JPS6283121A - Injection molding apparatus for concave lens - Google Patents

Abstract

PURPOSE:To obtain highly accurate plastic concave lens without occurrence of weldline by a method in which a side core is provided on the side of a cavity in the right-angle direction to the gate and the side core is advanced in the cavity in the early period of inflow of resin to the cavity. CONSTITUTION:A cavity 3 is formed by a fixed mount 1, a movable mount 2, a fixed insert 4, a movable insert 5 and side cores 6a and 6b located in the right-angled direction to a gate, slidable in the diametric direction of lens. The side cores 6a and 6b are advanced, and oil-pressure cylinders 8a and 8b are driven by an oil pressure controller 12 in such a way as to hold them on the most advanced position. A resin is injected from an injection molding machine and a plunger 20 is introduced through the gate 21 from a sprue and a runner into the cavity 3, whereupon the resin 20 flows on the central thin portion of a lens because the side cores 6a and 6b are present on the peripheral thick portion of the preceded lens. The occurrence of weld line on a concave plastic lens whose central thickness is smaller than the peripheral one can thus be prevented.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to an injection molding apparatus for a concave plastic lens molded by injection molding or injection compression molding.
In particular, the present invention relates to an injection molding apparatus for concave lenses suitable for preventing cut lines caused by concave shapes.

[Background of the invention]

Conventionally, when a concave plastic lens 51 as shown in FIG. 8 is molded by injection molding (however, FIG. 8 (α) is a plan view and FIG. 8 (6) is a side view), a gate 52 and A weld line 55 was formed on the opposite side. this is,
As shown in FIG. 9(α), the flow of resin flowing into the cavity 54 from the gate 52 first flows to the outer peripheral thick part 55 of the cavity 54 and then to the central thin part 56. This is because a weld line 55 is formed at the seam 57 where the flow from the outer periphery 55 of the cavity meets, as shown in (b). This weld line varies depending on the fluidity of the resin, but for example, it is 250 to 250 υ. In heated polycarbonate resin (hereinafter referred to as PC resin), this problem is likely to occur when the ratio of the outer peripheral wall thickness to the center wall thickness exceeds 2 times, and when the ratio exceeds 5 times, it occurs when controlling the gate shape and resin inflow speed. cannot be prevented. Also,
Such weld lines are a problem in terms of the appearance and optical properties of the lens, and lenses with weld lines cannot be used as products.

As a method for preventing this weld line, JP-A-55-
As shown in Japanese Patent No. 95850, there is a method of providing an overflow pocket outside the lens cavity. However, the lens molded using this method has a portion having the above-mentioned overflow pocket shape, and it was necessary to remove this portion by secondary processing when producing the product.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a concave lens injection molding apparatus suitable for injection molding a concave plastic lens by eliminating the drawbacks of the prior art and preventing the occurrence of weld lines.

[Summary of the invention]

In order to achieve the above object, the present invention reduces the flow cross-sectional area of the outer peripheral thick part where the resin conventionally flows before the lens central thin part at the initial stage of the resin flowing into the cavity from the gate. The mold structure is such that resin is actively flowed into the thin center part, and then the outer thick part is filled with resin to prevent weld lines from forming.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIGS. 1 to 5.

FIG. 1 is a sectional view of a mold for injection molding a plastic lens according to an embodiment of the present invention, and FIGS. 2 to 7 are enlarged views of the cavity 5 portion to explain the operation of the side cores 6α and 6b. It is.

The cavity 5 consists of a fixed frame 1, a movable frame 2, a fixed piece 4 provided in the fixed frame 1 whose surface in contact with the cavity 5'' is mirror-polished to a desired spherical or aspherical surface, and the movable frame. 2, a movable inserting piece 5 that is slidably provided in the lens thickness direction and whose surface in contact with the cavity 5 is mirror-polished to a desired spherical or aspherical surface, and a gate (not shown since it is perpendicular to the drawing). It is constituted by side cores 6α and 6b that are provided in the right angle direction and are slidable in the lens radial direction. Further, a hydraulic cylinder 7 for driving the movable inserting piece 5 in the lens thickness direction, and hydraulic cylinders 8α and 8b for driving the side cores 6α and 6b in the lens radial direction are provided in the movable frame 2. , these hydraulic cylinders 7.8α, Bb are connected to hydraulic piping 9α, t)b, 10α, 1o, 6, 1, respectively.
It is connected to the hydraulic control device 12 by 0C and 10d. In addition, in order to control the temperature of the fixed frame 1, movable frame 2, fixed insert piece 4, and movable insert piece 5, a heater and a heat medium flow path (not shown) are provided in each of them to control the mold temperature. Control device 15
It is a structure that can be controlled by In order to synchronize the operation of the hydraulic control device 12 and the mold temperature control device 15 with the operation of the injection molding machine (not shown), an injection molding machine opening device 14 and the hydraulic control device 12 that control the operation of the injection molding machine are provided. ．． The mold temperature side control device 15 has signal lines 16 and 17, respectively.
, 18 to the molding collateral device 15 .

Here, -1 As shown in FIGS. 2 and 5 ((5, FIG. 2 is an enlarged cross-sectional view of the cavity portion, and FIG. 5 is an enlarged plan view of the cavity portion), the aforementioned suite core 6α, The height d of 6A in the lens thickness direction is such that the gap C between the side cores 6α and 6A at the outer periphery of the lens that occurs when the side cores 6α and 6b move forward (indicated by dotted lines) is the same as the lens center thickness α;
It is desirably less than that, and the ratio with the center thickness of the lens is set to be 3 or less, preferably 2 or less. Further, the width t of the side cores 6α, 6h is set to a size that does not deform when the resin flows in the cavity 5 during injection, preferably about 173 times the lens diameter.

In addition, the surfaces of the side cores 6α and 6b in contact with the cavity at the time of the most retracted position are set to be at the same position or a retracted position as the side surfaces of the lens constituted by the fixed frame 1 and the movable frame 2, and when the side cores are fully advanced, The lengths of the closed cores 6α and 6h and the amount of protrusion of the hydraulic cylinder are set so that they do not come into contact with the fixed insert piece 4 and the movable insert piece 5.

Here, in this example, the process of molding a concave plastic lens will be explained using FIGS. 4 to 7.

First, before the injection molding machine injects the molten resin.

The fixed frame 1, the movable frame 2, the fixed insert piece 4, and the movable insert piece 5 are heated to a predetermined temperature by a mold temperature control device 15 using a heater and/or a heat medium, for example, in the case of PC resin, the glass transition temperature is 140. Heat to ~160v. Here, as shown in FIG. 4, the hydraulic cylinders 8α, 8A are driven by the hydraulic control device to advance the side cores 6α, 6b and hold them at the most advanced position. Here, the holding pressure of the side cores 6a and 6b is:

Cavity 5 during subsequent resin flow and filling
greater than the internal pressure, for example 400 in this example
~600Kq/c11K.

Next, by a known method, resin is injected from an injection molding machine, and the resin 20 is caused to flow into the cavity 5 through the gate 21 from the sprue and runner. Here, 0, the resin 20 flowing into the cavity 5 is the conventional one.

Since the side cores 6α and 6h are present in the thick portion of the outer periphery of the lens, the liquid flows through the thin portion of the center of the lens as shown in FIG.

Here, the gap between the side cores 6a, 6b and the outer periphery of the lens, ie, C in FIG. 2, must be equal to or smaller than the lens thickness.

This is necessary for the advance flow of the resin into the thin part of the lens.After this, as shown in FIG.
9, or after the injection pressure or amount of injected resin on the injection molding machine side, that is, the screw advance position reaches the set value, the side cores 6α, 6
B is retracted to the most retracted position by the resin pressure in the cavity 5 or the hydraulic cylinders 8α and Bh while resin injection continues. As a result, as shown in FIG. 7, the resin 20 can be filled into the cavity 5 while preventing the generation of weld lines. Immediately after the filling of the resin 20 into the cavity s and the retraction of the hidden cores 6α and 6A are completed. While maintaining the injection pressure,
In order to pressurize the resin 20 in the cavity s by the movable inserting piece 5, the hydraulic cylinder 7 is driven, and at the same time, the mold temperature is cooled by a heat medium.

After the resin in the gate portion 21 is cooled and solidified, the injection pressure is removed and preparations for the next resin injection are made using a known method. Further, the pressure applied by the movable inserting piece 5 is applied until the resin 20 in the cavity is cooled and solidified, and then the pressure is removed, the mold is opened by a known method, and the molded product including the lens portion is released from the mold.

As described above, according to the present embodiment, the occurrence of weld lines can be prevented in a concave plastic lens in which the thickness of the center part is thinner than that of the outer peripheral part.

And it can be molded with high precision.

Furthermore, in this embodiment, the resin 20 is injected into the cavity 3.
Immediately after filling, the hydraulic cylinder 8α is pressed again to pressurize the resin 20 in the cavity s from the side cores 61Z and 6hK simultaneously with the pressurization by the movable insert piece 5.

Driving the lens 8b helps improve the molding accuracy of the lens. This is because when the resin is cooled, the thin center part of the lens solidifies first, making it difficult to shape the lens surface by pressurizing the movable inserting piece 5, but at the same time, the thick part of the outer periphery is delayed in solidification. This is because by pressurizing this, it is possible to compensate for shrinkage due to cooling and solidification of the resin. At this time, before releasing the molded product, at the same time as removing the pressure from the movable insert piece 5, the side wall (Z,
6b needs to be depressurized and retreated.

〔Effect of the invention〕

According to the present invention, a side core is provided on the side surface of the cavity in a direction perpendicular to the gate, and the side core is advanced into the cavity at the initial stage of resin flowing into the cavity, thereby preventing the resin from flowing in the thick portion of the outer periphery of the lens. By allowing the resin to flow into the thin central part of the lens, it is possible to prevent the weld line that occurs conventionally due to the cavity shape, and it is possible to obtain a concave plastic lens with no defects and high precision. can.

[Brief explanation of drawings]

Fig. 1 is a sectional view showing an embodiment of the present invention, Fig. 2 is an enlarged sectional view of the cavity portion, Figs. 5 to 7 are enlarged plan views of the cavity portion, and Fig. 8 is a conventional concave lens. FIG. 9 is an enlarged plan view of a cavity showing a conventional molding process. 1... Fixed frame, 2... Movable frame, 5... Cavity% 4... Fixed inserted piece, 5... Movable inserted piece, 6α,
6h... Side core, 7.8α, 8h... Hydraulic cylinder %12... Hydraulic control device, 15... Mold temperature control device, 14... Injection molding machine control device, 15... Molding Side (capital) device, 19... Sensor, 20... Resin, 21... Gate portion, 55... Weld line, 5
5... Outer peripheral thick part, 56... Center thin part.

Claims (1)

[Scope of Claims] 1) Formed by a fixed frame, a movable frame, a fixed insert piece provided within the fixed frame, and a movable insert piece slidably provided within the movable frame. A concave lens-shaped cavity is filled with resin through a gate, and the movable insert piece is pushed out by a cylinder placed at the rear of the movable insert piece, thereby compressing the resin in the cavity and forming a concave lens. In the injection compression mold, a side core capable of sliding in a direction perpendicular to the gate is disposed on the side of the cavity, a cylinder for driving the side core is provided at the rear of the side core, and before the resin flows into the cavity, The side core is protruded into the cavity, and after the completion of the inflow of the resin into the center thin part of the concave lens is detected by a sensor provided at a position facing the gate, the side core is moved back, and after the resin has finished filling the cavity, the movable entry piece is moved. An injection molding device for a concave lens, characterized in that it is equipped with a pressure control device that controls pressurization on a lens surface. 2) Injection of a concave lens according to claim 1, characterized in that the pressure control device performs control to pressurize the side surface of the lens by the side core at the same time as the movable entry piece pressurizes the lens surface. Molding equipment. 3) When the side core advances into the cavity, it does not come into contact with the fixed insert piece and the movable insert piece, and the maximum value of the gap between the side core and the cavity is equal to or less than the thickness of the cavity. The injection molding apparatus for a concave lens according to claim 1, wherein the injection molding apparatus for a concave lens is configured to be at the same position as the side surface of the lens or at a position retracted when the lens is retracted.