JPH07316B2 - Formatting method for optical disc substrate with format - Google Patents

Description

Description: INDUSTRIAL APPLICABILITY The present invention relates to injection of a plastic substrate for a high density information recording carrier such as an optical disk such as an optical disk such as a ROM disk such as CD and VD, a DRAW disk or an E-DRAW disk. The present invention relates to a molding method and a mold used therefor.

2. Description of the Related Art A substrate for a high-density information recording carrier such as an optical disc is generally made of glass, metal, ceramics or plastic, but plastic is preferable from the viewpoint of lightness, strength and productivity.

However, the plastic substrates used for optical discs as described above are extremely thin and flat with a thickness of about 1.2 to 1.5 mm and a maximum diameter of about 300 mm, and acrylic resin or polycarbonate resin, which generally has poor fluidity, is used as the material. Therefore, it is difficult to injection-mold a plastic substrate that simultaneously completely satisfies optical properties such as birefringence and moldability such as transferability.

Among various performances required for this kind of disk substrate, the transfer performance for accurately transferring the surface shape of the stamper arranged in the mold, that is, the information pit row, is one of the most important factors.

Conventionally, as a mold for injection molding of a plastic substrate for an optical disc, a mold having a structure as shown in FIGS.

The mold shown in FIG. 1 has a molding cavity 3 formed by a pair of mold parts, that is, split molds, for example, a movable mold 1 and a fixed mold 2, and a part of the surface of this molding cavity (in the figure, A stamper 4 having submicron-order information bits, tracks, etc. on its surface is attached by a stamper holder 5 to the surface of the movable die 1. An outer peripheral ring 6 is attached on the surface of the fixed mold cavity. The resin is injected into the molding cavity 3 via the sprue 7.

FIG. 2 shows another conventional injection molding die. In FIG. 2, members corresponding to those in FIG. 1 are marked with dashes. The injection molding die shown in FIG. 2 eliminates the outer peripheral ring 6 in the case of FIG. 1 and eliminates the stamper holder 5 '.
On the tapered inner peripheral surface 10 of the fixed mold 2'opposing surface 19
Contact with each other to define the outer peripheral end surface of the molding cavity. This type of mold is generally called an inlay mold.

A method of molding a disc substrate using the mold of FIG. 1 will be described. First, a fixed mold 2 is mounted on a fixed plate for mounting a mold of an injection molding machine (not shown), and a movable mold 1 is mounted on a movable plate. Mounted. During molding, the molten resin is injected into the cavity 3 through the sprue 7 after closing the movable die and the fixed die. After that, the resin melt-injected into the cavity is cooled and solidified for a certain period of time, and then the mold clamping mechanism is driven to separate the movable mold from the fixed mold to open the mold, and at the same time, the air generated near the center of the fixed mold Air is blown from the ejector to release the molded substrate from the fixed mirror surface.

Therefore, the molded plastic substrate is opened in a form in which it is attached to the movable mirror surface, that is, the surface of the stamper 4. Next, after the mold is completely opened, air is blown from another air ejector provided near the center of the movable mold to separate the suntaper and the substrate, and the substrate is ejected using a mechanical ejector rod. By doing so, the substrate is completely released from the mold.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention Optical discs include a pre-format system and a post-format system.

In the case of the post-format system, only the groups (continuous grooves) to be the guide tracks are molded on the optical disk plastic substrate, and the required format is obtained by attaching the recording film to the grooved plastic substrate thus obtained. Written after the optical disc is installed in the drive. Therefore, in forming the substrate, it is sufficient to accurately transfer the groove from the stamper.

However, recently, in addition to the uneconomical effect of the post-formatting method, the so-called pre-formatting method, in which formatting is performed simultaneously with the group at the molding stage of the plastic substrate, has become mainstream due to advances in mastering or drive design technology. This preformatted signal is
Unlike the continuous guide track described above, it is composed of pits having a fixed length.

The pre-format signal is generally cut into a stamper by mastering, but when the stamper containing the pre-format signal is molded by the above-mentioned conventional mold in the above procedure, the "flow toward the inner peripheral direction of the pit which is not seen in the groove part""Phenomenon", that is, the uneven shape of the plastic substrate transferred / molded from the stamper "droops" and the transfer is not performed accurately.

The evaluation of the recording characteristics has revealed that the optical disk substrate in which the recording film is attached to the plastic substrate in which this phenomenon occurs has a bad influence on the amount of reflected light, and finally has a bad influence on the recording / reproducing characteristics.

As a result of extensive studies on this phenomenon, the present inventor has found that the above phenomenon occurs between the time when the mold is opened and the time when the molded disk substrate is released from the stamper surface, and a method for solving this is found. Invented

Therefore, the object of the present invention is to provide the above-mentioned "flow phenomenon" of pits.
(EN) Provided is a method for solving a decrease in transferability caused by the above, and a mold assembly used for the method.

Means for Solving the Problems The method for molding a plastic substrate for an optical disk provided by the present invention is a single-sided process including a step of supplying a liquid resin into a molding cavity formed by a pair of split molds having a stamper attached to one side. In a method of molding a plastic substrate for an optical disc having a format signal and / or a format signal having a guide groove, the optical disc substrate molded by mold opening after the resin supplied into the molding cavity is cooled and solidified. When the mold is released from the pair of split molds, the surface on which the format signal and / or the guide group on the stamper side is inserted is separated from the surface on the opposite side at least simultaneously with the mold.

The releasing operation may be performed by releasing the surface of the molded plastic substrate on the side of the stamper having the format signal and / or the guide group from the surface of the split mold earlier than the surface on the opposite side.

The molding method is generally injection molding, and the liquid resin is a molten resin.

First, the case where the optical disk substrate is molded by the conventional method as described above will be described.

The molten resin injected into the cavity tends to shrink inward as the cooling progresses, but while the mold is closed, it is pressed by the pressing force from the mold and the friction between the mold surface. As a result, stress occurs but contraction does not occur.

Next, when the mold begins to open and the signal surface of the substrate is still in close contact with the stamper, and the surface opposite to the signal surface of the molded substrate separates from the mold, that surface of the substrate peels inward. Begins contraction. At this point, the signal surface of the substrate is still in close contact with the stamper, so this signal surface tends to be held as it is due to the frictional force with the stamper surface. However, since the shrinkage force of the resin is greater, the force is unbalanced.

The "flow phenomenon" of pits is, so to speak, a trace made on the molded substrate by the pits of the stamper caused by the difference in shrinkage between the stamper and the disk substrate. Therefore, this phenomenon is affected by the height of the pit, and the higher the height, the longer the flow distance.

From the above analysis, the present inventor has completed the present invention by thinking that, in order to solve this phenomenon, it is sufficient to release the stamper from the stamper before the signal surface of the substrate is scratched by the opposite surface.

In the present invention, the known mold shown in FIG. 1 or 2 can be used as it is.

That is, for release of the molded plastic substrate at the start of the mold opening operation, release air supplied through an air blow ejector (not shown) provided near the center of the fixed die and the movable die. The blowout timing may be adjusted so that the stamper side and the opposite side simultaneously release the mold, or the stamper side releases the mold earlier.

Specifically, after the resin 10 melt-injected into the cavity is cooled and solidified for a certain period of time, at the start of the mold opening operation for taking out the molded plastic disc from the mold, the mold release of the molded plastic substrate is performed. Therefore, the air blown out through the air blow ejector near the center of the movable mold is released at the same time on the stamper side and the opposite side, or it is adjusted so that the stamper side releases earlier. Keep it. Also, in the early stages of mold opening,
Stop the air blow ejector of the fixed type,
It is also possible to blow air from the air blow ejector of the fixed mold after the mold has been opened a predetermined distance, for example, several tens of microns.

Then, after the mold is completely opened, the plastic substrate molded by using the mechanical protruding ring, the rod and the like is completely released from the mold.

Hereinafter, preferred embodiments of the present invention will be described, but the present invention is not limited thereto.

Example An improved spigot die shown in FIG. 1 has a groove depth of 800.
Install a stamper with a bit height of 1600Å at Å, use an M-70 injection molding machine manufactured by each machine manufacturer, and use a polycarbonate resin at a cylinder temperature of 330 ° C, a mold temperature of 110 ° C, and a diameter of 200 mm,
A 1.2 mm thick substrate was molded.

At this time, the procedure for releasing the molded substrate from the mold is to blow air from the air ejector provided near the center of the fixed mold and the movable mold at the same time as the mold opening signal so that the mold and the movable mold can be ejected almost simultaneously from both molds. The substrate was released.

No flow phenomenon was observed, as is apparent from FIG. 3 showing an electron micrograph of the bits of this molded product.

Comparative Example Molding was carried out using the same molding machine, mold and molding conditions as in the examples.

As a method of releasing the substrate, as is generally done in the past, first, at the same time as the mold opening signal, air is blown from the air ejector at the center of the fixed die to release it from the fixed die, and then the die is released. After making it completely open, air was blown from the central part of the movable mold to float the substrate from the mirror surface of the movable mold and mechanically eject the substrate with an ejector ring.

In this case, the molded substrate was first released from the fixed mold while being attached to the stamper.

As apparent from FIG. 4 showing an electron micrograph of the bit part of the obtained molded product, a flow phenomenon occurred.

Effects By using the method of the present invention, the “flow” phenomenon is eliminated as described above, and at the same time, the following effects are achieved.

(1) Since the signal surface is released at the same time when the mold is opened, the entire signal surface contracts uniformly. Therefore, the roundness of the groove is improved.

(2) Further, the signal surface is released at the same time when the mold is opened, and therefore the imbalance of the release is eliminated, so that the so-called cloud pattern, which is generally a problem in CD, is eliminated.

[Brief description of drawings]

1 and 2 are conceptual sectional views of an injection mold assembly used for molding a plastic substrate for an optical disc to which the present invention is applied. FIG. 3 is a copy of an electron micrograph of a bit portion of a plastic disk substrate molded according to the present invention. FIG. 4 is an electron micrograph of a bit portion of a plastic disk substrate molded by a conventional method. (Reference numeral in the figure) 1 ... Movable type, 2 ... Fixed type, 3 ... Molding cavity,
4 …… Stamper, 5 …… Stamper holder, 6 ……
Outer ring, 7 ... Sprue, 8 ... Parting line, 9, 10 ... Tapered surface

Claims (3)

[Claims] 1. An optical disk containing a format signal and / or a format signal having a guide groove on one side thereof, including a step of supplying a liquid resin into a molding cavity formed by a pair of split molds having a stamper attached to one side thereof. In the method of molding a plastic substrate for use in molding, when the resin supplied into the molding cavity is cooled and solidified, the optical disc substrate molded by mold opening is released from the pair of split molds by a format signal on the stamper side. And / or a molding method in which the surface containing the guide group and the surface on the opposite side are simultaneously released from the mold at least temporally. 2. The mold surface of the molded plastic substrate having the format signal and / or the guide groove on the stamper side is released from the split mold surface earlier than the surface on the opposite side. The method described. 3. The method according to claim 1, wherein the molding method is injection molding and the liquid resin is a molten resin.