JPH0315263B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an optical disk, and more particularly, the present invention relates to an optical disk that uses a 4-methylpentene polymer or a crosslinked product thereof as a disk base material, and has transparency, non-optical rotation (non-birefringence), moisture resistance, and resistance. This invention relates to an optical disk with excellent impact resistance, molding fidelity, etc. A recording layer with information bits engraved with a stamper on one side of the disk (hereinafter referred to as information bits)
Video discs, audio discs, etc. have been developed as information recording and reproducing discs in which a metal coating layer is formed on the exposed side and a laser beam is irradiated from the disc surface side to reproduce information. It is developing. Hard vinyl chloride resins, polycarbonate resins, polymethyl methacrylate resins, and the like have been studied as this type of disk material, and among these, polymethyl methacrylate resins are being put into practical use in some areas. However, these known optical disk materials have the following drawbacks, which are a major bottleneck in improving their versatility. In other words, with hard vinyl chloride resin, additives (such as plasticizers for improving moldability) bleed onto the disk surface and the light transmittance decreases over time.
There is a problem that the reproduction information deteriorates. On the other hand, if the amount of plasticizer added is small, problems such as optical distortion and optical rotation will occur during disk molding, which is critical for optical disk materials whose mission is high sensitivity and high precision. be. In addition, polycarbonate resin has excellent transparency, heat resistance, mechanical properties, etc.
Since it is hard, it has difficulty in molding, and optical distortion is likely to occur during molding (retardation value is large and optical rotation occurs). For this reason, errors (noise) are likely to occur during reproduction (reading) in optical discs manufactured using this resin. Moreover, since the moldability is poor, it is difficult to faithfully reproduce the fine irregularities for engraving information bits formed on the stamper, and the sensitivity and accuracy are still insufficient. On the other hand, polymethyl methacrylate polymers have excellent transparency and non-optical rotation, but have a problem that they have poor moisture resistance and absorb moisture in the air, causing the surface side to expand and warp. In order to deal with this problem, a reinforcing plate of the same thickness as the disk plate is laminated to prevent warping, but this is far from satisfactory. Moreover, this resin has poor mechanical strength, especially impact resistance, and is easily broken, and is hard, so there are problems with moldability. Although there is a movement to improve the problems caused by such high hardness by adding polyethyl methacrylate or polybutyl methacrylate, etc., the heat resistance becomes poor and becomes an impediment to practical use. The inventors of the present invention have focused on the above circumstances, and believe that in order to increase the versatility of optical disks, it is necessary to find the optimal resin that meets the required characteristics, and have conducted research along this line. I've made progress. We have conducted extensive research with the aim of developing an optical disk that can satisfy all of the required characteristics as shown below. It does not give optical distortion to the laser beam (non-optically active) and has enough transparency to transmit the laser beam. It is essential for optical discs to maintain flatness (no warping) so that reading errors do not occur, and hygroscopicity is thought to be the main cause of warping. Since a metal coating layer for reflecting laser beams is formed on the information bit side formed on one side of the optical disk, it is necessary to provide the transparent resin with moisture absorption resistance comparable to metal. Considering the manufacturing workability and handling during use of optical disks, a certain degree of mechanical strength is required, and audio disks for automobiles and the like also need heat resistance that can withstand temperatures of about 100°C. Materials for information disks that read information using laser beams have a high information recording density, so they must have moldability that can faithfully reproduce the fine irregularities of the stamper used to engrave information bits. The present invention was completed as a result of such research, and its structure is that information bits are engraved with a stamper on one side of an optically transparent plate made of a 4-methylpentene polymer or a crosslinked product thereof. The gist is that a recording surface is formed, a metal coating layer constituting a reflective surface is formed on the recording surface, and information can be reproduced by irradiating a laser beam from the reflective side of the metal coating layer. exist. The 4-methylpentene polymers used in the present invention include poly4-methylpentene-1, poly4-methylpentene-2, 4-methylpentene-1 and other olefins (ethylene, propylene, isoprene, butadiene, etc.). ), or blends of these with polymers that can be kneaded (polypropylene, polyethylene, polyisoprene, polyvinyl acetate, etc.), etc., all of which meet the requirements as resins for optical disks. Characteristic~
It has everything. However, if the content of the olefin or blending polymer in the copolymer or blend is too large, the transparency and non-optional rotation of the optical disc will decrease, and the characteristics of the present invention will be diminished. It should be kept below 50% by weight. In addition, these 4-methylpentene polymers have excellent properties as they are, but if they are crosslinked by adding an appropriate amount of organic peroxide or crosslinked by irradiation with radiation, Hygroscopicity etc. can be further improved. Although the timing of the crosslinking reaction is not particularly limited, it is most preferable to carry out the crosslinking reaction after forming information bits using a stamper, which will be described later, thereby preventing deterioration in moldability. Next, a method for manufacturing an optical disk according to the present invention will be briefly explained. As shown in FIG. 1 (schematic process diagram) and FIG. 2 (explanatory diagram of the molded product in each step), after forming a conductive film on the photoresist surface 1' of the glass substrate 1 by vapor deposition or electroless plating method. Nickel electroforming is performed to produce a master disk 1a, a mother disk 1b, and then a female mold (stamper) 2 for mass duplication. Next, using the stamper as a matrix, the 4-methylpentene polymer is extruded, compression molded, injection molded, etc., and the information bits 4 are engraved at the same time as the disk base 3 is formed. A metal coating layer 5 is formed. In the case where the disc base forming polymer is crosslinked, it may be carried out in any step after the information bits 4 are formed. The metal coating layer 5 is for reflecting the laser beam irradiated from the surface side of the transparent disk substrate 3 on the surface of the information bit 4, and the type of metal is not particularly limited, but the most common ones are aluminum, chromium,
The material may be gold, silver, copper, tin, etc., and all conventionally known methods such as vapor deposition, sputtering, ion plating, etc. can be used to form the coating layer 5. There are no particular restrictions on the thickness as long as the above-mentioned reflective ability is effectively exhibited, but in order to satisfy both the physical properties and economic efficiency of the coating layer, the most common thickness is about 500 to 1500 Å, preferably 700 to 700 Å. 800
It is about Å. The optical disk of the present invention achieves its purpose with the above configuration, but in order to prevent the metal coating layer 5 from peeling or tearing, the protective layer 6 (epoxy resin, methacrylic resin, urethane resin, or silicone resin) is required for practical use. It is preferable to form an inorganic resin such as Further, by forming a surface hardening protective layer 3' on the laser beam incident side surface of the disk base 3 for the same purpose, its life can be extended. Furthermore, in the above example, one disk substrate 3 was used so that the recorded information could be reproduced from only one side, but for example, as shown in FIG. If you combine it with agent 7, the table/
The back side can be used as a recording/playback surface. The present invention is roughly constructed as described above, and its effects can be summarized as follows. The 4-methylpentane polymer has extremely good transparency and non-optical rotation, and does not impede the directionality of the laser beam, which is the recording and reproducing source. In addition, its moisture absorption resistance is at a low level comparable to that of metal, so there is no risk of warping during storage, and it also has a moderate heat resistance, so it can be used for long-term storage of recorded information and high accuracy. maintain the regenerative ability of Since the 4-methylpentene polymer has excellent moldability, it can faithfully reproduce the minute and minute irregularities of the stamper, and has high accuracy in recording and reproducing information. Next, examples of the present invention will be shown, but the following examples are not intended to limit the present invention. In the following examples, maximum retardation value and moisture resistance refer to values measured by the following method. [Maximum retardation value (R value)] Measurement was performed using a Senarmont compensator (manufactured by Nippon Geikagaku Co., Ltd.) equipped with a polarizing microscope and using a sodium lamp as a light source. [Moisture Resistance] The obtained optical disk was left in an atmosphere of 95% RH and 40° C., and was taken out every hour to measure the warpage x as shown in FIG. Example 1 A pre-molded audio disk stamper was attached to the mold of an injection molding machine, and 4-methylpentene resin (TPX-RT18 manufactured by Mitsui Petrochemicals Co., Ltd.) was applied to it.
Apply cylinder temperature: 300℃, injection pressure: 250
Kg/cm ² , mold temperature: 60℃ injection molding, transparent disk base 3 with information bits 4 formed on one side
(diameter 120 mm, thickness 1.2 mm) was obtained. After forming an approximately 1000 Å thin aluminum film (metal coating layer 5) on the surface of the disk base 3 on which the information bits 4 are formed by vacuum evaporation, methyl methacrylate (40 parts by weight) and methyl acrylate (5 parts by weight) are coated on the surface. parts by weight), ethylene glycol dimethacrylate (15
(parts by weight), trimethylolpropane trimethacrylate (40 parts by weight), and benzoin ethyl ether (0.1 parts by weight) are applied, and cross-linked by irradiating the resin with ultraviolet light for about 20 minutes using an ultraviolet lamp to form a back surface with a thickness of about 15 μm. A protective layer 6 was formed. The cross-sectional structure of the obtained optical disk is as illustrated in FIG. 5. Example 2 In the same manner as in Example 1, a transparent disk base 3 with a diameter of 120 mm and a thickness of 1.2 mm was engraved with information bits 4.
was injection molded. This substrate was crosslinked by irradiation with γ-rays using C _p ⁶⁰ as a radiation source at a dose rate of 5 Mrad/hr for a total of 2 hours at room temperature in a nitrogen atmosphere. N-methylolbutoxymelamine (100 parts by weight) and P-
After coating and forming a 5 μm thick resin layer consisting of sodium toluenesulfonate (1 part by weight), the temperature was increased to 160°C.
The film was cured by heat treatment for 40 minutes to form a transparent and smooth surface protective layer 3'. Next, a metal coating layer 5 made of aluminum and a back surface protective layer 6 were formed on the surface on which the information bits 4 were formed in the same manner as in Example 1, and then
Two of these molded products were bonded together with the sides on which the metal coating layer 5 was formed, with a polybutadiene layer (adhesive layer 7) having a thickness of 20 μm interposed therebetween, to obtain a double-sided recyclable optical disc. The cross-sectional structure of this optical disk is as schematically illustrated in FIG. Example 3 4-methylpentene-1-ethylene copolymer (4-methylpentene-1/ethylene = 90/10:
A disk substrate 3 was prepared in the same manner as in Example 1, except that a monomer unit ratio (monomer unit ratio) was used, and a metal coating layer 4 and a back protection layer 5 were formed in the same manner to obtain a cross-sectional structure similar to that shown in FIG. I got an optical disc. Comparative Example 1 A transparent disk base with information bits 4 was injection molded in the same manner as in Example 1 except that a commercially available polymethacrylate resin was used (cylinder temperature: 260°C, injection pressure: 50Kg/cm ² , gold Mold temperature: 70
℃). A metal coating layer 5 and a back surface protection layer 6 were formed on the side of the disk substrate 3 on which the information bits 4 were formed in the same manner as in Example 1 to obtain an optical disk. Comparative Example 2 The disk base 3 was molded in substantially the same manner as in the example except that a commercially available polycarbonate resin was used as the injection molding material (however, the cylinder temperature was 290°C).
(°C, injection pressure: 800 Kg/cm ² , mold temperature: 80°C), and then a metal coating layer 5 and a back protection layer 6 were formed in the same manner to obtain an optical disk. Table 1 summarizes the characteristics of each optical disk obtained in the above Examples and Comparative Examples, as well as the characteristics of the intermediate transparent disk substrate.

[Table] As is clear from Table 1, the disk substrate made of methyl methacrylate resin (Comparative Example 1) had good light transmittance, refractive index, and maximum retardation value, but It has poor strength and poor moisture absorption resistance, and due to its poor moisture absorption resistance, it warps during storage, reducing the accuracy of reproducing recorded information. In addition, the one using a base made of polycarbonate resin (Comparative Example 2) has extremely good impact strength and sufficient moisture absorption resistance, but has a slightly low light transmittance, a high refractive index, and a maximum retardation value. is extremely bad. On the other hand, Examples 1 to 3, which satisfy all the requirements of the present invention, achieved excellent results in all required characteristics.

[Brief explanation of the drawing]

1 is a schematic process diagram illustrating a method for manufacturing an optical disk, FIG. 2 is an explanatory diagram of a molded product in each step of FIG. 1, and FIG. 3 is a schematic sectional view illustrating an optical disc according to the present invention. FIG. 4 is an explanatory view showing a method for measuring moisture absorption resistance, and FIGS. 5 and 6 are schematic cross-sectional views showing optical disks obtained in Examples. 1...Glass base, 2...Stamper, 3...
Disk base, 4... Information bit, 5... Metal coating layer, 6... Back protective layer, 3'... Surface protective layer.

Claims (1)

[Claims] 1. A recording surface on which information bits are engraved with a stamper is formed on one side of an optically transparent plate made of a 4-methylpentene polymer or a crosslinked product thereof, and a recording surface on which information bits are engraved is formed on the recording surface. An optical disk characterized by forming a metal coating layer. 2. In claim 1, the metal coating layer-formed plates described in the same claim are laminated with an adhesive so that the metal coating layer forming sides face each other, and both sides are subjected to recording and recording.
An optical disc configured to be playable. 3. The optical disk according to claim 1 or 2, wherein the optically transparent plate is crosslinked by blending an organic peroxide with a 4-methylpentene polymer. 4. The optical disk according to claim 1 or 2, wherein the optically transparent plate is a 4-methylpentene polymer crosslinked by radiation irradiation. 5. An optical disk according to any one of claims 1 to 4, wherein a back protective layer is formed on the exposed side of the metal coating layer.