JPH0421574B2 - - Google Patents

Description

[Detailed description of the invention]

(Field of Application of the Invention) The present invention relates to an injection compression molding method and apparatus for producing plastic lenses using a thermoplastic plastic molding material, and particularly to an injection compression molding method and apparatus for producing plastic lenses with high precision in shape. It is related to the device. (Background of the Invention) In recent years, with improvements in mold manufacturing technology and molding machine control technology, relatively high-precision plastic lenses have come to be manufactured using PS resin, PMMA resin, PC resin, etc. The highest quality plastic lenses are used in camera viewfinder lenses and instant camera lenses. However, these plastic lenses are significantly inferior in shape accuracy, such as lens surface accuracy and curvature radius accuracy, related to the optical performance of the lens, compared to glass lenses used in imaging lenses of medium to high-end cameras. Plastic lenses using thermoplastic resin are made using injection compression molding method (Plastics Age Encyclopedia).
dia 1981, P148-163). In the conventional normal injection compression molding method, molten thermoplastic resin heated to a high temperature of 190 to 260 degrees Celsius is injected into a mold maintained at a constant temperature of about 40 to 90 degrees Celsius, and then one side of the lens cavity is formed. Molding was performed by cooling and solidifying the resin while applying compressive force to the resin in the mold via insert pieces. However, when the shape of a plastic lens manufactured by such an injection compression molding method is measured with precision on the order of microns, there is always a drawback that molding distortion such as warpage and sink marks is present. The reason why such defects occur is considered to be due to the following reasons. In the conventional injection compression molding method described above, there is a large temperature difference between the mold and the resin injected into the mold cavity, and the high temperature molten resin injected into the cavity is 50 to 10℃/
It is rapidly cooled at a cooling rate of about minutes. Therefore, a large temperature difference occurs within the resin, and the resin is cooled and solidified while maintaining the large temperature difference. As a result, the shrinkage of the resin after molding becomes large and non-uniform, and sink marks occur in areas of the resin that were at high temperatures, and it is thought that the unbalance of the non-uniform temperature throughout the resin causes warping. This is considered to be the reason why plastic lenses as high precision as glass lenses cannot be obtained by conventional injection compression molding methods. The present inventors believe that the first drawback of the above-mentioned conventional injection compression molding method is large shrinkage, and have previously applied for a patent for a molding method having the following characteristics as an invention to improve this drawback. (Special application 1982-
105792). (1) During the pressure holding process after the mold cavity is filled with resin from the molding machine, compressive force is applied to the resin in the cavity to pre-shape the resin in the cavity. At the same time, the degree of adhesion between the resin in the cavity and the mold fixing and movable insert pieces is improved to ensure sufficient heat transfer between the resin in the cavity and the mold. (2) Next, while maintaining this state, the resin in the cavity is temporarily cooled or left to promote internal solidification. Thereafter, the temperature of the insert is increased to a temperature higher than the softening temperature of the resin, so that only the surface layer of the resin within the cavity is melted.
The reason why only the surface layer is melted is to reduce the amount of resin shrinkage that occurs during subsequent cooling. (3) Next, compressive force is again applied to the resin in the cavity to shape the molten surface layer.
At the same time, cooling of the fixed insertion piece and the movable insertion piece is started, and the compressive force applied to the resin in the cavity is controlled in accordance with this cooling temperature. In the manufacturing method of the above patent application explained above,
By molding a convex lens using PMMA resin, we were able to obtain a high-precision convex lens with significantly improved lens surface accuracy compared to the conventional injection compression molding method described above. The reason for this is that in the above-mentioned patent, only the lens surface layer is melted after the resin in the cavity is cooled. This is thought to be due to the fact that it can be made significantly smaller. It will be done. However, the manufacturing method of the above patent application includes the following (1)
Subsequent research revealed that there was a problem in (3). (1) When molding a concave lens, it is not possible to obtain a high-precision lens like that of a convex lens;
Double lens surface accuracy is poor. (2) Even convex lenses can be molded using PC resin.
The lens surface precision is 5 to 10 times lower than when PMMA resin is used. (3) When molding a concave lens using PC resin,
The lens surface accuracy is significantly higher (50 to 100 times more) than when convex lenses are molded using PMMA resin.
inferior to The reasons for the above drawbacks (1) to (3) are considered to be as follows. (A) The reason why concave lenses have inferior surface precision than convex lenses is that in convex lenses, the thickest part is at the center of the lens, but in concave lenses, the thickest part is on the outer periphery of the lens. For this reason, it is thought that the cooling contraction in the lens radial direction becomes larger than that of a convex lens. (B) The reason why the surface precision is inferior when making a convex lens using PC resin compared to when using PMMA resin is as follows.
In the manufacturing method of the patent application, only the lens surface layer is melted. Therefore, it is inevitable that temperature distribution occurs in the resin within the mold cavity. Additionally, the heat distortion temperature of PMMA resin is approximately 100℃, while that of PC resin is approximately 100℃.
PC resin has a higher heat distortion temperature than PMMA resin. Therefore, when heating the mold to melt only the lens surface layer, when using PC resin, it is necessary to heat the mold to a higher temperature than when using PMMA resin. Therefore, the temperature difference that occurs in the resin within the mold cavity increases, which increases the shrinkage of the resin that occurs as it cools and the non-uniformity of the contraction of each part of the resin. (C) The reason why the lens surface precision is significantly inferior when a concave lens is molded using PC resin is thought to be that the reasons (A) and (B) above act synergistically. (Object of the invention) The object of the present invention is to improve the drawbacks of the prior art (1) to (3) described above, and to
It is an object of the present invention to provide an injection compression molding method and an apparatus for the same, which can produce high-precision plastic lenses in any combination of convex lenses and concave lenses. (Summary of the Invention) The present invention is characterized by a sliding piece provided on one of a fixed mold and a movable mold that are arranged opposite to each other, and a mold or a piece opposite to this. In the injection compression molding method, resin is injected and filled into a cavity formed between the cavities, and a pressure cylinder applies pressure to the insert piece to apply compressive force to the resin in the cavity. After uniformizing the temperature distribution in the softening temperature range, the resin is gradually cooled to the heat distortion temperature that takes it out of the softening temperature range, thereby minimizing the occurrence of temperature unevenness in the resin due to cooling. The point is that it is designed to cool the air. Another feature of the present invention is a first temperature controller that heats the fixed mold, the movable mold, and the insertion piece at a constant temperature in the softening temperature range, and then gradually cools them to a heat distortion temperature that takes them out of the softening temperature range. and a second temperature controller that rapidly cools the fixed mold, the movable mold, and the inserted pieces before the constant temperature heating and after the slow cooling. (Example of the Invention) Prior to the present invention, the present inventors had an outer diameter of 46 mm, a center thickness of 1.9 mm, an outer diameter part thickness of 12.9 mm, and a radius of curvature of 250 mm.
Using an injection compression mold for a 30mm concave lens and PC resin, we conducted an experiment in which the mold temperature was maintained constant and then slowly cooled. In the experiment, the resin temperature during injection was set at 240°C, and the mold temperature to maintain a constant temperature was varied in the range of 130 to 180°C. Also, the time required to maintain the mold temperature constant is 5
The lens surface accuracy was measured by changing the time within a range of ~40 minutes. Furthermore, after maintaining the mold temperature constant for a predetermined period of time, the lens surface accuracy was measured by changing the cooling rate for slow cooling in the range of 0.5 to 10° C./min. FIG. 2 shows the measurement results of the former experiment, that is, the measurement results of the lens surface accuracy as the mold temperature maintenance time changes with the mold temperature maintained at a constant temperature as a parameter. As shown in Fig. 2, molding was performed by slow cooling at a common cooling rate of 1.5°C/min after maintaining the mold temperature constant. The mold temperature is determined from Figure 2.
By maintaining the temperature at 140℃ and increasing the mold temperature maintenance time,
It can be seen that the lens surface accuracy is improved. Figure 3 shows the measurement results of the latter experiment, that is, the measurement results of the lens surface accuracy as the cooling rate changes with the mold temperature as a parameter after maintaining the mold temperature constant at a predetermined temperature. . In each case in Figure 3, the time to maintain the mold temperature constant was 15 minutes. From Figure 3, it can be seen that the lens surface precision improves when the mold temperature is maintained at 140°C and the cooling rate is reduced. From the above experimental results, we found the following. That is, it can be said from FIG. 2 that the longer the time for maintaining the mold at a constant temperature, and from FIG. 3, the smaller the cooling rate, the more the lens surface precision can be improved. Furthermore, in both FIGS. 2 and 3, there is a mold temperature around 140° C. that provides the best lens surface accuracy. I used this
This is thought to be closely related to the fact that the heat distortion temperature range of PC resin is 130 to 150°C, and the glass transition temperature is 142°C. From the experimental results shown in Figs. 2 and 3, it is clear that when cooling and solidifying the resin in the compression process after injection, the smaller the temperature distribution width of the resin in the cavity within the softening temperature range of the resin, the more It is possible to derive the principle that molding shrinkage can be made uniform and the shape precision of plastic lenses can be made highly accurate. The present invention is based on this novel principle. The present invention will be explained below by way of examples. Fourth
The figure shows a mold for forming a plastic concave lens according to an embodiment of the present invention. FIG. 1 shows a block diagram of a molding control device according to an embodiment of the present invention. The same numbers in FIG. 4 and FIG. 1 indicate the same parts. In FIG. 4, 1 is a fixed type, 2 is a fixed type insertion piece, 3 is a fixed type auxiliary plate, and 4 is a spool bush. Said 1 to 4 are attached to a fixed platen (not shown) of an injection molding machine via a fixed type mounting plate 5,
Constitutes the fixed side of the lens mold. In addition, a movable mold 6, a movable auxiliary plate 7, a spacer 8
The movable mold inserting piece 9, the movable mold inserting piece auxiliary plate 10, and the hydraulic cylinder 11 are each attached to a movable platen (not shown) of the injection molding machine via a movable mold mounting plate 12, and constitute the movable side of the lens molding die. . The movable mold insertion piece 9 is integrated with the insertion piece auxiliary plate 10 and receives force from the hydraulic cylinder 11 to compress the resin in the cavity 13. It also serves to push the plastic lens out of the mold when the mold is opened. A surface 14 of the fixed mold insertion piece 2, a surface 15 of the movable mold 6, and a surface 16 of the movable mold insertion piece 9 form a lens cavity 13. A spool 17 is provided in the spool bush 4, and a runner gate 18 is provided in the movable mold 6.
These form a flow path that guides the resin injected from the cylinder (not shown) of the molding machine to the cavity 13. There is a cooling hole 1 near the surface 14 in the fixed type insert piece 2.
9, a heater 20, and a thermocouple 21 are installed.
A cooling hole 23 is provided in the fixed auxiliary plate 3 to connect the cooling hole 19 to a pipe 22 (shown in FIG. 1). On the other hand, inside the movable mold 6, a heater 24, a cooling hole 25, and a thermocouple 26 are installed around the cavity surface 15. There are cooling holes 25 in the movable auxiliary plate 7.
Cooling hole 2 that connects to piping 27 (shown in Figure 1)
8 is provided. Inside the insert piece 9 on the movable side,
Cooling holes 29, a heater 30, and a thermocouple 31 are installed near the surface 16. The heaters 20, 24, and 30 are means for realizing the mold initial temperature _T1 , which will be described later. A cooling hole 29 is provided in the piping 32 in the inserting piece auxiliary plate 10.
Cooling holes 33 are provided which communicate with the cooling holes 33 (shown in FIG. 1). Cooling holes 19, 23, 25, 28, 29
A heat medium in a first temperature controller 34 or a refrigerant in a second temperature controller 35, which will be described later, is sent to and 33. A pin 36 is installed in the center of the movable mold 6 to push out the cooled and solidified resin in the spool 17 and the runner gate 18 to the outside of the mold. The extrusion pin 36 is extruded by an extrusion rod 37 of the molding machine when the molds on the fixed side and the movable side are opened. In FIG. 1, numeral 34 is a first temperature controller composed of a heater 38, a first cooler 39, and a program controller 40, in which a heat medium (oil) is placed. The program controller 40 connects thermocouples 21 and 2 via a temperature recorder 41.
6 and 31, and thermocouples 21, 2
The heater 38 and the first cooler 39 are controlled to be turned on or off according to the detected temperature of either one of the heaters 6 and 31. It also has a program control function that maintains the temperature of the heat medium in the first temperature controller 34 constant, and a program control function that allows cooling at a constant cooling rate over time. The heat medium in the first temperature controller 34 is at the mold temperature, which will be described later.
This is a means of sharing the range of T ₂ to T ₃ . This heat medium enters the cooling holes 23-19, 28-25 and 33-29 through the solenoid valve 42 that opens and closes the feed pipes 22, 27 and 32, and the pipes 22, 27 and 32, respectively, and enters the return pipe. Return piping 43, 44 and 4 via piping 43, 44 and 45
5 through the solenoid valve 46 that opens and closes the temperature controller 3.
It circulates along the route that returns to step 4. With the above functions, the first temperature controller 34 maintains the temperature of the fixed mold insert 2, movable mold 6, and movable mold insert 9 at a constant temperature _T2 , and then changes the mold temperature from _T2. It can function as slow cooling to _T3 . 35 is a second temperature controller, which is composed of a heater 47 and a second cooler 48. The second temperature controller 35 contains a refrigerant (oil) that is the same material as the heating medium in the first temperature controller 34 . The refrigerant in the second temperature controller 35 is heated at a mold temperature T ₁ to _{T 2} to be described later.
and a means of sharing the rapid transition from T ₃ to _{T 4} .
This refrigerant passes through the feed pipe 49, passes through the solenoid valve 50 that opens and closes the pipe 49, passes through the pipes 22, 27, and 32, and then enters the cooling holes 23-19, 28, respectively.
-25 and 33-29, pipes 43, 44
and a return pipe 51 via 45;
It circulates through a solenoid valve 52 that opens and closes the air and returns to the second temperature controller 35. With the above functions, the second temperature controller 35 can quickly cool down the temperatures of the fixed mold inserting piece 2, the movable mold inserting piece 6, and the movable mold inserting piece 9. 53 is a hydraulic generator, 54 is an oil feed pipe, 5
5 is an oil return pipe and 56 is a feed pipe 54
It is a solenoid valve that opens and closes. The oil in the hydraulic pressure generator 53 is configured to be able to circulate through the solenoid valve 56, the feed pipe 54, and the hydraulic cylinder 11, and return to the return pipe 55. Further, 57a, 57b and 57c are heater controllers for fixed type, movable type and insert piece, respectively. These heater controllers control heaters 20, 24 and 30 and thermocouples 21, 2.
6 and 31, and the temperature recorder 41
displays the temperatures detected by thermocouples 21, 26, and 31. The heater controllers 57a, 57b and 57c respectively have thermocouples 21, 26 and 31.
When each detected temperature is below or above the temperature set for each thermocouple, the heater 2
It has a function of turning on or off energization to 0, 24, and 30. 58, 59, 60, and 61 are each connected to the control panel of the molding machine (not shown) by a timer installed in each control device, and the time is measured at the same time as molding starts, and the time when each control device starts operating. and indicates the point at which the operation stops. Now, FIG. 5 shows a control sequence during the injection compression molding process of the plastic lens according to this embodiment. Further, FIG. 6 shows the detected temperature curve of any one of the thermocouples 21, 26, and 31 during the injection compression molding process according to this embodiment by h, the estimated maximum temperature curve of the resin in the cavity 13 by k, The estimated minimum temperature curve is indicated by l. The resin temperature at each part within the cavity 13 changes between curves k and l. Next, the injection and compression process of the plastic lens according to this embodiment will be explained using FIGS. 5 and 6. Fifth,
In Figure 6, T ₀ is the resin temperature at the time of injection.
T ₁ is the initial mold temperature at the start of molding. The temperature was set at 175℃ or higher. Maintaining the initial mold temperature at _T1 can be achieved by adjusting the settings of heater controllers 57a, 57b, and 57c so that the temperatures detected by thermocouples 21, 26, and 31 are maintained at _T1 . T ₂ is the piece 9 that inserts the resin inside the mold cavity 13.
In order to enable compression molding by applying pressure and to make the resin temperature uniform, the metal must be maintained at a constant temperature within ±5℃ for at least 0.5 minutes within the range of the resin's heat distortion temperature to (heat distortion temperature + 40℃). This is the mold temperature. It is experimentally known that the accuracy deteriorates when the temperature exceeds (heat distortion temperature + 40°C). By the way, the thermal deformation temperature (the temperature at which it can be considered to have softened due to heat) of the resin used in plastic lenses is:
The temperature is approximately 95°C for PS resin, approximately 100°C for PMMA resin, and approximately 130°C for PC resin. The transition of the mold temperature from T ₁ to T ₂ is performed by the heater 20,
Stop heating by 24 and 30 and reduce temperature to T ₂
This can be achieved by circulating the heat medium in the first temperature controller 34, which is maintained in advance, into the mold. In FIG. 6, in order to shorten the molding cycle, after the heating by the heaters 20, 24 and 30 is stopped (time _t1 ), the temperature inside the second temperature controller 35, which has been maintained at a low temperature of 10 to 20°C, is heated. The refrigerant is circulated into the mold for a short time to rapidly cool the mold (time _t1 to _t2 ). Thereafter, the heat medium in the first temperature controller 34 was circulated into the mold (times _t2 to _t4 ). T ₃ is the mold temperature at which the resin is considered to have completely escaped the softening range by slowly cooling the mold while the insert piece 9 is pressurized. The mold temperature _T3 is suitably within the range from the heat distortion temperature to (heat distortion temperature -20°C) at which the resin is considered to be completely out of the softening range. To maintain the mold temperature at T ₂ and then gradually cool it to T ₃ (time t ₃ to _{t 5} ), the program controller 40 is set in two stages, with T 2 being kept constant at first, and then T ₂ being kept constant.
This can be achieved by subsequently setting a slow cooling gradient and circulating the heat medium in the first temperature controller 34 within the mold. Note that this gradual cooling gradient is preferably 5° C./min or less. T ₄ is the mold temperature at which the plastic lens is removed after the resin has cooled. Shifting the mold temperature from T ₃ to T ₄ (time t ₅ to t ₆ ) can be achieved by circulating the refrigerant in the second temperature controller 35 for a predetermined period of time. Further, when the mold temperature is shifted from T ₄ to T ₁ (time t ₇ to _{t 8} ), the circulation of the refrigerant of the second temperature controller 35 is stopped, and the temperature of the heater controller 57a, which has been set in advance to the temperature T ₁ , is changed. , 57b and 57c start heating the heaters 20, 24 and 30. Next, the injection compression molding method of this example will be explained. In FIGS. 5 and 6, t ₀ is the time point at which molding starts. At _t1 , the operation of the molding machine shifts from injection to holding pressure. At this point, the heaters 20, 24, and 30 that had been maintaining the mold temperature at _T1 stop generating heat, and the temperature is set to 10 to 20℃ in advance. The second tank containing the refrigerant
The solenoid valves 50 and 52 of the temperature controller 35 are opened to rapidly cool the mold for a short time. At the same time, the solenoid valve 5 of the hydraulic generator 53 is operated to apply pressure by the movable inserting piece 9.
Open 6. When the resin pressure in the cavity 13 falls below the pressure of the hydraulic cylinder 11 that operates the movable mold inserting piece 9, the movable mold inserting piece 9 is operated immediately before opening the mold to take out the plastic lens from the mold.
Continue to compress the resin in cavity 13 until T ₆ . t ₂ makes the temperature of the resin inside the cavity 13 uniform T ₂
The second temperature controller 35, which was being rapidly cooled in order to
This is the point in time when the solenoid valves 50 and 52 of the first temperature controller 34 are closed and the solenoid valves 42 and 46 of the first temperature controller 34, whose temperature of the heating medium is maintained at _T2 in advance, are opened. t ₃ is thermocouple 2
This is the point in time when the detected temperatures of Nos. 1, 26, and 31 reached _T2 . At _t4 , the constant temperature heating control that kept the mold temperature constant at _T2 is stopped, and the time is shifted to slow cooling control. At _t5 , when the detected temperatures of the thermocouples 21, 26, and 31 reach the above-described temperature _T3 or lower, the solenoid valves 42 and 46 of the first temperature controller 34 are closed, slow cooling is stopped, and the first temperature controller 34 is closed. This is the point in time when the solenoid valves 50 and 52 of the temperature controller 35 of No. 2 are opened again and rapid cooling of the mold is started. _t6 is set at the time when the pressurization by the insertion piece 9 is stopped and immediately before the mold is opened and the cooled and solidified plastic lens is taken out of the mold. At _t7 , after the plastic lens is removed from the mold, heating of the heaters 20, 24 and 30 is restarted in order to return the mold temperature to the initial temperature _T1 . _t8 is the end of one cycle when the mold temperature is returned to _T1 for the next cycle. As described above, when the resin is cooled and solidified in the compression process after injection, the smaller the temperature distribution of the resin in the cavity within the softening temperature range of the resin, the more uniform the molding shrinkage can be, and the higher the temperature. It is based on the principle that high-precision plastic cleansing can be achieved. Therefore, the thermal deformation temperature of the resin is between the set temperature T ₂ and T ₃ of the mold, and the period t ₃ - _{t 4} that maintains the mold temperature at T ₂ makes the resin temperature distribution in the cavity uniform. The cooling rate during slow cooling between t ₄ and _{t 5} , when the mold temperature transitions from T ₂ to T ₃ , is slow enough to not increase the unevenness of the resin temperature within the cavity. This is a condition for the establishment of the present invention. Therefore, it is necessary to set sufficiently long times between t ₃ and t ₄ and between t ₄ and _{t 5} . On the other hand, T ₃ is close to T ₂ and T ₀ , T ₁ , T ₂ and T ₄
The lower the temperature, the more t ₀ −t ₁ , t ₁ −t ₂ , t ₂ −t ₃ , t ₃ −t ₄ ,
It goes without saying that the shorter each _{of t 4 −t 5} . Therefore, the mold setting temperature T ₁ to T ₄ ,
When actually setting the operation start or stop times _t1 to _t8 of each control device, it is naturally necessary to consider molding cycle requirements as well as accuracy requirements. Next, a specific setting procedure for the resin temperature and mold set temperature T ₀ to T ₄ and operation start or stop times t ₁ to _{t 8} will be explained. First, it is necessary to find conditions that improve the overall quality of plastic lenses, including residual stress, including shape accuracy, surface gloss, and transparency. Regarding the shape accuracy, while observing the conditions for establishing the present invention, T ₁ and T ₂ are set at a higher temperature, T ₃ and T ₄ are set at a lower temperature, and each interval from t ₁ to _{t 7} is set at a higher temperature. It is best to set both of them to a long value. According to experiments, t ₁ ~
If the total time of _t8 is about 1 to 2 hours, it will never be too long and the quality of the plastic cleanser will deteriorate. After finding the conditions that satisfy the overall quality of the plastic cleanser mentioned above, each interval from t ₁ to _{t 8} should be made shorter, T ₀ , T ₁ , T ₂ and T ₄ should be made to the lower temperature side, and T ₃ should be made shorter than T 3. Change the temperature in small increments toward the one closest to ₂ at appropriate time or temperature intervals. If this is done, the shape accuracy of the plastic lens will eventually fall below an acceptable value. After finding the value just before the shape accuracy of the plastic lens falls below the allowable value for each of T ₀ to T ₄ and t ₁ to t ₈ , the same procedure is repeated several times in a cyclical manner. In this way, T ₀ to _{T 4} and t ₁ to _{t 8} all converge to specific values. With the above steps
T ₀ to T ₄ and t ₁ to _{t 8} can also be optimized from the viewpoint of the molding cycle. Next, Table 1 shows the results of specific examples based on this example. The lens shape of Example A has an outer diameter of 47 mm and a center thickness.
It is a concave lens with a diameter of 1.9 mm, an outer diameter of 12.7 mm, and a radius of curvature of 250 mm and 30 mm, and is made of PC resin. When this lens was manufactured by the method of the patent application mentioned above, only a surface accuracy with a deviation of 130 to 100 μm was obtained, but when manufactured under the manufacturing conditions shown in Table 1 according to this specific example, the lens surface accuracy was 3.0
~1.0μm, dramatically higher precision plastic

【table】

[Table] I was able to obtain a stick cleanse. In addition, the lens shape of specific example B has an outer diameter of 47 mm, a center thickness of 14.5 mm, an outer diameter thickness of 1.0 mm, and a radius of curvature of 88 mm.
A 31mm convex lens made of PC resin. on the other hand,
The lens shape of Example C has an outer diameter of 21 mm and a center thickness.
It is a concave lens with a diameter of 1.8 mm, an outer diameter of 5.8 mm, and a radius of curvature of 23 mm and 17 mm, and is made of PMMA resin. In any of these cases, the lens surface accuracy should be 2.0 to 1.0 μm.
We were able to obtain a high-precision plastic lens. In Table 1, during compression molding, the mold temperature is maintained at a constant temperature above the heat distortion temperature between t ₃ and t ₄ for 4 minutes in Example A, 5 minutes in Example B, and 1 minute in Example C. It is.
During the slow cooling period t ₄ - _{t 5} after t ₃ - t ₄ , specific example A is 6 minutes;
Specific example B takes 10 minutes, and specific example C takes 4 minutes. _t4 − _t5
The cooling rate during slow cooling in Example A was 1.7°C/min,
Specific example B is 3.0°C/min, and specific example C is 5.0°C/min. The time required to equalize the resin temperature in the mold cavity and the cooling rate to cool while maintaining a uniform temperature distribution are as shown in Table 1, depending on the lens shape to be molded, the resin used for molding, Naturally, it varies depending on the size of the mold. Therefore, the present invention is not limited to the manufacturing conditions shown in Table 1, but includes the temperature at which the mold temperature is maintained at a constant temperature _T2 in the softening temperature range of the resin, the interval _t3 - _t4 , and the slow cooling interval. _t4 − _t5 , _t4 − _t5
It goes without saying that the cooling rate between them may be determined depending on the lens shape, resin, mold size, etc. The specific example shown in Table 1 is a lens using PMMA resin and PC resin, but the present invention is not limited to this and can be applied to molding a plastic lens of any shape using any type of resin. Of course it can be done. It goes without saying that the present invention can also be applied to injection compression molding of plastic parts other than lenses that require high shape accuracy. (Effects of the Invention) According to the present invention, the temperature distribution during solidification of plastic during injection compression molding can be made uniform, so that the molding shrinkage of the plastic lens when it stabilizes at room temperature after molding can be made uniform, and in the order of microns. It is possible to manufacture a plastic lens with high shape accuracy and less wrinkles and warpage. This effect is especially noticeable for lenses with large thickness differences and significant shape asymmetry, such as concave lenses.
In the case of a concave lens made of PC resin with an outer diameter thickness of 12.7 mm, the surface accuracy, which had a deviation of 130 to 100 μm using conventional methods, was dramatically improved to 3.0 to 1.0 μm. According to the present invention, the optical performance of plastic lenses can be made much closer to that of glass lenses, and the applications of plastic lenses, which are lighter and lower cost than glass lenses, can be further expanded.

[Brief explanation of drawings]

Fig. 1 is a block diagram of a molding control device according to an embodiment of the present invention, Figs. 2 and 3 are graphs showing experimental data explaining the principle of the present invention, and Fig. 4 is an injection compression apparatus according to an embodiment of the present invention. FIG. 5 is a sectional view of a molding die, FIG. 5 is a sequence diagram of injection compression molding control according to an embodiment of the present invention, and FIG. 6 is a temperature-time curve diagram for explaining the operation of an embodiment of the present invention. . 1... Fixed type, 2... Fixed type inserting piece, 6... Movable type, 9... Movable type inserting piece, 11... Hydraulic cylinder, 13... Cavity, 19, 25, 29...
Cooling hole, 21, 26, 31...Thermocouple, 20, 2
4, 30... Heater, 34... First temperature controller, 3
5...Second temperature controller, 53...Hydraulic pressure generator, 57
a, 57b, 57c...Heater controller, 4
0...Program controller.

Claims (1)

[Claims] 1. Between a first insertion piece provided on one of the fixed and movable molds and a second insertion piece provided on the other mold, which are arranged opposite to each other. Inject and fill resin into the cavity formed in
In the injection compression molding method in which the resin is cooled and solidified, the temperature distribution of the resin in the cavity is once made uniform in the softening temperature range, and then the resin is slowly cooled to a heat distortion temperature that takes the resin out of the softening temperature range. An injection compression molding method characterized in that the resin is cooled while minimizing the occurrence of temperature non-uniformity. 2. The first and second insertion pieces are held within the temperature range of the heat distortion temperature of the resin to (heat distortion temperature + 40°C) ±
The injection compression molding according to claim 1, wherein the temperature distribution of the resin in the cavity is made uniform in the softening temperature range by once maintaining a constant temperature of 5°C. Method. 3. In the temperature range of (thermal distortion temperature of resin + 40°C) to (thermal distortion temperature - 20°C), the first and second insert pieces were slowly cooled at a cooling rate of 5°C/min or less. The first claim characterized in
The injection compression molding method described in Section 1. 4 A fixed mold and a movable mold arranged opposite to each other, a first insertion piece provided on either one of the fixed mold and the movable mold, and a second insertion piece provided on the other. In an injection compression molding apparatus that injects and fills a resin into a cavity formed between the first and second insert pieces, and cools and solidifies the resin, the first and second insert pieces are placed within the softening temperature range of the resin. a first temperature regulator that heats at a constant temperature and then gradually cools it to a heat distortion temperature that takes it out of the softening temperature range; and a first and second inserting piece before the constant temperature heating and after the slow cooling An injection compression molding apparatus characterized by comprising a second temperature controller for rapid cooling.