JP5917232B2 - Manufacturing method of plastic lens - Google Patents

Description

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

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

For example, Patent Document 1 discloses that a plastic lens is molded with high accuracy by controlling the mold temperature by inserting high-frequency heating means into the mold and heating the mold in the mold open state during mold clamping. A method is disclosed.
In addition, as a method for improving transferability when transferring the cavity shape in the injection molding method, Patent Document 2 discloses a method in which a mold is vibrated by ultrasonic waves when injecting and filling molten resin into the cavity. Patent Document 3 discloses a method of injecting carbon dioxide between the resin filled in the cavity and the cavity surface.

Japanese Patent Laid-Open No. 2-162007 JP 2001-1370 A JP 2002-52583 A

By the way, the steel material used for the mold has a very large thermal diffusivity compared to the resin, so cooling and solidification rapidly proceeds when the molten resin injected and filled into the mold cavity contacts the mold surface. Thus, if a solidified layer is formed on the surface of the molten resin, there is a concern that fluidity is impaired and transferability is lowered.
For this reason, in the injection molding method, in order to improve the transferability, as in the method disclosed in Patent Document 1, the temperature is controlled so that the temperature of the molding die when the molten resin is injected and filled becomes high. Is effective.

  However, if the temperature of the mold is raised, the formation rate of the solidified layer becomes slower and the fluidity of the molten resin is maintained, so that the transferability tends to improve. There is a problem that the time required for cooling the molten resin to be sufficiently solidified for taking out the resin becomes longer and the production efficiency is lowered.

Further, in the method disclosed in Patent Document 1, since heating can be performed only while the mold is opened, temperature control is required in consideration of a temperature change from when the mold is closed until filling is completed. Actually, it is not easy to perform the temperature control with high accuracy.
Further, the methods disclosed in Patent Documents 2 and 3 do not increase the temperature of the mold, but the method disclosed in Patent Document 2 uses a mold structure or ultrasonic wave for applying vibration to the mold. A generator is required, and in the method disclosed in Patent Document 3, in order to inject carbon dioxide, the mold structure must be changed in consideration of the flow path. For this reason, there is a problem that it is difficult to apply just by diverting an existing injection molding apparatus, and a new capital investment is required.

  The present invention has been made in view of the circumstances as described above, and even if the temperature of the molding die when injecting and filling the molten resin into the cavity is set low, the transferability does not decrease, and the cooling is performed. An object of the present invention is to provide a plastic lens manufacturing method that can shorten the time required for improving the productivity and can be easily applied to an existing injection molding apparatus.

  The method of manufacturing a plastic lens according to the present invention includes a step of injecting and filling a molten raw resin into a cavity formed between a pair of split molds to manufacture a plastic lens having a predetermined lens shape. In at least one of the molds, a molding surface that forms the cavity is formed by a heat insulating material made of a glass material, and the raw material resin that has flowed into the cavity fills the cavity and is completely filled. The temperature of the molding surface is controlled so as not to exceed the glass transition temperature of the raw material resin.

  According to the present invention, the productivity can be increased by shortening the molding cycle while maintaining the transferability.

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. It is explanatory drawing which shows an example of the method of measuring the surface temperature of a molding surface.

  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. 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 a movable mold 1 and a fixed mold 2 through a gate G together with two cavities 3 for molding a plastic lens of a predetermined shape. 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. Inside the insert guide member 5, an insert mold 11 as a cavity forming member is accommodated 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. Inside the insert guide member 9, an insert mold 12 as a cavity forming member is accommodated so as to be slidable in a direction perpendicular to the parting line PL.
The insert guide members 5 and 9, the insert molds 11 and 12, and the mold plates 6 and 10 are provided with a circulation mechanism for circulating a temperature control fluid supplied from a mold temperature control device (not shown).

  A molding die 50 having such a movable die 1 and a fixed die 2 includes an insert die 11 on the movable die 1 side and an insert die 12 on the fixed die 2 side between the movable die 1 and the fixed die 2. A cavity 3 including a molding surface formed in each is formed. The cavity 3 is formed corresponding to the shape of the plastic lens to be molded, and the molding surfaces of the insert molds 11 and 12 forming the cavity 3 are formed by heat insulating materials 11a and 12a made of a glass material. Yes.

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

  Examples of the heat insulating materials 11a and 12a that form the molding surfaces of the insert dies 11 and 12 include amorphous materials such as crown-based, flint-based, barium-based, phosphate-based, fluorine-containing, and fluorophosphate-based materials. The glass material can be used. Among these, it is preferable to appropriately select and use an amorphous glass material having a thermal conductivity of 0.4 to 1.3 W / m · K. 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.

  That is, in order to form a molding surface directly on an insert mold made of steel through a polishing process, a high-level technique and a laborious process are required, but a molding surface for molding an optical surface of a lens was formed. By forming the insert dies 11 and 12 by joining the heat insulating materials 11a and 12a to the insert main bodies 11b and 12b, the formation of the molding surface is facilitated and the number of manufacturing steps can be reduced. Thereby, it becomes possible to manufacture the insert molds 11 and 12 at low cost.

  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 main bodies 11b and 12b, a thermosetting resin having a low coefficient of linear expansion and excellent stability in a high temperature environment can be used as an adhesive. And what is necessary is just to join both by apply | coating with the brush etc. to the joint surface of insert main body 11b, 12b. As such a thermosetting resin, a sulfur-containing thermosetting resin obtained by reacting a thermosetting monomer containing sulfur is preferable. The sulfur-containing thermosetting resin has a low coefficient of linear expansion, is excellent in stability even in a high temperature environment, and is excellent in adhesiveness (adhesion) with a glass substrate. Furthermore, since the surface tension is low and it is possible to make it adhere to the surface to be bonded in the form of a liquid film in the state of the monomer before curing, the adhesion formed between the heat insulating materials 11a, 12a and the insert bodies 11b, 12b. The layer can be a very thin layer.

  The sulfur-containing thermosetting resin is preferably at least one resin selected from thiourethane resins and epithio resins. Here, the thiourethane resin refers to a resin obtained by reacting a polyisocyanate compound and a polythiol compound, and the epithio resin is obtained by reacting a lens raw material monomer having a compound having an epithio group as an essential component. Refers to the resin that is produced. It is particularly preferable to use a thiourethane resin as the sulfur-containing thermosetting resin because it is extremely excellent in adhesion to a glass substrate and is economical. Examples of commercially available thiourethane resins include MR series manufactured by Mitsui Chemicals, Inc., trade names “MR-6”, “MR-7”, “MR-8”, “MR-10”, and “MR-20”. “MR-1746” or the like is preferably used.

  The insert bodies 11b and 12b can be formed using a steel material such as maraging steel or beryllium copper alloy, but a steel material having a higher thermal diffusivity than the glass material used for the heat insulating materials 11a and 12a is used. Is preferred.

  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.

  Further, the mold mounting member 16 on the movable mold 1 side is provided with a hydraulic cylinder 19 corresponding to each of the insert molds 11, and the piston rod 21 connected to the piston 20 is connected to one end side of the hydraulic cylinder 19. It penetrates through the back insert 22 fixed to. A T-shaped clamp member 23 provided at the tip of each piston rod 21 is formed in a T-shaped groove 24 formed on the back surface of the insert mold 11 (the surface opposite to the surface on which the molding surface is formed). Engageable and detachable.

  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 mold 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 mold 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 insert molds 12, and a piston rod 28 connected to the piston 27 is provided in the mold mounting member 15. It penetrates. A T-shaped clamp member 29 provided at the tip of each piston rod 28 is formed in a T-shaped groove 30 formed on the back surface of the insert mold 12 (the surface opposite to the surface on which the molding surface is formed). Engageable and detachable.

  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 mold 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 mold 12 attached to the T-shaped clamp member 29 is housed inside 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 mounting member 16 presses the insert mold 11 via the back insert 22. Thereby, the volume of the cavity 3 at the time of mold clamping is made variable, and the molten resin injected and filled in the cavity 3 can be pressurized and compressed by the insert mold 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 mold 11 are also pressed and molded in the cavity 3. The lens is pushed out.
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 for adjusting the clamping force according to the characteristics of the plastic lens to be molded (lens shape, lens power, etc.) in advance in order to apply an appropriate pressure to the resin in the cavity 3 in advance. is there.

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 cross head 73 starts to advance, and when the cross head 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 50 is compressed. Pressed.

  In ST8, cooling is performed. For this purpose, the mold temperature is set so that the temperature of each part (insert mold, insert guide member, etc.) of the mold 50 is set to a temperature lower than the glass transition temperature of the raw resin according to the lens characteristics to be molded. The temperature of the temperature adjusting fluid is controlled by the adjusting device. 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 according to the above procedure, when the molten resin is injected and filled into the cavity 3 in ST5, if the temperature of the mold is set low in order to shorten the molding cycle, the transferability is lowered. There is a concern that

  In this embodiment, even if the temperature of the molding die when injecting and filling the molten resin into the cavity 3 is set low, transferability is suppressed by suppressing a decrease in the viscosity of the resin flowing on the surface of the cavity 3. In order not to decrease, the molding surface of the insert mold 11 on the movable mold 1 side forming the cavity 3 and the molding surface of the insert mold 12 on the fixed mold 2 side are formed by heat insulating materials 11a and 12a made of a glass material. doing. Then, the temperature of the temperature adjusting fluid is controlled by a mold temperature adjusting device, and the temperature is controlled so that the surface temperature of the molding surface of the insert molds 11 and 12 does not exceed the glass transition temperature of the raw material resin, thereby cooling process. This shortens the time required to improve productivity.

  When the molten resin injected and filled into the cavity 3 comes into contact with the molding surface of the mold, it is affected by the thermal diffusion of the mold, the temperature of the surface layer portion decreases, and conversely the surface temperature of the molding surface increases. . Since the thermal diffusivity of the glass material is very small as compared with a metal mold that is generally used, the surface layer of the molten resin is filled until the molten resin fills the cavity 3 and the filling is completed. The temperature can be maintained above the glass transition temperature, and the formation of the solidified layer can be delayed.

  In order to obtain good transferability, it is desirable to apply pressure in a state where the temperature of the surface layer portion of the molten resin is equal to or higher than the glass transition temperature. However, if the temperature at this time is too high, the time required for the cooling process becomes longer. , Reduce productivity. In particular, in a thick lens, the cooling time occupies most of the molding cycle, and the time required for the cooling process can be shortened by lowering the mold temperature.

  However, when the mold temperature is lowered, the transferability is lowered, and there is a limit to lowering the mold temperature. Therefore, in this embodiment, the heat insulating material 11a, 12a made of a glass material is used within a range in which the temperature of the surface layer portion of the molten resin at the time of filling can be maintained at a temperature equal to or higher than the glass transition point by utilizing the heat insulating effect of the glass material. The temperature of the molding surfaces of the insert molds 11 and 12 formed by the above can be set lower than in the conventional technique using a metal mold.

  In shortening the cooling time while maintaining the transferability, the heat insulating materials 11a and 12a forming the respective molding surfaces of the insert dies 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. When the above range is exceeded, it tends to be difficult to obtain a sufficient heat insulating effect. 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 example, as shown in FIG. 7, the surface temperature of the molding surface is such that a thermocouple T is disposed in a hole opened in the molding surface (heat insulating material 11a, 12a) of the insert dies 11, 12, and the hole It is possible to measure by filling the opening part with a metal putty P and fixing the temperature measuring part of the thermocouple T so as to be located in the vicinity of the molding surface.

In the present embodiment, the molding surfaces of the insert molds 11 and 12 are formed of the heat insulating materials 11a and 12a, thereby suppressing the temperature drop of the molten resin flowing into the cavity 3, while the In order to promote heat dissipation from the insert bodies 11b and 12b to which the heat insulating materials 11a and 12a are joined 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. It is preferable to form the insert body using
Furthermore, if the temperature of the surface layer portion of the raw material resin remains at the glass transition temperature or higher even after the filling of the raw material resin into the cavity 3, it becomes an obstacle to shortening the molding cycle. End up. For this reason, at the timing when the cavity 3 is filled with the raw material resin and filling is completed, various molding conditions are appropriately adjusted so that the temperature of the surface layer portion of the raw material resin is lower than the glass transition temperature, and injection molding is performed. More preferably.

  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 mold 11 on the movable mold 1 side and the molding surface of the insert mold 12 on the fixed mold 2 side has a thermal conductivity made of a crown glass material. 1.1 W / m · K heat insulating materials 11a and 12a were used.
With such an injection molding apparatus, polycarbonate is used as the raw material resin, the resin temperature is set to 290 ° C., and the set temperature of the molding surfaces of the insert molds 11 and 12 is set to 55 ° C. When the temperature is adjusted so as not to exceed the glass transition temperature (Tg: 145 ° C.) and the cooling time (time taken for ST8 described above) is used as a reference value, and when the time is increased by 30S from the reference value Thus, a plastic lens having a lens central portion thickness of 10 mm, a lens peripheral portion thickness of 12 mm, and a diameter of 77 mm was molded.
The power at the center of the molded plastic lens was measured, and the transferability was evaluated based on whether it was within the tolerance of the target power (D: -3.3). Those that are within tolerance are indicated by “◯”, those that are not within tolerance are indicated by “x”, and the results are shown in Table 1.

[Example 2]
A similar plastic lens was molded under the same molding conditions as in Example 1 except that the set temperature of the molding surfaces of the insert dies 11 and 12 was 85 ° C.
As in Example 1, Table 1 also shows the results of evaluating the transferability by measuring the power of the central part of the molded plastic lens.

[Comparative example]
Both the insert mold 11 on the movable mold 1 side and the insert mold 12 on the fixed mold 2 side are formed using maraging steel, the set surface temperature of the mold surface is 130 ° C., and the temperature of the mold surface is the raw material. A similar plastic lens was molded under the same molding conditions as in Example 1 except that the glass transition temperature of the polycarbonate used for the resin was allowed to be exceeded.
As in Example 1, Table 1 also shows the results of evaluating the transferability by measuring the power of the central part of the molded plastic lens.

  From these results, the molding surface set temperature was lowered to 85 ° C. (Example 2) and 55 ° C. (Example 1) with respect to the comparative example in which the molding surface temperature was set to 130 ° C. However, it was confirmed that the cooling time could be shortened without impairing the transferability.

  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, as a method of manufacturing a plastic lens for spectacles, a lens is molded in a semi-finished product that is thicker than the finished dimensions, and this semi-finished lens is finally processed by post-processing. A method of finishing in a shape, for example, a plurality of types of semi-finished lenses, which are molded as different optical surface shapes on the convex side and formed with a common concave surface on the concave side, are prepared according to the user's prescription from these There is known a method of manufacturing by selecting an appropriate lens, and cutting and polishing the concave side so as to satisfy the prescription to finish the final shape.

  When such a semi-finished lens is manufactured by an injection molding method, the quality of transferability of the surface to be post-processed does not matter. For this reason, when manufacturing a semi-finished lens, at least one of a pair of split molds forming a cavity (a mold that molds a surface that is not cut or polished by post-processing), the molding surface is made of glass. What is necessary is just to make it form with the heat insulating material which consists of a raw material.

In addition, the present invention can be applied regardless of the thickness of the plastic lens to be molded, and in particular, since a plastic lens having a very thin product thickness tends to solidify during injection, Although it corresponds to ultra-high speed injection molding or high temperature molding, if the present invention is applied, solidification of the resin during injection can be delayed, and it is expected that molding can be easily performed.
Furthermore, when there is a very fine pattern on the optical surface, it cannot be sufficiently transferred due to solidification during injection, and it is usually handled by high temperature molding. Therefore, it is expected that molding can be easily performed.

  INDUSTRIAL APPLICATION When manufacturing a plastic lens by the injection molding method, this invention can be utilized as a technique which can shorten the time which cooling requires and can improve productivity, without reducing transferability.

1 Movable type (split type)
2 Fixed type (split type)
3 Cavities 11 and 12 Insert molds 11a and 12a Thermal insulation materials 11b and 12b Insert body 50 Mold

Claims (4)

In manufacturing a plastic lens having a predetermined lens shape by injecting and filling a molten raw material resin into a cavity formed between a pair of split molds,
In at least one of the pair of split molds, a molding surface forming the cavity is formed by a heat insulating material made of an amorphous glass material having a thermal conductivity of 0.4 to 1.3 W / m · K ,
The temperature of the molding surface is controlled so that the surface temperature of the molding surface does not exceed the glass transition temperature of the raw material resin until the raw material resin flowing into the cavity fills the cavity and the filling is completed. Manufacturing method of plastic lens. By joining the heat insulating material to the insert body by using at least one resin selected from thiourethane resin and epithio resin as an insert mold housed in the split mold as a cavity forming member for forming the cavity The manufacturing method of the plastic lens of Claim 1 formed .   The temperature of the surface layer part of the raw material resin is maintained at the glass transition temperature or higher 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.   The method of manufacturing a plastic lens according to claim 3, wherein the temperature of the surface layer portion 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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