JP3270677B2 - Electrical insulating oil and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrical insulating oil using mineral oil as a base oil and a method for producing the same, and more particularly, to an oxidation stability and an electrical insulating property, in particular, an increase in dielectric loss tangent in the initial stage of oxidation, and hydrogen. The present invention relates to an electric insulating oil excellent in gas absorbability and a method for producing the same.

[0002]

2. Description of the Related Art Electrical insulating oil is used in transformers, high-voltage cables,
It is required to be filled in high-voltage electrical equipment such as high-voltage circuit breakers and condensers, and to maintain long-term stable oxidation resistance, electrical characteristics and metal corrosion resistance.

In order to transmit large-capacity power more economically,
With the introduction of 500,000 volt to 1 million volt ultra-high voltage power transmission technology, the problem of flow electrification has begun to be emphasized.
This is because charge separation occurs as the circulating amount of the electric insulating oil increases, which may result in dielectric breakdown due to discharge. This flow electrification phenomenon is observed as an increase in the dielectric loss tangent (tan δ, measured by a method specified in JIS C 2101; the same applies hereinafter) of the electric insulating oil. This is considered to be one of the causes of the conductive component generated in the oil, and a maximum value is generally observed at the beginning of oxidation. Therefore, the tendency of tan δ to increase in the early stage of oxidation (hereinafter referred to as “tan δ max” as necessary)
There is a demand for an electric insulating oil having a small value.

The applicant of the present invention has proposed that such a general deterioration of the dielectric loss tangent can be suppressed by setting the content of a specific component in the electric insulating oil to a specific range (Japanese Patent Laid-Open No. 6-325622). No.).

[0005]

According to the prior art such as Japanese Patent Application Laid-Open No. 6-325622, temporary deterioration of the dielectric loss tangent can be suppressed to some extent. However, long-term oxidation stability and tan δ max in the initial stage of oxidation are conflicting phenomena, and the technology described in JP-A-6-325622 optimizes these, but both are very excellent. Was not able to be said to exhibit the characteristics. For this reason, oxidation stability and tan δ m
There is a demand for an electrical insulating oil that can obtain both ax characteristics.

[0006] Therefore, the present invention provides an oxidative stability, tan δ m
It is an object of the present invention to provide an electric insulating oil having both the ability to suppress ax and the ability to absorb hydrogen gas, and a method for producing the same.
Specifically, according to the present invention, in terms of oxidation stability, the oxidation stability is 0.6 mgKOH / g or less (quality specified in JIS C 2320).
Of course, further satisfy 0.05 mg KOH / g or less,
In terms of tan δ max suppression, the tan δ max value is 0.3
It is an object of the present invention to provide an electric insulating oil and a method for producing the same, which satisfy the condition of not more than 0.1% and not more than 0.1% and have high hydrogen gas absorbability.

[0007]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have reached the present invention. That is, the electric insulating oil of the present invention uses a hydrorefined base oil, and in an electric insulating oil containing an antioxidant composed of a phenol compound, the total nitrogen content is 15 ppm or less, the sulfide sulfur content is 50 ppm or less, and the aromatic oil is aromatic. 15 hydrocarbons
The present invention relates to an electric insulating oil having a composition of about 40% by mass.

The method for producing an electrical insulating oil according to the present invention is characterized in that a mineral oil fraction having a boiling point range of 250 to 500 ° C., which is separated from crude oil by distillation, is hydrogenated at a temperature of 320 to 380 ° C. using a hydrorefining catalyst. To produce an electrical insulating oil base material having a total nitrogen content of 15 ppm or less, a sulfide sulfur content of 50 ppm or less, and an aromatic hydrocarbon composition of 15 to 40% by mass. Antioxidant consisting of 0.03 to 3
% By mass.

After the above-mentioned hydrogenation treatment, if necessary, a solvent for selectively extracting aromatic hydrocarbons is subjected to solvent extraction and purification at a raffinate yield of 60 to 90% by volume to obtain a total nitrogen content. Is less than 15ppm, sulfide type sulfur content is
An electric insulating oil base material having a composition of 50 ppm or less and an aromatic hydrocarbon content of 15 to 40% by mass can be produced.

In the method for producing an electric insulating oil according to the present invention, the following steps are carried out so that the basic nitrogen content is 1 ppm or less, the non-basic nitrogen content is 15 ppm or less, the sulfide type sulfur content is 50 ppm or less, Hydrocarbon content is 15-40% by mass
Can be produced.

(I) Boiling point range from 250 to 250
The mineral oil fraction at 500 ° C is converted to a temperature of 32 ° C using a hydrorefining catalyst.
Hydrotreating in the range of 0 to 380 ° C, if necessary, (ii)
After the hydrogenation treatment, by performing solvent extraction purification under conditions of a raffinate yield of 60 to 90% by volume with a solvent that selectively extracts aromatic hydrocarbons, the total nitrogen content is 15 ppm or less, and the sulfide-type sulfur content is reduced. An electric insulating oil base material having a composition of 50 ppm or less and an aromatic hydrocarbon content of 15 to 40% by mass is produced. Further, if necessary, (iii) a step of performing a dewaxing treatment before or after the hydrogenation treatment to obtain a predetermined pour point.
This dewaxing may be solvent dewaxing or hydrodewaxing. Further, if necessary, (iv) before or after mixing the alkylbenzene and the antioxidant with the electric insulating oil base, a solid adsorbent treatment is performed, and (v) 100 parts by weight of the mixed electric insulating oil base. On the other hand, 10 to 40 parts by weight of long-chain alkylbenzene is mixed, and (vi) an antioxidant composed of a phenol compound is added in an amount of 0.03 to 3% by mass based on the electric insulating oil base material.

Hereinafter, the contents of the present invention will be described in detail. First, terms used in the present specification will be described.

[0013] Total nitrogen (Nt); a value measured by the method specified in JIS K 2609 (1980) "Testing methods for nitrogen in crude oil and petroleum products", and the nitrogen content contained in oil as an organic nitrogen compound Means the total amount of

Basic Nitrogen (Nb); UOP Method, U.S.A., No. 313-70, "Nitrogen Bases in Petr
oleum Distillates by Color Indicator Titration ". In this measurement method, a sample oil is dissolved in glacial acetic acid, and crystal violet is used as an internal indicator, and titration is performed with perchloric acid in glacial acetic acid.

Non-basic nitrogen (Nn): It is determined from the above-mentioned Nt and Nb by the following equation. Nn = Nt-Nb Total nitrogen is a natural element in crude oil, and is a constituent element of organic nitrogen compounds modified by nuclear hydrogenation and dealkylation in the hydrorefining process. Representative nitrogen compounds in the fraction are quinoline, acridine, indole, pyrrole, and carbazole derivatives.
The basic nitrogen component is a constituent element of a nitrogen compound having basicity that can be detected by titration with perchloric acid as described above,
The difference between Nt and Nb is the non-basic nitrogen content.

Total sulfur (St): The total amount of sulfur constituting the organic sulfur compounds present in the oil. Such organic sulfur compounds include sulfides, thiophenes, and the like. St is measured by the method specified in JIS K 2541.

Sulfide-type sulfur (Sf);
It is the total amount of sulfur constituting the organic sulfur compound shown in (i) or (ii). That is, any of those originally contained in the mineral, those purified by nuclear hydrogenation of the thiophene-type organic sulfur compound during the hydrogenation treatment, and those newly added may be used. In the formula, R ₁ and R ₂ are carbon numbers
Represents 10 to 15 alkyl groups or aromatic hydrocarbons.
R ₃ and R ₄ represent a hydrogen atom or an alkyl group.

General formula (i): [R ₁ -SR ₂ ] General formula (ii)

Embedded image

The sulfide-type sulfur content in the present invention is a value which is separated and quantified by the method described below. Spray a 0.5 wt% hydrochloric acid-acidic acetone-water mixture of palladium chloride onto a thin-layer plate for thin-layer chromatography (for example, a glass plate coated with silica gel to a thickness of about 0.25 mm). After air-drying, 2 to 4 μl of the sample oil was spot-dried, and about 10 μl from the spotting position with carbon tetrachloride solution.
cm, chloroform / methanol (volume ratio 9)
/ 1) Further develop about 5 cm with the mixture.

By this operation, the compound is separated from sulfide-type sulfur compounds, hydrocarbons and other organic sulfur compounds, and shows yellow colored spots. A densitometer (for example, Shimadzu 2-wavelength chromato-scanner OS
(-910 type), irradiate visible light of 380 nm, and determine the absorbance.
When measuring the sample oil, a sample having a known sulfide concentration is simultaneously developed and the same measurement is performed. Thereby, the sulfide type sulfur content contained in the sample is determined.

In the present invention, the amount of aromatic hydrocarbon is
It is a value quantified by a method based on ASTM D2549-84. Similar results can be obtained by measuring with supercritical fluid chromatography (SFC) according to ASTM D5186-91.

Next, the electric insulating oil of the present invention will be described. The base oil used in the present invention has a viscosity of 5 to 30 cST (40
C) or a mixture of mineral oil and long-chain alkylbenzene. The long-chain alkylbenzene is known as an electric insulating oil, and specifically, an alkylbenzene substituted with a linear or branched alkyl group having 9 to 36 carbon atoms is preferable.

[0023] The electric insulating oil of the present invention comprises:
Basic nitrogen content Nb, non-basic nitrogen content Nn, sulfide sulfur content
Sf and the aromatic hydrocarbon content are in a specified amount to a specified range.

That is, in terms of oxidation stability, the acid value is 0.6 m
In order to improve the oxidation stability so as to satisfy g KOH / g or less (quality specified in JIS C 2320), the basic nitrogen content Nb is controlled to 1 ppm or less, preferably to 0. . Nn has no problem in increasing the acid value, but it causes hue deterioration, so it is preferably 15 ppm or less, and more preferably 7 ppm or less.
The following is preferred.

Since Sf interferes with the effect of the addition of the phenolic antioxidant, a smaller amount is desirable. However, it is 150 ppm or less, and there is no problem if the acid value satisfies 0.05 mg KOH / g. However, to keep tanδ max below 0.1%, Sf should be 50
ppm or less, more preferably 10 ppm or less.

In order to sufficiently impart the corona resistance required by the electric insulating oil, that is, the hydrogen gas absorbing property, an appropriate amount of aromatic hydrocarbon is required.
It is necessary that the content be 5% by mass or more, and preferably 20% by mass or more. Further, when the amount of the aromatic hydrocarbon is more than 40% by mass, the light stability is deteriorated.

To summarize the above, the basic nitrogen content Nb
Is 1 ppm or less, preferably zero, and the non-basic nitrogen content Nn is 15 ppm or less.
ppm or less, preferably 7 ppm or less, sulfide-type sulfur content
The content of Sf is 50 ppm or less, preferably 10 ppm or less, and the content of aromatic hydrocarbon is 15 to 40% by mass, preferably 20 to 40% by mass.

Next, a preferred embodiment of the hydrorefining treatment will be described. Using a hydrorefining catalyst, the mineral oil fraction is
Hydrogenation treatment in the range of 320 ° C to 380 ° C and, if necessary, solvent extraction purification with a solvent for selectively extracting aromatic hydrocarbons after the hydrogenation treatment under the conditions of 60 to 90% by volume of a ruffnate yield. To produce a refined mineral oil. As the hydrorefining catalyst, a catalyst in which one or two or more metals such as Ni, Co, Mo, and W are supported on a carrier such as silica, alumina, and silica-alumina can be used.

As conditions for the hydrorefining treatment, a temperature of 3
In addition to the temperature range of 20 ° C to 380 ° C,
It is preferably set in the range of 120 to 120 kg / cm ² , more preferably in the range of 60 to 100 kg / cm ² . Other conditions include the liquid hourly space velocity (LHS
V) is set to 0.2 to 2.0 Hr ^-1 . Further, the conditions are set so that the desulfurization rate is preferably 95% or more, more preferably 98% or more, and the conditions are set such that the desulfurization rate is preferably 95% or more, more preferably 98% or more. It is preferable to set the conditions so that the decomposition rate is 5% or less.

[Phenol compound] As the phenol compound serving as an antioxidant, phenol compounds represented by the following chemical formulas 2, 3, and 4 are preferable, and phenol compounds represented by the chemical formula 2 are most preferable.

[0031]

Embedded image In Chemical Formula 2, R ₁₁ and R ₁₃ represents a branched alkyl group having 3 to 12 carbon atoms, R _{1 2} denotes a -CH ₂ CH ₂ COOR ₁₄ methyl group or an ethyl group or a group. R ₁₄ has 1 carbon atom
Represents up to 20 alkyl groups. Preferred examples of this include 2,6
-Di-tert-butyl paracresol and stearyl-β- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

[0032]

Embedded image In Chemical Formula 3, R ₁₅ represents a branched alkyl group having 3 to 12 carbon atoms, R ₁₆ represents a methyl group or an ethyl group, and R ₁₇ represents an alkylidene group or a methylene group having 1 to 4 carbon atoms. Represent. Preferred examples thereof include 2,2'-methylenebis (6-tert-butyl-4-methylphenol) and 2-2'-methylenebis (6-tert-butyl-4-ethylphenol).

[0033]

Embedded image In Chemical Formula 4, R ₁₈ represents a branched alkyl group having 3 to 12 carbon atoms, and R ₁₉ represents hydrogen or an alkyl group having 1 to 12 carbon atoms. R ₂₀ is, if R ₁₉ represents hydrogen, a methyl group, if R ₁₉ represents an alkyl group having 1 to 12 carbon atoms, represents hydrogen. R ₂₁ represents a direct bond, a methylene group, or an alkylidene group having 1 to 4 carbon atoms. A preferred example thereof is 4,4'-methylenebis (2,6-di-tert-butylphenol).

The amount of the phenol compound added is 0.03 to 3% by mass based on the total weight of the electric insulating oil. When the content is less than 0.03% by mass, the oxidation stability of the electric insulating oil is low, and
If the amount is more than 10% by mass, not only oxidation stability commensurate with cost cannot be obtained, but also oxidation may be accelerated.
In this respect, the amount of the phenol compound to be added is preferably 0.1 to 1% by mass, and particularly preferably 0.2 to 0.5% by mass, based on the total weight of the electric insulating oil.

[Other Additives] The electrical insulating oil according to the present invention includes benzotriazole as a metal deactivator, derivatives thereof, polyalkyl methacrylate as a pour point depressant, ethylene-propylene copolymer, An alkylated naphthalene polycondensate can also be added.

[0036]

Hereinafter, the contents of the present invention will be described in more detail based on examples of the present invention, and the effects of the present invention will be illustrated. It should be noted that the present invention is not limited to the embodiments.

(Example 1) [Mineral oil fraction] From Arabian light crude oil by a conventional method
Separated by atmospheric distillation and vacuum distillation, the raw material base oil (40 ° C viscosity:
9.4 mm ² / g, total sulfur content: 2.54 mass%, total nitrogen content:
357 ppm, boiling point range 250 ° C to 400 ° C).

(Production of Insulating Oil Base 1) The above-mentioned base oil was hydrorefined under the following conditions to obtain a desulfurization rate of 99% and a denitrification rate of 99%.
A refined mineral oil was obtained with a degradation rate of 97% and a degradation rate of 2%. Hydrorefining is
1.0 mass% nickel on silica alumina support as catalyst
Molybdenum supported at 12.0% by mass, hydrogen partial pressure: 90 kg / cm ² G, reaction temperature 350 ° C, liquid hourly space velocity (LHSV)
Performed under the condition of 1.0 hr ^-1 .

A mixed solvent of methyl ethyl ketone / toluene (volume ratio 1/1) was added 2.6 times to this refined mineral oil, cooled to -32.5 ° C., and filtered to obtain a dewaxed oil having a pour point of −30 ° C. Obtained. Further, 1.5% by mass of activated clay is added,
After stirring at 20 ° C. for 20 minutes, the mixture was filtered to obtain an insulating oil base material 1. Table 1 shows the properties of the insulating oil base material 1.

The above base material 1 and DBPC (2,6-di-tert-butylparacresol) were mixed at a mass ratio of 99.7:
The mixture was mixed at 0.3 to obtain an electric insulating oil A as an example. The oxidation stability, dielectric loss tangent, maximum value of continuous tan δ, volume resistivity and hydrogen gas absorptivity of this electrical insulating oil A were evaluated and are shown in Table 1, and the time change of tan δ (continuous tan δ) is shown in FIG. It is shown in FIG.

[Production of insulating oil base material 2]
After hydrodewaxing, a hydrodewaxed oil was obtained. Further, after hydrorefining, a light fraction at 240 ° C. or lower was removed to obtain an insulating oil base material 2. The properties of the insulating oil base material 2 are shown in Table 1, and the time change of tan δ is shown in FIG.

In the hydrodewaxing, zeolite of ZSM-5 type is used as a catalyst, hydrogen partial pressure: 90 kg / cm ² G, reaction temperature:
The test was performed at 371 ° C. and a liquid hourly space velocity (LHSV) of 1.5 hr ⁻¹ . The hydrorefining was performed using a catalyst in which Mo, Ni, etc. were supported on an alumina carrier under the conditions of hydrogen partial pressure: 90 kg / cm ² G, reaction temperature: 339 ° C., and liquid hourly space velocity (LHSV): 0.6 hr ⁻¹ . Performed in

[Production of electrical insulating oil B] The above-mentioned hydrodewaxed base material treated with an alumina-based adsorbent and filtered through a filter paper,
PC (2,6-di-tert-butylparacresol) is mixed at a weight ratio of 99.7: 0.3 to obtain an electric insulating oil B as an example. The oxidation stability, dielectric loss tangent, maximum value of continuous tan δ, volume resistivity and hydrogen gas absorptivity of this electric insulator B were evaluated and are shown in Table 1, and the time change of tan δ is shown in FIG.

[Evaluation method] "Total sulfur content" was measured in accordance with JIS K 2541.
Compliant. "Total nitrogen content" was measured according to JIS K 2609. The amount of aromatic hydrocarbon was measured by supercritical fluid chromatography (SFC). "Oxidation stability"
Based on the oxidation stability test of SC 2101, evaluation was made based on the total acid value and the amount of sludge. "Dielectric loss tangent" and "Volume resistivity"
Was measured in accordance with JIS C2101. `` Continuous tan δ ''
`` Technical Data of Insulating Oil Subcommittee of Petroleum Institute of Japan '' (1985)
March)). In addition, the hydrogen gas absorbability is shown in Technical Data No. 6
It was measured by the method (subcommittee method) described in (1965).

[0045]

[Table 1]

[Comparative Example 1] The above-mentioned base oil was subjected to solvent extraction and purification using a furfural solvent, followed by solvent dewaxing using a mixed solvent of methyl ethyl ketone / toluene.
It is filtered at 32.5 ° C. and treated with activated clay to obtain a base material 3. The above-mentioned insulating oil base material 2 and this base material 3 are mixed at a mass ratio of 97: 3, treated with an alumina-based adsorbent, and filtered to obtain the electric insulating oil C of Comparative Example 1. The properties and evaluation results of the electric insulating oil C are shown in Table 2 and FIG.

[Comparative Example 2] Furfural was used as the insulating oil base material 1.
After contacting with a 250% solution at 80 ° C. at a raffinate yield of 55%, the mixture was treated with an alumina-based adsorbent and filtered. This was mixed with DBPC (2,6-di-tert-butylparacresol) at a weight ratio of 99.7: 0.3 to obtain an electric insulating oil D as Comparative Example 2.

Comparative Example 3 The above-mentioned base oil was hydrorefined under the following conditions to obtain a refined mineral oil 2 with a cracking rate of 15%.
In the hydrorefining, a silica-alumina carrier having nickel 1.0% and molybdenum 12.0% by mass supported thereon was used as a catalyst, hydrogen partial pressure: 100 kg / cm ² G, reaction temperature 395 ° C., and liquid hourly space velocity (LHSV) 0.5 hr. ^{Performed under} the condition of ^-1 .

The above-mentioned purified mineral oil 2 was mixed with methyl ethyl ketone / toluene mixed solvent (volume ratio: 1/1) in an amount of 2.
After adding 6 times and cooling to −32.5 ° C., the mixture was filtered to obtain a dewaxed oil having a pour point of −30 ° C. Further, 1.5% by mass of activated clay was added, and the mixture was stirred at 60 ° C. for 20 minutes.
I got This base material 4 and DBPC (2,6-di-tert-butylparacresol) were mixed at a weight ratio of 99.7: 0.3 to obtain an electric insulating oil E of Comparative Example 3. Oxidation stability, dielectric loss tangent, volume resistivity of these electric insulating oils D and E,
Table 2 shows the evaluation results of the hydrogen gas absorption.

Comparative Examples 4 and 5 A commercially available electric insulating oil containing no phenolic antioxidant was used as electric insulating oil F (Comparative Example 4). In addition, electric insulating oil F and DBPC (2,
6-di-tert-butylparacresol) in a weight ratio of 99.7: 0.3 to obtain an electric insulating oil G (Comparative Example 5). The properties and evaluation results of these electric insulating oils F and G are also shown in Table 2 and FIG.

[0051]

[Table 2]

As is clear from the above results, according to the electric insulating oils A and B of this embodiment, the dielectric loss tangent (tan δ) can be stably set to 0.1 without causing a maximum value in the time change of the continuous tan δ. % Or less. Further, it can be seen that the volume resistivity, the oxidation stability, and the like also show sufficient properties as an electric insulating oil.

Since the electric insulating oils D and E of the comparative examples have a low aromatic hydrocarbon content (aroma content), the hydrogen gas absorbency is a negative value, that is, hydrogen gas is generated. In the electric insulating oils C and F of the comparative examples, the maximum value occurs in the time change of tan δ, and the oxidation stability is low. In the electric insulating oil F, the dielectric loss tangent reaches 0.5%. In the electric insulating oil G of the comparative example, a phenol compound was added, but the dielectric loss tangent also changed over time with continuous tan δ.
Deteriorate to 0.3% or more.

[0054]

The electric insulating oil according to the present invention has a base material produced from a mineral oil fraction as a main component, contains 0.03 to 3% by mass of a phenol compound serving as an antioxidant, and has a total nitrogen content of 15 ppm Nt.
Below, sulfide sulfur content Sf 50 ppm or less, aromatic hydrocarbon
It is 15 to 40% by mass. According to the present invention, the dielectric loss tangent
(tanδ) can be lowered stably, and electrical properties such as volume resistivity, oxidation stability and corona resistance can be obtained. It is effective for proper driving.

[Brief description of the drawings]

FIG. 1 is a graph showing a time change of each tan δ of electric insulating oils A and B of an example of the present invention and electric insulating oils C, D and E of a comparative example.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI C10G 45/06 C10G 45/06 Z 67/04 67/04 (C10M 169/04 (C10M 169/04 101: 02 101: 02 129) : 10) 129: 10) C10N 30:00 C10N 30:00 Z 30:10 30:10 40:16 40:16 70:00 70:00 (56) References JP-A-6-325622 (JP, A) JP-A-53-35200 (JP, A) JP-A-4-227991 (JP, A) JP-A-59-160906 (JP, A) JP-A-60-101804 (JP, A) JP-A-61-4109 (JP, A) JP-A-52-98999 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C10M 169/04 C10M 101/02 C10M 129/10-129/14 C10M 177 / 00 C10N 30:00 C10N 30:10 C10N 40:16 C10N 70:00 C10G 21/16 C10G 45/06 C10G 67/04 H01B 3/20-3/22

Claims (3)

(57) [Claims] 1. An electric insulating oil using a hydrorefined base oil, wherein the total nitrogen content is 15 ppm or less and the sulfide sulfur content is 5 ppm or less.
0 ppm or less and an aromatic hydrocarbon content of 15 to 40% by mass.
An electric insulating oil characterized by containing by mass%. 2. An antioxidant comprising a phenol compound.
2. The composition according to claim 1, wherein the content is 0.1 to 1% by mass.
The electrical insulating oil according to the above. 3. A boiling point range of 250 to 500 separated from crude oil by distillation.
° C mineral oil fraction using a hydrorefining catalyst at a temperature of
Hydrotreating in the range of 80 ° C, total nitrogen content is 15 ppm or less, sulfide sulfur content is 50 ppm or less, and aromatic hydrocarbon is 15 to 40.
A method for producing an electric insulating oil, comprising: producing an electric insulating oil base having a composition of mass%, and adding an antioxidant composed of a phenol compound to the electric insulating oil base in an amount of 0.03 to 3 mass%. .