Mold for molding disk, having air passages for blowing compressed air to facilitate removal of molded disk

A mold for molding a disk substrate includes a stationary mold half having a first molding surface and a movable mold half having a second molding surface, which cooperate with each other to define therebetween a mold cavity. Each of at least one of the stationary and movable mold halves has at least one air supply passage for supplying compressed air, and a plurality of air blow passages having respective air inlets in communication with the at least one air supply passage and respective air outlets open to the mold cavity at respective circumferential positions of the mold cavity about a centerline of the mold, for introducing the compressed air from the air supply passage into the mold cavity, to facilitate removal of the molded substrate from the corresponding mold half or halves. The air supply passage and the air blow passages cooperate to provide a plurality of air passages ending at the air outlets which have a substantially same resistance to a flow of the compressed air therethrough.

The present invention is based on Japanese Patent Application No. 8-317325 
filed Nov. 28, 1996, the content of which is incorporated hereinto by 
reference. 
CROSS REFERENCE TO RELATED APPLICATIONS 
Not Applicable. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates in general to techniques associated with a 
mold for molding a disk, more precisely, a substrate of a compact disk 
(CD), a digital video disk (DVD), a magneto-optical disk, a phase-changing 
optical disk, or the like. More particularly, this invention is concerned 
with a mold which is provided with a plurality of air blow passages 
through which a stream of compressed air is introduced into a mold cavity, 
to facilitate removal of a molded disk substrate from the mold. 
2. Discussion of the Related Art 
There have recently been used optical disks and other disks as a data 
storage medium in various fields of the art. Disk substrates used for 
producing these disks are produced by a known mold, for example, by using 
a mold including a stationary mold half and a movable mold half, both of 
which have respective molding surfaces cooperating to define therebetween 
a mold cavity. The stationary and movable mold halves are brought to a 
closed position to define the mold cavity, and a material of the disk 
substrate is injected into the mold cavity. As a result, the disk 
substrate is molded. Then, the stationary and movable mold halves are 
brought to an open position, while the molded disk substrate is retained 
on the molding surface of one of the stationary and movable mold halves. 
The molded disk substrate is removed from the mold half by using a 
suitable mechanism, such as a mechanical ejector and an air blow device. 
Thus, the desired disk substrate is produced. The air-blow device is 
adapted to supply compressed air to the mold cavity for facilitating 
removal of the molded disk substrate from the mold cavity. This device is 
effective not only to aid the mechanical ejector to remove the molded disk 
substrate, but also to prevent local damage or deterioration or local 
sticking of the disk substrate in the process of cooling of the material 
in the mold cavity. Hence, the air blow device is preferably employed. 
The air blow device is generally provided for at least one of the 
stationary and movable mold halves such that an air passage is open on the 
molding surface of the stationary or movable mold half, at two or more 
outlets located at the suitable circumferential positions of the mold 
half. To facilitate the removal of the molded disk substrate from the mold 
half, compressed air is fed into the mold cavity through the air outlets 
open on the molding surface of the mold half. 
An extensive study of the air blow device by the present inventor revealed 
that the quality of the disk substrate is influenced by arrangement of the 
air blow device. Especially, the production. of the disk substrate used 
for a DVD which has a relatively thin thickness in comparison with those 
of a CD and a CD-ROM is significantly influenced by the arrangement of the 
air blow device. For instance, the molded disk substrate suffers from 
bending or buckling due to inadequate air blows, resulting in an increased 
ratio of reject of the molded disk substrate. 
A further study of the known air blow device in an effort to solve the 
above-described problem revealed that a variation of pressure of the 
compressed air injected from the air outlets may cause partial or local 
sticking of the molded disk substrate to the molding surface upon removal 
thereof from the mold half, so that the corresponding local area of the 
molded disk substrate tends to be bent or buckled, and otherwise 
deteriorated. 
SUMMARY OF THE INVENTION 
It is therefore an object of the present invention to provide a mold for 
molding a substrate of a disk, which is capable of producing the disk 
substrate with a desired quality, while preventing occurrence of surface 
deterioration and buckling or other deformation of the substrate due to 
variation of pressure of compressed air applied through the air outlets to 
the molded product. 
The object of the present invention may be achieved according to the 
principle of this invention, which provides a mold for molding a substrate 
of a disk, comprising: a stationary mold half having a first molding 
surface; and a movable mold half movable relative to the stationary mold 
half and having a second molding surface cooperating with the first 
molding surface to define therebetween a mold cavity. Each of at least one 
of the stationary and movable mold halves has at least one air supply 
passage for supplying compressed air and a plurality of air blow passages 
having respective air inlets in communication with the at least one air 
supply passage and respective air outlets open to the mold cavity at 
respective circumferential portions of the mold cavity about a centerline 
of the mold, for introducing the compressed air from the at least one air 
supply passage into the mold cavity, to facilitate removal of the molded 
substrate from the at least one of the stationary and movable mold halves. 
The at least one air supply passage and the air blow passages cooperate to 
provide a plurality of air passages ending at the air outlets. The 
plurality of air passage have a substantially same resistance to a flow of 
the compressed air therethrough. 
In the mold constructed according to the present invention, the pressure of 
the compressed air introduced into the mold cavity through air blow 
passages is effectively made even at the air outlets which are spaced from 
each other in the circumferential direction of the mold cavity or mold. 
That is, the compressed air injected from the air outlets of the plurality 
of air blow passages provides a substantially constant force acting on the 
surface of the molded disk substrate at each of the air outlets, so that 
undesired concentration of the compressed air pressure on local areas of 
the surface of the disk substrate may be effectively eliminated, by 
suitable positioning of the air outlets of the air blow passages, making 
it possible to prevent local sticking of the molded disk substrate to the 
molding surface and bending or buckling of the molded disk substrate. 
The number of the air blow passages is not specifically limited, but is 
preferably four or more. More preferably, these air blow passages are 
disposed such that the air outlets are evenly or equiangularly spaced from 
each other in the circumferential direction about the centerline of the 
mold or mold cavity. 
According to a first preferred form of the present invention, each of the 
above-indicated at least one of the stationary and movable mold halves has 
a circumferential communication channel communicating with an open end of 
each of the at least one air supply passage and the air inlets of the air 
blow passages, for thereby connecting the at least one air supply passage 
to the air blow passages. The air inlets are arranged in a circumferential 
direction of the circumferential communication channel such that the air 
inlets have a same circumferential distance from the open end of one of 
the at least one air supply passage. 
In the mold constructed according to the above first preferred form of the 
present invention, the compressed air supplied through the air supply 
passage or passages is fed to the air blow passages through the 
circumferential communication channel. Described in detail, the air inlets 
at which the air blow passages communicate with the communication channel 
have the same circumferential distance from the open end of one of the at 
least one air supply passage in the circumferential direction of the 
channel. Therefore, all of the air passages ending at the air outlets have 
the same resistance of flow of the compressed air therethrough, whereby 
the pressure of the compressed air injected through the air blow passages 
is made constant at the different air outlets open to the mold cavity. 
The number of the at least one air supply passage connected to the 
communication channel is not specifically limited. If more than three air 
blow passages are formed through the stationary or movable mold half, a 
plurality of air supply passages may be preferably provided in the 
corresponding mold half, and communicate at their open ends with the 
communication channel, such that the open end of each air supply passage 
is spaced from the adjacent air inlets of the air blow passage by the same 
distance in the circumferential direction of the communication channel. 
These air blow passages and the communication channel are dimensioned to 
have the same cross sectional area so that all of the air passages ending 
at the air outlets have the same overall flow resistance. 
In the present first preferred form of the mold, the air inlets of the air 
blow passages may be positioned along the communication channel with 
respect to the open end of each air supply passage such that the air 
inlets adjacent to the open end of one of the at least one air supply 
passage have the same distance from that open end in the circumferential 
direction of the communication channel. This arrangement permits even 
distribution of pressure of the compressed air injected from the air 
outlets of the air blow passages. More preferably, the air inlets of the 
air blow passages and the open ends of the air supply passages are 
positioned along the communication channel such that all of the air inlets 
have the same sum of the circumferential distances from all of the open 
ends of the air supply passages. This arrangement is more effective for 
uniform distribution of pressure of the compressed air at the different 
air outlets of the air blow passages. 
In one advantageous arrangement of the above first preferred form of the 
present invention, the air inlets of the air blow passages are equally 
spaced from each other in the circumferential direction, and the open end 
of each of the at least one air supply passage is located intermediate 
between adjacent ones of the air inlets. 
The air supply passages may communicate with respective divisions of the 
circumferential communication channel which are defined by the air inlets 
of the air blow passages, or alternatively with every other divisions. In 
this arrangement, the air inlets of all the air blow passages have the 
same sum of the circumferential distances from the open end of all the air 
supply passages. Thus, the compressed air is evenly injected through the 
air blow passages with high stability. When an even number of air blow 
passages are provided in the mold half, the open ends of the air supply 
passages may be open at the respective circumferential portions of the 
communication channel defined by the adjacent air inlets, or may be open 
at the every other circumferential portions defined by the adjacent air 
inlets. When an odd number of air blow passages are provided in the mold 
half, on the other hand, the open ends of the air supply passages are open 
at the respective circumferential portions of the communication channel. 
In both cases, the open ends of the air supply passages are equally spaced 
from each other in the circumferential direction of the communication 
channel. 
Preferably, the circumferential communication channel is coaxial with the 
mold cavity, and the air inlets of the air blow passages are equiangularly 
spaced from each other in the circumferential direction of the 
communication channel. In this arrangement, the compressed air may be 
effectively applied to the molded disk substrate, while avoiding a 
variation of the pressure of the compressed air in the circumferential 
direction of the disk substrate. 
According to a second preferred form of the present invention, each of the 
at least one of the stationary and movable mold halves has a 
circumferential communication channel communicating with an open end of 
each of the at least one air supply passage and the air inlets of the air 
blow passages, for thereby connecting the at least one air supply passage 
to the air blow passages, and at least one of the air blow passages has a 
flow restrictor for restricting a flow of the compressed air through each 
of the at least one of the air blow passages. 
In the mold constructed according to the second preferred form of the 
invention described above, the flow resistance of the compressed air of 
each air blow passage having the flow restrictor can be adjusted by means 
of the flow restrictor, relative to that of the other air blow passages. 
The air passages ending at the air outlets of the air blow passages may 
have different air flow resistances due to a difference of the 
circumferential distances between the open end of each air supply passage 
and the air inlets of the air blow passages, and a difference of length of 
the air blow passages. In this case, the overall flow resistance of the 
compressed air flowing through the air supply passage and the air blow 
passages can be adjusted by the flow restrictor or restrictors provided 
for the air blow passage or passages, to compensate for the difference of 
the flow resistance values of the air passages ending at the air outlets. 
Thus, the compressed air can be injected under the same pressure at the 
different air outlets of the air blow passages. 
To more effectively equalize the pressure of the compressed air injected 
through the air blow passages, the flow restrictors are preferably 
provided for all the air blow passages the flow resistances of which are 
different from the nominal value. The flow restrictors can be provided for 
all of the air blow passages, so as to adjust the distribution of the 
compressed air pressure at the air outlets. 
In one advantageous arrangement of the above second preferred form of the 
present invention, the flow restrictor may be manually operable to adjust 
the air flow resistance of the corresponding air blow passage. 
Namely, each flow restrictor may have a predetermined constant air flow 
resistance, but may preferably be arranged to manually operable to adjust 
the flow resistance of the corresponding air blow passage. In the latter 
arrangement, the pressures of the compressed air injected from the air 
blow passages can be effectively controlled, depending upon the specific 
configuration of the air passages. In the former arrangement, the flow 
restrictor for a given air blow passage may be changed to change the air 
flow resistance of that air blow passage. 
According to a third preferred form of the present invention, one of the 
stationary and movable mold halves includes an annular outer stamper 
holder for holding a radially outer portion of an annular stamper to be 
set on one of the first and second molding surfaces which corresponds to 
the one of the stationary and movable mold halves. The annular outer 
stamper holder has the plurality of air blow passages and cooperates with 
a radially outer portion of the one of the first and second molding 
surface to define an annular air chamber to which the air outlets of the 
air blow passages are open. The annular outer stamper holder cooperates 
with an exposed surface of the stamper to define therebetween a 
circumferential clearance communicating with a radially inner end of the 
annular air chamber, whereby the compressed air injected from the air 
outlets into the air chamber is fed to the exposed surface of the stamper 
through the circumferential clearance. 
In the mold constructed according to the third preferred form of the 
present invention, the compressed air is effectively applied to the 
radially outer portion of the surface of the molded disk substrate, 
facilitating the removal of the the molded disk substrate from the 
corresponding mold half, so as to improve the quality of the molded disk 
substrate. That is, the compressed air introduced into the air blow 
passages is fed to the exposed surface of the stamper through the annular 
air chamber partially defined by the annular outer stamper holder, so that 
pressure of the compressed air may be equalized in the circumferential 
direction of the annular stamper. This arrangement is effective to assure 
improved stability in removing the molded disk substrate from the mold, 
with even distribution of the removal force based on the air pressure.

DETAILED DESCRIPTION OF THE PRESENT EMBODIMENT 
Referring first to FIG. 1, there is shown a mold for molding a substrate of 
an optical disk. The mold has a stationary mold half 10 and a movable mold 
half 12. The stationary mold half 10 is attached to a stationary member of 
a mold clamping device (not shown), while the movable mold half 12 is 
attached to a movable member of the mold clamping device. The movable 
member of the mold clamping device is moved toward and away from the 
stationary member, so that the movable mold half 12 is moved toward and 
away from the stationary mold half 10. Thus, the mold has an open position 
and a closed position. 
In the closed position of FIG. 1 in which the stationary and movable mold 
halves 10, 12 are located close to each other, there is defined a mold 
cavity 14 therebetween having a thin-plate shape, for forming the disk 
substrate. That is, the mold cavity 14 is filled with a synthetic resin 
material, which is cooled to be solidified in the mold cavity 14, whereby 
the disk substrate is produced. 
More specifically described, the stationary mold half 10 includes a 
stationary base plate 18 to which are fixed an annular stationary mirror 
block 20 having a relatively large wall thickness and an annular mirror 
surface at its axial end, and an annular stationary abutting block 22 such 
that the stationary mirror block 20 is disposed on a radially center 
portion of one of the opposite axial end faces of the stationary base 
plate 18, while the stationary abutting block 22 is disposed on a radially 
outer or peripheral portion of the corresponding axial end face of the 
stationary base plate 18. The stationary base plate 18 and mirror block 20 
have center bores in which is received an outer bushing 24. The outer 
bushing 24 has a center bore in which is received a sprue bushing 26. The 
inner edge of the axial end of the outer bushing 24 on the side of the 
mirror block 20 serves as a female cutter, which cooperates with a male 
cutter 44 described below, to remove a central portion of the disk 
substrate. 
The stationary mold half 10 has a first molding surface 28, which is 
provided by the mirror surface of the stationary mirror block 20 and the 
corresponding axial end face of the outer bushing 24. Inside the 
stationary base plate 18 and the stationary mirror block 20, there is 
formed a first air passage 30 communicating with an annular gap between 
the contacting surfaces of the stationary mirror block 20 and the outer 
bushing 24. This annular gap opens on the first molding surface 28, so 
that a stream of compressed air which is supplied through the first air 
passage 30 is fed to the first molding surface 28 through the gap. 
The movable mold half 12 includes a movable base plate 32 to which there 
are fixed by screws an annular movable mirror block 34 having a relatively 
large wall thickness and an annular mirror surface at its axial end, and 
an outer stamper holder 36 in the form of a ring, such that the movable 
mirror block 34 is disposed on a radially center portion of one of the 
opposite axial end faces of the movable base plate 32, while the outer 
stamper holder 36 is disposed on a radially outer portion of the 
corresponding axial end face of the movable base plate 32. The outer 
stamper holder 36 has a radially outer annular surface 36a which is in 
contact with the movable base plate 32, and a radially inner annular 
surface 36b which faces the mirror surface of the movable mirror block 34. 
The movable mold half 12 further includes a cylindrical movable abutting 
block 37 having a relatively large wall thickness, which is disposed 
radially outwardly of and fixed to the outer circumferential surface of 
the movable base plate 32. The movable abutting block 37 protrudes from 
the axial end face of the movable base plate 32 toward the stationary mold 
half 10 by a predetermined distance in the axial direction of the movable 
mold half 12. The protruding axial end face of the abutting block 37 abuts 
on the corresponding axial end face of the abutting block 22 when the 
movable mold half 12 is moved toward the stationary mold half 10, so that 
the stationary and movable mold halves 10, 12 are axially positioned 
relative to each other to establish the closed position of the mold. 
The movable base plate 32 and mirror block 34 have center bores in which an 
inner stamper holder 38 having a generally cylindrical shape is 
accommodated and fixed thereto by screws or other suitable fasteners. The 
inner stamper holder 38 has a center bore in which is received a 
stationary guide sleeve 40 fixed to the movable base plate 32. The 
stationary guide sleeve 40 has a center bore in which an ejector sleeve 42 
is slidably movably received so that it is guided by the inner surface of 
the stationary guide sleeve 40. The ejector sleeve 42 has a center bore in 
which is axially slidably received the above-indicated male cutter sleeve 
44, which cooperates with the female cutter (outer bushing 24) of the 
stationary mold half 10 to remove the central portion of the molded disk 
substrate, for thereby forming a center hole in the disk substrate. The 
ejector sleeve 42 and the male cutter sleeve 44 are axially reciprocated 
by a suitable drive mechanism by a predetermined distance. 
The movable mold half 12 has a second molding surface 46, which is provided 
by the annular mirror surface of the movable mirror block 34 and the axial 
end faces of the inner stamper holder 38, stationary guide sleeve 40 and 
ejector sleeve 42 that are disposed radially inwardly of and 
concentrically or coaxially with the movable mirror block 34. Inside the 
abutting block 37, the movable base plate 32 and the stationary sleeve 40, 
there is formed a second air passage 47 communicating with an annular gap 
between the contacting surface of the inner stamper holder 38 and the 
stationary sleeve 40. The annular gap opens on the second molding surface 
46, so that a stream of compressed air supplied through the second air 
passage 47 is fed to the second molding surface 46 through the annular 
gap. 
On the mirror surface of the movable mirror block 34 which partially 
defines the second molding surface 46, there is placed an annular stamper 
48 which has an information bearing surface on which information in the 
form of pits or the like is stored. The stamper 48 is fixed on the second 
molding surface 46 such that the inner and outer peripheries of the 
stamper 48 are clamped by the inner and outer stamper holders 38, 36, 
respectively. More specifically described, the inner stamper holder 38 has 
an integrally formed annular retainer portion 50 at its axial end, which 
extends in the radially outward direction, so that the annular retainer 
portion 50 is disposed opposite to a radially inner peripheral portion of 
the mirror surface of the movable mirror block 34, with a certain axial 
spacing therebetween, for holding the inner periphery of the stamper 48 
onto the mirror surface of the movable mirror block 34. On the other hand, 
the outer stamper holder 36 has an integrally formed annular retainer 
portion 52 extending in the radially inward direction and having the 
radially inner annular surface 36b. The retainer portion 52 is disposed 
opposite to a radially outer peripheral portion of the mirror surface of 
the movable mirror block 34, with a certain axial spacing therebetween, 
for holding the outer periphery of the stamper 48 onto the mirror surface 
of the movable mirror block 34. 
The radially outer portion of the mirror surface of the movable mirror 
block 34, cooperates with the annular retainer portion 52 of the outer 
stamper holder 36 to define an annular air chamber 54 formed therebetween. 
In the radially outer portion of the mirror surface of the movable mirror 
block 34, there is formed a circumferential groove 58. Through the 
abutting block 37, the movable base plate 32 and the movable mirror block 
34, there is formed a third air passage 56 communicating with the 
circumferential groove 58, so that the third air passage 56 is connected 
to the annular air chamber 54 through the circumferential groove 58. The 
opening of the circumferential groove 58 is closed by the radially outer 
portion of the stamper 48, which extends into the air chamber 54, so that 
the stamper 48 is attracted to the second molding surface 46 at its 
radially outer portion by air suction applied thereto through the third 
air passage 56 and circumferential groove 58. 
In the radially outer portion of the axial end face of the movable base 
plate 32, there is formed a circumferential groove 59, which is closed by 
the radially outer annular surface 36a of the outer stamper holder 36, so 
that there is provided a circumferential communication channel 60 which 
extends in the circumferential direction with a constant cross sectional 
area, at an interface between the movable base plate 32 and the outer 
stamper holder 36. Through the movable abutting block 37 and the movable 
base plate 32, there are formed air supply passages in the form of two 
fourth air passages 62 communicating with the communication channel 60, as 
shown in FIG. 2. The outer stamper holder 36 has four air blow passages 
64. Each air blow passage 64 has an air inlet 64a open on the radially 
outer annular surface 36a and an air outlet 64b open on the radially inner 
annular surface 36b. These four air blow passages 64 are spaced from each 
other in the circumferential direction of the outer stamper holder 36, 
such that the air inlets 64a of the air blow passages 64 are open to the 
annular communication channel 60 at the respective four circumferential 
portions, while the air outlets 64b of the air blow passages 64 are open 
to the annular air chamber 54 at the respective four circumferential 
positions. A stream of compressed air supplied through the fourth air 
passages 62 is fed to the air blow passages 64 through the communication 
channel 60 and injected into the air chamber 54 at the respective air 
outlets 64b. The compressed air flows from the air chamber 54 onto the 
information bearing surface of the stamper 48 through a circumferential 
clearance 55 or gap between the outer circumferential surface of the 
stamper 48 and the annular retainer portion 52 of the outer stamper holder 
36. 
A desired disk substrate is produced by molding using the stationary and 
movable mold halves 10, 12 constructed as described above, according to 
the following procedure, for example. Initially, the stamper 48 is fixed 
to the movable mold half 12 by means of the inner stamper holder 38 and 
the outer stamper holder 36, while being attracted to the second molding 
surface 46 by air suction applied thereto through the third air passage 56 
which is connected to a suitable vacuum pump. Then, the movable mold half 
12 is moved toward the stationary mold half 10 to the closed position of 
the mold, to thereby define the mold cavity 14 therebetween. A suitable 
resin material for molding the disk substrate is injected into the mold 
cavity 14 through the sprue bushing 26 disposed in the stationary mold 
half 10 and connected to a nozzle of an injecting device (not shown). 
The resin material injected into the mold cavity 14 is cooled and 
solidified, whereby the desired disk substrate is molded. More 
specifically described, after the mold cavity is filled with the resin 
material, the male cutter sleeve 44 disposed in the movable mold half 12 
is moved toward the stationary mold half 10 and advanced into the center 
bore of the outer bushing 24 serving as the female cutter, whereby a 
center hole is cut in the molded disk substrate. After a predetermined 
period of time has passed, the movable mold half 12 is moved away from the 
stationary mold half 10 with the molded disk substrate fixed thereto. Then 
the ejector sleeve 42 is moved toward the stationary mold half 10 to 
remove the molded disk substrate from the movable mold half 12, whereby 
the desired disk substrate is produced. 
Upon opening the mold after the disk substrate is molded with the mold 
placed in the closed position, the compressed air is fed to the first 
molding surface 28 through the first air passage 30. In this arrangement, 
the molded disk substrate is effectively removed from the stationary mold 
half 10, while it is held on the second molding surface 46 of the movable 
mold half 12. To facilitate removal of the molded disk substrate from the 
movable mold half 12, the compressed air is fed to the second molding 
surface 46 through the second air passage 47, so that a suitable pressure 
is applied to a radially inner portion of the molded disk substrate, 
thereby aiding the ejector sleeve 42 to remove the molded disk substrate. 
In addition, the compressed air supplied through the two fourth air 
passages 62 is fed into the air blow passages 64 through the communication 
channel 60 and is introduced into the annular air chamber 54. The 
compressed air supplied to the annular air chamber 54 is then fed to the 
information bearing surface of the stamper 48, through the clearance 55 
between the annular retainer portion 52 of the outer stamper holder 36 and 
the stamper 48, so that a suitable pressure is applied to the radially 
outer portion of the molded disk substrate, to aid the ejector sleeve 42 
to remove the molded disk substrate. The compressed air supplied through 
the second and fourth air passages 47, 62 may be fed into the mold cavity 
14 not only upon removing the molded disk substrate from the movable mold 
half 12 after the mold is opened, but also upon opening of the mold after 
the material injected into the mold cavity 14 has been solidified to some 
extent. 
Referring next to FIG. 2, there are shown the four air inlets 64a which are 
open at the respective circumferential portions of the radially outer 
annular surface 36a of the outer stamper holder 36, namely, open to the 
annular communication channel 60 at the respective four circumferential 
positions, such that the four air inlet holes 64a are equiangularly spaced 
from each other in the circumferential direction of the radially outer 
annular surface 36a. More specifically described, the four air inlets 64a 
are located at the respective four points of intersection between the 
circumferential communication channel 60 and two straight lines L1 and L2 
which pass a centerline or axis 0 of the mold or mold cavity 14 and which 
are perpendicular to each other, lying in a plane parallel to the first 
and second molding surfaces 28, 46. The two air passages 62 communicate at 
respective open ends 62a thereof with the circumferential communication 
channel 60. The open ends 62a, 62a are located at respective points of 
intersection between the communication channel 60 and a straight line M 
which passes the centerline 0 and which is at 45.degree. with respect to 
the straight lines L1, L2. This straight line M also lies in the 
above-indicated plane. 
In this arrangement, the open ends 62a of the two fourth air passages 62 
are equally spaced from the adjacent air inlets 64a in the circumferential 
direction of the communication channel 60. That is, each of the four air 
inlets 64a is equiangularly spaced by 45.degree. from one of the two open 
ends 62a of the fourth air passages 62, and 135.degree. from the other 
open end 62a, in the opposite circumferential directions. This arrangement 
assures that two air inlets 64a adjacent to the corresponding open end 62a 
has the same sum of distances from the two open ends 62a in the 
circumferential direction of the channel 60. 
In the present arrangement of the two fourth air passages 62, 
circumferential communication channel 60 and four air blow passages 64, 
the compressed air is delivered to the air outlets 64b of the four air 
blow passages 64 over the same total flow distance, and with the same flow 
resistance. 
Therefore, the compressed air supplied through the air passages 62, 64 is 
fed to the radially outer portion of the molded disk substrate at a 
constant air pressure at the four air outlets 64b, at which the four air 
blow passages 64 are open to the annular air chamber 54 at the respective 
circumferential positions of the radially inner surface 36b of the outer 
stamper holder 36. The compressed air is evenly and stably applied to the 
surface of the disk substrate, so that pressure concentration on 
particular local areas of the surface of the disk substrate is effectively 
avoided, resulting in preventing partial sticking of the molded disk 
substrate to the stamper 48 and bending or buckling of the molded disk 
substrate. 
In the present embodiment, the compressed air which is evenly introduced 
from the four air blow passages 64 into the annular air chamber 54, is fed 
to the information bearing surface of the stamper 48 through the 
circumferential clearance 55. Thus, the compressed air can be uniformly 
applied to the molded disk substrate over its entire circumference, so 
that the partial sticking and bending of the molded disk substrate are 
more effectively prevented. 
While the first preferred embodiment of the present invention described 
above is provided with the two fourth air passages 62 and the four air 
blow passages 64, the number of these elements is not specifically 
limited. For instance, four fourth air passages 62 may be provided in the 
movable mold half 12 such that the open ends 62a of the four fourth air 
passages 62 are located at the respective circumferential positions of the 
circumferential communication channel 60, as shown in FIG. 3. Namely, the 
open ends 62a of the four passages 62 are located at respective four 
points of intersection between the circumferential communication channel 
60 and two mutually perpendicular straight lines M1 and M2 which pass the 
centerline 0 and which are at 45.degree. with respect to the straight 
lines L1 and L2. This arrangement has substantially the same advantages as 
described above with respect to the first embodiment. 
Referring next to FIG. 4, there is shown a part of a mold for molding a 
substrate of an optical disk, which mold is constructed according to the 
second embodiment of the present invention. The mold of the second 
embodiment has the same construction as the mold of the first embodiment, 
except the part illustrated in FIG. 4. 
The mold of the present embodiment includes the movable hold half 12 
wherein the outer stamper holder 36 has four air blow passages 64 formed 
therethrough, such that air inlets 64a are open in the radially outer 
annular surface 36a, while the air outlets 64b are open in the radially 
inner annular surface 36b. To the air inlets 64a, there are screwed flow 
restrictors 66, respectively. Each flow restrictor 66 has a restrictor 
passage 68 which extends in the axial direction of the mold and has a 
cross sectional area which is smaller than that of the corresponding air 
blow passage 64, as shown in FIG. 4. The compressed air supplied to the 
communication channel 60 is fed to the respective air blow passages 64 
through the respective restrictor passages 68. 
In the mold of the second embodiment, the pressure of the compressed air 
introduced to the annular air chamber 54 through each air blow passage 64 
is preferably adjusted or changed by selecting the flow restrictor 66, the 
restrictor passage 68 of which has a suitable cross sectional area. 
The mold of the present embodiment is capable of adjusting the flow 
resistance of the air passages from the fourth air passages 62 to the air 
outlets 64b, by selecting the appropriate flow restrictors 66 attached to 
the air inlets 64a. Thus, the compressed air can be evenly injected from 
the air outlets 64b at a constant pressure into the annular air chamber 
54, thereby providing the same advantages as in the first embodiment, such 
as prevention of the local sticking and bending of the molded disk 
substrate, even where only one fourth air passage 62 is provided as shown 
in FIG. 5. 
In the arrangement of FIG. 5, the air inlets 64a of the four air blow 
passages 64 are open to the circumferential communication channel 60 at 
the respective circumferential positions. On the other hand, the single 
fourth air passage 64 is open to the communication channel 60, at its open 
end 62a positioned intermediate between the adjacent air inlets 64a-1 and 
64a-2 in the circumferential direction of the communication channel 60 as 
shown in FIG. 5. In this case, the circumferential distance between the 
open end 62a of the passage 62 and the air inlets 64a-3, 64a-4 which are 
not adjacent to the open end 62a is longer than that between the open end 
62a and the adjacent air inlets 64a-1, and 64a-2. Thus, the flow 
resistance of the air passages connecting the open end 62a and the air 
inlets 64a-3 and 64a-4 (hereinafter referred to as "second air passages") 
is larger than that of the air passages connecting the open end 62a and 
the air inlet holes 64a-1 and 64a-2 (hereinafter referred to as "first air 
passages"), due to the dimensional difference between these first and 
second air passages. The difference of the flow resistance between the 
first and second air passages may cause a pressure difference of the 
compressed air injected through the first and second air passages. To 
avoid this difference of pressure of the compressed air, the flow 
restrictors 66 are provided at the air inlets 64a-1 and 64a-2 which are 
closer to the open end 62a than the other air inlets 64a-3 and 64a-4 in 
the circumferential direction of the communication channel 60. Each flow 
restrictor 66 has a suitable flow resistance, so that the first and second 
air passages have the same flow resistance. 
In the embodiment of FIG. 4, the movable mirror block 34 has an annular 
cutout 69 at the outer peripheral portion of the mirror surface. In other 
words, the outer peripheral portion of the mirror surface of the movable 
mirror block 34 is recessed to form an annular recess 69 having a depth in 
the axial direction of the mold. The stamper 48 is placed on the mirror 
surface of the movable mirror block 34 such that the outer periphery of 
the stamper 48 is positioned just above the annular cutout or recess 69. 
In this arrangement, the mirror surface of the movable mirror block 34 is 
effectively prevented from being scratched or damaged by burrs which may 
be formed on the outer periphery of the stamper 48, during manufacture of 
the stamper 48. 
The use of the flow restrictors 66 permits the compressed air to be 
injected into the air chamber 54 under a substantially constant pressure 
at the air outlets 64b of the air blow passages 64. Moreover, the flow 
restrictors 66 may be used to deal with a change in the flow resistance of 
the air passages involved, which change occurs for some reason or other. 
While the open end 62a of the single fourth air passage 62 and the air 
inlets 64a-1, 64a-2, 64a-3, 64a-4 of the four air blow passages 64 are 
open to the communication channel 60 at the appropriate circumferential 
portions of the communication channel 60, in the present embodiment, the 
numbers of these elements 62, 64 may be suitably selected. In the 
embodiment of FIGS. 4 and 5, the flow restrictors 66 are provided at the 
respective air inlets 64a-1 and 64a-2 which are adjacent to the open end 
62a of the fourth air passage 62, so as to adjust the flow resistances at 
these air inlets 64a-1 and 64a-2, on the basis of the flow resistances at 
the air inlets 64a-3 and 64a-4 which are remote from the open end 62a. 
However, the air inlets at which the flow restrictors 66 are provided may 
be suitably selected. Further, the flow restrictors 66 may be provided for 
all air inlets 64a. 
While the present invention has been described in detail in its presently 
preferred embodiments by reference to the accompanying drawings, for 
illustrative purpose only, it is to be understood that the invention is 
not limited to the detail of the illustrated embodiments. 
While the principle of the present invention is applied to the air passages 
62, 64 for applying air pressure to the radially outer portion of the 
molded disk substrate for facilitating the removal of the disk substrate 
from the movable mold half 12, in the illustrated embodiments, the 
principle of the present invention may be applied to air passages for 
applying the air pressure to a radially inner portion of the molded disk 
substrate. Further, the present invention may be applied to such air 
passages formed through the stationary mold half 10 for applying the air 
pressure to a desired portion of the molded disk substrate through a 
plurality of air outlets, for facilitating the removal of the disk 
substrate. 
In the second embodiment, the flow resistance of the air passages 64 is 
adjustable by using the appropriate flow restrictors at the air inlets 
64a. However, the individual air passages may be formed with suitable 
cross sectional areas and lengths, so that the pressure of injection of 
the compressed air into the mold cavity 14 is substantially constant at 
all of air outlets which are suitably arranged in the circumferential 
direction of the mold. The flow restrictors 66 may be replaced by flow 
restrictors 70 illustrated in FIG. 6, each of which is screwed in the 
outer stamper holder 36 such that the axial end of the flow restrictor 70 
partially defines the corresponding air blow passage 64. In this 
embodiment of FIG. 6, the cross sectional area of each air blow passage 64 
can be adjusted by changing the amount of protrusion of the flow 
restrictor 70 into the air blow passage 64. Thus, the flow restrictor 70 
is manually operable to change the resistance to the air flow through the 
air blow passage 64. 
It is to be understood that the present invention may be embodied with 
various other changes, modifications and improvements, which may occur to 
those skilled in the air, in the light of the foregoing teachings, without 
departing from the spirit and scope of the invention defined in the 
following claims.