JPS5849220A - Manufacture of plastic lens - Google Patents

Abstract

PURPOSE:To obtain the titled lens having a large aperture and thickness deviation, by compression molding a cut plastic lens material, which has been obtained by the casting method, in compression molds when only part of the material adjacent to the surface is melted to be flowable. CONSTITUTION:A monomer, a half polymer or a mixture of the monomer and the half polymer is cast in casting molds, and is bulk-polymerized to obtain the plastic material 2. The plastic material 2 is cut to have the surface roughness of 10-30mum by a lathe and preferably an NC lathe, and is set between cores 6, 7 associated with mold plates 1, 3, with the heated molds open. Then the molds are closed, and after they are left to stand until only part of the material adjacent to the surface is melted to be flowable, the material is compression molded. In this case, the circulation of the temperature controlling medium is stopped, and a cooling medium is passed through mold cooling medium flowing bores 12 thereby the molds are cooled.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a plastic lens.

Plastic lenses are becoming more widely used in optical products because they are lighter than traditional glass lenses, have the potential for mass production, and are expected to be inexpensive. . The resin currently mainly used as a plastic lens material is Jechi (
/ glycol bisallyl carbonate (hereinafter referred to as 0R-3
9) or polymethyl methacrylate (hereinafter referred to as PMM).

CR-39 is mainly used for eyeglass lenses, and PMM is often used for sunglasses and loupes. These lenses are relatively small in diameter, and in the case of PMM lenses, they are manufactured primarily by injection molding or by CR-39Fi casting.

By the way, attempts have recently been made to make lenses with relatively large diameters and large deviations in thickness from plastic. When manufacturing such lenses using the injection molding method, if you try to create a lens with good shape accuracy, pressure is applied along the resin flow path: cylinder nozzle - sprue - gate - product, resulting in insufficient product filling (short). However, strong pressure is applied to the cavity through the part of the lens product, especially near the gate, which tends to generate residual stress and result in distortion. In addition, sink marks are likely to occur in the thick parts of the lens due to differences in the thickness of the lens product part, which is called uneven thickness. As described above, it is difficult to obtain a plastic lens with high shape accuracy and little distortion by injection molding because of the application of high injection pressure and uneven thickness.

In view of the above points, the present invention provides a method for obtaining a plastic lens having a relatively large diameter and a large thickness deviation. That is, the present invention pours a monomer, a semi-polymer, a resin, or a mixture of a monomer and a polymer into a mold for cast molding, and produces a plastic lens material that is bulk-polymerized and has no cete distortion. After cutting this into a predetermined shape using a lathe, preferably an IC lathe, it is placed into a compression molding mold with a predetermined shape, and only the near surface (surface layer) of the lunz material melts, making it flowable. By compression molding when the
This makes it possible to manufacture plastic lenses with large diameters and uneven thickness.

Hereinafter, the manufacturing method of the present invention will be explained in more detail.

If the average molecular weight of the plastic lens material obtained by bulk polymerization is much larger than the average molecular weight of the injection molding material, it will be easier to grind than the injection molding material. 1' Because almost no unreasonable pressure is applied during bulk polymerization, residual stress may occur.
':, '6) is extremely rare compared to the injection molding method.The shape of this plastic lens material is preferably a flat plate of equal thickness from the viewpoint of a material that does not suffer from distortion, but it is extremely Plastic lens with large inner thickness deviation 1. For example, a convex lens with a center thickness of 40 mm and a burnt thickness of 4111 mm is made. If a flat plate is used, the amount of cutting will be significantly increased and it is not economical, so the shape may be made similar to the final lens shape. Also, methyl methacrylate is a material suitable for making plastic lens materials by bulk polymerization.

Transparent monomers such as styrene or polymers thereof are available.

Next, to cut the lens material obtained by bulk polymerization, a carbide tool can be used, but it is best to use a diamond tool. , preferably numerically controlled. The surface roughness of the lens material at this stage is 10~3o/
It is processed to a size of about 7m. After cutting, the lens is placed in a compression mold having a predetermined shape and compression molded. In the compression molding process, the entire plastic lens material is not melted, but only the vicinity of the surface of the lens material is melted into a fluid state. The reason for this is that when the entire lens material is melted, the thermal mass is large and it takes a long time, and the thinner parts of the lens solidify first during the cooling process, which causes sink marks as the thicker parts of the lens solidify. Because it will come.

In the compression molding of the present invention, even though the lens shape is a product with uneven thickness, the thickness of the part that can be melted and fluidized is constant throughout the lens, making it seem like a product with a constant thickness. The molding is done as if it were molded. In addition, the heating for melting the lens material can be done in advance outside the molding machine. In this case, only the near surface of the lens material is melted, and when it becomes flowable, the metal is added inside the molding machine. It is useful to perform preheating, etc. used in general compression molding, such as by transferring the mold and performing compression molding. Also, at the same time as compression pressure starts to be applied, cooling of the mold begins.

Hereinafter, the above-described compression molding process will be explained in more detail using the drawings. Figures 1 to 3 show the compression molding process in 3
It is a diagram showing an outline of the process divided into stages. In other words, Figure 1 shows the stage of setting the lens material cut in the previous process.
FIG. 2 is a diagram for explaining the pressurization and cooling stages, and FIG. 3 is a diagram for explaining the product removal stage.

In FIG. 1, the lens material 2 cut by an IC lathe in the previous step is placed between the cores 6 and 70 assembled in the templates 1 and 3 with the mold open. in this case,
The mold has a mold temperature control medium passage hole 1 to adjust the temperature.
Heat it to a constant temperature by flowing a temperature regulating medium (usually oil) through 1.

Next, the mold is closed as shown in FIG. 2 using a device not shown. However, since the mold is closed, almost no force should be applied to the mold. It is left in this state until only the vicinity of the surface of the lens material 2 melts and becomes fluid. Thereafter, compression molding is performed by applying a large pressure to the mold using a device (not shown). At that time, at the same time as starting to apply compression pressure, the circulation of the temperature regulating medium that was flowing through the mold temperature regulating medium passage hole 11 is stopped, and the cooling medium (oil, water, etc.) is allowed to flow through the mold cooling medium passage hole 12. This will start cooling the mold.

After reaching a temperature at which the molded product can be taken out, the mold is opened as shown in FIG. 3, and an ejector plate 5. The ejector sleeve (or ejector pin) 4 is activated to eject the final plastic lens 2'.

Examples of the present invention will be described below.

A biconvex lens with a diameter of 100M, and the radius of one spherical surface is 10
0111m s The radius of the other sphere is 200 mm
In order to obtain a plastic lens with a percent burnt thickness of 3rr1 m and a center thickness of 22.75 fi, first, uniformly thick flat plate lens materials were prepared by bulk polymerization. The method is to
Prepare two flat glass molds of 01H1, sandwich a gasket between the two molds so that the burnt thickness is 2!4 mtn, and pour the semi-polymerized material prepolymerized with methyl methacrylate into the molds. 40 hours at 60'C, then 1
Bulk polymerization was carried out at 10'C for 5 hours, and then cooled and released from the mold to obtain a flat plate of plastic lenses having a thickness of 24 mm. This lens material is cut using a lathe, and one spherical surface has a radius of 100 mm, the other spherical surface has a radius of 200 g, a scorch thickness of 3 mm, a center thickness of 22.8 fi, and a diameter of 1 oollll.
ll convex lens material was obtained. The spherical surface roughness of this lens material was approximately 30 μm. On the other hand, as shown in the drawing, a concave core with a diameter of 100 ml and a spherical radius of 100 mm and a concave core with a diameter of 100 mm and a spherical radius of 200 mm were prepared and assembled into the mold. Afterwards, this mold was heated to 150'C. after that,
This mold was opened, and the plastic lens material obtained in the cutting process was set on the core surface, then the mold was closed, and only the vicinity of the surface of the lens material was melted and allowed to flow for 20 seconds. Thereafter, a compression pressure of 50 kg/crll was applied for 10 minutes. At the same time as applying compression pressure, cooling of the mold began. After the compression pressure was released, the mold was opened to obtain the desired plastic lens.

As a result of measuring the shape of the obtained plastic lens using a coordinate measuring machine, the radius of the spherical surface was 1 oom.
The variation from the theoretical value on both sides of m and 200 mm is 13
It was within μm. When optical distortion was observed using the cut polarizing plate, almost no distortion was observed.

As described above, the present invention involves producing a plastic lens material by bulk polymerization in a casting mold, cutting it into a predetermined shape using a lathe, and finally producing a compression molding mold having a predetermined shape. By compressing and molding the lens material when only the surface near the surface has melted and can flow, it is possible to provide plastic lenses with large diameters and uneven thickness that could not be obtained with conventional methods. It is said that its industrial value is significant. It should be noted that, in the present invention, after compression molding, well-known zero treatments such as surface hardening treatment and anti-reflection coating may be performed.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are diagrams for explaining each step of compression molding in the present invention. 1.3... template, 2... lens cumulative moon,
2'...Final plastic lens, 4...
・Ejector sleeve (ejector bin), 6...
・Ejector plate, 6, 7... Core, 11
...Mold temperature control medium passage hole, 12...
Mold cooling medium passage hole.

Claims (1)

[Claims] A monomer, a semi-polymer, or a mixture of a monomer and a polymer is poured into a mold for cast molding, polymerized in bulk to create a plastic lens material, and then turned into a predetermined shape using a lathe. A method for manufacturing a plastic lens, which comprises cutting the lens material, placing it in a compression molding mold having a predetermined shape, and performing compression molding when only the vicinity of the surface of the lens material melts and becomes flowable.