JPH04285031A - Produciton of forming glass material and optical element - Google Patents

Abstract

PURPOSE:To prevent the cracking of a glass when formed and the contamination of the formed article and mold at the time of producing a glass material for press-forming an optical element by dipping the glass material in acid, and then heating the material under reduced pressure or in a dry atmosphere. CONSTITUTION:A glass material (e.g. silicate glass) used for press-forming an optical element is dipped in acid (e.g. nitric acid) to elute the component soluble in acid from the glass surface as a cation (e.g. Na<+>), the hydrogen ion of acid is diffused instead into the glass to exchange the cation, and a porous hydrated layer rich in SiO2 is formed on the glass surface. The glass material is then heated under reduced pressure or in a dry atmosphere to cause dehydration and condensation in the hydrated layer, hence the network structure of Si-O-Si is formed, and a dense glass layer rich in SiO2 is formed on the glass surface. Consequently, when the treated glass material is press-formed into an optical element, the fusion of the formed article to the mold member, the contamination due to the volatilization of the glass component, etc., are prevented.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a glass material for press molding, and a method for manufacturing an optical element using the glass material obtained by the method.

0002

[Prior Art] In recent years, a material for molding optical elements, such as a glass blank preformed to a certain degree of shape and surface accuracy, is housed in a mold with a predetermined surface accuracy and press-molded under heat. 2. Description of the Related Art A method for manufacturing an optical element having a high-precision optical functional surface that eliminates the need for post-processes such as grinding and polishing has been developed.

[0003] In such a press molding method, an upper mold member for molding and a lower mold member for molding are respectively arranged slidably facing each other in a molding body member, and these upper mold member, lower mold member and body are A molding material is introduced into the cavity formed by the mold member, and the atmosphere is set to a non-oxidizing atmosphere, such as a nitrogen atmosphere, to prevent oxidation of the mold member, and the molding material is heated to a moldable temperature, for example, a temperature at which the molding material becomes 108 to 1012 poise. The mold member is heated, the mold is closed and pressed for an appropriate time to transfer the surface shape of the mold member to the surface of the molding material, and the mold member temperature is cooled to a temperature sufficiently lower than the glass transition temperature of the molding material,
The press pressure is removed and the mold is opened to remove the molded optical element.

[0004] The molding material may be preheated to an appropriate temperature before being introduced into the mold member, or the molding material may be heated to a moldable temperature and then introduced into the mold member. Furthermore, while conveying the molding material together with the mold member, heating, pressing, and cooling can be performed at predetermined locations, thereby achieving continuity and high speed.

The above optical element press molding method and its apparatus are disclosed in, for example, Japanese Patent Application Laid-open No. 58-84134, Japanese Patent Application Laid-open No. 49-97009, and British Patent No. 37819.
9, JP-A-63-11529, JP-A-59
It is disclosed in Japanese Patent Laid-open No. 150728 and Japanese Patent Application Laid-open No. 61-26528.

However, in the press molding of optical elements as described above, the molding material and the mold member may fuse together at high temperatures during molding. Once fusion occurs, the element may crack or break due to the tensile force that acts on the element due to the difference in thermal expansion coefficient between the molded optical element and the mold member during cooling after pressing, or the element may crack or crack from within the mold. When taking out a molded optical element, a part of the element may adhere to and remain on the mold member, which may adversely affect subsequent molding.

[0007] In order to prevent the above-mentioned fusion, it is possible to use a mold release agent, but in the case of optical elements, where the optical functional surface requires a high level of smoothness, the use of a mold release agent is difficult. It is not preferable to use a mold release agent because its residue causes quality deterioration such as a decrease in smoothness and a decrease in transparency. Further, the properties of mold members that are less likely to cause fusion have been studied, but preventing fusion by using the material of the mold member narrows the range of selection of the mold member, which is disadvantageous in this respect.

As a means to solve the above problems, a method has been proposed in which a molding material is heat treated under reduced pressure at a temperature lower than the press molding temperature and then press molded (Japanese Patent Application Laid-Open No.
-315447). According to this method, it is possible to suppress the occurrence of fusion between the molded optical element and the mold member, and also to prevent the molding material and the molded optical element from being crushed.

[0009]

[Problem to be solved by the invention] However, JP-A-1-3
Even in the method of Publication No. 15447, the mold gets dirty due to volatile matter from the glass, and if molding continues, the dirt transfers to the molded product, so the mold needs to be cleaned frequently, and further improvements are needed. It was wanted.

Therefore, the objects of the present invention are to provide a method for producing a glass material for press molding that suppresses the volatilization of glass components and prevents staining of molded products and molds, and an optical element using the glass material obtained by the method. The purpose of this invention is to provide a method for manufacturing the same.

[0011]

[Means for Solving the Problems] According to the present invention, in a method for manufacturing a glass material used for press molding of an optical element, the glass material is immersed and then heated under reduced pressure or in a dry atmosphere. A method of manufacturing a glass material for use in glass materials, and a method of manufacturing an optical element using the glass material obtained by the method are provided.

In the present invention, the adhesion between the molded product and the mold member is reduced to prevent the occurrence of fusion, and microcracks on the surface of the molded product are suppressed to prevent the molded product from being crushed. It is possible to suppress the volatilization of and prevent staining of molded products and molds.

The present invention will be explained in more detail below. first,
The mechanisms of reducing adhesion, suppressing microcracks, and reducing glass volatile components in the present invention will be described. When silicate glass is immersed in acid, acid-soluble components from the glass surface are converted into cations (Ba2+, Li+, Na+
, K+, etc.), and hydrogen ions from the acid diffuse into the glass instead, causing ion exchange of cations. As a result, a porous hydrated layer rich in SiO2 is formed on the glass surface. Then, when heated under reduced pressure or in a dry atmosphere, a dehydration condensation reaction occurs in the surface hydration layer.
i-OH + Si-OH → Si-O-S
i occurs, and a Si-O-Si network structure is generated. As a result, a dense glass layer rich in SiO2 is formed on the glass surface, with acid-soluble components gradually decreasing toward the surface.

[0014] Furthermore, the glass transition point Tg of silicate glass
Tg is highest for SiO2 alone (silica glass), and as network structure modifying oxides such as alkali are added to this, Tg decreases. Therefore, in the glass material for press molding according to the present invention, the Tg becomes higher as it approaches the surface, and as a result, the adhesion between the glass and the mold during molding decreases and fusion is suppressed. Of course, since heating also involves removing water from the glass surface and reducing microcracks, there is also an effect of suppressing fusion by preventing mold oxidation and an effect of preventing glass from breaking. Furthermore, the components eluted during acid immersion are components that easily volatilize during molding compared to SiO2, and in the present invention, since these components are reduced in advance on the surface of the glass material for press molding, molded products and molds Prevents it from sticking to the surface and getting dirty.

[0015]

[Embodiments] The present invention will be explained below by showing embodiments based on the drawings. [Example 1] Figure 1 is a cross-sectional view of a glass material used for press molding obtained according to the present invention, where 1 is the inside of the glass material, 2 is a surface modified layer, 3 is an edge portion, and 4 and 5 are optical parts. It's functional. FIG. 2 shows the element concentration in the depth direction of the surface layer in the AA' cross section of FIG.

FIG. 3 is a process diagram of the method for manufacturing the glass material of the present invention. First, the SK12 (manufactured by Ohara) substrate 30 shown in FIG. 3 is set in an acid treatment jig, and the washing tank (1) 20,
After cleaning in a water washing tank (2) 21, the glass was immersed in a 3N nitric acid treatment tank 22 for 3 minutes to form a porous hydration layer (acid treatment layer) 31 rich in SiO2 on the glass surface. After that, the washing tank (
3) After washing in 23 and water washing tank (4) 24, it was placed in an IPA vapor tank 25 and then pulled up to dry and remove the solvent on the surface.

A porous hydrated layer 31 rich in SiO2 generated by the acid treatment remains on the surface of the glass substrate 30, and is then heated using an electric furnace capable of heating under reduced pressure or in a dry atmosphere. 400 under a vacuum of 2 Torr
It was heat-treated at ℃ for 4 hours. As shown in FIG. 2, a dense surface-modified layer 2 rich in SiO2 was formed on the surface of the glass substrate subjected to the above treatment, with acid-soluble components decreasing toward the glass surface.

Next, the adhesion between the glass and the mold during molding was measured as follows. The glass material and mold, which had been press-molded in advance under pressure and heat, were kept at a temperature between the strain point and the yield point, and the force required to separate the glass material from either the upper or lower mold was determined using a load cell. At this time, a flat plate was used as the mold to eliminate the shape factor.

Next, a molding test was conducted. After polishing SK12 glass into a biconvex lens with a diameter of 10 mm, a first surface 15R, and a second surface 32R, surface treatment was performed according to the method for manufacturing a glass material for press molding of the present invention. The glass material thus obtained was press-molded using an aspherical mold with a slightly different shape.

Table 1 shows the adhesion strength of glass materials obtained by various surface treatments, the frequency of fusion cracking during molding, and the mold cleaning interval. Regarding adhesion, the conventional example is not much improved compared to the untreated one. However, as a result of removing moisture from the glass surface, there was an effect of suppressing fusion by preventing mold oxidation, and the reduction of microcracks on the surface increased the strength of the glass and also had an effect of preventing cracking. As a result, in the conventional example, the frequency of fusion cracking was reduced to 14%, compared to 24% in the untreated case. On the other hand, in Example 1, in addition to the above-mentioned fusion crack prevention effect, the adhesion force between the glass and the mold was 0.28 kgf/m compared to the conventional example.
Reflecting the decrease in 0.17 kgf/mm2 compared to m2, the frequency of fusion cracks also decreased from 14% to 8%.

Next, the interval for cleaning the mold stains is as follows:
The conventional example shows almost no improvement compared to the untreated one. On the other hand, in Example 1, there are 72 shots compared to 33 shots in the conventional example.
It can be seen that it is more than twice as long as the shot.

[Example 2] Adhesion was measured under the same conditions as in Example 1, except that the heating conditions in the electric furnace were 10% humidity, 400°C, and 12 hours, and a molding test of a biconvex lens was conducted. . As shown in Table 1, almost the same results as Example 1 were obtained in terms of adhesion, frequency of fusion cracking, and mold cleaning interval.

[0023] The glass to which the present invention can be applied is S
It is not limited to K12, and any glass material containing SiO2 may be used. Further, as the acid for acid treatment, nitric acid, hydrochloric acid, sulfuric acid, acetic acid, etc. can be used depending on the glass composition. In SK12, sulfuric acid is not preferred for eluting Ba. If the thickness of the treated layer is too thin, the effect will be small, and if it is too thick, the treated layer itself may break and cause minute cracks on the surface of the molded product. It is preferable to decide on both.

[0024]

[Effects of the Invention] As explained above, according to the present invention,
After immersing the glass material in an acid, it is heated under reduced pressure or in a dry atmosphere to modify the surface layer of the glass material, thereby reducing the adhesion between the glass and the mold during and after press molding, and By suppressing microcracks on the surface of the molded product, it is possible to suppress fusion between the glass and the mold, and to prevent the glass from fracturing or cracking. Furthermore, since the easily volatile glass components are eluted during acid immersion, the volatilization of the glass components during molding can be suppressed, thereby preventing staining of the molded product and mold.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a glass material for press molding obtained by the present invention.

2 is a diagram showing the element concentration in the depth direction of the surface layer in the AA′ cross section of FIG. 1. FIG.

FIG. 3 is a process diagram of the method for manufacturing a glass material for press molding of the present invention.

[Explanation of sign]

1 Inside the glass material 2　Surface modified layer 3 Edge part 4,5 Optical functional aspect 20, 21, 23, 24 Washing tank 22 Acid treatment tank 25 IPA vapor tank 30 Glass substrate 31 Hydration layer (acid treatment layer)

Claims (2)

[Claims] 1. A method for producing a glass material for press molding, which comprises immersing the glass material and then heating it under reduced pressure or in a dry atmosphere. 2. A method for manufacturing an optical element, comprising press-molding a glass material obtained by the method according to claim 1.