JPH0759375B2 - Mold for plastic lens - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a molding die used when a molten plastic is injected and filled into a cavity of a mold to form a lens.

[0002]

2. Description of the Related Art When a molded product having a large difference in wall thickness distribution is injection-molded, cooling and solidification proceeds from a thin portion to a thick portion. Further, the shrinkage amount in the thin portion and the thick portion due to cooling and solidification varies depending on the difference in the rate and the difference in the cooling rate, and the transfer failure occurs due to the uneven shrinkage, so that the precision molding is difficult.

Therefore, when molding a lens that requires high dimensional accuracy, the entire body is compressed during the process of cooling and solidification, thereby preventing generation of flaws and transfer defects.

However, the amount of compression of the molded product by the mold is extremely small, and the thin portion is easily over-compressed, so it is technically difficult. Although internal strains such as orientated strains can be removed, it is difficult to completely remove shrinkage strains or converse compression strains caused by uneven cooling shrinkage.

As a means for removing shrinkage flaws by such non-uniform cooling, the solidification rate, which varies depending on the wall thickness distribution of the lens molded body, is forcibly promoted by cooling the thick wall portion and the thin wall portion is cooled. In the first place, an invention (refer to Japanese Patent Application No. 16423/1990) in which the heating is delayed and the temperature is controlled equally is made.

FIG. 1 shows a specific example of a molding die used for carrying out the invention. The molding die includes a fixed base die 1 and a movable base die 2, and the base die 1. , 2 and cylindrical insert dies 3 and 4 fitted in four places, and the base dies 1 and 2 are not shown in the drawing, but are similar to a normal die, A cooling water passage is provided to keep the mold temperature at a predetermined temperature.

The insert molds 3 and 4 are composed of front molds 3a and 4a and rear molds 3b and 4b, and a pair of front molds 3a and 4b.
A cavity 6 for molding a lens is formed in the parting part a.

The insert molds 3 and 4 are the base mold 1 and
The movable-side insert die 4 is connected to the pressing plate 10 at the tip of the compression plunger 9 by connecting the rear die 4b. hand,
It is fitted so as to be movable in the axial direction.

The cavity 6 is connected to the runner 11 provided on the parting part from the center of the fixed-side base mold 1 at the side portion, and through this runner 11, each of the four cavities 6 can be simultaneously injected and filled with molten plastic. It has become.

The front molds 3a, 4a of the insert molds 3, 4 are provided with a heating means 12 for delaying the cooling and solidification of the molten plastic forming the thin portion of the lens, and a molten plastic forming the thick portion of the lens. A temperature control flow path 13 for promoting cooling and solidification is provided. The setting positions of these two means are determined by the sectional shape of the lens to be molded.

As shown in the figures, in the insert molds 3 and 4 having the cavity 6 for molding a convex lens, the peripheral edge of the cavity 6 molds the thinnest part of the lens, so that the molten plastic in that part is cooled and solidified. Front mold 3 for restraining purposes
The heating means 12 including the electromagnetic coil 14 and the magnetic body 15 is provided around a and 4a, and the temperature control channel 13 is provided in the central portion forming the thick wall of the lens. Further, the temperature control flow path 13 is composed of a dual supply / discharge path 16 for the inside and outside.

In such a molding die, the electromagnetic coil 14
By passing a high frequency magnetic flux through the insert molds 3 and 4 made of a magnetic material to generate an eddy current inside the insert mold, and by the Joule heat generated by the eddy current and the specific resistance of the insert mold, The insert molds 3 and 4 can be heated to a temperature above the glass transition point.

The molten resin injected and filled into the cavity 6 is kept in a molten state because the lens moldings in the cavity do not solidify because the molds 3 and 4 are kept at a temperature above the glass transition point. maintain.

Therefore, when the movable mold die 4 is axially pressed by the compression plunger 9 after the filling is completed to compress the lens molded body in the molten state, the compression causes a filling strain or an orientation strain in the lens molded body. Internal strain is removed.

When cooling of the lens molded body is started in parallel with this compression operation, the solidification speed of each portion of the lens molded body due to cooling is different, and the melted portion disappears from the thin portion, which is eliminated. With the heating from the peripheral edge left unchanged, low-temperature oil is supplied to the flow passage 16 in the central portion so as to disappear entirely, and cooling of the thick portion is forcibly promoted.

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

[0017]

However, as shown in FIG.
A, as shown in FIG. 6A, in the molding die in which the flow path end surface 13a of the temperature control flow path 13 facing the cavity 6 is formed flat, the shape of the optical surface of the lens molded body 22 is uneven. Even if there is, it is difficult to control the temperature of the lens molded body, and uneven temperature distribution is likely to occur as shown in FIGS. 5B and 6B.

This poor temperature controllability is due to the annular corner of the end face of the flow path, and the annular corner causes a sudden change in the temperature control of the lens molded body 22.

Such a problem can be solved by forming the temperature control channel 13 as large as possible so that the end face of the channel faces the entire cavity. There is a limit to the size of the passage 13 and it is difficult to adopt such a means.

The present invention was conceived in order to solve the above problems, and its purpose is to improve the poor temperature controllability by the annular corner portion by a simple means, and to attribute it to the temperature distribution. It is to provide a new molding die for a plastic lens that can eliminate flaws and transfer defects of a product.

[0021]

The present invention according to the above object is provided in a fixed side base die and a movable side base die, a nesting die inside thereof, and a parting portion of the pair of nesting dies. A cavity for lens molding that forms an optical surface and a temperature control channel with dual inner / outer supply / discharge channels provided in the central portion of one or both of the insert molds. The end face of the flow path facing the cavity is formed in a convex spherical shape.

Further, the curvature r of the convex spherical end face of the flow path is r <R in relation to the curvature R of the optical surface on the cavity side, and the spherical region of the end face of the flow path is at least the center point O of the curvature r and the curvature. It exists from the line connecting the outer peripheral end R1 of R, and its temperature control flow path is formed in a spiral shape.

[0023]

[Operation] In the above configuration, since the flow path end surface of the temperature control flow path facing the cavity is formed in a convex spherical shape, even if the flow path end surface has a smaller diameter than the cavity and has an annular corner,
Since the end surface of the flow path faces the entire cavity and the heat conduction is radial, the temperature distribution in the injection-molded lens molded body does not change suddenly, and the temperature control is smoothly performed.

[0024]

Embodiments Embodiments shown in FIGS. 2 and 3 will be described below. The same parts as those in FIG. 1 are designated by the same reference numerals.

FIG. 2A shows a mold for molding a concave lens, and FIG. 3A shows a mold for molding a convex lens. Both molding dies, a cavity 6 for molding a lens that forms an optical surface provided on the parting portions of the pair of insert dies 3 and 4,
The insert mold 4 is provided with a temperature control flow path 13 formed by a dual supply / discharge path 16 provided inside and outside, and a flow path end face 13a of the temperature control flow path facing the cavity is formed in a convex spherical shape. There is.

As shown in FIG. 4, the flow path end surface 1 having a convex spherical surface shape.
The curvature r of 3a is r <R in relation to the curvature R of the optical surface on the cavity side, and the spherical region of the flow path end face is at least from the line connecting the center point O of the curvature r and the outer peripheral end R1 of the curvature R. And the supply passage 16a and the discharge passage 1 of the temperature control passage 16
6b is formed in a spiral shape.

The medium from the supply passage 16a flows into the flow passage end surface 13a while swirling, and because the flow passage end surface 13a has a convex spherical surface, the medium is discharged from the discharge passage 16b while rotating at the flow passage end surface 13a. It becomes difficult to cause the stagnation of the medium.

Even if the flow path end surface 13a has a smaller diameter than the cavity 6 and has an annular corner, the flow path end surface 13a has a convex spherical shape.
Since it faces the entire cavity, heat conduction is performed radially, a sudden change in the temperature distribution does not occur as shown in FIGS. 2B and 3B, and the temperature control of the lens molded body 22 is smoothly performed.

[0029]

As described above, according to the present invention, it is possible to prevent the lens molded body from being deformed due to the sudden temperature change and the defective transfer.
Moreover, since the temperature of the resin also changes uniformly, it is possible to obtain a lens molded body that is faithful to the cavity surface and has good transferability.

Further, since the flow path end surface is formed in a convex spherical shape and the supply path is formed in a spiral shape so that the medium rotates at the flow path end surface, the medium flows out without stagnating. There is very little heat loss due to stagnation, etc., and the temperature control efficiency is further improved compared to when the end face of the flow path is formed flat.
It has features such as enabling fine temperature control based on the temperature distribution.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a plastic lens molding die that can be used for carrying out the present invention.

FIG. 2 is an explanatory view showing a sectional view (A) of a main part and a temperature distribution diagram (B) of a concave lens molding die according to the present invention.

FIG. 3 is an explanatory view showing a sectional view (A) of a main part and a temperature distribution diagram (B) of a convex lens molding die according to the present invention.

FIG. 4 is an explanatory diagram related to the optical surface on the cavity side and the flow path end portion formed in a convex spherical shape .

FIG. 5 is an explanatory view showing a sectional view (A) of a main part and a temperature distribution diagram (B) of a concave lens molding die when a flow path end face is formed flat.

FIG. 6 is an explanatory view showing a cross-sectional view (A) of a main part and a temperature distribution diagram (B) of a convex lens molding die when the flow path end face is formed flat.

[Explanation of symbols]

 3 Nested Type 4 Nested Type 6 Cavity 13 Temperature Control Channel 13a Channel End Face 22 Lens Molded Body

Claims (3)

[Claims] 1. A cavity for lens molding, which forms an optical surface provided on a fixed side base mold and a movable side base mold, a nesting mold therein, and a parting portion of the pair of nesting molds. And a temperature control channel with dual inner and outer supply / discharge channels provided in the central part of one or both of the double-entry type, and the channel end surface of the temperature control channel facing the cavity is formed into a convex spherical shape. A plastic lens molding die characterized by being formed. 2. The curvature r of the convex end surface of the flow path is r <R in relation to the curvature R of the optical surface on the cavity side,
Moreover, the spherical region of the flow path end face has at least the center point O of the curvature r.
The molding die for a plastic lens according to claim 1, wherein the molding die exists from a line connecting the outer peripheral edge R1 of the curvature R and the outer peripheral edge R1. 3. The molding die for a plastic lens according to claim 1, wherein the temperature control channel is formed in a spiral shape.