JP7809965B2 - lubricating oil additives - Google Patents

Description

The present invention relates to a lubricating oil additive.

Lubricants have traditionally been used in internal combustion engines, automatic transmissions, and other mechanical devices to ensure their smooth operation. In recent years, in order to protect the global environment, the fuel-saving performance required of lubricants has become increasingly high, and there is a demand for further improvements in the viscosity index, which is one indicator of this performance.

The copolymer comprising structural units derived from a conjugated diene and structural units derived from an aromatic vinyl compound, disclosed in Patent Document 1, is used as a viscosity index improver for lubricating oils. Furthermore, the copolymer of alkyl (meth)acrylate, disclosed in Patent Document 2, is also used as a viscosity index improver for lubricating oils.

International Publication No. 2014/142001 JP 2017-197728 A

The viscosity index improver disclosed in Patent Document 1 has a problem in that when the content of structural units derived from aromatic vinyl compounds is high, the solubility in oil decreases.
The copolymer disclosed in Patent Document 2 is effective in improving the viscosity index of lubricating oils, but uses petroleum-derived monomers as raw materials, and does not meet recent social needs. In order to build a carbon-recycling society, there is a need to develop a different type of viscosity index improver that uses plant-derived monomers and has the same effect.

The present invention aims to provide a lubricating oil additive that contains structural units derived from a plant-derived monomer and that, when added to oil, has excellent viscosity index improving properties and oil solubility. The plant-derived monomer can be confirmed by measuring its radiocarbon concentration.

To solve the above problems, the present invention includes the following aspects.

[1]: A lubricating oil additive containing a polymer containing structural units derived from myrcene.

[2]: The lubricating oil additive described in [1], wherein the polymer further contains a structural unit a derived from an alkyl (meth)acrylate.

[3]: The lubricating oil additive described in [2], wherein the alkyl group in the structural unit a derived from the alkyl (meth)acrylate has 2 to 32 carbon atoms.

[4]: The lubricating oil additive according to either [2] or [3], wherein the content of the myrcene-derived structural units is 1 to 50 mass% and the content of the structural unit a is 50 to 99 mass% out of 100 mass% of the total of all structural units of the polymer.

[5]: A lubricating oil additive according to any one of [1] to [4], wherein the weight-average molecular weight of the polymer is 5,000 to 200,000.

The polymer contained in the lubricating oil additive of the present invention can be produced using plant-derived monomers as raw materials, and the lubricating oil additive of the present invention containing this polymer exhibits excellent viscosity index improving properties and oil solubility when added to a lubricating oil.

The following describes in detail an embodiment of the present invention. However, the following description of the components is merely an example of an embodiment of the present invention, and the present invention is not limited to these details. Various modifications can be made within the scope of the gist of the present invention.

[Terminology]
The following definitions of terms are used herein:
The term "structural unit" refers to a unit that constitutes a polymer derived from a monomer, i.e., a structural unit formed by polymerization of a monomer, or a structural unit in which a portion of the structural unit has been converted into a different structure by modifying a polymer.
The term "polymer" as used herein refers to a polymer containing a structural unit derived from myrcene and preferably further containing a structural unit a derived from an alkyl (meth)acrylate. Here, "(meth)acrylate" refers to either or both of an acrylate and a methacrylate.
In this specification, the terms "weight average molecular weight" and "number average molecular weight" refer to the weight average molecular weight and number average molecular weight measured by gel permeation chromatography (GPC) in terms of standard polystyrene.

The lubricating oil additive of the present invention is a lubricating oil additive containing a polymer containing structural units derived from myrcene (hereinafter, sometimes referred to as the "polymer of the present invention").

The polymer of the present invention contains a structural unit derived from myrcene (hereinafter sometimes referred to as a "myrcene unit") as an essential structural unit, but preferably also contains a structural unit a derived from alkyl (meth)acrylate, and may further contain structural units other than myrcene units and structural units a derived from alkyl (meth)acrylate (hereinafter sometimes referred to as "other structural units b").

[Structural units of polymer]
The myrcene unit, the structural unit a, and the other structural unit b that constitute the polymer of the present invention will be described in detail below.

<Myrcene units>
The polymer of the present invention contains a myrcene unit. Myrcene is available as a plant-derived monomer and is preferred from the perspective of building a carbon-recycling society.

When the total of all structural units of the polymer of the present invention is taken as 100% by mass, the lower limit of the myrcene unit content is preferably 1% by mass or more, more preferably 2% by mass or more, and even more preferably 3% by mass or more, from the viewpoint of solubility in oil and the inclusion of plant-derived raw materials. The upper limit of the myrcene unit content is preferably 50% by mass or less, more preferably 40% by mass or less, and even more preferably 30% by mass or less, from the viewpoint of improving the viscosity index. The proportion of myrcene units relative to 100% by mass of the total of all structural units of the polymer can be calculated from the amount of myrcene charged as a raw material monomer for the polymer of the present invention to introduce myrcene units.

<Structural unit a>
The polymer of the present invention preferably further contains, in addition to the myrcene unit, a structural unit a derived from an alkyl(meth)acrylate. Examples of the structural unit a derived from an alkyl(meth)acrylate include structural units derived from alkyl(meth)acrylates such as (meth)acrylates of linear or branched alkyl alcohols, such as methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate, propyl(meth)acrylate, hexyl(meth)acrylate, 2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, dodecyl(meth)acrylate, and tridecyl(meth)acrylate; and (meth)acrylates of cyclic alkyl alcohols, such as cyclohexyl(meth)acrylate.

In particular, from the viewpoint of improving the viscosity index of the oil and the solubility in oil, the lower limit of the number of carbon atoms in the alkyl group in the structural unit a derived from alkyl(meth)acrylate is preferably 2 or more, more preferably 4 or more, even more preferably 6 or more, and particularly preferably 8 or more. The upper limit of the number of carbon atoms in the alkyl group in the structural unit a derived from alkyl(meth)acrylate is preferably 32 or less, more preferably 20 or less, and even more preferably 15 or less.
The polymer of the present invention may contain only one type of structural unit a derived from these alkyl (meth)acrylates, or may contain two or more types.

When the total of all structural units of the polymer of the present invention is taken as 100% by mass, from the viewpoint of improving the viscosity index, the lower limit of the content of structural unit a derived from alkyl (meth)acrylate is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more. The upper limit of the content of structural unit a derived from alkyl (meth)acrylate is preferably 99% by mass or less, more preferably 98% by mass or more, and even more preferably 97% by mass or less. The proportion of structural unit a relative to 100% by mass of the total of all structural units of the polymer can be calculated from the amount of alkyl (meth)acrylate used to introduce structural unit a as a raw material monomer for the polymer of the present invention.

<Other structural units b>
The structural unit b is a structural unit other than the above-mentioned myrcene unit and structural unit a.
Other raw material monomers used to introduce the structural unit b into the polymer of the present invention include, for example, vinyl cyanide monomers such as acrylonitrile and methacrylonitrile; vinyl ether monomers such as vinyl methyl ether and vinyl ethyl ether; carboxylic acid vinyl monomers such as vinyl acetate and vinyl butyrate; olefin monomers such as ethylene, propylene, and isobutylene; halogenated vinyl monomers such as vinyl chloride and vinylidene chloride; maleimide monomers such as maleimide, N-phenylmaleimide, N-cyclohexylmaleimide, and N-methylmaleimide. These may be used alone or in combination of two or more.

The content of structural unit b is preferably 60% by mass or less, and more preferably 50% by mass or less, relative to 100% by mass of the total of all structural units of the polymer of the present invention. This is because a content of structural unit b of 60% by mass or less improves the solubility in oil when added to oil.

[Weight average molecular weight (Mw) of polymer]
From the viewpoint of the effect of improving the viscosity index of oil, the lower limit of the weight average molecular weight of the polymer of the present invention is preferably 5,000 or more, more preferably 10,000 or more. On the other hand, from the viewpoint of solubility in oil, the upper limit of the weight average molecular weight of the polymer of the present invention is preferably 200,000 or less, more preferably 150,000 or less.

[Number average molecular weight (Mn) of polymer]
From the viewpoint of the effect of improving the viscosity index of oil, the lower limit of the number average molecular weight of the polymer of the present invention is preferably 5,000 or more, more preferably 10,000 or more. On the other hand, from the viewpoint of solubility in oil, the upper limit of the number average molecular weight of the polymer of the present invention is preferably 150,000 or less, more preferably 100,000 or less.

[Method of producing polymer]
The method for producing the polymer of the present invention is not particularly limited, and the polymer can be produced by polymerizing the raw material monomers, in the above-mentioned suitable ratios, myrcene for introducing myrcene units, preferably the alkyl (meth)acrylate for introducing structural unit a, and, if necessary, other monomers for introducing structural unit b, by a known polymerization method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. Of these, solution polymerization is preferred from the viewpoint of compatibility with lubricating oil additives.
The method for producing the polymer of the present invention by solution polymerization will be described in detail below.

<Polymerization initiator>
The polymer of the present invention can be produced by a known method using a known radical polymerization initiator. Examples of the radical polymerization initiator include organic peroxides and azo compounds. The radical polymerization initiator can be used alone or in combination of two or more.

Specific examples of suitable organic peroxides used as radical polymerization initiators include t-butyl peroxypivalate, o-methylbenzoyl peroxide, bis-3,5,5-trimethylhexanoyl peroxide, octanoyl peroxide, cyclohexanone peroxide, benzoyl peroxide, methyl ethyl ketone peroxide, dicumyl peroxide, lauroyl peroxide, diisopropylbenzene hydroperoxide, t-butyl hydroperoxide, di-t-butyl peroxide, t-butylperoxy-2-ethylhexanoate, and 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate.
Specific examples of the azo compound include 2,2'-azobisisobutyronitrile, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobis(2,4-dimethyl-4-methoxyvaleronitrile).
Among these, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate and the like are preferred.

(Polymerization solvent)
In producing the polymer of the present invention, a general organic solvent can be used as the polymerization solvent, but paraffin oil is preferably used from the viewpoint of compatibility with the lubricating oil additive. In this case, the polymer in the paraffin oil used as the polymerization solvent can be used as the lubricating oil additive of the present invention.

[Lubricant Additives]
The lubricating oil additive of the present invention may contain, as a base oil together with the polymer of the present invention, one or more oil components selected from paraffinic, naphthenic, aromatic, etc. The lubricating oil additive of the present invention may contain only one polymer of the present invention, or may contain two or more polymers differing in the type or composition of the structural unit b.

The lubricating oil additive of the present invention may contain various additives other than the polymer of the present invention and the base oil, such as detergents, dispersants, antioxidants, oiliness improvers, friction and wear modifiers, extreme pressure agents, antifoaming agents, demulsifiers, and corrosion inhibitors.
The proportion of the polymer of the present invention in the lubricating oil additive of the present invention is preferably 0.1 to 100 mass% relative to 100 mass% of the total of all constituent components of the lubricating oil additive. When a base oil is contained, it is usually preferable that the polymer of the present invention is contained in an amount of 0.1 to 50 parts by mass relative to 100 parts by mass of the base oil.

When the lubricating oil additive of the present invention is used in various lubricating oils such as drive system lubricants, automatic transmission fluids, hydraulic fluids, and engine oils, the viscosity index, measured by the method described in the Examples section below, is preferably in the range of 140 to 250, and more preferably in the range of 150 to 200. When used in the above applications, a viscosity index within this range can reduce the fuel efficiency of vehicles, etc.

The present invention will be described in detail below using examples and comparative examples, but the present invention is not limited to the following descriptions.

<Proportion of constituent units>
The proportion of each structural unit in the polymer was calculated from the amount of monomer charged. The proportion of myrcene units relative to 100% by mass of the total of all structural units in the polymer was calculated from the amount of myrcene charged. The proportion of structural unit a relative to 100% by mass of the total of all structural units in the polymer was calculated from the amount of alkyl (meth)acrylate charged.

<Weight average molecular weight (Mw) and number average molecular weight (Mn)>
The weight average molecular weight (Mw) and number average molecular weight (Mn) of the polymer were determined by GPC (gel permeation chromatography) in terms of standard polystyrene. The measuring device and conditions are as follows:
Apparatus: HLC-8420GPC manufactured by Tosoh Corporation Separation column: TSK-GEL SUPER HM-H (exclusion limit molecular weight = 4 x 10 ⁸ )
6.0mmφ×150mm
Detector: RI (differential refractometer), UV
Eluent: tetrahydrofuran (THF)
・Flow rate: 0.600mL/min
Sample concentration: 0.02 g/10 mL
Column temperature: 40°C

<Solution state>
The transparency of the polymerization solution was visually confirmed and evaluated as follows.
◯: Transparent ×: Opaque or insoluble matter precipitated

<Kinematic viscosity>
The kinematic viscosity of the polymerization solution was measured at 40°C and 100°C in accordance with JIS K2283. Vk40 shown in Table 1 below represents the kinematic viscosity at 40°C, and Vk100 represents the kinematic viscosity at 100°C.

<Viscosity index (VI)>
The viscosity index of the polymerized solution was measured in accordance with JIS K 2283. The viscosity index is a physical property value that indicates the temperature dependency of the viscosity of a lubricating oil.

Example 1
A dried Schlenk tube was charged with 33.3 parts by mass of lubricating base oil (SK Lubricants Co., Ltd., trade name: YUBASE4), 80 parts by mass of alkyl methacrylate (Mitsubishi Chemical Corporation, trade name: ACRYESTER SL, alkyl group carbon number: 12 to 13), and 20 parts by mass of myrcene (Yasuhara Chemical Co., Ltd.). The atmosphere inside the Schlenk tube was thoroughly purged with nitrogen, and the temperature was raised to 100°C. Next, 2.2 parts by mass of 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate (NOF Corporation, trade name: Perocta O) was added as a polymerization initiator, and the reaction was carried out for 10 hours. The resulting polymerized solution was used as a lubricating oil additive and subjected to the various evaluations described above. The results are shown in Table 1.

Examples 2 to 6
A polymer solution was obtained in the same manner as in Example 1, using the amounts of ingredients shown in Table 1. Various evaluations were carried out using the obtained polymer solution. The results are shown in Table 1.

Comparative Example 1
Various evaluations were carried out using only a lubricating base oil (manufactured by SK Lubricants Co., Ltd., trade name: YUBASE4). The results are shown in Table 1.

In Table 1, the abbreviations for the raw material monomers are as follows:
SLMA: Acryester SL (manufactured by Mitsubishi Chemical Corporation, alkyl group carbon number: 12 to 13)
BMA: Acrylate B (manufactured by Mitsubishi Chemical Corporation, n-butyl methacrylate)
St: styrene monomer (manufactured by Nacalai Tesque, Inc.)

As shown in Table 1, Examples 1 to 6, which used the polymer of the present invention containing myrcene units and structural unit a derived from alkyl (meth)acrylate, all exhibited good solubility in base oil. Furthermore, Examples 1 to 6 all had better kinematic viscosity and viscosity index (VI) than Comparative Example 1, which did not use a polymer.

The lubricating oil additive of the present invention has excellent viscosity index improving ability and oil solubility, and is suitable for various lubricating oils such as drive system lubricating oils, automatic transmission oils, hydraulic oils, and engine oils.

Claims (5)

A lubricating oil additive containing a polymer containing structural units derived from myrcene ,
the polymer further contains a structural unit a derived from an alkyl (meth)acrylate,
the alkyl group in the structural unit a derived from the alkyl (meth)acrylate has 2 to 32 carbon atoms,
The lubricating oil additive, wherein the content of the structural unit derived from myrcene is 1 to 50 mass% and the content of the structural unit a is 50 to 99 mass% based on 100 mass% of the total of all structural units of the polymer . 2. The lubricating oil additive according to claim 1 , wherein the polymer has a weight average molecular weight of 5,000 to 200,000. 3. The lubricating oil additive according to claim 1, wherein the alkyl group in the structural unit a derived from the alkyl (meth)acrylate has 4 or more and 20 or less carbon atoms. The lubricating oil additive according to any one of claims 1 to 3, comprising the polymer and a base oil, wherein the base oil is one or more of paraffinic, naphthenic, and aromatic oil components. The lubricating oil additive according to claim 4, wherein the polymer is contained in an amount of 0.1 to 50 parts by mass per 100 parts by mass of the base oil.