JPS5948735B2 - Plastic lens molding correction method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for correcting molding of plastic lenses, and more specifically, to improving precision and quality of plastic lenses made of thermoplastic resin made by injection/compression molding or cast molding. The present invention relates to a molding correction method for a plastic lens.

As is well known, injection/compression molding methods, casting molding methods, and the like are generally used as molding methods for manufacturing plastic lenses using thermoplastic resins.

Next, an example of these molding methods will be explained based on the drawings.

FIGS. 1A to 1D are cross-sectional views of a molding machine showing the steps in making a plastic lens by the injection molding method described above.
In the figure, numeral 1 is a molded plastic lens;
2 is a spool runner, 3 is a gate, 4 is a movable plate, 5
is a fixed plate, 6 is a movable molding die attached to the movable platen 4, T is a fixed molding die attached to the fixed platen 5, 8
1 is an ejector pin, 9 is a spool head dowel pin, 10 is a molding material injection nozzle, 11 is a mold clamping ram, 12 is a heating cylinder, 13 is a molten plastic material 14 that is inserted into the nozzle 10.
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Concave portions 6b and 7b having curved surfaces equal to both lens surfaces of the plastic lens to be molded are formed on opposing surfaces of the movable mold 6 and the fixed mold 7, respectively. In the injection/compression molding method, as is well known, the molding material is heated and melted, injected into the cavity of the mold formed by the previously closed recesses 6b and 7b, and then cooled and solidified. This is a method of manufacturing molded products by

FIG. 1a shows a heating cylinder 12 in which a movable molding die 6 is attached to a movable platen 4, a fixed molding die 7 is attached to a fixed platen 5, and the heating cylinder 12 has a molten plastic material 14 made of thermoplastic resin inside. The nozzle 10 is shown in a state in which it is pressed and coupled to the injection hole 7a of the fixed molding die 7. From this state, the movable platen 4 is moved in the direction of the arrow a by the clamping ram 11, and the movable mold 6 is pressed against the opposing stationary mold 7, resulting in the state shown in FIG. 1b. Next, the heated and melted plastic material 14 in the heating cylinder 12 is forced into the injection hole 7a of the stationary mold 7 through the nozzle 10 of the screw 13. Then, through the gate grooves 6c and 7c formed in the abutting surfaces of the movable and fixed molds 6 and 7 connected to the injection hole 7a, the molten plastic material 14 enters the recesses 6b and 7c of the molds for molding the lens 1, respectively. 7b is filled. The molten plastic material 14 filled in the mold is then pressurized as shown in FIG.
It is cooled and solidified in this state. Next, after waiting for the filled plastic material 14 to solidify, the movable mold 6 is moved in the opposite direction to the arrow a by the mold clamping ram 11, and the plastic material 14 is attached to the mold 6. The molded plastic lens 1 and the gate 3 and runner 2 connected thereto are pushed out by the ejector pin 8 and spool lock pin 9 to the state shown in FIG. 1d. Then, the plastic lens 1 is obtained by cutting only the lens 1 from the extruded plastic molding material. In this way, the plastic lens 1 is manufactured by injection/compression molding. Next, the case of making a plastic lens by the casting method will be explained with reference to FIGS. 2a-c.

In FIGS. 2a to 2c, reference numeral 21 indicates a molded plastic lens, 22 and 23 are upper and lower casting molds, 24 is a plastic material for molding, and 25 is a guide for guiding the vertical movement of the upper mold 22. Each pillar is shown.

The abutting surfaces of the upper and lower molds 22 and 23 are provided with recesses 22a and 23a that are formed into the same curved surfaces as the upper and lower lens surfaces of the plastic lens 21 to be molded, respectively. In the casting molding method using the casting molds 22 and 23 configured in this way, first, the lower mold 2 is placed in the state shown in FIG. 2a, that is, with the upper mold 22 lifted upward.
A plastic material 24 made of thermoplastic resin softened into a fluid state is poured into the recess 23a of No. 3 in an amount equal to the volume of the lens to be molded, and then the upper mold 22 is pushed down, as shown in FIG. 2b. Next, the softened plastic material 24 is pressed between the concave portions 22a and 23a of the upper and lower molds 22 and 23 to form the desired lens 21. Plastic material 24 poured into the molds 22 and 23
is left for a certain period of time, and a polymerization reaction occurs in the mold using heat, a catalyst, light, etc., and it solidifies into a lens shape. Next, after waiting for the molded lens 21 to cool and harden, the upper mold 22 is pulled upward as shown in FIG.
1 is taken out. The above is the molding method for making plastic lenses, and all of the plastic lenses made in this way are molded and hardened plastic lenses 1, 21.
are taken out from the molds 6, 7, 22, 23 and used as products as they are. However, when the molten or softened plastic materials 14 and 24 are molded, cooled, and hardened, or polymerized and solidified, they shrink, and the thickness is different between the center and the periphery. The curved surface of the lens does not shrink evenly, causing plastic lenses 1 and 21.
Both lens curved surfaces are mold recessed parts 6b, 7b, 22a, 23a.
It has the disadvantage that the curved surface becomes different from the predetermined curved surface. This is a serious drawback in the optical performance of plastic lenses, and is the main reason why they cannot achieve the same optical performance as polished glass lenses. In view of the above points, an object of the present invention is to place a plastic thin piece of exactly the same material as the material of the lens on the curved lens surface of a plastic lens obtained by a conventional molding method, and to form a thin piece of plastic on the lens surface of the same lens. To provide a method for correcting the molding of a plastic lens, which improves the dimensional accuracy of the plastic lens by compensating for shrinkage of the plastic lens by heating, fusing and press-bonding the plastic lens.

According to the present invention, a piece of film made of exactly the same material as the lens is locally heated and fused and pressed onto the lens surface of a plastic lens made by a plastic molding method, so that shrinkage due to cooling and hardening is avoided. To provide a high-precision, high-quality plastic lens with minimal variation in dimensional accuracy, with minimal dimensional errors in the molded plastic lens since it is limited to only the fused and crimped portion of this thin layer and is uniform. I can do it.

Hereinafter, the present invention will be explained based on illustrated embodiments.

FIGS. 3a to 3c are diagrams showing each step of a method for correcting molding of a plastic lens according to an embodiment of the present invention. In the figure, reference numeral 30 denotes a molding correction attachment used in the molding correction method of the present invention, 31 a plastic lens obtained by a conventional molding method corrected by this method, 32 a movable crimping mold, and 33 34 is a sheet-like plastic thin piece made of the same material as the plastic lens 31; 35 is a guide member for vertical movement of the movable crimping mold 32; 36 is a lens molding member for both the pot molds 32 and 33. Curved surface 32
It is a plate-shaped heat insulating material disposed between the opposing surfaces except for a and 33a, and serves to prevent the heat of the heated crimping mold 32 from being conducted to the fixed mold 33. 3T indicates a plastic lens obtained by the molding and capturing method of the present invention. FIG. 3a shows a preparatory stage immediately before correction in the molding correction method of the present invention. The plastic lens 31 is placed on the upper surface of the fixed mold 33.
A lens mounting curved surface 33a is provided that follows one lens curved surface (lower surface), and the curved surface is a lens mounting surface formed of a spherical or aspherical surface. The lens mounting curved surface 33a on the lower surface of the crimping mold 32
A lens pressing curved surface 32a that follows a predetermined other lens curved surface of the plastic lens 31 is provided on the surface facing the plastic lens 31. Further, the movable press mold 32 is heated to the melting point temperature of the plastic lens 31 and the plastic thin piece 34. Next, a shaping correction method of the present invention using the shaping correction device 30 configured as described above will be explained. First, the plastic lens 31 is placed on the lens mounting curved surface 33a of the fixed mold 33 of the molding correction device 30, with one curved surface that follows the above-mentioned mounting curved surface 33a matching. Next, a sheet-like plastic thin piece 34 having substantially the same shape as the upper surface of the lens 31 is placed so as to cover the upper surface of the lens 31. Then, the movable pressing mold 32, which has already been heated to the melting point temperature of the lens 31 and the thin piece 34, is pushed down toward the fixed mold 33, and the lens pressing curved surface 32a of the mold 32 is held under high pressure. It is pressed onto the upper surface of the lens 31 via the thin piece 34. Then, the thin piece 34 melts, fuses and presses onto the upper surface of the plastic lens 31, and is integrated with the lens 31 to form a plastic lens 3T whose shrinkage has been corrected as shown in FIG. 3b. . Next, after stopping the heating of the movable crimping mold 32 and cooling and hardening the lens 37, the movable crimping mold 32 is turned off as shown in FIG.
Pull up and remove it. Each of the above steps has been described for the case of correcting the shrinkage of one lens surface (upper surface) of the plastic lens 31.
When correcting the shrinkage of the other lens surface (lower surface), the lens 31 is turned upside down and a movable press mold having a pressing curved surface formed on a predetermined other lens curved surface of the lens is used. The plastic foil may be fused and crimped to the other lens surface using the same process as described above.

Next, FIGS. 4A and 4B are process diagrams showing another embodiment of the present invention, and are sectional views of a forming correction device 40 used in this method. This molding correction device 40 has lens pressing curved surfaces 42a and 4 formed on a predetermined lens curved surface before shrinkage of a plastic lens 41 made by the above-mentioned molding method.
A movable mold 42 and a fixed mold 43 each having a
A guide member 45 for heating the molds 42 and 43 to a temperature higher than the melting point of the plastic material to press the movable mold 42 against the fixed mold 43 under high pressure, and a curved surface for pressing the lens. Both molds 42 and 43 except 42a and 43a
The curved surfaces 42a and 43a are arranged between the contact surfaces of the
It is composed of a heat insulating material 46 that prevents heat from being conducted to the outside. In order to correct the lens curved surface of the shrunken plastic lens 41 using this device 40, first, as shown in FIG.
As shown in FIG. 3, a sheet-like plastic thin piece 44 made of the same material as the lens 41 is placed on the lens pressing curved surface 43a of the fixed mold 43, and the shrunken plastic lens 41 is placed on top of it. Next, the sheet-shaped plastic thin piece 44 is also placed on the upper lens surface of the lens 41.
Thereafter, both the molds 42 and 43 are heated, and the movable mold 42 is pressed against the fixed mold 43 by the guide member 45 under high pressure.

Then, the molds 42 and 43, which are heated above the melting point temperature of the lens 41 and the thin piece 44, press the sheet-like thin piece 44 onto the upper and lower lens surfaces of the lens 41, respectively, using their lens pressing curved surfaces 42a and 43a. Press. When pressed in this manner, both the thin pieces 44 are melted, fused and pressed onto the upper and lower lens surfaces of the lens 41, and are integrated into the lens 41 to compensate for the shrinkage, as shown in FIG. 4b. A plastic lens 47 is formed. After that, heating of both molds 42 and 43 is stopped, the lens 47 is cooled and hardened, and the movable mold 42 is separated from the fixed mold 43,
Lens 47 is removed.

By the way, in the plastic lenses 37, 47 whose molding has been corrected in this way, the sheet-like thin pieces 34, 44
When fusing, the heating and fusing part is limited to an extremely thin layer along the lens surface, so shrinkage due to cooling is extremely small, and since the thin layers are approximately the same thickness, they are evenly bonded. Shrinked and completed plastic lens 37,
The molding surface 47 may correspond to the lens pressing curved surfaces 32a, 42a, 43a of the molds 32, 42, 43, that is, the predetermined lens curved surfaces that do not shrink the plastic lens.

As explained above, according to the present invention, a plastic lens made by a conventional molding method is corrected for its cylindrical shape,
It is possible to obtain a plastic lens with high precision comparable to a polished glass lens.

[Brief explanation of the drawing]

Figures 1 a to d are cross-sectional views of a molding machine showing the molding process of the injection compression molding method for plastic lenses, and Figures 2 a to c are cross-sectional views of the molding machine showing the molding processes of the cast length molding method for plastic lenses. , FIGS. 3a to 3c are cross-sectional views of a molding correction device according to an embodiment of the present invention, showing the correction steps of a plastic lens correction method, and FIGS. 4A and 4b are sectional views of another embodiment of the present invention. FIG. 3 is a cross-sectional view of a forming correction device, which is an example and shows a correction step of a forming correction method. 1, 21, 31, 37, 47... Plastic lens, 6, 7, 32, 33... Molding mold,
30, 40... Molding correction device, 32...
- Movable mold for crimping, 32a... Curved surface for pressing the lens, 33... Fixed mold, 33a... Curved surface for lens placement, 34, 44... ...Sheet plastic thin piece, 36,46...Insulating material, 42.
...Movable mold, 42a, 43a...Curved surface for pressing lens, 43...Fixed mold.

Claims (1)

[Scope of Claims] 1. A method for correcting a plastic lens made of thermoplastic resin made by injection molding or cast molding, which shrinks below a predetermined dimension during the molding process, A fixed mold having a curved surface for lens mounting that follows the curved surface of one of the lenses of the plastic lens, and a surface of the fixed mold opposite to the curved surface for lens mounting is provided with a predetermined shape of the plastic lens before shrinking. A movable mold for crimping is formed with a curved surface for pressing the lens that follows the curved surface of the other lens.The movable mold is heated to a temperature higher than the melting point of the plastic lens material, and the guide member is pressed against the fixed mold. At the same time, a heat insulating material is interposed between the abutting surfaces of both the molds except for the curved surface for lens mounting and the curved surface for pressing the lens, and the lens mounting surface of the fixed mold is Place the above-mentioned plastic lens on the curved surface for crimping so that the curved surface of one of the lenses follows the curved surface of the plastic lens, and place a sheet-shaped thin piece made of the same material as the lens on the curved surface of the other lens. A method for correcting molding of a plastic lens, the method comprising pressing a movable mold against a fixed mold to fuse and press the sheet-like thin piece to the other curved surface of the lens. 2. A method for correcting plastic lenses made of thermoplastic resin made by injection molding or cast molding, which have shrunk to below predetermined dimensions during the molding process; Using a movable mold and a fixed mold each having a lens pressing curved surface formed on a predetermined lens curved surface, both molds are heated to a temperature higher than the melting point of the plastic lens material, and the mold is pressed against the fixed mold. The movable mold is arranged so as to be pressed with high pressure by a guide member, and a heat insulating material is interposed between the contact surfaces of both molds except for the curved surface for pressing the lens, and the fixed mold is used for pressing the lens. The contracted plastic lens is placed on the curved surface via a sheet-like thin piece made of the same material as the lens, and the sheet-like thin piece is also placed between this lens and the lens pressing curved surface of the movable mold. . A method for correcting molding of a plastic lens, wherein the movable mold is pressed against a fixed mold to fuse and press the sheet-like thin pieces to both lens surfaces of the lens.