JPH07161032A - Magnetic recording medium - Google Patents

Abstract

PURPOSE:To improve the uniformity of a lubricant and the adhesive property to a protective layer by forming a polyorganosiloxane-contg. layer with ruggedness formed by hard fine particles dispersed in the matrix as the protective layer with a coating soln. contg. specified organosilicon compds. and specified hard fine particles. CONSTITUTION:A polyorganosiloxane-contg. layer as a protective layer 5 is formed on a magnetic layer 4 by applying and heat-curing a coating soln. contg. organosilicon compds. represented by the formulae R<1>nSi(R<2>)4-n such as a mixture of tetraethoxysmlane with gamma-hydroxytrimethoxysilane and hard fine particles such as fine silicon dioxide particles. Since the layer 5 is made rugged by the fine silicon dioxide particles dispersed in the polyorganosiloxane and silicon dioxide as the matrix, the uniformity of the lubricant of a lubricative layer 6 and the adhesive property to the protective layer 5 are improved. In the formulae, R<1> is hydroxyl, epoxy, mercapto, amino, etc., R<2> is alkoxy, acyloxy, isocyanato, etc., and (n) is 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 excellent CSS durability characteristics. More specifically, the toughness of the protective layer is improved and the adhesion between the lubricating layer and the protective layer is improved. The present invention relates to a magnetic recording medium.

[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 protects the magnetic layer from the external environment and prevents the magnetic layer from being damaged by direct contact with the magnetic head, while the lubricating layer serves to mitigate wear of the protective layer. The protective layer is composed 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. A liquid lubricant of perfluoropolyether type is used because of its properties such as chemical stability, low vapor pressure, low surface tension, boundary lubricity, and good adhesion to the protective layer. Further, in order to reduce friction between the magnetic recording medium and the magnetic head, a fine uneven surface is provided on the surface of the magnetic recording medium. By providing appropriate irregularities and lubricity on the surface of the magnetic recording medium, the synergistic effect between them has been attempted to improve the contact start stop (CSS) characteristics of the magnetic recording medium.

In Japanese Patent Laid-Open No. 61-229227 and Japanese Patent Laid-Open No. 61-732227, it is intended to form a protective layer for a magnetic layer of a magnetic recording medium and simultaneously form irregularities on the surface of the magnetic recording medium. It is disclosed that a protective layer is formed by applying a hydrolyzed solution of tetraalkoxysilane in which fine particles of silicon dioxide are dispersed on the magnetic layer and curing the solution. Further, Japanese Patent Laid-Open No. 2-137120 discloses a magnetic recording medium having a protective layer formed by dispersing silica fine particles having two or more kinds of average particle diameters in a silicon dioxide film.

[0004]

However, in the prior art in which silicon dioxide is used as a matrix with the protective layer in which the hard fine particles are dispersed, the uniform coating property of the lubricant and the adhesive force between the protective layer and the lubricant are not always sufficient. I couldn't say that. That is, the friction coefficient varies depending on the location on the surface of the protective layer, and the durability is not sufficient. For example, in the portion where the lubricating layer has disappeared, the friction coefficient increases remarkably and the silicon dioxide film is fragile, so that there is a problem that the wear of the protective layer progresses and eventually the magnetic layer is destroyed. The present invention has been made to solve the above problems, and provides a magnetic recording medium that reduces the friction between the magnetic head and the uniform coating property of the lubricant and the adhesion between the protective layer and the lubricant. With the goal.

[0005]

According to the present invention, in 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, a protective layer having the following general formula ( A magnetic recording medium comprising a polyorganosiloxane-containing layer formed by coating and curing a coating solution containing the organosilicon compound represented by 1) and (2) and hard fine particles on the magnetic layer.

R ¹ _n Si (R ² ) _4-n (1) Si (R ² ) ₄ (2) where R ^{1 has a} hydroxyl group, an epoxy group, a mercapto group, an amino group or a quaternary ammonium group. Organic groups, which may be the same or different from each other, 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 from each other, n: It is an integer of any one of 1 to 3.

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, and an organosilicon compound represented by the general formula (2) and / or a part thereof. It can be formed by coating a coating solution containing a hydrolyzed condensate and hard fine particles on the magnetic layer and then curing it by heating or the like. Here, the hydrolysis-condensation product is an alkoxy group, an alkoxyalkoxy group, an acyloxy group, an isocyanate group in the organosilicon compound represented by the general formulas (1) and (2), or a part or all of the chlorine element is a hydroxyl group. It is a substituted one or a partially condensed one.

Examples of the organosilicon compound represented by the general formula (1) used in the present invention include γ-hydroxypropyltrimethoxysilane, octadecyldimethyl [3- (trimethoxysilyl) propyl] ammonium chloride,
γ-mercaptopropyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane, N- (β-aminoethyl)-
γ-aminopropyltrimethoxysilane, 3- (N, N
-Diglycidyl) aminopropyltrimethoxysilane,
An example is γ-glycidoxypropylmethyldimethoxysilane. Examples of the organosilicon compound represented by the general formula (2) include tetramethoxysilane, tetraethoxysilane, tetraacetoxylan, tetraisocyanatesilane and the like. The organosilicon compound represented by the general formula (1) contains an organosilicon compound having a hydroxyl group, an amino group, an epoxy group, a mercapto group, a hydrocarbon group R ¹ having a quaternary ammonium group at its terminal, and / or a derivative thereof. When a lubricant such as perfluoropolyether is applied after forming the protective layer using the coating solution, the uniform coating property of the lubricant is improved and the functional group in the protective film and the lubricant are bonded via hydrogen bonds. The protective layer and the lubricating layer are firmly bonded to each other.

The mixing ratio of the organosilicon compounds represented by the general formulas (1) and (2) contained in the coating solution is R
^{_{1 n SiO (4-n)}} / represents in terms of the number of moles and the number of moles of the SiO ₂ as a ^{_{2, SiO 2 / R 1 n}} SiO (4-n) / 2
The ratio is preferably 1 to 10 ³ . As a protective layer of a magnetic recording medium if the value exceeds 10 ^3, reduces the uniform application of the lubricant, the friction coefficient at the time the magnetic head sliding varies by location on the surface of the protective layer is not preferable. Furthermore, the protective layer itself becomes brittle, which is not preferable. On the other hand, when it is less than 1, abrasion resistance of the protective layer becomes insufficient and abrasion strength as a magnetic recording medium decreases, which is not preferable. When the protective layer is applied and cured at a temperature at which changes in the magnetic properties of the magnetic layer do not affect recording and reproduction as a magnetic recording medium, the organic group R of the organosilicon compound represented by the general formula (1) is used.
¹ remains in the protective layer without decomposition. The organic group thus introduced into the protective layer has affinity with the lubricating layer, contributes to improvement of lubrication durability and imparting toughness of the protective layer, and the magnetic head is not comparable to the surface of the magnetic recording medium. Even in the case of a collision, it shows a large resistance to destruction.

In the present invention, in order to further reduce the coefficient of friction between the magnetic recording medium and the magnetic head, the surface of the magnetic recording medium is provided with an uneven surface having a difference between the convex portion and the concave portion of about 5 nm or more. You can In the present invention, the uneven surface shape is formed by the hard fine particles in the protective layer. As fine particles, aluminum, silicon, titanium,
Oxides such as zirconium, tin, antimony, and tantalum can be used, and among them, a sol in which the metal oxide fine particles are dispersed in a water or alcohol-based 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. What is silica sol?
A sol in which silica (silicon dioxide) fine particles 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 dispersed in an appropriate dispersion medium again. Is.

By controlling the concentration of the organosilicon compounds 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, protection having an optimum uneven shape is obtained. Layers can be formed.

In a preferred embodiment of the fine particles contained in the protective layer according to the present invention, fine particles having an average particle size of about 10 nm to about 300 nm, expressed as the number of moles of silicon element, are used.
To the general formula (1) and organosilicon compound (2) and the total amount of derivatives thereof are mixed so as to be 10 ^-5 10 ^-1 times. Thereby, the difference between the convex portion and the concave portion on the surface of the protective layer can be about 5 nm or more. More preferably, the fine particles having an average particle size of about 20 nm to about 100 nm in terms of the number of moles of silicon element are about 10 ⁻³ to about 10 with respect to the total amount of the general formulas (1) and (2) and their derivatives. 10
^{-Mix to} double. As a result, the difference between the convex portion and the concave portion on the surface of the protective layer is about 10 nm or more, the coefficient of friction with the magnetic head is low, and the durability against sliding of the magnetic head can be increased. It is not preferable to use fine particles having an average particle diameter of more than 300 nm because the distance between the magnetic head and the magnetic layer when using the magnetic recording medium increases and the recording / reproducing characteristics deteriorate. Two or more kinds of hard fine particles having different particle diameters may be used as long as the hard fine particles have a particle diameter of about 300 nm or less.

General formulas (1) and (2) in the above coating solution
So that the sum of the concentrations of the organosilicon compound and the fine particles of silicon dioxide is about 0.1 to about 10% in terms of the weight concentration converted into R ¹ _n SiO _{(4-n) / 2} , SiO _2, etc. Is preferred. Methanol, ethanol, isopropyl alcohol, ethoxyethanol, propylene glycol monomethyl ether or the like can be used as a solvent for adjusting the concentration.

After coating on the magnetic layer using such a coating solution, the coating film is cured to form a protective layer. The coating method is preferably a dip coating method or a spin coating method. After coating, changes in magnetic properties of the magnetic layer do not affect recording and reproduction, for example, heat curing at a temperature of about 400 ° C. or less, more preferably about 300 ° C. or less, or irradiation with ultraviolet rays, far ultraviolet rays, etc. Then, it can be cured to form a protective layer. Thus, 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 nm to about 250 nm.
The uneven shape of can be formed on the surface of the protective film. 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. Also, if the difference between the convex portion and the concave portion is about 5 nm or less, good CS
S durability is difficult to obtain, 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,
Any of inorganic oxides such as glass and ceramics and metals such as aluminum can be used. As the magnetic layer used in the present invention, an alloy magnetic film coated by sputtering or the like can be used. When a glass plate is used, the fire-polished surface or its surface is smoothed by polishing before use. When an aluminum substrate is used, it is used by coating it with a nickel-phosphorus film and smoothing its surface by polishing. As 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 oxidation of the magnetic layer when providing, the non-magnetic antioxidant layer may be provided prior to the formation of the protective layer.

[0016]

The protective layer of the present invention has toughness because it contains a polyorganosiloxane molecule having an organic group directly bonded to a silicon molecule. This prevents the magnetic head from breaking through the protective film and destroying the magnetic layer even if the magnetic head strongly contacts or collides with the surface of the protective layer. Further, the functional group bonded to the carbon chain of the organic group directly bonded to the silicon atom of the polyorganosiloxane present in the protective layer strengthens the bond between the protective layer and the lubricating layer coated on the protective layer. So
The sliding of the magnetic head moves the lubricating layer on the surface of the protective layer,
This prevents the protective layer from being locally exposed. Further, the hard fine particles in the protective layer of the present invention impart irregularities on the surface of the magnetic recording medium, 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 10 g of tetraethoxysilane, 1 g of γ-hydroxypropyltrimethoxysilane, 30 g of ethyl alcohol, 20 g of distilled water and 5 g of acetic acid were mixed and stirred at room temperature for 5 hours. After 25 g of this solution was diluted with 200 g of ethyl alcohol, 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, irregular shapes due to the silicon dioxide fine particles were 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 desired magnetic recording medium. Table 1 shows the results of measuring the static friction coefficient and the in-plane dynamic friction coefficient of the magnetic head after the CSS test was performed 20,000 times on this magnetic recording medium.

[0019]

[Table 1]

Example 2 Tetraethoxysilane 100 g, γ-glycidoxypropyltrimethoxysilane 10 g, ethyl alcohol 20
0 g, 35 g of distilled water and 3 g of acetic acid are mixed, and the temperature is about 50 ° C.
And stirred 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. The above coating solution was applied onto the magnetic layer on the surface of which no concavo-convex shape was formed, by a spin coating method, followed by heat treatment 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 observation with an atomic force microscope (AFM), the difference between the convex portion and the concave portion was about 20 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. This magnetic recording medium has a pin / disk wear test (the pin shape is approximately 2 mm
φ, 10 gf, 300 rpm) is shown in Table 2. This test shows that the longer the time until the protective film is destroyed, the lower the friction and the toughness of the protective film.

[0021]

[Table 2]

Example 3 The same procedure as in Example 1 was carried out except that flat alumina particles of about 10 nm × about 50 nm were used in place of the silicon dioxide particles having a particle size of 20 to 30 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 results of measuring the static friction coefficient and the in-plane dynamic friction coefficient of the magnetic head after the CSS test was performed 20,000 times on this magnetic recording medium.
As shown in Table 1, in the magnetic recording medium of the present invention, the absolute value of the friction coefficient when the magnetic head slides is kept low. Also, the in-plane variation of the dynamic friction coefficient is extremely small. The effect of using γ-hydroxypropyltrimethoxysilane as the organosilicon compound represented by the general formula (1) for forming the protective layer is clear. This is because the hydroxyl group of γ-hydroxypropyltrimethoxysilane improves the adhesive force between the protective layer and the lubricant and the uniform coating property of the lubricant, so that the protective layer and the magnetic head are not strongly adsorbed through the lubricating layer. It is presumed that.

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]

The protective layer of the magnetic recording medium of the present invention has a matrix of silicon dioxide containing polyorganosiloxane, and hard fine particles are dispersed in the matrix.
Furthermore, irregularities are formed on the surface. Therefore,
It has a higher toughness than that of a conventional protective layer having silicon dioxide as a matrix and hard fine particles dispersed therein. In addition, since the organic group directly bonded to the silicon atom of the polyorganosiloxane of the protective layer has a functional group having an affinity for the lubricating layer, the uniform coating property of the lubricating layer and the adhesiveness of the lubricant are improved. As a result, when the magnetic recording medium rotates or stops, the lubricating layer does not separate from the protective layer due to the sliding of the magnetic head.

[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 comprising a polyorganosiloxane-containing layer formed by applying a coating solution containing the organic silicon compound and hard fine 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) where R ¹ is an organic group having a hydroxyl group, an epoxy group, a mercapto group, an amino group or a quaternary ammonium group. R ² may be the same or different from each other, 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 from each other, n: 1 to 3 One of the integers. 2. The mixing ratio of the organosilicon compounds represented by the general formulas (1) and (2) in the coating solution is R ¹ _n S respectively.
It is characterized in that the ratio of SiO ₂ / R ¹ _n SiO _{(4-n) / 2} is 1 to 10 ³ when expressed in terms of iO _{(4-n) / 2} conversion number and SiO ₂ conversion number. The magnetic recording medium according to claim 1. 3. The magnetic recording medium according to claim 1, wherein R ^{1 of the} organosilicon compound represented by the general formula (1) is a hydrocarbon group having a hydroxyl group, an epoxy group or an amino group. 4. The average particle diameter of the hard fine particles is 10 to 30.
It is 0 nm, The magnetic recording medium of any one of Claim 1 thru | or 3 characterized by the above-mentioned. 5. The magnetic recording according to claim 1, wherein the hard fine particles in the protective layer are fine particles of silicon dioxide, and the average particle diameter is 20 to 100 nm. Medium. 6. The ratio of the hard fine particles to the total amount of the organosilicon compounds represented by the general formulas (1) and (2) is expressed by a molar ratio in terms of silicon element and is 10 ⁻⁵ to 10 ⁻¹ . The magnetic recording medium according to claim 5, wherein