + magnesium sulphate. If necessary, only one inorganic acid can be used, but the selection of acids that do not increase the risk of exceeding the parameters for dis charge into the sewer system is essential. For example, hydrochloric acid is to be avoided in order not to add a source of chlorides, which would inevitably move to the aqueous phase, exceeding the legal limits and compromising the possibility of discharging the aqueous phase itself downstream of the treat ment. If necessary, low concentration methanesulfonic acid can be used. The indicative dosage for breaking up the emulsion is 5-10 g of demulsifying agent per litre of emulsion to be treated.

The addition of the de-emulsifying agent allows to obtain two distinct phases: an oily phase with a very low percentage of water and an aqueous phase that must be further treated. The oily phase, consisting mainly of vege table and animal oils, can be used as a fuel for the production of energy or sold as a secondary raw material downstream of distillation/refining treat ments.

The aqueous phase requires a further clarification and neutralization operation to remove metals and other contaminants with cheap basic chemi cals such as lime, iron and aluminium salts, organic flocculants.

After the final treatment, the aqueous phase has physico-chemical characteristics that allow it to be discharged into the sewer or in other receiv ing body. As an alternative to the treatment aimed at disposal, the aqueous phase can be reused within the plant, for example in the cooling circuits with an evaporative tower.

Detailed description of the invention

Therefore, the present invention specifically provides is a metalworking fluid composition in emulsion or emulsifiable form comprising:

30-80% by weight of an oily base, consisting of vegetable oils or animal fats or mixtures thereof, and possibly containing not more than 5% by weight of mineral oily bases or synthetic hydrocarbons,

0-70% by weight of water, antiwear additives, friction modifiers, anticorrosives in a total concentra tion comprised from 20 to 40% by weight, antioxidants and biocides in a total effective concentration, not more than 2% by weight, and characterized in that it is free from boron-containing compounds, chlorine containing compounds, formaldehyde, non-ionic surfactants, amine- based buffers and coupling agents containing glycols, glycerol and/or glycol ethers.

According to a preferred embodiment, the metalworking fluid composi tion of the invention consists of an oil-in-water pre-emulsion comprising: from 35% to 50% by weight of said oily base, from 35% to 50% by weight of demineralized or osmotised water, the remainder comprising said antiwear additives, friction modifiers, an ti-corrosives, antioxidants and biocides, as well as alkalizing agents.

Further characteristics of the preferred embodiments of the invention are set forth in the further dependent claims.

Reported below is detailed information on the various components of the metalworking fluid compositions of the invention.

Oily bases

The common mineral bases, or the synthetic hydrocarbons, used in conventional metalworking fluids can be included in the formulation only if strictly necessary, and in any case in very low concentrations, i.e. lower than 5% by weight.

The fatty phases indicated for the invention are vegetable and animal oils and fats, alone or in a mixture with each other, such as palm oil, sunflower oil, lard oil, soybean oil, rapeseed oil, etc.

Natural or semi-synthetic esters such as, alone or in a mixture with the former, trimethylolpropane trioleate, pentaerythritol tetraoleate, 2-ethylhexyl- oleate, cetearyl-oleate, isopropyl-myristate, ethylhexyl-palmitate, methyl esters of fatty acids, etc are equally suitable.

Friction modifying additives

Friction modifying additives are substances which reduce friction in moderately heavy operations, such as dimerized, trimerized fatty acids, and polycondensed fatty acids (eg. Hostacor AL, also used as a corrosion inhibi tor). Polar fats are also suitable, such as fatty acids, fatty acid starches and fatty alcohols, e.g. oleyl alcohol, oleic acid, etc..

Anticorrosives

Anticorrosives have the task of helping the oily base to protect the met al surfaces from corrosion during mechanical processing and also afterwards. Active substances such as sodium and calcium sulphonates have been effec tively employed. Oxometalates such as sodium molybdate at a concentration of > 1%, vanadates, titanates are also effective. Also inorganic phosphates are effective in the formulation of metalworking fluids for which osmotic or de mineralized water is used to produce the emulsion,.

Antiwear additives

In the formulations according to the invention, organic phosphates and phosphonates were used. The former are preferable due to their lower toxicity, especially alkyl phosphates, which are less toxic than aryl phosphates. The most suitable antiwear additives are mono- and di-alkylphosphates with an al kyl chain > C12.

Ethoxylated alcohols, which are commonly used as antiwear additives, have not been used because they are very soluble and difficult to remove from the aqueous phase.

Anti-foam additives

They are mainly used in the formulation of metalworking fluids using osmotic or demineralized water in the preparation of the emulsion, but they are not required with water having a total hardness of 200-500 mg/I of CaCC>3. The antifoam additives usable in the present invention consist of polydime- thylsiloxanes of variable molecular weight.

Buffers

Buffers are necessary to maintain the operating pH in the 8-11 range. The usable buffers are inorganic substances based on sodium hydroxide, po tassium hydroxide or organic buffers such as amino alcohols, for example 2- aminoethanol at concentrations of 0.2% by weight.

If organic buffers are used, it is necessary to minimize the concentra- tion of use because, like all amino compounds, organic buffers contribute to the COD increase of the aqueous phase downstream of the breaking of the emulsion.

Biocides

The active substances must be effective and stable in the alkaline working pH and must not pose problems in the treatment of the wastewater emulsion. Benzoyl isothiazolinone, ortho-phenylphenol, octyl isothiazolinone, methyl-isothiazolinone, and sodium pyrithione were used. In line of principle, continuously dosed di-bromonitryl-propanamide can also be used.

The percentages of use have been selected in order to avoid the classi- fication of the entire composition as “dangerous for the environment” accord ing to the CLP ( Classification , Labeling and Packaging) Regulation, officially (CE) rRegulation No. 1272/2008.

Antioxidants

Antioxidants are required to avoid rancidity of fatty substances. The most suitable antioxidants for the invention are phenolic-type oxygenates, such as BHA, BHT or, preferably, high molecular weight phenolic antioxidants. The latter (such as Irganox L 135 from BASF) are safer for health.

Antioxidants of hydrophobic nature have been preferred in order to min imize the content of pollutants in the aqueous phase downstream of the emul- sion break.

Dyes , fragrances

Dyes and fragrances can be used in concentrations of 0.1 -0.3% by weight.

Water The water content in the metalworking fluid of the invention varies from

0 to 70% by weight. Such variability depends on the fact that the metalworking fluid is marketed in an oily solution form, to be diluted with water and emulsi- tied before use, or in the concentrated emulsion version (pre-emulsified), in the first case, polymeric emulsifiers such as alkylacrylate crosspolymers can be used.

As already noted, in the formulation of the invention the coupling agents are categorically absent, because these substances are fairly soluble in water and after the demixing of the emulsion they remain in the aqueous phase. They are difficult to be removed from the aqueous phase and they increase critically the Chemical Oxygen Demand (COD).

With the exclusions and limitations listed above, the metalworking fluid product according to the invention may contain one or more of the following compounds at the concentrations (% by weight) indicated below:

1) 30-80% oil base

2) 10-20% friction modifying additives

3) 5-20% anticorrosives 4) 5-20% antiwear additives

5) 0 to <1% anti-foam additives

6) 1-5% buffers

7) <1% biocides

8) <1% antioxidants 9) 0 to <1 % dyes, fragrances

10) 0-5% alkalizing agents

11 ) 0-70% water

As already noted, the selection of raw materials is studied on the basis of their tendency to move completely or partially in the oily phase upon break- ing of the emulsion, in order to minimize the concentration of pollutants found in the aqueous phase. Furthermore, the use of low-boiling raw materials, which are found in the aqueous condensate following the evaporation pro cess, has been avoided.

The metalworking fluid can be placed on the market as a pure fluid or pre-emulsified in water. The need to produce an already pre-emulsified ver sion is linked to operational aspects. In fact, potassium hydroxide (KOH) or sodium hydroxide (NaOH) must be added to the formulation to promote the in- timate mixing of water and oil before use in machine tools. Potassium or sodi um hydroxide cannot be added to the pure metalworking fluid formulation, as it cannot be mixed with the rest of the components present in the formulation. It must therefore be added to the pure fluid in situ, together with water, during the preparation of the emulsion.

To avoid the purchase, storage and management by users of an addi tional chemical compound, the option of the pre-mixed product is provided, to be diluted before use up to the most appropriate concentration.

A further advantage offered by the pre-emulsified version according to the invention consists in the possibility of using a non-combustible fluid, thus minimizing the risks for operators during transport, storage and handling.

The metalworking fluid proposed according to the invention is suitable for the machining of pieces made of carbon steel or stainless steel. Special precautions are required for the processing of cast iron, aluminium alloys and yellow metals.

EXAMPLES

Some specific embodiments of the metalworking fluid formulation ac cording to the present invention are described below by way of mere exam- pies but not of limitation, together with the results of the experiments carried out for the purpose of comparison with conventional metalworking fluids.

EXAMPLE 1

Pre-emulsion containing demineralized water to be diluted to the percentage of use with drinking water

The following composition represents an example of a pre-emulsified for mulation according to the invention:

The pre-emulsified metalworking fluid whose composition is shown in the above table appears as a whitish liquid with a pH between 10 and 11 .

The procedure for preparing the metalworking fluid was as fol- lows:

1 . mixing the first five raw materials at 40 °C until complete homogeneity to form the oily phase;

2. cold mixing of the last four raw materials, until the solids are com pletely dissolved, to form the aqueous phase; 3. slowly adding the oily phase to the aqueous phase under stirring to produce an oil-in-water emulsion;

4. mixing for 30-60 minutes with a propeller stirrer at 10-20000 rpm;

5. adjusting pH value in the 10-11 range. EXAMPLE 2

Metalworking fluid to be diluted to the percentage of use with drinking water and inorganic bases for pH correction

An example of a composition of the invention without water, to be mar keted as an undiluted fluid, is described below:

The formulation shown in the table requires the addition of potable water to reach the optimal concentration of use, as well as sodium or potassium hy droxide, to generate a whitish liquid with a pH between 10 and 11 .

The preparation of the metalworking fluid is carried out by slowly adding the materials to a mixing tank in the order shown in the list. The temperature must be brought and maintained at 40 °C and the mixing, with a propeller stir rer at 10-20000 rpm, must have a duration of 30-60 minutes, until a homoge neous mixture is obtained. EXAMPLE 3

Metalworking fluid to be diluted to the percentage of use with demineralized water and inorganic bases for pH correction

An example of a composition according to the invention without water, for use in plants that use demineralized water to prepare the emulsion, is shown below:

The formulation shown in the table is designed for use in plants qus- ing demineralized water to prepare the emulsion. It must be diluted to 3-6% by weight and requires the addition of sodium or potassium hydroxide to gener ate a whitish liquid with a pH between 10 and 11 . The metalworking fluid preparation method is carried out by slowly adding the materials to the mixing tank in the order shown in Table 3. The temperature must be brought and maintained at 40 °C and the mixing must last 30-60 minutes with propeller stirrer at 10-20000 rpm, until a homogeneous mixture is obtained.

Comparison of the invention with conventional metalworking fluids

The inventive step of the present invention can be clearly appreciat ed by comparing the characteristics of the product with those of four widely used metalworking fluids, produced by multinational companies in this sector. The products compared, which will be referred to below as A - D lubricants, are the following:

A) Hysol MB 50 (Castrol);

B) Ecocool Mach 20 (Fuchs);

C) Blasocut 940 (Blaser); D) Vanguard SuperSoloil 99 (Compagnia Italiana Lubrificanti).

The COD and the content of residual surfactants in the aqueous phase downstream of the treatment processes typically used in industry are com- pared below. The comparison was made starting from emulsions containing 5% by weight of metalworking fluid.

The most used method to break up an exhausted emulsion consists of acidification with mineral acids. The result of breaking the emulsion consists in 5 the unmixing in the following two phases:

• an oily phase, rich in oil and insoluble substances, which is positioned in the upper part of the reaction tank; this can be easily removed and treated to reduce the water content, and destined for secondary uses also by means of distillation/refining processes;

10 · an aqueous phase, rich in soluble organic substances, suspended sol ids and metal ions positioned in the lower part. The high content of pollutants requires a further clarification treatment using large quantities of lime, iron or aluminium salts and organic flocculants in order to increase the pH and pro mote the precipitation of metal ions and organic substances.

15 Even using large quantities of chemical products, the resulting aqueous phase has a content of organic substances and surfactants which do not allow discharge into the sewer system, or other receiving body, according to the le gal limits.

The following tables show the parameters measured in comparison, be-

20 fore and after the corresponding purification treatments. The percentage indi cated is the content by weight of the relevant product in drinking water.

Further treatments are therefore necessary (treatment in a biological plant, oxidative processes, evaporation followed by condensation, activated carbon filters, etc.).

As indicated in Table 2, the treatment of exhausted emulsions formu lated starting from conventional products, even if using large quantities of chemical agents, does not allow to reduce the COD values and the surfactant contents to levels compatible with the discharge into the sewer system.

Further treatments are therefore required (biological plant, oxidizing processes, absorption on activated carbon) to obtain waste that can be dis charged into the environment in accordance with the law.

On the contrary, the metalworking fluid products according to the inven- tion have been designed to be easily separable at the end of their life, and do not necessarily require the use of further treatments downstream of the chem ical-physical process in order to be reused (or disposed of, in the case of the aqueous phase).

As already noted, downstream of the emulsion breaking, the oily phase can be destined for other uses (e.g., fuel for energy production), or dis tilled/refined to be put back on the market.

The aqueous phase has a very low content of Chemical Oxygen De mand or COD (350-600 mg/I) and a negligible content of surfactants. The chemical-physical parameters of the aqueous phase are such as to allow, by means of a simple treatment, the discharge into the sewer system or other re ceiver body, in line with the legal limits.

On the other hand, the typical treatment for breaking conventional emulsions provides for the use of evaporators or chemical-physical treat ments, while in the case of the product of the present invention the treatment of the exhausted emulsion is even unnecessary, in circumstances where mix ing with other plant waste is possible. As an alternative to the treatment aimed at unloading, the aqueous phase can be reused within the plant, for example in the cooling circuits with an evaporative tower.

The present invention has been described with reference to some spe cific embodiments thereof, but it is to be understood that variations or modifi cations may be made to it by those skilled in the art without thereby departing from the relative scope of protection.