JPH0763991B2 - Mold for molding 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 Substrates for high-density information recording carriers such as optical discs are generally made of glass, metal, ceramics or plastics, but plastics are preferable from the viewpoints of lightness, strength and productivity.

However, the plastics substrate used for the above optical discs has a thickness of about 1.2 mm to 1.5 mm and a maximum diameter of about 300 mm.
In addition to being extremely thin and flat, acrylic resin or polycarbonate resin, which generally has poor fluidity, is used as the material, so a plastic substrate that satisfies the optical characteristics such as birefringence and the transferability at the same time to formability. Injection molding is difficult.

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. 2 has a molding cavity 3'formed by a pair of mold parts or split molds, for example, a movable mold 1'and a fixed mold 2 ', and a part of the surface of the molding cavity. A stamper 4'having information bits of sub-micron order, tracks, etc. on its surface is attached to (the surface of the movable die 1'in the figure) by a stamper holder 5 '. An outer peripheral ring 6'is mounted on the surface of the fixed mold cavity. Resin is sprue 7 '
And is injected into the molding cavity 3 '.

FIG. 3 shows another conventional injection molding die. In Fig. 3, a double dash (") is attached to the member corresponding to Fig. 2. The injection mold of Fig. 3 has the outer ring 6 'in the case of Fig. 2. The outer surface of the molding cavity is defined by contacting the opposed surface 9 ″ of the fixed mold 2 ″ with the tapered inner peripheral surface 10 ″ of the stamper holder 5 ″ so as to define the outer peripheral end surface of the molding cavity. Generally, it is called an inlay mold.

A method of molding a disk substrate will be described using the mold of FIG. 2. First, a fixed mold 2 ′ is fixed to a fixed plate for mounting a mold of an injection molding machine (not shown), and a movable mold 1 is set to a movable plate. 'Is attached. At the time of molding, after the movable die and the fixed die are closed, the molten resin is injected into the cavity 3'through the sprue 7 '. 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 while being attached to the movable mirror surface, that is, the surface of the stamper 4 '. Then, after the mold is completely opened, air is blown from another air ejector provided near the center of the movable mold to separate the stamper and the substrate, and
The substrate is completely released from the mold by ejecting the substrate with a mechanical ejector rod.

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 groove (continuous groove) to be the guide track is formed on the plastic substrate for optical disk, and the required format is obtained by attaching the grooved plastic substrate thus obtained to the recording film. 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 at the same time as the groove 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 by a mastering into a stamper, but when the stamper containing the pre-format signal is molded by the above-mentioned conventional mold in the above procedure, the "flow phenomenon in the inner circumferential direction of the pit which cannot be seen in the groove part is seen. That is, the uneven shape of the plastic substrate transferred / molded from the stamper “droops”, which causes a phenomenon that the transfer is not performed accurately.

The evaluation of the recording characteristics revealed that the optical disk substrate having the recording film attached to the plastic substrate in which this phenomenon occurred adversely affects the amount of reflected light and finally affects 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 A molding die for a plastic substrate for an optical disc containing a format signal provided by the present invention comprises a pair of split dies, a fixed die and a movable die, and one inner surface of the split die is a mirror surface. A stamper for transferring information pits is mounted on the other inner surface of the split mold, and a mold having a molding cavity defined by the mirror surface and the stamper, further comprising: In a mold in which each of the split molds is provided with an air blow ejector for releasing the molded plastic substrate, the stamper is attached to the fixed mold.

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, it is dragged to the point where the forces are balanced.

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.

That is, in the present invention, in order to solve the decrease in transferability due to the above-mentioned "flow phenomenon" of pits, the mounting surface of the stamper is changed from the movable mold surface to the fixed mold surface.

Even in the conventional mold, the above phenomenon can be solved by causing the air blow from the movable air ejector to work earlier than the air blow from the fixed air ejector when opening the mold. However, in that case, the molded plastic substrate is attached to the fixed mold, while the sprue is attached to the movable mold, so that the operation of an automatic take-out device such as a robot becomes complicated.

In the present invention, the above phenomenon can be solved by changing the mounting surface of the stamper from the movable type to the fixed type, and at the same time, the conventional technique is changed without changing the molding conditions and the operation of the take-out device as they are in the conventional molding device. There is a great advantage that it can be molded without doing.

Hereinafter, it will be described more specifically with reference to the accompanying drawings.

FIG. 1 shows a case where the present invention is applied to the conventionally known in-row type mold assembly shown in FIG.

In this FIG. 1, 1 is a movable die, 2 is a fixed die, 3 is a molding cavity, 4 is a stamper having guide grooves and / or format signal pits on its surface, 5 is an outer ring held by the fixed die, and 8 is Parting line,
Reference numeral 10 denotes a taper surface formed on the inner peripheral surface of the outer peripheral ring 5 and expanding in the mold opening direction, that is, a taper surface expanding in the movable mold direction, and 11 is a central stamper holder for holding the stamper at the center. The movable type 1
And the fixed mold 2 are attached to a movable platen and a fixed platen of a molding machine (not shown), respectively.

Hereinafter, the operation sequence when actually molding using the mold of FIG. 1 will be described.

First, the movable mold and the fixed mold are closed, and the molten resin 11 is injected and filled in the cavity. Next, after the resin melt-injected into the cavity is cooled and solidified for a certain period of time, a mold opening operation for taking out the molded plastic disc from the mold is started.

At the start of this mold opening operation, air is blown out through an air blow ejector (not shown) provided near the center of the fixed mold in order to release the molded plastic substrate. Therefore, the molded plastic substrate is first released from the stamper surface side, and the sprue is released simultaneously with the plastic substrate. The sprue can be mechanically cut out later.

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 movable 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.
With a Å bit and a bumper with a bit height of 1600 Å, and using an M-70 injection molding machine manufactured by Koki Seisakusho, a polycarbonate resin with a cylinder temperature of 330 ° C and a die temperature of 100 ° C with a diameter of 200 mm and a thickness of 1.2 mm Was molded.

At this time, the procedure for releasing the molded substrate from the mold is as follows. First, like the conventional method, the fixed mold, that is, the split mold to which the bumper 4 is attached is released, and after the mold is completely opened. The molded product was released from the movable mold.

As is clear from FIG. 4 showing an electron micrograph of this molded product bit, no flow phenomenon was observed.

The molding was continued for 100 short circuits, but no defective characteristics of the molded substrate or troubles during taking out occurred.

Comparative Example 1 Using the mold shown in FIG. 2, molding was performed under the same conditions as in Example 1.

In this case, the molded substrate was first released from the fixed mold 2'while being attached to the stamper.

As apparent from FIG. 5 showing an electron micrograph of the bit part of the obtained molded product, a flow phenomenon occurred.

Effects As is apparent from the above-described embodiments, according to the present invention, by mounting the stamper on a fixed mold, the operation of an automatic take-out device such as a robot is not complicated, and moreover, the above flow phenomenon can be solved, forming There is a great advantage that molding can be performed by using the conventional molding apparatus as it is as the conditions and the operation of the take-out apparatus without changing the conventional technology.

Further, the following effects can be obtained.

(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) Furthermore, 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 in general, CD
The so-called cloud pattern, which is a problem with, disappears.

(3) When the mold of the present invention is used in the injection-compression molding method, the compressive force from the mold is uniformly applied to the plastic substrate, so that the stress distribution of the entire substrate becomes uniform,
Therefore, the amount of deformation of the molded plastic substrate is small.

[Brief description of drawings]

FIG. 1 is a conceptual cross-sectional view of an injection mold assembly used for molding a plastic substrate for an optical disc according to an embodiment of the present invention. 2 and 3 are conceptual cross-sectional views of a conventionally known injection molding die assembly used for molding a plastic substrate for an optical disc. FIG. 4 is a copy of an electron micrograph of a bit portion of a plastic disk substrate molded according to the present invention. FIG. 5 is a copy of an electron micrograph of a bit portion of a plastic disk substrate molded by the conventional method. (Symbols in the figure) 1 ... Movable type, 2 ... Fixed type, 3 ... Molding cavity, 4 ... Stamper, 5 ... Outer ring, 7 ... Sprue, 8 ... Parting line, 10 ... Taper Surface 11 …… Center stamper holder

Claims (1)

[Claims] 1. A pair of split dies, a fixed die and a movable die, wherein one inner surface of the split die is a mirror surface and the other inner surface of the split die is a stamper for transferring information pits. Is a mold for molding a plastic substrate for an optical disc containing a format signal in which a molding cavity is defined by the mirror surface and the stamper, and further for releasing the molded plastic substrate. 2. A mold in which each of the split molds is equipped with the air blow ejector, wherein the stamper is attached to the fixed mold.