Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1999-02-03
2002-01-01
Yao, Sam Chuan (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S275700, C156S380900
Reexamination Certificate
active
06334925
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method for bonding together two discs having information recording layers and, more specifically, to an optimal method for manufacturing a DVD (“digital video disc” or “digital versatile disc”) employing are bonding method.
2. Description of the Related Art
In the conventional method for bonding two plate-like objects together employing a UV curable resin as an bonding agent, a UV curable composition is first coated uniformly to the bonding surfaces of the plates using a known technology such as spin coating, screen printing or the like. The two plates are then stacked so that the bonding surfaces meet. UV light is then irradiated in a continuous emission to cure the resin.
A high-pressure mercury lamp, metal halide lamp, mercury-xenon lamp or other such conventionally used device may be employed as the light source in the UV irradiation. However, since the lamp continuously emits light in this method, heat is readily generated, which can cause warping of the disc or impair its mechanical characteristics.
Further, in these types of continuous emission lamps, it generally requires several minutes or more for the light emission to stabilize once the lamp is turned on. Accordingly, since these lamps cannot be turned on and off readily, the lamp must be left on when a product is being produced continuously. For example, if a production cycle (i.e., the time required for a single bonding process) requires 5 seconds, the UV irradiation carried out for 2 seconds, then energy is wasted during the remaining 3 seconds in which the lamp is on but not needed.
Moreover, when bonding two plate-like objects together using a UV curable resin as an bonding agent, fewer problems occur if at least one of the two plate-like objects is UV transmissive.
However, when manufacturing a product such as a DVD, which is formed by bonding together two plate-shaped disc substrates, a thin metallic layer or other layer which does not readily transmit UV may be present under the bonding layer. In such cases, the intensity of the UV light is significantly weakened by these types of layers, so that efficient curing of the bonding agent may not occur.
Further, if the curing of the bonding agent is to be promoted, it then becomes necessary to provide a large capacity lamp so that the cost of the finished product unavoidably increases. Moreover, if a large capacity lamp is employed, then the heat given off by the lamp presents a problem in that it may give rise to warping or other deformations in the discs. In order to avoid this, it becomes necessary to provide separate cooling equipment around the lamp, making the device larger and more complicated.
Conversely, UV curing may be carried out using a small capacity lamp, but irradiation must then be performed for 20 to 30 seconds or more, making actual application of this approach difficult.
SUMMARY OF THE INVENTION
The present invention was conceived in consideration of the aforementioned problems, and has as its objective the provision of a method and device for bonding disc together which enables a high level of production, uses only a small amount of electric power, and requires only small, lightweight equipment.
After carrying out extensive research aimed at resolving the aforementioned problems, the present inventors were able to complete this invention upon the discovery that a method using flash emissions of UV in UV irradiation, rather than continuously emitting UV, enables a reduction in the electric power consumed and an increase in the number of discs bonded over a given period of time.
In other words, a first aspect of the present invention concerns a method for bonding together two disc substrates, each of which has a UV transmissive base, at least one disc substrate having a UV transmissive-visible light reflective information recording layer provided on the UV transmissive base, wherein the disc substrates are bonded together, so that the information recording layer of the disc substrate faces the other disc substrate, by irradiating UV light to cure a UV curable composition employed as a bonding agent, this method being characterized in that curing of the bonding agent is carried out by flash irradiation of UV light.
The second aspect of the present invention concerns a device for bonding together two disc substrates, each of which has a UV transmissive base, at least one disc substrate having a UV transmissive-visible light reflective information recording layer provided on the UV transmissive base, wherein the disc substrates are bonded together, so that the information recording layer of one disc substrate faces the other disc substrate, by irradiating UV to cure a UV curable composition employed as a bonding agent, this device being characterized in the employment of a light emission device which includes a flash-type discharge mechanism and a lamp that serves as the UV light source.
At least one of the two disc substrates employed in the bonding process in the present invention has an information recording layer provided on a UV transmissive base. The present invention includes both the case where each of the disc substrates have an information recording layer provided on a UV transmissive base, and the case where one disc substrate has an information recording layer provided on a UV transmissive base while the other disc substrate does not have an information recording layer which requires a UV transmissive base. In other words, the phrase “two disc substrates, at least one disc substrate having a UV transmissive-visible light reflective information recording layer provided on a UV transmissive base” as used in the present invention is intended to include both of the preceding cases. In either case, however, the UV transmissive layer ordinarily has a thickness of 0.3 to 1 mm.
Any of the known materials conventionally used may be employed as the UV transmissive base, with examples including heat-resistant thermoplastic synthetic resins such as acrylic resin, polycarbonate, amorphous polyolefin or the like. The information recording layer is provided to one of the bases, and has pits or indentations representing recorded information. This information recording layer is laminated with a UV transmissive-visible light reflective coating.
It is preferable that the material used for this coating is one which permits accurate confirmation of the pits by reflecting at a high rate the visible light used to read out the recorded information. In general, a coating which reflects visible light at a high rate will also demonstrate a high rate of reflection for UV light as well. A coating which does not transmit UV at all cannot be employed in the present invention. Examples of a UV transmissive-visible light reflective coating include UV-transmissive visible light-reflective metals such as aluminum, nickel, gold or alloys. Metals which may be employed as this coating are ones which have a rate of reflection of visible light in the range of 80 to 100%, and a rate of transmission of UV that is in the range of 0 to less than 10%, but preferably above 0 and less than 3%, across the entire UV wavelength region. The thickness of this coating in the information recording layer is between 200 to 800 angstroms.
The disc substrate employed in the present invention may be obtained by pouring the material which is to form the substrate into a stamper mold in which grooves of a specific size, thickness and shape have been formed which correspond to the audio or video information which is to be regenerated. The substrate is then molded, and a UV transmissive-visible light reflective coating is then laminated over the substrate. In general, this laminate can be formed by depositing the aforementioned metal to a specific thickness on the pitted surface of the substrate to form a thin metallic coating. In this way, an information recording layer may be formed in which the pits and coating are formed in a unitary construction.
In order to extend the recording time, distinct or continu
Ebisawa Shoei
Fukutomi Hiroshi
Murakami Kazuo
Armstrong Westerman Hattori McLeland & Naughton LLP
Dainippon Ink & Chemical, Inc.
Yao Sam Chuan
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