Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Solid hydrocarbon polymer
Reexamination Certificate
2001-06-08
2003-02-25
Howard, Jacqueline V. (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Solid hydrocarbon polymer
C585S012000, C585S018000
Reexamination Certificate
active
06525007
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a viscosity modifier for a lubricating oil and a lubricating oil composition. More particularly, the invention relates to a viscosity modifier for a lubricating oil capable of producing a lubricating oil composition having excellent low-temperature properties and a lubricating oil composition containing the viscosity modifier.
BACKGROUND ART
The viscosity of petroleum products generally varies greatly with temperature, and for lubricating oils for automobiles, the temperature dependence of the viscosity is desired to be small. In recent years, therefore, an ethylene/&agr;-olefin copolymer has been widely used as a viscosity modifier having an effect of improving viscosity index for the purpose of decreasing the temperature dependence of the lubricating oils.
When the surrounding temperature lowers, a wax component in a lubricating oil is crystallized and solidified to make the lubricating oil lose flowability, so that a pour point depressant is also contained in the lubricating oil to depress the solidification temperature. The pour point depressant functions to inhibit formation of a three-dimensional network attributed to crystallization of the wax component in the lubricating oil and to depress the pour point of the lubricating oil.
Of the low-temperature properties of a lubricating oil containing a viscosity modifier having an effect of improving viscosity index and a pour point depressant, the viscosity at a high shear rate is determined by compatibility of a lubricating oil base with the viscosity modifier, but on the other hand, the viscosity at a low shear rate is greatly influenced by the pour point depressant. It is known that when an ethylene/&agr;-olefin copolymer having specific composition is used as a viscosity modifier, the effect of the pour point depressant is markedly reduced because of an interaction between the copolymer and the pour point depressant (see U.S. Pat. Nos. 3,697,429 and 3,551,336).
Accordingly, the viscosity modifier to be blended with a lubricating oil which is required to have particularly excellent low-temperature properties is desired to exhibit an excellent effect of improving viscosity index and not to inhibit: the function of the pour point depressant.
As a viscosity modifier satisfying such requirements, an ethylene/&agr;-olefin copolymer, which has an uniform distribution of ethylene units and &agr;-olefin units in the molecules, an ethylene content of 30 to 80% by weight, a weight-average molecular weight of 20,000 to 750,000 and Mw/Mn of less than 2, is disclosed in Japanese Patent Publication No. 96624/1994.
The present inventors have earnestly studied under such circumstances as mentioned above, and as a result, they have found that an ethylene/propylene copolymer having a density, a molecular weight, a molecular weight distribution and a melting point in the specific ranges and having a specific relation between the density and the melting point and an ethylene/propylene copolymer having an ethylene content, a molecular weight, a molecular weight distribution and a melting point in the specific ranges and having a specific relation between the ethylene content and the melting point have an excellent effect of improving viscosity index and do not inhibit the function of the pour point depressant. Based on the finding, the present invention has been accomplished.
For reference, the ethylene/&agr;-olefin copolymer disclosed in the above publication satisfies neither the relation between the ethylene content and the melting point of the ethylene/propylene copolymer nor the relation between the density and the melting point of the ethylene/propylene copolymer specified by the present invention.
OBJECT OF THE INVENTION
It is an object of the present invention to provide a viscosity modifier for a lubricating oil, which comprises a specific ethylene/propylene copolymer and by which a lubricating oil composition having excellent low-temperature properties can be obtained, and to provide a lubricating oil composition containing the viscosity modifier and having excellent low-temperature properties.
DISCLOSURE OF THE INVENTION
One embodiment of the viscosity modifier for a lubricating oil according to the present invention comprises an ethylene/propylene copolymer (A) having the following properties (a-1) to (a-5):
(a-1) the density is in the range of 857 to 882 kg/m
3
,
(a-2) the weight-average molecular weight as measured by gel permeation chromatography is in the range of 80,000 to 400,000 in terms of polystyrene,
(a-3) Mw/Mn (Mw: weight-average molecular weight, Mn: number-average molecular weight), which is an indication of a molecular weight distribution, is not more than 2.3,
(a-4) the melting point as measured by a differential scanning calorimeter is in the range of 15 to 60° C., and
(a-5) the density (D (kg/m
3
)) and the melting point (Tm (° C.)) as measured by a differential scanning calorimeter satisfy the following relation (I)
Tm
≦1.247
×D
−1037 (I).
Another embodiment of the viscosity modifier for a lubricating oil according to the present invention comprises an ethylene/propylene copolymer. (B) having the following properties (b-1) to (b-5):
(b-1) the content of recurring units derived from ethylene is in the range of 70 to 79% by weight,
(b-2) the weight-average molecular weight as measured by gel permeation chromatography is not less than 80,000 and less than 250,000 in terms of polystyrene,
(b-3) Mw/Mn (Mw: weight-average molecular weight, Mn: number-average molecular weight), which is an indication of a molecular weight distribution, is not more than 2.3,
(b-4) the melting point as measured by a differential scanning calorimeter is in the range of 15 to 60° C., and
(b-5) the content (E (% by weight)) of recurring units derived from ethylene and the melting point (Tm (° C.)) as measured by a differential scanning calorimeter satisfy the following relation (II)
3.44
×E
−206
≧Tm
(II).
A further embodiment of the viscosity modifier for a lubricating oil according to the present invention comprises an ethylene/propylene copolymer (C) having the following properties (c-1) to (c-5):
(c-1) the content of recurring units derived from ethylene is in the range of 70 to 79% by weight,
(c-2) the weight-average molecular weight as measured by gel permeation chromatography is in the range of 250,000 to 400,000 in terms of polystyrene,
(c-3) Mw/Mn (Mw: weight-average molecular weight, Mn: number-average molecular weight), which is an indication of a molecular weight distribution, is not more than 2.3,
(c-4) the melting point as measured by a differential scanning calorimeter is in the range of 15 to 60° C., and
(c-5) the content (E (% by weight)) of recurring units derived from ethylene and the melting point (Tm (° C.)) as measured by a differential scanning calorimeter satisfy the following relation (III)
3.44
×E
−204
≧Tm
(III).
When the viscosity modifier for a lubricating oil according to the present invention is blended with a lubricating oil, a lubricating oil having excellent low-temperature properties can be obtained.
Embodiments of the lubricating oil composition according to the present invention include:
a lubricating oil composition comprising
(A) the ethylene/propylene copolymer having the above properties (a-1) to (a-5), and
(D) a lubricating oil base,
wherein the ethylene/propylene copolymer (A) is contained in an amount of 1 to 20% by weight;
a lubricating oil composition comprising
(B) the ethylene/propylene copolymer having the above properties (b-1) to (b-5), and
(D) a lubricating oil base,
wherein the ethylene/propylene copolymer (B) is contained in an amount of 1 to 20% by weight; and
a lubricating oil composition comprising
(C.) an ethylene/propylene copolymer having the above properties (c-1) to (c-5), and
(D) a lubricating oil base,
wherein the ethylene/propylene copolymer (C) is contained in an amount of 1 to 20% by weight.
Other embodiments of the lubricating oil composition accord
Kaneshige Ryousuke
Okada Keiji
Howard Jacqueline V.
Mitsui Chemicals Inc.
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