JP2003064030A - Partially fluorinated alkyl compound, lubricant comprising the compound and recording medium using the lubricant - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lubricant for a recording medium holding excellent lubricity under various working conditions, and keeping lubrication effect, and capable of imparting excellent trafficability, abrasion resistance, durability and the like for a long time. SOLUTION: For example, C18 H37 CH(COOCH(C11 H23 )CH2 COOH)CH2 COORf (Rf is a saturated or unsaturated partially fluorinated alkyl group) is used as a lubricant for a magnetic recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a partially fluorinated alkyl compound, a recording medium lubricant comprising the compound, and a recording medium on which a lubricating layer containing the lubricant is formed.

[0002]

2. Description of the Related Art A conventional recording medium, for example, a magnetic recording medium, is a so-called metal thin film type magnetic recording in which a ferromagnetic metal material is deposited on a non-magnetic support by a method such as vapor deposition and the magnetic layer is used as a magnetic layer. There is known a medium or a so-called coating type magnetic recording medium in which a magnetic coating material containing very fine magnetic particles and a resin binder is coated on a non-magnetic support and used as a magnetic layer. Since these conventional magnetic recording media have extremely good smoothness of the magnetic layer surface, the substantial contact area with a sliding member such as a magnetic head or a guide roller is large,
Therefore, there are many problems such that the friction coefficient becomes large and the adhesion phenomenon (so-called sticking) is likely to occur and running performance and durability are poor. Therefore, it has been studied to use various lubricants in order to improve these problems. Conventionally, higher fatty acids and their esters are internally added to the magnetic layer of the magnetic recording medium, or a top coat is used. Attempts have been made to suppress the friction coefficient by doing so.

However, the lubricant used for the magnetic recording medium is required to have very strict characteristics due to its properties.
At present, it is difficult to satisfy the requirement with the lubricants used conventionally.

That is, the lubricant used in the magnetic recording medium is (1) excellent in low temperature characteristics so as to ensure a predetermined lubricating effect when used in cold regions, and (2) a lubricant with a magnetic head. As pacing becomes a problem, it is necessary to be able to apply it extremely thinly, to exhibit sufficient lubrication characteristics even in that case, and (3) to endure long-term use or long-term use and to maintain the lubrication effect. To be done.

Incidentally, Japanese Unexamined Patent Publication No. 6-41561 discloses that
As a lubricant for a metal thin film type magnetic recording medium, a fluorine-containing alkyl succinic acid diester represented by the following general formula (i) has been proposed.

[0006]

Embedded image R1-CH (COOR2) CH ₂ COOR3 (i)

In the formula, R1 is an aliphatic alkyl group or an aliphatic alkenyl group, one of R2 and R3 is a fluoroalkyl ether group, and the other is a fluoroalkyl group,
It is either a fluoroalkenyl group, a fluorophenyl group, an aliphatic alkyl group, or an aliphatic alkenyl group. But,
The above-mentioned fluorine-containing alkyl succinate diester has a problem that it has a large friction coefficient.

[0008]

As described above, in the field of recording media, due to the lack of the ability of the lubricant used, for example, the reproduction output is lowered in the shuttle running test, and the practical characteristics are not achieved. I am dissatisfied. Therefore, the present invention, while maintaining excellent lubricity under various use conditions, the lubricating effect is maintained for a long time,
An object of the present invention is to provide a compound capable of providing excellent running property, abrasion resistance, durability, etc., a lubricant comprising the compound, and a recording medium.

[0009]

That is, the present invention provides the following general formula (1):

[0010]

Embedded image RCH (COOXCOOH) CH ₂ COORf (1)

(Wherein R represents a saturated or unsaturated aliphatic hydrocarbon group having 6 to 30 carbon atoms, Rf represents a saturated or unsaturated partial fluoroalkyl group, and X represents 2
A valent hydrocarbon group or aromatic ring group, a hydrocarbon group or an aromatic ring group substituted with an aromatic ring, or a hydrocarbon group substituted with an aromatic ring is shown. And a partially fluorinated alkyl compound.
The present invention also has the following general formula (1):

[0012]

Embedded image RCH (COOXCOOH) CH ₂ COORf (1)

(Wherein R represents a saturated or unsaturated aliphatic hydrocarbon group having 6 to 30 carbon atoms, Rf represents a saturated or unsaturated partial fluoroalkyl group, and X represents 2
A valent hydrocarbon group or aromatic ring group, a hydrocarbon group or an aromatic ring group substituted with an aromatic ring, or a hydrocarbon group substituted with an aromatic ring is shown. And a partially fluorinated alkyl compound represented by the formula (1). Furthermore, the present invention is a recording medium in which a recording layer and a lubricant layer made of a lubricant are formed at least in sequence on a support, and the lubricant has the following general formula (1):

[0014]

Embedded image RCH (COOXCOOH) CH ₂ COORf (1)

(Wherein R represents a saturated or unsaturated aliphatic hydrocarbon group having 6 to 30 carbon atoms, Rf represents a saturated or unsaturated partial fluoroalkyl group, and X represents 2
A valent hydrocarbon group or aromatic ring group, a hydrocarbon group or an aromatic ring group substituted with an aromatic ring, or a hydrocarbon group substituted with an aromatic ring is shown. And a partially fluorinated alkyl compound represented by the formula (1).

The partially fluorinated alkyl compound of the present invention is a novel substance, and when used as a lubricant for recording media, especially for magnetic recording media, excellent lubricity is maintained under various usage conditions. Thus, it is possible to provide a recording medium in which the lubrication effect is maintained for a long time and which has excellent running properties, abrasion resistance, durability and the like.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the case where the compound of the present invention is used as a lubricant for a magnetic recording medium will be described as an example.

In the partially fluorinated alkyl compound of the present invention, R has 6 to 30 carbon atoms, preferably 8 to 20 carbon atoms.
Is a saturated or unsaturated aliphatic hydrocarbon group. When the carbon number of R is less than 6 or more than 30, the solubility in an organic solvent decreases, and it becomes impossible to form a lubricating layer film on the carbon film layer using the organic solvent.

The partially fluorinated alkyl compound of the present invention is
For example, a succinic acid derivative containing an R group in the general formula (1) and a partial fluoroalkyl group (R
By mixing with an alcohol compound containing f), heating at about 150 ° C. and reacting, washing with an organic solvent or an inorganic solvent, liquid separation washing with a separating funnel, purification using column chromatography, etc. It can be synthesized by removing impurities and unnecessary substances, and then reacting the obtained purified product with the compound containing X and purifying.

Further, as described above, the partially fluorinated alkyl compound of the present invention can be suitably used as a lubricant for recording media, especially magnetic recording media. If necessary, various additives such as a rust preventive may be added to the lubricant. The rust preventive agent may be one used in conventional magnetic recording media, for example, phenols, naphthols, quinones, heterocyclic compounds containing nitrogen atom, heterocyclic compounds containing oxygen atom, sulfur. Examples thereof include heterocyclic compounds containing atoms.

The recording medium of the present invention comprises a lubricant layer containing the above-mentioned lubricant. For example, in the case of a magnetic recording medium, specifically, it is formed on a non-magnetic support by a method such as vapor deposition. A magnetic recording medium of a so-called metal thin film type in which a magnetic layer formed of the formed metal magnetic thin film, a carbon film layer, and a lubricant layer containing the partially fluorinated alkyl compound of the present invention are formed at least sequentially . Also,
If necessary, an underlayer may be formed between the non-magnetic support and the magnetic layer.

The non-magnetic support is not particularly limited, and a known one can be used. For example,
When a rigid substrate such as an Al alloy plate or a glass plate is used as the non-magnetic support, an oxide film such as an alumite treatment or a Ni-P film is formed on the substrate surface to harden the surface. May be.

The metal magnetic thin film forming the magnetic layer is not particularly limited, and known ones can be adopted. For example, it is formed as a continuous film by a method such as plating, sputtering, or vacuum evaporation.
e, Co, Ni and other metals, Co-Ni alloys, Co-P
t-based alloy, Co-Pt-Ni-based alloy, Fe-Co-based alloy, Fe-Ni-based alloy, Fe-Co-Ni-based alloy, Fe
-Ni-B system alloy, Fe-Co-B system alloy, Fe-Co
Examples include in-plane magnetization recording metal magnetic thin films made of —Ni—B type alloys, Co—Cr type alloy magnetic thin films, and the like. In particular, when an in-plane magnetization recording metal magnetic thin film is adopted, Bi, Sb, Pb, Sn, Ga, In, and
An underlayer of a low-melting point nonmagnetic material such as Ge, Si, or Tl is formed, and the above-mentioned metals are vapor-deposited or sputtered on the underlayer in a direction perpendicular to the underlayer, and these low-melting point nonmagnetic materials are formed in the metal magnetic thin film. The material may be diffused to eliminate the orientation, thereby ensuring the in-plane isotropic property and improving the anti-magnetism.

As a method for forming the carbon film layer, sputtering is generally used, but the method is not particularly limited, and any known method can be adopted. The thickness of the carbon film is preferably 2 to 100 nm, more preferably 5 to 30 nm.

The lubricant layer can be formed by topcoating the carbon film layer with a lubricant containing the partially fluorinated alkyl compound of the present invention by a conventional method. The coating amount of the lubricant, for example, preferably 0.5 to 100 mg / m ^2, more preferably 1 to 20 mg / m ^2. For application, a lubricant dissolved in an organic solvent such as hexane can be used. When a rust preventive agent is used, it may be used in combination with a lubricant, but if a rust preventive agent is applied on the carbon film layer and then a lubricant is applied to provide two or more layers, the rust preventive agent can be used. This is preferable because it enhances the rust effect.

The partially fluorinated alkyl compound of the present invention is
As described above, it is preferably used as a lubricant for recording media, especially magnetic recording media. However, the lubricant of the present invention can be applied not only to magnetic recording media but also to optical recording media, and its support is not limited to tapes and can be used for recording media such as disk media such as magnetic disks and optical disks. .

[0027]

In the conventional lubricant, a compound having a relatively large polarity such as a carboxylic acid or an amine salt of a carboxylic acid has a small friction coefficient but tends to have poor still durability. Small compounds have excellent still durability, but have a large friction coefficient. The partially fluorinated alkyl compound of the present invention has a carboxylic acid group of the general formula (1) and two ester groups as terminal polar groups, and thus has a small friction coefficient and excellent still durability. Particularly, when the partially fluorinated alkyl compound of the present invention is applied as a lubricant onto a carbon film layer, the carboxylic acid group of the general formula (1) and two ester groups of the polar base portion of the lubricant molecule are adsorbed onto the carbon film layer. However, due to the cohesive force between the hydrophobic groups, a lubricant layer having good durability can be formed. In addition, while a fluorine-based solvent is essential for applying a conventional fluorine-containing lubricant, the partially fluorinated alkyl compound of the present invention can be applied using a hydrocarbon-based solvent such as toluene or acetone. Therefore, the load on the environment is small, which is preferable. Thus, the magnetic recording medium using the partially fluorinated alkyl compound of the present invention as a lubricant,
Excellent lubricity is maintained under various usage conditions, and the lubrication effect is maintained for a long time, so that excellent running properties, wear resistance, durability, etc. can be provided.

[0028]

EXAMPLES The present invention will be further described below with reference to examples and comparative examples, but the present invention is not limited to the following examples.

Synthesis Example 1 (C ₁₈ H ₃₇ —CH (COOCH
_{(C 11 H 23) CH 2} COOH) CH 2 COO (CH 2)
Synthesis of ₂ (CF ₂ ) ₈ F) Octadecyl succinic anhydride is used as the succinic acid derivative containing the R group in the general formula (1), and fluorine is used as the compound containing the partial fluoroalkyl group (Rf) in the general formula (1). Alcohol F (CF ₂ ) ₈ CH ₂ CH ₂ OH,
3-hydroxymyristic acid CH ₃ (CH ₂ ) ₁₀ CH (OH) CH as the compound containing the X group in the general formula (1)
The partially fluorinated alkyl compound of the present invention was synthesized using ₂ COOH. The synthetic procedure is shown below. 17.7 g of octadecyl succinic anhydride C ₁₈ H ₃₇ C ₄ H ₃ O ₃ and 23.2 g of fluorinated alcohol F (CF ₂ ) ₈ CH ₂ CH ₂ OH.
Were mixed and refluxed at 150 ° C. for 3 hours. After the reaction,
The reaction product was dissolved in 200 ml of toluene and 10% NaO was added.
300 ml of H aqueous solution was added and shaken vigorously. The produced white solid (Na salt of the target product) was suction filtered with a glass filter. Further, 240 ml of water twice, 200 ml of toluene
The white solid was washed once on a glass filter. By this operation, the starting material octadecyl succinic anhydride could be removed. Next, the white solid was placed in a separating funnel, and 300 ml of toluene and 300 ml of 7.2% HCl were added for liquid separation washing and desalting. Further 7.2% HCl 300 ml
(2) and a sodium chloride aqueous solution (2) to perform liquid separation and washing. The toluene phase was recovered and dried over magnesium sulfate. 1
After hours, it was filtered and the toluene phase was concentrated. Subsequently, the recovered product was purified by column chromatography. The column conditions are column packing: silica gel, column temperature: room temperature, eluent: a mixed solvent of toluene and ethyl acetate 20% toluene 80%. The target substance is eluted when a mixed solvent of 20% ethyl acetate and 80% toluene is used. The collected amount was 33 g. The collected product was IR analysis, formula _{C 18 H 37 -CH (COOH)} CH 2 COO (CH 2)
It was found to have ₂ (CF ₂ ) ₈ F.

Further, purified C ₁₈ H ₃₇ --CH (COO
H) 5.0 g of thionyl chloride was added to 33 g of CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₈ F, and the mixture was refluxed at 50 ° C. for 2 hours. After completion of the reaction, the reaction product was concentrated and the target product was recovered.
The collected product was IR analysis, formula C ₁₈ H ₃₇ -CH
It was found to have (COCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₈ F.

Further, purified C₁₈H₃₇-CH (COC
l) CH₂COO (CH₂)₂(CF₂)₈3-hydro to F
Xymyristic acid CH₃(CH₂)_TenCH (OH) CH₂
12 g of COOH was added and refluxed at 100 ° C. for 2 hours.
After completion of the reaction, dissolve the reaction product in 200 ml of toluene,
Separation and washing with an aqueous sodium chloride solution twice in a separating funnel
Then, the toluene phase is recovered and dried with magnesium sulfate.
It was After 1 hour, it was filtered and the toluene phase was concentrated. Continued
Then, the recovered product is purified by column chromatography.
It was Column condition is column packing: silica gel, column
Temperature: room temperature, eluent: toluene and ethyl acetate 10%
It is a mixed solution of 90% toluene. The target product is ethyl acetate
Elutes when using a mixed solution of 10% toluene and 90%
It The recovered product was 37 g, and the recovery rate was about 70%.
IR analysis of the recovered material revealed that it had the general formula C ₁₈H₃₇-CH
(COOCH (C₁₁H_{twenty three}) CH₂COOH) CH₂COO
(CH₂)₂(CF₂)₈It was found to have F. Figure 1
The IR analysis results are shown in.

Synthesis Example 2 (C ₁₈ H ₃₇ —CH (COOC ₆ H ₄
COOH) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₈ F) Octadecyl succinic anhydride is used as the succinic acid derivative containing the R group in the general formula (1), and partial fluoroalkyl in the general formula (1) is used. Fluorinated alcohol F (CF ₂ ) ₈ CH ₂ CH ₂ OH is used as a compound containing a group (Rf),
The partially fluorinated alkyl compound of the present invention was synthesized using 4-hydroxybenzoic acid HOC ₆ H ₄ COOH as the compound containing the X group in the general formula (1). The synthetic procedure is shown below. First, under the same reaction conditions as in Synthesis Example 1, 17.7 g of octadecyl succinic anhydride and fluorinated alcohol F
By reacting 23.2 g of (CF ₂ ) ₈ CH ₂ CH ₂ OH, and by the same separation and purification method as in Synthesis Example 1, from IR analysis, the general formula C ₁₈ H ₃₇ —CH (COOH) CH ₂ COO (CH ₂ ) ₂
A reaction product having (CF ₂ ) ₈ F was obtained. Then, 33 g of this reaction product was reacted with 5 g of thionyl chloride under the same reaction conditions as in Synthesis Example 1 and, by the same separation and purification method as in Synthesis Example 1, from IR analysis to the general formula C ₁₈ H ₃₇ —CH ( C
OCl) CH ₂ COO (CH ₂ ) ₂ (CF ₂ ) ₈ F was obtained as the acid chloride.

Next, purified C₁₈H₃₇-CH (COC
l) CH₂COO (CH₂)₂(CF₂) ₈4-hydro on F
Xybenzoic acid HOC₆H_FourAdd 6.9g of COOH, 2:00
The mixture was refluxed at 100 ° C for a while. After the reaction, toluene 200
Dissolve the reaction product in ml and add sodium chloride in a separating funnel.
Separation and washing with an aqueous solution of water twice to recover the toluene phase
Dried with magnesium acidate. After 1 hour, filter and
The ene phase was concentrated. Then, column chromatography
The collected product was purified by. Column conditions are column packing
Substance: silica gel, column temperature: room temperature, eluent: toluene
And a mixed solution of 10% ethyl acetate and 90% toluene.
It The target product is a mixed solution of 10% ethyl acetate and 90% toluene.
Elute when the liquid is used. The collected product is 31g.
The yield was about 65%. IR analysis of the recovered material revealed that
General formula C₁₈H₃₇-CH (COOC₆H_FourCOOH) CH₂
COO (CH₂)₂(CF₂)₈Found to have F
It was FIG. 2 shows the IR analysis result.

If the same procedure as described above is adopted, the R group and the partial fluoroalkyl group (R
By setting f) arbitrarily, the partially fluorinated alkyl compound of the present invention can be synthesized. Specific examples thereof are shown in Tables 1 and 2 below.

[0035]

[Table 1]

[0036]

[Table 2]

Examples 1 to 23 Partially fluorinated alkyl compounds of the present invention having the structures shown in Table 3 below were synthesized by the same procedure as in the above-mentioned synthesis example, and used as lubricants in the following tests.

[0038]

[Table 3]

Comparative Examples 1 to 5 The compounds having the structures shown in Table 4 below were used as lubricants in the following tests.

[0040]

[Table 4]

Preparation of sample tape Co was vapor-deposited on a polyethylene terephthalate film having a thickness of 7.0 μm to form a magnetic layer composed of a metal magnetic thin film having a thickness of 180 nm. Next, a carbon film layer having a thickness of about 8 nm was formed on the magnetic layer using a magnetron sputtering device. Next, a 0.5 μm thick back coat layer made of carbon and polyurethane resin was formed on the surface of the polyethylene terephthalate film opposite to the surface on which the magnetic layer was formed. Subsequently, the compounds shown in Table 3 or Table 4 were dissolved in toluene and applied onto the surface of the carbon film layer so that the application amount of the compound was 5 mg / m ² . The obtained magnetic recording medium is 6.35 mm
The sample tape was cut into widths.

Evaluation of Durability and Travelability Using each sample tape prepared as described above,
The coefficient of friction was measured under the conditions of a temperature of 40 ° C. and a relative humidity of 80%, the still durability was measured under the conditions of a temperature of −5 ° C., and the shuttle durability was measured under the conditions of a temperature of 40 ° C. and a relative humidity of 20%. The results are shown in Table 5. It should be noted that these conditions in this example are considered to be the most severe usage conditions. A commercially available digital video camcorder (VX1000 manufactured by Sony Corporation) was used for measuring the still durability and the shuttle durability.

(1) Friction coefficient measuring method The friction coefficient was measured in a constant temperature bath at a temperature of 40 ° C. and a relative humidity of 8
Control the sample tape to 0% and set the sample tape to 1
The measurement was carried out by running 00 times. In addition, the numerical value after running 100 times is shown in the table as a friction coefficient. (2) Still Durability Measurement Method Still durability was measured in a constant temperature bath at -5 ° C, and the time until the reproduction output dropped by 3 dB was measured. (3) Shuttle durability measurement method Shuttle durability is measured in a thermostatic chamber at a temperature of 40 ° C and a relative humidity of 20.
%, The 60-minute length of the sample tape was run 100 times in the Play mode, and how many dB the playback output dropped from the initial output after running 100 times was measured.

Evaluation of Solubility in Solvents The lubricants used in Examples 1 to 23 and Comparative Example 3 were examined for solubility in ethanol, acetone and toluene. The evaluation was evaluated as ◯ when it was easily soluble in each solvent, and as x when the lubricant was insoluble in the solvent. Table 6 shows the results of the solubility evaluation of each lubricant.

[0045]

[Table 5]

[0046]

[Table 6]

From the above results, by using the partially fluorinated alkyl compound of the present invention as a lubricant for a magnetic recording medium, the friction coefficient and the still durability under various use conditions such as high temperature and high humidity, high temperature and low humidity, and low temperature. It can be seen that there is very little deterioration in durability or shuttle durability, and very good results are obtained.

[0048]

INDUSTRIAL APPLICABILITY The partially fluorinated alkyl compound of the present invention is particularly useful as a lubricant for magnetic recording media.
Further, when the above-mentioned partially fluorinated alkyl compound is used as a lubricant for a recording medium, excellent lubricity is maintained under various conditions of use, the lubricating effect is maintained for a long time, and excellent running property and durability are obtained. A recording medium that can provide abrasion resistance, durability, and the like can be obtained.

[Brief description of drawings]

FIG. 1 is a kind of partially fluorinated alkyl compound of the present invention, which is C ₁₈ H ₃₇ —CH (COOCH (C ₁₁ H ₂₃ ) CH ₂ C.
_{OOH) CH 2 COO (CH 2} ) 2 (CF 2) shows the IR analysis results of ₈ F.

FIG. 2 is a kind of partially fluorinated alkyl compound of the present invention
Some C₁₈H₃₇-CH (COOC ₆H_FourCOOH) CH₂C
OO (CH₂)₂(CF₂)₈In the figure which shows the IR analysis result of F
is there.

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G11B 5/725 G11B 5/725 // C10N 30:00 C10N 30:00 Z 30:06 30:06 40:18 40: 18 (72) Inventor Takahiro Kamei 6-735 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation (72) Inventor Kenichi Kurihara 6-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation ( 72) Inventor Hiroshi Iwamoto 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony Corporation (72) Inventor Toshinori Tsuboi 6-735 Kitashinagawa, Shinagawa-ku, Tokyo Sony F-term ( Reference) 4H006 AA01 AA03 AB60 BJ50 BM10 4H104 BD07A LA03 LA20 PA16 5D006 AA01 FA06

Claims (4)

[Claims] 1. The following general formula (1): RCH (COOXCOOH) CH ₂ COORf (1) (wherein R is a saturated or unsaturated aliphatic hydrocarbon having 6 to 30 carbon atoms). Rf is a saturated or unsaturated partial fluoroalkyl group, X is a divalent hydrocarbon group or an aromatic ring group, or an aromatic ring group substituted with a hydrocarbon group or an aromatic ring, or an aromatic ring. A partially fluorinated alkyl compound, which is represented by a substituted hydrocarbon group. 2. The following general formula (1): RCH (COOXCOOH) CH ₂ COORf (1) (wherein R is a saturated or unsaturated aliphatic hydrocarbon having 6 to 30 carbon atoms). Rf is a saturated or unsaturated partial fluoroalkyl group, X is a divalent hydrocarbon group or an aromatic ring group, or an aromatic ring group substituted with a hydrocarbon group or an aromatic ring, or an aromatic ring. And a partially fluorinated alkyl-based compound represented by a substituted hydrocarbon group). 3. A recording medium in which a recording layer and a lubricant layer made of a lubricant are sequentially formed on a support, wherein the lubricant has the following general formula (1): (COOXCOOH) CH ₂ COORf (1) (In the formula, R represents a saturated or unsaturated aliphatic hydrocarbon group having 6 to 30 carbon atoms, and Rf represents a saturated or unsaturated partial fluoroalkyl group. , X represents a divalent hydrocarbon group or an aromatic ring group, a hydrocarbon group, an aromatic ring group substituted with an aromatic ring, or a hydrocarbon group substituted with an aromatic ring. A recording medium containing an alkyl compound. 4. The recording medium according to claim 3, wherein the recording layer is a magnetic layer, and the recording medium is a magnetic recording medium.