JPH02310016A - Manufacture of optical disk board - Google Patents

Abstract

PURPOSE:To obtain a low birefringent optical disc board by eliminating inequalty in a temperature distribution on the surface of a cavity at the time of injection of resin, by a method wherein the surface of a cavity is heated by providing a temperature gradient where the surface becomes gradually high toward an inner circumferential part from an outer circumferential part by breaking a mold. CONSTITUTION:A high-frequency induction coil sheet 20 is constituted, for example, of a holding board 21 made of rectangular phenolic resin, a disk 22 made of the phenolic resin provided on one end part of both faces of the holding board 21 and a high-frequency induction coil 23 which is arranged on the disk 22 and in a spiral state and the high-frequency induction coil 23 is connected by a connecting device 25 with the other end part. A groove part 24 in the spiral state where the high-frequency induction coil 23 is arranged is formed in the disks 22 each and a depth of the groove part 24 is made shallow gradually toward an inner circumferential part from an outer circumferential part of the disk 22. When the high-frequency induction coil 23 is arranged along the groove 24, a position of the high-frequency coil 23 becomes high gradually toward the inner circumference from the outer circumference. With this constitution, it becomes that the surface of a cavity 7 is heated so as to negate influence from a heating medium flow path 17 for cooling of a sprue 9.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a method of manufacturing an optical disc substrate. .

[Background technology] It is difficult to manufacture optical disk substrates using plastic resins such as polycarbonate (PC) resins (due to distortion due to the orientation of molecular chains during injection molding and thermal stress due to uneven temperature distribution, Multilayer of the obtained optical disc substrate +
ii increases. Optical disks 7 with large birefringence (plates are preferable because they deteriorate the SN ratio during signal reproduction).
:1: Yes. In order to reduce this birefringence, we aim to create melting at high temperatures and uniform cooling.

Conventionally, in order to perform reef injection at high temperatures, there is a method of heating the surface of the cavity of the mold using a heat medium (Japanese Patent Application Laid-Open No. 64-42215'i; Publication, etc.), and a method of high-frequency heating 1. A method of heating using an oil has been proposed. There are methods using this high-frequency induction coil, depending on the person, a method of climbing the high-frequency induction coil buried in the mold (IRj Kaisho C; Publication No. 2-183320, etc.) and mold glue. (Heating method using a high-frequency induction coil placed in the
1-7961.4, etc.).

[Problems to be Solved by the Invention] According to the method of heating the surface of the cavity using a high-frequency induction coil placed outside the mold as described in 1, it is possible to heat the surface of the cavity so that the entire surface of the cavity has a uniform temperature. It's heating up. However, usually (1) the mold is equipped with a heat medium flow path for cooling the sprue, so even if the entire surface of the cavity is heated to a uniform temperature, the inner circumference of the cavity actually The temperature is lower than that of the outer periphery (this causes l
I+! Due to the non-uniformity of the power distribution, the occurrence of birefringence due to thermal stress on the optical disk substrate becomes unavoidable. Conventionally, the mold temperature during molding is usually 80 to I30' (
However, from the point of view of increasing the fluidity of the molten resin and improving its rolling properties, injection molding at a height of 614 is preferable.・It is desirable to maintain the

The present invention provides the advantages of 6. during high frequency heating. By making the temperature distribution on the surface of the two cavities uneven and making the temperature distribution of resin injection A uniform or C: 1 slightly higher on the inner periphery, the orientation of the resin and the occurrence of thermal stress are suppressed and the temperature distribution is reduced. The purpose of the present invention is to provide a manufacturing method for obtaining a birefringent optical fiber substrate.

"Means for solving the problem
- In a method for manufacturing an optical disk substrate in which resin is injected and filled into a cavity and then cooled and solidified, the cavity is heated with high frequency while the mold is open, and the surface of the cavity is heated from the outer periphery to the inside. This method of manufacturing an optical disk substrate is characterized in that heating is performed by providing a temperature gradient that gradually increases toward the periphery.

The predetermined molding pattern is a negative pattern for forming, for example, a concavo-convex pattern such as bits and grooves that will become a recording carrier on the optical disc substrate.

The high-frequency induction coil plate used in this method of manufacturing an optical disk substrate can be arranged such that the position of the high-frequency induction coil becomes gradually higher in a convex manner from the outer circumference toward the inner circumference.

In addition, the high frequency induction coil plate used is high frequency induction: I
The arrangement may be such that the density of the fibers gradually increases from the outer periphery to the inner periphery.

Furthermore, in this optical disc substrate manufacturing method, the heating temperature of the cavity surface is equal to or equal to the glass transition temperature T of the resin.
[or more]-, for example, in the case of polycarbonate] 8
0'C or more, preferably 200'C or more.

When the heating temperature is lower than the glass transition temperature, the fluidity of the molten resin decreases, and the transferability of the molding pattern to the resin decreases.

The molding resin used is polycarbonate with low impurities (Mv = 12,000 to 20,000) for optical polishing.
Polymethyl methacrylate-1-8 non-quality polyolefin and the like.

In the present invention, injection molding also includes injection compression molding.

[Function] When performing high-frequency heating on the cavity with the mold open, even if there is a temperature drop due to the heat medium flow path for cooling the sprue, the front surface of the cavity is heated from the outer periphery toward the inner periphery. By heating the resin with a temperature gradient that gradually increases, the temperature is made uniform over the entire surface during injection of the resin, or the temperature at the inner circumference is slightly higher. Kneading suppresses the orientation of the resin and the generation of thermal force.
As a result, a photon substrate with low birefringence can be obtained.

[Example 1: See one song! t4! Embodiments of the invention will be described.

As shown in FIG. 1, the injection molding die used in the non-example is attached to the fixed side tie brake
J4. Stainless steel was used for the steerer 1/stainless steel fixed mold 2 and the movable side die play 1-3! ! i
It is constructed by i'j j l-1J moving money Jν14. The surface of the fixed mold 2 is a mirror surface 2Δ. Then, a disc-shaped gap formed between the stationary mold 2 and the movable mold 4 on the surface of the fixed mold 2 and the movable mold 4 through the sliding plates 5 and 6 is used to mold the optical disk. cavity 7.

In the center of the fixed mold 2, there is a cylindrical sprue
. Also, inside this fixed mold 2 are: a plurality of annular heating media placed at an appropriate distance from the Toyahiti 7? A path 10 is formed.

A cylindrical hinge piece 11 is embedded in the center of the other movable mold 4, and a cutter bottle 12 is disposed along the center line of the center piece 11. Movable mold 4
Number: 11, recorded on the inner boundary surface (Bi-nod, which becomes l1 body,
Nll made vine bar 1 with uneven patterns such as grooves formed
Three stand bars 13 are provided, and the stand bars 13 are fixed with stand bar boulders 14.

Also, within this movable mold 4, a plurality of annular heat medium flow paths 15 are formed at appropriate distances from the =1-Yachti 7.

When the fixed mold 2 and the jiJ movable mold 4 are butted together, the gap formed by the sprue bush 8 and the center part 11 allows the molten resin to flow from the sprue 9 to the -1-Yachti 7. Days 1 to 16 are to be inserted.

A cooling annular heat medium flow path I7 is formed in the sprue bush 8 so as to surround the sprue 9, and an annular cooling heat medium flow path I7 is formed in the center member 11 so as to surround the canto pin 2. 18 are formed.

As shown in Part 1 and FIG. 2, the high frequency induction coil plate 20 used in this embodiment is provided on a rectangular phenol resin support substrate 21 and one end of both sides of this support substrate 2'1. phenolic resin disks 22 and spiral high frequency induction coils 2 arranged on these disks 22.
3, and a high frequency induction coil 23 at the other end.
is locked by a locking tool 25. A spiral groove 24 in which a high-frequency induction coil 23 is disposed is formed in each disk 22, and the depth of the groove 24 gradually becomes shallower from the outer circumference to the inner circumference of the disk 22. ing. By disposing the high-frequency induction coil 23 along this groove 24, the position of the high-frequency induction coil 23 is arranged so that it gradually becomes higher from the outer circumference toward the inner circumference, that is, it has a convex shape with a protruding center. A high frequency induction coil plate 20 is obtained. Note that this high frequency induction coil 23 has an outer diameter of 6
It consists of 514 tubes with an inner diameter of 3 mm and an inner diameter of 3 mm, through which cooling water flows.

Using this high frequency induction coil plate 20, an optical disk substrate is manufactured as follows.

As shown in FIG. 1, a high frequency induction coil plate 20 is inserted between the fixed mold 2 and the movable mold 4 in an open state, and high frequency oscillation is caused with an output of 10 to 15 kW. The current application time is suitably 3 to 10 seconds. When this high-frequency induction plate 20 is placed between both molds 2 and 4, the Ni of the stand bar 13 is more ferromagnetic than the stainless steel of the stationary mold 2 and is more easily heated by high-frequency waves, so the surface to be heated is In order to make the heating temperatures approximately equal, the distance between the disc 22 and the stand bar 13 is the distance L2 between the disc 22 and the fixed mold mirror surface 2Δ.
Set larger. After the high-frequency heating is finished, the high-frequency induction coil plate 20 is taken out from between both molds 2 and 4.

Next, the fixed mold 2 and the movable mold 4 are butted together, and a heat medium flow path 10.15 of the fixed mold 2 and the movable mold 4 is injected with
130°C pressurized water 20~1001/va in
Let it flow at a flow rate of Then, 250 to 350 kg of molten resin at 310 to 350°C is injected from the injection nozzle 19.
/ Inject into the sprue 9 with pressure of r, and gate part 1G
This molten resin is introduced into the cavity 7 through. The introduced molten resin is cooled and solidified in 10 to 20 seconds by pressurized water flowing into the heat medium channels 10.15 of the fixed mold 2 and the movable mold 4.

On the other hand, in the heat medium flow paths 17 and 18 of the sprue bush 8 and the center member 11, a cooling medium of 20 to 90°C
By flowing at a flow rate of 0 to 70 E/min, the molten resin in the sprue 9 is cooled and solidified.

After molding the optical disk substrate, the movable mold 4 is opened and the optical disk substrate is taken out from the cavity 7.

11 optical disk substrates were manufactured by setting the conditions in the above examples specifically as follows.

When the high frequency induction coil plate 20 is placed between the fixed mold 2 and the movable mold 4, the distance #l between the disk 22 and the stand bar 13
, 1 is 25. The distance L2 between the disk 22 and the fixed mold mirror surface 2A was 5 mm.

During high-frequency heating, the output of the high-frequency induction coil 23 is set to 10k.
W, the current application time was set to 5 seconds, and the temperature of the cavity surface during injection was set to 170'C, which is considerably higher than the conventional temperature.

During resin molding, the heat medium flow path 1 between the fixed mold 2 and the movable mold 4
The pressurized water flowing at 0.15°C had a temperature of 118°C and a flow rate of 80f/min.

The molten resin injected from the injection nozzle 19 was cooled in the cavity 7 for 15 seconds at an IAa degree of 330° C. and a resin pressure of 330 kg/(rice).

Heat medium flow path 1 between sprue bush 8 and center member 11
The temperature of the cooling medium flowing in step 7.18 was 70° C., and the flow rate was 10 fl/min.

Birefringence ΔN2 in the radial direction was measured for the optical disc substrate manufactured under these conditions.

Here, 8N z = ((n I+n 2 ) /
2-n31, as shown in FIG. 3, nl is the refractive index of the X-direction component of the optical disc substrate 30, n2 is the refractive index of the X-direction component, and n3 is the refractive index of the Z-direction component.

The measurement results of this birefringence ΔN2 are shown in the curves of FIG.

In addition, we use a high-frequency induction coil plate in which the height position of the high-frequency induction coil is equal on the outer circumference and the inner circumference,
An optical disc substrate according to Comparative Example 1 was manufactured under the same conditions as in the above experimental example. Regarding the optical disc substrate of Comparative Example 1, ΔN2 was also measured in the same manner as in the above experimental example. The results are shown in curve B in FIG.

Furthermore, an optical disk substrate according to Comparative Example 2 was manufactured under the same conditions as the above experimental example except that the high-frequency induction coil plate was not used. Regarding the optical disc substrate of Comparative Example 2, ΔN2 was also measured in the same manner as in the above experimental example. This result is shown in curve C in FIG.

According to these measurement results, the optical disc substrate obtained in this example has a ΔN2 of 4.0XIO-4 or less, and has lower birefringence than the optical disc substrates obtained in Comparative Examples 1 and 2. It can be seen that it has. Compared to the optical disc substrate obtained in Comparative Example 1, even if a high-frequency induction coil plate is used, if the height position of the high-frequency induction coil is equal on the outer and inner circumferences, the heated cavity It can be seen that the birefringence is still not very good because the non-uniformity of the temperature distribution on the surface is not improved. In particular, ΔN of Comparative Example 2, which was not subjected to high-frequency heating at all.
2 was approximately 6.0×10 −′, which was a much larger value than that of this example.

In the above embodiment, in order to heat the surface of the cavity 7 by providing a temperature gradient that gradually increases from the outer periphery to the inner periphery, the high frequency induction coil 23 changes its position from the outer periphery to the inner periphery. Although we have used high frequency induction coil plates arranged such that the heating temperature increases, high frequency induction coil plates of other configurations can also be used for such heating. For example, as shown in FIG. 5, the density of the high-frequency induction coil 23 increases from the outer circumference to the inner circumference as ff=Ji
You may use the high frequency induction coil temporary 26 arranged so that it becomes darker.

Further, in the above embodiment, when the temporary high-frequency induction coil 20 is placed between the two molds 2 and 4, the distance between the disk 22 and the stand bar 13 is L l in order to make the heating temperature of the heated surface substantially equal.
is set to be larger than the distance m L-2 between the disk 22 and the fixed mold mirror surface 2A, but instead of adjusting the distance, the outputs of the high-frequency induction coils 23 on both sides may be adjusted separately.

[Effect of the invention 1] According to the method for manufacturing an optical disk substrate according to the present invention, high-frequency heating under specific conditions eliminates uneven temperature distribution on the cavity surface during resin injection, resulting in low birefringence. An optical disc substrate is obtained.Furthermore, according to the present invention, it is possible to perform injection molding while maintaining a uniform high temperature state over the entire surface of the middle bit, so that transferability is improved.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing a method for manufacturing an optical disk substrate according to an example, Fig. 2 is a plan view of a high frequency induction coil plate used in the example, and Fig. 3 is an optical disk substrate used to explain the measurement of ΔN2. FIG. 4 is a graph showing the results of measuring ΔN2 for optical disk substrates obtained in Examples and Comparative Examples, and FIG. 5 is a cross section showing another example of a high-frequency induction coil plate. It is a diagram. 2... Fixed mold, 4... Movable mold, 7... Cavity, 20.26... High frequency induction coil plate, 23...
- High frequency induction coil, 30... optical disc board.

Claims (4)

[Claims] (1) In a method for manufacturing an optical disk substrate in which a molten resin is injected and filled into a cavity having a predetermined molding pattern formed on one side and then cooled and solidified, when the cavity is high-frequency heated with the mold open, the A method for manufacturing an optical disk substrate, characterized in that the surface of a cavity is heated by providing a temperature gradient that gradually increases from the outer periphery to the inner periphery. (2) In the method for manufacturing an optical disk substrate according to the first aspect, a high-frequency induction coil plate is used in which high-frequency induction coils are arranged in a convex manner so that the positions of the high-frequency induction coils are gradually raised from the outer circumference toward the inner circumference. A method for manufacturing a featured optical disk substrate. (3) The method for manufacturing an optical disk substrate according to claim 1, characterized in that a high-frequency induction coil plate is used in which high-frequency induction coils are arranged such that the density of the high-frequency induction coils gradually increases from the outer circumference to the inner circumference. A method for manufacturing an optical disc substrate. (4) The method for manufacturing an optical disk substrate according to any one of claims 1 to 3, characterized in that the heating temperature of the cavity surface is set to be higher than the glass transition temperature of the resin. .