JPH0295821A - Injection mold of optical disc board - Google Patents

Abstract

PURPOSE:To obtain an injection mold, the warpage of which is small and which has long service life, by a method wherein the surface of sintered SiC or of reaction-sintered Si and SiC is covered by dense SiC film developed by chemical vapor deposition. CONSTITUTION:Mixture, which is prepared by adding 0.7wt.% in external terms of B4C powder and 3wt.% in external terms of carbon-containing phenolic resin to SiC powder having particle diameter of 0.1mum, is mixed and ground in the presence of alcohol. The resultant mixture is compacted with a rubber press and fired so as to form annular plate-like core main body 1 and cavity main body 2. Next, dense SiC films having the thickness of 250mum are produced onto the inner surfaces (molding surfaces) of the respective main bodies 1 and 2 by chemical vapor deposition and, after that, ground with a diamond grinding wheel so as to realize the surface roughness of 0.02mum Rmax on the molding surface. An injection mold is made by forming a core mold 8 and a cavity mold 9 by mounting the respective main bodies 1 and 2 through annular holders 5 and 6 and a plurality of bolts 7 to a core main body mounting plate 3 and a cavity main body mounting plate 4 having two spiral heat radiating grooves 3a and 4a respectively on their backs.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an injection mold for optical disc substrates.

[Prior Art] Optical discs are made by coating a resin substrate made of synthetic resin such as PC (polycarbonate) or acrylic, or a glass substrate made of glass with a thin film of metal or metal compound as a recording/reading layer, and then forming a 411A film. formed and composed.

Glass substrates can be manufactured with good processing precision, but the glass plate must be cut and the surface must be ground and polished using a diamond grindstone or the like, which has the drawback of significantly increasing costs.

On the other hand, resin substrates are manufactured at low cost mainly by injection molding, but as optical disks progress from read-only (ROM) to write-once (FROM) and then to rewritable (RAM), processing precision is required. Warpage and surface flatness are now considered important.

Conventionally, an injection mold for injection molding the resin substrate is made of metal such as special stainless tool steel.

[Problems to be Solved by the Invention] However, the conventional injection molding mold for optical discs described above has the disadvantage that warping occurs due to thermal deformation because it is heated during injection molding. In addition, there was a problem that it was easily worn out, corroded, and scratched in a short period of time (approximately 10,000 shots).

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide an injection molding mold for an optical disk substrate that has a long life and less warpage.

[Means for Solving the Problems] In order to solve the above problems, the present invention coats the surface of a SiC sintered body or a 5t-SiC reaction sintered body with a dense SiC film by CVD.

The thickness of the SIC film is preferably 5 to 2000 μm, and the surface roughness of the molding surface is at least 0.02 μl.
It is preferable to set it as DRmax.

[Function] According to the above-mentioned means, thermal deformation during injection molding is reduced, and wear resistance and corrosion resistance are excellent, and scratches are less likely to occur.

Moreover, since the surface is coated by CVD, it becomes smooth.

The thickness of the SiC film is preferably within the above range; if it is less than 5 μm, the surface will not be smooth, and if it exceeds 2000 μm, strain will remain in the SiC film, making it easy to peel off.

The surface roughness of at least the molded surface is preferably 0.02 μm or less by diamond abrasive polishing, and 0.0
If it exceeds 2 μm, the surface roughness of the mold will be directly transferred to the molded product and remain as a scratch.

[Example] The present invention will be explained in detail below.

First Example: 0.1 um SiC powder with 0.7 wt% B4C
Powder and phenolic resin containing 3% by weight of carbon were added, alcohol was added, and the mixture was mixed and ground in a ball mill. This mixture was molded using a rubber press and then fired at 2000°C.
A circular plate-shaped core body 1 and cavity body 2 (see FIG. 1) having an outer diameter of 100 um, an inner diameter of 35 mm, and a thickness of 10 mm were made. Then, the inner surface (molding surface) of each main body 1.2 was coated with a thickness of 250 μm using the CVD method (chemical vapor deposition method).
After forming a dense SiC film (not shown), the surface roughness of the molded surface was reduced to 0.02μmR□8 by diamond abrasive polishing.
And so.

Next, as shown in FIGS. 1 and 2, each of the bodies 1 and 2 is mounted on a core body mounting plate 3 and a cavity body mounting plate 4, each having two spiral heat dissipation grooves 3a, 4a on the back surface.
A ring-shaped holding fitting 5.6 was attached via a plurality of bolts 7 to form a core mold 8 and a cavity mold 9, thereby making an injection mold.

The main body mounting plates 3, 4 and the holding fitting 5.6 are made of metal such as special stainless tool steel, and the outer end surface (lower surface in FIG. 1) of the holding fitting 6 of the cavity mold 9 is into which resin is pushed. In order to form the cavity 10, it is appropriately protruded from the molding surface of the cavity body 2.

When an optical disc substrate was injection molded using PC resin using the above injection molding mold, the warpage of the core body 1 and cavity body 2 during heating was 115 or less compared to conventional special stainless tool steel tools. Ta.

Furthermore, the injection mold is resistant to wear and damage, has excellent corrosion resistance, and has no problems during storage, and has a lifespan more than five times that of conventional molds.

Second Example 2% of phenol resin was added to 5 μm SiC powder, mixed and molded, cured at 200°C, and fired at 1500°C. Thereafter, it was reacted with molten silicon at 1500° C. to produce a core body and a cavity body having the same dimensions as in Example 1.

Then, the inner surface of each body is coated with a thickness of 250 μm using the CVD method.
After forming a dense S i cg, diamond abrasive polishing was performed to obtain a surface roughness of 0.02 μmR□8, and an optical disk substrate was injection molded, and the same effects as in Example 1 were obtained.

[Effects of the Invention] As described above, according to the present invention, thermal deformation during injection molding is reduced, so warpage can be reduced to 175 or less compared to conventional molds.

In addition, since it is resistant to wear (and scratches) and has excellent corrosion resistance, the re-polishing life can be extended by more than five times compared to conventional products.

Furthermore, since the surface is coated with a dense SiC film formed by CVD and is smooth, dimensional accuracy during molding is improved.

[Brief explanation of the drawing]

The figures show one embodiment of the present invention, and FIGS. 1 and 2 are a longitudinal sectional view and a bottom view of an injection mold for an optical disk substrate. 1... Core body 2... Cavity body 3.
...Core body mounting plate 4...Cavity body mounting plate 5.6...Press fitting 8...Core mold 9...Cavity mold 10...Cavity applicant Toshiba Ceramics Corporation

Claims (3)

[Claims] (1) An injection mold for an optical disk substrate, characterized in that the surface of a SiC sintered body or a Si-SiC reaction sintered body is coated with a dense SiC film by CVD. (2) The injection mold for an optical disk substrate according to claim 1, wherein the SiC film has a thickness of 5 to 2000 μm. (3) The surface roughness of the molding surface is at least 0.02μmR_
The injection mold for an optical disc substrate according to claim 1 or 2, characterized in that m_a_x.