JPH02160525A - Injection mold and molding method of disc board for which the same mold is used - Google Patents

Abstract

PURPOSE:To improve optical and mechanical properties of a molded product and shorten a molding cycle by providing a temperature control device independent of the vicinity of a gate part close by the outer circumference of a sprue. CONSTITUTION:The first annular heating medium flow path 13 of the cooling first temperature control device is formed within a sprue bushing 6 which is in a position close by a sprue 7 and separated from a gate part 12 so as to surround the outer circumference of the sprue 7 and the second annular heating medium flow path 14 of the second temperature control device for heat insulation is formed within the sprue bushing 6 close to the gate part 12. Different temperature controls are performed independently of the sprue 7 in the first temperature control device 13 and perform heat insulation of the vicinity of the gate part 12 in the second temperature control device 14. Consequently, since injected resin is filled out into a cavity 5 without being cooled by the gate part 12, a temperature distribution of the resin in the inner and outer circumferential parts of a board becomes uniform and the board whose optical and mechanical properties are favorable is obtained. Then since molten resin within the sprue is cooled and solidified swiftly, a molding cycle is made shorter.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an injection mold for plastic molded products and a method for molding a disk substrate using this mold.

[Prior Art] Injection molding is usually used to mold optical disk substrates, video disk substrates, and the like. According to the injection molding method using a conventional injection mold, during injection molding, a heat medium at a predetermined temperature, e.g. Run the water,
The molten resin injected into the cavity and the molten resin in the sprue are cooled and solidified.

[Problems to be Solved by the Invention] By the way, when the temperature of the water flowing into the heat medium flow path formed near the outer periphery of the sprue is set to a low temperature (for example, 10 to 40°C), the molten resin in the sprue Since it is quickly cooled and solidified, the molding cycle can be shortened. However, conversely, the temperature distribution at the inner and outer peripheries of the resin cooled in the cavity becomes uneven, resulting in variations in the birefringence distribution and warping of the resulting substrate, resulting in poor optical properties and mechanical properties. A problem arises regarding the physical characteristics. Also,
Since the outer periphery of the sprue is cooled, the mold temperature at the gate section is also relatively low, and the injected resin is cooled, causing an increase in pressure at the gate section due to the increase in viscosity, resulting in silver streaks.

On the other hand, the temperature of the water flowing through the heat medium flow path is set to a high temperature (for example, 50
When the temperature is set to 90'C), the temperature distribution in the inner and outer circumferences of the resin cooled in the cavity is made uniform, so that a substrate with excellent optical properties and mechanical properties can be obtained. However, for the molten resin in the sprue, not only does the cooling and solidification of the resin slow down, which lengthens the cycle time, but also leads to poor mold release due to insufficient cooling of the sprue, making continuous molding of substrates impossible. A problem arises.

According to Japanese Patent Application Laid-Open No. 61-217225, an injection molding die is disclosed in which a means for heating the sprue and a means for cooling the sprue are provided in the vicinity of the sprue.

However, according to this configuration, i. It is necessary to switch between heating and cooling, and the response at that time is slow, resulting in a long molding cycle, which is disadvantageous for continuous production.ii. It is difficult to control and stabilize the temperature of the spruce, and iii. The temperature of the entire spruce including the center of the base is uniformly cooled, so the resin is cooled too much, making it difficult to form the center hole. accompanies.

The present invention aims to provide an injection molding mold that can obtain a molded product with good optical properties and mechanical properties and shorten the molding cycle, and a method of molding a disk substrate using this mold. purpose.

[Means for Solving the Problems] The present invention provides a cavity formed on the abutting surfaces of a fixed mold and a movable mold, a sprue into which resin is melted and injected, and the resin is introduced into the cavity from the sprue. In the injection molding die having a gate portion, the invention is characterized in that a temperature control means is provided near the outer periphery of the sprue and is independent from the vicinity of the gate portion.

The temperature control means provided near the sprue may be configured, for example, by flowing a heat medium such as water at a predetermined temperature as a heat medium flow path, or by arranging a heating/cooling element such as a Peltier effect element. can.

In addition, near the gate, a temperature control means independent from the vicinity of the sprue, for example, a heat medium flow path through which a heat medium such as water at a predetermined temperature is flowed, or a heating endothermic element may be arranged.
Alternatively, a heat insulating layer may be formed between the sprue and the temperature control means provided in the vicinity of the sprue so that the gate portion is not cooled by cooling a portion of the sprue. Here, the heat insulating layer can be constructed by interposing a layer of a material with low thermal conductivity, such as air, a glass balloon, or various foams.

The plastic molded product to be molded by this injection mold is not particularly limited, and may be any such as an optical disk substrate, a video disk substrate, an eyeglass lens, etc., but it is particularly a molded product for an optical member.

The present invention also provides a disk substrate that uses the injection mold described above and injects molten resin from a sprue through a gate portion into a disk-shaped cavity formed at the abutting surface of a fixed mold and a movable mold. In the forming method, temperature control for cooling the sprue by a first temperature control means provided near the sprue and temperature control for keeping the gate portion warm by a second temperature control means provided near the gate portion are performed independently. It is characterized by being carried out.

Here, polycarbonate resin optical disk substrate [thickness 1
．． 2 am and a diameter of 130 m+a), for example, the first temperature control means provided near the sprue is used as a heat medium flow path, and the heat medium is flowed here for 20 to 70 m! It is appropriate to flow at a flow rate of /win and set the temperature to 20 to 40''C.

When the second temperature control means provided near the gate part is used as a heat medium flow path and the heat medium is flowed through the second temperature control means, the temperature of the heat medium is set at 40°C or higher, preferably 80°C or higher.
The temperature shall be 130°C. The flow rate of the heat medium is 20 to 70
1/sin is appropriate.

Next, instead of the heat medium flow path of the second temperature control means,
In the case of a structure in which a heat insulating layer is formed, the vicinity of the gate part is less affected by cooling by the first temperature control means, and is usually maintained at 80° C. or higher by the flow of high temperature resin. . In addition, in the present invention, semen control becomes possible by having two configurations: forming a heat insulating layer and providing a heat medium flow path.

The resin melted and injected from the sprue has a temperature of 31 to 3
A temperature of 50°C and a pressure of 250 to 350 kg/cnl are suitable.

The heat medium flowing through the heat medium channels formed along the cavities of the movable mold and the fixed mold respectively has a temperature of 100 to 13
0”C, m Jl 4; J: 20-70 e
/win is appropriate. Further, the appropriate cooling time for the molten resin injected into the cavity is 10-18 seconds.

Water or the like can be used as the heat medium to be passed through the heat medium flow path.

The molding resin used is polycarbonate resin (Mv
:12000-18000) is preferred, but acrylic resin, non-grade polyolefin, etc. are optional.

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

[Function] According to the molding method of the present invention, the first temperature control means is provided near the sprue, and the second temperature control means is provided near the gate.
The second temperature control means provided in the vicinity of the gate portion cools the outer periphery of the sprue, and the second temperature control means provided near the gate portion maintains heat in the vicinity of the gate portion, thus making it possible to perform different temperature controls independently. As a result, the resin injected into the cavity is filled into the cavity without being cooled at the gate, so the temperature distribution of the resin on the inner and outer peripheries of the substrate becomes uniform, resulting in good optical and mechanical properties. A substrate is obtained. At the same time, since the molten resin in the sprue is rapidly cooled and solidified after injection molding, the molding cycle can be shortened.

[Example] Referring to FIG. 1, an injection molding mold according to an example of the present invention and a method of molding a disk substrate using this mold will be described.

This injection mold has a fixed mold 2 attached to a fixed Goui plate 1 and a movable mold 4 attached to a movable Goui plate 3, and these are fixed via spacers 16 and 17. A disc-shaped gap formed between the surfaces where the mold 2 and the movable mold 4 are butted together becomes a cavity 5 for molding an optical disk substrate or the like.

A cylindrical sprue bush 6 is installed in the center of the fixed mold 2.
is buried to form a sprue 7 into which molten resin is injected along the center line of the sprue bush 6. In addition, a plurality of annular heat medium flow paths 15 are formed within the fixed mold 2 at appropriate distances from the cavity 5.

A cylindrical center member 8 is buried in the center of the other movable mold 4, and a cut bin 9 is arranged along the center line of the center member 8. A stamper IO, which serves as a recording carrier and has a focus, a groove, etc., is provided on the inner end surface of the movable mold 4, and this stamper 10 is fixed with a stamper holder 11. Also, a plurality of annular heat medium flow paths 15 are formed within the movable mold 4 at appropriate distances from the cavity 5.

When the fixed mold 2 and the movable mold 4 are butted against each other, the gap formed by the sprue bush 6 and the center member 8 serves as a gate portion 12 for introducing molten resin from the sprue 7 into the cavity 5. Become.

Then, a first annular heat medium flow path 13, which is a first temperature control means for cooling, is formed in the sprue bushing 6 at a position near the sprue 7 and away from the gate portion 12 so as to surround the outer periphery of the sprue 7. At the same time, a second annular heat medium flow path 14, which is a second temperature control means for heat retention, is formed in the sprue bush jL6 near the gate portion 12. In addition, a third annular heat medium flow path 13A for cooling is formed in the center member 8 at a position near the cut pin 9 and away from the gate part 12, and a third annular heat medium flow path 13A for cooling is formed in the vicinity of the gate part 12. A fourth annular heat medium flow path 14A is formed.

Next, a method of molding an optical disk substrate using the injection mold described above will be explained.

As shown in FIG. 1, the fixed mold 2 and the movable mold 4 are butted together, and the heat medium flow path 15 of the fixed mold 2 and the movable mold 4 is
Pressurized water at 120°C is allowed to flow at a flow rate of 4042/win.
, 80°C water is allowed to flow in an i amount of 4017thin through the fourth heat medium flow path 14° 14A.

Then, melted polycarbonate resin (M
v: 14800) from injection cylinder 17 to 300kg
/c11 pressure into the sprue 7, gate part 12
This molten resin is introduced into the cavity 5 through. The molten resin injected into this cavity 5 is transferred to the fixed mold 2
It is cooled and solidified in 12.5 seconds by pressurized water flowing into the heat medium flow path 15 of the movable mold 4.

On the other hand, 404 degrees of water at 35° C. is poured into the first and 30th heat medium channels 13.13A of the sprue bush 6 and the center member 8. /
By constantly flowing the resin at a flow rate of sin, the molten resin in the sprue 7 is cooled and solidified.

Regarding the optical disk substrate obtained by the above molding method,
The results of measuring birefringence are shown in Figure 2.

As a comparative example, an optical disk substrate was prepared in the same manner as in the above embodiment using an injection mold in which the second and fourth heat medium channels 14.14A were not formed in the spout bush 6 and the center member 8. was injection molded. The birefringence of this optical disk substrate is also shown in FIG. In the figure, curve A is the birefringence of the optical disk substrate according to the example, and curve B is the birefringence of the optical disk substrate according to the comparative example.

From this graph, in the case of the optical disk substrate according to the example,
Since the temperature distribution of the resin injected into the cavity 5 is made uniform by the second heat medium flow path 14, the variation in birefringence is suppressed within ±Ions (double pass), and from the inner circumference to the outer circumference of the substrate. It was about average. Furthermore, the change in birefringence over time did not change much even after the la period had elapsed, because the temperature distribution of the resin in the cavity 5 was made uniform and the thermal stress was reduced.

On the other hand, in the case of the optical disk substrate according to the comparative example, the birefringence at the inner circumference is +32n* (double pass) and the birefringence at the outer circumference is -20ns (double pass), which shows extremely large variations in the radial direction, and the optical characteristics is found to be defective.

Further, the change in birefringence over time was +5 to 10 nm (double pass) at the inner peripheral portion 24 hours after molding.

Next, the mechanical properties of the optical disk substrates according to these Examples and Comparative Examples were measured. The mechanical properties were measured for warpage, surface runout, skew angle, and surface runout acceleration. The measurement results are shown in Table 1 below.

Table 1 From the measurement results, the optical disk substrate of the example has smaller values of warpage, surface runout, skew angle, and surface runout acceleration than the optical disk substrate of the comparative example, and has good mechanical properties. I know what you're doing.

Further, according to this embodiment, the first heat medium flow path 13 formed near the sprue 7 in the sprue bush 6 allows
Because the molten resin in sprue 7 quickly cooled and solidified,
The effect of shortening molding time was also obtained. In addition, since a heat medium at a constant temperature is constantly flowing through the first heat medium flow path, the temperature of the injected resin is constant, and the performance of the molded disk substrate is consistent and stable. Met.

Furthermore, since the voltage increase at the gate portion 12 was small, no silver streaks were observed.

In the above embodiment, the third heat medium flow path 13A for cooling and the fourth heat medium flow path 14A for heat retention were also formed in the center member 9, but these were not provided. First, the first heat medium flow path 13 and the second heat medium flow path 14 are
It may be formed only in the sub-button 6.

[Effects of the Invention] According to the injection mold according to the present invention, a plastic molded product with good optical properties and mechanical properties can be obtained, and the molding cycle can be shortened.

According to the method of molding a disk substrate using this mold, a disk substrate with small variations in birefringence and changes over time and good mechanical properties with respect to warpage, surface runout, etc. can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an injection molding die according to an example of the present invention, and FIG. 2 is a graph showing measurements of birefringence of optical disk substrates obtained by molding methods according to an example and a comparative example. 2...Fixed mold, 4...Movable mold, 5...Cavity, 6...Subleu Bushe, 7...Sprue,
12... Gate portion, 13... First heat medium flow path, 1
4...Second heat medium flow path. Applicant Idemitsu Petrochemical Co., Ltd.

Claims (2)

[Claims] (1) An injection mold that has a cavity formed on the abutting surface of a fixed mold and a movable mold, a sprue into which resin is melted and injected, and a gate part that introduces the resin from the sprue into the cavity. An injection molding die, characterized in that a temperature control means independent from the vicinity of the gate portion is provided near the outer periphery of the sprue. (2) Using the injection mold according to the first claim, injecting molten resin from the sprue through the gate part into the disc-shaped cavity formed at the abutting surface of the fixed mold and the movable mold. In the method for molding a disk substrate, temperature control for cooling the sprue by a first temperature control means provided near the sprue, and temperature control for keeping the gate portion warm by a second temperature control means provided near the gate portion. A method for forming a disk substrate, characterized in that each control is performed independently.