Triblock polyalkylene glycol for two-phase lubricants

Abstract

A composition is disclosed that exhibits two phases at low temperatures (e.g., below about 50° C.) but only one phase at high temperatures (e.g., above about 90° C.). The composition includes a low-viscosity base oil that is a hydrocarbon oil, and a high-viscosity base oil that is a triblock polyalkylene glycol derived from a copolymer of 1,2-propylene oxide and 1,2-butylene oxide having a PO-BO-PO polymerization sequence with a PO / BO ratio of 25 / 75 to 90 / 10 wt %.

Description

[Technical Field]

[0001] This invention relates to a new type of material suitable for use as a lubricant. These materials are triblock polyalkylene glycols, which, when blended with hydrocarbon oils, tend to exhibit a two-phase state at one temperature and a single-phase state at a different temperature.

[0002] Introduction Industrial lubricants are typically single-phase, fixed-composition materials made from a base stock into which various performance-enhancing additives may be incorporated. Typically, lubricants are selected to optimize the performance, function, and protection of systems lubricated under intended operating conditions, such as gears, cam-driver pairs, roller bearings, fluid bearings, or pumps.

[0003] To optimize system performance, lubricants are formulated by selecting one or more base stocks and additives that meet the system's needs when combined. Viscosity characteristics are an important consideration when formulating lubricants, as the appropriate viscosity balances energy loss (due to viscous resistance) and wear (due to reduction in oil film thickness and viscosity). Anti-wear and anti-scuffing additives can help protect surfaces when the oil film between them becomes too thin. Depending on their composition, base stocks can have various beneficial properties, such as antioxidant properties, a good viscosity index, and low static friction.

[0004] While it is possible to optimize the lubricant selection for single-phase lubricants, optimal performance under dominant operating conditions (such as speed, load, and temperature) may be compromised when conditions change, or when the same lubricant is used to lubricate several parts, each with its own unique lubrication needs. Often, for simplicity's sake, one type of lubricant is used to lubricate a wide variety of machinery.

[0005] The use of single-phase lubricants requires a compromise between premature machine failure due to wear, fatigue, or scuffing caused by insufficient viscosity under one set of operating conditions, and excessive energy loss or overheating caused by lubricant viscosity being too high for a second set of operating conditions. Since machine or plant operators prefer to minimize downtime, this compromise usually favors higher viscosity lubricants, which reduce equipment failure but cause excessive energy loss during the low-temperature start-up period. When temperatures vary widely across the intended use of the lubricant, viscosity is typically optimized for use at its highest operating temperature, but a significant amount of energy is wasted due to the viscosity-temperature relationship, as the lubricant viscosity is too high at the normal, lower operating temperatures.

[0006] There has been significant innovation in developing lubricants that offer energy-efficient benefits that can improve fuel economy. This means that if a more energy-efficient lubricant is selected, less energy will be consumed when operating the equipment. One way to improve efficiency is to reduce friction losses in the equipment by developing a lubricant that reduces friction between moving parts. This can be achieved, for example, by using friction modifiers and / or by selecting a base oil that has an inherently low friction value. A second method is simply to reduce the viscosity of the lubricant. Lubricants with lower viscosity consume less energy in internal friction within the lubricant. However, if the viscosity of the lubricant is too low, excessive wear may occur, and ultimately, the equipment may be damaged due to an insufficient amount of lubricant film thickness.

[0007] Two-phase lubricants for improving cold-starting of automotive engines are disclosed in French Patent No. 2,205,931 and U.S. Patent No. 5,602,085. These references disclose a process for combining a denser, lower-viscosity phase with a lower-density, higher-viscosity phase such that a homogeneous phase with lubrication properties characteristic of conventional engine lubricants exists when the engine is at its operating temperature. When the engine is cold, the phases separate, so when the engine is started under cold conditions, only the low-viscosity, high-density fluid is drawn into the oil pump. This reduces viscous resistance, improving the engine cranking speed and making starting easier. The lubricant phases mix as the engine warms up, and the mixed lubricant behaves in a conventional manner, exhibiting a large viscosity change with temperature.

[0008] The lubricant should consist of a high-viscosity base oil and a low-viscosity base oil, with the high-viscosity base oil having a higher density than the low-viscosity base oil. Under low temperature and static conditions (e.g., when the device is not operating), the high-viscosity base oil separates to form a lower layer, while the low-viscosity base oil (having a lower density) forms an upper layer.

[0009] It is well known that a considerable amount of energy is consumed when conventional single-phase lubricants are pumped around the equipment during startup (single-phase lubricants remain single-phase over a wide operating temperature range). Energy loss due to viscous resistance can be more pronounced because the lubricant is more viscous at lower temperatures (than at higher temperatures).

[0010] In devices such as gear or transmission systems, the gears begin to rotate in the lubricant during startup. However, when the temperature is low (e.g., 20°C) during startup, if the lubricant is present as a two-phase lubricant, the gears will initially rotate in the low-viscosity base oil (upper phase). Therefore, the agitation energy loss is much lower than when the lubricant is homogeneous (single phase) and exists as a higher-viscosity fluid. This concept can improve energy efficiency through lubricant design and the method of lubricating equipment. As the lubricant temperature rises due to heat generated by friction, the high-viscosity and low-viscosity base oils mix to form a single phase of the lubricant, which then blends with each other.

[0011] Furthermore, it is well known that conventional lubricants, which are homogeneous (single-phase) at both low and high temperatures, exhibit a decrease in viscosity as the lubricant temperature rises, resulting in a thinner lubricant film and thus an increased probability of wear between friction surfaces. However, in a two-phase system, at higher temperatures, the high-viscosity base oil mixes with the low-viscosity base oil to create a more viscous lubricant, resulting in a thicker film and thus helping to prevent the occurrence of wear.

[0012] Therefore, there is a need for a novel lubricant solution or a method of using a novel lubricant solution that can provide improved energy efficiency compared to conventional lubricants while also achieving the primary goal of minimizing wear.

[0013] There is a constant need for new materials that can achieve a balance between energy efficiency and long-term wear resistance. [Overview of the project]

[0014] The present invention relates to a composition that exhibits two phases at low temperatures (e.g., below about 35°C) but only one phase at high temperatures (e.g., above about 90°C). This composition comprises a low-viscosity base oil, which is a hydrocarbon oil, and a high-viscosity base oil, which is a triblock polyalkylene glycol derived from a copolymer of 1,2-propylene oxide and 1,2-butylene oxide having a PO / BO ratio of 25 / 75 to 90 / 10% by weight and a polymerization order of PO-BO-PO. [Modes for carrying out the invention]

[0015] The present invention relates to a composition that exhibits two phases at low temperatures (e.g., about 30°C, 40°C, or even less than 50°C) but only one phase at high temperatures (e.g., about 100°C, 95°C, or even more than 90°C). The composition of the present invention comprises a low viscosity base oil which is a hydrocarbon oil and a high viscosity base oil which is a triblock polyalkylene glycol derived from a copolymer of 1,2-propylene oxide and 1,2-butylene oxide having a PO / BO ratio of 25 / 75 to 90 / 10% by weight and a polymerization order of PO-BO-PO.

[0016] The composition, i.e., lubricant system, of the present invention comprises two main components: a low-viscosity base oil which is a hydrocarbon oil, and a high-viscosity base oil which is an ABA triblock polyalkylene glycol derived from 1,2-propylene oxide as unit A and 1,2-butylene oxide as unit B. Block polymers are well known in the art and should be distinguished from random polymers in which units derived from PO and units derived from BO are polymerized simultaneously, resulting in a random distribution of monomers throughout the polymer backbone.

[0017] The American Petroleum Institute (API) classifies base oils into five categories (API 1509, Appendix E). Categories I-III are refined from crude petroleum. Group IV base oils are fully synthetic (polyalphaolefin) oils. Group V concerns other base oils not included in any of Groups I-IV. Groups I-III can be distinguished as follows: Group I has a sulfur content of less than 0.03% by weight and / or a saturated content of more than 90% by volume, and a viscosity index of 80-120. Group II has a sulfur content of 0.03% by weight or less, a saturated content of 90% by volume or more, and a viscosity index of 80-120. Group III has a sulfur content of 0.03% by weight or less, a saturated content of 90% by volume or more, and a viscosity index greater than 120.

[0018] The low-viscosity base oil used in this invention is selected from API classifications I to IV. The kinematic viscosity of the low-viscosity base oil at 40°C is preferably 8 to 100 mmHg. 2 The range of less than / s, more preferably 15-50 mm 2 It must be in the range of / s. The kinematic viscosity of the low viscosity base oil at 100°C is preferably 1.5 to 20 mm². 2 Range of / s, more preferably 2-15 mm 2 The range of / s, more preferably 3 to 10 mm 2 The range is / s. The density of the low viscosity base oil is preferably 0.80 to 0.90 g / cm³ at 15°C. 3 The range, more preferably 0.820 to 0.86 g / cm³ 3 This is within the range. It should be understood that two or more different types of low-viscosity base oils described herein can also be used in combination.

[0019] In general, Group I oils tend to be more soluble in the second component (i.e., ABA triblock polyalkylene glycol) than Group II oils, Group II oils are more soluble than Group III oils, and Group III oils are more soluble than Group IV oils. Therefore, Group IV oils tend to phase-separate more easily with the second component than Group I oils. This allows for some degree of control over the lubricant system, depending on the selected specific second component and the desired temperature for phase separation.

[0020] The second component of the lubricant system of the present invention is an ABA triblock polyalkylene glycol derived from 1,2-propylene oxide as unit A and 1,2-butylene oxide as unit B. The ratio of the unit derived from propylene oxide to the unit derived from butylene oxide is in the range of 1 / 3 to 10 / 1 by weight (i.e., the unit derived from BO constitutes 10% to about 76% by weight of the second component), preferably in the range of 1 / 3 to 3 / 1 by weight, and more preferably in the range of 1 / 2 to 2 / 1 by weight.

[0021] The kinematic viscosity of the high-viscosity polyalkylene glycol base oil at 40 °C is preferably in the range of 100 to 20,000 mm 2 / s, more preferably in the range of 200 to 5000 mm 2 / s, even more preferably in the range of 400 to 1000 mm 2 / s. The kinematic viscosity at 100 °C is preferably in the range of 20 to 500 mm 2 / s, more preferably in the range of 50 to 400 mm 2 / s, even more preferably in the range of 60 to 100 mm 2 / s. The density of the high-viscosity polyalkylene glycol base oil at 15 °C is in the range of 0.95 to 1.100 g / cm 3 , more preferably in the range of 0.960 to 1.05 g / cm 3 . It should be understood that two or more different types of high-viscosity base oils described herein can also be used in combination.

[0022] Typically, the ABA triblock polyalkylene glycol for use as the high-viscosity base oil of the present invention has a molecular weight in the range of 2000 to 8000 daltons, preferably 4000 to 6000 daltons, more preferably 4500 to 5500 daltons, when determined by OH value measurement.

[0023] Generally, higher levels of BO in the ABA triblock polyalkylene glycol tend to increase the solubility of the second component in the first component, which has also been found to allow for some adjustment of the system to reach a lubricant system that exhibits a good balance of efficiency and lubricity at different operating temperatures.

[0024] Typically, the lubricant system of the present invention comprises 40 to 95% by weight, more preferably 50 to 85% by weight of a low-viscosity base oil and 5 to 60% by weight, more preferably 15 to 50% by weight of a high-viscosity oil. It is to be understood that other oils or additives may be present in the lubricant system, and as a result, the weight percentages of the first and second components need not total 100%, but they may.

[0025] The lubricant system of the present invention may advantageously contain additives such as anti-wear agents, rust inhibitors, metal deactivators, hydrolysis inhibitors, antistatic agents, defoamers, antioxidants, dispersants, detergents, extreme pressure additives, friction modifiers, viscosity index improvers, pour point depressants, tackifiers, metal detergents, ashless dispersants, and corrosion inhibitors, which are generally known in the art. In some embodiments, the lubricant system of the present invention may be characterized by the substantially absence of any aliphatic esters.

[0026] The lubricant system of the present invention may be further characterized by its ability to exhibit two phases at low temperatures (e.g., about 30°C, 35°C, or even below 40°C) but only one phase at high temperatures (e.g., about 100°C, 95°C, or even above 90°C). The two phases can be demonstrated by either a clear boundary between the phases, or by a simple cloudiness or turbidity indicating that the phases are not miscible but there was not enough time to completely form completely separated layers. [Examples]

[0027] Table I lists the materials used in the examples.

[0028] [Table 1]

[0029] Synthesis of experimental polymers Synthesis of experimental OSP-A (75 / 25w / w PO / BO) A magnetically coupled stirrer head and temperature control device were installed in a 15 L conical reaction vessel, and 163.3 g of P400 (polypropylene glycol with a nominal molecular weight of 430 Daltons) and 20.0 g of 45% potassium hydroxide aqueous solution were added. The solution was stirred at 200 rpm and heated to a temperature of 115 °C. To remove water, a vacuum was applied and the solution was maintained at 30 mBar. The residual water was measured to be less than 1500 ppm after 2 hours under the above conditions using a Karl Fischer titrator. The solution was cooled to 110 °C, and the vacuum was released by introducing nitrogen into the reaction vessel.

[0030] The alkoxylation reaction is carried out in three steps. In the first step, 760 g of 1,2-propylene oxide is supplied to the solution at a rate of 7 g / min at 110°C while stirring at 320 rpm. After all the oxides have been supplied, the reaction is allowed to proceed at 110°C for 5 hours to decompose all the present oxides. In the second step, 930 g of 1,2-butylene oxide is supplied at a rate of 7 g / min at 130°C. After all the oxides have been supplied, the reaction is allowed to proceed at 130°C for 8 hours to decompose all the present oxides. In the third step, 1870 g of 1,2-propylene oxide is supplied at a rate of 5 g / min at 110°C. After all the oxides have been supplied, the reaction is allowed to proceed at 110°C for 18 hours to decompose all the present oxides. Throughout all three steps of the alkoxylation reaction, the pressure inside the reaction vessel is strictly monitored, and the oxide supply is restricted to ensure that the pressure does not exceed 3.5 bar.

[0031] Next, the solution is cooled to 80°C and mixed with 102 g of magnesium silicate at a stirring speed of 350 rpm for 1 hour. Subsequently, the resulting solution is removed from the reaction vessel and transferred to a porcelain Buchner filtration funnel equipped with filter paper having a pore size of 20 μm, and filtered under vacuum. The filtrate is maintained under a vacuum of less than 0.3 bar for 6 hours to obtain a clear solution.

[0032] Synthesis of experimental OSP-B (50 / 50 w / w PO / BO) A magnetically coupled stirrer head and temperature control device are attached to a 15 L conical reaction vessel, and 333.7 g of P400 and 29.7 g of 45% sodium hydroxide aqueous solution are added. The solution is stirred at 200 rpm and heated to a temperature of 115 °C. To remove water, a vacuum is applied and the solution is maintained at 30 mBar. The residual water is measured to be less than 1500 ppm after 2 hours under the above conditions using a Karl Fischer titrator. The solution is cooled to 110 °C, and the vacuum is released by introducing nitrogen into the reaction vessel.

[0033] The alkoxylation reaction is carried out in three steps. In the first step, 435 g of 1,2-propylene oxide is supplied to the solution at a rate of 7 g / min at 110°C while stirring at 320 rpm. After all the oxides have been supplied, the reaction is allowed to proceed at 110°C for 6 hours to decompose all the present oxides. In the second step, 3169 g of 1,2-butylene oxide is supplied at a rate of 10 g / min at 130°C. After all the oxides have been supplied, the reaction is allowed to proceed at 130°C for 14 hours to decompose all the present oxides. In the third step, 1915 g of 1,2-propylene oxide is supplied at a rate of 5 g / min at 110°C. After all the oxides have been supplied, the reaction is allowed to proceed at 110°C for 14 hours to decompose all the present oxides. Throughout all three steps of the alkoxylation reaction, the pressure inside the reaction vessel is strictly monitored, and the oxide supply is restricted to ensure that the pressure does not exceed 3.5 bar.

[0034] Next, the solution is cooled to 80°C and mixed with 104 g of magnesium silicate at a stirring speed of 350 rpm for 1 hour. Subsequently, the resulting solution is removed from the reaction vessel and transferred to a porcelain Buchner filtration funnel equipped with filter paper having a pore size of 20 μm, and filtered under vacuum. The filtrate is maintained under a vacuum of less than 0.3 bar for 7 hours to obtain a clear solution.

[0035] Synthesis of experimental OSP C (25 / 75 w / w PO / BO) In a 15 L conical reaction vessel equipped with a magnetically coupled stirrer head and a temperature control device, 201.5 g of P400 and 24.6 g of 45% potassium hydroxide aqueous solution are added. The solution is stirred at 200 rpm and heated to a temperature of 115°C. To remove water, a vacuum is applied and the solution is maintained at 30 mBar. The residual water is measured to be less than 1500 ppm after 2 hours under the above conditions using a Karl Fischer titrator. The solution is cooled to 110°C and the vacuum is released by introducing nitrogen into the reaction vessel.

[0036] The alkoxylation reaction is carried out in three steps. In the first step, 285 g of 1,2-propylene oxide is supplied to the solution at a rate of 10 g / min at 110°C while stirring at 320 rpm. After all the oxides have been supplied, the reaction is allowed to proceed at 110°C for 6 hours to decompose all the present oxides. In the second step, 2910 g of 1,2-butylene oxide is supplied at a rate of 7 g / min at 130°C. After all the oxides have been supplied, the reaction is allowed to proceed at 130°C for 12 hours to decompose all the present oxides. In the third step, 485 g of 1,2-propylene oxide is supplied at a rate of 5 g / min at 110°C. After all the oxides have been supplied, the reaction is allowed to proceed at 110°C for 14 hours to decompose all the present oxides. Throughout all three steps of the alkoxylation reaction, the pressure inside the reaction vessel is strictly monitored, and the oxide supply is restricted to ensure that the pressure does not exceed 3.5 bar.

[0037] Next, the solution is cooled to 80°C and mixed with 104 g of magnesium silicate at a stirring speed of 350 rpm for 1 hour. Subsequently, the resulting solution is removed from the reaction vessel and transferred to a porcelain Buchner filtration funnel equipped with filter paper having a pore size of 20 μm, and filtered under vacuum. The filtrate is maintained under a vacuum of less than 0.3 bar for 7 hours to obtain a clear solution.

[0038] Synthesis of experimental OSP D (50 / 50 w / w PO / BO) 234 g of B700 (polybutylene glycol with a nominal MW of 700 Da) and 18.3 g of 45% aqueous sodium hydroxide solution are placed in a 15 L conical reaction vessel equipped with a magnetically coupled stirrer head and a temperature control device. The solution is stirred at 200 rpm and heated to a temperature of 115 °C. To remove water, a vacuum is applied and the solution is maintained at 30 mBar. The residual water is measured to be less than 1500 ppm after 2 hours under the above conditions using a Karl Fischer titrator. The solution is cooled to 110 °C and the vacuum is released by introducing nitrogen into the reaction vessel.

[0039] The alkoxylation reaction is carried out in one step. 2042 g of 1,2-propylene oxide and 1851 g of 1,2-butylene oxide are co-supplied into the solution at a rate of 12 g / min at 130°C with stirring at 320 rpm. After supplying all the oxides, the reaction is allowed to proceed at 130°C for 4 hours to decompose all the present oxides. During the alkoxylation reaction, the pressure in the reaction vessel is strictly monitored, and the supply of oxides is restricted to ensure that the pressure does not exceed 3.5 bar.

[0040] Next, the solution is cooled to 80°C and mixed with 90 g of magnesium silicate at a stirring speed of 350 rpm for 1 hour. Subsequently, the resulting solution is removed from the reaction vessel and transferred to a porcelain Buchner filtration funnel equipped with filter paper having a pore size of 20 μm, and filtered under vacuum. The filtrate is maintained under a vacuum of less than 0.3 bar for 7 hours to obtain a clear solution.

[0041] Synthesis of experimental OSP E (25 / 75 w / w PO / BO) In a 15 L conical reaction vessel equipped with a magnetically coupled stirrer head and a temperature control device, 248.5 g of B700 (polybutylene glycol with a nominal MW of 700 Da) and 19.1 g of 45% aqueous sodium hydroxide solution are added. The solution is stirred at 200 rpm and heated to a temperature of 115°C. To remove water, a vacuum is applied and the solution is maintained at 30 mBar. The residual water is measured to be less than 1500 ppm after 2 hours under the above conditions using a Karl Fischer titrator. The solution is cooled to 110°C and the vacuum is released by introducing nitrogen into the reaction vessel.

[0042] The alkoxylation reaction is carried out in one step. 888 g of 1,2-propylene oxide and 2493 g of 1,2-butylene oxide are co-supplied into the solution at a rate of 14 g / min at 130°C with stirring at 320 rpm. After supplying all the oxides, the reaction is allowed to proceed at 130°C for 4 hours to decompose all the present oxides. During the alkoxylation reaction, the pressure in the reaction vessel is strictly monitored, and the supply of oxides is restricted to ensure that the pressure does not exceed 3.5 bar.

[0043] Next, the solution is cooled to 80°C and mixed with 95 g of magnesium silicate at a stirring speed of 350 rpm for 1 hour. Subsequently, the resulting solution is removed from the reaction vessel and transferred to a porcelain Buchner filtration funnel equipped with filter paper having a pore size of 20 μm, and filtered under vacuum. The filtrate is maintained under a vacuum of less than 0.3 bar for 7 hours to obtain a clear solution.

[0044] Blend preparation. Each 100 mL lubricant composition is prepared by adding each component to a 200 mL glass beaker using the weight percentages shown in the table below. The blends are stirred at ambient temperature using a magnetic stirrer. Some blends form a homogeneous, clear single-phase composition. For blends that do not form a homogeneous single-phase composition and instead appear as two phases at ambient temperature, their separation temperatures are measured according to the procedure described below.

[0045] Measurement of separation temperature and kinematic viscosity The separation temperature is measured only for compositions that exhibit two phases (either a separated phase or cloudiness / turbidity) at room temperature.

[0046] Add 50 mL of the lubricant composition at room temperature to a 100 mL beaker equipped with a thermometer and magnetic stirrer. Heat to 120 °C over 10–15 minutes with stirring, then stop heating and allow the lubricant composition to cool to room temperature. If the solution becomes cloudy or shows visual separation into two phases, record the temperature at which this occurs as the separation temperature. If the upper layer (called the supernatant) has separated into two phases at 40 °C, take a sample from it and measure the kinematic viscosity at 40 °C. If separation does not occur at 40 °C, simply measure the kinematic viscosity of the homogeneous single-phase composition at 40 °C. Also measure the kinematic viscosity of the homogeneous single-phase blend at 100 °C.

[0047] Examples (Ex.) and comparative examples (C.Ex.) of the present invention are shown below in different tables according to the selected low-viscosity oil and high-viscosity base oil.

[0048] [Table 2]

[0049] Table 3 VI = Viscosity Index

[0050] Table 4

[0051] Table 5

[0052] Table 6

[0053] Table 7

[0054] Table 8

[0055] Table 9

[0056] Table 10

[0057] Table 11

[0058] Table 12

[0059] [Table 13] * The phase separation temperature is very close to the sampling temperature (40°C), and therefore the sample state is not very stable.

[0060] [Table 14]

[0061] [Table 15]

[0062] [Table 16]

[0063] The Group III base oils and experimental OSP-A in Table 7, the Group III base oils and experimental OSP-B in Table 8, the Group IV base oils and experimental OSP-A in Table 11, the Group IV base oils and experimental OSP-B in Table 12, and the Group IV base oils and experimental OSP-C in Table 14 all exhibited similar phase separation temperatures. However, if desired, the mixture viscosity and VI could be increased by increasing the amount of high-viscosity PAG component. The Group III base oils and experimental OSP-C in Table 9 did not show separation during formulation. However, this example could be prepared to separate at a lower temperature by either moving the low-viscosity base oil to a higher classification level IV, or by reducing the relative amount of BO in the ABA triblock high-viscosity component.

[0064] Given the higher viscosity of high-viscosity PAG polymers used in two-phase lubricants, a higher VI can be achieved with the same amount of such PAG polymer, and it is highly desirable to use high-viscosity PAG with a kinematic viscosity exceeding 600 cst at 40°C. Since the fabricated random polymers (OSP-D and OSP-E) did not meet this goal, they were not tested with low-viscosity components to determine whether they exhibit the desired phase separation characteristics.

[0065] In the examples described in Table 16, experimental OSP-C exhibited significantly higher viscosity at a significantly lower theoretical MW than comparative example OSP-E, and experimental OSP-B exhibited significantly higher viscosity at a significantly lower theoretical MW than comparative example OSP-D. In the normal synthesis route of PO / BO copolymers (i.e., copolymers formed by the random addition of PO and BO units), side reactions (unsaturation due to isomerization of PO and BO) initiate alkoxylation, which can lead to an increase in molecular weight and, consequently, limit viscosity. Therefore, achieving a kinematic viscosity exceeding 600 cst at 40°C is considered extremely difficult. Experimental OSP-A, OSP-B, and OSP-C are prepared by supplying PO and BO separately at different temperatures. Since PO is supplied at 110°C, it is thought to result in a lower degree of unsaturation, a higher MW, and, consequently, a higher viscosity.

Claims

1. A lubricant system comprising a low-viscosity base oil and a high-viscosity base oil, The aforementioned low-viscosity base oil is a hydrocarbon oil included in classifications I to IV of the American Petroleum Institute. The aforementioned high-viscosity base oil is an ABA triblock polyalkylene glycol derived from 1,2-propylene oxide as unit A and 1,2-butylene oxide as unit B. The ratio of units derived from propylene oxide to units derived from butylene oxide is in the range of 1 / 3 to 10 / 1 by weight. The low-viscosity base oil has a kinematic viscosity in the range of 8 to less than 100 mm² / s at 40°C. A lubricant system wherein the high-viscosity base oil has a kinematic viscosity in the range of 100 mm² / s to 20,000 mm² / s at 40°C.

2. The lubricant system according to claim 1, wherein the ratio of units derived from propylene oxide to units derived from butylene oxide is in the range of 1 / 3 to 3 / 1 by weight.

3. The lubricant system according to claim 1, wherein the ratio of units derived from propylene oxide to units derived from butylene oxide is in the range of 1 / 2 to 2 / 1 by weight.

4. The lubricant system according to claim 1, wherein the low-viscosity base oil is an oil of API Group IV.

5. The lubricant system according to claim 1, wherein the ABA triblock polyalkylene glycol has a molecular weight in the range of 2,000 to 8,000 Daltons.

6. The lubricant system according to claim 1, wherein the low-viscosity base oil constitutes 40 to 95% by weight of the system.

7. The low viscosity base oil is 15 to 50 mm at 40°C. ２ The lubricant system according to claim 1, having a kinematic viscosity in the range of / s.

8. The aforementioned high-viscosity base oil is 400 mm at 40°C. ２ / s~1,000mm ２ The lubricant system according to claim 1, having a kinematic viscosity in the range of / s.

9. The low viscosity base oil is present at a concentration of 0.80 to 0.90 g / cm³ at 15°C. ３ The lubricant system according to claim 1, having a density in the range of [value].

10. The aforementioned high-viscosity base oil is present at a concentration of 0.95 to 1.10 g / cm³ at 15°C. ３ The lubricant system according to claim 1, having a density in the range of [value].

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