JPH11221842A - Method for molding concave lens and its molding mold - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a concave lens precisely and quickly by a method in which a mold for injection compression molding is filled with a material, and after the concave lenses are molded by compression, the material in an amount corresponding to the contraction due to the difference in thickness between the central and peripheral parts of the lens is supplied to the peripheral part of the molding. SOLUTION: First, with a core 7a and a pin 18 returned backward, a prescribed amount of a material is packed from a gate 21 into a cavity 11. Next, the core 7a is advanced by a core pushing piston 13, and the excess material is introduced into a tab 16b or returned to the gate 21 to mold a molding shape. Next, the pin 18 and an ejector pin 17 are advanced by a prescribed distance by a rod 14 for an ejector to correct the contraction of the material of the peripheral part 16a of a molding 16. A movable board 4 is retracted to divide a mold at a parting surface 8, and an ejector plate 10 is advanced by the rod 14 to drop the molding 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for molding a concave lens and a mold for molding the same, and more particularly, to an injection molding method for a concave shaped plastic lens and a mold for molding the same.

[0002]

2. Description of the Related Art In recent years, concave plastic lenses have
Widely used, such as myopic glasses, camera imaging systems, VTR camera imaging systems, and the like, there is a demand for further improvements in precision molding techniques for plastic lenses.

When a lens 23 having a concave shape as shown in FIG. 6 and having a large thickness difference between the center thickness A at the center and the edge thickness B at the peripheral portion (edge) is injection-molded, as shown in FIG. The flow of the material injected into the cavity 11 from the gate 21 changes from the state shown in FIG. 7A to the state shown in FIG.
4. Short shots 25 are likely to occur in the center.
Therefore, at the time of filling, it is necessary to maintain the mold temperature at a temperature at which the material does not solidify.

Conventionally, as a method of accurately molding a concave lens by injection molding, a mold is heated to a temperature at which a material to be filled can flow, and the material is filled in a cavity. Lowering the mold temperature and taking out the product after solidifying the material, or raising the mold above the glass transition temperature, filling the mold cavity with the material, and closing the gate with glass or metal balls And a method of gradually cooling the mold temperature at 1 ° C. for 60 seconds.

[0005] In addition, there is a method of using an injection compression molding die by a core compression method in order to facilitate filling of a material into a central portion.

FIG. 8 is a view showing an injection compression molding die by a core compression method for molding a convex lens. As shown in FIG. 1, the molding die includes a fixed-side mounting plate 2 mounted on a fixed platen 1, a cab plate 3 having one compression insert 31 mounted on the fixed-side mounted plate 2, and a movable platen. 4 has a movable side mounting plate 6 mounted via a core compression cylinder 32 and a compression insert 38 which is provided in an annular portion 6a formed on the movable side mounting plate 6 so as to be movable back and forth. Plate 33,
A runner plate 34 which can be brought into contact with and separated from the compression plate 33 and forms the parting surface 8 together with the cavity plate 3 is constituted.

On the runner plate 34 side of the compression plate 33, an ejector pin 17 for pressing the spool 15 to discharge the molded product 16, a compression plate 33 and the runner plate 3
A return pin 36 for guiding a compression plate returning spring 35 provided between the four is attached.

At the center of the core compression cylinder 32,
A hollow core compression piston 37 that advances the compression insert 38 through the compression plate 33 is attached. The movable platen 4 has an ejector rod 1 when the mold is opened.
4, the compression plate 33 is further advanced, and the molding 16 is formed by the compression insert 38 and the ejector pin 17.
Is mounted.

[0009]

However, any of the methods for increasing the mold temperature described in the prior art have a problem that the molding cycle time is long and the productivity is poor.

Further, in the method using an injection compression molding die, since a difference in material shrinkage occurs due to a difference in thickness between the central portion and the peripheral portion, it is difficult to improve accuracy due to sinking in the peripheral portion. In addition, in response to the peripheral portion by the pressure holding, the pressure is applied from the gate, and the central portion that is rapidly solidified is deformed.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of forming a concave lens capable of accurately and quickly producing a concave shaped pslatic lens, and a mold for forming the concave lens.

[0012]

The present invention has solved the above-mentioned problems as follows. That is, after filling a material into an injection compression molding mold and compressing to form a concave lens, the amount of shrinkage due to the difference in thickness between the central portion and the peripheral portion of the lens is applied to the peripheral portion of the molded product. Correct by replenishing. The mold temperature at the time of material filling is equal to or lower than the glass transition temperature.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described based on embodiments with reference to the drawings.

In the present invention, in order to mold a concave lens accurately and quickly by injection molding, the mold temperature at the time of filling should be equal to or lower than the glass transition temperature of the material (from the glass transition temperature to the glass transition temperature− (In the range of 20 ° C.), and after filling, the mold temperature is set to a temperature at which the material starts to be solidified, thereby shortening the solidification time. Even when the mold temperature is equal to or lower than the glass transition temperature, the flow of the material in the cavity is changed from the state shown in FIG. 7A to the state shown in FIG. As shown, a weld line 24 may be generated on the opposite side of the gate 21 and a short shot 25 may be generated at the center. Therefore, in the present invention, the molding die has the following configuration.

FIG. 1 is a sectional view showing a mold for forming a concave lens according to the present invention. Parts that are the same as or equivalent to the conventional example will be described using the same reference numerals.

As shown in FIG.
, A cabinet plate 3 attached to the fixed-side mounting plate 2 and having a plurality of recesses on its surface, and a movable-side mounted to a movable platen 4 via a heat insulating plate 5 or the like. A mounting plate 6, a core plate 7 that is configured to be able to contact and separate from an annular portion 6 a formed on the movable-side mounting plate 6,
A runner plate 9 forming a parting surface 8 together with the mold plate 3; and an ejector plate 10 provided in the annular portion 6a of the movable-side mounting plate 6 so as to be movable back and forth.
It is composed of

On the runner plate 9 side of the core plate 7, a plurality of cores 7a having a convex portion at the tip are formed. The core 7a is inserted into a plurality of through holes formed in the axial direction of the runner plate 9 so as to be able to move back and forth, and a convex portion at the tip is engaged with a concave portion of the cabinet plate 3 to form a cavity 11 therebetween. I do. In addition, on the surface of the runner plate 9, a concave portion for forming a plurality of tabs 16 b is formed on a peripheral portion 16 a of the molded product 16 and an outer peripheral side thereof.

A plurality of push rods 12 are mounted in the axial direction on the movable mounting plate 6 side of the core plate 7.
The push rod 12 is inserted into a plurality of through holes formed in the ejector plate 10 and the movable-side mounting plate 6 so as to be able to move back and forth, and is an annular core pushing piston provided at the center of the movable platen 4 so as to be able to move back and forth. 13 makes it possible to press. Further, the ejector plate 10 can be pressed by an ejector rod 14 which is provided in the hollow portion of the core pushing piston 13 so as to be able to move back and forth.

On the core plate 7 side of the ejector plate 10, an ejector pin 17 for pressing the spool 15 to discharge the molded product 16, and a peripheral portion 16a of the molded product 16
Are mounted. The ejector pins 17 and the pins 18 are inserted into through holes formed in the axial direction of the core plate 7 and the runner plate 9 so as to be able to move back and forth.

A spring 19 for returning the ejector plate is provided between the core plate 7 and the ejector plate 10, and a spring 20 for returning the core plate is provided between the runner plate 9 and the core plate 7. .

Next, the operation of the molding die will be described with reference to FIGS.

FIG. 1 shows a state where a predetermined amount of material is filled into the cavity from the gate 21. 2A and 2B are explanatory views showing a state in which a predetermined amount of material is filled in the cavity, wherein FIG. 2A is a front view and FIG. 2B is a side view. FIG.
FIG. 3 is a diagram showing a state in which the material in the cavity is compressed, (a) is a front view, and (b) is a side view.

First, as shown in FIGS. 1 and 2, with the core 7a and the pin 18 returned to the rear,
The cavity 11 is filled with a predetermined amount of material.

Next, as shown in FIG. 3, the core 7a is advanced by the core pushing piston 13 and excess material is removed from the tab 16b.
To form a molded product by flowing into the gate 21 or flowing backward to the gate 21. Next, the pin 18 and the ejector pin 17 are advanced by a predetermined distance by the ejector rod 14 to correct the contraction of the material in the peripheral portion 16a of the molded product 16.

Next, the movable platen 4 is retracted, the mold is divided at the parting surface 8, the ejector plate 10 is advanced by the ejector rod 14, and the molded product 16 is dropped. In the above embodiment, the compression of the peripheral portion 16a of the molded product 16 is performed by the pin 18, but may be performed by the sleeve 22 or the like as shown in FIG. Further, as shown in FIG. 5, a pin 18a may be provided on the tab 16b to compress the peripheral portion 16a. Further, the injection compression method is a core compression method, but may be a full-face compression method.

[0026]

The present invention has the following effects. (A) Since the mold temperature at the time of filling is set to the glass transition temperature, productivity is improved. (B) Injection compression (core compression method, etc.) prevents short shots in the center, and compensates for the shrinkage caused by the difference in thickness between the center and the periphery by replenishing material to the periphery. As a result, a highly accurate concave lens can be obtained. (C) A large concave lens having a thickness difference of 3 times or more between the central portion and the peripheral portion can be accurately molded.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a mold for forming a concave lens according to the present invention.

FIGS. 2A and 2B are explanatory views showing a state in which a material is filled in a cavity, wherein FIG. 2A is a front view and FIG. 2B is a side view.

FIGS. 3A and 3B are views showing a state in which a material in a cavity is compressed, wherein FIG. 3A is a front view and FIG. 3B is a side view.

FIG. 4 is a view showing a configuration in which a peripheral portion of a molded product is compressed by a sleeve.

FIG. 5 is a view showing a configuration in which a peripheral portion of a molded product is compressed by a pin provided on a tab.

FIG. 6 is a sectional view of a concave lens.

FIG. 7 is a diagram showing a flow of a material injected into a cavity when a concave lens is injection-molded. (A) at the time of filling,
(B) is a figure which shows the state at the time of completion of filling.

FIG. 8 is a configuration diagram of a conventional injection compression molding die using a core compression method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixed board 2 Fixed side mounting plate 3 Cabinet plate 4 Movable plate 5 Heat insulating plate 6 Movable side mounting plate 6a Annular part 7 Core plate 7a Core 8 Parting surface 9 Runner plate 10 Ejector plate 11 Cavity 12 Push rod 13 Core pushing piston 14 Ejector rod 15 Spool 16 Molded product 16a Peripheral portion 16b Tab 17 Ejector pin 18, 18a Pin 19, 20 Spring 21 Gate 22 Sleeve

Claims (6)

[Claims] 1. A mold for injection compression molding is filled with a material and compressed to form a concave lens. A method of forming a concave lens, wherein correction is performed by replenishment. 2. The method of molding a concave lens according to claim 1, wherein the mold temperature at the time of material filling is set to a glass transition temperature or lower. 3. An injection compression molding die, comprising an ejector plate (10), an ejector pin (17) for discharging a molded product (16), and a peripheral portion (16) of the molded product (16).
b) A mold for forming a concave lens, wherein a plurality of pins (18) for pressing the lens are formed. 4. A sleeve (22) is formed instead of the plurality of pins (18).
A molding die for the concave lens described in the above. 5. A peripheral portion (16a) of the molded article (16)
Instead of a plurality of pins (18) for pressing the molded product (1).
A plurality of tabs (1) provided on the outer periphery of the peripheral portion (16a) of (6).
The mold according to claim 3, characterized in that a plurality of pins (18a) for pressing 6b) are formed. 6. A core compression type mold for injection compression molding, wherein a core plate return spring (20) is provided on a front surface of a core plate (7) having a core (7a), and a core pressing piston (20) is provided on a back surface thereof. 13) acts on the core plate (7)
6. An ejector plate return spring (19) acting on a front surface of an ejector plate (10) provided on the back of the device, and an ejector rod (14) acting on a rear surface of the ejector plate (10). Mold for forming concave lenses.