JPS61125820A - Plastic cleansing heating compression molding equipment - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a heat compression molding apparatus for plastic lenses, and in particular, to heat compression molding of plastic lenses aimed at improving productivity and improving shape accuracy through multi-cavity K. It is related to the device.

[Background of the invention]

As a molding method for plastic optical parts that improves shape accuracy such as flatness by heating compression molding, for example, Japanese Patent Laid-Open No. 5
A correction type shown in Japanese Patent No. 7-113052 is known.

In this method, when the number of molds is increased for the purpose of improving productivity, the molding process is affected by fluctuations in the volume of the blank, which is a plastic molded product formed into a shape similar to the final shape by injection molding, etc. Retention decreases. That is, if the wall thickness, outer diameter, etc. of the blank vary and the blank volume fluctuates, a deviation occurs in the compression pressure applied between each cavity. As a result, an excessive compression pressure acts on the cavity whose blank volume has changed to a larger one, and a large uneven distribution of so-called internal strain observed due to birefringence occurs. This causes optical aberrations such as chromatic aberration, resulting in deterioration of optical performance.

10,000 In the cavity where the lens blank volume has changed to the smaller side, compression pressure is not applied sufficiently, so the mold transfer to the cavity surface is incomplete, and the correction of sink marks etc. is insufficient, resulting in a significant deterioration of shape accuracy. do.

[Purpose of the invention]

It is an object of the present invention to eliminate the drawbacks of the prior art described above. To provide a heating compression molding apparatus for a glass lens which can mold an excellent lens with higher efficiency than a multi-piece molding machine.

[Summary of the invention]

The present invention includes a hydraulic cylinder that pressurizes and compresses the lens surface of each cavity, a mold temperature sensor that measures the temperature of the mold pieces forming each cavity, and a mold temperature sensor that measures the temperature of the mold pieces that form each cavity. It is equipped with a flow valve that adjusts the flow rate of the medium, and is characterized by appropriately controlling the compression molding conditions of each cavity according to changes in the blank.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG. tl/
FIG. E1 is a configuration diagram showing an embodiment of a heating compression molding apparatus for a glass lens according to an embodiment of the present invention. f4
In Fig. 1, 2 is a molding die, 4 is a lens insert piece for molding the lens surface, and a cavity 5 is formed in the molding die fi2.
It is formed and numbered. Reference numeral 6 denotes a mold temperature flow path, which has the function of controlling the metal temperature of the lens insert piece 4 using a heating medium or a cooling medium supplied from the temperature controller 7 via the flow path control valve 8. . (The return line of the heating medium is not shown.) The molding die 2 is connected to a fixed platen 9 and a movable platen 10 of a compression molding machine.
from the hydraulic pressure source 11 to the electro-hydraulic control valve 12
The compression ram cylinder 13 is provided with a compression pressure corresponding to the hydraulic pressure supplied to the compression ram cylinder 13 via the ram cylinder 13.

The lens insert piece 4 is assembled into the molding die 2 via a compression cylinder 14. The compression cylinder 14a.

144 is a hydraulic pipe 15 on each forward side and backward side.
are connected by As a result, the cavity 5a,
Even if there is a difference in volume between the lens blanks supplied to the lens blanks 54, the structure is such that by adjusting the ram stroke of the compression cylinder 14, the same amount of compression pressure always acts on both lenses. When the volume of the lens blank changes in this way, each compression stroke is changed to a
An elastic body such as a spring or rubber can be used as a material having the function of balancing the compression pressure by adjusting the pressure. However, connected oil cylinders are the most reliable in terms of reliability against temperature or stability over repetition.

The control device of the present invention has a detection section according to its function.

It consists of a calculation section and a control section. The detection unit includes a pressure sensor 16 that detects compression pressure acting on the lens surface.
．． A pressure transducer 24 that amplifies the signal detected by this pressure sensor 16, a displacement sensor 11 that detects the compression stroke, and a displacement sensor 1a that detects the amount of opening of the mold parting surface.The signals detected by these displacement sensors A displacement converter 19 for amplifying the signal, a temperature sensor 2Q% for detecting the metal temperature of the lens input piece, and a temperature converter 21 for amplifying the signal detected by the temperature sensor 20 are also constructed. The calculation unit is a molding condition setter 2 that inputs appropriate molding conditions determined in consideration of lens material and lens shape.
2. Similar to the device, the control unit includes a controller 23 that controls and monitors compression pressure, metal temperature, etc. in order to maintain appropriate molding conditions based on input information of observation results of the molding state. By controlling the flow rate of the heating medium or cooling medium supplied to the electro-hydraulic control valve 1λ which adjusts the flow rate or pressure of the hydraulic oil supplied to the compression ram cylinder according to the output control signal, the input piece temperature can be adjusted. A flow rate control valve 8 for adjustment is also configured.

Next, the operation of the control device configured as described above will be explained. The molding die 2 is heated to a predetermined temperature by the heating medium supplied to the mold temperature regulating flow path 6 by controlling the flow rate regulating valve 8 based on the conditions of the molding condition setting device 220. When the temperature of the molding die 2 reaches a predetermined temperature, a lens blank is placed into each cavity 5as 54, and a fluidized bed is formed in the lens blank heating process. In the compression process,
The controller 25 uses the information from the molding condition setting device 22 to
The hydraulic electric control valve 21C outputs a control signal to heat and compress the lens blank. If there is a difference in the volume of the lens blanks supplied to the cavity 5't 54 K, the hydraulic oil flows through the hydraulic pipe 15 until the hydraulic pressures loaded on the forward side (compression side) of the pressure cylinders 14a and 144 are equal. Move via. Therefore, non-uniform compression pressure due to the difference in volume of the lens blank does not occur, resulting in fluctuations in the lens thickness. Variation in lens thickness affects the optical system as a variation in fish collection distance, but this variation can be easily adjusted during lens assembly work. Furthermore, when the volume variation of lens blanks that occurs during normal molding is converted into variation in lens thickness, the amount is small;
In reality, there is no need to make any adjustments during assembly. However, this variation in wall thickness affects the cooling uniformity conditions and the 41HC cooling rate, causing deterioration of the lens surface precision.

For this reason, the inventors of the present invention made various changes in the shape and weight of the lens blank, compression molding conditions, etc., and investigated the correlation with the V y X performance. As a result, it was found that fluctuations in the mold temperature and lens wall thickness of the insert piece that forms the lens surface have a large effect on the lens surface accuracy. In other words, the relationship between the compression pressure and the lens surface shape is as shown in FIG. 2. As the compression force increases, the lens surface shape changes to the inserted piece shape kI! get closer Furthermore, this phenomenon shows a remarkable tendency as the temperature of the pieces entering the cylinder increases. Further, FIG. 3 shows the relationship between birefringence and compression pressure, which is a measure of the generation of internal stress and is very important in terms of optical properties.

That is, the birefringence index tends to increase rapidly as the compression pressure increases. However, it was confirmed that there is a region where the occurrence of birefringence has almost no optical effect at compression pressures below a certain level. This region tends to expand as the temperature of the lens entering the lens increases.

As a result of the above, it was confirmed that by appropriately controlling the molding conditions, it is possible to prevent condensation and internal stress, that is, biased pressure of birefringence, when the lens surface accuracy is satisfied.

Furthermore, the lens shape shown in Fig. 4, outer diameter: DcmIhwk 150as, radius of curvature: R, -405, R, -565.

Center thickness: Hsm15.0m11 was used as a sample to observe the mold temperature of the lens insert and the deformation behavior of the lens. That is, the amount of deformation of the lens was evaluated as the amount of warpage from the reference surface using a plane passing through the center of the lens edge portion as a reference. As a result, as shown in Fig. 5, as the cooling rate of the lens insert increases, the lens surface tends to have a convex shape upward with the radius of curvature 4 side as the upper surface, and the amount of warpage increases. However, near 209C/win, the amount of warpage is 15.20μm.
Reach K. Furthermore, this tendency tends to increase as the lens thickness increases, and conversely tends to decrease as the lens thickness decreases. Therefore, if the lens thickness changes, it should be adjusted accordingly.

It was confirmed that the amount of warp occurring on the lens surface could be corrected by adjusting the cooling rate of the lens insert.

The amount of adjustment of the cooling rate with respect to the variation in lens thickness is as shown in Fig. 6 (depending on the radius of curvature of the lens surface. In other words, in the lens shape shown in Fig. 4, only the radius of curvature is 200"1500"). 1000m, and examined the amount of correction of the cooling rate to correct the amount of warpage caused by the amount of wall thickness change.As a result, it was found that when the wall thickness variation range is ±Q, !sIk from the reference value. It was found that the amount of modification of the cooling rate changes almost linearly.

Therefore, the wall thickness variation is ±(in the range of L5jllB,
By correcting the cooling rate by an amount obtained by multiplying the amount of thickness change by a predetermined correction coefficient, it is possible to prevent warp deformation of the lens surface. However, this correction coefficient has individual values depending on the lens base thickness, outer diameter, etc., in addition to the lens radius of curvature shown in FIG. Therefore, it is necessary to experimentally understand this correction coefficient at the time when the lens shape is determined. This operation can be relatively easily understood by intentionally changing the weight of the lens blank, molding and measuring it several times.

Based on the above study results, the thermocompression molding apparatus for plastic lenses according to the present invention has a function to prevent fluctuations in compression pressure by using a compression cylinder and to adjust the cooling rate according to fluctuations in lens thickness. ing.

That is, the controller 23 detects the opening amount of the mold parting surface during the compression stroke with the displacement sensor 18, and also detects the compression stroke of one compression cylinder 14 with the displacement sensors 171 and 174.

Based on this information, the controller 2'5 accurately measures the lens thickness -jdW in each of the cavities 5a and 54, and calculates the deviation from the basic thickness.

The controller 23 controls this wall thickness deviation and molding condition setting device.
An appropriate cooling rate for correcting warp deformation is calculated and determined based on the standard cooling rate and wall thickness-cooling rate correction coefficient input by . In the cooling process, the flow rate of the cooling medium is adjusted by the flow rate control valve 8 to achieve an appropriate cooling rate. Furthermore, the mold temperature is monitored by a temperature sensor 20, and feedback control is performed to ensure stable molding conditions at all times.

The above explanation has been made using an example of two cavities, but it goes without saying that a larger number of cavities K can also be applied.

〔Effect of the invention〕

As explained above, (1) the heat compression molding apparatus for plastic lenses according to the present invention makes it possible to maintain a constant compression pressure (related to variations in the volume of lens blanks) and to select the optimum cooling rate for the lens thickness. As a result, it became possible to produce a large number of lenses, and feedback control of the molding conditions resulted in good stability, making it possible to mold good plastic lenses with high efficiency and high yield.

Specifically, four plastic convex lenses with a lens outer diameter of 150 ml and a lens center thickness of 20 ml were taken and molded. As a result, the conventional molding tact is 1 piece/24
This has the effect of shortening the time to 1/4 of 76 minutes for one piece (724 minutes for four pieces). Furthermore, the yield rate of single-cavity molding was improved from 75 to 90.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of an embodiment of the heating compression molding apparatus according to the present invention, and FIG. 2 is a diagram of the relationship between lens surface shape and compression pressure.
Figure 5 is a diagram of the relationship between birefringence and compression pressure, Figure 4 is an explanatory diagram of the amount of lens surface warp, Figure 5 is a diagram of the relationship between the amount of lens surface warp and the cooling rate of the input piece, and Figure 6 is , is a relationship diagram between fluctuations in lens thickness and correction amount of cooling rate. 2- Molding mold 4... Lens insert piece 5... Cavity 6... Mold temperature control flow path 8... Flow rate control valve 14... Compression cylinder 15... Hydraulic pipe 25... ·controller

Claims (1)

[Scope of Claims] 1. In a heating compression molding device in which a lens blank with a larger wall thickness and a smaller outer diameter than a finished lens is put into a cavity of a molding die and molded into a plastic lens through a heating process and a compression process. , multiple lens blanks are simultaneously molded using a molding die having multiple cavities, and the lens thickness, which depends on the volume of the lens blank supplied to each cavity, is detected by the amount of movement of the mold parting surface,
A heating compression device for a plastic lens, characterized in that the cooling rate of a lens insert piece is controlled according to variations in the lens thickness. 2. Incorporate the lens insert into the mold via a compression cylinder to which a compressed medium is connected by a flexible pipe, etc. to configure each lens cavity, and a displacement sensor that detects the compression stroke of each cavity, and a mold parting. A displacement sensor that detects the amount of opening of the surface, a flow control valve that controls the flow rate of the temperature regulating heat medium supplied to the lens input piece, and a controller that outputs a control signal to the flow control valve. A heat compression molding apparatus for plastic lenses according to claim 1.