JP2501578B2 - Mold for molding - Google Patents

Description

TECHNICAL FIELD The present invention relates to a mold suitably used for molding an optical disc such as a compact disc or a laser disc.

"Prior Art" Compact discs are provided as audio records that can reproduce the original sound with high precision. A signal is recorded on this compact disc depending on the presence or absence of minute pits (recesses). Such an optical disc is generally manufactured by an injection molding method in which a thin disk (stamper) having protrusions corresponding to pits is attached to a molding die.

As shown in FIG. 3, a molding die used for molding an optical disc has a disk-shaped cavity 3 formed by a cavity surface 1a of a fixed mold 1 and a cavity surface 2a of a movable mold 2. The cavity surface 2a of the movable mold 2 of this mold is mirror-finished. A stamper 5 is detachably attached to the cavity surface 2a by utilizing the central recess 4. The stamper 5 is sequentially replaced according to the type of disc.

Conventionally, this type of molding die has been manufactured from a steel material such as Starbucks (trade name, manufactured by Woodeholm) for convenience of processing.

However, in this molding die, the cavity surface
There was a problem that 2a was easily scratched. If the cavity surface 2a is damaged, the thin stamper 5 is deformed due to the damage, and finally the thin stamper 5 is transferred to a molded disk, resulting in a large amount of defective products being produced.

Therefore, conventionally, when the cavity surface 2a is scratched, maintenance (re-polishing) of the cavity surface 2a must be performed each time, which is an obstacle to improving the disc production efficiency.

As a molding die capable of coping with such a problem, the present inventors previously proposed a molding die in which a part of the cavity 3 is formed of a ceramic sintered body in Japanese Patent Application No. 61-23594. .. FIG. 4 shows an example of this molding die, in which the cavity surface 2a of the movable die 2 to which the stamper 5 is attached is formed by a ceramic plate 6 made of a ceramic sintered body. According to this molding die,
There is an advantage that the frequency of mold maintenance can be greatly reduced.

However, since it is generally difficult to completely remove the pores from the ceramic sintered body, fine holes are distributed on the surface of the ceramic plate 6. Therefore, if a thin stamper 5 is used, these holes will be formed. Could be transferred to the molded product. Therefore, in the previously proposed molding die, the stamper 5 having a thickness of about 0.3 mm or more must be used, which causes the price of the stamper 5 manufactured by electroforming to soar.

"Means for Solving Problems" Therefore, the molding die of the present invention is a molding die to which a stamper is attached when molding an optical disc, and has Rockwell hardness (A scale) of 90 or more. The ceramic thin film layer is laminated on a ceramic substrate, and the thin film layer surface of the thin film layer is formed to 0.02S ~ 1.2S, by the thin film layer laminated surface of the ceramic member, at least the cavity stamper By forming the surface to be attached, the above problem was solved.

Hereinafter, the molding die of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of the molding die of the present invention.
The same components as those of the conventional example are designated by the same reference numerals to simplify the description.

In the molding die of this example, the cavity surface 2a to which the stamper 5 is attached is formed by the ceramic member 10.

The ceramic member 10 is a donut plate-shaped member
As shown in the figure, it is formed of a base material 10a and a thin film layer 10b. The central hole 10c of the ceramic member 10 forms a part of the stamper mounting recess 4. The ceramic member 10 can be mounted by using an adhesive, but the ceramic member 10 of the molding die of this example is a fixed frame.
It is sandwiched and fixed to the movable-side mold body 2b by 11.

The base material 10a of the ceramic member 10 is made of ceramics so that the difference from the coefficient of thermal expansion of the ceramic thin film layers 10b to be laminated is as small as possible. This base material 10a has a sintered density of 85% or more of the theoretical density (in the case of silicon carbide, it is 2.74 g / cm ³ or more).
It is suitable to use a ceramics sintered body of, especially 93% or more of the theoretical density (3.03 g / in case of silicon carbide /
cm ³ or more). When the sintered density becomes low, the pores in the ceramic sintered body become large, which causes a problem that the surface of the ceramic member 10 cannot be finished sufficiently smooth.

The ceramic thin film layer 10b laminated on the ceramic substrate 10a is a layer provided to close fine pores on the surface of the substrate 10a formed by pores present in the ceramic sintered body, and at least the stamper 5 Is formed so as to cover the cavity surface 2a to which is attached. The thin film layer 10b is formed of ceramics having a Rockwell hardness (A scale) of 90 or more. If the hardness of the thin film layer 10b is less than 90, the cavity surface 2a formed by the ceramic member 10 may be scratched due to the collision of a jig or the like when replacing the stamper 5 and the friction such as when cleaning the surface. This causes inconvenience that it becomes easy to attach.

The ceramic thin film layer 10b is formed by a dry coating method. Here, the dry coating method refers to a technique for forming a thin film in a vapor phase state, such as a physical vapor deposition method (PVD method) or a chemical vapor deposition method (CVD method). Examples of the PVD method include a vacuum vapor deposition method such as an electron beam vapor deposition method, a sputter method, an ion plating method, and a molecular beam epitaxy method.

The thickness of the thin film layer 10b formed by such means is preferably about 50 to 200 μm. Thin film layer 10b
If the film thickness is less than 50 μm, it may not be possible to close the fine pores on the surface of the base material 10a formed by the pores present in the ceramic sintered body. Also, the thin film layer 10
If the film thickness of b exceeds 200 μm, it is uneconomical.

Various ceramic materials can be used for forming the thin film layer 10b and the base material 10a. The thin film layer 10b and the base material 10a may be made of the same material, but may be made of different materials. However, when the thin film layer 10b and the base material 10a are formed of different materials, a material having a similar coefficient of thermal expansion is selected to prevent cracks in the thin film layer 10b or peeling of the thin film layer 10b. There is a need.

Specific examples of ceramic materials that can be used include silicon carbide, silicon nitride, alumina, aluminum nitride, zirconia,
Examples include spinel, titanium carbide, boron carbide and the like.

Among them, since silicon carbide has a high thermal conductivity, it has an advantage that cooling at the time of molding can be performed smoothly, the molding time can be shortened, and the molding cycle can be shortened.

There are α-type and β-type of silicon carbide, and any of the ceramic materials forming the ceramic member 10 can be used. As a sintering method of silicon carbide, there are a pressure sintering method, a pressureless sintering method, and a sintering method while reacting silicon (Si) and carbon (C). For the base material 10a of 10, a silicon carbide sintered body manufactured by any method can be used. Further, the silicon carbide sintered body is manufactured by adding a carbon source (C) or the like to fine powder of silicon carbide (SiC), which is the main component, and sintering the powder. Additives such as boron that facilitate the sintering more smoothly (for example, boron carbide (B
₄ C) etc.) have been added. Of course, any silicon carbide sintered body can be used for the molding die of the present invention.

When the thin film layer 10b of the ceramic member 10 is formed of a silicon carbide thin film, a sputtering target uses a silicon carbide target. Also, to form a silicon carbide thin film by the CVD method,
Using a gas obtained by mixing a source consisting of silicon tetrachloride-methane with hydrogen as a carrier gas, the substrate 10a was
Heat to about 400 ° C. In this case, propane can be used instead of methane. Further, the silicon carbide thin film can be formed by using a gas in which methylchlorosilane is mixed with hydrogen and a small amount of argon. In this case, the base material 10a is heated to about 1200 to 1500 ° C. under normal pressure.

In order to manufacture such a ceramic member 10 made of silicon carbide, first, a predetermined amount of a binder and an auxiliary agent is added to silicon carbide, and then a predetermined amount of water is added, and then they are sufficiently mixed with a hole mill or the like. To make a slurry. Next, the slurry is treated with a spray dryer or the like to form granules, and the granules are pressure-molded with a press or the like to form a molded body.
Next, the molded body is processed into a predetermined shape by a lathe, a milling machine, and the like, and then sintered, and a predetermined surface is subjected to polishing and the like to manufacture the base material 10a.

Next, the polished surface of the base material 10a is coated with silicon carbide by a CVD method or the like, and then the surface is subjected to finish processing such as polishing with a diamond lap to form a thin film layer 10b.
The ceramic member 10 is completed.

The surface roughness of the thin film layer 10b of the ceramic member 10 forming the cavity surface 2a is preferably about 0.02S to 1.2S.

The surface on which the thin film layer 10b is formed can be highly smoothed because the fine pores on the surface of the base material 10a made of a ceramics sintered body are closed by the thin film layer 10b.
It is desirable to keep the surface roughness to about 0.02S. When the surface roughness of the cavity surface 2a becomes small, the adhesive force with the attached stamper 5 becomes great, and the difference in thermal expansion between the stamper 5 and the ceramic member 10 easily causes an accident in which fine wrinkles occur in the stamper 5. Become. In this respect, there is a fundamental difference between the mold of the present invention and the conventional Starbucks (steel) mold, and it is said that the surface roughness of the Starbucks mold must be 0.01S or less. It was Further, if the surface roughness exceeds 1.2S, there is an increased risk that the unevenness of the cavity surface 2a will be transferred to the molded disk via the stamper.

The fixed mold 1 and the movable mold 2 of the molding die to which the ceramic member 10 is attached are respectively provided with cooling holes 12 for maintaining the die at a predetermined temperature during molding. ing.

"Operation" In the molding die having such a configuration, the stamper 5
Even when a jig or the like hits the cavity 2a of the movable-side mold 2 when exchanging, the damage such as transfer to the molded disk does not occur.

 The present inventor considers the reason as follows.

First, the cavity surface 2a of this mold is a ceramic member.
Since it is formed of 10, it is hard to get scratches even if it is hit by a jig. Also, even if a scratch is made, the scratch will be shallow.

Moreover, since ceramics are fragile materials unlike metal materials, even if the cavity surface 2a is damaged, it does not plastically deform and swell around the scratches unlike steel materials. Therefore, in the case of the conventional mold made of steel material, the molding pressure was concentrated on a part of the stamper 5 in contact with the raised portion and the deformation occurred there. However, in the mold of the present invention using the ceramic member, Even if the cavity surface 2a is scratched, swelling does not occur. Therefore, since the molding pressure is not concentrated on a part of the stamper 5 and the stamper 5 is not deformed, there is no problem even if the disk production is continued as it is.

Further, since the surface of the ceramic member 10 is formed by the ceramic thin film layer 10b, the micropores on the surface of the substrate 10a formed by the pores present in the ceramic sintered body are closed. . Therefore, even if the thin stamper 5 is attached to the cavity surface 2a formed by the ceramic member 10, there is no abnormality in the molded product due to the pores of the base material 10a. In addition, the cavity surface
Since the surface roughness of the thin film layer 10b of the ceramic member 10 forming 2a is 0.02S or more, the cavity surface 2a
It is possible to prevent fine wrinkles from occurring in the stamper 5 due to the difference in thermal expansion between the stamper 5 attached to the and the ceramic member 10. Since the surface roughness is 1.2 S or less, the unevenness of the cavity surface 2a is not likely to be transferred to the molded product via the stamper 5.

"Example" The molding die shown in Fig. 1 was prepared. First, a movable mold body 2b and a fixed mold 1 were manufactured using Starbucks. Next, using silicon carbide, outer diameter 140 mm, inner diameter 34 m
A doughnut-shaped ceramic sintered body having a size of m and a thickness of 12.7 mm was prepared as a base material 10a of the ceramic member 10. Next, this base material 10a was set in a CVD apparatus. After depressurizing the CVD apparatus, the base material 10a is heated to 1400 ° C., and then a mixed gas consisting of silicon tetrachloride-propane gas is mixed with hydrogen as a carrier gas and supplied to the apparatus, and one of the base material 10a A silicon carbide thin film layer 10b having a film thickness of 140 μm was formed on the surface to obtain a ceramic member 10.

Next, move the ceramic member 10 to the movable mold body.
It was fixed at a predetermined position of 2b using a fixing frame 11. After that, the surface of the ceramic member 10 is ground and then diamond-lapped to have a surface roughness of 0.2S, a parallelism of 0.002, and a flatness of 0.003.
Finished.

This molding die was used and its effect was confirmed.

First, after attaching this molding die to the injection molding machine,
Set a thin stamper 5 (0.1 mm thick) and have an outer diameter of 120
mm, an inner diameter of 15 mm, and a thickness of 1.2 mm were continuously formed into 1000 laser disks. Molding is performed by passing hot water at 80 ° C through the cooling holes 12, and then using molten polycarbonate resin at 300 ° C in the cavity 3.
It was injected into.

After molding, when the molded product and the stamper 5 were examined, no abnormalities were found in both the molded product and the stamper 5. According to this molding die, even if a thin stamper 5 such as 0.1 mm is used, the disc problem It turns out that it can be produced without.

Next, when this stamping die was used to perform a normal production in which the stamper 5 was replaced, the number of scratches on the die was reduced as compared with the conventional die. In the past, it was necessary to make a trial of about 10 to 15 shots until stable molding was performed after the stamper was replaced, but with this molding die provided with the silicon carbide ceramic member 10, about 3 shots is sufficient. It has been found that stable molding can be performed, and this molding die enables stable molding to be started in a short time after the stamper is replaced.

In the above-described embodiment, only a part (the surface 2a) of the cavity surfaces 1a and 2a forming the cavity 3 is formed by the ceramic member 10, but the entire cavity surface may be formed by the ceramic member 10. Of course good things.

Further, in the molding die of the embodiment, the cooling holes 12 ... Are provided in the movable die main body 2b, but the cooling holes 12 ... Can be provided in the ceramic member 10. In this case, it is desirable to fix the ceramic member 10 by providing a fixing spigot on the mold body 2b and locking the ceramic member 10 thereto. When the ceramic member 10 is provided with the cooling holes, the cavity surface 2a can be cooled more smoothly, and therefore, there is an advantage that even the ceramic forming the ceramic member 10 can be used even if its thermal conductivity is somewhat inferior.

[Advantages of the Invention] As described above, in the molding die of the present invention, at least a portion of the cavity surface forming the cavity to which the stamper is attached is formed of a ceramic member, and therefore, when used for molding an optical disc or the like. Even if the jig collides during the stamper replacement, it is less likely to be damaged, and the frequency of mold maintenance can be greatly reduced. Therefore, the molding die of the present invention is excellent in that it is easy to handle, it is possible to reduce the labor of die management, improve the use efficiency of the die, and thus improve the production efficiency of the disc. It has advantages.

In addition, since the ceramic member used in the molding die of the present invention has the ceramic thin film layer laminated on the surface of the base material, fine pores are formed on the surface of the base material due to the pores present in the ceramic sintered body. Even if the holes are formed, the fine holes are closed by the thin film layer. Therefore, according to the molding die of the present invention, the cavity surface formed by the ceramic member can be formed extremely smooth. Furthermore, since the surface roughness of the thin film layer of the ceramic member that forms the cavity surface is 0.02S to 1.2S, the stamper is not fine due to the difference in thermal expansion between the stamper attached to the cavity surface and the ceramic member. It is possible to prevent the occurrence of creases, and there is no fear that the unevenness of the cavity surface is transferred to the molded product via the stamper. As a result, with the molding die of the present invention, it is possible to manufacture a good molded product without problems even if a stamper that is thin and therefore inexpensive is used.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the molding die of the present invention,
FIG. 2 is an enlarged view of part A of the same embodiment, FIG. 3 is a sectional view showing a conventional molding die, and FIG. 4 is a sectional view showing the previously proposed molding die. 2a …… Cavity surface, 10 …… Ceramics member, 10a…
… Substrate, 10b… Thin film layer.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP 61-100425 (JP, A) JP 61-48492 (JP, A) JP 61-86221 (JP, A) JP 55- 80784 (JP, A) JP 61-222975 (JP, A) Actual development 61-143810 (JP, U)

Claims (3)

(57) [Claims] 1. A molding die used with a stamper attached when molding an optical disk, wherein a ceramic thin film layer having a Rockwell hardness (A scale) of 90 or more is laminated on a ceramic substrate. And a surface to which the stamper of at least the cavity is attached is formed by the thin film layer laminating surface of the ceramic member formed with the surface roughness of the thin film layer of 0.02S to 1.2S. Mold. 2. The molding die according to claim 1, wherein the thin film layer of the ceramic member is formed by a dry coating method. 3. The base material and thin film layer of the ceramic member are
The molding die according to claim 1 or 2, which is made of silicon carbide.