Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
1997-11-26
2001-08-07
Ball, Michael W. (Department: 1733)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S273300, C156S275500, C156S306900
Reexamination Certificate
active
06270611
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a multi-layer recording medium, such as a multi-layer optical disc, having plural information recording layers in which information signals are recorded by pits. The present invention also relates to a method for producing the multi-layer recording medium.
In a disc-shaped recording medium, for example, an optical disc or a magneto-optical disc, as a package medium for music or picture information or recording apparatus for computers, the recent tendency is towards higher recording density of information signals. For realizing this high density recording, there is proposed a multi-layer optical disc having a plurality of layered information recording layers functioning as a signal recording region.
Among a variety of multi-layer optical disc, there is a double-layer optical disc having two layered information recording layers functioning as an information recording region. Such double-layer optical disc
100
, shown in
FIG. 1
, includes a disc substrate
101
of a transparent synthetic resin material, such as polycarbonate, on one surface of which is formed a first information recording layer
101
a
having rows of pits, and a semi-transparent thin reflecting film
102
of a dielectric material, such as silicon nitride SiN, formed on the first information recording layer
101
a
. The double-layer optical disc
100
also includes an intermediate layer
103
of a transparent resin material having, on the surface thereof opposite to the recording layer
101
a
, a second information recording layer
103
a
also having rows of pits, and a reflecting film
104
of, for example, A1, formed on the second information recording layer
103
a
. In addition, the double-layer optical disc includes a protective layer
105
formed on the reflective film
104
.
For reading out the information signals from the double-layer optical disc, the focal position of a laser light radiated from an objective lens
106
of an optical pickup device shown in
FIG. 1
is changed in two steps. That is, for reading out the information signals on the first information recording layer
101
a
, the spot of a laser light beam L
1
is located on the row of pits recorded on the first information recording layer
101
a
. For reading out the information signals on the second information recording layer
103
a
, the spot of a laser light beam L
2
, shown by a broken line in
FIG. 1
, is located on the row of pits recorded on the second information recording layer
103
a
. If, in such case, it is desired to prohibit interference from being produced between the information recording layers
101
a
,
103
a
in the signal read-out or reproducing operation, it is necessary to set the thickness of the transparent intermediate layer
103
between the information recording layers to a larger value on the order of 30 to 60 &mgr;m, for example, 40 &mgr;m.
In such double-layer optical disc
100
, the intermediate layer
103
is formed by any of the following two methods. The first method is to spin-coat a UV curable resin (UV resin). The second method is to apply the UV resin dropwise into a space defined between the layers
101
and
105
by a spacer having a thickness corresponding to the thickness of the intermediate layer
103
for pressure bonding and curing the intermediate layer from both side layers.
For spin-coating the UV resin for forming the intermediate layer, since the UV resin can be applied to a thickness only of 10 &mgr;m by one coating operation, the process of application followed by curing needs to be repeated e.g., four times, thus consuming much time in the production of the multi-layer optical disc. In addition, if spin-coating is repeated a number of times, the UV resin is dripped or turned round to the peripheral portion thus producing thickness variations in the intermediate layer to obstruct production of the high precision multi-layer disc.
With the second method of dripping the UV resin into the spacer and pressure bonding and curing the resin from both side layers, it is necessary to set the spacer in position, thus necessitating a time-consuming operation in the production of the multi-layer optical disc, as in the first method explained above. On the other hand, the UV resin tends to leak from the spacer thus obstructing the production of the high precision multi-layer disc.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a multi-layer recording medium and a method for producing the multi-layer recording medium in which the distance between the information recording layers may be sufficiently increased and the information recording layers may be set to uniform thicknesses.
It is another object of the present invention to provide a multi-layer recording medium and a method for producing the multi-layer recording medium in which the recording medium may be produced in a shorter time with higher precision by simplifying the formation and prohibiting variations in thickness of the intermediate layer.
Basically, the multi-layer recording medium of the present invention is produced by interposing a photo-curable resin film between a substrate having formed thereon a first information recording layer and a master disc for transcription of a second information recording layer. The photo-curable resin film is pressure bonded to the substrate and the master disc, and the master disc is then peeled off for forming the intermediate layer.
In one aspect, the present invention provides a multi-layer recording medium including a light-transmitting substrate, a first information recording layer formed on the substrate, an intermediate layer at least part of which is formed of a photo-curable resin film, and which is formed on the first information recording layer, a second information recording layer formed on a surface of the intermediate layer opposite to the surface thereof facing the first information signal layer, and a protective layer formed on the second information signal layer.
In another aspect, the present invention provides a method for producing a multi-layer recording medium including the steps of pressure bonding a photo-curable resin film to a substrate having a first information recording layer formed thereon by a master disc for transcribing a pattern of micro-sized lands and recesses of a second information recording layer, photo-curing the photo-curable resin film by light irradiation, peeling off the master disc from the photo-curable resin film for forming an intermediate layer, forming the second information recording layer on the intermediate layer and forming a protective layer on the second information recording layer.
In yet another aspect, the present invention provides a method for producing a multi-layer recording medium including the steps of pressure bonding a photo-curable resin film to a substrate having a first information recording layer formed thereon, photo-curing said photo-curable resin film by light irradiation, interposing a liquid photo-curable resin between the photo-curable resin film and a master disc for transcription of a pattern of micro-sized lands and recesses of a second information recording layer and curing the liquid photo-curable resin by light irradiation; peeling off the master disc from the cured liquid photo-curable resin film for forming an intermediate layer, forming the second information recording layer on the intermediate layer and forming a protective layer on the second information recording layer.
With the above-described arrangement of the present invention, since the intermediate layer is formed between the information recording layer by the photo-curable resin film (dry photpolymer film) or the photo-curable film and the photo-curable resin layer by the 2P method, the intermediate film may be of a larger and uniform thickness.
With the method for producing the multi-layer recording medium according to the present invention, a photo-curable resin film is interposed between and bonded to a semi-transparent reflective film formed on the first informatio
Furuki Motohiro
Kashiwagi Toshiyuki
Ohki Hiroshi
Ball Michael W.
Kananen Ronald P.
Piazza Gladys
Rader Fishman & Grauer
Sony Corporation
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