JPH021778B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a press lens glass and a method for manufacturing a press lens. Since this press lens transfers the surface shape of a precision-machined mold by press molding, not only spherical lenses but also aspheric lenses can be manufactured, and it can be used for a wide range of lenses. [Prior Art] Various conventional press lens glasses and press lens manufacturing methods have been proposed, but optical glass is used as the glass, and the press lens manufacturing method involves preventing oxidation of the surface of the mold. Therefore, it is carried out in a non-oxidizing atmosphere. For example, in US Pat. No. 4,139,677, the glass for press lenses is flint (F) glass, and the flint glass is placed in a mold having a surface layer of SiC or Si ₃ N ₄ in a non-oxidizing atmosphere. We have proposed a method in which this glass is heated together with a mold until it becomes softened, and then the softened glass is press-molded using this mold. Here, a nitrogen gas atmosphere is mainly used as the non-oxidizing atmosphere. [Problem to be solved by the invention] However, when nitrogen gas is used, an oxide film is formed on the mold surface even by a small amount of oxygen, about several ppm, that is present in the nitrogen gas. However, there was a problem in that during press molding, the softened glass tended to fuse to the mold surface. In addition, when press forming is performed in a reducing atmosphere using the previously mentioned flint-based or heavy flint (SF) glass as the glass, PbO in the glass component is reduced and reduced particles (Pb) are precipitated on the surface of the pressed lens. Resulting in. As a result, reduced particles (Pb)
The reduced particles tend to fly out from the surface of the pressed lens, and when subjected to heat treatment, for example, the reduced particles evaporate, forming concave portions on the surface of the pressed lens, resulting in a significant decrease in surface roughness. [Means for Solving the Problems] The glass for press lenses and the method for manufacturing press lenses of the present invention have been made in order to solve the above problems.
A press comprising an inner glass and a glass surface layer formed on the surface of the inner glass, wherein the glass transition temperature of the glass surface layer is 15°C to 700°C higher than the glass transition temperature of the inner glass. The method for manufacturing a lens includes processing an inner glass into a shape that forms the basis of a finished shape, and forming a glass surface layer having a glass transition temperature 15 to 700°C higher than the glass transition temperature of the inner glass on the surface of the inner glass. The formed press lens glass is characterized in that the inner glass is softened and the glass surface layer is left unsoftened, and then press-molded using a mold. In the press lens glass and press lens manufacturing method of the present invention, the glass transition temperature of the glass surface layer is 15 to 700° C. higher than that of the inner glass. This glass transition temperature difference is due to the fact that the internal glass becomes a softened state and the glass surface layer becomes an unsoftened state during press forming. This is a state in which the inner glass can be elongated by molding, while the unsoftened state of the glass surface layer is a state that corresponds to the glass transition temperature difference (15 to 700°C) with the inner glass during the press molding. Since the viscosity is higher than that of the inner glass, it does not reach the softening state of the inner glass, but it is in a state where it can follow the elongation deformation of the inner glass and form a surface layer after press molding. Such a softened state of the inner glass and an unsoftened state of the glass surface layer can be obtained by heating the press lens glass together with the mold, or by heating the press lens glass before placing it in the mold. The practical range of glass surface layer thickness is 50~2000
Å (preferably 100 to 1000 Å); if it is less than 50 Å, the effect of forming this glass surface layer will decrease; if it exceeds 2000 Å, defects such as cracks will easily occur during press molding, and the transmittance and refraction will decrease. This causes a decrease in optical quality such as optical efficiency. As a method for forming this glass surface layer, a vacuum evaporation method, a sputtering method, an ion plating method, or the like can be used. In the method for manufacturing a pressed lens of the present invention,
"Shape that forms the basis of the finished shape" refers to the preforming of the glass before pressure forming, and the shape of this preform is the basic shape that can be made into the finished shape of the lens after pressure forming. For example, in the case of a lens with a convex or concave finished shape, the lens has a disc shape, a columnar shape, a spherical shape, or a spherical shape with approximately the same volume, and preferably a shape that is almost similar to the finished shape. The "mold" used in the press lens manufacturing method of the present invention has an important surface layer facing the press lens glass, has no defects such as pores, can be precisely processed into a dense and mirror-like shape, and is heated In the present invention, there is no need to particularly limit the material of the mold base material and its surface layer, as long as it meets the general requirements for a mold, such as having hardness and strength, such as silicon carbide. , silicon carbide and carbon mixtures, silicon nitride, molybdenum, 400 series stainless steel, electroless nickel, beryllium-nickel alloys, tungsten carbide, titanium nitride, titanium carbide, titanium boride, precious metals (platinum, rhodium, gold, etc.) , and _SiO2 - _{Al2O3 -} CaO-MgO-
A wide range of materials such as multi-component glass whose transition temperature is higher than that of the above-mentioned "inner glass and glass surface layer" such as ZanO-PbO glass (transition temperature 730℃, thermal expansion coefficient 43 × 10 ^-7 /℃) Materials are available. Further, the pressure for "press molding" may be sufficient as long as the surface shape of the mold is transferred to the press lens glass. Furthermore, regarding the atmosphere,
Since a non-oxidizing atmosphere is not necessarily required, the atmosphere may be used. [Function] During the press forming described above, the inner glass is in a softened state, and the alkali metal ions, alkaline earth metal ions, etc. in the inner glass components diffuse and blend with the glass surface layer, causing the inner glass and the glass surface to Increases layer adhesion. However, although the glass surface layer blends in with the internal glass, it is still in an unsoftened state, so even if the mold surface is oxidized, it prevents it from adhering to the mold surface during press molding. . In addition, since the glass surface layer covers the surface of the internal glass in an unsoftened state, the internal glass
Prevents reduction of PbO even in flint-based or heavy flint-based optical glasses containing a large amount of PbO. [Example] Next, in order to facilitate understanding of the present invention, examples of the present invention will be described in detail. [Example 1] Contains a large amount of PbO as an internal glass material
SF8 glass (composition (wt%): SiO ₂ ; 36.7,
PbO; 57.5, _K2O ; 4.2, _Na2O ; _0.8 , _B2O3 ;
0.8), LaK9 glass as the material for the glass surface layer (composition (wt%): SiO ₂ ; 5.0, B ₂ O ₃ ; 37.1,
La ₂ O ₃ ; 32.9, CaO; 9.6, ZnO; 13.4, Al ₂ O ₃ ;
2.0) respectively. The glass properties of SF8 and LaK9 are shown in Table 1.

[Table] Next, the SF8 material is preformed into a disc-shaped inner glass 1 (diameter: 9.7 mm, thickness: 2.5 mm) as shown in Figure 1a. Vacuum deposition method (deposition source: LaK9
glass surface layer 2 (thickness: 200 Å)
This is used as press lens glass 3 to be press-molded. As shown in Fig. 2, the press molding machine used in this example has an upper die 4 (material: tungsten carbide) and a lower die 5 (material: tungsten carbide), each having a convex spherical precision mirror-finished die surface. , a guide mold 6 (material: tungsten carbide) whose inner peripheral surface is precision mirror-finished, the upper mold 4 moves up and down, its outer peripheral surface slides on the inner peripheral surface of the guide mold 6, and the lower mold The outer peripheral surface of the mold 5 is slidably supported on the inner peripheral surface of the guide mold 6, and the molds 4, 5, and 6 are supported by a support base 8 (material: stainless steel). The push rod 7 (material: stainless steel) descends to the upper surface of the upper mold 4 and applies a load. The above mold structure is a silica tube 9
An induction heating coil 10 is arranged around the outer periphery of the silica tube, and the temperature is measured by a thermocouple 11 buried in the lower mold 5.
0 temperature control. Next, as described above, press the glass 3 for the press lens on top.
Place it in the lower molds 4, 5, create a 2% H ₂ + 98% N ₂ gas atmosphere, and heat the molds 4, 5, with the induction heating coil 10.
Glass 3 together with 6 was heated to 495°C (a temperature corresponding to the viscosity of inner glass 1 of 10 ⁹ poise, making inner glass 1 in a softened state, while glass surface layer 2 was in an unsoftened state). In the state, push rod 7
is lowered and a load is applied to the upper die 4 to perform press molding (pressure: 200 Kg/cm ² , press time: 30 seconds). Next, the pressure of the push rod 7 is removed and the molds 4, 5, 6 are removed.
While surrounding the press molded product inside, the inner glass 1
The lens 3' is slowly cooled to a transition temperature of 425° C., and then rapidly cooled to form a finished lens 3'. This lens 3' is shown in Fig. 1b.
As shown in Fig. 2, it is a biconcave spherical lens with a diameter of 10 mm consisting of an inner glass 1' and a glass surface layer 2', and there is no fusion with the mold, and the surfaces of the upper and lower molds 4 and 5 have a convex spherical shape. The concave spherical shape corresponding to the glass surface layer 2 is transferred as is, achieving high surface accuracy.
It was observed that due to the intervention of PbO, reduction of PbO did not occur, and optical qualities such as transmittance and refractive index were maintained well. Furthermore, since the coefficients of thermal expansion of the inner glasses 1, 1' and the glass surface layers 2, 2' are almost the same, cracks are prevented from occurring even at the heating temperature during press molding, and the refractive indexes are also almost the same, so they can be integrated into one piece. It can be used as a lens. [Example 2] Contains a large amount of PbO as an internal glass material
SF15 glass (composition (wt%): SiO ₂ ; 36.2,
PbO; 55.6, _K2O ; 4.8, _Na2O ; 1.5, _TiO2 ;
1.9), LaLF3 glass as the material for the glass surface layer (composition (wt%): SiO ₂ ; 17.6, B ₂ O ₃ ; 16.5,
La ₂ O ₃ ; 12.3, B ₂ O ₃ ; 16.6, CaO; 7.6, SrO;
22.8, ZrO ₂ ; 2.4, TiO ₂ ; 4.2), respectively. The glass properties of SF15 and LaLF3 are shown in Table 2.

[Table] Next, the SF15 described above is preformed into a spherical inner glass 12 (diameter: 6.3 mm) as shown in FIG. (evaporation source: LaLF3 powder) to form a glass surface layer 13 (thickness: 400 Å),
This is designated as press lens glass 14. The press molding machine used in this example is basically the same as that in Example 1, but in this example, since a biconvex spherical lens is manufactured from spherical glass 14, an upper mold 4' and a lower mold are used. The only difference is that each mold surface of the mold 5' is precisely mirror-finished into a concave spherical shape. Next, the glass 14 is placed in the upper and lower molds 4', 5', and the glass 14 is heated to 524°C (the viscosity of the inner glass 12 is 10 (at a temperature equivalent to ^8.7 poise, the inner glass 12 is softened, while the glass surface layer 13 is not softened), the push rod 7 is lowered and the upper mold 4' Apply a load and press-form (pressure: 500Kg/cm ² , press time: 60 seconds). Next, the pressure of the push rod 7 is removed, and while the press molded product is surrounded in the molds 4', 5', and 6, it is gradually cooled to the transition temperature (445°C) of the inner glass 12, and then rapidly cooled. , a biconvex spherical lens 1 consisting of an inner glass 12' and a glass surface layer 13', as shown in FIG. 3b, is molded into a finished shape.
4' (diameter: 8.0 mm, center wall thickness: 2.7 mm) and taken out. This lens 14' is of type 4', 5',
No fusion occurs with 6, and the convex spherical shape corresponding to the concave spherical shape of the surfaces of the upper and lower molds 4' and 5' is transferred as is, resulting in high surface accuracy and good optical quality. In addition, the same effects as in Example 1 were obtained. [Example 3] Contains a large amount of PbO as an internal glass material
F2 glass (composition (wt%): SiO ₂ ; 43.8, PbO;
46.6, CaO; 6.7, Na ₂ O; 2.9), borosilicate glass as the material for the glass surface layer (composition (wt%): SiO ₂ ; 65.0, B ₂ O ₃ ; 5.0, Li ₂ O ₃ ; 9.0 ，
_K2O ; 4.4, _Na2O ; 3.0, ZnO; 13.6) are used, respectively. The properties of the above F2 and borosilicate glasses are shown in Table 3.

〔Effect of the invention〕

As described above, according to the present invention, the glass for press lenses has an inner glass and a glass surface layer, and the glass transition temperature of the glass surface layer is 15°C to 700°C higher than that of the inner glass. Therefore, it is possible to prevent fusion with the mold during press molding, and even if the glass used contains PbO, reduction of PbO can be prevented. In addition, press molding can be performed in the atmosphere in addition to neutral gas or reducing gas, and there is no need to use expensive materials as mold materials, and mold materials can be appropriately selected from a wide range of materials.

[Brief explanation of drawings]

1A and 1B are cross-sectional views showing a press-molding glass and a lens after press-forming according to Example 1 of the present invention, FIG. 2 is a cross-sectional view showing a press-molding machine according to Example 1 of the present invention, and FIG. Figures a and b are cross-sectional views showing press molding glasses and lenses after press molding according to Examples 2 and 3 of the present invention, and Figure 4 is a cross-sectional view showing a press molding machine according to Examples 2 and 3 of the present invention. be. 1, 1', 12, 12'...inner glass, 2, 2',
13, 13'... Glass surface layer, 3, 14... Glass for press lens, 4, 4'... Upper die, 5, 5'... Lower die, 6... Guide die, 3', 14'... Press lens.

Claims (1)

[Scope of Claims] 1. Comprising an inner glass and a glass surface layer formed on the surface of the inner glass, wherein the glass transition temperature of the glass surface layer is 15°C to 700°C higher than the glass transition temperature of the inner glass. Glass for press lenses characterized by its high quality. 2. Glass for press lenses according to claim 1, wherein the glass surface layer has a thickness of 50 to 2000 Å. 3. The press lens glass according to claim 1, wherein the internal glass and the glass surface layer have substantially the same coefficient of thermal expansion. 4. The press lens glass according to claim 1, wherein the inner glass and the glass surface layer have substantially the same refractive index. 5 For press lenses in which the inner glass is processed into a shape that forms the basis of the finished shape, and a glass surface layer having a glass transition temperature 15 to 700°C higher than the glass transition temperature of the inner glass is formed on the surface of the inner glass. A method for manufacturing a press lens, characterized in that glass is press-molded using a mold with the inner glass in a softened state and the glass surface layer in an unsoftened state.