JPH07161031A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the toughness and hydrophobic property of a protective layer by using a polyorganosiloxane-contg. layer formed by curing a coating soln. contg. specified organosilicon compds. and specified hard fine particles as the protective layer. CONSTITUTION:A protective layer 5 and a lubricating layer 6 are laminated on a magnetic layer 4. When a coating soln. contg. organosilicon compds. represented by the formulae R S<1>n(R<2>)4-n and Si(R<2>)4 and hard fine particles of a metal oxide is applied to the smooth surface of the layer 4 and heat-cured and the resulting polyorganosiloxane-contg. layer is used as the protective layer 5, the layer 5 has improved toughness and hydrophobic property. In this case, the surface of the layer 5 is made rugged by the hard fine particles and the lubricating layer 6 with a rugged surface is formed on the layer 5. In the formulae, R<1> is satd. hydrocarbon or hydrocarbon contg. F or Cl, R<2> is alkoxy, alkoxyalkoxy, isocyanato or Cl and (n) is an integer of 1-3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic recording medium having a lubricating layer excellent in durability. More specifically, the present invention relates to a magnetic recording medium in which the toughness of the protective layer is improved and the adhesion between the protective layer and the lubricating layer is improved.

[0002]

2. Description of the Related Art Generally, a magnetic recording medium used in a contact start stop (hereinafter referred to as CSS) type magnetic disk device is manufactured by sequentially forming a magnetic layer, a protective layer and a lubricating layer on a non-magnetic substrate. It The protective layer has environmental resistance of the magnetic layer and damage prevention by direct contact with the magnetic head, and the lubricating layer plays a role of reducing wear of the protective layer. The protective layer is made of a metal oxide such as silicon dioxide, a metal nitride such as silicon nitride, or an inorganic substance such as amorphous carbon from the viewpoint of good wear resistance or lubricity. As the lubricating layer, a perfluoropolyether liquid lubricant is used because of its chemical stability, low vapor pressure, low surface tension, boundary lubricity, and good adhesion to the protective layer. Further, in order to reduce the friction between the magnetic recording medium and the magnetic head, fine irregularities are provided on the surface of the magnetic recording medium. It has been attempted to improve the CSS durability of the magnetic recording medium by providing the surface of the magnetic recording medium with appropriate irregularities and lubricity.

In JP-A-61-229227 or JP-A-61-732227, hard fine particles are dispersed on a magnetic layer for the purpose of forming such irregularities simultaneously with the formation of a protective layer. There is disclosed a magnetic recording medium having a protective layer formed by coating and curing a hydrolyzed solution of tetraalkoxysilane. In addition, JP-A-2-1371
Japanese Unexamined Patent Publication No. 20 discloses that the durability to the CSS test can be improved by limiting the particle size, the existing density of the hard fine particles dispersed in the protective layer, and the coating thickness of the recesses where the hard fine particles do not exist. .

[0004]

However, in the prior art in which silicon dioxide is used as a matrix to disperse the hard particles as a protective layer, the uniform coating property of the lubricating layer and the adhesive force between the protective layer and the lubricating layer are not always sufficient. I couldn't say that. That is, the coefficient of friction varies depending on the location on the surface of the protective layer, and its durability is not sufficient. For example, in the portion where the lubricating layer disappears, the friction coefficient increases remarkably, and since silicon dioxide is fragile, there is a problem that the protective layer eventually wears and breaks, and sometimes the magnetic layer also breaks. The present invention has been made to solve the above problems, and provides a magnetic recording medium in which abrasion and destruction of a protective layer by a magnetic head are reduced by improving the toughness and hydrophobicity of the protective layer. To aim.

[0005]

The present invention provides a magnetic recording medium in which a magnetic layer, a protective layer and a lubricating layer are sequentially formed on a non-magnetic substrate having a smooth surface, and the protective layer is formed by the following general formula: A magnetic recording medium characterized by forming a polyorganosiloxane-containing layer formed by applying a coating solution containing the organosilicon compound represented by (1) and (2) and hard fine particles onto the magnetic layer and curing the coating solution. Is.

R ¹ _n Si (R ² ) _4-n (1) Si (R ² ) ₄ (2) where R ^{1 is a} saturated hydrocarbon group, a hydrocarbon group containing fluorine or chlorine, and R ² may be the same or different, R ² : an alkoxy group, an acyloxy group, an alkoxyalkoxy group, an isocyanate group or a chlorine element, which may be the same or different, n: 1 to 3 , Which is an integer.

The protective layer of the present invention comprises an organosilicon compound represented by the general formula (1) and / or a partial hydrolysis-condensation product thereof (hereinafter referred to as a derivative), an organosilicon compound represented by the general formula (2), and It can be formed by applying a coating solution containing a hardened fine particle and / or a partially hydrolyzed condensate thereof (hereinafter referred to as a derivative) on the magnetic layer and curing it. Here, the hydrolysis-condensation product is represented by the general formula (1),
The alkoxy group, the alkoxyalkoxy group, the acylalkoxy group, the isocyanate group in the organosilicon compound represented by (2), the one in which some or all of the chlorine elements are substituted with a hydroxyl group, and the one in which some condensation has further proceeded Say.

Examples of the organosilicon compound represented by the general formula (1) used in the present invention include methyltriethoxysilane, phenyltrimethoxysilane, n-octyltriethoxysilane, γ-chloropropyltrimethoxysilane and 3,3. , 3-trifluoropropyltrimethoxysilane, heptadecafluorodecyltrimethoxysilane,
Dimethyldiethoxysilane, dimethyldichlorosilane,
Trimethylchlorosilane and the like can be mentioned as a typical example. Typical examples of the organosilicon compound represented by the general formula (2) used in the present invention include tetramethoxysilane, tetraethoxysilane, tetraacetoxysilane, and tetraisocyanatesilane.

When a lubricant such as perfluoropolyether is applied after forming a protective layer using the organosilicon compound represented by the general formula (1) and / or its derivative, it is possible to reduce friction and durability. Improvement is recognized. This is because even if the lubrication layer is not applied uniformly,
It is presumed that the durability of the protective layer is improved due to the low friction property and the contribution of the hydrophobic property of the protective layer itself.

The mixing ratios of the organosilicon compounds represented by the general formulas (1) and (2) contained in the coating solution are R ¹ _n SiO _{(4-n) / 2-} equivalent mole number and SiO ₂ -equivalent mole number, respectively. The SiO ₂ / R ¹ _n SiO _{(4-n) / 2} molar ratio is 1 to
It is preferably 10 ³ . If this value exceeds 10 ³ ,
As the protective layer of the magnetic recording medium, the effect of the organosilicon compound represented by the general formula (1) becomes small, the reduction of friction and the improvement of durability become insufficient, and the protective layer itself becomes brittle, which is not preferable. On the other hand, if this value is less than 1, the abrasion resistance of the protective layer is lowered, the durability as a magnetic recording medium is lowered, and the strength required for practical use cannot be obtained, which is not preferable. In the present invention in which the protective layer is cured at a temperature at which the change in the magnetic properties of the magnetic layer does not affect recording and reproduction, the organic group R ¹ derived from the organosilicon compound represented by the general formula (1) is contained in the protective layer. Remains in. The organic group thus introduced into the protective layer has a low friction property of the protective layer itself, and contributes greatly to improvement of lubrication durability and toughness of the protective layer.
Even when the magnetic head collides, it exhibits a large protective layer destruction resistance.

In the present invention, in order to further reduce the coefficient of friction between the magnetic recording medium and the magnetic head, it is possible to provide the surface of the protective layer with a concavo-convex shape in which the difference between the convex and concave portions is about 5 nm or more. it can. In the present invention, these irregularities can be formed by the hard fine particles in the protective layer. As the hard particles, oxides of aluminum, silicon, titanium, zirconium, tin, antimony, tantalum, etc. can be used, and among them, a sol in which the metal oxide particles are dispersed in a water or alcohol dispersion medium is preferable. In particular, silica sol is preferable in terms of stability at the time of preparing a coating solution, a large number of kinds available, and the like. Here, the case where silica sol is used as the hard fine particles will be described. A silica sol is a sol in which fine particles of silica (silicon dioxide) having a particle size of about 1 to 500 nm are dispersed in water or an alcohol-based dispersion medium, or a dry powder obtained by removing the dispersion medium from this sol is again used as an appropriate dispersion medium. It is a dispersed sol.

By adjusting the concentration of the organosilicon compound represented by the general formulas (1) and (2) contained in the coating solution and the particle size and concentration of the silica sol added thereto, the protective layer having the optimum unevenness. It is said that

Exemplifying the case where fine particles of silicon dioxide are used as the hard fine particles, the mixing ratio of silica sol is
To form unevenness with a difference between convex and concave of about 5 nm or more,
The silica sol fine particles having an average particle size of about 10 nm to about 300 nm are used for the total amount of the organosilicon compound of the general formulas (1) and (2) or / and the derivative of the organosilicon compound of the general formulas (1) and (2). And the molar ratio of elemental silicon is about 10
Mix ⁵ to about 10 ^-1 times. More preferably, the difference between the convex portion and the concave portion is about 10 nm or more, and the average particle diameter is about 20.
nm to about 100 nm in terms of the molar ratio of elemental silicon to about 10 ⁻³ to about 10 ⁻² times the total amount of general formula (1) and general formula (2) and / or their derivatives. To mix. By these, a protective layer having a low friction coefficient with the magnetic head and high durability against sliding of the magnetic head can be obtained. It is not preferable to use fine particles of more than 300 nm because the distance between the magnetic head and the magnetic layer increases and the recording / reproducing characteristics deteriorate. Two or more kinds of silicon dioxide fine particles having different particle diameters may be used as long as they are hard fine particles having a particle diameter of about 300 nm or less.

For the general formula (1), the sum of the concentrations of the general formulas (1) and (2) and the silicon dioxide fine particles in the coating solution is R ¹ _n SiO _{(4-n) / 2} , the general formula (2) ) And silicon dioxide fine particles are in a weight concentration converted to SiO ₂ .
It is preferable that it is about 0.1 to about 10%. Methanol, ethanol, isopropyl alcohol, ethoxyethanol, propylene glycol monomethyl ether or the like can be used as a solvent for adjusting the concentration. A magnetic layer is coated with such a coating solution and then cured to form a protective layer. The coating method is preferably a dip coating method or a spin coating method. After coating, changes in the magnetic properties of the magnetic layer do not affect recording and reproduction.
Hereinafter, more preferably, it may be heat-cured at a temperature of about 300 ° C. or lower, or may be irradiated with ultraviolet rays or deep ultraviolet rays to be cured to form a protective layer. In this way, the thickness of the concave portion is about 5 nm to about 50 nm and the difference between the convex portion and the concave portion is about 5 n.
It is possible to give the protective layer an uneven shape of m to about 250 nm. When the thickness of the concave portion is about 5 nm or less, the effect of protecting the magnetic layer against sliding of the magnetic head decreases, which is not preferable. On the other hand, if it exceeds 50 nm, the distance between the magnetic head and the magnetic layer increases and the recording / reproducing characteristics deteriorate, which is not preferable. Further, if the difference between the convex portion and the concave portion is about 5 nm or less, it is difficult to obtain good CSS durability, and if it exceeds about 250 nm, the recording / reproducing characteristics deteriorate, which is not preferable.

As the non-magnetic substrate used in the present invention,
Both an inorganic oxide type such as a glass plate and a ceramics plate and a metallic type such as an aluminum plate are used. When using a glass plate, the fired surface is used as it is, or the surface is polished and smoothed. When an aluminum substrate is used, it is used by coating it with a nickel-phosphorus film and polishing its surface. As the magnetic layer used in the present invention, an alloy magnetic film coated by sputtering or the like can be used. Further, for the lubricating layer of the present invention, a known lubricating oil composed of a fluorine-containing polymer compound such as perfluoropolyether can be used. Further, in the present invention, prior to coating the magnetic layer, an underlayer of chromium metal or the like for controlling crystallinity which affects the magnetic characteristics of the magnetic layer may be provided, and a protective layer may be provided on the magnetic layer. In order to prevent the magnetic layer from being oxidized when the protective layer is provided, a nonmagnetic antioxidant layer may be provided prior to the formation of the protective layer.

[0016]

Since the protective layer of the magnetic recording medium of the present invention contains polyorganosiloxane, it has a toughness as compared with the conventional protective layer made of silicon dioxide. This prevents the magnetic recording medium from being destroyed even when the magnetic head is in strong contact with the protective film. Further, since the silicon of the polyorganosiloxane skeleton contained in the protective layer has an organic group having lubricity and hydrophobicity, even if the lubricating layer provided on the protective layer is not uniformly applied,
Lubrication performance for the magnetic head is secured. Furthermore, the hard fine particles in the protective layer of the present invention impart irregularities on the surface of the protective layer, and improve CSS characteristics.

[0017]

EXAMPLES The present invention will be described in detail below with reference to examples and comparative examples, but the present invention is not limited to the following examples unless it exceeds the gist.

Example 1 Tetraethoxysilane 10 g, heptadecafluorodecyltrimethoxysilane 0.2 g, ethyl alcohol 30
g, 20 g of distilled water and 5 g of acetic acid were mixed and stirred at room temperature for 5 hours. 25 g of this solution was added to 200 ml of ethyl alcohol.
After diluting with g, 1 g of a solution in which 4% by weight of silicon dioxide particles having a particle diameter of 20 to 30 nm was dispersed in pure water was added to prepare a coating liquid for forming a protective layer. The coating solution was applied onto the magnetic layer on the surface of which the uneven shape was not formed, by a spin coating method, and then heat-treated at 290 ° C. for 1 hour to form a hardened protective layer. When the fracture surface was observed with a scanning electron microscope, irregularities due to the silicon dioxide fine particles were confirmed, and the thickness of the recess was about 15 nm. On the protective layer obtained above, a perfluoropolyether having a hydroxyl group at the end was applied by a spin coating method and then dried at 100 ° C. for 30 minutes to form a lubricating layer having a film thickness of about 2 nm. A magnetic recording medium was obtained. Table 1 shows the measurement results of the static friction coefficient of the magnetic head and the in-plane dynamic friction coefficient of this magnetic recording medium.

[0019]

[Table 1]

Example 2 Tetraethoxysilane 100 g, Methyltrimethoxysilane 15 g, Ethyl alcohol 200 g, Distilled water 35 g
And 3 g of acetic acid were mixed and stirred at about 50 ° C. for 20 hours. After 30 g of this solution was diluted with 250 g of ethyl alcohol, 3 g of a solution in which 2 wt% of silicon dioxide fine particles having a particle size of 30 to 40 nm were dispersed in pure water was added to prepare a coating liquid for forming a protective layer. After coating the coating liquid on the surface of the magnetic layer on which the uneven shape is not formed by the spin coating method,
A heat treatment was performed at 300 ° C. for 1 hour to form a protective layer by curing.
When the fracture surface was observed with a scanning electron microscope, the thickness of the protective layer recess was about 20 nm. As a result of observing with an atomic force microscope (AFM), the difference between the convex portion and the concave portion is about 20.
was nm. On the protective layer obtained above, a perfluoropolyether having a hydroxyl group at the end was applied by a spin coating method and then dried at 100 ° C. for 30 minutes to form a lubricating layer having a film thickness of about 2 nm. A magnetic recording medium was obtained. For this magnetic recording medium, a pin / disk wear test (the pin shape is about 2 mmφ, 10 gf, 30
Table 3 shows the results of carrying out 0 rpm). This test shows that the longer the time before the protective film is destroyed, the lower the friction and the toughness of the protective film.

[0021]

[Table 2]

Example 3 The procedure of Example 2 was repeated, except that the alumina dioxide particles having a particle size of 20 to 30 nm were replaced by the flat alumina particles having a particle size of about 10 nm * about 50 nm. The obtained magnetic recording medium showed good CSS durability.

Comparative Example 1 Tetraethoxysilane 11 g, ethyl alcohol 30
g, 20 g of distilled water and 5 g of acetic acid were mixed and stirred at room temperature for 5 hours. 25 g of this solution was added to 200 ml of ethyl alcohol.
After diluting with g, 1 g of a solution in which 4% by weight of silicon dioxide fine particles having a particle diameter of 20 to 30 nm was dispersed in pure water was added to prepare a coating liquid for forming a protective layer. The coating solution was applied onto the magnetic layer on the surface of which the uneven shape was not formed, by a spin coating method, and then heat-treated at 290 ° C. for 1 hour to form a hardened protective layer. When the fracture surface was observed with a scanning electron microscope, the irregular shape due to the silicon dioxide fine particles was confirmed,
The thickness of the recess was about 15 nm. After coating a perfluoropolyether having a hydroxyl group at the terminal by spin coating on the obtained protective layer, 100 ° C.
And dried for 30 minutes to form a lubricating layer having a film thickness of about 2 nm to obtain a magnetic recording medium. Table 1 shows the measurement results of the static friction coefficient of the magnetic head and the in-plane dynamic friction coefficient of this magnetic recording medium. As shown in Table 1, in the magnetic recording medium of the present invention, the static friction coefficient and the absolute value of the friction coefficient when the magnetic head slides are kept low. Also, the in-plane variation of the dynamic friction coefficient is extremely small. The effect of using heptadecafluorodecyltrimethoxysilane as the silicon compound represented by the general formula (1) for forming the protective layer is clear.

Comparative Example 2 Tetraethoxysilane 100 g, ethyl alcohol 17
5 g, distilled water 35 g and acetic acid 5 g were mixed and stirred for 5 hours at room temperature. 25 g of this solution was added to ethyl alcohol 20
After diluting with 0 g, 1 g of a solution in which 4% by weight of silicon dioxide particles having a particle diameter of 20 to 30 nm was dispersed in pure water was added to prepare a coating liquid for forming a protective layer. The same procedure as in Example 2 was carried out except that this coating solution was used. Table 2 shows the pin-disk wear test results of the obtained magnetic disks.

[0025]

Since the protective layer of the present invention has lubricity by itself, the lubricating performance required for a magnetic recording medium is excellent even if the lubricating layer is not uniformly applied.
Further, since the protective film itself has toughness, the magnetic recording medium has high resistance to breakage even when the magnetic head is in strong contact or collision.

[Brief description of drawings]

FIG. 1 is a partial cross-sectional view of an embodiment of a magnetic recording medium of the present invention.

[Explanation of symbols]

1 ... Magnetic recording medium, 2 ... Glass plate, 3 ... Underlayer, 4 ... Magnetic layer, 5 ... Protective layer, 6 ... Lubrication layer, 7 ... Hard fine particles

Claims (6)

[Claims] 1. A magnetic recording medium in which a magnetic layer, a protective layer and a lubricating layer are sequentially formed on a non-magnetic substrate having a smooth surface, and the protective layer is represented by the following general formulas (1) and (2). A magnetic recording medium characterized by forming a polyorganosiloxane-containing layer formed by applying a coating solution containing the organic silicon compound and hard particles shown on the magnetic layer and curing the coating solution. R ¹ _n Si (R ² ) _4-n (1) Si (R ² ) ₄ (2) Here, R ^{1 is a} saturated hydrocarbon group, a hydrocarbon group containing fluorine or chlorine, which are the same as each other. may be different from each even, R ^2: an alkoxy group, an acyloxy group, an alkoxyalkoxy group, an isocyanate group or a chlorine element may be different or mutually the same as each other, n: 1 to 3 either Is an integer of. 2. R ^{1 of the} organosilicon compound represented by the general formula (1) is a methyl group, an ethyl group, a propyl group, or a hydrocarbon group in which a part or all of hydrogen is substituted with fluorine. The magnetic recording medium according to claim 1, wherein: 3. The mixing ratio of the organosilicon compounds represented by the general formulas (1) and (2) is set to R ¹ _n SiO 2 respectively.
When expressed in _{(4-n) / 2} in terms of number of moles and SiO ₂ in terms of molar ratio, wherein characterized in that the SiO ₂ / R ¹ _n SiO _{(4-n) / 2} ratio from 1 to 10 ³ Item 3. The magnetic recording medium according to Item 1 or 2. 4. The magnetic recording medium according to claim 1, wherein the hard fine particles are metal oxides and have an average particle diameter of 10 to 300 nm. 5. When the content ratio of the metal oxide to the total amount of the organosilicon compounds represented by the general formulas (1) and (2) is expressed in terms of mol number of silicon element and mol number of metal element, respectively. The magnetic recording medium according to claim 4, wherein the magnetic recording medium has a thickness of 10 ^-5 to 10 ^-1 . 6. The metal oxide having an average particle size of 20 nm to
The magnetic recording medium according to claim 5, wherein the magnetic recording medium is 100 nm silicon dioxide.