EP0102088A2

EP0102088A2 - Methylpolysiloxane hydraulic fluids

Info

Publication number: EP0102088A2
Application number: EP83108576A
Authority: EP
Inventors: Takeshi Imai; Minoru Nishio
Original assignee: Toray Silicone Co Ltd
Current assignee: DuPont Toray Specialty Materials KK
Priority date: 1982-08-31
Filing date: 1983-08-31
Publication date: 1984-03-07
Also published as: JPS5941394A; EP0102088A3

Abstract

A methylpolysiloxane oil containing CH₃SiO_3/2, (CH₃)₂SiO, and/or (CH₃)₃SiO_1/2 units and having a specific gravity of 1.02 or greater has been found useful as an hydraulic fluid. The specific gravity of the hydraulic fluid allows for any water introduced into the system to collect as an upper layer above the hydraulic fluid where it can be removed easily. A particularly preferred methylpolysiloxane hydraulic fluid contains 0 to 10 mol percent (CH₃)₃SiO_1/2 units, 45-80 mol percent (CH₃)₂SiO units, and 20-45 CH₃SiO_3/2 units with a 1.65 to 1.80 CH₂/Si ratio.

Description

Background Of Invention

This invention relates to a hydraulic fluid. More specifically, this invention relates to a hydraulic fluid whose principal agent comprises a methylpolysiloxane oil with a specific gravity of 1.02 or greater at 25°C. This invention also relates to a process of transmitting power from one place to another via a hydraulic fluid medium where the hydraulic fluid medium is a methylpolysiloxane oil with a specific gravity of 1.02 or greater at 25°C.
Glycol ether base agents are typical examples of convention hydraulic oils used in automotive brake and clutch systems. The drawbacks of a glycol ether base hydraulic oil include the significant decline in both the boiling point and the temperature at which vapor lock occurs when the hydraulic fluid contains water either absorbed from the environment or introduced by accident. In order to eliminate these drawbacks, a large number of hydraulic oils with a silicone oil principal agent or base have been proposed to date. In particular, dimethylsilicone oils have been recognized as a hydraulic fluid and in particular as an automotive brake fluid because they exhibit a relatively insignificant variation in viscosity over a wide range of temperatures, a low solidification temperature and a high boiling point.
One important property required of a brake fluid, which comprises a major application of hydraulic fluids, is that the brake fluid can dissolve at least some quantity of water without separation or settling. With a brake fluid that can not dissolve any water, water mixed into the brake fluid accumulates in the lower regions of the pipe system of the operating mechanism and causes corrosion of the pipe system or solidifies in winter with a resulting loss of braking ability. The solubility of water in a dimethylsilicone oil is much lower than in a glycol ether system. Dimethylsilicone oil usually absorbs and dissolves at most 0.1 weight - percent water. For this reason, when the water content- is larger than the amount of a dimethylsilicone oil is capable of absorbing, the water is dispersed into the dimethylsilicone oil and eventually settles in the lower regions of the operating mechanism because the specific gravity of a dimethylsilicone oil is about 0.96 which is less than the specific gravity of 1.0 for water. In such a case the dimethylsilicone oi! will no longer function satisfactorily as a brake fluid. In order to eliminate the above drawbacks, U.S. Patent No. 3,725,287 (issued April 3, 1973) and Japanese Patent No. 53-21476 (78-21476) attempt to impart hydrophilici..ty by chemically modifying the dimethylsilicone oil. These attempts can increase the water absorptivity but require a special silicone starting material and are therefore disadvantageous from the standpoint of cost. Furthermore, the modified silicone are chemically unstable.

The Invention

The present invention relates to a hydraulic fluid comprising a methylpolysiloxane oil containing siloxane units of general formula (CH₃)_aSiO_(4-a)/2 where a is 1, 2, or 3 wherein said methylpolysiloxane oil has a specific gravity of 1.02 or greater at 25°C. The present invention also relates to a process of transmitting power from one place to another via a hydraulic fluid medium where the hydraulic fluid medium comprises a methylpolysiloxane oil containing siloxane units of general formula (CH₃)_aSiO_(4-a)/2 where a is 1, 2, or 3 wherein said methylpolysiloxane oil has a specific gravity of 1.02 or greater at 25°C.
The methylpolysiloxane oil of the present invention may be constituted of a single unit or of a combination of two or all three units from among CH₃SiO_3/2, (CH₃)₂SiO and (CH₃)₃SiO_1/2 siloxane units. However, it must exhibit a specific gravity of ^*1.02 at 25°C and be an oil at room temperature. Under these restrictions, the following four combinations are practical: CH₃SiO_3/2 units, alone; CH₃SiO_3/2 units and (CH3)2SiO units; CH₃SiO_3/2 units and (CH₃)₃SiO_1/2 units; CH₃SiO_3/2 units, (CH₃)₂SiO units and (CH₃)₃SiO_1/2 units. From the standpoint of ease of synthesis, the CH₃SiO_3/2 unit and (CH₃)₂SiO unit as well as the CH₃SiO_3/2 unit, (CH₃)₂SiO unit and (CH₃)₃SiO_1/2 unit comb.inations are preferred. In these cases, the methylpolysiloxane is generally a liquid at room temperature and generally exhibits a specific gravity of ^*1.02 for a molar ratio of CH₃SiO_3/2 units and (CH₃)₂SiO units in the range of 1:9 to 6:4.
Preferred methylpolysiloxane oils contain 0 to 10 mol percent (CH₃)₃SiO_1/2 units, 45-80 mol percent (_CH₃)_2SiO units, and 20-45 mol percent CH₃SiO_3/2 units. Preferred methylpolysi loxane oils also generally have a CH₃/Si ratio in the range of 1.65 to 1.80 in order to jnsure the specific gravity of the methylpolysiloxane is consistently greater than or equal to 1.02. Generally, if the CH₃lSi ratio is significantly outside the 1.65 to 1.80 range the methylpolysiloxane will either have too low a specific gravity or too high a viscosity to be useful as the hydraulic fluid of this invention.
The oxygen atoms in the CH₃SiO_3/2 and (CH₃)₂SiO units of the methylpolysiloxanes used in this invention will normally be in the form of siloxane bonds. Some of these oxygen atoms may however be in the form of hydroxyl or alkoxy groups. The molecule structure of the methylpolysiloxane may be network, cage, or branched chain configuration. To be most useful the hydraulic fluid of this invention should have a viscosity in the range of 10 to 10,000 cSt at 25°C.
The methylpolysiloxane oils of this invention may be readily produced by methods well known in the art. For example, these methylpotysiloxanes may be produced by the homo-hydrolytic or co-hydrolytic polycondensation of methylpolysiloxanes or methylalkoxysilanes. Preferred methylchlorosilanes include methyltrichlorosilane, dimethyldichlorosilane, and trimethylchlorosilane. Preferred methylalkoxysilanes include the methylmethoxysilanes and the methylethoxysilanes such as methyltrimethoxysilane, methyltriethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, and trimethylethoxysilane. The amounts of the various methylhalosilanes or methylalkoxysilanes used in the preparation of the methylpolysiloxane oil will be determined by the desired amounts of CH₃SiO_3/2, (CH₃)₂SiO, and (CH₃)₃SiO_1/2 units in the methylpolysiloxane which will in turn determine the specific gravity and viscosity of the hydraulic fluid. An organic solvent which can dissolve these silanes is preferably added in hydrolytic polycondensation. When an excess of silicon-bonded hydroxyl and alkoxyl groups remains after hydrolytic polycondensation, the polycondensation reaction is preferably continued at an elevated temperature under reduced pressure in order to significantly reduce the levels of these functional groups.
The hydraulic oil of this invention may contain only a methylpolysiloxane oil or may optional ly contain various additives. The various additives include dialkanol esters of dibasic acids (as rubber swell agents or lubricants), e.g., dioctyl sebacate, dihexyl adipate, trialkyl phosphates such as tributyl phosphate and trioctyl phosphate and corrosion inhibitors such as zinc naphthenate. Other conventional additives may also be used. These additives may comprise about 0.01 to 10 weight percent of the quantity of the methylpolysiloxane Oil.
Even if water is mixed into the hydraulic oil of this invention it can be readily separated and removed since it forms the upper layer. This oil is a satisfactory hydraulic oil and in particular a satisfactory brake fluid because it exhibits an insignificant change in viscosity over a wide temperature range, a low solidification temperature, a high boiling point, as well as chemical stability.
This invention is illustrated in the following example which is not intended to limit the invention. In the example, the viscosity and specific gravity were both measured at 25°C.

Example

Trimethylchlorosilane (220 g, 2.0 moles), dimethyldichlorosilane (4,515 g, 35.0 moles), methyltrichlorosilane (1.944 g, 13.0 moles) and toluene (2,000 g) were charged to a 10 L three-necked flask equipped with stirrer, addition funnel and reflux condenser. Water (810 g, 45 moles) was added dropwise over 3 hours with stirring temperatures of ^*50^PC. The vigorous evolution of hydrogen chloride was observed. After addition of the water, the mixture was heated to 60°C and then reacted for 1 hour. The reaction solution was combined with 2 L of water, stirred and then allowed to stand and the aqueous layer was subsequently removed. This washing procedure was conducted three times in order to remove residual hydrochloride from the methylpolysiloxane-containing layer. The methylpolysiloxane containing layer was then heated in order to remove water azeotropically with toluene. Toluene was removed by raising the temperature to 150°C.
The resulting methylpolysiloxane had a viscosity of 12.6 cSt and a specific gravity of 0.991. This methylpolysiloxane was combined with 30 g of acid clay and stirred at 120°C for 5 hours. The generation of water by polycondensation of silanol group bonds in the methylpolysiloxane was observed. After cooling, the reaction solution was combined with 50 g diatomaceous earth as a filter aid and then filtered under increased pressure. The filtrate was subjected to reduced pressure to remove low-boiling compounds. Finally, volatiles were removed at a temperature of 240°C under a reduced pressure of 10mm Hg. The product methylpolysiloxane oil (referred to hereafter as A) was colorless and transparent with a viscosity of 56 cSt and a specific gravity of 1.026. Component analysis by Si^29-NMR spectroscopy indicated that this methylpolysiloxane oil contained 4 mol percent of (CH₃)₃SiO_1/2 units, 71 mol percent of (CH₃)₂SiO units, and 25 mol percent of CH₃SiO_3/2 units. The methylpolysiloxane (A) had a 1.7₉ Me/Si ratio.
A co-hydrolytic polycondensation of methyltrichlorosilane (790 g, 5.3 moles), dimethyldichlorosilane (682 g, 5.3 moles) and trimethylchlorosilane (2,170 g, 20 moles) was prepared by a method identical to that used for methylpolysiloxane oil (A) to produce methylpolysiloxane oil (B) with a viscosity of 744 cSt and a specific gravity of 1.084. The co-hydrolytic polycondensation of methyltrichlorosilane (225 g, 1.8 moles) and dimethyldichlorosilane (775 g, 6.0 moles) was similarly conducted to produce methylpolysiloxane oil (C) with a viscosity of 65 cSt and a specific gravity of 1.021. Component analyses by Si²⁹-NMR spectroscopy indicated that methylpolysiloxane oil (B) contained 10 mol percent of (CH₃)₃SiO_1/2 units, 45 mol percent of (CH₃)₂SiO units, and 45 mole percent of CH₃SiO_3/2 units and that methylpolysiloxane oil (C) contained 80 mol percent (CH₃)₂SiO units and 20 mol percent of CH₃SiO_3/2 units. The CH₃/Si ratios for methylpolysiloxane oils (B) and (C) was 1.65 and 1.80, respectively.
For comparison purposes a dimethylsilicone oil (D) was prepared by the same procedure described above. The dimethylsiloxane oil (D) consisted of (CH₃)₃SiO_1/2 units (4 mol percent) and (CH₃)₂SiO units (96 mol percent). The dimethylsiloxane oil (D) had a Me/5i ratio of 204, a specific gravity of 0.96, and a viscosity of 50 cSt.
Each of these methylpolysiloxane oils (A), (B) and (C) and the dimethylsiloxane oil (D) was separately combined with 5 weight percent distilled water, agitated by shaking for 10 minutes and allowed to stand for 30 minutes in order to examine the water-oil separation. In the cases of the methylpolysiloxane oils (A), (B), and (C) the water and siloxane oil underwent complete separation with the water forming the upper layer. For the dimethylsiloxane oil (D) separation was observed with water forming the lower level.
Methylpolysiloxane oil (A) was examined at low temperatures for water resistance according to a test method for automotive brake fluids Japanese Industrial Standard (JIS) K2233. One hundred milliliters of methylpolysiloxane oil (A) was placed in a centrifuge tube to which was added 3.5 ml of distilled water. After shaking for 10 minutes the sample was allowed to settle for 5 minutes at which time the sample was cooled to -40°C. The sample remained at -40°C for 120 hours. After completion of the test the methylpolysiloxane oil (A) was found to have remained transparent. The water, which was totally located above the siloxane oil (A), was frozen. The test tube was then turned upside down. An air bubble reached the surface of the siloxane oil in about 5 seconds. Test method JIS K2233 requires that such an air bubble reach the surface of the test brake fluid in a time of less than 10 seconds. For comparison purpose a similar test was performed on dimethylsiloxane (D). After completion of this test a part of the water was found to have solified within the siloxane oil (D) and remain suspended therein and a part of the solified water had settled out.
The above comparison demonstrates that a brake fluid whose principal agent is methylpolysiloxane oil as described in this invention will not cause corrosion of the pipe system or vapor locking even when a large amount of water is mixed into the pipe system of the operating mechanism. This is due to the fact that water separates in the upper part of the brake system's master cylinder and can therefore be easily removed.
The metal corrosiveness and styrene butadiene rubber (SBR) swell of methylpolysiloxane oil (A) and dimethylsilicone oil (D) were also evaluated by the methods of JIS K2233. Each oil was combined with tributyl phosphate (5 weight percent) as a rubber shrinkage inhibitor before testing. Metal corrosiveness was determined using a clean panel (80 x 13 mn) of the appropriate metal. The metal panel was placed in the siloxane oil at 100°C for 120 hours and any changes in weight were noted. The rubber swell was determined by immersing the SBR cup at either 70 or 120°C for 70 hours.-The cup was washed with ethanol and the physical properties determined. The results are reported in Tables 1 and 2. As compared with dimethylsilicone oil (D), methylpolysiloxane oil (A) satisfied the properties of an automotive brake fluid in every measured respect.

Claims

1. A hydraulic fluid comprising a methylpolysiloxane oil containing siloxane units of the general formula (CH₃)_aSiO_(4-a)/2 where a is 1, 2, or 3 and wherein said methylpolysiloxane oil has a specific gravity of 1.02 or greater at 25°C.

2. A hydraulic fluid as described in claim 1 wherein said methylpolysiloxane oil has a viscosity of 10 to 10,000 cSt at 25°C.

3. A hydraulic fluid as described in claim 2 wherein said methylpolysiloxane oil contains (CH₃)₃SiO_1/2 units, (CH₃)₂SiO units, and CH₃SiO_3/2 units.

4. A hydraulic fluid as described in claim 2 wherein said methylpolysiloxane oil contains (CH₃)₂SiO units and CH₃SiO_3/2 units.

5. A hydraulic fluid as described in claim 2 wherein said methylpolysiloxane oil contains 0 to 10 mol percent (CH₃)₃SiO_1/2 units, 45-80 mol percent (CH₃)₂SiO units, and 20-45 mol percent CH₃SiO_3/2 units.

6. A hydraulic fluid as described in claim 2 wherein said methylpolysiloxane oil has a CH₃/Si ratio of 1.65 to 1.80.

7. A hydraulic fluid as described in claim 3 wherein said methylpolysiloxane oil has a CH₃/Si ratio of 1.65 to 1.80.

8. A hydraulic fluid as described in claim 4 wherein said methylpolysiloxane oil has a CH₃/Si ratio of 1.65 to 1.80.

9. A hydraulic fluid as described in claim 5 wherein said methylpolysiloxane oil has a CH₃/Si ratio of 1.65 to 1.80.

10. In a process of transmitting power from one place to another via a hydraulic fluid medium, characterized by using as the hydraulic fluid medium a hydraulic fluid comprising a methylpolysiloxane oil containing siloxane units of general formula (CH₃)_aSiO_(4-a)/2 where a is 1, 2, or 3 wherein said methylpolysiloxane oil has a specific gravity of 1.02 or greater at 25°C.