JPH07138589A - Lubricating composition and recording medium lubricated therewith - Google Patents

Abstract

PURPOSE:To obtain a lubricating composition which can be firmly held by the protective layer of a recording medium and has excellent sliding properties and sufficient durability by mixing a silicone oil and a fatty-acid-modified silicone as the essential components with a fatty acid ester as an optional component. CONSTITUTION:The composition comprises a silicone oil (a) and a fatty-acid- modified silicone (b) of the formula (wherein R is an aliphatic hydrocarbon group; m is 5-500; and n is 1 or greater) as the essential components and a fatty acid ester (c) as an optional component and satisfying the relationships: 0.1<=a/(a+b)<=0.98, 0.5<=b/(b+c)<=0.9, and 0.01<=c/(c+a)<=0.1 (wherein a, b and c are the amounts (pts.wt.) of the components, respectively) and the relationships: 1<=Ma/Mb<=100, 2<=Mb/Mc<=50, and 0.002<=Mc/Ma<=0.2 (wherein Ma, Mb and Mc are the number-average molecular weights, respectively). A recording medium which slidably contacts with the head is prepared by forming a recording layer on a transparent disc base, forming a protective coating layer comprising a synthetic resin on the recording layer, and applying the lubricating composition to form a 1nm to 1mum-thick lubricating layer on the protective layer.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to general purpose lubricating compositions. Above all, it is suitable for use in recording media such as magnetic recording, optical recording, and magneto-optical recording in the form of disks and tapes, and in particular, provides a useful lubricating composition with excellent sliding resistance. However, as shown below, it is particularly useful when applied to a magneto-optical recording medium for recording while sliding the magnetic head at a low speed.

[0002]

2. Description of the Related Art As a lubricant, a fatty acid-modified silicone,
Fatty acid esters, silicone oils, fluorine oils, etc. have been well known until now. In fact, these lubricants have been used extensively in various mechanical friction mechanisms to reduce sliding resistance. However, in many cases, mechanical parts are made of a strong metal, and minute scratches on the surface of the member due to sliding have not been a problem so much. Conventionally, different types of lubricants have been used together. That is, there were few opportunities to seriously consider the lubricating composition.

However, with the development of the precision industry, the design has been made under severe lubrication conditions such as the minute sliding contact of the minute parts made of synthetic resin, which cannot be expected to have high strength, and the durability against friction has been improved. The role of a lubricant that complements the performance of parts has come into the limelight during rigorous evaluation.
Along with this, even more stringent demands have been made for lubrication such as reduction of friction in mechanical parts of electronic devices.

Among them, a so-called recording medium is an example where such lubrication is most severely required. In particular, in magneto-optical recording media, the magnetic thin film is partially cured.
The basic principle is to raise the temperature beyond the point or the temperature compensation point to eliminate the coercive force in this part and to reverse the direction of the magnetization in the direction of the recording magnetic field applied from the outside. It is being put to practical use in an external storage device of a computer or a recording device for audio and video information. The general structure is to stack a recording magnetic layer, a reflective layer, and a dielectric layer that have an easy axis of magnetization in the direction perpendicular to the film surface and have a large magneto-optical effect on one surface of a transparent substrate made of polycarbonate or the like. The recording portion is formed, and a coating layer that plays a protective role is formed to protect the recording layer from corrosion and the like. As a material for the coating layer, that is, the protective layer, a soft ultraviolet curable resin (UV resin), a silicone resin or the like is no longer used as a metal.
Then, it is devised to read the signal by irradiating the laser beam from the transparent substrate side. Among the magneto-optical recording methods, the overwritable magnetic field modulation method writes an information signal in a magnetic thin film by reversing the applied magnetic field at a high speed. Done by the head.

In this case, a magnetic head applying a high-speed reversal magnetic field can generate only a very small magnetic field due to various restrictions, and it is necessary to bring the magnetic head as close to the recording magnetic layer as possible. However, a non-contact so-called flying head cannot be used like a hard disk in a rotation system of 1000 rpm or less, especially a low speed rotation system of a rotation speed of 300 to 800 rpm. Therefore, the magnetic head is slid on the magneto-optical recording medium. A magneto-optical recording method is conceivable for recording while recording. In this case, the magnetic head and coating layer (protective layer)
Sliding between them becomes a problem.

[0006]

If the friction between the magnetic head and the coating layer (protective layer) is high, the magnetic head vibrates while the magnetic head is running, and recording is hindered. The head itself cannot run. In addition, scratches and abrasion of the coating layer (protective layer) due to sliding pose problems. In order to solve this problem, it is necessary to reduce mutual friction between the two.

Conventionally, in order to reduce the friction between the recording medium and the magnetic head, a lubricant is applied like a magnetic disk, or a lubricant is added to a magnetic layer like a floppy disk (FD). Came. Known lubricants used in these are fatty acid-modified silicone, fatty acid ester, silicone oil, and fluorine oil.

However, the recording material of the magneto-optical recording medium, especially the magneto-optical disk is made of a magnetic material,
Since it itself is soft and easily scratched, it is covered with a coating layer (protective layer) of synthetic resin such as UV resin. If the conventional lubricant is simply applied here, there is a peculiar phenomenon that the lubricant is cut off during sliding, so that the sliding characteristics are deteriorated. Indeed, these lubricants have been shown to be useful in reducing the friction between metals and metal oxides. However, reduction between polymers such as UV resin, reduction of abrasion of polymers, reduction of friction at high speed sliding,
I was not able to say that it was exerting the effect to give enough satisfaction to.

This means that the lubrication means in the FD or hard disk cannot be transferred as it is. The possible causes of this are as follows. Unlike the magnetic disk in which the flying head slides at the start and stop, there is a unique phenomenon that the magnetic head or the support and the protective layer always slide at the time of recording. Therefore, unlike the floppy disk, it is impossible to prevent the lubricant from being broken by accumulating the lubricant in the voids of the magnetic layer. That is, since the interaction between the ultraviolet curable resin and the conventional lubricant is small like the metal thin film medium and the lubricant having a polar group, the lubricant cannot be strongly held in the medium. To overcome this problem, the present inventor has found the following means.

[0010]

Means for Solving the Problems That is, the inventors of the present invention have made various investigations in order to achieve the above-mentioned object. As a lubricating composition, the silicone oil (a) and the fatty acid-modified silicone ( When at least b) is contained, the lubricating effect is great and the lubricant is not broken. This is because the silicone oil (a) has a strong interaction with the protective layer due to the Van der Waals interaction and the fatty acid-modified silicone (b) having a strong oil film strength of itself.
This is because and are easily compatible with each other. Silicone oil (a)
When the fatty acid-modified silicone (b) was used alone, the lubricating effect was small, and when the fatty acid-modified silicone (b) alone had a small interaction with the protective layer of the UV-curable resin, the lubricant was broken. As a result, sufficient sliding resistance can be secured even when the recording medium is slid with the magnetic head or the magnetic head support. When the fatty acid ester (c) is further contained, the compatibility between the fatty acid-modified silicone (b) and the fatty acid ester (c) is good, so that the lubricating composition is strongly retained in the protective layer as described above. Further, since the fatty acid ester (c) has a further excellent lubricating function, the lubricating composition (a + b + c) containing the fatty acid ester has a further excellent sliding property, low friction and stable magnetic head running property, and sufficient durability against abrasion and damage. You can secure the sex.

As described above, since the roles of the silicone oil (a), the fatty acid-modified silicone (b) and the fatty acid ester (c) are subtly different, they can be used for recording media such as magnetic recording, optical recording and magneto-optical recording. In order to obtain a particularly suitable lubricating composition, the weight ratio of a and b is 0.1 ≦ a / (a + b) ≦ 0.98, and b and c
In the weight ratio of 0.5 ≦ b / (b + c) ≦ 0.9
9, in the weight ratio of c and a, 0.001 ≦ c / (c +
It is desirable to regulate each composition ratio such that a) ≦ 0.1. Also, in the number average molecular weight Ma of a and the number average molecular weight Mb of b, 1 ≦ Ma / Mb ≦ 100, and in the number average molecular weight Mb of b and the number average molecular weight Mc of c, 2 ≦ Mb / Mc ≦
In the number average molecular weight Mc of 50 and c and the number average molecular weight Ma of a, it is desirable to regulate the composition ratio of 0.002 ≦ Mc / Ma ≦ 0.2.

In particular, such a lubricating composition has 1000 rp
The effect is remarkable for a magneto-optical recording medium in which a signal is recorded by sliding contact with a magnetic head at a low speed rotation of m or less. This type of magneto-optical recording medium has a recording magnetic layer on a disk-shaped transparent substrate, and a coating layer containing a synthetic resin is formed on the recording magnetic layer, and a method such as coating on the surface of the coating layer is used. You can place it in.

FIG. 1 shows a sectional structure of an example of a magneto-optical recording medium according to the present invention. As is clear from this figure, as an example of the magneto-optical recording medium of the present invention, the first dielectric layer 2, the magnetic layer 3 and the second dielectric layer 4 are formed on the surface of the transparent substrate 1.
And a reflective layer 5 are sequentially laminated, the surface of the reflective layer 5 is covered with a protective layer 6, and a lubricating layer 7 is formed on the surface of the protective layer 6.

The transparent substrate 1 is formed of a transparent ceramic material such as glass, a transparent resin material such as a polycarbonate resin, a polymethylmethacrylate resin, a polyolefin resin, an epoxy resin, or the like into a desired shape and size. On one surface of the transparent substrate 1, a pre-format pattern such as a guide groove for a recording / reproducing laser beam or a pre-bit string is formed in a fine concavo-convex shape to form a signal surface. The method of forming the preformatted pattern and the arrangement of the preformatted pattern are well-known techniques and are not the subject matter of the present invention, so the description thereof is omitted. Appropriate known techniques can be applied to these depending on the type of the magneto-optical recording medium.

The first dielectric layer 2 is provided to cause multiple interference of the reproducing laser beam between the transparent substrate 1 and the magnetic layer 3 to increase the apparent magneto-optical effect. And is formed of an inorganic dielectric material having a refractive index larger than that of the transparent substrate 1. The magnetic layer 4 can be formed of any known material exhibiting a magneto-optical effect. However, since the magneto-optical effect such as the Kerr rotation angle or the Faraday rotation angle is large, the amorphous perpendicular magnetization of rare earth-transition metal system is used. Membranes are particularly suitable. The second dielectric layer 4 causes multiple reproduction laser beams to interfere between the magnetic layer 3 and the reflection layer 5,
It is provided to increase the apparent magneto-optical effect, and is formed of the same inorganic dielectric material as the first dielectric layer 2. The reflective layer 5 enhances the reflectance of the medium and enhances the reproduction signal output from the magneto-optical recording medium, and is formed of, for example, aluminum or gold, or an alloy containing each of these metals as a main component. The layers 2 to 5 can be continuously formed by a vacuum film forming method such as sputtering or vacuum evaporation.

The protective layer 6 is for preventing corrosion of the magnetic layer 3 due to the storage environment, and is preferably formed of an ultraviolet curable resin. As the ultraviolet curable resin, all known resins can be used. The thickness of the protective layer 6 is preferably about 0.1 μm to 50 μm. When the film thickness of the protective layer 6 exceeds 50 μm, the strength of the magnetic field reaching the magnetic layer 3 becomes small and a large recording current is required at the time of recording or erasing. On the contrary, the film thickness of the protective layer 6 is less than 0.01 μm. If so, sufficient impact resistance and the like cannot be exhibited. The protective layer 6 can be formed by a spray coating method, a spin coating method, or the like. The lubricating layer 7 reduces the frictional force between the protective layer and the magnetic head during magneto-optical recording, ensures stable running of the magnetic head, and protects the disk by sliding the magnetic head, and various films such as a magnetic film. To prevent wear and damage. The material constituting the lubricating layer is an important point in the present invention, and it is important to use a lubricating composition containing at least silicone oil and a fatty acid-modified silicone as a lubricant, or a lubricating composition further containing a fatty acid ester. is there.

As the silicone oil, dimethyl silicone oil, methyl phenyl silicone oil in which a part of the methyl group of dimethyl silicone oil is replaced with a phenyl group, and alkyl-modified silicone oil in which a part of the methyl group of dimethyl silicone oil is replaced with an alkyl group Etc. The viscosity of the silicone oil is preferably 10 cSt or more, more preferably 1000 cSt or more. The fatty acid-modified silicone may be any one of silicone oil whose terminal or side chain is modified with a fatty acid.

[0018]

[Chemical 2]

In the formula, R is an aliphatic hydrocarbon group,
It is preferable that m is an integer of 5 ≦ m ≦ 500 and n is an integer of 1 or more. R in this general formula (1) is an aliphatic hydrocarbon group, which may be linear or branched, and may further contain a double bond.

Examples of the fatty acid ester include fatty acids such as lauric acid, myristic acid, palmitic acid, stearic acid and oleic acid, and methyl alcohol, ethyl alcohol,
Any esterified alcohol such as butyl alcohol, octyl alcohol and oleyl alcohol may be used, and a double bond or a branch may be present in the molecule.

The thickness of the lubricating layer is preferably 1 nm to 1 μm. If this thickness exceeds 1 μm, problems such as sticking of the magnetic head to the disk may occur, which is a problem in running performance. On the contrary, if the thickness is less than 1 nm, it becomes difficult to secure sufficient durability.

The method of forming the lubricating layer in the present invention may be any method, but a solution obtained by dissolving the above lubricant in a solvent is applied onto the protective layer by a spin coater, a roll coater, a bar coater or the like. It can be formed by drying.

[0023]

By doing so, in a magneto-optical recording medium in which a protective layer such as an ultraviolet curable resin is formed, the conventional silicone oil, fluorine oil and fatty acid ester can be achieved by simply coating the protective layer. Can't
It is possible to exert the unique effect that the lubricant does not break even when sliding and maintains sliding characteristics, and sufficient sliding resistance even when sliding the magnetic head or magnetic head support and the recording medium. Can be secured.

[0024]

EXAMPLES Hereinafter, specific examples of the present invention will be described, but the present invention is not limited to these examples.

<Experiment with Polymethyl Methacrylate Disk> Example 1: On a polymethylmethacrylate disk having a thickness of 2 mm and a diameter of 70 mm, dimethyl silicone oil (average molecular weight about 38000) (viscosity about 50 parts by weight of 10000 cSt), 8 parts by weight of fatty acid-modified silicone (a) having the following structure with an average molecular weight of about 3300, 9 parts by weight of fatty acid-modified silicone (b), and methyl stearate (molecular weight 298). 1 part by weight, 2 parts by weight of oleyl oleate (molecular weight 532), and hexane 2500
A lubricating composition consisting of 0 parts by weight was applied. The structures of the fatty acid-modified silicones (a) and (b) are as follows.

[0026]

[Chemical 3]

[0027]

[Chemical 4]

Using a friction measuring machine having a plastic slider having a radius of curvature of 5 mm, the slider was brought into contact with the polymethyl methacrylate disk at a position of a radius of 25 mm, and the slider was attached to the slider. After applying a load of 7g, remove this plate for 500r
It was rotated at pm and the degree of scratches on the surface was examined. The degree of scratches was evaluated in the same manner as the determination of sliding scratches on the magneto-optical disk described later. As a result, there was no scratch, and the evaluation was A. Further, while fixing the molecular weight in Example 1 above, the amounts of dimethyl silicone oil A, fatty acid-modified silicone (a) B and methyl stearate C were varied as follows. Example 2, Example 3
The degree of scratches on the surface of the polymethylmethacrylate disk was evaluated. The results are shown in Table 1.

[0029]

[Table 1]

Subsequently, in Example 1, while fixing the blending amount,
The molecular weight Ma of the dimethyl silicone oil, the molecular weight Mb of the fatty acid-modified silicone (a), and the molecular weight Mc of the fatty acid ester were changed as follows, and the polymethyl methacrylate disk surface of Examples 4 to 9 was changed. The degree of scratching was evaluated. The results are shown in Table 2.

[0031]

[Table 2]

The degree of scratches on the polymethyl methacrylate plate was determined by magnifying a sliding mark after 20 passes by 50 times using a micrograph taking device manufactured by Olympus Co., and visually observed by 100 observers. After observing, the average value was taken and the comprehensive evaluation was calculated. As a result, 90 or more people judged that there were no sliding scratches A, and 60 or more people judged that there were no sliding scratches B. The degree of scratches was objectively evaluated as much as possible.

<Production of magneto-optical disk> Thickness 1.2 m
A magneto-optical disk was prepared by sequentially forming the following four layers on a disc-shaped transparent substrate (refractive index: 1.58) made of polycarbonate and having a diameter of 64 mm. The film thickness of each layer is as follows.

First dielectric layer Si3N4 1000A Recording magnetic layer Te-Fe-Co-Cr 230A Second dielectric layer Si3N4 500A Reflective layer Al 700A Protective layer UV curable resin 10 μm Example 10 Protective layer of this magneto-optical disc A lubricating composition similar to that used in Example 1 was applied on top.

Example 11 50 parts by weight of dimethyl silicone oil (average molecular weight about 38,000) was added on the protective layer of the above magneto-optical disk.
A lubricating composition containing 10 parts by weight of the fatty acid-modified silicone (a) used in Example 1, 10 parts by weight of the fatty acid-modified silicone (b), and 25,000 parts by weight of hexane was prepared and applied in the same manner as in Example 1. .

Comparative Example 1 70 parts by weight of dimethyl silicone oil (average molecular weight of about 38,000) was added on the protective layer of the above magneto-optical disk.
A lubricating composition containing 25,000 parts by weight of hexane was prepared and applied in the same manner as in Example 1.

Comparative Example 2 A lubricating composition comprising 70 parts by weight of fatty acid-modified silicone (a) and 25000 parts by weight of hexane was prepared on the protective layer of the above magneto-optical disk, and the same procedure as in Example 1 was carried out. Applied.

Comparative Example 3 A lubricating composition containing 70 parts by weight of butyl oleate and 25000 parts by weight of hexane was prepared on the protective layer of the above magneto-optical disk and applied in the same manner as in Example 1.

Comparative Example 4 50 parts by weight of dimethyl silicone oil (average molecular weight of about 38,000) was added on the protective layer of the above magneto-optical disk.
A lubricating composition consisting of 20 parts by weight of butyl oleate and 25000 parts by weight was prepared and applied in the same manner as in Example 1.

Comparative Example 5 A lubricating composition comprising 50 parts by weight of fatty acid-modified silicone (a), 20 parts by weight of butyl oleate, and 25000 parts by weight of hexane was prepared on the protective layer of the above magneto-optical disk. Application was carried out in the same manner as in Example 1.

The radius of curvature of the magneto-optical disk is 5
Using a friction measuring machine with a mm plastic slider, bring the slider into contact with the radius of 25 mm of the magneto-optical disk, apply a load of 3 g to the slider, and then rotate the magneto-optical disk at 500 rpm. After rotating, the coefficient of friction and the degree of scratching of the protective layer were examined.

[0042]

[Table 3]

The friction coefficient in this table was evaluated by measuring the friction coefficient after 20,000 passes. The degree of scratches on the surface of the protective layer was determined by enlarging the sliding marks after 20,000 passes by 50 times using a microphotographing apparatus manufactured by Olympus Co., Ltd., and taking an average value through visual observation by 100 observers. A comprehensive evaluation was calculated, and as a result, 90 or more people judged that there were no sliding scratches, A, 60 people or more judged that there were no sliding scratches, B, and 60 people or more partially. What was judged to have sliding scratches on the circumference was represented by C, and what was judged by 60 or more people to have sliding scratches on the entire circumference was represented by D, and the extent of the scratch was objectively evaluated as far as possible.

[0044]

As is apparent from the above table, the magneto-optical disks obtained in the examples have a low coefficient of friction and the degree of scratches on the protective layer is small. From this, it is understood that the magneto-optical recording medium obtained by the present invention has a further improved durability when the magnetic head is slid.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical disk according to the present invention.

[Explanation of symbols]

 1 Transparent Substrate 1 2 First Dielectric Layer 3 Magnetic Layer 4 Second Dielectric Layer 5 Reflective Layer 6 Protective Layer 7 Lubricating Layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication C10M 107: 50 139: 04 129: 70) C10N 20:04 40:18

Claims (8)

[Claims] 1. A lubricating composition containing at least a silicone oil (a) and a fatty acid-modified silicone (b). 2. The lubricating composition for a recording medium according to claim 1, further comprising a fatty acid ester (c). 3. The weight ratio of a to b is 0.1 ≦ a /
The lubricating composition according to claim 1, wherein (a + b) ≦ 0.98. 4. The number average molecular weight Ma of a and the number average molecular weight Mb of b are 1 ≦ Ma / Mb ≦ 100.
The lubricating composition described. 5. The lubricating composition according to claim 2, wherein the number average molecular weight Mb of b and the number average molecular weight Mc of c are 2 ≦ Mb / Mc ≦ 50. 6. The lubricating composition according to claim 2, wherein the number average molecular weight Mc of c and the number average molecular weight Ma of a are 0.002 ≦ Mc / Ma ≦ 0.2. 7. The fatty acid-modified silicone b has the general formula: (In the formula, R is an aliphatic hydrocarbon group,
It may be branched or may contain a double bond. m is an integer of 5 ≦ m ≦ 500, and n is 1
The lubricating composition according to claim 1, wherein the lubricating composition is represented by the above integers. 8. A recording medium in which signals are recorded by slidingly contacting a head, the recording medium having a recording layer on a disk-shaped transparent substrate, and a coating layer containing a synthetic resin formed on the recording layer. A recording medium having the lubricating composition according to claim 1 disposed on its surface.