WO2005112023A1

WO2005112023A1 - Optical disc and manufacturing method thereof

Info

Publication number: WO2005112023A1
Application number: PCT/JP2005/009018
Authority: WO
Inventors: Hideaki Yoshimura
Original assignee: Sony Disc & Digital Solutions Inc.
Priority date: 2004-05-14
Filing date: 2005-05-11
Publication date: 2005-11-24
Also published as: JP2005327391A

Abstract

A resin film is manufactured by melt extrusion by applying heat on a resin material for plasticization at the time of manufacturing the resin film to be used for a light transmitting layer of an optical disc. The molecular weight of the resin material to be used for the resin film is the same as that of a resin material to be used for a disc board. Since the shrinking ratio of the resin film can be almost the same as that of the disc board to be laminated on the resin film, the resin film and the disc board shrink by the same ratio, respectively, even with time, and disc warping can be prevented. Furthermore, since complicated processes suchas anneal processing and equipment for such processes are not required, a large quantity of discs can be manufactured at a low cost in a short time.

Description

Description Optical disc and method of manufacturing the same

The present invention relates to an optical disk and a method of manufacturing the same, and more particularly, to an optical disk manufactured using a light-transmitting film and a method of manufacturing the same. Background art

Optical discs used as information recording media today depend on their use, such as MD (Mini Disc), MO (Magneto Optical) disc, DVD (Digital Versatile Disc), B1 u-ray Disc (registered trademark), etc. Various formats have been proposed. Generally, the optical disc used in any of the formats is manufactured by injection molding of a resin material, thereby realizing a low-cost optical disc.

Among them, in recent years, there has been an increasing demand for high-capacity optical disks, and high-density optical recording disks such as Blu-rayDysc (hereinafter, appropriately referred to as BD) have been receiving attention. As shown in FIG. 1, a BD is made of a polycarbonate (hereinafter referred to as “PC” as appropriate) resin. A 1.1-mm-thick disk substrate 1 obtained by injection molding a resin. It is manufactured by forming a light-transmitting layer 6 having a thickness of 0.1 mm comprising a film 2, an adhesive layer 3, a PC film 4 and a hard coat layer 5 for preventing scratches.

In BDs, in order to improve the recording density, the wavelength of the laser beam is shortened, and the numerical aperture NA of the objective lens is increased. However, as the wavelength becomes shorter and the NA becomes higher, the allowable value of the tilt angle (tilt) of the disk with respect to the incident direction of the laser beam becomes smaller, and the spherical aberration due to a film thickness error increases. The For this reason, the PC film 4 used for the light transmitting layer 6 must have a small thickness and a small thickness variation.

Conventionally, solution casting has been used as a method for forming a PC film having a small thickness and a small thickness variation. In this method, a PC resin chip is dissolved approximately 5 times with a solvent such as methyl chloride and then filtered. Thereafter, as shown in FIG. 2, the solution is flowed in a curtain form from the slit of the die 11 to the belt 12. The solvent of the solution applied to the belt 12 evaporates in the drying step, and only the PC resin material remains to form the PC film 13. In the drying process, 4-5 of the solution is vaporized and removed, so both the variation in film thickness and the overall film thickness when the solution is flowed to the belt are 15 and excellent film thickness accuracy A film is formed.

At this time, since a high viscosity is required to form the PC resin into a sheet shape, a PC resin having an average molecular weight of about 350,000 is used. On the other hand, although a PC resin having an average molecular weight of about 1500 is used for the disk substrate, when a PC resin having an average molecular weight of about 1500 is used for forming a PC film, crystallization occurs due to low viscosity. It is easy to become cloudy. Conversely, if the average molecular weight of the PC resin used for injection molding of the optical disc substrate is about 350, the plasticized resin cannot be filled into the mold at high speed. Therefore, in order to improve moldability while maintaining strength, the appropriate average molecular weight is set to 1400 to 16000.

By the way, a laser beam having a short wavelength of about 400 nm is used for recording and reproducing BD. The difference between the structure of the BD and the structure of the CD is that the cover layer is used for protecting the disc in a CD, whereas the cover layer serves as an optical path in a BD. Strict conditions such as flatness of discs are required.

However, the disc substrate heats the resin during injection molding. Therefore, it undergoes heat history to plasticize, and shrinks when heat is applied later. However, since the resin film produced by solution casting uses a solvent, it does not receive heat history and does not shrink when heat is applied. Therefore, if heat is applied after the disk is completed, only the disk substrate shrinks as shown in Fig. 3 and warpage occurs.

Here, FIG. 4 shows that before bonding, the non-shrinkable PC film produced by solution casting and the shrinkable disk substrate produced by injection molding were subjected to 70% humidity at 50%. The relationship between the shrinkage ratio and the time when heating is continued is shown. While the PC film produced by solution casting hardly shrinks, the disc substrate made by injection molding shrinks about 0.027% after 100 hours. For this reason, the warp of the optical disk is within ± 0.7 degrees in the standard of the optical disk, whereas the warp of +0.7 degrees or more may occur in the optical disk manufactured by the conventional manufacturing method as described above. Here, the warpage toward the disk substrate side is represented by ten, and the warpage toward the opposite side is represented by one.

Therefore, in the past, an annealing process was performed on a disk substrate manufactured by injection molding to sufficiently shrink it, and then the disk substrate was bonded to a PC film. By using this method, the shrinkage of the disk substrate can be prevented, and the warpage of the disk can be kept within the standard. Japanese Patent Application Laid-Open No. 11-134728 discloses Japanese Patent Application Laid-Open No. 11-134728 as an example in which an annealing process is incorporated in the optical disk manufacturing process. Japanese Patent Application Laid-Open No. H11-1343472 discloses that in an optical disk having a structure in which two disk substrates each having a thickness of 0.6 mm are bonded to each other, at least one disk is required to suppress the warpage of the disk substrate. A method is described in which a disc substrate is annealed and then bonded.

However, equipment such as a thermostat is indispensable for performing annealing treatment. This requires capital investment. In addition, since it involves heating and cooling, it takes time to produce the final product. Particularly, it is not suitable for products that must meet short delivery times, such as ROM disks.

Accordingly, an object of the present invention is to provide a method of manufacturing an optical disk and an optical disk capable of manufacturing a disk at low cost and in a short time and suppressing warpage of the disk. Disclosure of the invention

In order to solve the above-mentioned problems, the present invention relates to a method for manufacturing an optical disk comprising a light-transmitting layer having a predetermined thickness on a disk substrate, wherein the optical disk is a disk substrate, and a signal layer is formed on the disk substrate. A method of manufacturing an optical disk, characterized in that a resin film is further laminated and the resin film has substantially the same average molecular weight as the disk substrate to be laminated and has undergone thermal history.

Further, the present invention provides an optical disk comprising a light-transmitting layer having a predetermined thickness on a disk substrate, wherein the resin film used for the light-transmitting layer has substantially the same average molecular weight as the disk substrate to be bonded, and receives heat history. An optical disc characterized by Brief Description of Drawings

FIG. 1 is a schematic diagram showing the structure of Blu-rayDisc. FIG. 2 is a schematic view showing an outline of an apparatus used for producing a PC film by solution casting.

FIG. 3 is a schematic view showing a state in which warpage occurs when heat is applied to an optical disk manufactured by laminating a PC film manufactured by solution casting and a disk substrate manufactured by injection molding. Fig. 4 shows the relationship between the shrinkage (%) and the time (h) when a heat of 70 was continuously applied to the PC film produced by solution casting and the disc substrate produced by injection molding. It is a graph. FIG. 5 is a schematic view showing a method of manufacturing a stamper used when manufacturing a disk substrate.

FIG. 6 is a schematic diagram showing a method for producing a PC film by melt extrusion and an apparatus used for the production.

FIG. 7 is a graph showing the relationship between shrinkage (%) and time (h) when a heat of 70% is continuously applied to a PC film produced by melt extrusion at a humidity of 50%.

FIG. 8 is a schematic diagram showing how to apply heat in an experiment for measuring the warpage of a disk.

Figure 9 shows the warpage (deg.) And time (h) when applying a heat of 70 to a disc produced by bonding a PC film produced by solution casting and a disc substrate produced by injection molding. It is a graph which shows the relationship of.

FIG. 10 shows the warpage (deg.) And time (°) when a heat of 70 was applied to a disc produced by bonding a PC film produced by melt extrusion and a disc substrate produced by injection molding. h) is a graph showing the relationship. BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. First, the manufacturing process of BD will be described with reference to FIG.

First, a master disk (hereinafter, appropriately referred to as a stamper) having a concavo-convex pattern corresponding to a pit or a group is manufactured using a laser light source. To do. A very thin resist (photosensitive agent) 31 is applied on the glass master 30 by spin coating or the like, and the glass master 30 is rotated and exposed to laser light 32 from a cutting device. A latent image having a pattern corresponding to a group or a pit is formed on the resist 31 by exposure. Thereafter, the developing solution 33 is dropped on the rotating glass master 30 and subjected to development processing, thereby forming a resist pattern having irregularities corresponding to the groups or pits of the optical disc on the glass master 30. A liquid such as an acid or an alkaline liquid is used as a developing solution, and an alkaline liquid used for the development is a tetramethylammonium hydroxide solution, KOH, Na〇H, Na ₂ CO ₃ or the like. Examples of the acidic solution include hydrochloric acid, nitric acid, sulfuric acid, and phosphoric acid. Next, a metal 34 such as nickel is deposited on the glass master 30 by plating, peeled off, and trimmed. Then stamper 35 is obtained. By mounting the stamper 35 on a mold of an injection molding apparatus and injecting a resin such as a PC into the cavity, a disk substrate on which the irregularities of the stamper are transferred is produced. At this time, the resin used for the disk substrate is plasticized by heat so that the mold can be filled at a high speed. After cooling the injection-molded disk substrate to 30 ° C. or less, a reflective film is formed by forming a thin metal film on the pit surface side using a sputtering device.

Next, an ultraviolet curing resin is dropped as an adhesive on the disk substrate on which the reflection layer is formed, and is uniformly applied by a spin coating method. After that, the surface of the disk substrate on which the ultraviolet-curing resin is applied and the PC film are held at a position facing each other, and then bonded. Lamination of the PC film is performed in the vacuum. This is to prevent wrinkles and gaps from being formed in the surface where the disc substrate and the PC film are bonded, resulting in reading errors. Next, the disc on which the PC film is bonded is irradiated with ultraviolet light to cure the ultraviolet curing resin, and the disc substrate and the PC film are bonded. In addition, a UV-curable hard coat agent is dropped onto the PC film bonded to the disc, applied uniformly by spin coating, and then irradiated again with UV light to cure the hard coat layer. Make it. This completes the disc.

The PC film used in the above-described disk manufacturing process is manufactured using a material having almost the same average molecular weight as the disk substrate. In addition, as shown in Fig. 6, the resin material of the PC film is heated in the same manner as the disc substrate, plasticized by an extruder 41, and then cooled from a T die 42 to a cooling roll 43. After being flowed and solidified into a film, the PC film 44 is wound around a roller 45. Such a manufacturing method is called melt extrusion.

When a disc is made using the above method, the heat history is applied to both the disc substrate and the PC film. If heat is applied after the disc is completed, both the disc substrate and the PC film shrink. In addition, since materials having almost the same average molecular weight are used, the properties of the materials are almost the same, and the shrinkage ratio is also a close value.

In FIG. 7, the solid line is a graph showing the relationship between the shrinkage (%) and the time (h) when the PC film produced by melt extrusion is continuously heated at 70% under a humidity of 50%. It is. In addition, the shrinkage rate (%) of the injection-molded disk substrate shown by the broken line is also shown. The shrinkage of the PC film produced by melt extrusion after 100 hours is about 0.024%, which is close to the shrinkage of the injection molded disk substrate of 0.027%.

When heat is applied to a disk manufactured by bonding a non-shrinkable PC film manufactured by solution casting and a shrinkable disk substrate manufactured by injection molding, deformation occurs as shown in FIG. 3 and warpage occurs. The warpage at this time is measured using the α angle (R – S kew) in Fig. 3. The environmental conditions at this time are a temperature of 70 degrees and a humidity of 50%.

The method for measuring the α angle will be described. As shown in Fig. 8, for example, when 7 O: heat is applied to a disk for Α hour, the ambient temperature is first raised from 25 to 70 over 12 hours. At this time, the humidity should always be kept at 50%. Start counting A hours when the ambient temperature reaches 70. After A hours, the ambient temperature is lowered from 25 to 25 over 70 to 12 hours, and the angle is measured after leaving it at 48 for 48 hours as the recovery time. At this time, the humidity should always be kept at 50%.

In order to measure the α angle through such a process, when measuring the disk heating time as 100 hours, if the environmental temperature rises (from 25 to 70 Τ:), 12 hours and 70 t: It takes 100 hours to heat the furnace, 12 hours to lower the ambient temperature (from 70 t: to 25), and 48 hours to recover, for a total of 1072 hours. Such heating is performed using one disk at each measurement point time shown in FIG. For example, heating is performed for 500 hours, the α angle is measured, and then heating is performed again for 100 hours, and the angle is measured. This is not the α angle at the time of heating for 600 hours.

FIG. 9 shows the relationship between disk warpage (deg.) And time (h) measured using the above method. In this case, the warp increases with time, and after about 800 hours, the warp becomes 0.7 degrees or more, and the required standard cannot be satisfied.

Next, a similar experiment is performed by applying heat to a disk manufactured by bonding a shrinkable PC film manufactured by melt extrusion and a shrinkable disk substrate manufactured by injection molding. Then, as shown in Fig. 10, the warpage of the disk fluctuates at less than 0.1 degrees, which is a result that sufficiently satisfies the standard. became.

Thus, by laminating a disc substrate and a PC film having almost the same average molecular weight to produce a disc, the disc shrinks at almost the same rate even after a lapse of time, and the occurrence of warpage can be prevented.

In addition, since the disk substrate and the PC film can be made of exactly the same material without requiring complicated processes and equipment, the cost can be reduced, and low cost and mass production can be achieved.

As described above, one embodiment of the present invention has been specifically described. However, the present invention is not limited to the above-described embodiment, and various modifications based on the technical idea of the present invention are possible.

For example, the numerical values given in the above-described embodiment are merely examples, and different numerical values may be used as needed.

Further, the present invention can be used not only for a single-layer optical disc but also for a multi-layer disc of two or more layers.

In addition, the present invention can be applied not only to a read-only disc, but also to a write-once or rewritable disc.

Further, the present invention can be applied to a disc without a hard coat layer enclosed in a cartridge.

Claims

The scope of the claims

1. In an optical disk in which a recording film is formed on a disk substrate and a resin film is bonded on the recording film,

The resin film is made by thinly extruding a resin material that has been heated and melted, and then cooling and extruding the thinly extruded resin material. The resin material has approximately the same average molecular weight as the resin material of the disk substrate. An optical disk characterized by the above-mentioned.

2. The optical disc according to claim 1, wherein the resin material has an average molecular weight of 140,000 to 1,600,000.

3. a step of forming a recording film on the disk substrate;

Laminating a resin film produced by melt-extruding a resin material having substantially the same average molecular weight as the disk substrate on the recording film,

The above-mentioned melt extrusion involves extruding a thin resin material melted by heating.

A method for manufacturing an optical disk, comprising a step of cooling the resin material extruded thinly.

4. The optical disc according to claim 3, wherein the resin material has an average molecular weight of 140,000 to 1,600,000.