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Description  |
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BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to optical media for recording information,
and more specifically to an optical information recording disk having a
pair of plates which form a space therebetween in which at least one of
the plates carries an information bearing layer on the inner surfaces
thereof.
2. Description of Background Information
Optical disks are popularly used for recording various information in which
the information is recorded in the form of a large number of minute pits
on the information bearing layer. The DRAW (Direct Read After Write) disk
is an example of optical information recording disk in which the reading
of the recorded information directly after writing is enabled.
Since the information is carried by the DRAW disk in the form of sequential
arrangement of the pits, it is quite important to protect the information
bearing layer in which the information is held as the series of pits.
To meet this condition, a conventional type of optical disk has been
developed which used a pair of disk-shaped substrates at least one of
which is transparent and carries the information bearing layer. Both of
the substrates are placed to face each other and combined together by
sandwiching an adhesive agent therebetween. Thus, the information bearing
layer carried by the substrate is formed between the inward surfaces of
the substrates.
On the other hand, for improving the recording characteristics of the DRAW
disk, it has been required to raise the sensitivity of the information
bearing layer so that the error ratio of the DRAW disk is reduced.
In the case of the above described dual substrate optical disks of
conventional design, a drawback is that the information bearing layer is
likely to become corroded by the adhesive agent used to combine two
substrates when the information bearing layer is made extremely sensitive.
Furthermore, another conventional type of optical disk is also been
developed in recent years. This type of DRAW disk comprises a pair of
disk-shaped substrates each of which has a center bore and at least one of
which substrate is transparent and carries the information bearing layer
on the main surface thereof; an inner annular spacer aligned with the
center bore and placed between the inner circumferential portion of the
main surface of the substrates; an outer annular spacer positioned
coaxially to the inner annular spacer and placed between the outer
circumferential portion of the main surface of the substrates, these inner
and outer annular spacers being respectively provided with circular
grooves on cylindrical surfaces thereof so that the circular grooves face
each other and having U-shaped cross-sections in the radial direction
thereof; and a circular partition which is supported by means of the outer
and inner annular spacers each having the circular groove so as to insert
the outer and inner circumferential portions of the partition into the
oppsite grooves of the spacers respectively. In this case, both of the
substrates are placed to face each other and combined together through the
inner and outer annular spacers so as to make a space therebetween. Thus,
the outer circumferential portion of the circular partition is slidably
fitted in the inward circular groove of the outer annular spacer, and the
inner circumferential portion of the circular partition is also slidably
fitted in the outward circular groove of the inner annular spacer, so that
the circular partition separates the space existing between the substrates
into two spaces. The information bearing layer formed on one of the
substrate is opposite to an inward surface of the other substrate through
the circular partition and the spaces.
In the case of this optical DRAW disk having gaps or spaces between the
substrates, the corrosion of the information bearing layer caused by the
adhesive agent, as the above described problem in the prior art, is almost
avoided since the adhesive agent hardly touchs the information bearing
layer except for the circumferential portions of the inward surfaces of
the substrates.
However, this optical DRAW disk having such annular spacers is weak,
because the substrates are slidably supported by only means of the inner
and outer annular spacers having specific forms at the inner and outer
circumferential portions thereof. Particularly, the outer annular spacer
sandwiched between the substrates is easily fragile, because a shearing
stress caused by the modification of the entire DRAW disk is concentrated
on the bottom of the inward circular groove of the outer spacer having the
U-shaped cross-section when such DRAW disk is loaded for playing in the
player.
Thus, it is a problem concerning the strength of the DRAW disk in this
conventional technique that the substrate must be manufactured with
thickness enough to maintain the stiffness of the entire DRAW disk
including its annular spacers, so that the apparatus for playing such DRAW
disk should be made relatively large in size. For example, there appears a
DRAW disk having a thickness of 8 mm in the market.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide a miniature
information recording disk such as a very thin DRAW disk maintaining the
high sensitivity of the information bearing layer and the stiffness
thereof.
According to the present invention, the recording disk is made up of a pair
of disk-shaped substrates each having a center bore, a reinforcement disk
provided with annular bank portions on the both main surfaces thereof at
the inner and outer circumferential portions of the main surfaces thereof,
in which the reinforcement disk is sandwiched between the substrates so as
to maintain two spaces between the inward main surfaces of the substrates,
and in which the cylindrical surface of the reinforcement disk is exposed
to the outside.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially enlarged sectional view of the outer circuferential
portion of a conventional information recording disk in its radial
direction;
FIG. 2 is a partially enlarged sectional view of the outer circuferential
portion of another conventional information recording disk in its radial
direction;
FIG. 3 is a partially enlarged sectional view of an embodiment of the
optical information recording disk according to the present invention in
its radial direction;
FIGS. 4A through 4F show sectional views of the annular spacers used in the
embodiments of the optical information recording disk according to the
present invention, showing enlarged views thereof in its radial direction;
FIG. 5 is a partially enlarged sectional view of another embodiment of the
optical information recording disk according to the present invention in
its radial direction; and
FIG. 6 is a perspective view of the information recording disk according to
the present invention, showing the same disk of FIG. 6.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Before entering into the explanation of the embodiments of the present
invention, conventional information recording disks will be outlined as
references.
Reference is first made to FIG. 1 which shows a partially enlarged
sectional view for illustrating the structure of the recording disk such
as the DRAW disk described in the above. As shown, this DRAW disk
comprises a pair of transparent substrates 1 and 2 which are formed of
synthetic resins for example, an information bearing layer 3 formed on the
substrate 1, and an adhesive layer 4 combining the substrates 1 and 2 so
that the substrates sandwich the information bearing layer 4 therebetween.
Reference is now made to FIG. 2 which shows a partially enlarged sectional
view for illustrating the structure of another DRAW disk hereinbefore
described. As shown, this DRAW disk comprises a pair of transparent
substrates 1 and 2 which have respectively center bores aligned with each
other and adhered to the annular surfaces of the inner and outer annular
spacers 5a and 5b via adhesive layers 4 and 4 so as to face each other
while maintaining a gap therebetween. An information bearing layer 3 is
formed on the inward main surface of the substrate 1. An inner annular
spacer 5a is aligned with the center bores of the substrates 1 and 2 and
is placed between the inner circumferential portions of the main surfaces
of the substrates 1 and 2. An outer annular spacer 5b is coaxially placed
with the inner annular spacer 5a between the outer circumferential
portions of the main surfaces of the substrates 1 and 2. The outer and
inner annular spacers are respectively provided with the circumferentially
extending grooves at the side surfaces thereof confronting each other. The
spacer has a U-shaped cross-section taken on a surface containing the
central axis thereof. The adhesive layers 4 and 4 are respectively formed
at the inner and outer circumferential portions of the main surfaces of
the substrates 1 and 2. A circular partition 7 is slidably supported by
these inner and outer spacers so that its outer circumference is fitted in
the inward circular groove of the outer annular spacer without using of
any adhesive agent and that its inner circumference is also fitted in the
outward circular groove of the inner annular spacer without using of any
adhesive agent. In this case, the circular partition 7 separates a space 6
existing between the substrates into two spaces. The features and
disadvantages of these conventional DRAW disks have been already
discussed.
Optical recording media according to the present invention will be
hereinafter described with reference to FIG. 3 through FIG. 6.
As shown in FIG. 3, an information recording disk as a double sided disk
according to the present invention is made up of a pair of transparent
disk-shaped substrates 11 and 12 each having a center bore which carry
information bearing layers 13 and 14 respectively thereon. A reinforcement
disk 17 having a center bore is provided with outer annular spacers 15b
and 15b adhered via adhesive layers 18b and 18b onto the outer
circumferential portions of the both main surfaces thereof respectively
and is likewise provided with inner spacers 15a and 15a adhered via
adhesive layers 18a and 18a onto the inner circumferential portion
thereof. Those outer and inner annular spacers form circular bank portions
of those outer and inner circumferences of the reinforcement disk 17,
while the reinforcement disk 17 is sandwiched between the substrates 11
and 12 through adhesive layers 16a, 16a, 16b and 16b which are formed at
the inner and outer circumferential portions of the substrates so that two
spaces 19 and 19 divided by the reinforcement disk are made between inner
main surfaces of the substrates 11 and 12.
In this embodiment as illustrated hereinabove, each of the annular spacers
has a radial cross-section of a rectangle. The annular spacers used in
other modifications may be provided in its radial cross-section with the
various shapes such as shown in FIGS. 4A through 4F, in which FIG. 4A
shows a trapezoid cross-section; FIG. 4B shows a parallelogram
cross-section; FIG. 4C shows a running track-shaped cross-section; FIG. 4D
shows a cross-section of a rectangle dented its oposite sides by oposite
semicircles; FIG. 4E shows a cross-section of a rectangle projected its
side by a triangle; and FIG. 4F shows a cross-section of a rectangle
dented its side by a triangle.
As shown in FIGS. 5 and 6, the second recording disk as a double sided disk
according to the present invention is made up of a pair of transparent
disk-shaped substrates 11 and 12 which carry information bearing layers 13
and 14 respectively thereon, and a reinforcement disk 17 integrally
provided with annular bank portions 17a, 17a, 17b and 17b as two pair of
inner and outer annular spacers at the outer and inner circumferences in
both sides. Each of the annular bank portions has a radial cross-section
of a trapezoid. The cicular bank portion is united with the reinforcement
disk 17 at the bottom thereof by means of the injection moulding method
with using of the same material such a synthetic resin. The inner bank
surface 17c of the annular bank portion is so inclined as to form an
obtuse angle together with the main surface of said renforcement disk (see
FIGS. 5 and 6). Then, the reinforcement disk 17 is sandwiched between the
substrates 13 and 14 through adhesive layers 16a, 16a, 16b and 16b. Each
of the adhesive layers are formed between the surface of the
circumferential portion of the substrate and the top surface of the
annular bank portion, so that the substrates 13 and 14 are firmly fixed to
the reinforcement disk 17 and that two spaces 19 and 19 are made between
inner surfaces of the substrates 13 and 14 respectively.
In these embodiments, the disk-shaped substrates 11 and 12 are made of the
transparent substances such as glass, polycarbonate resins, epoxy resins
and acrylic resins preferably. These materials can be used if smoothness
thereof is sufficient.
Futher, the guide tracks (not shown) may be formed on the substrate by
using the stamper with a guide track and the injection moulding process or
the spin coat process of such a synthetic resin. The guide tracks take the
form of a shallow groove formed coaxially or spirally around the center
bore of the substrate. With the method of the injection moulding process,
the substrate is produced directly, and the guide track is transferred
from the stamper to the substrate at the same time of the formation of the
substrate.
Then, upon the main surfaces of the prepared substrates, the information
bearing layer 13 and 14 are respectively formed by using the optical
recording material e.g. the substance being sublimated by a laser spot. In
the case of the examples shown in FIGS. 3 and 5, each substrate is coated
with the solution of such substance by using the spin coat process. After
that, the substrates are baked or dried for a pertinent period. Thus, the
substrate having the information bearing layer is preferably obtained.
In the first embodiment, the reinforcement disk 17, the substrates 13 and
14 and two pairs of annular spacers 15a, 15a, 15b and 15b are assembled
into a complete DRAW disk. The outer annular spacer 15b has a
predetermined outer diameter equal to the outer diameters of both the
substrate and the reinforcement disk so that the outer cylindrical surface
of the renforcement disk is exposed to the outside. Further, the inner
annular spacer 15a has a predetermined inner diameter equal to the inner
diameter of the center bores of both the substrates and the reinforcement
disk so that these center bores are aligned with the annular spacers and
the inner cylindrical surface of the renforcement disk is exposed to the
outside.
In the second embodiment, on the other hand, the reinforcement disk 17 is
integrated with annular spacers as circular bank portions 17a and 17b at
inner and outer circumferences in both sides. Therefore, it becomes facile
to manufucture the reinforcement disk with the circular bank portions.
When the injection moulding process is utilized in the producing of the
reinforcement disk, the formation of the annular bank portion having the
radially cross-section of a trapezoid is suitable for removing of the
moulded reinforcement disk from its mould, since the inner surface of each
of the annular bank portion is so inclined as to form an obtuse angle
together with the main surface of the renforcement disk. In this case, the
stiffness of the DRAW disk having the thus moulded renforcement disk is
higher than that of the DRAW disk assembled with annular spacers.
In either case, the reinforcement disk 17 and the substrates 11 and 12 are
pasted together with the adhesive agent on the top surface i.e. the
annular surface of the spacer 15 or the bank portion 17a so as to cover up
the information bearing layers 13 and 14 with spacers tightly.
In order to record the information on this recording disk, a laser beam
e.g. having the wave lenght of about 830 nm is irradiated on the thus
prepared recording disk. By the irradiation of the recording laser beam as
a spot, the desired portions of the information bearing layer are
sublimated and as a result a plurality of pits which carry the recording
information are fromed. The read out of the informaiton is preformed by
irradiating a read out laser beam and detecting the differece between the
intensity of the beam reflected from the pits and the intensity of the
beam reflected from the portion without pits.
Thus, according to the present invention, it is easy to produce the
information recording disk, beacuse the reinforcement disk is integrally
formed by the injection moulding process and the adhesive layer is almost
omitted.
The circular partition in the conventional information disk is also omitted
without decreasing the intensity of the disk as well as increasing the
corrosion by the ashesive agent on the information bearing layer.
This is because the simple structure of the recording disk according to the
present invention has a pair of substrates, an information bearing layer
formed on at least one of the substrates, and a reinforcement disk
provided with annular spacers or circular bank portions on its inner and
outer circumferences in both sides. The circular bank portions of the
reinforcement disk are integrally formed as annular spacers. The
reinforcement disk is only sandwiched tightly between the substrates on
the plan surface of the spacer or the bank portion so as to maintain the
information bearing layer in the DRAW disk.
The stiffness of the information recording disk as a DRAW disk is improved
by the use of this reinforcement disk provided with the circular bank
portions each of which has the radial cross-section of a trapezoid.
Furthermore, the stability of the information bearing layer of the DRAW
disk is maintained by the decrease of using amount of the adhesive agent.
The features of the present invention will be maintained advantageously
even if the DRAW disk is formed as a single sided disk.
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