Solid anti-friction devices – materials therefor – lubricant or se – Lubricants or separants for moving solid surfaces and... – Solid hydrocarbon polymer
Reexamination Certificate
2002-01-10
2004-07-20
McAvoy, Ellen M (Department: 1764)
Solid anti-friction devices, materials therefor, lubricant or se
Lubricants or separants for moving solid surfaces and...
Solid hydrocarbon polymer
C585S012000, C585S018000, C525S331700
Reexamination Certificate
active
06764985
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a viscosity modifier for lubricating oil and lubricating oil compositions. More particularly, the invention relates to a viscosity modifier for lubricating oil with which a lubricating oil composition excellent in low-temperature properties and handling properties at low temperatures is obtained, and lubricating oil compositions containing said viscosity modifier.
BACKGROUND OF THE INVENTION
The viscosity of petroleum products varies eminently with temperature. The viscosity of lubricating oil for automobiles, however, is desired to have small dependency on temperature. In order to control the temperature dependency of the lubricating oils, an ethylene/&agr;-olefin copolymer which has a viscosity index improvement effect, has been widely employed as a compounding agent.
The lubricating oils lose flowability at a low temperature because of crystal-solidification of its wax component. For the purpose of lowering a solidification temperature, the lubricating oils contain a pour-point depressant. The pour-point depressant blocks formation of three-dimensional network owing to the crystallization of wax component in the lubricating oil, and lead a pour point of the lubricating oil to lower.
Among the properties of the lubricating oils containing an ethylene/&agr;-olefin copolymer and a pour-point depressant at low-temperature, a viscosity under a high shear rate is determined by compatibility between a lubricating oil base and the ethylene/&agr;-olefin copolymer, and a viscosity under a low shear rate is remarkably influenced by the pour-point depressant. It is known that in case using a specifically composed ethylene/&agr;-olefin copolymer, the effect of the pour-point depressant is greatly deteriorated by the interaction between the pour-point depressant and the copolymer (see U.S. Pat. No. 3,697,429 and U.S. Pat. No. 3,551,336).
Accordingly, the ethylene/&agr;-olefin copolymer blended in lubricating oils is expected, particularly in the case where excellent low-temperature properties are conditioned, not to hinder the function of the pour-point depressant as well as to be satisfactory in the viscosity index improvement effect.
In order to prevent the interaction between the pour-point depressant and the ethylene/&agr;-olefin copolymer, a proposal has been made where an ethylene/&agr;-olefin copolymer having ununiform composition distribution and obtained by the use of a specific polymerization apparatus under specific polymerization conditions, is used as a viscosity index improver (JP A 60(1985)-228600). However, the lubricating oil having excellent low-temperature properties at any shear rate has not been produced.
As the method of the improvement of low-temperature properties of lubricating oils, it can be considered that an ethylene/propylene copolymer with a high ethylene content is added to the oils as a viscosity index improver. Although the high ethylene content leads to improvement of the low-temperature properties, it invites crystallization of ethylene sequences in the viscosity index improver at a low temperature to render a lubricating oil composition jellylike state, and results in the handling properties being occasionally deteriorated.
When the use of a copolymer with a high ethylene content as a viscosity modifier for lubricating oil is appropriate, even slight broadening in the composition distribution of the ethylene copolymer could cause gelling at a low temperature. Thus, property tolerance of the employed copolymer can not be so wide, and the properties need to be strictly controlled.
In view of such circumstances, the inventors of the present invention have worked earnestly to find out that by the use of a specific copolymer of ethylene, an &agr;-olefin of 3 or more carbon atoms and an &agr;-olefin of 4 or more carbon atoms, the interaction deteriorating the effect of the pour-point depressant is not caused and the compatibility between the copolymer and the lubricating oil base at a low temperature may be controlled, whereby a lubricating oil composition excellent in low-temperature properties at any shear rate and in handling properties at low temperatures is obtained. With the finding, the inventors completed the invention.
This invention aims to provide lubricating oil compositions excellent in low-temperature properties, oxidation stability, lubricity at high temperatures and fuel efficiency and also in handling properties at low temperatures, and a viscosity modifier for lubricating oil employed in said lubricating oil compositions.
DISCLOSURE OF THE INVENTION
A viscosity modifier for lubricating oil of the invention comprises an ethylene/&agr;-olefin copolymer (B) containing:
(i) ethylene,
(ii) an &agr;-olefin of 3 or more carbon atoms, and
(iii) a higher &agr;-olefin of 4 to 20 carbon atoms wherein the carbon number of (iii) is larger than that of (ii) by one or more, and
the ethylene/&agr;-olefin copolymer (B) has the following properties (1) and (2):
(1) a content of ethylene (i) is in the range of 40 to 80% by weight, a content of the &agr;-olefin of 3 or more carbon atoms (ii) is in the range of 15 to 59% by weight, and a content of the higher &agr;-olefin of 4 to 20 carbon atoms (iii) is in the range of 0.1 to 25% by weight with the proviso that the sum is 100% by weight; and
(2) a weight-average molecular weight (Mw) in terms of polystyrene as measured by GPC is between 80,000 and 400,000.
The ethylene/&agr;-olefin copolymer (B) preferably has a ratio of Mw/Mn being 2.4 or less (3).
The ethylene/&agr;-olefin copolymer (B) preferably has a melting point (Tm) being 60° C. or lower as measured by DSC (4).
It is preferable that the &agr;-olefin of 3 or more carbon atoms (ii) which is a constituent of the ethylene/&agr;-olefin copolymer (B), be propylene. Preferably, the higher &agr;-olefin (iii) which is another constituent of the ethylene/&agr;-olefin copolymer (B), has 6 to 20 carbon atoms.
It is preferable in the ethylene/&agr;-olefin copolymer (B) that ethylene (i) be contained in an amount of 60 to 80% by weight, likewise, the &agr;-olefin of 3 or more carbon atoms (ii) in an amount of 18 to 34% by weight, and the higher &agr;-olefin of 4 to 20 carbon atoms (iii) in an amount of 0.5 to 20% by weight.
One embodiment of the lubricating oil compositions of the invention comprises (A) a lubricating oil base and (B) the ethylene/&agr;-olefin copolymer in an amount of 1 to 30% by weight.
The other embodiment of the lubricating oil compositions of the invention comprises (A) a lubricating oil base, (B) the ethylene/&agr;-olefin copolymer in an amount of 0.1 to 5% by weight, and (C) a pour-point depressant in an amount of 0.05 to 5% by weight.
BEST MODE TO CARRY OUT THE INVENTION
The following are detailed descriptions on the viscosity modifier for lubricating oil and the lubricating oil compositions of the invention. In this specification, all the numbers for material amount, reaction conditions, molecular weight, carbon atoms, etc. should be read with the term “about” within the limit ensuring the good technical understanding except in the examples or unless otherwise mentioned.
Viscosity modifier for Lubricating Oil
The viscosity modifier for lubricating oil of the invention comprises a copolymer (B), which will be detailed later, containing ethylene (i), an &agr;-olefin of 3 or more carbon atoms (ii), and a higher &agr;-olefin of 4 to 20 carbon atoms (iii) in which the carbon number always exceeds that of said &agr;-olefin of 3 or more carbon atoms by a majority of 1 or more (said copolymer (B) will sometimes be referred to as an ethylene/&agr;-olefin copolymer (B) hereinafter).
Examples of the &agr;-olefin of 3 or more carbon atoms (ii) are propylene, 1-butene, 1-pentene, 1-hexene, 3-methyl-1-butene, 3-methyl-1-pentene, 3-ethyl-1-pentene, 4-methyl-1-pentene, 4-methyl-1-hexene, 4,4-dimethyl-1-hexene, 4,4-dimethyl-1-pentene, 4-ethyl-1-hexene, 3-ethyl-1-hexene, 1-octene, 1-decene, 1-dodecene, 1-tetradecene, 1-hexadecene and 1-octadecene. Those having 3 to 19 carbon atoms are preferable among
Kaneshige Ryousuke
Okada Keiji
McAvoy Ellen M
Mitsui Chemicals Inc.
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