JPH0244693B2 - ICHIGIMEYOSUPEESAA - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a positioning spacer used when assembling two molds for molding a plastic lens, and particularly to a positioning spacer made of a specific material.

Plastic lenses are sometimes manufactured by injection molding or compression molding of thermoplastic resins such as polycarbonate and poly(meth)acrylates, but cast molding is usually used to manufacture plastic lenses with excellent performance and physical properties. is used. Liquid curable compounds that serve as raw materials for plastic lenses include monomers and prepolymers thereof having one or more α,β unsaturated groups, and monomers and prepolymers having α,β unsaturated groups and condensation polymerizable groups such as epoxy groups. There are polymers and various other compounds that can be cured by polymerization. Specific examples include diethylene glycol bisallyl carbonate, (meth)acrylic acid ester, diallyl ester, and triallyl isocyanurate.

Among plastic lenses, especially eyeglass lenses, accurate prescription is required, as well as high physical properties such as impact resistance, scratch resistance, and transparency. Currently, diethylene glycol bisallyl carbonate called CR-39 is widely used as a raw material for eyeglass lenses. This homopolymer of CR-39 or a copolymer containing CR-39 as its main component has excellent physical properties such as transparency, impact resistance, and scratch resistance, making it the most excellent eyeglass lens.

Cast molding of plastic lenses involves (A) filling a plastic raw material such as a monomer into a cavity between two molds held together by a gasket;
It is usually done through three basic steps: (B) curing it by heating, etc., and (C) then removing the mold and taking out the lens. In step (A), the gasket is made of a flexible material such as rubber, elastomer, or relatively soft synthetic resin, and two molds, usually made of glass, are assembled to this gasket. The opposing surfaces of the two molds have the necessary curves to form the lens surface. Plastic raw materials such as monomers are filled into a cavity formed between these two molds and sealed to prevent leakage. In step (B), the mold filled with the raw material assembled in (A) is placed directly into a heating furnace or the like to harden the plastic raw material. In order to minimize distortion of the lens and ensure uniform polymerization, curing often takes at least several hours, usually over a day and a night. In the (C) process, the assembled mold is removed and the lens inside is taken out. At this time, the gasket is often cut to make it easier to remove, and the gasket is not reused, but the glass mold is Often reused for molding.

The biggest problem with cast molding of this plastic is the gasket. Plastic raw materials such as CR-39 have relatively large shrinkage during polymerization and curing. For this reason, the gasket needs to have a certain degree of flexibility, and if this flexibility is not sufficient, the volume between the molds will not be able to follow the shrinkage of the plastic raw material, and separation will occur between the mold and the plastic raw material. Further, since polymerization curing usually requires long heating, the gasket is also required to have heat resistance. In addition to both, the gasket material also needs to be inexpensive. That is, since gaskets are usually used only once, there is a problem that unless the materials and molding costs are low, the cost of gaskets in lens molding becomes too high.
For example, there are many problems with lenses, and the shapes of gaskets vary accordingly, making it necessary to prepare many different types of gaskets. Even if the material of the gasket is inexpensive, the cost of molding it (for example, the cost of the mold) cannot be ignored.

Additionally, the gasket requires features for mold alignment. For example, aligning the centers of the surfaces that form the plastic lens surfaces of two molds (i.e., spherical or aspherical surfaces), aligning the inclinations of these surfaces (i.e., making the axes coincide), This includes setting the distance between the surfaces to a predetermined distance (defining the thickness of the lens). For this reason, the gasket needs to be a molded product with an accurate shape. On the other hand, for the above-mentioned reasons, the material of the gasket needs to have a certain level of flexibility; therefore, gaskets made of such flexible materials are susceptible to misalignment of the mold, making it difficult to align the mold.

Therefore, the present inventors considered separating the functions of the gasket and aligning the mold without relying on the gasket. On the other hand, the inventors have discovered a method of molding plastic lenses using a sealing film without using a gasket. Therefore, the inventors of the present invention proceeded to study a method for assembling a mold in order to assemble the mold accurately and mold a plastic lens without using a gasket. As a result, they discovered a method for determining the positions of two molds by bringing them into contact via a positioning spacer with a predetermined shape. This positioning spacer is removed from between the two molds after the two molds have been positioned. When using a method that does not use a gasket, these two positioned molds are sealed by tightly sealing them with tape or the like.
A cavity is formed in which the plastic material is cured.

The invention regarding the method of assembling a mold using this positioning spacer has already been filed as an invention by the present inventors (Japanese Patent Publication No. 1983-1999-1).
(See Publication No. 29333 and Japanese Patent Publication No. 63-39409, etc.). These positioning spacers generally have a shape similar to a conventional gasket, which has a cylindrical frame and a lip (convex part in the previous application) on the inner surface of the frame, or have an improved shape as a positioning spacer. It was hot. Conventional gaskets were required to be flexible as described above, and therefore soft plastics were used as the material. For example, soft vinyl chloride resin,
Polyisobutylene-polyethylene mixed plastics (see Japanese Patent Publication No. 43-25830), ethylene-vinyl acetate copolymer as the main component (Japanese Patent Publication No. 1973-25830)
-3873), other soft plastics such as rubber and polyethylene are also known. In contrast, the positioning spacer according to the invention of the present inventors does not require flexibility. The positioning spacer is used when assembling the mold, but not during the curing of the plastic raw material, so it does not need properties to follow the shrinkage of the plastic raw material or to seal around the mold. It is. Furthermore, heat resistance is also unnecessary. Therefore, the main requirements for the positioning spacer are accurate shape and dimensional stability during repeated use, and since the spacer is used repeatedly, the economy of the material is not a big issue.

The present inventors have studied materials for the positioning spacer that can easily form the above-mentioned accurate shape and have excellent dimensional stability. Generally, such required performance can be achieved by using a hard material. However, as a result of further investigation, it was found that simply using a hard material was insufficient. First, the positioning spacer must not be fragile, since it is compressed by repeated molding and is also frequently attached and removed. Furthermore, since the mold is usually made of glass, it must not be hard enough to damage the glass mold. In addition, materials with high physical properties such as wear resistance are preferred. As a result of examining various materials that meet these required properties, the present inventor found that polyacetal resin is suitable. Other materials, such as metals, not only have a large coefficient of thermal expansion and undergo large changes in shape depending on usage conditions, but also have high hardness and easily damage the glass mold.
The present invention is a spacer for positioning a mold for forming a plastic lens of a specific shape, which is made of the polyacetal resin material described below.

This positioning spacer is used to position two molds for plastic lens molding, and is removed from between the molds after the positioning is completed, and the positioning spacer is made of polyacetal resin and has a cylindrical frame. A spacer for positioning a mold for molding a plastic lens, the spacer having a lip provided on the inner surface of the frame all or partially in the circumferential direction.

Figures 1 to 4 show four examples of the shape of the spacer of the present invention.
As shown in the figure. Each figure A is a plan view, and each figure B is a sectional view taken along a cutting line passing through the center of the cylindrical frame.
The positioning spacer shown in FIG. 1 consists of a cylindrical frame 1 and a lip 2, and the lip 2 is provided all around the inner surface of the cylindrical frame 1. It is preferable that the upper and lower surfaces of the lip 2 of this positioning spacer (the surfaces of the lip parallel to the paper plane in FIG. 1A) are flat. FIG. 2 shows a positioning spacer similar to that shown in FIG. 1, consisting of a cylindrical frame 3, a lip 4, and a convex portion 5 formed on the upper surface of the lip 3. The convex portion 5 of the lip 4 is provided for linear contact with the concave spherical surface of the mold for positioning. For more detailed information on the shape of the positioning spacers shown in FIGS. 1 and 2, how to use them, and other information, please refer to Japanese Patent Publication No. 63-394091, in which the aforementioned lost invention of the present inventors is described. sea bream.

The positioning spacer shown in FIGS. 3 and 4 has a further improved shape. Like the positioning spacers shown in Figures 1 and 2, this positioning spacer can be used not only to assemble molds with concave or convex spherical surfaces, but also to assemble molds with aspherical surfaces such as trick surfaces and cylindrical surfaces. It can also be used for assembly.
The positioning spacer shown in FIG. 3 consists of a cylindrical frame 6 and two arcuate lips 7, 8. Sectional view B shows the -' section of plan view A.
The positioning spacer shown in FIG. 4 consists of a cylindrical frame body 9 in which protrusions 12 and 13 are provided on the lips of the positioning spacer shown in FIG. 3, as in the case of FIG. 2, and two lips 10 and 11. be. Figure 4B
1 is a cross-sectional view showing the negative cross-section of A, and also shows a cross-section of the molds to show a state in which the two molds 14 and 15 are assembled and positioned. The mold 14 having a concave spherical surface 18 has a concave spherical surface 16
is positioned in linear contact with the convex portions 12 and 13 on the lip, and has a convex spherical surface 17.
is positioned with its convex spherical surface 17 in linear contact with the lips 10 and 11. The positioning mold shown in FIGS. 3 and 4 can also be used for positioning a mold having an aspherical surface such as a trick surface or a cylindrical surface. For example, if the mold in Figure 4B is 1
5, a mold having a convex trick surface is used, and this aspheric surface and the lips 10, 11 contact each other at four points on both ends of the lip in the circular direction, thereby positioning the aspheric surface. For details of the positioning spacers shown in FIGS. 3 and 4, please refer to the patent application (Japanese Patent Publication No. 22610/1989) filed on the same day as the original application of this application relating to the invention of the present inventors.

The polyacetal resin used in the present invention is an engineering plastic that has physical properties close to those of metal and is used as a metal substitute plastic. This polyacetal resin is a resin made of formaldehyde polymer or copolymer (trade name "Delrin" etc.), and has high strength and rigidity, good dimensional stability, excellent fatigue properties, and high wear resistance. The best material for positioning spacers. Polyacetal resin contains fillers,
A reinforcing agent, a stabilizer, a coloring agent and other additives may be added.

The method of molding a plastic lens using the positioning spacer of the present invention is not particularly limited, but it is preferable to use the method of the invention of the present inventors' previous application (the above-mentioned method of the present inventors' previous application). (See patent application for the invention). To explain one example of the method described in these applications, for example, a plastic lens is molded as follows. First, two molds are prepared, for example one having a concave spherical surface and the other having a convex trick surface. The mold is held in a movable mold holder with these two surfaces facing each other, and the positioning spacer of the present invention is sandwiched between the two surfaces, and the two surfaces are brought into contact with the positioning spacer. Perform positioning. This state is, for example, the state shown in FIG. Next, in this state, the mold holder is fixed to fix the mold position. However, the mold can only be moved in a direction parallel to the axis. Next, move the mold in a direction parallel to the axis, widen the space between the two surfaces, remove the positioning spacer from the two surfaces, and then
Bring the two surfaces together to a specified distance and fix them there. Next, a sealing film such as adhesive tape is tightly attached around the sides of the two molds to seal the space between the two sides and form a cavity.
After removing the assembly consisting of the two molds and the sealing film from the mold holder, the cavity of the assembly is filled with plastic material, or after the assembly cavity is filled with plastic material, the assembly is removed from the mold holder. Remove. Next, the assembled body filled with the plastic raw material is placed in a heating furnace or the like to harden the plastic raw material, and then taken out from the heating furnace and the sealing film and two molds are removed to obtain a plastic lens.

[Brief explanation of drawings]

1 to 4 are diagrams showing the shapes of four examples of the positioning spacer of the present invention, and each diagram A is a plan view;
B is a cross-sectional view. 1, 3, 6, 9... Cylindrical frame, 2, 4, 7,
8, 10, 11... Lip, 5, 12, 13...
Convex portions on the upper surface of the lip, 14, 15...mold.

Claims (1)

[Claims] 1. A positioning spacer that is used to position two molds for molding plastic lenses and is removed from between the molds after the positioning is completed, and the positioning spacer is made of polyacetal resin. A spacer for positioning a mold for forming a plastic lens, comprising a cylindrical frame and a lip provided on the inner surface of the frame all or partially in the circumferential direction. 2 a lip is provided in the circumferential direction of the inner surface of the cylindrical frame;
The positioning spacer according to claim 1, further comprising at least two notches.