JPS6029333B2 - How to assemble a mold for plastic lens molding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for assembling molds for molding plastic lenses, and more particularly to a method for accurately assembling two molds using a positioning spacer.

Plastic lenses are polycarbonate or poly(meth)
Although they may be manufactured by injection molding or compression molding of thermoplastic resins such as acrylates, cast molding is usually used to manufacture plastic lenses with excellent performance and physical properties. Liquid curable compounds that serve as raw materials for plastic lenses include monomers and their prepolymers that have one or more Q,P unsaturated groups, monomers that have vertically polymerizable groups such as Q,8 unsaturated groups, and epoxy groups, and their There are prepolymers 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 a main component is excellent in various physical properties such as transparency, impact resistance, and scratch resistance, and the most excellent eyeglass lenses can be obtained. In cast molding of plastic lenses, a plastic raw material such as a monomer is filled into a cavity between two molds held by a wind gasket.

This is usually done through three basic steps: curing the material by heating or the like, and then removing the mold and taking out the lens. In step (2), 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 combined with this gasket. The opposing surfaces of the two molds have the necessary curves for the lens.

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 materials assembled in step (■) is placed in a heating furnace, etc.
Harden plastic raw materials. In order to minimize lens distortion and ensure uniform polymerization, curing takes at least several hours.
It usually takes more than one day and night. (2) 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, and the gasket is not reused, but the glass mold can be used for the next casting. 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 of the mold gap 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. In addition, polymerization curing usually requires long heating, so
Gaskets are also required to be heat resistant. 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 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 cheap, 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 forming the lens surfaces of two molds (hereinafter referred to as optical surfaces), aligning the oblique angles of the optical surfaces (i.e., the optical axes coincide with each other), 2.
For example, setting the distance between the two optical surfaces to a predetermined distance (defining the thickness of the lens), etc. Furthermore, lenses for astigmatism and the like may require other alignment. 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 tend to cause misalignment of the mold, making it difficult to align the mold. Therefore, the present inventor considered separating the functions of the gasket and aligning the mold without using the gasket.

On the other hand, the present inventors discovered and developed a method for molding a plastic lens without using a gasket. Therefore, in order to accurately assemble a mold and mold a plastic lens without using a gasket, the inventor
We continued to consider how to assemble the mold. As a result, we discovered and developed a method for determining the position of two molds by bringing them into contact via a positioning spacer with a predetermined shape. This positioning base is 2
After the molds have been positioned, they are removed from between the molds. 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 to form a cavity.
The plastic raw material is hardened within this cavity.
The present invention relates to a method for assembling this mold, that is, a plastic lens is molded by curing a plastic raw material mainly composed of a liquid curable compound in a cavity formed between two molds. In the method of assembling the two molds in order to perform the process, the positioning spacer is held between the opposing surfaces of the two molds to position the molds, and then the spacer is removed from between the two molds. This method of assembling a plastic lens mold is characterized in that a cavity is formed around the side surfaces of the two molds by tightly adhering an adhesive tape across the two molds.

As an example of the method of the present invention, a method for assembling a mold for molding a meniscus type concave lens without using a gasket will be described with reference to the drawings.

FIG. 1 is a side view of a mold assembly apparatus shown for explaining the principle of assembling a mold. The two mold holding odors 1 and 2 that hold the two molds are
Column 7 by support village 3, 4 and support arm 5, 6 respectively
is attached to.

One mold holder 2 is fixed to a pillar 7. The other mold holder 1 is movable between it and the support village 3 and/or the support punch 3 and the support arm 5 and can be moved in the horizontal direction. The support arm 5 is also vertically movable along the column 7. These movable parts can be fixed by a method not shown if necessary. Using the apparatus shown in FIG. 1, the molds are held in mold holding smells 1 and 2, and a positioning spacer is placed between the two molds, and the two molds are brought close to each other and the two molds are moved between the two molds and the spacer. The movable parts are fixed in the horizontal direction, the molds are separated in the vertical direction, the baser is removed, the two molds are brought close to a predetermined distance again, and the molds are placed around the sides of the two molds.
Wrap adhesive tape around the two molds to make them stick together. A cross section of a mold assembly assembled in this manner is shown in FIG. The two molds 8 and 9 and the tape 1 that tightly adheres to the sides of the molds 8 and 9 are rolled to form the cavity 1.
1 is formed.

Positioning will be explained in more detail. FIG. 3 is a sectional view showing a state in which two molds 12 and 13 are holding a positioning spacer 14. Positioning surface
The cylinder 14 is a cylindrical body having an inner diameter that allows the molds 12 and 13 to penetrate therein, and has a convex portion 15 on its inner peripheral surface. The mold 12 has a concave spherical surface 16 (hereinafter referred to as an optical surface) forming one side of the lens, and the mold 13 similarly has an optical surface 17 consisting of a convex spherical surface. The optical axis 18 of the two optical surfaces is a line connecting the center of curvature of the optical surface and the center of the optical surface, and becomes the optical axis of the lens to be molded.

One requirement for alignment is to align the optical axes of the two optical surfaces, which is shown in the figure. The positioning of this mold is determined by the contact portion between the molds 12 and 13 and the baser 14. For example, in FIG. 3, the inner surface of the spacer 14 other than the part where the convex part 15 is present [contacts with the side surfaces of the molds 12 and 13], the surface where the optical surface 16 of the mold 12 and the convex part 15 of the baser 14 contact ,
Optical surface 17 of mold 13 and convex portion 15 of baser 14
This is the line where the ends of the lines touch. The distance between the two molds is determined by the inside of the convex portion 15 of the spacer 14.

By predetermining the length of the inside to a predetermined length, the distance between the centers of the two optical surfaces of the mold can be easily determined.
In order to perform positioning, at least one of the molds must be movable until the positioning is completed.

Further, when using a positioning spacer as shown in FIG. 3, it is necessary to move the mold to remove it from between the molds after positioning. When using the apparatus shown in FIG. 1, after determining the position of the mold in the state shown in FIG. To prevent mold movement in this direction, the mold is fixed in this direction. next,
The molds are moved in the direction of the optical axis 18 to increase the distance between the two molds and the positioning spacer 14 is removed from between the two molds. Next, the molds are brought closer to the optical axis 18 direction again, and the distance between the molds is set to a predetermined distance. If the distance between the molds at the time of positioning is determined in the convex portion 15 of the positioning spacer 14, then the position can be compared with the position after this movement to set the predetermined distance. can. Even if the distance between the molds is unknown at the time of positioning, the distance between the molds can be determined by touching the centers of both molds, determining the distance ○, and determining the distance between the molds by the subsequent movement distance. Distance can be determined. After the position in this optical axis direction is determined, the mold is also fixed in this direction. This fixation of the mold or the fixation of the mold in the direction perpendicular to the optical axis is sufficient to the extent that the position of the mold does not shift during the next handling in which a tape or the like is brought into close contact with the mold. Next, the tape is tightly attached around the two molds that have been positioned and fixed as described above. For example, place two pieces of adhesive tape with an adhesive layer on one side on the sides of two molds with the adhesive side inside.
Place it in close contact with the individual molds. It is preferable that the length of the adhesive tape is such that both ends overlap to some extent. FIG. 2 is a sectional view of a mold assembly in which a sealed cavity is formed by closely adhering adhesive tape. After this, the cavity is filled with plastic raw material. This filling of the plastic raw material can be carried out while the mold assembly shown in FIG. 2 is held in the mold holding odor, but it may also be carried out after the mold assembly is removed from the mold holding odor. The shape stability of this mold assembly is sufficiently high, and there is little risk of the mold shifting even if the mold is not fixed. Filling with plastic raw material is done by peeling off the outside of the overlapping part of the adhesive tape until just before the overlap occurs to form an injection port, and then injecting the plastic raw material from this injection port.A syringe needle is inserted between the tape and the side of the mold. This can be done by inserting a needle, etc., and injecting through the needle, etc. Of course, after filling the plastic material, the cavity is closed again. The examples of the present invention described above with reference to FIGS. 1 to 3 are typical examples, but the present invention is not limited to only this method.

Other possible methods are described below. In FIG. 1, only mold holding odor 1 is movable, but the other mold holding odor 2 may be movable, or both may be movable. The mold holders 1 and 2 may not only mechanically hold the mold, but also hold the mold by suction using a vacuum. Further, it is preferable that a distance scale or the like be attached to the pillar 7 to measure the moving distance of the mold. The optical surface of the mold shown in FIG.
It may be convex, convex, or other combinations. The present invention can mold not only a meniscus type concave lens but also various lenses such as a meniscus type convex lens, a planar lens, a flat lens, a trick lens, and a cylindrical lens by changing the mold. While changing the mold, positioning spacer
The shape of the lens may also need to be changed depending on the type of lens to be molded. In addition, it is possible to mold not only lenses of different thicknesses but also lenses of different curvatures using the same positioning spacer. For example, even if the curvature of the mold 13 shown in FIG. 3 changes, the positioning spacer can be used as is. The positioning of a mold with a concave optical surface (for example, mold 1 in FIG. 3) is different from the positioning of a mold with a convex optical surface (for example, mold 2 in FIG. 3).
It is more difficult than the positioning of

For example, in FIG. 3, the positioning substrate 14 and the optical surface of the mold 1 are aligned with the upper surface of the convex portion 15 of the substrate. Because this contact surface is a spherical surface or is in contact with a surface, there is a high possibility that the position will shift. Moreover, since the end of the optical surface of the mold 1 forms an acute angle with the side surface, there is a risk that when the mold 1 is pressed against the spacer 14, the spacer 14 may be deformed, thereby causing a positional shift. In order to solve this problem, it is possible to use a mold that has a concave optical surface, and a mold that has a flat surface, usually a flat surface perpendicular to the optical axis, formed around the optical surface, and a positioning spacer that has a flat surface that is in contact with that surface. preferable. Figure 4 shows the positioning spacer.
A cross section of is shown. The positioning spacer 19 is cylindrical and has a convex portion 20 on its inner surface, and the upper surface 21 of the convex portion 20 is a flat surface. The mold is shown by imaginary two-dot chain lines 22 and 23. By using this positioning spacer 19 and mold 22, the above problem is solved. Although the lens obtained by this method has a flat portion remaining around the periphery, this portion can be removed after forming the lens to obtain a lens with a normal shape. The shape of the positioning spacer is not limited to the cylindrical body having a convex portion on the inner surface as shown in FIGS. 3 and 4.

For example, the convex portion does not need to be present on the entire inner circumference of the cylindrical body, and positioning can be performed by contacting the mold at three points. Similarly, the entire periphery of the cylindrical body body does not need to be hugged by the side surface of the mold. In an extreme case, for example, it is also possible to position the mold using a ring consisting only of the convex portion 15 excluding the main body of the cylindrical body as shown in FIG. The positioning spacer does not need to be a cylindrical body, and may be a columnar body having a recessed portion on the upper and lower surfaces into which the mold penetrates. In this way, the positioning spacer is removed after the mold is positioned, so there is no need to form a cavity between the molds like a gasket, and there is no need to form a cavity between the molds. Since there is no need to seal the space, the shape is not limited as long as it has a function for positioning the mold. The method of removing the positioning spacer from between the molds after positioning the mold by sandwiching the positioning spacer is not limited to the above method. For example, if the positioning spacer is a splittable spacer, the positioning spacer can be disassembled and removed from between the molds without moving the mold at all in the state shown in FIG. Further, in order to remove the positioning spacer from between the molds, it is not necessarily necessary to relatively move the two molds in the optical axis direction. The positioning spacer can be removed by moving it in any direction if possible depending on the shape of the positioning spacer. What is required in this case is to return the mold to its original position. For example, the mold can be moved by touching and fixing a stopper on a positioned mold, moving the mold along a guide to remove the positioning baser, and then moving the mold back along the same guide until it contacts the stopper. It can be returned to its original position. Of course, these methods cannot change the distance between the two molds beyond the distance determined by the positioning spacer. Therefore, a type of positioning spacer is required depending on the thickness of the lens to be molded. The method of moving the mold in the direction of the optical axis is advantageous in that lenses of different thicknesses can be molded using one positioning spacer. The method of the present invention has many advantages over conventional methods of assembling molds using gaskets. First, the positioning spacer according to the present invention has some limitations in terms of material such as flexibility and heat resistance. For example, the positioning spacer can be made of a material that is slightly deformed and has a shape with high dimensional accuracy. Second, the positioning spacer has few restrictions in shape other than those necessary for positioning. For example, gaskets must seal cavities and require provision for injection of plastic materials. Thirdly, the positioning spacer is highly economical. The positioning spacer can be reused many times as long as it does not deform, and there are some restrictions on the material, so it can be used repeatedly for a long period of time using materials that do not deform. I can do it. Moreover, since it is possible to use a positioning spacer that can be used in common for lenses of different shapes to some extent, the number of types of positioning spacers is smaller than the number of types of lenses to be molded. Because it is more economical, it is also possible to use a positioning spacer with finer dimensional accuracy using higher quality materials. All of these advantages allow the mold to be loosened more accurately and thus to mold plastic lenses with higher dimensional accuracy. Adhesive tape, such as the tape described above, is preferably used to seal around the two mold gaps to form the cavity.

Adhesive tape is placed around the sides of the two molds to form a cavity between the two molds and the adhesive tape, and is used to prevent the plastic material from leaking out of this cavity when filled with plastic material. be done. The first feature when using this adhesive tape without using a gasket is that the adhesive tape, such as tape, can easily follow the shrinkage of the plastic raw material. The large shrinkage force generated when the plastic raw material hardens is applied in a direction that brings the two molds closer together, and this follows the movement of the molds by bending the tape toward the cavity side or the opposite side, or by shifting the surface in contact with the mold. Because the contraction force is much higher than the mold's gravitational force and is a force parallel to the optical axis, the tape can bend and will not displace the mold in any direction other than the optical axis. The second characteristic is that, whereas in the past it was necessary to prepare many types of gaskets to match the types of lenses, the method using tape does not require this at all. For example, all types of lenses can be molded with only one type of tape. Of course, the cost of molding the lens can therefore be greatly reduced. In addition, since the basic physical properties required of the tape are merely to have a certain level of strength, improvement in heat resistance can be easily achieved by changing the material. The adhesive tape is not particularly limited in its thickness or material.

The thickness thereof may be thick enough to have a certain degree of flexibility, and therefore, the "film" in the present invention may be referred to as a relatively thick "sheet."
Taking a tape-like material as an example, it only needs to be thick enough to be able to be wrapped around a mold and not peeled off due to the locking properties of the tape itself after it is adhered to the side surface of the mold with an adhesive or the like. Therefore, the thickness of the adhesive tape is not particularly limited, but when it is made of ordinary plastic, a thickness of about one rib or less is easy to use. The lower limit is the thickness that provides strength to the extent that buckling does not easily occur due to the weight of the mold when the mold is assembled. The material of the adhesive tape is also not particularly limited.

For example, it is possible to use a film that does not leak plastic raw materials such as plastic, rubber, paper, metal, cloth, etc. However, plastic is the most suitable material in terms of ease of use and economy. For example, polyolefin plastics such as polyethylene and polypropylene, polyvinyl chloride and polyvinyl chloride (or vinylidene) plastics such as polyvinyl chloride, polyester plastics such as polyethylene terephthalate, polystyrene plastics such as polystyrene and ABS, and nylon. Plastics such as polyamide plastics such as -6, cellulose plastics such as acetate, etc. can be used. These plastic films may be subjected to processing such as stretching or surface treatment, and may contain colorants, stabilizers, fillers, and other additives. The shape of the adhesive tape is most preferably tape-like as described above, but other shapes such as a tubular shape may also be used. Preferably, the tape has at least one surface coated with an adhesive or an adhesive. Various types of these are commercially available and can be easily obtained. Furthermore, it is possible to use a tape that does not have an adhesive or the like, and apply an adhesive or a saddle adhesive to the surface of the tape, the side surface of the mold, or both at the time of use. Tape and other adhesive tapes can be attached to the sides of the mold without the use of adhesives or adhesives. For example, a heat-shrinkable film can be used to heat and bring the film into close contact. Note that in the present invention, the term "tape" refers to a sealing film having a substantially constant inside and a length longer than the inside. The type of adhesive or adhesive is not particularly limited either.

The pressure-sensitive adhesive is generally rubber-based, and the adhesive is generally curable plastic-based. Among these,
Materials that easily dissolve in the plastic raw material are unsuitable, and materials that easily peel off due to the hydraulic pressure of the plastic raw material when the mold is assembled are unsuitable. Glass molds are the most common and widely used molds, but plastic molds have also been proposed.

Although a glass mold is most suitable for the present invention, it is not limited thereto, and molds made of materials other than glass can also be used. The liquid curable compound that is the raw material for the plastic lens in the present invention is not particularly limited either.

However, as mentioned above, diethylene glycol bisallyl carbonate called CR-39 is the most excellent raw material for plastic lenses. Of course, CR-39 is not only used alone;
Diallyl carbonate, diethylene glycol bismethallyl carbonate, ethylene glycol bisallyl carbonate, other allyl carbonates other than CR-39, unsaturated alcohol esters such as diallyl phthalate, triallyl isocyanurate, diallyl benzoate, methyl Unsaturated acid esters such as methacrylate, glycol dimethacrylate, diethylene glycol dimethacrylate, and glycidyl methacrylate, styrene, unsaturated polyester resins, and other Q and B liquids at room temperature.
It may be copolymerized with a monomer having an unsaturated group or a prepolymer thereof. However, monomers and prepolymers containing at least 4% by weight CR-39 and preferably 6% by weight are excellent raw materials for plastic lenses. In addition to the above-mentioned furyl carbonates, unsaturated alcohol esters, unsaturated esters, etc., curable compounds that can be used alone or copolymerized with other monomers or prepolymers containing CR-39 to form plastic lenses include the above-mentioned furyl carbonates, unsaturated alcohol esters, unsaturated esters, etc. Unsaturated polyester resin, epoxy resin and other Q,
8. There are monomers with unsaturated groups and their prepolymers. Plastic raw materials are mainly composed of the above-mentioned liquid curable compound, but usually also contain a small amount of a radical polymerization catalyst.

The radical polymerization catalyst may be any catalyst as long as it can initiate radical polymerization of the curable compound, but peroxides are preferred, such as penzoyl peroxide, diisopropyl peroxycycarbonate, etc. It is. Other plastic raw materials may also contain colorants such as dyes, ultraviolet absorbers, fillers, and other various additives.

[Brief explanation of drawings]

FIG. 1 is a side view of the mold assembly apparatus, and FIG. 2 is a cross-sectional view of the mold assembly. FIG. 3 is a cross-sectional view showing a mold positioned with a positioning spacer, and FIG. 4 is a cross-sectional view showing another example of the positioning spacer. 1, 2...
・Mold holder, 8, 9, 12, I3...mold,
10... Adhesive tape, 11... ．．・Cavity, 14, 19... Positioning baser. Tano drawing hair 2 drawing multi drawing hair 4 drawing

Claims (1)

[Claims] 1. A method of assembling two molds in order to mold a plastic lens by curing a plastic raw material containing a liquid curable compound as a main component in a cavity formed between the two molds. In this step, the molds are positioned by sandwiching a positioning spacer between the opposing surfaces of the two molds, and then the spacer is removed from between the two molds. A method for assembling a plastic lens mold, which comprises forming a cavity by closely adhering an adhesive tape across the two molds. 2. The method according to claim 1, wherein the positioning spacer is removed by relatively moving the two molds in the optical axis direction. 3. The method according to claim 1, wherein the adhesive tape has an adhesive layer or an adhesive layer provided on its surface.