NO179076B - Water-based hydraulic fluid - Google Patents

Abstract

A functional fluid composition for use as a hydraulic fluid, lubricant, cutting fluid or drilling fluid which comprises (a) from 20 to 98% by weight water (b) from 0 to 80% by weight of a glycol, and (c) from 0.5 to 25% by weight of a thickening agent prepared by (a) reacting one mole of a monofunctional active-hydrogen-containing compound having at least 10 carbon atoms with between 20 and 400 moles of one or more alkylene oxides and (b) thereafter reacting the product of step (a) with a diepoxide in an amount such that the molar ratio of diepoxide to hydroxyl groups in the product of step (a) is between 0.2:1 and 5:1. The fluid may further comprise functional components for preventing wear and corrosion and also 0.5 to 15% by weight of a non-ionic, cationic, anionic or amphoteric surfactant. i

Description

The present invention relates to a water-based hydraulic fluid.

Functional liquids based on mixtures of water and polyether glycols are well known, and are used in a number of different applications, e.g. such as cutting fluids, hydraulic fluids, etc. 1.

Typical formulations of water-based hydraulic fluids (known as HF-C fluids) comprise 15-30% of a high-viscosity polyether glycol, and 35-45% water, with the remainder (up to 50%) being simple glycol and small amounts of additives such as is known to the person skilled in the art. These hydraulic fluids typically have a viscosity of 32-68 cSt at 0°C.

However, there is a growing tendency to reduce the polyether glycol content in such functional liquids. In the last instance, it would e.g. be desirable to reduce the polyetherglycol content in hydraulic fluids to 10% or possibly even lower. There is also a tendency to produce what can be described as strongly water-based liquids (HWBFs) typically containing 50-98% water, by further removal of some or all of the glycol.

A problem arises when attempts are made to reduce the polyether glycol content in hydraulic fluids by reducing the hydraulic fluid's viscosity. This occurs because standard polyether glycol liquids do not possess sufficient thickening capacity. Simply increasing the viscosity of the polymer does not provide the required effect because the increase in solution viscosity becomes marginal and the polymer becomes unstable under high shear conditions.

It has previously been suggested e.g. in US patents 4,767,555 and 4,288,639 to achieve the desired viscosity of such hydraulic fluids by incorporating small amounts of materials which (a) are water compatible and (b) increase the viscosity of the hydraulic fluids by intramolecular association in solution. Such materials are known as associative thickeners.

The hydraulic fluids previously described as highly water-based fluids (HWBFs), which usually contain either no simple glycol, or only small amounts as an antifreeze, have a number of disadvantages compared to HFC water-glycol fluids, namely: ( i) although said HWBFs normally exhibit "permanent shear stability", i.e. the viscosity of the fluid remains stable over a longer period of operation, they nevertheless exhibit a temporary loss of viscosity in zones of high shear, as evidenced by a loss of flow rate and pump efficiency in hydraulic systems, m.a.o. they lack "temporary shear stability". (ii) Under such conditions with temporary viscosity loss, this also goes beyond the fluid's hydrodynamic lubrication ability. Lubrication is only maintained by additives that provide boundary lubrication (EP additives). Despite the fact that such additives are highly developed, these conditions can result in increased wear. Furthermore, the best of these additives are in many cases toxic, hydrolytically unstable, and environmentally undesirable. (ili) The viscosity index of such liquids is often poor, which can cause problems with starting pumps. (iv) HWBFs are sensitive to water loss, which has a

dramatic and undesirable effect on fluid viscosity.

US 3,538,033 describes a family of polyether derivatives of diepoxides which can be used as thickeners in textile printing emulsions, cosmetic emulsions, aqueous pigment suspensions, etc.

The problem to be solved is therefore to produce functional liquids, suitable for the applications described above, which have good permanent and temporary shear stability, contain low concentrations of the associative thickener, have good resistance to water loss in terms of viscosity change, has good apparent viscosity indices, and which maintains hydrodynamic lubrication under high shear conditions.

According to the present invention, a water-based hydraulic fluid is thus provided, which is characterized by the fact that it includes

(a) 20-98 wt-$ water,

(b) 0-80 wt-$ of a glycol, and

(c) 0.5-25 wt% of a thickening agent prepared by (a) relative reaction of 1 mole of a monofunctional compound containing active hydrogen and having at least 10 carbon atoms, with between 20 and 400 moles of one or more alkylene oxides , and (b) then reacting the product from step (a) with a diepoxide in an amount such that the molar ratio of diepoxide to hydroxyl groups in the product from step (a) is between 0.2:1 and 5:1.

The present invention solves the problem defined above by using a thickener of the type defined in US 3,538,033 in the applications mentioned above, together with the formulation technology detailed below.

If one first considers the water component of the hydraulic fluid, then it is preferred that it includes between 35 and 95$ of the hydraulic fluid, most preferably between 45 and 80$. Regarding the glycol, then this can in principle be any glycol which is miscible with water and includes monoethylene glycol and monopropylene glycol, and low molecular weight oligomers thereof (i.e. which have up to 6 ethylene and/or propylene glycol units. The glycol is preferably selected from monoethylene glycol, diethylene glycol and triethylene glycol It is preferred that the glycol comprises between 20 and 60% of the hydraulic fluid.

The first step in the production of the thickener involves reacting the monofunctional compound containing active hydrogen with one or more alkylene oxides. The term "compound containing active hydrogen" means a compound containing hydrogen which can be measured by the Zerewitinoff test for active hydrogen. Such compounds include alcohols, phenols, thiols, fatty acids and amines. The preferred compounds are C-j^-Cgo monohydric alcohol or thiols, ^ ib~^ 20 alkylphenols and C^5~<C>2o aliphatic amines.

The compound containing active hydrogen is alkoxylated with one or more alkylene oxides using either a base or a Lewis acid as catalyst. Typically, the alkylene oxide is one or more of ethylene oxide, propylene oxide or the isomers of butylene oxide. Suitably, between 20 and 400 mol of the alkylene oxide is added to the compound containing active hydrogen, of which 20-100 mol-$ (most preferably 65-85 mol-$) is ethylene oxide and 0-80$ (most preferably 15-35$) is propylene - and/or butylene oxide.

In the second manufacturing step, the product from the first step is reacted with a diepoxide. The diepoxide can in principle be any organic compound that has two epoxide groups. Suitable diepoxides are those having between 4 and 30 carbon atoms and include vinyl cyclohexene diepoxide, bisphenol A/epichlorohydrin condensate and the like. It is preferred to use the diepoxide in amounts such that the molar ratio of epoxide groups to hydroxyl groups (in the product from step 1) is in the range from 0.2:1 to 5:1. The second step in the process can also be catalyzed by either a base or a Lewis acid.

It is preferred that the thickener comprises between 2 and 10% by weight of the hydraulic fluid. It is also preferred that the thickener itself should have a net viscosity of over 4000 cSt at 40°C.

As for the anti-wear components, these are typically metal or amine salts of organosulphur, -phosphorus or boron derivatives or carboxylic acids. These typically include salts of £\- £>22 carboxylic acids, aliphatic or aromatic; sulfuric acids such as aromatic sulphonic acids, phosphoric acids, e.g. acid phosphate esters and analogous sulfur compounds, e.g. thiophosphoric acid and dithiophosphoric acid. Many additional anti-wear agents are suitable and are known to those skilled in the art.

Inhibitors for the corrosion of metals can be organic or inorganic, e.g. metal nitrites, hydroxyamines, neutralized fatty acid carboxylates, phosphates, sarcosines, and succinimides, etc. Most useful are amines such as alkanol amines, e.g. ethanolamine, diethanolamine and triethanolamine. Non-ferrous metal inhibitors include e.g. aromatic triazoles.

In the formulation it is preferred to include 0.5-15% of a surfactant as a co-thickener, which may be non-ionic, cationic, anionic or amphoteric. Examples of suitable surfactants include linear alcohol alkoxylates, nonylphenol ethoxylates, fatty acid soaps, amine oxides, etc. Most preferred are linear, secondary alcohol alkoxylates, e.g. those commercially available from BP Chemicals under the registered trademark Softanol. The surfactants act synergistically with the associative thickener so that a given viscosity can be achieved with a lower total content of thickener in the mixture compared to using the associative thickener alone.

In addition to what is mentioned above, the hydraulic fluid may also contain any components such as high pressure additives, antifoam agents, antimicrobial agents, etc., which are well known to the person skilled in the art. It is also possible to add further known thickeners and co-thickeners if this is desired.

Existing hydraulic fluids can be produced by mixing the four main components and any additional materials that are necessary in a container of suitable size.

In the preferred embodiments of the invention, that is the formulations containing 20% glycol or more, it has been found that temporary shear stability is provided to the liquids. This increases the fluid's ability to provide hydrodynamic lubrication under high shear conditions. The presence of 20% glycol or more and of the surfactant co-thickener also improves the apparent viscosity index of the fluids compared to fluids containing no glycol or surfactant.

In those embodiments of the invention that contain less than 20% glycol, the problem of temporary shearing is also taken into account by using associative thickeners according to the invention with high polymer viscosity (eg greater than 20,000 cSt at 40°C). In high shear environments, thickening achieved by association is lost when the fluids are subjected to temporary shear. However, the viscosity of the liquid is maintained at an intermediate level by the normal thickening of a high viscosity polymer, typically to a level of 10-20 cSt at 50°C. This limits the loss of pumping efficiency and ensures that hydrodynamic lubricity is maintained. This also promotes the liquid's properties in terms of viscosity change due to water loss and viscosity index.

Present water-based hydraulic fluids are particularly useful in hydraulic piston, gear or vane pumps, motors and general hydraulic systems, e.g. hydraulic rams, robots, etc.

The invention is illustrated by the following examples:

Example 1

A commercial sample of oleyl/cetyl alcohol (85/15) was catalyzed with potassium hydroxide (0.3 wt% of the target alkoxylate), dried and reacted with a 70/30 (w/w) mixture of ethylene oxide and propylene oxide at 115- 125°C to form an alkoxylate with an experimentally determined molecular weight of 6000 (by hydroxyl determination).

500 g of the above non-neutralized alkoxylate was reacted at 130°C with 15.9 g of bisphenol Å/epichlorohydrin condensate (Epikote 828 - ex Shell) for 3 hours. The remaining catalyst was removed by treatment with magnesium silicate to give an associative thickener with a net viscosity of 5000 cSt at 40°C. A viscosity for 10% aqueous solution was determined to be 193 cSt at 0°C.

Example 2

500 g of the above unneutralized alkoxylate from Example 1 was reacted at 130°C with 31.8 g of bisphenol A/epi-chlorohydrin condensate for 3 hours, the catalyst was removed by magnesium silicate treatment, and this gave an associative thickener with a net viscosity of 17,300 cSt at 40°C.

A viscosity for 10% aqueous solution was determined to be 2,100 cSt at 40°C.

Example 3

A commercial sample of oleyl/cetyl alcohol (85/15) was reacted in the manner described in Example 1 with an 80/20 mixture of ethylene oxide and propylene oxide to form an 6,000 molecular weight alkoxylate.

300 g of the above-mentioned unneutralized polyalkylene glycol was reacted with 14.0 g of vinylcyclohexene diepoxide for 3 hours at 140-150°C. The resulting associative thickener had a net viscosity of 4900 cSt at 40°C and a 10% aqueous solution viscosity of 1427 cSt at 0°C.

Example 4

A commercial sample of oleyl/cetyl alcohol (85/15) was reacted as described in Example 1 with a 75/25 mixture of ethylene oxide and propylene oxide to form an intermediate with a molecular weight of 2950, and then with additional ethylene oxide to form an alkoxylate with a molecular weight of 3100.

2000 g of the above unneutralized polyalkylene glycol was reacted with 175 g of vinyl cyclohexene diepoxide at 140-150°C for 6 hours to obtain an associative thickener with a 10% aqueous solution viscosity of 1742 cSt.

Examples 5-8

Dodecan-1-ol, tetradecan-1-ol, hexadecan-1-ol and octadecan-1-ol were reacted under base catalysis with 80-20 mixtures of ethylene oxide/propylene oxide to form 6000 molecular weight alkoxylates. 200 g of each alkoxylate was reacted with 9.4 g of vinylcyclohexene diepoxide in the manner described in Example 3 to obtain four associative thickeners. The products were used to provide a comparison of solution viscosity against hydrophobic chain length.

Example 9

The thickener (8$) from Example 1 was formulated into a hydraulic fluid of 46 cSt at 40°C containing water (36$), diethylene glycol (50$), a fatty acid and morpholine. This was subjected to a four-ball test (IP239) at 40 kg for 1 hour and produced a wear mark of 0.56 mm, a result similar to that of a similarly formulated hydraulic fluid using 15% of a conventional polyglycol thickener.

The same thickener at a level of 7$ in a strong water-based liquid of 46 cSt at 40°C was added for 50 passages in a Kurt Orban shear stability test device (IP294) and did not undergo any permanent loss of solution viscosity.

Example 10

The thickener from Example 4 was formulated at a level of 8% to a hydraulic fluid containing 30% diethylene glycol and 58% water, the remainder being a material comprising anti-wear and anti-corrosion agents. Said hydraulic fluid was circulated for 24 hours in a 7 kW Wickers PFB-5 axial piston pump at 50°C and 170 bar. The flow rate, which can be directly related to the fluid viscosity, was monitored to indicate viscosity in the high shear regions of the pump. The hydraulic fluid was compared to a similar hydraulic fluid containing only 10$ diethylene glycol and 80$ water, and to an additional hydraulic fluid based on a commercially available low viscosity associative thickener, a fatty alcohol ethoxylate terminated with an olefin epoxide, and without any diethylene glycol content .

Example 11

The thickener from Example 1 ($6.2) and a 5 mol ethoxylate of a linear, secondary C-12/14 alcohol ($1.55)

(Softanol 50 - ex BP Chemicals) was mixed with diethylene glycol ($40) and water ($50), the remainder consisting of functional anti-wear, anti-corrosion and anti-foam agents ($2.25) to obtain a hydraulic fluid of 45, 5 cSt at 40°C. The following data were determined.

Four-ball wear mark, mm (1 hour, 40 kg, IP239): 0.61 Shear stability (IP294), $ viscosity change: -7

Example 12

The associative thickener from Example 3 (3.6$) and a 5-mole ethoxylate of a linear secondary Cjl2/14 alcohol (0.9$) were mixed with diethylene glycol (20$) and water (73.4$), the remainder were additives (2$), to obtain a hydraulic fluid of 49.3 cSt at 40° C. The following data were determined.

Four-ball wear mark, mm (1 hour, 40 kg, IP239): 0.62 Shear stability (IP29), $ viscosity change: + 5

Example 13

The associative thickener from Example 3 (5.4$) and a 12 mol ethoxylate of a linear secondary C-12/14 alcohol (3.6$) (Softanol 120 - ex BP Chemicals) were mixed with diethylene glycol (39$) and water ($50), with the remainder consisting of anti-wear, anti-corrosion and anti-foam additives ($2) to obtain a hydraulic fluid of 46.8 cSt at 40°C. The following data were determined.

Four-ball wear mark, mm (1 hour, 40 kg, IP239): 0.61 Shear stability (IP294), $ viscosity change: +2.9

Example 14

The thickener from Example 2 (5.0$) and a 12 mol ethoxylate of a linear, secondary C-12/14 alcohol (1.25$) were mixed with diethylene glycol (20$) and water (70$), the residue consisting of anti-wear, anti-corrosion and anti-foam agents ($3.75) to obtain a hydraulic fluid of 46.1 cSt at 40°C. The following data were determined.

Four-ball wear mark, mm (1 hour, 40 kg, IP239): 0.68

Example 15

To demonstrate the effect of diethylene glycol on apparent viscosity index, two ISO 68 liquids were prepared from the thickener of Example 3. Liquid 1 contained 6.0% thickener, 30% diethylene glycol and 64% water. Liquid 2 contained 5.0$ thickener and 95$ water. The combined effect of the presence of diethylene glycol and the slightly elevated content of thickener in liquid 1 results in a liquid with a significantly lower viscosity at 20°C than that observed for liquid 2, demonstrating that the apparent viscosity index of liquid 1 is higher than the for liquid 2.

Example 16

To demonstrate the effect of co-thickeners on apparent viscosity index, two fluids of 550 cSt at 40°C were prepared as follows: Fluid 1 contained 6.0% thickener from Example 2, 4.0% of a 12 mol ethoxylate of a C 12/14 linear secondary alcohol, 10$ diethylene glycol and 80$ water. Liquid 2 contained 10.0 thickener from Example 2, 10% diethylene glycol and 80% water. The presence of surfactant in liquid and reduced content of thickener results in a liquid with significantly lower viscosity at 20°C than that observed for liquid 2, demonstrating that the apparent viscosity index of liquid 1 is higher than that of liquid 2.

Claims (7)

1. Water-based hydraulic fluid, characterized in that it includes (a) 20-98 wt-# of water, (b) 0-80 wt-$ of a glycol, and (c) 0.5-25 wt-$ of a thickener prepared by (a) relative reaction of 1 mol of a monofunctional compound containing active hydrogen and having at least 10 carbon atoms, with between 20 and 400 mol of one or more alkylene oxides, and (b) then reacting the product of step (a) with a diepoxide in an amount such that the molar ratio of diepoxide to hydroxyl groups in the product from step (a) is between 0.2:1 and 5:1. 2. Hydraulic fluid according to claim 1, characterized in that it further comprises functional components for preventing wear and corrosion. 3. Hydraulic fluid according to claim 1, characterized in that it comprises 35-95% water by weight. 4. Hydraulic fluid according to claim 1, characterized in that it comprises 20-60% glycol by weight. 5. Hydraulic fluid according to claim 1, characterized in that it comprises 2-10% by weight of the thickening agent. 6. Hydraulic fluid according to claim 1 or 4, characterized in that it further comprises 0.5-15% by weight of a non-ionic, cationic, anionic or amphoteric surfactant. 7. Hydraulic fluid according to claim 1, characterized in that it comprises 0-20 wt-$ of glycol and 0.5-25 wt-$ of a thickener which has a net viscosity of over 20,000 cSt at 40°C.