JPS59109325A - Mold for plastic lens - Google Patents

Abstract

PURPOSE:To obtain the titled mold that can provide a plastic lens having highly accurate optical surfaces, by pressing a cavity resiliently wherein a plastic raw material is sealed. CONSTITUTION:A top force 2 having a highly accurate optical finishing surface 1 and a resilient container 4 part of which is mated with the top force 2 and cooperate with the optical finishing surface 1 to form a cavity 3 are clamped by a holding frame 5 to seal the cavity 3. The container 4 can be deformed in conformity with the contraction of the plastic raw material so that the optical finishing surface 1 can be reflected accurately to make the optical surface of the intended lens highly accurate and the internal strain of the lens can be decreased. The surface opposite to the inner wall 7 of the container is finished by grinding, polishing or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a mold for molding a plastic lens, such as a plastic eyeglass lens or an optical lens.

In recent years, lenses for optical instruments and eyeglass lenses made of plastic have attracted attention. The reason for this is that plastic lenses have excellent impact resistance and transparency when loosened, are lightweight, and have other good optical properties. In addition, in recent years, plastic eyeglass lenses have become popular, and this has also spurred an increase in the use of plastic lenses.

This can be said to be because a crow lens does not have sufficient breaking strength, so if you try to manufacture something like Rei's dog, the resulting lens will be very expensive and heavy, making it unsuitable. Still, the cost of purchasing colored lenses such as Sunclas to make them fashionable is increasing, but it is not easy to tint crow lenses, whereas plastic lenses can be tinted relatively easily. Such plastic lenses are manufactured by injection molding of optically suitable thermoplastic resins such as polycarbonate I and volimegu acrylates, by compression molding, or by cast molding as in eyeglass lenses. has been done.

To introduce the commonly used cast molding of plastic lenses, for example, it is described in JP-A-56-2.7327, but as shown in Figure 1, a pair of plastic lenses made of glass are usually used. The upper mold A and the lower mold B are arranged so that a cavity E is formed between the optically finished surfaces C and 9 provided on each mold.
Fill the cavity L with plastic raw materials such as monomers and other polymerization initiators, hold the upper mold A and the lower mold B with a clamp F, and heat, etc. The raw materials are polymerized and hardened to form a plastic lens.Caskerat G used for this cast molding is made of a flexible material such as rubber, leek stone, or a relatively soft synthetic resin. , the upper and lower molds AX113.l!: a, which are usually glass molds, are used together, and the opposing optically finished surfaces C4 and D of the two glass molds have the necessary curve for the lens, forming a monomer. The plastic material is then filled into Chiyabitei E and sealed to prevent air from entering.Then, the casting mold filled with the raw material is placed in a heating furnace or the like to polymerize and harden the plastic raw material.At this time,
In order to minimize distortion of the lens and ensure uniform polymerization, it takes at least several hours for curing, and it often takes about an hour or more for hunting. Finally, the assembled casting mold is disassembled to remove the lens inside, or the gasket is often cut to facilitate disassembly, and the gasket is not reused. Glass molds are often reused for the next cast molding. The molded plastic lens is released from the crow mold by rapid cooling or impact, and the peripheral edge is completely deformed as shown in Figure 4, but the center part is trimmed as shown by the dotted line before use. Ru.

Cast molding of such plastic lenses has a problem in reversibility with respect to optically finished surfaces. Conventionally, the gasket (G) used for cast molding of plastic lenses has an approximately T-shaped cross-section with the legs facing inward in the radial direction and sandwiched between the upper and lower glass molds, as shown in Figure 1. It is an annular gasket, and a nullot S is carved in the center of the gasket, extending from the outer periphery toward the legs and facing inward in the radial direction so as to accommodate volume contraction. When the gasket G softens due to the heat between the polymerized and hardened particles of the plastic raw material, the upper and lower glass molds A
, IB move toward each other in response to the shrinkage of plastic and raw materials (CR-39 (trade name) has a yield rate of approximately 13%).

There, the gasket G conforms to the contracted shape of the plastic raw material under the pressure applied by the clamp F and falls inward under the intervention of the thrower S, but usually □
Shrinkage does not occur uniformly inside the mold; it shrinks unevenly.
When the polymerization and curing are completed, the upper mold A and the lower mold B are deformed as shown in FIG. If the gasket/cod is deformed in this way, the plastic lens L completed by molding will have optical axes 01 and 02 of the upper and lower optically finished surfaces I L and L2, as shown in Figure 3. As they match and disappear, the thickness of the lens also becomes 1,) 12
As a result, the reversibility with respect to the optically finished surface cannot also be uniform because it is not symmetrically uniform.

Therefore, in conventional cast molding, even if there is some variation in thickness or slight deviation in the optical axis of the vertically curved surface, as with eyeglass lenses, it is possible to easily adjust the optical axis of the plastic and there is no problem in practical use. The drawback is that it is not possible to mold lenses, but it is impossible to obtain high-precision plastic lenses such as those used in the optical systems of optical devices such as cameras and projectors.

Therefore, an object of the present invention is to provide a plastic lens casting mold that can obtain a plastic lens having a highly accurate optical surface by pressurizing a cavity that encloses a plastic raw material using comb elasticity. It is said that

Hereinafter, the details of this invention will be explained based on examples. In FIG. 5 showing the plastic lens casting mold according to the first embodiment of the present invention, the casting mold includes an upper mold 2 on which a highly accurate optically finished surface 1 is formed, and a part of the mold 2 that is fitted into the upper mold 2. and a container 4 made of a comb elastic body that cooperates with the optically finished surface 1 to form a cavity 3, and a presser frame 5 that tightens the container 4 to the upper die 2 from the outer periphery to seal the cavity 3. 4
ing.

The upper mold 2 is made of glass, metal, or other material,
It has a high A'ff Jx optical finish. The container 4 is made of a resilient material, such as polyvinyl chloride resin. The presser frame 5 is made of a rigid material such as steel.

In the first embodiment, the bottom surface of the inner wall 7 of the container is horizontal before polymerization.

To explain the operation of the plastic lens casting bottle of the first embodiment shown in FIG. , or a mixture (polymerization catalyst and other additives may be added as necessary) are pressurized and injected. This injection operation is performed with the upper mold 2 fitted into the container 4.

Thereafter, the cavity 3 is sealed with the presser frame 5.

Pressure may be applied from the outside by means such as the spring clamp 6 as necessary, such as when the internal pressure of the cavity is low or when there is concern about the ability to follow the shrinkage of the plastic raw material of the container 4.

After this, a polymerization operation is performed. Generally, the plastic raw material 1 shrinks during the polymerization operation. In the case of /ethylene glycol hisallyl carbonate-1, the volumetric shrinkage rate is about 13%. Therefore, the container/I deforms in sync with the contraction of the plastic raw material. As shown in FIG. 6, the container 4 has an inner wall 7
The plastic lens L is formed as a whole by following the deformation due to shrinkage of the plastic raw material. In this way, the shrinkage of the plastic raw material is followed by the entire inner wall 7 of the container 4, thereby improving the reversibility of the optical finishing surface 1, thereby eliminating the effects of increasing the precision of the optical surface and reducing internal distortion of the lens.

The plastic lens obtained by this plastic lens casting mold has only one highly accurate optical surface, and the surface of the inner wall 7 on the container side is finished by post-processing such as cutting and polishing to become a product.

FIG. 7 shows a second embodiment of the invention. Second
The embodiment is the same in construction as the first embodiment, or the container 4
have different shapes. The inner wall surface 7 of the container 4 facing the optically finished surface 1 of the upper mold 2 has the same shape as the plastic lens surface molded by the optically finished surface 1; By having a structure that keeps the wall surface 7 parallel, that is, by having the surface 7 of the container 4 facing the optically finished surface 1 having the same inverted shape as the optically finished surface 1, the cavity 3 is uniform. The thickness of the plastic lens is increased, and the internal distortion generated in the produced plastic lens is reduced due to the ability to follow the shrinkage of the plastic raw material due to the deformation of the container 4.

FIG. 8 shows a third embodiment of the invention. Third
The structure of this embodiment is similar to that of the first embodiment, but the container 4
The shapes of the shapes are different. Since the inner wall 7 of the container 4 is a smooth curve with no corners, the container 4 follows the shrinkage of the plastic raw material and is averaged, so that the distance between the plastic raw material and the container inner wall 7 during polymerization shrinkage is This reduces the occurrence of defects such as peeling.

FIG. 9 shows a fourth embodiment of the invention. Fourth
The structure of this embodiment is similar to that of the first embodiment, but the container 4
have different structures. Since the container 4 has a hollow structure 8, even if the volume change due to the shrinkage of the plastic raw material during polymerization shrinkage is large, the inner wall 7 on the container side can sufficiently follow the structure, making it possible to obtain a plastic lens of stable quality.

Furthermore, by combining the characteristic structures of each container 4 from the first embodiment to the fourth embodiment, the performance as a plastic lens casting mold can be improved.

Note that the optically finished surface 1 of the upper die 2 may be a flat surface, a convex surface, a concave surface, a spherical surface, an aspherical surface, a rotationally symmetric surface, a rotationally asymmetric surface, or the like.

As explained above, the present invention includes an upper mold for forming a lens surface, a container made of a rubber elastic body that partially fits into the upper mold to form a cavity, and a container that is tightened from the outer periphery to the upper mold. By pressurizing the cavity in which the plastic raw material is enclosed using comb elasticity, a plastic lens having an extremely precise optical surface can be obtained.

In particular, by making the entire inner wall of the container follow the shrinkage of the plastic raw material during polymerization, it is possible to improve the precision of the optical surface of the plastic lens by improving the reflectivity of the optical surface.
The effect of reducing internal distortion of the plastic lens can be obtained.

In addition, the inner wall surface of the container facing the optically finished surface of the upper mold or the optically finished surface (the same shape as the plastic lens surface to be molded by the child), and the container keeps the optically finished surface and the opposite inner wall surface parallel to each other. By having a more uniform structure, the cavity has a uniform wall thickness, the ability of the container to follow the shrinkage of the plastic raw material is improved, and the internal distortion that occurs in the produced plastic lens is reduced. It will be done.

Since the inner wall of the container still has a smooth curved structure, the shrinkage of the plasticine raw material is more averaged and multiplied by the container, and peeling between the plastic raw material and the inner wall of the container during polymerization shrinkage. This has the effect of reducing the occurrence of defects.

In addition, since the container has a hollow structure, even if the plastic raw material shrinks significantly, the inner wall of the container can sufficiently follow the shape of the container, resulting in the effect that a plastic lens of stable quality can be obtained.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing a conventional plastic lens casting mold, Fig. 2 is a sectional view showing gasket deformation of the casting mold shown in Fig. 1, and Fig. 3 is a sectional view showing the gasket deformation of the casting mold shown in Fig. 1. FIG. 4 is a partial sectional view illustrating a plastic lens to be used; FIG. 4 is a partial plan view showing a trimmed portion of the lens to be used after molding;
FIG. 5 is a sectional view showing a plastic lens pressing mold according to the first embodiment of this invention, FIG. 6 is a sectional view showing the action of the casting mold shown in FIG. 5, and FIG. A sectional view showing a plastic lens casting mold according to an embodiment, FIG. 8 is a sectional view showing a plastic lens casting mold according to a third embodiment of the present invention,
FIG. 9 is a sectional view showing a pre-stick lens casting mold according to a fourth embodiment of the present invention. ■...Pressing surface, 2...Upper mold, 3...Cavity, 4. Container, 5. Presser foot. Agent Patent Attorney Shoji Watanabe #5 Figure 2 Performance 7 Illustration Procedure Amendment June 13, 1980 Commissioner of the Japan Patent Office Kazuo Wakasugi 1, Indication of the Case 1989 Patent Application No. 218463 3 Person making the amendment Relationship of patent applicant Address: 2-43-2 Hatagaya, Shibuya-ku, Tokyo Name (
) (o37) Olympus Optical Industry Co., Ltd. Representative Shigeru Kitamura Male 4, Agent 227 Telephone 045-971-1
370 Address 20, 1165 Ichigao-cho, Midori-ku, Yokohama, Kanagawa Name (6708) Patent attorney Shoji Watanabe 5 Date of amendment order Voluntary order 6 Number of inventions increased by amendment □ 7. Subject of amendment (1) In the title of the invention in the application, the furigana for "casting mold" was corrected from "chuugatakata" to "chuukeigata." (2) Page 5, lines 7 to 8 of the specification “(CR-39
(product name) has a shrinkage rate of approximately 13%)" has been deleted. (3) On page 11, line 4 of the specification, the phrase "improvement of surface reflectivity" was corrected to "improvement of surface reversibility." List of attached documents (1) 1 application for correction

Claims (1)

[Scope of Claims] 1. A lens surface forming upper mold for molding one lens surface of a plastic lens, a container made of a comb elastic body that partially fits into the upper mold and forms a cavity, and A plastic lens casting mold characterized in that the container is formed from an upper mold for forming a lens surface and a presser frame that tightens the container from the outer periphery. 2. The plastic lens casting mold according to claim 1, wherein the surface of the container facing the upper lens forming surface is formed in the same inverted shape as the upper lens forming surface. 3. The plastic lens mold according to claim 1, wherein the entire inner wall constituting the cavity of the container is formed into a smooth curved shape. 4. The plastic lens mold according to claim 1, wherein the container has a hollow structure.