JP2001300970A - Method for manufacturing plastic disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a disk substrate generating no blister even if allowed to stand for a long time under high temperature and high humidity environment and low temperature environment, and a recording medium. SOLUTION: In a method for manufacturing the disk substrate by injection- molding a thermoplastic resin, the thermoplastic resin is injection-molded under such a condition that the temperature of the molten thermoplastic resin is not higher than Tg of the thermoplastic resin +220 deg.C and not lower than Tg+110 deg.C, the metering time thereof is 2.5-15 sec, the back pressure thereof at the time of metering is 5.4-15.7 MPa (55-160 kg/cm2) and mold clamping pressure is 1.5-15.7 MPa (15-160 kg/cm2).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a recording medium substrate mounted on an external storage device of a computer and other various recording devices for digital data, a recording medium constituted by the substrate, and a method of manufacturing the same. More specifically, the present invention relates to a magnetic recording medium substrate, a magnetic recording medium formed therefrom, and a method of manufacturing the same.

[0002]

2. Description of the Related Art With respect to a magnetic recording medium requiring a high surface precision, a high precision processing is required when a conventional non-magnetic metal substrate (such as Al) is used.

As a conventional non-magnetic metal substrate, generally, a metal material that has been heated and melted is rolled, heated and refined, and then heated.
A blank material processed to a specified size is used.
Next, the inner and outer diameters of the blank are processed. Further, after lapping for improving the surface accuracy is performed, 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 a surface roughness of Ra = 1 nm (10 °). After polishing to become
Final lapping is performed using diamond slurry. After that, for example, the CSS zone has a bump height of 19 nm (190 °) and a density of 1 in 30 μm square.
The substrate is subjected to laser zone texturing so that the substrate is precisely washed, and a substrate for a magnetic recording medium (magnetic disk substrate) is obtained.

[0004] Thereafter, the underlayer Cr layer was 50 nm (500 °), the Co-14Cr-4Ta magnetic layer was 30 nm (300 °), and the carbon protective layer was 8 nm (8 ° C) by DC sputtering.
0 °), tape burnishing is performed on the surface after sputtering, and a fluorine-based lubricating layer is then formed to a thickness of 2 nm (20 °) by dip coating or spin coating to obtain a magnetic recording medium.

An optical recording medium, for example, a compact disk, includes at least a reflective layer and a protective layer on an optical disk substrate, and reads information using light reflected from the reflective layer. Furthermore, a writable optical disk (C
DR, CD-RW, PD, etc.) have at least a recording layer, a reflective layer, and a protective layer laminated on an optical disk substrate, and read and write information on the recording layer using a laser beam. Things.

Further, the magneto-optical recording medium has a magnetic recording layer, a reflective film and a protective coat sandwiched between protective films, for example, on a magneto-optical disk substrate, and records information using laser light and magnetism. In addition, information is read using reflection of laser light by a magnetic layer.

However, the manufacturing methods and structures of the various disk substrates and various recording media are not limited to these.

Among the above, particularly with respect to the magnetic recording medium, the conventional method of manufacturing the magnetic disk substrate and the magnetic recording medium has become more and more complicated with the recent increase in the recording density, while maintaining high performance. There is a need for a magnetic recording medium that is less expensive than before. As a new magnetic disk substrate that solves the conflicting demands, a magnetic recording medium using plastic has been proposed (for example, Japanese Patent Application Laid-Open Nos. 5-4231, 5-6535, 5-28488). Please refer to Japanese Patent Publication No.

[0009]

However, magnetic disk substrates that require a high degree of shape stability and surface precision are generally required to have higher mechanical strength, e.g., tensile strength, elongation and elastic modulus than metal, glass or ceramic substrates. Plastic substrates with low mechanical strength and large thermal expansion coefficient are disadvantageous. In addition, in reliability tests under high temperature, high humidity and low temperature, blisters with a diameter of several μm and a height of several nm Many can occur.

In general optical recording media and magneto-optical recording media, blisters were generated by this environmental test, but no problem occurred because the distance between the laser and the substrate was large. However, in a device such as a hard disk, which requires a very high surface accuracy such that the head flies over a height of several tens of nanometers, the magnetic head does not float, and the actual reading and writing cannot be performed. .

Accordingly, the present invention has been proposed in view of such conventional circumstances, and has been proposed to minimize the occurrence of blisters on a substrate even when the substrate is left for a long time in a high-temperature, high-humidity, or low-temperature environment. And a recording medium.

[0012]

Means for Solving the Problems The present inventor has conducted intensive studies in order to achieve the above objects and objects, and as a result, it has been found that blisters on the substrate can be generated even when left for a long time in an environment of high temperature, high humidity and low temperature. In order to obtain a disk substrate and a recording medium that are minimized, moisture remaining inside the substrate and molding defects present on the substrate surface at the time of molding must be removed in the manufacturing process of the disk medium, and the source of moisture must be removed. Disk substrate, optical disk substrate, magneto-optical disk substrate, and recording medium using the same, by subjecting the substrate to injection molding under molding conditions having appropriate moisture permeability so as not to be localized and condensed Have been found, and the present invention has been completed.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The magnetic disk substrate according to the present invention is formed by injection-molding a high heat-resistant thermoplastic resin, and can be used for a long time in a high-temperature, high-humidity or low-temperature environment. In order to obtain a substrate that minimizes the occurrence of blisters on the surface, it is necessary to minimize the amount of moisture remaining inside the substrate and the number of molding defects existing on the substrate surface and to give the substrate an appropriate moisture permeability. It is a disk substrate manufactured under the molding conditions of the above.

The thermoplastic resin used in the present invention includes a polyolefin resin in addition to a polycarbonate resin and a polymethyl methacrylate resin generally used for a magneto-optical disk substrate. Especially high heat resistance
It is desirable to use a polyolefin resin having a low hygroscopicity and a rigid structure, such as a norbornene polycycloolefin resin. Further, the glass transition point (referred to as Tg in the present specification) derived from the resin structure is from 135 ° C. to 1 ° C.
70 ° C., and a higher Tg in this range is more desirable.

In the injection molding used in the present invention, it is preferable to use a screw-type injection molding apparatus in order to improve 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;
(Movable) screw 11 for melting, measuring, and injecting the resin, supply means 15 (such as a hopper) for supplying the resin to the screw 11, and for measuring and injecting the screw 11 And screw driving means 12. As the mold, a mold composed of two separable partial fixing portions 17 and a movable portion 18 is used. Further, a mold clamping pressure is applied to the mold, and the movable portion 18 is provided.
It is preferable to provide a driving means 19 for driving the driving mechanism, but the present invention is not limited to this.

In order to reduce blisters generated on a substrate when left in a high-temperature, high-humidity or low-temperature environment for a long period of time, it is necessary to eliminate molding defects serving as cores of blisters. This is because, when such a molding defect exists on the substrate surface, moisture condenses at the molding defect and becomes a core of blisters. It is preferable that the substrate is manufactured under molding conditions that can provide the substrate with appropriate moisture permeability so that localized moisture is not condensed together with the elimination of the molding defect.

The molding defects which are the cores of blisters are formed by (1) those caused by the deteriorated resin, (2) those caused by the residual resin melt, and (3) the gas generated by the resin. It is roughly divided into what you do. It is also desirable to remove as much as possible of ionic and metallic impurities in the resin. Hereinafter, details regarding the substrate and the molding conditions for eliminating the above-mentioned respective causes of formation will be described.

First, an attempt was made to remove molding defects caused by the degraded resin so that water would not condense and nuclei of blisters would not be formed. The deterioration of the resin in the injection molding is mainly due to the heat applied for melting the resin. When an attempt was made to inject molten resin at a temperature at which no degraded resin was generated in order to reduce the degraded resin in the molded substrate, the density at which blisters were generated could be significantly reduced.
The preferred maximum temperature of the molten resin at that time is Tg + 110 ° C.
Above was Tg + 220 ° C. or less. More preferably,
It was Tg + 130 ° C. or higher and Tg + 180 ° C. or lower (Tg is the glass transition point of the resin).

For the same purpose, the above-mentioned object can be achieved by shortening the measuring time from the start of the deterioration of the resin. The measuring time in the present invention means that the resin is supplied from the resin supply means 15 to the screw 11,
The resin is melted and mixed by the rotation of the screw 11 by the screw driving means 12 and the heating by the heating means 14.
Means the time during which the molten resin to be injected into the vicinity of the injection port 16 is accumulated and measured. However, since the measuring time is related to the time required for melting the resin, excessively shortening the measuring time may cause a residual resin such as resin balls to occur, thereby defining a lower limit of the measuring time.
Therefore, the appropriate weighing time was 2.5 seconds or more and 15 seconds or less, and the more appropriate time was 4 seconds or more and 10 seconds or less. By performing the molding with the resin temperature and the measuring time set to the above-mentioned appropriate values, the concentration of the deteriorated resin in the molded substrate was greatly reduced, and the density at which blisters were generated could be drastically reduced.

Next, an attempt was made to remove molding defects by reducing gas emission from the resin. For this purpose, the dependence of the density of blisters on the back pressure during weighing was measured. The back pressure during weighing means that the screw driving means 1
2 means the pressure applied to the screw 11. As a result, it was found that there was an appropriate back pressure value to reduce the number of defects and, consequently, the density of blisters.
The back pressure during proper weighing is 5.4 MPa (55 kg / cm
² ) Not less than 15.7 Mpa (160 kg / cm ² ). A more appropriate back pressure is 6.9 MPa (70 kg / c
m ² ) or more and 13.2 Mpa (135 kg / cm ² ) or less. If the back pressure is too small, the gas generated when the resin is melted will not be sufficiently discharged from the molten resin and will remain as bubbles, which will form molding defects and become cores of blisters. Can be Conversely, if the back pressure is too high, it becomes impossible to accumulate and measure the molten resin in the vicinity of the injection port 16 by the screw 11, so the upper limit of the back pressure is defined.

Finally, to prevent condensation of moisture in the substrate
Considered that. Even if there is a molding defect on the substrate surface
However, if water can be prevented from condensing there,
The occurrence of crepe can be reduced or eliminated. In fact,
Substrate with proper water permeability (moisture permeability)
Can reduce the density of blisters.
I also found it to work. To achieve this, the mold clamping pressure during molding
Forming is performed with the force below a certain value, and the bulk density of the substrate is
Needs to be smaller. However, too much mold clamping
Substrate shape when molding with low pressure
It will be difficult to keep it. Therefore, suitable mold clamping
The pressure is 1.5 MPa (15 kg / cm ^Two) 15.
7MPa (160kg / cm^Two) More suitable
The positive mold clamping pressure is 2.9 MPa (30 kg / cm^Two)
9.8 MPa (100 kg / cm^Two)
Was. The preferred bulk density of the substrate at that time is 0.75 to 1.
2g / cm^ThreeMet. More preferably, 0.8 to 1.1.
g / cm^ThreeMet.

[Operation] By using a disk substrate formed by injection molding the highly heat-resistant thermoplastic resin of the present invention,
In particular, it is possible to provide a disk substrate and a recording medium that have high environmental resistance and minimize the occurrence of blisters on the substrate even when left for a long time in an environment of high temperature, high humidity, and low temperature.

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

Example 1 A highly heat-resistant norbornene-based polycycloolefin resin (Tg) was used as a resin in a commercially available injection molding apparatus having a maximum injection molding pressure of 70 t using a mold having a stamper fixed thereto.
= 140 ° C), resin temperature 320 ° C, injection speed 12
0 mm / s, mold clamping pressure 5.4 MPa (55 kg / cm
² ), weighing time 4 seconds, back pressure 10.8MPa (110kg
f / cm ² ), mold temperature = fixed side 110 ° C / movable side 11
Injection molding is performed under the molding condition of 0 ° C, and the diameter is 95mm.
And a disk substrate having a thickness of 1.27 mm was obtained.

Example 2 A magnetic disk substrate was obtained in the same manner as in Example 1 except that the resin temperature was changed to 270 ° C.

Example 3 A magnetic disk substrate was obtained in the same manner as in Example 1 except that the resin temperature was changed to 350 ° C.

Example 4 A magnetic disk substrate was obtained in the same manner as in Example 1 except that the measuring time was changed to 8 seconds.

Example 5 A magnetic disk substrate was obtained in the same manner as in Example 1 except that the back pressure during weighing was changed to 6.4 MPa (65 kgf / cm ² ).

Example 6 The back pressure at the time of measurement was 15.7 MPa (160 kgf / c
A magnetic disk substrate was obtained in the same manner as in Example 1 except that m ² ) was set.

Example 7 The mold clamping pressure was 10.3 MPa (105 kgf / cm ² ).
A magnetic disk substrate was obtained in the same manner as in Example 1 except for the above.

Example 8 A magnetic disk substrate was obtained in the same manner as in Example 1, except that the mold clamping pressure was 1.5 MPa (15 kgf / cm ² ).

Example 9 The mold clamping pressure was 15.7 MPa (150 kgf / cm ² ).
A magnetic disk substrate was obtained in the same manner as in Example 1 except for the above.

Comparative Example 1 A magnetic disk substrate was obtained in the same manner as in Example 1 except that the resin temperature was set to 240 ° C.

Comparative Example 2 A magnetic disk substrate was obtained in the same manner as in Example 1 except that the resin temperature was changed to 370 ° C.

Comparative Example 3 A magnetic disk substrate was obtained in the same manner as in Example 1 except that the measuring time was changed to 1 second.

Comparative Example 4 A magnetic disk substrate was obtained in the same manner as in Example 1 except that the measuring time was changed to 2 seconds.

Comparative Example 5 A magnetic disk substrate was obtained in the same manner as in Example 1 except that the measuring time was changed to 16 seconds.

Comparative Example 6 A magnetic disk substrate was obtained in the same manner as in Example 1 except that the back pressure at the time of measurement was set to 2.9 MPa (30 kgf / cm ² ).

Comparative Example 7 The back pressure at the time of weighing was 18.6 MPa (190 kgf / c
A magnetic disk substrate was obtained in the same manner as in Example 1 except that m ² ) was set.

Comparative Example 8 The mold clamping pressure was 18.6 MPa (190 kgf / cm ² ).
A magnetic disk substrate was obtained in the same manner as in Example 1 except for the above.

(Evaluation Method) A magnetic layer was formed on the substrates prepared in Examples 1 to 9 and Comparative Examples 1 to 10 by sputtering, and thereafter an environmental test was performed. The density of blisters generated after the environmental test was determined. (The number of blisters per surface) was evaluated. First, the environmental test was performed in a high-temperature, high-humidity atmosphere (60 ° C
(80% RH) for 10 hours, then quickly cooled to -40 ° C and left there for 10 hours. Thereafter, the environment was promptly returned to the normal temperature and normal humidity environment, and the environmental test was completed. The evaluation items were the density of blisters, the weight density of the substrate, and the amount of degraded substances in the molded substrate. In addition, the amount of degraded products means the total amount of the degraded resin and the residual melt. If the blister density was 50 or less per surface, it was determined that the blister was suitable for use as a substrate for various recording media. In each of the above examples, five substrates were sampled for each condition, and the average value of the results of the five substrates was used as the evaluation result.

[Dependence of density of blisters on resin temperature] The resin temperature at the time of melting was changed, and the amount of degraded components of the resin on the substrate and the blister density were measured (Examples 1 to 3, and Comparative Examples 1 and 2). The result is shown in FIG.
As shown in the measurement results, it can be seen that there is an optimum value for the temperature of the resin to be melted, and that the amount of the degraded material increases when the temperature is too high or too low. If the temperature of the resin is too low, the resin cannot be melted sufficiently, and the screw will forcibly pulverize the pellets, resulting in an increase in the amount of degraded materials. On the other hand, if the temperature of the resin is too high, the deteriorated resin is used for molding, and the amount of degraded substances in the substrate increases. For this reason, it has been found that there is a resin temperature at which the amount of degraded substances is minimized, and that molding at that temperature also reduces the density of blisters. This is because when the resin deteriorates, it becomes a molding defect, and water condenses in that portion in an environmental test at high temperature, high humidity, and low temperature, and becomes a core of blisters. From this result, a suitable temperature for greatly reducing the density of blisters is Tg + 11
It was found that the temperature was 0 ° C. or higher and Tg + 220 ° C. or lower. More preferably, at Tg + 130 ° C. or higher, Tg + 18
It has been found that 0 ° C. or lower is preferable.

[Measurement Time Dependence of Swelling Density] The amount of degraded substrate and the swelling density of the substrate were measured by changing the measurement time of the resin (Examples 1 and 4, and Comparative Examples 3 to 5). . The result is shown in FIG. As shown in the measurement results, there is an optimum value for the weighing time as well as the resin temperature, and it can be seen that the amount of the degraded substance in the substrate increases when the measurement time is too long or too short. If the measuring time is too short, the resin cannot be melted sufficiently, and the screw that is not sufficiently melted will be forcibly crushed by the screw. ) Will increase. On the other hand, if the measuring time is too long, the resin is sufficiently melted, but the degradation of the resin starts, so that the amount of the deteriorated material (attributable to the deteriorated resin) increases. For this reason, it has been found that there is a measuring time for minimizing the amount of the degraded substance in the substrate, and that the density of blisters is reduced by performing molding during the measuring time. This is because if a degraded product, that is, a degraded resin and a molten residue are present in a substrate, it becomes a molding defect, and in that portion, moisture condenses in a high-temperature, high-humidity and low-temperature environmental test, and becomes a core of blisters. Because. From this result, it was found that the preferable weighing time for reducing the density of the blister is 2.5 seconds to 15 seconds, and a more appropriate time is 4 seconds to 10 seconds.

[Dependence of density of blister on back pressure during measurement] The back pressure during measurement was measured to measure the density of blisters (Examples 1, 5, and 6, and Comparative Examples 6 and 7). . The result is shown in FIG. As shown in the measurement results, it can be seen that the number of blisters is significantly reduced at a back pressure of 5.9 MPa (60 kgf / cm ² ) or more. This result is attributed to the fact that applying a back pressure of a certain value or more at the time of measurement makes it easier for gas components in the resin to escape from the molten resin, which is considered to reduce molding defects. However, 18.6 MPa (1
Above 90 kgf / cm ² ), the back pressure was too high and measurement was impossible. Therefore, the back pressure at the time of proper weighing is 15.4 MPa (55 kg / cm ² ) or more.
It was 7 MPa (160 kg / cm ² ) or less. A more appropriate back pressure was 6.9 MPa (70 kg / cm ² ) or more and 13.2 MPa (135 kg / cm ² ) or less.

[Dependence of Burr Density on Mold Clamping Pressure] The mold bulk pressure and the blister density of the substrate were measured by changing the mold clamping pressure during injection molding (Examples 1 to 7). 9 and Comparative Example 8). The result is shown in FIG. As shown in the measurement results, when the mold clamping pressure was increased, the bulk density of the substrate gradually increased. If the bulk density of the substrate is increased, the distance between the molecules of the resin will decrease, and the gap between the molecules will disappear, so it is thought that it will be difficult for moisture to pass through, but conversely, if the bulk density is reduced, it will be easier to transmit It is considered to be. When the mold clamping pressure is low, the density of blisters decreases,
It was found that the higher the permeability, the less the blisters could be. However, the mold clamping pressure is 9.8 MPa (10
It is known that when the weight is as small as kgf / cm ² ), the substrate shape is not stable. Therefore, a preferable mold clamping pressure is 1.5 MPa (15 kgf / cm ² ) or more.
It was 7 MPa (160 kg / cm ² ) or less. A more appropriate mold clamping pressure is 2.9 MPa (30 kg / cm ² ).
Above was 9.8 MPa (100 kg / cm ² ) or less. A suitable density at that time is 0.75 to 1.2 g / cm.
^{Was 3} . More preferably, it was 0.8 to 1.1 g / cm ³ .

[0046]

As is apparent from the above description, the disk substrate and the recording medium according to the present invention can reduce molding defects caused by various causes by controlling molding conditions within an appropriate range. In addition, by performing injection molding under molding conditions that maintain the transparency of the molded substrate, the number of blisters generated when an environmental test is performed at high temperature, high humidity, and low temperature can be minimized. If a disk substrate that suppresses the occurrence of such blisters can be obtained, a recording medium having high environmental resistance can be obtained.

Further, by using a substrate molded under the molding conditions proposed in the present invention, it becomes possible to produce a recording medium having high environmental resistance in a large amount and at a low cost. Value is great.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of an injection molding apparatus that can be used in the present invention.

FIG. 2 is a graph showing the relationship between the resin temperature at the time of melting and the densities of resin degradation products and blisters in a substrate.

FIG. 3 is a graph showing the relationship between the measurement time and the densities of resin degradation products and blisters in a substrate.

FIG. 4 is a graph showing the relationship between the back pressure during weighing and the density of blisters.

FIG. 5 is a graph showing a relationship between a mold clamping pressure, a substrate density, and a blister density.

Claims (4)

[Claims] 1. A method of manufacturing a disk substrate in which a thermoplastic resin is injection-molded, wherein the maximum temperature of the molten thermoplastic resin is Tg + 110 ° C. of the thermoplastic resin.
The above is the Tg of the thermoplastic resin + 220 ° C. or less, the weighing time is 2.5 seconds or more and 15 seconds or less, and the back pressure at the time of weighing is 5.4 MPa (55 kg / cm ² ).
And 15.7 Mpa (160 kg / cm ² ) or less, and the mold clamping pressure is 1.5 MPa (15 kPa).
g / cm ² ) or more and 15.7 MPa (160 kg
/ Cm ² ) A method for producing a disk substrate, which is injection-molded under the following conditions: 2. A disk substrate manufactured by the manufacturing method according to claim 1. 3. The disk substrate has a bulk density of 0.7.
^3. The disk substrate according to claim 2, wherein the amount is not less than 5 g / cm ^{3 and not} more than 1.2 g / cm ³ . 4. A magnetic recording medium comprising the disk substrate according to claim 2.