JPH0115366B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of molding a plastic lens, and particularly to a method of forming a cavity using two molds and a sealing film, and curing a plastic raw material within the cavity to mold a plastic lens. It is about the method.

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, eyeglass lenses in particular require accurate prescription and 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 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 distortion of the lens and ensure uniform polymerization, curing often takes at least several hours, usually over a day and a night. (C)
In the 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 can be used for the next cast molding. Often reused.

One of the problems in molding this plastic lens is the gasket. The gasket is CR―
It is necessary to seal the plastic material such as 39 to prevent it from leaking from the cavity until it polymerizes and hardens. For this reason, the gasket needs to have a certain degree of flexibility, and if this flexibility is not sufficient, the plastic material will easily leak out from the mold gap.

Furthermore, the gasket must serve to maintain a constant cavity thickness in order to mold a plastic lens of constant thickness. In addition to these, gaskets are also required to have properties that can follow the shrinkage of plastic raw materials during polymerization and hardening, and since polymerization and hardening usually require long-term heating, gaskets are also required to have heat resistance. In addition to these, the gasket material also needs to be inexpensive. That is,
Since gaskets are usually used only once, there is a problem in that unless the materials and molding costs are low, the cost of gaskets in lens molding becomes too high. For example, there are many types of lenses, and the shapes of gaskets vary accordingly, creating the problem of having to prepare many 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.

Therefore, the present inventor conducted various research studies in order to find a gasket that is satisfactory in sealing performance, heat resistance, and flexibility, can be used regardless of the type of lens, and is inexpensive. the result,
The surprising result was that the method of simply pasting a sealing film such as tape around the two molds was the best. The sealing film may be any film that does not allow the liquid plastic raw material to leak, and if a tape having an adhesive layer on one side, that is, an adhesive tape is used, it can be easily attached. This adhesive tape is used by placing it in close contact with the side of the mold.

As a result of studying a method of molding a plastic lens using this adhesive tape without using a gasket, the inventor of the present invention found that the mold holder used to assemble the two molds or another mold can be placed in a fixed position. We have discovered a method for molding plastic lenses by curing the plastic raw material inside the cavity while holding the mold using a jig that can be held in place. This method is less likely to cause misalignment of the mold than the method previously proposed by the present inventors, in which the area around the mold is sealed with a sealing film and the plastic raw material is cured while the mold is supported by the sealing film. Excellent. The gist of the present invention is this method, that is, a method for 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 plastic lens forming surfaces of the two molds are positioned opposite each other, and the two molds are placed around the side surfaces of the two molds.
The plastic raw material filled in the cavity of the mold assembly assembled by tightly adhering adhesive tape across the two molds was held by the mold holder used when assembling the two molds. This is a method for molding plastic lenses, which is characterized by curing the plastic raw material in the same state.

In order to explain the present invention, the mold will first be explained. In the present invention, two molds, which are usually made of glass and whose shape is usually cylindrical to disc-shaped, are used. The upper surface of the mold is provided with a surface forming a spherical or aspherical plastic lens surface. Hereinafter, unless otherwise specified, this surface will be referred to as an optical surface. This optical surface is usually a smooth curved surface such as a spherical surface, a trick surface, or a cylindrical surface, but it may also be a flat surface. FIG. 1 shows an example of a cylindrical mold having an optical surface consisting of a concave spherical surface. FIG. 2 shows a cross section cut along the diameter. The illustrated mold has an optical surface 1, a bottom surface 2 other than the optical surface, and a side surface 3. The center of the optical surface is called the center, and the line connecting the center of curvature of the spherical surface and the center of the optical surface is called the axis 4. The optical surfaces may be convex, with concave optical surfaces forming the convex surface of the lens and convex optical surfaces forming the concave surface of the lens. The bottom surface other than the optical surface may not be flat. There is no essential difference between a cylindrical mold and a disc-shaped mold, but a mold with almost constant thickness is called a disc-shaped mold.
Others will be referred to as cylindrical molds, and the cylindrical mold will be described below. Of course, in the present invention, it is not an essential requirement that the mold be cylindrical to disc-shaped. What is required is that there be a side surface of some width adjacent to the periphery of the optical surface.

FIG. 3 is a sectional view of a conventional mold assembly. Conventionally, two molds 5 and 6 are held by a gasket 7 with their optical surfaces facing each other, and the periphery of the molds is sealed with the gasket 7 to form a cavity 8, and the plastic raw material is hardened within this cavity 8. They were molding plastic lenses.

One of the requirements of the present invention is that the peripheries of the optical surfaces of two molds placed opposite to each other are sealed with adhesive tape. The combination of the optical surfaces of the two molds is not particularly limited. Although the diameters of the two molds may be different, normally those having the same diameter are used, and also in the present invention, it is preferable that the diameters of the two molds are the same or almost equal. An adhesive tape that seals around the space formed between the two optical surfaces is tightly attached to the sides of the two molds. This close contact is preferably through adhesive or adhesion, but the two may be in direct contact due to the shrinkage force of the adhesive tape or the like. It is preferable that this close contact is at least strong enough to prevent the mold and the adhesive tape from easily slipping or peeling. Adhesive tape is 2
It is tightly attached to the sides of two molds. That is, the adhesive tape adheres to both sides of the two molds. It is not preferable that the mold is in close contact with only one side of the two molds and not with the other side. However, it is not always necessary for the adhesive tape to be in close contact with the sides of the two molds at the same time. For example, the adhesive tape may be tightly attached to both sides as a whole, such as when relatively narrow tape is wound spirally with some parts overlapped. Of course, it is preferable to use a tape-like adhesive tape with a width equal to or greater than the distance between the circumferences of the two optical surfaces, with one end in the width direction
In this method, one end is wrapped tightly against one side of the mold, and the other end is wrapped tightly against the side of the other mold.

The purpose of using this adhesive tape is to seal the gap between two molds to form a cavity. The adhesive tape prevents the plastic material from leaking out of the cavity until the plastic material is filled into the cavity and cured. The use of adhesive tape also has the effect of preventing unwanted movement of the mold due to shrinkage during curing of the plastic material. For example, the shrinkage of the plastic material in the cavity can be followed by shrinkage of the adhesive tape, misalignment of the contact surfaces between the adhesive tape and the mold, or bending of the adhesive tape toward the cavity. Furthermore, the heat resistance of adhesive tapes can be easily improved by selecting the material, and there are no particular restrictions on the thickness, so using a thin adhesive tape can demonstrate flexibility regardless of the material. sell. However, unlike the case of gaskets, it is not necessarily necessary to have flexibility to follow the shrinkage of the plastic raw material. Also, unlike the case of using a gasket, adhesive tape does not require the function of positioning the mold or holding it at a constant gap. Therefore, as long as the adhesive tape has the necessary width, it can seal the mold gap without changing the type or shape. Needless to say, the amount of material used for the adhesive tape is extremely small compared to the amount of conventional gasket material, and for example, if a commercially available adhesive tape is used, there is no need for molding costs.

Another requirement of the present invention is to cure the plastic raw material without removing the mold holder or the like that holds the mold from the mold assembly assembled as described above and filled with the plastic raw material. The mold retainer fixes the position of the mold and holds the mold until the plastic stock is cured to prevent shrinkage or other mold displacement as the plastic stock cures. However, if the shrinkage of the plastic raw material is large, the mold may be allowed to move to some extent only in the thickness direction of the plastic lens, that is, in the axial direction. For example, when the plastic raw material shrinks significantly, such as when molding a thick plastic lens, the mold is elastically fixed in the direction of the optical axis so that it can move in this direction, and the mold follows the shrinkage. be able to be able to be able to be able to do so. Conventional gaskets have the role of sealing the cavity and positioning and fixing the mold, but in the present invention, the former role is given to the sealing film, and the latter role, especially fixing the mold, is given to the mold holder. It is something that

In order to explain one example of the method of the present invention, FIG. 4 shows a partial cross-sectional view of a mold holding device holding a mold. The two molds 9 and 10 are held by mold holders 11 and 12, respectively. The mold holder 12 at the bottom of the figure is fixed to a pedestal 13. The pedestal 13 is provided with a pillar 14,
The mold holder 11 in the upper part of the figure is attached to this column 14 with a support rod 15 and a rod 16. rod 1
6 is slidable on the pillar 14 and can be fixed at any position. An adhesive tape 17 is tightly wound around the side surfaces of the two molds 9 and 10, and this adhesive tape seals the gap between the molds and forms a cavity 18.

The illustrated mold assembly can be assembled, for example, as follows. That is, the molds 9 and 10 are attached to the mold holders 11 and 12, and then the rod body 16 is moved relative to the pillar 14,
After setting the distance between the two molds to a predetermined distance,
The rod body 16 is fixed to the pillar 14. Next, adhesive tape 17 is wound around the side surfaces of the two molds 9 and 10 to bring them into close contact, completing the assembly. In this method, the molds 9 and 10 are positioned by accurately determining the relative positions of the mold holders 10 and 11 in advance, and by moving the rod 16 to determine the distance between the molds by moving the molds in the optical axis direction. It is done by holding the If more accurate positioning is required, a positioning spacer is placed between the two molds, the two molds are brought into contact with this positioning spacer to determine the relative position of both molds, and then the rod is 16 relative to the pillar 14 to widen the gap between both molds, remove the positioning spacer, and bring both molds close to a predetermined distance again for positioning. In this case, the mold is preferably moved in the axial direction, but is not limited thereto. The mold positioning method using a positioning spacer is explained in detail in Japanese Patent Application No. 55-36928, Japanese Patent Application No. 55-36929, etc., which are related to the invention of the present inventors, and this invention also applies to this method. method can be used.

The two positioned molds are then sealed around the molds, such as by using an adhesive film and wrapping it around the molds. This forms a cavity surrounded by the two molds and the sealing film. The method of sealing, the type of adhesive tape, etc. are similarly explained in detail in the patent application filed by the present inventors, and these methods can also be used in the present invention. Preferably, a tape-shaped synthetic resin film is used as the adhesive tape,
In particular, a so-called adhesive tape or the like is used, in which a layer of adhesive or adhesive is previously provided on at least one side.

In the present invention, the assembly of the mold is not limited to the above method. For example, when using a mold holder as shown in Fig. 4 above, the rod 1
6 is rotatably coupled to the pillar 14 (for example, the fourth
In the figure, the rod 16 rotates on the paper surface), lift the mold 9 by rotating the rod 16 relative to the pillar 14, remove the positioning spacer, then return the rod 16 to its original position and seal it with adhesive tape or the like. Thus, the state shown in FIG. 4 can be obtained. In this case as well, if the position of the mold holder is accurately determined in advance, the mold can be assembled without using positioning spacers. Further, the mold can be assembled using a holder other than the one shown. For example, in FIG. 4, two pillars 14 can be provided and both ends of the rod 16 can be supported by the pillars. Furthermore, the mold holder 11 may be one that holds the cylindrical mold 9 only on the side surface or only on the bottom surface. Various applications can be considered for these holding methods, and the methods are not limited as long as they can achieve the purpose of fixing the mold.

The cavity of the mold assembly assembled as described above is then filled with plastic material. The filling of this plastic raw material is
This can also be done at the same time as sealing the mold gap with adhesive tape. For example, the tape is wound until the mold gap is completely sealed, and the plastic material is injected into the mold gap through the remaining hole.
The tape can then be applied until it overlaps to complete the seal. In the case of a mold assembly in which the sealing is completed and the cavity is completed, part of the adhesive tape is removed to form a hole leading to the cavity, and the plastic raw material is injected through there.
The cavity can then be filled with the plastic raw material by sealing it again, by inserting a syringe needle or the like through the contact surface between the adhesive tape and the mold, and injecting the plastic raw material, or by other methods.

After the cavity of the mold assembly shown in FIG. 4 is filled with plastic material, the fourth
In the state shown in the figure, ie without removing the mold holder, the mold assembly is placed in a heating furnace or the like to harden the plastic material within the cavity. Even when mold holders and supports other than those shown in FIG. 4 are used, the plastic material is cured without removing these holders and supports. Finally, the mold assembly is disassembled and the molded plastic lens is removed.

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 a plastic tape coated with an adhesive on one side, ie a so-called adhesive tape. 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 copolymerizable compound can be used alone or as a mixture with copolymerizable compounds other than CR-39. Examples of copolymerizable compounds 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 perspective view showing an example of a mold, and FIG. 2 is a sectional view thereof. FIG. 3 is a cross-sectional view of a mold assembly assembled using a conventional gasket. FIG. 4 shows a cross-sectional view of a mold assembly using the method of the present invention. 5, 6, 9, 10... Mold, 7... Gasket, 11, 12... Mold holder, 8, 18... Cavity.

Claims (1)

[Claims] 1. In a method of molding a plastic lens by curing a plastic raw material mainly composed of a liquid curable compound in a cavity formed between two molds, the surfaces forming the plastic lens surfaces of the two molds are The plastic raw materials filled in the cavities of the assembled molds were assembled by facing each other and adhering adhesive tape around the sides of the two molds. A method for molding a plastic lens, characterized by curing a plastic lens raw material while holding the mold with a mold holder used in assembling the mold.