JPS60176928A - Mold for press molding glass lens - Google Patents

Abstract

PURPOSE:The titled mold for molding, obtained by working a sintered hard alloy as a base material into a die of lens shape, and forming an A-SiC or alpha-SiC coating film of uniform thickness thereon, capable of easy mold working thereon, capable of easy mold working with a high accuracy, and having little reactivity with molded glass. CONSTITUTION:A mold for press molding, obtained by working a sintered hard alloy as a base material into a die having a pressing surface of lens shape for molding by electric discharge machining or grinding, etc. with a high accuracy, and forming a coating film of uniform thickness from a material consisting of one of A-SiC, alpha-SiC and a mixture of both, and capable of direct press molding optical glass of high accuracy. The above-mentioned base material having a composition of 98-80wt% WC and 2-20wt% Co has a thermal expansion coefficient in agreement with that of the above-mentioned coating film, and provides a strong adhesive powder. The use of the base material having 0.05-0.5mum grain size provides a glass lens having good surface roughness.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a mold for press-molding an optical glass lens that does not require a press-molding polishing process.

(Conventional Structure and its Problems) In recent years, there has been a trend toward aspheric optical glass lenses, which can simultaneously simplify the lens structure of optical equipment and make the lens portion lighter. To manufacture this aspherical lens,
Since the polishing method, which is a conventional optical lens manufacturing method, has difficulties in processability and mass production, direct press molding is viewed as promising. This direct press molding method involves heating a lump of optical glass, or press-molding a lump of pre-heated glass onto an aspherical mold that has been finished to the desired surface quality and precision in advance. ,
This is a method for manufacturing optical lenses without requiring a polishing process.

However, in the method for manufacturing an optical glass lens described above, the image forming quality of the obtained lens must be excellent after press molding. Especially in the case of an aspherical lens, it is required that it can be molded with high precision. Therefore, as a mold material, it should have minimal chemical action on glass at high temperatures, be resistant to damage such as scratches when glass is pressed into the mold, and have high fracture resistance due to thermal shock. is necessary. For this purpose, molds of materials such as silicon carbide (SIC), silicon nitride (513N4), or dense kerf 1? It is said that a mold in which a coating film of silicon carbide or the like is formed on top of the mold is suitable. However, materials such as silicon carbide and silicon nitride have extremely high hardness, so it is extremely difficult to process these materials to produce molds for molding spherical and aspherical lenses with high precision. Conventionally, these mold materials are of the sintered type, so At20. ,
B, 205, and other substances that easily react with glass are used, which has the drawback of not being able to mold lenses with high precision. 1
However, molds made by coating a high-density carpin molding with silicon carbide, etc., are also made of beta-silicon carbide (β-5ic), so they cannot be used with glass containing a large amount of sodium chloride or barium. The disadvantage was that it caused a reaction, making it impossible to mold high-precision glass lenses.

(Object of the invention) The object of the invention is to make the glass lens 1
Direct press molding for optical glass 17 lenses that can easily perform mold processing with the madder precision required for a sy-shaped mold, and can produce good images by using this mold. It is to provide a model.

(Structure of the Invention) The mold material for press molding of a glass lens of the present invention uses cemented carbide as a base material, processes this into a lens-shaped mold, and overlays amorphous silicon carbide, alpha A coating film of a material selected from the group consisting of silicon carbide and a mixture of amorphous silicon carbide and alpha silicon carbide is formed.

The cemented carbide used here can be processed not only by electric discharge machining, but also by general grinding using the highly hard silicon carbide, which is conventionally used as a mold for direct press molding of glass lenses. It is easier to process high-precision molds than silicon nitride or silicon nitride, and by reducing the viscosity of tungsten carbide to less than 5 μm, the maximum surface roughness of the glass lens can be reduced (Rmax).
It is possible to make it 0.02 μm. Further, the cemented carbide used as the base material has a coefficient of thermal expansion that closely matches that of the amorphous silicon carbide or alpha silicon carbide used as the coating film. In particular, the content of copal (Co), which is used as a binder for cemented carbide, is in good agreement with the amount of 2 to 20M. This provides strong circumferential adhesive strength that can withstand repeated use.

If the weight of cobalt exceeds 20%, the adhesive force of silicon carbide will work, making it unsuitable as a mold.If the weight of cobalt is less than 20%, it will be difficult to sinter tungsten carbide, making it impossible to obtain a good base material.

(Description of Embodiment) An embodiment of the present invention will be described based on FIG. 1 and FIG. 2.

Two cylindrical rods of cemented carbide with a diameter of 301 mm and a length of 50 mtn and an average grain size of 05 μm of tungsten carbide containing 2 weight percent cobalt were prepared, and by electric discharge machining, the circumference was formed as shown in Figure 1. A pair of press molding molds is formed, consisting of a concave upper mold 1 with a curvature radius of 46 mm and a concave lower mold 2 with a curvature radius of 200 mm. Press molding surfaces of these pair of blocks 3.
4 is mirror-polished using ultra-fine diamond abrasive grains to an accuracy of maximum surface roughness of 0,602 μm. Normally, processing can be performed in about 2 hours. Next, on this mirror surface,
A mold for glass press molding is manufactured by forming an amorphous silicon carbide film with a thickness of 2 μm by the taring method.

This mold was set in the press machine shown in Fig. 2, and 51
A borosilicate alkali optical glass consisting of 68% of 02, 11 parts of B2O3, 10 parts of Na20, 8% of K2O, and the rest is a trace amount, and 31 parts of 5102, B2
Two types of barium borosilicate optical glass with a radius of 20 m, consisting of 17 meters of O3, 50 meters of B, and a trace amount of residue.
A spherical raw material glass lump 5 of m is pressed and formed into a biconvex lens shape. At this time, press forming is performed by winding a heater 6 around the upper mold 1 and a heater 7 around the lower mold 2, holding the raw glass lump 5 with a raw glass supply jig 8, and using a glass preheating tunnel furnace 9. , the mold temperature was 800℃, the press pressure was 40kjI/1w'', and the mold temperature was 400℃.
Cool together with the mold to ℃ to sinter the molded product. This ejection is carried out through the outlet 10 of the molded product. Note that 11 is a piston cylinder for the upper mold, and 12 is a piston cylinder for the lower mold.

The results for the above borosilicate alkali glass are shown in Table 2, Sample A2, and the results for the borosilicate glass are shown in Table 2, Sample A2.

For comparison, all conventional molds of silicon carbide and silicon nitride were made, and they were installed in the press machine shown in Fig. 2 instead of the mold of the present invention, and the same glass lumps as above were pressed under the same conditions. I did the molding.

The silicon carbide and silicon nitride molds were manufactured by grinding them into the same shape as the cemented carbide after the electrical discharge machining, and the surfaces were mirror-polished using the same diamond abrasive grains. Even in this process of polishing the cast surface, the maximum surface roughness is 0.
It took 20 to 25 times as much time to finish to 0.02 μm as it did to finish with cemented carbide, that is, 40 to 50 hours. The results of press molding using this silicon carbide mold are also shown as comparative examples in Table 1 (Samples A 11 , 12 ) and Table 2 (Samples A 11 and 12 ).

As can be seen from Tables 1 and 2, the press molds for the sample molds 1 to 6 according to the present invention are superior to the conventional silicon carbide molds and can be manufactured easily. It's obvious. Also, the amount of cobalt is 2 to 20
Weight range and tungsten carbide particle size are 0
．． It is clear that molds in the range 0.05 μm to 0.5 μm are particularly superior to conventional molds.

(Effect of the invention) The mold for direct press molding of a glass lens according to the invention has the following features:
Compared to molds mainly made of silicon carbide or silicon nitride, which have been used in the past, it has less reactivity when molding glass, and also has the effect of allowing mold grinding to be performed more easily and with higher accuracy in a shorter time than conventional molds.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a mold for press molding a glass lens according to an embodiment of the present invention, and FIG. 2 is a perspective view of a press machine. 1... Upper die, 2... Lower die, 3... Pressing surface of upper die, 4... Pressing surface of lower die, 5... Raw glass lump, 6... For upper die. Heater, 7... Lower mold heater, 8.
... Raw material glass supply jig, 9... Force glass preheating tunnel furnace, 10... Molded product intake, 11... Piston cylinder for upper mold, 12... Piston cylinder for lower mold . Figure 1

Claims (3)

[Claims] (1) Using cemented carbide as a base material, process it into a molded lens-shaped mold and then apply amorphous silicon carbide (A-8IC) and alpha silicon carbide (α-5tC) to a uniform thickness.
and a press-molding mold for a glass lens, characterized in that a coating film is formed of one type of material selected from the group consisting of a mixture of amorphous silicon carbide and alpha silicon carbide. (2) The composition of the cemented carbide used as the base material is 98 to 80% by weight of tungsten carbide (WC) and 2 to 20% by weight of cobalt. Glass lens press molding mold. (3) Tungsten carbide used in cemented carbide)
The mold for press-molding a glass lens according to claim (1), wherein the viscosity of the (WC) is 0.05 μm to 0.5 μm.