JPH0420854B2 - - Google Patents

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. This invention relates to a method for obtaining optical elements such as lenses and prisms by placing a predetermined volume of optical element material between the molds, heating the material, and press-molding the material 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 or the like.
However, this method requires a great deal of labor and expense for grinding and polishing, and requires highly skilled techniques to maintain the surface precision. In particular, manufacturing aspherical lenses requires even more advanced technology, and it has been extremely difficult to produce large quantities of lenses at low cost. Many studies have been conducted to solve these problems, one of which is the U.S. Patent No.
No. 3,833,347 and the like disclose a method for molding a highly accurate optical element (for example, power is within 6 Newton rings and irregularity is within 3). but,
Traditionally, not much attention has been paid to the form of the molded material, and in order to eliminate the defect called "indentation" during molding, the sharp edges of the material are removed by barrel polishing, etc., resulting in a rounded overall shape. It was moderately hot. For this reason, if the surface of the material has irregularities, minute irregularities also occur on the surface of the pressure-molded optical element, making it impossible to use it as an optical element without post-processing. The present invention aims to provide a method for obtaining an optically satisfactory molded product that can be used as an optical element such as a lens or prism simply by press-molding an optical element material, and has no surface defects. Its characteristics are as follows: 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, and the surface roughness of the optical element is In order to obtain an accuracy of R _nax 0.02 μm or less, the surface of the preformed optical material processed in advance must have a surface roughness of at least R _nax 0.01 μm or less, and the surface roughness of the mold should be R _nax 0.02. The method of manufacturing an optical element is characterized in that the preform is processed to an accuracy of μm or less, and the preform is inserted into the mold and molded by heating and pressurizing. Furthermore, another object of the present invention is to provide a convex lens for cameras, etc.
It is an object of the present invention to provide a manufacturing method capable of mass producing various lenses while maintaining the same accuracy in an optical device in which a lens system is constructed by combining many lenses of a plurality of shapes such as concave lenses, spherical lenses, and aspheric lenses. 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 known pressure molding technology, an optical glass material is inserted into a mold with a predetermined volume and weight, and then the material in the mold is molded onto the mold surface by heating and pressurizing. If the shape of the optical material inserted inside is not determined 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, and the finish will deteriorate. Boundary surfaces (layers) are created in lenses that have been modified, which can cause distortion and affect optical properties such as light transmittance and refractive index of the lens.The above-mentioned purpose is to eliminate these problems. be. 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/irregularity) has been considered to satisfy the optical characteristics, but in the present invention, it is necessary to consider the surface accuracy as much as the finishing accuracy of the completed lens surface. Instead, you only need to remove surface defects such as scratches, cracks, protrusions, and depressions. Another method is to melt the material and pour it into a molten metal salt, such as 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. Figure 1 shows the final target convex lens, concave lens,
A schematic diagram of a molding device for heating and pressure molding Fresnel lenses, aspherical lenses, etc. is shown. Figures 2A and 2B show the molds (upper mold 3, lower mold 4) and preformed material 21 of the apparatus shown in Figure 1, and Figure 2A shows scratches and cracks between the molds 3 and 4. ·protrusion·
Removal of dents to achieve a specified surface finish accuracy (for example, as mentioned above, in the case of a camera lens, the surface roughness is 1/10)
From the diagram (Fig. 2 A) in which the preformed material preprocessed to an accuracy of 0μ or less is inserted, and the state of Fig. 2 A,
FIG. 2B is a diagram (FIG. 2B) in which the preformed material 21 is molded into the final target lens by applying pressure to the mold 4. 1 is an airtight container, 2 is a lid thereof, and 3 is an upper mold for molding an optical element, the surface 3a of which is finished to the same level as the functional surface of the optical element. 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, 12, 13, 1
4, 16, and 18 indicate 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 and remove the water cooling pipe 2.
0 and energize the heater 8. At this time, all valves are closed. Note that the exhaust oil rotary pump is always in operation. The valve 12 is opened to evacuate the airtight container, and when the degree of vacuum becomes 10 ^-2 Torr or less, the valve 12 is closed and the valve 16 is opened to introduce an inert gas (for example, N ₂ gas) 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. Note that the lower die 4 in the figure is made of the same material as the body die 6 and moves up and down while fitting with precision. Once the preformed material has been shaped into a predetermined shape, the temperature is gradually lowered. Once cooled sufficiently, remove the molded product from the equipment,
Finish the operation. The shape of the preformed material in the present invention is as shown in FIG. 2A.
It may be a disk with the surface defects of 1b removed, or a disk with the surface defects of 1b removed.
As shown in Figure A, the surfaces 21a and 21b of the material
may be formed into a spherical surface with a curvature approximating the shape of the optical element to be formed in advance. Particularly for thick lenses as shown in FIG. 3, it is effective to finish the lens to an approximate curvature in order to improve the precision of the molded product. As shown in FIG. 3, finishing the preformed material 21A with a curvature close to the final target shape of the lens 22A is achieved by inserting the preformed material 21A into the mold and
When pressure is applied to the preformed material 21A by the cylinder 10, pressure rod 9, and lower mold 4 shown in the figure, the process in which the preformed material 21A is transformed into the lens 22A having the final target shape by the pressure of the molds 3 and 4. In, preform material 2
When deforming 1A, a large pressure acts on a specific surface, for example, a point with a particularly large curvature, and this is useful for suppressing the stress concentration cause 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 (annealing work) that was previously required to remove strain becomes unnecessary. In material molding technology, lenses for intermediate models/lens apertures of 10φ to 20φ
In addition, it is a great achievement of the present invention that it can be applied to the production of large-diameter lenses for single-lens reflex cameras, with lens apertures of around 60φ. Furthermore,
As mentioned above, the fact that the preformed material 21A does not require strain removal work after hot-pressing forming is because conventionally it takes several hours to several tens of hours to remove strain after hot-pressing forming. As shown in Figure 3, a lot of time was wasted in the process of material - heating and pressing - forming - distortion removal - completion due to placement steps and adjustment of process work time. By finishing the outer surface shape with a curvature close to the final target lens shape, it is possible to send it to the next process, for example, the process of assembling it into a lens barrel, without going through the distortion removal process after the molding process. It is possible to significantly shorten the assembly process from the completion of the tube to the finished product process, and as a result, automation of the so-called assembly line process eliminates defective products, improves production efficiency, streamlines the production process, etc. It can make a significant contribution to the In order to further clarify the effects of the present invention, materials having various surface defects were molded using an apparatus implementing the present invention, and compared with molded products using materials from which surface defects had been removed in advance. The results are shown in Table 1 and Figure 4. The optical element material used to carry out the present invention is commonly known as
Using SF14 optical glass, its shape is 16.5mm in outer diameter.
It is a flat plate with a center thickness of 2.5mm. The surface 3a of the upper mold 3 was optically processed to have a curvature of 20.5 mm, and the surface 4a of the lower mold 4 was similarly optically processed to have a curvature of 55.5 mm. The molding conditions were to apply a pressure of 10 kg/cm ² for 3 minutes at 570°C. In Table 1, #1200, #600, #250, etc. indicate finishing accuracy according to Japanese Industrial Standards (JIS R 6001. Based on particle size distribution of fine powder according to JIS), and RMAX
indicates the maximum surface roughness. Incidentally, the blank in Table 1 and FIG. 4 refers to the above-mentioned preformed material. The correspondence between Table 1 and Figure 4 is that the surface roughness measurement results for the blank in Table 1 show the graph on the left in Figure 4, and
The measurement graph of the surface roughness of the final target lenses (lenses with curvature radii of 20.5 mm and 55.5 mm) using the polished blank is shown in the right figure of Figure 4. As shown on the right end of each graph in Figure 4, the degree of finishing of the blank (RMAX)
The graph scale of measured roughness is 0.02μ.
There is a large difference from m to 2 μm. This means that
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 0.01 μm or less and when it is set to RMAX 7 μm or less. In other words, the surface roughness of the blank is
If RMAX is set to 0.01μm or less, the surface roughness of the molded product will be
The RMAX was approximately 0.02 μm, and 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 of the molded product, RMAX 0.02μm, is the same value as the finish roughness of the molding die, and this means that if the surface roughness of the blank is RMAX0.01μm or less, the surface roughness of the molding mold will become the surface roughness of the molded lens. It means to be faithfully reproduced. In the case of a blank with a finishing grain size of #1200 to #250, the surface roughness of the lens of the molded product is 0.11 μm to 2 μm or more, as shown in Table 1 and Figure 4, and in particular, as shown in Figure 4, A ₁ ~ A ₄ , B ₁ ~ B ₃ , C ₁ ~ C ₄
A protruding point shown in is generated, and this protruding point greatly reduces optical properties such as light transmittance.
It was not suitable as a camera lens.
In addition, the pressing force in this example is based on the aforementioned shape and outer diameter.
The pressure on the cylinder mentioned above to obtain a lens of 16.5 mm, center thickness 2.5 mm, radius of curvature 20.5 mm, and 55.5 mm is approximately
It was ^about 10Kg/cm2. In this example, the surface roughness of the mold was 0.02 μm and the pressing force was 10 kg, but the above setting conditions can of course be changed depending on the optical characteristics of the lens, the size of the lens shape, and the size of the curvature. It is possible. 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 will have a surface roughness of 0.01 μm even if the surface roughness of the blank is 0.01 μm. It is understood from the above results that molding can be performed with the following high precision. As described above, the present invention provides an optical element molding method in which an optical material is inserted into a mold, and an optical surface is formed by molding the surface of the mold by heating and pressurizing the optical material. The optical material is preformed into a flat plate shape, surface defects such as scratches and cracks are removed, and the surface roughness is preprocessed to a certain degree to obtain a preformed material, and this preformed material is The molding method according to the present invention is characterized in that it is inserted into the mold and subjected to heating and pressure molding, and the molding method according to the present invention does not require post-processing or post-processing steps after molding in the mold, The desired optical finishing accuracy (surface roughness) can be obtained, and since the present invention uses a mold that has been finished to the final target curvature and roughness, material selection, heating conditions, and pressurizing conditions can be controlled. By making them the same, lenses with the same precision can be produced efficiently. Furthermore, by pre-processing the surface of the preformed material to a curvature close to the final target shape as shown in FIG. have. 【table】

[Brief explanation of drawings]

Figure 1 is a diagram showing an example of the apparatus used to carry out the method of the present invention, Figures 2A and B are sectional views showing a pair of molds, materials, and molded products, and Figures 3A and B are sectional views of the book. FIG. 7 is a sectional view showing another embodiment of the invention. Figure 4 shows the measurement results of the surface roughness of the raw material and the surface roughness of the molded product. 3, 4... Molding mold, 21, 22... Preforming material.

Claims (1)

[Claims] 1. An optical material is inserted into a mold, and the surface roughness is _reduced by applying heat and pressure to the optical material.
In a manufacturing method for molding an optical element with an accuracy of 0.02 or less, an optical material is processed to have a curvature that approximates the shape of the optical element, and the curvature surface is maintained at a surface roughness of at least R _nax 0.01 μm or less, The surface roughness of the mold is processed to an accuracy of R _nax 0.02 μm or less, and an optical material processed to an approximate curvature is inserted into the mold and molded by heating and pressure. A manufacturing method for molding an optical element.