JPS6131216A - Plastic lens shaping method - Google Patents

Abstract

PURPOSE:To manufacture a high-precision thermoplastic lens with a high rate of productivity by applying ultrasonic waves to a thermoplastic resin material. CONSTITUTION:When the radii of curvature R1, R2 are to be obtained on a lens, the top end 4 of the hole 1 is mirror-finished to the radius R1 and attached to an ultrasonic wave generating sorce. A lens blank 2 manufactured for example by injection molding is mounted on an anvil 3 having a lens shaping surface 5 which is mirror-finished to the radius of curvature R2. Then the hone 1 is dropped or the anvil 3 is lifted to apply ultrasonic vibration to the lens blank by the ultrasonic-vibrating hone 1. When the finished lens surface is convex, the lens blank 2 is a little smaller in the radius of curvature than the lens surface shaping part. When the finished lens surface is concave a little larger radius of curvature is used to the lens blank. The same basic principle is also used for an aspherical or a plane lens and the center part of the lens blank 2 first comes into contact with the anvil or the hone.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for manufacturing lenses made of thermoplastic plastics such as polymethyl methacrylate (hereinafter referred to as acrylic resin), and in particular, a method for efficiently manufacturing high-precision plastic lenses. It relates to a method for forming plastic lenses suitable for.

[Background of the invention]

Plastic lenses have come to be widely used because they are lightweight, hard to break, and inexpensive. However, conventional plastic lenses are manufactured using injection molding methods, compression molding methods, casting molding methods, etc., and are generally inferior in precision. In reality, the scope of its use was limited to soft lenses. On the other hand, many attempts have been made to process methods to improve the molding precision of plastic lenses. For example, in injection molding, as detailed in Japanese Patent Application No. 55-146407, there is a method in which the mold is cooled while rotating to apply centrifugal force to the injected resin, and a method that cools the surface layer of a lens blank. A method of heat-melting and thermal compression has been proposed. These methods are effective to a certain extent in improving precision, but the former requires complicated equipment and the cooling rate cannot be increased beyond a certain level in order to maintain the fluidity of the filled resin, and the latter increases the heat capacity. Since the lens blank is heated with a large mold, it wastes energy and takes time to heat and cool, both of which have the disadvantage of lower productivity and higher costs.

Another method has been proposed to increase precision by applying ultrasonic vibrations to the lens shaping surface of the cavity during injection molding, but when performing high precision molding, for example, with acrylic resin, the mold temperature is 90 to 100 C. There is no ultrasonic oscillator that can withstand long-term use at such high temperatures, and it is difficult to assemble the ultrasonic oscillator in a mold, making it difficult to realize it easily.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plastic lens shaping method that eliminates the above-mentioned drawbacks in manufacturing conventional plastic lenses and that allows high-precision thermoplastic lenses to be manufactured with good productivity.

[Summary of the invention]

The present invention was made based on the fact that by applying ultrasonic waves to a thermoplastic resin, the vicinity of the contact area of an ultrasonic tool horn and anvil (cradle) can be locally melted and shaped in a short time. be.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to the drawings.

First, the overall configuration will be explained using FIG. 1.

In Figure 1, 1 is a horn, 2 is a lens blank, and 3
is an anvil, and 8 is a positioning tool.

When trying to obtain the radius of curvature R,,R, of the lens, horn 1
The tip 4 of the lens is mirror-finished to a radius of curvature R by a known method, and attached to an ultrasonic generation source (not shown), and the lens-shaping surface (horn facing surface) 5 is mirror-finished to a radius of curvature R1 by a known method. A lens blank 2 manufactured by a known method (e.g. injection molding) is placed on the anvil 3, and the horn 1 is lowered or the anvil 5 is raised (the horn 1 is at the position indicated by the two-dot chain line in Fig. 1). Ultrasonic vibrations are applied by a horn 1 that vibrates sonically. At this time, it is important that the horn tip 4 and the vicinity of the center of the lens shaping surface 5 of the anvil are brought into contact with the lens blank 2 first. This is because the horn tip 4 or the periphery of the lens shaping surface of the anobile is first formed into the lens blank 2.
This is because when it comes into contact with the lens, it is melted and shaped from the contact area, creating an air pocket near the center and causing defects on the lens surface. Therefore, when the finished lens surface is convex, a lens blank with a radius of curvature that is slightly smaller than the radius of curvature of the horn or anvil's lens surface shaping part is used, and when the finished lens is concave, the lens blank is It is necessary to use a lens blank having a slightly larger radius of curvature, such as the lower surface 7' of the lens blank 2'. The basic idea is the same whether it is an aspherical or flat lens.
As shown in the example in which the upper surface 6' of the lens blank 2' is shaped into a flat surface, a lens blank is used in which the center portion contacts the umbilar or horn first. At that time, the gap l at the outer periphery of the lens was determined to be between '50 and 200 μm1 as a result of the experiment.
It has been found that the thickness is preferably 50 to 100 μm. If the gap is smaller than this range, air pockets are likely to occur, whereas if it is larger, defects such as incomplete shaping or eccentricity may occur.

When manufacturing an acrylic resin biconvex lens with a diameter of 20mm, radius of curvature on both sides of 20m and 40m, and thickness at the center of 5m+, the radius of curvature on both sides is approximately 195mm and 38mm, and the thickness at the center is 5mm.
A 15+m lens blank was made by injection molding and the gate portion was finished. The lens blank may be a normal injection molded product, even if it has some sink marks. The horn and anvil are machined from a block of stainless steel Assub Starbucks steel (trade name), and the tip of the horn is finished with a concave mirror finish with a radius of curvature of 40 meters, and the anvil is finished with a concave mirror finish with a radius of curvature of 20 m. I used it.

Assemble the device so that the central axis of the horn 1 and the central axis of the anvil 3 are aligned, and attach the anvil h5 (on the DV lens shaped surface 5,
Place the lens blank with the radius of curvature of 195 mm facing down, and fix the lens blank 2 with positioning tools 8 provided at three locations at 120° pitch on the outer circumference of the lens blank 2.
While applying ultrasonic vibrations of 5 KHz (width: 60 μm) to the horn 2, the horn was pressed with a force of 50 Kf. After applying ultrasonic oscillation for 5 seconds, static pressure (50 KF) was further applied for 10 seconds, and then the horn 1 was raised to remove the pressure. The shaped plastic lens is inspected using an eccentricity measuring device, and if eccentricity exceeds a permissible value, it is corrected by adjusting the position of the anobile and positioning tool.

At this time, if the lens blank surface is dirty with dirt, dust, etc., concentric clouding may occur on the shaped lens surface. This tendency is particularly strong as the lens diameter increases. To prevent this, after cleaning and drying the lens blank in advance, remove static electricity using a known method (in the experiment, the ionization effect of corona discharge was used. Last month's Erminostat model 8H5 was used), and then place it on the anvil. After placing it on the camera and fixing it with a positioning tool, as shown in FIG.
Uses a BPI type discharge air nozzle connected to SH5. It is preferable to apply ultrasonic vibrations while blowing ionized air onto the lens blank through a clean air filter 10. Soft vinyl chloride was used as the film material.

According to experiments, the ultrasonic amplitude was 30 to 90 μm, preferably 50 to 80 μm, and the pressing force was 10 to 60 Kf.

It is best to make the horn in one piece; the lens shaping surface, i.e. the tip, is made separately and attached to the horn (screwed or welded).
In this way, the mounting part is easily damaged. Since the length of the horn is approximately 150 degrees, it is difficult to polish a surface with a small radius of curvature, so it is better to use a larger radius of curvature on the horn side.

The lens is first shaped at the center of the horn side, and then at the periphery of the horn side, and at the same time, the anvil side is also shaped. Therefore, when the radius of curvature is small at the start of application of ultrasonic vibration, a large force is applied to move the lens blank in the lateral direction.

Although it is fixed with a positioning tool, if the fixing force is too strong, melting will occur at the fixed part, so it can only be fixed with strong force. From this point of view, it is better to have a larger radius of curvature on the horn side, where the lens surface shaping begins first.

In the manner described above, a desired lens surface was formed.

It should be noted that this shaping method that applies ultrasonic vibrations may sometimes cause flaky bleed-out. In such a case, the lens blank should be structured with a flange 11 as shown in Figure 4 to prevent the melting part 12 from having an adverse optical effect, or to prevent the lens from becoming eccentric even after finishing. The above explanation uses acrylic resin as an example, but it goes without saying that it can be similarly applied to hard thermoplastic materials such as polystyrene, polycarbonate, and acrylonitrile styrene copolymers.

〔Effect of the invention〕

As described above, according to the present explanation, high-precision lenses can be easily obtained by adding a small amount of time (about 20 seconds per lens) to the normal injection molding time.

As a result, the processing time, which used to account for 80-90% of the cost of plastic lenses, has been reduced to 1-9%, and the cost has also been reduced by 40%-90%.
I was able to reduce it by a certain amount.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the basic configuration of the present invention, and FIG. 2 is a sectional view showing the basic configuration of the present invention.
FIG. 3 is a cross-sectional view showing a situation in which a lens of another shape is formed; FIG.
The figure is a cross-sectional view of a lens with a flange that is designed to prevent defects even if melting occurs. 1...Horn, 2...Lens plastic/ri,
5... Anvil, 8... Positioning tool, 10
...Static elimination air port, 11...horn. 1st bacteria 31st! 3rd 4th

Claims (1)

[Claims] 1. In manufacturing thermoplastic lenses with finished radii of curvature R_1 and R_2 and center thickness T, when the finished lens has a convex surface, the radius of curvature R_1-ΔR_1R_2-ΔR_ is slightly smaller than the finished radius of curvature mentioned above.
2, and when the finished lens is concave, the radius of curvature R_1 + ΔR_1 is slightly larger than the finished radius of curvature.
A lens blank having R_2 + ΔR_2 and a center thickness T + ΔT slightly larger than the finished center thickness is placed on an anvil that has been mirror-finished to one finished radius of curvature, and a positioning tool that prevents lateral movement is used to prevent lateral displacement. At the same time, ultrasonic vibrations are applied to the lens blank through a horn having a mirror-finished tip with the other radius of curvature, and the lens blank is pressed, thereby shaping the lens blank sequentially from the center to the periphery. Shaping method.