JPS58224724A - Force for plastic lens molding - Google Patents

Abstract

PURPOSE:To obtain the plastic lens of a high precision, by making the ring gasket provided between a top force and a bottom force thick taper like (dovetail like) at its inside, also providing a stiff outer frame at the outer periphery of the gasket. CONSTITUTION:The ring gasket 6 which is attached between a top force 3 and a bottom force 4 shaping the optical finish faces 1 and 2 respectively and shapes a cavity 5 is formed by a top force supporting face 8, a bottom force supporting face 9 and a taper angle alpha which makes the inside thicker in a radial direction. Also, a stiff outer frame is attached to the outside of the ring gasket 6.

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, optical equipment lenses or eyeglass lenses made of plastic have attracted attention. The reason for this is that plastic lenses have extremely excellent impact resistance and transparency, are lightweight, and have other good optical properties. In recent years, plastic eyeglass lenses have become popular as fashion eyeglasses, and this is also spurring an increase in the use of plastic lenses. This can be said to be because if a glass lens were to be manufactured with a large diameter while having sufficient breaking strength, the resulting lens would be very expensive and would also increase in weight, making it unsuitable. In addition, there is an increasing demand for colored lenses, such as sunglasses, that can be fashionable, but it is not easy to color glass lenses, whereas plastic lenses can be colored relatively easily. Such glass lenses are manufactured by injection molding of a thermoplastic resin suitable for optical use such as polycarbonate or polymethacrylate, or by compression molding, or cast molding, as in the case of eyeglass lenses. ing.

To introduce the commonly used cast molding of glass lenses, for example, JP-A-56. Although it is also described in No. 27327, as shown in Figure 1, a pair of upper mold A and lower mold B usually made of glass are placed between the optically finished surfaces C and 0 provided on each mold. To form a cavity E,
Fill cavity E with plastic raw materials such as monomers and other polymerization catalysts, hold upper mold A and lower mold B with spring clamps F, etc., and polymerize and harden the plastic raw materials by heating etc. mold a plastic lens. Gasket G used for this cast molding
are made of a flexible material such as rubber, elastomer, or relatively soft synthetic resin, and are used in conjunction with upper and lower molds A and B, which are usually glass, and are made of two glass molds facing each other. The optically finished surfaces C and D have the necessary curves for the lens,
Plastic raw materials such as monomers are filled into a cavity E formed between two glass molds, and the cavity is sealed to prevent air from entering. Then, the mold filled with the raw material is directly placed in a heating furnace or the like to polymerize and harden the plastic raw material. At this time, in order to reduce distortion of the lens and ensure uniform polymerization,
Curing takes at least several hours, usually over a day or night. Finally, the assembled mold is disassembled and the lens inside is taken out, but at this time the gasket is often cut to facilitate disassembly, and the gasket is not reused. Glass molds are often reused for the next casting process. The molded plastic lens is released from the glass mold by rapid cooling or impact, and its periphery is deformed as shown in Figure 4, but the center part is trimmed as shown by the dotted line before use. Ru.

The biggest problem with cast molding of such plastic lenses is the gasket. The gasket must be such that the upper and lower molds can approach the lens in the thickness direction when the volume of the plastic raw material shrinks during the polymerization reaction, and the plastic raw material must still be able to reach the gasket wall W (
Premature separation from the gasket (Figure 1) may cause distortion, cranking, or other damage to the lens, so the plastic material must adhere to the gasket wall properly during molding. Conventionally, the gasket G used for cast molding of plastic lenses has an annular shape with a roughly T-shaped cross section, with the legs facing inward in the radial direction and sandwiched between upper and lower glass molds, as shown in Fig. 1. This gasket has a slot S oriented radially inward from the outer periphery to the legs in the center so as to accommodate volume contraction. When the gasket G is softened by the heat during the polymerization and hardening cycle of the plastic raw material, the upper and lower glass molds A,
B moves closer in accordance with the shrinkage of the plastic raw material (CR-39 (trade name) has a shrinkage rate of about 13%). Therefore,
The gasket G follows the contraction of the plastic raw material under the pressure applied by the clamp F and falls inward under the interposition of the slot S, but usually the yield Fi is uneven and does not occur uniformly inside the mold. Since the shrinkage is uniform, the upper mold A and the lower mold B are deformed in a misaligned manner by the time the polymerization and curing is completed, as shown in FIG. If the gasket G is deformed in this way, the plastic lens L completed by molding will no longer match the upper and lower optically finished surfaces and the optical axes o1 and 02 of L2, as shown in Figure 3. At the same time, the lens thickness is also 1. ) 12 and is not symmetrically uniform.

Therefore, with conventional cast molding using gaskets, 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 still practical within the range that can be easily adjusted by the eye. Although it is possible to mold plastic lenses without any problems, it has the disadvantage that it is impossible to obtain high-precision plastic lenses used in optical equipment such as cameras and groziers.

Therefore, an object of the present invention is to improve the annular gasket used in a plastinoclens mold, and to make it possible to obtain a high-precision plastic lens that can be used in many optical devices. The goal is to provide the following.

In this invention, the surface of the annular gasket on which the glass mold is seated is tapered so that the wall thickness becomes thicker inward in the radial direction, and a rigid outer frame that fits with the outer circumference of the gasket is provided. The high responsiveness of the peripheral wall reduces internal stress and prevents deformation of the lens upon completion of polymerization and curing, resulting in a plastic lens with high blueness.

Hereinafter, the details of this invention will be explained with reference to examples. In FIG. 5, which shows a mold for casting a plastic lens according to the first embodiment of the present invention, the mold is usually made of glass, and when the lens is stretched, the optically finished surfaces 1 and 2 of the scathe-type concave lens are formed. formed 1
Equipped with a pair of upper and lower molds 3 and 4, upper and lower glass molds 3 and 4
are supported at a fixed distance apart by an annular gasket 6, as shown in FIG. 6, to form a cavity 5 between the molds.

The annular gasket 6 includes an outer peripheral part 6a that fits with the upper and lower crow molds 3.4 at the inner diameter and surrounds them in an annular manner, and a gasket inner peripheral wall 7 that contacts the casting material and defines the outer periphery of the lens immediately after molding. It consists of an upper die support surface 8 and a lower die support surface 9 that extend inward in the radial direction from the outer circumferential portion 6a and on which the upper die 3 and the lower die 4 are seated. The upper mold support surface 8 and the lower mold support surface 9 are tapered to form an angle α so that the wall thickness becomes thicker inward in the radial direction. This angle α is determined by the properties of the casting material, the lens surface shape, the lens wall thickness, and the like.

Therefore, the upper mold seating surface 10 and the lower mold seating surface 11 that sit on the gaskets 6 of the upper molds 3 and 4 are supported by the entire surfaces of the upper mold supporting surface 8 and the lower mold supporting surface 9, as shown in FIG. Each has a corresponding taper. The annular gasket \6 is still elastically deformable in the radial direction. The outermost circumference of the annular gasket 6 fits into the inner diameter of the cylindrical ring-shaped outer frame 12. The outer frame 12 and the gasket 6 are fitted together by simple fitting without using any bonding means such as adhesive. Type seating surface 10
By seating the lower mold seating surface 11 on the upper mold support surface 8 and the lower mold support surface 9, a cast molding mold is assembled as shown in FIG. The outer periphery of the tab and cavity 5 is formed by the inner peripheral wall 7 of the gasket 6 fitted with the outer frame 12, and the lens surface is formed by the upper mold 3 and the lower mold 4. The casting mold configured as described above is held in place by a nokuneta lamp 13 or the like.

The annular gasket 6 is made of a suitable elastic material, such as soft polyvinyl chloride, polyolefin, or ethylene L! I is made from a composition of vinyl acetate copolymer. The outer frame 12 is made of a suitable rigid material, such as steel, stainless steel, aluminum, etc.

In the assembled casting mold, a plastic raw material such as a polymer (e.g. diethylene glycol his acrylic carbonate trade name cR-39) is placed in the cavity 5 which is configured and sealed as described above and polymerization starts. A plastic lens is formed by injecting a mixed liquid of the agent with a syringe or the like and hardening the plastic raw material during the polymerization process.

To explain the operation of the plastic lens casting mold of the first embodiment shown in FIG. In addition, the upper mold support surface 8 and the lower mold support surface 9 on which the upper and lower glass molds 3.4 are seated are radially inward in comparison with the conventional gasket structure. Because the surface is tapered to increase the wall thickness, a large response is achieved inward in the radial direction against the shrinkage of the plastic raw material in the thickness direction.
The gasket has sufficient adaptability to lens curing shrinkage, in particular, as the plastic raw material shrinks when the gasket is heated, the inner circumferential walls 7 of the gasket approach each other as shown in FIG. The outer frame 12 has the function of preventing the plastic raw material from flowing out in cooperation with the annular gasket 6, and with its rigid cylindrical body, the upper mold tray and the lower mold tray are simultaneously and coaxially connected via the gasket outer peripheral portion 6a. By supporting it, it has a function of aligning the optical axes of both lens surfaces 1 and 2.

In FIG. 7, as the gasket shell softens due to the heat generated during the polymerization process of the plastic raw material, the pressure applied by the clamp 13 causes the upper mold 3 and the lower mold 4 to move in the direction of the optical axis (the direction of entry in FIGS. 8(a) and 8(b)). )) and become closer to each other. At this time, since the upper mold support surface 8 and the lower mold support surface 9 are tapered, the contractile force in the input direction is dispersed in the B direction and the C direction, as shown in FIG. 8(A). Annular gasket 6
Since it can be elastically deformed, as shown in FIG. 8(b), the response of both opposing surfaces of the gasket inner circumferential wall 7 approaching each other in the D direction and shrinking compared to the conventional gasket due to the vector in the B direction. is high. At this time, the gasket 6 is prevented from deforming outward by the rigid outer frame 12, so that a portion of the gasket outer circumferential portion 6a separates from the outer frame 12, while both opposing surfaces of the gasket inner circumferential wall 7 approach each other. Transform.

As mentioned above, the glass mold 3. matches the shrinkage of the casting material.
4, the gasket inner circumferential wall 7 has a high responsiveness in which both inner opposing surfaces approach each other in conjunction with the contraction movement in the lens thickness direction (input direction). Separation can be avoided and the internal stress of the lens after polymerization is completed is minimized. Furthermore, since the outer circumferential portion 6a of the annular gas filter is supported by the rigid outer frame 12, there is no deviation of the optical axis due to deformation, and the lens thickness remains symmetrically uniform. In particular, a high-precision plastic lens can be obtained by reducing internal stress due to the high responsiveness of the gasket inner circumferential wall 7 and by preventing deformation of the lens at the time of completion of polymerization and curing.

9 and 10 show a second embodiment of the invention. The second embodiment has an upper die support surface 8 and a lower die support surface 9.
The inner peripheral part 6b of the gasket can support the upper and lower glass molds 3.4 at room temperature when the upper mold 3 and lower mold 4 are seated, and can be deformed in a high melting state when the casting material hardens. This embodiment is similar to the first embodiment except that it has a wall thickness width d, and the same members are given the same reference numerals. In the case of the second embodiment, the outer peripheral part 6a and the inner peripheral part 6b of the gasket
is a thin-walled part 6C that is thinner than the seating distance between the upper mold 3 and the lower mold 4.
The thin portion 6C and the upper mold 3 and lower mold 4 form an annular hollow groove 6d surrounding the lens optical axis 0. As in the first embodiment, the upper die support surface 8 and the lower die support surface 9 are tapered to form an angle α such that the wall thickness becomes thicker on the inner side in the radial direction. This angle α is determined by the properties of the casting material and the shape of the lens.

The structure, materials and operation of the second embodiment are completely the same as those of the first embodiment. In this embodiment, since the supporting surfaces 8 and 9 on which the clay mold 3.4 is seated have only a wall thickness d that can be deformed in a high temperature state, the inner circumferential wall 7 of the gasket approaches each other and contracts in a similar manner. .

FIG. 11 shows a third embodiment of the invention.

The third embodiment is similar to the second embodiment and includes the same members, except that a ring 14 is inserted into the hollow groove 6d to support the upper mold 3 and the lower mold 4 at a certain distance apart at room temperature. are given the same reference numerals.

In the case of the third embodiment, the wall thickness d of the inner circumferential portion 6b is set so that the upper mold 3 and the lower mold The glass mold 3.4 may be deformed inward in the radial direction without being able to support the glass mold 3.4 when the glass mold 3.4 is seated. The retaining ring 14 is inserted, and the ring 14 is made of a material that is rigid enough to support the upper mold 3 and lower mold 4 at room temperature and that can be deformed at the high temperature when the casting material hardens, such as polyester. It is made from vinyl chloride, polyolefin, synthetic rubber, etc.

The structure, materials, and operation of the third embodiment are completely the same as those of the second embodiment. In particular, in the third embodiment, the ring 14 defines the lens thickness of the plastic lens.

As explained above, the present invention includes a gasket that seats and supports a glass mold with a tapered surface that becomes thicker on the inside in the radial direction, and a rigid outer frame that fits with the outer periphery of the gasket. With this arrangement, it is possible to obtain a high-precision plastic lens that can be sufficiently used as a lens for optical equipment. Due to its special structure, it is able to fully accommodate the inherent shrinkage that occurs during the curing process of the lens, thus minimizing internal stresses in the lens and avoiding premature separation of the gasket. Still, compared to conventional cast molding molds using gaskets, it can clearly contribute to improved yield and quality.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing a conventional plastic lens mold, Fig. 2 is a cross-sectional view showing gasket deformation of the mold shown in Fig. 1, and Fig. 3 is a cross-sectional view showing the gasket deformation of the mold shown in Fig. 1. FIG. 4 is a partial plan view showing the trimming portion of the lens used after molding; FIG. 5 is an exploded view of the mold for molding a plastic lens according to the first embodiment of the present invention; Figure 6 is No. 5. , Figure 7 is a cross-sectional view showing the operation of the mold shown in Figure 6, and Figures 8 (a) and (b) are cross-sectional views showing the assembled state of the mold shown in Figure 6. 9 is a sectional view showing the plastic lens molding mold of the second embodiment of the present invention; FIG. 10 is a sectional view showing the action of the molding mold shown in FIG. 9; FIG. 2 is a sectional view showing a plastic lens molding mold according to a third embodiment of the present invention. 1 and 2...lens surface, 3...upper mold, 4...
・Lower mold, 5...cavity, 6...
Annular gasket, 6a... gasket outer periphery, 6b...
...Gasket inner peripheral part, 6d...Hollow groove, 7...Inner peripheral wall, 8.
... Upper die support surface, 9... Lower die support surface, 10.
... Upper mold seating surface, 11 ... Lower mold seating surface, 12
Outer frame, 14...Ring, α...Angle. Agent Patent Attorney Akira Watanabe Niji 1 Drawing Exhibition 5 - Steaming 7 Drawings (In Kou-1 8 Kuniri,... Tail 9 Drawings Steaming 1O (21 Drawings// Drawings)

Claims (1)

[Claims] ■. An upper mold for forming a lens surface for molding one lens surface of a plastic lens, a lower mold for forming a lens surface for molding the other lens surface of a plastic lens, and an upper mold. and an annular gasket forming a cavity between the lower molds.
The surface of the annular gasket on which the upper and lower molds are seated is tapered so that the wall thickness increases inward in the radial direction, and a rigid outer frame is provided that fits with the outer periphery of the gasket. A mold for molding plastic lenses. 2. A patent in which the inner periphery of a gasket, which has an upper mold support surface on which the upper mold is seated and a lower mold support surface on which the lower mold is seated, has a wall thickness that can be deformed by heat during curing of the casting material. A mold for molding a plastic lens according to claim 1. 3. The mold for molding a plastic lens according to claim 1, wherein a ring is inserted into a hollow groove formed between the outer circumference and the inner circumference of the gasket.