JPH10156889A - Mold for molding and method for injection molding thin plastic base sheet - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simultaneously prevent a diameter expanding part and an expanding part from being generated by a constitution wherein the inner peripheral side end part of a vacuum suction face is put in a row with a butting face to which the inner peripheral side end face of the stamper can be butted through an inclined face with an upward inclination toward the inner peripheral part from the outer peripheral part of a mold core to form a recessed mounting part. SOLUTION: A mold for molding is opened and stampers 71 and 72 are mounted on stamper mounting parts. In this case, inner peripheral side end parts of the stampers 71 and 72 are positioned very closely to butting faces and the surfaces of the stampers are made at the same level to the surface of a disk clamp face forming part. In addition, between the back faces of the stampers and a vacuum suction face and an upward inclined face, gaps 3d with an appropriate dimension are formed. A molding material 31 is filled into a cavity 4a to form a cavity and to form a center hole 31a, a disc clamp part 31b and a signal part 31c.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding technique for a thin plastic substrate, and more particularly, to an injection mold for a disk substrate such as a magnetic disk having a structure for performing a floating recording / reproducing method, and an injection molding method using the same. It is about.

[0002]

2. Description of the Related Art Hard disks made of aluminum alloy and flexible disks made of plastic such as polyester resin are known as magnetic disks. These magnetic disks have a flat surface coated with a magnetic material, and are set in a magnetic disk recording / reproducing device (disk drive device) while rotating at high speed.
A signal (data) is recorded / reproduced by a magnetic head of a floating recording / reproducing method or a contact reproducing method.

However, recently, as a substitute for such a magnetic disk, a new magnetic field in which a concave or convex signal portion (information recording portion) similar to a pit of an optical disk is formed on the surface of a thin plastic disk. Discs are being developed. This disc adopts a floating recording / reproducing method.

[0004] As a storage medium employing the contact reproduction method,
Various video discs have been developed in addition to the above. This video disc contains TED, VISC, CED, VH
D and other systems. The above-mentioned TED system reproduces the sound by bringing a diamond needle into contact with the signal groove of a thin-walled disc made of polyvinyl chloride.
The HD system regenerates with an electrode needle. or,
Hard disks have been developed and commercialized as recording media adopting the floating recording / reproducing method. In this floating recording / reproducing method, the head is lifted by the rotation of the disk, so that the flatness within the disk surface is required more.

As described above, as a storage medium adopting the levitation recording method, a storage medium having a concave or convex signal portion formed on a disk surface and a storage medium having a flat surface coated with a magnetic material are known. . In these discs, a center hole is formed at the center and a disc clamp surface is formed on the outer peripheral side. The center hole and the disk clamp surface are for setting and fixing the disk to the disk drive.

A substrate for manufacturing a disk having concave or convex signal portions formed on both sides, that is, a disk substrate,
For example, a prototype has been produced using an injection molding die (hereinafter, sometimes referred to as a molding die) shown in FIG. FIG. 8 is a cross-sectional view showing a main part structure of a molding die and an injection molding method using the same, showing a state where a stamper is mounted on the molding die and the die is closed (before injection and filling of the molding material). It is shown. FIG. 8 shows the right half of the drawing of the molding die, and the left half is symmetrical with the right half. FIG. 9 is a cross-sectional view showing a state when the injection and filling of the molding material into the molding die are completed.

In this molding die, the fixed die core 51 and the movable die core 52 are opposed to each other, and an outer peripheral forming member 61 for forming the outer peripheral surface of the disk substrate is formed on the outer peripheral portion of the opposing gap. The cavity 53 is formed by inserting the inner peripheral end of the cavity 53. Also, in this molding die, the concave mounting portions 54 and 55 for holding the stamper are formed on the die cores 51 and 52, respectively, and the stampers 71 and 72 are inserted into these concave mounting portions and mounted by vacuum holding. Is configured.

The surfaces of the concave mounting portions 54 and 55 (the surfaces forming the cavities 53) are mirror-finished, and these surfaces are provided with vacuum suction holes (both not shown) connected to a vacuum pump. Is formed. Also, the mold core 5
A center hole forming portion 56 is provided at the center of each of the center hole forming portions 1 and 52.
4 and 55, disk clamp surface forming portions 57 and 58 are formed near and in close proximity to these. Further, a sprue, a runner and a gate (not shown) are formed in this order at the center of the mold, and the gate communicates with the center hole forming portion 56.

The stampers 71 and 72 are for transferring a concave signal portion formed on the front surface to a molded product, similarly to the stamper for molding an optical disk substrate. The back surface is mirror-finished, and the center hole is formed by punching. Is formed. Then, the back surface of the stamper is brought into close contact with the surfaces of the concave mounting portions 54 and 55 by vacuum suction, and the surface of the stamper and the mold core 5 are pressed.
1 and 52 are flush with the disk clamp surface forming portions 57 and 58.

In the molding of the magnetic disk substrate by the molding die, similarly to ordinary plastic injection molding, a heat-melted molding material (eg, PC, amorphous polyolefin resin) is extruded from a screw (not shown). The cavity 53 is injected and filled through the gate. Then, after the molding material is cooled and solidified by cooling the molding die, the die is opened and the disk substrate is taken out. For the purpose of improving the transferability of the stamper to the disk substrate, an injection compression molding method of compressing the injected and filled molten molding material in the cavity may be adopted.

[0011]

However, in the case of forming a disk substrate having a diameter of up to about 90 mm in which the recording capacity is increased and the recording area is widened using the above-mentioned material,
As shown in FIG. 10, an enlarged diameter portion 84 is formed at a boundary between the disk clamp surface 82 of the disk substrate 81 and the signal portion 83, or a ring-shaped bulging portion (convex portion) is formed at the boundary as shown in FIG. There is a problem that 85 easily occurs.
The following is a description of this. 10 and 11, reference numerals 71a and 72b denote signal portions, and reference numeral 86 denotes a center hole.

FIG. 10 shows an enlarged diameter portion 84 formed on the inner peripheral portion of the magnetic disk substrate obtained by the injection molding method of FIG.
FIG. 4 is a cross-sectional view showing the relationship between the stamper and the stamper. FIG.
FIG. 9 is a cross-sectional view for explaining the cause of the occurrence of the ring-shaped bulging portion 85 on the magnetic disk substrate obtained by the injection molding method of FIG. 8. It shows the relationship between the shape of the substrate and the shape of the stamper.

For example, when a disk substrate having a recording area with a large diameter of up to about 90 mm is formed using the above-described material, the injection pressure must be increased to accurately transfer the signal portion of the stamper to the outer periphery of the substrate. Need to be raised. However, since the molding die has a structure in which the molding material is injected from the center of the cavity 53 toward the outer periphery, the pressure applied to the molding material increases as the position approaches the center.

Therefore, the disk clamp surface forming section 5
Since the molding material in 7, 58 is in a state of being more highly compressed than the molding material of the stamper mounting portion, the expansion rate of the molding material when the mold is opened after cooling and solidifying the molding material is: As a result, the molding material in the disk clamp surface forming portions 57 and 58 becomes larger, so that a molded product, that is, a disk substrate (even though the stamper surface of the molding die and the disk clamp surface forming portions 57 and 58 are flush with each other). In other words, the diameter-increased portion 84 having an upward gradient from the outer peripheral portion toward the center portion of the substrate is easily formed at the boundary between the disk clamp surface 82 and the signal portion 83.

Next, the cause of the occurrence of the bulging portion 85 will be described. As shown in FIG.
Are mounted on the concave mounting portions 54 and 55 with a small gap left between the inner peripheral surface thereof and the mold core. This is to prevent the inner peripheral surface from being damaged or deformed by colliding with the molding die when setting the stamper in the molding die. As described above, since the high-pressure molding material is injected in a state in which there is a gap between the inner peripheral surface of the stamper and the mold core, the molding material flows into this gap.
As shown in FIG. 1, the inner peripheral ends of the stampers 71 and 72 are deformed toward the disk substrate 81, and a bulge 85 having a shape corresponding to the deformation is generated.

When a magnetic disk of a discrete track type is manufactured from a substrate on which at least one of the enlarged portion 84 and the bulged portion 85 is formed, and the disk is set in a disk drive, the magnetic head and the slider are used during signal reproduction. In some cases, it was damaged by contact with the enlarged diameter portion 84 or the bulging portion 85.

On the other hand, unlike the molding die of FIG. 8, a disk substrate having a flat surface has been molded by using a stamperless molding die that does not form a concave signal portion on the substrate surface. This molding die molds a disk clamp surface forming portion and a portion for forming a signal forming portion of the disk substrate (a portion where a signal portion is to be formed on this substrate in a later step) (this is shown in FIG. 8 corresponds to a stamper mounting portion).

However, when a disk substrate having a large recording area and a diameter of up to about 90 mm is formed by using this molding die, the disk clamp surface of the disk substrate and the disk clamping surface of the disk substrate are formed for the same reason as in the molding die shown in FIG. In addition, since the enlarged diameter portion is easily formed at the boundary with the signal formation scheduled portion, the magnetic head and the slider are similarly damaged.

The present invention has been made in view of the above-mentioned problems of the prior art, and its object is to provide a disk clamp unit,
Manufactures a thin plastic disc substrate that does not have a radially enlarged portion from the outer peripheral portion to the inner peripheral portion of the substrate at the boundary with the concave signal portion or the portion where the signal is to be formed and that has no ring-shaped bulge at the boundary An object of the present invention is to provide an injection molding die and an injection molding method using the same.

A first object of the present invention is to improve the structure of the molding die in a technique for molding a thin plastic disc substrate provided with a concave signal portion by using a molding die equipped with a stamper. It is another object of the present invention to simultaneously prevent the occurrence of the enlarged diameter portion and the bulging portion at the boundary between the disc clamp portion and the portion where the concave or convex signal portion is formed.

A second object of the present invention is to obtain a substrate without the above-mentioned enlarged diameter portion in a technique for molding a thin plastic disk substrate provided with a signal forming portion using a stamperless molding die. is there.

[0022]

The gist of the present invention to achieve the first object is to improve the shape of a molten molding material filled in a cavity of a molding die, and to improve the shape of the disk clamp portion. At the boundary with the concave or convex signal portion, a gradient is formed from the outer peripheral portion to the inner peripheral portion of the disk substrate. That is, it is configured to compensate for the section.

The main point of the present invention for achieving the second object is that the shape of the molten molding material in the cavity is also improved so that the outer peripheral portion of the disk substrate is provided at the boundary between the disk clamp portion and the signal forming portion. The inner slope is formed so as to have a downward slope, and the downwardly inclined surface prevents the occurrence of the above-described enlarged diameter portion.

In the molding die for a thin plastic substrate according to the first aspect of the present invention, a cavity is formed by opposing a fixed-side mold core and a movable-side mold core, each of which has a mirror-finished surface, and the fixed-side mold core is formed. At least one of the mold core and the movable mold core is formed with a mirror-finished concave mounting portion for mounting a stamper having a signal surface on the front surface and a mirror-polished rear surface, forming the concave mounting portion. By suction-mounting the stamper with the vacuum suction surface to be formed, and by injecting the molding material into the cavity from the center to the outer periphery, a disk clamp surface is formed on both inner surfaces, and A thin plastic substrate such as a magnetic disk having a signal portion formed on the outer peripheral side of the disk clamp surface and extending to the outer peripheral side in close proximity to this surface is formed by injection molding. In the mold for making, the inner peripheral end surface of the vacuum suction surface is brought into contact with the inner peripheral end surface of the stamper through a slope that is inclined upward from the outer peripheral portion of the mold core toward the inner peripheral portion. The concave mounting portion is formed by connecting to a mating abutment surface.

In the above-mentioned molding die, the vacuum suction surface is a downward slope having a constant gradient from the outer peripheral portion to the inner peripheral portion of the mold core, and the vacuum suction surface and the inner peripheral side of the vacuum suction surface are formed. It is preferable that the concave mounting portion is formed by the upwardly inclined surface directly connected to an end portion and the abutment surface directly connected to the upwardly inclined surface.

According to a third aspect of the present invention, in the molding die for a thin plastic substrate, a molding material is formed in a cavity formed by opposing a fixed mold core and a movable mold core, each of which has been mirror-finished, and the molding material is formed in the cavity. By injecting from the central part toward the outer peripheral part, a disk clamp surface is formed on the inner peripheral part on both sides, and at least one side is a signal that spreads to the outer peripheral side of the disk clamp surface and spreads to the outer peripheral side in close proximity to this surface. In a mold for injection-molding a thin plastic substrate such as a magnetic disk on which a portion to be formed (a portion where a signal portion is to be formed) is formed, the portion to be signal-formed is formed on the die core surface. The vicinity of the inner peripheral end of the portion is an inclined surface having an upward slope from the outer peripheral portion to the inner peripheral portion of the mold core.

According to the third aspect of the present invention, the portion of the mold core surface on which the signal forming portion is to be formed is formed as a downward slope having a constant gradient from the outer peripheral portion to the inner peripheral portion of the mold core. ,
It is preferable that the upward slope be formed directly with the upward slope, and the inner peripheral end of the upward slope be positioned near the inner peripheral end of the signal forming portion.

According to a fifth aspect of the present invention, there is provided a method of injection-molding a thin plastic substrate having the above-described structure using the mold according to the first or second aspect, wherein the mold core is formed in a concave shape. The stamper is mounted on the portion, a suitable minute gap is formed between the back surface of the stamper and the vacuum suction surface, and discard molding is performed, and the stamper is moved toward the vacuum suction surface by injection pressure of a molding material. After forming the regular cavity by displacing, the main molding is performed using this molding die.

A molding method according to a sixth aspect is a method for injection-molding a thin plastic substrate by the method according to the fifth aspect using the mold according to the second aspect. Thus, the inner peripheral end of the stamper rear surface is brought into close contact with the upwardly inclined surface, and the other portion is brought into close contact with the vacuum suction surface.

[0030]

Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. 1 is a sectional view of a main part of a molding die, showing an opened state before a stamper is mounted. FIG. 2 is a partially enlarged view of FIG. FIG. 3 is a sectional view showing a state in which the stamper is mounted on the molding die of FIG. 1 and then closed (before injection and filling of molding material). FIG. 4 is a cross-sectional view showing a state where injection and filling of a molding material into the molding die of FIG. 3 are completed (before cooling and solidification) and a center hole is formed. 1 to 4 show the right half of the mold core, and the structure and shape of the left half are symmetrical with those of the right half. FIG. 5 is a sectional view showing a schematic shape of the right half of the magnetic disk substrate obtained by the molding die of FIG.

In the molding die shown in FIG. 1, each of a fixed core (mold core) 11 and a movable core 12 (mold core) opposed to each other has a center hole forming portion 1 extending from the center to the outer periphery. The disk clamp surface forming section 2 and the stamper mounting section (concave mounting section) 3 are provided in this order. The temporary cavities 4a are formed by mounting the stampers 71 and 72 on the stamper mounting portion 3. This cavity 4a is temporary, and as shown in FIG. 4, after the regular cavity 4 is formed by discard molding, the main molding for manufacturing a substrate is performed.

The stamper mounting portion 3 is a concave portion for mounting the stamper by suction using the vacuum suction surface 3a. The stamper mounting part 3 is a vacuum suction surface 3a that is a downward slope having a constant gradient from the outer peripheral part to the inner peripheral part of the mold core.
And an abutment surface 3c with which the ascending inclined surface 3b and the inner peripheral end surface of the stamper can abut (there is no actual abutment, and the inner peripheral end surface of the stamper and the abutment surface 3c , With an appropriate minute gap). The surfaces of the center hole forming portion 1, the disc clamp surface forming portion 2, and the stamper mounting portion 3 are mirror-finished. A large number of vacuum suction holes (not shown) are formed on the vacuum suction surface 3a, and these are connected to a vacuum pump (not shown). Other structures and shapes are the same as those of the conventional molding die shown in FIG.

As shown in FIG. 2, the height h ₁ of the abutment surface 3c is set equal to or slightly larger than the thickness of the stamper to be mounted. In addition, this molding die has a diameter of 90 made of PC or amorphous polyolefin resin.
mm, the height h ₂ of the upwardly inclined surface 3b is not less than ₂ μm and not more than 20 μm.
m or less.

Next, a method of forming a disk substrate using the above-described molding die and its operation will be described with reference to FIGS. The molding die is opened, and the stampers 71 and 72 are mounted on the stamper mounting portion 3 as shown in FIG. 3 (this figure shows a state in which the die is closed). In this case, the inner peripheral end of the stamper is located immediately adjacent to the abutment surface 3c, the surface of the stamper (signal surface) is flush with the surface of the disc clamp surface forming unit 2, and the back surface of the stamper is A gap 3d having an appropriate dimension is formed between the suction surface 3a and the upward inclined surface 3b.

Next, after forming the regular cavity 4 by throw-away molding, the main molding is performed. Close the mold,
After starting the vacuum pump, the molding material is injected and filled. As a result, the molding material 31 is filled in the cavity 4a of FIG. 3, and as shown in FIG. 4, the cavity 4 is formed, and the center hole 31a, the disk clamp portion 31b, and the signal portion 31c are formed.
In this filling operation, the molding material is injected into the center of the cavity 4a via the sprue, runner, and gate, and flows while spreading toward the outer periphery. At this time, the stamper is plastically deformed toward the gap 3d side by the injection pressure of the molding material and the vacuum action of the vacuum suction hole, and finally comes into close contact with the upwardly inclined surface 3b and the vacuum suction surface 3a, thereby forming the regular cavity 4. Is done. Next, after the molding material is cooled and solidified by cooling the mold, the mold is opened, the discarded substrate is taken out, and discarded.

The main molding is performed by the molding die in which the regular cavity 4 is formed as described above, and the disk substrate is manufactured. In the molding by this mold, as is clear from FIG. 4, the thickness of the molding material 31 in the stamper mounting portion 3 in the cavity 4 when the injection / filling operation is completed (the molding material is still in a molten state). is thicker by about 2 times the height h ₂ of the gap than the disk clamp portion 31b. In addition, since the molding material 31 has an injection pressure, the thickness of the disk substrate obtained by cooling and solidifying the molding material 31 is larger than that at the completion of the injection and filling operation.

Since the pressure of the molding material in the disk clamp portion 31b is higher than the pressure of the molding material in the stamper mounting portion 3, in the disk substrate finally obtained, the amount of the disk clamp corresponding to this pressure difference is increased. The thickness of the portion 31b tends to be larger than that of the stamper mounting portion 3.

However, the difference in wall thickness that is likely to occur due to the above-mentioned pressure difference is almost offset by the above-mentioned difference “about 2 × h ₂ ”. Therefore, as shown in FIG. The disk substrate 32 having almost the same thickness is obtained by the signal portion 32c and the signal portion 32c. Unlike the case where a conventional mold is used, the enlarged diameter portion 84 shown in FIG.
5 does not occur. In FIG. 5, 32
a is a center hall.

The upward inclined surface 3b of the molding die is
This is for forming d, and also for making the inner peripheral end of the stamper plastically deformable. In addition,
In FIG. 3, the stamper surface and the disk clamp surface forming portion 2
However, this is only a guide when the stamper is mounted in the mold, and if desired,
The surface of the stamper may be slightly displaced from the surface of the disk clamp surface forming portion 2 toward the gap 3d.

Embodiment 2 FIG. 6 is a cross-sectional view of a main part showing a stamper-less forming die constituted by providing die cores 21 and 22. In this molding die, of the mirror-finished surface (the surface forming the regular cavity 4) of the die core 21, the portion for molding the signal formation scheduled portion of the disk substrate is moved from the outer periphery of the mold core 21 to the inner periphery. The slope is formed by a downward slope 21a and an upward slope 21b having a constant gradient toward the portion, and the inner peripheral end of the upward slope 21b is positioned near the inner peripheral end of the signal forming portion. It is a thing. The shape of the mold core 22 is the mold core 2
1 is substantially plane-symmetrical, 22a is a downward slope, and 22b is an upward slope. When injection molding is performed using this molding die, the upwardly inclined surfaces 21b and 22b prevent the formation of the enlarged diameter portion 84 shown in FIG. 10, so that a disk substrate having almost the same thickness between the disk clamp portion and the signal portion can be obtained. can get.

The molding die shown in FIG. 4 is for molding a disk substrate having signal portions formed on both sides, but when a substrate having a signal portion only on one side is molded,
In the mold of FIG. 1, a stamper is mounted on one of the two stamper mounting portions, and a dummy stamper is mounted on the other stamper mounting portion (both surfaces are mirror-finished,
After forming a regular cavity in the same manner as described above, the main molding may be performed.

Embodiment 3 FIG. 7 is a sectional view of a main part showing another example of a molding die on which the stampers 71 and 72 are mounted. This molding die includes mold cores 41 and 42 which are substantially symmetrical with each other. The mold core 41 forms a concave vacuum suction portion 41a instead of the downward inclined surface 21a of the mold core 21 shown in FIG. Then, this is the upward slope 41
b. In this mold, the stamper 7
1 is inserted and attached to the vacuum suction part 41a. 42a is a vacuum suction part, and 42b is an upward slope. According to this mold, a disk substrate having the same shape as that of the mold shown in FIG. 4 can be formed.

[0043]

As is apparent from the above description, the present invention relates to a technique for molding a thin plastic disc substrate provided with a concave signal portion by using a molding die having a stamper mounted therein. The shape of the filled molten molding material is improved so that the slope between the outer periphery and the inner periphery of the disk substrate is lowered at the boundary between the disk clamp portion and the concave or convex signal portion. It is. Further, according to the present invention, the disk having neither the enlarged diameter portion nor the bulging portion at the boundary portion between the disk clamp portion and the portion where the concave or convex signal portion is formed due to the downward inclined surface of the molding die. There is an effect that the substrate can be formed.

According to the present invention, there is also provided a technique for molding a thin plastic disc substrate provided with a signal forming portion using a stamperless molding die, wherein the shape of the molten molding material in the cavity is improved as in the above invention. At the boundary between the disk clamp portion and the portion where the signal is to be formed, a gradient is formed from the outer peripheral portion to the inner peripheral portion of the disk substrate. According to the present invention, a thin plastic disc substrate having no diameter-increased portion having an upward gradient from the outer peripheral portion to the inner peripheral portion of the substrate at the boundary between the disk clamp portion and the signal forming portion is manufactured by the downward inclined surface. There is an effect that can be.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a molding die according to a first embodiment of the present invention.

FIG. 2 is a partially enlarged view of FIG.

FIG. 3 is a cross-sectional view showing a state in which a stamper is mounted on the molding die of FIG. 1 (before injection and filling of molding material).

4 is a cross-sectional view showing a state when injection and filling of a molding material into a molding die of FIG. 3 is completed.

FIG. 5 is a cross-sectional view showing a schematic shape of a magnetic disk substrate obtained by a molding die shown in FIG.

FIG. 6 relates to Embodiment 2 of the present invention and is a cross-sectional view of a main part of a molding die.

FIG. 7 relates to Embodiment 3 of the present invention and is a cross-sectional view of a main part of a molding die.

FIG. 8 is a cross-sectional view showing a main part structure of a conventional molding die and an injection molding method using the same, showing a state where a stamper is mounted on the molding die (before injection and filling of a molding material). is there.

9 is a cross-sectional view showing a state when injection and filling of a molding material into a molding die of FIG. 6 are completed.

10 is a cross-sectional view showing a relationship between a diameter-enlarged portion formed on an inner peripheral portion of a magnetic disk substrate obtained by the injection molding method of FIG. 6 and a stamper.

11 is a cross-sectional view for explaining the cause of the occurrence of a ring-shaped bulge in the magnetic disk substrate obtained by the injection molding method of FIG. 6; FIG. 4 shows the relationship between the shape of the magnetic disk substrate and the shape of the stamper.

[Explanation of symbols]

1,56 ... Center hole forming part, 2,32b, 5
7, 58... Disk clamp surface forming portion, 3... Stamper mounting portion (concave mounting portion), 3a.
… Upward inclined surface, 3c… Abutment surface, 3d …… Void, 4,4
a, 53: cavity, 11: fixed side core, 12:
... Movable core, 21, 22, 41, 42 ... Mold core,
21a, 22a: Downward slope, 21b, 22b, 41
b, 42b ... up slope, 31 ... molding material, 31
a, 32a, 86 ... center hall, 31b, 32b
... Disk clamp part, 32, 81 Disk substrate, 31c, 32c, 71a, 72a, 83 ... Signal part, 41a, 42a ... Vacuum suction part, 51 ... Fixed mold core, 52 ... Movable Side mold core, 54, 55 ... concave mounting portion, 61 ... outer peripheral forming member, 71, 72 ... stamper, 82 ... disk clamp surface, 84 ... enlarged diameter portion, 8
5 ... bulging part (convex part).

Claims (6)

[Claims] 1. A cavity is formed by opposing a fixed mold core and a movable mold core, both of which are mirror-finished, and a surface is formed on at least one of the fixed mold core and the movable mold core. A mirror-finished concave mounting portion is formed for mounting a stamper having a mirror-polished surface as a signal surface, and the stamper is suction-mounted by a vacuum suction surface forming the concave mounting portion, and the molding material is filled in the cavity. Injecting toward the outer peripheral portion from the center portion thereof forms a disk clamp surface on the inner peripheral portion on both surfaces, and at least one surface is on the outer peripheral side of the disk clamp surface and the outer peripheral portion is close to this surface. In a mold for injection-molding a thin plastic substrate such as a magnetic disk on which a signal portion extending to the side is formed, an inner peripheral end of the vacuum suction surface may be The concave mounting portion is formed by connecting an inner peripheral end surface of the stamper to an abutting surface that can abut via an inclined surface having an upward slope from the outer peripheral portion to the inner peripheral portion of the mold core. Mold for thin plastic substrates. 2. The vacuum suction surface is a downward slope having a constant gradient from the outer peripheral portion to the inner peripheral portion of the mold core, and is directly attached to the vacuum suction surface and the inner peripheral end of the vacuum suction surface. 2. The molding die for a thin plastic substrate according to claim 1, wherein the concave mounting portion is formed by the continuous up-slope surface and the abutment surface directly connected to the up-slope surface. 3. 3. A molding material is injected into a cavity formed by facing a fixed mold core and a movable mold core, both of which are mirror-finished, from the center to the outer periphery of the cavity. A thin-walled plastic such as a magnetic disk in which a disk clamping surface is formed on the inner peripheral portion of both surfaces and a signal forming portion is formed on at least one surface on the outer peripheral side of the disk clamping surface and on the outer peripheral side in close proximity to this surface. In a mold for injection molding a substrate, a portion of the mold core surface near an inner peripheral end of a portion where the signal forming portion is to be molded is moved upward from an outer peripheral portion of the mold core toward an inner peripheral portion. A molding die for a thin plastic substrate, characterized by having a sloped surface. 4. A portion of the mold core surface on which the signal forming portion is to be formed is formed by a downwardly inclined surface having a constant gradient from an outer peripheral portion to an inner peripheral portion of the mold core, and a portion directly connected to the inclined surface. 4. The thin plastic substrate according to claim 3, wherein the thin-walled plastic substrate is formed with an upwardly inclined surface, and the inner peripheral side end of the upwardly inclined surface is located near the inner peripheral side end of the signal forming portion. Molding mold. 5. A method for injection-molding a thin plastic substrate having the above-mentioned structure using the mold according to claim 1 or 2, wherein the stamper is mounted on a concave mounting portion of the mold core. After forming an appropriate minute gap between the back surface and the vacuum suction surface and performing discard molding, after forming the regular cavity by displacing the stamper to the vacuum suction surface side with the injection pressure of the molding material, An injection molding method for a thin plastic substrate, wherein a main molding is performed using the molding die. 6. A method for injection-molding a thin plastic substrate by the method according to claim 5 using the mold according to claim 2, wherein in the throw-away molding, an inner pressure of a stamper rear surface is determined by an injection pressure of a molding material. A method of injection-molding a thin plastic substrate, wherein a peripheral end portion is brought into close contact with the upwardly inclined surface, and another portion is brought into close contact with the vacuum suction surface.