Stock material or miscellaneous articles – Circular sheet or circular blank
Reexamination Certificate
2001-02-01
2003-06-10
Mulvaney, Elizabeth (Department: 2652)
Stock material or miscellaneous articles
Circular sheet or circular blank
C428S064400, C430S270110
Reexamination Certificate
active
06576317
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an improvement in an optical disc and an injection compression molding die for producing an optical disc substrate for the optical disc, and in particular to an optical disc that does not cause damages on a printing plate during screen printing on a printable plane of such disc, and an injection compression molding die for producing a substrate for such disc.
2. Description of the Related Art
Molding of a thin disc for lamination, such as that being used for DVD (Digital Versatile Disc), is generally carried out by the injection compression molding method in order to satisfy standards on birefringence or skew. A conventional die used for such injection compression molding will be explained referring to
FIGS. 8
to
9
.
FIG. 8
is a partial sectional view showing a tightened state of a conventional injection compression molding die for producing an optical disc substrate,
FIG. 9
is a partial sectional view showing a tightened state of another conventional die used for such injection compression molding for producing an optical disc substrate, and
FIG. 10
is a partial sectional view showing a structure of an optical disc using a substrate produced by the injection compression molding die shown in
FIGS. 8 and 9
.
First, a constitution and structure of the injection compression molding die
10
shown in
FIG. 8
will be described. The injection compression molding die
10
mainly comprises a fixed-side die
1010
composed of a mounting plate
1011
and a signal-side mirror
1012
mounted thereon, and a mobile-side die
1020
composed of a mounting plate
1021
and a readout-side mirror
1022
mounted thereon. The mounting plate
1011
, the signal-side mirror
1012
, the readout-side mirror
1022
and the mounting plate
1021
are arranged in a concentric manner. On an outer periphery of the signal-side mirror
1012
, a fixed-side interlock ring
1030
is located so as to be mounted on the mounting plate
1011
. To such fixed-side interlock ring
1030
, a cavity ring
1040
is joined and attached so as to allow free sliding on the outer peripheral plane of the readout-side mirror
1022
, while being constantly pressed toward such readout-side mirror
1022
by means of a spring not shown in the figure. A sprue bush
1050
is located at the center hole of the fixed-side die
1010
, and opposing to the sprue bush
1050
, a punch
1060
is located at the center hole of the mobile-side die
1020
. Now reference numerals
1013
,
1051
,
1023
and
1061
denote temperature controlling circuits for the signal-side mirror
1012
, the sprue bush
1050
, the readout-side mirror
1022
and the punch
1060
, respectively; a reference numeral
1024
denotes a degassing hole; and a reference numeral
1062
denotes a thrusting member.
The conventional injection compression molding die
20
shown in
FIG. 9
mainly comprises a fixed-side die
2010
composed of a mounting plate
2011
and a signal-side mirror
2012
mounted thereon, and a mobile-side die
2020
composed of a mounting plate
2021
and a readout-side mirror
2022
mounted thereon, in the similar manner as the injection compression molding die
10
. On an outer periphery of the signal-side mirror
2012
, a cavity ring
2040
engaging with a conical plane formed on the outer periphery of the readout-side mirror
2022
is joined and attached while being constantly pressed toward such readout-side mirror
2022
by means of a spring not shown in the figure. A reference numeral
2030
denotes a fixed-side interlock ring. A sprue bush
2050
is located at the center hole of the fixed-side die
2010
, and opposing to the sprue bush
2050
, a punch
2060
is located at the center hole of the mobile-side die
2020
. Now reference numerals
2013
,
2051
,
2023
and
2061
denote temperature controlling circuits for the signal-side mirror
2012
, the sprue bush
2050
, the readout-side mirror
2022
and the punch
2060
, respectively; and a reference numeral
2062
denotes a thrusting member.
When an optical disc substrate is molded using thus composed injection compression molding die
10
or
20
, a stamper S is mounted on the signal-side mirror
1012
or
2012
, a molten resin is injected from the sprue bushing
1050
or
2050
into a cavity C surrounded by the stamper S. the readout-side mirror
1022
or
2022
and the cavity ring
1040
or
2040
, to effect compression molding. This produces an optical disc substrate which is used for an optical disc D, an enlarged view of which is partially shown in FIG.
10
.
The optical disc substrate thus produced using the conventional injection compression molding die
10
or
20
, however, has on the outer periphery thereof a burr B with a height less than 10 &mgr;m. This is because the readout-side mirror
1022
and the cavity ring
1040
are kept in slide contact in the injection compression molding die
10
, or the readout-side mirror
2022
and the cavity ring
2040
are kept in engagement in the injection compression molding die
20
. Depending on the structure of the die, the burr B may have a sharp-edged tip as shown in FIG.
10
. The optical disc D having such burr B may undesirably make scratches on a printing plate P during screen printing on the printable plane of such optical disc D, which significantly reduces the service life of the printing plate P, and requires frequent exchange thereof. Alternatively, removal of the burr B before printing is required, which will however degrade the yield and thus push up the product cost of the optical disc.
An approach to reduce generation of the burr B requires an extremely high level of accuracy of the die structure, which will undesirably push up the production and maintenance costs of the die and significantly worsen the operation ratio of a molding machine.
SUMMARY OF THE INVENTION
To solve the foregoing problem, it is therefore an object of the present invention to provide an optical disc capable of preventing scratches from being produced on the printing plate with no special need of raising accuracy of the die, and to provide an injection compression molding die for producing such a disc substrate.
Hence a first aspect of the invention solves the foregoing problem by forming a ring-formed projected portion on an outer periphery of a printable plane of an optical disc.
In a second aspect of the present invention, the projected portion of the optical disc as described above has a continuous form.
In a third aspect of the present invention, the projected portion of the optical disc as described in the first aspect has a height of 10 &mgr;m to 50 &mgr;m.
In a fourth aspect of the present invention, the projected portion of the optical disc of the first or the second aspect of the present invention is formed in the inside and/or outside vicinity of a ring-formed burr generated on the outer periphery of the disc.
In a fifth aspect of the present invention, a ring-formed recessed portion formed on the outer periphery of the printable plane of the optical disc is formed so as to house a ring-formed burr.
Moreover, in a sixth aspect of the present invention, the foregoing problem is solved by an injection compression molding die which comprises a signal-side mirror; a readout-side mirror; a cavity ring joined to the signal-side mirror, and sliding on or being engaged with an outer periphery of the readout-side mirror; a sprue bush located at the center of the signal-side mirror; and a punch located at the center of the readout-side mirror; in which a molten resin is injected from the sprue bush into a cavity surrounded by a stamper mounted on the surface of the signal-side mirror, the surface of the readout-side mirror and an inner peripheral plane of the cavity ring, and compressed to be transferred with pits from the stamper, and is punched out by the punch to form a center hole of an optical disc substrate; wherein the surface of the readout-mirror and/or the inner peripheral plane of the cavity ring has a ring-formed recessed groove in an area around wh
Kishi Shinsuke
Yoshimura Hideaki
Kananen, Esq. Ronald P.
Mulvaney Elizabeth
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