Lubricating oil or lubricating oil composition and fuel oil composition

The present invention is directed towards a lubricating oil comprising a random copolymer of an .alpha.-olefin/aromatic vinyl compound, wherein the copolymer has a viscosity falling within a specific range and comprises ethylene, an aromatic vinyl compound, and optionally an .alpha.-olefin. The lubricating oil possesses excellent viscosity properties, thermal stability, oxidation stability, abrasion resistance, and compatibility with lubricating oil additives. The random copolymer having a different viscosity range is useful as a viscosity index improver and a compatibilizing agent for a lubricating oil. The invention also provides a lubricating oil composition comprising a base oil and the viscosity index improver or the compatibilizing agent. The invention further provides a fuel oil composition comprising a fuel oil fluidity improver based on the above random copolymer having a different viscosity range and a middle fraction fuel oil having a boiling point of 150 to 400.degree. C. The fuel oil composition prevents an increase in viscosity of the middle fraction fuel oil, lowers the clogging point and the flow point in a low-temperature filter, and inhibits the abrasion of a fuel jet nozzle.

TECHNICAL FIELD
 The present invention relates to lubricating oils and lubricating oil
 compositions. More particularly, the invention relates to lubricating oils
 comprising an .alpha.-olefin/aromatic vinyl compound random copolymer,
 lubricating oil compositions comprising the copolymer, and lubricating oil
 compositions comprising a base oil composed of a mineral oil and/or a
 hydrocarbon synthetic oil and an .alpha.-olefin/aromatic vinyl compound
 random copolymer.
 The present invention also relates to lubricating oil viscosity index
 improvers and lubricating oil compatibility improvers each comprising an
 .alpha.-olefin/aromatic vinyl compound random copolymer.
 The present invention further relates to fuel oil compositions having
 lubricating properties, which comprise a middle fraction fuel oil and an
 .alpha.-olefin/aromatic vinyl compound random copolymer.
 BACKGROUND ART
 Lubricating base oils, which comprise a mineral oil contained in petroleum
 or a synthetic oil such as an ethylene/.alpha.-olefin copolymer, have been
 hitherto known. Further, lubricating oil compositions containing a
 viscosity index improver or a lubricating oil additive each comprising an
 .alpha.-olefin polymer are also known.
 The lubricating base oils are desired to be excellent not only in viscosity
 properties (particularly low-temperature fluidity) but also in heat
 stability, oxidation stability and lubricating properties.
 The lubricating base oils are blended with additives such as an extreme
 pressure agent, but the lubricating base oils, particularly hydrocarbon
 synthetic oils, usually have poor compatibility with the lubricating oil
 additives, and therefore the kind and the amount of the viscosity index
 improver or the lubricating oil additives added to the lubricating oils
 have been markedly limited.
 Lubricating oil compositions wherein esters are added as compatibility
 improvers to improve the compatibility of the lubricating base oils with
 the lubricating oil additives are known.
 Even the lubricating oil compositions containing the viscosity index
 improver or the compatibility improver are desired to be further improved
 in the heat stability, oxidation stability, lubricating properties and
 compatibility with the lubricating oil additives. Further, lubricating
 base oils, which show sufficient compatibility with the lubricating oil
 additives even if no compatibility improver is used, are desired.
 By the way, when middle fraction fuel oils such as gas oil (light oil) and
 heavy oil are used or stored at low temperatures, crystals of waxes
 contained in the oils grow. If oils containing grown wax crystals are
 used, problems such as plugging (clogging) of pipes and extreme increase
 of viscosity of the whole oil to cause difficulty of oil flow are brought
 about. To cope with the problems, addition of a fluidity improver such as
 an ethylene/.alpha.-olefin copolymer to the middle fraction fuel oils is
 known.
 It is also known to add polybutadiene having hydroxyl end group and
 containing not less than 70% of 1,2-bonds or its hydrogenated product to
 the middle fraction fuel oils to lower a cold filter plugging point
 (CFPP).
 For purifying automobile exhaust gas, a low-sulfur gas oil, that is a
 diesel gas oil having a decreased sulfur content, tends to be used, and
 legal regulation is becoming severe. However, sulfur in the fuel oil
 contributes to lubricating properties of the fuel oil, and if the sulfur
 content in the fuel oil is decreased, the lubricating properties of the
 fuel oil are sometimes lowered to thereby cause abrasion of fuel injection
 nozzles. Accordingly, fuel oil fluidity improvers having excellent
 lubricating properties are desired.
 The present invention has been made under such circumstances as mentioned
 above, and it is an object of the invention to provide a lubricating oil
 and a lubricating oil composition each of which is excellent not only in
 compatibility with lubricating oil additives but also in viscosity
 properties, heat stability, oxidation stability and lubricating
 properties.
 It is another object of the invention to provide a lubricating oil
 composition having excellent properties, which comprises a base oil
 composed of a mineral oil and/or a hydrocarbon synthetic oil and a
 viscosity index improver comprising a specific .alpha.-olefin/aromatic
 vinyl compound random copolymer.
 It is a further object of the invention to provide a lubricating oil
 composition having excellent properties, which comprises a base oil
 composed of a mineral oil and/or a hydrocarbon synthetic oil, a
 compatibility improver comprising a specific low-molecular weight
 .alpha.-olefin/aromatic vinyl compound random copolymer and a lubricating
 oil additive.
 It is a still further object of the invention to provide a viscosity index
 improver comprising a specific .alpha.-olefin/aromatic vinyl compound
 random copolymer, and a lubricating oil compatibility improver comprising
 a specific low-molecular weight .alpha.-olefin/aromatic vinyl compound
 random copolymer.
 DISCLOSURE OF THE INVENTION
 The lubricating oil according to the present invention comprises an
 .alpha.-olefin/aromatic vinyl compound random copolymer comprising:
 40 to 75% by mol of constituent units derived from ethylene,
 0 to 45% by mol of constituent units derived from an .alpha.-olefin of 3 to
 20 carbon atoms, and
 1 to 40% by mol of constituent units derived from an aromatic vinyl
 compound,
 with the proviso that the total amount of the constituent units derived
 from ethylene and the constituent units derived from the .alpha.-olefin is
 60 to 99% by mol,
 said .alpha.-olefin/aromatic vinyl compound random copolymer having an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 0.01 to 0.50 dl/g.
 The first lubricating oil composition according to the present invention
 comprises the .alpha.-olefin/aromatic vinyl compound random copolymer and
 a lubricating oil additive.
 When the .alpha.-olefin/aromatic vinyl compound random copolymer is used as
 a lubricating base oil and blended with at least one additive selected
 from an extreme pressure agent, an abrasion resistance agent, an oiliness
 improver and a detergent-dispersant, a lubricating oil composition having
 excellent properties can be obtained.
 The second lubricating oil composition according to the present invention
 comprises:
 a base oil comprising a mineral oil and/or a hydrocarbon synthetic oil, and
 an .alpha.-olefin/aromatic vinyl compound random copolymer which comprises
 40 to 75% by mol of constituent units derived from ethylene, 0 to 45% by
 mol of constituent units derived from an .alpha.-olefin of 3 to 20 carbon
 atoms and 1 to 40% by mol of constituent units derived from an aromatic
 vinyl compound, with the proviso that the total amount of the constituent
 units derived from ethylene and the constituent units derived from the
 .alpha.-olefin is 60 to 99% by mol, and has an intrinsic viscosity
 [.eta.], as measured in decalin at 135.degree. C., of 0.1 to 5.0 dl/g.
 The third lubricating oil composition according to the present invention
 comprises:
 a base oil comprising a mineral oil and/or a hydrocarbon synthetic oil,
 a low-molecular weight .alpha.-olefin/aromatic vinyl compound random
 copolymer which comprises 40 to 75% by mol of constituent units derived
 from ethylene, 0 to 45% by mol of constituent units derived from an
 .alpha.-olefin of 3 to 20 carbon atoms and 1 to 40% by mol of constituent
 units derived from an aromatic vinyl compound, with the proviso that the
 total amount of the constituent units derived from ethylene and the
 constituent units derived from the .alpha.-olefin is 60 to 99% by mol, and
 has an intrinsic viscosity [.eta.], as measured in decalin at 135.degree.
 C., of 0.01 to 0.30 dl/g, and
 a lubricating oil additive.
 The viscosity index improver according to the present invention comprises
 the same .alpha.-olefin/aromatic vinyl compound random copolymer as the
 specific .alpha.-olefin/aromatic vinyl compound random copolymer
 employable in the second lubricating oil composition.
 The lubricating oil compatibility improver according to the present
 invention comprises the same low-molecular weight .alpha.-olefin/aromatic
 vinyl compound random copolymer as the specific low-molecular weight
 .alpha.-olefin/aromatic vinyl compound random copolymer employable in the
 third lubricating oil composition.
 The fuel oil composition according to the present invention comprises:
 a middle fraction fuel oil having a boiling point of 150 to 400.degree. C.,
 and
 an .alpha.-olefin/aromatic vinyl type fuel oil fluidity improver comprising
 an .alpha.-olefin/aromatic vinyl compound random copolymer which comprises
 60 to 90% by mol of constituent units derived from ethylene, 0 to 39% by
 mol of constituent units derived from an .alpha.-olefin of 3 to 20 carbon
 atoms and 1 to 40% by mol of constituent units derived from an aromatic
 vinyl compound, with the proviso that the total amount of the constituent
 units derived from ethylene and the constituent units derived from the
 .alpha.-olefin is 60 to 99% by mol, and has an intrinsic viscosity
 [.eta.], as measured in decalin at 135.degree. C., of 0.01 to 1.0 dl/g.
 BEST MODE FOR CARRYING OUT THE INVENTION
 The lubricating oil, the lubricating oil composition, the viscosity index
 improver, the lubricating oil compatibility improver and the fuel oil
 composition according to the invention are described in detail
 hereinafter.
 First, the lubricating oil according to the invention is described.
 The lubricating oil of the invention comprises an .alpha.-olefin/aromatic
 vinyl compound random copolymer obtained from ethylene, an aromatic vinyl
 compound, and optionally, an .alpha.-olefin of 3 to 20 carbon atoms.
 .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 The .alpha.-olefin/aromatic vinyl compound random copolymer for use in the
 invention is a random copolymer of ethylene and an aromatic vinyl compound
 (ethylene/aromatic vinyl compound random copolymer) or a random copolymer
 of ethylene, an .alpha.-olefin of 3 to 20 carbon atoms and an aromatic
 vinyl compound (ethylene/.alpha.-olefin/aromatic vinyl compound random
 copolymer).
 In the ethylene/aromatic vinyl compound random copolymer, the amount of
 constituent units derived from ethylene is in the range of 60 to 75% by
 mol, preferably 60 to 70% by mol, and the amount of constituent units
 derived from the aromatic vinyl compound is in the range of 25 to 40% by
 mol, preferably 30 to 40% by mol.
 Examples of the aromatic vinyl compounds include styrene; mono- or
 polyalkylstyrenes, such as o-methylstyrene, m-methylstyrene,
 p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene and
 p-ethylstyrene; functional group-containing styrene derivatives, such as
 methoxystyrene, ethoxystyrene, vinylbenzoic acid, methyl vinylbenzoate,
 vinylbenzyl acetate, hydroxystyrene, o-chlorostyrene, p-chlorostyrene and
 divinylbenzene; 3-phenylpropylene; 4-phenylbutene; and
 .alpha.-methylstyrene. Of these, preferable is styrene or
 4-methoxystyrene.
 In the ethylene/aromatic vinyl compound random copolymer, .alpha.-olefins
 other than ethylene and the vinyl aromatic compound may be copolymerized.
 Examples of such .alpha.-olefins include .alpha.-olefins of 3 to 20 carbon
 atoms, such as propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-butene,
 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene,
 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene,
 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene and
 1-eicosene. Of these, preferable is propylene, 1-butene, 1-pentene,
 1-hexene or 1-octene. These .alpha.-olefins can be used singly or in
 combination of two or more kinds.
 In the ethylene/.alpha.-olefin/aromatic vinyl compound random copolymer,
 the amount of constituent units derived from ethylene is in the range of
 40 to 75% by mol, the amount of constituent units derived from the
 .alpha.-olefin of 3 to 20 carbon atoms is in the range of not more than
 45% by mol, and the amount of constituent units derived from the aromatic
 vinyl compound is in the range of 1 to 40% by mol, with the proviso that
 the total amount of the constituent units derived from ethylene and the
 constituent units derived from the .alpha.-olefin is in the range of 60 to
 99% by mol. It is preferable that the amount of constituent units derived
 from ethylene is in the range of 40 to 70% by mol, the amount of
 constituent units derived from the .alpha.-olefin of 3 to 20 carbon atoms
 is in the range of not more than 40% by mol, and the amount of constituent
 units derived from the aromatic vinyl compound is in the range of 1 to 30%
 by mol, with the proviso that the total amount of the constituent units
 derived from ethylene and the constituent units derived from the
 .alpha.-olefin is in the range of 70 to 99% by mol.
 When the amount of the constituent units derived from ethylene, the amount
 of the constituent units derived from the .alpha.-olefin of 3 to 20 carbon
 atoms and the amount of the constituent units derived from the aromatic
 vinyl compound are within the above ranges, a lubricating base oil having
 good balance of various properties such as viscosity properties, heat
 resistance and lubricating properties can be obtained.
 Of such copolymers as mentioned above, preferable is an
 .alpha.-olefin/aromatic vinyl compound random copolymer wherein the total
 amount of the constituent units derived from the .alpha.-olefin of 3 to 20
 carbon atoms and the constituent units derived from the aromatic vinyl
 compound is in the range of 0.1 to 40% by mol.
 In the .alpha.-olefin/aromatic vinyl compound random copolymer, other
 monomers such as non-conjugated dienes may be copolymerized. Examples of
 the non-conjugated dienes include 1,4-pentadiene, 1,4-hexadiene,
 4-methyl-1,5-heptadiene, 5-methylene-2-norbornene,
 5-ethylidene-2-norbornene, 5-isopropenyl-2-norbornene, 2,5-norbornadiene,
 1,6-cyclooctadiene, 2-ethylene-2,5-norbornadiene,
 2-isopropenyl-2,5-norbornadiene, dicyclopentadiene, 1,6-octadiene,
 1,7-octadiene, tricyclopentadiene, and esters of
 dihydrodicyclopentadienyloxyethylene and unsaturated carboxylic acids
 (e.g., acrylic acid, methacrylic acid, itaconic acid, maleic acid and
 fumaric acid). These non-conjugated dienes can be used singly or in
 combination of two or more kinds.
 The .alpha.-olefin/aromatic vinyl compound random copolymer has an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 0.01 to 0.50 dl/g, preferably 0.02 to 0.40 dl/g.
 In the .alpha.-olefin/aromatic vinyl compound random copolymer for use in
 the invention, the proportion of the constituent units for forming
 sequences of two constituent units derived from the aromatic vinyl
 compound to all the constituent units derived from the aromatic vinyl
 compound is desired to be not more than 1%, preferably not more than 0.1%.
 The proportion of the sequences of two constituent units derived from the
 aromatic vinyl compound can be determined by means of .sup.13 C-NMR.
 The process for preparing the .alpha.-olefin/aromatic vinyl compound random
 copolymer will be described later.
 The lubricating oil of the invention comprising the .alpha.-olefin/aromatic
 vinyl compound random copolymer is excellent in compatibility with
 additives as well as in viscosity properties, heat stability, oxidation
 stability and abrasion resistance.
 Next, the first lubricating oil composition according to the invention is
 described.
 The first lubricating oil composition of the invention comprises a
 lubricating base oil, which comprises the same .alpha.-olefin/aromatic
 vinyl compound random copolymer as used for forming the above-mentioned
 lubricating oil, and a lubricating oil additive.
 Lubricating Oil Additive
 The lubricating oil additive for use in the invention is at least one
 additive selected from an extreme pressure agent, an abrasion resistance
 agent, an oiliness improver and a detergent-dispersant.
 Examples of the extreme pressure agents include sulfur type extreme
 pressure agents, such as sulfides, sulfoxides, sulfones, thiophosphinates,
 thiocarbonates, fats and oils, sulfurized fats and oils, and olefin
 sulfides; phosphoric acids, such as phosphoric esters, phosphorous esters,
 phosphoric ester amines and phosphorous ester amines; and halogen
 compounds, such as chlorinated hydrocarbons.
 Examples of the abrasion resistance agent include inorganic or organic
 molybdenum compounds, such as molybdenum disulfide; organoboron compounds,
 such as alkylmercaptyl borate; graphite; antimony sulfide; boron
 compounds; and polytetrafluoroethylene.
 Examples of the oiliness improvers include higher fatty acids, such as
 oleic acid and stearic acid; higher alcohols, such as oleyl alcohol;
 amines; esters; sulfurized fats and oils; and chlorinated fats and oils.
 Examples of the detergent-dispersants include metallic sulfonates, such as
 calcium sulfonate, magnesium sulfonate and barium sulfonate;
 thiophosphonates; phenates; salicylates; succinimides; benzylamine; and
 succinates.
 The first lubricating oil composition of the invention may further contain
 a viscosity index improver, an antioxidant, an anti-corrosion agent and an
 anti-foaming agent.
 As the viscosity index improvers, those generally added to lubricating oils
 are available, and examples thereof include natural resins, such as
 mineral oil, and synthetic resins, such as ethylene/.alpha.-olefin
 copolymer, .alpha.-olefin homopolymer, styrene/butadiene copolymer,
 poly(meth)acrylate and naphthalene condensate.
 Examples of the antioxidants include amine compounds, such as
 2,6-di-t-butyl-4-methylphenol; and sulfur or phosphorus compounds, such as
 zinc dithiophosphate.
 Examples of the anti-corrosion agents include carboxylic acids and their
 salts, such as oxalic acid; sulfonates; esters; alcohols; phosphoric acid
 and its salts; benzotriazole and its derivatives; and thiazole compounds.
 Examples of the anti-foaming agents include silicone compounds, such as
 dimethylsiloxane and silica gel dispersion; alcohol compounds; and ester
 compounds.
 Though the amount of the lubricating oil additive used varies depending on
 the lubricating properties requested, it is in the range of usually 0.01
 to 80 parts by weight, preferably 0.05 to 60 parts by weight, based on 100
 parts by weight of the .alpha.-olefin/aromatic vinyl compound random
 copolymer.
 The lubricating oil composition of the invention may further contain a
 mineral oil or a hydrocarbon synthetic oil in an amount of up to 50% by
 weight.
 Since the first lubricating oil composition of the invention contains the
 .alpha.-olefin/aromatic vinyl compound random copolymer as a base oil, the
 composition is excellent in compatibility with additives as well as in
 viscosity properties, heat stability, oxidation stability and abrasion
 resistance.
 Next, the second lubricating oil composition and the viscosity index
 improver according to the invention are described.
 The second lubricating oil composition of the invention comprises a base
 oil, which comprises a mineral oil and/or a hydrocarbon synthetic oil, and
 a specific .alpha.-olefin/aromatic vinyl compound random copolymer
 functioning as a viscosity index improver.
 The viscosity index improver of the invention comprises the same
 .alpha.-olefin/aromatic vinyl compound random copolymer as used in the
 second lubricating oil composition of the invention.
 Base Oil
 The base oil used in the second lubricating oil composition of the
 invention is a lubricating base oil comprising a mineral oil and/or a
 hydrocarbon synthetic oil. These oils can be used alone or as a mixture of
 two or more kinds without specific limitation, as far as they have a
 viscosity at 100.degree. C. of 1.5 to 40.0 mm.sup.2 /S, preferably 2.0 to
 10.0 mm.sup.2 /S.
 The mineral oil has a viscosity in the above range.
 The mineral oil is, for example, a refined oil obtained by subjecting a
 paraffin base crude oil or an intermediate base crude oil to atmospheric
 distillation or subjecting a residual oil of the atmospheric distillation
 to vacuum distillation and then refining the resulting distillate oil in a
 conventional manner, or a deep-dewaxed oil obtained by deep-dewaxing the
 refined oil obtained above. Examples of the refining methods include
 hydrogenation, dewaxing, solvent extraction, alkali distillation, sulfuric
 acid washing and clay treatment. These methods can be carried out singly
 or in appropriate combination, or the same method can be repeated plural
 times. In these cases, there is no specific limitation on the order of the
 methods and the number of repetition times. In the present invention, it
 is particularly preferable to use a mineral oil obtained by a solvent
 dewaxing process that is made under severe conditions or obtained by a
 deep-dewaxing process such as a catalytic hydrogenation dewaxing process
 using a zeolite catalyst.
 Examples of the hydrocarbon synthetic oils preferably used include
 oligomers obtained by polymerizing or copolymerizing olefins of 2 to 20
 carbon atoms or arbitrary mixtures of these olefins, such as an oligomer
 of 1-octene, an oligomer of 1-decene and an oligomer of 1-dodecene. In
 addition to the mineral oil and/or the hydrocarbon synthetic oil, also
 available are diesters, such as di-2-ethylhexyl sebacate, dioctyl adipate
 and dioctyl dodecanoate, and polyol esters, such as pentaerythritol
 tetraoleate and trimethylolpropane tripelargonate.
 The oligomers are obtained by (co)polymerizing olefins of 2 to 20 carbon
 atoms by conventional processes.
 In the second lubricating oil composition of the invention, the base oil is
 used in an amount of 50.0 to 99.8% by weight, preferably 60.0 to 95.0% by
 weight.
 .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 In the second lubricating oil composition of the invention, a specific
 .alpha.-olefin/aromatic vinyl compound random copolymer functioning as a
 viscosity index improver is used as the base oil or the viscosity index
 improver. This copolymer is similar to the .alpha.-olefin/aromatic vinyl
 compound random copolymer for forming the lubricating oil or the first
 lubricating oil composition of the invention mentioned above, and is a
 random copolymer of ethylene and an aromatic vinyl compound
 (ethylene/aromatic vinyl compound random copolymer) or a random copolymer
 of ethylene, an .alpha.-olefin of 3 to 20 carbon atoms and an aromatic
 vinyl compound (ethylene/.alpha.-olefin/aromatic vinyl compound random
 copolymer).
 The .alpha.-olefin/aromatic vinyl compound random copolymer for use in the
 second lubricating oil composition of the invention, however, has an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 0.1 to 5.0 dl/g, preferably 0.5 to 3.0 dl/g.
 The amount of the .alpha.-olefin/aromatic vinyl compound random copolymer
 functioning as the viscosity index improver is in the range of 1.0 to 50.0
 parts by weight, preferably 2.0 to 30.0 parts by weight, based on 100
 parts by weight of the base oil.
 The second lubricating oil composition of the invention has excellent
 lubricating oil properties because the base oil comprising the mineral oil
 and/or the hydrocarbon synthetic oil is blended with the
 .alpha.-olefin/aromatic vinyl compound random copolymer functioning as the
 base oil or the viscosity index improver.
 Next, the third lubricating oil composition and the lubricating oil
 compatibility improver according to the invention are described.
 The third lubricating oil composition of the invention comprises a base
 oil, which comprises a mineral oil and/or a hydrocarbon synthetic oil, a
 specific low-molecular weight .alpha.-olefin/aromatic vinyl compound
 random copolymer functioning as a compatibility improver, and a
 lubricating oil additive.
 The lubricating oil compatibility improver according to the invention is
 the same .alpha.-olefin/aromatic vinyl compound random copolymer as used
 for forming the third lubricating oil composition of the invention.
 Base Oil
 Examples of the base oils include the aforesaid mineral oils and
 hydrocarbon synthetic oils employable as the base oil of the second
 lubricating oil composition.
 .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 In the third lubricating oil composition of the invention, a specific
 low-molecular weight .alpha.-olefin/aromatic vinyl compound random
 copolymer functioning as a compatibility improver is employed. This
 copolymer is similar to the .alpha.-olefin/aromatic vinyl compound random
 copolymer for forming the lubricating oil or the first lubricating oil
 composition of the invention mentioned above, and is a random copolymer of
 ethylene and an aromatic vinyl compound (ethylene/aromatic vinyl compound
 random copolymer) or a random copolymer of ethylene, an .alpha.-olefin of
 3 to 20 carbon atoms and an aromatic vinyl compound
 (ethylene/.alpha.-olefin/aromatic vinyl compound random copolymer). The
 low-molecular weight .alpha.-olefin/aromatic vinyl compound random
 copolymer for use in the third lubricating oil composition of the
 invention, however, has an intrinsic viscosity [.eta.], as measured in
 decalin at 135.degree. C., of 0.01 to 0.30 dl/g, preferably 0.01 to 0.20
 dl/g.
 By the use of the low-molecular weight .alpha.-olefin/aromatic vinyl
 compound random copolymer functioning as the compatibility improver, the
 lubricating oil additive can be easily dissolved in the base oil.
 The amount of the .alpha.-olefin/aromatic vinyl compound random copolymer
 functioning as the compatibility improver is more than 0 part by weight
 and not more than 50 parts by weight, preferably more than 0 part by
 weight and not more than 30 parts by weight, based on 100 parts by weight
 of the base oil.
 The weight ratio of the low-molecular weight .alpha.-olefin/aromatic vinyl
 compound random copolymer to the lubricating oil additive is in the range
 of 0.01 to 4.0, preferably 0.01 to 2.0.
 Lubricating Oil Additive
 The third lubricating oil composition of the invention contains a
 lubricating oil additive, such as the aforesaid extreme pressure agent, an
 abrasion resistance agent, oiliness improver, detergent-dispersant,
 antioxidant, anti-corrosion agent or anti-foaming agent.
 Though the amount of the lubricating oil additive used varies depending on
 the lubricating properties requested, it is in the range of usually 0.01
 to 50% by weight, preferably 0.05 to 30% by weight in the lubricating oil
 composition.
 The third lubricating oil composition of the invention has excellent
 lubricating oil properties because the base oil comprising the mineral oil
 and/or the hydrocarbon synthetic oil is blended with the lubricating oil
 additive and the low-molecular weight .alpha.-olefin/aromatic vinyl
 compound random copolymer functioning as the base oil or the compatibility
 improver.
 Next, a process for preparing the .alpha.-olefin/aromatic vinyl compound
 random copolymer is described.
 The (low-molecular weight) .alpha.-olefin/aromatic vinyl compound random
 copolymer for use in the invention can be prepared by copolymerizing
 ethylene, the aromatic vinyl compound, and if necessary, an .alpha.-olefin
 of 3 to 20 carbon atoms, in the presence of, for example, a metallocene
 catalyst (a).
 As the metallocene catalyst (a), various metallocene type catalysts, such
 as those currently used as single site catalysts and those analogous
 thereto, can be employed without specific limitation. In particular, a
 catalyst comprising a metallocene compound (b) of a transition metal
 (transition metal compound), and an organoaluminum oxy-compound (c) and/or
 an ionizing ionic compound (d) is preferably employed.
 The metallocene compound (b) is, for example, a metallocene compound of a
 transition metal selected from Group 4 of the periodic table (long-form
 periodic table) of elements indicated by Group No. 1 to 18 according to
 IU Inorganic Nomenclature Rules, revised edition, (1989), specifically
 a metallocene compound represented by the following formula (1)
EQU ML.sub.x (1)
 In the formula (1), M is a transition metal selected from elements of Group
 4 of the periodic table, e.g., zirconium, titanium or hafnium, and x is a
 valence of the transition metal.
 L is a ligand coordinated to the transition metal. At least one ligand L is
 a ligand having a cyclopentadienyl skeleton which may have a substituent.
 Examples of the ligands having a cyclopentadienyl skeleton include alkyl or
 cycloalkyl substituted cyclopentadienyl groups, such as cyclopentadienyl,
 methylcyclopentadienyl, ethylcyclopentadienyl, n- or
 i-propylcyclopentadienyl, n-, i-, sec- or t-butylcyclopentadienyl,
 hexylcyclopentadienyl, octylcyclopentadienyl, dimethylcyclopentadienyl,
 trimethylcyclopentadienyl, tetramethylcyclopentadienyl,
 pentamethylcyclopentadienyl, methylethylcyclopentadienyl,
 methylpropylcyclopentadienyl, methylbutylcyclopentadienyl,
 methylhexylcyclopentadienyl, methylbenzylcyclopentadienyl,
 ethylbutylcyclopentadienyl, ethylhexylcyclopentadienyl and
 methylcyclohexylcyclopentadienyl.
 Further, an indenyl group, a 4,5,6,7-tetrahydroindenyl group and a
 fluorenyl group can be also mentioned.
 Those groups may be substituted with halogen atoms or trialkylsilyl groups.
 Of the above ligands, particularly preferred are alkyl substituted
 cyclopentadienyl groups.
 When the compound represented by the formula (1) has two or more ligands L
 having a cyclopentadienyl skeleton, two of the ligands having a
 cyclopentadienyl skeleton may be bonded to each other through an alkylene
 group such as ethylene or propylene, a substituted alkylene group such as
 isopropylidene and diphenylmethylene, a silylene group, or a substituted
 silylene group such as dimethylsilylene, diphenylsilylene or
 methylphenylsilylene.
 Examples of L other than the ligand having a cyclopentadienyl skeleton
 include a hydrocarbon group of 1 to 12 carbon atoms, an alkoxy group, an
 aryloxy group, a sulfonic acid-containing group (--SO.sub.3 R.sup.1), a
 halogen atom or hydrogen atom, where R.sup.1 is an alkyl group, an alkyl
 group substituted with a halogen atom, an aryl group, or an aryl group
 substituted with a halogen atom or an alkyl group.
 Examples of the hydrocarbon groups of 1 to 12 carbon atoms include alkyl
 groups, cycloalkyl groups, aryl groups and aralkyl groups, more
 specifically, there can be mentioned:
 alkyl groups, such as methyl, ethyl, n-propyl, isopropyl, n-butyl,
 isobutyl, sec-butyl, t-butyl, pentyl, hexyl, octyl, decyl and dodecyl;
 cycloalkyl groups, such as cyclopentyl and cyclohexyl;
 aryl groups, such as phenyl and tolyl; and
 aralkyl group, such as benzyl and neophyl.
 Examples of the alkoxy groups include methoxy, ethoxy, n-propoxy,
 isopropoxy, n-butoxy, isobutoxy, sec-butoxy, t-butoxy, pentoxy, hexoxy and
 octoxy.
 The aryloxy group is, for example, phenoxy.
 Examples of the sulfonic acid-containing group (--SO.sub.3 R.sup.1) include
 methanesulfonato, p-toluenesulfonato, trifluoromethansulfonate and
 p-chlorobenzenesulfonato.
 Examples of the halogen atoms include fluorine, chlorine, bromine and
 iodine.
 The metallocene compound (b) of the above formula (1) wherein the valence
 of the transition metal is 4 is more specifically represented by the
 following formula (2):
EQU R.sup.2.sub.K R.sup.3.sub.l R.sup.4.sub.m R.sup.5.sub.n M (2)
 wherein M is the above-mentioned transition metal, preferably zirconium or
 titanium, R.sup.2 is a group (ligand) having a cyclopentadienyl skeleton,
 R.sup.3, R.sup.4 and R.sup.5 may be the same or different, and are each
 independently a group having a cyclopentadienyl skeleton or the same as L
 other than the ligand having a cyclopentadienyl skeleton in the above
 formula (1), k is an integer of not less than 1, and k+l+m+n=4.
 In the present invention, a compound represented by the following formula
 (3) can be also employed as the metallocene compound (b).
EQU L.sup.1 M.sup.2 Z1.sub.2 (3)
 wherein, M.sup.2 is a metal of Group 4 of the periodic table or a metal of
 lanthanide series;
 L.sup.1 is a derivative of delocalization .pi. bond group and imparts
 restraint geometrical shape to the metal M.sup.2 active site; and
 the Z.sup.1 's are the same or different, and are each independently
 hydrogen, halogen, a hydrocarbon group of 20 or less carbon, silicon or
 germanium atoms, a silyl group or a germyl group.
 Of the metallocene compounds (b) of the formula (3), preferred are
 metallocene compounds represented by the following formula (4).
 ##STR1##
 In the formula (4), M.sup.3 is titanium, zirconium or hafnium, and Z.sup.1
 is the same as above.
 Cp is a cyclopentadienyl group which is .pi.-bonded to M.sup.3 in the
 .eta..sup.5 bonding way, a substituted cyclopentadienyl group or a
 derivative thereof.
 W.sup.1 is oxygen, sulfur, boron, an element of Group 14 of the periodic
 table or a group containing any of these elements.
 V.sup.1 is a ligand containing nitrogen, phosphorus, oxygen or sulfur.
 W.sup.1 and V.sup.1 may form together a fused ring. Further, Cp and W.sup.1
 may form together a fused ring.
 Examples of preferred groups indicated by Cp in the formula (4) include a
 cyclopentadienyl group, an indenyl group, a fluorenyl group and saturated
 derivatives of these groups. These groups or derivatives form a ring
 together with the metal atom (M.sup.3).
 Each carbon atom in the cyclopentadienyl group may be substituted or
 unsubstituted with the same or a different group selected from the group
 consisting of hydrocarbyl groups, substituted-hydrocarbyl groups wherein
 one or more hydrogen atoms is replaced by a halogen atom,
 hydrcarbyl-substituted metalloid groups wherein the metalloid is selected
 from Group 14 of the Periodic Table of the Elements, and halogen groups.
 In addition, two or more of the substituent groups may form together a
 fused ring. The preferred hydrocarbyl and substituted hydrocarbyl groups,
 which may be substituted for at least one hydrogen atom in the
 cyclopentadienyl group, will contain from 1 to 20 carbon atoms, and
 include straight and branched alkyl groups, cyclic hydrocarbon groups,
 alkyl-substituted cyclic hydrocarbon groups, aromatic groups and
 alkyl-substituted aromatic groups. Examples of the preferred
 organometalloid groups include mono-, di- and tri-substituted
 organometalloid groups of Group 14 elements, and each of the hydrocarbyl
 groups has 1 to 20 carbon atoms. Particular examples of the preferred
 organometalloid groups include trimethylsilyl, triethylsilyl,
 ethyldimethylsilyl, methyldiethylsilyl, phenyldimethylsilyl,
 methyldiphenylsilyl, triphenylsilyl, triphenylgermyl and trimethylgermyl.
 Examples of the groups indicated by Z.sup.1 in the formula (4) include
 hydrido, halo, alkyl, silyl, germyl, aryl, amido, aryloxy, alkoxy,
 phosphido, sulfido, acyl, pseudohalido (e.g., cyanide, azido),
 acetylacetonato and mixtures thereof. The groups indicated by Z.sup.1 may
 be the same as or different from each other.
 As the metallocene compound (b), the metallocene compound represented by
 the formula (3) is particularly preferable from the viewpoints of
 polymerization activity and transparency, rigidity, heat resistance and
 impact resistance of the resulting molded product. The metallocene
 compounds (b) mentioned above may be used singly or in combination of two
 or more kinds.
 The metallocene compound (b) for use in the invention may be diluted with a
 hydrocarbon or a halogenated hydrocarbon prior to use.
 Next, the organoaluminum oxy-compound (c) and the ionizing ionic compound
 (d) used for forming the metallocene catalyst (a) are described.
 The organoaluminum oxy-compound (c) for use in the invention may be
 aluminoxane conventionally known or a benzene-insoluble organoaluminum
 oxy-compound (c) exemplified in Japanese Patent Laid-Open Publication No.
 78687/1990.
 The aluminoxane is prepared by, for example, the following processes, and
 is generally recovered as a hydrocarbon solvent solution.
 (1) An organoaluminum compound such as trialkylaluminum is added to an
 aromatic hydrocarbon solvent suspension of a compound containing adsorbed
 water or a salt containing water of crystallization, e.g., magnesium
 chloride hydrate, copper sulfate hydrate, aluminum sulfate hydrate, nickel
 sulfate hydrate or cerous chloride hydrate, to thereby allow the
 organoaluminum compound to react with the adsorbed water or the water of
 crystallization, followed by recovering aluminoxane as its aromatic
 hydrocarbon solvent solution.
 (2) Water, ice or water vapor is allowed to directly act on an
 organoaluminum compound such as trialkylaluminum in a medium such as
 benzene, toluene, ethyl ether or tetrahydrofuran, followed by recovering
 aluminoxane as its aromatic hydrocarbon solvent solution.
 (3) An organotin oxide such as dimethyltin oxide or dibutyltin oxide is
 allowed to react with an organoaluminum compound such as trialkylaluminum
 in a hydrocarbon medium such as decane, benzene or toluene.
 Examples of the ionizing ionic compounds (d) includes Lewis acid, ionic
 compounds, borane compounds and carborane compounds. These ionizing ionic
 compounds are described in National Publications of international Patent
 No. 501950/1989 and No. 502036/1989, Japanese Patent Laid-Open
 Publications No. 179005/1991, No. 179006/1991, No. 207703/1991 and No.
 207704/1991, and U.S. Pat. No. 5,321,106.
 The Lewis acid which may be used as the ionizing ionic compound (d) is, for
 example, a compound represented by the formula BR.sub.3 (each R is the
 same or different and is a phenyl group which may have a substituent such
 as fluorine, methyl or trifluoromethyl, or a fluorine atom). Examples of
 such compounds include trifluoroboron, triphenylboron,
 tris(4-fluorophenyl)boron, tris(3,5-difluorophenyl)boron,
 tris(4-fluoromethylphenyl)boron and tris(pentafluorophenyl)boron.
 The ionic compound which may be used as the ionizing ionic compound (d) is
 a salt comprising a cationic compound and an anionic compound. The anionic
 compound reacts with the metallocene compound (b) to render the compound
 (b) cationic and to form an ion pair, whereby the transition metal cation
 seed is stabilized. Examples of such anions include organoboron compound
 anion, organoarsenic compound anion and organoaluminum compound anion.
 Preferable are anions which are relatively bulky and stabilize the
 transition metal cation seed. Examples of the cations include metallic
 cation, organometallic cation, carbonium cation, tripium cation, oxonium
 cation, sulfonium cation, phosphonium cation and ammonium cation. More
 specifically, there can be mentioned triphenylcarbenium cation,
 tributylammonium cation, N,N-dimethylammonium cation, ferrocenium cation,
 etc.
 Of these, preferable are the ionic compounds containing a boron compound as
 the anionic compound, and examples thereof include trialkyl-substituted
 ammonium salts, N,N,-dialkylanilinium salts, dialkylammonium salts and
 triarylphosphonium salts.
 Examples of the trialkyl-substituted ammonium salts include
 triethylammoniumtetra(phenyl)boron, tripropylammoniumtetra(phenyl)boron,
 tri(n-butyl)ammoniumtetra(phenyl)boron and
 trimethylammoniumtetra(p-tolyl)boron.
 Examples of the N,N,-dialkylanilinium salts include
 N,N-dimethylaniliniumtetra(phenyl) boron.
 Examples of the dialkylammonium salts include
 di(n-propyl)ammoniumtetra(pentafluorophenyl)boron and
 dicyclohexylammoniumtetra(phenyl)boron.
 Examples of the triarylphosphonium salts include
 triphenylphosphoniumtetra(phenyl)boron,
 tri(methylphenyl)phosphoniumtetra(phenyl)boron and
 tri(dimethylphenyl)phosphoniumtetra(phenyl)boron.
 Also available as the ionic compounds are
 triphenylcarbeniumtetrakis(pentafluorophenyl)borate,
 N,N-dimethylaniliniumtetrakis(pentafluorophenyl)borate and
 ferroceniumtetra(pentafluorophenyl)borate.
 Examples of borane compounds which may be used as the ionizing ionic
 compound (d) include decaborane (14); salts of anions, such as
 bis[tri(n-butyl)ammonium]nonaborate and
 bis[tri(n-butyl)ammonium]decaborate; and salts of metallic borane anions,
 such as tri(n-butyl)ammoniumbis(dodecahydridododecaborate)cobaltate(III)
 and bis[tri(n-butyl)ammonium]bis(dodecahydridododecaborate)nickelate(III).
 Examples of the carborane compounds which may be used as the ionizing ionic
 compound (d) include salts of anions, such as 4-carbanonaborane(14) and
 1,3-dicarbanonaborane(13); and salts of metallic carborane anions, such as
 tri(n-butyl)ammoniumbis(nonahydrido-1,3-dicarbanonaborate)cobaltate(III)
 and
 tri(n-butyl)ammoniumbis(undecahydrido-7,8-dicarbaundecaborate)ferrate(III)
 .
 The ionizing ionic compounds (d) mentioned above can be used singly or in
 combination of two or more kinds.
 The metallocene catalyst (a) used in the invention may optionally contain
 the following organoaluminum compound (e), in addition to the above
 components.
 The organoaluminum compound (e) which is optionally used is, for example,
 an organoaluminum compound represented by the following formula (5):
EQU (R.sup.6).sub.n AlX.sub.3-n (5)
 wherein R.sup.6 is a hydrocarbon group of 1 to 15 carbon atoms (preferably
 1 to 4 carbon atoms), X is a halogen atom or hydrogen, and n is 1 to 3.
 The hydrocarbon group of 1 to 15 carbon atoms is, for example, an alkyl
 group, a cycloalkyl group or an aryl group. Examples of such groups
 include methyl, ethyl, n-propyl, isopropyl and isobutyl.
 Examples of the organoaluminum compounds include:
 trialkylaluminums, such as trimethylaluminum, triethylaluminum,
 triisopropylaluminum, tri-n-butylaluminum, triisobutylaluminum and
 tri-sec-butylaluminum;
 alkenylaluminums represented by the formula (i-C.sub.4 Hg).sub.x Al.sub.y
 (C.sub.5 H.sub.10).sub.z (wherein x, y and z are each a positive number,
 and z.gtoreq.2x), such as isoprenylaluminum;
 dialkylaluminum halides, such as dimethylaluminum chloride and
 diisobutylaluminum chloride;
 dialkylaluminum hydrides, such as diisobutylaluminum hydride;
 dialkylaluminum alkoxides, such as dimethylaluminum methoxide; and
 dialkylaluminum aryloxides, such as diethylaluminum phenoxide.
 Copolymerization of ethylene, the aromatic vinyl compound, and if desired,
 the .alpha.-olefin of 3 to 20 carbon atoms may be carried out batchwise or
 continuously. When the copolymerization is carried out continuously, the
 metallocene catalyst (a) is used in the following concentration.
 The concentration of the metallocene compound (b) in the polymerization
 system is in the range of usually 0.00005 to 0.1 mmol/liter
 (polymerization volume), preferably 0.0001 to 0.05 mmol/liter.
 The organoaluminum oxy-compound (c) is used in such an amount that the
 ratio of the aluminum atom in the organoaluminum oxy-compound to the
 transition metal in the metallocene compound (b) in the polymerization
 system, Al/transition metal, is in the range of 0.1 to 10,000, preferably
 1 to 5,000.
 The ionizing ionic compound (d) is used in such an amount that the molar
 ratio of the ionizing ionic compound (d) to the metallocene compound (b)
 in the polymerization system (ionizing ionic compound (d)/metallocene
 compound (b)) is in the range of 0.1 to 20, preferably 1 to 10.
 The organoaluminum compound (e) is used in such an amount that the
 concentration of the organoaluminum compound (e) is in the range of
 usually 0 to 5 mmol/liter (polymerization volume), preferably 0 to 2
 mmol/liter.
 The copolymerization reaction to prepare the .alpha.-olefin/aromatic vinyl
 compound random copolymer is carried out under the conditions of a
 temperature of usually -30 to +250.degree. C., preferably 0 to 200.degree.
 C., and a pressure of usually more than 0 and not more than 80 kg/cm.sup.2
 (gauge pressure), preferably more than 0 and not more than 50 kg/cm.sup.2
 (gauge pressure).
 The reaction time (average residence time in case of continuous
 copolymerization) is in the range of usually 5 minutes to 3 hours,
 preferably 10 minutes to 1.5 hours, though it varies depending on the
 reaction conditions such as catalyst concentration and polymerization
 temperature.
 In the preparation of the .alpha.-olefin/aromatic vinyl compound random
 copolymer, ethylene, the aromatic vinyl compound and optionally the
 .alpha.-olefin of 3 to 20 carbon atoms are fed to the polymerization
 system in such amounts that the copolymer of aforesaid specific
 composition can be obtained. In the copolymerization, a molecular weight
 modifier such as hydrogen can be used.
 When ethylene, the aromatic vinyl compound and optionally the
 .alpha.-olefin of 3 to 20 carbon atoms are copolymerized as described
 above, the .alpha.-olefin/aromatic vinyl compound random copolymer is
 generally obtained as a polymerization solution containing it. The
 polymerization solution is treated in a conventional manner, whereby the
 .alpha.-olefin/aromatic vinyl compound random copolymer is obtained.
 Next, the fuel oil composition according to the invention is described.
 The fuel oil composition of the invention comprises:
 a middle fraction fuel oil having a boiling point of 150 to 400.degree. C.,
 and
 an .alpha.-olefin/aromatic vinyl compound random copolymer obtained from
 ethylene, an aromatic vinyl compound, and optionally, an .alpha.-olefin of
 3 to 20 carbon atoms.
 Middle Fraction Fuel Oil
 The middle fraction fuel oil for use in the invention has a boiling point
 of 150 to 400.degree. C., and a typical example of the middle fraction
 fuel oil is gas oil or fuel oil A. Particularly preferable is a middle
 fraction fuel oil having a difference between the 90% running point and
 the initial boiling point of not less than 110.degree. C. and, e.g., not
 more than 200.degree. C., preferably 115 to 190.degree. C., and having a
 cold filter plugging point of -10.degree. C. to +10.degree. C.
 The middle fraction fuel oil may be used alone or as a mixture of two or
 more kinds.
 .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 In the present invention, the .alpha.-olefin/aromatic vinyl compound random
 copolymer is used as a fuel oil fluidity improver. This copolymer is a
 random copolymer of ethylene and an aromatic vinyl compound
 (ethylene/aromatic vinyl compound random copolymer) or a random copolymer
 of ethylene, an .alpha.-olefin of 3 to 20 carbon atoms and an aromatic
 vinyl compound (ethylene/.alpha.-olefin/aromatic vinyl compound random
 copolymer).
 In the ethylene/aromatic vinyl compound random copolymer, the amount of
 constituent units derived from ethylene is in the range of 60 to 90% by
 mol, preferably 65 to 85% by mol, and the amount of constituent units
 derived from the aromatic vinyl compound is in the range of 10 to 40% by
 mol, preferably 15 to 35% by mol.
 Examples of the aromatic vinyl compounds include styrene; mono- or
 polyalkylstyrenes, such as o-methylstyrene, m-methylstyrene,
 p-methylstyrene, o,p-dimethylstyrene, o-ethylstyrene, m-ethylstyrene and
 p-ethylstyrene; functional group-containing styrene derivatives, such as
 methoxystyrene, ethoxystyrene, vinylbenzoic acid, methyl vinylbenzoate,
 vinylbenzyl acetate, hydroxystyrene, o-chlorostyrene, p-chlorostyrene and
 divinylbenzene; 3-phenylpropylene; 4-phenylbutene; and
 .alpha.-methylstyrene. Of these, preferable is styrene or
 4-methoxystyrene.
 In the ethylene/aromatic vinyl compound random copolymer, .alpha.-olefins
 other than ethylene and the vinyl aromatic compound may be copolymerized.
 Examples of such .alpha.-olefins include .alpha.-olefins of 3 to 20 carbon
 atoms, such as propylene, 1-butene, 3-methyl-1-butene, 4-methyl-1-butene,
 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene,
 1-decene, 1-undecene, 1-dodecene, 1-tridecene, 1-tetradecene,
 1-pentadecene, 1-hexadecene, 1-heptadecene, 1-octadecene, 1-nonadecene and
 1-eicosene. Of these, preferable is propylene, 1-butene, 1-pentene,
 1-hexene or 1-octene. These .alpha.-olefins can be used singly or in
 combination of two or more kinds.
 In the ethylene/.alpha.-olefin/aromatic vinyl compound random copolymer,
 the amount of constituent units derived from ethylene is in the range of
 60 to 90% by mol, the amount of constituent units derived from the
 .alpha.-olefin of 3 to 20 carbon atoms is in the range of not more than
 39% by mol, and the amount of constituent units derived from the aromatic
 vinyl compound is in the range of 1 to 40% by mol, with the proviso that
 the total amount of the constituent units derived from ethylene and the
 constituent units derived from the .alpha.-olefin is in the range of 60 to
 99% by mol. It is preferable that the amount of constituent units derived
 from ethylene is in the range of 65 to 85% by mol, the amount of
 constituent units derived from the .alpha.-olefin of 3 to 20 carbon atoms
 is in the range of 10 to 32% by mol, and the amount of constituent units
 derived from the aromatic vinyl compound is in the range of 5 to 25% by
 mol, with the proviso that the total amount of the constituent units
 derived from ethylene and the constituent units derived from the
 .alpha.-olefin is in the range of 75 to 95% by mol.
 When the amount of the constituent units derived from ethylene, the amount
 of the constituent units derived from the .alpha.-olefin of 3 to 20 carbon
 atoms and the amount of the constituent units derived from the aromatic
 vinyl compound are within the above ranges, the .alpha.-olefin/aromatic
 vinyl compound random copolymer is excellent in lubricating properties
 such as low-temperature fluidity improving effects.
 Of such copolymers as mentioned above, preferable is an
 .alpha.-olefin/aromatic vinyl compound random copolymer wherein the total
 amount of the constituent units derived from the .alpha.-olefin of 3 to 20
 carbon atoms and the constituent units derived from the aromatic vinyl
 compound is in the range of 6 to 39% by mol, preferably 13 to 32% by mol,
 more preferably 15 to 30% by mol.
 The .alpha.-olefin/aromatic vinyl compound random copolymer may be
 copolymerized with other monomers such as non-conjugated dienes. Examples
 of the non-conjugated dienes are the same as those previously described.
 The .alpha.-olefin/aromatic vinyl compound random copolymer has an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 0.01 to 1.0 dl/g, preferably 0.05 to 0.5 dl/g.
 In the fuel oil composition, the .alpha.-olefin/aromatic vinyl compound
 random copolymer functioning as the fuel oil fluidity improver is
 contained in an amount of 0.005 to 5.0% by weight, preferably 0.01 to 1.0%
 by weight.
 In the .alpha.-olefin/aromatic vinyl compound random copolymer for use in
 the invention, the proportion of the constituent units for forming
 sequences of two constituent units derived from the aromatic vinyl
 compound to all the constituent units derived from the aromatic vinyl
 compound is desired to be not more than 1%, preferably not more than 0.1%.
 The proportion of the sequences of two constituent units derived from the
 aromatic vinyl compound can be determined by means of .sup.13 C-NMR.
 The .alpha.-olefin/aromatic vinyl compound random copolymer can be prepared
 by the aforementioned process for preparing an .alpha.-olefin/aromatic
 vinyl compound random copolymer.
 EFFECT OF THE INVENTION
 The lubricating oil and the first lubricating oil composition according to
 the invention are excellent in compatibility with lubricating oil
 additives as well as in viscosity properties, heat stability, oxidation
 stability and abrasion resistance.
 The second lubricating oil composition according to the invention has
 excellent lubricating oil properties because the composition comprises a
 base oil composed of a mineral oil and/or a hydrocarbon synthetic oil and
 a viscosity index improver or a base oil each comprising the specific
 .alpha.-olefin/aromatic vinyl compound random copolymer.
 The third lubricating oil composition according to the invention has
 excellent lubricating oil properties because the composition comprises a
 base oil composed of a mineral oil and/or a hydrocarbon synthetic oil, a
 compatibility improver or a base oil each comprising the specific
 low-molecular weight .alpha.-olefin/aromatic vinyl compound random
 copolymer, a lubricating oil additive, and optionally, a viscosity index
 improver comprising the specific .alpha.-olefin/aromatic vinyl compound
 random copolymer.
 There are also provided by the invention a viscosity index improver
 comprising the specific .alpha.-olefin/aromatic vinyl compound random
 copolymer, and a lubricating oil compatibility improver comprising the
 specific low-molecular weight .alpha.-olefin/aromatic vinyl compound
 random copolymer.
 The .alpha.-olefin/aromatic vinyl type fuel oil fluidity improver for
 constituting the fuel oil composition of the invention prevents growth of
 wax crystals in the middle fraction fuel oil to thereby inhibit viscosity
 increase of the middle fraction fuel oil and to lower the cold filter
 plugging point (CFPP) and the pour point. Moreover, the fluidity improver
 has excellent lubricating properties. By virtue of these advantageous
 properties, fuel supply and air supply can be stabilized to achieve safety
 operation, and abrasion of fuel injection nozzles can be inhibited.
 Accordingly, the fuel oil composition of the invention is prevented from
 viscosity increase of the middle fraction fuel oil and is lowered in the
 cold filter plugging point and the pour point. Besides, the fuel oil
 composition contributes to inhibition of abrasion of fuel injection
 nozzles.

EXAMPLE
 The present invention is further described with reference to the following
 examples, but it should be construed that the invention is in no way
 limited to those examples.
 Example A-1
 Synthesis of .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 A 1-liter glass reactor equipped with a cooling tube and a stirrer was
 thoroughly purged with nitrogen. To the reactor were introduced 425 ml of
 toluene and 75 ml of styrene. Then, the reactor was saturated with
 ethylene while stirring. The temperature of the system was elevated to
 40.degree. C., and to the system were added 30.0 mM of methylaluminoxane
 (TOHSO AQUZO Co., 10 wt % toluene solution) and 0.06 mM of
 (t-butylamide)dimethyl(tetramethyl-.eta..sup.5
 -cyclopentadienyl)silanetitanium dichloride (0.01 mM toluene solution) so
 that the molar ratio of Al to the catalyst became 500. Then, ethylene was
 continuously fed at a rate of 100 N liter/hr to perform polymerization at
 80.degree. C. for 60 minutes.
 After the polymerization was completed, 250 ml of isobutyl alcohol and 10
 ml of hydrochloric acid were added, and the mixture was stirred at
 80.degree. C. for 30 minutes. The reaction solution containing isobutyl
 alcohol was transferred into a separatory funnel, washed twice with 250 ml
 of water, and separated into an oil phase and an aqueous phase. The oil
 phase portion was added to 3 liters of methanol to precipitate a polymer.
 The precipitated polymer was vacuum dried at 130.degree. C. for 12 hours
 to obtain 20 g of an ethylene/styrene random copolymer.
 In the copolymer (a), the molar ratio between ethylene and styrene
 (ethylene/styrene) was 69/31. The copolymer (a) had an intrinsic viscosity
 [.eta.], as measured in decalin at 135.degree. C., of 0.3 dl/g.
 The viscosity of the copolymer, the total acid number thereof and the
 properties thereof after heat resistance test are set forth in Table 1.
 The copolymer was used as a synthetic lubricating oil. As a result, the
 copolymer exhibited good performance.
 Example A-2
 Synthesis of .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 An ethylene/propylene/styrene random copolymer was synthesized in the same
 manner as in Example A-1, except that 450 ml of toluene and 50 ml of
 styrene were introduced into the reactor, and ethylene and propylene were
 continuously fed at rates of 95 N liter/hr and 5 Nl/hr, respectively.
 In the copolymer, the molar ratio among ethylene, propylene and styrene
 (ethylene/propylene/styrene) was 69/11/20. The copolymer (b) had an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 0.4 dl/g.
 The viscosity of the copolymer, the total acid number thereof and the
 properties thereof after heat resistance test are set forth in Table 1.
 The copolymer was used as a synthetic lubricating oil. As a result, the
 copolymer exhibited good performance.
 Example A-3
 Synthesis of .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 An ethylene/propylene/styrene random copolymer was synthesized in the same
 manner as in Example A-1, except that 450 ml of toluene and 50 ml of
 styrene were introduced into the reactor, and ethylene and propylene were
 continuously fed at rates of 85 N liter/hr and 15 Nl/hr, respectively.
 In the copolymer, the molar ratio among ethylene, propylene and styrene
 (ethylene/propylene/styrene) was 62/19/19. The copolymer (c) had an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 0.4 dl/g.
 The viscosity of the copolymer, the total acid number thereof and the
 properties thereof after heat resistance test are set forth in Table 1.
 The copolymer was used as a synthetic lubricating oil. As a result, the
 copolymer exhibited good performance.
 Example A-4
 Synthesis of .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 A 1-liter glass reactor equipped with a cooling tube and a stirrer was
 thoroughly purged with nitrogen. To the reactor were introduced 425 ml of
 toluene and 75 ml of styrene. Then, the reactor was saturated with
 ethylene while stirring. The temperature of the system was elevated to
 40.degree. C., and to the system were added 30.0 mM of methylaluminoxane
 (TOHSO AQUZO Co., 10 wt % toluene solution) and 0.06 mM of [(C.sub.5
 Me.sub.4)SiMe.sub.2 (N-t-Bu)]TiCl.sub.2
 ((t-butylamide)dimethyl(tetramethyl-.eta..sup.5
 -cyclopentadienyl)silanetitanium dichloride) (0.01 mM toluene solution) so
 that the molar ratio of Al to the catalyst became 500. Then, ethylene,
 propylene and hydrogen were continuously fed at rates of 85 N liter/hr, 15
 N liter/hr and 2 N liter/hr, respectively, to perform polymerization at
 80.degree. C. for 60 minutes. After the polymerization was completed, 250
 ml of isobutyl alcohol and 10 ml of hydrochloric acid were added, and the
 mixture was stirred at 80.degree. C. for 30 minutes. The reaction solution
 containing isobutyl alcohol was transferred into a separatory funnel,
 washed twice with 250 ml of water, and separated into an oil phase and an
 aqueous phase. The oil phase portion was added to 3 liters of methanol to
 precipitate a polymer. The precipitated polymer was vacuum dried at
 130.degree. C. for 12 hours to obtain an ethylene/propylene/styrene random
 copolymer.
 In the copolymer, the molar ratio among ethylene, propylene and styrene
 (ethylene/propylene/styrene) was 68/29/3. The copolymer (d) had an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 0.1 dl/g.
 The viscosity of the copolymer, the total acid number thereof and the
 properties thereof after heat resistance test are set forth in Table 1.
 The copolymer was used as a synthetic lubricating oil. As a result, the
 copolymer exhibited good performance.
 Example A-5
 Synthesis of .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 A 1-liter glass reactor equipped with a cooling tube and a stirrer was
 thoroughly purged with nitrogen. To the reactor were introduced 425 ml of
 toluene and 75 ml of styrene. Then, the reactor was saturated with
 ethylene while stirring. The temperature of the system was elevated to
 80.degree. C., and to the system were added 30.0 mM of methylaluminoxane
 (TOHSO AQUZO Co., 10 wt % toluene solution) and 0.06 mM of [(C.sub.5
 Me.sub.4)SiMe.sub.2 (N-t-Bu)]TiCl.sub.2
 ((t-butylamide)dimethyl(tetramethyl-.eta..sup.5
 -cyclopentadienyl)silanetitanium dichloride) (0.01 mM toluene solution) so
 that the molar ratio of Al to the catalyst became 500. Then, ethylene,
 propylene and hydrogen were continuously fed at rates of 51 N liter/hr, 9
 N liter/hr and 40 N liter/hr, respectively, to perform polymerization at
 80.degree. C. for 60 minutes.
 After the polymerization was completed, 250 ml of isobutyl alcohol and 10
 ml of hydrochloric acid were added, and the mixture was stirred at
 80.degree. C. for 30 minutes. The reaction solution containing isobutyl
 alcohol was transferred into a separatory funnel, washed twice with 250 ml
 of water, and separated into an oil phase and an aqueous phase. The oil
 phase portion was added to 3 liters of methanol to precipitate a polymer.
 The precipitated polymer was vacuum dried at 130.degree. C. for 12 hours
 to obtain an ethylene/propylene/styrene random copolymer.
 In the copolymer, the molar ratio among ethylene, propylene and styrene
 (ethylene/propylene/styrene) was 69/28/3. The copolymer (e) had an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 0.03 dl/g.
 The viscosity of the copolymer, the total acid number thereof and the
 properties thereof after heat resistance test are set forth in Table 1.
 The copolymer was used as a synthetic lubricating oil. As a result, the
 copolymer exhibited good performance.
 Example A-6
 An ethylene/propylene/styrene random copolymer was synthesized in the same
 manner as in Example A-5, except that isopropylidenebisindenylzirconium
 dichloride was used in place of the
 (t-butylamide)dimethyl(tetramethyl-.eta..sup.5
 -cyclopentadienyl)silanetitanium dichloride.
 In the copolymer, the molar ratio among ethylene, propylene and styrene
 (ethylene/propylene/styrene) was 72/25/3. The copolymer (f) had an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 0.01 dl/g.
 The viscosity of the copolymer, the total acid number thereof and the
 properties thereof after heat resistance test are set forth in Table 1.
 The copolymer was used as a synthetic lubricating oil. As a result, the
 copolymer exhibited good performance.
 Example A-7
 95.0 Parts by weight of the ethylene/propylene/styrene random copolymer (e)
 obtained in Example A-5 and 5.0 parts by weight of a load carrying
 additive were blended at about 60.degree. C. to prepare a blended oil.
 The kinematic viscosity and appearance (compatibility with the load
 carrying additive) of the blended oil are set forth in Table 2.
 Comparative Example A-1
 A blended oil was prepared in the same manner as in Example A-7, except
 that PAO-40 (oligomer of 1-decene, available from Mobil Co., trade name:
 SHF-401) was used in place of the ethylene/propylene/styrene random
 copolymer (e) obtained in Example A-5.
 The kinematic viscosity and appearance (compatibility with the load
 carrying additive) of the blended oil are set forth in Table 2.
 Comparative Example A-2
 90.0 Parts by weight of PAO-40 (oligomer of 1-decene), 5.0 parts by weight
 of an ester (DIDA: diisodecyl adipate, available from Daihachi Kagaku
 Kogyosho) and 5.0 parts by weight of a load carrying additive were blended
 at about 60.degree. C. to prepare a blended oil.
 The kinematic viscosity and appearance (compatibility with the load
 carrying additive) of the blended oil are set forth in Table 2.
 TABLE 1
 Examples
 A-1 A-2 A-3 A-4 A-5 A-6
 Intrinsic viscosity 0.3 0.4 0.4 0.1 0.03 0.01
 (.eta.) (dl/g)
 Viscosity *1 16,500 49,000 54,000 150 39 9.5
 (mPa.multidot.S) 100.degree. C.
 Total acid number 0.18 0.11 0.13 0.05 0.04 0.02
 *2 (mg-KOH/g)
 Lubricating
 properties
 Four ball load -- -- -- 4.0 3.0 2.5
 resistance test *3
 (kg/cm.sup.2)
 Properties after
 heat resistance
 test *4
 (200.degree. C. .times.
 6.5 hrs)
 Evaporation loss 0.8 0.5 0.5 3.0 13.0 20.5
 *5 (wt %)
 Total acid number 3.80 4.30 4.10 4.50 4.00 4.05
 *6 (mg-KOH/g)
 Remarks:
 *1: Measured by Brookfield viscometer (DV-II).
 *2: Measured by the method defined by JIS K 2501.
 *3: Measured by the method defined by JIS K 2519.
 *4: The heat resistance test was measured by the original method of our
 company, that is, 30 g of a sample contained in a cylindrical glass
 container (diameter: 55 mm, height 35 mm) was heated in an air oven at
 200.degree. C. for 6.5 hours.
 *5: The loss in weight after the heat resistance test (*4) was measured.
 *6: Measured by the method defined by JIS K 2501 after the heat resistance
 test (*4).
 TABLE 2
 Example Compar. Example
 A-7 A-1 A-2
 Component ratio of blended oil (wt %)
 Copolymer of Ex. A-5 95.0
 PAO-40 95.0 90.0
 Ester (DIDA) 5.0
 Load resistant additive 5.0 5.0 5.0
 Total (wt %) 100.0 100.0 100.0
 Properties of blended oil
 Kinematic viscosity *1 (mm.sup.2 /S)100.degree. C. 37.5 36.5 34.0
 Appearance *2 good bad good
 (compatibility with additives)
 Remarks:
 *1: Measured by the method defined by JIS K 2283.
 *2: Evaluated by visual observation.
 Example B-1
 Synthesis of .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 A 1-liter glass reactor equipped with a cooling tube and a stirrer was
 thoroughly purged with nitrogen. To the reactor were introduced 425 ml of
 toluene and 75 ml of styrene. Then, the reactor was saturated with
 ethylene while stirring. The temperature of the system was elevated to
 40.degree. C., and to the system were added 30.0 mM of methylaluminoxane
 (TOHSO AQUZO Co., 10 wt % toluene solution) and 0.06 mM of
 (t-butylamide)dimethyl(tetramethyl-.eta..sup.5
 -cyclopentadienyl)silanetitanium dichloride (0.01 mM toluene solution) so
 that the molar ratio of Al to the catalyst became 500. Then, ethylene was
 continuously fed at a rate of 100 N liter/hr to perform polymerization at
 80.degree. C. for 60 minutes.
 After the polymerization was completed, 250 ml of isobutyl alcohol and 10
 ml of hydrochloric acid were added, and the mixture was stirred at
 80.degree. C. for 30 minutes. The reaction solution containing isobutyl
 alcohol was transferred into a separatory funnel, washed twice with 250 ml
 of water, and separated into an oil phase and an aqueous phase. The oil
 phase portion was added to 3 liters of methanol to precipitate a polymer.
 The precipitated polymer was vacuum dried at 130.degree. C. for 12 hours
 to obtain 24 g of an ethylene/styrene random copolymer.
 In the copolymer, the molar ratio between ethylene and styrene
 (ethylene/styrene) was 71/29. The copolymer (g) had an intrinsic viscosity
 [.eta.], as measured in decalin at 135.degree. C., of 1.1 dl/g.
 Preparation of Lubricating Oil Composition
 The copolymer (g) was dissolved in a mineral oil A (available from Fuji
 Kosansha, 100 neutral oil) under heating in a concentration of 10% by
 weight based on the mineral oil A, to prepare a viscous liquid. The
 viscous liquid was blended with a mineral oil B (available from Fuji
 Kosansha, 150 neutral oil) in such a manner that the 100.degree. C.
 viscosity of the resulting blended oil became about 11 mm.sup.2 /S. The
 resulting blended oil was measured on the kinematic viscosity, viscosity
 index and oxidation stability. The results are set forth in Table 3.
 Example B-2
 Synthesis of .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 An ethylene/propylene/styrene random copolymer was synthesized in the same
 manner as in Example B-1, except that 450 ml of toluene and 50 ml of
 styrene were introduced into the reactor, and ethylene and propylene were
 continuously fed at rates of 95 N liter/hr and 5 Nl/hr, respectively.
 In the copolymer, the molar ratio among ethylene, propylene and styrene
 (ethylene/propylene/styrene) was 71/10/19. The copolymer (h) had an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 1.5 dl/g.
 Preparation of Lubricating Oil Composition
 A blended oil was prepared in the same manner as in Example B-1, except
 that the copolymer (h) was used.
 The kinematic viscosity, viscosity index and oxidation stability of the
 blended oil are set forth in Table 3.
 Example B-3
 Synthesis of .alpha.-Olefin/Aromatic Vinyl Compound Random Copolymer
 An ethylene/propylene/styrene random copolymer was synthesized in the same
 manner as in Example B-1, except that 450 ml of toluene and 50 ml of
 styrene were introduced into the reactor, and ethylene and propylene were
 continuously fed at rates of 85 N liter/hr and 15 Nl/hr, respectively.
 In the copolymer, the molar ratio among ethylene, propylene and styrene
 (ethylene/propylene/styrene) was 59/21/20. The copolymer (i) had an
 intrinsic viscosity [.eta.], as measured in decalin at 135.degree. C., of
 1.6 dl/g.
 Preparation of Lubricating Oil Composition
 A blended oil was prepared in the same manner as in Example B-1, except
 that the copolymer (i) was used.
 The kinematic viscosity, viscosity index and oxidation stability of the
 blended oil are set forth in Table 3.
 Example B-4
 A blended oil was prepared in the same manner as in Example B-1, except
 that the viscous liquid consisting of the ethylene/styrene random
 copolymer (g) and the mineral oil A (available from Fuji Kosansha, 100
 neutral oil) was blended with low-viscosity PAO-6 (oligomer of 1-decene,
 available from Shinnittetsu Kagaku K. K., trade name: Shinfluid 61) in
 place of the mineral oil B in such a manner that the 100.degree. C.
 viscosity of the resulting blended oil became about 11 mm.sup.2 /S. The
 resulting blended oil was measured on the kinematic viscosity, viscosity
 index and oxidation stability. The results are set forth in Table 3.
 Example B-5
 A viscous liquid was prepared in the same manner as in Example B-1, except
 that the ethylene/styrene random copolymer (g) was dissolved in
 low-viscosity PAO-4 (oligomer of 1-decene, available from Shinnittetsu
 Kagaku K. K., trade name: Shinfluid 41) in place of the mineral oil A
 under heating in a concentration of 10% by weight based on the PAO-4.
 Then, similarly to Example B-4, the viscous liquid was blended with
 low-viscosity PAO-6 (oligomer of 1-decene, available from Shinnittetsu
 Kagaku K. K., trade name: Shinfluid 61) in such a manner that the
 100.degree. C. viscosity of the resulting blended oil became about 11
 mm.sup.2 /S. The resulting blended oil was measured on kinematic
 viscosity, viscosity index and oxidation stability. The results are set
 forth in Table 3.
 Example B-6
 The viscous liquid obtained in Example B-1, which was a mixture of the
 ethylene/styrene random copolymer (g) and the mineral oil A, was blended
 with a detergent-dispersant, a low-molecular weight
 .alpha.-olefin/aromatic vinyl compound random copolymer
 (ethylene/propylene/styrene random copolymer, ethylene/propylene/styrene
 molar ratio: 69/11/20, intrinsic viscosity [.eta.] measured in decalin at
 135.degree. C.: 0.2 dl/g) as a compatibility improver and a base oil PAO-6
 (oligomer of 1-decene, available from Shinnittetsu Kagaku K. K., trade
 name: Shinfluid 61), to prepare a blended oil.
 The kinematic viscosity, viscosity index and appearance (compatibility with
 additive) of the blended oil are set forth in Table 4.
 Comparative Example B-1
 A blended oil was prepared in the same manner as in Example B-6, except
 that an ester (DIDA: diisodecyl adipate, available from Daihachi Kagaku
 Kogyosho) was used as the compatibility improver in place of the
 low-molecular weight .alpha.-olefin/aromatic vinyl compound random
 copolymer.
 The kinematic viscosity, viscosity index and appearance (compatibility with
 additive) of the blended oil are set forth in Table 4.
 Comparative Example B-2
 A blended oil was prepared in the same manner as in Example B-6, except
 that the low-molecular weight .alpha.-olefin/aromatic vinyl compound
 random copolymer as the compatibility improver was not used.
 The kinematic viscosity, viscosity index and appearance (compatibility with
 additive) of the blended oil are set forth in Table 4.
 TABLE 3
 Examples
 B-1 B-2 B-3 B-4 B-5
 Component ratio of
 viscous liquid (wt %)
 Copolymer of Ex. B-1 10.0 10.0 10.0
 Copolymer of Ex. B-2 10.0
 Copolymer of Ex. B-3 10.0
 Mineral oil A 90.0 90.0 90.0 90.0
 (100 netural)
 PAO-4 90.0
 Total (wt %) 100.0 100.0 100.0 100.0 100.0
 Component ratio of
 blended oil (wt %)
 Viscous liquid 24.0 18.5 15.5 25.3 25.8
 Mineral oil B 76.0 81.5 84.5
 PAO-6 74.7 74.2
 Total (wt %) 100.0 100.0 100.0 100.0 100.0
 Properties of blended oil
 Kinematic viscosity *1
 (mm.sup.2 /s)
 100.degree. C. 11.10 10.99 11.04 11.02 10.96
 40.degree. C. 68.8 67.5 68.1 61.9 60.3
 Viscosity index *2 153 154 153 172 176
 Properties after oxidation
 test *3
 Kinematic viscosity 0.66 0.68 0.65 0.75 0.73
 ratio *4 (40.degree. C.)
 Total acid number *5 5.6 5.1 5.0 4.0 3.8
 (mg-KOH/g)
 Remarks:
 *1: Measured by the method defined by JIS K 2283.
 *2: Calculated by the method defined by JIS K 2283.
 *3: Evaluated in accordance with the method defined by JIS K 2514.
 (165.5.degree. C. .times. 48 hrs)
 *4: Measured by the method defined by JIS K 2283. 40.degree. C. kinematic
 viscosity after oxidation test/40.degree. C. kinematic viscosity before
 oxidation test.
 *5: Measured by the method defined by JIS K 2501.
 TABLE 4
 Example Comp. Example
 B-6 B-1 B-2
 Component ratio of blended oil (wt %)
 (1) Viscous liquid (mixture of 14.0 14.0 14.0
 copolymer of Ex. B-1 and mineral
 oil A)
 (2) Detergent-dispersant 10.5 10.5 10.5
 (SH grade)
 (3) Compatibility improver
 (i) Low-molecular weight 5.0
 .alpha.-olefin/aromatic vinyl
 compound random copolymer
 (ii) Ester (DIDA) 5.0
 (4) Base Oil (PAO-6) 70.5 70.5 75.5
 Total (wt %) 100.0 100.0 100.0
 Properties of blended oil
 Kinematic viscosity *1 (mm.sup.2 /s)
 100.degree. C. 12.4 10.2 10.8
 40.degree. C. 72.2 56.1 62.1
 Viscosity index *2 170 172 166
 Appearance *3 good good bad
 (compatibility with additive)
 Remarks:
 *1: Measured by the method defined by JIS K 2283.
 *2: Calculated by the method defined by JIS K 2283.
 *3: Evaluated by visual observation.
 Example C-1
 (1) Synthesis of ethylene/styrene random copolymer (A)
 A 1-liter glass reactor equipped with a cooling tube and a stirrer was
 thoroughly purged with nitrogen. To the reactor were introduced 450 ml of
 toluene and 50 ml of styrene. Then, the reactor was saturated with
 ethylene while stirring. The temperature of the system was elevated to
 40.degree. C., and to the system were added 30.0 mM of methylaluminoxane
 (TOHSO AQUZO Co., 10 wt % toluene solution) and 0.06 mM of [(C.sub.5
 Me.sub.4)SiMe.sub.2 (N-t-Bu)]TiCl.sub.2
 ((t-butylamide)dimethyl(tetramethyl-.eta..sup.5
 -cyclopentadienyl)silanetitanium dichloride) (0.01 mM toluene solution) so
 that the molar ratio of Al to the catalyst became 500. Then, ethylene was
 continuously fed at a rate of 100 NL/hr to perform polymerization at
 80.degree. C. for 60 minutes. After the polymerization was completed, 250
 ml of isobutyl alcohol and 10 ml of hydrochloric acid were added, and the
 mixture was stirred at 80.degree. C. for 30 minutes. The reaction solution
 containing isobutyl alcohol was transferred into a separatory funnel,
 washed twice with 250 ml of water, and separated into an oil phase and an
 aqueous phase. The oil phase portion was added to 3 liters of methanol to
 precipitate a polymer. The precipitated polymer was vacuum dried at
 130.degree. C. for 12 hours to obtain an ethylene/styrene random copolymer
 (A).
 In the copolymer (A), the molar ratio between ethylene and styrene
 (ethylene/styrene) was 81/19. The copolymer (A) had an intrinsic viscosity
 [.eta.], as measured in decalin at 135.degree. C. of 0.4 dl/g.
 (2) Evaluation on performance of fuel oil composition
 To a commercially available gas oil No. 2 (sulfur content: 0.1% by weight),
 0.02% by weight of the ethylene/styrene random copolymer (A) was added.
 The resulting composition was evaluated on the pour point, cold filter
 plugging point (CFPP) and lubricating properties.
 The results are set forth in Table 5.
 Example C-2
 A fuel oil composition was prepared in the same manner as in Example C-1,
 except that the content of the ethylene/styrene random copolymer (A) in
 the fuel oil composition was varied to 0.10% by weight. The composition
 was evaluated in the same manner as in Example C-1.
 The results are set forth in Table 5.
 Example C-3
 (1) Synthesis of ethylene/propylene/styrene random copolymer (B)
 An ethylene/propylene/styrene random copolymer (B) was prepared in the same
 manner as in Example C-1, except that 4,750 ml of toluene and 25 ml of
 styrene were introduced into the reactor, and ethylene and propylene were
 continuously fed at rates of 100 NL/hr and 5 NL/hr, respectively.
 In the ethylene/propylene/styrene random copolymer (B), the molar ratio
 among ethylene, propylene and styrene (ethylene/propylene/styrene) was
 78/11/11. The copolymer (B) had an intrinsic viscosity [.eta.], as
 measured in decalin at 135.degree. C., of 0.3 dl/g.
 (2) Evaluation on performance of fuel oil composition
 Evaluation of a fuel oil composition was carried out in the same manner as
 in Example C-1, except that the ethylene/propylene/styrene random
 copolymer (B) was used.
 The results are set forth in Table 5.
 Example C-4
 A fuel oil composition was prepared in the same manner as in Example C-3,
 except that the content of the ethylene/propylene/styrene random copolymer
 (B) in the fuel oil composition was varied to 0.10% by weight. The
 composition was evaluated in the same manner as in Example C-3.
 The results are set forth in Table 5.
 Example C-5
 (1) Synthesis of ethylene/propylene/styrene random copolymer (C)
 An ethylene/propylene/styrene random copolymer (C) was prepared in the same
 manner as in Example C-1, except that 4,880 ml of toluene and 12 ml of
 styrene were introduced into the reactor, and ethylene and propylene were
 continuously fed at rates of 95 NL/hr and 6 NL/hr, respectively.
 In the ethylene/propylene/styrene random copolymer (C), the molar ratio
 among ethylene, propylene and styrene (ethylene/propylene/styrene) was
 79/16/5. The copolymer (C) had an intrinsic viscosity [.eta.], as measured
 in decalin at 135.degree. C., of 0.4 dl/g.
 (2) Evaluation on performance of fuel oil composition
 Evaluation of a fuel oil composition was carried out in the same manner as
 in Example C-1, except that the ethylene/propylene/styrene random
 copolymer (C) was used.
 The results are set forth in Table 5.
 Comparative Example C-1
 The commercially available gas oil No. 2 used in Example C-1 was evaluated
 on the pour point, cold filter plugging point and lubricating properties.
 The results are set forth in Table 5.
 Example C-6
 A fuel oil composition was prepared in the same manner as in Example C-3,
 except that the gas oil was replaced with a low-sulfur gas oil (sulfur
 content: not more than 0.01% by weight). The composition was evaluated in
 the same manner as in Example C-3.
 The results are set forth in Table 6.
 Example C-7
 A fuel oil composition was prepared in the same manner as in Example C-6,
 except that the content of the ethylene/propylene/styrene random copolymer
 in the fuel oil composition was varied to 0.10% by weight. The composition
 was evaluated in the same manner as in Example C-6.
 The results are set forth in Table 6.
 Comparative Example C-2
 The same gas oil (sulfur content: not more than 0.01% by weight) as used in
 Example C-7 was evaluated in the same manner as described above.
 The results are set forth in Table 6.
 TABLE 5
 Comp.
 Example Exam.
 C-1 C-2 C-3 C-4 C-5 C-1
 Component
 ratio of fuel oil
 composition
 (wt %)
 .alpha.- 0.02 0.10 0.02 0.10 0.02 --
 olefin/aromatic
 vinyl
 compound
 random
 copolymer
 Gas oil (sulfer 99.98 99.90 99.98 99.90 99.98 100.0
 content:
 0.1 wt %)
 Total (wt %) 100.0 100.0 100.0 100.0 100.0 100.0
 Properties of
 fuel oil
 composition
 Pour point -22.5 -25.0 -25.0 -30.0 -25.0 -15.0
 (.degree. C.)
 Cold filter -7 -8 -7 -9 -8 -3
 plugging
 point (.degree. C.)
 Lubricating 0.238 0.226 0.234 0.222 0.225 0.260
 properties
 (friction
 coefficient)
 TABLE 6
 Comp.
 Examples Example
 C-6 C-7 C-2
 Component ratio of fuel oil
 composition (wt %)
 .alpha.-olefin/aromatic vinyl 0.02 0.10 --
 compound random copolymer
 Low-sulfur gas oil
 (sulfur content: not more 99.98 99.90 100.0
 than 0.01 wt %)
 Total (wt %) 100.00 100.00 100.0
 Properties of fuel oil
 composition
 Pour point (.degree. C.) -25.0 -30.0 -17.5
 Cold filter plugging -8 -9 -4
 point (.degree. C.)
 Lubricating properties 0.246 0.234 0.272
 (friction coefficient)
 Evaluation methods:
 The pour point was measured in accordance with JIS K 2269.
 The cold filter plugging point was measured in accordance with JIS K 2288.
 The lubricating properties were evaluated based on the friction coefficient
 which was measured by a SRV friction tester (available from Optimol Co.)
 when the specimen was subjected to vibrating for 30 min. under the
 conditions of a test starting temperature of 60.degree. C., specimen
 contact of steel ball/plate, a load of 20 N, a frequency of 50 Hz and an
 amplitude of 1 mm.