JPH0652585A - Magneto-optic disk - Google Patents

Abstract

PURPOSE:To obtain a magneto-optic disk which has a small tilting angle, no adsorption, no contact of a floating magnetic head, no corrosion of a magneto- optic layer, and no double refraction malfunction in a board by forming a resin protective layer of a two-layer configuration, and specifying a thickness of a film, concentration-particle size of filler. CONSTITUTION:A magneto-optic layer 2 is formed on a main surface of a board 1 made or resin, such as polycarbonate, glass, etc., by sputtering, and a lower resin layer 3 with no filler and an upper resin layer 4 with filler 5 are formed by spin coating. Similarly, a hard coating layer 6 of ultraviolet curable resin is formed on the other main surface of the board 1 by spin coating. An average particle size (a) of the filler is set to 1-9mum, a concentration (x) of the filler is set to 0.5-40wt.%, a film thickness (y) of the layer 4 is so set to 2-13mum as to satisfy y/a >=1.45+0.033x.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin protective layer for a magneto-optical disk used in a magnetic field modulation recording system.

[0002]

2. Description of the Related Art It is known that a resin protective layer of a magneto-optical disk contains a filler to impart an appropriate surface roughness. (1) Japanese Patent Application Laid-Open No. 2-40149: A lubricant and a filler are mixed in an ultraviolet curable resin. (2) JP-A-3-157836: An ultraviolet curable resin contains a filler, an antistatic agent and a lubricant. (3) JP-A-3-157837: An ultraviolet curable resin contains a filler, an antistatic agent and a lubricant, and a resin protective layer comprises two layers, a lower layer without filler and an upper layer containing filler and the like. To do. (4) Japanese Patent Application Laid-Open No. 4-64936: A filler is added to an ultraviolet curable resin to have a surface roughness Ra of 10 to 50 nm.
And

In the above techniques (1) to (3), since the average particle size of the filler is as small as 1 μm or less, the required surface roughness cannot be obtained. Therefore, a lubricant is added to the resin protective layer and the floating type is used. Prevents head crash and magnetic attraction of the magnetic head. However, the addition of a lubricant is not preferable because it lowers the surface hardness of the resin protective layer. Next, in JP-A-4-64936, an appropriate surface roughness can be obtained, but since the resin protective layer is a single layer of resin containing a filler, birefringence abnormality occurs in the substrate due to the filler, and high temperature Corrosion occurs in the magneto-optical recording layer in high humidity.

[0004]

An object of the present invention is (1) the influence of the film thickness variation of the upper resin layer on the surface roughness is small, and (2) an appropriate surface roughness can be obtained without a lubricant, The upper resin layer can be formed, (3) the surface roughness is almost uniform over the entire surface, there are no local protrusions, and (4) because of these, there is no attraction or crash of the levitation type magnetic head, (Five)
An object of the present invention is to provide a magneto-optical disk which has a small tilt angle and which is free from corrosion of the magneto-optical recording layer and abnormal birefringence of the substrate.

[0005]

According to the present invention, in a magneto-optical disk in which at least a magneto-optical recording layer and a resin protective layer are laminated in this order on one surface of a synthetic resin substrate, the resin protective layer is a filler-free lower portion. It is composed of two layers, a resin layer and an upper resin layer to which a filler is added, the thickness of the lower resin layer is 2 to 13 μm, the concentration of the filler is x in wt% and the thickness of the upper resin layer is μm. And y is the average particle diameter of the filler in μm unit, 0.5 ≦ x ≦ 40, 2 ≦ y ≦ 13, 1 ≦ a ≦ 9, y / a ≧ 1.45 + 0.033x To do.

[0006]

According to the knowledge of the inventor, in the magneto-optical disk of the magnetic field modulation recording system, the surface roughness Ra of the contact surface of the disk with the floating magnetic head is 10n in terms of the center line average roughness.
mRa or more is required. If it is less than 10 nmRa, the adsorption of the head is likely to occur especially when there is an adhering substance such as tobacco dust on the surface of the resin protective layer. On the other hand, in order to stabilize the floating characteristics of the magnetic head, not only the surface roughness of 10 nmRa or more but also the surface roughness of the disk must be uniform. Further, in order to improve the mass productivity of the disc, it is preferable that the dependence of the surface roughness on the film thickness of the upper resin layer is small. In order to make the surface roughness uniform and reduce the film thickness dependency of the surface roughness, the film thickness y of the upper resin layer (unit: μm) and the average particle size of the filler (unit: μm) should be y / a ≧ 1. It suffices to have a relationship of 0.45 + 0.033x (1). In the range where equation (1) holds,
Since the film thickness y of the upper resin layer is sufficiently larger than the average particle diameter a of the filler, local protrusions due to the filler are eliminated in the upper resin layer, and the surface roughness of the disk becomes substantially uniform over the entire surface. For this reason, even if a flying magnetic head having a small flying height of about 2 μm is used, there is no head adsorption or head crash at any point of the disk, and the head can be stably floated. Moreover, the dependence of the surface roughness on the film thickness of the upper resin layer is small, and the fluctuation of the surface roughness due to the fluctuation of the film thickness can be prevented.

The surface roughness is determined by the average particle diameter a and the concentration x of the filler and the film thickness y of the upper resin layer. Surface roughness of 10 nm
To achieve Ra or higher, the filler content x is 0.5 wt%
As described above, it is necessary to set the average particle diameter a to 1 μm or more. Next, if the filler content x exceeds 40 wt%, the viscosity before spin coating increases drastically and spin coating becomes impossible. Although the manufacturing method of the upper resin layer is not limited to spin coating,
From the viewpoint of ease of forming the upper resin layer, the filler content x
Is 40 wt%. Therefore, the filler content x
Is 0.5 to 40 wt%. Average particle size a of filler
Is less than 1 μm, a surface roughness of 10 nmRa or more cannot be obtained as described above. When the average particle size a exceeds 9 μm,
The film thickness of the resin protective layer (the total of the lower resin layer and the upper resin layer) exceeds 15 μm. As shown below, the lower resin layer must have a film thickness of at least 2 μm or more, and if the average particle size a exceeds 9 μm, the film thickness y of the upper resin layer required to satisfy the formula (1) is 13 μm. And the total film thickness exceeds 15 μm
Exceed. If the total film thickness exceeds 15 μm, the tilt angle exceeds 5 mrad.

The film thickness of the resin protective layer is 2 μm in the lower resin layer.
If the thickness is less than 2 μm, birefringence anomaly occurs in the substrate due to the influence of the filler in the upper resin layer, and corrosion of the magneto-optical recording layer easily occurs. 2 μm on the upper resin layer
The above film thickness is required, and if it is less than 2 μm, the upper resin layer is peeled off due to contact with the head during a crash or the like. Next, when the total film thickness of the lower resin layer and the upper resin layer exceeded 15 μm, the tilt angle, which is one of the mechanical characteristics of the disc, exceeded 5 mrad. According to the ISO standard, the tilt angle is 5 mra
It is defined as d or less. From these facts, the film thickness of the lower resin layer becomes 2 to 13 μm, and the film thickness y of the upper resin layer also becomes 2-1.
It becomes 3 μm.

The filler material is, for example, SiO2, A
Insulating ceramic materials such as l2O3, Si3N4, SiC, CdS, ZnS, ITO, Sb-SnO2, Sb2
O3, IrO2, MoO2, NbO2, PtO2, RuO2,
Conductive oxides such as WO2, MoC, NbC, TaC, T
Conductive carbide such as iC, WC, NbN, Ta2N, Ti
Conductive nitrides such as N, ZrN, VN, melamine formaldehyde, polyethylene terephthalate, polyurethane, ABS, polyethylene homopolymer, acrylic resin cellulose, nylon, polycarbonate, polyester, polyethylene-sterene polymer, vinyl polymer,
Resins such as various copolymers may be used alone or in combination of two or more.

The resin material for the lower resin layer and the upper resin layer includes acrylic, epoxy, polyester, acrylic ester, urethane acrylic, and other ultraviolet curable resins, thermosetting resins, etc. An ultraviolet curable resin that is easy to process and has high mass productivity is preferable.

[0011]

EXAMPLE FIG. 3 shows the structure of a magneto-optical disk. In the figure, reference numeral 1 is a resin such as polycarbonate or a substrate such as glass, and a magneto-optical recording layer 2 is formed on one main surface by, for example, sputtering. By spin coating, a lower resin layer 3 made of a plain resin without a filler and an upper resin layer 4 with a filler added are formed. 5 is the upper resin layer 4
It is a filler added to. Similarly, a hard coat layer 6 of an ultraviolet curable resin is formed on the other main surface of the substrate 1 by spin coating.

In the embodiment, the magneto-optical recording layer 2 includes a silicon nitride first dielectric layer, a Gd-Dy-Fe based magneto-optical recording layer, a silicon nitride second dielectric layer, and an Al reflective layer in that order. A laminated product was used. For the hard coat layer 6, a conductive acrylic resin was used. The resin protective layer is composed of a lower resin layer 3 and an upper resin layer 4. The lower resin layer 3 is made of urethane acrylic UV curable resin having a thickness of 2 to 13 μm, and the upper resin layer 4 is made of acrylic UV light. 2 to 13 μm by including SiO2 filler 5 in the cured resin
A thick film was used.

The total film thickness of the lower resin layer 3 and the upper resin layer 4 is preferably 4 to 15 μm, and if it is 15 μm or more, the tilt angle increases. Further, the average particle size of the filler 5 is set to 1 to 9 μm, the film thickness y of the upper resin layer 4 and the average particle size a of the filler 5,
The concentration x of the filler 5 is determined so as to satisfy the formula (1).
In this specification, the film thickness y and the average particle size a are shown in μm unit, and the concentration x is shown in wt% unit.

In order to evaluate the characteristics of the magneto-optical disk, the film thickness of the lower resin layer 3 and the upper resin layer 4 and the particle diameter a of the filler 5 are evaluated.
And the concentration x were changed, and the samples shown in Table 1, Table 2 and FIG. 2 were produced. The surface roughness is 1 with a stylus type surface roughness meter.
mm scanning was performed and the center line average roughness Ra was measured.

[0015]

[Film Thickness and Filler Concentration] The film thickness of the lower resin layer 3 is 5 μm, and the average particle diameter a of the filler 5 contained in the upper resin layer 4 is a.
Of 1 to 9 μm and the filler concentration x in the range of 0.3 to 45 wt%, the film thickness y of the upper resin layer 4 and the surface roughness (R
The relationship of a) was investigated. Some of the results are shown in Table 1.

[0016]

[Table 1] Table 1 Sample Filler average concentration Upper resin layer y / a y / a Surface roughness Contact noise Judgment particle size a x Film thickness y Actual theoretical value (nmRa) Presence / absence A-1 1 40 2.5 2.5 2.77 132 Yes x A-2 1 40 3.1 3.1 2.77 43 No ○ A-3 1 40 5.2 5.2 5.2 2.77 42 No ○ A-4 4 10 6.7 1. 7 1.78 147 Yes × A-5 4 10 7.4 1.9 1.78 90 No ○ A-6 4 10 10.1 2.5 1.78 82 No ○ A-7 9 0.5 9. 8 1.1 1.47 96 Yes × A-8 9 0.5 13.3 1.5 1.57 17 No ○ A-9 9 0.5 16.2 1.8 1.8 1.47 15 No ○ A- 10 4 0.3 6.3 1.6 8 2) × A-11 445 1) × A-12 0.5 40 40 1.5 3.0 7 2) × 1) Viscosity is too high and spin coating is not possible. 2) When the tobacco mist is adhered to the resin layer surface Head adsorption 3) Contact noise indicates the presence or absence of noise due to contact with the magnetic head during the levitation test 4) The theoretical value of y / a indicates the lower limit of y / a in equation (1) 5) Judgment Is related to surface roughness and presence or absence of contact noise, presence or absence of magnetic head adsorption, and spin coating availability. In addition to this, the tilt angle must be examined for final determination.

A-10 having a filler concentration x of 0.3 wt%
The surface roughness was less than 10 nmRa due to the low concentration, and the resin viscosity rapidly increased at 45 wt% of A-11 due to the high concentration, which made spin coating impossible. Therefore, the filler concentration x was limited to 0.5 to 40 wt%. The surface roughness of A-1 to 9 is 10 nmRa or more, but there is a rapid change in the surface roughness between A-1 to 2, A-4 to 5, and A-7 to 8, which is expressed by the formula ( It corresponds to the change from outside the range of 1) to the film thickness within the range. And A that satisfies equation (1)
Among -2 to 3, A-5 to 6, and A-8 to 9, the dependence of the surface roughness on the film thickness y of the upper resin layer is small, and a stable surface roughness can be obtained. A levitation test was performed on these samples using a levitation type magnetic head with a small levitation amount. When the disk rotation speed was 3000 rpm, the head load was 6 gf, and the levitation amount was 2 μm, the formula (1) was not satisfied and the film thickness y rapidly increased. In A-1, 4, and 7 where various changes in surface roughness occur, a slight contact noise between the head and the disk is generated. On the other hand, equation (1)
And A-2, which has a stable surface roughness with respect to the film thickness y,
No contact noise was generated in Nos. 3, 5, 6, 8 and 9 and stable floating characteristics were exhibited.

In FIG. 2, the average particle diameter a of the filler 5 is 4 μm.
The relationship between the concentration x, the film thickness y, and the surface roughness is shown. Similar results were obtained with other average particle sizes. The region shown by the frame in FIG. 2 is the range of the present invention, and the upper left curve of the region connects the points at which the relationship between the film thickness and the surface roughness changes abruptly. As is clear from FIG. 2, when the film thickness y is increased beyond the point on this curve, the dependence of the surface roughness on the film thickness y decreases, and the surface roughness becomes almost constant. A plot of the points on this curve is shown in equation (1).
Is.

FIG. 1 shows the meaning of the equation (1). When the values of the inflection points of the relationship between the surface roughness and the film thickness y in FIG. 2 are plotted, seven points near the straight line in FIG. 1 are obtained. Equation (1) is a linear approximation of these points, and its meaning is the same as the fact that the film thickness is on the right side of the curve in FIG. The inventor conducted a similar experiment except that the average particle diameter a of the filler 5 was other than 4 μm, and the formula (1) was established. Next, the data in Table 1 are plotted according to Examples and Comparative Examples (judgment results in Table 1), and the symbols ◯ and ▲. The equation (1) can be used to express the characteristics relating to the surface roughness of the magneto-optical disk. As shown in Table 1, in the region where the film thickness y of the upper resin layer 4 is less than 2 μm, head adsorption or upper resin layer 4
Is a region where peeling is likely to occur. The filler concentration is 40
% Is a region where the viscosity increases and spin coating becomes difficult. Further, when the film thickness y exceeds 13 μm, the tilt angle has a problem due to the increase in the film thickness.

Returning to FIG. 2, let us consider the area shown on the right side of the chain line in the area surrounded by the frame. This is a more limited area of equation (1). If the average particle diameter of the filler is a, the concentration of the filler is x, and the film thickness of the upper resin layer 4 is y, this region is represented by the following inequality (2). When 0.5 ≦ x ≦ 1 wt% y ≧ 1.4a When 1 <x ≦ 5 wt% y ≧ 1.6a When 5 <x ≦ 10 wt% y ≧ 1.9a When 10 <x ≦ 20 wt% y ≧ 2.2a When 20 <x ≦ 30 wt% y ≧ 2.5a When 30 <x ≦ 40 wt% y ≧ 2.8a

[0021]

[Film Thickness and Average Particle Size of Filler] Samples B-1 to 6 satisfying the inequality (2) by changing the film thickness of the lower resin layer 3 and the upper resin layer 4
Was produced. The test results for this are shown in Table 2. When the read surface of the disk was observed with a polarizing microscope, birefringence anomaly was observed at the position where the filler 5 was present in B-6 without the lower resin layer, but it was not seen in the other samples with the lower resin layer. Next, using a floating magnetic head, contact start / stop test (disk rotation speed 300
0 rpm, head load 4 gf) 1 cycle 13 seconds 1
I've done it 100,000 times. In B-1 in which the film thickness of the upper resin layer 4 was 1.5 μm, peeling of the upper resin layer 4 occurred, but other 2 μm
It was not seen in the above samples. The tilt angle, which is one of the mechanical characteristics, is B- when the film thickness of the resin protective layer exceeds 15 μm.
5 exceeded 5 mrad, but the tilt angle was 5 mrad or less in the sample having a film thickness of 15 μm or less. ISO
According to the standard, the tilt angle is 5 mrad or less. Next, put these samples at 80 ° C. and 90% RH for 1000 hours,
When a visual inspection was conducted, corrosion occurred in the magneto-optical recording layer 2 at B-6, but no corrosion was found in the sample having another lower resin layer 3. From the above, in order to obtain reliability, the film thickness of the lower resin layer 3 is set to 2 to 13 μm, and the upper resin layer 4 is formed.
It was found that it is necessary to set the film thickness of 2 to 13 μm.

The average particle diameter a of the filler 5 is shown in Table 1.
In the sample A-12 having an average particle diameter of 0.5 μm, the surface roughness was less than 10 nmRa. When the average particle size of Sample B-5 in Table 2 is 10 μm, in order to satisfy the formula (1), the upper resin layer 4
Therefore, a film having a thickness of more than 13 μm is required. Therefore, the average particle size a of the filler 5 is preferably 1 to 9 μm.

[0023]

[Table 2] Table 2 Sample average particle size Filler concentration Resin protective layer Film thickness (μm) a (μm) x (wt%) Lower resin layer Upper resin layer Total B-1 1 40 10 1.5 11.5 B-2 1 40 10 2 12 B-3 1 40 12 12 14 B-4 9 0.5 2 13 15 B-5 10 0.5 0.5 2 14 16 B-6 9 0.5 0.5 0 12 12 Sample birefringent head Tilting angle (mrad) judgment abnormality due to peeling of upper layer B-1 No Yes 1.4 × B-2 No No 1.6 ○ B-3 No No 4.5 ○ B-4 No No 4.8 ○ B- 5 No No 5.6 × B-6 Yes No 4.5 1) × 1) Corrosion occurred

[0024]

According to the present invention, (1) the influence of the film thickness variation of the upper resin layer on the surface roughness is small, and (2) an appropriate surface roughness can be obtained without a lubricant, and the upper resin layer Layer formation is possible, (3) surface roughness is uniform over almost the entire surface, and there are no local protrusions. (4) Because of these, there is no attraction or crash of the floating magnetic head, and (5) It is possible to obtain a magneto-optical disk having a small tilt angle and free from corrosion of the magneto-optical recording layer and birefringence abnormality of the substrate.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a filler concentration x and a film thickness y of an upper resin layer in an example.

FIG. 2 is a characteristic diagram showing the relationship between the film thickness y of the upper resin layer and the surface roughness in the example.

FIG. 3 is a sectional view of the magneto-optical disk of the embodiment.

[Explanation of symbols]

 1 substrate 2 magneto-optical recording layer 3 lower resin layer 4 upper resin layer 5 filler 6 hard coat layer

Claims (1)

[Claims] 1. A magneto-optical disk in which at least a magneto-optical recording layer and a resin protective layer are laminated in this order on one surface of a synthetic resin substrate, wherein the resin protective layer includes a lower resin layer containing no filler, It is composed of two layers of the upper resin layer to which a filler is added, the thickness of the lower resin layer is 2 to 13 μm, the concentration of the filler is x in wt% unit, the thickness of the upper resin layer is y in μm unit, the filler A magneto-optical disk characterized in that the average particle size of is 0.5 μx unit, and 0.5 ≦ x ≦ 40, 2 ≦ y ≦ 13, 1 ≦ a ≦ 9, y / a ≧ 1.45 + 0.033x. .