Lubricating oil additive and lubricating oil composition containing the same

Abstract

To provide a lubricating oil additive that can impart a good wear prevention property to a lubricating oil base oil in addition to an excellent friction reduction property in various speed ranges, and a lubricating oil composition containing the same.SOLUTION: There is provided an additive for a lubricating oil, which comprises: a specific phosphite compound; and a specific ether compound, wherein a mass ratio of the phosphite compound to the ether compound (phosphite compound: ether compound) is 99.9: 0.1 to 90.0: 10.0, and a lubricating oil composition containing the additive for a lubricating oil.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a lubricating oil additive and a lubricating oil composition containing the same. More specifically, the present invention relates to a lubricating oil additive that can impart excellent friction reducing properties and good wear prevention properties to a lubricating oil base oil (hereinafter also referred to as base oil) over a variety of speed ranges, and to a lubricating oil composition containing the same. [Background technology]

[0002] Lubricants used in engine oils, hydraulic fluids, metalworking oils, etc. consist of base oils and additives with various functions. Lubricants used in metalworking oils, which are used under particularly harsh conditions, contain extreme pressure agents to improve extreme pressure and wear prevention. Examples of extreme pressure agents include chlorine-based, sulfur-based, and phosphorus-based agents. However, while chlorine-based extreme pressure agents have excellent extreme pressure properties, their use is avoided due to the risk of skin irritation and metal rust, which can lead to a deterioration of the working environment. Chlorine-based extreme pressure agents tend to be avoided, particularly in applications where mist is generated, such as metalworking oils. Sulfur-based compounds also have excellent lubricity and extreme pressure properties, but many of them have a distinctive odor, so they tend to be avoided in lubrication applications where they may come into contact with the human body. Therefore, phosphorus-based additives such as phosphate esters (salts) are used as alternatives to these chlorine- and sulfur-based extreme pressure agents. Patent Document 1, for example, discloses compounds such as amine salts of phosphate esters or phosphites having alkyl chains or polyoxyalkylene chains as such additives.

[0003] Furthermore, friction modifiers are used in metalworking oils and the like to reduce friction. Reducing the coefficient of friction is expected to extend tool life and improve workability. For example, Patent Document 2 discloses a lubricating oil composition in which a phosphite ester and a medium or higher fatty acid are combined and blended into a lubricating base oil, with the aim of reducing the coefficient of friction and achieving high extreme-pressure properties.

[0004] Meanwhile, in recent years, from the perspective of precision machining, lubricating oils have been increasingly made less viscous to enhance penetration, cooling, and cleaning effects. However, lowering viscosity results in thinner oil films, which can easily shift to the boundary lubrication region under operating conditions that were previously in the hydrodynamic lubrication region, potentially causing damage to equipment and tools due to increased friction coefficients and wear. In particular, at low speeds, such as when starting equipment, the boundary lubrication region increases, resulting in a higher friction coefficient and increased risk of wear. Therefore, there is a demand for additives that consistently demonstrate excellent friction reduction properties across a wide range of speeds while also providing good wear prevention.

[0005] However, the above-mentioned prior art has not sufficiently addressed the above problems, and there has been a demand for the development of an additive that stably exhibits excellent friction reduction properties even at low speeds and also has good anti-wear properties. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2001-81491 [Patent Document 2] Japanese Patent Application Laid-Open No. 2016-108492 Summary of the Invention [Problem to be solved by the invention]

[0007] As described above, an object of the present invention is to solve the above problems, and more specifically, to provide a lubricating oil additive that can impart good anti-wear properties to a lubricating oil base oil in addition to excellent friction reducing properties over a variety of speed ranges, and a lubricating oil composition containing the same. [Means for solving the problem]

[0008] As a result of intensive research into solving the above problems, the present inventors have found that the above problems can be solved by a lubricating oil additive comprising a specific quantitative ratio of the compounds represented by formula (1) and formula (2), and a lubricating oil composition containing the same in a base oil. That is, the present invention is the following [1] to [2].

[0009] [1] A lubricating oil additive comprising a phosphite ester compound represented by formula (1) and an ether compound represented by formula (2), wherein the mass ratio of the phosphite ester compound to the ether compound (phosphite ester compound:ether compound) is 99.9:0.1 to 90.0:10.0. [ka] [In formula (1), R 1 and R 2 each independently represents a hydrocarbon group having 1 to 22 carbon atoms. [ka] [In formula (2), R 3 and R 4 each independently represents a hydrocarbon group having 1 to 22 carbon atoms. [2] A lubricating oil composition containing 0.01 to 30 mass % of the lubricating oil additive according to [1] above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a lubricating oil additive that can impart excellent friction reducing properties over a variety of speed ranges to a lubricating oil base oil as well as good wear prevention properties, and a lubricating oil composition containing the same. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the lubricating oil additive of the present invention (hereinafter also referred to as "the additive of the present invention") and a lubricating oil composition containing the additive of the present invention and a lubricating oil base oil will be described in detail. In this specification, numerical ranges defined using the symbol "to" are inclusive of the numerical values ​​at both ends (upper and lower limits) of the symbol "to." For example, "2 to 5" means 2 or more and 5 or less.

[0012] [Lubricant additives] The additive of the present invention is a lubricating oil additive comprising a phosphite ester compound represented by the following formula (1) and an ether compound represented by the following formula (2), wherein the mass ratio of the phosphite ester compound to the ether compound (phosphite ester compound:ether compound) is 99.9:0.1 to 90.0:10.0. The phosphite ester compound represented by formula (1) and the ether compound represented by formula (2) are the main components of the lubricating oil additive, and the total amount of the phosphite ester compound represented by formula (1) and the ether compound represented by formula (2) in the lubricating oil additive is preferably 90 mass% or more, more preferably 95 mass% or more, and even more preferably 97 mass% or more.

[0013] <Phosphite ester compounds> The phosphite compound is represented by the following formula: [ka] In formula (1), R 1 and R 2 are each independently a hydrocarbon group having 1 to 22 carbon atoms, and the hydrocarbon group may be saturated or unsaturated, and may be either linear or branched. 1 and R 2 may be the same or different. R 1 and R 2Examples of the alkyl group include linear saturated hydrocarbon groups such as methyl, ethyl, propyl, butyl, hexyl, heptyl, octyl, decyl, lauryl, myristyl, palmityl, stearyl, and behenyl; branched saturated hydrocarbon groups such as isopropyl, isobutyl, t-butyl, isopentyl, isooctyl, 2-ethylhexyl, isononyl, 3,5,5-trimethylhexyl, isodecyl, isostearyl, 2-octyldecyl, 2-octyldodecyl, and 2-hexyldecyl; and unsaturated hydrocarbon groups such as allyl, palmitoyl, oleyl, and linoleyl. If the number of carbon atoms is 23 or more, sufficient wear prevention properties may not be obtained.

[0014] R 1 and R 2 From the viewpoint of anti-wear properties, R is preferably a linear or branched saturated or unsaturated hydrocarbon group having 4 to 18 carbon atoms, more preferably a branched saturated or unsaturated hydrocarbon group having 8 to 18 carbon atoms, and particularly preferably a branched saturated hydrocarbon group having 8 to 13 carbon atoms. 1 and R 2 is preferably a 2-ethylhexyl group, a lauryl group, or an oleyl group, and particularly preferably a 2-ethylhexyl group. The method for producing the phosphite ester compound represented by the above formula (1) is not particularly limited, but examples include a method in which phosphorous acid and an alcohol are subjected to an esterification reaction at, for example, 80 to 180° C. The esterification reaction for producing the present ester compound is preferably carried out using an alcohol in an amount at a molar ratio of at least two times that of the acid.

[0015] <Ether compounds> The ether compound is represented by the following formula: [ka] In formula (2), R 3 and R 4are each independently a hydrocarbon group having 1 to 22 carbon atoms, and the hydrocarbon group may be saturated or unsaturated, and may be either linear or branched. 3 and R 4 may be the same or different. R 3 and R 4 Examples of the alkyl group include linear saturated hydrocarbon groups such as methyl, ethyl, propyl, butyl, hexyl, heptyl, octyl, decyl, lauryl, myristyl, palmityl, stearyl, and behenyl; branched saturated hydrocarbon groups such as isopropyl, isobutyl, t-butyl, isopentyl, isooctyl, 2-ethylhexyl, isononyl, 3,5,5-trimethylhexyl, isodecyl, isostearyl, 2-octyldecyl, 2-octyldodecyl, and 2-hexyldecyl; and unsaturated hydrocarbon groups such as allyl, palmitoyl, oleyl, and linoleyl. If the alkyl group has 23 or more carbon atoms, the solubility in the base oil may be insufficient. R 3 and R 4 From the viewpoint of reducing the coefficient of friction, R is preferably a linear or branched saturated or unsaturated hydrocarbon group having 4 to 18 carbon atoms, more preferably a linear saturated or unsaturated hydrocarbon group having 8 to 18 carbon atoms, and particularly preferably a linear saturated hydrocarbon group having 8 to 12 carbon atoms. 3 and R 4 is preferably a 2-ethylhexyl group, a decyl group, a lauryl group, or an oleyl group, and particularly preferably a lauryl group. The method for producing the ether compound represented by the above formula (2) is not particularly limited, but for example, the Williamson ether synthesis method in which an alcohol and an alkyl halide are reacted under basic conditions can be mentioned.

[0016] <Phosphite monoester compound> From the viewpoint of anti-wear properties, the additive of the present invention preferably further contains a phosphite monoester compound in addition to the phosphite ester compound and the ether compound. The phosphorous monoester compound is represented by the following formula: [ka] [In formula (3), R 5 is a hydrocarbon group having 1 to 22 carbon atoms, and X is a hydrogen atom or an organic ammonium group.

[0017] In formula (3), R 5 represents a hydrocarbon group having 1 to 22 carbon atoms, and the hydrocarbon group may be saturated or unsaturated, and may be either linear or branched. R 5 If the number of carbon atoms is 23 or more, sufficient wear prevention properties may not be obtained. R 5 Examples of the alkyl group include linear saturated hydrocarbon groups such as methyl, ethyl, propyl, butyl, hexyl, heptyl, octyl, decyl, lauryl, myristyl, palmityl, stearyl, and behenyl groups; branched saturated hydrocarbon groups such as isopropyl, isobutyl, t-butyl, isopentyl, isooctyl, 2-ethylhexyl, isononyl, 3,5,5-trimethylhexyl, isodecyl, isostearyl, 2-octyldecyl, 2-octyldodecyl, and 2-hexyldecyl groups; and unsaturated hydrocarbon groups such as palmitoyl, oleyl, and linoleyl groups. R 5 From the viewpoint of anti-wear properties, R is preferably a linear or branched saturated or unsaturated hydrocarbon group having 4 to 18 carbon atoms, more preferably a branched saturated or unsaturated hydrocarbon group having 8 to 18 carbon atoms, and particularly preferably a branched saturated hydrocarbon group having 8 to 12 carbon atoms. 5 is preferably a 2-ethylhexyl group, a lauryl group, or an oleyl group, and particularly preferably a 2-ethylhexyl group.

[0018] In formula (3), X represents a hydrogen atom or an organic ammonium, and X is more preferably an organic ammonium. When X is an organic ammonium, it is an organic ammonium having a saturated or unsaturated hydrocarbon group having 1 to 24 carbon atoms bound to a nitrogen atom, and the hydrocarbon group may be saturated or unsaturated and may be linear or branched. Among the hydrocarbon groups contained in the organic ammonium, at least one is preferably a linear or branched saturated or unsaturated hydrocarbon group having 12 to 24 carbon atoms, more preferably a linear or branched saturated or unsaturated hydrocarbon group having 18 to 24 carbon atoms, and particularly preferably an unsaturated hydrocarbon group having 18 carbon atoms. Of these, among the hydrocarbon groups contained in the organic ammonium, at least one is preferably a linear or branched saturated or unsaturated hydrocarbon group having 12 to 24 carbon atoms, more preferably a linear or branched saturated or unsaturated hydrocarbon group having 18 to 24 carbon atoms, and particularly preferably an unsaturated hydrocarbon group having 18 carbon atoms. The hydrocarbon groups may be the same, or at least one hydrocarbon group may be different. Examples of organic ammonium include octylammonium, 2-ethylhexylammonium, laurylammonium, oleylammonium, stearylammonium, dioctylammonium, triethylamine, trioctylamine, dimethyllaurylamine, and dimethylstearylamine. From the viewpoint of anti-wear properties, laurylammonium, oleylammonium, dimethyllaurylammonium, and trioctylammonium are preferred, and oleylammonium is particularly preferred.

[0019] Next, a method for producing the phosphorous monoester compound represented by the above formula (3) will be described. The method for producing the phosphite monoester compound represented by formula (3) is not particularly limited, and when X is a hydrogen atom, for example, a method of esterifying phosphorous acid with an alcohol (hereinafter, referred to as the first step) can be mentioned. When X is an organic ammonium, the compound can be produced by the first step and a second step of neutralizing the phosphite monoester compound obtained in the first step with an amine compound.

[0020] The first step will be described. An example of such a method is to carry out an esterification reaction between an alcohol having a hydrocarbon group with 1 to 22 carbon atoms and phosphorous acid at a temperature of, for example, 80 to 180°C.

[0021] Next, the second step will be described. The phosphorous monoester compound and the amine compound produced by the production method in the first step can be neutralized at, for example, 20 to 60° C. From the viewpoint of stability over time, the molar ratio of phosphorous monoester to amine compound is preferably in the range of 60:40 to 40:60, more preferably 55:45 to 45:55, and particularly preferably 52:48 to 48:52.

[0022] In the lubricating oil additive of the present invention, the mass ratio of the phosphite ester compound to the ether compound (phosphite ester compound:ether compound) is 99.9:0.1 to 90.0:10.0. If the content of the phosphite ester compound in the lubricating oil additive is outside the above mass ratio range, the coefficient of friction will be high and prone to variation, resulting in poor anti-wear properties. The mass ratio of the phosphite compound to the ether compound (phosphite compound:ether compound) is preferably 99.9:0.1 to 92.0:8.0, more preferably 99.0:1.0 to 93.0:7.0, and particularly preferably 99.0:1.0 to 95.0:5.0. When the lubricating oil additive of the present invention contains a phosphite monoester compound, the content of the phosphite monoester compound is preferably 10 mass% or less, more preferably 5 mass% or less, and particularly preferably 3 mass% or less, based on the total mass of the phosphite ester compound and the ether compound, from the viewpoint of anti-wear properties, and is preferably 0.5 mass% or more, and more preferably 1 mass% or more.

[0023] [Lubricating oil composition] The lubricating oil composition of the present invention contains the additive of the present invention and a lubricating base oil. In the present invention, various lubricating base oils can be used as the lubricating base oil, including, for example, conventionally used lubricating base oils such as mineral oil, highly refined mineral oil, animal and vegetable oils and fats, synthetic esters, poly-α-olefins, and GTL (gas-to-liquid) oil. The content of the additive of the present invention in the lubricating oil composition of the present invention is 0.01 to 30 mass%, preferably 0.05 to 20 mass%, more preferably 0.1 to 10 mass%. If the content of the additive of the present invention is too low, sufficient stabilization of the friction coefficient and anti-wear properties may not be obtained. On the other hand, if the content of the additive of the present invention is too high, stabilization of the friction coefficient and anti-wear properties commensurate with the amount added may not be obtained. The content of the lubricating base oil in the lubricating oil composition of the present invention is 70 to 99.99 mass %, preferably 80 to 99.95 mass %, and more preferably 90 to 99.9 mass %. The lubricating oil composition of the present invention may contain additives other than the additive of the present invention, such as detergent-dispersants, viscosity index improvers, rust inhibitors, corrosion inhibitors, pour point depressants, and metal deactivators, as needed. The order of compounding, mixing, and adding each additive is not particularly limited, and various methods can be used. For example, a method of adding each compound represented by formula (1), formula (2), and formula (3) and various additives to a lubricating base oil and mixing them under heating, or a method of preparing a high-concentration solution of the additive in advance and mixing it with the lubricating base oil may be used. [Example]

[0024] The present invention will be described in more detail below with reference to examples and comparative examples.

[0025] Synthesis Examples 1 and 2 below show synthesis examples of the phosphite ester compound represented by formula (1), Synthesis Examples 3 and 4 below show synthesis examples of the ether compound represented by formula (2), Synthesis Example 5 below shows synthesis example of the phosphite monoester compound represented by formula (3), and Production Examples 1 and 2 below show production examples of additives comprising a phosphite ester compound, an ether compound, and a phosphite monoester compound.

[0026] [Synthesis Example 1, Compound 1-A of Formula (1)] A thermometer and nitrogen inlet tube were inserted into a 1-L four-neck flask, and 651 g (5 mol) of 2-ethylhexanol and 164 g (2 mol) of phosphorous acid were charged. The reaction was carried out at 120°C under reduced pressure of 200 Torr or less. The reaction was terminated when the decrease in acid value per hour reached 0.5 mg KOH / g or less. After the reaction was completed, unreacted raw materials were distilled off at 150°C under reduced pressure of 30 Torr or less to obtain compound 1-A of formula (1) shown in Table 1.

[0027] [Synthesis Example 2, Compound 1-B of Formula (1)] Compound 1-B of formula (1) shown in Table 1 was synthesized according to Synthesis Example 1, except that 2-ethylhexanol in Synthesis Example 1 was changed to lauryl alcohol.

[0028] [Table 1]

[0029] [Synthesis Example 3, Compound 2-A of Formula (2)] A thermometer and nitrogen inlet tube were inserted into a 1 L four-neck flask, and 184 g (0.99 mol) of lauryl alcohol, 224 g (0.90 mol) of 1-bromododecane, 32 g (0.09 mol) of tetrabutylammonium bromide, and 442 g of 48% aqueous sodium hydroxide solution were added and reacted at 70 °C. After the reaction was completed, the mixture was left to stand and the aqueous layer that separated into the lower layer was removed. The remaining reaction solution was washed five times with an equal amount of ion-exchanged water. Unreacted raw materials were then distilled off from the reaction solution at 150 °C under reduced pressure of 30 Torr or less, yielding compound 2-A of formula (2) shown in Table 2.

[0030] [Synthesis Example 4, Compound 2-B of Formula (2)] Compound 2-B of formula (2) shown in Table 2 was synthesized according to Synthesis Example 3, except that lauryl alcohol in Synthesis Example 3 was changed to 2-ethylhexanol and 1-bromododecane was changed to 1-bromo-2-ethylhexane.

[0031] [Table 2]

[0032] [Synthesis Example 5, Compound 3-A of Formula (3)] A thermometer and nitrogen inlet tube were inserted into a 1 L four-neck flask, and 260 g (2 mol) of 2-ethylhexanol and 180 g (2.2 mol) of phosphorous acid were charged. The reaction was carried out at 120 °C under reduced pressure of 200 Torr or less. The reaction was terminated when the decrease in acid value per hour reached 0.5 mg KOH / g or less. Subsequently, ion-exchanged water equivalent to 20% by mass of the reaction solution was added, stirred at 60 °C for 10 minutes, allowed to stand for 10 minutes, and the separated aqueous layer was removed. The mixture was then dehydrated by stirring at 100 °C for 1 hour at 30 Torr. After dehydration, 535 g (2 mol) of oleylamine was added and stirred at 25 °C for 0.5 hours to obtain compound 3-A of formula (3) shown in Table 3.

[0033] [Table 3]

[0034] [Production Example 1, Additive 1] A thermometer and a nitrogen inlet tube were inserted into a 1 L four-neck flask, and 480 g of compound 1-A synthesized in Synthesis Example 1, 10 g of compound 2-A synthesized in Synthesis Example 3, and 10 g of compound 3-A synthesized in Synthesis Example 5 were mixed and stirred at 25°C for 0.5 hours to obtain Additive 1.

[0035] [Production Example 2, Additives 2 to 8] Additives 2 to 8 shown in Table 4 were obtained by appropriately changing the compounding ratio of the compound of formula (1) and the compound of formula (2) in Production Example 1, adding the compound of (3) as needed, and performing the operations similar to Production Example 1. Note that lauryl alcohol was used as compound 2-C.

[0036] [Table 4]

[0037] [Preparation of Lubricating Oil Composition] Lubricating base oil (poly alpha olefin, kinematic viscosity (40 °C): approx. 50 mm 2 Additives 1 to 8 were blended at 0.5 mass % relative to the total mass of the lubricating oil (g / s), to obtain lubricating oil compositions of Examples 1 to 4 and Comparative Examples 1 to 4. The obtained lubricating oil compositions (test oils) were subjected to the following evaluation tests. The evaluation results are shown in Table 5 below.

[0038] (Friction test) The friction coefficient was evaluated using a multi-function friction and wear tester (BRUKER, UMT-TriboLab). The friction test was performed using a cylinder / disc. The cylinder was positioned 20 mm radius from the center of the disc. The cylinder had an outer diameter of 10 mm, a length of 14 mm, and was made of SUJ-2. The disc had an outer diameter of 70 mm, a width of 6.6 mm, and was also made of SUJ-2. The test conditions were a temperature of 25°C, a load of 20 N, and the rotation speed was gradually increased from 100, 50, 25, 10, 5, and 1 rpm. The friction coefficient was measured at each rotation speed. The measurement time at each rotation speed was 30 seconds. Each rotation speed was counted as one cycle, from 100 to 1 rpm, and the average friction coefficients of 10 cycles were calculated for 100, 10, and 1 rpm. The stability of the friction coefficient was calculated as the ratio of the friction coefficient at 100 rpm to that at 1 rpm (friction coefficient stability = friction coefficient at 100 rpm / friction coefficient at 1 rpm). The closer the stability of the friction coefficient is to 1, the more stable the friction reduction can be achieved regardless of the speed range.

[0039] In this test, the reduction in the friction coefficient was evaluated based on the friction coefficient at each rotation speed (100, 10, 1 rpm) according to the following criteria. ◎: Less than 0.120 〇: 0.120 or more and less than 0.150 ×: 0.150 or more

[0040] The stability of the friction coefficient (friction coefficient at 100 rpm / friction coefficient at 1 rpm) was evaluated according to the following criteria. ◎: 0.75 or higher ○: 0.74~0.60 ×: Less than 0.60

[0041] (wear test) Wear resistance was evaluated using an SRV tester (OPTIMOL Schwingungs Reihungundund Verschleiss Tester Model 4). The SRV test was performed using a ball and a disk, and the test specimens were made of SUJ-2. The test conditions were a test temperature of 120°C, a load of 100 N, an amplitude of 1 mm, and a vibration frequency of 50 Hz. The diameter of the wear scar was measured after 25 minutes of testing. The evaluation was based on the wear scar diameter and was carried out according to the following criteria. ◎: Less than 350 μm ○: 350 μm or more and less than 400 μm ×: 400μm or more

[0042] [Table 5]

[0043] As is clear from the results shown in Table 5, Additives 1 to 4 according to the present invention can reduce the coefficient of friction relative to the lubricating base oil, reducing variation and imparting good wear prevention properties. On the other hand, Additives 5 and 6, in which the mass ratio of the compounds of formula (1) and formula (2) was outside the range of the present invention, Additive 7, in which a compound other than formula (2) was blended, and Additive 8, which consisted of the compound of formula (2), had high and variable friction coefficients at low speeds, and were inferior in wear prevention properties.

Claims

1. A lubricating oil additive comprising a phosphite ester compound represented by formula (1) and an ether compound represented by formula (2), wherein the mass ratio of the phosphite ester compound to the ether compound (phosphite ester compound:ether compound) is 99.9:0.1 to 90.0:10.

0. 【Chemistry 1】 [In formula (1), R １ and R ２ each independently represents a hydrocarbon group having 1 to 22 carbon atoms.] 【Chemistry 2】 [In formula (2), R ３ and R ４ each independently represents a hydrocarbon group having 1 to 22 carbon atoms.]

2. A lubricating oil composition containing 0.01 to 30 mass % of the lubricating oil additive according to claim 1.

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