WO2008065158A1

WO2008065158A1 - Lubricating composition

Info

Publication number: WO2008065158A1
Application number: PCT/EP2007/062988
Authority: WO
Inventors: Tetsuya Kato; Koichi Numazawa; Takahiro Ozaki
Original assignee: Showa Shell Sekiyu KK; Shell Internationale Research Maatschappij BV
Current assignee: Showa Shell Sekiyu KK; Shell Internationale Research Maatschappij BV
Priority date: 2006-12-01
Filing date: 2007-11-29
Publication date: 2008-06-05
Anticipated expiration: 2009-06-01
Also published as: AR064021A1; CN101558141A; CL2007003447A1; JP5363722B2; EP2087086A1; US20090305920A1; JP2008156624A; TW200835786A; CA2671199A1

Abstract

The present invention aims to offer a lubricating composition with excellent heat resistance, mechanical stability, water resistance, corrosion resistance, load resistance and flame resistance. To this end the present invention suggests that from 2 to 68 % by weight of tricalcium phosphate relative to the total composition is added to a base oil, which may be a mineral oil and/or a synthetic oil. Surfactants are further added, and the whole is thoroughly mixed and kneaded to give a semi-solid lubricating composition. For the surfactants, non-ionic surfactants are most suitable, and fatty acid esters such as glycerine fatty acid esters, sorbitan fatty acid esters and sucrose fatty acid esters may be used. The amount used is from 0.2 to 18 % by weight relative to the total composition.

Description

LUBRICATING COMPOSITION

This invention relates to an improvement to lubricating compositions, and in particular relates to a semi-solid lubricating composition with excellent heat resistance, mechanical stability, load resistance, water resistance, corrosion resistance and flame resistance.

In the automobile industry, because of the requirements for high performance as well as compact and lightweight design, there is, with regard to the lubricating compositions used in constant velocity joints, bearings, gears and so on, a strong demand for products of high quality in respect of heat resistance, mechanical stability, load resistance and corrosion resistance. In order to meet this demand, grease compositions using a tricalcium phosphate as a thickening agent have been proposed. See Japanese I^aid-open Patent 197072 (1995) .

Grease compositions using this tricalcium phosphate as a thickening agent have a high dropping point and excellent heat resistance, and also perform extremely well in respect of mechanical stability and load resistance from ordinary temperatures up to high temperatures. At present, they are considered one of the preferred lubricating compositions.

However, whilst these grease compositions can fully exhibit their expected effect in environments not in contact with water, in environments in contact with large amounts of water, such as in the paper-making industry, or iron and steelmaking plant, severe corrosion occurs and the base oil and the powdered tricalcium phosphate which constitutes the thickening agent end up separating. The structure of the grease breaks down and it ends up losing its function as a grease, so that use in such environments is not possible.

Also, in chemical works, baking and finishing works and iron and ^■ steelmaking works, the manufacturing or working processes take place at elevated temperatures, and sparks may be scattered during these manufacturing and working processes, so that there is a risk that fly- off scale heated to high temperatures may come into contact with the grease and ignite it. To prevent such fires, it is desirable that the grease should have as much excellent flame resistance as possible.

For example, with greases used in iron and steelmaking plant where the lubricating conditions are the most rigorous, three elements in addition to lubricating performance need to be addressed: great heat, large quantities of water, and high loads. There are many cases where these may be a problem, and it is important that there should be no occurrence of grease sticking in feed pipes or roll -bearing greasing nipples, carbonisation, softening and leakage in bearings, or corrosion. Therefore, it is necessary to prevent hardening of the grease due to extremely high temperatures to ensure there are no blockages inside distribution pipes, and to inhibit occurrence of softening and leakage of greases outside bearings, as well as corrosion, due to insufficient water resistance. Further, there is also a risk that lubricating greases spilling on to floors may be ignited by fly-off scale heated to high temperatures, and so it is desirable that the greases should have as much flame resistance as possible so as to prevent fires. This invention provides a high-performance lubricating composition which has excellent heat resistance, mechanical stability, load resistance, corrosion resistance and water resistance and so can overcome all these problems.

Through this invention it is possible to obtain a lubricating composition which, because of the addition of a tricalcium phosphate to the base oil, which may be a mineral oil and/or synthetic oil, as well as addition of a surfactant, has excellent heat resistance, mechanical stability and load resistance, and at the same time has water resistance and corrosion resistance.

The aforementioned tricalcium phosphate is used m the proportion of from 2 to 68 % by weight relative to the total composition of the lubricating composition.

A non- ionic surfactant is suitable for the aforementioned surfactant, and m particular it is possible to use one of or a combination of the fatty acid esters glycerine fatty acid esters, sorbitan fatty acid esters and sucrose fatty acid esters.

This surfactant is preferably used in the proportion of from 0.2 to 18 % by weight relative to the total composition of the lubricating composition.

A urea compound may be used together with the aforementioned tricalcium phosphate as a thickening agent, and can lengthen bearing life and improve durability. The amount used thereof is preferably not more than 8 % by weight relative to the total composition of the lubricating composition. According to this invention the lubricating composition has excellent heat resistance, mechanical stability and load resistance, and also has corrosion resistance, water resistance and flame resistance, and further it can engender a substantial improvement in bearing life under high temperatures. Accordingly, it can be used in environments subjected to great heat, and can also be used effectively in environments in contact with water such as the paper-making industry and iron and steelmaking plant without giving rise to corrosion.

There is no particular restriction on the base oil used for the lubricating composition of this invention, and it is possible to use mineral oils and synthetic oils or suitable mixtures thereof within the viscosity range normally used for lubricating oils (2 - 40 mm²/s at 100⁰C) .

In particular it is possible to use, singly or as mixtures, base oils which belong to Group I, Group II, Group III, Group IV and so on of the API (American Petroleum Institute) base oil categories.

Group I base oils include, for example, paraffinic mineral oils obtained by appropriate use of a suitable combination of refining processes such as solvent refining, hydrorefining, and dewaxing in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil.

Group II base oils include, for example, paraffinic mineral oils obtained by appropriate use of a suitable combination of refining processes such as hydrorefining and dewaxing ^■ in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil. Group II base oils refined by hydrorefining methods such as the Gulf Company method have a total sulphur content of less than 10 ppm and an aromatic content of under 5% and so are suitable for this invention.

Group III base oils and Group 11+ base oils include, for example, paraffinic mineral oils manufactured by a high degree of hydrorefining in respect of lubricating oil fractions obtained by atmospheric distillation of crude oil, base oils refined by the Isodewax process which dewaxes and substitutes the wax produced by the dewaxing process with isoparaffins, and base oils refined by the Mobil wax isomerisation process. These, too, are suitable for use in this invention.

As examples of synthetic oils mention may be made of polyolefins, diester oils of dibasic acids such as dioctyl sebacate, polyol ester oils, alkylbenzenes, alkylnaphthalenes, esters, polyoxyalkylene glycols, polyoxyalkylene glycol esters, polyoxyalkylene glycol ethers, polyphenyl ethers, dialkyldiphenyl ethers, fluorine-containing compounds (perfluoropolyethers, fluorinated polyolefins) and silicone oils.

The above-mentioned polyolefins include polymers of various olefins or hydrides thereof. Any olefin may be used, and as examples mention may be made of ethylene, propylene, butene and α-olefins with five or more carbons. In the manufacture of polyolefins, one kind of the above-mentioned olefins may be used singly or two or more kinds may be used in combination. Particularly suitable are the polyolefins called poly-α-olefins (PAO) . These are base oils of Group IV. GTLs (gas to liquid derived base oils) synthesised by the Fischer-Tropsch method of converting natural gas to liquid fuel have a very low sulphur content and aromatic content compared with mineral oil base oils refined from crude oil and have a very high paraffin constituent ratio, and so have excellent oxidative stability, and because they also have extremely small evaporation losses, they are suitable as base oils for this invention. For the tricalcium phosphate used in this invention it is possible to use Ca₃ (PO₄) ₂ but in general any may be used which has the chemical structure of a hydroxyapatite composition that can be expressed as [Ca₃ (PO₄) ₂] ₃ • Ca (OH) ₂. Wherever below there is a reference to the amount contained in, this invention, it is to be taken as referring to the weight based on [Ca₃ (PO₄) ₂] 3 -Ca (OH) ₂.

This tricalcium phosphate is added to the aforementioned base oil, and is incorporated in the amount of from 2 to 68 % by weight relative to the total composition of the lubricating composition, but preferably in the amount of from 41 to 60 % by weight and more preferably in the amount of from 45 to 55 % by weight. If the amount of tricalcium phosphate in the blend is less than 2 % by weight, the lubricating composition softens and it is not possible to maintain hardness in a suitable semi-solid state. If the amount incorporated exceeds 68% by weight, the lubricating composition hardens and is not in a slippery semi-solid state, so that manufacture is too difficult.

Surfactants are used together with the tricalcium phosphate. These surfactants are preferably non-ionic surfactants and, in particular, it is possible to use fatty acid ester type surfactants. These fatty acid ester type surfactants include, for example, glycerine fatty acid esters, sorbitan fatty acid esters and sucrose fatty acid esters. The fatty acids used therein are preferably saturated or unsaturated fatty acids with from 12 to 22 carbons. They may be used singly or in mixtures.

As examples of the aforementioned glycerine fatty acid esters mention may be made of monoglyceride stearate, monoglyceride monooleate, and mono-diglycerides of stearic acid and oleic acid.

Also, as examples of sorbitan fatty acid esters mention be made of sorbitan monolaurate, sorbitan monopalmitate, sorbitan monostearate, sorbitan monooleate, sorbitan tristearate and sorbitan trioleate. As examples of sucrose fatty acid esters mention be made of sucrose palmitic acid ester and sucrose stearic acid ester. These surfactants may also be used in suitable mixtures .

These surfactants are used in the amount of from 0.2 to 18 % by weight relative to the total composition of the lubricating composition, but preferably in the amount of from 1 to 15 % by weight and more preferably from 2 to 10 % by weight. If the amount of these surfactants in the total composition is too much, the effect is either the same or may even be reversed.

When manufacturing the lubricating composition of this invention, the desired composition may be obtained in accordance with the usual method by adding the aforementioned tricalcium phosphate and one or more surfactants to the base oil, heating as appropriate and stirring, and then kneading well using, for example, a three-roll mill.

The tricalcium phosphate as mentioned above is barely soluble in water. In greases comprised only of base oil and tricalcium phosphate, when the grease mixes with water, the grease structure is normally destroyed within about 30 minutes, and it is not possible to maintain its gelled structure.

In the lubricating composition of this invention, by virtue of the fact that the aforementioned surfactants have been added, even when water is added to the lubricating composition, water of from 50 to 60 % by volume can be held with a certain degree of stability while keeping it in a finely dispersed state, and so by this means it is possible to maintain the gelled structure without destroying the semi-solid structure.

This differs in type from grease-m-water emulsions made by a soap, such as a sodium soap or potassium soap, insoluble in water, and because it makes a stable water- in-grease dispersion it may be inferred that the hardness of the composition is largely unaffected by the water.

Together with the aforementioned tricalcium phosphate it is possible to use a urea compound as a thickening agent. Lubricating compositions which use diurea compounds, tetraurea compounds and other urea compounds as thickening agents generally have superior heat-resisting properties, and by combining these with the tricalcium phosphate it is possible to produce lubricating compositions which have not only heat resistance and water resistance but also long bearing life at high temperatures and excellent durability.

These urea compounds are used by being incorporated in the amount of not more than 8 % by weight relative to the total composition. These urea compounds may be blended in suitable proportions with the tricalcium phosphate but normally it is more desirable if the amount of tricalcium phosphate is greater. The lubricating composition may be formed by mixing these urea compounds with the tricalcium phosphate, surfactants and base oil together. A lubricating composition may also be made by appropriately mixing together a lubricating composition containing mainly tricalcium phosphate and surfactants and a lubricating composition containing mainly a urea compound.

In addition to the aforementioned constituents, this lubricating composition, where necessary, may also be used in combination with additives such as anti-oxidants, anti-corrosion agents, extreme pressure .additives, anti- wear agents and solid lubricants.

Examples

Examples 1-13, Comparative Examples 1-4 The invention is explained below by means of examples but the invention is not limited in any way to these .

The base oils, tricalcium phosphate and surfactants shown below were blended into the compositions shown in Tables 1 and 2. After samples were added to the test kettle, they were heated to 100⁰C while stirring. Then they were treated in a three-roll mill to give a uniform consistency. This gave the lubricating compositions shown for Examples 1-13. The lubricating compositions shown for Comparative

Examples 1-4 were obtained in similar fashion, using the blend compositions shown in Table 3.

1. Base oils

(1) Mineral oil: paraffinic mineral oil with viscosity of 33 mm²/s at 100⁰C

(2) Poly-α-olefin oil: poly-α-olefin oil with viscosity of 40 mm²/s at 100⁰C

(3) Ether oil: alkyldiphenyl ether oil with viscosity of 13 mm²/s at 100⁰C (4) Ester oil: polyol ester oil with viscosity of 6 mm²/s at 100⁰C

2. Tricalcium phosphate: [Ca₃ (PO₄) ₂13 -Ca (OH) ₂

3. Surfactants (1) Stearic acid, oleic acid mono-diglycerides

(2) Sorbitan monolaurate

(3) Sorbitan tristearate

(4) Sorbitan trioleate Comparative Example 5: lubricating composition

Within 900 g of a refined mineral oil with a viscosity of approximately 33 mm²/s at 100⁰C and a viscosity of approximately 500 mm²/s at 40⁰C, 0.295 mol (38.12 g) of octylamine was reacted in 0.147 mol (36.88 g) of diphenylmethane-4 , 4 ' -diisocyanate, and then 0.08 mol (14.92 g) of laurylamine was added to 0.04 mol (10.08 g) of diphenylmethane-4 , 4 ' -diisocyanate and reacted therewith. 2 % by weight (20 g) of a diphenylamine anti-oxidant was added, and a lubricating composition was obtained by uniformly dispersing and treating in a three-roll mill. The amount of urea compound contained was 10% by weight. Examples 14-17

Example 14 was a lubricating composition which contained in Example 1, in the amount of 2 % by weight, the diphenylamine type of anti-oxidant used in Comparative Example 5.

Examples 15-17 were lubricating compositions with Example 14 and Comparative Example 5 mixed in the proportions shown in Table 4 Tests

Tests were carried out on the lubricating compositions of Examples 1-13 and Comparative Examples 1- 4 in respect Of penetration, dropping point, water resistance, mechanical stability and load resistance. Tests were also carried out on the lubricating compositions of Examples 14-17 and Comparative Example 5 in respect of flame resistance and bearing life at high temperatures .

(1) Penetration: based on JIS K2220 (ASTM D217) .

(2) Dropping point: based on JIS K2220 (ASTM D566) . (3) Water resistance: in accordance with ASTM D1831.

Water was added and mixed in the lubricating composition so that it formed 20 % by weight. Using a sample thereof, a shell roll test was carried out for 24 hours at room temperature. Then, a visual examination was made for the presence of rust 4 on each of the parts cylinder 1, inside roll 2 and top cover 3, and for any breakdown of the grease structure (see Figures IA, IB) .

If the grease structure of the lubricating composition was not destroyed and a normal grease state was maintained, the penetration was measured.

(4) Mechanical stability: in accordance with ASTM D1831. A shell roll test was carried out on the lubricating composition for 24 hours at room temperature, and then the penetration was measured. (5) Load resistance: a four-ball extreme pressure test was carried out following ASTM D2596.

Conditions: carried out at a speed of 1770 ± 60 rpm, time 10 seconds and room temperature.

Test item: the weld load WL (units kgf) and last non-seizure load LSNL (units kgf) were obtained.

(6) Bearing life at high temperatures: a bearing life test was carried out following ASTM D3527.

Conditions: carried out at a speed of 1000 ± 50 rpm and temperature of 16O⁰C. Test item: the bearing life based on overtorque

(hours) was obtained.

(7) Flame resistance: a grease burning test was carried out by the method introduced in NLGI (National Lubricating Grease Institute) Spokesman Nov. 1988. The outline of the test is as follows.

Outline of test: 4.00 + 0.01 g of specimen lubricating composition 12 was packed into a glass container 11 as used for the oxidative stability test of JIS K2220 (ASTM D942) , and to that a lighted match 13 was applied to examine the burning properties of the grease. If a flame 14 flared up and the grease burned 15, it was marked F (flammable) . If the match simply burnt out 16 and the grease did not burn 17, it was marked I (inflammable) . (see Figures 2A, 2B) . Test results

The results of the various tests are shown in Tables 1-4.

Table 1

Table 2

Table 3

Table 4

Discussion

In the case of Examples 1-4 shown in Tables 1 and 2, a tricalcium phosphate has been added to a mineral oil and the surfactants have been varied. In the case of Examples 5-10 surfactants have been used in mixtures. In the case of Examples 11-13 the type of base oil has been varied. Examples 1-13 exhibited a satisfactory grease state with a penetration of 227-345.

It can be seen also that Examples 1-13 also had excellent heat resistance, with dropping points of not less than 250⁰C in each case.

As regards load resistance, in the four-ball extreme pressure test the LNSL (last non-seizure load) was 160 kg for Examples 1-11 and 126 kg for Examples 12-13. The WL (weld load) was 400 kg for Examples 1-10 and 315 kg for Examples 11-13. Normally greases referred to as extreme- pressure greases would have an LSNL (last non-seizure load) of about 63 kg and WL (weld load) of about 250 kg, so that the examples have exhibited a high load resistance.

In the case of mechanical stability, in the shell roll tests Examples 1-13 exhibited values of 262-368, and so it is evident that their mechanical stability was satisfactory. In the case of water resistance, in the situation where the water content was 20% by weight, no occurrence of rust was seen in any of Examples 1-13 (Figure IA) , and no breakdown of the grease structure in the lubricating composition was observed. Also, the penetration exhibited excellent values of 287-409, and so it is evident that water resistance was extremely good.

In contrast, Comparative Examples 1-4 had no surfactants added yet the penetration was 267-272 and the EP2007/062988

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dropping point was not less than 25O⁰C, whilst good results were obtained in respect of the semi-solid state and heat resistance.

However, in the four-ball extreme pressure tests, in the case of Comparative Examples 1-4 the WL (weld load) was good at 315 kg but the LNSL (last non-seizure load) at 63 kg produced a significantly lower value than for the Examples, and so load resistance was inferior to the Examples . Furthermore, in the case of water resistance, bright red rust was generated on the entire surfaces of the cylinder 1, inside roll 2 and top cover 2 of the shell roll test apparatus in all of Comparative Examples 1-4 (Figure IB) . Also, the grease structure of the lubricating composition broke down and it was not possible to measure the penetration. It was evident, therefore, that the comparative examples were inferior in respect of water resistance.

Example 14 in Table 4 is a case of using a tricalcium phosphate as the thickening agent, and

Examples 15-i7 are cases of using a tricalcium phosphate and a urea compound together as thickening agents. Comparative Example 5 is a case of using a urea compound as the thickening agent . Examples 14-17 and Comparative Example 5 showed roughly the same performance in respect of penetration, dropping point, which shows heat resistance, mechanical stability and water resistance, but in the four-ball extreme pressure test for load resistance a big difference was seen: the LNSL (last non-seizure load) was 160 kg for Example 14 and 50 kg for Comparative Example 5, and the WL (weld load) was 400 kg for Example 13 and 126 kg for Comparative Example 5. The trend was that load resistance performance decreased as the 'amount of tricalcium phosphate was reduced.

Also, bearing life was 180 hours in the cases where tricalcium phosphate or a urea compound was used alone as a thickening agent, but when both were used together it was more than 300 hours, a satisfactory .result .

Further, in the case of flame resistance, whereas

Examples 14-17 did not burn (Figure 2A), Comparative

Example 5 did burn (Figure 2B) . A clear difference could be seen and it is evident that flame resistance has been improved in comparison with Comparative Example 5 of the prior art .

Brief Explanation of Drawings

Figure 1 is an exploded drawing of the various parts - cylinder, inside roll and top cover - in a shell roll tester for testing water resistance. Figure IA shows the state with no rust generated and Figure IB the state with rust generated.

Figure 2 is a drawing illustrating the test configurations in a flame resistance test. Figure 2A shows the configuration with the match not burning the grease and Figure 2B the configuration with the match burning the grease .

Explanation of symbols 1 Cylinder in shell roll test apparatus

2 Inside roll in shell roll test apparatus

3 Top cover of shell roll test apparatus

4 Rust generated in shell roll test apparatus 11 Glass container for flame resistance test 12 Specimen lubricating composition in glass container

13 Match

14 Match flame

16 Burnt-out match

Claims

C L A I M S

1. Lubricating composition comprising base oil, a tricalcium phosphate in the amount of from 2 to 68 % by weight relative to the total composition, and a surfactant .

2. Lubricating composition according to Claim 1 wherein the surfactant is a non-ionic surfactant.

3. Lubricating composition according to Claim 2 wherein the non-ionic surfactant is one of or a combination of the fatty acid esters glycerine fatty acid esters, sorbitan fatty acid esters and sucrose fatty acid esters.

4. Lubricating composition according to Claim 3 wherein the number of carbons of the fatty acid of the fatty acid ester type surfactant is from 12 to 22.

5. Lubricating composition according to any of Claims 1-4 wherein the amount of the surfactant is from 0.2 to

18 % by weight relative to the total composition.

6. Lubricating composition according to any of Claims 1-5 wherein a urea compound is incorporated in the amount of not more than 8 % by weight relative to the total composition.

7. Lubricating composition comprising a base oil, a mixture of a tricalcium phosphate and a urea compound in the amount of from 3 to 70 % by weight relative to the total composition, and a glycerine fatty acid ester and/or sorbitan fatty acid ester in the amount of from

0.2 to 18 % by weight relative to the total composition.

8. Use of the lubricating composition according to any^¬ one of Claims 1-7 for improving one or more properties selected from: (i) heat resistance; (ii) mechanical stability; (iii) water resistance; (iv) corrosion resistance; (v) load resistance; and (vi) flame resistance .