NO124315B - - Google Patents

Description

Base material for hydraulic fluids.

Products that are to be suitable for special purposes, such as for low-temperature stirring and operation of hydraulic mechanisms, require a combination of properties that ordinary products in many respects do not have. Properties that are necessary for safe and satisfactory

low-temperature operation includes a low pour point, so that pro-

the duct will work at least at temperatures as low as -40°c to

-50°C. Another important feature necessary for these appli-

else is a flat viscosity curve, i.e. a high viscosity index,

so that the material can be used over large temperature ranges of the kind encountered during the operation of aircraft. One of the key features that must

taken into account in the case of aircraft for military and commercial use, mini-

paint flammability. Other important characteristics include relatively high

boiling point, high corrosion resistance and high oxidation resistance.

Many products have been proposed for these purposes, e.g. lower trialkyl phosphates. However, these products have high wear properties, are rather flammable, partly due to their volatility, and at low temperatures they are not compatible with ordinary thickeners. To overcome these undesirable properties, it was proposed to modify trialkyl phosphates by adding to them a small amount of ketone. The addition of ketones, however, does not provide the properties required for hydraulic fluids. An example of such a mixture is described in U.S. Pat. patent no. 2,470,792.

Another attempt to use trialkyl phosphates consisted in adding to them a small amount of triaryl phosphate, e.g. diphenylcresyl phosphate, a certain amount of a linear polymer of methacrylic acid esters, and a small amount of an epoxide product, e.g. glycidyl hydrocarbyl ethers and hydrocarbon epoxides, see. U.S. pat. No. 2,636,861. However, these materials did not give very good results when used in aircraft hydraulic fluids, as the materials lack all of the above-mentioned combined properties.

It has been found that trialkyl phosphates can be successfully used as hydraulic fluids when, with certain limitations, they are combined with certain other materials which provide properties required for the hydraulic fluid. Thus, trialkyl phosphate can be combined with tricresyl phosphate, trixylenyl phosphate, a viscosity index improving agent, e.g. polymethacrylate, an anti-rust agent, a metal-deactivating agent, in specific amounts to provide a unique combination of materials that can be used as a hydraulic fluid and that have the desired properties.

Trialkyl phosphate which can be advantageously used in the invention can be present in an amount of from 50 to 90% by weight and preferably from 65 to 75% by weight. Trialkyl phosphates which give the best results are those where each alkyl group contains from 3 to 12 carbon atoms, preferably from 4 to 9 carbon atoms. The alkyl groups must have straight-chain configuration. A single trialkyl phosphate can contain: the same alkyl groups in all three positions or can contain a mixture of different alkyl groups. Mixtures of different trialkyl phosphates can be used. Suitable trialkyl phosphates that can be used in the base material according to the invention can include tripropyl phosphates, tributyl phosphates, trihexyl phosphates, trioctyl phosphates, dipropyloctyl phosphate, dibutyloctyl phosphate, dipropylhexyl phosphate, dihexyloctyl phosphate, dihexylpropyl phosphate, propylbutyloctyl phosphate and mixtures thereof.

The base material according to the invention must be combined with 50-10% by weight of triaryl phosphate, which is a mixture of tricresyl phosphate and trixylenyl phosphate which also acts as a thickener. The amount of tricresylphate and trixylenyl phosphate is between 5 and 25% by weight of each, preferably 5 to 15%. The combined mixture of tricresylphos-

barrel and trixylenyl phosphate have a viscosity between 145 and 230 Saybolt universal seconds measured at 38°c. The mixture of materials can then be combined with trialkyl phosphate in any known manner.

A conventional polymeric material is then mixed with the mixture of trialkyl phosphate and triaryl phosphate, and this polymeric material acts as a viscosity index improver.

The polymeric material which is mixed with the base material can be a mixture of 10 to 55% by weight polymethacrylates and polyacrylates, each of which contains from 1 to 20 carbon atoms. The polymeric materials can be in a solvent carrier, e.g. di-2-ethylhexyl sebacate, dioctyl adipate, di-2-ethylhexyl adipate or other conventional carriers. The polymeric material can be any combination of these materials. The material is thoroughly mixed with the combination of ingredients into a uniform material. The amount of material can be between 5 and 20% by weight.

The materials are then mixed with an anti-rust agent in a solvent carrier, e.g. an alkyl succinic acid and its derivatives. This agent may be present in amounts between 0.01 and 0.5% by weight. A corrosion inhibitor is then added to the mixture, e.g. benzotriazole, quinine or the like in an amount between 0.001 and 0.5% by weight and thoroughly mixed with it. A dye in an amount of 5 to 20 ppm is then added and mixed into the mixture in a known manner. A conventional silicone anti-foam agent is also added in

an amount between 5 and 50 ppm..

The aforementioned mixture of components has the necessary properties to be used as a hydraulic fluid.

The hydraulic fluids can be produced in a manner that is illustrated in the following examples:

EXAMPLE 1.

Tricresyl phosphate in an amount of 10.45 <y>ect% was thoroughly mixed

that with 8.55% by weight trixylenyl phosphate to achieve a viscosity of

155 Saybolt universal seconds measured at 37°C. This mixture was thoroughly mixed with 68.96 wt% tributyl phosphate. Then became thorough

mixed with 12% by weight of a mixture of approx. 40% polyalkyl methacrylate, and approx. 60% di-2-ethylhexylsebacato solvent-carrier. Then, a conventional alkylsuccinic acid-containing rust inhibitor was mixed in an amount of 0.02% by weight in a solvent carrier. Then 0.02% by weight of benzotriazole was thoroughly mixed together with a conventional dye and anti-foam agent in an amount of 10 and 15 ppm respectively. After the above-mentioned ingredients were thoroughly mixed into a homogeneous mixture, the hydraulic fluid was thoroughly examined and had the following properties:

EXAMPLE 2.

The thermal stability of a conventional hydraulic fluid was investigated and compared with the base material according to the invention. Thus, a sample of a commercially available material was examined in accordance with the method indicated in Table V. The active material was octyldiphenyl phosphate. The viscosity change measured in centistokes at 38°C was -0.25, while the neutralization number change, measured in milligrams of potassium hydroxide per gram, watt +7.57.

A comparison with the heat stability shown in Table V in Example 1 illustrates the superior properties of the product according to the invention.

Claims (2)

1. Base material for hydraulic fluids, essentially consisting of a mixture of 50-90% by weight trialkylphosphate, selected from the group consisting of tripropylphosphate, tributylphosphate, trihexylphosphate, trioctylphosphate, dipropyloctylphosphate, dibutyloctylphosphate. dipropylhexylphosphate, dihexyloctylphosphate, dihexylpropylphosphate, propylbutyloctylphosphate and mixtures thereof, and 50-10% by weight triaryl phosphate, characterized in that the triarylphosphate component consists of a mixture of 5-25% by weight of each tricresyl phosphate and trixylenyl phosphate, calculated on the entire composition, the mixture of tricresyl phosphate and trixylenyl phosphate has a viscosity of 145-230 Saybolt universal seconds, measured at 38°C. 2. Base material as stated in claim 1, characterized in that the trialkyl phosphate is present in an amount of from 65 to 75% by weight, and that tricresyl and trixylenyl phosphate are each present in amounts of from 5 to 15% by weight.