EP0129240A1

EP0129240A1 - Hydraulic fluids

Info

Publication number: EP0129240A1
Application number: EP84106971A
Authority: EP
Inventors: Franco Dr. Galati; Mario Dr. Musco
Original assignee: Montedison SpA
Current assignee: Montedison SpA
Priority date: 1983-06-21
Filing date: 1984-06-18
Publication date: 1984-12-27
Anticipated expiration: 2004-06-18
Also published as: JPH0458520B2; JPS6013892A; DE3470176D1; EP0129240B1; EP0129240B2; IT1163547B; IT8321698A0

Abstract

Fluids for hydraulic breaks are described which have a content in boron of from 0% to 1% by weight and essentially consist of:

(a) an alkylenglycol; (b) alkylenglycol monoalkylether;
(c) a polyalkylenglycol monoalkylether of the general formula:
wherein:
n = an integer which confers onto the compound a molecular weight comprised between 208 and 1000; and possibly
(d) the reaction product of (a) with a boron compound.

They display excellent characteristics, in particular high boiling points under wet conditions, and low viscosities at low temperatures.

Description

The present invention refers to liquid compositions that are suited as hydraulic fluids for the transmission of power, particularly as hydraulic break fluids having a content in boron of from 0% to 1% by weight, and consisting of mixtures of glycols, glycolethers of various molecular weights and, possibly, boric glycolesters.
The breaking systems for motorvehicles represent an important safety element, and the efficient working of the breaks is, to a large extent, determined by the cha racteristics of the hydraulic fluids used in said breaking systems. Therefrom results that on said fluids are imposed by the current regulations very strict requisites, such as concern the prescribed characteristics of: boiling point, viscosity at high and low temperatures, the pH value, the stability at low and high temperatures, re sistance to corresion attack on metals, the swelling action on rubbers.
Amongst the characteristics just cited above, par- ticul_krly decisive for the purposes of ascertaining the suitability or unsuitability of a break fluid, is theboi ling point at total reflux after humidification (WET PERT) and the viscosity at lew temperatures.
Said characteristics are closely bound to the hygro scopicity of the fluids in question.
In fact, it is knownthat the affinity fer water not oxly manifests itself in the absorption of water from ahumid gaseous surrounding (atmosphere), but also in determining the intensity of the intramolecular beads which affect the value of the total reflux boiling temperature at atmospheric pressure (PERT) and on the fluidity at lowtem peratures.
The gradual absorption of moisture by the breakflu ids, however this may occur, leads to a gradual lowering of the boiling point. This lowering of the boiling point makes the break fluid less reliable for use in breaks, since the modern motervehicles develop a considerable amount of friction heat which may cause the boiling of the breaking liquid, with a consequential formation of a vapor phase which frustrtes the uncempressibility of the liquid necessary for achieving the power transmission.
Since such a phenomenon occurs unfailingly, whatever the fluid, on the long run, attains a condition of unsuitability for its use. An effective remedy to this is the periodical change of the liquid of the breaking system.
However, since this is after all always a not too simple operation, and at any rate a somewhat expensive one, it would be desirable, the principle of the periodical change of the breaking fluid still remaining valid, to be able to dispose of a break-fluid having the charac teristic of attenuating the harmful effect of the absorb tion of water with the consequential prolongation of the period of operation under conditions of full suitability.
The hydraulic break-fluids normally used must meet all FMVSS 116, DOT-3 and DOT-4 (i.e.:Federal Motor-Vehicle Safety Standard - Department of Transportation) and SAE_J 1703 (Society of Automotive Engineers N.Y.) standards.
The break-fluid belonging to the classes DOT-3 and DOT-4 have the following characteristics:
It is known from the patent and scientific litera ture of the last decades that almost the totality of the hydraulic break-fluids consist of a mixture of ales hols, glycols, glycolethers, polyglycols, polyglycelethers and their derivatives.
For instance, French Pat. n°2.158.523 describes liquid compositions for breaks belonging to the class DOT-4, cen sisting of mixtures of tetraethylenglycol, other glycols and lower glycolethers. Said compositions possess a WET PERT slightly greater than 155°C (max. 156.5°C in example n°2), and high viscosity values at low temperatures, due to the presence of tetraethylenglycol (1590 cSt at -40°C in example 1).
It is quite obvious that a too high viscosity at low temperatures represents a negative characteristic forhy- draulic breaks, so much so as to compromise its actual use.
Numerous researches were carried out in the attempt of obtaining break-fluids having always a high WET PERT, greater than 155°C, but of a low viscosity at -40°C, not greater than 1500 cSt.
Said liquids named DOT-3 / DOT-4 have been six- gled out in the boric esters of the glycols, and more particularly in the products of the partial or total es terification with boric acid of one or more of the com ponents of the traditional formulations based on alcohols, glycols, glycolethers, polyglycols and polygly- colethers.
For instance, US.Pat. n°3.625.899, practically the first patent concerning boric esters, describes hydraulic break compositions consisting of mixtures of at least one boric ester of an etheric glycol; of a polyglycol and a monoether or diether glycols.
In the steps of this patent there were followed up different streams or currents of research, which differ from each other in the way of having each emphasized a particular type of boron ester, but all of them sharing with each other the fact that in order that the composition may fall within the DOT-4 class, there is neces sary the presence of boton in the composition, in concentrations greater than a limit value.
In said compositions part of the absorbed wateris removed by hydrolysis reactions of the esterwiththe contemporaneous undesired tendency of the boric acid to precipitate.
Moreover, the organoborates used in the process have the drawback of either causing consistent swellings in the rubbers (esters of etheric glycols) or to produce high viscosities (esters of glycols), and at any ratete cause an unavoidable greater cost in comparison with the traditional formulations.
For this reason the formulations containing organe borates have not met with a wide diffusion so far onthe market. Thus, there is felt the need for a break-fluid that may be a DOT-4 also in the absence of boron and, more in general, that it shall have superior characteris tics of resistance to moisture also in the presence of slight quantities of boric esters.
Thus, object of the present invention is that of providing compositions that be suited for use as hydraulic fluids which, though not containing boron com pounds, possess WET PERT greater than 155°C and viscosities at -40°C that be below 1500 cSt, that is, fluids belonging contemporaneously to the class DOT-3 (with refernce to the viscosity) and to DOT-4 (with reference to the WET PERT).
Still another object of this invention is that of providing compositions based on boric esters which, at an equal content in boron, will have WET PERT values greater than those of the compositions of the Prior Art.
A further object of the present invention is that of providing break fluids that will meet all the DOT-3 and DOT-4 specifications; more particularly that will meet the non-agressivity standards towards rubber and the metals present in the breaking system.
It has now, surprisingly been found that all the above listed objects as well as objects and advantages that may result from the description of this invention, are achieved by special liquid compositions having a content in boron comprised between 0% and 1% by weight, wherein the boron will be in the form of a glycol borate.
More particularly, the compositions based on the hydraulic fluids of this invention, consist of:

(a) 2 - 40% by weight, with respect to the composition, of an alkylenglycol;
(b) 15-65% by weight, with respect to the composition, of at least one alkylenglycol monoalkylether;
(c) 15-55% by weight, with respect to the composition, of at least one polyalkylenglycol monoalkylether of the formula:
(d) 0%-54% by weight, with respect to the composition, of at least one boric ester of (a).

Suitable alkylenglycols (a) consist of: monomethy lenglycol, diethylenglycol, triethylenglycol, monepro- pylenglycol, dipropylenglycol, tripropylenglycol. amongst these, the preferred ones are: diethylenglycol and triethylenglycol.
Suitable alkylenglycol monoalkylethers(b) consist of: C₁-C₄ monoalkylethers of alkylenglycols(a). Of these the preferred one is triethylenslycol monoethylether.
Suitable polyalkylenglycol monoalkylethers (c) are those in which in the above specified general formula:

_{R =} C₁-C₄ alkyl; R'₌ H, CH₃; n = such an integer that the molecular weight (M.W.) of the compound shall be comprised between 208 and 1000. Preferrential compounds are those wherein R' = H.

Suitable boric esters(d) are the reaction products of a boron compound with alkylenglycols(a). The preferred one is the reaction product from the reac tion of boric acid with diethylenglycol.
The liquid compositions obtained by means of the present invention display all a WET PERT greater than 155°C (lower limit of DOT-4 class), viscosity values at -40°C lower than 1500 cSt (top limit of class DOT-3), and PERT values of about 250°C and over.
Moreover, they are characterized by an almost total lack of aggressiveness towards the various types of rubber and metals present in the breaking systems, with a con sequential considerable advantage for the life of said systems; besides displaying all the typical properties of the traditional products of the highest quality.
Whenever required, the compositions of the present invention may be additioned with additives that have the purpose of boosting the performance of the breaking fluids. Amongst the various types of additives are com prised: buffering agents, corrosion inhibitors, anti- oxidizers, substances increasing the protective power with respect to ferrous metals in a humid and oxidizing environment, stabilizers, dyestuffs.
In generalthe quantity of additives that may be in corporated into the liquid compositions varies from0% to 10% on the total weight of the compositions. The preparation of the boric esters(a) is carried out at atmospheric pressure, preferably in the presence of an azeotropicsolvent, or at a reduced pressure in the absence of a solvent, at temperatures comprised between 50°C and 200°C.
The formulation of the hydraulic fluids according to the present invention is obtained by mixing together components(a), (b), (c) and (d) and additives in a mixer until achieving a thorough and complete homogenization. In general the mixing is carried out at atmospheric pressure, room temperature and, preferably, in the ab sence of humidity.
The present invention will be now further illustrated by the following non-limiting examples.

Example 1 :

A breaking, fluid was prepared by mixing together the following components:
This breaking fluid possess the following characteris- tics:
For comparative purposes example 1 of French Pat. Nr. 2.158.523, referring to the preparation of a mixture of the following composition, was rapegted:
On the fluid thus obtained the following characteristics were determined:

EXAMPLE 2 :

A hydraulic fluid was prepared by mixing together the following components:
This fluid showed the following characteristics:

EXAMPLE 3 :

EXAMPLE 4 :

A hydraulic break fluid was prepared by admixing the following components:
This fluid showed the following characteristics:

EXAMPLE 5 :

EXAMPLE 6 :

A hydraulic fluid w as prepared, containing 0.1% of boron, by mixing together the following components:
This fluid showed the following characteristics:
For comparative purposes there was prepared a fluid like the one described in example 3 of French Pat.Nr. 2.158.524, containing an equivalent quantity of boron
On the fluid thus obtained the following characteris tics were then determined:

EXAMPLE 7 :

A hydraulic fluid, containing 0.46% of boron, was prepared by mixing together the following components:
This fluid showed the following characteristics:
For comparative pàrposes there was prepared a fluid according to that of example 1 of French Pat.Nr. 2.158.522 containing an equal quantity of 0.46% boron and consis ting of:
On the fluid thus obtained the following characteris tics were determined:

EXAMPLE 8 :

A hydraulic fluid, containing 0.5 % of boron, was pre pared by mixing together the following components:
This fluid showed the following characteristics:

EXAMPLE 9 :

A hydraulic fluid, containing 0.7% of boron, was pre pared by mixing together the following components:
This fluid showed the following characteristics:

EXAMPLE 10 :

A hydraulic fluid, containing 0.46% of boron, was pre pared by mixing together the following components:
This fluid showed the following characteristics:

EXAMPLE 11 :

A hydraulic fluid, containing 0.5% of boron, was pre pared by mixing together the following components:
This fluid showed the following characteristics:

EXAMPLE 12 :

A hydraulic fluid, containing 0.43% boron, was pre pared by mixing together the following components:
This fluid showed the followng characteristics:
For comparative reasons there was prepared a fluid like the one of example 38 of US.Pat. Nr.3.711.410, containing 0.43% of boron, and consisting of the fol lowing basic components:
This flmid showed the following characteristics:

Claims

1. Hydraulic fluids with a boron content of from 0 to 1% by weight, and consisting essentially of:

a) 2-40% by weight, referred to the total weight of the fluid, of an alkylenglycol of general formu la (I):

wherein: Ra is an alkylene radical having from 2 to 3 carbon atoms; x is an integer comprised between 1 and 3;

b) 15-65% by weight, referred to the totalweight of the fluid, of an alkylenglycol monoalkylether of general formula (II);

wherein R_a and x have the above indicated meahings; R is a C₁-C₄ alkyl;

c) 15-55% by weight, referred to the total weight of the fluid, of at least one polyalkyleglycol monoalkylether of general formula (III) :

wherein R is a C₁-C₄ alkyl; R' is H or CH₃; n is an integer whereby the molecular weight of the compound will be comprised between 208 and 1000;

d) 0 - 54% by weight, referred to the total weight of the fluid, of the reaction product of H₃BO₃ with the alkylenglycols of formula (I), in a molar ratio of 1 : 1.5 - 3;

e) 0 - 10% by weight, referred to the total weight of the fluid, of at least one inhibitor.

2. Hydraulic fluids according to claim 1, characterized in that in component c) of formula (III), R' = H, while n is an integer such that the molecular weight of the compound turns out to be comprised between 208 and 340.

3. Hydraulic fluids according to claim 1, characterized in that said fluius have no boron and consist of:

a) 23-33% by weight, referred tu the total weight of the fluid, of an alkyleneglycol selected from the group consisting of diethylenglycol and triethylenglycol;

b) 20-45% by weight, referred to the total weight of the fluid, of triethylenglycol monomethylether;

c) 20-50% by weight, referred to the total weight of the fluid, of at least a polyalkylenglycol monomethylether, chosen out of the group consisting of the compounds of formula (III) having a mean molecular weight comprised between 208 and 600.

4. Hydraulic fluids according to claim 1, characterized in that said fluids contain boron and consist essentially of:

a) 2-25% by weight, with reference to the total weight of the fluid, of an alkylenglycol chosen out of the group consisting of diethylenglycol and triethylenglycol;

b) 40-60% by weight with reference to the total weight of the fluid, of triethylenglycol monomethylether;

c) 15-35% by weight, with reference to the total weight of the fluid, of at least one polyalkylenglycol monoalkylether chosen out of the group consisting of compounds of formula (III) having a mean molecular weight comprised between 208 and 600;

d) 3-34% by weight, with reference to the total weight of the fluid, of the reaction product between 1 mol of H₃BO₃ and 3 mols of an alkylenglycol chosen out of the group consisting of diethylenglycol and triethylenglycol.

5. Hydraulic fluids according to claim 4, characterized in that component d) represents from 3% to 24% by weight of the total weight of the fluid and is the reaction product of 1 mol of H₃BO₃ and 3 mols of diethyleneglycol.