JPH03219936A - Injection molding method and mold for plastic lens - Google Patents

Abstract

PURPOSE:To prevent a distortion from generating with uneven cooling shrinkage, by a method wherein a solidification speed which varies according to a thickness distribution of a lens molded body is controlled evenly by accelerating the speed forcibly with cooling in relation to thick part and delaying it with heating by magnetic induction heating or a heating fluid in relation to a thin prt. CONSTITUTION:A heating device 12 with a magnetic coil 14 and magnetic substance is provided on the circumference of front molds 3a, 4a for molding a convex lens and a device 13 with a flow path 16 of a cooling fluid is provided on the central part forming a thickness of a lens. The heating device 12 with an electromagnetic coil 14 is provided on the central part of the front molds 3a, 4a for molding a concave lens and a cooling device 13 with the flow path 16 is provided on the fringe part. At the time of molding of the convex lens, acceleration in solidification of a thick part is contrived by feeding the cooling fluid into the flow path 17 of the central part, a electromagnetic coil 20 in a flow path 18 of the fringe part is electrified and control of cooling and solidification of a thin part is contrived. Then at the time of molding of the convcave lens, electromagnetic coil 19 of the flow path 17 is electrified, the cooling fluid is fed into the flow path 18 and unification of cooling and solidification speeds is performed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of molding a lens by injecting and filling a cavity of a mold with molten plastic, and a mold for the same.

[Prior Art] When a molded product with a large difference in wall thickness distribution is injection molded, cooling and solidification progresses from thinner parts to thicker parts. Furthermore, shrinkage in thin and thick parts due to cooling and solidification differs greatly, and residual distortion occurs due to uneven shrinkage.

Therefore, when molding lenses that require dimensional accuracy,
During the cooling and solidification process, the entire product is compressed, thereby preventing distortion.

[Problem to be solved by the invention] However, the amount of compression of the molded product by the mold is extremely small, and thin-walled parts are likely to be overcompressed, so it is technically difficult to solve the problem using the conventional technology. Although it is possible to remove internal distortions such as filling distortion and orientation distortion through compression operations, it is difficult to completely eliminate shrinkage distortions caused by non-uniform cooling shrinkage.

This invention was conceived in view of the above circumstances, and its purpose is to eliminate the difference in solidification rate due to the difference in wall thickness distribution of the lens molded body, and to reduce the distortion caused by uneven cooling shrinkage by controlling the temperature around the cavity to 11J II. An object of the present invention is to provide a method for injection molding a plastic lens and a mold device that can easily prevent the occurrence of.

[Means for Solving the Problems 1] A feature of the plastic lens injection molding method of the present invention according to the above object is that when molding a lens by cooling the molten plastic injected into a cavity, the thickness distribution of the lens molded body is improved. The aim is to uniformly control the different assimilation rates by forcibly accelerating the thicker portions by cooling and delaying the thinner portions by heating with electromagnetic induction heating or heating fluid.

One of the mold devices used in the above method, when the molded product is a convex lens, includes a fixed and movable base mold equipped with a cooling means, a nested mold inside the base mold,
A cavity for molding a convex lens provided in the parting part of the pair of nested molds, a heating means using electromagnetic induction heating means or heating fluid provided around the cavity sides of both nested molds, and a heating means using heating fluid provided at the center of both nested molds. and a cooling means using a flow path provided in the section.

In addition, one of the features of the mold device is a cavity for molding a concave lens provided in the parting part of a pair of nested molds, and an electromagnetic induction heating or heating fluid provided in the center of the cavity side of both nested molds. It consists of a heating means and a cooling means using a flow path provided along the periphery of both nested molds.

Furthermore, the mold device includes a cooling channel provided concentrically in the center and periphery of the cavity side of both nested molds, and an electromagnetic induction system using an electromagnetic coil housed in each cooling channel. It consists of both a heating element, and can be used alternately for heating or cooling depending on the shape of the cavity provided therein, and can be used to mold both concave and convex lenses by replacing only the cavity. .

A plurality of sets of nesting molds equipped with the heating and cooling means described above are installed at required intervals in fixed and movable base molds equipped with cooling means, and the cavities in each nesting mold are placed on the fixed side. When a multi-cavity mold is constructed by connecting a runner placed from the center of the base mold, a cooling path that cuts off thermal interference between the nested molds is connected to the base mold. Provided between the child mold and the child mold.

[Function] In the injection molding method of the present invention, by accelerating the solidification rate by cooling the thick-walled parts and suppressing cooling assimilation by heating the thin-walled parts, the difference in the solidification rate of each part of the lens molded body due to cooling is greatly reduced. The melted layer becomes smaller and the melted layer covers the entire area, and the layer thickness becomes uniform and completely disappears.

[Example] The drawing shows a mold device for lens molding, which includes a base mold 1 on the fixed side, a base mold 2 on the movable side, and a cylinder fitted in four places on the base molds 1 and 2. Shape nesting type 3, 4
The base mold 1.2 is also provided with a cooling water channel 5 for keeping the mold temperature at a predetermined temperature, similar to a normal mold.

As shown in Figure 2 and below, the above insert mold 3.4 is the front mold 3.
It consists of a pair of front molds 3a and 4a and a rear mold 3b and 4b, and a cavity 6 for lens molding is formed in the parting part of the pair of front molds 3a and 4a.

Such a nesting die 3.4 is fitted into cylindrical receiving members 7 and 8 fitted to the base mold 1.2, respectively, but the movable nesting die 4 is used for compression. The rear mold 4a is connected to the press plate 10 at the tip of the plunger t9 and is fitted so as to be movable in the axial direction.

The cavity 6 is connected at the side to a runner 11 provided in the parting part from the center of the stationary base mold 1, and the cavities 6 on each of the four sides are connected through the runner 11.
can be simultaneously injected and filled with molten plastic.

The front molds 3a and 4a of the nested molds 3 and 4 are provided with a heating means 12 for delaying the cooling and assimilation of the molten plastic forming the thin part of the lens, and a heating means 12 for delaying the cooling and assimilation of the molten plastic forming the thick part of the lens. Further cooling means 13 are provided. The setting positions of these two means are determined by the cross-sectional shape of the lens to be molded.

As shown in Fig. 2, in the nested mold 3.4 equipped with a cavity 6 for molding a convex lens, the peripheral edge of the cavity 6 forms the thinnest part of the lens, so the molten plastic in that part is cooled and solidified. For the purpose of suppressing, the front type 3a, 4
The heating means 12 consisting of an electromagnetic coil 14 and a magnetic body 15 is provided around the lens a, and the heating means 12 is provided in the central part where the thick wall of the lens is formed.
The cooling means 13 are provided with cooling fluid channels 16 which facilitate cooling assimilation.

Furthermore, as shown in Fig. 3, in the nested mold 3.4 equipped with a cavity 6 for molding a concave lens, the thickness distribution of the lens is opposite to that of a convex lens, with the thickness being thinner at the center and thickening toward the periphery. Since the heating means 12 is formed in the center of the front molds 3a and 4a, the heating means 12 is provided with an electromagnetic coil 14,
A cooling means 13 formed by the flow path 16 is provided at the peripheral portion.

The example shown in FIG. 4 is the rear mold 3b of the nested molds 3 and 4.

Flow channels 17° 18 of the required width are concentrically provided in the center and peripheral portions of 4b, and electromagnetic coils 19° 20 are housed in each channel, so that both can be used alternately. .

With such mold equipment, when molding convex lenses,
Cooling fluid is supplied to the central channel 17 to promote assimilation of the thick walled portion, and the electromagnetic coil 20 in the peripheral channel 18 is energized to suppress cooling and solidification of the thin walled portion due to heating. be able to.

Also, when molding a concave lens, the electromagnetic coil 1 of the flow path 17
9 is energized and a cooling fluid is supplied to the flow path 18, the cooling solidification rate can be made uniform.

Therefore, the mold apparatus can be used for molding both concave and convex lenses by simply replacing the front molds 3a and 4a that form the cavity 6.

In addition, in a mold device equipped with a plurality of cavities 6, heat interference tends to occur between adjacent cavities; This can be prevented by providing cooling channels 21 that cut off heat between the nested molds.

In the above embodiment, electromagnetic induction heating is used as the heating means, but the heating means may also be a heating fluid.

Next, the present invention will be described in detail using injection molding of a convex lens using the mold apparatus shown in FIG. 2 as an example.

First, a nesting mold 3.degree. 4 is heated to a temperature above the glass transition point of the lens molding plastic (180.degree. to 190.degree. C.).

This heating is performed by energizing the electromagnetic coil 14 and passing a high-frequency magnetic flux through the nested molds 3 and 4 made of magnetic material, thereby generating an eddy current inside the nested mold. This can be easily done by the Joule heat generated by If necessary, heating may also be performed from the center of the nested mold by supplying roaring hot oil to the flow path 16.

Molten plastic is then injected into the mold apparatus to fill the cavity 6. Since the cavity 6 is maintained at a temperature above the glass transition point, the lens molded body 22 in the cavity shown in FIG. 5 does not solidify but maintains a molten state.

After filling is completed, the movable nesting mold 4 is pressurized in the axial direction using the compression plunger 9 to compress the molten lens molded body 22. This compression removes internal distortions such as filling distortions and orientation distortions in the lens molded body.

In parallel with this compression operation, cooling of the lens molded body is started. The rate at which each part of the lens molded body solidifies due to cooling is different, and the molten part disappears from the thinner part, so in order to eliminate this and completely disappear, heating from the periphery is left as it is, and the melted part disappears from the center part. Low-temperature oil is supplied to the flow path 16 to forcibly promote cooling of the thick-walled portion.

Such operations of promoting solidification by cooling and suppressing cold solidification by heating are performed in consideration of the solidification progress balance between thick and thin portions.

As a result, the lens molded body 22 is cooled with a temperature gradient symmetrical to the central axis, and the thickness of the internal molten layer 23 becomes uniform throughout.

This cooling operation is carried out until the melt [123] becomes almost uniform. After that, when the entire lens molded body is uniformly cooled, the molten layer 23 inside the lens molded body uniformly decreases in layer thickness and solidifies without being biased towards the thick side.

[Effects of the Invention] As described above, the present invention controls the solidification rate of the entire lens molded body by both cooling and heating, and completes cooling by making the thickness of the molten layer inside the molded body uniform. Therefore, even if there is a significant difference in wall thickness of the lens molded body, shrinkage distortion due to cooling does not occur, and a plastic lens with high shape accuracy can be injection molded more easily than before.

In addition, since the overall cooling temperature is controlled by both cooling and heating, it is easy to obtain a temperature gradient that corresponds to the wall thickness distribution of the lens molded object, and delicate temperature control is also possible. Injection molding can be carried out under the same means regardless of the

Furthermore, since the cavity is formed by a nested mold and a cooling means and a heating means are provided therein, lenses with different thickness distributions can be molded simply by replacing the nested mold.
With electromagnetic induction heating and heating with a heating fluid, it is easy to heat the entire thin wall part, and with electromagnetic induction heating in particular, it is easy to control the temperature, and it is easy to set the temperature balance for a specific molded object under the cooling means. It has characteristics.

[Brief explanation of drawings]

The drawings show an embodiment of a mold used for injection molding of a plastic lens according to the present invention. Fig. 1 is a front view with half of the movable mold cut away, and Fig. 2 is a diagram showing a convex lens mold. 3 is a plan sectional view of a mold for molding concave lenses;
FIG. 4 is a plan sectional view of the shared mold, and FIG. 5 is a sectional view showing the solidification process of the lens molded body. 1...Fixed side base mold 2...Movable side base mold 3...Fixed side nesting mold 4...Movable side nesting mold 6... Cavity 11... Runner 13... Cooling means 14.19.20... Electromagnetic coil 16.17.
18.21-...Cooling fluid flow path 22...
Lens molded body 23 --- Molten layer 3a --- Front mold 4a --- Rear mold 7.8 --- Receiving member 12 --- Heating Means 1 Figure 4 Procedural Amendment Written July 1991 Ueda 1, Display of the Case 1990 Patent Application No. 1E3423 Name of the Invention Plastic Lens Injection Molding Method and Molding Mold 3, Person Making the Amendment Related Applicant Name Nissei Jushi Kogyo Co., Ltd. 4゜Agent Address 1-1-5 Minami Aoyama-chome, Minato-ku, Tokyo Date of Notice of Reasons for Refusal (voluntary) Date of Heisei 7゜Contents of Amendment (1) Description No. Page 5, 1st line, ``Depending on the difference'' is corrected to ``Depending on the difference.'' ■ In the 3rd line of page 7, ``Construction'' has been corrected to ``Construction''. that's all

Claims (8)

[Claims] (1) When molding a lens by cooling the molten plastic injected into the cavity, the solidification rate of the lens molded body, which varies depending on the wall thickness distribution, is forcibly accelerated by cooling for thick parts, and A method for injection molding a plastic lens, characterized in that heating is delayed and equally controlled for each part. (2) The method of injection molding a plastic lens according to claim 1, wherein the thin portion is heated by electromagnetic induction heating. (3) The method of injection molding a plastic lens according to claim 1, wherein the thin portion is heated by a heating fluid. (4) fixed and movable base molds equipped with cooling means;
A nesting mold inside the base mold, a cavity for molding a convex lens provided in the parting part of the pair of nesting molds, and an electromagnetic induction heating means provided around the cavity side of both nesting molds; A mold for molding a plastic lens, characterized by comprising a cooling means using a flow path provided in the center of both nested molds. (5) fixed and movable base molds equipped with cooling means;
A nesting mold inside the base mold, a cavity for molding a concave lens provided in the parting part of the pair of nesting molds, and an electromagnetic induction heating means provided at the center of the cavity side of both nesting molds; A plastic lens molding die characterized by comprising a cooling means using a flow path provided along the periphery of both nested molds. (6) A plastic lens mold according to claim 4 or 5, characterized in that a fluid heating means is provided in place of the electromagnetic induction heating means. (7) fixed and movable base molds equipped with cooling means;
The nesting mold inside the base mold, the cavity for lens molding provided in the parting part of the pair of nesting molds, and the center and periphery of the cavity side of both nesting molds are arranged concentrically. 1. A mold for forming a plastic lens, characterized by comprising a cooling means formed by a flow path provided therein, and an electromagnetic induction heating means formed by an electromagnetic coil housed in each flow path. (8) fixed and movable base molds equipped with cooling means;
Multiple sets of nesting molds are installed inside the base mold at equal intervals, cavities for lens molding are provided in the parting part of each set of nesting molds, and each cavity is individually A multi-cavity mold comprising a solidification rate control means by cooling and heating provided in the base mold, and a runner disposed in each cavity from the center of the stationary base mold, the base mold and the nesting mold A mold for forming a plastic lens, characterized by having a cooling path for heat insulation between the mold and the mold.