Process for producing a roll stamper for molding a substrate sheet for information recording mediums

A process for producing a roll stamper which molds a substrate sheet for information recording mediums by continuously transferring preformat patterns on a resin sheet. The roll stamper has the feature that the preformat pattern on the roll stamper has a value b/a of greater than 1, where the length of the preformat pattern in the direction parallel to the direction in which the resin sheet is transported is defined as a and the length in the direction perpendicular thereto as b.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a roll stamper for continuously producing 
substrates for information recording mediums by forming preformats on a 
resin sheet. It also relates to a process for producing the roll stamper. 
2. Related Background Art 
Preformats such as track grooves or address pits are formed on substrates 
for information recording mediums such as optical disks. As a method of 
continuously mass-producing such substrates, Japanese Patent Application 
Laid-open No. 56-86721 discloses a method in which a thermoplastic 
synthetic resin sheet is heated and softened using an infrared lamp and 
thereafter signals in the form of grooves or pits are transferred using a 
molding roll. 
The roll stamper used in such a method is prepared by sticking a flat-plate 
thin stamper on a mirror-finished roll substrate with an adhesive or the 
like or mechanically fastening the stamper on the substrate by means of a 
jig or the like, or by directly forming a preformat pattern on the body of 
a roll substrate. 
As the preformat pattern formed on the roll stamper, a preformat pattern 
similar to those used in conventional methods is used in which the 
substrate is formed sheet by sheet as in the injection process, the 
compression process and the photopolymerization process (hereinafter "2P 
process"), which pattern is substantially circular, for example, in the 
case of a disk. 
With regard to the accuracy of the preformat pattern provided on the 
stamper used in the conventional injection process, compression process or 
2P process, tracking errors tend to occur unless a deviation from a circle 
is controlled to be not more than 100 .mu.m in the case of the disk. 
When preformats are, however, continuously formed on a resin sheet, a 
relatively large pressure is applied to the roll stamper or a shrinkage 
may occur with the cooling of resin, in the direction perpendicular to the 
direction in which the resin sheet is transported. Hence, in the case 
where the roll stamper on which the above substantially circular pattern 
has been formed is used, there is the problem that the preformat 
transferred onto the resin sheet causes a lowering of transfer accuracy, 
specifically, a lowering of the circularity or roundness. In particular, 
in the case of recording mediums like optical disks on which fine patterns 
are formed and information with a high density is recorded and reproduced, 
the lowering of the roundness may cause errors such as tracking-off. 
SUMMARY OF THE INVENTION 
The present invention was made taking into account the above problems. An 
object of the present invention is to provide a roll stamper used for 
molding a substrate sheet for information recording mediums, that can 
accurately form preformats in a continuous manner on a resin sheet, and a 
process for producing such a stamper. 
Another object of the present invention is to provide a process for 
producing a substrate sheet for information recording mediums, that can 
obtain an information recording medium substrate sheet on which preformats 
have been accurately formed. 
The roll stamper of the present invention for molding a substrate sheet for 
information recording mediums is a roll stamper which molds a substrate 
sheet for information recording mediums by continuously transferring 
preformat patterns on a resin sheet, wherein the preformat pattern on the 
roll stamper has a value of b/a of greater than 1 when the length of the 
preformat pattern in the direction parallel to the direction in which the 
resin sheet is transported is defined as a and the length in the direction 
perpendicular thereto as b. 
The process of the present invention for producing a substrate sheet for 
information recording mediums comprises continuously transferring 
preformat patterns on a resin sheet by the use of a roll stamper, wherein 
the preformat pattern on the roll stamper has a value of b/a of greater 
than 1 when the length of the preformat pattern in the direction parallel 
to the direction in which the resin sheet is transported is defined as a 
and the length in the direction perpendicular thereto as b. 
The process for producing the roll stamper of the present invention is a 
process for producing a roll stamper which molds a substrate sheet for 
information recording mediums by continuously transferring preformat 
pattern on a resin sheet, comprising the steps of; 
a) while an original plate having thereon a photoresist layer is rotated at 
a given number of revolutions per minute, vibrating a cutting head for 
cutting a pattern on the photoresist layer, corresponding to the preformat 
pattern, or vibrating the original plate, at a frequency twice the given 
number of revolutions per minute the original plate and in the diameter 
direction of the original plate, thereby cutting said pattern on the 
photoresist layer, followed by development to form a resist pattern in 
which each track is elliptical and which has an elliptical shape having a 
value of b/a of greater than 1 when the length of the minor axis is 
defined as a and the length of the major axis as b, at the outermost 
track; 
b) carrying out electroforming on the resist pattern to form a stamper 
having the preformat pattern; and 
c) fixing the stamper to a roll substrate in such a manner that the minor 
axis direction of said pattern is in accordance with the direction in 
which the resin sheet is transported. 
In this way the size of a preformat pattern is deviated from its standard 
shape in a specific range. It is thus possible to compensate the 
deformation of a preformat transferred onto a resin sheet, caused by the 
elongation of a stamper that may occur when a pattern is transferred onto 
a resin sheet and by the shrinkage due to cooling on the resin sheet, so 
that a very accurate preformat pattern can be formed on the resin sheet.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The roll stamper of the present invention for molding a substrate sheet for 
information recording mediums will be described below in detail with 
reference to the drawings. 
FIG. 1 diagramatically illustrates a preformat pattern 11 formed on the 
stamper of the present invention. In FIG. 1, the letter symbol a 
represents the diameter in the direction parallel to the direction in 
which a resin sheet is transported, corresponding to the diameter of the 
outermost track of a pattern formed on the stamper. The letter symbol b 
represents the diameter of this pattern in the direction perpendicular to 
the direction in which the resin sheet is transported. The roll stamper of 
the present invention is characterized in that the value of b/a (the value 
of b divided by a) is greater than 1. 
In this way a difference is given in the size ratio between the preformat 
pattern formed on the roll stamper and the standard shape of the preformat 
to be transferred to the resin sheet. It is thus possible to compensate 
for the deformation of a preformat pattern transferred onto a resin sheet, 
caused by the elongation of a stamper that may occur when the resin sheet 
and the stamper are brought into contact and by the shrinkage of the resin 
sheet, so that a preformat pattern can be very accurately formed on the 
resin sheet. 
In the roll stamper of the present invention, the relation between a and b 
should satisfy the following expression (1), and, particularly when the 
preformat is formed on a molten resin sheet, should preferably satisfy the 
following expression (2). 
EQU 0.05.ltoreq.(b-a)/a.times.100.ltoreq.2 (1) 
EQU 0.1.ltoreq.(b-a)/a.times.100.ltoreq.1 (2) 
Use of the stamper that satisfies the relation represented by the above 
expression makes it possible to particularly minimize the deformation of a 
preformat pattern transferred onto the resin sheet, caused by the 
elongation of a stamper that may occur when the preformat is transferred 
onto the resin sheet and by the shrinkage of the resin sheet that may 
occur after the transfer. 
There are no particular limitations on the shape and size of the preformat 
pattern formed on the roll stamper of the present invention and patterns 
with any shape and size can be used so long as they correspond to 
preformats formed on substrates of information recording mediums. 
Grooves or pits formed on a substrate of an optical recording medium such 
as an optical disk or optical card on which information is recorded or 
reproduced by means of light are exemplified by tracking grooves in the 
form of concentric circles, a spiral or stripes, having a groove width of 
from 0.1 .mu.m to 5 .mu.m, a pitch of from 1 .mu.m to 12 .mu.m and a depth 
of from 0.01 .mu.m to 0.4 .mu.m, or information pits with a size on the 
micron order. A slight elongation or shrinkage in size of such grooves or 
pits which may occur when they are transferred brings about defects in the 
optical recording medium. Stated specifically, when, for example, a 
tracking groove for an optical disk is transferred to a resin sheet, an 
elongation in size on its outer diameter produces an eccentricity in the 
optical disk to cause tracking errors, making it impossible to carry out 
recording and reproducing. Accordingly, in the case of a disk pattern, the 
deviation of the size on its outer diameter from a circle should 
preferably be not more than 90 .mu.m, particularly not more than 50 .mu.m, 
and more particularly not more than 30 .mu.m. 
Thus the roll stamper of the present invention is capable of accurately 
transferring such fine patterns on a resin sheet, and is particularly 
effective for the production of substrates for optical recording mediums 
such as optical disks and optical cards. 
As an example for the process for producing the roll stamper of the present 
invention, a photoresist layer is formed on a glass plate for a master and 
a pattern is drawn using a laser beam or electron beam, which is then 
developed to form a resist pattern. The resist pattern is subjected to 
Ni-electroforming, thereby to give a thin Ni stamper. Next, as shown in 
FIG. 2, this Ni stamper 21 is fixed to a mirror-finished roll substrate 22 
by using an adhesive or a jig. A roll stamper can be thus obtained. 
Alternatively, a preformat pattern may be formed directly on the roll 
substrate or on a pattern forming layer provided on the substrate. 
Here, the value of b/a of the preformat pattern on the stamper can be set 
to a given value in the following manner. For example, in the case of an 
optical disk, the pattern of tracking grooves is prepared in a circular 
form, and the stamper thus prepared is stretched by applying a tension 
thereto in the direction perpendicular to the direction in which a resin 
sheet is transported. The resulting stamper is fixed to the roll 
substrate. The roll stamper of the present invention can be thus obtained. 
In the case of a roll stamper for molding a substrate sheet for optical 
disks, the roll stamper can be produced in the following manner: In the 
step of producing the the above Ni stamper, when a photoresist layer is 
formed on the glass plate for a master and a pattern is drawn on this 
resist layer by irradiation with a laser beam or the like, an optical head 
for carrying out irradiation with the laser beam while the glass plate for 
a master is rotated (hereinafter "cutting head") is vibrated in the radial 
direction of the glass plate for a master at a frequency twice the number 
of revolutions per second of the glass plate. An elliptical pattern can 
thereby be drawn and at the same time the difference between the major 
axis and the minor axis of this elliptical form can be made twice as long 
as the amplitude of vibration of the cutting head. Then, the Ni stamper 
obtained by Ni-electroforming using this glass plate may be fixed to the 
roll substrate in the manner that the direction of the minor axis of the 
elliptical pattern is in accordance with the direction in which a resin 
sheet is transported. Thus the roll stamper of the present invention for 
molding the substrate sheet for an information recording medium can be 
produced. In this instance, a stamper having an elliptical pattern can be 
obtained without applying any tension to the stamper, and hence it is 
possible to prevent the stamper from being broken. 
FIG. 5 illustrates an embodiment of a drawing apparatus for the master used 
in the production of this roll stamper. 
In FIG. 5, the numeral 51 denotes a laser oscillator. A non-modulated laser 
beam is outputted from the laser oscillator 51. The numeral 53 denotes a 
modulated signal generator. A modulated signal corresponding to a pattern 
to be cut on a resist layer formed on an original plate 56, described 
later, for a master used for the stamper is outputted from the modulated 
signal generator 53. The numeral 52 denotes an optical modulator. In the 
optical modulator 52, the laser beam outputted from the above laser 
oscillator 51 is modulated corresponding to the modulated signal outputted 
from the above modulated signal generator 53, and the modulated laser beam 
is fed to a cutting head 54. Through the cutting head 54, the laser beam 
having been modulated through the optical modulator 53 is directed 
vertically downwards to converge on the surface of a resist layer on the 
original plate 56, made of glass, for a master used for the stamper 
(hereinafter "glass original plate 56") which is placed on a turn table 
57. The cutting head is supported in the manner that it is slidable in the 
diameter direction of the glass original plate 56 by means of a 
horizontally sliding mechanism (not shown), and a piezoeletric device 60 
is provided between the side of the above cutting head 54 and a machine 
frame 61. The piezoelectric device 60 expands or contracts according to an 
alternating voltage applied from a control means (not shown) and hence can 
reciprocate the above cutting head 54 in the diameter direction of the 
glass original plate 56. 
The glass original plate 56 is provided on its surface with a resist layer 
55. A pattern is cut on the resist layer 55 by means of the laser beam 
made to converge through the cutting head. Beneath the turn table 57, a 
motor 59 for direct drive is fitted, and its speed (i.e. the number of 
revolutions per minute) can be precisely controlled by the operation of 
the above control means and the turn table 57 can be rotated the turn 
table 57 around a spindle 62. The motor 59 is supported by a horizontally 
sliding mechanism 58 in the manner that it is slidable in the 
right-and-left direction shown in the drawing, and also is equipped with a 
feed mechanism (not shown) so that it can be slided to a given position by 
the operation of the above control means. The control means gives a 
command to the modulated signal generator 53 to cause a modulated signal 
to be outputted at a given speed. In accordance with the speed, it also 
controls the number of revolutions per minute of the motor 59, the 
frequency of vibration of the piezoelectric device 60 and the position of 
the cutting head 54 and changes the amplitude of vibration of the 
piezoelectric device 60 in accordance with the position of the cutting 
head 54. 
The process for producing the roll stamper according to the present 
invention will be described below with reference to FIG. 5. 
The motor 59 is rotated at a predetermined number of revolutions per minute 
under the control by the control means (not shown), and thus the turn 
table 57 and the glass original plate 56 are rotated by the rotation of 
the motor 59. In this state, the feed mechanism (not shown) is driven so 
that the motor 59, the turn table 57 and the glass original plate 56 are 
slid using the slide mechanism 58 to effect alignment. A laser beam and a 
modulated signal are then outputted from the laser oscillator 51 and the 
modulated signal generator 53, respectively, which are modulated in the 
optical modulator 52 and a modulated laser beam is outputted to the 
cutting head. Then the modulated laser beam is shot onto the resist layer 
55 on the surface of the glass original plate 56 and thus the cutting head 
54 cuts the resist layer to form a pattern corresponding to the modulated 
signal. At this time, the control means described above is operated to 
cause the piezoelectric device 60 to vibrate in the diameter direction of 
the glass original plate 56 synchronizing with the revolution of the motor 
54, thereby causing the cutting head 54 to vibrate at a frequency twice 
the number of revolutions per second of the motor 59. 
Here, the amplitude of vibration given to the cutting head 54 may be set in 
accordance with the value of b/a of the preformat pattern to be formed on 
the roll stamper. 
This amplitude of vibration may also be controlled as a function of the 
distance l between the center of the glass original plate 56 (or the 
spindle 62 of the turn table 57) and a laser beam spot on the resist layer 
55, in other words, the amplitude of variation may be made to vary for 
each track. This is preferred since the elliptical tracking groove or 
grooves having a constant ratio between the major axis and the minor axis 
can be formed over the whole track or tacks. As a proportional factor of 
the distance l, the factor may also be determined in accordance with the 
material for a disk substrate, the speed of molding, etc. so that the 
preformat pattern can be more round on a resin sheet. In particular, when 
this proportional factor is set to range from 0.001 to 0.04, particularly 
from 0.002 to 0.02, the tracking grooves for a die substrate can be 
accurately formed on a resin sheet. 
The cutting head may not be vibrated and instead the original master 56 may 
be vibrated as shown in FIG. 6. 
After the cutting for one track is completed in this way, the motor 59, the 
turn table 57 and the glass original plate 56 are slid for one pitch (step 
feed) in the same way as in the above alignment, and then the pattern is 
cut on the resist layer formed on the glass original plate 56, in the same 
way as in the cutting described above. This operation is successively 
repeated to cut the resist layer on the glass original plate 56 to form 
thereon a preformat pattern for a disk. A resist pattern obtained by 
developing the resist layer is subjected to known steps such as 
post-baking, nickel sputtering, nickel electroforming, back polishing and 
external finishing. Thus a stamper having the preformat pattern 11 as 
shown in FIG. 1 can be obtained. 
In FIG. 1, the letter symbol a represents the length of the minor axis of 
the outermost track; and b, the length of the major axis of the same 
track. The stamper having this preformat pattern is fixed to the roll 
substrate 22 in the manner that the direction of the minor axis of the 
above pattern may be in accordance with the direction in which a resin 
sheet is transported. Thus the roll stamper of the present invention for 
molding a substrate sheet for optical disks can be obtained. 
In the above method of making the master, the amplitude of variation in the 
above vibration may be made substantially constant when the preformat 
pattern may not be in an excessively flat elliptical form and also it is 
unnecessary for the ratio of the major axis to the minor axis to be 
strictly equal over the whole track or tracks. In such an instance, it 
becomes unnecessary to provide the means for changing the amplitude of 
variation in proportion to the distance l between the cutting head 54 and 
the center of the glass original plate 56, so that the cost can be 
lowered. 
In the present invention, metals, semiconductors, dielectrics or alloys may 
be used as materials for the roll substrate. For example, aluminum, glass, 
hard metal, mold steel (e.g. maraging steel) may be used, which are 
materials feasible for mirror-finishing. Particularly preferred is Cr 
steel, which can be mirror-finished with ease. 
The process for producing a substrate sheet for information recording 
mediums, using the roll stamper of the present invention, will be 
described below with reference to FIG. 4. FIG. 4 diagramatically 
illustrates an embodiment of the process for producing a substrate sheet 
for information recording mediums according to the present invention. 
In FIG. 4, the numeral 45 denotes an extruder for carrying out extrusion; 
46, a T-die; and 49, a pressure molding section, comprised of three rolls 
41, 42 and 43. 
At least one roll of these rolls serves as the roll stamper of the present 
invention. In the embodiment shown in FIG. 4, the roll 42 serves as the 
roll stamper, and the rolls 41 and 43 as mirror rolls. 
First, resin pellets 44 put into the extruder 45 are heated and melted in 
the barrel of the extruder, pressed forward by a screw, and then formed 
into a sheet through the T-die. The temperature of the resin at this time 
may be in the range of from 260.degree. C. to 330.degree. C., and 
preferably from 280.degree. to 320.degree. C., in the case of, for 
example, a polycarbonate resin. From the T-die, the resin is continuously 
extruded in the form of a transparent molten resin sheet 47. The T-die is 
disposed in the manner that this molten resin sheet is extruded between 
the rolls 41 and 42 in the pressure molding section 49. The space between 
the tip of the T-die and the rolls 41 and 42 may preferably be set to be 
not more than 100 mm so that the resin can be prevented from being cured 
before it comes into contact with the rolls. The atmosphere that surrounds 
the T-die and the rolls may preferably be heated to a temperature of 
60.degree. C. or more. 
Next, the resin sheet extruded between the rolls 41 and 42 is held between 
the heated roll 42 serving as the roll stamper and the roll 43 serving as 
a press roll, at which a preformat pattern is transferred to the resin 
sheet. 
The roll stamper of the present invention is kept at such a temperature 
that the resin used may not be cured on the rolls. 
More specifically, the roll stamper may preferably be heated to a 
temperature within the range of +20.degree. C. to -20.degree. C. of the 
temperature at which the resin used is thermally deformed. When, for 
example, a polycarbonate resin is used, the roll stamper may preferably be 
heated to have a surface temperature of from 120.degree. C. to 160.degree. 
C. Namely, when the temperature is controlled in the above range, the 
molten resin sheet is not rapidly cooled and hence no strain due to 
shrinkage or the like tends to be produced in the resin sheet. The 
temperature of the press roll 43 in the pressure molding section may 
preferably be set to be the same as or a little lower than that of the 
roll stamper 42. 
The temperature of these rolls can be controlled, for example, by 
electrically heating them using a heater casted in the roll or by 
circulating a heating medium at the center of the roll. 
Next, the resin sheet 47' on which preformat patterns have been formed is 
transported to take-off rolls 48. The take-off rolls 48 are rolls 
important to the continuous molding of the preformats, and are driven 
synchronously with the rolls in the pressure molding section 49. In other 
words, these two sets of rolls have the same peripheral speed, and are 
preferably constructed in the manner that no stress due to a stretch or 
the like may act on the resin sheet between them. Taking such construction 
makes it possible to prevent an optical anisotropy from being produced at 
the interior of the resin sheet. 
The thickness of the substrate sheet 47' for optical recording mediums 
depends on the gap or space between the rolls in the pressure molding 
section 49, the divergence between lips of the T-die, and the drawdown 
that is governed by the ratio of extrusion speed to stress rate, i.e., the 
degree of a stretch. 
The sheet thickness is commonly controlled by making the divergence between 
lips of the T-die greater by 20 to 200% than the desired sheet pressure so 
that the drawdown is increased. In the present invention, however, the 
drawdown should be controlled to be from 50 to 150% in order to prevent 
the optical anisotropy or sheet thickness uneveness caused by a strain 
ascribable to drawdown. 
Another manufacturing method of the present invention also provides a 
substrate sheet for information recording mediums having accurate 
preformats by heating and softening a resin sheet previously formed and 
then pressing the roll stamper of the present invention against it to 
transfer the preformat. 
As described above, the roll stamper of the present invention and the 
process for producing a substrate sheet for information recording mediums 
by the use of the roll stamper make it possible to accurately transfer 
preformat patterns onto a resin sheet. 
It has also become possible to continuously produce a resin sheet on which 
preformat patterns have been accurately transferred. 
EXAMPLES 
The present invention will be described below in greater detail by giving 
Examples. 
EXAMPLE 1 
Using the apparatus as shown in FIG. 5, cutting was carried out on a glass 
original plate having thereon a photoresist layer, at the part defined by 
the distance l of from 21 mm to 44.5 mm from the center of the glass 
original plate while the glass original plate was rotated at 900 rpm. At 
this time an alternating voltage of 900/60.times.2=30 Hz was applied to 
the piezoelectric device to cause the cutting head to vibrate in the 
diameter direction of the glass original plate. The amplitude of variation 
at this time was varied to be (0.0039/2).times.l (mm) in accordance with 
the distance l between the cutting head and the center of the glass 
original plate. The feed speed of the motor, the turn table and the glass 
original plate was set to be 24 .mu.m/s. 
After the cutting was carried out in this way, development was carried out 
to give a resist pattern in a spiral form with an elliptical shape of 
89.000 mm in length (a) of the minor axis and 89.174 mm in length (b) of 
the major axis, corresponding to a tracking groove having, at a convex 
part, a width of 0.6 .mu.m, a pitch of 1.6 .mu.m and a height of 1,000 
.ANG.. Next, this resist pattern was subjected to Ni electroforming to 
prepare a stamper. The resulting stamper was adhered with an adhesive 
(trade name: SC-55; available from Sony Chemicals K. K.) to a roll 
substrate in the manner that the direction of the minor axis of the 
stamper was in accordance with the direction in which a resin sheet is 
transported. A roll stamper was thus produced. 
Using this roll stamper, the apparatus for producing a substrate sheet for 
optical recording mediums, as shown in FIG. 4, was set up. In the manner 
as shown in FIG. 4, the substrate sheet for optical recording mediums was 
prepared using an extruder having an screw of 35 mm in diameter and a coat 
hanger type T-die of 20 cm in width, downwards provided to the body of the 
extruder. 
A polycarbonate resin (trade name: Panlite L-1250; available from Teijin 
Chemicals Ltd.) was used as the resin. The pressure molding section 49 was 
comprised of the rolls 41 and 43 serving as mirror rolls, and the roll 42 
serving as the roll stamper previously prepared. 
The resin sheet was extruded under conditions of extruder barrel 
temperatures of 300.degree. C. at the part a (Ta), 300.degree. C. at the 
part b (Tb) and 320.degree. C. at the part c (Tc) of the extruder 45 and a 
T-die temperature Td of 320.degree. C., under which a molten resin sheet 
was formed. At this time the resin temperature was in the range of 
280.degree. C. to 330.degree. C. 
The roll stamper 42 was kept at a temperature of 140.degree. C. The roll 41 
was kept at a temperature lower than that of the roll 42 by 1.degree. to 
2.degree. C., and the roll 43 was kept at a temperature higher than that 
of the roll 32 by 20.degree. to 21.degree. C. 
The space between the lips of the T-die and the pressure molding section 
was set to be 50 mm, and its surrounding was surrounded with a heating box 
to make control so that the atmosphere from the extrusion of the resin to 
the pressure molding section was kept at 60.degree. C. or higher. The 
divergence between the lips of the T-die was set to 0.48 mm and the gap 
between the rolls 41 and 42 in the pressure molding section was set to 1.2 
mm, under the conditions of which the preformat pattern of the roll 
stamper 42 was transferred to the resin sheet to carry out the production 
of a substrate sheet for optical recording mediums with a thickness of 1.2 
mm. 
The resin sheet was molded at a speed of 2 m/min. With respect to the 
preformat patterns thus formed on the substrate sheet for information 
recording mediums, the length of the preformat pattern in the direction 
parallel to the direction in which the resin sheet was transported was 
represented by a' and the length in the direction perpendicular thereto by 
b' as shown in FIG. 3. The lengths a' and b' were measured and the 
deviation of b' when viewed on the basis of a' was regarded as the amount 
of deviation from a circle. This measurement was made on three samples 
selected at random. Results obtained are shown in Table 1. 
TABLE 1 
______________________________________ 
Amount of 
Amount of 
Sam- deviation 
amplitude of 
ple a' b' from circle 
tracking error 
No. (mm) (mm) (.mu.m) signals 
______________________________________ 
1 88.689 88.684 5 AA 
2 88.687 88.683 4 AA 
3 88.689 88.685 4 AA 
______________________________________ 
Subsequently, substrates were cut out from the substrate sheet for optical 
recording mediums on which the above measurement was made. Thereafter, 
aluminum was deposited in a thickness of 1,000 .ANG. to produce optical 
disks. 
The resulting optical disks were evaluated using an optical disk evaluation 
apparatus (trade name: OMS-1000 Type III; manufactured by Nakamichi K. K.) 
by measuring the amplitude of tracking error signals. The case in which 
the amount of amplitude at this time was less than 0.2V was evaluated as 
"AA", the case of from 0.2V to less than 0.4V as "A", the case of from 
0.4V to less than 1.0V as "B", and the case of 1.0V or more up to 
tracking-off as "C". 
EXAMPLE 2 
Using the same apparatus as used in Example 1, cutting was carried out on a 
glass original plate having thereon a photoresist layer, at the part 
defined by the distance l of from 20 mm to 44.5 mm from the center of the 
glass original plate while the glass original plate was rotated at 1,200 
rpm. At this time an alternating voltage of 1,200/60.times.2=40 Hz was 
applied to the piezoelectric device to cause the cutting head to vibrate 
in the diameter direction of the glass original plate while the amplitude 
of variation was varied to be (0.0118/2).times.l (mm) in accordance with 
the distance l between the cutting head and the center of the glass 
original plate. 
In this way, a resist pattern was obtained in a spiral form with an 
elliptical shape of 89.000 mm in length (a) of the minor axis and 89.525 
mm in length (b) of the major axis, corresponding to a tracking groove for 
an optical disk. Next, this resist pattern was subjected to Ni 
electroforming to prepare a stamper. The resulting stamper was adhered 
with an adhesive to a roll substrate in the manner that the direction of 
the minor axis of the stamper was in accordance with the direction in 
which a resin sheet is transported. A roll stamper was thus produced. 
Subsequently, using this roll stamper, the substrate sheet for optical 
disks was prepared in the same manner as in Example 1 by continuously 
transferring optical disk preformat patterns onto the resin sheet formed 
by extrusion. 
With respect to the preformat patterns thus obtained on the substrate sheet 
for information recording mediums, the amount of deviation from a circle 
was measured in the same manner as in Example 1. Substrates for optical 
disks were also cut out from this substrate sheet to produce optical 
disks, and the amplitude of tracking error signals was measured. Results 
obtained are shown in Table 2. 
TABLE 2 
______________________________________ 
Amount of 
Amount of 
Sam- deviation 
amplitude of 
ple a' b' from circle 
tracking error 
No. (mm) (mm) (.mu.m) signals 
______________________________________ 
1 88.733 88.764 31 AA 
2 88.732 88.761 29 AA 
3 88.729 88.761 32 AA 
______________________________________ 
EXAMPLE 3 
In the same manner as in Example 1, the roll stamper of the present 
invention was prepared and preformat pattern for optical disks were 
transferred to the resin sheet formed by extrusion. In the present 
Example, the preformat pattern on the roll stamper was in an elliptical 
shape of 89.423 mm in length (a) in the direction parallel to the 
direction in which the resin sheet is transported and 89.793 in length (b) 
in the direction perpendicular to the direction in which the resin sheet 
is transported, and so formed as to correspond to tracking grooves having, 
at a convex part, a width at the land, of 0.6 .mu.m, a pitch of 1.6 .mu.m 
and a height of 1,000 .ANG.. 
With respect to the preformat patterns thus obtained on the substrate sheet 
for information recording mediums, measurement was made the same manner as 
in Example 1. On optical disks prepared from the substrate sheet, the 
amplitude of tracking error signals was also measured. Results obtained 
are shown in Table 3. 
TABLE 3 
______________________________________ 
Amount of 
Amount of 
Sam- deviation 
amplitude of 
ple a' b' from circle 
tracking error 
No. (mm) (mm) (.mu.m) signals 
______________________________________ 
1 88.996 88.992 4 AA 
2 88.995 89.001 6 AA 
3 89.000 88.995 5 AA 
______________________________________ 
EXAMPLE 4 
A substrate sheet for optical disks was continuously formed in the same 
manner as in Example 1 except that the preformat pattern formed on the 
roll stamper was made to be 89.023 in length (a) and 89.793 in length (b). 
With respect to the thus formed preformats of the substrate sheet for 
optical disks, thus formed, measurement and evaluation were made in the 
same manner as in Example 1. Results obtained are shown in Table 4. 
TABLE 4 
______________________________________ 
Amount of 
Amount of 
Sam- deviation 
amplitude of 
ple a' b' from circle 
tracking error 
No. (mm) (mm) (.mu.m) signals 
______________________________________ 
1 89.029 89.003 26 A 
2 89.021 88.989 32 A 
3 89.032 89.011 21 AA 
______________________________________ 
EXAMPLES 5 to 8 
Substrate sheets for optical disks were continuously formed in the same 
manner as in Example 1 except that the preformat patterns formed on the 
roll stampers were made to have the lengths a and b as shown in the 
following Table 5. With respect to the preformats formed on the substrate 
sheet for optical disks, measurement and evaluation were made in the same 
manner as in Example 1. 
REFERENCE EXAMPLES 1 and 2 
Substrates for optical disks were prepared in the same manner as in Example 
1 except that the preformat patterns formed on the roll stampers were made 
to have the lengths a and b as shown in Table 5. With respect to the 
preformats formed on the substrate sheet for optical disks, measurement of 
size and evaluation were made. 
Results of Examples 5 to 8 and Reference Example 1 and 2 are shown in Table 
5. 
TABLE 5 
__________________________________________________________________________ 
Preformat pattern 
Preformat on 
Amount of 
Amount of 
on stamper 
Sam- 
resin sheet 
deviation 
ampltitude of 
a b ple 
a' b' from circle 
tracking error 
(mm) 
(mm) No. 
(mm) 
(mm) 
(.mu.m) 
signals 
__________________________________________________________________________ 
Example: 
5 89.752 
89.797 
1 89.046 
89.005 
41 A 
(b-a/a) .times. 100 = 
2 89.056 
89.011 
45 A 
0.05 3 89.051 
89.008 
43 A 
6 89.685 
89.775 
1 89.001 
89.004 
3 AA 
(0.1) 2 88.999 
89.003 
4 AA 
3 89.001 
89.003 
2 AA 
7 88.981 
89.880 
1 88.980 
89.002 
22 AA 
(1) 2 88.979 
88.999 
20 AA 
3 88.983 
89.004 
21 AA 
8 88.192 
89.956 
1 88.989 
89.085 
96 B 
(2) 2 88.988 
89.086 
98 B 
3 88.992 
89.081 
89 A 
Reference Example: 
1 89.783 
89.792 
1 89.174 
88.994 
180 C 
(0.01) 2 89.179 
89.003 
176 C 
3 89.172 
88.989 
183 C 
2 87.518 
90.225 
1 88.906 
89.094 
188 C 
(3) 2 88.902 
89.090 
188 C 
3 88.903 
89.094 
191 C 
__________________________________________________________________________ 
EXAMPLE 9 
Using the apparatus as shown in FIG. 6, cutting was carried out on a glass 
original plate having thereon a photoresist layer, at the part defined by 
the distance l of from 20 mm to 44.5 mm from the center of the glass 
original plate while the glass original plate was rotated at 900 rpm. At 
this time an alternating voltage of 900/60.times.2=30 Hz was applied to 
the piezoelectric device to cause the motor, the turn table and the glass 
original plate to vibrate in the right-and-left direction. The amplitude 
of variation at this time was varied to be (0.0042/2).times.l (mm) in 
accordance with the distance l between the cutting head and the center of 
the glass original plate. 
After the cutting was carried out in this way, development was carried out 
to give a resist pattern in a spiral form with an elliptical shape of 
89.000 mm in length (a) of the minor axis and 89.187 mm in length (b) of 
the major axis, corresponding to a tracking groove having, at a convex 
part, a width of 0.6 .mu.m, a pitch of 1.6 .mu.m and a height of 1,000 
.ANG.. Next, this resist pattern was subjected to Ni electroforming to 
prepare a stamper. The resulting stamper was adhered with an adhesive 
(trade name: SC-55; available from Sony Chemicals K. K.) to a roll 
substrate in the manner that the direction of the minor axis of the 
stamper was in accordance with the direction in which a resin sheet is 
transported. A roll stamper was thus produced. 
Using this roll stamper, a plurality of preformats for optical disks were 
transferred onto a polycarbonate resin sheet formed by extrusion, in the 
same manner as in Example 1. A substrate sheet for optical disks was thus 
produced. With respect to the preformat patterns on this substrate sheet, 
measurement and evaluation were made in the same manner as in Example 1. 
EXAMPLE 10 
Using the same apparatus as used in Example 9, cutting was carried out on a 
glass original plate having thereon a photoresist layer, at the part 
defined by the distance l of from 20 mm to 44.5 mm from the center of the 
glass original plate while the glass original plate was rotated at 600 
rpm. At this time an alternating voltage of 600/60.times.2=20 Hz was 
applied to the piezoelectric device to cause the motor, the turn table and 
the glass original plate to vibrate in the diameter direction of the glass 
original plate while the amplitude of variation was varied to be 
(0.014/2).times.l (mm) in accordance with the distance l between the 
cutting head and the center of the glass original plate. 
After the cutting was carried out in this way, development was carried out 
to give a resist pattern in a spiral form with an elliptical shape of 
89.000 mm in length (a) of the minor axis and 89.623 mm in length (b) of 
the major axis, corresponding to a tracking groove having, at a convex 
part, a width at the land, of 0.6 .mu.m, a pitch of 1.6 .mu.m and a height 
of 1,000 .ANG.. Next, this resist pattern was subjected to Ni 
electroforming to prepare a stamper. The resulting stamper was adhered 
with an adhesive (trade name: SC-55; available from Sony Chemicals K. K. ) 
to a roll substrate in the manner that the direction of the minor axis of 
the stamper was in accordance with the direction in which a resin sheet is 
transported. A roll stamper was thus produced. 
Using this roll stamper, a plurality of preformats for optical disks were 
transferred onto a polycarbonate resin sheet formed by extrusion, in the 
same manner as in Example 1. A substrate sheet for optical disks was thus 
produced. With respect to the preformats on this substrate sheet, 
measurement and evaluation were made in the same manner as in Example 1. 
Results of the above Examples 7 and 8 are shown in Table 6. 
TABLE 6 
__________________________________________________________________________ 
Preformat pattern 
Preformat on 
Amount of 
Amount of 
on stamper 
Sam- 
resin sheet 
deviation 
ampltitude of 
a b ple 
a' b' from circle 
tracking error 
Example: (mm) 
(mm) No. 
(mm) 
(mm) 
(.mu.m) 
signals 
__________________________________________________________________________ 
7 89.000 
89.187 
1 88.563 
88.590 
27 AA 
(b-a/a) .times. 100 = 
2 88.559 
88.589 
30 AA 
0.21 3 88.611 
88.641 
30 AA 
8 89.000 
89.623 
1 88.849 
88.861 
12 AA 
(0.7) 2 88.842 
88.857 
15 AA 
3 88.854 
88.865 
11 AA 
__________________________________________________________________________