JPH02164516A - Molding method of plastic concave lens and die - Google Patents

Abstract

PURPOSE:To prevent generation of a weldline and shorten a molding time, by a method wherein a concave lens is molded by making a temperature of a die part forming the side of the outer circumference of a concave lens cavity a higher temperature than that of the die part forming an optical surface of the cavity. CONSTITUTION:At the time of pouring of thermoplastic resin within a die, only a sleeve 8 forming the side 8a of the outer circumference of a concave lens cavity 5 is heated and gas collected to a renotch of a weldline is discharged outside of a die cavity 5. In this instance, a stationary insertion piece 6 and movable insertion piece 7 forming the top 6a of an optical surface and the bottom 7a of the optical surface of the cavity 5 are cooled. Consequently, generation of the weldline on an injection-molded concave lens can be prevented, heat capacity of a die fluctuating a die temperature can be reduced, cooling of molten resin poured within the cavity 5 can be performed efficiently and a molding cycle of the concave lens can be shortened.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a plastic concave lens, and particularly to a molding method and mold for a plastic concave lens using a thermoplastic resin manufactured by an injection molding method or an injection compression molding method. It is something.

[Conventional technology]

Conventional plastic concave lens (hereinafter referred to as concave lens)
The molding method will be explained using FIGS. 4, 5, and 6. Fig. 4 is a sectional view showing the structure of a concave lens, Fig. 5 is a plan view of the concave lens in the molding process by a conventional molding method, and Fig. 6 is a sectional view taken along line AA in Fig. 5, where 1 is a concave lens, and 1a is a The upper surface of the concave lens, 1b is the lower surface of the concave lens, 1c is the side surface of the concave lens, 1d is the gate of the concave lens, 2a is the upper surface of the cavity of the concave lens, 2b is the lower surface of the cavity of the concave lens, 3 is the weld line, and 4 is the notch.

The opening and the arrow mark indicate the direction of resin flow.

As shown in FIG. 4, a concave lens
d is thicker than the center side. Therefore, when injection molding or injection compression molding is performed using a thermoplastic resin (PC resin or 1) MMA resin), the resin flowing through the gate branches once, as shown by A and C in Fig. 5. It flows ahead of the outer circumferential side surface 1d of the lens and merges again.

This results in a weld line 3, a joining line of resin flow.

According to the conventional method, 1. Using a normal concave lens molding mold (or referred to as a mold), the mold temperature is kept at a low temperature (below 150°C).
When the cross section of the weld line produced when molding is enlarged, as shown in FIG. 6, it becomes a V-notch 4 with a width and depth of about 1 to 5 μm. This v-notch 4 appears as a linear defect in appearance.

Therefore, in the method proposed in JP-A No. 61-19327, when injecting resin into a mold when molding a plastic concave lens, the mold temperature is set to the flow temperature of the resin (for PC resin and RMMA resin, 170 ℃), the resin in contact with the cavity surface of the mold is kept in a fluid state, and the weld line 3 is erased by fusing the resin at the location where the weld line 3 occurs.

[Problem to be solved by the invention]

In the conventional concave lens molding method described above, the temperature of the entire resin surface layer in contact with the cavity surface of the mold is made higher than the flow temperature of the resin during the resin injection stage, and the resin near the weld line is fused to close the weld line. In order to extinguish the metal, it was necessary to heat the entire mold to a high temperature as described above.

Furthermore, after the resin is injected into the mold, the entire mold needs to be cooled so that the lens molded product can be taken out.

In addition, in this concave lens molding method, in order to prevent weld lines, the temperature of the entire mold changes up and down during the molding cycle, so it takes time to change the temperature of the mold with a large heat capacity and to cool the resin. There was a problem in that it required electric power costs to raise and lower the mold temperature and the molding time became longer.

An object of the present invention is to reduce the cost required for raising and lowering the mold temperature, shorten the molding time, and make it possible to mold a plastic concave lens that can prevent the occurrence of weld lines.

[Means to solve the problem]

The main structure of the present invention adopted to solve the above-mentioned problems is that, in a method for molding a plastic concave lens, a concave lens is molded using a thermoplastic resin by an injection molding method or an injection compression molding method. In the molding method, when injecting the thermoplastic resin into a mold, the temperature of the mold part that forms the outer circumferential side of the concave lens is higher than the temperature of the mold part that forms the optical surface of the concave lens. In a molding mold for a plastic concave lens, the optical surface of the concave lens is formed in a molding mold for a plastic concave lens in which the concave lens is injection molded or injection compression molded using a thermoplastic resin. A mold member and a mold member forming the outer peripheral side surface of the concave lens are separated, the mold member forming the optical surface of the concave lens having a cooling means, and the mold member forming the outer peripheral side surface of the concave lens having cooling means. The mold member has built-in heating means and cooling means, or has means capable of switching between heating and cooling, or the mold member forming the optical surface of the concave lens has cooling means. , a mold member forming the outer circumferential side surface of the concave lens is made of a low thermal conductive material, and is provided in contact with a first mold member forming the outer circumferential side surface of the concave lens; It is characterized by comprising a second mold member that either incorporates heating means and cooling means or is provided with means that can switch between heating and cooling.

[Effect]

First, the mechanism by which weld lines and V-notches occur during molding of plastic concave lenses will be explained using drawings of embodiments of the present invention to be described later.

In the molding die according to the embodiment of the present invention shown in FIG. 1, a concave lens cavity (hereinafter referred to as cavity) 5 includes a fixed insert piece 6, a fixed die 13, a fixed heat insulating ring 22, a movable insert piece 7, and a movable die. 14, a movable sleeve (hereinafter referred to as sleeve) 8, and a movable heat insulating ring 23.

In this mold, when molding is performed at the same temperature as the mold part that forms the outer peripheral side surface of the concave lens and the mold part that forms the optical surface, after the molding starts.

When the resin is injected into the cavity 5 in the mold, the space volume of the part of the cavity 5 that is not filled with resin becomes smaller.
The air in the mold and the gas pressure of the volatile components emitted from the injected molten resin increase, and as a result, the gas (including air, hereinafter the same) in the mold increases as the pressure increases between the mating surfaces of the fixed and movable sides of the mold. The gap 28 formed by the parting surfaces 26 and 27 (see Fig. 2) (even if the parting surfaces 26 and 27 are mating surfaces, there is a gap when viewed microscopically) and the fixed insert forming the cavity 5. Piece 6. Gap 24 between movable insert piece 7 and sleeve 8
', 25', and 28 (see Figure 2), and most of it is discharged out of the mold. Then, at the stage M just before the resin completely fills the cavity 5, the 4+1 resin is applied to the parting surfaces 26 and 27, the fixed insert piece 6°, the movable insert piece 7, and the sleeve 8.
The gap 24'25' formed by the bonding surfaces of 28 and 28 fills the entrance and exit leading into the cavity 5. Therefore, the gas gathered at the V-notch 4 of the weld line 3 has nowhere to escape. As the resin pressure within the cavity 5 continues to rise, the gas collected at the weld line 3 is compressed.

When the mold temperature is low, the resin is cooled while trapping gas in the joint of the resin flow (weld line 3), so the part where the gas is trapped is as shown in Figure 6. It becomes V-notch 4.

Next, the main effects of the plastic concave lens molding method of the present invention will be explained.

If the molds are molded at the same temperature, the notch 4 will occur as described above.In contrast, in the present invention, the mold part that forms the outer peripheral side of the concave lens is heated to a high temperature, and the optical part of the concave lens is Since the mold part that forms the surface is molded at a low temperature, the fixed side (fixed insert piece 6, fixed mold 13, fixed side insulation ring 22, etc.) and movable side (movable insert piece 7. It is located between the sleeve 8 and the fixed insert piece 6 and movable insert piece 7 that constitute the cavity 5 and the gap 28 of the parting surfaces 26 and 27, which are the mating surfaces of the movable type 14 and the movable heat insulating ring 23, etc. Resin 30, 31 blocking the gap
．． 32 is a sleeve 8 forming the outer peripheral side surface 8a of the lens.
By means of heating means 12 provided therein, it is possible to maintain a high temperature molten state which can easily flow or deform.

Therefore, as the resin pressure inside the cavity 5 increases,
The gas gathered at the notch 4 of the weld line 3 is compressed and becomes high pressure, passes through the passage in the space along the weld line 3 formed by the notch 4, and passes through the gaps 24' and 2.
5', 28, the resin 30, 31. is maintained in a hot, easily flowing or deformable molten state.
．． 32 and escapes to the outside of the cavity 5, the gap 24,
It can be discharged out of the mold through the 25° 28, thereby making it possible to minimize the size of the notch 4 in the well line 3. Note that if the sleeve 8 is made of a low thermal conductivity material, while the sleeve 8 itself is kept at a high temperature, the heat released from the sleeve 8 to other mold materials can be minimized, and the temperature rise of other mold materials can be minimized. It can be done. With this configuration, while the sleeve 8 is kept at a high temperature, the fixed insert piece 6. which forms the optical surface upper surface 6a and the optical surface lower surface 7a. A fixed insert piece 6. A relatively low temperature medium is circulated through the cooling holes 9 and 10 provided in the movable insert piece 7 to form an upper optical surface 6a and a lower optical surface 7a, which occupy most of the surface area of the concave lens. The resin in contact with the movable insert piece 7 can be cooled.

After the gas collected in the V-notch 4 of the weld line 3 is discharged to the outside of the mold, the heater 12 provided on the sleeve 8 forming the outer peripheral side surface 8a of the concave lens stops generating heat, and the optical surface -
Fixed input pieces 6 that form the L field surface 6a and the lower surface 7a of the field surface. By making the cooling holes 9 and 10 provided in the movable human piece 7 and the cooling hole 11 provided in the sleeve 8 function together, the cavity 8
The entire resin inside can be cooled down to a temperature that allows it to be taken out.

Furthermore, a concave plastic lens without weld lines can be molded in a significantly shorter molding cycle than in the past.

〔Example〕

Examples will be described below.

FIG. 1 is a cross-sectional view of an embodiment of a molding die used in the method of molding a plastic concave lens of the present invention, and FIG. 2 is an explanatory diagram schematically showing an enlarged main part of FIG. The basic structure of the plastic concave lens injection mold used is the same as the conventional injection mold.

In these figures, 5 is a concave lens cavity, 6 is a fixed insert piece that forms the optical surface upper surface 6a of the concave lens cavity 5, and 7 is a fixed piece.
Similarly, 8 is a movable piece that forms the lower optical surface 7a, and 8 is a sleeve that also forms the outer peripheral side surface 8a.
is made of ceramic with low thermal conductivity, and cooling holes 9 and 10 are provided in the fixed insert piece 6 and the movable insert piece 7, respectively.
The sleeve 8 is provided with cooling holes 11 and a heater 12.

In other words, fixed input pieces 6. Movable piece 7. A concave lens cavity 5 is formed by the sleeve 8. The upper end of the sleeve 8 is located at almost the same position as the outer peripheral end of the fixed insert piece 6, but the lower end is located at a position where the heat from the sleeve 8 is transferred to the movable insert piece 7 when the heater 12 generates heat. In order to minimize this, the extended surface of the lens outer circumferential side surface 8a of the sleeve 8 contacts the outer diameter side surface 7b of the movable inserting piece 7, and the length of the temple part is shortened to a minimum of about 5 m. be.

13 is a fixed type, 14 is a movable type, 15 is a gate, 16 is a runner, 17 is a spool, 18 is a fixed side insulation plate, 19 is a fixed plate, 20 is a movable side insulation plate, 21 is a movable plate, 22 is a fixed side insulation plate The ring 23 is a movable heat insulating ring. Fixed side insulation board 18. Movable side insulation board 19. Fixed side insulation ring 2
2. Like the sleeve 8, the movable side insulation ring 23 is made of ceramic with low thermal conductivity, and when the heater 12 inside the sleeve 8 generates heat, it prevents the heat from the sleeve 8 from being transmitted to the entire mold. It is designed to play the role of

The fixed insert piece 6 and the fixed mold 13 face each other with a gap 24 in between, and the fixed insert piece 7 and the fixed side heat insulating ring 22 face each other with a gap 24 in between.
4', the movable insert piece 7 and the sleeve 8 face each other with gaps 25 and 25' in between, and the fixed side heat insulating ring 22
and fixed mold 13 and sleeve 8. The movable side insulation ring 23 and the movable mold 14 are parting surfaces 26 on the fixed side and the movable side.
．． The sleeve 8 and the movable mold 14 are opposed to each other with a gap 29 formed between them. Gap 24
, 25.29 serve as a heat insulating space, and the size of the gap is about 1 square inch. Further, the size of the gaps 24' and 25' is minute, about 5 to 10 μm, and the gap 28'
are even smaller minute gaps, and these gaps 24'
, 25', 28, even if the flow of the resin 30, 31, 32 enters, only a slight flash occurs.

During molding, a medium at a relatively low temperature of about 80° C. is constantly circulated through the cooling holes 9 and 10 to maintain the fixed insert piece 6 and the movable insert piece 7 at a low temperature.

The heater 12 inside the sleeve 8 starts generating heat when the resin is injected into the mold, and while the resin is being injected into the cavity 5, the sleeve 8 is kept at a temperature higher than the flow temperature of the resin (approximately 170°C for PC resin). Maintain at a high temperature. After the heater 12 stops generating heat, the cooling hole 11 in the sleeve 8 circulates the above-mentioned medium to bring the sleeve 8 to the same temperature as the fixed insert piece 6 and the movable insert piece 7.

That is, when molding is started, the flow of resin that has entered the cavity 5 is 42 in FIG.

As shown by the arrow C, one flow precedes the side surface 1c of the concave lens molded product, and the flow C merges at the weld line 3. The flow of resin flows through the spool 17, runner 16.
Gate 15. Most of the air collected while flowing through the cavity 5 and the gas released from the resin flow through the gaps 24' and 2.
4.25'25.28 and is discharged to the outside of the cavity 5.

However, before the resin completely fills the cavity 5, the aforementioned gases are collected in the V-notch 4 of the weld line 3 and the flow of resin 30, 31, 32 is directed to the gap 24', as shown in FIG. Fill the entrance and exit of cavity 5 of 25'28. However, during the resin injection stage, the sleeve 8 is maintained at a high temperature higher than the flow temperature of the resin due to the heat generated by the heater 12, so the resins 30, 31, and 32 filling the entrances and exits of the gaps 24', 25', and 28 remain at high temperatures. It is maintained in a molten state where it can easily flow or deform.

When the pressure of the resin in the cavity 5 increases and the gas gathered in the notch 4 of the weld line 3 is compressed and becomes high pressure, it passes through the passage formed by the notch 4 of the weld line 3 and flows into the gap 24'25. ' , 28, the molten resin 30°31.32, which is at a high temperature and can easily flow or deform, is pushed away, creating an escape route and opening the gap 2.
4'24.25', cavity 5 through 25.28
escape outside. In this way, most of the gas gathered in the notch 4 of the weld line 3 can be discharged out of the cavity 5, and the size of the notch 4 can be minimized.

During this time, the resin in contact with the optical surface upper surface 6a and the optical surface lower surface 7a forming the lens optical surface in the cavity 5 is maintained at a low temperature. It can be cooled by the movable input piece 7.

After the gas gathered in the V-notch 4 of the weld line 3 is discharged to the outside of the cavity S through the gaps 24', 24.25', and 25.28, the heater 1 in the sleeve 8 is
2, and the cooling hole 11 in the sleeve 8 also has about 8
The medium at 0''C begins to circulate. By doing this, all the resin in the cavity 5 can be cooled, so that it can be taken out as a plastic concave lens molded product.

As explained above, the sleeve 8, fixed insert piece 6°, movable insert piece 7. Gap 24', 2 between fixed side heat insulating ring 22
Since the resin 30°31.32 filling the entrances and exits of weld lines 5' and 28 can be maintained at a high temperature that can easily be buried or deformed, the gas collected in the V-notch 4 of the weld line 3 can be absorbed by the pressure of the gas itself. The flow of resin 30°31.32 filling the gaps 24', 25', and 28 can be pushed away, the aforementioned gas can be discharged out of the cavity 5, and the V-notch 4 of the weld line 3 of the concave lens can be minimized. can. Furthermore, during this time, the fixed insert piece 6 and the movable insert piece 7 that form the optical surface of the lens can be kept at a lower temperature than the sleeve 8, so that the resin can be efficiently cooled. Further, when raising or lowering the mold temperature, it is only necessary to raise or lower the temperature of the sleeve 8, which has a small heat capacity, so that the time required to raise or lower the mold temperature can be shortened. In this way, a plastic concave lens with virtually no weld lines can be molded in a shortened molding cycle.

According to the results of the experiment, the width and depth of the V-notch of the weld line were minute, 0.01 to 0.03 μm, and the weld line was invisible to the naked eye and could be virtually erased. Furthermore, in this embodiment, when increasing or decreasing the mold temperature, it is only necessary to change the temperature of the sleeve 8 that forms the lens outer circumferential side surface 8a. By fusing the resin, we can significantly reduce the heat capacity of the mold, which increases and decreases the mold temperature, compared to the case where weld lines were erased and molding took a long time. The optical surface upper surface 6a occupies the area.

Optical surface lower surface 7a, fixed input piece 6. Since the temperature of the movable insert piece 7 can be lowered to the lower temperature during molding, the cooling efficiency of the resin can be improved.
By eliminating weld lines, we were able to significantly shorten the molding cycle for plastic concave lenses compared to conventional methods, making it possible to mold in less than half the molding time.

FIG. 4 is a cross-sectional view of the main parts of another embodiment of the present invention.
The same parts as in the figures and FIG. 2 are given the same reference numerals. The difference between this embodiment and the embodiments shown in FIGS. 1 and 2 is that the sleeve 8 is connected to the first sleeve 8A on the side of the movable insert piece 7 and the movable die 1.
and a second sleeve 8B on the fourth side. The first sleeve 8A is made of ceramic, which is a low heat conductive material, and forms the outer circumferential side surface 8a of the concave lens.The second sleeve 8B is made of ordinary steel, in which the heater 12 and cooling holes 11 are provided. By controlling the temperature of the first sleeve 8B, the temperature of the first sleeve 8A forming the outer peripheral side surface 8a of the concave lens is indirectly controlled. can be reduced.

By using a low heat conductive material for the first sleeve 8A forming the outer circumferential side surface 8a of the concave lens, when the first sleeve 8A is heated, the fixing pieces forming the upper optical surface 6a and the lower optical surface 7a of the concave lens are heated. 6. Heat leakage to the movable input piece 7 can be reduced. In addition, the outer peripheral side surface 8 of the concave lens
The second sleeve 6 in contact with the first sleeve 8A forming a
If B is made of a copper-based alloy which is a highly thermally conductive material, the heating and cooling rate of the first sleeve 8A forming the outer circumferential side surface 8a of the concave lens can be increased, which has the effect of further shortening the molding cycle.

In addition, in the embodiments shown in FIGS. 1 and 2, the heater 12 and the cooling hole 11 are provided inside the sleeve 8 to heat and cool the sleeve 8, but only a medium passage inside the sleeve 8 is provided to allow the medium to flow therein. It goes without saying that the temperature of the sleeve 8 can be controlled by first switching the temperature of the medium to a high temperature and then to a low temperature.

〔Effect of the invention〕

According to the present invention, the gas collected in the V-notch of the weld line can be discharged to the outside of the cavity by heating only the sleeve 8 forming the outer circumferential side surface 8a of the lens, thereby virtually erasing the weld line, and at the same time, during this time, Fixed insert piece 5 forming the upper optical surface 6a and lower optical surface 7a of the concave lens. The movable insert piece 6 can be cooled. Therefore, it is possible to reduce the heat capacity of the mold which raises and lowers the mold temperature, and also to maintain the sleeve 8 forming the outer circumferential side surface 8a of the concave lens at a high temperature where the resin easily flows or deforms. A fixed insert piece 6. constitutes the upper surface 6a of the lens optical surface and the lower surface 7a of the optical surface, which occupy most of the surface area. Since the movable inserting piece 7 can be kept at a lower temperature than the sleeve 8, it is possible to improve the cooling efficiency of the resin compared to the conventional method and to mold a plastic concave lens with no weld lines in a shortened molding cycle.

In other words, the present invention enables the molding of a plastic concave lens that reduces the cost required for raising and lowering the mold temperature, shortens the molding time, and prevents the occurrence of weld lines. It is highly effective.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an embodiment of a molding die used in the method for molding a plastic concave lens of the present invention, FIG. 2 is an explanatory view schematically showing an enlarged main part of FIG. Similarly, FIG. 4 is a sectional view of another embodiment of the molding die, FIG. 4 is a sectional view showing the structure of the concave lens, FIG. 5 is a plan view of the concave lens in the molding process by the conventional molding method, and FIG. It is an AA sectional view. 5... Cavity (concave lens cavity), 6...
Fixed insert piece, 6a...Optical surface upper surface, 7... Movable insert piece,
7a... Optical surface lower surface, 8... Sleeve, 8a... Outer peripheral side, 9.10.11... Cooling hole, 12... Heater, 13... Fixed type, 14... Movable type , 22...
Fixed side insulation ring, 23... Movable side insulation ring, 8A
...First sleeve, Figure 1 inferior 2-Douuma 3 Figure 8a, -- Lido Torimata page 11

Claims (1)

[Claims] 1. In a method for molding a concave plastic lens using a thermoplastic resin by an injection molding method or an injection compression molding method, when injecting the thermoplastic resin into a mold, 1. A method for molding a plastic concave lens, characterized in that the temperature of a mold part that forms the outer peripheral side surface of the concave lens is higher than that of a mold part that forms the optical surface of the concave lens. 2. In a plastic concave lens molding method in which a concave lens is molded using a thermoplastic resin by an injection molding method or an injection compression molding method, the optical surface of the concave lens is formed when the thermoplastic resin is injected into a molding die. The mold member that forms the optical surface of the concave lens is heated to a lower temperature by a cooling means provided in the mold member that forms the optical surface of the concave lens; A method for molding a plastic concave lens, characterized in that molding is carried out by heating a mold member that forms the outer peripheral side surface of the concave lens to a high temperature by means of means and cooling means or means capable of switching between heating and cooling. 3. The method for molding a plastic concave lens according to claim 1 or 2, wherein the temperature of the mold portion forming the outer peripheral side surface of the concave lens is within the flow temperature range of the thermoplastic resin. 4. In a plastic concave lens molding mold for injection molding or injection compression molding a concave lens using thermoplastic resin,
A mold member forming an optical surface of the concave lens and a mold member forming an outer peripheral side surface of the concave lens are separated,
The mold member forming the optical surface of the concave lens has a cooling means, and the mold member forming the outer peripheral side surface of the concave lens,
A mold for forming a concave plastic lens, characterized by having a built-in heating means and a cooling means, or a means capable of switching between heating and cooling. 5. The mold for forming a plastic concave lens according to claim 4, wherein the mold member forming the outer circumferential side surface of the concave lens is made of a low heat conductive material. 6. In a plastic concave lens mold for injection molding or injection compression molding a concave lens using thermoplastic resin,
A mold member forming an optical surface of the concave lens and a mold member forming an outer peripheral side surface of the concave lens are separated,
The mold member forming the optical surface of the concave lens has a cooling means, and the mold member forming the outer peripheral side surface of the concave lens,
A first mold member made of a low thermal conductivity material and forming the outer circumferential side of the concave lens; and a first mold member provided in contact with the first mold member and having built-in heating means and cooling means, or heating and cooling means. A mold for molding a concave plastic lens, comprising a second mold member provided with a hand that can be switched. 7. The molding die for a plastic concave lens according to claim 6, wherein the low thermal conductivity material is ceramic. 8. The mold for forming a plastic concave lens according to claim 6, wherein the second mold member is made of a copper-based alloy. 9. At a position surrounding the mold member forming the optical surface of the concave lens at the part where the mold member forming the outer peripheral side surface of the concave lens and the mold member forming the optical surface of the concave lens are in contact, the outer periphery of the concave lens is placed. A mold for forming a plastic concave lens according to any one of claims 4 to 8, further comprising a heat shielding member for reducing heat leakage from the mold member forming the side surface.