JPH07210901A - Injection molding method of optical disk substrate - Google Patents

Abstract

PURPOSE:To provide a method for injection molding a substrate for optical disks which is substrate molding for optical disks of a board groove width, realizes a high transfer rate uniform over the entire surface of the substrate and is molded with lessened warpage. CONSTITUTION:A resin temp. is kept at 320 to 350 deg.C at the time of injection molding the optical disk substrate having the guide grooves and having the ratio W/P of 60 to 80% between the width W of these guide grooves and a track pitch P by using a polycarbonate resin. The metal mold temp. on a stamper mounting side is kept at 120 to 140 deg.C and the metal mold temp on the side facing the stamper is set lower by 20 to 5 deg.C than the metal mold temp. on the stamper mounting side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disk substrate injection molding method. Specifically, it relates to an injection molding method suitable for molding an optical disk substrate having a wide guide groove.

[0002]

2. Description of the Related Art Optical disk substrates are usually manufactured in terms of productivity.
It is formed using an injection molding method or an injection compression molding method. In these methods, a mold composed of two parts, a fixed side and a movable side, is used. To mold an optical disk substrate, an annular flat stamper with preformat information recorded as concave and convex information is attached to either the fixed side mold or the movable side mold, and a cavity is formed between both molds. It is performed by injecting a molten resin material into the inside.

Preformat information on the stamper surface is
Pits that carry information such as addresses, and recording / reproducing light guide grooves (grooves), etc., are reversed and transferred to the injection-molded resin substrate. That is, since the pits and grooves of the stamper are usually convex, concave pits and grooves are transferred and formed on the substrate side.

A portion sandwiched between the grooves is called a land. Optical discs can be roughly classified into two types: a type in which a signal is recorded in a land portion and a type in which a signal is recorded in a groove portion. Commercially available recordable compact disc (CD
-R) belongs to the groove recording type.

The groove width W of the CD-R substrate is about 0.4 μm
The track pitch P is 0.6 μm, the track pitch P is 1.6 μm, and the ratio W / P is about 0.25 to 0.38 (25% to 38%). That is, the groove width is narrower than the land width. Similarly, magneto-optical disks for recording music having a diameter of 120 mm and a diameter of 64 mm also belong to the groove recording type.

However, the groove shape of the substrate of these magneto-optical discs is very different from that of the recordable compact disc substrate, and the groove width W is 1.0 μm to 1.2 μm and the track pitch P is 1.6 μm. The ratio W / P is 60% or more. That is, the signal is recorded in this wide groove. One of the reasons for widening the groove width is the signal strength of the magneto-optical disk.

In a magneto-optical disk, a recording signal is read by utilizing a magneto-optical phenomenon called Kerr effect. The Kerr effect is a phenomenon in which the polarization direction of read light is slightly rotated left and right depending on the magnetization direction. Usually, since the rotation angle of the plane of polarization is very small, which is 1 degree or less, there is a drawback that it is weak against noise.

Further, the boundary between the groove and the land of the optical disk substrate, that is, the wall surface portion has unevenness, which causes noise.
Therefore, in order to eliminate the weakness against noise in a magneto-optical disk, when recording in a groove, it is necessary to widen the width of the groove and to make the groove shape U-shaped to suppress an increase in noise due to the wall surface portion. That is why.

However, widening the groove width causes a problem in injection molding the substrate. It is a problem that the groove (convex shape) of the stamper becomes difficult to be transferred to the substrate. In other words, the wide groove width of the substrate means
Since the unevenness is reversed on the stamper side, there are wide convex portions (groove forming portions) and narrow concave portions (land forming portions).

At the time of injection molding, the molten resin is filled under pressure into the mold cavity, but it is difficult for the molten resin to flow into the narrow concave portion (land forming portion) of the stamper, and the resin is filled at the tip of the concave portion. As a result, the land portion of the substrate is low and the groove is shallow. The decrease in the transfer rate does not occur uniformly on the entire surface of the substrate, but there is a problem that the transfer rate is decreased due to the radius, particularly at the outer circumference, and the distribution is caused depending on the angle even within the same radius.

[0011]

DISCLOSURE OF THE INVENTION The inventors of the present invention have conducted extensive studies to solve the above problems, and as a result, in injection molding using a polycarbonate resin, by molding under a special condition, It has been found that an injection molding method that can realize a uniform and high transfer rate over the entire surface of the substrate and can suppress the warp of the substrate to be small in molding a substrate having a wide groove width of the format can be provided. completed.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical disk substrate having a guide groove and a ratio W / P of the guide groove width W and the track pitch P of 60% to 80% to a polycarbonate resin. When using injection molding, set the resin temperature to 3
Set the mold temperature on the stamper mounting side to 1
An injection molding method for an optical disk substrate is characterized in that the mold temperature on the side facing the stamper is set to 20 ° C. to 140 ° C. and the mold temperature on the side facing the stamper is set to be 20 ° C. to 5 ° C. lower than the mold temperature on the stamper mounting side.

That is, in injection molding of an optical disk substrate having a ratio W / P of the groove width W to the track pitch P of 60% or more, the transferability is remarkably deteriorated, but the resin temperature is set to 320.
By setting the mold temperature on the stamper mounting side to 120 ° C or higher and 140 ° C or lower, the fluidity of the resin becomes high, and the recessed portion of the stamper (corresponding to the land portion of the substrate)
Further, the resin flows sufficiently and evenly over the entire surface of the stamper, so that a high transfer rate can be obtained.

Here, the temperature of the mold on the side facing the stamper is 20 ° C. higher than the temperature of the mold on the side on which the stamper is mounted.
By setting the temperature lower by 5 ° C., a substrate with less warp can be molded. Thus, according to the present invention, an optical disk substrate having a groove width W / track pitch P ratio W / P of 60% or more (usually up to 80%) can be molded with a high transfer rate and a small warpage. .

The present invention will be described in more detail below. A polycarbonate resin is used as the resin for molding the substrate in the present invention. In particular, the average molecular weight is 13500-15
A polycarbonate resin of about 500 is preferably used. The thickness of the molded substrate is 0.6 mm to 1.5 mm
Is standard.

The ratio W / P between the groove width W and the track pitch P is 6
In the injection molding of an optical disk substrate with 0% or more (60 to 80%), a decrease in transferability becomes a problem, but the resin temperature is 320 ° C or more, and the temperature of the die on the stamper mounting side is 12%.
By setting the temperature to 0 ° C. or higher, the fluidity of the molten resin becomes high, and the resin sufficiently flows into the concave portion of the stamper (corresponding to the land portion of the substrate) and uniformly flows over the entire surface of the stamper, and the transferability is improved.

Here, the condition that the mold temperature on the stamper mounting side is 120 ° C. or higher is particularly effective for improving the transferability. If the resin temperature exceeds 350 ° C, the polycarbonate resin will decompose, so the upper limit of the resin temperature is 350
℃. Also, the mold temperature on the side where the stamper is installed is 140 ° C.
If it exceeds, it takes a long time to cool and solidify the resin after injection, and as a result, the molded substrate is apt to be poor in solidification.

Since the warp of the substrate is likely to be large, the upper limit of the mold temperature on the stamper mounting side is 140 ° C.
And By the way, in the present invention, since the temperature of the mold is raised in order to improve the transferability, the warp of the substrate after molding tends to be large. Therefore, the temperature of the mold on the side facing the stamper, that is, on the side where the stamper is not mounted is set to 20 ° C. higher than the temperature of the mold on the side where the stamper is mounted.
Lower by ~ 5 ° C. By doing so, it is possible to reduce the warp of the substrate without impairing the transferability from the stamper.

Further, in order to suppress the warp of the substrate,
It is desirable to set the cooling time to 6 seconds or more.

[0020]

EXAMPLES The present invention is described in detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist. The groove shape of the stamper and the groove shape of the molded substrate in Examples and Comparative Examples were measured by an optical diffraction measurement method using a He—Ne laser and cross-sectional SEM observation. The groove width was measured at a position 90% of the land height of the substrate (near the top of the land).

Example 1 A groove width of 1.1 μm, a track pitch of 1.6 μm (W / P is about 69%), a groove depth of 70 ± 1 nm, and a groove shape U-shaped stamper are used. The optical disk substrate was injection-molded by mounting it on the fixed mold side. The optical disk substrate has a diameter of 120 mm and a thickness of 1.2 mm. Polycarbonate resin (average molecular weight 1
4300, glass transition point 139 ° C.) was used. The resin temperature was 330 ° C. The temperature of the fixed mold equipped with the stamper was 125 ° C, and the temperature of the movable mold facing the stamper was 115 ° C.

The cooling time was 7 seconds. Transfer rate (%) (groove depth of substrate / height of protrusion for groove formation of stamper) x 1
When defined as 00, the transfer rate of the substrate molded under these conditions was 94 to 96% over the entire surface. The warp of the substrate was 40 μm.

Comparative Example 1 The same stamper as in Example 1 was used, and the stamper was also mounted on the fixed metal side. The temperature of both the fixed mold and the movable mold was 110 ° C. Injection molding was performed under the same conditions as in Example 1 except for the mold temperature. The transfer rate of the molded substrate is 80 to 83% at a radius of 30 mm and a radius of 60 m.
It was 68 to 76% in m. That is, the transfer rate is low, and the transfer rate varies depending on the radius of the substrate or even in the same radius.

[0024]

EFFECT OF THE INVENTION In molding a substrate having a wide groove width, there is provided an injection molding method capable of realizing a uniform and high transfer rate over the entire surface of the substrate and suppressing the warp of the substrate to be small.

Claims (1)

[Claims] 1. An optical disk substrate having a guide groove and having a ratio W / P of the guide groove width W to the track pitch P of 60% to 80% is injection molded using a polycarbonate resin. The mold temperature of the stamper mounting side is set to 320 ° C. to 350 ° C., and the mold temperature of the side facing the stamper is set to 20 ° C. to 5 ° C. lower than the mold temperature of the stamper mounting side. Molding method for optical disk substrate.