JP2002264183A - Magnetic disk substrate, method for manufacturing the same and method for manufacturing magnetic recording medium using magnetic disk substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic disk substrate made of plastics, minimized in straightness, having excellent shape characteristics and excellent in the floating characteristics of a head, a method for manufacturing the same and a method for manufacturing a magnetic recording medium using the magnetic disk substrate. SOLUTION: The magnetic disk substrate is manufactured by an injection- molding method having at least a process for filling a mold with a thermoplastic resin through a gate and a process for cutting the gate within 0.03-0.47 sec after the filling of the mold with a thermoplastic resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a magnetic disk substrate using a thermoplastic resin. Further, the present invention relates to a method for manufacturing a magnetic recording medium using the magnetic disk substrate.

[0002]

2. Description of the Related Art When a conventional non-magnetic metal substrate (such as aluminum) is used as a magnetic disk substrate for a magnetic recording medium requiring a high surface precision, a high precision processing is required.

[0003] A conventional non-magnetic metal substrate is manufactured, for example, as follows. First, a metal material that has been heated and melted is rolled and heat-annealed, and then a blank material processed to a predetermined size is produced, and then the inner and outer diameters are processed. Further, after a lapping process is performed to improve the surface accuracy, a Ni-P plating layer is formed to a thickness of 13 μm for the purpose of improving the surface hardness, and the surface is polished to obtain a surface roughness Ra = 1. Polish to 0.0 nm (10 °) and perform final lapping using diamond slurry. Then, in the CSS (contact start / stop) zone, for example, the bump height is 1
By performing laser zone texturing so as to have a density of one bump per 9.0 nm (190 °), 30 μm square, and precision cleaning, a general magnetic disk substrate for a hard disk can be obtained.

On the magnetic disk substrate obtained as described above, a Cr underlayer 50 nm (500 °) and a CoCrTa magnetic layer (Co: Cr: Ta = 82: 14: 4) 30 nm.
(300 °) and a carbon protective layer of 8.0 nm (80
Å) is sequentially formed by a DC sputtering method, and a tape burnish is performed on the surface after the sputtering. Finally, a fluorine-based lubricating layer of 2.0 nm (20 °) is formed by dip coating or spin coating to obtain a magnetic recording medium for a hard disk.

[0005] However, the manufacturing method and configuration of the disk substrate and various recording media are not limited to those described above.

[0006] The conventional methods for manufacturing a magnetic disk substrate and a magnetic recording medium as described above are becoming more and more complicated with the recent increase in recording density. On the other hand, there is a need for a magnetic disk substrate and a magnetic recording medium that are less expensive than before while maintaining high performance. Magnetic disk substrates and magnetic recording media using a thermoplastic resin (plastic) have been proposed as new magnetic disk substrates satisfying these conflicting requirements (for example, Japanese Patent Application Laid-Open Nos. 5-4231, 5-5-231). 6535, JP-A-5-28488, etc.).

[0007]

However, when a magnetic disk substrate, which is required to have a high degree of shape stability and surface accuracy, is manufactured by injection molding of a plastic, there are cases where a magnetic disk substrate is manufactured from a metal, glass or ceramic substrate. In comparison, finish polishing (lapping, polishing, vanishing, etc.) cannot be performed due to low mechanical strength. Therefore, at the end of injection molding, it is necessary to adjust the surface accuracy (straightness, undulation, roughness, etc.) required for the magnetic disk substrate. However, there is a problem that the straightness of the substrate is not reduced (not improved) because the stress acting upon the resin molding locally remains on the substrate and the stress causes deformation such as undulation.

For a recording medium requiring extremely high surface accuracy, such as a hard disk in which a magnetic head floats above a substrate by several tens of nanometers for the purpose of improving the recording density, a large straightness ( When a substrate having poor surface accuracy) is used, a predetermined distance between the magnetic head and the recording medium cannot be maintained, and in the worst case, the magnetic head does not float and actual reading and writing are performed. Cause a problem that can not be.

SUMMARY OF THE INVENTION The present invention has been made in view of such a conventional situation, and provides a magnetic disk substrate and a magnetic recording medium having excellent head flying characteristics by minimizing the straightness of a plastic substrate. The purpose is to:

[0010]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to achieve the above-mentioned object, and as a result, after filling the resin into the mold, the resin has a length of 0.03 seconds or more and 0.47 seconds or less, more preferably 0% or less. It has been found that the straightness of the substrate can be significantly reduced by performing the gate cut within 0.07 seconds or more and within 0.35 seconds. It has been found that the straightness of the substrate is reduced to 8 μm or less, more desirably 4 μm or less, by performing injection molding satisfying this condition to produce a substrate.

In a first aspect of the present invention, a method for manufacturing a magnetic disk substrate by an injection molding method includes a step of filling a mold with a thermoplastic resin through a gate, and a step of completing the filling of the mold with the thermoplastic resin. 0.03 seconds or more after 0.47
And a step of cutting the gate at a time within seconds. Preferably, the gate cut may be performed at a time point of not less than 0.07 seconds and not more than 0.35 seconds after the filling of the mold with the thermoplastic resin.

A magnetic disk substrate according to a second aspect of the present invention has a straightness of 8 μm or less.
It is manufactured by the manufacturing method of the first aspect. Preferably,
It may have a straightness of 4 μm or less.

According to a third aspect of the present invention, a method for manufacturing a magnetic recording medium includes a step of manufacturing a magnetic disk substrate by the manufacturing method of the first aspect, and forming at least a magnetic recording layer on the magnetic disk substrate. It is characterized by including a step.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A magnetic disk substrate manufactured in the present invention can have a disk shape having a circular hole at the center. The center circular hole is used for mounting a spindle motor when a magnetic recording medium using the magnetic disk substrate is installed in a magnetic recording device. The diameter of the central circular hole and the disk depends on the design of the magnetic recording device.

In the injection molding used in the present invention, an injection molding apparatus known in the art can be used. It is preferable to use a screw-type injection molding device in order to increase the uniformity of the resin. It is possible to use a screw to melt and measure the resin and use a plunger to inject the resin.However, use an inline screw-type injection molding device that integrates the functions of melting, measuring and injection. Is preferred. FIG. 1 is a schematic sectional view of an in-line screw injection molding apparatus that can be used in the present invention. This in-line screw type injection molding apparatus comprises a heating cylinder 13 having a heating means 14 and an injection port 16 for a mold, and a (movable) screw in the heating cylinder 13 for melting, measuring and injecting the resin. 11 and screw 11
Supply means 15 (eg, hopper) for supplying resin to
And screw driving means 12 for measuring and injecting the screw 11. As the mold, a mold composed of two separable parts (fixed part 17 and movable part 18) is used, and a driving means 19 for applying a mold clamping pressure to the mold and driving the movable part 18 is provided. Preferably, but not exclusively.

FIG. 2 is a schematic sectional view of a mold that can be used in the present invention. FIG. 2A shows the mold at the time of filling the resin, and FIG. 2B shows the mold at the time of performing the gate cut. The mold has a space corresponding to the shape of the substrate to be manufactured (hereinafter, referred to as a substrate cavity 22), and a space connecting the substrate cavity and the injection port 16 (hereinafter, referred to as a sprue portion 21). A gate 23 is disposed between the substrate cavity 22 and the sprue 21, and the resin filled in the substrate cavity 22 and the sprue 2
Gate cutting means 24 for separating (gate cutting) from one resin is provided.

When manufacturing the magnetic disk substrate of the present invention, the resin melted and measured using the screw 11 is injected into the mold in the state shown in FIG. Sprue portion 21 and substrate cavity 22
Is filled with resin. Thereafter, the filled molten resin is cooled and hardened in a mold. During the cooling and hardening, as shown in FIG.
The magnetic disk substrate can be obtained by separating the resin of the substrate cavity portion 1 from the resin 1 and further cooling and hardening the resin.

The magnetic disk substrate of the present invention is manufactured with excellent straightness by performing a gate cut at an appropriate point in cooling. In this specification, “straightness” is a displacement amount in a direction perpendicular to the substrate surface in a linear region extending in a given radial direction on the disk substrate surface, and connects the innermost peripheral portion and the outermost peripheral portion of the recording region. The difference between the highest and lowest points of vertical displacement from a geometric straight line. Therefore, the value of straightness is an index for the undulation or roughness of the substrate surface, and a smaller value of straightness means a magnetic disk substrate having more excellent shape characteristics.

One of the reasons that the straightness is not improved in the injection molding is that a physical force acting during the curing process of the resin remains as a stress. More specifically, when the resin in the semi-solidified substrate cavity portion 22 and the resin in the sprue portion 21 are separated by the gate cut means 24 during the curing process of the resin injected into the mold, Force acts. The physical force at the time of the gate cut hardens while remaining as a stress on the inner peripheral portion, and the residual stress causes deformation of the substrate after the completion of the molding, and more specifically, swells on the inner peripheral portion of the substrate after the completion of the molding. It is believed that the straightness deteriorates (increases) to provide the components. The present inventors have found that it is desirable to perform gate cutting in a state where the viscosity of the resin immediately after resin filling is low. When gate cutting is performed in a state where the viscosity of the resin is low and the fluidity is maintained to some extent, the resin can flow to some extent even after the gate cut, so the physical force acting at the time of gate cutting is used as stress in the substrate as stress. Can be eliminated.

When manufacturing the magnetic disk substrate of the present invention, 0.03 to 0.47 seconds after the completion of the resin filling in the mold, preferably 0.07 to 0.47 seconds after the completion of the resin filling in the mold.
Gate cut is performed at 0.35 seconds to 0.35 seconds. When the molding is performed while satisfying this condition, the undulation component of the inner peripheral portion of the substrate can be reduced, and the straightness of the substrate can be significantly reduced. If gate cutting is performed at less than 0.03 seconds after the completion of resin filling, high pressure is generated in the mold due to insufficient volume shrinkage due to cooling and curing of the resin, and the resin viscosity is low. As a result, the resin enters the gaps of the mold, causing burrs. In addition, when gate cutting is performed 0.4 seconds or more after the completion of resin filling, the swell component due to the above-described stress is generated because the viscosity of the resin is high.

As described above, the magnetic disk substrate manufactured by performing gate cutting at an appropriate time has a thickness of 8 μm or less.
More preferably, it has a straightness of 4 μm or less.

It is preferable that the magnetic disk substrate manufactured as described above is subjected to an annealing treatment to reduce the stress remaining in the substrate. The annealing treatment is preferably performed at a temperature of (Tg-70) ° C. or more and (Tg-15) ° C. or less (Tg means a glass transition temperature of the resin) for 0.5 to 48 hours. The annealing temperature is preferably as high as possible, provided that it does not cause the deterioration of the resin and the local shape change of the substrate. The annealing treatment can be performed in an air atmosphere or a low oxygen atmosphere. In addition, in order to prevent the occurrence of bending due to the weight of the substrate during the annealing process, it is preferable to perform the annealing process with the substrate placed vertically. By performing sufficient annealing, the residual stress can be reduced, the shape change due to the release of the residual stress over time can be minimized, and the occurrence of local deformation can be prevented.

The thermoplastic resin used in the present invention contains a polyolefin resin in addition to a polycarbonate resin and a polymethyl methacrylate resin generally used for a magneto-optical disk substrate. In particular, it is preferable to use a polyolefin-based resin having a high heat resistance and a low moisture absorption and having a rigid structure, for example, a norbornene-based polycycloolefin resin. Further, the Tg derived from the resin structure is in the range of 135 to 170 ° C, and the higher the Tg in this range, the more preferable.

When a magnetic recording medium is manufactured using the magnetic disk substrate manufactured as described above, a magnetic recording layer is laminated on at least the substrate. Further, an underlayer, a protective layer, a lubricating layer, and the like can be provided as necessary. Depending on the application, the above-described layers can be provided on one or both sides of the magnetic disk substrate to obtain single-sided and double-sided magnetic recording media, respectively.

When manufacturing a magnetic recording medium of the horizontal recording type generally used in a hard disk drive or the like, it is preferable to provide an underlayer, a magnetic recording layer, a protective layer, and a lubricating layer in this order. For the purpose of improving the performance of the magnetic recording layer, an intermediate layer may be provided between the underlayer and the magnetic recording layer. In the case of manufacturing a perpendicular recording type magnetic recording medium that has recently attracted attention due to the possibility of improving the recording density, an underlayer, a soft magnetic backing layer, a magnetic recording layer, a protective layer, and a lubricating layer are arranged in this order. Preferably, it is provided. Also in this case, an intermediate layer may be provided between the underlayer and the soft magnetic underlayer and / or between the soft magnetic underlayer and the magnetic recording layer for the purpose of improving recording characteristics and the like.

Each of the above layers can be made from any material known in the art. For example,
The underlayer can be made of a nonmagnetic metal material of Cr or an alloy mainly composed of Cr, and the magnetic recording layer is made of Co and C
r can be made from magnetic materials such as alloys, and the protective layer is carbon (especially diamond-like carbon)
And the like. Further, the lubricating layer can be made of a liquid lubricant such as fluorine-containing polyether, and the soft magnetic backing layer is made of an amorphous Co alloy, a NiFe alloy, or a sendust (FeSiAl) alloy. Can be. As the intermediate layer, a material such as Ti or a TiCr alloy may be used.

Each of the above layers except for the lubricating layer is formed by a sputtering method,
It can be laminated on a magnetic disk substrate by a conventionally known method such as a vapor deposition method and a CVD method. In particular, it is preferable to use a sputtering method. Further, the lubricating layer can be formed by a method such as dip coating, spin coating, and spraying.

(Function) By using a high heat-resistant thermoplastic resin and performing injection molding while satisfying the conditions of the present invention, the straightness of the substrate is significantly reduced, and a magnetic disk substrate with improved shape characteristics is produced. Can be. By using the magnetic disk substrate, it is possible to provide a magnetic recording medium having excellent head flying characteristics.

[0029]

Embodiments of the present invention will be described below in detail with reference to the drawings.

Example 1 A mold having a stamper fixed thereto was mounted on a commercially available injection molding apparatus having a maximum injection molding pressure of 70 t. Using a norbornene-based polyolefin resin (Tg = 138 ° C.) as the resin, a resin temperature of 320
° C, injection speed 120mm / s, mold clamping pressure 120kg /
Injection molding was performed under the molding conditions of cm ² (about 11.8 MPa), mold temperature (fixed side / movable side) of 110 ° C./110° C., and gate cut timing of 0.2 seconds after completion of resin filling. Within one hour thereafter, the substrate was annealed at 90 ° C. for 10 hours in an air atmosphere with the substrate held vertically, having a central circular hole having a diameter of 25 mm, a diameter of 95 mm, and a thickness of 1.27 mm. A disk-shaped disk substrate having the following dimensions was obtained.

(Example 2) A disk substrate was obtained in the same manner as in Example 1 except that the timing of gate cutting was set to 0.1 second after completion of resin filling. (Example 3) A disk substrate was obtained in the same manner as in Example 1, except that the gate cut timing was set to 0.3 seconds after the completion of the resin filling. (Example 4) A disk substrate was obtained in the same manner as in Example 1, except that the gate cut timing was set to 0.4 seconds after the completion of the resin filling.

(Comparative Example 1) A disk substrate was obtained in the same manner as in Example 1 except that the timing of gate cutting was set to 0.0 seconds after completion of resin filling. (Comparative Example 2) A disk substrate was obtained in the same manner as in Example 1 except that the gate cut timing was set to 0.5 seconds after the completion of the resin filling. (Comparative Example 3) A disk substrate was obtained in the same manner as in Example 1, except that the timing of gate cutting was set to 0.6 seconds after completion of resin filling.

(Evaluation Method) For a linear area extending in the radial direction within the recording area from the inner diameter of 20 mm to the outer diameter of 45 mm of the substrate, the displacement of the substrate surface shape is measured by a non-contact optical surface roughness meter (MP2000 PLUS, manufactured by Chapman). )
Derived straightness. 4 every 90 degrees per board surface
Measurements were made at various locations, and the maximum straightness was determined as the straightness of the substrate surface.

(Evaluation Results) FIG. 3 shows the relationship between the gate cut timing and the straightness of the substrate. As is clear from FIG. 3, the straightness of the substrate was reduced as the timing of gate cutting was earlier after the end of resin filling. This result indicates that it is preferable to perform the gate cut as soon as possible before the resin is cured. However, Comparative Example 1
In the gate cut at 0.0 seconds, burrs occurred on the outer peripheral portion of the substrate. This is because gate cut was performed in a state where the melt viscosity of the resin was low and the pressure inside the mold was not sufficiently reduced due to the decrease in the volume of the resin due to cooling. It is considered that this is because the mold has entered the gap. If burrs are generated during molding, the burrs are broken or dropped in a later step, and a large amount of particles are generated, which is not preferable in terms of the process. In addition, when burrs occur, the releasability of the substrate from the mold deteriorates. The substrate was deformed by the residual stress at the time of mold release, and the straightness was increased more than when the gate cut was performed for 0.1 second. Therefore, it became clear that it was not appropriate to perform the gate cut at 0.0 seconds after the completion of the resin filling.

When the gate cut is performed at a time of 0.03 to 0.47 seconds after the completion of the resin filling, which is the molding condition of the present invention, the straightness of the obtained plastic substrate is 8 μm.
m or less. It is well known that the straightness of a substrate is greatly related to the flying characteristics of a head, and it is not possible to produce a magnetic disk substrate having excellent flying characteristics of a head or a magnetic recording medium using the substrate according to the present invention. it is obvious.

[0036]

As is apparent from the above description, in the disk substrate according to the present invention, the gate cutting timing is set to be 0.03 to 0.47 seconds, preferably 0.03 seconds after the resin filling is completed.
The substrate is manufactured by injection molding using molding conditions of 7 to 0.35 seconds, and the straightness of the substrate can be 8 μm or less, preferably 4 μm or less. Therefore, the magnetic disk substrate manufactured by the present invention and the magnetic recording medium using the substrate have excellent flying characteristics of the head.

Further, according to the method of the present invention, it is possible to mass-produce a plastic magnetic disk substrate having excellent shape characteristics in a large amount and at a low cost. As a result, a magnetic recording medium and a magnetic recording / reproducing apparatus using the plastic magnetic disk substrate can be produced. Can be mass-produced inexpensively. Therefore, the industrial value of the present invention is great.

[Brief description of the drawings]

FIG. 1 is a conceptual sectional view showing an example of an injection molding apparatus that can be used for manufacturing a magnetic disk substrate of the present invention.

FIG. 2 is a conceptual cross-sectional view showing an example of a mold that can be used for manufacturing a magnetic disk substrate according to the present invention, in which FIG.
FIG. 4B shows a state at the time of resin filling, and FIG. 4B shows a state at the time of gate cutting.

FIG. 3 is a graph showing the relationship between gate cut timing and straightness of a magnetic disk substrate manufactured according to each of Examples and Comparative Examples.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Screw 12 Screw drive means 13 Heating cylinder 14 Heating means 15 Supply means 16 Injection port 17 Mold fixed part 18 Mold movable part 19 Movable part drive means 21 Sprue part 22 Substrate cavity 23 Gate 24 Gate cut means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B29L 17:00 B29L 17:00 (72) Inventor Shoji Sakaguchi 1-1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-ku, Kawasaki-shi, Kanagawa No. F term in Fuji Electric Co., Ltd. (reference) 4F202 AH38 AM32 CA11 CB01 CK06 CK35 CK84 5D006 CB01 CB07 DA03 EA03 5D112 AA02 BA01 BA10

Claims (5)

[Claims] 1. A step of filling a mold with a thermoplastic resin through a gate; and 0.0 after the mold is filled with the thermoplastic resin.
At least a step of performing a gate cut at a time of not less than 3 seconds and not more than 0.47 seconds. A method of manufacturing a magnetic disk substrate by an injection molding method. 2. The method according to claim 1, wherein the gate cut is performed for at least 0.07 second after the completion of filling the mold with the thermoplastic resin.
2. The method for manufacturing a magnetic disk substrate by injection molding according to claim 1, wherein the method is performed at a time of less than one second. 3. The magnetic disk substrate manufactured by the manufacturing method according to claim 1, having a straightness of 8 μm or less. 4. A magnetic disk substrate manufactured by the manufacturing method according to claim 1, having a straightness of 4 μm or less. 5. A magnetic recording medium comprising: a step of manufacturing a magnetic disk substrate by the manufacturing method according to claim 1; and a step of forming at least a magnetic recording layer on the magnetic disk substrate. Method of manufacturing.