JPS5947974B2 - Method and apparatus for heat compression molding of plastic lenses - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a compression molding method and apparatus for manufacturing plastic lenses.

Large and thick lenses, such as the projection lenses used in projection televisions, are generally made by injection molding a lens blank from polycarbonate or acrylic resin, and then heat compression molding according to optical requirements. It is manufactured using the method.

However, plastic lenses manufactured by such conventional methods inevitably suffer from various aberrations, and no lens with satisfactory optical performance has yet been found. Next, the reason for this will be explained with reference to FIG. FIG. 1 is an explanatory diagram of a conventional plastic lens molding method, in which 1 shows a lens blank as a lens material, 2 a molding die, and 3 a molded lens.

The lens plank 1 shown in a of this figure is the lens 3 shown in d.
However, the volume is the same, the wall thickness is large, and the outer diameter is small. That is, the outer diameter and wall thickness of the lens 3 are set to D, 5- as shown in the figure.
From H to D-ΔD (5-H+ΔH) of the lens plank 1, the compression allowance is given.The lens plank 1 is charged into the molding die 2 as shown in b and heated to form a fluidized layer on the surface of the lens plank 1. Next, the process moves to the compression step c, where the lens 3 d is obtained by pressure molding and cooling. In such a conventional heat compression molding method, the lens plank 1 as a material is Variations in the volume of the lens have a large effect on the characteristics of the finished lens 3. That is, if the volume of the lens plank 1 is larger than the cavity volume of the mold (hereinafter simply referred to as mold volume), the mold parting surface 5 will be in close contact with each other. Therefore, mold compressive force is applied to the solidified layer inside the lens plank in addition to the fluidized bed of the lens plank 1. Therefore, depending on the conditions of this compressive force, internal stress may occur in the solidified layer. , birefringence is unevenly distributed in the lens 3. Therefore, various aberrations, especially chromatic aberration, are observed in the lens 3. Conversely, when the volume of the lens blank 1 is smaller than the mold volume ι, the mold parting surface is in close contact with the lens 3. Since the lens blank 1 is heated and formed while the lens blank 1 is being heated, the compression molding of the lens blank 1 is insufficient, the transferability of the surface is incomplete, and the lens surface precision and shape precision are poor. , the lens 3 causes various aberrations, resulting in a significant decrease in optical performance.The purpose of the present invention is to eliminate the above-mentioned conventional drawbacks, and to provide excellent optical performance by heat compression molding. Our goal is to provide a method and equipment for making plastic cleansers.

This method measures the hoop stress of the mold that occurs during the molding process, and uses the measured value to adjust and control the ram pressure of the heating compression molding machine, thereby ignoring variations in the volume of the lens plank. This makes it possible to obtain a lens 3 with excellent performance. Upon completion of the present invention, the inventor conducted detailed tests and studies on the correlation between lens molding conditions and the resulting optical performance.

That is, as a result of variously changing molding conditions such as the shape of the lens blank, heating temperature, and ram pressure of the compression molder, and observing the accompanying behavior of mold stress and lens physical properties,
It was confirmed that the hoop stress of the mold, which is stress acting in the direction of the outer circumference of the lens plank, has a large effect on the optical performance of the molded lens. The relationship between the hoop stress during compression molding, the surface precision representing the transferability of the lens surface to the inner surface of the mold, and the birefringence representing the degree of internal stress generation are shown in FIGS. 2 and 3, respectively. As is clear from FIG. 2, as the hoop stress increases, the surface precision of the lens improves and approaches the mold cavity surface precision of 4, that is, it becomes completely transferred. This phenomenon is caused by the heating temperature of the lens plank and the temperature of the inner surface of the mold (T1 to T
4. The higher Tl<T2<T3<T4), the smaller the hoop stress is and the higher the surface accuracy 4 of 10096 can be obtained. Also, as is clear from Figure 3, as the hoop stress increases,
The larger the birefringence index, which indicates the degree of internal stress, the greater the aberrations that occur in the molded lens. There is a region where the graph line in the figure and the horizontal axis coincide, and this region becomes larger as the mold temperature increases. The present invention has been made based on the above results, and when molding is performed with the volume of the lens blank approximately 1% larger than the mold volume by controlling the hoop stress of the mold during molding. The present invention takes advantage of the fact that it has been confirmed that a surface precision that is sufficiently satisfactory for practical use can be obtained, and that uneven distribution of internal stress and birefringence can be almost completely eliminated.

Hereinafter, the present invention will be explained in more detail with reference to the drawings. FIG. 4 shows a schematic diagram of an embodiment of a plastic lens molding apparatus according to the present invention. In this figure, 2 is a molding die that forms a cavity 9, 10 is a temperature control flow path through which a heat medium for heating and cooling the lens blank 1 is passed, 11 is a movable plate, and 12 is a fixed plate. The molding die 2 is held between the fixed plates 12, and the movable plate 11 is driven by the molding machine ram hydraulic pressure of the compression cylinder 13 driven by the hydraulic pressure generating source 25. Further, a detection section, a calculation section, and a control section are provided. The detection section is provided with a temperature sensor 14 that detects the temperature of the molding die 2 and a stress sensor 15 that detects the hoop stress of the shaping die 2, and preferably a temperature converter IT that amplifies the signals from these sensors and a stress sensor 15 that detects the hoop stress of the forming die 2. It is configured by providing a converter 21. The calculation section includes a standard mold temperature setter 16, a mold temperature calculator 18, and a standard hoop configured as shown in FIG. 4, for example, to obtain a control target value based on the mold temperature detected by the temperature sensor 14. Stress setting device 19, hoops dress calculator 2
0 is provided. Furthermore, a controller 22 is provided which compares and calculates the control target value output from the hoop stress calculator 20 and the hoop stress measurement value detected by the stress sensor 15, and outputs a control signal for controlling the molding machine ram hydraulic pressure. The control section includes a power amplifier 23 that amplifies this control signal.
and an electrohydraulic control valve 24 provided between the compression cylinder 13 and a hydraulic pressure generation source 25. The functions of the heat compression molding apparatus constructed in this way will be explained with reference to FIG.
In FIG. 5, the horizontal axis shows the molding process of this apparatus, that is, the mold heating process 30, the lens blank heating process 31. compression step 32;
The cooling process 33 is taken, and the vertical axis shows mold temperature 26, movable platen displacement 27, molding machine ram oil pressure 28, and molding mold houb stress 2.
9 is used to illustrate these changes. The molding die 2 is heated in a die heating step 30 according to a known technique.
It is heated by the heat medium supplied to the temperature control channel 10 and reaches a predetermined temperature. At that point, the lens blank 1 is inserted into the molding die 2 and proceeds to a lens blank heating step 31 to form a fluidized layer on the surface. Next, according to the compression molding method of the present invention, a compression step 32 is followed by a cooling step 33. Note that it is preferable that the supply control of the heating or cooling heat medium in each of the above steps be performed by the controller 22 based on the conditions set in the standard mold temperature setting device 16 and the standard hoop stress setting device 19, respectively. (This configuration is not shown in Figure 4). When moving to the compression step 32, the mold temperature is constantly measured by the temperature sensor 14,
At the same time, the stress sensor 15 measures the mold hoop stress.

On the other hand, based on the mold temperature and hoop stress values preset in the standard mold temperature setting device 16 and standard hoop stress setting device 19, respectively, the surface accuracy is excellent as shown in FIGS. 2 and 3. Standard molding conditions that do not cause birefringence are determined by the mold temperature calculator 18 and the hoop stress calculator 20. Next, the obtained standard molding conditions and the measured value of the mold temperature are compared, and the hoop stress control target value is output from the hoop stress calculator 20. Then, in the controller 22, the control target value and the hoop stress measurement value by the stress sensor 15 are compared and calculated to obtain a control signal for controlling the molding machine ram hydraulic pressure. This control signal drives the electro-hydraulic control valve 24, and the pressure and flow rate of the hydraulic oil supplied from the hydraulic pressure source 25 to the compression cylinder 13 are controlled so that the hoop stress measurement value follows the control target value. Ru. The procedure for determining the control target value according to the embodiment shown in FIG. 4 is as follows. That is, if there is a deviation between the measured value of the mold temperature and the set value of the standard mold temperature setting device 16,
The mold temperature calculator 18 converts the deviation amount into an equivalent hoop stress correction amount based on the empirically determined mold temperature that affects the relationship between hoop stress, surface accuracy, and birefringence. Next, in the hoop stress calculator 20, the equivalent hoop stress correction amount is corrected by the setting value of the standard hoop stress setting device 19, and is converted into a control target value or a hoop stress target value. In the cooling process, as in the compression process,
Mold temperature and hoop stress are constantly measured.

Then, as in the case of the compression process described above, a control target value is determined by the hoop stress calculator 20 based on the standard molding conditions determined empirically and the measured value of the mold temperature, and this control target value and the hoop A control signal is determined by the controller 22 based on the stress measurement value. Next, the pressure and flow rate of the hydraulic oil supplied to the compression cylinder are controlled by this control signal so that the measured hoop stress value follows the control target value. As described above, according to the present invention,
The hoop stress of the mold, which affects the optical performance of the plastic lens after molding, is properly managed.
A plastic lens with excellent surface precision and no birefringence can be obtained by compression molding.

Furthermore, since the molding state is constantly monitored and controlled, variations in molding conditions from molding cycle to molding cycle can be suppressed.
As a result, the molding defect rate is significantly reduced, for example to Z or less, compared to the conventional case.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the conventional plastic lens molding method, Figure 2 is a graph showing the relationship between hoop stress and surface accuracy during compression molding, and Figure 3 is a graph showing the relationship between hoop stress and birefringence. Graph diagram, Figure 4 is a schematic diagram of the compression molding apparatus according to the present invention, and Figure 5 is a graph diagram showing mold temperature, movable platen displacement, molding machine ram oil pressure, and mold hoop stress in each molding process. be. 1... Luns blank, 2... Molding mold, 11... Movable plate, 12... Fixed plate, 13... Compression cylinder 114 ...Temperature sensor, 15...Stress sensor, 16...
・・Standard mold temperature setting device, 18 ・・Mold temperature calculator, 19 ・・Standard hoop stress setting device, 2
0... Hoop stress calculator, 22...
・Controller, 24...Electrohydraulic control valve, 2
5... Hydraulic pressure source.

Claims (1)

[Claims] 1. In a method of molding a plastic lens by heating, compressing, and cooling a plastic lens blank, the temperature and hoop stress of the molding die in the compression process and the cooling process are measured, and A hoop stress control target value is determined by comparing the standard molding conditions determined by the mold temperature value and the hoop stress value with the measured mold temperature value, and the hoop stress control target value is determined by adding the value of the mold to the control target value. A method for heating and compression molding a plastic lens, characterized by controlling the pressure and flow rate of hydraulic oil supplied to a compression cylinder so that a hoop stress measurement value follows. 2. In an apparatus for heating and compression molding a plastic lens using a molding die 2 held between a fixed platen 12 and a movable platen 11 fixed to a ram hydraulically adjustable compression cylinder 13, the temperature of the molding die 2 is A detection section consisting of a temperature sensor 14 that detects hoop stress and a stress sensor 15 that detects hoop stress is provided, and then the measured value of the temperature sensor 14 and the mold temperature value preset in the standard mold temperature setting device 16 are combined. a hoop stress calculator 20 that compares and calculates a hoop stress value preset in a standard hoop stress setting device 19 and outputs a control target value; and a hoop stress calculator 20 that outputs a control target value and the control target value and the stress sensor 15.
A calculation unit is provided, which includes a controller 2, 2 that inputs and processes the measured values of , and outputs a control signal, and also generates hydraulic pressure via an electro-hydraulic control valve 24 that is controlled by the control signal. 1. A heat compression molding apparatus for plastic lenses, characterized in that the apparatus includes a control section that connects a source 25 and the compression cylinder 13.