Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Compositions to be polymerized by wave energy wherein said...
Patent
1998-02-12
2000-09-19
Sellers, Robert E.
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Compositions to be polymerized by wave energy wherein said...
3692751, 428414, 522 32, 522 66, 523427, 525524, C08F 248, C08L 6302, C08J 328, G11B 724
Patent
active
06121339&
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an epoxy resin composition initiating cationic polymerization upon irradiation with energy rays as well as an optical information recording medium such as an optical disk etc. using the resin composition as an adhesive layer.
BACKGROUND ART
Recently, attention is drawn to optical disks, particularly a digital video disk (DVD) that records a moving image and a sound in a digital system.
Generally, the optical disk e.g. a DVD requiring a large capacity has a structure so-called as a lamination type optical disk which includes, as shown in a schematic view of an optical disk 30 in FIG. 2, two disk substrates 24 having two transparent plastic substrates 21, each being formed on its one side with a recording and reflective layer 22 having formed with a concave and a convex (pits) corresponding to recording information and a protective layer 23 successively in this order, the disk substrates facing each other such that their recording layers (reflective layers) 22 are arranged inside and integrated via an adhesive layer 25.
Adhesives such as a hot-melt type adhesive or a radical polymerizable ultraviolet-curing adhesive have been used as the adhesive layer 25 for bonding the disk substrates 24, but they do not suffice for practical purposes in respect of thermal resistance and disk base warpage.
Under the circumstances, a method of manufacturing an optical disk is proposed as described in e.g. Japanese laid-open Publication No. 7-126577 in which a liquid cationic polymerizable, ultraviolet ray-curing adhesive layer is formed on a bonding face between 2 disks, irradiated with energy rays to effect the bonding and then two disks are bonded with pressure, followed by solidification of the layer.
Such a cationic polymerizable, ultraviolet-curing adhesive layer will initiate curing reaction whether in the air or in a dark place upon exposure to ultraviolet rays once and hence it is expected to have an significant effect on the improvement of the manufacturing process. The cationic polymerizable, ultraviolet-curing adhesive has the advantage of less warpage of disk substrates by virtue of less shrinkage at the time of the reaction, and the adhesive layer after curing becomes extremely hard.
However, even in cases where such cationic polymerizable, ultraviolet-curing adhesives are used, the resulting products cannot suffice under the circumstances of high temperature and high humidity.
For example, if the above-mentioned optical disk is stored under the circumstances of high temperature and high humidity, a tilt angle (i.e. angle from a horizontal plane) of the optical disk is enlarged due to distortion or warpage of the disk, causing an adverse effect on the reproduction of a recorded signal so that the recorded information cannot correctly be read out.
This is particularly a great problem for a DVD requiring high reading accuracy because a concave and a convex (pits) on the recording layer have been further minimized for large capacity.
Further, the laminated disk for a DVD is soft and thus tends to easily undergo warpage or bending because it is thinner than a conventional laminated disk such as a laser disk etc.
Furthermore, in the recording layer there occurs a trace of corrosion under the circumstances of high temperature and high humidity.
As a result of detailed examinations by the present inventors et al., it was estimated that the warpage or bending under the circumstances of high temperature and high humidity resulted from the inadequate thermal resistance and adhesiveness of the adhesive layer.
That is, under the circumstances of high temperature and high humidity, the adhesive layer generally requires thermal resistance. However, if thermal resistance is improved, the hardness of the adhesive layer is increased while its adhesiveness is lowered in many cases. In addition, if the moisture absorption property of the adhesive layer is high, the adhesive layer is easily swollen to lower adhesiveness. These reasons presumably cause the above distortion or war
REFERENCES:
patent: 4565859 (1986-01-01), Murai et al.
patent: 4835193 (1989-05-01), Hayase et al.
Chemical abstracts registry No. 1304-76-3 for bismuth oxide, 1966.
Chemical abstracts registry No. 10361-44-1 for bismuth nitrate, 1966.
Hayashi Kozaburo
Kominami Hiraku
Shibata Kazuki
Frommer William S.
Sellers Robert E.
Sony Chemicals Corporation
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