JPH0219774B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a mold for a disk base having an improved structure and a method for injection molding a disk base using such a mold, and more particularly to a mold for a disk base having an improved structure. The present invention relates to a disk substrate mold for stably manufacturing a substrate, especially an optical disk with good moldability, and an injection molding method using the same.

(Background Art) Conventionally, in the production of disk bases used for optical disks such as video disks and compact disks, a predetermined stamper is set in a product cavity formed by a movable mold and a fixed mold. An injection molding method is adopted in which a predetermined resin material is injected into the product cavity to form a disk base onto which the information on the stamper surface is transferred. In general, the mold clamping force required is enough to prevent the mold from opening even when the resin material is filled into the mold, for example 120
With a mmφ disc base, the mold clamping force is over 40 tons,
Furthermore, for a 300mmφ disc base, the mold clamping force must be over 200 tons.

On the other hand, when setting a stamper in the product cavity of a mold, the inner peripheral edge of the donut-shaped stamper is usually fixed to the movable mold side using an appropriate fixing means, and the outer peripheral edge of the stamper is is restrained by a stamper holding ring 2 as shown in FIG. and a gas venting section 10 for discharging to the outside the gas inside the product cavity that is extruded when a predetermined resin material is filled into the product cavity.
are formed with a predetermined gap: α.

However, in the case of such a conventional gas venting structure provided at the peripheral edge of the product cavity, the peripheral edge of the stamper 6 is connected to the stamper holding ring 2.
Since the stamper 6 is not completely constrained and there is a small gap, for example, about 2/100 mm between them, the thickness of the stamper 6 is The gap α of the gas venting portion 10 changes due to the variation in the height. For example, as the thickness of the stamper increases, this gap α becomes smaller, making it difficult for gas to escape and pressure is not applied to the end of the product.On the other hand, when the thickness of the stamper becomes thin, the gap α becomes larger. Therefore, the resin material 8 enters the gas venting part 10 having such a large gap under the injection pressure, causing problems such as burrs.

Moreover, the molding conditions change due to differences in gas release caused by differences in the thickness of the stamper 6, etc., and the molding conditions also have a narrow range, making it extremely difficult to select the optimal conditions. This has become a tedious task. In addition, because the range of such conditions is narrow, there are large variations in quality between products and poor yields. Pressure stripes are formed on the periphery of the disk substrate, causing variations in the quality of the product between the inner and outer circumferential sides, and in particular, the problem of changes in birefringence. For example, regarding this birefringence, in the case of a 120 mmφ compact disc, even if the 50 mmφ is 50 nm,
At a diameter of 90 mm, it is often close to 100 nm. Such a difference in birefringence causes variations in the information transferred to the surface of the disk substrate and variations in the reading of the transferred information, resulting in a decrease in the quality of the disk substrate. That's what happens.

(Problem to be solved) The present invention has been made against the background of the above circumstances, and its purpose is to discharge gas from the product cavity in injection molding of a disk base such as an optical disk. The destabilization of formability caused by variations in the size of gaps for gas venting and the resulting product variations can be effectively suppressed with a simple configuration, improving product stability and formability. The purpose of the present invention is to provide a mold for a disk base that can effectively suppress and equalize the birefringence when molding a disc base using such a mold. The object of the present invention is to provide an injection molding method for a disk base that can effectively improve product quality.

(Solution Means) In order to achieve such an object, in the present invention, a stamper is set in a product cavity formed by a movable mold and a fixed mold,
By injecting a predetermined resin material into the product cavity,
In the disc base forming mold capable of molding a disc base onto which information on the stamper surface has been transferred, a stamper holding member for restraining the outer peripheral edge of the stamper is provided on the movable mold side, and the fixed metal A stepped portion that can be fitted to the inner surface of the stamper holding member is formed on the mold side, and the product cavity is formed in a state where the stamper holding member and the stepped portion are fitted, and the inner surface of the stamper holding member is fitted. The end face of the product cavity is made up of a part of the product cavity.

In addition, in the method of the present invention, a stamper is set in a product cavity formed by a movable mold and a fixed mold, and a predetermined resin material is injected into the product cavity, thereby forming a surface of the stamper. In the method for molding a disk base onto which information has been transferred, a stamper holding member for restraining the outer peripheral edge of the stamper is provided on the movable mold side, and an end face of the product cavity is held on the inner surface of the stamper holding member. and a predetermined gap for degassing is formed between the rising wall surface of the stepped portion on the fixed mold side provided corresponding to the stamper holding member and the inner surface of the stamper holding member. In this step, the resin material is injected into the product cavity using a primary injection pressure that applies a mold opening force slightly larger than the mold clamping force to the movable mold, thereby injecting the resin material necessary to form the desired disk base. When the amount of resin is injected into the product cavity, the injection pressure is switched to a secondary injection pressure where the mold opening force acting on the movable mold is smaller than the mold clamping force. The material is filled into the product cavity by mold clamping force, and the gas inside the product cavity that is pushed out as a result of the filling is transferred between the inner surface of the stamper holding member and the rising wall surface of the step on the fixed mold side. It was designed so that it would be discharged from the gap between the two.

(Operations/Effects) According to the disk base forming mold according to the present invention, the gap for degassing provided at the peripheral edge of the product cavity is formed between the stamper holding member and the rising wall surface of the step on the fixed mold side. By providing the stamper so as to extend in the mold clamping direction, the gap for degassing can be kept constant with a simple configuration, regardless of variations in the thickness of the stamper. Therefore, unlike conventional molds in which a gap for degassing is formed between the stamper surface and the stationary ring in a direction perpendicular to the mold clamping direction, variations in the thickness of the stamper As a result, problems such as poor gas release and occurrence of burrs can be effectively prevented, and excellent product stability and moldability can be obtained.

Further, in the injection molding method according to the present invention, the mold according to the present invention is used, and in the mold, a gap for discharging gas in the product cavity is formed between the inner surface of the stamper holding member and the fixed mold. Since it is formed so as to extend in a direction parallel to the mold clamping direction between the side step part and the rising wall surface, the effects of the mold according to the present invention described above can be obtained as is, and Unlike conventional methods, the method of the present invention does not use injection pressure to fill the resin material into the product cavity, but instead injects the amount of resin necessary to form the desired disk base into the product cavity. After that, the cavity volume is compressed (reduced) using mold clamping force to fill the injected resin material up to the periphery of the product cavity. The resin material located in the mold also receives uniform pressure from the mold, making it possible to achieve a wide range of molding conditions, making it easy to optimize such molding conditions, and reducing variations between products. This not only improves yield and improves quality, but also reduces the difference in birefringence between the inner and outer peripheries of a single disk substrate. be.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

First, in Fig. 2, 12 is a movable plate;
Further, 14 is a fixed plate, and between them, as is well known, there is a product cavity for molding the target disk base (product) such as an optical disk such as a video disk or a compact disk. A movable mold 16 and a fixed mold 18 forming a mold according to the invention are attached. The movable mold 16 and the fixed mold 18 are clamped with a predetermined clamping force by a movable platen 12 that is moved by a clamping cylinder (not shown). On the other hand, a known injection molding machine 20 for injecting a predetermined resin material into a product cavity 22 in the mold formed by such mold clamping is arranged at the back of the fixed platen 14. The resin material injected from the injection molding machine 20 is guided to a product cavity 22 within the mold.

Further, a predetermined donut-shaped stamper 24 (generally, information is engraved on the surface) is disposed in a product cavity 22 formed between the movable mold 16 and the fixed mold 18, The inner peripheral edge portion on the center side is connected to the movable mold 16 in the same way as in the past.
While it is fixed to the side, its outer peripheral part is
As shown in FIGS. 3a and 3b, the stamper 24 is restrained by a hook-shaped stamper holding ring 26 attached to the movable mirror block 28 of the movable mold 16. , is set within the product cavity 22 on the movable mold 16 side. here,
The stamper presser ring 26 constitutes a stamper presser member that restrains the outer peripheral edge of the stamper 24.

Furthermore, a stepped portion (relief portion) 32 is formed on the fixed side mirror block 30 of the fixed mold 18 that forms the product cavity 22, corresponding to the stamper holding ring 26 provided on the movable side mirror block 28. When the mold is clamped, the fixed side mirror block 30 is fitted into the inner surface 34 of the stamper holding ring 26 at its stepped portion 32, so that the head of the stamper holding ring 26 does not interfere with the fixed side mirror block 30. has been done. and,
As a result, in the mold clamping state, a part of the inner surface 34 of the stamper holding ring 26 is attached to the product cavity 2.
2, and thereby the inner surface 34 constitutes the end surface of the product cavity 22, and the inner surface 34 and the rising wall surface 36 of the stepped portion 32 of the fixed side mirror block 30
in the mold clamping direction, that is, a in FIG. 3,
At b, a predetermined gap (gassing portion) 38 for venting gas in the vertical direction is formed.

By the way, the method of the present invention uses an apparatus having such a mold structure, and first, the movable mold 16 is
and the fixed mold 18 are clamped, and then the mold clamping force: Fc is slightly larger than the mold opening force: Fo which is applied to the movable mold 16 to the primary injection pressure: Pi _1. Then, a predetermined resin material 40 is injected from the injection molding machine 20 into the product cavity 22 of the mold. At this time, in order to make Fo>Fc, the mold clamping force is generally reduced to nearly half of the conventional one.For example, when molding a 120mmφ disc base,
Try to drop (lower) it to nearly a ton.
In this way, the mold clamping force Fc can be made smaller than the mold opening force Fo exerted on the movable mold 16 by the resin material injected at the normal primary injection pressure Pi ₁ . Then, in the product cavity 22, a resin material 4 necessary to form the intended disk base is placed.
0 is injected and before the inside of the product cavity 22 is filled (filled) with the injected resin, especially just before filling, the secondary injection pressure (holding pressure) lower than the primary injection pressure: Pi ₁ : Switch the injection pressure to Pi ₂ , for example, reduce the secondary injection pressure: Pi ₂ to less than half of the primary injection pressure: Pi ₁ , and change the mold opening force: Fo exerted by the resin material on the movable mold 16 to the mold clamping force: Fc. Make it smaller than.

Secondary injection pressure where injection pressure is applied: In the mold just before switching to Pi ₂ , the projected area of the product is large and the cavity internal pressure is high, so the mold opens slightly [see Figure 3 a]. Distance: d ₁ ], when the injection pressure is switched to the secondary injection pressure: Pi ₂ , the mold opening force: Fo exerted by the resin material on the movable mold 16 falls, and the mold clamping force: Fc becomes the mold opening force: Fo. The mold is closed again, which causes the resin material 4 injected into the product cavity 22 to
0 receives uniform pressure from the mold, and the cavity 22 is completely filled. This fully filled condition is shown in Figure 3b, where the distance between the molds, i.e. the thickness of the cavity 22: _d2 , varies from the primary injection pressure: Pi ₁ to the secondary injection pressure: The thickness of the cavity 22 just before switching to Pi ₂ is smaller than d ₁ (d ₁
> _d2 ).

Therefore, according to such an injection operation, the mold cavity 22 is filled with the resin material 40 after the injection pressure is changed from the primary injection pressure: Pi ₁ to the secondary injection pressure: Pi ₂ , and then the mold clamping force: Since this is performed during the mold closing operation based on Fc, in the conventional method, resin is supplemented from the center gate in response to resin contraction, so pressure is inevitably applied to the outer periphery and inner part of the cavity 22. In contrast, in the present invention, pressure is applied to the entire injected resin material 40 from the mold,
As a result, a uniform pressure is applied to the resin material 40 regardless of its location within the cavity 22, thereby eliminating residual stress generated between the inner and outer circumferential portions as in the conventional case. The occurrence of such a large difference can be effectively prevented, and therefore, the large fluctuation in the birefringence of the obtained disk substrate can be effectively suppressed.

In addition, adjustments to the quality of the disk base product, such as burrs, shorts, wall thickness, etc., can be resolved by adjusting the switching position of the mold clamping force: Fc and the injection pressure to the secondary injection pressure: Pi ₂ . It became possible,
Furthermore, the structure of the gas venting part 38, where burrs are likely to occur, has a gap extending in the mold clamping direction as described above, in other words, although the overlapping portion changes depending on the movement of the movable mold 16, the gap β is The inner surface 34 of the stamper holding ring 26 and the stepped portion 3 of the fixed side mirror block 30 facing thereto are always constant.
The gas inside the product cavity 22 that is forced out as the injected resin material 40 is filled into the product cavity 22 by the mold clamping force: Fc is Therefore, the gas is effectively and stably discharged from the gas venting section 38 to the outside. Moreover, since the gap β of the gas venting portion 38 can always be constant regardless of the thickness of the stamper 24 restrained by the stamper holding ring 36, the gap β of the gas venting portion 38 can be kept constant. This makes it possible to effectively suppress molding conditions from being affected by differences, etc., and the occurrence of burrs.
Even if there were variations (about m), it was possible to form a uniform product without any problems.

These effects widen the range of molding conditions, make it easier to optimize molding conditions, improve product-to-product variation, improve yields, and improve the disk substrates obtained. The quality of the product could be further improved, and the difference in birefringence between the inner and outer peripheries of a single disk substrate could be made extremely small. This makes it possible to improve the transfer state of information transferred from the stamper, and also to effectively improve the readout state when reading from the stamper.

The gap β of the gas venting portion 38 may be substantially constant in order to vent gas from the product cavity 22, and in this sense, the gap β between the inner surface 34 of the stamper holding ring 26 and the stepped portion 32 is If necessary, one or both of the rising surfaces 36 may be formed into a tapered surface having a slight inclination.

Furthermore, as is clear from the above description, the mold for disc base according to the present invention can be particularly suitably applied when molding a disc base according to the method of the present invention; Even when molding the disk base according to the conventional method of filling the cavity 22 with the resin material 40,
In this case as well, by adopting the same gas venting structure as in the above embodiment, the gas venting part 38 can be held constant,
The effect of successfully suppressing or preventing the occurrence of problems caused by variations in the size of the gas venting portion 38 can be achieved with a simple configuration.

In addition, although not listed one by one, the present invention is not to be construed as being limited to such illustrative specific examples, and various modifications and improvements may be made based on the knowledge of those skilled in the art, as long as they do not depart from the spirit of the present invention. , modification, etc., and it should be understood that the present invention includes such embodiments.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a main part for explaining the structure of a gas venting part of a conventional mold for a disk base.
FIG. 2 is a partially cutaway explanatory view showing the main parts of a mold clamping device equipped with a disk base mold according to the present invention, and FIGS. FIG. 1 is a sectional view of the main part corresponding to FIG. The figure shows the state in which the resin material is filled into the product cavity. 12... Movable plate, 14... Fixed plate, 16... Movable mold, 18... Fixed mold, 20... Injection molding machine, 22... Product cavity, 24... Stamper, 26... Stamper holding ring , 28...Movable side mirror block, 30...Fixed side mirror block, 32...Step part, 34...Inner surface, 36...Rising surface, 38...Gap (gas vent), 40...
resin material.

Claims (1)

[Claims] 1 A stamper is set in a product cavity formed by a movable mold and a fixed mold, and a predetermined resin material is injected into the product cavity, whereby information on the stamper surface is acquired. In a mold for a disc base that can mold a transferred disc base within the product cavity, a stamper holding member for restraining the outer peripheral edge of the stamper is provided on the movable mold side, and a stamper holding member for restraining the outer peripheral edge of the stamper is provided on the movable mold side, and the fixed mold A stepped portion that can be fitted to the inner surface of the stamper holding member is formed on the side, and the product cavity is formed in the fitted state of the stamper holding member and the stepped portion, so that the inner surface of the stamper holding member is formed. A mold for a disk base, characterized in that a part of the mold constitutes an end face of the product cavity. 2. Claim 1, characterized in that a predetermined gap is formed between the inner surface of the stamper holding member and the rising wall surface of the stepped portion for discharging gas in the product cavity. Molding mold for disk base as described in section. 3. A stamper is set in a product cavity formed by a movable mold and a fixed mold, and a predetermined resin material is injected into the product cavity to form a disk base onto which information on the stamper surface is transferred. In the method, a stamper holding member for restraining an outer peripheral edge of the stamper is provided on the movable mold side, and an end face of the product cavity is formed by an inner surface of the stamper holding member, and the stamper holding member Under the condition that a predetermined gap for degassing is formed between the rising wall surface of the stepped portion on the fixed mold side and the inner surface of the stamper holding member, the mold clamping force is slightly lower than the mold clamping force. The resin material is injected into the product cavity using a primary injection pressure that applies a large mold opening force to the movable mold, and the amount of resin necessary to form the desired disk base is injected into the product cavity. By switching the injection pressure to a secondary injection pressure in which the mold opening force acting on the movable mold is smaller than the mold clamping force, the injected resin material is heated by the mold clamping force. The gas in the product cavity is filled into the product cavity, and the gas in the product cavity that is pushed out due to the filling is discharged from the gap between the inner surface of the stamper holding member and the rising wall surface of the stepped portion on the fixed mold side. This is an injection molding method for disk bases.