Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2000-02-17
2002-06-18
Evans, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S065200
Reexamination Certificate
active
06406770
ABSTRACT:
TECHNICAL FIELD
The present invention relates to an optical disc represented by the digital video/versatile disc (hereinafter abbreviated as DVD) which adopts a laminating method, and a production method therefor.
BACKGROUND ART
Conventionally, when two plate-like objects are laminated using an ultraviolet curable composition as an adhesive, a radical polymerization-type ultraviolet curable composition is uniformly applied to an adhesion face by means of a spin coating method, a screen printing method, or the like which are existing techniques. After this, both adhesion faces are superposed so as to face each other, after which continuously radiative ultraviolet light is irradiated to cure the adhesive.
As a light source for the ultraviolet irradiation, a high-pressure mercury lamp, a metal halide lamp, a mercury-xenon lamp or the like have heretofore been used. With such methods, since the irradiance of the lamp is continuous, heat is easily generated, which causes a problem in that the heat may cause warping of the plate-like object, or may adversely affect the mechanical properties.
Moreover, with a continuously radiative type lamp, normally several minutes or more are necessary for the irradiance to stabilize after turning on the light. Hence turning on and off cannot be performed so often. Therefore, when a plate-like object is continually produced, the lamp must be kept turned on. If it is assumed that the time required for one adhesion (one cycle) (cycle time for the production) is 5 seconds, and of that the time required for ultraviolet irradiation is 2 seconds, then for the remaining 3 seconds energy is wastefully consumed.
When two plate-like objects are laminated using an ultraviolet curable composition as an adhesive, if at least one plate-like object of the two plate-like objects has ultraviolet transmissivity, there will be no particular problems.
With, for example, DVDs or the like produced by lamination however, there is a problem in that the ultraviolet intensity is greatly attenuated due to thin films and layers of Al and the like, before the ultraviolet rays reach the adhesive layer in which a radical polymerization type ultraviolet curable composition is used as an adhesive. Hence efficient curing and adhesion cannot be attained.
Therefore, there is a problem in that if an attempt is made to facilitate curing, lamp equipment having a large capacity becomes necessary. This inevitably leads to an increase in production costs. Moreover, when a lamp having a large capacity is used, there is a possibility of this causing problems such as deformation of the plate-like object due to the radiant heat from the lamp. To prevent this, cooling equipment around the lamp must be provided separately, which makes the whole apparatus large scale and more complicated.
On the other hand, if ultraviolet curing with lamp equipment having a small capacity is attempted, the irradiation time must be several tens of seconds or more, which is not practical.
A disc lamination method which solves the above problems is disclosed in Japanese Patent Application, First Publication No. Hei 9-193249. That is to say, the disc lamination method disclosed in Japanese Patent Application, First Publication No. Hei 9-193249 is characterized in that ultraviolet rays are not continuously radiated to a target, but are radiated in a flash. This method for radiating ultraviolet rays in a flash is a revolutionary method which enables an increase in the number of laminations per unit time compared to the case where ultraviolet rays are irradiated continuously, while suppressing the consumed power for the ultraviolet irradiation, and which is capable of preventing the generation of disc warping after lamination.
However, even this method using ultraviolet irradiation as a flash has problems as described below. That is to say, when a DVD is the laminated object, in view of the construction, ultraviolet rays will reach and cure the ultraviolet curable resin after being transmitted through an Al film having poor ultraviolet transmissivity. Hence if the Al film is thick to meet product specifications, the curing efficiency will be deteriorated. Moreover, among DVDs, in the case of the DVD-RAM where a film which does not substantially transmit ultraviolet rays (for example, ZnS—SiO
2
film which is typical of a dielectric film) exists, the method in which ultraviolet rays are irradiated in flashes onto an ultraviolet curable resin existing on the bonding faces of two discs to cure and bond this, cannot be adopted.
Japanese Patent Application, First Publication No. Hei 9-69239 discloses an effective lamination method with respect to the above problems. The method disclosed in Japanese Patent Application, First Publication No. Hei 9-69239 is characterized in that a slow acting cationic ultraviolet curable composition is used instead of the radical polymerization type ultraviolet curable resin being the conventional adhesive. More specifically, the cationic ultraviolet curable composition is applied to the whole surface of one disc to be laminated, and thereafter ultraviolet rays are irradiated onto the cationic ultraviolet curable composition. Then the other disc to be laminated is superposed thereon, pressure is applied thereto, and the cationic ultraviolet curable composition is allowed to cure.
The method using the cationic ultraviolet curable composition disclosed in Japanese Patent Application, First Publication No. Hei 9-69239 is an effective method, enabling adhesion even in the case where the Al film is thick, or with the DVD-RAM where the ZnS-SiO
2
film or the like which does not substantially transmit ultraviolet rays exists.
However, it is recognized that even with the method disclosed in Japanese Patent Application, First Publication No. Hei 9-69239, there are points to be improved. That is to say, as described above, with the method disclosed in Japanese Patent Application, First Publication No. Hei 9-69239, after the cationic ultraviolet curable composition is applied to the whole surface of one disc, the other disc is superposed thereon. At the time of superposition, there is a possibility that bubbles are trapped in large quantities, thereby deteriorating the adhesion performance.
That is to say, the resin in the vicinity of the bubbles is subject to inhibition of polymerization due to moisture (water content) contained in the bubbles, and curing may not be performed completely. Furthermore, there is a possibility that the product quality after lamination may be impaired. Moreover, if a disc in which bubbles are trapped is exposed to high temperature and high moisture for a long period of time, the inside air may expand, and in the worst case, the surface of the disc may swell.
Moreover, with the method disclosed in Japanese Patent Application, First Publication No. Hei 9-69239, two disc substrates are pressed together after being superposed. However, there is a possibility that damage may occur on the disc surface due to the mechanism used for pressing. This occurrence of damage becomes significant when the discs are produced continuously, and may lead to a decrease in product yield.
Furthermore, in view of the properties of the cationic ultraviolet curable composition, a predetermined period of time is required for curing after lamination. Therefore it is necessary to leave the disc substrate to stand for a certain period of time and to take measures so that deformation or displacement does not occur. This becomes a hindrance in constructing mass production equipment.
Moreover, there is a problem in that the cationic ultraviolet curable composition protruding from the bonding face becomes tacky, so that handling is troublesome.
Therefore, it is an object of the present invention is to provide an optical disc wherein even in the case where a cationic ultraviolet curable composition is used, trapping of bubbles in the adhesive layer is minimal, and uneven curing is suppressed. Moreover, it is another object of the present invention to provide a production method for optical discs which can eff
Ebisawa Shoei
Hashimoto Keiichi
Ito Daisuke
Oshima Kiyoshi
Tsunematsu Norio
Dainippon Ink and Chemicals Inc.
Evans Elizabeth
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