JPH0126860B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for molding a plastic lens, and in particular to a method for molding a plastic lens characterized by a method of peeling off a mold from a plastic raw material cured within a cavity.

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 cleansing include monomers containing one or more α, β unsaturated groups and their prepolymers, monomers containing α, β unsaturated groups and condensation polymerizable groups such as epoxy groups, etc. There are prepolymers and various other compounds that can be cured by polymerization. Specific examples include diethylene glycol bisallyl carbonate, (meth)acrylic ester, diallyl ester, and triallyl isocyanate.

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 mechanical lenses. This homopolymer of CR-39 or a copolymer containing CR-39 as a 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 lens distortion and ensure uniform polymerization, curing takes at least several hours.
Usually, it often takes more than one day and 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. Although the gasket is not reused, the glass mold is Often reused for molding.

The inventors had previously discovered a method of assembling two molds to form plastic lenses without using the gasket described above. In this method, two molds are positioned at predetermined positions, a sealing film such as adhesive tape is wrapped around the sides of the molds to seal the gap between the molds, and the two molds are surrounded by the sealing film. This is a method to obtain a plastic lens by curing the plastic raw material in a cavity. This method is extremely superior because it allows the mold to be positioned accurately and is more economical than using a gasket. However, there were problems with removing the mold after the plastic material had hardened within the cavity. That is, in the conventional method using a gasket, the plastic raw material was cured and the gasket removed, resulting in a state as shown in FIG. FIG. 1 shows a cross section of the mold assembly after the plastic material has hardened and the gasket has been removed. Between the two molds 1, 2 there is a hardened plastic raw material 3, ie a molded plastic lens. The cross section 4 of the gasket used is shown in broken lines on the right side of the figure. The diameter of the hardened plastic raw material 3 is smaller than the diameter of the molds 1 and 2, so after removing the gasket 4, there is a trace around the hardened plastic raw material 3 between the two molds where the gasket was removed. A recess 5 is formed. The mold is usually removed from the hardened plastic material 3 by driving a wedge 6 into the recess. The wedge 6 is a plastic raw material 3 made by hardening two molds 1 and 2.
The hardened plastic raw material 3, ie, the plastic lens, is thereby taken out.

On the other hand, it has been difficult to use this wedge in a method that does not use a gasket. FIG. 2 shows a cross section of a mold assembly in which the plastic raw material in this method is cured. This assembly consists of two molds 7, 8, a hardened plastic raw material 9, and a cavity formed between the two molds around the sides of the molds. The adhesive tape 10 is made of adhesive tape 10. Therefore,
Even if the adhesive tape 10 is removed, a recess into which a wedge can be driven is not formed, and the wedge cannot be used. In order to remove the two molds 7 and 8 from the hardened plastic raw material 9 in such a mold assembly, a method of applying an impact to the mold assembly with a mallet or the like has been adopted. However, this method is complicated and time-consuming, and is likely to damage the plastic lens, which is the hardened plastic raw material 9, and the molds 7, 8. In particular, when a convex lens is molded using a plastic raw material containing a curable compound such as CR-39 which has a large shrinkage upon curing, it is difficult to remove the mold. In other words, in the case of molding the concave lenses shown in Figures 1 and 2, the shrinkage is greater at the periphery of the lens than at the center of the lens, so the adhesion strength with the mold is greater than at the center, and peeling from the mold begins to occur. The peripheral area is smaller. In the case of molding a convex lens, the opposite is true, and removal from the mold is more difficult than in the case of a concave lens.

Therefore, in the above-mentioned plastic lens molding method that does not use a gasket, the inventor of the present invention conducted various studies and studies on how to remove the mold, and as a result, formed a handle for removing the mold around the cavity, especially at the injection hole for the plastic raw material. We have discovered a method of curing plastic raw materials by inserting strips made of a specific material. The gist of the present invention is this method,
That is, in a method of molding a plastic lens by curing a plastic raw material mainly composed of a liquid curable compound within a cavity formed between two molds, adhesive tape is tightly attached around the sides of the two molds. forming a cavity surrounded by the two molds and the adhesive tape, and providing a piece of material at the periphery of the cavity to form a handle for removing the mold; The plastic raw material is hardened in the cavity, and after the plastic raw material has hardened, the piece of material is removed.
This method of molding a plastic lens is characterized in that the mold is removed using the concave portion after removing the piece of material as a hook.

FIG. 3 is a cross-sectional view of the mold assembly with the plastic raw material cured, similar to FIG. 2. The present invention provides a hardened plastic raw material 14 in a cavity surrounded by two molds 11 and 12 and an adhesive tape 13, as well as a piece of material 15 at the periphery of the cavity, for example, a hole for activation of the plastic raw material. There is a characteristic in the way it is done. 4 is a plan view of the mold assembly of FIG. 3; FIG. Adhesive tape 13 closely adhered around the molds 11 and 12 is wound so that both ends overlap. This mold assembly is made, for example, as follows. After positioning the two molds 11 and 12 in accurate positions so as to face each other, as shown in FIG. Seal the mold gap. Next, the overlapping parts of both ends of this adhesive tape 13 are peeled off to form an injection hole into the cavity, and the plastic raw material is injected into the cavity through this injection hole.Finally, the strip 15 is put into the cavity through this injection hole. Close the cavity by reapplying the adhesive tape. This is then placed in a heating furnace to harden the plastic material in the cavity to obtain the mold assembly shown in FIGS. 3 and 4. To take out the plastic lens from this mold assembly, first remove the adhesive tape 13, then take out the strip 15, and drive a wedge into the recessed part as a gripping part.
12 is used. On the other hand, piece 1
A method may also be adopted in which the wedge is directly driven into the piece 15 without taking out the piece 5. The obtained plastic lens is made into a product by cutting off the peripheral part.

As for the material of the piece, it is preferable to use a material that is not strongly integrated with the plastic raw material and is easy to take out. For example, foamed plastics such as foamed polyethylene, foamed polystyrene, polyurethane foam with closed cells are used. In addition, various materials such as hollow materials such as hollow bags, soft materials such as elastomers and rubber, and non-adhesive plastics such as fluorine resins can be used. A particularly preferred material is a foamed plastic that does not adhere strongly to plastic raw materials.

On the other hand, as mentioned above, in the method where the piece is not removed, if the piece is made of foamed plastic or hollow material, the mold can be removed by driving a wedge into that part without taking out the piece. I can do it. Further, the piece of material may be present in the periphery of the cavity other than the injection hole for the plastic raw material. That is, before winding the adhesive tape, it is possible to place a piece of material around the mold gap and then wind the adhesive tape, but from the viewpoint of workability, it is difficult to place a piece of material around the injection hole where the plastic raw material is injected. It is most preferred to interpose the material. Furthermore, the shape of the piece is not particularly limited as long as it corresponds to the injection hole for the plastic raw material or is inserted around the cavity and is useful as a handle for removing the mold. It is also possible to use a method for removing the mold by using the concave portion of the piece left behind or the piece itself, or to use a method other than driving a wedge. For example, the mold can be peeled off by applying mechanical force to the concave portion of the left piece of material as a gripping portion so as to spread that portion.

The adhesive tape used in the present invention is not particularly limited in its thickness or material. The thickness may be thick enough to provide some flexibility. The material is plastic,
Although various materials such as paper and metal can be used, plastic is particularly preferred. The shape is preferably an elongated body with a constant width, that is, a tape-like shape, but is not particularly limited as long as it can seal around the mold gap. The most preferred adhesive tape is plastic tape coated with adhesive on one side. Furthermore, although a glass mold is most preferred as the mold, a plastic mold has also been proposed and can be used. The curable compound which is the main component of the plastic raw material is preferably the diethylene glycol bisallyl carbonate (CR-39) alone or a mixture thereof with another copolymerizable compound containing it as the main component. This copolymer compound can be used alone or as a mixture with a copolymerizable compound other than CR-39. Examples of the copolymerizable compound include allyl carbonates other than CR-39, esters of unsaturated alcohols and acids, and styrene. In addition to this curable compound, plastic raw materials usually require a polymerization catalyst, and if necessary, ultraviolet absorbers, colorants, and other additives may be added.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a mold assembly using a conventional gasket, and FIG. 2 is a sectional view of a mold assembly using a method that does not use a gasket.
3 is a sectional view of the mold assembly according to the present invention, and FIG. 4 is a plan view of the mold assembly of FIG. 3. In addition, in the figure, 1, 2, 7, 8, 11, 12 are molds, 3, 9, 14 are hardened plastic raw materials,
4 is a gasket, 6 is a wedge, 10 and 13 are adhesive tapes, and 15 is a piece of material.

Claims (1)

[Scope of Claims] 1. In a method of molding a plastic lens by curing a plastic raw material mainly composed of a liquid curable compound within a cavity formed between two molds, the periphery of the side surfaces of the two molds is Adhesive tape is closely attached to the molds to form a cavity surrounded by the two molds and the adhesive tape, and a piece of material is provided at the periphery of the cavity to form a handle for removing the mold. to cure the plastic raw material in the cavity, and after the plastic raw material has hardened, remove the piece material,
A method for molding a plastic lens, which comprises removing the mold using the concave portion after removing the piece. 2. The method according to claim 1, in which the mold is removed by driving a wedge into the recess after removing the piece of material. 3. The method of claim 1, wherein the piece is made of foamed plastic.