JPH0331124B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a convex plastic lens. More specifically, the present invention relates to a method of manufacturing a relatively thick, large-diameter, high-quality plastic convex lens by injection molding.

Recently, plastic lenses have come to be used as optical lenses, contributing to the weight reduction of optical equipment and the cost reduction of optical lenses.

Conventionally, methods for manufacturing plastic lenses have been disclosed in Japanese Patent Application Laid-open No. 110481/1983 and Japanese Patent Publication No. 52-29885.
JP-A-52-121642, etc.; JP-A-52-130865, JP-A-54-148055,
Injection molding methods such as those described in JP-A No. 55-39355 are known.

However, when using the cast molding method, the plastic lens that is molded and hardened in the molding mold shrinks when it is cooled and hardened, or when it is polymerized and hardened, especially at its center and periphery. Since the thickness is different between the two parts, the lens curved surface does not shrink evenly. For this reason, both curved surfaces of the resulting plastic lens do not shrink uniformly, resulting in a disadvantage that both curved surfaces of the lens end up being different from the predetermined curved surfaces of the mold recess.

On the other hand, when using the injection molding method, the molten resin is forced into a mold at high pressure at a temperature below the flow temperature of the resin, and is cooled and solidified, so that the orientation of the resin remains when the molten resin is pushed into the mold. Optical distortion may occur in the convex lens finally obtained. This optical distortion deteriorates the quality of the lens.

Furthermore, when manufacturing a relatively thick, large-diameter convex plastic lens for a projection television receiver using an injection molding method, it is difficult to manufacture the target object in one step. Therefore, methods of multilayer molding have been proposed, as described in Japanese Patent Application Laid-open Nos. 57-72822 and 1987-173136. When using the methods described in these publications, it is possible to manufacture relatively thick, large-diameter plastic convex lenses, but optical distortion occurs in the laminated parts, making it difficult to manufacture high-quality plastic convex lenses. It was difficult to manufacture.

In view of this situation, the present inventors have conducted extensive studies with the aim of providing a method for efficiently manufacturing a plastic convex lens that is relatively thick, has a large diameter, is free from optical distortion, and has excellent quality. As a result, the present invention was completed.

Therefore, the gist of the present invention is to (a) manufacture a convex plastic lens having a diameter of 50 to 500 mm and a center thickness of 10 to 100 mm by injection molding using a first injection mold; Approximately 1/2 of the thickness of the final convex lens
(b) the convex lenticular core produced in the first step,
In the cavity of the second injection mold, two cavity residual parts having substantially the same shape are formed and sandwiched between the respective curved surfaces of the convex lens-shaped core and the cavity surface of the second injection mold, and these two cavity residual parts are sandwiched. (c) In the first step, the cavity surface temperature of the first injection mold is adjusted to the temperature of the plastic injected into the first injection mold. After injecting the molten plastic, the cavity temperature of the first injection mold is cooled to below 100°C, and the convex lens-shaped core is taken out and transferred to the second injection mold. ) In the second step, the cavity surface temperature of the second injection mold is maintained at a temperature higher than the flow temperature of the plastic injected into the remaining parts of the two cavities, and after the molten plastic is injected, the second injection mold The present invention relates to a method for manufacturing a convex plastic lens, characterized by cooling the cavity temperature of the mold to about 100°C or less.

The present invention will be explained in detail below.

Plastic base materials used for manufacturing the plastic convex lens of the present invention generally include those having good visible light transmittance. Examples of such plastics include polyacrylic acid ester, polymethyl methacrylate, polycarbonate, polystyrene, acrylonitrile-styrene copolymer (AS resin), transparent ABS resin, cellulose acetate, cellulose acetate butyrate, polyacetal, polysulfone, polyethylene terephthalate, Examples include polyallyl diglycol carbonate. Among these plastics, polymethyl methacrylate and polycarbonate have physical properties such as weather resistance and impact resistance, as well as transparency and
It is particularly preferred because it has excellent optical properties such as refractive index.

In the present invention, a plastic convex lens is manufactured using an injection molding machine. As the injection molding machine that can be used in this case, conventionally known injection molding machines such as plunger type or screw type can be used without any restriction.

Hereinafter, the present invention will be described in detail based on the drawings, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

FIG. 1 is a schematic vertical cross-sectional view showing a state in which a convex lens-shaped core is manufactured using a first injection mold;
FIG. 2 is a schematic vertical cross-sectional view showing a state in which the convex lens-shaped core produced in the first step is sandwiched in the cavity of the second injection mold.

In the figure, 1 and 21 are fixed mold mounting plates, 2 and 22 are fixed mold blocks, 3,
23 are fixed nesting molds, 4 and 24 are movable mold blocks, 5 and 25 are movable molds, 6 and 26 are nozzles, 7 and 27 are gates, and 8 is a convex lens-shaped core cavity. ,
9 is a center core brim forming part, 28 is a convex lens-shaped center core, 2
8' and 28'' are the remaining parts of the cavity, 29 is the core collar holding part, 10 and 30 are the cylinder plates, and 1
1 and 31 are movable mold mounting plates, 12 and 32 respectively.
are spacer blocks, 13 and 33 are cylinders, 14 and 34 are piston rods, 15 and 35 are piston bodies, 16,
36 are gate shutter pin drive plates, 1
7 and 37 are gate shutter pins, 1
8 and 38 are movable nested pressure plates, 19 and 3, respectively.
9 is a solenoid switching valve, 20 is a melted plastic, and P is a pump.

In the present invention, first, a convex lens-shaped core is manufactured using a first injection mold, and then this convex lens-shaped core is placed in the cavity of a second injection mold, above and below the convex lens-shaped core. Two cavity residual parts are formed and sandwiched between the two cavities, and plastic is injected onto the curved surfaces of both lenses to integrate them, thereby manufacturing the desired plastic convex lens.

The method of the present invention has a diameter of 50 to 500 mm and a center thickness of
Suitable for efficiently manufacturing convex plastic lenses of 10 to 100 mm. Convex lenses with a diameter of less than 50 mm can be produced using a simple method other than the method of the present invention.
Although easy to manufacture, convex lenses with diameters exceeding 500 mm are difficult to manufacture by injection molding methods. Convex lenses with a center thickness of less than 10 mm, as well as lenses with a diameter of less than 50 mm, can be manufactured by a simple method other than the method of the present invention, and the method of the present invention is not preferred. Convex lenses with a center thickness exceeding 100 mm are difficult to manufacture by injection molding. Convex plastic lenses which are particularly easy to manufacture using the method of the invention have a diameter in the range 100 to 300 mm and a center thickness in the range 15 to 70 mm.

In the present invention, first, a convex lens-shaped core is manufactured using a first injection mold. As shown in FIG. 1 as a schematic vertical cross-sectional view, the first injection mold forms a cavity 8 for a convex lens-shaped core by a fixed insert mold 3 and a movable insert mold 5. This cavity 8 has a structure in which molten plastic 20 can be injected from the nozzle 6.

The convex lens-shaped core cavity 8 has a thickness that is approximately 1/2 of the thickness of the convex lens that will be finally obtained. This is because if it is too thick or too thin, the cycle for producing the convex lens-shaped core in the first molding die will not be balanced with the subsequent cycle in the second molding die, which is undesirable.

A flange forming portion 9 is carved into the convex lens-shaped core cavity 8 along the dividing plane between the fixed insert mold 3 and the movable insert mold 5 so as to cover either one or both of the insert molds. I'll keep it. The flange formed around the convex lens core by the flange forming portion 9 serves to hold the convex lens core in the flange holding portion of the second injection mold.

A gate shutter pin 17 is provided in the first injection mold, and this gate shutter pin 17 is
Advancing by the gate shutter pin drive plate 16,
It is preferable that the movable nesting mold 5 is provided in a structure that allows it to be moved toward and retracted from the fixed nesting mold 3 side. It is preferable that a medium passage be carved in the stationary nesting mold 3 and the movable nesting mold 5 so that a heating medium and a cooling medium can be sent to them from the outside.

In order to manufacture a convex lens-shaped core using the first injection mold, the first injection mold The surface temperature of the mold cavity is set to a temperature higher than the flow temperature of the plastic to be injected into it. Here, the flow temperature of plastic is ASTM (American Society for
Testing Materials) D569-59, using a Rossi Peaks flow tester,
At 1500 psi, a 1/8 inch diameter tube is
The temperature that flows in inches. The flow temperature varies depending on the type of plastic and, in the case of plastics of the same type, the molecular weight. For example, the temperature is about 150 to 250°C for polymethyl methacrylate used for injection molding, and about 200 to 330°C for polycarbonate used for injection molding.

When heating the cavity surface of the first injection mold to a temperature above the plastic flow temperature, other heating methods that can be used in combination with the heating method using a heating medium include infrared rays, nichrome wire, high frequency induction heating coils, etc. Examples include a method of directly roasting the cavity surface and a method of blowing hot air.

the first injection mold is heated to a temperature range above;
Clamp the mold and place it in the cavity 8 for forming the center core of the convex lens.
The molten plastic is injected, and after injection, the cavity surface temperature of the first injection mold is immediately adjusted to
Cool to below 100℃. In this first step,
The reason why the cavity surface of the first injection mold is cooled to 100°C or less is that the work when inserting the convex lens-shaped core obtained in this first step into the cavity of the second injection mold is 100 degrees Celsius or less. This is because it is easier to do this than at a temperature higher than 0.degree. C., and the flange formed around the convex lens-shaped core becomes appropriately hard, making it easier to hold it in the flange holding part of the second injection mold. At this time, if the cavity surface temperature of the first injection mold is made too low, optical distortion may occur in the final convex plastic lens, so it is preferably 50°C or higher, particularly preferably 70°C. It is better to set it to the above.

In order to quickly cool down the cavity surface temperature of the first injection mold, compressed air is passed through the medium passage of this mold to discharge the remaining heating medium.
It is preferable to adopt a method in which a cooling medium such as cooling water is then passed through.

If the cavity surface temperature of the first injection mold is quickly cooled, the molten plastic will undergo molding shrinkage, making it impossible to obtain a convex lens-shaped core with a uniformly curved surface. To prevent this, the cavity may be compressed after the molten plastic is injected. At this time, first move the gate shutter pin 17 forward and remove the gate 7.
It is preferable to close the mold completely, and then move the movable insert mold 5 closer to the fixed insert mold 3 to compress the molten plastic.

This operation will be explained based on FIG. When the injection of the molten plastic 20 into the cavity 8 for the convex lens core is completed, the electromagnetic switching valve 19 is switched by an appropriate detection device (not shown), and the pressure oil from the hydraulic pump P is transferred to the hydraulic cylinder 13. The piston rod 14 is raised. This rise causes the gate shutter pin drive plate 16 to rise, and the gate shutter pin 17 closes the gate 7. Piston rod 14
When further raised, the gate shutter pin driving plate 16 comes into contact with the movable nesting die press plate 18, and raises it, raising the movable nesting die 5, which releases the molten plastic in the cavity 8 for the center core of the convex lens. will be compressed.

After manufacturing the convex lens-shaped core by the above method, the first injection mold is opened, the piston rod 14 is moved back to its original position, and the gate shutter pin 17 is also moved back to its original position. Moving nesting type 5
is returned to the position shown in FIG. 1 when the mold is opened.

After the convex lens-shaped core is released, the cavity surface temperature of the first injection mold is raised to a predetermined temperature, and the mold is placed on standby for the next molding.

The convex lens-shaped core 28 produced in the first injection mold is held in the cavity of the second injection mold to carry out the second step. The convex lens-shaped core 28 may be transferred into the cavity of the second injection mold by any method such as an input method or a robot method.

The cavity of the second injection mold is constructed by fitting the flange of the convex lenticular core 28 into a flange holding part 29 carved along the mold dividing surface, clamping and holding the convex lenticular core 28. The structure is such that two cavity residual parts 28' and 28'' having substantially the same shape are formed by the respective curved surfaces of the mold and the surface of the second injection mold.
The remaining two cavities 28', 28'' are structured so that molten plastic can be injected from the nozzle 26.

Preferably, the two cavity remainders 28', 28'' have substantially the same shape and have substantially the same volume.The two cavity remainders 28', 28'' are preferably provided with molten plastic injected from the nozzle 26 almost evenly into these cavity remainders. It is preferable to provide a gate 27.

A gate shutter pin 37 is provided in the second injection mold in a structure capable of moving forward and backward by a gate shutter pin drive shaft 36.
It is preferable to provide a structure in which it is possible to approach and retreat from the fixed nesting die 23 side. The fixed nesting mold 23 and the movable nesting mold 25 are heated with a heating medium,
Preferably, medium passages are provided for the passage of cooling medium.

In order to manufacture the desired convex lens using the second injection mold, the heating medium is passed through the medium passage provided in the second injection mold, or other heating methods are used As with the mold, the cavity surface temperature is kept above the flow temperature of the plastic to be injected into it. here,
The plastic flow temperature has the same meaning as previously described.

When heating the cavity surface temperature of the second injection mold to a temperature higher than the flow temperature of the plastic,
Other heating methods that can be used in combination with the heating method using the heating medium are the same as in the case of the first injection mold.

The second injection mold is heated to an upper temperature range;
The mold is clamped by sandwiching the convex lens-shaped core, and molten plastic is injected into the remaining two cavities 28' and 28''. After injection, immediately lower the cavity surface temperature of the second injection mold to 100℃ or less. Cool to
In this second step, the cavity surface of the second injection mold is cooled to 100°C or less so that the convex lens obtained in this second step can be easily handled after being taken out from the second injection mold. Because there is. At this time, the cavity surface temperature of the second injection mold may be set to about 70° C., since if it is too low, the cooling time will be too long. The convex lens taken out from the second injection mold at this temperature is preferably held by a holder and immersed in warm to cold water to slowly cool it.

If the cavity surface temperature of the second injection mold is quickly cooled, the molten plastic will undergo molding shrinkage, making it difficult to obtain a convex lens with a uniform curved surface. To prevent this, the cavity may be compressed after the molten plastic is injected. At this time, it is preferable to first advance the gate shutter pin 37 to completely close the gate 27, and then move the movable nesting mold 25 closer to the fixed nesting mold 23 to compress the molten plastic.

This operation will be explained based on FIG. The molten plastic is poured into the remaining two cavities 28',
When injection is completed at 28'', an appropriate detection device (not shown) switches the electromagnetic switching valve 39 to send pressure oil from the hydraulic pump P to the head side of the hydraulic cylinder 33. The piston rod 34 is raised. This rise causes the gate shutter pin drive plate 36 to rise, and the gate shutter pin 37 closes the gate 27. When the piston rod 34 is further raised, the gate shutter pin drive plate 36 moves. abutting against the nested pressing plate 38;
This is raised, the movable nesting mold 25 is raised,
This causes the molten plastic molded into a convex lens shape to be compressed.

In the convex lens manufactured by the above method, the second injection mold is opened, the piston rod 34 is retracted to its original position, and the gate shutter pin 37 is also retracted to its original position. The movable nesting mold 25 is returned to the position shown in FIG. 2 when the mold is opened.

After the manufactured convex lens is released from the mold, the cavity surface temperature of the second injection mold is raised to a predetermined temperature, and the mold is placed on standby for the next molding.

In the method of the present invention, the desired plastic convex lens can be manufactured by performing the first step and the second step in succession. The plastics used in the first step and the second step may be of the same type or may be a combination of different types. In the latter case, it is preferable to use mutually compatible types of combinations.

The present invention is as described above, and has particularly remarkable effects as follows, and its industrial utility value is as follows:
It is extremely large.

(1) When using the method of the present invention, a convex lenticular core is manufactured in the first step, and then plastic is injected onto both curved surfaces of the convex lenticular core in the second step, so the thickness is relatively thick. It is possible to efficiently manufacture large diameter plastic convex lenses.

(2) When using the method of the present invention, in both the first and second steps, the surface temperature of the injection mold cavity is raised to a specific range before molten plastic is injected. Orientation hardly remains on the plastic when it is injected, and the convex lens finally obtained has no optical distortion and can be of excellent quality.

(3) If the volume of the cavity is made compressible after molten plastic is injected into the cavity of both the first injection mold and the second injection mold, volumetric contraction will occur as the molten plastic cools. However, this can be made completely inconspicuous, making it possible to obtain a plastic convex lens with high precision comparable to that of polished glass.

[Brief explanation of the drawing]

FIG. 1 is a schematic vertical cross-sectional view showing a state in which a convex lens-shaped core is manufactured using a first injection mold;
FIG. 2 is a schematic vertical cross-sectional view showing a state in which the convex lens-shaped core produced in the first step is sandwiched in the cavity of the second injection mold. In the figure, 1 and 21 are fixed mold mounting plates, 2 and 22 are fixed mold blocks, 3,
23 are fixed nesting molds, 4 and 24 are movable mold blocks, 5 and 25 are movable molds, 6 and 26 are nozzles, 7 and 27 are gates, and 8 is a convex lens-shaped core cavity. ,
9 is a center core brim forming part, 28 is a convex lens-shaped center core, 2
8' and 28'' are the remaining parts of the cavity, 29 is the core collar holding part, 10 and 30 are the cylinder plates, and 1
1 and 31 are movable mold mounting plates, 12 and 32 respectively.
are spacer blocks, 13 and 33 are cylinders, 14 and 34 are piston rods, 15 and 35 are piston bodies, 16,
36 are gate shutter pin drive plates, 1
7 and 37 are gate shutter pins, 1
8 and 38 are movable nested pressure plates, 19 and 3, respectively.
9 is a solenoid switching valve, 20 is a melted plastic, and P is a pump.

Claims (1)

[Scope of Claims] 1. In manufacturing a plastic convex lens having a diameter of 50 to 500 mm and a center thickness of 10 to 100 mm, (a) the final injection molding is performed using a first injection mold; Approximately 1/2 of the thickness of the resulting convex lens
(b) the convex lenticular core produced in the first step,
In the cavity of the second injection mold, two cavity residual parts having substantially the same shape are formed and sandwiched between the respective curved surfaces of the convex lens-shaped core and the cavity surface of the second injection mold, and these two cavity residual parts are sandwiched. (c) In the first step, the cavity surface temperature of the first injection mold is adjusted to the temperature of the plastic injected into the first injection mold. After injecting the molten plastic, the cavity temperature of the first injection mold is cooled to below 100°C, and the convex lens-shaped core is taken out and transferred to the second injection mold. ) In the second step, the cavity surface temperature of the second injection mold is maintained at a temperature higher than the flow temperature of the plastic injected into the remaining parts of the two cavities, and after the molten plastic is injected, the second injection mold A method for manufacturing a plastic convex lens characterized by cooling the cavity temperature of the mold to about 100°C or less. 2. The method of manufacturing a convex plastic lens according to claim 1, wherein in the first step, after injecting molten plastic into the cavity of the first injection mold, the cavity volume is compressed. 3. The plastic convex lens according to claim 1, wherein in the second step, after injecting molten plastic into the two cavity remaining parts of the second injection mold, the cavity volume is compressed. manufacturing method.