GB2063909A - High flashpoint hydraulic fluid - Google Patents

Abstract

A hydraulic fluid comprises a blend of 50-97% of an oleic acid ester of a polyol, 3-50% of a mixture of polyols and branched unsaturated C12-20 fatty acids, 0.01-2% of a phenolic antioxidant, 0.01-2% of a diphenyl amine antioxidant, and 1-1000 ppm each of (i) a mixture of a fatty acid partial ester, aliphatic hydrocarbon and silica and (II) a mixture of metal soaps in a hydrocarbon oil, as defoamants.

Description

SPECIFICATION High flashpoint hydraulic fluid This invention relates to hydraulic fluids that are less flammable than fluids based on mineral oils.

The fluids of the present invention are formulated without the use of base fluids which contain phosphorous and chlorine and have, moreover, improved oxidation stability, improved foaming resistance and a low neutralization factor.

Known hydraulic fluids based on esters of polyols with oleic acid or similar materials possess certain disadvantages even though they may be satisfactory in other respects. In particular, the oxidation stability may be unsatisfactory and they may possess high neutralization factors (over 4.0 mg KOH/g). They may also tend to resinify in the presence of air and light.

According to the present invention we provide a hydraulic fluid based on a blend of two basic oil components, a system of two antioxidants having a synergistic effect and a system of two foam inhibitors.

The individual components of the fluid are: (a) an oleic acid ester of a polyol, preferably pentaerythritol-tetraoleate or trimethylolpropanetrioleate, constituting preferably 50 to 97 percent of the blend; (b) a mixture of esters of polyols with branched, predominantly unsaturated C12-C20 fatty acids (neopentyl glycol or trimethylol propane being preferably employed as the polyol component), preferably constituting 3 to 50 percent of the blend; (c) 0.01 to 2.00 percent, preferably 0.20 to 1.00 percent of a phenol derivative having at least one sterically hindered phenol group, i.e. a phenolic hydroxy group immediately adjacent a substituent requiring much space, such as tertiary butyl, (preferably pentaerythrityl-tetrakis [ 3(3,5-di-tertia ry butyl4-hydroxyphenyl)propionate ] , as a phenolic antioxidant;; (d) 0.01 to 2.00 percent, preferably 0.20 to 1.00 percent of a diphenyl amine derivative (preferably a p,p'-dialkyl-diphenyl amine) as an amine antioxidant; (e) 1 to 1000 ppm, preferably 5 to 100 ppm of a mixture of a fatty acid partial ester, an aliphatic hydrocarbon, and finely dispersed silica as a foam inhibitor; and (f) 1 to 1000 ppm, preferably 5 to 100 ppm of a mixture of metal soaps in a hydrocarbon oil as foam inhibitor.

The main component of the product is a polyol-oleic acid ester according to (a). Inclusion of a certain amount of (b) in the formula surprisingly leads to a considerable improvement of the oxidation stability, as is shown in Table I below by comparing Lab. No. 2 and No. 5, without (in spite of the lower viscosity of (b)) affecting the flash point and thus, without noticeably impairing the low inflammability.

In addition, this leads to a more favorable air separating capacity (improvement of 1 to 2 min. at 500C, compared with formulae merely containing (a) as the base oil). Too great proportions of (b) lead to lower flash temperatures and higher inflammability.

Pentaerythrityl-tetrakis [3(3,5-di-tertiarybutyl-4-hydroxyphenyl) propionate] has proved particularly effective as compared with other phenolic antioxidants, as is shown in Table I by comparing Lab. Nos. 1 and 2.

The oxidation stability is further improved with lasting effect by adding (d), as is apparent from Table I by comparing Lab. Nos. 2 and 3 as well as Lab. Nos. 4 and 5.

The synergistic effect of the combination of (c) and (d) is particularly apparent from Table II, as shown by Lab. Nos. 7 and 9 compared with 8.

Although silicone defoamers generally effect sufficient foam inhibition, they also tend to cause a drastic deterioration in the air separating properties. For example, 0.01 percent of a 1 percent solution of dimethyl siloxane polymer in kerosene increases the separation time from 5 to 1 1 min. at 500 C.

Defoamers on the basis of polymeric acrylic acid esters are ineffective in the present ester fluids.

The use of either (e) or (f) by themselves as foam inhibitors results in moderate foam inhibition only, but the combination of (e) and (f) is surprising, and even in very small quantities (10 ppm each) foam formation is effectively inhibited, as can clearly be seen from Table III, while the air separating capacity is not materially impaired.

The hydraulic fluid developed according to the invention has a relatively low neutralization factor (typically about 0.6 mg K0H/g). This contributes to the improved hydrolytic stability of the fluid. In addition, the hydraulic fluid has very favorable toxicological properties and is less aggressive towards seal materials, paint coatings and synthetics than hydraulic fluids based on phosphorus or chlorine compounds.

The hydraulic fluids according to the invention may in addition contain also other agents, such as rust and corrosion inhibitors and metal deactivators.

TABLE I OXIDATION TEST

Pentaaerythrityl tetrakis [3(3,5- 4,4'-Methy- Neutralization di-tert.butylI-4- lene-bis(2,6- p,p'Diocryl Kin. viscosity Factor, Lab. Ester Ester hydroxyphenyl) di-tert. diphenil- Rust Metal (40 C) rise mg.

No. (a) (b) propionate] butylphenol) amine inhibitor Deactivator Rise % KOH/g wt. % 1 98.75 - - 0.50 0.50 0.20 0.05 195 2.0 2 98.75 - 0.50 - 0.50 0.20 0.05 114 1.0 3 99.25 - 0.50 - - 0.20 0.05 506 2.6 4 89.25 10.00 0.50 - - 0.20 0.05 377 2.4 5 88.75 10.00 0.50 - 0.50 0.20 0.05 28 0.4 Test Method: bubble air through sample for 24 hours at 130 C, 10 liters air/hour; oil sample contains steel, copper, aluminum and lead as catalysts.

TABLE Il DIFFERENTIAL THERMAL ANALYSIS 1800C (isotherm), 0.3 1 02/min.

size of sample: 10 mg

pentaerythrityl tetrakis [3(3,5 ester ester di-tert. butyl-4 Lab. accord. accord. hydroxyphenyl) p,p'-dialkyl- I induction No. to (a) to (b) propionate i diphenylamine I period wt. % min.

6 90.00 10.00 - - < 1 7 89.00 1.00 - - 7 8 89.00 10.00 0.50 0.50 14 9 89.00 10.00 - 1.00 1 < 2 Induction period = measured time up to oxidative collapse (strongly exothermic reaction) of fluid.

TABLE Ill FOAM BEHAVIOUR

Foam Test ASTM D Fluid- 892, Sequence I ml Base Fluid (a) 420/130 " + 100 ppm foam 100/5 inhibitor (e) " + 100 ppm foam 190/0 (free after inhibitor (f) 130 s.) 10 10 ppm foam 120/0 (free after inhibitor (e) 90 s.) + 10 ppm foam inhibitor (f)

Claims (7)

1. A hydraulic fluid comprising: (a) 50 to 97 percent of an oleic acid ester of a polyol; (b) 3 to 50 percent of a mixture of esters of polyols and branched, predominantly unsaturated C12-C20 fatty acids; (c) 0.01 to 2.00 percent of a phenolic antioxidant, having at least one sterically hindered phenol group; (d) 0.01 to 2.00 percent of a diphenyl amine antioxidant; (e) 1 to 1000 ppm of a mixture of a fatty acid partial ester, an aliphatic hydrocarbon, and finely dispersed silica; and (f) 1 to 1000 ppm of a mixture of metal soaps in a hydrocarbon oil.

2. A hydraulic fluid according to claim 1 in which the ester (a) is pentaerythritol tetraoleate or trimethylolpropane trioleate.

3. A hydraulic fluid according to claim 1 or 2 in which the ester (b) is an ester of a neopentyl glycol.

4. A hydraulic fluid according to claim 3 in which the neopentyl glycol is trimethylol propane.

5. A hydraulic fluid according to any of claims 1 to 4 in which the antioxidant (c) is pentaerythrityl tetrakis [ 3(3,5-di-tertiarybutyl-4-hydrnxyphenyl)prnpionate ] .

6. A hydraulic fluid according to any of claims 1 to 5 in which the diphenylamine antioxidant is a p,p'-dialky diphenylamine.

7. A hydraulic fluid according to claim 6 in which the diphenylamine antioxidant is p,p'-dioctyl diphenylamine.