WO2015046509A1 - 光学素子およびその製造方法 - Google Patents
光学素子およびその製造方法 Download PDFInfo
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- WO2015046509A1 WO2015046509A1 PCT/JP2014/075887 JP2014075887W WO2015046509A1 WO 2015046509 A1 WO2015046509 A1 WO 2015046509A1 JP 2014075887 W JP2014075887 W JP 2014075887W WO 2015046509 A1 WO2015046509 A1 WO 2015046509A1
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- glass
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- press
- oxide
- coating film
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- G—PHYSICS
- G02—OPTICS
- G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
- G02B3/00—Simple or compound lenses
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
- C03B11/00—Pressing molten glass or performed glass reheated to equivalent low viscosity without blowing
- C03B11/06—Construction of plunger or mould
- C03B11/08—Construction of plunger or mould for making solid articles, e.g. lenses
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C17/00—Surface treatment of glass, not in the form of fibres or filaments, by coating
- C03C17/22—Surface treatment of glass, not in the form of fibres or filaments, by coating with other inorganic material
- C03C17/23—Oxides
- C03C17/245—Oxides by deposition from the vapour phase
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- C—CHEMISTRY; METALLURGY
- C03—GLASS; MINERAL OR SLAG WOOL
- C03C—CHEMICAL COMPOSITION OF GLASSES, GLAZES OR VITREOUS ENAMELS; SURFACE TREATMENT OF GLASS; SURFACE TREATMENT OF FIBRES OR FILAMENTS MADE FROM GLASS, MINERALS OR SLAGS; JOINING GLASS TO GLASS OR OTHER MATERIALS
- C03C3/00—Glass compositions
- C03C3/04—Glass compositions containing silica
- C03C3/062—Glass compositions containing silica with less than 40% silica by weight
- C03C3/064—Glass compositions containing silica with less than 40% silica by weight containing boron
- C03C3/068—Glass compositions containing silica with less than 40% silica by weight containing boron containing rare earths
Definitions
- the present invention relates to an optical element and a manufacturing method thereof.
- a method of manufacturing an optical element such as a glass lens
- a method of press-molding a molding material hereinafter referred to as “a glass material for press molding” or “preform”
- a glass material for press molding or “preform”
- the glass material for press molding and the molding surface of the molding die adhere to each other under high temperature conditions, so that a chemical reaction occurs at the interface between them, so that fusion, spider, scratches, etc. Reaction traces or the like may occur, and the optical performance of the optical element obtained by press molding may deteriorate.
- Patent Document 1 proposes to provide a coating film on the surface of a glass material for press molding to suppress the reaction between the mold and the glass.
- Patent Document 2 proposes to provide a hydrogen capture film on the surface of a glass material for press molding in order to suppress the generation of linear marks.
- One embodiment of the present invention provides an optical element manufacturing method capable of suppressing the generation of bubbles in an optical element after press molding.
- One embodiment of the present invention provides: Oxide glass, A coating film covering at least part of the surface of the oxide glass; Have The above-described coating film is a metal oxide film in which oxygen is lost from the stoichiometric composition, and the metal oxide film is included in the oxide glass at a temperature equal to or higher than the glass transition temperature of the oxide glass. An optical element in which an oxygen atom is incorporated at a rate faster than a rate at which a metal atom contained in the metal oxide film diffuses into the oxide glass; About.
- a further aspect of the present invention provides: A step of preparing a glass material for press molding having an oxide glass and a coating film that covers at least a part of the surface of the oxide glass and is a metal oxide film in which oxygen is lost from the stoichiometric composition; , A press process for forming a press-molded body by press-molding a glass material for press molding; With The press-molded body described above includes the above-described coating film that has undergone a pressing process, and the coating film that has undergone the pressing process is a metal oxide film having a higher oxygen content than the coating film before the pressing process.
- Device manufacturing method About.
- the inventors have provided the above-described coating film on the surface of the glass material for press molding.
- a metal oxide film in which oxygen is deficient from the stoichiometric composition is in a state where oxygen is easily taken up. Therefore, with the metal oxide film in this state, oxygen that causes foaming during press molding can be removed from the inside of the glass, and generation of bubbles can be suppressed.
- the movement of oxygen atoms from the oxide glass to the coating film incorporation
- the movement of metal atoms from the coating film to the oxide glass Diffusion
- the diffusion rate of the metal atoms is faster than the rate at which oxygen atoms are taken into the coating film
- the diffusion proceeds in preference to the uptake.
- a remarkable reduction in film thickness or disappearance of the film occurs due to press molding, and it is difficult to suppress foaming inside the oxide glass.
- the above-mentioned coating film takes in oxygen atoms in preference to the diffusion of metal atoms, it efficiently takes in oxygen atoms that cause generation of bubbles from oxide glass and suppresses foaming. Can do.
- the above-described coating film that has undergone a pressing step is present.
- the coating film included in this optical element takes in oxygen from the oxide glass at the time of press molding, the content of oxygen atoms relative to metal atoms is higher than that contained in the glass material for press molding.
- the coating film included in the optical element is still in a state in which oxygen is lost from the stoichiometric composition.
- FIG. 1 shows an example of a press molding apparatus.
- FIG. 2 shows an optical micrograph of the lens (core glass: I-1 in Table 1) produced in Example 1.
- FIG. 3 shows an optical micrograph obtained by enlarging and photographing a part of the lens (core glass: I-1 in Table 1) produced in Comparative Example 2.
- FIG. 4 shows the depth direction analysis results of secondary ion intensity by TOF-SIMS after pressing (lens) for Example 1.
- FIG. 5 shows the depth direction analysis result of secondary ion intensity by TOF-SIMS before pressing (unpressed product) in Example 1.
- FIG. 6 shows the result of comparison of the secondary ion intensity ratio of ZrO 2 / ZrO in FIGS.
- FIG. 1 shows an example of a press molding apparatus.
- FIG. 2 shows an optical micrograph of the lens (core glass: I-1 in Table 1) produced in Example 1.
- FIG. 3 shows an optical micrograph obtained by enlarging and photographing a part of the lens (core glass: I-1 in
- FIG. 7 shows the depth direction analysis result of the secondary ion intensity of the lens produced in Comparative Example 2 by TOF-SIMS.
- FIG. 8 shows a result of superimposing the result of Example 1 shown in FIG. 4 and the result of Comparative Example 2 shown in FIG.
- FIG. 9 shows the results of depth direction analysis of secondary ion intensity by TOF-SIMS after pressing (lens) for Comparative Example 1.
- FIG. 10 shows the depth direction analysis result of the secondary ion strength by TOF-SIMS before pressing (unpressed product) in Comparative Example 1.
- press molding is performed using a glass material for press molding having a metal oxide film in which oxygen is lost from the stoichiometric composition as a coating film covering at least part of the surface of the oxide glass. I do.
- the above-mentioned coating film has the above-mentioned press-molding glass material in which the content of oxygen atoms relative to metal atoms is also present in at least a part of the surface of the press-molded body obtained by press-molding this press-molding glass material Is included as a metal oxide film that is higher than the coating film of the film.
- bubbles generated in the optical element after press molding are oxygen derived from oxide glass.
- a metal oxide film in which oxygen is deficient from the stoichiometric composition is considered to be in a state where oxygen can be easily taken in so as to approach the stoichiometric composition, which is a more stable state. Therefore, by applying at least a part of the surface of the oxide glass with a metal oxide film in which oxygen is deficient from the stoichiometric composition, the oxygen that causes foaming during the press is converted from the oxide glass to the metal.
- the metal oxide film remaining on the surface of the press-molded body (optical element) thus formed contains oxygen atoms taken from the oxide glass, the press-molding glass before press molding has it. It contains more oxygen atoms than the metal oxide film. That is, the press-molded body has a metal oxide film having a content rate of oxygen atoms with respect to metal atoms higher than that of the coating film of the press-molding glass material on at least a part of the surface.
- the metal oxide film is converted into oxide glass at a temperature equal to or higher than the glass transition temperature of the oxide glass.
- the rate at which oxygen atoms are incorporated is the rate at which metal atoms contained in the metal oxide film diffuse into the oxide glass (hereinafter, “metal atom diffusion rate”). )
- metal atom diffusion rate is the rate at which metal atoms contained in the metal oxide film diffuse into the oxide glass.
- the speed at which the above-described metal oxide film takes in oxygen atoms in the oxide glass during press molding depends on whether the metal atoms in the metal oxide film are oxides. Faster than the speed taken into the glass.
- uptake of oxygen atoms into the coating film during pressing proceeds in preference to the diffusion of metal atoms into the oxide glass. Therefore, after press molding, the metal oxide film in the above-described state can be present on the press-molded body.
- the glass material for press molding suitably used in the method for manufacturing an optical element according to one aspect of the present invention includes an oxide glass and a coating film that covers at least a part of the surface of the oxide glass.
- the metal oxide film is in a state where oxygen is deficient from the stoichiometric composition, and the oxygen atom uptake rate and the metal atom diffusion rate satisfy the above relationship.
- the optical element obtained through the step of press molding the glass material for press molding also has a metal oxide film in which the oxygen atom uptake rate and the metal atom diffusion rate satisfy the above-described relationship.
- the metal oxide film present on the optical element has a higher oxygen atom content to metal atoms than the metal oxide film before press molding. This is because oxygen atoms are taken from the oxide glass in press molding.
- the above-described glass material for press molding will be described in more detail.
- Coating film (metal oxide film)
- the coating film covering the oxide glass may be formed by a film formation method capable of forming a metal oxide film in which oxygen is lost from the stoichiometric composition.
- a film formation method capable of forming a metal oxide film in which oxygen is lost from the stoichiometric composition.
- core glass glass
- the lower limit of the film forming temperature (core glass temperature) is preferably 150 ° C. or higher, and more preferably 200 ° C. or higher.
- the upper limit is preferably less than the glass transition temperature of the core glass.
- the upper limit temperature is, for example, 450 ° C. or less.
- a plurality of core glasses formed in a predetermined shape are arranged in a tray and placed in a vacuum chamber, and the core glass is heated to about 300 ° C. by a heater while evacuating the vacuum chamber. To do. After evacuating until the degree of vacuum in the vacuum chamber becomes 1 ⁇ 10 ⁇ 5 Torr or less, Ar gas is introduced, the atmosphere gas in the vacuum chamber is replaced with Ar gas, and then a high frequency is applied to the target substrate. The raw material is turned into plasma, and a coating film is formed on the surface of the core glass.
- the film thickness of the coating film can be controlled to a desired film thickness by adjusting the pressure (vacuum degree) in the vacuum chamber, the power source power, and the film formation time.
- the coating film should just cover at least one part of the surface of core part glass. Therefore, the core glass after coating film formation may be in a state where a part of the surface is uncoated or the entire surface may be covered.
- An optical functional surface means a region within an effective diameter in an optical lens, for example.
- oxygen atoms can be taken from the core glass if the above-described coating film is present in at least a part of the surface of the glass material for press molding. .
- a metal that can form a metal oxide film in which the oxygen atom uptake rate and the metal atom diffusion rate satisfy the above-described relationship may be used.
- Specific examples of such metals include zirconium, titanium, niobium, tungsten, and tantalum.
- a preliminary experiment is performed as appropriate to confirm that the oxide film satisfying the above relationship can be formed by the oxygen atom uptake rate and the metal atom diffusion rate. It is possible to determine a metal that can form a metal oxide film that satisfies the above relationship. As a target in the above-described film forming method, it is preferable to use these metals alone.
- the film thickness of the coating film is preferably 0.5 nm or more and more preferably 1.5 nm or more in order to efficiently take in oxygen from the oxide glass. From the viewpoint of preventing spiders, the thickness of the coating film is preferably 15 nm or less, and more preferably 10 nm or less.
- the coating film described above is in a state where oxygen is lost from the stoichiometric composition.
- the stoichiometric composition is ZrO 2
- the coating film is a zirconium oxide film
- the composition is ZrOx (x ⁇ 2).
- x is not particularly limited as long as it is less than 2. The same applies to other metal oxide films.
- Oxide glass examples of the core glass whose surface is at least partially covered by the above-described coating film include optical glasses having various compositions that are usually used for producing optical elements.
- optical glasses having various compositions that are usually used for producing optical elements.
- Specific examples of such optical glass include boric acid-rare earth glass such as lanthanum borate glass, phosphate glass, and silicate glass.
- an oxide glass containing a relatively large amount of Nb 2 O 5 , TiO 2 , WO 3 , and Ta 2 O 5 as high refractive index imparting components can be mentioned.
- one or more high refractive index imparting components selected from the group consisting of Nb 2 O 5 , TiO 2 , WO 3 and Ta 2 O 5 are included, and the high refractive index
- the oxide glass having a total content (Nb 2 O 5 + TiO 2 + WO 3 + Ta 2 O 5 ) of the rate-imparting component of 10% by mass or more is used as the core glass, and the above-mentioned coating film is provided on the core glass.
- the total content (Nb 2 O 5 + TiO 2 + WO 3 + Ta 2 O 5 ) is more preferably 15% by mass or more.
- the total content (N b O 5 + TiO 2 + WO 3 + Ta 2 O 5 ) is 50% by mass or less, which suppresses an increase in press temperature due to a significant increase in the glass transition temperature Tg and the yield point Ts. Moreover, it is preferable from the viewpoint of easiness of vitrification, and more preferably 45% by mass or less.
- the pressing temperature is usually performed at a temperature equal to or higher than the glass transition temperature of the core glass, the higher the glass transition temperature, the higher the pressing temperature tends to be. On the other hand, a significant increase in the press temperature may promote the generation of bubbles. Therefore, as a preferable specific embodiment of the core glass, an oxide glass containing an appropriate amount of one or more glass components having an action of lowering the glass transition temperature can be exemplified.
- the glass component having an action of lowering the glass transition temperature include ZnO and an alkali metal oxide selected from the group consisting of Li 2 O, Na 2 O and K 2 O.
- the total content of ZnO and alkali metal oxide is preferably 5% by mass or more, and more preferably 10% by mass or more.
- the total content (ZnO + Li 2 O + Na 2 O + K 2 O) is preferably 25% by mass or less, and more preferably 20% by mass or less.
- Specific examples of the core glass include optical glass having a refractive index nd of 1.70 to 2.10 and an Abbe number ⁇ d of 20 to 55 from the viewpoint of the usefulness of the optical element.
- an optical glass satisfying one or both of glass transition temperature Tg of 630 ° C. or lower and yield point Ts of 680 ° C. or lower can also be illustrated.
- the method for manufacturing an optical element according to one embodiment of the present invention is not limited to the specific embodiment described above.
- the optical glass that can serve as the core glass
- the following glasses I, II, and III can be given, for example.
- the core glass may be an oxide glass, and the composition thereof is not particularly limited. Glasses I, II, and III are all suitable as optical glasses for producing optical elements. According to one embodiment of the present invention, such an optical glass can be press-molded to provide a high-quality optical element free from bubbles in the glass.
- B 3+ and Si 4+ in total 5 to 60% (however, B 3+ is 5 to 50%), Zn 2+ and Mg 2+ in total 5% or more, La 3+ , Gd 3+ , Y 3+ and Yb 3+ in total 10 to 50%, Ti 4+ , Nb 5+ , Ta 5+ , W 6+ and Bi 3+ in total 6 to 45% (provided that the total content of Ti 4+ and Ta 5+ exceeds 0% and W 6+ Content over 5%), Including The cation ratio of the Si 4+ content to the B 3+ content (Si 4+ / B 3+ ) is 0.70 or less, Ti 4+ and Ta 5+ content of the cation ratio of Ta 5+ to the total content of (Ta 5+ / (Ti 4+ + Ta 5+)) is not less 0.23 or more, The cation ratio of the W 6+ content to the total content of Nb 5+ and W 6+ (W 6+ / (N
- the glass I is a high refractive index glass, it can exhibit a low glass transition temperature, and thus is suitable as a glass for precision press molding.
- the glass transition temperature is 650 ° C. or lower.
- Optical glass having a glass transition temperature of 650 ° C. or lower can maintain the glass temperature during precision press molding in a relatively low temperature range, suppresses the reaction between the glass during press molding and the press molding surface, and is precise.
- the press formability can be maintained in a good state.
- the glass transition temperature is preferably 640 ° C. or less, more preferably 630 ° C. or less, further preferably 620 ° C.
- the glass transition temperature is preferably 500 ° C. or higher, and is preferably 520 ° C. or higher. More preferably, it is 540 degreeC or more, More preferably, it is 560 degreeC or more, It is still more preferable to set it as 570 degreeC or more.
- B 2 O 3 La 2 O 3 and ZnO are included, and expressed in mol%, B 2 O 3 20 to 60%, SiO 2 0 to 20%, ZnO 22 to 42%, La 2 O 3 5 to 24%, Gd 2 O 3 0 ⁇ 20% ( provided that the total of La 2 O 3 and Gd 2 O 3 is 10 ⁇ 24%), ZrO 2 0 ⁇ 10%, Ta 2 O 5 0 ⁇ 10%, WO 3 0 ⁇ 10%, Nb 2 O 5 0-10%, TiO 2 0-10%, Bi 2 O 3 0-10%, GeO 2 0-10%, Ga 2 O 3 0-10%, Al 2 O 3 0- 10%, BaO 0 to 10%, Y 2 O 3 0 to 10% and Yb 2 O 3 0 to 10%, and an Abbe number ( ⁇ d ) of 40 or more and substantially free of lithium Glass.
- ⁇ d Abbe number
- substantially free of lithium means that the amount of Li 2 O introduced is suppressed to a level that does not cause spiders or burns that hinder the use of the glass surface as an optical element. It is. Specifically, it means that the content is reduced to less than 0.5 mol% in terms of the amount of Li 2 O. Since the risk of spider and burns can be reduced as the amount of lithium is reduced, the amount of Li 2 O is preferably suppressed to 0.4 mol% or less, and more preferably to 0.1 mol% or less. Preferably, no introduction is more preferable.
- the transition temperature (T g ) is low in order to prevent wear of the press mold and damage to the release film formed on the molding surface of the mold.
- the temperature (T g ) is preferably 630 ° C. or lower, and more preferably 620 ° C. or lower.
- the amount of lithium in the glass is limited as described above. Therefore, if the transition temperature (T g ) is excessively decreased, the refractive index decreases or the glass Problems such as a decrease in stability of the product are likely to occur. Therefore, the transition temperature (T g ) is more preferably 530 ° C. or higher, and further preferably 540 ° C. or higher.
- Glass III exhibits a low-temperature softening property with a glass transition temperature of 650 ° C. or lower.
- a more preferable range of the glass transition temperature of the glass III is 640 ° C. or less, more preferably 630 ° C. or less, more preferably 620 ° C. or less, and still more preferably 610 ° C.
- the glass transition temperature is excessively decreased, it is difficult to achieve higher refractive index and lower dispersion and / or the stability and chemical durability of the glass tend to decrease.
- Is preferably 510 ° C. or higher, preferably 540 ° C. or higher, more preferably 560 ° C. or higher, and even more preferably 580 ° C. or higher.
- the preferred range of the yield point (Ts) of the glass III is 700 ° C. or less, more preferably 690 ° C. or less, further preferably 680 ° C. or less, more preferably 670 ° C. or less, and still more preferably 660 ° C. or less. .
- the yield point (Ts) is preferably 550 ° C. or higher, more preferably 580 ° C. or higher, even more preferably 600 ° C. or higher, and even more preferably 620 ° C. or higher.
- Core Glass Molding can be formed into a known shape as a preform for optical element molding using oxide glass by a known method as a preform molding method.
- a preform molding method Regarding the shape of the core glass and the forming method, reference can be made, for example, to paragraphs 0087 to 0106 of JP2011-1259A and description of examples, paragraphs 0040 to 0044 of JP2004250295A and description of examples.
- the glass material for press molding used in the method for producing an optical element according to one embodiment of the present invention is obtained by performing a film forming process for coating the above-described metal oxide film on the core glass described above. be able to.
- the glass material for press molding thus obtained has a structure in which the metal oxide film is in direct contact with the surface of the core glass. On the glass material for press molding having this configuration, one or more layers can be arbitrarily formed. Such a coating is effective for enhancing the mold releasability of the glass from the mold during press molding.
- a carbon-containing film can be exemplified.
- the carbon-containing film provides sufficient slipperiness with the mold when the glass material is supplied to the mold prior to pressing so that the glass material can move smoothly to a predetermined position (center position) of the mold.
- the glass material is softened and deformed by the press, the glass material is stretched according to the glass deformation on the surface of the glass material, and the glass material can be spread on the mold surface.
- it is useful in that the glass is easily separated from the surface of the mold when the molded body is cooled to a predetermined temperature after pressing, thereby assisting the mold release.
- laminating a carbon-containing film on the above-described metal oxide film is also effective in suppressing the occurrence of cracking in press molding.
- a film containing carbon as a main component is preferable, but a film containing a component other than carbon such as a hydrocarbon film may be used.
- a method for forming the carbon-containing film a known film forming method such as vacuum deposition using a carbon raw material, sputtering, ion plating method, plasma CVD (Chemical Vapor Deposition) can be used.
- a carbon-containing film may be formed by thermal decomposition of a carbon-containing material such as hydrocarbon.
- the film described as the first surface layer and the second surface layer in JP2011-1259A can be formed.
- the same publication can be referred to.
- optical element The glass material for press molding described above is prepared, and then the press molded body obtained by press molding itself or by subjecting the press molded body to a post-process such as film formation. An optical element according to one embodiment can be obtained.
- Press molding can be performed by a known press molding method as a method for molding an optical element.
- a known press molding method as a method for molding an optical element.
- a precision material made of a dense material having sufficient heat resistance and rigidity can be used.
- examples include metals such as silicon carbide, silicon nitride, tungsten carbide, aluminum oxide, titanium carbide, and stainless steel, or those whose surfaces are coated with a film of carbon, refractory metal, noble metal alloy, carbide, nitride, boride, etc. be able to.
- a film covering the molding surface a film containing carbon is preferable from the viewpoint that a glass material for press molding can be molded into a glass optical element without fusing, spidering, scratching, or the like. JP, 2011-1259, A paragraph 0116 can be referred to about a carbon content film.
- FIG. 1 shows an example of a press forming apparatus.
- press molding glass in which a core glass 1 is coated with the above-described coating film 2 in a molding die 6 including an upper die 3, a lower die 4 and a barrel die 5.
- the material PF is supplied and the temperature is raised to a temperature range suitable for pressing.
- the heating temperature is appropriately set depending on the type of oxide glass constituting the core glass 1, but the glass material PF and the mold 6 are temperatures at which the viscosity of the glass material PF becomes 10 5 to 10 10 dPa ⁇ s.
- the pressing temperature is more preferably, for example, a temperature at which the oxide glass constituting the core glass 1 is 10 6 to 10 8 dPa ⁇ s before and after 10 7.2 dPa ⁇ s, and the core glass 1 is equivalent to 10 7.2 dPa ⁇ s. It is more preferable to set the temperature so that Usually, the press temperature is set to a temperature equal to or higher than the glass transition temperature of the core glass.
- the core glass is covered with a metal oxide film in which oxygen is deficient from the stoichiometric composition and the oxygen atom uptake rate and the metal atom diffusion rate satisfy the above relationship.
- the glass material PF may be supplied to the mold 6 and the glass material PF and the mold 6 may be heated to a predetermined range, or the glass material PF and the mold 6 may be heated to a predetermined temperature range. Therefore, the glass material PF may be disposed in the mold 6. Further, the glass material PF is heated to a temperature equivalent to 10 5 to 10 9 dPa ⁇ s, the mold 6 is heated to a temperature corresponding to a glass viscosity of 10 9 to 10 12 dPa ⁇ s, and the glass material PF is placed in the mold 6. Then, a method of immediately press forming may be employed.
- the mold temperature can be relatively lowered, the temperature increase / decrease cycle time of the molding apparatus can be shortened, and deterioration of the mold 6 due to heat can be suppressed, which is preferable.
- cooling is started at the start or after the start of press molding, and the temperature is lowered while applying an appropriate load application schedule and maintaining the adhesion between the molding surface and the glass. Then, it molds and takes out a molded object.
- the mold release temperature is preferably 10 12.5 to 10 13.5 dPa ⁇ s.
- the metal oxide film provided on the glass material for press molding has taken in oxygen atoms from the core glass, so that the coating film has a higher oxygen content than before press molding. That is, there is a metal oxide film in which the content of oxygen atoms with respect to metal atoms is higher than the coating film of the glass material for press molding before press molding.
- This metal oxide film has been found by the present inventors to be in a state where oxygen is deficient rather than the stoichiometric composition.
- the obtained glass molded body can be shipped as an optical element as a final product as it is, or post-processing such as centering and film formation for forming an optical functional film such as an antireflection film on the surface. It can also be made into a final product after application.
- a desired antireflection film can be obtained by appropriately forming a film such as Al 2 O 3 , ZrO 2 —TiO 2 , MgF 2 on the glass molded body having the surface layer as a single layer or a laminated layer. Can be formed.
- the antireflection film can be formed by a known method such as vapor deposition, ion-assisted vapor deposition, ion plating, or sputtering.
- the vapor deposition material is heated by an electron beam, direct energization or arc in a vacuum atmosphere of about 10 ⁇ 4 Torr using a vapor deposition apparatus, and the material generated by evaporation and sublimation from the material is used.
- the antireflection film can be formed by transporting the vapor onto the substrate and condensing / depositing it.
- the substrate heating temperature can be about room temperature to about 400 ° C. However, when the glass transition temperature (Tg) of the substrate is 450 ° C. or lower, the upper limit temperature of the substrate heating is preferably Tg ⁇ 50 ° C.
- An optical element is a small-diameter, thin-walled small-mass lens, for example, a small imaging system lens, a communication lens, an optical pickup objective lens, a collimator lens, and the like mounted on a portable imaging device.
- the lens shape is not particularly limited, and various shapes such as a convex meniscus lens, a concave meniscus lens, a biconvex lens, and a biconcave lens can be taken.
- the glass transition temperature and yield point described below are values measured at a heating rate of 4 ° C./min with a thermomechanical analyzer of Rigaku Corporation.
- the refractive index (nd) and the Abbe number ( ⁇ d) were measured for the optical glass obtained at a slow cooling rate of ⁇ 30 ° C./hour.
- Example 1 Production of glass material for press molding Optical glass I-1 belonging to glass I and optical glass II- belonging to glass II described in Table 1 as optical glass to be core glass 1 of glass material PF for press molding 1 was used to form a zirconia oxide film on the surface by the following process. First, the optical glass to be the core glass 1 was dropped and cooled from a molten state onto a receiving mold, and a glass lump having a shape in which one side was a convex surface and the other side was a concave surface was preformed. A coating film (film thickness: about 5 nm) was formed on the preformed glass block by sputtering at a film forming temperature of 300 ° C.
- the film thickness was adjusted according to the sputtering conditions.
- the press-molding glass material thus obtained had an outer dimension of 10 to 11 mm and a center thickness of 7 to 8 mm.
- the glass material PF for press molding produced in the above (1) was press molded in a nitrogen gas atmosphere by a mold press molding apparatus.
- the core glass was heated to a temperature at which the viscosity of the core glass was 10 7.2 dPa ⁇ s, and supplied to a mold heated to a temperature equivalent to 10 8.5 dPa ⁇ s as the viscosity of the core glass.
- the glass material is pressed between the upper and lower molds (press temperature: 675 ° C.), cooled to a temperature below the annealing temperature of the core glass while maintaining the close contact between the glass and the upper and lower molds, and molded from within the mold.
- the body optical lens
- the molded body had an outer diameter of 20.0 mm and a center thickness of 0.70 mm.
- the outer periphery of the press-molded body was centered by grinding to obtain a concave meniscus aspheric glass lens with a diameter of 18 mm.
- Example 2 In the production of the glass material for press molding (1), a coating film having a film thickness of about 5 nm was formed on each of the core glass I-1 and II-1 using metal titanium (Ti) instead of metal zirconium. Otherwise, a concave meniscus aspheric glass lens was obtained in the same manner as in Example 1.
- Example 3 In the production of the glass material for press molding (1), a coating film having a film thickness of about 5 nm was formed on the core glass I-1 and II-1 using metal tantalum (Ta) instead of metal zirconium. Otherwise, a concave meniscus aspheric glass lens was obtained in the same manner as in Example 1.
- Example 4 In the production of the glass material for press molding (1), except that metal tungsten (W) was used instead of metal zirconium, and a coating film having a film thickness of about 5 nm was formed on the core glass II-1. A concave meniscus aspheric glass lens was obtained in the same manner as in Example 1.
- Example 5 In the production of the glass material for press molding (1), except that metal niobium (Nb) was used instead of metal zirconium, and a coating film having a film thickness of about 5 nm was formed on the core glass II-1. A concave meniscus aspheric glass lens was obtained in the same manner as in Example 1.
- Example 1 in the production of the glass material for press molding (1) except that a coating film having a thickness of about 5 nm was formed on the core glass I-1 using metal yttrium (Y) instead of metal zirconium. Similarly, a concave meniscus aspheric glass lens was obtained.
- Y metal yttrium
- Example 2 Similar to Example 1, except that the ZrO 2 film and the SiO 2 film, which are the surface layers in Examples 1 to 6 of JP 2011-1259 A, were formed in this order on the surface of the core glass I-1. A concave meniscus aspheric glass lens was obtained. The thicknesses of the ZrO 2 film and the SiO 2 film were each about 5 nm.
- FIG. 2 shows an optical micrograph of the lens (core glass: I-1 in Table 1) produced in Example 1. It can be confirmed that a homogeneous lens having high transparency without bubbles is obtained. On the other hand, in the lenses produced in Comparative Examples 1 and 2, many bubbles having a diameter of 50 ⁇ m or more were confirmed.
- FIG. 3 shows an optical micrograph obtained by enlarging and photographing a part of the lens (core glass: I-1 in Table 1) produced in Comparative Example 2.
- the coating film covering the core glass is a film having a stoichiometric composition such as a ZrO 2 film.
- a metal oxide film permeates oxygen liberated from the oxide glass at the time of press molding and is considered not to be taken into the film. Oxygen that has permeated the membrane is confined in the press mold and is not released to the outside. As a result, it is presumed that the film again passes through the film and returns to the glass, thereby causing foaming in the glass.
- Example 1 ⁇ Confirmation of coating film state before and after press molding (Example 1, Comparative Example 2)>
- TOF-SIMS Time-of-flight secondary ion mass spectrometer
- Depth direction analysis by TOF-SIMS Depth direction measurement was performed using TOF-SIMS300 manufactured by ION-TOF.
- TOF-SIMS is a technique for irradiating pulsed primary ions and detecting the generated secondary ions.
- FIG. 4 shows the depth direction analysis results of secondary ion intensity by TOF-SIMS after pressing (lens) for Example 1.
- FIG. 5 shows the depth direction analysis result of secondary ion intensity by TOF-SIMS before pressing (unpressed product) in Example 1.
- the unit of secondary ionic strength is an arbitrary unit. The same applies to the drawings described later.
- the film thickness of the zirconium oxide formed as the coating film on the core glass in Example 1 is about 5 nm.
- ZrO and ZrO 2 are described as secondary ions derived from zirconium oxide in each sample. Although not shown in the figure, Zr alone is detected in each sample.
- the coating films before and after pressing are all zirconium oxide.
- the analysis results of ZrO and ZrO 2 before pressing shown in FIG. 5 two peaks are recognized in the vicinity of the surface.
- the present inventors presume that the first peak near the surface is a natural oxide film, and the second peak is caused by reaction with glass during film formation.
- SiO 2 detected by the depth direction analysis of the secondary ion intensity by TOF-SIMS is derived from SiO 2 contained in the glass.
- Figure 6 is a ZrO 2/2 ion intensity ratio of ZrO (hereinafter. Referred to as "ZrO 2 / ZrO intensity ratio") result of comparison in FIGS.
- the ZrO 2 / ZrO intensity ratio is an index indicating the degree of oxidation in the zirconium oxide film.
- the range of about 2 nm from the surface of the zirconium oxide cannot be discussed because of the influence of the natural oxide film.
- the ZrO 2 / ZrO intensity ratio from the depth range of about 2 nm to about 5 nm is higher after pressing than before pressing. From this result, it can be confirmed that the oxidation of zirconium oxide was promoted by the press.
- the ZrO 2 / ZrO strength ratio described above is, for example, in the range of 0.5 to 1.9 before pressing.
- the coating can be a zirconium oxide film having a ZrO 2 / ZrO strength ratio in the range of, for example, 2.0 to 2.3 after pressing.
- Higher ZrO 2 / ZrO means that it is oxidized and contains more oxygen.
- the ZrO 2 / ZrO intensity ratio of this film can usually take a value of about 2.4 to 3.2.
- FIG. 7 shows the depth direction analysis result of the secondary ion intensity by TOF-SIMS of the lens produced in Comparative Example 2.
- FIG. 8 shows a result of superimposing the result of Example 1 shown in FIG. 4 and the result of Comparative Example 2 shown in FIG. Comparative Example 2 has a SiO 2 / ZrO 2 / glass structure, and it has been confirmed in advance that SiO 2 and ZrO 2 have a stoichiometric composition before and after pressing.
- the interface between SiO 2 and ZrO 2 is 0, and the SiO 2 portion is indicated by minus. Focusing on the region (depth 0 to 5 nm) showing ZrOx in FIG.
- the ZrO 2 / ZrO intensity ratio after pressing in Example 1 is smaller than that in Comparative Example 2. From this result, it can be seen that the degree of oxidation by the press of Example 1 is lower than that of Comparative Example 2. That is, it can be confirmed that the zirconium oxide after pressing in Example 1 is deficient in oxygen as compared with ZrO 2 having a stoichiometric composition in Comparative Example 2.
- Comparative Example 2 since the SiO 2 film was formed on the outermost surface of the press-molding glass material, it is not necessary to consider the influence of the natural oxide film. However, in Example 1, the region of about 2 nm from the surface is the natural oxide film. It is affected and cannot be the subject of discussion.
- Example 1 the zirconium oxide film had a composition in which oxygen was lost from the stoichiometric composition ZrO 2 both before and after pressing. It can be confirmed that the oxygen content of the zirconium oxide film is higher than that before pressing.
- Each of the metal oxide films produced on the core glass in Examples 2 to 5 was in a state where oxygen was lost from the stoichiometric composition before and after pressing by the same method. It was confirmed that the oxygen content was higher than before pressing.
- the glass III-1 shown in Table 2 below corresponding to the oxide glass III was also press-molded in the same manner as in Example 1, and it was confirmed that a homogeneous lens without bubbles was obtained.
- generation of bubbles after pressing can be suppressed.
- the total of the diameters of the bubbles does not exceed 50 ⁇ m can be used as an index that is a homogeneous optical element in which the generation of bubbles is suppressed.
- the number of bubbles having a diameter of 25 ⁇ m or more is less than 1 or the number of bubbles having a diameter of 10 ⁇ m or more is less than 3 when observed with an optical microscope at a magnification of 10 to 50 times, and the total diameter of the bubbles That does not exceed 25 ⁇ m can be used as an index that is a homogeneous optical element without bubbles. All the lenses manufactured in the above-described examples satisfy the preferable index and the more preferable index.
- the total diameter of the bubbles is, for example, 100 ⁇ m if there are two mills having a diameter of 50 ⁇ m.
- the diameter here refers to the diameter when the bubble is a circular bubble, the distance in the longitudinal direction when the bubble is elliptical, and the longest possible distance when the bubble is irregular.
- the diameter In the examples, almost the entire surface of the core glass surface was coated with a metal oxide film, but even if a portion was uncoated, oxygen was deficient from the stoichiometric composition and the oxygen atom uptake rate. Needless to say, the same effect can be obtained if a metal oxide film in which the diffusion rate of metal atoms and the diffusion rate of metal atoms satisfy the above-described relationship exists on the surface of the core glass.
- an oxide glass and a coating film that covers at least a part of the surface of the oxide glass are included, and the coating film has a stoichiometric composition.
- the rate at which the metal oxide film takes in oxygen atoms contained in the oxide glass at a temperature higher than the glass transition temperature of the oxide glass in a state where oxygen is more deficient is that the metal atoms contained in the metal oxide film It is possible to provide an optical element that is a metal oxide film faster than the speed of diffusion into oxide glass.
- the metal oxide is a metal oxide selected from the group consisting of zirconium, titanium, niobium, tungsten, and tantalum.
- the metal oxide film of the press-molded body obtained by press molding is in a state where oxygen is deficient due to the stoichiometric composition.
- the above-mentioned oxide glass contains one or more high refractive index imparting components selected from the group consisting of Nb 2 O 5 , TiO 2 , WO 3 and Ta 2 O 5 .
- the total content (Nb 2 O 5 + TiO 2 + WO 3 + Ta 2 O 5 ) of the high refractive index imparting component is preferably 10% by mass or more and 50% by mass or less.
- the above oxide glass contains one or more selected from the group consisting of ZnO and alkali metal oxides (Li 2 O, Na 2 O, K 2 O).
- the total content of ZnO and alkali metal oxide (ZnO + Li 2 O + Na 2 O + K 2 O) is 5% by mass or more and 25% by mass or less.
- heating during press molding is performed at a heating temperature of 650 ° C. or higher. According to the manufacturing method of the above-mentioned optical element, generation
- the oxide glass and a coating film covering at least a part of the surface of the oxide glass, the coating film described above is in a state in which oxygen is lost from the stoichiometric composition,
- the rate at which the metal oxide film takes in oxygen atoms contained in the oxide glass is faster than the rate at which the metal atoms contained in the metal oxide film diffuse into the oxide glass.
- a glass material for press molding which is a metal oxide film is also provided. This glass material for press molding is suitably used in the method for producing an optical element according to the above-described embodiment.
- the present invention is useful in the field of manufacturing optical elements such as glass lenses.
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Abstract
Description
特許文献1および英語ファミリーメンバーUS2012/135199A1、ならびに特許文献2の全記載は、ここに特に開示として援用される。
そこで本発明者らはガラス中の発泡を抑制する手段を見出すために、泡の発生原因について鋭意検討を重ねた。その結果、プレス成形後の光学素子に発生する泡は、非酸化性雰囲気(酸素含有率は数ppm)でプレス成形を行ったとしても多くの酸素を含んでいるという、予想外の現象を見出した。非酸化性雰囲気でのプレス成形における酸素の発生原因は酸化物ガラスのみであるため、酸化物ガラス由来の酸素が泡の発生に関与していると考えられる。
酸化物ガラスと、
この酸化物ガラスの表面の少なくとも一部を覆う被覆膜と、
を有し、
上述の被覆膜は、化学量論組成より酸素が欠損した状態にある金属酸化物膜であり、かつ
酸化物ガラスのガラス転移温度以上の温度における、金属酸化物膜が酸化物ガラスに含まれる酸素原子を取り込む速度は、金属酸化物膜に含まれる金属原子が酸化物ガラスへ拡散する速度より速い、光学素子、
に関する。
酸化物ガラスと、この酸化物ガラスの表面の少なくとも一部を覆う、化学量論組成より酸素が欠損した金属酸化物膜である被覆膜と、を有するプレス成形用ガラス素材を準備する工程と、
プレス成形用ガラス素材をプレス成形しプレス成形体を形成するプレス工程と、
を備え、
上述のプレス成形体は、プレス工程を経た上述の被覆膜を含み、かつ
プレス工程を経た被覆膜は、プレス工程前の被覆膜より酸素含有率が高い金属酸化物膜である、光学素子の製造方法、
に関する。
化学量論組成より酸素が欠損した状態にある金属酸化物膜は、酸素を取り込みやすい状態にある。したがって、この状態の金属酸化物膜であれば、プレス成形時に発泡を引き起こす酸素をガラス内部から取り除き、泡の発生を抑制することができる。
ただし、プレス成形時、被覆膜と酸化物ガラスとの間では、酸化物ガラスから被覆膜への酸素原子の移動(取り込み)とともに、被覆膜から酸化物ガラスへの金属原子の移動(拡散)も起こり得る。この金属原子の拡散速度が、酸素原子が被覆膜へ取り込まれる速度より速い金属酸化物膜は、拡散が取り込みに優先して進行する。このためプレス成形により膜厚の顕著な減少や膜の消失が生じ、酸化物ガラス内部での発泡を抑制することは困難である。これに対し、上述の被覆膜は、酸素原子の取り込みが金属原子の拡散に優先して進行するため、泡の発生を引き起こす酸素原子を酸化物ガラスから効率的に取り込み、発泡を抑制することができる。
こうして得られる光学素子には、プレス工程を経た上述の被覆膜が存在している。この光学素子に含まれる被覆膜は、プレス成形時に酸化物ガラスから酸素を取り込むため、プレス成形用ガラス素材に含まれていた状態より金属原子に対する酸素原子の含有率は高い。ただし、光学素子に含まれる被覆膜は依然として化学量論組成より酸素が欠損した状態にあることが、本発明者らの検討の結果、明らかとなった。
更に、本発明の一態様によれば、泡の発生のない均質な光学素子を提供することができる。
先に記載したように、本発明者らの鋭意検討により見出された新たな知見によれば、プレス成形後に光学素子に発生する泡は、酸化物ガラス由来の酸素であると推察される。これに対し化学量論組成より酸素が欠損した金属酸化物膜は、より安定な状態である化学量論組成に近づくべく酸素を取り込みやすい状態にあると考えられる。したがって、化学量論組成より酸素が欠損した状態の金属酸化物膜により酸化物ガラス表面の少なくとも一部を被覆した後にプレス成形を行うことで、プレス中に発泡を引き起こす酸素を酸化物ガラスから金属酸化物膜へ取り込むことができるため、プレス成形後の泡の発生が抑制された高品質な光学素子の提供が可能となる。そしてこうして形成されたプレス成形体(光学素子)の表面に残留している金属酸化物膜は、酸化物ガラスから取り込んだ酸素原子を含むものとなるため、プレス成形前のプレス成形用ガラスが有する金属酸化物膜よりも多く酸素原子を含むものとなる。即ち、プレス成形体は、表面の少なくとも一部に、金属原子に対する酸素原子の含有率が、プレス成形用ガラス素材が有する被覆膜より高い金属酸化物膜を有するものとなる。
先に記載した通り、プレス成形時、酸化物ガラスと、これを被覆する被覆膜との間では、酸化物ガラスから被覆膜への酸素原子の移動(取り込み)とともに、被覆膜から酸化物ガラスへの金属原子の移動(拡散)も起こり得る。プレス成形は、通常ガラス転移温度以上の温度で行われるため、プレス成形時に上述の金属酸化物膜が酸化物ガラス中の酸素原子を取り込む速度は、この金属酸化物膜中の金属原子が酸化物ガラスに取り込まれる速度よりも速い。このような性質を有する被覆膜であれば、プレス時に被覆膜への酸素原子の取り込みが酸化物ガラスへの金属原子の拡散に優先して進行する。したがって、プレス成形後、上述の状態の金属酸化物膜として、プレス成形体上に存在することができる。これに対し、酸化物ガラスへの金属原子の拡散速度が酸素原子が被覆膜へ取り込まれる速度より速い金属酸化物膜では、拡散が取り込みに優先して進行する。このため、プレス成形により膜厚の顕著な減少や膜の消失が生じ、酸化物ガラス内部での発泡を抑制することは困難である。なお、酸素原子の取り込み速度が金属原子の拡散速度よりも大きければ上述の効果を奏することができるため、酸素原子の取り込み速度と金属原子の拡散速度との差は、特に限定されるものではない。
以下、上述のプレス成形用ガラス素材について、更に詳細に説明する。
酸化物ガラスを覆う被覆膜は、化学量論組成より酸素が欠損した状態の金属酸化物膜が形成可能な成膜法により形成すればよい。例えば、酸化物ガラスからなるガラス塊(以下、「芯部ガラス」ともいう。)の表面に、ターゲットとして金属を用いて非酸化性雰囲気中でスパッタ法、真空蒸着法、CVD(Chemical Vapor Deposition)法などの公知の成膜法により成膜することで、上述の被覆膜を形成することができる。成膜温度(芯部ガラスの温度)は、下限は150℃以上であることが好ましく、200℃以上であることがさらに好ましい。上限は芯部ガラスのガラス転移温度未満であることが好ましい。上限温度は、例えば450℃以下である。
具体的態様としては、所定形状に形成した複数の芯部ガラスをトレーに配列して真空チャンバー内に配置し、真空チャンバー内を真空排気しながら、加熱ヒーターにより芯部ガラスを約300℃に加熱する。真空チャンバー内の真空度が1×10-5Torr以下になるまで排気した後、Arガスを導入し、真空チャンバー内の雰囲気ガスをArガスに置換した後にターゲット基材に高周波を印加して、原料をプラズマ化し、芯部ガラスの表面に被覆膜を成膜する。被覆膜の膜厚は、真空チャンバー内の圧力(真空度)、電源パワー、成膜時間を調整することによって所望の膜厚に制御することができる。なお、被覆膜は、芯部ガラスの表面の少なくとも一部を覆っていればよい。したがって、被覆膜成膜後の芯部ガラスは、表面の一部が未被覆の状態であってもよく、表面の全面が覆われていてもよい。一実施形態では、プレス成形用ガラス素材をプレス成形して光学素子を成形したときに、光学素子の光学機能面を形成することになる芯部ガラスの部位を少なくとも被覆することができる。光学機能面とは、例えば光学レンズにおいては有効径内の領域を意味する。ただし、上述の被覆膜がプレス成形用ガラス素材表面のどの部位にせよ少なくとも一部に存在すれば芯部ガラスから酸素原子を取り込むことができるため、上述の実施形態に限定されるものではない。
上述の被覆膜により表面の少なくとも一部が被覆される芯部ガラスとしては、光学素子作製に通常使用される各種組成の光学ガラスを挙げることができる。そのような光学ガラスの具体的態様としては、ホウ酸ランタン系ガラス等のホウ酸-希土類系ガラス、リン酸塩ガラス、ケイ酸塩ガラスを挙げることができる。
カチオン%表示で、
B3+およびSi4+を合計で5~60%(但し、B3+を5~50%)、
Zn2+およびMg2+を合計で5%以上、
La3+、Gd3+、Y3+およびYb3+を合計で10~50%、
Ti4+、Nb5+、Ta5+、W6+およびBi3+を合計で6~45%(但し、Ti4+およびTa5+の合計含有量が0%超、かつW6+の含有量が5%超)、
含み、
B3+の含有量に対するSi4+の含有量のカチオン比(Si4+/B3+)が0.70以下であり、
Ti4+およびTa5+の合計含有量に対するTa5+の含有量のカチオン比(Ta5+/(Ti4++Ta5+))が0.23以上であり、
Nb5+およびW6+の合計含有量に対するW6+の含有量のカチオン比(W6+/(Nb5++W6+))が0.30以上であり、
B3+およびSi4+の合計含有量に対するTi4+、Nb5+、Ta5+、W6+およびBi3+の合計含有量のカチオン比((Ti4++Nb5++Ta5++W6++Bi3+)/(B3++Si4+))が0.37を超え3.00以下であり、
La3+、Gd3+、Y3+およびYb3+の合計含有量に対するZn2+、Mg2+およびLi+の合計含有量のカチオン比((Zn2++Mg2++Li+)/(La3++Gd3++Y3++Yb3+))が0.40以上であり、
屈折率ndが1.90~2.00であり、かつアッベ数νdが下記(1)式:
25≦νd<(3.91-nd)/0.06 ・・・(1)
を満たす酸化物ガラス。
なお、ガラス転移温度を過剰に低下させるとガラスの安定性が低下したり、屈折率が低下する傾向を示すため、ガラス転移温度を500℃以上とすることが好ましく、520℃以上とすることがより好ましく、540℃以上とすることがさらに好ましく、560℃以上とすることが一層好ましく、570℃以上とすることがより一層好ましい。
B2O3、La2O3およびZnOを含み、モル%表示で、B2O3 20~60%、SiO2 0~20%、ZnO 22~42%、La2O3 5~24%、Gd2O3 0~20%(ただし、La2O3とGd2O3の合計量が10~24%)、ZrO2 0~10%、Ta2O5 0~10%、WO3 0~10%、Nb2O5 0~10%、TiO2 0~10%、Bi2O3 0~10%、GeO2 0~10%、Ga2O3 0~10%、Al2O3 0~10%、BaO 0~10%、Y2O3 0~10%およびYb2O3 0~10%、を含み、かつアッベ数(νd)が40以上で、実質的にリチウムを含まない酸化物ガラス。
モル%表示で、
SiO2 0~20%、
B2O3 5~40%、
SiO2+B2O3=15~50%、
Li2O 0~10%、
ZnO 12~36%、
ただし、3×Li2O+ZnO≧18%、
La2O3 5~30%、
Gd2O3 0~20%、
Y2O3 0~10%、
La2O3+Gd2O3=10~30%、
La2O3/ΣRE2O3=0.67~0.95%、
(但し、ΣRE2O3=La2O3+Gd2O3+Y2O3+Yb2O3+Sc2O3+Lu2O3)
ZrO2 0.5~10%、
Ta2O5 1~15%、
WO3 1~20%、
Ta2O5/WO3≦2.5(モル比)
Nb2O5 0~8%、
TiO2 0~8%
を含み、
屈折率ndが1.87以上、
アッベ数νdが35以上40未満
の酸化物ガラス。
芯部ガラスは、酸化物ガラスを光学素子成形用のプリフォームとして公知の形状に、プリフォームの成形法として公知の方法により成形することができる。芯部ガラスの形状および成形方法については、例えば、特開2011-1259号公報段落0087~0106および実施例の記載、特開2004-250295号公報段落0040~0044および実施例の記載を参照できる。
本発明の一態様にかかる光学素子の製造方法に用いられるプレス成形用ガラス素材は、以上説明した芯部ガラスに、上述の金属酸化物膜を被覆する成膜処理を行うことで得ることができる。こうして得られるプレス成形用ガラス素材は、芯部ガラスの表面に上述の金属酸化物膜が直接接する構成を取るものとなる。この構成のプレス成形用ガラス素材には、更に一層以上の被膜を任意に形成することができる。そのような被膜は、プレス成形において成形型からのガラスの離型性を高めることなどに有効である。
以上説明したプレス成形用ガラス素材を準備し、次いでプレス成形することにより得られたプレス成形体そのものとして、またはプレス成形体に被膜形成等の後工程を施すことにより、本発明の一態様にかかる光学素子を得ることができる。
屈折率(nd)およびアッベ数(νd)は、徐冷降温速度を-30℃/時にして得られた光学ガラスについて測定した。
(1)プレス成形用ガラス素材の作製
プレス成形用ガラス素材PFの芯部ガラス1となる光学ガラスとして、表1に記載したガラスIに属する光学ガラスI-1、ガラスIIに属する光学ガラスII-1を用いて、その表面に以下の工程によりジルコニア酸化物膜を成膜した。
まず、芯部ガラス1となる光学ガラスを、熔融状態から受け型に滴下、冷却し、片側を凸面、反対側を凹面とした形状のガラス塊を予備成形した。この予備成形されたガラス塊に対して、金属ジルコニウム(Zr)をターゲットに用いてAr100%の雰囲気中で成膜温度300℃でスパッタ法により被覆膜(膜厚:約5nm)を成膜した。膜厚は、スパッタ条件により調整した。こうして得られたプレス成形用ガラス素材の外形寸法は10~11mm、中心部肉厚は7~8mmであった。
次いで、上述の(1)で作製したプレス成形用ガラス素材PFをモールドプレス成形装置により窒素ガス雰囲気下でプレス成形した。すなわち、成形面にスパッタ法による炭素含有離型膜を形成したSiC製の上下型と、胴型からなる成形型を用い、成形装置のチャンバー内雰囲気を非酸化性のN2ガスで充満してから、芯ガラスの粘度が107.2dPa・sとなる温度に加熱し、芯ガラスの粘度で108.5dPa・s相当の温度に加熱した成形型に供給した。そして、供給直後に上下型間でガラス素材をプレスし(プレス温度675℃)、ガラスと上下型の密着を維持したまま、芯ガラスの徐冷温度以下の温度まで冷却し、成形型内から成形体(光学レンズ)を取り出した。成形体の外径寸法は20.0mm、中心肉厚は0.70mmであった。次いで、プレス成形体の外周部を研削加工により心取りを行い、φ18mmの凹メニスカス形状の非球面ガラスレンズを得た。
プレス成形用ガラス素材の作製(1)において、金属ジルコニウムに変えて金属チタン(Ti)を用いて芯部ガラスI-1、II-1にそれぞれ膜厚約5nmの被覆膜を成膜した点以外、実施例1と同様に凹メニスカス形状の非球面ガラスレンズを得た。
プレス成形用ガラス素材の作製(1)において、金属ジルコニウムに変えて金属タンタル(Ta)を用いて芯部ガラスI-1、II-1にそれぞれ膜厚約5nmの被覆膜を成膜した点以外、実施例1と同様に凹メニスカス形状の非球面ガラスレンズを得た。
プレス成形用ガラス素材の作製(1)において、金属ジルコニウムに変えて金属タングステン(W)を用いて、芯部ガラスII-1に膜厚約5nmの被覆膜を成膜した点以外、実施例1と同様に凹メニスカス形状の非球面ガラスレンズを得た。
プレス成形用ガラス素材の作製(1)において、金属ジルコニウムに変えて金属ニオブ(Nb)を用いて、芯部ガラスII-1に膜厚約5nmの被覆膜を成膜した点以外、実施例1と同様に凹メニスカス形状の非球面ガラスレンズを得た。
プレス成形用ガラス素材の作製(1)において、金属ジルコニウムに変えて金属イットリウム(Y)を用いて芯部ガラスI-1に膜厚約5nmの被覆膜を成膜した点以外、実施例1と同様に凹メニスカス形状の非球面ガラスレンズを得た。
芯部ガラスI-1の表面に、特開2011-1259号公報の実施例1~6における表面層であるZrO2膜とSiO2膜をこの順に成膜した点以外、実施例1と同様に凹メニスカス形状の非球面ガラスレンズを得た。ZrO2膜とSiO2膜の膜厚は、それぞれ約5nmとした。
実施例、比較例で作製した各レンズを光学顕微鏡で倍率50倍で観察し、レンズ内の泡の有無を確認したところ、実施例1~4で作製したレンズでは、泡はまったく観察されなかった。代表例として、図2に、実施例1で作製したレンズ(芯部ガラス:表1中のI-1)の光学顕微鏡写真を示す。泡のない高い透明性を有する均質なレンズが得られていることが確認できる。
これに対し比較例1、2で作製したレンズでは、直径50μm以上の泡が多数確認された。図3に、比較例2で作製したレンズ(芯部ガラス:表1中のI-1)の一部を拡大し撮影した光学顕微鏡写真を示す。泡が多数発生していることが確認できる。
比較例2において芯部ガラスを覆う被覆膜は、ZrO2膜等の化学量論組成の膜である。このような金属酸化物膜は、プレス成形時に酸化物ガラスから遊離した酸素を透過してしまい、膜中に取り込むことはできないと考えられる。膜を透過した酸素はプレス成形型内に閉じ込められ外部には放出されない。その結果、再び膜を透過してガラスに戻り、ガラス中で発泡を引き起こすと推察される。
比較例2で作製したレンズ(芯部ガラス:ガラスI-1)中の泡中の気体組成を、質量分析法(Mass Spectrometry)により分析したところ、N2:89%、O2:11%であり、窒素ガス雰囲気下でプレス成形を行ったにもかかわらず、10%超もの酸素が検出された。この結果は、先に説明した通り、酸化物ガラス由来の酸素が泡の発生原因となっていることを裏付けるものである。
芯部ガラスとしてガラスI-1を用いて実施例1、比較例2で作製されたレンズおよびこの成形に用いたプレス成形用ガラス素材と同じ条件で作製したプレス成形用ガラスについて、以下の方法によりTOF―SIMS(Time-of-flight secondary ion mass spectrometer:飛行時間型2次イオン質量分析法)により、表面から深さ方向の組成分析を行った。
TOF-SIMSによる深さ方向分析
ION-TOF社製TOF-SIMS300を用いて、深さ方向測定を実施した。TOF-SIMSは、パルス化された一次イオンを照射し、発生した二次イオンを検出する手法である。TOF-SIMSの深さ方向分析では、(i)一次イオンを照射、(ii)発生した二次イオンを計測、(iii)スパッタイオンを照射、以下(i)~(iii)の繰り返しでデータを取得する。
一次イオン源にはBi3 ++を用い、一次イオン源のカラムにかかる電圧は25kVとした。一次イオン源の電流を0.2pAとして測定を行った。一次イオン源の照射面積(=二次イオンを検出する測定領域)は100μm角とし、二次イオンは負イオンを検出した。
スパッタイオン源にはCsを用いた。スパッタイオン源の加速は1kV、電流値は75.4nAで調整を行った。スパッタイオン源の面積は400μm角でスパッタを行った。
実施例1で芯部ガラスに被覆膜として形成したジルコニウム酸化物の膜厚は、約5nmである。図中には、各試料におけるジルコニウム酸化物に由来する2次イオンとして、ZrOとZrO2を記載している。また、図からは省略しているが、各試料においてZr単体が検出されている。Zr2が検出されていないため、単体のZrは金属Zrに由来するものではなく、ジルコニウム酸化物に由来するものと考えられる。よって、プレス前後での被覆膜は、いずれもジルコニウム酸化物である。なお、図5に示すプレス前のZrO、ZrO2の分析結果では、表面近傍にそれぞれ2つのピークが認められる。本発明者らは、表面付近の一つ目のピークは自然酸化膜であり、2つ目のピークは成膜時にガラスとの反応により生じたものと推察している。TOF-SIMSによる2次イオン強度の深さ方向分析により検出されたSiO2は、ガラスに含まれるSiO2に由来する。各試料において、SiO2強度が表面付近で上昇している理由は表面にわずかに混入物(例えば、シロキサン等)が存在しているためと考えられる。
図6は、図4、5におけるZrO2/ZrOの2次イオン強度比(以降、「ZrO2/ZrO強度比」と記載する。)を比較した結果である。ZrO2/ZrO強度比は、ジルコニウム酸化物膜中の酸化の度合いを示す指標となるものである。ただし、ジルコニウム酸化物の表面から2nm程度の範囲内については、自然酸化膜の影響のため議論の対象とすることができない。図6に示す結果では、深さ2nm程度から5nm程度の領域までのZrO2/ZrO強度比は、プレス前に比べてプレス後の方が増加している。この結果から、プレスによってジルコニウム酸化物の酸化が促進したことが確認できる。
図8のZrOxを示す領域(深さ0~5nm)に注目すると、実施例1のプレス後のZrO2/ZrO強度比は比較例2に比べて小さいものとなっている。この結果から、実施例1のプレスによる酸化の度合いは、比較例2よりも低いことがわかる。すなわち、実施例1のプレス後のジルコニウム酸化物は比較例2の化学量論組成のZrO2に比べて酸素が欠損していることが確認できる。なお、比較例2はプレス成形用ガラス素材の最表面にSiO2膜を形成したため自然酸化膜の影響を考慮する必要はないが、実施例1については表面から2nm程度の領域は自然酸化膜の影響を受けているため、議論の対象とすることはできない。
芯部ガラスとしてガラスI-1を用いて比較例1で作製されたレンズおよびこの成形に用いたプレス成形用ガラス素材と同じ条件で作製したプレス成形用ガラスについて、上述の方法でTOF―SIMSによる2次イオン強度の深さ方向分析を行った。
図9は、比較例1に関するプレス後(レンズ)のTOF-SIMSによる2次イオン強度の深さ方向分析結果を示す。図10は、比較例1に関するプレス前(未プレス品)のTOF-SIMSによる2次イオン強度の深さ方向分析結果を示す。図9、図10に示す結果から、プレス後にはイットリウム酸化物膜が消失していることが確認できる。これは、比較例1で芯部ガラス上に成膜したイットリウム酸化物膜が、プレス成形時にイットリウム酸化物膜が芯部ガラスに含まれる酸素原子を取り込む速度よりも、イットリウム酸化物膜に含まれる金属原子(Y)が芯部ガラスへ拡散する速度が速いことを示す結果である。
実施例では、芯部ガラス表面のほぼ全面を金属酸化物膜で被覆したが、一部が未被覆であるとしても、化学量論組成より酸素が欠損した状態にあり、かつ酸素原子の取り込み速度と金属原子の拡散速度とが上述の関係を満たす金属酸化物膜が芯部ガラス表面に存在しているのであれば同様の効果が得られることはいうまでもない。
酸化物ガラスと、この酸化物ガラスの表面の少なくとも一部を覆う、化学量論組成より酸素が欠損した金属酸化物膜である被覆膜と、を有するプレス成形用ガラス素材を準備する工程と、
プレス成形用ガラス素材をプレス成形しプレス成形体を形成するプレス工程と、
を備え、
上述のプレス成形体は、プレス工程を経た上述の被覆膜を含み、かつ
プレス工程を経た被覆膜は、プレス工程前の被覆膜より酸素含有率が高い金属酸化物膜である、光学素子の製造方法、
が提供される。
Claims (5)
- 酸化物ガラスと、
前記酸化物ガラスの表面の少なくとも一部を覆う被覆膜と、
を有し、
前記被覆膜は、化学量論組成より酸素が欠損した状態にある金属酸化物膜であり、かつ
前記酸化物ガラスのガラス転移温度以上の温度における、前記金属酸化物膜が前記酸化物ガラスに含まれる酸素原子を取り込む速度は、前記金属酸化物膜に含まれる金属原子が前記酸化物ガラスへ拡散する速度より速い、光学素子。 - 前記金属酸化物は、ジルコニウム、チタン、ニオブ、タングステン、およびタンタルからなる群から選択される金属の酸化物である請求項1に記載のプレス成形用ガラス素材。
- 酸化物ガラスと、前記酸化物ガラスの表面の少なくとも一部を覆う、化学量論組成より酸素が欠損した金属酸化物膜である被覆膜と、を有するプレス成形用ガラス素材を準備する工程と、
前記プレス成形用ガラス素材をプレス成形しプレス成形体を形成するプレス工程と、
を備え、
前記プレス成形体は、前記プレス工程を経た前記被覆膜を含み、かつ
前記プレス工程を経た被覆膜は、プレス工程前の前記被覆膜より酸素含有率が高い金属酸化物膜である、光学素子の製造方法。 - 前記金属酸化物は、ジルコニウム、チタン、ニオブ、タングステン、およびタンタルからなる群から選択される金属の酸化物である請求項3に記載の光学素子の製造方法。
- 前記プレス成形体が有する金属酸化物膜は、化学量論組成より酸素が欠損した状態にある請求項3または4に記載の光学素子の製造方法。
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KR102219149B1 (ko) | 2021-02-22 |
JP6218536B2 (ja) | 2017-10-25 |
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