Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Light polarizing article or holographic article
Reexamination Certificate
1999-06-24
2001-08-28
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Light polarizing article or holographic article
C156S275500, C156S379600, C264S001380, C264S040500, C425S125000, C425S149000, C425S810000
Reexamination Certificate
active
06280660
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a technique for manufacturing an optical recording medium having an uneven pattern formed on the surface thereof. More particularly, the present invention provides a new method of producing a flat substrate to be used in manufacturing an optical recording medium by photopolymerization.
BACKGROUND ART
As a typical method of manufacturing an optical recording medium, i.e., an optical disk, photopolymerization has been used hitherto. Photopolymerization is a method in which a flat plate of plastic, glass, or the like (referred to as a “flat substrate”) is prepared, a photo curing resin, which is hardened by light energy such as ultraviolet rays, is filled between the flat substrate and a stamper, and the photocuring resin is hardened by irradiation with ultraviolet rays.
A conventional photopolymerization method is disclosed in, for example, Japanese Unexamined Patent Publication No. 53-86756. This publication describes a method in which a master (the “master” corresponds to a stamper hereinafter in this description) is formed of nickel by electroforming, and a pattern is transferred from the master onto a flat substrate made of polymethyl methacrylate, polycarbonate, or the like, by using an ultraviolet-curing resin.
Japanese Unexamined Patent Publication No. 5-62254 discloses a method in which silicon is used as a master, and a pattern is transferred from the master of a silicon wafer, which has an uneven pattern formed by etching, onto a flat substrate by using an ultraviolet-curing resin.
In the above conventional photopolymerization methods, a resin plate formed of polycarbonate by injection molding or extrusion is used as the flat substrate in order to improve mass productivity.
Since polycarbonate has a considerably strong optical anisotropy, however, the optical properties of a disk, which is obtained by working a sheet material formed by extrusion, vary depending on the reading direction of a pickup. In order to obtain stable reproduced signals, it is necessary that the optical properties not vary even when the reading direction of the pickup changes somewhat. Consequently, it is impossible to use polycarbonate as a material for the optical disk.
In contrast, when acrylic having a weak optical anisotropy is used instead of polycarbonate, the optical properties of a disk obtained by extrusion and working described above are improved. Acrylic is, however, highly hygroscopic, and thereby tends to cause deformation, such as warping of a disk. Moreover, when a reflecting film, a recording film, or the like is formed on the disk surface by vacuum forming, it takes substantial time to remove gas (in particular, moisture) from the disk.
In order to solve the above problems, it is preferable to use a polyolefin copolymer as a material for a resin plate that satisfies the requirements of desirable optical anisotropy, constant low hygroscopicity, and resistance to deformation. Even when polyolefin is used, however, as long as a resin plate is formed by injection molding, the following problems may arise. Therefore, it is necessary to suggest a new method of producing a resin plate. First, when polyolefin is heated to a high temperature for injection molding and is injected into a mold at a high pressure, decomposition or oxidation sometimes occurs, thereby deteriorating the properties of the optical disk. Furthermore, in injection molding, the resin plate sometimes deforms due to changes in pressure in the process of reducing the pressure immediately after molding. Moreover, in injection molding, after resin is heated to a high temperature to be melted, waiting is necessary for the resin to become sufficiently cooled. This may prolong production time, and increase production cost.
SUMMARY OF THE INVENTION
In view of the above problems, a first object of the present invention is to provide a technique for manufacturing an optical recording medium that has excellent optical properties and that is not apt to undergo failure during production.
A second object of the present invention is to provide an optical recording medium manufacturing technique in which the properties can be prevented from deteriorating due to oxidation of a resin plate.
A third object of the present invention is to provide an optical recording medium manufacturing technique in which deformation of a resin plate after molding is restricted.
A fourth object of the present invention is to provide an optical recording medium manufacturing technique that allows reduction in the time spent until a resin plate is molded.
The present invention achieves the above first object, and provides an optical recording medium manufacturing method for forming an optical recording medium by hardening a hardening resin between a resin plate and a template, wherein the resin plate is produced by a heating step for heating thermoplastic resin to a predetermined temperature to be melted; a feeding step for feeding the melted thermoplastic resin into a mold; and a molding step for compression-molding, into a resin plate, the thermoplastic resin fed into the mold. Preferably, the thermoplastic resin is a resin mainly containing a polyolefin copolymer.
The present invention achieves the above second object, in which the thermoplastic resin is compressed in the molding step below the temperature at which the thermoplastic resin undergoes oxidation.
The present invention achieves the above third object, in which the thermoplastic resin is compressed in the molding step at a pressure lower than the pressure at which the resin plate deforms due to reduction in pressure against the resin plate after molding.
The present invention achieves the above fourth object, and the method further includes a cooling step for cooling the molded resin plate after the resin plate is removed from the mold and transferred to another mold.
The method of the present invention further includes a mold switching step for accelerating the cooling of the resin plate by replacing a part of the mold with another mold after the resin plate is molded.
The present invention achieves the above first object, and provides an optical recording medium manufacturing apparatus for forming an optical recording medium by hardening a hardening resin between a resin plate and a template, which apparatus includes a mold structured so as to compression-mold thermoplastic resin fed into a cavity; a thermoplastic resin supplying mechanism for feeding thermoplastic resin into the cavity in the mold; and a hardening resin bonding apparatus for manufacturing an optical recording medium by putting melted hardening resin between a resin plate produced by compressing the thermoplastic resin by the mold and the template having a predetermined uneven pattern, and by hardening the hardening resin.
According to the present invention, the optical recording medium manufacturing apparatus includes a mold switching mechanism for replacing a part of the mold with another mold after the resin plate is molded, thereby accelerating the cooling of the resin plate.
According to the present invention, the optical recording medium manufacturing apparatus includes a plurality of molds, (a) a connecting mechanism structured to connect these molds and the thermoplastic resin supplying mechanism, (b) a mold switching mechanism for replacing a part of the mold with another mold, and (c) a removing mechanism for removing the resin plate from the mold whose part is replaced by another mold.
The connecting mechanism connects the thermoplastic resin supplying mechanism to the mold for producing a resin plate, and disconnects the mold and the thermoplastic resin supplying mechanism after the resin plate is molded in the mold.
The mold switching mechanism replaces a part of the mold with another mold after the resin plate is molded.
After the molded resin plate is cooled in the mold whose part has been replaced, the removing mechanism removes the resin plate from the mold.
The present invention offers the following four advantages:
(1) By adopting polyolefin for a resin p
Nebashi Satoshi
Nishikawa Takao
Takakuwa Atsushi
Harness & Dickey & Pierce P.L.C.
Seiko Epson Corporation
Vargot Mathieu D.
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