JPS5953858B2 - How to mold prescription lenses - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for molding prescription lenses.

Traditionally, most optical lenses have been made of glass, but recently surface hardening technology has been developed to make the surface of plastics as hard as glass, and plastic lenses are now being used for optical lenses as well. Ta.

However, since many plastic lenses are made by injection molding, it is difficult to completely eliminate molding distortion, and prescription lenses have thicker walls at the center of the lens, so the mold must be filled with plastic. When the molten resin is cooled, it undergoes volumetric contraction, resulting in "whiskers" in the thick parts.

The injection compression molding method is well known as the most effective method for preventing this "whisker", in which the volumetric shrinkage of the molten resin in the mold is recovered by compression.

In the conventional injection compression molding method, a combined mold is used, the cavity and gate are placed along the parting surface (separation surface of the mold), and the core is operated to compress the molten resin. It is also well known that it is commonly used. In this case, a hydraulic system is set up independent of the injection molding machine, and the core is operated by this hydraulic pressure. However, a multi-cavity mold has the drawback that a large hydraulic pressure is required to compress the molten resin, making the hydraulic system large and making it substantially difficult to attach it to the mold.

- The present inventors have eliminated the above drawbacks by utilizing the mold clamping force of an injection molding machine, and have invented an extremely simple method for molding prescription lenses that is free from "whiskers" and "distortion."

That is, in a lens molding mold having a gate and a cavity on the same separation line, one side of the moving core plate that accommodates the moving core so as to be able to slide through it is supported by the actuating plate via an elastic body, and the other side is supported by the actuating plate through an elastic body. The fixed core is abutted and supported by a fixed core plate that houses the fixed core, and the low mold clamping pressure obtained using the hydraulic pressure of the injection molding machine and the repulsive force of the above elastic body are combined into a θ balance that leaves a clamping margin for the moving core. Then, the cavity is filled with molten resin at an injection pressure lower than the above-mentioned low mold clamping pressure, and then the above-mentioned actuating plate is closed at the highest mold clamping pressure that can be obtained using the hydraulic pressure of the injection molding machine. Press to push the moving core by the above-mentioned moving core clamping margin, and at the same time, maintain the injection pressure to be sufficient to prevent backflow of molten resin from the gate due to the above c゛・5 high mold clamping pressure. This is a method for molding prescription lenses characterized by: One of the features of the present invention is that it has a very simple mold structure and can be used almost as is with an ordinary injection molding machine.

The present invention will be explained below based on illustrated embodiments.

FIG. 1 is a sectional view schematically showing a mold used in the method of the present invention, and FIG. 2 is a sectional view showing the state of the compression process.

The movable core plate 3, which houses the movable core 4 set on the actuating plate 8 so as to be able to slide through it, is supported by the fixed core plate 1 in contact with the parting surface 5, and the movable core plate 1 of the movable core plate 3
The opposite surface is supported by an actuation plate 8 via an elastic body 7.

Further, a fixed core 2 is set on the fixed core plate 1 at a position facing the movable core 4, and a cavity 6 is formed by the fixed core 2 and the movable core 4.

First, the movable core plate 3 is fixed to the fixed core plate 1 by pushing the actuating plate 8 with the low mold clamping pressure F1 obtained using the oil pressure of the injection molding machine 12.
The movable core is held at a position where this low mold clamping pressure F1 and the repulsive force of the elastic body 7 are balanced. At this time, an operating margin 9, that is, a movable core clamping margin is left between the moving core plate 3 and the operating plate 8, so that a cavity 6 containing the volumetric shrinkage of the molten resin is formed.

Next, the resin 10 melted by the injection molding machine 12 is transferred to the gate 1
1 into the cavity 6 at a pressure lower than the low mold clamping pressure, the mold clamping pressure is increased to the highest mold clamping pressure F2 of the injection molding machine 12, and the movable core 4 is pushed in and moved forward to close the cavity. At the same time, the injection pressure is increased to the above-mentioned maximum. Compression molding is performed by switching to a holding pressure sufficient to prevent the molten resin 10 from backflowing from the gate 11 due to the high mold clamping pressure F2. In the present invention, the optimum values for low mold clamping pressure, maximum mold clamping pressure, injection filling pressure, holding pressure, etc. can be determined depending on the properties of the resin to be molded and the specifications of the injection molding machine, but the injection filling pressure is 300~ 500kg/-, holding pressure is 60
0 to 1000 kg/CIIl2 is appropriate. Further, the elastic body is preferably a spring from the viewpoint of material and ease of use, but is not particularly limited. Comparative examples and examples are shown below.

[Comparative example]

Melt acrylic resin in an injection molding machine, mold temperature 80℃
, injection pressure was 900 kg/Cm2, and mold clamping force was 140 T0n.

Concentric "whiskers" were clearly observed on the resulting lens.

〔Example〕

The above acrylic resin is melted in the above injection molding machine, mold temperature is 80℃, low mold clamping force is 40T0n, and filling injection pressure is 400kg/
After filling the mold with molten resin under Aff conditions, the mold clamping pressure was increased to 140T0r1, and at the same time, the injection pressure was increased to 1000.
Molding was performed by switching to a holding pressure of kg/mash.

No "whiskers" were observed on the obtained lens.
As described above, the present invention fully utilizes the mold clamping force of an ordinary injection molding machine, and takes into consideration a mold with a simple structure, molding conditions, procedures, etc., thereby creating a prescription lens that does not have "whiskers" or "distortion." This is an extremely useful invention that can be molded.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view schematically showing the mold used in the method of the present invention, showing a state in which low mold clamping pressure and the repulsive force of the elastic body are balanced, and Figure 2 shows the molten metal filling the cavity. FIG. 3 is a cross-sectional view showing a state in which resin is compressed at maximum mold clamping pressure. In the figure, 1 is a fixed core plate, 2 is a fixed core, 3 is a moving core plate, 4 is a moving core, 6 is a cavity, 7 is an elastic body, and 8 is an actuating plate.

Claims (1)

[Claims] 1. In a lens molding mold having a gate and a cavity on the same separation line, one side of the moving core plate that accommodates the moving core so as to be able to slide through it is supported by an actuating plate via an elastic body, and the other side is supported by an actuating plate through an elastic body. The fixed core is abutted and supported by a fixed core plate that houses the fixed core, and the low mold clamping pressure obtained using the hydraulic pressure of the injection molding machine and the repulsive force of the elastic body are balanced so as to leave a clamping margin for the movable core. The mold is clamped, and then molten resin is filled into the cavity at an injection pressure lower than the above-mentioned low mold clamping pressure, and then the above-mentioned actuating plate is pressed with the maximum mold clamping pressure that can be obtained using the hydraulic pressure of the injection molding machine. A prescription lens characterized in that the movable core is pushed in by the movable core clamping margin while the injection pressure is maintained at a pressure sufficient to prevent backflow of molten resin from the gate due to the maximum mold clamping pressure. Molding method.