BACKGROUND ART In general, it is necessary to use lubricating agents in locations, where sliding motion takes place between the moving parts in machinery. A wide variety of grease compositions are commonly used as lubricating agents in locations where oil injection is difficult to perform. Such grease compositions consist basically of a grease containing a thickening agent and an oil. Poly alpha olefin oils and co- polymers thereof are commonly used as the oil in such grease compositions, because the resulting greases generally exhibit a relatively high lubricating performance and are typically inexpensive to prepare. Hence, poly alpha olefin oil based greases are widely used as lubricating agents offering excellent lubricating characteristics.

However, it is desirable to develop poly alpha olefin oils compositions with low coefficients of friction.

US 5,387,351 (equivalent to Japanese published patent application No.

H07-207293) provides a lubricating grease composition comprising a mineral/synthetic oil preferably an oligomer of poly alpha olefin, polybutene and polyethers (the oil) together with a thickening agent comprising a titanium alkoxide complex, carboxylic acids and fatty acids.

US 5,227,081 (equivalent to Japanese published patent application No.

H04-268376) claims a silicone grease composition comprising crosslinked organosiloxane gel and a thickening agent. Suggested thickening agents included alumina, boron nitride, silica, and titanium dioxide.

Japanese published patent application No. S73-38444 describes a fluorocarbon oil, polyperfluoroolefin-epoxide oil or fluorosilicon oil as the oil, a graphite thickener and optionally a finely powdered material such as silica gel, carbon, graphite, and titanium dioxide zirconium oxide or molybdenum disulfide.

DISCLOSURE OF THE INVENTION The present invention seeks to provide a poly alpha olefin grease composition possessing superior lubricating characteristics.

According to the present invention there is provided a poly alpha olefin grease composition comprising : a grease base comprising a poly alpha olefin oil and a thickener, and from 0.01 to 30 parts by weight of a titanium dioxide powder for each 100 parts by weight of the grease base.

BRIEF DISCRIPTION OF THE DRAWINGS FIG. I shows the method for light-load reciprocating motion test in Example 1.

BEST MODE FOR CARRYING OUT THE INVENTION Preferably the poly alpha olefin oil is a polymer or copolymer of C3 to Cao alpha olefin monomers, although a polymer substantially based on a single monomer is preferred. The alpha olefins may be linear or branched. Preferably where branching occurs it is situated at least three carbon atoms in the chain from the double bond.

Any appropriate alpha olefin monomers suitable for preparing the oil may be utilised. Examples include propylene, 1-butene, 1-pentene, 1-hexene, 1- heptene, 1-octene, 1-nonene, 1-decene, 4-methyl-1-pentene, 4-methyl-1-hexene, 5- methyl-1-hexene, 4,4-dimethyl-1-pentene, 4-methyl-1-heptene, 5-methyl-1-heptene, and 6-methyl-1-decene. A polymer of one or more C6 to C15 linear alpha olefins is particularly preferred. In the case of the oil being a poly alpha olefin co-polymer, the monomers for same may comprises any one of the above alpha olefin monomers and any other suitable monomer but is preferably a poly alpha olefin/ethylene co-polymer.

The poly alpha olefin oil preferably has a dynamic viscosity at 40°C of from 10 to 1000 mm2/s. A particularly preferred poly alpha olefin oil is a polymer, made substantially from 1-decene, having a molecular weight of between 250 and

2000 and a dynamic viscosity at 40°C of from 10 to 1000 mm2/s. It is however to be understood that, whilst such a polymer is formed predominantly from 1-decene, it is also likely to include a mixture of C8 to C12 alpha olefin monomers. The proportion of the poly alpha olefin oil contained in the grease base varies depending on its dynamic viscosity or, as will be described later, on the metal soap or solid lubricating agents used as thickening agents.

The thickener may be any one or more substance that possesses a thickening action sufficient to transform the poly alpha olefin oil into a grease, i. e. into a semi-solid or semi-liquid state. Any one or more suitable thickener (s) for thickening oils to form greases may be utilised in combination with the poly alpha olefin oil to form the grease of the present invention. Particularly preferred thickeners are metallic soaps and/or solid lubricating agents.

Metallic soaps which are suitable for use in the present invention are, for example reaction products of metallic hydroxides and fatty acids. Examples of suitable metallic soaps include the unsubstituted or hydroxy substituted stearate, oleate and palmitate salts of metals such as lithium, potassium, sodium, aluminum, barium, zinc, and calcium. The thickener may also be, for example, the reaction product of lithium azeleate and lithium 12-hydroxystearate or the reaction product of lithium 12-hydroxystearate and aluminium triisopropoxide and/or the like. The soaps can be used singly or in combination.

Solid lubricating agents which may be utilised in the present invention as thickeners include organic solid lubricating agents such as polytetrafluoroethylene powders, melamine isocyanate powders, organomolybdenum compounds such as sulfurized oxymolybdenum dibutyldithiocarbamate, molybdenum disulfide, graphite and boron nitride. The solid lubricating agents can be used singly or as a combination of two or more agents.

In the present invention, the thickening agent is preferably a metal soap in combination with a solid lubricating agent. When both a metal soap and a solid lubricant are used, the resultant grease compositions provide lower coefficients of friction because of the higher performance of the grease base itself.

The relative proportions of the poly alpha olefin oil and thickening agents contained in the grease will vary dependent on the solid lubricating agents and/or metal soaps used as the thickening agents.

For example, when the grease base is obtained by thickening a poly alpha olefin oil using a metal soap alone, said grease base may comprise as follows:- From 80 to 95 weight % of the poly alpha olefin oil and From 5 to 20 weight % of the metal soap.

When the grease base is obtained by thickening using a metal soap in combination with a solid lubricating agent, the grease base may comprise From 30 to 95 weight % of the poly alpha olefin oil, From 0 to 15 weight % of the metal soap, and From 5 to 70 weight % of the solid lubricating agent.

When the proportion of the thickening agent is outside the above- mentioned range, the grease base does not have the appropriate consistency, and, for this reason, uniform mixing of the titanium dioxide powder with the grease base becomes impossible, as a result of which sufficient enhancement of the lubricating performance of the grease composition based on the synergistic effect of the grease base and titanium dioxide powder is not obtained.

More preferably when the grease base is obtained by thickening using a metal soap in combination with a solid lubricating agent, the grease base may comprise:- from 35 to 85 weight % of poly alpha olefin oil, from 5 to 15 weight % of a metal soap and from 10 to 60 weight % of a solid lubricating agent as thickening agents, with the proportion of the poly alpha olefin oil to the metal soap being preferably from 80 to 95 weight % : 5 to 20 weight %.

When the proportion of the thickening agent is outside the above- mentioned range, the grease base does not have the appropriate consistency, and, for this reason, uniform mixing of the titanium dioxide powder with the grease base becomes impossible, as a result of which sufficient enhancement of the lubricating performance of the grease composition based on the synergistic effect of the grease base and titanium dioxide powder is not obtained.

In the poly alpha olefin grease composition of the present invention, the original lubricating performance provided by said grease base is improved based on a synergistic effect produced by compounding a titanium dioxide powder with the grease base described above. The resulting composition exhibits an improved lubricating performance with a low coefficient of friction.

Any form of titanium dioxide may be utilised for the present invention although rutile titanium dioxide is preferred. The titanium dioxide utilised in the present invention preferably has an average particle size of from 0.01 to 1 micrometers and is preferably surface-treated with a protective coating. The protective coating may comprise any standard treating agent for titanium dioxide, for example, it may comprise alumina alone or with silica, zinc oxide, a methylhydrogenpolysiloxane, a trimethylsiloxysilicate or a mixture of alumina, silica and a fatty acid. An example of a suitable titanium dioxide for the present invention is TR-700 from Fuji Titanium Industry Co. Ltd, which, it is understood, has an alumina and silica based coating.

The proportion of the titanium dioxide powder per 100 parts by weight of the grease base is from 0.01 to 30 parts by weight and preferably from 1 to 10 parts by weight. When the proportion of the titanium dioxide powder contained therein is less than 0.01 parts by weight, the resultant grease composition does not exhibit sufficient lubricating performance, and, on the other hand, when the proportion of the titanium dioxide powder exceeds 30 parts by weight, the titanium dioxide powder cannot be uniformly mixed with the grease base and, as a result, the grease composition does not exhibit sufficient enhancement of the lubricating performance due to the synergistic effects of the grease base and titanium dioxide powder.

So long as the lubricating performance is not impaired, appropriate additives such as surface active agents, dyes, pigments, dispersing agents and the like may be added into the poly alpha olefin grease composition as required.

The composition in accordance with the present invention may be prepared utilizing any suitable method, for example, the poly alpha olefin grease composition of the present invention can be produced by preparing a grease base of appropriate consistency by mixing the poly alpha olefin oil with one or more suitable thickener (s) and subsequently compounding a titanium dioxide powder with the resulting grease base. Alternatively, the poly alpha olefin oil, one or more suitable thickener (s) and the titanium dioxide powder may be mixed simultaneously. Where required heat may be utilised to assist in the formation of the grease base.

It is to be noted that in the case where a metal soap is being used as a thickener, the metal soap may be formed in situ, by introducing a metal hydroxide such as lithium hydroxide and for example stearic acid or 12-hydroxy stearic acid into the poly alpha olefin oil thereby forming lithium stearate or lithium 12- hydroxystearate, respectively, in sine.

In the case where at least one metal soap and at least one solid lubricating agent are used together as thickeners, the poly alpha olefin oil used in the preparation can be divided in two portions, a first portion comprising the poly alpha olefin oil and metal soap and a second portion comprising the solid lubricating agent along with the remaining portion of the poly alpha olefin oil, the resulting two mixtures being intermixed after their initial preparation.

The compounding of the titanium dioxide into the grease base may be carried out in any suitable mixer, such as by using butterfly mixers, twin mixers, double mixers, planetary mixers, 3-roll mills and the like.

The poly alpha olefin grease composition of the present invention is especially suitable for use in lubricating agents intended for reducing the coefficient of friction between metal members placed in contact, such as zinc-plated ball and

latch parts of door locks, sliding parts made of zinc-plated plates used in electrical household appliances, and the like.

In addition, when a metal soap and a solid lubricating agent are used together as thickening agents, in addition to the thickening action exerted on the poly alpha olefin oil, said solid lubricating agent possesses the function of improving the lubricating performance of the resultant grease base itself, which increases the lubricating performance of the grease base and leads to a synergistic effect between the titanium dioxide powder and the grease base exhibiting the lubricating performance enhanced by the solid lubricating agent, which allows for obtaining an even better low coefficient of friction.

Examples The invention will be more clearly understood with reference to the Drawing and the following examples.

Example 1-Grease Base Preparation A grease-like mixture (referred to hereafter as"grease base A") was prepared by mixing 86.9 weight % of a poly alpha olefin oil (referred to hereafter as PAO oil) with a dynamic viscosity of 29 mm2/s, 11.5 weight % of 12-hydroxystearic acid, and 1.6 weight % of lithium hydroxide at a temperature of 190°C for 10 minutes and as such substantially all water by-product of the reaction between the acid and base is evaporated off.

Hence the resulting Grease base A is considered to consist of 86.9 weight % of a poly alpha olefin oil and 13.1 weight % of lithium 12-hydroxystearate (a metal soap based thickening agent).

Preparation of Grease Composition (1) 0.1 parts by weight of a rutile titanium dioxide powder, having an average particle size of 0.3, um (TR-700 from Fuji Titanium Industry Co), (hereafter

referred to as titanium dioxide powder) were combined with 100 parts by weight of grease base A, the resulting mixture was mixed for 20 minutes using a butterfly mixer, and then milling in a 3-roll mill, to provide a grease composition (referred to hereafter as"Grease Composition (1)").

Evaluation of Grease Composition (1) The coefficient of friction of the resultant Grease Composition (1) was determined by the test depicted in Figure 1, in which grease composition (1) was first applied onto a zinc plated steel base plate 12 (SECC). Grease composition (1) was then subjected to a light-load reciprocating motion test by rolling roller 10, to which a 1 kg vertical load had been previously applied, over base plate 12 coated with grease composition (1) (Coating F). The roller stroke length was 8mm and the frequency of strokes of the roller over the plate was 30 strokes/min. A static coefficient of friction was determined using a load cell, and the coefficient of friction was calculated from the vertical load and the obtained static coefficient of friction. The results are shown in Table 1.

Examples (2), (3), (4) and (5) Four poly alpha olefin grease compositions (hereafter referred to as "Grease Compositions (2), (3), (4) and (5)"respectively) were prepared according to the same process as described in Example 1, with the exception that in each case the proportion titanium dioxide powder was different, as indicated in Table 1. The coefficients of friction were measured in the same manner as in Example 1 and the results are provided in Table 1.

Comparative Example 1 In this comparative example the coefficient of friction of grease base A was measured by carrying out the same friction coefficient measurement test as in Example 1 and the results thereof are shown in Table 1.

Comparative Example 2 A comparative composition (hereafter referred to as"Comparative Composition (1)") was obtained by compounding 10 parts by weight of titanium dioxide powder with 100 parts by weight of PAO oil. The coefficient of friction of the resulting comparative composition (1) was determined by using the test as hereinbefore described in Example 1. The results are shown in Table 1.

Reference Example 1 In this Reference example the coefficient of friction of PAO oil was measured by carrying out the same friction coefficient measurement test as in Example 1 and the results thereof are shown in Table 1.

Table 1 Comp. Comp. Ref. Ex 1 Ex. 2 Ex. 3 Ex. 4 Ex. Ex. 1 Ex. 2 Ex. 1 5 AmountGrease 100 100 100 100 100 100 base A (parts by weight) 0 Amount t) Titanium dioxide 0.1 1 10 20 30 0 10 0 U powder (parts by weight) PAO oil (parts by weight) 100 100 Grease 1 2 3 4 5 Base Comparative PAO Composition under A 1 oil test 300 0. 095 0.085 0.090 0.100 0.100 0.125 Impossible0. 100 , o strokes to measure 500 0. 100 0.085 0.095 0.095 0.105 0.135 Impossible 0. 105 strokes to measure U 1000 0. 130 0.100 0.095 0.100 0.105 0.190 Impossible 0. 105 strokes to measure

The above results, showed that the coefficients of friction obtained from Grease Compositions (1) to (5) were either on par with or better than the coefficient of friction obtained when using PAO oil alone (Reference Example 1) for the 300 and 500 stroke tests and with the exception of Grease composition (1) for the 1000 stroke tests. Furthermore, it will be seen that the rate of change in the coefficient of friction with increasing number of roller strokes (called"the rate of change of the coefficient of friction"herein below) was generally also reduced.

Whilst, it is evident that the PAO oil used in Reference Example 1 had a low coefficient of friction, its use, however, was limited because it was not grease- like. However, when the PAO oil was made into a grease (Grease Base 1), the coefficient of friction of the resulting grease base increased, as seen in Comparative Example 1.

Furthermore, as is evident from Comparative Example 2, when PAO oil was simply compounded with a titanium dioxide powder, a grease was not obtained, and no improvement could be achieved.

Hence, it will be appreciated that grease compositions (1) to (5) provided comparatively superior lubricating performances as compared to titanium dioxide free compositions which improved performance is thought to be due to an unexpected synergistic effect caused by the interaction between titanium dioxide powder and the grease base.

Example 6-Grease Base Preparation A grease base (hereafter referred to as"grease base Bol") was prepared by mixing grease base A with PAO oil in a weight ratio of 5: 1. The resulting grease base B1 therefore consisted of 89.1 weight % of a poly alpha olefin oil and 10.9 weight % of lithium 12-hydroxystearate.

Preparation of Grease Composition (6)

Grease composition (6) was obtained by compounding 19 parts by weight of titanium dioxide powder with 100 parts by weight of grease base B 1 according to the same process as described in Example 1. The coefficient of friction of said Grease composition (6) was measured by conducting the same friction coefficient measurement test as in Example 1. The results are shown in Table 2.

Comparative Example 3 In this comparative example the coefficient of friction of grease base B 1 was measured by carrying out the same friction coefficient measurement test as in Example 1 and the results thereof are shown in Table 2.

Table 2 Example 6 Comparative Example 3 Compositio Grease Type Base B1 Base B1 n base PAO oil (weight %) 89. 1 89. 1 Metal soap (weight %) 10. 9 10. 9 Amount of grease base (parts 100 100 by weight) Amount of titanium dioxide powder (parts 19 by weight) Evaluation Grease Composition under test Composition Base B1 (6) Coefficient of friction (u) (1000 strokes) 0. 12 2 0. 20 The results in Table 2 show that Grease composition (6) which contained the titanium dioxide powder, had a comparatively lower coefficient of friction as opposed to that of grease base B 1 used in Comparative Example 3, to which the titanium dioxide powder was not added.

Examples (7) to (10)

Four Grease bases (hereafter referred to as Grease bases (B2), (B3), (B4) and (B5) respectively) were prepared by adding the solid lubricating agents identified in Table 3 to Grease base (B 1). With reference to Table 3 it is to be understood that"MCA"stands for"melamine isocyanate adduct,"a solid lubricating agent,"PTFE"for"polytetrafluoroethylene,"a solid lubricating agent, and"MoDTC" for"sulfurized oxymolybdenum dibutyldithiocarbamate,"a solid lubricating agent.

Four Grease compositions (hereafter referred to as"Grease Composition (7), (8), (9) and (10)") were obtained by compounding titanium dioxide powder with 100 parts by weight of grease base (B2), (B3), (B4) and (B5) respectively in the proportions listed in Table 3. The grease compositions were prepared according to the same process as described in Example 1. The coefficients of friction thereof were measured by conducting the same friction coefficient measurement test as in Example 1. The results are shown in Table 3.

Comparative Example 4 A grease base (hereafter referred to as Grease bases (B6) was prepared by adding solid lubricating agents shown in Table 3 to Grease base (B1). The coefficient of friction thereof was measured by conducting the same friction coefficient measurement test as in Example 1. The result is shown in Table 3.

As seen in Table 3 below Grease Compositions (7) to (10) which contained the solid lubricating agents had lower coefficients of friction than Grease Composition (6) in Table 2, to which no solid lubricating agent was added. In addition, it can be seen that the coefficients of friction of Grease Compositions (7) to (10) were smaller than that of grease base B6 in Comparative Example 4, to which the solid lubricating agent was added and titanium dioxide powder was omitted.

Hence, it can be appreciated that grease compositions (7), (8), (9) and (10) provided a superior lubricating performance based on the synergistic effect created by the titanium dioxide powder and the grease base, whose lubricating performance was enhanced by the addition of the solid lubricating agents.

Also, it can be appreciated that whilst grease composition (6) in Table 2, did not contain a solid lubricating agent, it did contain titanium dioxide powder and is seen to provide a substantially equivalent lubricating performance with that of grease base B6, which contained a solid lubricating agent but omitted titanium dioxide.

Table 3 Comparative Ex. 7 Ex. 8 Ex. 9 Ex. 10 Ex. 4 Type Base B2 Base B3 Base B4 Base B5 Base B6 PAO oil (weight%) 81. 3 77. 9 77. 1 77. 1 74. 8 Metal soap 10 9. 6 9. 5 9. 5 9. 2 (weight %) Solid MCA 4. 35 6. 25 3. 1 3. 1 8 lubricatingPTFE 4. 35 6. 25 10. 3 9. 3 8 agent---- (weigh%) TC cl Total of metal soap 18.7 22.1 22.9 22.9 25.2 con and solid o U lubricating agent (weight%) Amount of grease 100 100 100 100 100 base (parts by weight) Amount of titanium 8. 7 4. 2 3. 1 3. 1- dioxide powder (parts by weight) Grease Composition Comp. 7 Comp. 8 Comp. 9 Comp. Base B6 under test 10 0 Coefficient of friction 0. 07 0. 07 0. 06 0. 05 0. 08 W (, u) (1000 strokes)