JPS60159021A - Mold for producing plastic lens - Google Patents

Abstract

PURPOSE:To make it easy to obtain the accuracy of shape and to reduce occurrence of internal strains, by providing temperature adjusting means, moving a cavity mold and a core mold when a resin is melted so that the resin in the cavity is separated from the runner, and applying a pressure to the resin in the cavity in accordance with the reduction of the volume of the resin in the cooling process. CONSTITUTION:A movable mold plate 6 and a fixed mold plate 17 are heated by a heater, the heat of them heats up a core mold 9 and a cavity mold 22, and in the injection step, a resin 31 such as acrylic resin or the like is injected into the heated cavity 30 through a runner 28 by an injection cylinder 27. At this time, the heating temperature is set between the glass transition point and the melting point of the resin 31. In the step of moving the cavity, a driving cylinder 12 is actuated to move a die plate forward to separate the resin from the runner 28. The movable mold plate 6 and the fixed mold plate 17 are quickly cooled by cooling means, so that the resin 31 is shrunk, but an auxiliary cylinder 26 is moved toward the core mold 9 in proportion to the shrinkage of the resin 31. After the resin 31 is cooled to prescribed temperature, the molds are opened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a manufacturing mold for injection molding of a plastic lens suitable as an optical head of a compact disc player or a lens of an optical device such as a video camera.

[Field of application of the invention]

In recent years, plastic lenses made by injection molding of thermoplastic resin have come to be used as lenses for optical devices such as optical heads of compact disc players. This is because conventional plastic molding methods can easily produce glass lenses in the desired shape, which reduces production costs, and when producing aspherical lenses, they are much more suitable than glass lenses. This is due to the fact that However, on the other hand, it has the disadvantage that it is difficult to achieve the shape accuracy of the lens surface, and furthermore, the optical performance becomes unstable due to internal distortion generated during molding.

The former causes of shape accuracy include volumetric contraction when the molten resin solidifies and volumetric contraction during the cooling process after solidification. The resin in the cavity could not make sufficient contact with the mold surface, and as a result, the shape accuracy of the lens surface deteriorated. Therefore, a conventional mold structure has been adopted in which after the resin in the cavity has solidified, compressive force is applied to the mold to press only one side of the lens curvature. A large pressing force is required to press the lens, which has the disadvantage of causing internal distortion in the lens.

Regarding the internal distortion that occurs during the latter molding process, in addition to the one that occurs when only one side of the lens curvature surface is pressed as described above, the internal distortion that occurs in the gate part due to the difference in internal pressure between the part that passes through the gate and becomes the lens and the part of the runner. Resin flow may occur and this may solidify, resulting in distortion, or the large temperature difference between the molten resin and the mold land may cause the surface of the injected resin to harden before the inside. Inner M
An example of this is a cap, in which the P resin is stretched by the surface layer resin and becomes distorted.

[Purpose of the invention]

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, and to provide a mold for manufacturing a plastic lens that facilitates achieving shape accuracy of the lens surface and generates less internal distortion. [Summary of the Invention] In order to achieve this object, the present invention provides a temperature control means for heating the cavity mold and the core mold to near the melting point of the injected resin and quickly cooling the cavity mold and the core mold when the resin is melted. The present invention is characterized by comprising a moving means for moving the mold to separate the resin in the cavity from the runner, and a compression means for applying compressive force to the resin in the cavity in response to volumetric contraction in the cooling process of the resin. .

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partial cross-sectional view of a plastic lens production mold according to an embodiment of the present invention in an open state, and FIGS. 2 and 3 show the plastic lens production mold shown in FIG. 1 in a closed state. FIG.

In these figures, 1 is the die plate of the movable mold,
2 is a mounting plate fixed to die plate 1, 3 is a movable plate facing die plate 1, 4 is a spring elastically installed between movable plate 3 and die plate 1, and 5 is fixed to movable plate i. A heat insulating plate 6 is a movable mold plate fixed to the movable plate 3 via a heat insulating plate 5, and the movable mold plate 6 is equipped with a heater and a cooler (both not shown). .

The mounting plate 2 has a guide bin 7, a drive bin 8, and a core mold 9.
are fixed, and a heat insulating material 1 is placed between the core mold 9 and the mounting plate 2.
0 is inserted. These guide bins 7 and drive bins 8
The core mold 9 is slidably fitted into the movable mold plate 6, and the tip 72 of the guide bin 7 is engaged with the movable mold plate 6, so that the movable mold plate 6 is connected to the die plate 1. It is designed to prevent it from falling off. Moreover, 11 is a guide post provided protrudingly at a plurality of locations on the movable mold plate 6, and 12 is a drive cylinder for moving the die rate in parallel.

13 is a die plate of the stationary mold, 14 is a mounting plate fixed to this die plate 13, 15 is a first spacer mold fixed to the mounting plate 14, and 16 is a first spacer mold 15.
17 is a fixed mold plate fixed to the second spacer mold 16 via a heat insulating plate 18, and the fixed mold plate 17 has a mold plate similar to the movable mold plate 6. is equipped with a heater and a cooler (both not shown).

19 is a movable bottle slidably fitted to the fixed mold plate 17, 20 is a movable plate fixed to the movable bottle 19, and 21 is a spring elastically installed between the movable plate 20 and the mounting plate 14. , the movable plate 20 is moved to the second spacer type 1 by the elastic force of the spring 21.
It is biased in the direction in which it comes into contact with 6. 22 is a cavity that is slidably fitted into the fixed mold plate 17! , 23 is a support fixed to the cavity mold 22 via a heat insulating material 24;
Reference numeral 25 denotes a spring elastically installed between the 7-run 9 portion of the support body 23 and the fixed mold plate 17, and the support body 23 is biased in the direction of contacting the movable plate 20 by the elastic force of the spring 25. It is supported at a position where it comes into contact with the movable plate 20. 26 is an auxiliary cylinder provided on the die plate 13, and the auxiliary cylinder 26, the support body 23, and the cavity mold 22 are arranged on the same axis. Further, 27 is an injection cylinder for injecting resin, 28 is a runner that serves as a passage for the resin injected from the injection cylinder 27, and 29 is a guide hole drilled at multiple locations in the fixed mold plate 17. This guide hole 29 is located at a position facing the guide post 11.

Next, a manufacturing process for manufacturing a plastic lens using the manufacturing mold configured as described above will be described.

First, in the first step, by operating the drive cylinder 12 of the movable mold in the mold open state shown in FIG.
The Goui plate 1 is advanced toward the stationary mold. When the Goui plate 1 is advanced, each guide boss 11 is inserted into the opposing guide hole 29, thereby positioning the fixed side mold and the movable side mold, and furthermore, the Goui plate 1
When moved forward, the movable mold plate 6 and the fixed mold plate 17 are butted against each other. When the movable mold plate 6 is advanced to the position where it butts against the fixed mold plate 17, the tip of the drive bin 8 comes into contact with the tip of the movable bin 19, and the movable plate 20 moves to the second position.
The spacer 16 moves in a direction away from the spacer 16. The movement of the movable plate 20 is detected by a detection means (not shown), and when the movable plate 20 starts moving, the operation of the drive cylinder 12 is stopped based on a signal from the detection means, and the fixed mold and the movable The side molds are in a closed state as shown in FIG.

In this mold closed state, the movable mold plate 6 and the fixed mold plate 17 are heated by the equipped heater, and the core mold 9 and the cavity mold 22 are heated by this heat.

The second process is an injection process, in which the cavity 30 is heated.
A resin 31 such as PMMA (acrylic resin) is injected into the interior through a runner 28 from an injection cylinder 27. At this time, the heating temperature of the core mold 9 and the cavity ring 22 is set to the resin 31.
If the heating temperature exceeds the melting point of the resin 31, the resin 31 will stick to the surface of the core mold 9 or the cavity mold 220, or the resin will decompose.On the other hand, if the heating temperature is below the glass transition point of the resin 31, the shape of the glass surface will change. A very large force is required to create the shape, and if you try to force the shape, it will cause cracks or large internal strains, so the heating temperature mentioned above is set between the glass transition point and melting point of the resin 31. It is necessary to set it.

The third step is a cavity moving step. In this third step, when the resin 31 is in a molten state, the driving cylinder 12
is operated to further advance the Goui plate 1 of the movable mold. When the Goui plate 1 is moved forward, the mounting plate 2 gradually approaches the movable plate 3, and the Goui plate 1 is moved to a position where the mounting plate 2 comes into contact with the movable plate 3, whereby the drive bin 8
The core mold 9 and Shizuka move forward toward the fixed side anaya.

When the drive bin 8 moves forward, the movable bin 19 and the movable plate 20 that contact the drive bin 8 move backward against the spring 21, so that the support body 23 and the cavity mold 22 integrated therewith also spring 25. The resin 31 in the cavity 30 and the runner 28 are separated from each other as shown in FIG. Note that the volume of the cavity 300 depends on the relative position between the core mold 9 and the middle cavity mold 22, that is, the drive beam/
8 and the moving bottle 19, the volume of the cavity 300 is constant while the resin 31 is moving. As a result, the resin 31 is no longer affected by the pressure from the runner 28 in subsequent steps.

The fourth step is a cooling step, in which the movable mold plate 6 and the fixed mold plate 17
It is rapidly cooled by the equipped cooler. Care should be taken to avoid a large difference in temperature between the core mold 9, the cavity mold 22, and the surface and interior of the resin 310 in the cavity 30. Varies depending on the resin used.

Further, the resin 31 in the cavity 30 contracts as it cools, but if the resin 31 in the cavity 30 is cooled in this state until the product is taken out, the resin 31 in the cavity 30 will not be able to make sufficient contact with the core mold 9 and the surface of the cavity mold 220. , the shape accuracy of the lens surface deteriorates. Therefore, in order to compensate for this, the auxiliary cylinder 26 is installed in the core mold 9 according to the amount of shrinkage of the resin 31.
The resin 31 in the cavity 30 is compressed. The relationship between the pressure of the auxiliary cylinder 26 and the temperature of the resin 31 at this time may be determined in advance for each type of resin used and controlled by a control means such as a microcomputer.

The fifth step is a mold opening and product removal step, in which the resin 31 is cooled to a predetermined temperature, and then the drive cylinder 12 is
The movable mold is moved back to the left from the position shown in FIGS. 2 and 3, and brought into the open state shown in FIG. By this operation, the main force from the movable mold is removed from the fixed mold, so that the movable bottle 19 and the movable plate 20 are moved by the spring 2.
1, the movable plate 20 moves to the second spacer type 16.
The cavity mold 22 and support body 23 are moved by the auxiliary cylinder 26 to a position where the cavity mold 22 protrudes from the fixed mold plate 17, and the product (plastic lens) is taken out.

The plastic lens manufactured in this way has a lens surface with a shape accuracy very close to that of the mold, little internal distortion, no decrease in transmittance, and stable optical performance. .

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a mold for manufacturing a plastic lens that facilitates achieving shape accuracy of the lens surface and that causes less internal distortion.

[Brief explanation of the drawing]

The figures are all explanatory diagrams of a manufacturing mold for a plastic lens according to the present invention, with FIG. 1 being a partial sectional view in the mold open state, and FIGS. 2 and 3 being partial sectional views in the mold closed state. 1...Die plate of the movable side mold, 4...
...Spring, 6...Movable mold plate, 7...
Guide bin, 8... Drive pin, 9...
Core type, 11... Guide post, 12...
... Drive cylinder, 13 ... Die rate of fixed side mold, 17 ... Fixed mold plate, 19 ...
...Moving pin, 20...Moving plate, 21...
... Spring, 22 ... Cavity type, 23 ...
...Support, 25...Spring. 26... Auxiliary cylinder, 27... Injection cylinder, 28... Runner, 29...
... Guide hole, 30 ... Cavity, 31.
·····resin. Figure 1 Figure 2

Claims (1)

[Claims] A manufacturing mold that has a cavity mold and a core mold, and molds a plastic lens in a desired lens shape by cooling a molten resin in the cavity constituted by the cavity mold and the core mold. Temperature adjustment means for heating or cooling the mold and core mold; moving means for moving the cavity mold and core mold to separate the runner/gate when the resin is melted; and compressive force applied to the resin in the cavity during the cooling process of the resin. A mold for manufacturing a plastic lens, characterized in that it is equipped with compression means for loading.