JP2013132866A - Method for producing plastic lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a plastic lens in which, without heating a die, a resin injected and filled into a cavity can be maintained at a temperature higher than a glass transition temperature of the resin only for a time until the filling of the resin into the cavity terminates, whereby production of a weld line can be prevented.SOLUTION: In producing a minus lens which is small in thickness at the lens center part and large in thickness at the lens peripheral edge part by injecting and filling a molten raw material resin into a cavity 3 formed between a movable die 1 and a fixed die 2, a part or all of a molding surface of at least one of inserts 11 and 12 as cavity forming members is formed by using insulating materials 11a and 12a made of a glass raw material.

Description

  The present invention relates to a method for manufacturing a plastic lens.

  Generally, a plastic lens for spectacles is manufactured by an injection molding method using a thermoplastic resin such as polycarbonate resin or methacrylic resin, and is a plastic lens having a complicated optical surface shape like a progressive power lens. However, high-precision molding is possible by transferring the cavity shape of the mold.

  However, when molding a plastic lens by injection molding, if the lens shape is uneven, the flow of resin in the cavity will be biased, and in a severe case, the quality of the molded plastic lens will be impaired. There is a problem that it ends up.

  For example, when the lens center is thin and the lens periphery is thick like a minus lens (concave lens), the resin injected into the cavity from the gate flows in the lens center. In this way, the resin flowing around the periphery of the lens wraps around the lens so as to fill the cavity, while filling the opposite side of the gate. For this reason, the lens peripheral part on the opposite side of the gate part tends to generate a line-like trace called a weld line when the resin flowing in the cavity wraps around the lens peripheral part and merges, If the weld line occurs, the quality of the molded plastic lens is adversely affected due to defects in appearance and a decrease in strength.

In a general technique related to injection molding, as an example of preventing the occurrence of such a weld line, for example, Patent Document 1 discloses a cavity surface by providing a cavity preheating unit that heats and supplies compressed air in a cavity. A method of preventing the generation of weld lines by spraying hot air and preheating the surface temperature to be higher than the glass transition temperature of the molding resin and then performing injection molding is disclosed.
Further, in Patent Document 2, a heating element is housed in a housing portion formed in a concave shape on the mold surface to heat a region of the mold surface that is expected to cause the generation of a weld line. An injection mold is disclosed.

JP-A-6-143319 JP 2003-80574 A

  However, in these conventional techniques, an apparatus for heating the mold and a mold structure for the apparatus are required, so that the durability decreases due to the complexity of the apparatus and the manufacturing cost increases. There's a problem. Furthermore, if the mold is heated, it takes time to cool and solidify the resin filled in the cavity, which not only lengthens the molding cycle, but also requires excessive energy to heat the mold. There is also a problem that.

  Therefore, the present inventors paid attention to the fact that the resin injected and filled into the cavity is usually set at a temperature higher than the mold temperature, and the cooling and solidification of the resin was injected into the cavity. Starting from the moment, the weld line occurs until the resin is completely filled in the cavity, so if the resin temperature can be maintained at a temperature higher than the glass transition temperature only during this period, the generation of the weld line is prevented. As a result of intensive studies from the viewpoint of being able to do so, the present invention has been completed.

  That is, according to the present invention, the resin injected and filled in the cavity is heated to a temperature higher than its glass transition temperature only until the filling of the resin into the cavity is completed without heating the mold. It is an object of the present invention to provide a method of manufacturing a plastic lens that can be maintained at the same temperature, thereby preventing the occurrence of weld lines.

  The plastic lens manufacturing method according to the present invention injects and fills a melted raw material resin into a cavity formed between a pair of split molds so that the lens center portion has a small thickness and the lens peripheral portion has a thickness. In manufacturing a thick minus lens, a part or the whole of the molding surface that forms the cavity is formed of a heat insulating material made of a glass material, and a raw material resin is injected into the cavity and filled into a predetermined lens shape. There is a way.

  According to the present invention, in manufacturing a minus lens having a thin lens center portion and a thick lens peripheral portion, the mold temperature during injection molding can be set low in order to shorten the molding cycle. Generation of weld lines can be prevented.

It is explanatory drawing which shows an example of an injection molding apparatus. It is sectional drawing which shows the outline of the shaping | molding die with which the injection molding apparatus shown in FIG. It is AA sectional drawing of FIG. It is BB sectional drawing of FIG. It is a principal part expanded sectional view which expands and shows the circumference | surroundings of the cavity in FIG. It is a flowchart which shows each step in embodiment of the manufacturing method of the plastic lens which concerns on this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Injection molding equipment]
FIG. 1 is an explanatory view showing an example of an injection molding apparatus, and the plastic lens manufacturing method according to this embodiment can be implemented by suitably using such an injection molding apparatus.

  The injection molding apparatus shown in FIG. 1 includes a mold 50 having a movable mold 1 and a fixed mold 2 as a pair of split molds divided by a parting line PL, and opening / closing and mold clamping of the mold 50 by a toggle link mechanism 65. A mold clamping device 60, and an injection device 80 that melts, kneads, and measures the raw material resin introduced from the hopper 81 and injects it from the nozzle 85.

[Injection device]
An injection apparatus 80 provided in the injection molding apparatus shown in FIG. 1 has a heating cylinder 82 having a nozzle 85 formed at the tip. Inside the heating cylinder 82, a screw whose rotation and forward / backward movement are controlled by the drive unit 84 is disposed.

  Further, a hopper 81 for feeding pellet-shaped raw material resin into the heating cylinder 82 is connected to the proximal end side of the heating cylinder 82. The raw material resin charged into the heating cylinder 82 from the hopper 81 is melted and kneaded by shearing heat and heating from the heater provided in the heating cylinder 82 while being sheared and pulverized by a screw rotating in the heating cylinder 82. Is sent to a cylinder front chamber formed between the front end of the nozzle and the nozzle 85 and weighed. Thereafter, a predetermined amount of raw material resin that is adjusted to a viscosity suitable for injection molding and in a molten state is injected from the nozzle 85. .

[Clamping device]
In the injection pressure molding apparatus shown in FIG. 1, the mold clamping device 60 has a plurality of tie bars 63 installed between a fixed die plate 61 and a rear plate 62 erected on a gantry 66 at a predetermined interval, and a movable die plate. 64 is configured to be moved by being guided by the tie bar 63. A molding die 50 is attached between the fixed die plate 61 and the movable die plate 64, and a toggle link mechanism 65 is attached between the rear plate 62 and the movable die plate 64.
As a result, when the toggle link mechanism 65 is driven, the movable die plate 64 is guided by the tie bar 63 to advance and retreat, and accordingly, the mold 50 is opened and closed and the mold is clamped.

  Here, the toggle link mechanism 65 is configured so that the screwed crosshead 73 moves along the ball screw 72 as the ball screw 72 connected to a motor (not shown) rotates. When the cross head 73 moves to the movable die plate 64 side, the toggle links 71A and 71B extend linearly by the connecting links 74A and 74B, and the movable die plate 64 moves so as to approach the fixed die plate 61 (advance). To do. On the contrary, when the cross head 73 moves to the rear plate 62 side, the toggle links 71A and 71B are bent inward by the connecting links 74A and 74B so that the movable die plate 64 is separated from the fixed die plate 61. Move (retreat).

[Molding mold]
FIG. 2 is a cross-sectional view showing a cross section of the molding die 50 shown in FIG. 1 cut along a plane perpendicular to the paper surface passing through the central axis, and shows an initial state in which the die is closed. 3 is a cross-sectional view taken along the line AA in FIG. 2, FIG. 4 is a cross-sectional view taken along the line BB in FIG. 2, and FIG. 5 is an enlarged cross-sectional view of the main part showing the periphery of the cavity 3 in FIG. FIG.

  In the examples shown in these drawings, a pair of split molds, a mold 50 and a movable mold 1 and a fixed mold 2 are sandwiched between two movable cavities 3 for molding a plastic lens of a predetermined shape and a gate G. Thus, a runner 49 as a resin flow path connected to each cavity 3 is formed. A sprue bush 47 that forms a sprue 48 connected to the runner 49 at a right angle is attached to the template 10 of the fixed mold 2.

The mold body 4 of the movable mold 1 has two insert guide members 5 and mold plates 6 and 7 for holding them. An insert 11 as a cavity forming member is accommodated inside the insert guide member 5 so as to be slidable in a direction perpendicular to the parting line PL.
The mold body 8 of the fixed mold 2 includes two insert guide members 9 and a template 10, and the insert guide member 9 is held by the template 10 and the mold attachment member 15. An insert 12 as a cavity forming member is accommodated inside the insert guide member 9 so as to be slidable in a direction perpendicular to the parting line PL.
The insert guide members 5 and 9 and the template plates 6 and 10 are provided with a circulation mechanism for circulating a temperature adjusting fluid supplied from a mold temperature adjusting device (not shown).

  A molding die 50 having such a movable die 1 and a fixed die 2 is formed between the movable die 1 and the fixed die 2 in each of the insert 11 on the movable die 1 side and the insert 12 on the fixed die 2 side. A cavity 3 including a molding surface is formed. The cavity 3 is formed corresponding to the shape of the plastic lens to be molded. In the present embodiment, a negative lens (concave lens) having a thin lens center portion and a thick lens peripheral portion is provided. It is a molding target.

  The molding surfaces of the inserts 11 and 12 forming the cavity 3 are formed by a heat insulating material made of a glass material. More specifically, in the insert 11 on the movable mold 1 side, the molding surface corresponding to one surface of the plastic lens to be molded (in the illustrated example, the surface on the concave surface side) is a heat insulating material 11a made of a glass material. The insert 11 is formed by joining the heat insulating material 11a to the insert body 11b. Similarly, the insert 12 on the fixed mold 2 side has a molding surface corresponding to the other surface of the plastic lens to be molded (in the illustrated example, the surface on the convex surface side) formed of a heat insulating material 12a made of a glass material, The insert 12 is formed by joining the heat insulating material 12a to the insert body 12b (see FIG. 5).

As the heat insulating materials 11a and 12a that form the molding surfaces of the inserts 11 and 12, for example, amorphous glass such as crown, flint, barium, phosphate, fluorine-containing, and fluorophosphate Although materials can be used, among these, it is preferable to select and use an amorphous glass material having a thermal conductivity of 0.4 to 1.3 W / m · K as appropriate. Such an amorphous glass material is suitable for forming a molding surface that requires high accuracy and can easily obtain a mirror surface by cutting or polishing, and has excellent moldability. It is suitably used in the present invention.
In addition, it is known that ceramics such as silicon nitride and aluminum titanate have a use as a heat insulating material. However, ceramics are not only brittle and easily cause thermal shock destruction, but also provide a mirror surface. Since high technology and cost are required, considering productivity, it is not suitable for the present invention.
The heat insulating materials 11a and 12a made of such an amorphous glass material have a thickness of 3 to 4 mm so as to sufficiently withstand the injection pressure and holding pressure at the time of injection molding in consideration of molding conditions. It is preferably formed, and surface treatment can be performed with tempered glass or DLC (diamond-like carbon) for the purpose of preventing damage during handling as well as during injection molding.

  Moreover, in order to join such heat insulating materials 11a and 12a to the insert bodies 11b and 12b, the thermosetting resin having a low coefficient of linear expansion and excellent stability in a high temperature environment is used as an adhesive. You can do it. Examples of such thermosetting resins include thiourethane resins using polyisocyanate compounds and polythiol compounds as raw materials, and episulfide resins using episulfide compounds as raw materials. A thiourethane resin which is advantageous in terms of cost is preferable.

  Moreover, although insert body 11b, 12b can be formed using steel materials, such as maraging steel and a beryllium copper alloy, it is preferable to use steel materials with a higher thermal diffusivity than the glass raw material used as a heat insulating material.

  In the mold 50 configured as described above, the mold body 4 of the movable mold 1 is fixed to the movable die plate 64 via the mold mounting member 16, and the mold body 8 of the fixed mold 2 is mounted to the mold. It is fixed to the fixed die plate 61 via the member 15. As a result, the mold 50 is attached between the fixed die plate 61 and the movable die plate 64 of the mold clamping device 60.

  The die mounting member 16 on the movable die 1 side is provided with a hydraulic cylinder 19 corresponding to each of the inserts 11, and a piston rod 21 connected to the piston 20 is fixed to one end side of the hydraulic cylinder 19. The back insert 22 is penetrated. And the T-shaped clamp member 23 provided at the front-end | tip of each piston rod 21 is engaged / disengaged in the T-shaped groove 24 formed in the back surface (surface on the opposite side to the surface in which the molding surface was formed) of the insert 11. It is freely engaged.

  Thus, with the mold 50 opened, the piston rods 21 of the respective hydraulic cylinders 19 are advanced, and the T-shaped clamp members 23 provided at the tips of the piston rods 21 are protruded from the insert guide members 5. Thus, the insert 11 can be exchanged according to the plastic lens to be molded. When the piston rod 21 of each hydraulic cylinder 19 is retracted, the insert 11 attached to the T-shaped clamp member 23 is housed inside the insert guide member 5.

  Similarly, a hydraulic cylinder 26 is provided in the mold mounting member 15 on the fixed mold 2 side so as to correspond to each of the inserts 12, and a piston rod 28 connected to the piston 27 penetrates the mold mounting member 15. doing. A T-shaped clamp member 29 provided at the tip of each piston rod 28 is engaged with or disengaged from a T-shaped groove 30 formed on the back surface of the insert 12 (the surface opposite to the surface on which the molding surface is formed). It is freely engaged.

  Thus, with the mold 50 opened, the piston rod 28 of each hydraulic cylinder 26 is advanced, and the T-shaped clamp member 29 provided at the tip of each piston rod 28 is projected from the insert guide member 9. Thus, the insert 12 can be exchanged according to the plastic lens to be molded. When the piston rod 28 of each hydraulic cylinder 26 is retracted, the insert 12 attached to the T-shaped clamp member 29 is accommodated in the insert guide member 9.

  When the mold body 4 of the movable mold 1 is fixed to the movable die plate 64, the mold body 4 is bolted to the mold mounting member 16 composed of the first member 16A and the second member 16B, as shown in FIG. 17 is attached. At this time, a plurality of disc springs 17 </ b> A inserted on the outer periphery of the bolt 17 are interposed between the mold body 4 of the movable mold 1 and the mold mounting member 16, and the mold body 4 and the mold of the movable mold 1 are interposed. A gap S is formed between the mounting member 16 and the mounting member 16.

The gap S is generated when the movable die plate 64 further advances after the molding die 50 is closed, and the die mounting member 16 guided by the guide pins 18 is pressed against the elastic force of the disc spring 17A. It is designed to be closed. Accordingly, in the illustrated example, each hydraulic cylinder 19 provided on the mold attachment member 16 presses the insert 11 via the back insert 22. Thereby, the volume of the cavity 3 when mold clamping is made variable, and the molten resin injected and filled in the cavity 3 can be compressed by the insert 11.
The guide pin 18 protrudes toward the fixed mold 2 so as to guide the opening / closing operation of the mold 50 and is inserted through an insertion hole formed in the fixed mold 2.

A pressure receiving member 32 is attached to the other end side of the hydraulic cylinder 19 provided on the die attaching member 16 on the movable die 1 side. When the eject rod 34 inserted from the hole 33 formed in the mold attachment member 16 presses the pressure receiving member 32, the hydraulic cylinder 19, the back insert 22 and the insert 11 are also pressed, and the lens molded in the cavity 3 is Extruded.
At the same time, an eject pin 35 is disposed at the center of the mold attachment member 16 so as to be movable back and forth in parallel with the opening / closing direction of the mold 50. When the pressure receiving member 36 attached to the eject pin 35 is pressed by the eject rod 38 inserted from the hole 37 formed in the mold attaching member 16, the eject pin 35 is pushed out.
Therefore, when the mold is opened, the ejected rods 34 and 38 are advanced to take out the molded product.

  As shown in FIG. 4, the spring force of the spring 42 wound around the outer periphery of the eject return pin 41 acts on the pressure receiving member 36 in the left direction in the figure. Although not particularly shown, the pressure receiving member 32 has the same structure so that a leftward spring force acts in the drawing. Thus, when the eject rods 34 and 38 are retracted, the pressure receiving members 32 and 36 are also retracted and returned to the standby position.

  Moreover, the shaping | molding die 50 has the nozzle shut mechanism 90 which obstruct | occludes the nozzle 85 of the injection apparatus 80, as shown in FIG. The nozzle shut mechanism 90 has a nozzle shut pin 91 as a blocking member protruding into the sprue 48 formed by the sprue bush 47. The nozzle shut pin 91 is connected to a piston rod 94 of a hydraulic cylinder 93 via a connecting piece 92, and the hydraulic cylinder 93 is fixed to the mold mounting member 15 by a cylinder mounting plate 95. As a result, when the hydraulic cylinder 93 is driven in a state where the nozzle 85 is in pressure contact with the sprue bush 47, the nozzle shut pin 91 projects into the sprue 48 and closes the nozzle 85, thereby preventing back flow of the resin. Yes.

[Plastic lens manufacturing method]
In order to manufacture a plastic lens using the injection molding apparatus as described above, for example, the steps (ST1 to ST10) shown in the flowchart of FIG. 6 can be sequentially performed.

  In ST1, a resin pressurizing condition is set. This is to adjust the clamping force according to the characteristics of the plastic lens to be molded (lens shape, lens power, etc.) in order to apply an appropriate pressure to the resin in the cavity 3 in advance. It is.

In ST2, weighing is performed. In the injection device 80, the pellet-shaped raw resin charged from the hopper 81 is melted and kneaded by shearing heat and heating from the heater provided in the heating cylinder 82 while being sheared and pulverized by a screw rotating in the heating cylinder 82. While being sent, it is sent to the cylinder front chamber formed between the tip of the screw and the nozzle 85 and weighed. Here, an amount of molten resin necessary for filling the cavity 3, the runner 49, and the sprue 48 is measured.
As the raw material resin, a thermoplastic resin such as a polycarbonate resin or an acrylic resin generally used for molding this type of plastic lens can be used.

  In ST3, the mold is closed at the parting line PL. Specifically, when the toggle link mechanism 65 is driven to advance the cross head 73, the toggle links 71A and 71B extend, and the movable die plate 64 advances toward the fixed die plate 61. 50 molds are closed. At this time, a gap S is maintained in a state where the disc spring 17A interposed between the mold body 4 of the movable mold 1 and the mold mounting member 16 is not compressed, and the fixed mold 2 and the movable mold 1 are separated by the parting line PL. Close the mold. In this state, the gap S is set to the maximum opening amount.

  In ST4, the cavity volume is set. In ST3, the crosshead 73 is further advanced to a preset position (cavity volume setting position) from the state in which the movable mold 1 and the fixed mold 2 are brought into close contact with each other by the parting line PL. As a result, the toggle links 71A and 71B are extended, and the movable die plate 64 is moved toward the fixed die plate 61 and moved to the cavity expansion position. The cavity enlargement amount is determined by setting the crosshead position. As a result, the gap S of the mold 50 is reduced leaving the cavity enlargement. At this time, the volume (thickness) of the cavity 3 is larger than the lens volume (thickness) to be molded, that is, the thickness of the extracted molded product. Further, since the disc spring 17A is compressed, some clamping force is generated as the reaction force.

  In ST5, injection is performed. The molten resin weighed in ST2 is injected into the mold 50 through the passage of the injection nozzle 85. That is, the molten resin introduced into the heating cylinder 82 of the injection device 80 and weighed is injected. Then, molten resin is injected from a nozzle 85 formed at the tip of the heating cylinder 82 and filled into the cavity 3 through the sprue 48, the runner 49, and the gate G. When the molten resin is filled into the cavity 3, the injection speed is controlled to be constant.

  In ST6, the resin is sealed in the mold. After injecting a predetermined amount of resin at T5, the cross head 73 is further advanced immediately before the injection filling of the molten resin is completed. Then, after the injection filling is completed, the nozzle shut pin 91 is protruded into the sprue 48 by the nozzle shut mechanism 90 and the nozzle 85 is closed. Thereby, the filled molten resin is enclosed in the mold 50 in a compressed and pressurized state.

  In ST7, resin pressurization is performed. In ST6, the crosshead 73 starts to advance, and when the crosshead 73 advances to the origin (zero position) and stops, the toggle links 71A and 71B extend, so that the molten resin contained in the mold 51 is compressed. Pressed.

  In ST8, cooling is performed. For this purpose, the temperature of each part (insert, insert guide member, etc.) of the mold 50 is adjusted by the mold temperature adjusting device 51 so that the temperature is set to the Tg point or less according to the lens characteristics to be molded. Perform fluid temperature control. When the molten resin contained in the mold 50 is cooled while being compressed and pressurized, the raw material resin injected and filled in the cavity 3 is solidified as the cooling progresses in the compressed state. By contracting, a plastic lens having a predetermined volume is molded.

  In ST9, a release operation is performed. In the mold release operation, the crosshead 73 of the toggle link mechanism 65 is moved backward toward the rear plate 62 to open the mold 50.

  In ST10, a molded product ejecting operation is performed. When the cross head 73 is retracted to the end, the distance between the movable die plate 64 and the fixed die plate 61 is maximized, and the mold 50 is divided and opened by the parting line PL. When opening the mold, the eject rods 34 and 38 are advanced to take out the molded plastic lens.

  In manufacturing a plastic lens in the above procedure, when the molten resin is injected and filled in the cavity 3 in ST5, the thickness of the center of the lens is the same as that of the minus lens to be molded in this embodiment. When manufacturing a thin plastic lens with a thick lens peripheral edge, the molten resin flowing into the cavity 3 from the gate G is prevented from flowing at the center of the lens by the hesitation phenomenon. The cavity 3 fills the cavity 3 so that the resin flowing around the periphery of the lens wraps around before filling the cavity 3, while filling the cavity 3 so as to merge on the opposite side of the gate G. For this reason, there is a tendency that a line-like trace called a weld line is likely to be generated at the lens peripheral portion opposite to the gate G when the resin flowing in the cavity 3 wraps around the lens peripheral portion and merges. .

In the present embodiment, in order to prevent the occurrence of such a weld line, each of the molding surface of the insert 11 on the movable mold 1 side and the molding surface of the insert 12 on the fixed mold 2 side, which form the cavity 3, respectively. Is formed by the heat insulating materials 11a and 12a made of a glass material. That is, by forming the molding surfaces of the inserts 11 and 12 with the heat insulating materials 11a and 12a made of a glass material, the mold temperature during injection molding can be set low in order to shorten the molding cycle. The temperature of the molten resin flowing into the cavity 3 is suppressed, and the molten resin in the cavity 3 is higher than its glass transition temperature until the molten resin fills the cavity 3 and the filling is completed. It becomes possible to maintain the temperature.
As a result, a decrease in the viscosity of the resin that wraps around the lens periphery and merges on the opposite side of the gate G is suppressed, so that a weld line is generated at the position so that the merged resins are sufficiently fused. Can be effectively avoided.

Thus, in preventing the generation of the weld line, the heat insulating materials 11a and 12a forming the respective molding surfaces of the inserts 11 and 12 have a thermal conductivity of 0.4 to 1.3 W as described above. It is preferable to use a glass material of / m · K.
In this embodiment, the glass material having such a thermal conductivity is used as the heat insulating materials 11a and 12a to form the molding surfaces of the inserts 11 and 12, and the filling of the raw material resin is completed by filling the cavity 3. Until the surface temperature of the raw material resin is maintained at a temperature higher than the glass transition temperature, the mold temperature and the resin temperature at the time of injection are set and injection molding is performed, so that the weld is more reliably performed. Generation of lines can be prevented. At this time, if the thermal conductivity of the glass material used as the heat insulating materials 11a and 12a exceeds the above range, a sufficient heat insulating effect tends to be hardly obtained. On the other hand, when it is less than the above range, the heat insulation effect becomes higher than necessary, and the time required for cooling becomes longer, which is not preferable for shortening the molding cycle.
Even after the filling of the raw material resin into the cavity 3, the surface temperature of the raw material resin remains higher than the glass transition temperature, which hinders shortening of the molding cycle. End up. Therefore, injection molding is performed by appropriately adjusting various molding conditions so that the surface temperature of the raw resin becomes lower than the glass transition temperature at the timing when the inside of the cavity 3 is filled with the raw resin and the filling is completed. Is more preferable.

  Further, in the present embodiment, the molding surfaces of the inserts 11 and 12 are formed by the heat insulating materials 11a and 12a, thereby suppressing the temperature drop of the molten resin flowing into the cavity 3, while the heat insulating material. In order to promote heat dissipation from the insert main bodies 11b and 12b to which 11a and 12a are joined and to shorten the cooling time after molding, a steel material having a higher thermal diffusivity than the glass material used for the heat insulating materials 11a and 12a is used. The insert body is preferably formed.

  Hereinafter, the present invention will be described in more detail with reference to specific examples.

[Example 1]
In the injection molding apparatus shown in FIG. 1, each of the molding surface of the insert 11 on the movable mold 1 side and the molding surface of the insert 12 on the stationary mold 2 side has a thermal conductivity of 1.1 W / of a crown glass material. It formed with the heat insulating material 11a and 12a of m * K.
With such an injection molding apparatus, injection molding is performed with the mold temperature set to 130 ° C. and the resin temperature set to 290 ° C., the lens central portion has a thickness of 1.3 mm, and the lens peripheral portion has a thickness of 6 mm. A negative lens having a diameter of 77 mm, which is 0.5 mm, was molded.
When the surface of the molded plastic lens was inspected, no weld line was confirmed.

[Example 2]
A plastic lens was molded in the same manner as in Example 1 except that the mold temperature was set to 85 ° C. lower than that of Example 1 and injection molding was performed. When the surface of the molded plastic lens was inspected, no weld line was confirmed.
Thus, by forming the molding surfaces of the inserts 11 and 12 with the heat insulating materials 11a and 12a made of a glass material, the temperature reduction of the molten resin flowing into the cavity 3 is suppressed, and the molten resin It is possible to maintain the molten resin in the cavity at a temperature higher than its glass transition temperature until the inside of the cavity 3 is filled and filling is completed. As a result, it was confirmed that no weld line was generated even when the mold temperature was set lower than that in Example 1.

[Comparative Example 1]
A plastic lens was molded in the same manner as in Example 1 except that both the insert 11 on the movable mold 1 side and the insert 12 on the fixed mold 2 side were formed using maraging steel. Inspection of the surface of the molded plastic lens revealed a weld line.

  Although the present invention has been described with reference to the preferred embodiments, the present invention is not limited to the above-described embodiments, and various modifications can be made within the scope of the present invention. Nor.

  For example, in the above-described embodiment, the entire molding surfaces of the inserts 11 and 12 are formed of the heat insulating materials 11a and 12a made of a glass material. However, at least a portion where a weld line is expected to occur in the plastic lens to be molded is determined. By forming with the heat insulating materials 11a and 12a, it is possible to prevent generation of weld lines.

INDUSTRIAL APPLICABILITY The present invention can be used as a technique for preventing the generation of weld lines when manufacturing a minus lens having a thin lens center portion and a thick lens peripheral portion by an injection molding method.

1 Movable type (split type)
2 Fixed type (split type)
3 Cavity 11, 12 Insert 11 a, 12 a Heat insulation material 11 b, 12 b Insert body 50 Mold 80 Injection device

Claims (4)

In manufacturing a minus lens in which the melted raw material resin is injected and filled into a cavity formed between a pair of split molds, and the lens center portion is thin and the lens peripheral portion is thick.
A part or the whole of the molding surface forming the cavity is formed by a heat insulating material made of a glass material,
A method for producing a plastic lens, comprising injecting and filling a raw material resin into the cavity to form a predetermined lens shape.   The method for producing a plastic lens according to claim 1, wherein the molding surface is formed using an amorphous glass material having a thermal conductivity of 0.4 to 1.3 W / m · K as the heat insulating material.   The surface temperature of the raw material resin is maintained at a temperature higher than the glass transition temperature until the raw material resin flowing into the cavity fills the cavity and is completely filled. The manufacturing method of the plastic lens of description.   4. The method of manufacturing a plastic lens according to claim 3, wherein the surface temperature of the raw material resin becomes lower than the glass transition temperature at a timing when the inside of the cavity is filled with the raw material resin and filling is completed.

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