JP2014129461A - Vacuum pump oil - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an improved vacuum pump oil having good thermal stability, excellent ultimate vacuum, a high flash point, favorable low-temperature startability, and excellent sealability at a high temperature.SOLUTION: A base oil produced by the Gas-To-Liquid process, having a kinetic viscosity at 100°C of 5-20 mm/s and a content of hydrocarbons with the carbon number of 30 or less of 3.0% or less is used. In this base oil, 0.01-5 mass% of a phenolic antioxidant and 3-15 mass% of a thickener of an olefin copolymer or a poly-α-olefin having a number average molecular weight of 2,000-30,000 are contained. Such a composition is adjusted such that a kinetic viscosity at 100°C thereof is 10.5 mm/s or more and a viscosity index thereof is 150 or more. Thereby, the vacuum pump oil of VG68 standard is provided.

Description

  The present invention relates to a vacuum pump oil, and more particularly to an improved vacuum pump oil that is excellent in thermal oxidation stability and ultimate vacuum, as well as low temperature startability and high temperature sealability.

Vacuum technology is widely used in fields such as semiconductor manufacturing, solar cells, aircraft, automobiles, optoelectronics, and the food industry.
In order to implement these vacuum technologies, mechanical vacuum pumps such as reciprocating vacuum pumps and rotary vacuum pumps, and high vacuum pumps such as oil rotary vacuum pumps and oil diffusion vacuum pumps have been widely used. Synthetic oil-based and mineral oil-based vacuum pump oils are used for the purpose of lubricating the movable parts of these vacuum pumps, increasing the vacuum, and extending the service life.

  In recent years, with the expansion of the application field of vacuum pumps, thermal stability and a high degree of vacuum have been required, and improvements to vacuum pump oils have been added to meet this demand. In particular, it is known that when the vacuum pump oil itself is highly evaporable, the oil is vaporized together with the exhaust gas, the pressure is increased, and the ultimate vacuum is deteriorated. (Non-Patent Document 1)

  In addition, the sliding part of the vacuum pump becomes hot due to friction, but when vacuum pump oil with poor thermal oxidation stability is used, sludge generated during operation is caught in the sliding part and the degree of vacuum reached May cause deterioration. Furthermore, there is a possibility of causing a device trouble when it is fixed to a valve or the like. For this reason, there existed a problem that productivity of the target product fell or the quality of a product was not obtained stably. Therefore, it is a problem to improve the thermal oxidation stability of the vacuum pump oil and reduce the amount of sludge generated.

In order to suppress the generation of sludge, it has also been proposed to use an antioxidant such as p-branched alkylphenyl-α-naphthylamine, but since it is an amine-based antioxidant, the decomposition component becomes a base, and vacuum is used. There are concerns that it may affect the system. (Patent Document 1)
Also, vacuum pumps may be used for sucking acidic gases such as carbon monoxide, and there is a concern that sludge may be formed due to the reaction between basic components and acidic gases. Is preferred.

  Further, in the field of application of vacuum technology, it is required to increase the productivity to shorten the time from the start of the vacuum pump to the steady operation. However, with known vacuum pump oils, especially when used in winter and cold regions, it takes a long time from start to steady operation, and improvements in low temperature startability are required. Yes.

  In addition, many oils such as petroleum and animal and vegetable oils are contained in flammable fluids stipulated as dangerous goods class 4 by the Fire Service Act and flammable liquids stipulated in designated combustibles. . Since these are flammable, they are designated as dangerous goods by the Fire Service Act. However, the lower the flash point, the higher the risk of fire, so depending on the flash point, the handling and storage amount is legal. Regulations are in place. An increase in the flash point increases safety in handling the fire and facilitates handling such as storage and management, so that facilities and management costs required for storage can be reduced.

  Thus, the higher the flash point, the higher the safety, and the easier it is to store and manage it easily and economically. Therefore, it is preferable that the flash point of the vacuum pump oil is also high. The flash point measured by the Cleveland open automatic flash point measuring device according to JIS K2265-4 is 200 ° C. or higher, preferably 250 ° C. or higher, more preferably 260 ° C.

Japanese Patent Laid-Open No. 7-252489

“Lubrication”, Vol. 33, No. 6 (1988), pages 454-457

  The present invention was made from the above viewpoint, and has improved thermal stability, excellent ultimate vacuum, high flash point, good low-temperature startability, and excellent high-temperature sealability. It is intended to provide an improved vacuum pump oil.

The present invention uses a base oil produced by a gas-to-liquid method having a kinematic viscosity at 100 ° C. of 5 to 20 mm ² / s and a hydrocarbon content of 30 or less carbon atoms of 3.0% or less. In this, 0.01 to 5% by mass of a phenolic antioxidant and 3 to 15% by mass of an olefin copolymer having a number average molecular weight of 2,000 to 30,000 or a polyalphaolefin thickener are contained. Thus, the VG68 standard vacuum pump oil is obtained by setting the kinematic viscosity at 100 ° C. to 10.5 mm ² / s or more and the viscosity index to 150 or more.

  According to the vacuum pump oil of the present invention, heat stability is high, and excellent results can be achieved even in the degree of vacuum that can be reached. In addition, since the vacuum pump oil in the present invention has a high flash point, the safety in handling the fire is increased, and the storage and management are facilitated. Can do. Furthermore, it has good low-temperature startability, can shift from start to steady operation at an early stage, and has excellent sealing performance at high temperatures, so that the vacuum pump can be operated efficiently and economically. become.

It is explanatory drawing which shows the system which measures a vacuum ultimate pressure.

As the base oil of the present vacuum pump oil, a base oil produced by a gas-to-liquid method (GTL method) is used.
In the present invention, the base oil produced by the gas-to-liquid method (GTL method) is produced using a condensation method by the Fischer-Tropsch method, and carbon monoxide and hydrogen are present in the presence of an appropriate catalyst. High temperature (for example 125-300 ° C., preferably 175-250 ° C.) and / or high pressure (for example 5 × 10 ⁵ to 10 ⁷ N / m ² , preferably 1.2 × 10 ^{5 to} 5 × 10 ⁶ N / m ² ) Can be converted to long chain, usually paraffinic hydrocarbons.

Some also produce isoparaffinic base oil from wax by the Fischer-Tropsch process.
These Fischer-Tropsch derived base oils tend to have excellent low temperature properties, such as low pour points, and very low evaporation losses, as well as the methods used to make these base oils are produced from mineral crude sources. Compared to a simple base oil production method, there is an advantage that it is relatively simple.

  This Fischer-Tropsch derived base oil is classified as a group III base oil in the API (American Petroleum Institute) base oil category, but it contains no or no sulfur and nitrogen. It is a standard. Also, it produces little or no aromatic component, usually less than 1% by weight, preferably less than 0.5% by weight, and more preferably less than 0.1% by weight (ASTM D-4629). It is. This improves the oxidative stability of the oil.

The base oil produced by this gas-to-liquid method has a kinematic viscosity at 100 ° C. of 5 to 20 mm ² / s, preferably 6 to 15 mm ² / s, more preferably 7 to 10 mm ² / s, and a carbon number of 30. The following hydrocarbons having a content of 3.0% or less, preferably 2.9% or less, more preferably 2.7% or less can be used.
About the content of the hydrocarbon having 30 or less carbon atoms, the content (%) of the peak area value of the fraction having a distillation temperature of 449 ° C. or less in the chromatogram is determined by gas chromatography method defined in ASTM D2887-08. ) To measure.

In order to obtain a high ultimate vacuum in a vacuum pump, it is preferable to use a base oil with a small amount of evaporation loss, and if the base oil has the same kinematic viscosity, the molecular weight of the base oil as described in the above non-patent document A narrow distribution is preferred. As a method for evaluating the evaporation loss amount of the base oil, there is a NOACK evaporability test defined by ASTM D5800.
Shell XHVI-8 (manufactured by Royal Dutch Shell), a base oil produced by the gas-to-liquid method, has an evaporation loss of only 2.0 mass% in the NOACK evaporability test and should be used suitably for vacuum pump oil. Can do. The value of the evaporation loss of the base oil of the vacuum pump oil is not particularly limited, but may be 2.8 mass% or less, preferably 2.4 mass% or less, more preferably 2 0.0 mass% or less may be sufficient.

On the other hand, as an existing highly refined base oil, Yu base 8 (manufactured by SK Innovation), which is an API group 3 base oil, is known. The Yu base 8 properties, it 40 ° C. kinematic viscosity 48.8mm ² / s, 100 ℃ kinematic viscosity 7.8 mm ² / s, viscosity index is 129,15 ° C. Density is 0.845 g / cm ^3. And the evaporation loss by NOACK evaporability test is as large as 3.1 mass%, and it is thought that it is not suitable for vacuum pump oil.

Moreover, PAO8 is marketed as a polyalpha-olefin which is a base oil of synthetic oil. Properties of this PAO8, it 40 ° C. kinematic viscosity 46.6mm ² / s, 100 ℃ kinematic viscosity 7.8 mm ² / s, viscosity index is 136,15 ° C. Density is 0.831 g / cm ^3. And the evaporation loss by a NOACK evaporability test is as large as 2.9 mass%, and it is thought that it is similarly unsuitable for vacuum pump oil.

Furthermore, the above-mentioned commercially available PAO8 is produced by polymerization of 1-decene, the main component is a 30-carbon component (molecular weight 422) which is a trimer, and a 40-carbon component (molecular weight) which is a tetramer. 562) is 65%, pentamer is 50% carbon component (molecular weight 702) is 2%, hexamer 60 carbon number component (molecular weight 842) is 10%, which is substantially low molecular weight. A mixture of ingredients.
Since these components have a discontinuous carbon number distribution as a mixture, a low molecular weight region is also present, and evaporation loss increases. Therefore, it is considered that these components are not suitable for vacuum pump oil.

A phenolic antioxidant is added to the base oil.
Examples of phenolic antioxidants include 2-t-butylphenol, 2-t-butyl-4-methylphenol, 2-t-butyl-5-methylphenol, 2,4-di-t-butylphenol, 2, 4-dimethyl-6-t-butylphenol, 2-t-butyl-4-methoxyphenol, 3-t-butyl-4-methoxyphenol, 2,5-di-t-butylhydroquinone (manufactured by Kawaguchi Chemical Co., Ltd .: ANTAGE DBH) 2,6-di-t-butylphenol, 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, etc. 2,6-di-t-, such as -butyl-4-alkylphenols, 2,6-di-t-butyl-4-methoxyphenol, 2,6-di-t-butyl-4-ethoxyphenol There are chill-4-alkoxy phenols.

  3,5-di-t-butyl-4-hydroxybenzyl mercapto-octyl acetate, n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate (manufactured by Yoshitomi Pharmaceutical Co., Ltd.) Yoshinox SS), n-dodecyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate, 2'-ethylhexyl-3- (3,5-di-tert-butyl-4-hydroxyphenyl) ) Propionate, alkyl-3- (3,5-benzenepropanoate 3,5-bis (1,1-dimethyl-ethyl) -4-hydroxy-C7-C9 side chain alkyl ester (manufactured by BASF: Irganox L135) Di-t-butyl-4-hydroxyphenyl) propionates, 2,6-di-t-butyl-α-dimethylamino-p-alkyl Sol, 2,2′-methylenebis (4-methyl-6-t-butylphenol) (manufactured by Kawaguchi Chemical Co., Ltd .: Antage W-400), 2,2′-methylenebis (4-ethyl-6-t-butylphenol) (Kawaguchi There are 2,2′-methylenebis (4-alkyl-6-tert-butylphenol) s such as those manufactured by Chemical Co .: Antage W-500).

  Further, 4,4′-butylidenebis (3-methyl-6-tert-butylphenol) (manufactured by Kawaguchi Chemical Co., Ltd .: Antage W-300), 4,4′-methylenebis (2,6-di-tert-butylphenol) (shell) -Japan company make: Ionox220AH), 4,4'-bis (2,6-di-t-butylphenol), 2, 2- (di-p-hydroxyphenyl) propane (shell Japan company make: bisphenol A), 2,2-bis (3,5-di-t-butyl-4-hydroxyphenyl) propane, 4,4′-cyclohexylidenebis (2,6-t-butylphenol), hexamethylene glycol bis [3- ( 3,5-di-tert-butyl-4-hydroxyphenyl) propionate] (manufactured by BASF: Irganox L109), triethylene glycol bis 3- (3-t-butyl-4-hydroxy-5-methylphenyl) propionate] (Yoshitomi Pharmaceutical Co., Ltd .: Tominox 917), 2,2′-thio- [diethyl-3- (3,5-di- t-butyl-4-hydroxyphenyl) propionate] (manufactured by BASF: Irganox L115), 3,9-bis {1,1-dimethyl-2- [3- (3-t-butyl-4-hydroxy-5-methyl) (Phenyl) propionyloxy] ethyl} 2,4,8,10-tetraoxaspiro [5,5] undecane (Sumitomo Chemical: Sumilizer GA80), 4,4′-thiobis (3-methyl-6-tert-butylphenol) ( There are bisphenols such as Kawaguchi Chemical Co., Ltd .: Antage RC) and 2,2′-thiobis (4,6-di-t-butyl-resorcin).

  Tetrakis [methylene-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate] methane (manufactured by BASF: Irganox L101), 1,1,3-tris (2-methyl-4-hydroxy -5-tert-butylphenyl) butane (Yoshitomi Pharmaceutical Co., Ltd .: Yoshinox 930), 1,3,5-trimethyl-2,4,6-tris (3,5-di-tert-butyl-4-hydroxybenzyl) Benzene (manufactured by Shell Japan: Ionox 330), bis- [3,3′-bis- (4′-hydroxy-3′-t-butylphenyl) butyric acid] glycol ester, 2- (3 ′, 5 ′ -Di-t-butyl-4-hydroxyphenyl) methyl-4- (2 ", 4" -di-t-butyl-3 "-hydroxyphenyl) methyl-6-t-butyl Polyphenols such as enol, 2,6-bis (2′-hydroxy-3′-tert-butyl-5′-methyl-benzyl) -4-methylphenol, condensates of pt-butylphenol and formaldehyde, p- Examples include phenol aldehyde condensates such as a condensate of t-butylphenol and acetaldehyde.

The said phenolic antioxidant can be used independently and can use it combining several things suitably.
This phenolic antioxidant is added in the range of 0.01 to 5% by mass, preferably 0.05 to 3% by mass, and more preferably 0.1 to 1% by mass in the total amount of the vacuum pump oil.

  A thickener is further added to the base oil. Examples of the thickener include an olefin copolymer, and examples thereof include an ethylene-propylene copolymer and an ethylene-isobutylene copolymer, and it is usually preferable to use an ethylene-propylene copolymer.

  Moreover, a poly alpha olefin can be used as a thickener. This poly alpha olefin is obtained by polymerizing one kind of alpha olefin having 5 or more carbon atoms alone or in combination of two or more kinds.

The ethylene-propylene copolymer and polyalphaolefin preferably have a number average molecular weight of about 2,000 to 30,000, more preferably about 3,000 to 20,000, and even more preferably 5 Those of about 8,000 to 8,000 are preferable.
If the molecular weight is too large, there is a possibility that the viscosity of the vacuum pump oil is reduced due to shearing at the sliding portion of the pump or sludge is generated under high temperature conditions. On the other hand, if the molecular weight is too small, the thickening effect is weakened, so it is necessary to add a large amount of thickening agent, which increases the cost of the lubricating oil product.
Such a thickener is used in the range of 3 to 15% by mass, preferably 4 to 14% by mass in the total amount of the vacuum pump oil.

In order to obtain a high degree of ultimate vacuum using a vacuum pump, it is desirable that the movable part be sealed with an oil film formed by the vacuum pump oil. When the kinematic viscosity of the vacuum pump oil is high and the oil film is sufficiently maintained, it is considered that the sealing effect by the lubricating oil is high.
On the other hand, when the kinematic viscosity is too low and the oil film is not sufficiently retained, a gap is generated in the sliding portion, and the ultimate vacuum is deteriorated.

Although the movable part of the vacuum pump is considered to have a high temperature exceeding 100 ° C. due to friction, it is necessary that the kinematic viscosity of the vacuum pump oil be maintained at a high value even under such a high temperature condition.
In the VG68 standard vacuum pump oil, the kinematic viscosity at 100 ° C. is preferably 10.5 mm ² / s or more, more preferably 10.7 mm ² / s or more, and further preferably 10.9 mm ² / s or more. is there.
Further, the kinematic viscosity at 120 ° C. is preferably 7.0 mm ² / s or more, more preferably 7.2 mm ² / s or more, and further preferably 7.4 mm ² / s or more.
Furthermore, the flash point of the vacuum pump oil of the present invention is preferably 260 ° C. or higher, more preferably 265 ° C. or higher, and further preferably 268 ° C. or higher.

  Various additives can be appropriately added to the present vacuum pump oil as necessary.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the present invention is not limited to these.
The following were prepared in order to produce Examples and Comparative Examples.

(Base oil)
Base oil 1: Fischer-Tropsch base oil, shell XHVI-8 (manufactured by Royal Dutch Shell) by gas-to-liquid method [Properties, etc .: Kinematic viscosity at 40 ° C .; 44.4 mm ² / s, kinematic viscosity at 100 ° C. 7.7 mm ² / s, content of hydrocarbon having 30 or less carbon atoms, determined by gas chromatography method specified in ASTM D2887-08; 2.6%, viscosity index; 142, 15 ° C. density; 0.828 g / cm ³ , evaporation loss in engine oil evaporability (NOACK method); 2.0 mass%]

(Additive)
Additive A1: Ethylene-propylene copolymer (LUCANT HC-1100 manufactured by Mitsui Chemicals)
(A) Number average molecular weight; 6,000
(B) Kinematic viscosity at 40 ° C .; 18,900 mm ² / s
(C) Kinematic viscosity at 100 ° C .; 1,100 mm ² / s
(D) Viscosity index; 270
(E) 15 ° C. density; 0.850 g / cm ³
Additive A2: Polyalphaolefin (SPECTRASYN ELITE 150 manufactured by ExxonMobil Chemical)
(A) Number average molecular weight; 7,000
(B) Kinematic viscosity at 40 ° C .; 1,731 mm ² / s
(C) Kinematic viscosity at 100 ° C .; 157 mm ² / s
(D) Viscosity index; 205
(E) 15 ° C. density; 0.850 g / cm ³

Additive A3: Polyisobutylene (Nisseki Polybutene HV300 manufactured by JX Nippon Oil & Energy Corporation)
(A) Number average molecular weight; 1,400
(B) Kinematic viscosity at 40 ° C .; 26,000 mm ² / s
(C) Kinematic viscosity at 100 ° C .; 590 mm ² / s
(D) Viscosity index; 155
(E) 15 ° C. density; 0.898 g / cm ³
Additive A4: High viscosity mineral oil (a) Number average molecular weight; 740 (calculated by calculation formula of ASTM D3238 ring analysis)
(B) Kinematic viscosity at 40 ° C .; 430 mm ² / s
(C) Kinematic viscosity at 100 ° C .; 31.4 mm ² / s
(D) Viscosity index: 105
(E) 15 ° C. density; 0.885 g / cm ³
Additive B: Phenolic antioxidant (IRGANOX L135 manufactured by BASF)

(Examples 1-2, Comparative Examples 1-2)
Using the materials described above, vacuum pump oils of Examples 1-2 and Comparative Examples 1-2 were prepared according to the compositions shown in Table 1. The compounding amount of the composition was expressed in mass%.

〔test〕
About the vacuum pump oil of Examples 1-2 and Comparative Examples 1-2, in order to see the property and performance, the test shown below was done.

[40 ° C kinematic viscosity]
According to JIS K2283.
[100 ° C kinematic viscosity]
According to JIS K2283.
Evaluation criteria: 10.5 mm ² / s or more
Less than 10.5 mm ² / s ・ ・ ・ ×
[120 ° C kinematic viscosity]
According to JIS K2283.
Evaluation criteria: 7.0 mm ² / s or more
Less than 7.0 mm ² /s...×

[Viscosity index]
According to JIS K2283.
Evaluation criteria: 150 or more
Less than 150 ...
[Pour point]
According to JIS K2269.
Evaluation criteria: less than −25 ° C.
-25 ℃ or higher

[Thermal stability test]
In order to prevent equipment trouble due to the sludge of the vacuum pump, it is desirable that the vacuum pump oil has a low sludge. The Cincinnati Milacron thermal stability test is known as a method for evaluating the sludge formation behavior of a lubricant under thermal oxidation conditions.
Therefore, a thermal stability test was performed in accordance with ASTM D2070.
In the test, first, 200 ml of test oil was put in a container and allowed to stand in a constant temperature bath at 120 ° C. for 45 days in the presence of a copper catalyst and an iron catalyst. The sample oil after completion of the test was filtered through a membrane filter having a pore size of 0.8 μm, and the weight of the generated sludge was measured.
Evaluation criteria: Less than 3.0 mg / 200 ml
3.0mg / 200ml or more

[Vacuum ultimate pressure]
In accordance with JIS B8316, the vacuum ultimate pressure of the oil rotary vacuum pump was measured with the system shown in FIG. The oil rotary vacuum pump used, test conditions and test procedure are shown below.
(A) Oil rotary vacuum pump: Alcatel M2010SD (Motor rated output 450W)
(B) Exhaust speed (50 Hz): 162 L / min (design exhaust speed), 142 L / m (effective exhaust speed)
(C) Removal volume at one compression (calculated value): 0.054L
(D) Test procedure: After opening the vacuum pump to the atmosphere, start the pump from a state where the oil temperature is about 35 ° C without gas ballast, and adjust the oil temperature to 50 ° C while cooling the pump with a cooling fan. To do. The oil temperature stabilizes at 50 ° C. about 50 minutes after the pump is started. The average value of the suction port pressure for 5 minutes from 55 minutes to 60 minutes after starting the pump was taken as the ultimate pressure. During the test, the temperature of the test dome was maintained at 25 ° C.
Evaluation criteria: Less than 0.1 Pa
0.1 Pa or more

[Vapor pressure]
Measured by the direct method (MST 0402-1).
Evaluation criteria: Less than 0.1 × 10 ⁻³ Pa.
0.1 × 10 ⁻³ Pa or more ··· ×

〔Test results〕
The test results are shown in Table 1.

[Discussion]
As shown in Table 1, in Example 1 using the olefin copolymer (additive A1) and Example 2 using the polyalphaolefin (additive A2), the viscosity index is 152, 154 and a high value of 150 or more. the shows a kinematic viscosity at 100 ° C. are both 11.0 mm ² / s, kinematic viscosity at 120 ° C. was good at both 7.4 mm ² / s and high values. The pour points were both −32.5 ° C. and −27.5 ° C. and less than −25.0 ° C. The amount of sludge in the Cincinnati Milacron thermal stability test was 0.8 mg / 200 ml and 1.3 mg / 200 ml, both of which were as low as less than 3.0 mg / 200 ml. The vacuum ultimate pressure is 0.091 Pa and 0.087 Pa, both less than 0.1 Pa, and a high degree of vacuum is achieved. The vapor pressures of 0.96 × 10 ⁻³ Pa and 0.50 × 10 ⁻³ Pa are both low and less than 1.0 × 10 ⁻³ Pa. In addition, the flash point is high at 268 ° C. and 276 ° C., which is highly safe.

On the other hand, in Comparative Example 1 using polyisobutylene (additive A3), the 100 ° C. kinematic viscosity, the 120 ° C. kinematic viscosity, and the viscosity index are lower than those in Example 1 and Example 2, and do not satisfy the evaluation standard value. . The pour point and the sludge amount in the Cincinnati Milacron thermal stability test satisfied the evaluation standard value, but the vacuum ultimate pressure was as large as 0.17 Pa, and the ultimate vacuum was not sufficient.
In Comparative Example 2 using the high-viscosity base oil (Additive A4), the 100 ° C. kinematic viscosity, the 120 ° C. kinematic viscosity, and the viscosity index are lower than those in Example 1 and Example 2, and do not satisfy the evaluation standard value. . The vacuum ultimate pressure and vapor pressure meet the evaluation standard values, but the pour point is also high, the amount of sludge in the Cincinnati Milacron thermal stability test is too large to meet the evaluation standard values, and it is not sufficient. It was.

As described above, in order to obtain a high ultimate vacuum using a vacuum pump, it is desirable that the movable part be sealed with an oil film formed by the vacuum pump oil. For example, kinematic viscosity at 100 ° C. is preferably at least 10.5 mm ² / s, Example 1 and Example 2 are high value and kinematic viscosity of 11.0 mm ² / s at 100 ° C. As described above, sufficient It is considered that the oil film is maintained and the sealing effect by the lubricating oil is high. On the other hand, the kinematic viscosity at 100 ° C. Comparative Example 1 is 10.1 mm ² / s, Comparative Example 2 is 10.2 mm ² / s and a low value.
Further, the kinematic viscosity at 120 ° C. is preferably 7.0 mm ² / s or more, and the kinematic viscosities at 120 ° C. of Example 1 and Example 2 are both 7.4 mm ² / s. Since 6.7 mm ² / s and Comparative Example 2 show a low value of 6.8 mm ² / s, there is a possibility that the oil film cannot be sufficiently retained at a high temperature.

Claims (3)

A phenolic antioxidant is added to a base oil produced by a gas-to-liquid method having a kinematic viscosity at 100 ° C. of 5 to 20 mm ² / s and a hydrocarbon content of 30 or less carbon atoms of 3.0% or less. In an amount of 0.01 to 5% by mass and an olefin copolymer having a number average molecular weight of 2,000 to 30,000 or 3 to 15% by mass of a polyα-olefin thickener, and a kinematic viscosity at 100 ° C. is 10. VG68 standard vacuum pump oil characterized by having a viscosity index of 150 or more at 5 mm ² / s or more. The VG68 standard vacuum pump oil according to claim 1, wherein the vacuum pump oil has a kinematic viscosity at 120 ° C of 7.0 mm ² / s or more.   The vacuum pump oil of the VG68 standard according to claim 1 or 2, wherein the vacuum pump oil has a flash point of 260 ° C or higher.

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