JPH07309B2 - Plastic lens and manufacturing method thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a plastic lens suitable for plasticizing a relatively large lens such as a video camera lens, and a manufacturing method thereof. 2. Description of the Related Art In recent years, along with the widespread use of video cameras, there has been a great demand for weight reduction and cost reduction of optical devices such as zoom lenses, and as one solution therefor, plastic lenses have come to be used. Came. Conventionally, a plastic lens is a so-called cast molding method in which a fluid plastic material such as a monomer or an oligomer is injected into a mold and polymerized by heat, radiation, or a thermoplastic polymer is melt-melted and shaped. It was molded by the injection molding method, compression molding method, or the like. However, these molding methods have the following drawbacks, and are particularly unsuitable for molding large plastic lenses. That is, in the cast molding method, when molding a lens such as a spectacle lens having a relatively small change in thickness,
Although a lens with few optical defects such as internal distortion can be obtained,
On the other hand, polymerization takes time, resulting in poor productivity. Also, when molding a lens with a large power that has an extreme difference in wall thickness, it is not possible to compensate for shrinkage due to polymerization, and it is possible to obtain a highly accurate lens. could not. Although the injection molding method has high productivity, a high-quality and high-precision lens cannot be obtained because of material flow, optical distortion due to cooling and solidification, and shrinkage due to molding shrinkage. Even in compression molding, which is said to be able to mold relatively high-precision lenses, when shaping
Since the material is heated to the melting or flowing temperature and then cooled and solidified, temperature non-uniformity occurs during cooling, warping occurs on the lens itself and heat shrinkage non-uniformity. The precision lens could not be formed. In order to eliminate these drawbacks, for example, in a casting method, a method of incorporating polymerization by radiation in order to increase the polymerization reaction rate has been proposed. There is a problem with the safety of. An object of the present invention is to provide a plastic lens which can improve the lens accuracy and prevent the occurrence of optical distortion and which is excellent in productivity, and a method for manufacturing the same, excluding the above-mentioned drawbacks of the prior art. In order to achieve the above object, the plastic lens according to the present invention comprises a plastic blank formed from a plastic material and free of optical distortion. A layer formed of a plastic material having a refractive index substantially the same as that of the material is polymerized by irradiation of ultraviolet rays. Further, in the method of manufacturing a plastic lens according to the present invention, the airtightness can be maintained at the time of assembly, the lens can be divided into at least two parts, and at least one of the portions forming the lens shaping surface is made of an ultraviolet-transparent material. Using
A lens blank having a substantially desired shape from which optical distortion has been removed is inserted into the cavity having the desired shape, and in the space between the lens blank and the mold surface of the cavity formed by the mold,
After filling with a fluid material that is polymerized by ultraviolet rays of a polymethylmethacrylate (including a copolymer) or polystyrene plastic material having a refractive index substantially the same as that of the lens blank after polymerization, ultraviolet rays are irradiated from the outside of the mold, The fluid layer is polymerized. In the plastic lens according to the present invention, the lens blank has a roughly desired shape because the optical distortion is removed. In some cases, the surface shape is deformed by removing the optical distortion. You may have something. Since the surface of this lens blank is provided with a layer polymerized by irradiation with ultraviolet rays, the surface shape of the entire lens becomes a predetermined shape. In this case, since the layer on the lens blank is formed by polymerization by ultraviolet irradiation, no optical distortion occurs in this layer, and this layer and the lens blank have approximately the same refractive index. Therefore, the deterioration of the optical characteristics due to the provision of this layer does not occur. Further, in the method of manufacturing a plastic lens according to the present invention, the cavity formed by the mold for inserting the lens blank is kept airtight, and the cavity is filled with a fluid plastic material of polymethylmethacrylate or polystyrene. The flowable plastic material then makes good contact over the entire mold surface. In this state, when the inside of the cavity is irradiated with ultraviolet rays through a mold made of an ultraviolet-transparent material, the fluid plastic material is polymerized and becomes integral with the lens blank. In this case, since the amount of polymerization shrinkage of the plastic material is small, a plastic lens whose surface shape accurately matches the mold surface of the mold can be obtained. Therefore, by setting the mold surface to a predetermined shape, A plastic lens with high shape precision can be obtained. Further, no optical strain is generated in the polymerized layer of the fluid plastic material, and since the polymerized layer and the lens blank have approximately the same refractive index, this polymerized layer is provided. There is no deterioration of optical characteristics. Embodiments of the present invention will be described below with reference to the drawings. First, a roughly shaped article is injection-molded with a lens material such as polymethylmethacrylate. As described above, while injection-molded plastic lenses can be manufactured with high efficiency, optical strain (birefringence,
Striae) is likely to occur. These defects are removed by so-called annealing. In the case of polymethylmethacrylate, annealing is performed at 80 ° C. for 4 hours. However, the shape imposed by injection molding is deformed by annealing. FIG. 2A shows the lens after injection molding,
Optical distortion 2 due to internal distortion is present near the gate 1. Figure 2
(B) shows the case where such a lens is annealed, and optical distortion is removed, but it is deformed. Deformation amount A, B, C
Varies depending on the shape of the lens, molding conditions, etc.
Each is about several tens of μm. 3 (a), 3 (b) and 3 (c) are schematic process diagrams for explaining the outline of each step of the method for producing a plastic lens according to the present invention, in which 3 is a lens blank,
4 is syrup, 5 and 5'is mold surface, 6 and 6'is mold, 7
Is a plastic lens and 8 is a cavity. As described above, the lens blank 3 is made of polymethylmethacrylate as a material and is obtained through the steps of injection molding and annealing. The imposed shape is deformed, but the optical distortion is removed. . Such lens blank 3
The methyl methacrylate syrup 4 containing a polymerization initiator is applied to the outer surface of the mold and placed in molds 6 and 6'having mold surfaces 5 and 5'having the finished curvature of the lens (Fig. 3).
(A)). Next, the two divided molds 6 and 6'are closed to form a lens-shaped cavity 8, and the temperature is 60 ° C to 80 ° C.
By heating the molds 6 and 6'with, the syrup 4 is polymerized and integrated with the lens blank 3 (Fig. 3).
(B)). The polymerization is kept warm for 4 to 10 hours. When the polymerization is completed, the molds 6 and 6'are cooled to room temperature and separated to obtain plastic lenses 7 (FIG. 3 (c)). As the syrup 4, a methyl methacrylate monomer added with a polymerization initiator such as benzoyl peroxide, an oligomer of methyl methacrylate, or a solution of polymethyl methacrylate (polymer) dissolved in methyl methacrylate monomer is used. The polymerization shrinkage ratio of these syrups is 5 to 10% by volume, but if the thickness of the syrup 4 is about 10 to 100 μm, the shrinkage amount (thickness) is about 0.2 to 3 μm, which is neglected in terms of optical characteristics. You will get the amount. By the way, when the polymerization is carried out by heating, not only a long time is required for the polymerization, but also bubbles may be introduced into the lens surface. Particularly, as the polymerization progresses, the syrup is insufficient near the outer peripheral portion of the lens (because of polymerization shrinkage). It is thought that) is likely to occur. Further, in the case of the thermal polymerization method, the lens blank itself is heated to the polymerization temperature,
After the polymerization of the syrup is completed, when the temperature is lowered to room temperature, the amount of heat shrinkage is not small, and the curvatures of the mold surfaces 5, 5'may not be transferred. Most of these trends are resolved by UV polymerization of the syrup rather than thermal polymerization. That is, in FIGS. 3A, 3B, and 3C, the mold 6,
6'with a silicate glass or Fe ₂ O ₃ content of 0.
It is made of UV-transparent glass such as soda lime glass of not more than 01% by weight, and as syrup 4, benzophenone,
The polymerization time is several tens of seconds by irradiating ultraviolet rays from the outside of the molds 6 and 6'at the time of polymerization by using a material whose ultraviolet polymerization property is improved by adding a sensitizer such as benzaldehyde.
In a few minutes, the temperature rise can be suppressed slightly. However, even if the UV polymerization method is used, it is not possible to completely suppress the generation of bubbles on the lens surface, especially on the outer peripheral portion. FIG. 1 is a cross-sectional view of a polymerization mold showing an embodiment of a method for producing a plastic lens according to the present invention, in which 6a and 6a 'are outer surfaces, 9 and 9'are frames 10 and 11'.
Is a communication pipe, 10 'and 11' are flow paths, 12 and 13 are valves, 14 is a parting surface, and 15 is an O-ring. The lens blank 3 produced by the above-mentioned method is held by the frames 9 and 9 ', and the final lens-shaped cavity 8 is formed by the molds 6 and 6'having a lens surface shape made of ultraviolet-transparent glass. Valve 12 provided in the middle of a flow path 10 ′ connected to a tank (not shown) containing the defoamed syrup through the communication pipe 10.
Is closed, and a valve 13 provided in the middle of a flow path 11 'for exhausting air in the cavity 8 through a communication pipe 11 to a vacuum pump (not shown) is opened to depressurize the inside of the cavity 8. Then, the valve 13 is closed and the valve 12 is opened, so that the syrup 4 is sucked into the cavity 8. At this time, if necessary, the tank containing the syrup may be pressurized and injected under pressure. When the syrup 4 is completely filled in the gap between the lens blank 3 formed in the cavity 8 and the mold surface, the bulb 12 is closed, and the mercury lamp is opened from the outer surface 6a, 6a 'side of the UV transparent mold 6, 6'. Ultraviolet rays are irradiated by (not shown) or the like. After the polymerization of the syrup 4 filled between the lens blank 3 and the mold surface is completed, the molds 6 and 6'and the frames 9 and 9'are divided from the parting surface 14 to obtain the final lens. In this embodiment, it is necessary to make an airtight fit between the molds 6 and 6'and the frames 9 and 9 ', and for that purpose, the O-ring 15 is put in a key position. In addition, the mercury lamp used for UV polymerization generates heat as well as UV light, and the mold 6,
6 ′ tends to heat up, so the frame 9,
A cooling water flow path is provided at 9 '. Next, materials will be described. The focus will be on polymethylmethacrylate (including copolymers), which is the most widely used plastic lens. Polymethylmethacrylate for injection molding usually has an average molecular weight of 10 to 10.
It is 150,000, and its refractive index is 1.4913 as measured by the D line at 20 ° C. On the other hand, a medium high pressure mercury lamp (3 kW) was added to methyl methacrylate containing 0.1, 0.2 and 0.3% by weight of benzoin as a sensitizer.
The polymer obtained by polymerizing by irradiation from a distance of cm has a molecular weight of 700 to 1,000,000, but the difference in refractive index from that for injection molding is 0.0004 or less. No defects will occur. The syrup may be a monomer alone, an oligomer, or a polymer in which a polymer is dissolved, and the point is that there is no particular limitation as long as it maintains fluidity and becomes the same as the refractive index of the lens blank at the end of polymerization. Benzophenone, benzanthrone, benzaldehyde, phenathraquinone and the like can be used as the sensitizer. The same applies to polystyrene used as a flint glass as a plastic lens. However, with the commercially available reagent styrene, the polymerization time is long. It is considered that this is because the polymerization inhibitor was added. This is not the case if styrene distilled under reduced pressure is used. Further, since the polymerization is carried out by ultraviolet rays, the polymerization reaction rate is higher than that of thermal polymerization. The plastic lens obtained as described above is formed by forming a polymerized plastic material layer on a lens blank from which optical distortion has been removed. This plastic material layer is completely filled in the cavity. The syrup that was in good contact with the entire mold surface was polymerized, and since the shrinkage amount of this syrup due to polymerization was minute, the surface shape of this plastic material layer was a highly accurate copy of the mold surface. Becomes Therefore, the surface shape of the obtained plastic lens has a desired shape with high accuracy. Further, since the plastic material layer is polymerized by ultraviolet rays, it does not cause optical distortion and has a refractive index substantially the same as that of the lens blank. Providing the plastic material layer does not deteriorate the optical characteristics of the obtained plastic lens. In this embodiment, a biconvex lens is shown.
It goes without saying that the shapes such as the biconcave and the unevenness are not particularly limited. The present invention can eliminate the weld line even in a concave lens where the weld line has an extreme change in wall thickness that cannot be avoided by injection molding. As described above, according to the present invention,
It is possible to mold a plastic lens with high accuracy without optical distortion, improve productivity, and provide a plastic lens having an excellent function not found in the prior art and a method for manufacturing the same.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of a polymerization mold showing an embodiment of a method for producing a plastic lens according to the present invention. FIG. 2 is an explanatory diagram showing optical distortion of a lens by injection molding and deformation after annealing. FIG. 3 is a schematic process drawing for explaining the outline of each process of the method for manufacturing a plastic lens according to the present invention. [Explanation of symbols] 3 lens blank 4 syrup 5, 5'mold surface 6, 6'mold 8 cavity

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location B29K 105: 32 B29L 11:00 (72) Inventor Masao Takagi 292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa Hitachi, Ltd. Household Appliances Research Laboratory (72) Inventor Norio Yatsuda 292 Yoshida-cho, Totsuka-ku, Yokohama, Kanagawa Prefecture

Claims (1)

[Claims] 1. On a lens blank made of a plastic material from which optical distortion has been removed, a layer made of a plastic material of polymethyl metal acrylate (including a copolymer) or polystyrene having substantially the same refractive index as that of the lens blank and polymerized by ultraviolet irradiation. A plastic lens, characterized in that the layer has a predetermined surface shape. 2. While maintaining airtightness at the time of assembly, it can be divided into at least two parts, and at least one of the parts forming the lens shaping surface is made of an ultraviolet-transparent material. After being inserted into the cavity having the desired shape, a polymethyl metal acrylate (copolymerization) having the same refractive index as that of the lens blank after polymerization is formed in the space between the lens blank and the mold surface of the cavity formed by the mold. A method for producing a plastic lens, which comprises filling a fluid material of a plastic material such as coalesce) or polystyrene, which is polymerized by ultraviolet rays, and then irradiating the fluid layer with ultraviolet rays to polymerize the fluid layer. 3. The method of manufacturing a plastic lens according to claim 2, wherein the void is decompressed and the fluid material is filled.