EP0436872B1 - Mineral oil based transmission fluid - Google Patents

Abstract

Hydraulic fluids, predominantly for hydrokinetic drives, also called automatic transmission fluids (ATF), are based on mineral oil, the base oil being a paraffin-based oil raffinate having viscosities of about 4 mm<2>s<-1> at 100 DEG C, with additives necessary for this application, with the exclusion of polyisobutylene-based dispersants, having been added thereto, and are formulated in such a way that they have Brookfield viscosities from less than 30,000 to less than 20,000 mPas at -40 DEG C. The decrease in viscosity at low temperatures is made possible by replacing the polyisobutylene-based dispersant by a dispersant based on polyalkyl (meth)acrylate.

Description

Field of the Invention

The invention relates to hydraulic fluids made from mineral oil for hydrokinetic power transmission, as they are also used as so-called "mobile hydraulics" in a wide variety of vehicles and aircraft. The invention relates in particular to the improvement of the low-temperature viscosity behavior of the power transmission fluids, which are also referred to in specialist circles as automatic transmission fluids (ATF).

State of the art

According to their character and their basic composition, ATF are gearbox oils that can be described as oils of the SAE class 75W-80W according to DIN 51512. The properties required for ATF are achieved by adding additives to the paraffin-based oil refinates used as base oils. According to the quality requirements to be met, ATF have high Additive levels. In practice, these power transmission oils show good VT behavior, are corrosion-resistant and highly aging-resistant (Ullmann, Encyclopedia of Industrial Chemistry, 4th edition, volume 20, pages 606-607). For extreme cold requirements, e.g. B. Use in automobiles at -40 ° C, show the well-known ATF, with today's values of approx. 40,000 mPas / -40 ° C, viscosities that are too high to meet the upcoming requirements of the new automatic transmission. In the future, viscosities of max. 30,000 mPas / -40 ° C, if not max. 20,000 mPas / -40 ° C. The typical ATF paraffinic base oil, often referred to in the mineral oil industry as 100 neutral oil and with a viscosity of approx. 4 mm²s⁻¹ / 100 ° C and a VI of approximately 100, is solid at -40 ° C; Brookfield viscosity measurement is not possible.

By adding a suitable pour point depressant, the viscosity at -40 ° C can be reduced to values below 20,000 mPas. Adding VI improvers, these are polymers, e.g. As polyalkyl methacrylates, causes the viscosity of the oil even at a higher temperature, for. B. at 100 ° C, is still sufficiently high without significantly deteriorating the viscosities obtained in the pour point reduction achieved.

Through the addition of other necessary additives (Ullmann, loc.cit.) Such as, in particular, antioxidants, friction reducers and detergents or dispersants, which are preferably and commercially available together in the form of packages, in the assembly of a wide variety of lubricating oils, including ATF assembly the -40 ° C viscosity value rises again to values of approx.40,000 mPas.

Possibilities for the production of hydraulic fluids (ATF) with better low-temperature behavior when using the package VI improver combination that is common today are the use of base oils of lower viscosity or the use of synthetic oils with the same viscosity or specially refined mineral oils, the so-called hydrocracked or extra high VI -Oil. ATFs that are manufactured with normal, low-viscosity base oils can allow potentially high wear, which cannot be prevented by alloying with wear protection additives due to the special friction coefficient requirements. A broader use of synthetic oils (polyolefins, ester oils) as ATF or as their base oils with good viscosity-temperature behavior should stand in the way of their high production costs. (Ullmann loc. Cit., Vol. 13, page 92).

US Pat. No. 4,036,768 describes combinations of polyalkyl methacrylates and liquid alkylbenzenes which are added to other ATF additives for the formulation of automatic transmission fluids. Such mixtures have Brookfield viscosities (mPas) of 27,000 to 33,200 at -40 ° C.

In addition to the upcoming, higher requirements already mentioned applies to the increased and easier use of non-military vehicles and aircraft as well as technical devices with hydrokinetic power transmission devices in regions with temperatures often below -20 to -40 ° C that the z. Z. usual hydraulic fluids based on mineral oil are not usable because of their high viscosity or can only be used with additional measures.

Task and solution

From this problem, the task arose to formulate hydraulic fluids based on mineral oil in which, for the temperature of -40 ° C, the viscosity currently around 40,000 mPas, if possible, to values below 30,000, possibly to values below Is reduced to 20,000 mPas.

Surprisingly, the problem of producing such hydraulic fluids based on mineral oil, the can be used both for high and very low use temperatures, and which further have the known desired properties, simply by solving that the polyisobutylene-based dispersants added to date have been largely or completely replaced by those based on polyalkyl methacrylate.

The invention thus relates to hydraulic fluids predominantly for the hydrokinetic drive, also called automatic transmission fluids (ATF), based on mineral oil, the mineral base oil being a paraffinic oil refinate with a viscosity of approx. 4 mm²s⁻¹ / 100 ° C and a V.I. of about 100, and the additives required for this purpose, with the exclusion of dispersants based on polyisobutylene, are added, and which, when formulated at -40 ° C., have Brookfield viscosities below 30,000 to 20,000 or less than 20,000 mPas.

The additive packages used mainly contain corrosion and oxidation inhibitors, wear protection agents, friction modifiers, etc. The dispersing action of the ATF must be present and is achieved by the exchange according to the invention, which also ensures the overall desired viscosity-temperature behavior and makes other additives for this effect superfluous. The ATF according to the invention can optionally also contain other conventional dispersing VI and pour point improvers in small amounts.

The hydraulic fluids according to the invention contain, as V.I. improvers, polymers, essentially those based on methacrylate. V.I.-improving polyalkyl methacrylates (PAMA) can also have detergent and dispersant properties through copolymerization with polar monomers.

The replacement of the dispersant based on polyisobutylene is carried out according to the invention with dispersing PAMA.
Through these measures, ATF are obtained that have the required viscosities at low temperatures down to -40 ° C without changing to low-viscosity base oils.

Advantages of the invention

The present invention improves the viscosity / temperature behavior of n-paraffin-containing mineral oils when used as a base oil for hydraulic fluids and opens them up to their use particularly at low temperatures under favorable viscosity conditions and without an annoying tendency towards crystallization of the n-paraffins. The increased use of paraffin-based mineral oils will be necessary in the future due to the fact that paraffinated mineral oils will increasingly dominate as base oils - exhaustion from other deposits - and secondly that low-viscosity Base oils, especially because of their unfavorable wear behavior, show technical disadvantages. However, the addition of wear protection additives is limited due to the special friction coefficient requirements. It is therefore important to maintain minimum base oil viscosities.

The measure according to the invention of replacing ashless dispersants based on polyisobutylene and the VI improver previously customary and the pour point improver with a dispersant based on PAMA has the further advantage that VI improvement and dispersion with an additive, a multipurpose additive multifunctional VI improver - namely an additive with a relatively low molecular weight. This is synonymous with minimal loss of viscosity and thus favorable wear behavior during the service life of the ATF.

The ashless dispersants for ATF of the conventional type are as polyisobutylene succinimides (Ullmann, loc. Cit., Vol. 20, p. 552 and US 4,036,768, example II) polymers which, in addition to the polyisobutene block (PIB), contain a strongly polar polyalkylene polyamine imide block. In contrast, in the ash-free PAMA-based dispersants, the polar groups are distributed over the polymer molecule. As a result, high overall dispersibility is achieved without interfering with friction and anti-wear additives.

In summary:

I.

Bessere, auf bisherigem Wege nicht erzielbare Tieftemperatureigenschaften.

II.

Vermeiden des Einsatzes niedrigerviskoser oder teurerer Grundöle.

III.

Drastische Verbesserung der Scherstabilität.

PAMA dispersants for ATF replace the previous PIB-based products as well as the VI improvers and pour point depressants used today. The following effects result:

I.

Better low-temperature properties that could not be achieved in the past.

II.

Avoid using low-viscosity or more expensive base oils.

III.

Drastic improvement in shear stability.

Implementation of the invention

• 1. Paraffin-based mineral oils are used as base oils (1) according to the invention, which are mainly obtained as solvent raffinates in crude oil processing and a viscosity at 100 ° C of about 4.0 mm²s⁻¹ and a pour point of no more than -10 ° C (Ullmann loc. Cit., Vol. 20, pp. 575-577, 606-607).
• 2. Flow improvers as additives to the base oil to improve the viscosity, the viscosity-temperature behavior and to lower the pour point are polymer additives, in particular based on (meth) acrylic acid alkyl ester (2). For this purpose, the oil-soluble polymers known as VI improvers of esters of methacrylic acid and / or acrylic acid with 1 to about 30 carbon atoms in the alkyl radical, predominantly as copolymers of the various esters and with a viscosity-average molecular weight of 5,000 to 200,000, preferably from 20,000 to 100,000 , mainly used from 10,000 to 50,000 (Ullmann loc. cit., vol. 13, p. 87; vol. 19, p. 26). Poly (meth) acrylic acid alkyl esters with polar monomers containing a hetero atom, such as, for example, hydroxyalkyl (meth) acrylates, 2-dimethylaminoethyl methacrylate, N-dimethylaminopropyl methacrylamide, vinyl pyridine, prepared as copolymers also have detergent and dispersant properties (Ullmann, loc.cit., volume 19, p. 26 and volume 20, p. 547, p. 552). These are known ash-free dispersants based on poly (meth) acrylate, which according to the invention are used as dispersing additives in hydraulic fluids Dispersants used and, as determined according to the invention, replace viscosity reductions at low temperatures which aggravate polyisobutenylsuccinimides. They can be used in combination with other known VI improvers, especially the known and described polyalkyl (meth) acrylates, as additives in the formulation of the hydraulic fluid based on mineral oil, or in their function as multifunctional additives all of the flow improver functions mentioned above and the dispersing action perceive in the ATF.
  They are prepared by copolymerization of (a), at least one C1 to C30 alkyl ester of methacrylic acid and / or acrylic acid and (b) at least one monomer with functional groups of the type described (polar monomers with hetero atom) in a molar ratio (a): (b) = 1: 0.01-0.2 especially 1: 0.02 to 0.2 and in particular in a molar ratio of 1: 0.02 to 0.15. The polymerization is preferably carried out in the mineral oil in which the dispersant is also primarily added as additives.
  Preparations of dispersing PAMAs with polar functional groups containing oxygen and / or nitrogen atoms are described, inter alia, in DE-C 28 05 826 (= US Pat. No. 4,281,081 and US Pat. No. 4,338,418), DE-A 33 39 103, DE-A 36 07 444, DE-A 36 13 992, US-P 4 290 925 or US-P 4 822 508.
  The viscosimetrically determined (method SN Chinai, RA Guzzi, J. Pol. Sci. 41 , 475 (1959)) determined molecular weights of the dispersing copolymers are in the range of 5,000 to 200,000.
• 3. To meet other required properties, such as oxidation stability, wear protection, aging, known active substances (Ullmann loc. Cit. Vol. 20, pp. 549-560, US Pat. No. 4,036,768) are used in a conventional manner, especially as an additive mixture (3), (additive package, DI package), according to the invention with the exclusion of any dispersants of the type of polyisobutenylsuccinimides contained therein, added to the ATF formulation.
• 4. The components (1), (2) and (3) specified under 1 to 3 are used in the ATF formulation in proportions (parts by weight) of:
  (1): (2): (3) = 80-95: 3-15: 2-10,
  especially in proportions of
  85-95: 3-10: 4-10
  used.

The ratio in parts by weight of the VI-improving PAMA additives with and without dispersing action can be
100: 0 to 10: 1
preferably at 99: 1 to 10: 1
lie.

Kinetische Viskosität

DIN 51550

Pour Point / Cloud Point

DIN 51597

Viskositätsindex (V.I.)

ISO 2909

Brookfield-Viskosität

DIN 51398

The following physical parameters can be used for characterization:

Kinetic viscosity

DIN 51550

Pour point / cloud point

DIN 51597

Viscosity index (VI)

ISO 2909

Brookfield viscosity

DIN 51398

EXAMPLES for ATF compositions Components used

• 1. Base oils:
  • (1.1) Paraffin-based raffinate (so-called 100 neutral) with the following data:
    viscosity

    mm²s⁻¹ / 100 ° C:

    4.25

    VI:

    107

    Pour Point ° C:

    -15

  • (1.2) Low-viscosity paraffinic raffinate:

    mm²s⁻¹ / 100 ° C:

    3.58

    VI:

    108

    Pour Point ° C:

    17th

• 2nd ATF package, commercial product: use concentration 8.0% by weight
• 3. ATF package without ashless dispersant based on polyisobutylene: use concentration 2.0% by weight
• 4.Dispersing V.I.-improver based on PAMA with pour point effect (commercial product): Use concentration 3.2% by weight PSSI (permanent shear stability index) according to DIN 51382 = 45.
• 5. PAMA-based pour point improver without
  Dispersing effect
  (commercial product) $$\text{PSSI = 15}$$
  
• 6. Ash-free PIB-based dispersing agent (polyisobutenyl succinimide, commercially available product).
• 7. Dispersing PAMA products to be used according to the invention, referred to internally as BID ( Brookfield Improving Dispersant ):
  
  These products have a pour point effect.
  The PSSI is = 5
  Polymer content 70% by weight
  Use concentration 7-10% by weight in the ATF.

EXAMPLES OF COMPOSITION OF THE BID OF THE INVENTION

Mol.-Verhältnis a : b = 1 : 0,17, wobei a Molzahl aus M₁ + M₂.

Mol.-Verhältnis a : b = 1 : 0,05, wobei a Molzahl aus M₁ + M₂.

Mol.-Verhältnis a : b = 1 : 0,18, wobei a Molzahl aus M₁ + M₂.

M₁ =

Methacrylsäure-n-C12-bis C18-alkylester

M₂ =

Methacrylsäuremethylester

M₃ =

N-Dimethylaminopropylmethacrylamid

M₄ =

Methacrylsäure-2-hydroxyethylester

Mol. Ratio a: b = 1: 0.17, where a number of moles from M₁ + M₂.

Mol. Ratio a: b = 1: 0.05, where a number of moles from M₁ + M₂.

Mol. Ratio a: b = 1: 0.18, where a number of moles from M₁ + M₂.

M₁ =

Methacrylic acid n-C12 to C18 alkyl esters

M₂ =

Methyl methacrylate

M₃ =

N-dimethylaminopropyl methacrylamide

M₄ =

2-hydroxyethyl methacrylic acid

The recipes are compared:

• A. Derzeit übliche ATF-Zusammensetzung.Basis Grundöl (1.1).
• B. Rezeptur mit BID 1 anstelle der in A enthaltenen PIB-Produkte, Basis Grundöl (1.1).
• C. Wie B, jedoch BID 1 mit ausgewählter PPD abgemischt.
• D. Wie A, jedoch auf Basis des niedrigerviskosen Grundöls (1.2).
• E. Wie B, jedoch bei Ersatz von nur 2/3 des PIB Produktes durch BID 1.
• F. Wie B, jedoch mit BID 2.

mit folgenden Zusammensetzungen und Viskositätsdaten:

• A. Current ATF composition based on base oil (1.1).
• B. Recipe with BID 1 instead of the PIB products contained in A, base oil (1.1).
• C. Like B, but BID 1 mixed with selected PPD.
• D. As A, but based on the low-viscosity base oil (1.2).
• E. As B, but when only 2/3 of the PIB product is replaced by BID 1.
• F. Like B, but with BID 2.

with the following compositions and viscosity data:

COMPOSITION OF THE ATF TO BE COMPARED AND THEIR VISCOSITY DATA

Claims (3)

1. Hydraulic fluids, mainly for the hydrokinetic drive, also known as Automatic Transmission Fluids (ATF), on mineral oil basis, containing

   1. 80 to 90 parts by weight of a paraffin-based oil raffinate as base oil, having a viscosity of about 4 mm²s⁻¹ at 100°C and

   2. 2 to 10 parts by weight of additives required for this application, such as flow-improvers, additives for oxidation stability, wear protection and ageing stability, under the exclusion of dispersant additives on polyisobutylene basis, characterised in that they contain

   3. 3 to 15 parts by weight of polymers on polyalkyl(meth)-acrylate basis as dispersant additives, which polymers are copolymers of (a) at least one C₁- to C₃₀-alkyl ester of methacrylic acid and/or acrylic acid and (b) at least one monomer with polar, oxygen and/or nitrogen atom-containing functional groups, and which are synthesised from the comonomers (a) and (b) in a molar ratio (a) : (b) = 1 : 0.01 to 0.2 and have a molecular weight of 5,000 to 200,000 ascertained by viscometry according to S.N. Chinai, R.A. Guzzi, J.Pol.Sci. 41,475 (1959),

   and which, when composed in this way, have Brookfield viscosities of below 30,000 to below 20,000 mPas at -40°C,
2. Hydraulic fluids according to claim 1, characterised in that the flow-improving, non-dispersing polyalkyl(meth)acrylate-additives are polyalkyl(meth)acrylates having C₁- to C₃₀-alkyl groups and the polyalkyl(meth)acrylates, acting as dispersants, are copolymers of C₁- to C₃₀-alkyl(meth)acrylates with comonomers carrying polar, oxygen and/or nitrogen atom-containing functional groups, and the ratio in parts by weight of the polyalkyl(meth)acrylate-additives without or with a dispersing effect is 1 : 10 to 1 : 99.
3. Hydraulic fluids according to claims 1 and 2, characterised in that the formulations mainly contain polyalkyl(meth)acrylate-additives which only carry functional groups and have a V.I., dispersion and pour point-improving effect.