JPS6210177B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for controlling heat compression molding, and its purpose is to produce a plastic that has a short molding time, excellent transferability from a molding die, and has good optical properties. The object of the present invention is to provide a method for controlling heating compression molding to obtain a lens. Large and thick plastic lenses, such as projection lenses for projection television receivers, are manufactured using a heat compression molding method to meet optical requirements.

The general steps of the molding method will be explained using FIG. 1. In other words, the finished lens volume (thickness H,
The outer diameter (D) is the same, and the wall thickness is Δ as the compression allowance.
A blank 1 as shown in FIG. 1a is prepared, which has a shape similar to a lens in which the outer diameter is increased by H and conversely reduced by ΔD. Next, in the heating step, the surface of the lens blank 1 is heated by the molding die 2 as shown in FIG. Next, in the compression process, the lens 3 shown in d is manufactured by pressure molding and cooling as shown in d. As a result of research conducted by the inventors, it has been found that in this conventional heating compression molding method, the curvature of the lens blank supplied to the molding die has a large effect on the physical properties of the lens. That is, when the curvature of the lens blank 1 is smaller than the cavity curvature as shown in FIG. 2, an air pocket 4 is created in the center of the lens surface during the compression process, and the adhesion of the lens blank surface to the mold is reduced. becomes incomplete, and the transferability of the lens surface becomes insufficient. It has also been found that similar defects are likely to occur even if the curvatures of both are made equal.

As a result, the lens surface accuracy or lens shape accuracy decreases, and optical characteristics deteriorate due to various aberrations that cause curvature of field and the like. Therefore, in the present invention, the lens blank 1 is selected to have a curvature larger than the curvature of the inner surface of the molding die 2, as shown in FIG. 2b. That is, the lens is shaped so that there is a gap G between the surface of the lens blank 1 at a distance D from the center axis CL of the lens blank 1 and the inner surface of the molding die 2 to be pressed against the surface, as shown by the chain line in the figure. A blank 1 is preformed. As a result of various tests and studies, we found that the above disadvantages cannot be eliminated unless the gap G is generally at least 0.1 mm (when D = 50 mm, however, if the outer diameter is 50 mm or less, consider an extended surface), and that the above drawback cannot be eliminated if the gap G is set too large. It was confirmed that this resulted in poor heat conduction between the molding die 2 and the lens blank 1, requiring a long time for compression molding, and making the finished lens more likely to generate internal stress that would cause aberrations. In addition, with this type of plastic lens made of acrylic resin, D
It was confirmed that transferability is completely ensured when G is 0.2 mm or more, and when G is 50 mm or more, internal stress becomes noticeable when it is about 0.5 mm or more.
The range of G is preferably 0.2 to 0.5 mm.

However, even in this shape, the contact area of the lens blank and the deformation resistance of the lens blank fluidized layer vary greatly depending on the movement state of the mold parting surface. For this reason, molding defects may occur due to variations in lens blank heating conditions such as mold temperature and compression ram speed.

Therefore, the present invention further provides a method for controlling hot compression molding that eliminates the above-mentioned drawbacks and produces a plastic lens with excellent optical properties. Therefore, in the present invention, in order to prevent molding defects and molding defects caused by fluctuations in molding conditions, the mold temperature during the lens blank heating process is measured and the compression ram speed is adjusted based on that information. The heating compression molding state can now be controlled.

Hereinafter, the method for controlling heat compression molding of a plastic lens according to the present invention will be described in detail with reference to the drawings.

FIG. 3 is a block diagram showing an example of a plastic lens heating compression molding apparatus and its control apparatus used in the practice of the present invention. In this figure, 2
1 is a molding die, 10 is a cavity formed in this molding die 2, and 11 is a mold temperature control flow path used for heating and cooling the lens blank 1. The compression molding machine includes a fixed platen 12, a movable platen 13, a compression ram 14 and a compression cylinder 15 for driving the movable platen 13, and is connected to a hydraulic pressure source 16 via an electro-hydraulic control valve 25. .

This control device can be divided into a detection section, a calculation section, and a control section according to their functions. The detection unit includes a speed sensor 19 that detects the moving speed of the parting surface of the molding die 2, and a speed changer 2 that amplifies the signal detected by the speed sensor 19.
0, and a temperature sensor 17 that measures the state of the heating heat source of the lens blank 1;
It consists of a temperature converter 18 which amplifies the signal detected by 7. The calculation unit outputs a control signal for the molding machine based on the input information detected by the standard mold temperature setter 21, standard deformation speed setter 22, and both sensors for setting standard heating conditions for the lens blank 1. controller 2
It consists of 3. The control unit includes a power amplifier 24 that amplifies the control signal and an electrohydraulic control valve 2 that converts the control signal into a state quantity of hydraulic fluid.
It consists of 5.

The operation of the control device configured as described above will be explained based on the fluctuation behavior of the heating state shown in FIG. Fourth
Graphs 30, 31, 32 and 32 show temporal changes in mold temperature, compression ram displacement, compression cylinder oil pressure, and compression ram speed, respectively, during the lens molding process of the present invention using the apparatus shown in FIG. 3
3 is exemplified.

As shown in the figure, in a mold heating step 34, the temperature of the molding mold 2 is raised by a heating medium supplied to the mold temperature control channel 11 based on the conditions of the standard mold temperature setting device 21.

Time a when the temperature of the molding die 2 rises to a predetermined temperature
Then, the lens blank 1 is put into the cavity 10, and a fluidized bed is formed in the lens blank heating step 35. Thereafter, the plastic lens is pressurized and molded in a compression step 36, and then passed through a cooling step 37 to produce a plastic lens.

In the lens blank heating step 35, the controller 23 captures the mold temperature that is the lens blank heating source, and compares that value with the standard mold temperature setting device 21.
Compare the setting values. If there is a deviation in the mold temperature, the amount of deviation is converted into a lens blank deformation speed at which the heating effect on the lens blank is equivalent. Further, the controller 23 calculates a lens blank deformation speed target value to be controlled based on the converted deformation speed correction amount and the setting value by the standard deformation speed setter 22.

The controller 23 monitors the heating state of the lens blank, and if a deviation from the control target occurs, outputs a correction signal according to the deviation, and performs compression molding via the power amplifier 24 and the electro-hydraulic control valve 25. control the machine. That is, the compression molding machine is controlled to stabilize the heating state of the lens blank by keeping the amount of heat supplied to the lens blank per unit deformation stroke of the lens blank constant.

As described above, according to the present invention, the lens blank shape, mold temperature, and lens blank deformation speed, which have important effects on optical properties, are managed so that the lens blank is heated to an appropriate state. It becomes possible to mold plastic lenses with excellent properties. Furthermore, since the molding state is tracked and controlled, fluctuations in the molding state for each molding cycle can be suppressed to a minimum.
As a result, the practical effect was that the molding defect rate could be reduced to less than 1/5 of the conventional rate.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the hot compression molding method, Fig. 2 is a schematic diagram of the lens blank shape, Fig. 3 is a schematic diagram of the control device according to the present invention, and Fig. 4 is a diagram showing temporal changes in the molding state according to the present invention. FIG. 1... Lens blank, 2... Molding die, 3... Lens, 17... Temperature sensor, 19... Speed sensor,
23...Controller, 25...Electro-hydraulic control valve, 3
4... Mold heating process, 35... Lens blank heating process, 36... Compression process, 37... Cooling process.

Claims (1)

[Claims] 1. In a method of molding a plastic lens by heating and compressing a lens blank with a larger wall thickness and a smaller outer diameter than a finished lens in the cavity of a molding die, the curvature of the lens blank is made larger than the curvature of the inner surface of the molding die, and , the mold temperature and the lens blank deformation speed in the lens blank heating process are measured, the standard mold temperature and the standard deformation speed are set in advance, and the change in the mold temperature in the lens blank heating process is measured. and controlling the pressure and flow rate of hydraulic oil supplied to a compression cylinder so that the molding state follows the control target obtained by calculation based on the standard molding state. Method.