JP4667930B2 - Optical element manufacturing method - Google Patents

Description

The present invention, glassware press molding a heated and softened glass material in a mold, in particular relates to the production how the optical element.

  There is a mold press method as a method for forming a precision optical glass element simply and with high productivity. In the mold press method, a glass material for molding, which has been preliminarily melted or solidified or cold processed into a predetermined shape, is supplied into the molding die, and this glass material is molded into a mold that can be molded by heat softening. In this method, the glass element is pressed and cooled in a state where the molded glass element is held in the mold. Since a precision-worked mold is used, according to this method, it is possible to eliminate the need to polish the molded surface of the glass element after molding.

  Here, it has been proposed to form various films on the surface of the glass material for molding, in order to solve the problem of fusing between the mold and the glass material and defects such as spiders and cracks.

  For example, it has been proposed to improve mold release by forming a hydrocarbon film on the surface of a forming glass material (see, for example, Patent Document 1).

  In addition, it has been proposed to form a thin carbon film on the surface of a glass material by thermal decomposition of hydrocarbons (see, for example, Patent Document 2).

Furthermore, it has been proposed to improve mold release by forming a carbon film having a film thickness of less than 5 nm, preferably less than 1 nm, on the surface of the glass material for molding by methane plasma treatment (see, for example, Patent Document 3). .
Japanese Examined Patent Publication No. 7-45329 JP-A-8-217468 Japanese Patent Laid-Open No. 9-286625

  According to the technologies disclosed in these patent documents, although a certain effect is seen, if the molding is repeated in the same mold, for example, 1000 times or more of continuous molding, the optical after molding is formed gradually or suddenly. The surface of the glass element was spoiled, cracked and poor in shape, which was not satisfactory. That is, when a glass material with insufficient film quality is subjected to press molding and continuous molding is performed, fusion between the glass material and the mold occurs, and the surface of the subsequent molded product (glass element) is spoiled, cracked, Form defects occur continuously. In particular, in high-efficiency production where continuous molding is performed hundreds or thousands of times using the same mold, this is a factor in yield reduction.

  In addition, even when a glass element is molded using a glass material for molding in which a predetermined thin film that suppresses fusion with the mold is formed on the glass surface, the timing at which the glass leaves the mold surface is uneven. Therefore, there is a problem that shape defects of the formed glass element are likely to occur, and the shape yield deteriorates. That is, when a glass element is molded by the mold press method, the glass material for molding and the mold are brought into close contact with each other in the press molding, and the shape of the mold is accurately transferred to the glass. Since press molding is performed at a temperature higher than the softening point of the glass, the heat shrinkage of the glass is larger than the heat shrinkage of the mold, so that the glass separates from the mold surface in the cooling process after the molding. The timing at which the glass leaves the mold surface is non-uniform and the shape of the molded glass element tends to be poor. In addition, in the adhesion between the glass and the mold surface at a high temperature, a reaction occurs at the interface between the glass and the mold, and a part of the glass is fused to the mold surface, and defects such as spiders and cracks are formed on the surface of the glass element. It has been difficult to obtain a good glass lens.

  Furthermore, when using a conventionally known hydrocarbon pyrolysis method, vacuum deposition method, sputtering method, plasma CVD method, etc., even if the device uses the same film formation principle, the film formation conditions between the devices It is difficult to make the film forming conditions completely uniform depending on the slight difference between the two and the position of the film forming object in the molding apparatus, and the possibility that the film quality on the surface of the glass material fluctuates must be considered in advance. Therefore, it is necessary to evaluate and select whether or not such a fluctuation factor is generated based on the film quality of the formed glass material.

  As described above, with the conventionally known film forming methods, it is not always possible to form only a film suitable for molding (good quality) on a glass material. In addition, it is possible to determine the quality of the film to some extent by inspecting the film thickness, color, and appearance of the film formed, but no method has been found to easily and reliably determine the quality of the film. .

In view of the above-mentioned problems, the problem of the present invention is to suppress fusion during press molding, and the spider or crack on the surface of the glass molded body resulting from it, and the timing at which the glass leaves the mold surface is uneven. becomes the shape of the glass element failure prevented caused by, is to provide a manufacturing how optical elements can be obtained in high yield and good quality glass products.

In order to solve the above-mentioned problem, in the present invention, in a method of manufacturing an optical element that softens a glass material by heating and press-molds, a glass material having a carbon-based film formed on the surface is prepared after preforming. The correlation between the dispersion term component of the surface free energy on the surface of the glass material on which the carbon-based film is formed and the shape defect rate when press-molding the glass material on which the carbon-based film is formed is obtained in advance, and the correlation On the basis of the above, a material having a dispersion term component of 85% or more in the surface free energy on the surface of the glass material after forming the carbon-based film is selected and continuously press-molded.

  Here, the surface free energy on the surface of the object corresponds to the sum of the dispersion force component (dispersion term component) and the polar force component. Therefore, in the present invention, the configuration based on the dispersion term component includes the meaning based on the polar force component.

In the present invention, a glass material having a dispersion term component in the surface free energy of 85% or more is selected and continuously press-molded as a glass material after the carbon-based film is formed. Therefore, an optical element can be produced stably without causing spoilage, cracks, or defective shape of the molded product.

We have purified water, CH ₂ I ₂ , By using the Owens-Wendt-Kaelble method from contact angle measurement using glycerin, isopentane, perfluorohexane, etc., due to the dispersion term component of the surface free energy of the film, the film quality (appropriateness for press molding) It was found that can be quantitatively evaluated.

Therefore, we investigated the correlation between the dispersion term ratio of the carbon-based thin film formed on the surface of the molding glass material and the shape defect rate, and searched for the preferred value of the ratio of the dispersion force component that would improve the yield of the molded lens. As a result, if glass materials with a dispersion term ratio of less than 85% are continuously supplied to press molding, the mold release timing on the mold molding surface will be non-uniform and the molded product (optical lens, etc.) will be defective. It was found that the rate was significantly increased and the yield decreased. The present invention has been made based on this result.

  In the present invention, the dispersion term component can be obtained by measuring a contact angle of a predetermined substance with respect to the surface of the glass material after film formation.

In the present invention, the formation of the carbon-based film on the glass material is simultaneously performed on a plurality of glass materials, and the glass material is selected for each lot formed, and the dispersion term component is 85% or more. It is preferable to carry out continuous press molding by selecting only those.

In the present invention, when a glass material is press-molded with a molding die to produce an optical element, a carbon-based film is formed in advance as a glass material on which a carbon-based film (a film containing carbon as a main component) is formed . Find the correlation between the dispersion term component of the surface free energy on the surface of the glass material and the shape defect rate when the glass material on which the carbon-based film is formed is press-molded. Based on the correlation, the dispersion of the surface free energy Since the component having a term component of 85% or more is selected and continuously press-molded, an optical element can be produced stably without causing defects in the shape of the spider, crack, or molded product.

(About surface free energy)
The present inventors have sought that the timing at which the forming glass material is separated from the surface of the forming mold (releasing property) greatly depends on the surface characteristics of the thin film formed on the surface of the forming glass material. Although it is difficult to evaluate the surface characteristics governing the releasability, the present inventors have used Owens- from the contact angle measurement using pure water, CH ₂ I ₂ , glycerin, isopentane, perfluorohexane and the like. The film quality (appropriate for press molding) can be quantitatively evaluated by the dispersion term component of the surface free energy of the film (calculated as the dispersion term ratio by the method described later) analyzed using the Wendt-Kaelble method. I found.

A surface having a large dispersion term ratio has a high component ratio of the dispersion term component in the interaction on the surface, and has a weak polar action that causes fusion and glass reactivity. The mold release depends on the polar action on the surface. If this action is small, the mold release is stable. On the contrary, when the polar action is increased, the releasability becomes unstable, and surface defects, shape defects such as asses and peculiarities occur. The correlation between the dispersion term ratio of the thin film mainly composed of carbon formed on the surface of the forming glass material and the shape defect rate was investigated.

The surface free energy on the object surface is decomposed into the dispersion force component gamma] s ^d and the polar force component gamma] s ^h. The dispersion force component γs ^d of the surface free energy is a van der Waals force, that is, a force that forms the core of a weak attractive force acting between molecules, and acts between all molecules including nonpolar molecules. On the other hand, polar force component gamma] s ^h in the surface free energy is that of the strong interaction forces between the polar groups represented by hydrogen bonding.

  Here, the “dispersion term ratio” is the ratio of the dispersion force component in the surface free energy, and the surface free energy can be measured using a known contact angle measuring device. That is, it is possible to measure and calculate the wetting angle (contact angle) of the surface to be measured using two different types of liquids.

For example, the surface free energy can be evaluated using the Owens-Wendt-Kaelble method from the measurement of the wetting angle of pure water and CH ₂ I ₂ as follows. The surface free energy (γ) is given by the sum of solid or liquid dispersion force γ ^d and solid or liquid polar interaction force γ ^p as shown in equation (1). It is done. Considering equation (1) with the surface free energy (γ _s ) of the solid, equation (2) is obtained. Here, the subscript s represents Solid.

  Similarly, in the case of a liquid, it is represented by the formula (3), and the subscript L represents Liquid.

As the surface free energy of the film, two kinds of liquids, water and CH ₂ I ₂ (diiodomethane), are dropped on the solid in the same amount, and the surface free energy is calculated from the obtained contact angle. That is, the calculation formula (4) was used by the Owens-Wendt-Kaelble method. The γ _L ^d and γ _L ^p of the two types of liquid use the literature values in Table 1, respectively, and γ _L of each of the two types of liquid is obtained from the equation (3).

  As shown in Table 1, for example, if the contact angle of water is 104.9 ° and the contact angle of diiodomethane is 72.0 °, the values in Table 1 are used for other energy values. As a result, the results represented by the equations (5) and (6) are obtained.

Therefore, when γ _s ^d obtained by the above equation (6) is substituted into the equation (5), the result shown in the equation (7) is obtained.

Therefore, by substituting the values of these equations (6) and (7) into equation (2),
γ _s = 21.76 + 0.59 = 22.35
The surface free energy γ _{s of the} solid is determined to be 22.35 mJ / m ^2, and the dispersion term ratio (γ _s ^d / γ _s ) is as follows: γ _s = 22.35 mJ / m ² , γ _s ^d = 21.76 mJ / m ²
∴γ _s ^d / γ _s = 97.36%
As shown, 97.36% is required.

(Glass material sorting method)
The formation (formation) of a carbon-based film containing carbon as a main component is formed by a technique such as a vapor deposition method, a sputtering method, a CVD method, a plasma method, or an ion plating method, which will be described later. If the glass material on which the film is formed is directly applied to the press molding process, the yield of molded lenses after press molding will vary due to differences in the film forming apparatus or film forming environment. focusing on the rate of dispersion KoNaru content in the surface free energy of the glass material after film was the yield of the molded lens is explored in the following preferred values of the proportion of dispersion term component becomes good.

  Table 2 shows the dispersion ratio of a thin film mainly composed of carbon formed on the surface of the molding glass material and the lens obtained by press molding for the molding glass material of glass A made of borate optical glass. Results are shown. The thin film mainly composed of carbon was formed by pyrolysis CVD of acetylene gas. The film thickness is 2 ± 1 nm. The lens is a convex meniscus lens (diameter φ 12.2 mm, edge thickness 0.4 mm).

  In Table 2, “dispersion term ratio * 1” indicates the dispersion term ratio of samples obtained by sampling a total of 25 samples from five trays of the same lot of 1000, and “defective rate * 2” is calculated for each lot. Fig. 5 shows the ratio of the number of defective shapes that are out of the standard value after 100 pieces of all press-formed products are inspected.

  In Table 2, the units in which the thin film mainly composed of carbon by acetylene gas pyrolysis CVD is simultaneously formed with the same apparatus are set as lots 1 to 4, and each lot is a tray on which 200 materials can be placed. Using 5 pieces, it consists of 1000 glass materials.

  The evaluation items of the molded lens are appearance evaluation such as spider and crack, and lens shape evaluation. The lens shape evaluation is a convex-spherical surface using a spherical interferometer (R = 19.92 mm, standard: 19.8862 to 19.9539). R value was evaluated.

  From this result, it can be seen that when the dispersion term ratio of the carbonaceous thin film formed on the surface of the forming glass material is 85% or more, the shape defect is drastically reduced. Conversely, if glass materials with a dispersion term ratio of less than 85% continue to be supplied to press molding, the mold release surface on the mold molding surface will become non-uniform and the molded product (optical lens, etc.) will be defective. The rate is significantly higher and the yield is reduced.

  The present invention has been made on the basis of the results of this investigation, and a glass material having a dispersion term ratio of a carbon-based film (film containing carbon as a main component) formed on the surface of the glass material is 85% or more. By selecting and press-molding using the selected glass material, it is possible to reduce the shape defect of the molded product (such as an optical lens), the occurrence of spiders and cracks. That is, when forming a carbon-based film containing carbon as a main component on the surface of a preformed glass material, and molding the glass material by pressing the glass material with a mold, the carbon-based film of the glass material It is determined whether or not the dispersion component of the surface energy at 85% or more is satisfied, and only the satisfied glass material is selected and subjected to glass forming. More specifically, after preforming, a glass material having a carbon-based film formed on the surface is prepared, and a dispersion term component of the surface free energy of the glass material on which the carbon-based film is formed, and the carbon-based film A correlation with the shape defect rate when the formed glass material is press-molded is obtained in advance, and based on the correlation, the surface free energy dispersion term component of the glass material on which the carbon-based film is formed is a predetermined ratio or more. Are selected and continuous press molding is performed. Therefore, according to the present invention, generation of spiders, cracks and shape defects is extremely small, and a glass product such as a desired optical element can be obtained.

The dispersion ratio of the glass material is, for example, using two types of liquid, water and CH ₂ I ₂ (diiodomethane), dropping the same amount on each solid, and calculating the surface free energy from the calculated contact angle. The dispersion term ratio can be obtained from the surface free energy.

(About carbon film)
In the present invention, the carbon-based film is a thin film mainly composed of carbon, and includes a film containing a component other than carbon (such as hydrogen).

The molding material is a glass material in which a thin film mainly composed of carbon having a dispersion term ratio of 85% or more is formed on the surface of the glass material. The surface free energy of a thin film mainly composed of carbon is 60 mJ / m ² or less, the film thickness is 0.1 nm or more and 1 μm or less, and the surface free energy of the glass material before film formation is 60 mJ / m ² or more. It is preferable.

The surface free energy of the glass material after preforming (before film formation) is a measure of organic contamination. When the surface free energy is high, there is little organic stain, and conversely, when the surface free energy is low, there is much organic stain. When there is a lot of organic contamination, reaction occurs at the interface based on this organic contamination, and many fusions of glass material to the mold surface or release film surface, especially sub-μm size fine fusion occur, For this reason, the mold surface or release film surface that has been subjected to optical mirror finish is rough and uneven. By transferring this, an appearance defect such as a spider is generated in the molded optical element. Further, cracking of the optical element occurs with the fused portion as a base point. Therefore, it is preferable that the forming glass material for forming carbon has a small amount of organic contamination, and specifically, the film is formed on the forming glass material having a surface free energy of 60 mJ / m ² or more.

Molding glass materials with a surface free energy of 60 mJ / m ² or more must be precisely cleaned as described above, stored in a clean environment with little organic contamination, and before forming a surface layer on the molding glass material. In addition, the surface free energy is inspected for each lot of forming glass material. Only the glass material for molding having a minimum surface free energy of 60 mJ / m ² or more is subjected to the surface layer forming step. The glass material for molding with a minimum surface free energy of less than 60 mJ / m ² is again subjected to precision cleaning. Similarly to the above, it is preferable to form the surface layer in advance when the variation of the surface free energy in the lot is a median value ± 5 mJ / m ² or less, preferably ± ² mJ / m ² or less.

  Thin films mainly composed of carbon provided on glass materials are diamond, diamond-like carbon film (hereinafter DLC), hydrogenated diamond-like carbon film (hereinafter DLC: H), tetrahedral amorphous carbon film (hereinafter ta- C) A hydrogenated tetrahedral amorphous carbon film (hereinafter referred to as ta-C: H), an amorphous carbon film (hereinafter referred to as aC), a hydrogenated amorphous carbon film (hereinafter referred to as aC: H) or the like.

  Further, the formation (formation) of a thin film containing carbon as a main component is formed by a technique such as vapor deposition, sputtering, CVD, plasma, or ion plating. The film thickness of the carbon-based thin film may be about 0.1 nm to 1 μm, and 0.5 nm to 100 nm is particularly preferable. If the film thickness is too thin, the releasability tends to decrease. If the film thickness is too thick, the effect of preventing fusion, spiders and cracks tends to be saturated, or the surface layer state of the glass material for molding is not uniform. And variations tend to increase.

Specifically, the carbon film is formed by vapor deposition using a known vapor deposition device, and the carbon material is heated by electron beam, direct current or arc in a vacuum atmosphere of about 10 ^-4 Torr, and evaporated from the material. In addition, carbon vapor generated by sublimation can be transported onto a substrate, condensed and deposited. For example, in the case of direct energization, a carbon material having a cross-sectional area of approximately 0.1 cm ² can be energized and heated by energizing approximately 100 V-50A. The substrate heating temperature is preferably about room temperature to 400 ° C. However, when the glass transition temperature (Tg) of the substrate is 450 ° C. or lower, the upper limit temperature for heating the substrate is preferably Tg-50 ° C.

  In this case, in order to control to a predetermined film thickness, the following can be performed. The film thickness of the carbon film can be measured from the reflectance change, transmittance change of the deposited film on the monitor glass or the actual measurement by QCM, and the carbon film thickness can be controlled by opening and closing the shutter, as with the normal optical thin film. .

In the case of the CVD method, a commercially available thermal decomposition CVD apparatus is used to heat the inside of a reaction vessel evacuated to about 10 ⁻¹ Torr to about 500 ° C., and hydrocarbon gas such as acetylene gas is put into this vessel for 20 minutes. By introducing up to about several tens of Torr over about 2 hours, a carbon-based thin film can be formed by condensing and precipitating carbon on the surface of the glass material.

  As the hydrocarbon gas, methane, ethane, ethylene, acetylene, propylene, benzene vapor, hexane vapor or the like can be used.

In the case of the plasma method, a hydrocarbon gas such as acetylene gas diluted with an inert gas such as Ar gas is introduced into a reaction vessel evacuated to about 10 ⁻¹ Torr using a commercially available plasma decomposition CVD apparatus. By applying high frequency power (13.56MHz) of about 500W to the reaction vessel, hydrocarbon molecules are decomposed into carbon and hydrogen plasma, and carbon is condensed and deposited on the surface of the glass material to form a carbon-based thin film. Can do.

  As the hydrocarbon gas, methane, ethane, ethylene, acetylene, propylene, benzene vapor, hexane vapor or the like can be used.

In the case of the sputtering method, using a known sputtering apparatus, a carbon target material is sputtered with argon ions in an argon atmosphere of about 10 ⁻² to 10 ⁻³ Torr, the sputtered carbon particles are transported, Carbon particles can be deposited on the surface of the material to form a carbon thin film. The substrate heating temperature is preferably about room temperature to 400 ° C. However, when the glass transition temperature (Tg) of the substrate is 450 ° C. or lower, the upper limit temperature for heating the substrate is preferably Tg-50 ° C. The film thickness of carbon can be measured from the change in reflectance or transmittance of the sputtered film on the monitor glass in the same manner as a normal optical thin film, and the carbon film thickness can be controlled by opening and closing the shutter.

In the case of the ion plating method, for example, using a known ion plating apparatus, a carbon material is heated by an electron beam in an argon atmosphere of about 10 ⁻² to 10 ⁻⁴ Torr, and evaporated and sublimated from the material. A carbon thin film can be formed by vapor-depositing the carbon vapor generated by the above process on a negatively biased substrate. The glow discharge between the filament and the substrate electrode improves the adhesion strength and uniformity of the deposition. The substrate heating temperature is preferably about room temperature to 400 ° C. However, when the glass transition temperature (Tg) of the substrate is 450 ° C. or lower, the upper limit temperature for heating the substrate is preferably Tg-50 ° C. In this case, the control of the predetermined film thickness can be performed in the same manner as the above evaporation method.

(Manufacturing method of optical element)
In the method for producing a glass product of the present invention, the preformed glass material described above is heated and softened, and then pressure-molded with a mold. The pressure molding of the glass material can be performed by a known means. For example, when a glass material is introduced into a precisely shaped mold, the viscosity is heated to a temperature equivalent to 10 ⁸ to 10 ¹² poise, softened, and pressed to make the molding surface of the mold a glass material. Transcript to. Alternatively, a glass material whose viscosity has been raised to a temperature equivalent to 10 ⁸ to 10 ¹² poise in advance is introduced into a precisely shaped mold and pressed to make the molding surface of the mold a glass material. Transcript to. The atmosphere during molding is preferably non-oxidizing. Thereafter, the mold and the glass material are cooled, and when the temperature is preferably equal to or lower than Tg, the mold is released and the molded optical element is taken out.

As the mold base material of the mold, in addition to SiC, WC, TiC, TaC, BN, TiN, AlN, Si ₃ N ₄ , SiO ₂ , Al ₂ O ₃ , ZrO ₂ , W, Ta, Mo, cermet, sialon A material selected from mullite, carbon composite (C / C), carbon fiber (CF), WC-Co alloy, and the like can be used.

Further, a mold release film is preferably formed on the molding surface of the mold to be used. For example, diamond-like carbon film (hereinafter referred to as DLC), hydrogenated diamond-like carbon film (hereinafter referred to as DLC: H), tetrahedral amorphous carbon film (hereinafter referred to as ta-C) hydrogenated tetrahedral amorphous carbon film (hereinafter referred to as ta-C: H), amorphous carbon film (hereinafter aC), hydrogenated amorphous carbon film (hereinafter aC: H), etc., carbon-based coating, Si ₃ N ₄ , TiAlN, TiCrN, CrN, Cr _X N _Y , AlN, TiN, etc. nitride coating or composite multilayer film or laminated film (AlN / CrN, TiN / CrN, etc.), Pt—Au, Pt—Ir—Au, Pt—Rh—Au, etc. A film such as a noble metal alloy film can also be used.

  The release film is formed by DC-plasma CVD method, RF-plasma CVD method, microwave plasma CVD method, ECR-plasma CVD method, plasma CVD method such as photo CVD method, laser CVD method, ion plating method, etc. Alternatively, a method such as ionized vapor deposition, sputtering, vapor deposition, or FCA (Filtered Cathodic Arc) may be used.

  The glass product produced by applying the present invention can be, for example, an optical element such as a lens, mirror, grating, prism, microlens, laminated diffractive optical element, and is a glass molded product other than the optical element. You can also.

  Hereinafter, the present invention will be described in more detail with reference to examples. Table 3 shows the conditions of the examples and comparative examples used in the following evaluations and the evaluation results. In Table 3, “dispersion term ratio value” means the minimum value of the dispersion term ratio in the entire set of samples prepared, and “lot ratio where the maximum value of the dispersion term ratio is less than 85%” In the prepared sample, the ratio of occurrence of lots with a maximum dispersion term ratio of less than 85% is shown. In the following evaluation, as an example, only a sample having a dispersion term ratio of 85% or more was selected from such a sample (lot) and used, and in the comparative example, the prepared sample (lot) was selected. It is a case where it uses as it is.

[Example 1]
As a glass material of the optical element molding material, borate glass A (optical glass having a glass transition temperature of 520 ° C., a refractive index of 1.69350, and a linear expansion coefficient of 69 × 10 ⁻⁷ / ° C.) is used. The glass material was cleaned with high precision by a wet cleaning method using a precision cleaning machine.

  100 glass materials are placed on each tray, and 15 trays (total of 1500 glass materials) are installed in the same film deposition system. The surface of this molding material is subjected to acetylene gas pyrolysis CVD. AC: H was deposited to a thickness of 2 ± 1 nm.

  The CVD method by thermal decomposition of acetylene gas was performed as follows. A glass material was placed on a quartz tray and placed in a bell jar (reaction vessel). The inside of the bell jar was evacuated to 0.5 torr or less by a vacuum pump, and then heated and maintained at 480 ° C. The introduction of nitrogen gas was stopped after purging for 30 minutes while maintaining the pressure at 160 torr by exhausting with a vacuum pump while introducing nitrogen gas into the bell jar. Further, after the inside of the bell jar was evacuated to 0.5 torr or less by a vacuum pump, acetylene gas was introduced at 40 torr in 20 minutes and the introduction was stopped. And after cooling, it returned to atmospheric pressure, diluting with nitrogen gas, and took out the glass raw material.

The surface free energy was evaluated using Owens-Wendt-Kaelble from the measurement of pure water and CH ₂ I ₂ wetting angles. In other words, as a result of sampling 5 glass materials from each of 15 trays and calculating the dispersion term ratio based on the surface free energy of each glass material, the minimum value of the dispersion term ratio for 13 trays is 91% or less, and the two trays contained a glass material (minimum value: 81%) with a dispersion ratio of less than 85%. Was stopped, and only the glass material of the 13 trays was added to the next process.

Subsequently, the glass material selected as described above is heated to 610 ° C. in a nitrogen gas atmosphere and pressurized with a mold at a pressure of 150 kg / cm ² for 1 minute. After releasing the pressure, the cooling rate was decreased to 480 ° C at -50 ° C / min, and then cooled at a rate of -200 ° C / min or more, and the temperature of the press molded product was lowered to 200 ° C or less. Thereafter, the molded product was taken out. As the mold, after using a polycrystalline SiC mold surface prepared by CVD method mirror-polished to Rmax = 18 nm, as a mold release film on the molding surface, using an ion plating film forming apparatus, A DLC: H film was used.

  Convex meniscus lens of the same type with a diameter of 16mmφ and edge thickness of 0.5mm is continuously pressed, and the appearance of the spider, crack, etc. of the lens up to 1000 times is magnified, and the first surface (spherical surface) is an interferometer. The second surface (aspheric surface) was inspected with a stylus type shape measuring instrument. The appearance inspection compared with the limit sample, and the shape inspection evaluated the quality based on the shape of the interference fringes and the measurement value by the measuring instrument. However, both the appearance and the shape were within the allowable range, and no defect was detected.

[Comparative Example 1]
In Example 1 above, the dispersion term ratio is obtained based on the surface free energy of the glass material, and all the glass materials placed on the two trays including the glass material having the dispersion term ratio of less than 85% are pressed. In Comparative Example 1, 150 glass materials selected from two trays that were unsuitable for press molding were subjected to continuous press molding under the same conditions as in Example 1 above. 150 convex meniscus lenses were obtained. For these glass materials, before press molding, 20 dispersion ratios were obtained from each tray based on the surface free energy, and 6 (30%) glass materials had a dispersion term ratio of less than 85%. (The lowest value was 78%).

  Next, with respect to the molded lens, the same inspection as in Example 1 was performed on all the lenses. As a result, there were 42 defects (17 appearance defects and 25 shape defects) (defective rate 28%). Was detected.

[Example 2]
A CVD method based on the thermal decomposition of acetylene gas was performed by evacuating the bell jar to 20 torr with a vacuum pump and then heating and maintaining at 440 ° C. As in Example 1, when the surface free energy of the glass material after film formation by CVD was evaluated using the Owens-Wendt-Kaelble method from the wetting angle measurement of pure water and CH ₂ I ₂ , the surface free energy was The maximum value was 60 mJ / m ² or less, the minimum value of the dispersion term ratio was 80%, and there were 22% of lots less than 85% that deviated from the claimed range of 85% or more. Therefore, continuous pressing was performed in the same manner as in Example 1 except for all the glass materials of the tray including the glass material having a dispersion term ratio of less than 85%. As a result of 1000 continuous presses, the incidence of shape defects was 2%.

[Examples 3 to 4]
In the same manner as in Example 2, only the tray (lot) having a minimum dispersion term ratio of 85% or more of the glass material on which the carbon-based thin film was formed was selected and continuously pressed under the same conditions. As a result of evaluating the shape of the optical element up to 1000 presses, as shown in Table 3, the occurrence rate of the shape defect was good or extremely good at less than 5%.

  In the above embodiment, a plurality of trays are set in the same apparatus, the glass material for each tray is sampled, the dispersion term ratio is obtained from the surface free energy, and the dispersion term ratio is 85% or more. In this example, 85% or more of the glass material on the tray is considered to be suitable for press molding, and it is used for the press molding process. If it is possible, the glass material for each processing unit (lot) can be sampled, and all the lots whose measured values satisfy the above conditions can be regarded as suitable for press forming.

Claims (3)

In the manufacturing method of the optical element that softens the glass material by heating and press-molds,
After preforming, prepare a glass material with a carbon-based film on the surface,
The correlation between the dispersion term component of the surface free energy on the surface of the glass material on which the carbon-based film is formed and the shape defect rate when the glass material on which the carbon-based film is formed is press-molded is obtained in advance.
Based on the correlation, optical elements dispersed term component in the surface free energy of the glass-containing material was deposited the carbon-based film is characterized in that a continuous press forming were selected more than 85% Production method. In claim 1,
The dispersion element component is obtained by measuring a contact angle of a predetermined substance with respect to the surface of the glass material after film formation . In claim 1 or 2,
The carbon-based film is formed on the glass material at the same time for a plurality of glass materials, and the glass material is selected for each lot formed, and only the lot having the dispersion term component of 85% or more is selected. An optical element manufacturing method comprising performing continuous press molding .