Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-08-05
2002-07-09
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C264S001330
Reexamination Certificate
active
06416609
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process and an apparatus of producing an optical disk (or an optical medium), and particularly a laminate type optical disk, and also relates to a process of producing a substrate to be laminated for the production of the optical disk. For example, such an optical disk includes those for DVD (Digital Video Disk) or the like.
2. Related Art
A process has been known in which a single optical disk for DVD is produced by laminating a plurality (usually two) of substrates each having predetermined irregularities for a recording layer on its one main surface so that the single optical disk has a plurality of the recording layers. Such a process and an apparatus therefor are disclosed in for example WO97/35720, parts of which are incorporated herein by this reference provided that they are relevant to the present invention described hereinafter.
Concretely, the optical disk is produced by the following process comprising the steps of:
(1) preparing a pair of same or different two substrates each of which has been injection molded of a transparent resin so as to provide with fine irregularities on its one main surface and each of which has a metal (gold, aluminum or the like) thin film on said one main surface (usually, each substrate is of a circular form having a center hole);
(2) supporting the substrates while keeping a narrow gap between them so that the metal layers on the substrates are facing to each other;
(3) supplying an adhesive such as a UV curable adhesive into the gap and spreading it throughout the gap so that a laminate of the pair of the substrate and the adhesive between them is obtained; and
(4) bonding the pair of the substrates together by curing the adhesive in order to join the substrates. For example, by irradiating UV on the laminate, the UV curable adhesive is cured.
Reading data (or information) from an optical disk or writing data into the optical disk is carried out by irradiating a laser beam having a predetermined wavelength onto the optical disk while the beam traversing the optical disk from its innermost or outermost periphery so that the beam passes through the transparent substrate and reaches a recording layer while the disk is being rotated at a high speed. Since a density of data which is to be recorded (or written in) or which has been recorded beforehand in the recording layer is extremely high, it is important that the laser beam is accurately focused onto a predetermined position of the optical disk. If flatness of the disk as a whole is not good, the laser beam cannot be focused onto the predetermined position of the optical disk so that data is likely to be incorrectly read or recorded.
Upon the production of the optical disk, it is therefore desirable that no deformation such as warpage or strain is observed in the optical disk as a final product, and also that occurrence of such deformation is suppressed after the production (i.e. during storing and/or using the optical disk), so that the produced optical disk has and keeps the improved flatness.
Considering the deformation which occurs in the optical disk, there comes one following possibility of a mechanism which causes the deformation:
The deformation of the optical disk is resulted from deformation with time of the substrate made of the transparent resin. Particularly, the substrate just after the molding which is in a dry condition at a considerably high temperature is likely to absorb moisture from its surrounding atmosphere, so that the substrate deforms as it absorbs the moisture.
Then, it has been proposed to subject the substrate to a treatment in which the molded substrate is left over an extended period to stabilize a moisture content of the substrate, and then subject to the metal film formation step as a subsequent step in which a metal thin film is deposited onto the substrate. The treatment may be also referred to as an “annealing treatment”, and generally it is carried out over a period between few hours and 24 hours.
However, it is very ineffective to include the annealing treatment requiring the extended period in an integrated production line when mass production of the optical disk is intended. In order to carry out the annealing treatment, a large space is required for temporarily storing a large number of the molded substrates. If conditions of an atmosphere for the annealing treatment are changed due to some reason, an extent of the effect derived from the annealing treatment varies, which results in the various substrates which have different moisture contents. Further, it takes a considerably long time to produce the optical disk as a final product since starting the molding of the substrate.
In addition, there is further warpage (or warp) which appears with time after completing the production of the optical disk as well as further warpage which appears depending on application conditions of the optical disk. Even though the produced optical disk has passed product testing so that it has been proved to have a warpage within a predetermined specification, the warpage of the optical disk sometimes increases while it is repeatedly used or stored for an extended period, which may adversely affect recording the data into or reading the data from the optical disk. This would be because an internal stress or strain contained in the optical disk during its production is released with time or due to its application conditions so that the warpage additionally occurs.
SUMMARY OF THE INVENTION
Considering the above related art, it is therefore an object of the present invention to suppress the occurrence of the warpage upon the production of the optical disk and the warpage of the optical disk with time so that the optical disk of the laminate type is efficiently produced which has better flatness.
In the first aspect, the present invention provides a process of producing a laminate type optical disk comprising the steps of:
(1) molding a pair of substrates of a transparent resin at least one of which substrates has irregularities on its one main surface;
(2) forming a metal thin film on said one main surface having the irregularities, and then
(3) laminating the pair of the substrates while the metal thin film is located inside and bonding the substrates by means of an adhesive which is supplied between the substrates,
the process being characterized in that after the step (1), a waiting treatment is carried out in which the molded substrates are cooled to such a temperature that a difference between said temperature and a temperature of an atmosphere surrounding the substrates is not greater than 5° C. while keeping a moisture (or water) content of the substrates not larger than 0.1% by weight, and then the step (2) is carried out.
In the present invention, at least one of the pair of the substrates has the fine irregularities on one of its main surfaces. That is, only one substrate may have the irregularities on its main surface, but generally each of the substrates has the irregularities on its main surface. When the optical disk is of a read only memory (ROM) type, the irregularities correspond to pits of recorded data. When the optical disk is of a random access memory (RAM) type or a recordable (or write once) (R) type, the irregularities correspond to lands and grooves. In any type of the optical disks, irregularities which correspond to format information inherently required for the optical disk may be included in said one main surface of either or both of the substrates.
The metal thin film is a layer formed on said one main surface of the substrate having the irregularities which layer reflects light, and the film may be semi-permeable to light (i.e. translucent). For example, the metal thin film is formed by sputtering gold or aluminum. The metal thin film functions as a reflecting layer which reflects a laser beam irradiated onto the optical disk. When the both substrates have the irregularities, the metal thin film is formed on said one main surface of each of the substr
Fujioka Toshiyuki
Higashida Takaaki
Imada Tetsuo
Inoue Mamoru
Namiki Shigeru
Ball Michael W.
Matsushita Electric - Industrial Co., Ltd.
Piazza Gladys
Wenderoth Lind & Ponack LLP
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