Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2001-03-13
2002-12-17
Mulvaney, Elizabeth (Department: 1774)
Stock material or miscellaneous articles
Circular sheet or circular blank
C369S282000
Reexamination Certificate
active
06495235
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to an optical disk used for information recording or reproduction, its substrate, and a mold for forming the substrate.
2. Related Background Art
Conventionally, an optical disk and its substrate have been proposed in a minidisk form disclosed in JP 5(1993)-303768 A.
FIG. 11
shows a schematic sectional view of a conventional optical disk. In
FIG. 11
, numeral
101
indicates an optical disk substrate, numeral
102
a handling surface, numeral
103
an information surface, numeral
104
a clamp plate retaining surface, numeral
106
a clamp plate, numeral
107
a groove, numeral
108
an information recording layer, numeral
109
a protective coating, and numeral
120
a rotation central axis. The functions of the optical disk configured as described above and its substrate are described as follows.
On the information surface
103
formed on one principal plane of the optically transparent disc-like substrate
101
made of polycarbonate, acrylic resin, or the like, a signal recording/reproduction layer or a reflection film is formed as the information recording layer
108
and the protective coating
109
is formed thereon. Thus, the optical disk is configured. The disc-like clamp plate
106
formed of an iron plate or magnetic stainless steel is attached to the clamp plate retaining surface
104
around the center of the substrate
101
. The clamp plate
106
is attracted magnetically to a disk table fixed to the tip of a spindle axis of a recording/reproducing device. Thus, the substrate
101
is rotated together with the disk table.
For instance, JP 5(1993)-89529 A describes a welding method using ultrasonic waves and an adhesion method using an ultraviolet curable resin as methods of holding the clamp plate
106
to the substrate
101
.
The welding method using ultrasonic waves is carried out as follows. As shown in
FIG. 11
, the clamp plate
106
is placed on the clamp plate retaining surface
104
. Then, a ring-like contact face of an ultrasonic horn tip is pressed against an inner circumferential side end portion of the handling surface
102
with a predetermined force. In this state, ultrasonic vibration is applied, so that the resin forming the portion against which the contact face has been pressed (hereinafter referred to as the “pressed portion”) is melted. The pressing force of the ultrasonic horn allows the resin thus melted to deform and the pressed portion to be displaced downward. In addition, the melted resin projects from a wall surface extending between the clamp plate retaining surface
104
and the handling surface
102
and thus a projection part
110
as shown in
FIG. 12
is formed. In
FIG. 12
, numeral
112
indicates a displaced surface formed by the displacement of part of the handling surface
102
on its inner circumferential side by the contact with the contact face of the ultrasonic horn. In this case, the projection amount of the projection part
110
toward the center corresponds to a displacement amount of the displaced surface
112
with respect to the handling surface
102
. As a result, an outer circumferential side flat portion (hereinafter referred to as an “outer flat portion”)
106
a
around the outer circumference of the clamp plate
106
is sandwiched between the clamp plate retaining surface
104
and the projection part
110
. Therefore, the clamp plate
106
is retained so as not to come off the clamp plate retaining surface
104
.
The adhesion method using an ultraviolet curable resin is carried out as follows. Initially, an ultraviolet curable resin is applied between the clamp plate retaining surface
104
and the outer flat portion
106
a
around the outer circumference of the clamp plate
106
. Then, the ultraviolet curable resin is irradiated with ultraviolet rays to be cured. Thus, the clamp plate retaining surface
104
and the clamp plate
106
are bonded and fixed.
The substrate
101
is manufactured by injection molding. The handling surface
102
functions as a suction face to be subjected to the suction of a vacuum suction pad attached to the end of a robot arm when the substrate
101
molded by injection molding is taken out from the mold using the robot arm. The inner circumferential side end of the handling surface
102
is defined by the outer circumferential side end of the clamp plate retaining surface
104
and the outer circumferential side end of the handling surface
102
is defined by the inner circumferential side end of the groove
107
. The groove
107
is formed as the reflection of the shape of a mold part required for holding a stamper incorporated into the mold. The inner circumferential side end of the information surface
103
(the inner circumferential side end in an area where grooves or pits are formed) is positioned at a predetermined distance from the outer circumferential side end of the groove
107
.
In the optical disk and its substrate, it is required to reduce the diameter and thickness of the disk so that the optical disk can be applied to portable equipment.
However, in the optical disk and its substrate with the clamp plate
106
sandwiched between the clamp plate retaining surface
104
and the projection part
110
as shown in
FIG. 12
, there has been the following problem in thickness reduction. In order to reduce the thickness of the substrate
101
, it is necessary to shorten the distance in the thickness direction between the handling surface
102
and the clamp plate retaining surface
104
. In
FIG. 12
, therefore, the displacement amount in the thickness direction of the displaced surface
112
with respect to the handling surface
102
is reduced. Thus, the projection amount of the projection part
110
is reduced. As a result, the reliability in retaining the clamp plate
106
decreases.
In order to solve the above mentioned problem, the following method might be considered. That is, a protrusion
114
is formed along the inner circumferential side end of the handling surface
102
as shown in
FIG. 13
, and then while the contact face of an ultrasonic horn is pressed against the protrusion
114
to suppress the occurrence of the difference in level between the handling surface
102
and the displaced surface
112
, the projection amount of the projection part
110
toward the center is increased. However, in this method, due to the formation of the protrusion
114
, the inner circumferential side end of the handling surface
102
is displaced radially outward. In order to take out the substrate
101
from the mold used for injection molding, it is necessary to form the handling surface
102
with a larger area than a predetermined area. Therefore, the outer circumferential side end of the handling surface
102
is required to be shifted radially outward. Accordingly, the inner and outer circumferential side ends of the groove
107
and the inner circumferential side end of the information surface
103
also are required to be shifted sequentially to the radially outer side. Therefore, in order to secure the same recording capacity, the outer diameter of the optical disk increases, which has been a problem.
On the other hand, in an optical disk and its substrate in which the clamp plate
106
is bonded and fixed to the clamp plate retaining surface
104
with an ultraviolet curable resin, the above-mentioned problem is not caused when the size and thickness of the disk are intended to be reduced. However, after being applied, the ultraviolet curable resin is solidified gradually with the passage of time. For instance, therefore, in the case where the environmental temperature varies, since the clamp plate
106
and the substrate
101
are different in material and thus in thermal expansion coefficient, the substrate
101
is distorted, which may cause noise generation.
SUMMARY OF THE INVENTION
The present invention intended to solve the above-mentioned problem. It is an object of the present invention to provide an optical disk and its substrate whose sizes and thicknesses can
Hanakawa Eiichi
Kurozuka Akira
Uchida Kiyoshi
Yamamoto Tomio
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
Mulvaney Elizabeth
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