JP2000015644A - Disk substrate molding die - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent formation of a thick part near an end face of an outer periphery of a board in the case of forming a disk by providing a protrusion-like step on an outer periphery of at least one side of opposed mold surfaces. SOLUTION: An outer peripheral ring 7 for forming an outer periphery of a cavity 12 is provided on an outer periphery of a movable mold 1 approaching to or separating from a fixed mold 8. 45-rpm record-like stampers 6, 6 for transferring pits or grooves as information to recording/reproducing area of a board are disposed on the board. A fixed side mirror surface bush 13 is provided on an outer periphery of the mold 8. A surface of the bush 13 is projected from a surface of the mold 8 to provide a step, while a movable side mirror surface bush 14 is provided on the outer periphery of the mold 1. A surface of the bush 14 is projected from a surface of the mold 1 to provide a step, and an interval of the cavity 12 is narrowed. Accordingly, formation of a thick part at an end face of an outer periphery of the board can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a disk molding die. More specifically, the present invention relates to a disk molding die for satisfactorily molding a synthetic resin disk having preformat information transferred to both surfaces.

[0002]

2. Description of the Related Art Optical recording media have been put to practical use as high-density, low-cost information recording media. For example, C for music
D (compact disk), LD (laser disk) for image use, magneto-optical disk for data recording, phase change disk, and the like are known. Recording and reproduction of information are performed by a change in reflectivity due to uneven pits provided on the substrate, a change in reflectivity due to crystallization and amorphization of the recording film, or a rotation of linearly polarized light due to a magnetization direction of a magnetic material.

With the increase in the capacity of these media, there has been a demand not only for increasing the density of the recording area but also for expanding the recording area to the outer periphery.

[0004]

A conventional method for forming a disk substrate will be described. FIG. 4 shows a conventional injection mold for a disk substrate having a format on both sides. The mold shown in FIG. 4 includes a movable mold 1 having a cylindrical movable-side stamper inner peripheral retainer 2 disposed at the center, and a sprue bush 4 through which a molten resin flows through a fixed-side bush 9. , And a fixed die 8 having a fixed-side stamper inner peripheral presser 3.

[0005] Further, a cut punch 10 for performing a gate cut is provided on the movable mold 1 which approaches and separates from the fixed mold 8.
A protruding pin 11 is provided so as to be able to protrude and retract for the purpose of taking out the sprue. An outer peripheral portion of the movable mold 1 is provided with an outer peripheral ring 7 forming an outer peripheral portion of the cavity 12. In the cavity 12, a stamper 6 on a donut board for transferring pits or grooves as information to a recording / reproducing area of the substrate is arranged. The inner circumference of the stamper 6
It is fixed to the surfaces of the dies 1 and 8 by the stamper inner peripheral retainers 2 and 3.

When resin injection molding is performed using this mold, the cooling rate of the outer peripheral portion of the disk substrate during molding is specifically increased due to the cooling effect of the outer peripheral ring at the outer peripheral end. At this time, since a temperature distribution occurs in the substrate, the resin is solidified in a state where the resin density at the outer peripheral portion of the substrate is high. Thereafter, in the cooling step or in releasing the mold clamping force after the mold is opened, the substrate shrinks and the resin density becomes uniform. At this time, the shrinkage is small at the outer edge where the density is originally high, and the shrinkage is large at other portions where the density is relatively small. As a result, the substrate thickness of the end face of the outer portion becomes thicker than other portions. Was.

That is, since the outer peripheral end portion, which is rapidly cooled after filling the resin, has a higher resin density than other regions, this region has a small amount of shrinkage after cooling or after the pressure is released. Is formed. Normally, the thickness gradually increases from the point of 1 to 2 mm from the outer peripheral edge of the substrate toward the outer peripheral edge, and at most is about 1 to 5% of the thickness of the central portion of the substrate.

Conventionally, since such a thick portion exists on the outer peripheral portion of a disk substrate, a defect of an information recording / reproducing signal, a crash of a head, and the like are likely to occur. The effect of the outer peripheral edge shape of the disk substrate on recording and reproduction will be described with reference to FIG. That is, as shown in FIG. 2A, when recording and reproduction are performed by irradiating light from the back surface of the substrate, since the substrate surface is inclined, the same effect as a large tilt occurs, and the recording / reproduction signal is likely to be defective. Become. In the case where recording and reproduction are performed by irradiating light from the film surface side as shown in FIG. 2 (b), the same effect occurs and the recording / reproduction signal is likely to be defective. Further, as shown in FIG. When a head is used, it is more serious, and the head cannot follow sharp irregularities on the substrate surface, and the head may collide with the substrate.

As a method for suppressing the outer peripheral thick portion, 1) the temperature of the outer peripheral portion of the mirror surface is independently adjusted to a high temperature. 2) A temperature control mechanism is provided on the outer ring to raise the temperature. In any case, however, there is a problem that the substrate is deformed after the mold is opened due to the high temperature of the outer peripheral portion.

An object of the present invention is to provide a disk molding die capable of suppressing formation of a thick portion near the end face of the outer peripheral portion of a substrate when molding a disk as described above.

[0011]

The present inventor has studied to solve the above-mentioned problems of the prior art, and as a result, by providing a step on the outer peripheral portion of the mold surface, it is possible to reduce a thick portion generated by ordinary molding. The inventors have found that the thickness can be reduced and the molded substrate can be flattened to the outer periphery, and the present invention has been completed.

That is, the gist of the present invention is a mold for molding an annular disk by injecting a synthetic resin, wherein cavities corresponding to the disk shape are formed opposite to each other, and the surfaces of the opposed molds are formed. A pair of molds provided with a stamper on at least one side, and an outer peripheral ring forming an outer peripheral portion of the disk, wherein a convex step is provided on at least one outer peripheral portion of the opposing mold surfaces. The disk substrate molding die to be used.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. FIG. 1 is an example of a mold of the present invention for molding a disk substrate having a format on both sides. A movable mold 1 having a cylindrical movable-side stamper inner peripheral retainer 2 disposed at the center, a sprue bush 4 through which a molten resin flows through a fixed-side bush 9, and a fixed-side stamper inner peripheral retainer. 3 and a fixed mold 8 having the same.

The movable mold 1 approaching and separating from the fixed mold 8 has a cut punch 10 for performing gate cutting,
A protruding pin 11 is provided so as to be able to protrude and retract for the purpose of taking out the sprue. An outer peripheral portion of the movable mold 1 is provided with an outer peripheral ring 7 forming an outer peripheral portion of the cavity 12. In the cavity 12, stampers 6, 6 'on a donut board for transferring pits or grooves as information to a recording / reproducing area of the substrate are arranged. The inner periphery of the stamper 6 is fixed to the surface of the movable mold 1 by the stamper inner periphery retainer 2. The inner periphery of the stamper 6 ′ is fixed to the surface of the fixed side 8 by the stamper inner periphery retainer 3.

In this example, the outer periphery of the fixed mold 8 and the movable mold 1 is divided, and the interval between the cavities 12 on the outer periphery is narrowed. That is, the fixed-side mirror surface bush 13 is provided on the outer periphery of the fixed mold 8, and the surface of the bush 13 is protruded from the surface of the fixed mold 8 to provide a step, while the outer periphery of the movable mold 1 is provided. Is provided with a movable mirror surface bush 14, the surface of the bush 14 is protruded from the surface of the movable mold 1 to provide a step, and the interval between the cavities 12 is reduced.

The convex step in the present invention may rise vertically from the mold surface, or may change smoothly such as by making it beveled or chamfered. If the step rises perpendicularly from the mold surface, there is a possibility that a trace of the step will be attached to the molded substrate, but if the stamper is arranged on top of the step, there will be no trace of the step on the molded substrate It is preferred.

The position where the step is provided is preferably within 2 mm from the outer edge of the disk substrate, more preferably 0.2 to 2 mm, and most preferably 0.2 to 1 mm inside. It is. The height of the step is
Preferably it is 100 μm or less, more preferably 50 μm or less. Further, it is preferably at least 2 μm. When the position where the step is provided and its height are within the above range, the effect of suppressing the thick portion at the outer peripheral end of the disk substrate is great.

The present invention is characterized in that a convex step is provided on the outer peripheral portion of the mold surface. The mold itself may have a convex step, but preferably, the mold is divided at the outer periphery and a convex step is separately provided. When a convex step is provided on the mold surface, it tends to be an obstacle in performing mirror polishing on the mold. Although not shown, the movable mold 1 and the fixed mold 8 are provided with a pressure reducing path for sucking and holding the stampers 6 and 6 '.

In the mold of the present invention, a substrate is manufactured in the following operation. First, the mold temperature is about 80 ~
After setting the temperature to 140 ° C., the movable mold 1 is closed to the fixed mold 8, and about 30
The cavity 12 is filled with a molten resin at 0 to 350 ° C. within about 2 seconds, the cut punch 10 is advanced to perform gate cutting, and a central portion of the molded resin is punched to form an opening.

At this time, the pressure on the substrate molding surface is about 5 to 50 M
The information of the stampers 6, 6 'is transferred to the resin at a mold clamping pressure of Pa, preferably 10 to 40 MPa. Thereafter, the substrate is cooled to form a substrate in the cavity 12.
After forming the substrate, the movable mold 1 is opened, for example, about 10 seconds after the start of the injection. In such opening of the mold, the stamper 6 'is released from the substrate, and the substrate remaining in the movable mold 1 is taken out by a discharge device provided separately.

Also, the cut punch 10 has a residue of the punched resin flow path 5 adhered thereto. The residue is pulled out from the fixed mold 8 as the mold is opened, and is disposed at the center of the cut punch 10. The protruding pin 11 is advanced from the movable mold 1 by moving the protruding pin 11 forward. In addition, when the mold temperature is increased, the cooling rate of the entire substrate is reduced,
This is preferable because it is difficult to form a thick portion near the outer peripheral end face. However, when the mold temperature is increased, the mechanical properties of the substrate tend to deteriorate. Therefore, the preferred mold temperature is 100
To 130 ° C, more preferably 115 to 125 ° C.

The substrate obtained by molding using the above mold is formed in the shape of a synthetic resin donut disk having a circular opening at the center. As a synthetic resin constituting the substrate, a polycarbonate resin, an acrylic resin, a polystyrene resin, a polyolefin resin, a liquid crystal polymer resin, or the like is used. The diameter of the substrate and the diameter of the opening are set according to the standard.

In the above, a case has been described in which a stamper is provided on both sides of a mold to form a disc on which information from the stamper is transferred on both sides of the disc. The present invention is also applicable to a case where information is transferred to only one side. According to the present invention, since a thick portion is prevented from being formed near the end surface of the outer peripheral portion of the disk substrate, a good signal can be obtained even if the recording / reproducing area is formed outside the outer peripheral end surface by more than 2 mm. Characteristics are obtained.

Also, since it is possible to prevent a head crash on the outer periphery of the substrate, it is very preferably used for an optical disk of a film incidence type in which the distance between the substrate and the optical head is short, an optical disk using a floating head, a contact head, and a magnetic disk. Can be.

[0025]

EXAMPLE 1 In the mold shown in FIG. 1, a fixed-side mirror bush 13 and a movable-side mirror bush 14 each having an inner diameter of 129 mm were used.
The step was provided such that the height from the mold surface was 10 μm.

Using this mold, a mold temperature of 120 ° C., a resin temperature of 350 ° C., a mold clamping force of 15 MPa, and an injection time of 0.5
A disk substrate having an inner diameter of 15 mm and an outer diameter of 130 mm was formed under the conditions of 0 seconds and a cooling time of 20.0 seconds. That is, the position of the step was 0.5 mm from the outer edge of the substrate.
About the obtained board | substrate, thickness t of the outer peripheral thick part shown in FIG.
Was measured using a surface roughness profile measuring device Surfcom558 (manufactured by Tokyo Seimitsu Co., Ltd.).

As a result of measurement at four angles of 0 °, 90 °, 180 °, and 270 °, the thickness t was 5 μm,
They were 3 μm, 3 μm and 3 μm. Example 2 A disk substrate was molded under the same conditions as in Example 1 except that the mold temperature was changed to 125 ° C.

When the thickness t of the outer peripheral thick part of the obtained substrate was measured at four points of angles 0 °, 90 °, 180 °, and 270 °, the thickness t was 3 μm,
They were 2 μm, 2 μm and 2 μm. Comparative Example 1 Example 1 except that a mold having a flat outer peripheral portion shown in FIG. 4 was used.
A disk substrate was formed under the same conditions as described above.

When the thickness t of the outer peripheral thick portion of the obtained substrate was measured, four angles of 0 °, 90 °, 180 °, and 270 ° were measured.
m, 15 μm, 12 μm, and 15 μm.

[0030]

According to the present invention, since a thick portion is prevented from being formed near the end face of the outer peripheral portion of the disk substrate,
For example, good signal characteristics can be obtained even if the recording / reproducing area is formed more than 2 mm outside the outer peripheral end face. In addition, since a head crash on the outer periphery of the substrate can be prevented, a film-surface incident type optical disk in which the distance between the substrate and the optical head is small,
It can be very preferably used for an optical disk or a magnetic disk using a flying head or a contact head.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of an example of a mold of the present invention.

FIG. 2 is a diagram for explaining the effect of the outer peripheral edge shape of a disk substrate on recording and reproduction;

FIG. 3 is a diagram for explaining a method of measuring an outer peripheral end shape;

FIG. 4 is a longitudinal sectional view of a conventional mold.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 movable mold 2 movable-side stamper inner-peripheral retainer 3 fixed-side stamper inner-peripheral retainer 4 sprue bush 5 resin flow path 6, 6 ′ stamper 7 outer peripheral ring 8 stationary mold 9 fixed-side bush 10 cut punch 11 protrusion pin 12 cavity 13 Fixed-side mirror surface bush 14 Movable-side mirror surface bush 15 Movable side bush 20 Disk substrate 21 Optical head 22 Optical head 23 Floating head

Claims (5)

[Claims] 1. A mold for injecting a synthetic resin to form an annular disk, wherein cavities corresponding to the disk shape are formed facing each other, and a stamper is provided on at least one of the facing mold surfaces. A pair of molds provided and an outer peripheral ring forming an outer peripheral portion of the disk, wherein a convex step is provided on at least one outer peripheral portion of the opposing mold surfaces. Mold. 2. The disk substrate molding die according to claim 1, wherein a stamper is provided on each of the opposing die surfaces. 3. The disk substrate molding die according to claim 1, wherein a convex step is provided on an outer peripheral portion of each of the opposing die surfaces. 4. The disk substrate molding die according to claim 1, wherein a step having a height of 100 μm or less is provided on an outer peripheral portion of a die surface corresponding to a position within 2 mm from an outer peripheral end of the disk. 5. The disk substrate molding die according to claim 1, wherein the die surface and the convex step portion are divided.