JPS63179728A - Manufacture of plastic lens - Google Patents

Abstract

PURPOSE:To eliminate securely weld lines for any type of concave lens and shorten the molding cycle by filling molten resin into a cavity almost on an optic axis of a plastic lens to be molded, molding the plastic lens and finishing a gate forming optical surface of said plastic lens smoothly after molding. CONSTITUTION:As a hot tip 9 of a plastic concave lens prepared by an injection molding die, shown in the drawing No.1, is positioned in the center of a cavity 4, resin is flowed radially just after being injected into the cavity 4 to eliminate forming joint sections of each resin or containing of capture of air which generates weld lines. Next, a hot cutter 18 is heated up to a given temperature by a heater 21 and lowered while being revolved facing downward in the axial direction. By said process, a gate 10 is cut and the cut surface is finished smoothly. After that, a given volume of a material 24 having almost similar refractive index as that of the lens 13 is dropped by a syringe 25 on the gate treating surface 23 side of the lens 13. A lens 26 to be laminated next is compressively adhered on the material 24 dropped.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing a plastic lens that is applied to projection televisions, video cameras, etc., and particularly relates to a method for manufacturing a plastic lens suitable for concave lenses. It is something.

[Conventional technology]

The conventional manufacturing method for this type of plastic lens is as follows:
As shown in FIG. 1, resin flows from a side gate 11 into a cavity 4 formed between a fixed fitting and a movable fitting. The inflowing resin flows along the cavity inner wall 4m as shown by arrow 12 because the thickness of the outer peripheral part of the concave lens is thicker than the thickness of the central part. A welded portion 4b between the resins is generated in the gap where the filling is completed, and due to air remaining in the space within the cavity, the resins cannot be brought into close contact and remain as a weld line.

Therefore, the injection molding method for lenses and lens blanks described in Japanese Patent Application Laid-open No. 53-93850 involves forcibly discharging the air or weld line remaining on the opposite side of the gate into the gap where the cavity has been filled to the outside of the cavity. , Weld countermeasures are being taken.

However, in the method described in the above-mentioned publication, a resin reservoir portion communicating with the cavity is constructed in consideration of the location where the weld line occurs, resulting in a poor resin yield.

Furthermore, optical materials that take heat resistance and moisture absorption resistance into consideration are expensive, so the lens cost also increases.

Furthermore, there is a problem in application to a concave lens in which the ratio of thickness change between the lens center and the periphery is large. The flow of the resin in the center becomes extremely poor, and it is difficult to remove the weld line by forced flow using the pooling method described above.

[Problem that the invention seeks to solve]

The above conventional technology is limited by the applicable lens shape;
There were problems such as an increase in the manufacturing cost of the lens due to the material yield, and the fact that molding had to be performed at a mold temperature in the thermal deformation region of the molding material, making it impossible to expect dramatic improvements in shortening the molding cycle.

The present invention was made to eliminate the above-mentioned problems, and its purpose is to reliably eliminate weld lines in any concave lens shape, dramatically shorten the molding cycle in lens molding, and It is an object of the present invention to provide a method for manufacturing a plastic lens without adversely affecting optical effects, impairing marketability, or increasing lens cost.

[Means for solving problems]

In order to achieve the above object, the present invention molds a plastic lens by filling a cavity with molten resin from almost on the optical axis of the plastic lens to be molded, and after molding, smooths the gate-forming optical surface of the plastic lens. It is characterized by the fact that it is finished.

[Effect]

In the method for manufacturing a plastic lens according to the present invention, the cavity is filled with resin from above the optical axis of the lens, so that the molten resin flows radially from the center, which is the thin wall portion.

Therefore, there is no residual air or a mating surface where resins merge together, and no weld lines are generated.

Furthermore, by smoothing and finishing the gate-forming optical surface of the lens after molding, the invasiveness on the gate-forming optical surface is improved and diffused reflection due to air entrainment can be prevented. Therefore, a lens can be obtained in which the gate marks do not have the same adverse effect optically or visually.

[Metal practice]

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic sectional view of an injection mold for carrying out the method of manufacturing a plastic lens of the present invention. In the figure, 1
indicates a mounting plate, which has a mounting hole (not shown) or flange 1a that is fixed between the molding machine die plates. 2 is a fixed mold plate, and 3 is a movable mold plate, both of which hold a fixed fitting 5 and a movable fitting 6 that constitute a cavity 4 for molding a lens.

A movable insert piece 7, which forms a part of the cavity 4, is slidably fitted into the movable insert 6.

This movable inserting piece 7 is connected to a hydraulic cylinder 8, and in order to compensate for the volumetric contraction caused by the cooling of the molten resin filled in the cavity 4 by the operation of the hydraulic cylinder, it moves in the lens thickness direction and cools and solidifies. It also has the function of extruding lenses from within the mold.

On the other hand, the fixed fitting 5 connects the tapered part 5a and the mounting plate 1 so that the chip part 9a of the hot chip 9 for filling the cavity 4 with resin protrudes by a predetermined dimension into the cavity space.
It is sandwiched between.

The above-mentioned hot chip 9 has a well-known function that is generally widely applied as a hot runner, and a heater (not shown) in the chip is heated in accordance with the injection timing of the molding machine to melt the The cavity is filled with resin.

The tip hole diameter, ie, the gate diameter d, is extremely small from the viewpoint of preventing internal strain.

Basically, any diameter is sufficient as long as the resin can pass through it at a given injection pressure and temperature, and according to this experiment, a diameter of at most 0.5M is sufficient for filling, and the internal strain is 0.
A value of 5° or less is preferable.

FIG. 2 is a model diagram showing the resin flow within the cavity 4 of a plastic concave lens obtained by the injection mold of FIG. 1 having the above-described configuration. As shown in FIG. 2, since the hot tip 9 is located at the center of the cavity 4, that is, on the optical axis of the lens, the resin flows radially immediately after being injected into the cavity 4, causing the resin to weld. No merging or air entrainment can occur.

However, although the gate 10 has an extremely small diameter, it remains on the lens surface after molding as a gate mark. Therefore, it is necessary to perform gate treatment on the lens surface as described below. To make the gate visually clear and optically unaffected, there should be no irregular light refraction and scattering on the gate.

Now, if we take an example in which a concave lens is molded with a gate provided on the incident light side, the ray diagram shown in FIG. 3 is obtained.

In other words, light that enters parallel to the optical axis from the optical surface 14 of the lens 13 obtained by optical design is directed to the optical surface 14 of the lens 13.
At gates 15 and 15, the light is refracted regularly with a predetermined refraction, as shown by the solid line, but at the gate 10, the light is refracted in a direction different from the optical surface, as shown by the broken line. Light refracted in a direction different from the optical surface not only affects optical performance but also can be visually observed, resulting in a significant loss of commercial value.

A solution to eliminate this obstacle is to form a new optical surface 16, as shown in FIG.

In this embodiment, the gate 10 is connected to the new optical surface 1
Gate 1 is hidden by the resin layer 17 forming Gate 6.
No unnecessary refraction at 0 occurs.

However, in order to prevent internal refraction from occurring at the boundary between the new resin layer 17 and the lens 13, it is important to select a material whose refractive index is close to that of the lens 13 for the resin layer 17.

Usually, polycarbonate resin is used as the concave lens material, and the refractive index of the resin is n=1.584.

Examples of materials used for the resin layer 17 forming the new optical surface 16 include styrene (n = 1.591) and chlorobenzyl methacrylate (n = 1.582).
), phenyl vinyl ketone (n = 1.586)
There is.

In the embodiment shown in FIG. 4, since the thickness t of the resin layer 17 is large, the applicable range is narrowed. Therefore, the embodiment described below relates to a method of configuring the thickness t of the resin layer to be extremely thin, and relates to a method of performing gate treatment before forming a new resin layer 17.

FIG. 5 is an example of an apparatus for carrying out this method. In FIG. 5, the same parts as those in FIG. It is directly connected to the rotating shaft 19. This rotating shaft 19 is movable in the axial direction.

21 is a heater fixed to the rotating shaft 19. The output of this heater 21 is variable, so that the temperature of the hot cutter 18 can be adjusted.

n is a stepped portion 22a that holds the flange portion 13a of the lens 13;
It is a lens holder with a This lens pedestal n is relatively arranged so that the center of the stepped portion 22a and the center of the hot cutter 18 are coaxially aligned.

In this apparatus having the above configuration, the lens 13 is arranged such that the gate 10 faces the hot cutter side, and the flange part 13
a into the stepped portion 22a, the center of the gate 10 and the center of the hot cutter are aligned and set up.

The hot cutter 18 is heated in advance to a predetermined temperature by the heater 21, and is lowered while rotating downward in the axial direction. As a result, the gate lO is cut and
The cutting surface is finished smoothly due to the heating effect.

The finished surface of the gate should be smooth enough to prevent light scattering due to air entrainment on the cutting surface when forming the new resin layer described above, and the temperature of the hot cutter 18 should be higher than the thermal deformation temperature of the lens 13. A temperature below the glass transition temperature is suitable.

Another example of obtaining such a smooth cut surface is to cut the gate in advance using a cutter such as a drill or milling cutter, and then finish it smoothly using a heated stylus (crimping tool). be. In either method, a suitable cut surface can be obtained.

Next, the lens 13 that has been cut by the method described above is
An example of a method for forming a new resin layer on the treated surface of the substrate will be described. FIGS. 6 and 7 show a manufacturing example in which a bonded lens for the front lens of a zoom lens is manufactured using a lens 13 that has been injection molded and then subjected to a cutting process.

First, as shown in FIG. 6, a predetermined amount of material having a refractive index similar to that of the lens 13 is dropped onto the gate-treated surface side of the lens 13 using a dispensing machine or a syringe 5.

Next, the process moves to the step shown in FIG. 7, and the lens 26 to be bonded is pressed onto the dropped material. The dropped material 24 spreads to the boundary between the lens 13 and the bonded lens 26, and excess resin spills out from the boundary shoulder 27.

In this case, by accurately measuring the weight of the drop,
The amount of overflow can be adjusted to a very small amount, and no wiping operation is necessary.

This bonding process is a method widely applied to glass lenses and the like, and can be accurately bonded without special techniques.

The composite lens obtained by the above method is completed as a lens in which not only the gate-treated surface % but also the presence of the resin layer has no influence optically or visually.

Another embodiment of the present invention relates to a method applicable when the center wall thickness of the concave lens is relatively thick. As shown in FIG. 5, this method can omit the step of gate processing using a cutter or the like.

FIG. 8 is a schematic sectional view of the gate portion showing this embodiment, and the line is a hot chip having the same function as the hot chip 9 shown in FIG. A needle valve 30 is built concentrically within this hot tip row, and a heater (not shown) is built therein.

A spring 32 is attached to the rear end 30a of this needle valve 30, and this spring constantly presses the needle valve 30 downward.

A resin flow path communicating with a molding machine nozzle (not shown) is formed on one side of the hot tip collar 28a.

This resin flow path communicates with a runner 34 formed in the manifold 29, and this manifold has a built-in heater that can heat the resin to a temperature that allows the resin to flow.

On the other hand, the tip 30b of the needle valve 30 is pressed by the action of the spring 32 and is in contact with the tapered portion 28c of the hot tip tip 28b. The hot tip tip 28b projects into the space of the cavity 4 by a distance t.

This protrusion amount t is set to be equal to or larger than the gate height 4) that remains as a gate mark after completion of molding.

Next, the functions of the apparatus having the above configuration will be explained. The resin is filled into the cavity 4 using a molding machine nozzle (not shown).
The melted resin is injected from the sprue part 34a. At this time, since the manifold 29 is heated to a temperature at which the resin can easily flow, the resin passes through the runner 34 and the resin flow path 35 and reaches the resin flow path 35 in the hot chip. Since the heater built into the spindle 3o is instantaneously heated in conjunction with the injection timing of the molding machine, the resin injected from the molding machine can instantly reach the resin flow path 35 in the hot chip.

The resin pressure in the resin flow path 35 increases, pressure is applied to the tapered portion 3°C against the force of the spring 32, and the spindle (9
) is pushed upward. Therefore, a gap is formed between the tapered portion 28c of the hot tip 4 and the needle valve tapered portion 30c, and the resin flows into the cavity 4.

As shown in FIG. 9, the thus obtained concave lens has a trapezoidal depression 35 with a depth t, and a gate 10 with a diameter of about dm and a height of 4 is formed in the center. . It is desirable that the height 4 of the gate 10 is smaller than the recess depth t.

The thus obtained concave lens 13 has a glossy and smooth surface because the depressions 35 and the gate 10 are formed at high temperature. Therefore, even if the resin for bonding is injected and the compound lens is exploded by the method explained in FIGS. 6 and 7, there will be no optical or visual problem. The shape of the recess 35 obtained by this method must not have sharp edges that may cause warping of the lens after molding. Preferably, an arcuate depression as shown in FIG. 10 is optimal.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, since the resin is filled into the cavity from almost on the optical axis of the plastic lens to be molded, it is not limited by the lens shape and can be applied to any kind of concave lens. Also, the occurrence of weld lines can be prevented. Along with this, restrictions on molding conditions are also lifted.

That is, since the mold temperature can be set low, the cooling time of the resin filled in the cavity can be shortened.

Furthermore, by forming a new resin layer on the gate-treated surface, an optical lens can be obtained that does not adversely affect optical performance and marketability.

When manufacturing a bonded lens, the process is the same as the conventional lens manufacturing process, so the manufacturing cycle is shortened, and the material yield is improved by creating a molded product without sprues or launches. Effects such as reduction in manufacturing costs are achieved.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an injection mold for carrying out the method of manufacturing a plastic lens of the present invention, and FIG. 2 is a plan view of a cavity showing the flow behavior of the filled resin in the method of manufacturing a plastic lens of the present invention.
Figures 3 and 4 are cross-sectional views of a plastic lens showing the principle of gate concealment, Figure 5 is a schematic diagram of the gate cutting machine, and Figure 6 is a schematic diagram of the gate cutting machine.
7 is a schematic diagram showing the procedure for bonding another optical lens to the plastic lens obtained by the manufacturing method of the present invention, and FIG.
The figure is a cross-sectional view of the hot tip part showing another injection mold for carrying out the method of manufacturing a plastic lens of the present invention, and FIGS. 9 and 10 are cross-sectional views of the plastic lens obtained by the method of manufacturing the present invention. , FIG. 11 is a plan view of a cavity showing the flow behavior of filled resin in a conventional manufacturing method. 4...Cavity 9...Hot chip 1
0, 11...Gate 13...Concave lens 1
7...New optical surface 18...Hot cutter 26...Laminated lens 27...Laminated resin agent Patent attorney/JS Katsuo Kawa-1゜1st
Fig. 2 - Kiyan 11 Fig. h '

Claims (11)

[Claims] (1) Molten resin is filled into a cavity from substantially on the optical axis of the plastic lens to be molded to mold the plastic lens, and after molding, the gate forming optic filled with the molten resin is smoothed and finished. A method of manufacturing plastic lenses. (2) The method for manufacturing a plastic lens according to claim (1), wherein the maximum diameter of the gate is 0.5 mm or less. (3) The method for manufacturing a plastic lens according to claim (1), wherein the molded plastic lens is a concave lens. (4) Claim (1) characterized in that a depression is formed around the gate so that the gate height is equal to or lower than the gate-forming optical surface.
2. Method for manufacturing a plastic lens described in Section 1. (5) The method for manufacturing a plastic lens according to claim (4), wherein the depression formed around the gate has an arc shape. (6) The method for manufacturing a plastic lens according to claim (1), wherein the gate is cut to be equal to or lower than the gate-forming optical surface. (7) The method for manufacturing a plastic lens according to claim (2), wherein the cut surface is finished smooth by heat. (8) Claim (6) characterized in that a resin having a refractive index almost equivalent to that of a plastic lens is formed on the gate cutting trace so that it is equal to or higher than the optical surface on which the gate is formed. The method for manufacturing a plastic lens according to item (7) or item (7). (9) In order to bond another optical lens to the gate-forming optical surface, a bonding resin having approximately the same refractive index as the plastic lens is injected into the gate-forming optical surface after cutting the gate. Said claim No. 6
) or (7), the method for producing a plastic lens. (10) A method of manufacturing a plastic lens according to claim (9), characterized in that the plastic lens is designed to be constructed in a front lens portion of a zoom lens. (11) A new optical surface is formed on the gate-forming optical surface using a resin having a refractive index almost the same as that of a plastic lens, and the thickness of this new optical surface is made equal to or thicker than the gate height. A method for manufacturing a plastic lens according to claim (1).