JPH11156897A - Mold for injecting molding of optical disk board, and molding board - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture an optical disk board for an information recording medium having a small refractive index of the board and no shrinkage fault by providing a heat insulation layer having low thermal conductivity on a surface of a mold member for forming a portion for transferring one plate thickness of the mold from a thick part and a thin part to the thick part. SOLUTION: An injection mold 21 has a thickly formed central part of a cavity 22 corresponding to a thick inner periphery of an optical disk board to thicken the inner periphery. This is performed by providing a step at an inner peripheral stamper retainer 26 mounted at a center of a movable side mirror surface member 23 and a center 23a of the member 23 to be recessed. A heat insulation layer 30 is provided on the retainer 26 including an oblique part transferred from the thick part to the thin part, the art 23a of the member 23 and a surface of an ejector 29. No shrinkage fault exists on a thick region of the inner periphery of the board and the disk board for an information recording medium having a small double refraction can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an injection molding die for manufacturing a substrate of an optical disk used as a high-density information recording medium.

[0002]

2. Description of the Related Art In recent years, research on a high-density optical information recording / reproducing system has been advanced as a recording device requiring a large capacity, such as an external storage device of a computer or a home video tape recorder. As an information recording medium of this optical information recording / reproducing method, a disk-shaped transparent substrate is provided with minute irregularities of a signal modulated by digital information, and various functional films such as a recording film or a reflection film are laminated thereon. An optical disk having a structure is generally used.

[0003] In the field of optical disks, in order to secure an optical margin and increase the surface recording density, a disk substrate having a reduced thickness and two thin disk substrates bonded together have been commercialized. In this case, the thickness in the information recording area is the thickness of the thin disk substrate single plate, and the thickness of the disk substrate near the clamp region outside the information recording region is twice as large as the thin disk substrate single plate.

On the other hand, there is a disk having a single-plate structure which is not the above-mentioned two-layered structure. In this case, in order to ensure compatibility with the two-layered structure disk, the thickness of the information recording area is reduced by the thin disk substrate. But the thickness in the clamp area is required to be twice the thickness of the thin portion. That is, in this case, the plate thickness differs between the information recording area and the clamp area.

If there is a difference in the plate thickness of the disk substrate as described above, a sink defect 5 occurs on the surface of the thick portion of the injection molded product as shown in FIG. Conventionally, in order to prevent the sink mark 5, in the field of injection molding, generally, a backflow at the time of injection filling is prevented, and a pressure setting called a holding pressure for controlling a pressure applied to a product from filling to solidification is increased. Or a method of extending the holding time.
However, when the holding pressure is increased or the holding time is increased in the optical disk substrate, the optical characteristics of the substrate called birefringence or retardation deteriorate as shown in FIG. 7 due to the orientation of the resin. Further, in order to prevent the sink failure 5, Japanese Patent Application Laid-Open No. 8-321072 discloses a method of providing a concave portion in a thick portion as shown in FIG. 8, but in this case, a sandwich type is provided from above and below the disk. In the clamping mechanism for sandwiching, there is a dent in the clamping area of the disc, so when clamping the disc, a method of clamping avoiding this recess or a clamping method utilizing this recess has been proposed, but in any of these methods This also limits the clamping method and is not mechanically preferable.

[0006]

As described above, the optical characteristics of the substrate of the information recording medium can be improved by increasing the holding pressure during the injection molding process or increasing the holding time in order to prevent sink marks. May cause deterioration. In particular, in an information recording medium such as an optical disk which records and reproduces information by using a laser beam, when the birefringence of the optical disk substrate increases, noise increases and an error occurs in reading of an information signal.

An object of the present invention is to provide an optical disk substrate for an information recording medium having a small birefringence of the substrate and free from sink marks.

[0008]

In order to achieve the above-mentioned object, the present invention employs the following means. In other words, in claim 1, an injection mold comprising a fixed mold and a movable mold for manufacturing an information recording medium substrate having a portion outside the information recording area and having a greater thickness than the information recording area. A mold for forming an information recording area on a surface of a mold member forming at least one of the fixed-side mold and the movable-side mold having the above-described thicker portion and a portion which transitions from the thinner portion to the thicker portion. An injection molding die is provided, wherein a heat insulating layer having a lower thermal conductivity than the mold member is provided. According to claim 2, the thickness of the sheet outside the information recording area is larger than the thickness of the sheet in the information recording area. In an injection mold comprising a fixed mold and a movable mold for manufacturing an information recording medium substrate having a thicker portion, at least one of the fixed mold and the movable mold has the thicker portion. Mold member to be formed Is the injection mold than the die member that forms an information recording area, characterized by using a low thermal conductivity insulating material.

According to a third aspect of the present invention, an injection mold comprising a fixed mold and a movable mold for manufacturing an information recording medium substrate having a portion outside the information recording area and having a greater thickness than the information recording area. In the mold, the surface roughness Ra of the mold member forming at least one of the fixed-side mold and the movable-side mold and the portion where the plate thickness increases and the portion where the plate thickness transitions from the thin portion to the thick portion is Ra. = 8 to 70 is defined.

According to a fourth aspect of the present invention, there is provided the injection molding die according to the first or second aspect, wherein ceramics is used as a heat insulating material having a low thermal conductivity. In claim 5, claim 1
The injection molding die according to any one of claims 3 to 3, wherein the injection molding die is characterized in that the injection molding die has a portion having a larger thickness in an inner peripheral portion than the information recording area. In the injection mold according to any one of claims 1 to 3, the thickness of the information recording area is at least 0.6 mm or less, and the thickness of the thick part is at least 1.3 mm. The following is defined. Claim 7 is the injection-molding mold according to any one of claims 1 to 6, wherein the mirror-surface member of the movable-side mold has the thicker portion. An injection molding die is characterized in that a nest using a heat insulating material is inserted into a certain central portion.

An eighth aspect of the present invention specifies an optical disk molded substrate formed by using the mold according to any one of the first to seventh aspects.

[0012]

As described above, in an injection molding die for manufacturing a substrate for an information recording medium having a portion outside the information recording area where the thickness is greater than the thickness in the information recording area, the thickness of the substrate is increased. A heat insulating layer having a lower thermal conductivity than the mold member forming the information recording area is provided on the mold member surface forming the portion. Alternatively, a heat-insulating material having a lower thermal conductivity than the mold member forming the information recording area is used for the mold member forming the portion where the board thickness of the substrate is increased, and the heat-insulating effect allows the board on the inner circumference of the substrate to be heated by the resin temperature. By increasing the temperature rise of the mold member in the thicker portion, the adhesion between the mold member and the resin is increased. Alternatively, by setting the roughness Ra of the surface of the mold member forming the portion where the thickness of the substrate is increased to Ra = 8 to 70, the adhesion between the mold member and the resin is increased, and the holding pressure during injection molding is increased. In addition, sink failure can be suppressed without extending the holding time. As a result, it is possible to obtain a disk substrate for an information recording medium which has no sink marks and a small birefringence in a portion having a large thickness outside the information recording area.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a sectional view of an optical disk substrate 1 manufactured by an optical disk substrate injection mold according to the present invention. The optical disc substrate 1 of the present embodiment is a disc-shaped transparent substrate having a circular hole 2 at the center, not shown, which serves as a rotation axis and into which a drive spindle is inserted. On 1a,
An information recording area 3 in which various functional films such as a recording film or a reflective film are laminated thereon, and an optical disc substrate 1 in an inner peripheral part outside the information recording area.
Has a clamping area 4 for rotation and support of the rotation. The thickness 4a of the clamp area 4 is equal to the information recording area 3
The thickness of the optical disc substrate 1 is about twice as large as the thickness 3a of the optical disc substrate 1 and has a medium thickness structure.

The dimensions of the optical disc substrate 1 in the present embodiment are, for example, that the thickness 3a of the information recording area 3 is 0.6 mm and the thickness 4a of the clamp area 4 is 1.2 mm.
mm. Actually, it is expected that the thickest portion will be about 1.3 mm in consideration of various tolerances.

FIG. 6 is a sectional view of an optical disk substrate 1 manufactured by a conventional optical disk substrate injection molding die. As shown in FIG. 6, sink marks 5 which cause poor appearance are seen on the upper surface of the region where the plate thickness of the inner peripheral portion is large.

FIG. 2 is a sectional view of an optical disk substrate injection mold 21 according to a first embodiment of the present invention. The configuration of the optical disk substrate injection mold 21 and the method of manufacturing the optical disk substrate 1 according to the present invention will be described. The optical disk substrate 1 is formed by injecting and filling a molten resin into a cavity 22 of an injection mold 21. Cavity 2
Reference numeral 2 denotes a stamper 25 and a fixed mirror member 24. The stamper 25 is a mirror-like member (hereinafter, referred to as a movable member) of the movable mold by an inner stamper holder 26 and an outer stamper holder 27.
The stamper 25 fixed to the movable mirror member 23
The irregularities formed on the surface of the optical disk substrate 1 are transferred to the surface of the optical disk substrate 1, and this area is
Becomes A cut punch 28 for punching a circular hole 2 of the optical disc substrate 1 is provided at the center of the movable mirror member 23.
And the optical disk substrate 1 when the optical disk substrate 1 is taken out.
An ejector 29 for projecting the image is provided. The injection molding die 21 of the present invention is used to mold the inner peripheral portion of the optical disc substrate 1 to be thick, so that the corresponding cavity 2 is formed.
The central part of 2 is formed thick. This is achieved by providing a step in the inner peripheral stamper retainer 26 attached to the central portion of the movable-side mirror member 23 and the central portion 23a of the movable-side mirror member 23 to make it concave. A heat insulating layer 30 is provided on the inner peripheral stamper retainer 26 including the inclined portion which transitions from the thick portion to the thin portion, the central portion 23a of the movable mirror member 23, and the surface of the ejector 29. The heat insulating layer 30 makes it possible to obtain a disc substrate for an information recording medium having no sink marks and a small birefringence in a region where the thickness of the inner peripheral portion of the optical disc substrate 1 is large.

The material of the heat insulating layer 30 is not particularly limited as long as a heat insulating effect can be obtained, but a ceramic layer formed by a thermal spraying method is preferable.

FIG. 3 is a schematic explanatory view for explaining a method of forming a heat insulating layer using a thermal spraying method. The working gas 32 (N ₂ , H ₂ , inert gas, etc.) sent into the thermal spraying device 31 is ionized by the discharge between the positive electrode 33 and the negative electrode 34, and coats the high-temperature and high-speed plasma jet 35 generated at this time. The thermal spray material powder 36 is fed, and the thermal spray material powder 36 is melted and accelerated in the plasma jet 35, and the thermal spray particles 39 are sprayed.
Becomes The thermal spray particles 39 collide with the base material 37, deform flatly and rapidly solidify, and the thermal spray particles 39 are laminated one after another to form a film 38. As described above, the cooling water 40 is circulated in the thermal spraying device 31 which is heated to a high temperature by the heat generated by the plasma shet 35.

With such a thermal spraying device 31, a heat insulating layer is formed on the inner peripheral stamper retainer 26, the central portion 23a of the movable mirror member 23, and the surface of the ejector 29.

FIG. 4 is a sectional view of an optical disk substrate injection molding die 41 according to a second embodiment of the present invention. In the first embodiment, the heat insulating layer is formed on the inner peripheral stamper retainer 26, the central portion 23a of the movable mirror member 23, and the surface of the ejector 29, but in the present embodiment, the inner peripheral stamper retainer 26 and the ejector 29 A ceramic material is used as the material, and a central portion 23 of the movable side mirror member 23 in FIG.
In this case, a member corresponding to a is a movable side insert 42 that is a separate member from the movable side mirror member 23, and a ceramic material is used as a material of the movable side insert 42. By using a heat insulating material such as a ceramic material for the mold of the thick part,
Improper surface shape due to sinking can be suppressed.

FIG. 5 aims to prevent sink marks by improving the adhesion between the molded product and the mold by providing minute irregularities on the mold corresponding to the thick portion in FIG. In particular, good results are obtained when the surface roughness Ra caused by the irregularities is in the range of Ra = 8 to 70.

Although the substrate injection molding die of the present embodiment has been described in the case where the stamper mounting side is a movable mirror member, the same applies to the case where the stamper mounting side is a fixed mirror member. Providing a heat insulating layer on the member,
Alternatively, it can be adapted by using a heat insulating material.

[0023]

According to the present invention, in an injection molding die for manufacturing a substrate for an information recording medium in which the thickness of the inner peripheral portion outside the information recording area is larger than the thickness of the information recording area, the inner peripheral plate is provided. A heat insulating layer having a lower thermal conductivity than the mold member forming the information recording area is provided on the surface of the mold member forming the thicker portion. Alternatively, a heat insulating material having a lower thermal conductivity than the mold member forming the information recording area is used for the mold member forming the portion where the thickness of the inner circumference of the substrate is increased, and the inner circumference of the substrate due to the resin temperature is reduced by the heat insulating effect. The temperature of the mold member in the portion where the plate thickness becomes large is increased. Alternatively, by setting the roughness Ra of the surface of the mold member forming the portion where the plate thickness of the substrate becomes thicker to Ra = 8 to 70, the adhesion between the mold member and the resin is increased, and the holding pressure during injection molding is reduced. It is high, and the beard defect can be suppressed without extending the holding time.
This makes it possible to obtain a disk substrate for an information recording medium with no sink marks and a small birefringence in a region where the inner peripheral portion has a large plate thickness, and mass production molding can be performed efficiently.

[Brief description of the drawings]

FIG. 1 is a sectional view of an optical disk substrate manufactured by an optical disk substrate injection mold according to the present invention.

FIG. 2 is a cross-sectional view of an optical disk substrate injection molding die according to the first embodiment of the present invention.

FIG. 3 is a basic configuration diagram of an apparatus for producing a ceramic heat insulating layer by a thermal spraying method.

FIG. 4 is a cross-sectional view of an optical disk substrate injection molding die according to a second embodiment of the present invention.

FIG. 5 is a sectional view of an optical disk substrate injection molding die according to a third embodiment of the present invention.

FIG. 6 is a cross-sectional view of a disk substrate in which sink failure occurs in a conventionally known optical disk.

FIG. 7 is data showing changes in birefringence characteristics depending on molding conditions.

FIG. 8 is a sectional view of an optical disk to which a conventionally known method is applied as a measure against sink marks.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Optical disk substrate 2 Circular hole 3 Information recording area 4 Clamp area 5 Poor sink 6 Depression 21 Optical disk substrate injection mold 22 Cavity 23 Movable mirror member 24 Fixed mirror member 25 Stamper 26 Inner stamper holder 27 Outer stamper holder 28 Cut punch 29 Ejector 30 Heat insulating layer 31 Thermal spraying device 32 Working gas 33 Positive electrode 34 Negative electrode 35 Plasma jet 36 Thermal spray material powder 37 Base material 38 Coating 39 Thermal spray particles 40 Cooling water 41 Optical disk substrate injection mold 42 Moving side insert

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroki Kuramoto 292, Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Prefecture, Hitachi, Ltd.

Claims (8)

[Claims] An injection molding mold comprising a fixed mold and a movable mold for manufacturing an information recording medium substrate having a portion whose thickness is larger than the thickness of the information recording area outside the information recording area. A mold member that forms an information recording area on a surface of a mold member that forms a portion where at least one of the fixed mold and the movable mold has a large thickness and a portion that transitions from a small thickness to a large thickness. An injection mold, wherein a heat insulating layer having a low thermal conductivity is provided. 2. An injection molding mold comprising a fixed mold and a movable mold for manufacturing an information recording medium substrate having a portion whose thickness outside the information recording area is greater than the thickness in the information recording area. A heat-insulating material having a lower thermal conductivity than a mold member forming an information recording area is used for a mold member forming a portion where the plate thickness of at least one of the fixed mold and the movable mold is increased. Injection mold. 3. An injection mold comprising a fixed mold and a movable mold for manufacturing an information recording medium substrate having a portion whose thickness is larger than the thickness of the information recording area outside the information recording area. The surface roughness Ra of the mold member forming at least one of the fixed mold or the movable mold and the portion where the plate thickness increases and the portion where the plate thickness transitions from the thin portion to the thick portion is Ra = 8 to 70. An injection molding die characterized in that: 4. The injection molding die according to claim 1, wherein ceramics is used as a heat insulating material having a low thermal conductivity. 5. The injection molding die according to claim 1, wherein the injection molding die has a thicker portion on an inner peripheral portion than an information recording area. 6. The injection mold according to claim 1, wherein the thickness of the information recording area is at least 0.6 mm or less, and the thickness of the thick part is at least 0.6 mm. An injection molding die having a diameter of 1.3 mm or less. 7. The injection molding die according to claim 1, wherein a heat insulating material is used in a central portion of the mirror member of the movable die, which is the thick portion. An injection molding die, wherein a metal mold is inserted. 8. An optical disk molded substrate formed by using the mold according to claim 1.