JPH0544329B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a lens molding method in which a cavity formed between a pair of lens molds is filled with a thermoplastic synthetic resin in the form of particles or tablets to mold a lens. The present invention relates to a method of molding a resin lens.

[Prior Art] The method for molding synthetic resin lenses using synthetic resin as a raw material differs depending on whether the raw synthetic resin is a thermoplastic synthetic resin or a thermosetting synthetic resin. . That is, in the case of thermoplastic synthetic resin, the raw material is usually in the form of particles such as pellets, and
Using a compression molding machine or an extrusion molding machine,
This is usually carried out by a so-called injection molding method, compression molding method, or extrusion molding method, in which the synthetic resin is plasticized by heating and then molded under high pressure. On the other hand, in the case of thermosetting synthetic resins, the raw material is usually used in a liquid form with a curing catalyst added to the monomer, and is sealed in a sealed system using two molds and a sealing material wrapped around the sides. This is done by a casting method in which a liquid raw material is injected into a cavity between formed molds and heated and cured at normal pressure.

[Problems to be Solved by the Invention] In the injection molding method, compression molding method, extrusion molding method, etc. as a method of molding a synthetic resin lens using the above-mentioned granular thermoplastic synthetic resin as a raw material, the molding conditions are High temperature heating and molding pressure, for example around 1000 kg/cm ² , are required to plasticize the raw material synthetic resin, making molding machines large and expensive. Moreover, since the heating mechanism heats from outside the molding machine, the efficiency for plasticizing the raw material synthetic resin is extremely low.In addition, applying high pressure requires the mold to withstand pressure, and the metal There is a restriction that a mold must be used. In particular, it is not easy to polish the finish of a metal mold, making it difficult to obtain a highly accurate mold.

Therefore, in injection molding, compression molding, or extrusion molding methods that use granular thermoplastic resin as raw material, it is difficult to mold high-precision molded products, such as high-mix, low-volume products such as eyeglass lenses. There is a problem in that the use of a metal mold is not appropriate due to the processing technology and cost of the mold.

In view of the above-mentioned problems, the present inventor has developed a method using granular or tablet-shaped thermoplastic synthetic resin as a raw material.
In molding methods for molded products that require high precision,
We conducted various studies and research on molding methods that reduce heating temperature and pressure. As a result, they discovered that by using a specific mold, it is possible to lower the heating temperature and pressing force, and that it is suitable for molding high-precision molded products, such as synthetic resin lenses, and completed the present invention. This is what led to this.

The present invention provides a novel, hitherto unknown molding method for molding synthetic resin lenses from granular or tablet-shaped thermoplastic synthetic resin.

[Means for Solving the Problems] The present invention is characterized by filling a synthetic resin raw material into a cavity formed between a pair of lens molds and a member wrapping around the side surfaces of the molds. A method for molding a synthetic resin lens, characterized in that the above-mentioned lens molding mold is filled with a thermoplastic synthetic resin in the form of particles or tablets into a cavity made of a glass mold, and molded under low pressure and heat. This is a method of molding a resin lens.

In the present invention, the lens forming mold consists of a pair of two glass molds. In the glass mold, the transfer surface of the lens can be processed with high precision, for example, by polishing, according to the desired curved surface of the lens to be molded. The size of the glass mold and the curvature of the transfer surface depend on the desired lens; for example, for eyeglass lenses, the diameter is 60 mm to 70 mm, and if it is a minus lens, the molded lens will be thick at the periphery, and if it is a plus lens, it will be thick at the center. Since it is thick, a curvature according to them is given,
If it is a negative lens, even a negative 8 diopter lens can be molded. The thickness of the glass mold is not particularly limited, but if uneven thickness appears in the molded lens, the uneven thickness can be prevented by increasing the thickness of the mold. The back side of the lens transfer surface of the mold is made of reinforcing material, such as metal material,
It may be lined with synthetic resin, synthetic resin composite material, plaster, etc.

A pair of lens molds has a cavity that corresponds to the desired lens thickness by means of a member wrapped around the side surfaces, and is different from a conventional cast mold in which a liquid monomer is filled and hardened. are constructed substantially identically. The part corresponding to the cavity formed by the lower mold and the member wrapping around the sides is filled with granular or tablet-shaped raw material synthetic resin, and the upper part and mold are placed on top of the raw material synthetic resin. The cast molding method differs from the cast molding method in that the filling method of the raw material synthetic resin is used. Naturally, the filling amount of the raw material synthetic resin is taken into consideration in advance in relation to shrinkage due to plasticization and melting, and the thickness of the molded lens.

The material of the wrapping member is not particularly limited, but
It is necessary that the material exhibits heat resistance at a temperature higher than the softening temperature of the raw material synthetic resin, and that it does not alter or discolor the plasticized or melted synthetic resin.
Examples of materials that satisfy these conditions include silicone rubber and fluorocarbon rubber. Since the molded product is a lens, the mold is also circular, and the member is preferably a cylindrical shape in that it is wrapped around the side surface of the mold. When the material is made of the above-mentioned material, it has elasticity, so it is preferable that the material can be brought into close contact with the periphery of the side surface of the mold by utilizing the elasticity. As another member, an adhesive tape coated with an adhesive on one side may be used, and the adhesive surface may be wrapped around the side surfaces of both molds and bonded. If it is a cylindrical member,
It is preferable that a stepped portion, for example a convex portion, for placing and positioning the mold is integrally formed on the inner surface side in contact with the mold. When using such a member, the diameter of the molded lens should be adjusted to match the stepped portion. It is necessary to take this into consideration in advance because it will be smaller by an amount corresponding to .

The assembly of the forming mold will be explained with reference to FIG. FIG. 1 is a cross-sectional view of a mold assembled for a minus lens, and shows
A cavity 4 is formed by the glass molds 1 and 2 and a cylindrical body 3 made of silicone rubber, which is a member wrapped around the side surfaces of the molds. The resin 5 is filled. Then, the glass mold 1 is inserted into the cylindrical body 3 and brought into close contact with the raw synthetic resin, and then a predetermined amount of synthetic resin is filled onto the transfer surface of the mold 1. Furthermore, the glass mold 2 is inserted into the cylindrical body 3 so that the transfer surface is in contact with the raw material synthetic resin 5, and is placed on the raw material synthetic resin. A release agent or the like may be applied to the transfer surfaces of the molds 1 and 2, if necessary. Although not shown in the drawings, a minute gap is provided at the portion where the glass mold 2 and the cylindrical body 3 are in contact with each other to allow air in the cavity to be discharged. Glass molds do not require special external pressure, but if necessary, the glass molds 1 and 2 may be clamped from the back side.
For example, it is pressurized to a low pressure using the elastic body 6 or the like. The mold is thus assembled.

The mold thus assembled is placed in a heating furnace or the like and heated at normal pressure.

The thermoplastic synthetic resin used in the present invention is preferably a transparent amorphous polymer such as polymethyl methacrylate, polycarbonate, or polystyrene as a raw material for a synthetic resin lens. Of course, such polymers are not limited to homopolymers, and may also be copolymers containing them. The above-mentioned thermoplastic synthetic resins are used in injection molding, compression molding, extrusion molding, etc., and are available in granular forms such as spheres, cylinders, disks, and dice of about 1 to 3 mm. These are commonly called pellets. In addition, the form of the thermoplastic synthetic resin used in the present invention may be in the form of a tablet, which is made by heating and plasticizing the thermoplastic synthetic resin in advance to form a crude product, and such a tablet may also be formed into a pellet. Similarly, a suitable lens molded product can be obtained.

The above-mentioned thermoplastic synthetic resins often have moisture adsorbed or attached to their surfaces, and this is known to cause residual bubbles in molded products and cause defects, so they are usually heated before molding. It is used after drying, for example, by heating and drying for several to ten-odd hours at a temperature slightly lower than the softening temperature of the synthetic resin. Also in the molding method of the present invention, it is essential to use a sufficiently dried synthetic resin for filling the mold in order to prevent the generation of residual bubbles.

In the synthetic resin lens molding method of the present invention,
The mold assembled as described above must be placed in a heating furnace and maintained for a sufficient time to heat and plasticize the thermoplastic synthetic resin within the cavity to at least the softening temperature. Thus, the heating temperature is considerably lower than the high temperature heating in conventional molding methods. Therefore, the heating temperature as a molding condition is not uniformly limited because the softening temperature varies depending on the type of synthetic resin used. Therefore, it is necessary to maintain the temperature at least above the softening temperature of the synthetic resin for a sufficient period of time to mold the lens. The heating temperature and holding time are interrelated; if the heating temperature tends to be low, the holding time may be long, and if the heating temperature is trending high, the holding time may be short.

Further, the heating may be carried out in several stages, for example, in two stages or three stages, by changing the heating temperature and the holding time. However, it is necessary to avoid uneven temperature distribution with respect to the mold under heating conditions.

High pressure is not required as a molding condition. As mentioned above, use an elastic body to cover the back of the mold.
Clamping with a low pressure of Kg/cm ² is sufficient.

Thus, after the molding process in which the mold is heated and held for the required time, the heating temperature is gradually lowered and the lens is gradually cooled while being held for several tens of minutes.After cooling to room temperature, the mold is dismantled and the lens is peeled from the mold. As a result, it is possible to obtain a synthetic resin lens that has no defects and has a highly precise shape.

The lens molding method of the present invention is suitable for molding eyeglass lenses that require high precision, but can also be used for molding other lenses such as microscope lenses, telescope lenses, camera lenses, etc.
Of course, it can be applied to molding various lenses such as Fresnel lenses.

[Example] Example 1 40g of polymethyl methacrylate pellets
It was kept in a dryer heated to 97°C for 16 hours to dry it. Next, as shown in Figure 1, a glass mold for lens forming with a diameter of 60 mm and a curvature of the transfer surface of -6 diopters was formed, and a cylindrical body made of silicone rubber was used as a member to wrap around the side of the mold. The above-mentioned dried pellets were filled into the molded cavity, and the glass mold was held from the back with elastic clips that applied a pressure of about 4 kgf.
Assembled the mold.

The mold assembled in this way is heated to about 110℃.
The lens was then placed in a furnace heated to approximately 130°C and held for 48 hours, and then heated to approximately 130°C and held for 64 hours to plasticize and melt the polymethyl methacrylate to form a lens. Next, the temperature was gradually lowered to about 105° C., about 80° C., and about 60° C., and the mold was slowly cooled by holding each for 30 minutes, and then the mold was taken out of the furnace and cooled to room temperature.

The assembled mold was dismantled, compressed air was blown onto the glass mold, and a slight impact was applied with a mallet to peel the molded lens from the mold, thereby obtaining a molded lens made of polymethyl methacrylate.

The molded lens has no residual bubbles or other defects, and the shape is precisely maintained at minus 6 diopters with high precision.Furthermore, there are no striae when inspected with a point light, and the quality is extremely excellent. It was warm.

Example 2 After pre-drying polymethyl methacrylate pellets, a tablet as a pre-formed product obtained by injection molding with an injection molding machine was dried at 95°C for 42 hours and then at 105°C for 18 hours. The mold was assembled by filling the cavity formed by the glass mold and the winding member in the same manner as in 1.

The mold assembled in this way is heated to about 150℃.
The lens was placed in a heated furnace for 2 hours to form a lens. Next, as in Example 1, slow cooling,
After cooling, the molded lens was taken out from the mold.

The quality of the obtained molded lens was extremely excellent, similar to the lens molded in Example 1.

[Effects of the Invention] The method for molding a synthetic resin lens of the present invention uses a glass mold, which is conventionally used for cast molding of liquid thermosetting resin, using granular or tablet-shaped thermoplastic synthetic resin as a raw material. This is a novel method that is characterized by molding under low pressure and heat.

In the case of conventional injection molding, compression molding, or extrusion molding, glass molds cannot be used because the molding is carried out under high pressure and high temperature. Since the molding method of the present invention uses a glass mold, the glass mold is advantageous in that the transfer surface can be processed with high precision and improves the precision of the lens to be molded. Because of the low pressure and relatively low temperature heating, the molded lenses have no defects, and the shape is highly accurate, making it possible to mold lenses of extremely high quality, especially for high-mix, low-volume production. The effect that it is suitable for is also recognized.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a mold assembled for a minus lens. In the figure,
1 and 2 are glass molds, 3 is a cylindrical body, 4 is a cavity, 5 is a raw material synthetic resin, and 6 is an elastic body.

Claims (1)

[Claims] 1. In a method of molding a synthetic resin lens by filling a synthetic resin raw material into a cavity formed between a pair of lens molds and a member wrapped around the side surfaces of the molds, the above lens molding method is performed. A method for molding a synthetic resin lens, which comprises filling a cavity in which the mold is made of glass with thermoplastic synthetic resin in the form of granules or tablets, and molding the resin under low pressure and heating.