JPS609716A - Manufacture of optical element - Google Patents

Abstract

PURPOSE:To obtain a molded article which is capable of using as an optical element, has no defect on the surface and is satisfactory from optical point of view, by making molding processing through heating and pressing actions by inserting reserve molded article obtained by processing an optical material in a predetermined surface roughness beforehand is inserted within a molding die. CONSTITUTION:A reserve molded material 21 obtained by molding in a predetermined shape and removing a flaw and a crack of the surface so that surface roughness is made less than 1/10mum desirably less than 1/100mum is placed on a bottom force 4, an upper force 3 and a weight 5 of the upper force 3 are set, a lid 2 of an airtight container 1 is closed, a water cooling pipe 20 is watered and a heater 8 is electrified. When a degree of vacuum has become less than 10<-2>Torr by opening a valve 12 and exhausting the inside of the airtight container 1 by an oil-seale rotary vacuum pump 11, inert gas is introduced into the container by closing a valve 12 and opening a valve 16. When an optical element is heated up to a temperature through which the optical element is capable of molding, pressure molding is performed by making a cylinder 10 act, pressing the bottom force 4 by a pressing rod 9 and applying pressure to the reserve molded material 21.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a pressure molding method for optical elements such as lenses and prisms. More specifically, the present invention relates to a method for pressure molding optical elements such as lenses and prisms. Place a predetermined capacity of optical element material between the molds and heat the material,
The present invention relates to a method for obtaining optical elements such as lenses and prisms by pressure molding using the pair of molds.

Conventionally, in order to produce lenses and prisms, a method has been adopted in which the material is ground with a diamond grindstone or the like, and then polished with cerium oxide (1) or the like. However, this method required a lot of labor for grinding and polishing, and required even more sophisticated technology, making it extremely difficult to produce lenses in large quantities at low cost. Many studies have been carried out in the past to solve these problems, one of which is U.S. Pat. A method for molding (up to 3 pieces) is disclosed. However, in the past, little attention was paid to the shape of the molded material, and in order to eliminate the so-called "injection" defect during molding, the sharp edges of the material were removed by barrel polishing, etc., giving it a rounded overall shape. For this reason, if the surface of the material has irregularities, minute irregularities will also occur on the surface of the pressure-molded optical element, so it is impossible to use it as an optical element without post-processing. It was possible.

(2) The present invention enables lenses to be formed simply by pressure molding optical element materials.
The aim is to provide a method for obtaining optically satisfactory molded products that can be used as optical elements such as prisms, have no surface defects, and are characterized by the removal of surface defects in advance as optical element materials. In other words, use a material made of a spherical or flat plate that has been formed into a predetermined shape so that the surface roughness is less than %μ, preferably less than Mooμ, and the scratches and cracks on the surface have been removed. It is in.

Furthermore, another object of the present invention is to mass produce the various types of lenses mentioned above in optical equipment such as cameras, in which a lens system is constructed by combining many lenses of a plurality of shapes, such as convex lenses, concave lenses, spherical lenses, and aspheric lenses, while maintaining the same precision. The purpose is to provide a manufacturing method that allows production. Still another object of the present invention is to provide a manufacturing method that does not require post-processing such as distortion removal for lenses formed by heating and pressurizing. According to the conventional and well-known pressure molding technology, an optical glass material is inserted into a mold (3) with a predetermined volume and weight, and then the material in the mold is molded onto the mold surface by heating and pressurizing action. However, if the shape of the optical material inserted into the mold is not fixed and there are convexes, concave parts, protrusions, needle-like acute angle protrusions, etc., these protrusions will be pushed down inside the material during the heating and pressurizing process. , a boundary surface (layer) is created in the finished lens, which causes distortion and affects optical properties such as light transmittance and refractive index of the lens, but the above purpose is to eliminate these problems. It's about doing.

One method of removing surface defects from a material is to remove surface defects by subjecting the material to a grinding and polishing process, as is widely known in the art. In this case, conventionally the surface accuracy (power,
Although irregularities (irregularities) have been considered to satisfy optical properties, in the present invention, there is no need to consider the finishing accuracy of the completed lens surface, but only scratches and cracks on the surface. Only surface defects such as cracks, protrusions, and depressions need to be removed.

Another method is to melt the material and pour it into a molten metal salt such as (4) tin, which is then cooled and solidified to remove surface defects.

An optical element is manufactured by pressure-molding the preformed material in this way. An embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a schematic diagram of a molding apparatus for heating and press-molding a preformed material obtained by preforming the optical material according to the present invention into a final target such as a convex lens, a concave lens, a Fresnel lens, an aspherical lens, etc.

2(A) and 2(B) show the molds (upper mold 3, lower mold 4) and preformed material 21 of the apparatus shown in FIG. 1, and FIG.
is a preformed material that has been preprocessed to have a predetermined surface finish accuracy (for example, in the case of a camera lens as described above, an accuracy of 'Aooμ or more) by removing scratches, cracks, protrusions, and depressions between the molds 3 and 4. (Fig. 2 (A)) and a view (Fig. 2 (B)) in which pressure is applied to the mold 4 to form the preformed material 21 into the final target lens from the state shown in Fig. 2. It is.

1 is an airtight container, 2 is its lid, and 3 is an upper mold for molding an optical element, the surface 3a of which is finished to the same degree as the surface of the optical bed (5). 4 is the lower mold, and its surface 4a is similarly finished. 8 is a heater, 9 is a pressurizing rod, 10 is a pressurizing cylinder, 11 is an exhaust oil rotary pump, and 12° 15.14, 16.18 are valves.

When molding an optical element, a preformed material 21 having a predetermined volume from which surface defects have been removed in advance, as referred to in the present invention, is placed on the lower mold 4, the upper mold 3 and the upper mold presser 5 are set, and the airtight container 1 is placed. Close the lid 2, pass water through the water cooling pipe 20, and turn on the heater 8.
energize.

At this time, all valves are closed. Note that the exhaust oil rotary pump is always in operation. When the pulp 12 is opened, the inside of the airtight container is evacuated, and when the degree of vacuum becomes 10 -2 Torr or less, the valve 12 is closed, the pulp 16 is opened, and an inert gas (for example, N2 gas) is introduced into the container. This is to prevent oxidation of the highly precisely finished surface of the mold. When the optical element is heated to a temperature at which it can be molded, the cylinder 10 is activated and the pressure rod 9 presses the lower mold 4 to apply pressure to the preformed material 21 to perform pressure molding. In addition, the lower mold (6) 4 in the figure is made of the same material as the net 6, and fits well and moves up and down. Once the preformed material has been formed into a predetermined shape, the temperature is gradually lowered. Once cooled sufficiently, the molded product is removed from the device and the operation is completed.

The shape of the preformed material in the present invention is shown in Figure 2 (A
) As shown in FIG. 6(A), it may be spherical, or it may be a disk with surface defects removed on the surfaces 21a and 21b of the material as shown in FIG. 6(A), as shown in FIG. 4(A). Similarly, the surfaces 21a and 21b of the material may be previously formed into spherical surfaces with a curvature approximating the shape of the optical element to be formed.

Particularly for a thick lens as shown in FIG. 4, it is effective to finish the lens to an approximate curvature in order to improve the density of the molded product.

Finishing the preformed material 21A with a curvature close to the final target shape of the lens 22A as shown in FIG. - When applying pressure to the preformed material 21A with the lower mold 4, the preformed material 21A is deformed by the pressure of the molds 3 and 4 into lenses (7) of the final target shape 22A. During deformation, a large pressure acts on a particular surface, for example, a point with a particularly large curvature, and this is useful for suppressing stress concentration, where stress is concentrated at or near that point, and the occurrence of distortion.

By suppressing this stress concentration and the occurrence of strain, the work to remove strain (runney ring work) that was previously required is no longer necessary. A major advantage of the present invention is that the glass material molding technology developed by the company can be applied not only to intermediate-level camera lenses with lens apertures of 10 to 20 φ, but also to large-diameter lenses for reflex cameras with lens diameters of around 60 φ. It was a success. Additionally, as mentioned above, the fact that there is no need for strain removal work after hot-pressing the preformed material 21A means that conventional strain-removing work requires several hours to several tens of hours for strain removal after hot-pressing forming. In short, a lot of time was wasted in the production process, such as adjusting the arrangement process and process work time, and the process of cable material - heating and pressing - forming - removing distortion - completion was (8) As shown in Figure 4, by finishing the outer surface shape of the preformed material to a curvature close to the final target lens shape, it is possible to carry out the next process, such as forming a lens barrel, without going through a distortion removal process after the forming process. The assembly process from materials to the completion of the lens barrel can be greatly shortened, and as a result, the so-called assembly process can be automated to eliminate non-defective products. It can make a great contribution to rationalization, such as improving production efficiency and streamlining the production process.

In order to clearly demonstrate the effects of the present invention, a material having surface defects on each ridge was molded using an apparatus implementing the present invention, and compared with a molded product using a material from which surface defects had been removed in advance. The results are shown in Table 1 and FIG.

The optical element material used to carry out the present invention is commonly known as 8II'14.
It is a flat plate with an outer diameter of 16.5 nm and a center thickness of 2.5 mm.

The surface 3a of the upper mold 3 was optically processed to have a curvature of 20.5 nm, and the surface 4a of the lower mold 4 was similarly optically processed to have a curvature of 55.5 tnm (9). Molding conditions are 570'O and 10 tons/
cI! A pressure of L2 was applied for 3 minutes.

In Table 1, +1200, +600, +250, etc. indicate finishing accuracy according to Japanese Industrial Standards (based on particle size distribution of fine powder according to JIB R6001/JIB), and RMAX
indicates the maximum surface roughness. Note that the blanks in Table 1 and FIG. 5 refer to the aforementioned preformed materials. The correspondence between Table 1 and Figure 5 is that the surface roughness measurement results for the blank in Table 1
The graph on the left of Figure 3 is shown, and the graph on the right of Figure 5 shows the measurement graph of the surface roughness of the final target lens (lens of 55.5 silk with a radius of curvature of 20.5 m1i) using a blank of the abrasive product.

As shown at the right end of each graph in FIG. 5, the graph scale of the measured roughness varies greatly from 0.02μ to 2μ depending on the finish level (HMAX) of the blank. This means that the degree of surface roughness of the molded product is completely different when the surface roughness of the blank is set to RMAX O, 01μ or less and when it is set to HMAX 7μ or less. That is, the surface roughness of the blank is RMAX Ooo
If it is 1μ or less (10), the surface roughness of the molded product will be about RMAX O,02μ,
This molded lens was able to pass the acceptance criteria for various optical characteristic factors such as lens surface flare and light transmittance. The surface roughness RMAXO002μ of the molded product is the same value as the finish roughness of the molding die, which means that if the surface roughness of the blank is RMAXO01μ, the surface roughness of the molding die will be the same as the surface roughness of the molding lens. It means to be faithfully reproduced.

In the case of a blank with a finished grain size of 1200 to 9250, the surface roughness of the lens of the molded product will be 0.11μ to 2μ or more, as shown in Table 1 and FIG. 5, and in particular, as shown in FIG. -A4, B1 to B3 Protruding points shown in degrees 01 to C4 were generated, and the optical properties, such as light transmittance, were significantly reduced due to the projecting points, making the lens unsuitable as a camera lens. In addition, the pressing force in the case of this example is the above-mentioned shape, outer diameter 16.5 mm, center thickness 2.5 mm,
In order to obtain a lens with a radius of curvature of 20.5 mm and a length of 55.5 mm, the pressure applied to the cylinder was approximately 10 kg 7 cm2. In this example, the surface roughness of the mold is 0.02μ,
(11) Although the pressing force was 110 Ic, it is of course possible to change the setting conditions according to the conditions of the optical characteristics of the lens, the size of the lens shape, and the size of the curvature.

In the above example, if the finishing roughness of the mold is further increased and the pressing force is increased, the finished surface of the molded product can be made such that even if the surface roughness of the blank is finished to 0.01μ, the surface roughness of the lens after molding is 0. It is understood from the above results that molding can be performed with a high precision of .01μ or more.

As described above, the present invention provides optical element molding in which an optical material is inserted into a mold, and an optical surface modeled after the mold surface of the mold is formed by heating and pressure molding the optical material. In the method, the optical material is preformed into a spherical, flat plate, shape, and surface defects such as scratches and cracks are removed, and the surface roughness is preprocessed to a certain extent to obtain a preformed material, The preformed material is inserted into the mold and subjected to heating and pressure molding,
The molding force (12) method according to the present invention does not require any post-processing or post-processing steps after molding using a mold, and can obtain the desired optical finishing accuracy (surface roughness). Since a mold that has been finished to the final target curvature and roughness is used, lenses with the same precision can be produced efficiently by making the material selection, heating conditions, and pressure conditions the same.

As shown in Example 4, by pre-processing the surface of the preformed material to a curvature close to the final target shape, the occurrence of distortion can be suppressed as described above, and production can be streamlined. It has the potential to be effective.

Table 1 (13)

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an example of the apparatus used to carry out the method of the present invention, Fig. 2 (A) and (B) are cross-sectional views showing a pair of molds, materials, and molded products, and Fig. 3 (A )(B), FIG. 4(A) (B) is a sectional view showing another embodiment of the present invention. Figure 5 shows the measurement results of the surface roughness of the raw material and the surface roughness of the molded product. 6.4...Molding mold 21.22...Preformed material applicant Canon Co., Ltd. (14)

Claims (1)

[Claims] A method for manufacturing an optical element, in which an optical material is inserted into a mold and an optical surface is formed by applying heat and pressure to the optical material, the optical material being brought to a predetermined surface roughness in advance. A method for manufacturing an optical element, comprising inserting the processed preform into the mold and performing molding by heating and pressurizing.