1. Field of the Invention
The present invention relates to an information recording disk such as an audio disk, a video disk and an optical or optomagnetic disk as a data file or buffer and, more particularly, to a disk which may be manufactured by transferring an information pattern to a support substrate of glass, plastic or the like by means of a mold called a stamper.
Further, the present invention relates to an information recording disk in which a resin forming an information transferring layer is a liquid precursor and the liquid precursor may be cured by applying light, heat or the like to form a cured resin layer integrated with a support having a transferred information pattern.
2. Description of the Prior Art
A record disk is well known as a conventional disk-like information medium. A stamper having a helical groove is used as a mold, and vinyl chloride is molded by injection or compression molding to manufacture records in mass production lines. The resin used in the manufacture of records is of a high molecular weight, and the high polymer resin is heated and melted for molding. In this process, the following problems are present: the flowability of resin melt is low; a thermal decomposition gas corrodes the stamper since molding requres a high temperature and a high pressure; the flow of resin melt or dust under a high pressure damages the surface pattern of the stamper; and the molecular orientation is distorted due to a heating/cooling cycle and a melt flow. Injection or compression molding has an advantage in mass production, but is not always advantageous for manufacturing disks with a high recording density.
Information recording disks such as audio, video and data processing optomagnetic disks have been commercially available in recent years. Typical structures of these disks will be described below.
FIG. 1 shows an example of an information recording disk. A transparent support substrate is made of plastic, glass or the like. Signal grooves or pits are formed in the surface of the support substrate 1. A reflecting layer 2 is formed on the support substrate 1 by depositing aluminum or the like thereon. The reflecting layer 2 is covered with a protective layer 3. An optical path 4 indicates a path for a signal read beam.
FIG. 2 shows another example of a two-side information recording disk. In this disk, two-side recording can be performed since the protective layers 3 of two information recording disks of FIG. 1 are adhered through an adhesive layer 5.
FIG. 3 shows still another example of a capacitive information recording disk. The disk comprises a support substrate 1, conductive layers 6 constituted of a thin metal film and dielectric layers 7
FIG. 4 shows an example of an optomagnetic information recording disk. Tracking grooves are formed in a support substrate 1 made of a transparent plastic, glass or the like. A magnetic recording layer 8 is formed by sputtering or the like. A protective layer 3 is formed on the magnetic recording layer 8.
FIG. 5 shows another example of an information recording disk as a two-side optomagnetic disk prepared by adhering the two single-side optomagnetic disks of FIG. 4 so that writing reading operation can be performed from the both surfaces.
These information recording disks require a particularly higher pattern shaping precision since the information recording disks have much higher recording density than conventional record disks. In order to manufacture these information recording disks, a molding method different from that used in manufacturing record disks is adapted and called a 2P or photo-polymer method. According to this method a liquid photo-setting resin is injected between a disk substrate and a stamper and is cured with light to transfer a pattern of the stamper, thereby preparing an integral structure consisting of the substrate and the pattern layer. Since the non-cured resin is a liquid having a relatively low molecular weight, it can be poured into the mold at atmospheric pressure. In addition, flowability of the resin is so good that the resin can be injected into the minute portions of the mold to obtain a replica with high precision. The molecular orientation due to flow of the resin does not substantially occur. Therefore, an information recording disk free from optical anisotropy can be fabricated.
Unlike in record disk fabrication, the stamper is not damaged due to molding at a high temperature and a high pressure. Ultraviolet curing provides a high reaction rate and is suitable for mass production. Heretofore, and acrylic acid ester or mothacryic acid ester compound has been used as a material for the transfer layer. This is mainly because the compound described above has proper properties to be polymerized and cured by irradiation with an ultraviolet ray for a short period of time. Furthermore, the compound is amorphous, has a small optical anisotropy and is convenient for an optical reading means.
When such an acrylic resin is used, however, there is not any acrylic resin capable of satisfying conditions that a replica, i.e., a transfer layer. can be easily released from the stamper and at the same time, the transfer layer has good adhesion to the support substrate, since easy release of the transfer layer from the stamper contradicts its good adhesion to the support layer.