JPH0751300B2 - Molding method for preformatted optical disk substrate and mold used therefor - Google Patents

Description

TECHNICAL FIELD The present invention relates to a plastic substrate injection molding for a high density information recording carrier such as an optical disk such as an optical disk such as a ROM disk such as a CD or VD, a DRAW disk or an E-DRAW disk. The present invention relates to a method and a mold used for the method.

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 substrate used for the optical disc as described above is extremely thin and flat with a thickness of about 1.2 to 1.5 and a maximum diameter of about 300 mm, and in general, acrylic resin or polycarbonate resin having poor fluidity is used as a material. Therefore, it is difficult to injection-mold a plastic substrate that simultaneously completely satisfies optical characteristics 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. 2 has a molding cavity 3 formed by a pair of mold parts, that is, a split mold, for example, a movable mold 1 and a fixed mold 2, and a part of the surface of the 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. 3 shows another conventional injection molding die. Incidentally, in FIG. 3, members corresponding to those in FIG. 2 are provided with dashes. The injection molding die shown in FIG. 3 eliminates the outer peripheral ring 6 in the case of FIG. 2 and eliminates the stamper holder 5 '.
Fixed type 2'on the tapered inner peripheral surface 10 of the diode of
Of the molding cavity are abutted against 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 disk substrate will be described with reference to the mold of FIG. 2. 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 stamper and the substrate, and further, the substrate is ejected using a mechanical ejector rod. 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 only necessary to accurately transfer the above group 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 in the inner circumferential direction of the pit which cannot be seen in the group part is seen. "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 An optical disk-shaped plastic substrate molding method provided by the present invention includes a step of supplying a liquid resin into a molding cavity formed by a pair of split molds. When the mold is released from the pair of split molds, the optical disk substrate molded first is released from at least the split mold surface corresponding to the uneven surface portion.

The above-mentioned molding method is generally an injection molding method, and therefore the liquid resin is generally a thermoplastic molten resin,
It can also be applied to other compression molding, casting method and the like.

The uneven surface portion may be constituted by a stamper attached to one of the split molds, and is generally a submicron order replica surface corresponding to a continuous guide track and / or preformat signal.

At the time of releasing the mold, it is preferable to eject a fluid between the molded optical disk substrate and the surface of the split mold.

A mold assembly for molding an optical disk-shaped plastic substrate provided by the present invention comprises a pair of inner surfaces defined by a pair of split dies, which face each other, and a ring shape attached to one outer peripheral portion of the split dies. It has a molding cavity defined by the inner surface of the member, one of the pair of inner surfaces facing each other is a mirror surface, and the other inner surface is uneven for transferring information pits to the molded disk. The inner surface of the ring-shaped member is a tapered surface that expands in the removal direction of the molded product, and the ring-shaped member is slidable in the mold opening direction. I am trying.

The pair of inner surfaces forming the cavity can be of the spigot type.

The ring-shaped member forming the female mold can hold the stamper.

It is preferable to form deaeration holes in the ring-shaped member.

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.

Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings, but the present invention is not limited thereto.

Embodiment FIG. 1 is a conceptual sectional view of a mold of a preferred embodiment embodying the present invention.

In the mold assembly shown in FIG. 1, 1 is a movable mold, 2 is a fixed mold, 3 is a molding cavity, 4 is a stamper having a guide group and / or a format signal pit on its surface, and 5 is held by the movable mold. Outer peripheral ring, 16 a pressing spring for pressing the outer peripheral ring in the mold opening direction, 7 a sprue, 8 a parting line, 9 conductive holes for letting air in the cavity escape, and 10 an outer peripheral ring 5. Is a taper surface formed on the inner peripheral surface of the tape and expanded in the mold opening direction.

Hereinafter, the operation sequence when actually molding using the mold of FIG. 1 will be described with reference to the conceptual diagrams shown in FIGS. 4 to 7.

First, FIG. 4 shows a state in which the movable mold 1 and the fixed mold 2 are attached to the movable platen and the fixed platen of a molding machine (not shown), respectively, and the molds are opened. At this time, the outer peripheral ring 5 is pushed up by the pressing spring 16 from the parting line 8 by an amount of length t. This length t is determined by the outer ring 5
Is smaller than the clearance t'between the holding portion and the stamper 4 by 0 to 40 μm, ideally 5 to 20 μm.

Next, in FIG. 5, the movable mold and the fixed mold are closed, and the molten resin 11
Shows the state in which the cavity is injection-filled. At this time, the outer peripheral ring 5 comes into contact with the fixed mold and is pushed into the movable mold by the distance t.

Next, FIG. 6 shows the resin 11 melt-injected into the cavity.
FIG. 7 is a diagram showing a state at the start of a mold opening operation for taking out the molded plastic disc from the mold after cooling and solidifying for a certain time.

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 movable mold to release the molded plastic substrate, but at the same time, The outer peripheral ring 5 is pushed out by the pressing spring 16 while the die is opened by the distance of the length t. On the inner peripheral surface of the outer peripheral ring 5, a tapered surface 10 is formed which is enlarged in the mold opening direction, so that the molded plastic substrate is separated from the stamper surface while the outer peripheral portion is held by the tapered surface 10. Mold.

Next, when the mold is opened by the distance t or more, the fixed mold and the molded plastic substrate are released from each other by the air blow of the fixed mold, and the molded substrate is stamped toward the movable mold as shown in FIG. Hold it above the surface.

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.

In addition, the above air blowing operation is supplied between the plastic substrate and the fixed mold at the same time as the movable air blow ejector through an air blow ejector (not shown) provided near the center of the fixed mold. However, it is necessary to release the molded plastic substrate first from at least the stamper surface side. Preferably, in the initial stage of mold opening in FIG. 6, the fixed-type air blow ejector is stopped and air is blown out from the fixed-type air blow ejector after the mold has opened a distance t. Is more effective. Further, in this case, since the air supplied from the movable air blow ejector flows out from the air escape conductive hole 9, the disc substrate held by the outer peripheral ring 5 is not released by the pressure.

An electron micrograph of the bit portion of the plastic disk substrate molded in this way is shown in FIG. As is clear from a comparison between this and FIG. 9 showing an electron micrograph of the same part formed by the conventional mold, the mold of the present invention has less deviation of the bit part, that is, “flow”. I understand.

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 group is improved.

(2) Furthermore, since the signal surface is released from the mold opening and the doji, and the imbalance of the mold release is eliminated, the so-called cloud-like gas pattern, which is generally a problem with CDs, is eliminated.

[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. 4 to 7 are explanatory views of respective steps in molding a plastic substrate for an optical disc using the injection molding die assembly shown in FIG. FIG. 8 is a copy of an electron micrograph of a bit portion of a plastic disk substrate molded according to the present invention. FIG. 9 is a copy of 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 ... Outer ring, 7 ... Sprue, 8 ... Parting line, 9 ... Conductive hole, 10 ...
Tapered surface, 11 …… Resin, 16 …… Pressing spring

Claims (3)

[Claims] 1. A method of molding a plastic substrate for an optical disc having an uneven surface portion on one surface, including a step of supplying a liquid resin into a molding cavity formed by a pair of split molds, wherein When releasing from the split mold, the method is characterized in that the optical disk substrate molded first is released from at least the split mold surface corresponding to the uneven surface portion. 2. The method of claim 1, wherein the textured surface portion is constituted by a stamper attached to one of the split molds. 3. The method according to claim 1, wherein a fluid is jetted between the molded optical disk substrate and the split mold surface at the time of demolding.