Optical disc having indication portion

An optical disc is provided with: a disc substrate of light transmissive type having an information record surface including an information recorded region, where pits or grooves carrying an information signal are coaxially or spirally formed, and an information not-recorded region, where the pits or grooves carrying the information signal are not formed; a light reflective layer wholly disposed on the information record surface in the information recorded region, and partially disposed on the information record surface in the information not-recorded region such that an indication pattern is formed of the partially disposed light reflective layer on the information record surface in the information not-recorded region; and a protection layer disposed on the light reflective layer and a portion of the information record surface in the information not-recorded region where the light reflective layer is not disposed.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention generally relates to an optical disc, and more 
particularly to an optical disc, on which an indication of visible 
information is provided at the disc surface. 
2. Description of the Related Art 
An optical disc, e.g. a video disc and a digital audio disc, has such a 
construction that fine concave and convex portions, which are so-called as 
"pits" to carry the information signal, are coaxially or spirally formed 
along a predetermined signal track at one surface (i.e. an information 
record surface) of a resin substrate of light transmissive type and are 
covered with a light reflective layer, and that the information signal of 
the pits are optically reproduced by irradiating the optical disc with a 
reading light beam from the other surface of the resin substrate. 
There is a method of providing a visible information onto the disc surface 
of the optical disc of this type, in related arts e.g. Japanese Patent 
Laid Open NO. Sho 58-100235. In this related art, characters, marks, the 
number etc. of the optical disc are recorded, as the indication portion on 
the disc surface, in the information not-recorded region, which is located 
at the inner circumferential area of the disc surface. 
During the step of light-exposing a glass original disc coated with 
photo-resist by a light beam which is modulated in accordance with the 
information signal to make the information recorded region, those 
characters, marks etc., are formed by light-exposing the information 
not-recorded region at the inner circumferential area of the disc surface 
by the light beam which is modulated in accordance with the characters, 
marks etc. to be indicated. This light-exposed glass original disc is 
developed. Then, a stamper is formed by nickel-electric-molding the 
developed disc. The composite resin of light transmissive type is 
injection-molded by use of this stamper. Finally, the light reflective 
layer and the protection layer are successively formed on the formed 
composite resin substrate, so that the optical disc is produced. The 
characters, the marks, etc. are indicated as the shapes of the portions 
where the pits or grooves exist. 
However, the indication portion of such characters, marks, etc., are 
visible by the light diffraction, the light interference, the light 
scattering of the light as the shapes of the portions where the pits or 
grooves exist, relative to the portions where the pits or grooves do not 
exist (i.e. the mirror finished surface). Thus, the contrast (i.e. the 
difference in the light intensity of the light sensed by a human eye) is 
rather little, and the indication clearness runs short, which is the 
problem. Further, the indication portion is the information not-recorded 
portion of the optical disc at the inner circumferential area thereof, the 
size of the indication portion is limited and rather small, so that it is 
difficult to visually recognize the content of the indication portion if a 
large amount of information is formed to be indicated. Furthermore, it is 
also difficult to make an indication of a picture or drawing in the 
indication portion. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide an optical 
disc having an indication portion and a method of forming such an 
indication portion of the optical disc, which can improve the contrast of 
the indication portion of the disc surface. 
The above object of the present invention can be achieved by a first 
optical disc provided with: a disc substrate of light transmissive type 
having an information record surface including an information recorded 
region, where pits or grooves carrying an information signal are coaxially 
or spirally formed, and an information not-recorded region, where the pits 
or grooves carrying the information signal are not formed; a light 
reflective layer wholly disposed on the information record surface in the 
information recorded region, and partially disposed on the information 
record surface in the information not-recorded region such that an 
indication pattern is formed of the partially disposed light reflective 
layer on the information record surface in the information not-recorded 
region; and a protection layer disposed on the light reflective layer and 
a portion of the information record surface in the information 
not-recorded region where the light reflective layer is not disposed. 
According to the first optical disc of the present invention, a disc 
substrate of light transmissive type has an information record surface 
including an information recorded region, where pits or grooves carrying 
an information signal are coaxially or spirally formed, and an information 
not-recorded region, where the pits or grooves carrying the information 
signal are not formed. A light reflective layer is wholly disposed on the 
information record surface in the information recorded region, and 
partially disposed on the information record surface in the information 
not-recorded region such that an indication pattern is formed of the 
partially disposed light reflective layer on the information record 
surface in the information not-recorded region. A protection layer is 
disposed on the light reflective layer and a portion of the information 
record surface in the information not-recorded region where the light 
reflective layer is not disposed. Accordingly, since the indication 
pattern is formed by the existence and non-existence of the light 
reflective layer in the information not-recorded region, the contrast of 
the indication pattern is quite high. 
In one aspect of the first optical disc of the present invention, pits or 
grooves carrying a dummy signal are coaxially or spirally formed on the 
information record surface in the information not-recorded region. In this 
case, by the light diffraction, light interference, light scattering etc. 
of the light due to the pits or grooves which are coaxially or spirally 
formed and carry the dummy signal, the indication portion can be seen in 
rainbow color etc., to improve the visual effect of the indication 
portion. On the other hand, a highly contrasty indication portion can be 
obtained by leaving the information not recorded region in the mirror 
finished surface condition without forming the pits or grooves carrying 
the dummy signal. 
As another aspect of the first optical disc of the present invention, the 
information recorded region is located at an inner circumferential side of 
the information not-recorded region. In this case, by recording the 
information signal from the inner circumferential side toward the outer 
circumferential side of the optical disc, a relatively large indication 
portion can be formed by use of the information not-recorded region 
located at the vicinity of the outer circumferential side of the optical 
disc. 
As another aspect of the first optical disc of the present invention, the 
disc substrate comprises resin, and the light reflective layer comprises 
metal. In this case, a high contrast of the indication portion can be 
obtained by virtue of the difference in optical properties between the 
resin and the metal. 
The above object of the present invention can be also achieved by a second 
optical disc provided with a first disc body, a second disc body which are 
coaxially disposed, and a bonding layer interposed between the first and 
second disc bodies for bonding the first and second disc bodies to each 
other. The first disc body is provided with: a first disc substrate of 
light transmissive type having a first information record surface 
including an information not-recorded region, where pits or grooves 
carrying the information signal are not formed; a first light reflective 
layer partially disposed on the first information record surface in the 
information not-recorded region such that an indication pattern is formed 
of the partially disposed first light reflective layer on the first 
information record surface in the information not-recorded region; and a 
first protection layer disposed on the first light reflective layer and a 
portion of the first information record surface in the information 
not-recorded region where the first light reflective layer is not formed. 
The second disc body is provided with: a second disc substrate of light 
transmissive type having a second information record surface including an 
information recorded region, where the pits or grooves carrying the 
information signal are coaxially or spirally disposed; a second light 
reflective layer wholly disposed on the second information record surface 
in the information recorded region; and a second protection layer disposed 
on the second light reflective layer. The first and second disc bodies are 
bonded by the bonding layer such that the first and second protection 
layers are opposed to each other. 
According to the second optical disc of the present invention, since the 
indication pattern is formed by the existence and non-existence of the 
light reflective layer in the information not-recorded region of the first 
disc body which is used exclusively for indicating the indication pattern, 
and since the second disc body is exclusively used for recording the 
information signal, the contrast of the indication pattern is quite high. 
At the same time, the size of the indication pattern can be made quite 
large at the side of the first disc body of the second optical disc. 
In one aspect of the second optical disc of the present invention, pits or 
grooves carrying a dummy signal are coaxially or spirally formed on the 
information record surface in the information not-recorded region. Thus, 
the indication portion can be seen in rainbow color etc., to improve the 
visual effect of the indication portion. 
The nature, utility, and further features of this invention will be more 
clearly apparent from the following detailed description with respect to 
preferred embodiments of the invention when read in conjunction with the 
accompanying drawings briefly described below.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to the accompanying drawings, an embodiment of the present 
invention will be now explained. 
First Embodiment 
FIG. 1 is a cross sectional view of a first embodiment of the present 
invention. 
In FIG. 1, an optical disc 1 is provided with a disc substrate 11 of light 
transmissive type, which comprises composite resin such as 
polymethylmethacrylate, polycarbonate, etc. The disc substrate 11 has an 
information recorded region 13, on which pits or grooves 12 for carrying 
an information signal are coaxially or spirally formed at one surface 
(i.e. an information record surface) thereof, and an information 
not-recorded region 15, where pits or grooves 14 for carrying a dummy 
signal are coaxially or spirally formed on the information record surface. 
The optical disc 1 is also provided with a light reflective layer 16. The 
light reflective layer 16 made of metal thin film comprising aluminum, 
aluminum alloy, gold, etc., is formed wholly on the information recorded 
region 13. On the contrary, the light reflective layer 16 is formed only 
partially on the information not-recorded region 15. Namely, on the 
information not-recorded region 15, the indication portion is formed by 
the pattern of the portion where the light reflective layer 16 is not 
formed or by the pattern of the portion where the light reflective layer 
16 is formed. The optical disc 1 is further provided with a protection 
layer 17, which is made from resin of the ultra-violet ray hardening type, 
and is formed on the upper surface of the light reflective layer 16 and 
the upper surface of the disc substrate 11 where the light reflective 
layer 16 is not formed. 
FIG. 2 is a surface plane view of the optical disc 1 of FIG. 1, from the 
side of the disc substrate 11. 
In FIG. 2, the information signal is recorded from the inner 
circumferential side toward the outer circumferential side of the optical 
disc 1. If there is only little amount of the information to be recorded, 
a relatively large empty region (i.e. the information not-recorded region) 
remains. In such a case, a large enough indication portion can be formed 
by use of the information not-recorded region at the outer circumferential 
area of the optical disc 1 as shown in FIG. 2. In FIG. 2, the character 
"A" is indicated in the information not-recorded region 15 by the 
indication portion as the pattern of the light reflective layer 16 on the 
substrate 11. In addition, if there is a large amount of information to be 
recorded so that the outer empty space is rather narrow, the indication 
portion may be formed in an information not-recorded region 18 at the 
inner circumferential area of the optical disc 1. Further, it is possible 
to improve the visual effect in such a manner that the indication portion 
can be visually rainbow-colored due to the light diffraction, the light 
interference, the light scattering, etc., by forming coaxially or spirally 
the pits or grooves 14 carrying the dummy signal at the information 
not-recorded regions 15 and/or 18 of the disc substrate 11. It goes 
without saying that a highly contrasty indication portion can be obtained 
by leaving the information not recorded regions 15 and/or 18 of the disc 
substrate 11 in the mirror finished surface condition without forming the 
pits or grooves 14 carrying the dummy signal thereat. 
Nextly, the method of producing the optical disc 1 will be explained with 
referring to FIG. 3. 
As shown in FIG. 3A, the disc substrate 11 is prepared which is made from 
composite resin and which has the information recorded region 13, where 
the pits or grooves 12 carrying the information signal are coaxially or 
spirally formed, and the information not-recorded region 15, where the 
pits or grooves 14 carrying the dummy signal are coaxially or spirally 
formed, on one surface (i.e. the information record surface) of the disc 
substrate 11. A mask 19, which has an aperture corresponding to the 
indication pattern of the characters, the marks, the graphics etc. to be 
indicated, is disposed over the information not-recorded region 15 of the 
disc substrate 11. Then, metal such as aluminum, aluminum alloy, gold 
etc., is deposited through the mask 19 onto the information record surface 
of the disc substrate 11 by means of vapor deposition or sputtering 
technique. 
As shown in FIG. 3B, the light reflective layer 16 made of metal thin film 
is formed wholly on the surface of the information recorded region 13. On 
the contrary, the light reflective layer 16 is partially formed on the 
surface of the information not-recorded region 15 in correspondence with 
the indication pattern of the mask 19. 
Then, as shown in FIG. 3C, the ultra-violet ray hardening type resin is 
spinner-coated and the protection layer 17 is formed on the light 
reflective layer 16 and at a portion of the disc substrate 11 where the 
light reflective layer 16 is not formed, so that the optical disc 1 of the 
present embodiment is produced. 
Second Embodiment 
FIG. 4 is a cross sectional view of a second embodiment of the present 
invention. 
In FIG. 4, an optical disc 2 is provided with two disc bodies 21 and 22, 
each of which is single side recording and reproducing type and which are 
bonded together through bonding agent layer 23 of hot melt type, in such a 
manner that the protection layers 17 and 17 are opposed to each other. The 
disc body 21 is provided with a disc substrate 24 of light transmissive 
type, which comprises composite resin such as polymethylmethacrylate, 
polycarbonate, etc. All over the information not-recorded region 15 of the 
disc substrate 24, the pits or grooves 14 for carrying the dummy signal 
are coaxially or spirally formed. Namely, the pits or grooves 12 for 
carrying the information signal are not formed at all on the disc body 21. 
The disc body 21 is also provided with the light reflective layer 16. The 
light reflective layer 16 made of metal thin film is only partially formed 
on the surface of the disc substrate 24 in accordance with the indication 
pattern such as characters, marks, graphics, etc. Namely, the indication 
portion is formed by the pattern of the portion where the light reflective 
layer 16 is not formed or by the pattern of the portion where the light 
reflective layer 16 is formed, on the disc body 21. The disc body 21 is 
further provided with the protection layer 17, which is made from resin of 
the ultra-violet ray hardening type, and is formed on the light reflective 
layer 16 and the disc substrate 24 where the light reflective layer 16 is 
not formed. 
On the other hand, the disc body 22 is provided with a disc substrate 25 of 
light transmissive type, which comprises composite resin such as 
polymethylmethacrylate, polycarbonate, etc. On the disc substrate 25, the 
pits or grooves 12 for carrying the information signal are coaxially or 
spirally formed at the information record surface 13 thereof. The disc 
body 22 is also provided with the light reflective layer 16. The light 
reflective layer 16 made of metal thin film is formed wholly on the 
information recorded region 13 of the disc substrate 25. The disc body 22 
is further provided with the protection layer 17, which is made from resin 
of the ultra-violet ray hardening type, and is formed on the light 
reflective layer 16. 
In this manner, while the first embodiment is constructed as an optical 
disc of single substrate type and single side recording and reproducing 
type, the second embodiment is constructed as an optical disc of double 
substrate type and single side recording and reproducing type, in which 
the information signal is recorded to only one of the two surfaces of the 
optical disc. The indication portion is exclusively formed onto the disc 
body 21, to which the information signal is not recorded, by the pattern 
of the portion where the light reflective layer 16 is not formed or by the 
pattern of the portion where the light reflective layer 16 is formed as 
shown in FIG. 5. Namely, since the whole one surface of the disc body 21 
is exclusively used for the indication portion, a large sized indication 
portion, which indicates "A" as shown in FIG. 2, can be obtained and, for 
example, a picture or drawing can be indicated by use of this indication 
portion. It goes without saying that a highly contrasty indication portion 
can be achieved by leaving the information record surface of the disc 
substrate 24 in the mirror finished surface condition without forming the 
pits or grooves 14 carrying the dummy signal. 
Third Embodiment 
FIG. 6 is a cross sectional view of a third embodiment of the present 
invention. 
In FIG. 6, an optical disc 3 is provided with two disc bodies 1a and 22a, 
each of which is single side recording and reproducing type and which are 
bonded together through bonding agent layer 23 of hot melt type, in such a 
manner that the protection layers 17 and 17 are opposed to each other. The 
disc body 1a has the same construction as the optical disc 1 of the first 
embodiment of FIG. 1. The disc bodies 22a has the same construction as the 
disc body 22 of the second embodiment of FIG. 4. 
Thus, while the first embodiment is constructed as an optical disc of 
single substrate type and single side recording and reproducing type, the 
third embodiment is constructed as an optical disc of double substrate 
type and both side recording and reproducing type, in which the 
information signal is recorded to both of the two surfaces of the optical 
disc 3. The indication portion is formed onto the disc body 1a at the 
information not-recorded portion, by the pattern of the portion where the 
light reflective layer 16 is not formed or by the pattern of the portion 
where the light reflective layer 16 is formed. Accordingly, the amount of 
information signals can be significantly large as compared with the first 
and second embodiments. It goes without saying that a highly contrasty 
indication portion can be achieved by leaving the information record 
surface of the disc substrate 11 in the information not-recorded region 15 
in the mirror finished surface condition without forming the pits or 
grooves 14 carrying the dummy signal. 
Fourth Embodiment 
FIG. 7 is a cross sectional view of a fourth embodiment of the present 
invention. 
In FIG. 7, an optical disc 4 is provided with two disc bodies 1a and 1b, 
each of which is single side recording and reproducing type and which are 
bonded together through bonding agent layer 23 of hot melt type, in such a 
manner that the protection layers 17 and 17 are opposed to each other. 
Each of the disc bodies 1a and 1b has the same construction as the optical 
disc 1 of the first embodiment of FIG. 1. 
Thus, while the first embodiment is constructed as an optical disc of 
single substrate type and single side recording and reproducing type, the 
fourth embodiment is constructed as an optical disc of double substrate 
type and both side recording and reproducing type, in which the 
information signal is recorded to both of the two surfaces of the optical 
disc 4. The indication portion is formed onto each of the disc bodies 1a 
and 1b at the information not-recorded portions respectively, by the 
pattern of the portion where the light reflective layer 16 is not formed 
or by the pattern of the portion where the light reflective layer 16 is 
formed. It goes without saying that a highly contrasty indication portion 
can be achieved by leaving the information record surface in the 
information not-recorded region 15 of the disc body 1a and/or 1b in the 
mirror finished surface condition without forming the pits or grooves 14 
carrying the dummy signal. 
As described above in detail, since the indication pattern is formed by the 
existence and non-existence of the light reflective layer 16 in the 
information not-recorded region, the contrast, the clearness and the 
distinctness of the indication pattern is quite highly improved according 
to the present embodiments. Especially, according to the second 
embodiment, since one disc surface is exclusively used for indicating the 
indication pattern, the indication portion of large size is realized as 
shown in FIG. 5. Especially, according to the third and fourth 
embodiments, since both side recording and reproducing operation is 
available, the information signal of large volume can be recorded and 
reproduced, while the contrast, the clearness and the distinctness of the 
indication pattern is high. 
The invention may be embodied in other specific forms without departing 
from the spirit or essential characteristics thereof. The present 
embodiments are therefore to be considered in all respects as illustrative 
and not restrictive, the scope of the invention being indicated by the 
appended claims rather than by the foregoing description and all changes 
which come within the meaning and range of equivalency of the claims are 
therefore intended to be embraced therein.