JPH05337975A - Apparatus and method for molding plastic lens - Google Patents

Abstract

PURPOSE:To mold a thick-walled plastic lens reduced in optical strain. CONSTITUTION:In an apparatus and method for molding a thick-walled plastic lens, a molten thermoplastic resin is supplied into a mold cavity and cooled and solidified while shearing force is applied to at least a part of the interior of a mold.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic lens molding apparatus and a molding method thereof. More specifically, the present invention relates to a molding apparatus and a molding method for manufacturing a thick plastic lens with little optical distortion.

[0002]

2. Description of the Related Art Recently, in optical devices and the like in which glass lenses have been used, demands for impact resistance and weight reduction have recently become strong, and PMMA, PS, P
Plastic lenses such as C have been used. However, with plastic lenses, resin shrinks as the resin in the mold cavity cools during molding, which tends to cause distortion and sink marks, resulting in poor surface accuracy and the appearance of distorted images. However, there is a drawback that it cannot be used in optical devices when particularly high accuracy is required.

In order to overcome such drawbacks, Japanese Patent Laid-Open Publication No.
JP-A No. 1-96855 discloses, "After injection molding a thermoplastic resin into a plate shape or a curved shape, the molded body is heated in advance to a softening point of the resin or higher to be deformed, put in a predetermined lens mold, and heated. "Manufacturing method of pressurized plastic lens", Japanese Patent Publication No. 59-47974, "By measuring the hoop stress of the mold generated in the molding process and adjusting and controlling the ram pressure of the heating compression molding machine by the measured value. , A method of obtaining a lens having excellent optical performance by ignoring the variation in the volume of the lens blank. However, these methods cannot form an excellent lens with a small optical distortion that can be used in high-performance optical equipment. Further, Japanese Patent Application Laid-Open No. 61-179715 discloses a molding method in which a molten thermoplastic resin is supplied to a mold and the resin is solidified while applying a shearing force to at least a part of the molten resin in the mold. However, there is a problem that a weld portion is generated.

[0004]

Means for Solving the Problems As a result of earnest studies on a molding apparatus and method for a high precision thermoplastic resin lens having a small optical distortion, the present inventor has found that it is not solidified before and during solidification filled in a mold cavity. The present invention has been completed by finding a method of molding a molten resin by using an apparatus for cooling the molten resin while repeatedly applying a shearing force to the molten resin. That is, the present invention is a molding apparatus for molding a plastic lens by injecting a molten thermoplastic resin into a mold cavity, and applying a shearing force to at least a part of the molten resin in the mold to melt the molten resin. The present invention relates to a plastic lens molding apparatus characterized by being cooled and solidified.

The thermoplastic resin which can be used in the present invention is a thermoplastic resin used in known plastic lenses, and examples thereof include PC, PMMA, PS and AS, and in the molding apparatus of the present invention. There is no particular limitation on the shape and thickness of the plastic lens that can be molded. The molding apparatus and molding method of the present invention will be described with reference to FIG. Reference numerals 1, 2, and 3 in FIG. 1 represent a cylinder, a screw, and a nozzle of an ordinary injection molding machine, respectively. Reference numeral 9 is a mold attached to the injection molding machine, and 5 and 6 between the nozzle and the cavity of the injection molding machine are devices for repeatedly applying shearing force to the molten resin in the mold.

The molten resin injected from the nozzle of the injection molding machine passes through the flow path 4 and fills the runner and the mold cavity. When the filling is completed, move the pistons 5 and 6 in the directions of the arrows to move the runner and the mold cavity 10.
The molten resin inside also moves in the direction of the arrow. Next, when the pistons 5 and 6 are moved in the direction opposite to the arrow, the runner and the molten resin in the mold also move in the direction opposite to the arrow. When the pistons 5 and 6 are alternately and continuously moved in the opposite direction in this manner, shearing force is repeatedly applied to the molten resin in the mold, and the resin causes shearing heat generation. Therefore, the mold temperature and the moving speed and movement of the piston are increased. By adjusting the distance, while controlling the cooling rate of the resin, the amount of contracted resin is replenished by the piston to reduce optical distortion.

Therefore, when molding a plastic lens using the molding apparatus of the present invention, it is desirable to mold it by the following operation. The molten resin is injected into the mold with the temperature of the mold being equal to or higher than the glass transition temperature of the thermoplastic resin used. The mold temperature is set to a temperature lower than the glass transition temperature while applying a shearing force to the molten resin by the pistons 5 and 6 to generate heat. When the movement of the pistons 5 and 6 is gradually slowed down, the molten resin begins to freeze from the surface of the molded product and the resin also contracts. Therefore, the molten resin is replenished by the pistons 5 and 6 by the amount of contraction. The movement cycle of the piston is preferably 0.1 to 20 seconds. After freezing to the center of the molded product, the movement of the pistons 5 and 6 is stopped, the mold is opened, and the molded product is taken out. By this operation, a lens with less freezing distortion can be molded. Depending on the required accuracy of the lens, the mold temperature may be lower than the glass transition temperature of the resin, or the shearing force applied to the resin by the piston may be adjusted.

The device of the present invention can also have a device for applying a shearing force to the mold as shown in FIG. 1 incorporated therein. That is, in a device that supplies a molten thermoplastic resin into a mold cavity and solidifies the resin while applying a shearing force to at least a part of the molten resin in the mold, the device that applies the shearing force is It is a mold with two or more hot runners communicating with the cavity and a piston installed on this hot runner. The piston also functions as a check valve that closes the flow path to the sprue-side runner when compressive force is applied. It is also possible to use a plastic lens molding device having a different structure. Next, in the case of a multi-cavity mold, when the resin is injected from the cylinder of the injection molding machine as shown in FIG. 1, the piston 6 is moved forward so that only one runner
When the molten resin is filled as shown by the arrow, the flow distance of the resin becomes long, and the resin temperature and injection pressure must be significantly increased.

Further, the resin heated between the piston 6 and the resin flow path 8 stays for a long time and causes thermal decomposition, which mixes in the molded product and becomes a defective product. In order to avoid this, the piston 6 in FIG. 1 is retracted like the piston 5,
It is better to fill the molten resin from the runner on the piston 6 side. However, in this case, if molding with a single die,
Since a weld line is generated in the center of the molded product,
As described above, it is preferable to use a mold of two or more even cavities and to arrange the cavities so that no weld line is generated in the molded product.

[0010]

By using the plastic lens molding apparatus of the present invention, it is possible to manufacture a thick plastic lens with little optical distortion.

EXAMPLES The present invention will be specifically described below with reference to examples and comparative examples.

Example 1 PMMA resin (manufactured by Mitsubishi Rayon Co., Ltd., trade name: Acrypet VH) was dried at 80 ° C. for 5 hours, then, the cylinder temperature was 250 ° C., the injection pressure was 1000 kg / cm ² , and the mold temperature was 140.
At 0 ° C., the mold set as shown in FIG. 1 was filled with molten resin. The lens had an outer diameter of 120 mm, a peripheral wall thickness of 6 mm, a central wall thickness of 4 mm, and a volume of about 60 cc.

Immediately after filling the mold with the molten resin, pressure 50 is applied.
While moving the pistons 5 and 6 at 0 kg / cm ² at a speed of 1 second per cycle, the flow path of the heat medium for controlling the mold temperature is switched.
A heating medium of 0 ° C. was flown through the mold temperature control pipe. Next, in the first 1 minute, the pistons 5 and 6 are moved in the directions opposite to each other at a speed of 1 second for 1 cycle, and then 1 cycle / 2 seconds, 1 cycle every 1 minute.
Cycle / 3 seconds, 1 cycle / 5 seconds, 1 cycle / 10 seconds, that is, 1 cycle is increased from 1 second to 10 seconds over 5 minutes,
The molded product was gradually cooled from the surface to the inside, after which the piston was stopped and 2 minutes later, the mold was opened and the molded product was taken out. After taking out the molded product, the flow path of the heat medium for controlling the mold temperature was switched, and the mold temperature was raised to 140 ° C. over 7 minutes. The molding cycle was 15 minutes. The obtained PMMA lens was subjected to an optical distortion test using a polarizing filter, and no optical distortion was found.

Comparative Example 1 A PMMA lens was molded in the same manner as in Example 1 except that the piston was not moved, and an optical distortion was inspected using a polarizing filter. As a result, optical distortion was observed over almost the entire surface of the lens. It was Example 2 A polycarbonate resin (manufactured by Mitsubishi Gas Chemical Co., Inc., trade name: Iupilon H3000) was dried at 120 ° C for 5 hours, then at a cylinder temperature of 300 ° C and an injection pressure of 1000 kg / cm.
^{2. At} a mold temperature of 170 ° C., a mold having four cavities arranged as shown in FIG. 2 was filled with molten resin. The shape of the lens is 100 mm in outer diameter and 7 mm in thickness at the outer circumference.
The thickness of the central portion was 5 mm and the volume was about 50 cc.

Immediately after the molten resin is filled in the mold cavity, the heat transfer medium for controlling the mold temperature is moved while the pistons 5 and 6 are moved in the opposite directions at a speed of 1 second per cycle for a period of 500 kg / cm ^2. And the heat medium at 90 ° C. was flown through the mold temperature control pipe. The movement cycle of the pistons 5 and 6 is 1 cycle / 1 second for the first 1 minute, 1 cycle / 2 seconds for the next 2 minutes, 1 cycle / 3 seconds for the following 2 minutes, and 1 cycle / 1 for the last 2 minutes.
It is set to 0 seconds, that is, the moving cycle of the piston is lengthened from 1 second to 10 seconds over 7 minutes and gradually cooled from the surface of the molded product to the inside, then the piston is stopped and the mold is opened 3 minutes later. I took out the item. After the molded product was taken out, the flow path of the heat medium for controlling the mold temperature was switched, and the mold temperature was raised to 170 ° C. over 10 minutes. The molding cycle was 20 minutes.
The obtained polycarbonate lens was examined for optical distortion using a polarizing filter, and no optical distortion was found.

COMPARATIVE EXAMPLE 2 A polycarbonate lens was molded in the same manner as in Example 2 except that the piston was not moved, and an optical distortion was inspected using a polarizing filter. As a result, optical distortion was observed over almost the entire surface of the lens. Was given.

[0016]

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an injection molding machine having a device for applying a shearing force.

FIG. 2 is a schematic sectional view of a mold having four cavities used in Example 2.

[Explanation of symbols]

 1 Cylinder 2 Screw 3 Nozzle 4 Resin Flow Path 5 Piston 6 Piston 7 Resin Flow Path 8 Resin Flow Path 9 Mold 10 Mold Cavity

Claims (5)

[Claims] 1. A molding apparatus for injecting a molten thermoplastic resin into a mold cavity to mold a plastic lens, wherein at least a part of the molten resin in the mold when the molten resin is cooled and solidified. An apparatus for molding a plastic lens, characterized in that a device for applying a shearing force is installed in the device. 2. The plastic lens molding apparatus according to claim 1, wherein the apparatus for applying a shearing force to at least a part of the molten resin is at least two hot runners between the injection molding machine and the mold cavity. A molding apparatus for a plastic lens, characterized in that it has a structure in which pistons that are alternately arranged and interlock in opposite directions are installed. 3. The plastic lens molding apparatus according to claim 1 or 2, wherein the number of mold cavities is two or more. 4. An injection molding machine is a device for applying a shearing force to at least a part of the molten resin when a molten thermoplastic resin is injected into a mold cavity by using an injection molding machine to mold a plastic lens. Pistons arranged in at least two hot runners between cavities, respectively, by cooling and solidifying the molten resin while alternately applying shearing force to one side of the piston and pressure reduction to the other side. A method of molding a plastic lens, characterized by: 5. The method for molding a plastic lens according to claim 5, wherein the periodic speeds of the pistons arranged in at least two hot runners between the injection molding machine and the cavities and interlocking in opposite directions, respectively. A method of molding a plastic lens, wherein is in the range of 0.1 to 20 seconds.