JP6888799B2 - Vacuum pump oil - Google Patents

Description

The present invention relates to vacuum pump oil.

Vacuum technology is widely used not only in the fields of semiconductors, solar cells, aircraft, automobiles, etc., but also in vacuum packing and retort processing in the food manufacturing process.
Examples of vacuum pumps for implementing vacuum technology corresponding to these fields include 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. A pump or the like is selected according to the application.

In recent years, as the application fields of vacuum pumps have expanded, the vacuum pump oil used in vacuum pumps has improved characteristics such as thermal stability and oxidation stability, depending on the application, in addition to the ultimate vacuum degree. Is required.
For example, Patent Document 1 aims to provide a vacuum pump oil having good thermal stability, excellent ultimate vacuum, high ignition point, good low-temperature startability, and excellent sealing performance at high temperature. , A phenolic antioxidant, an olefin copolymer having a molecular weight in a predetermined range, or poly α- in a base oil produced by a gas-to-liquid method in which the content of a hydrocarbon having 30 or less carbon atoms is set to a predetermined value or less. A VG68 standard vacuum pump oil containing an olefin thickener and having a viscosity index of 150 or more is disclosed.

Japanese Unexamined Patent Publication No. 2014-129461

By the way, in the vacuum pump for food processing used in vacuum packing processing, retort processing, etc., water is contained in the food itself, and water is often used in the processing process, and water may be mixed. There are many. When water is mixed in the vacuum pump oil used in the vacuum pump, the vacuum pump oil having excellent water separability can be easily separated into an aqueous layer and an oil layer, so that the aqueous layer may be removed.
However, the vacuum pump oil having poor water separability is easily emulsified by the mixing of water, which makes it difficult to separate the water, and as a result, it is liable to cause adverse effects such as a decrease in the degree of vacuum and a malfunction of the vacuum pump.
For example, a vacuum pump oil as described in Patent Document 1 may be emulsified by mixing with water due to the presence of an additive such as an antioxidant, which may cause a decrease in water separability. Further, the vacuum pump oil described in Patent Document 1 has a problem that it is inferior in shear stability because a viscosity index improver is added to adjust the viscosity of the entire composition.

On the other hand, vacuum pump oil containing no additives has good water separability and is therefore suitable for use in vacuum pumps for food processing, but is inferior in oxidative stability and thermal stability.
Therefore, the vacuum pump oil containing no additive is not suitable for application to applications requiring oxidative stability and thermal stability.
Further, when a vacuum pump oil containing no such additive is used, for example, in a vacuum pump provided in a vapor deposition apparatus, if a chemical substance such as a vapor deposition material is left in the vacuum pump oil in a state of being mixed, the vacuum pump oil may be allowed to stand. The chemical may polymerize to form a polymer. The presence of this polymer tends to cause adverse effects such as a decrease in the ultimate vacuum degree, a decrease in shear stability, and a malfunction of the vacuum pump.

Since such vacuum pumps are used in a wide variety of industrial fields, it is important to properly identify their applications and use vacuum pump oils suitable for them.
For example, a vacuum pump used for food processing is required to have vacuum pump oil having excellent water separability. Further, the vacuum pump provided in the vapor deposition apparatus is required to have a vacuum pump oil having excellent oxidative stability and a high degree of ultimate vacuum.
However, if the selection and management of the appropriate vacuum pump oil according to the application is insufficient, it may cause the vacuum pump to malfunction and cause serious troubles that are directly linked to production. is assumed.
Therefore, there is a demand for a vacuum pump oil that can be suitably applied to various applications without changing the formulation for each application.

The present invention has been made in view of the above matters, and is a vacuum pump which has a good ultimate vacuum degree, excellent water separability, oxidative stability, and shear stability, and can be adapted to various applications. The purpose is to provide oil.

The present inventor contains a mineral oil in which a temperature gradient of complex viscosity | Δη * | between two points of -10 ° C and -20 ° C is adjusted, and one or more compounds selected from phenol-based compounds and amine-based compounds. However, it has been found that a vacuum pump oil having a viscosity index of less than 150 can solve the above-mentioned problems.

That is, the present invention provides the following [1].
[1] Mineral oil having a complex viscosity temperature gradient | Δη * | between two points of -10 ° C and -20 ° C measured at an angular velocity of 6.3 rad / s using a rotary rheometer of 5 Pa · s / ° C or less ( A) and
Containing one or more compounds selected from a phenolic compound (B) and an amine compound (C),
Vacuum pump oil with a viscosity index less than 150.

The vacuum pump oil of the present invention has a good ultimate vacuum degree and is excellent in water separability, oxidation stability, and shear stability. Therefore, the vacuum pump oil of the present invention can be applied to various applications because such characteristics can be improved in a well-balanced manner.

As used herein, kinematic viscosity and viscosity index mean values measured in accordance with JIS K2283.

[Vacuum pump oil]
The vacuum pump oil of the present invention has a complex viscosity temperature gradient | Δη * | between two points of -10 ° C and -20 ° C measured at an angular velocity of 6.3 rad / s using a rotary rheometer of 5 Pa · s / ° C. It contains the following mineral oil (A) and one or more compounds selected from the phenolic compound (B) and the amine compound (C).
The vacuum pump oil according to one aspect of the present invention may contain synthetic oil as a base oil as long as the effects of the present invention are not impaired, and general-purpose additives other than the components (B) and (C) may be added. It may be contained.

In the vacuum pump oil of one aspect of the present invention, the total content of the components (A), (B) and (C) is preferably 70 to 100% by mass based on the total amount (100% by mass) of the vacuum pump oil. , More preferably 80 to 100% by mass, still more preferably 90 to 100% by mass, and even more preferably 97 to 100% by mass.

Further, the vacuum pump oil of the present invention has a viscosity index of less than 150.
In general, a large amount of viscosity index improver may be added to prepare a vacuum pump oil having a high viscosity index and conforming to the VG68 standard. Vacuum pump oil with a high viscosity index has excellent viscosity characteristics at low and high temperatures, but has a problem in shear stability. That is, with long-term use, the polymer component constituting the viscosity index improver is sheared, which deteriorates the performance of the vacuum pump oil and causes a malfunction of the vacuum pump.
On the other hand, the vacuum pump oil of the present invention has a viscosity index of less than 150 and imposes a limit on the content of the polymer component added as a viscosity index improver. Further, in the present invention, it is preferable to prepare the mineral oil (A) to be a vacuum pump oil conforming to the VG68 standard, and a polymer component (viscosity index improver) having a number average molecular weight (Mn) of 2000 or more is used. It is more preferable to prepare the mineral oil (A) without containing it to obtain a vacuum pump oil conforming to the VG68 standard.
Therefore, the vacuum pump oil of the present invention is excellent in shear stability, can maintain excellent performance even after long-term use, and can suppress malfunction of the vacuum pump.

From the above viewpoint, the viscosity index of the vacuum pump oil according to one aspect of the present invention is preferably 145 or less, more preferably 140 or less, still more preferably 135 or less.
Further, from the viewpoint of improving the viscosity characteristics at high and low temperatures, the viscosity index of the vacuum pump oil according to one aspect of the present invention is preferably 80 or more, more preferably 90 or more, still more preferably 100 or more, still more preferably. Is 110 or more.

In the vacuum pump oil of one aspect of the present invention, from the viewpoint of adjusting the viscosity index to the above range to obtain a vacuum pump oil having excellent shear stability, a polymer component having a number average molecular weight (Mn) of 2000 or more is used. The content is preferably less than 3% by mass, more preferably less than 1.5% by mass, still more preferably less than 0.9% by mass, still more preferably 0, based on the total amount (100% by mass) of the vacuum pump oil. It is less than 5.5% by mass.

In the present specification, the number average molecular weight (Mn) is a value in terms of standard polystyrene measured by a gel permeation chromatography (GPC) method, and the measurement conditions include the following conditions.
(Measurement condition)
-Gel permeation chromatograph device: "1260 type HPLC" manufactured by Agilent.
-Standard sample: Polystyrene column: Two "LF404" manufactured by Shodex, which are connected in sequence.
-Column temperature: 35 ° C
-Development solvent: Chloroform-Flow velocity: 0.3 mL / min

Hereinafter, details of each component contained in the vacuum pump oil of the present invention will be described.
<Mineral oil (A)>
The mineral oil (A) contained in the vacuum pump oil of the present invention is prepared so as to satisfy the following requirement (I).
-Requirement (I): Temperature gradient of complex viscosity between two points of -10 ° C and -20 ° C measured at an angular velocity of 6.3 rad / s using a rotary rheometer | Δη * | (hereinafter, "temperature of complex viscosity") Gradient | Δη * | ”) is 5 Pa · s / ° C or less.

The mineral oil (A) used in the present invention may be a mixed mineral oil composed of only one kind of mineral oil or two or more kinds of mineral oils.
When the mineral oil (A) is a mixed mineral oil composed of two or more kinds of mineral oils, the mixed mineral oil needs to satisfy the above requirement (I), but each mineral oil constituting the mixed mineral oil has the above requirement (I). ), It can be considered that "the mixed mineral oil also satisfies the above requirement (I)".

The "complex viscosity temperature gradient | Δη * |" defined in the above requirement (I) sets the value of the complex viscosity η * at -10 ° C and the value of the complex viscosity η * at -20 ° C independently. Alternatively, when the measurement is performed while continuously changing the temperature from -10 ° C to -20 ° C or -20 ° C to -10 ° C, and the value is placed on the coordinate plane of temperature-complex viscosity, -10 ° C and -20 ° C. It is a value indicating the amount of change (absolute value of the inclination) per unit of the complex viscosity between the two points. More specifically, it means a value calculated from the following formula (f1).
-Calculation formula (f1): Temperature gradient of complex viscosity Δη * = | ([Complex viscosity η * at -20 ° C]-[Complex viscosity η * at -10 ° C]) / (-20- (-10)) |
In the present specification, the complex viscosity η * at a predetermined temperature is a value measured under the above conditions, and specifically means a value measured by the method described in Examples.

Usually, when a phenol-based compound (B) or an amine-based compound (C) is added to mineral oil, the anti-emulsifying property is deteriorated. When the degree of deterioration of the anti-emulsifying property is large, the obtained vacuum pump oil has poor water separability, and can be applied to a device such as a vacuum pump for food processing, which is expected to be mixed with water. difficult.
The deterioration of anti-emulsifying property is caused by the addition of additives such as phenolic compounds and amine compounds. Therefore, if such an additive is not added, the anti-emulsifying property does not deteriorate, and it is possible to prepare a vacuum pump oil having good water separability.
However, vacuum pump oils that do not contain such additives have a particular problem in oxidative stability and are unsuitable for long-term use at high temperatures.

In response to such a problem, the present inventor is a means capable of suppressing deterioration of anti-emulsifying property due to the presence of the additive even when an additive such as a phenol-based compound or an amine-based compound is blended. Was repeatedly examined.
Then, the present inventor can use the mineral oil (A) prepared so as to satisfy the above requirement (I) as the base oil of the vacuum pump oil to obtain a phenolic compound (B), an amine compound (C), or the like. It was found that the deterioration of anti-emulsifying property due to the addition of additives can be effectively suppressed. The present invention has been made based on the findings.

By the way, the “complex viscosity temperature gradient | Δη * |” defined in the requirement (I) is a variety of properties relating to various components constituting the mineral oil (for example, the abundance ratio of branched-chain isoparaffin and linear paraffin; aromatic component. , Sulfur content, nitrogen content, naphthen content, etc.; wax content; refined state of mineral oil) can be said to be an index that comprehensively indicates the balance.

For example, since mineral oil contains a wax component, when the temperature of the mineral oil is gradually lowered, the wax component in the mineral oil is precipitated to form a gel-like structure. The wax content contains paraffin, naphthenic acid, and the like, but the precipitation rate of the wax content differs depending on the structure and content of these.
As a result of repeated studies, the precipitation rate of wax containing a large amount of linear paraffin (normal paraffin) is faster than that of branched-chain isoparaffin, and the value of the temperature gradient | Δη * | of complex viscosity is large, while the linearity is used. It was found that the precipitation rate of wax containing a large amount of branched-chain isoparaffin was slower than that of paraffin, and the value of the temperature gradient | Δη * | of the complex viscosity tended to be smaller.
That is, it can be said that the value of the temperature gradient | Δη * | of the complex viscosity is an index showing the ratio of the linear paraffin and the branched-chain isoparaffin.

Then, the present inventor considers that the mineral oil used has a larger proportion of branched-chain isoparaffin than that of straight-chain normal paraffin, depending on the addition of additives such as phenol-based compound (B) and amine-based compound (C). It was found that the effect of suppressing the deterioration of water separability (anti-emulsifying property) is high.
The reason is that when the proportion of isoparaffin in the mineral oil used increases, additives such as phenolic compound (B) and amine compound (C) are enclosed, and the same function as that of a surfactant is exhibited. It is thought that this is to be done.

Further, the mineral oil having a larger value of "temperature gradient of complex viscosity | Δη * |" defined in the requirement (I) tends to have a higher content of aromatics and sulfur in the mineral oil.
The presence of aromatics and sulfur also contributes to the deterioration of anti-emulsifying properties. In addition, it tends to cause sludge generation due to long-term use, and also causes a decrease in oxidative stability.

That is, the value of the temperature gradient | Δη * | of the complex viscosity of the mineral oil specified in the above requirement (I) deteriorates the water separability (anti-emulsifying property) when the additive is mixed in the target mineral oil. It is an index that comprehensively considers the characteristics of various components that can affect the inhibitory effect and oxidative stability.
Therefore, in the present invention, a vacuum pump oil that improves water separability and oxidative stability in a well-balanced manner by using mineral oil (A) prepared to have a complex viscosity temperature gradient | Δη * | of 5.0 Pa · ° C or lower. Can be.
On the contrary, when an additive such as a phenol compound (B) or an amine compound (C) is added to a mineral oil having a complex viscosity temperature gradient | Δη * | exceeding 5.0 Pa · ° C, the antiemulsifying property deteriorates. The water separability of the obtained vacuum pump oil is inferior.

From the above viewpoint, the temperature gradient | Δη * | of the complex viscosity defined in the requirement (I) of the mineral oil (A) is preferably 4.0 Pa · s / ° C or less, more preferably 3.0 Pa · s / ° C or less. It is more preferably 2.0 Pa · s / ° C or lower, even more preferably 1.0 Pa · s / ° C or lower, and particularly preferably 0.50 Pa · s / ° C or lower.
Further, the temperature gradient | Δη * | of the complex viscosity defined in the requirement (I) of the mineral oil (A) is preferably 0.05 Pa · s / ° C. or higher, more preferably 0.10 Pa · s / ° C. or higher, still more preferable. Is 0.20 Pa · s / ° C or higher.

The mineral oil (A) used in one embodiment of the present invention is, for example, an atmospheric residual oil obtained by atmospheric distillation of crude oils such as paraffin-based crude oil, intermediate base crude oil, and naphthen-based crude oil; the atmospheric residual oil. Distillate oil obtained by vacuum distillation; one of the refining treatments of the distillate oil, such as solvent removal, solvent extraction, hydrofinishing, solvent removal, contact removal, isomerization removal, vacuum distillation, etc. Examples thereof include mineral oils or waxes (slack wax, GTL wax, etc.) that have been subjected to the above treatment.

In one aspect of the present invention, the mineral oil (A) is classified into Group 3 in the API (American Petroleum Institute) category from the viewpoint of further improving the effect of suppressing the deterioration of water separability (anti-emulsifying property) due to the addition of additives. It is preferable to contain the classified mineral oil (A1) and the mineral oil classified into Group 2 (A2).
In addition to the above viewpoints, the mineral oil (A) is a mineral oil (A1) and a mineral oil (A1) from the viewpoint of making a vacuum pump oil conforming to the VG68 standard and improving the effect of suppressing sludge that may occur with long-term use. It is more preferable to include A2) together.

When the mineral oil (A) contains both the mineral oil (A1) and the mineral oil (A2), it is different from the mineral oil (A1) from the viewpoint of further improving the effect of suppressing the deterioration of water separability (anti-emulsifying property) due to the addition of the additive. The content ratio [(A1) / (A2)] with the mineral oil (A2) is preferably 50/50 to 95/5, more preferably 55/45 to 90/10, still more preferably 60 / in terms of mass ratio. It is 40 to 85/15, and even more preferably 65/35 to 82/18.

Further, in one aspect of the present invention, the mineral oil (A2) classified into Group 2 is a paraffin-based mineral oil from the viewpoint of further improving the effect of suppressing deterioration of water separability (anti-emulsifying property) due to the addition of additives. It is preferable to have.
% _{C P} of mineral oil (A2) is usually 50 or more, preferably 55 or more, more preferably 60 or more, more preferably 65 or more, and preferably 90 or less, more preferably 85 or less, more preferably 80 It is as follows.

% _{C N} mineral oil (A2) is preferably from 10 to 40, more preferably 15 to 35, more preferably from 20 to 32.
The% _{C A} mineral oil (A2), is preferably 0-10, more preferably 0-5, more preferably 0-2, more preferably more 0-1.
In this _{specification,% C P,%} C _N and% _{C A} means a value measured in conformity with ASTM D 3238 ring analysis (n-d-M method).

In one aspect of the present invention, the kinematic viscosity at 40 ° C. in mineral oil (A), preferably 61.2~74.8mm ² / s, more preferably 61.5~74.0mm ² / s, more preferably It is 62.0 to 73.8 mm ² / s.

In one aspect of the present invention, the viscosity index of the mineral oil (A) is preferably 80 or more, more preferably 90 or more, still more preferably 100 or more, even more preferably 110 or more, and preferably less than 150. It is more preferably 145 or less, still more preferably 140 or less, and even more preferably 135 or less.

Further, in the vacuum pump oil of one aspect of the present invention, the content of the mineral oil (A) is preferably 65% by mass or more, more preferably 70% by mass, based on the total amount (100% by mass) of the vacuum pump oil. The above is more preferably 75% by mass or more, further preferably 80% by mass or more, still more preferably 85% by mass or more, still more preferably 90% by mass or more, and preferably 99.98% by mass or less, more preferably. Is 99.90% by mass or less, more preferably 99.00% by mass or less.

<Example of preparation of mineral oil (A) satisfying requirement (I)>
The mineral oil (A) that satisfies the above requirement (I) can be prepared by appropriately considering the following items. The following items are examples of the preparation method, and can be prepared by considering other items.

(1) Selection of raw material oil as a raw material for mineral oil (A) As raw material oil for mineral oil (A), raw material oil containing petroleum-derived wax (slack wax, etc.), petroleum-derived wax and bottom It is preferably a raw material oil containing oil. Further, a raw material oil containing a solvent dewaxing oil may be used.
The mineral oil (A) contained in the vacuum pump oil according to one aspect of the present invention is preferably obtained by refining a raw material oil containing a petroleum-derived wax.

When a raw material oil containing petroleum-derived wax and bottom oil is used, the content ratio [wax / bottom oil] of the wax and the bottom oil in the raw material oil is preferably 50/50 to 99 / by mass ratio. 1, more preferably 60/40 to 98/2, even more preferably 70/30 to 97/3, and even more preferably 80/20 to 95/5.
As the proportion of bottom oil in the raw material oil increases, the value of the complex viscosity temperature gradient | Δη * | defined in the requirement (I) for mineral oil tends to increase.

As the bottom oil, a bottom fraction obtained when heavy fuel oil obtained from a vacuum distillation apparatus is hydrolyzed and decomposed to produce naphtha light oil in a normal fuel oil manufacturing process using crude oil as a raw material. From the viewpoint of reducing aromatic content, sulfur content, and nitrogen content, a bottom fraction obtained by hydrocracking heavy fuel oil is preferable.

As the wax, in addition to the wax separated by removing the bottom distillate from the solvent, the atmospheric residual oil obtained by atmospheric distillation of crude oils such as paraffinic mineral oil, intermediate base mineral oil, and naphthenic mineral oil. Wax obtained by removing the solvent from the distillate; wax obtained by removing the distillate oil obtained by distilling the atmospheric residual oil under reduced pressure with the solvent; the distillate oil was desorbed from the solvent, extracted with a solvent, and hydrogenated. Wax obtained by removing a substance from a solvent; GTL wax obtained by Fisher-Tropush synthesis and the like can be mentioned.

On the other hand, examples of the solvent-dewaxing oil include residual oil after solvent-dewaxing the above-mentioned bottom fraction and the like to separate and remove the above-mentioned wax. Further, the solvent dewaxing oil has been subjected to a refining treatment for solvent dewaxing, and is different from the above-mentioned bottom oil.

As a method for obtaining wax by solvent dewaxing, for example, a method in which a bottom fraction is obtained by mixing a mixed solvent of methyl ethyl ketone and toluene and removing precipitates while stirring in a low temperature region is preferable.
The specific temperature in the low temperature environment for solvent dewaxing is preferably lower than the temperature for general solvent dewaxing, and specifically, it is preferably -25 ° C. or lower, -30. More preferably, it is below ° C.

The oil content of the raw material oil is preferably 5 to 55% by mass, more preferably 7 to 45% by mass, further preferably 10 to 35% by mass, still more preferably 15 to 32% by mass, and particularly preferably 21 to 30% by mass. %.

(2) Setting of Refining Conditions for Raw Material Oil It is preferable to carry out refining treatment on the above raw material oil.
The purification treatment preferably includes at least one of a hydrogenation isomerization dewaxing treatment and a hydrogenation treatment. It is preferable that the type of refining treatment and the refining conditions are appropriately set according to the type of raw material oil used.

More specifically, it is preferable to select the refining treatment as follows according to the type of raw material oil used.
-When using a raw material oil (α) containing petroleum-derived wax and bottom oil in the above-mentioned content ratio, both the hydrogenation isomerization dewaxing treatment and the hydrogenation treatment are performed on the raw material oil (α). It is preferable to carry out a purification treatment including.
-When a raw material oil (β) containing a solvent dewaxing oil is used, it is preferable that the raw material oil (β) is subjected to a refining treatment including a hydrogenation treatment without performing a hydrogenation isomerization dewaxing treatment.

Since the above-mentioned raw material oil (α) contains bottom oil, the contents of aromatic, sulfur, and nitrogen tend to be high.
Aromatic components, sulfur components, and nitrogen components can be removed by hydrogenation isomerization dewaxing treatment, and the contents thereof can be reduced.
In the hydrogenation isomerization dewaxing treatment, the linear paraffin in the wax contained in the mineral oil is converted into branched-chain isoparaffin, so that the mineral oil (A) satisfying the requirement (I) can be easily prepared.

On the other hand, the above-mentioned raw material oil (β) contains wax, but since linear paraffin is precipitated and separated and removed in a low temperature environment by solvent dewaxing treatment, it has a complex viscosity specified in requirement (I). The content of linear paraffin that affects the value is low. Therefore, there is little need to perform "hydrogenation isomerization dewaxing treatment".

(Hydrogenation isomerization dewax treatment)
As described above, the hydrogenation isomerization and dewaxing treatment involves isomerization of linear paraffin contained in the raw material oil into branched-chain isoparaffin, conversion of the aromatic component by opening the ring, and sulfur content and nitrogen content. This is a purification process performed for the purpose of removing impurities such as paraffin. In particular, the presence of linear paraffin is one of the factors that increase the value of the temperature gradient | Δη * | of the complex viscosity specified in requirement (I). Therefore, in this treatment, the linear paraffin is converted to branched-chain isoparaffin. And the value of the temperature gradient | Δη * | of the complex viscosity is adjusted to be low.

The hydrogenation isomerization dewaxing treatment is preferably carried out in the presence of a hydrogenation isomerization dewaxing catalyst.
Examples of the hydrogenation isomerization dewaxing catalyst include nickel (Ni) / tungsten (W), nickel (Ni) / molybdenum (Mo), and cobalt (Co) on a carrier such as silica aluminophosphate (SAPO) or zeolite. / Examples thereof include catalysts supporting metal oxides such as molybdenum (Mo) and noble metals such as platinum (Pt) and lead (Pd).

The hydrogen partial pressure in the hydrogenation isomerization dewaxing treatment is preferably 2.0 to 220 MPa, more preferably 10 to 100 MPa, still more preferably 10 to 50 MPa, still more preferably 10 to 25 MPa.

The reaction temperature in the hydrogenation isomerization dewaxing treatment is preferably set higher than the reaction temperature in the general hydrogenation isomerization dewaxing treatment, specifically, preferably 270 to 480 ° C. It is more preferably 280 to 420 ° C, still more preferably 290 to 400 ° C, and even more preferably 300 to 370 ° C.
When the reaction temperature is high, the isomerization of the linear paraffin present in the raw material oil to the branched-chain isoparaffin can be promoted, and the preparation of the mineral oil (A) satisfying the requirement (I) becomes easy. ..

The liquid spatiotemporal velocity (LHSV) in the hydrogenation isomerization dewax treatment is preferably 5.0 hr ^-1 or less, more preferably 2.0 hr ^-1 or less, ^{still more preferably 1.5 hr -1} or less, and more. More preferably, it is 1.0 hr ^-1 or less.
Further, from the viewpoint of improving productivity, the LHSV in the hydrogenation isomerization dewaxing treatment is preferably 0.1 hr ^-1 or more, more preferably 0.2 hr ^-1 or more.

The feed rate of the hydrogen gas in the hydroisomerization dewaxing process, the raw material Oil 1 kiloliter supplied, preferably 100 to 1000 nm ^3, more preferably 300 to 800 nm ^3, more preferably at 300～650Nm ³ is there.
In addition, the product oil that has been subjected to hydrogenation isomerization dewaxing treatment may be subjected to vacuum distillation in order to remove light fractions.

(Hydrogenation)
The hydrogenation treatment is a refining treatment performed for the purpose of complete saturation of aromatic components contained in the raw material oil and removal of impurities such as sulfur and nitrogen.
The hydrogenation treatment is preferably carried out in the presence of a hydrogenation catalyst.
Examples of the hydrogenation catalyst include amorphous carriers such as silica / alumina and alumina and crystalline carriers such as zeolite, and nickel (Ni) / tungsten (W), nickel (Ni) / molybdenum (Mo), and cobalt (Co). ) / A catalyst supporting a metal oxide such as molybdenum (Mo) or a noble metal such as platinum (Pt) or lead (Pd).

The hydrogen partial pressure in the hydrogenation treatment is preferably set higher than the pressure in the general hydrogenation treatment, specifically, preferably 16 MPa or more, more preferably 17 MPa or more, still more preferably 20 MPa. It is more than that, and it is preferably 30 MPa or less, more preferably 22 MPa or less.

The reaction temperature in the hydrogenation treatment is preferably 200 to 400 ° C, more preferably 250 to 350 ° C, and even more preferably 280 to 330 ° C.

The liquid spatiotemporal velocity (LHSV) in the hydrogenation treatment is preferably 5.0 hr ^-1 or less, more preferably 2.0 hr ^-1 or less, ^{still more preferably 1.0 hr -1} or less, and of productivity. from the viewpoint, preferably 0.1 hr ^-1 or more, more preferably 0.2 hr ^-1 or more, still more preferably 0.3 hr ^-1 or more.

The feed rate of the hydrogen gas in the hydrotreating, the generated Oil 1 kiloliter obtained in step (3) is supplied, preferably 100 to 1000 nm ^3, more preferably 200 to 800 nm ^3, more preferably 250 to It is 650 Nm ^3.

In addition, hydrogenated produced oil may be subjected to vacuum distillation in order to remove light fractions. The conditions (pressure, temperature, time, etc.) of the vacuum distillation are appropriately adjusted so that the kinematic viscosity of the mineral oil (A) at 40 ° C. is within a desired range.

<Synthetic oil>
The vacuum pump oil according to one aspect of the present invention may contain a synthetic oil together with the mineral oil (A) as a base oil as long as the effects of the present invention are not impaired.
Examples of the synthetic oil include polyα-olefin (PAO), ester compounds, ether compounds, polyglycols, alkylbenzenes, alkylnaphthalene and the like.
The content of the synthetic oil is preferably 0 to 30 parts by mass, more preferably 0 to 20 parts by mass, and further preferably 0 to 10 parts by mass with respect to 100 parts by mass of the mineral oil (A) contained in the vacuum pump oil. Parts, more preferably 0 to 5 parts by mass.

<Phenolic compound (B)>
The phenolic compound (B) used in the present invention may be any compound having a phenolic structure, and may be a monocyclic phenolic compound or a polycyclic phenolic compound.
In one aspect of the present invention, the component (B) may be used alone or in combination of two or more.

Examples of the monocyclic phenol-based compound include 2,6-di-t-butyl-4-methylphenol, 2,6-di-t-butyl-4-ethylphenol, and 2,4,6-tri-t-. Butylphenol, 2,6-di-t-butyl-4-hydroxymethylphenol, 2,6-di-t-butylphenol, 2,4-dimethyl-6-t-butylphenol, 2,6-di-t-butyl- 4- (N, N-dimethylaminomethyl) phenol, 2,6-di-t-amyl-4-methylphenol, benzenepropanoic acid 3,5-bis (1,1-dimethylethyl) -4-hydroxyalkyl ester And so on.

Examples of the polycyclic phenolic compound include 4,4'-methylenebis (2,6-di-t-butylphenol), 4,4'-isopropyridenebis (2,6-di-t-butylphenol), and 2, 2'-Methylenebis (4-methyl-6-t-butylphenol), 4,4'-bis (2,6-di-t-butylphenol), 4,4'-bis (2-methyl-6-t-butylphenol) ), 2,2'-Methylenebis (4-ethyl-6-t-butylphenol), 4,4'-butylidenebis (3-methyl-6-t-butylphenol) and the like.

（上記式（ｂ−１）中、＊は結合位置を示す。） In the vacuum pump oil of one aspect of the present invention, the phenolic compound (B) is preferably a hindered phenolic compound having at least one structure represented by the following formula (b-1) in one molecule, preferably benzenepropane. Acid 3,5-bis (1,1-dimethylethyl) -4-hydroxyalkyl ester is more preferred.

(In the above formula (b-1), * indicates the bonding position.)

In one aspect of the present invention, the molecular weight of the phenolic compound (B) is preferably 100 to 1000, more preferably 150 to 900, still more preferably 200 to 800, from the viewpoint of providing a vacuum pump oil having a high degree of ultimate vacuum. Even more preferably, it is 250 to 700.

<Amine compound (C)>
The amine compound (C) used in one embodiment of the present invention is preferably an aromatic amine compound, and is selected from a diphenylamine compound and a naphthylamine compound, from the viewpoint of making a vacuum pump oil with further improved oxidative stability. More preferably, it is one or more.
In one aspect of the present invention, the component (C) may be used alone or in combination of two or more.

Examples of the diphenylamine-based compound include monoalkyldiphenylamine-based compounds having one alkyl group having 1 to 30 carbon atoms (preferably 4 to 30, more preferably 8 to 30) such as monooctyldiphenylamine and monononyldiphenylamine; 4 , 4'-dibutyldiphenylamine, 4,4'-dipentyldiphenylamine, 4,4'-dihexyldiphenylamine, 4,4'-diheptyldiphenylamine, 4,4'-dioctyldiphenylamine, 4,4'-dinonyldiphenylamine, etc. A dialkyldiphenylamine compound having two alkyl groups having 1 to 30 carbon atoms (preferably 4 to 30, more preferably 8 to 30); 1 carbon number such as tetrabutyldiphenylamine, tetrahexyldiphenylamine, tetraoctyldiphenylamine, tetranonyldiphenylamine, etc. Polyalkyldiphenylamine compounds having three or more alkyl groups of ~ 30 (preferably 4-30, more preferably 8-30); 4,4'-bis (α, α-dimethylbenzyl) diphenylamine and the like can be mentioned.

Examples of naphthylamine-based compounds include 1-naphthylamine, phenyl-1-naphthylamine, butylphenyl-1-naphthylamine, pentylphenyl-1-naphthylamine, hexylphenyl-1-naphthylamine, heptylphenyl-1-naphthylamine, and octylphenyl-1. Examples thereof include −naphthylamine, nonylphenyl-1-naphthylamine, decylphenyl-1-naphthylamine, dodecylphenyl-1-naphthylamine and the like.

In the vacuum pump oil of one aspect of the present invention, the amino compound (C) is preferably a diphenylamine compound, and contains 2 alkyl groups having 1 to 30 carbon atoms (preferably 1 to 20, more preferably 1 to 10). The dialkyldiphenylamine compound having one is more preferable.

In one aspect of the present invention, the molecular weight of the amine compound (B) is preferably 100 to 1000, more preferably 150 to 900, still more preferably 200 to 800, from the viewpoint of providing a vacuum pump oil having a high degree of ultimate vacuum. Even more preferably, it is 250 to 700.

<Contents of components (B) and (C)>
The vacuum pump oil of the present invention contains one or more compounds selected from the phenolic compound (B) and the amine compound (C), but at least from the viewpoint of making the vacuum pump oil more oxidatively stable. It is preferable to contain the phenolic compound (B), and it is more preferable to contain both the phenolic compound (B) and the amine compound (C).

In the vacuum pump oil of one aspect of the present invention, the content of the component (B) is the total amount (100 mass) of the vacuum pump oil from the viewpoint of making the vacuum pump oil having improved water separability and oxidative stability in a well-balanced manner. %) On a basis, it is preferably 0.01 to 10% by mass, more preferably 0.03 to 5% by mass, still more preferably 0.05 to 2% by mass, and even more preferably 0.07 to 1% by mass. ..

In the vacuum pump oil of one aspect of the present invention, the content of the component (C) is the total amount (100 mass) of the vacuum pump oil from the viewpoint of making the vacuum pump oil having improved water separability and oxidative stability in a well-balanced manner. %) On a basis, it is preferably 0.01 to 10% by mass, more preferably 0.05 to 5% by mass, still more preferably 0.07 to 2% by mass, and even more preferably 0.10 to 1% by mass. ..

Further, in the vacuum pump oil of one aspect of the present invention, the content ratio of the component (B) to the component (C) [(B) / (C) from the viewpoint of making the vacuum pump oil with further improved oxidative stability. )] Is a mass ratio, preferably 1/4 to 6/1, more preferably 1/3 to 5/1, still more preferably 1/2 to 4/1, still more preferably 1 / 1-3 /. It is 1.

In the vacuum pump oil of one aspect of the present invention, the total content of the components (B) and (C) is the vacuum pump oil from the viewpoint of making the vacuum pump oil having improved water separability and oxidative stability in a well-balanced manner. Based on the total amount (100% by mass) of, preferably 0.02 to 15% by mass, more preferably 0.05 to 10% by mass, still more preferably 0.10 to 5% by mass, still more preferably 0.15 to 5% by mass. 2% by mass.

<General-purpose additive>
The vacuum pump oil according to one aspect of the present invention may further contain general-purpose additives other than the components (B) and (C), if necessary, as long as the effects of the present invention are not impaired.
Examples of such general-purpose additives include antioxidants other than the components (B) and (C), metal inactivating agents, defoaming agents, and the like.
Each of these general-purpose additives may be used alone or in combination of two or more.
The content of each of these general-purpose additives can be appropriately adjusted according to the type of general-purpose additive within a range that does not impair the effects of the present invention.

In the vacuum pump oil of one aspect of the present invention, the total content of the general-purpose additives is preferably 0 to 30% by mass, more preferably 0 to 20 based on the total amount (100% by mass) of the vacuum pump oil. It is by mass%, more preferably 0 to 10% by mass, and even more preferably 0 to 3% by mass.

[Various properties of vacuum pump oil]
The vacuum pump oil of one aspect of the present invention preferably conforms to the VG68 standard of viscosity grade specified in ISO 3448.
Specifically, the kinematic viscosity of the vacuum pump oil according to one aspect of the present invention at 40 ° C. is preferably 61.2 to 74.8 mm ² / s, more preferably 61.5 to 74.0 mm ² / s, and further. It is preferably 62.0 to 73.8 mm ² / s.

In the vacuum pump oil of one aspect of the present invention, the content of sulfur atoms suppresses the formation of sludge with long-term use, and the total amount of the vacuum pump oil is considered to be a vacuum pump oil having excellent oxidative stability. On a (100 mass%) basis, it is preferably less than 200 mass ppm, more preferably less than 100 mass ppm, still more preferably less than 50 mass ppm, still more preferably less than 10 mass ppm.
In addition, in this specification, the content of a sulfur atom means a value measured according to JIS K2541-6.

The RPVOT value of the vacuum pump oil according to one aspect of the present invention is preferably 200 minutes or longer, more preferably 220 minutes or longer, still more preferably 240 minutes or longer.
In this specification, the RPVOT value of the vacuum pump oil means a value measured under the conditions described in Examples described later in accordance with the rotary cylinder type oxidation stability test (RPVOT) of JIS K2514-3. ..

When the vacuum pump oil of one aspect of the present invention is subjected to a water separability test at a temperature of 54 ° C. in accordance with JIS K2520, the degree of anti-emulsification indicating the time required for the emulsified layer to reach 3 mL is defined as the degree of anti-emulsification. It is preferably less than 20 minutes, more preferably 15 minutes or less, still more preferably 10 minutes or less, still more preferably 5 minutes or less.

The ultimate vacuum degree measured in accordance with JIS B8316 of the vacuum pump oil according to one aspect of the present invention is preferably less than 0.6 Pa, more preferably less than 0.5 Pa, and further preferably less than 0.4 Pa.

[Use of vacuum pump oil]
The vacuum pump oil of the present invention has a good ultimate vacuum degree and is excellent in water separability, oxidation stability, and shear stability. Therefore, the vacuum pump oil of the present invention can be applied to various applications because such characteristics can be improved in a well-balanced manner.
The use of the vacuum pump oil is not particularly limited, but is suitable as a lubricating oil for a vacuum pump used in the production of, for example, semiconductors, solar cells, aircraft, automobiles, foods with vacuum packing processing, retort processing, etc. is there.
The vacuum pump oil is not particularly limited, but for example, an oil rotary vacuum pump, a mechanical booster pump, a dry pump, a diaphragm vacuum pump, a turbo molecular pump, an ejector (vacuum) pump, an oil diffusion pump, a soap pump, and titanium. Examples thereof include a supplement pump, a sputter ion pump, a cryo pump, a swing piston type dry vacuum pump, a rotary blade type dry vacuum pump, and a scroll type dry vacuum pump.

That is, the present invention can also provide the following (1) vacuum pump and the following (2) method of using the vacuum pump oil.
(1) Mineral oil having a complex viscosity temperature gradient | Δη * | between two points of -10 ° C and -20 ° C measured at an angular velocity of 6.3 rad / s using a rotary rheometer of 5 Pa · s / ° C or less (1) A) and
Containing one or more compounds selected from a phenolic compound (B) and an amine compound (C),
A vacuum pump for the production of semiconductors, solar cells, aircraft, automobiles, or foods using vacuum pump oil with a viscosity index of less than 150.
(2) Mineral oil having a complex viscosity temperature gradient | Δη * | between two points of -10 ° C and -20 ° C measured at an angular velocity of 6.3 rad / s using a rotary rheometer of 5 Pa · s / ° C or less ( A) and
Containing one or more compounds selected from a phenolic compound (B) and an amine compound (C),
Vacuum pump oil with a viscosity index less than 150,
How to use vacuum pump oil for use in vacuum pumps for the manufacture of semiconductors, solar cells, aircraft, automobiles, or food.

[Vacuum pump oil manufacturing method]
The method for producing a vacuum pump oil of the present invention is a step of blending one or more compounds selected from a phenolic compound (B) and an amine compound (C) with a mineral oil (A) satisfying the above requirement (I). There is a method having.
At this time, if necessary, the above-mentioned general-purpose additive may be blended.
The suitable compounds, physical property values, blending amounts, and various properties of the obtained vacuum pump oil are as described above.

Next, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to these examples. The methods for measuring or evaluating various physical properties are as follows.

<Characteristics of base oil or vacuum pump oil>
(1) Dynamic viscosity at 40 ° C and 100 ° C Measured according to JIS K2283.
(2) Viscosity index Measured according to JIS K2283.

<Characteristics of base oil>
(3) aromatic content _{(% C} A), paraffins _{(% C} P), naphthenes _{(% C} N)
It was measured by ASTM D-3238 ring analysis (nd-M method).
(4) Complex viscosity η * at -10 ° C and -20 ° C
The measurement was carried out by the following procedure using a rheometer "Physica MCR 301" manufactured by Antonio Par.
First, the sample oil to be measured was inserted into a cone plate (diameter 50 mm, inclination angle 1 °) adjusted to either −10 ° C. or −20 ° C., and held at the same temperature for 10 minutes. At this time, care was taken not to give distortion to the inserted solution.
Then, at a predetermined measurement temperature, at each measurement temperature in vibration mode, under conditions of values appropriately set according to the measurement temperature in the range of an angular velocity of 6.3 rad / s and a strain amount of 0.1 to 100%. The complex viscosity η * was measured. The above-mentioned "strain amount" was set to "2.1%" in the measurement at −10 ° C. and “0.65%” in the measurement at −20 ° C.
Then, "Temperature gradient of complex viscosity | Δη * |" was calculated from the above calculation formula (f1) from the values of the complex viscosity η * at −10 ° C. and −20 ° C.

<Vacuum pump oil properties>
(5) Sulfur atom content Measured according to JIS K2541-6.

<Characteristics of vacuum pump oil>
(6) RPVOT value Based on the rotary cylinder type oxidation stability test (RPVOT) of JIS K 2514-3, the test was performed at a test temperature of 150 ° C. and an initial pressure of 620 kPa, and the time until the pressure decreased from the maximum pressure to 175 kPa (RPVOT value). ) Was measured. It can be said that the longer the time is, the more excellent the vacuum pump oil is in oxidative stability.
(7) Degree of anti-emulsification A water separability test was conducted at a temperature of 54 ° C. in accordance with JIS K2520. In Table 1, "volume of oil layer (ml)", "volume of aqueous layer (ml)", "volume of emulsified layer (ml)", and "elapsed time (minutes)" are listed in this order.
(8) Ultimate vacuum degree Measured according to JIS B8316. Specifically, after filling the compressor portion of the oil rotary vacuum pump with vacuum pump oil, the vacuum degree pump was started, and the degree of vacuum at the suction port one hour later was defined as the "reached vacuum degree".

<Various tests on vacuum pump oil>
(9) Shear Stability Test Based on the ultrasonic B method (JPI-5S-29), the measurement was performed under ultrasonic irradiation time of 30 minutes, room temperature (25 ° C.), and oil amount of 30 ml. The output voltage of the ultrasonic waves in the shear stability test was set to an output voltage at which the kinematic viscosity reduction rate at 40 ° C. was 15% after irradiating 30 ml of standard oil with ultrasonic waves for 10 minutes.
The kinematic viscosities at 40 ° C. and 100 ° C. and the viscosity index were measured before and after the shear stability test, and the kinematic viscosity reduction rate at each temperature was calculated by the following formula.
Formula: Shear stability (%) = ([Dynamic viscosity before test]-[Dynamic viscosity after test] / [Dynamic viscosity before test]) x 100
It can be said that the lower the value of the kinematic viscosity reduction rate, the better the shear stability of the vacuum pump oil. The kinematic viscosities and viscosity indexes at 40 ° C. and 100 ° C. were measured in accordance with JIS K2283.

(10) Indiana Oxidation Test (IOT)
In a sample container, 300 ml of sample oil, which is a vacuum pump oil, is placed in a cylinder container, a plate-shaped iron catalyst and a copper catalyst, which are catalysts, are added, and air is blown at 10 L / h through an air blowing tube at 150 ° C. 24. After heating for hours, an Indiana oxidation test was performed.
The kinematic viscosity of the sample oil after the test at 40 ° C., the acid value increase value, the RPVOT value, and the millipore value were measured by the methods shown below.
-"Dynamic viscosity at 40 ° C.": Measured in accordance with JIS K2283.
-"Acid value increase amount": The acid value of the sample oil before and after the test was measured in accordance with JIS K2501 (indicator method), and the difference was calculated.
-"RPVOT value": Based on the rotary cylinder type oxidation stability test (RPVOT) of JIS K2514-3, the test temperature is 150 ° C. and the initial pressure is 620 kPa, and the time until the pressure drops from the maximum pressure to 175 kPa (RPVOT value). ) Was measured.
-"Millipore value": According to SAE-ARP-785-63, the precipitate in 300 ml of the test oil after the above test was collected by filtration, and from the mass, the sample of the precipitate per 100 ml of the sample oil was taken as the "Millipore value". It was calculated as.

Examples 1 to 3 and Comparative Examples 1 to 5
Vacuum pump oils were prepared by blending various additives shown in Table 1 together with the base oils of the types and amounts shown in Table 1.
The details of the base oil used and various additives are as follows.

<Base oil>
・ Mineral oil (1):
The raw material oil, which contains slack wax and bottom oil obtained by hydrocracking heavy fuel oil and is a distillate oil of 1860 neutral or higher, is hydrogenated after being subjected to hydrogenation isomerization dewaxing treatment. A paraffinic mineral oil that has been subjected to a finishing treatment and is classified into Group 2 in the API category. 40 ° C. kinematic viscosity = 408.8mm ² / s, viscosity index _{= 107,% C A = 0} ,% C P = 70.0,% C N = 30.0.
The conditions for the hydrogenation isomerization dewax treatment are as follows.
Feed rate, the hydrogen gas: the starting Oil 1 kiloliter supplies, 250 Nm ³ or more 300Nm less than ^3.
-Hydrogen partial pressure: 3 MPa or more and less than 10 MPa.
-Liquid space velocity (LHSV): 0.5 to 1.0 hr ^-1 .
-Reaction temperature: 300 to 350 ° C.

・ Mineral oil (2):
It is a mixed oil obtained by mixing slack wax and bottom oil obtained by hydrocracking heavy fuel oil with a distillate oil of 150 neutral or more and a distillate oil of 500 neutral or more. A paraffinic mineral oil classified into Group 2 in the API category, which is obtained by subjecting the raw material oil to a hydrogenation isomerization dewaxing treatment and then a hydrofinishing treatment. 40 ° C. kinematic viscosity = 75.2mm ² / s, viscosity index _{= 98,% C A = 5.3} ,% C P = 66.8,% C N = 27.9.
The conditions for the hydrogenation isomerization dewax treatment are as follows.
Feed rate, the hydrogen gas: the starting Oil 1 kiloliter supplies, 250 Nm ³ or more 300Nm less than ^3.
-Hydrogen partial pressure: 3 MPa or more and less than 10 MPa.
-Liquid space velocity (LHSV): 0.5 to 1.0 hr ^-1 .
-Reaction temperature: 300 to 350 ° C.

・ Mineral oil (3):
The raw material oil, which contains slack wax and bottom oil obtained by hydrocracking heavy fuel oil and is a distillate oil of 200 neutral or more, is hydrogenated after being subjected to hydrogenation isomerization dewaxing treatment. Mineral oils that have been finished and are classified in Group 3 in the API category. 40 ° C. kinematic viscosity = 43.75mm ² / s, viscosity index _{= 143,% C A = 0} ,% C P = 94.7,% C N = 6.3.
The conditions for the hydrogenation isomerization dewax treatment are as follows.
^{-Hydrogen gas supply ratio: 300 to 400 Nm 3} for 1 kiloliter of raw material oil to be supplied.
-Hydrogen partial pressure: 10 to 15 MPa.
-Liquid space velocity (LHSV): 0.5 to 1.0 hr ^-1 .
-Reaction temperature: 300 to 350 ° C.

<Various additives>
-Phenolic compound: Benzene propanoic acid 3,5-bis (1,1-dimethylethyl) -4-hydroxyalkyl ester-Amine compound: 4,4'-dioctyldiphenylamine.
-Metal inactivating agent: 2- (2-hydroxy-4-methylphenyl) benzotriazole-Polymer component: Mn = 320,000 polyisobutene diluted with 150N mineral oil to improve the viscosity index by 4.9% by mass of resin Agent.

The vacuum pump oils prepared in Examples 1 to 3 conform to the VG68 standard, and result in excellent water separability, oxidation stability, and shear stability while maintaining a high ultimate vacuum degree. It was.
On the other hand, since the vacuum pump oils of Comparative Examples 1 and 2 used mineral oil having a high value of the temperature gradient of the complex viscosity between the two points of −10 ° C. and −20 ° C. The result was that the degree of vacuum was low and the water separability was also inferior.
Further, since the vacuum pump oils of Comparative Examples 3 and 5 do not contain both phenolic compounds and amine compounds, the RPVOT value is lower than that of the vacuum pump oils of Examples, and the acid after the Indiana oxidation test. The amount of increase in valence was large and deterioration was confirmed, resulting in inferior oxidative stability.
Further, the vacuum pump oils of Comparative Examples 4 and 5 were obtained by adding a certain amount of polymer component in order to conform to the VG68 standard, but the result was that the shear stability was inferior and the water separability was inferior. .. The vacuum pump of Comparative Example 4 has a high millipore value after the Indiana oxidation test, and there is a concern that sludge may be generated due to long-term use.

Claims (7)

The temperature gradient of complex viscosity between two points of -10 ° C and -20 ° C measured at an angular velocity of 6.3 rad / s using a rotary rheometer | Δη * | is 0.5 Pa · s / ° C or less, and is in the API category. Mineral oil (A) consisting only of mineral oil (A1) classified in group 3 and mineral oil (A2) classified in group 2 in the API category,
It contains a phenolic compound (B) as an antioxidant and an amine compound (C) as an antioxidant.
ASTM D-3238 ring analysis of the mineral oil (A1) aromatic content as measured by (n-d-M method) (% _{C A)} is 0, the aromatic content of mineral oil (A2) _{(% C} A) Is 2 or less,
The content of the mineral oil (A) is 65% by mass or more based on the total amount (100% by mass) of the vacuum pump oil.
The content of the phenolic compound (B) is 0.01 to 10% by mass based on the total amount (100% by mass) of the vacuum pump oil.
The content of the amine compound (C) is 0.01 to 10% by mass based on the total amount (100% by mass) of the vacuum pump oil.
Vacuum pump oil with a viscosity index less than 150. The vacuum pump oil according to claim 1, wherein the mineral oil (A2) is a paraffinic mineral oil. The vacuum pump oil according to claim 1 or 2, wherein the content ratio [(A1) / (A2)] of the mineral oil (A1) to the mineral oil (A2) is 50/50 to 95/5 in terms of mass ratio. .. The vacuum pump oil according to any one of claims 1 to 3, wherein the content of the polymer component having a number average molecular weight of 2000 or more is less than 3% by mass based on the total amount of the vacuum pump oil. The vacuum pump oil according to any one of claims 1 to 4, which conforms to the VG68 standard of the viscosity grade specified by ISO 3448. The vacuum pump according to any one of claims 1 to 5, wherein the total content of the components (A), (B) and (C) is 70 to 100% by mass based on the total amount of the vacuum pump oil. oil. The vacuum pump oil according to any one of claims 1 to 6, wherein the kinematic viscosity of the mineral oil (A) at 40 ° C. is 61.2 to 74.8 mm ^{2 / s.}